ergoline and mesulergine

We have evaluated 5 DA agonists-bromocriptine, lergotrile, lisuride, pergolide, and mesulergine in studies encompassing 278 patients with advanced PD. In most of our patients the DA agonist was added to levodopa. Most of our patients were no longer satisfactorily responding to levodopa. Previous attempts at managing these patients by changing the dose of levodopa (increasing or decreasing it), the treatment schedule, or the ratio of levodopa to carbidopa or by temporarily discontinuing levodopa [drug holiday] were unsuccessful. The majority of our patients had diurnal fluctuations in performance, either "wearing off" or "on-off" phenomena. The addition of a DA agonist resulted in a decrease in parkinsonian disability in most patients and a decrease in the severity of the diurnal fluctuations in performance. Improvement in many patients was maintained for at least 2 years. Adverse effects included mental changes, dyskinesias, orthostatic hypotension, and nausea. All of the adverse effects were reversible when the agonist was decreased or discontinued. As a group the agonists behaved similarly but individual patients often responded better to one agonist than another. The main role of agonists is in combination with levodopa in the treatment of patients with early PD who have not yet developed dyskinesias or diurnal fluctuations in performance.

Topics: Aged; Aged, 80 and over; Antiparkinson Agents; Dopamine; Ergolines; Female; Humans; Male; Middle Aged; Parkinson Disease; Receptors, Dopamine; Receptors, Dopamine D1; Receptors, Dopamine D2

Since the initiation of bromocriptine therapy for Parkinson's disease several newer dopamine agonists have been developed. Pergolide has reached the stage of Phase 3 clinical trials and will probably be available for general use sometime in the foreseeable future. Lisuride shows most promise in its parenteral form for infusion therapy of patients with severe fluctuations. Mesulergine, another ergot-derivative and ciladopa, a new non-ergot agonist, have been withdrawn from further clinical use due to tumorogenesis in rats. It is questionable how applicable these findings are to the use of the drugs in elderly humans with parkinsonism. Recently a small number of drugs have been found to have postsynaptic dopamine agonist properties only in the setting of denervated supersensitive dopamine receptors. These agents may be particularly effective in the early treatment of patients with Parkinson's disease. This paper will review a number of the dopamine agonists which have been developed since the introduction of bromocriptine therapy. Several of these have shown beneficial effects in early clinical trials while others show promise in preclinical studies of animal models of parkinsonism.

Topics: Antiparkinson Agents; Bromocriptine; Dopamine; Ergolines; Humans; Parkinson Disease; Piperazines

The current status of treatments designed to treat prolactinoma and other hyperprolactinaemic disorders is reviewed. The use of ergoline derivatives is described to correct prolactin levels, restore reproductive dysfunctions and reduce the size of prolactinomas. Side effects are minimal but withdrawal is almost always followed by a recurrence of the original condition. Radiation therapy is less effective and surgical resection of prolactinomas is effective, but the condition may recur. The authors recommend that dopaminergic drugs should be the primary therapies for prolactin-secreting adenomas and idiopathic hyperprolactinaemia, and surgery should be reserved for dopamine-resistant conditions.

Topics: Acromegaly; Bromocriptine; Delayed-Action Preparations; Dopamine; Ergolines; Female; Humans; Hyperprolactinemia; Lisuride; Pergolide; Pituitary Neoplasms; Pregnancy; Prolactin; Psychoses, Substance-Induced; Tamoxifen

Topics: Adenoma; Adrenocorticotropic Hormone; Bromocriptine; Dihydroergotoxine; Dopamine; Drug Administration Schedule; Ergolines; Growth Hormone; Levodopa; Lisuride; Metergoline; Methysergide; Pergolide; Pituitary Neoplasms; Prolactin; Tomography, X-Ray Computed

Topics: Adenoma; Adult; Diagnosis, Differential; Ergolines; Female; Follow-Up Studies; Galactorrhea; Genital Diseases, Female; Humans; Hypophysectomy; Hypothyroidism; Infertility, Female; Pergolide; Pituitary Neoplasms; Pregnancy; Pregnancy Complications, Neoplastic; Prolactin; Sella Turcica; Tomography, X-Ray Computed; Visual Field Tests

Topics: Animals; Antiparkinson Agents; Ergolines; Humans; Parkinson Disease; Receptors, Dopamine

Topics: Aged; Dopamine Agents; Dose-Response Relationship, Drug; Drug Therapy, Combination; Ergolines; Female; Humans; Levodopa; Male; Middle Aged; Neurologic Examination; Parkinson Disease

The efficacy and tolerance of treatment with an 8-alpha-amino-ergoline derivative CU32-o85, Mesulergine, were compared with levodopa/benserazide (Madopar) in a 3 month double-blind controlled trial in 31 patients with Parkinson's disease, not previously treated with levodopa. The two treatments were equally well tolerated, and neither dyskinesias nor dose-related fluctuations developed. In 90% of the patients treated with Mesulergine, Parkinsonian symptoms improved, and at the dose given the overall therapeutical response was two-thirds that of levodopa. During further 9 months of open study the beneficial effect was maintained equally well in both groups. Compared with other dopamine agonists Mesulergine has a considerable antiparkinsonian effect. Unfortunately, further clinical evaluation of the compound recently has been stopped owing to sex and species specific histological alterations in rats. It is suggested that Mesulergine derivatives might well be of value in future treatment of early Parkinson's disease and of late incompensated stages.

Topics: Aged; Antiparkinson Agents; Benserazide; Clinical Trials as Topic; Double-Blind Method; Drug Combinations; Ergolines; Female; Humans; Levodopa; Male; Middle Aged; Parkinson Disease; Random Allocation

We used a new D2 dopamine agonist, mesulergine (8-alpha-amino-ergoline, CU 32-085), to treat 20 patients (12 men and 8 women), mean age 62.6 (SEM = 1.7) and mean duration of illness 5.9 (SEM = 1.0) years. Wearing-off effect was the principal indication for new therapy in 15 patients, and the others had inadequate response to levodopa. All continued on levodopa therapy, and 10 patients were studied in a double-blind controlled test. The mean motor disability decreased from 2.8 (SEM = 0.12) to 1.6 (SEM = 0.18) with mesulergine (p less than 0.0001) and increased to 1.9 (SEM = 0.20) with placebo (p less than 0.001). Tremor improved most, followed by rigidity, bradykinesia, gait, and postural instability. Side effects included dyskinesia, light-headedness, hallucinations, nausea, vomiting, drowsiness, and ankle edema, but, in general, mesulergine was tolerated well.

Topics: Aged; Antiparkinson Agents; Clinical Trials as Topic; Ergolines; Female; Humans; Male; Middle Aged; Parkinson Disease; Placebos

The effect of a new dopamine agonist, CU 32-085 (8 alpha-amino-ergoline), on pituitary function in acromegaly was evaluated by a controlled, single blind study of 12 acromegalics. The study included a single dose placebo/drug (0.5 mg CU 32-085) trial and a long-term crossover trial with 3 month periods (placebo/CU 32-085 8 mg daily). The patients were evaluated clinically and biochemically (oral glucose tolerance (OGTT), TRH- and LHRH-tests) before and after each 3 month period. Nine patients completed this long-term trial; one died from myocardial infarction during the placebo period, and two dropped out because of side effects. The release of GH, judged from more than 9 h suppression of serum GH following the single dose, and from the response to OGTT after the long-term treatment, was significantly inhibited by CU 32-085. Serum GH reached normal values in 4 of 9 patients. Serum PRL was also markedly suppressed, to subnormal values after the 3 months in all but one hyperprolactinemic patient. Serum TSH, cortisol, FSH and LH were generally unaffected. Glucose tolerance was not significantly altered, although an improvement was found in six of nine patients. A semiquantitative evaluation of subjective symptoms showed a significant improvement following the long-term treatment, while objective signs of acromegaly were unaffected. The blood pressure was slightly lowered, both after a single dose and after 3 months' treatment. Seven patients experienced nausea and dizziness, two of them with vomiting, after a single dose of the drug. Four of these had similar symptoms initially during the long-term treatment, which forced two to interrupt the trial. We conclude that CU 32-085 caused a marked suppression of the release of GH and PRL and an improvement of the major symptoms of acromegaly, a therapeutic effect that is comparable to the previous experience with bromocriptine.

Topics: Acromegaly; Adult; Aged; Blood Pressure; Clinical Trials as Topic; Ergolines; Female; Growth Hormone; Hormones; Humans; Hydrocortisone; Male; Middle Aged; Prolactin

Twenty patients with Parkinson's disease were treated with the 8-alpha-ergoline derivative mesulergine. Participants were divided into two groups, and over a nine-week period, mesulergine dosage was increased to a maximum of either 10 or 20 mg daily. During this time levodopa-carbidopa (LD-CD) dosage was reduced and treatment was discontinued if possible. The dosage of LD-CD was reduced 75% in the 10 mg group and 74% in the 20 mg group. Patients in the low-dose group maintained their functional status and showed improvement in postural stability. Patients in the high-dose group showed improvement in each of the cardinal signs of parkinsonism. Adverse effects were generally mild and infrequent. Many adverse effects induced by LD-CD diminished or resolved. Our results suggest that mesulergine can be valuable in the management of Parkinson's disease, particularly in those individuals experiencing dose-limiting adverse effects from LD-CD.

Topics: Aged; Antiparkinson Agents; Clinical Trials as Topic; Double-Blind Method; Ergolines; Female; Humans; Male; Middle Aged; Parkinson Disease; Random Allocation

Previous studies with mesulergine (CU 32-085) demonstrated safety and efficacy in short-term observations of patients with Parkinson's disease. We compared mesulergine with bromocriptine in 20 patients with Parkinson's disease. Eighteen patients completed the randomized, double-blind, crossover study. Clinical assessments employed the UBC scale and "Mini-Mental State" examination; neurophysiologic measurements were undertaken on wrist rigidity and speed and accuracy of hand movement, and toxicity screening tests were compared. There were no significant differences between the effects of mesulergine (mean dosage, 27.4 mg/d) and bromocriptine (mean dosage, 40.8 mg/d).

Topics: Adult; Aged; Bromocriptine; Clinical Trials as Topic; Ergolines; Female; Humans; Male; Middle Aged; Movement; Nervous System; Parkinson Disease

CU 38085 (mesulergin) was given at doses ranging from 0.5 to 5 mg/day to 37 patients with pathological hyperprolactinaemia of varying aetiology. The effectiveness of this drug on the suppression of hyperprolactinaemia and on the recovery of gonadal functions was equivalent to that of bromocriptine previously given to a different group of 83 hyperprolactinaemic patients. Tumour shrinkage during treatment with CU 32085 was ascertained in two cases of macroprolactinoma. Histological examination after adenomectomy revealed extensive peri-vascular fibrosis in both cases. In most patients, the efficient doses of CU 32085 were 5-fold lower than those of bromocriptine. After acute oral administration in 10 previously untreated patients, 0.5 mg of CU 32085 had a more prolonged suppressive effect on Prl levels than 2.5 mg of bromocriptine (approximately 18 vs 12 h). According to this, 0.5 mg CU 32085 once a day was sufficient to maintain Prl levels within the normal range in 16 patients. Side-effects were similar in nature and frequency to those induced by bromocriptine and seemed to be dose-dependent. They can be avoided by slowly increases of dose at initiation of treatment.

Topics: Administration, Oral; Adolescent; Adult; Aged; Bromocriptine; Clinical Trials as Topic; Ergolines; Female; Gonads; Humans; Hyperprolactinemia; Male; Middle Aged; Pituitary Gland; Pituitary Neoplasms; Prolactin; Receptors, Dopamine; Tomography, X-Ray Computed

24 levodopa pretreated patients with advanced parkinsonism were split into two equal groups receiving mesulergine or bromocriptine respectively as an adjuvant therapy. The trial was carried out under double blind conditions the first three months and then continued as an open trial for one year. Clinical benefit was similar in both groups with minor differences in regard to single symptoms. While bromocriptine showed a beginning decline in efficacy after one year, mesulergine showed no decline. The mean mesulergine-dose, necessary to achieve good clinical improvement, was about half of bromocriptine. Side-effects were similar, except orthostatic hypotension requiring vasopressor medication, which was less frequent in mesulergine treated patients. This advantage of mesulergine might be explained by its special pharmacological pattern with biphasic action on dopaminergic receptors.

Topics: Adult; Aged; Blood Pressure; Bromocriptine; Drug Administration Schedule; Ergolines; Female; Heart Rate; Humans; Levodopa; Male; Middle Aged; Parkinson Disease; Time Factors

Two alpha-aminoergolines with different dopaminergic effects in rats were tried in two groups of Parkinson patients. CQ 32-084 was given in increasing doses up to 10 mg a day for 4 weeks to 10 Parkinson patients, 6 untreated cases and 4 cases with long-term levodopa treatment problems. The patients were checked every week by the Webster rating scale. All patients improved more or less, the earlier untreated patients more than the levodopa-treated patients. Most patients stopped at a dose of 15 mg a day. The side effects were slight. Another group of 10 patients with long-term levodopa treatment problems or insufficient effect of actual treatment were treated in a double-blind crossover trial with another ergoline derivative, CU 32-085. The dose was increased as in the first experiment up to 20 mg a day. Seven of the patients improved during the active drug period. In three cases, the hyperkinesia was increased during the active period, and in two cases it improved. Three patients found an obvious antidepressive effect during the active drug period. Five patients indicated slight decrease of on/off phenomena during the active period of treatment. A more extensive examination of these drugs seems indicated.

Topics: Adult; Aged; Blood Pressure; Clinical Trials as Topic; Disability Evaluation; Ergolines; Female; Humans; Male; Middle Aged; Parkinson Disease; Pilot Projects

Bromocriptine (CB-154) and the 8-alpha-ergoline CU 32-085, two dopamine receptor agonists, were administered at different times to two series of 22 patients with Parkinson's disease, most of whom took levodopa (plus benserazide) at optimum dosage. The addition of bromocriptine (mean daily dose 32 mg; after 6 months 40 mg) led to a 38.5% reduction of levodopa, while CU 32-085 (mean daily dose 15.2 mg; after 6 months 17.5 mg) permitted a 33.7% reduction in levodopa. The mean dose in two patients on CU 32-085 monotherapy was 55 mg/day. A total of 15 patients tolerated adequate doses of bromocriptine (5-75 mg/day, mean duration of treatment 7.5 months) and 15 patients long-term treatment up to 14 months with CU 32-085 (dose range 1-60 mg/day; mean duration 8.8 months). Both groups showed a significant improvement of "total disability score' at 6 months by 56% and 67%, respectively, and after 6 months by 69% and 69.4%, respectively, with a significant decrease of all types of disability. All patients with fluctuations and "on-off' effects rapidly improved on both compounds. Bromocriptine and CU 32-085 were discontinued in seven patients each (32%) because of adverse effect including mental changes (for with bromocriptine, two with CU 32-085), nausea and vomiting (one and two, respectively), hypotension (one each) and increased tremor plus vomiting (one with CU 32-085). Although adverse effects were similar to those observed with levodopa, CU 32-085 in general showed less severe dyskinesia and mental changes but more frequent nausea than bromocriptine and levodopa. While the results of treatment with bromocriptine and CU 32-085 were comparable, the antitremor effect of the latter drug developed more rapidly, even at low dosage. Both compounds were useful in the management of patients with advanced Parkinson's disease, CU 32-085 having a stronger effect on tremor, bradykinesia, fluctuations and "on-off' effects than bromocriptine.

Topics: Aged; Bromocriptine; Clinical Trials as Topic; Dose-Response Relationship, Drug; Drug Therapy, Combination; Ergolines; Female; Humans; Levodopa; Male; Middle Aged; Parkinson Disease; Receptors, Dopamine

The allosteric regulation of G protein-coupled receptors (GPCRs) is a well-known phenomenon, but there are only a few examples of allosteric modulation within the metabotropic serotonergic receptor family. Recently, we described zinc non-competitive interactions toward agonist binding at serotonin 5-HT

Topics: Allosteric Regulation; Cell Death; Cell Survival; Cyclic AMP; Ergolines; HEK293 Cells; Humans; Ions; Kinetics; Ligands; Phenols; Receptors, Serotonin; Sulfonamides; Zinc

Classically, ligands of GPCRs have been classified primarily upon their affinity and efficacy to activate a signal transduction pathway. Recent reports indicate that the efficacy of a particular ligand can vary depending on the receptor-mediated response measured (e.g. activating G proteins, other downstream responses, internalization). Previously, we reported that inverse agonists induce both homo- and heterologous desensitization, similar to agonist stimulation, at the Gs -coupled 5-HT7 receptor. The primary objective of this study was to determine whether different inverse agonists at the 5-HT7 receptor also induce internalization and/or degradation of 5-HT7 receptors.. HEK293 cells expressing 5-HT7(a, b or d) receptors were pre-incubated with 5-HT, clozapine, olanzapine, mesulergine or SB269970 and their effects upon receptor density, AC activity, internalization, recruitment of β-arrestins and lysosomal trafficking were measured.. The agonist 5-HT and three out of four inverse agonists tested increased internalization independently of β-arrestin recruitment. Among these, only the atypical antipsychotics clozapine and olanzapine promoted lysosomal sorting and reduced 5-HT7 receptor density (∼60% reduction within 24 h). Inhibition of lysosomal degradation with chloroquine blocked the clozapine- and olanzapine-induced down-regulation of 5-HT7 receptors. Incubation with SB269970 decreased both 5-HT7(b) constitutive internalization and receptor density but increased 5-HT7(d) receptor density, indicating differential ligand regulation among the 5-HT7 splice variants.. Taken together, we found that various ligands differentially activate regulatory processes governing receptor internalization and degradation in addition to signal transduction. Thus, these data extend our understanding of functional selectivity at the 5-HT7 receptor.

Topics: Antipsychotic Agents; Arrestins; Benzodiazepines; beta-Arrestins; Cells, Cultured; Chloroquine; Clozapine; Down-Regulation; Drug Inverse Agonism; Ergolines; HEK293 Cells; Humans; Ligands; Lysosomes; Olanzapine; Phenols; Radioligand Assay; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Signal Transduction; Sulfonamides

Neurotensin-like peptides acting as functional antagonists of serotonin receptors were revealed in the head-shaking test on mice. The neurotensin-like peptides block the serotonin-induced platelet aggregation in humans. Radioligand binding assay showed that neurotensin-like peptides modulate specifi c binding of 5НТ2 serotonin receptor antagonist ketanserin, but have no effect on binding of ligands of 5HT2c receptor mesulergine and 5HT1а receptors NAN-190. Similar effects of neurotensin-like peptides in the experiments in vivo and in vitro suggest that the mechanisms of the detected antipsychotic effect of the peptides can be mediated by serotonin receptors.

Topics: Animals; Antipsychotic Agents; Cell Membrane; Ergolines; Frontal Lobe; Ketanserin; Male; Mice; Neurotensin; Oligopeptides; Piperazines; Platelet Aggregation; Radioligand Assay; Rats; Serotonin; Serotonin Antagonists; Statistics, Nonparametric

Desired serotonin 5HT2 receptor pharmacology for treatment of psychoses is 5HT2A antagonism and/or 5HT2C agonism. No selective 5HT2A antagonist has been approved for psychosis and the only approved 5HT2C agonist (for obesity) also activates 5HT2A and 5HT2B receptors, which can lead to clinical complications. Studies herein tested the hypothesis that a dual-function 5HT2A antagonist/5HT2C agonist that does not activate 5HT2B receptors would be suitable for development as an antipsychotic drug, without liability for weight gain.. The novel compounds (+)- and (-)-trans-4-(4'-chlorophenyl)-N,N-dimethyl-2-aminotetralin (p-Cl-PAT) were synthesized, characterized in vitro for affinity and functional activity at human 5HT2 receptors, and administered by intraperitoneal (i.p.) and oral (gavage) routes to mice in behavioral paradigms that assessed antipsychotic efficacy and effects on feeding behavior.. (+)- and (-)-p-Cl-PAT activated 5HT2C receptors, with (+)-p-Cl-PAT being 12-times more potent, consistent with its higher affinity across 5HT2 receptors. Neither p-Cl-PAT enantiomer activated 5HT2A or 5HT2B receptors at concentrations up to 300-times greater than their respective affinity (Ki), and (+)-p-Cl-PAT was shown to be a 5HT2A competitive antagonist. When administered i.p. or orally, (+)- and (-)-p-Cl-PAT attenuated the head-twitch response (HTR) in mice elicited by the 5HT2 agonist (-)-2,5-dimethoxy-4-iodoamphetamine (DOI) and reduced intake of a highly palatable food in non-food-deprived mice, with (+)-p-Cl-PAT being more potent across behavioral assays.. The novel in vitro pharmacology of (+)-p-Cl-PAT (5HT2A antagonism/5HT2C agonism without activation of 5HT2B) translated in vivo to an orally-active drug candidate with preclinical efficacy to treat psychoses without liability for weight gain.

Topics: Amphetamines; Animals; Antipsychotic Agents; Cell Line, Transformed; Dose-Response Relationship, Drug; Ergolines; Food Preferences; Glycolates; Head Movements; Humans; Ketanserin; Mice; Mice, Inbred C57BL; Motor Activity; Protein Binding; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2B; Serotonin Antagonists; Serotonin Receptor Agonists; Tritium

Earlier autoradiographic studies with the 5-HT2 receptor agonist [(125)I](±)DOI in human brain showed unexpected biphasic competition curves for various 5-HT2A antagonists. We have performed similar studies in rat brain regions with selective 5-HT2A (M100907) and 5-HT2C (SB242084) antagonists together with ketanserin and mesulergine. The effect of GTP analogues on antagonist competition was also studied. Increasing concentrations of Gpp(NH)p or GTPγS resulted in a maximal inhibition of [(125)I](±)DOI-specific binding of approximately 50 %. M100907 competed biphasically in all regions. In the presence of 100 μM Gpp(NH)p, M100907 still displaced biphasically the remaining [(125)I](±)DOI binding. Ketanserin showed biphasic curves in some regions and monophasic curves in others. In the latter, Gpp(NH)p evidenced an additional high-affinity site. SB242084 competed biphasically in brainstem nuclei and monophasically in the other regions. In most areas, SB242084 affinities were not notably altered by Gpp(NH)p. Mesulergine competed monophasically in all regions without alteration by Gpp(NH)p. These results conform with the extended ternary complex model of receptor action: receptor exists as an equilibrium of multiple conformations, i.e. ground (R), partly activated (R*) and activated G-protein-coupled (R*G) conformation/s. Thus, [(125)I](±)DOI would label multiple conformations of both 5-HT2A and 5-HT2C receptors in rat brain, and M100907 and ketanserin would recognise these conformations with different affinities.

Topics: Aminopyridines; Animals; Autoradiography; Brain; Ergolines; Indoles; Ketanserin; Male; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Serotonin

To determine the effect of non-selective 5-HT2C antagonist mesulergine and 5-HT2C agonist mCPP (metachlorophenylpiperazine) on learning acquisition (LA), short-term memory (STM) and long-term memory (LTM).. Experimental study.. Department of Biochemistry, University of Karachi, from December 2009 to June 2010.. Twenty-four male albino Wistar rats were used in this study. The agonist and antagonist (mCPP and mesulergine) were injected intraperitoneally at a dose 3.0 mg/kg in volumes of 1 ml/kg. Control animals were injected with saline (1 ml/kg). Animals were randomly divided into four groups (n=6). 1st being control group, 2nd being mCPP injected group, 3rd being mesulergine injected group and 4th group being injected with both mesulergine and mCPP. Behavioural activities of rats were monitored after 30 minutes of injection. For assessment of memory functions, water maze apparatus was used.. Administration of mCPP impaired STM, LTM and LA of rats. Mesulergine injected rats exhibited no alteration in memory functions. However, when it was injected with mCPP then there were no memory deficits induced by mCPP.. Ability of 5-HT2C receptor antagonist mesulergine to block the memory impairment effect of mCPP indicated an important regulatory role of 5-HT2C receptors in cognitive processes.

Topics: Analysis of Variance; Animals; Behavior, Animal; Disease Models, Animal; Ergolines; Male; Maze Learning; Memory Disorders; Memory, Long-Term; Memory, Short-Term; Piperazines; Random Allocation; Rats; Rats, Wistar; Serotonin 5-HT2 Receptor Agonists; Serotonin 5-HT2 Receptor Antagonists

A series of substituted 4-arylpiperidines and a smaller family of 4-aryl-1,2,3,6-tetrahydropyridines were synthesized and their biological activity at the 5-HT(2C) receptor studied to determine whether either series showed noteworthy agonist activity. Structure-activity relationships were developed from the performed receptor binding assays and functional studies, and the results of the analysis are presented herein.

Topics: Animals; Appetite Depressants; Calcium; Ergolines; Humans; Kinetics; Piperidines; Protein Binding; Pyridines; Radioligand Assay; Receptor, Serotonin, 5-HT2C; Serotonin 5-HT2 Receptor Agonists; Serotonin Antagonists; Stereoisomerism; Structure-Activity Relationship

The 5-hydroxytryptamine 2C (5-HT(2C)) receptor has a single nucleotide polymorphism (SNP) site at amino acid position 23 in its N-terminal tail. The polymorphism involves conversion of a cysteine to serine. The site, designated C23S, is located within a 32 amino acid long predicted signal peptide. The aim of the present study was to investigate whether the 5-HT(2C) receptor indeed has a functional cleavable signal peptide. For this purpose, ten N-terminally modified 5-HT(2C) receptors were constructed. Modifications included addition of the influenza virus hemagglutinin signal peptide, addition of a FLAG epitope, truncation of the N-terminal tail, and combinations of these changes. The receptors were transiently expressed in COS-7 cells. The relative amounts of receptors expressed at the membranes were quantified by [(3)H]-mesulergine radioligand binding. In one of the receptor constructs the FLAG epitope was inserted just after the endogenous putative signal peptide. Immunostaining with the M1 antibody, which recognizes the FLAG epitope only as free N-terminal entity, was used to detect whether the putative signal peptide preceding the FLAG epitope was cleaved off. The results suggest the following conclusions. The predicted signal peptide in the N-terminal tail of the 5-HT(2C) receptor acts as a cleavable signal peptide. Cleaving of the signal peptide is important for translocation of the wild type receptor to the plasma membrane. The two amino acids differentially encoded by the C23S SNP are likely absent from the mature 5-HT(2C) receptor.

Topics: Amino Acid Sequence; Animals; Cell Membrane; Chlorocebus aethiops; COS Cells; Ergolines; Gene Expression Regulation; Humans; Molecular Sequence Data; Polymorphism, Single Nucleotide; Protein Sorting Signals; Protein Structure, Secondary; Proteolysis; Receptor, Serotonin, 5-HT2C; Transfection

Although haloperidol is widely prescribed for the treatment of schizophrenia, its beneficial effects are accompanied by extrapyramidal side effects (EPS). Role of 5-HT-2A/2C receptors in the attenuation of acute Parkinsonian-like effects of typical antipsychotics is investigated by prior administration of mianserin and mesulergine to rats injected with haloperidol. In the first part of study effects of various doses of haloperidol (0.5, 1.0, 2.5 and 5.0 mg/kg) were determined on motor activity and a selected dose (1 mg/kg) was used to monitor attenuation of parkinsonian effects by two different doses of 5-HT-2A/2C receptor antagonists mianserin (2.5 & 5.0 mg/kg) and mesulergine (1.0 & 3.0 mg/kg). Rats treated with haloperidol at doses of 0.5-5.0 mg/kg exhibited impaired motor coordination and a decrease in exploratory activity in an open field. The dose response curve showed that at a dose of 1 mg/kg significant and submaximal effects are produced on motor coordination and exploratory activity. Coadministration of mianserin and mesulergine attenuated and reversed haloperidol-induced motor deficits in a dose dependent manner. The mechanism involved in the attenuation / reversal of haloperidol-induced parkinsonian like symptoms by mianserin and mesulergine is discussed. Prior administration of mianserin or mesulergine may be of use in the alleviation of EPS induced by conventional antipsychotic drugs.The findings have potential implication in the treatment of schizophrenia and motor disorders.

Topics: Animals; Antipsychotic Agents; Catalepsy; Dopamine Agonists; Dyskinesia, Drug-Induced; Ergolines; Haloperidol; Male; Mianserin; Motor Activity; Parkinson Disease, Secondary; Psychomotor Performance; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Selective Serotonin Reuptake Inhibitors

The aim of this study was to analyze functional properties of the naturally occurring C23S variant of the human 5-HT2C receptor. In HEK293 cells transiently expressing the unedited forms of the variant receptor (VR) or the wild-type receptor (WTR), surface expression was determined by [3H]mesulergine binding to membrane fragments. Function was examined by an aequorin luminescence-based Ca2+ assay. Surface expression of the VR was 116% of that of the WTR. The 5-HT-induced increase in cytosolic Ca2+ ([Ca2+]i), and its inhibition by the inverse agonist SB 206553 did not differ between VR- or WTR-expressing cells. Preexposure of VR- or WTR-expressing cells to 0.5 μM 5-HT (3 min-4.5 h) led to a practically identical time course and extent in the reduction of the 5-HT-induced increase in [Ca2+]i. In contrast, prolonged preexposure to the inverse agonist SB 206553 (1 μM) elevated the 5-HT-induced increase in [Ca2+]i for both isoreceptors. A preexposure time of 4.5 h was necessary to significantly elevate the Ca2+ response of the WTR, but the VR produced this elevation within 1 h with virtually no further effect after 4.5 h of preexposure. In conclusion, prolonged preexposure to 5-HT caused equally rapid and strong desensitization of both isoreceptors. The different time course of SB 206553-induced resensitization of the two isoreceptors might be therapeutically relevant for drugs exhibiting inverse agonist properties at 5-HT2C receptors, such as atypical antipsychotics and certain antidepressants.

Topics: Adult; Aequorin; Base Sequence; Calcium; DNA, Complementary; Drug Inverse Agonism; Ergolines; HEK293 Cells; Humans; Indoles; Luminescent Measurements; Protein Binding; Pyridines; Receptor, Serotonin, 5-HT2C; Serotonin; Serotonin Antagonists; Time Factors

Abnormalities in both the hippocampal region and in serotonergic transmission are evident in patients with schizophrenia. We previously found that rats with serotonergic lesions targeting the dorsal hippocampus show altered psychotropic drug-induced hyperlocomotion and prepulse inhibition (PPI), behavioural paradigms relevant to aspects of schizophrenia. The present study explored the effect of serotonin depletion (>70%) along the dorsoventral axis of the hippocampus, or of partial serotonin depletion (∼50%) in the ventral hippocampus, on PPI modulation by acute antipsychotic drug treatment. We also used receptor binding autoradiography to investigate the neurochemical basis of behavioural effects. Following micro-injection of 5,7-dihydroxytryptamine, neither hippocampal serotonin depletion or partial serotonin depletion in the ventral hippocampus altered baseline PPI, startle magnitude or startle habituation. Acute treatment with clozapine or haloperidol had minimal effects on PPI in these lesioned rats or sham-operated controls. In contrast, risperidone treatment increased PPI to a significantly greater extent in rats with hippocampal serotonin depletion, an effect which was most prominent at low prepulse intensities. Partial serotonin depletion in the ventral hippocampus did not alter PPI modulation by risperidone. Neither type of serotonergic lesion altered the densities of 5-HT(1A) or 5-HT(2A) receptors in the hippocampus; serotonin transporters or 5-HT(1A) autoreceptors on raphe cell bodies; or dopamine transporters, D(1) or D(2) receptors in forebrain regions efferent to the hippocampus and implicated in schizophrenia, such as the nucleus accumbens. However, levels of [(3)H]mesulergine binding to 5-HT(2C) receptors were increased by approximately 70% in the dorsal hippocampus of rats with serotonin depletion in this region, while those in the ventral hippocampus were unaffected. Therefore, despite intact baseline PPI, abnormal PPI regulation in rats with >70% serotonin depletion in the hippocampus was unmasked by acute risperidone treatment. Selective upregulation of 5-HT(2C) receptors in the dorsal, but not ventral, hippocampus of these lesioned rats suggests that hippocampal 5-HT(2C) receptors vary in their adaptability to changes in serotonergic tone along the dorsoventral axis. These findings suggest that 5-HT(2C) receptors in the dorsal hippocampus may contribute to risperidone-induced enhancement of PPI.

Topics: Animals; Antipsychotic Agents; Behavior, Animal; Ergolines; Hippocampus; Male; Nerve Tissue Proteins; Neural Inhibition; Neurons; Organ Specificity; Random Allocation; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2C; Reflex, Startle; Risperidone; Schizophrenia; Serotonin; Serotonin 5-HT2 Receptor Antagonists; Serotonin Antagonists

Emotional disturbances, depressive mood, anxiety, aggressive behavior, and memory impairment are the common psychiatric features associated with temporal lobe epilepsy (TLE). The present study was carried out to investigate the role of Bacopa monnieri extract in hippocampus of pilocarpine-induced temporal lobe epileptic rats through the 5-HT(2C) receptor in relation to depression. Our results showed upregulation of 5-HT(2C) receptors with a decreased affinity in hippocampus of pilocarpine-induced epileptic rats. Also, there was an increase in 5-HT(2C) gene expression and inositol triphosphate content in epileptic hippocampus. Carbamazepine and B. monnieri treatments reversed the alterations in 5-HT(2C) receptor binding, gene expression, and inositol triphosphate content in treated epileptic rats as compared to untreated epileptic rats. The forced swim test confirmed the depressive behavior pattern during epilepsy that was nearly completely reversed by B. monnieri treatment.

Topics: Animals; Anticonvulsants; Bacopa; Carbamazepine; Disease Models, Animal; Epilepsy; Ergolines; Hippocampus; Inositol 1,4,5-Trisphosphate; Male; Pilocarpine; Plant Preparations; Protein Binding; Radioligand Assay; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2C; Serotonin Antagonists; Statistics, Nonparametric; Swimming; Tritium; Up-Regulation

Aminomethyl tetrahydronaphthalene biphenyl carboxamide MCH-R1 antagonists with greater selectivity over hERG were identified. SAR studies addressing two distinct alternatives for structural modifications leading to improve hERG selectivity are described.

Topics: Biphenyl Compounds; ERG1 Potassium Channel; Ergolines; Ether-A-Go-Go Potassium Channels; Humans; Indicators and Reagents; Mianserin; Naphthalenes; Potassium Channel Blockers; Receptor, Serotonin, 5-HT2C; Receptors, Somatostatin; Serotonin Antagonists; Structure-Activity Relationship

1. In the present study, we investigated how alloxan-induced diabetes affects the ability of 5-hydroxytryptamine (5-HT) to modulate bradycardia induced in vivo by electrical stimulation of the vagus nerve in pithed rats. We also analysed the type and/or subtype of 5-HT receptors involved. 2. Diabetes was induced in male Wistar rats with a single injection of alloxan (150 mg/kg, s.c.). Four weeks later, rats were anaesthetized, pretreated with atenolol and pithed. Electrical stimulation (3, 6 and 9 Hz) of the vagus nerve resulted in frequency dependent decreases in heart rate (HR). 3. In diabetic rats, intravenous bolus administration of high doses of 5-HT (100 and 200 microg/kg) increased the bradycardia induced by vagal electrical stimulation. Similarly, low doses (10 microg/kg) of the 5-HT(1/7) receptor agonist 5-carboxamidotryptamine (5-CT), increased vagally induced bradycardia. However, at high doses (50, 100 and 150 microg/kg), 5-CT reduced the bradycardia. Attenuation of the vagally induced bradycardia evoked by the higher doses of 5-CT was reproduced by L-694,247 (50 microg/kg), a selective agonist for the non-rodent 5-HT(1B) and 5-HT(1D) receptors. Enhancement of the vagally induced bradycardia elicited by low doses of 5-CT was reproduced by the selective 5-HT(1A) receptor agonist 8-hydroxydipropylaminotretalin hydrobromide (8-OH-DPAT; 50 microg/kg). These stimulatory and inhibitory actions on vagal stimulation-induced bradycardia in diabetic rats were also observed after administration of exogenous acetylcholine. 4. Vagally induced bradycardia in diabetic rats was not affected by administration of the selective 5-HT(2) receptor agonist alpha-methyl-5-HT (150 microg/kg), the selective 5-HT(3) receptor agonist 1-phenylbiguanide (150 microg/kg) or the selective 5-HT(1B) receptor agonist CGS-12066B (50 microg/kg). 5. Enhancement of the electrical stimulation-induced bradycardia in diabetic rats caused by 5-CT (10 microg/kg) or 8-OH-DPAT (50 microg/kg) was abolished by the selective 5-HT(2/7) receptor antagonist mesulergine (1 mg/kg) and the selective 5-HT(1A) receptor antagonist WAY-100,635 (100 microg/kg), respectively. Similarly, pretreatment with the non-selective 5-HT(1) receptor antagonist methiothepin (0.1 mg/kg) blocked the inhibitory effect of 5-CT (50 microg/kg) on the bradycardia induced by vagal electrical stimulation in diabetic rats. BRL-15572 (2 microg/kg), a selective 5-HT(1D) receptor antagonist, inhibited the action of L-694,247 (50

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Acetylcholine; Animals; Biphenyl Compounds; Blood Glucose; Bradycardia; Cholinergic Agents; Diabetes Mellitus, Experimental; Dose-Response Relationship, Drug; Electric Stimulation; Ergolines; Heart; Heart Rate; Injections, Intravenous; Male; Methiothepin; Oxadiazoles; Piperazines; Pyridines; Rats; Rats, Wistar; Receptors, Serotonin, 5-HT1; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tryptamines; Vagus Nerve

Although it has been well established that compounds that stimulate 5-HT(2C) and/or 5-HT(1B) receptors induce hypophagia by promoting satiety process, the relative role of these receptor subtypes in dietary choices remains to be fully determined. m-CPP is considered a useful probe of 5-HT(2C) receptor function in vivo and its administration reduces food intake and appetite in humans and rats. Conversely, the non-selective 5-HT(2C) receptor antagonist mesulergine elicits feeding in rats. Food intake and dietary choices were measured in a food-deprivation experimental protocol employing male Wistar rats. Animals were given access for a 4-h period to a pair of isocaloric diets. These two diets were enriched in protein or carbohydrate proportions, respectively, but fat content was held constant. The mixed 5-HT(2C/1B) receptor agonist, m-CPP, led to a dose-dependent hypophagia, due to substantial reduction in carbohydrate consumption while protein intake was spared (0.62, 1.25 and 2.50 mg/kg i.p., respectively). The non-selective 5-HT(2C) receptor antagonist and also D2 agonist, mesulergine, on its own produced a significant dose-dependent increase in both protein and carbohydrate diets (1.0 and 3.0 mg/kg i.p., respectively). Combined treatment with m-CPP, at its maximum effective dose, and mesulergine dose-dependently reversed m-CPP-induced hypophagia, during the 4-h test period. In order to clarify the effects of mesulergine on dietary choices since it is simultaneously a dopamine agonist besides its antiserotonergic properties, the D2 agonist apomorphine was also used. Apomorphine caused a dose-dependent increase in protein intake while carbohydrate and total food intake remained nearly unchanged (0.5 and 1.0 mg/kg i.p., respectively). It is concluded that the mesulergine-induced hyperphagic response on both diets is the expression of a dual mode of action, due to its 5-HT(2C) antagonist activity together with D2 agonist properties. The results further indicate that the activation of hypothalamic 5-HT(2C) receptors may be involved in both protein sparing and carbohydrate suppressing effects of 5-HT (m-CPP-like effect), whereas an important role in increase of protein consumption seems to have the dopaminergic system probably through D2 receptors (apomorphine-like and mesulergine-like effects, respectively).

Topics: Animals; Apomorphine; Behavior, Animal; Choice Behavior; Diet; Dopamine Agonists; Dose-Response Relationship, Drug; Eating; Ergolines; Food Deprivation; Male; Piperazines; Rats; Rats, Wistar; Serotonin Antagonists; Serotonin Receptor Agonists

5-HT receptors are predominantly located in the brain and are involved in pancreatic function and cell proliferation through sympathetic nervous system. The objective of this study was to investigate the role of hypothalamic 5-HT, 5-HT1A and 5-HT2C receptor binding and gene expression in rat model of pancreatic regeneration using 60% pancreatectomy. The pancreatic regeneration was evaluated by 5-HT content, 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus of sham operated, 72 h and 7 days pancreatectomised rats. 5-HT content was quantified by HPLC. 5-HT1A receptor assay was done by using specific agonist [3H]8-OH DPAT. 5-HT2C receptor assay was done by using specific antagonist [3H]mesulergine. The expression of 5-HT1A and 5-HT2C receptor gene was analyzed by RT-PCR. 5-HT content was higher in the hypothalamus of 72 h pancreatectomised rats. 5-HT1A and 5-HT2C receptors were down-regulated in the hypothalamus. RT-PCR analysis revealed decreased 5-HT1A and 5-HT2C receptor mRNA expression. The 5-HT1A and 5-HT2C receptors gene expression in the 7 days pancreatectomised rats reversed to near sham level. This study is the first to identify 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus during pancreatic regeneration in rats. Our results suggest the hypothalamic serotonergic receptor functional regulation during pancreatic regeneration.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Binding, Competitive; Down-Regulation; Ergolines; Gene Expression Regulation, Developmental; Hypothalamus; Male; Pancreas; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT1A; Receptor, Serotonin, 5-HT2C; Regeneration; Serotonin; Serotonin 5-HT1 Receptor Agonists; Serotonin 5-HT2 Receptor Antagonists; Serotonin Antagonists; Serotonin Receptor Agonists

We wanted to elucidate whether the proposed advantages of citalopram-buspirone combination treatment are related to changes in 5-HT(2A/C) receptor-mediated neurotransmission.. The affinity of buspirone to 5-HT2A and 5-HT2C receptors was measured in vitro, and the influence of buspirone on 5-HT2C receptor-mediated phosphoinositide hydrolysis was estimated. Four groups of rats received citalopram (10 mg/kg), buspirone (6 mg/kg), citalopram-buspirone combination, or saline once a day s.c. for 14 days. Treatment effects on 5-HT2A and 5-HT2C receptors were investigated by receptor autoradiography with antagonist and agonist radioligands.. Buspirone was found to be a weak 5-HT2C receptor antagonist, with a low affinity for 5-HT2A and 5-HT2C receptors. Repeated buspirone-citalopram combination treatment markedly decreased [3H]ketanserin and [125I]DOI binding to 5-HT2A receptors. Repeated administration of buspirone and buspirone-citalopram combination increased the affinity of [3H]mesulergine toward 5-HT2C receptors, and buspirone-citalopram combination also decreased [125I]DOI binding to 5-HT2C receptors.. We suggest that downregulation of brain 5-HT2A receptors and possibly of 5-HT2C receptor agonist sites is involved in the beneficial clinical effects of buspirone-SSRI augmentation treatment. Furthermore, a conversion of brain 5-HT2C receptors from high- to low-affinity state may provide an additional mechanism for the anti-anxiety effects of buspirone.

Topics: Amphetamines; Animals; Anti-Anxiety Agents; Antidepressive Agents; Autoradiography; Brain Chemistry; Buspirone; Cerebral Cortex; Choroid Plexus; Citalopram; Ergolines; Hydrolysis; Image Processing, Computer-Assisted; Ketanserin; Male; Phosphatidylinositols; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Serotonin Antagonists

Previously, we demonstrated that human serotonin (5-HT) 5-HT(7) receptors display marked constitutive activity. Here, we tested if the constitutive activation of adenylyl cyclase by 5-HT(7) receptors influenced both the desensitization properties of transfected 5-HT(7) receptors and the ability of endogenous G(s)-coupled receptors to activate adenylyl cyclase. Using membranes from stably transfected HEK293 cells expressing the recombinant human 5-HT(7) receptor splice variants (5-HT(7(a)), 5-HT(7(b)) and 5-HT(7(d))), we compared the effects of 1-h or 24-h preincubation of the agonist 5-HT, partial inverse agonists mesulergine and SB269970, and full inverse agonists clozapine and methiothepin on subsequent activation of adenylyl cyclase by both 5-HT through transfected 5-HT(7) receptors and the endogenous G(s)-coupled beta-adrenoceptors and prostaglandin receptors of HEK293 cells. The data show that stable expression of 5-HT(7) receptors is sufficient to attenuate adenylyl cyclase activation by endogenous G(s)-coupled receptors. Interestingly, preincubation with inverse agonists not only failed to result in the predicted resensitization of all receptor mediated adenylyl cyclase activation, but some inverse agonists further attenuated (desensitized) beta-adrenoceptor and prostaglandin-stimulated adenylyl cyclase activation similar to long-term agonist exposure by 5-HT. These effects were not correlated with inverse agonist efficacy, were not accompanied by receptor down-regulation and appear to be mediated by a protein kinase A (PKA) independent mechanism. It is concluded that the human 5-HT(7) receptor mediates heterologous desensitization of endogenous G(s)-coupled receptors through an unknown and potentially novel mechanism.

Topics: Adenylyl Cyclases; Alternative Splicing; Binding, Competitive; Cell Line; Cell Membrane; Clozapine; Colforsin; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Enzyme Activation; Ergolines; Gene Expression; Humans; Isoproterenol; Isoquinolines; Methiothepin; Multivariate Analysis; Phenols; Protein Isoforms; Protein Kinase Inhibitors; Radioligand Assay; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Sulfonamides; Time Factors; Tritium

The aim of this study was to examine the influence of different fat diets on serotonin receptor and transporter binding. Male Sprague-Dawley rats were fed a diet of either high saturated fat, omega-6 polyunsaturated fatty acid, omega-3 polyunsaturated fatty acid or low fat (control) for eight weeks. Using Beta-Imager quantification techniques, [(3)H]ketanserin, [(3)H]mesulergine and [(3)H]paroxetine binding to serotonin (5-HT)(2A), 5-HT(2C) receptors and 5-HT transporters (5-HTT) was measured throughout the brain in all four groups. All three high fatty acid diets influenced serotonin receptor binding, however the most pronounced effects were that compared with the low fat control group, i) 5-HT(2A) receptor binding was increased in the caudate putamen, but reduced in the mammillary nucleus in high saturated fat and high omega-6 polyunsaturated fatty acid diet groups; ii) 5-HT(2C) receptor binding was reduced in the mamillary nucleus of saturated fat group and reduced in prefrontal cortex of the omega-6 polyunsaturated fatty acid and omega-3 polyunsaturated fatty acid groups; and iii) 5-HTT binding was reduced in the hippocampus in the omega-6 polyunsaturated fatty acid group. Overall, the omega-6 polyunsaturated fatty acid diet exerted the most influence on serotonin receptor and transporter binding. These results may be of importance in relation to neuropsychiatric diseases such as schizophrenia, where associations between altered fatty acid levels and the serotonergic system have been made.

Topics: Analysis of Variance; Animals; Brain; Ergolines; Fatty Acids; Ketanserin; Male; Paroxetine; Protein Binding; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Selective Serotonin Reuptake Inhibitors; Serotonin Antagonists; Serotonin Plasma Membrane Transport Proteins

Selective serotonin reuptake inhibitors (SSRIs) bind directly to various neurotransmitter receptors. The clinical effects of SSRIs appear gradually during weeks of treatment, suggesting a role for adaptive changes in neurotransmitter receptors. Most clinically used antidepressants, e.g. fluoxetine, bind to 5-HT2C receptors. When administered chronically, many antidepressants elicit adaptive regulation of 5-HT2C receptors. The present study was conducted in order to determine the effects of acute and chronic fluoxetine and citalopram treatments on the density and function of 5-HT2C receptors in the rat choroid plexus. Acute and chronic treatments followed by phosphoinositide (PI) hydrolysis assays and quantitative receptor autoradiography were performed. Acute (single-dose) treatment with neither drug significantly affected basal or 5-HT-stimulated PI hydrolysis, but acute citalopram (20 mg/kg) treatment increased both agonist and antagonist binding to 5-HT(2C) receptors. Chronic (14 days) citalopram treatment (20 mg/kg) increased the maximal PI hydrolysis response by 40%, but fluoxetine lacked this effect. The present data suggest that sensitisation of 5-HT2C receptor-mediated intracellular signal transduction may play a role in the effects of citalopram. In contrast, fluoxetine treatment does not functionally sensitise 5-HT2C receptors. Thus, functional 5-HT2C receptor sensitisation is not a common effect of antidepressants, but the differential effects may explain some of the pharmacodynamic differences seen with these drugs, especially upon repeated administration.

Topics: Amphetamines; Animals; Choroid Plexus; Citalopram; Dose-Response Relationship, Drug; Ergolines; Fluoxetine; Hydrolysis; Inositol Phosphates; Male; Phosphatidylinositols; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2C; Second Messenger Systems; Selective Serotonin Reuptake Inhibitors; Serotonin 5-HT2 Receptor Agonists; Serotonin 5-HT2 Receptor Antagonists

The purpose of this study was to investigate the role of central 5-HT2C receptor binding in rat model of pancreatic regeneration using 60-70% pancreatectomy. The 5-HT and 5-HT2C receptor kinetics were studied in cerebral cortex and brain stem of sham operated, 72 h pancreatectomised and 7 days pancreatectomised rats. Scatchard analysis with [3H] mesulergine in cerebral cortex showed a significant decrease (p < 0.05) in maximal binding (Bmax) without any change in Kd in 72 h pancreatectomised rats compared with sham. The decreased Bmax reversed to sham level by 7 days after pancreatectomy. In brain stem, Scatchard analysis showed a significant decrease (p < 0.01) in Bmax with a significant increase (p < 0.01) in Kd. Competition analysis in brain stem showed a shift in affinity towards a low affinity. These parameters were reversed to sham level by 7 days after pancreatectomy. Thus the results suggest that 5-HT through the 5-HT2C receptor in the brain has a functional regulatory role in the pancreatic regeneration.

Topics: Animals; Binding, Competitive; Brain Stem; Cerebral Cortex; Ergolines; Pancreas; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2C; Regeneration; Serotonin; Serotonin Antagonists

The serotonin (5-hydroxytryptamine) 5-HT2 receptor subfamily consists of three members, 5-HT2A, 5-HT2B, and 5-HT2C. These receptors share high homology in their amino acid sequence, have similar signaling pathways, and have been indicated to play important roles in feeding, anxiety, aggression, sexual behavior, mood, and pain. Subtype-selective agonists and antagonists have been explored as drugs for hypertension, Parkinson's disease, sleep disorders, anxiety, depression, schizophrenia, and obesity. In this study, we report the development of homogeneous agonist binding assays in a scintillation proximity assay (SPA) format to determine the high-affinity binding state of agonist compounds for the human 5-HT2C, 5-HT2A, and 5-HT2B receptors. The 5-HT2 agonist 1-(4- [125I]iodo-2,5-dimethoxyphenyl)-2-aminopropane ([125I]DOI) was used to label the high-affinity sites for the 5-HT2A and 5-HT2C receptors. The high-affinity sites for the 5-HT2B receptor were labeled with [3H]lysergic acid diethylamide. Total receptor expression was determined with the 5-HT2 antagonist [3H]mesulergine for the 5-HT2B and 5-HT2C receptors, and [3H]ketanserin for the 5-HT2A receptor. The agonist high-affinity binding sites accounted for 2.3% (5-HT(2C) receptor), 4.0% (5-HT2A receptor), and 22% (5-HT2B receptor) of the total receptor population. Competition binding studies using known agonists indicated high Z' values of the agonist binding assays in SPA format (Z' > 0.70). The Ki values of 5-HT, (R)(-)DOI, and VER-3323 for the 5-HT2A, 5-HT2B, and 5-HT2C receptors by SPA format were equivalent to published data determined by filtration binding assays. These results indicate that agonist binding assays in SPA format can be easily adapted to a high throughput assay to screen for selective 5-HT2C receptor agonists, as well as for selectivity profiling of the compounds.

Topics: Amphetamines; Binding, Competitive; Calcium Signaling; Cell Line; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Ergolines; Humans; Ketanserin; Lysergic Acid Diethylamide; Radioligand Assay; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2B; Receptor, Serotonin, 5-HT2C; Serotonin; Serotonin 5-HT2 Receptor Agonists; Serotonin Antagonists; Serotonin Receptor Agonists; Transfection

1. The main aim of this investigation was to delineate the distribution of the 5-HT(7) receptor in human brain. Autoradiographic studies in guinea-pig and rat brain were also carried out in order to revisit and compare the anatomical distribution of 5-HT(7) receptors in different mammalian species. 2. Binding studies were performed in rat frontal cortex membranes using 10 nm [(3)H]mesulergine in the presence of raclopride (10 microm) and DOI (0.8 microm). Under these conditions, a binding site with pharmacological characteristics consistent with those of the 5-HT(7) receptors was identified (rank order of binding affinity values: 5-CT>5-HT>5-MeOT>mesulergine approximately methiothepin>8-OH-DPAT=spiperone approximately (+)-butaclamol>>imipramine approximately (+/-)-pindolol>>ondansetron approximately clonidine approximately prazosin). 3. The autoradiographic studies revealed that the anatomical distribution of 5-HT(7) receptors throughout the human brain was heterogenous. High densities were found over the caudate and putamen nuclei, the pyramidal layer of the CA2 field of the hippocampus, the centromedial thalamic nucleus, and the dorsal raphe nucleus. The inner layer of the frontal cortex, the dentate gyrus of the hippocampus, the subthalamic nucleus and superior colliculus, among others, presented intermediate concentrations of 5-HT(7) receptors. A similar brain anatomical distribution of 5-HT(7) receptors was observed in all three mammalian species studied. 4. By using [(3)H]mesulergine, we have mapped for the first time the anatomical distribution of 5-HT(7) receptors in the human brain, overcoming the limitations previously found in radiometric studies with other radioligands, and also revisiting the distribution in guinea-pig and rat brain.

Topics: 5-Methoxytryptamine; Amphetamines; Animals; Autoradiography; Brain; Cerebral Cortex; Corpus Striatum; Ergolines; Guinea Pigs; Humans; Male; Mammals; Radioligand Assay; Radionuclide Imaging; Rats; Rats, Wistar; Receptors, Serotonin; Tritium

The possible role of compensatory changes in 5-HT2C receptors in the reduced hypophagic action of d-fenfluramine in 5-HT1B knockout (KO) mice was assessed by comparing their response to d-fenfluramine and the 5-HT2C receptor agonist mCPP. In addition we measured 5-HT(2C/A) receptor binding in 5-HT1B KO and wild-type (WT) mice and examined the effects of 5-HT1B receptor antagonists on d-fenfluramine-induced hypophagia in WT mice.. Hypophagic responses to d-fenfluramine (1-30 mg/kg) and mCPP (1-5.6 mg/kg) were measured using a behavioural satiety sequence paradigm. The effects of the 5-HT1B receptor antagonists GR 127,935 and SB 224289 in opposing the hypophagic action of d-fenfluramine were evaluated in WT mice. The binding of [3H]-mesulergine was compared in the brains of both mouse strains.. The hypophagic effects of moderate doses of d-fenfluramine and mCPP were attenuated in 5-HT1B KO mice. Pretreatment of WT mice with the 5-HT(1B/1D) receptor antagonist GR 127,935, or food-deprived WT mice with the 5-HT1B receptor antagonist SB 224289, did not reproduce the reduction in sensitivity to the effects of d-fenfluramine on feeding behaviour observed in 5-HT1B KO mice. Estimates of 5-HT2C receptor binding were similar in 5-HT1B KO and WT mice.. The hypophagic effect of d-fenfluramine in mice is unlikely to be mediated by the 5-HT1B receptor. Instead, the evidence suggests that an adaptive change in 5-HT2C receptor function occurs in 5-HT1B receptor KO mice and contributes to their reduced response to d-fenfluramine.

Topics: Animals; Binding Sites; Cerebral Cortex; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Evaluation, Preclinical; Eating; Ergolines; Fenfluramine; Genotype; Injections, Intraperitoneal; Injections, Subcutaneous; Isomerism; Mianserin; Mice; Mice, Knockout; Piperazines; Piperidones; Receptor, Serotonin, 5-HT1B; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Satiation; Satiety Response; Serotonin 5-HT2 Receptor Agonists; Species Specificity; Spiperone; Spiro Compounds; Time Factors; Tritium; United Kingdom

Recombinant 5-hydroxytryptamine 5-HT7 receptors are known to express constitutive, i.e., agonist-independent activity. Nonselective ligands, like methiothepin, ritanserin or clozapine behave as full inverse agonists at 5-HT7 receptors. The aim of the present study was to evaluate the degree of inverse agonist activity of three selective 5-HT7 receptor antagonists ((R)-3,N-dimethyl-N-[1-methyl-3-(4-methyl-piperidin-1-yl)propyl]benzene sulfonamide or SB-258719, R-(+)-1-(toluene-3-sulfonyl)-2-[2-(4-methylpiperidin-1-yl)ethyl]-pyrrolidine or SB-258741 and (R)-3-(2-(2-(4-methylpiperidin-1-yl)ethyl)-pyrrolidine-1-sulfonyl)-phenol or SB-269970) in the same model. cAMP accumulation was measured in intact Chinese hamster ovary (CHO) cells expressing human recombinant 5-HT7a receptors. In these cells, 5-HT stimulated cAMP levels and a series of ligands antagonized the effect of 5-HT with a 5-HT7 receptor-like profile. SB-258719 had no inverse agonist activity, SB-258741 behaved as a partial inverse agonist and SB-269970 was a quasi-full inverse agonist (as compared to methiothepin). The inverse agonist effect of SB-269970 was antagonized in a concentration-dependent manner by SB-258719. The widespread spectrum of inverse agonist activities shown by these compounds should help assessing the physiological relevance of constitutive 5-HT7 receptor activity in native tissues.

Topics: Animals; Binding, Competitive; CHO Cells; Clozapine; Cricetinae; Cricetulus; Cyclic AMP; Dose-Response Relationship, Drug; Ergolines; Humans; Loxapine; Methiothepin; Phenols; Pimozide; Pindolol; Piperidines; Plasmids; Pyrrolidines; Radioligand Assay; Receptors, Serotonin; Ritanserin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Sulfonamides; Tosyl Compounds; Transfection

The effect of ligand pretreatment on human 5-hydroxytryptamine2C (5-HT2C) receptors was examined in CHO cells expressing high (CHO-1C7; 67+/-3 pmol/mg) or low (CHO-1C19; 72+/-10 fmol/mg) levels of the receptor. Seventy-two hours pretreatment of CHO-1C7 cells with various ligands did not affect receptor expression. Pretreatment with inverse agonists enhanced 5-HT-mediated inositol phosphate accumulation with no change in constitutive receptor activity. The enhanced agonist responsiveness was inversely correlated with the intrinsic activity of the pretreatment ligand. Seventy-two hours of pretreatment with the weak agonist, 5-methoxygramine, caused an elevation in constitutive activity but no alteration in 5-HT-mediated signaling. In CHO-1C19 cells, 24 but not 72 h of pretreatment with the inverse agonist mianserin enhanced 5-HT-mediated signaling, with no effect on basal signaling; pretreatment with 5-methoxygramine had no significant effect. These findings highlight differences in the pattern of chronic regulation of 5HT2C receptor signaling between high and low receptor expression levels in a common cellular background.

Topics: Algorithms; Analysis of Variance; Animals; Binding, Competitive; Cell Membrane; Chlorpromazine; CHO Cells; Cricetinae; Cricetulus; Dose-Response Relationship, Drug; Ergolines; Humans; Indoles; Indophenol; Inositol Phosphates; Kinetics; Ligands; Lisuride; Mianserin; Radioligand Assay; Receptor, Serotonin, 5-HT2C; Ritanserin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tritium; Tryptamines

We compared the ability of human 5-HT2C and 5-HT1A receptors to couple to selected G proteins expressed in insect Sf9 cells through simultaneous infection with recombinant baculoviruses. We also examined the coupling of G proteins to these same receptors in membranes derived from the Sf9 cells using in situ reconstitution with purified G proteins. Our data show that unoccupied 5-HT2C and 5-HT1A receptors can attain an activated conformation that is stabilized by interaction with specific G proteins. While high-affinity agonist binding to the 5-HT2C receptor was increased to a greater extent by Galphaq than by Galphai2, the high-affinity agonist binding to the 5-HT1A receptor was preferentially enhanced by Galphai2 coexpression. When the two 5-HT receptors were expressed in cells also expressing G proteins, both 5-HT2C and 5-HT1A receptors appear to activate Galphai2 in preference to Galphaq. In contrast, in situ reconstitution data show that 5-HT2C receptors robustly activate Galphaq and marginally activate Galphao or Galphai, whereas 5-HT1A receptors only marginally activate Galphaq and robustly activate Galphao and Galphai. These results suggest that the overexpression of receptor and potential G-protein coupling partners in Sf9 cells may lead to erroneous conclusions as to the signaling selectivity of receptors.

Topics: Animals; Cell Line; Dose-Response Relationship, Drug; Ergolines; Heterotrimeric GTP-Binding Proteins; Insecta; Protein Binding; Rats; Receptor, Serotonin, 5-HT1A; Receptor, Serotonin, 5-HT2C; Receptors, G-Protein-Coupled; Serotonin 5-HT1 Receptor Antagonists; Serotonin 5-HT2 Receptor Antagonists

The effects were studied of short-term (1 week) versus long-term (2-3 weeks) fluoxetine treatment of primary cultures of mouse astrocytes, differentiated by treatment with dibutyryl cyclic AMP. From previous experiments it is known that acute treatment with fluoxetine stimulates glycogenolysis and increases free cytosolic Ca2+ concentration ([Ca2+]i]) in these cultures, whereas short-term (one week) treatment with 10 microM down-regulates the effects on glycogen and [Ca2+]i, when fluoxetine administration is renewed (or when serotonin is administered). Moreover, antagonist studies have shown that these responses are evoked by activation of a 5-HT2, receptor that is different from the 5-HT2A receptor and therefore at that time tentatively were interpreted as being exerted on 5-HT2C receptors. In the present study the cultures were found by RT-PCR to express mRNA for 5-HT2A and 5-HT2B receptors, but not for the 5-HT2C receptor, identifying the 5-HT2 receptor activated by fluoxetine as the 5-HT2B receptor, the most recently cloned 5-Ht2 receptor and a 5-HT receptor known to be more abundant in human, than in rodent, brain. Both short-term and long-term treatment with fluoxetine increased the specific binding of [3H]mesulergine, a ligand for alL three 5-HT2 receptors. Long-term treatment with fluoxetine caused an agonist-induced up-regulation of the glycogenolytic response to renewed administration of fluoxetine, whereas short-term treatment abolished the fluoxetine-induced hydrolysis of glycogen. Thus, during a treatment period similar to that required for fluoxetine's clinical response to occur, 5-HT2B-mediated effects are initially down-regulated and subsequently up-regulated.

Topics: Animals; Astrocytes; Carrier Proteins; Cells, Cultured; Drug Administration Schedule; Ergolines; Fluoxetine; Glycogen; Membrane Glycoproteins; Membrane Transport Proteins; Mice; Nerve Tissue Proteins; Protein Isoforms; Receptor, Serotonin, 5-HT2B; Receptors, Serotonin; Selective Serotonin Reuptake Inhibitors; Serotonin Antagonists; Serotonin Plasma Membrane Transport Proteins; Up-Regulation

(R)-8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) depressed the monosynaptic reflex. This effect was not antagonized by 5-HT(1A) receptor antagonists. We examined whether 5-HT(1D) and 5-HT(7) receptors are involved in (R)-8-OH-DPAT-induced inhibition of the monosynaptic reflex in spinalized rats. Pretreatment with methiothepin and mesulergine, but not clozapine, inhibited (R)-8-OH-DPAT-induced monosynaptic reflex depression. Pretreatment with 2a-(4-phenyl-1,2,3,6-tetrahydropyridal)butyl)-2a,3,4,5-tetrahydrobenzo[c,d]indol-2(1H)-one (DR4004) and (R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrolidine (SB-269970), new selective 5-HT(7) receptors antagonists, and N-[methoxy-3-(4-methyl-l-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)[1,1-biphenyl]-4-carboxamide (GR127935), a selective 5-HT(1D) receptor antagonist, had no effect on (R)-8-OH-DPAT-induced depression. These results suggested that 5-HT(7) and 5-HT(1D) receptors are not involved in (R)-8-OH-DPAT-induced monosynaptic reflex depression.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Clozapine; Decerebrate State; Dose-Response Relationship, Drug; Ergolines; Indoles; Male; Methiothepin; Oxadiazoles; Phenols; Piperazines; Pyridines; Rats; Receptor, Serotonin, 5-HT1D; Receptors, Serotonin; Reflex, Monosynaptic; Serotonin Antagonists; Serotonin Receptor Agonists; Sulfonamides; Time Factors

1. The serotonin(2C) (5-HT(2C)) receptor couples to both phospholipase C (PLC)-inositol phosphate (IP) and phospholipase A(2) (PLA(2))-arachidonic acid (AA) signalling cascades. Agonists can differentially activate these effectors (i.e. agonist-directed trafficking of receptor stimulus) perhaps due to agonist-specific receptor conformations which differentially couple to/activate transducer molecules (e.g. G proteins). Since editing of RNA transcripts of the human 5-HT(2C) receptor leads to substitution of amino acids at positions 156, 158 and 160 of the putative second intracellular loop, a region important for G protein coupling, we examined the capacity of agonists to activate both the PLC-IP and PLA(2)-AA pathways in CHO cells stably expressing two major, fully RNA-edited isoforms (5-HT(2C-VSV), 5-HT(2C-VGV)) of the h5-HT(2C) receptor. 2. 5-HT increased AA release and IP accumulation in both 5-HT(2C-VSV) and 5-HT(2C-VGV) expressing cells. As expected, the potency of 5-HT for both RNA-edited isoforms for both responses was 10 fold lower relative to that of the non-edited receptor (5-HT(2C-INI)) when receptors were expressed at similar levels. 3. Consistent with our previous report, the efficacy order of two 5-HT receptor agonists (TFMPP and bufotenin) was reversed for AA release and IP accumulation at the non-edited receptor thus demonstrating agonist trafficking of receptor stimulus. However, with the RNA-edited receptor isoforms there was no difference in the relative efficacies of TFMPP or bufotenin for AA release and IP accumulation suggesting that the capacity for 5-HT(2C) agonists to traffic receptor stimulus is lost as a result of RNA editing. 4. These results suggest an important role for the second intracellular loop in transmitting agonist-specific information to signalling molecules.

Topics: Amphetamines; Animals; Arachidonic Acid; Binding, Competitive; Bufotenin; CHO Cells; Cricetinae; Dose-Response Relationship, Drug; Ergolines; Inositol Phosphates; Lysergic Acid Diethylamide; Piperazines; Protein Isoforms; Quipazine; Radioligand Assay; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; RNA Editing; Serotonin; Serotonin Receptor Agonists; Tritium

The distribution of serotonin 5-HT(2C) receptor mRNA in monkey brain was studied by in situ hybridization and compared with the distribution of [3H]mesulergine binding sites as visualized by receptor autoradiography. 5-HT(2C) receptor transcripts showed a widespread and heterogeneous distribution. The strongest hybridization signal was detected in choroid plexus. In neocortex, 5-HT(2C) mRNA was detected in layer V of all cortical regions examined except in the calcarine sulcus, which was devoid of signal. Several structures within the striatum and basal forebrain were strongly labeled: nucleus accumbens, ventral aspects of anterior caudate and putamen, septal nuclei, diagonal band, ventral striatum, and extended amygdala. Several thalamic, midbrain, and brainstem nuclei also contained 5-HT(2C) mRNA. Comparison of the distributions of 5-HT(2C) mRNA and specific [3H]mesulergine binding sites showed a good agreement in the majority of brain regions, suggesting a predominant somatodendritic localization of 5-HT(2C) receptors. A possible localization to axon terminals of 5-HT(2C) receptors is suggested by the disagreement observed in some regions such as septal nuclei and horizontal limb of the diagonal band (presence of mRNA with apparent absence of binding sites) and interpeduncular nucleus (presence of binding sites with apparent absence of mRNA). Comparison of 5-HT(2C) receptor and choline acetyltransferase mRNA distributions indicate that some regions where cholinergic cells are located are also enriched in cells containing 5-HT(2C) mRNA. Although the present methodology does not allow strict colocalization of both mRNA species to the same cells, the codistribution observed in several regions provides a possible anatomical substrate for the described modulation of acetylcholine release by 5-HT(2C) receptors.

Topics: Animals; Binding Sites; Brain; Choline O-Acetyltransferase; Ergolines; Female; Macaca fascicularis; Macaca mulatta; Male; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; RNA, Messenger; Serotonin Antagonists

The 5-HT(2A) and 5-HT(2C) receptors belong to the same subtype of the G-protein coupled receptor family and have several agonist and antagonist ligands in common. To gain more insight into the differences in the regulation of the two receptors, we studied the effect of agonist and antagonist pre-treatment on radioligand receptor binding and 5-HT-induced inositol phosphate formation on rat 5-HT(2A) and rat 5-HT(2C) receptors stable expressed in NIH 3T3 cells. We compared short (15 min) and prolonged (48 h) pre-treatment of the cells with the natural agonist, 5-HT and with the antagonist pipamperone, which can be readily washed out. The rat 5-HT(2C) receptor showed an agonist-induced down-regulation (decrease in B(max) of labelled agonist and antagonist binding) and desensitisation (decrease in 5-HT-induced inositol phosphate formation and potency of 5-HT). Antagonist pre-treatment induced an increase in rat 5-HT(2C) receptor-mediated inositol phosphate formation as well as increased agonist and antagonist radioligand binding. These findings are consistent with the classical model of G-protein coupled receptor regulation. In contrast, the rat 5-HT(2A) receptor expressed in the same host cell behaved differently, unlike the classical model. Pre-treatment with 5-HT for 15 min and 48 h did not change receptor levels measured by radioligand binding, but the signal transduction response (inositol phosphate formation) was significantly reduced. Pre-treatment with the antagonist pipamperone for 15 min and 48 h caused an increase in antagonist radioligand binding but a reduction in agonist radioligand binding and a decrease in inositol phosphate formation and potency of 5-HT. Hence, the rat 5-HT(2A) receptor apparently undergoes agonist desensitisation without down-regulation of the total receptor number. Antagonist pre-treatment causes a paradoxical desensitisation, possibly by uncoupling of the receptor from G-proteins. The uncoupled receptor does not bind 5-HT in the nanomolar range but retains its antagonist binding properties. Paradoxical antagonist-induced desensitisation of rat 5-HT(2A) receptors has also been observed in vivo.

Topics: 3T3 Cells; Animals; Benzamides; Binding Sites; Binding, Competitive; Butyrophenones; Dose-Response Relationship, Drug; Ergolines; Gene Expression; Inositol Phosphates; Iodine Radioisotopes; Membranes; Mice; Piperidines; Radioligand Assay; Rats; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin; Serotonin Agents; Serotonin Antagonists; Time Factors; Tritium

Human 5-HT7A receptors positively modulated adenylyl cyclases via Gs subtypes of G proteins in human embryonic kidney 293 cells, and bound 5-hydroxytryptamine (HT) with high and low affinity (K(I) values of 1.5 +/- 0.3 and 93 +/- 4 nM). More than 60% of 5-HT7A receptors, however, displayed the high-affinity 5-HT binding with no sensitivity to 5'-guanylylimidodiphosphate. In this study, we found that select amphipathic agents affected the high-affinity 5-HT binding to 5-HT7A. Oleic acid at low concentrations (<15 microM), but not palmitic, stearic, and arachidonic acids, increased maximal [3H]5-HT binding without affecting its K(D) value and [3H]mesulergine (antagonist) binding. Fatty acid-free bovine serum albumin (FF-BSA), a scavenger of fatty acids and lipid metabolites, substantially reduced maximal [3H]5-HT binding (no change in K(D) value and antagonist binding) but lost its action upon treatment with inactive stearic acid. FF-BSA and oleic acid produced no appreciable effects on [3H]5-HT binding to analogous 5-HT receptors 5-HT1D and 5-HT2C. Among various lysophospholipids, lysophosphatidyl choline (50 microM) decreased maximal [3H]5-HT binding, and a similar zwitterion, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS; 0.1%), increased it (no change in K(D)). Functionally, 5-HT-induced guanosine-5'-O-(3-[35S]thio)triphosphate (GTPgamma35S) binding was enhanced by oleic acid and CHAPS, but reduced by FF-BSA and lysophosphatidyl choline; the amphipathic agents and FF-BSA did not affect dopamine-induced GTPgamma35S binding at D1, a prototypic Gs-coupled receptor. At 5-HT7A, oleic acid, FF-BSA, CHAPS, and lysophosphatidyl choline also brought about corresponding changes in the half-maximal 5-HT concentration for cAMP production, without affecting the maximal and basal levels. We propose that endogenous, amphipathic lipid metabolites may modulate 5-HT7A receptors allosterically to promote high-affinity 5-HT binding and to enable receptors to couple more efficiently to Gs subtypes of G proteins.

Topics: Allosteric Regulation; Cells, Cultured; Ergolines; HeLa Cells; Humans; Oleic Acid; Oleic Acids; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Tritium

The present study was designed to investigate which subtype of spinal 5-HT receptors were involved in acetaminophen-induced antinociception using the paw-pressure test. Propacetamol (prodrug of acetaminophen, 400 mg/kg, injected intravenously, corresponding to 200 mg/kg of acetaminophen) produced a significant antinociceptive effect in this test. This effect was at least partially inhibited by intrathecal (i.t.) pretreatment with the 5-HT(1B) (penbutolol), 5-HT(2A) (ketanserin), 5-HT(2C) (mesulergine) receptor antagonists, but not by the 5-HT(1A) (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride, WAY 100635) and 5-HT(3) (granisetron) receptor antagonists. This profile was very close to that obtained recently with 5-HT, which suggests an implication of 5-HT in the spinal antinociceptive effect of acetaminophen. These results, the lack of binding of acetaminophen to 5-HT receptors and the increase of central 5-HT levels induced by this drug suggest that acetaminophen-induced antinociception could be indirectly mediated by 5-HT.

Topics: Acetaminophen; Analgesics; Animals; Ergolines; Granisetron; Injections, Spinal; Ketanserin; Male; Pain Threshold; Penbutolol; Piperazines; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT1B; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Receptors, Serotonin, 5-HT1; Receptors, Serotonin, 5-HT3; Serotonin Antagonists; Time Factors; Vocalization, Animal

The aim of the present study was to identify 5-hydroxytryptamine(7) (5-HT(7)) binding sites in the mouse ileum, where the presence of mRNA for the receptor has been reported. Studies were performed using [3H]mesulergine, an antagonist with high affinity at 5-HT(7) receptors. In the presence of a combination of masking drugs to inhibit the binding of the radioligand to other receptors at which it has affinity, such as 5-HT(2A), 5-HT(2C) and dopamine D(2) receptors as well as alpha(1)/alpha(2)-adrenoceptors, [3H]mesulergine labelled two sites with pK(D) values of 9.7+/-0.7 and 7.4+/-0.4 and B(max) values of 37.2+/-21.4 and 247.8+/-62.1 fmol mg protein(-1), respectively. Displacement studies also indicated the presence of non-homogenous binding sites, which showed a significant correlation (Pearson correlation factors of 0.91 and 0. 85) with the 5-HT(2C) and 5-HT(7) receptors, respectively. Total binding to the 5-HT(2C) receptor was minimal; <30% of the total specific receptor binding. The antagonist order of affinity at the greater proportion of receptors was: risperidone (pK(i)pindolol (5. 6). This receptor also showed a high affinity for 5-carboxamidotryptamine (5-CT; 10.6) and moderate affinity for (+/-)-2-dipropyl-amino-8-hydroxy-1,2,3,4,-tetrahydronaphthalene (8-OH-DPAT; 7.2), which is typical of the 5-HT(7) receptor profile.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Binding Sites; Ergolines; Female; Ileum; Male; Mice; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin; Serotonin Antagonists

The subthalamic nucleus (STN) is an important mediator of basal ganglia output. We studied the effects of STN microinjections of the serotonin-2 (5-HT2) antagonists clozapine, mesulergine and M100,907 on apomorphine-induced stereotypic activity in the rat. Each compound profoundly decreased the expression of stereotypic behavior, with particularly strong effects to reduce gnawing behavior. Because M100,907 does not have appreciable affinity for dopamine D1 and D2 receptors, and since all three agents are 5-HT2 antagonists, the current data suggest that basal ganglia output related to orofacial movements can be significantly modified by 5-HT2 receptors. The results suggest that antipsychotics with serotonergic properties may have direct actions on the STN that influence their potential to produce orofacial and other motor side effects.

Topics: Animals; Apomorphine; Behavior, Animal; Clozapine; Ergolines; Fluorobenzenes; Male; Mastication; Microinjections; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin Antagonists; Stereotypic Movement Disorder; Subthalamic Nucleus

Response properties of neurons in an auditory field in the frontal cortex of the mustached bat, Pteronotus parnellii, have not been studied before. We recorded neural responses to constant frequency (CF) stimuli from the frontal auditory field in awake animals. The majority (75%) of neurons in this area responded well and often exhibited low thresholds to CF stimuli. Most CF-responsive neurons exhibited sharp tuning with values of > 180 for Q10db, a quality factor expressing the sharpness of tuning at 10dB above threshold. Neurons at 13 recording sites exhibited combination sensitivity in that their responses were facilitated by presenting combinations of either CF1/CF2 and/or CF1/CF3 components of the mustached bat's echolocation signal. Unlike the typical on-responses to a 30 ms tone, observed in the mustached bat's auditory cortex and at subcortical levels, many frontal auditory neurons exhibited loosely time locked firing patterns that lasted for > 100 ms.

Topics: Animals; Apomorphine; Behavior, Animal; Clozapine; Ergolines; Fluorobenzenes; Male; Mastication; Microinjections; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin Antagonists; Stereotypic Movement Disorder; Subthalamic Nucleus

6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy) pyridin-3-ylcarbamoyl] indoline (SB242,084) is a novel, selective 5-HT(2C) receptor antagonist, but its actions at these sites have been little characterised at the cellular level. We employed a rapid and innovative approach to investigate its functional activity at phospholipase C (PLC)-coupled human 5-HT(2C) receptors expressed in CHO cells. PLC activity was determined as a decrease in the [3H]phosphatidylinositol ([3H]PI) content of cell membranes. Serotonin (5-HT) stimulated [3H]PI depletion (pEC50=8.74), and SB242,084, like mesulergine, completely reversed this action of 5-HT (pK(B)=9.25 and 9.01, respectively). Further, in Schild analysis, SB242,084 behaved as a high affinity competitive antagonist, inducing a parallel, rightward displacement of the 5-HT stimulation isotherm without loss of maximum efficacy. The pA2 of 9.50 was similar to its binding affinity (pKi=9.38). SB242,084 also displayed antagonist properties when PLC activity was examined by conventional determination of [3H]inositol phosphate generation. Employing this parameter, the potency of SB242,084 (pK(B)=9.21) and that of mesulergine (pK(B)=9.06) closely resembled those determined by [3H]PI depletion. In conclusion, determination of [3H]PI depletion constitutes a useful and novel technique to characterise agonist and antagonist properties of ligands at PLC-coupled receptors.

Topics: Aminopyridines; Animals; CHO Cells; Cricetinae; Ergolines; Humans; Indoles; Phosphatidylinositols; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Type C Phospholipases

This study examined the binding of serotonin receptor antagonists at the 5-HT(2A) and 5-HT(2C) receptors of the rabbit's cerebral cortex. The 5-HT(2A) receptor was characterized by the binding of [3H]MDL 100,907 (R(+)-alpha-(2, 3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine-methan ol) to cortical membranes and the 5-HT(2C) receptor by the binding of [3H]mesulergine in the presence of the selective 5-HT(2A) receptor ligand spiperone. Both [3H]MDL 100,907 and [3H]mesulergine demonstrated high affinity binding to single sites in rabbit membranes. Based on Scatchard plots of [3H]MDL 100,907 binding, the mean B(max) was 8.5+/-0.7 fmol/mg tissue and the mean K(d) was 33. 1+/-3.5 pM. For [3H]mesulergine binding the mean B(max) was 3.70+/-0. 58 fmol/mg tissue and the mean K(d) was 0.35+/-0.05 nM. Binding of [3H]MDL 100,907 to the 5-HT(2A) receptor and of [3H]mesulergine to the 5-HT(2C) receptor was confirmed by displacement studies with highly selective 5-HT(2A) and 5-HT(2C) receptor ligands. The pharmacological profile of these ligands in rabbits correlated highly with published values for 5-HT(2A) (r=0.91, P<0.001) and 5-HT(2C) (r=0.94, P<0.001) receptors in humans. There was also a high correlation between the profiles for human and rat 5-HT(2C) receptor (r=0.92, P<0.001), but not for 5-HT(2A) receptors (r=0.53, P>0.10). It was concluded that the rabbit provides an appropriate animal model for studies attempting to predict the pharmacology of human 5-HT(2A) and 5-HT(2C) receptors.

Topics: Animals; Cerebral Cortex; Ergolines; Female; Fluorobenzenes; Humans; Male; Piperidines; Rabbits; Rats; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin Antagonists

We aimed to develop a model to study in vivo the rabbit saphenous vein pharmacology and to investigate constrictions mediated by adrenoceptor and 5-HT receptor subtypes. We used the technique of high precision ultrasonic echo-tracking for direct measurement of saphenous vein diameters in pentobarbital anesthetized rabbits. Saphenous vein constrictions induced in rabbits by the alpha(1)-adrenoceptor agonist L-phenylephrine and the 5-HT(1B) receptor agonist sumatriptan were comparable with those induced in dogs but those induced by the 5-HT(1B) and 5-HT(7) receptor agonist 5-carboxamidotryptamine failed to appear in dogs. Dose-related constrictions of rabbit veins were obtained with L-phenylephrine and the alpha(2)-adrenoceptor agonist dexmedetomidine. Frequency-related constrictions of rabbit veins induced by nerve stimulation were partially inhibited by an alpha(1)-adrenoceptor or a postsynaptic alpha(2)-adrenoceptor antagonist (prazosin and SKF 104,078) but not affected by the pre- and post-synaptic alpha(2)-adrenoceptor antagonists BRL 44408 or rauwolscine. Constrictions of rabbit veins to sumatriptan and 5-CT were inhibited by GR 127935 and those induced by quipazine, a 5-HT(2) receptor agonist were prevented by ritanserin. The initial constrictions induced by 5-CT were followed by dilatations which were inhibited by the 5-HT(7) receptor antagonist mesulergine. These data indicate that rabbit saphenous veins, in vivo and at rest, respond to activation of 5-HT(1B) and 5-HT(2) receptors, alpha(1)- and alpha(2)-adrenoceptors and nerve stimulation; the dilator effect mediated by 5-HT(7) receptor activation was also detected. The data validate a new animal model to study superficial vein reactivity and its pharmacological sensitivity.

Topics: Adrenergic Agents; Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Anesthesia; Animals; Benzazepines; Blood Pressure; Dogs; Dose-Response Relationship, Drug; Ergolines; Imidazoles; Indoles; Injections, Intravenous; Isoindoles; Oxadiazoles; Peripheral Nervous System; Phenylephrine; Piperazines; Prazosin; Rabbits; Receptors, Adrenergic, alpha; Receptors, Serotonin; Saphenous Vein; Serotonin; Serotonin Agents; Serotonin Receptor Agonists; Sumatriptan; Tetrahydronaphthalenes; Time Factors; Ultrasonography, Doppler; Vasoconstrictor Agents

The involvement of abnormalities in nondopaminergic transmitter systems in Parkinson's disease is noteworthy because of the complications, such as dyskinesia, associated with long-term dopamine replacement therapy. The output regions of the basal ganglia, the substantia nigra pars reticulata, and the medial segment of the globus pallidus are overactive in Parkinson's disease but underactive in dyskinesia. 5-HT2C receptors are localized in these regions and are excitatory. A 5-HT2C receptor binding assay using [3H]-mesulergine and SB 200646A to define nonspecific binding was applied to postmortem tissue from patients with Parkinson's disease and from age-matched control patients. [3H]-mesulergine binding was increased in the substantia nigra pars reticulata by 108% in Parkinson's disease tissue as compared with control tissue. These data suggest abnormalities of 5-HT2C transmission in the basal ganglia of patients with Parkinson's disease.

Topics: Aged; Aged, 80 and over; Antiparkinson Agents; Autoradiography; Binding Sites; Brain; Dopamine Agonists; Dyskinesia, Drug-Induced; Ergolines; Female; Humans; Male; Parkinson Disease; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin Antagonists; Substantia Nigra

The function of the helix VII Tyr in the conserved Asn-Pro-X-X-Tyr segment of rhodopsin-like G protein coupled receptors has been investigated in many receptors. Various effects of site-directed mutation of this locus have been found, including altered coupling, sequestration and agonist affinity. We report the first constitutively active mutations of this Tyr. In the serotonin 5HT(2C) receptor, substituting Ala or Cys for Tyr resulted in a marked increase in the basal level of inositol phosphate accumulation in transfected COS-1 cells. This constitutive signaling was abolished by the inverse agonist SB206553. Introducing Phe at this locus eliminated both basal and agonist-stimulated signaling. All three mutant receptors showed an increase in binding affinity for the structurally dissimilar agonists 5-hydroxytryptamine (5HT), (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and quipazine, suggesting that both the activating and inactivating mutations stabilize a high affinity state. These results implicate the conserved Tyr in the conformational rearrangements that occur during agonist complexing and receptor activation.

Topics: Amino Acid Motifs; Amphetamines; Binding, Competitive; Cell Line; Conserved Sequence; Ergolines; Humans; Indoles; Inositol Phosphates; Ligands; Mianserin; Mutation; Protein Structure, Secondary; Pyridines; Quipazine; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Transfection; Tyrosine

The most prominent structural feature of the G protein-coupled receptor superfamily is their seven hydrophobic domains, which are postulated to form membrane-spanning alpha helices. Some members of the G protein-coupled receptor family, specifically several serotonin (5-HT) receptors, possess eight hydrophobic domains. The importance of this extra hydrophobic domain, located at the N terminus of the receptor, is unknown. This question was addressed by deleting the extra hydrophobic region from the 5-HT2C receptor and comparing its function and topology with those of the wild-type receptor. Immunofluorescence microscopy was used to determine the location of the N terminus of the epitope-tagged wild-type and mutant receptors. The N terminus of both receptors was extracellular, suggesting that the extra hydrophobic domain does not change the topology of this receptor and is unlikely to be a membrane-spanning alpha helix. Radioligand-binding studies in transfected cells and expression studies in Xenopus oocytes demonstrated that seven hydrophobic domains were sufficient for normal function in these assays. Interestingly, the mutant receptor, now containing seven hydrophobic domains, is expressed at higher levels in transfected cells than the wild-type receptor containing eight hydrophobic domains, suggesting that the extra hydrophobic domain does impact the activity of this receptor by regulating its expression.

Topics: Amino Acid Sequence; Animals; Binding, Competitive; Biological Transport; Chlorides; Ergolines; Fluorescent Antibody Technique; Gene Expression; GTP-Binding Proteins; Ligands; Molecular Sequence Data; Mutagenesis; Oocytes; Protein Structure, Secondary; Protein Structure, Tertiary; Receptors, Serotonin; Serotonin Antagonists; Transfection; Tritium; Xenopus laevis

To study specific serotonin (5-hydroxytryptamine [5-HT]) receptor subtype antagonists in an animal model of posthypoxic myoclonus.. Although serotonergic system dysfunction is implicated in posthypoxic myoclonus, anatomic specificity and linkage to receptor subtypes are not delineated.. The authors performed a pharmacologic study to identify specific serotonin receptor subtype antagonists effective in inhibiting myoclonus in posthypoxic rats. Sprague-Dawley rats underwent cardiac arrest for 8 minutes and were resuscitated. On the day of pharmacologic testing, animals were rated every 10 minutes at -30 minutes to time 0 (drug injection) and from +60 to +150 minutes. Using a blinded methodology, animals were injected with normal saline, vehicle, or one of seven serotonin antagonists given at a dose that maintains serotonin receptor subtype specificity: WAY100135 (5-HT1A), methiothepin mesylate (5-HT1B/1D/2), mesulergine hydrochloride (5-HT2A/2B), GR 127935 (5-HT1D), SR 46349 (5-HT2), ondansetron (5-HT3), or GR 125487 (5-HT4). Drugs that produced a significant decrease in myoclonus compared with the control were studied in a dose-response study with six doses across a range from the original dose studied to 10% of that dose.. Two drugs were significantly different from placebo: methiothepin mesylate and mesulergine hydrochloride. GR 127935 showed a trend toward reducing myoclonus. Dose-response studies showed that all doses of methiothepin mesylate and the three highest doses of mesulergine hydrochloride inhibited myoclonus effectively.. 5-HT1B, 5-HT2A/2B, and possibly 5-HT1D receptor subtypes likely play a role in posthypoxic myoclonus. More specific 5-HT antagonists that affect these receptor subtypes are candidates for future testing in this model and in Lance-Adams syndrome.

Topics: Acoustic Stimulation; Animals; Brain Chemistry; Disease Models, Animal; Dose-Response Relationship, Drug; Ergolines; Heart Arrest; Hypoxia; Hypoxia, Brain; Male; Methiothepin; Myoclonus; Oxadiazoles; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin Antagonists

1. The primary aim of this investigation was to determine whether binding sites corresponding to the 5-HT7 receptor could be detected in smooth muscle of the rat jejunum. Binding studies in rat brain (whole brain minus cerebellum) and guinea-pig ileal longitudinal muscle were also undertaken in order to compare the binding characteristics of these tissues. Studies were performed using [3H]-mesulergine, as it has a high affinity for 5-HT7 receptors. 2. In the rat brain and guinea-pig ileum, pKD values for [3H]-mesulergine of 8.0 +/- 0.04 and 7.9 +/- 0.11 (n = 3) and Bmax values of 9.9 +/- 0.3 and 21.5 +/- 4.9 fmol mg(-1) protein were obtained respectively, but no binding was detected in the rat jejunum. [3H]-mesulergine binding in the rat brain and guinea-pig ileum was displaced with the agonists 5-carboxamidotryptamine (5-CT) > 5-hydroxytryptamine (5-HT) > or = 5-methoxytryptamine (5-MeOT) > sumatriptan and the antagonists risperidone > or = LSD > or = metergoline > ritanserin > > pindolol. 3. Despite the lack of [3H]-mesulergine binding in the rat jejunum, functional studies undertaken revealed a biphasic contractile response to 5-HT which was partly blocked by ondansetron (1 microM). The residual response was present in over 50% of tissues studied and was found to be inhibited by risperidone > LSD > metergoline > mesulergine = ritanserin > pindolol, but was unaffected by RS 102221 (3 microM), cinanserin (30 nM), yohimbine (0.1 microM) and GR 113808 (1 microM). In addition, the agonist order of potency was 5-CT > 5-HT > 5-MeOT > sumatriptan. 4. In conclusion, binding studies performed with [3H]-mesulergine were able to detect 5-HT7 sites in rat brain and guinea-pig ileum, but not in rat jejunum, where a functional 5-HT7-like receptor was present.

Topics: 5-Methoxytryptamine; Animals; Binding Sites; Binding, Competitive; Brain; Dose-Response Relationship, Drug; Ergolines; Female; Free Radical Scavengers; Guinea Pigs; Ileum; In Vitro Techniques; Jejunum; Male; Muscle Contraction; Ondansetron; Radioligand Assay; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Spiro Compounds; Sulfonamides; Sumatriptan; Tritium

Many modern models of receptor-G protein function assume that there is a direct relationship between high-affinity agonist binding and efficacy. The validity of this assumption has been recently questioned for the serotonin 5-HT2A receptor. We examined the intrinsic activities of various ligands in activating phosphoinositide hydrolysis and measured their respective binding affinities to the high- and low-affinity states of the 5-HT2C (VNV isoform) and 5-HT(2A) receptors. Ligand binding affinities for the high-affinity state of the receptors were determined using 1-(4-[125I]iodo-2,5-dimethoxyphenyl)2-aminopropane, whereas [3H]mesulergine and N-[3H]methylspiperone were used, in the presence of excess guanine nucleotide [guanosine 5'-O-(3-thiotriphosphate)], to define binding to the low-affinity state of the 5-HT2C and 5-HT2A receptors, respectively. Antagonists labeled the high- and low-affinity states of each receptor with comparable affinities. Previously identified inverse agonists of the 5-HT2C receptor behaved as silent antagonists in our systems even when the receptor was overexpressed at a relatively high density. In contrast, the ability of agonists to bind differentially to the high- and low-affinity states of the 5-HT2A and 5-HT2C receptors was highly correlated (r2 = 0.86 and 0.96, respectively) with their intrinsic activities. These data suggest that high-affinity agonist states can account for agonist efficacy at human 5-HT2A or 5-HT2C receptors without the need for considering additional transition or active states of the receptor-ligand complex. The procedure described herein may expedite drug discovery efforts by predicting intrinsic activities of ligands solely from ligand binding assays.

Topics: Amphetamines; Binding, Competitive; Cell Line; Ergolines; Guanosine 5'-O-(3-Thiotriphosphate); Humans; Hydrolysis; Isomerism; Ligands; Models, Biological; Phosphatidylinositols; Receptors, Serotonin; Recombinant Proteins; Serotonin Antagonists; Serotonin Receptor Agonists; Spiperone

The release of acetylcholine (ACh) from the hippocampus of freely moving rats was studied after the systemic and local administration of the 5-HT agonist chlorophenylpiperazine (mCPP), utilising the in vivo microdialysis coupled to HPLC. Intraperitoneally (i.p.) given mCPP at a dose of 8 mg kg(-1)increased the release of ACh from the hippocampus by approximately 96%. This effect was not observed when the agonist was delivered locally through the dialysis tube (reverse dialysis). The mCPP-induced increase of ACh release was prevented by i.p. mesulergine, a 5-HT2A/2C receptor antagonist, at a dose of 2 mg kg(-1). A similar effect was found with the i.p. administration of isoteoline-a putative serotonergic antagonist. Both mesulergine and isoteoline have been shown to prevent also the mCPP-induced increase of ACh release from rat cortex. In the cortex experiments both antagonists were inactive by themselves. In the hippocampus, however, isoteoline, unlike mesulergine, increased significantly the output of ACh when used alone. This effect was haloperidol-sensitive, which implies a possible dopaminergic mechanism. The results of the present work suggest that (i) the effect of mCPP on ACh release could be attributed to stimulation of 5-HT2C receptors located outside the hippocampus and (ii) isoteoline antagonizes this mCPP-induced effect irrespective of its own enhancing action on ACh release.

Topics: Acetylcholine; Animals; Aporphines; Dopamine Antagonists; Dose-Response Relationship, Drug; Drug Administration Routes; Ergolines; Haloperidol; Hippocampus; Male; Piperazines; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists

Rat and human serotonin 5-HT2C receptor isoforms were evaluated for agonist-independent activation of inositol phosphate production in COS-7 cells. The nonedited isoform (5-HT(2C-INI)) displayed the greatest basal activity, stimulating inositol phosphate production fourfold over the fully edited isoform (5-HT(2C--VGV)). All of the other isoforms tested displayed intermediate levels of basal activity. Decreasing receptor expression levels by 50% produced a parallel decrease in basal activity. 5-HT stimulated inositol phosphate production twofold over basal levels through the 5-HT(2C-INI) receptor and eightfold over basal levels through the 5-HT(2C-VGV) receptor but produced similar maximal levels of inositol phosphate. 5-HT competition for [3H]mesulergine binding to 5-HT(2C-INI) best fit a two-site analysis with K(H) = 7.6 nM and K(L) = 160 nM, whereas 5-HT(2C-VGV) best fit a one-site model with Ki = 163 nM. [3H]5-HT labeled 36% of the total population of 5-HT(2C-INI) receptors labeled by [3H]mesulergine but only 12% of 5-HT(2C-VGV) receptors. [H]5-HT K(D) values increased from 5.1 nM for 5-HT(2C-INI) to 20 nM for 5-HT(2C-VGV). [3H]Mesulergine K(D) values were the same for both isoforms. 5-HT EC50 values for inositol phosphate production increased from 6.1 nM for 5-HT(2C-INI) to 30 nM for 5-HT(2C-VGV). These results demonstrate that RNA editing decreases 5-HT2C receptor basal activity, agonist affinity, and potency, indicating that RNA editing may play a role in regulating serotonergic signal transduction and response to drug therapy.

Topics: Animals; COS Cells; Ergolines; Humans; Inositol Phosphates; Kinetics; Mianserin; Mutagenesis, Site-Directed; Pargyline; Rats; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Recombinant Proteins; RNA Editing; Serotonin; Serotonin Antagonists; Signal Transduction; Transfection

The 5-HT(2C) receptor as heterologously expressed in various mammalian cells mediates inositol 1,4,5-triphosphate (IP(3)) signal by activating G(q/11) subtypes of G proteins, but minimally promotes agonist-induced GTPgamma35S binding in membranes due to slow GTP turnover rates of the G proteins. Here we discovered robust (over 200%) agonist-induced GTPgamma35S binding mediated by the human receptor expressed in human embryonic kidney (HEK) 293 cells, and investigated its pharmacology. Agonists concentration-dependently increased GTPgamma35S binding in isolated membranes, which was competitively blocked by antagonists. Intrinsic efficacies of agonists from GTPgamma35S binding were comparable to those from IP(3) measurement. Pertussis toxin treatment largely blocked serotonin-induced GTPgamma35S binding, serotonin high affinity sites by 70% without altering the total binding sites, and reduced IP(3) release by 40%. GTPgamma35S-bound Galpha subunits from serotonin-activated membranes were mainly Galpha(i), judging from immobilization studies with various Galpha-specific antibodies. Inhibition of forskolin-stimulated cAMP formation, however, was not observed. Apparently, the 5-HT(2C) receptor-mediated GTPgamma35S binding is a unique phenotype observed in HEK293 cells, reflecting its coupling to pertussis toxin-sensitive G(i) subtypes, which contribute to the IP(3) signal, along with pertussis toxin-insensitive G(q/11) subtypes.

Topics: Cyclic AMP; Ergolines; Guanosine 5'-O-(3-Thiotriphosphate); Humans; Inositol 1,4,5-Trisphosphate; Kidney; Pertussis Toxin; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Virulence Factors, Bordetella

Much interest is currently being directed towards serotonin (5-HT) receptors of type 2C (5-HT2C) because of their possible involvement in the control of different activities, such as the composition of the cerebrospinal fluid, locomotion, feeding, neuronal excitability and anxiety. The limited information regarding their distribution in the human brain prompted us to investigate, and to characterize the binding of [3H]mesulergine, a HT2C antagonist, in autopsy samples from 24 subjects. The results showed that the [3H]mesulergine binding represented 95% of the total binding and equilibrium saturation binding experiments resulted in a single straight line, consistent with the presence of one site only. The area with the highest density of [3H]mesulergine binding was the choroid plexus, followed at a significantly lower level by the hippocampus, substantia nigra, basal ganglia, amygdala, hypothalamus and prefrontal cortex. The pharmacological profile of the [3H]mesulergine binding was consistent with that of 5-HT2C receptors, since the most effective displacers were ritanserin, mesulergine and mianserine, followed by clozapine, ketanserine and m-CPP, while other compounds had a negligible or no effect. These findings, showing a wide distribution of [3H]mesulergine binding sites in the human brain, could provide anatomical bases for the different functions attributable to 5-HT2C receptors in humans.

Topics: Adult; Aged; Aged, 80 and over; Binding Sites; Binding, Competitive; Brain; Cell Membrane; Choroid Plexus; Dopamine Antagonists; Ergolines; Female; Humans; Male; Middle Aged; Postmortem Changes; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Selective Serotonin Reuptake Inhibitors; Serotonin Antagonists; Serotonin Receptor Agonists; Substantia Nigra; Substrate Specificity; Tissue Distribution; Tritium

The role of caudal brainstem 5-HT receptors in mediating the anorectic effect of the direct 5-HT2C/1B agonist, mCPP [1-(3-chlorophenyl)piperazine dihydrochloride], was evaluated. We demonstrated, first, that systemic injections of mCPP yielded a dose-related suppression of intra-oral intake of 12.5% glucose in intact rats and in chronically maintained supracollicular decerebrate rats. The results of the decerebrate experiment suggest that 5-HT receptors in the caudal brainstem are sufficient for mediating the drug's intake effect. We also showed a dose-related intake suppression when mCPP was delivered to the fourth ventricle of intact rats, with potent suppression obtained at doses well below threshold for systemic administration. Whether and to what extent the 5-HT2C/2A antagonist, mesulergine reverses the intake suppression that follows systemic or 4th i.c.v. injection of mCPP was examined. Fourth i.c.v. co-administration of mesulergine (60 microg) and mCPP (40 microg) eliminated the approximately 50% intake suppression observed when mCPP was delivered alone, a result that affirms the receptor selectivity of the 4th i.c.v. agonist effect. We showed, further, that 4th i.c.v.mesulergine (60 microg) completely reversed the intake suppression produced by systemic mCPP (2 mg/kg). The latter result indicates that stimulation of 5-HT receptors in the caudal brainstem is necessary for the intake suppression produced by systemic administration of this 5-HT agonist in the intact rat.

Topics: Animals; Appetite Depressants; Brain Stem; Decerebrate State; Dose-Response Relationship, Drug; Ergolines; Injections, Intraventricular; Male; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin Receptor Agonists

In guinea pigs, myoclonus can be induced by 5-hydroxytryptamine (5-HT, serotonin) precursors and synthetic 5-HT receptor agonists, yet the receptor subtype specificity of this behavior is not fully delineated. Guinea pigs were pre-treated with carbidopa (50 mg) followed by one of eight 5-HT antagonists: (-)-N-tert-butyl-3-[4-(2-methoxyphenyl) piperazin-1-yl]-2-phenyl propionamide ((-)-WAY 100135) (5-HT1A), N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridyl)-cy clohexancarboxamide (WAY 100635) (5-HT1A), methiothepin mesylate (5-HT1/2), mesulergine hydrochloride (5-HT2A/2C), N[4-methoxy-3-(4-methyl-L-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2 ,4-oxadizol-3-yl) (GR 127935) (5-HT1D), trans-4-[(3Z)3-(2-dimethylaminoethyl)oxyimino-3(2-fluorop hen yl) propen-1-yl]phenol, hemifumarate (SR 46349) (5-HT2), ondansetron hydrochloride (5-HT3), and [1-[2-[methylsulphonyl)amino]ethyl]-4-piperidinyl]methyl-5-fluoro-2-meth oxy-1H-indole-3-carboxylate (GR 125487) (5-HT4). Thirty minutes later, they received 5-hydroxytryptophan (5-HTP) (75 mg/kg, sc) and myoclonic jumping rates were assessed every 10 min for 200 min by a blinded observer. Repeated measures analysis of variance of drug-induced antagonism of 5-HTP-induced myoclonus revealed a significant effect for the 5-HT receptor antagonists methiothepin mesylate, GR127935, and mesulergine hydrochloride compared to placebo, and each of these drugs inhibited 5-HTP-induced myoclonus in a dose-dependent fashion. Based on the receptor profiles of the three effective antagonists, 5-HTP-induced myoclonus is influenced by the 5-HT1/2 receptor systems. The absence of a significant change with any other receptor subtype antagonist suggests that myoclonus is not related to diffuse activation of central serotonergic mechanisms.

Topics: Animals; Dose-Response Relationship, Drug; Drug Interactions; Ergolines; Guinea Pigs; Male; Methiothepin; Myoclonus; Oxadiazoles; Piperazines; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Substrate Specificity

Dopamine agonists are known to increase the incidence of Leydig cell hyperplasia/adenomas when administered to rats over periods of 1-2 years. We have examined the early changes in factors affecting luteinizing hormone (LH)-controlled signal transduction pathways and steroidogenesis in Leydig cells in vitro after chronic oral administration of one of these dopamine agonists, Mesulergine (CU327-085) (N-(1-6,dimethylergolin-8a-yl)-N',N'-dimethylsulphamide hydrochloride) to Sprague-Dawley (SD) rats. Eight-week-old rats were given this dopamine agonist (2 mg/kg body wt/day) in food for 1, 5, or 12 weeks. The Leydig cells from control and treated rats were purified by elutriation and density gradient centrifugation. The dopamine agonist treatment was found to decrease the specific binding of 125I-human chorionic gonadotrophin (hCG) binding to the Leydig cells: a decrease was detected as early as 1 week after treatment and was more pronounced after 5 and 12 weeks. This was found to be due to a decrease in the LH/hCG receptor numbers and not to a decrease in LH/hCG-receptor binding affinity. Both basal and LH-stimulated cAMP and testosterone production were also decreased; cAMP production was decreased by approximately 50% by all concentrations of LH added whereas testosterone production was only decreased with submaximum stimulating concentrations of LH. The formation of testosterone in response to dibutyryl cAMP was also decreased by approximately 50%, indicating additional lesions in the signal transduction pathway. The addition of the cell permeant 22R-hydroxycholesterol (22R) demonstrated that testosterone but not pregnenolone production was decreased by treatment with the dopamine agonist, thus indicating that the 17 alpha-hydroxylase/C17-20 lyase may have been inhibited. Supporting evidence for this was found because the dopamine agonist also increased aromatase activity in the Leydig cells and thus the potential to produce estrogens; previous studies have shown that estradiol is an inhibitor of the 17-20 lyase enzyme. The addition of the dopamine agonist directly to the Leydig cells did not inhibit cAMP production or testosterone production except at high concentrations. It is concluded that treatment of rats with the dopamine agonist indirectly (i.e., via the pituitary) affects Leydig cell function resulting in a rapid decrease in LH receptors and cAMP and testosterone production. Aromatase activity is increased and thus the capacity to produce estrogen

Topics: Administration, Oral; Animals; Aromatase; Cell Separation; Chorionic Gonadotropin; Cyclic AMP; Dopamine Agonists; Ergolines; Hydroxycholesterols; Iodine Radioisotopes; Leydig Cells; Male; Pregnenolone; Rats; Rats, Sprague-Dawley; Receptors, LH; Serotonin Antagonists; Signal Transduction; Testosterone

The effects of mesulergine (100 and 200 microg/kg s.c.), SB 206553 (1 and 2.5 mg/kg i.p.), RP 62203 (2.5 and 4 mg/kg i.p.) and ritanserin (630 microg/kg i.p.) were studied on the extracellular concentration of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens of chloral hydrate-anesthetized rats, using intracerebral microdialysis. Mesulergine, a non selective serotonin2C/2B/2A (5-HT2C/2B/2A) receptor antagonist, significantly increased DA release, which reached a peak level (+ 20%) 60 min after drug injection and slowly returned back to baseline values. Mesulergine also caused a dose-dependent increase in DOPAC outflow. Pretreatment with mesulergine (200 microg/kg) did not change the inhibition of DA release induced by apomorphine (100 microg/kg), whereas it prevented the reduction of DOPAC outflow induced by apomorphine (100 microg/kg). Administration of SB 206553, a selective blocker of 5-HT2C/2B receptors, dose-dependently increased DA outflow. The dose of 2.5 mg/kg SB 206553 caused a linear increase of DA output which reached a peak (+75%) 40 min after injection, while 1 mg/kg induced a more gradual increase of DA release which peaked (+54%) 60 min after administration of the drug. Treatment with RP 62203, a selective 5-HT2A receptor antagonist, did not produce any significant effect on DA outflow. Administration of ritanserin, a mixed 5-HT2A/2C receptor antagonist, did not cause any significant change of DA and DOPAC outflow. Taken together, these data indicate that selective blockade of 5-HT2/2B receptor subtypes increases DA release in the rat nucleus accumbens.

Topics: Animals; Apomorphine; Cyclic S-Oxides; Dopamine; Dopamine Agonists; Ergolines; Indoles; Microdialysis; Naphthalenes; Nucleus Accumbens; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2B; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Ritanserin; Serotonin Antagonists

1. The effects of mesulergine, a 5-hydroxytryptamine (5-HT) receptor antagonist with dopamine (DA) agonistic properties, on rats diet selection over a seven day period and on 5-HT and DA turnover was studied. 2. Three groups of male Wistar rats were individually caged and ad libitum fed with a standard (SD) and 50% sweet carbohydrate enriched diet (CED). Food intake was measured daily 4 hrs and 24 hrs after i.p. injections of mesulergine (1 and 3 mg/kg) or vehicle. 5-HT and 5-HIAA in hypothalamus (Hy), Striatum (St) and hippocampus (Hi) as well as DA and DOPAC in (Hy) and (St) were assayed at the 8th day of the experiment. 3. There was a dose dependent increase of SD consumption 4 hrs after mesulergine treatment while the CED remained unchanged with total food intake dose dependently increased as a consequence. At 24 hrs measurements SD consumption was increased only for the dose of 1 mg/kg of mesulergine, while a dose dependent decrease of CED intake was observed. Total food intake was unchanged for the dose of 1 mg/kg and decreased with the dose of 3 mg/kg consequently. A dose dependent decrease of rats body weight was observed too. 4. A significant increase of 5-HIAA/5-HT ratio in (Hy) and (St) for the dose of 1 mg/kg and in (Hi) for the dose of 3 mg/kg with no changes of DA turnover were found. 5. The above data suggest a dual mode of action of mesulergine presented as a short term hyperphagia due to simultaneous antiserotonergic and dopaminergic activity and long-term hypophagia due to long-term agonistic effects of dopaminergic neurons.

Topics: Animals; Body Weight; Brain Chemistry; Dietary Carbohydrates; Dopamine; Dopamine Agonists; Ergolines; Food Preferences; Male; Rats; Rats, Wistar; Serotonin; Serotonin Antagonists

The selective antagonist for the 5-HT2A serotonin receptor MDL 100,907, recently characterized autoradiographically in rat brain, has been characterized as a radioligand for the visualization of this receptor in human and monkey brain. In both species [3H]MDL 100,907 binding to brain sections was saturable, had sub-nanomolar affinity (Kd = 0.14-0.19 nM in human brain; Kd= 0.16-0.19 nM in monkey brain) and presented a pharmacological profile consistent with its binding to 5-HT2A receptors (rank order of affinity for [3H]MDL 100,907-labeled receptors: MDL 100,907 > spiperone > ketanserin > mesulergine). The autoradiographical signal obtained with [3H]MDL 100,907 was compared to the signal obtained with [3H]ketanserin, [3H]RP62203 and [3H]mesulergine in both species, and to the distribution of 5-HT2A receptor mRNA as determined by in situ hybridization in monkey brain. At variance with the other radioligands, [3H]MDL 100,907 showed a single population of binding sites with extremely low levels of non-specific binding. As expected, mesulergine showed low affinity for [3H]MDL 100,907-labeled receptors and the autoradiographic pattern shown by [3H]mesulergine confirmed the lack of labeling of the 5-HT2A receptor by this radioligand in primate brain. The similarity of the distribution of [3H]MDL 100,907-labeled receptors and 5-HT2A mRNA in monkey brain, supports the selectivity of this radioligand for 5-HT2A receptors and suggests a somatodendritic localization of these receptors. The present results confirm [3H]MDL 100,907 as the radioligand of choice at present for the autoradiographic visualization of 5-HT2A receptors in mammalian brain including post-mortem human brain.

Topics: Aged; Aged, 80 and over; Animals; Binding Sites; Binding, Competitive; Brain; Cyclic S-Oxides; Ergolines; Female; Fluorobenzenes; Humans; In Situ Hybridization; Ketanserin; Macaca fascicularis; Male; Naphthalenes; Piperidines; Radioligand Assay; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; RNA, Messenger; Tritium

In vagosympathectomised dogs pre-treated intravenously (i.v.) with mesulergine (300 microg/kg), 1-min intracarotid (i.c.) infusions of 5-hydroxytryptamine (5-HT; 0.3-30 microg/min) and sumatriptan (1-30 microg/min) dose-dependently decreased external carotid blood flow, without affecting mean blood pressure or heart rate. Treatment with the selective 5-HT1B receptor antagonist SB224289 (2,3,6,7-tetrahydro-1'-methyl-5-[2'-methyl-4'(5-methyl-1,2,4-oxadiazo l-3-yl) biphenyl-4-carbonyl]furo[2,3f]indole-3-spiro-4'-piperidine hydrochloride; 30-300 microg/kg, i.v.) produced a potent, specific and dose-dependent blockade of this response, whereas the selective 5-HT1D receptor antagonist BRL15572 (1-(3-chlorophenyl)-4-[3,3-diphenyl(2-(S,R) hydroxypropanyl)piperazine]hydrochloride; 30-300 microg/kg, i.v.) was ineffective. It is concluded that mainly 5-HT1B, but not 5-HT1D receptors mediate the canine external carotid vasoconstriction by 5-HT and sumatriptan.

Topics: Anesthesia; Animals; Biphenyl Compounds; Blood Pressure; Carotid Artery, External; Dogs; Dose-Response Relationship, Drug; Drug Interactions; Ergolines; Heart Rate; Norepinephrine; Piperazines; Piperidones; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Spiro Compounds; Sumatriptan; Sympathectomy; Vagotomy; Vasoconstriction

Previous studies have shown that mice bearing a targeted disruption of the 5-HT2C receptor gene exhibit an epilepsy syndrome associated with sporadic spontaneous seizures that occasionally result in death. In this study, we have defined the seizure susceptibility profiles of these 5-HT2C receptor mutant mice backcrossed onto a C57BL/6 background. Wild-type and mutant animals were either electrically kindled from the olfactory bulb, exposed to corneal electroshock, or tested with the chemoconvulsant, flurothyl. In all paradigms, mice lacking the 5-HT2C receptor were significantly more seizure susceptible than wild-type controls. Results indicate that mutants have lower focal seizure thresholds, increased focal seizure excitability, and facilitated propagation within the forebrain seizure system. Mutants also exhibit lower generalized seizure thresholds for the expression of both generalized clonic and generalized tonic seizures. Importantly, the 5-HT receptor antagonist, mesulergine (2 or 4 mg/kg), administered prior to electroshock testing, recapitulated the mutant phenotype in wild-type mice. Together, these data strongly implicate a role for serotonin and 5-HT2C receptors in the modulation of neuronal network excitability and seizure propagation globally, throughout the CNS.

Topics: Animals; Behavior, Animal; Brain Chemistry; Convulsants; Cornea; Disease Susceptibility; Dopamine Agonists; Electroshock; Epilepsies, Myoclonic; Epilepsy; Ergolines; Flurothyl; Kindling, Neurologic; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Mice, Knockout; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin

Previous studies from our laboratory have shown that the 5-HT2C serotonin receptor can be rendered constitutively active by changing amino acid 312 (third intracellular loop) from serine to lysine (S312K). In the present study, detailed radioligand binding analyses were performed to characterize the constitutively activated state of S312K mutant receptors. All agonists tested displayed high affinity for both [3H]5-HT and [3H]mesulergine binding to S312K receptors, but displayed low affinity for [3H]mesulergine binding to native 5-HT2C receptors. [3H]5-HT labeled the same total number of S312K binding sites as [3H]mesulergine. 5-HT2C antagonists inhibited S312K basal inositol phosphate production. These results suggest that S312K receptors mimic the active conformation of native 5-HT2C receptors and provide a good model system for evaluating drugs for inverse agonist activity. Also, S312K receptors may represent a new system for screening 5-HT2C agonist activity by comparing [3H]mesulergine binding to native and S312K mutant receptors.

Topics: 3T3 Cells; Amino Acid Substitution; Animals; Cell Membrane; Ergolines; Kinetics; Lysine; Mice; Mutagenesis, Site-Directed; Radioligand Assay; Rats; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Recombinant Proteins; Serine; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Transfection

The aim of this study was to demonstrate that 5-HT activates electrolyte transport directly via 5-HT2A receptor in rat colonic crypt cells. Patch-clamp whole cell recording was performed in isolated crypts to measure the 5-HT-induced changes in electrogenic K+ and Cl- currents. Superfusing 5-HT (10 microM) in the bath solution increased both K+ and Cl- currents, which were antagonized by the presence of ketanserin (1 microM), a selective 5-HT2A antagonist, in the bath solution. Mesulergine (1 microM) a 5-HT2A and 5-HT2C antagonist, had no inhibitory effect. Strong chelation of the intracellular Ca2+ by 5 mM BAPTA inhibited 5-HT-induced currents. 5-HT also failed to activate K+ and C1- currents in the presence of GDPbetaS (0.5 mM) in the pipette solution. Intracellular administration of GTPgammaS (0.1 mM) mimicked the stimulatory effect of 5-HT, that was inhibited by 5 mM BAPTA. H-7 (0.05 mM), an inhibitor of protein kinase C, A, and G, did not affect the currents. These data indicate that a G protein-coupled pathway is involved in the activation of electrolyte secretion via 5-HT2A receptor.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Biological Transport; Calcium; Cells, Cultured; Chlorides; Colon; Egtazic Acid; Electrolytes; Ergolines; Guanosine 5'-O-(3-Thiotriphosphate); Intestinal Mucosa; Male; Membrane Potentials; Patch-Clamp Techniques; Potassium; Protein Kinase Inhibitors; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; Serotonin

1. The mechanism of action of sumatriptan on coronary flow was examined before and after two different forms of endothelial ablation in guinea-pig isolated hearts. The mechanism was assessed in terms of the influence of the integrity of the coronary endothelium, the role of release of nitric oxide (NO) from the endothelium, and the receptor subtypes mediating the effects. 2. Continuous perfusion with sumatriptan reduced coronary flow, but the concentration-response curve was v-shaped. Sumatriptan (0.001-0.1 microM) caused a concentration-dependent decrease in coronary flow with the maximum effect achieved at 0.23 +/- 0.04 microM. The pEC50 was 8.49 +/- 0.07. At higher concentrations (0.1-10 microM) there was a concentration-dependent diminution of the vasoconstrictor effect. Endothelial ablation by saponin removed the diminution in the vasoconstrictor effect. In contrast pretreatment with NG-nitro L-arginine methyl ester (L-NAME) (100 microM. 45 min perfusion) did not affect it. This was despite both saponin and L-NAME being effective in reducing basal release of NO into the coronary effluent (measured by chemiluminescence) to the same extent (71 +/- 3 and 73 +/- 2%, respectively). 3. GR127935, a selective 5-hydroxytryptamine1D (5-HT1D) receptor antagonist (3 and 10 nM), which by itself had no effect on coronary flow or NO release, antagonized the vasoconstrictor response to sumatriptan and unmasked a sumatriptan-induced concentration-dependent increase in coronary flow and NO release. These increases in coronary flow and NO release were abolished by pretreatment with either saponin or L-NAME. 4. Mesulergine, a 5-HT2 receptor antagonist which had no effect by itself on basal coronary flow or NO release, inhibited the vasodilator response to sumatriptan that occurred in the presence of GR127935, and actually enhanced the vasoconstrictor response, increasing the max mum fall in coronary flow from -3.9 +/- 0.4 to -5.2 +/- 0.4 ml min-1 g-1 (P < 0.05). The diminution of vasoconstrictor effect of sumatriptan was abolished by mesulergine and by pretreatment with saponin, but not by L-NAME. 5. In conclusion, guinea-pig coronary arteries constrict to low concentrations of sumatriptan, causing a reduction in coronary flow. This effect appears to be caused by 5-HT1D agonism with the receptors located on the coronary vascular smooth muscle. With higher concentrations of sumatriptan this is partially offset by a weaker vasodilator effect, which is caused by low affini

Topics: Animals; Coronary Circulation; Coronary Vessels; Endothelium, Vascular; Enzyme Inhibitors; Ergolines; Guinea Pigs; Heart; In Vitro Techniques; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Oxadiazoles; Piperazines; Saponins; Serotonin Receptor Agonists; Sumatriptan; Vasoconstrictor Agents

We have investigated the role of serotonin-2C (5-HT2C) receptors in modulation of ocular dominance plasticity in kitten visual cortex. A small quantity of the 5-HT2C receptor blocker, mesulergine, was infused into the visual cortex of one hemisphere of 5- to 7-week-old kittens using osmotic minipumps, while the control hemisphere received vehicle solution. At the same time, one eyelid of the experimental animals was sutured shut. The ocular dominance distributions in the visual cortex (area 17) were assessed using extracellular recording methods after 1 week of combined mesulergine infusion and monocular deprivation. We found that the majority of the neurons remained binocularly responsive in the mesulergine-treated hemisphere, while most of the neurons recorded were either unresponsive or only weakly responsive to the deprived eye in the control hemisphere. Local infusion of mesulergine into the kitten visual cortex thus reduced the shift of ocular dominance that normally occurs in animals of these ages following monocular deprivation. The blocking effect seems to be distance-dependent and therefore dose-dependent: the farther away the recording sites were from the injection site, the fewer binocularly responsive cells were found. These results are relevant to previous findings indicating transient overexpression of 5-HT2C receptor in visual cortex of kittens at these ages. The data suggest that the 5-HT2C receptor system may be involved in the formation and modification of ocular dominance columns in the developing visual cortex.

Topics: Animals; Cats; Dominance, Cerebral; Electric Stimulation; Ergolines; Functional Laterality; Microelectrodes; Neuronal Plasticity; Neurons; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Serotonin Antagonists; Vision, Monocular; Visual Cortex; Visual Perception

Cyproheptadine is a drug that shows high affinity for type 2 (5-HT2) receptors. We studied a series of compounds obtained by modification of the tricyclic system of Cyp (dibenzocycloheptadiene): 2f (thioxanthene), 2g (xanthene), 2h (dihydrodibenzocycloheptadiene), 2j (diphenyl), 2i (fluorene), and 3b (phenylmethyl). Their activities at the rat cerebral cortex 5-HT2A receptor were (pKi +/- S.E.M.): 8.80 +/- 0.11 (Cyp), 8.60 +/- 0.07 (2f), 8.40 +/- 0.02 (2g), 8.05 +/- 0.03 (2h), 7.87 +/- 0.12 (2j), 6.70 +/- 0.02 (2i) and 6.45 +/- 0.02 (3b); those at the rat stomach fundus 5-HT2B receptor (pA2 +/- S.E.M.) were: 9.14 +/- 0.25 (Cyp), 8.49 +/- 0.07 (2f), 7.58 +/- 0.58 (2g), 7.02 +/- 0.14 (2h), 6.07 +/- 0.20 (2j), and undetectable (2i, 3b): and those at the pig choroidal plexus 5-HT2C receptor (pKi +/- S.E.M.) were: 8.71 +/- 0.08 (Cyp), 8.68 +/- 0.01 (2f), 8.58 +/- 0.20 (2g), 7.95 +/- 0.05 (2h), 7.57 +/- 0.04 (2j), 6.98 +/- 0.04 (2i) and 6.63 +/- 0.20 (3b). The slopes did not differ significantly from unity. The compounds exhibited the same order of activities at every type of receptor, and the most active molecules presented certain steric (butterfly conformation of the tricyclic system) and electrostatic (proton affinity on the top of the central rings) patterns. It is concluded that the activity of cyproheptadine derivatives at 5-HT2 receptors is related to these molecular features, which make feasible a common disposition to interact with all three 5-HT2 subtypes.

Topics: Animals; Binding, Competitive; Cerebral Cortex; Choroid Plexus; Cyproheptadine; Ergolines; Gastric Fundus; In Vitro Techniques; Ketanserin; Kinetics; Male; Models, Molecular; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin Antagonists; Structure-Activity Relationship; Swine

The role of 5-hydroxytryptamine (5-HT) receptor subtypes in acetylcholine (ACh) release induced by dopamine or neurokinin receptor stimulation was studied in rat striatal slices. The dopamine D1 receptor agonist SKF 38393 potentiated in a tetrodotoxin-sensitive manner the K(+)-evoked [3H]ACh release while SCH 23390, a dopamine D1 receptor antagonist, had no effect. [3H]ACh release was decreased by the dopamine D2 receptor agonist LY 171555 (quinpirole) and slightly potentiated by the dopamine D2 receptor antagonist haloperidol. The selective neurokinin NK1 receptor agonist [Sar9, met(O2)11]SP also potentiated K(+)-evoked release of [3H]ACh. GR 82334, a NK1 receptor antagonist, blocked not only the effect of [Sar9, met(O2)11]SP but also the release of ACh induced by the D1 receptor agonist SKF 38393. Among the 5-HT agents studied, only the 5-HT2A receptor antagonists ketanserin and ritanserin were able to reduce the ACh release induced by dopamine D1 receptor stimulation. Mesulergine, a more selective 5-HT2C antagonist, showed an intrinsic releasing effect but did not affect K(+)-evoked ACh release induced by SKF 38393. Methysergide and methiothepin, mixed 5-HT1/2 antagonists, as well as ondansetron, a 5-HT3 receptor antagonist, showed an intrinsic effect on ACh release, their effects being additive to that of SKF 38393. 5-HT2 receptor agonists were ineffective. However, the 5-HT2 agonist DOI was able to prevent the antagonism by ketanserin of the increased [3H]ACh efflux elicited by SKF 38393, suggesting a permissive role of 5-HT2A receptors. None of the above indicated 5-HT agents was able to reduce the ACh release induced by the selective NK1 agonist. The results suggest that 5-HT2 receptors, probably of the 5-HT2A subtype, modulate the release of ACh observed in slices from the rat striatum after stimulation of dopamine D1 receptors. It seems that this serotonergic control is exerted on the interposed collaterals of substance P-containing neurons which promote ACh efflux through activation of NK1 receptors located on cholinergic interneurons.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Acetylcholine; Animals; Benzazepines; Corpus Striatum; Dopamine Agonists; Dopamine Antagonists; Ergolines; Haloperidol; In Vitro Techniques; Ketanserin; Male; Neurokinin-1 Receptor Antagonists; Peptide Fragments; Physalaemin; Potassium; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; Ritanserin; Serotonin Antagonists; Substance P

It has been suggested that the late hypotensive response to serotonin (5-hydroxytryptamine; 5-HT) in vagosympathectomized rats is mediated by '5-HT1-like' receptors since this effect is mimicked by 5-carboxamidotryptamine (5-CT), is not modified by cyproheptadine, ketanserin or MDL 72222, but it is blocked by methysergide. The present study was set out to reanalyze this suggestion in terms of the classification schemes proposed in 1994 and 1996 by the NC-IUPHAR subcommittee on the classification and nomenclature of 5-HT receptors. I.v. bolus injections of 5-CT (0.01-0.3 microg x kg(-1)), 5-HT (1-30 microg x kg(-1)) and 5-methoxytryptamine (5-MeO-T; 1-30 microg x kg(-1)) produced dose-dependent hypotensive responses with a rank order of agonist potency: 5-CT >> 5-HT > 5-methoxytryptamine with sumatriptan (30-1000 microg x kg(-1)) inactive. The depressor responses to 5-HT and 5-CT were not attenuated by i.v. GR127935 (300-3000 microg x kg(-1)) or equivalent volumes of saline. In contrast, lisuride, methiothepin, mesulergine, metergoline and clozapine dose-dependently antagonized the responses to 5-HT and 5-CT; the rank order of apparent pA2 values against 5-HT and 5-CT, respectively, was: lisuride (7.7; 7.8) > methiothepin (6.8; 7.0) > or = mesulergine (6.4; 6.6) > clozapine (5.7; 5.8); metergoline displayed variable potencies (5.6; 6.4). Except for lisuride, which also affected isoprenaline-induced hypotension, the antagonism by the other drugs was selective. Based upon the above rank order of agonist potency, the blockade by a series of drugs showing high affinity for the cloned 5-ht7 receptor and the lack of blockade by GR127935, our results indicate that the 5-HT receptor mediating hypotension in vagosympathectomized rats is operationally similar to other putative 5-ht7 receptors mediating vascular and non-vascular responses (e.g. relaxation of the rabbit femoral vein, canine coronary and external carotid arteries and guinea-pig ileum as well as feline tachycardia).

Topics: 5-Methoxytryptamine; Adrenergic beta-Agonists; Animals; Blood Pressure; Clozapine; Ergolines; Heart Rate; Isoproterenol; Lisuride; Male; Metergoline; Methiothepin; Oxadiazoles; Piperazines; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Sumatriptan; Sympathectomy

We have assessed the ability of the serotonergic antagonist mianserin to modulate the number and functional activity of human 5-hydroxytryptamine2A (5-HT2A) and 5-HT2C receptors stably expressed in the human neuroblastoma cell line SH-SY5Y. Incubation of cells expressing the 5-HT2A receptor with mianserin (100 nM) for 24 h caused a significant decrease (48%) in the binding capacity of [3H] ketanserin. This receptor down-regulation was associated with a corresponding decrease in the maximal production of inositol phosphates induced by 5-HT but not by carbachol. Exposure of cells expressing the 5-HT2C receptor to mianserin (100 nM) for 72 h but not for 24 h similarly resulted in a significant reduction (44%) in [3H]mesulergine binding. Corresponding analysis of inositol phosphate production by 5-HT at the 5-HT2C receptor after incubation with mianserin showed no change in maximal response after 24 h. No change in the binding capacity of either radioligand was seen after incubation with mianserin for 1 h. A decrease in the binding affinity of both radioligands was also observed after mianserin treatment, but this decrease was similar after 1 h of incubation to that seen after 24 or 72 h, and was probably due to the retention of mianserin within the tissue. We conclude that antagonist down-regulation is evident at human 5-HT2A and 5-HT2C receptors stably expressed in a human neuroblastoma cell line and is probably mediated by a direct action of mianserin at the receptor.

Topics: Cell Membrane; DNA, Complementary; Down-Regulation; Ergolines; Humans; Ketanserin; Kinetics; Mianserin; Neuroblastoma; Phosphatidylinositols; Radioligand Assay; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Recombinant Proteins; Serotonin; Time Factors; Transfection; Tumor Cells, Cultured

Site-directed mutagenesis was performed to create a mutant serotonin 5-HT2C receptor that would mimic the active conformation of the native receptor. Structural alteration of receptor conformation was achieved by changing amino acid no. 312 from serine to phenylalanine (S312F) or lysine (S312K). After expression in COS-7 cells, the binding affinity of 5-HT for [3H]mesulergine-labeled 5-HT2C receptors increased from 203 nM (native) to 76 nM for S312F and 6.6 nM for S312K mutant receptors. 5-HT potency for stimulation of phosphatidylinositol (PI) hydrolysis increased from 70 nM (native) to 28 nM for S312F and 2.7 nM for S312K mutant receptors. The mutant receptors were constitutively active, stimulating PI hydrolysis in the absence of agonist. S312F and S312K mutations resulted in twofold and five-fold increases, respectively, in basal levels of PI hydrolysis. Mianserin and mesulergine displayed inverse agonist activity by decreasing basal levels of PI hydrolysis stimulated by S312K mutant receptors. [3H]5-HT and [3H]mesulergine labeled the same number of S312K mutant receptors and 5'-guanylylimidodiphosphate had no effect on [3H]5-HT binding. These results indicate that serine --> lysine mutation at amino acid no. 312 produces an agonist high-affinity state of the 5-HT2C receptor that spontaneously couples to G proteins and stimulates PI hydrolysis in the absence of agonist.

Topics: Animals; Binding Sites; COS Cells; Ergolines; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Kinetics; Lysine; Methysergide; Mianserin; Mutagenesis, Site-Directed; Phenylalanine; Phosphatidylinositols; Point Mutation; Protein Conformation; Radioligand Assay; Rats; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Recombinant Proteins; Serine; Serotonin; Serotonin Antagonists; Signal Transduction; Transfection

We analyzed the existence of an additional serotonin (5-HT) receptor subtype, sensitive to 5-carboxamidotryptamine, in the mammalian brain. Radioligand binding studies with [3H]5-HT were carried out in rat, guinea pig, and human brain membranes, in the presence of unlabeled drugs to mask the binding to all known 5-HT receptors, with the exception of 5-HT1E sites. Under these conditions, unlabeled 5-carboxamidotryptamine still showed a biphasic competition curve with a nanomolar affinity component. Saturation studies with 5-[3H]carboxamidotryptamine were carried out in the presence of (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin, mesulergine, and ergotamine, to mask the binding to all receptors known to be labeled by 5-carboxamidotryptamine. These studies showed the existence in cortex and hippocampus from guinea pig and human brain of a remaining binding site with high affinity (pK(D) = 7.8-8.1) and a unique pharmacological profile. 5-HT and 5-carboxamidotryptamine showed nanomolar affinity, whereas 5-methoxytryptamine recognized this binding site with intermediate affinity. Other drugs exhibited low or very low potency in inhibiting this binding. The addition of 5'-guanylylimidodiphosphate significantly reduced the number of binding sites labeled by 5-[3H]carboxamidotryptamine, in the presence of the masking drugs described above, indicating the interaction with a GTP-binding protein. Preliminary autoradiographic studies in human brain appear to indicate that this 5-HT binding site is present in areas such as the globus pallidus, neocortex, and hippocampus, among others.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Autoradiography; Binding Sites; Binding, Competitive; Brain; Cerebral Cortex; Ergolines; Ergotamine; Female; Guinea Pigs; Humans; Kinetics; Male; Mammals; Middle Aged; Organ Specificity; Radioligand Assay; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tritium

The recently developed 5-HT2A receptor selective antagonist [3H]MDL100,907 ((+/-)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol]) has been characterized as a radioligand for the autoradiographic visualization of these receptors. [3H]MDL100,907 binding to rat brain tissue sections was saturable, had sub-nanomolar affinity (Kd = 0.2-0.3 nM), and presented a pharmacological profile consistent with its binding to 5-HT2A receptors (rank order of affinity for [3H]MDL100,907-labelled receptors: MDL100,907 > spiperone > ketanserin > mesulergine). The distribution of receptors labelled by [3H]MDL100,907 was compared to the autoradiographical patterns obtained with [3H]Ketanserin, [3H]Mesulergine, and [3H]RP62203 (N-[3-[4-(4-fluorophenyl)piperazin-1-y1]propyl]-1,8-naphtalenes ultam) and to the distribution of 5-HT2A receptor mRNA as determined by in situ hybridization. As opposed to the other radioligands, [3H]MDL100,907 labelled a single population of sites (5-HT2A receptors) and presented extremely low levels of non-specific binding. The close similarity of the distributions of [3H]MDL100,907-labelled receptors and 5-HT2A mRNA further supports the selectivity of this radioligand for 5-HT2A receptors and suggests a predominant somatodendritic localization of these receptors. The present results point to [3H]MDL100,907 as the ligand of choice for the autoradiographic visualization of 5-HT2A receptors.

Topics: Animals; Autoradiography; Binding, Competitive; Brain; Cyclic S-Oxides; Ergolines; Fluorobenzenes; Guanylyl Imidodiphosphate; In Situ Hybridization; In Vitro Techniques; Ketanserin; Male; Naphthalenes; Piperidines; Protein Binding; Radioligand Assay; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; RNA, Messenger; Serotonin Antagonists

The changes in acetylcholine (ACh) release from the cortex of freely moving rats after systemic administration of chlorophenylpiperazine (mCPP), a 5-HT2C agonist, were measured utilising microdialysis coupled to high performance liquid chromatography. mCPP administered intraperitoneally (i.p.) increased cortical ACh release, but failed to do so when applied locally in the cortex. The effect of i.p. administered mCPP on cortical ACh release was prevented by i.p. injection of mesulergine, a 5-HT2A/2C receptor antagonist, and isoteoline, a compound previously shown to antagonize behavioural effects of mCPP. An increase of cortical ACh release was also found after the local administration of mCPP in nucleus basalis magnocellularis (NBM). The results of the present work suggest that 5-HT2C receptors located in NBM are involved in the modulation of cortical ACh release in the rat.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Aporphines; Cerebral Cortex; Ergolines; Male; Microdialysis; Piperazines; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Substantia Innominata

Audiogenic seizures can be induced in DBA/2J mice following intense auditory stimulation. A number of neurotransmitters, including 5-hydroxytryptamine (5-HT), are believed to be involved in mediating this effect since it has been shown previously that depletion of 5-HT or blockade of 5-HT receptors protects DBA/2J mice from these audiogenic seizures. The present study was undertaken to determine whether antagonism of the newly identified 5-HT7 receptor may protect DBA/2J mice from audiogenic seizures by attempting to correlate in vivo potency of compounds with their affinity at the 5-HT7 receptor. All compounds used in the correlation were shown to be antagonists at the 5-HT7 receptor and a statistically significant correlation was observed between 5-HT7 affinity and doses for half-maximal response (ED50) for protection of DBA/2J mice from sound-induced seizures (r = 0.80; P < 0.05). No significant correlation was observed between in vivo activity and affinity at either 5-HT1A, 5-HT2A or 5-HT2C receptors. It is also unlikely that interactions between the 5-ht5 receptor will protect DBA/2J mice from audiogenic seizures since metergoline and mesulergine which are both active in this in vivo model have no affinity for the 5-ht5 receptor. There are similarities between the pharmacology of the 5-HT7 receptor and that of the 5-HT1A receptor, however the correlation between the in vivo potency in DBA/2J mice and 5-HT1A affinity was not significant. Furthermore, the 5-HT1A receptor antagonist WAY 100135 did not protect DBA/2J mice from audiogenic seizures at doses that antagonise 5-HT1A receptor-mediated effects in mice. These data suggest that antagonism of 5-HT7 receptors may protect against audiogenic seizures in DBA/2J mice although a definitive conclusion must await studies with selective 5-HT7 antagonists.

Topics: Acoustic Stimulation; Animals; Anticonvulsants; CHO Cells; Cricetinae; Ergolines; Male; Methysergide; Mianserin; Mice; Mice, Inbred DBA; Receptors, Serotonin; Seizures; Serotonin Antagonists

G protein-coupled receptors (GPCRs) form a large superfamily of receptors that are characterised by a seven transmembrane helical motif. The functions they perform, such as binding ligands and G proteins, are related to the presence of certain amino acids in critical positions. We have developed a computational sequence pattern correlation technique for the recognition of such function-determining residues. The method searches for residues that are conserved in one class of proteins with a certain function but are different in other classes. The basic idea is that such residues are probably involved in this particular function. This technique was used to find residues that play a role in the binding of endogenous as well as exogenous ligands to various receptors. Many of the residues that were detected have been experimentally determined as important for ligand binding. More importantly, however, we also detected residues that are interesting targets for future mutation studies aimed at elucidating the sequence-function relationship in GPCRs. The information obtained may help improve three-dimensional GPCR models and can be useful for the study of receptor-ligand interactions.

Topics: Amino Acid Sequence; Binding Sites; Chlorpromazine; Ergolines; GTP-Binding Proteins; Ligands; Molecular Sequence Data; Molecular Structure; Pindolol; Propranolol; Receptors, Cell Surface; Receptors, Muscarinic; Receptors, Serotonin; Sequence Analysis; Sequence Homology, Amino Acid; Serotonin Receptor Agonists

An important determinant of the neurobehavioral responses induced by a drug is its relative receptor selectivity. The molecular basis of ligand selectivity of hallucinogenic and nonhallucinogenic compounds of varying structural classes for the human 5-hydroxytryptamine (5-HT)2A and 5-HT2C receptors was investigated with the use of reciprocal site-directed mutagenesis. Because these two closely related receptor subtypes differ in the amino acid present at position 5.46 (residues 242 and 222 in the sequences, respectively), the effects of corresponding substitutions in the 5-HT2A[S5.46(242)-->A] and 5-HT2C[A5.46(222)-->S] receptors were studied in tandem. By studying both receptors, the direct and indirect effects of mutations on affinity and selectivity can be distinguished. The ergolines studied, mesulergine (selective for the 5-HT2C receptor) and d-lysergic acid diethylamide (selective for the 5-HT2A receptor), reversed their relative affinity with mutations in each receptor, supporting a direct role of this locus in the selectivity of these ligands. However, interchange mutations in either receptor led to decreased or unchanged affinity for (+/-)-1-)(2,5-dimethoxy-4-iodophenyl)-2-aminopropane and ketanserin, which have higher affinity for the 5-HT2A receptor, consistent with little contribution of this locus to the selectivity of these ligands. The indoleamines studied were affected differently by mutations in each receptor, suggesting that they bind differently to the two receptor subtypes. Mutation of this locus in the 5-HT2A receptor decreased the affinity of all indoleamines, whereas the interchange mutation of the 5-HT2C receptor did not affect indoleamine affinity. These results are consistent with a direct interaction between this side chain and indoleamines for the 5-HT2A receptor but not for the 5-HT2C receptor. Furthermore, this analysis shows that the higher affinity of 5-HT and tryptamine for the 5-HT2C receptor than for the 5-HT2A receptors is not due to the difference at this locus. The hallucinogens studied [d-lysergic acid diethylamide, psilocin, bufotenin, and (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane] fell into different classes in this analysis. For the classes of ligand studied, the side-chain difference at this position directly determines relative ligand selectivity only for ergolines and may contribute to the specific effects of hallucinogens in this class.

Topics: Amino Acid Sequence; Animals; Binding Sites; Binding, Competitive; Cell Line; Chlorocebus aethiops; Ergolines; Hallucinogens; Humans; Ketanserin; Kinetics; Ligands; Lysergic Acid Diethylamide; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Phosphatidylinositols; Point Mutation; Protein Structure, Secondary; Rats; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Recombinant Proteins; Sequence Homology, Amino Acid; Structure-Activity Relationship; Transfection

Serotonin 5-HT2C receptor-mediated intracellular Ca2+ mobilization was investigated in 5-HT2C receptors expressed in Chinese hamster ovary (CHO) cells; and fura-2/AM was used to investigate the regulation of 5-HT2C receptor function. CHO cells, transfected with a cDNA clone for the 5-HT2C receptor, expressed 287 fmol/mg of the receptor protein as determined by mianserin-sensitive [3H]-mesulergine binding (kd = 0.49 nM). The addition of 5-HT mobilized intracellular Ca2+ in a dose-dependent fashion, ranging from basal level of 99 +/- 1.8 nM up to 246 +/- 21.2 nM, with an EC50 value for 5-HT of .015 microM. Exposure to 5-HT, a 5-HT receptor agonist, mCPP [1-(3-chlorophenyl)piperazine dihydrochloride], a 5-HT2C agonist, and DOI [1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane], a 5-HT2C and 5-HT2 agonist, resulted in increased intracellular Ca2+ levels. Mianserin, mesulergine, ritanserin, and ketanserin each blocked 5-HT-mediated intracellular Ca2+ mobilization more effectively than spiperone. Mianserin and amoxapine inhibited 5-HT-mediated intracellular Ca2+ mobilization completely; amitriptyline, nortriptyline, and imipramine reduced it about 50%. These results suggest that antagonism in CHO cells transfected with human 5-HT2C receptors is a component of the serotonergic properties of a number of established antidepressants.

Topics: Animals; Antidepressive Agents; Antidepressive Agents, Second-Generation; Calcium; Calcium Channels; CHO Cells; Cricetinae; Ergolines; Humans; Intracellular Fluid; Mianserin; Radioligand Assay; Receptors, Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Signal Transduction; Transfection

Membranes prepared after infection of Sf9 cells with recombinant baculovirus containing the rat 5HT2c receptor DNA, but not after infection with wild-type virus, expressed high affinity binding sites for 125I-lysergic acid diethylamide and [3H]mesulergine. The receptor site density reached an optimum of 50-70 pmol/mg membrane protein at 60 h postinfection. Extraction of peripheral membrane proteins from the postnuclear membrane fraction with 6 M urea depleted GTPgammaS-binding 4-fold without decreasing 5HT2c receptor binding activity. Urea-extracted Sf9 membranes expressing the 5HT2c receptor catalyzed the activation of squid retinal alphaq but not bovine retinal alphat or bovine alphao/alphai. Productive interaction of 5HT2c receptors with squid alphaq was enhanced by the addition of betagamma dimers prepared from either bovine brain or bovine rod outer segment discs. While the addition of serotonin increased 5HT2c receptor-catalyzed GTPgammaS binding to alphaq, the unoccupied receptor was also catalytically active. The 5HT2c receptor antagonists, mesulergine, mianserin, and ketanserin competitively inhibited 5HT activation of the receptor with predicted rank-order affinities; and mianserin and ketanserin markedly inhibited basal 5HT2c receptor activity. Interestingly, this "inverse agonist" efficacy did not correlate with antagonist affinity for the 5HT2c receptor. Baculoviral expression of the 5HT2c receptor and urea extraction of postnuclear Sf9 cell membranes have provided a high density of in situ, uncoupled, G-protein-linked receptor useful for reconstitution with purified G-protein subunits. This has allowed for independent manipulation of receptor and G-protein chemical concentrations and has revealed that a G-protein-linked receptor can possess a significant basal catalytic activity and that antagonist compounds can act as inverse agonists of this basal activity at the level of receptor activation of G-proteins.

Topics: Animals; Binding, Competitive; Cattle; Cell Line; Decapodiformes; Ergolines; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Triphosphate; Ketanserin; Mianserin; Photoreceptor Cells, Invertebrate; Rats; Receptor, Serotonin, 5-HT2C; Receptors, Cell Surface; Receptors, Serotonin; Recombinant Proteins; Serotonin

1. The murine 1C11 clone, which derives from a multipotential embryonal carcinoma cell line, has the features of a neuroectodermal precursor. When cultured in the presence of dibutyryl cyclic AMP, the 1C11 cells extend bipolar extensions and express neurone-associated markers. After 4 days, the resulting cells have acquired the ability to synthesize, take up, store and catabolize 5-hydroxytryptamine (5-HT). We have thus investigated the presence of 5-HT receptors during the 5-hydroxytryptaminergic differentiation of this inducible 1C11 cell line. 2. As shown by the binding of [125I]-GTI and the CGS 12066-dependent inhibition of the forskolin-induced cyclic AMP production, functional 5-HT1B/1D receptors become expressed on day 2 of 1C11 cell differentiation. The density of these receptors remained unchanged until day 4. 3. The same holds true for the 5-HT2B receptor, also identified by its pharmacological profile and its positive coupling to the phosphoinositide cascade. 4. On day 4 of 1C11 cell differentiation, a third 5-HT receptor, pharmacologically and functionally similar to 5-HT2A, had become induced. 5. Strikingly, the amounts of each transcript encoding 5-HT1B, 5-HT2A and 5-HT2B receptor did not very significantly during the time course of the 1C11 5-hydroxytryptaminergic differentiation. 6. The clone 1C11 may thus provide a useful in vitro model for studying regulation(s) between multiple G-linked receptors as well as the possible role of 5-HT upon the expression of a complete 5-hydroxytryptamine phenotype.

Topics: Animals; Antiparkinson Agents; Cells, Cultured; Colforsin; Cyclic AMP; Ergolines; Gene Expression; Quinoxalines; Receptors, Serotonin; Serotonin; Serotonin Receptor Agonists; Time Factors

The effects of chronic (for 14 days) citalopram and fluoxetine treatments with three doses (2.5, 10, and 20 mg/kg) and withdrawal times (24 hours, 68 hours, and 14 days) on 5-HT2C (formerly 5-HT1C) receptors in the rat brain choroid plexus were studied with quantitative receptor autoradiography in two separate experiments. Chronic citalopram treatment caused a consistent and dose-related increase in the density of 5-HT2C receptors (up to 90%). This effect was slightly more pronounced when measured with an antagonist ligand ([3H]mesulergine) than with an agonist ligand [(+/-)-1-(2,5-dimethoxy-4-[125I]iodophenyl)-2-aminopropane ([125I]DOI)]. The upregulation was most evident 24 hours after the last dose and disappeared thereafter rather rapidly. Chronic fluoxetine treatment also increased the density of 5-HT2C receptors 24 hours from the last dose, but the increase was accompanied by a reduced affinity and was less marked than that observed with citalopram. The changes in receptor characteristics were not observed consistently after the 68-hour withdrawal from fluoxetine. Furthermore, the upregulation of fluoxetine appeared not to be dose related or reflected by an increase in agonist binding. In conclusion, the results show that chronic citalopram and fluoxetine treatments induce an increase of choroid plexus 5-HT2C receptor density, but the effect is more marked with citalopram. These differences in the regulation of the 5-HT2C receptors may lead to pharmacodynamic differences between chronic citalopram and fluoxetine treatments.

Topics: Amphetamines; Animals; Antiparkinson Agents; Autoradiography; Choroid Plexus; Citalopram; Ergolines; Fluoxetine; Image Processing, Computer-Assisted; Male; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Selective Serotonin Reuptake Inhibitors; Serotonin Receptor Agonists; Up-Regulation

To examine the role of serotonin2C (5HT2C) receptors in alcohol drinking behavior, the binding indices of 5HT2C receptors were determined in various brain regions of alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. 5HT2C receptor-mediated phosphoinositide hydrolysis in the choroid plexus of P and NP rats was also determined. It was observed that the densities of 5HT2C receptors are significantly higher in the hippocampus, the amygdala, and the choroid plexus, but not in the cortex of P rats compared with NP rats. The Kd values of [3H]mesulergine binding to 5HT2C receptors were not different in these brain regions of P rats compared with NP rats. It was also observed that 5HT-stimulated [3H]inositol 1-phosphate formation was significantly higher in the choroid plexus of P rats compared with NP rats. The results of this study indicate that the numbers of 5HT2C receptors are higher in the hippocampus, the amygdala, and the choroid plexus, and that 5HT2C receptor-mediated phosphoinositide hydrolysis is more elevated in the choroid plexus of P rats compared with NP rats. Thus, it seems from these results that increased 5HT2C receptors may be involved in the genetic vulnerability to alcohol drinking behavior.

Topics: Alcohol Drinking; Alcoholism; Animals; Brain; Brain Mapping; Choroid Plexus; Ergolines; Hydrolysis; Male; Phosphatidylinositols; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Serotonin

Using transfected NIH 3T3 mouse fibroblast cell lines expressing the rat 5-HT2A and rat 5-HT2C receptor subtypes, and techniques of 2-[125I](+)-iodolysergic acid diethylamide ([125I]LSD) binding and serotonin (5-hydroxytryptamine, 5-HT)-stimulated phosphoinositide hydrolysis, we have characterized a new structural class of 5-HT receptor ligands, the aryloxyalkylimidazolines. These compounds were found to be potent competitors of [125I]LSD binding at both receptor subtypes (Ki approximately 5-200 nM) and to have efficacy ranging from potent competitive antagonists (IC50 approximately 25 nM) to moderately potent full agonists (EC50 approximately 200 nM). Some of these compounds are agonists at both receptor subtypes, while others are 5-HT2C receptor agonists with 5-HT2A receptor antagonist activity. None of the aryloxyalkylimidazolines reported here have 5-HT2A or 5-HT2C receptor selective antagonist activity. Since these compounds are novel structures, we compared them with a variety of reference 5-HT receptor ligands selected from other chemical classes that have previously been studied at 5-HT2A and 5-HT2C receptors in native tissues.

Topics: 3T3 Cells; Animals; Binding, Competitive; Dose-Response Relationship, Drug; Ergolines; Imidazoles; Lysergic Acid Diethylamide; Mice; Phosphatidylinositols; Rats; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists

Dopamine agonists are known to increase the incidence of Leydig cell hyperplasia/adenomas when administered to rats over periods of 1-2 years. We have examined the early changes in factors affecting Leydig cell growth/hyperplasia after chronic oral administration of one of these dopamine agonists, Mesulergine (CU32-085) [N-(1-6-dimethylergolin-8 alpha-yl)-N,N-dimethylsulphamide hydrochloride), to Sprague-Dawley (SD) rats. Eight-week-old rats were given the dopamine agonist (2 mg/kg body weight/day) in food for 5 or 57 weeks. The dopamine agonist treatment had no significant effect on food intake, body weight, and testis and seminal vesicle size, but significantly decreased testicular interstitial fluid volume at 5 weeks (by 51%). Leydig cells isolated from rats treated with the dopamine agonist for 5 weeks exhibited an increase in the rate of protein synthesis compared with the controls (by 28%). This treatment, however, had no significant effect on the number of Leydig cells or macrophages as assessed by histological examination of testicular sections. Treatment with the dopamine agonist for 57 weeks caused a 36 and 28% increase in the number of Leydig cells and macrophages, respectively. Nodules of Leydig cells, indicating the first signs of tumor development, were present in testes from the 57- but not the 5-week-treated animals or the controls of both groups, although an increase in the number of Leydig cells occurred with aging. Thick-walled arterioles were found in the intertubular spaces of the testis sections from rats treated for 57 weeks. These findings suggest that chronic treatment of male SD rats with the dopamine agonist causes hypertrophy of Leydig cells within 5 weeks (as assessed by [3H]methionine incorporation), followed by hyperplasia within 2 years, prior to the development of Leydig cell adenomas, which occur within 1-2 years after the initiation of treatment.

Topics: Adenoma; Animals; Antiparkinson Agents; Body Weight; Dopamine Agonists; Dose-Response Relationship, Drug; Ergolines; Extracellular Space; Hyperplasia; Leydig Cell Tumor; Leydig Cells; Male; Organ Size; Rats; Rats, Sprague-Dawley; Testicular Neoplasms

Stable transfection of the human neuroblastoma cell line SH-SY5Y with the human 5-hydroxytryptamine2A (5-HT2A) or 5-HT2C receptor cDNA produced cell lines demonstrating ligand affinities that correlated closely with those for the corresponding endogenous receptors in human frontal cortex and choroid plexus, respectively. Stimulation of the recombinant receptors by 5-HT induced phosphoinositide hydrolysis with higher potency but lower efficacy at the 5-HT2C receptor (pEC50 = 7.80 +/- 0.06) compared with the 5-HT2A receptor (pEC50 = 7.30 +/- 0.08). Activation of the 5-HT2A receptor caused a transient fourfold increase in intracellular Ca2+ concentration. Whole-cell recordings of cells clamped at -50 mV demonstrated a small inward current (2 pA) in response to 10 microM 5-HT for both receptors. There were no differences in potency or efficacy of phosphoinositide hydrolysis among four hallucinogenic [d-lysergic acid diethylamide (LSD), 1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane (DOI), 5-methoxy-N,N-dimethyltryptamine, and mescaline] and three nonhallucinogenic drugs (m-chlorophenylpiperazine, quipazine, and ergotamine). Comparison of equipotent doses producing 20% of the maximal response induced by 5-HT revealed selective activation of the 5-HT2A receptor by LSD and to a lesser degree by DOI, mescaline, and ergotamine. Quipazine and 5-methoxy-N,N-dimethyltryptamine were relatively nonselective, whereas m-chlorophenylpiperazine selectively activated the 5-HT2C receptor. It is unlikely therefore that hallucinosis is mediated primarily by activity at the 5-HT2C receptor, whereas activity at the 5-HT2A receptor may represent an important but not unique mechanism associated with hallucinogenic drug action.

Topics: Adrenergic alpha-Agonists; Amphetamines; Antiparkinson Agents; Calcium; Choroid Plexus; Electrophysiology; Ergolines; Ergotamine; Frontal Lobe; Hallucinogens; Humans; Hydrolysis; Ketanserin; Lysergic Acid Diethylamide; Mescaline; Methoxydimethyltryptamines; Neuroblastoma; Phosphatidylinositols; Piperazines; Quipazine; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Recombinant Proteins; RNA, Messenger; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tritium; Tumor Cells, Cultured

m-Chlorophenylpiperazine (mCPP), a major metabolite of the atypical antidepressant trazadone, has been observed to produce marked physiological and behavioral effects in both humans and animals. These effects have been attributed to the interaction of mCPP with serotonergic receptors. The present study was designed to characterize those interactions of mCPP with central serotonergic receptors which mediate mCPP-induced stimulus control. A series of serotonergic antagonists (mesulergine, pizotyline, ketanserin, spiperone, risperidone, ritanserin, metergoline, pirenpirone, and LY53857) was tested for the ability to block the mCPP stimulus. The affinity of these antagonists for 5-HT2A and 5-HT2C receptors was then correlated with maximal percent inhibition of the mCPP stimulus. Kd at the 5-HT2C receptor was inversely proportional (r = -0.75, P < 0.05), and Kd at the 5-HT2A receptor directly proportional (r = +0.67, P < 0.05) to the maximal percent inhibition of the mCPP stimulus. The 5-HT2C selectivity ratio [Kd(5-HT2A)/Kd(5-HT2C)] of the antagonists was directly proportional (r = +0.86, P < 0.01) to maximal percent inhibition of the mCPP stimulus. A multiple regressions analysis indicated that 81% of the variance in the ability of a given antagonist to block the mCPP stimulus could be predicted on the basis of its affinity for 5-HT2A and 5-HT2C receptors. It is concluded that the stimulus effects of mCPP are mediated predominantly by a combination of agonist activity at 5-HT2C receptors and antagonist activity at 5-HT2A receptors.

Topics: Animals; Antiparkinson Agents; Binding, Competitive; Dose-Response Relationship, Drug; Ergolines; Male; Piperazines; Rats; Rats, Inbred F344; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists

d-Fenfluramine (0.63 mg/kg i.p.), a serotonin (5-hydroxytryptamine, 5-HT) releaser and re-uptake inhibitor, reduced the eating caused by neuropeptide Y (235 pmol) injected into the paraventricular nucleus of the hypothalamus. The 5-HT1 and 5-HT2 receptor antagonist metergoline (1.0 and 2.0 mg/kg i.p.) and the 5-HT1A and 5-HT1B receptor antagonist (+/-)-cyanopindolol (3.0 and 8.0 mg/kg s.c.) significantly antagonized the effect of d-fenfluramine. The 5-HT2A and 5-HT2C receptor antagonist mesulergine (0.1 and 0.3 mg/kg s.c.) and the 5-HT2A receptor antagonist ketanserin (2.5 and 5.0 mg/kg i.p.) did not significantly modify the effect, nor did the 5-HT1A and 5-HT1B receptor antagonist (-)-propranolol (20-40 nmol), injected bilaterally into the paraventricular nucleus of the hypothalamus. The results suggest that d-fenfluramine reduces neuropeptide Y's hyperphagia by indirectly stimulating 5-HT1B receptors outside the paraventricular nucleus of the hypothalamus.

Topics: Analysis of Variance; Animals; Antiparkinson Agents; Drug Interactions; Eating; Ergolines; Fenfluramine; Hyperphagia; Hypothalamus; Injections, Intraperitoneal; Injections, Subcutaneous; Ketanserin; Male; Metergoline; Neuropeptide Y; Paraventricular Hypothalamic Nucleus; Pindolol; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT1B; Receptors, Serotonin; Serotonin Antagonists

Intraperitoneal administration of 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) produced significant decreases in the first-hour food intake on day 1 and on day 2 relative to saline-treated animals. Complete tolerance developed to DOI-induced hypophagia by day 3. However, there was no cross-tolerance to m-chlorophenyl-piperazine (m-CPP)-induced hypophagia. Similarly, complete tolerance developed to m-CPP-induced hypophagia by day 3, but again there was no cross-tolerance to DOI-induced hypophagia. These findings suggest that DOI and m-CPP-induced hypophagia are mediated by different mechanisms, most likely by selective stimulation of 5-HT2A receptors by DOI and 5-HT2C receptors by m-CPP. The functional sensitivity changes did not parallel changes in hypothalamic [3H]-mesulergine-labeled 5-HT2C receptors or [3H]-ketanserin-labeled 5-HT2A receptors following chronic m-CPP or DOI treatment, although both treatments significantly reduced 5-HT2A and 5-HT2C receptors in cortex. Thus, future studies investigating the effects of daily m-CPP and DOI administration on phosphoinositide hydrolysis or mRNA for 5-HT2C and 5-HT2A receptors in the hypothalamus might help explain the functional sensitivity changes observed in the present study.

Topics: Amphetamines; Animals; Binding, Competitive; Drug Tolerance; Eating; Ergolines; Frontal Lobe; Injections, Intraperitoneal; Ketanserin; Male; Piperazines; Propane; Radioligand Assay; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin Receptor Agonists; Time Factors

The effects of chronic clomipramine, imipramine and clorgyline on 5-HT1C receptors were studied in discrete brain regions, in male Wistar rats, using [3H]mesulergine to label the receptor binding sites. Clorgyline treatment significantly reduced [3H]mesulergine binding (Bmax values) in both the hypothalamus and striatum compared to saline-treated animals. There were no differences in the maximum number of [3H]mesulergine binding sites following clorgyline in the hippocampus, frontal cortex or brainstem. Neither clomipramine or imipramine treatment resulted in any significant changes in 5-HT1C receptor number in the brain regions examined here. Furthermore, the Kd values (receptor affinity) for [3H]mesulergine binding were not significantly different comparing treatment groups to control animals. The significant changes in discrete brain regions following chlorgyline treatment suggest that 5-HT1C receptors may be involved in the clinical efficacy for the treatment of depression and other neuropsychiatric disorders.

Topics: Animals; Brain; Clomipramine; Clorgyline; Ergolines; Imipramine; Male; Rats; Rats, Wistar; Receptors, Serotonin

1. In pithed rats, the receptor type of cardiac tissue mediating the tachycardiac response to 5-hydroxytryptamine (5-HT) was analysed. 2. Ketanserin, mesulergine and methiothepin, administered in doses which antagonized the pressor response to 5-HT, slightly reduced, considerably reduced and antagonized, respectively, its tachycardiac response. 3. 8-OH DPAT and RU 24969 produced no significant tachycardia, while DOI neither mimicked nor blocked the 5-HT-induced tachycardia. 4. The tachycardia was not affected by MDL 72222, metoclopramide and cocaine. 5. The hypothesis is proposed that in rats the tachycardiac response to 5-HT is mediated via 5-HT receptors belonging to an yet unclassified subtype of 5-HT1 or 5-HT2 receptors.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Blood Pressure; Ergolines; Female; Heart Rate; Ketanserin; Male; Methiothepin; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin

We studied the effects of acute clozapine and haloperidol treatments on 5-HT2C receptor binding characteristics and 5-HT2C receptor-mediated phosphoinositide hydrolysis in the rat choroid plexus. Scatchard analysis (with [3H]mesulergine) showed that acute clozapine treatment (10 and 25 mg/kg) decreased the density (Bmax) of 5-HT2C receptors by 20-25% with no marked change in the affinity (Kd). Quantitative autoradiography was in accordance with homogenate binding studies showing that acute clozapine treatment, unlike haloperidol (0.5 mg/kg), decreased the number of both agonist ([125I](+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, [125I]DOI) and antagonist ([3H]mesulergine) labeled 5-HT2C receptor binding sites. The decrease was more robust with the higher dose of clozapine. For comparison, both doses of clozapine, unlike haloperidol, decreased equally the density of 5-HT2A receptors in the frontal cortex by about 45%, whereas none of the treatments altered dopamine D2 receptor characteristics in the striatum. The Kd value of 5-HT2A receptors was significantly increased after the dose of 25 mg/kg of clozapine. These clozapine treatments failed to decrease the maximal 5-HT2C receptor-mediated phosphoinositide hydrolysis response. The higher dose of clozapine increased 5-HT-induced phosphoinositide hydrolysis response, but also decreased significantly the basal levels of phosphoinositide hydrolysis. Haloperidol did not significantly affect the 5-HT2C receptor-mediated phosphoinositide hydrolysis. To summarize, the present data show that a single injection of clozapine is able to reduce the density of 5-HT2C receptors but fails to cause functional desensitization of 5-HT2C receptors in the rat choroid plexus.

Topics: Amphetamines; Animals; Antiparkinson Agents; Autoradiography; Cerebral Cortex; Choroid Plexus; Clozapine; Ergolines; Haloperidol; Image Processing, Computer-Assisted; Injections, Subcutaneous; Male; Neostriatum; Phosphatidylinositols; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; Receptors, Serotonin; Serotonin Receptor Agonists

The 5-HT2C receptor gene is unique among the members of the 5-HT receptor family by virtue of its genomic organisation. The human 5-HT2C receptor gene, unlike many other genes for guanine nucleotide binding (G)-proteins, contains three introns which interrupt the coding sequence into four exons. The first two introns are at equivalent positions as compared to the intervening sequences previously found in the 5-HT2(A) receptor gene, suggesting a close evolutionary relationship between both genes. Southern blot analysis shows that the 5-HT2C receptor gene is a single copy gene. Furthermore, we report the functional expression of a complementary DNA for the 5-HT2C receptor, cloned from hippocampal RNA. Membranes prepared from NIH 3T3 cells stably expressing the 5-HT2C receptor cDNA, displayed a single population of high affinity sites for the antagonist [3H]mesulergine (Kd = 2.9 +/- 0.4 nM, Bmax = 44.3 +/- 7.2 pmol/mg protein) as well as for [3H]5-HT (Kd = 9.9 +/- 0.7 nM, Bmax = 13.6 +/- 1.0 pmol/mg protein). Displacement of [3H]mesulergine and [3H]5HT binding by ligands indicated a pharmacological similarity of these binding sites with porcine and rat choroid plexus 5-HT2C receptors. Furthermore, activation of the 5-HT2C receptor with 5-HT results in an increased phospholipase C activity.

Topics: 3T3 Cells; Amino Acid Sequence; Animals; Antiparkinson Agents; Base Sequence; Binding, Competitive; Blotting, Southern; Cloning, Molecular; DNA Primers; DNA, Complementary; Ergolines; Exons; Gene Expression Regulation; Hippocampus; Humans; Mice; Molecular Sequence Data; Polymerase Chain Reaction; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Restriction Mapping; RNA, Messenger; Transfection; Type C Phospholipases

5-HT2C receptor antagonists, such as mianserin and mesulergine, exhibit negative intrinsic activity, defined as a decrease in agonist-independent, receptor-mediated, phosphoinositide hydrolysis in cells transfected with the 5-HT2C receptor cDNA. These drugs are classified as inverse agonists. Guanine nucleotides reciprocally modulate the binding of an agonist and inverse agonist, suggesting that an inverse agonist binds preferentially to the G protein-uncoupled form of the 5-HT2C receptor. Another 5-HT2C receptor antagonist, 2-bromolysergic acid diethylamide, functions as a neutral antagonist with no intrinsic activity, but is able to block both agonist and inverse agonist. Chronic treatment of choroid plexus cells with an inverse agonist, but not with the neutral antagonist, causes 5-HT2C receptor down-regulation, suggesting that the biological effects of 5-HT2C receptor antagonists are not solely due to antagonism of endogenous agonist. These results provide evidence that constitutively active 5-HT2C receptors are biologically significant. The functionally distinct properties of inverse agonists and neutral antagonists may elucidate the mechanisms controlling basal receptor activity states and lead to novel approaches in the development of therapeutic agents.

Topics: 3T3 Cells; Animals; Antiparkinson Agents; Cell Membrane; Cells, Cultured; Choroid Plexus; Cloning, Molecular; DNA, Complementary; DOM 2,5-Dimethoxy-4-Methylamphetamine; Epithelium; Ergolines; Guanosine 5'-O-(3-Thiotriphosphate); Kinetics; Lysergic Acid Diethylamide; Mianserin; Mice; Radioligand Assay; Rats; Receptors, Serotonin; Serotonin Antagonists; Transfection

The serotonin2A and serotonin2C receptors are unique among receptors coupled to guanine nucleotide binding proteins in that chronic treatment in vivo with agonists as well as antagonists decreases receptor density. In an attempt to uncover molecular events involved in down-regulation of the serotonin2A receptor, the ability of agonists and antagonists to alter receptor density was examined in three heterologous expression systems, i.e., transfected NIH 3T3, transfected Madin-Darby canine kidney, and transfected AtT-20 cells. All three transfected cell lines exhibited pharmacological properties consistent with that predicted for cells expressing the serotonin2A receptor. However, the three cell lines displayed different receptor regulation properties in response to drugs acting at the serotonin2A receptor. In transfected NIH 3T3 cells, neither agonist nor antagonist treatment altered receptor density. Treatment with agonist as well as antagonist led to up-regulation of the serotonin2A receptor in transfected Madin-Darby canine kidney cells. In transfected AtT-20 cells, treatment with agonist led to receptor down-regulation, whereas antagonist treatment increased receptor density. Thus, the cellular background in which the serotonin2A receptor is expressed appears to determine the regulation properties of the receptor.

Topics: 3T3 Cells; Animals; Antiparkinson Agents; Binding, Competitive; Cell Line; Dogs; DOM 2,5-Dimethoxy-4-Methylamphetamine; Ergolines; Gene Expression Regulation; Ketanserin; Kidney; Kinetics; Mice; Pituitary Neoplasms; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; Recombinant Proteins; Transfection; Tumor Cells, Cultured

Electrophysiological techniques were used to study the effects of various serotonin (5-HT) agonists and antagonists on the activity of dopamine (DA) neurons in the ventral tegmental area (VTA) of rats. Systemic administration of the selective 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (1.25-80 micrograms/kg i.v.) increased the firing rate of the majority (75%) of DA cells studied and stimulated their bursting activity. A subpopulation (25%) of DA neurons was inhibited by 8-OH-DPAT. Selective lesions of 5-HT neurons by the neurotoxin 5-7-dihydroxytryptamine abolished completely the excitatory effect of 8-OH-DPAT on both firing rate and bursting activity of DA neurons. Microiontophoretic application of 8-OH-DPAT into the VTA did not cause any change in the firing rate of DA neurons. Treatment with the selective 5-HT1B agonist CGS 12066B (7-trifluoromethyl-4-(4-methyl-1-piperazinyl)-pyrolo[1,2-a] quinoxaline 1:2 maleate salt) (1.25-160 micrograms/kg i.v.) did not cause any change in basal firing rate of VTA DA cells. Systemic administration of trifluoromethylphenylpiperazine (TFMPP) (1.25-160 micrograms/kg i.v.) and m-chlorophenylpiperazine (mCPP) (1.25-320 micrograms/kg i.v.), two mixed 5-HT1B/5-HT1C receptor agonists, significantly reduced the firing rate of all VTA DA neurons studied. The effect of mCPP (maximal inhibition, 40%) was more pronounced compared to that of TFMPP (maximal inhibition, 25%). Microiontophoretic application of mCPP into the VTA caused a marked inhibition of the basal activity of DA neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Dopamine; Ergolines; Male; Motor Activity; Pindolol; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin; Ventral Tegmental Area

Expression of the 5-hydroxytryptamine type 2C (5-HT 2C) receptor in NIH/3T3 fibroblasts results in agonist-independent 5-HT2C receptor activation. Some 5-HT2c receptor antagonists decrease this activation and are termed inverse agonists. The present study uses this system to evaluate functional and receptor binding properties of other 5-HT2C receptor antagonists. A number of inverse agonists, including clozapine, and a neutral antagonist (methysergide) were identified in a functional assay. Guanine nucleotides increased the affinity of a radiolabeled inverse agonist ([3H]mesulergine), suggesting that inverse agonists bind the G protein-uncoupled form of the 5-HT2C receptor with high affinity. Competition binding was performed using conditions that separately labeled the G protein-coupled and -uncoupled forms of the receptor. These studies demonstrated that inverse agonists bound the uncoupled form of the 5-HT2C receptor with higher affinity, compared with the G protein-coupled form. Agonists, on the other hand, had higher affinity for the coupled form whereas neutral antagonists had equal affinity for both forms of the receptor. Thus, 5-HT2C receptor neutral antagonists exhibited functional and receptor binding properties consistent with those of classical receptor antagonists. However, 5-HT2C receptor inverse agonists displayed functional and receptor binding properties that were opposite those of agonists.

Topics: 3T3 Cells; Animals; Binding, Competitive; Cell Line; DOM 2,5-Dimethoxy-4-Methylamphetamine; Ergolines; Guanine Nucleotides; Hydrolysis; Mice; Phosphatidylinositols; Radioligand Assay; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Recombinant Proteins; Serotonin Antagonists; Serotonin Receptor Agonists

Chronic treatment with clozapine (14 days; 10 and 25 mg/kg/day) decreases 5-HT1C receptor density but not affinity in rat choroid plexus measured with [3H]mesulergine. We now report the effects of the same clozapine treatment regimens on the function of 5-HT1C receptors (measured by maximal stimulation of 5-HT1C receptor-mediated phosphoinositide hydrolysis) in relation to receptor changes in rat choroid plexus. Quantitative 5-HT1C receptor autoradiography indicated that chronic clozapine treatment decreased, in a dose-related manner, 5-HT1C receptor binding sites labeled by antagonist ([3H]mesulergine) and agonist ([125I](+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, [125I]DOI) radioligands. However, only the higher dose of clozapine decreased statistically significantly the maximal 5-HT1C receptor-mediated phosphoinositide hydrolysis response. Chronic administration of haloperidol (0.5 mg/kg/day) did not change any of the 5-HT1C receptor parameters. In conclusion, chronic clozapine treatment is able to modulate the function of 5-HT1C receptors. This further strengthens the possibility that 5-HT1C receptors may contribute to some of the atypical effects of clozapine.

Topics: Amphetamines; Animals; Autoradiography; Choroid Plexus; Clozapine; Ergolines; Haloperidol; Hydrolysis; Image Processing, Computer-Assisted; In Vitro Techniques; Male; Phosphatidylinositols; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Second Messenger Systems; Serotonin Receptor Agonists

Rats were trained to discriminate the 5-HT receptor agonist m-chlorophenylpiperazine (mCPP; 1 mg/kg) from saline using a two-lever, water-reinforced drug discrimination task. The antidepressant trazodone (1-8 mg/kg), the 5-HT1B/2C receptor agonists 1-(m-trifluoromethylphenyl)piperazine (TFMPP; 0.25-1 mg/kg) and MK 212 (0.125-1 mg/kg), and the mixed 5-HT1A/B receptor agonist RU 24969 (0.25-2 mg/kg) substituted fully for mCPP. The 5-HT2A/2C receptor agonists 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI; 0.25-1 mg/kg) and d-lysergic acid diethylamide (LSD; 0.02-0.08 mg/kg) and the 5-HT releaser fenfluramine (0.5-2 mg/kg) also mimicked mCPP. Agonists selective for the 5-HT1A or 5-HT3 receptor or the 5-HT reuptake site produced saline-lever responding. The ergoline derivative mesulergine (0.5-4 mg/kg) produced a partial agonist/antagonist profile. The 5-HT1/2 receptor antagonist metergoline (0.125-1 mg/kg) completely blocked the mCPP cue whereas the 5-HT2A/2C receptor antagonists ketanserin and LY 53857 as well as all other 5-HT receptor antagonists failed to block the mCPP cue. The dopamine receptor antagonists SCH 23390 and haloperidol were also ineffective mCPP antagonists. Following pretreatment with the 5-HT synthesis inhibitor p-chlorophenylalanine (pCPA; 100 mg/kg/day) for 3 consecutive days, the discriminability of low doses of mCPP increased, whereas the effects of fenfluramine decreased. The present results suggest that the discriminative stimulus effects of mCPP in rats are mediated primarily by postsynaptic 5-HT2C receptors.

Topics: Animals; Discrimination, Psychological; Dopamine Antagonists; Ergolines; Fenfluramine; Lysergic Acid Diethylamide; Male; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Trazodone

5HT modulates the rhythmic locomotor output of most vertebrates by enhancing the duration and intensity of motor bursts in each cycle, but there is little clear evidence on the pharmacological profile of the 5HT receptor subtype(s) involved. In this study we extend our previous work on the role of 5HT in the development and modulation of locomotor behaviour in newly hatched Xenopus tadpoles by examining the 5HT receptor type responsible for enhancing the swimming activity in immobilized preparations. By applying a range of agonists and antagonists against different 5HT receptor subtypes, we conclude that serotonergic modulation of swimming activity is accomplished via the activation of just one receptor type with a pharmacological profile similar to the mammalian 5HT1a receptor. The effects of 5HT on burst duration (an increase) and on episode length (a decrease) are mimicked by the 5HT1a receptor agonists, 5-carboxamidotryptamine (5CT) and R(+)-8-OH-DPAT, and reversed by the 5HT1a receptor antagonist NAN-190. Agents acting at other 5HT1, as well as 5HT2 and 5HT3, receptor subtypes were without noticeable effect on the 5HT-enhanced swimming rhythm.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Aging; Animals; Cyproheptadine; Ergolines; Ketanserin; Metamorphosis, Biological; Methysergide; Motor Activity; Piperazines; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Swimming; Xenopus laevis

Male Sprague-Dawley rats received injections of cocaine (20 mg/kg/dose, IP) every 12 h for 14 days and were sacrificed on the 15th day. The chronic cocaine treatment caused an increase in the levels of serotonin [5-hydroxytryptamine (5-HT)] and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus. 5-HIAA levels in the frontal cortex were also increased, but 5-HT levels were unaltered by the chronic cocaine treatment. Similarly, striatal levels of 5-HT and 5-HIAA were unchanged by repeated administration of cocaine. Chronic cocaine administration did not alter the density of [3H]8-OH(DPAT), [3H]mesulergine, or [3H]ketanserin binding in the hippocampus, choroid plexus, and frontal cortex, respectively. Furthermore, repeated injection of cocaine did not alter serotonergic-mediated inhibition of adenylate cyclase activity. Thus, repeated administration of cocaine causes region-specific alterations in 5-HT levels but does not change the properties of the 5-HT1A, 5-HT1C, or 5-HT2 receptors.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Adenylyl Cyclases; Animals; Antiparkinson Agents; Brain; Brain Chemistry; Cocaine; Ergolines; Hydroxyindoleacetic Acid; Ketanserin; Male; Nerve Tissue Proteins; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin

The anti-immobility effect of fluoxetine (40 mg kg-1) in the forced swimming test in mice was antagonized by the 5-HT1c/2 antagonist mesulergine (7.5 mg kg-1) and the dopamine D2 antagonist (+/-)-sulpiride (12.5 mg kg-1) but not by the 5-HT2/1C antagonist ritanserine (2 mg kg-1), the 5-HT1A/1B antagonist (-)-propranolol (20 mg kg-1) or the 5-HT3 antagonist DAU 6215 (0.1 mg kg-1). All compounds were administered intraperitoneally (i.p.) 6 min before fluoxetine, given i.p. 30 min before testing. The anti-immobility effect of fluoxetine was also prevented by pretreatment with p-chlorophenylalanine (300 mg kg-1 twice daily for 3 days) which produced an 80% reduction of 5-HT in brain. The results suggest that fluoxetine reduces immobility time in mice forced to swim, by acting indirectly through a mesulergine-sensitive site, probably the 5-HT1C receptor.

Topics: Animals; Behavior, Animal; Depression; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Ergolines; Fluoxetine; Immobilization; Male; Mice; Neurotransmitter Uptake Inhibitors; Receptors, Serotonin; Swimming

Both the 5-HT1C receptor and the 5-HT uptake binding sites were measured in Fawn-Hooded, Sprague-Dawley and Wistar rats. Five brain regions were examined: frontal cortex, hippocampus, striatum, hypothalamus, and brainstem. We found significant differences in the Bmax and Kd values in various brain regions comparing Fawn-Hooded rats, with Sprague-Dawley and Wistar animals. The regional differences in receptor number and affinity in both the 5-HT1C receptor and the 5-HT uptake site in the Fawn-Hooded strain, relative to Wistar and Sprague-Dawley animals, provide support for the use of the Fawn-Hooded rat in serotonin dysfunction studies.

Topics: Animals; Binding Sites; Brain; Brain Stem; Corpus Striatum; Ergolines; Frontal Lobe; Hippocampus; Hypothalamus; Male; Paroxetine; Rats; Rats, Sprague-Dawley; Rats, Wistar; Receptors, Serotonin; Serotonin

5-HT receptor denervation supersensitivity has been proposed to explain behavioural supersensitivity to L-5-HTP in rats with 5,7-dihydroxytryptamine (5,7-DHT) lesions. No upregulation of 5-HT2 binding sites was found despite supersensitivity to putative 5-HT2,1C drugs. To test the hypothesis that the 5-HT1C properties of these drugs are involved instead, dose-response and time-course studies of 5-HT1C and 5-HT2 receptors were performed using several different radioligands in rat brain after making neonatal 5,7-DHT lesions by intraperitoneal injection. 5-HT1C sites labelled with [3H]-mesulergine showed a distinct regional distribution: brainstem > diencephalon > cortex > hippocampus > cerebellum, constituting 65, 70, 31, 70, and 73% of total sites labelled by [3H]-mesulergine in the absence of 20 nM spiperone to block 5-HT2 sites, respectively. 5,7-DHT lesions did not significantly alter BMAX, KD, or nH of [3H]-mesulergine-labelled 5-HT1C sites in cortex or other regions but did reduce the density of cortical [3H]-paroxetine sites (-55%). Cortical 5-HT1C sites labelled by [3H]-5-HT or [3H]-mianserin, and cortical 5-HT2 sites labelled by [3H]-DOB or [3H]-ketanserin, were also unaffected. These data suggest that although denervation supersensitivity of 5-HT1C or 5-HT2 receptors may occur at the level of the receptor transducer-effector, there is no evidence it occurs at the receptor recognition site.

Topics: 5,7-Dihydroxytryptamine; Analysis of Variance; Animals; Animals, Newborn; Binding Sites; Brain Neoplasms; Brain Stem; Cerebellum; Cerebral Cortex; Diencephalon; Dose-Response Relationship, Drug; Ergolines; Female; Hippocampus; Injections, Intraperitoneal; Mianserin; Pregnancy; Radioligand Assay; Rats; Receptors, Serotonin; Serotonin; Time Factors; Tritium

The lesion of serotonergic neurons (by an intraventricular injection of 5,7-dihydroxytryptamine) potentiated the conditioned place aversion induced by the 5-hydroxytryptamine1C/5-hydroxytryptamine2 antagonist mianserin in rats. This effect was selective for mianserin as the same lesion suppressed the conditioned place aversion induced by the benzodiazepine inverse agonist FG-7142. Previous results had shown the involvement of the 5-hydroxytryptamine1C receptors in the conditioned place aversion induced by mianserin [Rocha et al. (1993) Behav. Pharmac. 4, 101-106]. It was thus of interest to investigate the effect of the lesion on these receptor binding sites. Autoradiographic binding studies showed that the lesion significantly increased the concentration of the 5-hydroxytryptamine1C binding sites in various brain regions, including the amygdala, the hippocampus and the nucleus accumbens. Contrastingly, in these same brain regions, in situ hybridization histochemistry did not reveal an alteration of the level of messenger RNA coding for these receptors. On the one hand, correlating potentiation of the aversive effects of mianserin and increase of 5-hydroxytryptamine1C binding sites in the limbic system represent an interesting step in the comprehension of the molecular and motivational effects of serotonergic drugs. On the other hand, showing a dissociation between the expression of 5-hydroxytryptamine1C receptors and their corresponding messenger RNA, suggest that post-transcriptional mechanisms are involved in the regulation of these receptors.

Topics: 5,7-Dihydroxytryptamine; Animals; Antiparkinson Agents; Autoradiography; Brain Chemistry; Carbolines; Conditioning, Operant; Ergolines; In Situ Hybridization; Male; Mianserin; Rats; Receptors, GABA-A; Receptors, Serotonin; RNA, Messenger; Transcription, Genetic

The effect of chronic ethanol consumption (60 days) on 5-HT1C receptors as measured by [3H]mesulergine binding in the hippocampus, cortex, and choroid plexus of rats was investigated. The 5-HT1C receptor-mediated phosphoinositide hydrolysis in rat choroid plexus was also investigated. It was observed that chronic ethanol treatment significantly increased the 5-HT-stimulated [3H]inositol 1-phosphate ([3H]IP1) formation, as well as the density (Bmax) of 5-HT1C receptors without causing a significant change in affinity (KD) of [3H]mesulergine binding in rat choroid plexus. It was also observed that chronic ethanol consumption had no significant effect on the Bmax or KD of 5-HT1C receptor binding sites in the hippocampus and cortex brain regions of rats. These results thus suggest that chronic ethanol consumption causes an up-regulation of both 5-HT1C receptors and 5-HT1C receptor-mediated phosphoinositide hydrolysis in rat choroid plexus but has no significant effects on the 5-HT1C receptors in brain. These results also suggest that 5-HT1C receptors and their functional response may be involved in the pathogenesis of alcohol dependence.

Topics: Animals; Antiparkinson Agents; Binding Sites; Brain; Cerebral Cortex; Choroid Plexus; Ergolines; Ethanol; Hippocampus; Hydrolysis; Male; Phosphatidylinositols; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Up-Regulation

Binding sites corresponding to 5-HT1E receptors were labelled in mouse, rat, and guinea-pig brains by using [3H]5-hydroxytryptamine ([3H]5-HT) in the presence of 5-carboxamidotryptamine (5-CT) (0.1 microM), and their distribution within the brain was studied by quantitative autoradiography. The results obtained with mouse brain show that 5-HT1E binding sites are particularly present in the cortex, caudate-putamen and claustrum, where they showed the highest density. Lower densities were measured in other regions. Saturation experiments showed that the affinity of [3H]5-HT for 5-HT1E binding sites (nanomolar range) was very similar in the different structures. The distribution of 5-HT1E binding sites was similar in rat and guinea-pig brains. In rat brain, selective lesioning of serotonergic fibres by intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT), a specific 5-HT neurotoxin, did not affect the density of 5-HT1E binding, indicating that these receptors are mainly localized on non-serotonergic neurones.

Topics: 5,7-Dihydroxytryptamine; Animals; Autoradiography; Binding, Competitive; Brain; Brain Chemistry; Ergolines; Guinea Pigs; In Vitro Techniques; Male; Membranes; Mice; Neurons; Radioligand Assay; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin; Serotonin Receptor Agonists

5-CT (5-carboxamidotryptamine)-insensitive (5-HT1E/5-HT1F) 5-HT1-like recognition sites have been mapped autoradiographically in rat and guinea pig brain using [3H]5-HT in the presence of 5-CT and mesulergine to mask 5-HT1A, 5-HT1B, 5-HT1D and 5-HT2C binding sites. Binding was more dense in the guinea pig but in both species 5-CT-insensitive 5-HT1-like sites were located in the olfactory tubercle, interpeduncular nucleus, caudate putamen, nucleus accumbens, substantia nigra, frontal cortex and hippocampus. These receptors were particularly marked in the claustrum of the guinea pig but not the rat.

Topics: Animals; Antiparkinson Agents; Autoradiography; Basal Ganglia; Brain Mapping; Ergolines; Guinea Pigs; Male; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Serotonin; Species Specificity

5-Hydroxytryptamine (5-HT) evoked potent contractile responses in phenoxybenzamine-treated ring segments of rat caudal artery, partially contracted with U46619. Responses were mimicked by 5-HT1-selective agonists with the potency order: RU24969 > 5-carboxamidotryptamine > 5-HT = CP-93,129 >> sumatriptan. 8-Hydroxy-N,N-dipropylaminotetralin was virtually inactive. Responses were unaffected by spiperone (0.1 microM) and mesulergine (1.0 microM), but were antagonized competitively by (+/-)-cyanopindolol affording agonist-independent pKB estimates of 8.4 to 8.9. The pharmacological profile of this receptor is consistent with that of the 5-HT1B subtype. Since the 5-HT1B receptor is the rodent homologue of the 5-HT1D beta subtype, it might be anticipated that 5-HT1D beta receptors will be found to mediate vasoconstrictor responses in non-rodent species.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Arteries; Ergolines; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth, Vascular; Pindolol; Prostaglandin Endoperoxides, Synthetic; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Spiperone; Vasoconstrictor Agents

In this study, quantitative autoradiography was used to determine the selectivity of RP 62203, a novel naphtosultam derivative, for 5-HT2 receptors in vitro and ex vivo, using [125I]7-amino-8-iodo-ketanserin ([125I]AMIK) and [3H]mesulergine as radioligands. The density of [125I]AMIK or [3H]mesulergine binding sites was determined by quantitative image analysis. In in vitro experiments, RP 62203 displaced [125I]AMIK from 5-HT2 receptors with an IC50 of 0.21 nM in rat frontal cortex. Its affinity for 5-HT1C receptors was 100-fold lower (IC50 25 nM versus [3H]mesulergine in rat choroid plexus). RP 62203 showed moderate affinity for alpha 1-adrenoceptors in the rat thalamus (IC50 14 nM) and for histamine H1 receptors in the guinea-pig cerebellum (IC50 13 nM). The tetrabenazine sites were not affected by RP 62203 at a concentration of 30 nM. In ex vivo experiments, RP 62203 was about 4 times more potent than ritanserin in displacing [125I]AMIK from 5-HT2 receptors (ED50 0.58 mg/kg p.o.). A dose of 10 mg/kg of RP 62203 did not displace [3H]mesulergine from 5-HT1C receptors or [125I]AMIK from alpha 1-adrenoceptors and tetrabenazine sites in the rat brain and from histamine H1 receptors in the guinea-pig brain. These results demonstrate that RP 62203 specifically recognizes 5-HT2 receptors in rodent brain.

Topics: Animals; Antiparkinson Agents; Autoradiography; Cerebellum; Choroid Plexus; Cyclic S-Oxides; Ergolines; Guinea Pigs; In Vitro Techniques; Ketanserin; Male; Naphthalenes; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha; Serotonin Antagonists; Thalamus

The molecular processes by which agonists and antagonists bind to serotonin2 [5-hydroxytryptamine (5-HT2)] receptors are currently unknown. Three molecular models have proposed that conserved aromatic residues help to anchor the phenyl ring of 5-HT via stacking or pi-pi-type interactions with the 5-HT2 receptor. To test these models we made single point mutations (Phe339-->Leu339 and Phe340-->Leu340) of two aromatic residues that are conserved among all guanine nucleotide-binding protein-coupled 5-HT receptors and a single point mutation (Phe125-->Leu125) that exchanges a 5-HT2 for a 5-HT1c sequence. [3H]Mesulergine binding was abolished by Phe340-->Leu340 and unchanged with the Phe339-->Leu339 and Phe125-->Leu125 mutations, whereas [3H]ketanserin binding affinity was diminished by the Phe339-->Leu339 mutation and unchanged by Phe340-->Leu340 and Phe125-->Leu125. We also found that the affinities of three ergot derivatives (mesulergine, methysergide, and lisuride) were decreased by 88-1079-fold with only the Phe340-->Leu340 mutation. We also discovered that 4-[125I]iodo-2,5-(dimethoxy)phenylisopropylamine (DOI) binding was abolished in COS-7 cells expressing 5-HT2 (Phe340-->Leu340) receptors but maintained in cells expressing the Phe339-->Leu339 and Phe125-->Leu125 mutations. Additionally, the Ki values for several agonists and partial agonists (5-HT, DOI, m-chlorophenylpiperazine, trifluoromethylphenylpiperazine, bufotenine, and MK-212) were greatly diminished (26-14,000-fold decrease) only with the Phe340-->Leu340 receptor mutation. Finally, the Phe340-->Leu340 mutant receptors displayed an attenuated or abolished ability to augment phosphoinositide hydrolysis in COS-7 cells with four separate agonists (5-HT, MK-212, bufotenine, and quipazine). Taken together, these results are consistent with the idea that agonists and certain ergot derivatives anchor to 5-HT2 receptors, in part, via specific interactions with aromatic residue Phe340 located in transmembrane region VI.

Topics: Amino Acid Sequence; Amphetamines; Animals; Base Sequence; Cell Line, Transformed; Chlorocebus aethiops; Ergolines; Hydrolysis; Ketanserin; Leucine; Molecular Sequence Data; Mutagenesis, Site-Directed; Phenylalanine; Phosphatidylinositols; Point Mutation; Radioligand Assay; Receptors, Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists

Radioligand binding measurements were performed in membranes of sheep caudate nucleus using [3H]5-hydroxytryptamine (5-HT). [3H]5-HT labeled a population of high affinity binding sites with a Kd of 1.9 +/- 0.1 nM and a Bmax of 19.8 +/- 2.2 fmol/mg tissue. Combined 5-HTID/E binding sites were the predominant 5-HT1 subtype, accounting for 78% of the total population of 5-HT1 binding sites. 5-Carboxamidotryptamine (5-CT) and sumatriptan yielded inhibition curves which best fitted a two-site model with high affinity values of 0.8 and 10.1 nM, and 1000 and 206 nM for their low affinity components. The proportion of the high affinity 5-CT and sumatriptan binding sites was 79 and 72%. The binding affinity profile of 5-HT1D binding sites [5-CT > 5-HT > d-LSD > 5-MeOT > sumatriptan > RU 24,969 > metergoline > tryptamine = rauwolscine = methylsergide > yohimbine = methiothepin > TFMPP = 8-OH-DPAT > 2-methyl-5-HT > mCPP = quipazine = CP 93,129 > ketanserin > (-)-propranolol = haloperidol = ipsapirone] compares well to that reported for 5-HT1D receptor sites in human caudate and cortex (correlation coefficient: 0.99 and 0.98). The present results indicate that sheep caudate nucleus is a valid tissue for studying interaction of compounds with 5-HT1D binding sites in the relative absence of 5-HT1E binding sites.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Binding Sites; Caudate Nucleus; Cell Membrane; Cerebral Cortex; Ergolines; Humans; Indoles; Rats; Selective Serotonin Reuptake Inhibitors; Serotonin; Sheep; Sulfonamides; Sumatriptan; Tritium

Postnatal changes in the distribution of 5-HT receptor subtypes in the visual cortex of cats were assessed both qualitatively and quantitatively using in vitro autoradiographic methods. The 5-HT 1A, 1C, 2, and 3 receptor subtypes and the 5-HT uptake (5-HTUp) site were visualized with 3H-8-hydroxy-2(di-n-propyl-amino)tetralin, 3H-mesulergine, (2,5-dimethoxy-4-125I-iodophenyl)-2-aminopropane, 3H-BRL43694, and 3H-cyanoimipramine, respectively. Although specific labeling of 5-HT3 receptors was not detected in the cat visual cortex at any age, each of the remaining 5-HT receptor subtypes exhibited unique temporal, regional, and laminar patterns of expression in visual cortical areas 17, 18, and 19 and lateral suprasylvian cortex (LS). 5-HT1A receptors were the earliest to demonstrate visual cortex-specific changes in expression. They exhibited peak levels of expression in all visual cortical areas, predominantly in supra- and infragranular layers, between postnatal day 10 (PD10) and PD30. Their levels in all areas declined progressively with increasing age. 5-HT1c receptors demonstrated their highest levels of expression in the deeper half of layer IV, but only in area 17, between PD40 and PD75. The most striking feature of their distribution throughout this period was that, in layer IV and extending into layer III, the 5-HT1c receptors were concentrated in columns that were 400 microns wide and had a center-to-center spacing of about 900 microns. This transient pattern of expression was not present beyond PD90. 5-HT2 receptors were most densely expressed in layer IV between PD40 and PD120, but they displayed a distinctly different distribution pattern. The densest binding of 5-HT2 receptors was limited to the upper half of layer IV and found in areas 17, 18, and LS. The distribution of layer 5-HT2 receptors along the dense band in layer IV of area 17 was discontinuous, exhibiting patches that were found in the same vertical columns as were the 5-HT1c receptors. Intermediate binding levels for the 5-HT2 receptors were found through layers I-III, the remainder of layer IV, and the subcortical white matter. The levels of 5-HT uptake sites increased gradually to reach adult levels by PD40, but with a distribution pattern that was basically homogeneous, both across cortical regions and across laminae.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Aging; Animals; Animals, Newborn; Antiparkinson Agents; Autoradiography; Cats; Ergolines; Granisetron; Organ Specificity; Receptors, Serotonin; Serotonin; Tritium; Visual Cortex

The 5-hydroxytryptamine1C (5-HT1C) receptor shares many features with the 5-HT2 receptor. To determine if the regulation of the sites is also similar we studied the effects of chronic treatment with drugs active at 5-HT1C/2 receptors on [3H]mesulergine-labelled 5-HT1C binding sites in spinal cord. The 5-HT receptor agonists 1-(3-chlorophenyl)piperazine (m-CPP) (-38%), 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (-35%), quipazine (-27%) and m-trifluoromethylphenylpiperazine (TFMPP) (-27%) significantly down-regulated spinal 5-HT1C sites with chronic injection compared to vehicle treatment. The 5-HT receptor antagonists methiothepin (-71%), mianserin (-24%), methysergide (-21%), and cyproheptadine (-27%) also induced down-regulation, and ritanserin and metergoline further reduced [3H]mesulergine specific binding to undetectable levels. There were no significant changes in Kd to implicate presence of residual drug except for mianserin, methiothepin, and TFMPP. Pindolol and spiperone had no significant effects. In acute dose-response studies, injection of a single dose of DOI did not result in a significant change in any receptor parameters. The capacity of a drug to lower Bmax correlated significantly with its pKd (r = 0.84, P < 0.0007). This drug regulation pattern for 5-HT1C sites of down-regulation by both 5-HT1C/2 receptor agonists and antagonists is similar to that for 5-HT2 receptors and is consistent with the classification of 5-HT1C and 5-HT2 receptors in the same superfamily.

Topics: Analysis of Variance; Animals; Binding Sites; Down-Regulation; Ergolines; Male; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Regression Analysis; Serotonin Antagonists; Serotonin Receptor Agonists; Spinal Cord

Quantitative in vitro receptor autoradiography was used to characterize the [3H]5-hydroxytryptamine binding sites which are not sensitive to 8-hydroxy-2-(di-N-propylamino)tetralin, mesulergine and serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide, in a non-5-hydroxytryptamine1A/1B/1C/1D receptor population, in rat brain. Displacement of [3H]5-hydroxytryptamine [in the presence of 100 nM 8-hydroxy-2-(di-N-propyl-amino)tetralin and mesulergine, to block 5-hydroxytryptamine1A and 5-hydroxytryptamine1C sites] with (-)pindolol, 5-hydroxy-3(4-1,2,5,6-tetrahydropyridyl)-4-azaindole, sumatriptan and serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide yielded complex competition curves suggesting the presence of 5-hydroxytryptamine1B and 5-hydroxytryptamine1D sites and an additional [3H]5-hydroxytryptamine-sensitive component in rat brain. The non-5-hydroxytryptamine1A/1B/1C/1D binding sites were localized in olfactory tubercle, several nuclei of the amygdala, bed nucleus of the stria terminalis, caudate-putamen, CA3 field of the hippocampus, the frontoparietal cortex (motor area) and parts of the striate cortex. All the drugs used had low affinity for the unknown recognition site, which therefore might be comparable to the [3H]5-hydroxytryptamine binding site reported to display low affinity for sumatriptan and 5-carboxamidotryptamine in the brains of various species, the so-called 5-hydroxytryptamine1E site. A comparison of the density of sites labelled with [125I]serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide (representing 5-hydroxytryptamine1B and 5-hydroxytryptamine1D sites) and [3H]5-hydroxytryptamine (under the conditions mentioned above) showed the density of [3H]5-hydroxytryptamine recognition sites to be higher in some structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Antiparkinson Agents; Autoradiography; Binding, Competitive; Brain Chemistry; Dipeptides; Ergolines; In Vitro Techniques; Iodine Radioisotopes; Kinetics; Male; Mesencephalon; Prosencephalon; Rats; Receptors, Serotonin; Serotonin

5-hydroxytryptamine (5-HT) is a mitogen for fibroblasts, vascular smooth muscle cells, renal mesangial cells, and jejunal crypt cells. The human carcinoid cell line (termed BON) that we established in our laboratory from a pancreatic carcinoid tumor produces and secretes 5-HT. In this study, therefore, we examined the effect of 5-HT on growth of BON cells. Furthermore, by use of selective 5-HT receptor antagonists, we examined receptor and post-receptor mechanisms by which 5-HT-induced responses were produced. 5-HT stimulated growth of BON cells. 5-HT stimulated phosphatidylinositol (PI) hydrolysis in a dose-dependent fashion and inhibited cyclic AMP production in a dose-dependent fashion. The 5-HT1A/1B receptor antagonist, SDZ 21-009, prevented the reduction of cyclic AMP production evoked by 5-HT and inhibited the mitogenic action of 5-HT. The 5-HT1C/2 receptor antagonist, mesulergine, competitively inhibited PI hydrolysis, but did not affect the mitogenic action of 5-HT. The mitogenic action of 5-HT and the reduction of cyclic AMP production evoked by 5-HT were also inhibited by pertussis toxin. These results suggest that 5-HT is an autocrine growth factor for BON cells and that mitogenic mechanism of 5-HT involves receptor-mediated inhibition of the production of cyclic AMP which may be linked to pertussis toxin-sensitive GTP binding protein. 8-bromo-cyclic AMP inhibited growth of BON cells whereas 8-bromo-cyclic GMP had no effect on cell growth. Involvement of protein kinase A in BON cell growth regulation was confirmed by the observation that a cAMP-dependent protein kinase antagonist (Rp-cAMPS) could stimulate BON cell growth.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Cell Division; Cyclic AMP; Cyclic GMP; Ergolines; Humans; Pancreatic Neoplasms; Pertussis Toxin; Phosphatidylinositols; Pindolol; Receptors, Serotonin; Second Messenger Systems; Serotonin; Serotonin Antagonists; Tumor Cells, Cultured; Virulence Factors, Bordetella

Choroid plexus epithelial cells are enriched in mRNA for proteins such as the iron carrier transferrin, which acts as a trophic factor in the brain. Choroid plexus epithelial cells also have a high density of 5-HT1C receptors linked to activation of the phosphoinositide (PI) hydrolysis second messenger system. The present studies show that the 5-HT1C/5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) potently increases PI hydrolysis and the levels of transferrin in primary cultures of rat choroid plexus epithelial cells. These effects are blocked by the 5-HT1C/5-HT2 receptor antagonists mesulergine and mianserin, but not by the 5-HT2 receptor-selective antagonist spiperone. Similarly, mesulergine and mianserin, but not spiperone, block the increases in transferrin levels and PI hydrolysis elicited by 5-carboxamidotryptamine (5-CT), a 5-HT1 receptor-selective agonist, and by serotonin. We conclude, therefore, that 5-HT1C receptor activation in the choroid plexus leads to an increase in the production of transferrin. By promoting transferrin synthesis in the choroid plexus, 5-HT may indirectly influence brain development and differentiation.

Topics: Amino Acid Isomerases; Animals; Blotting, Northern; Carrier Proteins; Cells, Cultured; Choroid Plexus; Cyclosporins; Epithelium; Ergolines; Fibroblasts; Kinetics; Male; Mianserin; Peptidylprolyl Isomerase; Phosphatidylinositols; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; RNA Probes; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Spiperone; Thymidine; Time Factors; Transferrin

5-Hydroxytryptamine (5HT)1C and 5HT2 receptors appear to be closely related, from a molecular viewpoint, displaying similar second messenger systems and a high degree of sequence homology. However, there are striking differences in the interactions of 5HT with 5HT1C and 5HT2 receptors; 5HT is generally more potent in stimulating responses mediated through 5HT1C receptors than responses mediated through 5HT2 receptors. Also [3H]5HT labels 5HT1C receptors and not 5HT2 receptors. In order to explore more fully the molecular rationale for these differences, radioligand binding studies were performed in rat, human, and porcine brain and choroid plexus tissues and in mammalian cells transfected with rat 5HT1C or 5HT2 receptors; second messenger studies (inositol phosphate accumulation) were performed in the transfected cells. The second messenger studies confirmed the approximately 10-fold higher potency of 5HT in stimulating intracellular responses through 5HT1C receptors (EC50 = 8.3 nM) than in stimulating intracellular responses through 5HT2 receptors (EC50 = 101 nM). An agonist radioligand selective for the 5HT1C and 5HT2 receptors, 2,5-dimethoxy-(4-[125I]iodo)phenylisopropylamine, was used, as well as [3H]5HT, [3H]mesulergine (antagonist radioligand for 5HT1C receptors), and [3H]ketanserin (antagonist radioligand for 5HT2 receptors). Computer-assisted analyses of the binding data revealed two agonist affinity states for the 5HT1C receptor. The agonist high affinity state of the receptor was modifiable by guanyl nucleotides. The proportion of agonist high affinity states, relative to the total receptor population, was approximately 10% for both receptors. The apparent higher affinity of 5HT for the radiolabeled 5HT1C receptors was due to the higher affinity 5HT displayed for the agonist low affinity state of the 5HT1C receptor, compared with the affinity of 5HT for the agonist low affinity state of the 5HT2 receptor. The correspondence between the higher affinity of 5HT for the agonist low affinity state of the 5HT1C receptor, relative to the 5HT2 receptor, and the higher potency of 5HT in stimulating 5HT1C responses indicates that 5HT interacts with the agonist low affinity state of the 5HT1C and 5HT2 receptors in initiating its biological effects. These observations indicate that guanine nucleotide-binding protein (G protein)-coupled receptors can exhibit high affinity for neurotransmitters in both the free receptor and the G protein-coupled states and th

Topics: 3T3 Cells; Amphetamines; Animals; Binding, Competitive; Brain; Cell Membrane; Choroid Plexus; Ergolines; Fibroblasts; GTP-Binding Proteins; Inositol Phosphates; Iodine Radioisotopes; Kinetics; Mice; Neurotransmitter Agents; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Stimulation, Chemical; Swine; Transfection; Tritium

Topics: Animals; Dihydropyridines; Ergolines; Isradipine; Leydig Cell Tumor; Male; Pituitary Hormones; Rats; Rats, Inbred Strains; Syndrome; Testicular Hormones; Time Factors

Mesulergine (N,N-dimethylsulphamide-N'-1,6-dimethyl-ergoline-8 alpha-yl) is an active semisynthetic ergot derivative with lower antiprolactin potency compared with bromocriptine or pergolide. Since no data are yet available on the effects of mesulergine on pituitary dopamine receptors, the present study has been designated to elucidate the influence of this drug on prolactin secretion in vivo and in vitro and 3H-spiperone binding by the anterior pituitary gland in female Wistar rats with experimentally induced hyperprolactinemia. Three weeks after bilateral ovariectomy and subcutaneous implantation of silastic tubes, containing 10 mg of diethylstilbestrol, a dramatic rise in serum prolactin levels was observed (1.67 +/- 0.23 vs. 80.82 +/- 3.80 ng/ml; P less than 0.001). Mesulergine attenuated the stimulatory effect of diethylstilbestrol on serum prolactin level in a time- and dose-dependent fashion. At concentration range between 10(-5) and 10(-7) M it also inhibited prolactin secretion from cultured rat pituitary cells to the medium during 180 min incubation in a dose-dependent manner. Scatchard analyses performed on the in vitro 3H-spiperone binding kinetics in a dispersed anterior pituitary cell culture, prepared from the pituitaries from rats treated for four weeks with diethylstilbestrol, showed that chronic mesulergine treatment (in dose of 3.0 mg/kg injected s.c. for 10 days) induced a significant decrease in the number of dopamine D2-binding sites (Bmax 28.00 +/- 4.20 vs. 42.80 +/- 4.76 fmol/10(6) cells; P less than 0.01) without any changes in D2-receptor affinity. Our results suggested that antiprolactin activity of mesulergine in vivo and in vitro is probably associated with agonistic effect of this drug on D2-dopamine receptors.

Topics: Animals; Antiparkinson Agents; Bromocriptine; Diethylstilbestrol; Dose-Response Relationship, Drug; Ergolines; Female; Hyperplasia; Hyperprolactinemia; Pergolide; Pituitary Gland, Anterior; Prolactin; Rats; Rats, Wistar; Receptors, Dopamine D2; Spiperone; Time Factors; Tritium

Administration of m-chlorophenylpiperazine [m-CPP, a serotonin (5-HT) agonist] to rats increases plasma concentrations of prolactin and corticosterone. Pretreatment with various doses of ritanserin (5-HT1C/5-HT2 antagonist), ICS 205-930 and MDL-72222 (5-HT3 antagonists), iodocyanopindolol or CG361A (beta adrenoceptor antagonists) and spiperone (5-HT1A/5-HT2 antagonist) did not attenuate m-CPP-induced increases in plasma concentrations of prolactin. In contrast, pretreatment with various doses of metergoline (5-HT1/5-HT2 antagonist), propranolol (beta adrenoceptor antagonist that also has binding affinity for 5-HT1A, 5-HT1B and 5-HT1C sites), mesulergine and mianserin (5-HT1C/5-HT2 antagonists) attenuated m-CPP-induced increases in plasma prolactin. On the other hand, m-CPP-induced increases in corticosterone concentrations were attenuated only by pretreatment with a low dose of mianserin and a high dose of spiperone. When administered without m-CPP, metergoline, mesulergine, ritanserin, ICS 205-930 and high doses of mianserin, spiperone and propranolol increased plasma corticosterone secretion. On the other hand, none of the antagonists used in the present study, except spiperone, had any significant effect on plasma prolactin secretion. These findings suggest that m-CPP-induced prolactin secretion is mediated by stimulation of 5-HT1C receptors while corticosterone secretion may be mediated either by an antagonistic effect at 5-HT3 receptor subtype or by nonserotonergic mechanisms. Alternatively, enhancement of corticosterone secretion by the 5-HT antagonists when administered alone may be responsible for their failure to block m-CPP-induced corticosterone secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Corticosterone; Ergolines; Male; Metergoline; Mianserin; Neurosecretory Systems; Piperazines; Prolactin; Rats; Rats, Wistar; Receptors, Serotonin; Ritanserin; Serotonin Antagonists; Spiperone

Serotonin [5-hydroxytryptamine (5-HT)] receptors are distinguished pharmacologically by their characteristic affinities for agonists and antagonists. Two serotonin receptors, the 5-HT2 and 5-HT1c, share a number of pharmacologic and structural properties while differing in their affinities for certain agonists and antagonists. To identify regions of the 5-HT2 and 5-HT1c receptors important for specifying their unique pharmacology, we constructed six chimeric 5-HT2/5-HT1c receptors in which domains of each receptor were exchanged. The abilities of several drugs to inhibit [3H]mesulergine bound to the chimeric and parent receptors transiently expressed in COS-7 cells were then examined. For spiperone and haloperidol (both butyrophenones), chimeras that exchanged transmembrane (TM) domains I and II or TMs I-III had the greatest effects on binding affinity. The binding affinity of cinanserin (a cinnamanilide) was significantly changed in all the chimeras studied. In contrast, the binding of ketanserin (a 4-fluorobenzoylpiperidine) was strongly influenced by chimeras that exchanged TMs I-III (but not I and II) and by chimeras that exchanged intracellular loop 3 to TM VII. 5-HT binding affinity was greatly altered for chimeras that exchanged domains of intracellular loop 3 to TM VII, with minor effects being noted for chimeras that exchanged TMs I and II and I-III. The affinities of the nonselective drugs mesulergine, mianserin, and m-chlorophenylpiperazine were relatively unaffected when domains of the 5-HT2 and 5-HT1c receptors were exchanged. Taken together, these results imply that structurally diverse 5-HT2 antagonists utilize distinct regions of the 5-HT2 receptor for high affinity binding.

Topics: Base Sequence; Binding, Competitive; Ergolines; Haloperidol; In Vitro Techniques; Ketanserin; Molecular Sequence Data; Oligodeoxyribonucleotides; Receptors, Serotonin; Recombinant Fusion Proteins; Spiperone; Structure-Activity Relationship; Transfection

Total 5-HT1, 5-HT1D and 5-HT1E binding sites were measured in homogenates of human frontal cortex, hippocampus, amygdala, globus pallidus, caudate and putamen. Combined 5-HT1D/1E sites were the predominant 5-HT1 subtype (66-95% of total 5-HT1 sites in all regions except hippocampus (38% of total 5-HT1 sites). Globus pallidus contained the highest density and the highest proportion of 5HT1D sites (74% of total 5-HT1 sites). 5HT1D sites in the other brain areas accounted for 19-27% of the total 5-HT1 sites. The highest densities and the highest proportions of 5-HT1E sites were in caudate (72%) and putamen (64%) and the lowest density and lowest proportion in hippocampus (16%).

Topics: Adult; Aged; Antiparkinson Agents; Brain; Brain Chemistry; Ergolines; Female; Humans; In Vitro Techniques; Kinetics; Male; Membranes; Middle Aged; Pindolol; Receptors, Serotonin

The effects of the new 5HT1A receptor antagonist (S)-UH-301 were investigated in several neurological and behavioral tests in rodents and monkeys. By itself, (S)-UH-301 was found to decrease palatable food consumption in rats, to exhibit anticonvulsant activity in mice, and anxiolytic-like properties in two rodent models of anxiety (light-dark test and elevated plus-maze test). (S)-UH-301 antagonized various symptoms and behaviors induced by the selective 5HT1A receptor agonist 8-OH-DPAT, such as lower lip retraction and flat body posture in rats, hyperphagia for palatable food in rats, and displacement activities (considered as indices of anxiety) in squirrel monkeys. These results further characterize (S)-UH-301 as an in vivo active 5HT1A receptor antagonist and suggest that this antagonistic activity might confer the compound with anxiolytic-like properties.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Acoustic Stimulation; Animals; Brain; Cerebral Ventricles; Conditioning, Operant; Conflict, Psychological; Ergolines; Exploratory Behavior; Feeding Behavior; Injections, Intraventricular; Ketanserin; Learning; Mice; Mice, Inbred DBA; Motor Activity; N-Methylaspartate; Rats; Receptors, Serotonin; Seizures; Serotonin; Serotonin Antagonists

[3H]5-Hydroxytryptamine ([3H]5-HT) and [3H]mesulergine were used to label 5-HT1C receptors expressed in NIH 3T3 mouse fibroblast cells. Using a rapid filtration assay, saturation analysis of the [3H]5-HT radioligand data indicate that the binding is biphasic. Based on computerized analysis of the data, a 2-site model of radioligand binding is significantly more consistent with the data than a one-site model (P less than 0.01). The KD values of [3H]5-HT for the 2 populations are 0.5 +/- 0.1 nM and 31 +/- 15 nM, while the Bmax values are 400 +/- 90 pmol/g protein and 3,000 +/- 600 pmol/g protein, respectively. A biphasic binding pattern is also observed with [3H]5-HT using a centrifugation assay (KD1 = 0.6 +/- 0.06 nM, KD2 = 60 +/- 10 nM; Bmax1 = 740 +/- 90 pmol/g, Bmax2 = 4,000 +/- 700 pmol/g). By contrast, saturation analysis of [3H]mesulergine binding is monophasic (KD = 4.7 +/- 0.7 nM) with a Bmax value (6,800 +/- 1,000 pmol/g protein) that is significantly greater than that obtained using [3H]5-HT (P less than 0.01). Drug competition studies confirm that both [3H]5-HT and [3H]mesulergine label at least 2 subpopulations of expressed 5-HT1C receptors in NIH 3T3 cells. 10(-4) M GTP eliminates the high affinity [3H]5-HT-labeled binding sites with minimal effect on the low affinity [3H]5-HT-labeled sites and no effect on [3H]mesulergine-labeled sites. These data demonstrate that at least 2 distinct subpopulations of 5-HT1C receptors in NIH 3T3 cells can be differentiated using radioligand binding techniques.

Topics: Animals; Antiparkinson Agents; Cell Line; Centrifugation; Clone Cells; Cold Temperature; Ergolines; Filtration; Guanosine Triphosphate; Mice; Radioligand Assay; Receptors, Serotonin; Serotonin

Developing embryos of the polychaete Ophryotrochal labronica were exposed to tritiated mesulergine, a selective antagonist of the serotonin receptors 5-HT1c and 5-HT2, that also has significant affinity to dopamine D-2 sites, and the labeling was analyzed by autoradiography. Already at the earliest developmental stages (1-4 cells), numerous silver grains visualizing 3H-mesulergine binding sites and possibly also serotonin receptors were recorded over the cytoplasm, mostly in association with decomposing yolk granules, but few grains were detected over the nuclear region. In advanced pregastrular embryos (3 days) the number of silver grains was greatly increased over nuclei, cell borders and non-yolk cytoplasmic elements, notably in the animal half of the embryos. For newly gastrulated embryos (4 days), more than 90% of the grains appeared over non-yolk cellular structures. Abundant access to serotonin receptors is probably a fundamental condition not only for gastrulation but also for the high mitotic activity of the cleavage period. An indication hereof is the observation that exposure of cleaving polychaete eggs/embryos to unlabeled mesulergine inhibited cytokinesis and chromosome movements, whereas spindle formation and chromosome duplication were unaffected.

Topics: Animals; Autoradiography; Cell Division; Cell Movement; Cell Nucleus; Chromosomes; Cytoplasm; Ergolines; Gestational Age; Polychaeta; Receptors, Serotonin; Serotonin Antagonists; Tritium

Certain phenylalkylamine derivatives have been considered to bind selectively at 5-HT2 serotonin receptors. It is now recognized that the most widely used derivatives, i.e., 1-(2,5-dimethoxy-4-X-phenyl)-2-aminopropanes where X = Me (DOM), Br (DOB), and I (DOI) (1-3, respectively) also bind at the more recently identified population of serotonin 5-HT1C receptors. The purpose of the present investigation was to determine whether simple phenylalkylamines bind selectively at one population of receptors over the other. An examination of 34 derivatives reveals (i) similar structure-affinity relationships and (ii) a significant correlation (r = greater than 0.9, n = 25) between 5-HT1C and 5-HT2 affinity. None of the compounds included in the present study displayed more than a 10-fold selectivity for one population of these receptors over the other; the results suggest that these compounds (including the widely used 5-HT2 agonists DOB and DOI) are 5-HT1C/5-HT2 agents.

Topics: Animals; Binding Sites; Binding, Competitive; Ergolines; Ketanserin; Male; Molecular Structure; Propylamines; Rats; Rats, Inbred Strains; Receptors, Serotonin; Structure-Activity Relationship; Tritium

5-Hydroxytryptamine1C (5-HT1C) recognition sites were characterized in rat spinal cord using [3H]mesulergine. In competition experiments with different 5-HT receptor agonists and antagonists, the rank order of drug potencies was consistent with drug affinities for the 5-HT1C receptor: mesulergine, mianserin, 5-HT greater than ketanserin, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane greater than 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)1H-indole, spiperone greater than 8-hydroxy-2-(di-n-propylamino)tetralin, pindolol. Bmax was 3.7 +/- 0.3 pmol/g and Kd 1.7 +/- 0.1 nM, with sites found in cervical, thoracic and lumbosacral cord. Inclusion of 20 nM spiperone to block potential 5-HT2 sites did not significantly alter drug affinities. There was a high correlation between drug affinities for [3H]mesulergine-labeled 5-HT1C sites in spinal cord and those reported in pig cortex (r = 0.94) and choroid plexus (r = 0.93), but poor correlation with 5-HT2 (high or low affinity states) or other 5-HT sites. Unlike [3H]mesulergine, the specific binding of [3H]5-HT, [3H]mianserin and [3H]ketanserin was low and no saturation studies could be performed with [3H]1-4-bromo-2-5-dimethoxy phenylisopropylamine. Limited competition studies suggest that [3H]5-HT labels 5-HT1C sites, [3H]ketanserin labels spinal 5-HT2 sites and [3H]mianserin labels both sites under the assay conditions studied, but the population of spinal 5-HT2 is small and not well characterized by these [3H]radioligands. In contrast, the population of spinal 5-HT1C receptors is substantial and [3H]mesulergine is the most useful [3H]radioligand for studies of spinal 5-HT1C sites.

Topics: Animals; Antiparkinson Agents; Binding Sites; Binding, Competitive; Ergolines; Male; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin Antagonists; Spinal Cord

Mesulergine (Cu32-085) is an active semisynthetic ergot alkaloid with unusual biphasic antagonistic-agonistic effect on dopamine (DA) turnover in the rat striatum. The present study has been made to elucidate the influence of the long-term treatment of this drug on prolactin secretion and prolactin cells morphology in the female Wistar rats with experimentally-induced hyperprolactinemia. Additionally, the effect of this drug was compared with bromocriptine and pergolide activity, applied in the same experimental conditions. It has been shown that prolonged mesulergine treatment attenuated the stimulatory effect of stilboestrol on prolactin secretion in vivo. It also decreased mean prolactin cells density, above all cells and lactotroph mitotic indexes, estimated in immunohistochemically-stained slides. However, antiproliferative activity of Cu 32-085 was weaker, when compared with bromocriptine and pergolide.

Topics: Animals; Antiparkinson Agents; Bromocriptine; Cell Division; Diethylstilbestrol; Drug Interactions; Ergolines; Female; Hyperprolactinemia; Immunohistochemistry; Pergolide; Pituitary Gland, Anterior; Prolactin; Rats

This study was aimed at exploring the role of 5-HT2/5-HT1C neurotransmission in male rat sexual behavior. The administration of the 5-HT2/5-HT1C agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (1 mg/kg), suppressed sexual activity in most of the animals. The suppressive effect of DOI was antagonized by treatment with amperozide, a selective 5-HT2 receptor antagonist, in doses which did not by themselves affect sexual activity. In addition, several other serotonin antagonists were tested with varying affinity profiles for 5-HT2/5-HT1C receptors, including ketanserin, ritanserin, and mesulergine. All these compounds antagonized the suppressive action of DOI. In contrast, no antagonizing effect was obtained by treatment with (-)-alprenolol, a 5-HT1A antagonist. The present findings suggest that 5-HT2/5-HT1C receptors might be involved in the neural control of male rat sexual behavior, presumably by exerting an inhibitory influence on the behavior.

Topics: Alprenolol; Amphetamines; Animals; Ergolines; Ketanserin; Male; Piperazines; Rats; Rats, Inbred Strains; Ritanserin; Serotonin Antagonists; Sexual Behavior, Animal

Quantitative receptor autoradiography was used to determine the distribution patterns of 5-CT-sensitive and 5-CT-insensitive binding of [3H]5-HT to high-affinity sites in human cortex, putamen, and globus pallidus. The binding of 3H-5-HT was limited to 5-HT1D sites (5-CT-sensitive) by co-incubating pindolol and mesulergine with [3H]5-HT, and by using 10 microM 5-HT to determine non-specific binding. The difference in the levels of binding between tissues exposed to the 5-CT-containing incubation media and tissue exposed to [3H]5-HT in the presence of 100 nM 5-CT was defined as 5-CT-insensitive binding (5-HT1E). The 5-HT1D receptor density in the frontal cortex was 189 fmol/mg, 226 fmol/mg was present in the globus pallidus, while the density in the putamen was only 28 fmol/mg. The 5-HT1E receptor density was 146 fmol/mg in frontal cortex, 224 fmol/mg in putamen and 140 fmol/mg in globus pallidus. The differential distribution patterns of the high-affinity, 5-CT-sensitive and 5-CT-insensitive [3H]5-HT binding sites indicate that these sites are expressed independently in human brain tissues. These data are supportive of and consistent with previous pharmacological data that led to the division of 5-HT1D receptors into 5-HT1D and 5-HT1E receptors and do not support the division of 5-HT1D receptors into 5-CT-sensitive and 5-CT-insensitive states.

Topics: Antiparkinson Agents; Autoradiography; Brain Chemistry; Ergolines; Humans; In Vitro Techniques; Pindolol; Receptors, Serotonin; Serotonin

Mesulergine displays approximately 50-fold higher affinity for the rat 5-HT2 receptor than for the human receptor. Comparison of the deduced amino acid sequences of cDNA clones encoding the human and rat 5-HT2 receptors reveals only 3 amino acid differences in their transmembrane domains. Only one of these differences (Ser----Ala at position 242 of TM5) is near to regions implicated in ligand binding by G protein-coupled receptors. We investigated the effect of mutating Ser242 of the human 5-HT2 receptor to an Ala residue as is found in the rat clone. Both [3H]mesulergine binding and mesulergine competition of [3H]ketanserin binding showed high affinity for rat membranes and the mutant human clone but low affinity for the native human clone, in agreement with previous studies of human postmortem tissue. These studies suggest that a single naturally occurring amino acid change between the human and the rat 5-HT2 receptors makes a major contribution to their pharmacological differences.

Topics: Amino Acid Sequence; Animals; Base Sequence; Binding, Competitive; Cell Line; Cell Membrane; Cloning, Molecular; DNA; Ergolines; Humans; Ketanserin; Molecular Sequence Data; Mutagenesis, Site-Directed; Rats; Receptors, Serotonin; Sequence Homology, Nucleic Acid; Species Specificity; Transfection

Behavioral, electrophysiological and biochemical evidence suggest that the 5HT2 receptor plays a role in the action of hallucinogenic agents. Considering the structural and functional similarities between the 5HT2 and 5HT1C receptors, we hypothesized that the 5HT1C receptor may also be an important site of action of hallucinogens. The present manuscript evaluates this hypothesis by examining the properties of hallucinogens in the phenalkylamine and indolealkylamine classes at 5HT1C receptors. Epithelial cells isolated from the rat choroid plexus have a high density of 5HT1C receptors linked to phosphoinositide hydrolysis. Comparison of the actions of drugs in cultured cells and whole choroid plexus confirmed that the cell culture system can serve as an in vitro model of 5HT1C receptor activation. 2,5-Dimethoxy-4-bromoamphetamine (DOB), 2,5-dimethoxy-4-methylamphetamine (DOM), 2,5-dimethoxy-4-iodoamphetamine (DOI) and 3,4-methylenedioxyamphetamine (MDA) were evaluated. The rank order of potency to activate 5HT1C receptors [(-)DOB greater than (+/-) DOI greater than (+)DOB greater than (-)DOM much greater than (-)MDA greater than (+) MDA] was consistent with the rank order of effective behavioral doses in rats and humans. The indolealkylamine hallucinogen, 5-methoxy-N,N-dimethyltryptamine was also a 5HT1C receptor agonist, as is the primary amine, 5-methoxytryptamine. These data, combined with previous studies showing that (+)LSD potently activates 5HT1C receptors, suggest that future investigations of the mechanism of action of hallucinogens should consider the role of 5HT1C receptors in addition to the more commonly investigated 5HT2 receptors.

Topics: 3,4-Methylenedioxyamphetamine; Amphetamines; Animals; Antiparkinson Agents; Cells, Cultured; Choroid Plexus; DOM 2,5-Dimethoxy-4-Methylamphetamine; Epithelial Cells; Ergolines; Hallucinogens; Male; Phosphatidylinositols; Quipazine; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Stereoisomerism

Topics: Animals; Antiparkinson Agents; Corticosterone; Ergolines; Hippocampus; Male; Piperazines; Rats; Rats, Inbred Strains; Receptors, Serotonin

Topics: Animals; Antiparkinson Agents; Corticosterone; Ergolines; Hippocampus; Male; Piperazines; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Serotonin

The affinity of a new serotonin (S) derivative, serotonin-O-carboxymethyl-glycyl-tyrosinamide (S-CM-GTNH2), for the various 5-hydroxytryptamine (5-HT)1 receptor subtypes was tested using quantitative autoradiography on rat and guinea pig brain sections. In the rat, S-CM-GTNH2 is 57 and 24 times more potent at 5-HT1B sites (IC50 = 28 nM) than at 5-HT1A (IC50 = 1600 nM) and 5-HT1C sites (IC50 = 670 nM), respectively. In the guinea pig, the affinity of S-CM-GTNH2 for 5-HT1D sites (IC50 = 67 nM) is 21 times higher than at 5-HT1A sites (IC50 = 1400 nM). S-CM-GTNH2 shows a low affinity (less than 10 microM) for 5-HT2 and 5-HT3 binding sites. This new ligand is therefore highly specific for 5-HT1B and 5-HT1D binding sites and can be used to further characterize the involvement of these subtypes in physiological studies focusing particularly on behavioral effects.

Topics: Animals; Binding Sites; Brain; Dipeptides; Ergolines; Guinea Pigs; Male; Membranes; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Tritium

1. Fozard & Gray (1989) proposed that migraine is mediated by stimulation of 5-HT1C receptors. We have examined the interaction of two effective anti-migraine agents, ergotamine and dihydroergotamine (DHE), with these receptors. Binding (inhibition of labelling by [3H]-mesulergine) and agonist activity (phosphoinositide hydrolysis) were measured in piglet choroid plexus, a tissue rich in 5-HT1C receptors. 2. The pKD for [3H]-mesulergine binding was 8.4. Ergotamine and DHE both inhibited [3H]-mesulergine binding with a pKD of 7.1. This was similar to the potency of m-chlorophenylpiperazine (m-CPP) (pKD 7.4) and rather less than that of 5-hydroxytryptamine (5-HT) (pKD 8.1). 3. Both ergotamine and DHE were full agonists (pEC50S 7.5 and 7.6 respectively) with potencies similar to that of 5-HT (pEC50 7.7) and greater than that of m-CPP (pEC50 7.1). Mesulergine 10(-7) M produced near-parallel rightward shifts of the concentration-response curves for all these agents of 1.8-2.2 log units, consistent with an action of the agonists at the same receptor. 4. There was no effect of prazosin, spiperone, mepyramine or atropine on the phosphoinositide hydrolysis induced by ergotamine, ruling out an action via alpha 1-adrenoceptors, 5-HT2, histamine H1, or muscarinic receptors. 5. It is concluded that, together with 5-HT, ergotamine and DHE are the most potent 5-HT1C agonists reported so far. These findings do not support the theory that 5-HT1C receptor activation causes migraine.

Topics: Animals; Binding, Competitive; Choroid Plexus; Dihydroergotamine; Ergolines; Ergotamine; In Vitro Techniques; Inositol Phosphates; Migraine Disorders; Piperazines; Receptors, Serotonin; Serotonin; Swine; Thermodynamics

We administered the serotonergic agents buspirone, mesulergine and ICS 205-930 during the last two weeks of a 4-week oral haloperidol chronic treatment regimen and determined dopamine receptor binding and apomorphine-induced stereotypic activity after a drug washout period. D1 receptor binding was not affected by any treatment. Chronic haloperidol treatment produced a significant increase in the density of D2 receptors for all groups, including the groups that were administered combination treatment of haloperidol and serotonergic compounds. Apomorphine-induced stereotypic activity measured 4 days after the last haloperidol treatment was elevated to the same extent for all haloperidol treated groups. Contrary to a previous report, subchronic treatment with buspirone did not significantly reverse neuroleptic-induced D2 receptor up-regulation.

Topics: Animals; Apomorphine; Buspirone; Corpus Striatum; Ergolines; Haloperidol; In Vitro Techniques; Indoles; Male; Rats; Rats, Inbred Strains; Receptors, Dopamine; Receptors, Dopamine D1; Receptors, Dopamine D2; Serotonin Antagonists; Stereotyped Behavior; Tropisetron; Up-Regulation

Anti-idiotypic antibodies were generated by immunizing rabbits with affinity-purified antibodies to serotonin (5-hydroxytryptamine; 5-HT). Anti-5-HT activity was removed from the resulting antisera by chromatography through a 5-HT affinity column. The anti-idiotypic antibodies were demonstrated by enzyme-linked immunosorbent assay to bind to affinity-purified whole anti-5-HT antibodies and their Fab fragments. Anti-idiotypic antibodies, purified by affinity chromatography on columns to which antibodies to 5-HT were coupled, competed with 5-HT (covalently bound to protein) for the binding sites on anti-5-HT antibodies and serotonin binding protein. The anti-idiotypic antibodies antagonized the binding of [3H]5-HT to membranes isolated from the cerebral cortex, striatum, and raphe area more than to membranes from hippocampus or cerebellum. The anti-idiotypic antibodies also blocked the binding of the 5-HT1B-selective ligand (-)-[125I]iodocyanopindolol (in the presence of 30 microM isoproterenol) to cortical membranes. In contrast, anti-idiotypic antibodies failed to inhibit binding of the 5-HT1A-selective ligand 8-hydroxy-2-(di-n-[3H]propylamino)-tetralin [( 3H]8-OH-DPAT) to raphe area membranes or hippocampal membranes. These observations suggested that the anti-idiotypic antibodies may recognize some 5-HT receptor subtypes but not others. This hypothesis was tested by ascertaining the ability of anti-idiotypic antibodies to immunostain cells transfected in vitro with cDNA encoding the 5-HT1C or 5-HT2 receptor or with a genomic clone encoding the 5-HT1A receptor. Punctate sites of immunofluorescence were found on the surfaces of fibroblasts that expressed 5-HT1C and 5-HT2 receptors, but not on the surfaces of HeLa cells that expressed 5-HT1A receptors. Immunostaining of cells by the anti-idiotypic antibodies was inhibited by appropriate pharmacological agents: immunostaining of cells expressing 5-HT1C receptors was blocked by mesulergine (but not ketanserin, 8-OH-DPAT, or spiperone), whereas that of cells expressing 5-HT2 receptors was blocked by ketanserin or spiperone (but not mesulergine or 8-OH-DPAT). The anti-idiotypic antibodies failed to inhibit the uptake of [3H]5-HT by serotonergic neurons. It is concluded that the anti-idiotypic antibodies generated with anti-5-HT serum recognize the 5-HT1B, 5-HT1C, and 5-HT2 receptor subtypes; however, neither 5-HT1A receptors nor 5-HT uptake sites appear to react with these antibodies.

Topics: Androstadienes; Animals; Antibodies, Anti-Idiotypic; Antiparkinson Agents; Brain; Carrier Proteins; Cell Line; Chromatography, Affinity; Enzyme-Linked Immunosorbent Assay; Ergolines; Fibroblasts; Fluorescent Antibody Technique; HeLa Cells; Humans; Immunohistochemistry; Iodine Radioisotopes; Iodocyanopindolol; Ketanserin; Mineralocorticoid Receptor Antagonists; Pindolol; Rabbits; Receptors, Serotonin; Serotonin; Thyroid Neoplasms; Tritium

The new antidepressant drugs, fluoxetine (and its enantiomers), citalopram, indalpine, paroxetine, and femoxetine show relatively weak affinities for 5-HT receptors as measured by radioligand binding to 5-HT-1(A,B,C and D), 5-HT-2, and 5-HT-3 subtypes. Fluoxetine and R(-)-fluoxetine, at near micromolar concentrations, inhibit 3H-mesulergine binding to 5-HT-1C receptors in bovine choroid plexus, and the R(-) enantiomer is 23 times more potent than the S(+) enantiomer. However, the near nanomolar potencies of these drugs as inhibitors of 5-HT uptake most likely account for their pharmacologic effects in animals.

Topics: Animals; Antidepressive Agents; Binding, Competitive; Cattle; Choroid Plexus; Ergolines; Fluoxetine; In Vitro Techniques; Male; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Stereoisomerism; Synaptosomes

SCH 39166 is a novel benzonaphthazepine, which has been characterized as a potent and selective D1 antagonist. Recently, its D1 selective benzazepine predecessor, SCH 23390, has been shown to bind to 5-HT1C binding sites in the choroid plexus. Therefore, the present studies were undertaken to determine if SCH 39166 has any measurable affinity for 5-HT1C binding sites. Our results indicate that SCH 39166 exhibited poor affinity for the 5-HT1C receptor, with a Ki of 1327 nM. In contrast, SCH 23390 inhibited [3H]-mesulergine binding to 5-HT1C receptors with a Ki of 30 nM. The non-selective 5-HT antagonist, methysergide, inhibited binding with a Ki of 2.4 nM. Finally, studies with the stereoisomers of SCH 39166 and SCH 23390 demonstrated that stereoselectivity at the 5-HT1C site is significantly less than for the D1 site.

Topics: Animals; Antiparkinson Agents; Benzazepines; Binding, Competitive; Choroid Plexus; Dopamine; Dopamine Antagonists; Ergolines; Receptors, Serotonin; Serotonin Antagonists; Swine

We determined the affinity of several typical and atypical antipsychotics for the 5-HT1C and 5-HT2 sites using radioligand binding assays. Most of the antipsychotics tested appeared to bind to 5-HT2 sites with affinities that were fairly high (i.e. pKi values between 7 and 9) and significantly higher than for 5-HT1C sites. In contrast, clozapine was found to have a significantly higher affinity for 5-HT1C than for 5-HT2 sites. Clozapine had the highest affinity for 5-HT1C sites of all the compounds tested. These findings are consistent with the hypothesis that an interaction with 5-HT2 receptors may be relevant to the clinical activity of typical antipsychotics. The findings also suggest, however, that an interaction with 5-HT1C sites may be relevant to the mechanism of clinical action of clozapine and, perhaps, of other atypical antipsychotics.

Topics: Animals; Antipsychotic Agents; Binding Sites; Choroid Plexus; Clozapine; Ergolines; In Vitro Techniques; Ketanserin; Kinetics; Receptors, Serotonin; Swine

This investigation evaluated the antagonist properties of (-)propranolol, (+)propranolol, metergoline and BMY 7378 on the known effect of 8-OH-DPAT (DPAT) to decrease motion sickness in cats. (-)Propranolol produced a greater decrease in the antiemetic effect of DPAT than did (+)propranolol. Although metergoline produced a decrease in the antiemetic effect of DPAT, the decrease could not be clearly attributed to interactions with 5-HT1A receptors because metergoline alone slightly enhanced motion sickness. Depletion of 5-HT with PCPA produced a weaker, nonsignificant enhancement of motion sickness, while mesulergine had no effect. As neither nonspecific 5-HT receptor blockade with metergoline nor depletion of 5-HT mimicked the antiemetic effect of DPAT, it was concluded that DPAT acts on postsynaptic 5-HT1A receptors to prevent emesis. BMY 7378 alone decreased the incidence of motion sickness. A dose just below this agonist range did not decrease the effects of DPAT.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Cats; Dose-Response Relationship, Drug; Ergolines; Female; Metergoline; Motion Sickness; Piperazines; Propranolol; Serotonin Antagonists; Stereoisomerism; Tetrahydronaphthalenes

To delineate the involvement of spinal 5-HT1C receptors in supersensitivity and recovery following neonatal 5,7-DHT lesions, we injected rats on postnatal days 2 and 5 with 5,7-DHT or vehicle by intraperitoneal (IP) or intracisternal (IC) injection. [3H]Mesulergine-labelled sites measured 4 or 14 weeks later exhibited a significant increase (+35% for IP and 27% for IC) in Bmax without changes in Kd or nH. Spinal 5-HT content was significantly reduced (-80 to 89%) by either route of 5,7-DHT injection. These data describe novel upregulation of spinal 5-HT1C receptors in rats with neonatal 5,7-DHT lesions. Spinal 5-HT1C receptor upregulation may contribute to the behavioral supersensitivity to L-5-hydroxytryptophan (L-5-HTP) in rats with 5,7-DHT lesions. It does not explain the behavioral recovery we found previously only after IP 5,7-DHT injection.

Topics: 5,7-Dihydroxytryptamine; Animals; Animals, Newborn; Antiparkinson Agents; Cisterna Magna; Ergolines; Female; In Vitro Techniques; Injections; Injections, Intraperitoneal; Kinetics; Male; Pregnancy; Rats; Rats, Inbred Strains; Receptors, Serotonin; Spinal Cord; Up-Regulation

Serotonin exerts its diverse physiological effects by interacting with multiple distinct receptor subtypes. We have isolated a rat brain 5HT2 serotonin receptor cDNA by virtue of its homology with the 5HT1c receptor. The 5HT2 receptor is a member of the family of receptors that are linked to guanine nucleotide-binding proteins and are predicted to span the lipid bilayer seven times. Overall sequence identity between the 5HT2 and 5HT1c receptors is 49%, but identity within the transmembrane domains is 80%. Expression of both the 5HT2 and 5HT1c receptors in transfected mouse fibroblasts activates phospholipase C signaling pathways and promotes cellular transformation. However, RNA blotting shows that these two receptor subtypes are differentially expressed in the central nervous system. In this manner, structurally and functionally homologous receptor subtypes may elicit distinct physiologic actions.

Topics: Amino Acid Sequence; Animals; Antiparkinson Agents; Brain; DNA; Ergolines; Fibroblasts; Gene Library; Genes; Mice; Molecular Sequence Data; Organ Specificity; Rats; Receptors, Serotonin; RNA, Messenger; Sequence Homology, Nucleic Acid; Spiperone; Transfection; Type C Phospholipases

The regional distribution and cellular localization of mRNA coding for the serotonin 1C receptor were investigated in tissue sections of mouse and rat brain by in situ hybridization histochemistry. Several 32P-labelled riboprobes derived from mouse genomic clones were used. The serotonin 1C receptor binding sites were visualized autoradiographically and quantified using [3H]mesulergine as ligand, in the presence of spiperone to block serotonin 1C receptors. Strong hybridization signal was observed in the choroid plexus of all brain ventricles. High levels of hybridization were also seen in the anterior olfactory nucleus, pyriform cortex, amygdala, some thalamic nuclei, especially the lateral habenula, the CA3 area of the hippocampal formation, the cingulate cortex, some components of the basal ganglia and associated areas, particularly the nucleus subthalamicus and the substantia nigra. The midbrain and brainstem showed moderate levels of hybridization. The distribution of the serotonin 1C receptor mRNA corresponded well to that of the serotonin 1C receptors. The highest levels of serotonin 1C receptor binding were observed in the choroid plexus. In addition, significant levels of the serotonin 1C receptor binding were seen in the anterior olfactory nucleus, pyriform cortex, nucleus accumbens, ventral aspects of the striatum, paratenial and paracentral thalamic nuclei, amygdaloid body and substantia nigra pars reticulata. The cingulate and retrosplenial cortices as well as the caudal aspects of the hippocampus (CA3) were also labelled. Binding in brainstem and medulla was low and homogeneously distributed. No significant binding was seen in the habenular and subthalamic nuclei. Similar findings were obtained in rat brain. These results demonstrate that, in addition to their enrichment in the choroid plexus, the serotonin 1C receptor mRNA and binding sites are heterogeneously distributed in the rodent brain and thus could be involved in the regulation of many different brain functions. The combination of in situ hybridization histochemistry with receptor autoradiography opens the possibility of examining the regulation of the serotonin 1C receptor synthesis after pharmacological or physiological alterations.

Topics: Animals; Antiparkinson Agents; Autoradiography; Blotting, Northern; Brain; Ergolines; Male; Mice; Mice, Inbred Strains; Nucleic Acid Hybridization; Organ Specificity; Rats; Rats, Inbred Strains; Receptors, Serotonin; RNA Probes; RNA, Messenger; Tritium

High-affinity, specific 3H-5-hydroxytryptamine (5-HT) binding was analyzed in membrane homogenates of human frontal cortex, caudate, and globus pallidus. 5-HT1A and 5-HT1C binding sites were pharmacologically blocked using 100 nM 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) and 100 nM mesulergine, respectively. The majority of 5-HT1 sites remained in each of the three brain regions under these conditions. The pattern of nucleotide interactions with these binding sites (GppNHp = GTP = GDP greater than GMP = adenine nucleotides) suggests a possible linkage to a G protein. RU 24969 competition studies confirmed the absence of 5-HT1B binding sites in human cortex, caudate, and globus pallidus. Drug interactions with putative 5-HT1D binding sites in bovine caudate membranes correlated significantly with their affinities for human membrane recognition sites labeled by 3H-5-HT in the presence of 100 nM 8-OH-DPAT + 100 nM mesulergine. We conclude that the majority of 3H-5-HT labeled recognition sites in human cortex, caudate, and globus pallidus represent 5-HT1D binding sites.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Adolescent; Adult; Aged; Binding, Competitive; Caudate Nucleus; Ergolines; Frontal Lobe; Globus Pallidus; Humans; Middle Aged; Receptors, Serotonin; Subcellular Fractions; Tetrahydronaphthalenes

Radioligand binding studies were performed to characterize serotonin 5HT1D binding sites in porcine and bovine brain. 3H-5HT binding, in the presence of 1 microM (+/-)pindolol (to block 5HT1A and 5HT1B receptors) and 100 nM mesulergine (to block 5HT1C receptors), was specific, saturable, and of high affinity. In porcine and bovine cortex and striatum the majority of 5HT1 sites (80%-90%) were of the 5HT1D subtype. In competition experiments 8-OH-DPAT, TFMPP, mesulergine, DOB, and ICS 205-930 had low affinity for 3H-5HT-labeled 5HT1D sites, indicating that the pharmacology of the 5HT1D site is distinct from previously identified 5HT1A, 5HT1B, 5HT1C, 5HT2, and 5HT3 sites. Guanyl nucleotides, GTPgammaS, and Gpp(NH)p, and divalent cations potently modulated the binding of 3H-5HT to 5HT1D sites in porcine and bovine striatum. Mg++ ions increased the number and affinity of 3H-5HT-labeled 5HT1D sites, while guanyl nucleotides decreased the number of 3H-5HT-labeled 5HT1D sites. These results demonstrate the presence of the 5HT1D receptors in porcine striatum and bovine cortex and provide direct demonstration that the radioligand binding assay for the 5HT1D receptor can monitor the interaction of this receptor with a GTP-binding protein.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Binding, Competitive; Brain; Cattle; Ergolines; GTP-Binding Proteins; In Vitro Techniques; Receptors, Serotonin; Swine; Tetrahydronaphthalenes

Serotonin-1 receptors were examined in post-mortem human brains, using quantitative in vitro autoradiography. [3H]Serotonin was used as a ligand. Serotonin-1 receptor subtypes were defined with 8-hydroxy-2-(di-n-propylamino)-tetralin and mesulergine. In the control human basal ganglia, the highest density of serotonin-1 binding sites was observed in both lateral and medial globus pallidus and substantia nigra reticulata. Lower densities were seen in the substantia nigra pars compacta, the nucleus accumbens, caudate and putamen. The majority of these serotonin-1 sites belonged to the serotonin-1D class. No significant alteration of the density and distribution of these sites was observed in Parkinson's disease brains. In contrast, a marked decrease in the density of the receptor binding was seen in the basal ganglia and the substantia nigra from patients dying with Huntington's disease. These results suggest that serotonin-1D receptors are expressed by cells intrinsic to the striatum which degenerate in Huntington's disease and project to the substantia nigra reticulata where these receptors are probably presynaptically localized. These observations in pathological human brains agree with the results of lesion studies in animal models and further support a role for serotoninergic mechanisms in movement control.

Topics: Aged; Basal Ganglia; Ergolines; Female; Humans; Huntington Disease; Male; Middle Aged; Parkinson Disease; Receptors, Serotonin

The regional distribution of high affinity [3H]5-HT recognition sites in the brain of several vertebrates (pigeon, rat, mouse, guinea-pig, cat, dog, monkey and human) was analyzed using in vitro autoradiography. The presence of subtypes of 5-HT1 binding sites was investigated by selective displacements with 8-OH-DPAT, mesulergine and (+/-)SDZ 21-009 at appropriate concentrations to block 5-HT1A, 5-HT1C and 5-HT1B sites respectively. In addition, 5-HT1A and 5-HT1C sites were directly visualized with the more selective radioligands [3H]8-OH-DPAT and [3H]mesulergine, respectively. In the pigeon brain, total [3H]5-HT binding sites were enriched in all telencephalic areas. Densely labelled regions were also present in the optic tectum and the brainstem. No binding was observed in the cerebellum. 8-OH-DPAT and mesulergine only displaced a small proportion of [3H]5-HT binding in most of the areas where high concentrations of 5-HT1 sites were found. (+/-)SDZ 21-009 did not affect [3H]5-HT binding in the regions examined. Taking into account our pharmacological studies, these results suggest that the majority of 5-HT1 sites belong to the 5-HT1D subtype in the pigeon brain. In the mammalian species investigated high levels of [3H]5-HT binding were found in the neo-cortex, hippocampal formation, basal ganglia and related structures (substantia nigra), raphe dorsalis, nucleus superior colliculus and choroid plexus. However, these brain areas were differentially enriched in subtypes of 5-HT1 recognition sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Aged; Animals; Autoradiography; Brain; Cats; Disease Models, Animal; Dogs; Ergolines; Female; Guinea Pigs; Humans; Macaca mulatta; Male; Mice; Movement Disorders; Receptors, Serotonin; Serotonin; Tetrahydronaphthalenes; Tritium

The effects of the serotonin agonist MK-212, on rat plasma ACTH were examined. MK-212 significantly increased plasma ACTH levels, and this effect was blocked by the 5-HT1C antagonists mesulergine and metergoline but not by spiperone, ketanserin, or (-)-pindolol. The results suggest that MK-212 activates the 5-HT1C receptor subtype to increase ACTH.

Topics: Adrenocorticotropic Hormone; Animals; Antiparkinson Agents; Ergolines; Ketanserin; Male; Metergoline; Pindolol; Piperazines; Pyrazines; Rats; Rats, Inbred Strains; Receptors, Serotonin; Spiperone

The action of m-trifluoromethylphenylpiperazine (TFMPP) and m-chlorophenylpiperazine (m-CPP), inhibiting the exploratory activity (ambulation and peeping) of the rat was studied in the open field test. The effects of both these drugs were antagonized by mesulergine, metergoline and mianserin, and partly by methysergide. Spiperone showed an antagonistic action in one (mean) dose only. The effects of TFMPP and m-CPP were not antagonized by ipsapirone, gepirone, cyanopindolol, compound 21009, cyproheptadine, ritanserine, ICS 205930, idazoxan or atropine. The lesion produced by p-chloramphetamine attenuated the effects of TFMPP and abolished those of m-CPP. The obtained results permit an assumption that the TFMPP- and m-CPP-induced decrease in the exploratory activity is mediated probably by 5-HT1C receptors.

Topics: Animals; Ergolines; Exploratory Behavior; Male; Metergoline; Mianserin; Piperazines; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Serotonin Antagonists; Spiperone

Using standard operant procedures with rats trained to discriminate the serotonin (5-HT) agonist 1-(3-trifluoromethylphenyl)piperazine (TFMPP) (0.5 mg/kg) from saline, tests of stimulus generalization and stimulus antagonism were conducted with propranolol, pindolol, and mesulergine. Neither propranolol nor mesulergine antagonized the TFMPP stimulus (pindolol was not evaluated as an antagonist). However, TFMPP-stimulus generalization occurred with all three agents. These results suggest that the TFMPP-stimulus may involve both a 5-HT1B and a 5-HT1C mechanism and further suggest that propranolol, pindolol, and mesulergine may be capable of acting as agonists at certain populations of serotonin receptors.

Topics: Adrenergic beta-Antagonists; Animals; Antiparkinson Agents; Drug Interactions; Ergolines; Generalization, Stimulus; Male; Pindolol; Piperazines; Propranolol; Rats; Rats, Inbred Strains

Male Sprague-Dawley rats deprived of food for 18 h were injected with the 5-HT agonists RU 24969, 1-(3-chlorophenyl)piperazine (mCPP) or 1-[3-(trifluoromethyl)phenyl)]piperazine (TFMPP) and 20 min later presented with their normal diet. Food intake was determined 1, 2 and 4 h later. All three drugs reduced intake over 1 and 2 h. Three out of four drugs with high affinity for 5-HT1C receptors (metergoline, mianserin, and mesulergine but not cyproheptadine) opposed hypophagia caused by mCPP. Another drug reported to have high affinity for the 5-HT1C site, 1-naphthyl-piperazine (1-NP), also blocked the hypophagic response to mCPP at doses which attenuated mCPP-induced hypolocomotion. Only one of the above drugs (metergoline) which also has high affinity for other 5-HT sites opposed hypophagia caused by RU 24969. Two out of three 5-HT1B receptor antagonists [(+/-) cyanopindolol, (-) propranolol, but not (-) pindolol)] which oppose hypophagia caused by RU 24969 (Kennett et al. 1987) also opposed hypophagia caused by mCPP. The 5-HT2 antagonists ketanserin and ritanserin, the 5-HT3 antagonist ICS 205-930 and the alpha 2 adrenoceptor antagonist idazoxan did not oppose the hypophagic effect of mCPP. In agreement with results for mCPP, hypophagia caused by TFMPP was opposed by both, mianserin and (+/-) cyanopindolol. Given alone, mianserin 1-NP and cyproheptadine but not ICS 205-930 increased food consumption of normally fed rats. The results suggest that RU 24969-induced hypophagia depends on 5-HT1B receptors but not on 5-HT1C receptors, while mCPP (and TFMPP)-induced hypophagia may depend on both receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adrenergic alpha-Antagonists; Animals; Ergolines; Feeding Behavior; Food Deprivation; Indoles; Male; Mianserin; Motor Activity; Pindolol; Piperazines; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin Antagonists; Tropisetron

The pharmacological characteristics of the presynaptic 5-HT receptor associated with the modulation of 5-HT release were investigated in a preparation of rat spinal cord synaptosomes (nerve terminals) superfused with a Tris-buffered Krebs solution containing fluoxetine (1 microM). The 5-HT receptor agonists serotonin (1-100 nM), lysergic acid diethylamide (10 nM-1 microM) and the 5-HT1B receptor agonists 1-(m-trifluoromethylphenyl)piperazine (100 nM-1 microM) and 1-(m-chlorophenyl) piperazine (100 nM-3 microM) concentration dependently decreased [3H]5-HT release, while 8-hydroxy-2-(di-n-propylamino)tetralin, a selective 5-HT1A receptor agonist, was inactive. The actions of the effective agonists were reversed by quipazine, an antagonist with high affinity for 5-HT1B binding sites, but not by spiperone, a 5-HT1A receptor antagonist. Furthermore, mesulergine, a 5-HT1C receptor antagonist was ineffective in reversing the action of 5-HT on [3H]5-HT release. These data indicate that the rat spinal cord nerve terminal autoreceptor has characteristics similar to the 5-HT1B binding site.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Ergolines; Male; Piperazines; Potassium; Quipazine; Rats; Receptors, Serotonin; Serotonin; Spinal Cord; Spiperone; Tetrahydronaphthalenes; Tritium

In human caudate and cortex membranes, [3H]serotonin ([3H]5-HT) labels 5-HT1A and 5-HT1C recognition sites which show nanomolar affinity for 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)-tetralin) and mesulergine respectively, whereas no 5-HT1B binding could be identified. However, the majority of the sites labelled by [3H]5-HT (greater than or equal to 60% in cortex, 90% in caudate) are different from 5-HT1A, 5-HT1B and 5-HT1C sites. Competition experiments were performed in human caudate membranes incubated with [3H]5-HT in the presence of 100 nM 8-OH-DPAT and 100 nM mesulergine. Under those conditions, [3H]5-HT labelled an apparently homogeneous population of 5-HT1-like sites which display nanomolar affinity for tryptamines (5-carboxamido-tryptamine, (5-CT) greater than 5-HT greater than or equal to 5-methoxytryptamine (5-MeOT) greater than tryptamine) and some ergolines (metergoline greater than methysergide). In contrast, these sites showed low affinity for drugs with high affinity and/or selectivity for 5-HT1A (8-OH-DPAT, buspirone), 5-HT1B (21-009, RU 24969), 5-HT1C (mesulergine, mianserin) and 5-HT2 sites (ketanserin, cinanserin). The pharmacological profile of these sites is different from that of 5-HT1A, 5-HT1B, 5-HT1C, 5-HT2 and 5-HT3 sites but is consistent with the pharmacology of a 5-HT1-like receptor. It is very similar to that of the 5-HT1D site recently described in bovine brain by Heuring and Peroutka.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Binding, Competitive; Brain Chemistry; Caudate Nucleus; Cerebral Cortex; Ergolines; Humans; Receptors, Serotonin; Tetrahydronaphthalenes

1) The binding characteristics of [3H]5-HT (5-hydroxytryptamine, serotonin) were investigated in membrane preparations of several regions from calf, pig and human brain in the presence of 100 nmol/l 8-OH-DPAT (8-hydroxy-2[di-n-dipropylamino]tetralin) and 100 nmol/l mesulergine in order to mask 5-HT1A and 5-HT1C sites. 2) [3H]5-HT bound rapidly, reversibly and stereo-selectively to a population of high affinity recognition sites in membranes from pig caudate, calf caudate and human cortex, caudate and substantia nigra. 3) Saturation experiments carried out with [3H]5-HT in the presence of 100 nmol/l 8-OH-DPAT and 100 nmol/l mesulergine revealed that non-5-HT1A non-5-HT1C sites represented from 50 to more than 90% of the total 5-HT1 sites (determined with [3H]5-HT in the absence of 8-OH-DPAT and mesulergine), depending on the tissue source. 4) The pharmacological profile of these sites was characterized in competition experiments performed with a variety of ligands in membranes of calf, pig and human caudate membranes. Under these conditions, [3H]5-HT labelled a population of "5-HT1-like" sites which display nanomolar affinity for tryptamines (5-carboxamidotryptamine greater than 5-HT greater than or equal to 5-methoxytryptamine greater than tryptamine) and some ergolines (metergoline greater than methysergide). In contrast, these sites showed low affinity for drugs with high affinity and/or selectivity for 5-HT1A (8-OH-DPAT, buspirone), 5-HT1B (21-009, RU 24969), 5-HT1C (mesulergine, mianserin) and 5-HT2 sites (ketanserin, cinanserin).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Antiparkinson Agents; Brain; Cattle; Caudate Nucleus; Ergolines; Humans; In Vitro Techniques; Kinetics; Membranes; Receptors, Serotonin; Serotonin Antagonists; Species Specificity; Swine; Tetrahydronaphthalenes

Pleuropulmonary disease has been observed in eight patients with Parkinson's disease treated with bromocriptine or its related compound, mesulergine. The pleuropulmonary changes included pleural effusions, pleural thickening, and parenchymal lung disease. The patients developed symptoms from nine months to four years after starting treatment with bromocriptine that varied in dosage from 22 to 50 mg daily, while the patient receiving mesulergine was taking 6 mg daily. No other cause was found for the pleuropulmonary changes. In six patients the medication was discontinued with subsequent clinical, physiologic, and radiologic improvement. In two patients bromocriptine treatment was continued for one to two years, and in one patient there was further physiologic and radiologic progression of the pleuropulmonary changes. These findings suggest a causal relationship between bromocriptine treatment and pleuropulmonary disease. We recommend a chest roentgenogram and pulmonary function evaluation prior to bromocriptine treatment with follow-up studies if the patient develops respiratory symptoms. Physicians prescribing bromocriptine should be aware of this side effect to ensure early recognition and prompt withdrawal of bromocriptine therapy.

Topics: Aged; Antiparkinson Agents; Bromocriptine; Ergolines; Humans; Lung Diseases; Male; Middle Aged; Parkinson Disease; Pleural Diseases; Radiography

In the presence of 1 microM ( +/- )-pindolol [to block 5-hydroxytryptamine (5-HT, serotonin) 5-HT 1A and 5-HT 1B receptors] and 100 nM mesulergine (to block 5-HT 1C receptors), 2.0 nM [3H]5-HT binding to rat cortical homogenates is specific, saturable, and reversible. Scatchard analysis of [3H]5-HT binding, in the presence of 1 microM ( +/- )-pindolol and 100 nM mesulergine, produced a KD of 3.2 nM and Bmax of 43 fmol/mg protein. Distribution studies show this site to be present in most rat brain regions. This site is also detectable in human caudate. The pharmacological profile of this site is distinct from the previously identified 5-HT receptor subtypes. Compounds with high affinity for 5-HT 1A (8-hydroxydipropylaminotetralin), 5-HT 1B (trifluoromethylphenylpiperazine), 5-HT 1C (mesulergine), 5-HT 2 (4-bromo-2,5-dimethoxyphenylisopropylamine), and 5-HT3 (ICS 205-930) receptors have low affinity for this site. These data suggest the presence of an additional, previously unidentified, 5-HT binding site in rat and human brain tissue. This putative novel 5-HT receptor has a similar pharmacology to the "5-HT 1D" site detected in bovine brain by Heuring and Peroutka.

Topics: Animals; Binding, Competitive; Brain; Brain Chemistry; Caudate Nucleus; Cerebral Cortex; Ergolines; Humans; Kinetics; Male; Middle Aged; Pindolol; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Tissue Distribution

3H-5-Hydroxytryptamine (5-HT) binding sites were analyzed in bovine brain membranes. The addition of either the 5-HT1A-selective drug 8-OH-DPAT (100 nM) or the 5-HT1C-selective drug mesulergine (100 nM) to the assay resulted in a 5-10% decrease in specific 3H-5-HT binding. Scatchard analysis revealed that the simultaneous addition of both drugs decreased the Bmax of 3H-5-HT binding by 10-15% without affecting the KD value (1.8 +/- 0.3 nM). Competition studies using a series of pharmacologic agents revealed that the sites labeled by 3H-5-HT in bovine caudate in the presence of 100 nM 8-OH-DPAT and 100 nM mesulergine appear to be homogeneous. 5-HT1A selective agents such as 8-OH-DPAT, ipsapirone, and buspirone display micromolar affinities for these sites. RU 24969 and (-)pindolol are approximately 2 orders of magnitude less potent at these sites than at 5-HT1B sites which have been identified in rat brain. Agents displaying nanomolar potencies for 5-HT1C sites such as mianserin and mesulergine are 2-3 orders of magnitude less potent at the 3H-5-HT binding sites in bovine caudate. In addition, both 5-HT2- and 5-HT3-selective agents are essentially inactive at these binding sites. These 3H-5-HT sites display nanomolar affinity for 5-carboxyamidotryptamine, 5-methoxytryptamine, metergoline, and 5-HT. Apparent Ki values of 10-100 nM are obtained for d-LSD, RU 24969, methiothepin, tryptamine, methysergide, and yohimbine, whereas I-LSD and corynanthine are significantly less potent. In addition, these 3H-5-HT labeled sites are regulated by guanine nucleotides and calcium. Regional studies indicate that this class of sites is most dense in the basal ganglia but exists in all regions of bovine brain. These data therefore demonstrate the presence of a homogeneous class of 5-HT1 binding sites in bovine caudate that is pharmacologically distinct from previously defined 5-HT1A, 5-HT1B, 5-HT1C, 5-HT2, and 5-HT3 receptor subtypes. We therefore suggest that this class of sites be designated the 5-HT1D subtype of binding sites labeled by 3H-5-HT.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Binding Sites; Binding, Competitive; Brain; Calcium; Cattle; Caudate Nucleus; Ergolines; Membranes; Nucleotides; Osmolar Concentration; Serotonin; Tetrahydronaphthalenes; Tritium

The anatomical distribution of serotonin-1 receptors in human postmortem brain tissue was studied by quantitative light microscopic autoradiography. [3H]Serotonin was used to label all the subtypes of serotonin-1 sites (serotonin-1A, serotonin-1B, serotonin-1C). Serotonin-1A receptors were specifically labelled with [3H]8-hydroxy-2-[N,N-di-N-propyl-amino]tetralin, while [3H]mesulergine was used to identify serotonin-1C receptors. Receptor densities were quantified by means of a computer-assisted microdensitometric system. Confirming previous findings, serotonin-1A and serotonin-1C receptors were found in the human brain, while sites with the pharmacological characteristics of serotonin-1B binding sites could not be identified in this tissue. In addition, serotonin-1C receptors appeared to present differences in terms of pharmacology, depending on the brain area analysed. The distribution of both serotonin-1A and serotonin-1C receptor subtypes throughout the human brain was heterogeneous. High or very high densities of serotonin-1A receptors were found over the Ca1 field of the hippocampus, raphé nuclei, layers I and II of the cortex and some nuclei of the thalamus and amygdala. The claustrum, posterior hypothalamus, mesencephalic and pontine central grey matter and substantia gelatinosa of the cervical spinal cord, among others, presented intermediate concentrations of serotonin-1A receptors. In contrast, high densities of serotonin-1C receptors were present in the choroid plexus, substantia nigra, globus pallidus and ventromedial hypothalamus, while low or very low amounts of this receptor subtype were found in many other human brain areas. The anatomical distribution of serotonin-1A and serotonin-1C receptors is discussed taking into account the distribution of serotonergic neurons and fibres, the central functions in which serotonin appears to be involved and the characteristics of the neurological and psychiatric disorders where changes in brain serotonin-1 receptors have been reported.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Adult; Aged; Aged, 80 and over; Autoradiography; Brain; Ergolines; Female; Humans; Male; Mianserin; Middle Aged; Receptors, Serotonin; Serotonin; Tetrahydronaphthalenes

High-affinity, specific [3H]5-hydroxytryptamine (5-HT) binding was analyzed in rat spinal cord homogenates. Drug competition studies were performed using 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) to compete selectively for 5-HT1A sites, RU 24969 to compete for 5-HT1B sites and mesulergine to compete for 5-HT1C sites. Competition data were analyzed by computer-assisted iterative curve-fitting analysis. The results demonstrate that 5-HT1A, 5-HT1B and 5-HT1C binding sites are present in rat spinal cord. In addition, approximately 33% of total 5-HT1 sites do not appear to represent either 5-HT1A, 5-HT1B or 5-HT1C binding sites. Therefore, 5-HT1D and/or some other 5-HT1 binding site subtype may also be present in rat spinal cord.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Binding Sites; Binding, Competitive; Ergolines; In Vitro Techniques; Indoles; Rats; Receptors, Serotonin; Serotonin; Spinal Cord; Tetrahydronaphthalenes

Topics: Antiparkinson Agents; Bromocriptine; Disability Evaluation; Drug Therapy, Combination; Ergolines; Humans; Levodopa; Lisuride; Long-Term Care; Parkinson Disease; Pergolide; Receptors, Dopamine

The cardiovascular effects of mesulergine were studied in anesthetized dogs. Intravenous (IV) administration (0.3 mg/kg) significantly decreased blood pressure in neurogenic hypertensive dogs without any change in heart rate. This effect was completely antagonized by IV administration of domperidone (0.5 mg/kg). Intracisternal administration of mesulergine (0.03, 0.3 and 3 mg/kg) did not produce any change in blood pressure. However, with the highest dose we observed a significant rise in heart rate during the first 2 min (which was probably nonspecific). These results suggest that mesulergine lowers blood pressure in sinoaortic-denervated dogs by means of a peripheral mechanism probably involving DA2 receptors. The findings confirm the potential interest of dopamine-receptor agonists as future antihypertensive agents.

Topics: Animals; Antihypertensive Agents; Antiparkinson Agents; Blood Pressure; Cisterna Magna; Dogs; Ergolines; Female; Injections; Injections, Intravenous; Male; Receptors, Dopamine

Seventeen hitherto untreated patients with mild Parkinson's disease were given the dopamine agonists mesulergine or pergolide. Of the 10 patients who received pergolide (mean dosage 3.7 mg/day) five failed to improve, four showed slight improvement and one gained moderate benefit. Of the seven patients who received mesulergine (mean dose 6.4 mg/day) three patients derived no benefit, two slight benefit and two moderate benefit. The incidence of adverse side-effects was high with both drugs despite the use of a peripheral dopamine receptor antagonist, domperidone, when required. These results are less encouraging than those reported from other centres both in respect of response rate and the severity of unwanted effects.

Topics: Aged; Antiparkinson Agents; Domperidone; Ergolines; Female; Humans; Male; Parkinson Disease; Pergolide

Twelve hyperprolactinemic women were administered the alpha aminoergoline derivative, CU 32-085 (Sandoz, Inc., East Hanover, NJ), in order to determine its effect on prolactin (PRL) secretion. The mean pretreatment serum PRL level was 145.0 +/- 11.5 ng/ml. Significant declines of serum PRL occurred with total daily doses of CU 32-085 of 0.1 to 0.5 mg (P less than 0.001). The magnitude of response to therapy was dose-related. In six patients, PRL levels were reduced to less than 25 ng/ml; this effect lasted at least 24 hours after intake of a single dose. In the other six patients, the response was less dramatic. No subjects developed adverse cardiovascular side effects. The results of this study demonstrate that CU 32-085 exhibits a clinically significant dopaminomimetic action on PRL secretion in hyperprolactinemic women.

Topics: Adenoma; Adult; Ergolines; Female; Humans; Hyperprolactinemia; Kinetics; Menstruation Disturbances; Pituitary Neoplasms; Prolactin

The effects of six putative dopamine receptor agonists on exploratory behaviour in rats were assessed: pergolide, (+)- and (-)-3-PPP, bromocriptine, mesulergine and CQ 32-084. Behaviour was automatically recorded in a holeboard apparatus and the data were analysed by the novel multivariate statistical method of partial least squares. All six substances suppressed exploratory behaviour at low doses. Pergolide and (+)-3-PPP-induced stereo-typed behaviour at higher doses. The suppression of exploration induced by pergolide was completely antagonised by sulpiride, partly antagonised by metoclopramide and weakly affected by haloperidol pretreatment. The effects of a low dose of (+)-3-PPP, bromocriptine or CQ 32-084, but not (-)-3-PPP or mesulergine, were antagonised by sulpiride. These findings support the hypotheses that pergolide, (+)-3-PPP, bromocriptine and CQ 32-084 inhibit exploration via stimulation of dopamine receptors. The present data do not substantiate the hypothesis that the suppression of exploration induced by (-)-3-PPP is mediated by stimulation of dopamine autoreceptors. A detailed analysis of the dose curves for pergolide and (+)-3-PPP indicates that the latter compound may have effects in addition to those of a dopamine receptor agonist.

Topics: Animals; Bromocriptine; Ergolines; Exploratory Behavior; Habituation, Psychophysiologic; Male; Motor Activity; Piperidines; Rats; Rats, Inbred Strains; Receptors, Dopamine

The presence, pharmacological properties and anatomical distribution of serotonin-1C and serotonin-2 receptor subtypes were studied in the human brain by both radioligand binding and autoradiographic procedures. Frontal cortex, hippocampus and choroid plexus from human brains obtained at autopsy without history of neurological diseases were used in this study. [3H]5-HT and [3H]mesulergine were used to label 5-HT1C recognition sites while [3H]ketanserin was used to label 5-HT2 receptors. The pharmacological profile of 5-HT1C sites which are very concentrated in the choroid plexus, was extremely similar to that of pig and rat 5-HT1C sites. These receptors were also detected in the hippocampus and the cortex from human brain. The general distribution of 5-HT1C sites in human and rat brain was similar although slight differences were observed. Human 5-HT2 receptors were concentrated in cortical areas but also found in the hippocampus. The pharmacological profile of these receptors was extremely similar in human and pig brain tissue, but differed in certain respects to that found in rat brain 5-HT2 receptors. The anatomical distribution of 5-HT2 receptors is similar in human and rat brain with some differences at the microscopic level. The importance of species differences in the development of 5-HT2 compounds is discussed.

Topics: Aged; Animals; Autoradiography; Binding Sites; Binding, Competitive; Brain; Cerebral Cortex; Choroid Plexus; Ergolines; Female; Humans; Ketanserin; Male; Membranes; Middle Aged; Piperidines; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Swine; Tissue Distribution; Tritium

The association of the serotonin recognition sites in the pig choroid plexus (5-HT-1C sites) with an adenylate cyclase was examined. The interaction of serotonin and mianserin with [3H]mesulergine binding was not affected by the stable GTP analogue GppNHp. The binding of [3H]serotonin to choroid plexus membranes was also unaffected by GppNHp while a dose-dependent decrease was observed in pig cortical and hippocampal membranes. The porcine choroid plexus contained a forskolin- and histamine-sensitive adenylate cyclase. Serotonin, however, was ineffective in this preparation. While forskolin-stimulated adenylate cyclase in the rat hippocampus was inhibited by serotonin forskolin-stimulated adenylate cyclase in the choroid plexus was insensitive to serotonin. These results indicate that the serotonin recognition sites in the choroid plexus are not linked in a stimulatory or inhibitory way to an adenylate cyclase, in contrast with other 5-HT-1 receptor subtypes.

Topics: Adenylyl Cyclases; Animals; Binding, Competitive; Cerebral Cortex; Choroid Plexus; Colforsin; Cyclic AMP; Dopamine; Ergolines; Hippocampus; Histamine; Kinetics; Mianserin; Rats; Receptors, Serotonin; Serotonin; Swine

The long-term effects of mesulergine, a new drug with dopamine agonistic properties, were studied in 28 patients with Parkinson's disease. In 18 patients with late side effects of levodopa, the addition of mesulergine (10.9 mg/day) induced significant decreases in the global (-48%), rigidity (-62%), and akinesia (-37%) scores. The drug was found to be very effective on tremor (-71%). Mesulergine was useful in cases of inefficacy of levodopa alone or persistent intolerable side effects. The decrease in levodopa dose and the addition of mesulergine permitted a significant reduction in dyskinesia. Used as sole therapeutic agent (10.9 mg/day), mesulergine was found to be active on tremor and rigidity scores but not on akinesia or global scores. Mesulergine induced few side effects. These results show the antiparkinsonian properties of mesulergine that seem to be of significant therapeutic value in patients with tremor or in combination with levodopa.

Topics: Adult; Aged; Antiparkinson Agents; Drug Administration Schedule; Ergolines; Female; Humans; Levodopa; Male; Middle Aged; Movement Disorders; Parkinson Disease; Time Factors

The mammalian choroid plexus is enriched in a newly described serotonin recognition site, the 5-HT1C site. In order to further characterize these sites, the binding characteristics of [125I]LSD, [3H]mesulergine and [3H]serotonin to pig choroid plexus membranes were compared. These ligands labelled with high affinity a similar number of sites. The binding profiles of the sites labelled with these radioligands are indistinguishable as illustrated by highly significant correlation parameters. These sites are very similar to those labelled by N1-methyl-2-[125I]LSD in pig and rat choroid plexus membranes. The data demonstrate that these ligands label 5-HT1C recognition sites in pig and rat choroid plexus membranes.

Topics: Animals; Cell Membrane; Cerebral Cortex; Choroid Plexus; Ergolines; Kinetics; Lysergic Acid Diethylamide; Radioligand Assay; Rats; Receptors, Serotonin; Serotonin; Species Specificity; Swine

The activity of pergolide, a clavine ergolene, and mesulergine, an 8-alpha amino ergoline, were compared in 18 patients with advanced Parkinson's disease. All of the patients were no longer satisfactorily responding to levodopa, and 16 patients had diurnal oscillations in performance. Pergolide, mean dose 2.7 mg, when added to levodopa resulted in a significant (27%) decrease in Parkinson disability and a significant improvement in diurnal oscillations in performance (136% increase in hours 'on'). Twelve of the 18 patients (67%) improved. However, after 2 years pergolide was discontinued in all of the patients because of decreased efficacy, adverse effects, or both. At this time, mesulergine, mean dose 9.3 mg., when added to levodopa resulted in a significant (37%) decrease in Parkinson disability and a significant improvement in diurnal oscillations (61% increase in hours 'on'). Twelve of the 18 patients (67%) improved. Adverse effects (dyskinesias) were less with mesulergine than with pergolide. A declining response to one agonist does not preclude a successful response to another agonist of a different class.

Topics: Aged; Antiparkinson Agents; Drug Therapy, Combination; Dyskinesia, Drug-Induced; Ergolines; Humans; Levodopa; Middle Aged; Parkinson Disease; Pergolide

The pharmacological characteristics of the binding of [3H]8-OH-DPAT ([3H]8-hydroxy-2(di-n-propylamino)tetralin, [125I]CYP ((-)[125I]iodocyanopindolol) (in the presence of 30 microM (-)isoprenaline) and [3H]mesulergine to 5-HT1 recognition sites were studied in rat and pig brain membranes. [3H]8-OH-DPAT bound in rat and pig cortex to the 5-HT1A recognition site characterized by high affinity for 5-CT (5-carboxamido-tryptamine), 8-OH-DPAT, 5-HT (5-hydroxytryptamine, serotonin) and low affinity for pirenperone, ketanserin and mesulergine. [125I]CYP bound in rat but not in pig cortex to the 5-HT1B site which shows high affinity for (-)21-009 (4[3-ter-butyl-amino-2-hydroxy-propoxy]indol-2-carbonic acid isopropyl ester), (+/-)ICYP (3-I-cyanopindolol), 5-HT, RU 24969 (5-methoxy-3-[1,2,3,6-tetrahydropyridon-4-yl]1H-indole) and low affinity for 8-OH-DPAT, mesulergine and pirenperone. [3H]Mesulergine bound in pig choroid plexus and in rat cortex (besides binding to 5-HT2 sites in rat cortex) to the 5-HT1C recognition site characterized by high affinity for metergoline, mesulergine, 5-HT and methergine and low affinity for (-)21-009, ICYP, 8-OH-DPAT and spiroperidol. The pharmacological profile of 5-HT1A sites in rat and pig cortex appears to be identical; 5-HT1C sites in pig choroid plexus and rat cortex show no differences. In contrast, it was not possible to label 5-HT1B sites with [125I]CYP in pig brain membranes indicating that like 5-HT2 receptors, 5-HT1 recognition sites show species differences. The pharmacological profiles of the three 5-HT1 recognition sites are clearly different from one another. Furthermore, the pharmacological profile of each individual 5-HT1 recognition site is also different from that of the 5-HT2 receptors labelled with [3H]ketanserin in rat cortex membranes although some similarities exist between 5-HT2 and 5-HT1C sites. Finally, the beta-adrenoceptor antagonist (-)21-009 which has different affinities for 5-HT1A, 5-HT1B and 5-HT1C recognition sites, yielded triphasic competition curves for [3H]5-HT binding in rat cortex membranes providing evidence that [3H]5-HT labels three distinct 5-HT1 sites in these membranes.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Brain Chemistry; Choroid Plexus; Ergolines; In Vitro Techniques; Iodocyanopindolol; Ketanserin; Male; Membranes; Pindolol; Piperidines; Rats; Rats, Inbred Strains; Receptors, Serotonin; Serotonin; Swine; Tetrahydronaphthalenes

Topics: Adenoma; Bromocriptine; Ergolines; Female; Humans; Lisuride; Metergoline; Pergolide; Pituitary Neoplasms; Pregnancy; Prolactin; Radiotherapy Dosage; Radiotherapy, High-Energy; Time Factors

We treated 12 patients with Parkinson's disease with an 8-alpha-amino-ergoline derivative, CU 32-085. The daily dosage was increased slowly to 7 mg over 9 weeks, held constant for 8 weeks, then replaced by placebo for 4 weeks. We found statistically significant benefit over placebo or pretreatment disability. The effect was seen at daily dosages of 3 mg or more. Its magnitude was dose related. There was no further improvement on prolonged treatment with 7 mg daily. Side effects were mild and did not require interruption of treatment.

Topics: Adult; Aged; Ergolines; Female; Humans; Male; Middle Aged; Neurologic Examination; Parkinson Disease; Psychomotor Performance

The effects of the 8-alpha-amino-ergoline CU 32-085 on central dopamine neuronal systems was investigated. Two h after administration of CU 32-085 a slight increase of dopamine levels was observed in the nucleus caudatus-putamen. Radioligand binding studies in vitro have shown that CU 32-085 has a low affinity for striatal dopamine receptors labeled by [3H]n-propylapomorphine or [3H]spiroperidol. However, CU 32-085 effectively displaces in vivo [3H]n-propylapomorphine and [3H]spiroperidol from their respective binding sites in the mouse striatum. Functional studies have shown that CU 32-085 elicits contralateral rotation in rats with unilateral 6-OH-dopamine induced lesions of the meso-striatal dopamine neurons, and ipsilateral rotation in rats with unilateral intrastriatal ibotenic acid lesions. CU 32-085 relieves tremor in monkeys with ventromedial tegmental lesions and produces only slight abnormal involuntary movements. The biochemical and functional studies suggest that CU 32-085 and/or its metabolite exerts central dopamine agonist activity in vivo. Studies in monkeys with ventromedial tegmental lesions suggest that CU 32-085 might be an effective antiparkinsonian agent which produces less dyskinesias than the other tested dopamine agonists.

Topics: Animals; Antiparkinson Agents; Brain; Chlorocebus aethiops; Corpus Striatum; Dopamine; Ergolines; Female; Male; Mice; Motor Activity; Rats; Rats, Inbred Strains; Receptors, Dopamine; Tremor

In 15 patients (8 men, 7 women), aged 44-81 years, with idiopathic parkinsonism, the effects of mesulergine (CU 32-085) were observed for up to 3 years. Of these patients, four had been without previous levodopa treatment, five had been on levodopa/decarboxylase inhibitor for 6.4 years and six patients had been on levodopa/decarboxylase inhibitor and bromocriptine for a period of 7.5 years. Mesulergine proved to be effective in all three groups of patients and for each main symptom of the disease. Rigidity and tremor showed a better response than akinesia. A decline in efficacy could be observed after 18 months of treatment. By increasing the levodopa dosage, the worsening of the symptomatology could be reduced again and after 3 years patients were slightly better off than before the introduction of mesulergine. Fine motor performance showed a longer-lasting improvement than walking, which was affected by an increase of freezing. Mesulergine was not fully sufficient when given in monotherapy and the levodopa saving effect was only temporary. Parallel with the decline in the therapeutic response as assessed by the rating scales, there was a worsening in the on/off symptomatology. The on/off symptoms, evaluated by patients themselves, had shown very small or no improvement at the beginning of mesulergine administration, contrasting with the findings reflected in the assessment scales. The most frequent side-effects were hallucinations and dyskinesias. Orthostatic hypotension did not prove a problem. Dyskinesias were not seen during monotherapy with mesulergine in de novo patients.

Topics: Adult; Aged; Antiparkinson Agents; Bromocriptine; Drug Therapy, Combination; Ergolines; Female; Humans; Levodopa; Male; Middle Aged; Parkinson Disease

The clinical activity of the new ergoline, mesulergine, was compared to pergolide in the treatment of hyperprolactinaemia. Mesulergine was given to 22 women and five men with hyperprolactinaemia. Serum prolactin was substantially lowered in 10 women; two subsequently conceived and completed normal pregnancies. Twelve women stopped treatment due to side-effects, usually nausea and vomiting, or inadequate responses. The side-effects were generally similar to those on bromocriptine; in one patient they were better and in four worse than on bromocriptine. The male patients were more tolerant of mesulergine, and substantial falls in serum prolactin were seen with evidence of tumour shrinkage. Twenty-seven women with hyperprolactinaemia received pergolide; serum prolactin was lowered or normalized in 16. Side-effects necessitating cessation of treatment were similar to those seen with bromocriptine. Nevertheless, four women tolerated pergolide better than bromocriptine and two women adequately treated with mesulergine had previously been intolerant of pergolide. We conclude that both pergolide and mesulergine may be useful and effective drugs in the treatment of hyperprolactinaemia as alternatives to bromocriptine.

Topics: Adenoma; Adult; Ergolines; Female; Humans; Male; Middle Aged; Pergolide; Pituitary Neoplasms; Pregnancy; Prolactin

Fifteen patients (12 male) with large pituitary tumours and serum prolactin levels below 1000 mU/l were given dopamine agonist therapy (bromocriptine, mesulergine or pergolide) for a mean of 9 months (range 3-36 months). Serum prolactin became undetectable in all. Despite this, significant suprasellar extensions and any associated neurological defect remained in 14 patients, who therefore were referred for surgery. In one patient there was evidence of spontaneous pituitary infarction unrelated to dopamine agonist therapy. At operation 12 patients had apparently functionless pituitary adenomas which failed to immunostain for prolactin, one had an epidermoid cyst and one a Rathke's pouch cyst. We conclude that patients with large pituitary tumours and only a mildly elevated serum prolactin are unlikely to have prolactinomas, and that such tumours are not likely to show significant tumour shrinkage with medical treatment with dopamine agonists.

Topics: Adenoma, Chromophobe; Adult; Bromocriptine; Dopamine; Ergolines; Female; Humans; Male; Middle Aged; Pergolide; Pituitary Neoplasms; Prolactin; Prospective Studies

185 patients with hyperprolactinaemia and prolactinoma were evaluated in a retrospective investigation. 128 patients were treated surgically whereby the prolactin serum level in 47% of the macroprolactinoma and 60% of the microprolactinoma patients was normalised (prolactin less than 25 ng/ml, no radiological evidence of tumor). Of those patients in whom the operation was less successful, a normal prolactin level could be achieved in 77% by additional therapy with dopamine agonists. Of 57 patients handled exclusively with drugs, the prolactin level was normalised by dopamine agonists in 78%. A small number of patients from both groups did not show a satisfactory fall in the prolactin level despite the use of markedly higher doses of dopamine agonists. During dopamine agonist therapy progressive tumor enlargement was detected radiologically in a previously operated patient.

Topics: Adolescent; Adult; Aged; Bromocriptine; Dopamine; Drug Therapy, Combination; Ergolines; Female; Humans; Hyperprolactinemia; Lisuride; Male; Middle Aged; Paraneoplastic Endocrine Syndromes; Prolactin

The therapeutic use of dopamine agonists for Parkinson's disease, clinical guidelines for their introduction into antiparkinson regimens, and their range of adverse effects are reviewed. The role played by the dopaminomimetic ergots in elucidating dopamine receptor function, and laboratory methods that identify dopamine agonists, are also examined.

Topics: Antiparkinson Agents; Apomorphine; Brain; Bromocriptine; Ergolines; Ergot Alkaloids; Humans; Levodopa; Lisuride; Neurons; Parkinson Disease; Pergolide; Piribedil; Receptors, Dopamine

Investigation of the influence of lithium upon the down-regulation of serotonin2 receptors in rat frontal cortex induced by long-term treatment with dibenzepin, an antidepressant without appreciable affinity to serotonin2 receptors. Groups of rats were treated orally for four weeks with either dibenzepin, lithiumcarbonate, or dibenzepine + lithium carbonate. Serotonin2 receptors were labelled with the new selective ligand [3H]mesulergine. Chronic treatment with dibenzepin caused down-regulation of serotonin2 receptors in the frontal cortex. Chronic treatment with lithiumcarbonate alone did not change the specific [3H]mesulergine binding. Given simultaneously with dibenzepin lithium did not prevent the down-regulation of serotonin2 receptors seen after dibenzepin alone.

Topics: Animals; Dibenzazepines; Ergolines; Frontal Lobe; Lithium; Male; Radioligand Assay; Rats; Receptors, Serotonin; Time Factors

The effect of an 8-alpha-amino-ergoline-derivative, CU 32-085, recently characterized as a dopamine agonist, was studied on blood pressure and heart rate in normotensive anesthetized rats. The effects of CU 32-085 and bromocriptine on dose-response curves to sympathomimetic agents (adrenaline, noradrenaline, methoxamine and clonidine), intravenously administered, were also studied. CU 32-085 slowed heart rate and lowered blood pressure. The hypotensive effect was antagonized by pretreatment with sulpiride. CU 32-085 and bromocriptine reduced the pressor effect of adrenaline, noradrenaline and methoxamine and the hypotensive action of clonidine. These results suggest that the hypotensive action of CU 32-085, like bromocriptine, is mainly due to an action on dopaminergic receptors. In addition, the data obtained with sympathomimetic agents suggest that CU 32-085 is a compound with mixed alpha 1 and alpha 2 antagonist properties, similar to bromocriptine.

Topics: Adrenergic alpha-Antagonists; Anesthesia; Animals; Antihypertensive Agents; Antiparkinson Agents; Blood Pressure; Bromocriptine; Clonidine; Epinephrine; Ergolines; Female; Heart Rate; Hemodynamics; Male; Methoxamine; Norepinephrine; Rats; Rats, Inbred Strains; Receptors, Dopamine

Dopamine agonists have yielded two important advances to our understanding of the basal ganglia--they have facilitated the subdivision of different classes of dopamine receptors, and they have established the fact that important dopaminergic effects can be achieved by activation of dopamine receptors in a manner that is unrelated to anoxal impulse traffic in dopaminergic neurons--a phenomenon similar in its diffuse, slow, characteristics to an endocrine effect. The tangible clinical benefit of dopamine agonists has been evident in patients with prominent dyskinesia or wearing off reactions. It is possible that earlier use of agonists, in low doses combined with similarly low doses of levodopa, may improve the long term treatment of Parkinson's disease, but as yet there is no firm evidence. In the future, we can expect to see agonists with more prolonged effects, deriving from the formation of active metabolites. We can also hope to gain further insight into the correlations between the various animal models of dopaminomimetic activity, and specific aspects of drug efficacy and toxicity in parkinsonian patients. Such information should allow the design of improved pharmacotherapy.

Topics: Bromocriptine; Dopamine; Drug Therapy, Combination; Ergolines; Ergot Alkaloids; Humans; Levodopa; Lisuride; Parkinson Disease; Pergolide; Receptors, Dopamine; Receptors, Dopamine D1; Receptors, Dopamine D2

We investigated the effects of single doses of mesulergine on basal and thyrotropin-releasing hormone (TRH)-stimulated serum levels of several anterior pituitary hormones in healthy men and defined its kinetics. We also compared the effects on serum prolactin (PRL) levels of three doses (0.1, 0.35, and 0.5 mg) of mesulergine to those in response to 2.5 mg bromocriptine. Secretory rates of PRL before the first dose of TRH were not affected by any dose of mesulergine or bromocriptine. TRH-stimulated PRL secretion was not altered by 0.1 mg mesulergine but was blunted by both the 0.35- and 0.5-mg doses at 10 A.M. and 1 P.M. Bromocriptine inhibited TRH-stimulated PRL secretion at 10 A.M. and 8 P.M. When analyzed as the 8 A.M. to 8 P.M. and the 8 P.M. to 9 A.M. (day 2) intervals, PRL secretion was not changed by 0.1 or 0.35 mg mesulergine but was suppressed during both periods by the 0.5-mg dose. A dose-response relationship was evident, however, between mesulergine and PRL secretion during both the 8 A.M. to 8 P.M. (R2 = 0.27) and the 8 P.M. to 9 A.M. (day 2; R2 = 0.18) intervals. Bromocriptine lowered PRL secretion during both intervals. Secretory rates of growth hormone during these intervals were not affected by 0.1 mg or 0.35 mg mesulergine but were increased during both intervals by the 0.5-mg dose. Neither the secretory rates of thyrotropin in response to TRH nor those of cortisol, luteinizing hormone, or follicle-stimulating hormone were changed by 0.1 or 0.35 mg mesulergine.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Absorption; Adult; Analysis of Variance; Biological Availability; Bromocriptine; Ergolines; Humans; Male; Pituitary Gland, Anterior; Pituitary Hormone-Releasing Hormones; Prolactin; Radioimmunoassay

Two novel 8 alpha-amino ergolines (CH 29-717 and CU 32-085) have been shown to inhibit secretion of prolactin in rats in vivo. However, when tested for dopaminomimetic potency on pituitary cell culture preparations in vitro, CH 29-717 inhibited prolactin release with an IC50 = 4 X 10(-9) M. In the same model the 1-methyl-derivative CU 32-085 was only weakly active even at high concentrations. When both compounds were incubated together, CU 32-085 displayed an inhibitory effect on the prolactin release restriction caused by CH 29-717. The activities were not time-dependent since similar results were obtained with incubation for 3 or 24 h. These results support the hypothesis that the 1-methyl ergoline derivative CU 32-085 is a partial agonist and becomes fully active in vivo only after metabolic conversion.

Topics: Animals; Cells, Cultured; Dopamine; Ergolines; Male; Pituitary Gland; Prolactin; Rats; Rats, Inbred Strains

The tolerance and prolactin (PRL) release-inhibiting action of the 8 alpha-aminoergoline, mesurlergine, were investigated. In a blind crossover study in six subjects with hyperprolactinemia, 0.5 mg mesulergine induced fewer side effects than did 2.5 mg bromocriptine, while the PRL release-inhibiting effect of the two was of the same order. Six different subjects with suspected PRL-secreting pituitary adenomas who (repeatedly) had to discontinue bromocriptine because of nausea, vomiting, or symptoms of orthostatic hypotension were treated for 20 mo with mesulergine (1 to 2 mg/day). Mesulergine did not induce side effects and its actions resembled those of bromocriptine. Mesulergine induced cessation of galactorrhea and resumption of normal menstrual cycles in five subjects, while in one subject an insufficient luteal phase persisted. No abnormalities in routine blood parameter estimations were observed. In two of three subjects there was shrinkage of a pituitary tumor after 12 to 15 mo on mesulergine. Mesulergine did not directly inhibit PRL release by cultured normal rat pituitary cells and human prolactinoma cells and it antagonized the action of dopamine in a dose-dependent manner. This suggests that the dopaminergic action is carried out by a metabolite of mesulergine, while the parent drug probably prevents the well-known side effects of dopamine-agonistic drugs by its dopamine receptor blocking activity. Because of its acceptability, mesulergine might be important in the treatment of hyperprolactinemia and perhaps also of acromegaly and Parkinson's disease.

Topics: Adenoma; Administration, Oral; Adult; Animals; Blood Pressure; Bromocriptine; Cells, Cultured; Dopamine Antagonists; Drug Evaluation; Ergolines; Female; Humans; Hypotension; Male; Menstruation; Middle Aged; Nausea; Pituitary Neoplasms; Prolactin; Radioimmunoassay; Random Allocation; Rats

The kinetic and pharmacological characteristics of the binding of [3H]ketanserin and [3H]mesulergine to frontal cortical brain membranes from rat, pig and human were studied. In the 3 species [3H]ketanserin labeled sites with the characteristics of the 5-HT2 receptors previously described in the rat. In contrast, [3H]mesulergine labeled 5-HT2 receptors in rat, but not in pig and human cortices. The characteristics of the sites labeled by [3H]mesulergine in pig cortex were similar to those of sites in the choroid plexus of rats, pigs and humans. While several reputed 5-HT2 ligands presented a similar affinity for the [3H]ketanserin binding sites in the 3 species, other such ligands, e.g. mesulergine, methysergide, cinanserin and LSD which displaced these sites with high affinity in rat brain, had lower affinities in pig and human brain. These results indicate that 5-HT2 receptors show different pharmacological profiles in different species. Caution should thus be exerted in extrapolating data from laboratory animals to humans.

Topics: Animals; Brain Chemistry; Cerebral Cortex; Ergolines; Humans; In Vitro Techniques; Ketanserin; Kinetics; Ligands; Male; Piperidines; Rats; Receptors, Serotonin; Species Specificity; Swine; Tritium

The kinetic and pharmacological characteristics of the binding of [3H]5-HT (serotonin), [3H]8-OH-DPAT (8-OH-2-di-n-propylaminotetraline), [3H]LSD, [3H]ketanserin and [3H]mesulergine to membranes from frontal cortex, hippocampus and choroid plexus of pig brain were studied. The binding of these ligands to frontal cortex and hippocampus demonstrated the presence of 5-HT1 and 5-HT2 sites in both tissues, although hippocampus was richer in 5-HT1 (subtype 5-HT1A) sites. [3H]5-HT, [3H]mesulergine and [3H]LSD labeled the pig choroid plexus with high affinity. The pharmacological profiles of [3H]5-HT and [3H]mesulergine binding to this tissue were closely comparable. Ligands reported as selective for 5-HT1A, 5-HT1B or 5-HT2 subtypes did not show high affinity for these binding sites. Therefore, these 5-HT binding sites in pig choroid plexus could be named 5-HT1C. Other drugs with a high affinity for these sites were methysergide and mianserine. In pig frontal cortex, [3H]5-HT labeled the different subtypes of 5-HT1 sites. In contrast, [3H]mesulergine bound in pig frontal cortex to a small population of sites with pharmacological properties similar to those of the choroid plexus 5-HT1C sites. Possible physiological functions in which these sites might be involved are discussed.

Topics: Animals; Binding, Competitive; Brain; Choroid Plexus; Ergolines; Frontal Lobe; In Vitro Techniques; Kinetics; Ligands; Receptors, Serotonin; Serotonin; Swine

Mesulergine, an 8-alpha-aminoergoline, is now proven to be of utility in the clinic as an antiparkinsonian drug. However, the molecule itself shows in vitro and in vivo antidopaminergic properties. Mesulergine is rapidly metabolized into several pharmacologically active DA agonists. The influence of mesulergine on central DA metabolism in rats is dependent on the route of drug administration. It was possible to determine the different metabolites of this drug in plasma as well as in rat striatum. A correlation between the actual present concentration of the parent drug and DAergic metabolites and the net action on striatal DA metabolism was found. It may be concluded that mesulergine itself lacks DAergic activity but occupies DA receptors and is very rapidly metabolized into potent DA agonists.

Topics: Animals; Corpus Striatum; Dopamine; Ergolines; Kinetics; Male; Rats; Receptors, Dopamine

Topics: Ergolines; Female; Humans; Male; Middle Aged; Parkinson Disease

Topics: Aged; Antiparkinson Agents; Bromocriptine; Drug Therapy, Combination; Ergolines; Female; Humans; Levodopa; Male; Middle Aged; Parkinson Disease

The clinical efficacy of CU 32-085, a novel ergoline derivative, in puerperal lactation inhibition was investigated in 41 healthy postpartum women and compared with serum concentrations of prolaction (PRL) and CU 32-085. The women received 0.5 mg CU 32-085 twice daily for 14 days. In 40 women (i.e. 97%) treatment with CU 32-085 successfully inhibited lactation; slight to moderate breast activity appearing during the first few days receded spontaneously. 1 woman experienced full milk let-down on day 5 of treatment. No rebound lactational phenomena were recorded. 5 h after the initial dose, mean serum PRL concentrations decreased by 82% (from 169 to 30 ng/ml), and PRL values remained at that level during the course of treatment. The mean serum concentrations of CU 32-085 showed an inverse pattern compared to PRL. CU 32-085 was well tolerated, with transient slight to moderate dizziness, headache and nausea reported by 12 women (29%) following the initial dose. These disappeared after an average of 3 h. Routine safety chemistries remained within the normal range, and no statistically significant differences between the treatment group and the control group (25 normal nursing postpartum women) were encountered. It is concluded that CU 32-085, a potent dopamine agonist, is an effective and well-tolerated treatment in the indication of postpartum lactation inhibition.

Topics: Adolescent; Adult; Chemical Phenomena; Chemistry; Depression, Chemical; Ergolines; Female; Humans; Lactation; Postpartum Period; Pregnancy; Prolactin

The antiparkinsonian activity of several dopamine agonists was investigated in an animal model and clinically in parkinsonian patients. The semisynthetic ergoline, pergolide, the partial ergoline, LY 141865 and the 8-alpha-aminoergoline, CU 32-085 were found to be effective antitremor agents in monkeys with ventromedial tegmental lesions. The administration of pergolide or LY 141865 results in a relief of tremor with a concomitant occurrence of severe abnormal involuntary movements, while the administration of CU 32-085 results in a relief of tremor with the occurrence of only minor abnormal involuntary movements. Clinical studies have revealed that pergolide is an effective drug in patients with advanced Parkinson's disease, and it reduces the "on-off" phenomena. The possible regulation of dopamine neurotransmission by the norepinephrine neuronal systems was reviewed. Preliminary data suggest that clonidine may interact with presynaptic dopamine receptors.

Topics: Adrenergic alpha-Agonists; Animals; Dopamine; Ergolines; Haplorhini; Humans; Neurons; Norepinephrine; Parkinson Disease; Pergolide; Quinpirole; Rats

Twenty patients with advanced progressing Parkinson's disease have been treated with the 8-alpha-ergoline CU 32-085 in combination therapy for 3 months. With a mean daily dose of 12.65 mg, CU 32-085 together with levodopa plus a decarboxylase inhibitor produced a significant reduction in akinesia, rigor and tremor. Adverse reactions were rare and mild; in one case the drug was discontinued because of dyskinetic movements. Many of the pre-existing side effects were reduced or eliminated, particularly the involuntary movements and the levodopa response swings. The compound was considered useful in the treatment of advanced, progressing Parkinson's disease.

Topics: Adult; Aged; Amantadine; Antiparkinson Agents; Bromocriptine; Carboxy-Lyases; Drug Therapy, Combination; Ergolines; Female; Humans; Levodopa; Male; Middle Aged; Parasympatholytics; Parkinson Disease

Mesulergine (CU 32-085), an 8 alpha-aminoergoline, has been reported to influence striatal dopamine turnover in a time-dependent biphasic manner, suggesting initial dopamine antagonistic and late dopamine agonistic effects. To clarify whether these opposing in vivo effects are due to a metabolic conversion in vivo or reflect mixed antagonist/agonist effects expressed at different dose levels, mesulergine and a 1,20-N,N-bidemethylated metabolite, identified in rat urine, were investigated in functional dopamine receptor models. Dopamine-sensitive adenylate cyclase in homogenates of rat striatum and modulation of electrically evoked tritium overflow from rat striatal slices previously labelled with [3H]choline were used as tests for D1- and D2-receptors, respectively. Mesulergine was found to antagonise D1-receptor responses at micromolar, and D2-receptor responses at nanomolar concentrations. In contrast, the bidemethylated metabolite of mesulergine stimulated both D1- and D2-receptors at micromolar and nanomolar concentrations, respectively. These in vitro results suggest that at dopamine receptors, mesulergine has antagonistic effects and that the late agonistic effects seen in vivo are mostly due to metabolic conversion into a potent dopaminomimetic drug.

Topics: Adenylyl Cyclases; Animals; Antiparkinson Agents; Chemical Phenomena; Chemistry; Choline; Corpus Striatum; Ergolines; In Vitro Techniques; Male; Rats; Receptors, Dopamine; Receptors, Dopamine D1; Receptors, Dopamine D2

Clinical responses to bromocriptine and three new ergoline derivatives, CM 29-712, CQ 32-084, and CU 32-085, in the treatment of Parkinson's disease were studied in new, non-levodopa-treated parkinsonian patients. All compounds elicited a significant but mostly only mild or moderate antiparkinsonian efficacy which seems to be less than that of levodopa. The therapeutic profile of the dopaminergic agonists studied was similar, and the improvement in tremor was considerably better than that in rigidity and hypokinesia. All of the compounds elicited clinical side effects typical of dopaminergic agonists but differed both quantitatively and qualitatively in certain respects. Fewer side effects, especially reduced blood pressure or the occurrence of postural hypotension, developed during treatment with CU 32-085. It is evident that more effective, specific, and tolerable dopaminergic agonists are needed before they can be considered a primary treatment of Parkinson's disease. At present, the main indications for dopaminergic agonists seem to be a deteriorating response to levodopa and daily fluctuations in performance.

Topics: Blood Pressure; Bromocriptine; Disability Evaluation; Domperidone; Dopamine; Ergolines; Follow-Up Studies; Humans; Levodopa; Parkinson Disease; Pleural Effusion; Receptors, Neurotransmitter; Time Factors

8-alpha-amino-ergoline (CU 32-085) is a dopamine receptor agonist that should have fewer side effects than most other dopamine agonists. We studied the effect of this drug in 19 parkinsonian patients. In untreated or levodopa-treated patients, there was considerable improvement of akinesia, rigidity, and tremor; on-off symptoms also improved in the levodopa-treated patients. In patients pretreated with levodopa/bromocriptine, about half the dose of CU 32-085 was necessary to obtain the same therapeutic results, but there was no further improvement of on-off symptoms. Side effects were less pronounced than with bromocriptine; no circulatory disturbances and no psychotic episodes were observed.

Topics: Activities of Daily Living; Adult; Aged; Antiparkinson Agents; Bromocriptine; Drug Therapy, Combination; Ergolines; Female; Humans; Hypotension, Orthostatic; Levodopa; Male; Middle Aged; Nausea; Parkinson Disease; Psychomotor Performance; Receptors, Dopamine

[3H]Mesulergine binds with high affinity to rat cerebral cortex membranes. (KD = 1.9 nM, Bmax = 11.3 pM/g tissue). The binding of this ligand is selective for serotonin-2 receptors: Its next highest affinity, which is for dopamine receptors labelled by neuroleptics, is about 50 times weaker than its affinity for serotonin-2 receptors. No significant affinity for serotonin-1, alpha 1-adrenergic or histamine H1 receptors was observed. Specific [3H]mesulergine binding was diminished in the presence of low concentrations of lithium ions.

Topics: Animals; Cations; Cerebral Cortex; Ergolines; Kinetics; Lithium; Male; Rats; Receptors, Dopamine; Receptors, Serotonin; Serotonin; Serotonin Antagonists

Topics: 3,4-Dihydroxyphenylacetic Acid; 4-Butyrolactone; alpha-Methyltyrosine; Animals; Corpus Striatum; Dopamine; Dose-Response Relationship, Drug; Ergolines; Homovanillic Acid; Male; Methyltyrosines; Rats; Time Factors; Tyrosine 3-Monooxygenase

The effect of lisuride, bromocriptine, CQ 32-084 and CU 32-085 on the specific binding of radiolabelled spiperone to homogenates of human putamen taken post-mortem has been investigated. In addition, the binding of 3H-lisuride to such preparations has been studied. Lisuride is found to inhibit spiperone binding to the dopamine receptor at very low concentrations and to bind to the beta-adrenergic receptor at somewhat higher levels. Lisuride binding to the dopamine receptor was found to be antagonist-like. A measure of the in vivo effect of lisuride was obtained from investigations of brain tissue taken from a patient treated with the drug before death.

Topics: Brain; Bromocriptine; Ergolines; Humans; Kinetics; Lisuride; Receptors, Dopamine; Spiperone