ergoline and talipexole

Although 6-hydroxydopamine-induced (6-OHDA-induced) rats are a well-known Parkinson's disease model, the effects of dopamine D2 agonists in mice with 6-OHDA-induced lesions are not completely understood. We produced mice with 6-OHDA-induced lesions and measured their total locomotion counts following administration of several dopamine D2 agonists (pramipexole, ropinirole, cabergoline, rotigotine, apomorphine, talipexole, and quinelorane). Cabergoline showed the longest duration of drug action, which was in agreement with its long-lived anti-Parkinson effects in rats and humans. In contrast, pramipexole and ropinirole had notably short durations of drug action. We demonstrated that mice with 6-OHDA-induced lesions accompanied with significant lesions in the striatum may be reasonable models to predict the action duration of anti-Parkinson drug candidates in humans.

Topics: Animals; Antiparkinson Agents; Apomorphine; Azepines; Benzothiazoles; Cabergoline; Corpus Striatum; Disease Models, Animal; Dopamine Agonists; Ergolines; Indoles; Injections, Intraventricular; Male; Mice; Motor Activity; Oxidopamine; Parkinsonian Disorders; Pramipexole; Quinolines; Receptors, Dopamine D2; Tetrahydronaphthalenes; Thiophenes

Topics: Aged; Antiparkinson Agents; Azepines; Benzothiazoles; Cabergoline; Carbidopa; Catatonia; Catechols; Drug Therapy, Combination; Electroconvulsive Therapy; Ergolines; Female; Humans; Levodopa; Nitriles; Parkinson Disease; Pramipexole

To investigate the frequency of cardiac valve regurgitation related with low dose dopamine agonists in patients with Parkinson's disease (PD), echocardiograms were analyzed in 527 consecutive PD patients (448 patients treated with dopamine agonists, 79 patients never treated with dopamine agonists as age-matched controls). The frequency of mild or above mild regurgitation of the aortic valve (AR) was significantly higher in the cabergoline group (13.7%, P < 0.05) compared with the controls (2.5%). Odds ratio adjusted by age and sex for AR was significantly higher in the cabergoline group (OR, 6.45; 95% CI, 1.46-28.60; P = 0.01): odds ratio was significantly higher in patients treated with higher daily doses (OR, 14.41; 95% CI, 3.08-67.38; P = 0.0007) and higher cumulative doses (OR, 15.29; 95% CI, 3.19-73.18; P = 0.0006). No statistical difference was identified in the frequency of the tricuspid and mitral regurgitation. None of the other dopamine agonist groups including pergolide gave higher frequency or higher odds ratio compared with the controls. None of our patients showed severe regurgitation or was operated for valvular heart disease. The question as to whether or not longer duration of low dose dopamine agonist treatment would yield the same results needs further studies.

Topics: Aged; Aortic Valve Insufficiency; Azepines; Benzothiazoles; Bromocriptine; Cabergoline; Dopamine Agonists; Ergolines; Female; Humans; Male; Mitral Valve Insufficiency; Parkinson Disease; Pergolide; Pramipexole; Prevalence

Paraquat (1,1'-dimethyl-4,4'-bipyridinium, PQ) is a herbicide to possibly induce Parkinson's disease (PD), since a strong correlation has been found between the incidence of the disease and the amount of PQ used. In this study, we examined PQ toxicity in rat organotypic midbrain slice cultures. PQ dose dependently reduced the number of dopaminergic neurons in cultured slices. Since this damage was prevented by GBR-12909, the dopamine transporter could be an initial step of the PQ induced dopaminergic neurotoxicity. The sequential treatments with lower PQ and 1-methyl-4-phenyl pyridinium (MPP+) doses, where each dose alone was not lethal, markedly killed dopamine neurons, suggesting that the exposure of a lower dose of PQ could lead to the vulnerability of dopaminergic neurons. This cell death was prevented by the inhibitors of NMDA, nitric oxide synthase (NOS), cycloheximide and caspase cascade. Neurons expressing NOS were identified inside and around the regions where dopamine neurons were packed. The cell death induced by the sequential treatments with PQ and MPP+ was also rescued by L-deprenyl and dopamine D2/3 agonists. These results strongly support that the constant exposure to low levels of PQ would lead to the vulnerability of dopaminergic neurons in the nigrostriatal system by the excitotoxic pathway, and might potentiate neurodegeneration caused by the exposure of other substances and aging.

Topics: 1-Methyl-4-phenylpyridinium; Analysis of Variance; Animals; Animals, Newborn; Azepines; Cabergoline; Caspases; Cell Count; Cycloheximide; Dizocilpine Maleate; Dopamine Agonists; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Enzyme Inhibitors; Ergolines; Excitatory Amino Acid Antagonists; Herbicides; Immunohistochemistry; Mesencephalon; NADPH Dehydrogenase; Neuroprotective Agents; NG-Nitroarginine Methyl Ester; Organ Culture Techniques; Paraquat; Piperazines; Protein Synthesis Inhibitors; Quinoxalines; Rats; Rats, Wistar; Selegiline; Tyrosine 3-Monooxygenase

The potencies for in vivo inhibition of substantia nigra pars compacta dopamine single cell firing were determined for apomorphine, BHT 920, N-0923, (+/-)-7-hydroxy-dipropylaminotetralin (7-OH-DPAT), (+)-3-(3-hydroxyphenyl)-N-propylpiperidine (3-PPP), pramipexole, quinelorane, quinpirole, RU 24926, U-86170, and U-91356. Significant correlation was obtained between the potencies of these 11 highly efficacious dopamine receptor agonists and the in vitro binding affinities at dopamine D3 receptors, but not at dopamine D2L receptors. These results support a functional role for the dopamine D3 receptor subtype in the autoreceptor-mediated regulation of dopamine cell activity, while a role for dopamine D2 receptors awaits further analysis. In addition, the results demonstrate the limitations of using currently available dopamine receptor agonists to delineate relative in vivo roles for the dopamine D2 and D3 receptor subtypes.

Topics: Aminoquinolines; Animals; Apomorphine; Azepines; Benzothiazoles; Binding, Competitive; CHO Cells; Cricetinae; Dopamine Agonists; Dose-Response Relationship, Drug; Ergolines; Imidazoles; Male; Neurons; Phenethylamines; Piperidines; Pramipexole; Quinolines; Quinpirole; Rats; Rats, Sprague-Dawley; Receptors, Dopamine; Receptors, Dopamine D2; Receptors, Dopamine D3; Structure-Activity Relationship; Substantia Nigra; Tetrahydronaphthalenes; Thiazoles; Thiophenes; Transfection

This study was undertaken to investigate the effect of chronic nicotine treatment on electrically evoked dopamine (DA) release from striatal slices and locomotor activity in rats under the influence of DA autoreceptor agonists and antagonist. Nicotine was supplied chronically by Alzet osmotic minipump for two weeks. B-HT920 and quinpirole decreased and (-)-sulpiride increased the evoked DA release from striatal slices. The B-HT920 and quinpirole-induced decrease and the (-)-sulpiride-induced increase in evoked DA release were enhanced by chronic treatment with nicotine. Nicotine itself has little effect on the evoked DA release. B-HT920 and quinpirole decreased and (-)-sulpiride, methamphetamine and apomorphine increased the locomotor activity in the rat. The B-HT920 and quinpirole-induced decrease and the (-)-sulpiride-induced increase in locomotor activity were enhanced by chronic treatment with nicotine. On the other hand, the methamphetamine and apomorphine-induced increase in locomotor activity were unaltered by chronic treatment with nicotine. Chronic nicotine treatment itself has no effect on locomotor activity. These data indicate that chronic treatment with nicotine caused a supersensitivity in presynaptic DA autoreceptors that modulate DA release from DA terminals in the rat striatum, and no change in the function of postsynaptic DA receptors.

Topics: Animals; Autoreceptors; Azepines; Corpus Striatum; Dopamine; Dopamine Agonists; Dopamine Antagonists; Drug Interactions; Ergolines; Locomotion; Male; Methamphetamine; Nicotine; Quinpirole; Rats; Rats, Wistar; Sulpiride

An electrophysiological study using cats anesthetized with alpha-chloralose was performed to elucidate whether or not talipexole (B-HT 920 CL2: 6-allyl-2-amino -5, 6, 7, 8-tetrahydro-4H-thiazolo [4, 5 -d] -azepine-dihydrochroride), a dopamine D2 agonist, acts on postsynaptic dopamine receptors in the caudate nucleus (CN) neurons receiving excitatory input from the pars compacta of substantia nigra (SN). Extracellular neuron activities were recorded in the CN using a glass-insulated silver wire microelectrode attached along a seven-barreled micropipette, each of which was filled with talipexole, quinpirole (dopamine D2 agonist), domperidone (dopamine D2 antagonist), glutamate and 2M NaCl. These drugs were microiontophoretically applied to the immediate vicinity of the target neuron. In the same neurons in which the spikes elicited by the SN stimulation were blocked by microiontophoretically applied domperidone, microiontophoretic application of talipexole and quinpirole induced a dose-dependent increase in spontaneous firing. This increase in firing by talipexole and quinpirole was blocked during simultaneous application of domperidone, although glutamate-induced firing remained unaffected by domperidone. In the CN neurons, in which the SN stimulation-induced spikes were not blocked by domperidone, spontaneous firing was not affected by talipexole or quinpirole. These findings suggest that talipexole activates CN neurons receiving a dopaminergic input from SN via D2 receptors, as does quinpirole.

Topics: Action Potentials; Animals; Azepines; Cats; Caudate Nucleus; Domperidone; Dopamine Agents; Electric Stimulation; Ergolines; Iontophoresis; Neurons; Quinpirole; Substantia Nigra

Narcolepsy is a genetically determined disorder of sleep characterized by excessive daytime sleepiness and abnormal manifestations of REM sleep that affects both humans and animals. Although its exact pathophysiologic mechanisms remain undetermined, recent experiments have demonstrated that in both humans and canines, susceptibility genes are linked with immune-related genes. A striking difference, however, is that the genes thought to be involved in the human pathology are autosomal dominant, whereas canine narcolepsy in Dobermans is transmitted as a single autosomal recessive gene with full penetrance (canarc-1). In this study, we have examined the development of narcoleptic symptoms in homozygous narcoleptic, heterozygous, and control Dobermans. Animals were behaviorally observed until 5 months of age and then treated at weekly intervals with cataplexy-inducing compounds that act on cholinergic or monoaminergic systems (alone and in combination). Our data indicate that cataplexy can be induced in 6-month-old asymptomatic heterozygous animals, but not in control canines, with a combination of drugs that act on the monoaminergic and cholinergic systems. This demonstrates that disease susceptibility may be carried by heterozygosity at the canarc-1 locus. Our data further suggest that cataplexy, a model of REM sleep atonia, is centrally regulated by a balance of activity between cholinergic and monoaminergic neurons.

Topics: Aging; Animals; Azepines; Biogenic Amines; Brain; Cataplexy; Chromosome Mapping; Crosses, Genetic; Dog Diseases; Dogs; Dopamine Agents; Ergolines; Female; Genes, Recessive; Genetic Predisposition to Disease; Heterozygote; Humans; Male; Narcolepsy; Parasympathomimetics; Pedigree; Physostigmine; Prazosin; Quinpirole; Sleep

The extent to which the putative dopamine (DA) autoreceptor agonists B-HT 920 (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5d]azepine dihydrochloride) and SND 919 (2-amino-4,5,6,7-tetrahydro-6-propylamino- benzthiazol dihydrochloride) and the potent D2 receptor agonist quinpirole have differential effects on pre- and postsynaptic DA receptors was determined by using in vivo microdialysis to monitor the effects of these compounds on extracellular concentrations of DA and acetylcholine (ACh) in the striata of freely moving rats. B-HT 920 and SND 919 reduced interstitial concentrations of DA, but not ACh, when administered s.c. at doses of 0.05 and 0.1 mg/kg. Quinpirole (0.05 and 0.2 mg/kg) decreased extracellular concentrations of both DA and ACh. Hence, relative to its effects on DA, quinpirole was more potent than the other drugs at DA receptors controlling ACh release. These results are consistent with the hypothesis that B-HT 920 and SND 919 have preferential actions on DA autoreceptors. Local application of the selective D2 receptor antagonist raclopride produced similar dose-dependent increases in DA and ACh release. It is unlikely therefore that differences in the degree to which endogenous DA inhibits transmitter release from nigrostriatal terminals and cholinergic neurons can account for the greater sensitivity of the former to the depressant actions of systemically administered B-HT 920 and SND 919. As was the case with systemic administration, local striatal application of B-HT 920 produced larger decreases in extracellular DA than ACh.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetylcholine; Animals; Azepines; Benzothiazoles; Corpus Striatum; Dopamine; Dopamine Agents; Ergolines; Male; Oxidopamine; Pramipexole; Quinpirole; Raclopride; Rats; Rats, Wistar; Receptors, Dopamine; Salicylamides; Thiazoles

The dopamine (DA) hypothesis of schizophrenia proposes hyperactivity of the mesocorticolimbic DA system, originating within the A10 DA cells of the ventral tegmental area (VTA), as a pathophysiological mechanism. Thus, reduction of activity in this system, including that produced by putative "autoreceptor-selective" DA agonists, may be of clinical utility. The present studies compared the ability of eight D2 DA receptor agonists to inhibit the firing of rat A10 DA neurons after i.v. administration. Both N-n-propyl-N-phenylethyl-p(3-hydorxyphenyl)ethylamine hydrochloride (RU 24213) and 2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]- azepine dihydrochloride (B-HT 920) were potent, high-efficacy agonists which completely inhibited the firing of A10 DA cells. The putative autoreceptor-selective DA agonists 3-(4-(4-phenyl-1,2,3,6-tetrahydropyridyl-(1)-butyl)-indole hydrochloride (EMD 23,448) and (+)-3-(3-hydroxy-phenyl)-N-n-propylpiperidine [(+)-3-PPP] were considerably weaker than RU 24213 and B-HT 920, but also exhibited "full" efficacy (i.e., they completely suppressed cell firing). The putative autoreceptor agonist preclamol [(-)-3-PPP] and its trans-fused congener (-)-HW 165 were weak partial agonists that failed to completely inhibit A10 DA cells. The new putative autoreceptor agonist N-[(8-alpha)-2-chloro-6-methylergoline-8-yl]-2,3]dimethylopropa namide (SDZ 208-911) was also a weak partial agonist that exhibited partial antagonist effects (reversed inhibition produced by the D2 agonist quinpirole), whereas its structural analog N-[(8-alpha)-2-chloro-6-methylergoline-8-yl]-2,2-dimethylopropa namide (SDZ 208-912) was nearly inactive as an agonist, but was an effective antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Azepines; Dopamine; Dopamine Agents; Electrophysiology; Ergolines; Indoles; Male; Neurons; Phenanthrenes; Rats; Rats, Sprague-Dawley

The present experiments were performed in order to investigate the effects of dopamine(DA)ergic drugs on the concentrations of extracellular glutamate (GLU) in the striatum of non-anaesthetised, freely moving rats by using microdialysis and to get further information about the interactions between glutamatergic and dopaminergic pathways. GLU was determined after pre-column derivatisation with o-phthaldialdehyde by HPLC and fluorescence detection. For increasing the fraction of extracellular GLU which is of neuronal origin, an enhanced release of this neurotransmitter was evoked by 100 mM K+ administered via the dialysis probe. This stimulation was applied twice in each experiment, at the second time after administration of a subcutaneously (s.c.) given DAergic drug. For basal conditions, a perfusion fluid containing 148.2 mM Na+, 4mM K+, 1.2 mM Ca2+ was used, for conditions of stimulation with 100 mM K+ the Na+ concentration was reduced correspondingly. Activation of the D1 receptor with the selective D1 sector agonist SKF 38393 ((+/-) 1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol) 15 mg/kg) failed to influence the stimulated release of GLU, and neither a combination of the selective D2 antagonist (-)sulpiride (150 mg/kg) with the mixed D1/D2 agonist apomorphine (1 mg/kg), nor a combination of sulpiride (150 mg/kg) with SKF 38393 (15 mg/kg) were effective. Also the two selective D2 agonists quinpirole (0.5 mg/kg) or talipexole (50 micrograms/kg) had no significant influence on the release of GLU. The results suggest that DA receptor agonists have less effect on the K(+)-stimulated GLU-release than might be expected from in vitro studies or behavioral experiments (Kornhuber and Kornhuber, 1986).

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Animals; Apomorphine; Azepines; Chromatography, High Pressure Liquid; Corpus Striatum; Dialysis; Dopamine Agents; Ergolines; Glutamates; Glutamic Acid; Male; Potassium; Quinpirole; Rats; Rats, Wistar; Spectrometry, Fluorescence; Stimulation, Chemical; Sulpiride

Topics: Animals; Autoreceptors; Azepines; Brain; Dopamine Agonists; Ergolines; In Vitro Techniques; Male; Quinpirole; Rats; Rats, Wistar; Receptors, Dopamine; Receptors, Dopamine D2; Synapses

Previous work in this laboratory, as well as observations reported in the literature, indicate that the adrenal medulla contains dopamine (DA) receptors of the D-2 subtype, which among other things are capable of controlling the DA level in rat adrenal glands. To further characterize the DA receptors involved in the control of the adrenal DA level, the effects of 9 DA receptor agonists with various intrinsic activities were compared. After various periods of drug administration the rats were killed by decapitation and the DA content of the adrenal glands and the DOPAC content of the forebrain were measured by high-performance liquid chromatography with electrochemical detection. All the investigated DA receptors agonists caused an increase in adrenal DA level, although statistical significance was not reached in one case [(-)-HW 165]. Domperidone, a DA D-2 receptor antagonist which does not readily cross the blood brain barrier, blocked the DA-elevating effects of apomorphine, quinpirole, B-HT 920 and both enantiomers of 3-PPP. For the two ergolines terguride and SDZ 208-920 the blockade by domperidone was not complete, suggesting that their effects are mediated not only through DA, but also through other receptor systems. The dose of domperidone used (3 mg/kg) had but a marginal influence on brain DOPAC levels, supporting the almost exclusively peripheral effect of this agent. Our data indicate that the DA D-2 receptors which control the DA level in the adrenal medulla in rats, have characteristics similar to, though not identical with the autoreceptors in the forebrain.

Topics: 3,4-Dihydroxyphenylacetic Acid; Adrenal Medulla; Animals; Apomorphine; Azepines; Diencephalon; Domperidone; Dopamine; Dopamine Agents; Epinephrine; Ergolines; Lisuride; Male; Norepinephrine; Phenanthrenes; Piperidines; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine; Telencephalon

Alterations both in the activity of the cortical EEG and behaviour were studied after administration of dopamine receptor agonists. In addition to apomorphine, which provided contrasting effects, both on the EEG and behaviour, when small and large doses were compared, alterations elicited by the D2 agonist, quinpirole and another agonist, with preference for dopamine D2 autoreceptors, talipexole (B-HT 920), were evaluated by using telemetric EEG recordings in rats. Similarly to apomorphine, quinpirole produced opposite effects after small and large doses: a small dose (0.05 mg/kg) led to sedation and an increase of EEG power spectra in all of the bands, except beta 2, whereas a larger dose (0.5 mg/kg) elicited stereotypy and desynchronization of the EEG, with a characteristic increase of power in the alpha 1 band. The effects on the EEG and on behaviour, obtained with the small dose of quinpirole were very similar to those of a small dose of apomorphine (0.05 mg/kg) and a small dose of talipexole (0.02 mg/kg) but even the large dose of talipexole (0.5 mg/kg) produced similar effects: all of these treatments produced behavioural sedation and an increase of power in the EEG in all of the bands, except beta 2; such increases appeared most pronounced in the delta band. The present study provides further evidence that drugs, which are assumed to activate dopamine autoreceptors, are effective in inducing sedation. This sedation was accompanied by a characteristic pattern, observed in EEG power spectra analysis.

Topics: Animals; Apomorphine; Azepines; Behavior, Animal; Dopamine Agents; Electrodes, Implanted; Electroencephalography; Ergolines; Male; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine; Receptors, Dopamine D2

Based on the results of in vivo studies, the thiazoloazepine derivative B-HT 920 has been proposed to be a selective agonist of dopamine autoreceptors. In the present study, we investigated the effects of B-HT 920 in two functional in vitro model systems of D2 receptors and compared these effects with the effects of the classical D2 agonist LY 171555. B-HT 920 and LY 171555 concentration dependently inhibited the electrically evoked release of radiolabeled dopamine and acetylcholine and the forskolin-induced stimulation of adenylate cyclase activity in rat striatal tissue slices with comparable efficacies. In striatal tissue slices prepared after 6-hydroxydopamine-induced destruction of dopaminergic terminals, both drugs were still able to inhibit forskolin-stimulated adenylate cyclase activity with a efficacy similar to that in tissue obtained from unlesioned rats. It is concluded that, in vitro, B-HT 920 is an agonist at both presynaptic and 'normosensitive' postsynaptic D2 receptors showing relatively high intrinsic activity.

Topics: Adenylyl Cyclases; Animals; Azepines; Colforsin; Corpus Striatum; Dopamine Agents; Ergolines; Hydroxydopamines; In Vitro Techniques; Male; Neurotransmitter Agents; Oxidopamine; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine; Stereoisomerism; Sympathectomy, Chemical

Yohimbine (2.5 or 4 mg/kg) reduced the percentage of open arm entries and the percentage of time spent on the open arms displayed by rats on an elevated plus-maze indicating anxiogenic activity. These effects were reversed by the alpha 2-adrenoceptor agonist clonidine (0.01 mg/kg) and by the dopamine receptor agonist apomorphine (0.57 mg/kg). The following failed to reverse the effects of yohimbine: the selective alpha 2-adrenoceptor agonists, guanfacine (0.25 and 1 mg/kg), B-HT920 (0.025 and 0.1 mg/kg), B-HT933 (1 and 10 mg/kg); the beta-blocker propranolol (2.5 and 10 mg/kg); the alpha 1-adrenoceptor agonist phenylephrine; the D1 agonist SK&F 38393 (5 and 10 mg/kg) and the D2 agonist LY 171555 (0.5 and 1 mg/kg). Therefore, it is unlikely that activity at only the alpha 1, alpha 2, beta, D1 or D2 sites can entirely account for the anxiogenic actions of yohimbine in the elevated plus-maze. Evidence that clonidine affects the dopaminergic system and that apomorphine affects the noradrenergic system suggest that yohimbine may produce its anxiogenic response by activity on both the noradrenergic and dopaminergic systems.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Adrenergic alpha-Agonists; Animals; Anxiety; Apomorphine; Azepines; Benzazepines; Clonidine; Dopamine Agents; Ergolines; Guanfacine; Guanidines; Learning; Male; Norepinephrine; Phenylacetates; Phenylephrine; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Adrenergic; Receptors, Dopamine; Yohimbine

The affinity of LY-171555 (quinpirole) and BHT-920 for both states of rat striatal dopamine D-1 and D-2 receptors was determined. Although these drugs have different pharmacological effects in experimental animals, we found that they had similar affinities for both D-1 and D-2 receptors.

Topics: Animals; Azepines; Benzazepines; Corpus Striatum; Dopamine Agents; Endothelins; Ergolines; Guanylyl Imidodiphosphate; In Vitro Techniques; Male; Peptides; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine

The putative autoreceptor-selective dopamine (DA) agonist B-HT 920 was tested using electrophysiological and behavioral models thought to reflect actions at postsynaptic D2 DA receptors. Direct iontophoretic application of B-HT 920 onto nucleus accumbens neurons caused a current-dependent inhibition of firing which could be attenuated by pretreatment with alpha-methyl-p-tyrosine (to deplete DA) and reinstated (enabled) by concurrent administration of the selective D1 DA receptor agonist SKF 38393. These findings suggest that, like other selective D2 DA receptor agonists, the postsynaptic effects of B-HT 920 require concurrent stimulation of D1 DA receptors. Behavioral indices of postsynaptic D2 DA receptor stimulation (stereotyped sniffing and rearing) were also evident following combined treatment with B-HT 920 and SKF 38393. Moreover, similar "low-level" stereotyped behaviors were also observed when B-HT 920 was administered alone following pretreatment with the alpha-2 adrenoceptor antagonists idazoxane and piperoxane, suggesting that alpha-2 agonist actions of B-HT 920, in some way, mask the expression of D2 receptor-mediated stereotyped responses. When B-HT 920 was combined with SKF 38393 following pretreatment with idazoxane, both the intensity and form (continual licking and gnawing) of stereotyped behavior was enhanced. Taken together, these electrophysiological and behavioral findings indicate that B-HT 920 possesses the properties of a selective D2 DA receptor agonist and cannot be considered as a DA autoreceptor-selective compound.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Action Potentials; Adrenergic alpha-Agonists; Animals; Azepines; Benzazepines; Dioxanes; Electrophysiology; Ergolines; Idazoxan; Iontophoresis; Male; Motor Activity; Nucleus Accumbens; Piperoxan; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine; Receptors, Dopamine D2; Stereotyped Behavior

The effect on dopamine (DA) release of D-1 and D-2 receptor agonists and antagonists applied locally in the caudate through a trans-striatal dialysis probe was studied in freely moving rats. D-2 agonists (LY 171555 and BHT 920) reduced DA release in a concentration-dependent manner. The same local application of haloperidol abolished the effect of 10 microM LY 171555 and BHT 920. A specific D-1 agonist, the catechol benzazepine SKF 38393, reduced DA release and this effect was not modified by systemic or local administration of the D-1 antagonist, SCH 23390, nor by the D-2 antagonist, haloperidol. In contrast, the non-catechol D-1 agonist, CY 208243, failed to modify DA release. Local application of the D-1 antagonist, SCH 23390, or of the D-2 antagonist, (-)-sulpiride, stimulated DA release in a concentration-dependent manner. The D-1 agonist, CY 20843, reversed the stimulatory effect of SCH 23390 but not that of (-)-sulpiride. It is concluded that D-1 and D-2 receptors located in the caudate control DA release separately in this area.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Animals; Azepines; Benzazepines; Brain; Dialysis; Dopamine; Dopamine Agents; Dopamine Antagonists; Ergolines; Haloperidol; Male; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine; Sulpiride

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; alpha-Methyltyrosine; Animals; Apomorphine; Appetite Depressants; Azepines; Behavior, Animal; Benzazepines; Ergolines; Methyltyrosines; Quinpirole; Rats; Receptors, Dopamine; Stereotyped Behavior

Using the technique of brain dialysis in freely moving rats we have investigated the effect of various dopamine (DA) receptor agonists on the release and metabolism of DA in two terminal dopaminergic areas, the nucleus accumbens and the dorsal caudate. Low doses of various DA receptor agonists such as apomorphine (12-100 micrograms/kg s.c.), LY 171555 (5-50 micrograms/kg s.c.), pergolide (5-25 micrograms/kg s.c.), (+)-3PPP (0.5-2.5 mg/kg s.c.) and BHT 920 (10-250 micrograms/kg s.c.) reduce DA release and elicit hypomotility. The potency of the drugs and their effectiveness is similar in the two areas. Inhibition of DA release appears related to the ability of the various agonists to stimulate D-2 rather than D-1 receptors. Thus, the reportedly selective D-1 agonist, SKF 38393, was inactive on DA release and metabolism even at doses fully active in eliciting D-1-mediated effects (grooming); on the other hand apomorphine, a D-1/D-2 agonist, and pergolide, a D-2 agonist with rather weak D-1 activity, reduced DA release in a manner which was related to their agonist activity at D-2 receptors; finally LY 171555, (+)-3PPP and BHT 920, which selectively stimulate D-2 receptors, were fully active at reducing DA release in vivo. Apomorphine, pergolide, LY 171555 and (+)-3PPP given at higher doses elicited behavioral stimulation. In contrast, BHT 920 failed to do so. In further contrast (-)-3PPP (0.1-10 mg/kg s.c.), which failed to reduce DA release at low doses, actually stimulated it at high doses (10 mg/kg s.c.) and elicited hypomotility, thus resembling DA receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; 3,4-Dihydroxyphenylacetic Acid; Animals; Apomorphine; Azepines; Behavior, Animal; Benzazepines; Brain; Dialysis; Dopamine; Ergolines; Homovanillic Acid; Isomerism; Male; Motor Activity; Neurons; Pergolide; Piperidines; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine; Time Factors

Low doses of BHT 920, LY 171555 and (+)3PPP, three dopamine agonists selective for D-2 receptors, induced yawning in rats. This effect was reduced by the selective D-1 antagonist SCH 23390 but the antagonism did not exceed a 50% reduction from the control values. In contrast, the selective D-2 antagonist (-)sulpiride completely abolished agonist-induced yawning. A 6 h reserpine pretreatment (5 mg/kg i.p.), which depletes brain dopamine (DA) by about 95%, reduced agonist-induced yawning by an extent similar to SCH 23390; in the reserpinized rats, SCH 23390 completely lost the property of blocking agonist-induced yawning while (-)sulpiride retained it. Two 5HT receptor antagonist, ketanserin and metergoline failed to influence agonist-induced yawning. The reportedly selective D-1 agonist, SKF 38393, failed to induce yawning in normal rats as well as in rats pretreated with reserpine 6 or 16 h earlier. If one excludes that SCH 23390 and the D-2 agonists interact with the same DA-receptors, the data are consistent with the possibility that stimulation of D-1 receptors by endogenous DA plays a permissive-facilitatory role for the behavioural expression of D-2 receptor activation.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Adrenergic alpha-Agonists; Animals; Azepines; Benzazepines; Brain Chemistry; Dopamine; Ergolines; Kainic Acid; Ketanserin; Male; Metergoline; Piperidines; Quinpirole; Rats; Rats, Inbred Strains; Receptors, Dopamine; Reserpine; Sulpiride; Yawning

Rat striatal synaptosomal tyrosine hydroxylation was inhibited dose- and pH dependently by a number of dopamine agonists. The catecholic agonists apomorphine and (-)N-n-propylnorapomorphine inhibited synaptosomal tyrosine hydroxylase completely, with IC50 values of around 0.3 mumol/l at pH 6.6. The noncatechol agonists pergolide and bromocriptine and the putative dopamine autoreceptor agonists 3-PPP(-), 3-PPP(+), HW-165 and B-HT 920 produced only partial inhibition of synaptosomal tyrosine hydroxylation at high concentrations. Comparison of the inhibition of synaptosomal and soluble tyrosine hydroxylase indicated that the inhibition produced by apomorphine could be ascribed to a direct effect on the enzyme, whereas this was not the case for the noncatechol agonists. The inhibition produced by pergolide and 3-PPP(-) was not antagonised by either dopamine receptor or alpha-adrenoceptor antagonists. The present results have been compared with results reported in the literature for inhibition of synaptosomal tyrosine hydroxylation and for two other tests of dopamine autoreceptor agonist activity (inhibition of dopamine release from striatal slices in vitro, and inhibition of the gamma-butyrolactone induced increase in dopamine synthesis in vivo). It is concluded that inhibition of striatal synaptosomal tyrosine hydroxylation by dopamine agonists does not fulfil the criteria required for it to be considered as a useful measure of dopamine autoreceptor function.

Topics: Adrenergic alpha-Agonists; Animals; Apomorphine; Azepines; Corpus Striatum; Depression, Chemical; Dopamine; Ergolines; Hydrogen-Ion Concentration; In Vitro Techniques; Male; Pergolide; Piperidines; Rats; Rats, Inbred Strains; Receptors, Dopamine; Receptors, Neurotransmitter; Synaptosomes; Tyrosine 3-Monooxygenase