clozapine and 4-iodo-2-5-dimethoxyphenylisopropylamine

Animal models with predictive and construct validity are necessary for developing novel and efficient therapeutics for psychiatric disorders.. We have carried out a pharmacological characterization of the Roman high- (RHA-I) and low-avoidance (RLA-I) rat strains with different acutely administered propsychotic (DOI, MK-801) and antipsychotic drugs (haloperidol, clozapine), as well as apomorphine, on prepulse inhibition (PPI) of startle and locomotor activity (activity cages).. RHA-I rats display a consistent deficit of PPI compared with RLA-I rats. The typical antipsychotic haloperidol (dopamine D2 receptor antagonist) reversed the PPI deficit characteristic of RHA-I rats (in particular at 65 and 70 dB prepulse intensities) and reduced locomotion in both strains. The atypical antipsychotic clozapine (serotonin/dopamine receptor antagonist) did not affect PPI in either strain, but decreased locomotion in a dose-dependent manner in both rat strains. The mixed dopamine D1/D2 agonist, apomorphine, at the dose of 0.05 mg/kg, decreased PPI in RHA-I, but not RLA-I rats. The hallucinogen drug DOI (5-HT2A agonist; 0.1-1.0 mg/kg) disrupted PPI in RLA-I rats in a dose-dependent manner at the 70 dB prepulse intensity, while in RHA-I rats, only the 0.5 mg/kg dose impaired PPI at the 80 dB prepulse intensity. DOI slightly decreased locomotion in both strains. Finally, clozapine attenuated the PPI impairment induced by the NMDA receptor antagonist MK-801 only in RLA-I rats.. These results add experimental evidence to the view that RHA-I rats represent a model with predictive and construct validity of some dopamine and 5-HT2A receptor-related features of schizophrenia.

Topics: Amphetamines; Animals; Antipsychotic Agents; Apomorphine; Avoidance Learning; Clozapine; Dizocilpine Maleate; Dopamine Agonists; Dopamine Antagonists; Excitatory Amino Acid Antagonists; Haloperidol; Locomotion; Male; Prepulse Inhibition; Rats; Receptor, Serotonin, 5-HT2A; Reflex, Startle; Schizophrenia; Serotonin 5-HT2 Receptor Agonists; Serotonin Antagonists

Topics: Amphetamines; Animals; Antipsychotic Agents; Clozapine; Inferior Colliculi; Male; Microinjections; Prepulse Inhibition; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Ritanserin; Serotonin 5-HT2 Receptor Agonists; Serotonin 5-HT2 Receptor Antagonists

G protein-coupled receptor (GPCR) signaling is modulated by endocytosis and endosomal sorting of receptors between degradation and recycling. Differential regulation of these processes by endogenous ligands and synthetic drugs is a poorly understood area of GPCR signaling. Here, we describe remarkable diversity in the regulation of trafficking of GPCR induced by multiple ligands. We show that the serotonin receptor 2A (5-HT(2A)), a prototypical GPCR in the study of functional selectivity at a signaling receptor, is functionally selective in endocytosis and recycling in response to five ligands tested: endogenous agonists serotonin (5-HT) and dopamine (DA), synthetic agonist 1-(2,5-dimethoxy-4-iodophenyl)-aminopropane (DOI), antagonist ketanserin, and inverse agonist and antipsychotic drug clozapine. Only four ligands (5-HT, DA, DOI, and clozapine) bring about receptor endocytosis. As we have earlier described with 5-HT and DA, there is ligand-specific requirement for protein kinase C (PKC) in endocytosis. We now show 5-HT(2A) phosphorylation by PKC is necessary for 5-HT-mediated and DOI-mediated receptor endocytosis, but DA-mediated and clozapine-mediated internalization is not affected if PKC is inhibited. Internalized receptors are recycled to the cell surface, but there is variability in the time course of recycling. 5-HT- and DA-internalized receptors are recycled in 2.5 hours while agonist DOI and antagonist clozapine bring about recycling in 7.5 hours. Recycling in response to those ligands that require PKC activation to effect receptor endocytosis is dependent on receptor dephosphorylation by protein phosphatase 2A (PP2A). Thus, internalization and phosphorylation/dephosphorylation cycles may play a significant role in the regulation of 5-HT(2A) by functionally and therapeutically important ligands.

Topics: Amphetamines; Animals; Clozapine; Dopamine; Drug Partial Agonism; Endocytosis; Enzyme Activation; HEK293 Cells; Humans; Ketanserin; Ligands; Phosphorylation; Protein Kinase C; Protein Phosphatase 2; Protein Transport; Rats; Receptor, Serotonin, 5-HT2A; Serotonin; Serotonin 5-HT2 Receptor Agonists; Serotonin 5-HT2 Receptor Antagonists; Signal Transduction

Clozapine, by virtue of its absence of extrapyramidal side effects and greater efficacy, revolutionized the treatment of schizophrenia, although the mechanisms underlying this exceptional activity remain controversial. Combining an unbiased cheminformatics and physical screening approach, we evaluated clozapine's activity at >2350 distinct molecular targets. Clozapine, and the closely related atypical antipsychotic drug olanzapine, interacted potently with a unique spectrum of molecular targets. This distinct pattern, which was not shared with the typical antipsychotic drug haloperidol, suggested that the serotonergic neuronal system was a key determinant of clozapine's actions. To test this hypothesis, we used pet1(-/-) mice, which are deficient in serotonergic presynaptic markers. We discovered that the antipsychotic-like properties of the atypical antipsychotic drugs clozapine and olanzapine were abolished in a pharmacological model that mimics NMDA-receptor hypofunction in pet1(-/-) mice, whereas haloperidol's efficacy was unaffected. These results show that clozapine's ability to normalize NMDA-receptor hypofunction, which is characteristic of schizophrenia, depends on an intact presynaptic serotonergic neuronal system.

Topics: Acoustic Stimulation; Action Potentials; Adrenergic Uptake Inhibitors; Amphetamines; Animals; Antipsychotic Agents; Behavior, Animal; Checkpoint Kinase 2; Clozapine; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Gene Expression Regulation; Ketanserin; Lysine; Mice; Mice, Knockout; Mitogen-Activated Protein Kinase 3; Motor Activity; N-Methyl-3,4-methylenedioxyamphetamine; Neurons; Patch-Clamp Techniques; Phencyclidine; Presynaptic Terminals; Protein Binding; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Radioligand Assay; Raphe Nuclei; Receptor, Serotonin, 5-HT1A; Reflex, Startle; Serotonin; Serotonin Antagonists; Stereotyped Behavior; Tritium; Tryptophan Hydroxylase

Atypical antipsychotic drugs, such as clozapine and risperidone, have a high affinity for the serotonin 5-HT(2A) G protein-coupled receptor (GPCR), the 2AR, which signals via a G(q) heterotrimeric G protein. The closely related non-antipsychotic drugs, such as ritanserin and methysergide, also block 2AR function, but they lack comparable neuropsychological effects. Why some but not all 2AR inhibitors exhibit antipsychotic properties remains unresolved. We now show that a heteromeric complex between the 2AR and the G(i)-linked GPCR, metabotropic glutamate 2 receptor (mGluR2), integrates ligand input, modulating signaling output and behavioral changes. Serotonergic and glutamatergic drugs bind the mGluR2/2AR heterocomplex, which then balances Gi- and Gq-dependent signaling. We find that the mGluR2/2AR-mediated changes in Gi and Gq activity predict the psychoactive behavioral effects of a variety of pharmocological compounds. These observations provide mechanistic insight into antipsychotic action that may advance therapeutic strategies for disorders including schizophrenia and dementia.

Topics: Amphetamines; Animals; Antipsychotic Agents; Clozapine; Dimerization; Dose-Response Relationship, Drug; Frontal Lobe; Methysergide; Mice; Oocytes; Potassium Channels, Inwardly Rectifying; Receptors, Adrenergic, beta-2; Receptors, Metabotropic Glutamate; Signal Transduction; Xenopus

Rat maternal behavior is a complex social behavior. Most antipsychotic drugs disrupt active maternal responses (e.g., pup retrieval, pup licking and nest building). Our previous work shows that typical antipsychotic haloperidol disrupts maternal behavior by blocking dopamine D(2) receptors, whereas atypical clozapine works by blocking 5-HT(2A/2C) receptors. The present study used c-Fos immunohistochemistry technique, together with pharmacological tools and behavioral observations, and delineated the neuroanatomical bases of the disruptive effects of haloperidol and clozapine. Postpartum female rats were treated with haloperidol (0.2 mg/kg sc) or clozapine (10.0 mg/kg sc), with or without pretreatment of quinpirole (a selective dopamine D(2)/D(3) agonist, 1.0 mg/kg sc) or 2,5-dimethoxy-4-iodo-amphetamine (DOI, a selective 5-HT(2A/2C) agonist, 2.5 mg/kg sc). They were then sacrificed 2 h later after a maternal behavior test was conducted. Brain regions that have been previously implicated in the regulation of rat maternal behavior and/or in the antipsychotic action were examined. Behaviorally, both haloperidol and clozapine disrupted pup retrieval, pup licking and nest building. Pretreatment of quinpirole, but not DOI, reversed the haloperidol-induced disruptions. In contrast, pretreatment of DOI, but not quinpirole, reversed the clozapine-induced deficits. Neuroanatomically, the nucleus accumbens (both the shell and core), dorsolateral striatum and lateral septum showed increased c-Fos expression to the treatment of haloperidol. In contrast, the nucleus accumbens shell showed increased expression of c-Fos to the treatment of clozapine. More importantly, pretreatment of quinpirole and DOI produced opposite response profiles in the brain regions where haloperidol and clozapine had an effect. Based on these findings, we concluded that haloperidol disrupts active maternal behavior primarily by blocking dopamine D(2) receptors in a neural circuitry involving the nucleus accumbens, dorsolateral striatum and lateral septum. In contrast, clozapine appears to disrupt maternal behavior mainly by blocking serotonin 5-HT(2A/2C) receptors in the nucleus accumbens shell.

Topics: Amphetamines; Animals; Animals, Newborn; Antipsychotic Agents; Biomarkers; Brain; Clozapine; Dopamine; Dopamine Agonists; Dopamine D2 Receptor Antagonists; Female; Haloperidol; Immunohistochemistry; Male; Maternal Behavior; Neostriatum; Nucleus Accumbens; Proto-Oncogene Proteins c-fos; Quinpirole; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2A; Receptors, Dopamine D2; Septum of Brain; Serotonin 5-HT2 Receptor Antagonists; Serotonin Receptor Agonists

Though transduction mechanisms recruited by heterologously expressed 5-HT(2A) receptors have been extensively studied, their interaction with specific subtypes of G-protein remains to be directly evaluated in cerebral tissue. Herein, as shown by an immunocapture/scintillation proximity analysis, 5-HT, the prototypical 5-HT(2A) agonist, DOI, and Ro60,0175 all enhanced [(35)S]GTPgammaS binding to G alpha q/11 in rat cortex with pEC(50) values of 6.22, 7.24 and 6.35, respectively. No activation of G o or G s/olf was seen at equivalent concentrations of DOI. Stimulation of G alpha q/11 by 5-HT (30 microM) and DOI (30 microM) was abolished by the selective 5-HT(2A) vs. 5-HT(2C)/5-HT(2B) antagonists, ketanserin (pK(B) values of 9.11 and 8.88, respectively) and MDL100,907 (9.82 and 9.68). By contrast, 5-HT-induced [(35)S]GTPgammaS binding to G alpha q/11 was only weakly inhibited by the preferential 5-HT(2C) receptor antagonists, RS102,221 (6.94) and SB242,084 (7.39), and the preferential 5-HT(2B) receptor antagonist, LY266,097 (6.66). The antipsychotic, clozapine, which had marked affinity for 5-HT(2A) receptors, blocked the recruitment of G alpha q/11 by 5-HT and DOI with pK(B) values of 8.54 and 8.14, respectively. Its actions were mimicked by the "atypical" antidepressant and 5-HT(2A) receptor antagonist, mirtazapine, which likewise blocked 5-HT and DOI-induced G alpha q/11 protein activation with pK(B) values of 7.90 and 7.76, respectively. In conclusion, by use of an immunocapture/scintillation proximity strategy, this study shows that native 5-HT(2A) receptors in rat frontal cortex specifically recruit G alpha q/11 and that this action is blocked by clozapine and mirtazapine. Quantification of 5-HT(2A) receptor-mediated G alpha q/11 activation in frontal cortex should prove instructive in characterizing the actions of diverse classes of psychotropic agent.

Topics: Adrenergic alpha-Antagonists; Amphetamines; Animals; Cerebral Cortex; Clozapine; GTP-Binding Protein alpha Subunits, Gq-G11; Male; Mianserin; Mirtazapine; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Scintillation Counting; Serotonin Antagonists; Serotonin Receptor Agonists

Many antipsychotic drugs disrupt active components of maternal behavior such as pup approach, pup retrieval and nest building at clinically relevant doses in postpartum female rats. However, the neurochemical mechanisms underlying such a disruptive effect remain to be determined. This study examined the neurochemical mechanisms that mediate the disruptive effects of haloperidol (a typical antipsychotic) and clozapine (an atypical antipsychotic) on rat maternal behavior. Postpartum rats were administered with haloperidol (0.2 mg/kg, sc) or clozapine (10.0 mg/kg, sc) together with either vehicle (saline or water), quinpirole (a selective dopamine D(2)/D(3) agonist, 0.5 or 1.0 mg/kg, sc), or 2,5-dimethoxy-4-iodo-amphetamine (DOI, a selective 5-HT(2A/2C) agonist, 1.0 or 2.5 mg/kg, sc), and their maternal behaviors were tested at different time points before and after drug administration. Haloperidol and clozapine treatment disrupted pup approach, pup retrieval, pup licking and nest building. Pretreatment of quinpirole, but not DOI, dose-dependently reversed the haloperidol-induced disruptions. In contrast, pretreatment of DOI, but not quinpirole, dose-dependently reversed the clozapine-induced disruptions. Quinpirole pretreatment even exacerbated the clozapine-induced disruption of pup retrieval and nest building. These findings suggest a double dissociation mechanism underlying the disruption of haloperidol and clozapine on rat maternal behavior. Specifically, haloperidol disrupts maternal behavior primarily by blocking dopamine D(2) receptors, whereas clozapine exerts its disruptive effect primarily by blocking the 5-HT(2A/2C) receptors. Our findings also suggest that 5-HT receptors are involved in the mediation of rat maternal behavior.

Topics: Amphetamines; Animals; Antipsychotic Agents; Clozapine; Dopamine Agonists; Dopamine Antagonists; Dose-Response Relationship, Drug; Drug Interactions; Female; Haloperidol; Maternal Behavior; Nesting Behavior; Postpartum Period; Pregnancy; Quinpirole; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Dopamine D2; Serotonin Receptor Agonists

Perceptual and psychic alterations and thought disorder are fundamental elements of schizophrenia symptoms, a pathology associated with an abnormal macro- and microcircuitry of several brain areas including the prefrontal cortex (PFC). Alterations in information processing in PFC may partly underlie schizophrenia symptoms.. The 5-HT(2A/2C) agonist DOI and antipsychotic drugs were administered to anesthetized rats. Single unit and local field potential (LFP) extracellular recordings were made in medial PFC (mPFC). Electrolytic lesions were performed in the thalamic nuclei.. DOI markedly disrupts cellular and network activity in rat PFC. DOI altered pyramidal discharge in mPFC (39% excited, 27% inhibited, 34% unaffected; n = 51). In all instances, DOI concurrently reduced low-frequency oscillations (.3-4 Hz; power spectrum: .25 +/- .02 and .14 +/- .01 microV(2) in basal conditions and after 50-300 microg/kg intravenous (i.v.) DOI, respectively; n = 51). Moreover, DOI disrupted the temporal association between the active phase of LFP and pyramidal discharge. Both effects were reversed by M100907 (5-HT(2A) receptor antagonist) and were not attenuated by thalamic lesions, supporting an intracortical origin of the effects of DOI. The reduction in low-frequency oscillations induced by DOI was significantly reversed by the antipsychotic drugs haloperidol (.1-.2 mg/kg i.v.) and clozapine (1 mg/kg i.v.).. DOI disorganizes network activity in PFC, reducing low-frequency oscillations and desynchronizing pyramidal discharge from active phases of LFP. These effects may underlie DOI's psychotomimetic action. The reversal by clozapine and haloperidol indicates that antipsychotic drugs may reduce psychotic symptoms by normalizing an altered PFC function.

Topics: Action Potentials; Amphetamines; Analysis of Variance; Animals; Antipsychotic Agents; Biological Clocks; Clozapine; Dose-Response Relationship, Drug; Electroencephalography; Electrolysis; Evoked Potentials; Fluorobenzenes; Fourier Analysis; Hallucinogens; Male; Neurons; Piperidines; Prefrontal Cortex; Rats; Rats, Wistar; Serotonin Antagonists; Thalamus

Clozapine is a prototype of atypical antipsychotics that has a profile not only to block D(2)/5-HT(2A) receptors but also to enhance N-methyl-D-aspartate (NMDA) receptor-mediated glutamatergic neurotransmission. This study hypothesized different effects between a single and repeated administration of clozapine on NMDA receptor-mediated neurotransmission, and examined effects of these treatments of clozapine on a non-competitive NMDA receptor antagonist, phencyclidine (PCP)-induced hyperlocomotion and acute increases in glutamate levels in the medial prefrontal cortex (mPFC), after short- and long-term withdrawal from this antipsychotic. Locomotor activity and extracellular levels of glutamate were measured by an infrared sensor and in vivo microdialysis respectively. A single administration of clozapine attenuated PCP-induced hyperlocomotion and blocked PCP-induced increases in glutamate levels in the mPFC at 48 hours, but not 11 days after the injection of clozapine. Repeated administration of clozapine attenuated PCP-induced hyperlocomotion not only at 48 hours, but also 11 days after the last injection of clozapine, with blocking PCP-induced increases in glutamate levels in the mPFC. Both a single and repeated administration of clozapine had no effect on methamphetamine (METH)-induced hyperlocomotion at 48 hours or 11 days after the treatment of clozapine. Considering fast dissociation of clozapine from dopamine D(2) receptors and no effect of a single or repeated administration of clozapine on METH-induced hyperlocomotion, the attenuated PCP-induced hyperlocomotion by a single and repeated clozapine treatments cannot be explained by clozapine occupancy of dopamine D(2) receptors. Repeated but not a single administration of clozapine inhibited a 5-HT(2A/2C) agonist, DOI-induced increases in the mPFC 11 days after the last injection of clozapine. These findings suggest that subchronically treated clozapine-induced long-lasting downregulation of 5-HT(2A) receptors may block the enhanced PCP-induced neurochemical and behavioral changes.

Topics: Amphetamines; Animals; Antipsychotic Agents; Clozapine; Glutamic Acid; Male; Motor Activity; Phencyclidine; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Mitogen-activated protein kinase (MAPK) signaling pathways respond to dopaminergic and serotonergic agents and mediate short- and long-term effects of intracellular signaling in neurons. Here we show that the antipsychotic agent, clozapine, selectively activates the MEK/ERK MAPK pathway, and inhibition of this pathway reverses clozapine's actions in the conditioned avoidance response (CAR) paradigm, a rodent behavioral assay of antipsychotic activity.. Phosphorylation patterns of MAPK pathway enzymes were determined by quantitative immunoblot analysis and immunohistochemistry of rat prefrontal cortex. Kinase inhibitors were used to assess the role of MAPK signaling pathways in mediating clozapine-induced suppression of CAR.. Clozapine administration selectively increased phosphorylation of MEK1/2 but had no effect on p38 or JNK phosphorylation. Pretreatment with the 5-HT2A agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride blocked the clozapine-induced increase in MEK1/2 phosphorylation. Immunohistochemistry revealed that clozapine treatment elevated the number of cells in the prefrontal cortex positive for phosphoERK, the downstream substrate of MEK1/2. Prior administration of MEK1/2 inhibitors U0126 or Sl327, or ERK inhibitor 5-iodotubercidin, reversed suppression of CAR induced by clozapine, whereas administration of vehicle, JNK or p38 inhibitors (L-JNK-1 and SB203580, respectively) had no effect. Inhibition of kinases upstream to MEK1/2 (PI-3K, PKC, and CaMKII) by administration of LY294002, bisindolylmaleimide, or KN-62, respectively, also reversed clozapine-induced suppression of CAR.. These data support the hypothesis that the MEK/ERK signal transduction cascade participates in clozapine's antipsychotic actions.

Topics: Amphetamines; Animals; Antipsychotic Agents; Avoidance Learning; Behavior, Animal; Blotting, Western; Clozapine; Conditioning, Psychological; Dose-Response Relationship, Drug; Drug Interactions; Extracellular Signal-Regulated MAP Kinases; Immunohistochemistry; Male; MAP Kinase Kinase Kinase 1; MAP Kinase Kinase Kinase 2; Phosphorylation; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Serotonin Receptor Agonists; Signal Transduction; Teprotide

Activation of 5-HT2A receptors has been shown to be an essential component of the discriminative stimulus effects of indoleamine and phenethylamine hallucinogens. The objective of the present study was to determine the neuroanatomical location of the 5HT2A receptors which may be responsible for the stimulus effects of the phenethylamine hallucinogen [-]2,5-dimethoxy-4-methylamphetamine (DOM). It was hypothesized that brain areas containing altered 5-HT2A receptor expression in the context of a similar alteration in DOM-induced stimulus control might be important in mediating the stimulus effects of DOM. Fisher 344 rats were treated with either clozapine (25 mg/kg/day) or DOM (2 mg/kg/day) for 7 days, and the consequences of these drug treatment regimens on DOM-induced stimulus control and on 5-HT2A receptor expression in several brain areas were determined. Chronic administration of clozapine was associated with a wide-spread decrease in levels of 5-HT2A/2C receptors. Conversely, treatment with DOM had varied effects including a neuroanatomically selective decrease in 5-HT2A/2C receptor levels that was restricted to the olfactory nucleus. Both chronic treatment with DOM and clozapine decreased the stimulus effects of DOM. The present findings suggest a role for the olfactory nucleus in producing the stimulus effects of DOM.

Topics: Amphetamines; Animals; Binding, Competitive; Brain; Clozapine; Discrimination, Psychological; DOM 2,5-Dimethoxy-4-Methylamphetamine; Hallucinogens; Iodine Radioisotopes; Male; Rats; Rats, Inbred F344; Receptor, Serotonin, 5-HT2A; Serotonin 5-HT2 Receptor Agonists; Serotonin 5-HT2 Receptor Antagonists; Serotonin Antagonists; Serotonin Receptor Agonists

Dorsal root-evoked stimulation of sensory afferents in the hemisected in vitro rat spinal cord produces reflex output, recorded on the ventral roots. Transient spinal 5-HT(2C) receptor activation induces a long-lasting facilitation of these reflexes (LLFR) by largely unknown mechanisms. Two Sprague-Dawley substrains were used to characterize network properties involved in this serotonin (5-HT) receptor-mediated reflex plasticity. Serotonin more easily produced LLFR in one substrain and a long-lasting depression of reflexes (LLDR) in the other. Interestingly, LLFR and LLDR were bidirectionally interconvertible using 5-HT(2A/2C) and 5-HT(1A) receptor agonists, respectively, regardless of substrain. LLFR was predominantly Abeta afferent fiber mediated, consistent with prominent 5-HT(2C) receptor expression in the Abeta fiber projection territories (deeper spinal laminae). Reflex facilitation involved an unmasking of polysynaptic pathways and an increased receptive field size. LLFR emerged even when reflexes were evoked three to five times/h, indicating an activity independent induction. Both the NMDA and AMPA/kainate receptor-mediated components of the reflex could be facilitated, and facilitation was dependent on 5-HT receptor activation alone, not on coincident reflex activation in the presence of 5-HT. Selective blockade of GABA(A) and/or glycine receptors also did not prevent reflex amplification and so are not required for LLFR. Indeed, a more robust response was seen after blockade of spinal inhibition, indicating that inhibitory processes serve to limit reflex amplification. Overall we demonstrate that the serotonergic system has the capacity to induce long-lasting bidirectional changes in reflex strength in a manner that is nonassociative and independent of evoked activity or activation of ionotropic excitatory and inhibitory receptors.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Amphetamines; Analysis of Variance; Animals; Animals, Newborn; Clozapine; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Female; Ganglia, Spinal; Immunohistochemistry; In Vitro Techniques; Male; Pyrazines; Rats; Rats, Sprague-Dawley; Reaction Time; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin, 5-HT2; Reflex; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Spinal Cord; Time Factors

Most studies of 5-HT(2) receptor regulation have been carried out on the central nervous system (CNS) (which expresses 5-HT(2A) and 5-HT(2C) receptors); very few in vitro studies have addressed the peripheral receptors 5-HT(2A) and 5-HT(2B). The aim of this investigation was to compare the possible short- and long-term processes regulating these peripheral receptors in the rat. The in vitro contractile response elicited by serotonin (5-HT, 10 micro M) in the rat gastric fundus (5-HT(2B) receptor system) was rapid and followed by a partial fade to a steady state, in contrast with the rat thoracic aorta response (5-HT(2A) receptor system), which was more stable, slower and sustained. To characterize drug-receptor interactions, cumulative concentration/response curves (CCRCs) for 5-HT were constructed ex vivo for rat tissues treated with drugs acting at these receptors. Rats were examined 4 or 24 h after a single, i.p. administration of (+/-)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane [(+/-)DOI, 1 or 2.5 mg/kg], clozapine, cyproheptadine or rauwolscine (10 mg/kg), 48 h after a single i.p. administration of (+/-)DOI (2.5 mg/kg), clozapine or cyproheptadine (10 mg/kg) or 24 h after the last of with 15 daily i.p. administrations of (+/-)DOI (1 or 2.5 mg/kg), clozapine, cyproheptadine or rauwolscine (10 mg/kg). In the aorta, E(max) (the maximum response elicited by 5-HT) was unchanged 4 h after a single dose of any of the drugs tested. However, 24 h after a single dose, E(max) was lower in animals treated with (+/-)DOI (2.5 mg/kg), clozapine or cyproheptadine than in controls, whilst 48 h after a single dose of (+/-)DOI (2.5 mg/kg), clozapine or cyproheptadine there was no difference in E(max) between experimental and control animals. After chronic treatment with (+/-)DOI (2.5 mg/kg), clozapine and cyproheptadine, E(max) was lower than in controls. In the gastric fundus, E(max) 4 h after a single dose of each drug was lower than in controls, and the response recovered by 24 or 48 h. Following chronic treatment, E(max) was significantly lower than in controls for each drug used. These findings suggest first, that regulation of peripheral 5-HT(2) receptors (5-HT(2A) and 5-HT(2B)) is a functionally significant phenomenon in vivo, and occurs after administration of both agonists and antagonists. Second, the kinetics of peripheral 5-HT(2) receptor regulation were similar in both in vivo and ex vivo experiments. The 5-HT(2B) receptors in rat gastric fundus are more

Topics: Amphetamines; Animals; Antipsychotic Agents; Aorta, Thoracic; Clozapine; Cyproheptadine; Gastric Fundus; In Vitro Techniques; Ligands; Male; Muscle Contraction; Muscle, Smooth; Muscle, Smooth, Vascular; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2B; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Yohimbine

Through the development of tolerance following long-term clozapine treatment, we investigated whether 5-HT(1A) and 5-HT(2A/2C) receptors participate in the clozapine-induced Fos-protein expression in the rat forebrain. Tolerance exists when the acutely increased Fos responses to a challenge dose of the 5-HT(1A) and 5-HT(2A/2C) agonists 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane-hydrochloride (DOI) and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), respectively, given simultaneously to rats, are attenuated after 3-week clozapine (20 mg kg(-1) day(-1) i.p.) pretreatment. As compared to the acute effects of clozapine, the Fos responses to concomitant administration of the 5-HT receptor agonists DOI (2.5 mg kg(-1) i.p. ) and 8-OH-DPAT (2.5 mg kg(-1) i.p.) were more pronounced in the prefrontal cortex, the nucleus accumbens core and the dorsomedial and ventromedial striatum, areas in which clozapine (20 mg kg(-1) i. p.) exhibited marginal effects. In the hypothalamic paraventricular nucleus, both clozapine and DOI/8-OH-DPAT induced a remarkably high number of Fos-positive nuclei. Long-term clozapine pretreatment attenuated the acutely induced Fos expression of the 5-HT receptor agonists in the nucleus accumbens core, the dorsomedial and ventromedial parts of the striatum and the lateral septum, indicating (partial) common sites of action of the agents in these brain regions. No tolerance was found in the nucleus accumbens shell and the hypothalamic paraventricular nucleus and the central amygdala, suggesting that the clozapine-induced Fos responses, though distinct in these regions, are independent of 5-HT receptors. The prefrontal cortex and the dorsolateral striatum indicated only a tendency towards tolerance. In addition, the involvement of the tested 5-HT receptor agonists in the clozapine-enhanced release of plasma corticosterone became apparent. The present results indicate that the clozapine-induced patterns of Fos expression in the rat forebrain can only be in part attributed to an interaction with 5-HT(1A/2A/2C) receptors.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Amphetamines; Animals; Antipsychotic Agents; Clozapine; Corticosterone; Immunohistochemistry; Male; Oncogene Proteins v-fos; Prosencephalon; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Receptors, Serotonin, 5-HT1; Serotonin Receptor Agonists

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

Low doses of the atypical antipsychotic drug risperidone are effective in patients with obsessive compulsive disorder (OCD) not responding to serotonin (5-HT) reuptake inhibitors, although higher doses have been reported to induce OCD symptoms in psychotic patients. Since such atypical antipsychotics exert, in addition to dopamine, 5-HT2 receptor antagonistic properties, it was deemed essential to investigate the electrophysiological effect of these agents on 5-HT2 receptors in the rat orbito-frontal cortex (OFc), a brain region implicated in OCD. Microiontophoretic application of the GABAA receptor antagonist bicuculline had no effect on the suppressant effect of neuronal activity in the OFc induced by microiontophoretic application of the preferential 5-HT2A and 5-HT2C receptor agonists (+)-1-(4-iodo-2, 5-dimethoxyphenyl)-2-aminopropane (DOI) and m-chlorophenyl-piperazine (mCPP), respectively, but it antagonized the effect of GABA on the same neurons. These results indicate a lack of involvement of GABA interneurons in the suppressant effect of DOI and mCPP. While the 5-HT2 receptor antagonist ritanserin (2 mg/kg, i.v.) attenuated the inhibitory effect of DOI and mCPP in the medial prefrontal cortex (mPFc), the inhibition was unaffected in the OFc. In the mPFc, the effect of DOI and mCPP was blocked by both clozapine (1.0 and 10 mg/kg, i.v.) and risperidone (0.1 and 1.0 mg/kg, i.v.). In the OFc, only the suppressant effect of mCPP was attenuated by both doses of clozapine but only by the high dose of risperidone. These results suggest that the 5-HT2 response in the OFc is more akin to the 5-HT2C subtype and that the deleterious effect sometimes observed with high doses of risperidone and clozapine may be due to a decrease in 5-HT neurotransmission. In contrast, the beneficial effect of low doses of risperidone may be due, in part, to the antagonism of dopamine receptors.

Topics: Amphetamines; Animals; Antipsychotic Agents; Bicuculline; Clozapine; Electrophysiology; GABA Antagonists; Iontophoresis; Male; Neurons; Piperazines; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2A; Receptors, GABA-A; Receptors, Serotonin; Risperidone; Ritanserin; Serotonin Antagonists; Serotonin Receptor Agonists

Clozapine is an atypical antipsychotic drug active on both positive and negative symptoms of schizophrenia which has a unique serotonergic and dopaminergic profile. Given the putative role of the medial prefrontal cortex (mPFC) in negative symptoms of schizophrenia, the aim of this study was to assess the effects of clozapine on the dopamine- and serotonin-responsive neurons in that particular brain structure. D1 and D2 agonists (SKF 38393 and quinpirole) as well as 5-HT2 and 5-HT3 agonists (1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, DOI, and phenylbiguanide) were applied by microiontophoresis alone and concurrently with clozapine while recording extracellularly mPFC neurons. Dopamine ejections inhibited firing activity while D1 and D2 agonists were ineffective. Clozapine did not change basal firing by itself, but was able to suppress the inhibition produced by dopamine and by the 5-HT2/5-HT3 receptor agonists. It is concluded that clozapine at the mPFC level exerts a complex modulatory activity on dopamine receptors, that is directly at the dopaminergic receptors and through 5-HT receptors on the same neurons.

Topics: Action Potentials; Amphetamines; Animals; Biguanides; Clozapine; Dopamine; Dopamine Agonists; Dopamine Antagonists; Iontophoresis; Neurons; Prefrontal Cortex; Rats; Rats, Wistar; Receptors, Dopamine D1; Receptors, Dopamine D2; Receptors, Serotonin; Receptors, Serotonin, 5-HT3; Serotonin Antagonists; Serotonin Receptor Agonists; Sodium Chloride; Sulpiride

S 16924 antagonized locomotion provoked by dizocilpine and cocaine, reduced conditioned avoidance responses and blocked climbing elicited by apomorphine, models predictive of control of the positive symptoms of schizophrenia: its median inhibitory dose (ID)50 was 0.96 mg/kg, s.c. vs. 1.91 for clozapine and 0.05 for haloperidol. Rotation elicited in unilateral, substantia nigra-lesioned rats by the D1 agonist, SKF 38393, and by the D2 agonist, quinpirole, was blocked equipotently by S 16924 (0.8 and 1. 7) and clozapine (0.6 and 2.0), whereas haloperidol preferentially blocked quinpirole (0.02) vs. SKF 38393 (1.8). S 16924 more potently inhibited the head-twitches elicited by 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and the locomotion provoked by phencyclidine than it inhibited the locomotion elicited by amphetamine (ID50s = 0.15 and 0.02 vs. 2.4). Clozapine showed a similar preference (0.04 and 0.07 vs. 8.6), but not haloperidol (0. 07 and 0.08 vs. 0.04). The discriminative stimulus (DS) properties of DOI were also blocked by S 16924 (ID50 = 0.17) and clozapine (0. 05) but not by haloperidol (>0.16). S 16924 fully (100%) generalized [effective dose (ED)50 = 0.7] to a clozapine DS and clozapine (0.23) fully generalized to a S 16924 DS whereas haloperidol (>/=0.08) only partially generalized (/=80.0) or clozapine (>/=80.0). Further, S 16924 (ID50 = 3.2) and clozapine (5.5) inhibited induction of catalepsy by haloperidol. This action of S 16924 was abolished by the 5-HT1A receptor antagonist, WAY 100,635 (0.16), which less markedly attenuated the anticataleptic action of clozapine. Further, although gnawing elicited by methylphenidate was inhibited by S 16924 (ID50 = 8.4), clozapine (19.6) and haloperidol (0.04), only the action of S 16924 was blocked by WAY 100,635 (0.16). Halop

Topics: Amphetamines; Animals; Antipsychotic Agents; Attention; Clozapine; Cognition; Discrimination Learning; Electroencephalography; Haloperidol; Humans; Male; Mice; Mice, Inbred ICR; Motor Activity; Prolactin; Pyrrolidines; Rats; Rats, Wistar; Receptors, Serotonin; Receptors, Serotonin, 5-HT1; Serotonin Receptor Agonists

Acute challenge with clozapine and haloperidol produce different anatomical patterns of c-fos expression in the forebrain. The pharmacological profile of atypical antipsychotics suggests that serotonin might contribute to the unique therapeutic benefits of these drugs. In order to test this possibility, we examined the abilities of 5-HT1A and 5-HT2A/2c agonists to modify the pattern of c-fos expression induced by haloperidol and clozapine. Various groups of rats were pretreated with either saline, DOI, 8-OH-DPAT, and 8-OH-DPAT + DOI 30 min prior to haloperidol or clozapine administration. Rats were killed 90 min after antipsychotic administration. In saline-pretreated rats, haloperidol produced intense Fos-LI in all four striatal quadrants while the effect of clozapine was restricted to the medial part of the striatum. Prior administration of 8-OH-DPAT significantly reduced haloperidol-induced Fos-LI in all four striatal quadrants while DOI and 8-OHDPAT + DOI significantly reduced Fos-LI only in dorso- and ventrolateral quadrants. In the nucleus accumbens, haloperidol induced intense Fos-LI in the core and the shell regions whereas clozapine induced c-fos expression only in the shell. Pretreatment with 8-OHDPAT in haloperidol treated rats reduced Fos-LI in the core region yielding to a c-fos pattern similar to that induced by clozapine. In the prefrontal cortex of saline-pretreated rats, haloperidol produced a moderate c-fos expression compared with the intense expression produced by clozapine. Pretreatment with serotonin agonists before haloperidol brought the number of FOS-positive neurons to the same level as in clozapine treated rats. These results show the ability of 5-HT agonists to transform the typical pattern of c-fos expression induced by haloperidol into a pattern resembling that of clozapine.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Amphetamines; Animals; Antipsychotic Agents; Clozapine; Haloperidol; Male; Prosencephalon; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Receptors, Serotonin; Receptors, Serotonin, 5-HT1; Serotonin Receptor Agonists

Latent inhibition (LI), a measure of the ability to learn to ignore irrelevant stimuli, is disrupted in acute schizophrenics and in rats treated with amphetamine; antipsychotics prevent amphetamine disruption of LI in rats. The 5-HT2A/C agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) has hallucinogenic properties in humans, and evidence suggests that 5-HT2 antagonism is an important component of atypical antipsychotic activity. Therefore, the ability of DOI to disrupt LI in rats was tested, and the ability of clinically-used and putative antipsychotics to reverse DOI disruption of LI was assessed. The method consisted of four phases. After habituation to the apparatus, thirsty rats underwent preexposure to a tone stimulus 24 h prior to two tone-shock conditioning trials. LI was demonstrated at testing (an additional 24 h later) by reduced lick suppression during tone presentation. When administered at the preexposure phase only, DOI disrupted LI. However, when administered at both preexposure and conditioning phases, DOI did not disrupt LI except at the highest dose, where lick suppression itself was also disrupted. Therefore, disruptive effects of DOI on LI are not easily dissociated from state-dependent learning effects. Additional experiments demonstrated that haloperidol, clozapine, risperidone, and the selective 5-HT2A antagonist MDL 100,907 prevented the disruptive effects of DOI on LI when administered at preexposure only. These results agree with findings that these compounds can also prevent other behavioral effects of DOI. Further experiments will be required to explore the possible involvement of state-dependent learning effects in the present results. However, if the disruptive effects of DOI on LI are due to an influence on attentional processes rather than state-dependent learning, this procedure may have potential as a method for detection of antipsychotic activity.

Topics: Amphetamines; Animals; Antipsychotic Agents; Clozapine; Conditioning, Operant; Fluorobenzenes; Haloperidol; Male; Piperidines; Rats; Rats, Sprague-Dawley; Reflex, Startle; Reinforcement, Psychology; Risperidone; Serotonin Antagonists; Serotonin Receptor Agonists

Described and evaluated here is a newly designed apparatus for the assessment of conditioned avoidance response (CAR) performance in rats. The system is computer-assisted using a design and system control development package based on the virtual instrument concept (LabView). The program, which allows for significant flexibility, greatly facilitated and simplified the process of timing and data acquisition. The apparatus was found effective and appropriately designed for CAR performance training, as well as for a reliable assessment of the effects of antipsychotic and potentially antipsychotic compounds on CAR in rats. The design presents a new, effective, and inexpensive option for laboratories involved in animal behavioral research.

Topics: Amphetamines; Animals; Antipsychotic Agents; Avoidance Learning; Benzazepines; Clozapine; Computers; Cross-Over Studies; Dopamine Antagonists; Fluorobenzenes; Haloperidol; Male; Physical Conditioning, Animal; Piperidines; Raclopride; Rats; Rats, Sprague-Dawley; Salicylamides; Serotonin Antagonists; Serotonin Receptor Agonists

CGS 10746B is an imidazole-derivative related to the atypical antipsychotic clozapine which produces a decrease in dopamine release without altering dopamine metabolism or occupying D2 receptors. Rats were trained on an appetitively-motivated, two-choice, operant task to discriminate 20.0 mg/kg CGS 10746B from its vehicle. CGS 10746B was highly discriminable, producing rapid acquisition of the discrimination, and its effects were dose-responsive allowing generation of an ED50 value of 6.16 mg/kg. Substitution tests were conducted with other typical and atypical antipsychotic compounds: haloperidol, chlorpromazine, clozapine and SCH 23390. Additional tests examined generalization from the CGS 10746B stimulus properties to the calcium channel blocker isradipine, as well as to the anticholinergics atropine, scopolamine and methylscopolamine, as well as to the serotonergic agonist DOI. Clozapine and SCH 23390 were the only substances to substitute for the CGS 10746B stimulus cue. Results are discussed in terms of potential D1 receptor selectivity of CGS 10746B.

Topics: Amphetamines; Animals; Antipsychotic Agents; Cholinergic Agents; Clozapine; Cues; Discrimination Learning; Discrimination, Psychological; Dose-Response Relationship, Drug; Generalization, Response; Male; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Serotonin Agents; Serotonin Receptor Agonists; Thiazepines

Classical antipsychotics exemplified by haloperidol (0.30), fluphenazine (0.070) and cis(Z)-flupentixol (0.088; ED50 values in mumol/kg are given in parentheses for all compounds) potently block the discriminative stimulus properties of D-amphetamine (1.0 mg/kg, IP) in rats. Newer antipsychotics have very different profiles: clozapine (7.2) and olanzapine (5.9) induce dose-dependent inhibition, while risperidone (> 6.1) and remoxipride (> 47) show weak inhibitory effects and sertindole (> 23), seroquel (> 20), amperozide (> 2.9) and the putative antipsychotic MDL 100151 (> 13; racemate with MDL 100907 as the active enantiomer) are ineffective. Antagonists of alpha 1-adrenoceptors (prazosin; > 6.0), 5-HT2A/2C (ritanserin; > 2.6) and histamine H1 receptors (mepyramine; > 50) are ineffective. Sertindole (0.076), risperidone (0.23), clozapine (0.39), olanzapine (0.088), MDL 100151 (0.0082), fluphenazine (0.13) and ritanserin (0.12) are potent inhibitors of the discriminative stimulus induced by the 5-HT2A/2C agonist DOI (0.63 mg/kg, IP), while haloperidol (approximately 0.4), cis(Z)-flupentixol (approximately 0.04), amperozide (approximately 0.5) and prazosin (> 12) show partial inhibition and remoxipride (> 23) and mepyramine (> 25) are ineffective. The results indicate that inhibition of D-amphetamine discrimination does not correlate with antipsychotic activity of newer antipsychotics, as has previously been suggested in the literature. Furthermore, the inhibitory potencies against D-amphetamine-induced discrimination (present study) and hypermotility (previous study in the same strain of rats) do not correlate either for several of the newer antipsychotics (e.g. for sertindole, risperidone, seroquel and remoxipride). The discrepancies cannot solely be explained by additional pharmacological effects of these compounds, e.g. 5-HT2 receptor blockade. The D-amphetamine discrimination is documented to depend on increased limbic dopamine function which in humans is associated with increased euphoria. Based on these results, it is hypothesized that D-amphetamine discrimination rather than a model for antipsychotic activity may reflect dysphoric or anhedonic activity.

Topics: Amphetamine; Amphetamines; Animals; Antipsychotic Agents; Clozapine; Discrimination Learning; Dose-Response Relationship, Drug; Haloperidol; Male; Rats; Rats, Wistar; Reward

In a drug discrimination paradigm, the 5-HT2A/2C receptor antagonists, ritanserin, ICI 169,369 (2-(2-dimethylaminoethylthio-3-phenylquinoline hydrochloride) and mianserin, and the preferential 5-HT2A receptor antagonist, ketanserin, antagonised the discriminative stimulus effects of the 5-HT2A/2C receptor agonist, DOI ((2,5-dimethoxy-4-iodohenyl)-2-aminopropan) (0.63 mg/kg i.p.). Effective dose50 (ED50) values were: 0.32, 0.39, 0.15 and 0.03 mg/kg s.c., respectively. While the novel, selective 5-HT2C receptor antagonist, SB 200,646 (N-(1-methyl-5-iodolyl)-N'-(3-pyridyl) urea hydrochloride) was inactive (10 mg/kg s.c. and 20 mg/kg p.o.), the highly selective 5-HT2A receptor antagonist, MDL 100,907 (R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl]-4- piperidine-methanol) very potently (ED50 = 0.0006) abolished the action of DOI. MDL 100,907 may display antipsychotic properties and the 'atypical' antipsychotics, clozapine, risperidone and sertindole, each of which possesses marked affinity at 5-HT2A receptors, abolished the discriminative stimulus effects of DOI (ED50 values of 0.07, 0.03 and 0.33 mg/kg, respectively). In contrast, haloperidol (0.16) was ineffective. These data demonstrate that 5-HT2A receptors mediate the discriminative stimulus effects of DOI and support the hypothesis that an antagonistic action at 5-HT2A receptors contributes to the in vivo actions of 'atypical' antipsychotics.

Topics: Amphetamines; Animals; Antipsychotic Agents; Behavior, Animal; Clozapine; Fluorobenzenes; Isoxazoles; Male; Motor Activity; Piperidines; Rats; Rats, Wistar; Receptors, Serotonin; Risperidone; Serotonin Antagonists

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 present study was designed to evaluate the roles of serotonin 5-HT1A and 5-HT2 receptors in the effects of neuroleptic drugs in the paw test. This behavioural test has been shown to model both the antipsychotic efficacy as well as the extrapyramidal side-effect liability of neuroleptic drugs. Whereas the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT) reduced the effects of the classical neuroleptic haloperidol, it increased the effects of the atypical neuroleptic clozapine. The 5-HT2 receptor antagonist ketanserin as well as the 5-HT1C/5-HT2 receptor antagonist ritanserin, on the other hand reduced the effects of haloperidol, whereas the 5-HT1C/5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) reduced the effects of clozapine. The most important finding, however, was that the behavioural effects of different (putative) neuroleptics (fluphenazine, SCH-39166, remoxipride, prothipendyl, thioridazine and risperidone) were differentially influenced by both 8-OHDPAT and DOI, suggesting that there are important differences between the neuronal mechanisms underlying the behavioural effects of these neuroleptic drugs, even within the subclasses of classical and atypical neuroleptics.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Amphetamines; Animals; Antipsychotic Agents; Basal Ganglia Diseases; Behavior, Animal; Clozapine; Haloperidol; Ketanserin; Male; Rats; Rats, Wistar; Receptors, Serotonin; Ritanserin; Serotonin Antagonists; Serotonin Receptor Agonists

Clozapine (7.5-30.0 mumol kg-1 s.c.) produced a decrease in core temperature in the rat. The temperature decrease caused by clozapine (7.5 mumol kg-1 s.c.) was fully antagonized by the selective dopamine D1 receptor antagonist SCH 23390 (0.3 mumol kg-1) s.c.) and a partial antagonism was obtained by the selective dopamine D2 receptor antagonist raclopride (1.6 mumol kg-1 s.c.). On the other hand, the hypothermia was not antagonized by alpha-adrenoceptor antagonists (idazoxan and prazosin), 5-HT receptor antagonists ((-)-pindolol and ritanserin) or by the muscarinic M1 receptor antagonist scopolamine. The hyperthermia produced by the 5-HT1C/2 receptor agonist DOI (0.75 mumol kg-1) was blocked by clozapine (3.0 mumol kg-1 s.c.). Clozapine did not antagonize hypothermia produced by selective dopamine D1 and D2 receptor agonists (A 68930 and quinpirole), the alpha 2-adrenoceptor agonist clonidine, the 5-HT1A receptor agonist 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin) or the muscarinic M1 receptor agonist oxotremorine. The present results suggest that clozapine may be a partial agonist at brain dopamine D1 receptors.

Topics: Amphetamines; Animals; Benzazepines; Body Temperature; Body Temperature Regulation; Chromans; Clonidine; Clozapine; Dopamine Agents; Dopamine D2 Receptor Antagonists; Ergolines; Hypothermia; Injections, Subcutaneous; Male; Oxotremorine; Quinpirole; Raclopride; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Salicylamides; Serotonin Antagonists

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

Microiontophoretic application (10-80 nA) of the relatively selective serotonin 2 (5-HT2) agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane [+/-)-DOI), suppressed medial prefrontal cortical (mPFc) cell's firing rate in a dose-dependent manner. This effect was antagonized by the antipsychotic drugs (APDs) clozapine (CLOZ) and spiperone (SPIP), with CLOZ displaying a greater potency in blocking DOI's action in the mPFc. In contrast, the typical APDs haloperidol (HAL) and L-sulpiride (SUL) failed to block DOI's effect. These results suggest that certain APDs interact with 5-HT2 receptors. Although 5-HT2 antagonism alone may not distinguish typical versus atypical APDs, it is possible that their 5-HT2/dopamine 2 (D2) binding ratio is important.

Topics: Amphetamines; Animals; Antipsychotic Agents; Clozapine; Dibenzazepines; Dose-Response Relationship, Drug; Evoked Potentials; Frontal Lobe; Haloperidol; Iontophoresis; Male; Rats; Rats, Inbred Strains; Receptors, Serotonin; Spiperone