norclozapine and xanomeline

3(3-Hexyloxy-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine (xanomeline) and N-desmethylclozapine are of special interest as promising antipsychotics with better efficacy, especially for negative symptoms and/or cognitive/affective impairment.. The guanosine-5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPγS) binding experiments were performed using (1) conventional filtration technique, (2) antibody-capture scintillation proximity assay, and (3) immunoprecipitation method, in brain membranes prepared from rat cerebral cortex, hippocampus, and striatum.. Xanomeline had agonistic activity at the M1 muscarinic acetylcholine receptor (mAChR) in all brain regions, as well as at the 5-HT1A receptor in the cerebral cortex and hippocampus. On the other hand, N-desmethylclozapine exhibited slight agonistic effects on the M1 mAChR, and agonistic properties at the 5-HT1A receptor in the cerebral cortex and hippocampus. This compound also behaved as an agonist at the δ-opioid receptor in the cerebral cortex and striatum. In addition, the stimulatory effects of N-desmethylclozapine on [(35)S]GTPγS binding to Gαi/o were partially mediated through mAChRs (most likely M4 mAChR subtype), at least in striatum.. The agonistic effects on the mAChRs (particularly M1 subtype, and also probably M4 subtype), the 5-HT1A receptor and the δ-opioid receptor expressed in native brain tissues, some of which are common to both compounds and others specific to either, likely shape the unique beneficial effectiveness of both compounds in the treatment for schizophrenic patients. These characteristics provide us with a clue to develop newer antipsychotics, beyond the framework of dopamine D2 receptor antagonism, that are effective not only on positive symptoms but also on negative symptoms and/or cognitive/affective impairment.

Topics: Animals; Antipsychotic Agents; Cerebral Cortex; Clozapine; Corpus Striatum; Hippocampus; Immunoprecipitation; Male; Muscarinic Agonists; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M1; Receptor, Serotonin, 5-HT1A; Thiadiazoles

N-desmethylclozapine (NDMC), a major circulating metabolite of the atypical antipsychotic drug, clozapine, and has M(1) muscarinic receptor partial agonistic property. The purpose of the present study was to examine whether in vivo behavioral effects of NDMC were elicited through the activation of muscarinic receptors. Both a non-selective muscarinic receptor agonist, oxotremorine (0.01-0.1mg/kg), and an M(1) and M(4) muscarinic receptor agonist, xanomeline (0.3-3mg/kg), decreased exploratory locomotor activity in mice. This effect was significantly antagonized by a non-selective muscarinic receptor antagonist, scopolamine, at a dose of 0.3mg/kg without affecting exploratory locomotor activity by itself. NDMC (3-30mg/kg) also decreased exploratory locomotor activity in a dose-dependent manner, and the reduced locomotor activity was significantly antagonized by scopolamine at doses of 0.1 and 0.3mg/kg. These results suggested that NDMC might decrease exploratory locomotor activity at least partly through the activation muscarinic receptors in vivo. NDMC (10-30mg/kg) and clozapine (0.3-1mg/kg) dose-dependently increased prepulse inhibition (PPI) in DBA/2J mice, as did xanomeline (1-3mg/kg). Scopolamine at a dose of 0.3mg/kg without altering PPI by itself significantly antagonized the increase of PPI caused by NDMC (30mg/kg), xanomeline (3mg/kg), and oxotremorine (0.06mg/kg). These findings suggest that the activation of muscarinic receptors may be at least partly responsible for exerting the antipsychotic-like effects of both NDMC and xanomeline in an animal model for schizophrenia.

Topics: Acoustic Stimulation; Animals; Antipsychotic Agents; Clozapine; Dose-Response Relationship, Drug; Drug Interactions; Mice; Motor Activity; Muscarinic Agonists; Neural Inhibition; Oxotremorine; Psychophysics; Pyridines; Receptors, Muscarinic; Scopolamine; Sensory Gating; Thiadiazoles

We have demonstrated that the main metabolite of clozapine, N-desmethylclozapine, has a significant role in the ability of clozapine to improve some aspects of cognition in schizophrenia. Furthermore, there is also evidence to suggest that it is the muscarinic M(1) receptor agonist effect of N-desmethylclozapine that underlies its cognitive effects. In the present study we examined the efficacy of two muscarinic receptor agonists xanomeline and sabcomeline to increase the efflux of acetylcholine and dopamine in rat medial prefrontal cortex and nucleus accumbens. Microdialysis in awake, freely moving rats was used to demonstrate that xanomeline at 10, but not 1 or 3 mg/kg (s.c.), significantly increased acetylcholine efflux in both the medial prefrontal cortex and nucleus accumbens. Sabcomeline, at 1 but not 0.1 or 0.5 mg/kg (s.c.), significantly increased acetylcholine efflux in the medial prefrontal cortex but not the nucleus accumbens. Both xanomeline and sabcomeline dose-dependently increased dopamine efflux in the medial prefrontal cortex but only high dose of xanomeline (10 mg/kg, s.c.) and sabcomeline (1 mg/kg, s.c.) increased that in the nucleus accumbens. The acetylcholine and dopamine efflux induced by xamomeline (10 mg/kg, s.c.) and sabcomeline (1 mg/kg, s.c.) were significantly blocked by the preferential muscarinic M(1) receptor antagonist telenzepine (3 mg/kg, s.c.), but significantly potentiated by the atypical antipsychotic drug risperidone (0.1 mg/kg, s.c.), which does not have much affinity for muscarinic receptor(s). According to the analysis of net-AUC (area under the curve) values of acetylcholine and dopamine levels, the rank order of ability of these drugs to increase acetylcholine or dopamine levels is sabcomeline>xanomeline approximately AC260584>N-desmethylclozapine. The present study suggests that the binding potency of muscarinic M(1) receptors is greatly related to their ability to increase cortical acetylcholine and dopamine efflux, and that this may have some relevance for treatment of the cognitive deficit of schizophrenia.

Topics: Acetylcholine; Animals; Antipsychotic Agents; Benzoxazines; Brain; Clozapine; Dopamine; Drug Synergism; Imines; Male; Nucleus Accumbens; Pirenzepine; Prefrontal Cortex; Pyridines; Quinuclidines; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M1; Receptor, Muscarinic M4; Risperidone; Thiadiazoles

Recent studies have suggested that the salutary actions of clozapine in schizophrenia may be due to selective activation of M(1) muscarinic receptors by clozapine and/or its major active metabolite N-desmethylclozapine.. We systematically tested this hypothesis by screening a large number of psychoactive compounds, including many atypical antipsychotic drugs, for agonist activity at cloned, human M(1), M(3) and M(5) muscarinic receptors.. Only three of the 14 atypical antipsychotic drugs we tested were found to possess partial agonist actions at M(1) muscarinic receptors (fluperlapine, JL13, clozapine). A few additional miscellaneous compounds had a modest degree of M(1) agonist actions. Only carbachol and N-desmethylclozapine had appreciable M(3) muscarinic agonism at M(3) muscarinic receptors, although several were M(5) partial agonists including MK-212, N-desmethylclozapine and xanomeline.. Although M(1) muscarinic receptor-selective partial agonists have shown promise in some preclinical antipsychotic drug models, these studies indicate that it is unlikely that the salutary actions of clozapine and similar atypical antipsychotic drugs are mediated solely by M(1) muscarinic receptor activation. It is possible, however, that the M(1) agonism of N-desmethylclozapine contributes to the uniquely beneficial actions of clozapine. Thus, these results are consistent with the notion that a balanced degree of activity at multiple biogenic amine receptors, including M(1) muscarinic agonism, is responsible for the uniquely beneficial actions of clozapine.

Topics: Animals; Antipsychotic Agents; CHO Cells; Clozapine; Cricetinae; Cricetulus; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Psychopharmacology; Pyridines; Receptors, Muscarinic; Thiadiazoles