In-vivo assessment of 5-HT2A and 5-HT2C antagonistic properties of newer antipsychotics.
The effects of serotonin (5-HT) receptor ligands on the MK 212 (6-chloro-2[1-piperazinyl]pyrazine) discriminative stimulus and quipazine-induced head twitches were studied in rats. 5-HT1A (8-OH-DPAT) and preferential 5-HT2A (DOI) receptor agonists did not generalize to the discriminative stimulus. The 5-HT2B/2C-receptor antagonist, SB 206553 (5-methyl-1-(3-pyridylcarbamoyl)-1,2,3,5-tetrahydropyrrolo[2 ,3-f]indole), and the 5-HT2A/2C-receptor antagonist, ritanserin, acted as potent antagonists, whereas the 5-HT2A-receptor antagonist, MDL 100.151 ([(+/-)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4- piperidine-methanol), produced minor and inconsistent inhibition. SB 206553 was a weak antagonist against quipazine-induced head twitches, whereas MDL 100.151 and ritanserin were potent antagonists. This suggests that the MK 212 discriminative stimulus is mediated by 5-HT2C receptors, while quipazine-induced head twitches are mediated primarily by 5-HT2A receptors. The effects on quipazine-induced head twitches were comparable to previously published effects on the DOI discriminative stimulus. 5-HT2A- and 5-HT2C-receptor antagonistic potencies of clozapine, olanzapine, risperidone, sertindole and ziprasidone were compared in the same models. Clozapine showed similar potencies in both models, while sertindole, olanzapine and risperidone inhibited quipazine-induced effects more potently than the MK 212 discriminative stimulus. Ziprasidone exerted a minor preference for 5-HT2A- compared to 5-HT2C-receptor-mediated effects. The ratio between in vivo inhibitory potencies at 5-HT2A and 5-HT2C receptors did not correlate with corresponding ratios from in-vitro affinity and ex-vivo occupancy studies in the literature.
Sánchez
C
C
Neuropharmacology Department, H. Lundbeck A/S, Valby, Denmark. CS@lundbeck.com
Arnt
J
J
D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology*; D006257:Head; D008024:Ligands; D008297:Male; D009068:Movement / Q000187:drug effects*; D011719:Pyrazines / Q000494:pharmacology; D011814:Quipazine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D014150:Antipsychotic Agents; D008024:Ligands; D011719:Pyrazines; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D011814:Quipazine; C014896:6-chloro-2-(1-piperazinyl)pyrazine