Y. Takahashi et al., IN-VIVO OCCUPATION OF DOPAMINE D-1, D-2 AND SEROTONIN(2A) RECEPTORS BY NOVEL ANTIPSYCHOTIC DRUG, SM-9018 AND ITS METABOLITE, IN RAT-BRAIN, Journal of neural transmission, 105(2-3), 1998, pp. 181-191
In vivo occupation of dopamine D-1, D-2 and serotonin (5-MT)(2A) recep
tors by a novel antipsychotic drug, SM-9018 (perospirone hydrochloride
-1-piperazinyl]butyl]cyclohexane-1,2-dicarboximide monohydrochloride)
and its major metabolite (ID-15036; isothiazol-3-yl)-1-piperazinyl]bu
tyl]-1-hydroxy-1, 2-cyclohexanedicarboximide) was measured in rat brai
n using N-ethoxycarbonyl-2-ethoxy-1 ,2-dihydroquinoline (EEDQ), an irr
eversible antagonist, at these receptor sites. SM-9018 and its metabol
ite, ID-15036, dose-dependently reversed EEDQ-induced 5-MT2A and D-2 r
eceptor inactivation, but not D-1 receptor inactivation. At lower dose
s (0.1 mg/kg i.p.), SM-9018 showed a preferential occupation of the 5-
MT2A receptors, with only a small effect on the D-2 receptors; while a
t higher doses (1.0 and 5.0 mg/kg i.p.): it was nearly equipotent in i
ts occupation of both the D-2 (77.8%) and the 5-HT2A receptors (78.6%)
. On the other hand, ID-15036 was more potent in occupying the 5-MT2A
than the D-2 receptors even at higher doses (1.0 and 5.0 mg/kg i.p.).
We previously reported that atypical antipsychotic drugs, such as cloz
apine, were characterized by a high occupancy of the 5-MT2A receptors,
with a low or minimum occupancy of the D-2 receptors in vivo. The pre
sent study suggests that SM-9018 and its metabolite ID-15036 show a pr
eferential tendency to occupy 5-MT2A receptors, and that the clozapine
-like atypical properties of SM-9018 may be due to some pharmacologica
l action of both the SM-9018 itself and its metabolite, ID-15063.