Remoxipride, a new potential antipsychotic compound with selective antidopaminergic actions in the rat brain

The novel substituted benzamide, remoxipride, preferentially blocked apomorphine-induced hyperactivity with weak effects on stereotypies. The potency of remoxipride was about 50 times higher than that of sulpiride. Remoxipride caused a weak, atypical form of catalepsy and showed a high separation between the ED50 for blockade of apomorphine-induced hyperactivity and the ED50 for induction of catalepsy (ratio 24). Remoxipride was shown to be a selective dopamine D2 receptor antagonist since it displaced [3H]spiperone (IC50 = 1570 nM) but not [3H]flupentixol (IC50 greater than 100 000 nM) in rat striatum, and did not inhibit striatal DA-sensitive Adenylate Cyclase in vitro (IC50 greater than 100 000 nM). Remoxipride is a potent antagonist of D2 receptors showing a dose-dependent blockade of [3H]spiperone and [3H]n-propylnorapomorphine in vivo binding with a potency equal to that of chlorpromazine. In contrast to haloperidol, remoxipride caused a preferential blockade of in vivo [3H]spierone binding in the mesolimbic DA rich areas and the substantia nigra with much less effect in the striatum. In addition, remoxipride produced a preferential increase of DA utilization following synthesis inhibition in the olfactory tubercle. Only minor changes in NA and 5-HT metabolism were observed while HVA and DOPAC levels were markedly elevated. Taken together, these results indicate that remoxipride is a potent, selective D2 receptor blocking agent with a preferential action in mesolimbic and extrastriatal dopamine-containing neurons.