The effect of butaclamol and of other neuroleptic agents on the apomorphine-elicited inhibition of synaptosomal tyrosine hydroxylase activity.

The effects of the two enantiomers of butaclamol and of several neuroleptics on the apomorphine-elicited inhibition of synaptosomal tyrosine hydroxylase activity was investigated. The (+) but not the (-) enantiomer of butaclamol reverses the apomorphine-elicited enzyme inhibition. (+) Butaclamol is more potent than the other tested neuroleptics. All the tested neuroleptics reverse the apomorphine-elicited enzyme inhibition but their relative potency differs. Using two criteria, namely the concentrations of neuroleptics required to reverse enzyme inhibition maximally or by 25%, the order of decreasing potency is as follows: (+) butaclamol, fluphenazine, haloperidol, pimozide, chlorpromazine. The results suggest that the reversal of apomorphine-elicited inhibition of synaptosomal tyrosine hydroxylase activity is a valid test model for screening antipsychotic drugs.