Blockade of apomorphine's discriminative stimulus properties: relation to neuroleptic activity in neuropharmacological and biochemical assays.

Using a food-reinforced two-lever operant conditioning procedure, rats were trained to discriminate 0.16 mg/kg apomorphine from saline. Eight neuroleptics of the phenothiazine, butyrophenone or diphenylbutylamine type were investigated for thsir ability to antagonize the discriminative stimulus properties of apomorphine. The same drugs were also assayed for in vivo antagonism of apomorphine-induced stereotyped behavior as well as for in vitro inhibition of stereospecific 3-H-haloperidol binding in rat striatal tissue preparations. The data are consistent with the hypothesis that apomorphine exerts its discriminative stimulus properties by a mechanism similar to that underlying its stereotypogenic action. The loci involved in these two phenomena are likely to be distinct.