Potentiation of apomorphine-induced stereotypies by naloxone and L-prolyl-L-leucyl-glycinamide.

We compared the influences of pretreatment with the narcotic antagonist drug naloxone and the neuropeptide L-prolyl-L-leucyl-glycinamide (PLG) upon apomorphine-induced stereotypic climbing activity in mice and apomorphine-induced contralateral rotational behavior in rats with unilateral 6-hydroxydopamine lesions of the substantia nigra. Naloxone produced dose-related potentiation in the mouse climbing model, while PLG was without effect. On the other hand, PLG produced dose-related potentiation in the rat rotational paradigm, while naloxone was without appreciable influence. These findings show an asymmetrical potentiation of apomorphine by naloxone and PLG in these two standard experimental models of striatal dopaminergic activity.