Influence of naloxone upon apomorphine-induced rotational behavior in rats with electrolytic versus chemolytical lesions of the substantia nigra.

In rats with unilateral electrolytic lesions of the substantia nigra, apomorphine induced ipsilateral rotational behavior that was significantly potentiated by naloxone. Yet, in rats with unilateral chemolytic (6-hydroxydopamine) lesions of the substantia nigra, apomorphine induced dose-dependent contralateral turning that was not influenced by pretreatment with even high doses of naloxone. High performance liquid chromatographic analysis of corpora striata from these rats revealed electrolytically-lesioned animals to have a 60-70% reduction in dopamine content while chemolytically-lesioned animals were virtually completely depleted of dopamine. These results suggest that striatal dopamine may be required for naloxone potentiation of apomorphine-induced effects in the rat rotational behavior paradigm.