Dopaminergic--GABA-ergic interaction in the nigrostriatal system.

Unilateral electrolytic lesion at the level of the substantia nigra resulted in ipsilateral rotation after the administration of different dopaminergic agonists such as d-amphetamine (5 mg/kg), apomorphine (3 mg/kg) and piribedil (50 mg/kg) in rats. The influence of the alteration of the GABA level was investigated on circling behaviour induced either by the presynaptic DA-ergic agonist d-amphetamine or by the postsynaptic stimulant apomorphine. Aminooxyacetic acid (12.5 mg/kg) as a GABA-transaminase inhibitor, decreased the rotation elicited by d-amphetamine or apomorphine. Picrotoxin pretreatment (1.5 mg/kg) acted reversely on the circling behaviour elicited by the presynaptic DA-ergic agonist. Picrotoxin pretreatment showed a trend to decrease the rotation induced by the postsynaptic DA-ergic agonists apomorphine and piribedil. It is concluded that the action of GABA in this behavioural test might appear not only presynaptically but also postsynaptically in the nigrostriatal system and even in different forms.