Turning behaviour induced by injection of muscimol or picrotoxin into the substantia nigra demonstrates dual GABA components.

Injection of the GABA agonist muscimol into rat caudal substantia nigra caused contralateral turning, whereas injection into the rostral substantia nigra caused ipsilateral turning. The GABA antagonist picrotoxin had the opposite effect. These findings support the hypothesis that GABA has dual actions in the substantia nigra. Ipsilateral turning induced by injection of muscimol into rostral nigra was abolished by haloperidol pretreatment, indicating the involvement of dopaminergic mechanisms. Haloperidol pre-treatment did not prevent turning induced by muscimol injected into the caudal nigra, supporting the existence of a non-dopaminergic nigral output system.