Behavioural stimulation induced by muscimol and other GABA agonists injected into the substantia nigra.

The unilateral injection of putative GABA agonists, muscimol, baclofen, imidazole acetic acid and GABA into the caudal area of substantia nigra (SN, zona reticulata) induced immediately a contralateral turning, whereas the antogonists picrotoxin and bicuculline methiodide induced ipsilateral turning. In the rostral area picrotoxin induced contralateral turning. Muscimol (10 ng bilaterally injected into SN) induced behavioural stimulation and antagonism of catelepsy in rats pretreated with high subcutaneous doses of perphenazine, haloperidol or reserpine and alpha-methyltyrosine. The muscimol behavioural stimulation seems dependent on a non-catecholaminergic neuronal pathway, probably present in the SN with GABA as the mediating neurotransmitter.