Dopamine mediates ipsi- and contraversive circling elicited from the substantia nigra

It was found that ipsiversive and contraversive circling could be induced by imposed stimulation of the lateral and median portions of the substantia nigra pars compacta (SNC), respectively. Stimulation of more ventral sites in the substantia nigra (SN) did not elicit circling. Pimozide, a dopamine (DA) antagonist, dose dependently blocked both ipsiversive and contraversive circling induced by imposed stimulation of the SN, but did not alter circling elicited from the non-dopaminergic cerebral peduncle. However, amphetamine, a catecholamine agonist, did not facilitate stimulation-induced circling elicited from the SN possibly because it releases DA on both sides of the brain and thus fails to exaggerate the imbalance of activity produced by stimulation. Taken together these results suggest that DA is involved in SN mechanisms mediating both ipsiversive and contraversive stimulation induced circling and provide further evidence that the lateral SN may be functionally antagonistic to the medial SN.