Opposite locomotor asymmetries elicited from the medial and lateral SN by modulation of SN DA receptors.

In combination with systemic d-amphetamine (1 mg/kg), apomorphine or alpha-flupenthixol were unilaterally injected into either the medial or lateral substantia nigra pars compacta (SNC) of adult male hooded rats. Direction and magnitude of circling were measured. Alpha-flupenthixol (5 and 15 micrograms) injected into the medial SNC caused rats to circle contraversive to the injected side while laterally placed injections produced ipsiversive circling. Apomorphine (5 and 15 micrograms) induced ipsiversive circling when injected into the medial SNC but had no effect in the lateral SNC. The results show that nigrostriatal mediated circling can be induced by modulation of dopamine (DA) receptors in the SNC. Furthermore, the findings support the notion that lateral SNC DA neurons are functionally antagonistic to medial SNC DA neurons with respect to circling. The results also suggest that there may be medial-lateral SNC differences in the type of DA receptors.