Reevaluation of the striatal role in the expression of turning behavior in the rat model of Parkinson's disease.

A traditional view holds the belief that the behavioral effects of l-dihydroxyphenilalanine (l-DOPA) in Parkinsonian patients are achieved through the action of the newly produced dopamine (DA) on striatal DA receptors. In contrast to this view, recent studies in the rat model of Parkinson's disease point to the substantia nigra pars reticulata as an important target for the behavioral effects of l-DOPA. In the present study, we tested the contribution of the substantia nigra vs. that of the striatum, in the expression of contralateral turning induced by l-DOPA in rats with unilateral dopaminergic depletion. Rats turned contralaterally to the lesion in response to either intrastriatal or systemic l-DOPA administration. Injections of lidocaine into the denervated striatum substantially decreased, and occasionally completely abolished, the contralateral turning after systemic l-DOPA. These findings indicate that activation of the DA depleted striatum is both sufficient and essential for the expression of behavioral response after systemic administration of l-DOPA. The contribution of the substantia nigra to this behavioral response seems to depend to a great extent on an active striatal outflow.