The ascending projections of the dopaminergic neurons of the substantia nigra, zona reticulata: a combined retrograde tracer-immunohistochemical study.

The efferent projections of the dopaminergic neurons in the zona reticulata of the substantia nigra were examined using a combined retrograde tracer-immunohistochemical method. These dopamine (DA) neurons were found to project exclusively to striatal targets in a topographically defined fashion. The zona reticulata DA neurons do not innervate mesolimbic or mesocortical dopaminergic terminal fields, nor do they project to the superior colliculus or the ventromedial thalamic nucleus. These data suggest that the dopaminergic neurons of the zona reticulata represent a ventrally placed subset of the nigrostriatal DA cells of the pars compacta.