Striatonigral projection neurons contain D₁ dopamine receptor-activated c-fos

Dopamine receptor agonists which stimulate the D₁ receptor have been shown to activate c-fos in the striatum ipsilateral to a 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal pathway. In the present study, striatal neurons ipsilateral to a 6-OHDA lesion of the medial forebrain bundle were retrogradely labelled by injection of the fluorescent tracer Fluoro-Gold into the substantia nigra pars reticulata. Five days later, c-fos was induced in the 6-OHDA-denervated striatum by injection of the selective D₁ agonist SKF 38393. C-fos-positive nuclei were frequently found in medium-sized striatal cell bodies labelled with Fluoro-Gold. These results indicate that D₁ agonists activate c-fos in medium-sized neurons that project to the substantia nigra pars reticulata.