Evidence that serotonergic projections to the substantia nigra in the rat arise in the dorsal, but not the median, raphe nucleus.

Following microinjections of the fluorescent retrograde tracer Fast blue into the substantia nigra, large numbers of retrogradely labeled cells were observed in the dorsal raphe nucleus. Using immunocytochemical techniques it could be demonstrated that the majority of these cells contained serotonin-like-immunoreactivity. In contrast, careful examination of the region of the median raphe nucleus revealed no suggestion of a significant projection from the median raphe to the substantia nigra.