Dorsal raphe cells with collateral projections to the caudate-putamen and substantia nigra: a fluorescent retrograde double labeling study in the rat.

The relationship between the dorsal raphe neurons projecting to the caudate-putamen and those projecting to the substantia nigra was investigated using a fluorescent retrograde double labeling technique in the rat. The majority of the dorsal raphe neurons projecting to the substantia nigra were found to project also to the caudate-putamen. In addition, a large population of dorsal raphe neurons innervating the caudate-putamen but not the substantia nigra was seen. The cells projecting to the substantia nigra were situated primarily in the dorsal part of the dorsal raphe, whereas those projecting to the caudate-putamen were located throughout the dorsal raphe.