Fluorescent retrograde double labeling: axonal branching in the ascending raphe and nigral projections.

Red fluorescent Evans blue and blue fluorescent DAPI-primuline were injected into the anterior-medial and lateral-caudal forebrains, respectively, of the same rats. Separate clusters of cells labeled by retrograde transport were observed in the substantia nigra, while in the dorsal raphe many cells were double-labeled. Thus, single raphe cells send divergent axon collaterals to widespread forebrain areas.