Ascending dopaminergic projections from the dorsal raphe nucleus in the rat

The projections of putative dopamine containing cells within the dorsal raphe nucleus (DR) were studied using a combination of tyrosine hydroxylase (TH) immunocytochemistry and fluorescent retrograde tracing. Substantial numbers of TH-immunoreactive cells in the DR were found to project to the nucleus accumbens. Progressively smaller numbers of cells were found to project to the lateral septum and medial prefrontal cortex. Very few TH-immunoreactive cells projected to the dorsal striatum, and none to the substantia nigra. TH-immunoreactive cells did not display serotonin-like immunoreactivity. These findings indicate that the projection pattern of TH-immunoreactive cells within the dorsal raphe more closely resembles that of dopaminergic cells within the ventral tegmental area (VTA) than that of serotonergic cells within the DR.