We have previously shown that electrical stimulation of the dorsal raphe nucleus (DRN) can increase or decrease cerebral blood flow (CBF). We now sought to determine whether the CBF responses are mediated by DRN neurons or fibers of passage. In anesthetized rat, the DRN was stimulated chemically (L-glutamate, kainate) and CBF in parietal cortex was measured by laser-Doppler flowmetry. Microinjection of kainate (5 nmol), but not L-glutamate, into DRN increased CBF (28 +/- 22%; P < 0.05). Decreased CBF to DRN stimulation was not observed. We conclude that stimulation of DRN neurons increases CBF.