Pressor response to electrical and chemical stimulation of nucleus raphe dorsalis in the cat

The dorsal raphe nucleus was stimulated electrically and chemically in 57 cats with blood pressure being measured by an arterial catheter. Blood pressure rose by a mean of 119.5 +/- 8.9% on stimulation of the dorsal raphe nucleus at a frequency of 200 sec-1. This pressor response was frequency-dependent over the range 0.2 to 200 sec-1 and the site of origin was localized to the dorsal raphe nucleus. The pressor response could also be obtained by the injection of D,L-homocysteic acid into the nucleus, and is therefore likely to be due to activation of cell bodies rather than axons of passage. The response was blocked by high spinal cord section but was not affected by bilateral clamping of the adrenal glands or supracollicular decerebration. The pressor response was significantly reduced by pretreatment of the cats with parachlorophenylalanine (PCPA) and abolished by the alpha receptor blocker phentolamine, suggesting that both serotonergic and noradrenergic synapses are involved.