Effect of stimulation of nucleus raphe dorsalis on carotid blood flow.

Injection of t&ho-mocysteic acid into the DRN reproduced the effect of electrical stimulation, indicating that the responses arose from excitation of cell bodies within the DRN, not from fibers of passage. The responses were mediated entirely within the brain stem since they remained intact after high spinal cord section. The vasodilator response was blocked by the intravenous administration of the nicotinic ganglion blocker hexamethonium but not by the a-adrenoceptor blocker phentolamine. The responses were unaffected by intravenous administration of methysergide but were markedly reduced after depletion of central serotonin by pretreatment with the serotonin depletor, p-chlorophenylalanine. A poststimulus constrictor response was mediated by release of catecholamines from the adrenal medulla and was blocked by the a-adrenoceptor antagonist phentolamine. No response involved supracollicular mechanisms since they persisted after decerebration. cell bodies; serotonin; carotid vascular resistance THE RAPHE NUCLEI of cat have been extensively mapped (17) and are largely similar to those of the monke