AJP - Regulatory, Integrative and Comparative Physiology, Vol 248, Issue 2 263-R269, Copyright © 1985 by American Physiological Society
Effect of stimulation of nucleus raphe dorsalis on carotid blood flow. II. The cat
P. J. Goadsby, R. D. Piper, G. A. Lambert and J. W. Lance
The dorsal raphe nucleus (DRN) and surrounding midbrain of 74 cats were
stimulated both electrically and chemically, and carotid flows were
measured with electromagnetic flow probes. Stimulation of the DRN caused a
frequency-dependent decrease in common carotid vascular resistance, which
was abolished by bilateral section of the facial nerve intracranially.
Injection of DL-homocysteic 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 alpha-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 alpha-adrenoceptor antagonist phentolamine. No
response involved supracollicular mechanisms since they persisted after
decerebration.
