Raphe magnus/pallidus neurons regulate tail but not mesenteric arterial blood flow in rats

In urethane-anesthetized rats with body temperature maintained at 39-40 deg reesC, electrical stimulation of raphe mapus/pallidus/parapyramidal region within 0.5 mm. of the ventral medullary surface reduced arterial blood flow to the tail cutaneous bed (measured with a chronically implanted Doppler u ltrasonic flowmeter) from 28 +/-5 to 6 +/-1 cm/s (P < 0.01), without changi ng mesenteric arterial blood flow, and with only small, variable changes in arterial pressure. Injection of bicuculline (50 pmol in 50 nl) at the same site reduced tail flow from 19 +/-2 to 3 +/-1 cm/s (P < 0.01), again witho ut significantly changing mesenteric flow, but with a moderate increase in arterial pressure. When the rat was cooled to reduce basal tail blood flow, injection of muscimol (1 nmol in 100 nl) or GABA (100 nmol in 100 nl) into the raphe site restored tail blood flow to 93 +/-4% of the pre-cooling lev el. These recordings are the first reported direct measurements of rat tail blo od flow changes elicited by alteration of neuronal function in the brainste m. The rostral medullary raphe controls the tail cutaneous vascular bed in a relatively selective manner. Our findings add to evidence that raphe magn us/pallidus/parapyramidal neurons are involved in regulating cutaneous bloo d flow in response to changes in body temperature in the rat. (C) 2001 IBRO . Published by Elsevier Science Ltd. All rights reserved.