Lower brainstem pathways regulating sympathetically mediated changes in cutaneous blood flow.

1. When the individual is alerted by painful or salient stimuli, there is a vigorous sympathetically mediated constriction of the cutaneous vascular bed. We investigated central pathways mediating this response using chronically implanted Doppler ultrasonic probes to measure cutaneous blood flow in the rabbit ear pinna and in the rat tail. 2. Blockade of neuronal function in the amygdala prevents cutaneous vasoconstriction elicited by salient stimuli, but does not prevent the response to painful stimuli. Blockade of neuronal function in raphe magnus/pallidus and the parapyramidal region in anesthetized rabbits prevents cutaneous vasoconstriction elicited by painful stimuli. A similar region of the medullary raphe regulates tail artery vasoconstriction in rats. Inhibition of neuronal function in this region reverses cutaneous vasoconstriction induced by cooling the animal. 3. Bulbospinal presympathetic neurons in the rostral medullary raphe region appear to regulate cutaneous blood flow responses occurring as part of the response to painful or dangerous environmental events and as part of the regulation of body temperature.