Inhibition of rostral medullary raphé neurons prevents cold-induced activity in sympathetic nerves to rat tail and rabbit ear arteries.

Sympathetically-mediated vasoconstriction of cutaneous vessels is critical for thermoregulation in the cold. We determined whether cold-induced sympathetic discharge depends on activity of neurons in the rostral medullary raphé. In urethane-anesthetized rats and rabbits, cooling the trunk skin by a water jacket reproducibly increased cutaneous sympathetic discharge recorded in the tail (rats) and the ear pinna (rabbits). When neurons in the rostral medullary raphé were inhibited by microinjection of glycine (30-100 nmol in 60-200 nl in rats), or muscimol (1 nmol in 100 nl in rabbits), cutaneous sympathetic activity was silenced and no longer responded to cooling (7+/-3 and 5+/-2% of pre-injection increase in rats and rabbits, respectively, P < 0.01). Our data demonstrate that activity of rostral medullary raphé neurons is important for the CNS mediation of cold-induced increases in sympathetic cutaneous vasomotor nerves.