Central pathways mediating skin cooling‐evoked sympathetic activation of brown adipose tissue thermogenesis

Abstract

In the regulation of body temperature in homeothermic animals, thermal afferents from the skin provide an important signal allowing rapid autonomic responses in peripheral thermoregulatory effectors to changes in ambient temperature. The preoptic area (POA) receives thermal information from the skin and sends efferent signals that alter peripheral effector activity to maintain body temperature. However, the central pathways mediating such autonomic responses to skin thermal information remain to be determined. In this study, we examined electrophysiologically the involvement of several autonomic brain regions in sympathetic thermogenic responses in brown adipose tissue (BAT) to skin cooling in urethane-chloralose-anesthetized rats. Cooling the skin (32–35°C) with a water jacket for 1–2 min, which did not affect rectal (core) or brain temperature, evoked increases in BAT sympathetic nerve activity (SNA). The skin cooling-evoked activation of BAT SNA was blocked by bilateral microinjections of muscimol, a GABAA receptor agonist, into the dorsomedial hypothalamic nucleus (DMH), but not by those into the ventrolateral part of the caudal periaqueductal gray. Furthermore, injection of muscimol or 8-OH-DPAT, a 5-HT1A receptor agonist, into the rostral raphe pallidus nucleus (rRPa) also blocked the skin cooling-evoked BAT SNA. These results suggest that the DMH and rRPa are involved in BAT sympathetic thermogenic responses to skin cooling, which are mediated by efferent neuronal pathways probably from the POA, and that these pathways can be modulated by serotonergic inputs to the medullary raphe. Supported by NIH grant NS40987.