Reflex changes in thermogenesis in the interscapular brown adipose tissue in response to thermal stimulation of the skin via sympathetic efferent nerves in anesthetized rats.

Reflex responses of both temperature in the interscapular brown adipose tissue (IBAT) and activity of the sympathetic efferent nerves innervating the IBAT to cutaneous thermal stimulation were examined in anesthetized rats. Thermal stimulation of the ear at 4 degrees C for 20 s produced a transient decrease in the temperature of the IBAT during this period, followed by a prolonged increase (lasting 7 min). This response was completely abolished in animals whose IBAT sympathetic nerves were bilaterally sectioned. Direct recording of IBAT sympathetic efferent activity revealed that thermal stimulation of the ear at 4 degrees C for 20 s increased activity for 80 s after the onset of stimulation. The threshold temperature of the cold stimulation for eliciting increased nerve activity was around 22 degrees C. However, warm stimulation up to 49 degrees C had no significant effect on activity. In addition to stimulation of the ear, cold stimulation of the face and neck at 4 degrees C also increased nerve activity, while warm stimulation at 49 degrees C of any skin area had no influence. The present results demonstrate that excitation of cutaneous cold receptors, but not warm or heat receptors, reflexly increases thermogenesis in the IBAT via excitation of sympathetic nerve activity, and that cold receptor afferents to cranial and cervical segments effectively increase nerve activity in the IBAT.