Activation of the habenula complex evokes autonomic physiological responses similar to those associated with emotional stress.

Neurons in the lateral habenula (LHb) discharge when an animal anticipates an aversive outcome or when an expected reward is not forthcoming, contributing to the behavioral response to aversive situations. So far, there is little information as to whether the LHb also contributes to autonomic physiological responses, including increases in body temperature (emotional hyperthermia) that are integrated with defensive behaviors. Vasoconstriction in cutaneous vascular bed and heat production in brown adipose tissue (BAT) both contribute to emotional hyperthermia. Our present study determines whether stimulation of the LHb elicits constriction of the tail artery and BAT thermogenesis in anesthetized Sprague-Dawley rats. Disinhibition of neurons in LHb with focal microinjections of bicuculline (1 nmol in 100 nl, bilaterally) acutely increased BAT temperature (+0.6 ± 0.1°C, n = 9 rats, P < 0.01) and reduced tail artery blood flow (by 88 ± 4%, n = 9 rats, P < 0.01). Falls in mesenteric blood flow, simultaneously recorded, were much less intense. The pattern of BAT thermogenesis and cutaneous vasoconstriction elicited by stimulating the habenula is similar to the pattern observed during stress-induced emotional hyperthermia, suggesting that the habenula may be important in this response.