Ventromedial hypothalamic lesions attenuate responses of sympathetic nerves to carotid arterial infusions of glucose and insulin.

The effects of intracarotid injections of glucose and insulin on the sympathetic firing of nerves to brown adipose tissue were measured in rats. The injection of glucose into the carotid artery of anesthetized rats increased the firing of nerve filaments from the sympathetic nerves which innervate brown adipose tissue. Injection of kainic acid into the ventromedial nucleus 6-9 days prior to the measurement of nerve recordings reduced the stimulatory effect of glucose by 60 percent. In contrast to the stimulation by glucose, injection of insulin into the carotid artery reduced the sympathetic firing rate of nerves to brown adipose tissue. Kainic acid destruction of neurons in the ventromedial hypothalamus also attenuated this effect by 40 percent. These experiments are consistent with the hypothesis that changes in the arterial concentration of glucose and insulin may modulate the firing rate of sympathetic nerves to brown adipose tissue, and that this effect is mediated, in part, by the ventromedial hypothalamus.