The effect of intrahypothalamic injections of glucose on sympathetic efferent firing rate.

Electrical stimulation of the ventromedial hypothalamus of anesthetized rats, produced an increase in temperature of brown adipose tissue. The magnitude of increase in temperature was linearly related to the frequency (Hz) of electrical stimulation of the hypothalamus. Microinjection of glucose into the ventromedial hypothalamus produced a dose-dependent increase in firing rate of the sympathetic nerves to brown adipose tissue, whereas comparable volumes of physiological saline had no effect. Destruction of neurons in the ventromedial hypothalamus with injections of kainic acid completely blocked the stimulatory effect of glucose on the firing rate of nerves to the brown adipose tissue. These studies support the hypothesis that glucose sensitive neurons in the ventromedial hypothalamus can directly modulate sympathetic nerves supplying brown adipose tissue.