Interaction of intracerebroventricular insulin and glucose in the regulation of the activity of sympathetic efferent nerves to brown adipose tissue in lean and obese Zucker rats.

The effects of injection of insulin and glucose into the third cerebral ventricle on the firing rate of the sympathetic efferent nerves to intercapsular brown adipose tissue was investigated in anaesthetized lean and obese Zucker rats. Injection of insulin resulted in a dose-dependent (70-480 pmol) inhibition of nerve firing rate, whereas in combination with glucose (140 pmol of insulin and 139 nmol of glucose), insulin strongly potentiated the increase in firing rate seen with glucose alone. Although basal levels of nerve firing rates were lower in the obese rat, responses to insulin, glucose, and insulin plus glucose were qualitatively similar to those seen in the lean rat. These results are consistent with the hypothesis that insulin acts in the central nervous system as a physiological signal in the control of thermogenesis after feeding, and that this effector system is intact in the obese rat.