Procaine into the VMH inhibits IBAT activation caused by frontal cortex stimulation in urethane-anesthetized rats

This experiment tested the effect of procaine injection into the ventromedial hypothalamus on the sympathetic and thermogenic activation induced by frontal cortex stimulation. Oxygen consumption, firing rate of the sympathetic nerves to interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures were monitored in fasted male Sprague-Dawley rats before and during 25 min after an electrical stimulation of the frontal cortex. The same variables were monitored in rats with administration of procaine into the ventromedial hypothalamus. The results show that cortical stimulation increases oxygen consumption, sympathetic firing rate, IBAT and colonic temperatures. The increase in sympathetic firing rate was reduced by procaine injection, and the increase in IBAT and colonic temperatures as well as oxygen consumption was fully inhibited by procaine. These findings suggest that the ventromedial nucleus plays an important role in the sympathetic and thermogenic changes induced by cortical stimulation.