ACUTE LESIONS OF THE VENTROMEDIAL HYPOTHALAMUS REDUCE SYMPATHETIC ACTIVATION AND THERMOGENIC CHANGES INDUCED BY PGE(1)

The aim of this experiment was to evaluate the effects of an intracere broventricular (icy) injection of prostaglandin El (PGE(1)) on the sym pathetic activation and the thermogenic changes in rats with acute les ions of the ventromedial hypothalamus (VMH). Four groups of six Spragu e-Dawley male rats were anesthetized with ethyl-urethane. The firing r ate of the sympathetic nerves innervating the interscapular brown adip ose tissue (IBAT) and the colonic and IBAT temperatures were monitored both before and after one of the following treatments: 1) VMH lesion plus icy injection of PGE(1) (500 ng); 2) VMH lesion plus icy injectio n of saline; 3) sham lesion plus icy injection of PGE(1); and 4) sham lesion plus icy injection of saline. PGE(1) induced an increase in the firing rate of IBAT nerves and the colonic and IBAT temperatures. The se effects were reduced by VMH lesion. The findings indicate that acut e lesions of the VMH reduce the effects of PGE(1) and seem to suggest a possible role played by the VMH in the control of the sympathetic ac tivation and the thermogenic changes during PGE(1) hyperthermia.