LESIONS OF THE VENTROMEDIAL HYPOTHALAMUS REDUCE POSTINGESTIONAL THERMOGENESIS

The aim of this experiment was to evaluate the effects of ventromedial hypothalamus lesions on the thermogenic changes that follow food inta ke. Four groups of six Sprague-Dawley male rats were used. Under anest hesia with pentobarbital, the animals in the first and second groups r eceived lesions at the ventromedial hypothalamus, and animals in the t hird and fourth groups received sham lesions. Body weight and food int ake were monitored daily until the experimental procedure began. Twent y days after lesion, oxygen consumption, firing rate of sympathetic ne rves to interscapular brown adipose tissue (IBAT), and IBAT temperatur e;were monitored for 45 min both before and after 5 g food intake in 2 4 h fasted rats from the first and third groups. The same variables we re measured in the animals of the second and fourth groups 50 days aft er receiving the lesions. Lesion placements were histologically verifi ed. The results showed that lesions produced hyperphagia and obesity. Firing rate of nerves to IBAT, IBAT temperature, and oxygen consumptio n increased after food intake in sham-lesioned rats. This increase was significantly reduced by the lesion at both the 20- and 50-day time p oints. These findings indicate that the ventromedial hypothalamus cont rols postingestional activation of sympathetic discharge to IBAT. The reduction of postingestional thermogenesis could be involved in: the d evelopment of obesity induced by lesion of the ventromedial hypothalam us. (C) 1997 Elsevier Science Inc.