Factors that contribute to the reduced weight gain following chronic ventromedial hypothalamic stimulation.

This report follows up our earlier finding that chronic ventromedial hypothalamic stimulation caused an inhibition of weight gain. In this study we examined the contribution of stimulation-induced activity and brown adipose tissue thermogenesis to the reduced weight gain following three sessions of low-level stimulation delivered every other day to the ventromedial hypothalamus and adjacent areas. During stimulation trials, activity level was ranked on a dichotomous scale. Weight gain and food intake were subsequently monitored for an additional 4 weeks, after which the effects of a 60-s stimulation trial on the temperature of core and interscapular brown adipose tissue were evaluated. The highest activity was associated with the ventromedial hypothalamic sites and this factor contributed significantly to the difference in weight gain and food intake resulting from stimulation of the ventromedial hypothalamus and other areas. These differences largely disappeared during the follow-up period. With little exception, none of the sites elicited temperature changes in brown adipose tissue. As demonstrated in acute work, the contribution of stimulation-induced activity must be dissociated from the metabolic changes that occur in response to ventromedial hypothalamic stimulation.