Heat production and body weight changes following lateral hypothalamic lesions

Factors causing rats with lateral hypothalamic (LH) aphagia to lose weight at a faster rate than food deprived controls were investigated in two experiments. In Experiment 1, the heat production of LH-lesioned and control rats was measured by indirect calorimetry for four days following surgery. A higher rate of energy expenditure was shown to account for the greater weight loss of the LH-lesioned rats. In Experiment 2, the heat production of rats receiving LH lesions either at normal or reduced body weights was measured continuously for 24 hours following surgery. Reducing body weight prior to lesioning attenuated postlesion heat production. It was also found that, though the heat production of LH-lesioned rats was consistently higher than that of nonlesioned rats of similar body weight, the fundamental relationship between body weight and heat production was unchanged by the lesion. These findings of higher rates of energy expenditure when at the same weight as nonlesioned animals, accompanied by normal adjustments in expenditure in response to weight change, are consistent with the view that LH-lesioned rats, both behaviorally and metabolically, regulate body weight at a reduced level. Their elevated rate of heat production following lesioning can be seen as an adaptive metabolic adjustment which, coupled with LH aphagia, leads to the rapid decline in body weight to a lower maintenance level.