Dissociative analysis of ventromedial hypothalamic obesity syndrome

Electrolytic lesions of the ventromedial hypothalamus (VMH) produce an obesity syndrome characterized by hyperphagia, adiposity, and heightened parasympathetic tone. Experiments were conducted to evaluate the possibility that these symptoms arise from damage to distinct and separated loci within the hypothalamus. Rats received either VMH lesions, perifornical hypothalamic (PFH) knife cuts, ventromedial hypothalamic nucleus (VMN) lesions, or sham surgery (Sham). When maintained ad libitum, VMH and PFH rats were hyperphagic, overweight, and became obese. VMN rats were not hyperphagic, nor did they gain excessive weight, but they did develop an obesity reflected as a significantly elevated level of carcass fat. Under restricted feeding conditions, both VMH and VMN rats became obese; PFH rats did not. Also, only VMH lesions and PFH knife cuts increased basal gastric acid secretion. These data demonstrate dissociations between hyperphagia and obesity, as well as between stomach secretion and obesity, in the VMH syndrome. The implications of these findings for a dissociative model of the VMH obesity syndrome are discussed.