Hyperinsulinemia: effects on body weight, obesity and motivated behaviors

Five experiments were performed to evaluate the physiological and behavioral similarities between lesions of the ventromedial hypothalamus (VMH) and injection-produced hyperinsulinemia. It was found that the rate of weight gain and fat deposition in both adult and weanling rats was essentially the same for both VMH and hyperinsulinemic rats. Measures of activity and taste preference measures yielded no differences between hyperinsulinemic rats and intact rats. Electric shock thresholds revealed a decrease in reactivity for hyperinsulinemic rats compared to intact rats. A hypothesis was suggested in which a combination of hypophysectomy, gonadectomy, and hyperinsulinemia might produce most of the physiological effects seen with VMH lesions. It was also suggested that since these physiological alterations radically modify the organism's internal environment, the behavioral effects of VMH lesions may be the results of the attempts of a brain-damaged animal to maintain new physiological conditions.