The immediate development of behavioral and biochemical changes following ventromedial hypothalamic lesions in rats

Abstract

The purpose of the present investigation was to determine the relationship between food intake, serum glucose, lipolysis attributable to epinephrine, and carcass composition in rats with ventromedial hypothalamic (VMH) lesions. These measures were made very shortly after surgery in order to gain some knowledge of the temporal development of both behavioral and biochemical changes immediately following VMH lesions. The study included repeated measures of food and water intake in VMH-damaged and sham Ss at 2, 4, 6, 8, and 24 hours postoperative, as well as at daily intervals for 12 days following surgery. Physiological measures were made at 2 hours, 8 hours, 24 hours, 3 days, 6 days, and 12 days postoperative. The findings indicated that hyperphagia following VMH lesions was two-staged. The first stage (acute dynamic stage) began immediately following surgery and lasted 4 to 6 hours. The second stage (chronic dynamic stage) began at approximately 3 days postoperative and lasted until termination of the study. The physiological measures also changed soon after surgery. Serum glucose levels and lipolytic rate were both decreased in the VMH-damaged Ss at 3 days postoperative. Changes in carcass content occurred at approximately 3 to 6 days following surgery. This change was found to be solely a function of increased fat deposition. Also, there was no substantial increase in the corrected body weight (total wt. minus gut contents) of the VMH-damaged Ss until 3 to 6 days postoperative. The results of the study suggested the following conclusions: (1) the dynamic stage of hyperphagia consists of two phases, an acute stage lasting 4 to 6 hours postoperative and a chronic stage beginning approximately 3 days after surgery; (2) the immediate hyperphagia may be attributable to neural shock produced by VMH damage, however, the possibility of hypoglycemia or other physiological changes immediately following surgery could not be eliminated; (3) the chronic dynamic stage may result from changes in metabolism which are themselves direct consequences of VMH damage; (4) no change in fat deposition occurs until after there is a decrease in lipolysis as a result of the VMH lesions; and (5) the increase in food intake is not reflected in corrected body weight until 6 days postoperative.