Food intake of weanling rats with lesions in the ventromedial and dorsomedial hypothalamic nuclei in response to intragastric loading and caloric density manipulation.

Male rats received bilateral electrolytic lesions shortly after weaning in the ventromedial (VMN) and dorsomedial (DMN) hypothalamic nuclei, respectively. A third group of rats served as sham-operated controls. The animals were subjected to intragastric preloading with 33% d-glucose and egg-white solutions and a 33% corn-oil suspension, and ad libitum feeding was assessed hourly for the first 7 hr after preloading. The pattern of food-intake depression was similar in all groups but the quantitative greatest depression was found in the DMN rats. The response of these three groups of animals to a diet diluted with 20% alpha cell, a nonnutritive bulker, showed an initial failure to meter calories by both VMN and DMN rats which, however, was compensated for during the remainder of the 24-hr test period. In response to a 50% glucose-chow mixture, both VMN and DMN rats, as well as the controls, showed the same pattern and behaved like mature dynamic hyperphagic rats inasmuch as they did not eat more of this mix than of the standard diet. After a 48-hr fast, both VMN and DMN rats showed refeeding hypophagia rather than hyperphagia. The data suggest that Panksepp's contention that the VMN in the mature rat is involved in long-term satiety regulation may be extended to the weanling rat with VMN destruction. Thus, this controlling role appears established early in ontogeny.