Choice of Diets of Differing Caloric Density by Normal and Hyperphagic Rats.

When bilateral lesions are made in the ventromedial nuclei of the hypothalamus, striking and characteristic changes are produced. These effects, first demonstrated in the rat, include an enormous increase in food intake (hyperphagia) and the development of obesity (Hetherington & Ranson, 1939; Brobeck, Tepperman & Long, 1943). The hyperphagia occurs immediately after the operation, the rat eating large quantities of food as soon as it has recovered from the anaesthetic. When maximum obesity is reached food intake falls, and the excessive weight is maintained with a normal food intake. Similar lesions produce the same sort of changes in cats, dogs and monkeys. It is now generally believed that the ventromedial nuclei of the hypothalamus are involved in the maintenance of normal body-weight by the control of food intake. In normal rats, food intake seems to be determined by calorie needs. Thus, Adolph (1947) has shown that, when rats were offered food diluted with kaolin or cellulose, they ate proportionately more food, so that their calorie intake remained constant. This ‘eating for calories’ was seen so long as the dilution was less than 30-50%; when the dilution was greater, the increase in food intake did not compensate for the dilution. Kennedy (1950) confirmed this observation for normal rats given kaolindiluted diets, but found that rats with hypothalamic lesions ate less of the diluted diets. This behaviour he put down to an increased discrimination of the hyperphagic and the obese rats against diets made unpalatable with kaolin. The purpose of the study reported here was to determine whether rats with lesions of the ventromedial nuclei, given a choice between two diets of differing caloric density, are able (I) to discriminate between the diets, and ( 2 ) to choose the proportion of the diets in relation to their calorie needs.