Feeding Studies in Weanling Rats with Dorsomedial Hypothalamic Lesions: Effect of High Fat and High Carbohydrate Diet and Nutrient Completeness on Food Choice and Intake

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Abstract
Weanling and mature rats with dorsomedial hypothalamic lesions (DMNL) show profound hypophagia. The present study was conducted to assess whether the hypophagia in the DMNL rat might be due to a disruption of systems subserving correct food (nutrient) choice, taste, or the sensing of dietary consistency. To this end, DMNL rats and shamoperated controls were exposed to three dietary regimens. During the first dietary regimen (14 days) the rats were fed a closed formula, cereal based stock diet. As previously reported, the DMNL rats were grossly hypophagic in comparison with the controls. During the second dietary regimen (18 days) the rats were fed a purified high-fat diet in addition to the stock diet. Both DMNL rats ate less of both of the two food mixtures when compared with the controls. During the third dietary period (19 days) commercial marshmallows were available in addition to stock diet. In contrast to the high fat diet, both DMNL rats and controls preferred the bland but more nutritious stock diet over the sweet marshmallows. Again, the DMNL rats ate less stock diet and marshmallows than the controls. The data indicate that hypophagia-producing DMN lesions, despite their grossly disruptive effect on spontaneous food intake, do not impair the animal's ability to choose between a nutritionally incomplete but sweet food (marshmallows) and a nutritionally complete but bland diet (stock diet). The data further show that when two nutritionally complete diets are available the DMNL rats, as do the controls, prefer the more palatable (high-fat diet) over the bland (stock diet) food mixture. The data also confirm previous findings that the DMNL-induced hypophagia does not disrupt energy metering. In conjunction with previous findings of normal body composition, growth hormone and insulin levels and normal gluconeogenesis in DMNL rats, the data are consistent with the hypothesis that DMN lesions “reset” food intake and/or body weight to a lower level at which the animal can subsist on a smaller energy intake.