Glucose preference and caloric regulation in weanling rats with ventromedial and dorsomedial hypothalamic lesions

Abstract

Weanling male rats received electrolytic lesions in the ventromedial (VMN) and dorsomedial (MDN) hypothalamic nuclei, respectively. A third group served as sham-operated controls (CON). After the two hypothalamic syndromes had been well established, the animals were subjected to (1) a glucose preference test assessing the choice between a 10% w/v and a 35% w/v d-glucose solution, and (2) a test examining the anorexigenic effect of intraperitoneally injected glucose. Weanling rats with VMN lesions, like their mature counterparts, consistently preferred the stronger over the weaker glucose solution throughout the experiment (16 days). Weanling DMN rats, on the other hand, showed a bimodal response, initially like that of the CON rat, toward the end of the experiment, like that of the VMN rats. The weanling CON animals behaved differently from their mature counterparts, inasmuch as their preference for the dilute solution became evident only toward the latter part of the test. An analysis of the calorie intake shows that calories from glucose are similar in all three groups of rats, that the pattern and magnitude of caloric intake in DMN and CON rats are almost identical, and that the total caloric intake (from chow plus glucose) is reduced in the DMN rats because the calorie component from chow is profoundly reduced. In response to intraperitoneally injected glucose, VMN rats show a longer depression of food intake than has been reported for mature VMN rats. The CON and DMN rats recovered quicker and reached preinjection levels of food intake sooner than the VMN rats. The data indicate that in the weanling VMN rat, as in its mature counterpart, the VMN are involved in long-term feeding behavior and do respond to the metabolic signal arising from administered glucose. Nevertheless, the principle factor in their preference seems to be taste rather than solely a metabolic signal. The data show that the DMN are less involved in this sensing and integrating mechanism. In essence, the DMN rat functions quite normally, but its control system is set at a subnormal level.