Effects of hypothalamic knife cuts on the ingestive responses to glucose and insulin

Parasagittal knife cuts through the perifornical hypothalamus either medial or lateral to the fornix produced hyperphagia and obesity and altered the rat's ingestive responses to dilute glucose solutions. The lateral knife cut rats drank less dilute glucose solution under both nondeprived and food deprived conditions and displayed less of a feeding suppressive response to glucose ingestion compared to controls. The lateral cut rats were also deficient in their feeding response to insulin-induced hypoglycemia, although their altered sensitivity to glucose and insulin did not appear to be causally related. The medial knife cuts decreased the responsivity to glucose, but less so than the lateral cuts, and did not alter the ingestive response to insulin. Both the medial and lateral knife cuts did not appear to change the rat's responsivity to concentrated blucose solutions. The neuroanatomical and functional nature of the disorder responsible for these effects and its relationship to the hyper-phagia-obesity syndrome are discussed.