Date of Award
Doctor of Philosophy (PhD)
Previous research has shown that rats with experimental lesions in the ventromedial area of the hypothalamus become obese due to hyperphagia. This striking effect on ad libitum food intake is sometimes accompanied by an increase and sometimes by a decrease in other measures of propensity to eat such as food-rewarded lever pressing. The current experiments attempt to discover the conditions under which these opposite effects on "food-motivated" behavior occur. Rats with ventromedial lesions made with steel electrodes showed a decrease relative to controls in lever pressing on a fixed ratio schedule. This effect was also seen in rats which had extensive pretraining on the fixed ratio task. Nonpretrained rats with lesions made with platinum electrodes showed a smaller, more variable deficit. However, rats with both platinum lesions and extended pretraining pressed reliably more than controls on schedules up to fixed ratio 256. The type of metal used in the lesion-producing electrode and the degree of pretraining are critical variables influencing the fixed ratio performance of rats with ventromedial hypothalamiC lesions. The importance of these variables will necessitate a reinterpretation of the role of the hypothalamus in operant and consumatory behavior. In further experiments, procaine anesthetization was found to also have disparate effects on eating and lever pressing. Eating was elicited within two minutes. Lever pressing on continuous reinforcement was less readily elicited and lever pressing on fixed ratio 64 appeared to be disrupted by a nonspecific increase in activity.
Larkin, Ronald Paul, "Effects of Ventromedial Hypothalamic Lesions on Food-Reinforced Fixed Ratio Responding" (1973). Student Theses and Dissertations. 543.