Pretraining: Effects on operant responding for food, frustration, and reactiveness to food-related cues in rats with VMH lesions

Abstract

Preoperative exposure to an ascending series of FR schedules in operant chambers (pretraining) attenuated the deficit in instrumental responding for food by rats with ventromedial hypothalamic (VMH) lesions. Subsequently, the same rats were tested in the Amsel double runway. VMH lesions depressed running speed, especially in the second alley, but did not enhance the magnitude of the frustration effect (FE). Pretraining increased running speeds in rats with VMH lesions, but did not affect the magnitude of the FE. The extremely slow performance in the second alley by the VMH group without pretraining seemed to result from an exaggerated attraction to the cues associated with feeding in the first goal box. Prefeeding animals in the start box produced a much larger reduction in running speed in the nonpretrained VMH group than in the pretrained VMH group or in controls. To test the possibility that deficits in operant performance might arise because the animals with VMH lesions spend more time investigating the food cup we examined performance of animals that were trained postoperatively on an ascending FR series in a modified operant chamber with the lever at one end and the food cup at the other. Under these conditions VMH lesions increased the time required to earn 50 reinforcements at all FR's tested, but the distribution of time spent between the end of the chamber with the response lever and the end with the food cup was not altered.