The Role of the Central Nucleus of the Amygdala in Feeding and Monitoring Internal State Cues in the Rat

Abstract

These experiments examined the role of the central nucleus of the amygdala (CN) in rats' ability to use internal and external cues as signals for shock. Half of the animals received Pavlovian discrimination training prior to ibotenate lesions of the CN while the other half were trained after surgery. Rats were placed on an alternating 24hr, Ohr food deprivation schedule and were shocked under one of the two levels of deprivation in combination with different auditory stimuli. During extinction, rats were tested with deprivation cues alone, then with auditory cues alone. Percentage of freezing under each condition served as the index of discrimination. Rats trained prior to surgery were able to learn to discriminate between shocked and non-shocked conditions. In postoperative extinction, they did not show discrimination between levels of deprivation, but did discriminate between auditory stimuli. Rats trained after surgery were unable to learn either discrimination. In a separate experiment, the amount of food and water consumed did not change, but CN rats were more active than controls. These results suggest that the CN plays an important role in acquisition, but not retention of fear conditioning. Furthermore, it appears that there are different mechanisms that underlie the utilization of internal and external cues. [From Abstract]