Instrumental reactions and food and water intake in medial amygdala rats.

Rats were trained preoperatively to perform instrumental reactions for food and water reward on a continuous reinforcement schedule. Two levers on two opposite sides of the Skinner box were available. Each press of the first lever delivered one drop of water and each press of the second lever - one pellet of solid food. After the electrolytic lesions of the medial part of the amygdaloid complex, rats were hypophagic and hypodipsic. Most of the animals showed, however, only small decreases of total unconditioned daily water and food intake. On the other hand, the instrumental performance was markedly impaired, in particular for water reinforcement. Histological verification showed that lesions were restricted to the amygdaloid complex and involved mainly the ventral part of medial nucleus.