Failure to discriminate conspecifics in amygdaloid-lesioned mice

An experiment was conducted to investigate the role of the amygdala in the discriminative behavior of mice using the conditioned individual preference (CIP) method, a modified conditioned place preference (CPP) paradigm. CIP training of the subject mice involved 6 consecutive days of alternate IP injections of morphine (3 mg/kg) or saline followed by associations with a stimulus mouse in one compartment of the preference box. After the CIP training, the subject mice were given a choice between the morphine-associated and the saline-associated stimulus mice. Normal and sham-operated mice showed preference for the morphine-associated stimulus mouse. On the other hand, mice receiving bilateral amygdala lesions before or after CIP training did not show any preference for either stimulus mouse. These results support the view that the amygdala influences expression and acquisition of conditioned discriminant behaviors of mice by possibly interacting centrally, through its opiate receptors, with the peripherally injected morphine.