Effects of muscimol applied to the basolateral amygdala on acquisition and expression of contextual fear conditioning in rats.

The amygdala is known to be important for normal aversive Pavlovian learning in the rat. The relative contribution of the amygdala to the learning vs. performance of conditional fear with the GABAa agonist muscimol was assessed. Rats were prepared with cannulas aimed at the basolateral amygdala and trained in a contextual fear conditioning paradigm in which each subject received a series of footshocks in a distinctive observation chamber. Conditional responses evoked after exposure to the observation chamber were assessed 24 hr later. Rats that were pretreated with muscimol before performance showed a significantly attenuated fear response, and injections made before acquisition resulted in a much smaller decrement in conditional fear measured 24 hr after training. These results indicate that acquisition-related processes that may be occurring within the amygdala are more difficult to disrupt than those associated with performance.