N-methyl-D-aspartate receptors in the basolateral amygdala are required for both acquisition and expression of conditional fear in rats

Three experiments examined the effects of intra-amygdaloid infusions of an N-methyl-D-aspartate (NMDA) receptor antagonist, D,L-2-amino-5-phosphonovalerate (APV), on contextual fear conditioning in rats. In Experiment 1, APV infusion into the basolateral amygdala (BLA), before training, disrupted the acquisition of contextual fear. In Experiment 2, APV produced a disruption of both the acquisition and expression of contextual fear. This blockade of contextual fear was not state dependent, not due to a shift in footshock sensitivity, and not the result of increased motor activity in APV-treated rats. In Experiment 3, fear conditioning was not affected by a posttraining APV infusion into the BLA. These results indicate that NMDA receptors in the BLA are necessary for both the acquisition and expression of Pavlovian fear conditioning to contextual cues in rats.