Complex Effects of NMDA Receptor Antagonist APV in the Basolateral Amygdala on Acquisition of Two-Way Avoidance Reaction and Long-Term Fear Memory

Although much has been learned about the role of the amygdala in Pavlovian fear conditioning, relatively little is known about an involvement of this structure in more complex aversive learning, such as acquisition of an active avoidance reaction. In the present study, rats with a pretraining injection of the N-methyl-D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonopentanoic acid (APV), into the basolateral amygdala (BLA) were found to be impaired in two-way active avoidance learning. During multitrial training in a shuttle box, the APV-injected rats were not different from the controls in sensitivity to shock or in acquisition of freezing to contextual cues. However, APV injection led to impaired retention of contextual fear when tested 48 h later, along with an attenuation of c-Fos expression in the amygdala. These results are consistent with the role of NMDA receptors of the BLA in long-term memory of fear, previously documented in Pavlovian conditioning paradigms. The APV-induced impairment in the active avoidance learning coincided with deficits in directionality of the escape reaction and in attention to conditioned stimuli. These data indicate that normal functioning of NMDA receptors in the basolateral amygdala is required during acquisition of adaptive instrumental responses in a shuttle box but is not necessary for acquisition of short-term contextual fear in this situation.