Increased training prevents the impairing effect of intra-amygdala infusion of the non-NMDA receptor antagonist CNQX on inhibitory avoidance expression

Abstract

Intra-amygdala infusion of the non-N-methyl-D-aspartate (NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) prior to testing impairs inhibitory avoidance retention test performance. Increased training attenuates the impairing effects of amygdala lesions and intra-amygdala infusions of CNQX. The objective of the present study was to determine the effects of additional training on the impairing effects of intra-amygdala CNQX on expression of the inhibitory avoidance task. Adult female Wistar rats bilaterally implanted with cannulae into the border between the central and the basolateral nuclei of the amygdala were submitted to a single session or to three training sessions (0.2 mA, 24-h interval between sessions) in a step-down inhibitory avoidance task. A retention test session was held 48 h after the last training. Ten minutes prior to the retention test session, the animals received a 0.5-µl infusion of CNQX (0.5 µg) or its vehicle (25% dimethylsulfoxide in saline). The CNQX infusion impaired, but did not block, retention test performance in animals submitted to a single training session. Additional training prevented the impairing effect of CNQX. The results suggest that amygdaloid non-NMDA receptors may not be critical for memory expression in animals given increased training.