INVOLVEMENT OF HIPPOCAMPAL NMDA RECEPTORS IN RETENTION OF SHUTTLE AVOIDANCE-CONDITIONING IN RATS

The purpose of this research nas to evaluate the role of hippocampal N -methyl-D-aspartate (NMDA) receptors in acquisition and consolidation of memory during shuttle avoidance conditioning in rats, Adult male Wi star rats were surgically implanted with cannulae aimed at the CAI are a of the dorsal hippocampus. After recovery from surgery, animals were trained and tested in a shuttle avoidance apparatus (30 trials, 0.5-m A footshock, 24-h training-test interval). Immediately before or immed iately after training, animals received a bilateral intrahippocampal 0 .5-mu l infusion containing 5.0 mu g of the NMDA competitive receptor antagonist aminophosphonopentanoic acid (AP5) or vehicle (phosphate-bu ffered saline, pH 7.4). infusion duration was 2 min per side. Pre-trai ning infusion of AP5 impaired retention test performance (mean +/- SEM number of conditioned responses (CRs) during retention test session w as 16.47 = 1.78 in the vehicle group and 9.93 +/- 1.59 in the AP5 grou p; P<0.05). Post-training infusion of AP5 did not affect retention (me an +/- SEM number of conditioned responses during retention test sessi on was 18.46 +/- 1.94 in the vehicle group and 20.42 +/- 2.38 in the A P5 group; P>0.10). This impairment could not be attributed to an effec t on acquisition, motor activity or footshock sensitivity since AP aff ected neither training session performance measured by the number of C Rs nor the number of intertrial crossings during the training session. These data suggest that NMDA receptors in the hippocampus ape critica l for retention of shuttle avoidance conditioning, in agreement with p revious evidence showing a role of NMDA receptors in fear memory.