MEMORY ENHANCEMENT BY INTRAHIPPOCAMPAL, INTRAAMYGDALA, OR INTRAENTORHINAL INFUSION OF PLATELET-ACTIVATING-FACTOR MEASURED IN AN INHIBITORY AVOIDANCE TASK

Platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosp hocholine), which is thought to be a retrograde messenger in long-term potentiation (LTP), enhances glutamate release and LTP through an act ion on presynaptic nerve endings. The PAF antagonist BN 52021 blocks C A1 LTP in hippocampal slices, and, when infused into rat dorsal hippoc ampus pre- or posttraining, blocks retention of inhibitory avoidance. Here we report that memory is affected by pre- or posttraining infusio n of the PAF analog yl-2-N-methylcarbamoyl-sn-glycero-3-phosphocholine (mc-PAF) into either rat dorsal hippocampus, amygdala, or entorhinal cortex. Male Wistar rats were implanted bilaterally with cannulae in t hese brain regions. After recovery from surgery, the animals were trai ned in step-down inhibitory avoidance or in a spatial habituation task and tested for retention 24 h later, mc-PAF (1.0 mu g per side) enhan ced retention test performance of the two tasks when infused into the hippocampus before training without altering training session performa nce. In addition, mc-PAF enhanced retention test performance of the av oidance task when infused into (i) the hippocampus 0 but not 60 min af ter training; (ii) the amygdala immediately after training; and (iii) the entorhinal cortex 100 but not 0 or 300 min after training. In conf irmation of previous findings, BN 52021 (0.5 mu g per side) was found to be amnestic for the avoidance task when infused into the hippocampu s or the amygdala immediately but not 30 or more minutes after trainin g or into the entorhinal cortex 100 but not 0 or 300 min after trainin g. These findings support the hypothesis that memory involves PAF-regu lated events, possibly LTP, generated at the time of training in hippo campus and amygdala and 100 min later in the entorhinal cortex.