REVERSIBLE CHANGES IN HIPPOCAMPAL H-3 AMPA BINDING FOLLOWING INHIBITORY AVOIDANCE TRAINING IN THE RAT

We have recently shown that inhibitory avoidance training produces a r apid, selective, and learning-specific increase in the number of H-3-A MPA glutamate receptors in several subfields of the dorsal hippocampal formation in the rat. In the present study we investigated the posttr aining temporal course of this enhancement by quantitative autoradiogr aphy of H-3-AMPA binding. Confirming previous results, rats submitted to a step-down inhibitory avoidance paradigm showed a marked increase (50-90%) in hippocampal H-3-AMPA binding that peaked 2 h posttraining. In CA(3) and dentate gyrus this increase persisted for at least 48 h following training. In contrast, 24 h after training the binding of H- 3-AMPA in the CA(1) subfield did not differ significantly from naive c ontrol values. In all hippocampal regions studied, the binding of H-3- AMPA at 168 h posttraining reached control values. No changes were obs erved in the shocked or free exploration groups in comparison with nai ve controls. The results suggest that hippocampal AMPA receptors under go rapid and reversible changes after inhibitory avoidance learning an d give further support to the hypothesis that changes in hippocampal A MPA receptors participate in the synaptic plasticity mediating certain forms of learning and memory. (C) 1996 Academic Press, Inc.