Reversible changes in hippocampal 3H-AMPA binding following inhibitory avoidance training in the rat

We have recently shown that inhibitory avoidance training produces a rapid, selective, and learning-specific increase in the number of 3H-AMPA glutamate receptors in several subfields of the dorsal hippocampal formation in the rat. In the present study we investigated the posttraining temporal course of this enhancement by quantitative autoradiography of 3H-AMPA binding. Confirming previous results, rats submitted to a step-down inhibitory avoidance paradigm showed a marked increase (50-90%) in hippocampal 3H-AMPA binding that peaked 2 h posttraining. In CA3 and dentate gyrus this increase persisted for at least 48 h following training. In contrast, 24 h after training the binding of 3H-AMPA in the CA1 subfield did not differ significantly from naive control values. In all hippocampal regions studied, the binding of 3H-AMPA at 168 h posttraining reached control values. No changes were observed in the shocked or free exploration groups in comparison with naive controls. The results suggest that hippocampal AMPA receptors undergo rapid and reversible changes after inhibitory avoidance learning and give further support to the hypothesis that changes in hippocampal AMPA receptors participate in the synaptic plasticity mediating certain forms of learning and memory.