ENHANCED SYNAPTIC TRANSMISSION IN CA1 HIPPOCAMPUS AFTER EYEBLINK CONDITIONING

CA1 field potentials evoked by Schaffer collateral stimulation of hipp ocampal slices from trace-conditioned rabbits were compared with those from naive and pseudoconditioned controls. Conditioned rabbits receiv ed 80 trace conditioning trials daily until reaching a criterion of 80 % conditioned responses in a session. Hippocampal slices were prepared 1 or 24 h after reaching criterion (for trace-conditioned animals) or after a final unpaired stimulus session (for pseudoconditioned animal s); naive animals were untrained. Both somatic and dendritic field pot entials were recorded in response to various stimulus durations. Recor ding and data reduction were performed blind to the conditioning state of the rabbit. The excitatory postsynaptic potential slope was greate r in slices prepared from trace-conditioned animals killed 1 h after c onditioning than in naive and pseudoconditioned controls (repeated-mea sures analysis of variance, F = 4.250, P < 0.05). Associative learning specifically enhanced synaptic transmission between CA3 and CA1 immed iately after training. This effect was not evident in the population f ield potential measured 24 h later.