Abstract: The changes of synaptic efficacy in the CA3 region of the rat hippo-campus during establishment, consolidation, extinction and re-estiblish-ment of the conditioned discrimination response have been examined. It is shown that the long-term potentiation (LTP) which appeared inthe CA3 of the hippocampus with the establishment of conditionedresponse, persisted with the consolidation of conditioned response andextinct with the experimental extinction of conditioned response.Yet, it reappeared with the reestablishment of the conditioned response.The development level and alteration of LTP were in advance of the dew- elopment level and alteration of conditioned behavior. The continuous in-vestigation made in one experiment substitutes for several experiments inthe past. The relevant appearance and alteration of the learning-dependentLTP in the CA3 that is a controllable effect on conditioned behavior wasobserved in the various phases of the continuous and rapid alteration inthe learning. All these are fresh and convincing evidences indicating thatthe learning-dependent LTP might be one of the neural substrates of lear-ing and memory.

Key words: Synaptic plasticity, Long-term potentiation, Hippocampus, Memory