Novelty acquisition is associated with induction of hippocampal long-term depression

Homosynaptic long-term depression (LTD) consists of a persistent nonpatholo gical decrease in synaptic transmission, which is induced by low-frequency stimulation. III vivo, low-frequency stimulation (1 Hz, 900 pulses) induces LTD in Wistar but not Hooded Lister rats. In this study, we investigated t he influence of behavioral learning and behavioral state on the expression of LTD in both rat strains. Recordings were taken from freely moving animal s that had undergone chronic implantation of a recording electrode in the h ippocampal CA1 region and a bipolar stimulating electrode in the ipsilatera l Schaffer collateral-commissural pathway. Exposure of the rat strains to s tress induced a significant elevation in serum corticosterone levels but di d not facilitate LTD expression. However, LFS given during exploration of a novel environment resulted in LTD expression in Hooded Lister, and LTD enh ancement in Wistar, rats. Reexposure to the same environment did not result in new expression of LTD. Behavioral comparison between the first and seco nd environmental exposure confirmed that the animals had habituated to the novel environment, These observations strongly implicate an association bet ween novelty acquisition and LTD.