HETEROSYNAPTIC INTERACTIONS BETWEEN LTP AND LTD IN CA1 HIPPOCAMPAL SLICES

Experiments in which several high and/or low frequency stimulation pat terns were applied to different groups of afferents in CA1 hippocampal slices revealed the existence of heterosynaptic interactions between LTP and LTD. Specifically, we report that repeated induction of LTD on one input was associated with a heterosynaptic reversal of the LTP pr eviously induced on a separate pathway. Reapplication of high frequenc y stimulation at the end of the experiment reinstated LTP. This hetero synaptic reversal occurred without modification of naive responses, an d it was prevented by D-AP5, an NMDA receptor antagonist, or cyclospor in A, a calcineurin inhibitor. Similarly, induction of LTP on one inpu t was found to reverse hetero-synaptically the LTD previously induced on a separate pathway. This effect was also sensitive to D-AP5, it occ urred without modification of naive pathways, and LTD could be reinsta ted by low frequency trains. These results indicate that repeated indu ction of LTP or LTD on one group of afferents can reset synaptic effic acy at other nonactivated synapses.