FLIP SIDE OF SYNAPTIC PLASTICITY - LONG-TERM DEPRESSION MECHANISMS INTHE HIPPOCAMPUS

There is growing interest in the phenomenon of long-term depression (L TD) of synaptic efficacy that, together with long-term potentiation (L TP), is a putative information storage mechanism in mammalian brain. I n neural network models, multiple learning rules have been used for LT D induction. Similarly, in neurophysiological studies of hippocampal s ynaptic plasticity, a variety of activity patterns have been effective at inducing LTD, although experimental paradigms are still being opti mized. In this review the authors summarize the major experimental par adigms and compare what is known about the mechanisms of LTD induction . Although all paradigms appear to initiate a cascade of events leadin g to an elevated level of Ca2+ postsynaptically, the extent to which t hese paradigms involve common expression mechanisms has not yet been t ested. The authors discuss several critical experiments that would add ress this latter issue. Numerous questions about the properties and me chanisms of LTD(s) in the hippocampuus remain to be answered, but it i s clear that LTD has finally arrived, and will soon be attracting atte ntion equal to its flip side, LTP. (C) 1994 Wiley-Liss, Inc.