Multideterminant role of calcium in hippocampal synaptic plasticity

Hippocampal CA1 cells possess several varieties of long‐lasting synaptic plasticity: two different forms of long‐term potentiation (LTP) and at least one form of long‐term depression (LTD). All forms of synaptic plasticity are induced by afferent activation, all involve Ca2+ influx, all can be blocked by Ca2+ chelators, and all activate Ca2+‐dependent mechanisms. The question arises as how different physiological responses can be initiated by activation of the same second messenger. We consider two hypotheses which could account for these phenomena: voltage‐dependent differences in cytosolic Ca2+ concentration acting upon Ca2+ substrates of differing Ca2+ affinities and compartmentalization of the Ca2+ and its substrates. © 1994 Wiley‐Liss, Inc.