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.