Selective induction of LTP and LTD by postsynaptic [Ca2+], elevation

Long-term potentiation (LTP) and long-term depression (LTD), two prominent forms of synaptic plasticity at glutamatergic afferents to CA1 hippocampal pyramidal cells, are both triggered by the elevation of postsynaptic intracellular calcium concentration ([Ca2+](i)). To understand how one signaling molecule can be responsible for triggering two opposing forms of synaptic modulation, different postsynaptic [Ca2+](i) elevation patterns were generated by a new caged calcium compound nitrophenyl-ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in CA1 pyramidal cells. We found that specific patterns of [Ca2+](i) elevation selectively activate LTP or LTD. In particular, only LTP was triggered by a brief increase of [Ca2+](i) with relatively high magnitude, which mimics the [Ca2+](i) rise during electrical stimulation typically used to induce LTP. In contrast, a prolonged modest rise of [Ca2+](i) reliably induced LTD. An important implication of the results is that both the amplitude and the duration of an intracellular chemical signal can carry significant biological information.