Involvement of postsynaptic G-proteins in hippocampal long-term potentiation

The guanine nucleotide binding proteins (G-proteins) are a family of proteins that couple membrane receptors to intracellular second messenger enzymes. Most subtypes of G-protein are highly expressed in hippocampal neurons, implying important roles of G-proteins in the modulation of synaptic transmission. In this article, we review recent studies on the involvement of G-proteins in tetanus-induced long-term potentiation (LTP) of synaptic efficacy in the hippocampus. Such an LTP has been demonstrated to be produced by several mechanisms. In Schaffer collateral-CA1 synapses where induction of LTP requires post- and presynaptic events, G-proteins may regulate the development of LTP presynaptically. In mossy fiber-CA3 synapses where only presynaptic elements are needed to initiate LTP, the contribution of G-proteins may also be localized at presynaptic sites. However, in fimbria-CA3 synapses where LTP is thought to be initiated by NMDA receptor activation at CA1 pyramidal cells, postsynaptic G-proteins are involved in the induction of LTP by affecting membrane depolarization and/or Ca2+ mobilization. The different contribution of G-proteins in the various forms of LTP at anatomically distinct synapses implies localized modification of synaptic transmission by endogenous neurotransmitters via G-protein-coupled receptors.