Group I metabotropic glutamate receptors are involved in TEA-induced long-term potentiation at mossy fiber-CA3 synapses in the rat hippocampus

Gq-protein-coupled Group I metabotropic glutamate receptors (mGluR) reportedly activate phospholipase C (PLC), leading to Ca2+ release from intracellular stores and the formation of diacylglycerol (DAG). We electrophysiologically examined the involvement of the Group I mGluR in tetraethylammonium (TEA)-induced long-term potentiation (LTP) at mossy fiber (MF)-CA3 synapses in the rat hippocampus. TEA-induced LTP was almost completely blocked under the selective blockade of either mGluR1 or mGluR5, both of which are Group I mGluR. This result was supported by the blockade of TEA-induced LTP even in the absence of these blockers under low temperature conditions, in which the activation of Group I mGluR is thought not to be fully effective. In addition, the blockade of mGluR1 resulted in lower short-term potentiation (STP) during TEA application compared with the blockade of mGluR5. These results demonstrate the crucial roles of Group I mGluR in the TEA-induced LTP at MF-CA3 synapses and the different contributions of mGluR1 and mGluR5 to the initial component of plasticity.