シナプス前性グルタミン酸受容体による視覚野抑制性シナプス伝達の制御

抄録

We studied the roles of presynaptic glutamate receptors in synaptic transmission and plasticity in cortical inhibitory connections. Whole-cell recording was conducted from layer 2/3 pyramidal cells in visual cortical slices of young mice. Inhibitory postsynaptic currents (IPSCs) were recorded at the reversal potential of excitatory synaptic transmission. The frequency of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin was increased by bath application of glutamate, AMPA and NMDA, while it was decreased by the AMPA receptor antagonist NBQX and the NMDA receptor antagonist APV. These compounds did not change mIPSC amplitude, suggesting that AMPA and NMDA receptors are present at the presynaptic terminal of inhibitory synapses and their activation facilitates inhibitory synaptic transmission. Indeed, application of either APV or NBQX decreased the amplitude of evoked IPSCs considerably with accompanying increases in both paired-pulse ratio and coefficient of variation of IPSC, consistent with presynaptic action of these antagonists. High-frequency stimulation produced long-term potentiation (LTP) of IPSCs in normal solution. The magnitude of LTP decreased in the presence of NBQX and LTP did not occur in the presence of NBQX and APV, suggesting that AMPA and NMDA receptors both contribute to the facilitation of LTP production. These results indicate that both AMPA and NMDA receptors are present at the presynaptic terminal of inhibitory synapses in layer 2/3 pyramidal cells and that their activation facilitates inhibitory synaptic transmission and LTP. [J Physiol Sci. 2006;56 Suppl:S33]