(S)- 3,5-Dihydroxyphenylglycine )an agonist for group I metabotropic glutamate receptors( induced synaptic potentiation at excitatory synapses on fast spiking GABAergic cells in visual cortex

Introduction: (S)- 3,5-Dihydroxyphenylglycine (DHPG) is an agonist for group I metabotropic glutamate receptors. DHPG-induced synaptic depression of excitatory synapses on hippocampal pyramidal neurons is well known model for synaptic plasticity studies. The aim of the present study was to examine the effects of DHPG superfusion on excitatory synapses on pyramidal and fast-spiking GABAergic cells (FS-GABA) of layer II/III of mice visual cortex. Methods: Effects of DHPG was examined in visual cortical slices of GAD67-GFP knock-in mice using whole-cell recordings of excitatory postsynaptic potentials (EPSPs) in layer II/III cells evoked by layer IV stimulation. In part of experiments, long term potentiation (LTP) was induced by theta burst stimulation (TBS) paired with postsynaptic depolarization. Results: DHPG induced potentiation of EPSPs of FS-GABA neurons in dose- and use-dependent manners but it has no effect on pyramidal cell excitatory synapses. An antagonist for type 5 metabotropic glutamate receptors (mGluR5) blocked DHPG-induced LTP, while an antagonist for mGluR1 was not effective. This potentiation and TBS-induced LTP occluded each other. Conclusion: Based on important role of FS-GABA cells in cortical neuronal circuit, mGlur5-dependent LTP may play a role in, enhancement or maintenance of synchronized activity of cortical pyramidal neurons.