The role of NMDA receptors in regulating group II metabotropic glutamate receptor-mediated long-term depression in rat medial prefrontal cortex

Previous work has shown that brief application of group II metabotropic glutamate receptor (mGluR) agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl) glycine (DCG-IV) can induce long-term depression (LTD) of excitatory transmission on layer V pyramidal neurons of rat medial prefrontal cortex (mPFC). An unusual feature of this LTD is that it relies on activation of both group II mGluRs and N-methyl-D-aspartate receptors (NMDARs). However, it is not known whether other specific group II mGluR agonists also induce LTD and whether they depend on the conjoint activation of group II mGluRs and NMDARs. We show here that the ability of DCG-IV to induce LTD was mimicked by a more selective group II mGluR agonist, LY379268. The induction of LTD by a lower concentration of DCG-IV (0.2 mu M) or LY379268 (0.03 mu M) was blocked by the NMDAR antagonist APV or the interruption of synaptic stimulation during drug application. In contrast, application of a higher concentration of DCG-IV (1 mu M) or LY379268 (0.1 mu M) can induce LTD that was independent of synaptic NMDAR activation. These results suggest that although molecular cooperation between group II mGluRs and synaptic NMDARs may facilitate the induction of group II mGluR-mediated LTD at excitatory synapses onto mPFC layer V pyramidal neurons, enhancing group II mGluR activation may remove NMDAR involvement in this form of synaptic plasticity. (C) 2008 Elsevier Ltd. All rights reserved.