mGlu and mGlu Negative Allosteric Modulators Divergently Enhance Thalamocortical Transmission and Exert Rapid Antidepressant-like Effects.

Non-selective antagonists of metabotropic glutamate receptor subtypes 2 (mGlu) and 3 (mGlu) exert rapid antidepressant-like effects by enhancing prefrontal cortex (PFC) glutamate transmission; however, the receptor subtype contributions and underlying mechanisms remain unclear. Here, we leveraged newly developed negative allosteric modulators (NAMs), transgenic mice, and viral-assisted optogenetics to test the hypothesis that selective inhibition of mGlu or mGlu potentiates PFC excitatory transmission and confers antidepressant efficacy in preclinical models. We found that systemic treatment with an mGlu or mGlu NAM rapidly activated biophysically unique PFC pyramidal cell ensembles. Mechanistic studies revealed that mGlu and mGlu NAMs enhance thalamocortical transmission and inhibit long-term depression by mechanistically distinct presynaptic and postsynaptic actions. Consistent with these actions, systemic treatment with either NAM decreased passive coping and reversed anhedonia in two independent chronic stress models, suggesting that both mGlu and mGlu NAMs induce antidepressant-like effects through related but divergent mechanisms of action.