Knockout mice mGluR5(-/-) displayed more depression-like behaviors (learned helplessness, social withdrawal and anhedonia) than control mice following exposure to stressful stimuli, whereas lentiviral 'rescue' of mGluR5 in the nucleus accumbens decreased these depression-like behaviors in mGluR5(-/-) mice.33 mGluR5 may be involved in the regulation of neural network activity and synaptic plasticity. The gene discussed is GRM5; the disease is major depressive disorder.