Pure cultures of rat cortical neurons were challenged with either 875 or 300 μM NMDA for 20 min in the absence or presence of DHPG and/or the mGlu3 receptor NAM, VU0650786. The experiment was carried out in the presence of the mGlu1 receptor NAM, JNJ16259685 (10 μM), to avoid the stimulation of mGlu1 receptors by DHPG. Neuronal toxicity was assessed by trypan blue staining. Values are means ± S.E.M. of 4 determinations. p < 0.05 (One-way ANOVA + Fisher’s LSD) vs. the respective basal values (*), the vehicle values of the same group (NMDA alone) (#), or vs. the respective DHPG values of the same group (§). F(11,36) = 177.91. This experiment was repeated twice and data were confirmed by using the MTT assay.