Acute injection of NAC inhibits radiant heat-induced nocifensive behavior in mice by activating mGlu2/3 receptors. Percentage of the maximum possible effect (%MPE) in the four tail-flick conditions: i) saline followed by saline; (ii) saline followed by N-acetyl-cysteine (NAC) (100 mg/kg); (iii) LY341495 (1 mg/kg) followed by saline; and (iv) LY341495 followed by NAC. NAC injection increased tail-flick latencies. Values are means + S.E.M. of 6–8 determinations. *p < 0.05 vs. all other values, F(3,22)=6.38, p=0.003.