NMDA receptor GluN2B subunit activity is required for trace fear memory. (A) We exposed mice to i.p. injections of either Ro25-6981 or ifenprodil (10 mg/kg @ 2 mg/ml), or saline, 30 min prior to trace fear conditioning and assessed freezing behavior in response to the CS in a new context 48 h later. (B-C) Mice exposed to either Ro25-6981 or ifenprodil prior to training exhibited normal learning behavior but a robust reduction in freezing behavior in response to the CS compared to mice exposed to saline, or to mice exposed to Ro25-6981 30 min prior to testing. (D) Treatment with Ro25-6981 30 min prior to training completely blocked trace fear induced membrane GluA1 upregulation in the ACC (saline: n = 7; Ro25-6981: n = 8; ifenprodil: n = 6; Ro25-6981 at test: n = 5; F = 6.64). (E) Mice displayed similar response latencies in the hot plate (55°C) and tail flick assays when treated with Ro25-6981 or saline 30 min before testing. (* P < 0.02 ).