Role of the NMDA receptor in consummatory successive negative contrast

Abstract

Four experiments using the partial agonist D-cycloserine (DCS) were conducted to investigate the role of the N-methyl D-aspartate (NMDA) receptor in consummatory successive negative contrast (cSNC), an animal model of loss-induced anxiety. . In Experiment 1, pretrial 11 and 12 administration of DCS (30 mg/kg) enhanced cSNC following the reward downshift from 32%-to-4% sucrose solution. In Experiment 2, posttrial 11 administration of DCS enhanced cSNC greatest at 30 mg/kg, following 32%-to-4%, and mildly following 32%-to-6%. In Experiment 3, DCS at 15 mg/kg and 60 mg/kg prolonged cSNC mildly (32%-to-4%). Experiment 4 suggested enhancement was not the result of conditioned taste aversion (CTA) to DCS (30 mg/kg); CTA to novel 4% solution failed to develop, compared to unpaired and saline controls. Results were interpreted to mean that activation of NMDA receptors via the glycine-modulatory site enhances the aversive memory associated with unexpected reward loss. Possible applications for therapeutic settings are discussed.