Long term potentiation (LTP) is a synaptic plasticity event used to investigate the cellular mechanisms involved in learning and memory (Bliss and Collingridge, 1993). Distinct temporal phases of LTP can be identified with an initial phase (0-3hrs) resulting from modifications to pre-existing proteins and a late-phase (>4hrs) requiring de-novo protein synthesis. The activation of NMDA receptors is known to be critical in initiating LTP whilst protein synthesis inhibitors have been shown to block the late phase (Krug et. al., 1984; Stanton & Sarvey, 1984). The nature of the majority of these de novo molecules is unknown. In this study we have investigated global changes of protein expression in an NMDA-dependent plasticity system using differential gel electrophoresis (DIGE).Hippocampal slices were prepared from male ICR mice (4-6 weeks) which were terminally anaesthetised with urethane (1500mg/kg i.p.). Following 1hr equilibration in artificial cerebrospinal fluid (ACSF), 4 horizontal slices (400µm) were held at interface in a humidified chamber incubated with either ACSF, glutamate (100µM) or glutamate (100µM) and the NMDA receptor blocker D-AP5 (50µM). The CA1 region of each hippocampal slice was harvested at 4hrs and snap frozen. Control (ACSF) and treated (glutamate, glutamate & D-AP5) lysates (n=4) together with internal standards were labeled with CyDye^TM DIGE fluors and subjected to 2-D gel electrophoresis. Gel images produced using a Typhoon^TM 9400 laser scanner were processed using DeCyder software (Amersham Biosciences).In total the expression levels of 79 proteins were shown to be significantly (p<0.05, students t-test) different from control following glutamate treatment. 35 of these molecules increased in expression (ratios 1.07 to 1.9, average ratio 1.29 ±0.0351). The remaining 44 decreased in expression (ratios −1.91 to −1.07, average ratio −1.29 ± 0.0287). Of these 79 proteins only 21 remained significantly different (p<0.05, students t-test) from control following coincubation of glutamate and D-AP5. Following in-gel tryptic digestion, Maldi-Tof/ Q-star mass spectrometry and database searching, several proteins have been identified. These include cytoskeletal proteins and proteins involved in vesicle trafficking, metabolism and ubiquitination.In conclusion, glutamate receptor activation results in changes in protein expression, which can be quantified and identified using proteomics and mass spectrometry.