STRESS-INDUCED SENSITIZATION AND FACILITATED-LEARNING REQUIRE NMDA RECEPTOR ACTIVATION

EXPOSURE to an inescapable stressor facilitates acquisition of a class ically-conditioned eyeblink response in the freely-moving rat. Here, w e tested the hypothesis that the facilitation is mediated via activati on of the N-methyl-D-aspartate (NMDA) type of glutamate receptor. Rats were injected with the competitive NMDA antagonist CGP-37849 (5 mg kg (-1)) or vehicle 2 h prior to exposure to restraint and 90, 1 mA, 1 s tail shocks. In contrast to the dramatic facilitation exhibited in str essed rats injected with the vehicle, rats whose NMDA receptors were b locked during exposure to the stressor did not exhibit any facilitatio n 24 h later. The antagonist alone had no effect on learning. These re sults demonstrate that the stress-induced facilitation of classical co nditioning is dependent on NMDA receptor activation and support the hy pothesis that stress is inducing a phenomenon similar in mechanism to that of long-term potentiation (LTP).