An in vitro slice preparation of rat amygdala was used to study the long-term modifications of synaptic efficacy following high-frequency stimulation of the ventral endopyriform nucleus. Delivery of brief tetani to the afferent fibers led to a long-term potentiation (LTP) of the amplitude and the initial slope of excitatory postsynaptic potential (EPSP). Pretreatment the slices with DL-2-amino-5-phosphonovaleate (DL-APV, 50 microM) blocked the induction of LTP, indicating that N-methyl-D-aspartate (NMDA) receptor activation is required for induction. NMDA receptor-mediated component of synaptic response (EPSPNMDA) was isolated by application of a solution containing 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX, 10 microM) and bicuculline (20 microM). Tetanic stimulation led to a lasting potentiation of the EPSPNMDA. These results suggest that brief repetitive stimulation of afferent pathway produces forms of LTP that share many properties of LTP seen in the CA1 region of the hippocampus.