MEDIAL AMYGDALA ENHANCES SYNAPTIC TRANSMISSION AND SYNAPTIC PLASTICITY IN THE DENTATE GYRUS OF RATS IN-VIVO

1. The present experiment was designed to test whether synaptic transm ission and synaptic plasticity in the dentate gyrus were modulated by the medial amygdala (MeA). Field potentials in the dentate gyrus (DG) evoked by stimulations of the medial perforant path (PP) were extracel lularly recorded in anesthetized rats. 2. Although single-pulse stimul ation of the MeA augmented PP stimulation-evoked population spike ampl itude in the DG transiently, high-frequency stimulation (100 Hz for 1 s) of the MeA induced long-lasting enhancement of synaptic transmissio n that was not occluded by PP tetanus-induced long-term potentiation ( LTP). 3. When high-frequency stimulation of the MeA was applied concur rently with weak tetanus of the PP, which alone induced only marginal LTP, the magnitude of LTP increased considerably. 4. These results dem onstrate that neuron activities in the MeA induce short- and long-last ing changes in the excitability of the PP-DG synapses and thereby enha nce their synaptic plasticity.