The induction of long-term potentiation at amygdalo-hippocampal synapses in vivo.

Electrical stimulation of the basolateral amygdala (BLA) evoked synaptic potentials in the dentate gyrus (DG) of the hippocampus in anesthetized rats. To determine if this pathway possesses synaptic plasticity, we investigated the impact of several conditions of high-frequency stimulation on BLA-DG synaptic potentials in these rats. Application of two trains of 100-pulse, 100-Hz stimulation or theta-burst stimulation to the BLA reproducibly induced long-term potentiation (LTP) of BLA-DG synaptic potentials. Paired-pulse facilitation was unchanged during LTP, suggesting that postsynaptic mechanisms are involved in the expression of LTP. In addition, the induction of LTP was not affected by the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate, suggesting that activation of NMDA receptors is not required. This novel form of LTP should be a valuable model for elucidating neural mechanisms underlying the formation of emotional memory.