공포조건화 소거에 따른전두엽-편도체 시냅스 강도의 역동적 조절

Abstract

Fear conditioning, in which a neutral conditioned stimulus (CS) is contingently paired with an aversive unconditioned stimulus (US) and acquires capacity to elicit conditioned response (CR), has been studied extensively to elucidate neural substrate of associative memory. It has been shown that the critical change for the fear memory is stored as a form of modified synaptic response in the lateral nucleus (LA) of the amygdala. On the other hand, extinction, in which the fear CR is reduced as a result of repeated exposure to the CS without the US, has been known to depend on the infralimbic cortex (IL) of the medial prefrontal cortex. However, little is known about the interaction between the IL and LA over the course of extinction process. In the current study, we investigated the synaptic changes in the IL-LA pathway by measuring evoked field potentials (EFPs) before and after fear extinction. Following fear conditioning in which the rats were presented with five parings of the CS and footshock US, they were subjected to two extinction sessions composed of 10 CS-only trials each. In addition, they received a retention test composed of three CS-only presentations. To measure synaptic plasticity, evoked field potentials (EFPs) were recorded in the lateral nucleus of the amygdala (LA) by stimulating the IL, six hours after every session. The recorded EFP was significantly increased after the first extinction but not after the subsequent sessions. These data indicate that dynamic regulation of IL-LA synaptic efficacy underlies the suppression of conditioned fear response following extinction and suggest that consolidation of memory extinction involves changes in other synapses than IL-LA pathway.