Neural substrates for the retrieval of conditioned taste aversion revealed by manganese-enhanced MRI

Memory is an important and dominant function of the brain. However, the neural mechanisms underlying memory function remain unclear. Conditioned taste aversion (CTA) is a useful model for the study of memory, in which a pairing of taste with visceral malaise produces robust aversive memory. Although many studies have investigated the brain regions involved in the acquisition of CTA, the neural mechanisms underlying the retrieval of CTA are a matter of debate. Because several lines of evidence indicate that the amygdala plays a role in CTA, we examined the activation of efferent projections from the basolateral nucleus of the amygdala (BLA) upon the retrieval of CTA memory, by using the manganese-enhanced MRI (MEMRI) technique. The rats presented with conditioned aversive saccharin showed enhanced activities of the neural projections from the BLA to the nucleus accumbens core (NAcC). Therefore, we also investigated whether CTA retrieval activates the output neurons in the NAcC predominantly projecting to the ventral pallidum (VP) by using MEMRI. The conditioned aversive saccharin induced stronger activation of the NAcC-VP projections than the normally preferred saccharin did. The NAcC-VP projections are mainly GABAergic. Further pharmacological and microdialysis studies clarified the involvement of VP GABAergic transmission in the retrieval of CTA memory. Thus, we conclude that the BLA-NAcC-VP pathway is a key component of the neural systems underlying CTA retrieval.