Activation of efferents from the basolateral amygdala during the retrieval of conditioned taste aversion.

ABSTRACT

The basolateral amygdala (BLA) is critical in the retrieval of conditioned taste aversion (CTA). Although BLA neurons have axonal connections with several brain regions, it is unclear which efferent pathways are functional in CTA. The present study investigated the involvement of efferents from BLA in CTA retrieval with manganese (Mn(2+))-enhanced magnetic resonance imaging (MEMRI). Rats receiving intraoral saccharin infusion paired with intraperitoneal administration of lithium chloride (LiCl) were presented with saccharin (C-S and BC-S groups) or water (C-W group) on the test day. The BC-S group was administered with LiCl 15 min before saccharin presentation on the conditioning day (backward conditioning, BC). Another two groups were injected with saline (S-S and S-W groups) instead of LiCl. On the test day, 50 nL of 40-mM manganese chloride (MnCl2) was injected into BLA before the intraoral fluid infusion. Using MRI, we analyzed Mn(2+) movements, which indicated the activation of efferent neurons. The C-S group showed the highest activities in several efferents from BLA. Of them, the activities of the efferents to the nucleus accumbens core (NAcC), the anterior part of the bed nucleus of the stria terminalis (aBNST), and the central amygdala (CeA) were larger in the C-S group than in the Q group, which was presented with a normally aversive quinine solution. Although rats equivalently rejected conditioned aversive saccharin and quinine, the aversive responses in the C-S group, and not the Q group, were due to CTA retrieval. Therefore, our results indicated that BLA efferents to NAcC, aBNST, and CeA were specifically activated during CTA retrieval, suggesting that these efferents are key components in the neural mechanisms of CTA.