Figure 3.

IC-to-BLA projecting neurons are necessary for the acquisition and retrieval but not for the extinction or maintenance of learned aversive memories. Adult (8–12 weeks) WT male mice were injected with viral constructs at the BLA (blue) and aIC (red), resulting in expression of inhibitory hMD4Gi in aIC-to-BLA neurons (A). Representative schematic overlays of the Cre-dependent expression of the chemogenetic receptors using the retroAAV systems is shown, demonstrating the expression to be restricted in the BLA and aIC (n = 12 slices). Animals were split into saline (light blue) and CNO (dark red) groups, and treated before CTA acquisition (B). Chemogenetic inhibition during CTA acquisition (C), significantly suppressed aversion upon retrieval compared with control animals (C). In separate experiments, similarly injected mice, were used to assess the role of the projection in CTA retrieval (D). Inhibition during CTA retrieval, significantly suppressed aversion compared with control animals (E). To test whether the projection is also involved in CTA memory maintenance, we inhibited 24 h after acquisition, and proceeded to test the animals 48 h later (F, G). Inhibition 24 h after conditioning, resulted in similar aversion upon retrieval testing in control and treated animals. Even though inhibition of the projection during the retrieval of CTA suppresses aversion to the CS (H), 24 h later, treated mice (I) exhibited similar aversion to control mice. After 14 unreinforced choice tests between water and saccharin, control and IC-BLA inhibited mice exhibited similar extinction of the conditioned response (I) and no significant differences were observed among the two groups due to our intervention. *p ≤ 0.05.