Oxytocin signaling in basolateral and central amygdala nuclei differentially regulates the acquisition, expression, and extinction of context-conditioned fear in rats

Abstract

The present study investigated how oxytocin (OT) signaling in the central (CeA) and basolateral (BLA) amygdala affects acquisition, expression, and extinction of context-conditioned fear (freezing) in rats. In the first set of experiments, acquisition of fear to a shocked context was impaired by a preconditioning infusion of synthetic OT into the CeA (Experiment 1) or BLA (Experiment 2). In the second set of experiments, expression of context fear was enhanced by a pre- or post-extinction CeA infusion of synthetic OT (Experiments 3-6) or a selective OT receptor agonist, TGOT (Experiment 4). This enhancement of fear was blocked by coadministration of an OT receptor antagonist, OTA (Experiment 5) and context fear was suppressed by administration of the antagonist alone (Experiment 6). In the third set of experiments, expression of context fear was suppressed, not enhanced, by a preextinction BLA infusion of synthetic OT or a selective OT receptor agonist, TGOT (Experiments 7 and 8). This suppression of fear was blocked by coadministration of the OT receptor antagonist, OTA (Experiment 8). Taken together, these findings show that the involvement of the CeA and BLA in expression and extinction of context-conditioned fear is dissociable, and imply a critical role for oxytocin signaling in amygdala-based regulation of aversive learning.

Figure 1.

Cannula placements for the 145 subjects in experiments targeting the CeA (left) and 124 subjects in experiments targeting the BLA (right). The filled circles represent the location of the cannula tips at five different rostral-caudal planes. The numbers represent the posterior coordinates (millimeters) from bregma.

Figure 2.

The effects of intra-amygdala infusions of OT on acquisition of context-conditioned fear. (A) Timeline of the experimental procedure; Cx+ and Cx− represent context–shock and context extinction sessions, respectively. (B) Mean (+SEM) percent freezing to the context across the acquisition (left) and test session (right) after intra-CeA infusions of saline (SAL) or OT in Experiment 1. The data from five rats were excluded from the analysis because of incorrect cannula placement yielding the following group sizes: Groups SAL, n = 9 and OT, n = 10. (*) P < 0.05, main effect of group. (C) Mean (+SEM) percent freezing to the context across the acquisition (left) and test session (right) after intra-BLA infusions of saline (SAL) or OT in Experiment 2. The data from six rats were excluded from the analysis of this experiment because of incorrect cannula placement yielding the following group sizes: Groups SAL, n = 10 and OT, n = 8. (#) P < 0.05, main effect of group and trend × group interaction.

Figure 3.

The effects of intra-CeA infusions on extinction of context-conditioned fear. Mean (+SEM) percent freezing to the context in the final minute of the second context-conditioning session (left panel), across the extinction (center panel) and test (right panel) sessions. (A) Timeline of the experimental procedure; Cx+ and Cx− represent context–shock and context extinction sessions, respectively. (B) Experiment 3, the effect of preextinction infusions of OT at various doses. The data from 12 rats were excluded from Experiment 3 because of incorrect cannula placement yielding the following group sizes: Groups SAL, n = 12, OT 0.6 ng, n = 9, OT 3 ng, n = 10, OT 15 ng, n = 8, and OT 75 ng, n = 8. (*) P < 0.05, main effect contrast testing SAL versus all OT groups. (C) Experiment 4, the effect of preextinction infusions of OT and the selective OT agonist (TGOT). The data for 10 rats were excluded from the analysis because of incorrect cannula placement yielding the following group sizes: Group SAL, n = 8, Group OT 15 ng, n = 10, Group TGOT 7 ng, n = 8. In extinction: (*) P < 0.05, main effect contrast testing SAL versus (OT and TGOT) groups. At test: (†) P < 0.05, comparison SAL versus OT. (D) Experiment 5, the effect of the selective OT antagonist alone (OTA) and in conjunction with OT (OT + OTA). The data from 12 rats were excluded from the analysis because of incorrect cannula placement yielding the following group sizes: Group SAL, n = 10, Group OT, n = 9, Group OTA, n = 9 and Group OT + OTA, n = 8. In extinction: (*) P < 0.05, main effect of group and group × trend contrast testing OT 15 ng versus remaining groups. (†) P < 0.05, contrast OTA 15 ng versus (SAL and OT + OTA) groups across the first 10 min of the extinction session. At test: (*) P < 0.05, main effect of group and group × trend contrast testing OT 15 ng versus remaining groups. (†) P < 0.05, contrast OTA 15 ng versus (SAL and OT + OTA) groups.

Figure 4.

The effects of pre- and post-extinction OT infusions into the CeA. (A) Timeline of the experimental procedure; Cx+ and Cx− represent context–shock and context extinction sessions, respectively. (B) Mean (+SEM) percent freezing to the context in Experiment 6 in the final minute of the second context conditioning session (left panel), across the extinction (center panel), and test (right panel) sessions. The data from nine rats were excluded from the analysis because of incorrect cannula placement yielding the following group sizes: Group SAL, n = 9, Group PRE OT, n = 10, Group POST OT, n = 8. In Extinction: (*) P < 0.05, main effect contrast testing PRE OT versus (POST OT and SAL) groups. At test: (*) P < 0.05, main effect contrast testing SAL versus (PRE OT and POST OT) groups.

Figure 5.

The effects of intra-BLA infusions on extinction of context-conditioned fear. Mean (+SEM) percent freezing to the context in the final minute of the second context-conditioning session (left panel), across the extinction (center panel) and test (right panel) sessions. (A,C) Timeline of the experimental procedures; Cx+ and Cx− represent context–shock and context–extinction sessions respectively. (B) Experiment 7, the effect of preextinction infusions of OT at various doses. The data from 18 rats were excluded from this experiment because of incorrect cannula placement yielding the following group sizes: group SAL, n = 8, group OT 0.6 ng, n = 9, group OT 3 ng, n = 8, group OT 15 ng, n = 8, group OT 75 ng, n = 9. In extinction: (*) P < 0.05, main effect contrast testing SAL versus (PRE OT and POST OT) groups. At test: (*) P < 0.05, main effect contrast testing SAL versus (0.6, 3, 15, and 75 ng OT) groups. (†) P < 0.05, main effect of group and group × trend contrast testing 0.6 ng OT versus (3, 15, and 75 ng OT) groups. (D) Experiment 8, the effect of pre- and post-extinction OT infusions, and the effect of the selective OT antagonist alone (OTA) and in conjunction with OT (OT + OTA). The data from 11 rats were excluded from the analysis because of incorrect cannula placement yielding the following group sizes: Group SAL, n = 10, Group PRE OT, n = 9, Group OT + OTA, n = 8, Group OTA, n = 9, Group POST OT, n = 10. In extinction: (*) P < 0.05, main effect contrast testing PRE OT versus (SAL, POST OT, OT + OTA, and OTA) groups. At test: (*) P < 0.05, main effect of group and group × trend contrast testing PRE OT versus (SAL, POST OT, OT + OTA, and OTA) groups.