Selective sub-nucleus effects of intra-amygdala oxytocin on fear extinction

Abstract

There is growing evidence that the neuropeptide oxytocin (OT) modulates fear and extinction in humans and rodents through actions in corticolimbic circuits including the central amygdala (CeA). Prior studies have, however, been limited to subjects that exhibit intact basal extinction, rather than extinction-impaired populations that could potentially therapeutically benefit from viable OT-targeting treatments. Here, we assessed the effects of pre-extinction training infusion of OT into the CeA, or basolateral amygdala (BLA), on extinction in an inbred mouse strain (S1) model of impaired extinction. We found that intra-CeA OT, at a dose of 0.01 μg, enabled extinction memory formation, as evidenced by lesser freezing as compared to vehicle-infused controls on a drug-free retrieval test. Conversely, infusion of a higher, 1.0 μg OT dose, markedly reduced freezing and increased grooming during extinction training and produced elevated freezing on drug-free retrieval. Infusion of the 0.01 μg dose into the BLA was without behavioral effects. Together, our data show that OT acts in a dose-dependent manner within the CeA to promote extinction in otherwise extinction-deficient mice. These findings provide further support for the potential utility of OT as an adjunctive treatment to extinction-based therapies for trauma and anxiety disorders.

Keywords: Basolateral amygdala; Central amygdala; Fear extinction; Impaired extinction; Mice; Microinfusion; Oxytocin.

Figure 1:. Experimental schematic for assessing fear extinction-related effects of intra-amygdala oxytocin (OT).

(A) Following implantation of guide cannulae directed at the CeA, mice underwent fear conditioning via 3 tone-shock pairings (Day 1). On experimental Day 2, vehicle, 0.01 or 1.0 μg OT infused into the CeA prior to extinction training, entailing 50 tone-CS presentations. On Day 3, extinction retrieval was tested via 3 tone-CS presentations. (B) After implantation of guide cannulae directed at the BLA, mice underwent testing as in A, but without the inclusion of the 1.0 μg OT dose. (C) Estimated cannula tip location for bilateral CeA infusions of vehicle (red triangles, n=9), 0.01 µg OT (orange circles, n=9) and 1 µg OT (blue circles, n=5). (D) Estimated cannula tip location for bilateral BLA OT infusions for vehicle (red triangles, n=6), 0.01 µg OT (orange circles, n=6).

Figure 2:. Dose-dependent effects of intra-CeA oxytocin (OT) on fear extinction.

(A) Freezing increased from the first to third CS-US pairing during conditioning. (B) Intra-CeA infusion of 1.0 μg OT (n=5, red circles) decreased freezing during extinction training and increased freezing on (drug-free) extinction retrieval, relative to vehicle (n=9, black empty circles). (C) Intra-CeA infusion of 0.01 μg OT (n=9 blue circles) prior to extinction training produced decreased freezing on (drug-free) extinction retrieval, relative to vehicle. (D) Grooming levels were very low during conditioning. Intra-CeA infusion of 1.0 μg, but not 0.01 μg, OT prior to extinction training increased grooming during extinction training (E) and decreased freezing on (drug-free) extinction retrieval (F), relative to vehicle controls. *P<0.05 versus vehicle. # P<0.05 versus first CS block in extinction. Data are means ± SEM. Abbreviations: CS: conditioned stimulus, US: unconditioned stimulus, b: baseline, AV: Average.

Figure 3:. Lack of effects of a single dose of intra-BLA oxytocin (OT) on fear extinction.

(A) Freezing increased from the first to third CS-US pairing during conditioning. (B) Intra-BLA infusion of 0.01 μg (n=6, blue circles) OT prior to extinction training did not affect freezing on extinction training (C) or (drug-free) extinction retrieval, as compared to vehicle controls (n=6, black empty circles). (D) Grooming was absent during conditioning. Intra-BLA infusion of 0.01 μg OT prior to extinction training did not affect grooming on extinction training (E) or extinction retrieval (F) compared to vehicle. Data are means ± SEM. Abbreviations: CS: conditioned stimulus, US: unconditioned stimulus, b: baseline, AV: Average.