Central Amygdala Angiotensin Type 2 Receptor (AT 2 R) Activation Reduces Fear‐Related Behavior

Background Previous retrospective clinical studies identify the renin‐angiotensin system (RAS) as a potential therapeutic target in post‐traumatic stress disorder (PTSD), however the mechanisms are unknown. We propose that brain RAS modulates inhibitory and excitatory fear circuits critical to the consolidation and extinction of fear memory in PTSD. Methods Using the angiotensin type 2‐receptor (AT 2 R)‐eGFP‐BAC reporter mouse combined with pharmacological and behavioral approaches, the aim of the study was to examine the role of the brain AT 2 R in fear memory. Results AT 2 R‐eGFP + immunoreactive cells co‐localized with the neuronal specific marker NeuN and were expressed in major subnuclei of the amygdala. They were predominately observed in the medial amygdala (203.8 ± 39.4 cells/mm 2 ) and the medial division of central amygdala (CeM) (224.7 ± 9.4 cells/mm 2 ), while the basolateral amygdala (11.7 ± 1.8 cells/mm 2 ) and lateral division of central amygdala (CeL) (3.2 ± 0.8 cells/mm 2 ) contained minimal to no AT 2 R‐eGFP expression (Fig. 1). Within the CeM, 96% of the AT 2 R‐eGFP + neurons expressed the GABAergic marker GAD1, while approximately 17% GABAergic AT2R‐eGFP + cells expressed interneuron markers, suggesting the remaining may be GABAergic projection neurons. Moreover, these AT 2 R‐eGFP + neurons were negative for the CeL marker PKC‐β. In C57Bl/6 mice, we used cue‐dependent and context‐dependent fear conditioning to examine the behavioral role of AT 2 R in fear memory. Twenty‐four hours after fear conditioning, bilateral intra‐CeA injection of the AT 2 R agonist C21 (0.06ug/ul) was administered and mice were exposed to the conditioned cue (30 second auditory tones) or context. Fear expression was quantified by percentage of freezing during cue stimuli or the context exposure. Compared to vehicle controls, mice receiving C21 into the CeA displayed a decreased freezing response to both the cue (61.7% ± 5.4 vehicle vs 42.1% ± 5.7 C21 group, p <0.05, n=10–12) and the context (64.6% ± 4.4 vehicle vs 48.3% ± 3.7 C21 group, p <0.05, n=16–17), indicating reduced fear expression (Fig. 2). These behavioral effects were also independent of generalized anxiety‐like behavior as determined by open‐field and EPM testing. Conclusion These findings suggest that CeM AT 2 R‐expressing neurons can modulate CeA outputs that play a role in fear expression and provide evidence for a novel angiotensinergic circuit in the regulation of fear. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .