Central amygdala angiotensin type 1 receptor (Agtr1) expressing neurons contribute to fear extinction

The renin-angiotensin system (RAS) has been linked to the pathophysiology of posttraumatic stress disorder (PTSD) however, the underlying neurobiological mechanism(s) remain elusive. Here we utilized angiotensin II receptor type 1 (AT1R) transgenic mice combined with neuroanatomical, behavioral, and electrophysiological approaches, to examine the role of the central amygdala (CeA) expressing AT1R neurons in fear and anxiety -related behavior. Within the major amygdala subdivisions, AT1R+ neurons were localized to gamma-aminobutyric acid (GABA) expressing neurons in the lateral division of the central amygdala (CeL), and the majority of them were identified as protein kinase C-delta positive (PKC delta+) neurons. Following CeA-AT1R deletion using cre-expressing lentiviral delivery in AT1R-Flox mice, generalized anxiety and locomotor activity as well as the acquisition of conditioned fear were unaltered while the acquisition of extinction learning, as measured by percent freezing behavior, was significantly enhanced. During electrophysiological recordings of CeL-AT1R+ neurons, the application of angiotensin II (1 mu m) increased the amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) and decreased the excitability of CeL-AT1R+ neurons. Overall, these findings demonstrate that CeL-AT1R-expressing neurons play a role in fear extinction, potentially through facilitated CeL-AT1R+ GABAergic inhibition. These results provide new evidence for mechanisms of angiotensinergic neuromodulation of the CeL and its role in fear extinction and may aid in further advancing targeted novel therapies for improving mal-adaptive fear learning processes associated with PTSD.

Automated summary

This study examined the role of angiotensin II receptor type 1 (AT1R) neurons in the central amygdala (CeA) in fear and anxiety-related behavior using AT1R transgenic mice. It was found that AT1R+ neurons were localized to GABA expressing neurons in the CeL, and their deletion enhanced extinction learning. Furthermore, the application of angiotensin II increased inhibitory synaptic currents and decreased the excitability of CeL-AT1R+ neurons. These findings provide new insights into the neurobiological mechanisms underlying fear extinction.