Sex-Dependent Effects of Angiotensin Type 2 Receptor Expressing Medial Prefrontal Cortex (mPFC) Interneurons in Fear Extinction Learning
Authors: Smith Hannah , Yu Zhe , Iyer Laxmi , Marvar Paul J 
Published: May 2024

Background: The renin-angiotensin system (RAS) has been identified as a potential therapeutic target for PTSD, though its mechanisms are not well understood. Brain angiotensin type 2 receptors (AT2Rs) are a subtype of angiotensin II receptors located in stress and anxiety-related regions, including the medial prefrontal cortex (mPFC). Their function and mechanism in the mPFC, however, remain unexplored. We therefore used a combination of neuroanatomical, chemogenetic, and behavioral methods to investigate mPFC-AT2R-expressing neuron involvement in fear learning. Methods: To characterize mPFC-AT2R-expressing neurons in the mPFC, AT2R-Cre/td-Tomato male and female brains were perfused and used for immunohistochemistry. Brain sections were stained with glutamatergic or interneuron markers, and density of AT2R+ cells and colocalization with each marker was quantified. To assess fear-related behaviors in AT2R-flox mice, we selectively deleted AT2R from mPFC neurons using an AAV-Cre or GFP virus. Mice then underwent Pavlovian auditory fear conditioning and anxiety-like and locomotor behavior testing using open field (OF) and elevated plus maze (EPM) tests. Results: IHC revealed that AT2R is expressed throughout the mPFC in males ( 208.6±48.8 cells/mm2) and females ( 139.0±59.8 cells/mm2) and has low co-expression on glutamatergic neurons ( TBR1 co-staining, males: 7.1%±1.8%; females: 13.2%±4.2%). Of the interneuron markers tested, AT2R is primarily expressed on somatostatin interneurons, and has higher colocalization in the mPFC of females than males ( males: 16.5%±1.2%, females: 31.8%±4.2%, p=0.02). Following fear conditioning and extinction, mPFC-AT2R deletion impaired extinction in female ( p=0.03) but not male ( p=0.76) mice. Locomotion in the OF was unaltered by mPFC-AT2R deletion in males or females ( total distance travelled; males: GFP 44.11m±5.92m, Cre 56.00m±10.29m, p=0.35; females: GFP 42.86m±4.85m, Cre 42.39m±4.97m, p=0.95), while AT2R-deleted females had increased exploratory behavior in the EPM ( open arm entries; males: GFP 12.38±1.02, Cre 13.22±1.54, p=0.66; females: GFP 12.50±0.96, Cre 20.00±2.81, p=0.02). Conclusion: These results lend support for mPFC-AT2R+ neurons as a novel somatostatin subgroup that influences fear extinction in a sex-dependent manner. This furthers underscores the role of mPFC in top-down regulation and a unique role for peptidergic (ie., angiotensin) mPFC regulation of fear and sex differences, and increases the understanding of circuitry and function of the brain RAS in disordered fear learning. This may lead to improved therapeutic treatments for PTSD. This research and PJM was supported by NIH1R01HL137103-01A1 and the American Heart Association 15CSA24340001. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.