Cellular and Circuit Mechanisms Underlying Observational Stress in Mice
Corticotropin releasing factor is a stress-associated neuropeptide that binds to Corticotropin-releasing factor receptor type 1 (CRF1) to encode arousing environmental stimuli. Oxytocin is a peptide that is released and binds to the oxytocin receptor (OXTR) in social contexts. Past research has shown that both neuropeptides are implicated in stress responses. This project sought to test the hypothesis that co-activation of CRFR1 and OXTR in the cortex is required for the behavioral manifestations of observational distress, defined as observing a conspecific directly exposed to a stressor. It has been previously shown that the anterior cingulate cortex (ACC) is critical for mediating observational fear behavior. Thus, I assessed CRFR1 and OXTR RNA expression in different areas of the cortex, including the ACC, and their respective level of activation (via cFos expression) in mice exposed to observational distress. Methods used include cryosectioning, in situ hybridization (RNAscope), epifluorescent imaging, and image analysis. Controls for this experiment included subjects that were directly stressed and mice that were in proximity to the stressor without the demonstrator present. Specifically, RNAscope was used to look at RNA for 3 different probes. We used image analysis software to measure the level of cFos RNA and co-expression between Crhr1, Oxtr, Fos mRNAs. Though data analysis is ongoing, our initial pilot studies (n = 1 in each group) indicated that there is a greater number of cFos+ cells in “Observer” mice exposed to an unfamiliar conspecific (“Demonstrator”) compared to a familiar conspecific. In addition, there appears to be an interesting lateralization of Crhr1/Oxtr/Fos expression, particularly in the “Observer” mouse exposed to a familiar demonstrator. This is consistent with observational fear studies that show differential contribution of the left and right cortical hemispheres. We are currently expanding our studies to investigate potential sex differences along with performing fully powered studies in male mice.