Mechanisms of sex selective enhancement of threat anticipation following early life adversity

PROJECT SUMMARY. Experiencing early life adversity (ELA), such as resource scarcity, is associated with anxiety-related disorders, including generalized anxiety disorder (GAD). Women have a two-fold greater prevalence of anxiety disorders, more robust presentation of symptoms, and poorer response to treatments. A debilitating and core feature of GAD is heightened anticipation of threat when it is not necessarily present. While responding to threat is adaptive, excessive anticipation in the absence of real threat can manifest as pathology. Examining the neural correlates underlying threat anticipation is critical to understanding sex- specific risk and developing effective treatments. ELA alters threat response circuitry, associated with excessive recruitment of the central amygdala (CeA), a region important for threat learning. A neuropeptide, corticotropin releasing hormone (Crh), within the CeA responds to threat-predictive cues and send long-range projections to the bed nucleus of the stria terminalis (BNST), a region known for behavioral modulation in response to stress. However, the impact of ELA on the Crh+ CeA to BNST projection and how sex-differences within this projection may alter threat anticipation remains unclear. Thus, examining the Crh CeA to BNST projection as a potential neurobiological target by which ELA enhances responses to threat will be central to understanding neural underpinnings of pathology and sex differences in risk. The startle response is an especially suitable endophenotype to study threat responding because it is reliably enhanced when threat is explicitly cued. It also provides a useful translational tool, as the behavior has been widely used in clinical settings. In preliminary studies, I used the limited bedding mouse model of ELA to test its effects on startle response as an index of threat anticipation. I found that mice who experience ELA exhibit enhanced startle to a loud noise both in the presence and absence of the conditioned tone, suggesting both heightened and maladaptive anticipation of threat. Importantly, this effect was exclusive to females. I hypothesize that anticipation of threat is driven by activation of CeACrh to BNST neurons and that ELA female mice show excessive activation of this circuit both when threat is present and absent. In Aim 1, I will test for sex- and ELA-specific differences of Crh CeA to BNST activity when threat is either present or absent by using fiber photometry to visualize calcium activity from a population of CeA Crh neurons projecting to BNST during the fear-potentiated startle task. In Aim 2, I will test the necessity of the CeA Crh to BNST projection for anticipated threat by optogenetically inhibiting Crh BNST terminals from CeA in the presence of threat. Ultimately, this knowledge may contribute to the development of proper treatments for anxiety disorders that are individualized to the experience and sex of the individual. The training I will gain through this F31 award will support my path towards becoming a well-rounded and independent research scientist focused on studying animal models of pathology and the consequences of ELA on emotional development.