Project Summary Elevated risk taking contributes not only to the development of substance use disorder (SUD) but also the likelihood of relapse. There has been significant progress in delineating the neural substrates underlying this causal relationship. Nonetheless, we are still faced with a significant barrier in translating these findings to the clinical setting because the majority of the work on this topic has used male subjects. This is despite the well- established sex differences in risk taking and aspects of SUD. This significant limitation in scientific advancement can be remediated by examining neurobiological mechanisms underlying decision making in females. The long-term goal of our lab is to identify the neural mechanisms mediating risk taking in females and how hormones contribute to these processes. To meet this goal, I will use a rodent model of risk taking in which females are more risk averse and exhibit greater sensitivity to risk of punishment than males. In this model, female risk aversion is largely mediated by estradiol (E2) and such E2-dependent risk aversion requires estrogen receptor (ER) β. We have also established a role for the basolateral amygdala (BLA) and its projections to the nucleus accumbens (NAc) shell in promoting risk averse behavior. Preliminary data reveal that activation of D2 dopamine receptors (D2Rs) in the BLA increases risk aversion in females, but not males. These findings suggest that differences in BLA function may underlie sex differences in risk taking, and specifically, promote risk aversion in females. Prior work shows sex differences in BLA-dependent behavior are due to the ability of E2 to modulate BLA activity and function. Given the role of the BLA in risk taking and the fact it is potently modulated by E2, it is therefore conceivable that risk aversion in females may be due to E2 regulation of BLA activity necessary for risk-based decision making. Consequently, the overall objective of this proposal is to dissect the neural mechanisms by which E2 promotes risk aversion in females. I hypothesize that E2 mediates female risk aversion through its modulation of ERβ and D2R function in the BLA and its projections to the NAc shell. I will test my hypothesis by carrying out three experimental aims. In Aim 1, I will identify the contributions of ERs in the BLA to E2-dependent risk aversion in females using RNA interference-mediated ER gene reduction. In Aim 2, I will identify the necessity of E2 modulation of D2R function in the BLA for risk aversion in females using optogenetic manipulation of BLA neurons that selectively express D2Rs. In Aim 3, I will identify the contribution of E2 modulation of BLA projections to the NAc shell to risk aversion in females using optogenetic manipulation of this circuit. This project is significant because the knowledge gained will advance our understanding of the neural mechanisms by which E2 mediates female risk aversion and provide a foundation from which we ...