PROJECT SUMMARY/ABSTRACT: For many psychiatric disorders, such as substance use disorder, sex is a critical biological variable and women represent a particularly vulnerable population. For cocaine use disorder women transition to addiction faster, take more cocaine, experience more adverse consequences, and have more difficulty remaining abstinent. Previous research has exposed significant sex differences in the mesolimbic dopamine system, a neural circuit critical in reward learning and motivation, and identified the gonadal hormone 17b-estradiol as a significant contributor to this vulnerability. The mesolimbic dopamine system - which originates in the ventral tegmental area and projects to the striatum - has been shown to be involved in the expression of sex-specific behavior especially as it relates to cocaine reward and motivation. To understand cocaine use disorder in females we need to understand the fundamental mechanisms by which drug responses are mediated and how this influences the systems these drugs act on – I focus here on the dopamine system. While substantial work has focused on sex differences in the anatomy of dopamine neurons and relative dopamine levels between males and females, an important characteristic of dopamine release from axon terminals in the striatum is that it is rapidly modulated by local regulatory mechanisms independent of somatic activity. The dopamine system contains a high density of estrogen receptors (ERa, ERb, and GPER-1 subtypes) that likely serve as important substrates through which ovarian hormones exert their influence on dopaminergic function. Indeed, there is robust dopamine system regulation by ovarian hormones where 17β-estradiol (E2) increases dopamine cell activity and release from dopamine terminals in the striatum. In Aim 1, I will combine analytical chemistry and optical imaging techniques with pharmacology to isolate dopamine terminals in the nucleus accumbens core and characterize the role of specific estrogen receptor subtypes in the modulation of presynaptic dopamine release. Further, previous work from our lab has shown selective increases in cocaine-evoked dopamine release, cocaine potency, and cocaine affinity for the dopamine transporter in estrus females (with high levels of circulating E2). In Aim 2, I will define how direct manipulation of estrogen receptors affects dopamine transporter-mediated clearance and potency of cocaine at terminals in the nucleus accumbens core. This work builds on the foundation set by innovators in the field to examine the role of estrogen receptors in presynaptic dopamine dynamics, and further proposes to investigate how these mechanisms modulate cocaine effects at the dopamine transporter. Importantly, this work provides me with an exceptional training opportunity while simultaneously providing answers to fundamental questions in the field, which are imperative in developing effective pharmacotherapies for cocaine use disorder. Together, understandi...