Project Summary Adverse childhood experiences (ACEs) have profound consequences for physiological development and are an important social determinant of health. ACEs can alter reproductive outcomes including age at menarche, engagement in risky sexual behaviors, and fertility. Early-life stress can also shape the way an individual responds to stress in adulthood, promoting either resiliency or susceptibility to later stress. Adult stress has been independently demonstrated to disrupt fertility. Two neuroendocrine axes play key roles regulating both the stress response (hypothalamo-pituitary-adrenal [HPA] axis) and reproduction (hypothalamo-pituitary- gonadal [HPG] axis). Corticotropin-releasing hormone (CRH) is the main central neurohormone for the hypothalamic component of the HPA axis, released by neurons in the paraventricular nucleus (PVN). CRH also serves as a signaling neuropeptide outside of the PVN, regulating other components of the stress response including emotional and behavioral aspects. Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus are the final common pathway for the central control of reproduction. GnRH neurons receive input from many afferent populations, including kisspeptin neurons in the anteroventral periventricular nucleus (AVPV). GnRH leads to the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland, thus stimulating synthesis of sex steroids. In females, estradiol switches from a negative to positive feedback action during the preovulatory stage, leading to a surge in GnRH and LH release that promotes ovulation. Critically, acute stress can disrupt this LH surge, and this disruption may involve CRH neurons. To investigate the neural mechanisms by which acute stress disrupts the LH surge, and to determine if a history of ACEs modulates this phenomenon, we must turn to animal models. Rodent models share core components of the reproductive system with humans, and they permit the use of genetic tools to interrogate biological circuits. Here, we will use a limited bedding and nesting (LBN) model for early-life stress and an acute, layered, psychosocial stress (ALPS) paradigm for adult stress. In Aim 1, we will investigate how these stressors alter the intrinsic electrophysiological properties of and fast-synaptic input to GnRH neurons on the afternoon of proestrus, corresponding to the timing of the LH surge. This aim will also test the hypothesis that early-life stress of the LBN model confers resilience to the effects of acute stress on reproduction in adulthood. In Aim 2, channelrhodopsin-assisted circuit mapping (CRACM) will be employed to interrogate the functional connection between CRH and GnRH neurons and AVPV kisspeptin neurons. In vivo chemogenetic tools will address if activation of CRH neurons that project to the AVPV is sufficient to disrupt the LH surge and necessary for stress to disrupt the surge on proestrus. The proposed studies will provide ke...