PROJECT SUMMARY Astrocytes are a glial subtype that are essential for numerous central nervous system functions. Dysregulation of astrocyte function is known to cause a variety of neurological and neuromuscular disorders. Interestingly, disruption of hypothalamic astrocytes has the capability to compromise fertility. Roughly one in five couples in the USA suffer from some type of infertility, thus elucidating the complete circuits underlying reproduction is essential. Gonadotropin-releasing hormone (GnRH) neurons in the preoptic area and hypothalamus form the final common pathway for the central control of fertility. Pulsatile GnRH secretion causes release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary, activating gonadal functions including steroidogenesis. An afferent network likely governs pulsatile GnRH secretion, including both steroid- sensitive kisspeptin neurons in the arcuate nucleus (KNDy neurons) and glia. Although pulsatile GnRH release is common to male and female reproduction, females exhibit unique processes including reproductive cycles and ovulation that could alter neural-glial interactions. Critically, astrocytes exhibit morphological plasticity and the levels of hypothalamic neuron ensheathment by glia change across cycle stages, pointing to potential astrocytic regulation that varies with respect to cycle stage. Astrocytic mediators like prostaglandin E2 (PGE2) can also regulate GnRH neuron activity, and PGE2 is required for timely sexual maturation and adult reproduction in rodents. To investigate the contexts in which astrocytes regulate reproductive neural circuits, a combination of electrophysiology, calcium imaging, and glial cell cultures will be used. Aim 1 will study if factors including sex, cycle stage, and time of day influence the ability of astrocytes to regulate GnRH and/or KNDy neuron firing rates. In vitro chemogenetic activation of astrocytes via the transduced Gq signaling receptor hM3D(Gq) will be employed to induce intracellular calcium transients that typify endogenous Gq-induced astrocyte activity, while monitoring the activity of identified neurons. In Aim 2, chemogenetic activation of primary astrocyte cultures followed by high-performance liquid chromatography of supernatants will be done to elucidate the gliotransmitter profiles of hypothalamic astrocytes. To compliment this, the endogenous Gq- coupled receptor profiles will be assessed in glial cultures and brain slices transduced with GFAP-GCaMP6f via treatment with candidate Gq ligands. These results will inform my subsequent experiments in which an endogenous Gq-coupled receptor will be knocked down in hypothalamic astrocytes and a gliotransmitter receptor in GnRH neurons, providing a test for the necessity of these components of glial-neural signaling for reproduction in vivo. Completion of the proposed work will clarify roles of astrocytes in the neuroendocrine control of fertility. Elucidating th...