SAT-426 Rabies-Mediated Monosynaptic Tract-Tracing of Sexually Dimorphic Estrogen-Sensitive Afferents to KNDy Neurons in the Mouse

Estradiol controls reproductive status and sexual behavior by acting upon a variety of neurochemical systems in the brain to mediate the sexually dimorphic release of gonadotrophins. However, the neural pathways that transmit steroid hormone information to gonadotropin-releasing hormone (GnRH) neurons are unclear. Kisspeptin/Neurokinin B/Dynorphin (KNDy) neurons of the arcuate nucleus (ARC) are critical for reproductive status and implicated to relay a number of peripheral signals, including gonadal steroids, to regulate GnRH secretion. We recently reported the distribution of primary afferents to KNDy neurons (Moore et al, International Congress for Neuroendocrinology, 2018), however, it is not known if KNDy neurons receive synaptic input from steroid hormone-sensitive cells. To address this, we utilized rabies-mediated tract-tracing to unequivocally determine the distribution of estradiol-sensitive monosynaptic inputs to KNDy neurons. Adult male (n=6) and female (n=4) Kiss1-Cre mice were stereotaxically injected in the ARC with Cre-dependent adenoassociated viruses (AAVs) to express avian receptor protein with GFP (TVA-GFP) and rabies glycoprotein (G) in ARC kisspeptin (KNDy) neurons. After three weeks, the glycoprotein-deleted rabies virus (RVdG) containing mCherry was injected in the same location. RVdG exclusively infects KNDy cells expressing TVA, and, as G is required for rabies to cross transynaptically, RVdG crosses into primary afferents of KNDy neurons to express mCherry. As RVdG induces toxicity in cells, a time-point trial determined mCherry-positive cells retain protein expression after 5 days. Mice were perfused and coronal sections immunolabeled for GFP to identify KNDy cells, mCherry to visualize KNDy afferents and estrogen receptor alpha (ERα). Immunoreactivity was mapped using fluorescent microscopy and slide scanning software (MBFbioscience) and dual labeled mCherry- and ERα- positive cells analyzed using confocal microscopy. Male and female mice were statistically compared using students t tests. Dual-labeled cells were detected within the bed nucleus of the stria terminalis and the hypothalamic rostral periventricular area, medial preoptic nucleus (MPON), ventromedial and anterior hypothalamus, ARC and premammillary nucleus. Compared to male mice, females exhibited a significantly higher percentage of dual-labeled cells in the periventricular nucleus (PeN, 46.7±16.4% in females, 7.8±5.1% in males, p<0.05) and MPON (34.3±7.2% in females, 10.9±6% in males, p<0.05). The PeN and MPON are critical for reproductive endocrine function and sexual behavior in the mouse, respectively. Together, these data indicate that sexually dimorphic estradiol-sensitive neuronal populations in the rostral hypothalamus may directly relay steroid hormone signals to KNDy neurons to regulate GnRH secretion and perhaps other functions.