https://academic.oup.com/endo 1 Endocrinology, 2021, Vol. 162, No. 3, 1–17 doi:10.1210/endocr/bqaa237 Research Article ISSN Online 1945-7170 © The Author(s) 2020. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com Research Article Indirect Suppression of Pulsatile LH Secretion by CRH Neurons in the Female Mouse Siew Hoong Yip, 1, * Xinhuai Liu, 1, * Sabine Hessler, 1 Isaiah Cheong, 1 Robert Porteous, 1 and Allan E. Herbison 1 1 Centre for Neuroendocrinology and Department of Physiology, University of Otago School of Biomedical Sciences, Dunedin 9054, New Zealand ORCiD number: 0000-0002-9615-3022 (A. E. Herbison). *These authors contributed equally. Received: 10 November 2020; Editorial Decision: 16 December 2020; First Published Online: 26 December 2020; Corrected and Typeset: 2 February 2021. Abstract  Acute stress is a potent suppressor of pulsatile luteinizing hormone (LH) secretion, but the mechanisms through which corticotrophin-releasing hormone (CRH) neurons inhibit gonadotropin-releasing hormone (GnRH) release remain unclear. The activation of para- ventricular nucleus (PVN) CRH neurons with Cre-dependent hM3Dq in Crh-Cre female mice resulted in the robust suppression of pulsatile LH secretion. Channelrhodopsin (ChR2)-assisted circuit mapping revealed that PVN CRH neuron projections existed around kisspeptin neurons in the arcuate nucleus (ARN) although many more fibers made close appositions with GnRH neuron distal dendrons in the ventral ARN. Acutely prepared brain slice electrophysiology experiments in GnRH- green fluorescent protein (GFP) mice showed a dose-dependent (30 and 300 nM CRH) activation of firing in ~20% of GnRH neurons in both intact diestrus and ovariectomized mice with inhibitory effects being uncommon (<8%). Confocal GCaMP6 imaging of GnRH neuron distal dendrons in acute para-horizontal brain slices from GnRH-Cre mice injected with Cre-dependent GCaMP6s adeno-associated viruses demonstrated no effects of 30 to 300 nM CRH on GnRH neuron dendron calcium concentrations. Electrophysiological recordings of ARN kisspeptin neurons in Crh-Cre,Kiss1-GFP mice revealed no effects of 30 -300 nM CRH on basal or neurokinin B-stimulated firing rate. Similarly, the optogenetic activation (2-20 Hz) of CRH nerve terminals in the ARN of Crh-Cre,Kiss1-GFP mice injected with Cre-dependent ChR2 had no effect on kisspeptin neuron firing. Together, these studies demonstrate that PVN CRH neurons potently suppress LH pulsatility but do not exert direct inhibitory control over GnRH neurons, at their cell body or dendron, or the ARN kisspeptin neuron pulse generator in the female mouse. Key Words: CRH, PVN, GnRH, kisspeptin, GCaMP, DREADD, electrophysiology, dendron Downloaded from https://academic.oup.com/endo/article/162/3/bqaa237/6052404 by guest on 28 June 2022