Changes in GABAergic Transmission to and Intrinsic Excitability of Gonadotropin-Releasing Hormone (GnRH) Neurons during the Estrous Cycle in Mice.

Xi Chen,Caroline Adams,Suzanne M Moenter

doi:10.1523/eneuro.0171-18.2018

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https://doi.org/10.1523/eneuro.0171-18.2018

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Journal: eNeuro	Publication Date: Sep 1, 2018
Citations: 20	License type: cc-by

Affiliation: University of Michigan–Ann Arbor

Abstract

Gonadotropin-releasing hormone (GnRH) neurons form the final common central output pathway controlling fertility and are regulated by steroid feedback. In females, estradiol feedback action varies between negative and positive; negative feedback typically regulates episodic GnRH release whereas positive feedback initiates a surge of GnRH, and subsequently luteinizing hormone (LH) release ultimately triggering ovulation. During the estrous cycle, changes between estradiol negative and positive feedback occur with cycle stage and time of day, with positive feedback in the late afternoon of proestrus in nocturnal species. To test the hypotheses that synaptic and intrinsic properties of GnRH neurons are regulated by cycle stage and time of day, we performed whole-cell patch-clamp studies of GnRH neurons in brain slices from mice at two times considered negative feedback (diestrous PM and proestrous AM) and during positive feedback (proestrous PM). GABAergic transmission can excite GnRH neurons and was higher in cells from proestrous PM mice than cells from proestrous AM mice and approached traditional significance levels relative to cells from diestrous PM mice. Action potential response to current injection was also greater in cells from proestrous PM mice than the other two groups. Interestingly, the hormonal milieu of proestrous AM provided stronger negative feedback on both GnRH neuron excitability and GABAergic postsynaptic current (PSC) amplitude than diestrous PM. These observations demonstrate elements of both synaptic and intrinsic properties of GnRH neurons are regulated in a cycle-dependent manner and provide insight into the neurobiological mechanisms underlying cyclic changes in neuroendocrine function among states of estradiol negative and positive feedback.

Highlights

Gonadotropin-releasing hormone (GnRH) neurons form the final hormonal output pathway through which the central nervous system controls reproduction
To lay a basis for understanding how synaptic and intrinsic properties of GnRH neurons change between conditions of estradiol negative and positive feedback within the normal estrous cycle, we examined the rates of GABAergic fast synaptic transmission, the primary fast synaptic input to GnRH neurons, as well as GnRH neuron excitability, measured as action potential firing rate in response to current injection, and action potential prop
To examine whether GABA transmission to GnRH neurons is modulated between phases of the estrous cycle during which physiologic negative versus positive feedback are obeNeuro.org served, GABAergic sPSCs were recorded from GnRH neurons in brain slices obtained from diestrous PM, proestrous AM, or proestrous PM mice

Summary

Introduction

Gonadotropin-releasing hormone (GnRH) neurons form the final hormonal output pathway through which the central nervous system controls reproduction. GnRH triggers the release of the anterior pituitary hormones, LH and follicle-stimulating hormone (Schally et al, 1971), which in turn promote sex steroid production and gametogenesis. In both sexes, gonadal steroid feedback controls GnRH release and pituitary response to GnRH (Levine and Ramirez, 1982; Karsch et al, 1987; Moenter et al, 1991). At the end of the follicular phase (proestrus in rodents), sustained rising levels of estradiol switch from suppressing GnRH/LH release to inducing a surge of GnRH/LH release (positive feedback; Moenter et al, 1991; Czieselsky et al, 2016).

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