THU190 Deletion Of The Glucocorticoid Receptor From GABAergic Neurons Causes Early Puberty In Male And Female Mice

Disclosure: S.A. Pereira: None. L. Arvizu-Sanchez: None. A.N. Fontes: None. R.S. Carroll: None. V.M. Navarro: None. U.B. Kaiser: None. Background and Objectives: Glucocorticoid (GC) secretion induced by various types of stress can negatively impact reproduction through effects at several levels of the hypothalamic-pituitary-gonadal (HPG) axis, including inhibition of gonadotrophin-releasing hormone (GnRH) secretion and suppression of luteinizing hormone (LH) release. KNDy neurons, expressing kisspeptin, neurokinin B and dynorphin A, are the GnRH and LH pulse generator and are key regulators of puberty. These neurons are proposed to play an important role in mediating the effects of stress and GC on reproduction. While the precise mechanisms by which stress affects regulation of KNDy neurons remain to be fully characterized, it is known that KNDy neurons are subject to regulation by multiple neural networks, among which GABAergic neurons appear to play a determinant role. Importantly, a large proportion of GABAergic neurons express glucocorticoid receptors (GR). We therefore hypothesized that stress, through the action of GC on GR in GABAergic neurons, affects the activity of KNDy neurons to impact puberty timing. Methods and Results: We generated mice with conditional deletion of GR in GABAergic neurons using Vgat(Cre) mice crossed with GR(lox/lox) mice to generate Vgat(Cre);GR(lox/lox) mice (GABA(GRKO)). The pubertal phenotypes of these GABA(GRKO) mice and their littermate controls (GR(lox/lox)) were characterized. Male GABA(GRKO) mice had earlier preputial separation compared to GR(lox/lox) littermate controls (GABA(GRKO) 29.8 ± 0.45 days vs. GR(lox/lox) 33.5 ± 0.57 days; p < 0.0001). Female GABA(GRKO) mice had a similar age of vaginal opening (GABA(GRKO) 25.7 ± 0.76 days vs GR(lox/lox) 24.5 ± 0.87 days; p = 0.2810) but had significantly earlier first estrus compared to their GR(lox/lox) littermate controls (GABA(GRKO) 32.4 ± 0.76 days vs GR(lox/lox) 37.9 ± 0.79 days; p < 0.0001). Male and female mice were euthanized at 30 days of age and their mediobasal hypothalamus (MBH) were collected for mRNA measurement by RT-qPCR of genes known to be related to pubertal development, including Kiss1, Tac2, Pdyn, Agrp and Pomc. Kiss1 and Pdyn expression were significantly higher in the MBH of GABA(GRKO) males compared to controls; in contrast, Pdyn expression was significantly lower in the MBH of GABA(GRKO) females and Kiss1 expression was unchanged compared to controls. Agrp expression was lower in the MBH of both GABA(GRKO) male and female mice compared to controls. No differences were observed in Tac2 and Pomc expression. Data sets are mean ± SEM. Statistical significance was considered at p < 0.05. Conclusions: The deletion of GR in GABAergic neurons results in early puberty onset, sexually dimorphic changes in Pdyn mRNA levels and downregulation of Agrp mRNA expression in male and female GABA(GRKO) mice. These findings suggest a role of glucocorticoids acting on GR in GABAergic neurons upstream of KNDy neurons to restrain the timing of their activation to initiate puberty. Presentation: Thursday, June 15, 2023