Lack of Functional GABA<sub>B</sub> Receptors Alters <b><i>Kiss1</i></b>, <b><i>Gnrh1 </i></b>and <b><i>Gad1</i></b> mRNA Expression in the Medial Basal Hypothalamus at Postnatal Day 4

Abstract

<b><i>Background/Aims:</i></b> Adult mice lacking functional GABA<sub>B</sub> receptors (GABA<sub>B1</sub>KO) show altered <i>Gnrh1</i> and <i>Gad1</i> expressions in the preoptic area-anterior hypothalamus (POA-AH) and females display disruption of cyclicity and fertility. Here we addressed whether sexual differentiation of the brain and the proper wiring of the GnRH and kisspeptin systems were already disturbed in postnatal day 4 (PND4) GABA<sub>B1</sub>KO mice. <b><i>Methods:</i></b> PND4 wild-type (WT) and GABA<sub>B1</sub>KO mice of both sexes were sacrificed; tissues were collected to determine mRNA expression (qPCR), amino acids (HPLC), and hormones (RIA and/or IHC). <b><i>Results:</i></b> GnRH neuron number (IHC) did not differ among groups in olfactory bulbs or OVLT-POA. <i>Gnrh1</i> mRNA (qPCR) in POA-AH was similar among groups. <i>Gnrh1</i> mRNA in medial basal hypothalamus (MBH) was similar in WTs but was increased in GABA<sub>B1</sub>KO females compared to GABA<sub>B1</sub>KO males. Hypothalamic GnRH (RIA) was sexually different in WTs (males > females), but this sex difference was lost in GABA<sub>B1</sub>KOs; the same pattern was observed when analyzing only the MBH, but not in the POA-AH. Arcuate nucleus <i>Kiss1</i> mRNA (micropunch-qPCR) was higher in WT females than in WT males and GABA<sub>B1</sub>KO females. <i>Gad1</i> mRNA in MBH was increased in GABA<sub>B1</sub>KO females compared to GABA<sub>B1</sub>KO males. Serum LH and gonadal estradiol content were also increased in GABA<sub>B1</sub>KOs. <b><i>Conclusion:</i></b> We demonstrate that GABA<sub>B</sub>Rs participate in the sexual differentiation of the ARC/MBH, because sex differences in several reproductive genes, such as <i>Gad1</i>,<i> Kiss1</i> and<i> Gnrh1,</i> are critically disturbed in GABA<sub>B1</sub>KO mice at PND4, probably altering the organization and development of neural circuits governing the reproductive axis.