Lack of Functional GABAB Receptors Alters Kiss1, Gnrh1 and Gad1 mRNA Expression in the Medial Basal Hypothalamus at Postnatal Day 4

Abstract

Background/Aims: Adult mice lacking functional GABA_B receptors (GABA_B1KO) show altered Gnrh1 and Gad1 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_B1KO mice. Methods: PND4 wild-type (WT) and GABA_B1KO mice of both sexes were sacrificed; tissues were collected to determine mRNA expression (qPCR), amino acids (HPLC), and hormones (RIA and/or IHC). Results: GnRH neuron number (IHC) did not differ among groups in olfactory bulbs or OVLT-POA. Gnrh1 mRNA (qPCR) in POA-AH was similar among groups. Gnrh1 mRNA in medial basal hypothalamus (MBH) was similar in WTs but was increased in GABA_B1KO females compared to GABA_B1KO males. Hypothalamic GnRH (RIA) was sexually different in WTs (males > females), but this sex difference was lost in GABA_B1KOs; the same pattern was observed when analyzing only the MBH, but not in the POA-AH. Arcuate nucleus Kiss1 mRNA (micropunch-qPCR) was higher in WT females than in WT males and GABA_B1KO females. Gad1 mRNA in MBH was increased in GABA_B1KO females compared to GABA_B1KO males. Serum LH and gonadal estradiol content were also increased in GABA_B1KOs. Conclusion: We demonstrate that GABA_BRs participate in the sexual differentiation of the ARC/MBH, because sex differences in several reproductive genes, such as Gad1, Kiss1 and Gnrh1, are critically disturbed in GABA_B1KO mice at PND4, probably altering the organization and development of neural circuits governing the reproductive axis.