18 January 2005
Previous work demonstrated a sexually dimorphic ontogenic expression of γ-aminobutyric acid receptors (GABA<sub>B</sub>R) in rat pituitary. As sex steroids determine sex-specific expression patterns, we now studied the effect of sex hormones on pituitary GABA<sub>B</sub>R expression. GABA<sub>B</sub>R subunits, measured by Western blot and by semi-quantitative RT-PCR and luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone measured by RIA were determined in two experimental designs: First experimental design: 8- and 15-day-old females (8F, 15F); 8F and 15F treated with 100 µg testosterone propionate (TP) on day 1 of life (8F100TP, 15F100TP), 8- and 15-day-old males (8M, 15M) and 8M and 15M castrated on day 1 (8MC, 15MC). Second experimental design: 8-day-old female and male animals: 8F, 8F100TP, 8F treated with 1 µg/day TP on days 1–4 (8F1TP), 8F treated with the androgen antagonist Flutamide (Flut: 2.5 mg/100 g BW of pregnant mother on days E17-E23) (8F-Flut), 8M, 8MC, 8M treated with Flut as above (8M-Flut) and 8MC-Flut. In these animals, in addition, GABA, glutamate, aspartate and taurine were measured by HPLC in hypothalami and cortex. In the first set of experiments, GABA<sub>B1</sub>R mRNA/protein expression was higher in 8F than in 15F, 8M or 15M. In 8F100TP, GABA<sub>B1</sub>R mRNA/protein decreased to male levels. TP treatment did not alter GABA<sub>B1</sub>R expression in 15F. There was no difference in GABA<sub>B1</sub>R expression between 8M and 15M and neonatal castration did not modify its expression. In the second set of experiments, TP (1 µg) or Flut did not modify GABA<sub>B1</sub>R in 8F, while 100 µg TP continued to decrease GABA<sub>B1</sub>R expression. In 8M, Flut, alone or with castration, increased GABA<sub>B1</sub>R mRNA/protein expression to 8F. Hypothalamic GABA content followed the same pattern as pituitary GABA<sub>B</sub>R expression in 8-day-old animals, suggesting a cross-regulation. With regard to hormonal levels, 100 µg, but not 1 µg TP altered gonadotropins at 8 days, although both treatments effectively androgenized females as evidenced by lack of cycling. We conclude that androgens, acting pre- and postnatally, decrease pituitary GABA<sub>B</sub>R subunit expression.