GABA_B1 Knockout Mice Reveal Alterations in Prolactin Levels, Gonadotropic Axis, and Reproductive Function

Abstract

γ-Aminobutyric acid (GABA) has been implicated in the control of hypophyseal functions. We evaluated whether the constitutive loss of functional GABA_B receptors in GABA_B1 knockout (GABA_B1^–/–) mice alters hormonal levels, under basal and stimulated conditions, and reproductive function. The serum hormone levels were measured by radioimmunoassay, the estrous cyclicity was evaluated by vaginal lavages, and the mating behavior was determined by the presence of vaginal plugs. A moderate hyperprolactinemic condition was observed, in which prolactin increase and thyroid-stimulating hormone decrease were similar between genotypes. Basal luteinizing hormone (LH), follicle-stimulating hormone, thyroid-stimulating hormone, and growth hormone levels were similar between genotypes in each sex. Analysis of the gonadotropin axis revealed no differences in puberty onset between female genotypes. In con trast, the estrous cyclicity was significantly disrupted in GABA_B1^–/– female mice, showing significantly extended periods in estrus and shortened periods in proestrus. Reproduction was significantly compromised in GABA_B1^–/– females, with a significantly lower proportion of mice (37.5%) getting pregnant during the first 30 days of mating as compared with wild-type controls (87.5%). Moreover, only 14% of vaginal plug positive GABA_B1^–/– females had successful pregnancies as compared with 75% in the controls. In addition, the postovariectomy LH rise was significantly advanced in GABA_B1^–/– mice, while the response to estradiol feedback was similar in both genotypes. In conclusion, our endocrine analysis of GABA_B1^–/– mice reveals that GABA_B receptors are involved in the regulation of basal prolactin titers. Moreover, the hypothalamic-hypophyseal-ovarian axis is seriously disturbed, with alterations in cyclicity, postcastration LH increase, and fertility indexes. The molecular mechanism underlying these hormonal disturbances remains to be addressed.

Postnatal development of the endocrine pancreas in mice lacking functional GABABreceptors

“…In addition to the results shown here, we have described previously that adult body weights showed no significant genotype differences for either sex (15), similar to PND4 mice. Moreover, fasted blood glucose did not differ between genotypes in adults, but fasted insulin levels were increased in adult GABA B1 KO males (7), suggesting insulin resistance in this sex.…”

“…Mice were genotyped by PCR analysis, as described previously (15). All animals were housed in groups and maintained at 22°C on a 12:12-h light-dark cycle with free access to laboratory chow and tap water.…”

“…Total RNA was isolated from TRIzol homogenates according to the manufacturer's protocol and kept at Ϫ70°C until use; 0.5 and 5 g of RNA, extracted from adult and PND4 tissue, respectively, were reversetranscribed in a 20-l reaction using Moloney murine leukemia virus reverse transcriptase (Epicentre, Madison, WI) and oligo(dT) 15 primers (Biodynamics, Buenos Aires, Argentina). The reverse transcriptase was omitted in control reactions, where the eventual absence of an amplification product indicated the isolation of RNA free from genomic DNA.…”

Withdrawal of dietary phytoestrogens in adult male rats affects hypothalamic regulation of food intake, induces obesity and alters glucose metabolism

“…Serum insulin was assessed by RIA using an anti-rat insulin antibody (Sigma, St. Louis, Missouri, USA) and standard rat insulin provided by Laboratorios Beta (Buenos Aires, Argentina). TSH was determined by competitive RIA according to the procedure outlined by Catalano et al (2005). The levels of total T4, estradiol and testosterone were measured using competitive RIA kits (Immunotech, Marseille, France).…”

Lack of functional GABAB receptors alters GnRH physiology and sexual dimorphic expression of GnRH and GAD-67 in the brain

“…In this regard, we showed that GABA B R subunits have particular ontogenic expression patterns in the rat hypothalamus and the pituitary (9,10) and that their expressions show sexual dimorphisms at early stages of development (8,9). In GABA B1 knockout (GABA B1 KO) mice, which lack functional GABA B Rs (79), we demonstrated that GABA B Rs are involved in regulating basal prolactin (PRL) release in males and that the hypothalamic-hypophyseal-ovarian axis is compromised in females, with significant alterations in cyclicity, postcastration LH increase, and reproduction indexes (14). Because GABA B receptors have been demonstrated to participate in the regulation of the gonadotropic axis, and taking into consideration our previous results in GABA B1 KO mice, we studied different parameters involved in the regulation of the hypothalamic-pituitary gonadotropic axis in adult male and female GABA B1 KO mice to establish the impact of the loss of functional GABA B Rs.…”