Sexual dimorphic expression of GABAB receptors between infantile male and female rat pituitaries is associated to baclofen-induced intracellular signalling differences.

MS BIANCHI; V CALVO; C LIBERTUN; V LUX-LANTOS

Washington DC. USA.

Congreso; The Endocrine Society (USA). 91th Annual Meeting. 2009; 2009

The Endocrine Society

Previously, we reported the presence of sexual differences in GABAB receptor (GABABR) expression in rat pituitaries at early stages of postnatal development, due to the perinatal circulating androgens in males (1,2). GABABR activation alters the activity state of transcription factors in the nucleus, such as CREB2 and ATFx, to regulate programs of gene expression (3). Therefore differences in GABABR expression may be associated to the pituitary sexual differentiation process through gene transcription modulation. Here our aim was to evaluate whether the sexual dimorphism in pituitary GABABR expression in infantile rats was associated to differential intracellular signalling post receptor activation. We performed primary pituitary cell cultures (PPCC) from male and female, 6-7 day-old Sprague-Dawley rats, which were stimulated with different concentrations of Baclofen, a GABABR agonist (Bac) or medium, as control. cAMP (RIA), inositol phosphates (ionic exchange cromatography after pre-incubation with 3H-inositol), MAPK and CREB2 phosphorylation (Western blots) were studied. Bac 10-4M inhibited basal adenilil ciclase activity, decreasing intracelular AMPc levels in female PPCC (51% from control, p<0.05) but not in males. No effect of Bac on forskolin-stimulated (5.10-7M) adenilil ciclase activity was observed in either sex. Bac 10-4M significantly decreased IP3 levels only in female PPCC after 30 minutes of incubation (IP3/total IPs: control: 0.0109±0.0013 vs Bac 10-4M: 0.0064±0.0010, p<0.05). Females also showed higher basal IP3 levels than males (p<0.05). As GABABR stimulation activates ERK1/2 in the nervous system and promotes CREB2-mediated gene transcription (4), PPCC from both sexes were incubated during 0, 5, 15, 30 and 60 minutes with either Bac or GnRH 10-7M (positive control) and ERK1/2 activation was determined. Bac 10-4M induced ERK1/2 phosphorylation only in female PPCCs, increasing significantly after 5 minutes stimulation and reaching basal level after 60 minutes. This sexual difference was stimulus specific, as no sex differences in the ERK1/2 response to GnRH was observed. Finally, the effect of Bac on CREB2 activation was determined at these same time points. Males showed higher basal CREB2 phosphorilation but Bac 10-4M was capabled to induce CREB2 activation only in females In conlusion, the sexual difference in pituitary GABABR expression is accompanied by marked differences in the intracellular pathways elicited post receptor activation. (CONICET, UBA, ANPCYT). 1Neuropharmacology 2001, 40:185-192 2Neuroendocrinology 2004, 80:129-142 3PNAS 2000, 97:13967-13972) 4Cell Signal. 2007, 19:1996-2002)