Estrogen Regulates Gaba Vesicular Contents via Modulation of Astrocyte Glutamate-Glutamine Cycle---Implications for Sex Difference

Males and females exhibit many different phenotypes throughout the body, including the brain. The rodent brain’s sexual differentiation is mostly dependent on steroid hormonal exposure, especially estradiol, during a “sensitivity period” starting in late gestation (embryonic 18) and ending in the early neonatal life (PN 7-10). The action of estradiol at this critical time period results a permanent determination of anatomical and physiological sexual dimorphisms in adult brain. However, the mechanism of estradiol mediating these changes is still elusive. The inhibitory neurotransmitter, GABA, is involved in regulation of sexually dimorphic patterns of behavior and gonadotropin secretion in the adult. Recent evidences suggest that estradiol could up-regulate the astrocytic glutamine synthetase, an enzyme involving in astrocytic glutamate-glutamine cycle which provides the main source of glutamate utilized for synthesis of vesicular GABA. The present proposal will explore cellular mechanism of estradiol contributes to brain sexual differentiations in several sexually dimorphic nucleus of neonatal males and females. Studies are designed to specifically test the central hypothesis: estradiol modulates GABA vesicular content via increasing astrocytic glutamine synthesis which concomitant enhances the efficacy of glutamate-glutamine cycle in sexually dimorphic nucleus of neonatal brains causing brain sexual differentiations. To test this hypothesis, the cellular properties of the brain preoptic areas and hypothalamic arcuate nucleus are to be studied in brain slices dissected from neonatal males and females, and pharmacological interventions in intact male pups and sexual behavior test in intact adult males are to be examined. Research directed at testing the central hypothesis will focus on 3 specific aims: Aim 1: To determine whether the glutamate-glutamine cycle regulates the inhibitory synaptic strength in brain’s sexually dimorphic nucleus such as preoptic areas, arcuate nucleus in either sex of neonatal animals during the critical period of sex differentiation. Aim 2: To assess whether the increase astrocyte glutamine synthesis effect of estrogen contributes to augmenting vesicular GABA content. Aim 3: To determine strategies to restore glutamate-glutamine cycle function for sustaining GABA transmission during the critical period in pups with malfunctioning sex differentiation. Using the combination of electrophysiological, pharmacological analyses and whole animal approaches, the present proposal will test 1) the roles of the astrocytic glutamate-glutamine pathway on the modulation of GABAergic synaptic strength in brain’s sexually dimorphic nucleus of both sex pups. 2) the cellular mechanisms of estrogen on modulation of GABAergic synaptic strength via glutamate-glutamine pathway during critical period of sexual differentiation. 3) whether the impairment of estrogen-induced sexual differentiation is reversible by pharmacological intervention during the critical period. This research would shed light on the mechanism of estrogen-induced brain sexual differentiation and the impairment of glutamate-glutamine cycle may link to cause malfunction of sex differentiation. Such knowledge should offer important insights into the cellular basis of brain sex differentiation and the development of new pharmacological agents in the prevention of brain malfunctioning sex differentiation during the critical period.

Project ID:PC9902-2175
External Project ID:NSC98-2320-B182-039-MY2