Role of Astrocyte Glutamate-Glutamine Cycle in the Regulation of Vesicular Glutamate Content during the Sensitive Period of Brain Sexual Differentiation

Synaptic vesicle content is dynamically in equilibrium with intraterminal neurotransmitter or its precursor concentration, e.g. increasing axon terminals concentration of glutamate (Glu) or its precursor, glutamine (Gln), will rapidly elevate the Glu vesicle content. Gln transported via astrocyte glutamate-glutamine cycle (GGC) is used for sustaining glutamatergic (Gluergic) synaptic transmission in the adult brain. Moreover, the sex difference of brain phenotypes is due to early exposure estrogen to the neonatal male, but not the female brain, during the sensitive period. Estrogen acts on its membrane receptors to increase release probability of Glu vesicles. Glu acting on Glu receptors determines permanently the sexual dimorphisms of spine morphology of the brain and behavioral differences of the animals. Recent studies demonstrate that estradiol (E2) up-regulates protein expressions of two GGC enzymes: Gln synthetase (GS) and glutaminase; E2 also increases extracellular Gln and Glu concentrations. We also found that the males express significantly higher GS and glutaminase proteins than the females during the sensitive period in the MBH. Blockade of neuronal Gln uptake significantly reduced protein expressions of glutaminase and spinophilin (spine marker) as well as vesicular Glu content of the males but not the females. Early exposure E2 to the neonatal females for mimicking the male brain reduced their adult lordosis behavior, which can be partially recovered by co-administration of E2 with the GS inhibitor. These data suggest that the E2-mediated sexual dimorphisms of the brain could be due to an up-regulation of the GGC efficacy and subsequent increase Glu vesicle content and Gluergic synaptic strength. The proposal will explore cellular mechanisms of E2-mediated sexual differentiation, focusing on the changes of GGC-mediated Glu vesicle content, in the sexually and non-sexually dimorphic brain nuclei including MBH, preoptic areas (POA) and hippocampus CA1. Study was designed to specifically test the central hypothesis: E2-mediated sex differences in spine morphology and behavior are due to E2 increases Glu vesicle content by enhancing the GGC efficacy, and subsequent increases Glu synaptic strength under active synapses. Therefore, malfunctions of adult reproductive behaviors, due to deprived the E2 exposure to the males or early exposure E2 to the females, can be recovered by manipulating the GGC efficacy during the sensitive period. To test the hypothesis, the changes of Glu vesicle content and Gluergic synaptic strength of MBH, POA and hippocampus CA1 neurons under pharmacologically manipulations of the GGC, the changes of protein expression of the GGC enzymes, and the changes of reproductive behavior in the adult animals will be examined. Research directed at testing the central hypothesis will focus on three specific aims: Aim 1: to assess whether the GGC regulates Glu vesicle content and Gluergic synaptic strength in the MBH, POA and hippocampus of neonates during the sensitive period of sexual differentiation. Aim 2: to examine whether E2 regulates Glu vesicle content and Gluergic synaptic strength under active synapses via modulation of the GGC efficacy in the neonatal MBH, POA, and hippocampus during the sensitive period. Aim 3: to determine strategies to restore the function of the GGC for maintaining Glu vesicle content and Gluergic synaptic transmission in neonates that are under the process of malfunctioning sexual differentiation during the sensitive period. This research would shed light on the cellular mechanism of E2-induced brain sexual differentiation and impairment of GGC may link to cause malfunction of sexual differentiation during the sensitive period.

Project ID:PC10308-0637
External Project ID:MOST103-2320-B182-006