Modulatory effects of GLT-1 enhancer, MC-100093, on glutamate uptake and associated signaling pathways in female and male alcohol preferring rats exposed to ethanol

Abstract

Background: Ethanol consumption disrupts glutamate homeostasis in several brain regions. The uptake of extracellular glutamate is regulated in the majority by the astrocytic glutamate transporter 1 (GLT-1), and cystine-glutamate exchanger (xCT) contributes to this regulatory effect. Chronic ethanol consumption is well known to downregulate GLT-1 expression in several reward brain regions, including the nucleus accumbens (NAc).

Objectives: Recently, we reported that a novel beta-lactam, MC-100093, attenuated ethanol consumption and normalized the expression of GLT-1 in the subregions of the NAc. Based on these findings, we aimed in this study to determine the dose-dependent effect of MC-100093 in attenuating ethanol consumption and whether this attenuating effect is associated with restoration of glutamate uptake. In addition, we focused on whether the effects of MC-100093 on GLT-1 are mediated through the mammalian target of rapamycin (mTOR), protein kinase B (Akt), and nuclear factor-kappa B (NF-κB) signaling pathways.

Methods: Male and female alcohol-preferring (P) rats are grouped into 4 groups. Other than control groups all the 3 groups had free access to ethanol (15% and 30% v/v), and water for 5 weeks. On week 6, rats received intraperitoneal injection (i.p.) of MC-100093 at a dosage of 100 or 150 mg/kg, or saline, for 5 days. The Na+ dependent and Na+ independent glutamate uptake is measured by radioactive glutamate uptake assay. The expression of GLT-1, xCT, mTOR, phospho-Akt (p-Akt), kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IkBa), and NF-κB are determined by Western blot analysis.

Results: MC-100093 treatment reduced ethanol drinking in male and female P rats. MC-100093 was associated with an increase in Na+-dependent and Na+-independent glutamate uptake. Furthermore, MC-100093 treatment attenuated ethanol-induced decrease in GLT-1, xCT, NF-κB, and p-Akt expression in the NAc.

Conclusions: These findings demonstrate that MC-100093 attenuated ethanol consumption and regulated glutamate uptake through normalizing GLT-1 expression.

Keywords: GLT-1; MC-100093; glutamate; nucleus accumbens; xCT.