Mechanisms of ethanol-induced damage of developing brain remain to be elucidated. In cultures of rat astrocytes or intact embryos, ethanol inhibits both glucose transport and glucose oxidation via the pentose phosphate pathway (PPP). Developmental changes in the expression of brain glucose transporters, GLUT 1 and GLUT 3, suggest that these genes are regulated to meet the changing metabolic requirements of immature brain. Glucose is not only the primary energy substrate of brain, but its oxidation via the PPP is essential for production of ribose-5-phosphate which is necessary for synthesis of nucleosides and polysaccharides. The PPP is also involved in the production of NADPH for removal of free radicals and synthesis of lipids and neurotransmitters. Brief exposure to ethanol during the brain growth spurt reduces glucose transport, as well as GLUT 1 and GLUT3 proteins of neurons and astrocytes. It is proposed that these reductions result from specific regulation of the GLUT1 and GLUT3 genes by ethanol. This regulation may differ for the two transporter isoforms, and is likely to involve post-transcriptional mechanisms. In vitro studies with astrocytes and rat embryos also show that ethanol specifically inhibits activity of the PPP. It is proposed that PPP is particularly vulnerable to reduced glucose transport and that reduced activity of this pathway has significant toxicological impact on cells with critical requirements for its products. Goals of the proposed research will be to identify and characterize the mechanism by which ethanol alters glucose transporter expression in neurons and glia of developing brain. Proposed studies will use immunocytochemistry and in situ hybridization histochemistry for detecting regional changes in transporter proteins and mRNAs and for quantitation of mRNAs by northern analysis and nuclear transcription assays in specific brain regions. Transporter proteins and mRNA stabilities and post-transcriptional mechanisms will be studied in cultured neurons, astrocytes and oligodendroglia. The second major aim will be to characterize alterations in glucose utilization, indicators of oxidative stress and parameters of cell function and viability under the same conditions and to define the toxicological significance of these effects, including those on intercellular relations which might affect growth or survival.
