Effects of ethanol exposure in neonatal mice on retinoic acid signaling in forebrain neurons and astrocytes

Toxicity of prenatal ethanol leading to fetal alcohol spectrum disorders (FASDs) has been linked to disturbances in retinoic acid (RA) signaling necessary for embryonic development. While ethanol exposure in the postnatal day 7 (P7) mice, which induces immediate neurodegeneration and long-lasting GABAergic cell loss and behavioral deficits, has been used for the third trimester FASD model, involvement of RA signaling in the process has not been well explored. Using RARE-LacZ reporter mice that express β-galactosidase (β-Gal) under the control of retinoic acid response element (RARE), we examined RA signaling activity of the forebrains of P8 and P30 mice with or without P7 ethanol treatment. In all experimental groups, β-Gal was expressed mainly in the hippocampus with the strongest expression in the granule cell layer of dentate gyrus. In addition, β-Gal was expressed in pyramidal neurons and parvalbumin (PV) neurons in CA1–3 pyramidal layer and in astrocytes scattered around the CA1–3 region although PV neurons were only examined at P30 because of the low PV expression at P8. β-Gal was also expressed in the anteroventral/anteromedial (AV/AM) thalamus and the retrosplenial (Rs) and Tbr1-positive (+) layer 6 cortices. β-Gal-expressing PV neurons were also found in the cortex such as Rs, while β-Gal was barely detected in somatostatin neurons in any brain regions examined. Such region and cell specific β-Gal expression was significantly higher in P8 brains than P30 brains in various brain regions. P7 ethanol reduced β-Gal expression in the CA1–3 pyramidal layer, Tbr1 + cortical layer 6, and the AV/AM thalamus at P8 or P30 or both. Although P7 ethanol decreased PV cells in CA2–3 pyramidal layers as reported, it decreased β-Gal+ PV cells more drastically. The active RA signaling found in PV neurons and the effects of P7 ethanol on the signaling suggest that reduced RA signaling by P7 ethanol may disturb PV cell maturation and enhance long-lasting brain abnormalities.