Effects of first trimester binge alcohol exposure on developing white matter in fetal sheep

Heavy prenatal alcohol exposure is associated with neurodevelopmental abnormalities. Neuropathologic and neuroimaging studies have shown a wide range of structural problems, including abnormal neuronal migration and volume reduction in specific brain regions, including white matter. We identified foci of significant fetal white matter microglia-macrophage immunoreactivity in a binge model of early prenatal alcohol exposure in sheep. Ewes of alcohol-exposed fetuses received daily 90 min alcohol (1.5 gm/kg i.v.) infusions at 30-60 d gestation (term = 147 d). Ewes of control fetuses received same volume infusions of normal saline intravenously. Near-term (125 d gestation) fetal brains were labeled with microglia-macrophages using HAM56 antibody. We quantified dense immunoreactive cellular regions across sections and anatomical locations using computer-assisted microscopy and quantitative morphometry. The proportional HAM56-positive area in cortical white matter was greater in the alcohol-exposed fetuses (1.6%) compared with the saline controls (0.7%). The areas were localized to the frontal gyral white matter, temporal gyral white matter, optic radiation, and others (corpus callosum, septum pellucidum, fasciculus subcallosus, and external capsule), with a greater distribution in the gyral white matter. The greater area of macrophage-rich regions in near-term fetal sheep brain suggests a vulnerability of developing white matter that is enhanced by early alcohol exposure.