Microglial activation in the developing rodent brain following single-day moderate binge-alcohol exposure

Alcohol has been shown to activate microglia, the immune cells of the brain, which may contribute to lasting deficits in cognitive functioning seen in humans with Fetal Alcohol Spectrum Disorders (FASD) and in rodent models of FASD. Previous studies using rat models have looked at microglial activation following alcohol exposure in the adolescent and adult brains, or the long-term effects of neonatal alcohol exposure. This current study adds to the newly growing literature on the short- term immune response of the brain to neonatal alcohol exposure, by expanding the timeline of microglial activation through measurement of microglial cell counts and inflammatory cytokine expression in the developing hippocampus. Cells were counted in three separate subregions of the three hippocampal subfields: Dentate gyrus: hilus, granule cell layer, molecular layer; CA1 and CA3: stratum oriens, pyramidal cell layer, stratum radiatum. Male and female rat pups were exposed to alcohol on postnatal day (PD) 4 to model a single binge-like exposure during the third trimester in humans, and effects within the hippocampus were measured on PD5 and PD8. We hypothesized that neonatal alcohol exposure would lead to an increase in microglial cell counts and inflammatory cytokine release, and that sex differences would be observed. The results support this hypothesis: an increase in PD5 microglial cell counts was seen in alcohol-exposed (AE) male rats in the hilus and molecular layer of the dentate gyrus compared to suckle controls (SC). Males generally had higher levels ix of microglia in all hippocampal subregions except for the hilus of the dentate gyrus, when compared with females. Females exhibited an opposite effect in the dentate gyrus: a decrease in cell counts following alcohol exposure in the granule cell layer and molecular layer when compared to sham-intubated (SI) controls. The increases in the pro-inflammatory cytokines CCL4 and IL-1β in alcohol exposed animals were not statistically significant compared to controls, but may reach significance upon further addition of animals. However, when the data from both sexes were combined, significant increases in CCL4 expression were seen in AE and SI animals compared to SC. following These findings are significant as they add to our knowledge of specific sex-dependent effects of alcohol on microglia in developing brain.University of Delaware, Department of Psychological and Brain SciencesM.S