Persistent Impairment of Hippocampal Neurogenesis in Young Adult Rats Following Early Postnatal Alcohol Exposure

Abstract

BACKGROUND: Prenatal alcohol exposure can cause damage to the developing fetus with outcomes including growth deficiency, facial dysmorphology, brain damage, and cognitive and behavioral deficits. Smaller brains in children with FASD have been linked both with reduced cell proliferation in the developing CNS and with apoptotic cell loss of postmitotic neurons. Prenatal alcohol exposure in rodents during the period of brain development comparable to that of the first and second trimesters of human pregnancy persistently alters adult neurogenesis. Long-term effects of alcohol exposure during the third trimester equivalent, which occurs postnatally in the rat, on adult neurogenesis have not been previously reported. The goal of this study was to examine the effect of postnatal binge-like alcohol exposure on cell proliferation and neurogenesis in hippocampal dentate gyrus during adolescence and young adulthood. METHODS: Male Long-Evans rat pups were assigned to 3 groups: alcohol-exposed (AE), sham-intubated (SI) or suckle control (SC). AE pups received ethanol in a milk formula in a binge manner (2 feedings, 2 hours apart, total dose 5.25 g/kg/day) on postnatal days (PD) 4-9. BrdU was injected every other day on PD30-50. Animals were perfused either on PD50 to examine cytogenesis and neurogenesis in hippocampal dentate gyrus at the end of BrdU injections or on PD80 to evaluate new cell survival. Dorsal hippocampal sections were immunostained for BrdU, a marker for proliferating cells, Ki67, endogenous marker of proliferation, and NeuN, a marker for mature neurons. RESULTS: Binge-like alcohol exposure on PD4-9 significantly reduced the number of mature neurons in adult hippocampal dentate gyrus (DG) both on PD50 and PD80, without altering cumulative cytogenesis on PD50. In addition, the number of new neurons, that were generated between PD30 and 50, was further reduced after 30 days of survival in all 3 groups (SC, SI, and AE). CONCLUSIONS: These observations suggest that early postnatal binge alcohol exposure results in long-term deficits of adult hippocampal neurogenesis, providing a potential basis for the deficits of hippocampus-dependent behaviors reported for this model.