Housing in Environmental Complexity Following Wheel Running Augments Survival of Newly-Generated Hippocampal Neurons in a Rat Model of Binge Alcohol Exposure during the Third Trimester Equivalent

Abstract

Background Binge-like alcohol exposure in neonatal rats during the brain growth spurt causes deficits in adult neurogenesis in the hippocampal dentate gyrus (DG). Previous data from our lab demonstrated that twelve days of voluntary wheel-running (WR) beginning on postnatal day (PD) 30 significantly increased the number of newly-generated cells evident in the DG on PD42 in both alcohol-exposed and control rats, but 30 days later a sustained beneficial effect of WR was evident only in control rats. This study tested the hypothesis that housing rats in environmental complexity (EC) following WR would promote survival of the newly-generated cells stimulated by WR, particularly in alcohol-exposed rats. Methods On PD4-9, pups were intubated with alcohol in a binge-like manner (5.25g/kg/day), sham-intubated, or reared normally. In Experiment 1, animals were either assigned to WR during PD30-42 or were socially housed (SH). On PD42, animals were injected with bromodeoxyuridine (BrdU; 200mg/kg) and perfused two hours later to confirm the WR-induced stimulation of proliferation. In Experiment 2, all animals received WR on PD30-42 and were injected with BrdU on the last full day of WR. On PD42, animals were randomly assigned either to EC (WR/EC) or SH (WR/SH) for 30 days and subsequently perfused and brains were processed for immunohistochemical staining to identify BrdU+, Ki67+ and BrdU+/NeuN+ labeled cells in DG. Results In Exp. 1, WR exposure significantly increased the number of proliferating cells in all three postnatal conditions. In Exp. 2, the alcohol-exposed rats given WR/SH had significantly fewer BrdU+ cells compared to control rats given WR/SH. However, WR/EC experience significantly increased the number of surviving BrdU+ cells in both the alcohol-exposed and sham-intubated groups compared to WR/SH rats of the same neonatal treatment. Approximately 80% of the surviving BrdU+ cells in the DG across the conditions were co-labeled with NeuN. Conclusions WR followed by EC could provide a behavioral model for developing interventions in humans to ameliorate hippocampal-dependent impairments associated with fetal alcohol spectrum disorders.