Chronic exposure of juvenile rats to environmental noise impairs hippocampal cell proliferation in adulthood

Increasing evidence indicates that chronic exposure to environmental noise may permanently affect the central nervous system. The aim of this study was to evaluate the long-term effects of early exposure to environmental noise on the hippocampal cell proliferation of the adult male rat. Early-weaned Wistar rats were exposed for 15 days to a rats' audiogram-fitted adaptation to a noisy environment. Two months later, the rats were injected with the cellular proliferation marker 5'bromodeoxiuridine (BrdU), and their brains were processed for immunohistochemical analysis. Coronal sections were immunolabeled with anti-BrdU antibodies to identify new-born cells in dentate gyrus (DG), cornu amonis areas CA1 and CA3. In addition, blood samples were obtained to evaluate corticosterone serum levels after noise exposure. All data are expressed as mean +/- standard deviation. For mean comparisons between groups, we used the Student t test. We found an increase in corticosterone serum levels after environmental noise exposure. Interestingly, noise-exposed rats showed a long-term reduction of proliferating cells in the hippocampal formation, as compared to controls. These findings indicate that chronic environmental noise exposure at young ages produces persistent non-auditory impairment that modifies cell proliferation in the hippocampal formation.