Long-term noise exposure causes abnormality of NMDAR2B expression and tau hyperphosphorylation and induction of apoptosis in rat hippocampus

Objective To explore the effects and mechanism of long-term noise exposure on hippocampus of rats.Methods Twenty four male Sprague-Dawley(SD) rats were grouped as control and noise exposure group.Expression of N-methyl-D-aspartic acid receptor 2B subunit(NR2B) and the level of phosphorylation of tau in hippocampus were measured after chronic noise exposure(100 dB SPL white noise,4 hours per day for 30 days).To explore the possible mechanism,we also detected neuronal cell apoptosis in hippocampus by terminal deoxynucleotidyl transfease-mediated dUTP nick end-labeling(TUNEL) reactivity.Results After long-term noise exposure,the expression of NR2B in the hippocampus decreased by 41%.Meanwhile,the chronic noise exposure also caused tau hyperphosphorylation,which was twice higher than the normal,and neuronal cell apoptosis accounted for 0.5%-1% total neuronal cells in the hippocampus.Immunohistochemistry assaies confirmed that tau hyperphosphorylation was most prominent in dentate gyrus(DG) and CA1 region in the hippcampus.Conclusion Long-term noise exposure induces abnormality of neurotransmitter system and hyperpbosphorylation of tau and the adverse effects could lead to neuronal cell apoptosis and cognition impairment.