Effects of chronic noise exposure on spatial learning and memory of rats in relation to neurotransmitters and NMDAR2B alteration in the hippocampus.

OBJECTIVES The purpose of this study was to examine the effects of noise exposure on spatial learning and memory and associated mechanisms in the hippocampus (HIP). METHODS Forty-eight male SD rats were grouped as: A, control; B, Morris water maze (MWM) training group; C, noise exposure group; and D, noise exposure followed by MWM training group. The influence of noise stress on spatial learning and memory in rats was assessed in hidden platform acquisition training and probe trial testing in MWM. Changes in morphology of Nissl bodies were observed in the CA1, CA3 and DG regions of HIP. In order to understand the possible mechanisms behind noise stress-induced changes, the concentration of amino acid neurotransmitters and the expression of NMDAR2B (NR2B) in HIP were also evaluated. RESULTS After noise exposure, the performance of spatial learning and memory in group D was decreased significantly compared to group B. The concentration of glutamate was significantly increased in groups C and D, whereas GABA decreased markedly. The mean optical density of Nissl bodies in groups C and D was reduced in the CA1, DG and CA3 regions. The expression of NR2B was significantly decreased in the CA1, CA3 and DG regions in group C, and in the CA1 and CA3 regions in group D as compared with groups A and B. CONCLUSIONS Excitotoxicity, impaired Nissl bodies and reduced expression of NR2B in rat HIP induced by chronic noise exposure might have caused the impairment of spatial learning and memory.