Mechanism of intermittent and persistent noise exposure-induced anxiety and depression-like behavior in rats / 中国职业医学

ABSTRACT

OBJECTIVE: To investigate the effects and mechanisms of intermittent and persistent noise exposure-induced anxiety and depression-like behavior in rats. METHODS: The specific pathogen free male SD rats were randomly divided into control group, four times/day intermittent noise exposure group, two times/day intermittent noise exposure group and persistent noise exposure group, with 15 rats in each group. The rats in the control group were housed in natural environment(background noise ≤50 dB), and the rats in other three exposure groups were exposed to noise with intensity of(95±2) dB of 20 to 20 000 Hz noise for four hours per day for 14 days; rats in the four times/day intermittent noise exposure group entered a five-hour quiet period every one hours of noise exposure, four times/day; rats in the two times/day intermittent noise exposure group entered a 10-hour quiet period every two hours of noise exposure, two times/day; rats in the persistent noise exposure group entered a 20-hour quiet period every four hours of noise exposure. After exposure, anxiety like behavior was evaluated by open field test and elevated cross maze test. The depression like behavior was evaluated by sugar preference test and forced swimming test. The pathological changes of neurons in the hippocampus were observed by hematoxylin-eosin(HE) staining, and the ultrastructural changes of hippocampal tissues were observed by transmission electron microscope. Chemiluminescence and colorimetry were used to detect the levels of reactive oxygen species(ROS), malondialdehyde, glutathione(GSH) and the activity of superoxide dismutase(SOD). RESULTS: In the behavioral experiment, the percentage of exercise time in the central area decreased in the three noise exposure groups(all P<0.01). The exercise distance in the central area and sugar preference index decreased in the persistent noise exposure group(both P<0.01). The percentage of open arm exercise time and open arm exercise distance decreased in the two times/day intermittent noise exposure group and persistent noise exposure group compared with the control group(all P<0.01). The open arm distance of rats in the persistent noise exposure group were lower than those in the four times/day intermittent noise exposure group(P<0.05), while the immobility time was longer than in control group and the four times/day intermittent noise exposure group(both P<0.05). The HE staining showed that the neuronal spacing in CA1 area of the hippocampus of rats was significantly widened, and the pyramidal cells showed degeneration and necrosis in the persistent noise exposure group. There was no obvious necrosis found in the neurons of the other three groups. The ultrastructure of neurons showed that most mitochondria of cells in the hippocampus of rats in the two times/day intermittent noise exposure group were swollen. In the persistent noise exposure group, some neurons of the hippocampus of rats were necrotic, the cell membrane was discontinuous, the mitochondria were swollen, and the cristae were broken, dissolved or even disappeared. The mitochondrial structure of the hippocampus of rats in the other two groups was normal. The activity of SOD in the hippocampus of rats decreased in the four times/day intermittent noise exposure group(P<0.05), and the activity of SOD and the level of GSH in the hippocampus of rats decreased in the two times/day intermittent noise exposure group(both P<0.05), compared with the control group. The level of ROS and malondialdehyde in the hippocampus of rats in the persistent noise exposure group increased(all P<0.05), while the SOD activity and GSH level decreased(all P<0.05), compared with the other three groups. CONCLUSION: Intermittent noise exposure causes less anxiety and depression-like changes in rats than persistent noise exposure. Noise may cause anxiety and depression in rats through oxidative stress pathways.