Chronic Noise Exposure Caused Low-anxiety In Mice And Its Molecular Mechanisms

Noise, unharmonious sound, is combined by a variety of different frequencies and intensity sounds, which is recognized as a serious health disruptor in our modern societies. Noise can result in the immune, respiration, cardiovascular system disorders. In recent years, the impact of noise in center nervous system is concerned. Chronic noise can not only damage cochlear system, resulting in hearing loss, but also can cause sleep disturbance, reduce work memory and neurogenesis. However, the report about the effects of noise on emotion and attention, especially in adolescence, is limited.In this paper, C57BL/6 male mice (postnatal 6 weeks) were continued exposure to noise environment for 30 days. Then the behavior of emotion and attention were detected by behavior tests and the potential molecular basis of behavior abnormal was analyzed using real time quantitative PCR.1. Showed low-anxiety behavior after mice exposure to chronic noiseTo explore the effects of noise on emotion and attention, the C57BL/6 male mice (postnatal six weeks) were exposed to noise, white noise, music and environment noise (control) stimulates separately (75 dB,8 h daily for 30 days), then their behaviors were analyzed. The behavioral results showed that the noise group explored the center portion of the environment (as a percentage of total exploratory activity) more than the other groups did in open field test. The noise mice explored the light compartment to a greater extent than the others did in light-dark box test and exhibited lower immobility time in forced swim test compared to the control group, with marked difference. These results demonstrated that chronic noise induced low-anxiety behavior in mice. In addition, in trace fear conditioning test, the freezing of baseline in training stage in noise group is lower than the others, while noise group mice showed lower latency to center region, which confirmed once again that the noise group mice exhibited low-anxiety behavior phenotype. Detecting the attention behavior, we obtained that chronic noise exposure didn't influence the attention behavior bases on the following results:the time spent freezing in the cued test was similar separately at each of three consecutive tones testing among the four groups; exploration time in new object also has no difference in novel object exploratory test; at the same time noise mice exhibited similar nest building ability.2. To explore the molecular mechanism resulting in low-anxiety by Q-PCR.We detected the mRNA expression of correlative molecules in hippocampus (including amygdale), prefrontal cortex and hypothalamus regions from the four groups using real time quantitative PCR. We found, in hippocampus, NR1 mRNA level in noise and white noise group increased compared to control and music group, and the NR2A/NR2B ratio in noise group was markedly lower than other three groups did; In prefrontal cortex, the ratio of noise and white noise group reduced compared to control and music group; And the ratio of noise group also showed lower than control mice in the hypothalamus. The expression of GAD65 mRNA, not GAD67 mRNA, decreased all in hippocampus, prefrontal cortex in noise and white noise group. In hippocampus and hypothalamus, we found that the GABAAα1/GABAAa3 ratio in noise mice was lower than control and music group, and the ratio in white noise mice also decreased compared to music group. In prefrontal cortex, the ratio of noise and white noise group also decreased compared to control and music group. Meanwhile, the expression level of BDNF and htr2a also reduced in noise group.These results showed the mice exhibited excited or low-anxiety behavior after being exposed to chronic noise, and the mechanism might be that the glutamatergic neurons activity was enhanced while the GABAergic neurons activity was reduced, and maybe also regulated by 5-HT receptor and BDNF. 3. The concentration of monoamine neurotransmitter in the brainBy using capillary electrophoresis assay, monoamine neurotransmitters in cortex, hippocampus, hypothalamus and other forebrain regions were detected in control and noise group mice. The results exhibited that the concentration of 5-serotonin(5-HT), epinephrine (E) and norepinephrine (NE) in the whole brain of the noise group mice decreased markedly, while the level of dopamine increased compared to control group mice. These results demonstrated that noise exposure can change the level of monoamine neurotransmitter. However, whether this is a direct result or not induced by noise needs to be further investigated.