Effect Of Medium Intensity White Noise Exposure On Cognitive Function Of Young Mice And Its Underlying Mechanisms

In this paper, we explored the effects of medium intensity white noise exposure on cognitive ability of young mice and its underlying mechanisms. 3-weeks-old mice were chosen as experimental animals (n = 110). Among the 110 mice, 22 young mice were exposed to medium intensity white noise (80 dB SPL) for 6 weeks and then were examined the basic sound response properties of inferior colliculus (IC) including minimal threshold (MT), latency (LAT), characterizing frequency (CF). The other 88 young mice were divided into 8 groups (11 in each group): 3 days' noise exposure group and its control group, 1 week's noise exposure group and its control group, 3 weeks' noise exposure group and its control group, 6 weeks' noise exposure group and its control group. The control groups were fed normally; the noise groups were exposed to 80 dB white noise 2 hours per day. After being exposed to noise for different time, we detected the learning and memory ability by Morris water maze and step down inhibitory avoidance tests; at the same time we also detected the value of malondialdehyde (MDA) and superoxide dismutase (SOD) of hippocampus (Hc), auditory cortex (AC) and inferior colliculus (IC) of the mice. We also detected the level of hyperphosphorylated tau of hippocampus of mice by Western-blot. The results were as follows: (1) The mice were scared and fidgety in the early period during noise treatment and in the late period of noise exposure, the mice were primness and moveless. (2) Compared with control, the avoidance latency was prolonged in Morris water maze and in step down inhibitory avoidance tests, the step down avoidance latency was shorten and the number of errors was increased after being exposured to medium intensity white noise. All the parameters above were positive association with the exposure time. (3) Compared with control, after 6 weeks' medium intensity white noise exposure, the minimum threshold of neurons in inferior colliculus rose, the latency of neurons in inferior colliculus increased, and the bandwidth of frequency tuning curve at MT+10 dB and MT+20 dB narrowed. (4) Compared with control, after 3 days' exposure, MDA level of hippocampus increased significantly, and the rate of SOD to MDA decreased significantly; after 1 week's exposure, MDA level of inferior colliculus also increased evidently; after 3 weeks' and 6 weeks' exposure, MDA level of hippocampus, auditory cortex and inferior colliculus were all increased, and the rate of SOD to MDA were all decreased. (5) Compared with control, after 1 week's, 3 weeks' and 6 weeks' exposure, the level of tau phosporylation in hippocampus increased significantly. All the results above indicated that medium intensity white noise exposure impaired the spatial and emotional learning and memory. At the same time, the sound response properties of neurons in inferior colliculus changed, oxidative stress increased in hippocampus, auditory cortex and inferior colliculus and tau was hyperphosphorylated in hippocampus. So, we presumed that the impairment of cognitive function induced by medium intensity white noise exposure was associated with the change of neurons' sound response properties of inferior colliculus, and the oxidative stress injury and tau hyperphosphorylation were all involved in .