Effect Of White Noise On Learning And Memory Of Mice And Its Underlying Mechanism

Noise can cause health injury and affect many systems, and the effect on the nervous system is most serious. The present study examines the effect of noise on spatial and emotional learning and memory of mice (Mus musculus Km) and underlying mechanism were probed. All young mice of 3-week old were divided into 2 experimental groups, the control and noise group. And noise group was exposed to 90 dB SPL white noise for two hours every day. At seventh week, the spatial and emotional learning and memory of mice were tested in Morris water maze and by step down test. To examine the the mechanism underlying effect of noise on learning and memory, the change of superoxide dismutase(SOD) activity and level of Malondialdehyde(MDA) in temporal cortex(TC), hippocampus(HIP) and inferior colliculus(IC) were detected after animals were exposed to white noise for one week, three weeks and six weeks. Besides, the change of newborn neurons in region CA3 of hippocampus were examined by 5-bromine uracil (5-BrdU) and the change of neuronal apoptosis were also examined using TUNELmethod.The experimental results were obtained as following: (1) The exposure to the noise caused growth retardation. Animals were very frightened, active very frequently in early phase, and their quantity of movement intensity decreased in later phase. (2) Compared with those mice in control group, the latency that the mice in noise group searched for a hidden under-water platform only prolonged markedly at second and third day. The latency that mice in noise group climbed on the stage were longer than those mice in control group when they were examined by step down test method. By calculating the errors made by mice in different groups, the times of happened mistakes by mice in noise group increased more markedly than the mice in control groups at first day. (3) Exposed to noise for one week, three weeks and six weeks, the SOD activity and the level of MDA in homogenate of 10% TC, HIP and IC taken from brains of mice in noise group were higher than those mice in control group. Prolonged exposure time, differences between noise group and control group decreased. (4) The newborn neurons labeled in region CA3 of hippocampus by 5-BrdU were calculated under the light microscope. The most of neurons in control group became positively colored ones, but there no positively colored neurons in noise group and they basically became vacuoles. The neuronal apoptosis in region CA3 of hippocampus was also examined with TUNEL method. The minority of neurons in control group, the large quantity of neurons in noise group by TUNEL.These experimental results described above demonstrated that long term 90 dB SPL white noise exposure (2h/day) lead to spatial and emotional learning and memory impaired. Noise exposure in the early phase increased reaction of oxidative stress in the body, and increase production of oxidative stress in the body, also enhanced the ability of anti-oxidative stress, enhanced the ability of removing the body's oxygen free radicals. In the later phase, the ability of oxygen free radicals impaired in the body, the number of neuronal apoptosis increased, while newborn neurons in the hippocampus of mice reduced.