Effect Of Noise On The Auditory System Of Mammalian

1 ObjectiveTo investigate the hearing levels and hair cell damages of guinea pigs, which were exposed to the music broadcasted by mp3 players though earphone.2 MethodsThe guinea pigs were randomly allocated into four groups: the control groups (A1 and B1) and the experiment groups (A2 and B2). The experiment groups were exposed to music broadcasted by mp3 players through earphone for 14 days (5 hour/day), while the control groups received no music exposure. Auditory function was assessed by auditory brainstem response (ABR) before, during, and after exposure. Surface preparations were made to observe the hair cell loss.3 Results During and after the exposure, the ABR thresholds in the experiment groups rose significantly, whereas no apparent change was found in the control groups. The differences between the two groups were evident. Surface preparation of cochlear basilar membrane showed partial absences of outer hair cells in the experiment groups after exposure. The degrees of absences varied with different turns of cochlea. The most severe absence was found in the basal turn, and the outer hair cells in the second and third row had greater damages than in the first row. The miss rates of outer hair cells were significantly different between the experiment and control groups.4 ConclusionMusic broadcasted by mp3 players through earphones could cause auditory system impairments in guinea pigs. Such impairments showed as rises of ABR thresholds and partial absences of outer hair cells. 1 ObjectiveTo observe the difference of the expression of NR1 mRNA in different parts of auditory pathway in rats.2 MethodsThirty rats served as subjects.The animals were randomly distributed into 5 groups:a control group,and four experimental groups including the group of 0 hours,24 hours ,3 days and 10 days after noise exposure. The four experimental groups were immersed in 110～115 dB SPL Broadband noise for 4 days(8 hours per day). Auditory function was assessed by auditory brainstem response (ABR) before and after noise exposure. Real-time quantitative RT-PCR(SYBR GreenⅠ)was done to detect the expression of NR1 mRNA in different parts of auditory pathway in rats.3 Results(1)The ABR thresholds in the group of 0 hours,24 hours and 3 days after noise exposure rose significantly( P<0.01).However, compared with control group, no apparent change was found in the group of 10 days(P≥0.05).(2)Compared with control group, the expression level of NR1 mRNA in auditory cortex tissues was reduced apparently in the group of 0 hours,24 hours, 3 days and 10 days after noise exposure. (3)Compared with control group, the expression level of NR1 mRNA in inferior colliculus tissues was reduced apparently in the group of 0 hours,24 hours, 3 days and 10 days after noise exposure.(4)Compared with control group, the expression level of NR1 mRNA in spiral ganglion tissues was increased apparently in the group of 0 hours,24 hours, 3 days and 10 days after noise exposure.4 ConclusionDepending on the difference in the expression of NR1, the function of NMDA receptor was similar in the auditory cortex and inferior colliculus, but different from that in the spiral ganglion. In noise-injured cochlear, NMDA receptor facilitated the healing processes during the neuron and synapsis regeneration. However, in the auditory cortex and inferior colliculus, NMDA receptor mediated the Glu excitotoxicity and led to neuron cell death during noise injury.