Study On The Mechanism Of Sound Conditioning In The Rats

Noise is a common industrial hazard. Exposure to intense noise induces hearing loss and mechanical insult to the cochlea. The mechanism is not clear yet. Recent studies have reported that noises can induce cochlea ischemia injury, over production of reactive oxygen species and excessive secretion in cochlea. Drugs which can upregulate cochlea blood flow and oxidative stress cleaner such as adenosine were used to treat with noise induced hearing loss.The best way to aviod noise induce hearing loss is keeping from noises. But it seemed to be impossible sometimes. Sound conditioning was first described in the 1963's by Miller. After that, the phenomenon of conditioning-related protection, whereby prior exposure to moderate-level, non-traumatic, sound protects the ear from subsequent traumatic exposure, has been documented in a number of mammalian species, include human being. So far, the menchanism is not clear.Hypoxia inducible factor-1alpha (HIF-1alpha) is a main responder to intracellular hypoxia. Hypoxia of tissue can active HIF-1alpha. Vascular endothelial growth factor (VEGF), one of the target of HIF-1alpha, up-expressed afterd hypoxia. VEGF can increase blood flow and upregulate concentration of oxygen in tissue. No report show the expression of HIF-1 alpha in cochlea and in noise induced hearing loss. On the other hands, recent studies of cochlear sensory cell damage resulting from noise provide due to reactive oxygen species (ROS). NADPH oxidase and inducible nitric oxide synthase (iNOS) play a important role in ROS producing.It is unkown wether"sound conditiong"effect on these two oxidase now.The current study builded a sound conditioning rat modle first. Cochlea patch technology, immunohistochemical method and RT-PCR were used to investigate the changes of HIF-1, VEGF, iNOS and P47 in cochlea metabolism after sound conditioning and subsequent more intense sound exposures.The contents of this paper are as follows:1. Building of sound conditioning rat modle 24Wistar rat were divided into 3 groups. Two sound conditioning protocols were used (Group 1 for 6h exposure and 6h rest, Group 2 for 6h exposure and 24h rest) For each protocol, both a condition pre trauma. Condition sound is octave-band noise (4 kHz at 90 dBSPL) and trauma is the same at 118 dBSPL. Group 3 were exposed to a traumatic noise only. 7 days after trauma, PTS of each group was measuered by ABR.No different was found among three groups before sound condition exposure. 7days after trauma, group 1 and 2 show less PTS compared with group 3(P<0.05). PTS of Group 2, which have a rest of 24h was obviously reduced than group 1.2. Mophological changes of cochleaSound conditioning protocols is 6h exposure and 24h rest. 28 Wistar rat were divided into 4 groups as follow, Group N(Normal without exposure), Group C(condition only), Group C+E(Condition pre trauma) and Group E (trauma only). Group C was scared 24h later after exposure, Group C+E and Group E were observed 7 days after trauma. Total cochlea patch were performed an 1% PI stained for each slide. Under the confocal laser microscopy, HC loss were counted by step of 1mm on the basilar memberance. Statistical analysis was done by SPSS10.0 then plot cochlea picture.In group N, no HC loss was detected and in group C have seldom HC loss. C+E group showed several HC loss while group E much. The cochlea picture showed HC loss mainly located in the middle range of basilar memberance and OHC loss is mostly. The OHC loss rate were 7.1±2.8% in group C, 17.3±5.9% in group C+E and 35.1±7.2% in group E.3. changes of HIF-1αand VEGF in cochlea after sound conditioning Immunohistochemical method was to detect the changes of HIF-1αand VEGF.PI staining and RT-PCR technology for HIF-1α.Both of HIF-1αand VEGF became highest density expression in group C. The expression level in group C+E (P<0.05)is higher than group E(P<0.05). In Group N,no obviouse stain was seen. By RT-PCR, trancription of HIF-1αmRNA become upregulated in group C, C+E and E, but no different in statistics(P>0.05).4. changes of iNOS and P47phox in cochlea in sound conditioningImmunohistochemical method and PI staining for iNOS was performed. RT-PCR technology was uesed to check P47.iNOS showed weak expression both in group N and group C (P>0.05). iNOS expression in group C+E was weaker than group E. P47phox was heaveyer in group E than group C+E(P<0.05).There were no different between group N and group C of P47phox (P>0.05).Conclusions:1. Sound condition can renduced PTS induced by folowed niose trauma. The effect of condition is related with the time during the two exposure. 2. Sound condition can reduce OHC loss obviously.3. Sound condition can up-regulate the expression of HIF-1αand VEGF expression which can increase blood flow in the cochlea to resist intracellular hypoxia.4. Sound condition reduce the expression of iNOS and P47phox, which can lead massive generation of ROS.It is the first report of expression of HIF-1αin cochlea and NIHL.It is the first study paper on the changes of oxidase of iNOS and P47 caused by sound conditioning.