| Infrasound refers to very low frequency sound, falling below what is usually considered to be the range of human hearing 20-20000Hz. Infrasound is found in natural and man-made environments and is related to thunder, tornadoes, rain, snow, ocean waves, etc. Because of their brief duration, low intensities and extremely low frequencies, naturally occurring infrasound has seldom been considered a problem. On the other hand, infrasound in working environment such as aircraft, automobiles, ships, subway, etc. may be considered potentially harmful, owing to longer exposures and greater intensities. Issues concerning the nature and biological effect of infrasound have brought forward in the 60s of 20th century. In 1972, Paris International Noise Professional Meeting gave a formal definition of infrasound, and discussed its exposure standards. Research for infrasound biological effect has been carried out in France, America, England, Japan and the former Soviet Union. Several studies has indicated that infrasound could affect the pituitary adrenocortical system, cardiovascular system, respiratory system, digestive organ and others of animals or human beings. Claim that infrasound adversely causes pilots visual deficit and substantially reduced visual acuity has not been clearly demonstrated in any experimental study. The purpose of this study is to evaluate the possible adverse effects of infrasound on the visual system from the electrophysiology points of view. Therefore, we try to explore the possible effect of infrasound on the rat's retinal function from visual electrophysiological, morphological points of view and the molecular mechanisms indicated by expression of VEGF and Occludin as well as it's signal transduction pathway by measuring changes of [Ca2+]j and ionic channel.Part One: The effect of infrasound on rat's visual electrophysiologyForty-eight mature male Sprague-Dawley rats randomised into 8 groups on the basis of exposure duration, 6 per group were used to study the effectsof infrasound at a frequency of 8Hz, 130dB sound pressure level. Treatment groups were given infrasound exposure 2 hours daily continuously for Id, 4d, 7d, lid, 14d, 18d, 2Id in the infrasonic pressure chamber respectively. According to exposure duration, FERG, Ops were performed before and after the exposure respectively in each time.The results showed that after exposure, treatment groups decreased in a, b, ZOPs amplitude (p<0.01), but there are no much linear relation with exposure time. Each index's amplitude decreased in various degree with the increase of exposure time. But under the whole trend of decrease, there was recover. When comparing the relationship between all the indexes' abnormity and exposure time, it showed that the changing trend of wave a and b is basically consistent with the changing of exposure time. But the main abnormity is the decrease of wave a when exposure to infrasound under Id. While the group with exposure for 4 days and 7 days, the decrease of wave b is larger than wave a. After that, prolong the exposure time, the main change is the abnormity of SOPs. The absolute value of the latent period of wave a and b prolong in various extent as the exposure time increase, especially on the 14th day, the changing is statistically meaningful.All indexes of ERG had different amplitude decreases with different exposure time to infrasound, and with the exposure time increase, the damaging went from the outer to inner, which show that infrasound causes extensive damage to all layers of the retina. While in different phrases, the damage is also different. It suggest that in the beginning exposure, the damaging effect of infrasound is mainly in the functional disorder of the outer layer of retina, while as the exposure time increases, infrasound has already damaged the Miiller cells of the retina, which is the cause of further functional disorder of retina, the evidence of which is the decrease of wave b larger than that of wave a. As the exposure time lasts longer, the main chang...
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