| Infrasound is a mechanical vibrational wave , as the same as the audible sound and ultrasound .whose frequency is below 20Hz. It has some unique feature due to its low frequency and long wavelength. For instance, infrasound hardly attenuates when it spreads through the air, with the wave-guide of atmosphere it can be spreaded throughwaveguided stratus to long distance but with low attenuation. The hearing threshold of infrasound is higher than that of audible voice. Infrasound usually can not be heard but be felt like "beat, beat" when the pressure reaches certain degree.Infrasound is ubiquitously around us. It can be detected during earthquake , typhoon and star shower. Vehicles like automobiles, planes, steamboats and trains can also produce infrasound. Machines, compressors, refrigerations in factories, washing machines and iceboxes at home can make infrasound too. Furthermore , infrasound can also be found in military affairs like moving tanks, submarines and rockets. Infrosonic weapon has been in use due to it difficult to be defended. Infrasound has effects on human organs because some organs' initial frequency are in the infrasonic range. With the development of industry and communication, infrasound is under people' s concern as one of the elements of environment pollution. Infrasound is the important compose of living and working noise, with the absorbing and separating measures been in use, infrasound' s specific gravity is becoming greater. Infrasound can make harmful influence on human when its pressure comes to certain degree. For example, reduces working ability, command and battle effectiveness. So it is important to investigate the biology effects of infrasuound on animals.Many paradigms have shown that infrasound can make series of biology effects on human and amimals, especially on central nervous system. Learning and memory is the seniorfunction of brain, it is the necessary process for animals to adapt to living surroundings, to survive and develop. Learning and memory is the important behavior of brain' s splasticity which is the major character of nervous system for both the developing and adult, peripheral and central system, neuron and nervous circle. Synaptic junction is the key point of nervous plasticity whose substantial bases are the physical and chemical changes of proteins, receptors, neurotransmitters, ions and messengers at synapses and in nervous cells.Many paradigms have shown that 5-HT, 5-HTR, RyR are the important substances for learning and memory. The effects of infrasound on amimal' s spacial learning and memory have not been found. Our work is to probe into the effects of 8Hz infrasound on achivements in Morris water maze and the expression of 5-HT, 5-HTR and RyR in hippocampus and temporal cortex of rats. By the way , we detected the recovery of those substances when rats were out of infrasound for 1 week or 2 weeks after 8Hz, 130dB infrasound exposure, making some theoretic bases for infrasound biology effects and its defence.We used the infrasonic storehouse made by the fourth military medical university at the assistance of Chinese acaidemy of sciences acoustic institute and the 41st research institute of aerospace industry company. The frequency was 8Hz and the pressure were 90dB, lOOdB and 130dB. Rats were under the exposure of infrasound for two hours each day .By the aid of Morris water maze we observedthe spacial learning achievement and by using immunohisto-chemistrial staining (ABC) we detected the expression of 5-HT, 5-HTR and RyR in hippocampus and temporal cortex of rats. We analyzed the pertinence of water maze results and the expression of 5-HT, 5-HTR, RyR. We also studied the change rules of 5-HT, 5-HTR and RyR in hippocampus and temporal cortex of-rats after long term exposure (l~42d) under those infrasonic parameter and the recovery of 5-HT, 5-HTR and RyR after leaving infrasound. At the same time we examined the ultrastructure changes in hippocampus after different time(l~42d) exposure of 8Hz, 90dB and 130dB infrasound. The results wer...
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