Study Of The Mechanism Of Influence From Infrasound On Rats' Procerebrum

Infrasound is mechanical oscillations whose frequency is ranged from 0. 0001～20 Hz. The conception of infrasound is brought up by French scientist Gavreau in 1966. Infrasound is extensively present in both the nature and the society. It has low frequency and large wavelength, which made it uneasy to be absorbed and attenuated while spreading, and can transmit a long way with powerful penetration, influencing enormously on living body. Infrasound of high intensity is detrimental to human body, therefore is an important part of producing and public noise. Long time exposure to infrasound can cause debility, apathy, depression, ear compression feeling, distraction, drowsiness, visceral vibration feeling, memory impairment, along with the diminutus of venous blood in cranial cavity.The basic function mechanism of infrasound on living body is the biological resonance, whose effects is so general and complex, involving the system, organs, tissues, cells, even molecules. According to former researches, brain is the most sensitive to infrasound among all the organs. Multiple kinds of neurotransmitters metabolism, the constructions and functions of tissues and cells are affected by infrasound. Infrasound of certain frequency and intensity can damage cortex, hippocampus, hypothalamus and limbic system et al in brain. The mechanism is complicated.Infrasound, which is a mechanical vibration wave, influencing human and animal through its resonance effects. However, the mechanism how the infrasound is detected and reacted remains unclear. To study the process of infrasound effect on procerebrum, we built the rat model of infrasound impaired brain, observed the immunohistochemical staining of TRPV4, GFAP and Fos in hippocampus, hypothalamus, nucleus amygdalae and cortex., intended to discover some clue of the infrasound sensing and responding mechanism and see the interaction between neurons and astrocytes. Living things must sense and respond to environmental changes.Some ion channels act as the cellular sensors that translate fluctuations in the external milieu into changes in membrane excitability and second messenger signals, particularly Ca2+. The channel family most intimately involved in this process is the transient receptor potential (TRP) family. TRP channels are the vanguard of our sensory systems, responding to temperature, touch, pain, osmolarity, pheromones, taste and other stimuli. TRPV4 is found to be necessary for normal thresholds in response to noxious mechanical/osmotic stimuliGlial fibrillary acidic protein (GFAP) , the principal intermediate filament in mature astrocytes of the central nervous system (CNS), is the standard marker of astrocyte. Its expression will be upregulated when astrocyts are activated and is well established to be used as the marker of active astrocyte. The immediate early gene c-fos is rapidly and transiently expressed in neurons in response to stimulation.Recently accumulating evidence suggests the existence of a complex bidirectional communication between glial cells and neurons and indicate an important active role of glial cells in the physiology of the nervous system .Astrocytes posses a form of excitability based on intracellular Ca2+ variations that can be triggered by synaptically-released neurotransmitters.These Ca2+elevations evoke Ca2+-dependent neurotransmitter release from astrocytes that can signal to adjacent neurons, leading to an astrocyte induced modulation of the neuronal excitability and synaptic transmission. Therefore we hypothesized the brain damage caused by infrasound is relevant with the interaction between astrocytes and neurons.We observed that in hippocampus, hypothalamus, nucleus amygdalae and cortex,1,The TRPV4 expression: TRPV4-IR(immunoreactive) neurons are rare in control group, while in 16Hz/130dB and 16Hz/90dB group the quantity of the IR-neurons were obviously enlarged compared with the control group. The majority IR-neurons distribution were found in hippocampus, nucleus paraventricularis hypothalami of hypothalamus, nucleus amygdalae and the whole cortex. The discrepancy among the groups is statistically significant(P<0.05). 2,The GFAP expression: Compared with control group. GFAP-IR astrocytes of 16Hz/130dB and 16HZ/90dB group were greater in size and number, the dendrites were pachier, the distribution were denser. The reaction was intenser in 16HZ/130dB group than in 16Hz/90dB group. The localization of GFAP-IR astrocytes are similar to TRPV4-IR neurons. The discrepancy among the groups is statistically significant(P<0.05).3,The Fos expression: Fos -IR(immunoreactive) neurons are rare in control group, while in 16Hz/130dB and 16Hz/90dB group the quantity of the IR-neurons were obviously enlarged compared with the control group. The localization of GFAP-IR astrocytes are similar to TRPV4-IR neurons. The discrepancy among the groups is statistically significant(P<0.05).These results that 16Hz/130dB and 16Hz/90dB infrasound can upregulate the expression of TRPV4 in dental gyrus of hippocampus, nucleus paraventricularis hypothalami of hypothalamus, nucleus amygdalae of rats, indicated that the mechanical stimuli of infrasound may be detected via TRPV4 channels of brain cells. The activation of neurons and astrocytes in these sites may be relevant with memory impairment and stress originated by infrasound.