| Backgrounds:Infrasound that generated by mechanical vibration is a wave with frequency below 20Hz,which exists widely in nature environment,work circumstance and et al.It spreads in all kinds of elastic media in the form of alternating waves between rarefaction and compact form.It has the same essence as ultrasound and audible sound.Due to low frequency,it has the character of long effecting distance,strong penetration ability,and et al.At first Gavreau brought up the question about character and biologic effects of infrasound in 1996.With the development of science,especially of communication and industry,people began to know infrasound existed widely in our environment,and more and more countries and scientific institutions cognized importance to the effects caused by infrasound and carried out lots of research work.The researches and studies have focused on damage effects of infrasound with high sound pressure level and how to protect them. Until now there are little research and few reports about biologic effects of infrasound with low sound pressure level.The action mechanism of infrasound is biological resonance.Foreign literatures once reported infrasound with below 90dB can cause light resonance with organism, physical effects,including mechanics,thermotics optics electricity and et al,were so slow and soft that it couldn't cause damage results.Infrasound could bringed out deep massage.such energy form was beneficial for each tissue and cell.Because of the characters with low frequency and long wave,it could spread in organism almost without much consumption of energy,so it could spread deeply in body,penetrate pathological tissues and cells and even make occlusive vessels in pathological tissues reopen,then improve blood circulation and create beneficial condition for delivering material such as oxygen,phagocyte,immu globulin to pathological tissue.These theories indicate infrasound with low sound pressure levels may be beneficial to cerebrovascular diseases,but there are few research about the aspect.The experiment treated rats with injury as objection,infrasound with low sound pressure level as treatment factor.And investigated its biological effects.Objective:To explore mechanisms and effects of infrasound with low sound pressure level on rats with focal cerebral ischemia-reperfusion injury,so as to furtherly clarify its biological effects.Methods:The middle cerebral artery occlusion model was established by filament method.Infrasound generated by Infrasound 8TM device was treated as a treatment,the acoustic spectrum of infrasound mainly focused on 4-20 Hz,change of the main frequency signals in the spectrum was random,and sound level of infrasound was at 79.75-86.11 dB.64 SD rats were divided into 3 groups:shamp group(n=16),model group(n=16) and infrasound group(n=32).The later group subdivided into 20-min and 120-min groups according to treatment time.Observe dymatically neurologica functional addition(2h,1d,3d,7d.).Half of each group was used HE stain and IGF immunohistochemistry.Another part was tested cerebral infraction reltive size by TTC stain.Results:1,Neurological function scoreScore of rat in Sham group was 0 point,.All of mode group and infrasound group came out different degree of left hemiplegia symptom.There was interaction effect between group and time(F=8.258,P＜0.05). Analying from single effect,there was significant defference on time after cerebral ischemia-reperfusion injury(P＜0.001),Neurological function symptom of rats in model group and infrasound group was improved obviously after 3 day;There was significant defference on groups(P＜0.05),neurological function symptoms of rats in 120-min infrasound was improved significantly.Compared 120-min infrasound group with the model group,there was statistical difference(P＜0.05);Compared 20-min infrasound group with the model group,there was no statistical differrence(P＞0.05).2,Cerebral infarction relative sizeInfarct area wasn't found in sham group,Model group and treatment group came out different degree of infarct area.There was significant defference on groups(F= 170.186,P＜0.001),Compared 20-min infrasound group with model group,there was no statistical differrence(P＞0.05).Compared with the model group,infarct area in 120-minute Infrasound group became smaller,there were significant differrence (P＜0.001).3 HE staining3.1 Sham groupMorphological structure in Sham group was clear,the number of neuron cell was rich,the cell arrangement was regular.Stain of caryon was deep,nuclear membrane was clear,nucleolus was obvious.Under High-power microscope:neuron cytoplasm was rich and had much staining-blue granular material,which indicated Nissl bodies was rich.3.2 Model groupIschemic penumbra in model group showed the organizational structure was irregular,rarefactive,glial filaments was sparse,glial cell proliferated slightly,the normal morphology of neuron disappeared,and the nucleus of some neurons pyknosised,cell body minificated and deformated,the residue neurons surrounding gap widened,cytoplasm was red-stained,uniform,ghosting cells was seen.Marginal zone under high-power microscope found morphology of neuron was almost normal, glial cells had no significant proliferation and glial filaments was rich.Marginal zone under the high-power microscope showed the stain of neurons cytoplasm was light or disappeared,wich indicated Nissl bodies decreased or disappeared.3.3 Infrasound 20-min group Compared the 20-minute infrasound group with the model group,there were no significant difference。Tissue in ischemic zone showed structure was irregular, glial cell prolifered and normal morphous of neuronal cells disappear,the residual atrophy red neurons appeared.Foam cells appeared,the phenomenon of macrophages was seen.Neurons in marginal zone had no obvious morphological abnormalities, glial cells had no obvious proliferation.Under the high-power microscope marginal staining-blue granular material which located in neurons cytoplasmic disappeared.3.4 Infrasound 120-min groupGliosis of Ischemic penumbra in infrasound 120-minute group was even more obvious,and neuronophgia and foamy cells can be seen.Marginal zone under the high-power microscope edge show obviously neuronal cytoplasm was blue-staining, particulate matter noticeably increased,which showed Nissl bodies was rich.Neurons form was even regular,caryon was deep-stained,nucleolus was clear。4 Expression of IGF-1 in cerebral cortexThe positive cells in the cerebral cortex expressed mainly in neurons,and expreesion of IGF-1 located mainly in cytoplasm of neurons,while other kind cells less expressed.The distribution of positive cell was almostly uniform.Comparison on stain extent within four groups:sham group was light,other three groups were deep. Comparison on the number of positive cells:There was significant defference on groups(F=379.941,P＜0.001),the number in model group was higher than that in sham group(P＜0.001),The number in 120-min infrasound group was higher than that in model group(P＜0.001);there was little different between 20-min infrasound group with model group(P＞0.05).Conclusions:The experimental results indicated infrasound with low sound level(120 minutes/d,7d)ould significantly improve neurological symptoms,reduce infarct size,active glial cells,strengthen neurons vitality.Infrasound with low sound levels played a protctetive role in rats with local cerebral ischemic-refusion injury,which was related to its effect of enhancing the expression of IGF-1.
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