The Preliminary In Structure Of Inner Ear And Hearing Function Of Tree Shrew

Objective:The tree shrew(Tupaia belangeri)is a small eutherian mammal,found predominantly in the tropical and subtropical zones of South-east Asia,and in the south-western region of Yunnan,Guangxi and Hainan provinces of China.Which occupies a unique phylogenetic niche.The tree shrew was reclassified as a member of the Primate order,before more recently being classified within its own order of Scandentia.At present,various kinds of animals including rodents such as guinea pigs,rats and nonhuman primates lemurs were experimented as animal models in hearing research at home and abroad.The study of experimental animals used in hearing function at home and abroad.The tree shrew is widely applied into medical and biological field,for instance,virology,Neurology,Gastroenterology,urology,genesiology,immunology,ophthalmology and sociobiology.The tree shrew was used to establish hepatitis animal model in Guangxi,but there was no related reports that the animal ear disease research model have been set up domestically.Auditory brainstem response might be an objective and sensitive electrophysiological indicator and might be of important value in evaluating the function state of auditory pathway.To explore hearing function of tree shrew via studying tree shrew auditory brainstem response(ABR)characteristics.Using light microscope and scanning electron microscope,the microstructure of the cochlea in tree shrew was analyzed.The research aimed to reveal the auditory characteristics of tree shrew.All this work provides the basis for the further experiments.Methods:Auditory threshold were assessed in tree shrew under anesthesia by testing click or tone pip evoked ABR using a Tucker-Davis Technologies System.After hearing was re-assessed,the tree shrew were sacrificed,and cochleae were quickly removed from the skull.Following fixation,all otocyst tissues were made into paraffin sections.Sections were stained with haematoxylin and eosin for light microscopic examination.All the stretching of cochlear basement membrane were stained haematoxylin and eosin for hair cell examination.Part of the cochlea was used scanning electron microscopy.Microscopic structure changes and ultrastructural feature of cells were observed by light microscopy and transmission electric microcopy.Results:(1)General observation of samples:The cochlea structures between Tree Shrew and other mammals are similar,it also have a typical screwy structure,and it have three point five circles aggregately.(2)Pathological examine,histologically,Stria vascularis,estibular membrane,spiral ganglion and corti organ structure clearly visible.The spiral ganglions are clear,which include big deeply dyed cells and small shallowly dyed cells.(3)The stretching of cochlear basement membrane showed that in tree shrew’ cochlea,the inner hair cells are arranged in a line,and outer hair cells are arranged in three rows.The length of basement membrane is about 13.6mm,the total number of cochlear hair cells is 6938,of which the total number of inner hair cells is 1471,the total number of outer hair cells is 5467.(4)Scanning electron microscopy showed that the structures of cochlea hair cells between Tree Shrew and other mammals are similar.The inner hair cells are arranged in a line,the stereocilia are arranged in arcuate.The stereocilia of the inner hair cells is longer than the outer hair cells at basal turn of cochlea,and shorter than the outer hair cells at top turn of cochlea.Outer hair cells are arranged in three rows,the stereocilia present a V-shape.The stereocilia from became longer gradually from the center to the outside,from the bottom to the top.(5)The ABR(click)test results:Six amplitude peaks were regularly recognized in click-evoked ABRs.At 80db SPL intensity,peaks latencies were 1.16 ± 0.07ms for Wave I,1.62 ±0.18ms for Wave II,1.96 ± 0.07ms for Wave Ⅲ,and 2.66 ± 0.13ms for Wave IV,3.60 ± 0.12ms for Wave V,4.62 ± 0.11ms for Wave Ⅵ.Respecqtively,which were quite variable.Among them,emergence rate of Wave Ⅱ is low,Wave Ⅲand Ⅴ are relatively stable.ABR peak amplitudes increased and latencies decreased as the click level was increased from 25 to 100db SPL.Wave Ⅲ of ABR is a reliable standard of judging auditory response threshold.ABR response reaction threshold shift was 26.19 ± 3.50 dB SPL in the tree shrews.(6)The ABR(tone pip)test results:The responses elicited by tone pip were similar in configuration to that by evoked-click.The latency of wave Ⅰ～Ⅵ extended with increasing of frequencies from 1 to 16 kHz and levels from 20 to 100 dB SPL.The threshold of tone pip evoked auditory brainstem responses(TP-ABR)was related to the threshold of click evoked ABR.ABR at 85dbSPL intensity of the sound,the frequencies of 4、8 kHz of TP-ABR have well differentiated waveform diagram.The threshold of TP-ABR was higher at the frequencies of 12 kHz from 1 to 16 kHz.The threshold of TP-ABR increased gradually from 2 to 8 kHz and decreased gradually from 12 to 16 kHz.Conclusion:(1)The tree shrew was widely considered to be a representative of one of the earliest forms of primate.Tree shrews are more closely related to humans than rodents such as guinea pigs,rats in auditory brainstem response hearing test.The ABR waveform analysis will provide reference bases for setting up tree shrew model in auditory pathway research in the next step.(2)Tree shrews were conduct the technology of sectioning with paraffin,the stretching of cochlear basement membrane and scanning electron microscopy.The anatomy and physiology characteristics of inner ear between tree shrew and other mammalian species are similar and suggest that the tree shrew may serve as an appropriate model of auditory development in man.It provide a efficient animal model and experimental basis for further study.Therefore we believe that the tree shrews as the otology animal model have a more important value.It will bridge laboratory experimentation to practical clinical settings.