Microscopic Anatomy And Significane Of The Tree Shrew Temporal Bone

Objective:The establishment and application of tree shrews as an emerging animal model has gradually become one of the recent research focus.’The classification of tree shrew is still unclear,most studies show that there is a high degree of similarity with the primate,tree shrew have a closer genetic relationship.Compared with rats,dogs and other animals,tree shrews are more similar to human because of their similarity in metabolism and gross anatomy,and tree shrews have a smaller size,lower price,easier breeding,domestication and breeding characteristics relative to other primate animals.Therefore,tree shrews have a broad application prospect in medical biology and they have been involved in the visual,neurological,endocrine,viral hepatitis,cancer,social behavior and psychology,and many other basic researches.They are still attracting the attention of scientists and so many models have been successfully established,such as the model of hepatitis virus,drug addiction,visual,sleep regulation and so on.There are no related reports about tree shrew in otology research and their temporal bone anatomy up to now.To explore whether tree shrews are good for otology research,we performed the study on the microanatomy observation and measurement of tree shrews’ temporal bone,middle ear and inner ear structure,detailed and compared the anatomy of ossicular chain with rats and guinea pigs.We hope that through this study we can fill the vacancy and provide a reference on the anatomy of tree shrews to otology models and to carry out other ear scientific researches.Methods:Twenty healthy tree shrews,rats and guinea pigs,which have positive Preyer’s reflex,the external auditory canal,integrated tympanic membrane and middle ear without infection,were selected.All animals were killed and fixed by cardiac perfusion with 4%paraformaldehyde solution.With a dissecting microscope and microsurgical techniques,the structure of temporal bone.middle ear and inner ear is observed and measured.We observed all of these structures:the surface markers of tree shrews temporal bone:including the listen to the bubble,external auditory canal,zygomatic process;structure of the middle ear:including the tympanic membrane,ossicular chain,eustachian tube,stapedius muscle,tensor tympanic,oval window,round window,facial nerve,etc;the inner ear structure:including the cochlea,three semicircular canals,internal auditory meatus,etc.Results:Measurement of rat,guinea pig and tree shrews tympanic membrane and ossicular chain data.1.Tree shrew’s listen bubble which is thin as paper located in superficial,and the structure of its ear is visible and easy to operate.2.The tree shrew’s ossicular chain differentiate into malleus,stapes and incus,it is more similar with human’s ossicular chain than rat and guinea pig.Furthermore,the pressurization mechanism of middle ear is similar to human.3.Semicircular canal can be positioned easily because it is clear to see and relatively bulky.It is also similar with the human’s structure and help to investigate the function of vestibular.4.The distribution and overall shape of facial nerve in tree shrew is very similar with human’s.5.Tree shrew’s cochlear structure which is similar to human’ s is prominent in the middle ear cavity.Though harder than the guinea pig,tree shrew’s cochlear can be operated without the polishing process.Anatomical structures in tree shrew temporal bone have greater similarity with human than other animals.Conclusions:Compared with rats and guinea pigs,tree shrews have a lot of advantages as an animal model in otology research and can be used in further researches.The anatomy of tree shrews have a greater similarity with human.These results will provide experimental bases for tree shrew model in otology research and are beneficial to the study about physiology of the middle ear and the inner ear.