Diffusion Tensor Imaging Of The Medial Geniculate Body Damage Model In Tree Shrews(Tupaia Belangeri Chinensis)

Objective: To establish a medial geniculate body(MGB)lesion model of tree shrews,and to investigate the damage and remodeling of nerve fiber bundles after MGB destruction by thetechnology of diffusion tensor imaging,which provides an experimental basis for the study of neurogenic hearing loss.Methods: Twenty-five(50 ears)of normal adult tree shrews were randomly selected.They were divided into normal control group and experimental group.Experimental group was divided into 3 days group,7days group,15 days group and 3months group after MGB damage,5 in each group.Auditory brainstem response(ABR)was measured with click and 1-60 kHz pure-tones stimulation.Then three tree shrews were randomly selected from each group.A total of 15 trees were used to collect T1 WI,T2W2,and DTI data from tree shrew brains on a Biospec 7T/20 cm small animal MRI,and deterministic fiber tracking and quantitative measurement of DTI were performed.Brain sections were HE stained and Nissl stained.The pathological changes of ABR waveforms,white matter fiber bundles,and neural cell structures at different time points after MGB injury were compared.Results: 1.In the click stimulus,the thresholds of ABR III and V waves gradually increased after 3 days and 7 days after MGB destruction.The latency period was prolonged and the amplitude was reduced.The threshold,latency and amplitude of III wave were recovered at 15 days and 3 months after surgery,but did not reach normal levels.V-wave latency gradually decreased at 15 days and 3 months,amplitude gradually increased at 15 days,slightly decreased at 3 months,and the threshold increased at 15 days.There was no statistical difference in threshold change between 3 months and 15 days.(p>0.05).2.In the 1-60 kHz pure-tones stimulation,the 1 kHz to 8 kHz threshold in the normal group gradually decreased,and the 4 kHz and 8 kHz thresholds were lower.This may be the frequency band in which the tree shrews sensitive frequency is located.The 8 kHz to 48 kHz threshold is gradually increased,and the 54 kHz and 60 kHz threshold is decreased.The thresholds of 3 days,7 days,and 15 days after MGB damage gradually increased,and the threshold decreased at 3 months,but did not return to the threshold level of the normal group.3.Compared with the normal group,the FA value,λ1 value,the number and length of nerve fiber bundles in the experimental groups decreased significantly,while there was no significant difference in the values of λ2,λ3 and ADC(p>0.05).4.In the HE staining of the brain tissue sections of the normal group tree shrews,the structure of the MGB region is clear,the neurons are intact,and the arrangement is dense and tidy.In the 3 days after operation,extensive infiltration of inflammatory cells was observed,and the normal structure of neurons gradually disappeared and the surrounding glial cells proliferated.In the 7 days after operation,a large number of neurons were pyknosis,lysis,and fragmentation.A large number of inflammatory cells infiltrated.Glial cells were extensively proliferated and tissues were edematous.In the 15 days after operation,the structure of normal neurons was significantly reduced,the arrangement of nerve cells was disordered,and non-uniform vacuoles appeared in the cytoplasm.In the 3 months group,necrotic tissue was gradually phagocytosed and cleared,the gap between cells and cells was larger,glial cells increased,and capillaries were hyperplastic.5.In Nissl’s stain of brain tissue sections in normal tree shrews,the NGB bodies enriched with blue particles in the MGB area were uniform in the neuronal cell body area.Nissl stained sections of the 3 days group after MGB lesions showed a decrease in the number of Nissl bodies,an increase in gaps,a loose network of nerve fibers,and more cytoplasmic vacuolization.In the 7 days group,the Nissl bodies were concentrated and darkly stained,and the cytoplasm vacuoles were enlarged and spongy.The number of Nissl bodies in the 15 days group and the 3 months group decreased or even disappeared,Nissl body lightly stained,and the cytoplasm vacuolated,forming a spongy,sieve-like structure.Conclusion: 1.Wallerian degeneration occurred after the destruction of bilateral MGB of tree shrews.The anatomic structure was difficult to recover within 3 months,and the functional remodeling was preceded by structural remodeling,which provides experimental basis for the study of hearing compensation in patients with neurogenic deafness.2.The tree shrew has a fiber-casting anatomy of the inferior colliculusmedial geniculate body-auditory cortex similar to humans.The tree shrew was used as a new animal in the research of otoneurology.The model of the otological animal model was expanded to provide further auditory study of the function of conduction pathways,especially providing the morphological basis for the multisensory integration,frequency coding,auditory plasticity,and the establishment of acoustic models.