Auditory Brainstem Response After Bilateral Electrolytic Lesions In Medial Geniculate Body Of Tree Shrews

Objective:Establish the tree shrew model of bilateral electrolytic lesions in medial geniculate body(MGB)in order to figure out the advantage of shrew model and reveal the auditory characteristics of pre-operation and post-operation of tree shrew by use auditory brainstem response(ABR).All this work provide the dates about the electrophysiology of the tree shrew and helped for the further diagnosis of central deafness.This experimental paradigm was also used towards analyzing the long-term evolution of post-lesion plasticity in the auditory system and its ability to self-repair.Methods:The tree shrews with positive Preyer's reflex,normal in the external auditory canal with otoscopy,tympanic membrane integrity,middle ear without infection were under anesthesia by testing ABR using a Tucker-Davis Technologies System.After hearing was re-assessed,the abnormal tree shrew were got rid of and we chose sixty healthy tree shrews to enter the test.The sixty tree shrews were randomly divided into two group.Group A were normal control,Group B were used to establish bilateral medial geniculate body ablated model.The two group were divided into three subgroup,a,b and c.Subgroup a was medial divisions of MGB(MGBm)lesion,b was dorsal divisions of MGB(MGBd)lesion,c was ventral divisions of MGB(MGBv)lesion.Group A/B tested by ABR pre-and post-operation 0h,24h,48h,72h,7d,15d and 30d to observed the change of hearing function in different time after the operation.The control group received an electrode insertion with no electricity.Results:(1)There was no difference pre-operation between experimental group and control group in ABR threshold(P>0.05).(2)Bilateral ablations group caused a statistically significant increase in ABR threshold of electrolytic damage group between pre-and post-operation(P<0.05).Threshold in post-operation at Oh raised fastest and was about 53-58 dB SPL at 72 h which reached the peak,and at 30d decreased slightly about 52 dB SPL.(3)There was a statistically significant increasing in the latencies in wave I after lesion MGBd at Oh,and a shortening in the interpeak latency of waves ?-?,?-?,?-? and ?-?at 24h,and a shortening in the interpeak latency of waves ?-? at 72h.There was a statistically significant increasing in the interpeak latency of waves ?-? after lesion MGBm at Oh and 7d.There was a statistically significant shortening in the interpeak latency of waves ?-? and increasing in the interpeak latency of waves ?-? after lesion MGBv at 24h,and a increasing in the interpeak latency of waves ?-? at 72h and 15d.Wave of lesion MGBd changed more obviously than the others,lesion MGBm group was the least.Latencies of wave after lesion MGBd and MGBm changed at Oh and lesion MGBv group changed at 24h.(4)The amplitudes of wave ? showed a significantly decrease after lesion MGBd,MGBm,MGBv at 0h,24h and 7d,compared to those values before the operation.Wave ? also showed a statistically significant decrease after lesion MGBd at 0h and 24h,and decrease in the amplitude of group lesion MGBv at 24h,48h,72h and 7d.The amplitudes of wave ? showed a significantly decrease after lesion MGBd at Oh and 24h,decrease in the amplitude of group lesion MGBm at 24h and 7d,and decrease in the amplitude of group lesion MGBv at 24h,48h,72h and 7d.The amplitudes of wave ? showed a significantly decrease after lesion MGBd at 24h and 48h,decrease in the amplitude of group lesion MGBm at 72h and 7d,and decrease in the amplitude of group lesion MGBv at 24h,48 h,72 h and 7d.Furthermore,it was more obviously decreasing in wave?,?,? amplitudes after bilateral MGBv lesion within 24 h-7 d than MGBm and MGBd group not only in the amplitudes and the range of time.The MGBm group was the opposite.Amplitude of wave ? and ? of MGBm group decreased firstly at 24h,while amplitude of wave ?,? and ? decreased in MGBd group at 0 h.Amplitude wave IV,V,VI of MGBv group decreased at 24h.These experimental groups had returned to preoperative levels during 15d-30d.Conclusion:(1)The lesion group suffered from the hearing loss,and not recover and was suggested that it was difficult to wholly repair when bilateral ablation.(2)Latencies and amplitude of Bilateral electrolytic lesion in medial geniculate body in 15d-30d could restore to pre-operation level,and it was suggested that part of the central nuclei lesion was reversibility.ABR waveforms changed more obviously when lesion in MGBv and MGBd than MGBm,indicating MGBv and MGBd fiber connection more complex in auditory pathway than MGBm.It was provided certain reference value in central deafness hearing loss patients caused by medial geniculate body injury.(3)The tree shrews as auditory animal model with a lot of advantages compared to other animal models were more complex in the brain structure and the auditory nuclei fiber connections,which made the results of the experiment more useful for clinical diagnosis compared with rat and guinea pig.This research successfully established the animal model of bilateral lesion in medial geniculate body and also lay the foundation of the function in the auditory nuclei model.