・388・ 经 Chin J Neurosurg Dis Res)2007:6(5 文章编号:1671—2897(2007)06—388—04 颅脑损伤机制与救治研究・ Changes of brainstem--auditory evoked potential in rat model with brain inj ury by lateral head rotation HE Xiaosheng ,ZHANG Xiang,FEl Zhou Department of Neurosurgery,Xijing Institute f oClinical Neuroscience,Fourth Military Medical University,Xi"an 710032,China Abstract Objective To study the change and mechanism of brainstem—auditory evoked potential (BAEP)in rat model with brain injury by lateral head rotation.Methods The model of brain injury by lateral head rotation was produced with 20 adult rats.The rats BAEP was measured before rotation and at 6 h after rotation.The test electrode was placed at the left C,on the headThe short click sound was given to .the left ear and continual sheltering was sent to the right ear.One thousand test results were added and then averaged.The latent period,wave・to—wave interval and amplitude of all waves in BAEP were recorded. Results Compared with the BAEP before head rotation,the latent period of wave I,V and the wave—to— wave interval of I一Ⅲ,Ⅲ一V were apparently prolonged,and the amplitude of wave 11I,V was markedly reduced at 6 h after rotation;on the other hand,no significant difference was found in the latent period of wave I,wave—to—wave interval of I,V and amplitude of wave 1.Conclusion Lateral head rotation leads to abnormal BAEP.It is related to the damage of special conductive pathways in brainstem.The diffusely—scattered axonal injury in brainstem is the pathological basis in this animal model by mechanic head rotation. Key words Brain injury; BAEP;Diffuse axonal injury(DAI);Laterla head rotation; Rat CLC number R 651.15 Document code A 大鼠头颅侧向旋转脑损伤模型脑干听觉诱发电位的变化 贺晓生 章翔 费舟(第四军医大学西京脑科医院神经外科,陕西西安710032) 摘要 目的探讨头颅侧向旋转致脑损伤大鼠模型脑干听觉诱发电位(BAEP)的变化及机制。 方法成年大鼠20只,制作头颅瞬间侧向旋转脑损伤模型,测量头颅旋转前及旋转后6 h的BAEP, 大鼠头颅旋转后6 h和V波潜伏期、I一Ⅲ和 测量电极置于颅顶左侧c2点,左耳予短暂click声刺激,右耳持续予噪声掩蔽,经1 000次叠加平均, 记录BAEP各波形的潜伏期、波问期和波幅值。结果V波波间期以及I波波幅无显著差异。结论Ⅲ~V波波间期明显较旋转前延长,I和V波波幅较旋转前明显降低,而旋转前后I波潜伏期、I~ 头颅瞬间侧向旋转可引起BAEP异常,此与脑干内特 殊传导通路的破坏有关,其结构基础为脑干广泛神经轴索损伤。 关键词脑损伤;BAEP;弥漫轴索损伤(DAI);头颅侧向旋转;大鼠 文献标识码A 中国图书资料分类号 R 651.15 Foundation:Supposed the National Natural Seience Foundation of China(30270534)and the Natural Science Foundation of Shannxi Province (2005C209) Biography:HE Xiaosheng,Professor,Tel:(029)84775567,E—mail: hexiaos@fmmu.edu.cn Corresponding author:HE Xiaosheng,Professor,Tel:(029) 84775567.E—mail:hexiaos@fmmu.edu.cn 维普资讯 http://www.cqvip.com 经 志(Chin J Neurosur ̄Dis Res)2007:6f5 ・389・ Normal conscious activity relies on the integrity of reticular structure in brainstem.It is well—known that conscious disorder often occurs in diffuse axonal iniu nr (DAI) and can be considered as the direct manifestation due to the abnormality of the function 0f the reticular structure in brainstem.We had produced brain DAI model in rats by lateral head rotation device. and observed the pathological changes of neuronal axon and micro—vasculature.In conclusion,it was found that the morphological evidences existed largely in the area of brainstem in this model[ ・ .In the present study.we tested the brainstem auditory evoked potential(BAEP) for this rat model in order to investigate the influence of morphological changes on the neuro・-electro・-physiological function in brainstem. MATERIALS AND METHoDS Animal grouping and model production Twelve male healthy Sprague—Dawley rats weighing 280 to 320 g were included in this study.All rats were anesthetized under peritoneal injection of 1%sodium pentobarbital(50 mg/kg).The scalp was incised at the midline and the cranial bone was exposed to the great extent. 矗el rotation by 90 Fig 1 Diagram of the device used to produce rat model of difuse axonal injury by lateral head rotation. ①tirgger;②reset nut;③rotation angle—determined hole at 0。;④ rotation angle—determined hole at 15。;⑤rotation angle—determined hole at 30。and its bolt;⑥drive spring;⑦ear pin;⑧horizontal a/nl;⑨ ante 0r tooth ho】e qhe lateral head rotation device was used in this study qhe mechanical,behavioral and pathological characteristics of the rat model produced by means of this device were described in our past publication l .The head of the anesthetized rat was horizontally secured to the rotati0n device by two lateral ear bars,a head clip and an anterior teeth hole,with its body 20 oblique to the top of laboratory table(Fig 1).After its tirgger was pressed downwards,the device rapidly rotated the rat head through a 90 angle laterally(i.e.in the coronal plane).It had been identiifed that the head rotation was ifnished in less than 2.09 ms with the angular velocity beyond 76 1 rad/s and the angular acceleration beyond 1.87×10 rad/s ll1. The recording electrode was placed at the left C2 point(5 mm back from coronal suture and 1 mm off the sagittal line)on the left.The bone hole was made by dental bur until the dural was exposed.The silver bulb electrode was inserted in the C2 hole and reached the dural in order to obtain the cerebral electric signals.The ground electrode was fixed underneath the skin of nose. The reference electrode was placed beneath the occipital scalp at the middle sagittla plane of the head.Then,the rat head was secured to the rotation device for next procedures. The standard stimulating conditions were as followed.The left ear was stimulated by short click sound with intensity of 75 dB,frequency 11.1 Hz,and duration 0.1 ms while the right ear was shielded by continuous buzz noise in intensity of 55 dB.The averages in 1 000 times for the latent period of wave, the wave・-to・-wave interval and the amplitude were calculated and printed out through the computer. A11 the indexes in BAEP were recorded for the rats prior to head rotation injury as the baseline value.After initiation of head rotation,the rat was freed from the injury device,either the recording or the stimulating or the reference electrode was discharged.Their incision was sutured before the rats were kept in cage for next procedure.And 6 hours later,the head—rotated rats were again anesthetized by peritoneal injection of 1% sodium pentobarbital and all the indexes were recorded and compared with those obtained prior to head rotation. The data concerning to the BAEP before and after head injury were calculated and analyzed by statistical s0ftware 0f SPLM[3]. 维普资讯 http://www.cqvip.com ・390・ 志(Chin J Neurosur ̄Dis Res)2007:6(5 RESULTS III~V.The amplitude of wave llI and V were markedly reduced. No significant difference was There was an obvious delay at 6 hours post lateral observed in the latent period of wave I.wave.to—wave interval of I~V,and the amplitude of wave I. head rotation for the latent period of wave llI and V, and the wave.to—wave interval of wave I~llI and wave Tab 1 The latent period,wave—to—wave interval and amplitude of all waves in BAEP before and after head rotation f n =20,x 4-s) Comparison before and after rotation: P<0.01“P<001 ..DISCUSSlON paths.The BAEP is a relatively sensitive method among neuro—electro—physiological tests.It reflects the nervous In the neural path connecting the sensory receptors and central nervous system,the sensory receptors often meet multiple external stimuli and hence serve as the origin of various nervous impulses.Large amount of function state of auditory conducting path, and demonstrates in the indirect way the severity of brainstem injury. There are five consecutive neurons that are involved in central neural path for auditory sensation.The acoustic hair cell is the first-grade neuron and also the receptor organ for hearing.When sound wave occurs, the stimulated hair cell initiates nerve impulses that pass to the brain via the cochlear division of the eighth cranial nerve.The second—grade neuron exists in cochlear nucleus in medullar oblongata.The third-grade neuron consists of olivary neucleus,inferior olivary activity potentials are delivered in unsynchronized way from the sensory receptors to the central brain.In this transmitting process, many activity potentials are counteracted,therefore,these impulses can not be recorded at the surface of the brain.On the other hand, fter a siangle and intensive and short stimulus exerts influence on the a designated sensory receptor,for example,short voice and flash respectively stimulating ears and eyes,a series of synchronized impulses are caused in the afferent neural fibers.These impulses are transmitted to the nucleus along the special path at the approximately same time,and then reach the fixed area at the cortex that result in synchronized depolarized changes in neural cells.These above changes are shown neueleus and lateral lemniscus in ports. and postgeminum in midbrain.Medial geniculate body in thalamus is the forth—grade neuron that forms the auditory radiation to the fifth—grade neuron in auditory cerebral cortex.Normal BAEP shows five to seven clear waves that are the representative of the designated site along the central auditory path.It is generally thought clearly in the baseline of the simultaneous potential activity of brain cortex.The lower the amplitude of simultaneous cortex potential is,the stronger the evoked potential will get[引.that I~VII is associated with auditory nerve.cochlear nucleus,superior olivary neucleus,lateral lemniscus, The deep anesthesia with sodium inferior colliculus,medial geniculate body,and auditory radiation.Hence,it is much valuable to analyze the BAEP for the aim of understanding the brainstem pentobarbital inhibits greatly the simultaneous cortex reactions and thus makes it easier to demonstrate the evoked potentials.The type,amplitude,and phase of the evoked potentials are related to the integrty of the sensory receptors,the special neural path,and the site of brain cortex.The evoked potential is possibly iluenced by the impairmentfn at any part of the afferent function and investigating the injury site.It has been documented that wave III and V were involved at earlier stage in rabbit model of increased ICP .It was speculated that superior olivary neueleus,lateral lemniscus,and inferior colliculus were damaged in this 维普资讯 http://www.cqvip.com 经 mode1. 志(Chin J Neurosurg Dis Res)2Q07;鱼( ・391・ axons,and the hemorrhages and ischemia,etc.which In the present study,there was an obvious delay at definitely inflicted the waves in BAEP by shortening the 6 hour post lateral head rotation for the latent period of wave 1II and V.and the wave—to—wave interval of wave I~11 and wave III~V.The amplitude of wave m and V were markedly reduced.No signiifcant difference was observed in the latent period of wave I,wave—to— wave interval of I V,and amplitude of wave I.It is suggested th at the possible impairment occurred in olivary nucleus, 1ateral lemniscus, and inferior collicu1us.These results were in concord with the ifndings we had in our previous research on the pathological evidences in rat brainstem in DAI post lateral head rotation _1.2 j.The differences in latent Deriod fl0r BAEP waves are related to many factors,such as neural impulse transmitting speed.the distance and way for transmitting path,the number of the delay of synapse,the degree of the demyelination of neural ifblers in transmitting path.The typical morphological changes of DAI occurred in the brainstem in this rat mode1 after lateral head rotation.These changes included the swelling and then disconnection of neural transmitting speed of neural impulses in various paths in brainstem and enhancing the shrinkage of the impulses along the neural paths.The neuro—electro—physiological mechanism for the delay of latent period and wave—to— wave interval and the decrease of the wave amplitude were acturally based on the morphological changes in brainstem. 1 Xiaosheng H,Shengyu Y.Xiang Z, et a1.Diffuse axonal injury due to lateral head rotation in a rat model[ J].J Neurosurg,2000,93(4): 626—633. 2 Xiaosheng H.Xiang Z,Zhou F,et a1.Calcium overloading in traumatic axonal injury by lateral head rotation:morphological evidence in rat model fj].J Clin Neurosci,2004,ll(4):402—407. 3 SPLM.f Statistical Program for Linear Modelling)中文统计软件.第四 军医大学卫生统计学教研室.1986. 4 Richard SS.Clinical and functional histology for medical student[M]. Fimt editi0n.B0st0n:Little,Brown and Company(1nc),1984:754— 771. (收稿日期:2007—08—30;修回日期:2007—09—15)
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