| Background and purposeDiabetes mellitus is a metabolic disorders characterized by abnormal metabolism of carbohydrate, fat and protein resulting from lack of insulin secretion, insulin action or both. Vestibular dysfunction is one of the complications of diabetes. Lindsey found that there is a high risk of falls and postural instability in diabetic patients, the incidence of falls in the diabetics aged over 65 was 39%, which is 3 times higher than the control group. Erdem compare the vestibular function among the 104 type 2 diabetes individuals and control group, found that statistically significant were present in gaze test, smooth persuit, saccade, opkinetic, and Dix-Hllpike tests in diabetes patients compared with the control group.Studies of vestibular functions in diabetes are very limited. For the research findings are not the same, which may be related to samples, age structure, the different duration. Cervical vestibular evoked myogenic potentials reflects vestibular activity that is elicited by high intensity sounds and detected as a change in sternocleidomastoid muscle potentials within the neck.The pathways of cVEMP include saccule, inferior vestibular nerve, vestibular mucleus and ipsilateral sternocleidomastoid, cVEMP is able to assess the otolith organ of vestibular especially the saccule and inferior vestibular nerve. Konukseven using cVEMP and oVEMP to assess 30 diabetes and prediabetes vestibular function in 2014, found that the mean latencies of both cVEMP and oVEMP pi, nl were significantly longer than the prediabetes group and the controls. To date, although there is a substantial number of clinical study have showed an association between diabetes mellitus and vestibular dysfunction, but the functional disturbance of the vestibular has not been reported because of the lack of a pathological model to explain the mechanism of the disease development. In this study, an diabetes rats model was established to observed the time when the threshold increased、the PI peak latency and Nl peak latency prolonged and amplitude decreased. Understanding this phenomenon may be useful to the physical therapist vestibular rat model of diabetes was in diabetic rats appear cVEMP threshold latency between P1, N1 latency and P1-N1 wave amplitude time exception occurs. Provide theoretical and experimental basis for the further investigation of pathogenic mechanisms help guide diabetes-related complications balance impairment early intervention, thereby reducing balance dysfunction due to diabetes caused by falls, disability and other serious consequences.Methods1. Animal Preparation:220 male SD rats weighing 300-350g were randomly divided into control group(n=20) and diabetes group(n=200), then diabetes rats were divided into 4,6,8, 10,12week groups(40 rats each group) according to the diabetes duration.2. The diabetes rats model:Male SD rats were injected with 1% STZ (55 mg/kg) which was dissolved in citric acid and sodium citrate buffer intraperitoneally. The control rats were intraperitoneally injected with citric acid and sodium citrate buffer of equal volume.3. ABR Test:Animals were anesthetized by an intraperitoneal injection of 2% pentobarbital sodium (0.2ml/100g). A pair of needle electrodes was placed onto the vertex and the ipsilateral retro-auricular region, with a ground electrode on the foot of rats. Click stimuli were delivered through a plastic tube inserted into the ear canal in order to record ABR. The repetition rate was 12.1/s, and 1000 sweeps were averaged. The electromyographic signals were amplified and band-pass filtered to 300 to 3000 Hz. The analysis time for each response was 20 ms, with 1024 responses being averaged for each run. The stimulus intensity was from 100 dB SPL initially, followed by 10 dB step decrement until the absence of the III waveforms, thus the threshold of ABR was determined.4. cVEMP Test:Animals were anesthetized by an intraperitoneal injection of 2% pentobarbital sodium (0.2ml/100g). A pair of active needle electrodes was fitted on both dorsal neck extensor muscles at the level of the third cervical vertebral bone (C3), while a reference electrode was placed on the occipital area at the midline. During the recording, each animal was fixed with its head elevated and neck extended in a prone position throughout the test. Click stimuli were delivered through a short tube inserted into the ear canal. During recording, electromyographic signals were amplified and band-pass filtered to 10 to 1000 Hz. Each animal underwent serial tests, with initial stimulus intensity of 100dB nHL. The stimulus intensity was then increased in steps of 10 dB nHL until the VEMP response reappeared, and the threshold was thus determined. The stimulation rate was 5 Hz and the analysis time for each response was 40 ms, with 204 responses being averaged for each run. The threshold, positive-negative polarities of biphasic waveforms were termed P1 and N1. The latencies of positive peak Ⅰ, negative peak Ⅱ, and peak-to-peak Ⅰ-Ⅱ amplitude were measured5. Morphological study:30 male SD rats were randomly divided into control group and diabetes group, then diabetes rats were divided into 4,6,8,10,12week groups according to the diabetes duration. Animals were anesthetized by an intraperitoneal injection of 2% pentobarbital sodium (0.2ml/100g). Then cut the thoracic cavity, exposing the heart, with saline and 4% paraformaldehyde solution from the left ventricle puncture perfusion fixation. Segregated otocyst from temporal bone quickly under the microscope, exposed cochlea, bored apical cochlea, took stapes out, opened ovoid window and round window, poured the 4% Polyoxymethylene through cochlea then fixed in it for one day, decalcificated with EDTA. After de-calcification, embedment, cutting sections in 4 μm and HE dyeing, the histological morphologies of the saccule in each group were observed under an optical microscope.6. TEM study:30 male SD rats were randomly divided into control group and diabetes group, then diabetes rats were divided into 4,6,8,10,12week groups according to the diabetes duration. Animals were anesthetized by an intraperitoneal injection of 2% pentobarbital sodium (0.2ml/100g).Then cut the thoracic cavity, exposing the heart, with saline and 2.5% GlutaricDialdehyde from the left ventricle puncture perfusion fixation. Segregated the sciatic nerve and the inferior vestibular nerve. Then fixed in it with 2.5% GlutaricDialdehyde for one day, After de-calcification, embedment, cutting sections and dyeing, the nerve sections were observed under a transmission electron microscopeistically significant.7. Statistical analysisOne-way analysis of variance (ANOVA) were used to conduct multiple comparisons between the threshold, latencies or amplitude of cVEMP. The results were analyzed with SPSS 17.0 software. A significant difference indicates P< 0.05.Results1. All diabetic groups appeared typical diabetic symptoms including polydipsia, polyuria, more food. Established rate of DM rat model is 76.5% and the cumulative death rate is 22.22%. The diabetes group weight loss(F= 17.44, P<0.01) and blood glucose elevation(F=64.07, P<0.01) compared with the control group.2. The threshold of ABR was significantly elevated (P<0.05) in the 6,8,10,12 week diabetic group. The threshold of ABR was significantly elevated in 6 week.3. Compared to normal group, the threshold of cVEMP was significantly elevated in 8 week(P<0.05),10 week(P<0.01),12 week(P<0.01) diabetes groups and the mean latency of P1 peak was significantly prolonged in 8 week(P<0.05),10 week(P<0.01),12 week (P<0.01). The mean latency of N1 peak was significantly prolonged in 10 week (P<0.01),12 week(P<0.01) compared to the control group. As to P1-N1 amplitude, there was no significantly difference in all groups(P>0.05)4. Morphological showed that the saccule microstructure of the diabetic model rats at 0 week were similar to those of the control group, the vestibular hair cells, supporting cell could be clearly identified under the microscope.5. Electron microscopy showed that sciatic nerve appeared morphological alterations changes earlier than the inferior vestibular nerve. In diabetic model rats at 4 weeks, the nerve fibers appeared loose in organization and with the extension of course, more serious morphological changes. The inferior vestibular nerve fibers of the diabetic model rats at 4 and 6 week were similar to those of the control group, with intact myelin sheaths, alternately dark and bright, concentric laminae medullares, and axons that were homogeneous in density and plump. At 8 weeks, the myelin sheaths of nerve fibers were segmental demyelination, but the axons are normal.At 10 weeks, the myelin sheaths of nerve fibers were segmental demyelination and the atrophy of axons more widespread, significant changes in morphology were observed in diabetic model rats in the 12 week group:the myelin sheaths were absent or separated and lysosomal enzyme can be found in axons or Schwann cells.Conclusions1. The study showed that the vestibular dysfunction appeared from the 8th week, including the threshold elevated and the mean latency of P1 peak prolonged. Diabetes may cause Peripheral vestibular dysfunction in the early period. The severity of disease and the duration may also influence the vestibular system. cVEMP can be used as an early diagnostic method. For further study we can extend the time of observation or do some treatment on the diabetes animal models, will help improve the diagnostic level of vestibular dysfunction in diabetes patients. In order to reduce the fall, disability and other serious consequences caused by the balance dysfunction in diabetic patients.2. In the present study, the sciatic nerve appeared morphological alterations changes earlier than the inferior vestibular nerve. In diabetic model rats at 4 weeks, the nerve fibers appeared loose in organization and with the extension of course, more serious morphological changes. But it was until the 8th the inferior vestibular nerve appeared loose in organization and with the extension of course. For further study we can extend the time of observation or do some treatment on the diabetes animal models, will help improve the diagnostic level of vestibular dysfunction in diabetes patients. In order to reduce the fall, disability and other serious consequences caused by the balance dysfunction in diabetic patients.3. In this study, the structure of the nerve fibers of the inferior vestibular nerve was changed and damaged in the eighth week of the diabetic rats. But compared to the control group, no obvious abnormality was found in the vestibular hair cells and supporting cells of the saccule in examined groups. To conclude that the vestibular hair cells and supporting cells of the saccule may not depend on the integrity and function of the inferior vestibular nerve. The abnormality of cVEMP in the eighth week may be related to the damage of the nerve fiber, And there was no significant association between the vestibular hair cells and the vestibular hair cells, Thus we suspected that the damage of vestibular nerve may play a more important role in the early stage of diabetes.In summary, vestibular damage of diabetic rat can occur in the early stage, and cVEMP can be an alternative method for early diagnosis. It is also found that morphological and structural changes in myelinated nerve fibers of inferior vestibular nerve appeared later than myelinated nerve fibers in diabetic rats, To further study its pathological mechanism, It provides a certain theoretical basis and experimental methods. When the symptoms of peripheral nervous system appear and the corresponding symptoms of vestibular function, Patients should be assessed the vestibular system function as early as possible in order to prevent and reduce the related complications that may cause injury to the balance function. In order to reduce the fall, disability and other serious consequences caused by the balance dysfunction in diabetic patients. The observation time of the animal model can be prolonged in later stage, And can be exerted intervention factors to observe the changes of vestibular function in rats with sciatic nerve lesion, To further study the mechanism of the effect of diabetes on vestibular function. These will help to improve the prevention and diagnosis of diabetic patients with vestibular dysfunction, and also improve the patients’quality life with diabetes. |
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