What does the video head impulse test tell us about post-caloric vestibular recruitment?

Abstract Objective: The vestibular recruitment observed in caloric testing is a new tool in the study of the vestibulo-ocular reflex. This study aimed to determine the sensitivity and specificity of the video head impulse test to detect post-caloric vestibular recruitment. Method: In this cross-sectional study, all participants underwent the standard otoneurological assessment of the service, caloric test, and video head impulse test. A non-linear mixed model was used to test for associations. Results: The study group consisted of 250 (89 male and 161 female) patients, with a mean age of 54.84 years. The control group comprised 35 participants, 18 men and 17 women, with a mean age of 40.42 years. Sex and age had no effect on group responses. There was no difference between the study and control groups regarding the interaction between recruitment and gain (p = 0.7487); recruitment and overt (p = 0.7002) and covert saccades (p = 1.0000); and recruitment and anti-compensatory saccades in the contralateral ear (p = 0.3050). The video head impulse test had a sensitivity of 51% and a specificity of 50% as a predictor of post-caloric recruitment. Conclusion: The video head impulse test results showed no relevance in predicting post-caloric vestibular recruitment.

Vestibular recruitment: new application for an old concept / Recrutamento vestibular: nova aplicação para um conceito antigo

Abstract Introduction Vestibular recruitment is a sign of hyperexcitability of central vestibular neurons and may be characteristic of peripheral vestibular damage. Objective To define the post-caloric recruitment index and its ability to predict the stage of vestibular compensation and peripheral lesion. Methods First of all, we demonstrated that larger values in the cold post-caloric stimulation compared to warm stimulation were equivalent to vestibular recruitment observed during the sinusoidal harmonic acceleration test. In the next step, patients with vestibular complaints and asymptomatic controls were submitted to the caloric test. We calculated post-caloric recruitment index for the control group. Among the study group, we analyzed the relation between post-caloric recruitment and unilateral weakness as well as the types of vestibular diagnoses. Results Mean post-caloric recruitment was 17.06% and 33.37% among the control and study group, respectively. The ratio between post-caloric recruitment and unilateral weakness was 1.3 in the study group. Among recruiting subjects, no significant difference of unilateral weakness from the lesioned or healthy side was observed. We found no differences in vestibular diagnoses between recruiting and non-recruiting subjects. Conclusion Post-caloric recruitment index identified asymmetric vestibular tonus and central compensation. The normal value was established at 17.06%.

Resumo Introdução O recrutamento vestibular é um sinal de hiperexcitabilidade dos neurônios vestibulares centrais e pode ser característico de lesão vestibular periférica. Objetivo Definir o índice de recrutamento pós‐calórico e sua capacidade de predizer o estágio de compensação vestibular e lesão periférica. Método Em primeiro lugar, demonstramos que valores maiores na estimulação pós‐calórica fria em relação à estimulação quente foram equivalentes ao recrutamento vestibular observado durante o teste de aceleração harmônica sinusoidal. Na etapa seguinte, os pacientes com queixas vestibulares e controles assintomáticos foram submetidos à prova calórica. Calculamos o índice de recrutamento pós calórico para o grupo controle. No grupo de estudo, analisamos a relação entre o recrutamento pós‐calórico e predomínio labiríntico, bem como os tipos de diagnósticos vestibulares. Resultados O recrutamento pós‐calórico médio foi de 17,06% e 33,37% nos grupos controle e estudo, respectivamente. A razão entre o recrutamento pós‐calórico e o predominício labiríntico foi de 1,3 no grupo de estudo. Nos sujeitos com recrutamento, não foi observada diferença significativa de predominício labiríntico do lado lesionado ou saudável. Não encontramos diferenças de diagnóstico vestibular entre sujeitos com recrutamento e sem recrutamento. Conclusão O índice de recrutamento pós‐calórico identificou tônus vestibular assimétrico e compensação central. O valor normal foi estabelecido em 17,06%.

Evaluation of Dizziness Handicap in Adolescents and Adults with Auditory Neuropathy Spectrum Disorder

Abstract Introduction Vestibular symptoms and damage to the vestibular branch of the eighth cranial nerve is reported in individuals with auditory neuropathy spectrum disorder (ANSD). However, the real life handicap caused by these vestibular problems in individuals with ANSD is not studied. Objective The present study attempted to evaluate the dizziness-related handicap in adolescents and adults with ANSD. Method The dizziness handicap inventory (DHI) was administered to 40 adolescents and adults diagnosed with ANSD. The study also attempted to determine if there is any gender effect on DHI scores and its correlation to the reported onset of hearing loss. Results The results of the study showed that adolescents and adults with ANSD had a moderate degree of dizziness-related handicap. The dizziness affected their quality of life, causing emotional problems. There was no gender effect, and the level of the handicap was greater in the cases in which the onset of the hearing loss was reported soon after the diagnosis of ANSD. There could be a vestibular compensation that could have resulted in a reduction in symptoms in individuals in whom the onset of the hearing loss was reported later on. Conclusion Thus, a detailed assessment of vestibular problems and their impact on quality of life is essential in adolescents and adults with ANSD. Appropriate management strategies should be considered to resolve their vestibular problems and improve their quality of life.

Reduction of long-term potentiation at Schaffer collateral-CA1 synapses in the rat hippocampus at the acute stage of vestibular compensation

Vestibular compensation is a recovery process from vestibular symptoms over time after unilateral loss of peripheral vestibular end organs. The aim of the present study was to observe time-dependent changes in long-term potentiation (LTP) at Schaffer collateral-CA1 synapses in the CA1 area of the hippocampus during vestibular compensation. The input-output (I/O) relationships of fEPSP amplitudes and LTP induced by theta burst stimulation to Schaffer's collateral commissural fibers were evaluated from the CA1 area of hippocampal slices at 1 day, 1 week, and 1 month after unilateral labyrinthectomy (UL). The I/O relationships of fEPSPs in the CA1 area was significantly reduced within 1 week post-op and then showed a non-significant reduction at 1 month after UL. Compared with sham-operated animals, there was a significant reduction of LTP induction in the hippocampus at 1 day and 1 week after UL. However, LTP induction levels in the CA1 area of the hippocampus also returned to those of sham-operated animals 1 month following UL. These data suggest that unilateral injury of the peripheral vestibular end organs results in a transient deficit in synaptic plasticity in the CA1 hippocampal area at acute stages of vestibular compensation.

Role of the Cerebral Cortex on Vestibular Compensation Following Unilateral Labyrinthectomy in Rats / 대한평형의학회지

OBJECTIVE: The cerebral cortex can modulate vestibular functions through direct control of neuronal activities in the vestibular nuclei. The purpose of this study was to investigate the effect of unilateral cortical lesion or cortical stimulation on static vestibular symptoms and vestibular nuclear activities at the acute stage of vestibular compensation following unilateral labyrinthectomy (UL) in rats. METHODS: The photothrombic ischemic injury using rose bengal was induced in the primary motor cortex or primary sensory cortex, and electrical stimulation was applied to the primary motor cortex, primary sensory cortex, or sencondary sensory cortex, respectively, in unilateral labyrinthectomized rats. Static vestibular symptoms including ocular movement and postural deficits, and expression of c-Fos protein in the medial vestibular nucleus (MVN) were measured. RESULTS: Lesion of the motor cortex produced a marked postural deficit with paralytic weakness in the hindlimb contralateral to UL. Number of spontaneous nystagmus in animals receiving cortical lesion was significantly increased 2, 6, and 12 hours after UL compared with animals being UL only. Lesion of the primary motor cortex or stimulation of the S2 sensory cortex decreased expression of c-Fos protein in MVN following UL compared with UL only group. Electrical stimulation of S2 sensory areas caused significant reduction of static vestibular symptoms and decreased expression of c-Fos protein in MVN 24 hours following UL. CONCLUSION: The present results suggest that cerebral cortex involves in recovery of static vestibular symptoms during vestibular compensation following UL.

Understanding of Structure and Function of Vestibular Cortex / 대한평형의학회지

The vestibular end-organs generate very sophisticated gravity sensory information about head movement by sensing head acceleration in three-dimensional space. Vestibular information is crucial for higher brain functions such as cognition of spatial orientation, spatial memory, and perception of self-motion. The term "vestibular cortex" represents cortical area where vestibular information is processed, converged with other sensory inputs to maintain cortical functions. The vestibular cortex gives rise to commend signals that control the vestibulosomatic reflex through the modulation of vestibular nuclear activity in the brainstem. The vestibular cortex includes such different cortical regions as the premotor region of the frontal cortex, parietal areas, temporal areas, and a central core region called parietoinsular vestibular cortex. This paper summarizes systemically animal and clinical research data concerned with the vestibular cortex in order to understand anatomy and functions of the vestibular cortex and to provide a basic literature for further study.

Temporal Changes of the Calcium-binding Proteins in the Medial Vestibular Nucleus following Unilateral Labyrinthectomy in Rats

Calcium (Ca2+) is an intracellular second messenger associated with neuronal plasticity of the central nervous system. The calcium-binding proteins regulate the Ca2+-mediated signals in the cytoplasm and buffer the calcium concentration. This study examined temporal changes of three calcium-binding proteins (calretinin, calbindin and parvalbumin) in the medial vestibular nucleus (MVN) during vestibular compensation after unilateral labyrinthectomy (UL) in rats. Rats underwent UL, and the changes in the expression of these proteins at 2, 6, 12, 24, 48, and 72 h were examined by immunofluorescence staining. The expression levels of all three proteins increased immediately after UL and returned to the control level by 48 h. However, the level of calretinin showed changes different from the other two proteins, being expressed at significantly higher level in the contralateral MVN than in the ipsilateral MVN 2 h after UL, whereas the other two proteins showed similar expression levels in both the ipsilateral and contralateral MVN. These results suggest that the calcium binding proteins have some protective activity against the increased Ca2+ levels in the MVN. In particular, calretinin might be more responsive to neuronal activity than calbindin or parvalbumin.

The Change in the Expression of Gamma-Amino Butyric Acid A Receptor Subunits in Rat's Flocculus / 听力学及言语疾病杂志

Objective To observe the expression of gamma-amino butyric acid A receptor(GABAA receptor)?3、?1、? subunits in rat flocculus following unilateral labyrinthectomy(UL).Methods 24 wistar rats were randomly divided into two groups.18 animals received unilateral labyrinthectomy while the others maintained labyrinthine well.After removing left labyrinthine,the change of GABAA receptor ?3、?1、? subunits was detected by immunohistochemistry.Results GABAA receptor ?1、? subunits in flocculus was induced on the operated side after unilateral labyrinthectomy.The most expression was on the 1st day flocculus of following UL.The expression is descending from the 3rd day to 7th day flocculus of following UL.The GABAA receptor ?3 subunit immunostaining in flocculus was weak and did not change in the process of vestibular compensation.Conclusion GABAA receptor ?1、? subunits were induced increase in the flocculus after unilateral labyrinthectomy.The alteration in the resting discharge of the central vestibular neurons may be caused by the increase of GABAA receptor ?1、? subunits in the flocculus.But the significance of the change of GABAA receptor ?1、? subunits in the vestibular compensation is still unknown.Our study suggests that GABAA receptor ?3 subunits may not participate in constructing GABAA receptor in the flocculus.

Spatio-temporal Changes on c-Fos Protein Expression in the Brain Stem Nuclei following Arsanilate-induced Unilateral Labyrinthectomy in Rats

Spatio-temporal changes on c-Fos protein expression were investigated in vestibular compensation following unilateral labyrinthectomy (UL) induced by injection of arsanilate into the middle ear cavity, chemical labyrinthectomy, or surgical labyrinthectomy in medial vestibular nuclei (MVN), prepositus hypoglossal nuclei (PrH), and inferior olivary nuclei (ION) of Sprague-Dawley rats. Number of spontaneous nystagmus in surgical labyrinthectomy group was 28.2+/-.2 beats/10 sec at post-op 2 hs and the nystagmus disappeared 76 hs after UL. In chemical labyrinthectomy group, spontaneous nystagmus occurred 6 hs after UL and increased up to maximum at 12 hs and disappeared 96 hs. Head deviation in surgical labyrinthectomy group reached a peak at post-op 2 hs and recovered to control level at 144 hs, but chemical labyrinthectomy produced head deviation 24 hs after UL and increased degree of the deviation over time till 144 hs. Expression of c-Fos protein in surgical labyrinthectomy group at post-op 2 hs was 81+/-9.4 cells in ipsilateral MVN to the lesion side and 212+/-0 cells in contralateral MVN, which showed severe asymmetry between bilateral MVN, and decrease of c-Fos protein expression was more in contralateral MVN than in ipsilateral MVN at 6 hs. Chemical labyrinthectomy expressed more c-Fos protein in contralateral MVN 6 hs after UL and in ipsilateral MVN 12 hs after UL, which showed asymmetry of c-Fos protein expression between bilateral MVN. And the expression in ipsilateral MVN of chemical labyrinthectomy group was increased gradually 48 hs after UL and reached a peak at 72 hs. In chemical labyrinthectomy group, expression of c-Fos protein in PrH was increased more in ipsilateral than in contralateral 6 hs after UL and more in contralateral 12 hs after UL, and ION showed more expression of c-Fos protein in contralateral than in ipsilateral 6 hs after UL through 72 hs. These results suggest that the course of vestibular compensation and the temporal expression of c-Fos protein in the brain stem nuclei following UL differed between surgical and chemical labyrinthectomy.

Effect of Ginkgo biloba on Expression of c-Fos Protein in the Vestibular Nuclear Complex following Unilateral Labyrinthectomy in Rats

BACKGROUND AND OBJECTIVES: The neuroprotective effect of Ginkgo biloba has been demonstrated in several in vivo and in vitro models. The effect of Ginkgo biloba on vestibular compensation following unilateral labyrinthectomy (UL) was investigated. Material and Methods: Spontaneous nystagmus and c-Fos protein expression were measured following UL in Sprague-Dawley rats with pretreatment of Ginkgo biloba (50 mg/kg, i.p.). RESULTS: After pretreatment with Ginkgo biloba (50 mg/kg, i.p.) expression of c-Fos protein in the vestibular nuclear complex and frequency of spontaneous nystagmus were measured till 24 hours after UL. UL produced spontaneous nystagmus with frequency of 124+/-.2 beats/min at post-op 2 hrs and 70+/-.1 beats/min at post-op 24 hrs. Pretreatment with Ginkgo biloba significantly decreased the frequency of spontaneous nystagmus till post-op 24 hrs compared to control group (p<0.05). UL produced marked expression of c-Fos protein in bilateral medial vestibular nucleus, inferior vestibular nucleus, and superior vestibular nucleus, and the number of expression was significantly higher in contralateral vestibular nuclei to the lesion than ipsilateral vestibular nuclei at post-op 2 hrs (p<0.01). The number of c-Fos protein expression was decreased with time and significantly higher in ipsilateral vestibular nuclei than contralateral ones at post-op 24 hrs (p<0.01). Pretreatment with Ginkgo biloba significantly decreased the number of c-Fos protein expression following UL (p<0.01) and abolished the asymmetry of c-Fos protein expression in bilateral vestibular nuclei at post-op 24 hrs. CONCLUSION: These results suggest that Ginkgo biloba may facilitate vestibular compensation following UL through modulation of neurotransmitters and neuroprotective effects.

Immunohistochemical Identification of Phosphorylated Extracellular Signal-Regulated Kinase1/2 in Rat Vestibular Nuclei by Unilateral Labyrinthectomy

This study evaluated the expression of phosphorylated signal-regulated kinase1/2 (pERK1/2), which is one of the main factors regulating transcription of the cfos oncogene in neurons, in the vestibular nuclei of Sprague-Dawley rats following unilateral labyrinthectomy (UL). Surgical UL was performed to eliminate afferent signals from the peripheral vestibular receptors in the inner ear, under a surgical microscope, 2 hours after anesthesia. Significant numbers of pERK1/2 immunoreactive neurons were seen in the superior, medial, and inferior vestibular nuclei. There were more pERK1/2 immunoreactive cells in the vestibular nuclei contralateral than in the vestibular nuclei ipsilateral to the injured labyrinth, which resulted in significant asymmetric expression of pERK1/2 immunoreactive cells. Subsequently, the pERK1/2 immunoreactivity decreased rapidly, disappearing 90 min after labyrinthectomy. No pERK1/2 labeling was seen in the lateral vestibular nucleus. These results suggest that intracellular signal pathways for the activation of extracellular signal-regulated kinase in the vestibular nuclei are involved in lesion-neural plasticity in the vestibular system

Roles of Nitric Oxide in Vestibular Compensation

The effects of nitric oxide on the vestibular function recovery following unilateral labyrinthectomy (UL) were studied. Sprague-Dawley male rats, treated with nitric oxide liberating agent sodium nitroprusside (SNP) and NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME), were subjected to destruction of the unilateral vestibular apparatus, and then spontaneous nystagmus was observed in the rat. To explore the effects of nitric oxide on the neuronal excitability, whole cell patch clamp technique was applied on isolated medial vestibular nuclear neurons. The frequency of spontaneous nystagmus in SNP treated rats was lesser than that of spontaneous nystagmus in control animals. In contrast, pre-UL treatment with L-NAME resulted in a significant increase in spontaneous nystagmus frequency. In addition, SNP increased the frequency of spontaneous action potential in isolated medial vestibular nuclear neurons. Potassium currents of the vestibular nuclear neurons were inhibited by SNP. After blockade of calcium dependent potassium currents by high EGTA (11 mM) in a pipette solution, SNP did not inhibit outward potassium currents. 1H-[1, 2, 4] oxadiazolo [4, 3-a] quinozalin-1-one (ODQ), a specific inhibitor of soluble guanylyl cyclase, inhibited the effects of SNP on the spontaneous firing and the potassium current. These results suggest that nitric oxide after unilateral labyrin- thectomy would help to facilitate vestibular compensation by inhibiting calcium-dependent potassium currents through increasing intracellular cGMP, and consequently would increase excitability in ipsilateral vestibular nuclear neurons.

Changes in Excitability of Neurons in Rat Medial Vestibular Nucleus Following Vestibular Neurectomy

Intrinsic excitabilities of acutely isolated medial vestibular nucleus (MVN) neurons of rats with normal labyrinth and with undergoing vestibular compensation from 30 min to 24 h after unilateral vestibular deafferentation (UVD) were compared. In control rats, proportions of type A and B cells were 30 and 70%, respectively, however, the proportion of type A cells increased following UVD. Bursting discharge and irregular firing patterns were recorded from 2 to 12 h post UVD. The spontaneous discharge rate of neurons in the ipsilesional MVN increased significantly at 2 h post-UVD and remained high until 12 h post-UVD in both type A and type B cells. After-hyperpolarization (AHP) of the MVN neurons decreased significantly from 2 h post-UVD in both types of cells. These results suggest that the early stage of vestibular compensation after peripheral neurectomy is associated with an increase in intrinsic excitability due to reduction of AHP in MVN neurons.

Activation of cAMP-Response Element Binding Protein in the Brain Stem Nuclei during Vestibular Compensation in Unilateral Labyrinthectomizied Rats / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The p-CREB (phospholyated form of cAMP/calcium response element binding protein) was known to be one of transcription factors for immediate early genes in the brain stem nuclei. The purpose of this present study was to evaluate time-dependent expression of p-CREB and investigate the effect of MK801, non-competitive NMDA channel blocker, on p-CREB expression following unilateral labyrinthectomy (ULX). MATERIALS AND METHODS: Adult Sprague-Dalwey rats weighing 250-300 g were divided into a control group and an unilateral labyrinthetomy (ULX) group. The intraperitoneal injection of MK801 was administered either 30 min before or 24 hrs after ULX. The ABC immunohistochemical staining and digital image analysis system were used to measure the p-CREB expression in neuronal cells. RESULTS: The peak level of p-CREB expressions in 4 major vestibular nuclei was observed bilaterally with the other brain stem nuclei including reticular formation and olivary complex at 30 min following ULX. Thereafter, the p-CREB immunoreactivity in these nuclei was reduced rapidly to the control level for 6 hrs after ULX. Treatment of MK801 for 30 min preceding ULX decreased p-CREB immunoreactivity significantly in both the injured and intact sides of the 4 major vestibular nuclei with dose-dependent relationship. However, MK801 did not affect the change of p-CREB immunoreactivity in bilateral vestibular complex 24 hrs after ULX. CONCLUSION: These results suggest that cAMP/calcium response element binding protein plays an important role in the initial events of vestibular compensation in which its activity is in part regulated by NMDA receptor.

Electrical stimulation can facilitate vestibular compensation following unilateral labyrinthectomy in rats

To investigate the effects of electrical stimulation on vestibular compensation, which is the recovery of vestibular symptoms following unilateral labyrinthectomy (UL), intermittent electrical stimulation was applied to the injured vestibular portion in Sprague-Dawley rats. Vestibuloocular and vestibulospinal reflexes, electrical activity and expression of c-Fos protein in medial vestibular nuclei (MVN) were measured with time following UL. Spontaneous nystagmus occurred with frequency of 2.9+/-0.2 beats/sec at 2 hours after UL and disappeared after 72 hours. Electrical stimulation decreased the frequency of nystagmus significantly till 24 hours after UL. Roll head deviation was 107+/-9.7degree at 2 hours after UL and the deviation was maintained till 72 hours, but electrical stimulation decreased the deviation significantly 6 hours after UL. Resting activity of type I neurons in ipsilateral MVN to the injured vestibular side decreased significantly compared with control at 6 and 24 hours after UL, but the activity of type I neurons was recovered to control level by electrical stimulation at 24 hours after UL. Gain of type I neurons induced by sinusoidal rotation of 0.1 Hz decreased significantly till 24 hours after UL, but electrical stimulation restored the activity at 24 hours. The gain of type II neurons decreased significantly at 6 hours after UL, but electrical stimulation restored the activity. Expression of c-Fos protein was asymmetric between bilateral MVN till 24 hours after UL, but the asymmetry disappeared by electrical stimulation 6 hours after UL. These results suggest that electrical stimulation to the injured vestibular portion facilitates vestibular compensation following UL by restoration of symmetry of neuronal activity between bilateral vestibular nuclei resulting from increased activity in ipsilateral vestibular nuclei to the injured side.

The Role of the Cerebellar Uvulonodulus on the Early Stage of Vestibular Compensation in Rats / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Many expeerimental evidences have beensupported that the vestibulocerebellum involved in recovery of vestibular compensation. The purpose of this study was to investigate effect of unilateral ablation of uvula and nodular lobes on early stage of vestibular compensation. MATERIALS AND METHODS: Adult Sprague-Dawley rats weighing 250~300 g were used and divided into control (CON) group receiving sham operation, unilateral labyrinthectomy (ULX) group, ULX plus left uvulonodulectomy (ULX+Lt-UNLX) group, and ULX plus right uvulonodulectomy (ULX+Rt-UNLX) group. UNLX was performed 1 hour following ULX. Spontaneous nystagmus (SN) and roll head tilt (RHT) were recorded for 3 days following ULX. Temporal change of c-Fos protein expression in the medial vestibular nuclei (MVN) was measured for 2 days following ULX. RESULTS: There were observed SN with contralateral direction to injured labyrinth and RHT toward ipsilateral side with flexion of ipsilateral limb and extenstion of contralateral one just after ULX. There was significant increase in SN frequency of ULX+Rt-UNLX group compared with that of ULX group. In addition, ULX+Rt-UNLX group resulted in severe postural asymmetry. ULX elicited prominent expression of c-Fos protein in contralateral MVN 2 hours but in ipsilateral one 6, 24 hours after ULX, respectively. In contrast, number of c-Fos positive neurons was higher in contralateral MVN. 24 hours after ULX higher expression of c-Fos protein in contralteral MVN was still remained in ULX+Rt-UNLX group but that in ipsilateral MVN was observed in ULX+Lt-UNLX group. CONCLUSION: These results suggest that UNLX have a different effect on the early stage of vestibular compensatory process and the uvulonodulus serves the restoration of balance between intervestibular nuclear activities after ULX by inhibition of vestibular nuclear complex through nhibitory Purkinje system.

Temporal changes in neuronal activity of the bilateral medial vestibular nuclei following unilateral labyrinthectomy in rats

To investigate the changes in the responses of vestibular neurons with time during vestibular compensation, the resting activity and dynamic responses of type I and II neurons in the medial vestibular nuclei to sinusoidal angular acceleration were recorded following unilateral labyrinthectomy (ULX) in Sprague-Dawley rats. The unitary extracellular neuronal activity was recorded from the bilateral medial vestibular nuclei with stainless steel microelectrodes of 3~5 MOMEGA before ULX, and 6, 24, 48, 72 hours, and I week after ULX under pentobarbital sodium anesthesia (30 mg/kg, i.p.). Gain (spikes/s/deg/s) and phase (in degrees) were determined from the neuronal activity induced by sinusoidal head rotation with 0.05, 0.1, 0.2, and 0.4 Hz. The mean resting activity before ULX was 16.7+/-8.6 spikes/s in type I neurons (n=67, M+-SD) and 14.5+/-8.4 spikes/s in type II neurons (n=43). The activities of ipsilateral type I and contralateral type 11 neurons to the lesion side decreased markedly till 24 hr post-op, and a significant difference between ipsilateral and contralateral type I neurons sustained till 24 hr post-op. The gain at 4 different frequencies of sinusoidal rotation was depressed in all neurons till 6 or 24 hr post-op and then increased with time. The rate of decrease in gain was more prominent in ipsilateral type I and contralateral type 11 neurons immediately after ULX. Although the gain of those neurons increased gradually after 24 hours, it remained below normal levels. The phase was significantly advanced in all neurons following ULX. These results suggest that a depression of activities in ipsilateral type I and contralateral type II neurons is closely related with the occurrence of vestibular symptoms and restoration of activities in those neurons ameliorates the vestibular symptoms.

Relationship between Recovery of Vestibuloocular Reflex and c-Fos Protein Expression in Medial Vestibular Nuclei Following Unilateral Labyrinthectomy in Rats / 대한이비인후과학회지

Relationships between recovery of vestibuloocular reflex and expression of c-fos immunoreactive cells in the medial vestibular nuclei following unilateral labyrinthectomy(ULX) were investigated in rats. Frequency of spontaneous nystagmus, velocity of eye movement induced by sinusoidal rotation of the whole body at frequencies of 0.1, 0.2, 0.5Hz, and the number of c-fos immunoreactive cells in the medial vestibular nuclei were measured for 72 hours after ULX. Frequency of spontaneous nystagmus was 3.9+/-0.5 beats/sec(M+/-SD) immediately after ULX and disappeared completely within 48 hours. On sinusoidal rotation, eye movement induced by rotation toward the lesioned side recovered normal pattern within 24 hours at 0.1Hz rotation, and 12 hours at 0.2, 0.5Hz. Directional preponderance which represents the symmetry of bilateral vestibular functions decreased to less than 20% at 72 hours, but did not recover normal limit. The number of c-fos immunoreactive cells in the bilateral medial vestibular nuclei was severe asymmetry till 24 hours of ULX. However, the symmetry was recovered after 48 hours. These results indicate that the recovery of vestibuloocular reflex correlates with the expression of c-Fos immunoreactive cells of the medial vestibular nuclei in the early stage of vestibular compensation following ULX. Therefore, the vestibular nuclei may play a key role in vestibular compensation.

Evaluation of Compensation in Peripheral Vestibulopathy / 대한이비인후과학회지

The initial severe and disabling symptoms of vestibular dysfunction diminish gradually by a process of compensation. Although the process is complex and not fully understood, knowledge of the extent of compensation makes physicians to identify the causes and to determine treatment choices of the dysfunction. In this report we present 2 common cases of peripheral vestibulopathy that result from different disease processes, and review the physiologic and functional changes as the compensation proceeds that can be evaluated by vestibular function tests including electronystagmography(ENG), rotation chair, and dynamic posturography. These tests are valuable tools in the assessment of the degree of compensation as well as the side and site of lesions in vestibulopathy.

Effects of electrical stimulation of the vestibular system on neuronal activity of the ipsilateral medial vestibular nuclei following unilateral labyrinthectomy in rats

The purpose of this study was to evaluate the effects of electrical stimulation on vestibular compensation following ULX in rats. Electrical stimulation (ES) with square pulse (100 ~ 300 uA, 1.0 ms, 100 Hz) was applied to ampullary portion bilaterally for 6 and 24 hours in rats receiving ULX. After ES, animals that showed the recovery of vestibular symptoms by counting and comparing the number of spontaneous nystagmus were selected for recording resting activity of type I, II neurons in the medial vestibular nuclei (MVN) of the lesioned side. And then the dynamic neuronal activities were recorded during sinusoidal rotation at a frequency of 0.1 Hz and 0.2 Hz. The number of spontaneous nystagmus was significantly different 24 hours (p< 0.01, n = 10), but not 6 hours after ULX+ES. As reported by others, the great reduction of resting activity only in the type I neurons ipsilateral to lesioned side was observed 6, 24 hours after ULX compared to that of intact labyrinthine animal. However, the significant elevation (p < 0.01) of type I and reduction (p < 0.01) of type II neuronal activity were seen 24 hours after ULX+ES. Interestingly, gain, expressed as maximum neuronal activity(spikes/sec)/maximum rotational velocity (deg/sec), was increased in type I cells and decreased in type II cells 24 hours after ULX+ES in response to sinusoidal rotation at frequencies of both 0.1 Hz and 0.2 Hz. This result suggests that accompanying the behavioral recovery, the electrical stimulation after ULX has beneficial effects on vestibular compensation, especially static symptoms (spontaneous nystagmus), by enhancing resting activity of type I neurons and reducing that of type II neurons.