Establishment of mice expressing EGFP in the placode-derived inner ear sensory cell lineage and FACS-array analysis focused on the regional specificity of the otocyst.

In this study, we established a novel enhanced green fluorescent protein (EGFP) reporter mouse line that enables the visualization of the placode-derived inner ear sensory cell lineage. EGFP was initially expressed in the otic placode and throughout its differentiation process into the inner ear sensory patches. At embryonic day 10.5 (E10.5), EGFP was expressed in the ventral and dorsomedial region of the otocyst. These regions could mainly give rise to the cochlea, including the organ of Corti, and the saccule, including the macula and the endolymphatic duct. The region could also give rise to cells that will develop as either prosensory cells or statoacoustic ganglion neuroblasts. By using this line and fluorescence-activated cell sorting (FACS)-array technology, we developed a new gene expression profile of the regional specificity of the otocyst. EGFP-positive regions include the Otx1-positive region, which could be clearly distinguished from EGFP-negative regions. The signal log ratio of microarray data showed high efficiency in predicting the genes expressed mainly in the ventral and/or dorsomedial otocyst and the data could be mined to uncover many novel genes involved in inner ear morphogenesis and cell fate regulation. Additionally, these data suggest that some novel genes enriched in EGFP-positive regions may be potentially involved in human congenital sensorineural hearing loss. This reporter line could play important roles in the use of animal models for detailed analysis of the differentiation process into the sensory patches and the identification of regional-specific gene networks and novel gene functions in the developing inner ear.

Vestibular drop attack secondary to Meniere's disease results from unstable otolithic function.

CONCLUSION: The otolithic organs of patients with vestibular drop attack (VDA) secondary to Meniere's disease were damaged but the damage was not complete. In other words, the otolithic functions of patients with VDA were unstable. OBJECTIVE: To evaluate otolithic function using vestibular evoked myogenic potential (VEMP) in patients with VDA secondary to Meniere's disease. PATIENTS AND METHODS: Clinical records of three patients with VDA secondary to Meniere's disease were reviewed with special reference to VEMP testing. RESULTS: The three patients were classified as stage II or III Meniere's disease. A long-term follow-up of VEMP in two patients showed reversible changes of VEMP reflexes, and VEMP testing with glycerol administration in two patients revealed the recovery of VEMP responses after taking glycerol, and the existence of saccular endolymphatic hydrops.

Tone burst-galvanic ratio of vestibular evoked myogenic potential amplitudes: a new parameter of vestibular evoked myogenic potential?

OBJECTIVE: To clarify whether the ratio of tone burst vestibular evoked myogenic potential (VEMP) amplitude to galvanic (electric) VEMP amplitude can be a useful indicator of peripheral vestibular disorders, especially labyrinthine disorders. METHODS: Twelve healthy volunteers and 12 patients with endolymphatic hydrops (EH) were enrolled in this study. VEMP was recorded using 500 Hz short tone bursts (135dBSPL, rise/fall time 1 ms, plateau time 2 ms) and galvanic stimulation (3 mA, 1 ms). Amplitudes of p13-n23 (tone burst) and p13g-n23g (galvanic) were corrected using background muscle activity. We defined the ratio of the corrected amplitude of p13-n23 to the corrected amplitude of p13g-n23g as TGratio. RESULTS: The mean+/-SD of logarithmic value of TGratio (LTGratio) of healthy volunteers was 0.34+/-0.12. LTGratios in patients were 0.002+/-0.24 on the affected side and 0.34+/-0.14 on the unaffected side. LTGratio on the affected side of patients was significantly smaller than the ratio on the unaffected side and the ratio of healthy volunteers. Among the 12 patients with EH, 8 patients (66%) had significantly decreased LTGratio (smaller than mean-2SD of healthy volunteers). CONCLUSIONS: Patients with EH had decreased ratio of tone burst VEMP amplitude to galvanic VEMP amplitude. SIGNIFICANCE: TGratio (or LTGratio) could be a new promising parameter of VEMP as it can be calculated from results of one side.

Development and regeneration of hair cells.

The vertebrate inner ear is derived from the otic placode and undergoes a complicated series of morphogenetic processes to differentiate into an elaborate structure harboring mechanosensory epithelia featuring hair cells, the mechanoreceptors of hearing and balance. Recently, the principal mechanisms producing hair cells and the key molecules involved in their fate determination and differentiation have been gradually unveiled. The in-depth understanding of hair cell development is consequently providing clues to strategies for mammalian hair cell regeneration. Among them, the identification and characterization of progenitor cells for the hair cell lineage, which is just emerging, is of particular interest. Herein, we review the molecular mechanisms of inner ear development with particular focus on perspectives for hair cell regeneration.

The lesion site of vestibular dysfunction in Ramsay Hunt syndrome: a study by click and galvanic VEMP.

Ramsay Hunt syndrome (RHS) is characterized by vestibulocochlear dysfunction in addition to facial paralysis and auricular vesicles. The present study investigated the lesion site of vestibular dysfunction in a group of 10 RHS patients. Caloric testing, vestibular evoked myogenic potentials by click sound (cVEMP) and by galvanic stimulation (gVEMP) were used to assess the function of the lateral semicircular canal, saccule, and their afferents. The results of caloric testing (all 10 cases showed canal paresis) mean the existence of lesion sites in lateral semicircular canal and/or superior vestibular nerve (SVN). Abnormal cVEMPs in 7 patients mean the existence of lesions in saccule and/or inferior vestibular nerve (IVN). Four of the 6 patients with absent cVEMP also underwent gVEMP. The results of gVEMP (2 absent and 2 normal) mean that the former 2 have lesions of the vestibular nerve, and the latter 2 have only saccular lesions concerning the pathway of VEMPs. Thus, our study suggested that lesion sites of vestibular symptoms in RHS could be in the vestibular nerve and/or labyrinth, and in SVN and/or IVN. In other words, in the light of vestibular symptoms, there is the diversity of lesion sites.

Extent of lesions in idiopathic sudden hearing loss with vertigo: study using click and galvanic vestibular evoked myogenic potentials.

OBJECTIVE: To clarify the extent of the vestibular lesions in idiopathic sudden hearing loss with vertigo using vestibular evoked myogenic potentials (VEMPs) in response to click (click-VEMP) and galvanic (galvanic-VEMP) stimulation, as well as caloric tests. DESIGN: Retrospective study. SETTING: University hospital. PATIENTS: We enrolled 22 patients with idiopathic sudden hearing loss with vertigo in this study. All patients underwent audiometry and click-VEMP and caloric tests. Eight patients underwent a galvanic-VEMP test. RESULTS: Among the 22 patients, 17 (77%) showed an absence of click-VEMPs on the affected side. In response to caloric testing, 10 patients (45%) showed a decreased response on the affected side. All 8 patients who underwent galvanic-VEMP testing showed normal responses. Most patients with decreased caloric responses (9 [90%] of 10 patients) showed an absence of click-VEMPs, whereas 9 (53%) of the 17 patients who showed abnormal click-VEMPs showed decreased caloric responses. Initial hearing level and hearing outcome significantly correlated with abnormalities on the vestibular test results. CONCLUSIONS: The lesion site of vestibular disorders in idiopathic sudden hearing loss with vertigo appeared to be within the labyrinth on the basis of galvanic-VEMP findings. Results of the click-VEMP and caloric tests suggested that the saccule could be involved more frequently than the semicircular canals. The combined use of click-VEMP and caloric tests is useful for evaluating vestibular functions in idiopathic sudden hearing loss with vertigo because the extent of vestibular abnormalities correlated well with hearing outcome.

Effect of stimulation repetition rate on galvanic-evoked vestibulo-collic reflexes.

CONCLUSION: Taking examination time and patient compliance into consideration, we propose that 5 Hz is the optimal stimulation rate of galvanic vestibular-evoked myogenic potentials for clinical use. OBJECTIVES: To evaluate the influence of stimulation repetition rate on galvanic-evoked vestibulo-collic reflexes and to propose the optimal stimulation rate for clinical use. MATERIAL AND METHODS: Both ears of 30 healthy adults were tested at 5 different galvanic stimulation rates (1, 3, 5, 7 and 9 Hz) in a random order. RESULTS: Responses were evident in all 60 ears only at 5 Hz; some ears showed no response at the other frequencies. The relative amplitudes in individual ears were higher at 1, 3 and 5 Hz than at 7 and 9 Hz. Comparison of the latencies of p13g and n23g showed no significant difference among the five stimulation rates.

Endothelin-1 regulates the dorsoventral branchial arch patterning in mice.

Endothelin-1 (ET-1), a 21-amino acid peptide secreted by the epithelium and core mesenchyme in the branchial arches as well as vascular endothelium, is involved in craniofacial and cardiovascular development through endothelin receptor type-A (EdnrA) expressed in the neural crest-derived ectomesenchyme. Here we show that ET-1(-/-) mutant mice exhibit a homeotic-like transformation of the lower jaw to an upper jaw. Most of the maxillary arch-derived components are duplicated and replaced mandibular arch-derived structures, resulting in a mirror image of the upper and lower jaws in the ET-1(-/-) mutant. As for hyoid arch-derivatives, the ventral structures are severely affected in comparison to the dorsal ones in the ET-1(-/-) mutant. Correspondingly, the expression of Dlx5 and Dlx6, Distalless-related homeobox genes determining the ventral identity of the anterior branchial arches, and of the mandibular marker gene Pitx1 is significantly downregulated in the ET-1(-/-) mutant, whereas the expression of Dlx2 and the maxillary marker gene Prx2 is unaffected or rather upregulated. These findings indicate that the ET-1/EdnrA signaling may contribute to the dorsoventral axis patterning of the branchial arch system as a mediator of the regional intercellular interactions.

Laterality of vestibular evoked myogenic potentials.

To clarify the laterality of acoustically evoked vestibulocollic reflexes with a short latency (vestibular evoked myogenic potentials, VEMPs). responses on the bilateral sternocleidomastoid muscles (SCMs) to unilateral acoustic stimulation were studied. Twenty-one healthy volunteers were enrolled. Surface electrodes were placed on the upper half of each SCM (active) and on the lateral end of the upper sternum (reference). Clicks and 500-Hz tone-bursts (95dB nHL) were used. All subjects showed positive-negative biphasic responses on the ipsilateral SCM by clicks and tone-bursts. Click-stimulation of 41 of the 42 ears did not evoke any response on the contralateral SCM. However, in one ear, positive-negative biphasic responses were evoked on the contralateral SCM. Recordings on the contralateral SCM by tone-bursts showed no response in 32 ears, small positive-negative biphasic responses in four ears, and small negative-positive biphasic responses in six ears. These findings show that VEMPs are ipsilateral-dominant, basically consistent with the hypothesis that they are of saccular origin.

Galvanic-evoked myogenic responses in patients with an absence of click-evoked vestibulo-collic reflexes.

OBJECTIVES: To show that galvanic-evoked responses on the sternocleidomastoid muscle (SCM) are useful for differentiating labyrinthine lesions from retro-labyrinthine lesions in patients with an absence of click-evoked vestibulo-collic reflexes. METHODS: We studied the average responses in the unrectified electromyographic (EMG) activities of the SCM to galvanic stimulation (3mA, 1ms). The cathodal electrode was on the mastoid, and the anodal electrode was on the forehead. Twenty-two healthy subjects and 28 patients with vestibular disorders were studied. All of the 28 patients showed the unilateral absence of vestibulo-collic reflexes evoked by 95dBnHL clicks on the affected side. RESULTS: In healthy subjects mastoid-forehead galvanic stimulation produced a positive-negative biphasic EMG response at short latency on the SCM ipsilateral to the cathodal electrode. All patients with labyrinthine lesions showed biphasic EMG responses even in the affected side. In contrast, almost all patients with retro-labyrinthine lesions (16/18) showed no response or a decreased response on the affected side. CONCLUSIONS: These results suggest that galvanic-evoked myogenic responses on the SCM may be useful in the differential diagnosis of labyrinthine lesions from retro-labyrinthine lesions in patients with an absence of vestibulo-collic reflexes evoked by clicks.