Disorders of cochlear blood flow

Cochlear modiolus and lateral semicircular canal in sudden deafness

CONCLUSION

This study demonstrated that precise analysis shows that the inner ear shape in sudden deafness (SD) is different from that in controls in that the fluid-filled area of SD labyrinths is significantly larger than that of controls. Reduced cochlear modiolus area and inner area of the lateral semicircular canal (LSCC) may be associated with insufficient maturation of the inner ear.

OBJECTIVE

The aim of this study was to quantify the morphologies of the cochlea and LSCC using magnetic resonance imaging (MRI) and to evaluate their relationships with clinical symptoms in SD.

SUBJECTS AND METHODS

Twenty-six unilateral SD patients with vertigo, 26 unilateral SD patients without vertigo and a matched control group without hearing loss were studied. The areas of cochlear modioli and LSCCs were traced on the MRI console and compared between SD patients with or without vertigo and control subjects. The ratio of the LSCC fluid-filled area to the total LSCC area was used to index the degree of dysplasia.

RESULTS

The cochlear modiolus area was significantly less in SD ears (4.1+/-0.2 mm2) than in controls (4.3+/-0.4 mm2). The LSCC inner area was significantly less in SD ears (6.9+/-1.7 mm2) than in controls (9.1+/-1.8 mm2). These results suggest that the fluid-filled area of SD labyrinths is significantly larger than controls. Morphology did not differ between affected and contralateral sides or between ears with or without vertigo in SD patients.

Three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging findings in a patient with cochlear otosclerosis

A 51-year-old man had progressive hearing loss over more than 15 years. He had bilateral sensorineural hearing loss (SNHL). Computed tomography (CT) showed extensive bilateral demineralization of the cochlear capsule, which is characteristic of diffuse cochlear otosclerosis. Three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) of magnetic resonance imaging before enhancement revealed high signals in the cochlea and vestibule. Postcontrast 3D-FLAIR revealed enhancement of the basal turn of the left cochlea. This is the first published case of the breakdown of the blood-labyrinth barrier in a patient with cochlear otosclerosis. Our findings suggest that the breakdown of the blood-labyrinth barrier is associated with a part of SNHL in cochlear otosclerosis.

Connexin30 deficiency causes instrastrial fluid-blood barrier disruption within the cochlear stria vascularis

The endocochlear potential (EP) is essential to hearing, because it provides approximately half of the driving force for the mechanoelectrical transduction current in auditory hair cells. The EP is produced by the stria vascularis (SV), a vascularized bilayer epithelium of the cochlea lateral wall. The absence of the gap junction protein connexin30 (Cx30) in Cx30(-/-) mice results in the SV failure to produce an EP, which mainly accounts for the severe congenital hearing impairment of these mice. Here, we show that the SV components of the EP electrogenic machinery and the epithelial barriers limiting the intrastrial fluid space, which are both necessary for the EP production, were preserved in Cx30(-/-) mice. In contrast, the endothelial barrier of the capillaries supplying the SV was disrupted before EP onset. This disruption is expected to result in an intrastrial electric shunt that is sufficient to account for the absence of the EP production. Immunofluorescence analysis of wild-type mice detected Cx30 in the basal and intermediate cells of the SV but not in the endothelial cells of the SV capillaries. Moreover, dye-coupling experiments showed that endothelial cells were not coupled to the SV basal, intermediate, and marginal cells. SV transcriptome analysis revealed a significant down-regulation of betaine homocysteine S-methyltransferase (Bhmt) in the Cx30(-/-) mice, which was restricted to the SV and resulted in a local increase in homocysteine, a known factor of endothelial dysfunction. Disruption of the SV endothelial barrier is a previously undescribed pathogenic process underlying hearing impairment.

Hematopoietic stem cells prevent hair cell death after transient cochlear ischemia through paracrine effects

Transplantation of hematopoietic stem cells (HSCs) is regarded to be a potential approach for promoting repair of damaged organs. Here, we investigated the influence of hematopoietic stem cells on progressive hair cell degeneration after transient cochlear ischemia in gerbils. Transient cochlear ischemia was produced by extracranial occlusion of the bilateral vertebral arteries just before their entry into the transverse foramen of the cervical vertebra. Intrascalar injection of HSCs prevented ischemia-induced hair cell degeneration and ameliorated hearing impairment. We also showed that the protein level of glial cell line-derived neurotrophic factor (GDNF) in the organ of Corti was upregulated after cochlear ischemia and that treatment with HSCs augmented this ischemia-induced upregulation of GDNF. A tracking study revealed that HSCs injected into the cochlea were retained in the perilymphatic space of the cochlea, although they neither transdifferentiated into cochlear cell types nor fused with the injured hair cells after ischemia, suggesting that HSCs had therapeutic potential possibly through paracrine effects. Thus, we propose HSCs as a potential new therapeutic strategy for hearing loss.

In vivo imaging of mammalian cochlear blood flow using fluorescence microendoscopy

AIMS

We sought to develop techniques for visualizing cochlear blood flow in live mammalian subjects using fluorescence microendoscopy.

BACKGROUND

Inner ear microcirculation appears to be intimately involved in cochlear function. Blood velocity measurements suggest that intense sounds can alter cochlear blood flow. Disruption of cochlear blood flow may be a significant cause of hearing impairment, including sudden sensorineural hearing loss. However, inability to image cochlear blood flow in a nondestructive manner has limited investigation of the role of inner ear microcirculation in hearing function. Present techniques for imaging cochlear microcirculation using intravital light microscopy involve extensive perturbations to cochlear structure, precluding application in human patients. The few previous endoscopy studies of the cochlea have suffered from optical resolution insufficient for visualizing cochlear microvasculature. Fluorescence microendoscopy is an emerging minimally invasive imaging modality that provides micron-scale resolution in tissues inaccessible to light microscopy. In this article, we describe the use of fluorescence microendoscopy in live guinea pigs to image capillary blood flow and movements of individual red blood cells within the basal turn of the cochlea.

METHODS

We anesthetized eight adult guinea pigs and accessed the inner ear through the mastoid bulla. After intravenous injection of fluorescein dye, we made a limited cochleostomy and introduced a compound doublet gradient refractive index endoscope probe 1 mm in diameter into the inner ear. We then imaged cochlear blood flow within individual vessels in an epifluorescence configuration using one-photon fluorescence microendoscopy.

RESULTS

We observed single red blood cells passing through individual capillaries in several cochlear structures, including the round window membrane, spiral ligament, osseous spiral lamina, and basilar membrane. Blood flow velocities within inner ear capillaries varied widely, with observed speeds reaching up to approximately 500 microm/s.

CONCLUSION

Fluorescence microendoscopy permits visualization of cochlear microcirculation with micron-scale optical resolution and determination of blood flow velocities through analysis of video sequences.

Expression of adhesion molecular proteins in the cochlear lateral wall of normal and PARP-1 mutant mice

Sound can damage peripheral cochlear function through a number of mechanisms, and emerging evidence suggests that inflammation may be one of them. Using immunohistochemistry and poly (ADP-ribose) polymerase-1 (PARP-1) mutant mice, we tested whether PARP-1 contributes to loud-sound induced cochlear lateral wall damage by triggering inflammatory effects, including upregulating intercellular adhesion molecule-1 (ICAM-1), P-selectin and platelet-endothelial cell-adhesion molecule-1 (PECAM-1). In control conditions, we found that there was no detectable poly-ADP-ribose (PAR) in the marginal cells and microvessels. ICAM-1 was expressed only at low levels in the vessels of the stria vascularis and the spiral ligament. P-selectin and PECAM-1 were barely detected and only in the vessels of the spiral ligament. Following loud-sound exposure, PAR was detected in numbers of marginal cells and some vessels of the spiral ligament. Also, an elevated expression of ICAM-1 was demonstrated in some vessels of the stria vascularis and spiral ligament. Increased expression of P-selectin and PECAM-1 were mainly located in the vessels of the spiral ligament, while increased populations of non-migrated and migrated leukocytes were observed in the area of the spiral ligament. However, neither increased expression of adhesion proteins nor increased population of leukocytes, were observed in the PARP-1 knockout mouse. We thus conclude that loud-sound stress activates the expression of adhesion molecular proteins in the lateral wall and that PARP-1 modulates inflammation-linked protein expression and leukocyte migration.

Three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging findings in patients with sudden sensorineural hearing loss

OBJECTIVE

To evaluate the inner ear in sudden sensorineural hearing loss (SNHL) using three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) magnetic resonance imaging (MRI) at 3 Tesla (T).

BACKGROUND

3D-FLAIR MRI has recently been developed to detect high concentrations of protein or hemorrhage. Application of this method to sudden SNHL has not been described.

METHODS

We used 3D-FLAIR at 3 T with and without gadolinium enhancement to evaluate eight patients with sudden SNHL.

RESULTS

In four of eight ears with idiopathic sudden SNHL, high precontrast signals were observed within the inner ear on 3D-FLAIR. The high-signal areas observed on 3D-FLAIR were not detected by T1- or T2-weighted MRI in any of these patients. In one of these four ears, significant gadolinium enhancement was observed on 3D-FLAIR.

CONCLUSION

Half the patients with sudden SNHL examined had high signals in the SNHL-affected ear on 3D-FLAIR at 3 T. High precontrast signals in the inner-ear fluid space may reflect minor hemorrhage, or an increased concentration of protein that had passed through blood vessels with increased permeability, or had originated from disrupted cells in the inner ear. Gadolinium enhancement in one ear suggested the breakdown of the blood-labyrinth barrier. 3D-FLAIR MRI should contribute markedly to the elucidation of pathologic conditions in the inner ears of patients with idiopathic sudden SNHL.

A model of peripherally developing hearing loss and tinnitus based on the role of hypoxia and ischemia

The incidence of sensorineural hearing loss often caused by direct damage to the cochlear hair cells is by far more frequent and more serious than disorders affecting the external ear or the middle ear. Mechanisms that are discussed to be relevant for the genesis of tinnitus and acquired hearing impairment are hair cell loss, signal transduction disturbances in the region of the outer and inner hair cells and the spiral ganglion, impairment of cochlear blood flow, mechanical disturbance, and hypoxia and ischemia. The present model surveys the possible cellular and molecular biological causes of peripherally developing hearing loss and tinnitus. In particular, the paper discusses the roles of hypoxia and ischemia in the cochlea and in the etiology of the neurosensory types of tinnitus. Peripheral origins of hearing disturbances and tinnitus may be: (a) damage to the stereocilia and the tip links, (b) dysfunction of potassium channels or (c) modification of the glutamate release. Moreover, the hypoxia inducible factor-1 may have an important role to play as a key transcription factor in the cells' adaptation to hypoxia and ischemia. An impairment of the cochlear blood flow may be induced by the expression of target genes like nitrogen monoxide synthase and endothelin-1 resulting in tinnitus. The paper discusses consequences resulting from the present model for the medical treatment of peripherally developing tinnitus and hearing loss.

Relationship between CT densitometry with a slice thickness of 0.5 mm and audiometry in otosclerosis

The appropriate cutoff Hounsfield unit (HU) value for the diagnosis of otosclerosis was determined and the correlation between the bone conduction threshold and the findings of computed tomography (CT) densitometry investigated. CT images, 0.5-mm thick, were evaluated in 24 ears with otosclerosis and 19 control ears. Eight regions of interest were set around the otic capsule. The mean HU values in the area anterior to the oval window (A-OW) and anterior to the internal auditory canal (A-IAC) were significantly lower in otosclerosis than in controls. Based on receiver operating characteristic (ROC) analysis, the cutoff HU value in A-OW was determined to be 2,187.3 HU. The mean HU value in retrofenestral otosclerosis was significantly lower in the area A-OW, A-IAC and around the cochlea than in controls. Based on ROC analysis, the cutoff HU value in the latter was determined to be 2,045 HU. A statistically significant correlation was found between the density of the area A-OW and the hearing level at 500 and 1,000 Hz, and between the density of the area around the cochlea and the hearing level at most frequencies. These results suggest the semi-automated diagnosis of otosclerosis may be possible.

Response of cochlear blood flow to prostaglandin E1 applied topically to the round window

CONCLUSIONS

The increase in cochlear blood flow (CBF) after administration of prostaglandin E1 (PGE1) to the round window depends on increased blood flow through the anterior inferior cerebellar artery (AICA).

OBJECTIVES

To evaluate the response of CBF to PGE1 applied topically to the round window, and to investigate the origin of blood flow changes after this topical application.

MATERIAL AND METHODS

The response of CBF to topically applied PGE1 was measured by placing the tip of a laser Doppler probe on the bony wall of the basal turn of the cochlea after the middle ear mucosa over the cochlea had been removed in guinea pigs and rats. In rats, the CBF response to PGE1 administration was investigated after occlusion of the AICA or stapedial artery.

RESULTS

CBF increased following PGE1 administration in both guinea pigs and rats. In rats, CBF increased from 100% to 132%+/-10% (mean+/-SD) after the topical application of 0.5 microl of a 0.014% PGE1 solution. CBF decreased after occlusion of the AICA or stapedial artery but did not increase after PGE1 administration during occlusion of the AICA. The CBF response to PGE1 administration was similar before and after occlusion of the stapedial artery.

Pharmakotherapie des akuten Tinnitus

Hypoxia/ischemia may play an important role in the pathogenesis of sensorineural tinnitus due to the characteristics of the cochlear blood supply. In addition, hypoxia modulates molecular processes both in the acute and chronic forms of tinnitus. Transcription factor HIF-1 (hypoxia-inducible factor) may play a key role in the cells' adaptation to hypoxia and ischemia, while under hypoxic/ischemic conditions, HIF-1 induces changes in the gene expression which may contribute to the remodeling of particular structures within the cochlea. Disturbances in the cochlear blood supply may result in membrane changes, perineural edema, inflammation, disturbances in ion homeostasis and in the formation of reactive oxygen species. Thus, the pharmacotherapy of acute tinnitus may be aimed at the improvement of cochlear blood supply and the prevention of acute processes leading to cell damage. Pharmacotherapies with colloidal plasma substitutes, vasodilators, calcium antagonists, procaine, and cortisone have been described in the literature and are discussed here. Many of the pharmacological treatments have not been validated in double blind studies. Although it is impossible to deduce the cause of tinnitus from a drug's efficiency, there is some evidence that it can be effectively suppressed by improving blood supply, at least at certain stages. The aim is to achieve an improved pharmacotherapy by means of sophisticated diagnostic instruments for classifying particular types of tinnitus.

Nuclear factor-kappa B nuclear translocation in the cochlea of mice following acoustic overstimulation

There is increasing evidence to suggest that the expression of many molecules in the lateral wall of the cochlea plays an important role in noise-induced stress responses. In this study, activation of the nuclear transcription factor nuclear factor-kappa B (NF-kappaB) was investigated in the cochlea of mice treated with intense noise exposure (4 kHz, octave band, 124 dB, for 2 h). The present noise exposure led to remarkable auditory brainstem response threshold shifts and cochlear damage on surface preparations. To assess the effects of noise exposure on NF-kappaB/DNA binding activity in the cochlea, we prepared nuclear extracts from the cochlea at different time points after noise exposure and carried out an electrophoretic mobility shift assay using a probe specific to NF-kappaB. NF-kappaB/DNA binding was significantly enhanced in the cochlea 2-6 h after noise exposure and returned to basal levels after 12 h. Supershift analysis using antibodies against p65 and p50 proteins, which are components of NF-kappaB, demonstrated that enhancement of NF-kappaB/DNA binding was at least in part due to nuclear translocation of p65. An immunohistochemical study also showed that nuclear translocation of both p65 and p50 was observed in the lateral wall after noise exposure and that there may be a possible close association between p65 and enhanced inducible nitric oxide synthase expression. These results suggest that NF-kappaB may have a detrimental role in the response to acoustic overstimulation in the cochlea of mice.

Morphological and functional alterations of the cochlea in apolipoprotein E gene deficient mice

The relationship between hyperlipidemia and sensorineural hearing loss remains obscure. In this study, we elucidate for the first time the cochlear morphological and auditory alterations and their relationships with hyperlipidemia, atherosclerosis, and endothelial dysfunction in apolipoprotein-E knockout (ApoE-KO) mice. Ten-week-old ApoE-KO mice were fed either atherosclerotic diet (1.25% cholesterol) or normal diet. Wild type mice (C57BL/6J) served as normal controls. Fourteen weeks later, marked hyperlipidemia, atherosclerosis, endothelial dysfunction, and hearing impairment, especially in the high frequencies, had developed in ApoE-KO mice as compared with C57BL/6J mice (P<0.001). A high positive correlation between hearing loss and the extent of atherosclerosis and plasma total cholesterol levels was found. Hearing loss, especially at high frequencies, was detected in all ApoE-KO mice. Hair cell loss mainly at the base turn, thickening of vascular intima, and lumen stenosis of the spiral modiolar artery (SMA) in cochlea were also found; these histological changes were exacerbated by the atherosclerotic diet. Furthermore, endothelial nitric oxide synthase (eNOS) in aortic wall and cochlea was distinctly reduced in ApoE-KO mice. These results demonstrate that hyperlipidemia and atherosclerosis can induce alterations in cochlear morphology and function. The stenosis of SMA, which may cause cochlear ischemia and hypoxia, endothelial dysfunction, and low eNOS activity, may contribute to hearing loss.

Sudden Sensorineural Hearing Loss Associated with Inner Ear Anomaly

OBJECTIVE

This study was conducted to evaluate the frequency of inner ear anomaly in patients with sudden sensorineural hearing loss and in control subjects.

STUDY DESIGN

Retrospective case review.

SETTING

A tertiary referral center.

PATIENTS AND INTERVENTION

We evaluated 366 patients (165 men and 201 women; age range, 3-91 yr) with sudden sensorineural hearing loss and 228 control subjects without sensorineural hearing loss using magnetic resonance imaging. Three hundred fifty-six patients had unilateral and 10 patients had bilateral sudden sensorineural hearing loss.

RESULTS

Eleven (2.9%) of 376 ears with sudden sensorineural hearing loss had inner ear anomaly. Nine patients (2.5%) had inner ear anomaly associated with sudden sensorineural hearing loss, but none of the 228 control subjects had the anomaly. The current study demonstrated that the frequency of inner ear anomaly in patients with sudden sensorineural hearing loss was significantly higher than in control subjects.

CONCLUSION

Our study reveals that inner ear anomaly may be associated with sudden sensorineural hearing loss in 2.5% of patients.

Age-related hearing loss: the status of Schuknecht’s typology

PURPOSE OF REVIEW

Recent developments in age-related hearing loss (ARHL) are reviewed with an emphasis on their relation to the framework advocated by Schuknecht. More than a classification scheme, Schuknecht's typology incorporates testable hypotheses about the bases of ARHL. Since there is presently no widely accepted competing framework, research in this area should be aimed at supporting, modifying, or replacing Schuknecht scheme. Only recently has our understanding of cellular changes and gene/environment interactions in ARHL achieved the level needed for hypothesis-driven experiments in this area.

RECENT FINDINGS

New findings largely support or amplify aspects of Schuknecht's framework. Consideration of the kinds of cells involved in ARHL has broadened to include more nonsensory and supporting cells. This should provide more complete criteria for comparing models, and for diagnosing particular forms of ARHL. Newly discovered genetic effects and more detailed comparisons have imparted mechanistic significance to the often-noted similarity between sensory ARHL and noise injury. Recent comparative studies, and studies of cell replacement in the cochlear lateral wall, suggest variations in the relation between strial and ligament pathology, and indicate why cell loss occurs during aging. Mouse models carrying mutations affecting processes that may give rise to ARHL are receiving increased attention, even as detailed studies bolster support for mice as valid ARHL models.

SUMMARY

Using Schuknecht's framework as a guide, basic research can now seek to model specific forms of ARHL by combining genetic defects and appropriate environmental conditions. Identification of distinct risk factors for age-related degeneration of organ of Corti, afferent neurons, and stria would verify a key tenet of Schuknecht's scheme, and point the way to interventions.

Contribution of stapedial artery to blood flow in the cochlea and its surrounding bone

This study was performed to elucidate the contribution of the stapedial artery (SA)--which has been considered to be independent of the vertebrobasilar system--to blood flow in the ear by observing ear blood flow in Sprague-Dawley rats. A laser-Doppler (LD) probe was positioned on the bony wall of the cochlear basal turn after removal of the middle ear mucosa. The LD output was measured while either or both the SA and the anterior inferior cerebellar artery (AICA) were occluded. The LD output decreased to 70.6+/-2.5% (mean+/-S.D.) of the baseline value following SA occlusion, and to 58.0+/-7.8% following AICA occlusion in 12 animals. The rebound phenomenon of blood flow, which is a type of autoregulation, was only observed after releasing AICA occlusion. Simultaneous occlusion of the SA and AICA decreased the LD output to 27.0+/-5.5% of the baseline value. The role of the contribution of the SA and AICA to the LD output is discussed.

A comparative study of intratympanic steroid and NO synthase inhibitor for treatment of cochlear lateral wall damage due to acute otitis media

We studied the damage to the cochlear lateral wall induced by otitis media and the therapeutic effects of intratympanic administration of steroid and nitric oxide (NO) synthase inhibitor. In Sprague-Dawley rats, right middle ear cavities were inoculated with lipopolysaccharide, followed after 30 min by intratympanic administration of dexamethasone, NOS-inhibitor or PBS. Twenty-four hours after lipopolysaccharide inoculation, cochlear blood flow was measured by laser-Doppler flowmetry. Prostaglandin E(1) was topically applied to the round window membrane of the right ear and changes in cochlear blood flow were calculated. Changes of cochlear blood flow were significantly different among the three groups. Increases in cochlear blood flow following PGE(1) application were higher in the group that received NOS-inhibitor. Electron microscopic examination revealed that changes in the stria vascularis were less severe in rats treated with dexamethasone or NOS-inhibitor. Our results show the effectiveness of intratympanic dexamethasone or NOS-inhibitor in treating cochlear lateral wall damage caused by otitis media.