Vestibular sensory epithelia in patients with acoustic neurinoma

Existence of nicotinic receptors in a subset of type I vestibular hair cells of guinea pigs

In mammals, vestibular hair cells (VHCs) are classified as type I and II according to morphological criteria. Acetylcholine (ACh) is identified as the primary efferent neurotransmitter. To date, cholinergic activities have been reported in mammalian type II VHCs, but similar activities in type I VHCs have not been pursued presumably because the body of type I VHCs were suggested to be totally surrounded by afferent nerve calyces. A few reports showed that part of type I VHCs were incompletely surrounded by calyces and received contact from the efferent nerve endings in the mammals studied. The possibility of the expression of cholinergic receptors, their subunit composition, and their function in mammals' type I VHCs are still unclear. In this study, nicotinic responses were investigated by the whole-cell patch clamp technique in isolated type I VHCs of guinea pigs. Of the cells, 7.3% were sensitive to cholinergic agonists and showed an excitatory current at -40 mV which was not sensitive to nifedipine, iberiotoxin (IBTX), and apamin. The main carriers of this current were Na⁺ and K⁺. The rank order of activation potency was nicotine > 1,1-dimethyl-4-phenyl-piperazinium (DMPP) > ACh. These nicotinic ACh receptors (nAChRs) were not blocked by strychnine and α-bungarotoxin (α-BTX), but sensitive to d-tubocurarine (dTC) and mecamylamine (Mec). The findings provide physiological evidence that some subtypes of nAChRs may be located in a subset of type I VHCs, which were different from α9α10 nAChRs.

Distribution of glucocorticoid receptors and 11β-hydroxysteroid dehydrogenase isoforms in the human inner ear

HYPOTHESIS

Glucocorticoids (GCs) are widely used as a therapeutic modality for the inner ear disorders including Ménière's disease (MD). The concentration of GCs in the target cells is known to be regulated by 11β-hydroxysteroid dehydrogenase (11β-HSD), an enzyme complex responsible for the conversion of hormonally active cortisol into inactive cortisone. There is no morphologic indication of glucocorticoid receptors (GRs) and 11β-HSD isoforms (11β-HSD1 and 2) in human inner ear.

OBJECTIVES

The objectives of this study are to determine whether GRs and the isoforms of 11β-HSD are present in human inner ear tissues and to reveal their precise distribution.

STUDY DESIGN

This study investigated the expression of GRs and 11β-HSD isoforms (11β-HSD1 and 2) in the human inner ear.

METHODS

In humans, immunostaining of GRs, 11β-HSD1, and 11β-HSD2 was performed in the stria vascularis (SV) and the vestibular tissues, whereas in the cochlear tissues except for the SV, only GRs were investigated.

RESULTS

Immunoreactivity of GRs was detected in the SV, outer hair cells, inner hair cell, spiral ligament, Reissner's membrane, vestibular hair cells, vestibular nerve, transitional cells, and dark cells of the crista ampullaris. 11β-HSD1 was observed in the SV, the apical area of the vestibular hair cells, the transitional cells, and the dark cells. However, no immunoreactivity of 11β-HSD2 was observed.

CONCLUSION

Those data indicate that different local steroid regulation by GRs and the isoforms of 11β-HSD is present in various parts of the human inner ear tissues and that the tissues are a direct therapeutic target of glucocorticoids in the inner ear diseases.

Histopathological and ultrastructural analysis of vestibular endorgans in Meniere's disease reveals basement membrane pathology

BACKGROUND

We report the systematic analysis of the ultrastructural and cytological histopathology of vestibular endorgans acquired from labyrinthectomy in Meniere's disease.

METHODS

17 subjects with intractable Meniere's disease and ipsilateral non-serviceable hearing presenting to the Neurotology Clinic from 1997 to 2006 who chose ablative labyrinthectomy (average age = 62 years; range 29-83 years) participated. The average duration of symptoms prior to surgery was 7 years (range 1-20 years).

RESULTS

Nearly all vestibular endorgans demonstrated varying degrees of degeneration. A monolayer of epithelial cells occurred significantly more frequently in the horizontal cristae (12/13 = 92%) (p < 0.001), the superior cristae (5/5 = 100%) (p < 0.005), the posterior cristae (2/2) compared with the utricular maculae (4/17 = 24%). Basement membrane (BM) thickening was more common in all of the cristae ampullares (18 out of 20) than the utricular maculae. Although only four saccular maculae were obtained, 3 out of 4 exhibited BM thickening and monolayer degeneration. Monolayer degeneration was highly significantly correlated with the presence of BM thickening (p < 0.001). Other degenerative changes noted equally among the five vestibular endorgans which were not significantly correlated with BM thickening or monolayer degeneration included hair cell vacuolization and stereocilia loss, microvesicles in the supporting cells, and increased stromal intercellular spaces. Transmission electron microscopy demonstrated disorganization of the BM collagen-like fibrils, and normal ultrastructural morphology of the nerve terminals and myelinated fibers. Stromal fibroblasts and endothelial cells of stromal blood vessels demonstrated vacuolization, and stromal perivascular BMs were also thickened.

CONCLUSION

Systematic histopathological analysis of the vestibular endorgans from Meniere's disease demonstrated neuroepithelial degeneration which was highly correlated with an associated BM thickening. Other findings included hair cell and supporting cell microvessicles, increased intercellular clear spaces in the stroma, and endothelial cell vacuolization and stromal perivascular BM thickening.

Ultrastructural findings of the macula utriculi in a case of a petrous apex cholesteatoma: a comparison with findings in a patient with an acoustic neuroma

The morphological characteristics of the vestibular sensory cells of the macula utriculi obtained during surgery in a patient with a petrous apex cholesteatoma were examined using scanning and transmission electron microscopy. Findings were compared to cells studied in a patient with acoustic neuroma. Scanning electron microscopy showed that compared to the apparently normal cells in the acoustic neuroma case, most sensory cells in the cholesteatoma case had large cuticular plates, irregular locations of cilia and no clear polarizations. Supporting cells showed profuse short microvilli on the whole surface. With transmission electron photomicrographs, type I hair cells were not seen and certain morphological changes were observed in type-II-like cells and supporting cells. We presume that the degenerative changes in the vestibular epithelia were due to circulatory disturbances and/or direct pressure applied to the vestibular nerve at the internal auditory canal, with subsequent involvement of the macula utriculi.

Observation of apical part and nerve terminals of human vestibular hair cells

The human vestibular sensory epithelia of macula utriculi in 3 cases of acoustic neurinoma were examined by conventional and intermediate voltage electron microscopes. The apical part and the nerve terminals of hair cells were studied by means of a computer-aided three-dimensional (3-D) reconstruction technique. The sensory epithelia were fairly well preserved. Most type I and all type II hair cells appeared as those described in the other reports. However, some type I hair cells were incompletely surrounded by nerve calyces and received direct contacts from the efferent nerve endings. These type I hair cells were also innervated by a few neighbouring afferent nerve calyces. The stereocilia and the cuticular plate of type I hair cells differed from those of type II hair cells. The mean diameter of type I hair cell stereocilia was 488 +/- 59 nm and that of type II hair cells was 373 +/- 21 nm. The cuticular plate of type I hair cells resembled a cone and was about several times as thick as that of type II hair cells which was similar to a flat disc.

Atypical innervation pattern of human vestibular hair cells

Human vestibular sensory epithelia of macula utriculi were examined in 3 cases with acoustic neurinoma by intermediate voltage electron microscope. The innervation pattern of vestibular hair cells was studied by means of computer aided three-dimensional reconstruction technique. The sensory epithelia were fairly well preserved. Most of type I and all of type II hair cells appeared normal. However, some type I hair cells were incompletely surrounded by nerve calyces and received direct contact from the efferent nerve endings. These type I hair cells were also innervated by a few neighboring afferent nerve calyces. These atypical type I hair cells constituted 5-8% of the total number of hair cells.