The ultrastructural organisation of "plana semilunata"

Novel cell types and developmental lineages revealed by single-cell RNA-seq analysis of the mouse crista ampullaris

This study provides transcriptomic characterization of the cells of the crista ampullaris, sensory structures at the base of the semicircular canals that are critical for vestibular function. We performed single-cell RNA-seq on ampullae microdissected from E16, E18, P3, and P7 mice. Cluster analysis identified the hair cells, support cells and glia of the crista as well as dark cells and other nonsensory epithelial cells of the ampulla, mesenchymal cells, vascular cells, macrophages, and melanocytes. Cluster-specific expression of genes predicted their spatially restricted domains of gene expression in the crista and ampulla. Analysis of cellular proportions across developmental time showed dynamics in cellular composition. The new cell types revealed by single-cell RNA-seq could be important for understanding crista function and the markers identified in this study will enable the examination of their dynamics during development and disease.

Transtympanic gentamicin in the treatment of Meniére's disease

Aminoglycosides enable a pharmacological approach, before resorting to surgery, to the treatment of Menière's disease (MD) proving unamenable to routine medical treatment. The staging of MD is an essential preliminary step in the implementation of a specific and personalized treatment with transtympanic gentamicin. The ideal condition is the presence of endolymphatic hydrops with little or no damage to the cochlear and vestibular hair cells. The technical aspects of the method are discussed. In 21 patients with unilateral Menière's disease in various stages, this treatment achieved the regression of vertigo in 86% of cases; hearing was better in 19% of cases, preserved in 62% and worse in 19%; tinnitus regressed totally or partially in 62% of cases; aural fullness also regressed totally or partially in 57% of cases.

INDEPENDENCE OF THE ENDOVESTIBULAR POTENTIAL IN HOMEOTHERMS

The endolymphatic potential was recorded from various vestibular parts of the labyrinth from which the cochlea (in the case of guinea pigs) or the cochlea, lagena, and sacculus (in the case of pigeons) had been removed. This endovestibular potential of the isolated vestibule declined during anoxia and recovered after anoxia in the same manner as the endovestibular potential of the intact labyrinth. Its non-anoxic level was the same as in the intact labyrinth; i.e., +5 to +8 mv in the pigeon and +2 to +5 mv in the guinea pig. It is, therefore, concluded that the endovestibular potential is independent of the cochlea, stria vascularis, and endocochlear potential.

Localization of the GM1 ganglioside in the vestibular system using cholera toxin

Cholera toxin is an ubiquitous activator of intracellular adenylate cyclase and is divided in two major components: A and B. The B-component consists of several subunits that specifically bind to the external cell membrane. The receptor for the toxin, the GM1 ganglioside, is concentrated in nervous tissues. The B subunit of the cholera toxin, conjugated to different molecules (i.e., choleragenoid) is therefore a sensitive anatomical tracer and has been used to detect the presence of GM1 in mammalian tissues. Using choleragenoid, unlabeled and labeled with FITC, we have determined the distribution of the GM1 ganglioside in the vestibular system of the chinchilla. Vestibular tissues were fixed in 4% paraformaldehyde in phosphate buffer, decalcified in 10% EDTA and prepared as either whole-mount, surface-preparations, or for radial cryosections. Positive control tissue consisted of binding to normal brain tissues. Negative controls consisted of several treatments: masking of the GM1 receptors with unlabeled choleragenoid, tissue extraction of GM1 using ethanol, and preabsorbing the choleragenoid with bovine GM1. In addition, to exclude staining of glycoproteins that may have a carbohydrate structure similar to GM1, tissues were digested with trypsin prior to choleragenoid exposure. In the vestibular system, a strongly positive reaction was observed in: the sensory stereocilia and supporting cells of the maculae and cristae, epithelial cells of the planum semilunatum, and polygonal cells of the semicircular canal. Positive but less strong reactivity was observed in the sensory cell body of maculae and cristae, nerve fibers, epithelial cells of utricle and ampulla walls and flattened epithelial cells of the semicircular canals. No reactivity was present in the supporting connective tissue cells and fibrils, blood vessels, gelatinous cupula of the cristae ampullaris and statoconial membranes. Brain tissue showed strong choleragenoid reactivity. The negative controls showed no or greatly reduced reactivity to choleragenoid. Trypsin digestion did not decrease reactivity to choleragenoid.

Planum semilunatum of the rat: new light and electron microscopy observations

Planum semilunatum (PSL) cells of the rat ampullae were studied by light, transmission, and scanning electron microscopy. The observed ultrastructure of rat PSL cells was similar to that described in other species, but is in disagreement with earlier reports of rat PSL cells, most probably because of previous divergent definitions of the PSL. Regions of PSL cells were easily distinguished from other nonsensory epithelia at the lateral ends of the crista ampullaris. The PSL region consisted of irregular-shaped columnar to cuboidal pentagonal or hexagonal cells that interdigitated with one another by lateral membrane infoldings. In the PSL region the subepithelial reticular layer appeared thickened and formed wartlike impressions in the basal surface of the PSL cells. These morphological characteristics of the subepithelial reticular layer were unique to the PSL region in the ampulla and may reflect special adaptations of the PSL region to mechanical stress. Furthermore, the thick subepithelial reticular layer may have implications for transport across the PSL region.

Immunohistochemical findings of IgG recognized in the planum semilunatum of the guinea pig

The planum semilunatum is located on the lateral side of the crista ampullaris of the semicircular canal. With regard to the functions of the planum semilunatum, some researchers assume the existence of secretory activity based on the microstructural features observed in isotopic experiments. In the present study, in order to confirm the existence of an immunological mechanism in the ampulla of the semicircular canal, the distribution of immunoglobulins in the semi-circular canal of guinea pigs was investigated immunohistochemically. Positivity of IgG was observed in the constituent cells of the planum semilunatum or beneath the basement membrane of the cells. It is concluded that ample IgG, which is an important constituent of the body fluids, is collected within this region. The planum semilunatum containing such ample amounts of IgG might be involved in the immunological mechanism operating in the ampullar of the semicircular canal.

Cytochemical study of K+-p-nitrophenyl phosphatase (K+-NPPase) in planum semilunatum and dark cells of the squirrel monkey

We examined the ultrastructure of the planum semilunatum, and also cytochemically demonstrated K+-dependent p-nitrophenyl phosphatase (K+-NPPase) activity in planum semilunatum and ampullary dark cells of the squirrel monkey. K+-NPPase activity was found in the basal part of the planum semilunatum. The reaction products were limited to the cytoplasmic side of the plasma membranes. A more intense reaction was found in the basal infoldings and the lateral interdigitations of the dark cells. On the other hand, the apical cell surface of both cell types showed no K+-NPPase activity. The present results show that both the planum semilunatum and the dark cells may both be involved in maintaining endolymph homeostasis.

Experiences with ESR (endolymphatic sac revascularization) in cases of sensorineural hearing-loss

Experience based on 14 cases of severe-to-total sensorineural deafness, treated with endolymphatic sac revascularization, operation, is presented. Changes seen in the endolymphatic sacs and lateral sinuses of these patients have been detailed. Irrespective of the degree and duration of deafness, significant hearing gain (with good improvement in speech discrimination) was obtained in nine out of 14 cases (64.28 per cent). There was no improvement at all in one out of 14 (7.14 per cent), and there was a relapse of the hearing-loss two months post-operatively in one case (7.14 per cent). Tinnitus disappeared in the operated ear in three out of five cases (60 per cent) and vertigo improved considerably in four out of six cases (66.66 per cent). The follow-up in this series has been up to two years.

Computer-aided and graphic reconstruction of the human endolymphatic duct and sac: a method for comparing Menière's and non-Menière's disease cases

The anatomy of the human endolymphatic duct system of three cases — one with Menière's syndrome (with no histopathological evidence of endolymphatic hydrops), one with Menière's disease (with histopathological evidence of endolymphatic hydrops), and one with no evidence of disease — has been studied by means of computer-aided and graphic reconstruction from serial sections of temporal bones. The reconstructions have revealed a canalicular arrangement of the epithelial lining of the rugose portion of the human endolymphatic sac. Accordingly, new nomenclature, “pars canalicularis,” is suggested for this portion. The computer produced lateral and medial views of the endolymphatic duct and sac of the patient with Menière's syndrome. The computer also calculated the luminal volume, the surface area of the epithelium, and the surface-to-volume ratio of the rugose portion of the sac.

In addition, the authors graphically reconstructed the rugose portion of the sac of all three cases. Measurements of the dimensions of these reconstructions were made, from which the luminal volume was estimated. The reconstructed images and the calculations allowed quantitative comparison of the microscopic anatomy of the rugose portion of the sac in the Menière's syndrome and Menière's disease ears with that in an ear without evidence of disease.

Significant differences were found in the volumes of the rugose portion of the sac of the three cases. The results suggest that the luminal volume of the rugose portion of the sac of Menière's disease patients may be significantly reduced. The authors speculate that endolymphatic hydrops may be the result of a loss of epithelial surface area in the canalicular portion, thus diminishing its resorptive function.

The computer and graphic reconstruction techniques in conjunction with their analytical capabilities provide a new method for studying inner ear structures. These techniques have the potential to expand the capabilities of quantitative morphology and provide the means for deriving clinically useful data from histopathological and ultrastructural material.

The importance of potassium in the function of frog semicircular canals

The slow potentials and afferent discharge of impulses in frog semicircular canals have been studied at different endolymphatic and perilymphatic K+ concentrations. Results indicate that the presence of K ions in the bathing fluids is essential for maintaining the receptor function in crista ampullaris, although very low concentrations of this ion in the perilymph are sufficient to preserve the receptor responsiveness to mechanical stimuli. The hypothesis is put forward that K+ may be pumped from the exterior of the canal towards the intracupular structures, where it accumulates. A K-rich endolymphatic environment does, however, appear to be necessary to ensure the resting activity of ampullar receptors and their ability to be "disfacilitated" during inhibitory cupula deflections.