Volume fraction and ultrastructure of age pigment in the saccular epithelium of old mice.

Age pigment in the sensory and supporting cells was a prominent characteristic distinguishing old saccules from young. However, the pigment was not distributed uniformly throughout the sensory epithelium but displayed cell-specific patterns of accumulation. The highest cytoplasmic volume density was in the old supporting cells followed by type I hair cells and then type II hair cells. The most common form of pigmented inclusion seen in old type I hair cells was a cluster of granules resembling melanin. This form was never seen in type II hair cells or supporting cells where a form containing a lipid-like droplet was prevalent. The differences in the amount of age pigment and the forms accumulated probably reflects metabolic differences between the three cell types.

Aberrant elemental composition of otoconia in the dancer mouse mutant with a semidominant gene causing a morphogenetic type of inner ear defect.

The elemental composition of otoconia from Jerker and Dancer mouse mutants was analysed in both maculae. A normal elemental content was found in otoconia from Jerker mutants, whereas in the Dancer mutant a large number of otoconia from both maculae contained very high concentrations of phosphorus. In these otoconia, the phosphorus calcium ratio was approximately 1:8, in Jerker (and normal) otoconia approximately 1:150-200. However, otoconia from Dancer mutants occurred with also a normal elemental composition. The increasing content of phosphorus in otoconia may possibly indicate an early onset of aging, i.e. corresponding to a phosphatization process as described in aging human otoconia.

X-ray microanalytic studies on developing otoconia.

The onset of otoconial development in the macula utriculi in CBA/CBA mice occurs on the fifteenth and sixteenth gestational days. Our study was concentrated on the early secretion of calcium in the areas of otoconial formation. The epithelial origin of otoconia is documented. Protrusions from supporting cells in the utricular and saccular epithelia contain very large quantities of calcium in addition to the normal cytoplasmic content of elements. The cell protrusions have an elemental composition clearly differing from that of otoconia as well as from neighbouring utricular cells with protrusions. A directed flow of calcium to developing otoconia from the supporting cells of the maculae is suggested.

Intermediate filaments in the newborn inner ear of the mouse.

The presence of intermediate filaments in the inner ear of the newborn mouse was analyzed with immunofluorescence techniques using antibodies against the five classes of intermediate filaments: cytokeratins, vimentin, desmin, neurofilaments and glial fibrillary acid protein (GFA). Neurofilaments were found in all nerve fibers from the ganglion cell to the hair cell. In the vestibular ganglion two subpopulations of ganglion cells were identified: a minor part staining intensively with neurofilament and the major part of cells lacking this immunofluorescence. Vimentin occurred in a number of supporting structures in the membranous labyrinth, but not in vestibular or cochlear ganglion cells. Cytokeratins, desmin or GFA were not identified in the inner ear.

Neuropeptides in macula utriculi and macula sacculi of guinea pig labyrinth. An immunohistochemical study.

The neuropeptides Substance P, beta-Endorphin, Prolactin, Cholecystokinin, and Glucagon were investigated by means of Sternbergers PAP technique in the neuroepithelium of the Maculae utriculi and sacculi of the labyrinth of newborn guinea pigs. This brief report will show the localization of some neuropeptides in the neuroepithelium of the Maculae utriculi and sacculi. We could not find information about similar studies on this topic in the literature. In connection with investigations of the sensory apparatus of the inner ear we have recently presented neuropeptides evidence for the presence of certain peptides in the Ggl. spirale and the hair cells of the organ of Corti. With this paper we continue to report on neuropeptides in the labyrinth of the juvenile guinea pig as revealed by immunohistochemistry (Nowak et al., in press).

Comparative crystallography of vertebrate otoconia.

Otoconial material was obtained from a number of vertebrates to determine the CaCO3 polymorph present. Otoconia and otoliths from bony fish, amphibians, and reptiles are primarily aragonitic; those from birds and mammals are calcitic. This paper summarizes data from all other investigators as well as presenting new data, particularly pertaining to reptiles. The significance, if any, of the relationship between taxonomic group and carbonate polymorph remains an intriguing question.

A re-examination of otoconia from the Shaker mouse.

We have studied saccular and utricular otoconia from Shaker-1 and Shaker-2 mice by X-ray diffraction and scanning electron microscopy. In contrast to previous reports, we found that the crystals were composed of calcite rather than polycrystalline hydroxylapatite. These crystals were indistinguishable mineralogically and morphologically from normal mouse otoconia. The reported occurrence of hydroxylapatite otoconia in the Shaker mouse is probably false.

Is substance P the neurotransmitter in the vestibular end organs?

The vestibular end organs of the rabbit were fixed intracardially with phosphate buffered 4% formaldehyde, sectioned for 15 micron cryostat sections and incubated with monoclonal substance P (SP) antibody. Specific SP-like immunoreactivity (SPLI) was observed within and below the sensory epithelia of both utricular and saccular maculae and ampullary cristae. Particularly strong SPLI was seen in the maculae which showed many SPLI-positive axons in the subepithelial space and a network of SPLI-positive structures in the basal zones of the sensory epithelium. The calyceal terminals of type I hair cells showed regularly SPLI. The possibility of a transmitter or modulator role for SP in the vestibular function is suggested.

Qualitative and quantitative analysis of otoconia in the normal and in the genetically deaf inner ear.

By using the energy dispersive x-ray microanalysis technique the elemental composition of otoconia was analyzed in the normal fetal and normal adult, Shaker-1 and Shaker-2 mouse. There are no statistically significant differences in Ca concentration between otoconia seen in normal nineteenth gestational day (CBA/CBA) fetuses and that seen in 2-month-old animals. However, the standard deviation is almost three times larger in fetal than in adult otoconia. In all analyses, in both normal and mutant species, the following, elements were identified: Na, Mg, P, S, Cl, K, and Ca. The present findings strongly indicate a calcite composition of otoconia in both normal and mutant species. Significant differences in Ca concentration (p less than 0.05) occurred between the central and peripheral parts of large otoconia in normal mice. No difference in the elemental composition of otoconia in adult normal and Sh-2 mutants was detected. Differences occurred between adult normal and Sh-1 otoconia (Na--p less than 0.05; Mg--p less than 0.001; K--p less than 0.001; Ca--p less than 0.02). It is, however, unlikely that the shaking-waltzing behavior of Sh-1 and Sh-2 mutants derives from a minimal derangement of the elemental composition of otoconia.

Calcite in the statoconia of amphibians: a detailed analysis in the frog Rana esculenta.

The otoconia of Amphibia, especially of the frog Rana esculenta, were studied by X-ray diffraction and scanning electron microscopy (SEM). The SEM studies showed that the membranous labyrinth of Amphibia contains two populations of crystals, which can easily be distinguished by their forms. The X-ray diffraction data indicated that these two populations consist of calcite and aragonite; the endolymphatic sac, the saccule and the lagena contain aragonite, whereas calcite is only found in the otolithic membrane of the utricle. The genetic and functional significance of the existence of two crystalline forms of calcium carbonate in the membranous labyrinth are discussed.

Immunohistochemical localization of several cytoskeletal proteins in inner ear sensory and supporting cells.

Several structural and contractile proteins have been searched for with immunohistochemical methods using antibodies directed against these proteins. Three types of preparations from the guinea pig have been used: isolated stereocilia from the utricle, organ of Corti fragments obtained by cellular dissociation and 0.2-1 micrometer sections obtained by cryoultramicrotomy. The main finding is that different sets of proteins compose the cytoskeleton in supporting cells and the mechanoreceptor structures of the sensory cells. Thus, actin was found in association with fimbrin in the mechanoreceptive region of hair cells, whereas supporting cells, although rich in actin, did not reveal fimbrin. Instead tubulin was seen together with actin in supporting cells which also exhibited prekeratin. Fimbrin appears to function as a protein capable of making bundles and networks from actin filaments. Its exclusive presence in the mechanosensitive region of the sensory cells is possibly related to the function of these cells as mechanoreceptors.

Scanning electron microscopic and x-ray diffraction studies of otoconia in the lizard Podarcis s. sicula.

The otoliths of embryos and young animals of the lizard Podarcis s. sicula were studied by X-ray diffraction and scanning electron microscopy. Two types of crystal that give different X-ray diffraction patterns were found in the membranous labyrinth of Podarcis. The crystals consist of calcite or aragonite and are easily distinguished by scanning electron microscopy because of their different morphology. The two calcium carbonate crystal forms are not mixed at random but are present in the embryo from the very beginning in specific sites. The endolymphatic sac contains aragonite crystals while the saccule contains calcite crystals adjacent to the wall, in addition to a preponderance of aragonite crystals. The utricle and lagena contain only calcite crystals. The presence of two crystal forms of calcium carbonate in the membranous labyrinth are discussed in terms of differing genetic and functional significance.

Magnets in guitarfish vestibular receptors.

Black magnetic particles are intermixed with white crystalline otoconia in the inner ear gravity receptors of a saltwater ray. Their size and composition suggest that they are multidomains of magnetite-ilmenite.