Synthesis of glycocalyx and associated structures in vestibular sensory cells

The ultrastructure of the glycocalyx with special reference to the synthesizing process was studied in the guinea pig vestibular sensory cells using the tannic acid staining technique. The glycocalyx emerged from the outer layer of the plasma membrane covering the entire length of the cilia. This glycocalyx also interconnected the ciliary structures tightly, such that a structural continuity was established between actin-membrane links and the glycocalyx. Interconnections between the actin filaments themselves were also noticed in the stereocilia as well as interconnections between individual actin filaments and the plasma membrane. These findings indicate that the glycocalyx and the ciliary interconnections may be closely related to the sensory hair transduction system. In the cellular cytoplasm, vesicles seemingly related to the synthesis of the glycocalyx were observed. These coated vesicles, which were synthesized by the Golgi complex and endoplasmic reticulum, interacted with the plasma membrane forming a coated pit. The lysosomal-like bodies also observed in the cell were closely related to the glycocalyx as well. Thus the glycocalyx seems to be synthesized by the endoplasmic reticulum and Golgi complexes and transferred through the coated vesicles or lysosomal-like bodies to the apical plasma membrane.

Carbohydrates of the guinea pig vestibular supporting cells

Ultrastructural localization of glycoconjugates with special reference to the synthesizing process was studied in the guinea pig vestibular supporting cells using the tannic acid and ruthenium red staining technique. The extracellular glycoconjugate (glycocalyx) was well stained by the ruthenium red which may be synthesized by GERL complex. The supporting cell has a numerous number of granules which also contain tannic acid positive glycoconjugate. These granules were closely related to the Golgi complex as well as the apical cell surface. It may be indicated that the glycoconjugate of the supporting cells is glycosylated at the Golgi complex, stored in the granules, transported, secreted, and form otoconial membrane and the cupula.

The presence and localization of receptors for atrial natriuretic peptide in the inner ear of the guinea pig

Atrial natriuretic peptide (ANP) is a cardiac hormone known to mediate increased capillary permeability, vasodilation, and natriuresis. Since specific receptors for ANP exist in both the eye and brain, possibly playing a role in ocular and cerebrospinal fluid regulation, we postulated that ANP might also be involved in inner ear fluid dynamics. Autoradiography was used to evaluate whether and where ANP receptors are present in the inner ear. Frozen sections of the cochlea and vestibular organ from guinea pigs (n = 18) were incubated in either 125J-ANP alone or together with an excess of unlabeled ANP (as control). ANP receptors were demonstrated in the stria vascularis of the cochlea and in the secretory epithelium of the ampulla and the utriculus, but not in the region of the sensory cells. These results indicate that (1) specific ANP receptors are present in the inner ear, and (2) their local distribution is congruent with those parts thought to regulate labyrinthine fluid composition and volume. We speculate that ANP contributes to the homeostasis of the inner ear fluids and may even play a role in the pathophysiology of Menière's disease.

Calbindin (CaBP 28 kDa) localization in the peripheral vestibular system of various vertebrates

Previous reports on calbindin, a 28 kDa vitamin D-induced calcium-binding protein, located in the mammalian peripheral vestibular system indicated that it is specifically distributed and postulated that it could play a role in the electrophysiological functioning of the sensory cells. This immunocytochemical investigation of the distribution of calbindin in the vestibular system of various vertebrates: fishes (goldfish and sea-perch), amphibia (frog), birds (chicken) and mammals (mouse, cat and baboon), was performed to verify these observations. In the vestibular ganglion, only a few neurons were faintly immunoreactive in the fishes and the frog, while the staining was more intense but still not present in all neurons of the chicken, the mouse and the cat. All the neurons were immunoreactive in the baboon. No immunoreactivity was observed in the sensory epithelia of the fishes. All hair cells were strongly immunoreactive in the frog. In the other species, most of the hair cells in the cristae were immunostained except those situated in the peripheral areas. In the maculae, the hair cells of the striola were either the only ones stained or were more intensely stained or were more intensely stained than the others. The localization of calbindin in specific cellular types and its increasing abundance from the fishes to the mammals suggest that calbindin is associated with the capacity of sensory and nerve cells to analyze precise mechanical or biochemical stimulations.

Calbindin (CaBP 28 kDa) appearance and distribution during development of the mouse inner ear

Previous reports of the distribution of calbindin, a 28 kDa vitamin D-induced calcium-binding protein, in the mammalian peripheral vestibular system postulated that this protein was involved in the calcium-dependent mechanisms occurring in the hair cells and ganglion cells. In this study, we examined the possibility of a relationship between the presence of calbindin and neurotransmission by comparing calbindin appearance in the inner ear to the sequence of synaptogenesis. Calbindin distribution was studied by immunocytochemistry, in the developing mouse inner ear from gestational day 12 to postnatal day 40. During the early development, calbindin was localized in non-neuronal structures: Kolliker's organ, spiral limbus and crista supporting cells; and in cochlear and vestibular ganglion neurons and sensory cells. At later stages and in the adult, no reactivity was observed in the non-neuronal cell populations and only certain sensory and nerve cells remained stained: inner hair cells, outer hair cells, vestibular hair cells of the apex of the cristae and of the striola in the maculae, all Corti's ganglion neurons and some vestibular ganglion neurons. The sequence of appearance of calbindin immunoreactivity in the sensory and nerve cells was not completely parallel to the maturation sequence of the inner ear, especially synaptogenesis. The dual distribution of calbindin during development and its expression in specific sensory and nerve cells opens new perspectives on its role in the inner ear.

Aminoglycoside binding sites in the inner ears of guinea pigs

With [125I]gentamicin as radioligand, the presence of aminoglycoside binding sites and kinetics of gentamicin binding to homogenates of organs of Corti, vestibular maculae, livers, spleens, and hearts of guinea pigs were investigated. The effects of temperature, osmolarity, 2,4-dinitrophenol, and digitonin on gentamicin binding were assessed. The affinities of several aminoglycosides for binding sites were tested. Gentamicin bound to cochlear and vestibular structures in a rapid and saturable fashion at a single class of noninteracting binding sites with Kds of 1.2.10(-6) and 3.10(-7) M and maximal binding capacities of 1.3 nmol and 43 pmol/mg of protein, respectively. In the liver, spleen, and heart, binding remained low and appeared to be nonspecific. In the organ of Corti, gentamicin uptake was unaffected by alterations in temperature or medium osmolarity or by 2,4-dinitrophenol, indicating that the uptake represented binding and not active transport. Digitonin at 10 nM increased markedly the uptake at 37 and 4 degrees C, suggesting the presence of internal binding sites. Various aminoglycosides compete for a common binding site.

Improvement of vestibular plasticity in the guinea pig with a calcium entry blocker

The influence of flunarizine on vestibular compensation was investigated in hemilabyrinthectomized guinea pigs. The results showed that the vestibular deficits from hemilabyrinthectomy disappeared more rapidly in the treated animals than in the controls. To elucidate the mechanism by which the drug could affect the compensatory process, further studies on the spontaneous and evoked activity of vestibular nuclei were performed in normal, labyrinthectomized and labyrinthectomized-cerebellectomized animals. These electrophysiological data implied that flunarizine improved the vestibular compensation by inhibiting the receptor and nuclear activities of the intact labyrinth. The drug excited the cerebellar cortex, which modulated the activity of the vestibular nuclei of both sides, restoring the balance disrupted by hemilabyrinthectomy.

Calcium transport in the endolymphatic space of cochlea and vestibular organ

Ca++ concentrations and d.c. potential within the endolymphatic space of the cochlear duct and the semicircular canal following acute anoxia or ethacrynic acid intoxication (100 mg/kg i.v.) were measured by means of double-barrelled microelectrodes. Ionic calcium content and d.c. potential were found to change in a roughly biphasic fashion after either intervention. The maximal increase in Ca++ concentration coincided with the decline in the d.c. potential, which after a rapid decline finally reached and maintained negative voltages. This phenomenon was more pronounced in the cochlear part than in the semicircular canal. A model of calcium homeostasis is proposed in an attempt to reconcile the data presented with earlier evidence.

[Receptor epithelium of the vestibular apparatus and cochlea in exposure to acceleration and noise]

The method for isolating and treating the vestibular and cochlear compartments of the inner ear was developed. Also, the procedure of histological treatment of temporal bones was modified. The pathogenesis of vestibulo-cochlear disorders due to acceleration and noise was investigated using histology, electron microscopy and histochemistry methods. It was found that exposure to acceleration of 10 Gx for 5 min and single and repeated (for 7 days) exposures to high-frequency noise of 100 dB produced histological changes and functional-morphological variations in all receptors located in the vestibular and cochlear compartments of the inner ear.

gamma-Aminobutyric acid stimulates chloride permeability across microdissected Deiters' neuronal membrane

Fluxes of 36Cl- across freshly prepared Deiters' neuronal membranes have been studied in a two-compartment microchamber simulating the extra- and the intracellular space. The rate of 36Cl- influx was enhanced by gamma-aminobutyric acid (GABA) (10(-4) M), the effect being reversed by picrotoxin (10(-4) M) and by bicuculline (10(-5) M). Diazepam (10(-8)-10(-7) M) did not potentiate the response to GABA and rather depressed it. However, a barbiturate site is most probably present in the GABA receptor complexes since pentobarbitone (10(-4) M) was able to stimulate 36Cl- permeability to the same extent as GABA itself.

Comparative uptake of gentamicin, netilmicin, and amikacin in the guinea pig cochlea and vestibule

The kinetics of the entry of three aminoglycosides into inner-ear tissues of the guinea pig after acute and chronic administration were compared: gentamicin toxic to the cochlea and the vestibule, amikacin preferentially cochleotoxic, and netilmicin of low ototoxic liability. During constant intravenous infusion, levels of the three drugs in plasma tended to reach a plateau after 1 h, while levels in perilymph did not reach a plateau within 6 h. The drug concentrations in both vestibular and cochlear tissues quickly reached saturation. Amikacin and gentamicin concentrations were similar in vestibular and cochlear tissues, while netilmicin values were somewhat lower. After 1 week of chronic treatment (100 mg of drug per kg of body weight daily subcutaneously), levels of gentamicin and amikacin in tissue were similar to each other and were not significantly different between cochlear and vestibular tissues. Netilmicin concentrations again were somewhat lower in the tissues, but identical to those of the other drugs in the perilymph. After 3 weeks of treatment, all of the drugs were equally distributed in the inner-ear tissues. Release of the drug from the tissues after the 3-week treatment was faster for amikacin (83% decrease after 20 days) than for netilmicin and gentamicin (approximately 50% decrease). There was no correlation, under any of the experimental conditions, between the drug concentrations and their degrees of toxicity. These results demonstrate that selective aminoglycoside ototoxicity cannot be explained by a preferential uptake or accumulation of drugs in the afflicted tissues or in the perilymph.

Specific [3H]gamma-aminobutyric acid binding to vestibular membranes of the chick inner ear

To support a postulated neurotransmitter character of gamma-aminobutyric acid (GABA) in the vertebrate vestibule, [3H]GABA binding was measured in a crude membrane preparation of chick inner ear ampullary cristae. In the absence of divalent cations bound [3H]GABA was displaced by unlabeled GABA, muscimol or bicuculline, but it was not displaced by (+/-)-baclofen. A single population of [3H]GABA binding sites with an equilibrium constant of 19.4 nM and a maximum binding capacity of 0.58 pmol/mg protein was found. These results suggest the possible existence of a synaptic GABAA receptor in the chick inner ear membranes and sustain the neurotransmitter role of GABA in the chick vestibule.

Carbohydrates detected by lectins in the vestibular organ

In the vestibular organ the presence of carbohydrates in the cupula and otoconia of young (6-day-old) and adult rats was investigated using fluorescent lectins. The following sugars have been identified in both young and adult rats: N-acetyl-glucosamine, galactose, mannose and fucose. In contrast, N-acetyl-galactosamine was not detected. In order to demonstrate the specificity of the reaction, control experiments were performed after preincubation of the lectin with its specific inhibitory sugar. The same sugars were identified in calcified (i.e. otoconia) and non-calcified (i.e. cupula) structures. The role of these sugars in the mineralization and fusion process of otoconia is discussed.

Perilymphatic and endolymphatic PO2. Variations during anoxia, hyperoxia, and hypercapnia

Cochlear microcirculation was studied with oxygen-sensitive microelectrodes simultaneously in all three scalas during anoxia, hyperoxia, and hypercapnia. The anoxia caused a sharp decline of Po2 in the scala media (SM), scala vestibuli (SV), and scala tympani (ST). Hyperoxia and hypercapnia resulted in an elevation of Po2 in all three scalas. During anoxia, the SM showed the earliest and largest decline in Po2, with the shortest recovery and reoxygenation time. When Po2 slopes (during anoxia) were compared, the SM to ST and the SM to SV were substantially different and remained different even when the partial pressures of oxygen quantified as oxygen in nanomoles. Our experiments also showed that changes in Po2 within the SM closely correlate with changes of endocochlear potential and BP.

GABA synthesis in isolated vestibulary tissue of chick inner ear

This study was undertaken to assess the possible participation of GABA in neurotransmission in the inner ear of higher vertebrates utilizing isolated chick vestibulary cristae as a model. GABA synthesis was investigated as a suitable criterion for postulating this amino acid as a putative neurotransmitter. Enzyme-mediated GABA synthesis was demonstrated implying a possible neurotransmitter role of this amino acid in the chick vestibule.

[On the glucose, pyruvate, and lactate concentration of perilymph, blood, and cerebrospinal fluid of unexposed and sound-exposed guinea pigs under ethyl urethane anesthesia (author's transl)]

Glucose, pyruvate, and lactate of perilymph (PL), blood, and cerebrospinal fluid (CSF) of unexposed and sound-exposed guinea pigs under ethyl urethane anesthesia were examined with due consideration of the principal sources of error. The animals had fasted for 15--20 h before the experiment to stabilize the blood glucose level. The metabolites were determined enzymatically by means of fluorescence measurements. It was found that the glucose levels depend not only on ingestion but also on the duration of anesthesia of the animals before sampling. The mean values of the scala tympani and scala vestibuli PL and CSF did not differ significantly, being about half those of blood or plasma immediately (10--20 min) after introducing anesthesia (Table 2). This concentration difference is in disagreement with the original ultrafiltration hypothesis of PL, suggesting a blood-PL barrier for glucose. The dependence on the duration of anesthesia and on the animals' ingestion before sampling appears to be an important cause of the differences in glucose data published in literature hitherto. No influence of anesthesia on pyruvate and lactate concentrations was observed. Data obtained on unexposed control animals (Tables 3 and 4) confirmed our earlier metabolite findings (Scheibe et al. 1976, 1981). No major changes in glucose, pyruvate, and lactate concentration of PL, blood, and CSF were detectable immediately after 1 h of exposure to wide-band noise at an intensity of 120 dB SPL. The present lactate findings confirmed our earlier exposure experiments (Scheibe et al. 1976), but they did not agree with the information given by Schnieder (1974).

Immunofluorescence localizations of proteins in semithin 0.2--1 micron frozen sections of the ear. A report of improved techniques including gelatin encapsulation and cryoultramicrotomy

The present work describes a high resolution technique for locating proteins in frozen sections of the inner ear by immunofluorescence. Dissected organs are encapsulated in gelatin, and sections 0.1--1 micron thick are cut at --100 degrees C in a cryoultramicrotome. These are labelled with antibodies against two cytoskeletal proteins, actin and tubulin. Actin, which had previously only been described in the sensory cells, is found in the supporting cells as well. Tubulin is identified in the supporting cells and in outer spiral nerve fibres.

Permeability of the labyrinthine windows in guinea pigs

Permeability of the labyrinthine windows in guinea pigs was investigated by electron microscopy using horseradish peroxidase (HRP). In the round window membrane, HRP particles were readily taken up by the epithelial cells and were transported to the subepithelial layer which was regarded as being bathed in the perilymph. The oval window also appears to allow the passage of the macromolecules in view of the HRP-labeled granules in the chondrocytes of the stapediovestibular joint. The transport of the HRP particles from the middle ear to the inner ear was confirmed by the uptake of those in the saccular epithelium after 30--40 min exposure to the tracer.

[Postmortem changes in the perilymphatic lactate and pyruvate concentrations of guinea pigs. (author's transl)]

Lactate and pyruvate of perilymph (PL) were studied 30, 60, and 120 min postmortem. During this period the mean lactate concentration of scala tympani and scala vestibuli increased from 4.8 mmol/l found intravitally to 17.8 and 15.1 mmol/l, respectively, whereas pyruvate decreased from an average of 0.33 to 0.10 mmol/l (fig. 1). These inverse changes of concentration yield postmortem lactate/pyruvate quotients which are more than one order of magnitude higher than the quotients found intravitally (Table 1). In comparative tests of blood samples carried out 30, 60, and 120 min after the sampling (Fig.1), the lactate increase was found to be markedly lower than in postmortem PL. The substantial metabolite changes in PL seem to be caused by glycolytic activity of all cochlear structures that are in direct contact with PL. The decrease of pyruvate level is probably due to a shift of the lactate-pyruvate equilibrium (lactate dehydrogenase system) in PL. The blood vessels in the perilymphatic space can be neglected as postmortem metabolite source of PL.

[Cellular detection of the in vivo incorporation of tritiated 2-deoxyglucose. Radioautographic study in the inner ear]

Inner ear injection of (3H) deoxyglucose was followed by in situ glutaraldehyde fixation and, after removal, by traditional preparation of the tissue for electron microscopy. Radioautography of semi-thin sections revealed preferential tracer accumulation in metabolically active structures such as the cochlear stria vascularis and the dark cells surrounding the basis of the vestibular cristae. Furthermore, in the vestibule, the perikaryon of some sensory cells was intensely labelled. These results show that an in vivo injection of deoxyglucose, followed by conventional histological processing can be used to mark active cells at both cellular and subcellular levels.

[Protein study on perilymph susbstitution during cerebrospinal fluid flow through cochlear aqueduct]

Total protein contents in the perilymphy of Scala vestibuli and Scala tympani as well as in the cerobrospinal fluid (CSF) of guinea-pigs were determined, by which specimens were taken under the following various conditions: With or without subarachnoidal puncture before perilymph collection, by varying the amount of perilymph taken from Scala tympani, by fractionating collection and under post mortem condition. The results suggest that under physiological conditions the CSF also flows through the cochleae aqueduct and the protein concentration in the Scala tympani decreases especially in the basal winding. Because the protein content in CSF is inaverage four times lower than in fluids of the inner ear it is of preference to consider the question of connection between the CSF and the fluids of the inner ear. In the specimens taken the blood contamination was estimated on the basisof erythrocytes in the connection capillaries under microscope. The protein content in the perilymph of Scala vestibuli was found significantly higher in relation to perilymph of Scala tympani.