Immunocytochemical reactivities of precursor cells and their progeny in the ear of a cichlid fish

Cell types in the inner ear of the fish Astronotus ocellatus were examined for the immunocytochemical reactivity to 31 commercial antibodies. Nine showed positive reactivity: vimentin, S-100, caldesmon, calbindin, MAP-1, MAP-2, parvalbumin, neurofilament, and GAP-43. The cell types examined were: hair cells, support cells, hair cell precursors, eighth nerve neurons, and neuronal precursors. The pattern of reactivities among these cell types lead to the following conclusions. First, hair cells and eighth nerve neurons have a striking immunocytochemical similarity. Second, the precursor cells for hair cells and neurons did not share immunoreactivity with these mature progeny. Third, the only antibody to react with supporting cells also reacted with the proliferating precursors that give rise to new hair cells and supporting cells. Taken with other available data, these finding suggest that in the oscar ear, hair cell precursors and supporting cells are closely related, if not the same cell type.

Immunocytochemical localization of 205 kDa microtubule-associated protein (205 kDa MAP) in the guinea pig organ of Corti

We have studied the immunocytochemical localization of microtubule-associated proteins (MAPs) in the guinea pig organ of Corti. Using immunological methods with antibodies against MAP1A, MAP1B, MAP2, tau and 205 kDa MAP, we have identified 205 kDa MAP as a major MAP of the sensory epithelium in the organ of Corti. Immunoperoxidase microscopic study has shown that both cochlear hair cells and supporting cells reacted with anti-205 kDa MAP antibody. Immunoelectron microscopy revealed that 205 kDa MAP was associated with most microtubules in the sensory epithelial cells. It was also associated with the microtubules of bundle structures within supporting cells, suggesting that this MAP might form a part of cross-bridges between microtubules and between microtubules and actin filaments in the bundle structure. In contrast, MAP1A, MAP1B and tau, which are known to be expressed in neuronal tissue, were localized only in nerve fibers in the organ of Corti, not in the sensory epithelium. MAP2, which is known to be localized in dendrites and soma of nerve cells, was not distributed in nerve fibers in the organ of Corti. These results suggest possible roles of the 205 kDa MAP in the formation and maintenance of the highly polarized morphology of the epithelial cells of the organ of Corti, through stabilization and modulation of microtubule networks of these cells.

Neurotrophic factors modulate hair cells and their potassium currents in chick otocyst explants

Neurotrophins, retinoids and their receptors are present in the sensory epithelia of the inner ear during development. We show that these factors modulate the proliferation of hair cells and their K+-currents when the embryonic day 3 (ED 3) presumptive inner ear (i.e. otocyst) is maintained in organ culture. All trans-retinoic acid (RA) increases hair cell differentiation and enhances the acquisition of outward currents, including a delayed rectifier and a fast activating, transient type, voltage-gated potassium current. In contrast, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) decrease ionic current activity, and the addition of RA with the neurotrophins enhances this inhibitory response in an age-dependent manner. We measured the total number of cells per explant over time to determine precisely when and how these factors inhibit explant growth. We found that high concentrations of BDNF and NT-3 administered together, and low concentrations of both neurotrophins combined and administered with RA suppress otocyst cell numbers after 24 h in vitro. This suppressive response is induced by RA and NT-3, not by RA and BDNF. The suppressive or inhibitory influence of NT-3 and RA is the result of NT-3 binding to the low affinity receptor, p75NTR, not the result of RA increasing mRNA levels for the high affinity receptor, trkC. However, trk may act with p75NTR, as disruption of trk signalling alleviates the inhibitory response induced by NT-3 and RA. Our data suggest that various combinations and/or concentration gradients of these factors can differentially regulate inner ear development and hair cell excitability.

Dystrophin expression in the hair cells of the cochlea

Dystrophin is normally expressed in a number of tissues including muscle, brain and the outer plexiform layer of the retina. In Duchenne and Becker muscular dystrophy abnormal or deficient dystrophin expression leads to muscle degeneration and has been implicated in mental retardation and a form of night blindness. We have examined the expression of dystrophin immunoreactivity in cochlear tissues of normal guinea-pig and mouse, and whether expression is perturbed in the cochlea of the dystrophic MDX mouse. A single band of approximately 427 kDa, corresponding to a full-length isoform of dystrophin was detected in guinea-pig and normal mouse but was absent from the MDX mouse. Cochleae from guinea-pig, normal and MDX mouse also showed a second dystrophin isoform of 116 kDa molecular weight with the C-terminal specific antibody. Immunostained guinea pig cochlear half turns were examined by laser scanning confocal microscopy. Dystrophin was localized in both inner and outer hair cells with staining patterns which were qualitatively similar with both antibodies. In the outer hair cells labelling of the lateral wall was especially distinctive. The synaptic region of both hair cell types was also strongly labelled.

NMDA receptors in frog semicircular canals

The effects of competitive (2-amino-5-phosphonovaleric acid) and noncompetitive (Mg2+, ketamine and kynurenic acid) NMDA receptor antagonists were tested in isolated semicircular canals of the frog. All these antagonists reduced the resting firing rate recorded from the whole ampullar nerve of the posterior canal. This suggests that NMDA receptors are present at the cytoneural junctions between hair cells and afferent nerve terminals in frog vestibular organs.

The cell adhesion molecule BEN defines a prosensory patch in the developing avian otocyst

The distribution of the cell adhesion molecule BEN in the developing chick inner ear is described. BEN is first detected in the otic placode at stage 11. As the placode begins to invaginate, BEN becomes concentrated in a ventromedial region extending from the anterior to the posterior end of the otic pit. BEN expression levels increase in this region as the pit closes to form the otocyst, and distinct boundaries become defined along the dorsal and ventral edges of the ventromedial band of BEN expression. BEN expression also becomes concentrated dorsally within the otic epithelium as the pit closes and is observed in the condensing otic ganglion. By stage 22, the ventromedial band of BEN expression splits into two distinct regions, a small caudal patch within which the posterior crista will develop, and a larger anterior patch. By stage 26, this larger anterior patch of cells expressing BEN becomes subdivided into five separate areas corresponding to the regions within which the anterior crista, the lateral crista, the utricle, the saccule, and both the basilar papilla and lagenar macula form. Hair cells only develop within these regions defined by BEN distribution. The data suggest that the ventromedial patch of BEN expression observed from stage 11 onwards defines a single sensory competent zone from which all sensory organs of the inner ear develop. BEN immunoreactivity in the inner ear declines after stage 38. In response to noise exposure, upregulation of BEN expression is mainly detected in regions of the posthatch papilla where the damage is severe and regenerating hair cells are not observed. The regenerating hair and supporting cells do not express BEN, highlighting a molecular difference between the processes of development and regeneration.

Glycoconjugates in the cochlea as revealed by the silver methenamine method

The glycoconjugates in the cochlea of the guinea pig were studied by staining samples by the silver methenamine method as well as after periodic acid-Schiff (PAS) staining. Results obtained by the two methods were similar but not identical. The silver methenamine method was much better in terms of resolution. However, this method of staining seemed less specific than the PAS reaction. When the silver methenamine method was used, the tectorial membrane and outer hair cells were specifically stained. Two types of fibrils were observed in the tectorial membrane. Thick fibrils were located in the fibrous layer. Thin fibrils were situated in the marginal band, the cover net, Hensen's stripe and the fibrous layer. The thick and thin fibrils appeared to correspond to type A and type B protofibrils, respectively. The outer hair cells were found to contain strongly stained particles which, presumably, consisted of glycogen. The basement membrane of the capillaries in the stria vascularis also gave a positive reaction, while that of other capillaries was essentially unstained. This finding suggests structural differences between these capillaries.

Efferent terminals in the cochlea of the mustached bat: quantitative data

Efferent terminals in the cochlea of the mustached bat were stained for acetylcholinesterase (AChE) and quantitative data were obtained for the number and size of the endings on the outer hair cells (OHCs) in each row, from base to apex. From TEM micrographs and AChE-stained, surface preparations it was determined that every OHC had a single, large terminal. The mean size of the terminals was significantly different in each row, with the largest occurring in the first row (7.1 microns 2); the mean size in the second and third rows was 5.7 and 5.0 microns 2 respectively. In specific frequency processing regions, the largest mean size (8.4 microns 2) for first row OHCs was consistently found in the distal densely innervated (DDI) area. This region has afferent neurons that are sharply tuned to the second harmonic, constant frequency component of the bat's biosonar signals. Sudden changes in the size of the terminals were observed exactly at the boundaries of the DDI with adjacent sparsely innervated regions. Similar, but less striking, size changes also occurred in and adjacent to the proximal densely innervated (PDI) region, a harmonically related, sharply tuned region, which processes the bat's 91.5 kHz, third harmonic, constant frequency signals. The region of the cochlea with the smallest first row terminals (mean 5.3 microns 2) was the large, sparsely innervated region of the basal turn, a region that does not appear to process biosonar signals. Although the significance of differences in efferent terminal size is not known, the data suggest a possible correlation between OHC stimulation and sharp tuning. The potentially greater influence of the efferent fibers on the first row of OHCs, compared to other rows, is consistent with observations made on other mammals; in the latter, however, the greater influence has been suggested more by number than size. Unlike other mammals, the OHC efferents in the mustached bat have no clear base-to-apex gradient in the number or size of the efferent terminals. It is suggested that this might reflect the high frequency nature of the ear (6-120 kHz) and absence of low frequency hearing.

Expression of a voltage-dependent potassium channel protein (Kv3.1) in the embryonic development of the auditory system

The present study traces the development of a voltage-dependent potassium channel protein (Kv3.1) in the avian homologue of the cochlear nucleus, in the cochleovestibular ganglion, and in the otic epithelium from early developmental stages until near hatching. Immunohistochemistry with antibodies to the carboxy terminus (recognizing the Kv3.1b splice variant) and to the amino terminus (recognizing either form of Kv3.1) was used on Hamburger-Hamilton-staged chicken embryos. There were three periods in the relative levels of immunostaining in these regions. Early (E2-6), when precursor cells proliferate, migrate, and form axons, there was staining when using either antibody. In the middle period (E6-11), marked by hair cell differentiation, dendritic growth, and early synapse formation, staining levels decreased. In the late period (E11-19), when auditory function begins, staining increased rapidly, especially for Kv3.1b. Early Kv3.1 expression occurs in neuronal and hair cell precursors before they differentiate or function. Later, in the otic epithelium, a high level of Kv3.1 in cilia may precede or coincide with the onset of hair cell function. In neurons, some features of its localization correlate with axon outgrowth and synapse formation, others with the onset of neural activity and function.

Immunohistochemical localization of S-100 protein in the saccule of the rainbow trout (Salmo gairdnerii R.)

The distribution of S-100-like immunoreactivity in the trout saccule (a presumed organ of hearing in fish) has been determined by means of immunohistochemistry. Within the sensory epithelium of the saccular macula, hair cells and myelinated saccular nerve fibers were found to be immunoreactive. Hair-cell immunoreactivity was relatively uniform throughout the macula except at the extreme periphery (rostral, caudal, ventral and dorsal), where staining was either decreased or absent. The immunoreactivity associated with myelinated nerve fibers was greatest at the peripheral edges of the nerve processes, a position corresponding to the location of Schwann cells. However, the nerve processes themselves (within and subjacent to the sensory epithelium), as well as cell bodies within the saccular nerve, were also immunoreactive. Thus, the immunoreactivity of the saccular nerve observed above the basal lamina can be attributed to the saccular nerve processes as well as to nerve-associated Schwann cells. Overall, the immunoreactivity displayed by hair cells was less intense than that associated with myelinated saccular nerve, as evidenced by a disappearance of signal in hair cells first, upon serial dilution of antibody. No S-100-like immunoreactivity was observed in supporting cells within the sensory epithelium or in epithelial cells in non-sensory regions. A concentration of S-100-like immunoreactivity in hair cells and saccular nerve is suggestive of the presence of S-100 calcium-binding protein-mediated activities in these cell types.

Sensory cells of the chick cochlea express synaptophysin

Previous evidence has shown expression of synaptophysin by sensory cells of the auditory and vestibular systems in the human, but not in other mammalian species. Using a monoclonal antibody, SBI 20.10, we investigated the expression of synaptophysin in the sensory cells of the avian cochlea. We present immunohistochemical data showing synaptophysin expression by cochlear hair cells in both late stage embryos and adult chickens. Immunoblotting of cochleae confirmed an antigen with an apparent molecular weight appropriate for synaptophysin that increases with development. Immunoreactivity in the apex of the cochlea occurred in hair cells on both neural and abneural sides, whereas immunoreactivity in the base of the cochlea was relegated to hair cells on the neural side. These observations indicate that, in the avian auditory system, like the human, synaptophysin is expressed in the sensory cells of both the embryo and adult.

Cellular localisation of taurine in the organ of Corti

The cellular localisation of taurine in the organ of Corti has been established using a monoclonal antibody and confocal fluorescence microscopy. The bulk of the taurine was found in the outer hair cells with very little present in the inner hair cells and supporting structures. The outer hair cells which probably function as an amplification/attenuation gain system, control inner hair cell output to the brain. Taurine is tentatively postulated as being related to calcium fluxes involved in outer hair cell response to sound or olivocochlear bundle stimulation. Other possibilities are also discussed.

Development of Ultrasensitive Biomimetic Auditory Hair Cells Based on Piezoresistive Hydrogel Nanocomposites

With an ageing population, hearing disorders are predicted to rise considerably in the following decades. Thus, developing a new class of artificial auditory system has been highlighted as one of the most exciting research topics for biomedical applications. Herein, a design of a biocompatible piezoresistive-based artificial hair cell sensor is presented consisting of a highly flexible and conductive polyvinyl alcohol (PVA) nanocomposite with vertical graphene nanosheets (VGNs). The bilayer hydrogel sensor demonstrates excellent performance to mimic biological hair cells, responding to acoustic stimuli in the audible range between 60 Hz to 20 kHz. The sensor output demonstrates stable mid-frequency regions (∼4-9 kHz), with the greatest sensitivity as high frequencies (∼13-20 kHz). This is somewhat akin to the mammalian auditory system, which has remarkable sensitivity and sharp tuning at high frequencies due to the "active process". This work validates the PVA/VGN sensor as a potential candidate to play a similar functional role to that of the cochlear hair cells, which also operate over a wide frequency domain in a viscous environment. Further characterizations of the sensor show that increasing the sound amplitude results in higher responses from the sensor while taking it to the depth drops the sensor outputs due to attenuation of sound in water. Meanwhile, the acoustic pressure distribution of sound waves is predicted through finite element analysis, whereby the numerical results are in perfect agreement with experimental data. This proof-of-concept work creates a platform for the future design of susceptible, flexible biomimetic sensors to closely mimic the biological cochlea.

Calcium-binding proteins in the inner ear of Xenopus laevis (Daudin)

Parvalbumin, S-100, calbindin-D28K and calmodulin-immunoreactive sensory hair cells were located in the inner ear of tadpoles and mature frogs of Xenopus laevis (Daudin). The relative number of immunoreactive cells varied in different compartments of the inner ear, depending on the Ca-binding protein studied.

Cytoskeletal network of intermediate filament proteins in the adult human vestibular labyrinth

The cytoskeleton of adult human vestibular hair cells lacks intermediate filament (IF) proteins, whereas in fetal material immunoreactivity for cytokeratin (cks; a subclass of IFs) occurs in both types of hair cells. The shift in the cytoskeletal composition can be hypothesized to their onset of physiological function. Since the IFs are extremely rigid intracellular structures, they provide considerable mechanical stability. The entire cytoplasm of all supporting cells in the epithelial lining of all five vestibular organs is filled with cks. In this way most vestibular hair cells become compartmentalized, each with a rigid shell surrounding it. The distinct delineation of IF proteins in adult tissues, in contrast to fetal inner ear organs in which often a rather general cytoplasmic expression occurs, probably reflects their anatomical basis for their function.

The localization of synaptophysin in the organ of Corti of the human as shown by immunoelectron microscopy

Synaptophysin, or p38, a polypeptide of molecular weight 38 kD, is a calcium-binding membrane protein found in synaptic vesicles of neurons and smooth surfaced vesicles of neuroendocrine cells. Six human neonatal and infant temporal bones were fixed in paraformaldehyde and glutaraldehyde, decalcified in EDTA and were than immunoreacted for synaptophysin (ICN Biomedicals) using the avidin-biotin reaction (ABC kit, Vector Labs). The tissue was then prepared for light microscopic surface preparation, radial sections of 5 microns, and serial section electron microscopy. At a light microscopic level, the inner spiral bundle, tunnel spiral bundle, upper tunnel crossing fibers and the base of outer hair cells were stained. At the base of outer hair cells, the immunoreactivity was seen to decrease from the base to the apex and from the first to third outer hair cells. At an electron microscopic level, immunoreactivity at the base of outer hair cells was limited to vesiculated efferent fibers. The degree of immunoreactivity between adjacent efferent fibers varied significantly. Immunoreactive vesiculated endings were also found in the supranuclear region of outer hair cells.

Substance P in the auditory hair cells in the guinea pig

Previous immunohistochemical and electrophysiological studies on various neurotransmitters revealed the tachykinin substance P (SP) as a neuromodulator in the auditory system of mammals. This study was performed in order to determine the immunohistochemical expression and distribution pattern of SP in the organ of Corti, especially in the inner (IHC) and outer hair cell (OHC) region of the guinea pig. We examined the immunoreactivity of SP of surface preparations by means of a fluorescence and a laser scanning microscope. The electrophysiological action of SP, N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were recorded at the subsynaptic afferent region of the IHCs using micro-iontophoretic techniques. The SP-like immunostaining could be detected at the basal and apical pole of the IHCs with a gradient distribution pattern from the basal to the apical turn. Furthermore, we could demonstrate SP-like immunoreactivity in OHCs with different occurrence in turns as well as in rows. Electrical activity was induced by applying SP, NMDA and AMPA perisynaptically to the IHCs. The selective SP antagonist spantide (D-Arg1, D-Trp7,9, Leu11-substance P) specifically blocked the SP-induced activity but without altering the activity of NMDA and AMPA. In contrast, specific NMDA or AMPA antagonists reversibly blocked either the NMDA- or AMPA-induced responses without affecting the SP-induced activity. These immunohistochemical and electrophysiological results confirm that SP may represent a neuromodulator function at the synapses of the IHCs in the guinea pig.

Electron-probe analysis of isolated goldfish hair cells: implications for preparing healthy cells

Electron-probe analysis provides an objective criterion for the physiological status of cells: whether they show the high potassium and low sodium that are expected of healthy animal cells. Preparing isolated goldfish hair cells that were healthy by this criterion required several precautions, including: limited exposure to enzymes and to simple salt solutions, a rest period between enzyme treatment and mechanical disruption of the tissue, and presence of bovine albumin in the medium both during the rest period and during mechanical dispersion and plating. Cells prepared with these precautions from the saccule and lagena and kept in an enriched medium had the following elemental composition (mole percentages with respect to phosphorus): K, 103; Na, 18; Cl, 23; S, 13; Mg, 8; Ca, 1.5. These mole percentages were close to these elements' total millimolar concentrations in the cells. If the precautions were not taken, cells with intact surface membranes (as assessed by exclusion and retention of dyes) could be obtained, but the cells had elevated cell sodium and low cell potassium.

G protein Gi2 alpha in the cochlea: cloning and selective occurrence in receptor cells

A cDNA library was made from the mouse cochlea and screened with a G protein-cDNA like molecule obtained from cochlear tissue by polymerase chain reaction. The nucleotide sequence of a clone, named cochlear Gi2 alpha, had 99.2% identity to mouse macrophage Gi2 alpha. Using an antibody which is selective for Gi2 alpha, expression of the cochlear Gi2 alpha was localized in outer and inner hair cells of the organ of Corti. Possible functional roles of this G protein in hair cells are discussed.

An analysis of actin isoforms expressed in hair-cell enriched fractions of the chick basilar papilla by the polymerase chain reaction technique

Actin mRNA was characterised in hair-cell enriched fractions of the chick basilar papilla, by means of the reverse-transcription polymerase chain reaction technique. Primers were directed against the 3' untranslated portions of the actin mRNAs. Evidence for beta-cytoplasmic and gamma-cytoplasmic actin mRNA was found; no evidence was found for alpha-skeletal, alpha-cardiac or type 5 cytoplasmic actin mRNAs. Since beta-actin is known to form bundles of filaments whereas gamma-actin does not, this suggests that the hair-cell stereocilia are composed of beta-actin.

AMPA-type glutamate receptor subunits are expressed in the avian cochlear hair cells and ganglion cells

The cellular localization of AMPA-type glutamate receptor subunits was examined in the pigeon inner ear using subunit specific polyclonal antibodies (GluR1-4). In the auditory ganglion cell bodies immunoreactivity for the subunits GluR2/3 and GluR4, but not for GluR1 was detected. The hair cells showed diffuse immunoreactivity for GluR4. Additionally, immunostaining for the subunits GluR2/3 and GluR4 was present below the hair cells. These results indicate that the AMPA type glutamate receptors play a role in neurotransmission at the hair cell afferent synapse in the avian auditory system.

Immunolocalization of myosin Ibeta in the hair cell's hair bundle

The hair bundle, the hair cell's sensory organelle, transduces acoustical or vestibular stimulation into a change in membrane potential. The actin-based stereociliary processes of the hair bundle contain a number of myosin isoforms that may be important to the bundle's function. One of these isoforms, myosin Ibeta, has been proposed to constitute an adaptation motor controlling sensitivity of the hair bundle to mechanical displacement. To gain insight into myosin Ibeta's function, its distribution within the hair bundle was examined. A polyclonal antibody was produced that recognizes a protein surface loop within the head domain of myosin Ibeta. This antibody was used to localize myosin Ibeta in the hair cell by indirect-immunofluorescence microscopy and indirect-immunoelectron microscopy. Within the hair bundle, myosin Ibeta immunoreactivity was located along the sides of the stereociliary actin core, concentrated in the distal two-thirds of the stereocilia. Within the hair cell soma, myosin Ibeta immunoreactivity was located throughout the cytoplasm exclusive of the cuticular plate.

Characterization of Two Transgene Insertional Mutations at Pirouette, a Mouse Deafness Locus

The mouse mutant 'pirouette' (pi) exhibits profound hearing loss and vestibular defects due to inheritance of a recessive mutation on chromosome 5. Dysfunction has been correlated with defects during maturation of sensory cells in the inner ear. As an initial step in characterizing pirouette at the genetic level, we have localized the candidate interval to a small region on central chromosome 5 by analysis of a congenic strain of pirouette mice. This region exhibits conserved synteny with human chromosome 4 and suggests that pirouette may be a genetic model of the human nonsyndromic deafness disorder DFNB25, which has been localized to 4p15.3-q12. In addition to the original spontaneous pirouette strain, we have identified and characterized 2 additional mouse strains with allelic mutations at the same locus. Analysis of the morphology in each of the 3 pirouette alleles indicated very similar early postnatal alterations in maturation of stereocilia and suggests that the gene affected in pirouette normally plays a role in building or maintaining these structures that are critical for sensory mechanotransduction.

Structure and composition of stereocilia cross-links in normal and hydropic cochleas of the guinea pig

Structure and composition of stereocilia cross-links were investigated cytochemically in normal and hydropic cochleas of the guinea pig. The electron-dense markers colloidal thorium and cationized ferritin were used for visualization. Side links as well as tip links were visualized using both markers. Cationized ferritin allowed a better visualization of the delicate cross-link substructure than did colloidal thorium. Following digestion with neuraminidase, cross-link reactivity for colloidal thorium was virtually abolished. However, the basic structure of the cross-links could still be observed as a result of routine post-fixation and contrast staining. In both 3- and 6-month hydropic cochleas glycocalyx reactivity of the stereocilia appeared to be unaltered, provided that stereocilia were still present. However, loss of cross-links of the outer hair cells - resulting in disarrangement of the stereociliary bundles - was observed in hydropic cochleas. Our results suggest that cross-links are a separate morphological and cytochemical entity, which is different from the glycocalyx. Furthermore, loss of stereocilia cross-links, with concomitant disarrangement of the outer hair cell stereociliary bundle, appears to be one of the early pathological features of surgically induced endolymphatic hydrops, which might be responsible for permanent sensorineural hearing loss.

Immunocytochemical localization of intermediate filaments in the guinea pig vestibular periphery with special reference to their alteration after ototoxic drug administration

The present study examined the immunocytochemical localization of various intermediate filaments (IFs), 68 kDa, 160 kDa and 200 kDa neurofilament protein (NFP), cytokeratin (CK) 1, 8, 10 and 19, vimentin, and glial fibrillary acidic protein (GFAP) in the vestibular end-organs and ganglia of normal and streptomycin-treated guinea pigs. In normal animals, 68 kDa, 160 kDa and 200 kDa NFP were found in afferent nerve fibers and nerve terminals (probably nerve chalices). Fine nerve fibers (probably efferent and/or sympathetic nerve fibers) were also immunoreactive to NFP. In the vestibular ganglia, 68 kDa and 160 kDa NFP were predominantly distributed in larger cells, whereas 200 kDa NFP was also found in some small ganglion cells. Cytokeratin 8 and 19 were located in supporting cells, transitional cells, dark cells of vestibular end-organs, and the epithelial cell lining of the membranous labyrinth. Vimentin was observed in the hair cells distributed in the central region of the end organs, supporting cells, most connective tissue cells, and Schwann cells of the vestibular ganglion. Although GFAP-like immunoreactivity was evident in glial cells of the proximal vestibular nerve, no immunoreactivity was detected in the distal portion of the vestibular nerve, vestibular ganglion, or vestibular end-organs. These highly distinct staining patterns of IFs indicated that they may play different roles in the different cell types, and that they may serve as a specific marker for each cell type. In streptomycin-treated guinea pigs, immunoreactivities for NFP and vimentin (found in the hair cells) decreased after treatment, whereas immunoreactivities for the other IFs were not affected.(ABSTRACT TRUNCATED AT 250 WORDS)