[Ultrastructural study of ampulla of mouse inner ear]

Objective: To observe the ultrastructure of the ampulla, and analyze its physiological and pathological significance. Methods: In this study, 20 Kunming mice were used, and scanning electron microscopy was used to observe the ultrastructure of the ampulla of inner ear. Results: Otoconia was found among the cilia bundles of different haircell(intercilla otoconia of ampulla). The cupula was attached to the lateral wall of the ampulla, and easily to be separated; after separated, a kind of slender crystal(surface otoconia of ampulla) could be seen between the cupula and lateral wall of the ampulla, both sides of ampullary crest were covered with slender crystals too. On the canal side of the ampulla wall, there was more particulate matter attached to the wall near the bottom of ampullary crest, partially embedded in the wall, and less on the utricle side of the ampulla wall. Conclusions: The observation of the ultrastructure of the ampulla is helpful for better understanding the physiological functions of the semicircular canals and the ampulla, and better understanding the pathogenesis and solution of some vertigo diseases.

Defects in vestibular sensory epithelia and innervation in mice with loss of Chd7 function: implications for human CHARGE syndrome

CHD7 is a chromodomain gene mutated in CHARGE syndrome, a multiple anomaly condition characterized by ocular coloboma, heart defects, atresia of the choanae, retarded growth and development, genital hypoplasia, and ear defects including deafness and semicircular canal dysgenesis. Mice with heterozygous Chd7 deficiency have circling behavior and semicircular canal defects and are an excellent animal model for exploring the pathogenesis of CHARGE features. Inner ear vestibular defects have been characterized in heterozygous Chd7-deficient embryos and early postnatal mice, but it is not known whether vestibular defects persist throughout adulthood in Chd7-deficient mice or whether the vestibular sensory epithelia and their associated innervation and function are intact. Here we describe a detailed analysis of inner ear vestibular structures in mature mice that are heterozygous for a Chd7-deficient, gene-trapped allele (Chd7(Gt/+)). Chd7(Gt/+) mice display variable asymmetric lateral and posterior semicircular canal malformations, as well as defects in vestibular sensory epithelial innervation despite the presence of intact hair cells in the target organs. These observations have important functional implications for understanding the clinical manifestations of CHD7 mutations in humans and for designing therapies to treat inner ear vestibular dysfunction.

Histopathology of the vestibular end organs after intratympanic gentamicin failure for Meniere's disease

CONCLUSION

To our knowledge, this is the first report of the histopathology of the vestibular end organs following intratympanic gentamicin for intractable Meniere's disease. There was relative sparing of the utricular macula, compared with the cristae ampullares. However, the utricular macula exhibited severe hair cell loss. Clinically, the patient has been free from vertigo spells for 3 years following labyrinthectomy.

OBJECTIVE

To describe the histopathology and morphometry of the vestibular end organs from a 59-year-old Meniere's patient who underwent transmastoid labyrinthectomy for recurrent vertigo after failed intratympanic gentamicin.

MATERIALS AND METHODS

Light and transmission electron microscopy were utilized; with unbiased stereology-physical fractionator for type I, type II hair cell, and supporting cell counts. Comparison with end organ histopathology in a 56-year-old with Meniere's disease without gentamicin treatment was carried out.

RESULTS

Histopathological analysis of the semicircular canal cristae ampullares showed severe atrophy of the neuroepithelium with undifferentiated cells, and fibrosis and edema of the stroma. The utricular macula had some remaining type I and type II vestibular hair cells, and nerve fibers and terminals within the underlying stroma. Morphometric measures were obtained from the utricular macula: 2000 type I and 500 type II hair cells, representing 7.3% of type I hair cells and 4.9% of type II hair cells compared with normative controls, and 24 000 supporting cells were obtained.

Single-channel L-type Ca2+ currents in chicken embryo semicircular canal type I and type II hair cells

Few data are available concerning single Ca channel properties in inner ear hair cells and particularly none in vestibular type I hair cells. By using the cell-attached configuration of the patch-clamp technique in combination with the semicircular canal crista slice preparation, we determined the elementary properties of voltage-dependent Ca channels in chicken embryo type I and type II hair cells. The pipette solutions included Bay K 8644. With 70 mM Ba(2+) in the patch pipette, Ca channel activity appeared as very brief openings at -60 mV. Ca channel properties were found to be similar in type I and type II hair cells; therefore data were pooled. The mean inward current amplitude was -1.3 +/- 0.1 (SD) pA at - 30 mV (n = 16). The average slope conductance was 21 pS (n = 20). With 5 mM Ba(2+) in the patch pipette, very brief openings were already detectable at -80 mV. The mean inward current amplitude was -0.7 +/- 0.2 pA at -40 mV (n = 9). The average slope conductance was 11 pS (n = 9). The mean open time and the open probability increased significantly with depolarization. Ca channel activity was still present and unaffected when omega-agatoxin IVA (2 microM) and omega-conotoxin GVIA (3.2 microM) were added to the pipette solution. Our results show that types I and II hair cells express L-type Ca channels with similar properties. Moreover, they suggest that in vivo Ca(2+) influx might occur at membrane voltages more negative than -60 mV.

Morphological aspects of potassium flow in the semicircular canal ampulla of the pigeon

Potassium ions are a prerequisite for the development and regulation of sensory cell stimulation in the inner ear. From the potassium-rich endolymph the ions flow into the sensory cells apically and are released basolaterally. After transport pathways of various lengths potassium is released again into the endolymph - in the cochlea by marginal cells of the stria vascularis, in the vestibular labyrinth by dark cells. While this long recycling pathway is relatively well-known in the cochlea, few studies have been conducted on the semicircular canal ampullae (SCCA) where its morphological basis is largely unknown. According to the present electron microscopic findings, potassium ions are initially released into the extracellular space during stimulation of the sensory cells and then absorbed by supporting and light cells. Finally they are transported transcellularly over numerous very long gap junctions into the region of the dark cells. From here they move to an extracellular compartment, which is more or less completely sealed off basally by basal plates of the light cells. Apically the intercellular space between light and dark cells is sealed by junctional complexes. This newly identified space in the SCCA corresponds to the extracellular compartment between the marginal and intermediate cells in the stria vascularis. At both sites, the cochlea and the SCCA, this probably serves as a regulatory valve, reservoir or storage space, particularly for potassium ions. It is likely that the different morphology of the ion transport pathways is related to the different flow levels of potassium ions expressed by the different levels of the so-called endocochlear potential and concomitant movement of other ions in the cochlea and SCCA.

Ultrastructural observations of efferent terminals in the crista ampullaris of the toadfish, Opsanus tau

The present study was conducted to visualize the ultrastructural features of vestibular efferent boutons in the oyster toadfish, Opsanus tau. The crista ampullaris of the horizontal semicircular canal was processed for and examined by routine transmission electron microscopy. The results demonstrate that such boutons vary in size and shape, and contain a heterogeneous population of lucent vesicles with scattered dense core vesicles. Efferent contacts with hair cells are characterized by local vesicle accumulations in the presynaptic terminal and a subsynaptic cistern in the postsynaptic region of the hair cell. Serial efferent to hair cell to afferent synaptic arrangements are common, particularly in the central portion of the crista. However, direct contacts between efferent terminals and afferent neurites were not observed in our specimens. The existence of serial synaptic contacts, often with a row of vesicles in the efferent boutons lining the efferent-afferent membrane apposition, suggests that the efferent influence on the crista may involve both synaptic and nonsynaptic, secretory mechanisms. Further, it is suggested that differences in more subtle aspects of synaptic architecture and/or transmitter and receptor localization and interaction may render the efferent innervation of the peripheral crista less effective in influencing sensory processing.

Self-treatment of benign paroxysmal positional vertigo: Semont maneuver vs Epley procedure

The authors compared the efficacy of a self-applied modified Semont maneuver (MSM) with self-treatment with a modified Epley procedure (MEP) in 70 patients with posterior canal benign paroxysmal positional vertigo. The response rate after 1 week, defined as absence of positional vertigo and torsional/upbeating nystagmus on positional testing, was 95% in the MEP group (n = 37) vs 58% in the MSM group (n = 33; p < 0.001). Treatment failure was related to incorrect performance of the maneuver in the MSM group, whereas treatment-related side effects did not differ significantly between the groups.

Quantitative analysis of stereociliary arrays on vestibular hair cells

We have developed a method for quantifying the number, spacing, and distribution of stereocilia on the apical surface of hair cells using spatial autocorrelation analysis and statistics for directional data. Here, we illustrate the method using idealized hair bundles, and we apply it to scanning micrographs of turtle hair cells from the utricle and posterior canal, and to freeze-fracture preparations of bullfrog saccule. The analysis suggests three common features of stereociliary bundles. First, bundle geometries form a continuum from 'loose' to 'tight' rather than two distinct groups. Second, interciliary spacing along the three hexagon axes is not equal; spacing is usually widest along the hexagon axis closest to the bundle's axis of bilateral symmetry (the presumptive excitatory axis). Third, spacing between stereocilia changes with distance from the kinocilium. All three features will influence predictions of the tip link tensions that accompany bundle deflection.

Circling behavior in the Ecl mouse is caused by lateral semicircular canal defects

The epistatic circler mouse (Ecl mouse) is a preexisting mutant, which displays a circling phenotype and hyperactivity. It has been shown that the circling phenotype in this mutant results from a complex inheritance pattern, but the vestibular pathology has not been analyzed. The present study deals with the morphological and functional basis responsible for the circling behavior in the Ecl mouse. Morphological examination of the inner ears revealed a bilateral malformation of the horizontal (lateral) semicircular canal and duct. No cochlear abnormalities were detected, and auditory brainstem response (ABR) measurements indicated that the auditory system is not affected. Investigation of the vestibuloocular reflex (VOR) in Ecl mice showed that their horizontal VOR on stimulation is virtually absent, which correlates with the morphological findings.

Ultrastructural observations of efferent terminals in the crista Ampullaris of the toadfish, opsanus tau

The present study was conducted to visualize the ultrastructural features of vestibular efferent boutons in the oyster toadfish, Opsanus tau. The crista ampullaris of the horizontal semicircular canal was processed for and examined by routine transmission electron microscopy. The results demonstrate that such boutons vary in size and shape, and contain a heterogeneous population of lucent vesicles with scattered dense core vesicles. Efferent contacts with hair cells are characterized by local vesicle accumulations in the presynaptic terminal and a subsynaptic cistern in the postsynaptic region of the hair cell. Serial efferent to hair cell to afferent synaptic arrangements are common, particularly in the central portion of the crista. However, direct contacts between efferent terminals and afferent neurites were not observed in our specimens. The existence of serial synaptic contacts, often with a row of vesicles in the efferent boutons lining the efferent-afferent membrane apposition, suggests that the efferent influence on the crista may involve both synaptic and nonsynaptic, secretory mechanisms. Further, it is suggested that differences in more subtle aspects of synaptic architecture and/or transmitter and receptor localization and interaction may render the efferent innervation of the peripheral crista less effective in influencing sensory processing.

Apoptosis during chick inner ear development: some observations by TEM and TUNEL techniques

In order to clarify the occurrence, distribution and possible role of apoptosis during inner ear development, the ultrastructural aspects (by TEM) (at 9-19 incubation day and 1 day after hatching) and the distribution of the apoptotic phenomenon (by the TdT-mediated dUTP nick end-labeling technique), were studied in the crista ampullaris of chick embryo at 5-19 days of incubation to hatching and of postnatal 1-day old chick. We found, in the sensorial epithelium, dark supporting cells in chick embryos and mainly dark hair cells in postnatal chicks, both with ultrastructural features consistent with those of apoptosis. The presence of apoptotic phenomena was confirmed by the TUNEL technique. According to our findings, it is hypothesized that apoptosis in the inner ear may be involved: 1) at first, in macroscopic remodelling of the membranous labyrinth in early developmental stages, 2) later, in the correct differentiation of the hair and of the supporting cells, leading to characteristic cellular pattern formation and 3) finally, in physiological cell turnover of the postnatal chicken sensorial epithelium of the crista.

Dehiscence of the bony roof of the superior semicircular canal in the middle cranial fossa

Spontaneous dehiscence of the superior semicircular canal (SSC) in the middle cranial fossa is rare and may cause clinical problems. This dehiscence was investigated in cadaveric and dried temporal bone specimens. One cadaveric specimen showed a spontaneous defect: the dehiscence was a symmetrical, elongated ellipse with smooth margins. Four of 244 dry bone specimens showed bony defects in the roof of the SSC, however, only one specimen was thought to have a spontaneous defect. Based on computer-simulation models, we hypothesized that spontaneous defects of the SSC may arise during the fetal period. Although rare, this defect may cause problems in middle cranial fossa surgery and may relate to certain vertiginous disorders.

Altered cupular mechanics: a cause of peripheral vestibular disorders?

It has taken many decades to arrive at today's concept of cupula mechanics in the stimulation of endolymphatic flows on the hair cells in the ampullae of the semicircular canal. While Steinhausen assumed free swing-door movement of the cupula in the 1930s, Hillman was the first to demonstrate firm cupula attachment to the ampulla wall as a physiological necessity in the 1970s. In contrast to the present clinical concepts of acute peripheral vestibular functional disorders (circulatory disturbances, viral or bacterial infection, altered electrolytes in the endolymph), this study examines the extent to which an impaired attachment mechanism can trigger peripheral vestibular disorders. For this purpose, we used a pigeon model (n = 8), in which mechanical detachment of the cupula from the ampulla wall was achieved by means of a targeted pressure increase in the ampulla of the lateral semicircular canal. In two additional animals the labyrinth was completely destroyed on one side in order to directly compare partial and complete vestibular disorders. In this way partial damage to the lateral semicircular canal ampulla presents a clinical picture whose symptoms are very similar to those of an idiopathic vestibular disorder in humans. Their intensity and course of compensation differ markedly from the symptoms of complete vestibular destruction. Subsequent histological examination revealed that the hair cells remained intact during the experimental detachment of the cupula. Our results thus show that only altered cupula mechanics seem to trigger the clinical picture of a peripheral vestibular disorder. This may result in completely new approaches to differential diagnosis and the therapy of vestibular neuronitis.

Subcellular immunolocalization of NMDA receptor subunit NR1, 2A, 2B in the rat vestibular periphery

The immunohistochemical localization of the NMDA glutamate receptor subunits NR1, NR2A, and NR2B was investigated in the rat vestibular periphery at the light and electron microscopy level using specific antipeptide antibodies. The afferent calyceal terminals and nerve fibers innervating type I vestibular hair cells were strongly NR1, NR2A, and NR2B immunoreactive. Under electron microscopy, the basolateral type I hair cell membrane was NR1 immunoreactive. The type II hair cell and its afferent boutons were NR1, NR2A, and NR2B non-immunoreactive. Nearly all of Scarpa's ganglion neurons were NR1 immunoreactive, but there was a subset of NR2A non-immunoreactive neurons. Additionally, the larger sized Scarpa's ganglia neurons were NR2B immunoreactive, while the smaller neurons were non-immunoreactive. These findings are strong evidence for functional NMDA receptor mediation or modulation of afferent excitatory neurotransmission from type I but not type II vestibular hair cells to the primary afferent nerve. The receptor subtype(s) may be a combination of NR1/NR2A, NR1/NR2B, and/or NR1/NR2A/NR2B.

Functional morphology of the crista ampullaris: with special interests in sensory hairs and cupula: a review

The functional significance of the ciliary interconnections and cupula has been reviewed. The ciliary interconnecting systems are divided into 2 types, i.e. side links and tip links. The side links acts to maintain the regular distance between the cilia thereby keeping the geometrical arrangement of the entire sensory hair bundle intact as well as to prevent close contact between neighbouring cilia. The tip links, stretching upwards from the tips of the shorter stereocilia to their taller neighbouring shafts, are actually involved in mechanoelectrical transduction. The cupula is composed of the cupula and subcupular meshwork. The subcupular meshwork consists of long branching filaments cross-bridged to one another. The cupula would function as a rigid plate and equally distribute the shear force of the cupula to all the ciliary bundles. The subcupular meshwork may play a role in the transmission of the shear strain force of the cupula to the ciliary bundle and may also exert an additional damping effect in order to prevent unwanted vibrations.

Effects of neurotrophin and neurotrophin receptor disruption on the afferent inner ear innervation

Two neurotrophins and their two receptors appear to regulate the survival of vestibular and cochlear neurons in the developing ear. Mice lacking either brain derived neurotrophic factor (BDNF) or its associated receptor, Trk B, show a severe reduction in the number of vestibular neurons and a loss of all innervation to the semicircular canals. Mice lacking NT-3 or its receptor, Trk C, show a severe reduction of spiral neurons in the basal turn of the cochlea. Mice lacking both BDNF and NT-3 or Trk B and Trk C, reportedly lose all innervation to the inner ear. These two neurotrophins and their associated receptors are necessary for the normal afferent innervation of the inner ear.

Abnormal vestibular control of gaze and posture in a strain of a waltzing rat

The waltzing behavior is usually attributed to vestibular dysfunction. However, the vestibular control of gaze and posture has not yet been measured quantitatively in any waltzing mutant. Therefore, this study was aimed at investigating the relationship between inner-ear morphology, the circling behavior, and the vestibular control of gaze and posture in a new strain of waltzing rats. Light- and electron-microscopy studies of these mutants did not reveal any structural abnormalities of the vestibular neural epithelia. In addition, the expression of Calretinin and 200-kD phosphorylated and non-phosphorylated neurofilaments was also found to be normal in the vestibular neural epithelia and ganglion cells. In contrast, the mutants showed severe dysfunctions of the vestibular control of gaze and posture. The skeletal geometry of the alert unrestrained animals was studied using cineradiography. At rest, waltzing rats held their heads tilted down: the horizontal semicircular-canal's plane was near the earth-horizontal's plane, instead of being tilted up as in Long Evans control rats. In addition, their cervical column was pitched more forward (33.6 degrees) than in the control group (6.9 degrees). The circling behavior was observed frequently, and the rats had episodes of circling in both directions. The episodes of circling amounted to an average of 17 turns, and the average angular velocity of the circling was 645 degrees/s. Unilateral labyrinthectomy induced the same postural and oculomotor syndromes in the waltzing and control groups. This indicates that the mutant vestibular nerve had a significant resting discharge before the lesion. Eye movements were recorded using acutely implanted search coils. Although waltzing rats were able to perform normal spontaneous eye movements, they showed a complete deficit of the horizontal vestibulo-ocular reflex (HVOR) and an impairment of the maculo-ocular reflex (MOR) during constant velocity, off-vertical axis rotation (OVAR). These results show, for the first time, that deficient transduction and/or processing of the horizontal-canal- and macular-related information can be causally related to the circling behavior and abnormal posture, respectively.

Examination of the cupula and stereocilia of the horizontal semicircular canal in the toadfish Opsanus tau

We imaged the horizontal semicircular canal (HSCC) crista and cupula of toadfish, Opsanus tau, by using a) confocal light microscopy of isolated vital HSCC; b) serial sections of fixed, trichrome-stained HSCC; and c) scanning electron microscopy of fixed HSCCs. HSCC were dissections which included an ampulla and an attached canal tube (long and slender canal portion), and, in some cases, a small portion of the utricular wall. Cupulae were seen as multipartite mucus connective tissue shells rising from the crista and extending toward the ampullary roof. They were composed of several refractile bands traversing the cupulae perpendicular to longitudinal fibers extending from the cupular base to its apex. Alcian green-stained cupulae showed an asymmetric alcianphilic, dark, X-shaped structure, indicating that the pillar is rich in mucin and carbohydrate, an interpretation supported by images of trichrome-stained sections. The cupular antrum is devoid of prominent refractile fibers. No tubes or channels were observed in the cupula or antrum of vital preparations. Cupular shell fibers cover the surface of the crista, are roughly parallel, and are associated with a translucent material having a refractive index greater than the surrounding endolymph. Stereocilia were thin, 100-microm-long structures, with little longitudinal curvature, which end with no end bulb. No strands extend from stereocilia to the roof or other portions of the cupular antrum. Gross movements of stereocilia were not seen in mechanically quiescent preparations. Within the cupular antrum, stereocilia were parallel to connective tissue fibers, all embedded in an isotropic gel. This fiber-reinforced gel and cupular matrix are sensitive to N-acetlyneuraminidase and beta-N-acetyl glucosaminidase, and minimally sensitive to beta-N-acetyl hexosaminidase. Connective tissue fibers may serve to stiffen the gel, whose matrix would restrict lateral motion of embedded fibers and stereocilia thereby providing mechanical support for stereocilia.

Effects of betahistine on vestibular receptors of the frog

Betahistine is widely used in the symptomatic treatment of peripheral and central vestibular disorders. However, its remains unknown whether the drug can act directly on inner ear sensory organs. To this end, the effects of betahistine (10(-7)-10(-2) M) were examined on isolated preparations of frog semicircular canal mounted in a double-celled bath which allowed drug administration both in the endolymphatic and in the perilymphatic fluid. The effects of betahistine were evaluated by recording ampullar receptor potentials and nerve firing rate both at rest and during mechanical stimulation of the isolated preparation. The results demonstrated that endolymphatic administration of betahistine had no effect, whereas its perilymphatic administration could reduce greatly ampullar receptor resting discharge but had little effect on mechanically evoked responses. This observation may explain the anti-vertigo effects of betahistine. Vertigo is normally due to uncontrolled changes in vestibular receptor resting discharge. It is therefore probable that any factor able to reduce the resting firing rate of vestibular receptors and, in consequence, its variations, may have an anti-vertigo action.

Localization of Ca-ATPase in frog crista ampullaris

The distribution of Ca-ATPase in frog crista ampullaris was mapped ultracytochemically by using a one-step lead citrate reaction. Electron-dense precipitates, as an expression of Ca-ATPase activity, were observed on the surface of stereocilia and on the apical membrane surrounding the cuticular plate of hair cells. Sensory cells of the isthmus region showed more reactivity than those of the peripheral regions of the crista. No reaction products were detectable on the basolateral membranes and in cytoplasmatic organelles. Supporting cells of the crista showed a quite variable Ca-ATPase reaction on microvilli and on basolateral membranes. The presence of an evident reactivity on the stereocilia is consistent with the existence of an apical calcium microdomain involved in the mechano-transduction process and supports the current view that calcium ions enter the stereocilia during natural stimulation. On the other hand, the lack of an observable reactivity on the basolateral membrane of hair cells suggests that in semicircular canals other mechanisms of active transport of calcium ions across the plasma membrane, such as Na-Ca exchange, may be involved in homeostasis of the ion.

Effect of cisplatin on the basement membrane anionic sites in the ampulla, macula, and stria vascularis of guinea pigs

Our objective was to compare changes in the basement membrane anionic sites (BMAs) in the ampulla, macula, and stria vascularis following the infusion of cisplatin (CDDP). After CDDP was administered to anesthetized Hartley guinea pigs, the bony labyrinth was immersed in a solution of polyethyleneimine (PEI). The size and distribution of PEI particles associated with BMAs in the stria vascularis and in the dark cell and sensory cell areas of the vestibular labyrinth were determined by electron microscopy. A significant reduction in the number and size of PEI particles was observed on CDDP-treated strial vessels. The number and size of PEI particles on the basement membranes of the vestibular labyrinth did not differ from those in the control. Our findings suggest that the BMAs of the vestibular labyrinth were not significantly affected by the administration of a single dose of CDDP.

Comparison of Five Agents in Protecting the Cochlea Against the Ototoxic Effects of Cisplatin in the Hamster

The purpose of this investigation was to study the ameliorating effects of four agents on cis-platin-induced ototoxicity. Hamsters were given a series of five cisplatin injections either alone or in combination with sodium thiosulfate (STS), diethyldihydrothiocarbamate (DDTC), and S-2(3-aminopropylamino) ethylphosphorothiolc acid (WR-2721), or fosfomycin. Ototoxicity was assessed anatomically by quantifying the extent of cochlear damage with the scanning electron microscope and physiologically with measures of the auditory brain stem response. When administered alone, cisplatin induced widespread loss of outer hair cells (OHCs) along much of the cochlea in the hamster, especially in the basal and middle turns, with an average survival of only 56% of the OHC population. In contrast, inner hair cells resisted cisplatin ototoxicity in the hamster. Thus the ameliorative effects of the different test agents were assessed by counting the number of surviving OHCs in each treatment group and comparing with cisplatin-treated controls. STS provided the most effective protection against the ototoxic effects of cisplatin, yielding 91% survival of OHCs. DDTC also reduced the ototoxic effects of cisplatin, yielding 68% survival of OHCs. Cotreatment with WR-2721 and fosfomycin yielded 45% and 52% OHC survival, respectively, and thus did not provide any chemoprotection. The results closely paralleled those based on auditory brain stem response recordings in that the magnitude of threshold shift was proportional to the amount of OHC loss; also, the amount of threshold shift at each frequency was in good agreement with the pattern of hair cell loss along the cochlear spiral. Thus both histologic and physiologic results suggest that STS and DDTC hold promise for ameliorating the ototoxic effects of cisplatin chemotherapy.

Anionic sites of charge barrier in the guinea pig crista ampullaris

In present studies we obtained anionic sites in the epithelial and capillary basement membranes in the dark cell area of the crista ampullaris in the guinea pig. The immersion method with cationic tracer polyethyleneimine (PEI) was applied. Electronmicroscopically, the arrangement of PEI particles was observed as two strata along the basement membrane. The number of particles could be counted and compared in each portion. The control test with protamine sulfate showed that the number of PEI particles decreased in both the epithelium and capillaries of the dark cell area. In the experiment using furosemide, the stria vascularis and the dark cells had changed, with pathological findings of interstitial edema and PEI particles reduced in number. It is suggested that the PEI particles reflect different conditions of charge in the basement membrane, which influences the production or absorption of the inner ear fluid.

Hair cell regeneration and recovery of the vestibuloocular reflex in the avian vestibular system

1. Although auditory and vestibular hair cells are known to regenerate after aminoglycoside intoxication in birds, there is only sparse evidence that the regenerated hair cells are functional. To address this issue, we examined the relation of hair cell regeneration to recovery of the vestibuloocular reflex (VOR), whose afferent signal originates at hair cells in the vestibular epithelium. Hair cell damage was produced by treating white Leghorn chicks (Gallus domesticus, 4-8 days posthatch) with streptomycin sulfate in normal saline (1,200 mg.kg-1.day-1 im) for 5 days. 2. In the 1st wk after treatment, the VOR gain was essentially 0, and hair cell density as assessed by light microscopy was approximately 40% of normal. Between the 1st and 3rd wk after treatment, the VOR was present. Although VOR gain varied considerably from one chick to another, it increased, on average, between the 1st and 3rd wk, as did the average hair cell density. At the end of 8-9 wk, the gain and phase of the VOR had returned to normal values, as had the average density of hair cells. 3. Therefore, despite the catastrophic initial effect of hair cell loss on the VOR, recovered hair cells appeared to restore the VOR completely. Average hair cell density increased with average VOR gain. VOR gain correlated better with recovery of type 1 hair cells than with recovery of type II hair cells. 4. In contrast to hair cell density, the appearance of the vestibular epithelia as assessed by hair cell stereocilia in scanning electron micrographs was a poor indicator of VOR gain. In both treated and control birds, epithelia with the same appearance could have quite different VOR gains, suggesting a variation in the functional viability of the hair cells. 5. This observation suggests that several factors, such as the repair of stereocilia, the efficacy of hair cell synapses on afferent fibers, and the extent of compensation by central vestibular pathways, may affect the recovery of VOR gain. However, our data suggest that hair cell regeneration plays an important role in this recovery.

Basophilic deposits on the cupula: preliminary findings describing the problems involved in studies regarding the incidence of basophilic deposits on the cupula

In this study, the possibility of whether basophilic deposits adhered to the cupulas in the semicircular canals was investigated histologically. Results indicated that basophilic deposits were present in all three cupulas of the semicircular canals. The overall incidence of basophilic deposits in the superior, lateral and posterior semicircular canal cupulas was 26%, 41% and 37%, respectively. The incidence of basophilic deposits bound to the cupulas increased with age. The possible origin of these basophilic deposits on the cupulas and the increased incidence of basophilic deposits with increasing age are discussed.

Comparative cytoskeletal analyses of the inner ear in man and the squirrel monkey

Serially sectioned human and squirrel monkey labyrinths were analyzed with high-resolution light microscopy after using 25 different monoclonal antibodies (mAbs) identifying all three main classes of cytoskeletal proteins. A high degree of similarity was found in labyrinths from man and squirrel monkey. Only 1 of 25 mAbs stained differently between the two species. In the squirrel monkey but not in the human the mAbs identifying S-100 proteins stained subpopulations of type I vestibular hair cells in the striola of the two macula and the summit of the cristae as compared to the same type of hair cells in the periphery of vestibular organs. Such an establishment of subpopulations of hair cells with the same ultrastructure has previously not been described in higher vertebrates. In contrast to the species differences in the distribution of neuroactive substances, the cytoskeletal architecture seems to be relatively unchanged and stable during evolution. Since each species has its own hearing and equilibrium function, neurotransmitters (neuropeptides, amino acids, etc.) could contribute to such species-specific functions.

Morphological features of different regions in frog crista ampullaris (Rana esculenta)

The cellular organization of different regions of the crista epithelium from the frog posterior semicircular canal was studied by light, transmission and scanning microscopy. The sensory epithelium consists of hair cells surrounded by supporting cells and basal cells located close to the basement membrane. Three types of hair cells, namely club-like, cylindrical and pear-like cells differentially distributed along the crista could be recognized on the basis of their shape. Club-like cells are located only in the peripheral regions, cylindrical cells both in the central and in the peripheral regions, and pear-like cells appear segregated into the intermediate regions. Sensory cells of the central region are characterized by a ciliary apparatus consisting of stereocilia usually shorter--and in some cases less numerous--than those of cells of the other regions. The presence of large evaginations of the apical membrane of hair cells and of several vesicles of microexocytosis demonstrates that receptor cells have a considerable secretory activity. This secretory activity is also proven by the presence in the supranuclear region of hair cells of numerous Golgi complexes. Moreover, the presence of two kinds of Golgi complexes, one constituted by dilated cisternae containing a moderately electron-dense material and the other made up of flattened electron-transparent cisternae, suggests a diversified secretion of material by the hair cells. This heterogeneous material may provide substances important for cupula formation and the composition of the endolymph.

Laser labyrinthectomy

Concepts and methods of laser labyrinthectomy have been proposed based on experimental studies in which the macula utriculi was irradiated with an argon laser beam through the oval window. In our previous reports, a single application of the beam (1.5 W, 0.5 s) eradicated the guinea pig macula within 5 weeks. The contour of the membranous labyrinth was normal and intact. The human macula utriculi was approached after stapedectomy and irradiated with an argon laser in a patient who developed persistent positional vertigo after closure of a perilymph fistula. Laser singular neurectomy was also done. Hearing remained unchanged, and the patient's vertigo disappeared. The human macula sacculi, however, cannot be irradiated, because of the presence of pigment in the saccular wall. In guinea pigs, the semicircular canals were irradiated from the outside. The lateral and posterior canals were approached through the middle ear, whereas the anterior canal was approached through the posterior fossa. Argon laser irradiation (1-1.5 W, 0.5 s) to the bony canal produced a charred area with or without perforation. The semicircular duct showed shrinkage and tearing of the trabecular meshwork immediately after irradiation. Several weeks later, the canal had been obliterated by ossification. Although laser labyrinthectomy can destroy the function of individual otolithic organs and eliminate dynamic impulses of the semicircular canals, hearing can be preserved.

Ultrastructural and immunocytochemical study of the subepithelial fiber component of the guinea pig inner ear

The connective tissues of the lateral cochlear wall and semicircular canal of the guinea pig were investigated by transmission electron microscopy, intermediate voltage electron microscopy and immunocytochemistry. In the spiral ligament, numerous fibroblasts and fiber bundles were intermingled with each other. Fibroblasts and fibers were also observed in the semicircular canal. Ultrastructurally, immuno-gold particles, indicating the presence of type II collagen, were found on the fibers in the spiral ligament and the semicircular canals. The present results revealed that both stria vascularis and the membranous semicircular canal were supported by a network of fibroblasts and type II collagen fibers.

Scanning electron microscopic evaluation of age-related changes in the rat vestibular epithelium

An ultrastructural study was performed to assess age-related changes in the vestibular end organs of Fischer 344 rats. The surfaces of the maculae and cristae from 3-, 12-, and 24-month-old Fischer 344 rats were observed by use of scanning electron microscopy. Age-related changes in the morphology of the vestibular neuroepithelium included a substantial loss of hair cells, as well as a reduction in the number of kinocilia and stereocilia on those that remained. These changes were greatest in the central upper regions of the three ampullae. In aged animals a greater area of the neuroepithelial surface was covered with microvilli, and in some instances, giant cilia were found among the microvillous surfaces. In contrast, there were few differences among the three age groups in the number and condition of hair cells in the saccules and utricles. The changes observed in the cristae may contribute to the age-associated impairment of vestibular function. If similar changes occur in human beings, these could in part account for the presbycusis observed in the elderly.

Ultrastructural changes of the vestibular sensory organs after streptomycin application on the lateral canal

Early changes in the vestibular sense organs resulting from the application of a streptomycin sulfate soaked Gelfoam pledget on the fenestra of the lateral semicircular canal were studied by transmission and scanning electron microscopy. Three days after the application, lesions were present in the central part of the lateral crista. The type I sensory cells were more affected than the type II cells. These sensory cells showed mitochondrial swelling, cytoplasm protrusion at the cell apex, inclusion of multiple vacuoles, fusion or loss of stereocilia, and pyknotic nuclei. Seven days after the drug application, the sensory cell damage extended to all three cristae and macula utriculi. The lesions were very extensive after ten days and the sensory cells had almost equally disappeared in all three cristae; the lesion in the macula utriculi was smaller and the macula sacculi was unaffected. At fourteen days, the lesions appeared less severe. Thus, a single application of a small amount of streptomycin on the lateral canal fenestra affected all vestibular sense organs, except the saccule, in a short time. The strong affinity of aminoglycosides for the cristae suggests possible entrapment of the drug at the ampullae. This local drug application technique to the canal will be useful in studying vestibular function in animals, and it is applicable to controlling severe vestibular symptoms in human patients.

Morphological correlations between spontaneously discharging primary vestibular afferents and vestibular nucleus neurons in the cat

Synaptic connections between physiologically classified primary vestibular afferents (PVAs) and their target vestibular nucleus (VN) neurons were examined by a combination of intra-axonal staining and electron microscopic techniques. PVAs originating from the horizontal semicircular canal were electrophysiologically classified as either regular- or irregular-type based on the regularity of their spontaneous discharge patterns, and were intra-axonally labeled with horseradish peroxidase (HRP). HRP-labeled PVAs of both types had many swellings along their course that contacted VN neurons. These swellings contained spherical synaptic vesicles and showed asymmetric postsynaptic specialization. Target VN neurons of both types of PVAs were distributed primarily in the superior, medial, and inferior VN. Irregular-type PVAs made more axosomatic contacts than did regular-type PVAs. The soma size of target VN neurons and the number of terminal boutons per target VN neuron were larger for irregular-type PVAs than for regular-type PVAs. Large VN neurons (presumably kinetic neurons) were innervated exclusively by irregular-type PVAs. Small VN neurons were innervated by PVAs of the regular-type and the irregular-type. These results demonstrate that there is a correlation between the physiological properties and morphological characteristics of PVAs and their target VN neurons.

The correlated blanching of synaptic bodies and reduction in afferent firing rates caused by transmitter-depleting agents in the frog semicircular canal

Synaptic bodies (SBs) associated with rings of synaptic vesicles and well-defined, pre- and post-synaptic membrane structures are indicators of maturity in most hair cell-afferent nerve junctions. The role of the SBs remains elusive despite several experiments showing that they may be involved in storage of neurotransmitter. Our results demonstrate that SBs of the adult posterior semicircular canal (SCC) cristae hair cells become less electron dense following incubation of the SCC with the transmitter-depleting drug tetrabenazine (TBZ). Objective quantification and comparison of the densities of the SBs in untreated and TBZ-treated frog SCC demonstrated that TBZ significantly decreased the electron density of SBs. This reduction in electron density was accompanied by a reduction in firing rates of afferent fibers innervating the posterior SCC. A second transmitter-depleting drug, guanethidine, previously shown to reduce the electron density of hair cell SBs, also reduced the firing rates of afferent fibers innervating the posterior SCC. In contrast, the electron density of dense granules (DG), similar in size and shape to synaptic bodies (SB) in hair cells, did not change after incubation in TBZ, thus indicating that granules and SBs are not similar in regard to their electron density. The role of SBs in synaptic transmission and the transmitter, if any, stored in the SBs remain unknown. Nonetheless, the association of the lessening of electron density with a reduction in afferent firing rate provides impetus for the further investigation of the SB's role in neurotransmission.

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.

The structure and development of the 'plana semilunata' of the labyrinth of the trout

Five plana semilunata consisting of tall epithelial cells were found in the semicircular canal ampullae of the trout labyrinth. All these areas began to develop after hatching. Their cells were cuboid at fry stages and prismatic in juveniles and adults. Cell outlines were smooth, with no basal infoldings of the plasma membrane or apical microvilli. The cell nucleus occupied basal locations in juveniles but migrated centrally in adults. The most conspicuous organelle, the smooth endoplasmic reticulum, was continuous with a well-developed vacuolar system. These cells stored numerous glycogen granules. The ultrastructural features of the plana semilunata strongly suggest their involvement in endolymph secretion.

Antidiuretic-hormone-induced morphological changes in the ampullary epithelium of the frog semicircular canal

Morphological changes induced by in vitro treatment with arginine-vasotocin, the frog antidiuretic hormone, were studied in the ampullary epithelium of the frog semicircular canal. Morphological changes appeared only in the apical side of the dark cells, while the basal part of these cells and the other cells lining the semicircular canal did not show any change. Changes consisted of the appearance of numerous small vesicles in the apical cytoplasm and the development of microvilli on the apical plasma membrane of the dark cells. These results suggest that arginine-vasotocin could play a role in the regulation of endolymph section.

Hyaluronan as a propellant for epithelial movement: the development of semicircular canals in the inner ear of Xenopus

The membranous labyrinth of the inner ear, with its three semicircular canals, originates from a simple spheroidal otic vesicle. The process is easily observed in Xenopus. The vesicle develops three dorsal outpocketings; from the two opposite faces of each outpocketing pillars of tissue are protruded into the lumen; and these paired ‘axial protrusions’ eventually meet and fuse, to form a column of tissue spanning the lumen of the outpocketing like the hub of a wheel, with a tube of epithelium forming the semicircular canal around the periphery. Each axial protrusion consists of epithelium encasing a core of largely cell-free extracellular matrix that stains strongly with alcian blue. In sections, at least 60% of the stainable material is removed by treatment with Streptomyces hyaluronidase. When Streptomyces hyaluronidase is microinjected into the core of a protrusion in vivo, the protrusion collapses and the corresponding semicircular canal fails to form. Hyaluronan (hyaluronic acid) in the core of the protrusion therefore seems to be essential in driving the extension of the protrusion. Autoradiography with tritiated glucosamine indicates that the hyaluronan-rich matrix is synthesised by the epithelium covering the tip of the protrusion; the basal lamina here appears to be discontinuous. These findings indicate that the epithelium of the axial protrusion propels itself into the lumen of the otocyst by localised synthesis of hyaluronan. Hyaluronan may be used in a similar way in the development of other organs, such as the heart and the secondary palate.

Adenylate cyclase in the semicircular canal. Hormonal stimulation and ultrastructural localization

The modulation of the cyclic AMP (cAMP) production and the cytochemical localization of adenylate cyclase were studied in isolated semicircular canal epithelium of the frog. The basal cAMP content, as measured by radioimmunoassay, was 344 +/- 37.8 fmoles/structure/5 min (mean +/- SEM, n = 41). This content was increased 6- to 8-fold by forskolin (10(-7) M to 10(-5) M). Among the tested drugs, only prostaglandin E2, isoproterenol, and vasotocin increased the cAMP production: 1.7-fold by prostaglandin E2 (1.5 X 10(-7) M) and isoproterenol (10(-6) M), and 1.3- and 3.3-fold by vasotocin at 10(-8) M and 10(-7) M, respectively. The addition of alpha 2-adrenergic agonists blunted the stimulatory effect of vasotocin. The adenylate cyclase was evidenced in both the basolateral and apical membranes of the dark cells. Vasotocin stimulated only the apical adenylate cyclase of dark cells. These results indicated that the adenylate cyclase located in the apical dark cells of the semicircular canal was stimulated by the antidiuretic hormone which may be involved in the regulation of the endolymph secretion.

Recovery mechanism of postural disturbance after vestibular neurectomy

Sectioning of the unilateral vestibular nerve of the bull frog resulted in tilting of the head and the body. The angle of head tilt was periodically measured. The angle returned to 0 degree in an average of 7.3 weeks. A morphological study demonstrated normal structure of the sensory epithelia and a well-regenerated nerve bundle. Also, discrete action potentials could be recorded from the nerve centrally to the cut site of the vestibular nerve. These results indicate that recovery from the tilting involves two mechanisms, one being central compensation and the other reactivation of the sensory cell-nerve unit.

Adenylate cyclase and carbonic anhydrase in the semicircular canal epithelium of the frog Rana esculenta. An ultrastructural cytochemical localization

Because the secretion of endolymph has been localized in the ampullar part of the frog semicircular canal, we attempted to determine by cytochemical methods the ultrastructural localization of two enzymes that are assumed to play a role in endolymph secretion: carbonic anhydrase and adenylate cyclase. Functionally, the epithelium of the frog semicircular canal can be schematically divided into three areas: sensory (crista ampullaris), secretory (dark cells), and non-sensory and nonsecretory (transitional and undifferentiated cells) areas. Carbonic anhydrase activity was widely distributed in dark cells. Dark cell labeling disappeared in the presence of acetazolamide. The other cells of the canal did not show any carbonic anhydrase labeling except for the supporting cells of the sensory cells. Adenylate cyclase activity was found on the basolateral and apical membranes of dark cells, and on the apical membrane of sensory cells; weak labeling was also observed in the other epithelial cells. In the apical membrane of the dark cells, adenylate cyclase labeling was dependent on the presence of vasotocin, the frog antidiuretic hormone. The dark cells of the frog semicircular canal thus possess the enzyme equipment needed for the secretion of endolymph and its possible hormonal regulation.

Hair cell tufts and afferent innervation of the bullfrog crista ampullaris

Within the bullfrog semicircular canal crista, hair cell tuft types were defined and mapped with the aid of scanning electron microscopy. Intracellular recording and Lucifer Yellow labeling techniques were used to study afferent responses and arborization patterns. Dye-filled planar afferent axons had mean distal axonal diameters of 1.6-4.9 microns, highly branched arbors, and contacted 11-24 hair cells. Dye-filled isthmus afferent axons had mean distal axonal diameters of 1.8-7.9 microns, with either small or large field arbors contacting 4-9 or 25-31 hair cells. The estimated mean number of contacts per innervated hair cell was 2.2 for planar and 1.3 for isthmus afferent neurons. Data on evoked afferent responses were available only for isthmus units that were observed to respond to our microrotational stimuli (less than 3 degrees/s peak rotational velocity). Of 21 such afferent neurons, 8 were successfully dye-filled. Within this small sample, high-gain units had large field arbors and lower-gain units had small field arbors. The sensitivity of each afferent neuron was analyzed in terms of noise equivalent input (NEI), the stimulus amplitude for which the afferent response amplitude is just equivalent to the RMS deviation of the instantaneous spike rate. NEI for isthmus units varied from 0.63 to 8.2 degrees/s; the mean was 3.2 degrees/s.

Morphophysiological and ultrastructural studies in the mammalian cristae ampullares

There are three kinds of afferent terminations in the cristae ampullares. Calyx units innervate a few neighboring type I hair cells. Bouton units contact several type II hair cells. Dimorphic units innervate both kinds of receptors. Axon diameters are largest for calyx fibers and smallest for bouton fibers. Dimorphic units supply all parts of the sensory epithelium. Calyx units are confined to the central zone of the crista and bouton units to its peripheral zone. Intra-axonal labeling was used to determine the innervation patterns of physiologically characterized afferents. Calyx units are irregularly discharging. Dimorphic units in the central zone have a more irregular discharge than those in the peripheral zone. Bouton units, which have also been identified by their slow conduction velocities, are regularly discharging. An afferent's discharge regularity, sensitivity to externally applied galvanic currents and response dynamics are more closely related to its epithelial location than to its branching pattern or to the types and number of hair cells it contacts. Of the various discharge properties studied, only the rotational gains seemed closely related to terminal morphology. Afferents innervating the central and peripheral zones differ in their innervation patterns and discharge properties. A preliminary ultrastructural study indicates that there also are regional variations in synaptic organization. Type II hair cells in the peripheral zone are contacted by many more afferent boutons than those in the central zone. Individual central boutons have multiple ribbon synapses with type II hair cells, whereas each peripheral bouton usually has a single synaptic contact. Synapses between type II hair cells and calyx endings are common centrally, but not peripherally. Two synaptic features did not vary regionally: 1) type I hair cells usually make 10-20 ribbon synapses with their calyx endings; and 2) each type II hair cell is contacted by 2-6 efferent endings. The number of efferent boutons in contact with each calyx ending declines slightly from the peripheral zone to the central zone. Reciprocal synapses were rare.

The ultrastructure of the supporting system in the guinea pig semicircular canal

The ultrastructure of the perilymphatic space of the guinea pig semicircular canal was examined, using thin sectioning, scanning electron microscopy and freeze-fracture methods. The perilymphatic space was divided into two parts: an area of fibrous matrix and an area of fibroblasts with bundles of fine filaments. In the area of fibroblasts, cell processes and filament bundles formed a meshed pattern. The cell processes were interconnected with each other by both intermediary and gap junctions. The inner surface of the osseous semicircular canal was covered with multilayers of cell processes of both fibroblasts and mesothelial cells. The fact that tight and gap junctions were observed between the cell processes suggests a functional significance in these structures.

Studies of solitary semicircular canal hair cells in the adult pigeon. I. Frequency- and time-domain analysis of active and passive membrane properties

1. Hair cells were enzymatically dissociated from the neuroepithelium (cristae ampullares) of the semicircular canals of white king pigeons (Columba livia). Those hair cells determined to be type II by an anatomic criterion, the ratio of the minimum width of the neck to the width of the cuticular plate, were studied with the use of the whole cell patch-clamp technique. 2. The mean +/- SD zero-current membrane potential, Vz, was found to be -54 +/- 12 mV for anterior crista hair cells (n = 71), -62 +/- 14 mV for posterior crista hair cells (n = 14), and -55 +/- 12 mV for lateral (horizontal) crista hair cells (n = 18). The mean +/- SD value of Vz for hair cells from all cristae (n = 103) was -56 +/- 13 mV. 3. Active and passive membrane properties were calculated in the time domain, in voltage- or current-clamp mode, from responses to voltage or current pulses and, in the frequency domain, by fitting a membrane model to admittance magnitude and phase data resulting from current responses to sum-of-sines voltages at different d.c. levels of voltage-clamp membrane potential. 4. The average value +/- SE of input resistance (Rin), over the range from -100 to -60 mV, was found to 1.5 +/- 0.3 G omega from a mean-voltage-as-a-function-of-current plot, V-I, (n = 7) and a mean of 1.4 +/- 0.3 G omega from individual (n = 15) current-as-a-function-of-voltage plots, I-V. A lower mean value 0.8 +/- 0.4 G omega was obtained for the input resistance from frequency-domain calculations for a different set of cells (n = 21). Also, in two different sets of cells, average input capacitance (Cin) was determined to be 12 +/- 3 pF (n = 7) from time-domain estimates and 14 +/- 3 pF (n = 21) from frequency-domain estimates. The (Rin)(Cin) product was 11 ms based on frequency-domain estimates and 17 ms from time-domain estimates. 5. I-V curves for hair cells voltage clamped at -60 mV showed some anomalous rectification for hyperpolarizations between -60 and -120 mV but no detectable N-shape for depolarizations between -50 and 90 mV. The I-V relation showed increasing slope with depolarization through the resting potential (Vz) and increased linearly between -40 and 80 mV; the best-fit straight-line maximum slope conductance for six cells over this range was 17.4 +/- 0.3 nS.(ABSTRACT TRUNCATED AT 400 WORDS)

[Mechanisms of development of the dome in the semicircular canals of birds. I. Cellular secretion]

A study of the crista ampullaris of the vestibular apparatus was carried out in chicken embryos. The study group included embryos between stages 24 and 39 of Hamburger-Hamilton. This study elucidates the relationship of the cupula with respect to the epithelium of the crista ampullaris. With electron microscopic examination, the rough endoplasmic reticulum of the crista epithelial sustentacular cells at developmental stage of 31 H-H, demonstrated dilatations containing secretory material. Vesicles, with adhering ribosomes appear to be formed from these dilatations. At later stages of development, the vesicular material took on the characteristics of the fibrillary material composing the cupula. In some cells, secretory vesicles are seen near the apical border of these cells, where they apparently secrete vesicular contents into the endolymphatic space, contributing to the formation of the cupula.