RESUMEN
Three-dimensional reconstructions of the inner ear of the pigeon (Columba livia domestica), from two-dimensional images, obtained with (conventional) light microscopy or orthogonal-plane fluorescence optical sectioning (OPFOS), are presented. The results are compared with available information on the dimensions and orientation of the semicircular canals.
Asunto(s)
Columbidae/anatomía & histología , Oído Interno/anatomía & histología , Procesamiento de Imagen Asistido por Computador , Imagenología Tridimensional , Canales Semicirculares/anatomía & histología , Animales , Colorantes Fluorescentes , Técnicas de Preparación HistocitológicaRESUMEN
The basilar papilla (BP) in the frog inner ear is a relatively simple auditory receptor. Its hair cells are embedded in a stiff support structure, with the stereovilli connecting to a flexible tectorial membrane (TM). Acoustic energy passing the papilla presumably causes displacement of the TM, which in turn deflects the stereovilli and stimulates the hair cells. Auditory neurons that contact the BP's hair cells are known to have nearly identical characteristic frequencies and frequency selectivity. In this paper, we present optical measurements of the mechanical response of the TM. Results were obtained from five specimens. The TM displacement was essentially in phase across the membrane, with the largest amplitudes occurring near the hair cells. The response was tuned to a frequency near 2 kHz. The phase accumulated over at least 270 degrees across the measured frequencies. The tuning quality Q(10dB) values were calculated; the average Q(10dB) was 2.0 +/- 0.8 (standard deviation). Our results are comparable to those of neural-tuning curves in the same and a similar species. Also, they are in agreement with the response of an associated structure-the contact membrane-in a closely related species. Our data provides evidence for a mechanical basis for the frequency selectivity of the frog's BP.
Asunto(s)
Órgano Espiral/fisiología , Rana pipiens/fisiología , Membrana Tectoria/fisiología , Estimulación Acústica , Animales , Fenómenos Biomecánicos/fisiología , Potenciales Evocados Auditivos/fisiología , Femenino , Células Ciliadas Auditivas/fisiología , Masculino , Mecanotransducción Celular/fisiología , Células Receptoras Sensoriales/fisiología , Membrana Tectoria/inervaciónRESUMEN
The first description of the presence of a utriculo-endolymphatic valve in human fetuses was given by Bast in 1928. Since then this valve-like structure is called Bast's valve. Its exact function has not yet been established. The general opinion is that it has a protective function by having the possibility to separate the superior endolymphatic compartments of the labyrinth from the inferior compartment. Phylogenetically seen birds are the first vertebrates with a cochlear duct and a distinct inferior and superior part of the labyrinth. A structure in the pigeon inner ear, resembling Bast's valve in mammals, is described.
Asunto(s)
Columbidae/anatomía & histología , Conducto Endolinfático/anatomía & histología , Sáculo y Utrículo/anatomía & histología , AnimalesRESUMEN
Three-dimensional (3D) reconstruction of anatomical structures can give additional insight into the morphology and function of these structures. We compare 3D reconstructions of the guinea pig inner ear, using light microscopy and orthogonal plane fluorescence optical sectioning microscopy. Applications of 3D reconstruction of the inner ear are further explored. For each method two bullas were prepared for 3D reconstruction. Both methods are explained. In general, the 3D reconstructions using orthogonal plane fluorescence optical sectioning microscopy are superior to light microscopy. The exact spiral shape of the cochlea could be reconstructed using orthogonal plane fluorescence optical sectioning microscopy and the length of the basilar membrane measured. When a resolution of 20 microm is sufficient, orthogonal plane fluorescence optical sectioning microscopy is a superior technique for 3D reconstruction of inner ear structures in animals.
Asunto(s)
Procesamiento de Imagen Asistido por Computador/métodos , Microscopía Fluorescente/métodos , Modelos Anatómicos , Animales , Cóclea/anatomía & histología , Cóclea/ultraestructura , Oído Interno/anatomía & histología , Oído Interno/ultraestructura , Femenino , Cobayas , Microscopía/instrumentación , Microscopía/métodos , Microscopía Fluorescente/instrumentaciónRESUMEN
The utriculo-endolymphatic valve was discovered by Bast in 1928. The function of Bast's valve is still unclear. By means of orthogonal-plane fluorescence optical sectioning (OPFOS) microscopy 3D-reconstructions of the valve and its surrounding region are depicted. The shape of the duct at the utricular side is that of a flattened funnel. In the direction of the endolymphatic duct and sac this funnel runs into a very narrow duct. The valve itself has a rigid 'arch-like' configuration. The opposing thin, one cell-layer thick, utricular membrane is highly compliant. We propose that opening and closure of the valve occurs through movement of the flexible base/utricular membrane away from and toward the relatively rigid valve lip.
Asunto(s)
Conducto Endolinfático , Imagenología Tridimensional , Procedimientos Quirúrgicos Otológicos/métodos , Procedimientos de Cirugía Plástica/métodos , Sáculo y Utrículo , Conducto Endolinfático/anatomía & histología , Conducto Endolinfático/fisiología , Conducto Endolinfático/cirugía , Humanos , Microscopía Fluorescente/métodos , Sáculo y Utrículo/anatomía & histología , Sáculo y Utrículo/fisiología , Sáculo y Utrículo/cirugíaRESUMEN
The round window membrane and cochlear aqueduct complex in the guinea pig are reconstructed with 3D-imaging, using orthogonal plane fluorescence optical sectioning (OPFOS). The 3D-images show that the periotic duct and the aqueduct are connected to a pouch-like extension of the round window. The function of this may be regulation of aqueduct flow resistance under the influence of a pressure difference between inner ear fluid and middle ear.
Asunto(s)
Acueducto Coclear/anatomía & histología , Cobayas/anatomía & histología , Imagenología Tridimensional/instrumentación , Ventana Redonda/anatomía & histología , Animales , Femenino , Imagenología Tridimensional/métodosRESUMEN
The role of the endolymphatic sac (ES) in endolymph volume homeostasis is speculative. The present study investigates changes of the ES's epithelia and luminal filling after induction of an acute endolymphatic hydrops. After microinjection of 1.1 mul artificial endolymph into scala media of the cochlea, guinea pigs were terminated immediately (n = 6) or after different time intervals ; 1/2 h (n = 3), 1 h (n = 4) and 2 h (n = 4). Inner ear specimens were processed for light and/or transmission electron microscopy. The non-injected contralateral ear served as a histological control. Correct injection was confirmed by detection of microspheres in the endolymphatic compartment after the same microinjection procedure. In all specimens, ribosome rich cells and intraluminal macrophages appeared to be actively involved in degradation of homogeneous substance (HS) by secreting lytic enzymes and digestion, respectively. Amazingly, in our study no ES differences were found between injected and non-injected ears and no distinct changes were observed in guinea pigs terminated after different time intervals. The ES's luminal HS was always present and often to a large extent. This is in contrast with [Hear. Res. 138, 81] dramatic changes were observed. Endolymph volume homeostasis is a complex mechanism, in which the role of HS remains obscure.
Asunto(s)
Hidropesía Endolinfática/patología , Saco Endolinfático/patología , Enfermedad Aguda , Animales , Conducto Coclear , Endolinfa , Hidropesía Endolinfática/etiología , Femenino , Cobayas , Microinyecciones , Microscopía Electrónica , Microesferas , Factores de TiempoRESUMEN
The resistance for fluid flow of the cochlear aqueduct was measured in guinea pigs for different positions of the round window membrane. These different positions were obtained by applying different constant pressures to the middle ear cavity. Fluid flow through the aqueduct was induced by small pressure steps superimposed on these constant pressures. It was found that the resistance for fluid flow through the aqueduct depended on the round window position but not on flow direction. The results can be explained by special fibrous structures that connect the round window with the entrance of the aqueduct. It was also found that the equilibrium inner ear pressure depends on middle ear pressure, indicating that the aqueduct does not connect the inner ear with a cavity with constant pressure.
Asunto(s)
Acueducto Coclear/fisiología , Líquidos Laberínticos/fisiología , Modelos Biológicos , Ventana Redonda/fisiología , Animales , Cobayas , PresiónRESUMEN
In this study freeze fracture, low-voltage cryo-SEM, SEM and TEM were used to characterise the glycocalyx and stereociliary interconnections in the hair cell bundle of the vestibular sensory epithelia of the guinea pig. The glycocalyx resembles a shell-like structure separately surrounding each stereocilium and kinocilium over its entire length. The lateral interciliary connections emerge from the glycocalyx layer, forming an extensive extracellular network maintaining the stereocilia as a bundle. These connections are morphologically similar to the glycocalyx, and grossly oriented in the same direction, indicative of a role in the mechanical transduction system. The matrix material around the glycocalyx also appears to be morphologically similar to the glycocalyx, suggesting the glycocalyx to be even more important in the mechanical transduction system. The tip-links are covered with a layer, which is a continuation of the glycocalyx covering the stereocilia.
Asunto(s)
Glicocálix/ultraestructura , Células Ciliadas Auditivas/ultraestructura , Vestíbulo del Laberinto/ultraestructura , Animales , Femenino , Técnica de Fractura por Congelación , Cobayas , Microscopía ElectrónicaRESUMEN
The inner ear fluid pressure of guinea pigs was measured during square wave middle ear cavity pressure variation. Time constants were derived for the slopes of the inner ear pressure recovery curves after middle ear pressure change. A "single exponential" function did not fit well and therefore more complicated functions were used for this purpose. For middle ear pressure increasing from zero to a few centimetres of water, returning to zero again, decreasing from zero to minus a few centimetres of water and then returning to zero again, time constants for the inner ear pressure recovery curves were on average 15.0, 8.6, 2.5 and 2.5 s, respectively. The results could not be described using a linear model with constant window membrane compliance and cochlear aqueduct flow resistance. A possible explanation for the large difference in time constants for positive or negative middle ear pressure changes is a dependence on aqueduct flow resistance or round window membrane position.
Asunto(s)
Oído Interno/fisiología , Oído Medio/fisiología , Animales , Acueducto Coclear/fisiología , Femenino , Cobayas , Líquidos Laberínticos/fisiología , Presión , Ventana Redonda/fisiología , TiempoRESUMEN
HYPOTHESIS: The aim of this study was to create a more dynamic animal model of Ménière's disease combining multiple causes, such as the role of endocrine factors and endolymphatic sac dysfunction, that may mimic the fluctuant characteristics of Ménière's disease. BACKGROUND: Endolymphatic hydrops remains to be considered a pathologic substrate in the etiology of Ménière's disease. The classic guinea pig model of inducing hydrops by total destruction of the endolymphatic sac is a nonphysiologic rigid model of Ménière's disease. METHODS: The authors developed the two-phase endolymphatic hydrops model by inducing hydrops by mild chronic endolymphatic sac dysfunction, in combination with increased endolymph production by aldosterone. Sensory cell damage was evaluated by low-voltage field emission scanning microscopy. RESULTS: This study describes a wide spectrum of morphologic effects of the outer hair cells in radial gradients, in which most effects were observed in the third to second row of outer hair cells, and longitudinal gradients in which the most severe effects were observed in the apical turns. Most affected were the ears that underwent distal endolymphatic sac dissection followed by the administration of aldosterone. Damaging effects proceeded from degeneration and absence of short stereocilia of outer hair cells and even some inner hair cells in the apical turns, to stereociliary disarrangement and atrophy, followed by degeneration and absence of outer hair cells, which were replaced by supporting cells. CONCLUSION: The two-phase endolymphatic hydrops model seems to represent a functional model that may mimic the fluctuant characteristics of Ménière's disease and emphasizes the influence of multiple and coexisting hydrops-inducing influences.
Asunto(s)
Hidropesía Endolinfática/patología , Ganglios Sensoriales/patología , Enfermedad de Meniere/diagnóstico , Animales , Saco Endolinfático/fisiopatología , Femenino , Estudios de Seguimiento , Cobayas , Células Ciliadas Auditivas Externas/patología , Enfermedad de Meniere/fisiopatología , Microscopía Electrónica de Rastreo/métodos , Degeneración Nerviosa , Órgano Espiral/patologíaRESUMEN
Previous studies have shown that pressure changes in the cerebrospinal fluid compartment are transmitted to the inner ear. The main route for pressure transfer is the cochlear aqueduct. about which little is known with regard to its dynamic properties. In the present study, sudden intracranial pressure changes (square waves and short pulses) were created in guinea pigs by means of an electronically controlled infusion system. Simultaneously with pressure manipulation, hydrostatic pressure was monitored in both the peridural space and the perilymphatic compartment of the inner ear. The onset of an inner ear pressure change following manipulation of intracranial pressure was immediate. Inner ear pressure increased or decreased without a measurable time lag, and equalized within a few seconds. During square wave intracranial pressure manipulation, inner ear pressure equalized somewhat more slowly after pressure increase than after pressure decrease. To a first approximation, the pressure equalization curves for the inner ear could be fitted with a single exponential function, rising or falling with a time constant in the range 1-3 s, and the system can be described as a low-pass filter composed of a constant compliance and a constant flow resistance. Detailed analysis, however, showed small deviations from a purely exponential recovery process. With a more complicated (non-linear) model, almost perfect fits to the inner ear pressure equalization curves could be obtained. This non-linearity may be a consequence of the dependence of the compliance and, or flow resistance on pressure.
Asunto(s)
Acueducto Coclear/fisiología , Presión Intracraneal/fisiología , Animales , Femenino , Cobayas , Perilinfa/fisiología , Factores de TiempoRESUMEN
In this study, short latency vestibular evoked potentials (VsEPs) were recorded in five guinea pigs in response to alternating linear acceleration pulses with and without acoustic masking. A steel bolt was implanted in the skull and coupled to a shaker. Linear acceleration pulses (n = 400) in upward, downward or alternating directions were given, with a peak acceleration of 4g after 0.5 msec. Tests were repeated with acoustic masking, after modiolus destruction and after application of KCl in the vestibule. Stimuli of the vestibular nerve were recorded with a platinum electrode in the bony facial nerve canal in the bulla. Unilateral linear acceleration showed a shallow plateau at 0.5 msec, which disappeared with alternating acceleration impulses and after modiolus destruction. Therefore all further tests were done with alternating impulses. After a latency time of 0.8 msec a multiwave response was seen, with a first positive peak P1 at 1.16 ms. These were followed by other positive and negative peaks (N1, P2, N2, P3, N3). With the elimination of cochlear influences by using acoustic masking, P1 remained stable, while subsequent peaks were altered or eliminated. After modiolus destruction, the P1 peak remained, although with a smaller amplitude due to vestibular damage. After application of a saturated KCl solution in the vestibule all responses, including P1, disappeared, thus confirming the vestibular origin of these responses. We conclude that the onset latency of the VsEP and the peak latency and level of the first positive peak P1 in response to alternating linear acceleration pulses without acoustic masking, measured in the facial canal, are good and stable parameters of vestibular function in guinea pigs.
Asunto(s)
Potenciales Evocados , Pruebas de Función Vestibular/métodos , Animales , Femenino , Cobayas , Enmascaramiento Perceptual , Nervio Vestibular/fisiologíaRESUMEN
The inner ear fluid pressure of guinea pigs was measured during a series of complex oscillating middle ear pressure changes induced by the Meniett20 (Pascal Medical, Sweden), a possible therapeutic pressure generator to be used by patients with Meniere's disease. Middle ear pressure changes were transferred instantly to the inner ear, although inner ear pressure declined while middle ear pressure stayed relatively stable. An average undershoot of -1.0 cm H2O with respect to the steady-state pressure was seen after application of a pressure pulse, which was released in a few seconds. The results did not fully comply with a simple linear model in which a constant flow resistance between the inner ear and cerebrospinal space was assumed.
Asunto(s)
Oído Interno , Animales , Diseño de Equipo , Femenino , Cobayas , PresiónRESUMEN
Two-phase endolymphatic hydrops is a subtle experimental model for Meniere's disease. Chronic dysfunction of the endolymphatic sac, induced by dissection of the most distal part without causing damage to the intermediate part, is combined with increased endolymph production induced by administration of aldosterone which stimulates the N/K-ATPase in the stria vascularis. A transmission electron microscopic study was performed on the endolymphatic sacs of four groups of guinea pig cochleas: controls: non-operated aldosterone-treated cochleas; operated (dissection of the endolymphatic sac) cochleas; operated and aldosterone-treated cochleas. Light and electron microscopy showed a normal morphology in the controls. Aldosterone treatment had no visible effect. Dissected ears revealed severe deviations. The epithelium of the intermediate sac was low, showed dilated lateral intercellular spaces indicating elevated fluid transport and displayed serious degenerative processes. Distally, the endolymphatic sac was completely blocked by newly formed bone. Additional aldosterone treatment had no cumulative effect on the dissected ears.
Asunto(s)
Hidropesía Endolinfática/patología , Saco Endolinfático/ultraestructura , Aldosterona/farmacocinética , Animales , Enfermedad Crónica , Hidropesía Endolinfática/fisiopatología , Saco Endolinfático/metabolismo , Saco Endolinfático/fisiopatología , Femenino , Cobayas , Enfermedad de Meniere/diagnóstico , Enfermedad de Meniere/fisiopatología , Microscopía Electrónica , ATPasa Intercambiadora de Sodio-Potasio/metabolismoRESUMEN
The classical guinea pig model for Meniere's disease, in which endolymphatic hydrops was achieved by destruction of the endolymphatic sac and obliteration of the endolymphatic duct, is a non-physiological profound model with shortcomings in relation to Meniere's disease as seen in patients. We developed a more subtle animal model; the two-phase endolymphatic hydrops. This model is based on a combination of chronic endolymphatic sac dysfunction, induced by slight destruction of the most distal part of the endolymphatic sac, and acute stress-induced endolymph production by stimulation of the Na/K-ATPase in the stria vascularis with aldosterone. Light microscopy of the fluid compartments of four groups of cochleas was used to examine them for the presence of endolymphatic hydrops: i) Normal (control) cochleas showed no hydrops; ii) some of the non-operated (no destruction) aldosterone-treated cochleas showed small degrees of hydrops mainly present in the basal turns; iii) mild dissection of the endolymphatic sac without administration of aldosterone produced a hydrops which was mainly present in the cochlear apex; iv) combination of chronic endolymphatic sac dysfunction and acute attacks of endolymph production by aldosterone administration revealed the most severe degrees of hydrops in all cochlear windings, damage to cochlear structures, and cellular disturbances of the epithelial lining of the endolymphatic sac. This new model may represent a more physiologic and dynamic approach to Meniere's disease and may explain the etiology of many symptoms in patients such as the fluctuant nature and the types of sensoneuronal hearing losses.
Asunto(s)
Modelos Animales de Enfermedad , Hidropesía Endolinfática/patología , Saco Endolinfático/patología , Aldosterona/farmacocinética , Aldosterona/farmacología , Animales , Cóclea/efectos de los fármacos , Cóclea/fisiopatología , Hidropesía Endolinfática/fisiopatología , Saco Endolinfático/efectos de los fármacos , Saco Endolinfático/fisiopatología , Femenino , Cobayas , Enfermedad de Meniere/patología , Enfermedad de Meniere/fisiopatología , ATPasa Intercambiadora de Sodio-Potasio/efectos de los fármacos , ATPasa Intercambiadora de Sodio-Potasio/metabolismoRESUMEN
Wiener kernel analysis was used to characterize the auditory pathway from tympanic membrane to single primary auditory nerve fibers in the European edible frog, Rana esculenta. Nerve fiber signals were recorded in response to white Gaussian noise. By cross-correlating the noise stimulus and the nerve fiber response, we computed (1) the full second-order Wiener kernel, and (2) the diagonals of the zeroth- to fourth-order Wiener kernels. These diagonals are usually referred to as polynomial correlation functions. The measured Wiener kernels were fitted with a 'sandwich' model. A new fitting procedure was used to compute the response characteristics of (1) the first filter, (2) the static nonlinearity, and (3) the second filter, which form the functional components of the model. The first filter is a bandpass filter. In the majority of low frequency fibers, with best excitatory frequency (BEF) < 800 Hz, this filter was tuned to two frequencies. This dual tuning mechanism gives rise to 'off-diagonal' components in the second-order Wiener kernel. The static nonlinearity resembles a rectifier, and is dominated by second-order (quadratic) nonlinearity. As a function of BEF, the shape of the nonlinearity changes systematically. Finally, the last filter in the model was a low pass filter. Across fibers, its cutoff frequency f-3dB ranged from 106 to 434 Hz.
Asunto(s)
Cóclea/fisiología , Modelos Teóricos , Ruido , Nervio Vestibulococlear/fisiología , Estimulación Acústica , Animales , Fibras Nerviosas/fisiología , Distribución Normal , Rana esculentaRESUMEN
The temperature dependence of the response of single primary auditory nerve fibers (n = 31) was investigated in the European edible frog, Rana esculenta (seven ears). Nerve fiber responses were analyzed with Wiener kernel analysis and polynomial correlation. The responses were described with a cascade model, consisting of a linear bandpass filter, a static nonlinearity, and a linear lowpass filter. From the computed Wiener kernels and the polynomial correlation functions, the characteristics of the three model components were obtained. With increasing temperature (1) tuning of the first filter increased in the majority (n = 16) of amphibian papilla fibers (best excitatory frequency, BEF < 1 kHz, n = 21) but remained unchanged in the majority (n = 10) of basilar papilla fibers (BEF > 1 kHz, n = 11), (2) the gain of the first filter remained unchanged, (3) the shape of nonlinear IO function remained unchanged, (4) the combined gain of the static nonlinearity and the second filter usually increased, but displayed considerable scatter across fibers (from -0.7 dB/degrees C to 3 dB/degrees C), and (5) the cutoff frequency of the second lowpass filter increases, with average 0.13 oct/degrees C. The immunity of the shape of the nonlinearity is considered evidence of a temperature independent gating mechanism in the transduction channels. The temperature dependence of the second filter may have resulted from a decrease of the hair cell membrane resistance, but may also reflect changes in subsequent staging of nerve fiber excitation.
Asunto(s)
Cóclea/fisiología , Ruido , Temperatura , Nervio Vestibulococlear/fisiología , Estimulación Acústica , Animales , Modelos Teóricos , Fibras Nerviosas/fisiología , Distribución Normal , Rana esculentaRESUMEN
In this study, a more subtle animal model of Menière's disease is investigated by damaging the distal portion of the endolymphatic sac by dissection or cauterization to produce mild dysfunction of endolymphatic outflow. Cauterization resulted in low degrees of hydrops without any correlation with the inflicted damage. Total dissection of the distal portion of the sac adjacent to the sigmoid sinus produced moderate to severe endolymphatic hydrops with interanimal variation. The consequences of these relatively severe effects, in relation to the mild damage of the endolymphatic sac, and the influence on damaged and undamaged parts of the endolymphatic sac will be discussed.
Asunto(s)
Modelos Animales de Enfermedad , Hidropesía Endolinfática/etiología , Saco Endolinfático/cirugía , Enfermedad de Meniere , Animales , Cauterización , Disección , Saco Endolinfático/anatomía & histología , Saco Endolinfático/patología , Femenino , Fibrosis , CobayasRESUMEN
The stereociliar structures of the guinea-pig cochlear organ of Corti were studied at low-voltage (1-5 kV) with field-emission scanning electron microscope (SEM) using various pre- and post-fixation methods, such as OTOTO (OsO4/thiocrbohydrazide/OsO4/thiocarbohydrazide/OsO4) and TAO (tannic acid/arginine/OsO4), and different dissection procedures of the cochlea. A perfusion and immersion pre-fixation with glutaraldehyde, in combination with removal of the bony wall and stria vascularis from the cochlea, followed by the TAO non-coating treatment gave the best result at 2 kV acceleration voltage. Due to these new technique, several interesting delicate structures of the stereocilia, in particular fine surface structures, were detected for the first time using SEM. These findings include the different types of cross-links and tip links, i.e., the fine surface morphology of the stereocilia and their attachments and imprints in the tectorial membrane (TM). One of the most interesting findings in this study is a network of long filamentous structures, which has been identified mainly at the top of the longest stereocilia and the undersurface of the TM and which may represent the glycocalyx. These findings and their possible implications in the process of mechanoelectrical transduction will be discussed.