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PubMed1986

Changes in endolymph chloride concentration following furosemide injection.

Endocochlear potential (EP) and chloride concentration in endolymph were monitored with microelectrodes in the basal turn of the cochlea of the chinchilla. After intravenous injection of furosemide (25-100 mg/kg), the EP dropped precipitously and rapidly reached its minimum value, however, the chloride activity in endolymph decreased more gradually. Possible mechanisms for this phenomenon include a reduced electrostatic attraction of chloride ions to the scala media due to a decreased EP and a reduction of passive influx of chloride into endolymph, resulting from a reduction of active inward potassium transport by furosemide.

Animals↗
PubMed1987

The Ca2+ activity of cochlear endolymph of the guinea pig and the effect of inhibitors.

The Ca2+ concentrations in cochlear perilymph and endolymph of the guinea pig were measured with double-barreled Ca2+-selective microelectrodes and showed 1.76 +/- 0.74 X 10(-3) M and 2.20 +/- 0.19 X 10(-5) M, respectively. The electrochemical potential gradient for Ca2+ between perilymph and endolymph was 23.2 mV and the existence of an active transport mechanism from the former to the latter was suggested. Vanadate given perilymphatically decreased the Ca2+ concentration in endolymph with a slight elevation of the endocochlear potential and was suspected of blocking the active transport. The Ca2+ concentration in endolymph was abruptly increased by anoxia or the intravenous administration of 60 mg/kg furosemide and was slightly increased by the intravenous administration of 30 mg/kg furosemide or 100 mg/kg acetazolamide. The endolymphatic pH measured with pH-microelectrodes under various conditions indicates that the mechanism of increase in the Ca2+ concentration is attributed not to the liberation of Ca2+ from the surrounding tissues caused by a fall in pH but to the increased influx of Ca2+ from perilymph due to the depression of the endocochlear potential.

Acetazolamide↗
PubMed1987

Antagonistic effects of perilymphatic calcium and magnesium on the activity of single cochlear afferent neurons.

The dependence of the spontaneous and sound driven activity of single cochlear nerve fibers on the calcium and magnesium content of the perilymph was studied by perfusion of the perilymphatic space. It was possible to study these effects under steady-state conditions by continuously perfusing scala tympani at low rates while simultaneously recording from units in the chinchilla auditory nerve. Preparations were stable for many hours. As previously reported [Robertson and Johnstone (1979) Pflügers Arch. 380, 7-12], perfusion with solutions containing elevated concentrations of magnesium reduces both the spontaneous and driven activity. When calcium was eliminated from the perfusate, activity was completely abolished for stimuli with sound pressure levels below 100 dB. During partial blocks, a relatively frequency-independent threshold elevation was seen for frequencies well below the characteristic frequency (CF) of the unit, with greater elevations closer to CF. When the threshold elevation at CF was 30-40 dB, the width of the 'tip' portion of the tuning curve was reduced, resembling that of naturally-occurring units with low spontaneous rates of discharge. These effects are similar to that of raising the criterion for response during threshold measurement and are probably related to a frequency-dependent nonlinearity exhibited by the motion of the basilar membrane. The dynamic range for the growth of average rate with level was increased and saturation was shifted to higher stimulus levels during elevated magnesium perfusion. Raising the calcium content of the perfusate increased both spontaneous and driven rates, even in the saturated portion of the rate-intensity plot. Under these conditions, the response of the unit may more directly correspond to the intracellular potential of the presynaptic hair cell. It is argued that the primary site of divalent cation interaction is in the control of transmitter release. Inner hair cells of the mammalian cochlea apparently do not release transmitter in the absence of a calcium influx. The size of the pool of 'readily-available' transmitter appears to be influenced by divalent cations. Even though this synapse is probably specialized for the transmission of auditory signals, the mechanism of synaptic transmission is probably not fundamentally different from that of other well-characterized synapses.

Animals↗
PubMed1987

Longitudinal flow of endolymph measured by distribution of tetraethylammonium and choline in scala media.

Longitudinal endolymph flow rate in the guinea pig cochlea was measured by determining the rate of migration of extrinsic ions, tetraethylammonium chloride (TEA) or choline, with a potassium sensitive ion-selective microelectrode (ISM). Low concentrations of iontophoretically injected TEA were detected with the ISM at various distances from the injection electrode. The results were variable when the ISM was used to record spread of TEA from turn II to turn I and vice versa. However, consistent data were obtained when the TEA spread was measured at different electrode separations (0.2, 0.5, 0.7 mm) within turn II. Electrode locations were systematically exchanged without changing their distance, i.e. the ISM electrode was placed basally or apically with respect to the TEA electrode. Comparison of data with a model, which combines the bulk diffusion of TEA and the flow of endolymph, is consistent with a rate of endolymph flow in turn II of about 0.2 mm/min, apex to base. A similar value was also obtained with the iontophoretic injection of choline. The endolymph flow rate may be different in turn I as indicated by measurements of compound action potential (CAP) changes. However, the results of experiments when TEA spread is measured at large distances must be interpreted cautiously because TEA may enter cellular walls of the cochlear duct and alternative routes of transport may be involved.

Action Potentials↗
PubMed1987

Longitudinal flow of macromolecules in the endolymphatic space of the rat. An autoradiographical study.

Secretion and resorption of sulphated glycoproteins by the epithelial lining of the endolymphatic space of the rat were studied autoradiographically with the use of 35SO4 as a selective marker. This isotope was found to be incorporated into the sensory area of cristae and maculae and a small area of epithelial cells adjacent to the sensory epithelium. Thereafter 35S-labelled glycoproteins were secreted into cupulae and otolithic membranes. No such process could be established in the tectorial membrane. From the gradual disappearance of 35S-labelled glycoproteins from cupulae and otolithic membrane coupled with an accumulation of this substance in the lumen of the endolymphatic sac, the existence of a longitudinal flow under physiological conditions could be concluded. Resorption of glycoproteins by the saccus epithelium was found to be very slow. Accumulation of 35S-labelled glycoproteins in the endolymphatic duct after saccus obstruction indicates that, in addition to the endolymphatic sac, also the duct contributes to the mechanism underlying the longitudinal flow of macromolecules.

Animals↗
PubMed1987

Uptake of horseradish peroxidase from perilymph by cochlear hair cells.

The specific mechanisms involved in the uptake of an exogenous protein, horseradish peroxidase (HRP), by cochlear hair cells were studied morphologically in light and electron microscopy. HRP was internalized by coated vesicles which formed from the plasma membrane only in the basal portion of the hair cells. Inner hair cells demonstrated relatively greater uptake than adjacent outer hair cells. The lateral plasma membrane of outer hair cells was unique in that reaction product was never bound to this portion of the membrane. Subsequent to endocytosis, HRP was transported to the Golgi and its associated system of endoplasmic reticulum and lysosomes. The exogenous protein was sequestered in a striking accumulation of secondary lysosomes and multivesicular bodies which were restricted to the infracuticular region of the hair cells and persisted for periods of at least 72 h after introduction of HRP. It is not clear whether the hair cells were slowly degrading the HRP or if the lysosomal enzymes necessary for its breakdown were lacking. The pathway demonstrated by HRP uptake and intracellular transport may represent one route by which macromolecules requisite for basic metabolic or nutritional requirements of the hair cells are supplied from the perilymph.

Animals↗
PubMed1988

Calcium transport mechanism in the endolymph of the chinchilla.

The Ca2+ transport mechanism between endolymph and perilymph was evaluated by the effects of vanadate and amiloride on the endocochlear potential (EP) and the Ca2+ concentration in endolymph using Ca2+-selective microelectrodes. Under normal conditions, the EP was 81.8 +/- 0.9 mV, and the Ca2+ concentrations in endolymph and perilymph were 16.6 +/- 1.3 microM and 1.85 +/- 0.11 mM (N = 12), respectively. Therefore, the uphill electrochemical potential gradient for Ca2+ from perilymph to endolymph, 20.2 +/- 2.0 mV, indicates the existence of an active uptake of Ca2+ into endolymph. Vanadate, the inhibitor of Ca2+-ATPase, topically applied to the round window membrane caused biphasic changes of the EP and the endolymph Ca2+ concentration; the former in a transient increase followed by a consistent decrease and the latter in a slow decrease followed by a slow increase. Amiloride induced a slight EP depression and a concomitantly slight elevation of the Ca2+ concentration in endolymph. The electrochemical potential gradient for Ca2+ between endolymph and perilymph vanished with the use of vanadate but was not affected by amiloride. These results suggest that Ca2+-ATPase, sensitive to vanadate, maintained the bulk of active Ca2+ transport in the cochlea and that the participation of Na+-Ca2+ exchange is negligible.

Amiloride↗
PubMed1988

Modulation of cochlear tuning by low-frequency sound.

An intense, low-frequency tone (about 30 Hz) modulates the sensitivity of the inner ear to high-frequency stimulation. This modulation is correlated with the displacement of the basilar membrane. The findings suggest that the modulation may also affect cochlear tuning. We have investigated modulation of cochlear tuning by low-frequency sound in the guinea pig. Applying indirect methods of measurement (narrow-band analysis of compound action potentials and compound-action-potential tuning curves), the results suggest a shift of the excitation pattern along the basilar membrane towards higher-frequency areas. The shift occurred for both scala tympani and scala vestibuli displacement of the cochlear partition. Tuning curves, obtained from single units in the cochlear nerve, show sensitivity loss and a tip shift towards lower frequencies. This was also found for both scala tympani displacement and scala vestibuli displacement. The shift of the tip of the tuning curve towards lower frequencies corresponds to the inferred high-frequency shift of the excitation pattern. The relationship of these phenomena with the pathophysiology of Ménière's disease and with possible active mechanisms in cochlear transduction is discussed.

Animals↗
PubMedDate not supplied

Ionic changes in cochlear endolymph of the guinea pig induced by acoustic injury.

The effects of acoustic overstimulation on the endocochlear potential (EP) and on concentrations of ions (K+, Na+, Cl-, H+, HCO3-, and Ca2+) in endolymph were investigated using ion-selective microelectrodes. A slight but significant elevation of the EP and alkalinization of the endolymph were induced by acoustic overstimulation, whereas there was little change in the K+, Na+, Cl-, and HCO3- concentrations. The changes in H+ and HCO3- concentrations implied a depression of PCO2, suggesting an increase in blood flow to the cochlea. On the other hand, the Ca2+ concentration increased abruptly to 48 times the pre-exposure value. In contrast, no significant change in the Ca2+ concentration was observed in cochleae with damaged hair cells. We discuss the mechanism of the tone-induced Ca2+ elevation in endolymph and its effect on hearing acuity.

Animals↗
PubMedDate not supplied

Cochlear potentials and their modulation by low-frequency sound in early endolymphatic hydrops.

Seventeen guinea pigs were unilaterally operated to produce endolymphatic hydrops. After 2 wk (9 animals) or 4 wk (8 animals), extracochlear electrophysiological responses to tone bursts of several frequencies were recorded in both the operated and non-operated ears. In addition, modulation by low-frequency (29 Hz sinusoidal bias) sound of the responses to 8 kHz tonebursts was measured. After the electrophysiological measurements, the animals were killed and examined histologically. Four weeks after the operation, cochlear microphonics in response to a 500 Hz tone burst and to the 29 Hz bias were significantly smaller in the operated ears. The summating potential showed a tendency to be larger in the operated ears. The compound action potential input-output curves for 2 kHz probes showed a small threshold shift accompanied by steep slopes, reminiscent of recruitment. Modulation of summating potentials by the low-frequency bias was smaller on the operated side. In most cochleae an endolymphatic hydrops was observed. Three cochleae showed a collapse of Reissner's membrane.

Acoustic Stimulation↗
PubMed1990

Alterations of CAP audiogram by increased endolymphatic pressure and its relation to hydrops.

Most current theories regarding the inner ear pathology of Menières disease assume that there is an augmentation of the endolymphatic pressure due to the presence of hydrops. In this study normal hearing pigmented guinea pigs were employed to investigate the effect of increased endolymphatic pressure on the compound action potential (CAP) audiogram. All animals were implanted with an electrode on the round window and the CAP audiogram was determined prior to further surgery. The endolymphatic canal was then visualised by a posterior fossa intra-dural surgical approach. A hole was pierced in the canal and a cannula inserted. The CAP audiogram was again determined before, and at frequent intervals after, the application of hydrostatic pressure (0.5-1 cm Hg). A similar sequence of CAP sensitivity losses was observed within 2 h for 0.5 cm Hg or 15 min for 1 cm Hg. There was at first a very high frequency loss, followed by a very low frequency loss and finally a mid frequency sensitivity loss rendered the audiogram flat and lying around 50 dB sound pressure level. Given that the first characteristic index for experimental hydrops is a low frequency loss the present data suggest that an increase in endolymphatic pressure, as in these experiments, is likely to be a rather late pathological feature of hydrops. Indeed we have shown that a high frequency loss develops at a second phase during the evolution of hydrops.

Action Potentials↗
PubMed1993

Effect of lymph composition on an in vitro preparation of the alligator lizard cochlea.

The effects of different artificial lymphs on the cochlear duct of the alligator lizard were studied in an in vitro preparation. The duct was dissected and cemented to the glass floor of a chamber that had been filled with an artificial lymph. The vestibular membrane was removed and latex beads (1-5 microns in diameter) were allowed to settle on the endolymphatic surface of the duct. During perfusion with an artificial lymph solution, the positions of beads were measured and video images of the duct were obtained. Artificial lymphs were isosmotic and included artificial endolymph (AE), artificial perilymph (AP), Leibovitz's L-15 culture medium, an AE solution whose calcium concentration was the same as that of AP, and AE and AP solutions in which gluconate was substituted for chloride ions. Results obtained in AE were consistently different from those in other lymphs. The displacements of beads, the projected area of the papilla, the occurrence of blebs, and direct observation of cells in the duct all indicated that the tissue swelled in AE (with or without 2 mmol/l Ca) but showed no consistent shrinking or swelling in any of the other artificial lymphs. Thus for the solutions we used, the presence of both potassium and chloride was required to elicit the swelling response to isosmotic artificial lymphs. There were some regional differences in the swelling response: the swelling of the endolymphatic surface of the tissue in a direction orthogonal to the basilar membrane surface was smaller on the free-standing region of the basilar papilla than either on the tectorial membrane or on the hyaline epithelial cells. The preparation was osmotically stable in AP and in both AE and AP solutions in which gluconate was substituted for chloride ions. After exposure to these solutions for as much as 300 min, the preparation showed no gross signs of deterioration visible with the light microscope, and continued to exhibit a highly specific osmotic response to the composition of the bathing medium.

Animals↗
PubMed1988

A mathematical approach enabling the calculation of the total endolymph flow in the semicircular ducts.

1. A mathematical treatment of the flow inside the vertebrate labyrinth is given. The main difference to former theories (e.g. the "torsion pendulum" theory) is that the entire system formed by the three semicircular ducts, interconnected by the crus commune and the utriculus, is considered, instead of a single duct circuit. 2. The theory consists of a geometrical description of a labyrinth rotating in space, the solution of the continuity equation, determination of the initial velocities in all the ducts in a "cupulometry" experiment and derivation of the equation of motion (e.o.m.). 3. Equations for a system consisting of two ducts and for the classical single-duct system are special cases of the three-duct system. 4. Three different methods for the solution of the e.o.m. are described: an analytical one, a Runge-Kutta simulation and an "asymptotic" method. The last method includes approximations of the solution of the e.o.m. on a long and a short time scale. Its advantage is that it gives an insight based on rather manageable formulae. 5. The physiological basis of the presented theory, biological applications and verification are given in a separate paper (Muller & Verhagen, 1988).

Animals↗
PubMed1983

Clinical features of female heterozygotes in the X-linked mixed deafness syndrome (with perilymphatic gusher during stapes surgery).

A new pedigree with 9 obligate and 10 probable female carriers of the X-linked mixed deafness syndrome is presented. In the male the syndrome is characterized by a perilymphatic gusher during stapes surgery, a severe progressive mixed hearing loss and lack or strong reduction of vestibular responses. Four of the 9 obligate heterozygote females show similar but much milder audiological abnormalities. The other five obligate female carriers have a normal audiogram. None of the obligate female carriers showed vestibular abnormalities such as observed in the affected males. Ten females, sisters of affected males, have a chance of 50% to be heterozygote carriers. Five of these females have also a hearing loss, the other 5 have normal audiograms. The relevance of these findings for genetic counseling and for identification of affected males is discussed.

Deafness↗
PubMed1980

Use of the glycerin test in the diagnosis of post-traumatic perilymphatic fistulas.

A new application of the glycerin test in the diagnosis of post-traumatic perilymphatic fistulas is described. Temporary disappearance of abnormal responses to the fistula and Quix tests and improvement in the hearing occurred. The glycerin test was useful in confirming the diagnosis of post-traumatic perilymphatic fistula in 13 patients in whom fistulas were found at middle ear exploration.

Adolescent↗