Biomedical subjects

M Kössl

Publications and source records attributed to M Kössl.

45 records · Page 3Linked to original sources

PubMed1992

Modulation of hair cell voltage responses to tones by low-frequency biasing of the basilar membrane in the guinea pig cochlea.

Inner (IHC) and outer (OHC) hair cell receptor potentials were recorded during stimulation with combinations of high-frequency (HF) tones and a 100 Hz tone burst of constant level (80 dB SPL). For frequencies at and below characteristic frequency (CF), OHC AC receptor potentials were suppressed by the 100 Hz tone at levels of the HF tone below about 70 dB SPL (the initial steep part of the AC/level function) and at levels that were frequency specific for frequencies above CF. Suppression was associated with a phase lead for frequencies at and close to the CF. For frequencies above CF, the OHC AC response was either suppressed or augmented at levels of the HF tone both below and above 70 dB SPL, depending on the frequency. The action of the 100 Hz tone on the AC response/level functions was to change nonmonotonic functions into monotonic functions or vice versa. IHC DC receptor potentials were suppressed maximally at the CF and at levels and frequencies where suppression of the OHC AC response and the appearance of the IHC DC response overlapped. For levels of the HF tone above 70 dB SPL, the amplitude of the responses of both IHCs and OHCs to the 100 Hz tone are suppressed and become more symmetrical through selective attenuation of the depolarizing phase of the IHC response and the hyperpolarizing phase of the OHC response. In IHCs from insensitive preparations, the response to the 100 Hz tone is augmented in the presence of the HF tone, which may indicate a shift in the operating point of transduction. At frequencies about one-half an octave below the CF, the phase of the 100 Hz voltage response of OHCs but not IHCs is inverted for levels of the HF tone above about 90 dB SPL. It is proposed that amplitude and phase changes in the response to the HF tone due to the presence of the 100 Hz tone are the result of changes in OHC feedback processes and in the mode of movement of the interface between OHC stereocilia and tectorial membrane. The interaction between the responses to HF and 100 Hz tones indicates that feedback contributes significantly to the voltage responses of OHCs throughout the frequency response range.

Acoustic Stimulation↗

PubMed1991

The voltage responses of hair cells in the basal turn of the guinea-pig cochlea.

1. Intracellularly recorded voltage responses to tones and to current injection were measured from inner (IHC) and outer (OHC) hair cells in the basal turn of the guinea-pig cochlea. 2. The voltage responses of IHCs to tones are increased by negative current and decreased by positive current. For any given current strength, the decrease in the receptor potential amplitude caused by positive current is less than the increase caused by negative current. This was attributed to the voltage-dependent rectification of the membrane conductance. 3. Estimates of the reversal potential of the receptor current were based on extrapolation of the slopes of the current-voltage relations for potentials more negative than -60 mV. The estimated reversal potentials were close to the measured endolymphatic potential. 4. Negative current increased the IHC membrane time constant and increased the transducer driving voltage. When receptor potentials to low-frequency tones were adjusted for constant driving voltage and for the membrane time constant, the positive DC component of the receptor potential was decreased relative to the AC component by current injection but the DC component in response to high-frequency tones near the best frequency of the IHC (16 kHz) was unchanged by negative current. 5. When compensated for constant driving voltage and low-pass filtering due to the basolateral membrane conductance, the proportion of the transducer conductance open in IHCs at rest is increased by negative current. 6. Negative current injection reduced the positive DC components of OHC voltage responses to low-frequency tones and may make them negative. In some cases negative current injection decreased the amplitude of the OHC receptor potential while positive current injection enhanced it. From these observations it is proposed that negative current injection shifts the operating point of the OHC transducer functions towards a positive, saturating region of the relationship and positive current decreases the proportion of the transducer conductance which is open at rest.

Acoustic Stimulation↗

PubMed1990

Stereocilia bundle stiffness: effects of neomycin sulphate, A23187 and concanavalin A.

The effects that the aminoglycoside antibiotic neomycin sulphate, the ionophore A23187 and the lectin Concanavalin A (Con A) have on the steady state stiffness of the hair-cell stereocilia bundle have been studied using organotypic cultures of the early postnatal mouse cochlea. In normal saline, stereocilia bundle stiffness is increased 1.5-2.0 fold by neomycin sulphate, 1.3-1.7 fold by the ionophore A23187 and 3.0-5.0 fold by Con A. In low-calcium saline neither neomycin sulphate nor A23187 cause increases in stiffness, and the stiffness increases elicited by these two agents in normal saline are reversed on washout with low-calcium saline. In normal saline neomycin sulphate has two independent effects on hair cells; one effect is a reversible inhibition of transduction and the other effect is to cause an irreversible increase in bundle stiffness. Neither Con A nor the ionophore A23187 block transduction. No obvious changes in stereocilia bundle morphology are associated with the increases in stiffness caused by neomycin sulphate, A23187 and Con A. Succinylated Con A binds to stereocilia bundles but does not cause an increase in stiffness, suggesting that the stiffness increase caused by native Con A results from receptor cross-linking. The effects of Con A and neomycin are non-additive, saturating concentrations of neomycin sulphate block the effects of low doses of Con A, and pretreatment of cells with succinylated Con A prevents subsequent neomycin sulphate treatment from causing an increase in stiffness suggesting that neomycin sulphate and Con A are acting via a similar mechanism at the cell surface. Ionophore treatment prevents the subsequent application of neomycin sulphate from causing a further increase in stiffness, but when cells are treated with neomycin sulphate followed by ionophore the effects of the two drugs are additive indicating that they are operating via different mechanisms. The possible nature of these mechanisms and their role in the control of steady state stereocilia bundle stiffness are discussed.

Animals↗

PubMed1989

The responses of cochlear hair cells to tonic displacements of the sensory hair bundle.

Hair bundle displacements and receptor potentials were recorded from outer hair cells (OHCs) in organotypic cultures of the mouse cochlea during force steps applied to the bundles with a silica probe of known stiffness. The receptor potentials of some OHCs adapt for excitatory displacements and the time constants of receptor potential adaptation and hair bundle force relaxation for excitatory displacements are very similar. Thus in these OHCs, the receptor potentials correspond to the applied force for excitatory displacements. For inhibitory displacements, the receptor potentials correspond to hair bundle displacement. Some OHC receptor potentials are nonadapting and follow displacement in both the excitatory and inhibitory directions. The hair bundles of nonadapting OHCs are less stiff than those of adapting OHCs and nonadapting OHCs are an order of magnitude less sensitive to hair bundle displacement than adapting OHCs. In response to a combination of excitatory, tonic, hair bundle displacement and current injection, the receptor potentials of nonadapting OHCs decline as the membrane potential is made more positive and reverse near 0 mV. When the receptor potentials of adapting OHCs measured during current injection are compensated for constant input resistance and driving voltage across the transducer conductance, the receptor potential amplitude at the offset of the step displacement is independent of the level and polarity of the injected current. Before adaptation, at the onset of the step displacement of the hair bundle, the amplitude of the receptor potential increases as the injected current becomes more positive. For adapting OHCs, the receptor potential amplitude is a linear function of excitatory bundle displacement for amplitudes less than 50 nm. With negative, but not positive, current injection the receptor potentials at the onset of the displacement tend to saturate and the slope of the function decreases. This voltage dependent control of OHC transducer operating range is proposed to have a role in regulating the sensitivity of the cochlea.

Adaptation, Physiological↗

PubMed1989

Noradrenaline enhances temporal auditory contrast and neuronal timing precision in the cochlear nucleus of the mustached bat.

In the mustached bat, Pteronotus parnellii, noradrenaline (NA) was applied iontophoretically to single units in the anteroventral cochlear nucleus. NA suppressed tonic components of auditory responses and enhanced phasic onset responses to pure tone stimuli. The enhancement of onset activity was most pronounced in awake bats and was due to a decrease in the latency jitter of the first tone-evoked spikes from 0.55 msec in controls to 0.28 msec during NA application. In addition, NA reduced spontaneous neuronal activity. Noradrenergic antagonists suppressed phasic onset activity and increased the latency jitter of onset spikes. Opposite to the effect of NA, the tonic response component increased during application of the beta-antagonist propranolol but decreased during injection of the alpha 1-antagonist corynanthine. Other putative transmitter substances tested, nonselectively depressed both phasic and tonic response components (GABA, glycine) or increased both components either similarly or had more pronounced effects on the tonic response components (ACh, glutamate). Thus, NA specifically enhances auditory temporal contrast in favor of transients and improves neuronal timing precision, which may be of relevance for auditory tasks like passive sound localization, echolocation, and recognition of temporal patterns.

Acetylcholine↗

PubMed1988

Distribution of catecholamine fibers in the cochlear nucleus of horseshoe bats and mustache bats.

The glyoxylic-acid-induced fluorescence technique was applied to demonstrate patterns of catecholaminergic innervation within the auditory brainstem of echolocating bats and the house mouse. In the cochlear nucleus of the rufous horseshoe bat (Rhinolophus rouxi) and the mustache bat (Pteronotus parnellii), species-specific catecholaminergic innervation patterns are found that contrast with the relatively homogeneous innervation in the rodent. In both bats the subnuclei of the cochlear nucleus receive a differentially dense supply of catecholaminergic fibers, and within the subnuclei, the catecholamine innervation densities can be correlated with the tonotopic frequency representation. The areas devoted to the high-frequency echolocation calls are less densely innervated than those regions which are responsive to lower frequencies. Apart from this common scheme, there are noteworthy distinctions between the two bats which correlate with specialized cytoarchitectural features of the cochlear nucleus. The marginal cell group, located medially to the anteroventral cochlear nucleus of Pteronotus, receives the densest supply of catecholaminergic fibers of all auditory nuclei. This plexus is formed by a morphologically distinct population of catecholaminergic fibers.

Animals↗

PubMed1987

Strychnine alters the fusiform cell output from the dorsal cochlear nucleus.

Anatomical and physiological evidence suggests that fusiform cells, the major output neurons of the dorsal cochlear nucleus (DCN), receive significant inhibitory input. Fusiform cells often display strongly non-monotonic rate-intensity functions and pauser-buildup or buildup tone-evoked temporal responses, patterns which may be mediated by inhibitory neurotransmitters. Other neurons located within the fusiform cell layer or in the more superficial molecular layer display varied rate-intensity functions and temporal responses. Neurons displaying response properties characteristic of fusiform cells are sensitive to iontophoretic application of the inhibitory amino acid neurotransmitter, glycine. Application of the glycine receptor antagonist, strychnine, alters the non-monotonic portion of the rate-intensity function at doses which do not alter spontaneous activity or near-threshold tone-evoked responses. These neurons are also sensitive to GABA and the GABAB agonist, (-)-baclofen, but are insensitive to the GABAA antagonist, bicuculline. DCN neurons which display monotonic rate-intensity functions and temporal response properties different than those associated with fusiform cells are sensitive to bicuculline, (-)-baclofen, and GABA. These data suggest that a glycinergic input onto fusiform cells may control the non-monotonic nature of the response of these neurons near characteristic frequency and therefore may contribute significantly to the nature of the output of the DCN.

Acoustic Stimulation↗

PubMed1985

The cochlear frequency map of the mustache bat, Pteronotus parnellii.

The frequency-place map of the cochlea of mustache bats was constructed by the analysis of HRP-transport patterns in spiral ganglion cells following iontophoretic tracer injections into cochlear nucleus regions responsive to different frequencies. The cochlea consists of 5 half turns (total length 14.3 mm) and the representation of certain frequency bands can be assigned to specific cochlear regions: The broad high frequency range between 70 and 111 kHz is represented in the most basal half turn within only 3.2 mm. This region is terminated apically by a distinct narrowing of the scala vestibuli that coincides with a pronounced increase in basilar membrane (BM) thickness. The narrow intermediate frequency range between 54 and 70 kHz is expanded onto 50% of cochlear length between 4.0 and 11.1 mm distance from apex. The frequency range around 60 kHz, where the tuning characteristics of the auditory system are exceptionally sharp, is located in the center of this expanded BM-region in the second half turn within a maximum of innervation density. These data can account for the vast overrepresentation of neurons sharply tuned to about 60 kHz at central stations of the auditory pathway. In the cochlear region just basal to the innervation maximum, where label from injections at 66 and 70 kHz was found, a number of morphological specializations coincide: the BM is maximally thickened, innervation density is low, the spiral ligament is locally enlarged, and the 'thick lining', a dense covering of the scala tympani throughout the basal halfturn, suddenly disappears. Low frequencies up to 54 kHz are represented within the apical half turns over a 4 mm span of the basilar membrane. The data are compared to the cochlea of horseshoe bats and the possible functional role of the morphological discontinuities for sharp tuning and the generation of otoacoustic emissions is discussed.

Animals↗

PubMed1985

Evoked acoustic emissions and cochlear microphonics in the mustache bat, Pteronotus parnellii.

In the echolocating bat, Pteronotus parnellii, otoacoustic responses at a frequency of 62 kHz are measurable in the external ear canal during continuous and after transient acoustic stimulation. These responses are interpreted to represent emissions from the cochlea. They can reach an amplitude as large as 70 dB SPL and occur in the frequency range most important for echolocation, namely on the average about 700 Hz above the constant frequency component of the orientation calls. A sharp maximum of the amplitude of cochlear microphonic potentials at about 62 kHz could be correlated with the emission frequency. In one bat an evoked otoacoustic response changed to a spontaneous otoacoustic emission. The frequency and amplitude of the evoked otoacoustic responses reversibly decreased after exposure for 1 min to continuous sounds of more than 85 dB SPL with frequencies of about 2.5-7.5 kHz above the emission frequency. Similar effects occurred during anaesthesia or cooling. A possible relation between the existence of otoacoustic emissions and morphological specializations of the cochlea is discussed.

Acoustic Impedance Tests↗