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P Dallos

Publications and source records attributed to P Dallos.

At least 55 records · Page 3Linked to original sources
PubMed1993

Longitudinal comparisons of IHC ac and dc receptor potentials recorded from the guinea pig cochlea.

Recordings were made from inner hair cells (IHC) at three locations distributed in the apical half of the guinea pig cochlea. Longitudinal variations in ac and dc components of receptor potentials produced in response to single-tone inputs were studied to further understand the ways in which IHCs communicate with their innervating afferent dendrites. While neural synchrony probably depends on the ac receptor potential, discharge rate may be controlled by the dc receptor potential generated by the IHC transducer plus an ac component derived from the phasic receptor potential. The latter reflects low-pass filtering inherent in the hair cell's basolateral membrane and calcium-dependent synaptic processes. By comparing the frequency dependence of ac and dc components in cells with different characteristic frequencies, it may be possible to learn how neural response areas are formed and why their shapes change along the cochlear spiral.

Acoustic Stimulation↗
PubMed1993

Theory of electrically driven shape changes of cochlear outer hair cells.

1. A theory of cochlear outer hair cell electromotility is developed and specifically applied to somatic shape changes elicited in a microchamber. The microchamber permits the arbitrary electrical and mechanical partitioning of the outer hair cell along its length. This means that the two partitioned segments are stimulated with different input voltages and undergo different shape changes. Consequently, by imposing more constraints than other methods, experiments in the microchamber are particularly suitable for testing different theories of outer hair cell motility. 2. The present model is based on simple hypotheses. They include a distributed motor associated with the cell membrane or cortex and the assumption that the displacement generated by the motor is related to the transmembrane voltage across the associated membrane element. It is expected that the force generated by the motor is counterbalanced by an elastic restoring force indigenous to the cell membrane and cortex, and a tensile force due to intracellular pressure. It is assumed that all changes take place while total cell volume is conserved. The above elements of the theory taken together permit the development of qualitative and quantitative predictions about the expected motile responses of both partitioned segments of the cell. Only a DC treatment is offered here. 3. Both a linear motor and an expanded treatment that incorporates a stochastic molecular motor model are considered. The latter is represented by a two-state Boltzmann process. We show that the linear motor treatment is an appropriate extrapolation of the stochastic motor theory for the case of small voltage driving signals. Comparison of experimental results with model responses permits the estimation of model parameters. Good match of data is obtained if it is assumed that the molecular motors undergo conformational length changes of 0.7-1.0 nm, that they have an effective displacement vector at approximately -20 degrees with the long axis of the cell, and that their linear density is approximately 80/microns. 4. An effort is made to parcel out motile response components that are a direct consequence of the motor action from those that are mediated by cytoplasmic pressure changes brought about by the concerted action of the motors. We show that pressure effects are of minor importance, and thus rule out models that rely on radial constriction/expansion-mediated internal pressure change as the primary cause of longitudinal motility. 5. As a consequence of the interaction between the Boltzmann process and the mechanical characteristics of the cell, the electromotile response is asymmetric.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

The location and mechanism of electromotility in guinea pig outer hair cells.

1. The microchamber method was used to examine the motile responses of isolated guinea pig outer hair cells to electrical stimulation. In the microchamber method, an isolated cell is drawn partway into a suction pipette and stimulated transcellularly. The relative position of the cell in the microchamber is referred to as the exclusion fraction. 2. The length changes of the included and excluded segments were compared for constant sinusoidal stimulus amplitude as functions of the exclusion fraction. Both included and excluded segments showed maximal responses when the cell was excluded approximately halfway. Both segments showed smaller or absent responses when the cell was almost fully excluded or almost fully included. 3. When the cell was near to, but not at, the maximum exclusion, the included segment response amplitude was zero, whereas the excluded segment response amplitude was nonzero. In contrast, when the cell was nearly fully included, the excluded segment response amplitude was zero, but the included segment response amplitude was still detectable. A simple model of outer hair cell motility based on these results suggests that the cell has finite-resistance terminations and that the motors are restricted to a region above the nucleus and below its ciliated apex (cuticular plate). 4. The function describing length change as a function of command voltage was measured for each segment as the exclusion fraction was varied. The functions were similar at midrange exclusions (i.e., when the segments were about equal length), showing nonlinearity and saturability. The functions were strikingly different when the segment lengths were different. The effects of exclusion on the voltage to length-change functions suggested that the nonlinearity and saturability are local properties of the motility mechanism. 5. The diameter changes of both segments were examined. The segment diameter changes were always antiphasic to the length changes. This finding implies that the motility mechanism has an active antiphasic diameter component. The diameter change amplitude was a monotonically increasing function of exclusion for the included segment, and a decreasing function for the excluded segment. 6. The voltage to length-change and voltage to diameter-change functions were measured for the same cell and exclusion fraction. The voltage to diameter-change function was smaller in amplitude than the voltage to length-change function. The functions were of opposite polarity to each other, but were otherwise similar in character. Thus it is likely that the same motor mechanism is responsible for both axial and diameter deformations.

Animals↗
PubMed1993

Acetylcholine controls the gain of the voltage-to-movement converter in isolated outer hair cells.

Sensitivity of the electromotility of isolated guinea pig outer hair cells (OHCs) to acetylcholine (ACh) was examined. OHCs were held in a partitioning microchamber in a position so that their ciliary poles were inserted and their somatic length changes measured. Transcellular square-wave stimuli were delivered to record voltage-to-movement conversion of the cells. ACh was applied to the synaptic poles. The transfer function of electromotility intimated shifts of the membrane potential with concomitant gain changes: gain decreases when the membrane potential is shifted in hyperpolarization direction and gain increases when the membrane potential is shifted in the opposite direction due to application of ACh in 100-500 microM concentration. Clear gain increase of the electromotility in basal turn OHCs to ACh was observed, whereas inconsistent results for apical turn OHCs were found. The latter is probably due to the pharmacological dose of ACh used. This possibility is further supported by results in which ACh abolished the sensitivity of the magnitude response of electromotility to DC depolarizing bias.

Acetylcholine↗
PubMed1992

Two-tone suppression in inner hair cell responses: correlates of rate suppression in the auditory nerve.

Inner hair cell (IHC) recordings were made from second turn of the guinea pig cochlea where characteristic frequencies are approximately 4000 Hz. In order to compare IHC responses with rate suppression measured in the auditory nerve, suppressors were introduced that produced little or no response in the hair cell. The effects of a variable-frequency suppressor on a constant-frequency probe, placed near characteristic frequency, were also investigated since this paradigm is commonly used in single unit experiments. Resulting magnitude changes were measured in the fundamental component of the ac receptor potential and/or in the total dc produced in the region of temporal overlap between the two stimulus inputs. This latter component is especially important when considering how changes in IHC responses relate to decreases in discharge rate in single auditory nerve fibers. Since the ac receptor potential is filtered by the hair cell's basolateral membrane, the dc component probably controls transmitter release at the characteristic frequency of these second-turn IHCs. Based on results from these and previous experiments, a proposal is advanced to explain the evolution of two-tone suppression in the peripheral auditory system. The paper also discusses the use of excitatory versus non-excitatory suppressors and includes a description of two-tone suppression areas at the mechanical, IHC and single unit levels. The explanation of low-side suppression areas is of special interest since hitherto they have been difficult to model (Kim, 1985).

Acoustic Stimulation↗
PubMed1992

Physiological correlates of off-frequency listening.

Recordings are made from inner hair cells (IHC) in the second turn of the guinea pig cochlea where characteristic frequencies (CF) are approximately 4000 Hz. Results from experiments using two stimulus inputs suggest that the characterization of two-tone suppression at this more-basal recording location is similar to the reported for IHCs in the third turn (Cheatham and Dallos, 1989, 1990a, 1990b). For example, introduction of a suppressor causes IHC frequency response functions to become narrower with the smallest magnitude reductions occurring between 1/2 to 1 octave below CF. In this frequency region, where suppression is minimal, it was also observed that suppressor magnitude was reduced by the probe. In other words, the mutual suppression of probe and suppressor may contribute to the sharpening of these functions. Since the peak of the frequency response function shifts to a lower frequency in the presence of the suppressor, these results may provide a physiological correlate of the psychophysical phenomenon known as 'off-frequency listening.'

Acoustic Stimulation↗
PubMed1992

The active cochlea.

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Acoustic Stimulation↗
PubMed1991

Nature of the motor element in electrokinetic shape changes of cochlear outer hair cells.

It is the prevailing notion that cochlear outer hair cells function as mechanical effectors as well as sensory receptors. Electrically induced changes in the shape of mammalian outer hair cells, studied in vitro, are commonly assumed to represent an aspect of their effector process that may occur in vivo. The nature of the motile process is obscure, even though none of the established cellular motors can be involved. Although it is known that the motile response is under voltage control, it is uncertain whether the stimulus is a drop in the voltage along the long axis of the cell or variation in the transmembrane potential. We have now performed experiments with cells partitioned in differing degrees between two chambers. Applied voltage stimulates the cell membrane segments in opposite polarity to an amount dependent on the partitioning. The findings show, in accordance with previous suggestions, that the driving stimulus is a local transmembrane voltage drop and that the cellular motor consists of many independent elements, distributed along the cell membrane and its associated cortical structures. We further show that the primary action of the motor elements is along the longitudinal dimension of the cell without necessarily involving changes in intracellular hydrostatic pressure. This establishes the outer hair cell motor as unique among mechanisms that control cell shape.

Animals↗
PubMed1991

Outer hair cell electromotility: the sensitivity and vulnerability of the DC component.

A technique was devised in order to study the fast electromechanical length changes of outer hair cells at low stimulus levels. Solitary outer hair cells were drawn into a glass microchamber. Length changes were evoked by the application of transcellular potentials and were detected with a photodiode. The method is non-invasive to the cell and offers superior sensitivity and stability for the recording of cell length changes. The function relating command voltage and cell length (V-delta L) change was determined. A nonlinearity, consisting of a DC component superimposed on the AC response, was shown to be present at the lowest stimulus levels measured. The nonlinearity was sensitive to imposed electrical bias as well as vulnerable to overstimulation. The observations are interpreted in reference to the V-delta L function. A parallel is suggested between the nonlinearity seen in the mechanical response and that observed in the responses of the intact cochlea.

Animals↗
PubMed1991

The role of outer hair cell motility in cochlear tuning.

The mammalian cochlea's remarkable sensitivity and frequency selectivity are thought to be mediated by the mechanical feedback action of outer hair cells. New tools for measuring the movement of cochlear elements, and recent advances in modeling are increasing our knowledge of cochlear mechanics.

Animals↗
PubMed1990

Neural coding in the chick cochlear nucleus.

Physiological recordings were made from single units in the two divisions of the chick cochlear nucleus-nucleus angularis (NA) and nucleus magnocellularis (NM). Sound evoked responses were obtained in an effort to quantify functional differences between the two nuclei. In particular, it was of interest to determine if nucleus angularis and magnocellularis code for separate features of sound stimuli, such as temporal and intensity information. The principal findings are: 1. Spontaneous activity patterns in the two nuclei are very different. Neurons in nucleus angularis tend to have low spontaneous discharge rates while magnocellular units have high levels of spontaneous firing. 2. Frequency tuning curves recorded in both nuclei are similar in form, although the best thresholds of NA units are about 10 dB more sensitive than their NM counterparts across the entire frequency range. A wide spread of neural thresholds is evident in both NA and NM. 3. Large driven increases in discharge rate are seen in both NA and NM. Rate intensity functions from NM units are all monotonic, while a substantial percentage (22%) of NA units respond to increased sound level in a nonmonotonic fashion. 4. Most NA units with characteristic frequencies (CF) above 1000 Hz respond to sound stimuli at CF as 'choppers', while units with CF's below 1000 Hz are 'primary-like'. Several 'onset' units are also seen in NA. In contrast, all NM units show 'primary-like' response. 5. Units in both nuclei with CF's below 1000 Hz show strong neural phase-locking to stimuli at their CF. Above 1000 Hz, few NA units are phase-locked, while phase-locking in NM extends to 2000 Hz. 6. These results are discussed with reference to the hypothesis that NM initiates a neural pathway which codes temporal information while NA is involved primarily with intensity coding, similar in principle to the segregation of function seen in the cochlear nucleus of the barn owl (Sullivan and Konishi 1984).

Acoustic Stimulation↗
PubMed1990

Comparison of low- and high-side two-tone suppression in inner hair cell and organ of Corti responses.

Two-tone interactions were measured from inner hair cells and from the organ of Corti fluid space in the third turn of the guinea pig cochlea. At relatively low stimulus levels, a low-side suppressor caused frequency response functions to become broader. Phase changes exhibited a lag/lead transition around the characteristic frequency in harmony with the change in magnitude. These patterns are similar to those previously documented for a high-side suppressor (Cheatham and Dallos 1989) and suggest that suppression is not simply an attenuation phenomenon since level reductions for single-tone inputs produce response patterns which are mirror images of those obtained for the two-tone conditions. In contrast to the low-level results, data measured at moderately high stimulus levels indicate that the magnitude changes produced by both low- and high-side suppressors are qualitatively similar to changes generated by reducing the input sound level. In other words, ac frequency response functions become narrower, partially reversing the broadening of these functions which occurs as sound level increases. Companion phase measures, however, demonstrate that low- and high-side suppressors, in spite of producing similar changes in filter shape, do not produce similar changes in response phase. In fact, neither of the two-tone conditions produce response patterns similar to the one associated with reducing the input sound level.

Acoustic Stimulation↗
PubMed1990

Two-tone interactions in inner hair cell receptor potentials: AC versus DC effects.

Two-tone suppression was studied in both ac and dc receptor potentials recorded from inner hair cells in the third turn of the guinea pig cochlea. Frequency response functions for the ac component obtained at moderate intensities indicate that frequency selectivity is enhanced when a high-side suppressor is added to the stimulus. This occurs because the largest reductions in magnitude take place well above and below the characteristic frequency (CF) of the cell. Changes near CF are relatively small. In contrast, frequency response functions for the dc receptor potential become broader in the presence of an excitatory suppressor. The significance of these findings for the processing of complex stimuli is considered.

Acoustic Stimulation↗
PubMed1990

Effects of electrical polarization on inner hair cell receptor potentials.

Ac and dc receptor potential components in response to tone-burst stimuli were measured from inner hair cells in the third cochlear turn of the guinea pig. Comparisons were sought between conditions when constant polarizing current was injected into the cell through the recording electrode and when there was no extrinsic current. Hyperpolarization of the cell increased all responses, while depolarization decreased them. The input-output functions were vertically translated by current injection. The extent of translation was a function of current level. In addition, the amount of current-induced change was frequency dependent. Largest changes were seen at low frequencies and the current-induced change tended toward a constant high-frequency asymptote between 1-2 kHz. Changes in the dc response component were considerably in excess of those for the fundamental ac response. The frequency-dependent effects are quantified with the aid of a hair cell circuit model [P. Dallos, Hear. Res. 14, 281-291 (1984)]. It is assumed that the quantity altered by polarizing current (actually by the transmembrane voltage) is the resistance of the cell's basolateral membrane.

Animals↗
PubMed1990

Intracellular recordings from supporting cells in the guinea pig cochlea: DC potentials.

1. Supporting cells and hair cells from the low-frequency region of the guinea pig cochlea were studied in vivo using intracellular recording and horseradish-peroxidase (HRP) marking techniques. 2. The response of third- and fourth-turn support cells to tone bursts is composed of a number of components: an AC component at the frequency of the stimulating tone, harmonic components, a DC component present at the onset of the stimulating tone (the early DC), a slowly developing depolarization, and a slowly decaying afterpotential. 3. The early DC of support-cell responses is generally less than or equal to that in the adjacent organ of Corti fluids [at the best frequency (BF) for an 80 or 90 dB sound pressure level (SPL) stimulus the average early DC of support-cell responses is 0.9 times that of the adjacent fluids; n = 71], and both are less than that seen in the hair cells [average early DC of inner hair-cell (IHC) responses at the same sound levels is 14.2 times that in the adjacent organ fluids, n = 15; average early DC of outer hair-cell (OHC) responses is 11.5 times that in nearby organ fluids, n = 2)]. 4. The end DC, magnitude of the DC response shortly before signal end, in responses of support cells deep into Corti's organ [e.g., pillar, inner phalangeal, border cells] is often greater than that recorded in the potentials of the adjacent organ fluids (e.g., for an 80 or 90 dB SPL stimulus at the BF with a 30 ms steady-state time, the average end DC of the support cells deep into the organ is 2 times that of the adjacent organ fluids, n = 42). In contrast, the end DC for the responses of peripheral support cells--the Hensen's cells--generally equals, or is smaller than, the extracellular-fluid counterpart (for an 80 or 90 dB SPL stimulus, the average end DC of Hensen's cells is 0.9 times that of the nearby, outer-tunnel fluids, n = 29). Thus a difference exists across support-cell type with respect to support-cell end DC vis-à-vis that of the adjacent organ of Corti fluids. 5. A slowly increasing depolarization is often present in moderate and high-level support-cell responses. It is not normally present in IHC or OHC responses. Magnitude of the slowly increasing depolarization, the slow DC, is dependent on stimulus duration and stimulus level.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1989

Developmental alterations in the frequency map of the mammalian cochlea.

The position of an auditory hair cell along the length of the cochlea determines the sound frequency to which it is most sensitive. Receptors located near the proximal end (base) of the cochlea are maximally stimulated by high-frequency sounds; those occupying successively more distal (apical) positions respond best to progressively lower frequencies. At present, it is unclear how this frequency place map emerges with respect to the development of the cochlea. It has been suggested, on the basis of acoustic trauma experiments with developing chicks and cochlear potential recordings from developing gerbils, that this map may arise through systematic changes in the spatial encoding of frequency along the cochlea. Others have inferred from frequency tuning curves derived from auditory-nerve recordings in developing mammals and chicks, that the cochlear frequency-place map remains stable throughout development. We analysed frequency tuning curves obtained from gerbil spiral ganglion cells at a constant location within the basal cochlea, and report here that these cells undergo significant increases (up to 1.5 octaves) in their best-response frequencies between the second and third weeks of postnatal life. These recordings provide direct evidence for developmental changes in the tonotopic organization of the mammalian cochlea.

Acoustic Stimulation↗