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T F Weiss

Publications and source records attributed to T F Weiss.

At least 37 records · Page 2Linked to original sources
PubMed1983

Components of cochlear electric responses in the alligator lizard.

Electric responses to clicks and tones were recorded at the round windows of anesthetized alligator lizards before and after tetrodotoxin (TTX) was added to scala tympani. By combining click responses obtained in the presence and absence of TTX and at high and low click repetition rates, we trisected click responses into three components: (1) a rate-insensitive, TTX-insensitive component (that we identify as the cochlear microphonic potential or CM); (2) a rate-sensitive, TTX-sensitive component (that we identify as the neural component); (3) a rate-sensitive, TTX-resistant component (which has not been identified previously and which we call component X). Component X is generated in the inner ear and has a latency between that of the CM and the neural component. Several possible origins for component X are discussed of which the most likely is that component X represents the compound post-synaptic potential of the nerve terminals. Measurements of responses to tones in the presence and absence of TTX demonstrate that the contribution of the neural component to the response is appreciable below 1.5 kHz and negligible above this frequency.

Animals↗
PubMed1983

Receptor potentials of lizard hair cells with free-standing stereocilia: responses to acoustic clicks.

Receptor potentials of single hair cells in the free-standing region of the basilar papilla of the anaesthetized alligator lizard were measured intracellularly with micropipettes. Stimuli were primarily acoustic pulses (clicks) delivered to the tympanic membrane. The receptor potential was independent of click repetition rate for the range 10-150 clicks/s. This property is presumed to be the basis of the rate independence of the extracellular cochlear microphonic potential. The receptor potential wave-form consisted of a fast oscillatory component (or oscillation) superimposed on a usually positive (depolarizing) slow component. Reversal of the stimulus polarity resulted in a reversal of the polarity of the oscillations; the polarity of the slow component remained unchanged. The relative magnitudes of the two components depended on click level. At the higher click levels the magnitudes of the slow and oscillatory components were comparable. The relation of the receptor potential to the stimulus was non-linear; the peak-to-peak magnitude of the receptor potential increased less than proportionately with increasing sound-pressure level, and reversal of the stimulus polarity did not result in a reversal of the receptor potential. The receptor-potential magnitude for high-level clicks ranged from 1-13 mV peak-to-peak with an average value of 3.5 mV. At the lower click levels the magnitude of the slow component was much smaller than that of the oscillatory component. The relation of the receptor potential to the acoustic stimulus approached that of a linear system, the magnitude of the receptor potential became approximately proportional to the sound-pressure level, and reversal of the stimulus polarity resulted in approximate reversal of the receptor potential. For low-level stimuli the frequency of the oscillations of the receptor potential in response to clicks was approximately equal to the frequency of maximal a.c. response to tones. Apparently, both phenomena reflect the frequency selectivity of the processes generating the receptor potential. The frequency of oscillations in the click response varied from one cell to another (range of 1.0-2.2 kHz in this study). The results are qualitatively consistent with a model (Weiss, Mulroy & Altmann, 1974) that contains a linear, band-pass filter followed by a rectifier followed by a low-pass filter.

Acoustic Stimulation↗
PubMed1983

Receptor potentials of lizard cochlear hair cells with free-standing stereocilia in response to tones.

Intracellular potentials were recorded with micropipettes from hair cells with free-standing stereocilia in the cochleae of anaesthetized alligator lizards. Wave forms of intracellular responses to click stimuli were classified into three types: hair cells, supporting cells, and untuned cells. We studied primarily the responses of hair cells to tonal stimuli. For most frequencies, f, and levels, P, of tone-burst stimuli, the response envelope of the receptor potential increases monotonically at the tone-burst onset, and decreases monotonically at tone-burst offset. Overshoot in the envelope of the response at the onset and offset of tone bursts is observed only for tone bursts of low f, high P, and short (approximately equal to 1 msec) rise/fall time. The steady-state response to tones consists of a positive (depolarizing) d.c. component, V0, plus a.c. components (e.g. a fundamental component, V1, second harmonic, V2, and third harmonic, V3). The magnitudes of a.c. and d.c. components are functions of f and P, and show three characteristics: frequency selectivity, non-linearity, and low-pass filtering. The receptor potential is frequency selective. The frequency selectivity of V0 and V1 components was measured by means of iso-voltage (iso-V0 and iso-V1) contours. Iso-V0 and iso-V1 contours are V-shaped: the maximum sensitivity occurs at a characteristic frequency (c.f.). The shapes of these contours near the c.f. depend on the values of V0 and V1 at which the contours were measured and are sharper for lower values of V0 and V1. The mean slopes of the low- and high-frequency sides of these contours are: -45.0 and +85.1 dB/decade for iso-V0 contours (n = 26), and -33.6 and +103.8 dB/decade for iso-V1 contours (n = 28). The receptor potential has non-linear properties. The magnitudes and phase angles of V0, V1, V2, and V3 receptor-potential components were measured as a function of P for different f. The slopes of level functions (the dependence of log V0 and log magnitude of V1 on log P) were measured at low levels for different f. For values of f differing from c.f. by more than a half-octave, the slope for V0 is between 1 and 2 with a mean of 1.3; the slope for V1 is about 1, i.e. magnitude of V1 increases approximately linearly with P. For frequencies near c.f., the slopes for V0 and V1 are approximately 0.8 and 0.5, respectively, indicating the presence of a compressive non-linearity.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1983

Frequency selectivity of hair cells and nerve fibres in the alligator lizard cochlea.

Receptor potentials of hair cells and spike discharges of cochlear nerve fibres were recorded with micropipettes from the free-standing region of the basilar papilla of anaesthetized alligator lizards in response to tones. In this region the hair-cell stereocilia are free-standing, i.e. they protrude directly into endolymph and are not in contact with a tectorial membrane. The frequency selectivity of hair-cell responses was measured by means of isovoltage contours of the d.c. (V0) and fundamental-a.c. (V1) component of the receptor potential, i.e. iso-V0 and iso-V1 contours. The frequency selectivity of the nerve-fibre discharge was measured by iso-rate (iso-V0) contours. Iso-V0, iso-V1 and iso-V0 contours are basically V-shaped with a characteristic frequency (c.f.) defined as the frequency at which minimum sound pressure (Pmin) is required to evoke the criterion value of the response. Receptor potential iso-V0 contours and neural iso-V0 contours have similar slopes: the mean slopes of the low-frequency sides (dB/decade) are -43.0 and -44.3; the slopes of the high-frequency sides are 85.0 and 80.2. The band widths of iso-V0 and iso-V0 contours away from c.f. are similar (mean values of Q30dB are 0.40 and 0.53, respectively). The band widths of iso-V0 contours near c.f. are narrower than those of iso-V0 contours (mean values of Q10dB are 2.34 and 1.20, respectively). However, the shapes of the contours near c.f. depend on the iso-response criteria, and we have not determined whether or not iso-V0 and iso-V0 contours are similar near c.f. The shapes of iso-V1 contours differ from those of iso-V0 and iso-V0 contours. Nerve fibre c.f.s are tonotopically organized in the nerve, with lowest c.f.s recorded from fibres innervating the border of free-standing and tectorial regions, a region in which hair-cell stereocilia are longest, and the highest c.f.s recorded from fibres innervating the end of the free-standing region in which hair-cell stereocilia are shortest. The c.f. of nerve-fibre response (and by implication hair-cell response) is, therefore, correlated with the height of the stereociliary tuft. The shapes of iso-V0 contours vary systematically with c.f. and, therefore, tonotopically with nerve position.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1982

Supporting-cell and extracellular responses to acoustic clicks in the free-standing region of the alligator lizard cochlea.

1. Acoustic clocks were delivered to the tympanic membrane of anesthetized alligator lizards, and electric responses were measured within the free-standing region of the cochlea using glass micropipettes. Responses were recorded intracellularly in supporting cells and extracellularly in the receptor organ and in the scalae. Gross responses were also recorded with wire electrodes in scala tympani. 2. Intra- and extracellular responses contain two components: (1) an early (with latent period less than 0.15 ms after the onset of the click), rate-independent component presumed to originate in the receptor cells, which we call the 'receptor component'; and (2) a later (with latent period from 2 to 5 ms after the onset of the click), rate-dependent component presumed to originate in the primary neurons, which we call the 'neural component'. 3. The receptor component consists of a positive, slow, polarity-independent potential which is superimposed on a small, oscillatory, polarity-dependent potential. The average magnitude of the receptor component in supporting cells (0.72 mV for -20 dB clicks) is about 10 times that in the extracellular spaces and about 1/5 of that recorded in receptor cells. This component depends nonlinearly on the sound stimulus in the -20 to -55 dB range of click levels. 4. The average magnitude of the neural component in supporting cells (0.3 mV for clicks at -20 dB and 10 clicks/s) is about 5-10 times larger than that in the extracellular spaces. 5. The receptor and neural components have different distributions within the cochlea. The slow potential of the receptor component has positive polarity within the receptor organ and in scala tympani, and negative polarity in scala media. In contrast, the neural component has approximately the same biphasic (negative then positive) waveform in all extracellular compartments where it was detected. However, the neural component has a larger magnitude and an inverted (positive then negative) waveform in supporting cells. The neural component has not been detected in receptor cells.

Acoustic Stimulation↗
PubMed1981

Proportionality of intracellular resistance changes and receptor potentials in hair-cell models.

Russell and Sellick (Russell, I.J. and Sellick, P.M. (1978): J. Physiol. (London) 284, 261-290) reported measurements in guinea pig inner hair cells of d.c. resistance and d.c. potential changes in response to tones delivered to the tympanic membrane. They reported that d.c. potential changes were proportional to d.c. resistance changes for a broad range of tone levels and frequencies, and concluded that this result is inconsistent with the variable-resistance model proposed by Davis (Davis, H. (1958): Ann. Otol, Rhinol, Laryngol. 67, 789-801). We show that this proportionality is consistent with the model. Furthermore, we show that such proportionality is a special case of a general property of a model that is a generalization of the Davis model. Namely, we show that the time-varying receptor potential is proportional to the time-varying resistance change.

Acoustic Stimulation↗
PubMed1978

Endolymphatic and intracellular resting potential in the alligator lizard cochlea.

Endolymphatic potential (EP) and intracellular resting potentials (RPs) in the cochlea of the alligator lizard were measured with micropipets. The EP (defined as the dc electric potential recorded between the endolymph in scala media and the perilymph in scala tympani or scala vestibuli) had a mean value of +16 mV (in 96 ears). The RPs (defined as the dc potentials recorded between the intracellular and perilymphatic spaces) were different in the distal portion of the cochlear nerve (range to -56 mV, mean of -23 mV in 158 cells) from those in the region of the basilar papilla (range to -154 mV, mean of -73 mV in 623 cells). In identified cells in the region of the basilar papilla, the mean values of RPs of hyaline epithelial cells (-113 mV in 7 cells) and supporting cells (-93 mV in 13 cells) were more negative than of hair cells (-73 mV in 5 cells). Differences in measured RPs could reflect differences in the resting potentials of these cells and/or their source resistances. RPs measured in the basilar papilla of the alligator lizard are compared with those obtained in other vertebrate hair cell organs.

Acoustic Stimulation↗
PubMed1976

Tuning of single fibers in the cochlear nerve of the alligator lizard: relation to receptor morphology.

(1) The general anatomy of the peripheral portion of the cochlear nerve in the alligator lizard is described. (2) Spike discharges of single units were recorded with micropipets placed in the peripheral portion of the cochlear nerve of anesthetized lizards. (3) In response to tone bursts, each unit is maximally sensitive to a charactertistic frequency (CF). There are two distinct populations of units having different CFs: a low CF population (CF in the range 0.2-0.8 kHz) recorded in the portion of the nerve that enters the apical region of the basilar papilla and a high CF population (CF in the range 0.9-4.0 kHz) recorded in the portion of the nerve that enters the basal region. The low CF units are more sharply tuned than the high CF units. (4) Comparison of cochlear nerve units of the alligator lizard with those of mammals shows that the tuning of low CF units resembles that of mammalian units of the same CF. The tuning of high CF lizard units differs significantly from mammalian units. (5) The distinct differences in tuning of low and high CF units are correlated with distinct differences in the structure of the basilar papilla in the apical and basal regions rather than with differences in the width of the basilar membrane.

Animals↗
PubMed1976

Tight and gap junctions in a vertebrate inner ear.

The auditory organ of the alligator lizard has been investigated with the transmission electron microscope using methods which distinguish between tight and gap junctions. There is a continuous zone of tight junctions located near the endolymphatic surface of the organ forming a boundary between the endolymph in scala media and the interstitial spaces between the cells. No such tight junctions were observed between the perilymph of scala tympani and the interstitial fluid within the organ. Small gap junctions occur between hair cells and supporting cells and large gap junctions occur between adjacent supporting cells. The locations of the tight junctions suggest that the composition of the intercellular fluid in the receptor organ is probably more like perilymph than like endolymph. The presence of gap junctions between hair cells and supporting cells provides a possible morphological basis for the occurrence of intracellular responses to sound in supporting cells, and for elctric coupling of receptor cells.

Animals↗