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Biomedical subjects

R Klinke

Publications and source records attributed to R Klinke.

At least 91 records · Page 5Linked to original sources
PubMed1983

Influence of temperature on tuning of primary-like units in the guinea pig cochlear nucleus.

The effect of temperature changes on the response area of primary-like single units recorded extracellularly in the anteroventral cochlear nucleus of the guinea pig was studied for cochlear temperatures in the range 27.4-40.3 degrees C, while maintaining a normal rectal temperature of 38.5 degrees C. A new approach to the cochlear nucleus was developed which involved opening of the temporal bone overlying the flocculus cavity and aspirating a small portion of the paraflocculus. Irrespective of characteristic frequency CF (0.8-16 kHz), hypothermia caused a reversible elevation of CF thresholds (1.6 dB/degrees C), a small loss of the sharpness of threshold tuning and reductions of the saturation and mean spontaneous rates. The CFs were unaffected, in contrast to single units in birds and cold-blooded animals. From a comparison of the effects of temperature on different species it is proposed that the processes that define CF and sharpness of tuning are different within a cochlea, and that these processes can be differentially influenced.

Animals↗
PubMed1982

The effects of intracochlear cyanide and tetrodotoxin on the properties of single cochlear nerve fibres in the cat.

1. Tuning properties and spontaneous discharge rate of single cochlear fibres in the anaesthetized cat were determined under conditions where millimolar concentrations of KCN were instilled into the scala tympani. 2. Short-term effects on the tuning properties were obtained, in which the threshold of the low threshold sharply tuned tip segment of the frequency-threshold ('tuning') curve (f.t.c.) was elevated by up to 40 db, without changes in the threshold of the low frequency 'tail' segment of the f.t.c., or necessarily changes in the spontaneous and maximally evoked activity. These changes were accompanied by a shift of the characteristic frequency tip segment towards lower frequencies. All these effects could be reversed. 3. The long-term effects of repeated KCN instillations produced irreversible changes similar to the short-term effects. 4. These changes correlated well with depression of the amplitude of the gross cochlear action potential but not with the cochlear microphonic potential, both recorded at the round window. 5. Instillations of tetrodotoxin (TTX) rapidly reduced and blocked the cochlear fibre discharges without effects on their tuning, in contrast to the effects of KCN.

Action Potentials↗
PubMed1982

The effects of intracochlear and systemic furosemide on the properties of single cochlear nerve fibres in the cat.

1. Tuning properties and spontaneous discharge rate of single cochlear fibres in the anaesthetized cat were determined during short- and long-term poisoning of the cochlea by locally and systemically applied furosemide.2. With intra-arterial administration of furosemide, short-term reversible elevation occurred of the low threshold sharply tuned ;tip' segment of the frequency threshold (;tuning') curve (f.t.c.) by up to 40 db, without substantial changes in the threshold of the low frequency ;tail' segment of the f.t.c. These changes could occur in part without changes in the spontaneous activity and entirely without changes in the maximal evoked activity. These effects were observed in all fibres examined, the characteristic frequencies of which ranged from 3.5 to 31 kHz.3. Intracochlear administration of furosemide in 0.9 mM concentrations produced similar changes, but these were not reversible.4. The changes correlated with the depression of the amplitude of the gross cochlear action potential. The cochlear microphonic potential, however, was either unchanged, or only slightly reduced.5. In long-term furosemide poisoning of the cochlea, fibres with anomalous response properties were found alongside fibres having normal tuning. The former exhibited either reduced excitability of the low threshold tip segment, or a tip segment attenuated in both excitability and threshold.6. It is concluded that the selective effects of furosemide on the tip segment of cochlear fibre f.t.c.s offer further evidence for a physiologically vulnerable ;second filter' in the cochlea. The selective influence of the furosemide on the low threshold tip segment provides support for the hypothesis that the normal f.t.c. is generated by two largely independent processes: one vulnerable, low threshold and sharply tuned, and the other less vulnerable, but high threshold and more broadly tuned.7. The findings, obtained with an agent known to produce reversible impairment of hearing in man, provide direct physiological evidence in support of the hypothesis that in sensorineural hearing loss of cochlear origin the frequency selectivity of cochlear nerve fibres is impaired.

Action Potentials↗
PubMed1980

Discharge properties of primary auditory fibres in Caiman crocodilus: comparisons and contrasts to the mammalian auditory nerve.

Single fibre recordings were performed from the auditory nerve of the caiman, Caiman crocodilus. All neurones were spontaneously active (1-80 imp/s). Clicks evoked multiple peaks in the post stimulus time histogram spaced at 1/CF. At high intensities irregularities were observed. The latencies of the first peak observable were intensity-dependent and related to CF. The number of peaks was correlated with tuning properties of the fibre. Frequency threshold curves were asymmetrical, with low frequency slopes less steep than high frequency slopes. Q10 dB was between 1.5 and 7 with best tuning at high CF. CF ranged from 30 Hz to 2.8 kHz, lowest thresholds down to 5 dB SPL. Intensity functions were nonmonotonic. In isointensity contours the best frequency shifted downwards with increasing stimulus level. At highest levels a response dip was observed above CF. Phase locking, two tone suppression and excitability by combination tones were observed. In comparison to the mammalian cochlea similarities and differences were found.

Acoustic Stimulation↗
PubMed1980

Discharge properties of afferent fibres of the goldfish semicircular canal with high frequency stimulation.

The horizontal semicircular canals of goldfish were sinusoidally stimulated 0.07 and 63 Hz (about 3 decades). Single afferent fibre recordings showed sinusoidal modulation of discharges. Above 4 Hz the discharges became phase-locked to the stimulus. With increasing frequency the number of spikes per period decreased so that finally only one spike per period remained. At 63 Hz a stimulus of as little as 0.005 degrees was sufficient to drive the units to far above their spontaneous activity. As cupular deflection is less than the angle of body movement, the cupular deflection threshold for modulation of afferent discharges must be much less than 0.005 degrees. Transfer functions of afferent activity were determined. The simple pendulum model does not fit the data. Additional introduction of a third time constant and the low pass properties of the receptor cell membrane, the synaptic delay and the leaky integrator of the post synaptic afferent terminal improve the fit.

Animals↗
PubMed1980

Efferent activity in the goldfish vestibular nerve and its influence on afferent activity.

Out of 326 fibres in the horizontal semicircular canal branch of the goldfish vestibular nerve, 7 fibres could be identified as efferents. They showed irregular spontaneous activity and responded to rotatory stimuli with double frequency. Additionally in the central stump of the dissected nerve, efferent fibres were found, the spontaneous and stimulus modulated activity of which could not be differentiated from afferents. Efferents could be driven by a number of stimuli (vestibular, visual, somatosensory). Disruption of the efferent influence upon the receptors by dissection of the nerve or by pharmacological means (Gallamine) led to an increase of spontaneous afferent activity by 50%, showing that there is tonic efferent inhibition. Transfer functions of afferents were not changed after release from efferent influence. Electrical stimulation of efferents in 41% of the fibres led to an increase of afferent activity instead of the expected inhibition, which was seen in another 32%.

Animals↗
PubMed1980

Interaural attenuation in the cat, measured with single fibre data.

Acoustic crosstalk was measured in the pentobarbital anesthetized cat using the responses of single units in the auditory nerve to ipsilateral and contralateral sound stimuli. The mean interaural attenuation (IATT) was found to be 76 dB between 350 and 18,000 Hz. No systematic variation of IATT with frequency was found although a large variation between different units with similar characteristic frequencies could be seen. We suggest that this scatter is due to the complex fine structure of the bone conduction pathways (Tonndorf (1966) Bone conduction. Acta Otolaryngol. Suppl. 213, 1-132). There are large discrepancies between these data and values obtained using cochlear microphonic potentials as an indicator. We suggest that cochlear microphonic crosstalk data in the literature should be treated with caution as it is extremely difficult to exclude the effect or direct electrical crosstalk on these analog signals.

Acoustic Stimulation↗
PubMed1979

[Physiological basis for a cochlear prosthesis (author's transl)].

For the attempt to develop a cochlear prosthesis, which allows some understanding of speech, it seems--at least for the first attempts--to be appropriate to mimic natural conditions as far as possible. The auditory nerve contains about 30,000 afferent fibres. Qualitatively, their behavior is similar but quantitative measures show considerably differences (2.3). Nothing certain can be said at present however about the spiral fibres originating from the outer hair cells. The quantitative differences between single afferents concern tuning, frequency selectivity, thresholds, intensity functions and--of particular interest for electrical stimulation--differences in timing of the activity pattern, brought about by differences in travelling time along the cochlear duct (2.3). The time differences seen in the activity pattern of different fibres are in the order of several ms (2.3.6;2.3.7). Actionpotentials elicited by natural acoustic stimuli show probabilistic behavior, that is they are not strictly determined. It is obvious that with artificial electrical stimulation not every surviving single fibre can be selectively stimulated. An electrode will always stimulate a group of fibres simultaneously. With any conceivable electrical stimulation all fibres in the suprathreshold region of the electrode will be synchronously activated (3.2); a fundamental difference to the natural situation. To estimate the number of channels, necessary to stimulate the auditory nerve with sufficient accuracy to allow speech perception we consider some psychoacoustic data. These have shown that the auditory system possesses the ability to differentiate a great number of different pitches, but on the other hand it is capable of integrating different frequency areas to a so called critical bandwidth. Sound energy falling into one critical bandwidth is integrated to a uniform auditory sensation. If one is to integrate various fibres of the auditory nerve to one channel of stimulation it seems to be adequate to use the critical bandwidth as a measure (3.1). According to this criterion 15 channels would have to be introduced into the speech region of the cochlea. This would allow 1.2 mm of cochlear length for each channel. Perfect electrical separation of the channels is required. Considering the severe distortions in neuronal activity pattern, introduced by electrical stimulation in comparison to the natural conditions it is not clear even whether the number given would be sufficient. On the other hand, current spreading would appear to prohibit any higher electrode density. As far as coding of sound parameters within one channel is concerned it is proposed that full use should be made of frequency analysis according to the place principle. In respect to coding of periodicity and loudness it is proposed to approach natural conditions as far as possible (3.3). Here delay times between the individual channels and a probabilistic character of the stimuli should be introduced to avoid dominance of periodicity pitch...

Action Potentials↗