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O Gleich

Publications and source records attributed to O Gleich.

32 records · Page 2Linked to original sources
PubMed1994

Inner-ear abnormalities and their functional consequences in Belgian Waterslager canaries (Serinus canarius).

Recent reports of elevated auditory thresholds in canaries of the Belgian Waterslager strain have shown that this strain has an inherited auditory deficit in which absolute auditory thresholds at high frequencies (i.e. above 2.0 kHz) are as much as 40 dB less sensitive than the thresholds of mixed-breed canaries and those of other strains. The measurement of CAP audiograms showed that the hearing deficit is already present at the level of the auditory nerve (Gleich and Dooling, 1992). Here we show gross abnormalities in the anatomy of the basilar papilla of Belgian Waterslager canaries at the level of the hair cell. The extent of these abnormalities was correlated with the amount of hearing deficit as measured behaviorally.

Acoustic Stimulation↗
PubMed1994

Excitation patterns in the starling cochlea: a population study of primary auditory afferents.

The excitatory effect of different test stimuli was quantified in a large sample of primary auditory units of the starling. In order to construct an excitation pattern, the level of excitation in many single units in response to a specific test stimulus was plotted as a function of their characteristic frequency (CF). The effects of stimulus frequency and stimulus sound-pressure level on the shapes of the excitation patterns were characterized by measuring excitation patterns in response to 33 different test stimuli which covered a range of frequencies (0.125 to 2.0 kHz) and sound-pressure levels (20 to 90 dB SPL). In contrast to the mammalian situation, excitation patterns in the starling showed a systematic asymmetry with the high-frequency side being, on average, twice as steep as the low-frequency side. In addition, the sound-pressure level had no systematic effect on the symmetry or on the high- and low-frequency slopes of the flanks of the excitation patterns. Thus, the nonlinear growth of excitation with increasing sound-pressure level that is typical for the high-frequency flank of mammalian excitation patterns, was not found in the starling. The differences in mammalian and avian excitation patterns are probably related to systematic differences in tuning characteristics of the respective hearing organs.

Animals↗
PubMed1993

The diameters of guinea pig auditory nerve fibres: distribution and correlation with spontaneous rate.

In the mammalian auditory nerve physiological recordings revealed that the spontaneous discharge rate of single auditory fibres correlates with the diversity of input-output functions which may be important for intensity discrimination (e.g., Sachs and Abbas, 1974, Liberman, 1978; Winter et al., 1990). In this study we determined if the spontaneous discharge rate of auditory nerve fibres in the guinea pig is correlated with an anatomical feature, namely the diameter of the respective fibres. The diameter of myelinated (Type I) guinea pig auditory nerve fibres was measured after staining with different techniques. Measurements were made on semithin sections using a video image analysis system. The diameters of fibres stained with toluidine blue from the portion of the auditory nerve containing fibres from the basal turn of the cochlea were found to have a normal distribution. Fibres were also labelled with horseradish peroxidase by bulk injection into the spiral ganglion. It was found that the presence of horseradish peroxidase within the fibres reduced the measured diameter in comparison to adjacent unlabelled fibres. A number of fibres were physiologically characterized with respect to spontaneous discharge rate and subsequently intracellularly labelled with horseradish peroxidase. Fibre diameter of a selected sample of intracellularly fibres was measured over a distance of 800 microns within the internal auditory meatus. At the positions nearest to the spiral ganglion fibres possessing low spontaneous rates were found to have smaller diameters than high spontaneous rate fibres. No difference in fibre diameter was found for the positions near the cochlear nucleus.

Animals↗
PubMed1991

Activity patterns of primary auditory-nerve fibres in chickens: development of fundamental properties.

We have examined the activity patterns of single auditory-nerve fibers in the chicken and tested for possible changes during post-hatching development. For this purpose, we recorded from fibres in the cochlear ganglion of chickens of two age groups (about P2 and P21) and investigated their spontaneous and sound-evoked activity patterns under nembutal-chloralhydrate anaesthesia. The spontaneous activity of primary auditory neurones was irregular, the average rates were between 20.5 (P2) and 23 (P21) spikes/s. Many low-frequency fibres from both age groups showed preferred intervals in their spontaneous activity. Tuning characteristics, including the range of characteristic frequencies, the presence of primary and two-tone suppression, the slopes of tuning-curve flanks and Q10dB values were similar to those previously reported for the starling and were statistically indistinguishable between the two age groups. However, there was a difference in fibre thresholds at the highest frequencies. Systematic differences were also present between the two age groups with regard to some characteristics of the rate-intensity functions. These data indicate that whereas the tuning properties of primary auditory fibres of the chicken cochlea are mature as early as post-hatching day 2, the intensity functions are not.

Acoustic Stimulation↗
PubMed1990

Effects of L-glutamate on auditory afferent activity in view of its proposed excitatory transmitter role in the mammalian cochlea.

This report describes the effects of L-glutamate (Glu) introduced into the perilymph of scala tympani on the spontaneous and tone-evoked activity of guinea pig single primary auditory afferents. Concentrations below 2 mmol/l were in general ineffective, while a concentration of 5 mmol/l caused a marked decrease of the neural activity. At 2 mmol/l, roughly 60% of the Glu-perfusions were effective and produced a variety of changes. The most prominent effect was a reduction of the tone-evoked activity without a change in spontaneous rate. Indeed, in some cells, the tone-evoked activity could be almost totally abolished without affecting the spontaneous activity. More rarely observed was a moderate, generally transient increase of the spontaneous activity which was occasionally followed by a decrease in both tone-evoked and spontaneous firing rate. The increase in firing rate was always small relative to the maximum discharge rate evoked by tone stimuli. Desensitization of the Glu-evoked response without an obvious change in the spontaneous activity was also found. In a few cells Glu caused a reduction of the discharge rate below the spontaneous firing rate during loud tone presentation. Higher Glu doses generally caused a reduction of spontaneous and tone-evoked activity without any sign of a preceding increase. Thus, the effects of Glu in the mammalian cochlea appear to be complex and on balance seem inconsistent with the effects predicted for an excitatory transmitter. The findings argue against the hypothesis that Glu is the afferent transmitter released by inner hair-cells. However, the results do not exclude an involvement of Glu as a neuromodulator or co-transmitter.

Acoustic Stimulation↗
PubMed1989

Auditory primary afferents in the starling: correlation of function and morphology.

Despite the independent evolution of birds and mammals, a number of structural similarities of their hearing organs have developed in parallel. By tracing the peripheral origin of functionally-characterized primary neurons, the present study demonstrates functional similarities between the respective hair cell populations of the hearing organs of birds and mammals. The space devoted to one octave on the starling's basilar papilla is not constant over the whole length; rather it increases from the apical low- to the basal high-frequency end. The finding that (with the exception of a specialized area near the apical end) only tall hair cells situated on the neural limbus receive active afferent innervation is a functional parallel to the mammalian inner hair cells. The thresholds of afferents increase with distance of the related hair cells from the neural side of the papilla and cover a range of more than 50 dB within the area of tall hair cells.

Acoustic Stimulation↗
PubMed1989

The organization of tip links and stereocilia on hair cells of bird and lizard basilar papillae.

Auditory papillae from three species of bird (pigeon, starling, and chick), and two species of European lizard (Podarcis muralis and Podarcis sicula) were examined by scanning electron microscopy. Hair bundles from all papillae showed tip links oriented along the direction of gradation in heights of the stereocilia (i.e. parallel to the hair-cell axis of bilateral symmetry, and so parallel to the excitatory-inhibitory axis for mechanotransduction). This orientation was seen irrespective of the overall orientation of the hair bundle within the papilla. The stereocilia formed columns, joined by the tip links, which ran parallel to the hair-cell axis of bilateral symmetry. The stereocilia within the same column tended to stay together, while those in different columns tended to separate during preparation. In many columns all the stereocilia tended to be a little taller, or a little shorter, than the equivalent stereocilia in adjacent columns, suggesting that all the stereocilia within one column had been affected by a common height determinant during development. In addition, links running laterally between stereocilia were seen, in a band near the base of the stereocilia. The results are consistent with the hypothesis that tip links are a universal feature of mechano-transducing acousticolateral hair cells, and that they are involved in sensory transduction. The results also support suggestions that the tip links may play a role in determining the heights of the stereocilia during development.

Animals↗
PubMed1988

Quantitative morphological analysis of the sensory epithelium of the starling and pigeon basilar papilla.

Several features of bird basilar papilla morphology were quantitatively studied in the starling and the pigeon in order to attempt a structure-function correlation. We confirmed and quantified several findings from earlier studies, but also obtained results contradictory to previous reports. The greatest discrepancies concerned the pattern of hair cell orientation. By including the results from other investigations, we describe a 'typical' avian basilar papilla and on this basis the specializations within individual species. These morphological specializations are discussed in the context of the available physiological data.

Animals↗
PubMed1988

The phase response of primary auditory afferents in a songbird (Sturnus vulgaris L.).

The effects of stimulus frequency and intensity on phase-locking characteristics of cochlear ganglion cells were studied in the starling. All cells showed phase-locking to tone stimuli within their response area. Phase-locking at CF is found on average 9 dB below discharge rate threshold. Phase-locking is best at 0.4 kHz and deteriorates with increasing frequency almost independently of CF. No phase-locking was evident for test frequencies above 3-4 kHz. Phase-locking in cells with CFs above 1.0 kHz is better below CF than at CF. For constant sound pressure, an increase in stimulus frequency always produced an increase in phase lag of the neural response. The phase vs. frequency data obtained at constant sound pressure can be reasonably approximated by straight line functions. The slopes of these functions indicate the latency of the neural response, and are correlated with the CFs of the respective cells; the latency tends to be longer in low-CF cells and shorter in high-CF cells. The latency decreases by 0.04 ms per 1 dB sound pressure increase. The response phase at CF is nearly stimulus level-independent. Increasing stimulus intensity causes increasing phase lag below CF and decreasing phase lag above CF. These results are compared to findings in other vertebrates and demonstrate the similarities of phase-locking characteristics despite the substantial anatomical differences among the vertebrate groups.

Animals↗
PubMed1985

Activity patterns of cochlear ganglion neurones in the starling.

Spontaneous activity and responses to simple tonal stimuli were studied in cochlear ganglion neurones of the starling. Both regular and irregular spontaneous activity were recorded. Non-auditory cells have their origin in the macula lagenae. Mean spontaneous rate for auditory cells (all irregularly spiking) was 45 spikes s-1. In half the units having characteristic frequencies (CFs) less than 1.5 kHz, time-interval histograms (TIHs) of spontaneous activity showed regularly-spaced peaks or 'preferred' intervals. The spacing of the peak intervals was, on average, 15% greater than the CF-period interval of the respective units. In TIH of lower-frequency cells without preferred intervals, the modal interval was also on average about 15% longer than the CF-period interval. Apparently, the resting oscillation frequency of these cells lies below their CF. Tuning curves (TCs) of neurones to short tone bursts show no systematic asymmetry as in mammals. Below CF 1 kHz, the low-frequency flanks of the TCs are, on average, steeper than the high-frequency flanks. Above CF 1 kHz, the reverse is true. The cochlear ganglion and nerve are tonotopically organized. Low-frequency fibres arise apically in the papilla basilaris and are found near non-auditory (lagenar) fibres. Discharge rates to short tones were monotonically related to sound pressure level. Saturation rates often exceeded 300 spikes s-1. 'On-off' responses and primary suppression of spontaneous activity were observed. A direct comparison of spontaneous activity and tuning-curve symmetry revealed that, apart from quantitative differences, fundamental qualitative differences exist between starling and guinea-pig primary afferents.

Acoustic Stimulation↗
PubMedDate not supplied

Cobalt labelling of single primary auditory neurones: an alternative to HRP.

We have labelled single, primary auditory neurones in three reptile and one bird species. After functional characterization of the neurones, hexamminecobaltic chloride was iontophoretically injected through the recording micropipette. Precipitation of cobalt sulfide followed by silver intensification of the cochlear duct as a whole-mount preparation revealed stained neurones in over 90% of cases. This method has several advantages over labelling with HRP.

Animals↗
PubMedDate not supplied

The postnatal growth of cochlear nucleus subdivisions and neuronal somata of the anteroventral cochlear nucleus in the Mongolian gerbil (Meriones unguiculatus).

We have analysed the postnatal volume increase of the cochlear nucleus subdivisions from birth to senescence in the Mongolian gerbil. All subdivisions showed the most prominent growth in the 2nd week of life before the onset of hearing on day 12. After the onset of hearing, the dorsal and the postero-ventral portion of the cochlear nucleus showed only a moderate degree of further growth. The antero-ventral cochlear nucleus, however, almost doubled in volume after the onset of hearing, reaching a maximum in 4-month-old animals. In ageing gerbils, we observed a small but systematic reduction of the cochlear nucleus volume. To further assess which elements contribute to the growth of the antero-ventral cochlear nucleus after the onset of hearing, we analysed the somal size of the neurones. Before the onset of hearing, somal and volume growth were highly correlated. However, somata had reached an adult size by the onset of hearing. We conclude that the growth of the antero-ventral cochlear nucleus after the onset of hearing is due to changes in the neuropil.

Age Factors↗
PubMedDate not supplied

Age-dependent effects of the onset of a conductive hearing loss on the volume of the cochlear nucleus subdivisions and the expression of c-fos in the mongolian gerbil (Meriones unguiculatus).

A monaural conductive hearing loss was induced by interrupting the chain of the middle ear ossicles on the right side in gerbils of four different age groups (P12-14, P20-21, P42 and P84). The volumes of the cochlear nucleus subdivisions and the number of cells that expressed immunoreactivity for c-fos after noise stimulation were determined on the left and right side in the deprived animals, and in undeprived control animals when they reached the age of 6 months. The anteroventral cochlear nucleus on the deprived side was reduced in volume when the deprivation started before the age of 3 months. The other cochlear nucleus subdivisions showed no systematic age-dependent reductions. The expression of c-fos in the dorsal cochlear nucleus appeared more resistant to a hearing loss, with deprivation being more effective in younger animals. c-fos expression was also dramatically reduced in the ventral cochlear nucleus, regardless of age at the onset of hearing loss.

Acoustic Stimulation↗