Biomedical subjects

C Köppl

Publications and source records attributed to C Köppl.

26 records · Page 2Linked to original sources

PubMed1994

Spontaneous otoacoustic emissions in the bobtail lizard. III: Temperature effects.

Spontaneous otoacoustic emissions (SOAE) in the ear canal of the Australian bobtail lizard are temperature sensitive. They shift their frequency up with an increase in temperature, an effect that is fully reversible. The degree of shift is dependent not only on the center frequency of the SOAE (lower-frequency SOAE show a smaller shift) but also on the temperature range in question. Rates of change of frequency are 0.014 to 0.04 oct/degrees C at 30 degrees C, and twice that at 22 degrees C. There was no strong and consistent effect of temperature on SOAE amplitudes. The above findings are very similar to those on the effect of temperature on SOAE of frogs and mammals. Suppression tuning curves of SOAE shifted with temperature, the largest effects being near the center frequency in the tuning-curve's tip region.

Animals↗

PubMed1993

Spontaneous otoacoustic emissions in the bobtail lizard. I: General characteristics.

Spontaneous otoacoustic emissions in the external ear canal of the bobtail lizard were identified on the basis of their consistent presence, their temperature- and hypoxia-dependence, and their suppressibility by external tones. They were found in 86% of ears investigated, and each ear generated on average 10 emissions. Their sound-pressure levels lay between -10 and 9.3 dB SPL, and their centre frequencies between 0.93 and 4.61 kHz at 30 degrees C body temperature. Previous studies have shown that these frequencies are processed in the basal basilar-papillar segment by hair-cell areas that are strictly bidirectionally oriented and are covered by tectorial sallets. In contrast, no spontaneous otoacoustic emissions were found in the frequency range known to be processed by the apical, low-frequency segment of the basilar papilla. The mean frequency distance between emissions varied systematically across the frequency range in a way consistent with the hypothesis that they are generated by anatomically-defined groups of hair cells and their tectorial sallets. The 3dB-bandwidth of the emissions depended on their amplitude above the noise, but was at least 9 Hz.

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

Morphology of the basilar papilla of the bobtail lizard Tiliqua rugosa.

The morphology of the basilar papilla of the bobtail lizard was investigated with standard light- and scanning-electron-microscopical methods. The papilla can be subdivided into two parts: a small apical segment which is rather uniform in structure and a long basal segment which displays various systematic changes along its length, for example in the density of the hair cells, the height and shape of the hair-cell stereovillar bundles, the number of stereovilli per bundle and the size of the tectorial structure. In addition, the tectorial structures overlying the two segments are very different in size and morphology. Both tectorial structures are probably sensitive to changes in their ionic environment. The possible functional implications of the papillar morphology described here are discussed with respect to a model of frequency tuning in the bobtail lizard.

Animals↗

PubMed1988

The basilar papilla of the barn owl Tyto alba: a quantitative morphological SEM analysis.

The barn owl has the longest basilar papilla (about 12 mm) of all bird species studied. In the apical half several morphological parameters change regularly: stereovillar number per hair cell, length of the stereovillar bundle and cell surface area decrease from basal to apical. Cell number across the papilla, width of stereovillar bundle, diameter of a single stereovillus and height of stereovilli increase in the same direction. The orientation of the stereovillar bundles' long axis is parallel (0 degrees) to the edges of the papilla at the neural and the abneural sides, whereas along the midline there is a zone with an orientation of 50 degrees towards the apex; apically, this change in orientation may increase up to 90 degrees. In the basal half of the owl papilla the situation is different: most parameters are fairly constant, e.g. stereovillar height, mean orientation of stereovillar bundles (0 degrees), bundle shape and stereovillar number per hair cell. As the basilar papilla of birds is known to be tonotopically organized, with the high frequency range being represented basally, the different organization of the basal half of the owl papilla may be a specialization related to the excellent high frequency hearing.

Animals↗

PubMed1988

Auditory peripheral tuning: evidence for a simple resonance phenomenon in the lizard Tiliqua.

The origin of the frequency selectivity of neurons in the vertebrate auditory periphery is one of the most important questions in auditory research today. In an attempt to delineate the extent to which structures outside the sensory cells play a role in determining peripheral auditory responses, we measured the mechanical displacement of the basilar membrane and the selectivity of nerve fibres at the same location in the bobtail lizard. These data indicate a contribution to frequency selectivity, the tuning of which resembles a high-pass resonant filter characteristic, arising subsequent to the basilar membrane motion. A comparison of these data with the tuning of auditory-nerve fibres originating from papillar areas in other lizard species without a tectorial membrane, suggests that it is the involvement of the tectorial membrane in a mechanical resonance which increases the frequency selectivity.

Acoustic Stimulation↗

PubMed1988

A neural map of interaural intensity differences in the brain stem of the barn owl.

The nucleus ventralis lemnisci lateralis pars posterior (VLVp) is the first binaural station in the intensity-processing pathway of the barn owl. Contralateral stimulation excites and ipsilateral stimulation inhibits VLVp cells. The strength of the inhibition declines systematically from dorsal to ventral within the nucleus. Cells selective for different intensity disparities occur in an orderly sequence from dorsal to ventral within each isofrequency lamina. Cells at intermediate depths in the nucleus are selective for a particular narrow range of interaural intensity differences independently of the absolute sound-pressure level. A simple model of the interaction between inhibition and excitation can explain most of the response properties of VLVp neurons. The map of selectivity for intensity disparity is mainly based on the gradient of inhibition.

Animals↗

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↗