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Biomedical subjects

G A Manley

Publications and source records attributed to G A Manley.

At least 55 records · Page 3Linked to original sources
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 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↗
PubMed1987

Developmental stability of the tonotopic organization of the chick's basilar papilla.

In the past, the damage patterns produced on the papilla of the chick by loud pure tones of different frequencies have been used to study the development of sound analysis by the hair cells of the basilar papilla. One conclusion from these data was that the best response frequency of individual hair cells changes substantially with age. However, this method has been criticized as unreliable. Now experiments have been performed in which single characterized nerve fibers were stained with horseradish peroxidase to permit the unequivocal localization of specific frequency responses in the papillae of chicks of different ages (2 and 21 days after hatching). There was no statistically significant change in the tonotopic organization of the papilla between the two groups of animals.

Aging↗
PubMed1987

Otoacoustic emissions in a song bird.

Synchronously evoked otoacoustic emissions (SEOAEs) were found in about two thirds (61%) of 56 ears of the starling Sturnus vulgaris. They appeared with rather broad synchronization widths (about 200 Hz) and predominantly at frequencies in the upper half of the hearing range of this bird. SEOAEs varied in level from below -30 dB to 2 dB SPL and showed typically nonlinear intensity functions. The emissions were present even following extirpation of the middle-ear muscle and could be suppressed by anaesthetics. Using Halothane, it was possible to determine the time course of this suppressive effect. Using second tones, typical iso-suppression tuning curves were obtained. The similarities and differences between the characteristics of these SEOAEs and emissions in other nonmammals and in mammals are discussed with regard to anatomical differences in inner-ear structure.

Acoustic Stimulation↗
PubMed1987

Potassium concentration in the inner sulcus is perilymph-like.

Using potassium-selective microelectrodes and an improved observation technique, it is shown that the potassium concentration in the fluid of the inner sulcus of the guinea pig is like that of perilymph. The implications for the common concepts about the role of potassium in the cochlea are discussed.

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↗
PubMed1980

Organ of Corti: observation technique in the living animal.

This paper describes a new technique for visualizing the organ of Corti in the living guinea pig. The various cell types and blood supply can be viewed at magnifications up to 625X through a microscope, as seen reflected by a tiny mirror in scala vestibuli. Glass microelectrodes can also be seen as they penetrate the tissues, and can be accurately localized.

Animals↗
PubMed1976

Analysis of spontaneous activity of auditory neurones in the spiral ganglion of the guinea-pig cochlea.

1. Spontaneous activity of single afferent neurones in the cochlea of the guinea-pig was studied by measurement of mean rates and computation of interspike interval histograms. 2. The shapes of interval histograms agreed with those found in cat cochlear nerve fibres. Modes of the histograms were less than 7 msec for all cells with mean rates ranging from 20 to 150 spikes/sec. 3. The distribution of mean rates showed higher maximum rates than those found in cat. Cells from animals with abnormally high thresholds showed lower mean rates than those from sensitive animals. 4. No correlation was found between mean spontaneous rate and sensitivity to acoustic stimulation. No discrete populations of cells could be discerned on any of the criteria used. 5. The simultaneous effects of hypoxia on cell thresholds, mean spontaneous rate and scala media potentials are reported. These and other results are discussed in relation to possible sites of generation of spontaneous activity in primary auditory afferents.

Action Potentials↗