Biomedical subjects

G A Manley

Publications and source records attributed to G A Manley.

At least 19 recordsLinked to original sources

PubMed1996

Brainstem connections of the macula lagenae in the chicken.

The macula lagenae, an otolithic hair-cell organ with probable vestibular function, lies close to the apical end of the avian auditory hair-cell epithelium, the papilla basilaris. In an earlier study in the pigeon in which lesioning techniques were used, Boord and Rasmussen ([1963] J. Comp. Neurol. 120:463-473) reported finding a projection of lagenar fibers to parts of the cochlear nuclei (nucleus magnocellularis and nucleus angularis). Subsequent to this report, it has been generally assumed that at least part of the cochlear nuclei has a vestibular or a combined vestibular-auditory function. In this study, we labeled fibers innervating the macula lagenae of the chicken by using a lipophilic fluorescent tracer. The analysis of Vibratome sections of the brainstem with epifluorescence illumination showed no projection to the cochlear nuclei. In cases in which the apical part of the papilla basilaris was contaminated with tracer, however, we found labeling of the cochlear nuclei in the same areas as described with the lesioning technique in the pigeon. Our results thus imply that there is no processing of information from the macula lagenae in the cochlear nucleus of the chicken. In addition, we studied the origin of the few labeled efferent neurons in the brainstem. The location of all somata encountered was restricted to an area medial to the nucleus facialis dorsalis and corresponded to the dorsal efferent cell group, from which efferents to other vestibular organs also originate.

Afferent Pathways↗

PubMed1996

Surface morphology of basilar papilla of the tufted duck Aythya fuligula, and domestic chicken Gallus gallus domesticus.

Quantitative details of the surface morphology of the hearing organ, the Papilla basilaris, as seen in the scanning electron microscope are described for the tufted duck Aythya fuligula and for comparison for the domestic chicken Gallus gallus domesticus, for which some published information is already available. As in the other avian species investigated to date, each papilla shows a unique constellation of features. The papilla of the tufted duck is 3.5 mm long in the unfixed state and contains 8,200 sensory hair cells. It shows systematic changes in its surface features along the length and across the width of the sensory epithelium. In general, its features and those of the chicken Papilla basilaris can be described as relatively primitive in comparison with other species. The tufted duck papilla does, however, show one feature that has so far been found to be well developed only in advanced papillae; the number of stereovilli per hair cell bundle is generally much higher on hair cells of the neural than those on the abneural side. This difference is only weakly developed in the chicken. It is clear that features considered to be evolutionarily advanced were acquired independently of one another during evolution and that each bird species can show a mosaic of primitive and advanced features.

Animals↗

PubMed1996

Spontaneous otoacoustic emissions in two gecko species, Gekko gecko and Eublepharis macularius.

Spontaneous otoacoustic emissions (SPOAE) of the gecko species Gekko gecko and Eublepharis macularius appear as broad spectral peaks (bandwidth 44 to 170 Hz) between 1 and 4.5 kHz that have peak levels of -7 to 10 dB SPL. Most ears showed SPOAE at many frequencies. In some ears, the peaks were superimposed on a broad baseline emission. The instantaneous frequency of any emission varied rapidly within its bandwidth limits and frequencies in the center of the band occurred most commonly, but not with higher levels than frequencies on the periphery of the band. SPOAE were temperature dependent, rising in frequency with an increase in temperature and falling with a decrease in temperature (rate of change from 54 to 107 Hz/degrees C), with no systematic changes in peak level except that at the temperature extremes, the SPOAE disappeared into the noise. External tones suppressed SPOAE peak level in a frequency-dependent way. Isosuppression tuning curves were V-shaped. In restricted frequency ranges, facilitation also occurred. External tones also caused shifts in the frequency of SPOAE; frequency "pushing" was more common than "pulling." The maximal frequency shift observed was 313 Hz. In general, the SPOAE characteristics strongly resemble those already reported in the bobtail lizard Tiliqua rugosa.

Animals↗

PubMed1995

A model of frequency tuning in the basilar papilla of the Tokay gecko, Gekko gecko.

This paper uses the quantitative details of the anatomy of the auditory papilla in the Tokay gecko Gekko gecko (as described in the companion paper) to make a quantitative model predicting the tonotopic organization of two of the three papillar areas. Assuming that hair-cell bundle stiffness is similar to that of other species, a model of resonance frequencies for the apical areas of the papilla was constructed, taking into account factors such as the number of hair cells per resonant unit, their bundle dimensions, the volume of the tectorial mass, etc. The model predicts that the apical pre- and postaxial areas, although anatomically adjacent, respond to different frequency ranges, a phenomenon not yet reported from any vertebrate. The model predicts that together, these areas respond best to frequencies between 1.1 and 5.3 kHz, close to the range found physiologically [Eatock et al. (1981) J. Comp. Physiol. 142, 203-218] (0.8 to 5 kHz) for the high-frequency range for this species. Only physiological experiments tracing responses to specific papillar nerve fibres can confirm or refute these interesting predictions of the model. The model also indicates that, compared to free-standing hair-cell bundles, the semi-isolated tectorial structures called sallets not only lower the range of characteristic frequencies but also increase the frequency selectivity of the attached hair cells.

Acoustic Stimulation↗

PubMed1995

Distortion-product otoacoustic emissions and their anaesthesia sensitivity in the European starling and the chicken.

The aim of the present experimental series was to provide further information on the distortion-product otoacoustic emissions (DP) of birds and contribute to a general understanding of DP generation. Basic characteristics of the DP 2f1-f2 and 2f2-f1 were measured in the ear canal of both awake and anaesthetized European Starlings and chickens. The effect of a third suppressive tone and the behaviour of the DP under anaesthesia were also studied. In general, the DP characteristics of both bird species resembled those of lizards and mammals, but first appeared at somewhat higher primary-tone levels. The best frequencies of third tones suppressing 2f1-f2 lay near the first primary tone (f1), but for 2f2-f1, the situation was more complex. Facilitation via a third tone was also seen for both DP, often at levels below those eliciting suppression. The DP 2f1-f2 disappeared completely at the onset of deep anaesthesia and recovered to its original magnitude when the anaesthesia was lightened, sometimes with a considerable delay. The compound action potential (CAP) was somewhat more sensitive to anaesthesia than the DP. Control experiments showed that the anaesthesia effect was not a result of hypoxia. Avian DP at low and intermediate sound levels are thus physiologically-sensitive manifestations of normal hair-cell function that are, in contrast to mammals, also anaesthesia-sensitive.

Acoustic Stimulation↗

PubMed1995

Filtering of distortion-product otoacoustic emissions in the inner ear of birds and lizards.

When the output magnitude of more than one order of distortion-product otoacoustic emission (DPOAE) is measured, they reach their maximum at the same DPOAE frequency. This fact led several authors to the assumption that, subsequent to their generation in the cochlea, the DPOAE are band-pass filtered. It was suggested that the tectorial membrane is the structure responsible for this filtering. In this report, we show that the same kind of "DPOAE tuning' is shown by animals which have hearing organs with tectorial structures of very different morphology, or even with no tectorial membrane at all. We therefore conclude that it is unlikely that the filter is the tectorial membrane.

Acoustic Stimulation↗

PubMed1995

The lessons of middle-ear function in non-mammals: improving columellar prostheses.

Due to the simplicity of their manufacture and placement, middle-ear prostheses are generally constructed using only a single 'ossicle'. The variety of pathologies frequently make it necessary to devise individual solutions and the results are often unsatisfactory. Many methods of improving the prostheses have been tried, with very mixed results. Even until recently, the fundamental assumptions underlying the use of single-ossicle, or columellar, prosthesis have been questioned, with suggestions that this type of prosthesis should be abandoned in favour of attempts to reconstruct a true three-ossicle middle ear. As some of the assumptions in the literature regarding columellar middle ears are incorrect and some published information is not easily accessible, a brief review of pertinent details of non-mammalian systems is given here.

Animal Population Groups↗

PubMed1995

[Indications of continuous hair cell regeneration in a song bird with genetically-induced cochlear hearing loss].

In recent years evidence has accumulated that birds in contrast to mammals have a great capacity to replace lost hair cells after cochlear trauma. Despite this capacity for cochlear repair, a hereditary hearing deficit for frequencies above 2 kHz has been described in a peculiar strain of canaries (Belgian Water-slagers). Because previous thresholds were determined by psychophysical methods, the origin of the hearing loss could not be identified. In order to determine if this loss originated in the cochlea and if these birds lack the potential for hair cell regeneration, we carried out physiological and morphological analyses of the hearing organ. Our results showed that most of the hair cells displayed severe pathologies. Also, found were small, microvilli-covered cells that resembled forms described during normal hair cell development. Small microvilli-covered cells with small sterovillar bundles have been described as regenerating hair cells in other birds after severe cochlear insults. These observations indicate that adult Belgian Waterslager canaries continuously produce new cochlear hair cells. They do not, however, succeed in reforming a normal basilar papilla. We believe that these birds are a promising model for future studies of cochlear hair cell repair mechanisms.

Animals↗

PubMed1994

Mechanical and electromechanical properties of the stereovillar bundles of isolated and cultured hair cells of the chicken.

Isolated single chicken hair cells and pieces of epithelium without the tectorial membrane, either freshly isolated or in tissue culture, were studied using water-jet stimulation of their stereovillar bundles and current injection. Responses were measured under enhanced video-microscopic observation or while using a differential photodiode technique sensitive down into the nanometer range. When stimulated with a water jet at low displacement amplitudes up to about 200 nm, the stereovillar bundle displacement was asymmetrical, indicating a lower stiffness in the excitatory direction, but the reverse was true at higher displacement amplitudes. Undamaged bundles showed no mechanical resonances below 1 kHz. In damaged bundles, however, such resonances were prominent and accompanied by splaying of the stereovilli. Hair cells in the epithelium showed small bundle movements (0.6 nm/mV) whose polarity depended on the polarity of the injected current. These movements probably resulted from activation of the bundle's adaptation motors.

Animals↗

PubMed1994

Cochlear and lagenar ganglia of the chicken.

Cochlear and lagenar components of the statoacoustical ganglion in the inner ear of one chicken were studied quantitatively in the TEM. Both myelinated and unmyelinated nerve fibers were present in these two parts of the ganglion and in a putative efferent bundle within the ganglion. The cochlear portion had the lowest, the efferent bundle the highest percentage of unmyelinated fibers. Compared to the other parts of the ganglia, the cochlear fibers had a high degree of homogeneity, especially in fiber size. Some gradients in the baso-apical direction were found, such as an increase in the size of myelinated cochlear fibers from the base to the apex. Based on the ultrastructure of cellular components, no distinct populations of cell bodies within the statoacoustical ganglion were definable. The ganglion contained some 8,000 cochlear and about 1,200-2,000 lagenar neurons. The putative efferent bundle had only 150-200 fibers. This cannot be the total number of efferents to the hair cells in both the basilar papilla and the lagenar. A large number of efferent fibers to the auditory papillae presumably run mingled among the afferent fibers.

Animals↗

PubMed1994

The cuticular plate of the hair cell in relation to morphological gradients of the chicken basilar papilla.

The aim of the present study was to provide details on the diversity and morphological gradients in the anatomy of the cuticular plate of hair cells in the chicken basilar papilla. The structure of the cuticular plate, which is mainly made up of a network of actin filaments, may be related to differences in the mechanical demands on the anchorage of the stereovillar bundle. We describe the morphological gradients in the cuticular plates as seen in transverse section for four positions along the basilar papilla. Three different shapes of cuticular plate could be distinguished. In general, cuticular plates in neurally-lying hair cells have their main mass on the neural side of the cells; for abneural cells, the converse is true. The shape of the plates changes gradually across the papilla; symmetrical forms exist. The hair-cell bundle orientation (and thus the preferred direction of stimulation of the bundle), as measured using scanning EM preparations, does not correlate with the shape of the plate in transverse section. The present data confirm the notion developed from other studies that (1) there are no distinct populations of hair cells, (2) there are no linear or monotonic morphological gradients, and (3) the gradients on the papilla are species- and position-specific.

Actins↗

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

Spontaneous otoacoustic emissions in the bobtail lizard. II: Interactions with external tones.

The response of spontaneous otoacoustic emissions to the presentation of external tones was studied in the Australian bobtail lizard. Three basic types of effects were observed: suppression (a reduction in the emission's amplitude), facilitation (an increase in the emission's amplitude) and frequency shifting. The suppressive effect was highly frequency selective. Iso-suppression tuning curves resembled the rate-threshold tuning curves of the high-frequency population of VIIIth nerve fibres in this species. The frequency with the lowest threshold for suppression corresponded, on average, to the emission's own frequency and did not show any systematic deviation from it. Facilitation of between 2 and 10 dB occurred, but only in response to frequencies within certain narrow ranges, and at sound pressure levels below those that suppressed. The most commonly-observed facilitation range lay between 0.2 and 0.6 octaves above the emission's own frequency and coincided in frequency with a characteristic notch in the iso-suppression tuning curve. In the same narrow frequency range, the input/output functions of amplitude suppression always showed a pronounced increase in slope. The emissions moved their own frequency away from that of an external tone. The observed shifts were comparatively large (up to -330 Hz) and were more pronounced in the downward direction.

Acoustic Stimulation↗

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↗

PubMed1994

Physiology of single putative cochlear efferents in the chicken.

1. An experimental approach was developed that allowed recording of neurophysiological activity from single putative cochlear efferents in the auditory brain stem of anesthetized chickens with the use of glass micropipettes. The aim of this study was to study spontaneous and tone-evoked activity from single efferent neurons in the chick and to compare their properties with those of other vertebrate hair cell organs. Because the birds, like mammals, have a complex hearing organ with different hair cell types and different afferent and efferent innervation, the purpose of this study was also to determine whether different types of efferents exist. 2. In the same electrode penetrations, putative trapezoid fibers were also isolated. In addition, the penetration angle permitted recordings from units in both cochlear nuclei, nucleus magnocellularis and nucleus angularis (probably mostly cochlear afferents), in the same animal. This allowed monitoring of the auditory sensitivity of the individual animal during the experiment. With the use of physiological criteria, it was possible to distinguish between trapezoid fibers and putative cochlear efferents. Possible alternative origins of the responses described are discussed. 3. Tuning curve characteristics of putative efferents were determined. They were as sensitive as ascending auditory neurons. Q10 dB values of efferent tuning curves were < 2.5 and thus showed poorer frequency selectivity than ascending fibers; in some cases they covered the entire hearing range of the chicken. 4. Latencies to tone pips were different for ascending neurons and putative efferent units. For trapezoid fibers and neurons from the cochlear nuclei, latencies usually did not exceed 5 ms, whereas latencies of efferents were always longer. 5. Because of the interaural canal that connects both middle ear cavities in birds, the measurement of the lateralization of the efferents was difficult. In any case, the majority of putative cochlear efferents responded more sensitively to sound stimulation of the contralateral side. 6. Of the efferent units, 28% showed no spontaneous activity. The others either showed regular spontaneous activity, or their time-interval histograms showed longer modes than ascending fibers. In general, mean spontaneous activity was lower than in ascending fibers, being < 30 spikes/s. 7. In contrast to reports from mammalian studies, in which efferents only showed on peristimulus time (PST) response pattern to tonal stimuli (chopper), two different response types were found in this study: two excitation types (chopper and primary-like) and one suppression type.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

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↗

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↗

PubMed1991

Innervation patterns and spontaneous activity of afferent fibres to the lagenar macula and apical basilar papilla of the chick's cochlea.

To investigate the origin of non-auditory fibres in the apical area of the avian cochlear ganglion, we recorded from nerve fibres in the young chick (87% of animals were aged between 5 and 10 days post-hatching). After characterization of their spontaneous activity patterns and, if present, their responses to sound, some fibres were stained with cobalt-ion injections and traced to their peripheral terminals. All stained fibres which were traced to the lagenar macula (N = 13) were non-auditory. They did not increase firing rate or phase-couple to sound stimuli. Their spontaneous activity was either regular (12 cases) or irregular (1 case). Regularly-firing cells all innervated several to very many hair cells, whereby there was no great difference in the pattern of spontaneous activity between those making calyx endings on relatively few hair cells in the striola region and those making small bouton endings on up to 80 hair cells outside the striola. All fibres that responded in any way to sound were irregularly spontaneously active. Three fibres, two of which only responded to sound with phase-coupling, innervated several hair cells in the apical, abneural region of the basilar papilla. Two other fibres traced to the basilar papilla are of previously undescribed types.

Acoustic Maculae↗