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PubMed1977

Echo-detecting characteristics of neurons in inferior colliculus of unanesthetized bats.

Neurons in the inferior colliculus of echolocating bats responded well to two stimuli presented in close temporal sequence. Favorable recovery of responsiveness was seen with stimuli having durations, intensities, and interpulse intervals similar to the natural biosonar signals reaching the ears during the various phases of echolocation. Some units responded to a subthreshold simulated echo but only when preceded by a loud initial pulse. These units appear to be specialized for echo-detection.

Action Potentials↗
PubMed2003

Effects of echo intensity on Doppler-shift compensation behavior in horseshoe bats.

Echolocating horseshoe bats respond to flight-speed induced shifts in echo frequency by adjusting the frequency of subsequent calls. Under natural conditions, Doppler effects may force the frequency of a returning echo several kilohertz above the original emission frequency. By lowering subsequent call frequencies, the bat can return echo frequencies to within a narrow spectral bandwidth to which its highly specialized auditory system is most sensitive. While Doppler-shift compensation (DSC) behavior specifically refers to frequency compensation, other parameters of the returning echo, such as delay, duration, and interaural time and intensity differences have been shown to influence DSC performance. Understanding the nature of these influences has already led to a better appreciation of the neurophysiology of DSC. Here we provide a quantitative analysis of the effects of a prominent feature of the returning echo, its intensity, on DSC performance in horseshoe bats. Although DSC performance generally tolerates echo attenuation up to approximately 40 dB relative to the outgoing emission intensity, a systematic decline in DSC performance can be observed over this range. Generally, the effects of echo attenuation are characterized by a reduction in 1) the overall amount of compensation relative to the size of the shift in echo frequency and 2) the rate at which the bat responds to perceived echo shifts. These effects appear to be the consequence of a systematic shift in the range of echo frequencies capable of inducing DSC behavior. In particular, the reference frequency (the minimum shift in echo frequency that will elicit DSC behavior) appears to be highly sensitive to echo intensity. Every 10-dB reduction in echo intensity shifts the reference upward nearly 250 Hz. Our results indicate that, even at the highest intensity levels, relatively minor changes in echo intensity critically influence frequency compensation during normal DSC. We conclude with a discussion of how these results might impact echolocation behavior of horseshoe bats under natural and experimental conditions.

Adaptation, Physiological↗
PubMed2002

Directional selectivity for FM sweeps in the suprageniculate nucleus of the mustached bat medial geniculate body.

Mustached bats emit echolocation and communication calls containing both constant frequency (CF) and frequency-modulated (FM) components. Previously we found that 86% of neurons in the ventral division of the external nucleus of the inferior colliculus (ICXv) were directionally selective for linear FM sweeps and that selectivity was dependent on sweep rate. The ICXv projects to the suprageniculate nucleus (Sg) of the medial geniculate body. In this study, we isolated 37 single units in the Sg and measured their responses to best excitatory frequency (BEF) tones and linear 12-kHz upward and downward FM sweeps centered on the BEF. Sweeps were presented at durations of 30, 12, and 4 ms, yielding modulation rates of 400, 1,000, and 3,000 kHz/s. Spike count versus level functions were obtained at each modulation rate and compared with BEF controls. Sg units responded well to both tones and FM sweeps. BEFs clustered at 58 kHz, corresponding to the dominant CF component of the sonar signal. Spike count functions for both tones and sweeps were predominantly non-monotonic. FM directional selectivity was significant in 53-78% of the units, depending on modulation rate and level. Units were classified as up-selective (52%), down-selective (24%), or bi-directional (non-selective, 16%); a few units (8%) showed preferences that were either rate- or level-dependent. Most units showed consistent directional preferences at all SPLs and modulation rates tested, but typically showed stronger selectivity at lower sweep rates. Directional preferences were attributable to suppression of activity by sweeps in the non-preferred direction (~80% of units) and/or facilitation by sweeps in the preferred direction (~20-30%). Latencies for BEF tones ranged from 4.9 to 25.7 ms. Latencies for FM sweeps typically varied linearly with sweep duration. Most FM latency-duration functions had slopes ranging from 0.4 to 0.6, suggesting that the responses were triggered by the BEF. Latencies for BEF tones and FM sweeps were significantly correlated in most Sg units, i.e., the response to FM was temporally related to the occurrence of the BEF in the FM sweep. FM latency declined relative to BEF latency as modulation rate increased, suggesting that at higher rates response is triggered by frequencies in the sweep preceding the BEF. We conclude that Sg and ICXv units have similar, though not identical, response properties. Sg units are predominantly upsweep selective and could respond to either or both the CF and FM components in biosonar signals in a number of echolocation scenarios, as well as to a variety of communication sounds.

Acoustic Stimulation↗
PubMed1978

A single-unit analysis of inferior colliculus in unanesthetized bats: response patterns and spike-count functions generated by constant-frequency and frequency-modulated sounds.

1. Single-unit activity evoked by constant-frequency (CF) and frequency-modulated (FM) sounds was recorded from the inferior colliculus of unanesthetized Mexican free-tailed bats. The FM bursts were designed to mimic the natural orientation cries emitted by this species. 2. The feature of greatest concern in this study is the response patterns evoked by acoustic signals. Four major types of response patterns are recognized: a) the phasic on patterns where up to 4 spikes were evoked with a total firing duration occurring within a period of about 5 ms, b) the on-off patterns characterized by a phasic on-response followed by a silent interval with a brief burst of impulses occurring to the off-set of the signal, c) the phasic burst patterns where the unit typically fired 3-7 spikes over a 5-10 ms (or longer) duration with the same response pattern being evoked by a wide range of signal durations, d) the tonic or sustained patterns characterized by a sustained firing whose duration faithfully followed the signal duration. 3. Constant frequency and FM signals were not equally effective for eliciting the various response patterns. While all of the major response categories and most of the subtypes were evoked with CF stimulation, FM signals, which mimicked the natural echolocation cries, evoked predominantly phasic on-responses and a much smaller number of phasic bursters. Tonic and on-off patterns were never observed with FM signals. 4. Many units exhibited a particular response pattern with CF signals which differed from the pattern evoked by FM signals. This finding demonstrated that utilizing CF signals to investigate encoding features relevant for echolocation is an inappropriate approach and can result in misleading conclusions. 5. In many electrode penetrations most units, and in some cases all units, had the same response pattern. This was observed for phasic constant-latency responders (pELRs), phasic erratic-latency responders (pELRs), phasic burst, and tonic units, and provides evidence that units having a particular response pattern are organized in vertical arrays within the volliculus. 6. Several of the response patterns were strongly correlated with a particular spike-count function. The pCLRs almost always had a steeply rising monotonic function, phasic bursters were always nonmonotonic but never upper threshold, while the tonic units typically had monotonic functions. The pELRs were heterogeneous with regard to spike counts having monotonic, nonmonotonic, and upper-threshold functions. Upper-threshold functions were observed only in pELRs.

Animals↗
PubMed1994

Frequency organization of delay-sensitive neurons in the auditory cortex of the FM bat, Myotis lucifugus.

1. The little brown bat, Myotis lucifugus, employs biosonar pulses containing broadband frequency-modulated (FM) sounds of only one harmonic during the initial phases of echolocation. Neurons throughout the auditory cortex exhibit delay-dependent facilitation to artificial pulses and echoes at particular echo delays. Extracellular unit recordings of these delay-sensitive neurons determined the essential frequency components in the sound pair and their relative timing for evoking maximum facilitation. 2. The entire 60-kHz sweep of both the simulated pulse and echo were divided into four equal spectral quarters (Ist, IInd, IIIrd, and IVth), each linearly sweeping 15 kHz downward in 1 ms, to determine the spectral parts essential for maximal facilitation. Maximal facilitation was evoked equally by pulse-echo pairs in which the sound components consisted of either the entire 60-kHz FM sweeps or only the essential quarters. Most neurons required the IVth quarter of the pulse and the echo for delay sensitivity. This is consistent with the hypothesis that the essential quarters swept excitatory frequencies just above inhibitory frequencies. 3. The spectral and temporal contributions to delay sensitivity were examined independently. The spectral content for each spectral quarter of echo was varied in echo delay, and the sound-pair responses were compared. Maximal facilitation in individual delay-sensitive neurons required both a specific part of the echo spectrum and a specific echo delay. 4. The FM sweeps of the essential pulse and echo quarters were further narrowed to their minimum bandwidth, and the essential pulse frequencies (EPFs) and essential echo frequencies (EEFs) were determined. Both the EPFs and EEFs averaged approximately 8 kHz in FM bandwidth and represented different spectral parts of the echolocation pulse emitted by this FM bat. All neurons showed delay sensitivity to search stimuli in which pulse-echo stimuli consisted of 15-kHz FM pairs. 5. Delay sensitivity in virtually all neurons required pulse and echo components whose essential frequencies differed. However, some spectral overlap was found between the pulse and echo in 39% of these neurons. The majority of neurons (81%) required a pulse and echo in which their mean frequencies differed by < or = 16 kHz. This includes neurons with pulse and echo overlapping spectrally and those with sound components showing no overlap but separated by a relatively small frequency range. 6. The facilitative frequency-tuning curves of individual neurons were measured with their essential pulse and echo frequencies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Response selectivity for multiple dimensions of frequency sweeps in the pallid bat inferior colliculus.

1. While hunting, the pallid bat uses passive sound localization at low frequencies to find terrestrial prey, and echolocation for general orientation. It must therefore process two different types of acoustic input at the same time. The pallid bat's echolocation pulse is a downward frequency-modulated (FM) sweep from 60 to 30 kHz. This study examined the response selectivity of single neurons in the pallid bat's central nucleus of the inferior colliculus (ICC) for FM sweeps, comparing the response properties of the high-frequency population, tuned to the biosonar pulse, with the low-frequency population, tuned below the pulse. The working hypothesis was that the high-frequency population would exhibit a response selectivity for downward FM sweeps that was not present in the low-frequency population. 2. Neurons were tested for their selectivity for FM sweep direction, duration, frequency range and bandwidth, and rate of frequency change. The extent to which they responded exclusively to tones, noise, and FM sweeps was also examined. Significant differences in the response properties of neurons in the two populations were found. In the low-frequency population, all neurons responded to tones, but only 50% responded to FM sweeps. Only 23% were selective for sweep direction. In the high-frequency population, all neurons responded to FM sweeps, but 31% did not respond to tones. Over one-half of this population was selective for sweep direction, and of those that were selective, all preferred the downward sweep direction of the biosonar pulse. A large percentage (31%) responded exclusively to downward sweeps, and not to tones or upward sweeps. None of the cells in either population responded to noise, or did so only at very high relative thresholds. 3. Both populations contained neurons that were selective for short stimulus durations that approximated the duration of the biosonar pulse, although the percentage was greater in the high-frequency population (58% vs. 20%). In the high-frequency population, 31% of the neurons tested for duration responded exclusively to both the sweep direction and duration of the biosonar pulse. 4. Downward FM-selective neurons, with one exception, were generally insensitive to the rate of frequency change of the FM sweep, as well as the frequency range and bandwidth of the sweep. They responded similarly to both the full 60- to 30-kHz sweep and to 5-kHz bandwidth portions of the full sweep.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Neural selectivity and tuning for sinusoidal frequency modulations in the inferior colliculus of the big brown bat, Eptesicus fuscus.

Most communication sounds and most echolocation sounds, including those used by the big brown bat (Eptesicus fuscus), contain frequency-modulated (FM) components, including cyclical FM. Because previous studies have shown that some neurons in the inferior colliculus (IC) of this bat respond to linear FM sweeps but not to pure tones or noise, we asked whether these or other neurons are specialized for conveying information about cyclical FM signals. In unanesthetized bats, we tested the response of 116 neurons in the IC to pure tones, noise with various bandwidths, single linear FM sweeps, sinusoidally amplitude-modulated signals, and sinusoidally frequency-modulated (SFM) signals. With the use of these stimuli, 20 neurons (17%) responded only to SFM, and 10 (9%) responded best to SFM but also responded to one other test stimulus. We refer to the total 26% of neurons that responded best to SFM as SFM-selective neurons. Fifty-nine neurons (51%) responded about equally well to SFM and other stimuli, and 27 (23%) did not respond to SFM but did respond to other stimuli. Most SFM-selective neurons responded to a limited range of modulation rates and a limited range of modulation depths. The range of modulation rates over which individual neurons responded was 5-170 Hz (n = 20). Thus SFM-selective neurons respond to low modulation rates. The depths of modulations to which the neurons responded ranged from +/-0.4 to +/-19 kHz (n = 15). Half of the SFM-selective neurons did not respond to the first cycle of SFM. This finding suggests that the mechanism for selective response to SFM involves neural delays and coincidence detectors in which the response to one part of the SFM cycle coincides in time either with the response to a later part of the SFM cycle or with the response to the first part of the next cycle. The SFM-selective neurons in the IC responded to a lower and more limited range of SFM rates than do neurons in the nuclei of the lateral lemniscus of this bat. Because the FM components of biological sounds usually have low rates of modulation, we suggest that the tuning of these neurons is related to biologically important sound parameters. The tuning could be used to detect FM in echolocation signals, modulations in high-frequency sounds that are generated by wing beats of some beetles, or social communication sounds of Eptesicus.

Acoustic Stimulation↗
PubMed2002

Morphology of the external nose in Hipposideros diadema and Lavia frons with comments on its diversity and evolution among leaf-nosed Microchiroptera.

In some bats, a noseleaf is thought to help focus echolocation calls emitted through the nostrils. I studied the ontogenetic mode of the rhinarial cartilages and the associated facial muscles to assess how these rhinarial infrastructures interact with the noseleaf, and the inferred function of such a rhinarial complex. This study focuses on developmental stages of Hipposideros diadema and Lavia frons. Based on new data on these two rhinolophoids and a review of former studies concerning rhinopomatids, rhinolophoids and phyllostomids, the functional and phylogenetic implications of the rhinarial complex among leaf-nosed Microchiroptera are evaluated by the current study. Nasal emitting forms evolved several times independently in the Microchiroptera and share various features, irrespective of their phylogenetic position: the nostrils lie dorsally; the noseleaf has a well-developed horseshoe-shaped plate; the cartilago cupularis bears a large processus cupularis; M(iv) is extended on the lateral plate of the processus alaris superior. The unique similarities of the ontogenetic process of the nasal 'resonators' support the assumption that the rhinolophids + megadermatids and rhinopomatids may represent a natural group. In some features, the rhinolophids + megadermatids differ significantly from the phyllostomids. The noseleaf has a median flap and anterior-facing pockets. The processus alaris superior is half-tube-shaped or included in the lateral wall of the cupula nasi anterior. The cartilago accessoria and the attendant musculature perform an important function for supporting and moving the noseleaf. Similar emission of the echolocation pulses but alternative constructional designs of the external nose structures suggest that a separate history of rhinolophoids and phyllostomids might account for these differences.

Animals↗
PubMed2001

Artificial ears for a biomimetic sonarhead: from multiple reflectors to surfaces.

This work presents an evolutionary approach to pinna design. Narrowband echolocating bats move the pinna to alter the directional sensitivity of their perceptual systems. Adding pinnae to RoBat--a biomimetic sonarhead mounted on a mobile robot--is the goal of this work. After a description of the earlier work on artificial pinnae consisting of multiple reflectors around the transducer, an acoustic model, inspired by a physical model of sound diffraction and reflections in the human concha, is described and revisited as the model to use for evolving complex shapes. A genetic algorithm evolved the shape of the pinnae with respect to desired features of the directivity pattern of the receiver transducers. Some interesting paraboloid shapes for specific echolocating behaviors were evolved, improving performance with respect to the bare transducer's performance.

Animals↗
PubMed2003

Auditory encoding during the last moment of a moth's life.

The simple auditory system of noctuoid moths has long been a model for anti-predator studies in neuroethology, although these ears have rarely been experimentally stimulated by the sounds they would encounter from naturally attacking bats. We exposed the ears of five noctuoid moth species to the pre-recorded echolocation calls of an attacking bat (Eptesicus fuscus) to observe the acoustic encoding of the receptors at this critical time in their defensive behaviour. The B cell is a non-tympanal receptor common to all moths that has been suggested to respond to sound, but we found no evidence of this and suggest that its acoustic responsiveness is an artifact arising from its proprioceptive function. The A1 cell, the most sensitive tympanal receptor in noctuid and arctiid moths and the only auditory receptor in notodontid moths, encodes the attack calls with a bursting firing pattern to a point approximately 150 ms from when the bat would have captured the moth. At this point, the firing of the A1 cell reduces to a non-bursting pattern with longer inter-spike periods, suggesting that the moth may no longer express the erratic flight used to escape very close bats. This may be simply due to the absence of selection pressure on moths for auditory tracking of bat echolocation calls beyond this point. Alternatively, the reduced firing may be due to the acoustic characteristics of attack calls in the terminal phase and an acoustic maneuver used by the bat to facilitate its capture of the moth. Although the role of less sensitive A2 cell remains uncertain in the evasive flight responses of moths it may act as a trigger in eliciting sound production, a close-range anti-bat behaviour in the tiger moth, Cycnia tenera.

Acoustic Stimulation↗
PubMed1998

Hearing and hunting in red bats (Lasiurus borealis, Vespertilionidae): audiogram and ear properties.

We examined aspects of hearing in the red bat (Lasiurus borealis) related to its use of biosonar. Evoked potential audiograms, obtained from volume-conducted auditory brainstem responses, were obtained in two bats, and the sound pressure transformation of the pinna was measured in three specimens. Field-recorded echolocation signals were analysed for comparison. The fundamental sonar search calls sweep from 45 to 30 kHz (peak energy at 35 kHz), approach-phase calls sweep from 65 to 35 kHz (peak 40 kHz) and terminal calls sweep from 70 to 30 kHz (peak 45 kHz). The most sensitive region of the audiogram extended from 10 kHz to 45-55 kHz, with maximum sensitivity as low as 20 dB SPL occurring between 25 and 30 kHz. A relative threshold minimum occurred between 40 and 50 kHz. With increasing frequency, the acoustic axis of the pinna moves upwards and medially. The sound pressure transformation was noteworthy near 40-45 kHz; the acoustic axis was closest to the midline, the -3 dB acceptance angles showed local minima, and the pinna gain and interaural intensity difference were maximal. These results are related to the known echolocation and foraging behavior of this species and match the spectral components of approach- and final-phase calls. We conclude that co-evolution with hearing prey has put a higher selective pressure on optimizing localization and tracking of prey than on improving detection performance.

Animals↗
PubMed2001

Algorithms for the generation of complex sounds for auditory physiology studies.

The pallid bat (Antrozous pallidus) is a member of a small class of bats known as gleaners. These bats use echolocation to avoid obstacles in flight while using passive listening to localize terrestrial prey. The echolocation pulses are 60-30 KHz downward frequency modulated sweeps that last 3-5 milliseconds. The prey-generated sounds are broadband noise transients in the 5-35 KHz range [1]. The frequency components of these sounds are beyond the range of commonly available sound cards, but the availability of fast, low-cost computers makes it possible to use host-based digital signal processing techniques to generate more complex sound patterns using existing equipment. The new capabilities allow new types and combinations of behaviorally relevant sounds to be generated, permitting the functions and topology of the auditory cortex to be mapped with increased detail. This paper describes the algorithms used to generate the amplitude and frequency modulated tones and band-pass filtered noise signals used as stimulus sounds.

Animals↗
PubMed1982

[Hearing mechanisms in dolphins and baleen whales (author's transl)].

Dolphins have the most highly developed acoustical system in nature. They are not only able to hear far into the realm of ultrasound, but they have also developed a magnificent echolocation system. Baleen whales, on the other hand, are specialists for extremely low frequencies, without echolocation. In order to overcome technical problems it was necessary to drastically alter the construction of the hearing organ, of the entire skull, and even the skin. A short review of the current knowledge is presented, along with a discussion of the biotechnology involved.

Animals↗
PubMed1988

Existence of vocal folds in the larynx of odontoceti (toothed whales).

Odontocetes (toothed whales) vocalize for communication and echolocation. The mechanisms of sound production, however, remain unclear. Their larynx has long been thought to lack vocal folds and, thus, was considered incapable of generating sounds. This study investigates internal anatomy of the odontocete larynx to: 1) describe the morphology of any folds found, 2) determine any structural homologies between these folds and the vocal folds of terrestrial mammals, and 3) assess their possible function in sound production. Larynges of 24 odontocetes representing ten genera (Delphinus, Stenella, Lagenorhynchus, Tursiops, Grampus, Delphinapterus, Globicephala, Kogia, Mesoplodon, and Phocoena) were studied post mortem. Nine specimens were cut midsagittally, and the remainder were dorsally opened to reveal internal anatomy. Results show that, contrary to established belief, vocal folds are consistently present. They are not isolated bands or "cords," but appear continuous with the internal laryngeal membrane. The attachments of these folds are the same as in terrestrial mammals, thus indicating homology with true mammalian vocal folds. These folds extend from the midline of the thyroid cartilage to the base of the arytenoid cartilages, sometimes to a discrete process. The vocal folds are elongated and oriented in a vertical plane, parallel to airflow direction. Vocal fold morphology varies, appearing as true bifurcated structures, a trifurcated fold, or a single midline fold. Laryngeal ventricles and vestibular folds are also consistently found lateral to the vocal folds. The vocal folds may divide the airstream within the larynx into three separate air currents. Fold vibrations may produce initial laryngeal sound used in echolocation or communication.

Animals↗
PubMed1985

Projections from the cochlear nuclei in the mustache bat, Pteronotus parnellii.

Ascending projections of the cochlear nuclei in the mustache bat were analyzed by anterograde transport of [3H]-leucine and by retrograde transport of HRP. We were particularly interested in pathways to two parts of the system: (1) to the medial superior olive, because this nucleus is missing in most echolocating bats, but appears to be present in the mustache bat, and (2) to the intermediate and ventral nuclei of the lateral lemniscus, because these nuclei are hypertrophied and highly differentiated in all echolocating bats that we have examined. The results show a highly systematic projection from the anteroventral cochlear nucleus to all of the auditory nuclei in the brain stem. After an injection of [3H]-leucine in the anterior and dorsal part of the anteroventral cochlear nucleus, presumably in a region sensitive to low frequencies, label is seen in the following locations: ipsilateral to the injection in the lateral part of the lateral superior olive; bilaterally in the dorsal part of the medial superior olive; contralateral to the injection in the dorsal parts of the intermediate and ventral nuclei of the lateral lemniscus; and in the anterolateral part of the central nucleus of the inferior colliculus. After an injection of [3H]-leucine in a posterior part of the anteroventral cochlear nucleus, presumably in a region sensitive to high frequencies, labeling is in the same set of nuclei, but within each nucleus the label is now in a different location: medially in the lateral superior olive, ventrally in the medial superior olive, ventrally in each division of the ventral and intermediate nuclei of the lateral lemniscus, and medially in the central nucleus of the inferior colliculus. Projections from the entire anteroventral cochlear nucleus to the inferior colliculus are confined to the ventral two-thirds of the central nucleus. The dorsal one-third of the central nucleus of the inferior colliculus is the principal target of the dorsal cochlear nucleus and may be a target of the posteroventral cochlear nucleus. Both of these nuclei appear to project sparsely to the ventral parts of the inferior colliculus. We conclude first that the bilateral input to the medial superior olive in the mustache bat is similar to the input seen in other mammals. Thus this bat has a neural structure which is associated with the analysis of binaural time differences and which usually is seen only in animals with heads large enough to create interaural time differences greater than those available to Pteronotus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Distribution of catecholamine fibers in the cochlear nucleus of horseshoe bats and mustache bats.

The glyoxylic-acid-induced fluorescence technique was applied to demonstrate patterns of catecholaminergic innervation within the auditory brainstem of echolocating bats and the house mouse. In the cochlear nucleus of the rufous horseshoe bat (Rhinolophus rouxi) and the mustache bat (Pteronotus parnellii), species-specific catecholaminergic innervation patterns are found that contrast with the relatively homogeneous innervation in the rodent. In both bats the subnuclei of the cochlear nucleus receive a differentially dense supply of catecholaminergic fibers, and within the subnuclei, the catecholamine innervation densities can be correlated with the tonotopic frequency representation. The areas devoted to the high-frequency echolocation calls are less densely innervated than those regions which are responsive to lower frequencies. Apart from this common scheme, there are noteworthy distinctions between the two bats which correlate with specialized cytoarchitectural features of the cochlear nucleus. The marginal cell group, located medially to the anteroventral cochlear nucleus of Pteronotus, receives the densest supply of catecholaminergic fibers of all auditory nuclei. This plexus is formed by a morphologically distinct population of catecholaminergic fibers.

Animals↗
PubMed1992

Ultrastructure of the horseshoe bat's organ of Corti. I. Scanning electron microscopy.

The organ of Corti of the echolocating horseshoe bat (Rhinolophus rouxi) was investigated with scanning electron microscopy in order to provide a comparison with non-echolocating mammals. Throughout the cochlea of horseshoe bats, each outer hair cell (OHC) possesses three rows of stereocilia and there are no morphological distinctions among the different rows of OHCs. However, there are morphological differences between different regions along the cochlea. In the lower and upper basal turn, the receptor surfaces of OHCs are characterized by extremely wide W-shaped stereocilia bundles and wingshaped cuticular plates. The cuticular plates of OHCs of the middle and outermost rows are arranged parallel to each other. Stereocilia length is only 0.8 microns and there is an exaggerated angle of inclination of the shortest row of stereocilia towards the next taller one. Stereocilia arrangements in the apex of the horseshoe bat's cochlea closely resembles those observed in the midbasal region of the rat cochlea. Inner hair cells (IHC) in the lower basal turn appear specialized. They possess only two rows of stereocilia and only 7-8 stereocilia per row. Their cuticular plates are small and oval and widely separated from one another in the longitudinal direction. IHCs at all other locations possess three and up to four rows of stereocilia and 17-20 stereocilia per row. Their cuticular plates are elongated and closely spaced. The transition from specialized to typical mammalian morphology occurs abruptly (over a distance of about 100-150 microns) at the border between the lower and the upper basal turn. This transition is not accompanied by a change in OHC morphology. In the subsurface of the tectorial membrane, throughout the cochlea, there are distinct imprints of the tallest row of stereocilia of all three rows of OHCs and of the IHCs. Data are discussed in relation to specialized aspects of the cochlear frequency map in horseshoe bats and as possible micromechanical adaptations to ultra-high frequency hearing.

Animals↗
PubMed1979

A morphometric study of the cochlea of the little brown bat (Myotis lucifugus).

A detailed morphometric study of the basilar membrane was made from serial sections and graphic reconstructions of the cochlea of three little brown bats. Four distinct morphometric changes were observed within the basilar membrane. First, between 0-1.4 mm from the basal end of the cochlea, there is a rapid increase in width and cross-sectional area of the basilar membrane. Secondly, between 1.4-2.5 mm, there is little change in width of the basilar membrane (its cross-sectional area is at its greatest in this region). Thirdly, between 2.7-3.1 mm, there is a sudden decrease in cross-sectional area concomitant with an increase in the width of the basilar membrane. Finally, between 3.1 mm and the apex, there is a gradual decrease in cross-sectional area concomitant with an increase in the width of the basilar membrane. The magnitudes of the cross-sectional areas of the scalae media and vestibuli decrease from base to apex, but this is not true for the scala tympani. The cross-sectional area of the scala tympani appears to decrease from the base to 0.7 mm, then it increases up to 1.4 mm, and then it decreases to the apex. These morphometric changes in the basilar membrane of the little brown bat are compared to those in other echolocating and non-echolocating mammals. The significance of these changes is discussed in relation to the range of hearing in the little brown bat.

Animals↗