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PubMed1983

Lipid composition of the spinal cord in the fruit bat Rousettus aegyptiacus.

Spinal cords were removed from ten Egyptian fruit bats Rousettus aegyptiacus and the lipids analysed. The major phosphatides were choline glycerophosphatide (32.3%), ethanolamine glycerophosphatide (29.3%), serine glycerophosphatide (15.2%) and phosphatidylinositol (8.4%). Sphingomyelin accounted for 13.8% of the phospholipid. Glycosphingolipids amounted to 43.2 mol/100 mol lipid phosphorus, plasmalogens 32.5 mol/100 mol P and cholesterol 159.5 mol/100 mol P. The fatty acid composition of whole cord, sphingomyelin and non-hydroxy cerebroside were determined. The results were compared with data from other species.

Animals↗
PubMed1986

Isolation and properties of creatine kinase from the breast muscle of tropical fruit bat, Eidolon helvum (Kerr).

Creatine kinase, from fruit bat breast muscle, has been purified to homogeneity. The mol. wt of the enzyme was estimated to be about 78,000-80,000 with two subunits of 42,500. There are nine thiol residues/mol of the enzyme and two of these react readily with DTNB leading to total inactivation of the enzyme. The metal ion specificity was in order Mg2+ greater than Zn2+ greater than Co2+. Initial velocity and product inhibition studies of the reverse reaction are consistent with sequential reaction but of either rapid equilibrium random or ordered type.

Animals↗
PubMedDate not supplied

Histoenzymological mapping of alkaline phosphatase and 5-nucleotidase in the medulla oblongata of a microchiropteran bat (Taphozous melanopogon Temminck).

The contribution deals with the distribution of alkaline phosphatase and 5-nucleotidase in the medulla oblongata of Taphozous melanopogon (a Microchiroptera), for the first time. The main highlights of the study are: (1) Cranial nerve nuclei demonstrate intense activity of alkaline phosphatase, whereas except nucleus tractus spinalis n. trigemini, rest of the nuclei show much variations of 5-nucleotidase distribution. (2) The vestibular nuclei are very intensely positive for 5-nucleotidase but exhibit variable activity of alkaline phosphatase. (3) Three subdivisions of nucleus olivaris inferior, i.e. nucleus olivaris accessorius medialis, nucleus olivaris accessorius dorsalis and nucleus olivaris inferior, which were not reported in the earlier neuroanatomical studies, have been identified. These nuclei show very intense alkaline phosphatase and relatively less intense 5-nucleotidase activities. (4) In general, the activity of alkaline phosphatase is stronger in neurons than in neuropil and that of 5-nucleotidase is stronger in neuropil than in neurons. (5) Blood capillaries are completely negative for alkaline phosphatase and intensely positive for 5-nucleotidase. A comparison is made between the distribution of these enzymes in the medulla oblongata of bat and other mammals so far studied.

Alkaline Phosphatase↗
PubMed1980

Cochlear innervation in the greater horseshoe bat: demonstration of an acoustic fovea.

The innervation of the cochlea of the greater horseshoe bat was investigated by different methods. The regional densities of the spiral ganglion neurons and of the inner and outer receptors were determined from surface specimens and histological sections. The pattern of the unmyelinated fibers was reconstructed in EM serial sections and the efferent pattern separately by localization of cholinesterase activity. The study reveals three regions each adapted to different auditory functions: (1) The region 1.3--5.4 mm from the basal end where the constant frequency segment of the orientation signal (around 83 kHz) is analysed. The neuronal structures of this region are similar to other mammals studied. Since, however, this region has widely expanded frequency mapping, the innervation density per octave is very high. In the region of this 'acoustic fovea' 25% of the receptors and 21% of the spiral ganglion neurons of the cochlea represent 10% of a single octave. (2) The region from 5.4 to 8 mm with frequencies from 40--80 kHz encompasses the frequency modulated segment of the orientation signal. This region is characterized by a high density of spiral ganglion neurons together with a short spiral course of the afferent fibers to the outer receptors. (3) The region from 8 mm to the apex (16 mm) represents frequencies lower than 40 kHz. Here neuronal elements, except for the efferents, are comparable to those of other mammalian cochleae. As important and surprising finding was that there is no efferent fiber to the outer hair cells in any part of the cochlea.

Animals↗
PubMed1981

Time and Frequency domain processing in the inferior colliculus of echolocating bats.

Tone bursts and frequency-modulated (FM) signals were presented to Mexican free-tailed bats and tuning curves, discharge patterns, and discharge latencies of single units in the inferior colliculus were recorded. Cells were broadly tuned to tone bursts, with most Q 10 values ranging from 3 to 20. However, in response to FM stimulation the discharges of neurons were closely synchronized to the time of occurrence of restricted frequency components within the FM sweep. These excitatory frequencies (EFs) were generally unaffected by changes in the starting frequency or intensity of the stimulus. Thus, in response to FM signals, the cells exhibited a much greater frequency selectivity than that observed following tone burst stimulation. Across the population of neurons sampled, EFs covering a wide frequency range were found, and the different EFs were represented in a systematic fashion within the colliculus. The frequencies in an FM biosonar signal or echo will thus be neurally represented both by the time of occurrence of neuronal discharges and by the location of the discharging cells within the nucleus. The potential role of this dual frequency coding in spectral and temporal processing of biosonar signals and echoes is discussed, with emphasis on the neural coding of target range.

Acoustic Stimulation↗
PubMed1982

Cochlear microphonic potentials elicited by biosonar signals in flying bats, Pteronotus p. parnellii.

Cochlear microphonic (CM) potentials were recorded from the bat, Pteronotus p. parnellii during tethered flight and during simulated flight on a pendulum. For each emitted signal the frequency of the ca. 61 kHz constant frequency (CF) component was compared with the frequency response characteristics of the animals's ear. The majority of "resting pulses' had CF components with the maximum frequency approximately 200 Hz below the best frequency (BF) of the CM audiogram. Doppler shift compensation occurred only during forward swings of the pendulum and in such a way that the echo CF components were always maintained near the BF, but on the low frequency slope of the CM audiogram. CM responses to emitted pulses were usually small in amplitude and in some animals no responses were seen. Echoes Doppler shifted upward, however, evoked high amplitude potentials. Echo CF components estimated to be at least 43 dB fainter than the emitted pulses evoked higher amplitude CM potentials than the loud emitted pulses. Echoes from large surfaces up to 4.5-5.0 meters away evoked CM potentials as high in amplitude as those elicited by emitted pulses, even when there was no Doppler shift. Beats in the CM were observed on many occasions and occurred as a result of pulse-echo and echo-echo interactions.

Animals↗
PubMed1983

Basilar membrane tuning properties in the specialised cochlea of the CF-bat, Rhinolophus ferrumequinum.

The greater horseshoe bat has greatly expanded frequency mapping, and morphological specialisations, in the first half turn of its cochlea and a sudden transition to normal mapping. Amplitude and phase of vibration have been measured on various structures in the expanded and normal regions and have not revealed any sharply tuned responses. Amplitudes are much lower than those found in other species and frequently show a deep notch in the 77-84 kHz region. The high-frequency cut-off frequencies are tonotopically organised but deviate from the Bruns map, so that hair-cell tuning appears to occur at a frequency at which basilar membrane vibration is small. In the basal region, phase differences were frequently found between the inner and outer parts of the basilar membrane. These appear to be due to interaction between two components of motion and are probably not indicative of a further filtering mechanism. There is no evidence for reflection of the travelling wave at the transition.

Acoustic Stimulation↗
PubMed1985

Echo intensity compensation by echolocating bats.

When mounted on a swinging pendulum, mustache bats, Pteronotus p. parnellii, emit ultrasonic pulses as they move toward and away from fixed targets. During forward swings they systematically decrease the intensity of their emitted pulses and during backward swings they increase the intensity. In this way, echo strength is continuously adjusted and apparently optimized for signal analysis. We have called this behavior echo intensity compensation. Pteronotus simultaneously Doppler and echo intensity compensate during forward swings of the pendulum but during backward swings they only echo intensity compensate. Pteronotus can regulate the intensity of both the constant frequency and frequency modulated components of their pulses; this regulation is independent of vestibular cues, pulse repetition rates, pulse durations and pulse-echo intervals.

Animals↗
PubMed1986

Directional sensitivity of the auditory midbrain in the mustached bat to free-field tones.

To ascertain the directional characteristics of the auditory system in the mustached bat, Pteronotus parnellii, we measured the summated neural response at the lateral lemniscus (N4) in response to pure tones at 30, 60 and 90 kHz, frequencies that are typical of the harmonics of this species' biosonar signal. Stimuli were presented at various vertical and horizontal locations in the contralateral hemifield. Intensity-response functions were measured at different horizontal locations for the second harmonic, and showed no variation in shape with variations in azimuth. There was little difference in directionality measured from either threshold or amplitude of N4 potentials. Our results show that areas of maximum sensitivity (best areas) were significantly different for each of the harmonics (P less than 0.05). The centers of the best areas were: first harmonic (30 kHz), 39 degrees azimuth and -19 degrees elevation; second harmonic, 20 degrees azimuth and 0 degrees elevation; and third harmonic, 12 degrees azimuth and -11 degrees elevation. Thus, with increasing frequency best areas shifted toward the vertical midline. Directionality to first harmonic stimuli was broader than to either of the two higher harmonics.

Acoustic Stimulation↗
PubMed1988

Intracellular labeling of afferents to the lateral superior olive in the bat, Eptesicus fuscus.

An in vitro tissue slice preparation of the bat brain stem was used to label intracellularly individual axons projecting to the lateral superior olive from two different sources: the medial nucleus of the trapezoid body (MNTB) and the anteroventral cochlear nucleus (AVCN). The tracing of individually labeled MNTB axons into the lateral superior olive reaffirms the long accepted indirect route by which information from the contralateral ear reaches the lateral superior olive. While the MNTB appears to relay input from the contralateral AVCN, information from the ipsilateral ear reaches the lateral superior olive via a direct projection from the ipsilateral AVCN. Axons from the contralateral and ipsilateral pathways have different distribution patterns upon the fusiform cells of the lateral superior olive. Axon terminals of MNTB principal cells have a perisomatic and proximal dendritic distribution pattern. Axon terminal varicosities from the ipsilateral anteroventral cochlear nucleus are distributed primarily to more distal dendrites.

Animals↗
PubMed1991

The organ of Corti in the bat Hipposideros bicolor.

The bat Hipposideros bicolor (Hipposideridae, Microchiroptera) is the mammalian species with the highest upper limit of hearing in which the structure of the organ of Corti has been studied. H. bicolor emits pure tone echo-locating signals of 153 kHz, compensates for Doppler shifts in the echo and hears ultrasonic frequencies up to 200 kHz (Neuweiler et al., 1984). The organ of Corti was investigated qualitatively and quantitatively using the technique of semi-thin sectioning. Some complementary ultra-thin sections were also examined. Length, width and cross-sectional area of the basilar membrane, the tectorial membrane, the hair cells with their stereocilia and the organ of Corti were measured at equi-distant positions on the basilar membrane. The organ of Corti of H. bicolor is composed of elements similar to those found in the cochleae of other eutherian mammals studied. However, in H. bicolor some of these elements show species-specific differences when compared to auditorily unspecialized mammals. The most basal region of the cochlea is characterized by miniaturization and re-inforcement of macro- and micro-mechanically important elements. This is interpreted as an adaptation for hearing extremely high frequencies. Specialized structures as well as local maxima of 'normal' elements in the basal and middle cochlear region are associated with evaluation of the echos of emitted pure tones. Besides the basal specializations. Hipposideros also shows specializations in the apical, low frequency, region which can be correlated with passive acoustic orientation.

Animals↗
PubMed1991

Specializations for sharp tuning in the mustached bat: the tectorial membrane and spiral limbus.

The sense of hearing in the mustached bat, Pteronotus parnellii, is specialized for fine frequency analysis in three narrow bands that correspond to approx 30, 60 and 90 kHz constant frequency harmonics in the biosonar signals used for Doppler-shift compensation and acoustic imaging of the environment. Previous studies have identified anatomical specializations in and around the area of the cochlea that processes the dominant second harmonic component, but similar features have not been found in areas related to sharp tuning and high sensitivity for the first or third harmonics. In this report we call attention to the large size of the tectorial membrane and spiral limbus in all three areas that appear to process the harmonically related constant frequency components. These structures are especially pronounced in the regions of the cochlea that respond to the approx 61 kHz, second harmonic and 91.5 kHz, third harmonic bands; they correspond specifically to areas where the density of afferent nerve fibers is high and where very sharply tuned neurons occur. These data for cochleae with multiple specializations lend strong support to the idea that the mass of the tectorial membrane can be an important factor in establishing the response properties of the cochlea.

Animals↗
PubMed1992

High frequency distortion products from the ears of two bat species, Megaderma lyra and Carollia perspicillata.

In two echolocating bat species, Megaderma lyra and Carollia perspicillata 2f1-f2 distortion products were measured acoustically in the outer ear canal for f1 frequencies between 5 and 95 kHz in an attempt to study nonlinear cochlear processes at high frequencies. Similar to other mammals, the input/output (I/O) functions of 2f1-f2 show non-monotonicities and notches at f1 levels between 40-70 dB SPL. The slope of the initial rise of the 2f1-f2 I/O functions increased with f1 frequency from 0.73 (5 kHz) to 1.41 (95 kHz) in Megaderma and from 0.66 (7.5 kHz) to 1.47 (95 kHz) in Carollia. With increasing f1 frequency the optimum frequency ratio f2/f1 in order to evoke maximum distortion level decreases from 1.18 (5 kHz) to 1.09 (95 kHz) in Megaderma and from 1.21 (7.5 kHz) to 1.11 (95 kHz) in Carollia. This is taken as indication of a general increase of the quality of tuning of the distortion generating mechanism with frequency. The f1 levels that were sufficient to elicit distortion levels of -10 dB SPL were used to construct iso-distortion threshold curves which lay on average 37.2 dB (Megaderma) and 33.9 dB (Carollia) above the neuronal threshold curves [Rübsamen et al., J. Comp. Physiol. A 163 (1988); Sterbing et al., Proc. 18th Göttingen Neurobiol. Conf. Thieme Verlag, Stuttgart (1990)] and roughly paralleled these. Highest distortion levels (40-50 dB SPL with f1 levels of 80 dB SPL) and lowest distortion thresholds were measured in the f1 frequency range of 10-30 kHz (Megaderma) and 15-30 kHz (Carollia).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Processing of pure-tone and FM stimuli in the auditory cortex of the FM bat, Myotis lucifugus.

FM bats perceive their surroundings during echolocation by analyzing frequency-modulated (FM) acoustic signals. Results from this study indicate a cortical organization in Myotis lucifugus which is largely made up of neurons sensitive to FM sounds (FM-sensitive neurons). Three types of neurons were distinguished by their responses to pure-tone and FM stimuli: (1) Type I FM-sensitive units (83%), Type II FM-sensitive units (13%) and pure-tone sensitive units (4%). Type I FM-sensitive units responded to pure tones, but exhibited greater response magnitudes to FM stimuli when the best FM swept through the BF. An orderly frequency representation was found when the frequencies of pure tones essential for response (EPTs) in Type I units were mapped along the cortical surface. The EPTs for Type I neurons were usually found within the last millisecond of a downward FM sweep. As outlined by two neuronal network models, both the responses of Type I and II units could likely result from the convergence of excitatory and inhibitory lower level neurons with slightly differing BFs. Type II units were selective for an FM sweep and showed negligible to no response to pure-tone stimuli. Pure-tone sensitive units exhibited weak or no responses to FM stimuli. These neurons were clustered in a small area located rostrodorsal to the tonotopic zone and had significantly lower best frequencies than adjacent EPT frequencies of Type I FM-sensitive neurons.

Acoustic Stimulation↗
PubMed1993

The effects of GABAergic inhibition on monaural response properties of neurons in the mustache bat's inferior colliculus.

The effects of GABAergic inhibition on response properties of neurons in the inferior colliculus were investigated. The experimental animals were mustache bats and responses were monitored from neurons in the hypertrophied 60 kHz isofrequency contour of the inferior colliculus. The features we report on here are: 1) the maximum discharge rates evoked by tone bursts at each unit's best frequency; 2) the forms of the rate-level functions; 3) the discharge patterns evoked by best frequency tone bursts; and 4) the changes in these response features that were observed when GABAergic inhibition was blocked with bicuculline, an antagonist specific for GABAA receptors. There were three main findings. The first is that bicuculline caused the discharge rate to increase in the majority of neurons. The maximum firing rates in more than half of the units increased by at least 100%, and in 15% of the cells the maximum spike-count increased 400% or more. Of particular interest were the 13 cells that were nearly unresponsive to any tone burst, but responded vigorously to the same stimuli after application of bicuculline. The second main finding is that the increased discharge rates were due either to a change from a phasic to a tonic discharge pattern, or to a change in overall excitability with no change in discharge pattern. The third main finding was that bicuculline changed the shape of the rate-level functions in almost half of the cells studied. The general trend was that units whose pre-drug rate-level functions were upper-threshold were most likely to be changed, followed by regular nonmonotonic and non-saturated monotonic. Units with saturated monotonic functions were the least likely to be affected by bicuculline. These results lead us to suggest that GABAergic inhibition acts on collicular cells in two principal ways. The first way is to modify the effects of the excitatory innervation and thereby shape the response features of collicular neurons. The formation of rate-level functions is but one illustration of the shaping action of GABAergic inhibition. Other features that are shaped by GABAergic inhibition include discharge patterns, thresholds, latencies and tuning curves. The second way is to provide a regulated suppression of evoked activity. We propose that the suppression is situation dependent and may act to enhance the operating range of collicular neurons in situations of particular importance to the animal, such as during periods of selective attention and perhaps in other situations as well.

Acoustic Stimulation↗
PubMed1995

The shape of 2f1-f2 suppression tuning curves reflects basilar membrane specializations in the mustached bat, Pteronotus parnellii.

Iso-suppression tuning curves (STCs) of the 2f1-f2 distortion product (dp) were measured over a primary frequency range of 20 to 93 kHz in mustached bats, Pteronotus parnellii parnellii. Primary levels were chosen to produce dp levels between 0 and 7 dB SPL. At frequencies outside the ranges of 60-72 kHz and 90-93 kHz the shapes of the STCs were symmetrical or asymmetrical with a steep high frequency slope. In the vicinity of 61 kHz where a strong stimulus frequency otoacoustic emission (SFOAE) is present, the asymmetry of the STCs was inverted with a very steep low frequency slope (max. -89 dB/kHz) and a shallow high frequency slope. The inverted STCs resemble neuronal tuning curves of the same species with best frequencies at about 61 kHz. Close to 61 kHz the STCs were sharply tuned with Q10dB values up to 177. The STC-thresholds were about 20 dB above the neuronal thresholds. Thickenings of the basilar membrane located just basal to the cochlear place of the SFOAE frequency are probably involved in creating the asymmetric STCs. Cochlear resonance at the SFOAE frequency and an increased longitudinal coupling within the thickened basilar membrane region are thought to contribute to the specialized STC shape. In the range of 90-93 kHz, the STCs are also sharply tuned with inverted asymmetry which is probably not due to an harmonic effect of the specialized cochlear mechanics in the 60 kHz region but may be caused by an independent mechanism.

Acoustic Stimulation↗
PubMed1994

Tuned hair cells for hearing, but tuned basilar membrane for overload protection: evidence from dolphins, bats, and desert rodents.

A cochlear model is presented suggesting that the organ of Corti (OC) and the basilar membrane (BM) are both tuned resonant systems, but have different functions. The OC provides frequency filtering and amplification by means of tuned outer hair cells. The BM provides resonant absorption of excessive vibrational energy as an overload protection for vulnerable elements in the OC. Evidence supporting this model is demonstrated in dolphins, bats, and desert rodents. Specialized auditory capabilities correlate with cochlear deviations, some of them dramatically changing BM compliance. In characteristic regions along the cochlea there are BM thickenings and, on both sides of the OC, hypertrophied supporting cells. Structures of striking similarity have evolved independently across orders or families, revealing multiple events of convergent evolution. In all cases, the locations of deviating structures rule out a BM function in auditory frequency selectivity but support one in resonant absorption. Cochlear microphonics and BM responses demonstrate strongest high-level absorption in the frequency bands most vital for the tested species. The assumed cause is increased internal damping in the enlarged structures during BM motion. Species with intermediate specializations supply further evidence that resonant absorption is universally the genuine function of BM mechanics in mammals, providing complementary high-level protection of low-level sensitivity.

Absorption↗
PubMed1994

AChE-staining of type II ganglion cells, processes and terminals in the cochlea of the mustached bat.

There have been a number of reports showing that ganglion cells of sensory neurons may be stained by traditional acetylcholinesterase (AChE) histochemical techniques commonly used to demonstrate efferent nerve fibers and terminals. AChE-staining has been described for cell bodies in the vestibular and spiral ganglia; staining of peripheral and central processes, however, is rare and the presence of reaction product in afferent terminals has not been reported. The outer hair cells of mustached bats, Pteronotus parnellii, differ from those of most mammals in that they typically have a single, large efferent terminal surrounded by 5-7 small, afferent terminals. In this animal an AChE-positive reaction was found not only in efferent fibers and terminals but also in type II ganglion cells, their peripheral and central processes and in outer hair cell terminals. The stained cell bodies were smaller than the unstained type I ganglion cells and they were much fewer in number. The processes of the stained cells could be followed from the soma. The central processes were dispersed throughout the VIIIth nerve trunk. Stained peripheral processes were evident in the osseous spiral lamina, floor of the tunnel of Corti and first space of Nuel and in the outer spiral plexus along the sides of the outer phalangeal (Deiters') cells. AChE-stained afferent terminals were easy to identify after transection of the crossed olivocochlear bundle (COCB) and subsequent degeneration of large efferent terminals. These results are of interest in that assessments of efferent nerve histochemistry after COCB transection need to recognize the potential contribution of AChE reaction product in afferent terminals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗