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At least 1,135 records · Page 63Linked to original sources
PubMed1984

Vitamin B12 deficiency alters the distribution of membrane proteins on linear sucrose gradients in the fruit bat brain.

Total particulate material prepared by homogenization in water and centrifugation at 100,000 g for 60 min from the brains of normal and vitamin B12-deficient fruit bats was fractionated on linear sucrose gradients (0.1 M-1.4 M sucrose). Animals were made vitamin B12-deficient by dietary deprivation or as a result of exposure to nitrous oxide. Based on absorbance at 280 nm three peaks were seen in material derived from the B12-deficient fruit bat brain and only two peaks in the normal animal. Myelin proteins were observed over a larger range of molarities of sucrose in the deficient brain than in the control tissue. Animals rendered vitamin B12-deficient by nitrous oxide treatment showed membrane protein patterns similar to those observed in the control animal.

Animals↗
PubMed1996

Corticofugal control of central auditory sensitivity in the big brown bat, Eptesicus fuscus.

Using bats as a model auditory system, we studied corticofugal control of auditory sensitivity of neurons in the inferior colliculus. We demonstrate for the first time that the corticocollicular pathway continuously regulates acoustic signal processing in the inferior colliculus by increasing the threshold, reducing the auditory spatial response area, and sharpening the frequency tuning curve of recorded inferior collicular neurons. Regulation of auditory sensitivity of recorded inferior collicular neurons was observed when the corticocollicular pathway was activated by electrical stimulation in the auditory cortex. The effect of this corticofugal regulation of auditory sensitivity in inferior collicular neurons can also be produced by ionophoretical application of GABA to the collicular recording site. This regulation of ascending acoustic information by commands originating from higher brain centers may provide the bat with a mechanism to actively control acoustic signal processing and thus optimize acoustic signal analysis.

Animals↗
PubMed1980

Utilization of [2-14C]tetrahydropteroylglutamic acid and 5-[G-3H]methyltetrahydropteroylglutamic acid as substrates for folate polyglutamate synthesis in fruit bats: effect of vitamin B-12-deficiency.

[2-14C]Tetrahydropteroylglutamic acid and 5-[G-3H]methyltetrahydropteroylglutamic acid were given intraperitoneally to fruit bats. Folate polyglutamates were formed in the liver from both substrates in different amounts and at different rates. The methylfolate pool appeared to remain separate from the tetrahydrofolate pool. More polyglutamate was formed from tetrahydropteroylglutamic acid than from 5-methyltetrahydropteroylglutamic acid. There was a fall in the folate content of the liver in the vitamin B-12-deficient bat and a more rapid incorporation of folates into polyglutamates but thereafter a more rapid loss of the labelled folate from liver.

Animals↗
PubMed1978

Enzymes of heterotherms: LDH of hibernating and normothermic little brown bats, Myotis lucifugus.

1. Lactate dehydrogenase (LDH) was isolated from pectoral or flight muscle, liver and heart of hibernating and normothermic bats, Myotis lucifugus. 2. Activities at high substrate concentrations and the interactions between substrate and enzyme were studied to evaluate possible adaptations associated with the extended period of depressed metabolism of this bat. 3. Activity levels in all tissues decreased with hibernation, although the magnitude was dependent upon both temperature and substrate concentration. In general, the extent of decrease was in the order pectoral muscle greater than liver much greater than heart. 4. No correlation was found between the temperature sensitivity of the tissue LDHs as estimated by Ea-values, and the physiological state. 5. However, affinity parameters as estimated by Km-values were less temperature sensitive in hibernator tissues in contrast to the marked perturbations exhibited at temperature extremes in the normotherm enzymes. 6. It is suggested that changes in subunit quantities are in part responsible for these kinetic differences, and not major qualitative isozyme changes. 7. The net result of these effects is a reduced carbon flux to lactate during hibernation, but the maintenance of a potential for LDH catalyses during arousal.

Animals↗
PubMed1987

Erythrocyte biochemistry of the grey-headed fruit bat (Pteropus poliocephalus).

1. Several haematological and biochemical parameters were measured in the erythrocytes of the grey-headed fruit bat. 2. The level of 2,3-diphosphoglycerate was almost twice that found in human erythrocytes. Similarly pyruvate kinase activity was more than twice that of man. 3. The activities of other enzymes of the glycolytic pathway were similar to those found in man. 4. The level of reduced glutathione (GSH) and the GSH regeneration rate in the erythrocytes of the bat were comparable to those found in man.

2,3-Diphosphoglycerate↗
PubMed1982

The cells of Boettcher in the bat, Pteronotus p. parnellii.

The structural characteristics, distribution and intercellular relationships of the cells of Boettcher were studied in the mustache bat, Pteronotus P. parnellii. The cells of Boettcher have many structural features similar to those described in other mammals, but in Pteronotus they are distributed throughout the cochlea and are associated with relatively large amounts of secretory and/or absorptive material. Much of this material seems to be derived from or contribute to, a darkly staining upper layer of the basilar membrane. This material accumulates in elaborate microvillus-filled intercellular channels which are restricted to an area near the basilar membrane. The channels communicate with the basilar membrane surface through wide intercellular spaces and through small canals. The microvillus-filled channels are confluent with large extracellular spaces between Boettcher's cells and a single row of cells which form the floor of the outer tunnel. The latter have irregular shaped nuclei, contain many vacuoles and like Boettcher's cells, are associated with large amounts of basilar membrane-like material. Observations on Pteronotus, as well as other species of bats, do not support concepts relating Boettcher's cells to hair cell innervation patterns or to high frequency hearing.

Animals↗
PubMed1983

Middle-ear mechanics in the CF-bat Rhinolophus ferrumequinum.

The acoustic vibrations of the eardrum at the umbo and of the stapes have been measured in the greater horseshoe bat. The displacement amplitude response of the eardrum shows a second-order low-pass characteristic, typical of a lumped mass and stiffness system with a resonance frequency of about 55 kHz. The effective mass was calculated to be about 8 micrograms, and the specific stiffness 40 X 10(6) dyne/cm3, which is one hundred times greater than guinea pig. The measured level ratio appears to be greater (3X - 5X) than the geometric ratio (2X) probably due to flexing of the manubrium. The umbo-stapes phase lag exceeds 1 cycle at high frequencies, suggesting a system of at least four reactances. This is not consistent with the relatively slight change in lever ratio with frequency. One possibility for reconciling the two results is that the distributed mass and stiffness of the ossicles act as a transmission line for transverse vibrations. There is no evidence for a sharply peaked middle-ear response (although it is more sharply tuned than some species), nor for resonant absorption by the cochlea in the region of 83 kHz - the 'constant' frequency of this bat. The eardrum shows theoretically optimal matching to the air at 55 kHz and is reasonably efficient from 15 kHz to at least 110 kHz.

Acoustic Stimulation↗
PubMed1984

Spatial tuning of auditory neurons in the superior colliculus of the echolocating bat, Myotis lucifugus.

The azimuthal selectivity of auditory neurons was examined in the superior colliculus of the little brown bat, Myotis lucifugus. Frequency-modulated (FM) sounds, synthesized to mimic biosonar signals the echolocating bat naturally hears, were delivered from a loudspeaker moving across the front of the unanesthetized animal. Neurons were classified on the basis of their spatial tuning into two general classes: (i) hemifield units (34%) were broadly tuned to the contralateral side irrespective of sound pressure level; (ii) azimuth-sensitive units (66%) were sharply tuned to different azimuths at sound pressures near their minimum thresholds (MTs). A distinguishing feature of these azimuth-sensitive neurons is that they responded maximally to a sound source located at a preferred azimuth (best azimuth) for levels as high as 30 dB above their MT. Mapping experiments provide evidence of a sequential representation of best azimuth along the rostrocaudal extent of the superior colliculus, with sounds originating from 0-10 degrees ipsilateral coded at the rostral end, and from 30-40 degrees contralateral coded at the caudal end. The highly directional echolocation system of Myotis probably accounts for the limited azimuthal representation of echo-source spanning mainly 40 degrees to either side of its line of flight.

Acoustic Stimulation↗
PubMed1985

Evoked acoustic emissions and cochlear microphonics in the mustache bat, Pteronotus parnellii.

In the echolocating bat, Pteronotus parnellii, otoacoustic responses at a frequency of 62 kHz are measurable in the external ear canal during continuous and after transient acoustic stimulation. These responses are interpreted to represent emissions from the cochlea. They can reach an amplitude as large as 70 dB SPL and occur in the frequency range most important for echolocation, namely on the average about 700 Hz above the constant frequency component of the orientation calls. A sharp maximum of the amplitude of cochlear microphonic potentials at about 62 kHz could be correlated with the emission frequency. In one bat an evoked otoacoustic response changed to a spontaneous otoacoustic emission. The frequency and amplitude of the evoked otoacoustic responses reversibly decreased after exposure for 1 min to continuous sounds of more than 85 dB SPL with frequencies of about 2.5-7.5 kHz above the emission frequency. Similar effects occurred during anaesthesia or cooling. A possible relation between the existence of otoacoustic emissions and morphological specializations of the cochlea is discussed.

Acoustic Impedance Tests↗
PubMed1988

Time is traded for intensity in the bat's auditory system.

Disparities in time and intensity are the two chief cues animals use for localizing a sound source in space. Echolocating bats belonging to the family Molossidae emit brief, ultrasonic signals for orientation that sweep downward about an octave over the duration of the pulse. Due to acoustic shadowing and the directional properties of the ears, pronounced interaural intensity disparities are created that vary as a function of azimuth. However, due to the small headwidth of these animals, azimuthal changes create small interaural time disparities that are at most 30 microseconds. The experiments in this report are concerned with the binaural processing of time and intensity disparities using brief FM signals that simulate the animal's natural echolocation calls. Binaural neurons receiving excitation from one ear and inhibition from the other (E-I neurons) were recorded from the inferior colliculus of Mexican free-tailed bats. The majority of units sampled were highly sensitive for temporal disparities of 100-300 microseconds, and a few had significant changes in discharge probability when interaural time was changed by 10-20 microseconds. However, all E-I neurons were also sensitive to intensity disparities. With only one exception, all E-I neurons traded time for intensity. On the average, each decibel difference in intensity could be compensated for by advancing or delaying the inhibitory sound by 47 microseconds. The main conclusion is that the auditory system processes interaural disparities by transforming level differences at the two ears into latency differences. Thus the discharge probability of each binaural neuron is determined largely by the arrival times of the discharges from the excitatory and inhibitory ears. In view of the substantial time-intensity trading ratios, the small interaural time disparities produced by azimuthal locations off the midline play no role in shaping the response properties of these neurons. Specific examples of how time-intensity trades can translate into a high spatial selectivity are presented.

Animals↗
PubMed1991

Cochlear and CNS tonotopy: normal physiological shifts in the mustached bat.

The ear of the mustached bat (Pteronotus parnellii) shows marked cochlear resonance near 60 kHz and many sharply tuned neurons throughout the brain have best frequencies (BF) near the cochlear resonance frequency (CRF). Controlled changes in the normal physiological range of body temperature (approx 37-42 degrees C) were used to change the CRF and to study the tuning properties of neurons in the cochlear nucleus (CN) and inferior colliculus (IC). In all cases there were concomitant shifts in the CRF and the BFs. Results were the same for single and multi-units, and for CN and IC units. Although the BF reliably changed with shifts in the CRF, the majority of the units showed no change in minimum threshold or the sharpness (Q10 dB) of tuning. The temperature-induced effects on cochlear tuning were similar to those previously described in nonmammalian vertebrates. The physiological data reveal that, within a narrow frequency band, cochlear and CNS tonotopy are labile in the mustached bat. The lability of tuning is further substantiated by adaptations of biosonar emission behavior with shifts in CRF (Henson et al., 1990).

Acoustic Stimulation↗
PubMed1992

Enkephalin-like immunoreactivity in cochlear efferents in the bat, Rhinolophus ferrumequinum [corrected].

The cochlear efferent of the bat is anatomically different from other mammals. The olivocochlear bundle of the greater horse shoe bat, Rhinolophus ferrumequinum, projects only to inner hair cells. To examine the neurochemical nature of the olivocochlear bundle, we examined methionine-enkephalin-like immunoreactivity in this species. We observed immunoreactivity in the inner spiral bundles and in nerve fibers in the osseous spiral lamina. Sometimes immunostained inner spiral bundles were found to project towards inner hair cells. These data, as well as data from previous studies, suggest that cochlear efferents of different species of mammals share some common neurochemical features [corrected].

Animals↗
PubMed1993

The influence of temporal pattern of stimulation on delay tuning of neurons in the auditory cortex of the FM bat, Myotis lucifugus.

In echolocating bats, delay-sensitive neurons show facilitative responses to simulated pulse-echo pairs at particular echo delays. Three experiments examined how the temporal pattern of stimulation affected the delay tuning of neurons in the auditory cortex of the awake FM bat, Myotis lucifugus. First, delay tuning was compared using a series of pulse-echo pairs fixed in echo delay ('standard' stimuli), and a series of pulse-echo pairs in which successive sound pairs decreased by a fixed echo-delay step ('approach' stimuli). Similar best delays were measured with both stimulation patterns presented at repetition rates in which the neuron was delay-sensitive. At the higher delay-sensitive pulse repetition rates, approach stimuli evoked larger delay-dependent responses. Second, approach stimuli were fixed at different intertrial intervals. The best delay was unaffected by intertrial interval, although some neurons showed larger responses for longer intertrial intervals (0.5, 1.0 s), especially at the higher delay-sensitive pulse repetition rates. Third, approach stimuli were fixed at different echo-delay steps to simulate target velocity. The majority of neurons showed some sensitivity to echo-delay step, with clear preference for target velocity mainly between 1.8-7.0 m/s. This suggests that delay-sensitive neurons compute target velocity by rate of change of echo delay over successive echoes. Thus, response properties of cortical neurons are influenced by dynamic acoustic conditions found in target-directed flight.

Acoustic Stimulation↗
PubMed1994

After-discharges in the auditory cortex of the mustached bat: No oscillatory discharges for binding auditory information.

Action potentials of single or multi-neurons were recorded from the DSCF, FM-FM and DF areas in the auditory cortex of the mustached bat to study stimulus-induced neural oscillation in the auditory system. Out of 125 neurons 120 recorded in these three areas showed after-discharges to a best stimulus. Durations of after-discharges of 120 neurons ranged between 4.8 and 217 ms. In the remaining 5 neurons, the duration of the discharges was shorter that of the stimulus. The PST histograms displaying responses of these 125 neurons showed no oscillatory component locked to the stimulus. 98% of the autocorrelograms of responses (122/125) showed no sign of oscillation, but the remaining two percent showed a very weak oscillatory component that was not stimulus-locked. The duration of the after-discharges had no correlation with the best delay or cortical depth of neurons. After-discharges are common in the auditory cortex of the mustached bat, but oscillatory discharges are very rare, so that neural oscillations play no role in binding various types of biosonar information processed in the different 'specialized' areas in the auditory cortex.

Action Potentials↗
PubMed1994

Evidence for a mechanical filter in the cochlea of the 'constant frequency' bats, Rhinolophus rouxi and Pteronotus parnellii.

To investigate the function of basilar membrane (BM) thickenings in the cochlea of bats which use constant frequency (CF) echolocation calls, acoustic distortion products were measured while placing the primary stimuli f1 and f2 at frequencies which are represented in the thickened BM regions. In Rhinolophus, for primary stimuli between about 80-100 kHz, pronounced maxima of the level of distortion products (2f1-f2, 3f1-2f2, 4f1-3f2) can be measured if the frequency separation between the two primary tones is chosen so that the resulting distortion frequency matches the dominant CF frequency (resting frequency, RF). The distortion maxima extend from the individual RF down to frequencies which are 2-4 kHz lower. The data indicate that the thickened BM region in the basal halfturn of the cochlea strongly oscillates at the bats' RF and slightly below. The hearing threshold, however, is at a maximum at the RF (see Kössl 1993). Therefore, the RF oscillations are thought to be involved in absorbing the respective frequency such that the more apically located frequency place of the RF is insensitive and a mechanical notch filter is established. In Pteronotus, there are maxima of the level of 2f1-f2 at distortion frequencies around the RF of about 61.5 kHz up to the frequency of a strong stimulus-frequency otoacoustic emission (SFOAE) which is a few hundred Hz higher. Pronounced distortions in the RF range can only be elicited when the stimulus frequencies are between about 62 to 72 kHz. Similar to the situation in Rhinolophus, this frequency band is represented on a stretch of thickened BM.

Acoustic Stimulation↗
PubMed1995

The effect of contralateral stimulation on cochlear resonance and damping in the mustached bat: the role of the medial efferent system.

In the unanesthetized mustached bat, stimulation of the ear with an acoustic transient produces damped oscillations which are evident in the cochlear microphonic potential. In this report we demonstrate how the decay time of these oscillations is affected by broadband noise presented to the contralateral ear (CLN). In the absence of CLN, the mean decay time was 1.94 +/- 0.23 ms, but during the presentation of CLN the decay time consistently decreased. The changes were finely graded, the higher the CLN, the greater the change. The effect could be maintained at a constant level for extended periods of time and this was evident when the CLN exceeded 40 dB SPL. The latency of the reflex for 64 dB noise was about 11 ms and near maximum changes occurred within 15 ms of CLN onset. Sectioning medial efferent nerve fibers in the floor of the fourth ventricle or the administration of a single dose of gentamicin eliminated changes produced by CLN. The prominence of CM responses to damped oscillations and the robust changes in response to CLN make the mustached bat an excellent model for studying the influence of the medial efferent system on cochlear mechanics.

Acoustic Stimulation↗
PubMed1996

Further studies on the mechanics of the cochlear partition in the mustached bat. I. Ultrastructural observations on the tectorial membrane and its attachments.

From semithin and ultrathin sections of the mustached bat cochlea, baso-apical gradients in ultrastructural composition, shape and attachment site of the tectorial membrane (TM) were determined in relation to gradients in hair cell size and stereocilia size. These provide a data base for estimates of the mechanical properties of the organ of Corti as they relate to specialized aspects of the cochlear frequency map (Kössl and Vater, 1996). As in other mammals, the TM is composed to type A and type B protofibrils. Measurements of the packing density of type A protofibrils reveal gradients in both the radial and longitudinal direction. Distinct variations in packing density of type A protofibrils across the radial extent of the TM allow the definition of more subregions than in other mammals. Throughout the cochlea, packing density is highest in the 'stripe' region located close to the spiral limbus. The centrally located 'core' region of the middle zone contains distinctly fewer type A protofibrils than the laterally located 'mantle' region of the middle zone. The TM in the specialized basal turn (first and second half-turns) features a higher packing density of type A protofibrils in the 'mantle' than the TM in the apical cochlea (upper third to fifth half-turns), and in incorporation of longitudinally directed type A protofibrils in the marginal zone. Among cochlear turns, there are pronounced changes in cross-sectional area of the TM and the extent of its limbal attachment site. Within the densely innervated second half-turn that contains an expanded representation of the 60 kHz constant frequency (CF) component of the echolocation signal, both the cross-sectional area (see also Henson and Henson, 1991) and the attachment site of the TM are enlarged. An extended limbal attachment site is also observed in the densely innervated region of the lower first half-turn that represents the upper harmonics of the call. Within the sparsely innervated region of the upper first half-turn, the limbal attachment site of the TM is significantly diminished. Size of outer hair cells (OHC) ranges between 12 and 13 microns throughout the basal 80% of cochlear length and reaches maximal values of 20 microns in the apex. Size of OHC stereocilia ranges between 0.7 and 0.8 microns throughout the basal 60% of cochlear length and reaches a maximal size of 2.2 microns in the apex. These data corroborate and extend previous notions that morphological specializations of the TM in concert with specializations of the basilar membrane and perilymphatic spaces play an integral role in creating specialized cochlear tuning in the mustached bat.

Animals↗
PubMed1996

The course and distribution of medial efferent fibers in the cochlea of the mustached bat.

The course and distribution of medial olivocochlear (MOC) nerve fibers were studied in the cochlea of the mustached bat. This animal is of interest because of the very sharp tuning of the ear and fine frequency resolution in small frequency bands near 60 and 90 kHz. The MOC fibers arise from about 400 cells in the dorsomedial periolivary (DMPO) nucleus and they are distributed to approximately 4500 outer hair cells (OHCs), resulting in an average OHC unit size of 11.25. Individual fibers appear to have a small number of branches and each branch entering the tunnel of Corti terminates on a patch of OHCs. The patch size is typically 1-3 OHCs with the smallest average patch sizes in the regions tuned to 60 and 90 kHz. The majority of the MOC terminals are derived from the contralateral DMPO. Contralateral vs. ipsilateral projecting fibers are not preferentially distributed within any of the three rows of OHCs or within specific regions throughout most of the cochlea. It can be concluded that the main differences between the mustached bat's MOC system and that of most other mammals are: (1) origin from a single nucleus; (2) relatively small sizes of the patches; (3) a single terminal on each OHC; (4) a gradient in the size of the terminals but not in the number of terminals from row to row or from base to apex.

Acetylcholine↗