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At least 433 records · Page 24Linked to original sources
PubMed1993

An audio-vocal interface in echolocating horseshoe bats.

The control of vocalization depends significantly on auditory feedback in any species of mammals. Echolocating horseshoe bats, however, provide an excellent model system to study audio-vocal (AV) interactions. These bats can precisely control the frequency of their echolocation calls by monitoring the characteristics of the returning echo; they compensate for flight-induced Doppler shifts in the echo frequency by lowering the frequency of the subsequent vocalization cells (Schnitzler, 1968; Schuller et al., 1974, 1975). It was the aim of this study to investigate the neuronal mechanisms underlying this Doppler-shift compensation (DSC) behavior. For that purpose, the neuronal activity of single units was studied during spontaneous vocalizations of the bats and compared with responses to auditory stimuli such as playback vocalizations and artificially generated acoustic stimuli. The natural echolocation situation was simulated by triggering an acoustic stimulus to the bat's own vocalization and by varying the time delay of this artificial "echo" relative to the vocalization onset. Single-unit activity was observed before, during, and/or after the bat's vocalization as well as in response to auditory stimuli. However, the activity patterns associated with vocalization differed from those triggered by auditory stimuli even when the auditory stimuli were acoustically identical to the bat's vocalization. These neurons were called AV neurons. Their distribution was restricted to an area in the paralemniscal tegmentum of the midbrain. When the natural echolocation situation was stimulated, the responses of AV neurons depended on the time delay between the onset of vocalization and the beginning of the simulated echo. This delay sensitivity disappeared completely when the act of vocalization was replaced by an auditory stimulus that mimicked acoustic self-stimulation during the emission of an echolocation call. The activity of paralemniscal neurons was correlated with all parameters of echolocation calls and echoes that are relevant in context with DSC. These results suggest a model for the regulation of vocalization frequencies by inhibitory auditory feedback.

Adaptation, Physiological↗
PubMed1997

Efficacy and toxicity of 67Cu-2IT-BAT-Lym-1 radioimmunoconjugate in mice implanted with human Burkitt's lymphoma (Raji).

Radioimmunotherapy has shown promising results for treatment of radiosensitive malignancies such as lymphoma. Positive responses have been reported in patients with non-Hodgkin's lymphoma treated with 131I-radiolabeled Lym-1, a mouse anti-lymphoma monoclonal antibody. In this study, the efficacy of 67Cu-radiolabeled Lym-1 was examined. Nude mice bearing human Burkitt's lymphoma (Raji) tumors (20-524 mm3) were treated with 12.4, 14.8, 18.5, and 23.3 MBq of 67Cu-2IT-BAT-Lym-1. Tumor size was measured to assess efficacy, and mouse weight, blood counts, and mortality were monitored to assess toxicity. In mice treated with 12.4, 14.8, and 18.5 MBq of 67Cu-2IT-BAT-Lym-1, 50% (9 of 18), 42% (5 of 12), and 50% (3 of 6) of tumors achieved remission or cure; 33% of tumors were cured overall; and significant regrowth delay was observed. The 23.3 MBq dose group did not yield meaningful efficacy data because of high mortality. In control groups receiving 14.8 and 18.5 MBq of the isotype-matched nonspecific monoclonal antibody radioimmunoconjugate, 67Cu-2IT-BAT-L6, 0% (0 of 15) and 17% (2 of 12) of tumors achieved a response; hence, targeted delivery of radiation was the dominant antitumor mechanism of 67Cu-2IT-BAT-Lym-1. LD50/30 for mice treated with 67Cu-2IT-BAT-Lym-1 and -L6 were 21.6 and 20.6 MBq, respectively. In conclusion, 67Cu-2IT-BAT-Lym-1 provided a therapeutic and frequently curative dose of radiation to tumored mice with modest toxicity.

Animals↗
PubMed1998

Ultrastructure of the binary parotid glands in the free-tailed bat, Tadarida thersites. I. Principal parotid gland.

BACKGROUND: Many species of bats have two sets of submandibular glands, principal and accessory. The accessory gland may resemble the principal one but more often shows wide morphological divergence. The free-tailed bat, Tadarida thersites, is very unusual in that it has two sets of parotid glands rather than binary submandibular glands. We studied the ultrastructure of the principal parotid gland to establish a baseline for comparison with the accessory parotid. METHODS: Two specimens of adult free-tailed bats, one male and one female, were live-trapped in western Kenya. Parotid glands were fixed for electron microscopy using a protocol expressly designed for field fixation and then embedded by conventional means. RESULTS: Histologically, the principal parotid is a typical serous gland. The secretory granules of the endpiece cells have an unusual substructure in that they contain variable numbers of lucent halos and one or several spherules. Intercalated duct cells contain a significant number of dense, serous-like granules. Striated ducts have the usual basal configuration of mitochondria and folded plasma membranes, but the supranuclear cytoplasm contains many small, dense granules, so that these ducts resemble the granular convoluted tubules found in the submandibular glands of many families of rodents. The apices of the duct cells have a peculiar contour--the luminal surfaces obliquely invaginate into the apical cytoplasm, so that in thin section the luminal membranes appear to be underlaid by a layer of vacuoles. CONCLUSION: Although the principal parotid gland of the free-tailed bat shows some distinctive, species-specific ultrastructural features, it basically is similar to the parotid gland in two other molossid bats, Tadarida brasiliensis and Molossus molossus. The distinctive features in the principal parotid gland of T. thersites might relate to its feeding on hard-bodied insects and perhaps to the production of lysozyme.

Animals↗
PubMed1998

Intercellular material in the basal and lateral folds of parotid serous cells in four species of bats.

BACKGROUND: Basal folds are slender plications at the basal surface of acinar cells in the salivary glands of many mammalian species. These largely organelle-free folds increase the surface area of the basal plasmalemma manyfold and are unquestionably involved in the translocation of organic and inorganic molecules and water into the acinar cells. METHODS: Specimens of salivary glands were obtained from over 230 species of live-trapped bats from major areas of the globe. Tissues for electron microscopy were fixed and processed by conventional means. RESULTS: A number of the bat species examined had dense material in the intercellular spaces between basal and lateral folds of serous cells in the parotid gland. This intercellular material was particularly prominent in three species of New World bats, viz., Pteronotus parnellii, P quadridens, and Phyllostomus latifolius, and in one species of Old World bats, Chalinolobus argentatus. This dense material, which has a farinaceous texture, appears not to pass through tight junctions, so it is excluded from the lumina of intercellular canaliculi and acini. The dense material originates in the acinar cells--it is carried to the membranes of the folds via coated vesicles, which empty their dense content by exocytosis into the intercellular space. Similar dense material is present in the intercellular spaces of the basal labyrinth of striated ducts in the two species of Pteronotus. The manner in which this material accumulates in the striated duct is unclear. CONCLUSIONS: Although the function of the intracellular dense material is undetermined, it appears to be placed strategically to influence molecular traffic into acinar cells or to modulate the paracellular pathway. From a comparative evolutionary perspective, we hypothesize that, in bats, the combination of basal folds and extracellular densities is associated with insectivory. Similar morphologies appear to be lacking in frugivorous or nectarivorous species.

Animals↗
PubMed1998

Rapid and nonisotopic SSCP-based analysis of the BAT-26 mononucleotide repeat for identification of the replication error phenotype in human cancers.

Microsatellite instability is an important new form of genetic alteration that characterizes tumors of the replication error phenotype (RER+). The RER status of tumors has been determined until now by analyzing several microsatellite loci for size variations compared with matching normal DNA. This has been done by separating isotopically labeled PCR products on denaturing gels. We recently showed that deletions within BAT-26, a polyadenine tract within the hMSH2 gene, could be used to establish the RER status of tumors without the need for matching normal DNA. We now propose a rapid and nonisotopic method of determining RER status based on PCR-SSCP analysis of the BAT-26 poly(A) tract. Compared with conventional means of examining RER+, this method reduces the PCR and gel manipulations involved by 10-fold. Size variations of as little as 2 bp in the BAT-26 sequence were readily detected using mini-sized, silver-stained SSCP gels run for 2.5 h. The incidence of RER+ detected in 183 right-sided colonic, 121 gastric, and 123 endometrial carcinomas was 20%, 10%, and 5% respectively, using this method. Frameshift mutations in the mononucleotide repeat of the TGF-beta RII gene were found in 86% (42/49) of RER+ but less than 1% (1/237) of RER- colon and gastric tumors identified by BAT-26 analysis. Our results demonstrate that nonisotopic PCR-SSCP of the poly(A) BAT-26 tract is a specific, sensitive and rapid method for determining the RER status of human tumors.

DNA Replication↗
PubMed2005

Neurobiological specializations in echolocating bats.

Although the bat's nervous system follows the general mammalian plan in both its structure and function, it has undergone a number of modifications associated with flight and echolocation. The most obvious neuroanatomical specializations are seen in the cochleas of certain species of bats and in the lower brainstem auditory pathways of all microchiroptera. This article is a review of peripheral and central auditory neuroanatomical specializations in echolocating bats. Findings show that although the structural features of the central nervous system of echolocating microchiropteran bats are basically the same as those of more generalized mammals, certain pathways, mainly those having to do with accurate processing of temporal information and auditory control of motor activity, are hypertrophied and/or organized somewhat differently from those same pathways in nonecholocating species. Through the resulting changes in strengths and timing of synaptic inputs to neurons in these pathways, bats have optimized the mechanisms for analysis of complex sound patterns to derive accurate information about objects in their environment and direct behavior toward those objects.

Animals↗
PubMed1988

Origin of ascending projections to an isofrequency region of the mustache bat's inferior colliculus.

The inferior colliculus of the mustache bat is similar in most respects to the inferior colliculus of more commonly studied mammals, but one isofrequency contour, the dorsoposterior division, is greatly overrepresented. The present study utilizes this specialization of the auditory system in the mustache bat to determine the total set of ascending projections to a single isofrequency contour of the inferior colliculus. Within the dorsoposterior division, neurons are all very narrowly tuned to 60 kHz, the major component of this bat's echolocation call. The afferent projections to this isofrequency contour were identified by making deposits of horseradish peroxidase (HRP) within the dorsoposterior division after physiologically defining its borders. Two other frequency representations are present in the central nucleus of the inferior colliculus of the mustache bat, the anterolateral division in which there is an orderly progression of frequencies from 59 down to 20 kHz, and the medial division in which frequencies from 63-120 kHz are represented. In additional experiments, the afferent projections to the medial and anterolateral divisions were examined, providing an anatomical description of the tonotopicity of the lower auditory nuclei. Deposits of HRP in the DPD labeled cells in each of the lower brainstem auditory nuclei that have previously been shown to project to the entire central nucleus of the inferior colliculus. The ascending projections to the dorsoposterior division include contralateral projections from the cochlear nucleus and inferior colliculus, ipsilateral projections from the medial superior olive, ventral and intermediate nuclei of the lateral lemniscus, and bilateral projections from the lateral superior olive and dorsal nucleus of the lateral lemniscus. In most of the nuclei, labeled cells were confined to specific portions of the nuclei, often forming "slabs" of labeled cells across the rostrocaudal extent of most nuclei. These slabs presumably represent the 60 kHz representation in each of the lower nuclei. When deposits of HRP were made into other frequency band representations of the inferior colliculus, in either the medial or anterolateral division, labeled cells again formed slabs in each lower nucleus. However, the location of the slab varied as a function of the best frequency of neurons at the deposit site, and labeled cells were not present within the 60 kHz representation. These results show the general tonotopy of the mustache bat's brainstem auditory nuclei, and with respect to the dorsoposterior division, clearly reveal the total set of projections to a single isofrequency region.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1989

Functional organization of mustached bat inferior colliculus: I. Representation of FM frequency bands important for target ranging revealed by 14C-2-deoxyglucose autoradiography and single unit mapping.

The representation in the inferior colliculus of the frequency modulated (FM) components of the first (25-30 kHz) and second (50-60 kHz) harmonic of the sonar signal of the mustached bat, which may be important for target range processing, was investigated by using the 2-deoxyglucose (2-DG) technique and single-unit mapping. In the 2-DG experiments, bats presented with second harmonic FM stimuli alone showed uptake of label in specific regions of the central nucleus and dorsal cortex of the inferior colliculus, and the nucleus of the brachium. In the central nucleus, a dorsoventrally and mediolaterally elongated slab at the caudal border of the anterolateral division was observed. Labeling in the dorsal cortex was contiguous with this band. Bats stimulated with pairs of first and second harmonic FM stimuli separated by short time delays showed similar patterns of labeling, with the addition of another dorsoventrally elongated region of uptake in the more rostral part of the anterolateral division, associated with label in the dorsal cortex. By comparison to control cases exposed to delayed pairs of first and third harmonic signals, or to a second harmonic constant-frequency tone burst at the bat's reference frequency (ca. 60 kHz), we deduced that this additional region of uptake was attributable to the first harmonic FM component. To elucidate further the details of the tonotopic organization and to correlate the frequency representation with anatomical features of the IC, fine-grained maps of single-unit best frequencies were obtained in the central nucleus. Isofrequency contours were reconstructed by computer from five bats after focal, iontophoretic injection of horseradish peroxidase to locate the penetrations and trace connections of the FM2 area. We found that the tissue volume representing FM2 frequencies (50-60 kHz) showed approximately a sixfold overrepresentation for this frequency band. This region occupied most of the caudal portion of the anterolateral division of the central nucleus. Only a single tonotopic representation was found in the central nucleus, consistent with the pattern seen in other mammals. However, isofrequency contours in the anterolateral division were oriented dorsoventrally, approximately parallel to the coronal plane. The small band of frequencies (ca. 60-62 kHz) associated with the dominant constant-frequency component of the biosonar signal was even more dramatically overrepresented (40x) and was confined to the dorsoposterior division, as previously reported by Zook et al. (1985, 530-456).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1989

Connections and frequency representation in the auditory brainstem of the mustache bat, Pteronotus parnellii.

The goals of this study were to describe the cochlear frequency map of the mustache bat, Pteronotus parnellii, and to relate the organization of cochlear primary afferents to that of the second-order projections from the cochlear nucleus to the superior olivary complex. Small deposits of horseradish peroxidase (HRP) were placed in the cochlear nucleus at sites that were physiologically characterized with respect to unit-best frequency. From the deposits, labeled fibers were traced in the retrograde direction to the cochlea and in the anterograde direction to the superior olive. Cochleas from both experimental and control animals were examined with light and electron microscopy. The peripheral axons of spiral ganglion neurons were counted in order to quantify the unusual variation in the innervation density along the cochlear spiral of the mustache bat. Regions of increased innervation density were found at the beginning and end of the basal turn of the cochlea. The highest cochlear innervation density consistently occurred in the upper basal turn. In horseradish peroxidase tracing experiments, this region contained labeled fibers only when HRP deposits were made at sites within the cochlear nucleus with unit-best frequencies around 60 kHz. These findings support the suggestion (Kössl and Vater, '85) that the cochlear sites of increased innervation density are related to the neural and behavioral emphasis that this echolocating bat places upon the analysis of the 60 kHz frequency band. The general arrangement of tonotopic maps within the cochlea, cochlear nucleus, and superior olive was consistent with previous observations in this bat and other mammalian species. At all three levels, there was evidence of a disproportionately large representation of frequencies around 60 kHz, similar to the enlarged representation reported within the inferior colliculus and auditory cortex of the mustache bat. In all cases there was a consistent relation between the size of the HRP deposit and the number and distribution of retrogradely labeled neurons in the cochlea. For most cases there was a similar relation between the size of the deposit and the terminal arborization field of anterogradely labeled fibers in the superior olive. However, in cases with deposits associated with the 60 kHz frequency band, the size of the labeled arborization field was more than twice as large as expected from the size of the deposits and from the extent of labeling in the cochlea. These cases suggest that the representation of frequencies around 60 kHz, already overrepresented in both the cochlea and cochlear nucleus, may be further expanded at the level of the superior olivary complex.

Acoustic Stimulation↗
PubMed1992

GAD- and GABA-immunoreactivity in the ascending auditory pathway of horseshoe and mustached bats.

A comparative study of the immunostain to antibodies directed against glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) in the ascending auditory pathway was carried out in horseshoe bats (Rhinolophus rouxi) and mustached bats (Pteronotus parnellii). In both species GAD/GABA-positive puncta (presumed axonal boutons) and GAD/GABA-positive cells were found in the cochlear nucleus, the superior olivary complex, the nuclei of the lateral lemniscus the inferior colliculus, and the medial geniculate body. General features of the immunostaining pattern in the auditory pathway agree with observations in other mammals. Quantitative analysis of puncta distribution shows that many auditory centers are characterized by subregional differences in puncta density and distribution. This indicates local differences in putatively inhibitory input related to connectivity and tonotopic organization. The following species characteristic features were found: 1) The dorsal non-laminated portion of the dorsal cochlear nucleus in horseshoe bats lacks the GAD/GABA-immunoreactive cells typical for the ventral laminated portion and the dorsal cochlear nucleus of other species. Clearly, a cytoarchitectonic specialization is accompanied by a loss of putatively GABAergic local inhibitory circuits. 2) The ventral division of the medial geniculate body of the mustached bat lacks GAD/GABA-immunopositive cells. Such cells are present in the horseshoe bat and other mammals. This finding implies functional differences in the organization of the medial geniculate body within the same mammalian order.

Animals↗
PubMed1994

Anatomy and projection patterns of the superior olivary complex in the Mexican free-tailed bat, Tadarida brasiliensis mexicana.

The superior olivary complex (SOC) is the first station in the ascending auditory pathway that receives binaural projections. Two of the principal nuclei, the lateral superior olive (LSO) and the medial superior olive (MSO), are major sources of ascending projections to the inferior colliculus. Whereas almost all mammals have an LSO, it has traditionally been thought that only animals that hear low frequencies have an MSO. Recent reports, however, suggest that the medial part of the SOC in bats is highly variable and that at least some bats have a well-developed MSO. Thus, the main goal of this study was to evaluate the cytoarchitecture and connections of the principal superior olivary nuclei of the Mexican free-tailed bat, with specific attention directed at the MSO. Cell and fiber stained material revealed that the LSO and the medial nucleus of the trapezoid body (MNTB) are similar to those described for other mammals. There are two medial nuclei we refer to as dorsomedial periolivary nucleus (DMPO) and MSO. Tracer experiments exhibited that the DMPO receives bilateral projections from the cochlear nucleus, and additional projections from the ipsilateral MNTB. The DMPO sends a strong projection to the ipsilateral inferior colliculus. Positive staining for acetylcholinesterase indicates that the DMPO is a part of the olivocochlear system, as it is in other animals. The MSO in the free-tailed bat meets many of the criteria that traditionally define this nucleus. These include the presence of bipolar and multipolar principal cells, bilateral innervation from the cochlear nucleus, a strong projection from the ipsilateral MNTB, and the absence of cholinergic cells. The major difference from traditional MSO features is that it projects bilaterally to the inferior colliculus. Approximately 30% of its cells provide collateral projections to the colliculi on both sides. Functional implications of the MSO for the free-tailed bat are considered in the Discussion.

Acetylcholinesterase↗
PubMed1995

Ultrastructural and immunocytochemical observations on the superior olivary complex of the mustached bat.

This study investigates the functional organization of the superior olivary complex of the mustached bat with classical transmission electron microscopy and postembedding immunocytochemistry for gamma-aminobutyric acid (GABA) and glycine antisera in semithin serial sections. The ultrastructure and distribution of terminal types in the lateral superior olive (LSO) and the medial nucleus of the trapezoid body (MNTB) closely resemble that of other mammals; the organization within the medial superior olive (MSO) differs significantly. The differences concern the relative proportion of putatively inhibitory boutons, which appear as symmetrical synapses with flattened vesicles on MSO somata. In the bat, inhibitory boutons comprised 75-100% of perisomatic boutons, a value identical to that observed in the LSO. These terminals most likely arise from the MNTB. In other species, putatively inhibitory terminals form a much smaller proportion of perisomatic boutons in MSO. This difference suggests that in the bat MSO excitatory input to cell somata is considerably reduced and outweighed by inhibitory input. This suggestion is corroborated by immunocytochemical data. Glycine-immunoreactive puncta encrust somata of LSO and MSO cells to a similar degree and in rather homogeneous patterns throughout these nuclei. Putatively GABAergic terminals are located mainly on distal dendrites of MSO and LSO cells. Regional variations in the density of GABA-immunoreactive puncta in LSO suggest that different tonotopic zones are under differential modulatory influence. Both the LSO and MSO of the mustached bat contain significant amounts of putatively inhibitory projection cells. Coexistence of both antigens was commonly observed in subsets of cells. Quantitative analyses of labeling patterns and comparisons with other mammals suggest that the mix of neurotransmitters in projection cells of LSO and MSO is phylogenetically flexible, and thus the details of the functions of ascending pathways are species specific. In contrast to other mammals, the bat MSO forms parallel output pathways with excitatory and inhibitory components. Data are discussed in relation to specialized physiological response features.

Animals↗
PubMed2002

Basic properties and annual changes of follicle-stimulating hormone receptors in the testis of horseshoe bats, Rhinolophus ferrumequinum.

The unique reproductive patterns, delayed fertilization in females, and asynchrony between spermatogenesis and mating behavior in males are well documented in bats living in temperate latitudes. The present study was undertaken to examine follicle-stimulating hormone (FSH) receptors in the testis of bats, Rhinolophus ferrumequinum, during the annual reproductive cycle. Male bats were captured at natural roosting sites and testicular preparations were subjected to a radioligand binding assay for FSH receptors. The weight of paired testes increased considerably in the spermatogenic period and decreased from the mating to hibernation periods. Meiotic division in the testis was observed in the spermatogenic period but not the mating period. Serum testosterone concentrations increased in the spermatogenic period and rapidly decreased in the mating period. The binding of FSH was specific for mammalian FSHs and detected primarily in the testis. Scatchard plot analyses of the binding of FSH to bat testicular preparations showed straight lines, suggesting the presence of a single class of binding sites. The affinities (equilibrium association constant) of FSH receptors were consistent throughout the annual reproductive cycle. The specific binding per unit weight of testis and total binding in the paired testes were highest in the mating period and in the spermatogenic period, respectively, among reproductive periods. The accumulation of cyclic adenosine 3', 5'-monophosphate to FSH stimulation was higher in the spermatogenic period than in the hibernation period. These findings suggest that testicular function of bats is associated with seasonal changes in the number of binding sites, while the number per target cell and the activation of adenylate cyclase led by FSH-receptor complex considerably decreases in the hibernation period.

Adenylyl Cyclases↗
PubMed1976

Feeding adaptations in the hairs and tongues of nectar-feeding bats.

Scales on the hairs of pollinating bats spread out at an angle to the main hair shaft. In contrast, the hairs of most bats not associated with plants are relatively smooth. Both megachiropteran and microchiropteran flower-feeding bats show this divaricate scale structure which may aid in the collection of a heavy coating of pollen. Some of the pollen is transferred to subsequent flowers, but most is groomed from the fur and ingested as the only reliable nitrogen source for the bat. The tongues of nectar-feeding bats also show structural modifications which allow efficient uptake of the carbohydrate fraction of the diet. Structural specializations of the hiars and tongue are analogous to those seen in other nectar-feeding animals.

Adaptation, Biological↗
PubMed1990

Convergence of temporal and spectral information into acoustic images of complex sonar targets perceived by the echolocating bat, Eptesicus fuscus.

1. FM echolocating bats (Eptesicus fuscus) were trained to discriminate between a two-component complex target and a one-component simple target simulated by electronically-returned echoes in a series of experiments that explore the composition of the image of the two-component target. In Experiment I, echoes for each target were presented sequentially, and the bats had to compare a stored image of one target with that of the other. The bats made errors when the range of the simple target corresponded to the range of either glint in the complex target, indicating that some trace of the parts of one image interfered with perception of the other image. In Experiment II, echoes were presented simultaneously as well as sequentially, permitting direct masking of echoes from one target to the other. Changes in echo amplitude produced shifts in apparent range whose pattern depended upon the mode of echo presentation. 2. Eptesicus perceives images of complex sonar targets that explicitly represent the location and spacing of discrete glints located at different ranges. The bat perceives the target's structure in terms of its range profile along a psychological range axis using a combination of echo delay and echo spectral representations that together resemble a spectrogram of the FM echoes. The image itself is expressed entirely along a range scale that is defined with reference to echo delay. Spectral information contributes to the image by providing estimates of the range separation of glints, but it is transformed into these estimates. 3. Perceived absolute range is encoded by the timing of neural discharges and is vulnerable to shifts caused by neural amplitude-latency trading, which was estimated at 13 to 18 microseconds per dB from N1 and N4 auditory evoked potentials in Eptesicus. Spectral cues representing the separation of glints within the target are transformed into estimates of delay separations before being incorporated into the image. However, because they are encoded by neural frequency tuning rather than the time-of-occurrence of neural discharges, the perceived range separation of glints in images is not vulnerable to amplitude-latency shifts. 4. The bat perceives an image that is displayed in the domain of time or range. The image receives no evident spectral contribution beyond what is transformed into delay estimates. Although the initial auditory representation of FM echoes is spectrogram-like, the time, frequency, and amplitude dimensions of the spectrogram appear to be compressed into an image that has only time and amplitude dimensions.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1994

Echo SPL influences the ranging performance of the big brown bat, Eptesicus fuscus.

Four bats of the species Eptesicus fuscus were trained in a two-alternative forced-choice procedure to discriminate between two phantom targets that differed in range. The rewarded stimulus was located at a distance of 52.7 cm, while the other unrewarded stimulus was further away. Only one target was presented at a time. In the first experiment we measured the range discrimination performance at an echo SPL of -28 dB relative to the bat's sonar transmission. A 75% correct performance level was arbitrarily defined as threshold and was obtained at a delay difference of 80 microseconds, corresponding to a range difference of 13.8 mm. In the second experiment the delay difference was fixed at 150 microseconds and the echo SPL varied between -8 and -48 dB relative to sonar emissions. The performance of the bats depended on the relative echo SPL. AT -28 dB the bats showed the best performance. It deteriorated at an increase of the relative echo SPL to -18 dB and -8 dB. The performance also deteriorated when the relative echo SPL was reduced to -38 dB and -48 dB. Only at low relative echo SPLs did the bats partially compensate for the reduction in echo SPL and increased the SPL of their emitted signals by a few dB. Our results support the hypothesis that neurons exhibiting paradoxical latency shift may be involved in encoding target range. This hypothesis predicts a decrease in performance at high echo SPLs as we found it in our experiments. The observed reduction in performance at very low echo SPLs may be due to a decrease in S/N ratio.

Animals↗
PubMed1996

The degradation of distance discrimination in big brown bats (Eptesicus fuscus) caused by different interference signals.

The ability of two big brown bats (Eptesicus fuscus) to discriminate the distance to an electronically synthesized "phantom" target by echolocation was tested in the presence of interfering signals presented slightly before the target echo. Interfering signals were chosen to have differing degrees of similarity to the typical echolocation emission used by the bat in this task (which was the signal used to create the phantom target), and we predicted that the degree of disruption of ranging would be proportional to the similarity of the interference to the target echo. This prediction was not confirmed; rather, all interference signals not identical to the target echo increased the threshold to about twice that found with no interference. When the interference was identical to the target echo, the threshold increased to about 4 times that with no interference. When each bat was presented with phantom target "echoes" appropriate for the other bat, its range discrimination threshold increased about ten fold, and in this case the degree of interference of different signals was related to their similarity to the target echo, not to their similarity to the bat's "normal" signal. We suggest that Eptesicus may suppress interference by a more sophisticated strategy than simple linear matched filtering.

Animals↗
PubMed1996

The orientation behaviour of the lesser spearnosed bat, Phyllostomus discolor (Chiroptera) in a model roost. Concurrence of visual, echoacoustical and endogenous spatial information.

The orientation behaviour of bats (Phyllostomus discolor, Phyllostomidae), flying inside an octagonal "roost-like" chamber (phi: 100 cm; h: 150 cm) was examined. It has been shown that the bats begin turning manoeuvres during flight by turning their head towards the direction they intend to proceed to. During early phases of the flights, cumulative navigation errors were evident, indicating that endogenous spatial information plays a major role in the orientation of the bats. During later phases of the flight this error is diminished again. So it can be concluded that the bats start to use exogenous spatial information for orientation while approaching the target. In order to investigate the relative importance of vision, echolocation and endogenous spatial information for approaching the roost, the landing lattices inside the test arena were changed for non-grid dummies. We found that: 1. combined visual and endogenous information are more important than echoacoustical cues, 2. the bats learned quickly to switch their orientation behaviour in order to get a better performance in avoiding the dummies, 3. the learning performance was influenced by the visual similarity of dummies and the real landing lattice.

Animals↗