Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “BATS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52Linked to original sources
PubMed2002

Selectivity for echo spectral interference and delay in the auditory cortex of the big brown bat Eptesicus fuscus.

The acoustic environment for an echolocating bat can contain multiple objects that reflect echoes so closely separated in time that they are almost completely overlapping. This results in a single echo with a spectrum characterized by deep notches due to interference. The object of this study was to document the possible selectivity, or lack thereof, of auditory neurons to the temporal separation of biosonar signals on a coarse (ms) and fine (micros) temporal scale. We recorded single-unit activity from the auditory cortex of big brown bats while presenting four protocol designs using wideband FM signals. The protocols simulated a pair of partially overlapping echoes where the separation between the first and second echo varied between 0 and 72 micros, a pulse followed by a single echo at varying delay from 0 to 30 ms, a pulse followed at a fixed delay by a pair of partially overlapping echoes that had a varying temporal separation of 0-72 micros, and a pulse followed, with a varying delay between 0 and 30 ms, by a pair of echoes that themselves had a fixed temporal separation on a microsecond time scale. About half of the cortical units showed increased spike counts to pairs of partially overlapping echoes at particular separations (6-72 micros) compared with a baseline stimulus at 0-micros separation. For many neurons tested with a pulse followed by two overlapping echoes, we observed a sensitivity to the coarse delay between the pulse and pair of overlapping echoes and to the separation between the two echoes themselves. The sensitivity to the partial overlap between the two echoes was not tuned to a single temporal separation. For bats, this means that the absolute range to the closest reflector and range between reflectors may be jointly encoded across a small population of single units. There are several possible neuronal mechanisms for encoding the separation between two nearby echoes based on the sensitivity to spectral notches.

Acoustic Stimulation↗
PubMed1991

Combination-sensitive neurons in the medial geniculate body of the mustached bat: encoding of relative velocity information.

1. Orientation sounds (pulses) emitted by the mustached bat (Pteronotus parnellii) consist of up to four harmonics (H1-4); each harmonic contains a constant frequency (CF) component and a terminal frequency modulated (FM) component, so that there are eight components in total (CF1-4 and FM1-4). By referring the echo from a target to the emitted pulse, the mustached bat derives velocity information from Doppler shift and distance information from echo delay. In this study, the responses of single neurons in the medial geniculate body (MGB) to synthetic biosonar signals were investigated. Stimuli consisted of CF, FM, and CF-FM sounds. Paired CF-FM sounds were used to mimic any two harmonics of pulse-echo pairs. The dorsal and medial divisions of the MGB were found to contain combination-sensitive neurons. These neurons responded poorly to individual sounds regardless of frequency and amplitude and were facilitated by paired sounds presented at particular frequencies, amplitudes and inter-component intervals (simulated echo delay). Combination-sensitive neurons were tuned to the frequencies that characterize particular components of natural biosonar signals and were classified according to the components of pulse-echo pairs that best matched the spectral selectivity of the neuron. Two classes of combination-sensitive neurons were found, CF/CF and FM-FM. This paper focuses on CF/CF combination-sensitive neurons, which extract velocity information from paired CF components, and on CF2 and CF3 neurons, which, although not combination-sensitive, are tuned to the frequencies of the CF2 and CF3 components of biosonar signals. 2. CF2 and CF3 neurons were sharply tuned in frequency. The best frequencies of the most sharply tuned CF2 neurons were all approximately equal to 61.17 kHz (SD = 370 Hz), which closely matches the frequency at which P. parnellii stabilizes the CF2 component of an echo when compensating for Doppler shift. Thus CF2 neurons are specialized for a fine analysis of Doppler-compensated echoes. 3. Tuning curves of CF2 and CF3 neurons remained narrow regardless of stimulus level. When compared at high stimulus levels (30 and 50 dB above minimum threshold), bandwidths of tuning curves of CF2 and CF3 neurons were much smaller than those of peripheral auditory neurons turned to CF2 or CF3 frequencies but were about the same as those of cortical neurons tuned to CF2 or CF3 frequencies. Thus the sharpening of neural tuning curves by the bat's central auditory system occurs within or before the MGB.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1991

Binaural properties of single units in the superior olivary complex of the mustached bat.

1. Previous studies of the superior olive of echolocating bats suggest that the lateral superior olive (LSO) retains the same structure and function as in other mammals but that the medial superior olive (MSO) is different in structure and possibly also in function. The present study is an examination of this idea in Pteronotus parnellii, a bat that has a large and well-defined MSO. 2. Using pure tones presented via earphones, we obtained data on frequency tuning for 60 single units and 96 multiunits in LSO and 94 single units and 154 multiunits in MSO. Of these we also obtained binaural response characteristics from 55 single units in LSO and 72 single units in MSO. 3. LSO and MSO each have a complete tonotopic representation, arranged in a sequence similar to that of other mammals studied. However, in both LSO and MSO there is an expanded representation of the frequencies around 60 kHz, the main frequency component of the bat's echolocation call; there is another expanded representation of the range around 90 kHz, the third harmonic of the call. The expansion of these frequency ranges suggests that the functions of LSO and MSO in Pteronotus are related to echolocation behavior. 4. The binaural characteristics of cells in LSO were essentially the same as those seen in other mammals. Most LSO units (93%) were excited by the ipsilateral ear and inhibited by the contralateral ear. The responses of nearly all LSO units were completely suppressed when the sound level at the two ears was equal. 5. The binaural characteristics of cells in MSO were different from those in nonecholocating mammals. Most MSO units (72%) were excited by the contralateral ear but were neither excited nor inhibited by the ipsilateral ear. Of the remaining units, 21% were excited by the contralateral ear and inhibited by the ipsilateral ear, and only 6% were excited by both ears. 6. The temporal discharge patterns of units in MSO differed from the tonic response pattern seen in LSO. Most MSO units had phasic response patterns, with a few spikes at the onset or offset of the stimulus; the response often changed from ON to OFF depending on stimulus frequency. 7. The results support the idea that in evolution LSO has remained unchanged, whereas MSO has undergone adaptation. The function of LSO in Pteronotus seems to be identical to that in other mammals, i.e., analysis of interaural sound level differences to derive azimuthal location. The function of MSO in Pteronotus must be different from that in nonecholocating mammals.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1991

Are the initial frequency-modulated components of the mustached bat's biosonar pulses important for ranging?

1. FM-FM neurons in the auditory cortex of the mustached bat, Pteronotus parnellii, are specialized to process target range. They respond when the terminal frequency-modulated component (TFM) of a biosonar pulse is paired with the TFM of the echo at a particular echo delay. Recently, it has been suggested that the initial FM components (IFMs) of biosonar signals may also be important for target ranging. To examine the possible role of IFMs in target ranging, we characterized the properties of IFMs and TFMs in biosonar pulses emitted by bats swung on a pendulum. We then studied responses of FM-FM neurons to synthesized biosonar signals containing IFMs and TFMs. 2. The mustached bat's biosonar signal consists of four harmonics, of which the second (H2) is the most intense. Each harmonic has an IFM in addition to a constant-frequency component (CF) and a TFM. Therefore each pulse potentially consists of 12 components, IFM1-4, CF1-4, and TFM1-4. The IFM sweeps up while the TFM sweeps down. 3. The IFM2 and TFM2 depths (i.e., bandwidths) were measured in 217 pulses from four animals. The mean IFM2 depth was much smaller than the mean TFM2 depth, 2.87 +/- 1.52 (SD) kHz compared with 16.27 +/- 1.08 kHz, respectively. The amplitude of the IFM2 continuously increased throughout its duration and was always less than the CF2 amplitude, whereas the TFM2 was relatively constant in amplitude over approximately three-quarters of its duration and was often the most intense part of the pulse. The maximum amplitude of the IFM2 was, on average, 11 dB smaller than that of the TFM2. Because range resolution increases with depth and the maximum detectable range increases with signal amplitude, the IFMs are poorly suited for ranging compared with the TFMs. 4. FM-FM neurons (n = 77) did not respond or responded very poorly to IFMs with depths and intensities similar to those emitted on the pendulum. The mean IFM2 depth at which a just-noticeable response appeared was 4.48 +/- 1.98 kHz. Only 14% of the pulses emitted on the pendulum had IFM2 depths that exceeded the mean IFM2 depth threshold of FM-FM neurons. 5. Most FM-FM neurons responded to IFMs that had depths comparable with those of TFMs. However, when all parameters were adjusted to optimize the response to TFMs and then readjusted to maximize the response to IFMs, 52% of 27 neurons tested responded significantly better to the optimal TFMs than to the optimal IFMs (P less than 0.05, t test).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

GABAergic circuits sharpen tuning curves and modify response properties in the mustache bat inferior colliculus.

1. The influence of bicuculline on the tuning curves of 65 neurons in the inferior colliculus of the mustache bat was investigated. Single units were recorded with multibarrel electrodes where one barrel contained bicuculline, an antagonist specific for gamma-amino-butyric acid (GABA)A receptors. Fifty-nine tuning curves were recorded from units that were sharply tuned to 60 kHz, the dominant frequency of the bat's orientation call, but six tuning curves were also recorded from units tuned to lower frequencies and whose tuning curves were broader than the 60 kHz cells. Tuning curves were constructed from peristimulus time (PST) histograms obtained over a wide range of frequency-intensity combinations. Thus tuning curves, PST histograms evoked by frequencies within the tuning curve, and rate-level functions at the best frequency were obtained before iontophoresis of bicuculline and compared with the tuning curves and response properties obtained during the administration of bicuculline. 2. Three general types of tuning curves were obtained: 1) open tuning curves that broadened on both the high- and low-frequency sides with increasing sound level; 2) level-tolerant tuning curves in which the width of the tuning curve remained uniformly narrow with increasing sound level; and 3) upper-threshold tuning curves, which did not discharge to high-intensity tone bursts at the best frequency, thereby creating closed or folded tuning curves. 3. One major finding is that GABAergic inhibition plays an important role in sharpening frequency tuning properties of many neurons in the mustache bat inferior colliculus. In response to blocking GABAergic inputs with bicuculline, the tuning curves broadened in 42% of the neurons that were sharply tuned to 60 kHz. The degree of change in most units varied with sound level: tuning curves were least affected, or not affected at all, within 10 dB of threshold and showed progressively greater changes at higher sound levels. These effects were seen in units that had open, level-tolerant, and upper-threshold tuning curves. 4. A second key result is that bicuculline affected rate-level functions and/or temporal discharge patterns in many units. Bicuculline transformed the rate-level functions of 13 cells that originally had nonmonotonic rate level functions, from strongly nonmonotonic into weakly nonmonotonic or monotonic functions. It also changed the temporal discharge patterns in 22 cells, and the changes were often frequency specific.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1993

Differences in response properties of neurons between two delay-tuned areas in the auditory cortex of the mustached bat.

1. The orientation sound (pulse) of the mustached bat, Pteronotus parnellii parnellii, consists of four harmonics (H1-4), each containing a long constant-frequency component (CF1-4) followed by a short frequency-modulated component (FM1-4). The auditory cortex of this species contains several "combination-sensitive" areas: FM-FM, dorsal fringe (DF), ventral fringe (VF), CF/CF, and H1-H2. The FM-FM, DF, and VF areas each consist of neurons tuned to particular delays of echo FMn (n = 2, 3, or 4) from pulse FM1, and have an echo-delay (target-range) axis. This delay axis is from 0.4 to approximately 18 ms in the FM-FM area, to approximately 9 ms in the DF area, and to approximately 5 ms in the VF area. Therefore we hypothesized that the VF area was more specialized for the processing of range information in the terminal phase of echolocation than was the FM-FM area. The aim of our present studies was to find differences in response properties between neurons with best delays shorter than 6 ms in the VF and FM-FM areas and thus to test our hypothesis. 2. In the terminal phase of target-directed flight, the rate of pulse emission becomes higher, pulse duration (in particular, CF duration) becomes shorter, echo delay becomes shorter, and echoes (both the CF and FM components) are less Doppler shifted. Therefore, a "temporal-pattern-simulating (TPS)" stimulus was designed to mimic the train of pulse-echo pairs that would be heard by the bat during the terminal phase, and responses of single neurons to the TPS stimulus and other types of stimuli were recorded from the VF and FM-FM areas of the auditory cortex of unanesthetized bats with a tungsten-wire microelectrode. 3. Best delays of the neurons studied range between 0.9 and 5.5 ms (2.64 +/- 0.72 ms, N = 181) for the VF area, and between 0.6 and 6.0 ms (3.64 +/- 1.14, N = 144) for the FM-FM area. More neurons in the VF area than those in the FM-FM area showed no response or a poor response to the TPS stimulus. Therefore VF neurons are less suited than neurons in the FM-FM area for processing target ranges in the terminal phase of target-directed flight. Facilitative delay-tuning curves were commonly sandwiched between inhibitory delay-tuning curves. The lack of response or poor response to the TPS stimulus can be explained by this inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Tonotopic and functional organization in the auditory cortex of the big brown bat, Eptesicus fuscus.

1. In Eptesicus the auditory cortex, as defined by electrical activity recorded from microelectrodes in response to tone bursts, FM sweeps, and combinations of FM sweeps, encompasses an average cortical surface area of 5.7 mm2. This area is large with respect to the total cortical surface area and reflects the importance of auditory processing to this species of bat. 2. The predominant pattern of organization in response to tone bursts observed in each cortex is tonotopic, with three discernible divisions revealed by our data. However, although cortical best-frequency (BF) maps from most of the individual bats are similar, no two maps are identical. The largest division contains an average of 84% of the auditory cortical surface area, with BF tonotopically mapped from high to low along the anteroposterior axis and is part of the primary auditory cortex. The medium division encompasses an average of 13% of the auditory cortical surface area, with highly variable BF organization across bats. The third region is the smallest, with an average of only 3% of auditory cortical surface area and is located at the anterolateral edge of the cortex. This region is marked by a reversal of the tonotopic axis and a restriction in the range of BFs as compared with the larger, tonotopically organized division. 3. A population of cortical neurons was found (n = 39) in which each neuron exhibited two BF threshold minima (BF1 and BF2) in response to tone bursts. These neurons thus have multipeaked frequency threshold tuning curves. In Eptesicus the majority of multipeaked frequency-tuned neurons (n = 27) have threshold minima at frequencies that correspond to a harmonic ratio of three-to-one. In contrast, the majority of multipeaked neurons in cats have threshold minima at frequencies in a ratio of three-to-two. A three-to-one harmonic ratio corresponds to the "spectral notches" produced by interference between overlapping echoes from multiple reflective surfaces in complex sonar targets. Behavioral experiments have demonstrated the ability of Eptesicus to use spectral interference notches for perceiving target shape, and this subpopulation of multipeaked frequency-tuned neurons may be involved in coding of spectral notches. 4. The auditory cortex contains delay-tuned neurons that encode target range (n = 99). Most delay-tuned neurons respond poorly to tones or individual FM sweeps and require combinations of FM sweeps. They are combination sensitive and delay tuned.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Interaction of excitation and inhibition in processing of pure tone and amplitude-modulated stimuli in the medial superior olive of the mustached bat.

1. In mammals with good low-frequency hearing, the medial superior olive (MSO) processes interaural time or phase differences that are important cues for sound localization. Its cells receive excitatory projections from both cochlear nuclei and are thought to function as coincidence detectors. The response patterns of MSO neurons in most mammals are predominantly sustained. In contrast, the MSO in the mustached bat is a monaural nucleus containing neurons with phasic discharge patterns. These neurons receive projections from the contralateral anteroventral cochlear nucleus (AVCN) and the ipsilateral medial nucleus of the trapezoid body (MNTB). 2. To further investigate the role of the MSO in the bat, the responses of 252 single units in the MSO to pure tones and sinusoidal amplitude-modulated (SAM) stimuli were recorded. The results confirmed that the MSO in the mustached bat is tonotopically organized, with low frequencies in the dorsal part and high frequencies in the ventral part. The 61-kHz region is overrepresented. Most neurons tested (88%) were monaural and discharged only in response to contralateral stimuli. Their response could not be influenced by stimulation of the ipsilateral ear. 3. Only 11% of all MSO neurons were spontaneously active. In these neurons the spontaneous discharge rate was suppressed during the stimulus presentation. 4. The majority of cells (85%) responded with a phasic discharge pattern. About one-half (51%) responded with a level-independent phasic ON response. Other phasic response patterns included phasic OFF or phasic ON-OFF, depending on the stimulus frequency. Neurons with ON-OFF discharge patterns were most common in the 61-kHz region and absent in the high-frequency region. 5. Double tone experiments showed that at short intertone intervals the ON response to the second stimulus or the OFF response to the first stimulus was inhibited. 6. In neuropharmacological experiments, glycine applied to MSO neurons (n = 71) inhibited any tone-evoked response. In the presence of the glycine antagonist strychnine the response patterns changed from phasic to sustained (n = 35) and the neurons responded to both tones presented in double tone experiments independent of the intertone interval (n = 5). The effects of strychnine were reversible. 7. Twenty of 21 neurons tested with sinusoidally amplitude-modulated (SAM) signals exhibited low-pass or band-pass filter characteristics. Tests with SAM signals also revealed a weak temporal summation of inhibition in 13 of the 21 cells tested.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Processing of amplitude-modulated signals that mimic echoes from fluttering targets in the inferior colliculus of the little brown bat, Myotis lucifugus.

1. Neurophysiological recordings were undertaken to determine how neurons in the central nucleus of the inferior colliculus (ICc) of the little brown bat, Myotis lucifugus, extract amplitude modulations that span across a series of tone pulses (i.e., signals that simulate echoes from fluttering targets). Two types of stimuli were presented to the bats. The first served as a control and consisted of an unmodulated train of tone pulses having different repetition rates (TPu, 5-400 pulses per second). The second was a train of tone pulses that were sinusoidally amplitude modulated (TPm, 5-110 Hz) across sequential pulses. The modulated trains of pulses were presented at five different repetition rates (25, 50, 100, 200, and 400 pulses per second) encompassing the range of biosonar emission rates in these bats at different stages of target-directed flight. 2. One hundred fifty-two single neurons were isolated in the ICc of M. lucifugus; their basic response properties and temporal firing patterns were characterized. The best frequencies (BFs) ranged from 10 to 80 kHz and the minimum thresholds at BF were distributed widely (10-95 dB SPL). The frequency tuning selectivity ranged widely, from very broadly tuned (Q10dB = 1.3) to narrowly tuned (Q10dB = 89). Units with very narrow frequency tuning (Q values > 20) were restricted to BFs of 30-50 kHz. The temporal firing pattern of ICc units could be categorized into primary-like (PL), chopper (C), onset-immediate (OI), and onset-late (OL). 3. In response to TPu ICc units exhibited varying degrees of response selectivities as evidenced by their count-based response functions (using the spike count as a measure) versus repetition rate. The count-based response functions of ICc units exhibited five filtering characteristics including band-pass, low-pass, high-pass, band-suppression, and all-pass characteristics. The temporal firing pattern of a unit showed certain correlations with its count-based response function. For example, the majority of OI and OL units, and about half of the C units, showed tuned band-pass response functions. The remaining C and onset types showed mostly low-pass response functions. In contrast, PL neurons showed mostly high-pass response functions, but one third displayed band-pass response functions. 4. The ability of ICc neurons to time-lock their discharges to the individual pulses in a train was characterized by using the synchronization coefficient (SC) as a measure. The SC was plotted against the repetition rate to construct units' synchronization-based response function.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
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↗
PubMed1999

Delay-tuned neurons in the inferior colliculus of the mustached bat: implications for analyses of target distance.

We examined response properties of delay-tuned neurons in the central nucleus of the inferior colliculus (ICC) of the mustached bat. In the mustached bat, delay-tuned neurons respond best to the combination of the first-harmonic, frequency-modulated (FM1) sweep in the emitted pulse and a higher harmonic frequency-modulated (FM2, FM3 or FM4) component in returning echoes and are referred to as FM-FM neurons. We also examined H1-CF2 neurons. H1-CF2 neurons responded to simultaneous presentation of the first harmonic (H1) in the emitted pulse and the second constant frequency (CF2) component in returning echoes. These neurons served as a comparison as they are thought to encode different features of sonar targets than FM-FM neurons. Only 7% of our neurons (14/198) displayed a single excitatory tuning curve. The rest of the neurons (184) displayed complex responses to sounds in two separate frequency bands. The majority (51%, 101) of neurons were facilitated by the combination of specific components in the mustached bat's vocalizations. Twenty-five percent showed purely inhibitory interactions. The remaining neurons responded to two separate frequencies, without any facilitation or inhibition. FM-FM neurons (69) were facilitated by the FM1 component in the simulated pulse and a higher harmonic FM component in simulated echoes, provided the high-frequency signal was delayed the appropriate amount. The delay producing maximal facilitation ("best delay") among FM-FM neurons ranged between 0 and 20 ms, corresponding to target distances </=3.4 m. Sharpness of delay tuning varied among FM-FM neurons with 50% delay widths between 2 and 13 ms. On average, the facilitated responses of FM-FM neurons were 104% greater than the sum of the responses to the two signals alone. In comparing response properties of delay-tuned, FM-FM neurons in the ICC with those in the medial geniculate body (MGB) from other studies, we find that the range of best delays, sharpness of delay tuning and strength of facilitation are similar in the ICC and MGB. This suggests that by the level of the IC, the basic response properties of FM-FM neurons are established, and they do not undergo extensive transformations with ascending auditory processing.

Animals↗
PubMed2000

Modulation of responses and frequency tuning of thalamic and collicular neurons by cortical activation in mustached bats.

In the Jamaican mustached bat, Pteronotus parnellii parnellii, one of the subdivisions of the primary auditory cortex is disproportionately large and over-represents sound at approximately 61 kHz. This area, called the Doppler-shifted constant frequency (DSCF) processing area, consists of neurons extremely sharply tuned to a sound at approximately 61 kHz. We found that a focal activation of the DSCF area evokes highly specific corticofugal modulation in the inferior colliculus and medial geniculate body. Namely a focal activation of cortical DSCF neurons tuned to, say, 61. 2 kHz with 0.2-ms-long, 100-nA electric pulses drastically increases the excitatory responses of thalamic and collicular neurons tuned to 61.2 kHz without shifting their best frequencies (BFs). However, it decreases the excitatory responses of subcortical neurons tuned to frequencies slightly higher or lower than 61.2 kHz and shifts their BFs away from 61.2 kHz. The BF shifts are symmetrical and centrifugal around 61.2 kHz. These corticofugal effects are larger on thalamic neurons than on collicular neurons. The cortical electrical stimulation sharpens the frequency-tuning curves of subcortical neurons. These corticofugal effects named "egocentric selection" last </=2.5 h after the cessation of a 7-min-long cortical electrical stimulation. In the mustached bat, corticofugal modulation serves to increase the contrast in neural representation of sound at approximately 61 kHz, which is an important component of an echo bearing velocity information. It is also most likely that the corticofugal system plays an important role in plasticity of the central auditory system. Another subdivision of the auditory cortex of the mustached bat is called the FM-FM area. This area consists of delay-tuned combination-sensitive neurons, called FM-FM neurons, and has the echo-delay axis for the systematic representation of target distances. A focal electric stimulation of the FM-FM area evokes changes in the responses of collicular and thalamic FM-FM neurons. These changes are basically the same as those described in the present paper. Therefore corticofugal modulation takes place for frequency domain analysis in exactly the same way as it does in time domain analysis.

Acoustic Stimulation↗
PubMed1998

Coexistence of FMRFAMIDE-like and LHRH-like immunoreactivity in the terminal nerve and forebrain of the big brown bat, Eptesicus fuscus.

The coexistence of molluscan cardioexcitatory neuropeptide (FMRFAMIDE) and luteinizing hormone-releasing hormone (LHRH) was studied in the nervous system of the big brown bat, Eptesicus fuscus, with immunocytochemistry. Within mammals, this is the first report of the coexistence of these neuropeptides in the terminal nerve. In juvenile and adult bats, both neuropeptides are distributed identically throughout the terminal nerve (tn), and they coexist in many parts of the prosencephalon from the olfactory bulb as far caudally as the interpeduncular nucleus. Peripherally, on the basal surface of the forebrain, fibers and a few perikarya, which may belong to the tn, form a loose plexus. Within the brain wall, regions of maximal immunoreactivity (ir) are the habenula, medial preoptic area, arcuate nucleus, and the infundibulum. Whereas in most areas of the prosencephalon (e.g., stria terminalis and bed nuclei, amygdaloid complex) fibers show stronger immunoreactivity to FMRFAMIDE, labeling of fibers in the habenula and infundibulum is largely identical for both neuropeptides. The arcuate nucleus contains a large number of perikarya and is the major source of both FMRFAMIDE- and LHRH-ir within the forebrain. A number of fibers run along the ependyma of the ventricular system and seem to terminate here; this is particularly evident in the median eminence and infundibular stalk. In the big brown bat, there seems to exist a continuum of FMRFAMIDE- and LHRH-ir throughout the tn and those structures of the forebrain that are known to be engaged in the control of mating behavior, reproduction, and rhythmicity. Concerning the hypothalamo-hypophyseal-gonadal axis, the arcuate nucleus may serve as a central hub between the olfactory/terminal input and superior areas including the limbic system. In contrast to LHRH immunoreactivity, FMRFAMIDE-like ir extends throughout the brainstem and cervical spinal cord. This system may also be involved in the processing and modulation of autonomic input via the parabrachial and solitary nuclei, the rhombencephalic central gray, and its projection into the hypothalamus (paraventricular nucleus), thus facilitating feed-back of gonadotropic influences of the terminal nerve and prosencephalon.

Animals↗
PubMed1999

Encephalization, adaptation and evolution of chiroptera: A statistical analysis with further evidence for bat monophyly.

As part of a large-scale study on brain morphometrics and adaptations in mammals, we addressed the problem of chiropteran evolution. A specific statistical framework was designed to test which of two competing hypotheses (bat monophyly vs. diphyly) is more strongly supported by quantitative brain data. Our analyses, based on 120 species, revealed that megabats and microbats were more closely related to each other than to primates, and illustrated the convergent adaptations of the brain of bats to similar trophic (i.e. feeding related) niches. Ecologically-corrected characters were then used to derive a new phylogeny which also supports the chiropteran clade. The monophyletic origin of bats is the preferred hypothesis to explain brain quantitative evolution in chiropterans and primates.

Adaptation, Physiological↗
PubMed2006

Karyotype relationships of six bat species (Chiroptera, Vespertilionidae) from China revealed by chromosome painting and G-banding comparison.

The Vespertilionidae is the largest family in the order Chiroptera and has a worldwide distribution in the temperate and tropical regions. In order to further clarify the karyotype relationships at the lower taxonomic level in Vespertilionidae, genome-wide comparative maps have been constructed between Myotis myotis (MMY, 2n = 44) and six vesper bats from China: Myotis altarium (MAL, 2n = 44), Hypsugo pulveratus (HPU, 2n = 44), Nyctalus velutinus (NVE, 2n = 36), Tylonycteris robustula (TRO, 2n = 32), Tylonycteris sp. (TSP, 2n = 30)and Miniopterus fuliginosus (MFU, 2n = 46) by cross-species chromosome painting with a set of painting probes derived from flow-sorted chromosomes of Myotis myotis. Each Myotis myotis autosomal probe detected a single homologous chromosomal segment in the genomes of these six vesper bats except for MMY chromosome 3/4 paint which hybridized onto two chromosomes in the genome of M. fuliginosus. Our results show that Robertsonian translocation is the main mode of karyotype evolution in Vespertilionidae and that the addition of heterochromatic material also plays an important role in the karyotypic evolution of the genera Tylonycteris and Nyctalus. Two conserved syntenic associations (MMY9 + 23 and 18 + 19) could be the synapomorphic features for the genus Tylonycteris. The integration of our maps with the published maps has enabled us to deduce chromosomal homologies between human and these six vesper bats and provided new insight into the karyotype evolution of the family Vespertilionidae.

Animals↗
PubMed1987

Interspecific comparisons of immunohistochemical localization of retinal neurotransmitters in four species of bats.

Four ecologically distinctive Neotropical bat species of the family Phyllostomidae were collected and their retinae surveyed immunohistochemically for the presence of neurotransmitter candidates: glucagon, somatostatin, vasoactive intestinal peptide, substance P (SP), methionine enkephalin, serotonin (5-HT) and two enzymes, glutamic acid decarboxylase (GAD) and tyrosine hydroxylase (TOH). In all four species immunoreactivity (IR) to GAD, TOH and SP was found. GAD-IR and SP-IR showed little interspecies variation whereas TOH-IR differed interspecifically in a pattern that matched the systematic relationships and the ecological characteristics of the bats. 5-HT-IR, which has not previously been reported from mammalian retinae, was found in fibers in the inner nuclear layer and in the outer and inner plexiform layers of Macrotus waterhousii, which is a relatively underived insectivorous phyllostomid bat, but was not found in the retinae from frugivorous or nectarivorous species.

Animals↗
PubMed1983

Distribution of carboxylic esterases in the telencephalon and diencephalon of a microchiropteran bat (Taphozous melanopogon Temminck).

The contribution deals with the histoenzymological makeup of telencephalon and diencephalon of a microchiropteran bat which is considered to have a primitive type of brain. Three esterases, namely acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and nonspecific esterase (NSE), have been studied. In comparison with other mammalian brains the telencephalon and diencephalon of the bat demonstrate a high concentration of enzyme, especially in the nucleus caudatus and putamen, stria medullaris and the nuclei of the thalamus. AChE concentration is higher in neurons, while BChE is seen in almost all fibrous areas of the telencephalon and diencephalon. NSE activity is prominent in neurons and neuropil of neocortex, thalamus and hypothalamus. All the above data indicate that the brain of echolocating microchiropteran bats is metabolically much more active than that of other mammals. This is specifically true of the auditory system which is considerably specialized in these animals; this is also confirmed by the present histoenzymological study.

Acetylcholinesterase↗
PubMed1983

The ultrastructure of the sinu-atrial node of the bat.

The sinu-atrial node (SAN) of the bat, Pipistrellus subflavus, is capable of generating a wide range of spontaneous activity varying from 20 bpm when hibernating to bursts of 800 bpm during active flight. Electrophysiological studies have shown an absence of arrhythmias even below 4 degrees C body temperature. In order to determine whether these physiological capabilities are based upon unique ultrastructural features of the bat SAN, the present study was conducted. We found that the structure of the SAN of the bat is typically mammalian. Diameters of all three cell types in the SAN (nodal, transitional, and atrial) are smaller than those observed in any other mammalian species. A morphometric analysis of cell junctions reveals that nodal-nodal and transitional-transitional cell contacts are primarily undifferentiated with few nexuses. Atrial-atrial cell contacts have a dominance of fasciae adherentes-type junctions with a small area left undifferentiated. Nexuses are much more prevalent in atrial-atrial cell contacts.

Action Potentials↗