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PubMed1994

Sensorimotor model of bat echolocation and prey capture.

A model of the bat sensorimotor system is developed using acoustics, signal processing, and control theory to illustrate the fundamental issues in accomplishing prey capture with echolocation. This model indicates that successful nonpredictive tracking of an ideal prey can be accomplished with a very simple system. Circular apertures approximate the mouth and ears for deriving acoustic beam patterns, using the big brown bat Eptesicus fuscus as a model. Fundamental and overtone frequency components in the emissions allow two simultaneous acoustic beams to be defined. A pair of nonlinear, time-variable, sampled-data controllers alter the bat's heading by applying yaw and pitch heading corrections. The yaw correction attempts to position the prey in the midsagittal plane by nulling the interaural intensity difference of the fundamental component. The pitch correction compares the intensities of the overtone and fundamental components and acts to null their difference. By initiating pitch correction when the overtone intensity first exceeds that of the fundamental, the ambiguity problem is solved and the prey is directed to the capture region. Simulations of passive prey capture indicate that the capture probability decreases as the prey speed increases. Both quick and sluggish prey are considered, with sluggish prey found to be caught with slightly better efficiency. The magnitude of the prey's lateral motion just prior to capture is observed to be an important factor determining capture. The presence of a blind stage is considered, during which the interference of the emission with the echo is assumed to disrupt any sonar information. The presence of such a blind stage is found to have negligible effect on capture efficiency.

Acoustics↗

PubMed1965

HISTOPLASMA CAPSULATUM FROM THE LIVER OF A BAT IN COLOMBIA.

Of 135 bats (eight species), one of the species Glossophaga sorcina sorcina, a nectar-feeding bat from Girardot, Colombia, harbored Histoplasma capsulatum. The microorganism was cultured from the liver. This is the second report of recovery of this fungus from bat tissue.

Animals↗

PubMed1967

Radio tracking of homing bats.

Neotropical bats, Phyllostomas hastatus, were released 10 kilometers from their home roost, and their homeward flights were tracked by radio. Flights of bats with unimpeded vision were strongly oriented in the homeward direction, while the flights of blindfolded bats did not show this marked orientation.

Animals↗

PubMed1979

Perception of echo phase information in bat sonar.

Echolocating bats (Eptesicus fuscus) can detect changes as small as 500 nanoseconds in the arrival time of sonar echoes when these changes appear as jitter or alternations in arrival time from one echo to the next. The psychophysical function relating the bat's performance to the magnitude of the jitter corresponds to the half-wave rectified cross-correlation function between the emitted sonar signals and the echoes. The bat perceives the phase or period structure of the sounds, which cover the 25- to 100-kilohertz frequency range, as these are represented in the auditory system after peripheral transformation. The acoustic image of a sonar target is apparently derived from time-domain or periodicity information processing by the nervous system.

Animals↗

PubMed1979

Neural axis representing target range in the auditory cortex of the mustache bat.

In echolocating bats, the primary cue for determining distance to a target is the interval between an emitted orientation sound and its echo. Whereas frequency is represented by place in the bat cochlea, no anatomical location represents of primary range. Target range is coded by the time interval between grouped discharges of primary auditory neurons in response to both the emitted sound and its echo. In the frequency-modulated-signal processing area of the auditory cortex of the mustache bat (Pteronotus parnellii rubiginosus), neurons respond poorly or not at all to synthesized orientation sounds or echoes alone but respond vigorously to echoes following the emitted sound with a specific delay from targets at a specific range. These range-tuned neurons are systemically arranged along the rostrocaudal axis of the frequency-modulated-signal processing area according to the delays to which they best respond, and thus represent target range in terms of cortical organization. The frequency-modulated-signal processing area therefore shows odotopic representation.

Animals↗

PubMed1979

Harmonic-sensitive neurons in the auditory cortex of the mustache bat.

Human speech and animal sounds contain phonemes with prominent and meaningful harmonics. The biosonar signals of the mustache bat also contain up to four harmonics, and each consists of a long constant-frequency component followed by a short frequency-modulated component. Neurons have been found in a large cluster within auditory cortex of this bat whose responses are facilitated by combinations of two or more harmonically related tones. Moreover, the best frequencies for excitation of these neurons are closely associated with the constant-frequency components of the biosonar signals. The properties of these neurons make them well suited for identifying the signals produced by other echolocating mustache bats. They also show how meaningful components of sound are assembled by neural circuits in the central nervous system and suggest a method by which sounds with important harmonics (or formants) may be detected and recognized by the brain in other species, including humans.

Action Potentials↗

PubMed2004

Genetic analysis of European bat lyssavirus type 1 isolates from France.

European bat lyssavirus type 1a (EBLV-1a) was first identified in central France from a serotine bat (Eptesicus serotinus) collected at the end of 2002. Rabies was diagnosed by reference rabies diagnosis methods and molecular tools. Phylogenetic analysis of 14 viral isolates obtained from French bats infected with EBLV-1 between 1989 and the end of 2002 against 47 nucleoprotein sequences showed a north-west to east distribution of EBLV-1a virus and a south to north distribution of EBLV-1b virus, isolates of which could be divided into two groups: group 1 in north-eastern France and group 2 in central and north-western France.

Animals↗

PubMed1985

Thermogenesis and BAT activity in hypophysectomized rats with and without corticotropin replacement.

Surgical hypophysectomy (Hypox) suppressed body weight, body energy gain, and net energetic efficiency when compared with pair-fed, sham-operated controls but caused marked increases in the thermic response to food, brown adipose tissue (BAT) mass, protein content, and BAT thermogenic activity (estimated from mitochondrial purine nucleotide binding). Chronic replacement of Hypox rats with ACTH restored adrenal weight, plasma corticosterone levels, body energy gain, energetic efficiency, and the thermic response to food to normal. However, the Hypox-replaced animals were apparently fatter (greater carcass energy density) and retained a greater mass of brown fat than controls. Purine nucleotide binding to BAT mitochondria was lower in the ACTH-replaced group than in Hypox rats but remained above the level in controls. These data indicate that hypophysectomy stimulates thermogenesis, probably as a result of decreased adrenal steroid release. However, ACTH does not totally prevent the effects of Hypox, and an involvement of other pituitary hormones and/or hypothalamic-releasing factors cannot be excluded.

Adipose Tissue, Brown↗

PubMed1986

Thermogenesis and sympathetic activity in BAT of overfed rats after adrenalectomy.

Resting oxygen consumption was elevated by 30% in young rats fed a cafeteria diet compared with their chow-fed controls and by 22% in cafeteria-fed, adrenalectomized (ADX) rats compared with the ADX chow-fed group, but injection of propranolol reduced oxygen consumption in the cafeteria-fed animals and abolished these differences. Brown adipose tissue (BAT) mass was increased by cafeteria feeding, and the activity of the mitochondrial proton conductance pathway (assessed from purine nucleotide binding) was enhanced by adrenalectomy and by cafeteria feeding. Norepinephrine turnover in BAT (determined from the time-dependent loss of tissue [3H]norepinephrine specific activity) was increased by 105% in sham-operated, cafeteria-fed rats, by 142% in chow-fed ADX rats, and by 400% in cafeteria-fed ADX rats, compared with chow-fed controls. Cardiac norepinephrine turnover was elevated by 80% in sham-operated, cafeteria-fed rats, but unaffected by adrenalectomy. These data indicate that the enhanced thermogenesis and BAT activity induced by adrenalectomy in chow- or cafeteria-fed rats is due to increased sympathetic activity in the tissue.

Adipose Tissue, Brown↗

PubMed1988

Adaptive changes in individual acyl-CoA esters from hamster BAT during cold acclimation.

Long-chain fatty acyl-CoA esters (LCFACoAE) were extracted from freeze-clamped powdered brown adipose tissue (BAT) obtained from thermoneutral control and cold-acclimated hamsters and the CoA esters individually separated by high-performance liquid chromatography. LCFACoAE of carbon chain length C12 to C20 were identified by increasing column retention time in the following order: C12:0, C14:1, C14:0, C16:1, C18:2, C16:0, C18:1, C18:0, and C20:4. The mean total LCFACoAE concentrations were 235 +/- 40 nmol/g protein for the control hamsters and 648 +/- 105 nmol/g protein for the 22-day cold-acclimated hamsters. A rapid fourfold increase in the levels of C16:0, C18:0, and C18:1 occurred within hours after initiation of the cold temperature, whereas the concentrations of the other six LCFACoAE either increased only slightly or remained unchanged. Almost 50% of the total LCFACoAE in the BAT of cold-acclimated hamsters was made up of C16:0, C18:0, and C18:1. These results, which demonstrate some dynamic changes in adipose tissue LCFACoAE, are consistent with their proposed role in the initiation and maintenance of BAT thermogenesis.

Acclimatization↗

PubMed1993

Spontaneous contractions of isolated bat wing venules are inhibited by luminal flow.

The hypothesis that spontaneous contractions of bat wing venules could be modulated by luminal flow was tested. Single venules (114 +/- 5 microns diam) from the wings of anesthetized pallid bats were dissected, cannulated, and pressurized in vitro. A dual reservoir system was used to independently control luminal pressure and flow. In the absence of flow, and with pressure set to 10 cmH2O, all venules contracted spontaneously at rates between 20 and 40 cycles/min. Pressure elevation over the range of 3-10 cmH2O caused a rapid increase in contraction frequency and decrease in amplitude; pressure reduction caused a rapid decrease in contraction frequency and increase in amplitude. In contrast, initiation of flow resulted in a delayed and gradual reduction of contraction amplitude and/or frequency (sometimes to zero). The net effect of flow was to increase mean diameter and decrease the product of frequency x cross-sectional area. Flow-induced inhibition of venular contraction was eliminated by endothelial denudation but persisted in the presence of NG-monomethyl-L-arginine (10(-4) M) or indomethacin (10(-5) M) in concentrations that blocked the effects of exogenously applied ATP or arachidonic acid, respectively. The flow-induced venular response also persisted in the presence of superoxide dismutase (55 U/ml). Denuded venules responded to flow when placed downstream (i.e., perfused in series) from venules with intact endothelium. These results indicate that luminal flow can modulate the contractile function of bat wing venules via release of a transferable substance from the endothelium. The exact nature of the substance is not yet known but it does not appear to be classical endothelium-derived relaxing factor, a prostaglandin, or an oxygen radical.

Adenosine Triphosphate↗

PubMed2002

Vampire bat, shrew, and bear: comparative physiology and chronic renal failure.

In the typical mammal, energy flux, protein metabolism, and renal excretory processes constitute a set of closely linked and quantitatively matched functions. However, this matching has limits, and these limits become apparent when animals adapt to unusual circumstances. The vampire bat and shrew have an extremely high protein intake, and the glomerular filtration rate (GFR) is not commensurate with the large urea load to be excreted. The vampire bat is chronically azotemic (blood urea concentration 27-57 mmol/l); yet there is no information as to how this animal has adjusted to such an azotemic internal environment. A high protein intake should also lead to chronic glomerular hyperfiltration; yet neither animal appears to develop progressive renal failure. The American black bear, on the other hand, has adapted to a prolonged period without intake or urine output. Despite continued amino acid catabolism with urea production, this mammal is able to completely salvage and reutilize urea nitrogen for protein synthesis, although the signals that initiate this metabolic adaptation are not known. The vampire bat, shrew, and bear are natural models adapted to circumstances analogous to chronic renal failure. Unraveling these adaptations could lead to new interventions for the prevention/treatment of chronic renal failure.

Adaptation, Physiological↗

PubMed1990

Increase in cytochrome oxidase capacity of BAT and other tissues in cold-acclimated gerbils.

To determine the effects of cold acclimation on the oxidative capacity of different tissues and their possible role in nonshivering thermogenesis (NST) in a desert rodent, the gerbil (Gerbillus campestris), measurements of cytochrome oxidase activity (COX) were performed on homogenates of liver, brown adipose tissue (BAT), and subsarcolemmal (SS) and intermyofibrillar (IMF) fractions of skeletal muscle. Total organ mass was also measured. Gerbils were maintained either at thermoneutrality (TN) or cold [4 degrees C, ambient temperature (Ta)] for 4 (CA4) or 8 (CA8) wk. A comparative study was made with mice (Mus musculus). Total and relative masses of BAT increased significantly in both gerbils and mice during cold acclimation, whereas muscle mass decreased in CA4 gerbils. Specific and total COX (TCOX) increased in the three tissues. A considerable increase (+170%, P less than 0.05) of TCOX and protein content in liver of CA4 gerbils compared with controls was observed, whereas no significant changes occurred in liver of CA4 mice. In muscle, an increase of TCOX in SS and a reduction in IMF cell compartments were noted. The increase in BAT oxidative capacity in CA4 gerbils represented only a small portion of that in liver (36%) and in SS fraction of muscle (41%) at the same stage of acclimation. The ability of the three tissues to contribute to components of thermogenesis in vivo was evaluated. The sum of oxidative capacity of the three tissues was largely above the peak metabolic rate (PMR), whereas that of muscle exceeded maximum shivering thermogenesis, which developed both in TN and CA4 gerbils.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1993

BAT thermogenic activity and capacity are reduced during lactation in ground squirrels.

The effect of lactation on brown adipose tissue (BAT) thermogenic activity and capacity as well as on uncoupling protein (UCP) gene expression has been studied in the 13-lined ground squirrel. Lactating animals were studied after approximately 21 days of lactation. Parameters of thermogenesis were also studied in a group of postpregnant animals from which litters had been removed at 1-2 days postpartum. A group of animals that did not bear litters served as nonpregnant controls. BAT pad weights, protein concentration, and mitochondrial mass were all significantly decreased relative to nonpregnant controls and postpregnant animals. Specific binding of GDP and total GDP bound were significantly decreased in lactating animals relative to both nonpregnant and postpregnant animals. Scatchard analysis of GDP binding indicated that binding affinity (Kd) was unaffected by treatment. UCP concentrations were reduced by 26% during lactation, whereas total UCP content was reduced by 70%. A 3-wk period after pup removal was sufficient for UCP concentrations to return to nonpregnant levels, although total UCP content remained reduced. The changes in UCP concentrations were accompanied by parallel alterations of gene expression. UCP mRNA-to-beta-actin mRNA ratios during lactation were 30% of the levels found in nonpregnant controls and postpregnant animals. The results presented here clearly indicate that BAT activity and capacity are suppressed during lactation in the 13-lined ground squirrel.

Adipose Tissue, Brown↗

PubMed1995

Seasonal influences on the control of plasma sex hormone-binding globulin by T4 in male little brown bats.

Male little brown bats showed a well-defined seasonal cycle of plasma thyroxine (T4). Total T4 concentrations increased during hibernation, reached peak levels in May at spring emergence, and subsequently declined to lowest levels in September. Thyroxine-binding globulin (TBG) activity increased only in summer, and seasonal changes in non-TBG-bound T4 generally paralleled those of total T4. During the fall and early hibernation period, bats studied under feral conditions or following photoperiod manipulation showed coincident changes in plasma T4 and sex hormone-binding globulin (SHBG) levels. In contrast, males studied during late hibernation or following spring arousal exhibited declining plasma T4 levels during periods of increased SHBG activity. Additionally, the prehibernation decline in SHBG did not depend on changing environmental conditions. Bats maintained under summerlike conditions during the fall showed normal seasonal reductions in SHBG and T4. These studies indicate that T4 is the likely physiological regulator of plasma SHBG activity during the fall and early hibernation, but that other factors modulate the timing of SHBG induction in the spring.

Animals↗

PubMed1996

High plasma cholesterol, but low triglycerides and plaque-free arteries, in Mexican free-tailed bats.

Female mammals typically become hyperphagic from mid- to late pregnancy and during lactation. Mexican free-tailed bats, Tadarida brasiliensis mexicana, double their nightly food intake from late pregnancy to peak lactation and consume an insect diet that is exceptionally high in fat. During late pregnancy and throughout lactation, fasting plasma levels of cholesterol in this insectivorous bat are high (215 +/- 8 mg/dl) and are nearly 10-fold higher than in three species of Old World frugivorous bats. Fasting triglycerides were unexpectedly low in T. brasiliensis (25 +/- 2 mg/dl), despite evidence of high fat intake during nightly feeding bouts (postprandial cholesterol and triglycerides, 268 +/- 18 and 122 +/- 20 mg/dl, respectively). High-density lipoprotein (HDL) cholesterol levels were extraordinarily high (124 +/- 5 mg/dl) and unaffected by feeding. Low-density lipoprotein cholesterol levels were correspondingly low (86 +/- 7 mg/dl). This unusual plasma lipid profile was not associated with coronary or aortic atherosclerosis, nor was there evidence of hyperglycemia or hyperinsulinemia. A high-fat diet and high levels of cholesterol in T. brasiliensis are not correlated with cardiovascular disease or (possibly) insulin resistance. Among several possible factors that might account for these observations, nightly bouts of powered flight (commuting and foraging for food) may contribute to elevated HDL cholesterol, which may protect this species from developing atherosclerosis.

Animals↗

PubMed2006

Neural mechanisms underlying selectivity for the rate and direction of frequency-modulated sweeps in the auditory cortex of the pallid bat.

Frequency-modulated (FM) sweeps are common in vocalizations, including human speech. Selectivity for FM sweep rate and direction is present in the auditory cortex of many species. The present study sought to determine the mechanisms underlying FM sweep selectivity in the auditory cortex of pallid bats. In the pallid bat inferior colliculus (IC), two mechanisms underlie selectivity for FM sweep rate. The first mechanism depends on duration tuning for tones that arises as a consequence of early inhibition generated by an excitatory tone. The second mechanism depends on a narrow band of delayed high-frequency inhibition. Direction selectivity depends on a broad band of early low-frequency inhibition. Here, the contributions of these mechanisms to cortical FM sweep selectivity were determined in pentobarbital-anesthetized pallid bats. We show that the majority of cortical neurons tuned to echolocation frequencies are selective for the downward direction and rate of FM sweeps. Unlike in IC neurons tuned in the echolocation range, duration tuning is rare in cortical neurons with similar tuning. As in the IC, consistent spectrotemporal differences exist between low- and high-frequency sidebands. A narrow band of delayed high-frequency inhibition is necessary for FM rate selectivity. Low-frequency inhibition has a broad bandwidth, early arrival time, and creates direction selectivity. Cortical neurons respond better to slower FM rates and exhibit broader rate tuning than IC neurons. Relative arrival time of high-frequency inhibition is slower in the cortex than in the IC. Thus whereas similar mechanisms shape direction selectivity of neurons tuned in the echolocation range in the IC and the cortex, only one of the two mechanisms underlying rate selectivity in the IC is present in the cortex.

Acoustic Stimulation↗

PubMed2004

Lateral inhibition for center-surround reorganization of the frequency map of bat auditory cortex.

Repetitive acoustic stimulation, auditory fear conditioning, and focal electric stimulation of the auditory cortex (AC) each evoke the reorganization of the central auditory system. Our current study of the big brown bat indicates that focal electric stimulation of the AC evokes center-surround reorganization of the frequency map of the AC. In the center, the neuron's best frequencies (BFs), together with their frequency-tuning curves, shift toward the BFs of electrically stimulated cortical neurons (centripetal BF shifts). In the surround, BFs shift away from the stimulated cortical BF (centrifugal BF shifts). Centripetal BF shifts are much larger than centrifugal BF shifts. An antagonist (bicuculline methiodide) of inhibitory synaptic transmitter receptors changes centrifugal BF shifts into centripetal BF shifts, whereas its agonist (muscimol) changes centripetal BF shifts into centrifugal BF shifts. This reorganization of the AC thus depends on a balance between facilitation and inhibition evoked by focal cortical electric stimulation. Unlike neurons in the AC of the big brown bat, neurons in the Doppler-shifted constant-frequency (DSCF) area of the AC of the mustached bat are highly specialized for fine-frequency analysis and show almost exclusively centrifugal BF shifts for focal electric stimulation of the DSCF area. Our current data indicate that in the highly specialized area, lateral inhibition is strong compared with the less-specialized area and that the specialized and nonspecialized areas both share the same inhibitory mechanism for centrifugal BF shifts.

Acoustic Stimulation↗