bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tympanic membrane oscillations and auditory receptor activity in the stridulating cricket Gryllus bimaculatus
Authors: Poulet J. F. A. , Hedwig B. 
Published: April 2021

ABSTRACT
The ears of stridulating crickets are exposed to loud self-generated sounds that might desensitise the auditory system and reduce its responsiveness to environmental sounds. We examined whether crickets prevent self-induced auditory desensitisation, and measured the responsiveness of the peripheral auditory system of the cricket (acoustic spiracle, tympanic membrane and tympanic nerve) during pharmacologically induced sonorous (two-winged) and silent (one-winged) stridulation.
The acoustic spiracles remained open during stridulation, so the self-generated auditory signal had full access to both the external side and the internal side of the tympanic membrane. When the spiracles shut in resting crickets, the responsiveness of the tympanic membrane to acoustic stimuli varied according to the phase of ventilation and was minimal during expiration. The tympanic membrane oscillated in phase with the self-generated sounds during sonorous chirps and did not oscillate during silent chirps. In both sonorously and silently singing crickets, the responses of the tympanic membrane to acoustic stimuli were identical during the chirps and the chirp intervals.
Bursts of activity were recorded in the tympanic nerve during sonorous chirps; however, activity was minor during silent chirps. In sonorously and in silently singing crickets, the summed nerve response to acoustic stimuli in the chirp intervals was the same as in resting crickets. The response to stimuli presented during the syllable intervals of sonorous chirps was slightly reduced compared with the response in the chirp intervals as a consequence of receptor habituation. In silently singing crickets, acoustic stimuli elicited the same summed nerve response during chirps and chirp intervals. These data indicate that in the cricket no specific mechanism acts to reduce the responsiveness of the peripheral auditory pathway during stridulation.
Mechanisms of frequency-specific responses of ω neuron 1 in crickets (Teleogryllus oceanicus): a polysynaptic pathway for song?
Authors: Faulkes Zen , Pollack Gerald S. 
Published: April 2021

ABSTRACT
In crickets (Teleogryllus oceanicus), the auditory interneuron omega neuron 1 (ON1) responds to sounds over a wide range of frequencies but is most sensitive to the frequency of conspecific songs (4.5 kHz). Response latency is longest for this same frequency. We investigate the mechanisms that might account for the longer latency of ON1 to cricket-like sounds. Intracellular recordings revealed no evidence for appropriately timed postsynaptic inhibition of ON1 that might increase its latency, nor was latency affected by picrotoxin. The onset of excitatory postsynaptic potentials (EPSPs) was delayed for 4.5 kHz stimuli compared with ultrasound stimuli, pointing to a presynaptic locus for the latency difference. When ON1 is stimulated with high frequencies, discrete, apparently unitary EPSPs can be recorded in its dendrite, and these are latency-locked to spikes recorded simultaneously in the auditory nerve. This suggests that input to ON1 from high-frequency-tuned auditory receptor neurons is monosynaptic. In agreement with this, brief ultrasound stimuli evoke a single, short-latency EPSP in ON1. In contrast, the EPSP evoked by a brief 4.5 kHz stimulus consists of an early component, similar in latency to that evoked by ultrasound and possibly evoked by ultrasound-tuned receptors, and a later, dominant component. We interpret the early peak as arising from a monosynaptic afferent pathway and the late peak from a polysynaptic afferent pathway. Multiple-peak EPSPs, with timing similar to those evoked by sound stimuli, were also evoked by electrical stimulation of the auditory nerve.
Prey detection in selective plankton feeding by the paddlefish: is the electric sense sufficient?
Authors: Wilkens Lon A. , Wettring Barbara , Wagner Eva , Wojtenek Winfried , Russell David 
Published: April 2021

ABSTRACT
The long rostrum of the paddlefish Polyodon spathula supports an extensive array of ampullary electroreceptors and has been proposed to function as an antenna for detecting planktonic prey. Evidence in support of this hypothesis is presented in experiments that preclude the use of other sensory mechanisms for plankton detection. Paddlefish swimming in a recirculating observation chamber are shown to feed normally in the dark when prey-related chemical and hydrodynamic sensory cues are masked or attenuated. Specifically, we demonstrate that the spatial distribution of plankton captured by paddlefish is little changed when the plankton are individually encapsulated in agarose, when a high background concentration of plankton extract is added to the chamber, when the nares are plugged and under turbulent water flow conditions. Paddlefish also discriminate between encapsulated plankton and ‘empty’ agarose particles of the same size. Although capture distributions differed somewhat under certain conditions, the general pattern and effectiveness of prey capture were not disrupted by these procedures. These results support the conclusion that paddlefish, as zooplanktivores, rely on their passive electric sense for prey detection.
Count and spark? The echo response of the weakly electric fish Gnathonemus petersii to series of pulses
Authors: Schuster Stefan 
Published: April 2021

ABSTRACT
Weakly electric fish of the pulse type electrolocate objects in the dark by emitting discrete electric organ discharges (EODs) separated by intervals of silence. Two neighbouring pulse-type fish often reduce the risk of discharging simultaneously by means of an ‘echo response’: one fish will respond to a neighbour’s EOD with a discharge of its own following at a fixed short latency so that its EOD will occur long before the next EOD of its neighbour. Although working elegantly for two partners, this simple strategy should fail in larger groups because two fish could discharge in response to the same EOD of a third fish. Here, I show that the mormyrid fish Gnathonemus petersii could use a simple mechanism to reduce this problem. Individuals were stimulated with two closely spaced pulses, the second following so as to coincide with an echo given in response to the first. All the fish examined were able to respond more to the second pulse so that most of their echoes did not collide with the second pulse. An analysis was made of how echoing more to the second pulse depends on (i) the delay at which the stimulus followed the last spontaneous EOD, (ii) the spontaneous firing rate, (iii) the intensity of the stimulus, (iv) the number of stimulus pulses, (v) the interval between stimulus pulses, and (vi) the level of previous stimulation with double pulses. The results suggest that echoing more in response to the second pulse is probably because the first pulse causes an after-effect whose inferred properties would be compatible with the properties of the mormyromast afferences thought to be involved in the echo response.
Copper transport by lobster hepatopancreatic epithelial cells separated by centrifugal elutriation: measurements with the fluorescent dye Phen Green
Authors: Chavez-Crooker P. , Garrido N. , Ahearn G. A. 
Published: April 2021

ABSTRACT
The hepatopancreas of the American lobster (Homarus americanus) possesses four types of epithelial cells arranged along blind-ended tubules. At the distal tips of these tubules, stem cells termed E-cells differentiate into three other cell types, R-cells, F-cells and B-cells, each of which have different absorptive and secretory roles in the biology of the overall organ. This investigation uses centrifugal elutriation to separate the individual hepatopancreatic epithelial cell types of Homarus americanus and to investigate their plasma membrane copper transport properties using the copper-sensitive fluorescent dye Phen Green. Results show highly dissimilar endogenous concentrations of copper in each cell type and within the vacuoles (vesicles) released from these cells during the centrifugation process ([copper] in vacuoles&gt;E-cells&gt;R-cells&gt;F-cells≈B-cells). All four cell types were able to absorb copper from external concentrations ranging from 0.01 to 8 μmol l−1, but considerable differences in transport rates occurred between the cell types. External calcium (0–10 mmol l−1 ) stimulated the uptake of external copper in a saturable fashion, suggesting the occurrence of carrier-mediated metal uptake. Addition of the Ca2+ channel blocker verapamil (30 μmol l−1 ) to the external medium reduced the uptake rate of copper by all four cell types, but to different extents in each type of cell. External zinc (0–1000 nmol l−1 ) was a competitive inhibitor of copper influx in E- and R-cells, suggesting that the two metals shared the same binding and transport mechanism. A model is proposed which suggests that copper may enter all hepatopancreatic epithelial cell types by a divalent cation antiport process that exchanges intracellular Ca2+ (or other cations) with either external copper or zinc. Verapamil-sensitive Ca2+ channels may allow access of external calcium to cytoplasmic exchange sites on the antiporter or to activator sites on the same transport protein. The results suggest that elutriation is an excellent technique for the separation of complex invertebrate organ systems into their separate cell types and for analyzing the physiological properties of each cell type in isolation.
Boxfishes (Teleostei: Ostraciidae) as a model system for fishes swimming with many fins: kinematics
Authors: Hove J. R. , O’Bryan L. M. , Gordon M. S. , Webb P. W. , Weihs D. 
Published: April 2021

ABSTRACT
Swimming movements in boxfishes were much more complex and varied than classical descriptions indicated. At low to moderate rectilinear swimming speeds (&lt;5 TL s−1, where TL is total body length), they were entirely median- and paired-fin swimmers, apparently using their caudal fins for steering. The pectoral and median paired fins generate both the thrust needed for forward motion and the continuously varied, interacting forces required for the maintenance of rectilinearity. It was only at higher swimming speeds (above 5 TL s−1 ), when burst- and-coast swimming was used, that they became primarily body and caudal-fin swimmers. Despite their unwieldy appearance and often asynchronous fin beats, boxfish swam in a stable manner. Swimming boxfish used three gaits. Fin-beat asymmetry and a relatively non-linear swimming trajectory characterized the first gait (0–1 TL s−1 ). The beginning of the second gait (1–3 TL s−1 ) was characterized by varying fin-beat frequencies and amplitudes as well as synchrony in pectoral fin motions. The remainder of the second gait (3–5 TL s−1 ) was characterized by constant fin-beat amplitudes, varying fin-beat frequencies and increasing pectoral fin-beat asynchrony. The third gait (&gt;5 TL s−1 ) was characterized by the use of a caudal burst- and-coast variant. Adduction was always faster than abduction in the pectoral fins. There were no measurable refractory periods between successive phases of the fin movement cycles. Dorsal and anal fin movements were synchronized at speeds greater than 2.5 TL s−1, but were often out of phase with pectoral fin movements.
Physiological and biochemical correlates of brood size and energy expenditure in tree swallows
Authors: Burness Gary P. , Ydenberg Ronald C. , Hochachka Peter W. 
Published: April 2021

ABSTRACT
Intra-population variation in many fitness-related traits (e.g. clutch size) is often attributed to variation in individual parental quality. One possible component of quality is the level at which each individual can expend energy while provisioning dependent young. We used breeding tree swallows (Tachycineta bicolor) to test whether adults with large, natural-sized broods and/or nestlings in good nutritional condition had relatively high daily energy expenditures (DEEs). Adults with high DEEs were predicted to have large internal organs and high metabolic capacities. We first measured the growth rate of nestlings in natural broods of five, six and seven over a 4-day period and then measured parental DEE using doubly labelled water. Adults were then dissected for analyses of body composition and to determine maximum enzyme activities in the pectoral muscle. Although the total mass gain of large broods was greater than that of small broods, parental DEE was independent of brood size. We hypothesize that adults matched their clutch size (and consequently, brood size) to their individual foraging efficiencies. When statistically controlling for the effects of brood size, in one of two years there was a positive correlation between DEE and brood mass. This suggests that among individuals rearing the same-sized broods there were reproductive benefits of a relatively high DEE. There was no correlation between either brood size or DEE and the mass of any internal organ or the metabolic capacity of the pectoral muscle.
Branchial Co2 receptors and cardiorespiratory adjustments during hypercarbia in Pacific spiny dogfish (Squalus acanthias)
Authors: Mckendry J. E. , Milsom W. K. , Perry S. F. 
Published: April 2021

ABSTRACT
Adult Pacific spiny dogfish (Squalus acanthias) were exposed to acute (approximately 20 min) hypercarbia while we monitored arterial blood pressure, systemic vascular resistance (RS), cardiac output and frequency (fH) as well as ventilatory amplitude (VAMP) and frequency (fV). Separate series of experiments were conducted on control, atropinized (100 nmol kg−1 ) and branchially denervated fish to investigate putative CO2-chemoreceptive sites on the gills and their link to the autonomic nervous system and cardiorespiratory reflexes.
In untreated fish, moderate hypercarbia (water CO2 partial pressure; mmHg) (1 mmHg= 0.133 kPa) elicited significant increases in VAMP (of approximately 92 %) and fV (of approximately 18 %) as well as decreases in fH (of approximately 64 %), (approximately 29 %) and arterial blood pressure (of approximately 11 %); RS did not change significantly.
Denervation of the branchial branches of cranial nerves IX and X to the pseudobranch and each gill arch eliminated all cardiorespiratory responses to hypercarbia. Prior administration of the muscarinic receptor antagonist atropine also abolished the hypercarbia-induced ventilatory responses and virtually eliminated all CO2-elicited cardiovascular adjustments. Although the atropinized dogfish displayed a hypercarbic bradycardia, the magnitude of the response was significantly attenuated (36±6 % decrease in fH in controls versus 9±2 % decrease in atropinized fish; means ± S.E.M.).
Thus, the results of the present study reveal the presence of gill CO2 chemoreceptors in dogfish that are linked to numerous cardiorespiratory reflexes. In addition, because all cardiorespiratory responses to hypercarbia were abolished or attenuated by atropine, the CO2 chemoreception process and/or one or more downstream elements probably involve cholinergic (muscarinic) neurotransmission.
Sarcomere Length Operating Range of Vertebrate Muscles During Movement
Authors: Burkholder Thomas J. , Lieber Richard L. 
Published: April 2021

ABSTRACT
The force generated by skeletal muscle varies with sarcomere length and velocity. An understanding of the sarcomere length changes that occur during movement provides insights into the physiological importance of this relationship and may provide insights into the design of certain muscle/joint combinations. The purpose of this review is to summarize and analyze the available literature regarding published sarcomere length operating ranges reported for various species. Our secondary purpose is to apply analytical techniques to determine whether generalizations can be made regarding the ‘normal’ sarcomere length operating range of skeletal muscle. The analysis suggests that many muscles operate over a narrow range of sarcomere lengths, covering 94±13 % of optimal sarcomere length. Sarcomere length measurements are found to be systematically influenced by the rigor state and methods used to make these measurements.
Ventilatory Modes And Mechanics Of The Hedgehog Skate (Leucoraja Erinacea): Testing The Continuous Flow Model
Authors: Summers Adam P. , Ferry-Graham Lara A. 
Published: April 2021

ABSTRACT
The movement of water across the gills of non-ram-ventilating fishes involves the action of two pumps: a pressure pump that pushes water across the gills from the oropharyngeal to the parabranchial cavity, and a suction pump that draws water across the gills from the oropharyngeal into the parabranchial cavity. Together, the two are thought to keep water flowing continuously antero-posteriorly through the head of the respiring animal. However, there is evidence that the pressure and suction pumps do not always work in perfect phase in elasmobranch fishes, leading to periods of higher pressure in the parabranchial than in the oropharyngeal cavity. We investigated the existence and consequence of such pressure reversals in the hedgehog skate Leucoraja erinacea using pressure transducers, sonomicrometry and flow visualization including internal visualization using endoscopy. We noted four patterns of respiration in the experimental skates distinguished by the flow pattern at the three openings into the respiratory system: (1) in through the spiracle only, (2) in through the mouth + spiracle, (3) in through the mouth only, and (4) the mouth held open throughout the respiratory cycle. The first two were by far the dominant modes recorded from experimental animals. We determined that pressure reversals exist in the hedgehog skate, and that the gill bars adducted during such pressure reversals. Direct observation confirmed that these pressure reversals do correspond to pulsatile flow across the gills. During mouth+spiracle ventilation the flow completely reversed direction, flowing from the parabranchial chambers back across the gills and into the oropharyngeal cavity. Finally, we addressed the utility of sonomicrometry as a technique for determining kinematics in aquatic animals. Despite some problems involving errors inherent to the system design, we found the technique useful for complementing such techniques as pressure measurements and endoscopy.
Reduction in the Rates of Protein and Amino Acid Catabolism to Slow Down the Accumulation of Endogenous Ammonia: A Strategy Potentially Adopted by Mudskippers (Periophthalmodon Schlosseri and Boleophthalmus Boddaerti) During Aerial Exposure in Constant Darkness
Authors: Lim Cheng B. , Chew Shit F. , Anderson Paul M. , Ip Yuen K. 
Published: April 2021

ABSTRACT
This study was designed to elucidate the strategies adopted by mudskippers to handle endogenous ammonia during aerial exposure in constant darkness. Under these conditions, specimens exhibited minimal locomotory activity, and the ammonia and urea excretion rates in both Periophthalmodon schlosseri and Boleophthalmus boddaerti decreased significantly. As a consequence, ammonia accumulation occurred in the tissues of both species of mudskipper. A significant increase in urea levels was found in the liver of P. schlosseri after 24 h of aerial exposure, but no similar increase was seen in the tissues of B. boddaerti. It is unlikely that these two species of mudskipper detoxified ammonia to urea during aerial exposure since B. boddaerti does not possess a complete ornithine–urea cycle (OUC) and, although all the OUC enzymes were present in P. schlosseri, the activity of carbamoyl phosphate synthetase present in the liver mitochondria was too low to render the OUC functional for ammonia detoxification. Peritoneal injection of 15 NH4Cl into P. schlosseri showed that this mudskipper was capable of incorporating some of the labelled ammonia into urea in its liver. However, aerial exposure did not affect this capability and did not induce detoxification of the accumulated ammonia to urea. Mudskippers exposed to terrestrial conditions and constant darkness did, however, show significant decreases in the total free amino acid content in the liver and blood, in the case of P. schlosseri and in the muscle of B. boddaerti. No changes in the alanine or glutamine content of the muscle were found in either species. Analyses of the balance between the reduction in nitrogenous excretion and the increase in nitrogenous accumulation further revealed that these two species of mudskipper were capable of reducing their protein and amino acid catabolic rates. Such adaptations constitute the most efficient way to avoid the build-up of internal ammonia, and would render unnecessary the detoxification of ammonia through energetically expensive pathways. This finding may be the first report of a teleost fish showing a reduction in proteolysis and amino acid catabolism in response to aerial exposure.
Effects of Serotonin, Dopamine and Ergometrine on Locomotion in the Pulmonate Mollusc Helix Lucorum
Authors: Pavlova Galina A. 
Published: April 2021

ABSTRACT
The terrestrial snail Helix lucorum crawls using waves of muscular contraction (pedal waves) that spread along the sole of its foot. Crawling speed depends on wave generation frequency (step frequency) and the distance the snail moves forwards during each wave (step length). In a previous study, video recordings of a crawling snail showed that its sole length varied over a wide range and was directly correlated with mollusc speed. Speed depended on step length, which was directly related to sole length, rather than on step frequency, which remained rather constant. In the present study, the effects of dopamine, ergometrine (a blocker of dopamine receptors in molluscs) and serotonin injection on the linear relationship between sole length and locomotor speed in Helix lucorum were studied. In crawling snails, dopamine caused sole contraction, and locomotion slowed down or ceased. Ergometrine stimulated locomotion, which resembled rapid crawling with an extended sole, as observed under normal conditions. Serotonin stimulated locomotion and accelerated crawling significantly without causing changes in sole length. The acceleration of locomotion induced by serotonin injection was due to pedal wave (step) elongation. It is proposed that, during each locomotor episode, dopamine controls snail speed by regulating sole length, which determines the amplitude of contraction of the muscle cells involved in pedal waves and, as a result, step length; serotonin determines the basic step length and shifts the linear relationship between sole length and mollusc speed upwards along the axis of mollusc speed. The efficiency of the serotonergic system depends on the physiological state of the mollusc (e.g. that characteristic of summer or winter).