bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Role of the Muscle Receptor Organ in the Control of Abdominal Extension in the Crayfish Cherax Destructor
Authors: Mccarthy Bernard J. , Macmillan David L. 
Published: April 2021

ABSTRACT
A platform was lowered from beneath suspended crayfish, Cherax destructor, to evoke slow abdominal extension. The movements were filmed and the length between segments plotted as a function of time. Unlike abdominal flexion, which starts posteriorly and progresses anteriorly, extension occurs at all joints simultaneously. Although the duration of extension varied from trial to trial for an individual, the movement was organised in a stereotyped manner: the abdomen achieved a consistent position for any given proportion of the time for complete extension. We examined the role of the abdominal muscle receptor organs (MROs) in extension by cutting the nerves of selected MROs to abolish their input. The extension movement was measured before and after nerve section for animals with either unloaded or loaded abdomens. Removal of MRO input had no significant effect on extension of the unloaded abdomen. In animals with a loaded abdomen, the extension at joints spanned by sectioned MROs was slowed, whereas that at joints with intact MROs was not. The findings are consistent with the hypothesis that the MRO is an error detector in a servo-loop controlling abdominal position. The results provide the first demonstration that this load-compensating reflex loop operates during naturally evoked extension of the abdomen under constant load.
The Avian Lung: Is There an Aerodynamic Expiratory Valve?
Authors: Brown Richard E. , Kovacs Christopher E. , Butler James P. , Wang Ning , Lehr John , Banzett Robert B. 
Published: April 2021

ABSTRACT
The unidirectional gas-flow pattern through the avian lung is thought to result from ‘aerodynamic valves’; support for this hypothesis lies mainly in the failure to find any evidence for anatomical valves. During expiration, air flows from the caudal air sacs through the major exchange area of the lung, the paleopulmonic parabronchi, instead of bypassing the lungs via the intrapulmonary bronchus. We tested whether the effectiveness of this expiratory flow control mechanism depends on aerodynamic factors, especially convective inertial forces that depend on gas density and flow velocity. In pump-ventilated, anaesthetized geese, a bolus of tracer gas was introduced into both the right and left caudal thoracic air sacs during an end-inspiratory pause. During the first expiration, the rise of tracer levels within the caudal trachea was measured. Valve efficacy was positively correlated with the AO rate of expiratory gas flow, (range 8–200 ml s-1). At flows assumed to occur during exercise in geese , the expiratory valve efficacy was approximately 95 %; it was less effective at lower flows. Surprisingly, the density (ρ) of the background gas (ρ of He/O2=0.43 g l-1, Ar/O2=1.72 g l-1 or SF6/O2=5.50 g l-1) had no effect on expiratory valving. We suggest two possible mechanisms that might explain this unusual combination of flow dependence without density dependence. (1) If airway geometry changes occurred between experiments with different gases, flow in the vicinity of the expiratory valve may have varied independently from flow measured at the airway opening. (2) Alternatively, valving may depend on dynamic compression of the intrapulmonary bronchus, which could depend mainly on viscous resistance and thus on flow velocity but not gas density.
Effect of Dietary Salt Load on Transepithelial Na+ Exchange in Freshwater Rainbow Trout (Oncorhynchus Mykiss)
Authors: SMITH N. F. , EDDY F. B. , TALBOT C. 
Published: April 2021

ABSTRACT
Dietary Na+ loads (0.5–70 mmol kg-1 fish) were almost completely absorbed within 7 h, and branchial Na+ excretion commenced within 1 h. Na+ loads of less than 1 mmol kg-1 were lost through the gills through a significant decrease in Na+ influx with unaltered Na+ efflux rate (compared with Na+ fluxes in unfed fish). At higher salt loads (&gt;18 mmol kg-1 ), Na+ loss increased as a result of significantly higher Na+ efflux rates, with no further decrease in Na+ influx rate. Tissue Na+ concentrations were unchanged, apart from a significant increase in blood plasma Na+ concentration in fish loaded above 18 mmol kg-1 . The results show that branchial Na+ fluxes may be rapidly adjusted in response to prevailing conditions, and possible control mechanisms are discussed.
Variations on a segmental theme: muscle receptor organs and extensor neuromusculature in the squat lobster Munida quadrispina (Anomura, Galatheidae)
Authors: Wallis E. J. , Paul D. H. , Antonsen B. L. , Hollenberg R. 
Published: April 2021

ABSTRACT
Extensor neuromusculature and the muscle receptor organs (MROs) associated with them have been conserved during the evolution of malacostracan crustaceans, despite species-specific differences between homologous segments in divergent taxa. Investigations of these differences could provide insight into how sensory and neuromuscular elements are modified to accommodate changing behavioural patterns. The most obvious differences between squat lobsters (galatheid anomurans) and macruran decapods, such as crayfish, are the greater dorso-ventral flattening of the galatheid abdomen and its flexed resting posture. To investigate whether the evolution of this altered posture affected extensor neuromusculature and MRO morphology and physiology, we used Methylene Blue staining, cobalt backfilling and extracellular recording techniques to describe these elements in the caudal thoracic and six abdominal segments of the squat lobster Munida quadrispina and compared our results with published descriptions of homologous elements in macrurans. In M. quadrispina, there is segmental variation both in the orientation of the MROs along the abdomen and in their physiological responses to stretch: apparent sensitivity is higher in caudal than rostral MROs. Homologues of three of the four accessory neurones found in crayfish occur, but AN#1 has a major dendrite not present in crayfish. Intersegmental differences in size and morphology of extensor motoneurones occur in M. quadrispina, as have been reported in crayfish, but are dissimilar in the two: abdominal ganglion 5 extensor motoneurones are the largest in M. quadrispina and the smallest in crayfish; this difference correlates with the difference in relative size of axial muscles along the abdomen reported previously for these species. M. quadrispina also differs from macrurans in having a single tonic, and no phasic, MRO on each side of the last abdominal segment. Together, these observations suggest that galatheids have evolved modified or additional neurobehavioural control(s) for the abdomen and tailfan.
Epaxial muscle function during locomotion in a lizard (Varanus salvator) and the proposal of a key innovation in the vertebrate axial musculoskeletal system
Authors: Ritter Dale 
Published: April 2021

ABSTRACT
The pattern of electromyographic activity in the epaxial muscles of walking and running lizards (water monitors, Varanus salvator) was quantified with high-speed video and synchronized electromyography. Muscle denervation experiments were performed and ground reaction forces were recorded to evaluate hypotheses of muscle function. Water monitors exhibit unilateral, uniphasic activation of the epaxial muscles ipsilateral to rear limb support. The iliocostalis and longissimus dorsi muscles are active throughout the support phase of the rear limb, while the transversospinalis is active only during the second half of the support phase. The timing of muscle activity does not support the presumed locomotor function of the epaxial muscles of lizards (lateral bending of the trunk). Bilateral denervation of the two most lateral epaxial muscles (iliocostalis and longissimus dorsi) caused no significant change in the amplitude of lateral trunk bending. These two epaxial muscles do not appear to be necessary for lateral bending of the trunk, nor do they appear to be involved in resisting lateral bending of the trunk. On the basis of the data reported in this study, as well as a re-evaluation of previously existing data, it is proposed that the locomotor function of the epaxial muscles of lizards is to stabilize the trunk against the vertical component of the ground reaction forces; i.e. the epaxial muscles function in a postural role during locomotion in lizards, as they do in other amniotes. This proposed postural role of the epaxial muscles may represent a key innovation of amniotes, made possible by the loss of an aquatic larval stage in their common ancestor.
The role of the pericardium and the effects of adrenaline and changes in oxygen tension on the performance of an in situ perfused crocodile heart
Authors: Axelsson Michael , Franklin Craig E. 
Published: April 2021

ABSTRACT
An in situ perfused crocodile (Crocodylus porosus) heart preparation was used to examine the mechanical responses of the heart to increases in adrenaline concentration, to a decrease in oxygen tension and to opening of the pericardium. Starling and power curves were constructed before and after these experimental manipulations. Increasing adrenaline concentration in the perfusate from 5 nmol l−1 to 0.5 μmol l−1 produced a significant increase in heart rate and a decrease in stroke volume, leaving cardiac output unchanged. With maximal adrenergic stimulation, the left ventricle was able to generate greater power outputs at high right aortic output pressures; however, the right ventricle showed a decrease in performance with increasing output pressure.
Decreasing the of the perfusate to 10 kPa resulted in a significant bradycardia. Both the flow and pressure-generating capabilities of the perfused heart preparation were reduced, although the heart was able to maintain low work levels at this .
Opening the pericardium permitted greater movement/expansion of the cardiac chambers and resulted in an increase in heart rate. Higher flows were generated at low filling pressures during the input pressure challenge as a result of an increase in the sensitivity of the Starling response.
Glycerol synthesis in the rainbow smelt Osmerus mordax
Authors: Raymond James A. 
Published: April 2021

ABSTRACT
Rainbow smelt, Osmerus mordax, maintain high glycerol levels in winter to avoid freezing. After intramuscular injection of 14C-labeled glucose, [14C]glycerol was found in the blood, liver and muscle, indicating that glycogen is a source of glycerol. Levels of both the active and inactive forms of glycogen phosphorylase were higher in muscle in winter than in autumn, although the fraction in the active form did not change significantly. More of the phosphorylase was in the active form in the liver than in the muscle. Short-term starvation resulted in a significant decrease in the level of glycogen soon after the stomachs were emptied, presumably to replace glycerol lost to the water. However, tissue glycerol levels remained relatively high, despite a near depletion of glycogen reserves. Triglyceride levels increased slightly during starvation, indicating that triglycerides were not involved in glycerol synthesis. After intramuscular injection of 14C-labeled pyruvate, [14C]glycerol was found in the blood, liver and muscle, indicating a second route, presumably from muscle protein, to glycerol synthesis. Liver phosphoenolpyruvate carboxykinase activity was slightly higher in winter, possibly to assist in the conversion of pyruvate to glycerol.
Potassium Transport in the Freshwater Bivalve Dreissena Polymorpha
Authors: Wilcox Shawn J. , Dietz Thomas H. 
Published: April 2021

ABSTRACT
Potassium transport and blood ion composition were examined in the freshwater bivalve Dreissena polymorpha. Animals acclimated to artificial pondwater (APW, [K+]=0.05 mmol l−1) for 4 weeks gradually lost Na+ and Cl−, but the blood K+ concentration remained constant near 0.5 mmol l−1. Blood [K+] in D. polymorpha declined by 41% after 1 week of exposure to K+-free APW. Conversely, blood [K+] rose to 1.52±0.05 mmol l−1 (mean ± S.E.M.) 24 h after exposure to 0.5 mmol l−1 K+ APW. Total tissue K+ content remained stable in animals maintained in APW, but fell significantly in animals exposed to K+-free APW for 2 weeks. The net K+ flux (Jnet) for animals incubated in APW, with an average K+ concentration of 0.07 mmol l−1, was -0.27±0.06 µequiv g−1 dry tissue h−1, significantly different from the value of 0.50±0.08 µequiv g−1 dry tissue h−1 for animals transferred to 0.30 mmol l−1 K+ APW. A transepithelial membrane potential of -3.6±0.7 mV (blood negative compared with the bathing medium) was measured in APW-acclimated mussels. Potassium influx was measured with 42K and displayed Michaelis–Menten saturation kinetics at dilute K+ concentrations. The Km was 0.084±0.054 mmol l−1 and the Jmax was 1.74±0.39 µequiv g−1 dry tissue h−1. Both the Km and Jmax for animals exposed to K+-free APW for 7 days were unchanged. Using 86Rb, qualitatively similar transport characteristics were observed for animals incubated in K+-free, Rb+ APW, but the 22 day K+ depletion time significantly increased Jmax. D. polymorpha compensated for changes in the ionic composition of the acclimation medium by tolerating alterations in blood solute composition and adjusting ion transport rates.
Neural Control of Hindleg Steering in Flight in The Locust
Authors: Lorez M. 
Published: April 2021

ABSTRACT
Corrective flight steering with the hindlegs was investigated in intact tethered flying locusts inside a wind tunnel as well as in animals dissected for intracellular recording and showing fictive flight activity.
In intact tethered flying animals, activity in the second coxal abductor muscle (M126) was highly correlated with hindleg steering and was coupled to the elevator phase of the flight cycle.
Fictive flight and steering could also be elicited in animals dissected for intracellular recording of motoneurones innervating M126. During fictive flight activity, motoneurones 126 were rhythmically excited in the elevator phase, presumably from central elements of the neuronal oscillator generating the flight motor pattern, as is the case for motoneurones innervating wing muscles. During fictive straight flight, this input was subthreshold, and it could be demonstrated that simulated deviation from the flight course resulted in recruitment of motoneurones 126.
Statistical analysis of the latencies of fast muscle spikes in M126 and in one wing elevator muscle showed that both received common input during flight steering. One source of this common input was identified as the sensory information from the lateral ocelli, which play an important role in the detection of course deviation.
The experiments demonstrated that processing in the sensory-motor system for hindleg steering is probably organized in a very similar way to that responsible for steering with the wings.
Serotonergic Modulation of Swimming Speed in the Pteropod Mollusc Clione Limacina:I. Serotonin Immunoreactivity in the Central Nervous System and Wings
Authors: Satterlie Richard A. , Norekian Tigran P. , Jordan Sheryl , Kazilek Charles J. 
Published: April 2021

ABSTRACT
Serotonin-immunoreactive somata in the pteropod mollusc Clione limacina were restricted to the cerebral and pedal ganglia. 10–14 pairs of cells were consistently found in the cerebral ganglia, including one large pair that had soma positions and axon branching patterns reminiscent of those of the metacerebral cells of other molluscs. Two clusters of somata were found on the midline near the cerebral commissure, one on the anterio-lateral margin and one posterio-laterally. A distinct paired cluster of up to nine somata was found on the dorso-lateral margin of the pedal ganglia, near the emergence of the pedal commissure. Up to five of these cells innervated the ipsilateral wing via the wing nerve. Dye-fills of these cells showed that they branch repeatedly in the ipsilateral wing and innervate the swim musculature. Double-labelling experiments indicated that the filled neurons were also serotonin-immunoreactive. Neurobiotin fills that were processed for electron microscopy revealed two types of terminals associated with the swim musculature: direct contacts and reactive terminals adjacent to non-labelled presynaptic terminals. Additional immunoreactive neurons in the pedal ganglia included the asymmetrical heart excitor neuron of the left pedal ganglion and up to nine ventral somata.
Serotonergic Modulation of Swimming Speed in the Pteropod Mollusc Clione Limacina:II. Peripheral Modulatory Neurons
Authors: Satterlie Richard A. 
Published: April 2021

ABSTRACT
A symmetrical cluster of serotonin-immunoreactive neurons in the pedal ganglia of Clione limacina has been described morphologically and physiologically. At least five of the cluster neurons send axons to the ipsilateral wing that branch throughout the entire wing area. Activation of these cells did not produce a motor effect in non-swimming preparations, but did enhance contractility in swimming preparations. Activity in the pedal neurons did not produce detectable central effects as neither swim interneuron nor swim motor neuron activities were altered. Most notable was a lack of a change in swim frequency, a characteristic of swim acceleration. Activity in the pedal neurons did enhance the size of muscle junctional potentials and spike-like responses, but only in slow-twitch muscles. The peripheral modulatory effect was blocked by the serotonin antagonist mianserin.
Regulatory Responses of the Coxal Organs and the Anal Excretory System to Dehydration and Feeding in the Spider Porrhothele Antipodiana (Mygalomorpha: Dipluridae)
Authors: Butt A. G. , Taylor H. H. 
Published: April 2021

ABSTRACT
The roles of coxal and anal excretion in the regulation of haemolymph osmolality, [Na+] and [K+] were studied in the mygalomorph spider Porrhothele antipodiana (mass 0.7–1.0 g) under differing conditions of feeding and hydration state. Dehydration of starved spiders by removal of drinking water caused progressive mass loss at a rate of about 2.5 % of initial body mass per day and was associated with increases in the whole-body [Na+] and [K+] and in the osmolality, [Na+] and [K+] of the haemolymph. On provision of prey, feeding partially restored this mass loss but further elevated body and haemolymph ion concentrations. Dehydration reduced fluid excretion by the anal excretory system and the four coxal organs in both starved and feeding spiders. Starved hydrated spiders initially produced anal urine at 5 μl day-1 and this was progressively reduced to zero after 4 days of water deprivation. Spiders dehydrated to less than 12 % mass loss would nevertheless feed and this initiated a small post-prandial anal diuresis (&lt;5 μl day-1 compared with &gt;30 μl day-1 in fed hydrated spiders). Coxal fluid was produced by dehydrated spiders only during feeding and was delivered into the prey, the rate of production by single organs decreasing from about 19 μl h-1 g-1 body mass in hydrated spiders to about 4 μl h-1 g-1 body mass in spiders dehydrated to 11 % mass loss.
There was an increase in urine [K+] and in the rate of anal K+ excretion associated with ad libitum feeding in dehydrated spiders. However, urine [Na+] and the rate of anal excretion of Na+ were not increased by feeding. This was associated with an increase in [K+] of the stercoral fluid above that observed in either fed or starved hydrated spiders, but no significant change in [Na+]. Conversely, [Na+] of the coxal fluid produced during feeding was increased by dehydration whereas [K+] was not. These observations are consistent with the previously postulated roles of the coxal organs (Na+) and anal system (K+) in the excretion of ions ingested with the prey.
Full elimination of the prey ions was accomplished only after drinking water was resupplied, which initiated further anal and coxal diureses. Smaller anal and coxal diureses also occurred on rehydration of unfed spiders. The production of coxal fluid in the absence of prey is further evidence that the coxal organs have a true excretory function besides, presumably, assisting ingestion. During dehydration and feeding, P. antipodiana, unlike many insects, is unable simultaneously to conserve water and to eliminate ions by production of a highly concentrated excretory fluid. Both coxal fluid and anal urine were approximately iso-osmotic to the haemolymph and the urine was markedly hypo-ionic.
Extensive Erythrocyte Deformation in Fish Gills Observed by In Vivo Microscopy: Apparent Adaptations for Enhancing Oxygen Uptake
Authors: Nilsson Göran E. , Löfman Carl O. , Block Mats 
Published: April 2021

ABSTRACT
The secondary lamellae of the gills are the primary sites of oxygen uptake in fish. We have used epi-illumination microscopy in vivo to observe the microcirculation directly in secondary lamellae of rainbow trout (Oncorhynchus mykiss) and roach (Rutilus rutilus).
Our observations point at previously unrecognised factors in fish respiratory physiology. Erythrocytes passing through secondary lamellae became greatly deformed. We propose that this deformation plays a role in oxygen uptake by diminishing the diffusion boundary layer (adhesion layer) of fluid around the erythrocyte and possibly also by mixing intracellular haemoglobin molecules. Moreover, the erythrocytes were apparently slowed down and forced to travel over an extended path to pass through the lamella, making it tempting to speculate that plasma passes more readily than erythrocytes through the lamella, resulting in a local elevation of the haematocrit.
Scaling the Feeding Mechanism of the Largemouth Bass (Micropterus Salmoides): Motor Pattern
Authors: Wainwright Peter C. , Richard Barton A. 
Published: April 2021

ABSTRACT
We present the first analysis of scaling effects on the motor pattern of a feeding vertebrate. Data are presented for the effects of body size on the pattern of activity in four head muscles during prey capture in the largemouth bass, Micropterus salmoides. Electromyographic (EMG) recordings were made from three expansive-phase muscles (the epaxialis, the sternohyoideus and the levator arcus palatini) and one compressive-phase muscle (the adductor mandibulae), during the capture of small fish prey. Recordings were made of 181 prey-capture events from 19 bass that ranged in size from 83 to 289 mm standard length. We measured seven variables from the myogram of each capture to quantify the temporal pattern of muscle activation, including the duration of activity in each muscle and the onset time of each muscle, relative to the onset of the sternohyoideus muscle. Regressions of the mean value of each variable for the 19 individuals on standard length revealed that only the onset time of the adductor mandibulae changed with fish body size. The increase in onset time of the adductor muscle appears to reflect the longer time taken to open the mouth fully in larger fish. Other research shows that the kinematics of the strike in this species slows significantly with increasing body size. The combined results indicate that the duration of the EMG signal is not directly correlated with the duration of force production in muscles when compared between fish of different sizes. The lack of scaling of burst duration variables suggests that the reduced speeds of prey-capture motion are explained not by changes in the envelope of muscle activity, but rather by the effects of scale on muscle contractile kinetics. These scaling effects may include changes in the relative resistance of the jaw and head structures to movement through water and changes in the intrinsic contractile properties of the muscles of the feeding apparatus.