bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vagal Regulation of Intracardiac Shunting in the Turtle Pseudemys Scripta
Authors: Hicks James W. , Comeau Stephen G. 
Published: April 2021

ABSTRACT
Two principal hypotheses account for intracardiac shunting in reptiles. The ‘pressure shunting’ hypothesis proposes that there is no fuctional separation between the ventricular cava during systole. The ‘washout shunting’ hypothesis suggests that the cavum pulmonale is functionally separated from the rest of the ventricle during systole. The purpose of this study was to test the two principal hypotheses in a turtle, Pseudemys scripta, after inducing a right-to-left shunt by electrical stimulation of the vagus nerve. Animals were anaesthetized with sodium pentobarbital (30–40 mg kg-1), tracheotomized and mechanically ventilated. Two experimental groups were used. Both groups had the right and left cervical vagi exposed and sectioned and silver bipolar electrodes were attached for electrical stimulation. In addition, cardiac function was evaluated by determining the pulmonary blood flow, pulmonary arterial pressure, peak systolic pressure in the cavum pulmonale, central arterial pressure, pulmonary vascular resistance and heart rate. In group I, hydrogen electrodes were inserted into the right aorta, the left aorta and the pulmonary artery. Hydrogen, dissolved in saline, was infused into the left atrium, jugular vein and cavum pulmonale. Blood flow from these sites was deduced from detection of a H2 signal in the right and left aortae and the pulmonary artery. In group II, catheters were inserted in the left and right atria and aortae for the measurement of blood gases. For both groups, the protocol consisted of control periods and periods of electrical stimulation of the efferent and afferent ends of the vagus nerve. During the control periods, infusion of a H2 solution into either the left atrium or the jugular vein resulted in the detection of H2 in the right and left aortae and the pulmonary artery. This suggested that both right-to-left and left-to-right intracardiac shunts were present. H2 infused into the cavum pulmonale was always detected in the pulmonary artery but never in the left or right aortae. During stimulation of the right vagal efferents, a bradycardia developed (heart rate declined by 65 %), pulmonary blood flow was reduced by 73 % and pulmonary vascular resistance increased by 158 %. This was accompanied by a reduction in the of both the right and left aortae, although the of the left and right atria remained constant. Under these conditions, H2 infused into the jugular vein and the left atrium was detected in the right and left aortae and the pulmonary artery of all animals studied. Infusion of H2 into the cavum pulmonale was detected in the right and left aortae in only two animals. The results supported the washout mechanism for right-to-left intracardiac shunting.
Effect of coronary ablation and adrenergic stimulation on in vivo cardiac performance in trout (Oncorhynchus Mykiss)
Authors: Gamperl A. K. , Pinder A. W. , Boutilier R. G. 
Published: April 2021

ABSTRACT
In fish, catecholamine-induced changes in cardiac performance in vivo are the result of complex interactions between the direct adrenergic effects on the heart and peripheral circulation and the reflex responses to increased blood pressure. In addition, coronary artery transport of catecholamines and oxygen to the compact myocardium may be essential for maximal in vivo cardiac performance during adrenergic stimulation. Cardiac output (Q̇), heart rate (fH), stroke volume (Vs) and dorsal aortic pressure (PDA) were measured in trout with intact or ablated coronary arteries at rest and following intra-arterial administration of 0.2, 0.5, 1.0 and 2.0 µg kg−1 adrenaline. Resting Q̇, fH, Vs and PDA were the same in fish with intact and ablated coronaries at 48 h post-surgery, averaging approximately 18 ml min−1 kg−1, 42 beats min−1, 0.42 ml kg−1 and 2.2 kPa, respectively. All cardiovascular variables showed a strong relationship between response magnitude and adrenaline dose. However, our results indicate that adrenaline doses above 0.5 µg kg−1 may have a limited ability to increase Q̇ (ED50 0.22 µg kg−1). Coronary artery ablation had little effect on post-injection Q̇, Vs, PDA or fH at any dose of adrenaline. In both intact and ablated groups, two types of responses in Q̇ were observed following adrenaline injection. In the ‘type 1’ response, Q̇ increased shortly (15–30 s) after adrenaline administration, as increases in Vs more than compensated for a pressor-stimulated reflex bradycardia. In the ‘type 2’ response, alterations in Q̇ were biphasic. In the initial minutes post-injection, Q̇ fell and reached a minimum level at 1–2 min, the result of an immediate drop in fH and a delayed post-injection increase in Vs. Thereafter, Q̇ gradually increased as a result of concordant increases in fH and Vs. Although time to maximum Q̇ was 5–6 min longer for fish exhibiting type 2 responses, there was no difference in maximum Q̇ increase or in the time courses for changes in fH and PDA between response types. Our results suggest (1) that during normoxic conditions, cardiac performance does not depend highly on coronary blood flow; (2) that the capacity of adrenaline to increase Q̇ may be limited by elevations in output pressure and/or by the low dose (concentration) of adrenaline required to achieve near maximal adrenergic stimulation of the heart; and (3) that fish exhibiting type 2 responses have an increased barostatic gain (% fH per unit PDA) compared with those with type 1 responses.
Effects of diluted natural water and altered ionic environments on gustatory responses in rainbow trout (Oncorhynchus mykiss)
Authors: Kitada Y. , Hara T. J. 
Published: April 2021

ABSTRACT
The effects of adaptation to diluted natural water (NW) and various salt solutions on the gustatory responses recorded from the palatine nerve in rainbow trout (Oncorhynchus mykiss) were studied. The magnitude of the response to 1 mmol l−1 L-proline (L-Pro) decreased when the perfusing NW was diluted with artificial fresh water (AFW) that maintained concentrations of major cations. AFW suppressed the responses to L-Pro by about 70 %. The responses to 1 mmol l−1 L-Pro, 0.1 mmol l−1 quinine–HCl (Q-HCl) and 10 nmol l−1 taurolithocholic acid (TLCA) were eliminated or reduced (to &lt;10 %) by adapting the palate to distilled water (DW). The addition of 0.1–100 mmol l−1 salts (NaCl, KCl, CaCl2, MgCl2) and choline chloride restored the gustatory responses to about 50 % of those in NW. The addition of salts to NW had no effect on the gustatory responses. The gustatory responses to 5 % CO2 were similarly reduced when the palate was adapted to solutions that contained no NW (DW, AFW, 10 mmol l−1 NaCl in DW). However, the reduction was independent of salt concentration, suggesting a different transduction mechanism for CO2. Tetrodotoxin (1 µmol l−1) had no effect on the gustatory responses to L-Pro.
We conclude that NW is required and that cations alone are not sufficient to support maximal gustatory responses. The results suggest that an unknown substance(s) contained in NW plays an essential role in gustatory reception and that permeation of cations through the apical membrane of gustatory cells is not involved in gustatory transduction in rainbow trout.
Concealed transepithelial potentials and current rectification in tsetse fly malpighian tubules
Authors: Isaacson L. C. , Nicolson S. W. 
Published: April 2021

ABSTRACT
Electrophysiological techniques have been applied to tsetse fly Malpighian tubules for the first time. In either Cl− or SO42− Ringer, both non-perfused and perfused tubules displayed transtubular potentials (Vt) at or close to 0 mV. Exposure to cyclic AMP elicited a marked secretory response and, in SO42− Ringer, a sharp (lumen-positive) increase in Vt. In Cl− Ringer, despite more than double the secretory response, there was little or no change in Vt. Replacing Cl− with SO42− Ringer, in the presence of cyclic AMP, promptly increased Vt. In perfused tubules, this occurred irrespective of the Cl− or SO42− composition of the perfusate. In Cl− Ringer, the transepithelial resistance (Rtrans) was less than half that previously reported in Malpighian tubules of other species. Cyclic AMP reduced Rtrans still further, whether tubules were bathed in Cl− or SO42− Ringer. Current–voltage (I/V) plots often displayed current rectification, both before and more frequently after exposure to cyclic AMP, thus permitting estimation of both the electromotive force of the Na+ transport mechanism (ENa) and of the shunt resistance (Rshunt). Both ENa and Rshunt were markedly lower in tubules bathed in Cl− than in SO42− Ringer. Cyclic AMP was without effect on ENa and Rshunt, in either Cl− or SO42− Ringer. In terms of the equivalent electrical circuit, the secretory response to cyclic AMP was due solely to a fall in resistance of the active transport pathway (Rseries). The absence of an appreciable Vt, in Cl− Ringer, is consistent with an apical Cl− shunt.
Molecules that become redistributed during regeneration of the leech central nervous system
Authors: Lüthi T. E. 
Published: April 2021

ABSTRACT
A search has been made for molecules other than laminin that change their distribution during axonal regrowth after injury. Two monoclonal antibodies, generated against a protein extract of leech central nervous system (CNS), stain distinct regions of leech CNS and, following lesions, show changes in distribution with time.
Monoclonal antibody NP17 stained two bands of Mr 80×103 and 60×103 on Western blots of protein extracted from whole CNS. On cryosections of leech CNS, staining was predominantly within the neuropile. A second antibody, mAb CT16, stained a collagen-associated molecule of the extracellular matrix. It labelled the outer capsule, which surrounds the neuronal cell packets, and the inner capsule, which envelops the neuropile. In the connectives, CT16 immunoreactivity was restricted to the connective capsule and was not associated with nerve fibres or glia. When the connectives were crushed, immunocytochemical studies revealed changes in distribution of both mAb NP17 and mAb CT16. After 3 days, a time when fibres begin to sprout and form connections, an increase in NP17 immunoreactivity appeared at the site of the lesion. Staining levels remained elevated for several weeks. In contrast, CT16 immunoreactivity did not change for several days after damage. After 10 days, fibre-like staining appeared at the site of the crush; for several weeks it continued to spread throughout the connective. These results show that regeneration of the leech CNS involves the redistribution of at least two molecules. Using monoclonal antibodies, these two molecules, which are situated in distinct regions of the CNS, have been visualized at different stages of the repair process. It has been shown that they alter their distribution at distinct times during regeneration.
EMG–force relationship of the cat soleus muscle studied with distributed and non-periodic stimulation of ventral root filaments
Authors: Guimaraes A. C. , Herzog W. , Hulliger M. , Zhang Y. T. , Day S. 
Published: April 2021

ABSTRACT
Distributed stimulation of ventral root (VR) filaments and pseudo-random interpulse intervals (based on a Gaussian distribution with a coefficient of variation of 12.5 %) were used to modulate electromyographic activity (EMG) and force of the cat soleus muscle to assess the EMG–force relationship. A protocol consisting of addition and rate modulation of ten VR filaments that contain alpha motoneurones to the soleus muscle was adopted. EMG was measured using indwelling electrodes and forces were measured at the distal tendon using a strain transducer. EMG records obtained using this approach were similar in the time and frequency domains to those obtained during voluntary contractions. Force records obtained from stimulation of single VR filaments showed summation effects typical of irregular interpulse intervals. The overall relationship between integrated rectified EMG (IEMG) and mean force was found to be non-linear. At low and high stimulation levels, IEMG tended to increase proportionally more than mean force. In the intermediate stimulation region (i.e. producing forces between approximately 5 % and 88 % of the maximal tetanic force), the IEMG–mean force relationship was virtually linear. Muscles with a homogeneous fibre type composition, such as the cat soleus muscle, have been reported to have a linear EMG–force relationship.
Sound production and hearing in the pyralid mothSymmoracma minoralis
Authors: Heller Klaus-Gerhard , Krahe Rüdiger 
Published: April 2021

ABSTRACTMales of the moth Symmoracma minoralis (Snellen) (Lepidoptera: Pyralidae, Nymphulinae) were observed producing a high-intensity calling song (95 dB SPL at a distance of 10 cm) with a complex amplitude and frequency modulation (peaks of carrier frequency at 60 and 120 kHz). This sound is produced by a hitherto unknown type of sound organ located in the last abdominal (genital) segment, which may act as a tymbal. The observed directionality of sound output is probably achieved by means of a hollow cone surrounding the sound organ. Electrophysiological recordings revealed that the tympanal organs of S. minoralis are most sensitive in the frequency range from 50 to at least 100 kHz, which is distinctly higher than the minimum threshold levels in most other moths yet examined. The origin of genital sound production is discussed with respect to abdominal pheromone glands and pheromone-releasing movements.
Gas exchange through the lungs and gills in air-breathing crabs
Authors: Farrelly Caroline A. , Greenaway Peter 
Published: April 2021

ABSTRACT
Lung and gill performance in gas exchange have been evaluated in eight species of air-breathing crabs with two different lung circulatory designs, those with portal systems and smooth lung linings, and those without portal systems and with invaginated and evaginated lung linings. In all species, the lungs were extremely effective in oxygen uptake whilst the performance of the gills was inferior. An exception to this was Gecarcoidea natalis, which has gills highly modified for aerial gas exchange; its gills and lungs were equally efficient in O2 uptake. The relative efficiencies of the lungs and gills in CO2 excretion differed between species, with the gills being the major site of CO2 loss in the more amphibious species and the lungs having an increasingly important role in the more terrestrial crabs. The presence or absence of lung portal systems was not found to correlate with either saturation rates or efferent oxygen concentrations, with both lung types being extremely efficient in O2 uptake. The lungs with portal systems showed a large increase in oxygen content in the first lacunar bed and progressively smaller increases in the next two; these lungs may, therefore, have some reserve for exercise.
Thermal acclimation, neuromuscular synaptic delay and miniature end-plate current decay in the frog rana temporaria
Authors: Tiiska A. J. , Lagerspetz K. Y. H. 
Published: April 2021

ABSTRACT
The effects of 1 or 2–3 weeks of acclimation to 4 °C and 24 °C of overwintering grass frogs (Rana temporaria) on the synaptic delay and on the time constant of the decay phase (τ) of miniature end-plate currents (MEPCs) in the neuromuscular junction of sartorius muscle were studied. In order to equalize the possible effects of differential starvation, the animals were usually cross-acclimated to the two temperatures. Synaptic delay was not affected by temperature acclimation but was slightly prolonged by the more profound starvation at the higher temperature when the cross-acclimation procedure was not used. The average Q10 of synaptic delay between 4 and 24 °C was 2.60 and of minimum synaptic delays, 2.64. The corresponding values for apparent activation energy (Ea) were 65.79 and 66.48 kJ mol−1. The time constant of the decay phase of MEPCs was not affected by temperature acclimation. The average Q10 between 4 and 24 °C was 2.27. The corresponding Ea value was 56.02 kJ mol−1. The function of peripheral neuromuscular synapses is well regulated and changes in its time relationships do not appear to be involved in the thermal acclimation of frogs.
Partial purification, tissue distribution and modulatory activity of a crustacean cholecystokinin-like peptide
Authors: Turrigiano G. G. , Van Wormhoudt A. , Ogden L. , Selverston A. I. 
Published: April 2021

ABSTRACT
Reversed-phase chromatography was used to separate several forms of cholecystokinin-like peptides (CCKLP) from the pericardial organs (PCOs) of the spiny lobster Panulirus interruptus. Fast protein liquid chromatography of PCOs, stomatogastric ganglia (STGs) and eyestalks revealed five peaks of CCKLP (peaks A–E) that were common to all three tissues, as well as two additional peaks (peaks F and G) in the STG. Peaks A–E were present in the hemolymph of fed, but not starved, lobsters. The bioactivity of peaks A–E was tested on the gastric mill rhythm of the isolated STG. Only peak E elicited activity. The effects of peak E included activating the gastric mill rhythm in quiescent preparations and strengthening existing rhythms in a dose-dependent manner. Further purification of peak E by high performance liquid chromatography resolved this peak into two immunoreactive peaks, one of which retained its bioactivity. The effects of peak E were blocked by the CCK antagonist proglumide. These results are consistent with a role for peak E in the feeding-induced activation of the gastric mill.
Scaling modulus as a degree of freedom in the design of locust legs
Authors: Katz Stephen L. , Gosline John M. 
Published: April 2021

ABSTRACT
Previous work has shown that the scaling of mechanical behaviour in bending of the metathoracic tibiae of the African desert locust (Schistocerca gregaria) is not predicted by the scaling of external dimensions. The flexural stiffness of the tibia scales to (body mass)1.53, which is similar to the predictions of the elastic similarity model of scaling. The external dimensions, however, scale in a manner that produces relatively more elongate limb segments – an observation that differs from the predictions of any existing scaling model. In this paper, we examined two alternative hypotheses to explain this uncoupling of morphology and mechanics: (1) that the load-bearing cuticular material is distributed in the legs in a manner that is not indicated by changes in external dimensions, or (2) that the stiffness of the cuticular material is altered to produce the observed scaling of flexural stiffness.
The second moment of area (I) scaled to (body mass)1.19, which was similar to scaling I to (tibial radius)4. This indicates that the relationship between the external dimensions of the tibiae and the specific distribution of load-bearing material is conserved independently of scale. Therefore, the locust achieves the observed scaling of flexural stiffness by altering the modulus of the load-bearing cuticular material. In fact, the time-dependent modulus (E′) scales to (body mass)0.311. In essence, the scaled material stiffness provides a degree of freedom in design in addition to external morphological dimensions in accommodating the changing demands placed on a skeletal structure with increases in body size.
Contractile properties of a high-frequency muscle from a crustacean: II. Contraction kinetics
Authors: Stokes Darrell R. , Josephson Robert K. 
Published: April 2021

ABSTRACT
The flagella (small appendages on the maxillipeds) of the crab Carcinus maenas beat regularly when active at about 10 Hz (15 °C). The beat of a flagellum is due to contraction of a single small muscle, the flagellum abductor (FA). The optimal stimulus frequency for tetanic contraction of the FA was about 200 Hz. When the muscle was stimulated at 10 Hz with paired stimuli per cycle, the interstimulus interval that maximized peak force was 2–4 ms, which corresponded well to the interspike intervals within bursts recorded from motor axons during normal beating. Contraction of the isolated FA showed pronounced neuromuscular facilitation and many stimuli were needed to activate the muscle fully. The dependence on facilitation in isolated muscles appeared to be greater than that in vivo. It is suggested that neuromodulators in the blood of the crab enhance neuromuscular transmission and reduce the dependency on facilitation in intact animals. The FA had a narrow length–tension curve. Tetanic tension became vanishingly small at muscle lengths less than about 90 % of the maximum in vivo length. The maximum length change of the muscle during in vivo contraction was about 5 %. The maximum isometric force of the FA was low (about 6 N cm-2) but its shortening velocity was high. Vm, the maximum shortening velocity determined from isotonic shortening, was 4.0 muscle lengths s−1; V0, the maximum shortening velocity from slack test measurements, was about 8 lengths s−1. The structure and physiology of the FA are compared with those of locust flight muscle, chosen because it too is a muscle capable of long-duration, high-frequency performance.
Contractile properties of a high-frequency muscle from a crustacean: III. Mechanical power output
Authors: Josephson Robert K. , Stokes Darrell R. 
Published: April 2021

ABSTRACT
The mechanical power output during oscillatory contraction was determined for the flagellum abductor muscle of the crab Carcinus maenas using the work loop technique. Measurements were made at 10 Hz, which is the normal operating frequency of the muscle. The temperature was 15 °C. Increasing the number of stimuli per cycle (given at an interstimulus interval of 3.3 ms) decreased the number of cycles required to reach a work plateau and increased the work per cycle at the plateau to a maximum at 4–5 stimuli per cycle. The maximum mechanical power output was 9.7 W kg−1 muscle (about 26 W kg−1 myofibril). The optimum strain for work output (5.7 %) was close to the estimated muscle strain in vivo (5.2 %).
Auditory threshold change in singing cicadas
Authors: Hennig R. M. , Weber T. , Huber F. , Kleindienst H.-U. , Moore T. E. , Popov A. V. 
Published: April 2021

ABSTRACT
The hearing sensitivity in singing cicadas is reduced during sound production by a folding of the tympanal membranes. Using electrophysiological recording and nerve stimulation techniques, we have shown an effect of the folded tympanum on the auditory threshold of two species of cicadas, Tibicen linnei and Okanagana rimosa. Auditory thresholds of both species increased by about 20 dB when the tympana folded during singing. In T. linnei the increase in threshold affected the whole frequency range, from 1 to 16 kHz, in a similar way. Electrical stimulation of one or both auditory nerves resulted in a folding of both tympanal membranes in a way very similar to that seen in singing animals. We have demonstrated that a cicada male is able to adjust its auditory threshold within a range of about 20 dB by the tympanal folding mechanism.