bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Pharmacological Blockade on Cardiovascular Responses to Voluntary and Forced Diving in Muskrats
Authors: Signore Pierre E. , Jones David R. 
Published: April 2021

ABSTRACT
Neural control of free and forced diving bradycardia and peripheral resistance was studied in the muskrat (Ondatra zibethicus) by means of acute pharmacological blockade with the muscarinic blocker atropine, the α-adrenergic blocker phentolamine and the β-adrenergic blockers nadolol and propranolol. Saline injection was used as a control. Heart rate in control animals increased before voluntary dives and dropped markedly as soon as the animals submerged. Heart rate started increasing towards the end of voluntary dives and reached pre-dive values within the first 5 s of recovery. Pre-dive and post-dive tachycardia were reduced in β-blocked animals, emphasizing the role of the sympathetic system during the preparatory and recovery periods of voluntary dives. Diving bradycardia and the acceleration in heart rate before surfacing were abolished by atropine and unaffected by nadolol, demonstrating the importance of vagal efferent activity during diving. The results after blockade with nadolol suggest that there is an accentuated antagonism between the two branches of the autonomic nervous system during diving, so that parasympathetic influences on the heart predominate. Propranolol-treated muskrats had a higher diving heart rate than saline-and nadolol-treated animals, which may be due to a sedative effect caused by propranolol crossing the blood–brain barrier, a blockade of central catecholaminergic pathways or a peripheral neural effect, due to the anaesthetic properties of propranolol. Phentolamine did not affect diving bradycardia, indicating that diving bradycardia occurs independently of peripheral vasoconstriction. Compared with voluntary dives, heart rate was lower before forced dives in unrestrained animals and fell to lower values during diving. Underwater endurance in forced dives was markedly reduced after atropine and phentolamine treatment (either individually or combined) compared with that of control animals. Hence, bradycardia and peripheral vasoconstriction are necessary for maximum underwater endurance. A puzzling finding was that animals without bradycardia and/or peripheral vasoconstriction still dived voluntarily for periods as long as the calculated aerobic dive limit of muskrats and survived 5 min of forcible submergence. We hypothesize that anaerobic metabolism may play an important role during diving in muskrats.
Characterization and Modulation of Na+ and Ca2+ Currents Underlying the Action Potential in Bag Cells of two Species of Aplysia
Authors: Fieber Lynne A. 
Published: April 2021

ABSTRACT
The neurosecretory bag cells of Aplysia produce long trains of action potentials (afterdischarge) to release hormones important to egg laying. These ionic currents are modulated by second messengers. Modulation of excitability in bag cells is incompletely understood partly because the currents that are modulated have not been fully characterized. Whole-cell voltage-clamp experiments were executed in cultured cells from sexually mature A. californica and A. brasiliana to characterize the inward voltage-gated currents for Na+ and Ca2+. These species had similar Na+ and Ca2+ current characteristics. The Na+ currents activated at voltages less negative than -30 mV and peaked at between +10 and +20 mV in artificial sea water. The time course and pharmacology of bag cell Na+ currents were similar to those of fast Na+ current in other excitable cells. Na+ currents were abolished in Na+-free extracellular solution and were not inhibited by Cd2+. The KD for inhibition by tetrodotoxin was 2.6 nmol l−1. The Na+ current was relatively insensitive to depolarized holding potentials (Vh), maintaining approximately 65 % of peak current amplitude throughout the activation range at Vh=-30 mV. In experiments using a 1 s depolarized Vh prior to a test pulse, the half-inactivation voltage (V1/2) was -21 mV. The time constant of recovery from steady-state activation was 2.9 ms at Vh=-70 mV and 6.8 ms at Vh=-30 mV. The Ca2+ currents activated near -10 mV and peaked at approximately +20 mV with 11 mmol l-1 Ba2+ as the charge carrier. The pharmacology and V1/2 of bag cell Ca2+ current were similar to those of L-type Ca2+ currents. In extracellular solution without Na+, but containing Ba2+, Cs+ and tetraethylammonium, the Ca2+ current was inhibited by 25–100 % by nifedipine (10 µmol l−1), mean 42 %, and was unaffected in the majority of cells by w-conotoxin (10 µmol l−1). The Ca2+ current was insensitive to Ni2+ (100 µmol l−1), but was abolished by 100 µmol l−1 Cd2+. Like the Na+ current, the Ca2+ current was relatively insensitive to depolarized Vh, maintaining more than 80 % of peak current amplitude throughout the activation range at Vh=-40 mV. With a 1 s depolarized Vh prior to a test pulse, the V1/2 was -30 mV. The activation thresholds for Na+ and Ca2+ currents as well as the relative insensitivity of both currents to depolarized Vh as low as -30 mV are characteristics that would be required for spontaneous depolarizations during afterdischarge. After a 1 h treatment with phorbol 12-myristate 13-acetate (25 nmol l−1), the amplitude of Na+, Ca2+ and outward currents in individual bag cells was increased compared with control amplitudes from the same cells. Phorbol ester treatment did not change the activation and inactivation ranges, time course, V1/2 or pharmacology of the inward currents.
Enteric Reflexes and Nitric Oxide in the Fish Intestine
Authors: Karila Paul , Holmgren Susanne 
Published: April 2021

ABSTRACT
The aim of the present study was to elucidate the possible regulation of peristalsis in the intestine of the Atlantic cod Gadus morhua. For this purpose, the mid intestine was dissected out and placed in a partitioned bath. Balloon distension (0.1–0.4 ml) and intramural field stimulation (8 Hz, 10 V) were carried out and the responses of the circular muscle were recorded 1.5 cm orally and anally to the stimulus using force transducers. The preparations developed spontaneous contractions propagating in the anal direction with a frequency of about one contraction per 2 min. Distension of the muscle wall with a balloon did not evoke any recordable peristaltic reflexes. Intramural stimulation caused a contraction oral to the stimulation and a relaxation anal to the stimulation in most cases. Tetrodotoxin abolished the responses to electrical stimulation in both directions. Atropine reduced and methysergide abolished the oral contractions caused by electrical stimulation. Administration of the nitric oxide synthesis inhibitor L-NG -nitro-arginine methyl ester (L-NAME) abolished the anal relaxation caused by electrical stimulation and augmented the oral contractions. The results indicate the presence in teleost fish intestine of an ascending excitatory peristaltic reflex which involves a cholinergic–serotonergic pathway and a descending inhibitory reflex involving a nitrergic pathway. These observations suggest a high degree of conservation of peristaltic mechanisms during vertebrate evolution.
Several forms of callitachykinins are distributed in the central nervous system and intestine of the blowfly Calliphora vomitoria
Authors: Nässel Dick R. , Kim Min-Yung , Lundquist C. Tomas 
Published: April 2021

ABSTRACT
We have examined the distribution of two tachykinin-related neuropeptides, callitachykinin I and II (CavTK-I and CavTK-II), isolated from whole-animal extracts of the blowfly Calliphora vomitoria. Extracts of dissected brains, thoracic–abdominal ganglia and midguts of adult blowflies and the entire central nervous system of larval flies were analysed by high performance liquid chromatography (HPLC) combined with enzyme-linked immunosorbent assay (ELISA) for the presence of CavTKs. To identify the two neuropeptides by HPLC, we used the retention times of synthetic CavTK-I and II as reference and detection with an antiserum raised to locustatachykinin II (shown here to recognise both CavTK-I and II). The brain contains only two immunoreactive components, and these have exactly the same retention times as CavTK-I and II. The thoracic–abdominal ganglia and midgut contain immunoreactive material eluting like CavTK-I and II as well as additional material eluting later. The larval central nervous system (CNS) contains material eluting like CavTK-I and II as well as a component that elutes earlier. We conclude that CavTK-I and II are present in all assayed tissues and that additional, hitherto uncharacterised, forms of tachykinin-immunoreactive material may be present in the body ganglia and midgut as well as in the larval CNS. An antiserum was raised to CavTK-II for immunocytochemistry. This antiserum, which was found to be specific for CavTK-II in ELISA, labelled all the neurones and midgut endocrine cells previously shown to react with the less selective locustatachykinin antisera. It is not clear, however, whether CavTK-I and II are co-localised in all LomTK-immunoreactive cells since there is no unambiguous probe for CavTK-I.
Crustacean cardioexcitatory peptides may inhibit the heart in vivo
Authors: McGaw I. J. , Wilkens J. L. , McMahon B. R. , Airriess C. N. 
Published: April 2021

ABSTRACT
Peptide neurohormones exist as functionally similar analogues in a wide variety of invertebrate and vertebrate phyla, and many have been implicated as cardiovascular regulators. In decapod crustaceans, these include the pentapeptide proctolin, crustacean cardioactive peptide (CCAP) and the FMRFamide-related peptides F1 and F2, all of which are found in the pericardial organs located immediately upstream of the heart. Cardioexcitatory activity has been demonstrated by these four peptides in both isolated and semi-isolated arthropod hearts; CCAP, however, has minimal effects on the heart of Cancer magister. In the present study, we determined the effects of proctolin, F1 and F2 on the heart of the crab C. magister in both in vitro (semi-isolated heart) and in vivo (whole animal) preparations. In semi-isolated hearts, infusion of each peptide caused cardioexcitation, increasing the rate and stroke volume of the heart. In whole crabs, the peptides were cardioinhibitory; the strongest effects were observed with F1 and F2, which dramatically decreased heart rate, cardiac stroke volume and cardiac output. These results cast doubt on current perceptions of the functional role of cardioactive peptides in the regulation of invertebrate cardiovascular performance in vivo.
Roles of energy status, KATP channels and channel arrest in fish brain K+ gradient dissipation during anoxia
Authors: Johansson Dan , Nilsson Göran E. 
Published: April 2021

ABSTRACT
The crucian carp (Carassius carassius L.) is one of the most anoxia-tolerant vertebrates known, being able to maintain ion homeostasis in its brain for many hours of anoxia. This study aims to clarify the importance of glycolysis during anoxia and also to investigate whether the extreme tolerance to anoxia could be due to down-regulation of K+ permeability (‘channel arrest’) and/or activation of ATP-sensitive K+ (KATP) channels. The latter was also tested in rainbow trout (Oncorhynchus mykiss).
The results suggest that, during anoxia, the crucian carp brain is completely dependent on glycolysis, since blocking glycolysis with iodoacetic acid (IAA) rapidly caused an increase in [K+]o that coincided with a drastic drop in ATP level and energy charge. Testing the channel arrest hypothesis by measuring the K+ efflux rate after Na+/K+-ATPase had been blocked by ouabain revealed no change in K+ permeability in crucian carp brain in response to anoxia. Furthermore, superfusing the brain of anoxic crucian carp with the KATP channel blocker glibenclamide did not alter the efflux rate of K+ after glycolysis had been inhibited with IAA. Glibenclamide had no effect on K+ efflux rate in rainbow trout brain during anoxia.
Ultrasound acoustic startle response in scarab beetles
Authors: Forrest T. G. , Farris H. E. , Hoy R. R. 
Published: April 2021

ABSTRACT
We discovered an auditory sense in a night-flying scarab beetle, Euetheola humilis, the first scarab to be shown to hear airborne sounds. In the field, beetles were captured beneath speakers broadcasting ultrasound that simulated bat echolocation pulses. Apparently, the beetles took evasive action from a potential bat predator and flew into the traps. Using another behavioral assay in laboratory studies, the beetles were sensitive to frequencies ranging from 20 to 70 kHz at levels between 60 and 70 dB SPL. One component of the behavioral response, a head roll, was graded with stimulus intensity, and the number of potentials in electromyographic recordings from muscles involved in the roll increased as stimulus intensity increased. The response latency was about 40 ms at threshold, decreasing to about 30 ms at 20 dB above threshold. The beetle’s short response latency is ideally suited for predator avoidance behavior and the frequency tuning of the response suggests that it could function in evasion from insectivorous bats. The beetle’s acoustic sensitivity is remarkably similar to that of other night-flying insects showing ultrasound-induced startle and it should provide these scarab beetles with a similar advance warning of predation risk.
A novel proline, glycine: K+ symporter in midgut brush-border membrane vesicles from larval Manduca sexta
Authors: Bader Amy L. , Parthasarathy R. , Harvey William R. 
Published: April 2021

ABSTRACT
Alkali-cation-dependent uptake of proline and glycine into brush-border membrane vesicles from the midgut of the larval tobacco hornworm Manduca sexta was investigated using rapid filtration assays. Uptake of both amino acids was by electrophoretic symport, with K+ being the favored cation at pH 10. Counterflow accumulation of proline was elicited by glycine and vice versa, suggesting that the two amino acids are transported by a common symporter, which we designate the pro, gly: K+ symporter. L-α-Aminoisobutyric acid was the only other amino acid that elicited the accumulation of both proline and glycine. D-Proline was not symported; L-proline, glycine and L-α-aminoisobutyric acid appear to be the only substrates of the pro, gly: K+ symporter. Neutral amino acids with relatively short sidechains elicit glycine accumulation, suggesting that glycine may also be symported by the well-established neutral amino acid system. Since proline does not utilize the broad-spectrum, neutral system, its symport appears to be exclusively through the pro, gly: K+ symporter. Proline symport was found mainly in posterior midgut vesicles, suggesting that the pro, gly: K+ symporter may be localized in this region of the midgut.
Immunolocalization of the 17 kDa vacuolar H+-ATPase subunit c in Heliothis virescens midgut and malpighian tubules with an anti-peptide antibody
Authors: Pietrantonio Patricia V. , Gill Sarjeet S. 
Published: April 2021

ABSTRACT
The transmembrane sector of V-ATPases is involved in proton conduction across the membrane where a 15–17 kDa proteolipid forms a putative proton channel. An affinity-purified rabbit polyclonal antibody was developed to an antigenic and putatively extracellular region of a cloned 17 kDa proteolipid. In larval tissue sections, this antibody labeled the midgut goblet cell apical membrane in Heliothis virescens (Lepidoptera: Noctuidae) and the apical membrane in Malpighian tubules from H. virescens and Manduca sexta (Lepidoptera: Sphingidae). The antibody also recognized the 17 kDa protein in an immunoblot of H. virescens Malpighian tubule homogenate. Northern blot analysis revealed the presence of two transcript sizes in the midgut (1.9 and 1.2 kb) and Malpighian tubules (2.2 and 1.9 kb). Our results strongly support the hypothesis that the 17 kDa protein is a component of the V-ATPase, where it is thought to be the proton-conducting subunit. This polyclonal antibody may provide a powerful tool for V-ATPase regulation studies, while the use of the anti-peptide antibody approach may be helpful for the immunolocalization of other ductins.
Dye coupling in the muscles controlling squid chromatophore expansion
Authors: Reed Candida M. 
Published: April 2021

ABSTRACT
Dye coupling between the cone-shaped radial muscle fibres, which control the expansion and closing of a squid chromatophore organ, was investigated in the squid Loligo vulgaris. Particular attention was paid to the role of the myomuscular junctions located between the muscle fibres. Lucifer Yellow was injected ionophoretically into single muscle fibres under normal artificial sea water (ASW) and under various concentrations of calcium in ASW. Under ASW, 44 % of muscle fibres examined were dye-coupled, 82 % were coupled under calcium-free sea water and 67 % were coupled under sea water containing high concentrations of calcium. Dye transfer was blocked by octanol. Muscle fibres were never seen to link adjacent chromatophore organs. Results are discussed in terms of the role of the myomuscular junctions in the regulation of chromatophore expansion in the living animal.
Wing-Beat Coupling Between Flying Locust Pairs: Preferred Phase and Lift Enhancement
Authors: Camhi J. M. , Sumbre G. , Wendler G. 
Published: April 2021

ABSTRACT
Pairs of locusts flying in tandem in a wind tunnel are known to couple their wing-beats intermittently. The rhythmically oscillating air flow from the front locust’s wing-beat, detected by the rear individual, appears to convey the timing information for coupling. Three predictions of this arrangement were tested quantitatively in this study. (1) Given that the oscillating air flow has a wavelength of 7.5 cm, placing the rear locust 7.5 or 15 cm behind the front one should produce the same phase of coupling, whereas placing it at an intermediate distance of 11 cm should produce an opposite phase. (2) At any distance, the preferred phase at which wing-beat coupling occurs should depend, in part, on the difference in the wing-beat frequencies of the two locusts just before the coupling began. (3) At the moment that the wing-beats of the two locusts become coupled, a change should be observed consistently in the wing-beat frequency of the rear individual only. Each of these three predictions was fulfilled.
We also recorded the instantaneous lift of the rear locust by tethering it to a laser torque meter. Lift varied with the phase of the wing-beats between the two locusts. For a given distance between the two locusts, lift was greater by a mean of 16% of the locust’s body mass at those phases where coupling most commonly occurred than at opposite phases. This lift effect was seen even if the wing-beats of the two locusts drifted through these preferred phases without actually coupling. These results are discussed in terms of a possible energetic advantage conferred to the rear locust by flying in tandem and by coupling its flight rhythm to the leader’s wing-beat.
Extraordinary Flight Performance of Orchid Bees (Apidae: Euglossini) Hovering in Heliox (80% He/20% O2)
Authors: Dudley Robert 
Published: April 2021

ABSTRACT
Limits to insect flight performance are difficult to evaluate because the full range of aerodynamic capabilities cannot be easily elicited or controlled. Invasive experimental manipulations, such as tethering and weight addition, may adversely affect the biomechanics of the flight system as a whole. Because air density is a major determinant of aerodynamic force production, gas mixtures of variable density can be used to investigate insect flight performance non-invasively. Three species of orchid bee hovering in heliox (80% He/20% O2) exhibited dramatic increases in lift and power output relative to flight in normal air. Stroke amplitude increased significantly in heliox, while wingbeat frequency was unchanged; the Reynolds numbers of the wings decreased on average by 41%. Although lift performance of airfoils generally degrades at lower Reynolds numbers, mean lift coefficients in heliox increased significantly relative to values for hovering in normal air. Mean muscle mass-specific power output for flight in heliox mixtures ranged from 130 to 160 W kg−1, substantially exceeding values determined from isolated asynchronous muscle preparations as well as limits postulated from the results of load-lifting experiments. The use of variable-density gas mixtures to examine animal flight performance is a simple yet powerful manipulation that will permit a new evaluation of both insect and vertebrate flight mechanics.
Locomotor Behavior of Nocturnal Ghost Crabs on the Beach: Focal Animal Sampling and Instantaneous Velocity From Three-Dimensional Motion Analysis
Authors: Weinstein Randi B. 
Published: April 2021

ABSTRACT
Previous laboratory measurements of the energetics and biomechanics of locomotion have defined performance limits for the ghost crab Ocypode quadrata. To discover whether these animals naturally operate within these limits, a novel infrared videotaping system was used to observe nocturnally active ghost crabs in the field for three-dimensional motion analysis (N=27) and focal animal sampling (N=24). Instantaneous movement velocity, movement duration, pause duration and stride frequency were determined from video tapes. Voluntarily active crabs moved at a mean instantaneous velocity of 8 cm s−1. Stressed crabs (i.e. those captured and released into the field site) moved at a mean velocity of 83 cm s−1. The mean movement and pause period durations of voluntarily active animals moving along the beach were 11.2 and 23.4 s, respectively. Stressed crabs had much shorter movement (1.4 s) and pause (7.6 s) durations. Despite the differences in mean movement and pause duration, both voluntarily active and stressed crabs moved for an average of approximately 30% of the observation period. These data indicate that voluntarily active ghost crabs primarily move at velocities that can be sustained aerobically and that their performance is not likely to be altered by moving intermittently. By contrast, stressed crabs move at faster speeds that are closer to the limits of their continuous locomotor performance (e.g. escape behavior and aggressive encounters). In the laboratory, the endurance capacity of crabs moving continuously at these rapid speeds is only a few seconds. However, in the field, the stressed crabs are able to move intermittently for more than a few seconds, yet they do not fatigue. These observations suggest that the performance limits of the stressed crabs are increased by moving intermittently.