bluuebunny/crossref_metadata_2025 huggingface dataset:
Epithelial Glucose Transport By Lobster Antennal Gland
Authors: Behnke Rachel D. , Busquets-Turner Liz , Ahearn Gregory A.
Published: April 2021

Transport of D-[3H]glucose into lobster (Homarus americanus) brush-border membrane vesicles (BBMVs) prepared by Mg2+ precipitation from antennal gland labyrinth–coelomosac tissue was examined. Influx of D-glucose occurred primarily by a phlorizin-sensitive, Na+-dependent carrier similar to that found in vertebrate renal epithelium. An inwardly directed Na+ gradient drove concentrative D-glucose uptake, whereas similar gradients of Li+ and K+ did not. Stimulation by the Na+ gradient was further enhanced by the imposition of an inside-negative potential difference and also by increases in the pH of the vesicle and incubation media. An analysis of cis inhibition of D-glucose uptake by a number of sugars and sugar derivatives indicated that the transporter requires (a) that the sugar substrate be a D-pyranose in the C1 chair conformation and (b) that the hydroxyl groups at C2 and C3 of the ring be unmodified and equatorial. Apparent kinetic parameters for glucose uptake were determined under zero-trans, short-circuited conditions. Maximal influx of D-glucose into vesicles was estimated to be 96 pmol mg−1 protein s−1. Half-maximal influx was determined to occur at 0.20 mmol l−1 D-glucose. The relationship between external Na+ concentration and glucose influx was sigmoidal, and the stoichiometry of Na+-dependent glucose transport found to be 3 Na+:1 glucose using the static head method.
Intensity Responses of the Single Auditory Receptor of Notodontid Moths: A Test of the Peripheral Interaction Hypothesis in Moth Ears
Authors: Fullard James H. , Forrest Evelyn , Surlykke Annemarie
Published: April 2021

It has been proposed that the most sensitive auditory receptor cell (A1) in the two-celled ears of certain noctuoid moths is inhibited by its partner, the A2 cell, at high stimulus intensities. We used the single-celled ears of notodontid moths, also noctuoids, to test this hypothesis. The A1 cells of all but one of the moths tested exhibited non-monotonic firing rates, with reduced firing rates at high stimulus intensities and showing no relationship to the firing rate of the only other receptor, the non-auditory B cell. These results challenge the peripheral interaction hypothesis for A1 firing patterns in two-celled moth ears. An examination of notodontid A1 adaptation rates and laser vibrometry results suggests that receptor adaptation and tympanal motion non-linearity are more likely explanations for the non-monotonic receptor firing observed in both single- and multi-celled moth ears.
Changes In the Ultrastructure Of Surviving Distal Segments Of Severed Axons Of The Rock Lobster
Authors: Parnas I. , Shahrabany-Baranes O. , Feinstein N. , Grant P. , Adelsberger H. , Dudel J.
Published: April 2021

Peripheral axons of lobsters can survive for many months after axotomy. We have investigated the structural and ultrastructural changes seen after axotomy using confocal microscopy and electron microscopy. While the proximal stump had a normal appearance, the distal part of the cut axon became lobulated, and glial cells penetrated the original glial tube (axon tube) in which the axon normally runs. The changes proceeded from the cut end towards the muscle. As time elapsed, the axon tube seemed to be filled with glial cells, but interposed small profiles of the original axon could be identified by injection of a fluorescent dye into the axon. The glial cells send cytoplasmic projections deep into folds of the axolemma, and nuclei were found at the end of these long processes. Proliferation of glial cells was also seen.
Thermal Control of Metabolic Cold Defence In Pigeons Columba Livia
Authors: Østnes Jan Eivind , Bech Claus
Published: April 2021

Metabolic rate (MR) and various body temperatures were recorded in pigeons Columba livia during gradual lowering of the ambient temperature (Ta) and during cold exposure (−10 °C) for an entire circadian cycle. The aim was to study how changes in MR accorded with the observed body temperature displacements and our knowledge of regional cold sensitivity. When Ta was lowered from 28 to −10 °C, the threefold increase in MR was accompanied by a significant increase in deep-body and spinal cord temperatures. Cold exposure also resulted in a distinct rise in breast skin temperature, whereas the skin temperatures of the neck, back and leg decreased significantly. Thus, during acute cold exposure of pigeons, peripheral thermosensors seem to have the primary effect in mediating metabolic cold defence, while internal thermosensors are apparently of minor importance. By using differential weightings of various skin areas, cold-sensitivity values of between −3.9 and −14.7 W kg−1 °C−1 were estimated. These values indicate a much higher skin thermosensitivity of birds than has been previously suggested. When cold-exposed for an entire circadian cycle, the pigeons usually maintained a low leg skin temperature. However, during these experiments, the pigeons showed regular distinct increases in leg skin temperature, obviously due to cold-induced vasodilatations (CIVDs). The flushing of cold peripheral blood through the body in connection with these CIVDs resulted in a decrease in deep-body temperature (Tb), to which the pigeons responded with a distinct increase in MR. From the concomitant changes in MR and Tb, a total body cold sensitivity of −8.0W kg−1 °C−1 was calculated, a value that is close to the previously published cold-sensitivity value of pigeons. This shows that, at least under some naturally occurring conditions, internal thermosensors will provide a significant error signal in the control of metabolic cold defence. Furthermore, the results of our study show that the relative importance of various thermosensitive sites in the control of metabolic cold defence is contextual.
Pulsatile Urea Excretion In Gulf Toadfish (Opsanus Beta): Evidence For Activation Of A Specific Facilitated Diffusion Transport System
Authors: Wood Chris M. , Gilmour K. M. , Perry S. F. , Part P. , Laurent P. , Walsh Patrick J.
Published: April 2021

When toadfish are made ureotelic by a crowding/ confinement protocol, they excrete approximately 90 % of their urea nitrogen (urea-N) production in large, irregular pulses (1–2 pulses per day) from the gill region. We investigated three hypotheses as to the mechanism of pulsatile excretion: (i) the presence of an active reabsorptive ‘back-transport’ mechanism that is periodically inhibited to allow urea-N excretion to occur; (ii) the periodic occurrence of a generalized, non-specific increase in gill permeability; and (iii) the presence of a specific facilitated diffusion transport system that is periodically activated. Exposure of toadfish during non-pulse periods to treatments designed to block a ‘back-transport’ mechanism (Na+-free sea water or the urea analogues 30 mmol l−1 thiourea or 30 mmol l−1 acetamide in the external water) did not stimulate a leakage of urea-N, thereby opposing the first hypothesis. The second hypothesis was opposed by several results. Neither injection of the potent branchial vasodilator L-isoprenaline (10−5 mol l−1) nor infusion of NH4Cl, the latter at levels known to stimulate urea-N efflux in perfused gills, had any effect on urea-N excretion. Furthermore, during natural pulse events, when the normally very low gill permeability to urea (3×10−7 cm s−1) increased at least 35-fold, there was no accompanying increase in permeability to either 3H2O (1.5×10−5 cm s−1) or the paracellular marker [14C]PEG-4000 (10−8 cm s−1). However [14C]thiourea permeability (1.5×10−7 cm s−1) increased approximately fivefold, in support of the third hypothesis. Furthermore, when 30 mmol l−1 urea was placed in the external water, a concentration (60 000 μmol-N l−1) approximately three times that of blood (20 000 μmol-N l−1), each efflux pulse event (measured with [14C]urea) was accompanied by a net uptake, such that blood urea-N levels rose rather than fell. A proportional 1:1 relationship between influx per unit external concentration and efflux per unit internal (i.e. plasma) concentration indicated a fully bidirectional transport system. The simultaneous presence of 60 mmol l−1 thiourea in the external water inhibited the influx component by 73 %, further supporting this conclusion. These data, together with recent molecular, morphological and endocrinological evidence, strongly suggest that pulsatile urea-N excretion is caused by the periodic activation of a facilitated urea transporter in the gills, similar to the vasopressin-regulated urea transporter in the mammalian kidney.
Proliferation And Differentiation Properties Of Permanent Schwann Cell Lines Immortalized With A Temperature-Sensitive Oncogene
Authors: Thi Anh Do , Evrard Claudine , Rouget Pierre
Published: April 2021

Permanent Schwann cells lines have been established in culture after stable transfection of newborn rat Schwann cells with the pJC-SVLTtsA vector, expressing a thermosensitive oncogene driven by the early promoter-enhancer region of the gliotropic GS/B variant of the papovavirus JC. The proliferation and differentiation of two clonal cell lines have been studied. The cells of these lines display the morphology of primary Schwann cells and express Schwann cell differentiation markers such as the S-100 protein, laminin, the low-affinity receptor to nerve growth factor and the glial fibrillary acidic protein. One of the lines is able to differentiate further. Indeed, in the presence of dorsal root ganglion neurones, the cells synthesize the myelin Po protein and are capable of some myelination, although to a lesser extent than secondary Schwann cells.
Long-Term Memory of an Operantly Conditioned Respiratory Behaviour Pattern in Lymnaea Stagnalis
Authors: Lukowiak Ken , Cotter Ralph , Westly Jackie , Ringseis Erika , Spencer Gaynor , Syed Naweed
Published: April 2021

The freshwater snail Lymnaea stagnalis breaths bimodally either through its skin (cutaneous respiration) or via a rudimentary lung opening called the pneumostome (aerial respiration). Aerial respiratory behaviour can be operantly conditioned. Animals placed in an aquatic, hypoxic environment received a tactile stimulus to the pneumostome area every time they attempted to breathe. Over a period of five training sessions (2.5 days), the animals learned not to breathe, and the number of stimuli received in the fifth session was significantly lower than in the first session. These changes in the respiratory behaviour following the operant paradigm were shown to persist for at least 24 h. We aimed to determine whether the changes in the learned behaviour would persist for longer. We obtained direct evidence that the behavioural changes following operant conditioning persisted for at least 4 weeks following the last training session. However, we found that the persistence of this memory was dependent upon the training procedure used. Memory persisted longer following a spaced training procedure (4 weeks) as opposed to a massed training procedure (2 weeks). Yoked control animals showed no changes in their respiratory behaviour over the same time periods. However, if these yoked control animals were subjected to an operant conditioning procedure, their ability to learn was not impeded. This study demonstrated that operant conditioning of a behaviour pattern in a molluscan preparation can result in long-term memory and that the persistence of the memory is contingent on the training procedure used.
Whole-Body Composition of Xenopus Laevis Larvae: Implications for Lean Body Mass During Development
Authors: Territo Paul R. , Smits Allan W.
Published: April 2021

Body composition in developing animals has been extensively investigated in fish larvae and bird embryos. However, no studies to date have attempted to determine whole-animal body composition or lean body mass (MLB) in developing amphibians. The present study investigates how body composition changes during development in Xenopus laevis and the potential implications of MLB for substrate turnover, energy stores, oxygen consumption and other physiological measures. Whole-animal composition was determined during development from eggs (NF stage 1) to 2 weeks post-feeding (NF 50–51), which represents two-thirds of the developmental period. Wet and dry masses were found to be highly correlated, with water content remaining constant at 93% of wet mass. Whole-animal nucleic acid content was linearly correlated with both wet and dry masses, and declined relative to mass as development progressed. Similarly, total protein content was linearly correlated with wet and dry masses; however, total protein content increased with developmental stage. Amounts of individual neutral lipids were variable although, overall, total neutral lipid content declined progressively with development. The stoichiometric ene.rgy balance paralleled the changes seen in mass-specific with the energy primarily from lipids fueling respiration up to NF 44–45. Quantification of total body composition revealed that lipid stores greatly influenced the calculations of MLB and therefore had profound underestimating effects on the mass-specific expression of numerous physiological measures through development.
Strategies for Hearing in Noise: Peripheral Control Over Auditory Sensitivity in the Bushcricket Sciarasaga Quadrata (Austrosaginae: Tettigoniidae)
Authors: Römer Heiner , Bailey Winston
Published: April 2021

The carrier frequency of the call of the Australian bushcricket Sciarasaga quadrata is unusually low for tettigoniids at 5 kHz. The sound transmission measured in the habitat of the insect reflects the advantages of producing low-rather than high-frequency signals; attenuation is explained almost entirely by the spherical spreading of sound. The natural vibration frequency of the wings is controlled by size and stiffness. The small tegmina are unusually fleshy, with an order-of-magnitude higher water content than in comparable sagine species. Reduced stiffness allows the insect to call at low carrier frequencies, albeit at lower intensity levels (60 dB SPL at 1 m), than bushcrickets of comparable size (80–90 dB SPL). The responses of the tympanic nerve and a first-order interneurone (omega neurone) in the afferent auditory pathway showed that the hearing system is most sensitive to frequencies of 15–20 kHz, an effective mismatch to the conspecific call resulting in a reduced sensitivity of approximately 20 dB at the carrier frequency of the call. S. quadrata can occlude its spiracular opening, which increases the sensitivity of the ear to lower frequencies. Under such conditions, the best frequency of the ear matched that of the carrier frequency of the call. We measured the activity of auditory neurones in the field, noting the ability of the open and partially closed ear to filter out potentially masking calls of congenerics. At the same time, the directionality of the system was only slightly reduced in the closed relative to the open spiracle status. We discuss the evolutionary advantages of an insect both calling with a low carrier frequency and having the ability to close down the tracheal system to avoid the effects of masking. In addition, we consider the advantages of such a signalling system in avoiding the most significant predator of the male, the ormine fly Homotrixa alleni.
Scaling of Intrinsic Contractile Properties and Myofibrillar Protein Composition of Fast Muscle in the Fish Myoxocephalus Scorpius L
Authors: James Rob S. , Cole Nicholas J. , Davies Melissa L. F. , Johnston Ian A.
Published: April 2021

Contractile properties were determined for fast muscle fibres from short-horn sculpin (Myoxocephalus scorpius L.) ranging from 5 to 35 cm total body length (L) and from 2.0 to 758 g body mass. Maximum unloaded shortening velocity (V0) decreased with increasing body size, scaling as 19.5L−0.34, and isometric twitch activation and tetanus relaxation times became longer, scaling as 12.0L0.31 and 19.5L0.42 respectively. Myofibrillar Mg2+/Ca2+-ATPase activity scaled as 2.51L−0.28. In order to investigate the mechanisms underlying the scaling of contractile properties, myofibrillar protein composition and I filament lengths were determined. One-dimensional SDS–PAGE and two-dimensional isoelectric focusing/non-equilibrium isoelectric focusing–PAGE revealed no differences in the myofibrillar protein isoforms of myosin light chains, actin, tropomyosin, troponin-T and troponin-C in fish of differing body size. Peptide maps of purified myosin heavy chains digested with eight different proteolytic enzymes were also similar in all fish examined. Three isoforms of troponin-I were present in fish less than 20 cm in total length with relative molecular masses of 17 (TnIf3), 22 (TnIf2) and 23 (TnIf1). The ratio of TnI isoforms varied with body length, and only TnIf3 was present in fish greater than 28 cm total length. The length of I filaments was independent of body length. Thus, although the expression of TnI isoforms changes during growth, the underlying mechanism responsible for increased shortening velocity with decreased body size remains unknown.
Morphological Characterization of the Bursting and Nonbursting Neurones in the Olfactory Centre of the Terrestrial Slug Limax Marginatus
Authors: Watanabe Satoshi , Kawahara Shigenori , Kirino Yutaka
Published: April 2021

We investigated the morphological characteristics of physiologically characterized neurones in the procerebrum (PC) of the terrestrial slug Limax marginatus. The electrophysiological characteristics of the neurones were determined using the perforated patch recording technique. By comparing the shapes and sizes of somata, we found that the somata of bursting neurones were larger and had more oblong shapes than those of nonbursting neurones, indicating that the bursting and nonbursting neurones in the PC could be discriminated on the basis of the sizes and shapes of their soma. Injection of fluorescent dyes into the bursting and nonbursting neurones revealed morphological differences in the neurites. The bursting neurones had extensive projections within the cell body layer, and the major neurites of the bursting neurones were oriented along the dorsal–ventral axis. In contrast, the nonbursting neurones had neurites extending into the neuropile layers, where terminals of both sensory and presumed output neurones exist.
Development of Heart Rate in the Precocial King Quail Coturnix Chinensis
Authors: Pearson James T. , Tsudzuki Masaoki , Nakane Yoshifumi , Akiyama Ryuichi , Tazawa Hiroshi
Published: April 2021

Our aim was to examine changes in heart rate (fH) during the embryonic and posthatching periods of the smallest precocial avian species, Coturnix chinensis. In experiment I, repeated measurements of mean fH were made for individual quail by ballistocardiogram (BCG) during incubation, and by both piezo-electric film and electrocardiogram (ECG) during the posthatching period (resting and thermoneutral conditions). Mean fH of all embryos increased during the second half of incubation and the first week posthatching, but a few embryos experienced a very brief period of decreased fH prior to internal pipping. After the first week, fH of posthatching quail was maintained at high levels (550–650 beats min−1), then decreased with age and increase in body mass. The maximal fH of quail chicks represents a greater posthatching increase in fH than is found in larger precocial chickens, this difference being attributable to the higher demands of thermoregulation at small body masses in the quail. In experiment II, the mean fH of quail embryos (day 2–16) was recorded by ECG, and embryonic stage, yolk-free embryo mass (wet and dry) and water content were measured. Mean fH was linearly related to embryo mass throughout incubation, except on the day prior to internal pipping, when the fH of a few embryos declined below this linear relationship. Measurements of instantaneous fH of late incubation embryos, young and adult quail all showed spontaneous fluctuations in fH. Two main frequency components of fH fluctuations were identified for the first time in an avian species. Low-frequency (mean 0.09 Hz, 12.6 s) and high-frequency (1.4 Hz, 0.9 s) oscillations in both young chicks and adult quail were detected and are considered to reflect baroreflex mediation of fH and respiratory sinus arrhythmia, respectively.
Air-Breathing During Activity in the Fishes Amia Calva and Lepisosteus Oculatus
Authors: Farmer C. G. , Jackson D. C.
Published: April 2021

Many osteichthyan fishes obtain oxygen from both air, using a lung, and water, using gills. Although it is commonly thought that fishes air-breathe to survive hypoxic aquatic habitats, other reasons may be more important in many species. This study was undertaken to determine the significance of air-breathing in two fish species while exercising in oxygen-rich water. Oxygen consumption from air and water was measured during mild activity in bowfin (Amia calva) and spotted gar (Lepisosteus oculatus) by sealing a fish in an acrylic flume that contained an air-hole. At 19–23°C, the rate of oxygen consumption from air in both species was modest at rest. During low-level exercise, more than 50% of the oxygen consumed by both species was from the air (53.0±22.9% L. oculatus; 66.4±8.3% A. calva).
Estimating Velocities and Accelerations of Animal Locomotion: A Simulation Experiment Comparing Numerical Differentiation Algorithms
Authors: Walker Jeffrey A.
Published: April 2021

Functional biologists employ numerical differentiation for many purposes, including (1) estimation of maximum velocities and accelerations as measures of behavioral performance, (2) estimation of velocity and acceleration histories for biomechanical modeling, and (3) estimation of curvature, either of a structure during movement or of the path of movement itself. I used a computer simulation experiment to explore the efficacy of ten numerical differentiation algorithms to reconstruct velocities and accelerations accurately from displacement data. These algorithms include the quadratic moving regression (MR), two variants of an automated Butterworth filter (BF1–2), four variants of a method based on the signal’s power spectrum (PSA1–4), an approximation to the Wiener filter due to Kosarev and Pantos (KPF), and both a generalized cross-validatory (GCV) and predicted mean square error (MSE) quintic spline. The displacement data simulated the highly aperiodic escape responses of a rainbow trout Oncorhynchus mykiss and a Northern pike Esox lucius (published previously). I simulated the effects of video speed (60, 125, 250, 500 Hz) and magnification (0.25, 0.5, 1 and 2 screen widths per body length) on algorithmic performance. Four performance measures were compared: the per cent error of the estimated maximum velocity (Vmax) and acceleration (Amax) and the per cent root mean square error over the middle 80% of the velocity (VRMSE) and acceleration (ARMSE) profiles.

The results present a much more optimistic role for numerical differentiation than suggested previously. Overall, the two quintic spline algorithms performed best, although the rank order of the methods varied with video speed and magnification. The MSE quintic spline was extremely stable across the entire parameter space and can be generally recommended. When the MSE spline was outperformed by another algorithm, both the difference between the estimates and the errors from true values were very small. At high video speeds and low video magnification, the GCV quintic spline proved unstable. KPF and PSA2–4 performed well only at high video speeds. MR and BF1–2 methods, popular in animal locomotion studies, performed well when estimating velocities but poorly when estimating accelerations. Finally, the high variance of the estimates for some methods should be considered when choosing an algorithm.
Energy Absorption During Running by Leg Muscles in a Cockroach
Authors: Full Robert J. , Stokes Darrell R. , Ahn Anna N. , Josephson Robert K.
Published: April 2021

Biologists have traditionally focused on a muscle’s ability to generate power. By determining muscle length, strain and activation pattern in the cockroach Blaberus discoidalis, we discovered leg extensor muscles that operate as active dampers that only absorb energy during running. Data from running animals were compared with measurements of force and power production of isolated muscles studied over a range of stimulus conditions and muscle length changes.We studied the trochanter-femoral extensor muscles 137 and 179, homologous leg muscles of the mesothoracic and metathoracic legs, respectively. Because each of these muscles is innervated by a single excitatory motor axon, the activation pattern of the muscle could be defined precisely. Work loop studies using sinusoidal strains at 8 Hz showed these trochanter-femoral extensor muscles to be quite capable actuators, able to generate a maximum of 19–25 W kg−1 (at 25°C). The optimal conditions for power output were four stimuli per cycle (interstimulus interval 11 ms), a strain of approximately 4%, and a stimulation phase such that the onset of the stimulus burst came approximately half-way through the lengthening phase of the cycle. High-speed video analysis indicated that the actual muscle strain during running was 12% in the mesothoracic muscles and 16% in the metathoracic ones. Myographic recordings during running showed on average 3–4 muscle action potentials per cycle, with the timing of the action potentials such that the burst usually began shortly after the onset of shortening. Imposing upon the muscle in vitro the strain, stimulus number and stimulus phase characteristic of running generated work loops in which energy was absorbed (−25W kg−1) rather than produced. Simulations exploring a wide parameter space revealed that the dominant parameter that determines function during running is the magnitude of strain. Strains required for the maximum power output by the trochanter-femoral extensor muscles simply do not occur during constant, average-speed running. Joint angle ranges of the coxa–trochanter–femur joint during running were 3–4 times greater than the changes necessary to produce maximum power output. None of the simulated patterns of stimulation or phase resulted in power production when strain magnitude was greater than 5%. The trochanter-femoral extensor muscles 137/179 of a cockroach running at its preferred speed of 20 cm s−1 do not operate under conditions which maximize either power output or efficiency. In vitro measurements, however, demonstrate that these muscles absorb energy, probably to provide control of leg flexion and to aid in its reversal.
Atmospheric Oxygen, Giant Paleozoic Insects and the Evolution of Aerial Locomotor Performance
Authors: Dudley Robert
Published: April 2021

Uniformitarian approaches to the evolution of terrestrial locomotor physiology and animal flight performance have generally presupposed the constancy of atmospheric composition. Recent geophysical data as well as theoretical models suggest that, to the contrary, both oxygen and carbon dioxide concentrations have changed dramatically during defining periods of metazoan evolution. Hyperoxia in the late Paleozoic atmosphere may have physiologically enhanced the initial evolution of tetrapod locomotor energetics; a concurrently hyperdense atmosphere would have augmented aerodynamic force production in early flying insects. Multiple historical origins of vertebrate flight also correlate temporally with geological periods of increased oxygen concentration and atmospheric density. Arthropod as well as amphibian gigantism appear to have been facilitated by a hyperoxic Carboniferous atmosphere and were subsequently eliminated by a late Permian transition to hypoxia. For extant organisms, the transient, chronic and ontogenetic effects of exposure to hyperoxic gas mixtures are poorly understood relative to contemporary understanding of the physiology of oxygen deprivation. Experimentally, the biomechanical and physiological effects of hyperoxia on animal flight performance can be decoupled through the use of gas mixtures that vary in density and oxygen concentration. Such manipulations permit both paleophysiological simulation of ancestral locomotor performance and an analysis of maximal flight capacity in extant forms.
Quiescence in Artemia Franciscana Embryos: Reversible Arrest of Metabolism and Gene Expression at Low Oxygen Levels
Authors: Hand Steven C.
Published: April 2021

Depression of the production and consumption of cellular energy appears to be a prerequisite for the survival of prolonged bouts of anoxia. A correlation exists between the degree of metabolic depression under anoxia and the duration of anoxia tolerance. In the case of brine shrimp (Artemia franciscana) embryos, oxygen deprivation induces a reversible quiescent state that can be tolerated for several years with substantial survivorship. A global arrest of cytoplasmic translation accompanies the transition into anoxia, and rates of protein synthesis in mitochondria from these embryos appears to be markedly reduced in response to anoxia. Previous evidence suggests that the acute acidification of intracellular pH (pHi) by over 1.0 unit during the transition into anoxia contributes to the depression of biosynthesis, but message limitation does not appear to play a role in the down-regulation in either cellular compartment. The ontogenetic increase in mRNA levels for a mitochondrial-encoded subunit of cytochrome c oxidase (COX I) and for nuclear-encoded actin is blocked by anoxia and aerobic acidosis (artificial quiescence imposed by intracellular acidification under aerobic conditions). Further, the levels of COX I and actin mRNA do not decline appreciably during 6 h bouts of quiescence, even though protein synthesis is acutely arrested across this same period. Thus, the constancy of mRNA levels during quiescence indicates that reduced protein synthesis is not caused by message limitation but, instead, is probably controlled at the translational level. This apparent stabilization of mRNA under anoxia is mirrored in an extension of protein half-life. The ubiquitin-dependent pathway for protein degradation is depressed under anoxia and aerobic acidosis, as judged by the acute drop in levels of ubiquitin-conjugated proteins.

Mitochondrial protein synthesis is responsive to both acidification of pHi and removal of oxygen per se. Matrix pH declines in parallel with pHi, and evidence from experiments with nigericin indicates that mitochondrial protein synthesis is depressed directly by acidification of matrix pH. The oxygen dependency of organellar protein synthesis is not explained by blockage of the electron transport chain or by the increased redox state. Rather, this cyanide- and antimycin-insensitive, but hypoxia-sensitive, inhibitory signature for the arrest of protein synthesis suggests the presence of a molecular oxygen sensor within the mitochondrion.
Two Visual Pigments In A Single Photoreceptor Cell: Identification And Histological Localization Of Three Mrnas Encoding Visual Pigment Opsins In The Retina Of The Butterfly Papilio Xuthus
Authors: Kitamoto Junko , Sakamoto Katsuhiko , Ozaki Koichi , Mishina Yuji , Arikawa Kentaro
Published: April 2021

This paper describes the localization of newly identified visual pigment opsins in the tiered retina of the Japanese yellow swallowtail Papilio xuthus. We first cloned three cDNAs encoding visual pigment opsins, PxRh1, PxRh2 and PxRh3, and then carried out histological in situ hybridization to localize their mRNAs in the retina. By combining the present data with our previous electrophysiological results, we concluded that both PxRh1 and PxRh2 correspond to visual pigments expressed in photoreceptor cells sensitive in the green wavelength region (green receptors), whereas PxRh3 corresponds to a pigment in red receptors. The in situ hybridization studies showed that some photoreceptor cells express two opsin mRNAs. In the ventral half of the eye, all green receptors in the distal tier were labelled by both PxRh1 and PxRh2 probes. The labelling by the PxRh2 and PxRh3 probes was detected throughout the eye in the proximal tier; in 18 % of ommatidia, the probes labelled the same photoreceptor cell. These results suggest that the possible co-localization of two different visual pigments will broaden the sensitivity spectrum of the photoreceptor cells.
Rhodopsin-Like Proteins in Planarian Eye and Auricle: Detection and Functional Analysis
Authors: Asano Yoshiya , Nakamura Satoshi , Ishidas Sachiko , Azuma Katsu , Shinozawa Takao
Published: April 2021

The presence of rhodopsin-like proteins in the eyes and auricles of the freshwater planarian Dugesia japonica was confirmed using anti-frog-rhodopsin rabbit IgG. The apparent relative molecular masses of these proteins were 65×103 and 62×103, and positive reactions to IgG were localized to the microvilli of the photoreceptor cells in the eyes and to the sensory cilia, rootlets and microvilli in the auricles. Eye- or head-excised planarians showed no negative phototaxis, whereas intact or auricle-excised planarians did. During regeneration in head-excised planarians, the appearance of rhodopsin-like proteins in the regenerating eyes corresponded to the recovery of negative phototaxis behaviour. Head or auricle excision enhanced asexual fission under continuous illumination. However, eye excision had no such effect. These results suggest that the rhodopsin-like proteins in the eyes work as photoreceptors for negative phototaxis behaviour and that, in the auricles, they are involved in asexual fission originating from the circadian rhythm.
Curve Walking in Freely Moving Crayfish (Procambarus Clarkii)
Authors: Domenici Paolo , Jamon Marc , Clarac François
Published: April 2021

The curve walking of freely moving crayfish trained to walk along a curved path during homing behaviour was investigated using a video-analysis system. The leg kinematics and leg phase relationships, as well as the relationship between stepping patterns and body axis rotation measured relative to external references, were studied.

The anterior and posterior extreme positions of the power stroke (AEP and PEP, respectively) and step amplitudes were analysed. As in a previous study on crayfish curve walking on a treadmill, PEPs were more posterior in outer legs (the legs on the outside of the turn) than in the inner legs. As a result, outer legs showed larger step amplitudes than inner legs. Leg kinematics varied within each walking sequence. AEP leg angles (the angles between the body and leg axes at the AEP) tended to decrease over time for inner legs and increase for outer legs. This leg angle drift was present mainly in the anterior legs and it suggests that these legs did not completely compensate for the body rotation after each step. In addition, leg angle asymmetries in a direction opposite to that of leg angle drift were observed at the start of each curve-walking sequence, suggesting that the extensive training (3 weeks) may have allowed crayfish to anticipate the leg angle drift.

The rotational component of curve walking showed a discontinuous pattern, with the animal’s body axis turning towards the inside of the curve only periodically. Analysis of cross-correlation functions showed that the angular acceleration of the body axis in the direction of the turn occurred during the power strokes of inner legs 2 and 5 and outer leg 4. While the tripod formed by these three legs showed in-phase relationships, the legs of the corresponding contralateral tripod (outer legs 2 and 5 and inner leg 4) were not in phase. We hypothesize that inner legs 2 and 5 and outer leg 4 act synergically causing the inward body rotation observed in curve-walking crayfish and that some of the asymmetries found in step geometry may be a passive phenomenon due to the body rotation.
Orthodromically and Antidromically Evoked Local Field Potentials in the Crayfish Olfactory Lobe
Authors: Sandeman D. C. , Sandeman R. E.
Published: April 2021

A local field potential, consistent in form and duration, can be recorded from the olfactory lobe of crayfish following electrical stimulation of the outer flagellum of the antennule. The field potential is reversibly blocked by perfusion of the brain with low-[Ca2+] saline or γ-aminobutyric acid and, to a lesser extent, histamine. Paired shocks to the antennule and antidromic electrical stimulation of olfactory lobe output neurones also partially block the field potential. Comparing the field potential with simultaneously recorded intracellular responses of olfactory interneurones reveals a coincidence between excitatory and inhibitory effects in the interneurones and the appearance of identifiable components of the field potential. We interpret the field potential to reflect the response of neural elements in the olfactory lobe to orthodromic activity in the axons of the olfactory receptor neurones on the antennule. We conclude from the blocking experiments that the greater part of the field potential stems from neurones in the olfactory lobe that are postsynaptic to olfactory receptor neurones. As such, it provides a robust indication of olfactory neurone activity.
The Impact of Endurance Training on Arterial Plasma K+ Levels and Swimming Performance of Rainbow Trout
Authors: Holk Karin , Lykkeboe Gunnar
Published: April 2021

Arterial plasma K+ and lactate concentrations ([K+]a and [lactate]a), as well as blood oxygenation status, were measured in relation to increasing swimming speeds in rainbow trout Oncorhynchus mykiss. Neither [K+]a nor [lactate]a changed at swimming speeds below 1.5 BL s−1, where BL is total body length. Between 1.5 and 2.0 BL s−1, [K+]a started to increase, and above 2.0 BL s−1 both [K+]a and [lactate]a increased with swimming speed. Training shifted the onset of these increases to higher swimming speeds and increased the critical swimming speed (Ucrit) from 2.4 to 3.0 BL s−1. Blood oxygen content showed no changes in control fish, whereas in trained fish it increased by 22 % at the final swimming speed. From the [K+]a data, we suggest that no loss of K+ occurred from the working muscle at low swimming speeds, allowing an unlimited endurance, whereas moderate and higher speeds were probably associated with a loss of K+ from the working muscles, indicating a limited endurance.
Tissue and Whole-Body Extracellular, Red Blood Cell and Albumin Spaces in the Rainbow Trout as a Function of Time: A Reappraisal of the Volume of the Secondary Circulation
Authors: Bushnell P. G. , Conklin D. J. , Duff D. W. , Olson K. R.
Published: April 2021

[58Co]EDTA, [51Cr]RBC and [125I]albumin spaces in the whole body and 28 tissue samples were examined at timed intervals over 16 h in rainbow trout Oncorhynchus mykiss. [58Co]EDTA space (which approximates extracellular fluid volume; ECF) in fins, skin, gallbladder and eye are reported for the first time. After a 16 h equilibration, ECF volume was large (376–726 µl g−1 wet tissue mass) in kidney, swimbladder, skin and fins, moderate (219–313 µl g−1 wet tissue mass) in stomach, skull, spleen, liver, intestine, gills, eye and cecum, and small (53–181 µl g−1 wet tissue mass) in red muscle, fat, brain, gallbladder and white muscle. Whole-body ECF was 387±10.6 µl g−1 (mean ± S.E.M.; N=11). [51Cr]RBC space relative to [58Co]EDTA space was large in spleen, liver, intestine and gill, and low in skin, fins, stomach and skull. Whole-body [51Cr]RBC space was 9.9±0.6 µl g−1 body mass (N=17). Blood volume calculated from [51Cr]RBC space at 16 h and a dorsal aortic hematocrit of 24.5 % was 40.4 µl g−1 body mass. Whole-body [125I]albumin space at 16 h was 118.0±7.4 µl g−1 body mass (N=6), which resulted in an estimated blood volume of 156.6 µl g−1 body mass, nearly four times that estimated from the [51Cr]RBC space. Tissue hematocrits, calculated from [125I]albumin and [51Cr]RBC spaces, were significantly lower than dorsal aortic hematocrit in all tissues except spleen, kidney and liver. [58Co]EDTA and [51Cr]RBC spaces reached equilibrium in nearly all tissues within 1 h, whereas [125I]albumin continued to accumulate in many tissues up 24 h. The disparity between [125I]albumin distribution kinetics compared with the kinetics of [58Co]EDTA and [51Cr]RBC distribution, as well as the accumulation of [125I]albumin in tissues not known to have a secondary circulation, indicates that [125I]albumin is a poor marker of plasma volume in trout and that previous studies based on [125I]albumin clearance from the plasma have overestimated both the volume and the turnover rate of the secondary system. Revised estimates of secondary circulation volume, based on [58Co]EDTA distribution rate, indicate that it is no more than 10–20 % of the volume of the primary circulation.
Neuromuscular Sensitivity to Hydrogen Sulfide in the Marine Invertebrate Urechis Caupo
Authors: Julian David , Dalia Wendy E. , Arp Alissa J.
Published: April 2021

Hydrogen sulfide (HS) is a well-known inhibitor of aerobic respiration via its reversible binding of mitochondrial cytochrome c oxidase, but recent studies have suggested that HS may have other non-respiratory actions. We have studied the effects of HS on spontaneous and evoked contractions in vitro under hypoxic and anoxic conditions in nerve–muscle preparations from the echiuran worm Urechis caupo. Contraction amplitude in response to electric field stimulation under anoxic conditions was completely abolished by HS within minutes in a classic dose–response relationship (Kd=31 mmol l−1, r2=0.86). Exposure of body wall and esophagus to HS in vitro for up to 6 h demonstrated that the contraction amplitude and frequency of spontaneous activity were relatively insensitive to anoxia, but that the sensitivity to HS was similar to that seen in field-stimulated muscle (Kd=2.7–32 mmol l−1). The toxic effects of HS were reversible, with almost complete recovery under anoxic conditions within the first hour. These data indicate that HS at millimolar concentrations can directly inhibit muscle contraction. Although the mechanism of this action is unknown, it does not appear to involve metabolic pathways or oxygen transport.
Cell Volume Regulation In Proximal Renal Tubules From Trout (Salmo Trutta)
Authors: Kanli Hilde , Norderhus Eli
Published: April 2021

Regulatory volume decrease (RVD) following hypo-osmotic stimulation was studied using videometric methods in isolated proximal renal tubules from trout (Salmo trutta). The relative tubule diameter increased by 132.0±4.8 % (maximum swelling within 1 min at 15 and 25 °C and within 4 min at 10 °C) following a change from iso-osmotic (290 mosmol kg−1) to hypo-osmotic (160 mosmol kg−1) Ringer’s solution. The tubule diameter subsequently decreased to approximately one-quarter of the maximal value. Ouabain (1 mmol l−1) reduced cell swelling and inhibited the RVD response by 28.0±10.5 %. Furthermore, increasing the bath K+ concentration by 30 mmol l−1 inhibited RVD by 76.5±3.6 %. The K+ channel blocker quinine, but not Ba2+ (1 and 2 mmol l−1), significantly decreased the RVD response (by 25.0±5.4 and 72.3±5.1 % at 0.1 and 0.5 mmol l−1, respectively). Similarly, increasing the Cl− concentration in the bath from 47 to 102 mmol l−1 induced a significant reduction (45.2±7.9 %) in RVD. The RVD response was also markedly reduced (by 54.7±5.3 %) by the Cl− channel blocker indacrinone (MK-196; 0.5 mmol l−1), but only marginally by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB; 1, 5, 8 and 10 µmol l−1). Addition of the K+/Cl− symport inhibitor furosemide (0.1 mmol l−1) resulted in a 39.8±3.9 % inhibition of RVD. This inhibition could be completely overcome by simultaneous administration of 1 µmol l−1 tributyltin (anion exchanger) and furosemide.

Chelation of either extracellular (1 mmol l−1 EGTA) or both extra- and intracellular Ca2+ (1 mmol l−1 EGTA, 10 µmol l−1 A23187) had no effect on this RVD process. Furthermore, as measured using the fluorescent dye Fura-2/AM, there was no increase in the intracellular free Ca2+ concentration upon hypo-osmotic stimulation. Administration of the 5-lipoxygenase antagonist ETH 615-139 (20 µmol l−1), however, induced a 60 % inhibition of RVD. Simultaneous addition of ETH-615 and either the K+ ionophore gramicidin (0.5 mmol l−1) or the anion exchanger tributyltin (1 µmol l−1) could not reverse the ETH 615-139 inhibition. Finally, administration of the cycloxygenase inhibitor indomethacin had only a small, but significant, effect on RVD.

We conclude that RVD following hypo-osmotic swelling is in these cells a temperature- and ouabain-sensitive process that appears to be the result of K+ efflux through quinine-sensitive, Ba2+-insensitive K+ channels and Cl− efflux through an MK-196- and furosemide-sensitive Cl− conductance that is relatively unaffected by NPPB. This KCl efflux seems to be regulated by eicosanoids produced by the 5-lipoxygenase. Arachidonic acid metabolites from the cycloxygenase pathway are not involved in this process. Similarly, neither extra-nor intracellular Ca2+ appears to be important for the signalling of RVD.
Experimental Approaches Towards Interpreting Dolphin-Stimulated Bioluminescence
Authors: Rohr Jim , Latz Michael I. , Fallon Stewart , Nauen Jennifer C. , Hendricks Eric
Published: April 2021

Flow-induced bioluminescence provides a unique opportunity for visualizing the flow field around a swimming dolphin. Unfortunately, previous descriptions of dolphin-stimulated bioluminescence have been largely anecdotal and often conflicting. Most references in the scientific literature report an absence of bioluminescence on the dolphin body, which has been invariably assumed to be indicative of laminar flow. However, hydrodynamicists have yet to find compelling evidence that the flow remains laminar over most of the body. The present study integrates laboratory, computational and field approaches to begin to assess the utility of using bioluminescence as a method for flow visualization by relating fundamental characteristics of the flow to the stimulation of naturally occurring luminescent plankton.

Laboratory experiments using fully developed pipe flow revealed that the bioluminescent organisms identified in the field studies can be stimulated in both laminar and turbulent flow when shear stress values exceed approximately 0.1 N m−2. Computational studies of an idealized hydrodynamic representation of a dolphin (modeled as a 6:1 ellipsoid), gliding at a speed of 2 m s−1, predicted suprathreshold surface shear stress values everywhere on the model, regardless of whether the boundary layer flow was laminar or turbulent. Laboratory flow visualization of a sphere demonstrated that the intensity of bioluminescence decreased with increasing flow speed due to the thinning of the boundary layer, while flow separation caused a dramatic increase in intensity due to the significantly greater volume of stimulating flow in the wake. Intensified video recordings of dolphins gliding at speeds of approximately 2 m s−1 confirmed that brilliant displays of bioluminescence occurred on the body of the dolphin. The distribution and intensity of bioluminescence suggest that the flow remained attached over most of the body. A conspicuous lack of bioluminescence was often observed on the dolphin rostrum and melon and on the leading edge of the dorsal and pectoral fins, where the boundary layer is thought to be thinnest. To differentiate between effects related to the thickness of the stimulatory boundary layer and those due to the latency of the bioluminescence response and the upstream depletion of bioluminescence, laboratory and dolphin studies of forced separation and laminar-to-turbulent transition were conducted. The observed pattern of stimulated bioluminescence is consistent with the hypothesis that bioluminescent intensity is directly related to the thickness of the boundary layer.