bluuebunny/crossref_metadata_2025 huggingface dataset:
Cellular distribution of a high-affinity glutamate transporter in the nervous system of the cabbage looperTrichoplusia ni
Authors: Gardiner Richard B. , Ullensvang Kyrre , Danbolt Niels C. , Caveney Stanley , Donly B. Cameron
Published: April 2021

Glutamate functions as a neurotransmitter in the central nervous system(CNS) and neuromuscular junctions in insects. High-affinity glutamate transporters are responsible for keeping the resting levels of excitatory amino acids below the synaptic activation threshold by removing them from the extracellular fluid, thereby preventing them from reaching toxic levels. Peptides representing the N- and C-terminal regions of a glutamate transporter cloned from the cabbage looper caterpillar (Trichoplusia ni) were synthesized and used to generate polyclonal antibodies. The antibodies produced immunohistochemical staining in both muscular and nervous system T. ni tissues. Neuromuscular junctions in the skeletal muscles produced the most intense labelling, but no visceral muscle or sensory nerves were labelled. In the CNS, the neuropile of the ganglia, but not the connectives, gave a diffuse staining. Electron microscopical examination of ganglia and neuromuscular junctions showed that the plasma membrane of glial cells, but not that of neurons was labelled, in agreement with the notion that most of the glutamate uptake sites in this insect are in glial cells.
Cutaneous blood flow in the pigeonColumba livia: its possible relevance to cutaneous water evaporation
Authors: Ophir E. , Arieli Y. , Marder J. , Horowitz M.
Published: April 2021

The heat-acclimated rock pigeon is thought to use cutaneous water evaporation (CWE) as the `preferred' route for heat dissipation, and this mechanism is controlled by adrenergic signaling. In the present study, we tested the hypothesis that adjustments in skin blood flow are a crucial component of this adaptation. Skin blood flow was measured by laser Doppler flowmetry and by ultrasonic flowmetry in heat-acclimated (HAc) and non-acclimated (NAc) pigeons. Skin blood flow, CWE and rectal and skin temperatures were measured under heat exposure(Ta=50°C) or following propranolol (1.3 mg kg-1) or clonidine (80 μg kg-1) administration. Using laser Doppler flowmetry, we found a significant increase (1.3-fold) in skin blood flow in the dorsal skin of HAc pigeons following propanolol administration. In contrast, a significant decrease (0.7-fold) was observed in NAc birds. Injection of clonidine resulted in a significant decrease in skin blood flow in both HAc and NAc pigeons (0.4- and 0.5-fold, respectively). Heat exposure increased blood perfusion in both groups (2.5- and 1.8-fold,respectively). Using ultrasonic flowmetry, we showed that both propanolol and clonidine increase the arterial blood flow (Qa) in HAc pigeons, while venous blood flow (Qv) decreases. In contrast, no significant changes were found in NAc pigeons. As shown by the effect of clonidine, augmentation of skin blood flow is not a prerequisite for CWE, but normally coincides with a greater difference in arterial—venous pressure. Possible regulatory mechanisms are discussed.
How fins affect the economy and efficiency of human swimming
Authors: Zamparo P. , Pendergast D. R. , Termin B. , Minetti A. E.
Published: April 2021

The aim of the present study was to quantify the improvements in the economy and efficiency of surface swimming brought about by the use of fins over a range of speeds (v) that could be sustained aerobically. At comparable speeds, the energy cost (C) when swimming with fins was about 40 %lower than when swimming without them; when compared at the same metabolic power, the decrease in C allowed an increase in v of about 0.2 ms-1. Fins only slightly decrease the amplitude of the kick (by about 10 %) but cause a large reduction (about 40 %) in the kick frequency. The decrease in kick frequency leads to a parallel decrease of the internal work rate (Ẇint, about 75 %at comparable speeds) and of the power wasted to impart kinetic energy to the water (Ẇk, about 40 %). These two components of total power expenditure were calculated from video analysis (Ẇint) and from measurements of Froude efficiency(Ẇk). Froude efficiency(ηF) was calculated by computing the speed of the bending waves moving along the body in a caudal direction (as proposed for the undulating movements of slender fish); ηF was found to be 0.70 when swimming with fins and 0.61 when swimming without them. No difference in the power to overcome frictional forces(Ẇd) was observed between the two conditions at comparable speeds. Mechanical efficiency[Ẇtot/(Cv), where Ẇtot=Ẇk+Ẇint+Ẇd]was found to be about 10 % larger when swimming with fins, i.e. 0.13±0.02 with and 0.11±0.02 without fins (average for all subjects at comparable speeds).
Interplay among energy metabolism, organ mass and digestive enzyme activity in the mouse-opossumThylamys elegans: the role of thermal acclimation
Authors: Nespolo Roberto F. , Bacigalupe Leonardo D. , Sabat Pablo , Bozinovic Francisco
Published: April 2021

The potential for thermal acclimation in marsupials is controversial. Initial studies suggest that the thermoregulatory maximum metabolic rate (MMR)in metatherians cannot be changed by thermal acclimation. Nevertheless, recent studies reported conspicuous seasonality in both MMR and in basal metabolic rate (BMR). We studied the role of thermal acclimation in the Chilean mouse-opossum, Thylamys elegans, by measuring MMR and BMR before and after acclimation to cold or warm conditions. Following acclimation we also measured the mass of metabolically active organs, and the activity of a key digestive enzyme, aminopeptidase-N. No significant effect of thermal acclimation (i.e. between cold- and warm-acclimated animals) was observed for body mass, MMR, body temperature or factorial aerobic scope. However, the BMR of cold-acclimated animals was 30 % higher than for warm-acclimated individuals. For organ mass, acclimation had a significant effect on the dry mass of caecum, liver and kidneys only. Stepwise multiple regression using pooled data showed that 71 % of the variation in BMR is explained by the digestive organs. Overall, these results suggest that MMR is a rather rigid variable, while BMR shows plasticity. It seems that T. elegans cannot respond to thermal acclimation by adjusting its processes of energy expenditure (i.e. thermogenic capacity and mass of metabolically active organs). The lack of any significant difference in aminopeptidase-N specific activity between warm- and cold-acclimated animals suggests that this response is mainly quantitative (i.e. cell proliferation) rather than qualitative (i.e. differential enzyme expression). Finally, as far as we know, this study is the first to report the effects of thermal acclimation on energy metabolism, organ mass and digestive enzyme activity in a marsupial.
Oxygen transfer during aerobic exercise in a varanid lizardVaranus mertensiis limited by the circulation
Authors: Frappell Peter , Schultz Tim , Christian Keith
Published: April 2021

Oxygen transfer during sustained maximal exercise while locomoting on a treadmill at 0.33 m s-1 was examined in a varanid lizard Varanus mertensi at 35 °C. The rate of oxygen consumption(V̇O2) increased with locomotion from 3.49±0.75 (mean ± S.D.) to 14.0±4.0 ml O2 kg-1 min-1. Ventilation(V̇E) increased, aided by increases in both tidal volume and frequency, in direct proportion to V̇O2. The air convection requirement(V̇E/V̇O2=27)was therefore maintained, together with arterial PaCO2 and PaO2. The alveolar—arterial PO2 difference(PAO2—PaO2)also remained unchanged during exercise from its value at rest, which was approximately 20 mmHg. Pulmonary diffusion for carbon monoxide(0.116±0.027 ml kg-1 min-1 mmHg-1) was double the value previously reported in V. exanthematicus and remained unchanged with exercise. Furthermore, exercise was associated with an increase in the arterial—venous O2 content difference(CaO2—CvO2),which was assisted by a marked Bohr shift in the hemoglobin saturation curve and further unloading of venous O2. During exercise the increase in cardiac output (Q̇tot) did not match the increase in V̇O2, such that the blood convection requirement(Q̇tot/V̇O2)decreased from the pre-exercise value of approximately 35 to 16 during exercise. Together, the results suggest that ventilation and O2transfer across the lung are adequate to meet the aerobic needs of V. mertensi during exercise, but the decrease in the blood convection requirement in the presence of a large arterial—venous O2content difference suggests that a limit in the transport of O2 is imposed by the circulation.
Fluid-dynamic characteristics of a bristled wing
Authors: Sunada S. , Takashima H. , Hattori T. , Yasuda K. , Kawachi K.
Published: April 2021

Thrips fly at a chord-based Reynolds number of approximately 10 using bristled rather than solid wings. We tested two dynamically scaled mechanical models of a thrips forewing. In the bristled design, cylindrical rods model the bristles of the forewing; the solid design was identical to the bristled one in shape, but the spaces between the `bristles' were filled in by membrane. We studied four different motion patterns: (i) forward motion at a constant forward velocity, (ii) forward motion at a translational acceleration, (iii) rotational motion at a constant angular velocity and (iv)rotational motion at an angular acceleration. Fluid-dynamic forces acting on the bristled model wing were a little smaller than those on the solid wing. Therefore, the bristled wing of a thrips cannot be explained in terms of increased fluid-dynamic forces.
Olfactory sensitivity to changes in environmental [Ca2+] in the freshwater teleostCarassius auratus: an olfactory role for the Ca2+-sensing receptor?
Authors: Hubbard P. C. , Ingleton P. M. , Bendell L. A. , Barata E. N. , Canário A. V. M.
Published: April 2021

Olfactory sensitivity to changes in environmental Ca2+ has been demonstrated in two teleost species; a salmonid (Oncorhynchus nerka)and a marine/estuarine perciform (Sparus aurata). To assess whether this phenomenon is restricted to species that normally experience large fluctuations in external ion concentrations (e.g. moving from sea water to fresh water) or is present in a much wider range of species, we investigated olfactory Ca2+ sensitivity in the goldfish (Carassius auratus), which is a stenohaline, non-migratory freshwater cyprinid. Extracellular recording from the olfactory bulb in vivo by electroencephalogram (EEG) demonstrated that the olfactory system is acutely sensitive to changes in external Ca2+ within the range that this species is likely to encounter in the wild (0.05-3 mmol l-1). The olfactory system responded to increases in external calcium with increasing bulbar activity in a manner that fitted a conventional Hill plot with an apparent EC50 of 0.9±0.3 mmol l-1 (close to both ambient and plasma free [Ca2+]) and an apparent Hill coefficient of 1.1±0.3 (means ± S.E.M., N=6). Thresholds of detection were below 50 μmol l-1. Some olfactory sensitivity to changes in external [Na+] was also recorded, but with a much higher threshold of detection (3.7 mmol l-1). The olfactory system of goldfish was much less sensitive to changes in [Mg2+] and [K+]. Preliminary data suggest that Ca2+ and Mg2+ are detected by the same mechanism, although with a much higher affinity for Ca2+. Olfactory sensitivity to Na+ may warn freshwater fish that they are reaching the limit of their osmotic tolerance when in an estuarine environment. Olfaction of serine, a potent odorant in fish, was not dependent on the presence of external Ca2+ or Na+. Finally, the teleost Ca2+-sensing receptor (Ca-SR) was shown to be highly expressed in a subpopulation of olfactory receptor neurones by both immunocytochemistry and in situ hybridisation. The olfactory sensitivity to Ca2+ (and Mg2+) is therefore likely to be mediated by the Ca-SR. We suggest that olfactory Ca2+ sensitivity is a widespread phenomenon in teleosts and may have an input into the physiological mechanisms regulating internal calcium homeostasis.
Incubation temperature modulates post-hatching thermoregulatory behavior in the Madagascar ground gecko, Paroedura pictus
Authors: Blumberg Mark S. , Lewis Sean J. , Sokoloff Greta
Published: April 2021

All vertebrates regulate body temperature within narrow limits, regardless of their physiological capabilities. When do these limits develop, and can they be modified by manipulations of the developmental thermal environment? We addressed these questions by incubating the eggs of the Madagascar ground gecko, Paroedura pictus, at three temperatures and by assessing thermoregulatory behavior in hatchlings. Thermoregulatory behavior was assessed using a two-choice shuttle paradigm, and skin temperatures were measured non-invasively using infrared thermography. The shuttling behavior of hatchlings was systematically affected by the temperature at which they were incubated, and follow-up tests suggested that this effect persisted for at least three weeks post-hatching. The body temperature data from the shuttling experiment were used to model thermoregulatory behavior in a complex thermal environment; the model predicted systematic effects of incubation temperature on thermal preference. The specificity of the alteration in thermoregulatory behavior by incubation temperature is compelling and provides evidence for powerful pre-hatching influences on a fundamental, life-sustaining behavioral process.
The role of the frontal ganglion in locust feeding and moulting related behaviours
Authors: Zilberstein Yael , Ayali Amir
Published: April 2021

In the desert locust, Schistocerca gregaria, the frontal ganglion(FG) plays a key role in control of foregut movements, and constitutes a source of innervation to the foregut dilator muscles. In this work we studied the generation and characteristics of FG motor outputs in two distinct and fundamental behaviours: feeding and moulting. The FG motor pattern was found to be complex, and strongly dependent on the locust's physiological and behavioural state. Rhythmic activity of the foregut was dependent on the amount of food present in the crop; animals with food in their crop demonstrated higher FG burst frequency than those with empty crop. A very full gut inhibited the FG rhythm altogether. When no feeding-related foregut pattern was observed, the FG motor output was strongly correlated with the locust's ventilation pattern. This ventilation-related rhythm was dominant in pre-moulting locusts. During the moult, synchronization with the ventilation pattern can be transiently switched off, revealing the endogenous(feeding-related) FG pattern. This presumably happens during vigorous air swallowing, and could also be induced experimentally. Our findings suggest that the FG central pattern generator can be modulated to generate a variety of motor outputs under different physiological conditions and behavioural contexts.
Post-prandial blood flow to the gastrointestinal tract is not compromised during hypoxia in the sea bassDicentrarchus labrax
Authors: Axelsson Michael , Altimiras Jordi , Claireaux Guy
Published: April 2021

The hypothesis that the increase in post-prandial splanchnic blood flow will be reduced during hypoxia to prioritise blood flow to other organs was tested by measuring cardiac output and gut blood flow during a stepwise hypoxic challenge (five steps, from 20.6 to 3.9 kPa, 5 min of exposure to each level) before and after feeding (equivalent to 2.9% of body mass). Splanchnic blood flow, both absolute and relative to cardiac output, increased after feeding. Mean post-prandial gut blood flow increased by 71% (from 9.6±1.6 to 14.9±1.6 ml min-1 kg-1, means± S.E.M.). Before feeding, gut blood flow was 24.0% of cardiac output,and this increased significantly 24 h after feeding to 34.0%. The absolute post-prandial increase in gut blood flow (5.3±0.9 ml min-1kg-1) was paralleled by an increase in cardiac output(5.4±2.1 ml min-1 kg-1). Hypoxia decreased gut blood flow significantly from 9.6±1.6 to 3.7±1.1 ml min-1 kg-1, corresponding to a decrease in relative gut blood flow from 24 % to 13%. Contrary to our initial hypothesis, and although post-prandial absolute blood flow decreases during hypoxia, the relative proportion of cardiac output reaching the gut did not decrease (34.6%pre-hypoxia versus 26.7% during hypoxia), unlike the situation in non-feeding fish. We propose that, following feeding, relative gut blood flow is maintained because splanchnic hyperaemia occurs as a result of the release of local factors; consequently the reflex vasoconstriction of the gastrointestinal vasculature during hypoxia is not as effective in decreasing gut blood flow as it was before feeding because local hyperaemia out-competes the reflex regulation.
Adaptive mechanisms of intracellular calcium homeostasis in mammalian hibernators
Authors: Wang Shi Qiang , Lakatta Edward G. , Cheng Heping , Zhou Zeng Quan
Published: April 2021

Intracellular Ca2+ homeostasis is a prerequisite for a healthy cell life. While cells from some mammals may suffer dysregulation of intracellular Ca2+ levels under certain deleterious and stressful conditions, including hypothermia and ischemia, cells from mammalian hibernators exhibit a remarkable ability to maintain a homeostatic intracellular Ca2+ environment. Compared with cells from non-hibernators, hibernator cells are characterized by downregulation of the activity of Ca2+ channels in the cell membrane, which helps to prevent excessive Ca2+ entry. Concomitantly, sequestration of Ca2+ by intracellular Ca2+ stores, especially the sarcoplasmic/endoplasmic reticulum, is enhanced to keep the resting levels of intracellular Ca2+ stable. An increase in stored Ca2+ in heart cells during hibernation ensures that the levels of Ca2+messenger are sufficient for forceful cell contraction under conditions of hypothermia. Maintenance of Na+ gradients, viaNa+—Ca2+ exchangers, is also important in the Ca2+ homeostasis of hibernator cells. Understanding the adaptive mechanisms of Ca2+ regulation in hibernating mammals may suggest new strategies to protect nonhibernator cells, including those of humans, from Ca2+-induced dysfunction.
Design, limitations and sustained metabolic rate: lessons from small mammals
Authors: Bacigalupe Leonardo D. , Bozinovic Francisco
Published: April 2021

Physiological limitations affect an organism's capacity to acquire and expend energy over long periods of activity. These limitations could be related to the central machinery used for acquiring, processing and allocating energy, or by the energy-consuming machinery. Another possibility is that the capacities of central and peripheral organs and tissues are co-adjusted,implying an optimized design. Given the important consequences that rates of energy expenditure have on many ecological aspects of animal life, we need to understand which factors impose ceilings on sustained metabolic rate. Ceilings on sustainable energy expenditure represent the limit below which all the activities performed by an individual must occur. There have been many studies of design constraints on energy budgets, but the different procedures used to identify the type of physiological limitation do not necessarily resolve which factors actually impose metabolic ceilings in small mammals, which precludes a clear understanding of the ecological and evolutionary consequences of design constraints on energy budgets. We propose that the following steps are necessary to identify the physiological limits on sustained metabolic rate:(1) combining peak energy demands to differentiate a central limitation from a peripheral limitation; (2) pushing the animals to their physiological limits(e.g. asymptotic food intake); (3) testing for a central excess capacity (if the limit is set peripherally), or a peripheral excess capacity (if there is a central limitation); (4) utilizing different levels of energy demand to test for symmorphosis.
Magnetite-based magnetoreception in birds: the effect of a biasing field and a pulse on migratory behavior
Authors: Wiltschko Wolfgang , Munro Ursula , Wiltschko Roswitha , Kirschvink Joseph L.
Published: April 2021

To test the hypothesis that single domain magnetite is involved in magnetoreception, we treated Australian silvereyes Zosterops l. lateralis with a strong, brief pulse designed to alter the magnetization of single domain particles. This pulse was administered in the presence of a 1 mT biasing field, either parallel to the direction of the biasing field (PAR group) or antiparallel (ANTI group). In the case of magnetoreceptors based on freely moving single domain particles, the PAR treatment should have little effect, whereas the ANTI treatment should cause remagnetization of the magnetite particles involved in a receptor and could produce a maximum change in that receptor's output for some receptor configurations. Migratory orientation was used as a criterion to assess the effect on the receptor. Before treatment, both groups preferred their normal northerly migratory direction. Exposure to the biasing field alone did not affect their behavior. Treatment with the pulse in the presence of the biasing field caused both the PAR and the ANTI birds to show an axial preference for the east—west axis, with no difference between the two groups. Although these results are in accordance with magnetite-based magnetoreceptors playing a role in migratory orientation, they do not support the hypothesis that single domains in polarity-sensitive receptors are free to move through all solid angles. Possible interpretations, including other arrangements of single domains and superparamagnetic crystals, are discussed.
Serotonergic modulation of nonspiking local interneurones in the terminal abdominal ganglion of the crayfish
Authors: Nagayama Toshiki
Published: April 2021

The modulatory effect of serotonin on local circuit neurones forming the uropod motor control system of the crayfish Procambarus clarkiiGirard was analysed electrophysiologically. Bath application of 10 μmol l-1 serotonin caused a decrease in the tonic spike activity of the exopodite reductor motor neurone. The inhibitory effect of serotonin on the motor neurone was dose-dependent and its spike discharge was completely suppressed for long periods by 1 mmol l-1 serotonin perfusion. Nonspiking local interneurones in the terminal abdominal ganglion showed either a membrane depolarization (N=6) or hyperpolarization(N=9) of 10-30 mV in amplitude when 100 μmol l-1serotonin was perfused for 3-5 min. By contrast, spiking local interneurones and intersegmental ascending interneurones showed no observable excitatory responses to the perfusion of serotonin but instead some showed a small membrane hyperpolarization of 2-5 mV. These results indicate that the nonspiking interneurones could contribute substantially to the level of tonic excitation of the uropod motor neurones.

Sensory stimulation elicited depolarizing or hyperpolarizing potentials in the nonspiking interneurones and excitatory postsynaptic potentials (EPSPs)and spikes in the spiking interneurones. The sensory responses of spiking interneurones increased during bath application of serotonin and were reduced after 20-30 min of washing with normal saline. In the nonspiking interneurones, the amplitude of both depolarizing and hyperpolarizing potentials increased without any direct correlation with the serotonin-mediated potential change. This effect of serotonin was long-lasting and continued to enhance the responses of the nonspiking interneurones after washing. This postserotonin enhancement persisted for over 1 h.
Low-temperature protein metabolism: seasonal changes in protein synthesis and RNA dynamics in the Antarctic limpet Nacella concinna Strebel 1908
Authors: Fraser Keiron P. P. , Clarke Andrew , Peck Lloyd S.
Published: April 2021

Protein synthesis is a fundamental and energetically expensive physiological process in all living organisms. Very few studies have examined the specific challenges of manufacturing proteins at low ambient temperatures. At high southern latitudes, water temperatures are continually below or near freezing and are highly stable, while food availability is very seasonal. To examine the effects of low temperature and a highly seasonal food supply on protein metabolism, we have measured wholebody protein synthesis, RNA concentrations, RNA:protein ratios and RNA translational efficiencies in the Antarctic limpet Nacella concinna at four times of the year. From summer to winter, protein synthesis rates decreased by 52%, RNA concentrations decreased by 55% and RNA:protein ratios decreased by 68%, while RNA translational efficiencies were low and very variable. Protein synthesis rates in N. concinna approached those measured in temperate mussels, while RNA:protein ratios were considerably higher than in temperate species. Interspecific comparisons show that species living at low temperatures have elevated RNA:protein ratios, which are probably needed to counteract a thermally induced reduction in RNA translational efficiency. Calculations using theoretical energetic costs of protein synthesis suggest that Antarctic species may allocate a larger proportion of their metabolic budget to protein synthesis than do temperate or tropical species.
Nitric oxide regulation of the central aortae of the toad Bufo marinus occurs independently of the endothelium
Authors: Broughton Brad R. S. , Donald John A.
Published: April 2021

Nitric oxide (NO) signalling pathways were examined in the lateral aortae and dorsal aorta of the cane toad Bufo marinus. NADPH diaphorase histochemistry and nitric oxide synthase (NOS) immunohistochemistry found no evidence for endothelial NOS in the endothelium of toad aortae, but it could be readily demonstrated in rat aorta that was used as a control. Immunohistochemistry using a specific neural NOS antibody showed the presence of neural NOS immunoreactivity in the perivascular nerves of the aortae. The anatomical data was supported by in vitro organ bath physiology,which demonstrated that the vasodilation mediated by applied acetylcholine(10-5 mol l-1) was not dependent on the presence of the vascular endothelium; however, it was significantly reduced in the presence of a neural NOS inhibitor, vinyl-L-NIO (10-4 mol l-1). In addition, atropine (10-6 mol l-1) (a muscarinic receptor inhibitor), L-NNA (10-4 mol l-1) (a NOS inhibitor) and ODQ (10-5 mol l-1) (an inhibitor of soluble guanylyl cyclase) abolished the vasodilatory effect of applied acetylcholine. In conclusion, we propose that an endothelial NO system is absent in toad aortae and that NO generated by neural NOS in perivascular nerves mediates vasodilation.
The effects of lipid location on non-invasive estimates of body composition using EM-SCAN technology
Authors: Unangst Edward T. , Merkley Lance A.
Published: April 2021

We evaluated the effect of lipid location on body-composition estimation accuracy using electromagnetic scanning (EM-SCAN), a non-invasive [total body electrical conductivity (TOBEC)] method. Molds were constructed that simulated a `general' small mammal, either 93% lean/7% lipid (control) or 82% lean/18%lipid (lipid-location groups). In the 18% lipid molds, we varied the location of the fat; simulating all the fat in the head, tail or midsection or simulating homogenous distribution. Comparisons were made between the EM-SCAN output of each lipid-location group, and multiple-regression techniques were performed to derive body-composition estimation equations for both lipid mass(ML) and fat-free mass (MFF). Device output varied significantly for all lipid-location groups even though all groups contained 18% body fat, showing a lipid-location effect on device output. Calibration equations derived for each lipid-location condition estimated both ML and MFF accurately,but an independent equation was required for each lipid-location condition. In situations where species significantly vary body fat content and location, for example during hibernation or reproductive periods, we suggest deriving a calibration equation that is more representative of the actual body composition to improve ML and MFFestimation accuracy using non-invasive EM-SCAN methods.
The superfast extraocular myosin (MYH13) is localized to the innervation zone in both the global and orbital layers of rabbit extraocular muscle
Authors: Briggs Margaret M. , Schachat Fred
Published: April 2021

Extraocular muscles (EOMs) are the most molecularly heterogeneous and physiologically diverse mammalian striated muscles. They express the entire array of striated muscle myosins, including a specialized myosin heavy chain MYH13, which is restricted to extraocular and laryngeal muscles. EOMs also exhibit a breadth of contractile activity, from superfast saccades to slow tracking and convergence movements. These movements are accomplished by the action of six ultrastructurally defined fiber types that differ from the type IIa, IIb, IIx and I fibers found in other skeletal muscles. Attempts to associate different eye movements with either the expression of different myosins or the activity of particular EOM fiber types are complicated by the molecular heterogeneity of several of the fiber types, and by electromyography studies showing that the majority of extraocular motor units participate in both fast and slow eye movements. To better understand the role of MYH13 in ocular motility, we generated MYH13-sequence-specific antibodies and used SDS-PAGE to quantify the regional distribution of myosin in EOM and to characterize its heterogeneity in single fibers. These studies demonstrate that MYH13 is preferentially expressed in the majority of orbital and global fibers in the central innervation zone of rabbit EOM. Many individual fibers express MYH13 with the fast IIb myosin and varying amounts of IIx myosin. The differential localization of MYH13, coupled with specialization of the sarcoplasmic reticulum and thin filament systems, probably explains how activation of the endplate band region enables the majority of EOM fibers to contribute to superfast contractions.
Vibrometric studies of the middle ear of the bullfrog Rana catesbeiana I. The extrastapes
Authors: Mason Matthew J. , Narins Peter M.
Published: April 2021

Laser vibrometry was used to measure the vibration velocity at different points on the ossicular apparatus of the bullfrog Rana catesbeiana in response to free-field sound. The ascending process of the extrastapes,neglected in most accounts of frog middle ear mechanics, supports a rocking motion of the extrastapes and is critical to the normal function of the ossicular apparatus. The articulation between extrastapes and the bony stapes shaft acts as a hinge, although movement at this hinge is usually small. The ratio of tympanic membrane to footplate vibration velocity is significantly greater in male frogs than in female frogs. Differences in this ratio between male and female frogs are probably mainly due to flexion between the extrastapes and stapes rather than to differences in the coupling between tympanic membrane and extrastapes. It is argued that flexibility in the ossicular system represents a protective mechanism in frogs, and functional analogies are drawn between the stapes/extrastapes system of frogs and the tri-ossicular system of mammals.
Individual variation in metabolic traits of wild nine-banded armadillos(Dasypus novemcinctus), and the aerobic capacity model for the evolution of endothermy
Authors: Boily Patrice
Published: April 2021

A fundamental assumption of the aerobic capacity model for the evolution of endothermy is that basal (BMR) and peak (PMR) metabolic rates are functionally linked at the intraspecific level. The purpose of this study was to use the nine-banded armadillo Dasypus novemcinctus as a model to test this assumption. Measurements of BMR, PMR, mass and rectal temperature were obtained over two summers from wild, adult individuals from a population in Louisiana, USA. BMR and PMR were positively correlated (r=0.62), and both were significantly higher (by 46% for BMR and by 35% for PMR) in 1999 than in 1998. Similar results were obtained whether metabolic rates were expressed in whole-animal or mass-independent units. These results suggest the existence of a functional link between BMR and PMR and are therefore consistent with the aerobic capacity model. In addition, this study confirmed that, compared with most eutherian mammals, the nine-banded armadillo exhibits low and highly variable basal and peak metabolic rates (20-60% the predicted values; 23% and 27% coefficients of variation) and rectal temperatures (range 32.7-35.3°C). Such metabolic traits are, however, consistent with the general pattern previously observed for other members of the order Xenarthra and with the hypothesis that low metabolic rates in armored mammals evolved as a result of unbalanced selection in which, because of low predation risks,selection for a high aerobic capacity was much weaker than the opposing selection for energy conservation.
Thermal acclimation changes DNA-binding activity of heat shock factor 1(HSF1) in the gobyGillichthys mirabilis: implications for plasticity in the heat-shock response in natural populations
Authors: Buckley Bradley A. , Hofmann Gretchen E.
Published: April 2021

The intracellular build-up of thermally damaged proteins following exposure to heat stress results in the synthesis of a family of evolutionarily conserved proteins called heat shock proteins (Hsps) that act as molecular chaperones, protecting the cell against the aggregation of denatured proteins. The transcriptional regulation of heat shock genes by heat shock factor 1(HSF1) has been extensively studied in model systems, but little research has focused on the role HSF1 plays in Hsp gene expression in eurythermal organisms from broadly fluctuating thermal environments. The threshold temperature for Hsp induction in these organisms shifts with the recent thermal history of the individual but the mechanism by which this plasticity in Hsp induction temperature is achieved is unknown. We examined the effect of thermal acclimation on the heat-activation of HSF1 in the eurythermal teleost Gillichthys mirabilis. After a 5-week acclimation period (at 13, 21 or 28°C) the temperature of HSF1 activation was positively correlated with acclimation temperature. HSF1 activation peaked at 27°C in fish acclimated to 13°C, at 33°C in the 21°C group, and at 36°C in the 28°C group. Concentrations of both HSF1 and Hsp70 in the 28°C group were significantly higher than in the colder acclimated fish. Plasticity in HSF1 activation may be important to the adjustable nature of the heat shock response in eurythermal organisms and the environmental control of Hsp gene expression.
Temperature affects the ontogeny of sexually dimorphic cuticular hydrocarbons inDrosophila melanogaster
Authors: Savarit Fabrice , Ferveur Jean-François
Published: April 2021

Hydrocarbons on the cuticle of mature Drosophila melanogasterflies play a crucial role in mate recognition, and protect against dehydration. We measured the effect of temperature on mature cuticular hydrocarbons (CHs) by (i) rearing two control strains at different temperatures, (ii) shifting the temperature after metamorphosis and (iii)inducing a single heat-shock pulse in control and heat-sensitive transgenic strains, over a period of 3 days following adult eclosion. This study describes the time course of the events involved in the production of male-and female-predominant CHs. We also found that `immature' CHs, sexually monomorphic CHs on younger flies, were not affected by these treatments.
Quantification of the wake of rainbow trout (Oncorhynchus mykiss) using three-dimensional stereoscopic digital particle image velocimetry
Authors: Nauen Jennifer C. , Lauder George V.
Published: April 2021

Although considerable progress has been made within the last decade in experimental hydrodynamic analyses of aquatic locomotion using two-dimensional digital particle image velocimetry (two-dimensional DPIV), data have been limited to simultaneous calculation of two out of the three flow velocity variables: downstream (U), vertical (V) and lateral(W). Here, we present the first biological application of stereo-DPIV, an engineering technique that allows simultaneous calculation of U, V and W velocity vectors. We quantified the wakes of rainbow trout (Oncorhynchus mykiss, 16.5-21.5 cm total body length, BL), swimming steadily in a recirculating flow tank at a slow cruising speed of 1.2 BL s-1. These data extend the comparative basis of current hydromechanical data on the wakes of free-swimming fishes to the salmoniforms and are used to test current hypotheses of fin function by calculations of mechanical performance and Froude efficiency.

Stereo-DPIV wake images showed three-dimensional views of oscillating jet flows high in velocity relative to free-stream values. These jet flows are consistent with the central momentum jet flows through the cores of shed vortex rings that have been previously viewed for caudal fin swimmers using two-dimensional DPIV. The magnitude and direction of U, V and W flows in these jets were determined over a time series of 6-8 consecutive strokes by each of four fish.

Although the fish swam at the same relative speed, the absolute magnitudes of U, V and W were dependent on individual because of body size variation. Vertical flows were small in magnitude (<1 cm s-1) and variable in direction, indicating limited and variable vertical force production during slow, steady, forward swimming. Thus, in contrast to previous data from sunfish (Lepomis macrochirus) and mackerel (Scomber japonicus), the trout homocercal caudal fin does not appear to generate consistent vertical forces during steady swimming. U flows were of the order of 3-6 cm s-1; lateral flows were typically strongest, with W magnitudes of 4-6 cm s-1. Such strong lateral flows have also been shown for more derived euteleosts with homocercal caudal fins.

The ratios of the magnitudes of wake flow, U/(U+V+W), which is a flow equivalent to mechanical performance, were also dependent on individual and ranged from 0.32 to 0.45, a range similar to the range of mechanical performance values previously determined using standard two-dimensional DPIV methods for caudal fin locomotion by more derived euteleosts. Strong lateral jet flow appears to be a general feature of caudal fin locomotion by teleosts and may reflect the nature of undulatory propulsion as a posteriorly propagated wave of bending. Froude efficiency (ηp) was independent of individual; meanη p was 0.74, which is similar to previous findings for trout.
Sensitivity to novel feedback at different phases of a gymnotid electric organ discharge
Authors: Schuster Stefan , Otto Natalie
Published: April 2021

Weakly electric fish communicate and electrolocate objects in the dark by discharging their electric organs (EOs) and monitoring the spatiotemporal pattern of current flow through their skin. In the South-American pulse-type gymnotid fish these organs often are intriguingly complex, comprising several hundreds of electrogenic cells (electrocytes) of various morphologies,innervation patterns and abilities to generate a spike, distributed over nearly the full length of the fish. An attractive idea is that different parts of the organ may serve distinct functions in electrocommunication and electrolocation. Recent studies support this notion and suggest that the currents produced during the final phase of the electric organ discharge (EOD)are used for communication. Here, we explore a method to directly assess the relevance of the various currents for electrolocation. In this new method, the pattern of current flow during a gymnotid EOD is changed selectively at distinct phases of the EOD so that currents generated by known electrocyte groups are affected. We have studied the roles played by the various currents for the detection of novel feedback at the trunk/tail region of the gymnotid fish Gymnotus carapo. An experimental animal rested in a cage and two electrodes were placed at a close distance to its trunk and tail. An electronic switch briefly connected these electrodes during a selected phase within an EOD and the shunting of EOD current that resulted from switch closure was directly monitored. G. carapo responded with an acceleration of its discharge rate to novelties in the EOD feedback that occurred only for a fraction of a single EOD. Controls in which the switch was closed during the silent intervals between successive EODs showed that the fish responded to the changes in EOD feedback and not to unrelated artefacts of the brief switch closure. Fish responded to shunting of current during all phases; the sensitivity was highest during the final headnegative phase but the magnitude of shunted current was largest in the preceeding phase. The current produced during the final part of the EOD is thus not reserved for communication as previously suggested but plays a predominant role in electrolocation at the trunk and tail region of G. carapo.
Increased blood oxygen affinity during digestion in the snakePython molurus
Authors: Overgaard Johannes , Wang Tobias
Published: April 2021

Many snakes exhibit large increases in metabolic rate during digestion that place extensive demands on efficient oxygen transport. In the present study,we describe blood oxygen affinity following three weeks of fasting and 48 h after feeding in the Burmese python (Python molurus). We also report simultaneous measurements of arterial blood gases and haematological parameters. Arterial blood was obtained from chronically implanted catheters,and blood oxygen-dissociation curves were constructed from oxygencontent measurements at known oxygen partial pressure(PO2) values at 2% and 5% CO2. Arterial pH remained constant at approximately 7.6 after feeding, but digestion was associated with an approximately 6 mmol l-1 increase in [HCO3-], while CO2 partial pressure(PCO2) increased from 2.21±0.13 kPa in fasted animals to 2.89±0.17 kPa at 48 h after feeding. Blood oxygen affinity in vivo was predicted on the basis of pH in vivoand the blood oxygen-dissociation curves obtained in vitro. The blood oxygen affinity in vivo increased during digestion, with P50 values decreasing from 4.58±0.11 kPa to 3.53±0.24 kPa. This increase was associated with a significant decrease in the red blood cell [NTP]/[Hb4] ratio (relationship between the concentrations of organic phosphates and total haemoglobin) and a significant decrease in mean cellular haemoglobin content, which is indicative of swelling of the red blood cells. Our data for blood oxygen affinity and arterial oxygen levels, together with previously published values of oxygen uptake and blood flows, allow for a quantitative evaluation of oxygen transport during digestion. This analysis shows that a large part of the increased metabolism during digestion is supported by an increased venous extraction, while arterial PO2(PaO2) and haemoglobin saturation do not vary with digestive status. Thus, we predict that venous PO2 (PvO2) is reduced from a fasting value of 5.2 kPa to 1.6 kPa during digestion.
Metabolite diffusion in giant muscle fibers of the spiny lobster Panulirus argus
Authors: Kinsey Stephen T. , Moerland Timothy S.
Published: April 2021

The time- and orientation-dependence of metabolite diffusion in giant muscle fibers of the lobster Panulirus argus was examined using 31P- and 1H-pulsed-field gradient nuclear magnetic resonance. The 31P resonance for arginine phosphate and the 1H resonances for betaine, arginine/arginine phosphate and-CH2/-CH groups were suitable for measurement of the apparent diffusion coefficient, D. Diffusion was measured axially, D∥, and radially, D⊥, in fibers over diffusion times of 20 to 300 ms. Diffusion was strongly anisotropic, and D∥ was higher than D⊥ at all times. Radial diffusion decreased with time until a steady-state value was reached at a diffusion time of ≈100 ms. Changes in D⊥ occurred over a time scale that was consistent with previous measurements from fish and mammalian muscle,indicating that diffusion is hindered by the same types of barriers in these diverse muscle types. The time dependence indicated that the sarcoplasmic reticulum is the principal intracellular structure that inhibits mobility in an orientation-dependent manner in skeletal muscle. The abdominal muscles in P. argus are used for anaerobic, burst contractions during an escape maneuver. The fact that these muscle fibers have diameters that may exceed hundreds of microns in diameter, and nearly all of the mitochondria are localized near the sarcolemmal membrane, suggests that barriers that hinder radial diffusion of ATP equivalents may ultimately limit the rate of post-contractile recovery.
Behavioral observations and computer simulations of blue crab movement to a chemical source in a controlled turbulent flow
Authors: Weissburg Marc J. , Dusenbery David B.
Published: April 2021

The behavior of crabs tracking odor in turbulent chemical plumes was compared to the performance of computer simulations of search behavior operating in similar chemical signal environments. The movement of blue crabs(Callinectes sapidus) towards a source of food odor was studied in controlled flow conditions in a flume. The evolving chemical stimulus field of a similar chemical source in an equivalent flow environment was captured by recording concentration patterns of a fluorescent tracer. Hypotheses about the sensory mechanisms employed by the crabs were tested by computer simulation using the recorded fluorescence as the stimulus. The results demonstrate that a simple model combining chemotropotaxis (simultaneous, spatial comparisons of chemical signals) and odor-stimulated upstream movement (rheotaxis) is sufficient to explain the efficient movements towards the source displayed by foraging crabs. Spatial integration around each sensor improves performance significantly, but the number of sensors does not have a large impact on performance. The weighting of information from chemical versus flow signals can substantially change simulation performance, resulting in more or less congruence between the behavior of simulations and that of crabs, which suggests the general importance of both sources of information for successful odor-guided navigation.
The relationship between heat flow and vasculature in the dorsal fin of wild bottlenose dolphinsTursiops truncatus
Authors: Meagher Erin M. , McLellan William A. , Westgate Andrew J. , Wells Randall S. , Frierson Dargan , Pabst D. Ann
Published: April 2021

The dorsal fin of the bottlenose dolphin Tursiops truncatuscontains blood vessels that function either to conserve or to dissipate body heat. Prior studies have demonstrated that heat flux, measured from a single position on the dorsal fin, decreases during body cooling and diving bradycardia and increases after exercise and at the termination of the dive response. While prior studies attributed changes in heat flux to changes in the pattern of blood flow, none directly investigated the influence of vascular structures on heat flux across the dorsal fin. In this study we examined whether heat flux is higher directly over a superficial vein,compared to a position away from a vein, and investigated the temporal relationship between heart rate, respiration and heat flux. Simultaneous records of heat flux and skin temperature at three positions on the dorsal fins of 19 wild bottlenose dolphins (with the fin in air and submerged) were collected, together with heart rate and respiration. When the fin was submerged, heat flux values were highest over superficial veins, usually at the distal tip, suggesting convective delivery of heat, via blood, to the skin's surface. Conversely, in air there was no relationship between heat flux and superficial vasculature. The mean difference in heat flux (48 W m-2) measured between the three fin positions was often equal to or greater than the heat flux that had been recorded from a single position after exercising and diving in prior studies. Tachycardia at a respiratory event was not temporally related to an increase in heat flux across the dorsal fin. This study suggests that the dorsal fin is a spatially heterogeneous thermal surface and that patterns of heat flux are strongly influenced by underlying vasculature.