bluuebunny/crossref_metadata_2025 huggingface dataset:
Does Blood Acid–Base Status Modulate Catecholamine Secretion in the Rainbow Trout (Oncorhynchus Mykiss)?
Authors: Julio Alejandra E. , Montpetit Colin J. , Perry Steve F.
Published: April 2021

The direct and modulating effects of acidosis on catecholamine secretion in rainbow trout (Oncorhynchus mykiss) were assessed in vivo using cannulated fish and in situ using a perfused cardinal vein preparation. In situ, acidosis (a reduction in perfusate pH from 7.9 to 7.4) did not elicit catecholamine release or modulate the secretion of catecholamines evoked by the non-specific cholinergic receptor agonist carbachol (3×10−7 to 10−5 mol kg−1) or the muscarinic receptor agonist pilocarpine (10−7 mol kg−1). Acidosis, however, significantly increased the secretion rates of noradrenaline and adrenaline in response to nicotine (10−8 to 10−7 mol kg−1). In vivo, intra-arterial injections of nicotine (300–600 nmol kg−1) into normocapnic or moderately hypercapnic fish (water or 0.67 kPa) caused a dose-dependent elevation of circulating catecholamine levels. At the highest dose of nicotine, the rise in plasma catecholamine levels was significantly enhanced in the hypercapnic fish.

Acute hypoxia in vivo caused an abrupt release of catecholamines when arterial haemoglobin O2-saturation was reduced to approximately 55–60 %; this catecholamine release threshold during hypoxia was unaltered in hypercapnic fish. However, the hypoxia-induced catecholamine release was significantly greater in hypercapnic fish than in normocapnic fish.

The results of this study suggest that blood acid–base status, while not influencing catecholamine secretion directly or influencing the blood O2 content threshold for catecholamine release during hypoxia, may modulate the secretory process specifically in response to nicotinic receptor stimulation of chromaffin cells.
An Analysis of Synthetic Processing of Odor Mixtures in the Honeybee (Apis Mellifera)
Authors: Chandra Sathees , Smith Brian H.
Published: April 2021

Both sensory transduction and central processing of odor mixtures can give rise to several different kinds of interaction, which can influence how well individual components are perceived and processed. In particular, odor mixtures are believed to give rise to ‘configural’ or ‘synthetic’ properties that are not characteristic of the components. However, the exact nature of these effects, particularly with regard to their expression in behavior, remains to be examined in detail. Here we use feature-negative and transwitching conditioning paradigms to show that honeybees can use configural cues in odor processing. However, the nature of these configural cues is not similar to that predicted by some models of conditioning. We propose that configural models may be capable of accounting for a substantial portion of odor mixture processing.
A Respirometric Analysis of Fuel Use During Aerobic Swimming at Different Temperatures in Rainbow Trout (Oncorhynchus Mykiss)
Authors: Kieffer James D. , Alsop Derek , Wood Chris M.
Published: April 2021

Instantaneous fuel usage at 5 °C or 15 °C was assessed by measurement of rates of O2 consumption , CO2 excretion and nitrogenous waste excretion (Ṁnitrogen =ammonia-N + urea-N) in juvenile rainbow trout (Oncorhynchus mykiss) at rest and during swimming at 45 % and 75 % of aerobic capacity (Ucrit). After 2 weeks of training at approximately 1 body length s−1 (BL s−1), critical swimming speeds (approximately 3.0 BL s−1) and whole-body energy stores (total protein, lipids and carbohydrates) were identical in fish acclimated to 5 °C or 15 °C. and increased with swimming speed at both temperatures and were higher at 15 °C than at 5 °C at all speeds, but the overall Q10 values (1.23–1.48) were low in these long-term (6 weeks) acclimated fish. The respiratory quotient (, approximately 0.85) was independent of both temperature and swimming speed. In contrast to and , the rate of ammonia excretion was independent of swimming speed, but more strongly influenced by temperature (Q10 1.4–2.8). Urea excretion accounted for 15–20 % of Ṁnitrogen, was unaffected by swimming speed and showed a tendency (P<0.07) to be positively influenced by temperature at one speed only (45 % Ucrit). Nitrogen quotients (NQ) were generally higher in warm-acclimated fish, remaining independent of swimming speed at 15 °C (0.08), but decreased from about 0.08 at rest to 0.04 during swimming at 5 °C. Instantaneous aerobic fuel use calculations based on standard respirometric theory showed that both acclimation temperature and swimming speed markedly influenced the relative and absolute use of carbohydrates, lipids and proteins by trout. At rest, cold-acclimated trout used similar proportions of carbohydrates and lipids and only 27 % protein. During swimming, protein use decreased to 15 % at both speeds while the relative contributions of both lipid and carbohydrate increased (to more than 40 %). On an absolute basis, carbohydrate was the most important fuel for fish swimming at 5 °C. In contrast, resting fish acclimated to 15 °C utilized 55 % lipid, 30 % protein and only 15 % carbohydrate. However, as swimming speed increased, the relative contribution of carbohydrate increased to 25 %, while the protein contribution remained unchanged at approximately 30 %, and lipid use decreased slightly (to 45 %). On an absolute basis, lipid remained the most important fuel in fish swimming at 15 °C. These results support the concept that lipids are a major fuel of aerobic exercise in fish, but demonstrate that the contribution of protein oxidation is much smaller than commonly believed, while that of carbohydrate oxidation is much larger, especially at higher swimming speeds and colder temperature.
Dynamic gearing in running dogs
Authors: Carrier David R. , Gregersen Colin S. , Silverton Natalie A.
Published: April 2021

Dynamic gearing is a mechanism that has been suggested to enhance the performance of skeletal muscles by maintaining them at the shortening velocities that maximize their power or efficiency. We investigated this hypothesis in three domestic dogs during trotting and galloping. We used ground force recordings and kinematic analysis to calculate the changes in gear ratio that occur during the production of the external work of locomotion. We also monitored length changes of the vastus lateralis muscle, an extensor muscle of the knee, using sonomicrometry in four additional dogs to determine the nature and rate of active shortening of this muscle. During both trotting and galloping, the gear ratios of the extensor muscles of the elbow, wrist and ankle joints were relatively constant early in limb support, but decreased rapidly during the second half of support. The gear ratio at the hip exerted an extensor moment initially, but decreased throughout limb support and became negative midway through support. This pattern of decreasing gear ratio during the second half of support indicates that dynamic gearing does not maximize muscle power or efficiency at the elbow, wrist, hip and ankle joints. In contrast, the extensor muscles of the shoulder and knee joints exhibited an increase in gear ratio during limb support. In two dogs, the vastus lateralis muscle shortened at a relatively constant rate of 3.7–4 lengths s−1 during intermediate-speed galloping. This pattern of increasing gear ratio and constant velocity of muscle shortening at the knee joint is consistent with the hypothesis of dynamic gearing. Given the amount of work done at the knee and shoulder joints of running dogs, dynamic gearing may contribute to the economy of constant-speed running and may be important to integrated limb function.
Fiber capillarization and ultrastructure of pigeon pectoralis muscle after cold acclimation
Authors: Mathieu-Costello O. , Agey P. J. , Quintana E. S. , Rousey K. , Wu L. , Bernstein M. H.
Published: April 2021

We investigated the effect of 2 months of exposure to cold conditions (0–5 °C) on capillarization and on fiber size, distribution and ultrastructure in the pectoralis muscle of nine pigeons (Columbia livia; mean body mass 700±31 g) and compared the results with measurements from four control birds (mean mass 715±42 g) kept at normal ambient temperature (22–23 °C) for the same period. Superficial and deep portions of the muscles, taken from the central area of the right or left pectoralis major muscle, were perfusion-fixed in situ, processed for electron microscopy and analyzed by morphometry. Aerobic fibers represented the vast majority of fibers (93±1 %, mean ± S.E.M.) in all samples. After cold-acclimation, fiber sectional area was reduced and capillary density increased proportionally. There was no change in the degree of orientation (anisotropy) of capillaries, capillary-to-fiber ratio or fiber type distribution compared with controls. The volume density of mitochondria and lipid droplets in aerobic fibers and capillary diameter increased in response to cold, while the linear relationship between capillary length per fiber volume and fiber mitochondrial volume density remained unchanged. Capillary surface area, intrafiber lipid deposition and fiber mitochondrial volume density were all correlated in cold-acclimated pigeons. The results indicate a close match between the aerobic capacity of the highly aerobic fibers of the pectoralis muscle and their vascularization to meet the increased energetic demand of shivering.
Effect of a magnetic pulse on the orientation of silvereyes, zosterops l. lateralis, during spring migration
Authors: Wiltschko Wolfgang , Munro Ursula , Ford Hugh , Wiltschko Roswitha
Published: April 2021

The orientation behaviour of Australian silvereyes, Zosterops l. lateralis, was tested during their spring migration, when they head southward to their Tasmanian breeding grounds. With only the local geomagnetic field as a cue, the birds significantly preferred their normal southerly migratory direction. Treatment with a short, strong magnetic pulse designed to alter the magnetization of single-domain magnetite led to a significant deflection towards the east for the next 4 days. This was followed by a period of non-oriented behaviour. From day 10 onwards, the birds returned to their original southerly headings. Together with previous findings, these data suggest that the navigational ‘map’ of these birds includes magnetic parameters and that a magnetite-based receptor provides them with information about their position. The transient nature of the effect is not easily explained on the basis of single-domain magnetite.
Looking all Around: Honeybees use Different Cues in Different Eye Regions
Authors: Lehrer Miriam
Published: April 2021

Based on results of early as well as recent behavioural studies, the present review compares the performance of different eye regions in exploiting information on shape, colour and motion, relevant to the honeybee’s foraging task. The comparisons reveal similarities, as well as differences, among the performances of various eye regions, depending on the visual parameter involved in the task under consideration. The outcome of the comparisons is discussed in the light of anatomical and optical regional specializations found in the bee’s peripheral visual pathway, as well as in the light of the foraging bee’s natural habits. It is concluded that the functional differences found among different eye regions are based on neural mechanisms subserving the bee’s natural needs, rather than on peripheral specializations.
Electrophysiology of the In Situ Contractile Vacuole Complex of Paramecium Reveals its Membrane Dynamics and Electrogenic Site During Osmoregulatory Activity
Authors: Tominaga Takashi , Allen Richard D. , Naitoh Yutaka
Published: April 2021

In the freshwater protozoan Paramecium multomicronucleatum, excess cytosolic water, acquired osmotically, is segregated and expelled to the cell exterior through the activity of the contractile vacuole complex. This process keeps the cell volume constant. The electrophysiological parameters of the organelle were measured in situ using a fine-tipped microelectrode inserted into the contractile vacuole, the exocytotic vesicle of the organelle to which the segregated fluid is transported before being expelled to the exterior. The input capacitance decreased markedly immediately before fluid expulsion and regained its previous value when fluid filling resumed after fluid expulsion. This change in the capacitance proved that the contractile vacuole became disconnected from its radial arms, which project from the vacuole, before fluid expulsion occurred and then reconnected with the arms after fluid expulsion. A positive electrical potential was recorded from the contractile vacuole only when it was connected to the radial arms.

This implies that the electrogenic mechanism resides exclusively in the radial arms and supports the idea that the decorated spongiomes, V-type proton-pump-covered terminal tubules of the radial arms that end blindly in the cytosol, are electrogenic. The linear current–voltage relationship of the contractile vacuole membrane also implies that few voltage-activated ion channels are present in the membrane. To explain the movement of water into the contractile vacuole complex, we favour the hypothesis that the potential generated across the decorated spongiome membrane can be used to drive counter-anions from the cytosol into the lumen of the complex. The anions could then act as an osmolite to pull cytosolic water into the lumen of the organelle.
Embryonic Temperature Modulates Muscle Growth Characteristics in Larval and Juvenile Herring
Authors: Johnston Ian A. , Cole Nicholas J. , Abercromby Marguerite , Vieira Vera L. A.
Published: April 2021

The influence of embryonic and larval temperature regime on muscle growth was investigated in Atlantic herring (Clupea harengus L.). Eggs of spring-spawning Clyde herring were incubated at 5 °C, 8 °C or 12 °C until hatching and then reared until after metamorphosis at rising temperatures to simulate a seasonal warming. Metamorphosis to the juvenile stage was complete at 37 mm total length (TL), after an estimated 177 days as a larva at 5 °C, 117 days at 8 °C and 101 days at 12 °C. Growth rate and the development of median fins were retarded in relation to body length at 5 °C compared with 8 °C and 12 °C. Between hatching (at 8–9 mm TL) and 16 mm TL, there was a threefold increase in total muscle cross-sectional area, largely due to the hypertrophy of the embryonic red and white muscle fibres. The recruitment of additional white muscle fibres started at approximately 15 mm TL at all temperatures, and by 37 mm was estimated to be 66 fibres day−1 at 5 °C and 103 fibres day−1 at 8 °C and 12 °C. Peptide mapping studies revealed a change in myosin heavy chain composition in white muscle fibres between 20 and 25 mm TL. Embryonic red muscle fibres expressed fast myosin light chains until 24–28 mm TL at 5 °C and 22 mm TL at 12 °C, and new red fibres were added at the horizontal septum starting at the same body lengths. Following metamorphosis, the total cross-sectional area of muscle was similar at different temperatures, although the number of red and white fibres per myotome was significantly greater at the warmest than at the coldest regime. For example, the mean number of white muscle fibres per myotome in 50 mm TL juveniles was calculated to be 23.4 % higher at 12 °C (12 065) than at 5 °C (9775). In other experiments, spring-spawning (Clyde) and autumn-spawning (Manx) herring were reared at different temperatures until first feeding and then transferred to ambient seawater temperature and fed ad libitum for constant periods. These experiments showed that, for both stocks, the temperature of embryonic development influenced the subsequent rate of muscle fibre recruitment and hypertrophy as well as the density of muscle nuclei. Labelling experiments with 5′-bromo-2-deoxyuridine showed that both the hypertrophy and recruitment of muscle fibres involved a rapidly proliferating population of myogenic precursor cells. The cellular mechanisms underlying the environmental modulation of muscle growth phenotype are discussed.
Seasonal Changes in the Cardiovascular, Respiratory and Metabolic Responses to Temperature and Hypoxia in the Bullfrog Rana Catesbeiana
Authors: Rocha Priscila L. , Branco Luiz G. S.
Published: April 2021

We assessed seasonal variations in the effects of temperature on hypoxia-induced alterations in the bullfrog Rana catesbeiana by measuring the heart rate, arterial blood pressure, breathing frequency, metabolic rate, blood gas levels, acid–base status and plasma glucose concentration. Regardless of the season, decreased body temperature was accompanied by a reduction in heart and breathing frequencies. Lower temperatures caused a significant decrease in arterial blood pressure during all four seasons. Hypoxia-induced changes in breathing frequency were proportional to body temperature and were more pronounced during winter, less so during spring and autumn and even smaller during summer. Season had no effect on the relationship between hypoxia and heart rate. At any temperature tested, the rate of oxygen consumption had a tendency to be highest during summer and lowest during winter, but the difference was significant only at 35 °C. The and pH values showed no significant change during the year, but was almost twice as high during winter than in summer and spring, indicating increased plasma bicarbonate levels. Lower temperatures were accompanied by decreased plasma glucose levels, and this effect was greater during summer and smaller during autumn. Hypoxia-induced hyperglycaemia was influenced by temperature and season. During autumn and winter, plasma glucose level remained elevated regardless of temperature, probably to avoid dehydration and/or freezing. In winter, the bullfrog may be exposed not only to low temperatures but also to hypoxia. These animals show temperature-dependent responses that may be beneficial since at low body temperatures the set-points of most physiological responses to hypoxia are reduced, regardless of the season.
Nitric oxide and cyclic GMP modulate photoreceptor cell responses in the visual system of the locust
Authors: Schmachtenberg Oliver , Bicker Gerd
Published: April 2021

Nitric oxide (NO) is a membrane-permeant messenger molecule which activates the cyclic GMP (cGMP)-synthesizing enzyme soluble guanylyl cyclase. Using cytochemical techniques, we recently reported NO-induced cGMP immunoreactivity in the photoreceptor cells of the compound eye of the locust Schistocerca gregaria and also detected NADPH diaphorase staining, a marker of NO synthase, in a subset of the monopolar cells of the lamina. By recording the corneal electroretinogram (ERG), we found that the application of neurochemicals that raise NO/cGMP levels in the optic lobe increased the ERG amplitude, whereas the experimental reduction of NO levels caused a decrease in the response to light. An increase in the light response was also found in intracellular recordings after application of a NO donor, suggesting that the NO-induced changes in the ERG are not caused by changes in the resistive isolation of the retina. Our cytochemical and electrophysiological data are both consistent with the hypothesis that NO synthesized in monopolar cells is a retrograde messenger to the presynaptic photoreceptor neurones.
Chloride channels in the eel intestine
Authors: Bicho A. , Ferreira H. Gil , Ferreira K. Gil
Published: April 2021

Patches of freshly isolated epithelial cells from eel Anguilla anguilla intestine bathed by the same solution on both sides in the cell-attached configuration had conductances of 57.0±1.8 pS (for positive voltages) and 13.3±0.7 pS (for negative voltages) (means ± S.E.M., N=25). Electrical activity was spontaneous in the cell-attached configuration, but was frequently lost after excision. In inside-out patches, channel activity was restored by strong hyperpolarization (−150 mV for 5 s) or depolarization (+150 mV for 5 s). Channel activity was inhibited by the Cl− transport blocker DIDS (1 mmol l−1).

The membrane potential measured using the nystatin slow whole-cell technique in primary cultured eel intestine epithelial cells was −35.4±1.0 mV (N=14), similar to the expected equilibrium potential for Cl− (−38.2 mV). Removal of Cl− from the bath or application of DIDS caused 16 mV and 6–7 mV depolarizing shifts in reversal potential, respectively. In one experiment, DIDS also induced a reduction in cell conductance from 0. 011±0.014 to 0.002±0.005 nS. The addition of 0.5 mmol l−1 8-(4-chlorophenylthio)-adenosine 3′,5′-cyclic monophosphate (a membrane-permeable analogue of cyclic AMP) to the bath caused an increase in conductance without affecting the reversal potential.
Load–Elongation Characteristics Of in vivo Human Tendon and Aponeurosis
Authors: Maganaris Constantinos N. , Paul John P.
Published: April 2021

In the present study, we measured the in vivo load–elongation characteristics of the human tibialis anterior tendon and its central aponeurosis. Measurements were taken in five men using dynamometry, muscle electrical stimulation and ultrasonography. Percutaneous tetanic stimulation of the muscle at successive voltages corresponding to 20, 40, 60, 80 and 100 % of maximum isometric dorsiflexion moment was applied. During electrical stimulation, we recorded the displacements of the tibialis anterior tendon origin and its aponeurosis proximal end using B-mode ultrasonography. Aponeurosis displacement was calculated by subtracting tendon displacement from the displacement of the aponeurosis proximal end. Tendon and aponeurosis displacements increased curvilinearly from 1.3 to 4 mm and from 3.7 to 12 mm, respectively, as a function of dorsiflexion load. Scaling of the displacements recorded to the resting lengths (measured over the skin) yielded strain values that increased curvilinearly with load, from 0.8 to 2.5 % in the tendon and from 2.1 to 7 % in the aponeurosis. Tendon strain was smaller by between 61 and 64 % compared with aponeurosis strain at any given contraction level. These findings are in line with reports from in vitro isolated material testing and have important implications for muscle modelling.
Effects Of Complex Radiative And Convective Environments On The Thermal Biology Of The White-Crowned Sparrow (Zonotrichia Leucophrys Gambelii)
Authors: Wolf Blair O. , Wooden K. Mark , Walsberg Glenn E.
Published: April 2021

The energy budgets of small endotherms are profoundly affected by characteristics of the physical environment such as wind speed, air temperature and solar radiation. Among these, solar radiation represents a potentially very large heat load to small animals and may have an important influence on their thermoregulatory metabolism and heat balance. In this investigation, we examined the interactive effects of wind speed and irradiance on body temperature, thermoregulatory metabolism and heat balance in the white-crowned sparrow (Zonotrichia leucophrys gambelii). We measured changes in metabolic heat production by exposing birds to different wind speeds (0.25, 0.5, 1.0 and 2.0 m s−1) and irradiance combinations (<3W m−2 and 936±11 W m−2; mean ± S.D.) at an air temperature of 10 °C.

Body temperature was not affected by wind speed, but was significantly higher in animals not exposed to simulated solar radiation compared with those exposed at most wind speeds. In the absence of solar radiation, metabolic heat production was strongly affected by wind speed and increased by 30 % from 122 to 159 W m−2 as wind speed increased from 0.25 to 2.0 m s−1. Metabolic heat production was even more strongly influenced by wind speed in the presence of simulated solar radiation and increased by 51 % from 94 to 142 W m−2 as wind speed increased from 0.25 to 2.0 m s−1. Solar heat gain was negatively correlated with wind speed and declined from

28 to 12 W m−2 as wind speed increased from 0.25 to 2.0m s−1 and, at its maximum, equaled 11 % of the radiation intercepted by the animal. The overall thermal impact of the various wind speed and irradiance combinations on the animal’s heat balance was examined for each treatment. Under cold conditions, with no solar radiation present, an increase in wind speed from 0.25 to 2.0m s−1 was equivalent to a decrease in chamber air temperature of 12.7 °C. With simulated solar radiation present, a similar increase in wind speed was equivalent to a decrease in chamber air temperature of 16 °C. Overall, shifting environmental conditions from a wind speed of 0.25 m s−1 and irradiance of 936 W m−2 to a wind speed of 2.0m s−1 with no short-wave radiation present was equivalent to decreasing chamber air temperature by approximately 20 °C.

The sensitivity to changes in the convective environment, combined with the complex effects of changes in irradiance levels revealed by re-analyzing data published previously, significantly complicates the task of estimating the heat balance of animals in nature.
Spray Mechanism of the Most Primitive Bombardier Beetle (Metrius Contractus)
Authors: Eisner Thomas , Aneshansley Daniel J. , Eisner Maria , Attygalle Athula B. , Alsop David W. , Meinwald Jerrold
Published: April 2021

The bombardier beetle Metrius contractus discharges its defensive secretion as a froth that clings to its body. When attacked from the rear, it allows the froth to build up over the gland openings near the abdominal tip; when attacked from the front, it conveys the secretion forwards along special elytral tracks. M. contractus has two-chambered defensive glands typical of bombardier beetles, and its secretion, like that of other bombardiers, is quinonoid and hot. Its frothing mechanism, however, is unique for bombardiers and possibly illustrative of the ancestral glandular discharge mechanism of these beetles. M. contractus, thus, could be the least derived of extant bombardiers.
Ocellar Pigmentation and Phototaxis in the Nematode Mermis Nigrescens: Changes During Development
Authors: Burr A. H. Jay , Wagar Donna , Sidhu Parmjit
Published: April 2021

After 1 or 2 years of dormancy in the soil, Mermis nigrescens females emerge to lay eggs on vegetation where their grasshopper hosts are likely to feed. Females collected at this life stage exhibit a strong positive phototaxis and have a tubular region of pigmentation near the anterior tip consisting of concentrated oxyhaemoglobin. A previous investigation of the scanning motion of the ‘head’ and orientation of the ‘neck’ has implicated the shadowing of a photoreceptor inside the tube as the mechanism for identifying the direction of light during phototaxis. Here, we describe the development of the pigment in young adult females and investigate phototaxis in early developmental stages that lack the pigment. The orientation of the neck to a horizontal 420 nm stimulus (intensity 1013 photons s−1 cm−2) was measured for unpigmented fourth-stage larvae and immature adult females as well as mature females with pigmented ocelli. The orientation of the larvae and immature adults was weakly negative, whereas that of the mature adults was strongly positive. Head and neck movements were otherwise the same in the three stages. Thus, the pigmentation appears to be required for positive phototaxis, and the results provide further support for the shadowing role of ocellar haemoglobin.
Energy Metabolism of the Virginia Opossum During Fasting and Exercise
Authors: Weber Jean-Michel , O’connor Timothy
Published: April 2021

Rates of oxygen consumption and CO2 production were measured in Virginia opossums (Didelphis virginiana) during fasting and prolonged exercise to quantify changes in total energy expenditure and oxidative fuel selection. We hypothesized that fasting would cause metabolic depression and a progressive shift towards lipid utilization to spare alternative substrates. It was also predicted that prolonged exercise would cause the same relative changes in fuel preference as fasting, but on a compressed time scale. The results show that hypometabolism is not used by the Virginia opossum to cope with food deprivation. However, a rapid exhaustion of limited carbohydrate reserves is prevented through a sixfold reduction in the percentage contribution of carbohydrates to total energy expenditure made possible by an increase in lipid utilization. No protein sparing is observed in this species. Prolonged low-intensity exercise elicits a potent mobilization of lipids that allows maximal running time to be extended by delaying the depletion of limited carbohydrate reserves. We conclude that fasting and prolonged low-intensity exercise cause similar changes in the relative use of lipids and carbohydrates, but on a different time scale, supporting the idea that endurance exercise is the metabolic equivalent of ‘accelerated fasting’. The absence of metabolic depression and protein sparing during fasting shows that such physiological strategies have not been necessary for the rapid range expansion towards the North recently shown by this species.
The Effect Of Metabolic Depression on Proton Leak Rate in Mitochondria From Hibernating Frogs
Authors: St-Pierre J. , Brand M.D. , Boutilier R.G.
Published: April 2021

Futile cycling of protons across the mitochondrial inner membrane accounts for 20 % or more of the total standard metabolic rate of a rat. Approximately 15 % of this total is due to proton leakage inside the skeletal muscle alone. This study examined whether the rate of proton leak is down-regulated as a part of a coordinated response to energy conservation during metabolic depression in cold-submerged frogs. We compared the proton leak rate of skeletal muscle mitochondria isolated from frogs at different stages of hibernation (control, 1 month and 4 months of submergence in normoxia and hypoxia). The kinetics of mitochondrial proton leak rate was unaltered throughout normoxic and hypoxic submergence. The state 4 respiration rates did not differ between control animals and frogs hibernating in normoxia. In contrast, the state 4 respiration rates obtained from frogs submerged in hypoxic water for 4 months were half those of control animals. This 50 % reduction in respiration rate in hypoxic hibernation was due to a reduction in electron transport chain activity and consequent decrease in mitochondrial membrane potential. We conclude that proton leak rate is reduced during metabolic depression as a secondary result of a decrease in electron transport chain activity, but that the proton conductance is unchanged. In addition, we show that the rate of proton leakage and the activity of the electron transport chain are lower in frogs than in rats, strengthening the observation that mitochondria from ectotherms have a lower proton conductance than mitochondria from endotherms.
Effects of Fish Size and Temperature On Weakfish Disturbance Calls: Implications For the Mechanism of Sound Generation
Authors: Connaughton M. A. , Taylor M. H. , Fine M. L.
Published: April 2021

To categorize variation in disturbance calls of the weakfish Cynoscion regalis and to understand their generation, we recorded sounds produced by different-sized fish, and by similar-sized fish at different temperatures, as well as muscle electromyograms. Single, simultaneous twitches of the bilateral sonic muscles produce a single sound pulse consisting of a two-to three-cycle acoustic waveform. Typical disturbance calls at 18 °C consist of trains of 2–15 pulses with a sound pressure level (SPL) of 74 dB re 20 μPa at 10 cm, a peak frequency of 540 Hz, a repetition rate of 20 Hz and a pulse duration of 3.5 ms. The pulse duration suggests an incredibly short twitch time. Sound pressure level (SPL) and pulse duration increase and dominant frequency decreases in larger fish, whereas SPL, repetition rate and dominant frequency increase and pulse duration decreases with increasing temperature. The dominant frequency is inversely related to pulse duration and appears to be determined by the duration of muscle contraction. We suggest that the lower dominant frequency of larger fish is caused by a longer pulse (=longer muscle twitch) and not by the lower resonant frequency of a larger swimbladder.
Allometric Relationships Between Embryonic Heart Rate and Fresh Egg Mass in Birds
Authors: Tazawa Hiroshi , Pearson James T. , Komoro Takashi , Ar Amos
Published: April 2021

Previously, we have measured daily changes (developmental patterns) in embryonic heart rate (fH) in altricial and semi-altricial (ASA) birds (range of mean fresh egg mass approximately 1–20 g), semi-precocial seabirds (egg mass approximately 38–288 g) and precocial birds (egg mass approximately 6–1400 g). An allometric relationship between embryonic fH at 80 % of incubation duration (ID) and fresh egg mass (M) has been derived for six species of precocial bird (fH at 80 % ID=429M−0.118). In the present study, additional measurements of embryonic fH in three ASA species, the barn owl Tyto alba, the cattle egret Bubulcus ibis and the lanner falcon Falco biarmicus, were made to extend the egg mass range (20–41 g), and the allometric relationships of embryonic fH for these ASA birds and the precocial and semi-precocial (PSP) groups were investigated from published data. The developmental patterns of embryonic fH in three relatively large ASA species did not show a significant increase prior to the pipping period, unlike those in small ASA birds, but tended to be constant, with a subsequent increase during pipping. The allometric relationship derived for ASA birds was Fh at 80 % ID=371M−0.121 (r=−0.846, P<0.001, N=20) and that for PSP birds was fH at 80 % ID=433M−0.121 (r=−0.963, P<0.001, N=13). The slopes were parallel, but fH of ASA embryos was low compared with that of PSP embryos with the same egg mass. In ASA birds, embyronic fH was maximal during the pipping (perinatal) period, and the maximum fH (fHmax) was significantly related to fresh egg mass: fHmax=440M−0.127 (r=−0.840, P<0.001, N=20). The allometric relationships for fH at 80 % ID in PSP and fHmax in ASA embryos were statistically identical. Accordingly, embryonic fH at 80 % ID in PSP birds and fHmax during pipping in ASA birds can be expressed by a single allometric equation: fH=437M−0.123 (r=−0.948, P<0.001, N=33).
Molecular Characterization Of V-Type H+-ATPase (B-Subunit) In Gills Of Euryhaline Crabs And Its Physiological Role In Osmoregulatory Ion Uptake
Authors: Weihrauch Dirk , Ziegler Andreas , Siebers Dieter , Towle David W.
Published: April 2021

The vacuolar-type H+-ATPase (V-ATPase) has been implicated in osmoregulatory ion uptake across external epithelia of a growing variety of species adapted to life in fresh water. In the present study, we investigated whether the V-ATPase may also function in a euryhaline species that tolerates brackish water (8 ‰ salinity) but not fresh water, the shore crab Carcinus maenas. cDNA coding for the regulatory B-subunit of the V-ATPase was amplified and sequenced from C. maenas gills and partially sequenced from four other crab species. Two isoforms differing in the 3′-untranslated region were found in C. maenas. In this species, the abundance of B-subunit mRNA was greater in the respiratory anterior gills than the ion-transporting posterior gills and was not increased by acclimation to dilute salinity. Immunocytochemical analysis showed that the B-subunit protein is not targeted to the apical membrane but is distributed throughout the cytoplasmic compartment. Physiological studies of isolated perfused gills indicated that the V-ATPase inhibitor bafilomycin had no effect on transepithelial potential difference. Thus, in contrast to the freshwater-tolerant Chinese crab Eriocheir sinensis, in which the V-ATPase appears to play an important osmoregulatory role, the V-ATPase in C. maenas probably functions in acidification of intracellular organelles but not in transbranchial NaCl uptake.
Contractile Properties of the Elasmobranch Rectal Gland
Authors: Evans David H. , Piermarini Peter M.
Published: April 2021

The importance of the rectal gland in elasmobranch osmoregulation is well established. The rate of secretion by the gland is under the control of a variety of secretagogues and inhibitors. Early morphological work suggested that a band of smooth muscle cells surrounds the periphery of the shark rectal gland between the secretory tubules and the connective tissue capsule. To confirm the presence of the muscle ring, we examined histological sections from two species of shark, Squalus acanthias and Carcharodon carcharius, and from the stingray Dasyatis sabina and stained sections from S. acanthias with the actin-specific ligand phalloidin. In all three species, a distinct band of what appeared to be smooth muscle cells was evident, and the putative muscle ring in S. acanthias stained specifically with phalloidin. Moreover, isolated rings of rectal gland tissue from S. acanthias constricted when acetylcholine or endothelin was applied and responded to nitric oxide with an initial dilation, followed by a more substantial constriction. Subsequent addition of porcine C-type natriuretic peptide dilated the rings, but two prostanoids (carbaprostacyclin and prostaglandin E1) did not change ring tension significantly. The rings did not respond to the endothelin-B-specific agonist sarafotoxoin S6c, suggesting that the response to endothelin was mediated via endothelin-A-type receptors. Our data confirm the presence of a smooth muscle ring in the periphery of the elasmobranch rectal gland and demonstrate that the gland responds to a suite of smooth muscle agonists, suggesting that changes in the dimensions of the whole rectal gland may play a role in its secretory function.
The Boundary Layer of Swimming Fish
Authors: Anderson Erik J. , Mcgillis Wade R. , Grosenbaugh Mark A.
Published: April 2021

Tangential and normal velocity profiles of the boundary layer surrounding live swimming fish were determined by digital particle tracking velocimetry, DPTV. Two species were examined: the scup Stenotomus chrysops, a carangiform swimmer, and the smooth dogfish Mustelus canis, an anguilliform swimmer. Measurements were taken at several locations over the surfaces of the fish and throughout complete undulatory cycles of their propulsive motions. The Reynolds number based on length, Re, ranged from 3×103 to 3×105. In general, boundary layer profiles were found to match known laminar and turbulent profiles including those of Blasius, Falkner and Skan and the law of the wall. In still water, boundary layer profile shape always suggested laminar flow. In flowing water, boundary layer profile shape suggested laminar flow at lower Reynolds numbers and turbulent flow at the highest Reynolds numbers. In some cases, oscillation between laminar and turbulent profile shapes with body phase was observed. Local friction coefficients, boundary layer thickness and fluid velocities at the edge of the boundary layer were suggestive of local oscillatory and mean streamwise acceleration of the boundary layer. The behavior of these variables differed significantly in the boundary layer over a rigid fish. Total skin friction was determined. Swimming fish were found to experience greater friction drag than the same fish stretched straight in the flow. Nevertheless, the power necessary to overcome friction drag was determined to be within previous experimentally measured power outputs.

No separation of the boundary layer was observed around swimming fish, suggesting negligible form drag. Inflected boundary layers, suggestive of incipient separation, were observed sporadically, but appeared to be stabilized at later phases of the undulatory cycle. These phenomena may be evidence of hydrodynamic sensing and response towards the optimization of swimming performance.
Sarcomere Number Regulation Maintained After Immobilization In Desmin-Null Mouse Skeletal Muscle
Authors: Shah Sameer B. , Peters David , Jordan Kimberly A. , Milner Derek J. , Fridén Jan , Capetanaki Yassemi , Lieber Richard L.
Published: April 2021

The serial sarcomere number of skeletal muscle changes in response to chronic length perturbation. The role of the intermediate filament desmin in regulating these changes was investigated by comparing the architectural adaptations of the tibialis anterior, extensor digitorum longus (EDL) and soleus from wild-type mice with those of homozygous desmin knockout mice after hindlimb immobilization. After 28 days, serial sarcomere number increased significantly in the lengthened wild-type tibialis anterior (by approximately 9 %) and EDL (by approximately 17 %). Surprisingly, muscles from desmin knockout mice also experienced significant serial remodeling, with the serial sarcomere number of the tibialis anterior increasing by approximately 10 % and that of the EDL by approximately 27 %. A consistent result was observed in the shortened soleus: a significant decrease in sarcomere number was observed in the muscles from both wild-type (approximately 26 %) and knockout (approximately 12 %) mice. Thus, although desmin is not essential for sarcomerogenesis or sarcomere subtraction in mouse hindlimb muscles, the results do suggest subtle differences in the nature of sarcomere number adaptation. We speculate that desmin may play a role in regulating the optimal arrangement of sarcomeres within the muscle or in sensing the magnitude of the immobilization effect itself.
A Novel Mechanism of Body Mass Regulation
Authors: Adams Christopher S. , Korytko Andrew I. , Blank James L.
Published: April 2021

While significant attention has been devoted to the identification of hormonal factors that control body mass, little attention has been paid to the role of mechanical loading on animal mass. Here, we provide evidence that intraperitoneal implantation of metabolically inert mass results in a compensatory reduction in tissue mass. Deer mice (Peromyscus maniculatus) were surgically implanted with weights of 1, 2 or 3 g. There was a resulting loss of tissue mass (total body mass minus implant mass) that was proportional to the mass of the implant. This reduction in tissue mass followed a reduction in food intake in animals with 3 g implants. Evaluation of body composition failed to identify any single component that contributed to the loss of tissue mass. Removal of implants led to a transient restoration of body mass to levels similar to the total body mass of those control animals in which the implant had not been removed. However, within 12 days of implant removal, body mass again declined to the level seen before implant removal. These results suggest the existence of a set point that is sensitive to changes in the perception of mass and that is transduced via neural pathways.
Three-Dimensional Kinematics of Skeletal Elements in Avian Prokinetic and Rhynchokinetic Skulls Determined By Roentgen Stereophotogrammetry
Authors: Gussekloo Sander W. S. , Vosselman M. George , Bout Ron G.
Published: April 2021

Several different types of cranial kinesis are present within modern birds, enabling them to move (part of) the upper bill relative to the braincase. This movement of the upper bill results from movement of the quadrate and the pterygoid–palatine complex (PPC). The taxon Palaeognathae is characterised by a very distinct PPC and a special type of cranial kinesis (central kinesis) that is very different from that found in the Neognathae. This has led some authors to hypothesise that there is a functional relationship between the morphology of the PPC and the type of cranial kinesis.

This hypothesis is tested here by analysing the movement pattern of both the upper bill and the PPC in birds with three different types of cranial kinesis: prokinesis, distal rhynchokinesis and central rhynchokinesis. Movement patterns were determined using a Roentgen stereophotogrammetry method, which made it possible to detect very small displacements (0.5 mm) of bony elements in three dimensions, while the jaw muscles and ligaments remained intact.

We found that in all types of kinesis investigated the movements of the quadrate, jugal bars and PPC are similar. Movement of the quadrate is transferred to the upper beak by the jugal bar and the PPC, which moves almost exclusively forwards and backwards, thereby elevating or depressing the upper bill. The differences between the types of kinesis lie only in the position of the point of rotation.

These findings indicate that there is no correlation between the specific morphology of the PPC and the type of cranial kinesis. Several other factors, including the external forces applied during food acquisition, may influence the morphology of the PPC. Differences in PPC morphology therefore appear to be the result of different functional demands acting on the system simultaneously but with different strengths, depending on the species.
The Anisotropic Young’s Modulus of Equine Secondary Osteones and Interstitial Bone Determined by Nanoindentation
Authors: Rho Jae-Young , Currey John D. , Zioupos Peter , Pharr George M.
Published: April 2021

The equine radius is a useful subject for examining the adaptation of bone histology to loading because in life the anterior cortex is loaded almost entirely in tension, the posterior cortex in compression. The histology of the two cortices is correspondingly different, the osteones and the interstitial lamellae in the posterior cortex having a more transversely oriented fibre arrangement than those in the anterior cortex. Presumably as a result of this histological difference, the posterior cortex is stronger in compression than the anterior cortex; the anterior cortex is stronger in tension than the posterior cortex. We here use nanoindentation to examine how the Young’s modulus of elasticity of secondary osteones and interstitial lamellae in the anterior and posterior cortices varied as a function of angle.

The anterior osteones were stiffer than the posterior osteones when tested in the direction parallel to the bone’s long axis, but became progressively relatively less stiff as the angle increased; at 90 °, they were less stiff than the posterior osteones. Although the interstitial lamellae were stiffer than their neighbouring osteones, the same relationship between anterior and posterior interstitial lamellae as a function of angle was found as for the osteones. The anisotropy of these Young’s moduli determined by nanoindentation shows a close relationship with what was to be expected from the histological findings.