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PubMed2005

The selective glucocorticoid receptor antagonist ORG 34116 decreases immobility time in the forced swim test and affects cAMP-responsive element-binding protein phosphorylation in rat brain.

Glucocorticoid receptor (GR) antagonists can block the retention of the immobility response in the forced swimming test. Recently, we showed that forced swimming evokes a distinct spatiotemporal pattern of cAMP-responsive element-binding protein (CREB) phosphorylation in the dentate gyrus (DG) and neocortex. In the present study, we found that chronic treatment of rats with the selective GR antagonist ORG 34116 decreased the immobility time in the forced swim test, increased baseline levels of phosphorylated CREB (P-CREB) in the DG and neocortex and affected the forced swimming-induced changes in P-CREB levels in a time- and site-specific manner. Overall, we observed that, in control rats, forced swimming evoked increases in P-CREB levels in the DG and neocortex, whereas in ORG 34116-treated animals a major dephosphorylation of P-CREB was observed. These observations underscore an important role of GRs in the control of the phosphorylation state of CREB which seems to be of significance for the immobility response in the forced swim test and extend the molecular mechanism of action of GRs in the brain.

Administration, Oral↗
PubMed1990

Swimming causes myosin adaptations in the rat cardiac isograft.

To investigate the contributions of humoral and hemodynamic factors to cardiac adaptations associated with chronic exercise, female Fischer 344 rats were subjected to chronic swimming, infrarenal cardiac transplantation, or both. Swimming resulted in hypertrophy (11-12%) of the in situ hearts in both the unoperated and operated animals compared with the matched sedentary controls. The cardiac isograft exhibited atrophy (32-35%), which was not attenuated by swimming. The cardiac isograft was also associated with a decrease in the percent of V1 myosin isoenzyme, which was attenuated by swimming (45 +/- 5% versus 66 +/- 6%). Swimming also increased the percent of this isomyosin in the in situ hearts of operated rats. These data suggest that hemodynamic load and/or neural innervation are necessary for hypertrophy associated with chronic conditioning by swimming, whereas myosin isoenzyme control is significantly mediated by humoral factors.

Adaptation, Physiological↗
PubMedDate not supplied

Cardiovascular responses to swimming.

The authors examined cardiovascular responses to long-distance fin swimming as compared to freestyle swimming. Elite male fin swimmers (n = 17) swam 8 km in the open sea (group A) and 17 top freestyle endurance swimmers (group B) swam 6 km in the open sea. The swimming times of the 2 groups did not differ significantly. The heart rate and mean blood pressure were higher in group B than in group A after exercise. As estimated from the systolic time intervals (STI), total electromechanical systole index (QS(2)I) and electrical systole index (QTI) increased and QT-QS(2) decreased in both types of swimming. These changes were more marked in fin swimmers. Moreover, the preejection period (PEPI) and the preejection period to left ventricular ejection time ratio (PEP/LVET) significantly decreased in both groups, while LVET remained constant in the 2 swimming events. Likewise, the amount of change in PEP/LVET was more pronounced in group A. Finally, only the QT-QS(2) changes were associated with performance efforts in both groups. Therefore, there are quantitative cardiovascular differences between these types of swimming that should be primarily attributed to the different muscle mass effort involved.

Adolescent↗
PubMed1985

A mutant of Chlamydomonas reinhardtii that lacks the flagellar outer dynein arm but can swim.

A new type of Chlamydomonas mutant, which lacks the outer dynein arm but can swim, was isolated. Sodium dodecyl sulphate/polyacrylamide gel electrophoresis showed that four of the ten high-molecular-weight bands of dynein present in the wild-type axoneme are missing or diminished in the mutant axoneme. The mutant has a swimming rate of about 35 micrometers/s and a flagellar beat frequency of about 25 Hz, both of which are about 1/2.5 to 1/3 of those of the wild type. The mutant flagella beat with an asymmetric, cilia-type pattern, similar to the forward-swimming mode of the flagellar beating pattern of the wild type. However, unlike wild-type flagella, the mutant flagella never beat with a symmetrical waveform: when the cells were stimulated by intense light, the mutant transiently stopped beating its flagella, whereas the wild-type cell transiently swam backwards with the two flagella beating with a symmetrical waveform. Both wild-type and mutant cells could be demembranated by Nonidet P40 and their swimming reactivated by addition of Mg-ATP in the virtual absence of Ca2+. Double reciprocal plots of the beat frequency against ATP concentrations showed a linear relationship for both strains, yielding maximal frequencies of 44 Hz (wild-type) and 23 Hz (mutant). The mutant axonemes can be reactivated only when the Ca2+ concentration is lower than 10(-6) M: at pCa4, the wild-type axonemes beat with a symmetrical waveform, but the mutant axonemes showed no movement. These findings indicate that the outer dynein arm is dispensable for flagellar beating of the asymmetric waveform (forward-swimming mode), but not for beating of the symmetrical waveform (backward-swimming mode), and thus suggest the importance of the outer dynein arm in the switching of flagellar waveforms.

Chlamydomonas↗
PubMed2004

Kinematics and hydrodynamics of swimming in the mayfly larva.

The kinematics and hydrodynamics of free-swimming mayfly larvae (Chloeon dipterum) were investigated with the aid of a simple wake visualisation technique (tracer dyes) and drag measurements on dead insects. The basic swimming movement consists of a high-amplitude dorso-ventral undulation and, during continuous swimming, this produces a wake of ring vortices shed alternately to the dorsal and ventral sides of the body. The ring vortices propagate laterally away from the body at an angle of approximately 80 degrees relative to dead aft of the swimming line. Thus, mayfly larvae, like damsel-fly larvae, resemble eels in producing a wake consisting of separate vortices that propagate laterally rather than the reverse von Karman vortex street characteristic of most caudal fin swimming fish. The thrust estimated from the momentum in the wake of swimming mayfly larvae was comparable with the drag measured on dead specimens. Possible sources of error in these estimates are discussed, but the conclusion is reached that even though only 14% of the total force generated by vortex production is directed forwards, it is still sufficient to account for the thrust required for steady locomotion.

Animals↗
PubMed2004

The hydrodynamics of eel swimming: I. Wake structure.

Eels undulate a larger portion of their bodies while swimming than many other fishes, but the hydrodynamic consequences of this swimming mode are poorly understood. In this study, we examine in detail the hydrodynamics of American eels (Anguilla rostrata) swimming steadily at 1.4 L s(-1) and compare them with previous results from other fishes. We performed high-resolution particle image velocimetry (PIV) to quantify the wake structure, measure the swimming efficiency, and force and power output. The wake consists of jets of fluid that point almost directly laterally, separated by an unstable shear layer that rolls up into two or more vortices over time. Previously, the wake of swimming eels was hypothesized to consist of unlinked vortex rings, resulting from a phase offset between vorticity distributed along the body and vorticity shed at the tail. Our high-resolution flow data suggest that the body anterior to the tail tip produces relatively low vorticity, and instead the wake structure results from the instability of the shear layers separating the lateral jets, reflecting pulses of high vorticity shed at the tail tip. We compare the wake structure to large-amplitude elongated body theory and to a previous computational fluid dynamic model and note several discrepancies between the models and the measured values. The wake of steadily swimming eels differs substantially in structure from the wake of previously studied carangiform fishes in that it lacks any significant downstream flow, previously interpreted as signifying thrust. We infer that the lack of downstream flow results from a spatial and temporal balance of momentum removal (drag) and thrust generated along the body, due to the relatively uniform shape of eels. Carangiform swimmers typically have a narrow caudal peduncle, which probably allows them to separate thrust from drag both spatially and temporally. Eels seem to lack this separation, which may explain why they produce a wake with little downstream momentum while carangiform swimmers produce a wake with a clear thrust signature.

Analysis of Variance↗
PubMed2004

Effects of swimming on metabolic recovery from anoxia in the painted turtle.

Anoxic submergence in the Western painted turtle results in a severe metabolic acidosis characterized by high plasma lactate and depressed arterial pH, a response similar to that seen in other vertebrates following exhaustive exercise. We tested the hypothesis that 1 or 2 h of aerobic swimming following anoxic submergence would enhance the rate of lactate disappearance from the blood just as sustained aerobic exercise does in mammals and fishes following strenuous exercise. Following 2 h of anoxic submergence at 25 degrees C and 1 h of recovery, the pattern of plasma lactate disappearance in turtles previously trained to swim in a flume and swum aerobically (2-3x resting V(O(2))) for 1 or 2 h did not differ significantly from that in trained and untrained non-swimming turtles. Turtles were fully recovered by 7-10 h post-anoxia. The response patterns also did not differ between treatments for arterial P(O(2)), P(CO(2)), pH, and plasma glucose and HCO(3)(-). Blood pH and plasma HCO(3)(-) recovered by 1 and 4 h, respectively. Despite the large lactate load, painted turtles are able to sustain periods of continuous swimming for at least 2 h without compromising metabolic recovery. Although this activity did not consistently enhance recovery, the rate of lactate disappearance was positively correlated with oxygen consumption rate in actively and passively recovering turtles. We suggest that active recovery was not a more important enhancer of recovery either because swimming may have had an inhibitory effect on hepatic gluconeogenesis or that there is variation in fuel utilization during the swimming period.

Analysis of Variance↗
PubMed2004

Swimming of larval zebrafish: fin-axis coordination and implications for function and neural control.

Adult actinopterygian fishes typically perform steady forward swimming using either their pectoral fins or their body axis as the primary propulsor. In most species, when axial undulation is employed for swimming, the pectoral fins are tucked (i.e. adducted) against the body; conversely, when pectoral fins are beating, the body axis is held straight. In contrast to adults, larval fishes can combine their pectoral fin and body-axis movements during locomotion; however, little is known about how these locomotor modes are coordinated. With this study we provide a detailed analysis of the coordinated fin and axial movements during slow and fast swimming by examining forward locomotion in larval zebrafish (Danio rerio L.). In addition, we describe the musculature that powers pectoral fin movement in larval zebrafish and discuss its functional implications. As larvae, zebrafish alternate their pectoral fins during slow swimming (0.011+/-0.001 mm ms(-1)) in conjunction with axial undulations of the same frequency (18-28 Hz). During fast swimming (0.109+/-0.030 mm ms(-1); 36-67 Hz), the fins are tucked against the body and propulsion occurs by axial undulation alone. We show that during swimming, larval fishes can use a similar limb-axis coordination pattern to that of walking and running salamanders. We suggest that the fin-axis coordination observed in larval zebrafish may be attributed to a primitive neural circuit and that early terrestrial vertebrates may have gained the ability to coordinate limbs and lateral bending by retaining a larval central pattern generator for limb-axis coordination in the adult life history stage.

Animals↗
PubMed2006

Swim speeds and stroke patterns in wing-propelled divers: a comparison among alcids and a penguin.

In diving birds, the volume and resulting buoyancy of air spaces changes with dive depth, and hydrodynamic drag varies with swim speed. These factors are important in the dive patterns and locomotion of alcids that use their wings both for aerial flight and underwater swimming and of penguins that use their wings only for swimming. Using small data-loggers on free-ranging birds diving to 20-30 m depth, we measured depth at 1 Hz and surge and heave accelerations at 32-64 Hz of four species of alcids (0.6-1.0 kg mass) and the smallest penguin species (1.2 kg). Low- and high-frequency components of the fluctuation of acceleration yielded estimates of body angles and stroke frequencies, respectively. Swim speed was estimated from body angle and rate of depth change. Brünnich's (Uria lomvia) and common (Uria aalge) guillemots descended almost vertically, whereas descent of razorbills (Alca torda), rhinoceros auklets (Cerorhinca monocerata) and little penguins (Eudyptula minor) was more oblique. For all species, swim speed during descent was within a relatively narrow range. Above depths of 20-30 m, where they were all positively buoyant, all species ascended without wing stroking. During descent, little penguins made forward accelerations on both the upstroke and downstroke regardless of dive depth. By contrast, descending alcids produced forward accelerations on both upstroke and downstroke at depths of <10 m but mainly on the downstroke at greater depths; this change seemed to correspond to the decrease of buoyancy with increasing depth. The magnitude of surge (forward) acceleration during downstrokes was smaller, and that during upstrokes greater, in little penguins than in alcids. This pattern presumably reflected the proportionally greater mass of upstroke muscles in penguins compared with alcids and may allow little penguins to swim at less variable instantaneous speeds.

Animals↗
PubMed2006

Development of swimming behaviour in the larva of the ascidian Ciona intestinalis.

The aim of this study was to characterize the swimming behaviour of C. intestinalis larvae during the first 6 h after hatching by measuring tail muscle field potentials. This recording method allowed a quantitative description of the responses of the larva under light and dark conditions. Three different larval movements were distinguished by their specific frequencies: tail flicks, 'spontaneous' swimming, and shadow response, or dark induced activity, with respective mean frequencies of about 10, 22 and 32 Hz. The shadow response develops at about 1.5 h post hatching (h.p.h.). The frequency of muscle potentials associated with this behaviour became higher than those of spontaneous swimming activity, shifting from 20 to 30 Hz, but only from about 2 h.p.h. onwards. Swimming rate was influenced positively for about 25 s after the beginning of the shadow response. Comparison of swimming activity at three different larval ages (0-2, 2-4 and 4-6 h.p.h.) showed that Ciona larvae swim for longer periods and more frequently during the first hours after hatching. Our results provide a starting point for future studies that aim to characterize the nervous control of ascidian locomotion, in wild-type or mutant larvae.

Action Potentials↗
PubMed2007

Quantitative analysis of tethered and free-swimming copepodid flow fields.

We quantified the flow field generated by tethered and free-swimming Euchaeta antarctica using the particle image velocimetry (PIV) technique. The streamlines around the free-swimming specimens were generally parallel to the body axis, whereas the streamlines around all of the tethered copepodids demonstrated increased curvature. Differences noted in the streamline pattern, and hence the vorticity, dissipation rate and strain rate fields, are explained by considering the forces on the free-swimming specimen compared to the tethered specimen. Viscous flow theory demonstrates that the force on the fluid due to the presence of the tether irrevocably modifies the flow field in a manner that is consistent with the measurements. Hence, analysis of the flow field and all associated calculations differ for tethered versus free-swimming conditions. Consideration of the flow field of the free-swimming predatory copepodid shows the intensity of the biologically generated flow and the extent of the mechanoreceptive signal quantified in terms of shear strain rate. The area in the dorso-ventral view surrounded by the 0.5 s(-1) contour of e(xy), which is a likely threshold to induce an escape response, is 11 times the area of the exoskeletal form for the free-swimming case. Thus, mechanoreceptive predators will perceive a more spatially extended signal than the body size.

Animals↗
PubMed1984

Development of swimming movements and musculature of larval herring (Clupea harengus).

A kinematic analysis was made of swimming of larval herring Clupea harengus L. Swimming style was found to change with growth and development; the amplitude of swimming movements of early post-yolk-sac larvae increases linearly towards the tail, a style of swimming which relies mainly on resistive forces for propulsion. Later, after the caudal and dorsal fins have developed, the swimming style changes, in response to an increase in Reynold's Number, such that inertial forces are more important. In this type of swimming the amplitude increases more rapidly than linearly towards the tail. The distribution of red and white muscle fibre types was studied in relation to development. On hatching, red muscle fibres were found to be arranged as a single layer on the outside of the myotomes. They develop into the adult distribution, concentrated at the midline of the flank near the skin, only after the gills and circulation become fully functional.

Animals↗
PubMed1986

Swim initiation in the leech by serotonin-containing interneurones, cells 21 and 61.

Two pairs of serotonin-containing neurones, designated cells 21 and 61, were characterized physiologically and anatomically in the hirudinid leeches Macrobdella decora and Hirudo medicinalis. Both of these cells are bilaterally paired interneurones and each cell is weakly electrically coupled to the other serotonin-containing cells both intra- and interganglionically. Cells 21 and 61 are excited polysynaptically by individual identified mechano-sensory neurones. Segmental nerve shock sufficient to elicit an episode of swimming strongly excites cells 21 and 61, which then tend to generate bursts of impulses that are phase-locked to the swim motor pattern. Intracellular stimulation of either cell 21 or cell 61 often causes the initiation of swimming, acting in parallel with the nonserotonergic swim-initiator cell 204. Cells 61 and 204 are also weakly electrically coupled. The latency to swim onset by stimulating cell 21 or 61 is similar to that of cell 204 and different from that of the serotonergic Retzius cell. This result, with those in the accompanying paper (Nusbaum, 1986), suggests that unlike the Retzius cell and similar to cell 204, cells 21 and 61 synaptically contact cells of the swim central pattern generator (CPG).

Animals↗
PubMed1988

Kinematics and estimated thrust production of swimming harp and ringed seals.

The propulsive motions of swimming harp seals (Phoca groenlandica Erxleben) and ringed seals (Phoca hispida Schreber) were studied by filming individuals in a flume. The seals swam at velocities ranging from 0.6 to 1.42 m s-1. Locomotion was accomplished with alternate lateral sweeps of the hind flippers generated by lateral flexions of the axial body in conjunction with flexion of the flippers. The frequency of the propulsive cycle increased linearly with the swimming velocity, and the maximum angle of attack of the flipper decreased, but the amplitude remained constant. The kinematics and morphology of this hind flipper motion indicated that phocid seals do not swim in the carangiform mode as categorized by Lighthill (1969), but in a distinct mode that mimics swimming by thunniform propulsors. The hind flippers acted as hydrofoils, and the efficiency, thrust power and coefficient of thrust were calculated from unsteady wing theory. The propulsive efficiency was high at approximately 0.85. The thrust power increased curvilinearly with velocity. The drag coefficient ranged from 0.012 to 0.028 and was found to be 2.8-7.0 times higher than the theoretical minimum. The drag coefficient was high compared with that of phocid seals examined during gliding or towing experiments, indicating an increased drag encumbered by actively swimming seals. It was determined that phocid seals are capable of generating sufficient power for swimming with turbulent boundary layer conditions.

Animals↗
PubMed1992

The influence of temperature on muscle function in the fast swimming scup. II. The mechanics of red muscle.

To understand better how scup can swim twice as fast as carp with its red muscle, we measured the mechanical properties of red muscle bundles in scup. The values of the mean maximum velocity of shortening (Vmax) at 10 degrees C (3.32 muscle lengths s-1) and at 20 degrees C (5.55 muscle lengths s-1; Q10 = 1.69) were nearly the same as those in carp. Isometric force, however, was approximately 50% greater (183 kN m-2; Q10 = 1.08). The maximal power generation was correspondingly about 50% greater in scup than in carp (71 W kg-1 at 10 degrees C and 134 W kg-1 at 20 degrees C; Q10 = 1.88). The larger power output of its muscle may be important in the faster swimming of the scup. In addition, the fact that scup use a less undulatory style of swimming means that, when they are swimming twice as fast, their red muscle shortens at the same velocity (V) and with the same V/Vmax (0.37, i.e. where maximum power is generated) as that of carp. The importance of V/Vmax is further shown by the comparison of scup swimming at different temperatures. The 1.69-fold higher Vmax at 20 degrees C than at 10 degrees C enables scup to swim with a 1.67-fold faster V at 20 degrees C. Thus, at both 10 degrees C and 20 degrees C, red muscle is used only over the same narrow range of V/Vmax (0.17-0.37), where experiments on isolated muscle suggest that power and efficiency are maximal. Therefore, V/Vmax appears to be an important design constraint that limits the range of velocities over which muscle is used in vivo, both at different temperatures and in fast- and slow-locomoting species.

Animals↗
PubMed1996

Squid (Lolliguncula brevis) life in shallow waters: oxygen limitation of metabolism and swimming performance.

Squid (Lolliguncula brevis) were exercised in a tunnel respirometer during a stepwise increase in water velocity in order to evaluate the anaerobic threshold, i.e. the critical swimming speed above which anaerobic metabolism contributes to energy production. The average anaerobic threshold was found at speeds of 1.5-2 mantle lengths s-1. Above this velocity, alpha-glycerophosphate, succinate and octopine started to accumulate in the mantle tissue. ATP levels fell and phospho-L-arginine was progressively depleted, while the levels of glucose 6-phosphate and inorganic phosphate rose. The finding of a simultaneous onset of anaerobic metabolism in the cytosol and the mitochondria indicates that a limited oxygen supply to the mitochondria elicits anaerobic energy production. This finding is opposite to the situation found in many other vertebrate and invertebrate species, in which energy requirements in excess of aerobic energy production are covered by anaerobic metabolism, with mitochondria remaining aerobic. In L. brevis, swimming at higher speeds is associated with a small factorial increase in metabolic rate based on a high resting rate of oxygen consumption. Pressure recordings in the mantle cavity support this finding, indicating a high basal level of spontaneous activity at rest and a small rise in mean pressure at higher swimming velocity. Bursts of higher pressures from the jet support elevated swimming speeds and may explain the early transition to anaerobic energy production which occurs when pressure amplitudes exceed 1.2-1.5 kPa or when mean pressure rises above 0.22-0.25 kPa. The finding of mitochondrial hypoxia at a low critical speed in these squid is interpreted to be related to their life in shallow coastal and bay waters, which limits the necessity to maintain high swimming velocities. At increased swimming velocities, the animals oscillate between periods of high and low muscular activity. This behaviour is interpreted to reduce transport cost and to permit a longer-term net use of anaerobic resources when speed exceeds the critical value or when the squid dive into hypoxic waters. The simultaneous onset of anaerobic metabolism in the cytosol and the mitochondria emphasizes that squid generally make maximal use of available oxygen under resting conditions, when their energy requirements are the highest among marine invertebrates.

Adenosine Triphosphate↗
PubMed1997

Energetics of swimming by the platypus Ornithorhynchus anatinus: metabolic effort associated with rowing.

The metabolism of swimming in the platypus Ornithorhynchus anatinus Shaw was studied by measurement of oxygen consumption in a recirculating water flume. Platypuses swam against a constant water current of 0.45-1.0 ms-1. Animals used a rowing stroke and alternated bouts of surface and submerged swimming. Metabolic rate remained constant over the range of swimming speeds tested. The cost of transport decreased with increasing velocity to a minimum of 0.51 at 1.0 ms-1. Metabolic rate and cost of transport for the platypus were lower than values for semiaquatic mammals that swim at the water surface using a paddling mode. However, relative to transport costs for fish, the platypus utilized energy at a similar level to highly derived aquatic mammals that use submerged swimming modes. The efficient aquatic locomotion of the platypus results from its specialised rowing mode in conjunction with enlarged and flexible forefeet for high thrust generation and a behavioral strategy that reduces drag and energy cost by submerged swimming.

Animals↗
PubMed2000

Influence of tail shape on tadpole swimming performance.

Many tadpoles respond to insect predators by developing deeper, and sometimes longer, tails. It has been assumed that the larger tail enhances aspects of swimming performance, because deep-tailed tadpoles survive well when confronted with hunting predators. We tested this hypothesis using both naturally occurring and surgically created variation in tail morphology of Hyla versicolor tadpoles. We measured swimming performance (maximum speed, time to reach a 2.5 cm radius, and angle of escape) and morphology (size and shape of the body and tail) in 288 tadpoles, of which half possessed the predator-induced morphology and the other half were from predator-free ponds. Large tadpoles swam faster than small ones, and shape was significantly correlated with size-corrected swimming performance. The fastest tadpoles had relatively shallow bodies and tail fins, and short tails; there was no difference in swimming performance between predator-induced and no-predator tadpoles. We performed an experiment to create independent variation in tail depth and length by surgically manipulating tail shape in 270 tadpoles. Three tail-length treatments reduced the length of the tail fin by 21 %, 34 % and 55 %; three tail-depth treatments reduced the maximum depth of the tail fin by 11 %, 34 % and 59 %; two additional treatments controlled for the effects of anaesthesia and surgery. The angle of escape was unaffected by surgery. Maximum speed and minimum escape time were both significantly impaired by the high-removal treatments, but showed no evidence of decline until 30 % of the tail (length or depth) was removed. These results suggest that the relatively deep tails in predator-induced tadpoles (approximately 10 % deeper than in no-predator tadpoles) do not improve performance in burst swimming. Thus, predator-induced tadpoles are less vulnerable to predation for reasons other than enhanced swimming performance.

Animals↗