The influence of temperature on power production during swimming. II. Mechanics of red muscle fibres in vivo. (57/2436)

We found previously that scup (Stenotomus chrysops) reduce neither their stimulation duration nor their tail-beat frequency to compensate for the slow relaxation rates of their muscles at low swimming temperatures. To assess the impact of this 'lack of compensation' on power generation during swimming, we drove red muscle bundles under their in vivo conditions and measured the resulting power output. Although these in vivo conditions were near the optimal conditions for much of the muscle at 20 degrees C, they were far from optimal at 10 degrees C. Accordingly, in vivo power output was extremely low at 10 degrees C. Although at 30 cm s(-)(1), muscles from all regions of the fish generated positive work, at 40 and 50 cm s(-)(1), only the POST region (70 % total length) generated positive work, and that level was low. This led to a Q(10) of 4-14 in the POST region (depending on swimming speed), and extremely high or indeterminate Q(10) values (if power at 10 degrees C is zero or negative, Q(10) is indeterminate) for the other regions while swimming at 40 or 50 cm s(-)(1). To assess whether errors in measurement of the in vivo conditions could cause artificially reduced power measurements at 10 degrees C, we drove muscle bundles through a series of conditions in which the stimulation duration was shortened and other parameters were made closer to optimal. This sensitivity analysis revealed that the low power output could not be explained by realistic levels of systematic or random error. By integrating the muscle power output over the fish's mass and comparing it with power requirements for swimming, we conclude that, although the fish could swim at 30 cm s(-)(1) with the red muscle alone, it is very unlikely that it could do so at 40 and 50 cm s(-)(1), thus raising the question of how the fish powers swimming at these speeds. By integrating in vivo pink muscle power output along the length of the fish, we obtained the surprising finding that, at 50 cm s(-)(1), the pink muscle (despite having one-third the mass) contributes six times more power to swimming than does the red muscle. Thus, in scup, pink muscle is crucial for powering swimming at low temperatures. This overall analysis shows that Q(10) values determined in experiments on isolated tissue under arbitrarily selected conditions can be very different from Q(10) values in vivo, and therefore that predicting whole-animal performance from these isolated tissue experiments may lead to qualitatively incorrect conclusions. To make a meaningful assessment of the effects of temperature on muscle and locomotory performance, muscle performance must be studied under the conditions at which the muscle operates in vivo.  (+info)

Aerobic and anaerobic swimming performance of individual Atlantic cod. (58/2436)

Individual Atlantic cod (Gadus morhua) were exercised using three different measures of swimming performance. (1) An endurance test (critical swimming speed, U(crit), protocol) designed to assess predominantly aerobic endurance swimming (duration hours). (2) An acceleration test (U(burst)), in which the fish were required to swim against a rapidly increasing current until exhausted (duration minutes). This test was designed to assess predominantly glycolytic-based swimming capacity. (3) A sprint test that examined the animals' ability to swim away from a sudden stimulus (duration seconds). Rates of oxygen consumption ( mdot (O2)) during the endurance test and various morphological variables of the individual fish were also measured. Both aerobic and anaerobic swimming performance of individual cod were found to be significantly repeatable over a 3 month period. mdot (O2) during the U(crit) protocol was also significantly repeatable at intermediate to high swimming speeds, but not at low speeds. Our results support extrapolation from metabolic rates at incremented swimming speeds to zero activity as the best way to measure standard metabolic rate in cod. While performance in the U(crit) test and the sprint test were positively correlated, there was a negative correlation between performance in the U(crit) test and performance in the U(burst) test. This implies a potential trade-off in individual cod between stamina and the ability to use glycolytic-based locomotion. Inter-individual variation in swimming performance during these protocols, while substantial, was not correlated with individual variation in fin surface areas, age or morphology. However, U(burst) performance was dependent upon the sex of the animals, while performance during the U(crit) protocol was significantly correlated with their aerobic scope for activity.  (+info)

Effect of repeated electroconvulsive shock treatment on a depression model, mouse forced swimming. (59/2436)

Mouse forced swimming is one of the behavioral depression models and repeated electroconvulsive shock (ECS) treatment has been used to human depression. In order to investigate the mechanism of the anti-depressive effect induced by repeated ECS, we investigated the effect of repeated ECS with the mouse forced swimming model. The 5 times par-day ECS remarkably increased the typical anti-depressive behavior climbing 24 hours after the final treatment. The anti-depressive activity was declined by a dopamine 1 antagonist SCH-23390 at the doses of 1 and 0.1 mg/kg, but not by the other dopamine, serotonin and adrenoceptor antagonists at the dose of 1 mg/kg. The present findings strongly suggest that the late anti-depressive effect of repeated ECS is mediated by the dopamine 1 receptor activity. The present findings will also contribute to the further investigations of the effect of repeat ECS treatments on human depression.  (+info)

Spatial working memory in rats: no differences between the sexes. (60/2436)

In a number of mammalian species, males appear to have superior spatial abilities to females. The favoured explanations for this cognitive difference are hormonal, with higher testosterone levels in males than females leading to better spatial performance, and evolutionary, where sexual selection has favoured males with increased spatial abilities for either better navigational skills in hunting or to enable an increased territory size. However, an alternative explanation for this sex difference focuses on the role of varying levels of oestrogen in females in spatial cognition (the 'fertility and parental care' hypothesis). One possibility is that varying oestrogen levels result in variation in spatial learning and memory so that, when tested across the oestrous cycle, females perform as well as males on days of low oestrogen but more poorly on days of high oestrogen. If day in the oestrous cycle is not taken into account then, across an experiment, any sex differences found would always produce male superiority. We used a spatial working memory task in a Morris water maze to test the spatial learning and memory abilities of male and female rats. The rats were tested across a number of consecutive days during which the females went through four oestrous cycles. We found no overall sex differences in latencies to reach a submerged platform in a Morris water maze but, on the day of oestrus (low oestrogen), females took an extra swim to learn the platform's location (a 100% increase over the other days in the cycle). Female swim speed also varied across the oestrous cycle but females were no less active on the day of oestrus. These results oppose the predictions of the fertility and parental care hypothesis.  (+info)

Electrically evoked fictive swimming in the low-spinal immobilized turtle. (61/2436)

Fictive swimming was elicited in low-spinal immobilized turtles by electrically stimulating the contralateral dorsolateral funiculus (cDLF) at the level of the third postcervical segment (D(3)). Fictive hindlimb motor output was recorded as electroneurograms (ENGs) from up to five peripheral nerves on the right side, including three knee extensors (KE; iliotibialis [IT]-KE, ambiens [AM]-KE, and femorotibialis [FT]-KE), a hip flexor (HF), and a hip extensor (HE). Quantitative analyses of burst amplitude, duty cycle and phase were used to demonstrate the close similarity of these cDLF-evoked fictive motor patterns with previous myographic recordings obtained from the corresponding hindlimb muscles during actual swimming. Fictive rostral scratching was elicited in the same animals by cutaneous stimulation of the shell bridge, anterior to the hindlimb. Fictive swim and rostral scratch motor patterns displayed similar phasing in hip and knee motor pools but differed in the relative amplitudes and durations of ENG bursts. Both motor patterns exhibited alternating HF and HE discharge, with monoarticular knee extensor (FT-KE) discharge during the late HF phase. The two motor patterns differed principally in the relative amplitudes and durations of HF and HE bursts. Swim cycles were dominated by large-amplitude, long-duration HE bursts, whereas rostral scratch cycles were dominated by large-amplitude, long-duration HF discharge. Small but significant differences were also observed during the two behaviors in the onset phase of biarticular knee extensor bursts (IT-KE and AM-KE) within each hip cycle. Finally, interactions between swim and scratch motor networks were investigated. Brief activation of the rostral scratch during an ongoing fictive swim episode could insert one or more scratch cycles into the swim motor pattern and permanently reset the burst rhythm. Similarly, brief swim stimulation could interrupt and reset an ongoing fictive rostral scratch. This shows that there are strong central interactions between swim and scratch neural networks and suggests that they may share key neural elements.  (+info)

Scratch-swim hybrids in the spinal turtle: blending of rostral scratch and forward swim. (62/2436)

Turtles with a complete transection of the spinal cord just posterior to the forelimb enlargement at the D2-D3 segmental border produced coordinated rhythmic hindlimb movements. Ipsilateral stimulation of cutaneous afferents in the midbody shell bridge evoked a rostral scratch. Electrical stimulation of the contralateral dorsolateral funiculus (DLF) at the anterior cut face of the D3 segment activated a forward swim. Simultaneous stimulation of the ipsilateral shell bridge and the contralateral DLF elicited a scratch-swim hybrid: a behavior that blended features of both rostral scratch and forward swim into each cycle of rhythmic movement. This is the first demonstration of a scratch-locomotion hybrid in a spinal vertebrate. The rostral scratch and the forward swim shared some characteristics: alternating hip flexion and extension, similar timing of knee extensor activity within the hip cycle, and a behavioral event during which force was exerted against a substrate. During each cycle, each behavior exhibited three sequential stages, preevent, event, and postevent. The rostral scratch event was a rub of the foot against the stimulated shell site. The forward swim event was a powerstroke, a hip extension movement with the foot held in a vertical position with toes and webbing spread. The two behaviors differed with respect to several features: amount of hip flexion and extension, electromyogram (EMG) amplitudes, and EMG duty cycles. Scratch-swim hybrids displayed two events, the scratch rub and the swim powerstroke, within each cycle. Hybrid hip flexion excursion, knee extensor EMGs, and hip flexor EMGs were similar to those of the scratch; hybrid hip extension excursion and hip extensor EMGs were similar to those of the swim. The hybrid also had three sequential stages during each cycle: 1) a combined scratch prerub and swim postpowerstroke, 2) a scratch rub that also served as a swim prepowerstroke, and 3) a swim powerstroke that also served as a scratch postrub. Merging of the rostral scratch with the forward swim was possible because of similarities between the sequential stages of the two forms, making them biomechanically compatible for hybrid formation. Kinematic and myographic similarities between the rostral scratch and the forward swim support the hypothesis that the two behaviors share common neural circuitry. The common features of the sequential stages of each behavior and the production of scratch-swim hybrids provide additional support for the hypothesis of a shared core of spinal cord neurons common to both rostral scratch and forward swim.  (+info)

Power production during steady swimming in largemouth bass and rainbow trout. (63/2436)

Steady swimming in fishes is powered by the aerobic or red muscle, but there are conflicting theories on the relative roles of the anterior and posterior red muscle in powering steady swimming. To examine how red muscle is used to power steady swimming in rainbow trout (Oncorhynchus mykiss), electromyographic (EMG) and sonomicrometry recordings were made of muscle activity in vivo. These data were used in in vitro work-loop studies of muscle power production. Data on in vitro power production were also collected for largemouth bass (Micropterus salmoides) red muscle from previously published data on in vivo muscle activity. The in vivo data collected from swimming trout were similar to those for other species. The anterior red muscle of these fish has the longest duty cycle, the smallest phase shift between the onset of EMG activity and maximum muscle length during each tailbeat and undergoes the smallest strain or length change. For both trout and largemouth bass, work-loop experiments indicate that the majority of power for steady swimming is generated by the posterior muscle, as has been observed in other species.  (+info)

The distribution of NADPH-diaphorase-labelled interneurons and the role of nitric oxide in the swimming system of Xenopus laevis larvae. (64/2436)

The possible involvement of the free radical gas nitric oxide (NO) in the modulation of spinal rhythm-generating networks has been studied using Xenopus laevis larvae. Using NADPH-diaphorase histochemistry, three putative populations of nitric oxide synthase (NOS)-containing cells were identified in the brainstem. The position and morphology of the largest and most caudal population suggested that a proportion of these neurons is reticulospinal. The possible contribution of nitrergic neurons to the control of swimming activity was examined by manipulating exogenous and endogenous NO concentrations in vivo with an NO donor (SNAP, 100-500 micromol l(-)(1)) and NOS inhibitors (l-NAME and l-NNA, 0.5-5 mmol l(-)(1)), respectively. In the presence of SNAP, swim episode duration decreased and cycle period increased, whereas the NOS inhibitors had the opposite effects. We conclude from these data that the endogenous release of NO from brainstem neurons extrinsic to the spinal cord of Xenopus laevis larvae exerts a continuous modulatory influence on swimming activity, functioning like a 'brake'. Although the exact level at which NO impinges upon the swimming rhythm generator has yet to be determined, the predominantly inhibitory effect of NO suggests that the underlying mechanisms of NO action could involve modulation of synaptic transmission and/or direct effects on neuronal membrane properties.  (+info)