Effects of swimming training on aerobic capacity and exercise induced bronchoconstriction in children with bronchial asthma. (17/2436)

BACKGROUND: A study was undertaken to determine whether swimming training improved aerobic capacity, exercise induced bronchoconstriction (EIB), and bronchial responsiveness to inhaled histamine in children with asthma. METHODS: Eight children with mild or moderate asthma participated in swimming training every day for six weeks. The intensity of training was individually determined and set at 125% of the child's lactate threshold (LT), measured using a swimming ergometer. Another group of eight asthmatic children served as control subjects. Aerobic capacity and the degree of EIB were assessed by both cycle ergometer and swimming ergometer before and after swimming training. RESULTS: The mean (SD) aerobic capacity at LT increased by 0.26 (0.11) kp after training when assessed with the swimming ergometer and by 10.6 (4.5) W when assessed with the cycle ergometer, and these changes were significantly different from the control group. The mean (SD) maximum % fall in forced expiratory volume in one second (FEV1) to an exercise challenge (cycle ergometer) set at 175% of LT decreased from 38.7 (15.4)% before training to 17.9 (17.6)% after training, but with no significant difference from the control group. There was, however, no difference in histamine responsiveness when compared before and after the training period. CONCLUSION: A six week swimming training programme has a beneficial effect on aerobic capacity but not on histamine responsiveness in children with asthma.  (+info)

Long-term regulation of locus ceruleus sensitivity to corticotropin-releasing factor by swim stress. (18/2436)

Corticotropin-releasing factor (CRF) acts as a putative neurotransmitter in the locus ceruleus (LC) to mediate its activation by certain stressors. In this study, we quantified LC sensitivity to CRF 24 h after swim stress, at a time when behavioral depression that is sensitive to antidepressants is apparent. Rats were placed in a tank with 30 cm (swim stress) or 4 cm water and 24 h later, either behavior was monitored in a forced swim test or LC discharge was recorded. Swim stress rats were more immobile than control animals in the swim test. LC neurons of swim stress rats were sensitized to low doses of CRF (0.1-0.3 microgram i.c.v.) that were ineffective in control animals and were desensitized to higher doses. Swim stress selectively altered LC sensitivity to CRF because neither LC spontaneous discharge nor responses to other agents (e.g., carbachol, vasoactive intestinal peptide) were altered. Finally, the mechanism for sensitization was localized to the LC because neuronal activation by low doses of CRF was prevented by the intracerulear administration of a CRF antagonist. CRF dose-response curves were consistent with a two-site model with similar dissociation constants under control conditions but divergent dissociation constants after swim stress. The results suggest that swim stress (and perhaps other stressors) functionally alters CRF receptors that have an impact on LC activity. Stress-induced regulation of LC sensitivity to CRF may underlie behavioral aspects of stress-related psychiatric disorders.  (+info)

Sensory feedback can coordinate the swimming activity of the leech. (19/2436)

Previous studies showed that sensory feedback from the body wall is important and sometimes critical for generating normal, robust swimming activity in leeches. In this paper, we evaluate the role of sensory feedback in intersegmental coordination using both behavioral and physiological measurements. We severed the ventral nerve cord of leeches in midbody and then made video and in situ extracellular recordings from swimming animals. Our electrophysiological recordings unequivocally demonstrate that active intersegmental coordination occurs in leeches with severed nerve cords, refuting earlier conclusions that sensory feedback cannot coordinate swimming activity. Intersegmental coordination can in fact be achieved by sensory feedback alone, without the intersegmental interactions conveyed by the nerve cord.  (+info)

Separate effects of a classical conditioning procedure on respiratory pumping, swimming, and inking in Aplysia fasciata. (20/2436)

We examined whether swimming and inking, two defensive responses in Aplysia fasciata, are facilitated by a classical conditioning procedure that has been shown to facilitate a third defensive response, respiratory pumping. Training consisted of pairing a head shock (UCS) with a modified seawater (85%, 120%, or pH 7.0 seawater--CSs). Animals were tested by re-exposing them to the same altered seawater 1 hr after the training. For all three altered seawaters, only respiratory pumping is specifically increased by conditioning. Swimming is sensitized by shock, and inking is unaffected by training, indicating that the conditioning procedure is likely to affect a neural site that differentially controls respiratory pumping. Additional observations also indicate that the three defensive responses are differentially regulated. First, different noxious stimuli preferentially elicit different defensive responses. Second, the three defensive responses are differentially affected by shock. Inking is elicited only immediately following shock, whereas swimming and respiratory pumping are facilitated for a period of time following the shock. Third, swimming and respiratory pumping are differentially affected by noxious stimuli that are delivered in open versus closed environments. These data confirm that neural pathways exist that allow Aplysia to modulate separately each of the three defensive behaviors that were examined.  (+info)

Enhanced hippocampal long-term potentiation and learning by increased neuronal expression of tissue-type plasminogen activator in transgenic mice. (21/2436)

Adult cortical neurons can produce tissue-type plasminogen activator (tPA), an extracellular protease that plays a critical role in fibrinolysis and tissue remodelling processes. There is growing evidence that extracellular proteolysis may be involved in synaptic plasticity, axonal remodelling and neurotoxicity in the adult central nervous system. Here we show that transgenic mice overexpressing tPA in post-natal neurons have increased and prolonged hippocampal long-term potentiation (LTP), and improved performance in spatial orientation learning tasks. Extracellular proteolysis catalysed by tPA may facilitate synaptic micro-remodelling, and thereby play a role in activity-dependent neuronal plasticity and learning.  (+info)

Mechanical versus physiological determinants of swimming speeds in diving Brunnich's guillemots. (22/2436)

For fast flapping flight of birds in air, the maximum power and efficiency of the muscles occur over a limited range of contraction speeds and loads. Thus, contraction frequency and work per stroke tend to stay constant for a given species. In birds such as auks (Alcidae) that fly both in air and under water, wingbeat frequencies in water are far lower than in air, and it is unclear to what extent contraction frequency and work per stroke are conserved. During descent, compression of air spaces dramatically lowers buoyant resistance, so that maintaining a constant contraction frequency and work per stroke should result in an increased swimming speed. However, increasing speed causes exponential increases in drag, thereby reducing mechanical versus muscle efficiency. To investigate these competing factors, we have developed a biomechanical model of diving by guillemots (Uria spp.). The model predicted swimming speeds if stroke rate and work per stroke stay constant despite changing buoyancy. We compared predicted speeds with those of a free-ranging Brunnich's guillemot (U. lomvia) fitted with a time/depth recorder. For descent, the model predicted that speed should gradually increase to an asymptote of 1.5-1.6 m s-1 at approximately 40 m depth. In contrast, the instrumented guillemot typically reached 1.5 m s-1 within 10 m of the water surface and maintained that speed throughout descent to 80 m. During ascent, the model predicted that guillemots should stroke steadily at 1.8 m s-1 below their depth of neutral buoyancy (62 m), should alternate stroking and gliding at low buoyancies from 62 to 15 m, and should ascend passively by buoyancy alone above 15 m depth. However, the instrumented guillemot typically ascended at 1.25 m s-1 when negatively buoyant, at approximately 1.5 m s-1 from 62 m to 25 m, and supplemented buoyancy with stroking above 25 m. Throughout direct descent, and during ascent at negative and low positive buoyancies (82-25 m), the guillemot maintained its speed within a narrow range that minimized the drag coefficient. In films, guillemots descending against high buoyancy at shallow depths increased their stroke frequency over that of horizontal swimming, which had a substantial glide phase. Model simulations also indicated that stroke duration, relative thrust on the downstroke versus the upstroke, and the duration of gliding can be varied to regulate swimming speed with little change in contraction speed or work per stroke. These results, and the potential use of heat from inefficient muscles for thermoregulation, suggest that diving guillemots can optimize their mechanical efficiency (drag) with little change in net physiological efficiency.  (+info)

The prevalence of chronic knee injury in triathletes. (23/2436)

OBJECTIVES: To add to the area of triathlon research by providing much needed prevalence data on knee injury in triathletes. METHOD: An incidental "in field" sampling technique was used to interview 58 triathletes aged between 15 and 55 years about knee injury during a triathlon event. The sample comprised 46 men and 12 women. RESULTS: Most knee injuries occurred during the running event (72%) and affected the lateral side of the knee (38%). In all, 78% of the sample sought treatment from a healthcare professional. CONCLUSION: The study has provided much needed prevalence data on chronic knee injury in triathletes.  (+info)

Simulations of neuromuscular control in lamprey swimming. (24/2436)

The neuronal generation of vertebrate locomotion has been extensively studied in the lamprey. Models at different levels of abstraction are being used to describe this system, from abstract nonlinear oscillators to interconnected model neurons comprising multiple compartments and a Hodgkin-Huxley representation of the most relevant ion channels. To study the role of sensory feedback by simulation, it eventually also becomes necessary to incorporate the mechanical movements in the models. By using simplifying models of muscle activation, body mechanics, counteracting water forces, and sensory feedback through stretch receptors and vestibular organs, we have been able to close the feedback loop to enable studies of the interaction between the neuronal and the mechanical systems. The neuromechanical simulations reveal that the currently known network is sufficient for generating a whole repertoire of swimming patterns. Swimming at different speeds and with different wavelengths, together with the performance of lateral turns can all be achieved by simply varying the brainstem input. The neuronal mechanisms behind pitch and roll manoeuvres are less clear. We have put forward a 'crossed-oscillators' hypothesis where partly separate dorsal and ventral circuits are postulated. Neuromechanical simulations of this system show that it is also capable of generating realistic pitch turns and rolls, and that vestibular signals can stabilize the posture during swimming.  (+info)