bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deciphering the organization and modulation of spinal locomotor central pattern generators
Authors: Gordon Ian T. , Whelan Patrick J. 
Published: May 2006

SUMMARY
Networks within our spinal cord generate the basic pattern underlying walking. Over the past decade, much progress has been made in our understanding of their function in a variety of vertebrate species. A significant hurdle has been the identification of candidate populations of neurons that are involved in pattern generation in the spinal cord. Recently,systems neuroscientists in collaboration with molecular biologists have begun to dissect the circuitry underlying spinal locomotor networks. These advances have combined genetic and electrophysiological techniques using in vitro preparations of the mouse spinal cord. This review will discuss new advances in the field of spinal locomotor networks with emphasis on the mouse.
Many of the behaviors fundamental to animal life, such as breathing,chewing and locomotion, are rhythmic activities controlled by neuronal networks. Discerning which neurons are members of these networks, their synaptic connectivity and their individual electrophysiological properties is essential to our understanding of how rhythmic motor behaviors are produced. It is well known that the spinal cord contains the basic circuitry to produce locomotion. However, identifying neurons and connections within spinal networks is challenging because cells that comprise the locomotor network form part of a heterogeneous mix of interneurons within the ventral spinal cord. Recently, the merging of electrophysiological and genetic approaches has provided new tools to identify classes of interneurons within the spinal cord that contribute to network function. These new findings will be discussed in this review.
The energetic costs of trunk and distal-limb loading during walking and running in guinea fowlNumida meleagris
Authors: Marsh Richard L. , Ellerby David J. , Henry Havalee T. , Rubenson Jonas 
Published: May 2006

SUMMARYWe examined the energetic cost of loading the trunk or distal portion of the leg in walking and running guinea fowl (Numida meleagris). These different loading regimes were designed to separately influence the energy use by muscles used during the stance and swing phases of the stride. Metabolic rate, estimated from oxygen consumption, was measured while birds locomoted on a motorized treadmill at speeds from 0.5 to 2.0 m s-1, either unloaded, or with a mass equivalent to 23% of their body mass carried on their backs, or with masses equal to approximately 2.5% of their body mass attached to each tarsometatarsal segment. In separate experiments, we also measured the duration of stance and swing in unloaded, trunk-loaded, or limb-loaded birds. In the unloaded and limb-loaded birds, we also calculated the mechanical energy of the tarsometatarsal segment throughout the stride.Trunk and limb loads caused similar increases in metabolic rate. During trunk loading, the net metabolic rate (gross metabolic rate - resting metabolic rate) increased by 17% above the unloaded value across all speeds. This percentage increase is less than has been found in most studies of humans and other mammals. The economical load carriage of guinea fowl is consistent with predictions based on the relative cost of the stance and swing phases of the stride in this species. However, the available comparative data and considerations of the factors that determine the cost of carrying extra mass lead us to the conclusion that the cost of load carrying is unlikely to be a reliable indicator of the distribution of energy use in stance and swing. Both loading regimes caused small changes in the swing and/or stance durations, but these changes were less than 10%.Loading the tarsometatarsal segment increased its segmental energy by 4.1 times and the segmental mechanical power averaged over the stride by 3.8 times. The increases in metabolism associated with limb loading appear to be linked to the increases in mechanical power. The delta efficiency (change in mechanical power divided by the change in metabolic power) of producing this power increased from 11% in walking to approximately 25% in running. Although tarsometatarsal loading was designed to increase the mechanical energy during swing phase, 40% of the increase in segmental energy occurred during late stance. Thus, the increased energy demand of distal limb loading in guinea fowl is predicted to cause increases in energy use by both stance- and swing-phase muscles.
Balancing the competing requirements of saltatorial and fossorial specialisation: burrowing costs in the spinifex hopping mouse,Notomys alexis
Authors: White Craig R. , Matthews Philip G. D. , Seymour Roger S. 
Published: May 2006

SUMMARYSemi-fossorial animals (burrowing surface foragers) need to balance the competing morphological requirements of terrestrial and burrowing locomotion. These species rarely show the same degree of claw, forelimb and pectoral girdle structural development that fully fossorial forms (burrowing subterranean foragers) do, but nevertheless invest considerable amounts of energy in burrow systems. The compromise between terrestrial and burrowing locomotion was investigated by measuring net costs of burrowing and pedestrian transport in the spinifex hopping mouse, Notomys alexis, a species that forages in open areas in arid environments and is adapted for saltatorial locomotion. The net cost of transport by burrowing of hopping mice was found to be more expensive than for specialised fossorial species, and burrows were estimated to represent an energy investment equivalent to the terrestrial locomotion expected to be incurred in 17-100 days. A phylogenetically independent-contrasts approach revealed that morphological specialisation for burrowing was associated with low maximum running speeds in fossorial mammals and, for non-fossorial rodents and marsupials, maximum running speed was positively correlated with an index of habitat structure that ranged from arboreal to open desert. The high terrestrial speeds attainable by this semi-fossorial species by saltatory locomotion apparently outweigh the energetic savings that would be associated with burrowing specialisation.
Adaptive value of ambling gaits in primates and other mammals
Authors: Schmitt Daniel , Cartmill Matt , Griffin Timothy M. , Hanna Jandy B. , Lemelin Pierre 
Published: May 2006

SUMMARYAt speeds between the walk and the gallop, most mammals trot. Primates almost never trot, and it has been claimed that they transition directly from a walk to a gallop without any distinctive mid-speed running gait. If true,this would be another characteristic difference between the locomotion of primates and that of most other quadrupedal mammals. Presently, however, few data exist concerning the actual presence or absence of intermediate-speed gaits (i.e. gaits that are used between a walk and a gallop) in primates. Video records of running in twelve primate species reveal that, unlike most other mammals, all the primates studied almost exclusively adopt an `amble' -an intermediate-speed running gait with no whole-body aerial phase - rather than trot. Ambling is also common in elephants and some horses, raising the question of why ambling is preferred over trotting in these diverse groups of animals. Mathematical analyses presented here show that ambling ensures continuous contact of the body with the substrate while dramatically reducing vertical oscillations of the center of mass. This may explain why ambling appears to be preferable to trotting for extremely large terrestrial mammals such as elephants and for arboreal mammals like primates that move on unstable branches. These findings allow us to better understand the mechanics of these unusual running gaits and shed new light on primate locomotor evolution.
Locomotor function of the pectoral girdle `muscular sling' in trotting dogs
Authors: Carrier David R. , Deban Stephen M. , Fischbein Timna 
Published: May 2006

SUMMARY
In therian mammals, gravitational and locomotor forces are transferred between the forelimb and trunk primarily, or entirely, through the muscles that connect the limb and trunk. Our understanding of this force transmission is based on analyses of shoulder anatomy and on a handful of descriptive electromyographic studies. To improve our understanding, we manipulated the locomotor forces of trotting dogs and monitored the resulting change in recruitment of five extrinsic muscles of the forelimb: m. serratus ventralis thoracis, m. serratus ventralis cervicis, m. pectoralis superficialis transversus, the anterior portion of the m. pectoralis profundus, and m. rhomboideus thoracis. Locomotor forces were modified as the dogs trotted at constant speed on a motorized treadmill by (1) adding mass to the trunk, (2)inclining the treadmill so that the dogs ran up and down hill, (3) adding mass to the wrists and (4) applying horizontally directed force to the trunk through a leash. These experiments indicate that the thoracic portion of the serratus ventralis muscle is the main antigravity muscle of the shoulder during trotting in dogs. Its activity increased when we added mass to the trunk and also when we ran the subjects downhill. In contrast, the cervical portion of the serratus ventralis did not show a consistent increase in activity in response to added mass. Instead, its activity increased when we ran the subjects up hill and added mass to their wrists, suggesting that it functions to stabilize the fulcrum of the forelimb in the cranial-caudal direction during active retraction of the forelimb. The thoracic portion of the rhomboideus muscle also appears to provide this cranial-caudal stabilization during active retraction of the forelimb. The force manipulations indicate that the transverse pectoralis muscle acts to both protract and retract the forelimb, depending on the position of the limb. In contrast, the anterior portion of the pectoralis profundus muscle acts as a retractor of the forelimb during the end of swing phase and the beginning of support phase. We found that adding mass to the trunk did not increase the activity of forelimb retractor muscles, suggesting that the ground reaction force vector passes through, or very near, the fulcrum of the shoulder during a trotting step. Whether or not the functions of these extrinsic appendicular muscles in dogs characterize therian mammals or represent specializations for high-speed, economical running remains to be determined.
Time-domain signal divergence and discrimination without receptor modification in sympatric morphs of electric fishes
Authors: Arnegard Matthew E. , Jackson B. Scott , Hopkins Carl D. 
Published: May 2006

SUMMARYPolymorphism in an animal communication channel provides a framework for studying proximate rules of signal design as well as ultimate mechanisms of signal diversification. Reproductively isolated mormyrid fishes from Gabon's Brienomyrus species flock emit distinctive electric organ discharges(EODs) thought to function in species and sex recognition. Species boundaries and EODs appear congruent in these fishes, with the notable exception of three morphs designated types I, II and III. Within the species flock, these morphs compose a monophyletic group that has recently been called the magnostipes complex. Co-occurring morphs of this complex express distinctive EODs, yet they appear genetically indistinguishable at several nuclear loci. In this study, we investigated EOD discrimination by these morphs using both behavioral and physiological experiments. During the breeding season, wild-caught type I and type II males showed evidence that they can discriminate their own morph's EOD waveform from that of a sympatric and genetically distinct reference species. However, we found that type I and type II males exhibited an asymmetry in unconditioned responses to paired playback of EODs recorded from type I versus type II females. Males of the type II morph responded preferentially to EODs of type II females,whereas type I males did not appear to discriminate homotypic and heterotypic EODs in our experimental paradigm. Part of this behavioral asymmetry may have resulted from a previously undetected difference in adult size, which may have enhanced apparent discrimination by the smaller morph (type II) due to a relatively higher risk of injury from the larger morph (type I). Knollenorgan receptors, which mediate electrical communication in mormyrids, showed similar spectral tuning in type I and type II. These electroreceptors coded temporal features of any single magnostipes-complex EOD with similar patterns of time-locked spikes in both morphs. By contrast, Knollenorgans exhibited distinctive responses to different EOD waveforms. These results suggest that discrete EOD variation in this rapidly diversifying complex is functional in terms of morph-specific advertisement and recognition. Time-domain signal divergence has outpaced frequency-domain divergence between sympatric morphs,requiring little to no change in receptor response properties. We discuss our findings in light of a model for EOD time-coding by the Knollenorgan pathway,as well as evolutionary hypotheses concerning sympatric signal diversification in the magnostipes complex.
Activation of a sensorimotor pathway in response to a water temperature drop in a teleost fish
Authors: van den Burg E. H. , Verhoye M. , Peeters R. R. , Meek J. , Flik G. , Van der Linden A. 
Published: May 2006

SUMMARYWhen common carp, Cyprinus carpio L., experience a rapid temperature drop, the cerebral blood volume is strongly reduced to dampen the temperature drop in the brain. Simultaneously, the preoptic area and pituitary gland are activated to launch whole-body adaptive responses. However, the preferred reaction of fish to a temperature change is an escape reaction,which implies activation of a sensorimotor pathway. Here, we used blood oxygenation level-dependent (BOLD)- and cerebral blood volume (CBV)-weighted functional magnetic resonance imaging (fMRI) to identify a sensorimotor pathway, during a 10°C temperature drop in common carp. Transient activation was observed in the region where the sensory root of the trigeminal nerve enters the brain, and in the valvula cerebelli. In both regions,metabolic activity increased (increased deoxyhemoglobin content demonstrated by a decreased BOLD signal) within 30 s after the onset of the temperature drop, peaked after 2-3 min, and then decreased, even though the temperature continued to drop for another 2 min. These brain structures appear to respond to temperature change, rather than to the absolute temperature. Thus, during a temperature drop, the sensorimotor pathway consisting of the trigeminal nerve,the primary sensory trigeminal nucleus, the valvula cerebelli and some motornuclei, is active, in line with perception of temperature change in the buccal cavity, leading to motor activity for escape. This pathway operates in parallel to an acclimation pathway, which involves the preoptic area to pituitary gland pathway.
Steroid-induced cardiac contractility requires exogenous glucose,glycolysis and the sarcoplasmic reticulum in rainbow trout
Authors: Farrar Richard S. , Battiprolu Pavan K. , Pierson Nicholas S. , Rodnick Kenneth J. 
Published: May 2006

SUMMARYRecent data from our laboratory suggest that sex steroids promote contractile function in cardiac muscle of rainbow trout (Oncorhynchus mykiss Walbaum), and there are sex differences in hormone signaling and cardiac function. The current study investigated whether steroid-induced inotropism in electrically paced (0.5 Hz, 14°C) ventricle strips at 90%Lmax (1) has a metabolic requirement for exogenous glucose and (2) is associated with enhanced intracellular Ca2+ storage and release from the sarcoplasmic reticulum (SR). We also explored whether sex differences exist in extracellular Ca2+(Ca2+o) or cardiac sensitivity to Ca2+o. In the absence or at low concentrations (1 or 2 mmol l-1) of exogenous glucose, resting tension and relaxation time were increased selectively in cardiac tissue from females. Increasing glucose promoted twitch force in a bell-shaped manner, with 5 mmol l-1representing the optimal concentration for both sexes. The positive inotropic effects of physiological concentrations of testosterone (T) and 17β-estradiol (E2) in male and female trout ventricle strips,respectively, developed slowly (10-45 min) and were not apparent in glucose-free medium, in medium containing iodoacetate (IAA), an inhibitor of glycolysis, or medium containing 5 mmol l-1 lactate or pyruvate. Male ventricle strips had increased inotropic responses to glucose and T compared with female strips exposed to glucose and E2. Furthermore, sexually maturing males showed a greater inotropic response than immature males or females. Pretreatment with ryanodine (a specific blocker of SR Ca2+release) also eliminated the inotropic effects of sex steroids and exogenous glucose and reduced the post-rest potentiation of contractile force (a marker of SR Ca2+ storage). By contrast, the inotropic effects of epinephrine (Epi) or elevated Ca2+o were faster(developing within 1-3 min) and were not diminished by the presence or absence of glucose or by pretreatment with IAA or ryanodine. Sex differences were also found in responsiveness to caffeine (males &gt; females) and the relationship between Ca2+ concentration and force development above baseline. The Ca2+50 was lower in female cardiac tissue than males, suggesting greater Ca2+ sensitivity, and although plasma albumin was higher in females, total and ionized plasma Ca2+ did not differ between the sexes. For the first time, our study highlights the importance of extracellular glucose, glycolytic activity and SR Ca2+ storage and release for sex steroid-induced inotropism in the trout ventricle. Conversely, the inotropes Epi and elevated[Ca2+o] do not require the presence or metabolism of exogenous glucose or the SR for signaling their positive effects on contractility. These results also demonstrate novel sex-related differences in cardiac reliance on exogenous glucose, Ca2+ sensitivity and SR function and thus should be considered in future studies.
Fast-swimming hydromedusae exploit velar kinematics to form an optimal vortex wake
Authors: Dabiri John O. , Colin Sean P. , Costello John H. 
Published: May 2006

SUMMARYFast-swimming hydromedusan jellyfish possess a characteristic funnel-shaped velum at the exit of their oral cavity that interacts with the pulsed jets of water ejected during swimming motions. It has been previously assumed that the velum primarily serves to augment swimming thrust by constricting the ejected flow in order to produce higher jet velocities. This paper presents high-speed video and dye-flow visualizations of free-swimming Nemopsis bachei hydromedusae, which instead indicate that the time-dependent velar kinematics observed during the swimming cycle primarily serve to optimize vortices formed by the ejected water rather than to affect the speed of the ejected flow. Optimal vortex formation is favorable in fast-swimming jellyfish because,unlike the jet funnelling mechanism, it allows for the minimization of energy costs while maximizing thrust forces. However, the vortex `formation number'corresponding to optimality in N. bachei is substantially greater than the value of 4 found in previous engineering studies of pulsed jets from rigid tubes. The increased optimal vortex formation number is attributable to the transient velar kinematics exhibited by the animals. A recently developed model for instantaneous forces generated during swimming motions is implemented to demonstrate that transient velar kinematics are required in order to achieve the measured swimming trajectories. The presence of velar structures in fast-swimming jellyfish and the occurrence of similar jet-regulating mechanisms in other jet-propelled swimmers (e.g. the funnel of squid) appear to be a primary factor contributing to success of fast-swimming jetters, despite their primitive body plans.
Hypoxia induces a complex response of globin expression in zebrafish(Danio rerio)
Authors: Roesner Anja , Hankeln Thomas , Burmester Thorsten 
Published: May 2006

SUMMARY
Unlike most mammals, many fish species live and survive in environments with low or changing levels of oxygen. Respiratory proteins like hemoglobin or myoglobin bind or store oxygen, thus enhancing its availability to the respiratory chain in the mitochondria. Here we investigate by means of quantitative real-time PCR the changes of hemoglobin, myoglobin, neuroglobin,cytoglobin and globin X mRNA in zebrafish (Danio rerio) exposed to mild (PO2=∼8.6 kPa) or severe(PO2=∼4.1 kPa) hypoxia. Neuroglobin and myoglobin protein levels were investigated by western blotting. Whereas mild hypoxia caused only minor changes of mRNA levels, strong hypoxia enhanced mRNA levels of the control genes (lactate dehydrogenase A and phosphoglycerate kinase 1). Surprisingly, levels of hemoglobin α and β mRNA were significantly reduced under severe hypoxia. Myoglobin mRNA and protein in heart mildly increased, in line with its proposed oxygen supply function. Likewise,neuroglobin mRNA and protein significantly increased in brain (up to 5.7-fold at the protein level), but not in eye. This observation, firstly, suggests physiological differences of zebrafish eye and brain under hypoxia, and secondly, indicates an important role of neuroglobin in oxidative metabolism,probably oxygen supply within neurons. There was little change in the expression of the two cytoglobin genes. Globin X mRNA significantly decreased under hypoxia, pointing to a functional linkage to oxygen-dependent metabolism.