Importance of mechanics and kinematics in determining the stiffness contribution of the vertebral column during body-caudal-fin swimming in fishes

Whole-body stiffness in fishes has important consequences for swimming mode, speed and efficiency, but the contribution of vertebral column stiffness to whole-body stiffness is unclear. In our opinion, this lack of clarity is due in part to the lack of studies that have measured both in vitro mechanical properties of the vertebral column as well as in vivo vertebral kinematics in the same species. Some lack of clarity may also come from real variation in the mechanical role of the vertebral column across species. Previous studies, based on either mechanics or kinematics alone, suggest species-specific variation in vertebral column locomotor function that ranges from highly stiff regimes that contribute greatly to whole-body stiffness, and potentially act as a spring, to highly compliant regimes that only prohibit excessive flexion of the intervertebral joints. We review data collected in combined investigations of both mechanics and kinematics of three species, Myxine glutinosa, Acipenser transmontanus, and Morone saxatilis, to illustrate how mechanical testing within the context of the in vivo kinematics more clearly distinguishes the role of the vertebral column in each species. In addition, we identify species for which kinematic data are available, but mechanical data are lacking. We encourage further investigation of these species to fill these mechanical data gaps. Finally, we hope these future combined analyses will identify certain morphological, mechanical, or kinematic parameters that might be associated with certain vertebral column functional regimes with respect to body stiffness.     

Scaling of feeding biomechanics in the horn shark Heterodontus francisci: ontogenetic constraints on durophagy

Organismal performance changes over ontogeny as the musculoskeletal systems underlying animal behavior grow in relative size and shape. As performance is a determinant of feeding ecology, ontogenetic changes in the former can influence the latter. The horn shark Heterodontus francisci consumes hard-shelled benthic invertebrates, which may be problematic for younger animals with lower performance capacities. Scaling of feeding biomechanics was investigated in H. francisci (n=16, 19–59 cm standard length (SL)) to determine the biomechanical basis of allometric changes in feeding performance and whether this performance capacity constrains hard-prey consumption over ontogeny. Positive allometry of anterior (8–163 N) and posterior (15–382 N) theoretical bite force was attributed to positive allometry of cross-sectional area in two jaw adducting muscles and mechanical advantage at the posterior bite point (0.79–1.26). Mechanical advantage for anterior biting scaled isometrically (0.52). Fracture forces for purple sea urchins Strongylocentrotus purpuratus consumed by H. francisci ranged from 24 to 430 N. Comparison of these fracture forces to the bite force of H. francisci suggests that H. francisci is unable to consume hard prey early in its life history, but can consume the majority of S. purpuratus by the time it reaches maximum size. Despite this constraint, positive allometry of biting performance appears to facilitate an earlier entry into the durophagous niche than would an isometric ontogenetic trajectory. The posterior gape of H. francisci is significantly smaller than the urchins capable of being crushed by its posterior bite force. Thus, the high posterior bite forces of H. francisci cannot be fully utilized while consuming prey of similar toughness and size to S. purpuratus, and its potential trophic niche is primarily determined by anterior biting capacity.     

The strain-generated electrical potential in cartilaginous tissues: a role for piezoelectricity

The strain-generated potential (SGP) is a well-established mechanism in cartilaginous tissues whereby mechanical forces generate electrical potentials. In articular cartilage (AC) and the intervertebral disc (IVD), studies on the SGP have focused on fluid- and ionic-driven effects, namely Donnan, diffusion and streaming potentials. However, recent evidence has indicated a direct coupling between strain and electrical potential. Piezoelectricity is one such mechanism whereby deformation of most biological structures, like collagen, can directly generate an electrical potential. In this review, the SGP in AC and the IVD will be revisited in light of piezoelectricity and mechanotransduction. While the evidence base for physiologically significant piezoelectric responses in tissue is lacking, difficulties in quantifying the physiological response and imperfect measurement techniques may have underestimated the property. Hindering our understanding of the SGP further, numerical models to-date have negated ferroelectric effects in the SGP and have utilised classic Donnan theory that, as evidence argues, may be oversimplified. Moreover, changes in the SGP with degeneration due to an altered extracellular matrix (ECM) indicate that the significance of ionic-driven mechanisms may diminish relative to the piezoelectric response. The SGP, and these mechanisms behind it, are finally discussed in relation to the cell response.     

Regional variation in morphology of vertebral centra and intervertebral joints in striped bass,Morone saxatilis

The vertebral column of fishes has traditionally been divided into just two distinct regions, abdominal and caudal. Recently, however, developmental, morphological, and mechanical investigations have brought this traditional regionalization scheme into question. Alternative regionalization schema advocate the division of the abdominal vertebrae into cervical, abdominal, and in some cases, transitional regions. Here, we investigate regional variation at the level of the vertebrae and intervertebral joint (IVJ) tissues in the striped bass, Morone saxatilis. We use gross dissection, histology, and polarized light imaging to quantify vertebral height, width, length, IVJ length, IVJ tissue volume and cross‐sectional area, and vertical septum fiber populations, and angles of insertion. Our results reveal regional differences between the first four (most rostral) abdominal vertebrae and IVJs and the next six abdominal vertebrae and IVJs, supporting the recognition of a distinct cervical region. We found significant variation in vertebral length, width, and height from cranial to caudal. In addition, we see a significant decline in the volume of notochordal cells and the cross‐sectional area of the fibrous sheath from cranial to caudal. Further, polarized light imaging revealed four distinct fiber populations within the vertical septum in the cervical and abdominal regions in contrast with just one fiber population found in the caudal region. Measurement of the insertion angles of these fiber populations revealed significant differences between the cervical and abdominal regions. Differences in vertebral, IVJ, and vertical septum morphology all predict greater range of motion and decreased stiffness in the caudal region of the fish compared with the cervical and abdominal regions. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.     

Accuracy of non-differential GPS for the determination of speed over ground

Accurate determination of speed is important in many studies of human and animal locomotion. Some global positioning system (GPS) receivers can data log instantaneous speed. The speed accuracy of these systems is, however, unclear with manufacturers reporting velocity accuracies of 0.1–0.2 ms⁻¹. This study set out to trial non-differential GPS as a means of determining speed under real-life conditions.

A bicycle was ridden around a running track and a custom-made bicycle speedometer was calibrated. Additional experiments were performed around circular tracks of known circumference and along a straight road. Instantaneous speed was determined simultaneously by the custom speedometer and a data logging helmet-mounted GPS receiver. GPS speed was compared to speedometer speed. The effect on speed accuracy of satellite number; changing satellite geometry, achieved through shielding the GPS antenna; speed; horizontal dilution of precision and cyclist position on a straight or a bend, was evaluated. The relative contribution of each variable to overall speed accuracy was determined by ANOVA. The speed determined by the GPS receiver was within 0.2 ms⁻¹ of the true speed measured for 45% of the values with a further 19% lying within 0.4 ms⁻¹ (n=5060). The accuracy of speed determination was preserved even when the positional data were degraded due to poor satellite number or geometry. GPS data loggers are therefore accurate for the determination of speed over-ground in biomechanical and energetic studies performed on relatively straight courses. Errors increase on circular paths, especially those with small radii of curvature, due to a tendency to underestimate speed.     

Perceptual strain index for heat strain assessment in an experimental study: An application to construction workers

Although the physiological strain index (PhSI) is universal and comprehensive, its restrictions are recognized in terms of invasive on-site measurements and the requirement of accurate instruments. The perceptual strain index (PeSI) has been proposed as a user-friendly and practical indicator for heat strain. However, the application of this index in assessing the heat strain of construction workers has yet to be examined and documented. This study aims to ascertain the reliability and applicability of PeSI in an experimental setting that simulates a stressful working environment (i.e., environment, work uniform, and work pace) experienced by construction workers. Ten males and two females performed intermittent exercise on a treadmill while wearing a summer work uniform at 34.5 °C and 75% relative humidity in a climatic chamber. Physiological parameters (core temperature, heart rate) and perceptual variables (thermal sensation, perceived exertion) were collated synchronously at 3 min intervals. The results of two-way repeated measures analysis of variance (clothing×time) revealed that the PeSI was useful in differentiating the heat strain levels between different work uniforms. Not only did the PeSI change in the same general manner with the PhSI, but it was also powerful in reflecting different levels of physiological strain. Thus, the PeSI offers considerable promise for heat strain assessment under simulated working conditions.     

Elastic,permeability and swelling properties of human intervertebral disc tissues: A benchmark for tissue engineering

The aim of functional tissue engineering is to repair and replace tissues that have a biomechanical function, i.e., connective orthopaedic tissues. To do this, it is necessary to have accurate benchmarks for the elastic, permeability, and swelling (i.e., biphasic-swelling) properties of native tissues. However, in the case of the intervertebral disc, the biphasic-swelling properties of individual tissues reported in the literature exhibit great variation and even span several orders of magnitude. This variation is probably caused by differences in the testing protocols and the constitutive models used to analyze the data. Therefore, the objective of this study was to measure the human lumbar disc annulus fibrosus (AF), nucleus pulposus (NP), and cartilaginous endplates (CEP) biphasic-swelling properties using a consistent experimental protocol and analyses. The testing protocol was composed of a swelling period followed by multiple confined compression ramps. To analyze the confined compression data, the tissues were modeled using a biphasic-swelling model, which augments the standard biphasic model through the addition of a deformation-dependent osmotic pressure term. This model allows considering the swelling deformations and the contribution of osmotic pressure in the analysis of the experimental data. The swelling stretch was not different between the disc regions (AF: 1.28±0.16; NP: 1.73±0.74; CEP: 1.29±0.26), with a total average of 1.42. The aggregate modulus (Ha) of the extra-fibrillar matrix was higher in the CEP (390 kPa) compared to the NP (100 kPa) or AF (30 kPa). The permeability was very different across tissue regions, with the AF permeability (64 E⁻¹⁶ m⁴/N s) higher than the NP and CEP (~5.5 E⁻¹⁶ m⁴/N s). Additionally, a normalized time-constant (3000 s) for the stress relaxation was similar for all the disc tissues. The properties measured in this study are important as benchmarks for tissue engineering and for modeling the disc's mechanical behavior and transport.     

Bone strain magnitude is correlated with bone strain rate in tetrapods: implications for models of mechanotransduction

Hypotheses suggest that structural integrity of vertebrate bones is maintained by controlling bone strain magnitude via adaptive modelling in response to mechanical stimuli. Increased tissue-level strain magnitude and rate have both been identified as potent stimuli leading to increased bone formation. Mechanotransduction models hypothesize that osteocytes sense bone deformation by detecting fluid flow-induced drag in the bone''s lacunar–canalicular porosity. This model suggests that the osteocyte''s intracellular response depends on fluid-flow rate, a product of bone strain rate and gradient, but does not provide a mechanism for detection of strain magnitude. Such a mechanism is necessary for bone modelling to adapt to loads, because strain magnitude is an important determinant of skeletal fracture. Using strain gauge data from the limb bones of amphibians, reptiles, birds and mammals, we identified strong correlations between strain rate and magnitude across clades employing diverse locomotor styles and degrees of rhythmicity. The breadth of our sample suggests that this pattern is likely to be a common feature of tetrapod bone loading. Moreover, finding that bone strain magnitude is encoded in strain rate at the tissue level is consistent with the hypothesis that it might be encoded in fluid-flow rate at the cellular level, facilitating bone adaptation via mechanotransduction.     

Prey capture by Luciocephalus pulcher: implications for models of jaw protrusion in teleost fishes

Synopsis Luciocephalus pulcher possesses one of the most protrusible jaws known among teleosts, the premaxillae extending anteriorly a distance of 33% of the head length during feeding. Jaw bone movement during feeding proceeds according to a stereotypical pattern and resembles that of other teleosts except for extreme cranial elevation and premaxillary protrusion. Anatomical specializations associated with cranial elevation include: a highly modified first vertebra with a separate neural spine, articular fossae on the posterior aspect, greatly enlarged zygapophyses on the second vertebra with complex articular condyles, and highly pinnate multi-layered epaxial musculature with multiple tendinous insertions on the skull. Luciocephalus, despite the extreme jaw protrusion, does not use suction during prey capture: rather, the prey is captured by a rapid lunge (peak velocity of about 150 cm per sec) and is surrounded by the open mouth. Previous hypotheses of the function of upper jaw protrusion are reviewed in relation to jaw movements inLuciocephalus. Protrusion is not obligatorily linked with suction feeding; behavioral aspects of the feeding process limit the possible range of biological roles of a given morphological specialization, and make prediction of role from structure risky.     

Calcium regulation in wild populations of a freshwater cartilaginous fish, the lake sturgeon Acipenser fulvescens

Lake sturgeon, Acipenser fulvescens, are one of a few species of cartilaginous fishes that complete their life cycle entirely in freshwater. Sturgeons maintain very low concentrations of circulating calcium (Ca²⁺) compared with other vertebrates, and therefore, face unique challenges in regard to Ca²⁺ regulation, which are likely to be magnified during vitellogenic stages of the reproductive cycle. In the present study, Ca²⁺ concentrations and associated hormones of female and male lake sturgeon were examined in two wild populations, and were related to reproductive stage. In both populations, free, bound and total Ca²⁺ were low, peaking in mid-late vitellogenic females. Internal Ca²⁺ and phosphate (PO₄³⁻) concentrations were inversely related to environmental concentrations, suggesting that these ions are preferentially retained and that mechanisms for mobilization are up-regulated under diminished environmental concentrations. Plasma 17β-estradiol, 11-ketotestosterone and testosterone, peaked in mid-late vitellogenic females, while the androgens peaked in spawning males. Urine Ca²⁺ was more tightly regulated than other divalent ions and decreased in spawning fish. Therefore, the increases in free plasma Ca²⁺, the very low circulating concentrations of free and total Ca²⁺, and the increase in PO₄³⁻ and bound Ca²⁺ in low Ca²⁺ environments indicate unique adaptations to Ca²⁺ regulation in the lake sturgeon.     

L-乳酸生产菌种选育技术

随着聚乳酸作为生物可降解塑料的迅速发展,采用现代高新技术来选育L-乳酸纯度高、产量高、转化率高、能够利用木塘和适于发酵生产工艺要求的优良菌株,已成为国内外研究机构和企业关注的热点.本文对L-乳酸生产菌株的选育技术进展进行综述.     

Gradients of strain and strain rate in the hollow muscular organs of soft-bodied animals

The cylindrical shape of soft-bodied invertebrates is well suited to functions in skeletal support and locomotion, but may result in a previously unrecognized cost—large non-uniformities in muscle strain and strain rate among the circular muscle fibres of the body wall. We investigated such gradients of strain and strain rate in the mantle of eight long-finned squid Doryteuthis pealeii and two oval squid Sepioteuthis lessoniana. Transmural gradients of circumferential strain were present during all jets (n = 312); i.e. for a given change in the circumference of the outer surface of the mantle, the inner surface experienced a greater proportional change. The magnitude of the difference increased with the amplitude of the mantle movement, with circular muscle fibres at the inner surface of the mantle experiencing a total range of strains up to 1.45 times greater than fibres at the outer surface during vigorous jets. Differences in strain rate between the circular fibres near the inner versus the outer surface of the mantle were also present in all jets, with the greatest differences occurring during vigorous jetting. The transmural gradients of circumferential strain and strain rate we describe probably apply not only to squids and other coleoid cephalopods, but also to diverse soft-bodied invertebrates with hollow cylindrical or conical bodies and muscular organs.     

Importance of material parameters and strain energy function on the wall stresses in the left ventricle

Patient-specific estimates of the stress distribution in the left ventricles (LV) may have important applications for therapy planning, but computing the stress generally requires knowledge of the material behaviour. The passive stress-strain relation of myocardial tissue has been characterized by a number of models, but material parameters (MPs) remain difficult to estimate. The aim of this study is to implement a zero-pressure algorithm to reconstruct numerically the stress distribution in the LV without precise knowledge of MPs. We investigate the sensitivity of the stress distribution to variations in the different sets of constitutive parameters. We show that the sensitivity of the LV stresses to MPs can be marginal for an isotropic constitutive model. However, when using a transversely isotropic exponential strain energy function, the LV stresses become sensitive to MPs, especially to the linear elastic coefficient before the exponential function. This indicates that in-vivo identification efforts should focus mostly on this MP for the development of patient-specific finite-element analysis.     

鸡毒支原体强毒株与F疫苗株双重PCR检测方法的建立

目的建立能同时检测MG强毒株和F疫苗株的双重PCR技术。方法根据鸡毒支原体(MG)R株的PvpA基因序列和F疫苗株假定的α磷酸海藻糖酶基因序列,设计2对引物R1、R2和F1、F2,在单一PCR的基础上,建立检测MG强毒株和F疫苗株的双重PCR方法,并运用该双重PCR方法对临床样品进行检测。结果在330 bp和444 bp处分别出现预期的特异性DNA扩增条带,敏感性试验显示该体系能检测出0.45 ng的MG R株DNA和0.25 ng的MG F疫苗株DNA。临床样品MG强毒株阳性检出率为79.69%,高于常规分离培养鉴定法。结论成功建立检测两种毒株的双重PCR技术,为根除鸡群中MG野毒株、建立无MG的阴性鸡群提供新的技术手段。     

Thirty Years of Luminescent Solar Concentrator Research: Solar Energy for the Built Environment

Research on the luminescent solar concentrator (LSC) over the past thirty‐odd years is reviewed. The LSC is a simple device at its heart, employing a polymeric or glass waveguide and luminescent molecules to generate electricity from sunlight when attached to a photovoltaic cell. The LSC has the potential to find extended use in an area traditionally difficult for effective use of regular photovoltaic panels: the built environment. The LSC is a device very flexible in its design, with a variety of possible shapes and colors. The primary challenge faced by the devices is increasing their photon‐to‐electron conversion efficiencies. A number of laboratories are working to improve the efficiency and lifetime of the LSC device, with the ultimate goal of commercializing the devices within a few years. The topics covered here relate to the efforts for reducing losses in these devices. These include studies of novel luminophores, including organic fluorescent dyes, inorganic phosphors, and quantum dots. Ways to limit the surface and internal losses are also discussed, including using organic and inorganic‐based selective mirrors which allow sunlight in but reflect luminophore‐emitted light, plasmonic structures to enhance emissions, novel photovoltaics, alignment of the luminophores to manipulate the path of the emitted light, and patterning of the dye layer to improve emission efficiency. Finally, some possible ‘glimpses of the future’ are offered, with additional research paths that could result in a device that makes solar energy a ubiquitous part of the urban setting, finding use as sound barriers, bus‐stop roofs, awnings, windows, paving, or siding tiles.     

Negatively correlated firing: the functional meaning of lateral inhibition within cortical columns

Lateral inhibition is a well documented aspect of neural architecture in the main sensory systems. Existing accounts of lateral inhibition focus on its role in sharpening distinctions between inputs that are closely related. However, these accounts fail to explain the functional role of inhibition in cortical columns, such as those in V1, where neurons have similar response properties. In this paper, we outline a model of position tracking using cortical columns of integrate-and-fire and Hodgkin-Huxley-type neurons which respond optimally to a particular location, to show that negatively correlated firing patterns arise from lateral inhibition in cortical columns and that this provides a clear benefit for population coding in terms of stability, accuracy, estimation time and neural resources.     

A comparison of complete genome sequences of the attenuated RC-HL strain of rabies virus used for production of animal vaccine in Japan, and the parental Nishigahara strain

In order to establish the molecular basis of the pathogenicity of the attenuated RC-HL strain of rabies virus used for the production of animal vaccine in Japan, the complete genome sequence of this strain was determined and compared with that of the parental Nishigahara strain which is virulent for adult mice. The viral genome of both strains was composed of 11,926 nucleotides. The nucleotide sequences of the two genomes showed a high homology of 98.9%. The homology of the G gene was lower than those of N, P, M and L genes at both nucleotide and deduced amino acid levels, and the percentage of radical amino acid substitutions on the G protein was the highest among the five proteins. These findings raise the possibility that the structure of the G protein is the most variable among the five proteins of the two strains. Furthermore, we found two clusters of amino acid substitutions on the G and L proteins. The relevance of these clusters to the difference in the pathogenicity between the two strains is discussed.