Skeletal Adaptations Research Articles

BODY WEIGHT INFLUENCES MUSCULOSKELETAL ADAPTATION TO LONG-TERM VOLUNTARY WHEEL RUNNING DURING AGING

Abstract Frailty is a key hallmark of aging and exercise has been shown to delay aging effects. This study was initiated based on the hypothesis that voluntary wheel running (VWR) starting at 12 mo until 18 or 22 mo of age would benefit the female murine musculoskeletal system. Based on the final body weight, the mice were separated into high (HBW) and low body weight (LBW) subgroups. Beneficial effects of VWR were observed on soleus muscle mass and contractile force at both ages, although HBW led to greater increases at 22 mo. VWR increased fiber cross-sectional area by 20%, leading to more type I and fewer IIA fibers in soleus. HBW mice were resistant to age-related decline in Extensor digitorum longus (EDL) mass and contractile force. EDL in 18 mo HBW also showed 15% higher contractile force following VWR while muscle from 18 & 22 mo LBW responded to VWR with greater osteocyte protective factor secretion. Skeletal adaptation to VWR was also dependent on body weight, with HBW showing higher femoral cortical thickness and area under sedentary conditions. VWR maintained osteocyte dendrite number in HBW. VWR increased periosteal and endosteal circumferences in HBW, suggesting compensation for loss of material strength. Consistent with this, VWR maintained higher bone mechanical properties in 18mo LBW. In summary, VWR alters musculoskeletal parameters depending on body weight with HBW contributing to more muscle mass and strength to prevent sarcopenia while bone retains better mechanical properties in LBW but HBW contributes structural modification to prevent osteopenia.

Deletion of osteopontin or bone sialoprotein induces opposite bone responses to mechanical stimulation in mice

Osteopontin (OPN) and Bone Sialoprotein (BSP) are co-expressed in bone and display overlapping and complementary physiological properties. Both genes show a rapid expression response to mechanical stimulation. We used mice with single and double deletions (DKO) of BSP and OPN to assess the specificity of their roles in skeletal adaptation to loading. Two-month-old Wild-Type (WT), BSP knockout (BSP−/−), OPN−/− and DKO male mice were submitted to two mechanical stimulation regimen (n = 10 mice/group) respectively impacting trabecular bone (Hypergravity, HG) and cortical bone (Whole Body Vibration, WBV). HG increased trabecular bone volume (BV/TV) in WT femur through reduced resorption, and in BSP−/− mice femur and vertebra through increased bone formation. In contrast, HG increased the turnover of OPN−/− bone, resulting in reduced femur and vertebra BV/TV. HG did not affect DKO bones. Similarly, WBV increased cortical thickness in BSP−/− mice and decreased it in OPN−/−, without affecting structurally WT and DKO bone. Vibrated BSP−/− mice displayed increased endocortical bone formation with a drop in Sclerostin expression, and reduced periosteal osteoclasts with lower Rankl and Cathepsin K expression. In contrast, vibrated OPN−/− endocortical bone displayed decreased formation and increased osteoclast coverage. Therefore, under two regimen (HG and WBV) targeting distinct bone compartments, absence of OPN resulted in bone loss while lack of BSP induced bone gain, reflecting divergent structural adaptations. Strikingly, absence of both proteins led to a relative insensitivity to either mechanical challenge. Interplay between OPN and BSP thus appears as a key element of skeletal response to mechanical stimulation.

Influence of Chronic Lameness on Thoracolumbar Musculus Multifidus Structure in the Horse

The clinical relationship between equine limb lameness and secondary back dysfunction is largely unknown. Proper function of the spine is critical to maintain the integrity of the kinetic chain and attenuate forces from the appendicular skeleton. The musculus multifidus (m. multifidus) is the primary muscle providing spinal intersegmental stabilization and a functional relationship between m. multifidus hypertrophy and equine postural stability has been established. The relationship between equine thoracolumbar m. multifidus cross-sectional area (CSA) and limb lameness is unknown. The objective was to evaluate ultrasonographic changes in thoracolumbar m. multifidus CSA in horses with chronic single limb lameness, compared with sound horses. We hypothesized that the CSA of m. multifidus, ipsilateral to the lame limb would be smaller than the contralateral side, and within the sound group there would be no difference between sides. Thirty-six horses were enrolled, with twelve horses per group: sound, forelimb lame, and hindlimb lame. M. multifidus CSA was measured ultrasonographically at multiple spinal levels and compared between groups, spinal levels, and sides. M. multifidus CSA at the spinal level T18 was significantly larger than at all other measured levels, regardless of group (P ≤ .05). CSA at all levels was significantly larger in sound horses than the forelimb lame group, regardless of side (P = .002). This is the first study to evaluate the impact of chronic lameness on the axial skeleton and showed a decrease in m. multifidus CSA with forelimb lameness. These results support that axial skeletal adaptation occurs in response to naturally occurring chronic lameness.

Bone and calcium metabolism markers as an indicator of skeletal adaptation and stress fracture risk in military personnel

Introduction: The purpose of the talk is to identify the physical and behavioural characteristics likely to be associated with bone stress injury. Over the past decades many risk factors for bone stress injury have been reported for athlete and military populations. The data on which those reports have been based, however, has not always been of the highest quality. The result has been a plethora of suspects but a dearth of certainty around the biological, morphological, behavioural, and functional characteristics that should be the focus of preventative and therapeutic measures for bone stress injury.

Dynamic finite-element simulations reveal early origin of complex human birth pattern

Human infants are born neurologically immature, potentially owing to conflicting selection pressures between bipedal locomotion and encephalization as suggested by the obstetrical dilemma hypothesis. Australopithecines are ideal for investigating this trade-off, having a bipedally adapted pelvis, yet relatively small brains. Our finite-element birth simulations indicate that rotational birth cannot be inferred from bony morphology alone. Based on a range of pelvic reconstructions and fetal head sizes, our simulations further imply that australopithecines, like humans, gave birth to immature, secondary altricial newborns with head sizes smaller than those predicted for non-human primates of the same body size especially when soft tissue thickness is adequately approximated. We conclude that australopithecines required cooperative breeding to care for their secondary altricial infants. These prerequisites for advanced cognitive development therefore seem to have been corollary to skeletal adaptations for bipedal locomotion that preceded the appearance of the genus Homo and the increase in encephalization.

A cholinergic neuroskeletal interface promotes bone formation during postnatal growth and exercise.

SummaryThe autonomic nervous system is a master regulator of homeostatic processes and stress responses. Sympathetic noradrenergic nerve fibers decrease bone mass, but the role of cholinergic signaling in bone has remained largely unknown. Here, we describe that early postnatally, a subset of sympathetic nerve fibers undergoes an interleukin-6 (IL-6)-induced cholinergic switch upon contacting the bone. A neurotrophic dependency mediated through GDNF-family receptor-α2 (GFRα2) and its ligand, neurturin (NRTN), is established between sympathetic cholinergic fibers and bone-embedded osteocytes, which require cholinergic innervation for their survival and connectivity. Bone-lining osteoprogenitors amplify and propagate cholinergic signals in the bone marrow (BM). Moderate exercise augments trabecular bone partly through an IL-6-dependent expansion of sympathetic cholinergic nerve fibers. Consequently, loss of cholinergic skeletal innervation reduces osteocyte survival and function, causing osteopenia and impaired skeletal adaptation to moderate exercise. These results uncover a cholinergic neuro-osteocyte interface that regulates skeletogenesis and skeletal turnover through bone-anabolic effects.

Skeletal Structure and Training Adaptability of Athletes Based on Biomechanical Analysis.

According to the kinematics analysis of the human body, a set of exoskeleton mechanical structures is designed to imitate the physiological structure and movement characteristics of the lower limbs of humans. To study the biomechanical characteristics of the exoskeleton in two different phases during walking and to provide a research basis for the design and optimization of the exoskeleton. Doctors and engineers are actively committed to the basic understanding and improvement of the tissue characteristics, structure, and function of the human musculoskeletal system. Firstly, according to the gait analysis of the lower limbs, the exoskeleton mechanical structure is designed by using three-dimensional modeling software. After the solid model is generated, the assembly, meshing, and element attribute assignment are carried out by using finite element software. And the face-to-face contact relationship between each building is established, and the stress distribution of the exoskeleton is simulated and analyzed. The stress distribution of the exoskeleton under different working conditions is significantly different. Since the calculation does not take into account uncertainties such as shocks that may occur during walking, it is necessary to consider and multiply a certain safety factor when designing the optimized exoskeleton.

Equids from the late Middle Pleistocene to Early Holocene of the Apulia Peninsula (southern Italy): reassessment of their taxonomy and biochronology

The Apulian Peninsula represents a key-region for the study of climatic changes and paleoenvironmental dynamics during the Quaternary. Both large and small-sized horses are well documented in this region during the Pleistocene and are frequently found associated. The caballoid horses from Middle to Late Pleistocene of Europe show a large intraspecific ecomorphological variation, emphasizing a strong link between skeletal adaptations and specific aspects of the palaeoenvironment. This large variability led to an extended debate concerning the taxonomy of equids and their evolutionary history. In the Italian Peninsula, fossils from the Middle to the Late Pleistocene have been historically referred to several species (or even subspecies), emphasizing the uncertainty of the taxonomic attribution. Here, a large craniodental sample of Equidae fossils from late Middle Pleistocene to the Early Holocene localities of the Apulia Peninsula are described for the first time. The comparison of the protocone index allowed us to determine the first occurrences of Equus mosbachensis von Reichenau, 1903 in the Apulian Peninsula, from a few localities chronologically referred to late Middle Pleistocene. Most of the material from the late Middle to the end of the Late Pleistocene is instead attributed to Equus ferus Boddaert, 1785. The results of this work thus add novel information on the biochronology of Italian fossil equids and their evolutionary history through the Middle and Late Pleistocene.

Technical note: Mapping of trabecular bone anisotropy and volume fraction in 3D using μCT images of the human calcaneus

AbstractTrabecular bone anisotropy, describing preferential trabecular co‐alignment, is a proxy for its long‐term loading history. Trabecular anisotropy varies locally, thus rendering averaged calculations across an entire bone inutile. Here we present a 3D trabecular anisotropy mapping method using vector fields where each vector reflects the extent of local co‐alignment of the elementary units of surface. 3D anisotropy maps of hundreds of thousands of vectors were visualized by their magnitude and direction. Similarly, volume fraction was mapped as 3D scalar fields. We constructed anisotropy and volume fraction maps using micro‐computed tomography of four presumably nonpathologic human calcanei and compared their anisotropy signature with pathologically loaded calcanei in club foot and calcaneonavicular ankylosis. In the nonpathologic calcaneus, a pattern of four anisotropy trajectories (bands) was consistently identified as dorsal, plantar, Achilles', and peroneal bands. Both pathologic specimens deviated from the nonpathologic maps. The calcaneus in the congenitally disused club foot showed very low local anisotropy values, no co‐oriented bands, and low volume fraction. The ankylosed calcaneus showed lower anisotropy than the nonpathologic calcaneus, but not to the same extent as the club foot, and showed patchy high volume fraction. The directionality of co‐oriented bands was barely discernable in the ankylosed calcaneus as compared to nonpathologic calcaneus. The anisotropy signature of the nonpathologic calcaneus is consistent with a kinetic loading pattern attributable to walking. The loss of this kinetic loading results in an absent/vanishing anisotropy signature. Such 3D mapping adds new dimensions to quantitative bioimaging of bone and the understanding of skeletal adaptation.

Impaired bone quality in the superolateral femoral neck occurs independent of hip geometry and bone mineral density

Skeletal adaptation is substantially influenced by mechanical loads. Osteocytes and their lacuno-canalicular network have been identified as a key player in load sensation and bone quality regulation. In the femoral neck, one of the most common fracture sites, a complex loading pattern with lower habitual loading in the superolateral neck and higher compressive stresses in the inferomedial neck is present. Variations in the femoral neck-shaft angle (NSA), i.e., coxa vara or coxa valga, provide the opportunity to examine the influence of loading patterns on bone quality. We obtained femoral neck specimens of 28 osteoarthritic human subjects with coxa vara, coxa norma and coxa valga during total hip arthroplasty. Bone mineral density (BMD) was assessed preoperatively by dual energy X-ray absorptiometry (DXA). Cortical and trabecular microstructure and three-dimensional osteocyte lacunar characteristics were assessed in the superolateral and inferomedial neck using ex vivo high resolution micro-computed tomography. Additionally, BMD distribution and osteocyte lacunar characteristics were analyzed by quantitative backscattered electron imaging (qBEI). All groups presented thicker inferomedial than superolateral cortices. Furthermore, the superolateral site exhibited a lower osteocyte lacunar density along with lower lacunar sphericity than the inferomedial site, independent of NSA. Importantly, BMD and corresponding T-scores correlated with microstructural parameters at the inferomedial but not superolateral neck. In conclusion, we provide micromorphological evidence for fracture vulnerability of the superolateral neck, which is independent of NSA and BMD. The presented bone qualitative data provide an explanation why DXA may be insufficient to predict a substantial proportion of femoral neck fractures. Statement of significanceThe femoral neck, one of the most common fracture sites, is subject to a complex loading pattern. Site-specific differences (i.e., superolateral vs. inferomedial) in bone quality influence fracture risk, but it is unclear how this relates to hip geometry and bone mineral density (BMD) measurements in vivo. Here, we examine femoral neck specimens using a variety of high-resolution imaging techniques and demonstrate impaired bone quality in the superolateral compared to the inferomedial neck. Specifically, we found impaired cortical and trabecular microarchitecture, mineralization, and osteocyte properties, regardless of neck-shaft angle. Since BMD correlated with bone quality of the inferomedial but not the superolateral neck, our results illustrate why bone densitometry may not predict a substantial proportion of femoral neck fractures.

Paranasal sinus system and upper respiratory tract evolution in Mesozoic pelagic crocodylomorphs.

Thalattosuchians were a predominately marine clade of Mesozoic crocodylomorphs, including semi-aquatic teleosauroid and obligately pelagic metriorhynchid subclades. Recent advances in our understanding of thalattosuchian endocranial anatomy have revealed new details of the evolutionary transition from terrestrial to marine to pelagic taxa. Paranasal sinuses, however, have received little attention. Herein, we investigate the evolution of the paranasal sinus system and part of the upper respiratory system (nasopharyngeal ducts) in Thalattosuchia, by reconstructing the nasal and paranasal anatomy in CT scans of seven thalattosuchian skulls: one teleosauroid, two basal metriorhynchoids and four metriorhynchids. Our outgroups were: three extant crocodylian species (including adult and subadult skulls) and the basal crocodyliform Protosuchus. We found thalattosuchians exhibit exceptionally reduced paranasal sinus systems, solely comprising the antorbital sinus, as has been previously proposed. The semi-aquatic basal thalattosuchians Palgiopthalmosuchus gracilirostris and Pelagosaurus typus both have an antorbital sinus partially located medial to a reduced external antorbital fenestra and broadly communicating with the dorsal alveolar canal. In pelagic metriorhynchids, the antorbital cavity is more extensive than in basal taxa and possibly had an active function associated with a hypothesized accessory suborbital diverticulum, but our reconstructions are insufficient to confirm or reject the presence of such a diverticulum. The nasopharyngeal ducts of metriorhynchids are dorsoventrally enlarged, possibly enabling stronger ventilation. The sequence of acquisition of craniofacial adaptations show a mosaic pattern and appears to predate many skeletal adaptations, suggesting these changes occurred early in the thalattosuchian marine transition.

Extreme flow simulations reveal skeletal adaptations of deep-sea sponges.

Since its discovery1,2, the deep-sea glass sponge Euplectella aspergillum has attracted interest in its mechanical properties and beauty. Its skeletal system is composed of amorphous hydrated silica and is arranged in a highly regular and hierarchical cylindrical lattice that begets exceptional flexibility and resilience to damage3-6. Structural analyses dominate the literature, but hydrodynamic fields that surround and penetrate the sponge have remained largely unexplored. Here we address an unanswered question: whether, besides improving its mechanical properties, the skeletal motifs of E. aspergillum underlie the optimization of the flow physics within and beyond its body cavity. We use extreme flow simulations based on the 'lattice Boltzmann' method7, featuring over fifty billion grid points and spanning four spatial decades. These in silico experiments reproduce the hydrodynamic conditions on the deep-sea floor where E. aspergillum lives8-10. Our results indicate that the skeletal motifs reduce the overall hydrodynamic stress and support coherent internal recirculation patterns at low flow velocity. These patterns are arguably beneficial to the organism for selective filter feeding and sexual reproduction11,12. The present study reveals mechanisms of extraordinary adaptation to live in the abyss, paving the way towards further studies of this type at the intersection between fluid mechanics, organism biology and functional ecology.

Ecophysiological steps of marine adaptation in extant and extinct non-avian tetrapods.

Marine reptiles and mammals are phylogenetically so distant from each other that their marine adaptations are rarely compared directly. We reviewed ecophysiological features in extant non-avian marine tetrapods representing 31 marine colonizations to test whether there is a common pattern across higher taxonomic groups, such as mammals and reptiles. Marine adaptations in tetrapods can be roughly divided into aquatic and haline adaptations, each of which seems to follow a sequence of three steps. In combination, these six categories exhibit five steps of marine adaptation that apply across all clades except snakes: Step M1, incipient use of marine resources; Step M2, direct feeding in the saline sea; Step M3, water balance maintenance without terrestrial fresh water; Step M4, minimized terrestrial travel and loss of terrestrial feeding; and Step M5, loss of terrestrial thermoregulation and fur/plumage. Acquisition of viviparity is not included because there is no known case where viviparity evolved after a tetrapod lineage colonized the sea. A similar sequence is found in snakes but with the haline adaptation step (Step M3) lagging behind aquatic adaptation (haline adaptation is Step S5 in snakes), most likely because their unique method of water balance maintenance requires a supply of fresh water. The same constraint may limit the maximum body size of fully marine snakes. Steps M4 and M5 in all taxa except snakes are associated with skeletal adaptations that are mechanistically linked to relevant ecophysiological features, allowing assessment of marine adaptation steps in some fossil marine tetrapods. We identified four fossil clades containing members that reached Step M5 outside of stem whales, pinnipeds, sea cows and sea turtles, namely Eosauropterygia, Ichthyosauromorpha, Mosasauroidea, and Thalattosuchia, while five other clades reached Step M4: Saurosphargidae, Placodontia, Dinocephalosaurus, Desmostylia, and Odontochelys. Clades reaching Steps M4 and M5, both extant and extinct, appear to have higher species diversity than those only reaching Steps M1 to M3, while the total number of clades is higher for the earlier steps. This suggests that marine colonizers only diversified greatly after they minimized their use of terrestrial resources, with many lineages not reaching these advanced steps. Historical patterns suggest that a clade does not advance to Steps M4 and M5 unless these steps are reached early in the evolution of the clade. Intermediate forms before a clade reached Steps M4 and M5 tend to become extinct without leaving extant descendants or fossil evidence. This makes it difficult to reconstruct the evolutionary history of marine adaptation in many clades. Clades that reached Steps M4 and M5 tend to last longer than other marine tetrapod clades, sometimes for more than 100 million years.

Complex sexually dimorphic traits shape the parallel evolution of a novel reproductive strategy in Sulawesi ricefishes (Adrianichthyidae)

BackgroundPelvic brooding is a form of uni-parental care, and likely evolved in parallel in two lineages of Sulawesi ricefishes. Contrary to all other ricefishes, females of pelvic brooding species do not deposit eggs at a substrate (transfer brooding), but carry them until the fry hatches. We assume that modifications reducing the costs of egg carrying are beneficial for pelvic brooding females, but likely disadvantageous in conspecific males, which might be resolved by the evolution of sexual dimorphism via sexual antagonistic selection. Thus we hypothesize that the evolution of pelvic brooding gave rise to female-specific skeletal adaptations that are shared by both pelvic brooding lineages, but are absent in conspecific males and transfer brooding species. To tackle this, we combine 3D-imaging and morphometrics to analyze skeletal adaptations to pelvic brooding.ResultsThe morphology of skeletal traits correlated with sex and brooding strategy across seven ricefish species. Pelvic brooding females have short ribs caudal of the pelvic girdle forming a ventral concavity and clearly elongated and thickened pelvic fins compared to both sexes of transfer brooding species. The ventral concavity limits the body cavity volume in female pelvic brooders. Thus body volumes are smaller compared to males in pelvic brooding species, a pattern sharply contrasted by transfer brooding species.ConclusionsWe showed in a comparative framework that highly similar, sexually dimorphic traits evolved in parallel in both lineages of pelvic brooding ricefish species. Key traits, present in all pelvic brooding females, were absent or much less pronounced in conspecific males and both sexes of transfer brooding species, indicating that they are non-beneficial or even maladaptive for ricefishes not providing extended care. We assume that the combination of ventral concavity and robust, elongated fins reduces drag of brooding females and provides protection and stability to the egg cluster. Thus ricefishes are one of the rare examples where environmental factors rather than sexual selection shaped the evolution of sexually dimorphic skeletal adaptations.

A new darwinopteran pterosaur reveals arborealism and an opposed thumb

Pterosaurs, which lived during the Mesozoic, were the first known vertebrates to evolve powered flight.1,2 Arboreal locomotion has been proposed for some taxa,3,4 and even considered to have played a role in the origin of pterosaur flight.5,6 Even so, there is still need for comprehensive quantitative ecomorphological analyses.3,4 Furthermore, skeletal adaptations correlated to specialized lifestyles are often difficult to recognize and interpret in fossils. Here we report on a new darwinopteran pterosaur that inhabited a unique forest ecosystem from the Jurassic of China. The new species exhibits the oldest record of palmar (or true) opposition of the pollex, which is unprecedented for pterosaurs and represents a sophisticated adaptation related to arboreal locomotion. Principal-coordinate analyses suggest an arboreal lifestyle for the new species but not for other closely related species from the same locality, implying a possible case of ecological niche partitioning. The discovery adds to the known array of pterosaur adaptations and the history of arborealism in vertebrates. It also adds to the impressive early bloom of arboreal communities in the Jurassic of China, shedding light on the history of forest environments.

The TrkA agonist gambogic amide augments skeletal adaptation to mechanical loading.

The periosteal and endosteal surfaces of mature bone are densely innervated by sensory nerves expressing TrkA, the high-affinity receptor for nerve growth factor (NGF). In previous work, we demonstrated that administration of exogenous NGF significantly increased load-induced bone formation through the activation of Wnt signaling. However, the translational potential of NGF is limited by the induction of substantial mechanical and thermal hyperalgesia in mice and humans. Here, we tested the effect of gambogic amide (GA), a recently identified robust small molecule agonist for TrkA, on hyperalgesia and load-induced bone formation. Behavioral analysis was used to assess pain up to one week after axial forelimb compression. Contrary to our expectations, GA treatment was not associated with diminished use of the loaded forelimb or sensitivity to thermal stimulus. Furthermore, dynamic histomorphometry revealed a significant increase in relative periosteal bone formation rate as compared to vehicle treatment. Additionally, we found that GA treatment was associated with an increase in the number of osteoblasts per bone surface in loaded limbs as well as a significant increase in the fold change of Ngf, Wnt7b, and Axin2 mRNA expression as compared to vehicle (control). To test the effect of GA on osteoblasts directly, we cultured MC3T3-E1 cells for up to 21days in osteogenic differentiation media containing NGF, GA, or vehicle (control). Media containing GA induced the significant upregulation of the osteoblastic differentiation markers Runx2, Bglap2, and Sp7 in a dose-dependent manner, whereas treatment with NGF was not associated with any significant increases in these markers. Furthermore, consistent with our in vivo findings, we observed that administration of 50nM of GA upregulated expression of Ngf at both Day 3 and Day 7. However, cells treated with the highest dose of GA (500nM) had significantly increased apoptosis and impaired cell proliferation. In conclusion, our study indicates GA may be useful for augmenting skeletal adaptation to mechanical forces without inducing hyperalgesia.

New Advances in Osteocyte Mechanotransduction.

Skeletal adaptation to mechanical loading plays a critical role in bone growth and the maintenance of bone homeostasis. Osteocytes are postulated to serve as a hub orchestrating bone remodeling. The recent findings on the molecular mechanisms by which osteocytes sense mechanical loads and the downstream bone-forming factors are reviewed. Calcium channels have been implicated in mechanotransduction in bone cells for a long time. Efforts have been made to identify a specific calcium channel mediating the skeletal response to mechanical loads. Recent studies have revealed that Piezo1, a mechanosensitive ion channel, is critical for normal bone growth and is essential for the skeletal response to mechanical loading. Identification of mechanosensors and their downstream effectors in mechanosensing bone cells is essential for new strategies to modulate regenerative responses and develop therapies to treat the bone loss related to disuse or advanced age.

Sex differences in the effect of diet, obesity, and exercise on bone quality and fracture toughness.

Bone fragility and obesity are both diseases that are multifactorial in etiology and pathology. The contributing role of high fat diet (HFD) versus energy overconsumption on bone health is controversial. Exercise is often prescribed for improving bone health, but it is unclear whether HFD or overconsumption influences skeletal adaptations to exercise. Female and male Wistar rats were fed HFD or low fat diet (LFD) for 10weeks, starting at 8weeks of age. Within HFD, rats were labeled Obesity-Resistant (OR) or Obesity-Prone (OP) based on weight and fat gain. Within each diet and phenotype group, rats were randomized to treadmill exercise or sedentary control (SED) for the final 4weeks. Femurs were assessed for fracture toughness. Cortical lamellar and nonlamellar bone microscale material behavior and chemistry were assessed using nanoindentation and Raman spectroscopy. Female bones had higher fracture toughness and mineral: matrix ratio than male bones. Diet and energy overconsumption affected bone characteristics in a sex-dependent manner, where the divergence between OP and OR in response to HFD occurred more rapidly in males. Diet composition, in general, had a stronger effect on bone quality than overconsumption. HFD dramatically decreased bone size and lamellar mineral:matrix compared to LFD. Effects of short-term exercise training on microscale tissue properties were generally more robust with LFD. Exercise enhanced the contrast between lamellar and nonlamellar bone for nanoindentation modulus but decreased this contrast for plastic work. Our data demonstrate the complexities in the relationship between diet and obesity and highlight the importance of addressing both aspects when characterizing bone quality and fracture resistance.

A morphological analysis of the cervical spine of the dolphin

Objective:Morphology of bones of cervical vertebrae of dolphin was studied. When compared to human vertebrae the structural modifications in terms of functional needs are evaluated.Material:Morphological analysis of duly prepared bones of species D. delphis was carried out.Result:The craniocervical junction and cervical spine of the dolphin (Delphinus delphis) has unique adaptations to allow for dorsoventrally undulating swimming movements as well as leaping out of water. The key differences from the human cervical spine include the absence of an odontoid process limiting rotatory movements, disproportionately short and wide vertebral bodies and a unilaterally elongated transverse process of the axis. Moreover, the cervical spine of the dolphin is disproportionally short compared to humans. These modifications give strength and stability to the cervical spine allowing maximal agility for flexion-extension movements of the lumbocaudal spine, which are keys for propulsion. The unilaterally elongated transverse process likely allows for rotatory spinning, suggesting possible lateral dominance of rotatory spin in this species.Conclusions:Despite the skeletal adaptations, the cervical spine is strongly resonant of a mammalian heritage with a remarkably similar form and structure to house neurovascular contents and to allow muscular attachments.

New manual unguals of Trierarchuncus prairiensis from the Hell Creek Formation, Montana, and the ontogenetic development of the functional alvarezsaurid hand claw

The Alvarezsauridae comprise a clade of small-bodied theropod dinosaurs with highly-specialized skeletal adaptations, primarily reduced but proportionately robust forelimbs which have been hypothesized as relating to an insectivorous ecology. Alvarezsaurids are known predominantly from Mongolia, China, and South America, with a comparatively sparse North American record, where alvarezsaurid remains are among the most rarely recovered vertebrate fossils from the Upper Cretaceous Western Interior. North American alvarezsaurids include Albertonykus borealis from the lower Maastrichtian Horseshoe Canyon Formation of Alberta, Canada, known from a partial skeleton and additional isolated remains, and the recently named Trierarchuncus prairiensis from the upper Maastrichtian Hell Creek Formation of eastern Montana, USA, known previously from isolated specimens, including three manual D-I unguals, a partial radius, and a partial metatarsal III. Here we describe two new manual D-I unguals referable to the alvarezsaurid Trierarchuncus from the Hell Creek Formation of eastern Montana, USA. These new unguals contribute additional detail to the currently known ontogenetic series of Trierarchuncus manual D-I unguals and indicate the sequence and degree of change that occurred through growth within these alvarezsaurid hand claws. These changes appear to be modifications and reinforcement related to stresses induced from the hypothesized ecology of alvarezsaurids as insectivores which would tear apart substrates in search of insect prey, and as such can be characterized as ecologically-driven ontogenetic changes. Additionally, we demonstrate morphological indicators for determining whether isolated alvarezsaurid manual D-I unguals pertain to the right or left manus.