Epaxial Research Articles

Clinical efficacy and cardiorespiratory effects of intramuscular administration of alfaxalone alone or in combination with dexmedetomidine in cats

ObjectiveTo investigate the sedative, anaesthetic and cardiorespiratory effects of intramuscular (IM) administration of alfaxalone alone or in combination with dexmedetomidine in cats. Study designBlinded, randomized crossover study with a washout period of 15 days. AnimalsSeven adult cats, weighing 3.5 ± 0.7 kg. MethodsCats were assigned randomly to each of three treatments: A5 (alfaxalone 5 mg kg-1), D20A5 (dexmedetomidine 20 μg kg-1 and alfaxalone 5 mg kg-1) and D40A5 (dexmedetomidine 40 μg kg-1 and alfaxalone 5 mg kg-1). Drugs were administered IM into the epaxial muscles. Sedation or anaesthesia scores were evaluated by a modified numerical rating scale. Times to extubation, head-lift, sternal recumbency and standing were recorded. Heart and respiratory rates, systolic arterial pressure, arterial oxygen saturation of haemoglobin, end-tidal carbon dioxide tension and rectal temperature were measured at 5, 10, 15, 20, 30, 45, 60, 90, 120 and 150 minutes after drug administration. Adverse events were recorded. Data were analysed by one-way anova with Tukey’s post-hoc test for parametric values and, for non-normally distributed parameters, a Kruskal–Wallis test and Mann–Whitney U-test for two independent samples (p < 0.05). ResultsSedation scores were significantly different among the treatments. Cats in A5 were deeply sedated, whereas cats administered dexmedetomidine were anaesthetized. The onset of action and the duration of anaesthesia were related to the dose of dexmedetomidine. Cardiorespiratory parameters remained stable in the A5 group. Lower heart rates, higher systolic blood pressures and occasional low pulse oximetry readings were observed in the dexmedetomidine groups. A limited number of adverse events (hyperkinesia, emesis) occurred during recovery. Conclusions and clinical relevanceAlfaxalone administered IM induced sedation in cats. The addition of dexmedetomidine to alfaxalone induced general anaesthesia with a mild decrease in the heart rate and arterial oxygen saturation of haemoglobin.

Mercury and selenium in fish of Fountain Creek, Colorado (USA): possible sources and implications.

Fountain Creek in Colorado USA is a major tributary that confluences with the Arkansas River at Pueblo, Colorado, the result being the tributary’s influence on Arkansas River water quality affecting down-stream users. In a previous study, we found that bryophytes (aquatic plants) accumulated selenium in Fountain Creek watershed and this finding prompted us to investigate the extent of the metalloid in the whole-body tissues of fish. One hundred 11 fish (six species) were collected and analyzed for Se by inductively-coupled plasma emission mass spectrometry. Analysis of all analytical data also showed mercury in all of the fish whole bodies and selected tissues. There was a general increase in selenium but a decrease in mercury in fish with downstream travel-distance. The highest whole-body selenium was in Pueblo, Colorado (3393 µg/kg, dry weight; 906 µg/kg, wet weight); the highest mercury in fish was in the Monument Creek tributary north of Colorado Springs, Colorado (71 µg/kg, dry weight; 19 µg/kg, wet weight). In four tissues of 11 female fish captured, selenium was highest in the livers at eight sites but highest in the ovaries at three sites. Mercury was highest in the epaxial muscle at all sites. Selenium availability could be due to the watershed lithology and land uses; however, mercury could be carried by atmospheric deposition from coal-fired power plants and historic mining activities. Selenium in fish tissues and water samples were compared to U.S. national water quality criteria.

Development of the Epaxial Muscles in the Human Embryo

BackgroundThe appearance of the true muscles of the back is dominated by three muscle columns, but a division into a lateral sacrospinal compartment with longissimus (medial) and iliocostal (lateral) divisions, and a medial compartment with transversospinal muscles is presently more often used. Although back muscles are defined by their embryological origin and innervation pattern, no detailed study on their development is available.MethodsHuman embryos (5–10 weeks development) were studied, using Amira® and Cinema4D® remodeling software for visualization.ResultsAt Carnegie Stage (CS)15, the epaxial portions of the myotomes became identifiable laterally to the developing vertebrae. At CS16, these portions fused to form a longitudinal muscle column, which became innervated by the dorsal branch of the spinal nerve. At CS17, the longitudinal muscle mass segregated into medial and lateral columns (completed at CS18). At CS18, the medial column segregated again into intermediate and medial columns (completed at CS20). Between CS20 and CS23, the cervical portions of the three columns segregated again form lateral to medial resulting ventrolaterally in rod‐like continuations of the caudal portions of the columns and dorsomedially in spade‐like portions. The lateral and intermediate columns did not separate in the lower lumbar and sacral region. The observed topography identifies the iliocostalis and splenius as belonging to the lateral column, the longissimus to the intermediate column, and the multifidus and (semi‐)spinalis to the medial column. The medial group acquired its transverso‐spinal course during closure of the vertebral arches in the early fetal period.ConclusionEpaxial muscle growth is characterized by cranio‐caudal and latero‐medial gradients in development. Our ontogenetic approach shows that all back muscles can be classified as components of the erector spinae.Support or Funding InformationNFP (Netherlands Fellowship Programmes)

Assessing the reproducibility of fractional rates of protein synthesis in muscle tissue measured using the flooding dose technique

The flooding dose technique of Garlick et al. (1980) has become the main method for measuring tissue and whole-animal rates of protein synthesis in ectotherms. However, single tissue samples are used to determine rates of protein synthesis and no studies have examined the pattern of flooding in large tissues such as the white muscle in fishes, which can comprise up to 55% of the wet body mass of a fish and which is poorly perfused. The present study has examined, for the first time, the patterns of flooding and measured rates of protein synthesis in five different regions of the white muscle in the Arctic charr Salvelinus alpinus ranging in size from 25g to 1.6kg following a flooding dose injection of L-[3H]-phenylalanine. The results indicate that the degree of flooding (i.e. free pool specific radioactivity relative to that of the injection solution) and elevation in free phenylalanine concentrations can vary between regions but the calculated fractional rates of protein synthesis were similar in four of the five regions studied. The variability in rates of protein synthesis increased with body size with greater variability observed between regions for fish >1kg in body mass. For consistency between studies, it is recommended that samples are taken from the epaxial muscle in the region below the dorsal fin when measuring fractional rates of white muscle synthesis in fishes.

Role of skeletal muscle in motor neuron development.

The current paper is a continuation of our work most recently described in Kablar, 2011. Here, we show lists of up- and down-regulated genes obtained by a cDNA microarray analysis that compared developing mouse MyoD-/- limb musculature (MyoD-dependent, innervated by Lateral Motor Column motor neurons) and Myf5-/- back (epaxial) musculature (Myf5-dependent, innervated by Medial Motor Column motor neurons) to the control and to each other, at embryonic day 13.5 which coincides with the robust programmed cell death of motor neurons and the inability of myogenesis to undergo its normal progression in the absence of Myf5 and MyoD that at this embryonic day cannot substitute for each other. We wanted to see if/how the myogenic program couples with the neurotrophic one, and also to separate Lateral from Medial column trophic requirements, potentially relevant to Motor Neuron Diseases with the predilection for the Lateral column. Several follow-up steps revealed that Kif5c, Stxbp1 and Polb, differentially expressed in the MyoD-/- limb muscle, and Ppargc1a, Glrb and Hoxd10, differentially expressed in the Myf5-/- back muscle, are actually regulators of motor neuron numbers. We propose a series of follow-up experiments and various ways to consider our current data.

Rapid and simple method for in vivo ex utero development of mouse embryo explants

The in utero development of mammals drastically reduces the accessibility of the mammalian embryo and therefore limits the range of experimental manipulation that can be done to study functions of genes or signaling pathways during embryo development. Over the past decades, tissue and organ-like culture methods have been developed with the intention of reproducing in vivo situations. Developing accessible and simple techniques to study and manipulate embryos is an everlasting challenge. Herein, we describe a reliable and quick technique to culture mid-gestation explanted mouse embryos on top of a floating membrane filter in a defined medium. Viability of the cultured tissues was assessed by apoptosis and proliferation analysis showing that cell proliferation is normal and there is only a slight increase in apoptosis after 12h of culture compared to embryos developing in utero. Moreover, differentiation and morphogenesis proceed normally as assessed by 3D imaging of the transformation of the myotome into deep back muscles. Not only does muscle cell differentiation occur as expected, but so do extracellular matrix organization and the characteristic splitting of the myotome into the three epaxial muscle groups. Our culture method allows for the culture and manipulation of mammalian embryo explants in a very efficient way, and it permits the manipulation of in vivo developmental events in a controlled environment. Explants grown under these ex utero conditions simulate real developmental events that occur in utero.

Three-dimensional movements of the pelvis and the lumbar intervertebral joints in walking and trotting dogs

Current knowledge of the physiological range of motion (ROM) in the canine axial system during locomotion is relatively limited. This is particularly problematic because dogs with back-related dysfunction frequently present for routine consultations. To collect detailed kinematic information and describe the three-dimensional motions of the pelvis and the lumbar spine (i.e. intervertebral joints S1/L7–L2/L1), we recorded ventro-dorsal and latero-lateral X-ray videos of three walking and trotting dogs and reconstructed their pelvic and intervertebral motions using X-ray reconstruction of moving morphology and scientific rotoscoping.Pelvic roll displayed a monophasic motion pattern and the largest ROM with on average 13° and 11° during walking and trotting, respectively. Pelvic yaw had the smallest ROM with on average 5° (walk) and 6° (trot). A biphasic pattern was observed for pelvic pitch with a mean ROM of 8°. At both gaits, the greatest intervertebral motions occurred either in S1/L7 or L7/L6. The intervertebral motions were mono- or biphasic in the horizontal and the transverse body planes and biphasic in the sagittal plane. Cranial to L6/5, the ROM tended to decrease from 3° to <1.5° in all three planes. Our results confirm that pelvic displacement and intervertebral joint movements are tightly linked with pelvic limb action at symmetrical gaits. The overall small movements, particularly cranial to L5, are consistent with the epaxial musculature globally stabilising the spine against the external and internal limb forces acting on the pelvis and the trunk during walking and trotting.

Striped Bass, Morone saxatilis, a New Intermediate Host for the Heterophyid Ascocotyle nana

ABSTRACT: Striped bass, Morone saxatilis (Moronidae), collected from several rivers in South Carolina, U.S.A., were found to be infected with heterophyid metacercariae whose morphology was consistent with Ascocotyle (Phagicola) nana on the basis of descriptions from the literature and via comparison with reference specimens of metacercariae from largemouth bass, Micropterus salmoides (Centrarchidae), a known intermediate host for A. nana. Morphology of metacercariae from both fish species was similar and partial sequencing of their 18S ribosomal DNA gene confirmed that metacercariae from both fish belonged to the same heterophyid species. Young-of-the-year striped bass were not infected and over 65% of the population sampled (N = 39) age 1 yr and older were infected with up to 49 metacercariae per gram of somatic muscle. Mid-line red muscle (lateralis superficialis) had a significantly higher density of metacercariae than epaxial and hypaxial white muscle. Some metacercariae showed signs of degradation...

Canine chondrodystrophic intervertebral disc disease (Hansen type I disc disease)

Intervertebral disc disease (IVDD) is the most common spinal disease in dogs. Chondrodystrophic dogs, which have disproportionably short and curved limbs, are predisposed to Hansen type I IVDD and of these the miniature Dachshund is over represented [1,2], is more likely to be presented at an earlier age [3] and is at greater risk of a severe spinal cord injury [4]. The tendency for IVDD in Dachshunds is inherited [5,6] and a major locus on chromosome 12 harbours genetic variations affecting the development of intervertebral disc calcification [7]. Hansen type I disc degeneration is thought to occur because of loss of notochordal cells which produce proteoglycans which “hold water” in the disc. Chondrodystrophic dogs have a primary deficiency of notochordal cells, a study found that large notochordal cells in the nucleus pulposus of chondrodystrophoid dogs formed 13% of the cell population in young dogs and fell to 0.4% in adults, whereas they were the predominant cell type in the nonchondrodystrophoid dogs at all ages [8]. Thus chondrodystrophoid dogs suffer early degenerative changes in the disc and a concomitant reduction in proteoglycan content, increased collagen, and loss of water content making the discs likely to herniate [8]. Certain lifestyle factors may increase or decrease risk of IVDD and this is currently under investigation. There is a suggestion that exercise (including stair climbing) reduces the incidence of disc calcification [9]. By contrast it has been hypothesized that obesity/lack of postural muscle strength may increase risk. Dachshunds with intervertebral disc extrusion had significantly smaller cross sectional area and greater fat infiltration in the epaxial muscles (muscles which lie dorsal to the horizontal septum of the vertebrae which mobilize and globally stabilize the trunk [10]) compared to dogs presenting with fibrocartilagenous embolism (another acute onset intervertebral disc related spinal disease) [11]. In addition chondrodystrophic dogs may have increased risk of IVVD if they have a more extreme conformation e.g. Dachshunds that have a longer back and shorter limbs are more at risk [12] and breeds with a comparatively heavy head such as the Bassett Hound may be more at risk of cervical disc disease. Breeds with a tendency for kyphoscoliosis such as the French Bulldog may be more at risk of IVDD in the IVDs adjacent to a vertebral malformation [13,14]. This presentation details the pathogeneis, clinical presentation, diagnosis and treatment of IVDD in chondrodystrophic dogs.

Differential Accumulation of Mercury and Selenium in Brown Trout Tissues of a High-Gradient Urbanized Stream in Colorado, USA.

Total mercury (THg) and selenium (Se) were analyzed by Inductively Coupled Plasma Mass Spectrometry in 11 internal and external tissues and stomach contents from 23 brown trout, Salmo trutta, of a 22.9-km reach of a high-gradient stream (upper Fountain Creek) in Colorado, USA, impacted by coal-fired power plants, shale deposits, and urbanization. Trout and water were sampled from four sites ranging from 2335 to 1818m elevation. Lengths, weights, and ages of fish between pairs of the four sites were not significantly different. The dry weight (dw) to wet weight (ww) conversion factor for each tissue was calculated with egg-ovary highest at 0.379 and epaxial muscle fourth highest at 0.223. THg and Se in stomach contents indicated diet and not ambient water was the major source of Hg and Se bioaccumulated. Mean THg ww in kidney was 40.33µg/kg, and epaxial muscle second highest at 36.76µg/kg. None of the tissues exceeded the human critical threshold for Hg. However, all 23 trout had at least one tissue type that exceeded 0.02mg/kg THg ww for birds, and four trout tissues exceeded 0.1mg/kg THg ww for mammals, indicating that piscivorous mammals and birds should be monitored. Se concentrations in tissues varied depending on ww or dw listing. Mean Se dw in liver was higher than ovary at the uppermost site and the two lower sites. Liver tissue, in addition to egg-ovary, should be utilized as an indicator tissue for Se toxicity.

Dorsal fin function in spiny dogfish during steady swimming

AbstractDorsal fins of actinopterygian fishes are known to function to varying degrees as stabilizers and as propulsive elements that augment thrust from the caudal fin. However, little is known about the ability of elasmobranchs to control three‐dimensional conformation of the dorsal fins during swimming, which may alter the force balance during locomotion. In this study, dorsal fin function was investigated in spiny dogfish, Squalus acanthias, swimming steadily at 0.5 and 0.75 BL s−1, using three‐dimensional kinematics and electromyography. Points on the dorsal and caudal fins were tracked in dorsal and lateral views with dual high‐speed video at 125 f s−1. Electrodes were implanted in three points along each dorsal fin muscle and in the adjacent red epaxial muscle. Conformational changes were detected in both dorsal fins at both speeds. Speed was found to influence lateral displacement of the first dorsal fin relative to trunk undulation, with larger magnitudes at 0.5 BL s−1. The first dorsal fin oscillates at a different phase lag than predicted by position on the body, while the second dorsal fin moves in synchrony with the axial musculature. Muscles of the first dorsal fin show synchronous bilateral activation, while there is no clear pattern in the second dorsal fin. This study provides evidence that spiny dogfish control movements of the first dorsal fin during steady swimming to stabilize body position. In contrast, the second dorsal fin appears to be capable of thrust generation. Thus, there is a dual dorsal fin function in spiny dogfish during steady swimming.

Development of the ventral body wall in the human embryo.

Migratory failure of somitic cells is the commonest explanation for ventral body wall defects. However, the embryo increases ~ 25-fold in volume in the period that the ventral body wall forms, so that differential growth may, instead, account for the observed changes in topography. Human embryos between 4 and 10 weeks of development were studied, using amira reconstruction and cinema 4D remodeling software for visualization. Initially, vertebrae and ribs had formed medially, and primordia of sternum and hypaxial flank muscle primordium laterally in the body wall at Carnegie Stage (CS)15 (5.5 weeks). The next week, ribs and muscle primordium expanded in ventrolateral direction only. At CS18 (6.5 weeks), separate intercostal and abdominal wall muscles differentiated, and ribs, sterna, and muscles began to expand ventromedially and caudally, with the bilateral sternal bars fusing in the midline after CS20 (7 weeks) and the rectus muscles reaching the umbilicus at CS23 (8 weeks). The near-constant absolute distance between both rectus muscles and approximately fivefold decline of this distance relative to body circumference between 6 and 10 weeks identified dorsoventral growth in the dorsal body wall as determinant of the 'closure' of the ventral body wall. Concomitant with the straightening of the embryonic body axis after the 6th week, the abdominal muscles expanded ventrally and caudally to form the infraumbilical body wall. Our data, therefore, show that the ventral body wall is formed by differential dorsoventral growth in the dorsal part of the body.

Comparison of isotopic turnover dynamics in two different muscles of a coral reef fish during the settlement phase

The temporal variation in carbon and nitrogen isotopic compositions (noted as δ13C and δ15N) was investigated in the convict surgeonfish (Acanthurus triostegus) at Moorea (French Polynesia). Over a period of 24 days, juveniles were reared in aquaria and subjected to two different feeding treatments: granules or algae. The dynamics of δ13C and δ15N in two muscles (the adductor mandibulae complex and the epaxial musculature) having different functions were compared. At the end of experiments, a steady-state isotopic system in each muscle tissue was not reached. Especially for the algal treatment, we found different patterns of variation in isotopic compositions over time between the two muscles. The turnovers of δ13C showed opposite trends for each muscle but differences are mitigated by starvation and by the metamorphosis. Our study highlighted that the metabolism of coral reef fish may be subjected to catabolism or anabolism of non-protein precursors at settlement, inducing variation in isotopic compositions that are not linked to diet change.

Gymnastic Training and Dynamic Mobilization Exercises Improve Stride Quality and Increase Epaxial Muscle Size in Therapy Horses

The objective was to evaluate the efficacy of gymnastic training (GYM) and dynamic mobilization exercises (DMEs) on stride length (SL) and epaxial muscle size in therapy horses. Nine cross-bred hippotherapy horses that performed three, 25-minute therapeutic riding sessions per week throughout the study period were randomly assigned to three experimental groups: a control group in which the horses were sedentary with no additional physical activity; a group that performed DMEs; and a group that performed both DMEs and additional GYM including pelvic tilting, backing, turning in small circles, and walking over a raised rail to strengthen the abdominal and pelvic stabilizer muscles. The exercises were performed 3 days per week for 3 months, with evaluations at the start and end of the study. Stride quality was assessed by measuring SL and tracking distance (TD). Epaxial muscle size was monitored by ultrasonographic measurement of m. longissimus dorsi (LD) thickness and m. multifidi (MM) cross-sectional area. Paired t tests were used to compare within groups across time, and between groups were detected using analysis of variance with Tukey post hoc test. When walking at 1.3 m/s, SL and TD at walk increased significantly (P < .05) in horses subjected to GYM. Thickness of LD did not change in any group, but cross-sectional area of MM increased significantly by 3.55 cm2 (DME) and 3.78 cm2 (GYM). It was concluded that GYM training improved stride quality and DME-stimulated MM hypertrophy which has been shown to improve intervertebral joint stability in other species.

Epaxial muscle fiber architecture favors enhanced excursion and power in the leaper Galago senegalensis.

Galago senegalensis is a habitual arboreal leaper that engages in rapid spinal extension during push-off. Large muscle excursions and high contraction velocities are important components of leaping, and experimental studies indicate that during leaping by G. senegalensis, peak power is facilitated by elastic storage of energy. To date, however, little is known about the functional relationship between epaxial muscle fiber architecture and locomotion in leaping primates. Here, fiber architecture of select epaxial muscles is compared between G. senegalensis (n = 4) and the slow arboreal quadruped, Nycticebus coucang (n = 4). The hypothesis is tested that G. senegalensis exhibits architectural features of the epaxial muscles that facilitate rapid and powerful spinal extension during the take-off phase of leaping. As predicted, G. senegalensis epaxial muscles have relatively longer, less pinnate fibers and higher ratios of tendon length-to-fiber length, indicating the capacity for generating relatively larger muscle excursions, higher whole-muscle contraction velocities, and a greater capacity for elastic energy storage. Thus, the relatively longer fibers and higher tendon length-to-fiber length ratios can be functionally linked to leaping performance in G. senegalensis. It is further predicted that G. senegalensis epaxial muscles have relatively smaller physiological cross-sectional areas (PCSAs) as a consequence of an architectural trade-off between fiber length (excursion) and PCSA (force). Contrary to this prediction, there are no species differences in relative PCSAs, but the smaller-bodied G. senegalensis trends towards relatively larger epaxial muscle mass. These findings suggest that relative increase in muscle mass in G. senegalensis is largely attributable to longer fibers. The relative increase in erector spinae muscle mass may facilitate sagittal flexibility during leaping. The similarity between species in relative PCSAs provides empirical support for previous work linking osteological features of the vertebral column in lorisids with axial stability and reduced muscular effort associated with slow, deliberate movements during anti-pronograde locomotion.

Cranial Morphology of the Brachystelechid 'Microsaur' Quasicaecilia texana Carroll Provides New Insights into the Diversity and Evolution of Braincase Morphology in Recumbirostran 'Microsaurs'.

Recumbirostran ‘microsaurs,’ a group of early tetrapods from the Late Carboniferous and Early Permian, are the earliest known example of adaptation to head-first burrowing in the tetrapod fossil record. However, understanding of the diversity of fossorial adaptation within the Recumbirostra has been hindered by poor anatomical knowledge of the more divergent forms within the group. Here we report the results of μCT study of Quasicaecilia texana, a poorly-known recumbirostran with a unique, broad, shovel-like snout. The organization of the skull roof and braincase of Quasicaecilia is found to be more in line with that of other recumbirostrans than previously described, despite differences in overall shape. The braincase is found to be broadly comparable to Carrolla craddocki, with a large presphenoid that encompasses much of the interorbital septum and the columella ethmoidalis, and a single compound ossification encompassing the sphenoid, otic, and occipital regions. The recumbirostran braincase conserves general structure and topology of braincase regions and cranial nerve foramina, but it is highly variable in the number of ossifications and their extent, likely associated with the reliance on braincase ossifications to resist compression during sediment compaction and mechanical manipulation by epaxial and hypaxial musculature. Expansion of the deep ventral neck musculature in Quasicaecilia, autapomorphic among recumbirostrans, may reflect unique biomechanical function, and underscores the importance of future attention to the role of the cervical musculature in contextualizing the origin and evolution of fossoriality in recumbirostrans.

Kudoa spp. (Myxozoa) infection in musculature of Plagioscion squamosissimus (Sciaenidae) in the Amazon region, Brazil.

Ninety specimens of Plagioscion squamosissimus captured using fishing tackle in the Outeiro district, state of Pará, were examined. Fish were placed in plastic bags containing water, under conditions of artificial aeration, and transported live to the Carlos Azevedo Research Laboratory (LPCA), in Belém, Pará. They were anesthetized, euthanized and necropsied; small fragments of the epaxial and hypaxial muscles were removed for examination of fresh histological sections by means of optical microscopy. In 100% of the specimens analyzed, parasitic pseudocysts were seen to be interspersed within and between the skeletal muscle. These contained pseudoquadrate and/or star-shaped spores that presented four valves and four polar capsules, which were identified from their morphology as belonging to the genus Kudoa. This is the first report of Kudoa in P. squamosissimus in the Amazon region, Pará, Brazil.

Reevaluating Musculoskeletal Linkages in Suction-Feeding Fishes with X-Ray Reconstruction of Moving Morphology (XROMM)

Suction-feeding fishes encompass a vast diversity of morphologies and ecologies, but during feeding they all rely on musculoskeletal linkages and levers to transform the shortening of muscle into 3D expansion of the mouth cavity. To relate the shape of these skeletal elements to their function in expansion of the mouth, four-bar linkage models have been developed and widely used in studies of ecology, evolution, and development. However, we have lacked the ability to test the predictions of these 2D linkage models against the actual 3D motions of fishes' skulls. A new imaging method, X-ray Reconstruction of Moving Morphology (XROMM), now makes it possible to measure 3D skeletal motions relative to other bones within the head and relative to the fish's body, and thereby to examine directly the proposed linkages. We used XROMM to examine the opercular linkage, in which shortening of the levator operculi muscle is hypothesized to retract the operculum, and thereby the interoperculum and interoperculomandibular ligament to generate depression of the lower jaw about the quadratomandibular joint. XROMM animations of suction strikes in largemouth bass revealed that the operculum is indeed retracted relative to the suspensorium as the levator operculi muscle shortens and the jaw depresses. However, the four-bar model of this linkage overestimates the depression of the jaw by nearly a factor of two. Therefore, caution should be used in interpreting and applying the predictions of this linkage model. When we measured kinematics relative to the fish's body, we found that the operculum was relatively stable, whereas the suspensorium was elevated along with the neurocranium, pushing the quadratomandibular joint forward to produce depression of the jaw. Thus, it is the epaxial muscles elevating the neurocranium that powers depression of the jaw through the opercular linkage. However, the levator operculi muscle plays a crucial role in stabilizing the operculum to allow elevation of the head to produce depression of the lower jaw. These results support the role of cranial muscles in controlling and transmitting power from the axial muscles, rather than generating substantial power themselves. We also demonstrate the utility of XROMM for assessing the function of this, and other, cranial linkages in suction-feeding fishes.

Estimating maximal force output of cetaceans using axial locomotor muscle morphology

AbstractCetaceans span a large range of body sizes and include species with the largest known locomotor muscles. To date, force output and thrust production have only been directly measured in the common bottlenose dolphin (Tursiops truncatus), although thrust forces have been hydrodynamically modeled for some whales. In this study, two metrics of epaxial muscle size—cross‐sectional area (CSA) and mass—were used to estimate force output for 22 species (n = 83 specimens) ranging in size from bottlenose dolphins to blue whales (Balaenoptera musculus). Relative to total body length (TL), maximum force output estimated based upon both muscle CSA (TL1.56 ± 0.05) and mass (TL2.64 ± 0.07) scaled at rates lower than those predicted by geometric scaling, suggesting relative force output decreases with increasing body size in cetaceans. Estimated maximal force outputs were compared to both published drag forces and to the breaking strengths of commercial fishing lines known to entangle whales. The breaking strengths of these lines are within the same order of magnitude, and in some cases, exceed the estimated maximal force output of whales. These results suggest that while powerful animals, large whales may be unable to break the extremely strong fishing line used today.

Life-Long Transgene Expression in Skeletal Muscle Without Transduction of Satellite Cells Following Embryonic Myogenic Progenitor Transduction by Lentivirus Administered in Utero.

Embryologic events in mammalian myogenesis remain to be fully defined. Recent evidence supports the presence of a common progenitor arising in the dermomyotome that gives rise to both embryologic and adult muscle and postnatal myogenic stem cells (satellite cells). In this study, we utilize the technique of early intra-amniotic gene transfer to target nascent muscle progenitors as they traverse the primitive streak before formation of the dermomyotome. This technique robustly transduced both epaxial and hypaxial muscle groups. Marker gene expression is observed in up to 100% muscle fibers in the lower extremities and is sustained for the lifetime of the mouse. We next analyzed transduced muscle for satellite cell transduction using highly sensitive methodology. Surprisingly, despite high levels of sustained transgene expression in muscle fibers, satellite cells lacked the marker transgene. Our data suggest that dermatomyotome is a heterogeneous structure and that not all myogenic progenitors of dermatomyotome give rise to satellite cells.