The distribution of motoneurons supplying hind limb muscles in the clawed toad, Xenopus laevis

The distribution of motoneurons in the lumbar spinal cord (spinal segments 8-10) of the clawed toad, Xenopus laevis, was studied with the horseradish peroxidase technique. In a total of 13 different hind limb muscles this tracer was applied in a slow-release gel. Motoneurons innervating a particular hind limb muscle were clustered in longitudinally arranged motor pools. Motor pools of different muscles did show considerable overlap both in the rostrocaudal and transverse plane. But, the various motor pools clearly show a somatotopic organization of motoneurons even in such a condensed lumbar spinal cord as in Xenopus laevis. Motoneurons innervating more distally positioned muscles are generally found in more caudal segments, while proximal muscles (with the exception of the m. adductor magnus) are supplied by motoneurons more or less throughout the lumbar enlargement. Flexor muscles usually are innervated by motoneurons situated ventrolaterally in the ventral horn, extensor muscles by dorsomedially found motoneurons. This pattern is particularly apparent for proximal (thigh) muscles, less so for more distal (shank and foot) muscles. The present data are in keeping with those obtained with the retrograde cell degeneration technique in ranid frogs and are consistent with observations in other tetrapods, although a more clear separation of motor pools is evident in "higher" vertebrates such as birds and mammals.     

Reformation of specific neuromuscular connections during axolotl limb regeneration: evidence that the first contacts are correct

Retrograde neuronal tracing with horseradish peroxidase was used to determine the position in the spinal cord of the motor neurone pools of a proximal (biceps) and a distal (extensor digitorum) limb muscle at various times during axolotl limb regeneration. It was found that from the earliest stages of muscle redifferentiation (as judged by light and electron microscopic analysis) the vast majority of axons innervating the regenerating muscles came from cells within the bounds of the normal motor neurone pool for each muscle. A few incorrect projections were noted in that the regenerating proximal muscle was sometimes innervated by some cells caudal to its normal motor neurone pool. The results are discussed in terms of mechanisms that may be operating in the regenerating limb to ensure that specific neuromuscular connections are made.     

Functional organization of locomotor interneurons in the ventral lumbar spinal cord of the newborn rat

Although the mammalian locomotor CPG has been localized to the lumbar spinal cord, the functional-anatomical organization of flexor and extensor interneurons has not been characterized. Here, we tested the hypothesis that flexor and extensor interneuronal networks for walking are physically segregated in the lumbar spinal cord. For this purpose, we performed optical recordings and lesion experiments from a horizontally sectioned lumbar spinal cord isolated from neonate rats. This ventral hemi spinal cord preparation produces well-organized fictive locomotion when superfused with 5-HT/NMDA. The dorsal surface of the preparation was visualized using the Ca(2+) indicator fluo-4 AM, while simultaneously monitoring motor output at ventral roots L2 and L5. Using calcium imaging, we provided a general mapping view of the interneurons that maintained a stable phase relationship with motor output. We showed that the dorsal surface of L1 segment contains a higher density of locomotor rhythmic cells than the other segments. Moreover, L1 segment lesioning induced the most important changes in the locomotor activity in comparison with lesions at the T13 or L2 segments. However, no lesions led to selective disruption of either flexor or extensor output. In addition, this study found no evidence of functional parcellation of locomotor interneurons into flexor and extensor pools at the dorsal-ventral midline of the lumbar spinal cord of the rat.     

Forearm compartment syndrome: anatomical analysis of surgical approaches to the deep space

Forearm compartment syndrome is a surgical emergency that usually requires release of the superficial muscle compartments. In some clinical situations it is imperative to also explore the deep muscle compartments. There are no anatomical guides for surgical exploration of the deep compartments that would minimize collateral damage to surrounding vessels, nerves, and muscles. Surgical injury in the setting of ischemia, especially vascular injury, compounds the tissue damage that has already occurred. The authors evaluated four surgical approaches (three volar and one dorsal) to the deep forearm by performing detailed anatomical dissections on 10 embalmed and plastinated cadavers. They used a scoring system to rate the approaches for their ability to visualize the deep space without causing iatrogenic injury to superficial muscles, arteries, and nerves. In the volar forearm, an ulnar approach to the deep space is simple, causes the least iatrogenic surgical injury, and provides access to the deep volar forearm structures. The plane of dissection is between the flexor carpi ulnaris and the flexor digitorum superficialis. Dividing one or two distal segmental branches of the ulnar artery to the distal flexor digitorum superficialis exposes the pronator quadratus. Lifting the ulnar neurovascular bundle with the flexor digitorum superficialis in the middle third of the forearm exposes the flexor digitorum profundus and the flexor pollicis longus. This approach to the deep space requires no sharp dissection. In the dorsal forearm, a midline approach between the extensor digitorum communis and the extensor carpi radialis brevis is simple and safe.     

Analysis of "Teno-uchi" maneuver in releasing Japanese-style bows based on muscle activities and forces acting on the bow

Since a Japanese-style bow has a very complicated shape and structure, an archer has to apply the "Teno-uchi" maneuver including horizontally twisting torque, or "Nejiri", and sagittally down-pushing torque, or "Uwa-oshi", to the restoring bow in order to hit the target. The purpose of this study was to investigate the biomechanical relationship between the muscular activities of the left forearm and the operation of "Teno-uchi" maneuver. Surface EMG of left forearm muscles and the two kinds of torque acting on the bow around the time of release were recorded in 10 experienced subjects during arrow shooting. The "Biku", an involuntary resignation from release happening in the shooting, was also examined. Close analyses of the results revealed that activation of the extensor carpi ulnaris and extensor digitorum muscles together with inhibition of the flexor carpi ulnaris muscle brought about "Nejiri", while activation of the extensor carpi ulnaris as well as flexor carpi ulnaris muscles and inhibition of the extensor carpi redialis longus and extensor digitorum muscles gave rise to "Uwa-oshi", thus causing activities of trade-off nature in the extensor digitorum and flexor carpi ulnaris muscles for the "Nejiri" and "Uwa-oshi. The trade-off activities were presumably actualized through time-sharing coordination between the muscles.     

Postnatal growth and differentiation in three hindlimb muscles of the rat

Summary The postnatal development, between 0 and 90 days, of three hindlimb muscles and diaphragm of the rat was investigated with respect to fiber types and diameter (histochemistry) and substrate oxidation rates and enzyme activities (biochemistry). The process of muscle fiber differentiation into mature patterns was evaluated by visual classification into 3 or 4 groups having different staining intensities for 3 enzyme-histochemical reactions, enabling 26 fiber types to be distinguished. These exhibited specific sizes and growth rates that varied among the muscles. One of the hindleg muscles (flexor digitorum brevis) remained much more immature than soleus and extensor digitorum longus.The histochemical and biochemical findings correlated well. The capacity for pyruvate and palmitate oxidation, and the activities of cytochrome c oxidase and citrate synthase, increased markedly between 9 and 37 days in soleus and extensor digitorum longus (except citrate synthase in the latter) but not in flexor digitorum brevis. Creatine kinase activity increased in all hindlimb muscles. Both the capacity and the activity of pyruvate oxidation (determined in homogenates and intact isolated muscles, respectively), were in accordance with the fiber type composition. In contrast to oxidation capacity, the activity of pyruvate oxidation decreased after birth until the mature stage, when a value of 18–42% of that of early postnatal muscles was recorded.     

Electromyographic and kinematic studies of tail movements during falling in cats

When falling from an inverted position, EMG activities of tail muscles (the m. extensor caudae lateralis, m. abductor caudae externus, m. flexor caudae longus) and tail movements were recorded in 7 long-tailed adult cats. After being released from an elevated position, cat rotates the tail in a reverse direction to rotation of other parts of the cat's body then lands on four legs. Rotation of the tail was started by EMG activities of the tail muscles on one side. Both synchronized and alternating groups of discharge occur between its left and right side, while extensor and flexor movements and displacements of its tail appear in the air. After transection of ventral roots from the coccygeal spinal segments innervating tail muscles, cats often fail to land on four legs. These facts suggest that that tail movements control body balance in the air when falling from an inverted position.     

Functional identification of interneurons responsible for left-right coordination of hindlimbs in mammals

Local neuronal networks that are responsible for walking are poorly characterized in mammals. Using an innovative approach to identify interneuron inputs onto motorneuron populations in a neonatal rodent spinal cord preparation, we have investigated the network responsible for left-right coordination of the hindlimbs. We demonstrate how commissural interneurons (CINs), whose axons traverse the midline to innervate contralateral neurons, are organized such that distinct flexor and extensor centers in the rostral lumbar spinal cord define activity in both flexor and extensor caudal motor pools. In addition, the nature of some connections are reconfigured on switching from rest to locomotion via a mechanism that might be associated with synaptic plasticity in the spinal cord. These results from identified pattern-generating interneurons demonstrate how interneuron populations create an effective network to underlie behavior in mammals.     

Identifying tasks to elicit maximum voluntary contraction in the muscles of the forearm

Maximum voluntary contractions (MVCs) are often used for the normalisation of electromyography data to enable comparison of signal patterns within and between study participants. Recommendations regarding the types of tasks that are needed to collect MVCs for the muscles of the forearm have been made, specifically advocating the use of resisted moment tasks to get better estimates of forearm MVCs. However, a protocol detailing which specific tasks to employ has yet to be published. Furthermore, the effects of limb dominance on the collection of MVCs have not been considered previously. Muscle activity was monitored while 23 participants performed nine isometric, resisted tasks. The tasks that are likely to elicit MVC in the flexor carpi ulnaris, flexor carpi radialis, flexor digitorum superficialis, extensor carpi ulnaris, extensor carpi radialis, extensor digitorum communis, and pronator teres were identified. Thus, targeted protocols can be designed to mitigate against fatigue. Hand dominance had limited effect, with differences being found only in the finger flexors and extensors (p< 0.03). Thus, use of the contralateral flexor digitorum superficialis and extensor digitorum communis muscles to obtain baselines for activation levels and patterns may not be appropriate.     

Structure of tendon organs of the rat after neonatal de-efferentation

Summary The number, size and structure of tendon organs were examined in leg muscles of the rat 3–19 weeks after de-efferentation performed in newborn animals by removal of the lumbosacral spinal cord. After this operation, tendon organs differentiated and grew in disused muscles and were innervated by primary sensory neurons, the dorsal roots of which had been disrupted.Three weeks after de-efferentation extensor digitorum longus muscles contained 14.1±1.0 (mean±standard error) and soleus muscles had 14.2±1.6 tendon organs, which corresponds to the mean number of tendon organs in the respective control muscles. The mean size of tendon organs was, however, changed. Tendon organs became on the average by 53% longer and by 35% thinner in de-efferented extensor digitorum longus muscles that were prolonged due to immobilization, as compared with shorter and wider tendon organs in de-efferented soleus muscle that remained in the shortened position.The ultrastructural differentiation of tendon organs was completed after the operation as under normal conditions. Thus it can be concluded that elimination of muscle function during the period of postnatal development indirectly affects the mean size of these receptors, but does not otherwise interfere with their morphogenesis.     

Increase of CGRP Expression in Motor Endplates Within Fore and Hind Limb Muscles of the Degenerating Muscle Mouse (<Emphasis Type="Italic">Scn8a</Emphasis><Superscript><Emphasis Type="Italic">dmu</Emphasis></Superscript>)

The distribution of calcitonin gene-related peptide (CGRP) was examined in skeletal muscles of fore and hind limb as well as in oral and cranio-facial regions of the degenerating muscle (dmu) mouse, which harbours a null mutation in the voltage-gated sodium channel gene Scn8a. In limb, oral and cranio-facial muscles of wild type mice, only a few motor endplates contained CGRP-immunoreactivity. However, many CGRP-immunoreactive motor endplates appeared in the triceps brachii muscle, the biceps brachii muscle, the brachialis muscle, and the gastrocnemius muscle of dmu mice. CGRP-immunoreactive density of motor endplates in the skeletal muscles was also elevated by the mutation. In these muscles, the atrophy of muscle fibers could be detected and the density of cell nuclei in the musculature increased. In the flexor digitorum profundus muscle, the flexor digitorum superficialis muscle, and the soleus muscle as well as in oral and cranio-facial muscles, however, the distribution of CGRP-immunoreactivity was barely affected by the mutation. The morphology of muscle fibers and the distribution of cell nuclei within them were also similar in wild type and dmu mice. In the lumbar spinal cord of dmu mice, CGRP-immunoreactive density of spinal motoneurons increased. These findings suggest that the atrophic degeneration in some fore and hind limb muscles of dmu mice may increase CGRP expression in their motoneurons.     

Nerve stimulation with a multi-contact cuff electrode: validation of model predictions

The recruitment characteristics of muscle selective nerve stimulation by a multi-contact nerve cuff electrode, as predicted by computer modeling, have been investigated in acute experiments on rabbits. A nerve cuff containing five or six dot electrodes was placed around the sciatic nerve in five rabbits. M-waves were recorded with wire electrodes from the lateral gastrocnemius, soleus, tibialis anterior, and extensor digitorum longus muscles. The muscle recruitment performances of three contact configurations (monopole, transverse bipole, transverse tripole) were compared. The selectivity was quantified by the recruitment of two muscles (one extensor and one flexor) in response to a particular stimulus. The results showed that only in a few cases, transverse bi- and tripolar stimulation provided a better selectivity than monopolar stimulation. Neither of the two extensors, nor of the two flexors could be stimulated separately. In accordance with the results of the modeling studies, bi- and tripolar stimulation required higher stimulus currents than monopolar stimulation, whereas maximum recruitment and slopes of recruitment curves were lower. The rabbit sciatic nerve appears to be a less suitable preparation for reproducible selectivity experiments, due to the variability in the number and size of the fascicles and their position in this nerve.     

Cryptic organisation within an apparently irregular rostrocaudal distribution of interneurons in the embryonic zebrafish spinal cord

The molecules and mechanisms involved in patterning the dorsoventral axis of the developing vertebrate spinal cord have been investigated extensively and many are well known. Conversely, knowledge of mechanisms patterning cellular distributions along the rostrocaudal axis is relatively more restricted. Much is known about the rostrocaudal distribution of motoneurons and spinal cord cells derived from neural crest but there is little known about the rostrocaudal patterning of most of the other spinal cord neurons. Here we report data from our analyses of the distribution of dorsal longitudinal ascending (DoLA) interneurons in the developing zebrafish spinal cord. We show that, although apparently distributed irregularly, these cells have cryptic organisation. We present a novel cell-labelling technique that reveals that DoLA interneurons migrate rostrally along the dorsal longitudinal fasciculus of the spinal cord during development. This cell-labelling strategy may be useful for in vivo analysis of factors controlling neuron migration in the central nervous system. Additionally, we show that DoLA interneurons persist in the developing spinal cord for longer than previously reported. These findings illustrate the need to investigate factors and mechanisms that determine “irregular” patterns of cell distribution, particularly in the central nervous system but also in other tissues of developing embryos.     

Menadione-linked α-glycerophosphate dehydrogenase activity of motoneurons in rat soleus and extensor digitorum longus neuron pools

After injection of horseradish peroxidase into the soleus (slow twitch) and extensor digitorum longus (fast twitch) muscles, glycolytic enzyme activity as reflected by -glycerophosphate dehydrogenase activity of labeled motoneurons in the neuron pool was examined. No differences were found in glycolytic enzyme activity of motoneurons between slow twitch and fast twitch neuron pools.     

Analysis of Rat Hindlimb Muscle Proteins by Two-Dimensional Gels Following Spinal Cord Injury

Proteins from extensor digitorum longus (EDL), plantaris (PLN), and soleus (SOL) muscles of adult, female rats were examined by high resolution two-dimensional gel electrophoresis up to 4 weeks following spinal cord transection. The electrophoretograms were analyzed by computer imaging and densitometry. Reproducible and significant changes in the relative concentrations of several proteins in each muscle type were detected. Whereas changes involving the largest number of proteins were observed in SOL, changes in EDL and PLN were also detected. In SOL, approximately 50% of the altered proteins increased in concentration and the remaining decreased: Actin and myosin light chains LCF-1 and LCF-2 were among those proteins whose concentrations increased, whereas myosin light chains LCS-1 and LCS-2 were among those proteins whose concentrations decreased. The present findings regarding the reversal in myosin light chain composition provide biochemical support for previously published data on changes in contractile properties of muscles following spinalization. In EDL, the relative concentration of only one protein was elevated in a time-dependent manner. The concentrations of two protein species in PLN were increased following cord transection. These findings provide new biochemical markers on the effects of spinal cord on gene expression in specific hindlimb skeletal muscles.     

The Effects of Direction of Exertion,Path, and Load Placement in Nursing Cart Pushing and Pulling Tasks: An Electromyographical Study

The purpose of this study was to explore the effects of direction of exertion (DOE) (pushing, pulling), path (walking in a straight line, turning left, walking uphill), and load placement (LP) (the 18 blocks were indicated by X, Y and Z axis; there were 3 levels on the X axis, 2 levels on the Y axis, and 3 levels on the Z axis) on muscle activity and ratings of perceived exertion in nursing cart pushing and pulling tasks. Ten participants who were female students and not experienced nurses were recruited to participate in the experiment. Each participant performed 108 experimental trials in the study, consisting of 2 directions of exertion (push and pull), 3 paths, and 18 load placements (indicated by X, Y and Z axes). A 23kg load was placed into one load placement. The dependent variables were electromyographic (EMG) data of four muscles collected bilaterally as follows: Left (L) and right (R) trapezius (TR), flexor digitorum superficialis (FDS), extensor digitorum (ED), and erector spinae (ES) and subjective ratings of perceived exertion (RPE). Split-split-plot ANOVA was conducted to analyze significant differences between DOE, path, and LP in the EMG and RPE data. Pulling cart tasks produced a significantly higher activation of the muscles (RTR:54.4%, LTR:50.3%, LFDS:57.0%, LED:63.4%, RES:40.7%, LES:36.7%) than pushing cart tasks (RTR:42.4%, LTR:35.1%, LFDS:32.3%, LED:55.1%, RES:33.3%, LES:32.1%). A significantly greater perceived exertion was found in pulling cart tasks than pushing cart tasks. Significantly higher activation of all muscles and perceived exertion were observed for walking uphill than walking in a straight line and turning left. Significantly lower muscle activity of all muscles and subject ratings were observed for the central position on the X axis, the bottom position on the Y axis, and the posterior position on the Z axis. These findings suggest that nursing staff should adopt forward pushing when moving a nursing cart, instead of backward pulling, and that uphill paths should be avoided in the design of work environments. In terms of distribution of the load in a nursing cart, heavier materials should be positioned at bottom of the cabinet, centered on the horizontal plane and close to the handle, to reduce the physical load of the nursing staff.     

The specificity of motor innervation of the chick wing does not depend upon the segmental origin of muscles

In vertebrate embryos, motor axons originating from a particular craniocaudal position in the neural tube innervate limb muscles derived from myoblasts of the same segmental level. We have investigated whether this relationship is important for the formation of specific nerve-muscle connections, by altering the segmental origin of muscles and examining their resulting innervation. First, by grafting quail wing somites to a new craniocaudal position opposite the chick wing, we established that the segmental origin of a muscle can be altered: presumptive muscle cells migrated according to their new, rather than their original, somitic level, colonizing a different subset of muscles. However, after reversal of a length of brachial somitic mesoderm along the craniocaudal axis, or exchange or shift of brachial somites, the craniocaudal position of wing muscle motoneurone pools within the spinal cord was undisturbed, despite the new segmental origin of the muscles themselves. While not excluding the possibility that muscles and their motor nerves are labelled segmentally, we conclude that specific motor axon guidance in the wing does not depend upon the existence of such labels.     

Reinnervation of murine muscle following fetal sciatic nerve transection

A technique is reproted that permits transection of the sciatic nerve of mouse fetuses without interfering with fetal viability. Sciaticotomy was performed on Swiss Webster mice at day 17 of gestation; the contralateral side served as a control. Six weeks later the extensor digitorum longus (EDL) muscles on both sides were injected with horseradish peroxidase (HRP). Examination of the lumbar spinal cord revealed that while a substantial number of motor neurons in the region of the spinal cord giving rise to the sciatic nerve died, the EDL muscle did become reinnervated. The size of the EDL motor neuron pool on the denervated-reinnervated side was ～43% of that seen on the control side. While the control EDL motor neuron pool was located in lumbar segments L3–L5, the location of the pool to the denervated-reinnervated EDL was shifted cranially to L2–L4. Denervated-reinnervated EDL muscles were analyzed immunohistochemically to study the effect of fetal denervation on the neuronal cell adhesion molecule (N-CAM) expression. At 2 weeks postnatal, N-CAM immunoreactivity in control muscle was segregated to the motor end plate region, while fetally denervated muscle continued to express N-CAM along the length of the sarcolemma. Thus fetally denervated muscle does not develop the same pattern of N-CAM expression as normal, innervated muscle. By 6 weeks of age, the denervated-reinnervated muscle showed the same level and distribution of N-CAM immunoreactivity as did age-matched control muscle, indicating that most, if not all, of its myofibers had been reinnervated.     

Estimation of instantaneous moment arms of lower-leg muscles

Muscle moment arms at the human knee and ankle were estimated from muscle length changes measured as a function of joint flexion angle in cadaver specimens. Nearly all lower-leg muscles were studied: extensor digitorum longus, extensor hallucis longus, flexor digitorum longus, flexor hallucis longus, gastrocnemius lateralis, gastrocnemius medialis, peroneus brevis, peroneus longus, peroneus tertius, plantaris, soleus, tibialis anterior, and tibialis posterior. Noise in measured muscle length was filtered by means of quintic splines. Moment arms of the mm. gastrocnemii appear to be much more dependent on joint flexion angles than was generally assumed by other investigators. Some consequences for earlier analyses are mentioned.