Intersegmental Muscles Research Articles

The thoracic muscular system and its innervation in third instar Calliphora vicina Larvae. I. Muscles of the pro‐ and mesothorax and the pharyngeal complex

An anatomical description is given by the muscles in the pro- and mesothorax, and those associated with the feeding apparatus (cephalopharyngeal skeleton, CPS) that participate in feeding behavior in third instar Calliphora larvae. The body wall muscles in the pro- and mesothoracic segments are organized in three layers: internal, intermedial, and external. The muscles were labeled with roman numerals according to the nomenclature in use for the abdominal segments. Muscles associated with the CPS are labeled according to their function. The prothorax bears five pairs of lateral symmetrically longitudinal segmental body wall muscles and lacks the transversal muscle group present in the mesothorax and abdominal segments. Additionally, four pairs of intersegmental muscles project from the prothorax to the second, fourth, and fifth segment. The mesothorax bears 15 pairs of segmental longitudinal and 18 pairs of transversal muscles. The accessory pharyngeal muscles span the CPS and the cuticle. Three pairs of protractors and retractors and two pairs of mouth hook accessors (MH(AC)) exist, which move the CPS relative to the body. The pharyngeal muscles are exclusively attached to the structures of the CPS. The mouth hook elevators and depressors, which mediate the hooks rotation are attached to the ventral arm of the CPS and project to a dorsal (elevators) or ventral (depressors) protuberance of the mouth hooks. The cibarial dilator muscles (CDM) span the dorsal arms of the CPS and the dorsal surface of the esophagus and mediate food ingestion. The labial retractors (LRs) lack antagonists and project from the ventral surface of the CPS to the unpaired labium. Contractions of these muscles open the mouth cavity.

Neuromuscular systems in the fifth instar larva of silkworm Bombyx mori (Lepidoptera: Bombycidae): I-Cephalothoracic musculature and its innervation

The cephalo-thoracic musculature of the fifth instar larva of Bombyx mori comprises distinct groups of segmental muscle bands arranged in a stereotyped pattern. It includes dorsal, ventral, tergopleural, tergocoxal, lateral intersegmental, pleurosternal, sternocoxal, pleurocoxal and spiracular muscles. The cephalothoracic segments are innervated by the nerves of brain, suboesophageal ganglion (SG) and three thoracic ganglia (TG1, TG2, TG3).The brain gives nerves for compound eyes, antennae, labrum, frontal ganglion and the integument in the head. The SG, TG1,TG2,and TG3 give out a pair of lateral segmental nerves each, called the dorsal (DN) and ventral (VN) nerves. The DN of SG innervates muscles in the cephalic region, while its VN innervates muscles in the prothorax. The DN of thoracic ganglia innervates muscles in the dorsal, lateral and ventral regions of the hemi-segment while the VN innervates muscles in the ventral region. The innervation pattern indicates the presence of mixed nerves and multiple innervations that facilitate coordinated body movements and locomotion.

Regulation of muscle differentiation and survival by Acheron

Acheron (Achn), a phylogenetically-conserved member of the Lupus antigen family of RNA binding proteins, was initially identified as a novel cell death-associated gene from the intersegmental muscles of the tobacco hawkmoth Manduca sexta. C 2C 12 cells are a standard model for the study of myogenesis. When deprived of growth factors, these cells can be induced to: form multinucleated myotubes, arrest as quiescent satellite-like reserve cells, or undergo apoptosis. Achn expression is induced in myoblasts that form myotubes and acts upstream of the muscle specific transcription factor MyoD. Forced expression of ectopic Achn resulted in the formation of larger myotubes and massive reserve cell death relative to controls. Conversely, dominant-negative or antisense Achn blocked myotube formation following loss of growth factors, suggesting that Achn plays an essential, permissive role in myogenesis. Studies in zebrafish embryos support this hypothesis. Reduction of Achn with antisense morpholinos led to muscle fiber loss and an increase in the number of surviving cells in the somites, while ectopic Achn enhanced muscle fiber formation and reduced cell numbers. These results display a crucial evolutionarily conserved role for Achn in myogenesis and suggest that it plays key roles in the processes of differentiation and self-renewal.

Differential control of cell death and gene expression during two distinct phases of hormonally-regulated muscle death in the tobacco hawkmoth Manduca sexta

In larvae of the tobacco hawkmoth Manduca sexta, the intersegmental muscles (ISMs) span eight abdominal segments and represent the major muscle group. Following pupation, the ISMs in the first two and last two segments undergo programmed cell death (PCD), while the remaining four segments persist until the time of adult eclosion, when they too undergo PCD. ISM death at adult eclosion is initiated by a decline in the circulating ecdysteroid titer and requires de novo gene expression. In this study we have investigated the hormonal regulation and the patterns of gene expression that accompany both early and late ISM death. We find that distinct endocrine cues regulate these two periods of muscle death. Even though the middle segments of ISMs are exposed to the same endocrine environment as the adjacent cells that die following pupation, they do not express death-associated transcripts until they are specifically signaled to die following adult eclosion. These data indicate that subsets of homologous muscles appear to make segment-specific decisions to couple their endogenous cell death programs to distinctly different developmental cues. Nevertheless, once cell death is initiated, they utilize many of the same molecular components.

Acheron, an novel LA antigen family member, binds to cask and forms a complex with id transcription factors

Acheron, a Lupus antigen ortholog, was identified as a novel death-associated transcript from the intersegmental muscles of the mothManduca sexta. Acheron is phylogenetically-conserved and represents a new sub-family of Lupus antigen proteins. Acheron is expressed predominantly in neurons and muscle in vertebrates, and regulates several developmental events including myogenesis, neurogenesis and possibly metastasis. Using Acheron as bait, we performed a yeast two-hybrid screen with a mouse embryo cDNA library and identified CASK-C, a novel CASK/Lin-2 isoform, as an Acheron binding partner. Acheron and CASK-C bind via the C-terminus of Acheron and the CaMKII-like domain of CASK-C. Co-immunoprecipitation assays verify this interaction and demonstrate that Acheron also forms a complex with all members of the Id (inhibitor of differentiation) proteins. Taken together, these data suggest a mechanism by which Acheron may regulate development and pathology.

Honoring contributions of Richard A Lockshin to the field of cell death

On 10 December 2007, a scientific symposium was organized at The Rockefeller University by Zahra Zakeri and Hermann Steller to honor Dr. Richard Lockshin for his contributions to the field of cell death. Over 300 scientists attended this meeting. The speakers and chairs included distinguished scientists in the field, from 20 countries, who have contributed to this special issue. Richard Lockshin is one of the pioneers in the field of cell death contributing to the field for over the past 40 years and still remains one of the field’s primary scientists. Rick was born in Columbus, Ohio in December 1937. His fascination and interest in the natural sciences from an early age led him to become a scientist. He obtained his bachelor’s degree at Harvard University (1959), where he continued his doctoral studies with Carroll M Williams and received his PhD in 1963. The topic of his dissertation was published in a series of five landmark papers, beginning with ‘Endocrine potentiation of the breakdown of the intersegmental muscles of silkmoths’ coining the term ‘programmed cell death’ in 1964. H Robert Horvitz (one of the recipients of the Nobel Prize in 2002) and Lockshin acknowledged the possibility that cell death may be regulated using nonmammalian model systems such as Caenorhabditis elegans and moths. This idea led to the elucidation of the genetic pathways of programmed cell death and has proven operative in mammals as well and has become a major area of scientific endeavor, as evidenced by the existence of this journal. Cell death is now the focus of much research not only in the area of basic science but also in understanding and controlling many diseases such as cancer, degenerative diseases, infection, and many others. Richard has studied the underlying mechanisms involved in programmed cell death using insects, and more recently, zebrafish, as model systems. He was among the first to report on alternative ways of cell death and the involvement of different proteases in cell killing. This finding now has blossomed into a major area of research in the field of cell death. His current research is a continuation of this in the developing embryo. Collaborating with several individuals, he was among the first to recognize and seek new proteins synthesized during programmed cell death; to study the physiology of dying cells and to question why they shrank; to recognize that the regulation of oncogenes was important in cell death; and to emphasize that not all deaths were by classical apoptosis. He continued to work on cell death and development, with a brief excursion into embryology, where he was among the first to initiate studies on gene activity in early embryos as a postdoctoral fellow at the University of Edinburgh until 1965. Upon his return to the United States, he took the position of Assistant Professor at the University of Rochester School of Medicine and Dentistry. He moved to St. John’s University in 1975 as an associate professor, becoming a professor 1 year later, and served for 9 years as the chair of the department. He has mentored more than 30 graduate students and many undergraduates. He has been and remains a role model and a great help to young researchers and faculty all over the world. He has a tremendous love for teaching and it is this love that has made him the author of a book entitled ‘The Joy of Science’ to enlighten the students about the process of scientific inquiry. For his teaching, he has been honored with the Outstanding Achievement Award, St. John’s University, 1987; the Presidential Award, Long Island University, 1987; and the Outstanding Achievement Award, New York City, 1982. Another dimension of Richard’s contribution to the field is his cofounding of the International Cell Death Society, for which he also served as President from 1998 to 2002. He has received the Society’s award for ‘great contributions to the field’ given to a few others including Drs. John Kerr, Shigekazu Nagata, Peter Krammer, Junying Yuan, and Robert Horvitz. Richard, who is also the founding Chair of the first Gordon Conference on Cell Death, is on the Editorial Boards of Cell Death and Differentiation, Apoptosis, and the Journal of Biological Chemistry. He has served as the organizer and chair of numerous meetings in the field. In collaboration with Dr. Zahra Zakeri, he has established a focus group of researchers that work in enhancing scientific communication and knowledge to the third world countries and less privileged areas by the creation of the organization of Scientists Without Borders (Frontiers), whose aim is to advance teaching and scientific communication. A quotation from Richard Lockshin is the banner for the Scientists Without Borders group, which is as follows: ‘Science should be like a monarch butterfly. It

Elan vital, élan létal: one life but multiple deaths

When Richard Lockshin coined the expression ‘programmed cell death’ (PCD), more than 40 years ago, he modestly and accurately described the unique morphological and biochemical features of a developmental cell-death process that affected the intersegmental muscles of silkmoths. En passage, he developed the important notion that PCD would be controlled by a combination of cell-extrinsic and cell-intrinsic factors, yet would be executed through a plethora of genetically controlled catabolic reactions, from inside of the self-destroying cell. In retrospect, it is hard to believe that Richard did not foresee that his discovery – a mixture of dedicated and inventive bench work and visionary extrapolation – would be one of the major breakthroughs in cell biology of the 20th century. More interestingly, the process he observed was not apoptosis but one of the emerging new mechanisms of PCD, in a story that is now just unfolding. The concept of PCD, as initially formulated by Richard and then extended and applied by a panoply of follow-up studies, is most intriguing because it introduces the notion of constructive death into the science of life, biology. Perhaps this is the reason why there has been a strong tendency in the field, in particular between 1980 and 2000, to envisage two simplistic approaches to the problem. First, there has been a tendency to believe that there would be just one single important PCD mechanism in animals, namely apoptosis. Second, based on the discovery of the Caenorhabditis elegans death (CED) genes, many non-specialists have thought that there would be a sort of specialized device, the ‘apoptotic machinery’, whose building blocks would be exclusively dedicated to the execution of PCD, yet would not have any relevant function in normal life, as if elan vital and elan letal were necessarily opposed and separate entities. Both these (dogmatic) tendencies toward simplification have been broken, and the field is now open again, as open as during the early days when Lockshin translated his microscopic observations into data and concepts. The present special issue of Cell Death Diffferentiation, which celebrates Richard Lockshin’s 70th birthday, perfectly illustrates this regained spirit of freedom. Although apoptosis undoubtedly represents an important modality of PCD in many animal species, there are other forms of PCD that can be distinguished by simple morphological observation. For example, the linker cell of C. elegans succumbs to a PCD that morphologically resembles necrosis and that does not require any among the quintessential apoptotic (CED) genes. Autophagic processes may also play a major role in the development of the mammalian neural tube, although there may be an important cross talk between apoptotic and autophagic pathways. Human cancer cells do not only succumb to classical apoptosis when their DNA is damaged by chemotherapy or radiotherapy but also can die through mitotic catastrophe, a process in which cell death occurs during or after a prolonged mitotic arrest, often in cells that have undergone microor multinucleation. This mitotic catastrophe can lead to secondary apoptosis and necrosis, and it can be debated whether it constitutes a separate entity of cell death. Irrespective of semantic issues, it appears that there is not just one single cell-death program and that cells can die through multiple distinct subroutines. It has become increasingly clear that none of the individual proteins that participate in the major self-destructive events linked to apoptosis, mitochondrial outer-membrane permeabilization (MOMP) and caspase activation, is exclusively dedicated to self-destructive reactions. Rather, all of them also exert some function in normal, death-unrelated processes. Night killers have day jobs. Thus, two archetypical ‘cell death genes’, egl-1 and ced-4, turned out to play a major role in the adaptation of C. elegans cells to starvation and DNA damage, respectively. Mammalian caspases have also many death-unrelated functions, as illustrated for caspase-8 that participates in the activation of T and B lymphocytes, as well as in macrophage differentiation, among other processes. Caspase-12 turns out to be essential for the induction of cytoprotective autophagy in the context of stress affecting the endoplasmic reticulum. Bcl-2-like proteins, which regulate the cell death-associated mitochondrial membrane permeabilization as well as mitochondrial fission, have been discovered to play a cardinal role in synaptic plasticity. The mutation of Itch, an E3 ubiquitin ligase that plays an important role in determining the stability of p73, induces inflammatory lesions as well as lymphoid hyperplasia, illustrating how one single cell-death regulator can affect multiple cellular functions. Finally, phosphatidylserine exposure, one of the cardinal features of apoptotic cell death, may play an important role in conveying anti-inflammatory

Atrophy and programmed cell death of skeletal muscle

Striated skeletal is subject to nonlethal cycles of atrophy in response to a variety of physiological and pathological stimuli, including: starvation, disuse, denervation and inflammation. These cells can also undergo cell death in response to appropriate developmental signals or specific pathological insults. Most of the insights gained into the control of vertebrate skeletal muscle atrophy and death have resulted from experimental interventions rather than natural processes. In contrast, the intersegmental muscles (ISMs) of moths are giant cells that initiate sequential and distinct programs of atrophy and death at the end of metamorphosis as a normal component of development. This model has provided fundamental information about the control, biochemistry, molecular biology and anatomy of naturally occurring atrophy and death in vivo. The ISMs have provided a good complement to studies in vertebrates and may provide insights into clinically relevant disorders.

Skeletomuscular differences in the thorax of winged and non-winged forms of Camponotus camelinus (Smith) (Hym., Formicidae)

Comparative study of the thorax between the non-winged and winged forms of the ant Camponotus camelinus Smith brings to light some interesting skeletomuscular differences. In the winged form, the pro-, the meso-, and the metathoracic components of the thorax are loosely associated, while the pronotum is reduced. The mesoalinotum and mesopectus are differentiated into sclerites by sutures and ridges as in other winged Hymenoptera, but absent in the non-winged form. The metanotum is demarcated from the mesonotum, the propodeum and the metapectus. The metapectus follows the same pattern as does the mesopectus. The first and second phragmata are present. The meso- and meta-endosternites are stout and connected to each other by intersegmental muscles. The different wing sclerites and processes are differentiated from the surrounding components of the thorax. The muscle controlling the wing movements are well developed. Some other muscles which are present in the non-winged form are either displaced or are absent in the winged form.

Extracardiac haemocoelic pulsations and the autonomic neuroendocrine system (coelopulse) of terrestrial insects

AbstractTerrestrial insects exhibit extracardiac pulsations (ExP) in haemocoelic pressure, similar in some respect to the human blood pressure pulse. The pulsations are produced by large intersegmental abdominal musculature (abdominal pressure pump). The dorsal vessel of insects is a relatively weak organ which is unable to pump haemolymph against an increased gradient of pressure. The weak cardiac pulsations (myogenic nature) and strong ExP (neurogenic nature) occasionally occur hand in hand during similar periods with similar, but not identical frequencies. This increases the possibility of their mutual confusion. ExP can be recorded directly from haemocoelic cavity by means of hydraulic transducers or, indirectly from the body surface by recording movements of some flexible segments. In most cases, we recorded pulsations in haemocoelic pressure indirectly by recording movements of the terminal abdominal segments in immobile pupal stages. The movements caused by ExP are generally very small and invisible, only in the μm range. However, the corresponding abdominal movements or changes in haemocoelic pressure associated with the heartbeat are 30- to 500-fold smaller, in the range of nanometers. During the past three decades we have recorded cardiac and extracardiac pulsations in haemocoelic pressure in a number of insects and ticks. Practical examples of extracardiac pulsation patterns and their distinction from the heartbeat is described here for all major groups of terrestrial insects. The results obtained with monitoring of haemocoelic pulsations have revealed that terrestrial insects and possibly other arthropods posses a brain-independent, neuroendocrine system, called coelopulse. This type of newly discovered, autonomic, cholinergic system of insects shows apparent structural and functional analogy with the parasympathetic system of vertebrate animals. It regulates a number of homeostatic physiological and developmental functions, using pulsations in haemocoelic pressure for controlling circulatory and respiratory functions. The regulatory nervous center of the coelopulse system is located within thoracic ganglia of the ventral nerve cord (in analogy with parasympathetic centers in the spinal cord). Nerve impulses are dispatched from neurons of the thoracic ganglia through connectives and abdominal ganglia into large intersegmental abdominal muscles, whose contractions cause large peaks in haemocoelic pressure. The described coelopulse system controls a number of important physiological functions. For instance: 1) ExP in haemocoelic pressure cause rapid circulatory inflow and outflow of haemolymph between thoracic and abdominal parts of the body; 2) The relatively strong pressure changes caused by ExP can vigorously move tissue and organs against each other, thus preventing occlusion of haemolymph among densely packed organs; 3) Large extracardiac peaks in haemocoelic pressure open or close passively, one-way valves or tissue fold and promote circulation of haemolymph to destinations that cannot be reached by the heartbeat, i.e. ventral perineural sinus, appendages; 4) Strong ExP in haemocoelic pressure produce rhythmic, up and down compressions of tracheal tubes and air sacs, resulting in actively regulated inspirations or expirations of air through individual spiracles, i.e. actual insect breathing; 5) ExP controlled by the coelopulse neuroendocrine system causes unidirectional ventilation of the determined spiracles during emergency hypoxia, or during enzymatically produced outbursts of CO2; 6) The coelopulse system effectively controls various homeostatic physiological functions, like respiratory water loss, water retention, isoosmosis, optimum body volume, or economic gaseous exchange; 7) ExP in haemocoelic pressure plays an important roles in execution of special developmental events, like ecdysis, oviposition or pupariation. I am convinced that knowledge of the autonomic, parasympathetic-like neuroendocrine system in terrestrial arthropods may open new avenues for comparative animal physiology and pharmacology.

A TRIBUTE TO Professor Richard A. Lockshin on his 70th birthday

A TRIBUTE TO Professor Richard A. Lockshin on his 70th birthday

Proteomic Profiling of the Silkworm Skeletal Muscle Proteins during Larval−Pupal Metamorphosis

The silkworm is a typical holometabolous insect going through drastic morphological changes upon metamorphosis from larvae to pupae. Comprehensive studies focusing on the changes help elucidate understanding of a biogenic mechanism. Here, we report the initial profile of the intersegmental muscle (ISM) proteins of the silkworm during larval-pupal metamorphosis. In total, 258 protein spots were resolved by two-dimensional gel electrophoresis (2-DE). Fifty-seven larval proteins were identified, where 3 proteins were exclusively detected in larval samples. Fifty-four other proteins were common in pupal samples. Of these, 12 proteins belonging to the contractile apparatus, metabolism, regulation, and signal transduction were altered in their contents during the metamorphosis from larvae to pupae. Three pupa-defective proteins were identified as isoforms of troponin I, followed by an immunoblotting validation. This data will be helpful in understanding the biochemistry of an insect ISM.

Acheron, a novel member of the Lupus Antigen family, is induced during the programmed cell death of skeletal muscles in the moth Manduca sexta

In order to identify novel genes associated with the initiation of programmed cell death during development, we employed a differential screening protocol to isolate cDNAs that were induced when the intersegmental muscles (ISM) of the moth Manduca sexta become committed to die at the end of metamorphosis. In this report we provide the first description of Acheron (Achn), a novel protein that was isolated in this screen. Acheron contains three Lupus antigen (La) repeats, nuclear localization and export (NLS and NES) signals, and an RNA recognition motif. Achn defines a new subfamily of La proteins that appears to have branched from authentic La protein relatively late in metazoan evolution. Achn is widely expressed in various insect, mouse and human tissues. Consistent with its expression during ISM death, Achn has been shown in separate studies to control muscle differentiation and apoptosis in both mice and zebrafish. These data define Achn as a newly discovered regulatory molecule that presumably mediates a variety of developmental and homeostatic processes in animals.

Electrically Stimulated Rectus Abdominis Muscle Flap to Achieve Enterostomal Continence: Development of a Functional Canine Model

Dynamic myoplasty has many clinical applications and has proven to be a versatile surgical procedure with great promise. This procedure has been used to achieve fecal/urinary continence, as in the dynamic graciloplasty, and to augment cardiac ventricular function, as is commonly seen with dynamic latissimus cardiomyoplasty. In the present study, the authors describe a functional innovative island flap sphincter created from the rectus abdominis muscle in a large-animal model to provide stomal continence for future clinical studies. The caudal region of the rectus abdominis muscle in eight mongrel canines (23 to 25 kg) was investigated through anatomical dissections during which the location of the neurovascular pedicles and the intersegmental muscle dimensions between the muscle inscriptions were noted. The rectus abdominis muscle was used to create functional dynamic stomal sphincters that were trained with subcutaneously implanted pulse stimulators. The neurovascular pedicles were consistently found in similar locations along the posterior medial aspect of the caudal portion of the canine's rectus abdominis muscle. The vertical height of the deep inferior epigastric pedicle and caudal intercostal nerve muscular mean entry points were 6.75 +/- 1.89 cm and 7.44 +/- 0.86 cm, respectively. The mean caudal intersegmental muscle length of the rectus abdominis muscle used to create the sphincter was 9.69 +/- 1.81 cm. The canine rectus abdominis muscle has reliable anatomical locations where the neurovascular pedicle may be found. This canine muscle may be used to create a continent island flap stomal sphincter. This large-animal sphincter model is versatile, durable, and easy to manipulate, with minimal morbidity to the animal.

Common and specific inhibitory motor neurons innervate the intersegmental muscles in the locust thorax

The inhibitory innervation of the intersegmental (body wall) muscles between the first and the second thoracic segment of the migratory locust, Locusta migratoria, was investigated using neuroanatomical, immunocytochemical and electrophysiological techniques. Three neurons located in the prothoracic ganglion show GABA-like immunoreactivity and project into the intersegmental nerve. Two are common inhibitors. One of those innervates the oblique intersegmental muscle M59 and two dorsal longitudinal muscles (M81 and M82). The second common inhibitor also innervates M59 and the ventral longitudinal muscle M60. The third neuron innervates M60 exclusively and, for that reason, has to be regarded as the first specific inhibitor ever observed in insect neuromuscular assemblies. According to their innervation pattern, we term these neurons CI(59/60), CI(59/81/82), and SI(60). CI(59/81/82) and CI(59/60) appear to be segmentally homologous to CI(a) and CI(b) neurons, respectively, in the other body segments.

Up- and downregulated genes in muscles that undergo developmentally programmed cell death in the insect Manduca sexta

This study was designed to investigate changes in gene expression associated with stage-specific programmed cell death (PCD) in intersegmental muscles (ISMs) of the moth, Manduca sexta. The technique of differential display reverse transcription PCR was applied to compare mRNA levels before and after the onset of PCD in ISMs. Expression of E75 B transcription factor was repressed while another factor, βFTZ-F1, stayed at a very low level. However, gene coding for a translation-initiation factor ( eIF1A) was upregulated. Expression of these genes had not been previously reported to be altered in dying ISMs. An ecdysteroid agonist, RH-5849, that prevented PCD in ISMs also blocked these changes.

Inhibitors of ubiquitin‐dependent proteolysis can delay programmed cell death of adult intersegmental muscles in the moth Manduca sexta

In the moth Manduca sexta, intersegmental muscles (ISMs) undergo rapid programmed cell death (PCD) within 48 hr of adult emergence. ISM PCD involves ubiquitin-dependent proteasomal degradation accompanied by the down-regulation of expression of actin genes and the up-regulation of degradative gene expression such as ubiquitin. Hemin chloride and N-acetyl-leu-leu-norleucinal (ALLN), both inhibitors of proteasomal activity, administered before adult emergence delayed PCD for up to 5 days in ISMs maintained from the larval stage, such as the dorsal internal medial muscle in abdominal segment 4 (DIM-A4). ISMs that developed during metamorphosis from respecified larval muscles such as the DIM-A2 were less dramatically affected. The increase in polyubiquitinated proteins and the decrease in actin mRNA expression accompanying maintained ISM PCD were delayed after inhibitor application. No changes were detected in respecified ISMs. These results reveal a regulatory role for proteasomal activity in an early stage of maintained ISM cell death.

Determining the stabilizing role of individual torso muscles during rehabilitation exercises.

A systematic biomechanical analysis involving an artificial perturbation applied to individual lumbar muscles in order to assess their potential stabilizing role. To identify which torso muscles stabilize the spine during different loading conditions and to identify possible mechanisms of function. SUMMARY OF BACKGROUND DATA.: Stabilization exercises are thought to train muscle patterns that ensure spine stability; however, little quantification and no consensus exists as to which muscles contribute to stability. Spine kinematics, external forces, and 14 channels of torso electromyography were recorded for seven stabilization exercises in order to capture the individual motor control strategies adopted by different people. Data were input into a detailed model of the lumbar spine to quantify spine joint forces and stability. The EMG signal for a particular muscle was replaced either unilaterally or bilaterally by a sinusoid, and the resultant change in the stability index was quantified. A direction-dependent-stabilizing role was noticed in the larger, multisegmental muscles, whereas a specific subtle efficiency to generate stability was observed for the smaller, intersegmental spinal muscles. No single muscle dominated in the enhancement of spine stability, and their individual roles were continuously changing across tasks. Clinically, if the goal is to train for stability, enhancing motor patterns that incorporate many muscles rather than targeting just a few is justifiable.

Changes in contractile properties of skeletal muscle during developmentally programmed atrophy and death.

Skeletal muscle atrophy and death are protracted processes that accompany aging and pathological insults in mammals. The intersegmental muscles (ISMs) from the tobacco hawkmoth Manduca sexta are composed of giant fibers that undergo distinct hormonally-regulated programs of atrophy and death at the end of metamorphosis. Atrophy occurs during the 3 days preceding adult emergence and results in a 40% reduction of mass, whereas death takes place during the subsequent 30 h and results in the complete loss of the fibers. There are no significant changes in tetanic force or calcium sensitivity in skinned fiber preparations during atrophy. However, the size of caffeine-induced contractions fell by about 50%. With the onset of the death phase, dramatic reductions occur in ISM: tetanic force, twitch amplitude, resting potential, caffeine-induced contractions, calcium sensitivity, and Hill coefficients. Several lines of evidence suggest that ISM atrophy is caused by an increase in protein turnover without significant modification of fiber organization. In contrast, ISM death is accompanied by disorganization of the contractile apparatus and concomitant loss of contractile function.

A simplified conceptual model of the human cervical spine for evaluating force transmission in upright static posture

Objective: To develop a simplified graphical model appropriate for the evaluation of proposed theoretical force transmission mechanisms in the upright static cervical spine. The model is used to demonstrate in a visual format the underlyingmechanical principles contributing to an optimal mechanical configuration of the cervical spine in upright posture. The model is also used to explore the relative mechanical efficiency of 2 different force transmission methods. Method: A graphical model was developed to illustrate relevant force vectors acting on the head and neck in upright posture. This model was used to calculate theoretical static loading on the structures of the neck under various loading conditions resulting from specific configurations of passive elements and active supportive muscle effort. Results: From the information gained from the model, a theorized optimal mechanical configuration and theorized role of various components of the cervical spine in static upright posture is presented. The model is used to test the mechanical validity of a concurrent force system with intersegmental muscle force rather than the parallel force system presented in the literature. The alternate models are examined in relation to their predictions and theoretical implications with respect to force transmission in the cervical spine. Conclusion: A simplified model has been developed that facilitates the graphical representation of forces involved in maintaining static upright posture in the human cervical spine. The model is used to explore the optimal spinal configuration of the major mechanical components of the neck. (J Manipulative Physiol Ther 2002;25:306-17)