A biomechanical paradox in fish: swimming and suction feeding produce orthogonal strain gradients in the axial musculature

The axial musculature of fishes has historically been characterized as the powerhouse for explosive swimming behaviors. However, recent studies show that some fish also use their ‘swimming’ muscles to generate over 90% of the power for suction feeding. Can the axial musculature achieve high power output for these two mechanically distinct behaviors? Muscle power output is enhanced when all of the fibers within a muscle shorten at optimal velocity. Yet, axial locomotion produces a mediolateral gradient of muscle strain that should force some fibers to shorten too slowly and others too fast. This mechanical problem prompted research into the gearing of fish axial muscle and led to the discovery of helical fiber orientations that homogenize fiber velocities during swimming, but does such a strain gradient also exist and pose a problem for suction feeding? We measured muscle strain in bluegill sunfish, Lepomis macrochirus, and found that suction feeding produces a gradient of longitudinal strain that, unlike the mediolateral gradient for locomotion, occurs along the dorsoventral axis. A dorsoventral strain gradient within a muscle with fiber architecture shown to counteract a mediolateral gradient suggests that bluegill sunfish should not be able to generate high power outputs from the axial muscle during suction feeding—yet prior work shows that they do, up to 438 W kg−1. Solving this biomechanical paradox may be critical to understanding how many fishes have co-opted ‘swimming’ muscles into a suction feeding powerhouse.

Dual function of epaxial musculature for swimming and suction feeding in largemouth bass

The axial musculature of many fishes generates the power for both swimming and suction feeding. In the case of the epaxial musculature, unilateral activation bends the body laterally for swimming, and bilateral activation bends the body dorsally to elevate the neurocranium for suction feeding. But how does a single muscle group effectively power these two distinct behaviours? Prior electromyographic (EMG) studies have identified fishes' ability to activate dorsal and ventral epaxial regions independently, but no studies have directly compared the intensity and spatial activation patterns between swimming and feeding. We measured EMG activity throughout the epaxial musculature during swimming (turning, sprinting, and fast-starts) and suction feeding (goldfish and pellet strikes) in largemouth bass ( Micropterus salmoides ). We found that swimming involved obligate activation of ventral epaxial regions whereas suction feeding involved obligate activation of dorsal epaxial regions, suggesting regional specialization of the epaxial musculature. However, during fast-starts and suction feeding on live prey, bass routinely activated the whole epaxial musculature, demonstrating the dual function of this musculature in the highest performance behaviours. Activation intensities in suction feeding were substantially lower than fast-starts which, in conjunction with suboptimal shortening velocities, suggests that bass maximize axial muscle performance during locomotion and underuse it for suction feeding.

The Developmental Phases of Zebrafish Myogenesis

The development and growth of vertebrate axial muscle have been studied for decades at both the descriptive and molecular level. The zebrafish has provided an attractive model system for investigating both muscle patterning and growth due to its simple axial musculature with spatially separated fibre types, which contrasts to complex muscle groups often deployed in amniotes. In recent years, new findings have reshaped previous concepts that define how final teleost muscle form is established and maintained. Here, we summarise recent findings in zebrafish embryonic myogenesis with a focus on fibre type specification, followed by an examination of the molecular mechanisms that control muscle growth with emphasis on the role of the dermomyotome-like external cell layer. We also consider these data sets in a comparative context to gain insight into the evolution of axial myogenic patterning systems within the vertebrate lineage.

Difficult to Treat Focal, Stiff Person Syndrome of the Left Upper Extremity

Background. Stiff person syndrome (SPS) is a rare neurologic disorder characterized by muscle rigidity. It is a disorder of reduced GABA activity leading to increased muscle tone and often painful spasms. It generally presents in the axial musculature but rarely can involve only one limb, typically a lower extremity. In rare cases it can be paraneoplastic which generally resolves on treatment of the underlying neoplasm. Case Report. A 46-year-old male with a history of Hodgkin’s Lymphoma in remission presented with left upper extremity pain secondary to a diagnosis of Stiff Person Syndrome limited to his left upper extremity. He had previously benefitted from plasmapheresis and was on diazepam and baclofen at home with relatively good control of his symptoms. SPS had previously been diagnosed with EMG and anti-GAD-65 antibody titers and was confirmed by an elevated anti-GAD-65 antibody titer. He was treated with plasmapheresis and maximum doses of medical treatment including botulinum toxin with only transient mild improvement in his symptoms. Conclusion. This case represents a case of a rare disease that was refractory to all known therapies. It outlines the need for further understanding of this disorder in order to provide better symptomatic treatment or potentially more definitive care.

Skeletal muscle development in vertebrate animals

This review covers the pre- and post-natal development of skeletal muscle of vertebrate animals with cellular and molecular levels. The formation of skeletal muscle initiates from paraxial mesoderm during embryogenesis of individuals which develops somites and subsequently forms dermomyotome derived myotome to give rise axial musculature. This process (myogenesis) includes stem and progenitor cell maintenance, lineage specification, and terminal differentiation to form myofibrils consequent muscle fibers which control muscle mass and its multiplication. The main factors of muscle growth are proliferation and differentiation of myogenic cells in prenatal stage and also the growth of satellite cells at postnatal stage. There is no net increase in the number of muscle fibers in vertebrate animals after hatch or birth except fish. The development of muscle is characterized by hyperplasia and hypertrophy in prenatal and postnatal stages of individuals, respectively, through Wnt signalling pathway including environment, nutrition, sex, feed, growth and myogenic regulatory factors. Therefore further studies could elucidate new growth related genes, markers and factors to enhance meat production and enrich knowledge on muscle growth.Asian J. Med. Biol. Res. June 2015, 1(2): 139-148

Early vestibular processing does not discriminate active from passive self-motion if there is a discrepancy between predicted and actual proprioceptive feedback

Most of our sensory experiences are gained by active exploration of the world. While the ability to distinguish sensory inputs resulting of our own actions (termed reafference) from those produced externally (termed exafference) is well established, the neural mechanisms underlying this distinction are not fully understood. We have previously proposed that vestibular signals arising from self-generated movements are inhibited by a mechanism that compares the internal prediction of the proprioceptive consequences of self-motion to the actual feedback. Here we directly tested this proposal by recording from single neurons in monkey during vestibular stimulation that was externally produced and/or self-generated. We show for the first time that vestibular reafference is equivalently canceled for self-generated sensory stimulation produced by activation of the neck musculature (head-on-body motion), or axial musculature (combined head and body motion), when there is no discrepancy between the predicted and actual proprioceptive consequences of self-motion. However, if a discrepancy does exist, central vestibular neurons no longer preferentially encode vestibular exafference. Specifically, when simultaneous active and passive motion resulted in activation of the same muscle proprioceptors, neurons robustly encoded the total vestibular input (i.e., responses to vestibular reafference and exafference were equally strong), rather than exafference alone. Taken together, our results show that the cancellation of vestibular reafference in early vestibular processing requires an explicit match between expected and actual proprioceptive feedback. We propose that this vital neuronal computation, necessary for both accurate sensory perception and motor control, has important implications for a variety of sensory systems that suppress self-generated signals.

Metamorphosis-Induced Changes in the Coupling of Spinal Thoraco-Lumbar Motor Outputs During Swimming in Xenopus laevis

Anuran metamorphosis includes a complete remodeling of the animal's biomechanical apparatus, requiring a corresponding functional reorganization of underlying central neural circuitry. This involves changes that must occur in the coordination between the motor outputs of different spinal segments to harmonize locomotor and postural functions as the limbs grow and the tail regresses. In premetamorphic Xenopus laevis tadpoles, axial motor output drives rostrocaudally propagating segmental myotomal contractions that generate propulsive body undulations. During metamorphosis, the anterior axial musculature of the tadpole progressively evolves into dorsal muscles in the postmetamorphic froglet in which some of these back muscles lose their implicit locomotor function to serve exclusively in postural control in the adult. To understand how locomotor and postural systems interact during locomotion in juvenile Xenopus, we have investigated the coordination between postural back and hindlimb muscle activity during free forward swimming. Axial/dorsal muscles, which contract in bilateral alternation during undulatory swimming in premetamorphic tadpoles, change their left-right coordination to become activated in phase with bilaterally synchronous hindlimb extensions in locomoting juveniles. Based on in vitro electrophysiological experiments as well as specific spinal lesions in vivo, a spinal cord region was delimited in which propriospinal interactions are directly responsible for the coordination between leg and back muscle contractions. Our findings therefore indicate that dynamic postural adjustments during adult Xenopus locomotion are mediated by local intraspinal pathways through which the lumbar generator for hindlimb propulsive kicking provides caudorostral commands to thoracic spinal circuitry controlling the dorsal trunk musculature.

OBSERVATIONS ON SPINE DEFORMITY AND SYRINGOMYELIA

OBJECTIVE Spine deformities, notably scoliosis, are known to occur in conjunction with syringomyelia. This study aims to analyze the effect of laminectomies performed in the course of treatment of syringomyelia. It examines the incidence, severity, and type of spine deformity as it relates to the extent and location of laminectomies performed. METHODS Records of 169 patients were analyzed for evidence of spinal deformity on imaging studies for the extent of the syringomyelic cavities and for previous surgical procedures on the spine. This analysis included patients with syringomyelia related to Chiari malformation, as well as patients with primary spinal pathology. RESULTS Spinal deformities were encountered in 41% of Chiari-syringomyelia patients who had not undergone previous surgery and in 57% of such patients who underwent reoperation. Scoliosis, the most common type of deformity encountered, was likely to be mild in patients who had not undergone previous surgery and severe in reoperated patients. Spine deformity was significantly more common in those patients who had more extensive bone removal. CONCLUSION Complete laminectomy should be avoided whenever possible in patients with syringomyelia because local denervation of the axial musculature, added to loss of medial anterior horn cells from syringomyelia, favors the development of spine deformities. This is particularly true of laminectomies performed at the junctional areas of the spine, i.e., cervical-thoracic and thoracolumbar. Hemilaminectomy usually suffices for shunt placement; instrumented stabilization should be considered in patients undergoing full laminectomy, especially those considered to be at high risk of developing deformity.