A Biological Micro Actuator: Graded and Closed-Loop Control of Insect Leg Motion by Electrical Stimulation of Muscles

In this study, a biological microactuator was demonstrated by closed-loop motion control of the front leg of an insect (Mecynorrhina torquata, beetle) via electrical stimulation of the leg muscles. The three antagonistic pairs of muscle groups in the front leg enabled the actuator to have three degrees of freedom: protraction/retraction, levation/depression, and extension/flexion. We observed that the threshold amplitude (voltage) required to elicit leg motions was approximately 1.0 V; thus, we fixed the stimulation amplitude at 1.5 V to ensure a muscle response. The leg motions were finely graded by alternation of the stimulation frequencies: higher stimulation frequencies elicited larger leg angular displacement. A closed-loop control system was then developed, where the stimulation frequency was the manipulated variable for leg-muscle stimulation (output from the final control element to the leg muscle) and the angular displacement of the leg motion was the system response. This closed-loop control system, with an optimized proportional gain and update time, regulated the leg to set at predetermined angular positions. The average electrical stimulation power consumption per muscle group was 148 µW. These findings related to and demonstrations of the leg motion control offer promise for the future development of a reliable, low-power, biological legged machine (i.e., an insect–machine hybrid legged robot).     

Enthalpy efficiency of the soleus muscle contributes to improvements in running economy

During human running, the soleus, as the main plantar flexor muscle, generates the majority of the mechanical work through active shortening. The fraction of chemical energy that is converted into muscular work (enthalpy efficiency) depends on the muscle shortening velocity. Here, we investigated the soleus muscle fascicle behaviour during running with respect to the enthalpy efficiency as a mechanism that could contribute to improvements in running economy after exercise-induced increases of plantar flexor strength and Achilles tendon (AT) stiffness. Using a controlled longitudinal study design (n = 23) featuring a specific 14-week muscle–tendon training, increases in muscle strength (10%) and tendon stiffness (31%) and reduced metabolic cost of running (4%) were found only in the intervention group (n = 13, p < 0.05). Following training, the soleus fascicles operated at higher enthalpy efficiency during the phase of muscle–tendon unit (MTU) lengthening (15%) and in average over stance (7%, p < 0.05). Thus, improvements in energetic cost following increases in plantar flexor strength and AT stiffness seem attributed to increased enthalpy efficiency of the operating soleus muscle. The results further imply that the soleus energy production in the first part of stance, when the MTU is lengthening, may be crucial for the overall metabolic energy cost of running.     

Cholinergic regulation of body-wall muscle contraction of the ascidian Styela rustica (Linnaeus, 1767)

The regulation of body-wall muscle contraction in the ascidian Styela rustica was studied. Acetylcholine (ACh, 1?C10 ??M) induced a significant contraction of isolated muscle strips. The ACh-induced contractile response was potentiated and prolonged in the presence of proserine (15 ??M), which confirms acetylcholinesterase activity in the S. rustica body-wall muscle. Atropine (1?C100 ??M, M-cholinoreceptor blocker) did not prevent the ACh-induced contractile response, while d-tubocurarine (1?C100 ??M, N-cholinoreceptor blocker) progressively reduced muscle contraction induced by 10 ??M ACh. Thus, neuromuscular transmission in the S. rustica body-wall muscle is mediated by nicotinic-like ACh-receptors. Procaine reduced ACh-induced (10 ??M) muscle contraction. As well, our experiments showed spontaneous rhythmic contractile activity in isolated muscle strips of S. rustica. Atropine, d-tubocurarine, procaine, and proserine did not alter rhythmic activity. Myogenic automaticity is suggested as a possible cause of the rhythmic contraction of the ascidian body-wall muscle.     

Design and synthesis of potent myostatin inhibitory cyclic peptides

Myostatin is a negative regulator of skeletal muscle growth and myostatin inhibitors are promising lead compounds against muscle atrophic disorders such as muscular dystrophy. Previously, we published the first report of synthetic myostatin inhibitory 23-mer peptide 1, which was identified from a myostatin precursor-derived prodomain protein. Our structure-activity relationship study afforded the potent inhibitory peptide 3. In this paper, we report an investigation of the synthesis of conformationally-constrained cyclic peptide based on the linear peptide 3. To examine the potency of side chain-to-side chain cyclized peptides, a series of disulfide-, lactam- and diester-bridged derivatives were designed and synthesized, and their myostatin inhibitory activities were evaluated. The diester-bridged peptide (11) displayed potent inhibitory activity with an in vitro IC₅₀ value of 0.26?µM, suggesting that it could serve as a new platform for development of cyclic peptide inhibitors.     

Mechanical properties of muscle spindles in Xenopus laevis

Mechanical properties of isolated living muscle spindles from Xenopus laevis were examined in order to determine their role in sensory transduction. The reticular zone of the intrafusal muscle fibers was identified microscopically by: (1) its position beneath the sensory endings, (2) its length, 50–100 μm, (3) its extension during intrafusal muscle contraction, and (4) its coarse striations with a period of about 1.5 times the normal sarcomere length. The reticular zone in the passive muscle spindle did not extend until the spindle was stretched to about 1.05–1.1 its maximal length in the animal (L _m ). Evidence was obtained that the absence of extension of the reticular zone at normal muscle lengths was due to the presence of the spindle capsule which acted as a stiff element in parallel with the sensory region. At those lengths at which the reticular zone did extend (> L _m ), no rate — sensitive mechanical properties were detected in response to step and ramp extensions. The sensory discharge of the spindle showed no dynamic transient in response to ramp extensions if the reticular zone were not extended. During extension of the reticular zone a dynamic sensory transient appeared. It is concluded that current notions on the mechanical origin of the rate — sensitive properties of the sensory discharge of the muscle spindle do not apply to Xenopus laevis. In addition, it is not likely that the passive spindle in this animal is a sensitive stretch receptor.     

A dynamometer for evaluation of dynamic muscle work

The validation of a new dynamometer for evaluation of dynamic muscle work is presented. The device was based on a precise measurement of load displacements of any machine using gravitational loads as external resistance. It allowed, through a sensor consisting of an infrared photo interrupter, the calculation of velocity, force and power during concentric, eccentric and stretch-shortening cycle activity. To validate the dynamometer 33 male and female track and field athletes (12 throwers and 21 jumpers) participated in the study. The throwers (4 women and 8 men) were asked to perform half-squat exercises on a slide machine with a load of 100% of the subject's body mass. The day-to-day reproducibility of half-squat exercises gave a correlation coefficient ofr = 0.88, 0.97 and 0.95 for average push-off force (AF), average push-off velocity (AV), and average push-off power (AP) respectively. Comparison of half-squat measurements was performed against jumping and running test evaluation by the jumpers (7 women and 14 men). The interrelationships among the different variables studied demonstrated a strong correlation between AF, AV and AP and sprinting and jumping parameters (r = 0.53–0.97;P < 0.05–0.001). Using values of AF, AV and AP developed in half-squat exercises executed with different loads, ranging from 35% to 210% of the subject's body mass, it was also possible to establish the force-velocity and power-velocity relationships for both male and female jumpers. In any individual case, the maximal error due to the measurement system was calculated to be less than 0.3%, 0.9% and 1.2% for AF, AV, and AP respectively. Given the accuracy of the ergometer, the high reliability found between 2 days of measurements, and the specificity of the results it is suggested that the dynamic dynamometer would be suitable for evaluation of athletes performing specific skills. In addition, because single and multiple joint movements involving appropriate muscle groups can be easily performed, physiological characteristics could be evaluated for both athletic and rehabilitation purposes. Therefore, because of its simplicity of use and application, and its low cost the dynamometer would be suitable for both laboratory and field conditions.     

Consistency of growth response to precipitation by Pseudopiptadenia contorta in two Atlantic Forest remnants

Tree growth sensitivity to climate can vary over space and time. This variability generates inconsistency in growth response to climate, which makes it difficult to assess the effects of past climate and global climate change on tree growth. A previous short-term study of Pseudopiptadenia contorta found a consistent growth response to climate in distinct locations, which raises the question, is the growth response of P. contorta to climate consistent over the long-term? We aimed to assess whether there is a common pattern of variation in tree-ring width, build tree-ring width chronologies, and verify the consistency of the climate-growth response of P. contorta in two Atlantic Forest remnants. Wood samples were collected in Reserva Biológica de Poço das Antas (RBPA) and Reserva Biológica de Tinguá (RBT) in the state of Rio de Janeiro, Brazil. Conventional dendrochronology methods were used for cross-dating, to build chronologies and to assess the climate-growth relationship. A common growth pattern was detected for P. contorta, and two tree-ring width chronologies were constructed. A congruent growth response was found for trees of RBPA and RBT to annual and spring precipitation as well as precipitation in the rainy months. Other climate-growth relationships were detected with other precipitation and temperature variables. Considering that P. contorta is a widespread species, occurring in other Brazilian biomes and forest formations, it is a promising model for developing further dendrochronological research including regional networks of replicated site chronologies, which could facilitate the reconstruction of historical climatic series and predictions of future impacts of climate change in tropical areas.     

Ciliary muscle contraction force and trapezius muscle activity during manual tracking of a moving visual target

Previous studies have shown an association of visual demands during near work and increased activity of the trapezius muscle. Those studies were conducted under stationary postural conditions with fixed gaze and artificial visual load. The present study investigated the relationship between ciliary muscle contraction force and trapezius muscle activity across individuals during performance of a natural dynamic motor task under free gaze conditions. Participants (N = 11) tracked a moving visual target with a digital pen on a computer screen. Tracking performance, eye refraction and trapezius muscle activity were continuously measured. Ciliary muscle contraction force was computed from eye accommodative response. There was a significant Pearson correlation between ciliary muscle contraction force and trapezius muscle activity on the tracking side (0.78, p < 0.01) and passive side (0.64, p < 0.05). The study supports the hypothesis that high visual demands, leading to an increased ciliary muscle contraction during continuous eye–hand coordination, may increase trapezius muscle tension and thus contribute to the development of musculoskeletal complaints in the neck–shoulder area. Further experimental studies are required to clarify whether the relationship is valid within each individual or may represent a general personal trait, when individuals with higher eye accommodative response tend to have higher trapezius muscle activity.     

FOXP3+ T Cells Recruited to Sites of Sterile Skeletal Muscle Injury Regulate the Fate of Satellite Cells and Guide Effective Tissue Regeneration

Muscle injury induces a classical inflammatory response in which cells of the innate immune system rapidly invade the tissue. Macrophages are prominently involved in this response and required for proper healing, as they are known to be important for clearing cellular debris and supporting satellite cell differentiation. Here, we sought to assess the role of the adaptive immune system in muscle regeneration after acute damage. We show that T lymphocytes are transiently recruited into the muscle after damage and appear to exert a pro-myogenic effect on muscle repair. We observed a decrease in the cross-sectional area of regenerating myofibers after injury in Rag2^-/- γ-chain^-/- mice, as compared to WT controls, suggesting that T cell recruitment promotes muscle regeneration. Skeletal muscle infiltrating T lymphocytes were enriched in CD4⁺CD25⁺FOXP3⁺ cells. Direct exposure of muscle satellite cells to in vitro induced Treg cells effectively enhanced their expansion, and concurrently inhibited their myogenic differentiation. In vivo, the recruitment of Tregs to acutely injured muscle was limited to the time period of satellite expansion, with possibly important implications for situations in which inflammatory conditions persist, such as muscular dystrophies and inflammatory myopathies. We conclude that the adaptive immune system, in particular T regulatory cells, is critically involved in effective skeletal muscle regeneration. Thus, in addition to their well-established role as regulators of the immune/inflammatory response, T regulatory cells also regulate the activity of skeletal muscle precursor cells, and are instrumental for the proper regeneration of this tissue.     

Neuromuscular response amplitude to mechanical stimulation using large-array surface electromyography in participants with and without chronic low back pain

Purpose: The present study aimed to compare the neuromuscular response under various mechanical stimulations of the lumbar spine in participants with and without chronic low back pain (cLBP). Methods: Four mechanical stimulations, characterized by forces ranging from 75 to 225 N, were delivered using a servo-controlled linear actuator motor to the L3 spinous process of 25 healthy participants and 26 participants with cLBP. Lumbar neuromuscular responses were recorded using 64-electrodes large surface electromyography arrays. Between-group differences in the dose–response relationship (neuromuscular response amplitude according to each force level) were assessed using mixed model ANOVAs. Results: No differences between groups were shown (all p values > .05). A significant linear relationship was observed between forces and neuromuscular response amplitudes (p < .001) indicating an increase in response amplitudes with increasing stimulation force. Responses were observed throughout the lumbar region with highest response amplitudes in the vicinity of the contacted vertebra. Conclusion: The neuromuscular response amplitude triggered by localized lumbar mechanical stimulations does not differ between participants with and without cLBP. Moreover, even though stimulations were delivered at specific spinal segment, a neuromuscular response, although rapidly decreasing, was observed in areas distant from the contact site.     

Intrinsic Feedback Factors Producing Inertial Compensation in Muscle

An attempt was made to determine the factors causing the load-inertia compensation that has been observed in skeletal muscle. Cat skeletal muscle force output was determined as a function of the two variables, length and stimulus pulse rate. The results were represented in a system diagram from which it becomes apparent that: (a) the length-tension relationship in muscle forms a functional, non-neural servo feedback; (b) the force-velocity curve appears as an oscillation-damping, velocity feedback in the muscle servo; (c) the nonlinear action of pulse rate on response is, in effect, in the input element to the muscle servo system. For purpose of analysis of the motor system it appears that these signal handling characteristics of muscle make it more nearly a “position servo” than a “force motor.”     

An In Vitro Adult Mouse Muscle-nerve Preparation for Studying the Firing Properties of Muscle Afferents

Muscle sensory neurons innervating muscle spindles and Golgi tendon organs encode length and force changes essential to proprioception. Additional afferent fibers monitor other characteristics of the muscle environment, including metabolite buildup, temperature, and nociceptive stimuli. Overall, abnormal activation of sensory neurons can lead to movement disorders or chronic pain syndromes. We describe the isolation of the extensor digitorum longus (EDL) muscle and nerve for in vitro study of stretch-evoked afferent responses in the adult mouse. Sensory activity is recorded from the nerve with a suction electrode and individual afferents can be analyzed using spike sorting software. In vitro preparations allow for well controlled studies on sensory afferents without the potential confounds of anesthesia or altered muscle perfusion. Here we describe a protocol to identify and test the response of muscle spindle afferents to stretch. Importantly, this preparation also supports the study of other subtypes of muscle afferents, response properties following drug application and the incorporation of powerful genetic approaches and disease models in mice.     

Pleonal muscle development in the shrimp Penaeus (Litopenaeus) vannamei (Crustacea: Malacostraca: Decapoda: Dendrobranchiata)

Penaeoidean shrimp pleonal muscle is a valuable economic resource worldwide, but little is known of its development during larval stages. The development of pleonal muscle in Penaeus (Litopenaeus) vannamei was studied by rhodamine-phalloidin staining and laser-scanning confocal microscopy. Dorsal pleonal muscle was first evident at the protozoea I stage while ventral pleonal muscle was present by the protozoea II stage. Identifiable ventral pleonal muscles were evident by the protozoea III stage and all ventral muscle types were present in the mysis I. The tail flex response began at the mysis stage and growth of existing pleonal muscles continued. The pleopods formed during the mysis stages, with coxal and basis muscles developed by mysis III. The pleopods became functional beginning with the first post-larval stage. We conclude that the pleonal muscle pattern of P. vannamei larvae is similar to that of adult Penaeus setiferus, and that homologous muscles are present. The major formation of dorsal pleonal muscles occurs during the protozoea II stage, while significant development of ventral pleonal muscles occurs during the protozoea III stage.     

Alkaline phosphatase activity sensitive to environmental salinity and dopamine in muscle of the euryhaline crab Cyrtograpsus angulatus

The occurrence, characteristics and response to environmental salinity and dopamine of alkaline phosphatase (AP) activity were studied in chela muscle of the euryhaline crab Cyrtograpsus angulatus from Mar Chiquita coastal lagoon (Buenos Aires Province, Argentina). Chela muscle exhibited a high AP activity with a Michaelis-Menten kinetic (K_m=1.21 mM). AP activity was strongly inhibited by EDTA (I₅₀=2.26 mM). AP activity appeared to be sensitive to environmental salinity. In crabs acclimated to low salinity (10‰) AP activity was lower than in 35‰ salinity. Upon an abrupt change to reduced salinity a short-term decrease of AP activity occurred, concomitant with the transition to hyperregulation. Furthermore, AP activity appeared to be under hormonal control since it was inhibited “in vivo” by 10⁻⁴ M dopamine. The response to both environmental salinity and dopamine suggests that AP activity could be a component of muscle regulatory mechanisms at the biochemical level secondary to hyperregulation of C. angulatus. The possible functional relationship of AP activity with Na⁺/K⁺ ATPase in muscle is discussed.     

Genetic variability affects the response of skeletal muscle to disuse

Objective:To examine whether genetic variability plays a role in skeletal muscle response to disuse.Methods:We examined skeletal muscle response to disuse in five different strains of mice: CAST/EiJ, NOD/ShiLtJ, NZO/HILtJ, 129S1/SvImJ and A/J. Mice had one limb immobilized by a cast for three weeks.Results:Response to immobilization was dependent on the strain of mice. Skeletal muscle mass/body weight was decreased by immobilization in all strains except 1291/SvImJ. Immobilization decreased absolute skeletal muscle mass in quadriceps and gastrocnemius in NOD/ShiltJ and NZO/HILtJ mice. Three weeks of immobilization resulted in an increase in quadriceps levels of atrogenes in CAST/EiJ. Immobilization resulted in an increase in quadriceps and gastrocnemius levels of Myh4 in CAST/EiJ. A similar trend was observed for Myh7 in gastrocnemius muscle. Immobilization resulted in a decrease of the p-p70S6K1/total p706SK1 ratio in quadriceps of NOD/ShiLtJ mice and the gastrocnemius of A/J mice. Immobilization did not affect the p-4EBP1/total 4EBP1 ratio in quadriceps of any of the strains examined. However, the p-4EBP1/total 4EBP1 ratio in gastrocnemius was greater in immobilized, relative to control, limbs in CAST/EiJ mice.Conclusion:Genetic variability affects the response of skeletal muscle to disuse.     

Muscle weakness during tricaine anesthesia

An isolated preparation of tadpole tail muscle was used to assess the peripheral effects of tricaine (3-aminobenzoic acid ethyl ester) at anesthetic concentrations and under physiological conditions. The drug effect on the electrically-evoked twitch was tested using short-pulse durations that elicited synaptically mediated effects or longer-duration pulses that stimulated the muscle directly. Tricaine reduced both types of response at anesthetic and even subanesthetic concentrations. At steady state concentrations that produced surgical anesthesia in vivo, tricaine reduced the directly evoked response by about half. It is concluded that tricaine anesthesia has a pronounced peripheral effect on neuromuscular function and that direct effect(s) on muscle are a major component.     

Studies on histamine H2 receptors coupled to cardiac adenylate cyclase Effects of guanylnucleotides and structural requirements for agonist activity

In particular preparations from guinea-pig ventricle, histamine in the concentration range 10^?6–10^?3 M caused a 3–5-fold stimulation of adenylate cyclase activity which was dependent on the presence of GTP. The effects of fourteen analogs of histamine were examined on this cyclase preparation. Five of the compounds studied proved to be partial agonists relative to histamine while nine others had essentially the same intrinsic activity as histamine. The intrinsic activities of the partial agonists were increased by GppNHP to the extent that dimaprit, which was a partial agonist in the presence of GTP, became a full agonist in the presence of GppNHp. The relative potencies of the full agonists as activators of the cyclase were found to correlate with the relative potencies on physiologically defined H₂ receptor systems. Activation of the cyclase by histamine, as well as by several of the agonist analogs, including dimaprit and tolazoline, was completely blocked by the H₂ antagonist cimetidine, but was not affected by pharmacologically relevant concentrations of the H₁ antagonist mepyramine, the β-blocker alprenolol, or the α-blocker phentolamine. The results suggest that all the agonists studied probably interact with a common H₂ receptor site on the cardiac muscle cell leading to activation of adenylate cyclase. The accompanying increase in cyclic AMP is presumably responsible for the chronotropic and inotropic effects of histamine and related compounds on cardiac muscle.