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MiniVStimA: A miniaturized easy to use implantable electrical stimulator for small laboratory animals. PLoS One 2020; 15:e0241638. [PMID: 33125415 PMCID: PMC7598460 DOI: 10.1371/journal.pone.0241638] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 10/16/2020] [Indexed: 01/17/2023] Open
Abstract
According to PubMed, roughly 10% of the annually added publications are describing findings from the small animal model (mice and rats), including investigations in the field of muscle physiology and training. A subset of this research requires neural stimulation with flexible adjustments of stimulation parameters, highlighting the need for reliable implantable electrical stimulators, small enough (~1 cm3), that even mice can tolerate them without impairing their movement. The MiniVStimA is a battery-powered implant for nerve stimulation with an outer diameter of 15 mm and an encapsulated volume of 1.2 cm3 in its smallest variation. It can be pre-programmed according to the experimental protocol and controlled after implantation with a magnet. It delivers constant current charge-balanced monophasic rectangular pulses up to 2 mA and 1 ms phase width (1 kΩ load). The circuitry is optimized for small volume and energy efficiency. Due to the variation of the internal oscillator (31 kHz ± 10%), calibration measures must be implemented during the manufacturing process, which can reduce the deviation of the frequency related parameters down to ± 1%. The expected lifetime of the smaller (larger) version is 100 (480) days for stimulation with 7 Hz all day and 10 (48) days for stimulation with 100 Hz. Devices with complex stimulation patterns for nerve stimulation have been successfully used in two in-vivo studies, lasting up to nine weeks. The implant worked fully self-contained while the animal stayed in its familiar environment. External components are not required during the entire time.
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Schmoll M, Unger E, Sutherland H, Haller M, Bijak M, Lanmüller H, Jarvis JC. SpillOver stimulation: A novel hypertrophy model using co-contraction of the plantar-flexors to load the tibial anterior muscle in rats. PLoS One 2018; 13:e0207886. [PMID: 30458051 PMCID: PMC6245836 DOI: 10.1371/journal.pone.0207886] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Accepted: 11/07/2018] [Indexed: 01/22/2023] Open
Abstract
The influence of loading on muscular hypertrophy has previously been studied in rodents by removal of synergistic muscles or various weight-lifting regimes. We present a novel model, evoking hypertrophy in the rat's tibialis anterior (TA) muscle by means of an implanted single channel electrical nerve stimulator. The amount of load experienced by the TA was measured in acute experiments in anaesthetized rats with contractions over a range of stimulation frequency and amplitude. A novel electrode configuration allowed us to elicit concentric, isometric and eccentric contractions within the same setup. This was achieved by 'SpillOver' stimulation in which we adjusted the amount of co-activation of the stronger antagonistic plantarflexors by increasing the stimulus above the level that caused full recruitment of the dorsiflexor muscles. The effect of loading on hypertrophy of the TA was tested in 3-4 week stimulation experiments in two groups of freely-moving rats, with a protocol that resembles typical resistance-training in humans. One group performed concentric contractions with no antagonistic co-contraction (unloaded, UNL, n = 5). In the other group the TA was loaded by simultaneous co-contraction of the antagonistically acting plantarflexors (SpillOver, n = 5). The wet mass of the stimulated TA increased in both groups; by 5.4 ± 5.5% for the UNL-group and 13.9 ± 2.9% for the SpillOver-group, with significantly greater increase in the SpillOver-group (p<0.05). Our results correlate well with values reported in literature, demonstrating that SpillOver-stimulation is a suitable model in which to study muscular hypertrophy. Even higher gains in muscle-mass may be possible by optimizing and adjusting the stimulation parameters according to the principles of progressive resistance training.
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Affiliation(s)
- Martin Schmoll
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
- School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
- * E-mail: (MS); (JCJ)
| | - Ewald Unger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Hazel Sutherland
- School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
| | - Michael Haller
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Manfred Bijak
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Hermann Lanmüller
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Jonathan Charles Jarvis
- School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
- * E-mail: (MS); (JCJ)
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Schmoll M, Unger E, Bijak M, Stoiber M, Lanmüller H, Jarvis JC. A novel miniature in-line load-cell to measure in-situ tensile forces in the tibialis anterior tendon of rats. PLoS One 2017; 12:e0185209. [PMID: 28934327 PMCID: PMC5608493 DOI: 10.1371/journal.pone.0185209] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 09/10/2017] [Indexed: 11/19/2022] Open
Abstract
Direct measurements of muscular forces usually require a substantial rearrangement of the biomechanical system. To circumvent this problem, various indirect techniques have been used in the past. We introduce a novel direct method, using a lightweight (~0.5 g) miniature (3 x 3 x 7 mm) in-line load-cell to measure tension in the tibialis anterior tendon of rats. A linear motor was used to produce force-profiles to assess linearity, step-response, hysteresis and frequency behavior under controlled conditions. Sensor responses to a series of rectangular force-pulses correlated linearly (R2 = 0.999) within the range of 0–20 N. The maximal relative error at full scale (20 N) was 0.07% of the average measured signal. The standard deviation of the mean response to repeated 20 N force pulses was ± 0.04% of the mean response. The step-response of the load-cell showed the behavior of a PD2T2-element in control-engineering terminology. The maximal hysteretic error was 5.4% of the full-scale signal. Sinusoidal signals were attenuated maximally (-4 dB) at 200 Hz, within a measured range of 0.01–200 Hz. When measuring muscular forces this should be of minor concern as the fusion-frequency of muscles is generally much lower. The newly developed load-cell measured tensile forces of up to 20 N, without inelastic deformation of the sensor. It qualifies for various applications in which it is of interest directly to measure forces within a particular tendon causing only minimal disturbance to the biomechanical system.
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Affiliation(s)
- Martin Schmoll
- Center for Medical Physics and Biomedical Engineering, Medical University Vienna, Waehringer Guertel, Vienna, Austria
- School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
- * E-mail: (MS); (JCJ)
| | - Ewald Unger
- Center for Medical Physics and Biomedical Engineering, Medical University Vienna, Waehringer Guertel, Vienna, Austria
| | - Manfred Bijak
- Center for Medical Physics and Biomedical Engineering, Medical University Vienna, Waehringer Guertel, Vienna, Austria
| | - Martin Stoiber
- Center for Medical Physics and Biomedical Engineering, Medical University Vienna, Waehringer Guertel, Vienna, Austria
| | - Hermann Lanmüller
- Center for Medical Physics and Biomedical Engineering, Medical University Vienna, Waehringer Guertel, Vienna, Austria
| | - Jonathan Charles Jarvis
- School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
- * E-mail: (MS); (JCJ)
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Schmoll M, Unger E, Sutherland H, Haller M, Bijak M, Lanmüller H, Jarvis JC. In-situ measurements of tensile forces in the tibialis anterior tendon of the rat in concentric, isometric, and resisted co-contractions. Physiol Rep 2017; 5:e13245. [PMID: 28420761 PMCID: PMC5408282 DOI: 10.14814/phy2.13245] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2017] [Revised: 03/16/2017] [Accepted: 03/16/2017] [Indexed: 11/24/2022] Open
Abstract
Tensile-force transmitted by the tibialis anterior (TA) tendon of 11 anesthetized adult male Wistar rats (body-mass: 360.6 ± 66.3 g) was measured in-situ within the intact biomechanical system of the hind-limb using a novel miniature in-line load-cell. The aim was to demonstrate the dependence of the loading-profile experienced by the muscle, on stimulation-frequency and the resistance to shortening in a group of control-animals. Data from these acute-experiments shows the type of loading achievable by means of implantable electrical stimulators activating agonists or agonist/antagonist groups of muscles during programmed resistance-training in freely moving healthy subjects. Force-responses to electrical stimulation of the common peroneal nerve for single pulses and short bursts were measured in unloaded and isometric contractions. A less time-consuming approach to measure the force-frequency relationship was investigated by applying single bursts containing a series of escalating stimulus-frequencies. We also measured the range of loading attainable by programmed co-contraction of the TA-muscle with the plantar-flexor muscles for various combinations of stimulation-frequencies. The maximal average peak-force of single twitches was 179% higher for isometric than for unloaded twitches. Average maximal isometric tetanic-force per gramme muscle-mass was 16.5 ± 3.0 N g-1, which agrees well with other studies. The standard and time-saving approaches to measure the force-frequency relationship gave similar results. Plantar-flexor co-activation produced greatly increased tension in the TA-tendon, similar to isometric contractions. Our results suggest that unloaded contractions may not be adequate for studies of resistance-training. Plantar-flexor co-contractions produced considerably higher force-levels that may be better suited to investigate the physiology and cell-biology of resistance-training in rodents.
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Affiliation(s)
- Martin Schmoll
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
- School of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
| | - Ewald Unger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Hazel Sutherland
- School of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
| | - Michael Haller
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Manfred Bijak
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Hermann Lanmüller
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Jonathan C Jarvis
- School of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
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Jarvis JC. The Relationship Between Activity Pattern and Muscle Adaptation in Skeletal Muscle. Artif Organs 2015; 39:863-7. [DOI: 10.1111/aor.12622] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Jonathan C. Jarvis
- School of Sport and Exercise Science; Liverpool John Moores University; Liverpool UK
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Herzig D, Maffiuletti NA, Eser P. The Application of Neuromuscular Electrical Stimulation Training in Various Non-neurologic Patient Populations: A Narrative Review. PM R 2015; 7:1167-1178. [DOI: 10.1016/j.pmrj.2015.03.022] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Revised: 03/24/2015] [Accepted: 03/27/2015] [Indexed: 12/16/2022]
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Anderson CM, Hu J, Barnes RM, Heidt AB, Cornelissen I, Black BL. Myocyte enhancer factor 2C function in skeletal muscle is required for normal growth and glucose metabolism in mice. Skelet Muscle 2015; 5:7. [PMID: 25789156 PMCID: PMC4364460 DOI: 10.1186/s13395-015-0031-0] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 01/28/2015] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Skeletal muscle is the most abundant tissue in the body and is a major source of total energy expenditure in mammals. Skeletal muscle consists of fast and slow fiber types, which differ in their energy usage, contractile speed, and force generation. Although skeletal muscle plays a major role in whole body metabolism, the transcription factors controlling metabolic function in muscle remain incompletely understood. Members of the myocyte enhancer factor 2 (MEF2) family of transcription factors play crucial roles in skeletal muscle development and function. MEF2C is expressed in skeletal muscle during development and postnatally and is known to play roles in sarcomeric gene expression, fiber type control, and regulation of metabolic genes. METHODS We generated mice lacking Mef2c exclusively in skeletal muscle using a conditional knockout approach and conducted a detailed phenotypic analysis. RESULTS Mice lacking Mef2c in skeletal muscle on an outbred background are viable and grow to adulthood, but they are significantly smaller in overall body size compared to control mice and have significantly fewer slow fibers. When exercised in a voluntary wheel running assay, Mef2c skeletal muscle knockout mice aberrantly accumulate glycogen in their muscle, suggesting an impairment in normal glucose homeostasis. Consistent with this notion, Mef2c skeletal muscle knockout mice exhibit accelerated blood glucose clearance compared to control mice. CONCLUSIONS These findings demonstrate that MEF2C function in skeletal muscle is important for metabolic homeostasis and control of overall body size.
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Affiliation(s)
- Courtney M Anderson
- Cardiovascular Research Institute, University of California San Francisco, 555 Mission Bay Blvd, South, MC 3120, San Francisco, CA 94158-2517 USA
| | - Jianxin Hu
- Cardiovascular Research Institute, University of California San Francisco, 555 Mission Bay Blvd, South, MC 3120, San Francisco, CA 94158-2517 USA
| | - Ralston M Barnes
- Cardiovascular Research Institute, University of California San Francisco, 555 Mission Bay Blvd, South, MC 3120, San Francisco, CA 94158-2517 USA
| | - Analeah B Heidt
- Cardiovascular Research Institute, University of California San Francisco, 555 Mission Bay Blvd, South, MC 3120, San Francisco, CA 94158-2517 USA
| | - Ivo Cornelissen
- Cardiovascular Research Institute, University of California San Francisco, 555 Mission Bay Blvd, South, MC 3120, San Francisco, CA 94158-2517 USA
| | - Brian L Black
- Cardiovascular Research Institute, University of California San Francisco, 555 Mission Bay Blvd, South, MC 3120, San Francisco, CA 94158-2517 USA ; Department of Biochemistry and Biophysics, University of California San Francisco, 555 Mission Bay Blvd, South, MC 3120, San Francisco, CA 94158-2517 USA
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Salmons S. An interesting study of the relationship between electromyographic activity in jaw muscles and their fibre type composition. J Anat 2010; 216:417; author reply 417. [PMID: 20447250 DOI: 10.1111/j.1469-7580.2009.01206_1.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Salmons S. Adaptive change in electrically stimulated muscle: a framework for the design of clinical protocols. Muscle Nerve 2009; 40:918-35. [PMID: 19902542 DOI: 10.1002/mus.21497] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Adult mammalian skeletal muscles have a remarkable capacity for adapting to increased use. Although this behavior is familiar from the changes brought about by endurance exercise, it is seen to a much greater extent in the response to long-term neuromuscular stimulation. The associated phenomena include a markedly increased resistance to fatigue, and this is the key to several clinical applications. However, a more rational basis is needed for designing regimes of stimulation that are conducive to an optimal outcome. In this review I examine relevant factors, such as the amount, frequency, and duty cycle of stimulation, the influence of force generation, and the animal model. From these considerations a framework emerges for the design of protocols that yield an overall functional profile appropriate to the application. Three contrasting examples illustrate the issues that need to be addressed clinically.
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Affiliation(s)
- Stanley Salmons
- Department of Human Anatomy and Cell Biology, School of Biomedical Sciences, University of Liverpool, The Sherrington Buildings, Ashton Street, Liverpool L69 3GE, UK.
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Duffell LD, Donaldson NDN, Perkins TA, Rushton DN, Hunt KJ, Kakebeeke TH, Newham DJ. Long-term intensive electrically stimulated cycling by spinal cord-injured people: Effect on muscle properties and their relation to power output. Muscle Nerve 2008; 38:1304-11. [DOI: 10.1002/mus.21060] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Ashley Z, Sutherland H, Russold MF, Lanmüller H, Mayr W, Jarvis JC, Salmons S. Therapeutic stimulation of denervated muscles: The influence of pattern. Muscle Nerve 2008; 38:875-86. [DOI: 10.1002/mus.21020] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Sutherland H, Salmons S, Ramnarine IR, Capoccia M, Walsh AA, Jarvis JC. Adaptive conditioning of skeletal muscle in a large animal model (Sus domesticus). J Anat 2007; 209:165-77. [PMID: 16879597 PMCID: PMC2100312 DOI: 10.1111/j.1469-7580.2006.00598.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Recognition of the adaptive capacity of mammalian skeletal muscle has opened the way to a number of clinical applications. For most of these, the fast, fatigue-susceptible fibres need to be transformed stably to fast, fatigue-resistant fibres that express the 2A myosin heavy chain isoform. The thresholds for activity-induced change are size-dependent, so although the requisite patterns of electrical stimulation are known for the rabbit, in humans these same patterns would produce type 1 fibre characteristics, with an undesirable loss of contractile speed and power. We have used histochemistry, immunohistochemistry and electrophoretic separations to evaluate a possible conditioning regime in a large animal model. Stimulation of the porcine latissimus dorsi muscle with a phasic 30-Hz pattern for up to 41 days converted all type 2X and 2A/2X fibres to 2A with only a small increase in the type 1 population, from 17% to 22%. Stimulation for longer periods increased the proportion of type 1 fibres to 52%. Based on this model, stimulation regimes designed to achieve a stable 2A phenotype in humans should deliver fewer stimulating impulses, possibly by a factor of 2, than the pattern assessed here. Any such pattern needs to be tested for at least 8 weeks.
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Affiliation(s)
- Hazel Sutherland
- Department of Human Anatomy and Cell Biology, University of Liverpool, UK
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Graham GM, Thrasher TA, Popovic MR. The effect of random modulation of functional electrical stimulation parameters on muscle fatigue. IEEE Trans Neural Syst Rehabil Eng 2006; 14:38-45. [PMID: 16562630 DOI: 10.1109/tnsre.2006.870490] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Muscle contractions induced by functional electrical stimulation (FES) tend to result in rapid muscle fatigue, which greatly limits activities such as FES-assisted standing and walking. It was hypothesized that muscle fatigue caused by FES could be reduced by randomly modulating parameters of the electrical stimulus. Seven paraplegic subjects participated in this study. While subjects were seated, FES was applied to quadriceps and tibialis anterior muscles bilaterally using surface electrodes. The isometric force was measured, and the time for the force to drop by 3 dB (fatigue time) and the normalized force-time integral (FTI) were determined. Four different modes of FES were applied in random order: constant stimulation, randomized frequency (mean 40 Hz), randomized current amplitude, and randomized pulsewidth (mean 250 micros). In randomized trials, stimulation parameters were stochastically modulated every 100 ms in a range of +/-15% using a uniform probability distribution. There was no significant difference between the fatigue time measurements for the four modes of stimulation. There was also no significant difference in the FTI measurements. Therefore, our particular method of stochastic modulation of the stimulation parameters, which involved moderate (15%) variations updated every 100 ms and centered around 40 Hz, appeared to have no effect on muscle fatigue. There was a strong correlation between maximum force measurements and stimulation order, which was not apparent in the fatigue time or FTI measurements. It was concluded that a 10-min rest period between stimulation trials was insufficient to allow full recovery of muscle strength.
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Affiliation(s)
- Geoffrey M Graham
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada.
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Thrasher A, Graham GM, Popovic MR. Reducing muscle fatigue due to functional electrical stimulation using random modulation of stimulation parameters. Artif Organs 2005; 29:453-8. [PMID: 15926981 DOI: 10.1111/j.1525-1594.2005.29076.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A major limitation of many functional electrical stimulation (FES) applications is that muscles tend to fatigue very rapidly. It was hypothesized that FES-induced muscle fatigue could be reduced by randomly modulating the pulse frequency, amplitude, and pulse width in a range of +/-15%. Seven subjects with spinal-cord injuries participated in this study. FES was applied to quadriceps and tibialis anterior muscles using surface electrodes. Isometric force was measured, and the time for the force to drop by 3 dB (fatigue time) was compared between trials. Four different modes of FES were applied in random order: constant stimulation, randomized frequency, randomized amplitude, and randomized pulse width. There was no significant difference between the fatigue-time measurements for the four modes of stimulation (P=0.329). Therefore, random modulation appeared to have no effect. Based on an observed correlation between maximum force measurements and trial order, we concluded that having 10-min rest periods between trials was insufficient.
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Affiliation(s)
- Adam Thrasher
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada.
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Abstract
The review explains why the myotoxic phospholipases A2 and cardiotoxins are such important tools in the study of the regeneration and maturation of mammalian skeletal muscle. The role of satellite cells as precursors of cell-based regeneration is discussed and recent controversies on the origin of myogenic cells involved in the regeneration of mature skeletal muscle are addressed. This is followed by discussions of sarcomere reconstruction, myosin and sarcoplasmic reticulum ATPase expression, the electrophysiological properties of regenerating muscle, and the reconstruction of the neuromuscular junction. The emphasis throughout is on the plastic changes of major structural and functional proteins that occur during regeneration, and on other influences that determine the final outcome of regenerative activity such as innervation, thyroid status, mechanical work and the functional integrity of the microcirculation. The review closes with a discussion of some of the factors--such as active regeneration--that influence the success of gene-based therapies applied to inherited muscle disease.
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Affiliation(s)
- J B Harris
- School of Neurology, Neurobiology and Psychiatry, Faculty of Medical Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
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