[show abstract][hide abstract] ABSTRACT: Current methods for applying multi-site vibratory stimuli to the skin typically involve the use of multiple, individual vibrotactile stimulators. Limitations of such an arrangement include difficulty with both positioning the stimuli as well as ensuring that stimuli are delivered in a synchronized and deliberate manner. Previously, we reported a two-site tactile stimulator that was developed in order to solve these problems (Tannan et al., 2007a). Due to both the success of that novel stimulator and the limitations that were inherent in that device, we designed and fabricated a four-site stimulator that provides a number of advantages over the previous version. First, the device can stimulate four independent skin sites and is primarily designed for stimulating the digit tips. Second, the positioning of the probe tips has been re-designed to provide better ergonomic hand placement. Third, the device is much more portable than the previously reported stimulator. Fourth, the stimulator head has a much smaller footprint on the table or surface where it resides. To demonstrate the capacity of the device for delivering tactile stimulation at four independent sites, a finger agnosia protocol, in the presence and absence of conditioning stimuli, was conducted on seventeen healthy control subjects. The study demonstrated that with increasing amplitudes of vibrotactile conditioning stimuli concurrent with the agnosia test, inaccuracies of digit identification increased, particularly at digits D3 and D4. The results are consistent with prior studies that implicated synchronization of adjacent and near-adjacent cortical ensembles with conditioning stimuli in impacting TOJ performance (Tommerdahl et al., 2007a,b).
Journal of neuroscience methods 12/2011; 204(2):215-20. · 2.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: To investigate the clinical correlates of central nervous system alterations among women with vulvodynia. Altered central sensitization has been linked to dysfunction in central nervous system-inhibitory pathways (e.g., γ-aminobutyric acidergic), and metrics of sensory adaptation, a centrally mediated process that is sensitive to this dysfunction, could potentially be used to identify women at risk of treatment failure using conventional approaches.
Twelve women with vulvodynia and 20 age-matched controls participated in this study, which was conducted by sensory testing of the right hand's index and middle fingers. The following sensory precepts were assessed: (1) vibrotactile detection threshold; (2) amplitude discrimination capacity (defined as the ability to detect differences in intensity of simultaneously delivered stimuli to 2 fingers); and (3) a metric of adaptation (determined by the impact that applying conditioning stimuli have on amplitude discriminative capacity).
Participants did not differ on key demographic variables, vibrotactile detection threshold, and amplitude discrimination capacity. However, we found significant differences from controls in adaptation metrics in 1 subgroup of vulvodynia patients. Compared with healthy controls and women with a shorter history of pain [n=5; duration (y) = 3.4 ± 1.3], those with a longer history [n=7; duration (y) = 9.3 ± 1.4)] were found to be less likely to have adaptation metrics similar to control values.
Chronic pain is thought to lead to altered central sensitization, and adaptation is a centrally mediated process that is sensitive to this condition. This report suggests that similar alterations exist in a subgroup of vulvodynia patients.
The Clinical journal of pain 05/2011; 27(9):755-63. · 3.01 Impact Factor
[show abstract][hide abstract] ABSTRACT: While it is well known that skin physiology - and consequently sensitivity to peripheral stimuli - degrades with age, what is less appreciated is that centrally mediated mechanisms allow for maintenance of the same degree of functionality in processing these peripheral inputs and interacting with the external environment. In order to demonstrate this concept, we obtained observations of processing speed, sensitivity (thresholds), discriminative capacity, and adaptation metrics on subjects ranging in age from 18 to 70. The results indicate that although reaction speed and sensory thresholds change with age, discriminative capacity, and adaptation metrics do not. The significance of these findings is that similar metrics of adaptation have been demonstrated to change significantly when the central nervous system (CNS) is compromised. Such compromise has been demonstrated in subject populations with autism, chronic pain, acute NMDA receptor block, concussion, and with tactile-thermal interactions. If the metric of adaptation parallels cortical plasticity, the results of the current study suggest that the CNS in the aging population is still capable of plastic changes, and this cortical plasticity could be the mechanism that compensates for the degradations that are known to naturally occur with age. Thus, these quantitative measures - since they can be obtained efficiently and objectively, and appear to deviate from normative values significantly with systemic cortical alterations - could be useful indicators of cerebral cortical health.
Frontiers in Aging Neuroscience 01/2011; 3:18. · 5.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: A significant number of studies that evaluated tactile-pain interactions employed heat to evoke nociceptive responses. However, relatively few studies have examined the effects of non-noxious thermal stimulation on tactile discriminative capacity. In this study, the impact that non-noxious heat had on three features of tactile information processing capacity was evaluated: vibrotactile threshold, amplitude discriminative capacity, and adaptation. It was found that warming the skin made a significant improvement on a subject's ability to detect a vibrotactile stimulus, and although the subjects' capacities for discriminating between two amplitudes of vibrotactile stimulation did not change with skin heating, the impact that adapting or conditioning stimulation normally had on amplitude discrimination capacity was significantly attenuated by the change in temperature. These results suggested that although the improvements in tactile sensitivity that were observed could have been a result of enhanced peripheral activity, the changes in measures that reflect a decrease in the sensitization to repetitive stimulation are most likely centrally mediated. The authors speculate that these centrally mediated changes could be a reflection of a change in the balance of cortical excitation and inhibition.
Brain research 09/2009; 1302:97-105. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: The internal anal sphincter (IAS) is a specialized circular smooth muscle that maintains rectoanal continence. In vitro models are needed to study the pathophysiology of human IAS disorders. We bioengineered sphincteric rings from human IAS smooth muscle cells (SMC) and investigated their response to cholinergic stimulation as well as investigated whether protein kinase C (PKC) and Rho kinase signaling pathways remain functional.
3-Dimensional bioengineered ring (3DBR) model of the human IAS was constructed from isolated human IAS SMC obtained from surgery. Contractile properties and force generation in response to acetylcholine, PKC inhibitor calphostin-C, Rho/ROCK inhibitor Y-27632, permeable Rho/ROCK inhibitor c3-exoenzyme, and PKC activator PdBU was measured.
The human IAS 3DBR has the essential characteristics of physiologically functional IAS; it generated a spontaneous myogenic basal tone, and the constructs were able to relax in response to relaxants and contract in response to contractile agents. The constructs generated dose-dependent force in response to acetylcholine. Basal tone was significantly reduced by calphostin-C but not with Y-27632. Acetylcholine-induced force generation was also significantly reduced by calphostin-C but not with Y-27632. PdBU generated force that was equal in magnitude to acetylcholine. Thus, calphostin-C inhibited PdBU-induced force generation, whereas Y-27632 and c3 exoenzyme did not.
These data indicate that basal tone and acetylcholine-induced force generation depend on signaling through the PKC pathway in human IAS; PKC-mediated force generation is independent of the Rho/ROCK pathway. This human IAS 3DBR model can be used to study the pathophysiology associated with IAS malfunctions.
[show abstract][hide abstract] ABSTRACT: The traditional two-point discrimination (TPD) test, a widely used tactile spatial acuity measure, has been criticized as being imprecise because it is based on subjective criteria and involves a number of non-spatial cues. The results of a recent study showed that as two stimuli were delivered simultaneously, vibrotactile amplitude discrimination became worse when the two stimuli were positioned relatively close together and was significantly degraded when the probes were within a subject's two-point limen. The impairment of amplitude discrimination with decreasing inter-probe distance suggested that the metric of amplitude discrimination could possibly provide a means of objective and quantitative measurement of spatial discrimination capacity.
A two alternative forced-choice (2AFC) tracking procedure was used to assess a subject's ability to discriminate the amplitude difference between two stimuli positioned at near-adjacent skin sites. Two 25 Hz flutter stimuli, identical except for a constant difference in amplitude, were delivered simultaneously to the hand dorsum. The stimuli were initially spaced 30 mm apart, and the inter-stimulus distance was modified on a trial-by-trial basis based on the subject's performance of discriminating the stimulus with higher intensity. The experiment was repeated via sequential, rather than simultaneous, delivery of the same vibrotactile stimuli.
Results obtained from this study showed that the performance of the amplitude discrimination task was significantly degraded when the stimuli were delivered simultaneously and were near a subject's two-point limen. In contrast, subjects were able to correctly discriminate between the amplitudes of the two stimuli when they were sequentially delivered at all inter-probe distances (including those within the two-point limen), and improved when an adapting stimulus was delivered prior to simultaneously delivered stimuli.
Subjects' capacity to discriminate the amplitude difference between two vibrotactile stimulations was degraded as the inter-stimulus distance approached the limit of their two-point spatial discriminative capacity. This degradation of spatial discriminative capacity lessened when an adapting stimulus was used. Performance of the task, as well as improvement on the task with adaptation, would most likely be impaired if the cortical information processing capacity of a subject or subject population were systemically altered, and thus, the methods described could be effective measures for use in clinical or clinical research applications.
[show abstract][hide abstract] ABSTRACT: A quantitative understanding of the bulk excitability of skeletal muscle tissues is important for the design of muscle tissue bioreactor systems, implantable muscle stimulators, and other systems where electrical pulses are employed to elicit contractions in muscle tissue both in vitro and in vivo. The purpose of the present study is to systematically compare the excitability of mammalian (rat) skeletal muscle under a range of conditions (including neonatal development, denervation, and chronic in vivo stimulation of denervated muscle) and of self-organized muscle tissue constructs engineered in vitro from both primary cells and cell lines. Excitability is represented by rheobase (R(50), units = V/mm) and chronaxie (C(50), units = microseconds) values, with lower values for each indicating greater excitability. Adult skeletal muscle is the most excitable (R(50) ~ 0.29, C(50) ~ 100); chronically denervated whole muscles (R(50) ~ 2.54, C(50) ~ 690) and muscle engineered in vitro from cell lines (C2C12 + 10T1/2) (R(50) ~ 1.93, C(50) ~ 416) have exceptionally low excitability; muscle engineered in vitro from primary myocytes (R(50) ~ 0.99, C(50) ~ 496) has excitability similar to that of day 14 neonatal rat muscle (R(50) ~ 0.65, C(50) ~ 435); stimulated-denervated muscles retain excellent excitability when chronically electrically stimulated (R(50) ~ 0.40, C(50) ~ 100); and neonatal rat muscle excitability improves during the first 6 weeks of development, steadily approaching that of adult muscle.
[show abstract][hide abstract] ABSTRACT: The purpose of this study is to measure abdominal wall myopathic histologic and mechanical changes during incisional herniation and its effect on incisional hernia repairs.
Unloaded skeletal muscles undergo characteristic atrophic changes, including change in fiber type composition, decreased cross-sectional area, and pathologic fibrosis. We hypothesize that these atrophic changes decrease muscle elastic properties and may contribute to the high laparotomy wound failure rate observed following incisional hernia repair.
A rat model of chronic incisional hernia formation was used. Failing midline laparotomy incisions developed into incisional hernias. Controls were uninjured and sham laparotomy (healed) groups. Internal oblique muscles were harvested for fiber typing, measurement of cross-sectional area, collagen deposition, and mechanical analysis. Mesh hernia repairs were performed on a second group of rats with chronic incisional hernias or acute anterior abdominal wall myofascial defects.
The hernia group developed lateral abdominal wall shortening and oblique muscle atrophy. This was associated with a change in the distribution of oblique muscle fiber types, decreased cross-sectional area, and pathologic fibrosis consistent with myopathic disuse atrophy. These muscles exhibited significant decreased extensibility and increased stiffness. The healed (sham) laparotomy group expressed an intermediate phenotype between the uninjured and hernia groups. Recurrent hernia formation was most frequent in the chronic hernia model, and hernia repairs mechanically disrupted at a lower force compared with nonherniated abdominal walls.
The internal oblique muscles of the abdominal wall express a pattern of changes consistent with those seen in chronically unloaded skeletal muscles. The internal oblique muscles become fibrotic during herniation, reducing abdominal wall compliance and increasing the transfer of load forces to the midline wound at the time of hernia repair.
Annals of Surgery 02/2007; 245(1):140-6. · 6.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: Prolonged denervation of skeletal muscles results in atrophy and poor recovery of motor function following delayed reinnervation. Electrical stimulation reduces denervation atrophy. We hypothesized that electrical stimulation of denervated extensor digitorum longus (EDL) muscles during a prolonged period between nerve axotomy and opportunity for reinnervation by motoneurons after nerve-repair would enhance the recovery of muscle mass, force and motor-function.
The EDL muscles of rats were denervated for 3.5 months by peroneal nerve axotomy, then repaired with an end-to-end neurorrhaphy, and allowed to recover for 6.5 months. During the period of denervation, some of the rats received a protocol of electrical stimulation that had previously been shown to dramatically attenuate the effects of denervation atrophy through 4 months. Other experimental groups included unoperated control muscles, denervated muscles, and axotomy followed immediately by nerve-repair. Final evaluations included walking track analysis, maximum force measured in situ by indirect stimulation of the nerve, and muscle mass.
The hypothesis was not supported. Electrical stimulation during the period of denervation did not enhance recovery of muscle mass, force or motor function.
The primary factors that inhibited reinnervation and recovery following delayed reinnervation were not alleviated by the electrical stimulation during the period of muscle denervation.
Restorative neurology and neuroscience 02/2007; 25(5-6):601-10. · 2.93 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report the completion of Phase II of a technological development program for the production of living muscle mechanical actuators for robotic and prosthetic applications. Our primary objectives were to engineer living skeletal muscle actuators in culture using integrated bioreactors to guide tissue development and to maintain tissue contractility, to achieve 50% of adult phenotype muscular contractility, and then to install the engineered muscles into a centimeter-scale hybrid swimming robotic platform. Outcomes by milestone: (1) Develop integrated tissue culture bioreactor systems: completed all but bulk perfusion (2) Develop appropriate tissue interfaces in culture: full success, muscle-tendon & nerve (3) Achieve 50% of adult muscle functional capacity: excellent progress but not 50% (4) Swimming robotic platform with muscle: 50% success due to inadequate muscle performance Overall, this project resulted in many planned and collateral technological advances, including sub-cm scale cardiac muscle powered swimming actuators, functional tendon and nerve tissue interfaces, integrated rapid manufactured tissue bioreactors and improved contractility.
[show abstract][hide abstract] ABSTRACT: Denervation or inactivity is known to decrease the mass and alter the phenotype of muscle. The mechanical response of tendon to inactivity that has been determined experimentally differs from what is reported by patients. We investigated the hypothesis that this difference was the result of artifacts of the testing process and did not represent what occurred in vivo. To test this hypothesis, a novel approach was used to determine the mechanical properties of the tibialis anterior (TA) tendon by optically measuring the end-to-end mechanical strains as well as the local strains at specific regions of excised TA tendon units. When the end-to-end strain of normal TA tendon is determined, stress-strain response curves show considerably more extensibility than when strain is measured across only the midsection of the tendon (mid-tendon). The strain experienced by the region close to the muscle (muscle tendon) is five times greater than the strain in either the mid-tendon or near the bone (bone-tendon). Five weeks of denervation decreased muscle mass by 67%; increased tendon mass by 10%; and changed the entire shape of the nonlinear response curve, including a loss in regional variation in strain, a 3.9-fold increase in end-to-end tangent modulus, and a 70% reduction in the toe region, as a result of a drastic reduction of the extensibility in the muscle-tendon region. The stress-strain response in the mid-tendon region of a normal TA tendon is therefore not indicative of its overall ability to deform in vivo as it transmits forces from muscle to bone.
Journal of Applied Physiology 11/2006; 101(4):1113-7. · 3.48 Impact Factor
[show abstract][hide abstract] ABSTRACT: In vitro studies have used protein markers to distinguish between myogenic cells isolated from fast and slow skeletal muscles. The protein markers provide some support for the hypothesis that satellite cells from fast and slow muscles are different, but the data are equivocal. To test this hypothesis directly, three-dimensional skeletal muscle constructs were engineered from myogenic cells isolated from fast tibialis anterior (TA) and slow soleus (SOL) muscles of rats and functionality was tested. Time to peak twitch tension (TPT) and half relaxation time (RT(1/2)) were approximately 30% slower in constructs from the SOL. The slower contraction and relaxation times for the SOL constructs resulted in left shift of the force-frequency curve compared with those from the TA. Western blot analysis showed a 60% greater quantity of fast myosin heavy chain in the TA constructs. 14 days of chronic low-frequency electrical stimulation resulted in a 15% slower TPT and a 14% slower RT(1/2), but no change in absolute force production in the TA constructs. In SOL constructs, slow electrical stimulation resulted in an 80% increase in absolute force production with no change in TPT or RT(1/2). The addition of cyclosporine A did not prevent the increase in force in SOL constructs after chronic low-frequency electrical stimulation, suggesting that calcineurin is not responsible for the increase in force. We conclude that myogenic cells associated with a slow muscle are imprinted to produce muscle that contracts and relaxes slowly and that calcineurin activity cannot explain the response to a slow pattern of electrical stimulation.
[show abstract][hide abstract] ABSTRACT: As tissue-engineered muscle constructs increase in scale, their size is limited by the need for a vascular supply. In this work, the authors demonstrate a method of producing three-dimensional contractile skeletal muscles in vivo by incorporating an axial vascular pedicle.
Primary myoblast cultures were generated from adult F344 rat soleus muscle. The cells were suspended in a fibrinogen hydrogel contained within cylindrical silicone chambers, and situated around the femoral vessels in isogeneic adult recipient rats. The constructs were allowed to incubate in vivo for 3 weeks, at which point they were explanted and subjected to isometric force measurements and histologic evaluation.
The resulting three-dimensional engineered skeletal muscle constructs produced longitudinal contractile force when electrically stimulated. Length-tension, force-voltage, and force-frequency relationships were similar to those found in developing skeletal muscle. Desmin staining demonstrated that individual myoblasts had undergone fusion to form multinucleated myotubes. Von Willebrand staining showed that the local environment within the chamber was richly angiogenic, and capillaries had grown into and throughout the constructs from the femoral artery and vein.
Three-dimensional, vascularized skeletal muscle can be engineered in vivo. The resulting tissues have histologic and functional properties consistent with native skeletal muscle.
Plastic and reconstructive surgery 07/2006; 117(7):2235-42. · 2.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: An improved understanding of load-bearing soft tissue repair suggests that the mechanism for the improved outcomes after alloplastic incisional herniorrhaphy involves more than simple tissue replacement or material strength. We test the hypothesis that postrepair abdominal wall elastic properties are most predictive of successful abdominal wall reconstruction.
A rodent model of chronic incisional hernia formation was used. Midline incisional hernias were repaired primarily with suture (n = 24) or polypropylene mesh (n = 24). Rodents were sacrificed at serial postoperative time points over 60 days. Intact abdominal wall strips were cut perpendicular to the wound for tensiometric analysis. Biopsies of wound provisional matrix were obtained for biochemical analysis.
Recurrent incisional hernia formation was significantly decreased in the mesh-repair group, compared with the suture-repair group (5/24 vs 14/24, P = .02). Mesh-repaired abdominal walls demonstrated significantly more elongation (P < .01) and less stiffness (P < .01). Toughness was equal between wounds, although the suture-repaired wounds had increased recovery of tensile strength (P < .01). There were no significant differences in collagen deposition after postoperative day 7.
Mesh incisional herniorrhaphy increases abdominal wall elastic properties as measured by increased elongation and reduced stiffness. Increased abdominal wall elasticity after incisional hernia repair in turn results in lower recurrence rates.
Surgery 07/2006; 140(1):14-24. · 3.37 Impact Factor
[show abstract][hide abstract] ABSTRACT: Denervated skeletal muscles lack contractile activity and subsequently lose mass and force generation. Prolonged periods of denervation prior to nerve-implant grafting limit the recovery of mass and force. We hypothesized that electrical stimulation during a period of denervation that maintains mass and force above the levels of denervated muscles enhances the recovery of mass and force following nerve-implant grafting.
The extensor digitorum longus (EDL) muscles of anesthetized rats were denervated, and a stimulator was implanted. Following 4 or 7 months of denervation, with or without electrical stimulation, the EDL muscles were removed, evaluated in vitro for mass and contractile properties, and then nerve-implant grafted into syngeneic rats. Unoperated, contralateral muscles were also evaluated and grafted.
The hypothesis was not supported by the experimental data. Compared with values for 4- or 7-month denervated muscles, the stimulated-denervated muscles maintained higher mass and force, less prolonged time-to-peak tensions and half-relaxation times, and higher excitability. Nevertheless, the recovery of mass and force following grafting was not improved.
The factors within long-term denervated muscles that hinder recovery following grafting appear to be related primarily to factors associated with the duration of denervation and not to the level of atrophy and weakness prior to grafting.
Restorative neurology and neuroscience 02/2006; 24(1):41-54. · 2.93 Impact Factor
[show abstract][hide abstract] ABSTRACT: Previously, we have engineered three-dimensional (3-D) skeletal muscle constructs that generate force and display a myosin heavy-chain (MHC) composition of fetal muscle. The purpose of this study was to evaluate the functional characteristics of 3-D skeletal muscle constructs cocultured with fetal nerve explants. We hypothesized that coculture of muscle constructs with neural cells would produce constructs with increased force and adult MHC isoforms. Following introduction of embryonic spinal cord explants to a layer of confluent muscle cells, the neural tissue integrated with the cultured muscle cells to form 3-D muscle constructs with extensions. Immunohistochemical labeling indicated that the extensions were neural tissue and that the junctions between the nerve extensions and the muscle constructs contained clusters of acetylcholine receptors. Compared to muscles cultured without nerve explants, constructs formed from nerve- muscle coculture showed spontaneous contractions with an increase in frequency and force. Upon field stimulation, both twitch (2-fold) and tetanus (1.7-fold) were greater in the nerve-muscle coculture system. Contractions could be elicited by electrically stimulating the neural extensions, although smaller forces are produced than with field stimulation. Severing the extension eliminated the response to electrical stimulation, excluding field stimulation as a contributing factor. Nerve- muscle constructs showed a tendency to have higher contents of adult and lower contents of fetal MHC isoforms, but the differences were not significant. In conclusion, we have successfully engineered a 3-D nerve-muscle construct that displays functional neuromuscular junctions and can be electrically stimulated to contract via the neural extensions projecting from the construct.
[show abstract][hide abstract] ABSTRACT: The ability to engineer cardiac tissue in vitro is limited by the absence of a vasculature. In this study we describe an in vivo model which allows neovascularization of engineered cardiac tissue. Three-dimensional cardiac tissue, termed "cardioids," was engineered in vitro from the spontaneous delamination of a confluent monolayer of cardiac cells. Cardioids were sutured onto a support framework and then implanted in a subcutaneous pocket in syngeneic recipient rats. Three weeks after implantation, cardioids were recovered for in vitro force testing and histological evaluation. Staining for hematoxylin and eosin demonstrated the presence of viable cells within explanted cardioids. Immunostaining with von Willebrand factor showed the presence of vascularization. Electron micrographs revealed the presence of large amounts of aligned contractile proteins and a high degree of intercellular connectivity. The peak active force increased from an average value of 57 microN for control cardioids to 447 microN for explanted cardioids. There was also a significant increase in the specific force. There was a significant decrease in the time to peak tension and half relaxation time. Explanted cardioids could be electrically paced at frequencies of 1-5 Hz. Explanted cardioids exhibited a sigmoidal response to calcium and positive chronotropy in response to epinephrine. As the field of cardiac tissue engineering progresses, it becomes desirable to engineer larger diameter tissue equivalents and to induce angiogenesis within tissue constructs. This study describes a relatively simple in vivo model, which promotes the neovascularization of tissue-engineered heart muscle and subsequent improvement in contractile performance.
[show abstract][hide abstract] ABSTRACT: Fecal incontinence affects people of all ages and social backgrounds and can have devastating psychological and economic consequences. This disorder is largely attributed to decreased mechanical efficiency of the internal anal sphincter (IAS), yet little is known about the pathophysiological mechanisms responsible for the malfunction of sphincteric smooth muscle at the cellular level. The object of this study was to develop a three-dimensional (3-D) physiological model of the IAS bioengineered in vitro from isolated smooth muscle cells. Smooth muscle cells isolated from the IAS of rabbits were seeded in culture on top of a loose fibrin gel, where they migrated and self-assembled in circumferential alignment. As the cells proliferated, the fibrin gel contracted around a 5-mm-diameter SYLGARD mold, resulting in a 3-D cylindrical ring of sphincteric tissue. We found that 1) the bioengineered IAS rings generated a spontaneous basal tone, 2) stimulation with 8-bromo-cAMP (8-Br-cAMP) caused a sustained decrease in the basal tone (relaxation) that was calcium-independent, 3) upon stimulation with ACh, bioengineered IAS rings showed a calcium- and concentration-dependent peak contraction at 30 s that was sustained for 4 min, 4) addition of 8-Br-cAMP induced rapid relaxation of ACh-induced contraction and force generation of IAS rings, and 5) bioengineered sphincter rings show striking functional differences when compared with bioengineered rings made from isolated colonic smooth muscle cells. This is the first report of a 3-D in vitro model of a gastrointestinal smooth muscle IAS. Bioengineered IAS rings demonstrate physiological functionality and may be used in the elucidation of the mechanisms causing sphincter malfunction.
[show abstract][hide abstract] ABSTRACT: Loss of innervation in skeletal muscles leads to degeneration, atrophy, and loss of force. These dramatic changes are reflected in modifications of the mRNA expression of a large number of genes. Our goal was to clarify the broad spectrum of molecular events associated with long-term denervation of skeletal muscles. A microarray study compared gene expression profiles of 2-mo denervated and control extensor digitorum longus (EDL) muscles from 6-mo-old rats. The study identified 121 genes with increased and 7 genes with decreased mRNA expression. The expression of 107 of these genes had not been identified previously as changed after denervation. Many of the genes identified were genes that are highly expressed in skeletal muscles during embryonic development, downregulated in adults, and upregulated after denervation of muscle fibers. Electrical stimulation of denervated muscles preserved muscle mass and maximal force at levels similar to those in the control muscles. To understand the processes underlying the effect of electrical stimulation on denervated skeletal muscles, mRNA and protein expression of a number of genes, identified by the microarray study, was compared. The hypothesis was that loss of nerve action potentials and muscle contractions after denervation play the major roles in upregulation of gene expression in skeletal muscles. With electrical stimulation of denervated muscles, the expression levels for these genes were significantly downregulated, consistent with the hypothesis that loss of action potentials and/or contractions contribute to the alterations in gene expression in denervated skeletal muscles.
[show abstract][hide abstract] ABSTRACT: Stimulation protocols for denervated muscles distribute the generated contractions either within treatment sessions followed by hours of rest, or repeated 24 h per day with each contraction followed by a constant interval of rest. Our purpose was to directly compare the effects of the same number of identically generated contractions having different temporal daily distributions. For 5 weeks in denervated extensor digitorum longus muscles of rats, between 100 and 800 contractions were generated daily, distributed either within worksets that alternated periods of activity and rest, or separated by constant intervals of rest. Most of the tested protocols maintained muscle mass and maximum force near values of innervated controls. Although 100 contractions daily generated at constant intervals were sufficient to maintain mass and force, 100 contractions during a 4-h treatment session followed by 20 h of rest were not sufficient, and mass and force were not different from values of denervated muscles.