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PubMed2000

Magnetic resonance imaging of denervated muscle: comparison to electromyography.

The purpose of the study is to further assess the usefulness of short TI (time to inversion) recovery (STIR) magnetic resonance imaging (MRI) in detecting denervation of skeletal muscle compared to needle electromyography (EMG). Ninety subjects with clinical evidence of peripheral nerve injury or radiculopathy underwent STIR MRI and EMG of the affected limb. In 74 (82%) of these subjects, a positive correlation was found between STIR MRI and EMG (P < 0.009). STIR MRI has a relative sensitivity of 84% and specificity of 100% for detecting denervation. A subset of 28 subjects underwent quantitative assessments of signal intensity ratio (SIR) from the STIR MRI. The rank order correlation coefficient between the SIR and abnormal spontaneous activity on EMG was 0.70 (P < 0.001). Increased signal intensity on STIR MRI corresponds closely with spontaneous activity on EMG in denervated muscle. Although less sensitive than EMG in detecting muscle denervation, STIR MRI may be a useful adjunctive diagnostic tool in this setting.

Adult↗
PubMed1980

The visualization of myosatellite cells in normal and denervated muscle: a new light microscopic staining technique.

A new light microscopic staining technique allows the visualization of satellite cells on the surface of myofibers. Either prior to or during fixation, whole frog sartorius muscles are bathed in an acidic buffered solution containing lead nitrate and subsequently exposed to ammonium sulfide. The staining of the satellite cells resulting from this procedure reveals their positions, and the outlines of their cell processes which occasionally branch. Electron microscopy shows that the staining is due to lead deposits localized between apposing membranes of satellite cells and associated myofibers. Prior exposure to N-ethyl-maleimide (NEM) does not alter the formation of the lead deposits on the satellite cell, but reduces the amount of Pb deposits on the muscle surface and connective tissue. This technique has been applied to determine the effects of denervation on the satellite cells of frog sartorius muscles. Four weeks after denervation, the number of satellite cells is essentially the same in both denervated muscles and the intact muscles of the contralateral side. However, denervation results in a subpopulation of satellite cells with altered shapes. They have elongated cytoplasmic processes which often branch. It is suggested that these supernumerary cytoplasmic processes represent an intermediate phase in the transition of satellite cells to myoblasts.

Animals↗
PubMed1983

A quantitative ultrastructural analysis of satellite cells in denervated fast and slow muscles of the mouse.

Mononucleated cells located between the external lamina and sarcolemma of denervated muscle fibers within the extensor digitorum longus (EDL) and soleus muscles of adult mice were quantified and examined ultrastructurally from 3 to 65 days after ligating and removing a section of the sciatic nerve. During the first 2 weeks postdenervation, mononucleated cells in denervated muscles were morphologically indistinguishable from satellite cells observed in control muscles. With time, however, many of these satellite-like cells appeared more active as evidenced by a decrease in their nucleocytoplasmic ratio and an increase in their mean percentage of euchromatin material. The number of satellite cells (expressed as a ratio of satellite cell nuclei to satellite cell nuclei plus myonuclei) did not increase significantly until 30 days postdenervation, at which time the mean percentage for the soleus muscle had risen from a control value of 4.1-8.5%, and for the EDL from 1.2-4.1%. Small-diameter, presumably regenerating, myofibers were occasionally observed but only after 30 days denervation. The ultrastructural evidence plus comparisons of euchromatin distributions between myonuclei and satellite cell nuclei support the concept that an increase in the number of satellite-like cells during denervation is more likely due to satellite cell proliferation than to the formation of mononucleated fragments utilizing preexisting myonuclei.

Animals↗
PubMed1985

Partial denervation of the ovaries by transection of the suspensory ligament does not inhibit ovulation in rats treated with pregnant mare serum gonadotropin.

Adrenergic nerves reach the ovary via two routes: along the arteries to the ovary and via the suspensory ligament. Results from earlier investigations suggest that denervation of the nerves along the arteries does not influence the ovulatory process. In the present study we have examined whether denervation by transection of the ovarian suspensory ligament influences the ovulatory process. Partial denervation of the ovary by transection of the ovarian suspensory ligament, sham operation, or only anesthesia were performed on immature 25-day-old rats. To induce ovulation, pregnant mare serum gonadotropin (PMSG) was injected in the morning (0800-0930), when the rats were 26 days old. This PMSG treatment normally induces ovulation around 0200 in the early morning of day 29 with subsequent formation of corpora lutea. Rats were killed 5-8 hr, 3 days, and 5 days after this ovulation time. Ovarian interstitial norepinephrine levels were markedly decreased after transection of the suspensory ligament. Ovulations had occurred in all denervated, as well as sham-operated, and control rats. The various groups did not differ in the number of ovulations per rat. Thus, the adrenergic nerves in the suspensory ligament appear not to be necessary for ovulation. Whether catecholamines themselves play a role in the ovulatory process cannot be elucidated from this experiment, since the norepinephrine content in the ovary was not totally depleted. It seems unlikely that adrenergic nerves reach the corpus luteum via the suspensory ligament, since transection of this structure did not change the luteal content of norepinephrine.

Animals↗
PubMed1986

Effects of denervation and delayed amputation on forelimb regeneration in Xenopus laevis froglets.

Left forelimbs of postmetamorphic Xenopus laevis froglets were repeatedly denervated prior to and following amputation. Amputations were performed 14, 21, 28, or 42 days after the original denervation. A tissue-regenerative response resulting in the formation of a spike-shaped, heteromorphic outgrowth was found in the sham-denervated and control animals, but dedifferentiation of the stump tissues was not apparent. Tissue-regenerative outgrowths were not observed in the denervated cases; instead, dermal wound healing and stump and scar formation occurred. In both control and experimental cases, however, a periosteal proliferative response to amputation injury led to the development of a greatly thickened periosteum the length of the amputated radius-ulna as well as a cap of cartilage at the distal end of these bones. We conclude from these results that forelimbs of postmetamorphic froglets are incapable of adjusting to a prolonged nerveless state sufficient to allow the normal tissue-regenerative response of spike outgrowth formation.

Animals↗
PubMed1989

Effect of selected denervations on glycoconjugate composition and tissue morphology during the initiation phase of limb regeneration in adult Ambystoma.

This study was undertaken to assess the effects of various quantities of neural tissue on the temporal relationship of matrix glycoconjugates to the regeneration morphology. 1) Denervation before amputation revealed that a threshold level of nervous tissue was necessary to activate a regeneration response from the tissue, i.e., appearance of regeneration-specific morphologies and glycoconjugates. 2) Denervation after amputation demonstrated that the level of neural tissue necessary to maintain these responses was below the level necessary to activate the regeneration response. If neural tissue was completely removed there was a concomitant loss of regenerate morphologies and glycoconjugates. 3) Bilateral amputation of a neurogenically intact limb and its completely denervated contralateral limb revealed that the regeneration response was a localized phenomenon during the first 30 days after amputation. After 30 days the regeneration response appeared within the previously degenerated denervating limb. The results suggest that the factors controlling the regenerative response in adult Ambystoma are large diffusible substances that can be transported by the circulation and can affect the regenerative response in remote, previously activated, tissues.

Ambystoma↗
PubMed2003

Regeneration of myenteric plexus in the mouse colon after experimental denervation with benzalkonium chloride.

Recent reports suggest a far greater plasticity in nerve tissue than previously believed. As the digestive tract is exposed to a variety of insults, this question is relevant to enteric nerves, but little is known about their ability to recover from damage. To address this problem, we ablated the myenteric plexus of the mouse colon with the detergent benzalkonium chloride (BAC) and followed the ensuing morphologic changes for up to 60 days by using light- and electron microscopy. We found that, 2 days after BAC application, the treated area was essentially devoid of intact nerve elements. From day 7, new nerve fibers were observed within the denervated region. This growth progressed until, at days 30-60, newly grown nerve fibers were present in most of this region, and the pattern of muscle innervation was similar to the normal one. At least part of these fibers originated at neurons within intact ganglia surrounding the denervated region. The cross-sectional area of neurons near the denervated region at day 14 was 52% greater than controls. Glial cells were closely associated with the regenerating nerve fibers. From day 14 onward, we observed undifferentiated cells and differentiating neurons in ganglia surrounding the denervated region, and by day 30, new neurons were present in the myenteric region, along with regenerating nerve fibers. We conclude that the myenteric plexus is endowed with a considerable ability of regeneration and plasticity. The results provide evidence for the presence of stem cells and for an adult neurogenesis in this plexus.

Animals↗
PubMed1990

Specificity of corticospinal axon arbors sprouting into denervated contralateral spinal cord.

Previous studies have reported considerable plasticity in the rodent corticospinal pathway in response to injury. This includes sprouting of intact axons from the normal pathway into the contralateral spinal cord denervated by an early corticospinal lesion. We carried out the present study to obtain detailed information about the time course, origin, and degree of specificity of corticospinal axons sprouting in response to denervation. Hamsters (Mesocricetus auratus) ranging in age from 5 to 23 days received unilateral lesions of the left medullary pyramidal tract. Two weeks after the lesion, small regions of the right sensorimotor cortex opposite the lesion were injected with the plant lectin Phaseolus vulgaris leucoagglutinin (PHA-L). After a further 2 week survival period, immunohistochemistry was carried out on frozen sections of the fixed brains and spinal cords. Detailed morphological analysis of PHA-L labeled corticospinal axons revealed that sprouting from the intact corticospinal pathway into the contralateral denervated spinal cord occurred only at local spinal levels and not at the pyramidal decussation. Arbors sprouting into the denervated cord frequently arose from corticospinal axons that branched into the normal side of the cord as well. Sprouting was maximal after early lesions (5 days) and declined with lesions at later ages up to 19 days. Sprouting corticospinal axons arborized with the same degree of functional and topographic specificity as previously reported for normal corticospinal arbors (Kuang and Kalil: J. Comp. Neurol. 292:585-598, '90), such that axons arising from somatosensory cortex projected only to the dorsal horn, those from motor cortex innervated only the ventral horn, and normal forelimb and hindlimb topography was preserved. Sprouting fibers also had normal branching patterns. Parallel studies of developing corticospinal arbors showed that sprouting could not be attributed to maintenance or expansion of early bilateral connections. These results suggest that local signals, most likely similar to those governing normal corticospinal development, elicit corticospinal sprouting and determine specificity of axon arbors.

Aging↗
PubMed1991

Localized denervation demonstrates the innervation pattern of olfactory bulb glomeruli and second order cells.

Sensory systems rely upon spatially organized projections for the faithful transfer of receptor activity into the central nervous system. While the mammalian olfactory nerve shows a regional topographical organization, data on the sources of variation within this projection are scarce. We evaluated the degree of precision of olfactory bulb glomerular innervation from the olfactory nerve layer (ONL) by making small cuts across the trajectory of the olfactory nerve fibers and assessing the resulting denervation by wheat germ agglutinin-horseradish peroxidase (WGA-HRP) labeling of primary nerve fibers. In control animals (no ONL cut), the ONL and glomerular layer showed intense labeling around the entire circumference of the bulb. Transneuronal labeling of the mitral cell layer and the external plexiform layer was also observed in animals surviving at least 2 days, which allowed us to study the nerve fiber innervation of second order cells as well. ONL cuts on the lateral face of the bulb produced a stripe of denervation, as evidenced by the absence of primary and transneuronal label in a well-defined region. Fascicles of fibers within the ONL were never observed to enter the denervated region from more than one or two glomerular widths away, indicating a relatively tight limit of variation in the spatial termination of olfactory nerve fibers on the lateral bulb surface. This limit of variation does not hold around the circumference of the bulb since similar ONL cuts on the dorsal surface failed to produce a distinct stripe of denervation. Field potential measurements from the ONL after similar cuts supported the anatomic findings. These results show that primary olfactory axons and their terminals lie in parallel along the lateral face of the olfactory bulb. These spatial relationships of olfactory input to the bulb are maintained in the second order connections. This organization allows one to study the spatial aspects of interneuronally mediated synaptic mechanisms involved in olfactory coding.

Animals↗
PubMed2001

Role of nitric oxide and nitric oxide synthases in experimental models of denervation and reinnervation.

Nitric oxide (NO) is a short-living free molecule synthesized by three different isoforms of nitric oxide synthases (NOS)-neuronal NOS, endothelial NOS, and inducible NOS-associated with neuromuscular transmission, muscle contractility, mitochondrial respiration, and carbohydrate metabolism in skeletal muscle. Neuronal NOS is constitutively expressed at the muscle fiber sarcolemma linked to the dystrophin-glycoprotein complex and concentrated at the neuromuscular endplate. There is increasing evidence that altered expression of neuronal NOS plays a role in muscle fiber damage in neuromuscular diseases such as dystrophinopathies and denervating disorders. Although there have been some previous conflicting results on the neuronal NOS expression pattern in denervated muscle fibers, it is now well established that denervation is associated with a down-regulation and disappearance of sarcolemmal neuronal NOS at synaptic/extrasynaptic or both sites. As NO has been shown to induce collapse and growth arrest on neuronal growth cones, down-regulation of sarcolemmal neuronal NOS may contribute to axonal regeneration and attraction to muscle fibers aiming at the formation of new motor endplates providing reinnervation and reconstitution of NOS expression. As NO serves as a retrograde messenger, it may trigger structural downstream events responsible for neuromuscular synaptogenesis and preventing polyneural innervation. Nevertheless, decreased NO production in denervation reduces the cytoprotective scavenger function of NO for superoxide anions promoting oxidative stress that is likely to be involved in muscle fiber damage and death. However, the multifaced role of NOS and NO under physiological and pathological conditions remains poorly understood on the basis of the current knowledge.

Animals↗
PubMed1989

Ability of various injuries to promote resorption of denervated, nerve independent regenerates of adult newts.

Young blastemas of the newt resorb if the limb is denervated, and are thus called "nerve dependent". Late bud and later stage regenerates are termed "nerve independent" because, while denervation inhibits their growth, they proceed through differentiation to form a normally patterned regenerate. Schotté and Liversage ('59) found that reamputation of a denervated nerve independent regenerate causes it to resorb. The present study asked whether injuries of varying severity are equally effective at promoting resorption. Newt forelimbs were amputated through the mid-radius/ulna. At nerve independent stages, the regenerates were denervated and injured in one of a variety of ways, then monitored for signs of resorption. Reamputation of the tip or incisions which created large gaps in the wound epidermis promoted resorption in 77-90% of the cases. Histology showed that the tissue removed by tip reamputation was a small proportion of the entire regenerate, suggesting that blastema resorption is not determined simply by the number of cells directly affected by the injury. Pin prick injuries, which created small disruptions of the wound epidermis, never caused resorption. Devascularization, caused by severing the brachial artery, promoted resorption in 17% of cases. These results are not consistent with the hypothesis that avascularity is a major causative factor in nerve dependence.

Animals↗
PubMed1992

Ganglia implantation as a means of supplying neurotrophic stimulation to the newt regeneration blastema: cell-cycle effects in innervated and denervated limbs.

Regulation of blastema cell proliferation during amphibian limb regeneration is poorly understood. One unexplained phenomenon is the relatively low level of active cell cycling in the adult newt blastema compared to that of larval axolotls. In the present study, we used ganglia implantation as a means of "superinnervating" normally innervated adult newt blastemas to test whether blastema cell subpopulations are responsive to nerve augmentation. The effectiveness of implanted ganglia to provide neurotrophic stimulation was demonstrated in denervated blastemas. Blastemas implanted with 2 dorsal root ganglia and simultaneously denervated 14 days after amputation exhibited control levels of cell cycle activity 6 days later, as measured by 3H-thymidine pulse labeling. Denervated blastemas that were sham-operated or implanted with pituitary glands exhibited cell-cycle declines similar to those of denervated blastemas without implanted ganglia. Thus, 2 implanted ganglia provide neurotrophic stimulation equivalent to that of the normal nerve supply. Dorsal root ganglia implanted into normally innervated blastemas, which should effectively double neurotrophic activity to the blastema, had no effect on cell-cycle activity, innervated blastemas implanted with ganglia for 6 days exhibited pulse labeling indices similar to those of normally innervated blastemas. These data indicate that neurotrophic stimulation is not normally limiting in innervated limbs, and that some other factor, whether extrinsic or intrinsic to blastema cells, accounts for the relatively low level of active cell cycling in the adult newt blastema.

Animals↗
PubMed1992

Combined effect of acute denervation and ischemia on the microcirculation of skeletal muscle.

Using direct in vivo videomicroscopy and a fluorescein dye technique, reperfusion injury after 3 h of ischemia was studied in the acutely denervated cremaster muscle of the rat. Compared with normally innervated controls, ischemia-induced reperfusion injury was more severe in the denervated group and included a delay of blood flow recovery, vortex formation, edema, hemorrhage, and vessel spasm. Vessel size was reduced at the arteriole and small artery level, and there was a decrease of reactive hyperemia. The injury mechanism may be related to a loss of active vasomotion and vascular response to vasoactive substances after denervation. The results suggest that shortening the ischemia time of denervated tissues may reduce ischemia-induced reperfusion injury. Similarly, given the same ischemia time, improved tissue reperfusion may be expected if the nerve supply is maintained.

Animals↗
PubMed1993

Effect of denervation on endothelium-derived relaxing factor-dependent relaxation in the rat cremaster muscle.

Endothelium-derived relaxation mediated primarily by endothelium-derived relaxing factor/nitric oxide (EDRF/NO) is essential in the maintenance of vascular tone. However, little is known about the effects of denervation on EDRF-mediated relaxation in the microcirculation after reimplantation. Using intravital videomicroscopy in the rat cremaster model, this study assessed the effect of acute and chronic denervation of the muscle, produced by severing the genitofemoral nerve, on EDRF-mediated vasorelaxation. The results demonstrated that acetylcholine-induced EDRF relaxation (10(-6)M) significantly relieved norepinephrine-induced vasoconstriction in small arteries (40-80 microns diameter) in both the acute and chronic denervated muscles. There was no significant difference in the relaxant response between the denervated or innervated controls in each group or between the acute or chronic groups. This relaxation was prevented by methylene blue (10(-4) M). These findings suggest that EDRF-mediated relaxation in the microcirculation is not dependent on tissue innervation. Thus the use of potent endothelial dependent agonists may be of use in cases of vasospasm postreimplantation.

Acetylcholine↗
PubMedDate not supplied

Experimental myotonia induced in denervated muscles by 2,4-D.

Rats were denervated in one hind limb and injected with 2,4-dichlorophenoxyacetic acid (2,4-D). Isotonic tetanic contractions of the muscles treated with 2,4-D after more than 10 days of denervation revealed prolonged relaxation times similar to those of the intact side and characteristic of clinical myotonia. No myotonic discharges were observed in the muscles denervated for more than 10 days and treated with 2,4-D. The increase in threshold for action potential generation secondary to denervation is suggested as the factor limiting the initiation of the repetitive discharges.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1989

Org.2766 stimulates collateral sprouting in the soleus muscle of the rat following partial denervation.

The influence of melanocortins on the process of collateral sprouting has been investigated in rat soleus muscle. The soleus muscle was partially denervated by transecting and ligating the L5 mixed nerve. Collateral sprouting was assessed by means of isometric twitch tension measurements of soleus motor units that remained following L5 transection. The smaller the number of remaining soleus motor units, the larger the extent of collateral sprouting. Seven days following partial denervation, the index of sprouting (ratio between twitch tension of motor units in partly denervated muscles and in normal muscles) was significantly increased by treatment with the ACTH4-9 analog Org.2766 (1 microgram/48 hours). This increase appeared to be present also 28 days following partial denervation. The electrophysiological results were confirmed by histological investigations. The results provide evidence that Org.2766 increases the motor neuron collateral sprouting capacity of peripheral nerve. Org.2766 did not induce muscle fiber hypertrophy.

Adrenocorticotropic Hormone↗
PubMed1976

Effects of denervation and colchicine treatment on the chloride conductance of rat skeletal muscle fibers.

Membrane potentials, cable parameters, and component resting conductances were measured in extensor digitorum longus (EDL) muscle fibers from adult rats in vitro at 24 degrees C, after 15 to 18 days of denervation by nerve section, and at seven to ten days following epineural injection of 100 to 450 mug of colchicine in the peroneal nerve. The denervated muscles were paralyzed throughout the experimental period, whereas the colchicine-treated preparations showed no clinical paralysis except for the first day or two. The EDL from the untreated side served as a control. Both the denervated and colchicine-treated fibers were depolarized, showed signs of fibrillation, had tetrodotoxin-resistant potentials, and membrane resistance was increased two- to sevenfold. In the denervated fibers, mean chloride conductance GC1 dropped from a control value of 3196 to 596 mumhos/cm2 while mean potassium conductance GK showed a tendency to rise from 260 to 332 muhos/cm2. Colchicine-treated fibers while showing a similar fall in mean GC1 from 2993 to 1066 mumhos/cm2, also showed a significant fall in mean GK from 213 to 116 mumhos/cm2. It was concluded that factors transported by the microtubular system are important for the maintenance of the high resting GC1 of mammalian skeletal muscle fibers.

Action Potentials↗
PubMed1995

Spontaneous bursting and long-lived local correlation in normal and denervated tectum of goldfish.

The formation of fine retinotopic order by growing optic fibers in the goldfish is thought to be mediated by the correlated firing of optic fibers from neighboring retinal ganglion cells. Although the activity of the tectal cells must also be important for this activity-dependent refinement, few studies have analyzed the pattern and local correlation of the intrinsic activity of tectal neurons and the effect of denervation on this activity. To address this issue, spontaneous (nonoptic driven) activity was analyzed and cross-correlograms were computed between individual tectal neurons using single and double electrode extracellular recordings. Recordings were made in normally innervated tectum in which the contribution of optic activity was eliminated by short-term intraocular blockade with tetrodotoxin and in denervated tecta in which the optic nerve had been severed several weeks prior. Several observations were relevant to activity-dependent refinement: First, coupling between neighboring tectal cells is weak. Second, the time duration for local correlation is relatively long, as long as 200 ms. Third, tectal neurons exhibit spontaneous bursting. Fourth, denervation increased the level of spontaneous activity in the tectum. The increased spontaneous activity and bursting following denervation implies that tectal neurons are more excitable when optic fibers are beginning to reinnervate the tectum. This could make it possible for optic fibers to drive tectal neurons at a time when their input to individual neurons is severely weakened by a lack of spatial convergence. The weak coupling between tectal cells and the consequent long-time constant for correlated activity implies a constraint on the duration of correlated retinal activity that is used for activity-dependent refinement. Since optic fibers likely need to detect the postsynaptic activity of a local group of tectal neurons, rather than that of a single neuron, the long tectal time constant means that retinal activity need not be correlated with precision much better than 200 ms because the postsynaptic circuitry cannot generate shorter correlations.

Animals↗