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PubMed1975

Synthesis of acetylcholine receptor by denervated rat diaphragm muscle.

Acetylcholine receptor was purified by affinity chromatography from denervated rat hemidiaphragms that had been incubated in organ culture for 24 hr in medium containing [35-S] methionine. Radioactive acetylcholine receptor was identified in purified preparations by zone sedimentation in a sucrose gradient, by isoelectric focusing, and by precipitation with an antiserum to the acetylcholine receptor from electric eel. When innervated and denervated hemidiaphragms were incubated with [35-S] methionine in organ culture, and the acetylcholine receptors from each were purified separately, only the preparation from denervated muscles contained radioactive receptor as determined by zone sedimentation. We conclude that newly synthesized receptor is accumulated as a result of muscle denervation.

Acetylcholine↗
PubMed1996

Characterization and molecular reaction scheme of a chloride channel expressed after axotomy in crayfish.

The nerve to the deep extensor abdominal muscle (DEAM) in crayfish species Astacus astacus, containing four excitatory and one inhibitory motor axons, was cut in the third segment on one side of the animal. The distal axon stump was not subject to phagocytosis but was present for months after the axotomy. The two lateral bundles of the DEAM were prepared 4-6 weeks after the axotomy. The gamma-aminobutyric-acid-(GABA-) activated chloride channel of these bundles was characterized by applying pulses of GABA to outside-out patches of the muscle membrane and measuring the responses. Based on the dose/response relationship of the peak current and of the rise time as well as on single-channel kinetics, a detailed molecular scheme for the reaction of the channel with GABA was derived. This scheme contains four binding steps of the agonist to the receptor and two open states. Simulations of the dose/response relationships with this model resulted in a set of rate constants which generate proper fits. In comparison to the channels present in innervated muscles, the channels of denervated muscles have a higher affinity for GABA, a lower single-channel conductance, four versus five binding steps, and non-cooperative binding. The first three of these adaptations of denervated muscles correspond to similar changes in denervated vertebrate muscles.

Abdominal Muscles↗
PubMed1982

The distribution of nodal sprouts in a paralysed or partly denervated mouse muscle.

The right gluteus maximus muscles of young adult mice were paralysed with botulinum toxin for up to 21 days or partly denervated by spinal root section for up to 63 days; the intramuscular and extramuscular nerves were then examined in the electron microscope in thin sections of tissue fixed conventionally or stained with zinc iodide-osmium tetroxide. Contralateral muscles were also examined as controls. The distribution of nodal sprouts in the nerves of the paralysed or partly denervated muscles was determined by calculating the mean ratios of unmyelinated to myelinated axons in nerve profiles containing different numbers of myelinated axons (intact or degenerating) and comparing these with control ratios. In paralysed muscles there was a significantly higher proportion of nerve profiles containing one or two unmyelinated axons alongside a single myelinated axon. Nerve profiles containing two or more myelinated axons did not show any increase in the proportion of unmyelinated axons. Thus, there is probably nodal sprouting in paralysed muscles which is restricted to the most distal nodes of the intramuscular nerves. In muscles partly denervated for 8 days there were significant increases in the proportion of unmyelinated axons in nerve profiles which had contained up to 5-10 myelinated axons. After 21 days of partial denervation, similar increases may have occurred in the larger intramuscular nerve profiles and after 63 days there were large increases in the proportion of unmyelinated axons in the main intramuscular nerve branches and in the extramuscular nerve. Nodal sprouting in response to partial denervation is therefore localised initially to the smaller, more distal nerve branches; at later times, some sprouts probably grow slowly in a disto-proximal direction along denervated Schwann cell pathways. The existence of nodal sprouts in paralysed muscles and their restricted distribution in paralysed and partly denervated muscles suggest that the nodal sprouting stimulus is produced by the muscle and acts only at distal nodes.

Animals↗
PubMed1975

Neurogenic control of muscle ribosomal protein synthesis.

In vitro protein synthesis of ribosomes extracted from leg muscles of 20 Sprague-Dawley rats denervated 3 and 14 days (high sciatic transections) and 10 control rats was studied. The concentration/mg protein of total ribosomes extracted from the 14-day denervated muscle showed a significant increase. Distribution of muscle polyribosomes on sucrose density gradients was normal in all cases. Noncollagen protein synthesis of the heavy polyribosomes from both early and late denervated muscles showed a significant decrease. SDS polyacrylamide gels suggested that this decrease affected the synthesis of heavy chains of myosin, while the light chains of myosin, actin and tropomyosin had normal structure and amounts. Collagen synthesis of heavy polyribosomes showed slight to moderate increase in only 50 per cent of the cases. Supplementation of ribosomes extracted from denervated muscles with normal muscle soluble enzymes increased their noncollagen synthesis by 66 per cent. This suggests that the neurogenic control of ribosomal protein synthesis is accomplished by hormonal trophic substances contained in the muscle soluble enzymes.

Animals↗
PubMed1983

Rapid decline in acetylcholine release and content of rat extensor digitorum longus muscle after denervation.

The amount of acetylcholine (ACh) and choline (Ch) in normal and denervated rat extensor digitorum longus (EDL) muscles, as well as that released spontaneously from these muscles, was determined by an extremely sensitive gas chromatographic-mass spectrometric assay method. We found decreases in ACh content and spontaneous, resting ACh release as early as 8 h after denervation. The ACh content decreased to a plateau of 30% of control by 11 h; ACh release attained a plateau of 50% of control several hours later. These results showed that in denervated EDL muscles ACh content and spontaneous release (measured biochemically) decreased before nerve-evoked and spontaneous quantal release (measured physiologically) ceased at most synapses. The rapid reduction in ACh, or possibly in other substances that may be released with ACh, may be an important factor in initiating postsynaptic degenerative changes after nerve transection. Choline content and choline resting release increased significantly at both 1 and 3 days after nerve transection. These increases may be related to onset of postsynaptic neuromuscular degenerative changes.

Acetylcholine↗
PubMed1999

Reduced glycogen phosphorylase activity in denervated hindlimb muscles of rat is related to muscle atrophy and fibre type.

Changes in the activity of muscle glycogen synthase or phosphorylase (GP) may be responsible for the deregulation of glycogen synthesis and storage which occurs in diabetes mellitus. To clarify the relationship between muscle atrophy, fibre type, insulin-stimulated glucose uptake and GP activity during insulin resistance, we used sciatic nerve severance to induce insulin resistance in rat hindlimb muscles and compared the above parameters in muscles with a range of fibre types. Changes were analysed by comparison with the contralateral hindlimb, which bears more weight due to denervation of the opposing limb, as well as the sham-operated and contralateral limb of a separate rat. Denervation caused a decrease in insulin-stimulated glucose uptake by 1 day after denervation and a decline of GP activity after 7 days in all muscles investigated. GP activity decreased by 73% in soleus, 36% in red gastrocnemius, 35% in tibialis and 13% in white gastrocnemius, which was related to the degree of muscle atrophy and inversely related to the overall GP activity in non-denervated muscles. GP activity in muscles of the contralateral limb from the denervated rat did not differ from either hindlimb of the sham-operated rat. We conclude that the fibre-type related reduction in insulin-stimulated glucose uptake of denervated muscle determines the change in its metabolism and it is this metabolic change which determines the mechanism, rate and degree of muscle atrophy, which is directly related to the decline in GP activity.

Animals↗
PubMed1978

Tetrodotoxin blocks mechanical response in mammalian muscle in the presence of tetrodotoxin-resistant action potentials.

The effect of tetrodotoxin (TTX) (10(-5)-10(-6)M) on the mechanical activity and on the action potential of innervated and denervated muscle of the rat was studied. The twitch tension was reduced to 10 % of the control values within 20 min of TTX 10(-6) introduction. This effect was reversible. The mean twitch tension in the presence of 10(-6)M TTX expressed as a percentage of control was 9.3 +/- 2.4 (SEM) for innervated muscle and 10.9 +/- 2.5 for denervated muscle. The dose-effect twitch relation for denervated muscles was not significantly different from that observed in control innervated muscles in the 10(-3)-10(-6) TTX range. Action potentials of innervated muscles could not be elicited in 10(-6)M TTX. In the presence of this (TTX) fibers of chronically denervated muscles consistently responded to stimulation with action potentials which were slower and smaller but still with overshoot, contrasting with fibrillation potentials that had been described to be blocked by TTX.

Action Potentials↗
PubMed2002

Effect of a nitric oxide donor on microcirculation of acutely denervated skeletal muscle during reperfusion.

The authors have shown that exogenous nitric oxide (NO) protects innervated skeletal muscle against reperfusion injury. This study further evaluated the effects of exogenous NO donor on denervated skeletal muscle. Forty-eight denervated rat cremaster muscles underwent 3 hr of ischemia, followed by 90 min of reperfusion, and received systemic infusion of 100 nmol/min s-nitroso-n-acetylcysteine (SNAC) or an equal amount of phosphate-buffered saline (PBS). Results showed that the average diameter in 10 to 20 microm arterioles was between 107 percent and 123 percent of baseline in the SNAC group, and between 55 percent and 84 percent in the PBS group during 90 min of reperfusion. These values in 21 to 40 microm and 41 to 70 microm arteries were between 100 percent and 110 percent in the SNAC group, and between 70 percent and 90 percent in the PBS group from 20 to 90 min of reperfusion. Compared to the PBS group, the SNAC group had a statistically significantly greater vessel diameter in both 10 to 20 microm (p<0.001) and 21 to 40 microm arterioles (p<0.01) during 90 min of reperfusion, and in 41 to 70 microm arteries (p<0.02) from 20 to 90 min of reperfusion. The overall blood flow of the muscle in the SNAC group increased from 37 percent of baseline at 10 min to 108 percent at 40 min of reperfusion, and remained above baseline thereafter. In contrast, this value in the PBS group was only between 27 percent and 68 percent of baseline during 90 min of reperfusion. The blood flow was statistically significantly (p<0.03) greater in the SNAC group than in the PBS group from 40 to 90 min of reperfusion. Among the conclusions were: (1) NO donor SNAC improves the microcirculation of denervated skeletal muscle during early reperfusion; and (2) this protection against reperfusion injury is independent of innervation in skeletal muscle.

Acetylcysteine↗
PubMed1984

Myoglobin in rat hind limb muscles after denervation and during reinnervation.

Radioimmunoassay of myoglobin (Mb) was performed in rat hind limb muscles after surgical denervation and during reinnervation following cryolesion of the sciatic nerve. Muscles of the contralateral leg served as controls. After resection of the sciatic nerve, decreased Mb concentrations were noted on the fourth day in the tibialis anterior, peroneus longus, and extensor digitorum longus (EDL) muscles. Thereafter, the levels increased up to the last observation on day 32. The increases in Mb levels in the tibialis anterior and EDL muscles were considerably more pronounced (305% and 324%, respectively) than in the peroneus longus and soleus muscles (148% and 137%, respectively). After cryolesion of the sciatic nerve, the Mb concentrations in the tibialis anterior, peroneus longus, and EDL muscles increased, reaching maximal values on days 16-21. The levels then decreased and normal values were observed 2 months postoperatively. The normalization of the Mb levels during reinnervation corresponded fairly well in time with the clinical recovery and neurophysiological findings observed in a previous study.

Animals↗
PubMed1979

Some ultrastructural observations on the denervated skeletal muscle of frog.

The frog skeletal muscle resists atrophy for a long time after denervation. If, however, the entry of the nerve is prevented for more than 3.5 months, small muscle portions, sometimes containing nucleus, are sequestered from the parent muscle fibre. The basal lamina does not dissociate from these detached muscle portions.

Animals↗
PubMed1995

Reinnervation of a denervated slow muscle triggers high extrajunctional expression of the asymmetric molecular forms of acetylcholinesterase.

Expression of acetylcholine receptor and of the asymmetric molecular forms of acetylcholinesterase (AChE) in the extrajunctional regions of rat muscles is suppressed during early postnatal development. In mature muscles, the extrajunctional synthesis of acetylcholine receptor, but not of the asymmetric molecular forms of AChE, becomes reactivated after denervation. The hypothesis that a denervated muscle needs reinnervation in order to revert transiently to an immature state characterized by high extrajunctional production of the asymmetric AChE forms, was examined in rat muscles recovering after nerve crush. Molecular forms of AChE were analysed by velocity sedimentation. Activity of the asymmetric A12 AChE form in the extrajunctional regions of the slow soleus (SOL) muscle increased during the first week after reinnervation to about 9 times its control level, remained high for about one week, and declined towards normal thereafter. If the nerve was crushed close to the muscle and reinnervation occurred very rapidly, the extrajunctional increase of the A12 AChE form still occurred but was less pronounced than after late reinnervation. In contrast, a transient paralysis of the SOL muscle due to acetylcholine receptor blockade by alpha-bungarotoxin, followed by spontaneous recovery of muscle activity after 3-5 days, did not revert AChE regulation into an immature state. Disuse of the SOL muscle caused by leg immobilization, which is known to change the tonic pattern of neural stimulation of the SOL muscle into a phasic one, did not prevent the reversion of AChE regulation during reinnervation. This indicates that neural stimulation pattern is not crucial for this reversion.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗
PubMed1976

Altered patterns of innervation in frog muscle after denervation.

The pattern of reinnervation of muscle fibres after a nerve crush was examined in the cutaneous pectoris muscle of the frog by microscopy and electrophysiology. Normally, about 16% of the muscle fibres are innervated by more than one motor neuron. Two months after reinnervation, about 50% of the fibres are polyneuronally innervated and this high incidence persists for at least seven months. The total number of neurons reinnervating the muscle, as well as the number of muscle fibres comprising the muscle, are normal. However, nerve fibres sprout branches at the site of the crush, and, therefore, the number of axons entering the muscle is greater than normal. Regenerating axons contact muscle fibres precisely at the original synaptic sites and the terminal branches from different axons that end on the same muscle fibre often run side by side occupying stretches or original postsynaptic membrane normally covered by one terminal. Our findings indicate that the amount of synaptic contact during regeneration is limited by the amount of original postsynaptic membrane and that any number of axons that reach vacant portions of original postsynaptic membrane can make synaptic contact with it. Surprisingly, control cutaneous pectoris muscles, situated contralaterally to those that were denervated, also exhibited an abnormal pattern of innervation. Although neither nerve nor muscle was disturbed by the operation, there was a higher incidence of polyneuronal innervation (27% vs 16%) than in muscles of normal animals.

Animals↗
PubMed1999

Long-term denervation modulates differentially the accumulation of myogenin and MRF4 mRNA in adult Xenopus muscle.

In adult Xenopus laevis, we analyzed, using reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization, the influence of long-term muscle denervation on the accumulation of MRF4 and myogenin transcripts. The brachial muscle was denervated by cutting the brachial nerve and was examined after 4 months. MRF4 mRNA levels decreased about two-fold in denervated muscle as compared with contralateral muscle. Myogenin mRNA levels, by contrast, were induced about five-fold by denervation. This report shows that muscle denervation persistently reduces the levels of MRF4 transcripts suggesting that MRF4 expression may be induced by innervation and hence may be involved in mediating transcriptional responses to innervation. The up-regulation of myogenin by denervation suggests that myogenin expression may compensate for the down-regulation of MRF4 gene.

Animals↗