Ultra-Low Frequency Transcutaneous Electrical Nerve Stimulation on Pain Modulation in a Rat Model with Myogenous Temporomandibular Dysfunction.

Masticatory myofascial pain (MMP) is one of the most common causes of chronic orofacial pain in patients with temporomandibular disorders. To explore the antinociceptive effects of ultra-low frequency transcutaneous electrical nerve stimulation (ULF-TENS) on alterations of pain-related biochemicals, electrophysiology and jaw-opening movement in an animal model with MMP, a total of 40 rats were randomly and equally assigned to four groups; i.e., animals with MMP receiving either ULF-TENS or sham treatment, as well as those with sham-MMP receiving either ULF-TENS or sham treatment. MMP was induced by electrically stimulated repetitive tetanic contraction of masticatory muscle for 14 days. ULF-TENS was then performed at myofascial trigger points of masticatory muscles for seven days. Measurable outcomes included maximum jaw-opening distance, prevalence of endplate noise (EPN), and immunohistochemistry for substance P (SP) and µ-opiate receptors (MOR) in parabrachial nucleus and c-Fos in rostral ventromedial medulla. There were significant improvements in maximum jaw-opening distance and EPN prevalence after ULF-TENS in animals with MMP. ULF-TENS also significantly reduced SP overexpression, increased MOR expression in parabrachial nucleus, and increased c-Fos expression in rostral ventromedial medulla. ULF-TENS may represent a novel and applicable therapeutic approach for improvement of orofacial pain induced by MMP.

l-Theanine and NEP1-40 promote nerve regeneration and functional recovery after brachial plexus root avulsion.

Brachial plexus root avulsion causes severe sequelae Treatments and prognosis face many problems, including inflammatory reaction, oxidative damage, and myelin related inhibitory effect. l-Theanine has anti-inflammatory, anti-oxidative, and neuroprotective effects. NEP1-40 competitively inhibits Nogo-66 receptor (NgR1) promotes axonal regeneration. Forty-eight Sprague-Dawley rats were randomly assigned into four groups to establish an animal model of brachial plexus root avulsion. Inflammation and oxidative damage were evaluated by spectrophotometry and motor function of the upper limbs was assessed via Terzis grooming test after modeling. Immunofluorescence and hematoxylin and eosin staining were utilized to determine the content of reactive oxygen species, activation of microglial cells, neuroprotection, and nerve regeneration. Compared with the control group, the L-Theanine + NEP1-40 group had significantly decreased myeloperoxidase, malondialdehyde, interleukin-6, reactive oxygen species, and microglial cells, significantly increased score on the Terzis grooming test, increased motor neuron content, and thickened muscle fibers, increased area, and appearance of large and clear motor endplate structures. The results of this study suggest that l-Theanine combined with NEP1-40significantly promoted nerve regeneration after brachial plexus root avulsion, and may be a potential treatment for promoting nerve regeneration. Possible mechanisms underlying these results are alleviation of oxidative damage and inflammatory responses in the injured area and antagonism of myelin inhibition.

TGF-ß/SMAD signaling inhibits intermittent cyclic mechanical tension-induced degeneration of endplate chondrocytes by regulating the miR-455-5p/RUNX2 axis.

A mechanical stimulation plays a pivotal role in maintaining normal cartilage function. Our objective was to reveal the mechanism of action of the tension-sensitive molecule miR-455-5p in the degeneration of endplate chondrocytes and to identify whether the transforming growth factor beta (TGF-ß)/SMAD signaling pathway has a regulatory effect on it. The expression profiles of members of the TGF-ß/SMAD pathway, miR-455-5p, and RUNX2 were determined by microRNA microarray analysis, reverse transcription quantitative polymerase chain reaction, luciferase reporter assay, and Western blot analysis. Intermittent cyclic mechanical tension (ICMT) induced the degeneration of endplate chondrocytes without affecting their viability. The tension-sensitive molecule miR-455-5p specifically bound to RUNX2, a gene involved in the degeneration of endplate chondrocytes. Activation of the TGF-ß/SMAD signaling pathway upregulated miR-455-5p expression and thus inhibited RUNX2 levels. Therefore, the TGF-ß/SMAD signaling pathway inhibits the ICMT-induced degeneration of endplate chondrocytes by regulating the miR-455-5p/RUNX2 axis.

Adenosine A2A receptors activation facilitates neuromuscular transmission in the pre-symptomatic phase of the SOD1(G93A) ALS mice, but not in the symptomatic phase.

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease leading to motor neuron dysfunction resulting in impairment of neuromuscular transmission. A2A adenosine receptors have already been considered as a potential therapeutical target for ALS but their neuromodulatory role at the neuromuscular junction in ALS remains to be clarified. In the present work, we evaluated the effects of A2A receptors on neuromuscular transmission of an animal model of ALS: SOD1(G93A) mice either in the pre-symptomatic (4-6 weeks old) or in the symptomatic (12-14 weeks old) stage. Electrophysiological experiments were performed obtaining intracellular recordings in Mg2+ paralyzed phrenic nerve-hemidiaphragm preparations. Endplate potentials (EPPs), quantal content (q. c.) of EPPs, miniature endplate potentials (MEPPs) and giant miniature endplate potential (GMEPPs) were recorded. In the pre-symptomatic phase of the disease (4-6 weeks old mice), the selective A2A receptor agonist, CGS 21680, significantly enhanced (p<0.05 Unpaired t-test) the mean amplitude and q.c. of EPPs, and the frequency of MEPPs and GMEPPs at SOD1(G93A) neuromuscular junctions, the effect being of higher magnitude (p<0.05, Unpaired t-test) than age-matched control littermates. On the contrary, in symptomatic mice (12-14 weeks old), CGS 21680 was devoid of effect on both the amplitude and q.c. of EPPs and the frequency of MEPPs and GMEPPs (p<0.05 Paired t-test). The results herein reported clearly document that at the neuromuscular junction of SOD1(G93A) mice there is an exacerbation of A2A receptor-mediated excitatory effects at the pre-symptomatic phase, whereas in the symptomatic phase A2A receptor activation is absent. The results thus suggest that A2A receptors function changes with ALS progression.

HnRNP L and hnRNP LL antagonistically modulate PTB-mediated splicing suppression of CHRNA1 pre-mRNA.

CHRNA1 gene, encoding the muscle nicotinic acetylcholine receptor alpha subunit, harbors an inframe exon P3A. Inclusion of exon P3A disables assembly of the acetylcholine receptor subunits. A single nucleotide mutation in exon P3A identified in congenital myasthenic syndrome causes exclusive inclusion of exon P3A. The mutation gains a de novo binding affinity for a splicing enhancing RNA-binding protein, hnRNP LL, and displaces binding of a splicing suppressing RNA-binding protein, hnRNP L. The hnRNP L binds to another splicing repressor PTB through the proline-rich region and promotes PTB binding to the polypyrimidine tract upstream of exon P3A, whereas hnRNP LL lacking the proline-rich region cannot bind to PTB. Interaction of hnRNP L with PTB inhibits association of U2AF(65) and U1 snRNP with the upstream and downstream of P3A, respectively, which causes a defect in exon P3A definition. HnRNP L and hnRNP LL thus antagonistically modulate PTB-mediated splicing suppression of exon P3A.

Muscle-specific kinase myasthenia gravis IgG4 autoantibodies cause severe neuromuscular junction dysfunction in mice.

Myasthenia gravis is a paralytic disorder with autoantibodies against acetylcholine receptors at the neuromuscular junction. A proportion of patients instead has antibodies against muscle-specific kinase, a protein essential for acetylcholine receptor clustering. These are generally of the immunoglobulin-G4 subclass and correlate with disease severity, suggesting specific myasthenogenic activity. However, immunoglobulin-G4 subclass antibodies are generally considered to be 'benign' and direct proof for their pathogenicity in muscle-specific kinase myasthenia gravis (or other immunoglobulin-G4-associated disorders) is lacking. Furthermore, the exact electrophysiological synaptic defects caused at neuromuscular junctions by human anti-muscle-specific kinase autoantibodies are hitherto unknown. We show that purified immunoglobulin-G4, but not immunoglobulin-G1-3, from patients with muscle-specific kinase myasthenia gravis binds to mouse neuromuscular junctions in vitro, and that injection into immunodeficient mice causes paralysis. Injected immunoglobulin-G4 caused reduced density and fragmented area of neuromuscular junction acetylcholine receptors. Detailed electrophysiological synaptic analyses revealed severe reduction of postsynaptic acetylcholine sensitivity, and exaggerated depression of presynaptic acetylcholine release during high-rate activity, together causing the (fatigable) muscle weakness. Intriguingly, compensatory transmitter release upregulation, which is the normal homeostatic response in acetylcholine receptor myasthenia gravis, was absent. This conveys extra vulnerability to neurotransmission at muscle-specific kinase myasthenia gravis neuromuscular junctions. Thus, we demonstrate that patient anti-muscle-specific kinase immunoglobulin-G4 is myasthenogenic, independent of additional immune system components, and have elucidated the underlying electrophysiological neuromuscular junction abnormalities.

Accelerating axonal growth promotes motor recovery after peripheral nerve injury in mice.

Although peripheral nerves can regenerate after injury, proximal nerve injury in humans results in minimal restoration of motor function. One possible explanation for this is that injury-induced axonal growth is too slow. Heat shock protein 27 (Hsp27) is a regeneration-associated protein that accelerates axonal growth in vitro. Here, we have shown that it can also do this in mice after peripheral nerve injury. While rapid motor and sensory recovery occurred in mice after a sciatic nerve crush injury, there was little return of motor function after sciatic nerve transection, because of the delay in motor axons reaching their target. This was not due to a failure of axonal growth, because injured motor axons eventually fully re-extended into muscles and sensory function returned; rather, it resulted from a lack of motor end plate reinnervation. Tg mice expressing high levels of Hsp27 demonstrated enhanced restoration of motor function after nerve transection/resuture by enabling motor synapse reinnervation, but only within 5 weeks of injury. In humans with peripheral nerve injuries, shorter wait times to decompression surgery led to improved functional recovery, and, while a return of sensation occurred in all patients, motor recovery was limited. Thus, absence of motor recovery after nerve damage may result from a failure of synapse reformation after prolonged denervation rather than a failure of axonal growth.

Factors contributing to failure of neuromuscular transmission in myasthenia gravis and the special case of the extraocular muscles.

Acetylcholine receptors (AchRs) and Na(+) channels (NaChs) are concentrated on neuromuscular junction (NMJ) postsynaptic folds; both are depleted in myasthenia gravis (MG), reducing the safety factor (SF) for neuromuscular transmission, especially in extraocular muscles (EOM). Studies of human myasthenic nerve-muscle preparations indicate that loss of endplate AChRs accounts for 59%, and NaChs for 40%, of SF reduction. Rodent models of MG indicate that NaChs and AChRs losses are due to complement-mediated destruction of postsynaptic folding. Saccades in MG show stereotyped, conjugate initial components, similar to normal but different from early disconjugacy with ocular nerve palsies. Loss of AChRs, NaChs, and postsynaptic folding all contribute to SF reduction in MG. EOM seem more susceptible to MG because of poor postsynaptic folding, lower baseline SF, and lower levels of intrinsic complement inhibitors. Initial conjugacy of saccades in MG reflects selective sparing of neuromuscular transmission of fast, pale global fibers, which have better developed postsynaptic folding.

Motor end plate innervation loss in diabetes and the role of insulin.

Retraction of distal sensory axons is a prominent feature in diabetic peripheral neuropathy (DPN), a process amenable to insulin therapy. Nevertheless, diabetic patients and long-term diabetic mice develop motor deficits after longer durations of DPN, a process that may be related to insulin deficiency. To compare the efficacy of intranasal delivery of insulin (IN-I) and subcutaneous insulin (Subc-I) in preventing motor deficits in a long-term mouse model of DPN, IN-I or Subc-I, 0.87 IU daily or placebo was delivered in separate cohorts of diabetic and nondiabetic CD1 mice for 8 months. Radiolabeled detection was used to assess insulin delivery and biodistribution. Biweekly behavioral tests and monthly electrophysiological and multipoint quantitative studies assessed motor function deficits. Morphometric analysis of spinal cord, peripheral nerve, muscle innervation, and specific molecular markers were evaluated at and before the end point. Despite progressive distal axonal terminal loss, numbers and caliber of motor neurons were preserved. There were no differences in glycemia between IN-I and Subc-I-treated mice. Intranasal delivery of insulin and, to a lesser extent, Subc-I, protected against electrophysiological decline, loss of neuromuscular junctions, and loss of motor behavioral skills. Intranasal delivery of insulin was associated with greater preservation of the phosphatidylinositol 3-kinase signaling pathway involving Akt, cyclic AMP response element binding protein,and glycogen synthase kinase 3ß but did not alter extracellular signal-regulated kinase, mitogen-activated protein kinase/extracellular signal-regulated kinase, or c-Jun amino-terminal kinase. Thus, direct delivery of insulin to the nervous system might prevent motor deficit in human type 1 diabetes by preservation of the phosphatidylinositol 3-kinase-Akt pathway rather than only affecting glycemic levels; the effects of insulin on other signaling pathways may, however, play additional roles.

Imaging the back pain patient.

Imaging is an integral part of the clinical examination of the patient with back pain; it is, however, often used excessively and without consideration of the underlying literature. The primary role of imaging is the identification of systemic disease as a cause of the back or limb pain; magnetic resonance imaging (MRI) excels at this. Systemic disease as a cause of back or limb pain is, however, rare. Most back and radiating limb pain is of benign nature, owing to degenerative phenomena. There is no role for imaging in the initial evaluation of the patient with back pain in the absence of signs or symptoms of systemic disease. When conservative care fails, imaging may be undertaken with due consideration of its risks: labeling the patient as suffering from a degenerative disease, cost, radiation exposure, and provoking unwarranted minimally invasive or surgical intervention. Imaging can well depict disc degeneration and disc herniation. Imaging can suggest the presence of discogenic pain, but the lack of a pathoanatomic gold standard obviates any definitive conclusions. The imaging natural history of disc herniation is resolution. There is very poor correlation between imaging findings of disc herniation and the clinical presentation or course. Psychosocial factors predict functional disability due to disc herniation better than imaging. Imaging with MRI, computed tomography (CT), or CT myelography can readily identify central canal, lateral recess, or foraminal compromise. Only when an imaging finding is concordant with the patient's pain pattern or neurologic deficit can causation be considered. The zygapophysial (facet) and sacroiliac joint are thought to be responsible for axial back pain, although with less frequency than the disc. Imaging findings of the structural changes of osteoarthritis do not correlate with pain production. Physiologic imaging, either with single-photon emission CT bone scan, heavily T2-weighted MRI sequences (short-tau inversion recovery), or gadolinium enhancement, can detect inflammation and are more predictive of an axial pain generator.

Pre- and postsynaptic neuromuscular junction abnormalities in musk myasthenia.

Autoantibodies to muscle-specific kinase (MuSK) can cause myasthenia gravis (MG). The pathophysiological mechanism remains unknown. We report in vitro electrophysiological and histological studies of the neuromuscular junction in a MuSK MG patient. Low levels of presynaptic acetylcholine release and small miniature endplate potentials were found. This combination of pre- and postsynaptic abnormalities was supported by histology, revealing partially denervated postsynaptic areas, and some degeneration of postsynaptic folds. Results suggest that anti-MuSK antibodies reduce the stability of muscle-nerve contact.

The effect of plasma from muscle-specific tyrosine kinase myasthenia patients on regenerating endplates.

Muscle-specific tyrosine kinase (MuSK) is essential for clustering of acetylcholine receptors (AChRs) at embryogenesis and likely also important for maintaining synaptic structure in adult muscle. In 5 to 7% of myasthenia gravis (MG) cases, the patients' blood contains antibodies to MuSK. To investigate the effect of MuSK-MG antibody on synapse regeneration, notexin was used to induce damage to the flexor digitorum brevis muscle. We administered aliquots of MuSK-MG patients' plasma to the flexor digitorum brevis twice daily for a period up to 21 days, and muscles were investigated ex vivo in contraction experiments. AChR levels were measured with (125)I-alpha-bungarotoxin, and endplates were studied with quantitative immunohistochemistry. In normal muscles and in 14-day regenerated muscles, MuSK plasma caused impairment of nerve stimulus-induced contraction in the presence of 0.35 and 0.5 mmol/L Ca(2+) with or without 100 to 400 nmol/L tubocurarine. Endplate size was decreased in regenerated muscles relative to controls; however, we did not observe such differences in muscle not treated with notexin. MuSK plasma had no effect on the amount and turnover rate of AChRs. Our results suggest that anti-MuSK antibodies influence the activity of MuSK molecules without reducing their number, thereby diminishing the size of the endplate and affecting the functioning of AChRs.

Monozygous twins with neuromuscular transmission defects at opposite sides of the motor endplate.

Disorders affecting the postsynaptic side of the neuromuscular junction include autoimmune myasthenia gravis (MG) as well as some of the congenital myasthenic syndromes (CMS). Lambert-Eaton myasthenic syndrome (LEMS) is an acquired autoimmune neuromuscular disorder in which autoantibodies are directed against the presynaptic calcium channels. Here we describe two monozygous twin brothers: case 1 was diagnosed with an indeterminate form of acquired postsynaptic neuromuscular junction defect at age 32 and case 2 with LEMS at age 47. Case 1 presented clinically with mild generalized myasthenic weakness, neurophysiological examination revealed disturbed neuromuscular transmission along with probable myositis and serum analysis regarding antibodies against the acetylcholine receptor and muscle-specific tyrosine kinase was negative. Case 2 presented with proximal muscle fatigue accompanied by areflexia at rest and antibodies against the P/Q-type voltage-gated calcium channels were present. Neurophysiologically, case 2 had reduced baseline compound motor action potential amplitudes on neurography, decrement on low-frequency repetitive nerve stimulation (RNS) and pathological increment on high frequency RNS. To our knowledge this is the first case report of its kind and adds an intriguing contrast to the more common diagnosis of CMS in monozygous twins.

Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.

Schwartz-Jampel syndrome (SJS) is a recessive neuromyotonia with chondrodysplasia. It results from hypomorphic mutations of the gene encoding perlecan, leading to a decrease in the levels of this heparan sulphate proteoglycan in basement membranes (BMs). It has been suggested that SJS neuromyotonia may result from endplate acetylcholinesterase (AChE) deficiency, but this hypothesis has never been investigated in vivo due to the lack of an animal model for neuromyotonia. We used homologous recombination to generate a knock-in mouse strain with one missense substitution, corresponding to a human familial SJS mutation (p.C1532Y), in the perlecan gene. We derived two lines, one with the p.C1532Y substitution alone and one with p.C1532Y and the selectable marker Neo, to down-regulate perlecan gene activity and to test for a dosage effect of perlecan in mammals. These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG). An inverse correlation between disease severity and perlecan secretion in the BMs was observed at the macroscopic and microscopic levels, consistent with a dosage effect. Endplate AChE levels were low in both lines, due to synaptic perlecan deficiency rather than major myofibre or neuromuscular junction disorganization. Studies of muscle contractile properties showed muscle fatigability at low frequencies of nerve stimulation and suggested that partial endplate AChE deficiency might contribute to SJS muscle stiffness by potentiating muscle force. However, physiological endplate AChE deficiency was not associated with spontaneous activity at rest on EMG in the diaphragm, suggesting that additional changes are required to generate such activity characteristic of SJS.

How myasthenia gravis alters the safety factor for neuromuscular transmission.

Myasthenia gravis (MG), the most common of autoimmune myasthenic syndromes, is characterized by antibodies directed against the skeletal muscle acetylcholine receptors (AChRs). Endplate Na(+) channels ensure the efficiency of neuromuscular transmission by reducing the threshold depolarization needed to trigger an action potential. Postsynaptic AChRs and voltage-gated Na(+) channels are both lost from the neuromuscular junction in MG. This study examined the impact of postsynaptic voltage-gated Na(+) channel loss on the safety factor for neuromuscular transmission. In intercostal nerve-muscle preparations from MG patients, we found that endplate AChR loss decreases the size of the endplate potential, and endplate Na(+) channel loss increases the threshold depolarization needed to produce a muscle action potential. To evaluate whether AChR-specific antibody impairs the function of Na(+) channels, we tested omohyoid nerve-muscle preparations from rats injected with monoclonal myasthenogenic IgG (passive transfer model of MG [PTMG]). The AChR antibody that produces PTMG did not alter the function of Na(+) channels. We conclude that loss of endplate Na(+) channels in MG is due to complement-mediated loss of endplate membrane rather than a direct effect of myasthenogenic antibodies on endplate Na(+) channels.

Bone marrow-derived mesenchymal stem cell transplantation does not improve quality of muscle reinnervation or recovery of motor function after facial nerve transection in rats.

Recently, we devised and validated a novel strategy in rats to improve the outcome of facial nerve reconstruction by daily manual stimulation of the target muscles. The treatment resulted in full recovery of facial movements (whisking), which was achieved by reducing the proportion of pathologically polyinnervated motor endplates. Here, we posed whether manual stimulation could also be beneficial after a surgical procedure potentially useful for treatment of large peripheral nerve defects, i.e., entubulation of the transected facial nerve in a conduit filled with suspension of isogeneic bone marrow-derived mesenchymal stem cells (BM-MSCs) in collagen. Compared to control treatment with collagen only, entubulation with BM-MSCs failed to decrease the extent of collateral axonal branching at the lesion site and did not improve functional recovery. Post-operative manual stimulation of vibrissal muscles also failed to promote a better recovery following entubulation with BM-MSCs. We suggest that BM-MSCs promote excessive trophic support for regenerating axons which, in turn, results in excessive collateral branching at the lesion site and extensive polyinnervation of the motor endplates. Furthermore, such deleterious effects cannot be overridden by manual stimulation. We conclude that entubulation with BM-MSCs is not beneficial for facial nerve repair.

ISSLS prize winner: A study of diffusion in human lumbar discs: a serial magnetic resonance imaging study documenting the influence of the endplate on diffusion in normal and degenerate discs.

STUDY DESIGN: An in vivo serial magnetic resonance imaging study of diffusion characteristics in human lumbar discs over 24 hours in healthy volunteers and patients with low back pain. OBJECTIVES: To document the temporal pattern of diffusion in normal human lumbar discs and to study the influence of the vascularity of bone and the status of endplate on diffusion in the normal and degenerate discs. SUMMARY OF BACKGROUND DATA: Diffusion is the only source of nutrition to the discs, but no firm data are available on pattern of diffusion in humans. More data on this important subject are required to improve our understanding of disc degeneration and to probe research possibilities for preventing the same. METHODS: The diffusion pattern over 24 hours following gadodiamide injection was studied in 150 discs (96 normal and 54 degenerate). Signal intensity values for three regions of interest in bone (i.e., vertebral body, subchondral bone, and endplate zone) and seven in the disc were calculated, and normal percentiles of diffusion were derived for these regions. Enhancement percentage for each time period, peak enhancement percentage for each region, and the time taken to achieve peak enhancement percentage (Tmax) were used to define and compare diffusion characteristics and plot a time-intensity curve to document the 24-hour temporal pattern. The correlation of blood flow of the bone as measured by peak enhancement percentage of vertebral body, the status of the endplate zone as measured by the peak enhancement percentage, and Tmax of the endplate zone were correlated with the diffusion of the disc.Univariate analysis of variance, multiple comparisons, appropriate tests for significance, and stepwise linear regression analysis were used for analysis of the data using SPSS software. RESULTS: In normal discs, a "diffusion march" from the vertebral body to the center of disc was noted with the SImax being observed at 5 min in the vertebral body and subchondral bone, at 2 hours in the endplate zone, and at 6 hours in the nucleus pulposus. A significant difference in mean peak enhancement percentage was observed between that of the body and the discs in those less than 10 years and those above the age of 20 years (P < 0.001). Alterations in endplate zone produced distinct magnetic resonance imaging signs of disturbance in diffusion, which offered a reliable noninvasive method of identifying endplate cartilage damage. Stepwise linear regression analysis showed that the significant variable influencing diffusion to the center of the nucleus pulposus of the total sample was peak enhancement percentage of endplate zone (R2 = 0.216; P < 0.001), that of degenerate discs was peak enhancement percentage of endplate zone (R2 = 0.322; P < 0.001), and that of normal discs (R2 = 0.324; P < 0.001) was age. CONCLUSIONS: Serial postcontrast magnetic resonance imaging studies offer a reliable method of assessing the diffusion of the discs and the functional status of the endplate cartilage. Endplate cartilage damage increases with age and produces considerable changes in diffusion. The present study has described reliable signs by which these damages can be identified in vivo. Aging and degeneration have been shown to be two separate processes by documenting clear-cut differences in diffusion. The present data encourage use of diffusion studies as a noninvasive method to assess the physiologic status of the disc and endplate and to study the effect of drugs, smoking, mechanical loading, exercises, etc. on the physiology of the disc.

Are MuSK antibodies the primary cause of myasthenic symptoms?

OBJECTIVE: To investigate the morphologic, electrophysiologic, and molecular correlates of muscle-specific tyrosine kinase-seropositive [MuSK(+)] myasthenia gravis (MG). BACKGROUND: Anti-MuSK antibodies are detected in some of acetylcholine receptor-seronegative [AChR(-)] patients with MG with prominent facial, bulbar, and respiratory muscle involvement. The morphologic and electrophysiologic correlates of MuSK(+) MG have not been investigated to date. METHODS: Immunohistochemistry, electron microscopy, and in vitro electrophysiology studies were performed on an intercostal muscle specimen of a patient with MuSK(+) MG and in control subjects. MUSK was directly sequenced, and the nucleotide changes were traced with allele-specific PCR in control subjects. RESULTS: A man aged 34 years has had facial weakness since childhood and progressive bulbar and respiratory muscle weakness and intermittent diplopia since age 21 years. He has thin temporalis and masseter muscles, a high-arched palate, and an atrophic tongue. EMG shows a 36% decrement in facial muscles. His mother has similar facial features. His endplates (EPs) show no AChR or MuSK deficiency, but the amplitudes of the miniature EP potentials and currents are reduced to 35% and 55% of normal, respectively. EP ultrastructure is well preserved, but some junctional folds immunostain faintly for immunoglobulin G. Mutation analysis of MUSK reveals one rare and two common DNA polymorphisms. CONCLUSIONS: 1) The circulating anti-muscle-specific tyrosine kinase antibodies caused neither muscle-specific tyrosine kinase nor acetylcholine receptor deficiency at the endplates; 2) the reduced intercostal miniature endplate potential and current amplitudes were not accounted for by acetylcholine receptor deficiency; 3) the faint immunoglobulin G deposits at the endplates may or may not represent anti-muscle-specific tyrosine kinase antibodies; and 4) the anti-muscle-specific tyrosine kinase antibodies may not be the primary cause of myasthenic symptoms in this patient.

[Secondary nerve reconstruction in the upper extremity in children--results with respect to number of motor units]. / Sekundäre Nervenrekonstruktionen an Extremitäten im Kindesalter--Ergebnisse unter Betrachtung der Anzahl motorischer Einheiten.

After nerve injury, the therapy of choice is primary suture. If this, however, is not possible or inadequate, a secondary reconstruction must be carried out within a suitable period of time. This study shows results after nerve transplantation within a timeframe of six weeks. Seventeen children with peripheral nerve injuries of the upper extremity were treated. Secondary nerve reconstruction was accomplished by sural nerve transplantation. Eight children, aged from 5 to 13 years, were examined. The median nerve was affected in three and the ulnar nerve in five cases. The examination included clinical and electrophysiological assessments. The length of grafts was correlated with the clinical result. Besides the calculation of sensitive and motor nerve conduction velocity the number of motor units from the flexor pollicis brevis muscle or abductor digiti minimi muscle were determined by motor-unit-estimation (MUE) on both sides. The observation time period was on an average 2.9 years. Results were good to excellent. A persisting Hoffmann-Tinel's sign was found only once in median nerve lesion. Loss of sensitivity following harvesting of sural nerve was not noted as a problem by any of these children. Length of grafts did not affect the results. Standard values were reached in every case in the electrophysiological examination. The number of motor units of the abductor pollicis brevis muscle and abductor digiti minimi muscle decreased to approximately 50% compared to the healthy side. Sural nerve grafting resulted in good motor and sensory function. We recommend grafting within six weeks, as Wallerian degeneration is completed and regeneration from the proximal nerve stump is optimal. Although children have a very good regeneration potential, the examined cases did not achieve a complete restoration of all motor units of the muscles.

Presynaptic failure of neuromuscular transmission and synaptic remodeling in EA2.

OBJECTIVE: To further investigate the basis of abnormal neuromuscular transmission in two patients with congenital myasthenic syndrome associated with episodic ataxia type 2 (EA2) using stimulated single fiber EMG (SFEMG) and in vitro microelectrode studies. METHODS: Two patients with genetically characterized EA2 previously shown to have abnormal neuromuscular transmission by voluntary SFEMG were studied with stimulated SFEMG and anconeus muscle biopsy with microelectrode studies and electron microscopy of the neuromuscular junction. RESULTS: In vivo stimulated SFEMG showed signs of presynaptic failure, with jitter and blocking that improved with increased stimulation frequency. Additional evidence of presynaptic failure was provided by the in vitro microelectrode studies, which showed marked reduction of the end plate potential quantal content in both patients. Of note, the end plate potentials showed high sensitivity to N-type blockade with omega-conotoxin not seen in controls. The ultrastructural studies revealed some evidence of small nerve terminals apposed to normal or mildly overdeveloped postsynaptic membranes, suggesting an ongoing degenerative process. CONCLUSIONS: The authors demonstrated presynaptic failure of neurotransmission in patients with heterozygous nonsense mutations in CACNA1A. The contribution of non-P-type calcium channels to the process of neurotransmitter release in these patients likely represents a compensatory mechanism, which is insufficient to restore normal neuromuscular transmission.