Differences in excitability properties of FDI and ADM motor axons

The first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles are innervated by the same ulnar nerve, but studies have shown that the former is much more severely affected in amyotrophic lateral sclerosis. In this study, threshold tracking was used to investigate whether membrane properties differ between FDI and ADM motor axons. In 12 normal subjects, compound muscle action potentials were recorded from FDI and ADM after ulnar nerve stimulation at the wrist. The strength-duration time constant was significantly longer in the FDI axons than in the ADM axons, and latent addition studies showed greater threshold changes at the conditioning-test stimulus of 0.2 ms in FDI than in ADM axons. These findings suggest that nodal persistent sodium conductances are more prominent in FDI axons than in ADM axons, and therefore excitability is physiologically higher in FDI axons. Even in the same nerve at the same sites, membrane properties of FDI and ADM motor axons differ significantly, and thus their axonal/neuronal responses to disease may also differ.

Structural characterization of Tn916-like element in Streptococcus parauberis serotype II strains isolated from diseased Japanese flounder

AIMS

To screen for the existence and determine the structure of Tn916-like element in Streptococcus parauberis serotype II strains isolated from cultured Japanese flounder in western Japan.

METHODS AND RESULTS

In this study, the structure of Tn916-like element and the flanking regions were characterized by polymerase chain reaction (PCR) and inverse PCR, followed by cloning and sequencing. The Tn916-like element is 18 031 bp in length and composed of 22 ORFs. Southern blot hybridization analysis showed that the HincII-digested internal structures of Tn916-like elements yielded two patterns among S. parauberis serotype II strains. The flanking sequences were identical with the corresponding region of S. parauberis serotype I strain except for the addition of 6-bp coupling sequence (ATCATA) being adjacent to the upstream of the element.

CONCLUSION

The Tn916-like element exhibited high homology (more than 99%) with Tn916 observed in other streptococci and enterococci and was integrated in the same site of chromosome for all of the tested S. parauberis serotype II strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results indicate that the Tn916-like element encoding tet(M) gene is present in all of the tested S. parauberis serotype II strains, which are disseminated in the flounder-culturing areas in western Japan.

Thalidomide reduces serum VEGF levels and improves peripheral neuropathy in POEMS syndrome

BACKGROUND

Polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes (POEMS) syndrome is a rare multi-system disorder associated with plasma-cell dyscrasia. Several case series and reports have suggested that high-dose chemotherapy with autologous peripheral blood stem-cell transplantation is efficacious treatment, but this transplantation is not indicated for elderly patients and patients with renal failure.

OBJECTIVE

To investigate the effects of thalidomide treatment for POEMS syndrome.

METHODS

Nine patients, who were not indicated for high-dose chemotherapy, were treated with thalidomide. Neurological disability scores, nerve conduction studies and serum levels of vascular endothelial growth factor (VEGF) were prospectively examined. VEGF levels were measured by an enzyme-linked immunosorbent assay.

RESULTS

During follow-up periods of 8-23 months (mean, 15 months), all patients showed substantial clinical improvement (n = 6) or stabilisation of symptoms (n = 3). Serum VEGF levels decreased in all patients and were normalised in five patients. Nerve conduction velocities in the median nerve increased in seven patients. There were no serious adverse effects, including thalidomide neuropathy.

CONCLUSION

Thalidomide treatment should be further studied as a treatment for POEMS syndrome, particularly for patients who are not indicated for transplantation therapy.

Evaluation of plasma C-terminal atrial natriuretic peptide in healthy cats and cats with heart disease

BACKGROUND

The clinical implications of evaluating C-terminal atrial natriuretic peptide (ANP) concentration in cats are still controversial.

HYPOTHESIS

The objective of this study was to investigate the relationship between plasma C-terminal ANP concentration and left atrial pressure (LAP) in healthy cats with volume overload (study 1), and to compare plasma C-terminal ANP in normal cats and cats with cardiomyopathy (study 2).

ANIMALS

Five healthy adult cats were used in study 1, and clinically healthy cats (n=8) and cats with cardiomyopathy (n=14) were used in study 2.

METHODS

In study 1, cats were anesthetized and given acetated Ringer's solution (100 mL/kg/h for 60 minute) via the cephalic vein. Hemodynamic measurements and blood samples, collected from the jugular vein, were performed at 10-min intervals. In study 2, blood samples from normal cats and cats with cardiomyopathy were collected from the cephalic vein. The plasma C-terminal ANP concentration was determined by radioimmunoassay for human alpha-ANP.

RESULTS

In study 1, volume overload significantly increased the C-terminal ANP concentration and LAP from baseline. The C-terminal ANP concentration was strongly correlated with the mean LAP. In study 2, age, E wave velocity, and the ratios of the left atrium to aorta were significantly higher in the cats with cardiomyopathy compared with the normal cats. The C-terminal ANP concentration was significantly higher in the cats with cardiomyopathy compared with the normal cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our results suggest that the measurement of plasma C-terminal ANP in cats may provide additional information for the diagnosis of heart disease.

Effects of age on excitability properties in human motor axons

OBJECTIVE

The threshold tracking technique is a new approach to non-invasively assess biophysical properties of axonal membrane in human subjects. The aim of this study was to evaluate the effects of age and gender on excitability properties of human motor axons.

METHODS

Computerized threshold tracking was used to measure multiple excitability indices in median motor axons of 93 normal subjects (50 men; age, 20-86 years).

RESULTS

Regression analyses showed that the higher age was associated with longer strength-duration time constant (p=0.03), smaller threshold changes in depolarizing threshold electrotonus (p=0.02), smaller supernormality (p=0.01), and steeper slope of the current-threshold relationship for hyperpolarizing currents (p<0.001). There were slight sex differences in rheobase, threshold electrotonus, supernormality, late subnormality, and current-threshold slope, though they were significant only in the subgroup with age <50 years.

CONCLUSIONS

Aging may increase persistent sodium currents, inward rectification, and possibly, outward potassium currents. The combination of changes raises the possibility of slight membrane depolarization in elderly people. For the sex-related differences, further studies will be required with the evaluation of sex hormonal effects.

SIGNIFICANCE

Age-related effects on excitability properties are subtle, but should be taken into consideration in the clinical application of nerve excitability testing, particularly in elderly subjects.

Changes in Na(+) channel expression and nodal persistent Na(+) currents associated with peripheral nerve regeneration in mice

Patients with peripheral neuropathy frequently suffer from positive sensory (pain and paresthesias) and motor (muscle cramping) symptoms even in the recovery phase of the disease. To investigate the pathophysiology of increased axonal excitability in peripheral nerve regeneration, we assessed the temporal and spatial expression of voltage-gated Na(+) channels as well as nodal persistent Na(+) currents in a mouse model of Wallerian degeneration. Crushed sciatic nerves of 8-week-old C57/BL6J male mice underwent complete Wallerian degeneration at 1 week. Two weeks after crush, there was a prominent increase in the number of Na(+) channel clusters per unit area, and binary or broad Na(+) channel clusters were frequently found. Excess Na(+) channel clusters were retained up to 20 weeks post-injury. Excitability testing using latent addition suggested that nodal persistent Na(+) currents markedly increased beginning at week 3, and remained through week 10. These results suggest that axonal regeneration is associated with persistently increased axonal excitability resulting from increases in the number and conductance of Na(+) channels.

Genetically confirmed Huntington's disease masquerading as motor neuron disease

We describe a patient with Huntington's disease (HD) who showed asymmetrical upper limb amyotrophy as a main manifestation. Chorea and psychiatric symptoms were not prominent. Electromyography revealed generalized active and chronic denervation and fasciculations. A genetic test showed 46 CAG repeats in the huntingtin gene. Asymmetrical amyotrophy restricted to the upper limb has been reported in some patients with progressive chorea and amyotrophy without acanthocytosis, but genetically proven cases of HD have rarely been reported. It is not known why only a few HD patients show the motor neuronal loss; however, certain as-yet-unidentified genetic factors combined with some environment factors and the underlying cellular dysfunctions by polyglutamine aggregation could be responsible for the motor neuronal loss similar to that in amyotrophic lateral sclerosis.

[Altered axonal ion channel function in amyotrophic lateral sclerosis]

Fasciculation is a characteristic feature of amyotrophic lateral sclerosis (ALS). The ectopic firing of motor units usually arises from the motor nerve terminals, and occasionally from the motor neurons, indicating a wide-spread abnormality in axonal excitability properties. ALS is a multi-factorial disease; some gene abnormalities and environmental factors lead to a cell death through a complex cascade, including oxidative stress, mitochondrial dysfunction, excitotoxicity, and impaired axonal transport. It is important to elucidate the pathophysiology of axonal excitability in ALS, because increased axonal excitability would enhance oxidative stress and excitotoxicity, and therefore contribute to motor neuronal death. So far, two kinds of axonal ion channel abnormalities have been found; (1) increased persistent sodium currents, and (2) reduced potassium currents, both increasing axonal excitability and responsible for generation of fasciculations. In excitability testing, findings in ALS are characterized prolonged strength-duration time constant, suggesting increased persistent sodium currents, and greater threshold changes in depolarizing threshold electrotonus and greater supernormality, suggestive of impaired potassium channels. In relation to disease stage, persistent sodium currents increase in the early phase of the disease, possibly associated with collateral sprouting, and then, potassium currents decline. These serial changes in axonal properties could provide new insights into the pathophysiology of ALS, and implications for future therapeutic options.

Anti-GQ1b antibody does not affect neuromuscular transmission in human limb muscle

Anti-ganglioside GQ1b antibody induces neuromuscular blocking on mouse phrenic nerve-diaphragm preparations. Several reports suggest that patients with this antibody show abnormal neuromuscular transmission in the facial or limb muscles, but limb muscle weakness is unusual in Miller Fisher syndrome that is often associated with anti-GQ1b antibody. To determine whether anti-GQ1b sera affect neuromuscular transmission in human limb muscles, axonal-stimulating single fiber electromyography was performed in the forearm muscle of seven patients with anti-GQ1b antibody. All showed normal jitter and no blocking. Anti-GQ1b antibody does not affect neuromuscular transmission in human limb muscles. The different findings in mouse and human may be explained by the extent of expression of GQ1b on the motor nerve terminals in the muscle examined.

Is excitation–contraction coupling impaired in myasthenia gravis?

OBJECTIVE

To investigate whether excitation-contraction (E-C) coupling of muscle is impaired in patients with myasthenia gravis (MG).

METHODS

In 51 patients with generalized MG and 35 normal subjects, compound muscle action potentials (CMAPs) of the abductor pollicis brevis, and movement-related potentials using an accelerometer placed at the thumb tip were simultaneously recorded after median nerve stimulation at the wrist. The E-C coupling time (ECCT) was estimated by a latency difference between CMAP and movement-related potential. Antibodies against acetylcholine receptor (AChR), ryanodine receptor (RyR), and muscle specific receptor tyrosine kinase (MuSK) were measured by immunoassays.

RESULTS

The mean ECCT was significantly longer in patients with MG (mean+/-SEM; 2.79+/-0.1 ms; p=0.002) than in normal controls (2.52+/-0.1 ms). Among MG patients, the mean ECCT was longer for patients with thymoma than for those without it (P=0.04), and was shorter for patients treated with FK506 (an immunosuppressant and also an enhancer of RyR related Ca(2+) release) than for those not receiving this treatment (p=0.04). ECCT had no significant correlation with anti-AChR, anti-RyR, or anti-MuSK antibodies.

CONCLUSIONS

In MG, E-C coupling appears to be impaired, particularly in patients with thymoma, and FK506 possibly facilitates E-C coupling.

SIGNIFICANCE

The functional implication of impaired E-C coupling is not established, but it may contribute to muscle weakness in patients with MG.

Median-radial sensory nerve comparative studies in the detection of median neuropathy at the wrist in diabetic patients

OBJECTIVE

Median-ulnar comparative studies (MUCS) play an important role in the electrodiagnosis of carpal tunnel syndrome, but in diabetes concomitant involvement of Guyon's canal (ulnar nerve compression at the wrist) would reduce the sensitivity of MUCS. This study tested the utility of median-radial comparative studies (MRCS) in diabetic patients.

METHODS

Anti-dromic MUCS and MRCS were prospectively performed in 120 patients with diabetes, and 64 normal controls. In 28 diabetic patients, latent addition using threshold tracking was performed in superficial radial sensory axons to estimate persistent nodal sodium currents.

RESULTS

MUCS was abnormal in 49% of the diabetic patients, and MRCS was abnormal in 58%. Median motor distal latencies were prolonged in 38%, and median sensory nerve conduction velocities were slowed in 40%. The longer latency differences in MRCS were associated with smaller persistent sodium currents, suggesting that intra-axonal sodium accumulation mediated by hyperglycemia enhances nerve compression.

CONCLUSIONS

MRCS appears to be the most sensitive electrodiagnostic test in the detection of median neuropathy at the wrist in diabetic patients. Nerve conduction slowing across the carpal tunnel may be associated with metabolic abnormalities under hyperglycemia.

SIGNIFICANCE

Assessment of nerve conduction across the common entrapment sites could provide new insights into the pathophysiology of diabetic neuropathy related to metabolic factors.

Paroxysmal kinesigenic choreoathetosis (PKC): confirmation of linkage to 16p11-q21, but unsuccessful detection of mutations among 157 genes at the PKC-critical region in seven PKC families

Paroxysmal kinesigenic choreoathetosis (PKC) is a paroxysmal movement disorder of unknown cause. Although the PKC-critical region (PKCCR) has been assigned to the pericentromeric region of chromosome 16 by several studies of families from various ethnic backgrounds, the causative gene has not yet been identified. In the present study, we performed linkage and haplotype analysis in four new families with PKC, as well as an intensive polymerase chain reaction (PCR) based mutation analysis in seven families for a total of 1,563 exons from 157 genes mapped around the PKCCR. Consequently, the linkage/haplotype analysis revealed that PKC was assigned to a 24-cM segment between D16S3131 and D16S408, the result confirming the previously defined PKCCR, but being unable to narrow it down. Although the mutation analysis of the 157 genes was unsuccessful at identifying any mutations that were shared by patients from the seven families, two nonsynonymous substitutions, i.e., 6186C>A in exon 3 of SCNN1G and 45842A>G in exon 29 of ITGAL, which were segregated with the disease in Families C and F, respectively, were not observed in more than 400 normal controls. Thus, one of the two genes, SCNN1G and ITGAL, could be causative for PKC, but we were not able to find any other mutations that explain the PKC phenotype.

The effects of physiological fluctuation of serum potassium levels on excitability properties in healthy human motor axons

OBJECTIVE

Previous axonal excitability studies suggest hyperkalemia or hypokalemia can significantly alter membrane potential and thereby, excitability properties. We studied whether physiological fluctuation of serum potassium levels affects axonal excitability in normal human axons.

METHODS

Threshold tracking was used to measure strength-duration properties, refractory periods, supernormality, and threshold electrotonus in median motor axons of 12 normal volunteers. In each subject, the excitability indices and serum potassium levels were measured three times (baseline, 2h later, and 2 weeks later).

RESULTS

The pooled data (n=36) showed significant correlation of the relative refractory period, supernormality, and depolarizing threshold electrotonus with potassium levels. Among each trial (12 subjects) the correlation did not reach statistical significance occasionally. Strength-duration properties, refractoriness, late subnormality, and hyperpolarizing threshold electrotonus were not significantly affected by serum potassium levels.

CONCLUSIONS

Even in the normal range, serum potassium levels could slightly alter axonal excitability of human axons. Among excitability indices, the relative refractory period, supernormality, and threshold electrotonus are sensitive to potassium levels.

SIGNIFICANCE

Physiological fluctuation of serum potassium levels could partly be responsible for inter- and intra-subject variability of excitability indices.

Time course of axonal regeneration in acute motor axonal neuropathy

Patients with acute motor axonal neuropathy (AMAN) generally recover well. We reviewed clinical and electrophysiologic recovery in 13 patients for up to 5 years. Twelve patients showed rapid recovery over 12 months, whereas in the remaining one the recovery was slow and incomplete at 5 years. In AMAN, axonal degeneration appears to develop predominantly in the motor nerve terminals, and only occasionally more proximally in the nerve roots. Nerve terminal degeneration-regeneration presumably provides a mechanism for good recovery.

RCA/IAEA third external dosimetry intercomparisons in East Asia region

Several intercomparison exercises were organised by the International Atomic Energy Agency (IAEA) on the determination of operational quantities at the regional or interregional basis. In East Asia region, a third phase of the intercomparison finished in mid 2004. It was organised within the frame of the Regional Cooperation Agreement (RCA) as a follow-up to previous exercises carried out during 1990-1992 and 1995-1996. The results of this intercomparison for the determination of operational quantities were satisfactory for all Member States. The laboratories demonstrated a good performance in quantities tested. The purpose of this paper is to present the results of the RCA/IAEA intercomparison and the future of RCA activities in support of assessment of occupational exposure by organising intercomparison runs.

Gangliosides contribute to stability of paranodal junctions and ion channel clusters in myelinated nerve fibers

Paranodal axo-glial junctions are important for ion channel clustering and rapid action potential propagation in myelinated nerve fibers. Paranode formation depends on the cell adhesion molecules neurofascin (NF) 155 in glia, and a Caspr and contactin heterodimer in axons. We found that antibody to ganglioside GM1 labels paranodal regions. Autoantibodies to the gangliosides GM1 and GD1a are thought to disrupt nodes of Ranvier in peripheral motor nerves and cause Guillain-Barré syndrome, an autoimmune neuropathy characterized by acute limb weakness. To elucidate ganglioside function at and near nodes of Ranvier, we examined nodes in mice lacking gangliosides including GM1 and GD1a. In both peripheral and central nervous systems, some paranodal loops failed to attach to the axolemma, and immunostaining of Caspr and NF155 was attenuated. K(+) channels at juxtaparanodes were mislocalized to paranodes, and nodal Na(+) channel clusters were broadened. Abnormal immunostaining at paranodes became more prominent with age. Moreover, the defects were more prevalent in ventral than dorsal roots, and less frequent in mutant mice lacking the b-series gangliosides but with excess GM1 and GD1a. Electrophysiological studies revealed nerve conduction slowing and reduced nodal Na(+) current in mutant peripheral motor nerves. The amounts of Caspr and NF155 in low density, detergent insoluble membrane fractions were reduced in mutant brains. These results indicate that gangliosides are lipid raft components that contribute to stability and maintenance of neuron-glia interactions at paranodes.

Failure of treatment with anti-VEGF monoclonal antibody for long-standing POEMS syndrome

We present the case of a 71-year-old woman with polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome. Overproduction of vascular endothelial growth factor (VEGF), secreted by plasmacytoma, is considered responsible for the characteristic symptoms, and therefore anti-VEGF monoclonal antibody (bevacizumab) could be a therapeutic option. The patient was treated with bevacizumab 7 years after onset. Despite a dramatic decrease in serum VEGF levels, there was no clinical improvement, possibly because aberrant angiogenesis had already developed systemically. We suggest that careful consideration should be taken for indication of bevacizumab therapy, and this agent may be used in selected patients with a short duration POEMS syndrome.

Increased nodal persistent Na+ currents in human neuropathy and motor neuron disease estimated by latent addition

OBJECTIVE

To investigate the changes in nodal persistent Na(+) currents in human neuropathy and motor neuron disease. In human motor axons, approximately 1.0% of total Na(+) channels are active at rest, termed "persistent" Na(+) channels, and the conductance can be non-invasively estimated by the technique of latent addition in vivo.

METHODS

Latent addition was performed in median motor axons of 93 patients with axonal neuropathy (n=38), lower motor neuron disorder (LMND; n=19) or amyotrophic lateral sclerosis (ALS; n=36) and in 27 age-matched normal subjects. Brief hyperpolarizing conditioning current pulses were delivered, and threshold change at the conditioning-test interval of 0.2 ms was measured as an estimator of the magnitude of persistent Na(+) currents. Threshold electrotonus and supernormality were also measured as indicators of resting membrane potential.

RESULTS

Threshold changes at 0.2 ms were significantly greater in patients with neuropathy or LMND (p<0.05), and tended to be greater in ALS patients (p=0.075) than in normal controls. Threshold electrotonus and supernormality did not differ in each patient group and normal controls, suggesting that membrane potential is not altered in patients. In the recovery phase of axonal neuropathy, the threshold changes increased in parallel with an increase in amplitudes of compound muscle action potential.

CONCLUSIONS

Persistent Na(+) currents appear to increase commonly in disorders involving lower motor neurons, possibly associated with axonal regeneration or collateral sprouting or changes in Na(+) channel gating.

SIGNIFICANCE

The increased axonal excitability could partly be responsible for positive motor symptoms such as muscle cramping frequently seen in lower motor neuron disorders.

Rho-kinase inhibition enhances axonal regeneration after peripheral nerve injury

In injured adult neurons, the process of axonal regrowth and reestablishment of the neuronal function have to be activated. We assessed in this study whether RhoA, a key regulator of neurite elongation, is activated after injury to the peripheral nervous system. RhoA is activated in motoneurons but not in Schwann cells after mouse sciatic nerve injury. To examine whether the activation of RhoA and its effector, Rho-kinase, retards axon regeneration of injured motoneurons, we employed a Rho-kinase inhibitor, fasudil. Amplitudes of distally evoked compound muscle action potentials are increased significantly faster after axonal injury in mice treated with fasudil compared with controls. Histological analysis shows that fasudil treatment increases the number of regenerating axons with large diameter, suggesting that axon maturation is facilitated by Rho-kinase inhibition. In addition, fasudil does not suppress the myelination of regenerating axons. These findings suggest that RhoA/Rho-kinase may be a practical molecular target to enhance axonal regeneration in human peripheral neuropathies.

Distal excitability changes in motor axons in amyotrophic lateral sclerosis

OBJECTIVE

Previous axonal excitability studies in amyotrophic lateral sclerosis (ALS) have suggested that impaired potassium channel function could be responsible for the generation of fasciculations, but the ectopic activity arises predominantly from the motor nerve terminals. This study tested the hypothesis that dysfunction of potassium channels is more pronounced in the more distal parts of axons.

METHODS

Threshold electrotonus was used to compare accommodation at the motor point of abductor pollicis brevis, and at the wrist portion of the median nerve, between 22 patients with ALS and 19 normal subjects. As target responses for motor point stimulation, movement-related potentials were recorded using an accelerometer.

RESULTS

Compared to normal subjects, ALS patients showed greater threshold changes to depolarizing conditioning currents at both the motor point and wrist, suggesting less accommodation by potassium currents. Differences in the threshold electrotonus curves between the normal and ALS groups were much more prominent at the motor point than at the wrist.

CONCLUSIONS

In ALS, axonal potassium channels are impaired more prominently in distal portions of axons than at the nerve trunk, and this is consistent with evidence that fasciculations mostly arise from the nerve terminals.

SIGNIFICANCE

Excitability testing at the motor point provides additional information about the pathophysiology of ALS.

Aldose reductase inhibition alters nodal Na+ currents and nerve conduction in human diabetics

BACKGROUND

In diabetic nerves, activation of the polyol pathway via an aldose reductase and the resulting impairment of the Na(+)-K(+) pump would lead to a decreased transaxonal Na+ gradient and thereby reduced nodal Na+ currents.

OBJECTIVE

To investigate whether the aldose reductase inhibitor (ARI) epalrestat improves nodal Na+ currents and nerve conduction in human diabetic neuropathy.

METHODS

The authors conducted a 6-month, open clinical trial with an ARI, epalrestat, in 30 patients with mild-to-moderate diabetic neuropathy. The latent addition technique and measurements of the strength-duration time constant were used to estimate nodal persistent Na+ currents in median motor axons. Excitability testing and extensive nerve conduction studies including F-wave analyses were performed before and 1 and 6 months after the initiation of treatment with oral epalrestat.

RESULTS

Within a month of the start of treatment, there was a significant improvement in nerve conduction, particularly in conduction times across the carpal tunnel and F-wave latencies. The results of latent addition (p < 0.05) and strength-duration time constant (p = 0.06) suggested increased nodal persistent Na+ currents. At 6 months, nerve conduction continued to improve.

CONCLUSIONS

Aldose reductase pathway inhibition could rapidly increase nodal Na+ currents and thereby improve the slowing of nerve conduction, presumably because of a restoration of the membranous Na+ gradient.

Autologous peripheral blood stem cell transplantation for POEMS syndrome

Polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes syndrome is a rare multisystem disorder. Overproduction of vascular endothelial growth factor (VEGF) by plasmocytoma could be responsible for the symptoms. The authors treated four patients with high-dose chemotherapy and autologous peripheral blood stem cell transplantation. Within 6 months, symptoms associated with rapid normalization of serum VEGF levels improved.

Latent addition in human motor and sensory axons: Different site-dependent changes across the carpal tunnel related to persistent Na+ currents

OBJECTIVE

To compare site-dependent changes across the carpal tunnel in axonal persistent Na+ conductances in motor and sensory axons. Positive sensory symptoms are prominent features in carpal tunnel syndrome, and a persistent Na+ current is a major determinant of axonal excitability.

METHODS

The technique of latent addition was used to estimate persistent Na+ currents in median motor and sensory axons at the wrist and palm of 10 normal subjects. Brief hyperpolarizing conditioning current pulses were delivered, and threshold change at the conditioning-test interval of 0.2 ms was measured as an indicator of persistent Na+ currents.

RESULTS

Threshold changes at 0.2 ms were greater in sensory than in motor axons at both the wrist and palm. In motor axons, the threshold changes were significantly smaller at the palm (mean, 4.9%) than at the wrist (10.0%). By contrast, the threshold changes were similar at the two sites of sensory axons (12.6 and 13.1%). The passive membrane time constant was similar for motor and sensory axons at the palm and wrist.

CONCLUSIONS

Nodal persistent Na+ conductances have substantial site-dependent changes decreasing distally across the carpal tunnel in median motor axons, but not in sensory axons.

SIGNIFICANCE

Whereas sensory axons generally have higher excitability than motor axons, the sensory-motor differences become more prominent across, and possibly at the carpal tunnel than the nerve trunk, and it is suggested that this contributes to the predominance of positive sensory symptoms in carpal tunnel syndrome.

Nodal persistent Na+ currents in human diabetic nerves estimated by the technique of latent addition

OBJECTIVE

To investigate the effects of hyperglycemia on persistent Na+ currents in human diabetic nerves, eliminating the factors of passive membrane properties as a factor. Previous studies show that strength-duration time constant of a nerve is shortened under hyperglycemia, suggesting reduced axonal persistent Na+ currents. However, the time constant is also affected by changes in passive membrane properties. Latent addition using computerized threshold tracking is a new method that can separately evaluate Na+ currents and passive membrane properties.

METHODS

Latent addition was used to estimate nodal Na+ currents in median motor axons of 83 diabetic patients. Brief hyperpolarizing conditioning current pulses were delivered, and threshold changes at the conditioning-test interval of 0.2 ms were measured as an indicator of nodal persistent Na+ currents. Seventeen patients were examined before and after insulin treatment.

RESULTS

There was an inverse linear relationship between hemoglobin A1c levels and threshold changes at 0.2 ms (P=0.02); the higher hemoglobin A1c levels were associated with smaller threshold changes. After insulin treatment, there was a significant improvement in nerve conduction velocities associated with greater threshold changes at 0.2 ms (P=0.03), suggesting an increase in persistent Na+ currents. The fast component of latent addition, an indicator of passive membrane properties, was not affected by the state of glycemic control.

CONCLUSIONS

Hyperglycemia could suppress nodal persistent Na+ currents, presumably because of reduced trans-axonal Na+ gradient or impaired Na+ channels, and this can be rapidly restored by glycemic control.

SIGNIFICANCE

Reduced nodal Na+ currents may partly contribute to the pathophysiology of human diabetic neuropathy.

Altered axonal excitability properties in amyotrophic lateral sclerosis: impaired potassium channel function related to disease stage

Fasciculations are a characteristic feature of amyotrophic lateral sclerosis (ALS), and can arise proximally or distally in the motor neuron, indicating a widespread disturbance in membrane excitability. Previous studies of axonal excitability properties (i.e. threshold electrotonus, strength-duration time constant) have suggested respectively that change in potassium or sodium channels may be involved. To reinvestigate these changes and explore their correlation with disease stage, multiple axonal excitability properties (threshold electrotonus, strength-duration time constant, recovery cycle and current-threshold relationship) were measured for the median nerve at the wrist in 58 ALS patients, and compared with 25 age-matched controls. In ALS, there were greater changes in depolarizing threshold electrotonus (i.e. less accommodation) (P < 0.001) and greater supernormality in the recovery cycles (P < 0.001). These abnormalities were more prominent in patients with moderately reduced CMAP (1-5 mV). Modelling the excitability changes in this group supported the hypothesis that axonal potassium conductances are reduced, resulting in increased supernormality despite membrane depolarization. The tendency for strength-duration time constant to be prolonged in ALS was only significant for patients with normal CMAP amplitude (>5 mV). Patients with severely reduced CMAP (<1 mV) alone showed reduced threshold changes to hyperpolarizing current. These results suggest a changing pattern of abnormal membrane properties with disease progression. First, persistent Na+ conductance increases, possibly associated with collateral sprouting, and then K(+) conductances decline. Both changes cause axonal hyperexcitability, and may contribute to the generation of fasciculations. These serial changes in axonal properties could provide insights into the pathophysiology of ALS, and implications for future therapeutic options.

Temperature-dependent Luttinger surfaces

The Luttinger surface of an organic metal (TTF-TCNQ), possessing charge order and spin-charge separated band dispersions, is investigated using temperature-dependent angle-resolved photoemission spectroscopy. The Luttinger surface topology, obtained from momentum distribution curves, changes from quasi-2D (dimensional) to quasi-1D with temperature. The high temperature quasi-2D surface exhibits 4kF charge-density-wave (CDW) superstructure in the TCNQ derived holon band, in the absence of 2kF order. Decreasing temperature results in quasi-1D nested 2kF CDW order in the TCNQ spinon band and in the TTF surface. The results establish the link in momentum space between charge order and spin-charge separation in a Luttinger liquid.

Meningitis-retention syndrome. An unrecognized clinical condition

BACKGROUND

A combination of acute urinary retention and aseptic meningitis has not been well known. This combination can be referred to as meningitis-retention syndrome (MRS), when accompanied by no other abnormalities.

OBJECTIVE

To describe the results of a uro-neurological assessment in our patients with MRS.

METHODS

In three patients (two men, one woman; age, 34-68 years), we performed urodynamic studies and relevant imaging and neurophysiological tests, in addition to cerebrospinal fluid (CSF) examination.

RESULTS

All three patients developed acute urinary retention along with headache, fever and stiff neck. None had obvious neurological abnormalities, other than a slightly brisk reflex in the lower extremities. One had previously experienced generalized erythematous eruptions, but none had pain, hypalgesia or skin eruptions in the sacral dermatomes suggestive of Elsberg syndrome (infectious sacral polyradiculitis; mostly genital herpes). Brain/spinal/lumbar plexus MRI scans and nerve conduction studies were normal. CSF examination showed mild mononuclear pleocytosis, increased protein content, and normal to mildly decreased glucose content in all patients; increased myelin basic protein suggestive of central nervous system demyelination in one; and increased viral titers in none. Urodynamic study revealed, during the voiding phase, an underactive detrusor in all patients and an unrelaxing sphincter in one. These clinical manifestations were ameliorated within 3 weeks.

CONCLUSIONS

We reported three cases of MRS, a peculiar syndrome that could be regarded as a mild variant of acute disseminated encephalomyelitis (ADEM). Urinary retention might reflect acute shock phase of this disorder. Although MRS has a benign and self-remitting course, management of the acute urinary retention is necessary.

Axonal potassium conductance and glycemic control in human diabetic nerves

OBJECTIVE

To investigate the effects of hyperglycemia on axonal excitability and potassium conductance in human diabetic nerves.

METHODS

Threshold tracking was used to measure excitability indices, which depend on potassium channels (supernormality, late subnormality, threshold electrotonus, and a current/threshold relationship) in median motor axons of 96 diabetic patients. The effects of hyperglycemia on these indices were analyzed.

RESULTS

Among diabetic patients, higher serum hemoglobin A1c (HbA1c) levels were significantly associated with greater supernormality (P = 0.04) and smaller late subnormality (P = 0.02), suggestive of reduced nodal/paranodal potassium currents under hyperglycemia. Threshold electrotonus and current/threshold relationships did not correlate with HbA1c levels, but partly related with nerve conduction slowing.

CONCLUSIONS

Hyperglycemia could reduce nodal potassium conductances, possibly due to reduced membranous potassium gradient or suppression of potassium channels. In contrast, internodal potassium conductances may be determined by both metabolic factors and structural changes such as exposure of internodal channels by demyelination.

SIGNIFICANCE

Measurements of the excitability indices could provide new insights into nodal and internodal axonal membrane properties in human diabetic neuropathy, whereas multiple factors can affect especially internodal properties.