ISSN:0148-639X    

DOI:10.1002/mus.880161202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0148-639X    

DOI:10.1002/mus.880161203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA 5.5‐year‐old girl had myasthenic symptoms since birth. Tests for antiacetylcholine receptor (AChR) antibodies were negative. To investigate the character of the neuromuscular transmission defect, an intercostal muscle specimen was obtained at age 27 months. Immune deposits were absent from the endplates. On electron microscopy, most postsynaptic regions appeared normal, but the density of AChR on the junctional folds was diffusely reduced. In vitro microelectrode studies revealed that the number of transmitter quanta released by nerve impulse was normal. The amplitude of miniature of endplate potentials and currents was abnormally low. A study of the kinetic properties of AChR by analysis of acetylcholine‐induced current noise demonstrated a significant decrease in mean channel open‐time; the mean channel conductance was normal. The safety margin of neuromuscular transmission in this disorder is likely to be compromised by the deficiency and abnormal kinetic properties of AChR. The findings are unique among those patients with congenital AChR deficiency described to date. © 1993 John Wiley&S

ISSN:0148-639X    

DOI:10.1002/mus.880161204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA 21‐year‐old woman had myasthenic symptoms since birth that responded poorly to anticholinesterase therapy. Tests for acetylcholine receptor (AChR) antibodies were negative. An intercostal muscle specimen was obtained to investigate the character of the neuromuscular transmission defect. There were no immune deposits at the endplates. The quantal content of the endplate potential was normal. Miniature endplate potentials and currents were very small, but the number of AChR per endplate was normal. On electron microscopy, the synaptic vesicles were of normal size, the junctional folds were intact, and the density and distribution of AChR on the folds was normal. The kinetic properties of AChR were studied by analysis of acetylcholine (ACh)‐induced current noise. The mean single channel conductance was normal. The noise power spectrum was abnormal, containing two components of different time course. This could result from an abnormal interaction of ACh with AChR, or from two populations of AChR at the endplate. The second possibility is unlikely because if two populations of AChR were present at the endplate, then both would have to have low conductance to explain the small miniature endplate current, but the average conductance of the channels that did open was normal. © 1993 John Wiley&Son

ISSN:0148-639X    

DOI:10.1002/mus.880161205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe distribution of motor fiber conduction velocities (FCVs) of the ulnar and peroneal nerves in patients with polyneuropathy was estimated using F tacheodispersion, a technique based on F wave latencies. Twenty‐three ulnar and 23 peroneal nerves were studied. Three groups of nerves were identified according to conventional, M response, and F wave measurements: those with all parameters normal (group 1), those with abnormal F wave parameters only (group 2), and those with all parameters abnormal (group 3). Application of F tacheodispersion to nerves in group 1 revealed a shift of the distribution of FCVs toward the lower normal values in 6 of 7 nerves. In group 2, a significant proportion of FCVs were below the lower normal limits despite normal maximum conduction velocity estimated by the M response. In group 3, all nerve fibers were abnormally slow. The results indicate that application of F tacheodispersion in clinical practice will increase sensitivity of nerve conduction studies and enable quantitative estimation of conduction in a motor nerve fiber population. © 1993 John Wiley&Sons, I

ISSN:0148-639X    

DOI:10.1002/mus.880161206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe identified 5 of 44 consecutive children (11%) with Guillain–Barré syndrome who had electrophysiologic evidence of severe reduction of the mean amplitude of the compound motor action potentials (mean CMAP amplitude10% of lower limit of normal. Children in the first group were more likely to require assisted ventilation (60% vs. 6.2%) and were more frequently quadriplegic at the peak of their disability (80% vs. 18.7%). They also required longer periods to improve one functional grade (mean 63.6 days vs. 16.6 days) and to become ambulatory (mean 156 days vs. 17.6 days). Moreover, only the children in the first group had distal atrophy of four limbs after 1 year of follow‐up. Severe reduction of the mean amplitude of the CMAPs in children with GBS identifies a subgroup of patients with axonal damage that produces more severe weakness and delayed recovery. © 1993 John Wiley&Sons

ISSN:0148-639X    

DOI:10.1002/mus.880161207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe examined the mechanism(s) which allow terbutaline, a β2‐adrenergic agonist, to increase isometric force in bundles of normal and denervated rat soleus fibers. Terbutaline (10 μmol/L) potentiated tetanic contractions during exposure to 1 mmol/L ouabain, 10 μmol/L nifedipine, or 0.5 mmol/L iodoacetate. Terbutafine induced equivalent increases in submaximal potassium (K+) contracture and tetanic force: these effects were mimicked by 2 mmol/L dibutyrl‐cyclic AMP. Therefore, terbutaline increased force by a cyclic AMP‐dependent mechanism other than enhancement of sodium‐pump activity, dihydropyridine sensitive Ca2+currents, glycolysis, or action potentials. Pretreatment with 1 mmol/L caffeine induced submaximal potentiation of peak tetanic force but prevented further potentiation by terbutaline. This suggested that terbutaline did not influence the myofilaments, but acted on the sarcoplasmic reticulum (SR) to increase the myoplasmic Ca2+concentration and hence force production. We speculate that force is potentiated following β‐adrenoceptor activation by a cyclic AMP‐dependent phosphorylation of Ca2+release channels to facilitate SR calcium release during tetanic stimulation. © 1993 John

ISSN:0148-639X    

DOI:10.1002/mus.880161208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to compare two fundamentally different methods of deriving the average surface‐detected motor unit action potential (S‐MUAP) size from which to calculate a motor unit number estimate (MUNE), namely: (1) the simple arithmetic average of S‐MUAP parameter values; and (2) a computer‐derived datapoint by datapoint average waveform which takes account of differences in S‐MUAP shapes and durations. Multiple point stimulation was used to collect representative samples of between 11 and 20 S‐MUAPs (mean 15 ± 2 SD) from the median‐innervated thenar muscles of 20 healthy control subjects between 20 and 76 years of age (mean 48 ± 19 SD). The average S‐MUAP size based on peak‐to‐peak amplitude, negative peak amplitude, and negative peak area measurements was calculated using the two different methods. The mean S‐MUAP sizes based on the average waveform were significantly lower in all cases than those based on the simple average of S‐MUAP parameter values. Differences tended to be greatest for MUNEs based on peak‐to‐peak amplitude (35%), less for negative peak amplitude (20%), and least for negative peak area (16%)

ISSN:0148-639X    

DOI:10.1002/mus.880161209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIt is controversial whether acetylcholine receptors (AChR) or AChR‐like proteins exist in human thymus. To evaluate this question we isolated RNA from paraffin‐embedded thymic tissue of 5 myasthenics and 5 nonmyasthenics. RNA was subjected to reverse transcription followed by polymerase chain reaction (RT‐PCR) using primers specific for β‐actin, subunits of the fetal‐ and adult‐type AChR, andMyf‐4, a gene product which regulates AChR expression in muscle. β‐Actin transcripts were identified in specimens from 8 of 10 patients. In these 8 patients α‐and ε‐subunit transcripts were identified. Presence of these transcripts did not correlate with thymic pathology or clinical presentation. No γ‐subunit (specific for the fetal‐type AChR) orMyf‐4 transcripts were found. Our results indicate that mRNA for subunits of the adult‐type AChR are expressed in thymic tissue by mechanisms not involvingMyf‐4. AChR subunits in pathological thymus may provide a target for immune attack in MG. However, as AChR subunits were found in thymus tissue from myasthenics and nonmyasthenics, the presence of AChR subunits in the thymus alone is not sufficient to produce myasthenia g

ISSN:0148-639X    

DOI:10.1002/mus.880161210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe measured the peak voltage induced in a sensing loop by a Magstim 200 magnetic stimulator. Coil output varied little for repeated stimulation at the same intensity over a wide range of coil output. In contrast, the first stimulus immediately after a change in intensity was of larger amplitude and showed greater variability than subsequent stimuli. The effect was seen for changes in intensity of 5% and 60% and was greater for reductions than for increases in stimulation intensity. Stimulation immediately after a reduction in intensity from 100% to 40% resulted in peak induced voltages as high as those recorded for repeated stimulation at 43% of maximum coil output. Increased coil output following changes in stimulation intensity may affect measurement of the threshold for motor cortical stimulation. The effect of a change in intensity could be minimized by delaying stimulation for at least 30 s or discarding the first stimulus after the change. © 1993 John Wiley&Sons, Inc

ISSN:0148-639X    

DOI:10.1002/mus.880161211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY