Influence of temperature on neuromuscular transmission in myasthenia gravis

Summary The effect of local cooling was studied in 28 patients with myastenia gravis. We stimulated the ulnar nerve with single stimuli and trains at 3/s for 2s and at 50/s for 1.5s. The compound muscle action potential (MAP), the muscle twitch and the isometric tetanic force of the adductor pollicis were registered. 1. At 3/s stimulation the pathological decrement of the MAP decreased after slight cooling. 2. The amplitude of the single MAP was higher at lower temperature when compared to normal temperature. The same increase is however to be found in healthy subjects. 3. After slight cooling, the maximum tetanic force was higher. However, the decrement of the force was higher also, therefore ruling out a practicable application of cooling for the patient. 4. After severe cooling (18–22°C) the tetanic force was much lower and in many cases a complete failure of the neuromuscular transmission occured.

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Zusammenfassung Der Einfluß lokaler Kühlung wurde an 28 Patienten mit Myasthenia gravis untersucht. Wir reizten den N. ulnaris mit einzelnen Impulsen und mit Serien von 3/s für 2s und von 50/s für 1.5s. Das Summenaktionspotential (MAP), die Muskelzuckung und die isometrische tetanische Kraft des Adduktor pollicis wurden registriert. 1. Bei Reizung mit 3/s war das pathologische Dekrement des MAP nach leichter Kühlung geringer. 2. Die Amplitude des MAP war größer. Diese Amplitudenzunahme tritt jedoch auch bei Gesunden nach Kühlung auf. 3. Nach leichter Kühlung war die maximale tetanische Kraft größer. Jedoch nahm die Kraft während der Reizung nach dem Maximum wieder schnell ab. Der praktische Nutzen einer Kühlung ist deshalb für den Patienten gering. 4. Nach starker Kühlung (18–22°C) war die maximale tetanische Kraft sehr niedrig. In vielen Fällen kam es zu einem vollständigen Versagen der neuromuskulären Impulsübertragung.

     

Some features of different motor units in human biceps brachii

Summary Use has been made of the method of selective leading-off of impulses from individual motor units at high isometric muscle tension, the maximum one including. Two types of motor units have been distinguished in m. biceps brachii in man on the basis of the dependence between the firing frequency and the level of the muscle tension. Characteristic of the first (tonic) type is the rise in the frequency at lower tensions and constant frequency at higher tensions. The second (phasic) type shows an approximately linear rise of the frequency with increase of tension. The tonic motor units are smaller in size, with lower threshold, they are less fatiquable and their transient pattern of firing depends on the rate of increase of tension. They contribute less to the growth of the muscle tension. The phasic motor units are bigger in size with higher threshold, more fatiguable, their transient pattern of firing does not depend on the rate of increase of tension. They contribute essentially to the growth of the muscle tension.     

The fine structure of de-and reinnervated muscle spindles

Summary Sensory and motor nerve endings in lower lumbrical muscles of rats were surprisingly well reconstituted following a single crush lesion of the sciatic nerve. No motor nerve endings were noted in the equatorial region, nor sensory endings in the polar regions of the muscle spindles examined.1 and 2 months after the lesion, multiple axonal sprouts reinnervated an increased number of intrafusal Schwann cells and, occasionally, of intrafusal muscle fibers. This frequently resulted in abnormal contact relationships between multiple Schwann cell processes and muscle fibers, nerve terminals and muscle fibers, and nerve terminals and Schwann cell processes. In addition, the remaining or newly formed basement membranes of the respective Schwann cells, axons, or muscle fibers were often irregularly arranged. Freely floating basement membranes adjacent to intrafusal muscle fibers of Schwann cells were more frequently observed than in normal spindles. The internal structure of regenerated nerve terminals varied considerably; however, there was a wide range of variability in the structure of normal nerve terminals too.Most endings, at 14 and 24 months after the lesion, had a normal appearance although some altered relations between nerve terminals and muscle, fibers were still present. Some proliferated Schwann cells or Schwann cell processes as well as basement membranes were not reinnervated. These could represent the only evidence of the preceding lesion.Presented in part at the 3rd Symposium on Neuromuscular Disorders, September 12–14, 1973 in Janské Láznê, SSR.     

Excitation-contraction uncoupling in skeletal muscle by dantrolene sodium

Summary Dantrolene sodium, a skeletal muscle relaxant, inhibits the twitch response by direct action on the muscle. The action potentials from dantrolene sodium depressed muscles have been examined by taking their first derivative, and membrane capacitance has been measured with cable analysis techniques. It is concluded that dantrolene sodium has no effect on the electrical excitability of the muscle and uncouples excitation-contraction mechanisms.     

Relationship between the size of the capillary bed and oxidative capacity in various cat skeletal muscles

The size of the capillary bed, assessed by capillary density (CD), capillary per muscle fibre ratio (C/F), total capillary length, surface area and volume was related to the oxidative capacity, assessed by the volume density of mitochondria and O₂max in cat muscles with a different composition of glycolytic and oxidative fibres: predominantly glycolytic gracilis, purely oxidative soleus and gracilis transformed towards oxidative by chronic low frequency (10 Hz) electrical stimulation. Maximal blood flow and lactate output were measured in the muscles during isometric contractions.When capillary supply was estimated by C/F ratio, there was a close correlation between various parameters only in stimulated gracilis. The combined data of all muscles showed a significant correlation between the total volume of mitochondria, O₂max and total capillary surface area. Capillary volume showed a tight correlation with maximal blood flow in both control and stimulated gracilis, but not in soleus. Maximal blood flow was correlated withVO₂max in oxidative muscles (stimulated gracilis and soleus) but not in control glycolytic gracilis. Moreover normal gracilis did not show any relationship between the volume density of mitochondria and the size of the capillary bed. The latter was inversely correlated with the output of lactate which was greater in muscles with a lower C/P ratio.The data on gracilis indicates that the capillary bed can adapt to the increased demand for oxygen and a greater oxidative capacity induced by long-term activity imposed on a glycolytic muscle, while it may be more important for the removal of lactate in the glycolytic muscles under their normal activity. The factors involved in the regulation of blood flow in control soleus — when the morphological size of the vascular bed is not related to blood flow — are discussed.     

A case of femoral compressive neuropathy in AL amyloidosis

We describe a case of a 54-yr-old AL amyloidosis patient who developed femoral compressive neuropathy due to iliopsoas pseudohypertrophy. The patient, who presented with end stage renal disease, was referred to our clinic because of lower extremity weakness and polyarthritis. Finally, he was diagnosed as having kappa-AL amyloidosis, complicated by femoral compressive neuropathy, hypertrophic amyloid myopathy, amyloid arthropathy, carpal tunnel syndrome, and end stage renal disease. Femoral compressive neuropathy has never been reported in association with amyloid induced iliopsoas hypertrophic myopathy. This report expands the clinical spectrum of AL amyloidosis.     

Enhanced expression of brain interferon-alpha and serotonin transporter in immunologically induced fatigue in rats

Immunologically induced fatigue was induced in rats by intraperitoneal injection of a synthetic double-stranded RNA, polyriboinosinic : polyribocytidylic acid (poly I:C). An injection of poly I:C (3 mg/kg) decreased the daily amounts of spontaneous running wheel activity to approximately 60% of the preinjection level until day 8. Quantitative analysis of mRNA levels demonstrated that interferon-alpha (IFN-alpha) and p38 mitogen-activated protein kinase mRNAs increased in the medial preoptic, paraventricular and ventromedial hypothalamic nuclei and in cortex on both days 1 and 8, while interleukin-1beta and an inhibitor of nuclear factor kappaB (IkappaB)-beta mRNAs increased on day 1, but recovered within a week. Serotonin transporter (5-HTT) mRNA also increased on days 1 and 8 after poly I:C injection in the same brain regions where IFN-alpha mRNA increased. The increased 5-HTT had a functional significance, because in vivo brain microdialysis revealed that an i.p. injection of poly I:C induced a decrease in the extracellular concentration of 5-HT in the prefrontal cortex; the decrease was blocked by local perfusion with a nonselective 5-HT reuptake inhibitor, imipramine. Finally, the poly I:C-induced fatigue was attenuated by a 5-HT1A receptor agonist but not by 5-HT2, 5-HT3 or dopamine D3 agonists. These findings, taken together, suggest that disorders in brain IFN-alpha and 5-HTT expression may be involved in the neuronal mechanisms of the poly I:C-induced fatigue.     

The structure and response properties of Golgi tendon organs in control and hypodynamia-hypokinesia rats

The Golgi tendon organs (GTOs) are encapsulated mechano-receptors that, in normal conditions, monitor via Ib afferent fibers the contractile force. A 14-day period of hypodynamia, absence of weight bearing and hypokinesia, and reduction of motor activity (HH) is known to induce changes in postural muscles such as the soleus. At present, there is no data available regarding the Ib afferent feedback in normal rats (CONT group) and in rats after a hypodynamia-hypokinesia (HH group) period. Consequently, the aim of our study was to determine the HH effects on the morphological (histochemistry on gross morphology) and electrophysiological properties of the GTOs in rat soleus muscle. In the histological study, nine CONT and nineteen HH GTOs of the soleus muscle were identified. The results demonstrated that HH GTOs were morphologically similar to the CONT GTOs. Regarding the electrophysiological study, a L2-L6 laminectomy was performed under deep anesthesia (sodium pentobarbital, 60 mg kg(-1)). Responses in single Ib fibers from the L5 dorsal root to the isometric twitch and tetanic fused contractions of "in-series" motor units (MUs) were recorded. Twenty-three and twenty-eight GTO/MU pairs were studied in the CONT and HH groups, respectively. In the HH group, the Ib afferent response exhibited a decrease in dynamic peak for the high stimulation frequencies and an increase in static sensitivity for all stimulation frequencies. Our results suggest that after an HH period, the GTOs continue to fulfil their mechano-sensory function to signal the contractile force but with a higher static sensitivity.     

Electrical stimulation restores the specificity of sensory axon regeneration

Electrical stimulation at the time of nerve repair promotes motoneurons to reinnervate appropriate pathways leading to muscle and stimulates sensory neurons to regenerate. The present experiments examine the effects of electrical stimulation on the specificity of sensory axon regeneration. The unoperated rat femoral cutaneous branch is served by 2-3 times more DRG neurons than is the muscle branch. After transection and repair of the femoral trunk, equal numbers of DRG neurons project to both branches. However, 1 h of electrical stimulation restores the normal proportion of DRG neurons reinnervating skin and muscle. To ask if the redistribution of stimulated neurons results from enhanced specificity of target reinnervation, we developed a new technique of sequential double labeling. DRG neurons projecting to the femoral muscle branch were prelabeled with Fluoro Gold 2 weeks before the nerve was transected proximally and repaired with or without 1 h of 20-Hz electrical stimulation. Three weeks after repair, the muscle nerve was labeled a second time with Fluororuby. The percentage of regenerating neurons that both originally served muscle and returned to muscle after nerve repair increased from 40% without stimulation to 75% with stimulation. Electrical stimulation thus dramatically alters the distribution of regenerating sensory axons, replacing normally random behavior with selective reinnervation of tissue-specific targets. If the enhanced regeneration specificity resulting from electrical stimulation is found to improve function in a large animal model, this convenient and safe technique may be a useful adjunct to clinical nerve repair.