Muscle membrane properties in A pig sepsis model: Effect of norepinephrine.

Introduction: Sepsis-induced myopathy and critical illness myopathy are common causes of muscle weakness in intensive care patients. This study investigated the effect of different mean arterial blood pressure (MAP) levels on muscle membrane properties following experimental sepsis.

Methods: Sepsis was induced with fecal peritonitis in 12 of 18 anesthetized and mechanically ventilated pigs.

In vivo assessment of muscle membrane properties in myotonic dystrophy.

Introduction: Myotonia in myotonic dystrophy types 1 (DM1) and 2 (DM2) is generally attributed to reduced chloride-channel conductance. We used muscle velocity recovery cycles (MVRCs) to investigate muscle membrane properties in DM1 and DM2, using comparisons with myotonia congenita (MC).

Methods: MVRCs and responses to repetitive stimulation were compared between patients with DM1 (n = 18), DM2 (n = 5), MC (n = 18), and normal controls (n = 20).

Muscle velocity recovery cycles: Comparison between surface and needle recordings.

Introduction: Recording of muscle velocity recovery cycles (MVRCs) has been developed as a technique to investigate the pathophysiology of muscle diseases. MVRCs have been measured by direct muscle stimulation and concentric electromyographic needle recording. This study was undertaken to determine whether recordings can be made with surface electrodes.

Arginine butyrate per os protects mdx mice against cardiomyopathy, kyphosis and changes in axonal excitability.

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by lack of dystrophin, a sub-sarcolemmal protein, which leads to dramatic muscle deterioration. We studied in mdx mice, the effects of oral administration of arginine butyrate (AB), a compound currently used for the treatment of sickle cell anemia in children, on cardiomyopathy, vertebral column deformation and electromyographic abnormalities. Monthly follow-up by echocardiography from the 8th month to the 14th month showed that AB treatment protected the mdx mice against drastic reduction (20-23%) of ejection fraction and fractional shortening, and also against the ≈20% ventricular dilatation and 25% cardiac hypertrophy observed in saline-treated mdx mice.

Potassium and the excitability properties of normal human motor axons in vivo.

Hyperkalemia is an important cause of membrane depolarization in renal failure. A recent theoretical model of axonal excitability explains the effects of potassium on threshold electrotonus, but predicts changes in superexcitability in the opposite direction to those observed. To resolve this contradiction we assessed the relationship between serum potassium and motor axon excitability properties in 38 volunteers with normal potassium levels.

Chloride channels in myotonia congenita assessed by velocity recovery cycles.

Introduction: Myotonia congenita (MC) is caused by congenital defects in the muscle chloride channel CLC-1. This study used muscle velocity recovery cycles (MVRCs) to investigate how membrane function is affected.

Methods: MVRCs and responses to repetitive stimulation were compared between 18 patients with genetically confirmed MC (13 recessive, 7 dominant) and 30 age-matched, normal controls.

Peripheral nerve hyperexcitability with preterminal nerve and neuromuscular junction remodeling is a hallmark of Schwartz-Jampel syndrome.

Schwartz-Jampel syndrome (SJS) is a recessive disorder with muscle hyperactivity that results from hypomorphic mutations in the perlecan gene, a basement membrane proteoglycan. Analyses done on a mouse model have suggested that SJS is a congenital form of distal peripheral nerve hyperexcitability resulting from synaptic acetylcholinesterase deficiency, nerve terminal instability with preterminal amyelination, and subtle peripheral nerve changes. We investigated one adult patient with SJS to study this statement in humans.

Membrane dysfunction in Andersen-Tawil syndrome assessed by velocity recovery cycles.

Introduction: Andersen-Tawil syndrome (ATS) due to Kir2.1mutations typically manifests as periodic paralysis, cardiac arrhythmias and developmental abnormalities but is often difficult to diagnose clinically. This study was undertaken to determine whether sarcolemmal dysfunction could be identified with muscle velocity recovery cycles (MVRCs).

Muscle velocity recovery cycles: effects of repetitive stimulation on two muscles.

Introduction: We sought to characterize the excitability properties of tibialis anterior (TA) and brachioradialis (BR) muscles at rest and during electrically induced muscle activation in normal subjects.

Methods: Two centers recruited 10 subjects each. Multi-fiber velocity recovery cycles (VRCs) were recorded from TA (both centers) and BR (one center).

Validity of multi-fiber muscle velocity recovery cycles recorded at a single site using submaximal stimuli.

Objective: To examine the validity of multi-fiber muscle velocity recovery cycles (VRCs) recorded by direct muscle stimulation with submaximal stimuli.

Methods: VRCs were recorded from tibialis anterior muscle in normal volunteers with 1, 2 and 5 conditioning stimuli. Recordings were made with 6 different amplitudes of conditioning stimuli.

A mouse model of Schwartz-Jampel syndrome reveals myelinating Schwann cell dysfunction with persistent axonal depolarization in vitro and distal peripheral nerve hyperexcitability when perlecan is lacking.

Congenital peripheral nerve hyperexcitability (PNH) is usually associated with impaired function of voltage-gated K(+) channels (VGKCs) in neuromyotonia and demyelination in peripheral neuropathies. Schwartz-Jampel syndrome (SJS) is a form of PNH that is due to hypomorphic mutations of perlecan, the major proteoglycan of basement membranes. Schwann cell basement membrane and its cell receptors are critical for the myelination and organization of the nodes of Ranvier.

A model of mouse motor nerve excitability and the effects of polarizing currents.

This study was undertaken to develop a theoretical model of mouse motor nerve excitability, and to validate it by application to recordings from mouse axons with membrane potential altered by polarizing currents. Multiple excitability tests were performed on the caudal motor nerves of 12 mice. Membrane potential was artificially modified by injecting polarizing currents through the stimulating electrodes (±20% of threshold for 1 ms pulse).

Nerve excitability changes after intravenous immunoglobulin infusions in multifocal motor neuropathy and chronic inflammatory demyelinating neuropathy.

Intravenous immunoglobulin (IVIg) infusions may provide clinical benefits in multifocal motor neuropathy (MMN) and chronic inflammatory demyelinating polyneuropathy (CIDP). The short delay in the clinical response to IVIg therapy is not consistent with a process of remyelination or axonal regeneration. We assessed whether or not the efficacy of IVIg infusions in MMN and CIDP could reflect changes in axonal membrane properties and nerve excitability.

Excitability properties of mouse motor axons in the mutant SOD1(G93A) model of amyotrophic lateral sclerosis.

Non-invasive excitability studies of motor axons in patients with amyotrophic lateral sclerosis (ALS) have revealed a changing pattern of abnormal membrane properties with disease progression, but the heterogeneity of the changes has made it difficult to relate them to pathophysiology. The SOD1(G93A) mouse model of ALS displays more synchronous motoneuron pathology. Multiple excitability measures of caudal and sciatic nerves in mutant and wild-type mice were compared before onset of signs and during disease progression (4-19 weeks), and they were related to changes in muscle fiber histochemistry.

Excitability properties of motor axons in the maturing mouse.

Non-invasive excitability tests have been developed to appraise axonal membrane properties in peripheral nerves and are contributing to our understanding of neuropathies and neuronopathies. These techniques have been adapted to in vivo and in vitro rat models, but little data are available on mice, although mice provide more transgenic models of neurological disorders. This study was therefore undertaken to assess the suitability of mice to model human nerve excitability measurements and to document changes during maturation.

Neuromuscular excitability properties in myotonic dystrophy type 1.

Objective: To study neuromuscular excitability in patients with dystrophia myotonica type 1 (DM1).

Methods: The neuromuscular recovery cycle following motor nerve stimulation was assessed in 16 DM1 patients who had no sign of peripheral neuropathy or diabetes. Compound muscle action potentials were recorded from the adductor digiti minimi muscle to ulnar nerve stimulation at the wrist.

[Nerve conduction blocks and peripheral neuropathies].

A motor nerve conduction block is defined as a reduction of either amplitude or area of the compound motor action potential elicited by proximal vs. distal motor nerve stimulation. The pathophysiological mechanisms leading to a figure of conduction block include segmental demyelination, recent axonal interruption, or various axonal excitability abnormalities due to ion channel dysfunction or membrane potential changes.

[Inflammatory demyelinating neuropathies: classification, evolution and prognosis].

Inflammatory demyelinating neuropathies can be classified according to the topography of the nervous lesion. Acute and chronic polyradiculoneuritis are characterized by diffuse and multifocal, but predominantly proximal lesions, multifocal motor and sensory-motor neuropathies with persistent conduction blocks are restricted to some nerve trunks, while neuropathies due to monoclonal IgM with anti-MAG (Myelin Associated Glycoprotein) activity show distal and symmetric distribution. The clinical characteristics of inflammatory demyelinating neuropathies vary according to the type of neuropathy.

Alteration of motor nerve recovery cycle in multiple sclerosis.

Objective: To study peripheral motor nerve excitability in patients with multiple sclerosis (MS).

Methods: Twenty MS patients with normal nerve conduction parameters and no predisposing factors for peripheral neuropathy were included. Compound muscle action potentials were recorded from the abductor digiti minimi muscle to paired-pulse stimulation of the ulnar nerve at the wrist, with various interstimuli intervals (ISIs) ranging from 1 to 7 ms.

Central and peripheral fatigue after electrostimulation-induced resistance exercise.

Purpose: To investigate central and peripheral fatigue induced by a typical session of electromyostimulation (EMS) of the triceps surae muscle.

Methods: A series of neuromuscular tests including voluntary and electrically evoked contractions were performed before and immediately after 13 min of EMS (75 Hz) in 10 healthy individuals.

Results: Maximal voluntary contraction torque of the plantar flexor muscles significantly decreased (-9.

A reappraisal of various methods for measuring motor nerve refractory period in humans.

Objective: To compare various techniques of stimulation and methods of analysis to estimate absolute (ARP) and relative (RRP) refractory periods in motor nerve trunks of humans.

Methods: Double collision (DC) technique and two types of paired pulse (PP) technique, with test stimulation of supramaximal (PP(supra)) or submaximal (PP(sub)) intensity, were applied to 32 healthy subjects. The ulnar nerve was stimulated either at a single site (wrist) for the PP techniques or at two sites (wrist and elbow) for the DC technique, with various distal interstimuli intervals (ISIs).