James F. Howard

High-Pressure Transvenous Perfusion of the Upper Extremity in Human Muscular Dystrophy: A Safety Study with 0.9% Saline

We evaluated safety and feasibility of high-pressure transvenous limb perfusion in an upper extremity of adult patients with muscular dystrophy, after completing a similar study in a lower extremity. A dose escalation study of single-limb perfusion with 0.9% saline was carried out in nine adults with muscular dystrophies under intravenous analgesia. Our study demonstrates that it is feasible and definitely safe to perform high-pressure transvenous perfusion with 0.9% saline up to 35% of limb volume in the upper extremities of young adults with muscular dystrophy. Perfusion at 40% limb volume is associated with short-lived physiological changes in peripheral nerves without clinical correlates in one subject. This study provides the basis for a phase 1/2 clinical trial using pressurized transvenous delivery into upper limbs of nonambulatory patients with Duchenne muscular dystrophy. Furthermore, our results are applicable to other conditions such as limb girdle muscular dystrophy as a method for delivering regional macromolecular therapeutics in high dose to skeletal muscles of the upper extremity.

Chapter 12 Neurotoxicology of neuromuscular transmission.

Publisher Summary The neuromuscular junction (NMJ) is sensitive to the effects of neurotoxins. The neurotoxins directed to the NMJ come from many sources. Many occur as natural substances of plants or animals, others are prescribed pharmaceutical compounds and still others are environmental hazards or weapons of terror. Drugs that produce worsening of neuromuscular function can be categorized as (1) drugs that have a direct effect on neuromuscular transmission (NMT) in otherwise normal individuals; (2) drugs that disturb the immune system and result in the development of myasthenia gravis (MG); (3) drugs that unmask subclinical MG or worsen muscle strength in patients with disorders of NMT; (4) drugs that delay recovery of strength, particularly respiratory function, following general anesthesia during which neuromuscular blocking agents have usually been used. The clostridial neurotoxins are gram-positive, anaerobic, spore-forming bacteria found ubiquitously in the environment. The neurotoxins of clostridial organisms produce botulism and tetanus by the inhibition of neurotransmitter release via their metalol-proteolytic activity directed against SNARE proteins, although the site of action and clinical picture of each is quite different. Heavy metal intoxication is a rare cause of clinical neuromuscular toxicity. The metals include barium, erbium, cadmium, cobalt, gadolinium, lanthium, manganese, nickel, praseodymium, triethyltin, and zinc. Nearly all of these have multiple effects on synaptic transmission but they block the release of acetylcholine (ACh) from the presynaptic nerve terminal. The inadvertent use of potentially NMJ toxic drugs is a matter of concern. Health care personnel must carefully assess each patients potential complications and risk of adverse events before prescribing these agents to someone whose neuromuscular transmission is perturbed.

Automated data acquisition and analysis of neural evoked potentials.

A software system to collect, analyze and store trains of neural evoked potentials is presented. Real-time waveform capture permits sampling of a variable-duration data window of 6 to 399.6 ms with a sample delay accurately adjustable up to 1 001 ms (20 microseconds resolution). The digitized representation of each waveform is stored for individual analysis. Off-line processing determines 17 parameters of each waveform, including an arrow-selected amplitude and time. Individual processing of waveforms preserves all degrees of freedom for statistical analysis across waveforms. Ensemble averages may optionally be formed from the individual waveforms with processing performed on the averaged responses. The software provides MENU-selectable support functions including stimulus-to-artifact timing, storage and retrieval of data and calculated parameters, digital display of waveforms, data calibration and gain modification, table referenced data editing, file management, simple statistics, hardcopy output, and optional database interfacing with output formatted for compatibility with a statistics package (SAS).

In Vivo Viscoelastic Response (VisR) Ultrasound for Characterizing Mechanical Anisotropy in Lower-Limb Skeletal Muscles of Boys with and without Duchenne Muscular Dystrophy

Our group has previously found that in silico, mechanical anisotropy may be interrogated by exciting transversely isotropic materials with geometrically asymmetric acoustic radiation force excitations and then monitoring the associated induced displacements in the region of excitation. We now translate acoustic radiation force-based anisotropy assessment to human muscle in vivo and investigate its clinical relevance to monitoring muscle degeneration in Duchenne muscular dystrophy (DMD). Clinical anisotropy assessments were performed using Viscoelastic Response ultrasound, with a degree of anisotropy reflected by the ratios of Viscoelastic Response relative elasticity (RE) or relative viscosity (RV) measured with the asymmetric radiation force oriented parallel versus perpendicular to muscle fiber alignment. In vivo results from rectus femoris and gastrocnemius muscles of boys aged ∼7.9-10.4 y indicate that RE and RV anisotropy ratios in rectus femoris muscles of boys with DMD were significantly higher than those of healthy control boys (RE: DMD = 1.51 ± 0.87, control = 0.99 ± 0.69, p = 0.04, Wilcoxon rank sum test; RV: DMD = 1.04 ± 0.71, control = 0.74 ± 0.22, p = 0.02). In the gastrocnemius muscle, only the RV anisotropy ratio was significantly higher in dystrophic than control patients (DMD = 1.23 ± 0.35, control = 0.88 ± 0.31, p = 0.04). In the dystrophic rectus femoris muscle, the RE anisotropy ratio was inversely correlated (slope = -0.03/lbf, r = -0.43, p = 0.07, Pearson correlation) with quantitative muscle testing functional output measures but was not correlated with quantitative muscle testing in the dystrophic gastrocnemius. These results suggest that Viscoelastic Response RE and RV measures reflect differences in mechanical anisotropy associated with functional impairment with dystrophic degeneration that are relevant to monitoring DMD clinically.

Chapter 3 Structure and function of the neuromuscular junction

Publisher Summary This chapter reviews the normal anatomy and physiology of the neuromuscular junction (NMJ) and the associated mechanisms necessary for synaptic transmission. The goal of neuromuscular transmission is the rapid amplification of small neuronal signals and the modulation of neurotransmitter release to effect repeated and robust communication with muscle. The acetylcholine receptor (AChR) is the functional unit of the postsynaptic membrane of skeletal muscle and encodes the ionotropic channel. The chapter illustrates the mechanism of synaptic transmission at the mammalian neuromuscular junction. A nerve action potential arriving at the presynaptic nerve terminal causes voltage-gated Ca 2+ channels at active release zones to open. The opening of these voltage-gated calcium channels results in a high concentration of Ca 2+ near the active zone, which, in turn, causes vesicles containing neurotransmitter to fuse with the presynaptic membrane, thereby releasing ACh into the synaptic cleft. ACh diffuses across the synaptic cleft to bind with AChRs on the postjunctional membrane; this causes ionic channels to open, allowing Na + to enter the muscle cell, thereby resulting in the depolarization of the membrane and the generation of an action potential.

Passive Myasthenia Gravis Induced in SCID Mice by Transfer of Blood Cells from Myasthenie Patients

More than 25 years ago, experiments that involved daily injections into mice of immunoglobulins purified from serum of myasthenia gravis (MG) patients demonstrated that this procedure reproduced in the mice the characteristic clinical and electrophysiologic features of MG [1]. During the same years other seminal experiments demonstrated that administration to mice of purified monoclonal antibodies against the acetylcholine receptor (AChR) also reproduced the clinical and electrophysiologic symptoms of MG (rev. in [2]). Those findings proved that autoantibodies against the AChR at the neuromuscular junction cause the symptoms of MG.