Long-term neuromuscular dysfunction produced by passive transfer of amyotrophic lateral sclerosis immunoglobulins.

We investigated the role of the immune system in the pathogenesis of amyotrophic lateral sclerosis (ALS) by studying the long-term consequences of ALS immunoglobulin (Ig) application on the levator auris muscle of the mouse. We applied Ig from seven ALS patients, four disease controls, and a pool of normal Ig (6 mg of Ig in 2 weeks) by subcutaneous injection; removed the muscles 4 to 12 weeks after the beginning of treatment; and recorded both spontaneous and evoked release of transmitter. None of the control Ig induced changes in transmitter, whereas five of seven ALS Ig induced a significant increase in the rate of spontaneous release, and all ALS Ig produced significant changes in the quantal content of evoked release. In muscles treated with one of the ALS Igs, synaptic activity was completely absent. Cholinesterase and silver staining demonstrated intact neuromuscular junctions in the control Ig-treated muscles and also in many areas of ALS Ig-treated muscles. Axonal degeneration and denervation were present in most muscles treated with ALS Ig. There was complete denervation when no synaptic activity could be recorded. Thus, ALS Ig appears to lead to long-lasting effects at the neuromuscular junction, and such effects may be an early stage in the immune-mediated pathogenesis of ALS.

Effect of omega-conotoxin GVIA on neurotransmitter release at the mouse neuromuscular junction.

The effect of omega-conotoxin GVIA (omega-CgTx) was studied on spontaneous, K(+)-induced and electrically evoked neurotransmitter release at the neuromuscular junction of mouse diaphragm. omega-CgTx decreased the frequency and amplitude of basal and K(+)-induced miniature end plate potentials. This effect was abolished by raising the extracellular Ca2+ concentration. omega-CgTx had no effect on the quantal content of the electrically evoked release in this preparation.

Ca2+ role on the effect of phorbol esters on the spontaneous quantal release of neurotransmitter at the mouse neuromuscular junction.

The effect of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on the release process was studied in presence of different extracellular Ca2+ concentrations, in the mouse phrenic-diaphragm preparation. Hemidiaphragms were incubated for 2 h at room temperature in the presence or absence of TPA. TPA increased the basal frequency of miniature end plate potentials (mepp's) in a dose-dependent manner, resulting in a maximal increase of 280% at a concentration of 0.5 microM. An inverse relationship between extracellular Ca2+ concentration and TPA effect was observed: at high extracellular concentrations of Ca2+ the action of TPA decreased significatively, while at low Ca2+ concentrations the effect of TPA was remarkably augmented. The highest effect of TPA was obtained when tested in a calcium-free medium. TPA also increased mepp frequency stimulated by 10 mM K+. As at basal conditions, the effect of TPA was higher at lower concentrations of extracellular calcium. The results suggest that the effect of stimulation of PKC on neurotransmitter release at the mice neuromuscular junction is not exerted at the level of calcium influx to the nerve terminal. Moreover the action of calcium and TPA seems to be superimposed. The effect of K+ on neurotransmitter release could be explained not only by depolarization of the nerve terminal but by increasing the pool of activable PKC.