Comparison of the Action of Types A and F Botulinum Toxin at the Rat Neuromuscular Junction

摘要

Blockade of neuromuscular transmission was produced in the lower hind limb of the rat by local injection of either type A or type F botulinum toxin (BoTx). At 1, 3, 7 and 10 days after injection, the extensor digitorum longus (edl) nerve-muscle preparation was excised and analyzed for alterations in muscle mechanical properties or spontaneous and nerve stimulus-evoked quantal transmitter release. Muscles receiving type A toxin were paralyzed up to and including 7 days after injection. Muscles treated with type F toxin, although completely paralyzed at 1 and 3 days, twitched in response to nerve stimulation by 7 days after injection. Both toxins induced a marked decrease in the frequency of miniature endplate potentials, but type A did so to a great extent. At 1 and 3 days after toxin injection nerve impulse evoked transmitter release was reduced for both type A- and type F-treated muscles. However, 3,4-diaminopyridine (3,4-DAP), an agent which increases nerve-evoked transmitter release by increasing Ca2+ influx, was more effective in reversing the paralysis in type A- than in type F-treated muscles.