title: Different effects of types A and B botulinum toxin on transmitter release at the rat neuromuscular junction.
abstract: Blockade of neuromuscular transmission was produced in the lower hind limb of the rat by local injection of either crystalline type A botulinum toxin or purified type B botulinum neurotoxin. At 1, 3, 5 and 7 days after injection, the extensor digitorum longus nerve-muscle preparation was excised and analyzed in vitro for alterations in 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 B toxin, although completely paralyzed at 1 and 3 days, twitched in response to nerve stimulation at 5 and 7 days after injection. Both toxins induced a marked decrease in the frequency of miniature endplate potentials but type A did so to a greater extent. The remaining population of miniature endplate potentials contained a greater frequency of potentials with small or large amplitudes and prolonged rise times compared to normal muscle. These changes were more pronounced with type A toxin than with type B toxin. In the presence of alpha-dinitrophenol (1 mM), high frequency, fast-rising miniature endplate potentials of uniform size reappeared. High K+ (20 mM) was less effective in this respect. At 3 days after toxin injection nerve impulse evoked transmitter release was reduced more for type A treated muscles than for type B. However, 3,4-diaminopyridine, 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 B-treated muscles.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives*; D000077770:Amifampridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology*; D004140:Dinitrophenols / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D008297:Male; D009045:Motor Endplate / Q000502:physiology; D009469:Neuromuscular Junction / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D009435:Synaptic Transmission / Q000187:drug effects
chemical_list: D000631:Aminopyridines; D004140:Dinitrophenols; D018377:Neurotransmitter Agents; D015761:4-Aminopyridine; D001905:Botulinum Toxins; D000077770:Amifampridine