Acute and chronic effects of botulinum neurotoxin a on the mammalian neuromuscular junction.
BACKGROUND
Botulinum neurotoxin A (BoNT/A) cleaves SNAP-25 and inhibits acetylcholine (ACh) release at the neuromuscular junctions (NMJ) to cause neuroparalysis. Previous reports indicate a dyssynchrony between the inhibitory effect of BoNT/A on ACh release and SNAP-25 cleavage.


METHODS
We tested the in vitro (acute; 90 min) and in vivo (chronic; 12 h) effects of BoNT/A on stimulus-evoked ACh release (SEAR), twitch tension, and SNAP-25 cleavage in isolated extensor digitorum longus (EDL) nerve-muscle preparations (NMP).


RESULTS
In vitro or in vivo BoNT/A poisoning inhibited SEAR and twitch tension. Conversely, SNAP-25 cleavage and inhibition of spontaneous release frequency were observed only in NMP poisoned with BoNT/A in vivo. Moreover, chronic treatment of BoNT/A inhibited ionomycin stimulated Ca(2+) signals in Neuro 2a cells.


CONCLUSIONS
These results demonstrate that the inhibition of SEAR precedes SNAP-25 cleavage and suggest involvement of a more complex mechanism for the inhibitory effect of BoNT/A at the NMJ.
School of Pharmacy, 1000 East University Avenue, University of Wyoming, Laramie, Wyoming, 82071.
Padmamalini
P
Baskaran
Baskaran
B
Thyagarajan
D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000494:pharmacology; D000109:Acetylcholine / Q000378:metabolism; D000110:Acetylcholinesterase / Q000378:metabolism; D000077770:Amifampridine; D000818:Animals; D019274:Botulinum Toxins, Type A / Q000633:toxicity*; D061207:Calcium Ionophores / Q000494:pharmacology; D045744:Cell Line, Tumor; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000187:drug effects*; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D009447:Neuroblastoma / Q000473:pathology; D009465:Neuromuscular Agents / Q000633:toxicity*; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D012018:Reflex / Q000187:drug effects; D013997:Time Factors
D061207:Calcium Ionophores; D009465:Neuromuscular Agents; D026902:Potassium Channel Blockers; D015759:Ionomycin; D015761:4-Aminopyridine; D000110:Acetylcholinesterase; D019274:Botulinum Toxins, Type A; D000109:Acetylcholine; D000077770:Amifampridine
SNAP-25; acetylcholine release; botulinum neurotoxin; end plate currents; spontaneous release; twitch tension