Acute and chronic effects of botulinum neurotoxin A on the mammalian neuromuscular junction
Copyright © 2013 Wiley Periodicals, Inc., a Wiley company
- Accepted manuscript online: 12 NOV 2013 01:11AM EST
- Manuscript Accepted: 7 NOV 2013
- Manuscript Revised: 30 OCT 2013
- Manuscript Received: 13 MAY 2013
- National Institute of General Medical Sciences
- National Institutes of Health. Grant Number: 8P20GM103432-12
- American Association of Colleges of Pharmacy
- botulinum neurotoxin;
- acetylcholine release;
- twitch tension;
- end plate currents;
- spontaneous release
Introduction: 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 hr.) 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 Ca2+ signals in Neuro 2a cells.
Discussion: These results demonstrate that 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. © 2013 Wiley Periodicals, Inc.