Abstract
Botulinum neurotoxin A (BoNT/A), the most toxic, naturally occurring protein, cleaves synapse-associated protein of 25 kDa and inhibits acetylcholine release from motor nerve endings (MNEs). This leads to paralysis of skeletal muscles. Our study demonstrates that capsaicin protects mouse neuromuscular junctions from the neuroparalytic effects of BoNT/A. Bilateral injection of BoNT/A near the innervation of the Extensor digitorum longus (EDL) muscle of adult Swiss-Webster mice inhibited the toe spread reflex (TSR). However, when capsaicin was coinjected bilaterally, or injected 4 or 8 h before injecting BoNT/A, the TSR remained normal. In animals that were pretreated with capsazepine, capsaicin failed to protect against the neuroparalytic effects of BoNT/A. In vivo analyses demonstrated that capsaicin protected muscle functions and electromygraphic activity from the incapacitating effects of BoNT/A. The twitch response to nerve stimulation was greater for EDL preparations isolated from mice injected with capsaicin before BoNT/A. Capsaicin pretreatment also prevented the inhibitory effects of BoNT/A on end-plate currents. Furthermore, pretreatment of Neuro 2a cells with capsaicin significantly preserved labeling of synaptic vesicles by FM 1-43. This protective effect of capsaicin was observed only in the presence of extracellular Ca2+ and was inhibited by capsazepine. Immunohistochemistry demonstrated that MNEs express transient receptor potential protein of the vanilloid subfamily, TRPV1, the capsaicin receptor. Capsaicin pretreatment, in vitro, reduced nerve stimulation or KCl-induced uptake of BoNT/A into motor nerve endings and cholinergic Neuro 2a cells. These data demonstrate that capsaicin interacts with TRPV1 receptors on MNEs to reduce BoNT/A uptake via a Ca2+-dependent mechanism.
- BoNT, botulinum neurotoxin
- αBnTX, alpha bungarotoxin
- BoNT/A, botulinum neurotoxin A
- CAP, capsaicin
- CPZ, capsazepine
- CMAP, compound muscle action potential
- EDL, Extensor digitorum longus
- EPP, end-plate potentials
- EPC, end-plate currents
- MNE, motor nerve ending
- TRPV1, transient receptor potential protein 1 of vanilloid subfamily
- TS, triangularis sterni
- TSR, toe spread reflex
- ACh, acetylcholine
- HC, heavy chain
- LC, light chain
- PBS, phosphate-buffered saline
- YFP, yellow fluorescence protein.
Footnotes
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This work was supported by The Defense Threat Reduction Agency [Grant HDTRA1-07-C-0031 CBT BAA]; the National Institutes of Health [Grant 2R01-NS045979]; the Kirby Foundation; and the Toohey Foundation.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.109.156901
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↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- Received May 29, 2009.
- Accepted August 3, 2009.
- © 2009 by the American Society for Pharmacology and Experimental Therapeutics
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