Capsaicin protects mouse neuromuscular junctions from the neuroparalytic effects of botulinum neurotoxin a.
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 Ca(2+) 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 Ca(2+)-dependent mechanism.
Thyagarajan
Baskaran
B
Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, New Jersey MedicalSchool, Newark, New Jersey 07103, USA. mcardle@umdnj.edu
Krivitskaya
Natalia
N
Potian
Joseph G
JG
Hognason
Kormakur
K
Garcia
Carmen C
CC
McArdle
Joseph J
JJ
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D019274:Botulinum Toxins, Type A / Q000037:antagonists & inhibitors* / Q000633:toxicity*; D002211:Capsaicin / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D002460:Cell Line; D004594:Electrophysiology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D051379:Mice; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000187:drug effects; D053580:Muscle Strength / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation; D009411:Nerve Endings / Q000187:drug effects; D009465:Neuromuscular Agents / Q000037:antagonists & inhibitors* / Q000633:toxicity*; D009469:Neuromuscular Junction / Q000187:drug effects*; D018696:Neuroprotective Agents; D013569:Synapses / Q000187:drug effects; D050916:TRPV Cation Channels / Q000378:metabolism
D009465:Neuromuscular Agents; D018696:Neuroprotective Agents; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D019274:Botulinum Toxins, Type A; C071423:capsazepine; D000109:Acetylcholine; D002211:Capsaicin