title: Botulinum neurotoxin type A (BoNTA) decreases the mechanical sensitivity of nociceptors and inhibits neurogenic vasodilation in a craniofacial muscle targeted for migraine prophylaxis.
abstract: The mechanism by which intramuscular injection of BoNTA into the craniofacial muscles decreases migraine headaches is not known. In a blinded study, the effect of BoNTA on the mechanical and chemical responsiveness of individual temporalis muscle nociceptors and muscle neurogenic vasodilation was investigated in female rats. Mechanical threshold was measured for 3h following intramuscular injection of BoNTA or vehicle, and for 10 min after a subsequent injection of the algogen glutamate. Injection of BoNTA significantly increased the mechanical threshold of muscle nociceptors without altering the muscle surface temperature and blocked glutamate-induced mechanical sensitization and neurogenic vasodilation. None of these effects were reproduced by pancuronium-induced muscle paralysis. Western blot analysis of temporalis muscles indicated that BoNTA significantly decreased SNAP-25. Measurement of interstitial glutamate concentration with a glutamate biosensor indicated that BoNTA significantly reduced glutamate concentrations. The mechanical sensitivity of muscle nociceptors is modulated by glutamate concentration through activation of peripheral NMDA receptors. Immunohistochemical experiments were conducted and they indicated that half of the NMDA-expressing temporalis nerve fibers co-expressed substance P or CGRP. Additional electrophysiology experiments examined the effect of antagonists for NMDA, CGRP and NK1 receptors on glutamate-induced effects. Glutamate-induced mechanical sensitization was only blocked by the NMDA receptor antagonist, but muscle neurogenic vasodilation was attenuated by NMDA or CGRP receptor antagonists. These data suggest that injection of BoNTA into craniofacial muscles acts to decrease migraine headaches by rapidly decreasing the mechanical sensitivity of temporalis muscle nociceptors through inhibition of glutamate release and by attenuating the provoked release of CGRP from muscle nociceptors.
authors: The Faculty of Pharmaceutical Sciences, The University of British Columbia, Vancouver, BC, Canada Center for Sensory-Motor Interaction (SMI), Dept. of Health Science and Technology, Aalborg University, Aalborg, Denmark.
authors: Parisa
authors: P
authors: Gazerani
authors: Sammy
authors: S
authors: Au
authors: Xudong
authors: X
authors: Dong
authors: Ujendra
authors: U
authors: Kumar
authors: Lars
authors: L
authors: Arendt-Nielsen
authors: Brian E
authors: BE
authors: Cairns
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D019274:Botulinum Toxins, Type A / Q000494:pharmacology*; D005152:Facial Muscles / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D007150:Immunohistochemistry; D016202:N-Methylaspartate / Q000378:metabolism; D009412:Nerve Fibers / Q000187:drug effects / Q000378:metabolism; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D017288:Pain Threshold / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012684:Sensory Thresholds; D013373:Substance P; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D013373:Substance P; D018698:Glutamic Acid; D016202:N-Methylaspartate; D019274:Botulinum Toxins, Type A