Antinociceptive Effect of Botulinum Toxin A in Persistent Muscle Pain Rat Model

ABSTRACT

OBJECTIVE: To investigate the effects of botulinum toxin on the mechanical hyperalgesia, electrophysiology and motor functions in the persistent muscle pain rat model. METHOD: A secondary mechanical hyperalgesia in the bilateral hindpaws of Sprague-Dawley rats was produced by the repeated injections of acidic saline into gastrocnemius. Botulinum toxin A (BTX-A(4) 4 U/kg, BTX-A(7) 7 U/kg) was administrated into same muscle 24 hours after a second injection of saline. The mechanical hyperalgesia was measured with withdrawal threshold to von Frey filament. The grade of muscle paralysis was evaluated with electrophysiology and the locomotor performance using inclined plane board. RESULTS: The mechanical hyperalgesia was significantly decreased from 5 days to 2 weeks in BTX-A(7) group in the injected side. The dose-dependent decreased amplitude of compound muscle action potential and reduced prevalence of endplate noise from the first day of botulinum toxin injection lasted for 4 weeks in both gastrocnemius. The maximum angle maintained at initial position on the inclined plane board did not change. CONCLUSION: Local muscular injection of botulinum toxin A reduced ipsilateral hyperalgesia dose-dependently in persistent muscle pain rat model without motor deficit. The antinociceptive mechanism of botulinum toxin might act at a local or peripheral rather than a systemic or central effect due to ineffectiveness of contralateral hyperalgesia. Clinically, botulinum toxin A might be useful for the treatment of local and referred pain of muscle origins.