Subcutaneous administration of botulinum toxin A reduces formalin-induced pain

Botulinum toxin type A (BoNT-A) produced by the bacterium Clostridium botulinum is a potent inhibitor of acetylcholine release in the neuromuscular junction and has been used to treat many disorders related to excessive muscle contraction. However, BoNT-A has recently been used in pain therapy to treat myofascial pain, low back pain and various types of headaches, including migraine. The purpose of this study is to investigate the antinociceptive effect of BoNT-A and its underlying mechanism in the rat formalin inflammatory pain model. BoNT-A (3.5, 7, 15 and 30 U/kg) or vehicle was administered to the plantar surface of the right hindpaw of male Sprague-Dawley rats. BoNT-A dose-dependently (P