title: Subcutaneous administration of botulinum toxin A reduces formalin-induced pain.
abstract: 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<0.05) inhibited formalin-induced nociceptive behavior during phase 2 but not during phase 1 when administered 5 h to 12 days before formalin challenge. The onset of the antinociceptive effect started at 5 h after pre-treatment and this effect lasted for at least 12 days. BoNT-A (7 U/kg) also reduced edema. Consistent with the lack of effect in the formalin phase 1, BoNT-A, at 15 U/kg, had no effect on acute thermal nociception; no local muscle weakness was observed at this dose. Pre-treatment of rats with BoNT-A (3.5, 7 or 15 U/kg) all significantly reduced formalin-evoked glutamate (Glu) release. These results demonstrate that local peripheral injection of BoNT-A significantly reduces formalin-induced nociceptive behaviors with the absence of obvious muscle weakness. Such an antinociceptive effect of BoNT-A is associated with the inhibition of formalin-induced release of Glu (and/or neuropeptides) from primary afferent terminals.
authors.affiliation: Department of Biological Sciences, Allergan Pharmaceut Inc., RD-2C, 2525 Dupont Drive, PO Box 19534, Irvine, CA 92623, USA. cui_minglei@allergan.com
authors.forename: Minglei
authors.initials: M
authors.lastname: Cui
authors.forename: Sid
authors.initials: S
authors.lastname: Khanijou
authors.forename: John
authors.initials: J
authors.lastname: Rubino
authors.forename: Kei Roger
authors.initials: KR
authors.lastname: Aoki
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D019274:Botulinum Toxins, Type A / Q000627:therapeutic use*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004487:Edema / Q000188:drug therapy / Q000473:pathology; D005557:Formaldehyde; D018698:Glutamic Acid / Q000378:metabolism; D007266:Inhibition, Psychological; D007279:Injections, Subcutaneous / Q000379:methods*; D008297:Male; D009020:Morphine / Q000627:therapeutic use; D009043:Motor Activity / Q000187:drug effects; D009294:Narcotics / Q000627:therapeutic use; D009465:Neuromuscular Agents / Q000627:therapeutic use*; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy* / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D013997:Time Factors
chemical_list: D009294:Narcotics; D009465:Neuromuscular Agents; D005557:Formaldehyde; D018698:Glutamic Acid; D009020:Morphine; D019274:Botulinum Toxins, Type A