title: Study of crotoxin on the induction of paralysis in extraocular muscle in animal model.
abstract: OBJECTIVE
  Crotoxin is the major toxin of the venom of the South American rattlesnake Crotalus durissus terrificus, capable of causing a blockade of the neurotransmitters at the neuromuscular junction. The objective of this study was to appraise the action and effectiveness of the crotoxin induced paralysis of the extraocular muscle and to compare its effects with the botulinum toxin type A (BT-A).
  
  
  METHODS
  The crotoxin, with LD50 of 1.5 µg, was injected into the superior rectus muscle in ten New Zealand rabbits. The concentration variance was 0.015 up to 150 µg. Two rabbits received 2 units of botulinum toxin type A for comparative analysis. The evaluation of the paralysis was performed using serial electromyography. After the functional recovery of the muscles, which occurred after two months, six rabbits were sacrificed for anatomopathology study.
  
  
  RESULTS
  The animals did not show any evidence of systemic toxicity. Transitory ptosis was observed in almost every animal and remained up to fourteen days. These toxins caused immediate blockade of the electrical potentials. The recovery was gradual in the average of one month with regeneration signs evident on the electromyography. The paralysis effect of the crotoxin on the muscle was proportional to its concentration. The changes with 1.5 µg crotoxin were similar to those produced by the botulinum toxin type A. The histopathology findings were localized to the site of the injection. No signs of muscle fiber's necrosis were seen in any sample. The alterations induced by crotoxin were also proportional to the concentration and similar to botulinum toxin type A in concentration of 1.5 µg.
  
  
  CONCLUSIONS
  Crotoxin was able to induce transitory paralysis of the superior rectus muscle. This effect was characterized by reduction of action potentials and non-specific signs of fibrillation. Crotoxin, in concentration of 1.5 µg was able to induce similar effects as botulinum toxin type A.
authors.affiliation: Strabismus Service, Universidade Federal de Minas Gerais - UFMG, Belo Horizonte (MG), Brazil. gbarrosribeiro@gmail.com
authors.forename: Geraldo de Barros
authors.initials: Gde B
authors.lastname: Ribeiro
authors.forename: Henderson Celestino de
authors.initials: HC
authors.lastname: Almeida
authors.forename: David Toledo
authors.initials: DT
authors.lastname: Velarde
authors.forename: Maria Lygia Vaz de Melo
authors.initials: ML
authors.lastname: Sá
mesh_terms: D000818:Animals; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage / Q000494:pharmacology*; D003439:Crotoxin / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D056965:Injections, Intraocular; D023421:Models, Animal; D009465:Neuromuscular Agents / Q000008:administration & dosage / Q000494:pharmacology*; D009469:Neuromuscular Junction / Q000187:drug effects*; D009801:Oculomotor Muscles / Q000187:drug effects* / Q000473:pathology; D009886:Ophthalmoplegia / Q000139:chemically induced*; D011817:Rabbits
chemical_list: D009465:Neuromuscular Agents; D003439:Crotoxin; D019274:Botulinum Toxins, Type A