Histologic Analysis of the Myotoxic Change by Bupivacaine and Ricin mAb 35 on Extraocular Muscle in Rabbits

ABSTRACT

PURPOSE: To analyze the acute histologic change of extraocular muscles (EOM) induced by injection of bupivacaine or Ricin mAb 35. METHODS: The superior rectus and inferior rectus of white rabbits were injected with either bupivacaine (0.4 mg in 0.3ml) or Ricin mAb 35 (0.2 micro gram/kg in 0.3 ml). One, two, and four weeks after injection, the rectus muscles were harvested and the post-injection changes were histologically analyzed. RESULTS: Both the orbital and the global layers of EOM showed myotoxic changes induced by bupivacaine and Ricin mAb 35. However, the inflammation and destruction of myofiber by bupivacaine injection were localized to the injection site, whereas changes induced by Ricin mAb 35 were diffuse. Regenerating myofibers with a central nucleus were found at one week after myotoxin injection. Four weeks after injection, the acute changes induced by these two toxins were much recovered with prominent myofiber regeneration. Bupivacaine-induced myotoxic change was more prominent in the global layer in contrast to the more prominent damage in the orbital layer induced by Ricin mAb 35. CONCLUSIONS: We found that EOM have a superb ability to recover from the acute injury induced by bupivacaine or Ricin mAb 35 and that the two myotoxins cause unique damage including the predilection of muscle layers and the duration for which the damage persisted. Further investigation into the functional change during recovery from the myotoxin-induced injury of EOM is needed.