Effects of botulinum toxin type A on the superior cervical ganglia in rabbits

Sympathetic neurolysis is very important in treating chronic pain, especially sympathetically maintained pain. However, conventional neurolytic agents destroy nerve fibers nonselectively and may leave serious complications. Botulinum toxin type A (BTA) selectively acts on cholinergic nerves and inhibits the secretion of acetylcholines (Ach) at the involved nerve endings. Because cholinergic nerves also exist in autonomic ganglia, it is believed that BTA has pharmacological effects on sympathetic ganglia. In this study, after the administration of BTA into the superior cervical ganglion (SCG) in rabbits, the possible clinical use of BTA as a neurolytic agent was evaluated. In the normal saline-treated control group, miosis was not observed in all 12 rabbits. However, in the BTA-treated group, 15 cases of miosis were observed among 40 rabbits (37.5%). Furthermore, BTA induced miosis in a dose-dependent manner, though onset time and duration of miosis varied. Mean time of onset and duration were 1.8 days and 5.3 weeks, respectively. By eosin-hematoxylin (H&E) staining finding, no significant chronological and histological changes between the control and the experimental groups were observed. In conclusion, BTA was found to have a sympathetic ganglion blocking effect over a period of more than 1 month without causing considerable pathologic changes in the SCG, that is, this toxin may be used in the case of sympathetically maintained pain control as a sympatholytic.