Effect of OnabotulinumtoxinA on Intramural Parasympathetic Ganglia: An Experimental Study in the Guinea Pig Bladder

Purpose: We investigated whether onabotulinumtoxinA injected in the bladder would affect preganglionic parasympathetic nerve endings in intramural ganglia. Materials and Methods: Guinea pig bladders were injected with 5 U of botulinum toxin. At 24 hours bladders were collected and processed for immunohistochemistry using tyrosine hydroxylase, and intact and cleaved SNAP-25. To identify the different populations of affected fibers coursing the ganglia we performed double immunoreactions for cleaved SNAP-25 and VAChT, TH or CGRP. Results: VAChT immunoreactive fibers were identified in axons and varicosities of presynaptic to postganglionic parasympathetic neurons. Those fibers were also immunoreactive to SV2 and SNAP-25. The rare CGRP and TH immunoreactive fibers coursing in the ganglia did not express SV2 or SNAP-25. After onabotulinumtoxinA injection the cleaved form of SNAP-25 was abundantly expressed in parasympathetic fibers. Conclusions: Botulinum toxin injection in the bladder wall affects preganglionic parasympathetic nerve terminals. This could contribute to the strong effect of botulinum toxin on bladder smooth muscle activity.