Purchase this article with an account.
Y.-W. Suh, M. J. Chang, S.-H. Kim, C.-S. Uhm, Y. A. Cho; The Ultrastructural Changes of Palisade Nerve Endings in the Exotraocular Muscle After Injection of Botulinum Toxin. Invest. Ophthalmol. Vis. Sci. 2009;50(13):654.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study was to investigate the ultrastructural changes of palisade nerve endings after the injection of botulinum toxin A (Botox) into the extraocular muscles.
Under the general anesthesia, the medial and superior recti muscles of 12 cats (24 eyes) were exposed. A dose of 5 IU of Botox (0.1 mL) was injected into the exposed extraocular muscles of one eye and 0.1 ml of normal saline was injected into the muscles of the other eye. The injection site was about 10 mm proximal to the myotendinous junction to minimize mechanical trauma of palisade nerve endings. The myotendinous junctional area was harvested at 1, 4 and 12 weeks after the injection, 4 cats at each time period. The samples were examined under electron microscope. The myotendinous junction of 4 normal cats were also examined as a normal control.
There was no morphological difference between normal control group and saline injection group. The proximal portion of palisade nerve endings in control group was encapsulated structure containing collagen, myelinated and unmyelinated nerve fiber. At distal palisade endings, myelinated fibers were absent, and encapsulated nerve endings contained unmyelinated fiber and collagen. At pre-terminal region, the capsular structure became incomplete. However, axon of unmyelinated fiber were completely covered with Schwann cell. In botox injection group, separation of myelin sheath, increase of neurofilament in axons of myelinated and unmyelinated nerve fiber were observed 1 week after injection, which persisted to 12 weeks. Around terminal nerve endings, incomplete Schwann cell with axonal exposure were found, and fibroblast-like change of Schwann cells were also occurred. At 12 weeks, palisade endings which was not related to the muscle fiber due to Botox induced muscle atrophy were also found.
Botulinum toxin injected into the extraocular muscle induced ultrastructural changes of palisade nerve endings. Those alteration can influence proprioception of the extraocualr muscles. The possibility that those changes can diminish proprioception of the extraocualr muscle should be considered when botulinum toxin is used for the treatment of strabismus.
This PDF is available to Subscribers Only