Glycerol gangliotomy of the second dorsal cervical root in rats: An experimental study to evaluate a minimal invasive approach for the treatment of the chronic cervicogenic headache

Glycerol is a known agent in the therapy of chronic tic douloureux. It has been used for about 20 years in percutaneous, retrogasserian minimal-invasi ve rhizotomy, although the pharmacological mechanism of the pain relief inv olved remains unclear. To investigate glycerol treatment as a possible repl acement for invasive approaches in the therapy of chronic cervicogenic head aches, we performed an experimental study on the pathomorphologic action of anhydrous glycerol injection into the second upper cervical dorsal root ga nglion (DRG) of rats. Glycerol injections into the second cervical ganglion were investigated light- and electron-microscopically in a series of 40 ra ts for survival times of up to 30 days. We detected an unspecific overall e ffect on sensory neurons and satellite cells, as well as on myelinated and unmyelinated axons and Schwann cells. This could be detected after 5 days a nd sometimes led to degeneration of most of the neurons. Contralateral sali ne injections as a control showed no morphological effects. The loss of aff erent fiber connections to the posterior horn of the myelon could be detect ed by immunohistochemical labeling of reactive astrocytes. Our results show a glycerol-induced deterioration of the cytoarchitecture of the neurons an d their glial satellite cells. The effects on the ganglion cells appear to have been mediated by membrane disturbances and loss of glial integrity. Th ese observations are contrary to previously reported results indicating the specific effect of glycerol on thin myelinated sensory axons.