Effects of Ciliary Ganglionectomy on Contractile Responses in the Dilator Muscle of the Rat Iris

Abstract

Effects of removing the ciliary ganglion (CGR) on contractile responses of the rat iris dilator muscle to agonists were examined and compared with those after removing the superior cervical ganglion (SCGR). Denervations were considered successful if the atropine or phentolamine-sensitive mechanical responses to transmural nerve stimulation were abolished. After CGR, muscle sensitivity to noradrenaline (NA) increased two to three times in terms of their ED50, whereas the ED50 for methoxamine did not change. The sensitivity of both the control and denervated dilator muscles to NA increased after treatment with 30μM cocaine, and resulted in similar ED50s. The content of NA in the whole iris decreased by about 27% after CGR. Maximal responses of the dilator muscle to NA and 5-hydroxytryptamine were significantly increased by CGR, but decreased by SCGR. These results indicate that sympathetic post-ganglionic nerves running through the CG and short ciliary nerves contribute about 27% of the total sympathetic innervation of the iris region. The CGR, therefore, induced a small presynaptic supersensitivity specific to NA. The non-specific increase in the maximal responses to agonists after CGR may be attributable to a parasympathetic denervation since sympathectomy by SCGR decreased the maximal responses.