Effects of denervations on the acetylcholinesterase-containing and fluorescent nerves of the rat iris.

The thiocholine method for the demonstration of AChE-containing fibres and the formaldehyde-induced fluorescence technique for the visualization of adrenergic fibres were employed to study the innervation of the albino rat iris. The following denervations were performed in order to verify the origins of different nerve types: (1) extirpation of the ciliary ganglion, (2) extirpation of the superior cervical ganglion, (3) stereotactic coagulation of the ophthalmic division of the trigeminal nerve, and (4) all possible combinations of the above-mentioned procedures. The denervations disclosed three main types of AChE-containing nerves in the iris: (1) nerve fibres degenerating after ciliary ganglionectomy, (2) thick nerve bundles in the dilator region disappearing after trigeminal neurotomy, and (3) fibres remaining intact after any type of denervation. Cervical sympathectomy had no effect on AChE-positive fibres. Under electron microscope AChE activity could be seen in the axolemma both in unmyelinated and in myelinated fibres. All fluorescent fibres vanished after ipsilateral cervical sympathectomy. Most of these fibres also disappeared after trigeminal neurotomy and the remaining fibres degenerated after subsequent ciliary ganglionectomy. On the basis of the present findings, the following conclusions can be drawn: (1) Most AChE-containing fibres of the rat iris originate in the ciliary ganglion. (2) The majority of the myelinated sensory fibres of the rat iris also contain AChE. (3) There is no AChE in the adrenergic fibres of the rat iris. (4) All adrenergic fibres of the rat iris originate in the ipsilateral superior cervical ganglion, and (5) these fibres enter the iris along with both the long and short ciliary nerves.