Silver impregnation of intrinsic sensory innervation of rat iris in toto.

A silver impregnation technique (Linder, 1978) has been applied to whole mounts of the rat iris. The results suggest that only sensory fibres, both myelinated and non-myelinated, are stained. They disappear only after a trigeminal lesion and their distribution is different from that of catecholaminergic intrinsic fibres. Staining of the iris reveals a conspicuous pattern of innervation, characterised by a circular bundle and a thin plexus in the ciliary body, and by prominent bundles of fibres with a loose network of thin smooth fibres in the external part of the dilator plate and with a denser network in the central area. Nerve endings are seen on the dilator plate, in the sphincter as well as in the ciliary body. It is possible by a slight modification of the technique to stain myelinated and non-myelinated fibres separately. It results in a deep staining of the myelin while thin fibres are relatively clear. This method provides clear and reproducible staining of the nerves of the iris. It can be combined with various histochemical and immunocytochemical techniques. This will permit further studies to be made on the development of sensory and central nervous tissues, when grafted to the normal or the selectively denervated iris.