[An immunoelectron microscopic study of distribution and density of nerve fibers innervating the rat iris]

We studied the sympathetic, parasympathetic and sensory nerve fibers in the rat iris using electron microscopic immunohistochemical techniques. Antibodies raised against tyrosine hydroxylase (TH), substance P (SP), and calcitonin gene-related peptide (CGRP) were used alone or combined together to characterize the nerve fibers. The ratios of the TH-positive, SP/CGRP-positive and TH/SP/CGRP-negative fibers were 18%, 37%, and 45% in the anterior half of the dilator stroma, 11%, 3%, and 86% in the posterior half of the dilator stroma, 45%, 26%, and 29% in the sphincter stroma, and 23%, 1%, and 76% in the sphincter muscle layer. These results confirm that the sympathetic and parasympathetic fibers doubly innervate both rat iris sphincter and iris dilator muscles, whereas sensory nerve fibers innervate mainly the stroma.