Ultrastructural analysis of tyrosine hydroxylase-, substance P-, and calcitonin gene-related peptide-immunoreactive nerve fibers in the rat iris.

Different patterns of distribution of chemically different nerve fibers in the rat iris were studied by immunoelectron microscopy. The iris was immunostained either singly for tyrosine hydroxylase (TH), or doubly for substance P (SP) and calcitonin gene-related peptide (CGRP), or triply for TH, SP and CGRP. TH-positive fibers were distributed in the stroma near the iris dilator and within the iris sphincter. SP/CGRP-positive fibers were found mainly in the anterior half of the stroma and partly in the stroma close to the sphincter, but were hardly ever seen in the stroma near the dilator or within the sphincter. Fibers neither positive for TH, SP nor CGRP were observed in the stroma near the dilator and within the sphincter.