Calcitonin gene-related peptide immunoreactive nerve fibers in the rat conjunctiva

Calcitonin gene-related peptide (CGRP) immunoreactive nerve fibers were studied in the rat conjunctiva by using indirect immunohistochemistry. Their origin was evaluated in a series of experiments where the animals were denervated by electrocoagulating the two first branches of the trigeminal nerve or by surgically extirpating the superior cervical ganglion. The CGRP-immunoreactive nerve fibers were seen mainly as thin varicose fibers in the epithelium and in the stroma. Many of the stromal fibers showed no apparent destination. However, CGRP-immunoreactive fibers were commonly found in association with stromal blood vessels, the smooth muscle of Müller, and the meibomian glands. Approximately 40% of the ganglion cells in the trigeminal ganglion were immunoreactive to CGRP. In the superior cervical ganglion, a few CGRP-immunoreactive fibers were seen although the ganglion cells were negative. After trigeminal denervation, all the epithelial and most of the stromal CGRP-immunoreactive nerve fibers disappeared. Sympathectomy had no effect on the presence of the CGRP-immunoreactive fibers. These observations indicate that most of the CGRP-immunoreactive nerve fibers in the rat conjunctiva are sensory nerves originating in the trigeminal ganglion. A few of the demonstrated fibers are, however, resistant to the sensory denervation and may be parasympathetic in their origin.