Calcitonin Gene-related Peptide (CGRP) Immunoreactive Sensory Nerves in the Human and Guinea Pig Uvea and Cornea

The presence of calcitonin gene-related peptide (CGRP) immunoreactive nerves in the uvea and cornea of human and guinea pig eyes was evaluated using immunohistochemical techniques. CGRP immunoreactivity was found in thin, varicose nerve fibers in both species. Most of the fibres were localized in the ciliary body, and were mainly associated with blood vessels. In the human ciliary body, a moderate number of CGRP immunoreactive nerves were also seen in the ciliary muscle. In the iris and cornea, CGRP immunoreactive fibres were relatively uncommon. In the iris, they were mostly found associated with blood vessels, while in the cornea they were seen sub-epithelially or as free nerve endings in the epithelium. In the trigeminal ganglion, small sized ganglion cells displayed CGRP immunoreactivity. About 40% of all ganglion cells were immunoreactive nerves in the guinea pig, while sympathetic denervation did not change the staining pattern of CGRP immunoreactivity. The present findings, together with previous physiological data, suggest that CGRP might play a role in the regulation of the blood flow, aqueous humour dynamics, and neurogenic inflammation, not only in experimental animals but also in man.