Elevated levels of secretoneurin in the rabbit aqueous humor in response to formaldehyde irritation

Abstract

The neuropeptide secretoneurin has been detected in the anterior segment of the eye for the first time. The elevation of secretoneurin in formaldehyde-treated eyes may be induced by an enhanced release from the iris/ciliary body complex, as formaldehyde is known to provoke neurogenic inflammation in the anterior segment via release of sensory peptides originating from the trigeminal ganglion. This is why our results indicate a sensory origin of secretoneurin in the eye.

Secretoneurin in the Peripheral Ocular Innervation

“…The demonstration of nerve fibers in the iris/ciliary body complex together with the expression of SgII mRNA in nonpigmented ciliary epithelial cells 60,61 completes the picture of the innervation pattern in this tissue. SN has been detected in significant amounts in the rabbit 41 and human aqueous humor (manuscript submitted) indicating either secretion from the nonpigmented ciliary epithelium and/or release from nerve fibers of the iris/ciliary body complex. Sensory neuropeptides in the iris/ciliary body complex are well known to provoke the irritative response in the eye, which represents a classic model for neurogenic inflammation in lower mammals (for a review, see Ref.…”

“…29 SN may be involved in the neurogenic inflammation of the eye, as this represents also a process with the function of neurons to maintain homeostasis in the face of irritation to the tissue, as SN is a constituent of C-fibers in the rat iris/ciliary body complex, which are known to mediate the response and as the peptide is released by formaldehyde irritation into the rabbit aqueous humor. 41 Another main finding that may be clinically relevant concerns the clear association of SN-immunoreactive nerves with blood vessels. Very recently a potent angiogenic effect of SN comparable to that of VEGF was reported in the eye.…”

“…First, topical application of formaldehyde elevates the concentration of SN in the rabbit aqueous humor. 41 This kind of irritation is well known to provoke neurogenic inflammation exclusively by releasing sensory peptides that derive from the trigeminal ganglion, in particular substance P (SP) and calcitonin gene-related peptide (CGRP) (for a review, see Ref. 42).…”