Existence Of The Neuropeptide Alarin In The Eye Of Various Species

Abstract

Purpose: : Alarin is a lately discovered neuropeptide of the galanin peptide family with vasoconstrictor acitivity in murine skin. In the eye, ocular blood flow and aqueous humor production are essential for ocular homeostasis and a pool of intrinsic and extrinsic neuropeptides is involved to fulfill this task. Alarin might be an additional regulatory peptide in these processes.

Methods: : Eyes of human (meeting the Declaration of Helsinki), mouse, and rat were processed for immunohistochemistry against alarin using affinity purified antibodies. Confocal laser-scanning microscopy was used for documentation and quantitative RT-PCR was performed to detect alarin mRNA expression in human eyes.

Results: : Alarin-like immunoreactivity (alarin-LI) was detected in corneal epi- and endothelium of human, mouse, and rat, as well as in the conjunctiva of mouse and rat. Alarin-LI was found in the iris of all the species investigated and, in humans, was concentrated around blood vessels. All three species showed distinctive alarin-LI in the non-pigmented epithelium of the ciliary body. In the retina of mouse and rat, maximum signals were detected in the outer nulear and opticus ganglion cell layer, whereas in humans a strong alarin-LI was found around retinal blood vessels and in intrinsic choroidal neurons (ICN). Quantitative RT-PCR in human revealed higher alarin mRNA expression in the choroid than retina.

Conclusions: : Alarin is widely distributed in the eyes of species investigated. The existence around blood vessels/ in ICN might indicate an involvement in ocular blood flow regulation. Alarin in the non-pigmented epithelium of the ciliary body might be involved in aqueous humor production.

Keywords: neuropeptides • neurotransmitters/neurotransmitter systems • anatomy