Urocortin in the chicken eye: distribution and origin

Abstract

Purpose : Neuroregulatory peptides are important contributors in ocular homeostasis, and fulfill multiple functions. The neuroregulatory peptide urocortin-1 (UCN) has been recently identified in human eye tissue, but its exact role is unclear. To establish a possible animal model, in which UCN function can be studied, we here screen the chicken eye for the presence of UCN-innervation including possible sources of ocular UCN.

Methods : Chicken eyes and cranial autonomic ganglia (pterygopalatine ganglion, PPG; ciliary ganglion, CIL; superior cervical ganglion, SCG) were prepared for immunohistochemistry of UCN, neuronal nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), and vesicular monoamine-transporter 2 (VMAT2). For documentation, confocal laser-scanning microscopy was applied

Results : In the chicken anterior eye, UCN was detected in corneal epi- and endothelium and stromal keratinocytes. Few UCN+ stromal nerve fibres were present. In contrast in the choroid, numerous UCN+ nerve fibres were detected within the ciliary nerves, most of which lacking nNOS immunoreactivity, while few co-expressed nNOS. Many stromal choroidal nerve fibres were UCN+, but lacked nNOS, VIP, or VMAT2. UCN immunoreactivity was not observed in perivascular nerve fibers and intrinsic choroidal neurons lacked UCN. In cranial autonomic ganglia, UCN-immunoreactivity was expressed in numerous neurons of the SCG and in small and large neurons of the CIL, but was not detectable in the PPG

Conclusions : UCN is a neuroregulatory peptide in the chicken eye. While its function in the cornea is not clear, the lack of UCN in the vascular supply and its presence in choroidal stroma suggests an impact for stromal non-vascular smooth muscle cells. Since intrinsic choroidal neurons and neurons of the PPG lacked UCN, and while a co-localization with VMAT2 (SCG-origin) was not detected, the main input of choroidal stromal UCN is thought to originate from the UCN-positive neurons in the CIL. Future functional studies will clarify the role of UCN in ocular homeostasis.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.