Galanin receptor detection in the human eye: first results

Abstract

Purpose: The neuropeptide galanin (GAL) is widely distributed within intrinsic and extrinsic sources supplying the eye. It is involved in regulation of the vascular tone, thus important for ocular homeostasis. Since the presence/distribution of its receptors is unknown, we here screen for the presence of the various GAL receptors in the human eye.

Methods: Meeting the Helsinki-Declaration, human eyes (n=6; 45 -83 years of age, of both sex, post mortem time 10-19 hrs) were obtained from the cornea bank and prepared for immunohistochemistry against GAL receptors 1 to 3 (GALR1-GALR3). Over-expressing cell assays served as positive controls and confocal laser-scanning microscopy was used for documentation.<br />

Results: In the cornea, GALR1-GALR3 were detected in basal layers of the epithelium, stroma, endothelium, as well as in adjacent conjunctiva. In the iris, GALR1-GALR3 were detected in iris sphincter, dilator and iris vessels. In the ciliary body, GALR1-GALR3 were detected in ciliary muscle, with highest signal for GALR3, and in ciliary body epithelium (GALR1 >>GALR3> GALR2), while ciliary body vessels were positive for GALR3 only. In the retina, GALR1 was present in fibers of the IPL/NFL, many cells of the INL and only few cells of the ONL. GALR3 and GALR2 were present in few neurons of the INL, while GALR2 was also found surrounding retinal vessels. In the choroid, GALR1-3 were detectable in nerve fibers surrounding vessels and in intrinsic choroidal neurons.

Conclusions: This is the first report of the various GALRs in the human eye. While the presence of GALR in cornea is enigmatic, the detection of GALR1-3 in ocular vessels (iris, choroid) highlights the role of GAL in vessel dynamics. High GALR3 presence in ciliary body vessels might indicate importance for aqueous humor production, whereas retinal GALR distribution might contribute to signal transduction.