Chapter 4 - The Ciliary Body: A Potential Multifaceted Functional Neuroendocrine Unit

Abstract

Publisher Summary The Ciliary Body (CB), the site of aqueous humor secretion, is comprised of a bilayered secretory polarized neuroepithelium, the Pigmented (PE) and the Non-Pigmented (NPE) Ciliary Epithelium (CE), overlapping the ciliary muscle and stroma containing blood vessels. Both epithelial cell layers of the CE and the iris share a common embryological origin with the multiple cell layers of the retina and with the Retinal Pigment Epithelium (RPE). These tissues derive from the optic cup during development as four distinct structures: the iris, the CB, the retina and the RPE. The CE is formed at the rim of the optic cup, whereas the retina and RPE are formed around the optic cup. The PE cell layer of the CE is continuous with the RPE, and the NPE cell layer is related to the neural retina. The expression of neuroendocrine peptides in the CE is of particular interest, since many of them are restricted to neuroendocrine cells and tissues around the body. Neuropeptides can function as neurotransmitters, neurohormones, or neuromodulators depending of the distance and effect mediated by the neuropeptide. Their expression in the CE has been confirmed by the detection of their mRNA, by conventional RT-PCR or by Northern blotting analysis, and by radioimmunoassay. Further analysis by indirect immuno-fluorescence had also helped to verify their cellular distribution along the CE.