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Jiucheng He, Haydee E P Bazan; Mapping the entire nerve architecture and sensory neuropeptide distribution of rabbit iris. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4446. doi: https://doi.org/.
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To disclose the entire architecture and sensory neuropeptide content of rabbit iridal innervation.
Ten New Zealand albino rabbits were euthanatized and the whole irises were excised and fixed. The tissues were stained with antibodies against a neuronal-class β-tubulin III, calcitonin gene-related peptide (CGRP), substance P (SP), and vasoactive intestinal polypeptide (VIP) and whole-mount images were acquired to build a whole view of the iridal nerve architecture. To obtain the relative contents of the neuropeptides in the iris, after neuropeptide staining, the specimens were double stained with β-tubulin III. Relative nerve fiber densities for each fiber population were assessed quantitatively on the basis of whole mount view of the entire nerve architecture by computer-assisted analysis.
The iris nerves are extensions of the ciliary nerves. The thick nerves run in the iris stroma close to the anterior epithelia, forming 4-5 stromal nerve rings from the iris periphery to the pupillary margin. In the anterior surface, fine divisions derivate from the stromal nerves constitute a nerve network-like structure to innervate the epithelial cells, with the pupillary margin having the densest innervation. In the posterior side, the nerve bundles run along with the pupil dilator muscles in a radial pattern around the pupil. The morphology of iris nerves in both sides changes with the pupil sizes. Double staining showed that in the anterior epithelia, CGRP-positive nerve fibers constitute about 60%, while SP-positive nerves constitute about 30% of the total nerve contents. In the posterior side, CGRP-positive nerve fibers are about 75% of total nerve contents, while SP take up only 20%. In addition, there is a very small amount of VIP-positive nerve fibers (less than 1%).
This is the first study to show a three dimensional map of the entire iris nerve architecture. Considering the anatomical location, the high expression of CGRP and SP implies that these neuropeptides may play important role in the pathogenesis of anterior uveitis, glaucoma, cataracts and chronic ocular pain.
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