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Jiucheng He, Thang Luong PHAM, Haydee E P Bazan; Comparative nerve architecture and CGRP content between rat and guinea pig corneas. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3950.
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Corneal innervation in both rat and guinea pig models have been extensively investigated, but no studies have provided an entire map of their nerve architecture or the content of one of the most abundant neuropeptides, calcitonin gene-related peptide (CGRP). We here used our modified technique of immunofluorescence and imaging to compare the anatomic features and total CGRP nerve content between these two animal models.
Adult albino rats and guinea pigs of both genders were euthanized, and the whole corneas were excised and fixed. The corneas were stained with the primary monoclonal rabbit anti-PGP9.5 antibody, and whole-mount images were acquired to build an entire view of the corneal nerve architecture. To obtain the relative content of CGRP, the specimens were double stained with monoclonal mouse anti-CGRP antibody. To obtain the transected view, the same corneas were cryosectioned. Relative nerve fiber densities for each fiber population were assessed on the basis of a whole mount view of the entire nerve architecture by computer-assisted analysis.
There was no significant difference in both the shape and the number of thick stromal nerves between the corneas of rats (18.7±2.4, n=10 eyes) and guinea pigs (19.3±2.36, n=8 eyes). However the shape and density of subbasal nerves were different between the two animals. In the rat, the subbasal bundles run as long and straight branches towards the center of the cornea, while in the guinea pig, the subbasal bundles are short and scattered. Subbasal nerve density of central cornea, calculated as the percentage of total area, was significantly higher (p<0.05) in the rat (21.76 ± 1.94%, n=10 eyes) than that in the guinea pig (11.46±1.75%, n=8 eyes). Nerve terminals budding from the bundles, calculated as the number of terminals/mm2, were also greater in the rat (831±57) than in the guinea pig (663±50). Double staining showed that in the central cornea CGRP-positive nerve fibers in the rat (47.62±3.51%) were significantly higher (p<0.05) than those in the guinea pig (10.81±2.28%).
Our results indicate that corneal epithelial innervation of the two animals have a different morphology and density. While the rat looks more similar to the human and mouse corneas, the guinea pig has a different architecture and distribution of CGRP. These differences need to be considered when extrapolating results from animal models to humans.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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