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F. Schroedl, M. E. De Stefano, A. Brehmer, W. L. Neuhuber, D. Nickla; On the Way to the Denervated Eye as a Key for Understanding the Intrinsic Choroidal Innervation: First Results. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1310.
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Autonomic input to the choroid regulates blood flow (and thereby may influences IOP), however, its role in other possible processes such as choroidal thickness changes in response to defocus is unknown. The aim of this study was to eliminate extrinsic autonomic innervation, as a basis for studies to determine extrinsic versus intrinsic control of ocular homeostasis.
In adult chickens, transections of the sympathetic pathway via lesioning the superior cervical ganglion (SCG), and both parasympathetic pathways via lesioning the ciliary ganglion (CG), and the preganglionig input to the pterygopalatine ganglion (PPG), were performed. IOP (n=4) was measured in both eyes using a Tonopen at various intervals. 9 days after the transections, immunohistochemistry for nNOS, VIP, CGRP, Somatostatin (SOM), ChAT, TH and VMAT2 was done in choroids, PPG and SCG in experimental and control birds.
Immunohistochemistry shows almost complete absence of SOM and TH-positive fibers in the ipsilateral choroid, indicating a loss of much of the SCG and CG input. A few ChAT-positive fibres remained in nasal parts of the choroid, presumably originating from intact ChAT/VIP-positive PPG neurons. There was also an increase in CGRP-positive fibers in ipsilateral ciliary nerves. The VIP/nNOS-positive intrinsic choroidal neurons (ICNs) remained unaffected. In ipsilateral PPG there was a notable loss of SOM-positive boutons around PPG neurons; it otherwise appeared normal. Because SOM is not found in neurons of the PPG and SCG, these boutons presumably stemmed from choroid neurons of the CG.Both eyes showed a significant decrease in IOP that occurred within 7 days of the surgery (post-surgery minus pre-surgery; ipsilateral and contralateral, respectively: -5.8 and -2.7 mm Hg; p<0.05). By day 10, the IOP of the experimental eyes had increased (11.2 vs 7.4 mm Hg; p<0.01) but were still lower than pre-surgery (p=0.05), while the fellow eyes had returned to normal.
Deafferenting the PPG did not result in loss of staining in the neurons over the 9 days. The loss of the SOM-positive boutons however, indicates an interganglionic input from the CG. There was no loss of ICNs, and a possible intact input from the PPG. The ipsilateral rebound toward normal IOP might be mediated by primary afferent fibres (via CGRP) or ICNs. This technique has potential for studying the functional attributes of these choroidal inputs.
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