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Bettina Hohberger, Carmen Jessberger, Franz Hermann, Matthias Zenkel, Antonio Bergua, Winfried Neuhuber; Circadian Rhythm of VIP in Chicken Intrinsic Choroidal Neurons. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4654.
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© ARVO (1962-2015); The Authors (2016-present)
Intrinsic choroidal neurons (ICN), one component of the autonomic neuronal regulation system of the eye, are decreased in glaucoma. Three targets of ICN are known: blood vessels, non-vascular smooth muscle cells (NVSMC) and choroidal melanocytes. Co-expression of vasoactive intestinal peptide (VIP) and neuronal nitric oxide synthase (nNOS) in ICN suggested that ICN can relax vascular smooth muscle and NVSMC, resulting in increased choroidal thickness. This might have an impact on choroidal accommodation, blood flow and intraocular pressure (IOP). As a circadian variation of blood flow and IOP was described in humans and birds, the aim of this study was to investigate a potential circadian rhythm of VIP, nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and nNOS in avian ICN.
Immunohistochemistry for VIP and nNOS and histochemical NADPH-d staining was performed in 12 whole-mount choroids of chicken, sacrificed at 8.00-9.30 a.m. or 8.00 p.m., respectively. Analysis of number and topography of ICN and their axons was performed. VIP concentrations in 18 choroids of chicken, sacrificed either in the morning or evening, were analysed using an ELISA (EIAab®, Wuhan, China).
(1) NADPH-d positive ICN showed no circadian rhythm (p>0.05; morning: 848.4±364.7; evening: 567.9±945.8). (2) nNOS positivity in ICN was stable throughout the day (p>0.05; morning: 721.8±404.9; evening: 1014.7±592.3). (3) Topography and number of nNOS positive ICNs correlated with NADPH-d positivity, accumulating temporo-cranially. (4) VIP positive ICN showed a circadian rhythm (p=0.018; morning: 239.17±113.9; evening: 550.83±245.7). (5) VIP positive ICNs accumulate temporo-cranially in the evening, whereas they were distributed more temporo/naso-cranially in the morning. At both daytimes axons of VIP positive ICNs crossed the whole choroid. In the evening, a dense network could be seen in temporo/naso-cranial regions, being much denser than in the morning. (6) By ELISA choroidal VIP displayed a significantly (p=0.014) higher concentration in the evening (227.89±112.6 pg/ml) as compared to the morning (140.39±49.7 pg/ml).
VIP positive ICNs accumulate near retinal regions of high visual acuity. Additionally VIP concentration varies during daytime, not regarding NADPH-d and nNOS. This suggests circadian influences on ocular circulation and regulation of IOP.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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