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X. Zhu, Y. Liu, J. Wallman; Glucagon Increases Choroidal Thickness of Chick Eyes by Acting on the Retinal Pigment Epithelium . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3338.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Chick eyes compensate rapidly for imposed myopic or hyperopic defocus by changing both the choroidal thickness and the rate of ocular elongation in appropriate directions. Because glucagonergic amacrine cells show opposite modulation of immediate early gene expression to wearing positive and negative lenses (Fischer et al., 1999), and glucagon and its antagonist modulate both choroidal thickness and ocular elongation (Zhu et al., ARVO 2001; Feldkaemper and Schaeffel, 2002), glucagon may be an important signaling molecule in emmetropization. In particular, the abundance of glucagon receptors in the Retinal Pigment Epithelium (Koh and Chader, 1984; Buck et al., 2004) raises the possibility that glucagon is an output signal from the retina to the RPE. We asked whether the effect of glucagon on choroidal thickness requires the RPE. Methods: To maximize our opportunity to see choroidal thickening, we had chicks wear diffusers over both eyes (except for a small open sector in each) for 3 days so that their choroids were thinned. Then eyes were hemisected to make eyecups with the retina removed, in some cases leaving the RPE attached to the choroid, in others removing the RPE. Eyecups were cultured in L–15 medium with or without glucagon (10 µM). Choroidal thickness of eyecups was measured using A–scan ultrasound after 4 hrs of incubation. Results: The thickness of choroids in cultured eyecups could be measured reliably (SD from repeated measurements: 9 µm). In eyecups cultured with the RPE attached, 14 out of 17 choroids incubated with glucagon were thicker than the fellow choroids without glucagon, compared to 4 out of 9 choroids in eyecups without the RPE, a significant difference (Chi–square = 3.97, p < .05). Furthermore, the amount of choroidal thickening caused by glucagon compared to the eyecup of the fellow eye was significantly greater in the pairs of eyecups incubated with the RPE (250 ± 14 µm vs. 201 ± 14 µm [Mean ± SEM], p < .05), but not in those incubated without the RPE. Conclusions: Glucagon appears to modulate choroidal thickness by acting through the RPE.
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