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MP Feldkaemper, E Burkhardt, F Schaeffel; Expression Patterns of the Glucagon Receptor in the Chick Retina, With and Without Intravitreal Application of a Glucagon Agonist . Invest. Ophthalmol. Vis. Sci. 2002;43(13):205.
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Purpose: Glucagon amacrine cells respond to growth-modulating visual stimuli with alterations in the synthesis of the transcription factor ZENK. Moreover, the amount of retinal glucagon mRNA increases during treatment with positive lenses and glucagon itself is an inhibitor of lens-induced myopia. However, the distribution and regulation of glucagon receptors in the retina are not known. Methods:(1) In situ hybridization with digoxigenin labeled riboprobes was used to demonstrate the cellular localization of glucagon receptors in the retina of 14 to 21 day-old chicks. Kidney and liver tissue served as a positive control for receptor detection. (2) Six chicks were intravitreally injected every other day with 2.5 nmol of the glucagon agonist Lys17,18,Glu21-glucagon into one eye and saline into the contralateral eye. At this concentration, the agonist inhibits lens-induced myopia development completely. After 6 days, receptor expression in both eyes was compared. Results:(1) Glucagon receptor mRNA expression was found in about 50% of the cells in the ganglion cell layer. Moreover, receptor expression was demonstrated in many cells in the inner nuclear layer. (2) The glucagon agonist Lys17,18,Glu21-glucagon led to a prominent reduction of glucagon mRNA labeling in 5 of 6 chicks. Conclusion: Even though only about 1 percent of the amacrine cells are glucagonergic, glucagon receptor expression was demonstrated in many cells in the inner nuclear layer, most of them presumably amacrine cells, and in the ganglion cell layer. These cells are, therefore, possible sites for glucagon action and perhaps also for eye growth regulation. The glucagon agonist regulates glucagon receptor expression through a negative feedback loop, a regulation which has already been described for other tissues.
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