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Alexander Greif, Julia Wiedemann, Gopenath Thangaraj, Paul G. Layer; BDNF and Forskolin act on Retinal Development in a Ganglion Cell-free Novel Explant System of the Chick Embryo. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6290.
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After its retrograde transport from the optic tectum, BDNF is strictly required to ensure survival of ganglion cells in the vertebrate retina. Not much is known, however, about i) possible further functions of this cytokine on development of the other retinal layers, and ii) whether such functions could be independent of the presence of ganglion cells. These two topics were approached by applying a novel explant system (1), where ganglion cells die off quickly in vitro, but otherwise differentiation of the retina pursues normally for 2-3 weeks.
The preparation of explants from E6 chicken embryonic retina has been described (see ref.). At onset of cultures, explants were supplied with 10 ng/ml BDNF and/or 5 µM forskolin, a plant diterpene increasing intracellular levels of cAMP. Cellular and laminar differentiation were documented immunohistochemically, using cell type-specific antibodies, e.g. Brn3a for ganglion cells, choline acetyltransferase (ChAT) for cholinergic amacrine cells, CERN 901 for rhodopsin; cell proliferation was studied by BrdU uptake and apoptosis by TUNEL assay.
Treatment with BDNF or forskolin led to an extended survival of ganglion cells, as shown by Brn3a. BrdU studies showed strongly increased rates of proliferation in the future INL and ONL. Apoptosis was reduced in the GCL, but not much in other retinal layers. Noticeably, differentiation of the inner plexiform layer (IPL) was much advanced, as documented by ChAT. Similarly advanced was the differentiation of rod photoreceptors. Some of these effects were particularly pronounced after combination of both agents.
This study provides evidence that BDNF not only supports the survival of ganglion cells, but rather has pronounced retina-internal functions, e.g. IPL and photoreceptor differentiation. Further, it also shows that these processes can occur in the absence of ganglion cells.
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