Retinal cell death occurs in the absence of retinal disc invagination: Experimental evidence in papaverine-treated chicken embryos

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Abstract
In an attempt to clarify the relationship between the presence of retinal cell death and the invagination of the optic vesicle, we have tested the occurrence and cytological characteristics of the retinal necrotic areas in the embryonic chicken after the administration in ovo of papaverine. Papaverine, a Ca2+ antagonist, was found to prevent the invagination of the optic vesicle. All embryonic retinae presented two distinct necrotic areas. However, these areas of cell death appeared abnormally located in the experimental, uninvaginated retina. One area was located at the transition between the retinal disc and the ventral wall of the optic vesicle; a second area was located in the dorsal wall of the optic vesicle, close to the optic stalk. We suggest that these necrotic areas represent the normal necrotic areas, should the invagination of the retinal disc have taken place. Retinal cell death appears to beprogrammed; it occurs whether the retinal disc invaginates or not. Cell death appears, in this experimental model, as a natural marker giving evidence that the embryonic retinal cells move from the optic stalk into the invagination retinal disc during normal eye cup formation. In addition to the uninvaginated optic vesicle the lens placode failed to invaginate in 45% of the cases, forming a lens vesicle in 55% of the remaining cases. This suggests that the two processes of invaginate in 45% of the cases, forming a lens vesicle in 55% of the remaining cases. This suggests that the two processes of invagination are governed by a different set of factors.