Influence of Vitamin a on The Regeneration of Eye from Damaged Retinal Pigmented Epithelium Cells in Tadpoles of the toad, Bufo melanostictus

In the present study complete eye was found to regenerate from a small part of retinal PECs in external gill stage tadpoles of Bufo melanostictus. More than half of the eye balls (including lens) were removed keeping a small part of neural retina intact in 40 tadpoles of external gill stage. Half (20) of the operated tadpoles were reared in tap water which served as control and remaining half (20) were reared in vitamin A (15 IU/ml) solution for five days and then transferred to water upto the day of termination of experiment (10th day after operation). Differences in retinal differentiation and the appearance of the new lens were noted between the two groups of tadpole. Although regeneration of eye was found in the both untreated as well as vitamin A treated tadpoles. However, vitamin A increased the percentage of eye regeneration. In the tadpoles of control group eye regeneration occurred only in 4 (20%) out of 20 whereas, it was in 16 (80%) out of 20 tadpoles of vitamin A treated group of the same age. Morphological and histological study revealed that newly regenerated complete eyes were similar to that of normal functional eyes.Similar experiment was performed on mature tadpoles of 5-toe stage. Vitamin A could induce eye regeneration in 12 (60%) out of 20 but regenerated eyes were found smaller in size. However, eye regeneration was not reported even in a single operated 5-toe stage tadpoles of untreated control group. This experimental model is the first to show that vitamin A can induce the developmental potency of neural retinal pigmented epithelial cells to regenerate not only the lost retinal cells but also the complete eye. Thus the results provide the basis for a new hypothesis concerning cytodifferentiation.