All life on earth exists under rhythmically changing cycles. The light/dark cycle is the most important cycle for retinal activity, circadian rhythms have been reported for several molecules and retinal function. The light is the most important cue to synchronize the endogenous clock with the environment and it is an essential stimulus for a correct development of retinal circuitry. The purpose of this project was to analyze the relationship between light experience, during the critical period of retinal development, and circadian rhythms in the rat retina.

Three experimental groups of animals were used. Control animals, dark-reared animals born and raised in complete darkness, and recovery animals born and raised in complete darkness and then returned to normal conditions. The levels of different molecules were analyzed at different time of the day by immunohistochemistry and Western Blot technique. We also analyzed retinal function by electroretinogram (ERG) technique.

In dark-reared animals, the expression of several molecules involved in rod bipolar pathway, was modified. In particular, in dark-reared animals, the expression of Tyrosine Hydroxylase is drastically reduced and the Parvalbumin immunoreactivity, in AII amacrine cells, and retinal function were no longer regulated by circadian rhythms.

Light experience, during the critical period of development, is essential in regulating retinal circadian rhythms and in maintaining a normal retinal function.