Aim: 

It has been recently shown that dark rearing permanently modifies the receptive field (RF) properties of RGCs and strongly alters functional and structural properties of retinal circuits. Here we report data to test whether dark rearing also modifies permanently the circadian regulation of several critical molecules in selected cell populations.

Methods: 

Long-Evans and Sprague-Dawley rats were born and raised in complete darkness for 1 or 3 months, some animals were then returned to normal cyclic illumination for at least 1 to 6 months (dark-reared/recovered: DR/R). The animals were sacrificed at fixed daily time and the retinas were quickly removed, fixed, cryosectioned and immunolabelled with antibodies against TH, PV, and PKC. Some retinas were whole mount for Chat immunolabelling.

Results: 

Our data show that tyrosine hydroxilase (TH), parvalbumine (PV) and PKC are no longer regulated by circadian rhythms with the exception of PKC and they do not recover even after prolonged exposure to normal cyclic illumination. Dark-rearing also produced a reduction in the number of cholinergic amacrine cells as well as it modified their characteristic mosaic pattern. In addition, the levels of expression of ISLET-1, a marker for early developmental stages, also seemed to be strongly reduced in dark-reared animals. Some recovery is detected in the cholinergic mosaic.

Conclusion: 

Taken together these results show that light is essential in regulating retinal development and the deleterious effects are more prominent in inhibitory neurons.