Previous studies have shown that, in the Royal College of Surgeon rat,
circadian rhythms in the
retinal dopaminergic and melatonergic systems are still present after the photoreceptors have degenerated, thus demonstrating that
circadian rhythmicity in the mammalian
retina can be generated independently from the photoreceptors. The aim of the present study was to investigate the pattern of expression of the
clock genes in the
retina of the Royal College of Surgeons rat under different lighting conditions. Expression of
clock genes was investigated in the
retina of normal and dystrophic Royal College of Surgeons rats under 12 h of light/12 h of
dark (LD), constant
darkness (DD) and constant light (LL) using Real Time Quantitative
RT-PCR. Our data indicate that, in control animals, Period1, Period2, Cryptochrome1, Cryptochrome2, Clock, Rora, Rev-Erb alpha and Npas2
mRNA levels showed a significant variation over the sampling period in LD cycles and in DD, whereas Bmal1
mRNA did not show any significant variation. In LL, the transcripts for Per1, Per2, Clock and Rev-Erb alpha showed significant
temporal variations. In the dystrophic
retina, only Per1 and Per2
mRNA levels showed a
temporal variation over the 20-h period. Our work indicates that degeneration of the
photoreceptor cells dramatically affected the expression levels and patterns of many
clock genes. Finally, the present study suggests that investigating the expression pattern of
clock genes using the whole
retina or animals with photoreceptor degeneration may not provide any definitive answers about the working of the
retinal circadian clock system.
