Abstract
The mammalian retina has an endogenous oscillator that regulates circadian melatonin production. We examined this mechanism in the retina of rats under restricted feeding (RF) by investigating the expression rhythms of the mRNA for serotonin N-acetyltransferase (NAT), which is the rate limiting enzyme for melatonin synthesis. Northern blots showed that RF shifted the phase of circadian mRNA expression rhythms of a circadian clock gene rat period 2 and a clock-controlled gene D-site binding protein. However, the NAT mRNA showed a bimodal rhythm pattern with one peak at midnight and the other at midday after RF, although the mRNA expression showed a single peak at midnight after ad libitum feeding. Our results suggest that NAT mRNA in the rat retina is regulated by at least two circadian oscillatory mechanisms: one is affected by feeding and the other can oscillate independent to the imposed feeding cycles.
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