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We describe a hypothalamus-specific mRNA that encodes preprohypocretin, the putative precursor of a pair of peptides that share substantial amino acid identities with the gut hormone secretin. The hypocretin (Hcrt) protein products are restricted to neuronal cell bodies of the dorsal and lateral hypothalamic areas. The fibers of these neurons are widespread(More)
Many physiological, cellular, and biochemical parameters in the retina of vertebrates show daily rhythms that, in many cases, also persist under constant conditions. This demonstrates that they are driven by a circadian pacemaker. The presence of an autonomous circadian clock in the retina of vertebrates was first demonstrated in Xenopus laevis and then,(More)
Several investigations have shown that illumination at night reduces melatonin level in the mammalian pineal, but the effect of night illumination on the retina is not known. In this study retinas were cultured in a flow-through apparatus and then were exposed to light at ZT 18. Light exposure reduced melatonin levels to the daytime level within 30 min. The(More)
The aim of the present study was to investigate the in vitro expression of Period 1 (Per1), Period 2 (Per2) and arylalkylamine N-acetyltransferase (AA-NAT) genes in the rat pineal gland to understand the mechanism(s) regulating the expression of these genes in this organ. Pineals, when maintained in vitro for 5 days, did not show circadian rhythmicity in(More)
Melatonin is synthesized in retinal photoreceptor cells and acts as a neuromodulator imparting photoperiodic information to the retina. The synthesis of melatonin is controlled by an ocular circadian clock and by light in a finely tuned mechanism that ensures that melatonin is synthesized and acts only at night in darkness. Here we report that the circadian(More)
Several studies have established that melatonin synthesis occurs in the retina of vertebrates, including mammals. In mammals, a subpopulation of photoreceptors (probably the cones) synthesize melatonin. Melatonin synthesis in the retina is elevated at night and reduced during the day in a fashion similar to events in the pineal gland. Both the MT1 and MT2(More)
Arylalkylamine N-acetyltransferase (AA-NAT) is the key regulatory enzyme in the melatonin biosynthetic pathway. Previous investigations have reported that Aa-nat mRNA in rat is only detected in a sub-population of photoreceptor cells that resemble cones in shape and size. In the present study, we investigated Aa-nat expression in the rat retina by using in(More)
The newly discovered multi-oscillatory nature of the mammalian circadian clock system and the cloning of the genes involved in the molecular mechanism that generates circadian rhythmicity have opened new approaches for understanding how mammals are temporally organized and how the mammalian circadian system reacts to the lack of normal synchronization cues.(More)
BACKGROUND Nocturnin was originally identified by differential display as a circadian clock regulated gene with high expression at night in photoreceptors of the African clawed frog, Xenopus laevis. Although encoding a novel protein, the nocturnin cDNA had strong sequence similarity with a C-terminal domain of the yeast transcription factor CCR4, and with(More)
Several studies have demonstrated that the mammalian retina contains an autonomous circadian clock. Dopaminergic and other inner retinal neurons express many of the clock genes, whereas some of these genes seem to be absent from the photoreceptors. This observation has led to the suggestion that in mammalian retina the circadian pacemaker driving retinal(More)