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The hypothesis is advanced that the circadian pacemaker in the mammalian suprachiasmatic nucleus (SCN) is composed at the molecular level of a nonredundant double complex of circadian genes (per1, cry1, and per2, cry2). Each one of these sets would be sufficient for the maintenance of endogenous rhythmicity and thus constitute an oscillator. Each would have(More)
125I-Melatonin was used to localize and characterize the melatonin receptor sites in the rat hypothalamus. Autoradiography revealed that displaceable 125I-melatonin binding occurred in suprachiasmatic nuclei and median eminence only. Further studies performed on crude membrane fractions from median eminences revealed high affinity (Kd = 21 pM) melatonin(More)
Rhythmicity of the rat suprachiasmatic nucleus (SCN), a site of the circadian clock, develops prenatally. A molecular clockwork responsible for the rhythmicity consists of clock genes and their negative and positive transcriptional-translational feedback loops. The aim of the present study was to discover the development of the clockwork during ontogenesis.(More)
A recently reported circadian rhythm in the spontaneous c-Fos immunoreactivity in the rat suprachiasmatic nucleus (SCN) is expressed mostly in the dorsomedial (dm) SCN, where vasopressinergic cells are located. The aim of the present study is to find out whether day length, i.e., photoperiod, affects the dm-SCN rhythm and, if so, how the rhythm adjusts to a(More)
The SCN as a site of the circadian clock itself exhibits rhythmicity. A molecular clockwork responsible for the rhythmicity consists of clock genes and their negative and positive transcriptional-translational feedback loops. The authors' previous work showed that rhythms in clock gene expression in the rat SCN were not yet detectable at embryonic day (E)(More)
Rhythmicity of the rat suprachiasmatic nucleus (SCN), a site of the circadian pacemaker, is affected by daylength; that is, by the photoperiod. Whereas various markers of rhythmicity have been followed, so far there have been no studies on the effect of the photoperiod on the expression of the clock genes in the rat SCN. To fill the gap and to better(More)
Within the suprachiasmatic nucleus (SCN) is a pacemaker that not only drives circadian rhythmicity but also directs the circadian organization of photoperiodic (seasonal) timekeeping. Recent evidence using electrophysiological, molecular, and genetic tools now strongly supports this conclusion. Important questions remain regarding the SCN's precise role(s)(More)
Seasonal changes of daylength (photoperiod) affect the expression of hormonal and behavioral circadian rhythms in a variety of organisms. In mammals, such effects might reflect photoperiodic changes in the circadian pace-making system [located in the suprachiasmatic nucleus (SCN) of the hypothalamus] that governs these rhythms, but to date no functionally(More)
In rats maintained for 2 days in constant darkness, the suprachiasmatic nucleus exhibited a circadian rhythm in c-Fos immunoreactivity, with the maximum in the morning and trough during the subjective night. In contrast to the night-time photic c-Fos induction occurring in the ventrolateral part of the nucleus, the spontaneous rhythmic c-Fos induction in(More)
In the Djungarian hamster, short photoperiods induce regression of testes and accessory glands. There is evidence that the length of time melatonin levels are elevated is the signal conveying the photoperiodic effects to the neuroendocrine axis. When the temporal course of decompression of the pattern of pineal melatonin content was followed after a change(More)