Helena Illnerová

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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)
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)
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)
Melatonin content in the rat pineal decreases at night after exposure of animals to light, from 20 to 2 pmol/gland in 15 min. Melatonin concentration in serum fell precipitously in a manner almost identical to the drop in pineal melatonin only with a 5 min time lag. It is concluded that the rapid decrease in the pineal melatonin content is mainly due to an(More)
Recent studies have shown that the waveform of the rhythm of c-Fos photoinduction in the ventrolateral (vl) part of the suprachiasmatic nucleus (SCN) and that of the rhythm in the spontaneous c-Fos production in the dorsomedial (dm) part of the SCN in rats released into constant darkness depend on the photoperiod under which the animals were previously(More)
In the Djungarian hamster Phodopus sungorus, the daily temporal pattern of synthesis and release of pineal hormone melatonin, mainly the length of the period of elevated melatonin levels, may be involved in transferring the information on day length to the neuroendocrine-gonadal axis. The present study investigated the time course of adjustment of the(More)
To ascertain how photic stimuli disturbing overt circadian rhythms affect the endogenous rhythmicity of the suprachiasmatic nucleus (SCN), rats were subjected to constant light (LL) or to a 9-h light pulse encompassing midnight, and rhythms of abundance of the c-Fos-immunoreactive (c-Fos-ir) and the PER1-immunoreactive (PER1-ir) cells were studied during(More)
Entrainment of the circadian rhythm in the pineal N-acetyltranferase activity by prolonged periods of light was studied in rats synchronized with a light:dark regime of 12∶12 h by observing phase-shifts in rhythm after delays in switching off the light in the evening or after bringing forward of the morning onset of light. When rats were subjected to delays(More)