The Institute of Physiology of the Czech Academy of Sciences (CAS) has been involved in the field of chronobiology, i.e., in research on temporal regulation of physiological processes, since 1970. The review describes the first 35 years of the research mostly on the effect of light and daylength, i.e., photoperiod, on entrainment or resetting of the pineal rhythm in melatonin production and of intrinsic rhythms in the central biological clock. This clock controls pineal and other circadian rhythms and is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. During the early chronobiological research, many original findings have been reported, e.g. on mechanisms of resetting of the pineal rhythm in melatonin production by short light pulses or by long exposures of animals to light at night, on modulation of the nocturnal melatonin production by the photoperiod or on the presence of high affinity melatonin binding sites in the SCN. The first evidence was given that the photoperiod modulates functional properties of the SCN and hence the SCN not only controls the daily programme of the organism but it may serve also as a calendar measuring the time of a year. During all the years, the chronobiological community has started to talk about "the Czech school of chronobiology". At present, the today´s Laboratory of Biological Rhythms of the Institute of Physiology CAS continues in the chronobiological research and the studies have been extended to the entire circadian timekeeping system in mammals with focus on its ontogenesis, entrainment mechanisms and circadian regulation of physiological functions. Key words: Pineal, Melatonin, AA-NAT rhythm, Light entrainment, Photoperiod, SCN clock.

• MeSH
• Academies and Institutes MeSH
• Biological Clocks physiology   MeSH
• Circadian Clocks physiology   MeSH
• Circadian Rhythm * physiology   MeSH
• History, 20th Century MeSH
• History, 21st Century MeSH
• Pineal Gland * metabolism   physiology   MeSH
• Photoperiod MeSH
• Humans MeSH
• Melatonin metabolism   MeSH
• Brain metabolism   physiology   MeSH
• Suprachiasmatic Nucleus physiology   metabolism   MeSH
• Animals MeSH
• Check Tag
• History, 20th Century MeSH
• History, 21st Century MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Historical Article MeSH
• Review MeSH
• Names of Substances
• Melatonin MeSH

Entertainment 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 in switching off the light of up to 10 h and then were released into darkness, phase-delays of the evening N-acetyltransferase rise during the same night corresponded roughly to delays in the light switch off. However, phase-delays of the morning decline were much smaller. After a delay in the evening switch off of 11 h, no N-acetyltransferase rhythm was found in the subsequent darkness. The evening N-acetyltransferase rise was phase-delayed by 6.2 h at most 1 day after delays. Phase-delays of the morning N-acetyltransferase decline were shorter than phase-delays of the N-acetyltransferase rise by only 0.7 h to 0.9 h at most. Hence, 1 day after delays in the evening switch off, the period of the high night N-acetyltransferase activity may be shortened only slightly. The N-acetyltransferase rhythm was abolished only after a 12 h delay in switching off the light. Rats were subjected to a bringing forward of the morning light onset and then were released into darkness 4 h before the usual switch off of light. In the following night, the morning N-acetyltransferase decline, but not the evening rise, was phase advanced considerably. Moreover, when the onset of light was brought forward to before midnight, the N-acetyltransferase rise was even phase-delayed. Hence, 1 day after bringing forward the morning onset of light, the period of the high night N-acetyltransferase activity may be drastically reduced. When rats were subjected to a 4 h light pulse around midnight and then released into darkness, the N-acetyltransferase rhythm in the next night was abolished. The data are discussed in terms of a two-component pacemaker controlling the N-acetyltransferase rhythm. It is suggested that delays in the evening switch off of light may disturb the N-acetyltransferase rhythm the next day only a little, as the morning component may adjust to phase-delays of the evening component almost within one cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

• MeSH
• Acetyltransferases metabolism   MeSH
• Arylamine N-Acetyltransferase metabolism   MeSH
• Circadian Rhythm radiation effects   MeSH
• Pineal Gland enzymology   radiation effects   MeSH
• Rats, Inbred Strains MeSH
• Rats MeSH
• Environment, Controlled MeSH
• Light MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetyltransferases MeSH
• Arylamine N-Acetyltransferase MeSH