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Entrainment of the Circadian Rhythm in Rat Pineal N‐Acetyltransferase Activity Under Extremely Long and Short Photoperiods
Author(s) -
Illnerová Helena,
Vaněček Jiří
Publication year - 1985
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1985.tb00628.x
Subject(s) - circadian rhythm , evening , morning , darkness , entrainment (biomusicology) , endocrinology , medicine , photoperiodism , biology , rhythm , melatonin , botany , physics , astronomy
Entrainment of a pacemaker driving the circadian rhythm in rat pineal N‐acetyltransferase activity was studied under extremely long and short photoperiods. Adult male rats maintained under the light‐dark regime (LD) 18:6 or under the regime LD 6:18 were exposed to a I‐min light pulse at different times at night, then they were released into darkness, and the next night phaseshifts of the evening N‐acetyltransferase rise and of the morning N‐acetyltransferase decline caused by light pulses were determined. The evening rise was phase‐delayed by at most 0.5 h under LD 18:6, but by as much as 2.8h under LD 6:18. The morning decline was phase‐advanced by at most 1.9 h under LD 18:6, but by as much as 3.5 h under LD 6: 18. Hence, the magnitude of phaseshifts and consequently patterns of phase‐response curves, which show possibilities of discrete entrainment, depend on the photoperiods under which animals are maintained. A 1‐min light pulse applied within 1 h before the end of the dark period phase‐advanced the morning N‐acetyltransferase decline under LD 18:6 as well as under LD 6:18, while a pulse applied within 1 h after the beginning of the dark period phase‐delayed the evening N‐acetyltransferase rise only in rats maintained under LD 18:6, but not in those kept under LD 6:18. It seems that under very long photoperiods, the N‐acetyltransferase rhythm may be entrained by evening as well as by the morning light, while under very short photoperiods the rhythm may be synchronized by morning light only.