Circadian Rhythm in Pineal N-Acetyltransferase Activity: Phase Shifting by Dark Pulses (III) |
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Authors: | Sue Binkley Karen Mosher Beatrix H White |
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Institution: | Biology Department, Temple University, Philadelphia, Pennsylvania, U.S.A. |
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Abstract: | N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is thought to be responsible for melatonin circadian rhythms. The enzyme has circadian properties--its rhythm persists in constant conditions, and it is precisely controlled by light and dark. Experiments are reported in which 4-h light or dark pulses were imposed on chicks (Gallus domesticus) over a 24-h period. Pineal NAT profiles were measured during and subsequent to the pulses. The phase of the NAT cycle following pulses was plotted to obtain phase-response curves. Light pulses produced a maximum phase shift (advance of 5 h) 8 h after the expected time of lights-out; dark pulses produced a maximum phase shift (advance of 4 h) 3 h after the expected time of lights-out. Maximum phase delays (-2 h) occurred 1-2 h after the expected lights-out for light pulses and 8 h after expected lights-on for dark pulses. |
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Keywords: | Pineal gland Circadian N-Acetyltransferase |
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