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When chicken pineal glands were organ-cultured in darkness, serotonin N-acetyltransferase activity was low during daytime, increased at midnight, and decreased on the next morning. The autonomous increase of N-acetyltransferase activity was suppressed by illumination of the glands. When pineal glands were cultured under a light-dark cycle (LD 12:12), the change of N-acetyltransferase activity continued to oscillate in phase with the light-dark cycle for 3 days.
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Takeo Deguchi (1979) studied this question.
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