種々の光周期変化に対するニワトリひな松果体におけるセロトニンN-アセチルトランスフェラーゼ活性の変動

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タイトル別名
  • Rhythmic Changes in Serotonin N-Acetyltransferase Activity in the Pineal Gland of the Chick Exposed to Different Photoperiods
  • シュジュ ノ ヒカリ シュウキ ヘンカ ニ タイスル ニワトリ ヒナ ショウカ

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We investigated effects of various photoperiodic changes on serotonin N-acetyltrasferase (NAT) activity in the pineal gland of the chick in vivo. The NAT activity in the pineal gland of 16- and 42-day-old chicks fluctuated with a marked rhythmicity under a 14hr light (lights on at 05:00 and off at 19:00) and 10hr dark photoperiodic condition (14L:10D). The level of pineal NAT activity at 42 days of age elevated in both light and dark periods of a 14L:10D photoperiod compared to that at 16 days of age. Chicks which were raised under a 14L:10D photoperiod for 16 days after hatching were exposed to a 4-5hr darkness during the expected. dark period (19:00-05:00) and maintained under continuous light for two consecutive days. In continuous light, the peak time of NAT rhythm on the first day was delayed for about 5hr, and this enzymatic activity was suppressed by light on the first day to about half of the normal nocturnal level of the corresponding time of 14L:10D. The NAT activity of the chick exposed. to darkness for 4hr after the expected lights off (19:00) showed the natural rhythmicity, because the lights-off time of this treated group was the same hour as that of 14L:10D. But exposure to darkness for 4 to 5hr at both 22:00 to 03:00 and 01:00 to 05:00 caused the peak of NAT activity to delay for about 2 and 4hr, respectively. When the position of a 4hr light period during the expected light period of 14L:10D was shifted(at 05:00-09:00, 08:00-12:00, 12:00-16:00 and 15:00-19:00), the NAT rhythm was entrainable in all cases according to the lights-off time. The findings show that the onset of darkness may be a major signal for the phase-shift of the NAT rhythm in the pineal gland of the chick. Furthermore, we studied the effect of the duration time of the dark period as signals on the rhythmic change of NAT activity in the pineal gland. Since the NAT rhythm was not entrainable when the length of the dark treatment was 1-2hr, it seems that exposure of at least 3hr darkness is needed for the entrainment of NAT rhythm to external light-dark cycle. The chick NAT rhythm at 16 days of age on the second day of continuous light showed a different pattern compared to that at 42 days of age; the NAT rhythm free-ran at 16 days of age but not at 42 days of age (showing the same rhythm as that of 14L:10D), indicating that the pineal gland of the chicken gradually decreases a capacity to react to light with advancing age.

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