Entrapment of the adrenal cortical rhythm and of the locomotor activity rhythm by ahemeral photoperiods in the quail

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Abstract
The actographically recorded locomotor activity and the plasma corticosterone content were measured in male quail, which had been first preadapted to a control 12L/12D photoperiod, and then switched for 4 weeks to ahemeral photoperiods of 35 hrs (26L/9D) or (9L‐26D), or 13 hrs (6L/7D). Despite the extension of the three photoperiods investigated for beyond the range of the classical circadian periodicity (20 to 28 hrs), and in spite of the very low light intensities used (3–5 Lux), the entrainment of both physiological rhythms, as checked by mathematical procedures, was found complete. In a further experiment, where both physiological parameters were tested during the transition periods from the 12L/12D photoperiod to a 26L/9D schedule, it could be shown that the entrainment of both physiological parameters occurred almost immediately.

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