Formal properties of the circadian and photoperiodic systems of Japanese quail: Phase response curve and effects of T-cycles

A role for the circadian system in photoperiodic time measurement in Japane se quail is controversial. The authors undertook studies of the circadian a nd photoperiodic system of Japanese quail to try to identify a role for the circadian system in photoperiodic time measurement. The circadian studies showed that the circadian system acts like a low-amplitude oscillator: It i s readily reset by Light without significant transients, has a Type 0 phase response curve (PRC), and has a large range of entrainment. In fact, a cyc le length that is often used in resonance protocols (LD 6:30) is within the range of entrainment. The authors employed T-cycle experiments; that is, L D cycles with 6- and 14-h photoperiods and period lengths ranging from 18 t o 36 h to test for circadian involvement in photoperiodic time measurement. The results did not give evidence for circadian involvement in photoperiod ic time measurement: T-cycles utilizing 6-h photoperiods were uniformly non inductive (that is, did not stimulate the reproductive system), whereas T-c ycles utilizing 14-h photoperiods were inductive (stimulatory). A good matc h was observed between the phase-angles exhibited on the T-cycles employing 6-h photoperiods and the predicted phase-angles calculated from a FRC gene rated from 6-h light pulses.