Summary
The effects on Drosophila eclosion rhythm of two light interruptions applied at different phases of the circadian cycle, were studied.
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1.
When two light interruptions were applied, the first one at a point in the circadian cycle known to phase delay the subsequent peaks and the second one known to phase advance if offered as a solitary pulse, the peaks in the steady state occurred after a pronounced delay.
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2.
Anticipating a discrete and instantaneous phase-shift by the first pulse it was possible to apply the second light interruption at a point in the circadian oscillation as to restore the subsequent peaks to normalcy.
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3.
The transient oscillations induced by the first light pulse did not respond to the second light pulse in the same manner as does the original state oscillation.
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4.
It is concluded that Pittendrigh's assumption that the underlying light sensitive oscillation in Drosophila is phase-shifted by light interruptions even on day 1 to the extent observed in the steady state later, is valid.
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The studies upon which this paper is based were supported by Scholarships from the German Academic Exchange Service and the Alexander von HumboldtStiftung. I am especially grateful to Professor E. Bünning for provision of working space and facilities in his laboratory, his continued interest in the work and encouragement. I have greatly bene fited by the stimulating discussions I had with my colleagues Dr. W. Engelmann and Mr. Hans-Willi Honegger regarding this work.
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Chandrashekaran, M.K. Studies on phase-shifts in endogenous rhythms. Zeitschrift für vergleichende Physiologie 56, 154–162 (1967). https://doi.org/10.1007/BF00340507
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DOI: https://doi.org/10.1007/BF00340507