Colin S. Pittendrigh

A functional analysis of circadian pacemakers in nocturnal rodents

Summary1.The circadian pacemakers controlling activity rhythms in four species of rodents are compared, as freerunning systems in constant darkness. In analyzing their stability the distinction is made between (1) spontaneous day-to-day instability of frequency, and (2) a longer-term lability, some of which is traceable to identified causes.2.Serial correlation analysis indicates that the precision (day-to-day stability) of the pacemakers period is ca. twice as good (estimated s.d.=0.6% of

A Functional Analysis of Circadian Pacemakers in Nocturnal Rodents. V. Pacemaker Structure: A Clock for All Seasons

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A Functional Analysis of Circadian Pacemakers in Nocturnal Rodents. I. The Stability and Lability of Spontaneous Frequency

inMus musculus) as the already remarkable precision of the activity rhythm it drives (average s.d.=1.2% of

Circadian Systems: Entrainment

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A Functional Analysis of Circadian Pacemakers in Nocturnal Rodents. III. Heavy Water and Constant Light: Homeostasis of Frequency?

).3.Identifiable causes of long-term lability include age and several features of prior entrainment by light. The period and photoperiod of a light cycle have a predictable influence on the subsequent freerunning period (τ) of the pacemaker; they cause “after-effects”. So do single light pulses causing a phase-shift in the freerunning system. Constant light also has an after-effect opposite in sign from the after-effect of long photoperiods.4.After-effects of “skeleton” photoperiods support the hypothesis that the transitions of light to darkness vv. are involved in the entrainment process which leads to changes in τ.5.Both day-to-day instability and long term lability are most pronounced in species (Peromyscus maniculatus, Mus musculus) whose