Chronoclippings

Foundational Observations of Circadian Science

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The Scottish Spitsbergen Expedition: Can human physiology acclimate to a 21h day? Simpson, Lobban, and Halberg (1970) used fast-running wrist watches and polar summer to find out. Figure from Arctic Anthropology, Vol. 7, No. 1. pp. 144-164.

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Autoradiographs (top row) of coronal brain sections  from rats injected with radiolabled deoxyglucose. Daytime on the left. Nighttime on the right.  A clear rhythm in glucose utilization is apparent in the SCN (arrows). Nissl stains shown below display general brain architecture (Schwartz and Gainer 1977 Science. Vol. 197, pp. 1089-1091 DOI: 10.1126/science.887940).

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Rats whose Suprachiasmatic Nuclei (SCN) had been bilaterally lesioned display homeostatic sleep rebound following 24-h total sleep deprivation.  “I-DL” indicates an intact control under a 12:12 Dark:Light (DL) cycle.  “SCN-DL” indicates a lesioned rat under 12:12 DL.  “SCN-DD” indicates a lesioned rat under constant darkness.

From Milstlberger et al. (1983) Sleep 6:217-233.  “Recovery Sleep Following Sleep Deprivation in Intact and Suprachiasmatic Nuclei-Lesioned Rats.”

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The free-running periods displayed by wild-type and tau mutant hamsters before the bilateral ablation of suprachiasmatic nuclei (SCN) and after the reinstatement of free-running rhythms by the implantation of fetal SCN from hamsters of a different genotype in to the 3rd ventricle. “Host” indicates the free-running periods displayed by hamsters before ablations were made. “Restored” indicates the free-running periods displayed after recovery from SCN implantation.  The reinstated free-running periods match genotype of the implanted SCN, not those of the host. The vertical gray bars on the right indicate the normal range of periods displayed by the genotypes used as the source of the implanted SCN.  Homozygous tau mutants were used in A, heterozygotes were used in B.  From Ralph et al. (1990) Science. 247:975-978.

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Time-course of Gonyaulax luminescence under a 14-hour light dark cycle (i.e., LD 7:7) followed by free-running luminescence under constant darkness (filled circles) or constant dim light (unfilled circles).  The near-24-hour period of the free-running rhythms under DD and dim LL is clearly not a memory of the previous Zeitgeber.  From Hastings and Sweeney (1958) Biol. Bull. 115: 440-458.

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Phase responses, or lack thereof, of free-running flying squirrels to 10-minute light pulses.  Light was delivered during the subjective day (A), early subjective night (B), and late subjective night ( C).  Activity was recorded under constant darkness and 20 deg. G. Intensity of light pulses was 0.5 foot-candles.  The figure is from DeCoursey (1960) “Phase Control in a Rodent.” Cold Spring Harbor Symposia on Quantitative Biology, Vol. XXV., pg. 53.

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Isolated lizards, Laeerta viridis (V1-4 above) and Laerta agilis (A1-2 above) develop locomotor rhythms with circadian periods despite never having experienced a rhythmic environment.  Eggs were transferred to constant darkness and temperature immediately upon being laid.  The abscissa, labeled MEZ, refers to local time, the ordinate indicates days after hatching and the data points indicate the phase of daily activity.  Periods are approximated in the parentheses placed alongside the plots linking data points for each lizard.  The figure is from Hoffman, K. (1957) “Angeborene Tagesperiodik bei Eidechsen” Naturwissenschaften Vol. 44, pp. 359-360.

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The effect of light intensity on the free-running period (a.k.a., the spontaneous frequency) of circadian rhythms under constant light for several animals and plants.  Aschoff’s rules were based on such comparisons across phyla.  The figure is taken from Aschoff’s chapter on “Exogenous and Endogenous Components” from the Cold Spring Harbor Symposium on Quantitative Biology on Biological Clocks in 1960: http://library.cshl.edu/symposia/1960/contents.html

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An arrhythmic (or perhaps unsynchronized) population of Drosophila psuedoobscura is rendered rhythmic (or perhaps synchronized) by a single 4-hour pulse of light.  In populations of Drosophila reared under constant darkness and temperature for many generations, no clear rhythmicity in adult emergence is apparent (A). However, the light pulse results in a persistent population rhythm in adult emergence (B and C).  This was taken as powerful evidence in favor of the existence of an endogenous and inherited biological clock mechanism, as the rhythmic population had never experienced a rhythmic environment. The figure is taken from  CS Pittendrigh’s “Perspectives in the Study of Biological Clocks,” included in “Perspectives in Marine Biology,” (1958) Edited by AA Buzati-Traverso, pp. 239-268.

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Prolonged exposure to constant light stops the diurnal rhythm of leaf movements of the bean plant Phaseolus multifloras (a). The exposure of these plants to single dark periods of durations shorter than 18 hours fails to induce subsequent diurnal leaf movement rhythms (b-f). A dark exposure of 18 hours of darkness (g) produces robust daily rhythms under subsequent constant light conditions. From Wasserman (1959) “Die Auslösung endogentagesperiodischer Vorgänge bei Pflanzen durch einmalige Reize.” Planta 53: 647-669

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Activity records of five chaffinches held under constant light and temperature. The bird shown in panel I (top) was exposed to a light intensity of 5 lux. The birds shown in panels II-V were exposed to an order of magnitude dimmer light. Here Aschoff’s focus is on the relationships between the free-running period (τ) and the two major components of the actogram, activity (α) and rest (ρ). Quoting Aschoff: “It may be asked whether, under constant conditions, the variability of the whole period τ is simply the summation of the variabilities of α and ρ or whether τ is more or less stable than its two components.” Aschoff was also working out the best way to assess the precision of τ. The figure is taken from chapter one of the book “Biochronometry,” edited by Michael Menaker, which is a record of the proceedings of a symposium held at Friday Harbor, Washington in September 1969, published by the National Academy of Sciences.

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Eclosion rhythms of Drosophila psuedoobscura under a 12h:12h light:dark cycle in the presence of temperature oscillations (not defined by the author) in 12 different cultures for which light and temperature rhythms were delivered with different relative phases.  The onset of heating corresponds to lights-on in culture number one and was delayed by two hour intervals for cultures two to twelve.  The figure is taken from Pittendrigh CS (1958) “Perspectives in the Study of Biological Clocks,” included in the book “Perspectives in Marine Biology,” Edited by AA Buzati-Traverso, pp. 239-268.

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Illustration of the daytime (a) and nighttime (b) positions of Mimosa piduca leaflets from W. Pfeffer’s book “Die periodischen Bewegungen der Blattorgane,” published in 1875.  The oscillation between these two positions in constant darkness was the phenomenon that captured Jean Jacques d’Ortous de Mairan’s attention in the 18th century.

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As a test of the hypothesis that leaf rhythms were driven by a rhythmic environment rather than the product of an endogenous time-sense, R. Semon reared Acacia lophantha under a 12-hour day, consisting of 6 hours of light and 6 hours of darkness.  After several such cycles, he released the plants into constant light of an intensity dim enough to support prolonged free-running rhythms.  The plant clearly failed to entrain to the 12-hour day and free-ran with period that was about twice as long as the previous 12-hour light dark cycle. The results supported the notion that the plant had an inherited endogenous rhythm. The figure is taken from R. Semon (1905) Über die Erblichkeit der Tagesperiod. Biol. Zentralbl. Vol. 25, pp. 241-252.

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The leaf movements of Acacia lophantha (a.k.a. Paraserianthes lophantha), recorded under constant darkness by W. Pfeffer and first reported in his book “Die periodischen Bewegungen Der Blattorgane,” published in 1875.  The rhythm appears to decrease rapidly in amplitude as time passes.  This led Pfeffer to suggest that the rhythms were produced by external rhythmic cues that had after-effects on the leaves for a only few cycles.   The results were consistent with plant rhythms being a passive response to light/dark cycles.  But the complete absence of light leads to an alternative explanation, particularly for a plant.  The figure is taken from the second edition of B. M. Sweeney’s “Rhythmic Phenomena in Plants,” published by Academic Press in 1987.

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Human physiological and behavioral rhythms under temporal isolation recorded in an underground bunker consisting of a “comfortable bed-sitting room” attached to a shower and small kitchen. Circadian changes in urination, core body temperature, and sleep and wakefulness are apparent. The subject in this case was the author J. Aschoff.  From  J. Aschoff (1965) Circadian Rhythms in Man. Science. Vol. 148, pp. 1427-1432

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We are dealing with a self-sustained oscillation which is free-running under constant conditions and has its own inherent frequency. An increasing number of experimental results demonstrated that we are right in using this technical terminology and that the "clock" on which the overt rhythms are based has all the characteristics of an active oscillator, as was first outlined by Pittendrigh... [The opposing hypothesis, that in constant conditions the rhythm is controlled by an unknown exogenous 24- hour input of, possibly, cosmic origin, has been criticized several times ... with sufficient thoroughness; I there- fore refrain from discussing it again.]

J. Aschoff (1965) Circadian Rhythms in Man. Science. Vol. 148, pp. 1427-1432