J. Aschoff

Circadian rhythms of finches in light-dark cycles with interposed twilights

Abstract 1. 1. In 24 hr cycles of light and dark, interposed with twilight of gradual-changing intensity, Greenfinches and Bullfinches show the typical pattern of activity with a major peak at dawn and a minor peak at dusk. 2. 2. With an increase of light-time from 7·5 to 15·5 hr, the activity-time of the bird increases, but to a lesser extent. 3. 3. The phase-angle difference, measured between midpoint of activity-time and midpoint of the light-cycle (“noon”), follows the circacian rule, becoming more positive with an increase in light-time. Onset and end of activity change their relative position in opposite directions, indicating that, under these conditions, these two phases are not useful to measure the phase-angle difference between organism and light-cycle. 4. 4. With an increase in the duration of twilight from 160 min to 420 min, the phase-angle difference becomes more positive, as predicted by a circadian mathematical model. 5. 5. The results are in full agreement with three rules, describing the activity cycles of wild birds in the field at different seasons.

Twenty-four-hour rhythms of rectal temperature in humans: Effects of sleep-interruptions and of test-sessions

SummaryRectal temperature has been recorded continuously in 6 male subjects in groups of two on a rigorous time-schedule with 7 h sleep in an isolation chamber, first for 8 days in a 16:8-h light-dark cycle (LD), thereafter for 4 days in complete darkness (DD). Urine samples have been collected and performance tests made in 3-h intervals during the daytime and also at 02:00 and 05:00 h on 7 of the 12 nights. The overall picture of the rhythm of rectal temperature is similar in all subjects, showing minima towards the end of sleep-time and maxima in the second half of wakefulness. Superimposed on this general curve are small increases of rectal temperature accompanying each test session; we consider these increases to be due to emotional stress (“psychogenic fever”). There is no difference between LD- and DD-conditions with regard to phase, mean level and range of oscillation of the temperature rhythm. Similarly, no significant difference exists between the curve averaged from days with uninterrupted sleep and the curve averaged from days with sleep interrupted twice.

Brain temperature as related to gross motor activity in the unanesthetized chicken

Abstract Brain temperature was recorded, together with activity, continuously for up to 8 days at various depths of the tissue in awake, but moderately restrained chicken. The animals were kept in a small round arena with a movable floor and exposed to either a light-dark cycle or constant dim illumination. In entrained as well as in free running rhythms, the circadian rise of temperature preceded onset of activity by several hours. Circadian rhythms of brain temperature were clearly expressed in animals showing no activity rhythm. Short bursts of activity were positively correlated with increases in temperature during the time of circadian low temperatures (sleep) but not during high temperatures (wakefulness). It is concluded that brain temperature and gross motor activity are only loosely coupled to each other, and that especially the circadian rhythm of temperature does not depend on a concurrent rhythm of activity.

Brain temperature in the unanaesthetized chicken: its circadian rhythm of responsiveness to light

Temperatures were recorded continuously for up to 4 days in the brain of 8 unanaesthetized, moderately restrained male chickens, kept in light-dark cycles (LD) of 30:30 or 60:60 min duration. In all cases, brain temperature was higher in L than in D. Temperatures increased or decreased immediately after the light was turned on or off, respectively, but did not reach a new level until after about 30 min. Average values of temperature obtained during the last 10 min in L and D were used for further analysis. The changes of brain temperature due to changes in light intensity were super imposed to marked circadian oscillations. The computed differences between L- and D-values were found to be a function of the circadian phase. For 4 out of the 8 chickens a uniform circadian rhythm of responsiveness to light could be demonstrated, with two maxima coinciding with the ascending and descending circadian slope, respectively. In view of the evidence suggesting brain temperature as a reliable measure of the degree of arousal, it is concluded that light has a stronger arousing effect on the chicken in the morning and in the evening than in the middle of the day or the night.

Brain temperature responses to light in unanesthetized chicken

We have measured the formation of carbamate in hemoglobin solutions using the stopped flow rapid pH technique described previously. For human adult hemoglobin carbamate concentrations were determined in a wide range of pH (pH 6 pH 8.5) and pC02 (30-140 Torr) in fully oxygenated and fully deoxygenated solutions. Analysis of the results indicated that 3 kinds of groups participate in carbamate formation of deoxyhemoglobin: 2s-NH2 groups (u-chains), 2a-NH 2 groups (S-chains), and -15 c-NH2 groups. Upon oxygenation the contribution of thea-NH 2 groups of the S-chains appeared to vanish. AHbCO2/AHb02, the fraction of oxylabile carbamate, is -0.2 for stripped HbA with pH=7.2 and pCO2=40 Torr. Using a least squares procedure the carbamate equilibrium constants, Kc, and the ionization constants, Kz, were calculated for the three types of groups.