Seasonal changes of circadian pattern in human rectal temperature rhythm under semi-natural conditions

A phase delay of the circadian rectal temperature rhythm existed in three human subjects leading normal lives under semi-natural conditions: the rectal temperature began to increase later in summer than in the other three seasons.     

Entrainment of human circadian rhythms by artificial bright light cycles

Summary Artificial bright light cycles (LD 816) of about 5000 lux during the light period were applied to two subjects in a temporal isolation unit, who had shown free-running circadian rhythms in sleep-wakefulness and rectal temperature. The circadian rhythms were successfully entrained by the artificial light cycle, but the phase relation of the rhythms to the light cycle was substantially different between the two subjects. The result indicated that the artificial bright lights are able to reset human circadian rhythms.     

Entrainment of human circadian rhythms by artificial bright light cycles

Artificial bright light cycles (LD 8:16) of about 5000 lux during the light period were applied to two subjects in a temporal isolation unit, who had shown free-running circadian rhythms in sleep-wakefulness and rectal temperature. The circadian rhythms were successfully entrained by the artificial light cycle, but the phase relation of the rhythms to the light cycle was substantially different between the two subjects. The result indicated that the artificial bright lights are able to reset human circadian rhythms.     

Behavioural entrainment of circadian rhythms

This paper reviews the discovery and characterization of a behavioural system for entrainment of circadian rhythms. This behavioural system depends on non-photic inputs but interacts with the light-entrainment system. Non-photic stimuli can be powerful quantitatively: behavioural events can shift rhythms by several hours. Non-photic entrainment offers scope for rephasing biological rhythms in circumstances where light input from the environment is inadequate.     

Behavioural entrainment of circadian rhythms

Summary This paper reviews the discovery and characterization of a behavioural system for entrainment of circadian rhythms. This behavioural system depends on non-photic inputs but interacts with the light-entrainment system. Non-photic stimuli can be powerful quantitatively: behavioural events can shift rhythms by several hours. Nonphotic entrainment offers scope for rephasing biological rhythms in circumstances where light input from the environment is inadequate.     

Seasonal changes in the circadian variation of oral temperature during wakefulness.

The circadian change of oral temperature in 26 subjects was compiled for December, March and June. Average peak time delays up to 70 min, and a reduced daytime temperature rise were found in June compared with December.     

Sex differences in human circadian rhythms: Intrinsic periods and sleep fractions

Summary The period of freerunning circadian rhythms is significantly shorter and the fraction of sleep is significantly larger in human females than in males, as long as the rhythms run internally synchronized. The sex difference in the period could be a property either of the whole circadian system or of only one of the oscillators in a multi-oscillator system. The sex difference in the sleep fraction could be a fixed property of the sleep-wake rhythm or could depend on interactions in the multi-oscillator system. To investigate these questions, a sample of 33 long-term experiments, in which the rhythms ran internally synchronized in one section and internally desynchronized in another section, were analyzed. The periods of rhythms in rectal temperature were different in females and males during internal synchronization, but became identical during internal desynchronization. In contrast, sex differences in sleep-wake periods were more pronounced when the rhythms were desynchronized than when they were internally synchronized. This result provides evidence that the sex difference in periodicity is a property only of the sleep-wake rhythm; the intrinsic periods of temperature rhythms are identical in females and males, whereas those of sleep-wake rhythms are distinctly shorter in females than in males. In the state of internal synchronization, the joint period is a compromise between the intrinsic periods of the rhythms involved, and therefore it shows a small but significant sex difference. Moreover, the transition from internally synchronized to desynchronized rhythms is combined with a highly significant reduction in the sleep fraction, which is considerably greater in females than in males. These results suggest that the occurrence of internal desynchronization strongly affects the sleep-wake rhythm, and that the influence of rhythm disorders is considerably greater in females than in males.     

Phase-dependent shift of free-running human circadian rhythms in response to a single bright light pulse

Responsiveness of free-running human circadian rhythms to a single pulse of bright light was examined in a temporal isolation unit. Bright light (5000 lx) of either 3 or 6 h duration, applied during the early subjective day, produced phase-advance shifts in both the sleep-wake cycle and the rhythm of rectal temperature; the light pulse had essentially no effect on the phase of the circadian rhythms, when it was introduced during the late subjective day or the early subjective night. The results indicate that bright light can reset the human circadian pacemaker.     

Effect of high lipid diet on circadian rhythms of tissue glycogen

Summary The well defined circadian rhythms of glycogen content in heart, diaphragm and liver of the rat are drastically altered by a high lipid diet as shown by changes in amplitude, phase and tissue glycogen levels. If sampling times had been restricted to certain hours of the day the profound effect of the high fat diet on tissue glycogen would not have been apparent.Supported by USPHS grants HL 16041-03 and HL 07094-03.     

Functional absence of brain photoreceptors mediating entrainment of circadian rhythms in the adult rat

Summary The photic energy penetrating into the brain was increased in adult rats sustaining craniotomies sealed with transparent plastic. After blinding, these animals failed to entrain their circadian food intake rhythm to light-dark cycles. Short pulses of light did not phase-shift the freerunning rhythm. We conclude that adult rats lack brain photoreceptors mediating entrainment of circadian rhythms.     

Zeitgeber-schedule dependent resynchronization of circadian rhythms in nocturnal mammals (Primates and Chiroptera)

Summary Changing the L: D time ratio of an entraining light-dark regime leads to characteristic alterations of the resynchronization behaviour of the circadian activity rhythms in night monkeys (Aotus trivirgatus) and African fruit bats (Rousettus aegyptiacus) after 8 h advance and delay shifts of the LD-Zeitgeber. Reduced speed of re-entrainment and occurrence of antidromic resynchronization point to a lower Zeitgeber strength of 24-h LD-cycles with a prolonged D-phase.Supported by the Deutsche Forschungsgemeinschaft (Er 59/8).     

Timing of single daily meal influences relations among human circadian rhythms in urinary cyclic AMP and hemic glucagon,insulin and iron

Summary Relations among circadian rhythms in serum iron, glucagon and insulin and urinary cyclic AMP excretion differ drastically when diurnally active, nocturnally resting human adults consume all daily food for one week as breakfast only and for another week as dinner only—a finding of interest to diverse fields, e.g., for optimizing certain kinds of therapy or for a better utilization of calories.Supported by grants (No. RR-400 from the General Clinical Research Centers Program of the Division of Research Resources, National Institutes of Health, USPHS and Nos. 5-K6-GM-13, 981 and 1RO1-CA-14445-01) and grant No. 20, Fondation de l'industrie pharmaceutique pour la recherche.     

Timing of single daily meal influences relations among human circadian rhythms in urinary cyclic AMP and hemic glucagon, insulin and iron.

Relations among circadian rhythms in serum iron, glucagon and insulin and urinary cyclic AMP excretion differ drastically when diurnally active, nocturnally resting human adults consume all daily food for one week as breakfast only and for another week as dinner only - a finding of interest to diverse fields, e.g., for optimizing certain kinds of therapy or for a better utilization of calories.     

Ultradian and other rhythms in human respiration rate

Summary Twelve male subjects had their respiration rate (RR) measured at 3 min intervals for 6 h. Although there were substantial individual differences, most subjects demonstrated a 90±15 min rhythm of RR, with several subjects also showing 60±10 min and 30±3 min rhythms.     

Pentobarbital-induced phase shifts of circadian rhythms of locomotor activity are not mediated through stimulated activity in mice

The possibility that phase shifts of circadian rhythms of locomotor activity induced by pentobarbital injections are mediated through hyperactivity after recovery from the sedative condition was tested in DBA/2 mice. The mice were restrained for 3 h in a tube immediately after injections of pentobarbital at either CT 9 or CT 0. The results indicated that immobilization did not block the phase shifts, suggesting that pentobarbital-induced phase shifts are not due to increasing the level of activity.     

Bilateral lesions of suprachiasmatic nucleus eliminate circadian rhythms of oxygen consumption and the respiratory quotient in rats

Summary Bilateral lesions of the suprachiasmatic nucleus of the hypothalamus of rats abolished circadian rhythms of oxygen consumption and of the respiratory quotient (RQ). The RQ remained constant at a level intermediate between the maximum (about 1.0) and minimum (about 0.9) values in control animals.