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.     

Vertebrate circadian rhythms: Retinal and extraretinal photoreception

Summary ERRs Both the pineal and the SCN are elements of the vertebrate multioscillator system although the relative importance of these 2 areas probably varies between, and possibly within, the different vertebrate classes. Extraretinal photoreception is a universal feature of submammalian vertebrates, and possibly of neonatal mammals, but is absent in adult mammals. Although the pineal systems of sumammalian vertebrates are photosensitive, the pineal system has been directly implicated as an extraocular site for the perception of entraining light cycles only in amphibians. In all other submammalian vertebrates extraretinal entrainment can occur in the absence of the pineal system although it is certainly conceivable that the pineal system may act as an alternate route of photoreception. These extraretinal-extrapineal receptors are located within the brain but the exact location(s) of these receptors within the brain is unknown. The hypothalamus would be likely area for this extraretinal photoreception, however, for several reasons: 1. Neurophysiological studies have identified light sensitive neurons in the frog's hypothalamus⁴³. 2. The avian hypothalamus is a site of photoperiodic photoreception^100–103. 3. The only other light sensitive structures known in vertebrates—the pineal system and the lateral eyes—are all derived embryologically from the hypothalamus. 4. The hypothalamus appears to be the site of a circadian clock and there may be advantages in having the photoreceptors and the clock anatomically close to one another. These considerations, of course, do not exclude the possibility that other brain areas may be involved as well. The reason behind the loss of extraretinal photoreception in mammals is uncertain. The shift to exclusive retinal photoreception in mammals may have been dictated by the extensive reorganization that occurred during the evolution of the mammalian brain. Or, perhaps, the increased size of the mammalian skull and overlying tissue made direct photoreception difficult and necessitated a shift to retinal photoreception. The persistence of extraretinal photoreceptors in submammalian vertebrates, however, underscores their importance in the sensory repertoire of vertebrates.     

Antidepressant drugs elevate rat pineal and plasma melatonin

Summary Acute administration in the mid-light phase of a number of antidepressant drugs of different pharmacological profiles elevated pineal and plasma melatonin (measured by radioimmunoassay). Following chronic treatment with the tricyclic antidepressant clomipramine, the elevation was significantly reduced. This may be an effect of reduced -adrenergic receptor sensitivity after chronic clomipramine administration, analogous to other findings of reduced -adrenergic receptor binding and reduced noradrenaline-sensitive adenylate-cyclase response.These collaborative studies were made possible by a Twinning Grant from the European Training Programme for Brain and Behaviour Research; J.A. was supported by the Medical Research Council of Great Britain. We thank M. Lichtsteiner for excellent technical assistance. This paper was written during a Fellowship of the Swiss Biomedical Research Foundation to A.W.-J. Hofmann-LaRoche AG, Basel kindly provided the 1-5HTP-ester (Ro 11-5940) and Ro 11-2465, CIBA-Geigy AG, Basel, the maprotiline, clomipramine, and imipramine, USV, New York, the desmethylimipramine.     

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.     

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.     

Seasonal changes of circadian rhythms of human birth in northern Finland

Zusammenfassung Die Verteilung der Geburten im finnischen Lappland auf die Tagesstunden zeigt eine jahreszeitliche Schwankung der Phasenlage in der Geburtenrhythmik. Zur Mittwinterzeit fallen die meisten Geburten in die Zeit von 08.00 bis 20.00 Uhr, während sie in den anderen Jahreszeiten auf die Nacht und den Vormittag fallen.

---

---

Supported by a grant from the National Research Council for Sciences (Finland).     

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.     

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).     

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.     

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.     

Dynamic mechanistic explanation: computational modeling of circadian rhythms as an exemplar for cognitive science

We consider computational modeling in two fields: chronobiology and cognitive science. In circadian rhythm models, variables generally correspond to properties of parts and operations of the responsible mechanism. A computational model of this complex mechanism is grounded in empirical discoveries and contributes a more refined understanding of the dynamics of its behavior. In cognitive science, on the other hand, computational modelers typically advance de novo proposals for mechanisms to account for behavior. They offer indirect evidence that a proposed mechanism is adequate to produce particular behavioral data, but typically there is no direct empirical evidence for the hypothesized parts and operations. Models in these two fields differ in the extent of their empirical grounding, but they share the goal of achieving dynamic mechanistic explanation. That is, they augment a proposed mechanistic explanation with a computational model that enables exploration of the mechanism’s dynamics. Using exemplars from circadian rhythm research, we extract six specific contributions provided by computational models. We then examine cognitive science models to determine how well they make the same types of contributions. We suggest that the modeling approach used in circadian research may prove useful in cognitive science as researchers develop procedures for experimentally decomposing cognitive mechanisms into parts and operations and begin to understand their nonlinear interactions.     

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.     

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

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.     

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

Summary 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.     

Effect of precocene II on circadian rhythms of feeding and mating behavior in the milkweed bug,Oncopeltus fasciatus

Summary Oncopeltus fasciatus adults were treated with the antiallatotropin, precocene II and the circadian rhythms of feeding and mating behavior were monitored at 2-h intervals from lights on to lights off under 2 photoperiod regimes. Females ovariectomized as 5th instars were monitored for feeding and mating behavior at 2–3-h intervals from lights on to lights off as well. Neither precocene treatment nor ovariectomy was found to affect the mating or feeding behavioral rhythms under any photoperiod regime.Acknowledgment. This work was supported by a National Science Foundation Grant number PCM76-10560 to M.A.R.