Entrainment Of Circadian Activity Rhythms Research Articles

Retinal pathways influence temporal niche

In mammals, light input from the retina entrains central circadian oscillators located in the suprachiasmatic nuclei (SCN). The phase of circadian activity rhythms with respect to the external light:dark cycle is reversed in diurnal and nocturnal species, although the phase of SCN rhythms relative to the light cycle remains unchanged. Neural mechanisms downstream from the SCN are therefore believed to determine diurnality or nocturnality. Here, we report a switch from nocturnal to diurnal entrainment of circadian activity rhythms in double-knockout mice lacking the inner-retinal photopigment melanopsin (OPN4) and RPE65, a key protein used in retinal chromophore recycling. These mice retained only a small amount of rod function. The change in entrainment phase of Rpe65(-/-);Opn4(-/-) mice was accompanied by a reversal of the rhythm of clock gene expression in the SCN and a reversal in acute masking effects of both light and darkness on activity, suggesting that the nocturnal to diurnal switch is due to a change in the neural response to light upstream from the SCN. A switch from nocturnal to diurnal activity rhythms was also found in wild-type mice transferred from standard intensity light:dark cycles to light:dark cycles in which the intensity of the light phase was reduced to scotopic levels. These results reveal a novel mechanism by which changes in retinal input can mediate acute temporal-niche switching.

Extremely low threshold for photic entrainment of circadian activity rhythms in molossid bats (Molossus molossus; Chiroptera – Molossidae)

Summary Circadian rhythms usually deviate from 24 h and must be synchronized (entrained) to the outer 24 h day by certain environmental periodicities called Zeitgebers. For almost all organisms the most efficient Zeitgeber is the light-dark cycle (LD). In mammals the photic Zeitgeber cues are exclusively received via retinal photoreceptors. It is still in debate whether this circadian photoreception is mediated by rods, cones, and/or other retinal cells. From recent results in mouse mutants a circadian photoreception via non-rod/non-cone retinal receptors was deduced. However, earlier observations in bats indicating a very low threshold for photic entrainment imply that circadian photoreception may be mediated by rod-like receptors. In the present study the threshold for photic entrainment was determined in the neotropical mastiff bat Molossus molossus. Six test animals (3 m, 3 f) were kept isolated in recording cages situated in light-tight and sound-attenuating wooden boxes with a special lighting device on top. Under constant ambient temperature of 25 ± 1°C, relative humidity of 60 ± 5%, and an irregular ad libitum feeding schedule, the bats were exposed intermittantly for longer times to constant physiological darkness (LD-X) or 12:12 h light dark cycles with physiological darkness during the dark time (D) and varying low light-time illuminances (L). Half of the bats had an extremely low threshold for photic entrainment, about 10−5 lux, while the other individuals’ free-running activity rhythm was entrained by LD cycles with 10−4, 10−2 and 10−1 lux in L. The illuminance of only 10−5 lux is the lowest threshold value for photic entrainment found thus far in vertebrates. Plausibility considerations suggest circadian photoreception via rod-like retinal receptors to be most probably involved in this case.

Entrainment of Circadian Activity Rhythms in Rats to Melatonin Administered at T Cycles Different from 24 Hours

Entrainment of running wheel activity in DD was studied in adult male Long Evans rats exposed to cycles of a constant dose of melatonin (MEL; 100 µg/h) infused subcutaneously. The period (T) of the MEL cycle was initially kept at 24 h until stable entrainment was established; T was then changed in a stepwise manner, and each new T value was maintained for at least 20 cycles. Entrainment by phase advance occurred near circadian time 12 (activity onset), and the range of entrainment was between 30 and 35 min. The negative phase angle difference between activity onset and MEL onset increased as T values approached the entrainment limit, whereas no change in the duration of daily activity periods was found. No difference was observed between pre- and posttreatment values of the endogenous circadian period; hence, no aftereffects were found for any T value. These results indicate that the functional properties of entrainment to MEL are similar to those of entrainment to light, suggesting that both zeitgebers share a common timing mechanism.

Unraveling the enigma: the role of melatonin in seasonal processes in birds.

Birds, unlike mammals, do not use the annual profile of pineal melatonin secretion to coordinate their reproductive efforts with a favorable time of year. Melatonin in birds mediates the entrainment of circadian activity rhythms, and thus helps to time hatching of eggs and facilitate migration. However, the role of melatonin as a reliable indicator of day length for seasonal processes has remained equivocal for many years. Recently, the influence of melatonin on two physiological processes involved in aspects of seasonal reproduction has been identified in European starlings: 1) the regulation of seasonal changes in immune function, and 2) neuroplasticity in the song control system. Melatonin can enhance cell-mediated immune function and acts as an inhibitory hormone on the song control system. Melatonin receptor (MelR) density in a forebrain song control nucleus, Area X, is regulated as a function of reproductive state; there is marked downregulation of MelR in Area X during the breeding season in starlings. Seasonal regulation of immune function and neural plasticity within the song control system, and the efficacy of the action of melatonin on these two processes, appears to be modified by the same central, thyroid-dependent mechanism that controls the reproductive state of birds. These data indicate that the interaction of day length and hormones of different classes affects the ability of melatonin to affect seasonal processes in birds. The downstream consequences of MelR regulation within the song control system are discussed with regard to the cellular action of melatonin and its possible interaction with immediate-early genes and transcription factors.

Maternal entrainment in the circadian activity rhythm of laboratory mouse (C57BL/6J)

Maternal entrainment of circadian activity rhythm was studied in the laboratory mouse (C57BL/6J). Pregnant mice gave birth in constant dim light and the mother raised the pups until Postnatal Day 18 (weaning). The wheel running activity of these pups was individually monitored from Day 18. It was found that the phases of pups' activity on the day of weaning were similar to the phases of their mother's rhythm ( p < 0.001), indicating that maternal entrainment occurs in the C57BL/6J pups. When the mother mouse was cyclically presented to the pups for 12 h of a day, thereby creating presence–absence (PA) cycles of 12:12 h, it was found that the pups' activity rhythm entrained to the imposed cycles. The onset of activity of the pups coincided with the beginning of the mother's 12-h absence period. It is proposed that the social contact between the mother and the pups is taken by the pups as subjective day (rest time) and absence of the mother as subjective night (activity time). This maternal (nonphotic) entrainment, however, does not continue beyond Postnatal Days 23–26, despite ongoing PA cycles. These results indicate that the PA cycles of the mother are a transient zeitgeber, and are effective in entraining the rhythm of pups only for about 4 weeks after birth.

O-64 - Potentiating action of MKC-242, a selective 5-HT1A receptor agonist, on photic entrainment of circadian activity rhythm in hamsters

O-64 - Potentiating action of MKC-242, a selective 5-HT1A receptor agonist, on photic entrainment of circadian activity rhythm in hamsters

Lack of Social Entrainment of Circadian Activity Rhythms in the Solitary Golden Hamster and in the Highly Social Mongolian Gerbil

This study compared the capability for social entrainment of the circadian locomotory rhythms of solitary versus socially living nocturnal small mammals. Therefore single adult golden hamsters and Mongolian gerbils of both sexes were kept under LD 12:12 and then transferred in their cages to a dark chamber (DD), which was covered with an opaque material, but located permanently in a room with other conspecifics exposed to a light regime (LD 12:12). The animal in the chamber was able to detect acoustical and olfactorial stimuli of the conspecifics outside the chamber. Under these experimental conditions all the golden hamsters and gerbils investigated developed free-running rhythms of activity with an individual-specific spontaneous period. In golden hamsters these free-running rhythms were never entrained or masked. In 5 out of 6 gerbils the free-running of activity rhythms stopped after a few days and the rhythms were more or less pronounced entrained or masked. Unexpectedly the response was not induced via signals from the conspecifics but quite probably by the caretaking procedures in the animal room. Therefore, our results suggest that in neither investigated species did social entrainment of the circadian activity rhythms occur.

A possible retinal information route to the circadian pacemaker through pretectal areas in the hagfish, Eptatretus burgeri

By recording the locomotor activity rhythm of hagfish, Eptatretus burgeri, in which surgical lesions of the pretectal areas were made, we searched for the route of light information from the eyes to the circadian pacemaker, which is considered to be located in the preoptic nucleus. The entrainment of circadian activity rhythm to the light dark cycle, under 12 h light 12 h dark (12L:12D) was lo animals whose pretectum was ablated with a pair of scissors and the animals then showed a free-running rhythm. Destruction of the pretectal areas with a high-frequency lesion generator also caused a free-running rhythm under 12L:12D. These findings indicate that retinal information may entrain the circadian rhyth, via the pretectal areas, which have retinofugal connections.

Nonphotic entrainment of circadian activity rhythms in suprachiasmatic nuclei-ablated hamsters.

Nonphotic entrainment of circadian activity rhythms in suprachiasmatic nuclei-ablated hamsters.

Nonphotic entrainment of circadian activity rhythms in suprachiasmatic nuclei-ablated hamsters.

This study examined the role of the suprachiasmatic nuclei (SCN) in nonphotic entrainment. The wheel-running activity of SCN-ablated hamsters was recorded in constant dark (DD) and then under prolonged schedules of 2-hr daily cage changes, restricted food availability, and daily light-dark (LD) cycles. Some hamsters with very large lesions subsuming the SCN and surrounding areas exhibited significant, albeit unstable, circadian activity rhythms in DD. Some hamsters with similar ablations also showed entrained rhythms to daily cage change schedules. All hamsters showed robust rhythms entrained to a daily feeding schedule, but no hamsters showed entrainment to LD cycles. Competent circadian oscillators evidently exist outside the SCN, at least 0.5 mm or more away, and at least some are nonphotically entrainable. Weaker entrainment in animals with larger lesions suggests that nonphotically entrainable oscillators also exist within the SCN or its immediate vicinity.

Social Entrainment of Circadian Activity Rhythms in Common Marmosets, Callithrix j. jacchus (Primates)1

AbstractLong‐term recordings of the locomotor activity of 9 common marmosets, Callithrix j. jacchus, show that under certain preconditions, social entrainment of the free‐running circadian rhythm can occur in these non‐human primates. However, there exist considerable interindividual differences in the Zeitgeber effect of the various forms of social contact. Findings indicate that both the level of acquaintance and the individual differences in spontaneous period of individuals involved are important, and that daily, or circadian, social cues have a cumulative effect. Because of the low Zeitgeber strength of social stimuli, however, desynchronization of different individual rhythms can arise spontaneously among animals kept as a pair in the same cage, even after months of harmonized free‐running rhythms. It is discussed that social entrainment in primates and other mammals is more likely to be a coincidental, rather than an essential, characteristic of the circadian system. Arousal triggered by social stimuli is thereby ascribed a key role.

Characteristics of Food-Entrained Orcadian Rhythms in Rats During Long-Term Exposure to Constant Light

Rats possess a system of circadian oscillators that permit entrainment of circadian activity rhythms independently to 24 hr cycles of light-dark and food access. The nature of interactions between food- and light-entrainable oscillators was examined by observing the generation and persistence of food-entrained circadian rhythms in rats whose light-entrainable rhythms were eliminated by long-term exposure to constant light. Most of these rats showed a delayed generation of food-entrained rhythms and only one of eight animals showed persistence of food associated rhythms during a 4-day food deprivation test. Rats whose light-entrainable rhythms are eliminated by suprachiasmatic nuclei ablation show, in contrast, normal generation and persistence of food-entrained rhythms. The results suggested a disruptive influence of constant light on non-photic entrainment, possibly due to coupling forces between damped light-entrainable oscillators and the food-entrainable oscillators.

Acoustical Entrainment of Circadian Activity Rhythms in House Sparrows: Constant Light is not Necessary

AbstractCycles of presence/absence of social factors can sometimes entrain the circadian activity rhythms of diurnal animals kept under constant light. This might represent a special case of photic entrainment; social factors might awaken the subjects and make them see the light at times when they are normally unaware of it because of sleep. The present study attempted to falsify this hypothesis by entraining the activity rhythms of house sparrows (Passer domesticus) kept in constant darkness. The zeitgebers used were daily 2‐h playbacks of conspecific vocalizations, and daily 1.5‐h acoustical (non‐conspecific) disturbance. 7 birds were tested; four (all males) entrained to both stimuli, while the other three (all females) mostly showed relative coordination. Entrainment took place when the stimuli coincided with the late part of the birds' normal sleep time. No anticipatory activity preceded the daily stimulus presentations. In a second experiment, 8 more male sparrows in constant darkness began their free‐running activity earlier (phase‐advanced) on days that followed the presentation of a single 2‐h bout of acoustical disturbance in the last half of their normal sleep time. Stimulus presentations at other times had no effect. Opening the eyes and seeing the light are not necessary for acoustical (and social) entrainment, but other physiological consequences or correlates of sleep interruption may be involved.

Restricted feeding and circadian activity rhythms of a predatory marsupial, Dasyuroides byrnei

There is considerable disagreement as to whether food availability entrains circadian activity rhythms in omnivorous laboratory rodents. However, in carnivorous mammals a restricted feeding regime could act as a zeitgeber because the predator should hold a periodism correlated to that of the prey. Nevertheless, a restricted feeding schedule does not dominate the LD cycle for entrainment of circadian activity rhythms of the nocturnal predator Dasyuroides byrnei, nor does it entrain the free-running activity rhythms in DD. Anticipatory wheel running prior to food availability was observed in most animals. Some evidence for weak coupling between LD-entrained and meal-associated oscillators was indicated by occurrences of relative coordination. This species does not appear to have a dominance hierarchy of zeitgebern different to that reported for laboratory rodents. One would have predicted that it would have been ecologically adaptive for cycles of food availability to be more important than the LD cycle in this species.

Recovery of anticipatory activity to restricted feeding in rats with ventromedial hypothalamic lesions

Entrainment of circadian activity rhythms to a fixed daily mealtime was measured in intact and ventromedial hypothalamic (VMH) lesioned rats housed in tilt-cages. Intact rats showed a clear increase in activity for 2–3 hr prior to the 2 hr daytime feeding period. Anticipatory activity in lesioned rats was attenuated or absent during restricted feeding 5–9 weeks after surgery, but was evident in all rats, even those bearing apparently total VMH damage, during a second restricted feeding schedule 14–21 weeks after surgery. These results show recovery of function and argue against a necessary role for the VMH in food entrained rhythms.

Dark switch in the entrainment of circadian activity rhythms in night monkeys, Aotus trivirgatus Humboldt

1. 1. The locomotor activity of the night monkey ( Aotus trivirgatus) has been shown to be related to light intensity by an optimum function; here entrainment by LD cycles is examined to see whether the mechanism of synchronization of circadian periodicity in Aotus is based on this function. 2. 2. Eleven night monkeys of various ages, previously in either a free-running phase or in LD 12:12 (10 2:10 −1 lux), were recorded in LD 12:12 with the optimal intensity (10 −1 lux) in the light part of the cycle and a suboptimal intensity (10 −1 lux) in the dark part. 3. 3. In all cases the monkeys synchronized in such a way that their activity phase fell in the dark part of the LD cycle. 4. 4. The implication is that Aotus is a true dark-active species, that the illumination-dependent activity maximum at 10 −1 lux does not affect the synchronization mechanism, and that the differential (direction of change) rather than proportional (absolute level) actions of light provide the decisive cue for synchronization of the circadian activity rhythm.

Circadian organization and neural mediation of hamster reproductive rhythms

(1) Circadian rhythms mediate various cycles of the hamster's reproductive physiology and behavior. (2) Destruction of the suprachiasmatic nuclei interfered with the integration and/or generation of coherent circadian rhythms of wheel-running behavior and also abolished photoperiodic regulation of the testes, which remain large and functional after the lesion regardless of photoperiod or presence of the eyes. (3) The retinohypothalamic tract is the principal visual projection for the entrainment of circadian activity rhythms to the light: dark cycle and also appears necessary and sufficient for mediating the effects of photoperiod on the reproductive physiology of the male hamster. (4) The hamster estrous cycle free-ran under constant dim illumination with a period significantly different from 4 days; regression analyses of concurrently recorded free-running heat onsets and wheel-running behavior showed that the period of the estrous cycle was a multiple (× 4) of the circadian activity period. This implies a circadian organization of the estrous cycle and mediation of both activity and estrous behaviors by a common circadian system. Implications of these findings for contemporary views of sexual differentiation of gonadotrophin release are considered. (5) Estradiol influenced the phase angle of entrainment of wheel-running behavior by ovariectomized hamsters. The period of the free-running activity rhythm was significantly shortened in blind ovariectomized hamsters implanted with Silastic capsules containing estradiol benzoate. The functional significance of these hormone-mediated changes in rhythm periodicity is discussed. (6) Exposure of male hamsters to short daily photoperiods reduced the frequency of copulation. Castrated males maintained on short daily photoperiods were less responsive than those on long days to the activational effects of testosterone on copulation. The significance of this photoperiodically induced refractoriness to hormones, which in this species appears limited to the male, is discussed.

Entrainment of Circadian Activity Rhythms in Squirrels

Entrainment behavior of circadian activity rhythms in squirrels apparently results from the interaction of an endogenous rhythm with environmental parameters. Red squirrels were placed in LD cycles which were out of phase with normal activity time. The time course of entrainment was a gradual, orderly process which often culminated in decreasing overshooting and undershooting. Animals placed in LD conditions which were insufficient to cause entrainment showed the predicted oscillatory free runs. The same analysis technique was used to examine entrainment data from other studies. Responsiveness varied, presumably depending on individual differences and the type and amplitude of the synchronizer. Generally, the stable entrainment-phase angle for diurnal animals was about 180 degrees from that for nocturnal animals. To examine the complex relation between period and phase during the entrainment process, 21 light-pulse experiments were conducted. It was found that, at least with red squirrels, phase and period shifting occur together and presumably act synergistically.

Photic entrainment of circadian activity rhythms by direct brain illumination in the cockroach Blaberus craniifer

The activity rhythms of male Blaberus craniifer adults having a small glass ‘window’ implanted in the vertex were studied in contrast to the rhythms of surgical control and untreated cockroaches. Results indicate that entrainment occurred in insects having a ‘window’ in the absence of functional cephalic photoreceptors when exposed to a 12L : 12D photoperiod. Activity rhythms of cockroaches possessing the ‘window’ were comparable to the rhythms of the surgical control and untreated insects.

Relationship of the Phase-Response Curve for Light to the Free-Running Period of the Kangaroo Rat Dipodomys merriami

Previous articleNext article No AccessRelationship of the Phase-Response Curve for Light to the Free-Running Period of the Kangaroo Rat Dipodomys merriamiJohn J. NataliniJohn J. Natalini Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 45, Number 2Apr., 1972 Article DOIhttps://doi.org/10.1086/physzool.45.2.30155579 Views: 2Total views on this site Citations: 16Citations are reported from Crossref Journal History This article was published in Physiological Zoology (1928-1998), which is continued by Physiological and Biochemical Zoology (1999-present). PDF download Crossref reports the following articles citing this article:S. Daan, D. G. M. Beersma Circadian Frequency and Its Variability, (Jan 2002): 24–37.https://doi.org/10.1007/978-3-662-06085-8_3Andrew J.P Francis, Grahame J Coleman Phase Response Curves to Ambient Temperature Pulses in Rats, Physiology & Behavior 62, no.66 (Dec 1997): 1211–1217.https://doi.org/10.1016/S0031-9384(97)00202-3Vijay Kumar Sharmad Light-Induced Phase Response Curves of the Circadian Activity Rhythm in Individual Field Mice, Mus Booduga, Chronobiology International 13, no.66 (Jul 2009): 401–409.https://doi.org/10.3109/07420529609020911D. J. G. Ford, A. Cook Responses to pulsed light stimuli in a pulmonate slug ( Limax pseudoflavus ), Journal of Zoology 214, no.44 (Mar 2009): 663–672.https://doi.org/10.1111/j.1469-7998.1988.tb03765.xRonald D. Gettinger, Charles L. Ralph Thermoregulatory responses to photoperiod by kangaroo rats (Dipodomys ordii): Influence of night lighting on nonshivering thermogenesis and resting metabolism, Journal of Experimental Zoology 234, no.33 (Jun 1985): 335–340.https://doi.org/10.1002/jez.1402340302F. A. Brown The biological clock phenomenon: Exogenous timing hypothesis, Journal of Interdisciplinary Cycle Research 14, no.22 (Sep 2008): 137–162.https://doi.org/10.1080/09291018309359807Ziad Boulos, Benjamin Rusak Circadian phase response curves for dark pulses in the hamster, Journal of Comparative Physiology ? A 146, no.44 (Jan 1982): 411–417.https://doi.org/10.1007/BF00609437F. A. Brown Interrelations Between Biological Rhythms and Clocks, (Jan 1978): 215–234.https://doi.org/10.1007/978-1-4757-4460-6_9G. J. Kenagy Seasonality of endogenous circadian rhythms in a diurnal rodentAmmospermophilus leucurus and a nocturnal rodentDipodomys merriami, Journal of Comparative Physiology ? A 128, no.11 (Jan 1978): 21–36.https://doi.org/10.1007/BF00668370Serge Daan, Colin S. Pittendrigh A Functional analysis of circadian pacemakers in nocturnal rodents, Journal of Comparative Physiology ? A 106, no.33 (Oct 1976): 253–266.https://doi.org/10.1007/BF01417857Frank A. Brown Biological clocks: Endogenous cycles synchronized by subtle geophysical rhythms, Biosystems 8, no.22 (Jul 1976): 67–81.https://doi.org/10.1016/0303-2647(76)90010-1K. R. Kramm Phase control of circadian activity in the antelope ground squirrel, Journal of Interdisiplinary Cycle Research 7, no.22 (Jun 1976): 127–138.https://doi.org/10.1080/09291017609359513K. E. Mills, R. B. Lockard, D. H. Owings Search for lunar periodicity in the bannertail kangaroo rat (Dipodomys spectabilis), Journal of Interdisciplinary Cycle Research 6, no.44 (Sep 2008): 323–333.https://doi.org/10.1080/09291017509359497 Kenneth R. Kramm Entrainment of Circadian Activity Rhythms in Squirrels, The American Naturalist 109, no.968968 (Oct 2015): 379–389.https://doi.org/10.1086/283008 T. Pavlidis The Free-Run Period of Circadian Rhythms and Phase Response Curves, The American Naturalist 107, no.956956 (Oct 2015): 524–530.https://doi.org/10.1086/282855 References, (Jan 1973): 187–204.https://doi.org/10.1016/B978-0-12-547350-7.50014-6