Circadian entrainment of the squirrel monkey by extreme photoperiods: Interactions between the phasic and tonic effects of light

To examine the role that the phasic and tonic aspects of the light-dark (LD) cycle play in entraining the circadian timing system of primates, squirrel monkeys (Saimiri sciureus) were exposed to 24 hr LD cycles in which the light duration (photoperiod) was varied from 1 sec to 23 hr. The monkeys were maintained in isolation and the circadian rhythm of drinking was monitored. The photoperiod was first gradually shortened until constant darkness was reached. Even in extremely short photoperiods of only one second of light per day, the drinking rhythm remained synchronized to the 24 hr period of the LD cycle. In the second set of experiments, the photoperiod was gradually lengthened until constant light was achieved. The drinking rhythm of all monkeys was synchronized by 21 hr photoperiods (LD 21:3), but free-ran in 23 hr photoperiods (LD 23:1) which provided a 1 hr dark pulse each day. The tonic effects of light may contribute to the difference between the ability to entrain to short versus long photoperiods. In constant darkness the free-running period was close to 24 hr, thus reducing the phase-resetting necessary to achieve entrainment to a 24 hr period by short light pulses. However, in constant light or in the long photoperiods which did not entrain (LD 23:1) the free-running period of the drinking rhythm was greater than 25 hr, thus requiring a much larger daily phase shift to achieve entrainment to a 24 hr period.     

Effect of reproductive state on circadian periodicity in the rat

The circadian activity rhythms of adult female rats maintained under a light-dark cycle of 14 hr light, 10 hr dark (LD 14:10) or constant dim illumination (dim LL) were recorded during their 4 or 5 day estrous activity cycles and when they were pseudopregnant. In LD 14:10 both the phase angle difference (ψ), which defines the temporal relationship between the onsets of activity and darkness, and the period (τ) of locomotor activity differed significantly among the days of the 4 and 5 day estrous cycle. Activity-time (α) varied reliably only over the days of the 5 day estrous cycle. The period of the free-running activity rhythm in dim LL also differed significantly among the days of the estrous cycle. In both LD and dim LL the most positive ψ, shortest τ and longest α were observed on the day of estrus. Pseudopregnancy diminished the amplitude and altered the daily pattern of the estrous activity rhythm. We conclude that the periodicity of circadian activity systematically varies as a function of the stage of the estrous cycle and in a manner that cannot be solely explained by corresponding alterations in endogenous estrogen.     

Direct and circadian control of sparrow behavior by light and dark

House sparrows, Passer domesticus, have perch-hopping activity (1) which was elicited by light (direct), and (2) which exhibited daily rhythms that were entrained by environmental light-dark cycles (circadian). When photoperiod was more than 14 hr, the sparrows' activity coincided with the light; when it was less than 14 hr, the birds were also active in the dark according to circadian predictions. Bimodality was dependent on photoperiod with the maximum incidence (75%) in LD16:8. Sparrows placed in LD1:11 (skeleton of 13:11) synchronized the onsets of their activity with the light beginning 8-18 hr after the time of the last L/D irrespective of when the birds experienced the first 1 hr light. Thirty-five percent of the sparrows advanced when they entrained to LD1:11 with the first pulse 8 hr after the last L/D; 76-87% of the sparrows delayed when they entrained to LD1:11 with the first pulse 2, 5 or 18 after the last L/D. Sparrows kept in exotic light-dark cycles (with periods of 10 min, 1.5 hr, 3.0 hr, 6.0 hr, 12 hr) were active in the light. Some birds displayed circadian rhythms superimposed on short period patterns. The period lengths of the circadian rhythms were shorter (22.8 hr) than in constant dark (24.2 hr). When sparrows subjected to LD1.5:1.5 or 36 hr of constant light were placed in constant dark, the phase of their activity onsets extrapolated to 15 hr after the last lights-off.     

Circadian rhythms in the rat: Constant darkness,entrainment to T cycles and to skeleton photoperiods

Free running activity and drinking rhythms of male Sprague-Dawley rats were observed in constant darkness (DD) for up to 44 days. The average period of the rhythms ($\text{τ}{}_{\mathrm{<mtext>dd</mtext>}}$) was 24.2 hr (±0.12 hr) and the activity time was near one half of the circadian cycle. In the second experiment, rats were entrained to T cycles (T=period) with 2 hr of light per cycle. At T=23 and T=26 about one half of the rats entrained indicating that these periods are near the limits of entrainment. T=23 induced a lasting aftereffect on $\text{τ}{}_{\mathrm{<mtext>dd</mtext>}}$ while T=26 affected $\text{τ}{}_{\mathrm{<mtext>dd</mtext>}}$ only briefly. In contrast to some other nocturnal rodents, activity time was not compressed as T neared the limits of entrainment. In the third experiment, rats and hamsters were entrained to 24 hr skeleton photoperiods (two 1 hr light pulses/cycle). Rats phase jumped to the longer subjective night when the interval between the light pulses was reduced to 6 or 5 hr, while most hamsters phase jumped at 3.5 hr. Furthermore, all rats phase jumped by means of delaying transients while most hamsters showed advancing transients. Finally, while skeleton photoperiods compressed activity time in hamsters to 6 hr or less, activity time remained fairly constant in rats. These results demonstrate considerable differences in the organization of the circadian system among commonly studied nocturnal rodents.     

Role of the pineal gland in circadian organization of diurnal ground squirrels

Golden-mantled ground squirrels, Spermophilus lateralis, pinealectomized (pinx) or sham-pinx at 70 days of age, were maintained in a LD 10:14 photoperiod; phase angles of activity onset were 1.6 +/- 0.3 and 1.9 +/- 0.3 hr in advance of light onset, respectively, and did not differ significantly between the groups. Rates of phase shifting of the activity rhythm after a 6 hr phase advance in the LD cycle also were comparable for the two groups and stable re-entrainment was achieved in 11 days. The period of the free-running activity rhythm in constant light did not differ between the groups. As demonstrated previously in nocturnal rodents, the pineal gland exerts little if any influence on generation or entrainment of the ground squirrel diurnal circadian activity rhythm. The rodent pineal is neither a master circadian oscillator nor a significant component of the transduction process by which light entrains the circadian activity rhythm.     

Photoperiodic regulation of the time of birth in rats: involvement of circadian endogenous mechanisms

A resonance experiment was undertaken to demonstrate that photoperiod regulates birth time by endogenous circadian mechanisms. Pregnant rats were maintained on a standard light-dark (LD) cycle (14L-10D; lights on from 0600 to 2000 hr) or on fixed LD cycles with periods of 12, 24, 36 and 48 hours after day 8 of gestation. In these groups, the light phase (2 hr) started between 0600 and 0800 hr or between 1800 and 2000 hr illuminating exclusively (for periods of 24 and 48 hr) or alternatively (for periods of 12 and 36 hr) the hours corresponding to morning (M) or evening (E) of the standard light regimen. At the end of gestation, the general activity was manifested mainly at moments corresponding to the night of the standard regimen in most groups; it was delayed in the two groups lit up exclusively at E hours. In groups receiving light exclusively at M hours, birth times were delayed compared to the deliveries in groups receiving light at E hours only. An intermediate distribution of birth times was observed when M and E hours were stimulated every 12 hr but not every 36 hr. The apparent stability of the diurnal rhythm of activity and the difference in birth time distributions due to the period of light phase indicate that the regulation of birth time by photoperiod is due to a circadian mechanism in rats. This mechanism implicates at least two endogenous systems which are apparently antagonists with regard to birth.     

Daytime sleep-wake cycle in the rat.

The daytime sleep-wake cycle of 20 male, albino rats was observed for a 8:00 a.m. to 8:00 p.m. period. EEG, EMG, gross body movement and eyelid position were continuously monitored throughout the 12 hr observation period. Based on percent of total time the results indicate that the rat's sleep-wake activities during the day are: awake, 24% (active, 17%; restings, 7%); SWS, 67% (light SWS, 13%; deep SWS, 54%); PS, 9%; and total sleep, 76%. The rats had a mean of 396 wake-ups from either SWS and PS per day. Visual observations revealed a sleep phenomenon not previously reported for the rat and termed “paradoxical awake”; an animal would generate typical light and deep SWS, EEG waves with either one or both eyes opened. The present results compared to previous findings revealed significant variability in estimates of the rat's sleep-wake activities which may be a function of illumination cycles, sleep observation times or duration of the adaptation periods.     

Effects of restricted feeding cycle on the locomotor activity rhythm in the mouse Mus booduga

The effect of restricted feeding (RF) cycles on the circadian locomotor activity rhythm was studied in the nocturnal field mouse Mus booduga. Mice were presented with a 2-h meal schedule every 24 h in continuous darkness (DD), in continuous light (LL), and in a light-dark (LD) cycle. Additionally, in DD, two groups of mice were subjected to RF cycles of periodicities 22 (T22) and 26 h (T26), respectively, in order to assess the limits of entrainment. The T22 and T26 RF cycles failed to produce any entrainment of the locomotor activity rhythm, whereas some of the animals that had a free-running period (tau) close to 24 h showed stable entrainment or "relative coordination" to daily (T24) RF cycle. In LD, the locomotor activity rhythm phase advanced under the influence of the daily RF cycle when the food presentation preceded the light to dark (L to D) transition by 5-6 h. However, when the timing of food presented in the RF cycle coincided with the L to D transition, locomotor activity rhythm dissociated into two components. Some of the mice whose locomotor activity rhythm disappeared in LL showed prominent meal-AA. These results suggest that RF modifies the expression of the light-entrainable pacemaker (LEP) directly and also that in the absence of the expression of the LEP, RF can induce meal-AA.     

Conditioned stimulus control in the rat circadian system depends on clock resetting during conditioning

The authors examined the ability of a conditioned stimulus (CS; mild air disturbance) previously paired with an entraining light pulse to reset the circadian pacemaker in rats. Rats were entrained to a single 30-min light stimulus delivered every 25 hr or 24 hr (T cycle). Each daily light presentation was paired with the CS. After at least 20 days of stable entrainment to each of the T cycles, the rats were allowed to free run and were then presented with the CS at circadian time 15. CS-induced phase shifts in wheel-running activity rhythms were taken as evidence for conditioning. For the most part, conditioning occurred after CS-light pairings on the 25-hr but not 24-hr T cycle. The results suggest that CS control of the circadian clock phase depends on the effect that the entraining light pulse has on the clock during conditioning.     

Feeding time synchronizes primate circadian rhythms.

Circadian rhythms of squirrel monkeys maintained in constant light and temperature can be entrained by 24 hr cycles of food availability with eating for 3 hr and fasting for 21 hr (EF 3:21). Rhythms of drinking, body temperature and urinary potassium and water excretion exhibited periods which matched the 24 hr period of the EF 3:21 cycle. These results suggest that temporal patterns of food intake are capable of synchronizing the circadian timekeeping system which underlies the observed rhythms.     

Pretreatment circadian period in free-running blind people may predict the phase angle of entrainment to melatonin.

To date, we have entrained (synchronized) eight totally blind people with free-running circadian rhythms to a nightly dose of 10 mg of melatonin. Each person entrained at a different phase angle of entrainment (PAE), which is the interval in hours between the time of the melatonin dose and the time of the endogenous melatonin onset. When the PAE was plotted against the pretreatment free-running (i.e. slightly different than 24.0 h) circadian period (tau), the fitted regression line revealed a significant correlation, which is consistent with previous findings on light entrainment of rest-activity rhythms in free-running rodents [Pittendrigh and Daan, J. Comp. Physiol., 106 (1976) 291-331].     

Activity rhythms in the circadian domain appear in suprachiasmatic nuclei lesioned rats given methamphetamine

Female rats were lesioned in the suprachiasmatic nuclei (SCN) electrolytically and treated with methamphetamine. The SCN lesions abolished the circadian locomotor rhythm completely. When methamphetamine was administered in the drinking water, robust rhythmicities in locomotor activity appeared in the SCN lesioned rats, which did not entrain to the 24 hr light cycle. The period of the activity rhythm was dose-dependent; the lower the concentration of methamphetamine was, the shorter the period of the rhythm became. When rats were treated with 0.005% methamphetamine, the mean period was 26.4 hours. In addition, activity time () became shorter, rest time () longer and / ratio lower, when methamphetamine concentration was decreased. After methamphetamine withdrawal, the rhythmicity disappeared and locomotor activity became aperiodic again. When methamphetamine was administered continuously by means of an osmotic minipump, similar rhythmicities appeared in locomotor activity of the SCN lesioned rats. It is concluded that methamphetamine manifests an activity rhythm whose period is in the circadian range. The rhythmicity is independent of the SCN and is not entrained by the light-dark cycle.     

Cytotoxicity by Tumor Necrosis Factor is Linked with the Cell Cycle But Does Not Require DNA Synthesis

Abstract

The relationship between the kinetics of cell death induced by TNF and the cell cycle in L929.10 target cells was investigated by comparison of growing, asynchronous cells with target cells synchronized at G₁/S using a double thymidine block. The induction phase of lysis, the time following TNF addition but before loss of cell viability, was shortened in asynchronous cells by increasing the level of saturation of the TNF receptor. However, in synchronized target cells, the length of the induction phase showed no dependence on receptor occupancy. Almost all cell death occurred within a 3 hr period 4-7 hr after the addition of TNF regardless of the concentration of TNF. Target cell lysis in Synchronized cells was concomitant with mitosis as verified by flow cytometry and DNA staining with propidium iodide. The narrow window of cytotoxicity was not due to cell cycle-related changes in the expression of the TNF receptor as measured by [¹²⁵I]TNF binding. Treatment with TNF did not accelerate or retard the progression of cells through S and G₂/M nor did target cells accumulate at G₂/M. When the kinetic experiments were repeated in the presence of 2 MM thymidine, TNF-treated cells died with identical dose and kinetic responses as those in which the thymidine block had been removed. Under these conditions, flow cytometric analysis revealed that DNA synthesis remained inhibited. These results suggest that TNF-induced cytotoxicity is linked to cell cycle-associated processes and that TNF is capable of overriding the normal cellular controls that coordinately link the DNA replicative cycle with the mitotic cycle. In the L929.10 target cell, TNF may induce a fatal mitosis-linked event.     

Circadian rhythms in house sparrows: lighting ad lib

House sparrows, Passer domesticus, have circadian rhythms of locomotor activity that can be entrained by light-dark cycles. Perch-hopping activity was studied in house sparrows that were given control of their own lighting. In one series of experiments, sparrows permitted to select their own lighting most commonly chose circadian freerunning cycles. The period of the selected freerunning cycles was 23.2 hr (0.9 hr shorter than the period length the sparrows exhibited in constant dark). The average self-imposed "photoperiods" in the selected freerunning cycles ranged from 8.2-10.0 hr. In a second series of experiments, sparrows were exposed to LDLD1:6:1:16. This cycle can be interpreted ambiguously as the skeleton of a short photoperiod, LD8:16, or of a long photoperiod, LD18:6. All the birds (13 birds; 23 trials) interpreted the skeleton cycle as a short photoperiod because they entrained to it as they would to LD8:16.     

Effect of progesterone on the estrous activity cycle of the rat

Two, 3 or 4 Silastic capsules of progesterone were implanted sc for 24–35 days, removed for a 12–14 day interval and re-implanted into the same adult female rats from which they were taken. A control group received cholesterol capsules. For approximately 4–10 days, Silastic capsules of progesterone suppressed estrous activity cycles. Thereafter, amplitude of running increased progressively and definite periodicities re-emerged. Following a 12 day recovery period, the same capsules were re-implanted and activity was again suppressed. During the first implantation, the number of estrous cycles with greater than 4-day periods significantly increased. Progesterone was also found to delay the daily onset of activity in relation to the light/dark cycle (phase angle difference). Phase angle difference prior to the first implantation was negatively correlated with the rate of recovery. The data support the conclusion that progesterone affects parameters of estrous activity by antagonizing the actions of estrogen and suggest that animals may make internal adjustments to high titers of progesterone.     

Kinetics of parvovirus replication,cytopathic effects,and mitotic arrest in synchronized bovine fetal spleen cells

Initiation of autonomous parvovirus replication depends on the S phase of host cells actively traversing the cell cycle. The parvoviruses Lu III and H-1 inhibit synchronized cells from entering mitosis, implying that parvoviruses rapidly shut down cell cycle traverse during G2 phase. Bovine parvovirus (BPV) did not inhibit the entry into mitosis of hydroxyurea synchronized bovine fetal spleen cells. Mitotic indexes of infected cultures were as much as 60-fold higher than those of mock-infected controls. Mitosis in control and infected cultures peaked at 10 hr after infection corresponding to the end of the BPV eclipse period. Cytopathic changes, including morphological alteration of mitotic chromosomes, were detected in mitotic cells from infected cultures by light and electron microscopy. Arrest of BPV-infected cells in mitosis may explain these results. Not all infected cells were killed in mitosis, since some developed intranuclear inclusions and became pycnotic as nucleated, interphase cells. Inclusion formation was coincident with viral morphogenesis in interphase nuclei at 16 to 18 hr postinfection, late in the viral replication cycle. The cell cycle stage at which parvovirus-infected cells are arrested and cytopathic events ensue may be determined by the cellular progression rate from S phase through G2 and M.     

Effects of acute ovariectomy on the lordosis response of female rats

The sexual receptivity of intact females with 4- or 5-day estrous cycles was compared to that of other females which had been ovariectomized at particular times during their cycles. The quality and frequency of lordosis responding were more degraded the earlier during the cycle ovariectomy was performed. This effect was more pronounced in 4-day than in 5-day cyclic females. Because exogenous progesterone was administered to all ovariectomized females, these behavioral deficits were attributed to removal of ovarian estradiol. Ovariectomy 6 hr before the critical period for luteinizing hormone release significantly shortened the duration of behavioral estrus, even though it had no effect when lordosis was tested at the time intact estrous females are maximally receptive. These findings are consistent with the hypothesis that the continual availability of estradiol throughout the 18--24 hr interval perior to the onset of behavioral estrus is essential for optimal conditioning of sexual receptivity to occur under physiological conditions. The relevance of triggering and maintenance functions of estradiol to these results is discussed.     

细胞周期对细胞ADPRT基础活性及DNA损伤剂诱发活性的影响

真核细胞染色质中的腺苷二磷酸核糖基转移酶(ADPRT)是维持有效DNA切除修复所必需的。本研究证明在通透化了的FL细胞中ADPRT活性呈细胞周期依存性波动。它的活性峰值见于DNA合成峰值后的4～6小时;同步培养于G_1期的细胞在按触DNA-损伤剂,甲基硝基亚硝基胍(MNNG)、甲磺酸甲酯(MMS)及4-硝基喹啉氧化物(4NQO)后ADPRT活性明显升高。在细胞周期的不同阶段,MNNG/4NQO对ADPRT的刺激作用与细胞周期对它的影响呈叠加作用。但MMS对ADPRT活性的刺激作用却完全依存于基础酶活性。在基础酶活性最高时,MMS几乎不显示其ADPRT刺激作用。因而认为DNA-损伤剂引起的ADPRT刺激作用有不止一个机制存在。同步于G_1期的细胞最适合于显示DNA损伤后的ADPRT活性升高。上述细胞周期性影响可能同细胞周期中DNA修复的顺序性变化以及细胞对致癌物敏感性的周期性变化有关。     

Effects of feeding and light cycles on activity rhythms of maternally isolated rat pups

Motor activity of infant rat pups was measured continuously between days 3 and 18 of postnatal age. Mother-reared rats on a 12:12 LD cycle exhibited significant rhythmic activity in the circadian range as early as day 5 of postnatal age. Some of the pups reared in isolation from maternal and sibling contact and kept on 12:12 LD cycles, feeding cycles, or combinations of feeding, temperature, and LD cycles also showed rhythmic activity but it was less persistent and of a lower amplitude than the rhythms of the mother-reared group. In the isolated rat pups nocturnal partitioning of activity was strengthened in the presence of both a light-dark cycle and a feeding cycle but only when the feeding resembled more natural nursing rhythms. In animals kept on constant light and a feeding cycle, activity occurred slightly more often during the 12-hr interval of decreased food intake. The addition of a temperature cycle--cooler nocturnal temperature--decreased the proportions of nocturnal motor activity. These results indicate that feeding and light-dark cycles may contribute to the synchronization of activity rhythms during the early postnatal period.     

Rapid eye movement stage of sleep participates in the generation of the nocturnal meal pattern in the rat

Twenty-four hour cycles of food intake were continuously recorded in eight male rats on a $\text{12}\text{12}$ hr light/dark schedule during baseline conditions and rapid eye movement sleep deprivation. The results suggest that food intake in the rat is controlled by two different mechanisms, one serving control of immediate caloric demands during the dark part of the LD cycle and the other, activated prior to the beginning of the inactive light hours, being responsible for the intake of a few large meals covering the total energy requirement for this time period. The correct timing of the consumption of these large meals with respect to the LD cycle seems to be dependent on undisturbed rapid eye movement sleep.