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 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.     

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.     

Sleep architecture in unrestrained rhesus monkeys (Macaca mulatta) synchronized to 24-hour light-dark cycles

STUDY OBJECTIVES: To characterize the sleep patterns of unrestrained, diurnal nonhuman primates entrained to 24-hour light-dark cycles. DESIGN: EEG, EMG, and EOG were recorded continuously via implanted telemetry from 5 unrestrained male rhesus monkeys housed individually under a 16:8 light-dark cycle (LD 16:8; L = 13 lux; D = 0 lux). RESULTS: In a LD 16:8 cycle, all 5 monkeys demonstrated a long period of consolidated sleep during the 8-h dark period. On average, sleep accounted for 89.2% of the 8-h dark period and 25.2% of the 16-hour light period. REM sleep occupied 23% of total sleep time over 24 h, or 10.7% of the total time. The average length of the consolidated sleep (CS) period was 10.5 h, although the time of CS onset was variable. In contrast, the end of CS, and thus the onset of consolidated wakefulness (CW) demonstrated very little variation, typically occurring within 2 min of light onset. Ultradian NREM-REM cycles with periods of approximately 60 min were also observed. EEG delta activity during NREM sleep, thought to reflect the homeostatic sleep process, peaked at 3-4 h after CS onset. CONCLUSIONS: The present study demonstrates the feasibility of long-term, unrestrained sleep monitoring in nonhuman primates using fully-implantable biotelemetry. With minor exceptions, most notably a delay in peak delta activity, sleep-wake architecture, regulation, and consolidation in rhesus monkeys strongly resembles that of humans. These results demonstrate that the unrestrained rhesus monkey is an excellent biomedical model for human sleep.     

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.     

Lengthening of the photoperiod influences sleep characteristics before and during total sleep deprivation in rat

The photoperiod has been evidenced to influence sleep regulation in the rat. Nevertheless, lengthening of the photoperiod beyond 30 days seems to have little effect on the 24‐hr baseline level of sleep and the response to total sleep deprivation. We studied the effects of 12:12 (habitual) and 16:8 (long) light–dark photoperiods on sleep, locomotor activity and body core temperature, before and after 24 hr of total sleep deprivation. Eight rats were submitted for 14 days to light–dark 12:12 (lights on: 08:00 hours–20:00 hours) followed by total sleep deprivation, and then for 14 days to light–dark 16:8 (light extended to 24:00 hours) followed by total sleep deprivation. Rats were simultaneously recorded for electroencephalogram, locomotor activity and body core temperature for 24 hr before and after total sleep deprivation. At baseline before total sleep deprivation, total sleep time and non‐rapid eye movement sleep per 24 hr and during extended light hours (20:00 hours–24:00 hours) were higher (13% for total sleep time) after light–dark exposure compared with habitual photoperiod, while percentage delta power in non‐rapid eye movements and rapid eye movements were unchanged. Locomotor activity and body core temperature were lower, particularly during extended light hours (20:00 hours–24:00 hours). Following total sleep deprivation, total sleep time and non‐rapid eye movements were significantly lower after long photoperiod between 20:00 hours and 24:00 hours, and between 10:00 hours and 12:00 hours, and unchanged per 24 hr. The percentage delta power in non‐rapid eye movements was lower between 08:00 hours and 11:00 hours. Total sleep deprivation decreased locomotor activity and body core temperature after habitual photoperiod exposure only. Fourteen days under long photoperiod (light–dark 16:8) increased non‐rapid eye movements sleep, and decreased sleep rebound related to total sleep deprivation (lower non‐rapid eye movements duration and delta power). This may create a model of sleep extension for the rat that has been found to favour anabolism in the brain and the periphery.     

Effects of a short light-dark cycle on the sleep-wake patterns of the cat.

The purpose of this study was to measure the effect of a short, 106 min, light-dark (LD) cycle on the sleep-wake (SW) patterns of the cat. Eight cats prepared for chronic sleep studies were observed with electrographic tracings for 48 hr on a regular 12:12 hr LD schedule and again after 2 weeks of adaptation to a 27 min light and 79 min dark schedule. Each 1 min of data was scored as either alert, drowsy, slow wave sleep (SWS) or REM sleep. The parameters studied were percent electrographic state, state epoch length, polycyclic SW cycle, and mean vigilance. The short LD cycle caused a significant increase in alert state accompanied by reductions in drowsy, SWS, and REM sleep states. Although the effect was more pronounced during lights-on intervals, the trend was also present in dark intervals. Alert episodes of about all lengths increased. There were decreases in longer episodes of the other three states and a tendency for shorter episodes to increase in number. Episodes of the polycyclic SW cycle did not tend to follow the short LD cycle. The mean length of both sleep and wake episodes increased rather than decreased. However, mean vigilance values increased toward wakefulness at or near the light interval. Analyses showed that both the amplitude and phase relationship of this increase was significantly related to the 27 min light interval in comparison to base-line data. It was hypothesized that both light-dark and dark-light transitions represent alerting cues to the cat. Differences between the SW response of the cat and the rat to LD cycles are discussed.     

Entrainment and masking of circadian drinking rhythms in primates: Influence of light intensity

The entrained drinking rhythms of squirrel monkeys were studied during exposure to 24 hr illumination cycles of three different intensities (60:0; 66:6; 76:16 lux). Increasing the intensity of ambient illumination significantly delayed the offset of drinking but had no effect on either the onset or the total amount of daily drinking behavior. Comparison of drinking behavior under an alternating schedule of LD 66:6 lux and constant light of 6 lux indicated that the twice daily light transitions consistently altered the temporal distribution of drinking behavior. The daily timing of squirrel monkey drinking behavior thus, depends not only on the mechanisms of circadian entrainment to the LD cycle, but also on the ability of the LD cycle to directly influence, or “mask” behavior.     

Scheduled daily exercise or feeding alters the phase of photic entrainment in Syrian hamsters

Single daily bouts of appropriately timed activity can phase-shift or entrain circadian rhythms in rodents maintained in constant dark (DD). Whether this apparent feedback of behavioral activity to the circadian pacemaker has any adaptive significance is unclear; circadian rhythms are normally entrained by light-dark (LD) cycles, and this may override any effects of activity. To address this issue, the phase of entrainment to LD cycles was examined in hamsters exposed to a daily exercise schedule (3 h of induced wheel running). Hamsters exercised late in the dark showed a significant delay of entrained phase in LD (i.e., they became relative “night owls”) and lengthening of free-running periodicity in DD, compared to controls and hamsters exercised in midlight. Hamsters fed in midlight (arousal without wheel running) showed a significant advance of LD entrained phase (i.e., they became “early birds”). These observations provide the necessary rationale for further examination of the functional significance of behavioral feedback for the normal entrainment process. In addition, they raise the possibility that the entrained phase of human circadian rhythms can be similarly manipulated by behavioral procedures such as timed exercise.     

Daily rhythm of locomotor activity is abolished during rapid eye movement sleep deprivation in the rat

Applying a modified flowerpot technique, which made it possible to use a test animal as its own control, twenty-four hour cycles of locomotor activity were recorded in eight juvenile male rats on 12/12 hr light/dark (LD) schedule during six days of rapid eye movement (REM) sleep deprivation. It was found that the LD difference in locomotor activity unrelated to feeding was instantaneously abolished during REM sleep deprivation. The daily rhythm of food-directed activity, however, was only gradually attenuated. Due to this equalisation in the light and dark activity the rats gave an impression of hyperactivity during the light hours although the total daily motor output after an initial increase returned close to the baseline value.     

Sparrow circadian rhythm responses to rotated light-dark schedules

House sparrows, Passer domesticus, were individually subjected to light-dark regimens while their perching activity was continuously monitored. The sparrows resynchronized in 5 days when LD8:16 (8 hr of light alternating with 16 hr of dark) was advanced by 8 hr; however, the sparrows were 1.7 hr from resynchronization after 5 days when the schedule was delayed 8 hr. Sparrows subjected to two simultaneously presented light-dark schedules (rotated LD8:16 provided by one light source imposed together with LD12:12 provided by a second light source) did not ignore either cycle; instead the sparrows responded as to a sequence of photoperiods; they resynchronized the onsets of their activity with the first time of lights-on of the collective photoperiod provided by the two light sources.     

Central visual pathways and the distribution of sleep in 24-hr and 1-hr light-dark cycles

The role of the central visual pathways in determining the distribution of sleep in light-dark (LD) cycles in the circadian and ultradian range was examined. EEG, EMG, and brain temperature were recorded under 24-hr (LD 12:12 or LD 10:14) and 1-hr (LD 0.5:0.5) cycles in rats which received either (1) no lesion, (2) primary optic tract lesions, (3) lesions of dorsal and lateral terminal nuclei of the accessory optic system, (4) lesions of medial terminal nucleus of the accessory optic system, or (5) retinohypothalamic tract-suprachiasmatic nucleus lesions. Under 24-hr cycles, about 40% of sleep occurred in the dark in intact rats. Retinohypothalamic tract-suprachiasmatic nucleus lesions abolished this entrainment of sleep to the LD cycle. Under 1-hr cycles, 90% of REM sleep occurred in the dark periods in intact rats. While primary optic tract lesions attenuated this response, it was not completely abolished by any of the visual system lesions. The characteristic LD distributions of sleep in circadian and ultradian cycles may therefore be under separate neural control by the central visual system.     

Prehatch entrainment of circadian rhythms in the domestic chick using different light regimes

The onset of circadian rhythms in many animals occurs during prenatal development. We conducted four experiments, using the domestic chick as a model, to assess when these rhythms can first be entrained and the type of light zeitgeber necessary. In Experiment 1, the presence of circadian rhythms was assessed using tonic immobility, an antipredator behavior, whereas in Experiments 2 to 4 body temperature was studied. We demonstrate that (a) circadian rhythms can be entrained during the late stage of the chick's 21-day incubation period (prehatch Days 13-18), (b) only 1 day of light cues [12:12 hr light:dark (12L:12D)] on prehatch Day 13 is necessary for entrainment, and (c) short bouts of light, which simulate the light cues embryos typically experience during natural incubation, can act as zeitgebers although they are not as effective as 12L:12D. The onset of entrainment is earlier than predicted and suggests that the brain structures mediating circadian rhythms mature sooner than proposed by previous research.     

Partial isolation of the suprachiasmatic nuclei: Effects on circadian rhythms of rat drinking behavior

The rat's daily pattern of contact with a drinking tube was observed in a light-dark cycle (LD 12:12) and in constant light (LL) after partial isolation of the suprachiasmatic nuclei (SCN) with a wire microknife that transected their lateral, dorsal, and caudal connections or the passage of a wire microknife through the SCN. Animals whose SCN had been partially isolated remained entrained to an LD cycle and phase shifted drinking behavior when the LD cycle was delayed 4 hr. Disintegration of circadian rhytmicity was observed when these rats were exposed to LL. Passage of the knife through the SCN resulted in immediate and persistent disruption of circadian rhythmicity as severe as that seen after electrolytic lesions of the SCN. These data confirm the necessity of the SCN in regulating circadian behavior and suggest that the SCN may mediate entrainment and freerunning rhythms via different neural systems.     

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.     

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.     

Disorganization of the rat activity rhythm by chronic treatment with methamphetamine

Remarkable changes in the circadian activity rhythm of rats were observed when they were chronically treated with methamphetamine dissolved in drinking water. The circadian rhythm was phase-delayed with respect to the light-dark (LD) cycle, and showed signs of relative coordination. In some rats, the circadian organization was disturbed and two activity components appeared, with one component free-running and the other entrained by the LD cycle. After methamphetamine withdrawal, these changes disappeared rapidly but there were transient periods of 2-3 days before establishment of a stable entrainment to the LD cycle. The changes in the circadian rhythm persisted even in constant darkness (DD). The period around 24 hr in DD was significantly shorter during methamphetamine treatment than after the drug withdrawal. These results indicate that neither alteration of the sensitivity to light nor lengthening of the intrinsic period is involved in the methamphetamine induced disorganization of the circadian rhythm. Possible mechanisms are discussed in terms of a multi-oscillatory system.     

Effects of aging on sleep in the golden hamster

The golden hamster (Mesocricetus auratus) has been a model organism for the study of circadian rhythmicity and, in particular, the effects of age on the circadian system. Surprisingly, nothing is known about the effects of advanced age on sleep in this species. As a first step in determining the effects of aging on sleep in the golden hamster, we recorded sleep for 24 hours in 12 young (3 months) and 18 old (17-18 months) golden hamsters entrained to a 14:10 light:dark (LD) cycle. Aged hamsters exhibited small but significant increases in overall NREM sleep time, primarily due to an increase in time the old animals spent in the NREM sleep state during the dark period relative to the young hamsters. There were no significant differences in REM sleep, median sleep episode length, or the number of arousals. The most striking differences between the sleep of young and old hamsters was in NREM delta (0.5-4 Hz) power per epoch. Old hamsters showed approximately 27% less (p=0.0004) delta power per NREM epoch than young hamsters. It is possible that increased NREM sleep time in the old hamsters may be a failed attempt to maintain cumulative delta power; ie, old hamsters may have more NREM sleep in order to make up for the lower intensity of their sleep. This decline in delta power with age parallels earlier findings in cats and humans, although has it not been previously reported in rodents.     

Coupling between feeding- and light-entrainable circadian pacemakers in the rat

Activity of the rat can be entrained to LD cycles (light-entrainable rhythm = LER) and to periodic food access (feeding-entrainable rhythm = FER) and these responses appear to be mediated by separate circadian pacemaking systems. The purpose of this study was to explore interactions between these systems. In Experiment I, after entrainment of activity to a LD cycle and to restricted feeding, the LD cycle was phase delayed by 4 hr and rats were food deprived for 3 days. Delaying transients were observed in both the LER and FER although food was no longer a Zeitgeber. In Experiment II, food was scheduled at 3 different phases of the LD cycle. Food access was then phase delayed by 8 hr and rats were placed in DD. When the new food access fell into the subjective day, the phase of the LER was not affected but transients in the FER persisted for up to 18 days, 3 to 5 times longer than reported for rats with suprachiasmatic nucleus lesions. When the new food access fell into the early subjective night, the "free-running" LER was phase advanced by over 3 hr but no delaying transients in the FER were observed. When the new food access fell into the late subjective night, the LER was not phase advanced but its period remained close to 24 hr and no delaying transients in the FER were observed. In Experiment III, food was presented at two phases of the LD cycle and restricted feeding was continued in DD without phase shifts.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of light on sleep and the EEG of young rats

Sleep states, the power spectra of the cortical electroencephalogram (EEG) and cortical temperature (T _crt) were determined in young rats (age 23–24 days). Recordings were made for 1 day under habitual 12 h light: 12 h dark (LD 1212) conditions and on the subsequent day under continuous darkness (DD). The amount and distribution of the vigilance states differed little between experimental conditions. Sleep occurred predominantly during the actual (LD) or habitual (DD) 12-h light period. The EEG power density in the actual light period was lower than in the habitual light period. These differences were largest in the delta range for the EEG of non-rapid eye movement of sleep (NREMS) and in the theta range for the EEG of REM sleep (REMS) and waking. EEG power density in NREMS was somewhat lower in the LD dark period than in the corresponding DD period. The typical 24-h pattern of EEG power density in NREMS, which reflects processes underlying sleep regulation, was little affected by the experimental conditions. It is concluded that the light during an LD 1212 schedule suppresses the EEG but has little effect on the vigilance states.