Response of the Sleep-Wake Rhythm to an 8-Hour Advance of the Light-Dark Cycle in the Rat

We have studied the effects of an 8-h advance of the environmental light-dark (LD) cycle on the sleep-wake rhythm in the rat. Electroencephalograms and electromyograms were recorded simultaneously on chart paper through a two-channel telemetry system for 3 days before phase shift (baseline) and 8 days during and after phase shift. Phase advance of the LD cycle led to an increase in both non-rapid eye movement (NREM) and REM sleep. The amount of NREM sleep in the light period correlated positively with that in the preceding dark period for 4 days after phase advance. The duration of REM sleep in the light period correlated negatively with that in the preceding dark period. The results suggest that homeostatic control of the amount of NREM sleep between the preceding dark period and the following light period is disturbed by phase advance of the LD cycle.     

A probabilistic model for the ultradian timing of REM sleep in mice

A salient feature of mammalian sleep is the alternation between rapid eye movement (REM) and non-REM (NREM) sleep. However, how these two sleep stages influence each other and thereby regulate the timing of REM sleep episodes is still largely unresolved. Here, we developed a statistical model that specifies the relationship between REM and subsequent NREM sleep to quantify how REM sleep affects the following NREM sleep duration and its electrophysiological features in mice. We show that a lognormal mixture model well describes how the preceding REM sleep duration influences the amount of NREM sleep till the next REM sleep episode. The model supports the existence of two different types of sleep cycles: Short cycles form closely interspaced sequences of REM sleep episodes, whereas during long cycles, REM sleep is first followed by an interval of NREM sleep during which transitions to REM sleep are extremely unlikely. This refractory period is characterized by low power in the theta and sigma range of the electroencephalogram (EEG), low spindle rate and frequent microarousals, and its duration proportionally increases with the preceding REM sleep duration. Using our model, we estimated the propensity for REM sleep at the transition from NREM to REM sleep and found that entering REM sleep with higher propensity resulted in longer REM sleep episodes with reduced EEG power. Compared with the light phase, the buildup of REM sleep propensity was slower during the dark phase. Our data-driven modeling approach uncovered basic principles underlying the timing and duration of REM sleep episodes in mice and provides a flexible framework to describe the ultradian regulation of REM sleep in health and disease.     

Light-Dark Difference in Arterial Pressure Variability During REM Sleep in the Rat

We have observed mean arterial pressure (MAP) variability during rapid eye movement (REM) sleep and brain temperature (Tb) in the rat during both light and dark periods over 24 h. MAP was measured using a telemetric device with a computer data capture and analysis system. As markers of MAP variability, the maximum and coefficient of variation (CV%) of MAP during REM sleep were determined. The following results were obtained: (a) there was a light-dark difference in MAP during non-REM (NREM) sleep and Tb during both NREM and REM sleep; (b) the increase of MAP in going from NREM to REM sleep in the light period was greater than that in the dark period, whereas the increase of Tb in the light period was not different from that in the dark period; (c) the maximum and CV% for MAP during REM sleep in the light period were greater than those in the dark period; (d) there was a negative correlation between the average Tb and MAP CV% during REM sleep. We suggest that phasic fluctuation of MAP during REM sleep may be influenced, in part, by a factor independent of sleep mechanisms.     

Light-Dark Difference in Arterial Pressure Variability During REM Sleep in the Rat

We have observed mean arterial pressure (MAP) variability during rapid eye movement (REM) sleep and brain temperature (Tb) in the rat during both light and dark periods over 24 h. MAP was measured using a telemetric device with a computer data capture and analysis system. As markers of MAP variability, the maximum and coefficient of variation (CV%) of MAP during REM sleep were determined. The following results were obtained: (a) there was a light-dark difference in MAP during non-REM (NREM) sleep and Tb during both NREM and REM sleep; (b) the increase of MAP in going from NREM to REM sleep in the light period was greater than that in the dark period, whereas the increase of Tb in the light period was not different from that in the dark period; (c) the maximum and CV% for MAP during REM sleep in the light period were greater than those in the dark period; (d) there was a negative correlation between the average Tb and MAP CV% during REM sleep. We suggest that phasic fluctuation of MAP during REM sleep may be influenced, in part, by a factor independent of sleep mechanisms.     

Altered sleep and behavioral activity phenotypes in PER3-deficient mice

Sleep homeostasis and circadian rhythmicity interact to determine the timing of behavioral activity. Circadian clock genes contribute to circadian rhythmicity centrally and in the periphery, but some also have roles within sleep regulation. The clock gene Period3 (Per3) has a redundant function within the circadian system and is associated with sleep homeostasis in humans. This study investigated the role of PER3 in sleep/wake activity and sleep homeostasis in mice by recording wheel-running activity under baseline conditions in wild-type (WT; n = 54) and in PER3-deficient (Per3(-/-); n = 53) mice, as well as EEG-assessed sleep before and after 6 h of sleep deprivation in WT (n = 7) and Per3(-/-) (n = 8) mice. Whereas total activity and vigilance states did not differ between the genotypes, the temporal distribution of wheel-running activity, vigilance states, and EEG delta activity was affected by genotype. In Per3(-/-) mice, running wheel activity was increased, and REM sleep and NREM sleep were reduced in the middle of the dark phase, and delta activity was enhanced at the end of the dark phase. At the beginning of the baseline light period, there was less wakefulness and more REM and NREM sleep in Per3(-/-) mice. Per3(-/-) mice spent less time in wakefulness and more time in NREM sleep in the light period immediately after sleep deprivation, and REM sleep accumulated more slowly during the recovery dark phase. These data confirm a role for PER3 in sleep-wake timing and sleep homeostasis.     

Essential Roles of GABA Transporter-1 in Controlling Rapid Eye Movement Sleep and in Increased Slow Wave Activity after Sleep Deprivation

GABA is the major inhibitory neurotransmitter in the mammalian central nervous system that has been strongly implicated in the regulation of sleep. GABA transporter subtype 1 (GAT1) constructs high affinity reuptake sites for GABA and regulates GABAergic transmission in the brain. However, the role of GAT1 in sleep-wake regulation remains elusive. In the current study, we characterized the spontaneous sleep-wake cycle and responses to sleep deprivation in GAT1 knock-out (KO) mice. GAT1 KO mice exhibited dominant theta-activity and a remarkable reduction of EEG power in low frequencies across all vigilance stages. Under baseline conditions, spontaneous rapid eye movement (REM) sleep of KO mice was elevated both during the light and dark periods, and non-REM (NREM) sleep was reduced during the light period only. KO mice also showed more state transitions from NREM to REM sleep and from REM sleep to wakefulness, as well as more number of REM and NREM sleep bouts than WT mice. During the dark period, KO mice exhibited more REM sleep bouts only. Six hours of sleep deprivation induced rebound increases in NREM and REM sleep in both genotypes. However, slow wave activity, the intensity component of NREM sleep was briefly elevated in WT mice but remained completely unchanged in KO mice, compared with their respective baselines. These results indicate that GAT1 plays a critical role in the regulation of REM sleep and homeostasis of NREM sleep.     

Sleep and cortical temperature in the Djungarian hamster under baseline conditions and after sleep deprivation

The Djungarian hamster (Phodopus sungorus) is a markedly photoperiodic rodent which exhibits daily torpor under short photoperiod. Normative data were obtained on vigilance states, electroencephalogram (EEG) power spectra (0.25–25.0 Hz), and cortical temperature (T_CRT) under a 168 h light-dark schedule, in 7 Djungarian hamsters for 2 baseline days, 4 h sleep deprivation (SD) and 20 h recovery.During the baseline days total sleep time amounted to 59% of recording time, 67% in the light period and 43% in the dark period. The 4 h SD induced a small increase in the amount of non-rapid eye movement (NREM) sleep and a marked increase in EEG slow-wave activity (SWA; mean power density 0.75–4.0 Hz) within NREM sleep in the first hours of recovery. T_CRT was lower in the light period than in the dark period. It decreased at transitions from either waking or rapid eye movement (REM) sleep to NREM sleep, and increased at the transition from NREM sleep to waking or REM sleep. After SD, T_CRT was lower in all vigilance states.In conclusion, the sleep-wake pattern, EEG spectrum, and time course of T_CRT in the Djungarian hamster are similar to other nocturnal rodents. Also in the Djungarian hamster the time course of SWA seems to reflect a homeostatically regulated process as was formulated in the two-process model of sleep regulation.Abbreviations EEG electroencephalogram - EMG electromyogram - N NREM sleep - NREM non-rapid eye movement - R REM sleep - REM rapid eye movement - SD sleep deprivation - SWA slow-wave activity - T_CRT cortical temperature - TST total sleep time - VS vigilance state - W waking     

Sleep EEG spectral analysis in a diurnal rodent:Eutamias sibiricus

1. Sleep was studied in the diurnal rodent Eutamias sibiricus, chronically implanted with EEG and EMG electrodes. Analysis of the distribution of wakefulness, nonrapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep over the 24 h period (LD 12:12) showed that total sleep time was 27.5% of recording time during the 12 h light period and 74.4% during the 12 h dark period. Spectral analysis of the sleep EEG revealed a progressive decay in delta power density in NREM sleep during darkness. Power density of the higher frequencies increased at the end of darkness. Power density of the higher frequencies decreased and that of the lower frequencies increased during light. 2. Analysis of the distribution of vigilance states under three different photoperiods (LD 18:6; 12:12; 6:18) revealed that changes in daylength mainly resulted in a redistribution of sleep and wakefulness over light and darkness. Under long days the percentage of sleep during light was enhanced. The time course of delta power density in NREM sleep was characterized by a long rising part and a short falling part under long days, while a reversed picture emerged under short days. As a consequence, the power density during days. As a consequence, the power density during light was relatively high under long days. 3. After 24 h sleep deprivation by forced activity, no significant changes in the percentages of wakefulness and NREM were observed, whereas REM sleep was slightly enhanced. EEG power density, however, was significantly increased by ca. 50% in the 1.25-10.0 Hz range in the first 3 h of recovery sleep. This increase gradually decayed over the recovery night. 4. The same 24 h sleep deprivation technique led to a ca. 25% increase in oxygen consumption during recovery nights. While the results of the EEG spectral analysis are compatible with the hypothesis that delta power density reflects the 'intensity' of NREM sleep as enhanced by prior wakefulness and reduced by prior sleep, such enhanced sleep depth after sleep deprivation is not associated with reduced energy expenditure as might be anticipated by some energy conservation hypotheses on sleep function.     

Nonphotic enhancement of adjustment to new light-dark cycles: masking interpretation discounted

The adjustment of hamsters to advanced light-dark (LD) cycles can be greatly accelerated by scheduling a single 3-hr bout of extra activity in a novel running wheel, starting about 7 hr before the time when the animals become active in the preceding LD cycle. The present experiments were designed to provide stronger evidence that this effect depends on a shift in the pacemaker rather than on masking. It was shown that when hamsters were put into continuous darkness (DD) 1 day after the exercise-accelerated phase shift, their free-running rhythms took off from a time nearer to the onset of darkness in the new LD cycle than in the preceding LD cycle. An incidental finding was that in DD the free-running period of the hamsters with the accelerated phase shifts was longer than that of the control animals. Further evidence that the 3-hr exercise pulse had produced a greater phase advance than that occurring in undisturbed control animals was obtained by giving a light pulse at the same clock time to all animals after they had been in DD for 8 days. The animals that had previously exercised for the additional 3-hr phase-advanced in response to the light pulse, while the undisturbed control animals phase-delayed.     

Subchronic 17alpha-ethinyl estradiol differentially affects subtypes of sleep and wakefulness in ovariectomized rats

In ovariectomized (OVX) Sprague-Dawley rats, estradiol benzoate (EB) has been reported to decrease rapid eye movement (REM) and non-REM (NREM) sleep during the dark phase for up to 3 days. It is unknown, however, if estrogenic effects on sleep extend beyond 3 days or if other estrogens could induce the same changes. Furthermore, it is unclear whether the increased wakefulness in the dark phase was due to changes in active or quiet wakefulness. Therefore, we examined the effects of daily injections of 17alpha-ethinyl estradiol (EE) for 6 days on sleep and wakefulness in the OVX rat. After 3 days of baseline recording using a telemetric system, rats were administered sesame oil (sc) for 3 days followed by injection with EE (20 mug/rat/day, sc) for 6 days. After treatment, sleep was recorded during hormone withdrawal for an additional 5 days. A few sporadic but statistically significant increases in light phase sleep occurred during the last 3 days of EE treatment. Starting on day 2 of the study, EE caused statistically significant decreases in dark phase REM sleep that were maintained throughout the treatment period and persisted until the 3rd day of hormone withdrawal. During the dark phase, statistically significant decreases in NREM sleep and increases in active wakefulness started on the second day of treatment and abated by the end of treatment. This study demonstrated that EE had similar effects on sleep-wakefulness to EB and demonstrates the utility of telemetric polysomnographic recording of the female OVX rat as a model for understanding the estrogen-induced changes on sleep-wakefulness.     

Racial Differences in the Human Endogenous Circadian Period

The length of the endogenous period of the human circadian clock (tau) is slightly greater than 24 hours. There are individual differences in tau, which influence the phase angle of entrainment to the light/dark (LD) cycle, and in doing so contribute to morningness-eveningness. We have recently reported that tau measured in subjects living on an ultradian LD cycle averaged 24.2 hours, and is similar to tau measured using different experimental methods. Here we report racial differences in tau. Subjects lived on an ultradian LD cycle (1.5 hours sleep, 2.5 hours wake) for 3 days. Circadian phase assessments were conducted before and after the ultradian days to determine the change in circadian phase, which was attributed to tau. African American subjects had a significantly shorter tau than subjects of other races. We also tested for racial differences in our previous circadian phase advancing and phase delaying studies. In the phase advancing study, subjects underwent 4 days of a gradually advancing sleep schedule combined with a bright light pulse upon awakening each morning. In the phase delaying study, subjects underwent 4 days of a gradually delaying sleep schedule combined with evening light pulses before bedtime. African American subjects had larger phase advances and smaller phase delays, relative to Caucasian subjects. The racial differences in tau and circadian phase shifting have important implications for understanding normal phase differences between individuals, for developing solutions to the problems of jet lag and shift work, and for the diagnosis and treatment of circadian rhythm based sleep disorders such as advanced and delayed sleep phase disorder.     

Light-Dark Entrainment of Circadian Activity Rhythms of the Diurnal Indian Palm Squirrel (Funambulus pennanti)

A recent focus of chronobiological studies has been to establish diurnal models as alternatives to the more frequently used nocturnal rodents. In the present study, light-dark (LD) entrainment characteristics were examined in one diurnal species, the Indian palm squirrel ( Funambulus pennanti ). Palm squirrels showed strongly diurnal locomotor activity rhythms (~ 88 percent) under light-dark (LD) cycles, with activity bimodally distributed during the L phase. In comparison to a dim LD cycle, exposure to a bright LD cycle caused a phase advance in the onset of activity, an increase in daily activity levels and an increase in the duration of activity. Percentage diurnality, however, did not vary between bright and dim LD cycles. Activity rhythms reentrained in significantly fewer days after an 8 hour phase delay of the LD cycle compared to an 8 hour phase advance. In both cases, the direction of reentrainment followed the direction of the LD shift. When exposed to single light pulses (1 hour) presented at the same time each day, 6/7 squirrels entrained. Under a skeletal photoperiod cycle (2 x 1 hour light pulses each day), 6/8 squirrels showed stable entrainment. The remaining squirrels exhibited rhythm splitting, with each component synchronising in an unstable manner with one of the light pulses. Under entrainment to single light pulses and to the skeletal photoperiod cycle, the phase angle of entrainment was negatively correlated with t. Finally, when exposed to a skeletal scotoperiod cycle (2 x 1-hour dark pulses each day), only 3/8 squirrels entrained, while the others free-ran. Two of the entrained squirrels showed spontaneous phase reversals during entrainment. As with other species, the activity rhythm of palm squirrels appears to be controlled by two separate self-sustaining oscillators. The strongly diurnal nature of palm squirrels make them a promising diurnal model for studies examining endogenous and exogenous influences on circadian functioning.     

Light-Dark Entrainment of Circadian Activity Rhythms of the Diurnal Indian Palm Squirrel (Funambulus pennanti)

A recent focus of chronobiological studies has been to establish diurnal models as alternatives to the more frequently used nocturnal rodents. In the present study, light-dark (LD) entrainment characteristics were examined in one diurnal species, the Indian palm squirrel (Funambulus pennanti). Palm squirrels showed strongly diurnal locomotor activity rhythms (? 88 percent) under light-dark (LD) cycles, with activity bimodally distributed during the L phase. In comparison to a dim LD cycle, exposure to a bright LD cycle caused a phase advance in the onset of activity, an increase in daily activity levels and an increase in the duration of activity. Percentage diurnality, however, did not vary between bright and dim LD cycles. Activity rhythms reentrained in significantly fewer days after an 8 hour phase delay of the LD cycle compared to an 8 hour phase advance. In both cases, the direction of reentrainment followed the direction of the LD shift. When exposed to single light pulses (1 hour) presented at the same time each day, 6/7 squirrels entrained. Under a skeletal photoperiod cycle (2 x 1 hour light pulses each day), 6/8 squirrels showed stable entrainment. The remaining squirrels exhibited rhythm splitting, with each component synchronising in an unstable manner with one of the light pulses. Under entrainment to single light pulses and to the skeletal photoperiod cycle, the phase angle of entrainment was negatively correlated with t. Finally, when exposed to a skeletal scotoperiod cycle (2 x 1-hour dark pulses each day), only 3/8 squirrels entrained, while the others free-ran. Two of the entrained squirrels showed spontaneous phase reversals during entrainment. As with other species, the activity rhythm of palm squirrels appears to be controlled by two separate self-sustaining oscillators. The strongly diurnal nature of palm squirrels make them a promising diurnal model for studies examining endogenous and exogenous influences on circadian functioning.     

Characteristics of the circadian activity rhythm in common marmosets (Callithrix j. jacchus)

The circadian activity rhythm of the common marmoset, Callithrix j. jacchus was investigated by long-term recording of the locomotor activity of 15 individuals (5 males, 10 females) from 1.5 to 8 years old, both under constant illumination and under LD 12:12. The mean period of the spontaneous circadian rhythm was 23.2 ± 0.3 h. Neither sex-specific differences nor a systematic influence of light intensity on the spontaneous period were observed, but the period was dependent on the duration of the trial and on the age of the individual. Due to the short spontaneous period, in LD 12:12 there was a distinct advance of the activity phase with respect to the light time and a masking of the true onset of activity by the inhibitory direct effect of low light intensity during the dark time. After an 8 h delay shift of the LD 12:12, re-entrainment of the circadian activity rhythm required an average of 6.8 ± 0.7 days; the average re-entrainment time after an 8 h phase advance of the LD cycle was 8.6 ± 1.3 day. This directional effect is ascribed to characteristics of the phase-response curve. No ultradian components were observed, either in the LD-entrained or the free-running circadian activity rhythm.     

Melatonin accelerates reentrainment of the circadian rhythm of its own production after an 8-h advance of the light-dark cycle

Summary The rhythm in melatonin production in the rat is driven by a circadian rhythm in the pineal N-acetyltransferase (NAT) activity. Rats adapted to an artificial lighting regime of 12 h of light and 12 h of darkness per day were exposed to an 8-h advance of the light-dark regime accomplished by the shortening of one dark period; the effect of melatonin, triazolam and fluoxetine, together with 5-hydroxytryptophan, on the reentrainment of the NAT rhythm was studied.In control rats, the NAT rhythm was abolished during the first 3 cycles following the advance shift. It reappeared during the 4th cycle; however, the phase relationship between the evening rise in activity and the morning decline was still compressed.Melatonin accelerated the NAT rhythm reentrainment. In rats treated chronically with melatonin at the new dark onset, the rhythm had already reappeared during the 3rd cycle, in the middle of the advanced night, and during the 4th cycle, the phase relationship between the evening onset and the morning decline of the NAT activity was the same as before the advance shift. In rats treated chronically with melatonin at the old dark onset or in those treated with melatonin 8 h, 5 h and 2 h after the new dark onset during the 1st, 2nd and 3rd cycle, respectively, following the advance shift, the NAT rhythm reappeared during the 3rd cycle as well but in the last third of the advanced night only.Neither triazolam nor fluoxetine together with 5-hydroxytryptophan administered around the new dark onset facilitated NAT rhythm reentrainment after the 8-h advance of the light-dark cycle.Abbreviations NAT N-acetyltransferase - LD cycle light-dark cycle - CT circadian time - LD xy light dark cycle comprising x h of light and y h of darkness     

Serotonin neurons and sleep. I. Long term recordings of dorsal raphe discharge frequency and PGO waves

Brain stem transection studies suggest that pontine neurons play a key role in regulating the mammalian sleep cycle. The serotonin (5-HT) hypothesis originally postulated that pontine 5-HT containing neurons directly initiated and maintained synchronized or NREM sleep and "primed" rapid eye movement (REM) sleep. Contrary to the predictions of this hypothesis, single unit recordings from the serotonergic dorsal raphe nucleus (DRN) have uniformly shown that DRN discharge rate is positively correlated with behavioral arousal but negatively correlated with both the NREM and REM phases of sleep. These findings required revision of the original 5-HT hypothesis and suggested instead that DRN discharge may influence the maintenance of behavioral arousal and, by ceasing to discharge, may contribute to the generation of NREM and REM sleep. The purpose of this paper was to quantitatively assess the strength of the correlation between DRN discharge, REM sleep, and PGO waves following the experimental perturbations of the sleep cycle. Since forced locomotor activity is known to powerfully alter the timing of sleep and wakefulness, the present experiments used forced activity in an attempt to dissociate DRN discharge from the sleep cycle. It was hypothesized that such dissociations would suggest DRN discharge is not involved in sleep cycle regulation. Contrastingly, preserved correlations would support the hypothesis of a possible causal relationship between DRN discharge, PGO waves activity, and the timing of sleep and wakefulness. Extracellular recordings were obtained from single cells in the DRN of intact, undrugged cats across greater than 300 sleep cycles with durations ranging from about 8 to 80 mins. Forced activity significantly reduced the amount of time spent in wakefulness and increased the number but not the duration of REM sleep epochs. The results revealed that DRN discharge rate was altered as a function of sleep cycle duration. In no case, however, was forced activity able to completely dissociate the characteristic DRN discharge rates from PGO waves or the ultradian sleep cycle. The inability of forced activity to disrupt the faithful relationships between DRN discharge, PGO waves, and sleep cycle phase thus provides a new form of correlative evidence consistent with the hypothesis that the DRN is involved in sleep cycle regulation.     

An ether stressor increases REM sleep in rats: possible role of prolactin

Sleep alterations after a 1-min exposure to ether vapor were studied in rats to determine if this stressor increases rapid eye-movement (REM) sleep as does an immobilization stressor. Ether exposure before light onset or dark onset was followed by significant increases in REM sleep starting approximately 3-4 h later and lasting for several hours. Non-REM (NREM) sleep and electroencephalographic slow-wave activity during NREM sleep were not altered. Exposure to ether vapor elicited prolactin (Prl) secretion. REM sleep was not promoted after ether exposure in hypophysectomized rats. If the hypophysectomy was partial and the rats secreted Prl after ether exposure, then increases in REM sleep were observed. Intracerebroventricular administration of an antiserum to Prl decreased spontaneous REM sleep and inhibited ether exposure-induced REM sleep. The results indicate that a brief exposure to ether vapor is followed by increases in REM sleep if the Prl response associated with stress is unimpaired. This suggests that Prl, which is a previously documented REM sleep-promoting hormone, may contribute to the stimulation of REM sleep after ether exposure.     

Restricted daytime feeding attenuates reentrainment of the circadian melatonin rhythm after an 8-h phase advance of the light-dark cycle

It is well established that in the absence of photic cues, the circadian rhythms of rodents can be readily phase-shifted and entrained by various nonphotic stimuli that induce increased levels of locomotor activity (i.e., benzodiazepines, a new running wheel, and limited food access). In the presence of an entraining light-dark (LD) cycle, however, the entraining effects of nonphotic stimuli on (parts of) the circadian oscillator are far less clear. Yet, an interesting finding is that appropriately timed exercise after a phase shift can accelerate the entrainment of circadian rhythms to the new LD cycle in both rodents and humans. The present study investigated whether restricted daytime feeding (RF) (1) induces a phase shift of the melatonin rhythm under entrained LD conditions and (2) accelerates resynchronization of circadian rhythms after an 8-h phase advance. Animals were adapted to RF with 2-h food access at the projected time of the new dark onset. Before and at several time points after the 8-h phase advance, nocturnal melatonin profiles were measured in RF animals and animals on ad libitum feeding (AL). In LD-entrained conditions, RF did not cause any significant changes in the nocturnal melatonin profile as compared to AL. Unexpectedly, after the 8-h phase advance, RF animals resynchronized more slowly to the new LD cycle than AL animals. These results indicate that prior entrainment to a nonphotic stimulus such as RF may "phase lock" the circadian oscillator and in that way hinder resynchronization after a phase shift.     

Reduction of rapid eye movement (REM) sleep by glucose alone or glucose and insulin in rats

Administration of a high dose of glucose (2.5 g/kg, i.p.) that is known to produce severe hyperglycemia in euglycemic rats suppressed rapid eye movement (REM) sleep time significantly during the first three hours of 8 hr total electroencephalogram (EEG) recording period. Co-administration of glucose (2.5 g/kg, i.p.) and a non-convulsive dose of insulin (1.0 I.U./kg, i.p.) produced a significant reduction in REM sleep time during 1st through 5th hour and an increase in slow-wave sleep (NREM) time in the 3rd and 4th hour of 8 hr total EEG recording period. However, awake, NREM and REM sleep time in the 8 hr total EEG recording period were unaffected by either glucose alone or glucose plus insulin treatments. These results strongly suggest that the insulin's effects on the sleep-awake cycle i.e. reduction in REM and a slight increase in NREM sleep times of rats is not due to indirect effects of insulin on the central nervous system via hypoglycemia as reported by us previously, but could possibly be due to its direct effects on brain chemistry of neurotransmitters such as serotonin, catecholamines and acetylcholine which are believed to modulate the sleep-awake cycle pattern in rats.     

Circadian Rhythm in Pineal N-Acetyltransferase Activity: Phase Shifting by Dark Pulses (III)

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is thought to be responsible for melatonin circadian rhythms. The enzyme has circadian properties--its rhythm persists in constant conditions, and it is precisely controlled by light and dark. Experiments are reported in which 4-h light or dark pulses were imposed on chicks (Gallus domesticus) over a 24-h period. Pineal NAT profiles were measured during and subsequent to the pulses. The phase of the NAT cycle following pulses was plotted to obtain phase-response curves. Light pulses produced a maximum phase shift (advance of 5 h) 8 h after the expected time of lights-out; dark pulses produced a maximum phase shift (advance of 4 h) 3 h after the expected time of lights-out. Maximum phase delays (-2 h) occurred 1-2 h after the expected lights-out for light pulses and 8 h after expected lights-on for dark pulses.