Yujiro Yamanaka

Physical exercise accelerates reentrainment of human sleep-wake cycle but not of plasma melatonin rhythm to 8-h phase-advanced sleep schedule

Effects of timed physical exercise were examined on the reentrainment of sleep-wake cycle and circadian rhythms to an 8-h phase-advanced sleep schedule. Seventeen male adults spent 12 days in a temporal isolation facility with dim light conditions (<10 lux). The sleep schedule was phase-advanced by 8 h from their habitual sleep times for 4 days, which was followed by a free-run session for 6 days, during which the subjects were deprived of time cues. During the shift schedule, the exercise group (n = 9) performed physical exercise with a bicycle ergometer in the early and middle waking period for 2 h each. The control group (n = 8) sat on a chair at those times. Their sleep-wake cycles were monitored every day by polysomnography and/or weight sensor equipped with a bed. The circadian rhythm in plasma melatonin was measured on the baseline day before phase shift: on the 4th day of shift schedule and the 5th day of free-run. As a result, the sleep-onset on the first day of free-run in the exercise group was significantly phase-advanced from that in the control and from the baseline. On the other hand, the circadian melatonin rhythm was significantly phase-delayed in the both groups, showing internal desynchronization of the circadian rhythms. The sleep-wake cycle resynchronized to the melatonin rhythm by either phase-advance or phase-delay shifts in the free-run session. These findings indicate that the reentrainment of the sleep-wake cycle to a phase-advanced schedule occurs independent of the circadian pacemaker and is accelerated by timed physical exercise.

Scheduled exposures to a novel environment with a running-wheel differentially accelerate re-entrainment of mice peripheral clocks to new light-dark cycles.

Effects of scheduled exposures to novel environment with a running‐wheel were examined on re‐entrainment to 8 h shifted light–dark (LD) cycles of mouse circadian rhythms in locomotor activity and clock gene, Per1, expression in the suprachiasmatic nucleus (SCN) and peripheral tissues. Per1 expression was monitored by a bioluminescence reporter introduced into mice. The animals were exposed to the novel environment for 3 h from the shifted dark onset for four cycles and released into constant darkness. In the phase‐advance shift, the circadian rhythm in locomotor activity fully re‐entrained in the exposed group, whereas it was in transients in the control. On the other hand, the circadian rhythm of Per1 expression in the SCN almost completely re‐entrained in both the control and exposed groups. In the skeletal muscle and lung, the circadian rhythm fully re‐entrained in the exposed group, whereas the rhythms in the control did not. In the phase‐delay shift, the circadian rhythms in locomotor activity and Per1 expression almost completely re‐entrained in both groups. These findings indicate that the scheduled exposures to novel environment with a running‐wheel differentially accelerate the re‐entrainment of the mouse peripheral clocks to 8 h phase‐advanced LD cycles.

Loss of circadian rhythm and light-induced suppression of pineal melatonin levels in Cry1 and Cry2 double-deficient mice.

Cryptochrome 1 and 2 (Cry1 and Cry2) are considered essential for generating circadian rhythms in mammals. The role of Cry1 and Cry2 in circadian rhythm expression and acute light‐induced suppression of pineal melatonin was assessed using Cry1 and Cry2 double‐deficient mice (Cry1−/−/Cry2−/−) developed from the C3H strain that synthesizes melatonin. We examined the circadian variation of pineal melatonin under a 12:12‐h light–dark (LD) cycle and constant darkness (DD). Light suppression of pineal melatonin concentration was analyzed by subjecting a 30‐min light pulse at the peak phase of melatonin concentration. Wild‐type mice showed significant rhythmicity in pineal melatonin concentration with the highest level at Zeitgeber time 22 (ZT22, where time of light on was defined as ZT0) under LD or ZT18 on the first day of DD. In contrast, Cry1−/−/Cry2−/− mice did not show significant circadian rhythmicity, with only a small peak observed at ZT22 in LD. Nevertheless, a significant daily variation could be observed under DD, with a small increase at ZT6 and ZT18 h. Melatonin concentration was significantly suppressed by acute light pulse at ZT22 in wild‐type mice but not in Cry1−/−/Cry2−/− mice. The present results suggest that Cry genes are required for regulating pineal melatonin synthesis via circadian and photic signals from the suprachiasmatic nucleus of the hypothalamus (SCN).

Differential regulation of circadian melatonin rhythm and sleep-wake cycle by bright lights and nonphotic time cues in humans

Our previous study demonstrated that physical exercise under dim lights (<10 lux) accelerated reentrainment of the sleep-wake cycle but not the circadian melatonin rhythm to an 8-h phase-advanced sleep schedule, indicating differential effects of physical exercise on the human circadian system. The present study examined the effects of bright light (>5,000 lux) on exercise-induced acceleration of reentrainment because timed bright lights are known to reset the circadian pacemaker. Fifteen male subjects spent 12 days in temporal isolation. The sleep schedule was advanced from habitual sleep times by 8 h for 4 days, which was followed by a free-run session. In the shift session, bright lights were given during the waking time. Subjects in the exercise group performed 2-h bicycle running twice a day. Subjects in the control kept quiet. As a result, the sleep-wake cycle was fully entrained by the shift schedule in both groups. Bright light may strengthen the resetting potency of the shift schedule. By contrast, the circadian melatonin rhythm was phase-advanced by 6.9 h on average in the exercise group but only by 2.0 h in the control. Thus physical exercise prevented otherwise unavoidable internal desynchronization. Polysomnographical analyses revealed that deterioration of sleep quality by shift schedule was protected by physical exercise under bright lights. These findings indicate differential regulation of sleep-wake cycle and circadian melatonin rhythm by physical exercise in humans. The melatonin rhythm is regulated primarily by bright lights, whereas the sleep-wake cycle is by nonphotic time cues, such as physical exercise and shift schedule.

Daily exposure to a running wheel entrains circadian rhythms in mice in parallel with development of an increase in spontaneous movement prior to running-wheel access

Entrainment of circadian behavior rhythms by daily exposure to a running wheel was examined in mice under constant darkness. Spontaneous movement was individually monitored for more than 6 mo by a thermal sensor. After establishment of steady-state free running, mice were placed in a different cage equipped with a running-wheel for 3 h once per day at 6 AM. The daily exchange was continued for 80 days. The number of wheel revolutions during exposure to the running wheel was also measured simultaneously with spontaneous movement. In 13 out of 17 mice, circadian behavior rhythm was entrained by daily wheel exposure, showing a period indistinguishable from 24 h. The entrainment occurred in parallel with an increase in spontaneous movement immediately prior to the daily wheel exposure. A similar preexposure increase was observed in only one of four nonentrained mice. The preexposure increase appeared in 19.5 days on average after the start of daily wheel exposure and persisted for 36 days on average after the termination of the exposure schedule. The preexposure increase was detected only when daily wheel exposure came into the activity phase of the circadian behavior rhythm, which was accompanied by an increase in the number of wheel revolutions. These findings indicate that a novel oscillation with a circadian period is induced in mice by daily exposure to a running wheel at a fixed time of day and suggest that the oscillation is involved in the nonphotic entrainment of circadian rhythms in spontaneous movement.

Morning and evening physical exercise differentially regulate the autonomic nervous system during nocturnal sleep in humans

Effects of daily physical exercise in the morning or in the evening were examined on circadian rhythms in plasma melatonin and core body temperature of healthy young males who stayed in an experimental facility for 7 days under dim light conditions (<10 lux). Sleep polysomnogram (PSG) and heart rate variability (HRV) were also measured. Subjects performed 2-h intermittent physical exercise with a bicycle ergometer at ZT3 or at ZT10 for four consecutive days, where zeitgeber time 0 (ZT0) was the time of wake-up. The rising phase of plasma melatonin rhythm was delayed by 1.1 h without exercise. Phase-delay shifts of a similar extent were detected by morning and evening exercise. But the falling phase shifted only after evening exercise by 1.0 h. The sleep PSG did not change after morning exercise, while Stage 1+2 sleep significantly decreased by 13.0% without exercise, and RE sleep decreased by 10.5% after evening exercise. The nocturnal decline of rectal temperature was attenuated by evening exercise, but not by morning exercise. HRV during sleep changed differentially. Very low frequency (VLF) waves increased without exercise. VLF, low frequency (LF), and high frequency (HF) waves increased after morning exercise, whereas HR increased after evening exercise. Morning exercise eventually enhanced the parasympathetic activity, as indicated by HRV, while evening exercise activated the sympathetic activity, as indicated by increase in heart rate in the following nocturnal sleep. These findings indicated differential effects of morning and evening exercise on the circadian melatonin rhythm, PSG, and HRV.

Cardiovascular autonomic nervous response to postural change in 610 healthy Japanese subjects in relation to age

To determine the effect of aging on the cardiovascular response to postural change, we examined the cardiovascular sympathetic and parasympathetic response to active standing in 610 healthy Japanese subject (6-83 years) measuring the initial heart rate (HR) response for 3 min in the supine and standing position, we also measured the coefficient of variation of R-R interval (CV(R-R)). As a result, the cardiovascular response to active standing demonstrated a different change with aging between sympathetic and parasympathetic. Sympathetic function was in a sthenia state in young subjects, and that this function declined with age increasing. Whereas, parasympathetic function was immature enough to inhibit the sympathetic tone in young subjects and matured at 20 years of age, and had an ability to inhibit sympathetic tone. CV(R-R) show a linear change that decline with age increasing. These results indicated that the cardiovascular parasympathetic response to active standing shows a characteristic change with aging that differs from cardiovascular parasympathetic at rest represented by CV(R-R). The present study is the first report to demonstrate the cardiovascular response to standing in relation to aging in large population. These results suggested that the cardiovascular response to postural change is dependent on subjects age.

Daily exposure to cold phase-shifts the circadian clock of neonatal rats in vivo

Maternal rhythms entrain the prenatal and neonatal circadian clock in the suprachiasmatic nucleus (SCN) before light entrainment is established. However, the responsible time cues for maternal entrainment are not identified. To examine the role of cyclic changes of ambient temperature in maternal entrainment, blind neonatal rats carrying a clock gene (Per2) bioluminescence reporter were exposed to either of three ambient temperatures (10, 20 or 30 °C) during 6‐h maternal separation in the early light phase. Cold exposure was performed from postnatal day 1 (P1) to P5. On P6, the SCN was harvested and cultured for photometric monitoring of the circadian rhythm in Per2 expression. Here we demonstrate that the daily cold exposure phase‐delayed the circadian Per2 expression rhythms at P6 in a temperature‐dependent manner. Exposure to 10 °C produced the largest phase‐shift of 12.7 h, and exposure to 20 and 30 °C yielded moderate shifts of 4.1 and 4.5 h, respectively. There was no significant difference in the phase‐shifts between the latter two temperatures, indicating that ambient temperature is not the sole factor for the phase‐shift. Behavioral rhythms that developed after weaning reflected the phase‐shift of clock gene expression rhythm in the SCN. These findings indicate that a daily exposure to an ambient temperature of 10 °C during the neonatal period is capable of resetting the circadian clock in the SCN, but other factors yet unidentified are also involved in maternal entrainment.

Mistimed wheel running interferes with re-entrainment of circadian Per1 rhythms in the mouse skeletal muscle and lung.

Previously, we showed the acceleration of re‐entrainment to 8‐h phase‐advanced light/dark cycles (LD) in the circadian Per1 expression rhythms of the mouse lung and skeletal muscle by 3‐h wheel running (WR) at the beginning of shifted dark phase. In the present study, the effects of WR at the end of shifted dark phase were examined on the re‐entrainment in mice. LD was advanced by shortening and was delayed by lengthening the first light period in the phase‐advance and phase‐delay protocol, respectively. Shifted LD was continued for 4 days, which was followed by constant darkness (DD). Per1 expression was measured in the cultured tissues obtained on the first day of DD from mice carrying a bioluminescence reporter of Per1 expression. In the phase‐advance protocol, re‐entrainment was not influenced by WR in any circadian rhythm examined. In the phase‐delay protocol, re‐entrainment of the circadian locomotor rhythm was not affected by WR. However, re‐entrainment of circadian Per1 rhythm was significantly decelerated in the skeletal muscle and lung. These findings indicate that the effects of WR on re‐entrainment depend on the time of day and the peripheral tissues. Mistimed WR interferes with re‐entrainment of circadian rhythms in the lung and skeletal muscle.

Two Coupled Circadian Oscillators Are Involved in Nonphotic Acceleration of Reentrainment to Shifted Light Cycles in Mice

The onset and offset of an activity band in the circadian behavioral rhythm are known to differentially reentrain to shifted light-dark cycles (LD). Differential reentrainment could be explained by different light responsivities of circadian oscillators underlying these phase-markers. In contrast, reentrainment is accelerated by exposure to nonphotic time cues such as timed wheel-running. However, the relationship between the 2 oscillators and nonphotic acceleration of reentrainment is largely unknown. We examined phase-shifts of the mouse behavioral rhythm in response to an 8-h phase-advanced shift of LD and effects of behavioral interventions: maintained in a home cage (HC), exposed to a running wheel (RW) in HC (HC+RW), transferred to a new cage (NC), and exposed to RW in NC (NC+RW). Each intervention was given for 3h from the beginning of the shifted dark period and repeated for 4 days. Following the last dark period, the mice were released into constant darkness (DD). As a result, activity onset and offset were differentially phase-shifted. The activity onset on the first day of DD (DD1) was phase-advanced from the baseline slightly in HC and HC+RW, substantially in NC+RW, but not significantly in NC. The amount of phase-shift was significantly larger in the NC+RW than in the other groups. In contrast, the activity offset was significantly advanced in all groups by 6 to 8 h. The differential phase-shifts resulted in shortening of the activity band (α compression). The α compression was gradually relieved upon exposure to DD (α decompression), and the activity band finally became stable. Interestingly, the magnitude of phase-shifts of activity offset, but not of activity onset, in the following DD was negatively correlated with the extent of α compression in DD1. These findings indicate that the 2 circadian oscillators underlying activity onset and offset are involved in asymmetric phase-shifts and nonphotic acceleration of reentrainment.