Biomedical subjects

Shin Yamazaki

Publications and source records attributed to Shin Yamazaki.

31 records · Page 2Linked to original sources

PubMed2005

Effects of preparation time on phase of cultured tissues reveal complexity of circadian organization.

The phases of central (SCN) and peripheral circadian oscillators are held in specific relationships under LD cycles but, in the absence of external rhythmic input, may damp or drift out of phase with each other. Rats exposed to prolonged constant light become behaviorally arrhythmic, perhaps as a consequence of dissociation of phases among SCN cells. The authors asked whether individual central and peripheral circadian oscillators were rhythmic in LL-treated arrhythmic rats and, if rhythmic, what were the phase relationships between them. The authors prepared SCN, pineal gland, pituitary, and cornea cultures from transgenic Period1-luciferaserats whose body temperature and locomotor activity were arrhythmic and from several groups of rhythmic rats held in LD, DD, and short-term LL. The authors measured mPer1gene expression by recording light output with sensitive photomultipliers. Most of the cultures from all groups displayed circadian rhythms. This could reflect persistent rhythmicity in vivo prior to culture or, alternatively, rhythmicity that may have been initiated by the culture procedure. To test this, the authors cultured tissues at 2 different times 12 h apart and asked whether phase of the rhythm was related to culture time. The pineal, pituitary, and SCN cultures showed partial or complete dependence of phase on culture time, while peak phases of the cornea cultures were independent of culture time in rhythmic rats and were randomly distributed regardless of culture time in arrhythmic animals. These results suggest that in behaviorally arrhythmic rats, oscillators in the pineal, pituitary, and SCN had been arrhythmic or severely damped in vivo, while the cornea oscillator was free running. The peak phases of the SCN cultures were particularly sensitive to some aspect of the culture procedure since rhythmicity of SCN cultures from robustly rhythmic LD-entrained rats was strongly influenced when the procedure was carried out at any time except the 2nd half of the day.

Animals↗

PubMed2005

[An estimation of the prevalence of excessive daytime sleepiness based on age and sex distribution of epworth sleepiness scale scores: a population based survey].

OBJECTIVES: To describe the distribution of subjective daytime sleepiness among local residents using the Epworth Sleepiness Scale (ESS) and estimate the prevalence of excessive daytime sleepiness (EDS) in a general Japanese adult population. METHODS: Subjects consisted of all residents aged 20 years and over from a self-governing body of approximately 10,000 people located in the Hokkaido region. Questionnaires, which included a Japanese version of the ESS, were distributed and later collected by a health promoter who visited subjects' residences between October and December 2000. Subjects of the analysis were restricted to those who answered five items or more out of a total of eight items. Means and standard deviations of the ESS global score were calculated for each age group by gender. And differences with reference to sex and age were examined by ANOVA. The prevalence of EDS in the Japanese general population was estimated from this study's results by direct age adjustment using the Japanese census figures for 2000. Factors related to EDS were also examined. RESULTS: A total of 5,327 residents responded to the survey (86.0%). Of these, 4,412 (71.2%) were entered for analysis. The average (+/- standard deviation) ESS global score were with 5.18 +/- 3.75 (males 5.25 +/- 3.89, females 5.12 +/- 3.75). Differing significantly age, regardless of sex (P<0001). From the overall prevalence of EDS of 9.2% (males 9.6%, females 8.8%), the estimated prevalence in the Japanese general population was to be 8.9% (males 9.3%, females 8.4%). EDS was found to be related to age, sleep duration under six hours and to snoring (P=0.002, P=0.008 and P<0.001). CONCLUSION: This study provided baseline data for the distribution by sex and age group of subjective daytime sleepiness in a community using the ESS and was used to generate the first ever estimated prevalence of EDS in the general Japanese adult population. The finding should prove useful for clinicians and researchers interested in (1) screening for daytime sleepiness, (2) evaluating changes between pre and post-interventions, (3) comparing epidemiological findings across studies, and lastly, (4) making of health policy. Daytime sleepiness estimated by ESS differs with the sex and age, possibly related to bio-medical and socio-medical factors. Further research is need to detail this problem.

Activities of Daily Living↗

PubMed2004

PERIOD2::LUCIFERASE real-time reporting of circadian dynamics reveals persistent circadian oscillations in mouse peripheral tissues.

Mammalian circadian rhythms are regulated by the suprachiasmatic nucleus (SCN), and current dogma holds that the SCN is required for the expression of circadian rhythms in peripheral tissues. Using a PERIOD2::LUCIFERASE fusion protein as a real-time reporter of circadian dynamics in mice, we report that, contrary to previous work, peripheral tissues are capable of self-sustained circadian oscillations for >20 cycles in isolation. In addition, peripheral organs expressed tissue-specific differences in circadian period and phase. Surprisingly, lesions of the SCN in mPer2(Luciferase) knockin mice did not abolish circadian rhythms in peripheral tissues, but instead caused phase desynchrony among the tissues of individual animals and from animal to animal. These results demonstrate that peripheral tissues express self-sustained, rather than damped, circadian oscillations and suggest the existence of organ-specific synchronizers of circadian rhythms at the cell and tissue level.

Animals↗

PubMed2004

Plasticity of circadian behavior and the suprachiasmatic nucleus following exposure to non-24-hour light cycles.

Period aftereffects are a form of behavioral plasticity in which the free-running period of circadian behavior undergoes experience-dependent changes. It is unclear whether this plasticity is age dependent and whether the changes in behavioral period relate to changes in the SCN or the retina, 2 known circadian pacemakers in mammals. To determine whether these changes vary with age, Per1-luc transgenic mice (in which the luciferase gene is driven by the Period1 promoter) of different ages were exposed to short (10 h light: 10 h dark, T20) or long (14 h light: 14 h dark, T28) light cycles (T cycles). Recordings of running-wheel activity in constant darkness (DD) revealed that the intrinsic periods of T20 mice were significantly shorter than of T28 mice at all ages. Aftereffects following the shorter light cycle were significantly smaller in mice older than 3 months, corresponding with a decreased ability to entrain to T20. Age did not diminish entrainment or aftereffects in the 28-h light schedule. The behavioral period of pups born in DD depended on the T cycle experienced in utero, showing maternal transference of aftereffects. Recordings of Per1-luc activity from the isolated SCN in vitro revealed that the SCN of young mice expressed aftereffects, but the periods of behavior and SCN were negatively correlated. Enucleation in DD had no effect on behavioral aftereffects, indicating the eyes are not required for aftereffects expression. These data show that circadian aftereffects are an age-dependent form of plasticity mediated by stable changes in the SCN and, importantly, extra-SCN tissues.

Age Factors↗

PubMed2003

Circadian gene expression in mammalian fibroblasts revealed by real-time luminescence reporting: temperature compensation and damping.

Mammalian cells such as rat-1 fibroblasts have been shown to exhibit daily oscillations in the expression of several gene transcripts in culture. After induction, these oscillations persist with a period of approximately 24 h for several days. This characteristic suggests that the oscillations are controlled by a circadian clock, but the crucial criterion of temperature compensation has not been demonstrated for rat-1 fibroblasts. We have developed an automated assay of circadian expression of the mPer1 promoter in rat-1 fibroblasts that have been stably transfected with a luciferase reporter. Using this cell culture-based in vitro luminescent reporter assay, we found that the daily oscillation of mPer1 promoter activity in rat-1 cells is temperature compensated over the range of 28.5-36.5 degrees C. This finding means that these oscillations are bona fide circadian rhythms. Moreover, the circadian clock of these homeothermic mammalian cells not only is temperature compensated but also is overcompensated such that it runs faster at cooler temperatures (Q10 of 0.85-0.88). The oscillations in rat-1 fibroblasts damp more rapidly at cooler temperatures, and damping is not due to cells becoming unhealthy because a second stimulus will reinitiate a robust rhythm. These data show that rat-1 cell cultures that are stably transfected with luminescence reporters are an excellent model system for studying circadian clocks at the cellular level in mammals.

Animals↗

PubMed2003

Dissociation between circadian Per1 and neuronal and behavioral rhythms following a shifted environmental cycle.

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus contains a major circadian pacemaker that imposes or entrains rhythmicity on other structures by generating a circadian pattern in electrical activity. The identification of "clock genes" within the SCN and the ability to dynamically measure their rhythmicity by using transgenic animals open up new opportunities to study the relationship between molecular rhythmicity and other well-documented rhythms within the SCN. We investigated SCN circadian rhythms in Per1-luc bioluminescence, electrical activity in vitro and in vivo, as well as the behavioral activity of rats exposed to a 6-hr advance in the light-dark cycle followed by constant darkness. The data indicate large and persisting phase advances in Per1-luc bioluminescence rhythmicity, transient phase advances in SCN electrical activity in vitro, and an absence of phase advances in SCN behavioral or electrical activity measured in vivo. Surprisingly, the in vitro phase-advanced electrical rhythm returns to the phase measured in vivo when the SCN remains in situ. Our study indicates that hierarchical levels of organization within the circadian timing system influence SCN output and suggests a strong and unforeseen role of extra-SCN areas in regulating pacemaker function.

Animals↗

PubMed2003

Courses of cervical disc herniation causing myelopathy or radiculopathy: an analysis based on computed tomographic discograms.

STUDY DESIGN: The courses of protruded masses in cervical disc herniations were traced on preoperative computed tomography discograms of patients with myelopathy or radiculopathy. OBJECTIVE: To characterize the courses of protruded masses in cervical disc herniation. SUMMARY OF BACKGROUND DATA: No studies have been reported on the varied courses of protruded masses in cervical disc herniation. METHODS: This study investigated the preoperative CT discograms of 150 patients with myelopathy and 50 patients with radiculopathy who had undergone anterior cervical discectomy and fusion for disc herniation. The courses of herniations were traced from the penetration sites on the deep layer of the posterior longitudinal ligament through their locations in the spinal canal, and were divided into one median, two paramedian, and two lateral sections. RESULTS: Of the 150 discs in the patients with myelopathy, 87% had a median penetration and 13% had a paramedian one. No discs had a lateral penetration. It was found that 45% of the median penetrations led to median herniation through a straight course and 55% to paramedian herniation through an oblique course, and that 95% of the paramedian penetrations led to paramedian herniation through a straight course. Of the 50 discs in the patients with radiculopathy, 70% had a median penetration, 26% a paramedian penetration, and 4% a lateral penetration. Lateral penetration was observed only at C7-T1. All of the median penetrations led to the paramedian or lateral herniation, and 92% of the paramedian penetrations led to lateral herniation through oblique courses. CONCLUSIONS: In the cervical spine, most herniated masses penetrate the deep layer of the posterior longitudinal ligament in the middle, where the posterior intervertebral space is widest. Oblique courses to paramedian or lateral herniation are common. Only at C7-T1, where there are no Luschka joints, lateral penetration was observed. The narrow space of the Luschka joint may prevent fragments from penetrating laterally. Preoperative information from the CT discograms on the characteristic courses of the herniation may facilitate the complete removal of herniated mass in anterior decompressive surgery.

Adult↗

PubMed2003

SCN: ringmaster of the circadian circus or conductor of the circadian orchestra?

The mammalian circadian system is composed of multiple circadian oscillators in both the brain and the periphery. Unravelling the organization of this system is a major challenge that the field is only beginning to take on. Clearly the suprachiasmatic nucleus of the hypothalamus (SCN) plays a key role and sits at or near the top of the organizational hierarchy, the details of which are largely unknown. The SCN has often been characterized as a 'master oscillator' that controls other oscillators downstream in the hierarchy, but there is little information about the nature of that control or how rigid or flexible it may be. Indeed, characterization of the SCN as 'master' may be exaggerated since other central circadian pacemakers are known to exist and the extent of feedback onto the SCN from other oscillators remains unexplored. We have tried to make some of the issues concerning the role of the SCN within the entire system more explicit using the somewhat fanciful metaphor referred to in the title.

Animals↗

PubMed2002

Effects of aging on central and peripheral mammalian clocks.

Circadian organization changes with age, but we do not know the extent to which age-related changes are the result of alterations in the central pacemakers, the peripheral oscillators, or the coupling mechanisms that hold the system together. By using transgenic rats with a luciferase (luc) reporter, we assessed the effects of aging on the rhythm of expression of the Period 1 (Per1) gene in the suprachiasmatic nucleus (SCN) and in peripheral tissues. Young (2 months) and aged (24-26 months) Per1-luc transgenic rats, entrained to light-dark cycles, were killed, and tissues were removed and cultured. Per1-luc expression was measured from 10 tissues. In the SCN, the central mammalian pacemaker, Per1-luc expression was robustly rhythmic for more than 7 weeks in culture. The only difference between SCN rhythmicity in young and old rats was a small but significant age-related shortening of the free-running period. Circadian rhythmicity in some peripheral tissues was unaffected by aging, whereas rhythmicity in other tissues was either phase advanced relative to the light cycle or absent. Those tissues that were arrhythmic could be induced to oscillate by application of forskolin, suggesting that they retained the capacity to oscillate but were not being appropriately driven in vivo. Overall, the results provide new insights into the effects of aging on the mammalian circadian system. Aging seems to affect rhythms in some but not in all tissues and may act primarily on interactions among circadian oscillators, perhaps attenuating the ability of the SCN to drive damped oscillators in the periphery.

Aging↗

PubMed2002

Food-anticipatory activity and liver per1-luc activity in diabetic transgenic rats.

The mammalian Per1 gene is an important component of the core cellular clock mechanism responsible for circadian rhythms. The rodent liver and other tissues rhythmically express Per1 in vitro but typically damp out within a few cycles. In the liver, the peak of this rhythm occurs in the late subjective night in an ad lib-fed rat, but will show a large phase advance in response to restricted availability of food during the day. The relationship between this shift in the liver clock and food-anticipatory activity (FAA), the circadian behavior entrained by daily feeding, is currently unknown. Insulin is released during feeding in mammals and could serve as an entraining signal to the liver. To test the role of insulin in the shift in liver Per1 expression and the generation of FAA, per-luciferase transgenic rats were made diabetic with a single injection of streptozotocine. Following 1 week of restricted feeding and locomotor activity monitoring, liver was collected for per-luc recording. In two separate experiments, FAA emerged and liver Per1 phase-shifted in response to daytime 8-h food restriction. The results rule out insulin as a necessary component of this system.

Animals↗

PubMed2002

Circadian rhythms in isolated brain regions.

The suprachiasmatic nucleus (SCN) of the mammalian hypothalamus has been referred to as the master circadian pacemaker that drives daily rhythms in behavior and physiology. There is, however, evidence for extra-SCN circadian oscillators. Neural tissues cultured from rats carrying the Per-luciferase transgene were used to monitor the intrinsic Per1 expression patterns in different brain areas and their response to changes in the light cycle. Although many Per-expressing brain areas were arrhythmic in culture, 14 of the 27 areas examined were rhythmic. The pineal and pituitary glands both expressed rhythms that persisted for >3 d in vitro, with peak expression during the subjective night. Nuclei in the olfactory bulb and the ventral hypothalamus expressed rhythmicity with peak expression at night, whereas other brain areas were either weakly rhythmic and peaked at night, or arrhythmic. After a 6 hr advance or delay in the light cycle, the pineal, paraventricular nucleus of the hypothalamus, and arcuate nucleus each adjusted the phase of their rhythmicity with different kinetics. Together, these results indicate that the brain contains multiple, damped circadian oscillators outside the SCN. The phasing of these oscillators to one another may play a critical role in coordinating brain activity and its adjustment to changes in the light cycle.

Animals↗

PubMed2002

Interaction of the retina with suprachiasmatic pacemakers in the control of circadian behavior.

The suprachiasmatic nucleus (SCN) is the central circadian pacemaker governing the circadian rhythm of locomotor activity in mammals. The mammalian retina also contains circadian oscillators, but their roles are unknown. To test whether the retina influences circadian rhythms of locomotor behavior, the authors compared the activity of bilaterally enucleated hamsters with the activity of intact controls held in constant darkness (DD). Enucleated hamsters showed a broader range of free-running periods (tau) than did intact hamsters held for the same length of time in DD. This effect was independent of the age at enucleation (on postnatal days 1, 7, or 28). The average tau of intact animals kept in DD from days 7 or 28 was significantly longer than that of intact animals kept in DD from day 1 or any of the enucleated groups. This indicates that early exposure to light-dark cycles lengthens the tau and that the eye is required to maintain this effect even in DD. These data suggest that hypothalamic circadian pacemakers may interact continuously with the retina to determine the tau of locomotor activity. Enucleation caused a large decrease in glial fibrillary acidic protein in the SCN but has no (or slight) effects on calbindin, neuropeptide Y, vasopressin, or vasoactive intestinal polypeptide, which suggests that enucleation does not produce major damage to the SCN, an interpretation that is supported by the fact that enucleated animals retain robust circadian rhythmicity. The presence of an intact retina appears to contribute to system-level circadian organization in mammals perhaps as a consequence of interaction between its circadian oscillators and those in the SCN.

Animals↗

PubMed2001

Photic and circadian expression of luciferase in mPeriod1-luc transgenic mice invivo.

A conserved transcription-translation negative feedback loop forms the molecular basis of the circadian oscillator in animals. Molecular interactions within this loop have been relatively well characterized in vitro and in cell culture; however, in vivo approaches are required to assess the functional significance of these interactions. Here, regulation of circadian gene expression was studied in vivo by using transgenic reporter mouse lines in which 6.75 kb of the mouse Period1 (mPer1) promoter drives luciferase (luc) expression. Six mPer1-luc transgenic lines were created, and all lines express a daily rhythm of luc mRNA in the suprachiasmatic nuclei (SCN). Each mPer1-luc line also sustains a long-term circadian rhythm of luminescence in SCN slice culture. A 6-h light pulse administered during the early subjective night rapidly induces luc mRNA expression in the SCN; however, high luc mRNA levels are sustained, whereas endogenous mPer1 mRNA levels return to baseline, suggesting that posttranscriptional events mediate the down-regulation of mPer1 after exposure to light. This approach demonstrates that the 6.75-kb mPer1 promoter fragment is sufficient to confer both circadian and photic regulation in vivo and reveals a potential posttranscriptional regulatory mechanism within the mammalian circadian oscillator.

3T3 Cells↗