BACKGROUND AND OBJECTIVE: Natural light exposure has important effects on the biological timing systems. One could suppose that this exposure might promote a better adjustment between biological rhythms and early working times among outdoor diurnal workers. The aim of this study was to compare the morningness/eveningness preferences and the relationship between actual and ideal timing to work on diurnal workers exposed to different light conditions.
METHODS: The study was conducted with two groups of workers (n=49) living in a rural area and exposed to similar social conditions. One group worked indoor (n=20, mean age 30.8 years (21-50); standard deviation=9.8), and the other group worked outdoor (n=29, mean age 30.8 years (17-50); standard deviation=10.0). The workers filled out a morningness-eveningness questionnaire (MEQ). A one-way ANOVA was carried out in order to compare MEQ scores between the two groups of workers.
RESULTS: As expected, Outdoor Environment Group (OEG) showed a higher average when compared to Indoor Environment Group (IEG), which means a trend to a morning preference (OEG: 58.4±7.9; IEG: 47.4±6.4), with a significant difference (F=26.22; p<0.001). According to the reported data related to working times, the OEG would like to postpone the working time by 31 minutes, while the IEG would postpone by 96 minutes their actual working time (F=7.71; p<0.01).
CONCLUSIONS: The results of this study suggested that natural light exposure may promote better adjustment to early working hours.
Keywords: Chronobiology phenomena; Work hours; Night work; Sleep deprivation; Rural workers
BACKGROUND AND OBJECTIVE: Considering that chronotype is an individual differential characteristic reflecting the time of day when individuals have their best performances, some people prefer to wake up early in the morning and are more alert in the first part of the day, others prefer to wake up later, as their peak time of the day is in the evening, and they prefer to go to bed late at night. The purpose of this study was to analyze the chronotype of undergraduate dental students and to identity the relationship between chronotype and periods of both physical activity and study, as well as to verify the correlation to age.
METHODS: Seventy-five first-year students, who participated voluntarily in the study, both genders, whose mean age was 19 years old (±1.5), answered the Horne and Ostberg Questionnaire (1976), which was modified and validated by Benedito-Silva et al. or Brazilian population and was applied at the Dental School of the University of São Paulo, Ribeirão Preto (USP).
RESULTS: The results revealed a predominance of "Indifferent" chronotype, followed by "Moderately eveningness", "Moderately morningness" and "Definitely eveningness" chronotypes. A significant statistical correlation was not observed between chronotypes and individual characteristics.
CONCLUSIONS: There was a predominance of indifferent chronotype among dental students and we did not find any correlation between chronotype, time of study, physical activity, gender and age.
Keywords: Circadian rhythm; Exercise; Students, dental
BACKGROUND AND OBJECTIVE: Permission to take a nap during the night shift may compensate for shorter daytime sleep duration at home and improve alertness on the job. This study aimed to describe the importance of napping and characterize the environmental and organizational conditions of taking a nap during a night shift.
METHODS: This is a qualitative study in which 20 registered nurses and nurse assistants of a hospital in the city of São Paulo were interviewed.
RESULTS: The results showed that, despite the permission to nap, the occurrence of napping depended on the workload. Although there was a location designated for napping, there was insufficient space and couches for everyone. In this event, many workers improvised other locations to nap. Although the conditions were not always adequate, participants reported napping/rest as an important factor for physical and mental rest and for maintaining alertness during the night shift.
CONCLUSIONS: The statements of the participants emphasize that, in order to obtain satisfactory benefits from napping, adequate conditions for this purpose should be implemented.
Keywords: Night work; Work schedule tolerance; Nursing staff; Sleep deprivation; Arousal; Shift work; Working environment; Workload; Sleep disorders; Circadian rhythm
BACKGROUD AND OBJECTIVE: To evaluate onset and stability of therapeutic effect of 4-week melatonin treatment for chronic sleep onset insomnia in elementary school-aged children.
METHODS: Retrospective analysis of unpublished data obtained from two previously published randomized, double-blind and placebo-controlled trials on melatonin treatment efficacy for childhood insomnia in children with chronic sleep onset insomnia, age 6-12 years (n=49). Intervention consisted of placebo (n=25) or melatonin 5 mg (n=24) administered at 6 (n=9) or 19h (n=40) during four weeks. Collected data were "light-out time", "sleep onset latency", "sleep onset", "total sleep time", "wake-up time", and subjective sleep measures recorded in a diary.
RESULTS: Melatonin treatment showed a phase-advance of lights out of 21h15 (1.05) to 20h28 (1.07); sleep onset advanced from 22h05 (0.93) to 20h45 (1.09) and sleep latency decreased from 53 (39) to 18 minutes (16). After the 4-week trial period, these values were 20h44 (1.27), 21h09 (1.33), 25 minutes (39).
CONCLUSIONS: Melatonin advances sleep latency and sleep onset and increases total sleep time starting right from the first treatment night in children with chronic sleep onset insomnia. Evidence is provided that the onset of melatonin treatment effect can be expected within a few days after commencement and, then, remains stable.
Keywords: Sleep initiation and maintenance disorders/drug therapy; Melatonin/therapeutic use; Education, primary and secondary; Child
BACKGROUND AND OBJECTIVE: Due to circadian disturbances observed among bipolar disorder (BD) patients, several studies have analyzed a possible link with genes involved in the molecular generation of biological rhythms. Some of these genes have been previously associated with diurnal preference (i.e., chronotype) in healthy individuals. In this study, we aimed to establish the influence of two genetic polymorphisms on chronotypes among two local populations of healthy subjects and individuals affected by bipolar disorders.
METHODS: The polymorphisms analyzed were a variable number of tandem repeats (4 or 5-repeat alleles; 4R or 5R) in exon 18 of hper3, and a T/C single nucleotide polymorphism in clock. Chronotypes of healthy individuals (n=39) and patients (n=37) were determined by the Horne and Ostberg Questionnaire, and the control population was divided into three groups according to results.
RESULTS: No difference in allele or genotype frequencies was detected between control and bipolar disorder populations. In controls, the 5R allele in hper3 and the C allele in clock were sub-represented among evening-type individuals (p<0.05). Moreover, subjects homozygous for the 4R allele of hper3 had significantly lower scores (evening preference) than 5R allele carriers among both controls (p<0.05) and patients (p<0.001).
CONCLUSIONS: We have confirmed the strong correlation of hper3 variable number of tandem repeats (VNTR) polymorphism with diurnal preference on a local population, even when not taking into account chronotype classification. This correlation was replicated with an even stronger robustness, on patients with bipolar disorders. These findings add to the growing body of evidence supporting an important role for hper3 on human circadian physiology.
Keywords: Chronobiology disorders; Bipolar disorder; Polymorphism, genetic; Sleep/physiology; Phenotype; Minisatellite repeats
BACKGROUND AND OBJECTIVE: Food-anticipatory behavioral rhythms are observed in several species, including mammals. It is reported that acute ingestion of glucose phase-shifts the food-entrainable oscillator (FEO) in rats. Here, we intended to extend the knowledge about the role of glucose on anticipatory behavioral rhythms by submitting rats to a long period of scheduled glucose availability.
METHODS: Adult Wistar rats were under 12:12 hours light-dark cycle for three days with ad libitum feeding (Baseline) prior to being submitted to ten days of scheduled glucose restriction (GR) (three hours duration) starting at Zeitgeber time (ZT) 06 and two days of meal (glucose) omission.
RESULTS: The animals anticipated glucose availability by increasing motor activity in the two hours preceding ZT 06. The anticipatory behavior observed during the glucose restriction persisted on the second day of glucose omission (i.e. when glucose was not offered). That is, this anticipatory behavior was self-sustained, evidencing the true entrainment of the rhythm.
CONCLUSION: Glucose ingestion was a sufficient temporal cue for inducing endogenously-generated circadian anticipatory behavior in the rat.
Keywords: Glucose/administration & dosage; Circadian rhythm; Feeding behavior; Rats; Models, neurological; Signal transduction
BACKGROUND AND OBJECTIVE: The increased risk of developing prostate cancer (PC) observed in recent decades in industrialized countries has showed to be related at least partially to the elevated exposure to artificial light at night and to long photoperiod during all the year. However, the precise effects of light and photoperiod manipulations on prostate cancer cell proliferation in vivo have not been reported to the same extent.
METHODS: We exposed male C57BL/6 mice to short or long photoperiods (short day, SD, and long day, LD). After inoculation of TRAMP-C2 cells, half of the SD mice were also exposed to light interference at night while half of the LD mice were treated with melatonin.
RESULTS: Under LD-acclimation, tumours were significantly larger compared to SD conditions. Melatonin treatment to LD mice reduced tumour size significantly, while light interferences to SD mice tended to increase it.
CONCLUSIONS: we conclude that exposure to LD and light interference may promote cancer growth via changes in melatonin production and secretion. Our results strongly support a novel link between temporal variables and cancer incidence. Accordingly, we anticipate our findings to increase the awareness of scientists as well as health officials and policy makers to the adverse effects of illumination misuse during the night.
Keywords: Light; Circadian rhythm; Climate; Sunlight; Prostatic neoplasms; Environment; Melatonin; Photoperiod; Chronobiology disorders
BACKGROUND AND OBJECTIVE: The circadian timing system (CTS) is composed of a group of specialized neuronal structures that establish a temporal organization of physiological and behavioral processes within precise patterns. The central components of this system are the suprachiasmatic nucleus of the hypothalamus (SCN) and the intergeniculate leaflet of the thalamus (IGL). The objective of this study was to verify the presence of the neuron-specific nuclear protein (NeuN) in the circadian timing system of capuchin monkeys (Cebus apella) using immunohistochemical techniques.
METHODS: Capuchin monkeys (Cebus apella) were anesthetized and transcardially perfused with 4% paraformaldehyde in 0.1 M phosphate buffer, and then their brains were removed and frozen. A microtome was used to make 30 µm sections in the coronal plane. One of the series was used for Nissl staining (thionin) to demarcate the cytoarchitecture, and the remainders of the sections were processed for immunohistochemical detection of NeuN (ABC protocol).
RESULTS: NeuN-positive neurons were observed in the suprachiasmatic nucleus of the capuchin monkey. The pregeniculate nucleus (PGN), a structure equivalent to the ventral lateral geniculate nucleus (vLGN) and to the IGL in rodents, did not have any NeuN-positive neurons.
CONCLUSIONS: In this primate species, only the suprachiasmatic nucleus neurons of the central structures of the circadian timing system express the NeuN protein.
Keywords: Circadian rhythm; Suprachiasmatic nucleus; Nuclear proteins; Immunohistochemistry/methods; Geniculate bodies; Neurons; Animals; Cebus
BACKGROUND AND OBJECTIVE: In mammals, the main biological clock that is synchronized by light is located in the suprachiasmatic nucleus of the hypothalamus, which can be divided into two distinct regions: the ventrolateral and the dorsomedial. Both behave as separate oscillators that interact with each other to form the circadian rhythm.
METHODS: Our objective was to develop a mathematical model to understand how these regions of the suprachiasmatic nucleus coordinate the circadian rhythm of motor activity in rats. To accomplish this, we performed simulations with light-dark cycles of 24 (T24) and 22 hours (T22) and simulations with constant darkness (CD). In the model, we developed equations to describe the circadian rhythm of a clock protein.
RESULTS: For the two light-dark and constant darkness cycles, the model was able to reproduce the synchronization with T24, the dissociation with T22, and the free-running rhythm with constant darkness. The results show that the intensity of coupling between the two oscillators and their periods define the output of the rhythm.
CONCLUSIONS: The proposed model is consistent with data in the literature and suggests new experimental approaches. This model will contribute to a better understanding of the interaction between the two regions of the suprachiasmatic nucleus.
Keywords: Mathematical models; Circadian rhythms; Motor activity; Suprachiasmatic nucleus; CLOCK proteins; Biological clocks/physiology; Animal; Rats
BACKGROUND AND OBJECTIVE: The sleep-wake cycles of medical students are affected by their academic demands and class starting times. Despite their different sleep needs and characteristics (such as chronotype), all students must follow the same schedule. Therefore, it is necessary to know whether chronotype is related to sleep quality and daytime sleepiness.
METHODS: A study was carried out with the assessment of 234 students in their 1st through 4th years of medical school at the Federal University of Rio Grande do Norte. The Pittsburgh Sleep Quality Index (PSQI) was used to evaluate subjective sleep quality. Values below 5 indicated good sleep quality, while values above 5 indicated poor sleep quality. The Epworth Sleepiness Scale (ESS), in which values above 10 indicate extreme daytime sleepiness, was used to evaluate daytime sleepiness. A Portuguese version of a questionnaire for the "eveningness-morningness" dimension developed by Horne and Östberg (1976) was used to classify participants with regard to their chronotypes.
RESULTS: Chronotype had a normal distribution. Students of second through fourth years of medical school had sleep quality values above 5, while students of the first year had sleep quality values below 5. Daytime sleepiness was homogenous across groups, with an average of 8.9 (SD=3.55). Chronotype and sleep quality had a linear relationship (p<0.001); evening types had worse sleep quality than morning types. The relationship between chronotype and daytime sleepiness was not statistically significant.
CONCLUSIONS: The medical students evaluated in this study had low sleep quality, particularly those of extreme evening type.
Keywords: Sleep; Students, medical; Sleep stages; Chronobiology phenomena
BACKGROUND AND OBJECTIVE: To explore the role of the suprachiasmatic nucleus (SCN) for masking by light in rats bearing bilateral complete or partial lesions of the suprachiasmatic nucleus.
METHODS: Rats were submitted to electrolytic SCN lesions, and their spontaneous activity was monitored to verify arrhythmia in different lighting conditions, under light/dark cycle and constant darkness.
RESULTS: Rats bearing a partial suprachiasmatic nucleus lesion presented arrhythmic activity patterns when assessed in constant darkness; however, in a light-dark cycle, rats show a diurnal pattern. Partial lesions were evidenced through histological analysis.
CONCLUSIONS: We conclude that when behavioral indicators are used evidence suprachiasmatic nucleus lesions, animals should be tested at least in two lighting conditions; we also conclude that the suprachiasmatic nucleus is necessary for masking by light.
Keywords: Circadian rhythm; Darkness; Light; Suprachiasmatic nucleus/injuries; Perceptual masking
BACKGROUND AND OBJECTIVES: Constant environmental conditions can lead to changes in the synthesis of melatonin. In vitro studies have shown that this hormone modulates the efficiency of mitochondrial respiration. Therefore, this work examined whether the efficiency of mitochondrial respiration changes in rats that have been subjected to constant illumination or darkness for a short period.
METHODS: Rats were randomly distributed in three groups: Control, Constant Illumination (72 hours) and Constant Darkness (72 hours). Upon completion of treatment, rats were sacrificed and mitochondria from the pineal gland, Harderian gland, thymus and spleen were isolated. Subsequently, mitochondrial respiratory control was quantified from the removed tissues in the three experimental groups.
RESULTS: Our findings show that brief treatments of continued illumination or continued darkness had no significant effect on mitochondrial respiratory control in spleen, thymus or Harderian glands. In contrast, we observed a slight increase in mitochondrial respiratory control in the pineal gland of animals exposed to constant illumination.
CONCLUSIONS: Our results suggest that brief treatment with continuous light or darkness does not have a significant effect on the efficiency of mitochondrial activity in spleen, thymus or Harderian gland. This is probably due to the endogenous circadian rhythms that tightly regulate mitochondrial enzymatic activity in these tissues.
Keywords: Mitochondria; Cell respiration; Pineal gland; Circadian rhythm; Disease models, animal; Rats, Wistar
BACKGROUND AND OBJECTIVE: Circadian variations have been found in the performance of many human activities. The performance of many tasks depends on basic cognitive processes, such as executive functions. One of the components of these functions is the capacity to adjust behavior to environmental changes. The objective of this study was to identify circadian rhythms in the capacity to adjust behavior to environmental changes.
METHODS: Three college students were recorded in a constant routine protocol for 29 hours, starting at noon. Rectal temperature was measured every minute, and their performance on a tracking task was assessed every 1 hour and 40 minutes. In this task, each participant observed a circle following a linear path with a constant speed. Each time the circle appeared, the participant had to place a cursor inside the circle and press the left button of the mouse. After a variable number of circles, the path and speed were modified, and the participants' capacity to efficiently respond to these changes was measured.
RESULTS: All participants showed a decreased capacity to adjust their behavior to changes in the tracking task at night and early in the morning.
CONCLUSIONS: Circadian variations were observed in people's capacity to adjust their behavior to changes in the tracking task. This capacity was reduced at night and early in the morning. This impairment might lead to errors and accidents in night-shift workers.
Keywords: Circadian rhythm; Environment; Human activities