Western Diet Affects the Murine Circadian System Possibly Through the Gastrointestinal Microbiota

Consumption of a high-fat diet characteristic of human Western diet has been shown to affect the circadian system of laboratory rodents. The present study confirms an effect of Western diet on the circadian system of mice, specifically a shortening of the free-running circadian period of running-wheel activity, in addition to increased weight gain. Decimation of the gut microbiota by broad spectrum antibiotic treatment reversed the effect of Western-diet feeding on the free-running period, which suggests that the effect of Western-diet feeding on the circadian system is mediated by the gastrointestinal microbiota. This finding is particularly relevant in view of recent studies describing a relationship between gut microbes, circadian clock function, and obesity

Variability of Behavioral Chronotypes of 16 Mammalian Species Under Controlled Conditions

Human chronotypes (differences in preference for early or late rising each day) have been extensively studied in recent years, but no attempt has been made to compare human chronotypes with the chronotypes of other animal species. We evaluated behavioral chronotypes in 16 mammalian species along a body size gradient of five orders of magnitude (from mice to cattle). Individuals of all species were studied under a 12L:12D photoperiod in a thermoneutral environment with food and water available at all times. Rhythms of locomotor activity were analyzed for onset time, acrophase, and robustness. Neither of these rhythmic parameters was significantly related to body size, but onset time and acrophase varied considerably from species to species, thus characterizing diurnal and nocturnal species. Chronotype spreads ranged from less than an hour in sheep to almost 24 hours in cats, thus extending both below and above the human chronotype spread of 6 hours. The variability of chronotype (as quantified by the standard deviation of group means) was much larger between species than within species and also larger between individuals of a species than within individuals on consecutive days. These results help situate the matter of human chronotypes within the broader context of variability in the phase angle of entrainment of circadian rhythms in animals

Parameters of photic resetting of the circadian system of a durnal rodent, the nile grass rat

Research on circadian rhythms has been hampered by the lack of a suitable rodent model with diurnal habits. The goal of this study was to characterize the parameters of photic entrainment of the circadian system of the Nile grass rat, a small rodent that can potentially serve as a model for the study of circadian rhythms in diurnal animals. The state of the circadian system was accessed through the rhythm of running-wheel activity and manipulated by photic stimulation (white light). The results indicated that the grass rat exhibits a robust rhythm of running-wheel activity with a mean free-running period of 23.9 hours (range: 23.6 to 24.3 hours). The animal is clearly diurnal and starts activity daily approximately 50 minutes before lights-on under an L12:D12 light-dark cycle. Its photic phase-response curve shows a dead zone during most of subjective day, a phase delay region during early subjective night (maximal delay: 1.5 hours), and a phase advance region during late subjective night (maximal advance: 2.2 hours). When exposed to constant illumination, the grass rat exhibits longer circadian periods as the intensity of illumination increases, with a ceiling between 100 and 1,000 lux. Finally, its range of entrainment extends from at least 23.0 to 25.0 hours (from 22.0 to 25.5 in some animals)

Time for sex: nycthemeral distribution of human sexual behavior

BACKGROUND: Nycthemeral (daily) oscillation has been documented in a variety of physiological and behavioral processes. The present study was carried out to evaluate the existence of a nycthemeral rhythm of human sexual behavior and to identify environmental factors responsible for the rhythmic pattern. METHODS: Non-traditional university students (ages 18 to 51 years) recorded the times of day when they went to sleep, when they woke up, and when they had sex for 3 consecutive weeks. They also answered a questionnaire designed to identify the causes of their selection of time for sex. RESULTS: The majority of sexual encounters took place at bedtime (11 pm to 1 am). The most common explanations for this temporal pattern were the rigidity of the professional work schedule and family obligations and the availability of the partner, which reduced the opportunity for sexual encounters at other times of the day. CONCLUSION: Most sexual encounters take place around bedtime. Although the presence of an endogenous component responsible for this temporal pattern cannot be excluded, the evidence indicates strong environmental forcing, particularly from the work/family schedule of the individuals and from partner availability

Daily Activity Patterns of 2,316 Men and Women from Five Countries Differing in Socioeconomic Development

Daily rhythmicity in the locomotor activity of laboratory animals has been studied in great detail for many decades, but the daily pattern of locomotor activity has not received as much attention in humans. We collected waist-worn accelerometer data from more than 2,000 individuals from five countries differing in socioeconomic development and conducted a detailed analysis of human locomotor activity. Body mass index was computed from height and weight. Individual activity records lasting 7 days were subjected to cosinor analysis to determine the parameters of the daily activity rhythm: mesor (mean level), amplitude (half the range of excursion), acrophase (time of the peak), and robustness (rhythm strength). The activity records of all individual participants exhibited statistically significant 24-hour rhythmicity, with activity increasing noticeably a few hours after sunrise and dropping off around the time of sunset, with a peak at 1:42 pm on average. The acrophase of the daily rhythm was comparable in men and women in each country but varied by as much as 3 h from country to country. Quantification of the socioeconomic stages of the five countries yielded suggestive evidence that more developed countries have more obese residents, who are less active, and who are active later in the day than residents from less developed countries. These results provide a detailed characterization of the daily activity pattern of individual human beings and reveal similarities and differences among people from five countries differing in socioeconomic development

São Paulo, centro e periferia: a retórica ambiental e os limites da política urbana

The text, referring to the Metropolitan Region of São Paulo, puts a focus on the urban environmental issue, in whish the environment consists not only of natural processes and dynamics, but also includes the relations between them and the social processes and dynamics. Two extreme situations highlight the matter: i) the outlying settlements on the fringes along the water supply areas and environmentally sensitive areas; ii) the decrease of population at the central and consolidated areas, which have a potential to increase density. From this point, the urban projects made for the central area of São Paulo, the core of the metropolitan area are discussed. It turns evident then that the inclusion of the environmental dimension in the urban issue, in a sense that is not just rhetoric, brings to light the intrinsic limitations of Urban Policies.O texto, referenciando-se na Região Metropolitana de São Paulo, coloca um foco na questão ambiental urbana, onde o ambiente não consiste apenas em dinâmicas e processos naturais, mas inclui as relações entre estes e as dinâmicas e os processos sociais. Duas situações extremas expressam a questão: os assentamentos precários nas franjas periféricas junto aos mananciais e em áreas ambientalmente sensíveis e áreas centrais, consolidadas, que perdem população, mas têm potencial de adensamento. A partir desse ponto, são discutidos os projetos urbanos formulados para a área central do município de São Paulo, núcleo da Região Metropolitana. Evidencia-se, então, que a inserção da dimensão ambiental na questão urbana, de modo que não seja apenas retórica, traz à luz as próprias limitações das políticas urbanas

Chronotype, Class Times, and Academic Achievement of University Students

Numerous studies over the years have documented an effect of human chronotypes on physiological and psychological processes. Studies evaluating the impact of an individual’s chronotype on his/her academic achievement have indicated that morning chronotypes have an academic advantage over evening chronotypes. However, these studies did not account for the time of day in which the participants were being evaluated. The goal of the present study was to examine whether morning chronotypes do have an academic advantage over evening chronotypes when the time-of-day of classes and exams is taken into consideration. We obtained morningness-eveningness scores and course grades from 207 university students who took classes (and exams) at different times of the day. We confirmed that morning chronotypes attain better grades than evening chronotypes, although the association is weak (r2 = 0.02). The difference persisted even after the time-of-day of classes and exams was taken into consideration. This is probably due to the fact that evening chronotypes are generally more sleep deprived than morning chronotypes as a result of the early schedule of most schools, which can impair their performance both early and late in the day

Daily Activity and Nest Occupation Patterns of Fox Squirrels (\u3cem\u3eSciurus niger\u3c/em\u3e) Throughout the Year

The authors investigated the general activity and nest occupation patterns of fox squirrels in a natural setting using temperature-sensitive data loggers that measure activity as changes in the microenvironment of the animal. Data were obtained from 25 distinct preparations, upon 14 unique squirrels, totaling 1385 recording days. The animals were clearly diurnal, with a predominantly unimodal activity pattern, although individual squirrels occasionally exhibited bimodal patterns, particularly in the spring and summer. Even during the short days of winter (9 hours of light), the squirrels typically left the nest after dawn and returned before dusk, spending only about 7 hours out of the nest each day. Although the duration of the daily active phase did not change with the seasons, the squirrels exited the nest earlier in the day when the days became longer in the summer and exited the nest later in the day when the days became shorter in the winter, thus tracking dawn along the seasons. During the few hours spent outside the nest each day, fox squirrels seemed to spend most of the time sitting or lying. These findings suggest that fox squirrels may have adopted a slow life history strategy that involves long periods of rest on trees and short periods of ground activity each day

Circadian Rhythms of Body Temperature and Locomotor Activity in the Antelope Ground Squirrel, \u3cem\u3eAmmospermophilus leucurus\u3c/em\u3e

We studied circadian rhythms of body temperature and locomotor activity in antelope ground squirrels (Ammospermophilus leucurus) under laboratory conditions of a 12L:12D light-dark cycle and in constant darkness. Antelope ground squirrels are diurnally active and, exceptionally among ground squirrels and other closely related members of the squirrel family in general, they do not hibernate. Daily oscillations in body temperature consisted of a rise in temperature during the daytime activity phase of the circadian cycle and a decrease in temperature during the nighttime rest phase. The body temperature rhythms were robust (71% of maximal strength) with a daily range of oscillation of 4.6 °C, a daytime mean of 38.7 °C, and a nighttime mean of 34.1 °C (24-h overall mean 36.4 °C). The body temperature rhythm persisted in continuous darkness with a free-running period of 24.2 hours. This pattern is similar to that of hibernating species of ground squirrels but with a wave form more similar to that of non-hibernating rodents. Daily oscillations in body temperature were correlated with individual bouts of activity, but daytime temperatures were higher than nighttime temperatures even when comparing short episodes of nocturnal activity that were as intense as diurnal activity. This suggests that although muscular thermogenesis associated with locomotor activity can modify the level of body temperature, the circadian rhythm of body temperature is not simply a consequence of the circadian rhythm of activity