Carolina Virginia Macêdo de Azevedo

INFLUENCE OF SEASONALITY ON CIRCADIAN MOTOR ACTIVITY RHYTHM IN COMMON MARMOSETS DURING PUBERTY

The effect of puberty on circadian rhythmicity in nonhuman primates has been little studied, even though it has been demonstrated that puberty-related changes in circadian activity rhythm occur in a number of species, including humans. To characterize the motor activity rhythm during puberty in common marmosets (Callithrix jacchus), six animals was continuously monitored by actimeters between their 5th and 12th months of age. The animals were housed with their families in outdoor cages under seminatural conditions. Onset of puberty was determined from fecal estrogen and progesterone levels in females and androgen levels in males. The spectral power of the circadian component stabilized later in the last two animals to enter puberty. The bimodal characteristic of the active phase in this species became progressively more apparent over the course of the months in which the mean temperature was highest, irrespective of the animals age. Although the onset of activity advanced after entry into puberty, this parameter showed a strong correlation with sunrise, indicating that seasonality influences this variable. Neither age nor climatic factors included in the regression model influenced the differences in phase angles between sunrise and onset of activity, and between sunset and offset of activity. Total activity was the only parameter influenced by age in the regression model, showing an increase after entry into puberty. Despite the evidence of pubertal influence on both the circadian component and total activity, under seminatural conditions seasonal factors may have a more important effect on motor activity rhythm in common marmosets. (Author correspondence: E-mail: carolina@cb.ufrn.br)

Effect of Nest Box Availability on the Circadian Activity Rhythm of Common Marmosets (Callithrix jacchus)

The effect of nest box availability on the circadian activity rhythm (CAR) was compared in a diurnal primate kept in two conditions: with and without nest box, in a light-dark (LD) cycle (12:12) and constant light (LL). Marmosets kept in LD without nest box showed a longer duration of the activity phase (α), smaller day-to-day variability in activity onset and offset and higher levels of activity, particularly towards the end of the activity time. In LL, all animals maintained with nest box expressed free-running CAR, but without nest box, 3 of the 4 individuals showed relative coordination with the outdoor LD cycle, possibly due to social synchronization with captive marmosets maintained outdoors. All animals showed longer α and higher levels of activity without nest box. Thus, the availability of a nest box is an important aspect in maintaining marmosets, influencing CAR expression in this diurnal primate in LD and LL conditions, possibly due to differences in light exposure that induces masking. Further studies are needed to evaluate the effects of the unavailability of a nest box on CAR in LL conditions.

Socially Adjusted Synchrony in the Activity Profiles of Common Marmosets in Light-Dark Conditions

Synchronized state of activity and rest might be attained by mechanisms of entrainment and masking. Most zeitgebers not only act to entrain but also to mask circadian rhythms. Although the light-dark (LD) cycle is the main zeitgeber of circadian rhythms in marmosets, social cues can act as weaker zeitgebers. Evidence on the effects of social entrainment in marmosets has been collected in isolated animals or in pairs where activity is not individually recorded. To characterize the synchronization between the daily activity profiles of individuals in groups under LD conditions, the motor activity of animals from five groups was continuously monitored using actiwatches for 15 days during the 5th, 8th, and 11th months of life of juveniles. Families consisting of twins (4 ♂♀/1 ♂♂) and their parents were maintained under controlled lighting (LD 12:12 h), temperature, and humidity conditions. Synchronization was evaluated through the synchrony between the circadian activity profiles obtained from the Pearson correlation index between possible pairs of activity profiles in the light and dark phases. We also calculated the phase-angle differences between the activity onset of one animal in relation to the activity onset of each animal in the group (ψon). A similar procedure was performed for activity offset (ψoff). By visual analysis, the correlation between the activity profiles of individuals within each family was stronger than that of individuals from different families. A mixed-model analysis showed that within the group, the correlation was stronger between twins than between twins and their parents in all families, except for the family in which both juveniles were males. Because a twin is an important social partner for juveniles, a sibling is likely to have a stronger influence on its twin’s activity rhythm than other family members. Considering only the light phase, the second strongest correlation was observed between the activity profiles of the individuals in the reproductive pair. Regarding the parameters ψon and ψoff, the juvenile/juvenile dyad had lower values than the other dyads, but these differences did not reach statistical significance in relation to all dyads. Comparing the results of the ψon and ψoff, and correlation indices, we suggest that the latter could detect differences between the animals that were not observed in the results of the phase-angle differences. These differences could be related to changes that occur during the active phase but not only in a particular phase, such as the temporal changes during the activity phase that characterize unimodal or bimodal patterns. Based on the differences in the correlations between individuals subjected to the same LD routine, we suggest that social cues modulate the circadian activity profiles of marmosets as a result of interactions between the animals within each group. Future studies are necessary to characterize the mechanisms of synchronization that are involved in this social modulation. (Author correspondence: carolina@cb.ufrn.br)

Sleep patterns of teachers and adolescents who attend school in the morning

Late sleeping times characteristic of adolescence, when associated with the morning shift for school, reduce sleep duration on school days and increase sleep–wake cycle (SWC) irregularity. Furthermore, teachers start work in the morning and finish at night, in addition to working at home. In order to compare SWC patterns, daytime sleepiness and sleep quality, 165 adolescents and 55 secondary school teachers completed a “Health and Sleep” questionnaire and a sleep diary for seven days. The results showed that both woke up earlier during the week (class start time: about 7:15 h), and this was associated with less time spent in bed, worse sleep quality and increased daytime sleepiness. These parameters improved during the weekends, albeit less in teachers. Therefore, it is suggested that class time starting in the morning have a negative effect on teachers as well as to their adolescent students, reinforcing the need for changes in the start time of morning school.

The influence of social cues on circadian activity rhythm resynchronisation to the light–dark cycle in common marmosets Callithrix jacchus

The influence of a previously synchronised conspecific of the same sex on the circadian activity rhythm resynchronisation rate to the LD cycle was assessed in five adult male marmosets during a 6 h LD cycle delay, followed by a 6 h advance, in the absence and presence of a donor. After phase delay with donor, activity onset and offset were resynchronised in fewer days. During the transients, the occurrence of a mid-activity delay, an activity increase in the L-phase and a decrease in the D-phase indicates a faster resynchronisation. After phase advance, activity onset resynchronised promptly and the number of transients for the offset and mid-activity during the transients did not differ. Daily activity increased at phase shifts. Social cues may influence photic synchronisation in marmosets, probably due to direct effects of socially-induced arousal on the circadian pacemaker or by indirect effects, thus increasing photic input or masking.

Influence of different light intensities on the daily grooming distribution of common marmosets Callithrix jacchus.

The daily distribution of autogrooming was evaluated in adult marmosets submitted to different illumination intensities in the light phase of the light-dark cycle. Autogrooming and locomotor activity were monitored and the faecal cortisol level assessed as a stress indicator. The distribution of autogrooming showed two distinct tendencies: when the light intensity varied from 500 to 200 lux, a slight increase in frequency and duration was observed, while a significant decrease in both variables occurred at 10 lux. Varying light intensities did not inhibit rhythm synchronization. The daily profile of autogrooming was mainly unimodal with an acrophase in the first half of the light phase. Faecal cortisol levels tended to increase in animals submitted to 100 and 10 lux, but these results are not conclusive. We suggest keeping captive marmosets in light intensities of at least 200 lux in the light phase, allowing animals to maintain autogrooming levels in order to reduce the discomfort caused by captivity and isolation.

Evidence for age-related changes in the circadian activity rhythm of the diurnal primate Callithrix jacchus: a case report

Abstract Many cross-sectional studies have shown that circadian rhythms change with age, but such age-related modifications are gradual and may be insufficiently described by cross-sectional studies. In this case study, circadian activity rhythm (CAR) was evaluated longitudinally, in both LD (12:12) and LL conditions, on two occasions in a single male marmoset: when ‘adult’ (3 y.o.) and when ‘old’ (9 y.o.). When adult, the CAR synchronized with positive phase angles for the onset and offset of activity. In LL, the rhythm free-ran with τ < 24 h. When old, the animal showed a significant phase delay of its activity rhythm with respect to the LD cycle (t-test, p < 0.01) and a reduction on total daily activity (t-test, p < 0.01), with signs of lesser stability, greater fragmentation and some loss of photic synchronization. In LL, the period free-ran with τ > 24 h. We conclude that aging is associated with attenuation of photic synchronization and expression of CAR in LL in the marmoset. Further studies with a larger number of individuals are needed to confirm these findings.

Conspecific vocalisations modulate the circadian activity rhythm of marmosets

Conspecific vocalisations have an important ecological role for marmosets and likely modulate the circadian timing system. However, the effect of this specific cue on circadian activity rhythm (CAR) has not been evaluated. To analyse the synchroniser effect of conspecific vocalisations on CAR in marmosets, the motor activity of five isolated adult males was continuously recorded in rooms with constant dim light (~2 lx) and attenuated sound. All animals presented positive masking, four presented relative coordination and three presented temporary entrainment associated with the daily pattern of vocalisations from animals kept outdoors, similarly to previous studies that assessed social cues. Furthermore, most animals displayed a shortened circadian period in response to conspecific vocalisation pulses that were reproduced daily for 30 days under total darkness. This is evidence that a non-photic cue with ecological significance can modulate the CAR, reinforcing the role of conspecific vocalisation as an important zeitgeber for marmosets.

Circadian activity rhythm in pre-pubertal and pubertal marmosets (Callithrix jacchus) living in family groups.

In marmosets, a phase advance was observed in activity onset in pubertal animals living in captivity under semi-natural conditions which had stronger correlation with the times of sunrise over the course of the year than the age of the animal. In order to evaluate the effect of puberty on the circadian activity rhythm in male and female marmosets living in family groups in controlled lighting conditions, the activity of 5 dyads of twins (4 ♀/♂ and 1 ♂/♂) and their respective parents was continuously monitored by actiwatches between the 4th and 12th months of age. The families were kept under LD 12:12 h with constant humidity and temperature. The onset of puberty was identified by monitoring fecal steroids. Juveniles showed higher totals of daily activity and differences in the daily distribution of activity in relation to parents, in which the bimodal profile was characterized by higher levels in evening activity in relation to morning activity. Regarding the phase, the activity onset and offset, occurred later in relation to parents. After entering puberty, the activity onset and offset occurred later and there was an increase in total daily activity. On the other hand, when assessing the effect of sex, only females showed a delay in the activity offset and an increase in total daily activity. Therefore, the circadian activity rhythm in marmosets has peculiar characteristics in the juvenile stage in relation to the total of daily activity, the onset and offset of the active phase, and the distribution of activity during this phase. Besides, the entering puberty was associated with a phase delay and increase on total daily activity, with differences between sexes, possibly due to hormonal influences and/or social modulation on rhythm.

Gender differences in sleep habits and quality and daytime sleepiness in elementary and high school teachers

ABSTRACT The extensive workload of teachers inside and outside the classroom may contribute to sleep problems. Such problems may occur more frequently in women due to the combination of professional demands, domestic tasks, and their relatively greater sleep needs compared to men. The objective of this cross-sectional study was to evaluate the influence of gender on sleep habits and quality, and daytime sleepiness in a sample of 243 teachers (77 men and 166 women) using questionnaires. Linear regression models were used to examine the effect of gender on sleep measures; the unadjusted model considered only gender and the adjusted model considered chronotype and work characteristics as potential confounders. Bedtimes of women were significantly earlier than men during the week, but not on weekends, in the unadjusted and adjusted models. Time in bed was longer for women throughout the week and weekend in the unadjusted model. However, in the adjusted model, this statistical significance disappeared, and longer time in bed during the week was associated with teaching in one shift and for both levels of education. In addition, the female gender was associated with higher sleepiness scores compared to males in both models, and worse sleep quality in the adjusted model. Also, sleep quality was worse in subjects working in three shifts and in both types of schools (public and private). The tendency to eveningness was associated with later bedtimes and wake up times during both week days and weekends, higher irregularity of bedtimes and wake up times, and higher sleepiness scores in the adjusted model. Therefore, we suggest that female teachers do not fulfill their sleep needs and show higher levels of diurnal sleepiness and poor sleep quality that can be modulated by chronotype and some work characteristics. More studies are needed to evaluate the role of double workload on this pattern.