0303 Heart Rate and Systolic Blood Pressure Increase During Experimental Sleep Restriction

Introduction

Experimental sleep restriction is associated with elevated daytime cardiac activity, including heart rate (HR) and blood pressure (BP). However, some studies have found changes in systolic (SBP) but not diastolic blood pressure (DBP) or found changes in neither. Although findings are mixed, there may be a dose-response effect of cumulative sleep loss on daytime cardiac activity, such that HR and BP increase above basal levels with additional nights of insufficient sleep. This study examined changes in cardiac activity during experimental sleep restriction.

Methods

We used multilevel models with random effects for individuals to analyze data from 15 healthy males (M=22.3 years old, SD=2.8) in an 11-day inpatient protocol consisting of three nights of 10-hour/night baseline sleep opportunity, five nights of sleep restriction (5-hour/night sleep opportunity), and then two recovery nights (10-hour/night sleep opportunity). HR and BP were measured approximately every two hours during wake.

Results

HR increased 0.75 beats/minute with each successive night of sleep restriction (SE=0.18, p<0.001). HR was 5.13 beats/minute higher during the recovery condition than during baseline or sleep restriction (SE=1.05, p<0.001). During sleep restriction only, HR was lower in the later morning and evening compared to the earliest morning timepoint of the day, F(10, 743)=10.44, p<0.001. SBP increased 0.33 mmHg following each successive night of sleep restriction (SE=0.16, p=0.041); however, SBP was only marginally higher during the sleep restriction condition than during baseline (b=1.90, SE=1.09, p=0.082).

Conclusion

Our findings suggest that HR and SBP increase with each additional day of experimental sleep restriction, even after accounting for diurnal effects on HR and SBP. HR did not recover to baseline levels following a night of recovery sleep, suggesting that longer recovery sleep may be necessary to recover from a week of sleep restriction.

Support

Grant UL1TR000127 (Chang PI), Clinical and Translational Science Institute; College of Health and Human Development at Pennsylvania State University.

0360 Neighborhood Disadvantage is Associated with Lower Quality Sleep and More Variability in Weeknight Sleep Duration Among Urban Adolescents

Introduction

Differential social and contextual environments may contribute to adolescent sleep disparities. Yet, most prior studies are limited to self-reported sleep data, and the actigraphic studies of sleep are not conducted at a national level, thus limiting the variation in neighborhood contexts. This study examined the association between neighborhood disadvantage and actigraphic assessment of adolescent sleep.

Methods

Participants (682 adolescents, mean age 15.4 years) were racially/ethnically diverse (44% Black, 26% Hispanic, 17% White, 14% other race/ethnicity), sampled from 20 large US cities in the Fragile Families and Child Wellbeing Study. Neighborhood disadvantage was calculated from American Community Survey 2015 census data using the Standardized Neighborhood Deprivation Index (SNDI), consolidating five variables (proportion of female-headed households, public assistance recipients, households in poverty, adults without high school degrees, and unemployed) into an index. SNDI quartiles 1-3 fell below national averages of SNDI variables (“most disadvantaged”) and were compared to quartile 4 (“least disadvantaged”). Sleep indicators (duration, quality, and timing) were measured over ≥5 nights using wrist-worn accelerometers. Separate multilevel models estimated differences in sleep indicators, adjusting for weekday/weekend and summer/school year. General linear models used within-person standard deviations of sleep indicators (controlling for number of days) to test for associations between neighborhood disadvantage and consistency of weeknight sleep patterns. Models adjusted for individual-level sociodemographic covariates (age, sex, race/ethnicity, household income, caregiver education, and family structure).

Results

In fully adjusted models, adolescents living in more disadvantaged neighborhoods spent more time awake after falling asleep (4.0 minutes/night, p<0.05), spent greater percentage of nighttime sleep intervals awake (1%, p<.01), and had less consistent sleep duration (11.7% higher standard deviation, p<.05). Sleep duration and timing did not differ across neighborhood groups.

Conclusion

Living in more disadvantaged neighborhoods is associated with lower quality adolescent sleep; more research is needed to identify causal mechanisms.

Support

Research was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) of the National Institutes of Health (NIH), award numbers R01HD073352 (PI: Hale), R01HD36916, R01HD39135, and R01 HD40421, and private foundations. The content is the responsibility of the authors and does not represent official NIH views.

0296 Less Self-Reported Alertness and Motivation During Sleep Restriction are Associated with Decreased Attentional Performance

Introduction

Some individuals demonstrate more performance decrements on the psychomotor vigilance task (PVT) after sleep restriction (SR). We investigated whether individuals who reported less alertness and/or less motivation after SR demonstrated poorer performance on the PVT.

Methods

Fifteen healthy men (22.3±2.8 years) participated in a 10-night inpatient protocol with three nights of 10-hour baseline time in bed (TIB), five nights of SR (5-hour TIB), then two recovery (10-hour TIB) nights. Participants completed the 10-minute PVT (Joggle Research® battery) approximately every two hours during wake. Outcomes included number of false starts (<100 ms reaction time, RT) and number of lapses (≥500 ms RT). Participants reported alertness and motivation levels after each PVT. Median splits were used to characterize changes in alertness (“sleepy,” n=8, versus “alert,” n=7) and motivation (“unmotivated,” n=7, versus “motivated,” n=8) from the last day of baseline to the last day of SR. Outcomes were analyzed in mixed models with the predictor day*alertness or day*motivation, excluding the first three baseline days to preclude practice effects.

Results

There were significant interactions between day and alertness (p=.025) and day and motivation (p=.043) for false starts. False starts followed a quadratic inverted-U shape across days in sleepy (b=-0.16, p=.003) and unmotivated (b=-0.16, p=.004) participants, but not in alert or motivated participants (p>.05). There was a significant interaction between day and alertness for lapses (p=.008); lapses followed a quadratic inverted-U shape across days with a stronger effect in sleepy (b=-0.43, p<.001) versus alert (b=-0.15, p=.031) participants. There was no interaction between day and motivation for lapses.

Conclusion

Participants reporting less alertness were more likely to make both false starts and lapses after SR; those reporting less motivation were more likely to make false starts, but not lapses. Findings suggest greater motivation is sufficient to preserve inhibitory control but not vigilance after sleep restriction. In contrast, greater alertness despite sleep restriction was sufficient to preserve inhibitory control and resulted in lower vigilance decrements.

Support

This study was funded by grant UL1TR000127 from the Clinical and Translational Science Institute and the College of Health and Human Development at the Pennsylvania State University (Chang PI).

0085 Vulnerability to Sleep Restriction is Associated with Decreased Working Memory Performance

Introduction

We investigated whether individuals with more lapses on the psychomotor vigilance task (PVT) after sleep restriction (SR) demonstrated poorer working memory compared to those with fewer PVT lapses.

Methods

Fifteen healthy men (22.3±2.8 years) participated in a 10-night inpatient protocol with three nights of 10-hour baseline time in bed (TIB), five nights of SR (5-hour TIB), then two recovery (10-hour TIB) nights. Participants completed the Visual Object Learning Task (VOLT) and Fractal 2-Back (F2B; visual n-back) measuring working memory and the PVT (Joggle Research® battery) approximately every two hours during wake. During the VOLT, participants indicated whether presented images had been shown previously. Outcomes included number of misses and false alarms. During the F2B, participants tapped the screen when an image appeared that had been shown 2 images previously. Outcomes included sensitivity and specificity. Median split of mean PVT lapses after the last night of SR was used to categorize participants into “vulnerable” (n=8) versus “resistant” (n=7) groups. Outcomes were analyzed in mixed models with the predictor day*vulnerability, excluding the first three baseline days to preclude practice effects.

Results

There was a significant interaction between day and attentional vulnerability for VOLT misses (p<.001); misses increased linearly across days in vulnerable (b=.18, p<.001) but not resistant (p=.956) participants. There was no interaction between day and vulnerability for VOLT false alarms, which did not change across days. There was a significant interaction between day and attentional vulnerability for F2B sensitivity (p=.002); sensitivity increased linearly across days in resistant (b=.02, p<.001) but not in vulnerable (p=.273) participants. There was no interaction between day and vulnerability for F2B specificity, which did not change across days.

Conclusion

Performance on the VOLT decreased in vulnerable participants only; performance on the F2B improved in resistant participants likely due to practice effects not seen in vulnerable participants. Findings indicate vulnerability to attentional lapses after SR is a marker of vulnerability to working memory decrements.

Support

This study was funded by grant UL1TR000127 from the Clinical and Translational Science Institute (Chang PI) and the College of Health and Human Development at the Pennsylvania State University.

0033 Recurrent Circadian Disruption While Minimizing Sleep Loss in Humans Impairs Glucose Tolerance Only in The Presence of High-Fat Diet

Introduction

Nearly 14% of Americans experience chronic circadian disruption due to shift work, increasing their risk of obesity and cardiometabolic disorders. These disorders are also exacerbated by modern eating habits such as frequent snacking and consumption of high-fat foods. Here we used a forced desynchrony protocol to investigate the effect of 3 weeks of recurrent circadian disruption (RCD) with minimal sleep loss on glucose metabolism in humans on a lower or higher fat diet (LFD and HFD, respectively).

Methods

Six healthy adults (38-69yrs; 3f) participated in a 37-day inpatient protocol with LFD (25–27% fat) and 15.67-hr fasting duration, or HFD (45–50% fat) and 13-hr fasting duration. The protocol included three weeks of RCD consisting of 28-hr “days” with 11.67-hr sleep opportunities (=10hrs/24hr). Glucose and insulin responses to a standardized breakfast were conducted at baseline, at an aligned circadian phase after 2–3 weeks of exposure to RCD, and after 1 week of recovery. Frequent blood samples were assayed for glucose and insulin; the Area-Under-Curve was calculated from start of breakfast through postprandial minute 180.

Results

Total Sleep Time was similar in Baseline and RCD in both groups. Participants on the LFD showed no change in glucose AUC during RCD compared to Baseline. Insulin AUC was lower during RCD (p=0.0269) and Recovery (p=0.0443) than Baseline. In contrast, participants on the HFD showed a significant increase in glucose AUC during RCD compared to Baseline (p<0.0001); AUC returned to Baseline during Recovery. There was no significant change in insulin AUC on the HFD.

Conclusion

RCD (in the absence of sleep loss) led to impaired glucose tolerance when combined with HFD, but not when combined with LFD. These results suggest that LFD may be part of healthy strategies for people experiencing RCD.

Support

Study supported by P01AG009975 and conducted in the Brigham and Women’s Hospital Center for Clinical Investigation, part of Harvard Clinical and Translational Science Center supported by UL1TR001102. Authors supported by a fellowship from the Finnish Cultural Foundation (KMZ); T32HL007901 and F32HL143893 (RKY); T32HL007901 and F32AG051325 (NV); K24HL105664 (EBK); R01HL118601 (FAJLS).

0371 Educational Disparities in U.S. Elementary School Children are Related to Sleep Duration and Bedtimes

Introduction

Sleep is vital for healthy development in children. Suboptimal sleep health may play an under-appreciated role in educational achievement gaps among vulnerable student populations. Students of color, students from economically disadvantaged homes, and students with disabilities are especially likely to experience poor sleep. Sleep deficiency could interfere with school functioning, including academic achievement.

Methods

Longitudinal data from the nationally-representative Early Childhood Longitudinal Study (ECLS-K: 2011) included ~12,000 students. We tested the hypothesis that parent-reported child sleep duration (typical hours per night) was associated with academic achievement trajectories (3rd-5th grade). We further tested the extent to which this relation is linked to parent-reported bedtimes in kindergarten. Preregistered analyses (osf.io) used structural equation path modeling, stratified by racial/ethnic group (White, Black, Hispanic, Asian), disability status, and socioeconomic status (SES) tertiles. Students were assessed using psychometrically-validated standardized academic achievement tests.

Results

Children with later kindergarten bedtimes had shorter sleep duration across 3rd-5th grade. Children with shorter sleep duration also had poorer achievement in 3rd grade. The path by which sleep associates with achievement differed by vulnerable subgroups. Among children from average- or high-SES families, earlier bedtimes were related to higher reading achievement growth across 3rd-5th grade, but not among children from low-SES families. For children with disabilities, longer sleep duration was significantly and positively associated with growth in reading achievement across 3rd-5th grade, but this relation among children with disabilities was not evident within racial or ethnic groups or SES strata.

Conclusion

Sleep duration, a modifiable behavioral factor, may be a promising target of intervention in families for promoting healthy childhood sleep health behaviors. Results provide evidence that age-appropriate bedtimes and adequate sleep duration could be promoted among vulnerable populations including students with disabilities. For instance, although most screening instruments do not currently evaluate sleep or sleep disorders, assessing and treating disability or behavioral difficulties could include such evaluations for clinical and parent consideration.

Support

Penn State Center for Educational Disparities Research

0320 Psychological Correlates of Morningness/Eveningness in Latinx Pre-Adolescents

Introduction

Chronotype refers to a preference for morning hours (morningness) vs. evening hours (eveningness) when individuals tend to feel their best (e.g., higher energy levels). People may be classified at either end of this spectrum or along a continuum between these preferences. Among adolescents, eveningness is positively related to depression and anxiety, whereas morningness is negatively related to depression. However, less is known about the relationship of chronotype and psychological health in pre-teens and Latinx youth. The present study explored associations of morningness/eveningness with anxiety symptoms, depressive symptoms, and perceived stress among Latinx pre-adolescents in Southern California.

Methods

A purposive sample of 100 Latinx children, ages 10-12 years old, completed self-report surveys in their homes or a preferred location chosen by the parent. Measures included the Morningness/Eveningness Scale for Children (higher scores indicate morning preference), Revised Child Anxiety and Depression Scale and the Perceived Stress Scale (higher scores indicate higher anxiety, depression and stress, respectively). Associations were tested with Pearson correlations.

Results

The sample was 47% male with a mean±SD age of 10.9±0.8 years. Average score for morningness/eveningness was M=30.2±4.4 (range: 18-41), for anxiety symptoms was M=0.7±0.7 (range: 0-2.8), for depression symptoms was M=0.5±0.4 (range: 0-1.9) and for perceived stress was M=15.2±5.8 (range: 2-30). Greater morningness/eveningness scores, indicating more morningness, were associated with lower scores for anxiety symptoms (r=-.41, p<.001), depressive symptoms (r=-.36, p<.001) and perceived stress (r=-.33, p=.001).

Conclusion

As has been found for adolescents, higher morningness in Latinx pre-teens was related to less frequent anxiety and depression symptoms, as well as lower perceived stress. Youth experience a circadian phase delay during adolescence, shifting their preference toward eveningness, which may exacerbate stressors and negative mental health. Therefore, interventions to promote psychological well-being in pre-adolescents may help prevent worse psychological outcomes in Latinx children as they transition to adolescence.

Support

This work was supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Numbers UL1GM118979, TL4GM118980, and RL5GM118978.

0858 Impact Of Actigraphic Sleep Measures On Ambulatory Cognitive Performance In A Community-Based Sample Of Older Adults

Introduction

Few longitudinal studies link objectively assessed sleep and cognition, especially day to day differences in sleep as they relate to daily cognitive performance in ecologically-valid, natural environments. We examine the associations of sleep (actigraphy) with ambulatory ecological momentary assessments (EMA) of cognitive performance.

Methods

Analyses involved 225 participants enrolled in The Einstein Aging Study, a community based longitudinal cohort of older adults free of dementia at enrollment (Mage=77.27 years; 33% males; 47% Caucasian, 39% African American, 13% Hispanic). We examined between-person associations between actigraphic sleep duration and wake after sleep onset (WASO) with mean and variability across the day in cognitive performance. Cognitive performance was assessed via validated, smartphone-based EMA over a mean of 18 days. Six assessments/day included Symbol Match (processing speed), Color Dot (working memory), and Color Shape (memory binding). Models controlled for age, gender, ethnicity, education (years), clinically assessed mild cognitive impairment, and learning effects. Actigraphy data was collected throughout the study period.

Results

Sleep duration had a significant effect on within-person variability on ambulatory cognition: Color Dot, Symbol Match, and Color Shape (all p’s <0.001). Older adults with longer mean nightly sleep duration exhibited more stable cognitive performance over time versus those with shorter sleep duration; sleep duration did not predict mean levels of daily cognitive performance. Person-level means of WASO (0.99±0.45 hours/night) predicted mean levels on cognitive tests, independent of sleep duration. Older adults with less WASO/night exhibited better cognitive performance. One half hour less nightly WASO predicted 175ms shorter Symbol Match response time (p=0.004), 1.5% lower Color Dot error proportion (p=0.048), 0.07 points higher Color Shape accuracy (p<0.001). Older adults with less WASO/night also had less within-person variations in Color Dot (p<0.001), Symbol Match (p<0.001) and Color Shape performance (p=0.01).

Conclusion

Ambulatory cognitive performance assessed using EMA was related to actigraphic sleep. Poor sleep health may be a target for prevention of early cognitive changes that may precede onset of cognitive impairment and AD.

Support

Research was supported by the National Institute on Aging (NIA) award numbers P01AG003949 and R01AG056538.

Rapid suppression of bone formation marker in response to sleep restriction and circadian disruption in men

We describe the time course of bone formation marker (P1NP) decline in men exposed to ~ 3 weeks of sleep restriction with concurrent circadian disruption. P1NP declined within 10 days and remained lower with ongoing exposure. These data suggest even brief exposure to sleep and circadian disruptions may disrupt bone metabolism.

INTRODUCTION

A serum bone formation marker (procollagen type 1 N-terminal, P1NP) was lower after ~ 3 weeks of sleep restriction combined with circadian disruption. We now describe the time course of decline.

METHODS

The ~ 3-week protocol included two segments: "baseline," ≥ 10-h sleep opportunity/day × 5 days; "forced desynchrony" (FD), recurring 28 h day (circadian disruption) with sleep restriction (~ 5.6-h sleep per 24 h). Fasted plasma P1NP was measured throughout the protocol in nine men (20-59 years old). We tested the hypothesis that PINP would steadily decline across the FD intervention because the magnitude of sleep loss and circadian misalignment accrued as the protocol progressed. A piecewise linear regression model was used to estimate the slope (β) as ΔP1NP per 24 h with a change point mid-protocol to estimate the initial vs. prolonged effects of FD exposure.

RESULTS

Plasma P1NP levels declined significantly within the first 10 days of FD ([Formula: see text] = - 1.33 μg/L per 24 h, p < 0.0001) and remained lower than baseline with prolonged exposure out to 3 weeks ([Formula: see text] = - 0.18 μg/L per 24 h, p = 0.67). As previously reported, levels of a bone resorption marker (C-telopeptide (CTX)) were unchanged.

CONCLUSION

Sleep restriction with concurrent circadian disruption induced a relatively rapid decline in P1NP (despite no change in CTX) and levels remained lower with ongoing exposure. These data suggest (1) even brief sleep restriction and circadian disruption can adversely affect bone metabolism, and (2) there is no P1NP recovery with ongoing exposure that, taken together, could lead to lower bone density over time.

24-hour profile of serum sclerostin and its association with bone biomarkers in men

The osteocyte's role in orchestrating diurnal variations in bone turnover markers (BTMs) is unclear. We identified no rhythm in serum sclerostin (osteocyte protein). These results suggest that serum sclerostin can be measured at any time of day and the osteocyte does not direct the rhythmicity of other BTMs in men.

INTRODUCTION

The osteocyte exerts important effects on bone remodeling, but its rhythmicity and effect on the rhythms of other bone cells are not fully characterized. The purpose of this study was to determine if serum sclerostin displays rhythmicity over a 24-h interval, similar to that of other bone biomarkers.

METHODS

Serum sclerostin, FGF-23, CTX, and P1NP were measured every 2 h over a 24-h interval in ten healthy men aged 20-65 years. Maximum likelihood estimates of the parameters in a repeated measures model were used to determine if these biomarkers displayed a diurnal, sinusoidal rhythm.

RESULTS

No discernible 24-h rhythm was identified for sclerostin (p = 0.99) or P1NP (p = 0.65). CTX rhythmicity was confirmed (p < 0.001), peaking at 05:30 (range 01:30-07:30). FGF-23 levels were also rhythmic (p < 0.001), but time of peak was variable (range 02:30-11:30). The only significant association identified between these four bone biomarkers was for CTX and P1NP mean 24-h metabolite levels (r = 0.65, p = 0.04).

CONCLUSIONS

Sclerostin levels do not appear to be rhythmic in men. This suggests that in contrast to CTX, serum sclerostin could be measured at any time of day. The 24-h profiles of FGF-23 suggest that a component of osteocyte function is rhythmic, but its timing is variable. Our results do not support the hypothesis that osteocytes direct the rhythmicity of other bone turnover markers (CTX), at least not via a sclerostin-mediated mechanism.

Feasibility of actigraphy wristband monitoring of atopic dermatitis in children

BACKGROUND/PURPOSE

Actigraphy monitors are used to monitor sleep and scratching. Previous studies have implemented these monitors to evaluate behavior in adult patients with atopic dermatitis. However, such monitoring devices have been implemented in a paucity of studies involving pediatric patients with atopic dermatitis. The purpose of this study was to assess the feasibility of actigraphy monitoring in children with mild-to-severe atopic dermatitis.

METHODS

A total of six pediatric subjects were recruited. The severity of atopic dermatitis at the wrist area was assessed prior to placement of the wristband monitor. After wearing the wristbands for 7 days, subjects returned to clinic to undergo reassessment of the wrist area to determine if atopic dermatitis was exacerbated by the wrist-worn device. Data on sleep quality and how often patients wore the wristband monitors were also collected. No subjective data from the subjects or parents/caregivers were collected on tolerability of the monitors.

RESULTS

None of the subjects exhibited exacerbation of atopic dermatitis at the wrist area after wearing the actigraphy monitors for 7 days. No adverse events were reported. Pediatric patients with atopic dermatitis exhibited less total sleep time compared with children evaluated in previous actigraphy studies.

CONCLUSION

Actigraphy wristband monitoring can be used to continuously assess disease severity in children with atopic dermatitis.

Racial disparities in job strain among American and immigrant long-term care workers

BACKGROUND

Nursing homes are occupational settings, with an increasing minority and immigrant workforce where several psychosocial stressors intersect.

AIM

This study aimed to examine racial/ethnic differences in job strain between Black (n = 127) and White (n = 110) immigrant and American direct-care workers at nursing homes (total n = 237).

METHODS

Cross-sectional study with data collected at four nursing homes in Massachusetts during 2006-2007. We contrasted Black and White workers within higher-skilled occupations such as registered nurses or licensed practical nurses (n = 82) and lower-skilled staff such as certified nursing assistants (CNAs, n = 155).

RESULTS

Almost all Black workers (96%) were immigrants. After adjusting for demographic and occupational characteristics, Black employees were more likely to report job strain, compared with Whites [relative risk (RR): 2.9, 95% confidence interval (CI) 1.3 to 6.6]. Analyses stratified by occupation showed that Black CNAs were more likely to report job strain, compared with White CNAs (RR: 3.1, 95% CI: 1.0 to 9.4). Black workers were also more likely to report low control (RR: 2.1, 95% CI: 1.1 to 4.0). Additionally, Black workers earned $2.58 less per hour and worked 7.1 more hours per week on average, controlling for potential confounders.

CONCLUSION

Black immigrant workers were 2.9 times more likely to report job strain than White workers, with greater differences among CNAs. These findings may reflect differential organizational or individual characteristics but also interpersonal or institutional racial/ethnic discrimination. Further research should consider the role of race/ethnicity in shaping patterns of occupational stress.

Circadian variation in Cushing's disease and pseudo-Cushing states by analysis of F and ACTH pulsatility

Distinguishing pituitary-dependent Cushing's disease from pseudo-Cushing's states can present a diagnostic challenge. Although many studies potentially discriminate between the 2, only the dexamethasone-suppressed corticotropin-releasing hormone (CRF) stimulation test at 15 minutes is 100% sensitive or specific. We measured baseline profiles of F and ACTH in 31 Cushing's disease patients, 11 with pseudo-Cushing's and 17 controls. Venous blood was collected at 30 minute intervals for 24-h. Subjects also had CRF stimulation tests and 2.0 mg/day dexamethasone suppression tests. F and ACTH profiles were analyzed for circadian rhythmicity, variability, and pulsatility. Relative circadian amplitude was decreased in Cushing's disease compared to both pseudo-Cushing's and normal states. Relative pulse amplitude was reduced in Cushing's disease. Because of this dampening of circadian and pulsatile variations, the overall variability of F and ACTH levels around their mean levels as quantified by the intra-series coefficient of variation (CV), was also decreased in Cushing's disease compared to pseudo-Cushing's and normal states. A F 24-h CV<40% was able to distinguish Cushing's disease from pseudo-Cushing's with 100% sensitivity (95% confidence interval (CI), 88-100%) and specificity (CI, 71-100%). An ACTH CV<40% had 97% sensitivity (CI, 83-100%) and 100% specificity (CI, 71-100%). An overnight 8-h F CV <40% also distinguished Cushing's disease from pseudo-Cushing's with 100% sensitivity (CI, 88-100%) and specificity (CI, 71-100%). These data show that a simple index of total temporal variability (the intra-series CV) derived from the analysis of basal F profiles, provides a useful method to distinguish Cushing's disease from pseudo-Cushing's. A F or ACTH CV <40% discriminates Cushing's disease from pseudo-Cushing's and reflects reduced circadian and pulsatile variations.

A benzodiazepine hypnotic facilitates adaptation of circadian rhythms and sleep-wake homeostasis to an eight hour delay shift simulating westward jet lag

STUDY OBJECTIVES

To determine whether appropriately timed administration of a short-acting benzodiazepine hypnotic, which has proven effective in an animal model of jet lag, also facilitates adaptation of circadian rhythmicity and sleep-wake homeostasis in a human model of jet lag.

DESIGN

Subjects participated in two double-blind, placebo-controlled studies of adaptation to an 8-hr delay shift of sleep-wake and dark-light cycles simulating westward travel. Each 9-day laboratory study began with a 3-day habituation period followed by a 24-hr study to obtain basal hormonal and sleep profiles (23:00-07:00). Subjects were then kept awake until 07:00 the next day and slept in darkness 07:00-15:00 for the next five 24-hr spans post-shift.

SETTING

N/A.

PARTICIPANTS

6 normal, healthy men 24-31 years of age.

INTERVENTIONS

Oral Triazolam (0.5 mg) or placebo given at 04:00 before the first shifted sleep/dark period (3 hours before bedtime) and at 07:00 (at bedtime) on days 2-5 post-shift.

MEASUREMENTS AND RESULTS

Sleep recordings and 24-hr cortisol and growth hormone profiles were obtained at baseline and on the first, third, and fifth days post-shift. Global measures of treatment efficacy were calculated for multiple endpoints representing circadian rhythmicity and sleep-wake homeostasis. With placebo, the shift induced disturbances of sleep and hormonal secretion, and a gradual re-entrainment of circadian rhythmicity. Triazolam significantly facilitated adaptation by accelerating re-entrainment of circadian rhythms (chronobiotic effect) and normalizing markers of sleep/wake homeostasis (hypnotic effect).

CONCLUSIONS

Appropriately timed administration of a benzodiazepine hypnotic appears to facilitate the adaptation of both circadian rhythmicity and sleep-wake homeostasis to a shifted dark/sleep cycle. Compounds with combined chronobiotic/hypnotic properties may be useful in conditions of jet lag or night work.

Twenty-four-hour profiles of serum leptin in siberian and golden hamsters: photoperiodic and diurnal variations

Serum leptin concentrations were obtained from male Siberian hamsters (Phodopus sungorus) and golden hamsters (a.k.a. Syrian, Mesocricetus auratus) housed on long [light:dark (LD) 16:8] and short (LD 6:18) photoperiods for 10-11 weeks. Blood samples were collected at 45-min intervals for 24 h from individual animals using an in-dwelling atrial catheter. In Siberian hamsters, exposure to short photoperiods as compared to long photoperiods reduced body weight (32.5 +/- 1.5 vs 47.7 +/- 1.1 g) and leptin (24-h mean: 5.3 +/- 0.4 ng/ml vs 18.6 +/- 2.1 ng/ml). Although photoperiod influenced the temporal distribution of leptin in golden hamsters, the main effect of photoperiod on leptin levels in golden hamsters did not reach significance (24-h mean: 7.1 +/- 1.0 ng/ml vs 5.1 +/- 0.8 ng/ml.). Body weights of golden hamsters did not vary significantly following exposure to short photoperiod for 11 weeks (178.3 +/- 3.6 g in LD 6:18 vs 177.8 +/- 7.3 g in LD 16:8). There was no nocturnal increase in serum leptin in either species. Marked interindividual differences were apparent in individual leptin profiles. Periodogram analysis revealed that only a few animals exhibited 24-h periodicities; the presence of a significant 24-h periodicity was more common in hamsters exposed to short days. Photoperiod-associated differences in the 24-hour profile of leptin secretion may be the result of photoperiod-associated changes in feeding behavior or metabolism. A full understanding of the regulation of leptin secretion in multiple time domains may enhance our understanding of the function of leptin.

Locomotor response to an open field during C57BL/6J active and inactive phases: differences dependent on conditions of illumination

Time of day has proven to be a source of variability in diverse behavioral measures. Knowledge of the pattern of this temporal effect as well as its origin (exogenous or endogenous) is essential for a precise description of any behavior. This study analyzed the effect of the external light-dark cycle and the internal rest-activity rhythm on the response of C57BL/6J mice to a novel environment. In a first experiment, animals maintained in a 12:12-h light-dark cycle were tested in an open field at six different times of day. A diurnal rhythm of ambulation in the open field was observed with greater levels of activity exhibited by those groups tested at night. Long-term and short-term behavioral habituation to spatial novelty were also affected by phase of the light-dark cycle. A second experiment was designed to control for any direct effect of the light-dark cycle by keeping the animals in dim green light where entrainment was maintained by a skeleton photoperiod (two 15-min bright-light pulses separated by 12 hours of green, dim light). This second group of animals was tested at two different circadian phases under the same conditions of illumination. One group was tested during the subjective night and another group during the subjective day, i.e., 2 or 14 h after the onset of the active phase, as assessed by wheel-running behavior. No effect of circadian phase on ambulation or habituation of this response to the open field was observed in these animals. Taken together, these results suggest that spatial novelty is equally arousing regardless of circadian phase and that the conditions of illumination can dramatically alter the response to a novel environment.

Daytime naps in darkness phase shift the human circadian rhythms of melatonin and thyrotropin secretion

To systematically determine the effects of daytime exposure to sleep in darkness on human circadian phase, four groups of subjects participated in 4-day studies involving either no nap (control), a morning nap (0900-1500), an afternoon nap (1400-2000), or an evening nap (1900-0100) in darkness. Except during the scheduled sleep/dark periods, subjects remained awake under constant conditions, i.e., constant dim light exposure (36 lx), recumbence, and caloric intake. Blood samples were collected at 20-min intervals for 64 h to determine the onsets of nocturnal melatonin and thyrotropin secretion as markers of circadian phase before and after stimulus exposure. Sleep was polygraphically recorded. Exposure to sleep and darkness in the morning resulted in phase delays, whereas exposure in the evening resulted in phase advances relative to controls. Afternoon naps did not change circadian phase. These findings indicate that human circadian phase is dependent on the timing of darkness and/or sleep exposure and that strategies to treat circadian misalignment should consider not only the timing and intensity of light, but also the timing of darkness and/or sleep.

Effects of aging on sleep in the golden hamster

The golden hamster (Mesocricetus auratus) has been a model organism for the study of circadian rhythmicity and, in particular, the effects of age on the circadian system. Surprisingly, nothing is known about the effects of advanced age on sleep in this species. As a first step in determining the effects of aging on sleep in the golden hamster, we recorded sleep for 24 hours in 12 young (3 months) and 18 old (17-18 months) golden hamsters entrained to a 14:10 light:dark (LD) cycle. Aged hamsters exhibited small but significant increases in overall NREM sleep time, primarily due to an increase in time the old animals spent in the NREM sleep state during the dark period relative to the young hamsters. There were no significant differences in REM sleep, median sleep episode length, or the number of arousals. The most striking differences between the sleep of young and old hamsters was in NREM delta (0.5-4 Hz) power per epoch. Old hamsters showed approximately 27% less (p=0.0004) delta power per NREM epoch than young hamsters. It is possible that increased NREM sleep time in the old hamsters may be a failed attempt to maintain cumulative delta power; ie, old hamsters may have more NREM sleep in order to make up for the lower intensity of their sleep. This decline in delta power with age parallels earlier findings in cats and humans, although has it not been previously reported in rodents.

Effects of exercise on neuroendocrine secretions and glucose regulation at different times of day

To study the effects of time of day on neuroendocrine and metabolic responses to exercise, body temperature, plasma glucose, insulin secretion rates (ISR), and plasma cortisol, growth hormone (GH) and thyrotropin (TSH) were measured in young men, both at bed rest and during a 3-h exercise period (40-60% maximal O2 uptake). Exercise was performed at three times of day characterized by marked differences in cortisol levels, i.e., early morning (n = 5), afternoon (n = 8), and around midnight (n = 9). The subjects were kept awake and fasted, but they received a constant glucose infusion to avoid hypoglycemia. Exercise-induced elevations of temperature were higher in the early morning than at other times of day. The exercise-induced glucose decrease was approximately 50% greater around midnight, when cortisol was minimal and not stimulated by exercise, than in the afternoon or early morning (P < 0.05). This effect of time of day appeared unrelated to decreases in ISR or increases in temperature and GH. Robust TSH increases occurred in all exercise periods and were maximal at night. The results demonstrate the existence of circadian variations in neuroendocrine and metabolic responses to exercise.

Acute and delayed effects of exercise on human melatonin secretion

Accumulating evidence suggests that exercise may have both rapid and delayed effects on human melatonin secretion. Indeed, exercise may acutely (i.e., within minutes) alter melatonin levels and result in a shift of the onset of nocturnal melatonin 12 to 24 h later. The presence and nature of both acute and delayed effects appear to be dependent on the timing of exercise. The presence of a detectable acute effect also depends on the duration, intensity, and type of exercise. Late evening exercise during the rising phase of melatonin secretion may blunt melatonin levels. High-intensity exercise during the nighttime period, when melatonin levels already are elevated, consistently results in a further (nearly 50%) elevation of melatonin levels. No effect of low-intensity exercise performed at the same circadian phase could be detected. Irrespective of intensity, exercise near the offset of melatonin secretion or during the daytime has no consistent acute effect on melatonin secretion. Nighttime exercise, whether of moderate or high intensity, results in phase delays of the melatonin onset on the next evening. In support of the concept that a shift of the melatonin onset on the day after nighttime exercise represents a shift of intrinsic circadian timing is the observation that similar phase shifts (in both direction and magnitude) may be observed simultaneously for the onset of the circadian elevation of thyrotropin secretion. The observation of exercise-induced phase shifts of the onset of melatonin secretion is, therefore, interpreted as evidence that, in humans as in rodents, increased physical activity during the habitual rest period is capable of altering circadian clock function.

Roles of intensity and duration of nocturnal exercise in causing phase delays of human circadian rhythms

To determine the roles of intensity and duration of nocturnal physical activity in causing rapid phase shifts of human circadian rhythms, eight healthy men were studied three times under constant conditions with no exercise, a 3-h bout of moderate-intensity exercise, or a 1-h bout of high-intensity exercise. Exercise stimulus was centered at 0100. Circadian phase was estimated from the onsets of the nocturnal elevation of plasma thyrotropin (TSH) and melatonin. Mean phase shifts of TSH onsets were -18 +/- 8 (baseline), -78 +/- 10 (low-intensity exercise, P < 0.01), and -95 +/- 19 min (high-intensity exercise, P < 0.01). Mean phase delays of melatonin onsets were -23 +/- 10 (baseline), -63 +/- 8 (low-intensity exercise, P < 0.04), and -55 +/- 15 min (high-intensity exercise, P < 0.12). Taken together with our previous findings, this study indicates that nocturnal physical activity may phase delay human circadian rhythms and demonstrates that phase-shifting effects may be determined with exercise durations and intensities compatible with the demands of a real-life setting.

Synchronizing circadian rhythms in early infancy

Entrainment to the 24-hour light-dark cycle is of adaptive significance to mammals. Human infants are no exception, but some postnatal care habits prevalent in developed countries can interfere with the physiological mechanisms underlying circadian synchronization. We describe the physiological mechanisms of entrainment to the light-dark cycle in fetuses and newborns, and some common parental care behaviors which subject the developing circadian system of the newborn to conflicting temporal cues. Improvements in parental care are proposed which may improve the circadian synchronization of newborns, and their parents or caregivers.