Circadian Insights into Motivated Behavior

Mechanisms of microbial coexistence in a patchy ecosystem: Differences in ecological niche overlap and species fitness between rhythmic and non-rhythmic species

Resource patchiness caused by external events breaks the continuity and homogeneity of resource distribution in the original ecosystem. For local organisms, this leads to drastic changes in the availability of resources, breaks down the co-existence of species, and reshuffles the local ecosystem. West Lake is a freshwater lake with resource patchiness caused by multiple exogenous disturbances that has strong environmental heterogeneity that prevents clear observation of seasonal changes in the microbial communities. Despite this, the emergence of rhythmic species in response to irregular changes in the environment has been helpful for observing microbial communities dynamics in patchy ecosystems. We investigated the ecological mechanisms of seasonal changes in microbial communities in West Lake by screening rhythmic species based on the ecological niche and modern coexistence theories. The results showed that rhythmic species were the dominant factors in microbial community changes and the effects of most environmental factors on the microbial community were indirectly realised through the rhythmic species. Random forest analyses showed that seasonal changes in the microbial community were similarly predicted by the rhythmic species. In addition, we incorporated species interactions and community phylogenetic patterns into stepwise multiple regression analyses, the results of which indicate that ecological niches and species fitness may drive the coexistence of these subcommunities. Thus, this study extends our understanding of seasonal changes in microbial communities and provides new ways for observing seasonal changes in microbial communities, especially in ecosystems with resource patches. Our study also show that combining community phylogenies with co-occurrence networks based on ecological niches and modern coexistence theory can further help us understand the ecological mechanisms of interspecies coexistence.

Qualitative and quantitative evidence of motivation states for physical activity, exercise and being sedentary from university student focus groups

Motivation for physical activity and sedentary behaviors (e.g., desires, urges, wants, cravings) varies from moment to moment. According to the WANT model, these motivation states may be affectively-charged (e.g., felt as tension), particularly after periods of maximal exercise or extended rest. The purpose of this study was to examine postulates of the WANT model utilizing a mixed-methods approach. We hypothesized that: (1) qualitative evidence would emerge from interviews to support this model, and (2) motivation states would quantitatively change over the course of an interview period. Seventeen undergraduate students (mean age = 18.6y, 13 women) engaged in focus groups where 12 structured questions were presented. Participants completed the "right now" version of the CRAVE scale before and after interviews. Qualitative data were analyzed with content analysis. A total of 410 unique lower-order themes were classified and grouped into 43 higher order themes (HOTs). From HOTs, six super higher order themes (SHOTs) were designated: (1) wants and aversions, (2) change and stability, (3) autonomy and automaticity, (4) objectives and impulses, (5) restraining and propelling forces, and (6) stress and boredom. Participants stated that they experienced desires to move and rest, including during the interview, but these states changed rapidly and varied both randomly as well as systematically across periods of minutes to months. Some also described a total absence of desire or even aversion to move and rest. Of note, strong urges and cravings for movement, typically from conditions of deprivation (e.g., sudden withdrawal from exercise training) were associated with physical and mental manifestations, such as fidgeting and feeling restless. Urges were often consummated with behavior (e.g., exercise sessions, naps), which commonly resulted in satiation and subsequent drop in desire. Importantly, stress was frequently described as both an inhibitor and instigator of motivation states. CRAVE-Move increased pre-to-post interviews (p < .01). CRAVE-Rest demonstrated a trend to decline (p = .057). Overall, qualitative and quantitative data largely corroborated postulates of the WANT model, demonstrating that people experience wants and cravings to move and rest, and that these states appear to fluctuate significantly, especially in the context of stress, boredom, satiety, and deprivation.

Motivation states to move, be physically active and sedentary vary like circadian rhythms and are associated with affect and arousal

Introduction

Motivation to be physically active and sedentary is a transient state that varies in response to previous behavior. It is not known: (a) if motivational states vary from morning to evening, (b) if they are related to feeling states (arousal/hedonic tone), and (c) whether they predict current behavior and intentions. The primary purpose of this study was to determine if motivation states vary across the day and in what pattern. Thirty adults from the United States were recruited from Amazon MTurk.

Methods

Participants completed 6 identical online surveys each day for 8 days beginning after waking and every 2-3 h thereafter until bedtime. Participants completed: (a) the CRAVE scale (Right now version) to measure motivation states for Move and Rest, (b) Feeling Scale, (c) Felt Arousal Scale, and (d) surveys about current movement behavior (e.g., currently sitting, standing, laying down) and intentions for exercise and sleep. Of these, 21 participants (mean age 37.7 y; 52.4% female) had complete and valid data.

Results

Visual inspection of data determined that: a) motivation states varied widely across the day, and b) most participants had a single wave cycle each day. Hierarchical linear modelling revealed that there were significant linear and quadratic time trends for both Move and Rest. Move peaked near 1500 h when Rest was at its nadir. Cosinor analysis determined that the functional waveform was circadian for Move for 81% of participants and 62% for Rest. Pleasure/displeasure and arousal independently predicted motivation states (all p's < .001), but arousal had an association twice as large. Eating, exercise and sleep behaviors, especially those over 2 h before assessment, predicted current motivation states. Move-motivation predicted current body position (e.g., laying down, sitting, walking) and intentions for exercise and sleep more consistently than rest, with the strongest prediction of behaviors planned for the next 30 min.

Discussion

While these data must be replicated with a larger sample, results suggest that motivation states to be active or sedentary have a circadian waveform for most people and influence future behavioral intentions. These novel results highlight the need to rethink the traditional approaches typically utilized to increase physical activity levels.

Mistimed restricted feeding disrupts circadian rhythms of male mating behavior and female preovulatory LH surges in mice

In rodents, eating at atypical circadian times, such as during the biological rest phase when feeding is normally minimal, reduces fertility. Prior findings suggest this fertility impairment is due, at least in part, to reduced mating success. However, the physiological and behavioral mechanisms underlying this reproductive suppression are not known. In the present study, we tested the hypothesis that mistimed feeding-induced infertility is due to a disruption in the normal circadian timing of mating behavior and/or the generation of pre-ovulatory luteinizing hormone (LH) surges (estrogen positive feedback). In the first experiment, male+female mouse pairs, acclimated to be food restricted to either the light (mistimed feeding) or dark (control feeding) phase, were scored for mounting frequency and ejaculations over 96 h. Male mounting behavior and ejaculations were distributed much more widely across the day in light-fed mice than in dark-fed controls and fewer light-fed males ejaculated. In the second experiment, the timing of the LH surge, a well characterized circadian event driven by estradiol (E2) and the SCN, was analyzed from serial blood samples taken from ovariectomized and E2-primed female mice that were light-, dark-, or ad-lib-fed. LH concentrations peaked 2 h after lights-off in both dark-fed and ad-lib control females, as expected, but not in light-fed females. Instead, the normally clustered LH surges were distributed widely with high inter-mouse variability in the light-fed group. These data indicate that mistimed feeding disrupts the temporal control of the neural processes underlying both ovulation and mating behavior, contributing to infertility.

Circadian rhythm disruption in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Implications for the post-acute sequelae of COVID-19

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a common and disabling disorder primarily characterized by persistent fatigue and exercise intolerance, with associated sleep disturbances, autonomic dysfunction, and cognitive problems. The causes of ME/CFS are not well understood but may coincide with immune and inflammatory responses following viral infections. During the current SARS-CoV2 coronavirus pandemic, ME/CFS has been increasingly reported to overlap with persistent “long COVID” symptoms, also called the post-acute sequelae of COVID-19 (PASC). Given the prominence of activity and sleep problems in ME/CFS, circadian rhythm disruption has been examined as a contributing factor in ME/CFS. While these studies of circadian rhythms have been pursued for decades, evidence linking circadian rhythms to ME/CFS remains inconclusive. A major limitation of older chronobiology studies of ME/CFS was the unavailability of modern molecular methods to study circadian rhythms and incomplete understanding of circadian rhythms outside the brain in peripheral organ systems. Major methodological and conceptual advancements in chronobiology have since been made. Over the same time, biomarker research in ME/CFS has progressed. Together, these new developments may justify renewed interest in circadian rhythm research in ME/CFS. Presently, we review ME/CFS from the perspective of circadian rhythms, covering both older and newer studies that make use of modern molecular methods. We focus on transforming growth factor beta (TGFB), a cytokine that has been previously associated with ME/CFS and has an important role in circadian rhythms, especially in peripheral cells. We propose that disrupted TGFB signaling in ME/CFS may play a role in disrupting physiological rhythms in sleep, activity, and cognition, leading to the insomnia, energy disturbances, cognition problems, depression, and autonomic dysfunction associated with ME/CFS. Since SARS-like coronavirus infections cause persistent changes in TGFB and previous coronavirus outbreaks have caused ME/CFS-like syndromes, chronobiological considerations may have immediate implications for understanding ME/CFS in the context of the COVID-19 pandemic and possibly suggest new avenues for therapeutic interventions.

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Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is characterized by ​disrupted ​sleep ​and activity ​implicating ​circadian clocks.

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The incidence of ME/CFS is expected to increase as a result of the post-acute sequelae of COVID-19.

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Biomarker studies in ME/CFS patients implicate Transforming Growth Factor B (TGFB).

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TGFB has roles in synchronizing circadian rhythms in peripheral cells.

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Identification of biomarkers and new methodologies may facilitate progress in the chronobiological basis of ME/CFS.

Light at night disrupts biological clocks, calendars, and immune function

Light at night is a pervasive problem in our society; over 80% of the world’s population experiences significant light pollution. Exacerbating this issue is the reality that artificially lit outdoor areas are growing by 2.2% per year and continuously lit areas brighten by 2.2% each year due to the rapid growths in population and urbanization. Furthermore, the increase in the prevalence of night shift work and smart device usage contributes to the inescapable nature of artificial light at night (ALAN). Although previously assumed to be innocuous, ALAN has deleterious effects on the circadian system and circadian-regulated physiology, particularly immune function. Due to the relevance of ALAN to the general population, it is important to understand its roles in disrupting immune function. This review presents a synopsis of the effects of ALAN on circadian clocks and immune function. We delineate the role of ALAN in altering clock gene expression and suppressing melatonin. We review the effects of light at night on inflammation and the innate and adaptive immune systems in various species to demonstrate the wide range of ALAN consequences. Finally, we propose future directions to provide further clarity and expansion of the field.

The habenula clock influences response to a stressor

The response of an animal to a sensory stimulus depends on the nature of the stimulus and on expectations, which are mediated by spontaneous activity. Here, we ask how circadian variation in the expectation of danger, and thus the response to a potential threat, is controlled. We focus on the habenula, a mediator of threat response that functions by regulating neuromodulator release, and use zebrafish as the experimental system. Single cell transcriptomics indicates that multiple clock genes are expressed throughout the habenula, while quantitative in situ hybridization confirms that the clock oscillates. Two-photon calcium imaging indicates a circadian change in spontaneous activity of habenula neurons. To assess the role of this clock, a truncated clocka gene was specifically expressed in the habenula. This partially inhibited the clock, as shown by changes in per3 expression as well as altered day-night variation in dopamine, serotonin and acetylcholine levels. Behaviourally, anxiety-like responses evoked by an alarm pheromone were reduced. Circadian effects of the pheromone were disrupted, such that responses in the day resembled those at night. Behaviours that are regulated by the pineal clock and not triggered by stressors were unaffected. We suggest that the habenula clock regulates the expectation of danger, thus providing one mechanism for circadian change in the response to a stressor.

Adrift in time: the subjective experience of circadian challenge during COVID-19 amongst people with mood disorders

Social distancing/lockdown policies during the coronavirus (COVID-19) pandemic may alter social rhythms of people through imposition of restrictions on normal daily activities. This may in turn challenge circadian function, particularly in people with mood disorders. Although objective data describing the relationship between circadian disturbances and mood disorders exist, data regarding the subjective experience of circadian challenge is sparse, and its association with mood symptoms is unclear. The present qualitative study was one component of a mixed-methods multi-national project, which took advantage of widespread disruption to daily routines due to Government COVID-related lockdowns during 2020. The Behavior Emotion and Timing during COVID-19 (BEATCOVID) survey study included three open questions generating qualitative data on participants' subjective experience of social disruption due to social distancing/lockdown policies, two of which asked about the barriers and opportunities for stabilizing routines. Responses were coded and analyzed using Thematic Analysis. A total of N = 997 participants responded to at least one of the free-text questions. Four themes were identified: 1) loss of daily timed activities, 2) role of social interaction, 3) altered time perception and 4) disruption to motivation and associated psychological effects. Themes were organized into a provisional heuristic map, generating hypotheses for future research centered on the new concept of 'psychological drift.'

Effects of Time-of-Day Training Preference on Resistance-Exercise Performance

Purpose: The purpose of this study was to investigate how time-of-day training preference influences resistance-exercise performance. Methods: Resistance trained males (n = 12) were recruited for this study. In a crossover, counterbalanced design, participants completed two separate bench-press exercise trials at different times of day: (a) morning (AM; 8:00 hr) and (b) evening (PM; 16:00 hr). Participants answered a questionnaire on time-of-day training preference and completed a preferred (PREF) and nonpreferred (NON-PREF) time-of-day trial. For each trial, motivation was measured using a visual analog scale prior to exercise. Participants completed 2 sets × 2 repetitions at 75% 1-RM with maximum explosiveness separated by 5 min of rest. Mean barbell velocity was measured using a linear position transducer. Participants then completed 1 set × repetitions to failure (RTF) at 75% 1-RM. Rate of perceived exertion (RPE) was measured immediately following exercise. Results: Regardless of preference, velocity (p = .025; effect size (ES) = 0.43) was higher during the PM versus AM trial. However, there were no significant differences in velocity (p = .368; ES = 0.37) between PREF and NON-PREF time of day. There were no significant differences for repetitions between PREF and NON-PREF times (p = .902; ES = 0.03). Motivation was higher in the PREF time versus NON-PREF (p = .015; ES = 0.68). Furthermore, RPE was significantly lower during the PREF time of day (p = .048; 0.55). Conclusions: Despite higher barbell velocity collectively at PM times, time-of-training preference did not largely influence resistance-exercise performance, while motivation is higher and RPE is lower during preferred times.

Tubulin Polymerization Promoting Protein Affects the Circadian Timing System in C57Bl/6 Mice

The circadian timing system (CTS) is a complex set of cyclic cellular mechanisms which serve to synchronize discrete cell groups across multiple organ systems to adapt the bodys physiology to a (roughly) 24-hour clock. Many genes and hormones have been shown to be strongly associated with the CTS, some of which include the genes Bmal1, Period1, Period2, Cryptochrome1, and Cryptochrome2, and the hormone melatonin. Previous data suggest that microtubule dynamics play an important role in melatonin function as it relates to the CTS in vitro, though this relationship has never been explored in vivo. The purpose of this study was to determine whether disruption of microtubule regulation in C57Bl/6 mice results in measurable changes to the CTS. To study the potential effects of microtubule dynamics on the CTS in vivo, we utilized a mouse model of microtubule instability, knocked out for the tubulin polymerization promoting protein gene (Tppp -/-), comparing them to their wild type (WT) littermates in three categories: locomotor activity (in light/dark and dark/dark photoperiods), serial clock gene expression, and serial serum melatonin concentration. These comparisons showed differences in all three categories, including significant differences in locomotor characteristics under dark/dark conditions. Our findings support and extend previous reports that microtubule dynamics are a modulator of circadian rhythm regulation likely through a mechanism involving melatonin induced phase shifting.

The role of chronotype and reward processing in understanding social hierarchies in adolescence

INTRODUCTION

Circadian rhythms shift toward an evening preference during adolescence, a developmental period marked by greater focus on the social domain and salience of social hierarchies. The circadian system influences maturation of cognitive architecture responsible for motivation and reward, and observation of responses to reward cues has provided insights into neurocognitive processes that underpin adolescent social development. The objective was to investigate whether circadian phase of entrainment (chronotype) predicted both reward-related response inhibition and social status, and to explore whether mediator and moderator relationships existed between chronotype, reward processing, and social status outcomes.

METHODS

Participants were 75 adolescents aged 13-14 years old (41 females) who completed an eye tracking paradigm that involved an inhibitory control task (antisaccade task) within a nonsocial reward (Card Guessing Game) and a social reward (Cyberball Game) context. Chronotype was calculated from weekend midsleep and grouped into early, intermediate, and later terciles. Participants indicated subjective social status compared with peers in seven domains.

RESULTS

An intermediate and later chronotype predicted improved inhibitory control in the social versus nonsocial reward context. Chronotype also predicted higher perceived social status in two domains (powerful, troublemaker). Intermediate chronotypes reported higher "Powerful" status whereas later chronotypes were higher on "Troublemaker." Improved social reward-related performance predicted only the higher powerful scores and chronotype moderated this relationship. Improved inhibitory control to social reward predicted higher subjective social status in the intermediate and later chronotype group, an effect that was absent in the early group.

CONCLUSION

This behavioral study found evidence that changes toward a later phase of entrainment predicts social facilitation effects on inhibitory control and higher perceived power among peers. It is proposed here that circadian delayed phase in adolescence is linked to approach-related motivation, and the social facilitation effects could reflect a social cognitive capacity involved in the drive to achieve social rank.

Light at Night and Disrupted Circadian Rhythms Alter Physiology and Behavior

Life on earth has evolved during the past several billion years under relatively bright days and dark nights. Virtually, all organisms on the planet display an internal representation of the solar days in the form of circadian rhythms driven by biological clocks. Nearly every aspect of physiology and behavior is mediated by these internal clocks. The widespread adoption of electric lights during the past century has exposed animals, including humans, to significant light at night for the first time in our evolutionary history. Importantly, endogenous circadian clocks depend on light for synchronization with the external daily environment. Thus, light at night can derange temporal adaptations. Indeed, disruption of natural light-dark cycles results in several physiological and behavioral changes. In this review, we highlight recent evidence demonstrating how light at night exposure can have serious implications for adaptive physiology and behavior, including immune, endocrine, and metabolic function, as well as reproductive, foraging, and migratory behavior. Lastly, strategies to mitigate the consequences of light at night on behavior and physiology will be considered.

Risk assessment of cardiotoxicity to zebrafish (Danio rerio) by environmental exposure to triclosan and its derivatives

Triclosan (TCS) and its two derivatives (2,4-dichlorophenol and 2,4,6-trichlorophenol) are priority pollutants that coexist in aquatic environments. Joint exposure of TCS, 2,4-dichlorophenol and 2,4,6-trichlorophenol, hereafter referred to as TCS-DT, contributes severe toxicity to aquatic organisms. There is currently a paucity of data regarding TCS-DT molecular toxicity, especially on cardiac diseases. We used zebrafish (Danio rerio) as a model organism, and evaluated the molecular-level cardiotoxicity induced by TCS-DT from embryonic to adult stages. TCS-DT exposure prominently led to phenotypic malformations, such as pericardial cysts, cardiac bleeding, increased SV-BA distance, decreased heart rate and reduced ejection fraction, as well as abnormal swimming behavior. Analyses of the GO and KEGG pathways revealed enrichment pathways related to cardiac development and screened for significantly down-regulated adrenaline signaling in cardiomyocytes. The cardiac marker genes (amhc, cmlc2, vmhc, and nkx2.5) were obtained through protein-protein interaction (PPI) networks, and expressed as down-regulation by WISH. After chronic exposure to TCS-DT from 30 to 90-dpf, both body mass and heart indexes prominently increased, showing myocardial hypertrophy, abnormal heart rate and histopathological injury. Heart tissue damage included disordered and ruptured myocardial fibers, broken and dissolved myofilaments, nuclear pyknosis, mitochondrial injury and inflammatory cell infiltration. Further, abnormal changes in a series of cardiac functions-related biomarkers, including superoxide dismutase, triglyceride, lactate dehydrogenase and creatinine kinase MB, provided evidence for cardiac pathological responses. These results highlight the molecular mechanisms involving TCS-DT induced cardiac toxicity, and provide theoretical data to guide prevention and treatment of pollutant-induced cardiac diseases.

Equation representing the dark-entrained transition from inaction to action in male and female mice

The activation of behaviour in a daily rhythm governed by the light cycle is a universal phenomenon among humans, laboratory mammals and other vertebrates. For mice, the active period is during the dark. We have quantified the increase in activity when the lights shut off (Light to Dark, L to D) using a generalized CNS arousal assay with 20 ms resolution, rather than traditional running wheels. Data analysis yielded the rare demonstration of an equation which precisely tracks this behavioural transition and, surprisingly, its reverse during D to L. This behavioural dynamic survives in constant darkness (experiment 2) and is hormone-sensitive (experiment 3). Finally (experiment 4), mice on a light schedule analogous to one which proved troublesome for U.S. Navy sailors, had dysregulated activity bursts which did not conform to the transitions between D and L. These experiments show the lawfulness of a behavioural phase transition and the consequence of deviating from that dynamic pattern. And, in a new way, they bring mathematics to the realm of behavioural neuroscience.

AI-Based Early Change Detection in Smart Living Environments

In the smart environments we live today, a great variety of heterogeneous sensors are being increasingly deployed with the aim of providing more and more value-added services. This huge availability of sensor data, together with emerging Artificial Intelligence (AI) methods for Big Data analytics, can yield a wide array of actionable insights to help older adults continue to live independently with minimal support of caregivers. In this regard, there is a growing demand for technological solutions able to monitor human activities and vital signs in order to early detect abnormal conditions, avoiding the caregivers’ daily check of the care recipient. The aim of this study is to compare state-of-the-art machine and deep learning techniques suitable for detecting early changes in human behavior. At this purpose, specific synthetic data are generated, including activities of daily living, home locations in which such activities take place, and vital signs. The achieved results demonstrate the superiority of unsupervised deep-learning techniques over traditional supervised/semi-supervised ones in terms of detection accuracy and lead-time of prediction.

Circadian disruption of food availability significantly reduces reproductive success in mice

Circadian disruptions impair reproductive health in human populations and in animal models. We tested the hypothesis that mistimed food, a common disruptive feature of shift work, impairs reproductive success in mice. Male and female mPer2^Luc mice on a C57BL/6 background were fed during the light or dark phase in two experiments. Food-induced internal misalignment of the liver clock was verified by in vivo bioluminescence in anesthetized mice in both experiments. In Experiment 1, food-restricted pairs were monitored for litters for 18 weeks. In the light-fed group, birth of the first litter was significantly delayed, and total reproductive output was significantly reduced by 38%. In Experiment 2, estrous cycling was monitored for 3 weeks, and then after pairing, copulatory plugs, pregnancy, litter sizes, and uterine implantation sites were measured. Fewer light-fed females birthed litters (25% versus 73%). This was attributable to a difference in behavior as mating success was significantly reduced in light-fed mice: 42% were observed with a copulatory plug compared to 82% for dark-fed mice. The proportion of mice displaying uterine implantation sites was the same as the proportion observed with copulatory plugs, suggesting no deficit in initiating pregnancy after mating. Estrous cycling and pregnancy maintenance did not differ between the groups. We conclude that mistimed feeding inhibits reproduction in mice by reducing successful mating behavior.

Rhythmicity of Mood Symptoms in Individuals at Risk for Psychiatric Disorders

Despite emerging evidence that disruption in circadian rhythms may contribute to the pathophysiology of psychiatric disorders, there is a significant knowledge gap on the rhythmicity of psychological symptoms. Here, we aimed at investigating the rhythmicity of mood symptoms in individuals at risk for psychiatric disorders. 391 Brazilian and 317 Spanish participants completed the Self-Reporting Questionnaire-20 for non-psychotic mental disorders; the Mood Rhythm Instrument was used to assess rhythmicity of mood symptoms and the Munich ChronoType Questionnaire to assess sleep patterns. We found that the rhythmicity of specific mood-related symptoms and behaviors, particularly pessimism and motivation to exercise, were associated with being at risk for psychiatric disorders, even after controlling for sleep timing, sleep deficit, and season of data collection. We also found that the peak of some mood symptoms and behaviors were different between individuals at high vs. low risk for psychiatric disorders, with specific differences between countries. These results are consistent with previous research showing that circadian misalignment is associated with higher risk for mental health conditions. These findings also suggest that lifestyle changes preventing circadian misalignment might be useful to reduce the risk of psychiatric disorders, where cultural differences must be taken into account.

Chronic BMY7378 treatment alters behavioral circadian rhythms

The mammalian circadian clock is synchronized to the day : night cycle by light. Serotonin modulates the circadian effects of light, with agonists inhibiting response to light and antagonists enhancing responses to light. A special class of serotonergic compounds, the mixed 5-HT_1A agonist/antagonists, potentiates light-induced phase advances by up to 400% when administered acutely. In this study, we examine the effects of one of these mixed 5-HT_1A agonist/antagonists, BMY7378, when administered chronically. Thirty adult male hamsters were administered either vehicle or BMY7378 via surgically implanted osmotic mini pumps over a period of 28 days. In a light : dark cycle, chronic BMY7378 advanced the phase angle of entrainment, prolonged the duration of the active phase and attenuated the amplitude of the wheel-running rhythm during the early night. In constant darkness, chronic treatment with BMY7378 significantly attenuated light-induced phase advances, but had no significant effect on light-induced phase delays. Non-photic phase shifts to daytime administration of a 5-HT_1A/7 agonist were also attenuated by chronic BMY7378 treatment. qRT-PCR analysis revealed that chronic BMY7378 treatment upregulated mRNA for 5-HT_1A and 5-HT_1B receptors in the hypothalamus and downregulated mRNA for 5-HT_1A and monoamine oxidase-A in the brainstem. These results highlight adaptive changes of serotonin receptors in the brain to chronic treatment with BMY7378 and link such up- and downregulation to changes in important circadian parameters. Such long-term changes to the circadian system should be considered when patients are treated chronically with drugs that alter serotonergic function.

Circadian behavior of adult mice exposed to stress and fluoxetine during development

INTRODUCTION

Women of child-bearing age are the population at greatest risk for depression. The stress experienced during pregnancy and the associated antidepressant treatments can both affect fetal development. Fluoxetine (FLX) is among the most common antidepressants used by pregnant women. We have previously demonstrated that perinatal exposure to FLX can alter expression of circadian rhythms in adulthood. Here, we examine the combined effects of maternal stress during pregnancy and perinatal exposure to the antidepressant FLX on the circadian behavior of mice as adults.

METHODS

Mouse dams were exposed to chronic unpredictable stress (embryonic (E) day 7 to E18), FLX (E15 to postnatal day 12), a combination of both stress and FLX, or were left untreated. At 2 months of age, male offspring were placed in recording chambers and circadian organization of wheel running rhythms and phase shifts to photic and non-photic stimuli were assessed.

RESULTS

Mice exposed to prenatal stress (PS) had smaller light-induced phase delays. Mice exposed to perinatal FLX required more days to re-entrainment to an 8-h phase advance of their light-dark cycle. Mice subjected to either perinatal FLX or to PS had larger light-induced phase advances and smaller phase advances to 8-OH-DPAT. FLX treatment partially reversed the effect of PS on phase shifts to late-night light exposure and to 8-OH-DPAT.

CONCLUSIONS

Our results suggest that, in mice, perinatal exposure to either FLX, or PS, or their combination, leads to discernible, persistent changes in their circadian systems as adults.

The cholinergic forebrain arousal system acts directly on the circadian pacemaker

Sleep and wake states are regulated by a variety of mechanisms. One such important system is the circadian clock, which provides temporal structure to sleep and wake. Conversely, changes in behavioral state, such as sleep deprivation (SD) or arousal, can phase shift the circadian clock. Here we demonstrate that the level of wakefulness is critical for this arousal resetting of the circadian clock. Specifically, drowsy animals with significant power in the 7- to 9-Hz band of their EEGs do not exhibit phase shifts in response to a mild SD procedure. We then show that treatments that both produce arousal and reset the phase of circadian clock activate (i.e., induce Fos expression in) the basal forebrain. Many of the activated cells are cholinergic. Using retrograde tract tracing, we demonstrate that cholinergic cells activated by these arousal procedures project to the circadian clock in the suprachiasmatic nuclei (SCN). We then demonstrate that arousal-induced phase shifts are blocked when animals are pretreated with atropine injections to the SCN, demonstrating that cholinergic activity at the SCN is necessary for arousal-induced phase shifting. Finally, we demonstrate that electrical stimulation of the substantia innominata of the basal forebrain phase shifts the circadian clock in a manner similar to that of our arousal procedures and that these shifts are also blocked by infusions of atropine to the SCN. These results establish a functional link between the major forebrain arousal center and the circadian system.

Phase shifts to light are altered by antagonists to neuropeptide receptors

The mammalian circadian clock in the suprachiasmatic nucleus (SCN) is a heterogeneous structure. Two key populations of cells that receive retinal input and are believed to participate in circadian responses to light are cells that contain vasoactive intestinal polypeptide (VIP) and gastrin-releasing peptide (GRP). VIP acts primarily through the VPAC2 receptor, while GRP works primarily through the BB2 receptor. Both VIP and GRP phase shift the circadian clock in a manner similar to light when applied to the SCN, both in vivo and in vitro, indicating that they are sufficient to elicit photic-like phase shifts. However, it is not known if they are necessary signals for light to elicit phase shifts. Here we test the hypothesis that GRP and VIP are necessary signaling components for the photic phase shifting of the hamster circadian clock by examining two antagonists for each of these neuropeptides. The BB2 antagonist PD176252 had no effect on light-induced delays on its own, while the BB2 antagonist RC-3095 had the unexpected effect of significantly potentiating both phase delays and advances. Neither of the VIP antagonists ([d-p-Cl-Phe6, Leu17]-VIP, or PG99-465) altered phase shifting responses to light on their own. When the BB2 antagonist PD176252 and the VPAC2 antagonist PG99-465 were delivered together to the SCN, phase delays were significantly attenuated. These results indicate that photic phase shifting requires participation of either VIP or GRP; phase shifts to light are only impaired when signalling in both pathways are inhibited. Additionally, the unexpected potentiation of light-induced phase shifts by RC-3095 should be investigated further for potential chronobiotic applications.

Circadian Mechanisms Underlying Reward-Related Neurophysiology and Synaptic Plasticity

Evidence from clinical and preclinical research provides an undeniable link between disruptions in the circadian clock and the development of psychiatric diseases, including mood and substance abuse disorders. The molecular clock, which controls daily patterns of physiological and behavioral activity in living organisms, when desynchronized, may exacerbate or precipitate symptoms of psychiatric illness. One of the outstanding questions remaining in this field is that of cause and effect in the relationship between circadian rhythm disruption and psychiatric disease. Focus has recently turned to uncovering the role of circadian proteins beyond the maintenance of homeostatic systems and outside of the suprachiasmatic nucleus (SCN), the master pacemaker region of the brain. In this regard, several groups, including our own, have sought to understand how circadian proteins regulate mechanisms of synaptic plasticity and neurotransmitter signaling in mesocorticolimbic brain regions, which are known to be critically involved in reward processing and mood. This regulation can come in the form of direct transcriptional control of genes central to mood and reward, including those associated with dopaminergic activity in the midbrain. It can also be seen at the circuit level through indirect connections of mesocorticolimbic regions with the SCN. Circadian misalignment paradigms as well as genetic models of circadian disruption have helped to elucidate some of the complex interactions between these systems and neural activity influencing behavior. In this review, we explore findings that link circadian protein function with synaptic adaptations underlying plasticity as it may contribute to the development of mood disorders and addiction. In light of recent advances in technology and sophisticated methods for molecular and circuit-level interrogation, we propose future directions aimed at teasing apart mechanisms through which the circadian system modulates mood and reward-related behavior.

Circadian regulation of metabolic homeostasis: causes and consequences

Robust circadian rhythms in metabolic processes have been described in both humans and animal models, at the whole body, individual organ, and even cellular level. Classically, these time-of-day-dependent rhythms have been considered secondary to fluctuations in energy/nutrient supply/demand associated with feeding/fasting and wake/sleep cycles. Renewed interest in this field has been fueled by studies revealing that these rhythms are driven, at least in part, by intrinsic mechanisms and that disruption of metabolic synchrony invariably increases the risk of cardiometabolic disease. The objectives of this paper are to provide a comprehensive review regarding rhythms in glucose, lipid, and protein/amino acid metabolism, the relative influence of extrinsic (eg, neurohumoral factors) versus intrinsic (eg, cell autonomous circadian clocks) mediators, the physiologic roles of these rhythms in terms of daily fluctuations in nutrient availability and activity status, as well as the pathologic consequences of dyssynchrony.