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Circadian rhythms are fundamental biological processes that recur approximately every 24 h, with the sleep–wake cycle or circadian behavior being a well‐known example. In the field of chronobiology, mice serve as valuable model animals for studying mammalian circadian rhythms due to their genetic similarity to humans and the availability of various genetic tools for manipulation. Monitoring locomotor activity in mice provides valuable insights into the impact of various conditions or disturbances on circadian behavior. In this review, we summarized the effects of disturbance of biological rhythms on circadian behavior in mice. External factors, especially light exert a significant impact on circadian behavior. Additionally, feeding timing, food composition, ambient temperature, and physical exercise contribute to variations in the behavior of the mouse. Internal factors, including gender, age, genetic background, and clock gene mutation or deletion, are effective as well. Understanding the effects of circadian disturbances on murine behavior is essential for gaining insights into the underlying mechanisms of circadian regulation and developing potential therapeutic interventions for circadian‐related disorders in humans. [ABSTRACT FROM AUTHOR]

In chronobiology, shifting light/dark cycles is a common method to disrupt circadian rhythms. While the direction and magnitude of a phase shift (e.g., +6 denoting a 6‐h advanced shift) dictate the temporal change before and after the shift, little attention has been paid to the duration and relative proportion of daytime and nighttime during the shift, leading to a critical, unexamined variable in circadian research. In this study, we introduce the concepts of "L‐shift" (longer light phase on the shift day) and "D‐shift" (longer dark phase), and investigate how these variations impact the adaptability of mice to jet lag. By examining multiple phase shifts (12L vs. 12D, +6L vs. +6D, −6L vs. −6D), we demonstrate that L‐shifts not only facilitate faster adaptation but also significantly reduce the severity of sepsis in a jet lag‐sensitive lipopolysaccharide‐induced sepsis model. Further investigations with additional phase shifts at 1‐h intervals (+8 to +11) reinforced the enhanced fitness of mice under L‐shifts. Mechanistically, L‐shifts were found to increase sleep duration, thereby improving circadian entrainment, with sleep deprivation nullifying the adaptability differences between lighting protocols. These findings underscore a previously unrecognized factor in circadian biology and suggest that optimizing lighting protocols could profoundly improve adaptability to circadian disruptions. This research opens new avenues for enhancing therapeutic strategies and refining experimental designs in the field of chronobiology. [ABSTRACT FROM AUTHOR]

Animals invest crucial resources in foraging to support development, sustenance, and reproduction. Foraging and feeding behaviors are rhythmically expressed by most insects. Rhythmic behaviors are modified by exogenous factors like temperature and photoperiod, and internal factors such as the physiological status of the individual. However, the interactions between these factors and the circadian clock to pattern feeding behavior remains elusive. As Drosophila, a standard insect model, spends nearly all its life on food, we rather chose to focus on the adults of a non-model insect, Agrotis ipsilon, a nocturnal cosmopolitan crop pest moth having structured feeding activity. Our study aimed to explore the impact of environmental cues on directly measured feeding behavior rhythms. We took advantage of a new experimental set-up, mimicking an artificial flower, allowing us to specifically monitor feeding behavior in a naturalistic setting, e.g., the need to enter a flower to get food. We show that the frequency of flower visits is under the control of the circadian clock in males and females. Feeding behavior occurs only during the scotophase, informed by internal clock status and external photic input, and females start to visit flowers earlier than males. Shorter duration visits predominate as the night progresses. Importantly, food availability reorganizes the microstructure of feeding behavior, revealing its plasticity. Interestingly, males show a constant number of daily visits during the 5 days of adult life whereas females decrease visitations after the third day of adult life. Taken together, our results provide evidence that the rhythmicity of feeding behavior is sexually dimorphic and controlled by photoperiodic conditions through circadian clock-dependent and independent pathways. In addition, the use of the new experimental set-up provides future opportunities to examine the regulatory mechanisms of feeding behavior paving the way to investigate complex relationships between feeding, mating, and sleep-wake rhythms in insects. [ABSTRACT FROM AUTHOR]

Animals invest crucial resources in foraging to support development, sustenance, and reproduction. Foraging and feeding behaviors are rhythmically expressed by most insects. Rhythmic behaviors are modified by exogenous factors like temperature and photoperiod, and internal factors such as the physiological status of the individual. However, the interactions between these factors and the circadian clock to pattern feeding behavior remains elusive. As Drosophila, a standard insect model, spends nearly all its life on food, we rather chose to focus on the adults of a non-model insect, Agrotis ipsilon, a nocturnal cosmopolitan crop pest moth having structured feeding activity. Our study aimed to explore the impact of environmental cues on directly measured feeding behavior rhythms. We took advantage of a new experimental set-up, mimicking an artificial flower, allowing us to specifically monitor feeding behavior in a naturalistic setting, e.g., the need to enter a flower to get food. We show that the frequency of flower visits is under the control of the circadian clock in males and females. Feeding behavior occurs only during the scotophase, informed by internal clock status and external photic input, and females start to visit flowers earlier than males. Shorter duration visits predominate as the night progresses. Importantly, food availability reorganizes the microstructure of feeding behavior, revealing its plasticity. Interestingly, males show a constant number of daily visits during the 5 days of adult life whereas females decrease visitations after the third day of adult life. Taken together, our results provide evidence that the rhythmicity of feeding behavior is sexually dimorphic and controlled by photoperiodic conditions through circadian clock-dependent and independent pathways. In addition, the use of the new experimental set-up provides future opportunities to examine the regulatory mechanisms of feeding behavior paving the way to investigate complex relationships between feeding, mating, and sleep-wake rhythms in insects.

Circadian symptoms have long been observed in Alzheimer's disease (AD) and often appear before cognitive symptoms, but the mechanisms underlying circadian alterations in AD are poorly understood. We studied circadian reentrainment in AD model mice using a "jet lag" paradigm, observing their behavior on a running wheel after a 6 h advance in the light:dark cycle. Female 3xTg mice, which carry mutations producing progressive amyloid beta and tau pathology, re-entrained following jet lag more rapidly than age-matched wild type controls at both 8 and 13 months of age. This re-entrainment phenotype has not been previously reported in a murine AD model. Because microglia are activated in AD and in AD models, and inflammation can affect circadian rhythms, we hypothesized that microglia contribute to this re-entrainment phenotype. To test this, we used the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX3397, which rapidly depletes microglia from the brain. Microglia depletion did not alter re-entrainment in either wild type or 3xTg mice, demonstrating that microglia activation is not acutely responsible for the re-entrainment phenotype. To test whether mutant tau pathology is necessary for this behavioral phenotype, we repeated the jet lag behavioral test with the 5xFAD mouse model, which develops amyloid plaques, but not neurofibrillary tangles. As with 3xTg mice, 7-monthold female 5xFAD mice re-entrained more rapidly than controls, demonstrating that mutant tau is not necessary for the re-entrainment phenotype. Because AD pathology affects the retina, we tested whether differences in light sensing may contribute to altered entrainment behavior. 3xTg mice demonstrated heightened negative masking, a circadian behavior measuring responses to different levels of light, and re-entrained dramatically faster than WT mice in a jet lag experiment performed in dim light. 3xTg mice show a heightened sensitivity to light as a circadian cue that may contribute to accelerated photic re-entrainment. Together, these experiments demonstrate novel circadian behavioral phenotypes with heightened responses to photic cues in AD model mice which are not dependent on tauopathy or microglia. [ABSTRACT FROM AUTHOR]

Circadian symptoms have long been observed in Alzheimer’s disease (AD) and often appear before cognitive symptoms, but the mechanisms underlying circadian alterations in AD are poorly understood. We studied circadian re-entrainment in AD model mice using a “jet lag” paradigm, observing their behavior on a running wheel after a 6 h advance in the light:dark cycle. Female 3xTg mice, which carry mutations producing progressive amyloid beta and tau pathology, re-entrained following jet lag more rapidly than age-matched wild type controls at both 8 and 13 months of age. This re-entrainment phenotype has not been previously reported in a murine AD model. Because microglia are activated in AD and in AD models, and inflammation can affect circadian rhythms, we hypothesized that microglia contribute to this re-entrainment phenotype. To test this, we used the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX3397, which rapidly depletes microglia from the brain. Microglia depletion did not alter re-entrainment in either wild type or 3xTg mice, demonstrating that microglia activation is not acutely responsible for the re-entrainment phenotype. To test whether mutant tau pathology is necessary for this behavioral phenotype, we repeated the jet lag behavioral test with the 5xFAD mouse model, which develops amyloid plaques, but not neurofibrillary tangles. As with 3xTg mice, 7-month-old female 5xFAD mice re-entrained more rapidly than controls, demonstrating that mutant tau is not necessary for the re-entrainment phenotype. Because AD pathology affects the retina, we tested whether differences in light sensing may contribute to altered entrainment behavior. 3xTg mice demonstrated heightened negative masking, a circadian behavior measuring responses to different levels of light, and re-entrained dramatically faster than WT mice in a jet lag experiment performed in dim light. 3xTg mice show a heightened sensitivity to light as a circadian cue that may contribute to accelerated photic re-entrainment. Together, these experiments demonstrate novel circadian behavioral phenotypes with heightened responses to photic cues in AD model mice which are not dependent on tauopathy or microglia.

Abstract Dysfunction of striatal dopaminergic circuits has been implicated in motor impairment and Parkinson’s disease (PD)-related circadian perturbations that may represent an early prodromal marker of PD. Cyclin-dependent kinase 5 (CDK5) negatively regulates dopamine signaling in the striatum, suggesting a critical role of CDK5 in circadian and sleep disorders. Here, we used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing to produce mice with a dorsal striatum (DS)-specific knockdown (KD) of the Cdk5 gene (referred to as DS-CDK5-KD mice) and investigate its role in vivo. DS-CDK5-KD mice exhibited deficits in locomotor activity and disturbances in activity/rest behavior. Additionally, Golgi staining of neurons in the DS revealed that CDK5 deletion reduced dendrite length and the number of functional synapses, which was confirmed by significant downregulation of MAP2, PSD-95, and synapsin I. Correlated with this, DS-CDK5-KD mice displayed reduced phosphorylation of Tau at Thr181. Furthermore, whole-cell patch-clamp recordings of green fluorescent protein-tagged neurons in the striatum of DS-CDK5-KD mice revealed a decreased frequency of spontaneous inhibitory postsynaptic currents and altered excitatory/inhibitory synaptic balance. Notably, anterograde labeling showed that CDK5 KD in the DS disrupted long-range projections to the secondary motor cortex, dorsal and ventral thalamic nuclei, and basolateral amygdala, which are involved in the regulation of motor and circadian rhythms in the brain. These findings support a critical role of CDK5 in the DS in maintaining the striatal neural circuitry underlying motor functions and activity/rest associated with circadian rhythms that are perturbed in neurodegenerative disorders.

Circadian rhythms play a crucial role in regulating behavior, physiology, and health. Sexual dimorphism, a widespread phenomenon across species, influences circadian behaviors. Additionally, post-mating physiological changes in females are known to modulate various behaviors, yet their effects on circadian rhythms remain underexplored. Here, using Drosophila melanogaster , a powerful model for studying circadian mechanisms, we systematically assessed the impact of sex and mating status on circadian behavior. We measured circadian period length and rhythm strength in virgin and mated males and females, including females mated to males lacking Sex Peptide (SP), a key mediator of post-mating changes. Across four wild-type and control strains, we found that males consistently exhibited shorter circadian periods than females, regardless of mating status, suggesting that circadian period length is a robust sexually dimorphic trait. In contrast, rhythm strength was influenced by the interaction between sex and mating status, with female mating generally reducing rhythm strength in the presence of SP signaling. Notably, genetic background significantly modulated these effects on rhythm strength. Our findings demonstrate that while circadian period length is a stable sex-specific trait, rhythm strength is shaped by a complex interplay between sex, mating status, and genetic background. This study advances our understanding of how sex and mating influence circadian rhythms in Drosophila and provides a foundation for future research into sexually dimorphic mechanisms underlying human diseases associated with circadian disruptions., Competing Interests: Conflict of Interest The authors declare no competing financial interests.

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Dysfunction of striatal dopaminergic circuits has been implicated in motor impairment and Parkinson's disease (PD)-related circadian perturbations that may represent an early prodromal marker of PD. Cyclin-dependent kinase 5 (CDK5) negatively regulates dopamine signaling in the striatum, suggesting a critical role of CDK5 in circadian and sleep disorders. Here, we used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing to produce mice with a dorsal striatum (DS)-specific knockdown (KD) of the Cdk5 gene (referred to as DS-CDK5-KD mice) and investigate its role in vivo. DS-CDK5-KD mice exhibited deficits in locomotor activity and disturbances in activity/rest behavior. Additionally, Golgi staining of neurons in the DS revealed that CDK5 deletion reduced dendrite length and the number of functional synapses, which was confirmed by significant downregulation of MAP2, PSD-95, and synapsin I. Correlated with this, DS-CDK5-KD mice displayed reduced phosphorylation of Tau at Thr181. Furthermore, whole-cell patch-clamp recordings of green fluorescent protein-tagged neurons in the striatum of DS-CDK5-KD mice revealed a decreased frequency of spontaneous inhibitory postsynaptic currents and altered excitatory/inhibitory synaptic balance. Notably, anterograde labeling showed that CDK5 KD in the DS disrupted long-range projections to the secondary motor cortex, dorsal and ventral thalamic nuclei, and basolateral amygdala, which are involved in the regulation of motor and circadian rhythms in the brain. These findings support a critical role of CDK5 in the DS in maintaining the striatal neural circuitry underlying motor functions and activity/rest associated with circadian rhythms that are perturbed in neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

ABSTRACT: The paper aimed to study the effects of light regime on circadian rhythmic behavior and reproductive parameters in a native laying hen, Beijing You Chicken (BYC) during 22 to 30 wk. A total of 630 19-wk-old BYC female chicken were allocated to 6 light regime groups with 3 replicates per group and 35 birds per replicate, reared in individually lit floor pens with separate outdoor areas. A 2 × 3 factorial experiment (2 lighting patterns: continuous and intermittent lighting; 3 photoperiods: 16 h, 14 h, 12 h) was arranged, including 16L:8D for group 1; 12L:2D:4L:6D for group 2; 14L:10D for group 3; 10L:2D:4L:8D for group 4; 12L:12D for group 5, and 8L:4D:4L:8D for group 6, respectively. The circadian rhythmic behavior of the hens, including feeding, egg-laying and sleeping behaviors were observed by scan sampling and target sampling method for consecutive 3 d every other week during 22 to 30 wk. Infrared cameras were set outside each pen to record the rhythmic behaviors of the birds every other hour (6:00–7:00;8:00–9:00;10:00–11:00;12:00–13:00;14:00–15:00;16:00–17:00;18:00–19:00;20:00–21:00;22:00–23:00;0:00–1:00;2:00–3:00;4:00–5:00). Theovarian weight, oviduct weight, oviduct length, the number of large yellow follicles (LYF), and small yellow follicles (SYF) were measured at the end of 30 wk. The egg-laying rate during 22 to 30 wk was measured. The results showed that the highest feeding frequency was given by the 16L:8D, and the lowest given by the 12L:12D (P < 0.05). The average feeding duration was the longest in the 8L:4D:4L:8D at 6:00 to 8:00 (18.67 min/hen) (P < 0.05), and the shortest in the 8L:4D:4L:8D at 18:00 to 20:00 (3.75 min/hen) (P < 0.05). The highest egg-laying frequency was given by the 8L:4D:4L:8D (0.28), the lowest given by the 10L:2D:4L:8D (0.21) (P < 0.05). The shortest egg-laying duration occurred at 6:00 to 8:00, was given by the 16L:8D (8 min/hen), and the longest egg-laying duration occurred at 18:00 to 20:00, was given by 16L:8D and 8L:4D:4L:8D (>20.5 min/hen) (P < 0.05). The highest sleeping frequency was given by the 12L:2D:4L:6D, the lowest was given by the 12L:12D (P < 0.05). At 6:00 to 8:00, the shortest sleeping duration was given by 12L:2D:4L:6D (1.5 s/hen), at 18:00 to 20:00, the longest given by 8L:4D:4L:8D (14.3 s/hen) (P < 0.05). Lighting pattern and photoperiod alone or in interaction had no effect on egg-laying rate during 22 to 30 wk (P > 0.05), but had significant effects on ovarian weight, oviduct weight, oviduct length, the number of LYF and SYF (P < 0.05), and the continuous groups were all significantly higher than the intermittent groups (P < 0.05). The present study indicated that light regimes affected the frequency and duration of circadian behavior in BYC laying hens, and the continuous light was more beneficial to the reproductive development than the intermittent light in the early laying period.

Rationale: Selective serotonin reuptake inhibitor (SSRI) antidepressants are increasingly prescribed during pregnancy. Changes in serotonergic signaling during human fetal development have been associated with changes in brain development and with changes in affective behavior in adulthood. The suprachiasmatic nucleus (SCN) is known to be modulated by serotonin and it is therefore assumed that SSRIs may affect circadian rhythms. However, effects of perinatal SSRI treatment on circadian system functioning in the offspring are largely unknown. Objective: Our aim was to investigate the effects of perinatal exposure to the SSRI fluoxetine (FLX) on circadian behavior, affective behavior, and 5-HT1A receptor sensitivity in female rats. In addition, we studied the expression of clock genes and the 5-HT1A receptor in the SCN, as they are potentially involved in underlying mechanisms contributing to changes in circadian rhythms. Results: Perinatal FLX exposure shortened the free-running tau in response to the 5-HT1A/7 agonist 8-OH-DPAT. However, FLX exposure did not alter anxiety, stress coping, and 5-HT1A receptor sensitivity. No differences were found in 5-HT1A receptor and clock genes Per1, Per2, Cry1, and Cry2 SCN gene expression. Conclusions: Perinatal FLX exposure altered the response to a phase-shifting challenge in female rats, whether this may pose health risks remains to be investigated. [ABSTRACT FROM AUTHOR]

Rationale: Few effective treatments exist for cocaine use disorders due to gaps in knowledge about its complex etiology. Genetically defined animal models provide a useful tool for advancing our understanding of the biological and genetic underpinnings of addiction-related behavior and evaluating potential treatments. However, many attempts at developing mouse models of behavioral disorders were based on overly simplified single gene perturbations, often leading to inconsistent and misleading results in pre-clinical pharmacology studies. A genetically complex mouse model may better reflect disease-related behaviors. Objectives: Screening defined, yet genetically complex, intercrosses of the Collaborative Cross (CC) mice revealed two lines, RIX04/17 and RIX41/51, with extreme high and low behavioral responses to cocaine. We characterized these lines as well as their CC parents, CC004/TauUnc and CC041/TauUnc, to evaluate their utility as novel model systems for studying the biological and genetic mechanisms underlying behavioral responses to cocaine. Methods: Behavioral responses to acute (initial locomotor sensitivity) and repeated (behavioral sensitization, conditioned place preference, intravenous self-administration) exposures to cocaine were assessed. We also examined the monoaminergic system (striatal tissue content and in vivo fast scan cyclic voltammetry), HPA axis reactivity, and circadian rhythms as potential mechanisms for the divergent phenotypic behaviors observed in the two strains, as these systems have a previously known role in mediating addiction-related behaviors. Results: RIX04/17 and 41/51 show strikingly divergent initial locomotor sensitivity to cocaine with RIX04/17 exhibiting very high and RIX41/51 almost no response. The lines also differ in the emergence of behavioral sensitization with RIX41/51 requiring more exposures to exhibit a sensitized response. Both lines show conditioned place preference for cocaine. We determined that the cocaine sensitivity phenotype in each RIX line was largely driven by the genetic influence of one CC parental strain, CC004/TauUnc and CC041/TauUnc. CC004 demonstrates active operant cocaine self-administration and CC041 is unable to acquire under the same testing conditions, a deficit which is specific to cocaine as both strains show operant response for a natural food reward. Examination of potential mechanisms driving differential responses to cocaine show strain differences in molecular and behavioral circadian rhythms. Additionally, while there is no difference in striatal dopamine tissue content or dynamics, there are selective differences in striatal norepinephrine and serotonergic tissue content. Conclusions: These CC strains offer a complex polygenic model system to study underlying mechanisms of cocaine response. We propose that CC041/TauUnc and CC004/TauUnc will be useful for studying genetic and biological mechanisms underlying resistance or vulnerability to the stimulatory and reinforcing effects of cocaine. [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) are highly persistent and ubiquitously distributed environmental pollutants. Based on their chemical structure, PCBs are classified into non- ortho -substituted and ortho -substituted congeners. Non- ortho -substituted PCBs are structurally similar to dioxin and their toxic effects and mode of action are well-established. In contrast, very little is known about the effects of ortho -substituted PCBs, particularly, during early development. The objective of this study is to investigate the effects of exposure to an environmentally prominent ortho -substituted PCB (2,2',4,4',5,5'-hexachlorobiphenyl; PCB153) on zebrafish embryos. We exposed zebrafish embryos to 3 different concentrations of PCB153 starting from 4 to 120 hours post-fertilization (hpf). We quantified gross morphological changes, behavioral phenotypes, gene expression changes, and circadian behavior in the larvae. There were no developmental defects during the exposure period, but starting at 7 dpf, we observed spinal deformity in the 10 μM PCB153 treated group. A total of 633, 2227, and 3378 differentially expressed genes were observed in 0.1 μM (0.036 μg/ml), 1 μM (0.36 μg/ml), and 10 μM (3.6 μg/ml) PCB153-treated embryos, respectively. Of these, 301 genes were common to all treatment groups. KEGG pathway analysis revealed enrichment of genes related to circadian rhythm, FoxO signaling, and insulin resistance pathways. Behavioral analysis revealed that PCB153 exposure significantly alters circadian behavior. Disruption of circadian rhythms has been associated with the development of metabolic and neurological diseases. Thus, understanding the mechanisms of action of environmental chemicals in disrupting metabolism and other physiological processes is essential. [ABSTRACT FROM AUTHOR]

Many animals rely heavily on visual cues from their environment, and therefore show circadian rhythmicity in their behavioral activities. In group living animals, individuals' activity rhythms must be synchronized not only with diel light–dark cycle but also with other group members. Increasing evidence has recently shown that circadian behaviors of animals are consistent within individuals and different between individuals, but the sources and consistency of diel activity variation in social c [ABSTRACT FROM AUTHOR]

We describe a genome-wide microRNA (miRNA)-based screen to identify brain glial cell functions required for circadian behavior. To identify glial miRNAs that regulate circadian rhythmicity, we employed a collection of "miR-sponges" to inhibit miRNA function in a glia-specific manner. Our initial screen identified 20 glial miRNAs that regulate circadian behavior. We studied two miRNAs, miR-263b and miR-274, in detail and found that both function in adult astrocytes to regulate behavior. Astrocyte-specific inhibition of miR-263b or miR-274 in adults acutely impairs circadian locomotor activity rhythms with no effect on glial or clock neuronal cell viability. To identify potential RNA targets of miR-263b and miR-274, we screened 35 predicted miRNA targets, employing RNA interference-based approaches. Glial knockdown of two putative miR-274 targets, CG4328 and MESK2, resulted in significantly decreased rhythmicity. Homology of the miR-274 targets to mammalian counterparts suggests mechanisms that might be relevant for the glial regulation of rhythmicity. [ABSTRACT FROM AUTHOR]

Regulatory systems required to maintain behavioral arousal remain incompletely understood. We describe a previously unappreciated role that toll-like receptor 2 (Tlr2, a membrane bound pattern recognition receptor that recognizes specific bacterial, viral, and fungal peptides), contributes toward regulation of behavioral arousal. In 4–4.5 month old mice with constitutive loss of Tlr2 function (Tlr2−/− mice), we note a marked consolidation in the circadian pattern of both active and inactive states. Specifically, Tlr2−/− mice demonstrated significantly fewer but longer duration active states during the circadian dark cycle, and significantly fewer but longer duration inactive states during the circadian light cycle. Tlr2−/− mice also consumed less food and water, and moved less during the circadian light cycle. Analysis of circadian rhythms further suggested that Tlr2−/− mice demonstrated less day-to-day variability in feeding, drinking, and movement behaviors. Reevaluation of this same mouse cohort at age 8–8.5 months revealed a clear blunting of these differences. However, Tlr2−/− mice were still noted to have fewer short-duration active states during the circadian dark cycle, and continued to demonstrate significantly less day-to-day variability in feeding, drinking, and movement behaviors. These results suggest that Tlr2 function may have a role in promoting transitions between active and inactive states. Prior studies have demonstrated that Tlr2 regulates sickness behaviors including hypophagia, hyperthermia, and decreased activity. Our work suggests that Tlr2 function also evokes behavioral fragmentation, another aspect of sickness behavior and a clinically significant problem of older adults.

Regulatory systems required to maintain behavioral arousal remain incompletely understood. We describe a previously unappreciated role that toll-like receptor 2 (Tlr2, a membrane bound pattern recognition receptor that recognizes specific bacterial, viral, and fungal peptides), contributes toward regulation of behavioral arousal. In 4-4.5 month old mice with constitutive loss of Tlr2 function (Tlr2-/- mice), we note a marked consolidation in the circadian pattern of both active and inactive states. Specifically, Tlr2-/- mice demonstrated significantly fewer but longer duration active states during the circadian dark cycle, and significantly fewer but longer duration inactive states during the circadian light cycle. Tlr2-/- mice also consumed less food and water, and moved less during the circadian light cycle. Analysis of circadian rhythms further suggested that Tlr2-/- mice demonstrated less day-to-day variability in feeding, drinking, and movement behaviors. Reevaluation of this same mouse cohort at age 8-8.5 months revealed a clear blunting of these differences. However, Tlr2-/- mice were still noted to have fewer short-duration active states during the circadian dark cycle, and continued to demonstrate significantly less day-to-day variability in feeding, drinking, and movement behaviors. These results suggest that Tlr2 function may have a role in promoting transitions between active and inactive states. Prior studies have demonstrated that Tlr2 regulates sickness behaviors including hypophagia, hyperthermia, and decreased activity. Our work suggests that Tlr2 function also evokes behavioral fragmentation, another aspect of sickness behavior and a clinically significant problem of older adults. [ABSTRACT FROM AUTHOR]

Serotonin (5-HT) is a crucial neuromodulator linked to many psychiatric disorders. However, after more than 60 years of study, its role in behavior remains poorly understood, in part because of a lack of methods to target 5-HT synthesis specifically in the adult brain. Here, we have developed a genetic approach that reproducibly achieves near-complete elimination of 5-HT synthesis from the adult ascending 5-HT system by stereotaxic injection of an adeno-associated virus expressing Cre recombinase (AAV-Cre) into the midbrain/pons of mice carrying a loxP-conditional tryptophan hydroxylase 2 (Tph2) allele. We investigated the behavioral effects of deficient brain 5-HT synthesis and discovered a unique composite phenotype. Surprisingly, adult 5-HT deficiency did not affect anxiety-like behavior, but resulted in a robust hyperactivity phenotype in novel and home cage environments. Moreover, loss of 5-HT led to an altered pattern of circadian behavior characterized by an advance in the onset and a delay in the offset of daily activity, thus revealing a requirement for adult 5-HT in the control of daily activity patterns. Notably, after normalizing for hyperactivity, we found that the normal prolonged break in nocturnal activity (siesta), a period of rapid eye movement (REM) and non-REM sleep, was absent in all animals in which 5-HT deficiency was verified. Our findings identify adult 5-HT as a requirement for siestas, implicate adult 5-HT in sleep-wake homeostasis, and highlight the importance of our adult-specific 5-HT-synthesis-targeting approach in understanding 5-HT's role in controlling behavior. [ABSTRACT FROM AUTHOR]

Animals use circadian rhythms to anticipate daily environmental changes. Circadian clocks have a profound effect on behavior. In Drosophila, for example, brain pacemaker neurons dictate that flies are mostly active at dawn and dusk. miRNAs are small, regulatory RNAs (≈22 nt) that play important roles in posttranscriptional regulation. Here, we identify miR-124 as an important regulator of Drosophila circadian locomotor rhythms. Under constant darkness, flies lacking miR-124 (miR-124KO) have a dramatically advanced circadian behavior phase. However, whereas a phase defect is usually caused by a change in the period of the circadian pacemaker, this is not the case in miR-124KO flies. Moreover, the phase of the circadian pacemaker in the clock neurons that control rhythmic locomotion is not altered either. Therefore, miR-124 modulates the output of circadian clock neurons rather than controlling their molecular pacemaker. Circadian phase is also advanced under temperature cycles, but a light/dark cycle partially corrects the defects in miR-124KO flies. Indeed, miR-124KO shows a normal evening phase under the latter conditions, but morning behavioral activity is suppressed. In summary, miR-124 controls diurnal activity and determines the phase of circadian locomotor behavior without affecting circadian pacemaker function. It thus provides a potent entry point to elucidate the mechanisms by which the phase of circadian behavior is determined. [ABSTRACT FROM AUTHOR]

Fragile X Syndrome (FXS) is the most common heritable form of intellectual impairment as well as the leading monogenetic cause of autism. In addition to its canonical definition as a neurodevelopmental disease, recent findings in the clinic suggest that FXS is a systemic disorder that is characterized by a variety of heterogeneous phenotypes. Efforts to study FXS pathogenesis have been aided by the development and characterization of animal models of the disease. Research efforts in Drosophila melanogaster have revealed key insights into the mechanistic underpinnings of FXS. While much remains unknown, it is increasingly apparent that FXS involves a myriad of spatially and temporally specific alterations in cellular function. Consequently, the literature is filled with numerous discordant findings. Researchers and clinicians alike must be cognizant of this dissonance, as it will likely be important for the design of preclinical studies to assess the efficacy of therapeutic strategies to improve the lives of FXS patients. [ABSTRACT FROM AUTHOR]

The paper aimed to study the effects of light regime on circadian rhythmic behavior and reproductive parameters in a native laying hen, Beijing You Chicken (BYC) during 22 to 30 wk. A total of 630 19-wk-old BYC female chicken were allocated to 6 light regime groups with 3 replicates per group and 35 birds per replicate, reared in individually lit floor pens with separate outdoor areas. A 2 × 3 factorial experiment (2 lighting patterns: continuous and intermittent lighting; 3 photoperiods: 16 h, 14 h, 12 h) was arranged, including 16L:8D for group 1; 12L:2D:4L:6D for group 2; 14L:10D for group 3; 10L:2D:4L:8D for group 4; 12L:12D for group 5, and 8L:4D:4L:8D for group 6, respectively. The circadian rhythmic behavior of the hens, including feeding, egg-laying and sleeping behaviors were observed by scan sampling and target sampling method for consecutive 3 d every other week during 22 to 30 wk. Infrared cameras were set outside each pen to record the rhythmic behaviors of the birds every other hour (6:00–7:00;8:00–9:00;10:00–11:00;12:00–13:00;14:00–15:00;16:00–17:00;18:00–19:00;20:00–21:00;22:00–23:00;0:00–1:00;2:00–3:00;4:00–5:00). Theovarian weight, oviduct weight, oviduct length, the number of large yellow follicles (LYF), and small yellow follicles (SYF) were measured at the end of 30 wk. The egg-laying rate during 22 to 30 wk was measured. The results showed that the highest feeding frequency was given by the 16L:8D, and the lowest given by the 12L:12D (P < 0.05). The average feeding duration was the longest in the 8L:4D:4L:8D at 6:00 to 8:00 (18.67 min/hen) (P < 0.05), and the shortest in the 8L:4D:4L:8D at 18:00 to 20:00 (3.75 min/hen) (P < 0.05). The highest egg-laying frequency was given by the 8L:4D:4L:8D (0.28), the lowest given by the 10L:2D:4L:8D (0.21) (P < 0.05). The shortest egg-laying duration occurred at 6:00 to 8:00, was given by the 16L:8D (8 min/hen), and the longest egg-laying duration occurred at 18:00 to 20:00, was given by 16L:8D and 8L:4D:4L:8D (>20.5 min/hen) (P < 0.05). The highest sleeping frequency was given by the 12L:2D:4L:6D, the lowest was given by the 12L:12D (P < 0.05). At 6:00 to 8:00, the shortest sleeping duration was given by 12L:2D:4L:6D (1.5 s/hen), at 18:00 to 20:00, the longest given by 8L:4D:4L:8D (14.3 s/hen) (P < 0.05). Lighting pattern and photoperiod alone or in interaction had no effect on egg-laying rate during 22 to 30 wk (P > 0.05), but had significant effects on ovarian weight, oviduct weight, oviduct length, the number of LYF and SYF (P < 0.05), and the continuous groups were all significantly higher than the intermittent groups (P < 0.05). The present study indicated that light regimes affected the frequency and duration of circadian behavior in BYC laying hens, and the continuous light was more beneficial to the reproductive development than the intermittent light in the early laying period. [ABSTRACT FROM AUTHOR]

Abstract: The dorsomedial hypothalamic nucleus (DMH) has been proposed as a candidate for the neural substrate of a food-entrainable oscillator. The existence of a food-entrainable oscillator in the mammalian nervous system was inferred previously from restricted feeding-induced behavioral rhythmicity in rodents with suprachiasmatic nucleus lesions. In the present study, we have characterized the circadian rhythmicity of behavior in Wfs1-deficient mice during ad libitum and restricted feeding. Based on the expression of Wfs1 protein in the DMH it was hypothesized that Wfs1-deficient mice will display reduced or otherwise altered food anticipatory activity. Wfs1 immunoreactivity in DMH was found almost exclusively in the compact part. Restricted feeding induced c-Fos immunoreactivity primarily in the ventral and lateral aspects of DMH and it was similar in both genotypes. Wfs1-deficiency resulted in significantly lower body weight and reduced wheel-running activity. Circadian rhythmicity of behavior was normal in Wfs1-deficient mice under ad libitum feeding apart from elongated free-running period in constant light. The amount of food anticipatory activity induced by restricted feeding was not significantly different between the genotypes. Present results indicate that the effects of Wfs1-deficiency on behavioral rhythmicity are subtle suggesting that Wfs1 is not a major player in the neural networks responsible for circadian rhythmicity of behavior. [Copyright &y& Elsevier]

DBP, a PAR leucine zipper transcription factor, accumulates according to a robust circadian rhythm in liver and several other tissues of mouse and rat. Here we report that DBP mRNA levels also oscillate strongly in the suprachiasmatic nucleus (SCN) of the hypothalamus, believed to harbor the central mammalian pacemaker. However, peak and minimum levels of DBP mRNA are reached about 4 h earlier in the SCN than in liver, suggesting that circadian DBP expression is controlled by different mechanisms in SCN and in peripheral tissues. Mice homozygous for a DBP-null allele display less locomotor activity and free-run with a shorter period than otherwise isogenic wild-type animals. The altered locomotor activity in DBP mutant mice and the highly rhythmic expression of the DBP gene in SCN neurons suggest that DBP is involved in controlling circadian behavior. However, since DBP-/- mice are still rhythmic and since DBP protein is not required for the circadian expression of its own gene, dbp is more likely to be a component of the circadian output pathway than a master gene of the clock. [ABSTRACT FROM AUTHOR]

Arginine vasopressin (AVP) is a neurohormone that alters cellular physiology through both endocrine and synaptic signaling. Circadian rhythms in AVP release and other biological processes are driven by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. Loss of vasopressin signaling alters circadian behavior, but the basis of these effects remains unclear. Here we investigate the role of AVP signaling in circadian timekeeping by analyzing behavior and SCN function in a novel AVP-deficient mouse model. Consistent with previous work, loss of AVP signaling increases water consumption and accelerates recovery to simulated jetlag. We expand on these results to show that loss of AVP increases period, imprecision and plasticity of behavioral rhythms under constant darkness. Interestingly, the effect of AVP deficiency on circadian period was influenced by sex, with loss of AVP lengthening period in females but not males. Examining SCN function directly with ex vivo bioluminescence imaging of clock protein expression, we demonstrate that loss of AVP signaling modulates the period, precision, and phase relationships of SCN neurons in both sexes. This pattern of results suggests that there are likely sex differences in downstream targets of the SCN. Collectively, this work indicates that AVP signaling modulates circadian circuits in a manner influenced by sex, which provides new insight into sexual dimorphisms in the regulation of daily rhythms. • Vasopressin expression is reduced in the hypothalamus of AVP-IRES-Cre mice. • Vasopressin loss in this model increases water intake and speeds jetlag recovery. • Three novel effects on circadian behavior manifest in a sex-dependent manner. • Phenotypic differences in behavior reflect changes in master clock function. • Clocks constructed differently despite comparable overt rhythms in males and females. [ABSTRACT FROM AUTHOR]

Glial astrocytes of vertebrates and invertebrates are important modulators of nervous system development, physiology, and behavior. In all species examined, astrocytes of the adult brain contain conserved circadian clocks, and multiple studies have shown that these glial cells participate in the regulation of circadian behavior and sleep. This short review summarizes recent work, using fruit fly (Drosophila) and mouse models, that document participation of astrocytes and their endogenous circadian clocks in the control of rhythmic behavior. This article is categorized under: Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms Nervous System Development > Flies., (© 2019 Wiley Periodicals, Inc.)

Summary ATAXIN-2 (ATX2) has been implicated in human neurodegenerative diseases, yet it remains elusive how ATX2 assembles specific protein complexes to execute its physiological roles. Here we employ the posttranscriptional co-activator function of Drosophila ATX2 to demonstrate that LSM12 and ME31B/DDX6 are two ATX2-associating factors crucial for sustaining circadian rhythms. LSM12 acts as a molecular adaptor for the recruitment of TWENTY-FOUR (TYF) to ATX2. The ATX2-LSM12-TYF complex thereby stimulates TYF-dependent translation of the rate-limiting clock gene period ( per ) to maintain 24 hr periodicity in circadian behaviors. In contrast, ATX2 contributes to NOT1-mediated gene silencing and associates with NOT1 in a ME31B/DDX6-dependent manner. The ME31B/DDX6-NOT1 complex does not affect PER translation but supports high-amplitude behavioral rhythms along with ATX2, indicating a PER-independent clock function of ATX2. Taken together, these data suggest that the ATX2 complex may switch distinct modes of posttranscriptional regulation through its associating factors to control circadian clocks and ATX2-related physiology. [ABSTRACT FROM AUTHOR]

Summary The suprachiasmatic nucleus (SCN) of the hypothalamus orchestrates daily rhythms of physiology and behavior in mammals. Its circadian (∼24 hr) oscillations of gene expression and electrical activity are generated intrinsically and can persist indefinitely in temporal isolation. This robust and resilient timekeeping is generally regarded as a product of the intrinsic connectivity of its neurons. Here we show that neurons constitute only one “half” of the SCN clock, the one metabolically active during circadian daytime. In contrast, SCN astrocytes are active during circadian nighttime, when they suppress the activity of SCN neurons by regulating extracellular glutamate levels. This glutamatergic gliotransmission is sensed by neurons of the dorsal SCN via specific pre-synaptic NMDA receptor assemblies containing NR2C subunits. Remarkably, somatic genetic re-programming of intracellular clocks in SCN astrocytes was capable of remodeling circadian behavioral rhythms in adult mice. Thus, SCN circuit-level timekeeping arises from interdependent and mutually supportive astrocytic-neuronal signaling. [ABSTRACT FROM AUTHOR]

We describe a genome-wide microRNA (miRNA)-based screen to identify brain glial cell functions required for circadian behavior. To identify glial miRNAs that regulate circadian rhythmicity, we employed a collection of "miR-sponges" to inhibit miRNA function in a glia-specific manner. Our initial screen identified 20 glial miRNAs that regulate circadian behavior. We studied two miRNAs, miR-263b and miR-274, in detail and found that both function in adult astrocytes to regulate behavior. Astrocyte-specific inhibition of miR-263b or miR-274 in adults acutely impairs circadian locomotor activity rhythms with no effect on glial or clock neuronal cell viability. To identify potential RNA targets of miR-263b and miR-274, we screened 35 predicted miRNA targets, employing RNA interference-based approaches. Glial knockdown of two putative miR-274 targets, CG4328 and MESK2, resulted in significantly decreased rhythmicity. Homology of the miR-274 targets to mammalian counterparts suggests mechanisms that might be relevant for the glial regulation of rhythmicity., (Copyright © 2018 by the Genetics Society of America.)

Animals use circadian rhythms to anticipate daily environmental changes. Circadian clocks have a profound effect on behavior. In Drosophila, for example, brain pacemaker neurons dictate that flies are mostly active at dawn and dusk. miRNAs are small, regulatory RNAs (≈22 nt) that play important roles in posttranscriptional regulation. Here, we identify miR-124 as an important regulator of Drosophila circadian locomotor rhythms. Under constant darkness, flies lacking miR-124 (miR-124(KO)) have a dramatically advanced circadian behavior phase. However, whereas a phase defect is usually caused by a change in the period of the circadian pacemaker, this is not the case in miR-124(KO) flies. Moreover, the phase of the circadian pacemaker in the clock neurons that control rhythmic locomotion is not altered either. Therefore, miR-124 modulates the output of circadian clock neurons rather than controlling their molecular pacemaker. Circadian phase is also advanced under temperature cycles, but a light/dark cycle partially corrects the defects in miR-124(KO) flies. Indeed, miR-124(KO) shows a normal evening phase under the latter conditions, but morning behavioral activity is suppressed. In summary, miR-124 controls diurnal activity and determines the phase of circadian locomotor behavior without affecting circadian pacemaker function. It thus provides a potent entry point to elucidate the mechanisms by which the phase of circadian behavior is determined., Significance Statement: In animals, molecular circadian clocks control the timing of behavioral activities to optimize them with the day/night cycle. This is critical for their fitness and survival. The mechanisms by which the phase of circadian behaviors is determined downstream of the molecular pacemakers are not yet well understood. Recent studies indicate that miRNAs are important regulators of circadian outputs. We found that miR-124 shapes diurnal behavioral activity and has a striking impact on the phase of circadian locomotor behavior. Surprisingly, the period and phase of the neural circadian pacemakers driving locomotor rhythms are unaffected. Therefore, miR-124 is a critical modulator of the circadian output pathways that control circadian behavioral rhythms., (Copyright © 2016 the authors 0270-6474/16/362007-07$15.00/0.)