Phase-delay in the light-dark cycle impairs clock gene expression and levels of serotonin, norepinephrine, and their metabolites in the mouse hippocampus and amygdala

Chronic blue light exposure induced spatial anxiety in an adolescent mouse model: Per2 upregulation and altered brain resting-state functional activity

BACKGROUND

Blue light (BL) is the primary component of light emitted from 3C devices. The use of 3C (computers, consumer electronics, and communication) devices has been increasing among all age groups. How social interaction and spatial cognition are affected in adolescents after long-term 3C device usage at night remains unclear.

METHODS

Five-week-old mice were exposed to BL. Subsequently, these mice were subjected to social behavior tests, functional magnetic resonance imaging, and histopathologic analyses.

RESULTS

BL exposure increased spatial anxiety but did not affect sociability, social novelty, or motor coordination. Also, BL exposure altered brain connectivity in the hippocampus (Hip), thalamus, and striatum, and it reduced brain activity in the retrosplenial cortex and dorsal part of the Hip. Spatial anxiety was associated with brain alterations. Although BL exposure reduced the size of retinal oligodendrocytes and increased the expression of the Period 2 circadian protein, it did not result in brain inflammation, at least not in the Hip.

CONCLUSION

Our findings highlight that long-term BL exposure in adolescents induces spatial anxiety. The underlying mechanisms include changes in brain activity and connectivity and the disruption of the circadian rhythm.

The neurobiological mechanisms of photoperiod impact on brain functions: a comprehensive review

Variations in day length, or photoperiodism, whether natural or artificial light, significantly impact biological, physiological, and behavioral processes within the brain. Both natural and artificial light sources are environmental factors that significantly influence brain functions and mental well-being. Photoperiodism is a phenomenon, occurring either over a 24 h cycle or seasonally and denotes all biological responses of humans and animals to these fluctuations in day and night length. Conversely, artificial light occurrence refers to the presence of light during nighttime hours and/or its absence during the daytime (unnaturally long and short days, respectively). Light at night, which is a form of light pollution, is prevalent in many societies, especially common in certain emergency occupations. Moreover, individuals with certain mental disorders, such as depression, often exhibit a preference for darkness over daytime light. Nevertheless, disturbances in light patterns can have negative consequences, impacting brain performance through similar mechanisms albeit with varying degrees of severity. Furthermore, changes in day length lead to alterations in the activity of receptors, proteins, ion channels, and molecular signaling pathways, all of which can impact brain health. This review aims to summarize the mechanisms by which day length influences brain functions through neural circuits, hormonal systems, neurochemical processes, cellular activity, and even molecular signaling pathways.

Molecular mechanisms of artificial light at night affecting circadian rhythm disturbance

Artificial light at night (ALAN) pollution has been regarded as a global environmental concern. More than 80% of the global population is exposed to light pollution. Exacerbating this issue, artificially lit outdoor areas are growing by 2.2% per year, while continuously lit areas have brightened by 2.2% each year due to rapid population growth and expanding urbanization. Furthermore, the increasing prevalence of night shift work and smart device usage contributes to the inescapable influence of ALAN. Studies have shown that ALAN can disrupt endogenous biological clocks, resulting in a disturbance of the circadian rhythm, which ultimately affects various physiological functions. Up until now, scholars have studied various disease mechanisms caused by ALAN that may be related to the response of the circadian system to light. This review outlines the molecular mechanisms by which ALAN causes circadian rhythm abnormalities in sleep disorders, endocrine diseases, cardiovascular disease, cancer, immune impairment, depression, anxiety and cognitive impairments.

Artificial light at night and risk of depression: a systematic review and meta-analysis

BACKGROUND

Artificial light at night (ALAN) has been increasingly recognized as a potential environmental risk factor for mental health issues. However, no meta-analyses have been conducted to summarize the findings. This study aimed to evaluate the pooled associations between outdoor and indoor ALAN exposures and the risk of depression.

METHODS

Adhering to the PRISMA guideline, we conducted systematic searches across PubMed, Web of Science, EMBASE, Cochrane, and Ovid databases for studies published before May 1st, 2024.

RESULTS

A total of 7 studies (5 for outdoor ALAN and 2 for indoor ALAN) with a combined total of 560,219 participants were included in the meta-analysis. Specifically, a 1 nW/cm2/sr increase in outdoor ALAN was associated with a 0.43% (95% CI: 0.21%, 0.65%) increase in depression risk. Meanwhile, a 1 lux increase in indoor ALAN was associated with a 3.29% (95% CI: 0.85%, 5.79%) increase in depression risk. No potential heterogeneity was observed for outdoor ALAN exposure and indoor ALAN exposure. Subgroup analyses for outdoor ALAN indicated that development level, sample size, age group, sex, study design, modality of depression assessment, or adjustment of sleep-related variables in models may not be potential sources of heterogeneity. Sensitivity analyses confirmed the robustness of the findings, while evidence of publication bias was observed for studies on outdoor ALAN.

CONCLUSIONS

Our findings suggest that both outdoor and indoor ALAN exposures are associated with increased risk of depression. These results underscore the importance of considering outdoor and indoor ALAN in public health strategies aimed at reducing depression risk. Nevertheless, further studies with prospective design are still warranted considering the limited study numbers.

Chronic jetlag accelerates pancreatic neoplasia in conditional Kras-mutant mice

Misalignment of the circadian clock compared to environmental cues causes circadian desynchrony, which is pervasive in humans. Clock misalignment can lead to various pathologies including obesity and diabetes, both of which are associated with pancreatic ductal adenocarcinoma - a devastating cancer with an 80% five-year mortality rate. Although circadian desynchrony is associated with an increased risk of several solid-organ cancers, the correlation between clock misalignment and pancreas cancer is unclear. Using a chronic jetlag model, we investigated the impact of clock misalignment on pancreas cancer initiation in mice harboring a pancreas-specific activated Kras mutation. We found that chronic jetlag accelerated the development of pancreatic cancer precursor lesions, with a concomitant increase in precursor lesion grade. Cell-autonomous knock-out of the clock in pancreatic epithelial cells of Kras-mutant mice demonstrated no acceleration of precursor lesion formation, indicating non-cell-autonomous clock dysfunction was responsible for the expedited tumor development. Therefore, we applied single-cell RNA sequencing over time and identified fibroblasts as the cell population manifesting the greatest clock-dependent changes, with enrichment of specific cancer-associated fibroblast pathways due to circadian misalignment.

Circadian regulation of memory under stress: Endocannabinoids matter

Organisms ranging from plants to higher mammals have developed 24-hour oscillation rhythms to optimize physiology to environmental changes and regulate a plethora of neuroendocrine and behavioral processes, including neurotransmitter and hormone regulation, stress response and learning and memory function. Compelling evidence indicates that a wide array of memory processes is strongly influenced by stress- and emotional arousal-activated neurobiological systems, including the endocannabinoid system which has been extensively shown to play an integral role in mediating stress effects on memory. Here, we review findings showing how circadian rhythms and time-of-day influence stress systems and memory performance. We report evidence of circadian regulation of memory under stress, focusing on the role of the endocannabinoid system and highlighting its circadian rhythmicity. Our discussion illustrates how the endocannabinoid system mediates stress effects on memory in a circadian-dependent fashion. We suggest that endocannabinoids might regulate molecular mechanisms that control memory function under circadian and stress influence, with potential important clinical implications for both neurodevelopmental disorders and psychiatric conditions involving memory impairments.

Hypnotic and Melatonin/Melatonin-Receptor Agonist Treatment in Bipolar Disorder: A Systematic Review and Meta-Analysis

BACKGROUND

Bipolar disorder (BD) is a chronic relapsing-remitting psychiatric disorder. Sleep and circadian rhythm disturbances persist during acute mood episodes of the disorder and during euthymia. However, the treatment potential of hypnotic agents that might be used to manage sleep disturbance in BD is not well understood. Similarly, melatonin and medications with a melatonin-receptor agonist mechanism of action may have chronotherapeutic potential for treating people with the disorder, but the impact of these substances on sleep and circadian rhythms and core symptoms in BD is unclear.

OBJECTIVE

Our aim was to conduct a systematic review and meta-analysis evaluating the current evidence for hypnotic and melatonin/melatonin-receptor agonist pharmacotherapy for symptoms of sleep disturbance, mania, and depression in patients with BD.

METHODS

AMED, Embase, MEDLINE and PsychINFO databases were searched for studies published in English from the date of inception to 31 October 2021. Studies included in this review were randomised controlled trials (RCTs) and non-controlled/non-randomised studies for BD that examined hypnotic medications selected based on a common pattern of usage for treating insomnia (i.e. chloral, clomethiazole, diphenhydramine, doxepin, doxylamine, promethazine, suvorexant, zaleplon, zolpidem, zopiclone, and eszopiclone) and melatonin and the melatonin-receptor agonist drugs ramelteon and agomelatine. Risk of bias was assessed using the RoB2 and AXIS tools. Pooled effect sizes for RCT outcomes were estimated using random-effects models.

RESULTS

A total of eleven studies (six RCTs and five experimental feasibility studies) involving 1279 participants were included. Each study examined melatonin or melatonin-receptor agonists. No studies of hypnotics were found that fulfilled the review inclusion criteria. Pilot feasibility studies suggested beneficial treatment effects for symptoms of sleep disturbance, depression, and mania. However, the pooled effect of the two available RCT studies assessing sleep quality via Pittsburgh Sleep Quality Index scores was not statistically significant (g = - 0.04 [95% CI - 0.81 to 0.73]) and neither was the pooled effect for depressive symptoms (four studies; g = - 0.10 [95% CI - 0.27 to 0.08]). Some RCT evidence suggests ramelteon might prevent relapse into depression in BD. The largest efficacy signal detected was for manic symptoms (four studies; g = - 0.44 [95% CI - 1.03 to 0.14]) but there was substantial heterogeneity between studies and patient characteristics. In the two RCTs assessing manic symptoms during acute mania, adjunctive melatonin demonstrated superior treatment effects versus placebo.

CONCLUSIONS

There is a paucity of studies examining pharmacological interventions for sleep and circadian rhythm disturbance in BD. Few studies assessed sleep-related symptoms, and none quantitatively examined endogenous melatonin patterns or other circadian rhythms. Melatonin may be a promising candidate for the adjunctive treatment of bipolar mania. However, dose-finding studies and studies with larger sample sizes are needed to confirm its efficacy. We recommend parallel monitoring of sleep and circadian rhythms in future trials. Chronobiology-informed trial designs are needed to improve the quality of future studies.

PROTOCOL REGISTRATION

PROSPERO (CRD42020167528).

Circadian rhythms and pain

The goal of this review is to provide a perspective on the nature and importance of the relationship between the circadian and pain systems. We provide: 1) An overview of the circadian and pain systems, 2) a review of direct and correlative evidence that demonstrates diurnal and circadian rhythms within the pain system; 3) a perspective highlighting the need to consider the role of a proposed feedback loop of circadian rhythm disruption and maladaptive pain; 4) a perspective on the nature of the relationship between circadian rhythms and pain. In summary, we propose that there is no single locus responsible for producing the circadian rhythms of the pain system. Instead, circadian rhythms of pain are a complex result of the distributed rhythms present throughout the pain system, especially those of the descending pain modulatory system, and the rhythms of the systems with which it interacts, including the opioid, endocrine, and immune systems.

Changes in Locomotor Activity and Oxidative Stress-Related Factors after the Administration of an Amino Acid Mixture by Generation and Age

Amino acids, as nutrients, are expected to improve sleep disorders. This study aimed to evaluate the generation- and age-dependent sleep-improving effects of γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP) coadministration. The differentially expressed genes and generation-related behavior after the administration of a GABA/5-HTP mixture were measured in a Drosophila model, while age-related changes in gene expression and oxidative stress-related parameters were measured in a mouse model. The GABA/5-HTP-treated group showed significant behavioral changes compared to the other groups. Sequencing revealed that the GABA/5-HTP mixture influenced changes in nervous system-related genes, including those involved in the regulation of the expression of behavioral and synaptic genes. Additionally, total sleep time increased with age, and nighttime sleep time in the first- and third-generation flies was significantly different from that of the control groups. The GABA/5-HTP mixture induced significant changes in the expression of sleep-related receptors in both models. Furthermore, the GABA/5-HTP mixture reduced levels of ROS and ROS reaction products in an age-dependent manner. Therefore, the increase in behavioral changes caused by GABA/5-HTP mixture administration was effective in eliminating ROS activity across generations and ages.

Dual orexin receptor antagonist (DORA-12) treatment affects the overall levels of Net/maoA mRNA expression in the hippocampus

The orexinergic system plays a significant role in regulating proper sleep/wake maintenance. Dual orexin receptor antagonist (DORA) is widely prescribed for insomnia symptoms. The antagonist acts on orexin 1 and 2 receptors located in certain brain areas, including the locus coeruleus and dorsal raphe. Nevertheless, its effects on monoamine-related gene expression remain unclear. Here, we measured the expression levels of monoamine-related genes in DORA-treated mice. DORA treatment significantly affected overall levels of noradrenalin transporter/monoamine oxidases A mRNA expression in the hippocampus. Our findings suggest that DORA contributes to noradrenalin-related gene expression regulation in the central nervous system.

Memory and the circadian system: Identifying candidate mechanisms by which local clocks in the brain may regulate synaptic plasticity

The circadian system is an endogenous biological network responsible for coordinating near-24-h cycles in behavior and physiology with daily timing cues from the external environment. In this review, we explore how the circadian system regulates memory formation, retention, and recall. Circadian rhythms in these memory processes may arise through several endogenous pathways, and recent work highlights the importance of genetic timekeepers found locally within tissues, called local clocks. We evaluate the circadian memory literature for evidence of local clock involvement in memory, identifying potential nodes for direct interactions between local clock components and mechanisms of synaptic plasticity. Our discussion illustrates how local clocks may pervasively modulate neuronal plastic capacity, a phenomenon that we designate here as circadian metaplasticity. We suggest that this function of local clocks supports the temporal optimization of memory processes, illuminating the potential for circadian therapeutic strategies in the prevention and treatment of memory impairment.

Gamma oryzanol impairs alcohol-induced anxiety-like behavior in mice via upregulation of central monoamines associated with Bdnf and Il-1β signaling

Adolescent alcohol exposure may increase anxiety-like behaviors by altering central monoaminergic functions and other important neuronal pathways. The present study was designed to investigate the anxiolytic effect of 0.5% γ-oryzanol (GORZ) and its neurochemical and molecular mechanisms under chronic 10% ethanol consumption. Five-week-old ICR male mice received either control (14% casein, AIN 93 M) or GORZ (14% casein, AIN 93 M + 0.5% GORZ) diets in this study. We showed that GORZ could potentially attenuate alcohol-induced anxiety-like behaviors by significantly improving the main behavioral parameters measured by the elevated plus maze test. Moreover, GORZ treatment significantly restored the alcohol-induced downregulation of 5-hydroxytryptophan and 5-hydroxyindole acetic acid in the hippocampus and improved homovanillic acid levels in the cerebral cortex. Furthermore, a recovery increase in the level of 3-methoxy-4-hydroxyphenylglycol both in the hippocampus and cerebral cortex supported the anxiolytic effect of GORZ. The significant elevation and reduction in the hippocampus of relative mRNA levels of brain-derived neurotrophic factor and interleukin 1β, respectively, also showed the neuroprotective role of GORZ in ethanol-induced anxiety. Altogether, these results suggest that 0.5% GORZ is a promising neuroprotective drug candidate with potential anxiolytic, neurogenic, and anti-neuroinflammatory properties for treating adolescent alcohol exposure.

Circadian regulation of membrane physiology in neural oscillators throughout the brain

Twenty-four-hour rhythmicity in physiology and behavior are driven by changes in neurophysiological activity that vary across the light-dark and rest-activity cycle. Although this neural code is most prominent in neurons of the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus, there are many other regions in the brain where region-specific function and behavioral rhythmicity may be encoded by changes in electrical properties of those neurons. In this review, we explore the existing evidence for molecular clocks and/or neurophysiological rhythms (i.e., 24 hr) in brain regions outside the SCN. In addition, we highlight the brain regions that are ripe for future investigation into the critical role of circadian rhythmicity for local oscillators. For example, the cerebellum expresses rhythmicity in over 2,000 gene transcripts, and yet we know very little about how circadian regulation drives 24-hr changes in the neural coding responsible for motor coordination. Finally, we conclude with a discussion of how our understanding of circadian regulation of electrical properties may yield insight into disease mechanisms which may lead to novel chronotherapeutic strategies in the future.

Evaluation of neuroactive effects of ethanol extract of Schisandra chinensis, Schisandrin, and Schisandrin B and determination of underlying mechanisms by zebrafish behavioral profiling

Schisandra chinensis, a traditional Chinese medicine (TCM), has been used to treat sleep disorders. Zebrafish sleep/wake behavioral profiling provides a high-throughput platform to screen chemicals, but has never been used to study extracts and components from TCM. In the present study, the ethanol extract of Schisandra chinensis and its two main lignin components, schisandrin and schisandrin B, were studied in zebrafish. We found that the ethanol extract had bidirectional improvement in rest and activity in zebrafish. Schisandrin and schisandrin B were both sedative and active components. We predicted that schisandrin was related to serotonin pathway and the enthanol extract of Schisandra chinensis was related to seoronin and domapine pathways using a database of zebrafish behaviors. These predictions were confirmed in experiments using Caenorhabditis elegans. In conclusion, zebrafish behavior profiling could be used as a high-throughput platform to screen neuroactive effects and predict molecular pathways of extracts and components from TCM.

Anxiolytic effects of γ-oryzanol in chronically- stressed mice are related to monoamine levels in the brain

AIMS

The present study was aimed to investigate the anxiolytic effect of γ-oryzanol (GORZ) during chronic restraint stress treatment (CRST), which is a well-documented model of stress-related disorders, like anxiety, and its potential molecular mechanisms.

MATERIALS AND METHODS

In this experiment, 5-week-old male ICR mice were used and the concentration of GORZ was fixed at 0.5% in the mouse standard diet (14% casein, AIN 93 M). Mice were immobilized daily for 3 h from ZT 2.5 to 5.5 (ZT0 was designated as light-on time) for 20 consecutive days, followed by behavioral testing, including the open field test (OFT) and elevated plus maze (EPM) test. The concentration of serum corticosterone (CORT) was measured. In addition, the expression of central monoamine neurotransmitters with their metabolites in the hippocampus, cerebral cortex, and amygdala of the brain were examined.

KEY FINDINGS

0.5% GORZ partially blocked stress-induced reduction of body weight gain while stressed mice had significantly lower body weights during the entire experimental period. Further, 0.5% GORZ treatment could significantly improve the main behavioral parameters even in CRST situations. The significant increase in serum CORT levels indicated CRST-induced stress, which was almost unaffected by 0.5% GORZ treatment. Moreover, 0.5% GORZ also supported the anxiolytic mechanism with enhancement of 5-HIAA and NE levels in the amygdala of brain after CRST.

SIGNIFICANCE

Taken together, our studies suggested that 0.5% GORZ is a potential therapeutic drug candidate against anxiety under chronic stress conditions.

Age-dependent motor dysfunction due to neuron-specific disruption of stress-activated protein kinase MKK7

c-Jun N-terminal kinase (JNK) is a member of the mitogen-activated protein kinase family and controls various physiological processes including apoptosis. A specific upstream activator of JNKs is the mitogen-activated protein kinase kinase 7 (MKK7). It has been reported that MKK7-JNK signaling plays an important regulatory role in neural development, however, post-developmental functions in the nervous system have not been elucidated. In this study, we generated neuron-specific Mkk7 knockout mice (MKK7 cKO), which impaired constitutive activation of JNK in the nervous system. MKK7 cKO mice displayed impaired circadian behavioral rhythms and decreased locomotor activity. MKK7 cKO mice at 8 months showed motor dysfunctions such as weakness of hind-limb and gait abnormality in an age-dependent manner. Axonal degeneration in the spinal cord and muscle atrophy were also observed, along with accumulation of the axonal transport proteins JNK-interacting protein 1 and amyloid beta precursor protein in the brains and spinal cords of MKK7 cKO mice. Thus, the MKK7-JNK signaling pathway plays important roles in regulating circadian rhythms and neuronal maintenance in the adult nervous system.

Circadian Rhythms in Fear Conditioning: An Overview of Behavioral, Brain System, and Molecular Interactions

The formation of fear memories is a powerful and highly evolutionary conserved mechanism that serves the behavioral adaptation to environmental threats. Accordingly, classical fear conditioning paradigms have been employed to investigate fundamental molecular processes of memory formation. Evidence suggests that a circadian regulation mechanism allows for a timestamping of such fear memories and controlling memory salience during both their acquisition and their modification after retrieval. These mechanisms include an expression of molecular clocks in neurons of the amygdala, hippocampus, and medial prefrontal cortex and their tight interaction with the intracellular signaling pathways that mediate neural plasticity and information storage. The cellular activities are coordinated across different brain regions and neural circuits through the release of glucocorticoids and neuromodulators such as acetylcholine, which integrate circadian and memory-related activation. Disturbance of this interplay by circadian phase shifts or traumatic experience appears to be an important factor in the development of stress-related psychopathology, considering these circadian components are of critical importance for optimizing therapeutic approaches to these disorders.