Light Affects Mood and Learning through Distinct Retina-Brain Pathways

The Influence of Artificial Light at Night on Asthma and Allergy, Mental Health, and Cancer Outcomes: A Systematic Scoping Review Protocol

Artificial light at night (ALAN) exposure is associated with the disruption of human circadian processes. Through numerous pathophysiological mechanisms such as melatonin dysregulation, it is hypothesised that ALAN exposure is involved in asthma and allergy, mental illness, and cancer outcomes. There are numerous existing studies considering these relationships; however, a critical appraisal of available evidence on health outcomes has not been completed. Due to the prevalence of ALAN exposure and these outcomes in society, it is critical that current evidence of their association is understood. Therefore, this systematic scoping review will aim to assess the association between ALAN exposure and asthma and allergy, mental health, and cancer outcomes. This systematic scoping review will be conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement. We will search bibliographic databases, registries, and references. We will include studies that have described potential sources of ALAN exposure (such as shift work or indoor and outdoor exposure to artificial light); have demonstrated associations with either allergic conditions (including asthma), mental health, or cancer-related outcomes; and are published in English in peer-reviewed journals. We will conduct a comprehensive literature search, title and abstract screening, full-text review, and data collection and analysis for each outcome separately.

Divergent outer retinal circuits drive image and non-image visual behaviors

Image- and non-image-forming vision are essential for animal behavior. Here we use genetically modified mouse lines to examine retinal circuits driving image- and non-image-functions. We describe the outer retinal circuits underlying the pupillary light response (PLR) and circadian photoentrainment, two non-image-forming behaviors. Rods and cones signal light increments and decrements through the ON and OFF pathways, respectively. We find that the OFF pathway drives image-forming vision but cannot drive circadian photoentrainment or the PLR. Cone light responses drive image formation but fail to drive the PLR. At photopic levels, rods use the primary and secondary rod pathways to drive the PLR, whereas at the scotopic and mesopic levels, rods use the primary pathway to drive the PLR, and the secondary pathway is insufficient. Circuit dynamics allow rod ON pathways to drive two non-image-forming behaviors across a wide range of light intensities, whereas the OFF pathway is potentially restricted to image formation.

luox: validated reference open-access and open-source web platform for calculating and sharing physiologically relevant quantities for light and lighting

Light exposure has a profound impact on human physiology and behaviour. For example, light exposure at the wrong time can disrupt our circadian rhythms and acutely suppress the production of melatonin. In turn, appropriately timed light exposure can support circadian photoentrainment. Beginning with the discovery that melatonin production is acutely suppressed by bright light more than 40 years ago, understanding which aspects of light drive the 'non-visual' responses to light remains a highly active research area, with an important translational dimension and implications for "human-centric" or physiologically inspired architectural lighting design. In 2018, the International Commission on Illumination (CIE) standardised the spectral sensitivities for predicting the non-visual effects of a given spectrum of light with respect to the activation of the five photoreceptor classes in the human retina: the L, M and S cones, the rods, and the melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs). Here, we described a novel, lean, user-friendly, open-access and open-source platform for calculating quantities related to light. The platform, called luox, enables researchers and research users in vision science, lighting research, chronobiology, sleep research and adjacent fields to turn spectral measurements into reportable quantities. The luox code base, released under the GPL-3.0 License, is modular and therefore extendable to other spectrum-derived quantities. luox calculations of CIE quantities and indices have been endorsed by the CIE following black-box validation.

Dim Blue Light at Night Induces Spatial Memory Impairment in Mice by Hippocampal Neuroinflammation and Oxidative Stress

Light pollution is one of the most serious public problems, especially the night light. However, the effect of dim blue light at night (dLAN-BL) on cognitive function is unclear. In this study, we evaluated the effects of exposure to dLAN-BL in C57BL/6J mice for 4 consecutive weeks. Our results showed dLAN-BL significantly impaired spatial learning and memory and increased plasma corticosterone level in mice. Consistent with these changes, we observed dLAN-BL significantly increased the numbers and activation of microglia and the levels of oxidative stress product MDA in the hippocampus, decreased the levels of antioxidant enzymes Glutathione peroxidase (GSH-Px), Superoxide dismutase (SOD), Gluathione reductase (Gsr), total antioxidants (T-AOC) and the number of neurons in the hippocampus, up-regulated the mRNA expression levels of IL6, TNF-α and the protein expression levels of iNOS, COX2, TLR4, p-p65, Cleaved-Caspase3 and BAX, and down-regulated the mRNA expression levels of IL4, IL10, Psd95, Snap25, Sirt1, Dcx and the protein expression level of BCL2. In vitro results further showed corticosterone (10uM)-induced BV2 cell activation and up-regulated content of IL6, TNF-α in the cell supernatant and the protein expression levels of iNOS, COX2, p-p65 in BV2 cells. Our findings suggested dLAN-BL up-regulated plasma corticosterone level and hippocampal microglia activation, which in turn caused oxidative stress and neuroinflammation, leading to neuronal loss and synaptic dysfunction, ultimately leading to spatial learning and memory dysfunction in mice.

Daily changes in light influence mood via inhibitory networks within the thalamic perihabenular nucleus

Exposure to irregular lighting schedules leads to deficits in affective behaviors. The retino-recipient perihabenular nucleus (PHb) of the dorsal thalamus has been shown to mediate these effects in mice. However, the mechanisms of how light information is processed within the PHb remains unknown. Here, we show that the PHb contains a distinct cluster of GABAergic neurons that receive direct retinal input. These neurons are part of a larger inhibitory network composed of the thalamic reticular nucleus and zona incerta, known to modulate thalamocortical communication. In addition, PHbGABA neurons locally modulate excitatory-relay neurons, which project to limbic centers. Chronic exposure to irregular light-dark cycles alters photo-responsiveness and synaptic output of PHbGABA neurons, disrupting daily oscillations of genes associated with inhibitory and excitatory PHb signaling. Consequently, selective and chronic PHbGABA manipulation results in mood alterations that mimic those caused by irregular light exposure. Together, light-mediated disruption of PHb inhibitory networks underlies mood deficits.

External light‐dark cycle shapes gut microbiota through intrinsically photosensitive retinal ganglion cells

Gut microbiota are involved in many physiological functions such as metabolism, brain development, and neurodegenerative diseases. Many microbes in the digestive tract do not maintain a constant level of their relative abundance but show daily oscillations under normal conditions. Recent evidence indicates that chronic jetlag, constant darkness, or deletion of the circadian core gene can alter the composition of gut microbiota and dampen the daily oscillation of gut microbes. However, the neuronal circuit responsible for modulating gut microbiota remained unclear. Using genetic mouse models and 16s rRNA metagenomic analysis, we find that light-dark cycle information transmitted by the intrinsically photosensitive retinal ganglion cells (ipRGCs) is essential for daily oscillations of gut microbes under temporal restricted high-fat diet conditions. Furthermore, aberrant light exposure such as dim light at night (dLAN) can alter the composition, relative abundance, and daily oscillations of gut microbiota. Together, our results indicate that external light-dark cycle information can modulate gut microbiota in the direction from the brain to the gut via the sensory system.

Multimodal Tuning of Synaptic Plasticity Using Persistent Luminescent Memitters

Mimicking memory processes, including encoding, storing, and retrieving information, is critical for neuromorphic computing and artificial intelligence. Synaptic behavior simulations through electronic, magnetic, or photonic devices based on metal oxides, 2D materials, molecular complex and phase change materials, represent important strategies for performing computational tasks with enhanced power efficiency. Here, a special class of memristive materials based on persistent luminescent memitters (termed as a portmanteau of "memory" and "emitter") with optical characteristics closely resembling those of biological synapses is reported. The memory process and synaptic plasticity can be successfully emulated using such memitters under precisely controlled excitation frequency, wavelength, pulse number, and power density. The experimental and theoretical data suggest that electron-coupled trap nucleation and propagation through clustering in persistent luminescent memitters can explain experience-dependent plasticity. The use of persistent luminescent memitters for multichannel image memorization that allows direct visualization of subtle changes in luminescence intensity and realization of short-term and long-term memory is also demonstrated. These findings may promote the discovery of new functional materials as artificial synapses and enhance the understanding of memory mechanisms.

Evening light environments can be designed to consolidate and increase the duration of REM-sleep

Evening exposure to short-wavelength light has disruptive effects on circadian rhythms and sleep. These effects can be mitigated by blocking short-wavelength (blue) frequencies, which has led to the development of evening blue-depleted light environments (BDLEs). We have previously reported that residing 5 days in an evening BDLE, compared with residing in a normal indoor light environment of similar photopic lux, advances circadian rhythms and increases the duration of rapid eye movement (REM) sleep in a randomized cross-over trial with twelve healthy participants. The current study extends these findings by testing whether residing in the evening BDLE affects the consolidation and microstructure of REM sleep in the same sample. Evening BDLE significantly reduces the fragmentation of REM sleep (p = 0.0003), and REM sleep microarousals in (p = 0.0493) without significantly changing REM density or the latency to first REM sleep episode. Moreover, the increased accumulation of REM sleep is not at the expense of NREM stage 3 sleep. BDLE further has a unique effect on REM sleep fragmentation (p = 0.0479) over and above that of circadian rhythms phase-shift, indicating a non-circadian effect of BDLE. If these effects can be replicated in clinical populations, this may have a therapeutic potential in disorders characterized by fragmented REM sleep.

The Retinal Basis of Light Aversion in Neonatal Mice

Aversive responses to bright light (photoaversion) require signaling from the eye to the brain. Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) encode absolute light intensity and are thought to provide the light signals for photoaversion. Consistent with this, neonatal mice exhibit photoaversion before the developmental onset of image vision, and melanopsin deletion abolishes photoaversion in neonates. It is not well understood how the population of ipRGCs, which constitutes multiple physiologically distinct types (denoted M1-M6 in mouse), encodes light stimuli to produce an aversive response. Here, we provide several lines of evidence that M1 ipRGCs that lack the Brn3b transcription factor drive photoaversion in neonatal mice. First, neonatal mice lacking TRPC6 and TRPC7 ion channels failed to turn away from bright light, while two photon Ca2+ imaging of their acutely isolated retinas revealed reduced photosensitivity in M1 ipRGCs, but not other ipRGC types. Second, mice in which all ipRGC types except for Brn3b-negative M1 ipRGCs are ablated exhibited normal photoaversion. Third, pharmacological blockade or genetic knockout of gap junction channels expressed by ipRGCs, which reduces the light sensitivity of M2-M6 ipRGCs in the neonatal retina, had small effects on photoaversion only at the brightest light intensities. Finally, M1s were not strongly depolarized by spontaneous retinal waves, a robust source of activity in the developing retina that depolarizes all other ipRGC types. M1s therefore constitute a separate information channel between the neonatal retina and brain that could ensure behavioral responses to light but not spontaneous retinal waves.SIGNIFICANCE STATEMENT At an early stage of development, before the maturation of photoreceptor input to the retina, neonatal mice exhibit photoaversion. On exposure to bright light, they turn away and emit ultrasonic vocalizations, a cue to their parents to return them to the nest. Neonatal photoaversion is mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs), a small percentage of the retinal ganglion cell population that express the photopigment melanopsin and depolarize directly in response to light. This study shows that photoaversion is mediated by a subset of ipRGCs, called M1-ipRGCs. Moreover, M1-ipRGCs have reduced responses to retinal waves, providing a mechanism by which the mouse distinguishes light stimulation from developmental patterns of spontaneous activity.

Differential diagnosis and theories of pathophysiology of post-traumatic photophobia: A review

BACKGROUND: Photophobia is a common sensory symptom after traumatic brain injury (TBI) that may have a grave impact on a patient’s functional independence, neurorehabilitation, and activities of daily living. Post-TBI photophobia can be difficult to treat and the majority of patients can suffer chronically up to and beyond one year after their injury. OBJECTIVES: This review evaluates the current theories of the pathophysiology of photophobia and the most-common co-morbid etiologies of light sensitivity in TBI to help guide the differential diagnosis and individualized management of post-TBI photophobia. METHODS: Primary articles were found via PubMed and Google Scholar search of key terms including “photophobia” “light sensitivity” “photosensitivity” “photo-oculodynia” “intrinsically photosensitive retinal ganglion cells” “ipRGC” and “concussion” “brain injury” “dry eye”. Due to paucity of literature papers were reviewed from 1900 to present in English. RESULTS: Recent advances in understanding the pathophysiology of photophobia in dry eye and migraine and their connection to intrinsically photosensitive retinal ganglion cells (ipRGC) have revealed complex and multifaceted trigeminovascular and trigeminoautonomic pathways underlying photophobia. Patients who suffer a TBI often have co-morbidities like dry eye and migraine that may influence the patient’s photophobia. CONCLUSION: Post-traumatic photophobia is a complex multi-disciplinary complaint that can severely impact a patient’s quality of life. Exploration of underlying etiology may allow for improved treatment and symptomatic relief for these patients beyond tinted lenses alone.

Neurobiological and behavioral mechanisms of circadian rhythm disruption in bipolar disorder: A critical multi-disciplinary literature review and agenda for future research from the ISBD task force on chronobiology

AIM

Symptoms of bipolar disorder (BD) include changes in mood, activity, energy, sleep, and appetite. Since many of these processes are regulated by circadian function, circadian rhythm disturbance has been examined as a biological feature underlying BD. The International Society for Bipolar Disorders Chronobiology Task Force (CTF) was commissioned to review evidence for neurobiological and behavioral mechanisms pertinent to BD.

METHOD

Drawing upon expertise in animal models, biomarkers, physiology, and behavior, CTF analyzed the relevant cross-disciplinary literature to precisely frame the discussion around circadian rhythm disruption in BD, highlight key findings, and for the first time integrate findings across levels of analysis to develop an internally consistent, coherent theoretical framework.

RESULTS

Evidence from multiple sources implicates the circadian system in mood regulation, with corresponding associations with BD diagnoses and mood-related traits reported across genetic, cellular, physiological, and behavioral domains. However, circadian disruption does not appear to be specific to BD and is present across a variety of high-risk, prodromal, and syndromic psychiatric disorders. Substantial variability and ambiguity among the definitions, concepts and assumptions underlying the research have limited replication and the emergence of consensus findings.

CONCLUSIONS

Future research in circadian rhythms and its role in BD is warranted. Well-powered studies that carefully define associations between BD-related and chronobiologically-related constructs, and integrate across levels of analysis will be most illuminating.

Effect of light therapy on delirium in older patients with Alzheimer's disease-related dementia

Light therapy has been used as a non-pharmacologic treatment to modulate biorhythms in patients with mental and psychological conditions. These conditions include affective disorders and depression. Delirium is a syndrome characterized by an acute change in a patient's mental status. We hypothesized that light therapy might suppress delirium in patients with Alzheimer's disease (AD). A 4-week randomized controlled trial was conducted in which AD participants were randomly assigned to a treatment group or a control group. Delirium, defined by the Confusion Assessment Method (CAM), was evaluated at baseline and after 4 weeks. The Neuropsychiatric Inventory (NPI) and Zarit Caregiver Burden Interview (ZBI) were also conducted to assess the behavior of patients and the burden of their caregivers. For this study, 61 participants were initially recruited. A total of 34 and 27 participants were included in the treatment and control groups, respectively. After treatment with light therapy, the CAM score decreased during the second and fourth week. The NPI score in the therapy group also decreased during the second and fourth week. From the caregiver's perspective, after light therapy, the ZBI score significantly decreased during the second and fourth week. Compared with the control group, patients who underwent CAM and NPI assessments showed a small but significant improvement after 4 weeks of light therapy. In conclusion, a course of 4-week light therapy significantly suppressed delirium in patients with AD. The combined effects of light therapy and conventional treatment were superior to that of conventional treatment alone.

Feature Detection by Retinal Ganglion Cells

Retinal circuits transform the pixel representation of photoreceptors into the feature representations of ganglion cells, whose axons transmit these representations to the brain. Functional, morphological, and transcriptomic surveys have identified more than 40 retinal ganglion cell (RGC) types in mice. RGCs extract features of varying complexity; some simply signal local differences in brightness (i.e., luminance contrast), whereas others detect specific motion trajectories. To understand the retina, we need to know how retinal circuits give rise to the diverse RGC feature representations. A catalog of the RGC feature set, in turn, is fundamental to understanding visual processing in the brain. Anterograde tracing indicates that RGCs innervate more than 50 areas in the mouse brain. Current maps connecting RGC types to brain areas are rudimentary, as is our understanding of how retinal signals are transformed downstream to guide behavior. In this article, I review the feature selectivities of mouse RGCs, how they arise, and how they are utilized downstream. Not only is knowledge of the behavioral purpose of RGC signals critical for understanding the retinal contributions to vision; it can also guide us to the most relevant areas of visual feature space. Expected final online publication date for the Annual Review of Vision Science, Volume 8 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Adaptation and Pilot Study of a Behavioral Intervention Targeting Morning Activation Deficits in Dementia Caregivers: Scheduling Activity and Monitoring Mornings (SAMM)

OBJECTIVES

Morning activation deficits (MADs) correlate with depression symptom persistence in older dementia caregivers. To clarify the potential of MADs as a target for depression interventions, we aimed to: 1) adapt an existing behavioral activation program, Engage therapy, to target mornings; and 2) evaluate effects on self-reported MADs and depression symptoms.

METHODS

While trialing the 9-week Engage adaption (targeting mornings) in six older dementia caregivers, we incorporated feedback and finalized an adapted program called Scheduling Activity and Monitoring Mornings (SAMM). We delivered the SAMM protocol to 13 dementia caregivers (all female; mean age = 69, standard deviation = 7). We report modifications made/rationale, as well as changes in subjective MADs (relevant items from the Composite Scale of Morningness) and depression symptoms (Patient Health Questionnaire - 9).

RESULTS

Using caregiver and expert input, we adapted the protocol to: include educational materials/content describing the potential relationship between morning inactivity and depression; target activity scheduling within 2 hours of awakening (preferably earlier); and focus only on the main components of morning activity scheduling, planning, and monitoring. This program was associated with decreases in subjective MADs averaging 29% at week 4, 52% at week 6, and 57% by week 9 (all p's <0.005). Initial depression symptoms were significantly reduced, by 62%, at week 9.

CONCLUSIONS

These preliminary findings suggest that subjective MADs can be modified pragmatically, and that doing so may have antidepressant effects. A controlled trial with measures of the putative mechanism is needed to clarify whether, and if so how, targeting MAD with SAMM causally perturbs depression's mechanisms.

Influence of External Natural Environment Including Sunshine Exposure on Public Mental Health: A Systematic Review

The COVID-19 pandemic has been raging around the world and public health measures such as lockdowns have forced people to go out less often, reducing sunlight exposure time, green space use, and physical activity. It is well known that exercise has a positive impact on mental health, but the impact of external environmental factors such as sunlight exposure and green space use on mental health has not been systematically reviewed. In this review, we categorized the major factors that may affect people’s mental health into (1) external environmental factors such as exposure to sunlight and green spaces, (2) internal life factors such as physical activity and lifestyle, and (3) mixed external and internal factors, and systematically examined the relationship between each factor and people’s mental health. The results showed that exposure to sunlight, spending leisure time in green spaces, and physical activity each had a positive impact on people’s mental health, including depression, anxiety, and stress states. Specifically, moderate physical activity in an external environment with sunlight exposure or green space was found to be an important factor. The study found that exposure to the natural environment through sunbathing and exercise is important for people’s mental health.

The Effects of Light and the Circadian System on Rhythmic Brain Function

Life on earth has evolved under the influence of regularly recurring changes in the environment, such as the 24 h light/dark cycle. Consequently, organisms have developed endogenous clocks, generating 24 h (circadian) rhythms that serve to anticipate these rhythmic changes. In addition to these circadian rhythms, which persist in constant conditions and can be entrained to environmental rhythms, light drives rhythmic behavior and brain function, especially in nocturnal laboratory rodents. In recent decades, research has made great advances in the elucidation of the molecular circadian clockwork and circadian light perception. This review summarizes the role of light and the circadian clock in rhythmic brain function, with a focus on the complex interaction between the different components of the mammalian circadian system. Furthermore, chronodisruption as a consequence of light at night, genetic manipulation, and neurodegenerative diseases is briefly discussed.

Rapid-acting antidepressants and the circadian clock

A growing number of epidemiological and experimental studies has established that circadian disruption is strongly associated with psychiatric disorders, including major depressive disorder (MDD). This association is becoming increasingly relevant considering that modern lifestyles, social zeitgebers (time cues) and genetic variants contribute to disrupting circadian rhythms that may lead to psychiatric disorders. Circadian abnormalities associated with MDD include dysregulated rhythms of sleep, temperature, hormonal secretions, and mood which are modulated by the molecular clock. Rapid-acting antidepressants such as subanesthetic ketamine and sleep deprivation therapy can improve symptoms within 24 h in a subset of depressed patients, in striking contrast to conventional treatments, which generally require weeks for a full clinical response. Importantly, animal data show that sleep deprivation and ketamine have overlapping effects on clock gene expression. Furthermore, emerging data implicate the circadian system as a critical component involved in rapid antidepressant responses via several intracellular signaling pathways such as GSK3β, mTOR, MAPK, and NOTCH to initiate synaptic plasticity. Future research on the relationship between depression and the circadian clock may contribute to the development of novel therapeutic strategies for depression-like symptoms. In this review we summarize recent evidence describing: (1) how the circadian clock is implicated in depression, (2) how clock genes may contribute to fast-acting antidepressants, and (3) the mechanistic links between the clock genes driving circadian rhythms and neuroplasticity.

Ocular and extraocular roles of neuropsin in vertebrates

The ability to detect and adapt to different levels of ambient light is critical for animal survival. Light detection is the basis of vision, but light also regulates eye development and drives several non-image-forming functions, including synchronizing circadian rhythms to the daily light/dark cycle, restricting pupils in response to changes in light intensity, and modulating mood in response to light. Until the early 2000s, these functions were thought to be solely mediated by ocular photoreceptors. However, neuropsin (OPN5), a UV-sensitive opsin, has been receiving growing attention, as new methods have revealed previously unappreciated functions of OPN5. In fact, OPN5-mediated extraocular and deep-brain photoreception have recently been described for the first time in mammals. This review aims to synthesize current knowledge of the properties and functions of OPN5 across vertebrates.

The effect of ultraviolet radiation on the incidence and severity of major mental illness using birth month, birth year, and sunspot data

Background and objectives

The evaluation of the severity of patients afflicted with major mental illness (MMI) has been problematic because of confounding variables and genetic variability. There have been multiple studies that suggest several human diseases, especially schizophrenia, are predisposed to be born in certain months or seasons. This observation implied an epigenetic effect of sunlight, likely ultraviolet radiation (UVR), which is damaging to DNA, especially in an embryo. This paper outlines a method to evaluate the severity of schizophrenia (SZ), bipolar disorder (BPD), and schizoaffective disorder (SZ-AFF) using the month/year of birth of those affected compared to the month/year of birth of the general population (GP).

Relevance

Our previous research found that more intense UVR (equal to or greater than 90 sunspot number (SSN)) had a negative effect on the average human lifespan. Also, human birth rates vary in frequency by month of birth reflecting variables like availability of food, sunlight, and other unknown epigenetic factors. We wanted to see if the patient month of birth varied from the average birth months of the general population and if UVR has an epigenetic effect promoting these diseases.

Methods

We obtained the month and year of birth of 1,233 patients admitted over a 15-year period to Maine's largest state psychiatric hospital and counted the months of birth for each diagnosis of SZ, BPD, and SZ-AFF, and compared these results to the general population's birth months of 4,265,555 persons from U. S. Census Year 2006. The number of patients in each month was normalized to August and compared with the normalized birth months of the general population (GP). Plots of the normalized months were considered rates of change (e.g., derivatives) and their respective integrals gave domains of each mental illness relative to the GP. Normalizing the GP to unity was then related to the factor 1.28, e.g., 28% more entropy, deduced from the Sun's fractal dimension imprinted on biological organisms.

Results

The percent of patients meeting our criterion for severity: SZ = 27%; BPD = 26%; SZ-AFF = 100%.

Conclusions

High UVR intensity or a rapid increase in UVR in early gestation are likely epigenetic triggers of major mental illness. BPD is more epigenetically affected than SZ or SZ-AFF disorders. We found that 52% of 1,233 patients comprised the core function of a tertiary-care psychiatric hospital. Also, mental illness exacerbated when the median SSN doubled. This work also validates the Kraeplinian dichotomy.

What is new in this research

This paper offers a new paradigm for evaluating the severity of MMI and supports significant epigenetic effects from UVR.

Cannabidiol prevents depressive-like behaviors through the modulation of neural stem cell differentiation

Chronic stress impairs radial neural stem cell (rNSC) differentiation and adult hippocampal neurogenesis (AHN), whereas promoting AHN can increase stress resilience against depression. Therefore, investigating the mechanism of neural differentiation and AHN is of great importance for developing antidepressant drugs. The nonpsychoactive phytocannabinoid cannabidiol (CBD) has been shown to be effective against depression. However, whether CBD can modulate rNSC differentiation and hippocampal neurogenesis is unknown. Here, by using the chronic restraint stress (CRS) mouse model, we showed that hippocampal rNSCs mostly differentiated into astrocytes under stress conditions. Moreover, transcriptome analysis revealed that the FoxO signaling pathway was involved in the regulation of this process. The administration of CBD rescued depressive-like symptoms in CRS mice and prevented rNSCs overactivation and differentiation into astrocyte, which was partly mediated by the modulation of the FoxO signaling pathway. These results revealed a previously unknown neural mechanism for neural differentiation and AHN in depression and provided mechanistic insights into the antidepressive effects of CBD.

Adult Neurogenesis under Control of the Circadian System

The mammalian circadian system is a hierarchically organized system, which controls a 24-h periodicity in a wide variety of body and brain functions and physiological processes. There is increasing evidence that the circadian system modulates the complex multistep process of adult neurogenesis, which is crucial for brain plasticity. This modulatory effect may be exercised via rhythmic systemic factors including neurotransmitters, hormones and neurotrophic factors as well as rhythmic behavior and physiology or via intrinsic factors within the neural progenitor cells such as the redox state and clock genes/molecular clockwork. In this review, we discuss the role of the circadian system for adult neurogenesis at both the systemic and the cellular levels. Better understanding of the role of the circadian system in modulation of adult neurogenesis can help develop new treatment strategies to improve the cognitive deterioration associated with chronodisruption due to detrimental light regimes or neurodegenerative diseases.

Nighttime lights, urban features, household poverty, depression, and obesity

Nighttime Light Emission (NLE) is associated with diminished mental and physical health. The present study examines how NLE and associated urban features (e.g., air pollution, low green space) impact mental and physical wellbeing. We included 200,393 UK Biobank Cohort participants with complete data. The study was carried out in two steps. In Step1, we assessed the relationship between NLE, deprivation, pollution, green space, household poverty and mental and physical symptoms. In Step2, we examined the role of NLE on environment-symptom networks. We stratified participants into high and low NLE and used gaussian graphical model to identify nodes which bridged urban features and mental and physical health problems. We then compared the global strength of these networks in high vs low NLE. We found that higher NLE associated with higher air pollution, less green space, higher economic and neighborhood deprivation, higher household poverty and higher depressed mood, higher tiredness/lethargy and obesity (Rtraining_mean = 0.2624, P training_mean < .001; Rtest_mean = 0.2619, P test_mean < .001). We also found that the interaction between environmental risk factors and mental, physical problems (overall network connectivity) was higher in the high NLE network than in the low NLE network (t = 0.7896, P < .001). In areas with high NLE, economic deprivation, household poverty and waist circumference acted as bridge factors between the key urban features and mental health symptoms. In conclusion, NLE, urban features, household poverty and mental and physical symptoms are all interrelated. In areas with high NLE, urban features associate with mental and physical health problems at a greater magnitude than in areas with low NLE.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12144-022-02754-3.

Reading on a smartphone affects sigh generation, brain activity, and comprehension

Electronic devices have become an indispensable part of our daily lives, while their negative aspects have been reported. One disadvantage is that reading comprehension is reduced when reading from an electronic device; the cause of this deficit in performance is unclear. In this study, we investigated the cause for comprehension decline when reading on a smartphone by simultaneously measuring respiration and brain activity during reading in 34 healthy individuals. We found that, compared to reading on a paper medium, reading on a smartphone elicits fewer sighs, promotes brain overactivity in the prefrontal cortex, and results in reduced comprehension. Furthermore, reading on a smartphone affected sigh frequency but not normal breathing, suggesting that normal breathing and sigh generation are mediated by pathways differentially influenced by the visual environment. A path analysis suggests that the interactive relationship between sigh inhibition and overactivity in the prefrontal cortex causes comprehension decline. These findings provide new insight into the respiration-mediated mechanisms of cognitive function.

Circadian Influences on the Habenula and Their Potential Contribution to Neuropsychiatric Disorders

The neural circadian system consists of the master circadian clock in the hypothalamic suprachiasmatic nuclei (SCN) communicating time of day cues to the rest of the body including other brain areas that also rhythmically express circadian clock genes. Over the past 16 years, evidence has emerged to indicate that the habenula of the epithalamus is a candidate extra-SCN circadian oscillator. When isolated from the SCN, the habenula sustains rhythms in clock gene expression and neuronal activity, with the lateral habenula expressing more robust rhythms than the adjacent medial habenula. The lateral habenula is responsive to putative SCN output factors as well as light information conveyed to the perihabenula area. Neuronal activity in the lateral habenula is altered in depression and intriguingly disruptions in circadian rhythms can elevate risk of developing mental health disorders including depression. In this review, we will principally focus on how circadian and light signals affect the lateral habenula and evaluate the possibility that alteration in these influences contribute to mental health disorders.

The Suprachiasmatic Nucleus Regulates Anxiety-Like Behavior in Mice

Individuals suffering from mood and anxiety disorders often show significant disturbances in sleep and circadian rhythms. Animal studies indicate that circadian rhythm disruption can cause increased depressive- and anxiety-like behavior, but the underlying mechanisms are unclear. One potential mechanism to explain how circadian rhythms are contributing to mood and anxiety disorders is through dysregulation of the suprachiasmatic nucleus (SCN) of the hypothalamus, known as the "central pacemaker." To investigate the role of the SCN in regulating depressive- and anxiety-like behavior in mice, we chronically manipulated the neural activity of the SCN using two optogenetic stimulation paradigms. As expected, chronic stimulation of the SCN late in the active phase (circadian time 21, CT21) resulted in a shortened period and dampened amplitude of homecage activity rhythms. We also repeatedly stimulated the SCN at unpredictable times during the active phase of mice when SCN firing rates are normally low. This resulted in dampened, fragmented, and unstable homecage activity rhythms. In both chronic SCN optogenetic stimulation paradigms, dampened homecage activity rhythms (decreased amplitude) were directly correlated with increased measures of anxiety-like behavior. In contrast, we only observed a correlation between behavioral despair and homecage activity amplitude in mice stimulated at CT21. Surprisingly, the change in period of homecage activity rhythms was not directly associated with anxiety- or depressive-like behavior. Finally, to determine if anxiety-like behavior is affected during a single SCN stimulation session, we acutely stimulated the SCN in the active phase (zeitgeber time 14-16, ZT14-16) during behavioral testing. Unexpectedly this also resulted in increased anxiety-like behavior. Taken together, these results indicate that SCN-mediated dampening of rhythms is directly correlated with increased anxiety-like behavior. This work is an important step in understanding how specific SCN neural activity disruptions affect depressive- and anxiety-related behavior.

Multi-Level Processes and Retina-Brain Pathways of Photic Regulation of Mood

Light exerts powerful biological effects on mood regulation. Whereas the source of photic information affecting mood is well established at least via intrinsically photosensitive retinal ganglion cells (ipRGCs) secreting the melanopsin photopigment, the precise circuits that mediate the impact of light on depressive behaviors are not well understood. This review proposes two distinct retina–brain pathways of light effects on mood: (i) a suprachiasmatic nucleus (SCN)-dependent pathway with light effect on mood via the synchronization of biological rhythms, and (ii) a SCN-independent pathway with light effects on mood through modulation of the homeostatic process of sleep, alertness and emotion regulation: (1) light directly inhibits brain areas promoting sleep such as the ventrolateral preoptic nucleus (VLPO), and activates numerous brain areas involved in alertness such as, monoaminergic areas, thalamic regions and hypothalamic regions including orexin areas; (2) moreover, light seems to modulate mood through orexin-, serotonin- and dopamine-dependent pathways; (3) in addition, light activates brain emotional processing areas including the amygdala, the nucleus accumbens, the perihabenular nucleus, the left hippocampus and pathways such as the retina–ventral lateral geniculate nucleus and intergeniculate leaflet–lateral habenula pathway. This work synthetizes new insights into the neural basis required for light influence mood

Pilot Study of the Effects of Bright Ambient Therapy on Dementia Symptoms and Cognitive Function

Light therapy potentially improves dementia symptoms. In this study, we examined the effects of bright light therapy on neuropsychiatric behaviors and cognitive function. Thirty-five participants were assigned to either the experimental or comparison group. The experimental group was exposed to bright light at 2,500 lux, and the comparison group was exposed to 114–307 lux. The instruments used were the Neuropsychiatric Inventory and the Mini-Mental State Examination. The experimental group showed a significant improvement in Neuropsychiatric Inventory scores; these scores, which were calculated using generalized estimating equations with medication (benzodiazepines) as a covariate, were reduced by 65% (P < 0.001) and 78% (P = 0.001) by the 5th and 9th weeks, respectively. At the same time, Mini-Mental State Examination scores increased by 19% (P = 0.007) and 28% (P = 0.04), respectively. However, differences in outcomes between the 5th and 9th weeks were not significant. A 4-week regimen of bright light therapy was the most effective, with higher adherence and acceptability.

Rodent models in translational circadian photobiology

Over the last decades remarkable advances have been made in the understanding of the photobiology of circadian rhythms. The identification of a third photoreceptive system in the mammalian eye, in addition to the rods and cones that mediate vision, has transformed our appreciation of the role of light in regulating physiology and behavior. These photosensitive retinal ganglion cells (pRGCs) express the blue-light sensitive photopigment melanopsin and project to the suprachiasmatic nuclei (SCN)-the master circadian pacemaker-as well as many other brain regions. Much of our understanding of the fundamental mechanisms of the pRGCs, and the processes that they regulate, comes from mouse and other rodent models. Here we describe the contribution of rodent models to circadian photobiology, including both their strengths and limitations. In addition, we discuss how an appreciation of both rodent and human data is important for translational circadian photobiology. Such an approach enables a bi-directional flow of information whereby an understanding of basic mechanisms derived from mice can be integrated with studies from humans. Progress in this field is being driven forward at several levels of analysis, not least by the use of personalized light measurements and photoreceptor specific stimuli in human studies, and by studying the impact of environmental, rather than laboratory, lighting on different rodent models.

Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes: A cross-sectional and longitudinal study in over 400,000 UK Biobank participants

BACKGROUND

Light has powerful effects on mood, sleep, and the circadian system. Humans evolved in an environment with a clear distinction between day and night, but our modern environments have blurred this distinction. Negative effects of light exposure at night have been well characterized. The importance of daytime light exposure has been less well characterized. Here we examine the cross-sectional and longitudinal associations of time spent in daytime outdoor light with mood, sleep, and circadian-related outcomes.

METHODS

Participants were drawn from the UK Biobank cohort, a large study of UK adults (n = 502,000; 37-73 years old; 54% women).

RESULTS

UK Biobank participants reported spending a median of 2.5 daylight hours (IQR = 1.5-3.5 h) outdoors per day. Each additional hour spent outdoors during the day was associated with lower odds of lifetime major depressive disorder (95% CI OR:0.92-0.98), antidepressant usage (OR:0.92-0.98), less frequent anhedonia (OR:0.93-0.96) and low mood (OR:0.87-0.90), greater happiness (OR:1.41-1.48) and lower neuroticism (incident rate ratio, IRR:0.95-0.96), independent of demographic, lifestyle, and employment covariates. In addition, each hour of daytime light was associated with greater ease of getting up (OR:1.46-1.49), less frequent tiredness (OR:0.80-0.82), fewer insomnia symptoms (OR:0.94-0.97), and earlier chronotype (adjusted odds ratio; OR:0.75-0.77). Auto-Regressive Cross-Lagged (ARCL) models were used to examine the longitudinal association of time spent in outdoor light at baseline with later mood-, sleep- and circadian-related outcomes reported at time point 2. Overall, longitudinal associations support cross-sectional findings, though generally with smaller effect sizes.

LIMITATIONS

Future studies that examine the intensity of daytime light exposure at the ocular level are needed.

CONCLUSIONS

Our findings suggest that low daytime light exposure is an important environmental risk factor for mood, sleep, and circadian-related outcomes.

Melanopsin phototransduction: beyond canonical cascades

Melanopsin is a visual pigment that is expressed in a small subset of intrinsically photosensitive retinal ganglion cells (ipRGCs). It is involved in regulating non-image forming visual behaviors, such as circadian photoentrainment and the pupillary light reflex, while also playing a role in many aspects of image-forming vision, such as contrast sensitivity. Melanopsin was initially discovered in the melanophores of the skin of the frog Xenopus, and subsequently found in a subset of ganglion cells in rat, mouse and primate retinas. ipRGCs were initially thought to be a single retinal ganglion cell population, and melanopsin was thought to activate a single, invertebrate-like Gq/transient receptor potential canonical (TRPC)-based phototransduction cascade within these cells. However, in the 20 years since the discovery of melanopsin, our knowledge of this visual pigment and ipRGCs has expanded dramatically. Six ipRGC subtypes have now been identified in the mouse, each with unique morphological, physiological and functional properties. Multiple subtypes have also been identified in other species, suggesting that this cell type diversity is a general feature of the ipRGC system. This diversity has led to a renewed interest in melanopsin phototransduction that may not follow the canonical Gq/TRPC cascade in the mouse or in the plethora of other organisms that express the melanopsin photopigment. In this Review, we discuss recent findings and discoveries that have challenged the prevailing view of melanopsin phototransduction as a single pathway that influences solely non-image forming functions.

The circadian clock in the mouse habenula is set by catecholamines

Circadian rhythms are those variations in behavioral and molecular processes of organisms that follow roughly 24 h cycles in the absence of any external cue. The hypothalamic suprachiasmatic nucleus (SCN) harbors the principal brain pacemaker driving circadian rhythms. The epithalamic habenula (Hb) contains a self-sustained circadian clock functionally coupled to the SCN. Anatomically, the Hb projects to the midbrain dopamine (DA) and serotonin (5-HT) systems, and it receives inputs from the forebrain, midbrain, and brainstem. The SCN is set by internal signals such as 5-HT or melatonin from the raphe nuclei and pineal gland, respectively. However, how the Hb clock is set by internal cues is not well characterized. Hence, in the present study, we determined whether DA, noradrenaline (NA), 5-HT, and the neuropeptides orexin (ORX) and vasopressin influence the Hb circadian clock. Using PER2::Luciferase transgenic mice, we found that the amplitude of the PER2 protein circadian oscillations from Hb explants was strongly affected by DA and NA. Importantly, these effects were dose-and region (rostral vs. caudal) dependent for NA, with a main effect in the caudal part of the Hb. Furthermore, ORX also induced a significant change in the amplitude of PER2 protein oscillations in the caudal Hb. In conclusion, catecholaminergic (DA, NA) and ORXergic transmission impacts the clock properties of the Hb clock likely contributing to the circadian regulation of motivated behaviors. Accordingly, pathological conditions that lead in alterations of catecholamine or ORX activity (drug intake, compulsive feeding) might affect the Hb clock and conduct to circadian disturbances.

Light therapy improved depression-like behavior induced by chronic unpredictable mild stress in Mongolian gerbils

Progress has been made in elucidating the mechanism by which light modulates depressive-like behaviors. However, almost all of these studies ignore an important issue, namely, that examining the effects of light therapy in nocturnal animals may be difficult because the influences of light on behavioral responses differ between nocturnal and diurnal animals. To date, few diurnal rodents have been utilized to establish animal models that closely mimic clinical depression. Herein, the chronic unpredictable mild stress model, which is the most representative, reliable, and effective rodent model of depression, was implemented in diurnal Mongolian gerbils for the first time. The gerbils were subjected to two hours of light therapy or fluoxetine treatment for 2 weeks. Our work revealed that Mongolian gerbils subjected to chronic unpredictable mild stress showed depression-like behaviors. Interestingly, we also found that light therapy improved anhedonic behavior more effectively than fluoxetine after two weeks of treatment. In summary, our study is the first to use diurnal Mongolian gerbils, which have the same circadian rhythm as humans, to establish an effective, economical, and practical animal model of depression and confirmed that light therapy could improve depression-like behavior more effectively than fluoxetine to some extent in diurnal Mongolian gerbils, which establishes a good foundation for clarifying the neural mechanism of light therapy for depression.

Iterative Metaplasticity Across Timescales: How Circadian, Ultradian, and Infradian Rhythms Modulate Memory Mechanisms

Work in recent years has provided strong evidence for the modulation of memory function and neuroplasticity mechanisms across circadian (daily), ultradian (shorter-than-daily), and infradian (longer-than-daily) timescales. Despite rapid progress, however, the field has yet to adopt a general framework to describe the overarching role of biological rhythms in memory. To this end, Iyer and colleagues introduced the term iterative metaplasticity, which they define as the "gating of receptivity to subsequent signals that repeats on a cyclic timebase." The central concept is that the cyclic regulation of molecules involved in neuroplasticity may produce cycles in neuroplastic capacity-that is, the ability of neural cells to undergo activity-dependent change. Although Iyer and colleagues focus on the circadian timescale, we think their framework may be useful for understanding how biological rhythms influence memory more broadly. In this review, we provide examples and terminology to explain how the idea of iterative metaplasticity can be readily applied across circadian, ultradian, and infradian timescales. We suggest that iterative metaplasticity may not only support the temporal niching of neuroplasticity processes but also serve an essential role in the maintenance of memory function.

Deletion of AMPA receptor GluA1 subunit gene (Gria1) causes circadian rhythm disruption and aberrant responses to environmental cues

Dysfunction of the glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 subunit and deficits in synaptic plasticity are implicated in schizophrenia and sleep and circadian rhythm disruption. To investigate the role of GluA1 in circadian and sleep behaviour, we used wheel-running, passive-infrared, and video-based home-cage activity monitoring to assess daily rest-activity profiles of GluA1-knockout mice (Gria1-/-). We showed that these mice displayed various circadian abnormalities, including misaligned, fragmented, and more variable rest-activity patterns. In addition, they showed heightened, but transient, behavioural arousal to light→dark and dark→light transitions, as well as attenuated nocturnal-light-induced activity suppression (negative masking). In the hypothalamic suprachiasmatic nuclei (SCN), nocturnal-light-induced cFos signals (a molecular marker of neuronal activity in the preceding ~1-2 h) were attenuated, indicating reduced light sensitivity in the SCN. However, there was no change in the neuroanatomical distribution of expression levels of two neuropeptides-vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP)-differentially expressed in the core (ventromedial) vs. shell (dorsolateral) SCN subregions and both are known to be important for neuronal synchronisation within the SCN and circadian rhythmicity. In the motor cortex (area M1/M2), there was increased inter-individual variability in cFos levels during the evening period, mirroring the increased inter-individual variability in locomotor activity under nocturnal light. Finally, in the spontaneous odour recognition task GluA1 knockouts' short-term memory was impaired due to enhanced attention to the recently encountered familiar odour. These abnormalities due to altered AMPA-receptor-mediated signalling resemble and may contribute to sleep and circadian rhythm disruption and attentional deficits in different modalities in schizophrenia.

How Smart Is It to Go to Bed with the Phone? The Impact of Short-Wavelength Light and Affective States on Sleep and Circadian Rhythms

Previously, we presented our preliminary results (N = 14) investigating the effects of short-wavelength light from a smartphone during the evening on sleep and circadian rhythms (Höhn et al., 2021). Here, we now demonstrate our full sample (N = 33 men), where polysomnography and body temperature were recorded during three experimental nights and subjects read for 90 min on a smartphone with or without a filter or from a book. Cortisol, melatonin and affectivity were assessed before and after sleep. These results confirm our earlier findings, indicating reduced slow-wave-sleep and -activity in the first night quarter after reading on the smartphone without a filter. The same was true for the cortisol-awakening-response. Although subjective sleepiness was not affected, the evening melatonin increase was attenuated in both smartphone conditions. Accordingly, the distal-proximal skin temperature gradient increased less after short-wavelength light exposure than after reading a book. Interestingly, we could unravel within this full dataset that higher positive affectivity in the evening predicted better subjective but not objective sleep quality. Our results show disruptive consequences of short-wavelength light for sleep and circadian rhythmicity with a partially attenuating effect of blue-light filters. Furthermore, affective states influence subjective sleep quality and should be considered, whenever investigating sleep and circadian rhythms.

Comparative Efficacy of Multiple Therapies for the Treatment of Patients With Subthreshold Depression: A Systematic Review and Network Meta-Analysis

Background: Subthreshold depression (SD) is considered to be the precursor stage of major depression, which is correlated with functional impairment and increased suicide rate. Although there are multiple therapies for the treatment of SD, the comparison and efficacy of various methods has yet to be evaluated. This study aimed to evaluate the efficacy of different therapies by performing a Bayesian network meta-analysis.

Methods: We searched eight databases on April 3, 2021. Center for Epidemiologic Studies Depression Scale (CES-D), Beck Depression Inventory scale (BDI), the Patient Health Questionnaire-9 (PHQ-9), and the Kessler Screening Scale for Psychological Distress (K-6) were used as efficacy outcomes. This Bayesian network meta-analysis used a fixed-effects model.

Findings: Twenty-one randomized controlled trials involving 5,048 participants were included in this study. The results suggested that electroacupuncture (MD −12.00, 95% CrI −15.00, −10.00), conventional acupuncture plus wheat-grain moxibustion (MD −9.70, 95% CrI −14.00, −5.30), and the Chinese traditional peripateticism pill plus group counseling (MD −9.00, 95% CrI −11.00, −6.70) had better efficacy than the control group (CG) in improving CES-D. For BDI outcome, bright light therapy (MD −9.70, 95% CrI −13.00, −6.00), behavioral activation program (MD −5.70, 95% CrI −6.10, −5.40), and dim light therapy (MD −6.30, 95% CrI −10.00, −2.20) were better than the CG. Tai chi (MD −3.00, 95% CrI −4.00, −2.00) was better than CG for PHQ-9 outcomes. Telephone-based cognitive behavioral treatment (MD −2.50 95% CrI −2.70, −2.30) was better than the CG for K-6 scores.

Conclusion: Our results suggest that electroacupuncture or bright light therapy appear to be the better choices in the treatment of SD. This study provide new insights into clinical treatment selection and may aid the development of guidelines for the management of SD.

Ambient bright lighting in the morning improves sleep disturbances of older adults with dementia

BACKGROUND

Ambient light therapies are potentially effective in improving sleep disturbances and circadian rhythms. This study created a new lighting intervention model for elderly patients with dementia. It is hypothesized that exposure to bright ambient light in the morning is more effective than general lighting in improving sleep disturbances and circadian rhythms.

METHODS

A single-blind longitudinal-group experimental design was employed. The dementia participants came from the community and nursing homes. Those in the experimental group were exposed to ambient light at 2500 lux, and those in the comparison group were exposed to 114-307 lux. The corresponding sleep disturbances and circadian rhythms were determined using an accelerometer (XA-5). A longitudinal experimental design was adopted to observe the time to an effective response.

RESULTS

The covariates of benzodiazepine use and total activity during the day were analyzed using generalized estimating equations. The experimental group showed significant sleep efficiency improvement, with mean increases of 41.9% (P < 0.001) and 31.7% (P = 0.002), sleep time increases of 141 min (P = 0.001) and 135 min (P = 0.008), awakening time decreases of 116 min (P = 0.001) and 108 min (P = 0.002), and sleep onset advancements of 60-84 min/sleep offset delays of 57-79 min upon the fifth and ninth week, respectively. A 4-week bright ambient light intervention was the most effective.

CONCLUSIONS

This study found that bright ambient light in the morning is beneficial for improving sleep disturbances and was driven by stabilizing circadian rhythms.

Spectral tuning and deactivation kinetics of marine mammal melanopsins

In mammals, the photopigment melanopsin (Opn4) is found in a subset of retinal ganglion cells that serve light detection for circadian photoentrainment and pupil constriction (i.e., mydriasis). For a given species, the efficiency of photoentrainment and length of time that mydriasis occurs is determined by the spectral sensitivity and deactivation kinetics of melanopsin, respectively, and to date, neither of these properties have been described in marine mammals. Previous work has indicated that the absorbance maxima (λmax) of marine mammal rhodopsins (Rh1) have diversified to match the available light spectra at foraging depths. However, similar to the melanopsin λmax of terrestrial mammals (~480 nm), the melanopsins of marine mammals may be conserved, with λmax values tuned to the spectrum of solar irradiance at the water's surface. Here, we investigated the Opn4 pigments of 17 marine mammal species inhabiting diverse photic environments including the Infraorder Cetacea, as well as the Orders Sirenia and Carnivora. Both genomic and cDNA sequences were used to deduce amino acid sequences to identify substitutions most likely involved in spectral tuning and deactivation kinetics of the Opn4 pigments. Our results show that there appears to be no amino acid substitutions in marine mammal Opn4 opsins that would result in any significant change in λmax values relative to their terrestrial counterparts. We also found some marine mammal species to lack several phosphorylation sites in the carboxyl terminal domain of their Opn4 pigments that result in significantly slower deactivation kinetics, and thus longer mydriasis, compared to terrestrial controls. This finding was restricted to cetacean species previously found to lack cone photoreceptor opsins, a condition known as rod monochromacy. These results suggest that the rod monochromat whales rely on extended pupillary constriction to prevent photobleaching of the highly photosensitive all-rod retina when moving between photopic and scotopic conditions.

Dim light in the evening causes coordinated realignment of circadian rhythms, sleep, and short-term memory

In modern societies, people are regularly exposed to artificial light (e.g., light-emitting electronic devices). Dim light in the evening (DLE) imposes an artificial extension of the solar day, increasing our alertness before bedtime, delaying melatonin timing and sleep onset, and increasing sleepiness in the next morning. Using laboratory mice as a model organism, we show that 2 wk of 4-h, 20-lux DLE postpones rest–activity rhythms, delays molecular rhythms in the brain and body, and reverses the diurnal pattern of short-term memory performance. These results highlight the biological impact of DLE and emphasize the need to optimize our evening light exposure if we are to avoid shifting our biological clocks.

Light provides the primary signal for entraining circadian rhythms to the day/night cycle. In addition to rods and cones, the retina contains a small population of photosensitive retinal ganglion cells (pRGCs) expressing the photopigment melanopsin (OPN4). Concerns have been raised that exposure to dim artificial lighting in the evening (DLE) may perturb circadian rhythms and sleep patterns, and OPN4 is presumed to mediate these effects. Here, we examine the effects of 4-h, 20-lux DLE on circadian physiology and behavior in mice and the role of OPN4 in these responses. We show that 2 wk of DLE induces a phase delay of ∼2 to 3 h in mice, comparable to that reported in humans. DLE-induced phase shifts are unaffected in Opn4^−/− mice, indicating that rods and cones are capable of driving these responses in the absence of melanopsin. DLE delays molecular clock rhythms in the heart, liver, adrenal gland, and dorsal hippocampus. It also reverses short-term recognition memory performance, which is associated with changes in preceding sleep history. In addition, DLE modifies patterns of hypothalamic and cortical cFos signals, a molecular correlate of recent neuronal activity. Together, our data show that DLE causes coordinated realignment of circadian rhythms, sleep patterns, and short-term memory process in mice. These effects are particularly relevant as DLE conditions―due to artificial light exposure―are experienced by the majority of the populace on a daily basis.

Chemogenetic activation of nigrostriatal dopamine neurons in freely moving common marmosets

To interrogate particular neuronal pathways in nonhuman primates under natural and stress-free conditions, we applied designer receptors exclusively activated by designer drugs (DREADDs) technology to common marmosets. We injected adeno-associated virus vectors expressing the excitatory DREADD hM3Dq into the unilateral substantia nigra (SN) in four marmosets. Using multi-tracer positron emission tomography imaging, we detected DREADD expression in vivo, which was confirmed in nigrostriatal dopamine neurons by immunohistochemistry, as well as by assessed activation of the SN following agonist administration. The marmosets rotated in a contralateral direction relative to the activated side 30-90 min after consuming food containing the highly potent DREADD agonist deschloroclozapine (DCZ) but not on the following days without DCZ. These results indicate that non-invasive and reversible DREADD manipulation will extend the utility of marmosets as a primate model for linking neuronal activity and natural behavior in various contexts.

Distinct Opsin 3 (Opn3) Expression in the Developing Nervous System during Mammalian Embryogenesis

Opsin 3 (Opn3) is highly expressed in the adult brain, however, information for spatial and temporal expression patterns during embryogenesis is significantly lacking. Here, an Opn3-eGFP reporter mouse line was used to monitor cell body expression and axonal projections during embryonic and early postnatal to adult stages. By applying 2D and 3D fluorescence imaging techniques, we have identified the onset of Opn3 expression, which predominantly occurred during embryonic stages, in various structures during brain/head development. In addition, this study defines over twenty Opn3-eGFP-positive neural structures never reported before. Opn3-eGFP was first observed at E9.5 in neural regions, including the ganglia that will ultimately form the trigeminal, facial and vestibulocochlear cranial nerves (CNs). As development proceeds, expanded Opn3-eGFP expression coincided with the formation and maturation of critical components of the central and peripheral nervous systems (CNS, PNS), including various motor-sensory tracts, such as the dorsal column-medial lemniscus (DCML) sensory tract, and olfactory, acoustic, and optic tracts. The widespread, yet distinct, detection of Opn3-eGFP already at early embryonic stages suggests that Opn3 might play important functional roles in the developing brain and spinal cord to regulate multiple motor and sensory circuitry systems, including proprioception, nociception, ocular movement, and olfaction, as well as memory, mood, and emotion. This study presents a crucial blueprint from which to investigate autonomic and cognitive opsin-dependent neural development and resultant behaviors under physiological and pathophysiological conditions.

[Intrinsically photosensitive retinal ganglion cells]

Hintergrund

Melanopsin exprimierende, intrinsisch-photosensitive retinale Ganglienzellen (ipRGCs) bilden neben Stäbchen und Zapfen die dritte Klasse von retinalen Photorezeptoren. Diese kleine, heterogene Zellfamilie vermittelt ein weites Spektrum an Aufgaben überwiegend des nicht-bildformenden Sehens.

Fragestellung

Diese Arbeit soll einen Einblick in das aktuelle Verständnis der Funktion und der funktionellen Diversität der ipRGCs geben sowie klinisch und translational relevante Aspekte beleuchten.

Material und Methoden

Narrative Übersichtsarbeit.

Ergebnisse

ipRGCs machen etwa 1–2 % aller retinalen Ganglienzellen aus und bilden dabei 6 spezialisierte Subtypen. Mit ihrem Photopigment Melanopsin sind sie in der Lage, unabhängig von synaptischem Input Lichtinformationen an das Gehirn weiterzuleiten oder lichtabhängig zu modifizieren. Je nach Subtyp vermitteln sie so nichtvisuelle Aufgaben wie die Synchronisation der inneren Uhr oder den Pupillenreflex, greifen aber auch in das bildformende System ein. ipRGCs weisen eine differenzielle Widerstandskraft gegenüber Optikusschädigung auf, was sie zu einem attraktiven Studienobjekt für die Entwicklung neuroprotektiver Therapieansätze macht. Melanopsin rückt zudem als optogenetisches Werkzeug, etwa in der prosthetischen Gentherapie, in den Fokus.

Schlussfolgerungen

Häufige klinische Beobachtungen lassen sich nur mit Kenntnis des ipRGC-Systems verstehen. Ihre neuronale Vernetzung und die intrazelluläre Signalverarbeitung sind Gegenstand aktiver Forschung, die neue translationale Ansätze hervorbringt.

Melanopsin-driven pupil response in summer and winter in unipolar seasonal affective disorder

A retinal subsensitivity to environmental light may trigger Seasonal Affective Disorder (SAD) under low wintertime light conditions. The main aim of this study was to assess the responses of melanopsin-containing retinal ganglion cells in participants (N= 65) diagnosed with unipolar SAD compared to controls with no history of depression. Participants attended a summer visit, a winter visit, or both. Retinal responses to light were measured using the post-illumination pupil response (PIPR) to assess melanopsin-driven responses in the non-visual light input pathway. Linear mixed-effects modeling was used to test a group*season interaction on the Net PIPR (red minus blue light response, percent baseline). We observed a significant group*season interaction such that the PIPR decreased from summer to winter significantly in the SAD group while not in the control group. The SAD group PIPR was significantly lower in winter compared to controls but did not differ between groups in summer. Only 60% of the participants underwent an eye health exam, although all participants reported no history of retinal pathology, and eye exam status was neither associated with outcome nor different between groups. This seasonal variation in melanopsin driven non-visual responses to light may be a risk factor for SAD, and further highlights individual differences in responses to light for direct or indirect effects of light on mood.

Light therapy for seasonal affective disorder in visual impairment and blindness - a pilot study

OBJECTIVE

Seasonal and non-seasonal depression are prevalent conditions in visual impairment (VI). We assessed the effects and side effects of light therapy in persons with severe VI/blindness who experienced recurrent depressive symptoms in winter corresponding to seasonal affective disorder (SAD) or subsyndromal SAD (sSAD).

RESULTS

We included 18 persons (11 with severe VI, 3 with light perception and 4 with no light perception) who met screening criteria for sSAD/SAD in a single-arm, assessor-blinded trial of 6 weeks light therapy. In the 12 persons who completed the 6 weeks of treatment, the post-treatment depression score was reduced (p < 0.001), and subjective wellbeing (p = 0.01) and sleep quality were improved (p = 0.03). In 6/12 participants (50%), the post-treatment depression score was below the cut-off set for remission. In four participants with VI, side effects (glare or transiently altered visual function) led to dropout or exclusion.

CONCLUSION

Light therapy was associated with a reduction in depressive symptoms in persons with severe VI/blindness. Eye safety remains a concern in persons with residual sight.

Temporal vision: measures, mechanisms and meaning

Time is largely a hidden variable in vision. It is the condition for seeing interesting things such as spatial forms and patterns, colours and movements in the external world, and yet is not meant to be noticed in itself. Temporal aspects of visual processing have received comparatively little attention in research. Temporal properties have been made explicit mainly in measurements of resolution and integration in simple tasks such as detection of spatially homogeneous flicker or light pulses of varying duration. Only through a mechanistic understanding of their basis in retinal photoreceptors and circuits can such measures guide modelling of natural vision in different species and illuminate functional and evolutionary trade-offs. Temporal vision research would benefit from bridging traditions that speak different languages. Towards that goal, I here review studies from the fields of human psychophysics, retinal physiology and neuroethology, with a focus on fundamental constraints set by early vision.

Summary: Simple measures of temporal vision such as the critical flicker frequency can be useful for modelling natural vision only if their relationship to photoreceptor responses and retinal processing is understood.

The effects of bright light treatment on affective symptoms in people with dementia: a 24-week cluster randomized controlled trial

BACKGROUND

The majority of people with dementia have behavioral and psychological symptoms of dementia (BPSD), including depression, anxiety and agitation. These may be elicited or aggravated by disrupted circadian rhythms. Bright light treatment (BLT) is a promising non-pharmacological approach to the management of BPSD, but previous research has yielded mixed results.

METHODS

Eight nursing home dementia units (1 unit = 1 cluster) with 78 patients were invited to participate in a cluster randomized controlled trial from September 2017 to April 2018 investigating the effects of BLT on sleep and circadian rhythms (primary outcome) and BPSD (secondary outcome). Ceiling mounted LED-panels were installed in the intervention group (four units), providing light at 1000 lx and 6000 K (vertically at 1.2 m) between 10 a.m. and 3 p.m., with lower values in the mornings and evenings. Standard indoor light was used in the control group (four units). BPSD were assessed with The Cornell Scale for Depression in Dementia (CSDD) and the Neuropsychiatric Inventory Nursing Home Version (NPI-NH). Data collection took place at baseline and after 8, 16 and 24 weeks. Multilevel regression models with and without false discovery rate correction were used for the analysis, with baseline values and dementia stage entered as covariates.

RESULTS

Sixty-nine patients were included in the study at baseline. Compared to the control group, the intervention group had a larger reduction on the composite scores of both the CSDD (95% CI = - 6.0 - - 0.3) and the NPI-NH (95% CI = - 2.2 - - 0.1), as well as on the NPI-NH Affect sub-syndrome, and the CSDD Mood related signs sub-scale at follow-up after 16 weeks. With FDR correction, the group difference was significant on the CSDD Mood related signs sub-scale (95% CI = - 2.7 - - 0.8) and the NPI-NH Affect sub-syndrome (95% CI = - 1.6 - - 0.2). No differences were found between conditions at weeks 8 or 24.

CONCLUSION

Compared to the control condition, affective symptoms were reduced after 16 weeks in the group receiving BLT, suggesting BLT may be beneficial for nursing home patients with dementia.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03357328 . Retrospectively registered on November 29, 2017.

Effect of lighting illuminance and colour temperature on mental workload in an office setting

The mental workload of subjects was tested under different lighting conditions, with colour temperatures ranging from 3000 to 6500 K and illuminance ranging from 300 to 1000 lx. We used both psychological and physiological responses for evaluation. The former was based on NASA Task Load Index (NASA-TLX, NASA), and the latter was based on the electroencephalogram (EEG) P3b analysis of event-related potentials using the “oddball” paradigm experimental task. The results show that as illuminance increases, and the response time becomes longer with a colour temperature of 3000 K (P < 0.01). However, when the colour temperature is set at 6500 K, the response time becomes shorter as the illuminance increases (P < 0.01). P3b amplitudes were significantly affected by colour temperature (P = 0.009) and illuminance (P = 0.038) levels. The highest amplitudes occurred at 3000 K and 750 lx, which is consistent with the trend shown by the subjective scale. The data analysis of error rates is not significant. These results suggest that an office environment with a colour temperature of 3000 K and illumination of 750 lx, which exerts the lowest mental workload, is the most suitable for working. However, the interaction between colour temperature and illuminance in affecting the mental workload of participants is not clear. This work provides more appropriate lighting choices with colour temperature and illuminance to reduce people’s mental workload in office settings.

Opsins outside the eye and the skin: a more complex scenario than originally thought for a classical light sensor

Since the discovery of melanopsin as a retinal non-visual photopigment, opsins have been described in several organs and cells. This distribution is strikingly different from the classical localization of photopigments in light-exposed tissues such as the eyes and the skin. More than 10 years ago, a new paradigm in the field was created as opsins were shown, to detect not only light, but also thermal energy in Drosophila. In agreement with these findings, thermal detection by opsins was also reported in mammalian cells. Considering the presence of opsins in tissues not reached by light, an intriguing question has emerged: What is the role of a classical light-sensor, and more recently appreciated thermo-sensor, in these tissues? To tackle this question, we address in this review the most recent studies in the field, with emphasis in mammals. We provide the present view about the role of opsins in peripheral tissues, aiming to integrate the current knowledge of the presence and function of opsins in organs that are not directly affected by light.