Melanopsin (Opn4) requirement for normal light-induced circadian phase shifting

Discrete photoentrainment of mammalian central clock is regulated by bi-stable dynamic network in the suprachiasmatic nucleus

The biological clock synchronizes with the environmental light-dark cycle through circadian photoentrainment. While intracellular pathways regulating clock gene expression after light exposure in the suprachiasmatic nucleus are well studied in mammals, the neuronal circuits driving phase shifts remain unclear. Here, using a mouse model, we show that chemogenetic activation of early-night light-responsive neurons induces phase delays at any circadian time, potentially breaking the photoentrainment dead zone. In contrast, activating late-night light-responsive neurons mimics light-induced phase shifts. Using in vivo two-photon microscopy, we found that most neurons in the suprachiasmatic nucleus exhibit stochastic light responses, while a small subset is consistently activated in the early subjective night and another is inhibited in the late subjective night. Our findings suggest a dynamic bi-stable network model for circadian photoentrainment, where phase shifts arise from a functional circuit integrating signals to groups of outcome neurons, rather than a labeled-line principle seen in sensory systems.

Examining the role of the photopigment melanopsin in the striatal dopamine response to light

The mesolimbic dopamine system is a set of subcortical brain circuits that plays a key role in reward processing, reinforcement, associative learning, and behavioral responses to salient environmental events. In our previous studies of the dopaminergic response to salient visual stimuli, we observed that dopamine release in the lateral nucleus accumbens (LNAc) of mice encoded information about the rate and magnitude of rapid environmental luminance changes from darkness. Light-evoked dopamine responses were rate-dependent, robust to the time of testing or stimulus novelty, and required phototransduction by rod and cone opsins. However, it is unknown if these dopaminergic responses also involve non-visual opsins, such as melanopsin, the primary photopigment expressed by intrinsically photosensitive retinal ganglion cells (ipRGCs). In the current study, we evaluated the role of melanopsin in the dopaminergic response to light in the LNAc using the genetically encoded dopamine sensor dLight1 and fiber photometry. By measuring light-evoked dopamine responses across a broad irradiance and wavelength range in constitutive melanopsin (Opn4) knockout mice, we were able to provide new insights into the ability of non-visual opsins to regulate the mesolimbic dopamine response to visual stimuli.

Circadian clock communication during homeostasis and ageing

Maintaining homeostasis is essential for continued health, and the progressive decay of homeostatic processes is a hallmark of ageing. Daily environmental rhythms threaten homeostasis, and circadian clocks have evolved to execute physiological processes in a manner that anticipates, and thus mitigates, their effects on the organism. Clocks are active in almost all cell types; their rhythmicity and functional output are determined by a combination of tissue-intrinsic and systemic inputs. Numerous inputs for a specific tissue are produced by the activity of circadian clocks of other tissues or cell types, generating a form of crosstalk known as clock communication. In mammals, the central clock in the hypothalamus integrates signals from external light-dark cycles to align peripheral clocks elsewhere in the body. This regulation is complemented by a tissue-specific milieu of external, systemic and niche inputs that modulate and cooperate with the cellular circadian clock machinery of a tissue to tailor its functional output. These mechanisms of clock communication decay during ageing, and growing evidence suggests that this decline might drive ageing-related morbidities. Dietary, behavioural and pharmacological interventions may offer the possibility to overcome these changes and in turn improve healthspan.

Two-photon activation, deactivation, and coherent control of melanopsin in live cells

Intrinsically photosensitive retinal ganglion cells are photoreceptors discovered in the last 20 years. These cells project to the suprachiasmatic nucleus of the brain to drive circadian rhythms, regulated by ambient light levels. The photopigment responsible for photoactivation in these cells, melanopsin, has been shown to exhibit many unique activation features among opsins. Notably, the photopigment can exist in three states dependent on the intensity and spectrum of ambient light, which affects its function. Despite increasing knowledge about these cells and melanopsin, tools that can manipulate their three states, and do so with single-cell precision, are limited. This reduces the extent to which circuit-level phenomena, and studying the implications of melanopsin tri-stability in living systems, can be pursued. In this report, we evoke and modulate calcium transients in live cells and intrinsically photosensitive retinal ganglion cells from isolated retinal tissues following two-photon excitation using near-infrared light pulses. We demonstrate that two-photon activation of melanopsin can successfully stimulate melanopsin-expressing cells with high spatio-temporal precision. Moreover, we demonstrate that the functional tri-stability of the photopigment can be interrogated by multiphoton excitation using spectral-temporal modulation of a broadband, ultrafast laser source.

Beyond vision: effects of light on the circadian clock and mood-related behaviours

Light is a crucial environmental factor that influences various aspects of life, including physiological and psychological processes. While light is well-known for its role in enabling humans and other animals to perceive their surroundings, its influence extends beyond vision. Importantly, light affects our internal time-keeping system, the circadian clock, which regulates daily rhythms of biochemical and physiological processes, ultimately impacting mood and behaviour. The 24-h availability of light can have profound effects on our well-being, both physically and mentally, as seen in cases of jet lag and shift work. This review summarizes the intricate relationships between light, the circadian clock, and mood-related behaviours, exploring the underlying mechanisms and its implications for health.

Pulsed alternating wavelength system lighting does not negatively impact production or welfare but reduces dopamine activity and may improve bone growth in grow-out Pekin ducks: Effects of PAWS lighting on meat ducks

The production and welfare of Pekin ducks can be affected by the lighting type they are housed under. There is no standard lighting system in industry and little data evaluating effects of different light systems on duck production and welfare. Pulsed Alternating Wavelength System (PAWS) is a novel LED technology that delivers multiple wavelengths of light in pulsating patterns. This study aimed to determine the effects of PAWS on brain serotonin turnover and skeletal quality in ducks. Ducks housed under PAWS were hypothesized to have lower brain serotonin turnover and equal bone quality compared to those housed under control lights (fluorescent with digital ballasts, 4500K, ∼40 lux). Ducks were placed in floor pens under PAWS or control lighting (1200 ducks/pen, n = 4 pens/treatment) at day of hatch until processing at 30 days of age (DOA). Body weights and feed intake were monitored weekly. Brains, femurs, tibiae, and humeri were collected on days 7, 14, 21 and 29 (n = 6 ducks/age/lighting type). Brain serotonin and metabolites were measured. Bone length, width, breaking strength, and ash were determined. Serotonin data were analyzed using 2-way ANOVA for age and lighting treatment with a post-hoc Fisher's LSD test. Bone data were analyzed with independent t-tests between treatments within each age. Ducks housed under PAWS were heavier by 29 DOA than controls (P < 0.001) with no differences in feed conversion. Brain analyses revealed no differences in serotonin turnover between lighting types. Early interstitial growth of PAWS femur and tibia was increased (P < 0.05), and PAWS femurs had increased bone mineral content at 29 DOA (P = 0.001). At 29 DOA, the PAWS humeri were wider than controls (P = 0.025) and had increased geometrical bone mechanical properties (P < 0.003), but no differences in breaking stress were evident. Results suggest that PAWS may have benefits for production traits and skeletal quality, however, a complete understanding of the welfare effects need further study.

Loss of Bmal1 impairs the glutamatergic light input to the SCN in mice

Introduction

Glutamate represents the dominant neurotransmitter that conveys the light information to the brain, including the suprachiasmatic nucleus (SCN), the central pacemaker for the circadian system. The neuronal and astrocytic glutamate transporters are crucial for maintaining efficient glutamatergic signaling. In the SCN, glutamatergic nerve terminals from the retina terminate on vasoactive intestinal polypeptide (VIP) neurons, which are essential for circadian functions. To date, little is known about the role of the core circadian clock gene, Bmal1, in glutamatergic neurotransmission of light signal to various brain regions.

Methods

The aim of this study was to further elucidate the role of Bmal1 in glutamatergic neurotransmission from the retina to the SCN. We therefore examined the spontaneous rhythmic locomotor activity, neuronal and glial glutamate transporters, as well as the ultrastructure of the synapse between the retinal ganglion cells (RGCs) and the SCN in adult male Bmal1-/- mice.

Results

We found that the deletion of Bmal1 affects the light-mediated behavior in mice, decreases the retinal thickness and affects the vesicular glutamate transporters (vGLUT1, 2) in the retina. Within the SCN, the immunoreaction of vGLUT1, 2, glial glutamate transporters (GLAST) and VIP was decreased while the glutamate concentration was elevated. At the ultrastructure level, the presynaptic terminals were enlarged and the distance between the synaptic vesicles and the synaptic cleft was increased, indicative of a decrease in the readily releasable pool at the excitatory synapses in Bmal1-/-.

Conclusion

Our data suggests that Bmal1 deletion affects the glutamate transmission in the retina and the SCN and affects the behavioral responses to light.

Construction of a circadian rhythm-related gene signature for predicting the prognosis and immune infiltration of breast cancer

Objectives

In this study, we constructed a model based on circadian rhythm associated genes (CRRGs) to predict prognosis and immune infiltration in patients with breast cancer (BC).

Materials and methods

By using TCGA and CGDB databases, we conducted a comprehensive analysis of circadian rhythm gene expression and clinicopathological data. Three different machine learning algorithms were used to screen out the characteristic circadian genes associated with BC prognosis. On this basis, a circadian gene prediction model about BC prognosis was constructed and validated. We also evaluated the association of the model's risk score with immune cells and immune checkpoint genes, and analyzed prognostic genes and drug sensitivity in this model.

Results

We screened 62 DEGs, including 30 upregulated genes and 32 downregulated genes, and performed GO and KEGG analysis on them. The above 62 DEGs were included in Cox analysis, LASSO regression, Random Forest and SVMV-RFE, respectively, and then the intersection was used to obtain 5 prognostic related characteristic genes (SUV39H2, OPN4, RORB, FBXL6 and SIAH2). The Risk Score of each sample was calculated according to the expression level and risk coefficient of 5 genes, Risk Score= (SUV39H2 expression level ×0.0436) + (OPN4 expression level ×1.4270) + (RORB expression level ×0.1917) + (FBXL6 expression level ×0.3190) + (SIAH2 expression level × -0.1984).

Conclusion

SUV39H2, OPN4, RORB and FBXL6 were positively correlated with Risk Score, while SIAH2 was negatively correlated with Risk Score. The above five circadian rhythm genes can construct a risk model for predicting the prognosis and immune invasion of BC.

Non-image-forming photoreceptors improve visual orientation selectivity and image perception

It has long been a decades-old dogma that image perception is mediated solely by rods and cones, while intrinsically photosensitive retinal ganglion cells (ipRGCs) are responsible only for non-image-forming vision, such as circadian photoentrainment and pupillary light reflexes. Surprisingly, we discovered that ipRGC activation enhances the orientation selectivity of layer 2/3 neurons in the primary visual cortex (V1) of mice by both increasing preferred-orientation responses and narrowing tuning bandwidth. Mechanistically, we found that the tuning properties of V1 excitatory and inhibitory neurons are differentially influenced by ipRGC activation, leading to a reshaping of the excitatory/inhibitory balance that enhances visual cortical orientation selectivity. Furthermore, light activation of ipRGCs improves behavioral orientation discrimination in mice. Importantly, we found that specific activation of ipRGCs in human participants through visual spectrum manipulation significantly enhances visual orientation discriminability. Our study reveals a visual channel originating from "non-image-forming photoreceptors" that facilitates visual orientation feature perception.

Direct photoreception by pituitary endocrine cells regulates hormone release and pigmentation

The recent discovery of nonvisual photoreceptors in various organs has raised expectations for uncovering their roles and underlying mechanisms. In this work, we identified a previously unrecognized hormone-releasing mechanism in the pituitary of the Japanese rice fish (medaka) induced by light. Ca2+ imaging analysis revealed that melanotrophs, a type of pituitary endocrine cell that secretes melanocyte-stimulating hormone, robustly increase the concentration of intracellular Ca2+ during short-wavelength light exposure. Moreover, we identified Opn5m as the key molecule that drives this response. Knocking out opn5m attenuated melanogenesis by reducing tyrosinase expression in the skin. Our findings suggest a mechanism in which direct reception of short-wavelength light by pituitary melanotrophs triggers a pathway that might contribute to protection from ultraviolet radiation in medaka.

Effects of Illumination Color on Hypothalamic Appetite-Regulating Gene Expression and Glycolipid Metabolism

Irregular illumination is a newly discovered ambient factor that affects dietary and metabolic processes. However, the effect of the modulation of long-term light exposure on appetite and metabolism remains elusive. Therefore, in this current study, we systematically investigated the effects of up to 8 weeks of exposure to red (RL), green (GL), and white light (WL) environments on appetite, food preferences, and glucose homeostasis in mice on both high-fat and low-fat dietary patterns. It was found that the RL group exacerbated high-fat-induced obesity in mice compared with GL- or WL-treated mice. RL-exposed mice exhibited worsened metabolic profiles, including impaired glucose tolerance/insulin sensitivity, elevated lipid levels, and reduced serum insulin levels. Serological analyses showed that RL exposure resulted in decreased leptin levels and increased levels of orexigenic and hunger hormones in mice. Further qPCR analysis showed that the expression levels of the hypothalamic appetite-related genes NPY and AgRP mRNA were upregulated in RL-treated mice, while the expression level of the appetite suppressor gene POMC mRNA was downregulated. The results of this study will be instructive for the regulation of appetite and metabolism from the perspective of illumination colors.

Genomic signatures of sensory adaptation and evolution in pangolins

BACKGROUND

Pangolin is one of the most endangered mammals with many peculiar characteristics, yet the understanding of its sensory systems is still superficial. Studying the genomic basis of adaptation and evolution of pangolin's sensory system is expected to provide further potential assistance for their conservation in the future.

RESULTS

In this study, we performed a comprehensive comparative genomic analysis to explore the signature of sensory adaptation and evolution in pangolins. By comparing with the aardvark, Cape golden mole, and short-beaked echidna, 124 and 152 expanded gene families were detected in the genome of the Chinese and Malayan pangolins, respectively. The enrichment analyses showed olfactory-related genomic convergence among five concerned mammals. We found 769 and 733 intact OR genes, and 704 and 475 OR pseudogenes in the Chinese and Malayan pangolin species, respectively. Compared to other mammals, far more intact members of OR6 and OR14 were identified in pangolins, particularly for four genes with large copy numbers (OR6C2, OR14A2, OR14C36, and OR14L1). On the genome-wide scale, 1,523, 1,887, 1,110, and 2,732 genes were detected under positive selection (PSGs), intensified selection (ISGs), rapid evolution (REGs), and relaxed selection (RSGs) in pangolins. GO terms associated with visual perception were enriched in PSGs, ISGs, and REGs. Those related to rhythm and sound perception were enriched in both ISGs and REGs, ear development and morphogenesis were enriched in ISGs, and mechanical stimulus and temperature adaptation were enriched in RSGs. The convergence of two vision-related PSGs (OPN4 and ATXN7), with more than one parallel substituted site, was detected among five concerned mammals. Additionally, the absence of intact genes of PKD1L3, PKD2L1, and TAS1R2 and just six single-copy TAS2Rs (TAS2R1, TAS2R4, TAS2R7, TAS2R38, TAS2R40, and TAS2R46) were found in pangolins. Interestingly, we found two large insertions in TAS1R3, distributed in the N-terminal ectodomain, just in pangolins.

CONCLUSIONS

We found new features related to the adaptation and evolution of pangolin-specific sensory characteristics across the genome. These are expected to provide valuable and useful genome-wide genetic information for the future breeding and conservation of pangolins.

Circadian Disruption in Glaucoma: Causes, Consequences, and Countermeasures

This review explores the intricate relationship between glaucoma and circadian rhythm disturbances. As a principal organ for photic signal reception and transduction, the eye plays a pivotal role in coordinating the body's circadian rhythms through specialized retinal ganglion cells (RGCs), particularly intrinsically photosensitive RGCs (ipRGCs). These cells are critical in transmitting light signals to the suprachiasmatic nucleus (SCN), the central circadian clock that synchronizes physiological processes to the 24-hour light-dark cycle. The review delves into the central circadian body clock, highlighting the importance of the retino-hypothalamic tract in conveying light information from the eyes to the SCN. It underscores the role of melanopsin in ipRGCs in absorbing light and initiating biochemical reactions that culminate in the synchronization of the SCN's firing patterns with the external environment. Furthermore, the review discusses local circadian rhythms within the eye, such as those affecting photoreceptor sensitivity, corneal thickness, and intraocular fluid outflow. It emphasizes the potential of optical coherence tomography (OCT) in studying structural losses of RGCs in glaucoma and the associated circadian rhythm disruption. Glaucomatous retinal damage is identified as a cause of circadian disruption, with mechanisms including oxidative stress, neuroinflammation, and direct damage to RGCs. The consequences of such disruption are complex, affecting systemic and local circadian rhythms, sleep patterns, mood, and metabolism. Countermeasures, with implications for glaucoma management, are proposed that focus on strategies to improve circadian health through balanced melatonin timing, daylight exposure, and potential chronotherapeutic approaches. The review calls for further research to elucidate the mechanisms linking glaucoma and circadian disruption and to develop effective interventions to address this critical aspect of the disease.

Hierarchy or Heterarchy of Mammalian Circadian Timekeepers?

Mammalian circadian biologists commonly characterize the relation between circadian clocks as hierarchical, with the clock in the suprachiasmatic nucleus at the top of the hierarchy. The lineage of research since the suprachiasmatic nucleus (SCN) was first identified as the clock in mammals has challenged this perspective, revealing clocks in peripheral tissues, showing that they respond to their own zeitgebers, coordinate oscillations among themselves, and in some cases modify the behavior of the SCN. Increasingly circadian timekeepers appear to constitute a heterarchical network, with control distributed and operating along multiple pathways. One reason for the continued invocation of hierarchy in mammalian circadian biology is that it is difficult to understand how a heterarchical system could operate effectively so as to maintain the organism. Evolved mechanisms, however, need not respect hierarchy and those that have survived have demonstrated the ability of heterarchical organizaton to maintain organisms.

Differential susceptibility to hypoxia in hypoxia-inducible factor 1-alpha (HIF-1α)-targeted freshwater water flea Daphnia magna mutants

The water flea, Daphnia magna, serves as a key model organism for investigating the response of aquatic organisms to environmental stressors, including hypoxia. Hypoxia-inducible factor 1-alpha (HIF-1α) is a central regulatory protein involved in the cellular response to hypoxic conditions. In this study, we used CRISPR/Cas9 gene editing to create D. magna mutant lines with targeted alterations in the HIF-1α gene. Mutants demonstrated decreased survival and reproductive output and down-regulated genes for the HIF-1α-mediated pathway in low-oxygen conditions. These findings suggest that the HIF-1α pathway is a critical component of resistance to hypoxia in D. magna. This study provides novel insights into the molecular basis of hypoxia tolerance of HIF-1α in D. magna and expands our understanding of how aquatic organisms can adapt to or be challenged by changing oxygen levels in the face of global environmental changes.

Impacts of circadian disruptions on behavioral rhythms in mice

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

Circadian de(regulation) in physiology: implications for disease and treatment

Time plays a crucial role in the regulation of physiological processes. Without a temporal control system, animals would be unprepared for cyclic environmental changes, negatively impacting their survival. Experimental studies have demonstrated the essential role of the circadian system in the temporal coordination of physiological processes. Translating these findings to humans has been challenging. Increasing evidence suggests that modern lifestyle factors such as diet, sedentarism, light exposure, and social jet lag can stress the human circadian system, contributing to misalignment; i.e., loss of phase coherence across tissues. An increasing body of evidence supports the negative impact of circadian disruption on several human health parameters. This review aims to provide a comprehensive overview of how circadian disruption influences various physiological processes, its long-term health consequences, and its association with various diseases. To illustrate the relevant consequences of circadian disruption, we focused on describing the many physiological consequences faced by shift workers, a population known to experience high levels of circadian disruption. We also discuss the emerging field of circadian medicine, its founding principles, and its potential impact on human health.

Developmental control of rod number via a light-dependent retrograde pathway from intrinsically photosensitive retinal ganglion cells

Photoreception is essential for the development of the visual system, shaping vision's first synapse to cortical development. Here, we find that the lighting environment controls developmental rod apoptosis via Opn4-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs). Using genetics, sensory environment manipulations, and computational approaches, we establish a pathway where light-dependent glutamate released from ipRGCs is detected via a transiently expressed glutamate receptor (Grik3) on rod precursors within the inner retina. Communication between these cells is mediated by hybrid neurites on ipRGCs that sense light before eye opening. These structures span the ipRGC-rod precursor distance over development and contain the machinery for photoreception (Opn4) and neurotransmitter release (Vglut2 & Syp). Assessment of the human gestational retina identifies conserved hallmarks of an ipRGC-to-rod axis, including displaced rod precursors, transient GRIK3 expression, and ipRGCs with deep-projecting neurites. This analysis defines an adaptive retrograde pathway linking the sensory environment to rod precursors via ipRGCs prior to eye opening.

Active state structures of a bistable visual opsin bound to G proteins

Opsins are G protein-coupled receptors (GPCRs) that have evolved to detect light stimuli and initiate intracellular signaling cascades. Their role as signal transducers is critical to light perception across the animal kingdom. Opsins covalently bind to the chromophore 11-cis retinal, which isomerizes to the all-trans isomer upon photon absorption, causing conformational changes that result in receptor activation. Monostable opsins, responsible for vision in vertebrates, release the chromophore after activation and must bind another retinal molecule to remain functional. In contrast, bistable opsins, responsible for non-visual light perception in vertebrates and for vision in invertebrates, absorb a second photon in the active state to return the chromophore and protein to the inactive state. Structures of bistable opsins in the activated state have proven elusive, limiting our understanding of how they function as bidirectional photoswitches. Here we present active state structures of a bistable opsin, jumping spider rhodopsin isoform-1 (JSR1), in complex with its downstream signaling partners, the Gi and Gq heterotrimers. These structures elucidate key differences in the activation mechanisms between monostable and bistable opsins, offering essential insights for the rational engineering of bistable opsins into diverse optogenetic tools to control G protein signaling pathways.

The Role of Season, Sunlight, and Light Sensitivity in Self-Reported Depressive Symptoms by Adults With Visual Impairment

Purpose

Depression is common in people with visual impairment, and the onset may be influenced by aspects related to light. The aim was to explore the associations of season, sunlight, and light sensitivity with depressive symptoms in this population.

Methods

Data regarding self-reported depressive symptoms from seven cross-sectional studies conducted between 2009 and 2018 were combined with information concerning sensitivity to light, season on the date of self-report, and potential sunlight exposure in the 2 weeks prior to self-report. The latter was calculated by summing up the daily sunlight hours detected by the weather station nearest to the residence of each participant. Logistic regression analyses were performed to investigate the associations.

Results

Participants (N = 1925) experienced clinically significant depressive symptoms most often in winter (32.8%), followed by summer (27.4%), spring (26.2%), and fall (24.2%). The odds of experiencing depression in fall were significantly lower compared with winter (odds ratio [OR] = 0.67, P = 0.007). An increase in the hours of sunlight in the participant's environment was associated with lower odds to experience depressive symptoms (OR = 0.995, P = 0.011). People who were sensitive to bright light had higher odds of experiencing depressive symptoms (OR = 1.80, P < 0.001). Other differences found between subgroups were not consistent.

Conclusions

It seems likely that season, sunlight, and light sensitivity play a role in depression among people with visual impairment. Further research is needed, exploring the experiences in this population, the actual sunlight exposure using objective measures, and treatment options.

Translational Relevance

Clinicians should consider these factors when treating visually impaired patients with depressive symptoms.

Ultradian rhythms of activity in a wild subterranean rodent

Many animals adapt their activity patterns to the best environmental conditions using daily rhythms. African mole-rats are among the mammals that have become models for studying how these rhythms can be entrained by light or temperature in experimental laboratory studies. However, it is unclear whether they exhibit similar circadian rhythms in their natural lightless, subterranean environment. In this study, we used biologging to investigate the activity rhythms of wild, highveld mole-rats. We show that their activity cycle exhibited an ultradian rhythm with a length between 4 and 8 h. On an individual level, mole-rats displayed about five activity bouts per day, occurring at various times during the day and night. On a population level, activity peaked in the afternoon, coinciding with the peak in ambient temperature. Our research suggests that wild subterranean mammals, which experience reduced environmental variation, are unlikely to show clear circadian rhythmicity in activity patterns. Instead, activity periods are distributed over several bouts throughout the day and night, and activity coincides with the peak in daily temperature. We propose that ultradian rhythms in activity may be more common than previously thought and discuss how physiological processes may generate differences in periodicity between laboratory and wild populations.

Circadian rhythm disruption and retinal dysfunction: a bidirectional link in Alzheimer's disease?

Dysfunction in circadian rhythms is a common occurrence in patients with Alzheimer's disease. A predominant function of the retina is circadian synchronization, carrying information to the brain through the retinohypothalamic tract, which projects to the suprachiasmatic nucleus. Notably, Alzheimer's disease hallmarks, including amyloid-β, are present in the retinas of Alzheimer's disease patients, followed/associated by structural and functional disturbances. However, the mechanistic link between circadian dysfunction and the pathological changes affecting the retina in Alzheimer's disease is not fully understood, although some studies point to the possibility that retinal dysfunction could be considered an early pathological process that directly modulates the circadian rhythm.

Striatal projection neurons coexpressing dopamine D1 and D2 receptors modulate the motor function of D1- and D2-SPNs

The role of the striatum in motor control is commonly assumed to be mediated by the two striatal efferent pathways characterized by striatal projection neurons (SPNs) expressing dopamine (DA) D1 receptors or D2 receptors (D1-SPNs and D2-SPNs, respectively), without regard to SPNs coexpressing both receptors (D1/D2-SPNs). Here we developed an approach to target these hybrid SPNs in mice and demonstrate that, although these SPNs are less abundant, they have a major role in guiding the motor function of the other two populations. D1/D2-SPNs project exclusively to the external globus pallidus and have specific electrophysiological features with distinctive integration of DA signals. Gain- and loss-of-function experiments indicate that D1/D2-SPNs potentiate the prokinetic and antikinetic functions of D1-SPNs and D2-SPNs, respectively, and restrain the integrated motor response to psychostimulants. Overall, our findings demonstrate the essential role of this population of D1/D2-coexpressing neurons in orchestrating the fine-tuning of DA regulation in thalamo-cortico-striatal loops.

Dynamic endocannabinoid-mediated neuromodulation of retinal circadian circuitry

Circadian rhythms are biological rhythms that originate from the "master circadian clock," called the suprachiasmatic nucleus (SCN). SCN orchestrates the circadian rhythms using light as a chief zeitgeber, enabling humans to synchronize their daily physio-behavioral activities with the Earth's light-dark cycle. However, chronic/ irregular photic disturbances from the retina via the retinohypothalamic tract (RHT) can disrupt the amplitude and the expression of clock genes, such as the period circadian clock 2, causing circadian rhythm disruption (CRd) and associated neuropathologies. The present review discusses neuromodulation across the RHT originating from retinal photic inputs and modulation offered by endocannabinoids as a function of mitigation of the CRd and associated neuro-dysfunction. Literature indicates that cannabinoid agonists alleviate the SCN's ability to get entrained to light by modulating the activity of its chief neurotransmitter, i.e., γ-aminobutyric acid, thus preventing light-induced disruption of activity rhythms in laboratory animals. In the retina, endocannabinoid signaling modulates the overall gain of the retinal ganglion cells by regulating the membrane currents (Ca2+, K+, and Cl- channels) and glutamatergic neurotransmission of photoreceptors and bipolar cells. Additionally, endocannabinoids signalling also regulate the high-voltage-activated Ca2+ channels to mitigate the retinal ganglion cells and intrinsically photosensitive retinal ganglion cells-mediated glutamate release in the SCN, thus regulating the RHT-mediated light stimulation of SCN neurons to prevent excitotoxicity. As per the literature, cannabinoid receptors 1 and 2 are becoming newer targets in drug discovery paradigms, and the involvement of endocannabinoids in light-induced CRd through the RHT may possibly mitigate severe neuropathologies.

Flp-recombinase mouse line for genetic manipulation of ipRGCs

Light has myriad impacts on behavior, health, and physiology. These signals originate in the retina and are relayed to the brain by more than 40 types of retinal ganglion cells (RGCs). Despite a growing appreciation for the diversity of RGCs, how these diverse channels of light information are ultimately integrated by the ~50 retinorecipient brain targets to drive these light-evoked effects is a major open question. This gap in understanding primarily stems from a lack of genetic tools that specifically label, manipulate, or ablate specific RGC types. Here, we report the generation and characterization of a new mouse line (Opn4FlpO), in which FlpO is expressed from the Opn4 locus, to manipulate the melanopsin-expressing, intrinsically photosensitive retinal ganglion cells. We find that the Opn4FlpO line, when crossed to multiple reporters, drives expression that is confined to ipRGCs and primarily labels the M1-M3 subtypes. Labeled cells in this mouse line show the expected intrinsic, melanopsin-based light response and morphological features consistent with the M1-M3 subtypes. In alignment with the morphological and physiological findings, we see strong innervation of non-image forming brain targets by ipRGC axons, and weaker innervation of image forming targets in Opn4FlpO mice labeled using AAV-based and FlpO-reporter lines. Consistent with the FlpO insertion disrupting the endogenous Opn4 transcript, we find that Opn4FlpO/FlpO mice show deficits in the pupillary light reflex, demonstrating their utility for behavioral research in future experiments. Overall, the Opn4FlpO mouse line drives Flp-recombinase expression that is confined to ipRGCs and most effectively drives recombination in M1-M3 ipRGCs. This mouse line will be of broad use to those interested in manipulating ipRGCs through a Flp-based recombinase for intersectional studies or in combination with other, non-Opn4 Cre driver lines.

A Comprehensive Overview of the Neural Mechanisms of Light Therapy

Light is a powerful environmental factor influencing diverse brain functions. Clinical evidence supports the beneficial effect of light therapy on several diseases, including depression, cognitive dysfunction, chronic pain, and sleep disorders. However, the precise mechanisms underlying the effects of light therapy are still not well understood. In this review, we critically evaluate current clinical evidence showing the beneficial effects of light therapy on diseases. In addition, we introduce the research progress regarding the neural circuit mechanisms underlying the modulatory effects of light on brain functions, including mood, memory, pain perception, sleep, circadian rhythm, brain development, and metabolism.

Differential Photosensitivity of Fibroblasts Obtained from Normal Skin and Hypertrophic Scar Tissues

It is unclear whether normal human skin tissue or abnormal scarring are photoreceptive. Therefore, this study investigated photosensitivity in normal skin tissue and hypertrophic scars. The expression of opsins, which are photoreceptor proteins, in normal dermal fibroblasts (NDFs) and hypertrophic scar fibroblasts (HSFs) was examined. After exposure to blue light (BL), changes in the expression levels of αSMA and clock-related genes, specifically PER2 and BMAL1, were examined in both fibroblast types. Opsins were expressed in both fibroblast types, with OPN3 exhibiting the highest expression levels. After peripheral circadian rhythm disruption, BL induced rhythm formation in NDFs. In contrast, although HSFs showed changes in clock-related gene expression levels, no distinct rhythm formation was observed. The expression level of αSMA was significantly higher in HSFs and decreased to the same level as that in NDFs upon BL exposure. When OPN3 knocked-down HSFs were exposed to BL, the reduction in αSMA expression was inhibited. This study showed that BL exposure directly triggers peripheral circadian synchronization in NDFs but not in HSFs. OPN3-mediated BL exposure inhibited HSFs. Although the current results did not elucidate the relationship between peripheral circadian rhythms and hypertrophic scars, they show that BL can be applied for the prevention and treatment of hypertrophic scars and keloids.

Contribution of the eye and of opn4xa function to circadian photoentrainment in the diurnal zebrafish

The eye is instrumental for controlling circadian rhythms in mice and human. Here, we address the conservation of this function in the zebrafish, a diurnal vertebrate. Using lakritz (lak) mutant larvae, which lack retinal ganglion cells (RGCs), we show that while a functional eye contributes to masking, it is largely dispensable for the establishment of circadian rhythms of locomotor activity. Furthermore, the eye is dispensable for the induction of a phase delay following a pulse of white light at CT 16 but contributes to the induction of a phase advance upon a pulse of white light at CT21. Melanopsin photopigments are important mediators of photoentrainment, as shown in nocturnal mammals. One of the zebrafish melanopsin genes, opn4xa, is expressed in RGCs but also in photosensitive projection neurons in the pineal gland. Pineal opn4xa+ projection neurons function in a LIGHT ON manner in contrast to other projection neurons which function in a LIGHT OFF mode. We generated an opn4xa mutant in which the pineal LIGHT ON response is impaired. This mutation has no effect on masking and circadian rhythms of locomotor activity, or for the induction of phase shifts, but slightly modifies period length when larvae are subjected to constant light. Finally, analysis of opn4xa;lak double mutant larvae did not reveal redundancy between the function of the eye and opn4xa in the pineal for the control of phase shifts after light pulses. Our results support the idea that the eye is not the sole mediator of light influences on circadian rhythms of locomotor activity and highlight differences in the circadian system and photoentrainment of behaviour between different animal models.

Precision medicine in endocrinology: Unraveling metabolic health through time-restricted eating

As a promising avenue in nutrition, intermittent fasting, particularly time-restricted eating like the 8/16 protocol, requires careful individualization. This approach involves voluntary food restriction interspersed with normal eating, aiming to align with inner circadian rhythms for potential benefits in metabolism and weight management. Endocrinologists, responding to patient interest and backed by evidence-based medicine, can now delve into the intricacies of time-restricted eating. They consider each patient's unique medical history and expectations, integrating this approach into tailored treatment plans in a personalized medicine approach. Ongoing research is essential to deepen our comprehension of how time-restricted eating influences metabolic health, enabling the development of precise recommendations suitable for diverse populations and various clinical conditions. While time-restricted eating is a relevant metabolic approach, endocrinologists should exercise caution to prevent the promotion of eating disorders due to its restrictive nature.

Entrainment to gradual vs. immediate 8-hour phase advance shifts with and without short-wavelength enriched polychromatic green light

OBJECTIVES

For optimal health and well-being the sleep episode and the circadian timing system should be properly aligned. We evaluated the effectiveness of different dynamic light and sleep/wake shift schedules for rapid circadian entrainment following an 8-hour advance of sleep.

METHODS

Forty-three healthy participants completed an 8-day inpatient protocol in which the 8-hour sleep episode was advanced by 8 hours. Participants were assigned to one of five conditions: (1) dim ambient WHITE light and GRADUAL shift in which the sleep episode was incrementally advanced over 5days; (2) dim GREEN, short-wavelength (∼504 nm) polychromatic light and GRADUAL shift; (3) dim WHITE light and SLAM shift, including an abrupt 8-hour advance on day 3 following an extended 32-hour wake episode; (4) GREEN light and SLAM shift; or (5) COMBINED (higher illuminance WHITE plus GREEN) light and modified SLAM shift with 2 short naps scheduled on the day prior to the abrupt advance. Phase shifts of the plasma dim light melatonin onset and sleep measures were compared to examine effects of protocol condition.

RESULTS

After 5days, the COMBINED light/modified SLAM shift condition showed larger phase advances of dim light melatonin onset (4.02 ± 1.13 hours) compared to the other 4 conditions (range 1.50 ± 0.96-2.83 ± 2.23 hours; p < .05) and resulted in increased REM sleep duration and fewer sleep disruptions.

CONCLUSIONS

Consideration of the type of shift and the illuminance and wavelength of light may assist in designing lighting countermeasures to sleep and circadian disruption, which has implications for jetlag, shiftwork, and circadian rhythm sleep disorders.

Melanopsin enhances image persistence

Contributions of the inner retinal photopigment melanopsin to human visual perception are incompletely understood. Here, we use a four-primary display to produce stimuli differing in melanopsin versus cone contrast in psychophysical paradigms in eight subjects with normal color vision. We address two predictions from electrophysiological recordings of the melanopsin system in non-human mammals: melanopsin influences color and/or supports image persistence under visual fixation. We first construct chromatic contrast sensitivity contours for stimuli differing in melanopsin excitation presented as a central annulus (10°) or peripheral (22.5°) spot. We find that although including melanopsin contrast produces modest changes in the average chromatic coordinates in both eccentricities, this occurs equally at low (0.5 Hz) and higher (3.75 Hz) temporal frequencies, arguing that it reflects divergence in cone spectral sensitivity in our participants from that captured in standardized cone fundamentals rather than a melanopsin contribution to color. We continue to ask whether the established ability of melanopsin to sustain firing of visual neurons under extended light exposure has a visual correlate, using the optical illusion of Troxler fading in which blurred spots in periphery disappear during visual fixation. We find that introducing additional melanopsin contrast (+28% Michelson contrast) to either bright or dark spots increases fading latency by 35% ± 8.8% and 41% ± 13.6%, respectively. Our data argue that the primary contribution of melanopsin to perception under these conditions is not to provide a color percept but rather to enhance persistence of low spatial frequency patterns during visual fixation.

Teneurin-3 regulates the generation of non-image-forming visual circuitry and responsiveness to light in the suprachiasmatic nucleus

Visual system function depends upon the elaboration of precise connections between retinal ganglion cell (RGC) axons and their central targets in the brain. Though some progress has been made in defining the molecules that regulate RGC connectivity required for the assembly and function of image-forming circuitry, surprisingly little is known about factors required for intrinsically photosensitive RGCs (ipRGCs) to target a principal component of the non-image-forming circuitry: the suprachiasmatic nucleus (SCN). Furthermore, the molecules required for forming circuits critical for circadian behaviors within the SCN are not known. We observe here that the adhesion molecule teneurin-3 (Tenm3) is highly expressed in vasoactive intestinal peptide (VIP) neurons located in the core region of the SCN. Since Tenm3 is required for other aspects of mammalian visual system development, we investigate roles for Tenm3 in regulating ipRGC-SCN connectivity and function. Our results show that Tenm3 negatively regulates association between VIP and arginine vasopressin (AVP) neurons within the SCN and is essential for M1 ipRGC axon innervation to the SCN. Specifically, in Tenm3-/- mice, we find a reduction in ventro-medial innervation to the SCN. Despite this reduction, Tenm3-/- mice have higher sensitivity to light and faster re-entrainment to phase advances, probably due to the increased association between VIP and AVP neurons. These data show that Tenm3 plays key roles in elaborating non-image-forming visual system circuitry and that it influences murine responses to phase-advancing light stimuli.

Short-Wavelength Light-Blocking Filters and Oral Melatonin Administration in Patients With Retinitis Pigmentosa: Protocol for a Randomized Controlled Trial

BACKGROUND

The medical community is beginning to recognize that retinitis pigmentosa (RP), due to its disabling progression, eventually leads to a reduction in the patient´s quality of life, a direct economic impact, and an increase in the burden on the health care system. There is no curative treatment for the origin of the disease, and most of the current interventions fail in reducing the associated negative psychological states, such as anxiety and depression, which lead to increased variability of vision and pose a continuous threat to the patient's independence.

OBJECTIVE

The aim of this study is to assess the effect of oral melatonin (OM) administration alone and combined with short-wavelength light (SWL)-blocking filters on patients with RP and test their effectiveness in improving the level of stress and sleep problems in many of these patients.

METHODS

We have developed a low-cost therapy protocol for patients with RP with sleep disorders and negative psychological stress. Patients will be randomized to receive a combined intervention with SWL-blocking filters and OM, SWL-blocking filters alone, or OM alone. There will also be a nonintervention arm as a control group. This study will be conducted across 2 retinal units in patients with RP with sleep disorders and high perceived stress and anxiety score reports. Patients will be assessed in the preintervention period, weekly during the 4 weeks of intervention, and then at 6 months postintervention. The primary outcomes are the differences in changes from baseline to postintervention in hormone release (α-amylase, cortisol, and melatonin) and sleep quality, as measured with the visual analog scale. Secondary outcome measures include clinical macular changes, as measured with optical coherence tomography and optical coherence tomography angiography; retinal function, as measured using the visual field and best-corrected visual acuity; sleep data collected from personal wearables; and several patient-reported variables, such as self-recorded sleep diaries, quality of life, perceived stress, and functional status.

RESULTS

This project is still a study protocol and has not yet started. Bibliographic research for information for its justification began in 2020, and this working group is currently seeking start-up funding. As soon as we have the necessary means, we will proceed with the registration and organization prior to the preliminary phase.

CONCLUSIONS

In this feasibility randomized clinical controlled trial, we will compare the effects of SWL blocking alone, administration of OM alone, and a combined intervention with both in patients with RP. We present this study so that it may be replicated and incorporated into future studies at other institutions, as well as applied to additional inherited retinal dystrophies. The goal of presenting this protocol is to aid recent efforts in reducing the impact of sleeping disorders and other psychological disorders on the quality of life in patients with RP and recovering their self-autonomy. In addition, the results of this study will represent a significant step toward developing a novel low-cost therapy for patients with RP and validating a novel therapeutic target.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/49196.

Melanopsin activates divergent phototransduction pathways in intrinsically photosensitive retinal ganglion cell subtypes

Melanopsin signaling within intrinsically photosensitive retinal ganglion cell (ipRGC) subtypes impacts a broad range of behaviors from circadian photoentrainment to conscious visual perception. Yet, how melanopsin phototransduction within M1-M6 ipRGC subtypes impacts cellular signaling to drive diverse behaviors is still largely unresolved. The identity of the phototransduction channels in each subtype is key to understanding this central question but has remained controversial. In this study, we resolve two opposing models of M4 phototransduction, demonstrating that hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are dispensable for this process and providing support for a pathway involving melanopsin-dependent potassium channel closure and canonical transient receptor potential (TRPC) channel opening. Surprisingly, we find that HCN channels are likewise dispensable for M2 phototransduction, contradicting the current model. We instead show that M2 phototransduction requires TRPC channels in conjunction with T-type voltage-gated calcium channels, identifying a novel melanopsin phototransduction target. Collectively, this work resolves key discrepancies in our understanding of ipRGC phototransduction pathways in multiple subtypes and adds to mounting evidence that ipRGC subtypes employ diverse phototransduction cascades to fine-tune cellular responses for downstream behaviors.

Watching the clock in glioblastoma

Glioblastoma (GBM) is the most prevalent malignant primary brain tumor, accounting for 14.2% of all diagnosed tumors and 50.1% of all malignant tumors, and the median survival time is approximately 8 months irrespective of whether a patient receives treatment without significant improvement despite expansive research (Ostrom QT, Price M, Neff C, et al. CBTRUS statistical report: primary brain and other central nervous system tumors diagnosed in the United States in 2015-2019. Neurooncology. 2022; 24(suppl 5):v1-v95.). Recently, important roles for the circadian clock in GBM tumorigenesis have been reported. Positive regulators of circadian-controlled transcription, brain and muscle ARNT-like 1 (BMAL1), and circadian locomotor output cycles kaput (CLOCK), are highly expressed also in GBM and correlated with poor patient prognosis. BMAL1 and CLOCK promote the maintenance of GBM stem cells (GSCs) and the establishment of a pro-tumorigenic tumor microenvironment (TME), suggesting that targeting the core clock proteins may augment GBM treatment. Here, we review findings that highlight the critical role the circadian clock plays in GBM biology and the strategies by which the circadian clock can be leveraged for GBM treatment in the clinic moving forward.

Immediate responses to ambient light in vivo reveal distinct subpopulations of suprachiasmatic VIP neurons

The circadian rhythm pacemaker, the suprachiasmatic nucleus (SCN), mediates light entrainment via vasoactive intestinal peptide (VIP) neurons (SCNVIP). Yet, how these neurons uniquely respond and connect to intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing melanopsin (Opn4) has not been determined functionally in freely behaving animals. To address this, we first used monosynaptic tracing from SCNVIP neurons in mice and identified two SCNVIP subpopulations. Second, we recorded calcium changes in response to ambient light, at both bulk and single-cell levels, and found two unique activity patterns in response to high- and low-intensity blue light. The activity patterns of both subpopulations could be manipulated by application of an Opn4 antagonist. These results suggest that the two SCNVIP subpopulations connect to two types of Opn4-expressing ipRGCs, likely M1 and M2, but only one is responsive to red light. These findings have important implications for our basic understanding of non-image-forming circadian light processing.

The genetics and chronobiology of cluster headache

BACKGROUND/HYPOTHESIS

Cluster headache displays uniquely rhythmic patterns in its attack manifestation. This strong chronobiological influence suggests that part of the pathophysiology of cluster headache is distinctly different from migraine and has prompted genetic investigations probing these systems.

METHODS

This is a narrative overview of the cluster headache chronobiological phenotype from the point of view of genetics covering existing knowledge, highlighting the specific challenges in cluster headache and suggesting novel research approaches to overcome these.

RESULTS

The chronobiological features of cluster headache are a hallmark of the disorder and while discrepancies between study results do exist, the main findings are highly reproducible across populations and time. Particular findings in subgroups indicate that the heritability of the disorder is linked to chronobiological systems. Meanwhile, genetic markers of circadian rhythm genes have been implicated in cluster headache, but with conflicting results. However, in two recently published genome wide association studies two of the identified four loci include genes with an involvement in circadian rhythm, MER proto-oncogene, tyrosine kinase and four and a half LIM domains 5. These findings strengthen the involvement of circadian rhythm in cluster headache pathophysiology.

CONCLUSION/INTERPRETATION

Studying chronobiology and genetics in cluster headache presents challenges unique to the disorder. Researchers are overcoming these challenges by pooling various data from different cohorts and performing meta-analyses providing novel insights into a classically enigmatic disorder. Further progress can likely be made by combining deep pheno- and genotyping.

Transcriptomic Analysis of Light-Induced Genes in Nasonia vitripennis: Possible Implications for Circadian Light Entrainment Pathways

Circadian entrainment to the environmental day-night cycle is essential for the optimal use of environmental resources. In insects, opsin-based photoreception in the compound eye and ocelli and CRYPTOCHROME1 (CRY1) in circadian clock neurons are thought to be involved in sensing photic information, but the genetic regulation of circadian light entrainment in species without light-sensitive CRY1 remains unclear. To elucidate a possible CRY1-independent light transduction cascade, we analyzed light-induced gene expression through RNA-sequencing in Nasonia vitripennis. Entrained wasps were subjected to a light pulse in the subjective night to reset the circadian clock, and light-induced changes in gene expression were characterized at four different time points in wasp heads. We used co-expression, functional annotation, and transcription factor binding motif analyses to gain insight into the molecular pathways in response to acute light stimulus and to form hypotheses about the circadian light-resetting pathway. Maximal gene induction was found after 2 h of light stimulation (1432 genes), and this included the opsin gene opblue and the core clock genes cry2 and npas2. Pathway and cluster analyses revealed light activation of glutamatergic and GABA-ergic neurotransmission, including CREB and AP-1 transcription pathway signaling. This suggests that circadian photic entrainment in Nasonia may require pathways that are similar to those in mammals. We propose a model for hymenopteran circadian light-resetting that involves opsin-based photoreception, glutamatergic neurotransmission, and gene induction of cry2 and npas2 to reset the circadian clock.

Distribution and synaptic organization of substance P-like immunoreactive neurons in the mouse retina

Substance P (SP), a neuroprotective peptidergic neurotransmitter, is known to have immunoreactivity (IR) localized to amacrine and/or ganglion cells in a variety of species' retinas, but it has not yet been studied in the mouse retina. Thus, we investigated the distribution and synaptic organization of SP-IR by confocal and electron microscopy immunocytochemistry in the mouse retina. SP-IR was distributed in the inner nuclear layer (INL), inner plexiform layer (IPL), and ganglion cell layer (GCL). Most of the SP-IR somas belonged to amacrine cells (2.5% of all) in the INL and their processes stratified into the S1, S3, and S5 layers of the IPL, with the most intense band in the S5 layer. Some SP-IR somas can also be observed in the GCL, which were identified as displaced amacrine cells (82%, 1269/1550) and ganglion cells (18%, 281/1550) by antibodies against AP2α and RBPMS, respectively. Such SP-IR ganglion cells (1.2% of all RGCs) can be further divided into 3 subgroups expressing SP/α-Synuclein (α-Syn), SP/GAD67, and/or SP/GAD67/α-Syn. Possible physiological and pathological roles of these ganglion cells are discussed. Further, electron microscopy evidence demonstrates that SP-IR amacrine cells receive major inputs from other SP-IR amacrine cell processes (146/242 inputs) and output mostly to SP-negative amacrine cell processes (291/673 outputs), suggesting series inhibition among amacrine cells. These results reveal for the first time an explicit distribution, novel ganglion cell features, and synaptic organization of SP-IR in the mouse retina, which is important for the future use of mouse models to study the roles of SP in healthy and diseased (including Parkinson's disease) retinal states.

Designing artificial circadian environments with multisensory cares for supporting preterm infants' growth in NICUs

Previous studies suggest the importance of stable circadian environments for fetuses to achieve sound physiology and intrauterine development. This idea is also supported by epidemiological and animal studies, in which pregnant females exposed to repeated shifting of light-dark cycles had increased rates of reproductive abnormalities and adverse pregnancy outcomes. In response to such findings, artificial circadian environments with light-dark (LD) cycles have been introduced to NICUs to promote better physical development of preterm infants. Such LD cycles, however, may not be fully effective for preterm infants who are less than 30 weeks gestational age (WGA) since they are too premature to be adequately responsive to light. Instead, circadian rhythmicity of incubated preterm infants less than 30 WGA may be able to be developed through stimulation of the non-visual senses such as touch and sound.

The impact of shift-work light conditions on tissue-specific circadian rhythms of canonical clock genes: insights from a mouse model study

Background: The natural day-night cycle synchronizes our circadian rhythms, but modern work practices like night shifts disrupt this pattern, leading to increased exposure to nighttime light. This exposure is linked to various health issues. While some studies have explored the effects of night shifts on human circadian rhythms, there is limited research on the consequences of long-term exposure to shift-work light conditions. Rodents can provide valuable insights into these effects. This study aimed to examine how short- or long-term exposure to rotating shifts and chronic jetlag affects the core circadian oscillators in the liver and skin of mammals. Methods: C57BL/6J male mice were subjected to simulated shift-work light conditions, including short-term or long-term rotating shifts and chronic jet-lag conditions. Liver and skin samples were collected every four hours over a 24-hour period on the second day of constant darkness. RNA was extracted and qRT-PCR analysis was conducted to measure the circadian gene expression in liver and skin tissues. Circadian rhythm analysis using CircaCompare compared the control group to mice exposed to shift-work light conditions. Results: The liver's circadian clock is significantly altered in mice under long-term rotating shift conditions, with a lesser but still noticeable impact in mice experiencing chronic jetlag. However, short-term rotating shift conditions do not significantly affect the liver's circadian clock. Conversely, all three simulated shift conditions affect the skin's circadian clock, indicating that the skin clock is more sensitive to shift-work light conditions than the liver clock. Compared to the liver, the skin's circadian clock is greatly affected by long-term rotating shift conditions. Conclusions: The study findings indicate more pronounced disturbances in the canonical clock genes of the skin compared to the liver under simulated shift-work light conditions. These results suggest that the skin clock is more vulnerable to the effects of shift-work.

The impact of shift-work light conditions on tissue-specific circadian rhythms of canonical clock genes: insights from a mouse model study

Background: The natural day-night cycle synchronizes our circadian rhythms, but modern work practices like night shifts disrupt this pattern, leading to increased exposure to nighttime light. This exposure is linked to various health issues. While some studies have explored the effects of night shifts on human circadian rhythms, there is limited research on the consequences of long-term exposure to shift-work light conditions. Rodents can provide valuable insights into these effects. This study aimed to examine how short- or long-term exposure to rotating shifts and chronic jetlag affects the core circadian oscillators in the liver and skin of mammals. Methods: C57BL/6J male mice were subjected to simulated shift-work light conditions, including short-term or long-term rotating shifts and chronic jet-lag conditions. Liver and skin samples were collected every four hours over a 24-hour period on the second day of constant darkness. RNA was extracted and qRT-PCR analysis was conducted to measure the circadian gene expression in liver and skin tissues. Circadian rhythm analysis using CircaCompare compared the control group to mice exposed to shift-work light conditions. Results: The liver's circadian clock is significantly altered in mice under long-term rotating shift conditions, with a lesser but still noticeable impact in mice experiencing chronic jetlag. However, short-term rotating shift conditions do not significantly affect the liver's circadian clock. Conversely, all three simulated shift conditions affect the skin's circadian clock, indicating that the skin clock is more sensitive to shift-work light conditions than the liver clock. Compared to the liver, the skin's circadian clock is greatly affected by long-term rotating shift conditions. Conclusions: The study findings indicate more pronounced disturbances in the canonical clock genes of the skin compared to the liver under simulated shift-work light conditions. These results suggest that the skin clock is more vulnerable to the effects of shift-work.

Enhanced human contrast sensitivity with increased stimulation of melanopsin in intrinsically photosensitive retinal ganglion cells

The intrinsically photosensitive retinal ganglion cells (ipRGCs) are known to serve non-image-forming functions, such as photoentrainment of the circadian rhythm and pupillary light reflex. However, how they affect human spatial vision is largely unknown. The spatial contrast sensitivity function (CSF), which measures contrast sensitivity as a function of spatial frequency, was used in the current study to investigate the function of ipRGCs in pattern vision. To compare the effects of different background lights on the CSF, we utilized the silent substitution technique. We manipulated the stimulation level of melanopsin (i.e., the visual pigment of ipRGCs) from the background light while keeping the cone stimulations constant, or vice versa. We conducted four experiments to measure the CSFs at various spatial frequencies, eccentricities, and levels of background luminance. Results showed that melanopsin stimulation from the background light enhances spatial contrast sensitivity across different eccentricities and luminance levels. Our finding that melanopsin contributes to CSF, combined with the receptive field analysis, suggests a role for the magnocellular pathway and challenges the conventional view that ipRGCs are primarily responsible for non-visual functions.

In light of breathing: environmental light is an important modulator of breathing with clinical implications

In vertebrate animals, the automatic, rhythmic pattern of breathing is a highly regulated process that can be modulated by various behavioral and physiological factors such as metabolism, sleep-wake state, activity level, and endocrine signaling. Environmental light influences many of these modulating factors both indirectly by organizing daily and seasonal rhythms of behavior and directly through acute changes in neural signaling. While several observations from rodent and human studies suggest that environmental light affects breathing, few have systematically evaluated the underlying mechanisms and clinical relevance of environmental light on the regulation of respiratory behavior. Here, we provide new evidence and discuss the potential neurobiological mechanisms by which light modulates breathing. We conclude that environmental light should be considered, from bench to bedside, as a clinically relevant modulator of respiratory health and disease.

Cry1 expression during postnatal development is critical for the establishment of normal circadian period

The mammalian circadian system generates an approximate 24-h rhythm through a complex autoregulatory feedback loop. Four genes, Period1 (Per1), Period2 (Per2), Cryptochrome1 (Cry1), and Cryptochrome2 (Cry2), regulate the negative feedback within this loop. Although these proteins have distinct roles within the core circadian mechanism, their individual functions are poorly understood. Here, we used a tetracycline trans-activator system (tTA) to examine the role of transcriptional oscillations in Cry1 and Cry2 in the persistence of circadian activity rhythms. We demonstrate that rhythmic Cry1 expression is an important regulator of circadian period. We then define a critical period from birth to postnatal day 45 (PN45) where the level of Cry1 expression is critical for setting the endogenous free running period in the adult animal. Moreover, we show that, although rhythmic Cry1 expression is important, in animals with disrupted circadian rhythms overexpression of Cry1 is sufficient to restore normal behavioral periodicity. These findings provide new insights into the roles of the Cryptochrome proteins in circadian rhythmicity and further our understanding of the mammalian circadian clock.

Altered circadian behavior and light sensing in mouse models of Alzheimer's disease

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

Long-term artificial/natural daytime light affects mood, melatonin, corticosterone, and gut microbiota in rats

The desynchronization of circadian rhythms affected by light may induce physiological and psychological disequilibrium. We aimed to elucidate changes of growth, depression-anxiety like behaviors, melatonin and corticosterone (CORT) secretion, and gut microbiota in rats influenced by long-term light inputs. Thirty male Sprague-Dawley rats were exposed to a 16/8 h light/dark regime for 8 weeks. The light period was set to 13 h of daylight with artificial light (AL group, n = 10), or with natural light (NL group, n = 10), or with mixed artificial-natural light (ANL group, n = 10), and 3 h of artificial night light after sunset. The obtained findings indicated that the highest weight gain and food efficiency were observed in the AL group and the lowest in NL group. In the behavioral tests, the NL and ANL groups showed lower anxiety level than AL group, and ANL groups showed lower depression level than AL group. The NL and ANL groups had delayed acrophases and maintained higher concentrations of melatonin compared to AL group. The circadian rhythm of CORT was only found in ANL group. At the phylum level, the mixed light contributed to a lower abundance of Bacteroidetes. The genus level results recommend a synergistic effect of artificial light and natural light on Lactobacillus abundance and an antagonistic effect on the Lachnospiraceae_NK4A136_group abundance. The study indicated that the mixture of artificial and natural light as well as the alignment of the proportions had beneficial influences on depression-anxiety-like levels, melatonin and corticosterone secretion, and the composition of the gut microbiota. KEY POINTS: • The mixed light can reduce the depression-anxiety level • The mixed light can maintain the secretion rhythm of melatonin and CORT • The mixed light can increase Lactobacillus and decrease Lachnospiraceae_NK4A136_group.

Nonphotic entrainment of central and peripheral circadian clocks in mice by scheduled voluntary exercise under constant darkness

In mammals, the central circadian pacemaker in the suprachiasmatic nucleus (SCN) entrains to an environmental light-dark (LD) cycle and organizes the temporal order of circadian rhythms in physiology and behavior. Previously, some studies have demonstrated that scheduled exercise could entrain the free-running behavior rhythm in nocturnal rodents. However, it remains unknown whether entrainment by scheduled exercise alters the internal temporal order of the behavioral circadian rhythms or clock gene expression in the SCN, extra-SCN brain regions, and peripheral organs when mice are entrained to the scheduled exercise under constant darkness (DD). In the present study, we examined circadian rhythms in locomotor activity and clock gene Per1 expression by bioluminescence reporter (Per1-luc) in the SCN, arcuate nucleus (ARC), liver, and skeletal muscle of mice entrained to an LD cycle, mice free-running under DD, and mice entrained to daily exposure to a new cage with a running wheel (NCRW) under DD. All mice showed a steady-state entrainment of behavioral circadian rhythms to NCRW exposure under DD in parallel with shortening of the α when compared with that under DD. The temporal order of behavioral circadian rhythms and the Per1-luc rhythms in the SCN and peripheral tissues but not in the ARC were maintained in the mice entrained to the NCRW and LD cycles; in contrast, the temporal order was altered in the mice under DD. The present findings reveal that the SCN entrains to daily exercise, and daily exercise reorganizes the internal temporal order of behavioral circadian rhythms and clock gene expression in the SCN and peripheral tissues.