Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity

Red Light Sensitivity of Non-image and Image Forming Visual Systems of Laboratory Rodents: Circadian Disruption and Behavioral Detection

The mammalian circadian system regulates all biological processes, thereby ensuring optimal function at the appropriate times of day. Animal studies that examine neurobehavioral processes at different times of day, including during the animal's active phase, may provide important new biomedical insights. A logistical problem for the study of nocturnal laboratory rodents is the potential confounding influence of nighttime light exposure, which may cause circadian disruption and alteration of behavior. The historical solution has been to use red light illumination, which is widely believed to be undetected by the rodent visual system. However, some recent studies have questioned this belief. We, therefore, tested the effects of nighttime exposure to commonly used red light conditions on the circadian non-image forming and the image forming visual systems of female and male laboratory rodents. We found that brief dim red light exposure to a range of red light wavelengths produces strong activation of the suprachiasmatic nucleus master clock, rapid suppression of melatonin secretion, and a subsequent phase shift in daily activity onsets. We also found in an operant behavioral task that rats are able to detect long wavelengths of red light, but not near-infrared light. Thus, both the non-image and image forming visual systems of laboratory rodents are responsive to red light conditions that are often used in animal research. The use of red light for laboratory rodent research and animal care should be carefully considered in terms of its possible confounding influences on research objectives.

Improving children's alertness and neuromuscular response by using a blue-enriched white light in the kindergarten playroom

Preschool children, who spend most of their time indoors, and the effects of artificial light on children's health and performance are important. Previous studies show that blue-enriched white light (BWL) has significant effects on human bodies, but only a few studies have specifically examined its effects in young children. Moreover, due to the significant physiological differences between children and adults, findings from BWL studies in adults cannot be directly applied to children. Therefore, investigating the effects of BWL on young children living in indoor environments is crucial. We recruited 24 preschool children (age: 5 ± 0.8 years; 12 girls and 12 boys) to participate in a within-subject, randomized crossover study involving common white light (CWL) (450 lx, Melanopic EDI: 354.04 lx) and BWL (450 lx, Melanopic EDI: 746.05 lx) in a kindergarten playroom. Under different light conditions, the children underwent tests for cardiac activity and critical flicker fusion frequency (CFF), as well as psychomotor vigilance task (PVT) and ruler drop test (RDT). The results indicated that BWL had significant effects on preschool children. Compared to CWL exposure, BWL exposure significantly improved cardiac activity, alertness, and neuromuscular response but slightly increased visual fatigue. Our study reveals that BWL has significant potential to improve children's physiological and cognitive functions, particularly to improve cardiac activity, alertness, and neuromuscular response. This study broadens the understanding of the effects of indoor lighting on children and provides a theoretical basis for designing a healthy indoor environment for children.

Photoneuroendocrine, circadian and seasonal systems: from photoneuroendocrinology to circadian biology and medicine

This contribution highlights the scientific development of two intertwined disciplines, photoneuroendocrinology and circadian biology. Photoneuroendocrinology has focused on nonvisual photoreceptors that translate light stimuli into neuroendocrine signals and serve rhythm entrainment. Nonvisual photoreceptors first described in the pineal complex and brain of nonmammalian species are luminance detectors. In the pineal, they control the formation of melatonin, the highly conserved hormone of darkness which is synthesized night by night. Pinealocytes endowed with both photoreceptive and neuroendocrine capacities function as "photoneuroendocrine cells." In adult mammals, nonvisual photoreceptors controlling pineal melatonin biosynthesis and pupillary reflexes are absent from the pineal and brain and occur only in the inner layer of the retina. Encephalic photoreceptors regulate seasonal rhythms, such as the reproductive cycle. They are concentrated in circumventricular organs, the lateral septal organ and the paraventricular organ, and represent cerebrospinal fluid contacting neurons. Nonvisual photoreceptors employ different photopigments such as melanopsin, pinopsin, parapinopsin, neuropsin, and vertebrate ancient opsin. After identification of clock genes and molecular clockwork, circadian biology became cutting-edge research with a focus on rhythm generation. Molecular clockworks tick in every nucleated cell and, as shown in mammals, they drive the expression of more than 3000 genes and are of overall importance for regulation of cell proliferation and metabolism. The mammalian circadian system is hierarchically organized; the central rhythm generator is located in the suprachiasmatic nuclei which entrain peripheral circadian oscillators via multiple neuronal and neuroendocrine pathways. Disrupted molecular clockworks may cause various diseases, and investigations of this interplay will establish a new discipline: circadian medicine.

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.

The Circadian Response to Evening Light Spectra in Early Childhood: Preliminary Insights

Although the sensitivity of the circadian system to the characteristics of light (e.g., biological timing, intensity, duration, spectrum) has been well studied in adults, data in early childhood remain limited. Utilizing a crossover, within-subjects design, we examined differences in the circadian response to evening light exposure at two different correlated color temperatures (CCT) in preschool-aged children. Healthy, good sleeping children (n = 10, 3.0-5.9 years) completed two 10-day protocols. In each protocol, after maintaining a stable sleep schedule for 7 days, a 3-day in-home dim-light circadian assessment was performed. On the first and third evenings of the in-home protocol, dim-light melatonin onset (DLMO) was assessed. On the second evening, children received a 1-h light exposure of 20 lux from either 2700 K (low CCT) or 5000 K (high CCT) (~9 and ~16 melanopic equivalent daylight illuminance (mEDI lux), respectively) centered around their habitual bedtime. Children received the remaining light condition during their second protocol, with the order counterbalanced across participants. Salivary melatonin was collected to compute melatonin suppression and circadian phase shift resulting from each experimental light condition. Melatonin suppression across the 1-h light stimulus was significantly greater during exposure to the high CCT light (M = 56.3%, SD = 19.25%) than during the low CCT light (M = 23.90%, SD = 41.06%). Both light conditions resulted in marked delays of circadian timing, but only a small difference (d = -0.25) was observed in the delay between the 5000 K (M = 35.3 min, SD = 34.3 min) and 2700 K (M = 26.7 min, SD = 15.9 min) conditions. Together, these findings add to a growing literature demonstrating high responsivity of the circadian clock to evening light exposure in early childhood and provide preliminary evidence of melatonin suppression sensitivity to differences in light spectrum in preschool-aged children.

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.

Decades of Night-Shift Work Induce Diurnal Disruption and Corneal Adaptations: Evidence from Pentacam Analysis

We aimed to determine the effects of night-shift work on corneal parameters in thirty-five healthy individuals (24-59 years) in a retrospective cohort study. Among them, 12 hospital nurses regularly worked two shifts, spending a third of their nights awake, whereas 23 age-matched controls never worked shifts and slept regularly. Measurements were performed at least five times within 12 h. We analyzed the keratometric parameters of the corneal front (F) and back (B) surfaces, including the refractive power in the flattest and steepest axes (K1, K2), astigmatism (Astig); and corneal pachymetry (Pachy) at the thinnest corneal point and pupil center, volume relative to the 10 mm corneal diagonal (Vol D10); and surface variance index (ISV). A multilevel mixed-effects linear regression adjusted for age was applied to 905 measurements. All parameters exhibited significant periodic fluctuations (p ≤ 0.005). The two groups also showed significantly different periodic fluctuations (p ≤ 0.008), except in K1B and AstigB. K1/K2 (F and B), AstigF, Pachy, and ISV differed significantly (p < 0.0001). Surprisingly, prolonged night shift work did not increase the ISV, and no evidence of age-related corneal thinning was observed. Long-term night-shift exposures change various corneal parameters, reflecting both concomitant and adaptive effects. This study highlights the impact of consistent sleep deprivation on corneal properties, warranting further research into understanding the long-term effects of night-shift work.

Characteristics of objectively-measured naturalistic light exposure patterns in U.S. adults: A cross-sectional analysis of two cohorts

Light is an environmental feature important for human physiology. Investigation of how light affects population health requires exposure assessment and personal biomonitoring efforts. Here, we derived measures of amount, duration, regularity, and timing from objective personal light (lux) measurement in >4000 participants across two United States (US)-based cohort studies, the Multi-Ethnic Study of Atherosclerosis (MESA) and the Hispanic Community Health Study / Study of Latinos (HCHS/SOL), encompassing eight geographic regions. Objective light and actigraphy data were collected over a week using wrist-worn devices (Actiwatch Spectrum). Cohort-stratified light exposure metrics were analyzed in relation to sex, season, time-of-day, location, and demographic and sleep health characteristics using Spearman correlation and linear and logistic regressions (separately by cohort) adjusted for age, sex (where applicable), and exam site. Light exposure showed sex-specific patterns and had seasonal, diurnal, geographic, and demographic and sleep health-related correlates. Results between independent cohorts were strongly consistent, supporting the utility and feasibility of light biomonitoring. These findings provide a fundamental first characterization of light exposure patterns in a large US sample and will inform future work to incorporate light as a biologically relevant exposure in environmental public health and key component of the human exposome.

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.

Perceptual Visual Acuity Declines With Age in a Rat Model of Retinitis Pigmentosa While Light Perception is Maintained

Purpose

Retinitis pigmentosa (RP) is a leading cause of blindness and genetically induces impairment of the retinal epithelium and photoreceptors. In this study, we investigated the decline in the visual response and visual ability during disease progression. This understanding is crucial for disease staging in patients, establishing therapeutic plans in advance, and evaluating the effects of interventional treatments.

Methods

We used a rat model of inherited RP (Royal College of Surgeons [RCS] rats) and evaluated form visual acuity and light perception using behavioral tests and electrophysiological recordings in the dorsal lateral geniculate nucleus, superior colliculus, and primary visual cortex.

Results

The perceptual form vision (detection of grating stimulus) was attenuated by 9 weeks old. The neural responses in the three early visual areas to flashing grating stimuli with various contrasts and spatial frequencies showed similar degeneration progress as the behavioral evaluations. Light perception (detection of a bright uniform light source) was maintained until at least 11 weeks old. The neural responses to the uniform flashlight stimulus in the three early visual areas were maintained during the same period.

Conclusions

Our findings suggest that form vision is primarily affected by the progression of RP, whereas non-form vision is potentially robust to retinal degeneration. This maintenance of light perception is likely due to the preserved function of intrinsically photosensitive retinal ganglion cells. These results provide useful and fundamental knowledge for evaluating the protective or restorative effects of experimental treatments for RP.

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.

Time-restricted feeding does not improve daily rhythms in locomotion and drinking disrupted by artificial light at night

Exposure to artificial light at night (ALAN) disrupts natural darkness and desynchronizes daily rhythms in physiological processes and behavior. Previously, in rats, we have shown that dim ALAN disturbed the central circadian control and the temporal organization of behavior, and hormonal and metabolic pathways. The measurements of undisturbed daily behavioral (locomotor activity, feeding and drinking) patterns revealed reduced amplitudes and a transitory activity peak in the middle of the light (i.e. resting) period. Recent studies indicated that time-restricted feeding during the active period (TRFd) can strengthen daily rhythms and improve metabolic health. Therefore, the aim of our study was to prevent the dim ALAN-induced attenuation of daily behavioral rhythms by applying TRFd. Male Wistar rats were kept in a 12/12 light/dark cycle in metabolic cages for one week with free access to food and water. After acclimation, rats were divided into two groups: 1) ad libitum food or 2) time-restricted food during the dark period. After one week, both groups were exposed to dim ALAN for two weeks. Despite the enhanced amplitude of the daily feeding rhythm in TRFd animals, ALAN still suppressed the rhythm of locomotor activity, induced the extra peak during the resting period and reduced the bimodal pattern during the night. Furthermore, TRFd did not prevent the drop in anticipatory thirst caused by ALAN at the end of the active period. In conclusion, TRFd was not able to fully prevent the weakning of daily behavioral rhythms by dim ALAN.

Melatonin Alters Preference to Move Toward Monochromatic Lights in Female Syrian Hamsters: A Behavior Associated With Circadian Rhythm

Different light colors have different effects on endogenous melatonin. The preference for light colors has been studied in various animal species, except hamsters. Additionally, no research has been done on how melatonin affects color preference. In this study, I investigated whether melatonin can influence Syrian hamsters' preferences for various light colors. Eighteen female Syrian hamsters were divided into a control group and a test group orally administered 0.01 mg melatonin daily for 30 days. On Day 31, I placed each hamster in the test box at four stages: dark mid-phase; beginning, middle, and end of day. The box had four areas with red, yellow, green, and blue lamps. In each stage, the hamsters' movements were recorded for 5 min. I tested the effects of color, stage, and melatonin treatment using a mixed model analysis. The preferences of both groups changed between the stages (p < 0.001) with the except stages 1 and 4 of the control group (p = 0.012); and stages 2 and 3 of the test group for the yellow color (p = 0.104). There was a significant difference between the test and the control groups in all stages and all colors (p < 0.001) except the green light color in stage 2 (p = 0.007). The results suggest that exogenous melatonin controls the preference for monochromatic light by an unknown mechanism. Circadian endogenous melatonin levels are also effective. Scientists must consider melatonin levels in studies evaluating responses to light.

Spatial distribution and functional integration of displaced retinal ganglion cells

The retina contains distinct types of ganglion cells, which form mosaics with cells of each type at each position of the visual field. Displaced retinal ganglion cells (dRGCs) occur with cell bodies in the inner nuclear layer (INL), and regularly placed RGCs with cell bodies in the ganglion cell layer. An example of mammalian dRGCs are M1-type intrinsically photosensitive ganglion cells (ipRGCs). Little is known, however, about their relationship with regularly placed ipRGCs. We identified mouse ipRGC types M1, M2, and M4/sONɑ by immunohistochemistry and light microscopy. Reconstruction of immunolabeled mosaics from M1 and sONɑ RGCs indicated that dRGCs tiled the retina with their regular RGC partners. Multi-electrode array recordings revealed conventional receptive fields of displaced sONɑ RGCs which fit into the mosaic of their regular counterparts. An RGC distribution analysis showed type-specific dRGC patterns which followed neither the global density distribution of all RGCs nor the local densities of corresponding cell types. The displacement of RGC bodies into the INL occurs in a type-dependent manner, where dRGCs are positioned to form complete mosaics with their regular partners. Our data suggest that dRGCs and regular RGCs serve the same functional role within their corresponding population of RGCs.

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.

Hypothalamic opsin 3 suppresses MC4R signaling and potentiates Kir7.1 to promote food consumption

Mammalian opsin 3 (OPN3) is a member of the opsin family of G-protein-coupled receptors with ambiguous light sensitivity. OPN3 was first identified in the brain (and named encephalopsin) and subsequently found to be expressed in other tissues. In adipocytes, OPN3 is necessary for light responses that modulate lipolysis and glucose uptake, while OPN3 in human skin melanocytes regulates pigmentation in a light-independent manner. Despite its initial discovery in the brain, OPN3 functional mechanisms in the brain remain elusive. Here, we investigated the molecular mechanism of OPN3 function in the paraventricular nucleus (PVN) of the hypothalamus. We show that Opn3 is coexpressed with the melanocortin 4 receptor (Mc4r) in a population of PVN neurons, where it negatively regulates MC4R-mediated cAMP signaling in a specific and Gαi/o-dependent manner. Under baseline conditions, OPN3 via Gαi/o potentiates the activity of the inward rectifying Kir7.1 channel, previously shown to be closed in response to agonist-mediated activation of MC4R in a Gαs-independent manner. In mice, we found that Opn3 in Mc4r-expressing neurons regulates food consumption. Our results reveal the first mechanistic insight into OPN3 function in the hypothalamus, uncovering a unique mechanism by which OPN3 functions to potentiate Kir7.1 activity and negatively regulate MC4R-mediated cAMP signaling, thereby promoting food intake.

Visible Exocytosis of the Non-Photic Signal Neuropeptide Y to the Suprachiasmatic Nucleus in Fasted Transgenic Mice Throughout Their Circadian Rhythms

Organisms maintain circadian rhythms corresponding to approximately 24 h in the absence of external environmental cues, and they synchronize the phases of their autonomous circadian clocks to light-dark cycles, feeding timing, and other factors. The suprachiasmatic nucleus (SCN) occupies the top position of the hierarchy in the mammalian circadian system and functions as a photic-dependent oscillator, while the food-entrainable circadian oscillator (FEO) entrains the clocks of the digestive peripheral tissues and behaviors according to feeding timing. In mammals, neuropeptide Y (NPY) from the intergeniculate leaflet (IGL) neurons projected onto the SCN plays an important role in entraining circadian rhythms to feeding conditions. However, the relationship between the FEO and SCN has been unclear under various feeding conditions. In this study, novel NPY::Venus transgenic (Tg) mice, which expressed the NPY fused to Venus fluorescent protein, were generated to investigate the secretion of NPY on the SCN from the IGL. NPY-containing secretory granules with Venus signals in the SCN slices of the Tg mice could be observed using confocal and super-resolution microscopy. We observed that the number of NPY secretory granules released on the SCNs increased during fasting, and these mice were valuable tools for further investigating the role of NPY secretion from the IGL to the SCN in mediating interactions between the FEO and the SCN.

Integrating Assessment of Circadian Rhythmicity to Improve Treatment Outcomes for Circadian Rhythm Sleep-Wake Disorders: Updates on New Treatments

Purpose of Review

Despite advancements in basic circadian research, development of new diagnostic and treatment strategies for circadian rhythm sleep-wake disorders (CRSWDs) has been slow. Here, we review the most recent innovations in human circadian assessment and emerging new therapies for CRSWDs.

Recent Findings

Researchers have improved existing circadian assessment methods to overcome logistical barriers and developed novel circadian assessment methods. New treatments for CRSWDs involve pharmacological and behavioral treatments that modulate circadian phase, amplitude, and/or robustness of the central circadian clock.

Summary

Commercialization of these emerging tools will require overcoming barriers, such as additional testing to confirm the underlying pathology and mechanism of action of potential treatments. Clinicians and scientists are also called to survey adjacent fields and adopt existing diagnostic tools that may offer diagnostic clarity in CRSWDs. Lastly, we must continue to advocate for medical insurance coverage of current and future tools and technologies to improve patient care.

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.

Expression of Osteopontin in M2 and M4 Intrinsically Photosensitive Retinal Ganglion Cells in the Mouse Retina

Purpose

Melanopsin-expressing intrinsically photosensitive (ip) retinal ganglion cells (RGCs) can be divided into six different subtypes (M1 - M6). Yet, specific markers exist for only some of these subtypes that could be employed to study the function of individual subtypes. Osteopontin (Spp1) marks αRGC, suggesting that, across ipRGCs, it would only mark the M4-ipRGC subtype (synonymous to ON-sustained αRGCs). Recent evidence suggests that osteopontin expression could spread to other ipRGC subtypes. Therefore, this study aims to characterize the expression pattern of osteopontin across ipRGC subtypes in mice.

Methods

Single-cell RNA (scRNA-seq) sequencing data from murine RGCs were analyzed to identify expression patterns of Spp1 across ipRGCs. Immunohistochemistry (IHC) was performed on retinal cryosections and flatmounts from C57BL/6J mice to characterize the localization of osteopontin across ipRGCs. Neurite tracing was employed to study dendritic morphology and identify individual ipRGC subtypes.

Results

scRNA-seq analysis revealed Spp1 expression in two distinct clusters of ipRGCs. IHC confirmed osteopontin colocalization with neurofilament heavy chain, an established marker for αRGCs, including M4-ipRGCs. Spp1 immunoreactivity was moreover identified in one additional group of ipRGCs. By dendritic morphology and stratification, those cells were clearly identified as M2-ipRGCs.

Conclusions

Our findings demonstrate that osteopontin is expressed in both M2- and M4-ipRGCs, challenging the notion of osteopontin as a marker exclusively for αRGCs. IHC double-labeling for osteopontin and melanopsin provides a novel method to identify and differentiate M2 ipRGCs from other subtypes. This will support the study of ipRGC physiology in a subtype -specific manner and may, for instance, foster research in the field of optic nerve injury.

The electroretinography to identify biomarkers of idiopathic hypersomnia and narcolepsy type 1

Hypersomnia spectrum disorders are underdiagnosed and poorly treated due to their heterogeneity and absence of biomarkers. The electroretinography has been proposed as a proxy of central dysfunction and has proved to be valuable to differentiate certain psychiatric disorders. Hypersomnolence is a shared core feature in central hypersomnia and psychiatric disorders. We therefore aimed to identify biomarkers by studying the electroretinography profile in patients with narcolepsy type 1, idiopathic hypersomnia and in controls. Cone, rod and retinal ganglion cells electrical activity were recorded with flash-electroretinography in non-dilated eye of 31 patients with idiopathic hypersomnia (women 84%, 26.6 ± 5.9 years), 19 patients with narcolepsy type 1 (women 63%, 36.6 ± 12.7 years) and 43 controls (women 58%, 30.6 ± 9.3 years). Reduced cone a-wave amplitude (p = 0.039) and prolonged cone (p = 0.022) and rod b-wave (p = 0.009) latencies were observed in patients with narcolepsy type 1 as compared with controls, while prolonged photopic negative response-wave latency (retinal ganglion cells activity) was observed in patients with idiopathic hypersomnia as compared with controls (p = 0.033). The rod and cone b-wave latency clearly distinguished narcolepsy type 1 from idiopathic hypersomnia and controls (area under the curve > 0.70), and the photopic negative response-wave latency distinguished idiopathic hypersomnia and narcolepsy type 1 from controls with an area under the curve > 0.68. This first original study shows electroretinography anomalies observed in patients with hypersomnia. Narcolepsy type 1 is associated with impaired cone and rod responses, whereas idiopathic hypersomnia is associated with impaired retinal ganglion cells response, suggesting different phototransduction alterations in both hypersomnias. Although these results need to be confirmed with a larger sample size, the electroretinography may be a promising tool for clinicians to differentiate hypersomnia subtypes.

Ambient chemical and physical approaches for the modulation of sleep and wakefulness

Humans spend a third of their lives asleep. While the sleep-wake behaviors are primarily modulated by homeostasis and circadian rhythm, several ambient chemical and physical factors, including light, sound, odor, vibration, temperature, electromagnetic radiation, and ultrasound, also affect sleep and wakefulness. Light at different wavelengths has different effects on sleep and wakefulness. Sound not only promotes but also suppresses sleep; this effect is mediated by certain nuclei, including the pedunculopontine nucleus and inferior colliculus. Certain sleep-promoting odorants regulate sleep through the involvement of the olfactory bulb and olfactory tubercle. In addition, vibrations may induce sleep through the vestibular system. A modest increase in ambient temperature leads to an increase in sleep duration through the involvement of the preoptic area. Electromagnetic radiation has a dual effect on sleep-wake behaviors. The stimulation produced by the ambient chemical and physical factors activates the peripheral sensory system, which converts the chemical and physical stimuli into nerve impulses. This signal is then transmitted to the central nervous system, including several nuclei associated with the modulation of sleep-wake behaviors. This review summarizes the effects of ambient chemical and physical factors on the regulation of sleep and wakefulness, as well as the underlying neurobiological mechanisms.

Circadian rhythm and the influence of light on parameters related to calcium metabolism in stroke patients admitted for rehabilitation

Hospitalized stroke patients are at high risk of developing circadian disruption due to lack of natural sunlight. This may affect the circadian rhythm of the calcium metabolism. This study is a secondary explorative analysis from a Randomized Controlled Trial. Acute stroke patients requiring a minimum of two weeks of rehabilitation were randomized to an Intervention unit (IU) equipped with naturalistic light or a Control unit (CU) with standard indoor lighting. Blood was drawn across 24 h at inclusion and discharge in 45 patients, 25 from the IU and 20 from the CU. Calcium showed significant rhythmicity at inclusion and discharge in both groups. Alkaline phosphatase, parathyroid hormone (PTH), and Vitamin D exhibited no significant rhythmicity at inclusion or discharge in either group while phosphate exhibited rhythmicity at discharge in the CU. PTH levels were elevated in the CU group compared to the IU group at time of discharge. Of the measured parameters, only calcium exhibited circadian rhythmicity after stroke. Naturalistic light did not have any influence on the rhythmicity, indicating that light may not be the main circadian regulator of the circadian oscillations that regulate calcium metabolism. PTH seems to be decreased by naturalistic light.

The relationship between the vestibular system and the circadian timing system: A review

This review attempts to analyze the relationship between the vestibular system and the circadian timing system. The activity of the biological clock allows an organism to optimally perform its tasks throughout the nychtemeron. To achieve this, the biological clock is subjected to exogenous factors that entrain it to a 24h period. While the most powerful synchronizer is the light-dark cycle produced by the Earth's rotation, research has led to the hypothesis of the vestibular system as a possible non-photic time cue used to entrain circadian rhythms. Demonstrated neuroanatomical pathways between vestibular nuclei and suprachiasmatic nuclei could transmit this message. Moreover, functional evidence in both humans and animals has shown that vestibular disruption or stimulation may lead to changes in circadian rhythms characteristics. Vestibular stimulations could be considered to act synergistically with other synchronizers, such as light, to ensure the entrainment of biological rhythms over the 24-h reference period.

Evaluation of the Digital Ventilated Cage® system for circadian phenotyping

The study of circadian rhythms has been critically dependent upon analysing mouse home cage activity, typically employing wheel running activity under different lighting conditions. Here we assess a novel method, the Digital Ventilated Cage (DVC®, Tecniplast SpA, Italy), for circadian phenotyping. Based upon capacitive sensors mounted under black individually ventilated cages with inbuilt LED lighting, each cage becomes an independent light-controlled chamber. Home cage activity in C57BL/6J mice was recorded under a range of lighting conditions, along with circadian clock-deficient cryptochrome-deficient mice (Cry1-/-, Cry2-/- double knockout). C57BL/6J mice exhibited a 24 h period under light/dark conditions, with a free-running period of 23.5 h under constant dark, and period lengthening under constant light. Animals displayed expected phase shifting responses to jet-lag and nocturnal light pulses. Sex differences in circadian parameters and phase shifting responses were also observed. Cryptochrome-deficient mice showed subtle changes in activity under light/dark conditions and were arrhythmic under constant dark, as expected. Our results show the suitability of the DVC system for circadian behavioural screens, accurately detecting circadian period, circadian disruption, phase shifts and mice with clock defects. We provide an evaluation of the strengths and limitations of this method, highlighting how the use of the DVC for studying circadian rhythms depends upon the research requirements of the end user.

Neuropeptidergic Input from the Lateral Hypothalamus to the Suprachiasmatic Nucleus Alters the Circadian Period in Mice

In mammals, the central circadian clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus, which transmits circadian information to other brain regions and regulates the timing of sleep and wakefulness. Neurons in the lateral hypothalamus (LH), particularly those producing melanin-concentrating hormone (MCH) and orexin, are key regulators of sleep and wakefulness. Although the SCN receives nonphotic input from other brain regions, the mechanisms of functional input from the LH to the SCN remain poorly understood. Here, we show that orexin and MCH peptides influence the circadian period within the SCN of both sexes. When these neurons are ablated, the circadian behavioral rhythms are lengthened under constant darkness. Using anterograde and retrograde tracing, we found that orexin and MCH neurons project to the SCN. Furthermore, the application of these peptides to cultured SCN slices shortened circadian rhythms and reduced intracellular cAMP levels. Additionally, pharmacological reduction of intracellular cAMP levels similarly shortened the circadian period in SCN slices. These findings suggest that orexin and MCH peptides from the LH contribute to the modulation of the circadian period in the SCN.

Spatial Mapping of Activity Changes across Sensory Areas Following Visual Deprivation in Adults

Loss of a sensory modality triggers global adaptation across brain areas, allowing the remaining senses to guide behavior more effectively. There are specific synaptic and circuit plasticity observed across many sensory areas, which suggests potential widespread changes in activity. Here we used a cFosTRAP2 mouse line to drive tdTomato (tdT) expression in active cells to spatially map the extent of activity changes in various sensory areas in adult mice of both sexes following two modes of visual deprivation. We found that in the primary visual cortex (V1), both dark exposure (DE) and enucleation (EN) caused an initial loss of active cells followed by a partial rebound, which occurred relatively more in the superficial layers. A similar pattern was observed in the secondary visual cortex, especially in the lateral areas (V2L). The spared primary sensory cortices adapted distinctly. In the primary somatosensory barrel cortex (S1BF), there was a change in the density of active cells dependent on the duration and the mode of visual deprivation. In the primary auditory cortex (A1), there was a relative reduction in the density of active cells in the superficial layers without a significant change in the overall density. There were minimal changes in the active cell density in the secondary cortices of the spared senses and the multisensory retrosplenial cortex (RSP). Our results are consistent with cross-modal recruitment of the deprived visual cortex and compensatory plasticity in the spared primary sensory cortices that can support enhanced processing and refinement of the spared senses.

Meta-analysis of retinal transcriptome profiling studies in animal models of myopia

Objective

Myopia prevalence is increasing at alarming rates, yet the underlying mechanistic causes are not understood. Several studies have employed experimental animal models of myopia and transcriptome profiling to identify genes and pathways contributing to myopia. In this study, we determined the retinal transcriptome changes in response to form deprivation in mouse retinas. We then conducted a transcriptome meta-analysis incorporating all publicly available datasets and analyzed how the results related to the genes associated with refractive errors in human genome-wide association studies (GWAS).

Methods

Form deprivation was induced in three male C57BL6/J mice from postnatal day 28 (P28) to P42. Retinal gene expression was analyzed with RNA sequencing, followed by differential gene expression analysis with DESeq2 and identification of associated pathways with the Kyoto Encyclopedia of Genes and Genomes (KEGG). A systematic search identified four similar retinal transcriptomics datasets in response to experimental myopia using chicks or mice. The five studies underwent transcriptome meta-analyses to determine retinal gene expression changes and associated pathways. The results were compared with genes associated with human myopia.

Results

Differential gene expression analysis of form-deprived mouse retinas revealed 235 significantly altered transcripts, implicating the BMP2 signaling pathway and circadian rhythms, among others. Transcriptome-wide meta-analyses of experimental myopia datasets found 427 differentially expressed genes in the mouse model and 1,110 in the chick model, with limited gene overlap between species. Pathway analysis of these two gene sets implicated TGF-beta signaling and circadian rhythm pathways in both mouse and chick retinas. Some pathways associated only with mouse retinal changes included dopamine signaling and HIF-1 signaling pathway, whereas glucagon signaling was only associated with gene changes in chick retinas. The follistatin gene changed in both mouse and chick retinas and has also been implicated in human myopia. TGF-beta signaling pathway and circadian entrainment processes were associated with myopia in mice, chicks, and humans.

Conclusion

This study highlights the power of combining datasets to enhance statistical power and identify robust gene expression changes across different experimental animal models and conditions. The data supports other experimental evidence that TGF-beta signaling pathway and circadian rhythms are involved in myopic eye growth.

Temporal and spatial layout of endocannabinoid system components in the mouse suprachiasmatic nucleus

Environmental light serves as the main entraining signal for the central circadian pacemaker, the suprachiasmatic nucleus of the hypothalamus (SCN). To shift clock timing with the changing environment, minute adjustments are necessary and the endocannabinoid system (ECS) acts as a neuromodulatory signaling mechanism in the SCN. These systems exert bidirectional effects on one another, still, limited knowledge exists about the role of endocannabinoids in circadian rhythm regulation. Therefore, we investigated the temporal and spatial molecular layouts of the ECS in the SCN of male and female C57BL/6J mice. We utilized laser capture microdissection and quantitative RT-PCR to investigate the ECS temporal layout in the SCN, detected 13 of 19 examined ECS components, and followed up with two 24-hour time course experiments, one under 12:12 light/dark and one under constant dark conditions. All enzymatic machinery related to endocannabinoid synthesis and degradation investigated were found present; however, only cannabinoid receptor 1 (Cnr1) was detected from the 6 ECS related receptors investigated. Cosinor analysis revealed circadian rhythms in many components in both sexes and lighting conditions. Next, we investigated the spatial localization of ECS components in the SCN with RNAscope in situ hybridization. Some genes, such as Cnr1, were more highly expressed in neurons with others, such as Fabp7, were elevated in astrocytes. Cnr1 levels were highest in neurons that do not express the neuropeptides Avp or Vip, and lowest in Vip neurons. Our results support the idea that locally regulated ECS signaling through neuronal CB1 modulates circadian clock function.

A time for sex: circadian regulation of mammalian sexual and reproductive function

The circadian clock regulates physiological and biochemical processes in nearly every species. Sexual and reproductive behaviors are two processes controlled by the circadian timing system. Evidence supporting the importance of proper clock function on fertility comes from several lines of work demonstrating that misalignment of biological rhythms or disrupted function of the body's master clock, such as occurs from repeated shift work or chronic jet lag, negatively impacts reproduction by interfering with both male and female fertility. Along these lines, dysregulation of clock genes leads to impairments in fertility within mammals, and disruption of circadian clock timing negatively impacts sex hormone levels and semen quality in males, and it leads to ovulatory deficiencies in females. Here, we review the current understanding of the circadian modulation of both male and female reproductive hormones-from animal models to humans. Further, we discuss neural circuits within the hypothalamus that may regulate circadian changes in mammalian sexual behavior and reproduction, and we explore how knowledge of such circuits in animal models may help to improve human sexual function, fertility, and reproduction.

Light-eye-body axis: exploring the network from retinal illumination to systemic regulation

The human body is an intricate system, where diverse and complex signaling among different organs sustains physiological activities. The eye, as a primary organ for information acquisition, not only plays a crucial role in visual perception but also, as increasing evidence suggests, exerts a broad influence on the entire body through complex circuits upon receiving light signals which is called non-image-forming vision. However, the extent and mechanisms of light's impact on the body through the eyes remain insufficiently explored. There is also a dearth of comprehensive reviews elucidating the intricate interplay between light, the eye, and the systemic connections to the entire body. Herein, we propose the concept of the light-eye-body axis to systematically encapsulate the extensive non-image-forming effects of light signals received by the retina on the entire body. We reviewed the visual-neural structure basis of the light-eye-body axis, summarized the mechanism by which the eyes regulate the whole body and the current research status and challenges within the physiological and pathological processes involved in the light-eye-body axis. Future research should aim to expand the influence of the light-eye-body axis and explore its deeper mechanisms. Understanding and investigating the light-eye-body axis will contribute to improving lighting conditions to optimize health and guide the establishment of phototherapy standards in clinical practice.

Effect of hydrogen-rich saline on melanopsin after acute blue light-induced retinal damage in rats

Excessive exposure to blue light can cause retinal damage. Hydrogen-rich saline (HRS), one of the hydrogen therapies, has been demonstrated to be effective in eye photodamage, but the effect on the expression of melanopsin in intrinsically photosensitive retinal ganglion cells (ipRGCs) is unknown. In this study, we used a rat model of light-induced retinal injury to observe the expression of melanopsin after HRS treatment and to determine the effect of HRS on retinal ganglion cell protection. Adult SD rats were exposed to blue light (48 h) and treated with HRS for 0, 3, 7, and 14 days. Real-time polymerase chain reaction (qRT-PCR) and Western blotting (WB) were performed to find the expression of genes and proteins, respectively. The function of retinal ipRGCs was measured by pattern-evoked electroretinography (pERG). The number and morphological changes of melanopsin-positive ganglion cells in the retina were observed by immunofluorescence (IF). Acute blue light exposure caused a decrease in ipRGC function, decreased expression of melanopsin protein and the melanopsin-positive RGCs, and diminished immunoreactivity in dendrites. However, over time, melanopsin showed a tendency to self-recovery, with an increase in melanopsin protein expression and the number of melanopsin-positive RGCs, with incomplete recovery of function within two weeks. HRS treatment accelerated the recovery process, with a significant increase in melanopsin expression and the number of melanopsin-positive RGCs, and an improvement in the pERG waveform within two weeks.

Lactic acid contributes to the emergence of depression-like behaviors triggered by blue light exposure during sleep

The threat posed by light pollution to human health is increasing remarkably. As demand for high-efficiency and bright lighting increases, so does the blue light content from artificial sources. Although animal studies suggested blue light induced depression-like behaviors, human evidence remained limited, and the mechanisms by which blue light affects depression remained elusive. This study aimed to investigate the association between blue light exposure and depression in humans, and explored the underlying mechanisms that driving depression-like behaviors induced by blue light. Our population findings showed that the high-blue-light exposure at night was positively associated with depressive symptoms. Lactic acid was relevant to depression with Mendelian randomization analysis. Moreover, animal studies demonstrated that exposure to blue light during sleep (BLS) induced depression-like behaviors in the animals. Metabolomics and colorimetric analyses revealed elevated levels of lactic acid in the cerebrospinal fluid and lateral habenula (LHb) of rats with depression-like behaviors induced by BLS. The administration of a lactate inhibitor (Oxamate) alleviated these behaviors, along with changes in neuronal excitability, synaptic function, and morphology in the LHb. Overall, our study suggests that excessive exposure to high blue light-content artificial light at night links to increased depressive symptoms, revealing possible molecular mechanisms and prevention strategies, which are crucial for addressing environmentally related mental health issues.

Effects of light on biological functions and human sleep

The nonvisual effects of light in humans are mainly conveyed by a subset of retinal ganglion cells that contain the pigment melanopsin which renders them intrinsically photosensitive (= intrinsically photosensitive retinal ganglion cells, ipRGCs). They have direct connections to the main circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus and modulate a variety of physiological processes, pineal melatonin secretion, autonomic functions, cognitive processes such as attention, and behavior, including sleep and wakefulness. This is because efferent projections from the SCN reach other hypothalamic nuclei, the pineal gland, thalamus, basal forebrain, and the brainstem. The ipRGCs also directly impact the prefrontal cortex and the perihabenular nucleus (mood). In particular, light suppresses the secretion of melatonin in a dose-dependent manner, mainly depending on irradiance and spectral composition of light. There is evidence that exposure to light-emitting devices from luminaires and screens before bedtime can impact on sleep onset latency, sleep duration, and sleep quality. Likewise, light exposure during daytime modulates sleep architecture, duration, and sleep quality during the subsequent night. Therefore, the integration of acute, circadian, and long-term effects of light together influence sleep-wake quality and behavior in healthy individuals, as well as in patients with psychiatric or medical disorders.

Distinct retinal ganglion cell types in strictly subterranean, naturally microphthalmic mammals

African mole-rats (Bathyergidae, Rodentia) are subterranean rodents that live in extensive dark underground tunnel systems and rarely emerge aboveground. They can discriminate between light and dark but show no overt visually driven behaviours except for light-avoidance responses. Their eyes and central visual system are strongly reduced but not degenerated. Here, we focus on retinal ganglion cells (RGCs). Sighted mammals have numerous RGC types with distinct morphological and functional properties that encode different aspects of a visual scene. We analysed the morphological diversity of 216 intracellularly dye-injected RGCs in the giant mole-rat (Fukomys mechowii) and 48 RGCs in Ansell's mole-rat (Fukomys anselli). Using a hierarchical cluster analysis on 11 morphological parameters, we show that both species possess at least five RGC types with distinct dendritic field sizes and branching patterns. These resemble some RGC types of the mouse and rat, but mole-rat RGCs feature overall sparser and more asymmetric branching patterns. The dendritic trees of most RGCs in all clusters are monostratified in the inner plexiform layer, but bistratified and multistratified/diffuse cells also exist. Thus, although RGC morphologies have become disorganized, the basic retinal organization principle of parallel information processing by distinct RGC types is retained.

Axon guidance during mouse central nervous system regeneration is required for specific brain innervation

Reconstructing functional neuronal circuits is one major challenge of central nervous system repair. Through activation of pro-growth signaling pathways, some neurons achieve long-distance axon regrowth. Yet, functional reconnection has hardly been obtained, as these regenerating axons fail to resume their initial trajectory and reinnervate their proper target. Axon guidance is considered to be active only during development. Here, using the mouse visual system, we show that axon guidance is still active in the adult brain in regenerative conditions. We highlight that regenerating retinal ganglion cell axons avoid one of their primary targets, the suprachiasmatic nucleus (SCN), due to Slit/Robo repulsive signaling. Together with promoting regeneration, silencing Slit/Robo in vivo enables regenerating axons to enter the SCN and form active synapses. The newly formed circuit is associated with neuronal activation and functional recovery. Our results provide evidence that axon guidance mechanisms are required to reconnect regenerating axons to specific brain nuclei.

Light modulates glucose and lipid homeostasis via the sympathetic nervous system

Light is an important environmental factor for vision and for diverse physiological and psychological functions. Light can also modulate glucose metabolism. Here, we show that in mice, light is critical for glucose and lipid homeostasis by regulating the sympathetic nervous system, independent of circadian disruption. Light deprivation from birth elicits insulin hypersecretion, glucagon hyposecretion, lower gluconeogenesis, and reduced lipolysis by 6 to 8 weeks in male, but not female, mice. These metabolic defects are consistent with blunted sympathetic activity, and indeed, sympathetic responses to a cold stimulus are substantially attenuated in dark-reared mice. Further, long-term dark rearing leads to body weight gain, insulin resistance, and glucose intolerance. Notably, metabolic dysfunction can be partially alleviated by 5 weeks exposure to a regular light-dark cycle. These studies provide insight into circadian-independent mechanisms by which light directly influences whole-body physiology and better understanding of metabolic disorders linked to aberrant environmental light conditions.

Elevated Bile Acids Induce Circadian Rhythm Sleep Disorders in Chronic Liver Diseases

BACKGROUND & AIMS

Sleep disorders (SDs) are common in chronic liver diseases (CLDs). Some SDs arise from impaired internal clock and are, hence, circadian rhythm SDs (CRSDs). Bile acids (BAs), whose levels are increased in many CLDs, reciprocally interact with circadian rhythm. This study explores the mechanisms underlying CRSDs in CLDs and novel therapies.

METHODS

We monitored the sleep of patients with CLD using actigraphic watch and established male mouse cholemia models by feeding with BA or bile duct ligation. Sleep-wake cycle and circadian rhythm were analyzed by electroencephalogram-electromyography and locomotor wheel-running experiments.

RESULTS

Patients with CLD showed CRSD-like phenotypes including increased night activity and early awakening, which were strongly correlated with increased BA levels (ie, cholemia). CRSDs, including shortened circadian period, were recapitulated in 2 cholemic mouse models. Mechanistically, elevated BAs in the suprachiasmatic nucleus (SCN) activated BA receptor Takeda G protein-coupled receptor 5 (Tgr5), which, in turn, increased the level and phosphorylation of Period2 (Per2), a master rhythm regulator, through extracellular signal-regulated kinase (Erk) and casein kinase 1ε (CK1ε). Per2 phosphorylation inhibited its nuclear import, which would release its transcriptional inhibition and expedite the circadian cycle. Cholemia also blunted the light entrainment response and light-induced phase change of SCN mediated by the neurons expressing gastrin releasing peptide through Tgr5-Per2 axis. BA sequestrant or CK1 inhibitor reversed the CRSDs in cholemic mice by restoring Per2 distribution.

CONCLUSIONS

Cholemia is a major risk factor for CRSDs in CLDs and, hence, a promising target in future clinical study.

Clinical benefits of modifying the evening light environment in an acute psychiatric unit: A single-centre, two-arm, parallel-group, pragmatic effectiveness randomised controlled trial

BACKGROUND

The impact of light exposure on mental health is increasingly recognised. Modifying inpatient evening light exposure may be a low-intensity intervention for mental disorders, but few randomised controlled trials (RCTs) exist. We report a large-scale pragmatic effectiveness RCT exploring whether individuals with acute psychiatric illnesses experience additional benefits from admission to an inpatient ward where changes in the evening light exposure are integrated into the therapeutic environment.

METHODS AND FINDINGS

From 10/25/2018 to 03/29/2019, and 10/01/2019 to 11/15/2019, all adults (≥18 years of age) admitted for acute inpatient psychiatric care in Trondheim, Norway, were randomly allocated to a ward with a blue-depleted evening light environment or a ward with a standard light environment. Baseline and outcome data for individuals who provided deferred informed consent were used. The primary outcome measure was the mean duration of admission in days per individual. Secondary outcomes were estimated mean differences in key clinical outcomes: Improvement during admission (The Clinical Global Impressions Scale-Improvement, CGI-I) and illness severity at discharge (CGI-S), aggressive behaviour during admission (Broset Violence Checklist, BVC), violent incidents (Staff Observation Aggression Scale-Revised, SOAS-R), side effects and patient satisfaction, probabilities of suicidality, need for supervision due to suicidality, and change from involuntary to voluntary admission. The Intent to Treat sample comprised 476 individuals (mean age 37 (standard deviation (SD) 13.3); 193 (41%) were male, 283 (59%) were female). There were no differences in the mean duration of admission (7.1 days for inpatients exposed to the blue-depleted evening light environment versus 6.7 days for patients exposed to the standard evening light environment; estimated mean difference: 0.4 days (95% confidence interval (CI) [-0.9, 1.9]; p = 0.523). Inpatients exposed to the blue-depleted evening light showed higher improvement during admission (CGI-I difference 0.28 (95% CI [0.02, 0.54]; p = 0.035), Number Needed to Treat for clinically meaningful improvement (NNT): 12); lower illness severity at discharge (CGI-S difference -0.18 (95% CI [-0.34, -0.02]; p = 0.029), NNT for mild severity at discharge: 7); and lower levels of aggressive behaviour (difference in BVC predicted serious events per 100 days: -2.98 (95% CI [-4.98, -0.99]; p = 0.003), NNT: 9). There were no differences in other secondary outcomes. The nature of this study meant it was impossible to blind patients or clinical staff to the lighting condition.

CONCLUSIONS

Modifying the evening light environment in acute psychiatric hospitals according to chronobiological principles does not change duration of admissions but can have clinically significant benefits without increasing side effects, reducing patient satisfaction or requiring additional clinical staff.

TRIAL REGISTRATION

Clinicaltrials.gov NCT03788993; 2018 (CRISTIN ID 602154).

Selecting, implementing and evaluating control and placebo conditions in light therapy and light-based interventions

Introduction: Light profoundly influences human physiology, behaviour and cognition by affecting various functions through light-sensitive cells in the retina. Light therapy has proven effective in treating seasonal depression and other disorders. However, designing appropriate control conditions for light-based interventions remains a challenge.Materials and methods: This article presents a novel framework for selecting, implementing and evaluating control conditions in light studies, offering theoretical foundations and practical guidance. It reviews the fundamentals of photoreception and discusses control strategies such as dim light, darkness, different wavelengths, spectral composition and metameric conditions. Special cases like dynamic lighting, simulated dawn and dusk, complex interventions and studies involving blind or visually impaired patients are also considered.Results: The practical guide outlines steps for selection, implementation, evaluation and reporting, emphasizing the importance of α-opic calculations and physiological validation.Conclusion: In conclusion, constructing effective control conditions is crucial for demonstrating the efficacy of light interventions in various research scenarios.

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.

Retinal ganglion cell circuits and glial interactions in humans and mice

Retinal ganglion cells (RGCs) are the brain's gateway for vision, and their degeneration underlies several blinding diseases. RGCs interact with other neuronal cell types, microglia, and astrocytes in the retina and in the brain. Much knowledge has been gained about RGCs and glia from mice and other model organisms, often with the assumption that certain aspects of their biology may be conserved in humans. However, RGCs vary considerably between species, which could affect how they interact with their neuronal and glial partners. This review details which RGC and glial features are conserved between mice, humans, and primates, and which differ. We also discuss experimental approaches for studying human and primate RGCs. These strategies will help to bridge the gap between rodent and human RGC studies and increase study translatability to guide future therapeutic strategies.

Post-chemotherapy changes in retinal pigment epithelium in retinoblastoma eyes

OBJECTIVE

Histopathological analysis of the retinal pigment epithelial (RPE) changes in retinoblastoma (RB) cases who received pre-surgical chemotherapy.

DESIGN

Laboratory-based observational study.

METHODS

Five-year analysis was performed to identify Retinoblastoma cases who underwent enucleation after receiving systemic chemotherapy. Grossly, RPE cells were observed in flat preparation in small calottes by staining with fluorescein stain in the raw specimens. They were documented under the objective of compound microscope and compared with hematoxylin and eosin-stained slides in the permanent tissue sections.

RESULTS

Out of 51 cases of RB, post-chemotherapy enucleation was performed in 17 cases. Mean age of enucleation was 3.2 years. Endophytic RB (11 cases, 64.71%) was more common than the exophytic variety. Choroidal involvement was noted in 8 cases (47.06%), and optic nerve involvement was seen in 5 cases (29.4%). Focal and diffuse RPE changes were seen in one case each (5.88%). Central RPE cell changes near the cell nucleus were seen in all 17 cases (100%), which were documented by both fluorescein and Hematoxylin and eosin stain (100%). Drusens were observed in 8 cases (47.06%), and RPE proliferations were seen in 3 cases (17.65%).

CONCLUSION

The study highlights the characteristic histopathological RPE changes after systemic chemotherapy in RB cases. These changes may be attributable to cell nucleus damage after chemotherapy.

Behavioural determinants of physiologically-relevant light exposure

Light exposure triggers a range of physiological and behavioural responses that can improve and challenge health and well-being. Insights from laboratory studies have recently culminated in standards and guidelines for measuring and assessing healthy light exposure, and recommendations for healthy light levels. Implicit to laboratory paradigms is a simplistic input-output relationship between light and its effects on physiology. This simplified approach ignores that humans actively shape their light exposure through behaviour. This article presents a novel framework that conceptualises light exposure as an individual behaviour to meet specific, person-based needs. Key to healthy light exposure is shaping behaviour, beyond shaping technology.

What can the eye see with melanopsin?

A subpopulation of human retinal ganglion cells contains the melanopsin photopigment, allowing them to act as a fifth photoreceptor class. These ganglion cells project to the visual cortex, but to reveal its intrinsic contribution to conscious vision is technically challenging as it requires melanopsin to be separated from the responses originating in the rods and three cone classes. Using a display engineered to isolate the melanopic visual response, we show that it detects lowpass spatial (≤0.35 cycles per degree) and temporal image content (≤1 Hz) but cannot reconstruct the stimulus form necessary for object recognition. We demonstrate that a model of the spatially diffuse intrinsically-photosensitive retinal ganglion cells' sampling structure is predictive of the measured image reconstruction limits of melanopic spatial vision. Separately, we find that under five-photoreceptor silent substitution conditions, rod pathways alone can support form vision in bright lighting when typically thought to be in saturation. Form vision that is absent from melanopsin can be only perceived in mixtures of both melanopsin and rod signals because it is the rod pathway that sees the form. Our findings show that melanopsin's unique tuning to the diffuse and slow-changing elements in the world provides a stabilized reference point for vision.

Circadian Regulation in Diurnal Mammals: Neural Mechanisms and Implications in Translational Research

Diurnal and nocturnal mammals have evolved unique behavioral and physiological adaptations to optimize survival for their day- or night-active lifestyle. The mechanisms underlying the opposite activity patterns are not fully understood but likely involve the interplay between the circadian time-keeping system and various arousal- or sleep-promoting factors, e.g., light or melatonin. Although the circadian systems between the two chronotypes share considerable similarities, the phase relationships between the principal and subordinate oscillators are chronotype-specific. While light promotes arousal and wakefulness in diurnal species like us, it induces sleep in nocturnal ones. Similarly, melatonin, the hormone of darkness, is commonly used as a hypnotic in humans but is secreted in the active phase of nocturnal animals. Thus, the difference between the two chronotypes is more complex than a simple reversal, as the physiological and neurological processes in diurnal mammals during the day are not equivalent to that of nocturnal ones at night. Such chronotype differences could present a significant translational gap when applying research findings obtained from nocturnal rodents to diurnal humans. The potential advantages of diurnal models are being discussed in a few sleep-related conditions including familial natural short sleep (FNSS), obstructive sleep apnea (OSA), and Smith-Magenis syndrome (SMS). Considering the difference in chronotype, a diurnal model will be more adequate for revealing the physiology and physiopathology pertaining to human health and disease, especially in conditions in which circadian rhythm disruption, altered photic response, or melatonin secretion is involved. We hope the recent advances in gene editing in diurnal rodents will promote greater utility of the diurnal models in basic and translational research.

Supercapacitively Liquid-Solid Dual-State Optoelectronics

Photo-transduction of solid-state optoelectronics occurs in semiconductors or their interfaces. Considering the confined active area and interfacial capacitance of solid-state materials, solid-state optoelectronics faces inherent limitations in photo-transduction, especially for bionic vision, and the performance is lower than that of living systems. For example, a photoreceptor generates pA-level photocurrent when absorbing a single photon. Here, a liquid-solid dual-state phototransistor is demonstrated, in which photo-transduction and modulation take place at the microporous interface between semiconductors and water, mimicking principles of the photoreceptor. When operating in the water, an orderly stacked photo-harvesting covalent organic framework layer generates supercapacitively photogating modulation of the channel conductivity via a dual-state interface, achieving responsivity of 4.6 × 1010 A W-1 and detectivity of 1.62 × 1016 Jones at room temperature, several orders of magnitude higher than other photodetectors. Such bio-inspired dual-state optoelectronics enables high-contrast scotopic neuromorphic imaging with responsivity greater than photoreceptors, holding promise for constructing optoelectronic systems with performance beyond conventional solid-state optoelectronics.