A Visual Circuit Related to Habenula Underlies the Antidepressive Effects of Light Therapy

Efficacy evaluation and facial expressions biomarker of light therapy in youths with subthreshold depression: A randomized control trial study

BACKGROUND

Simpler and more feasible light therapy protocols, and objective indicators for assessing its effectiveness is lacking. We aimed to evaluate the efficacy of light therapy on subthreshold depression (SD) among college students and explore facial expressions as an objective biomarker across different treatment groups.

METHODS

From September 13, 2021, to January 4, 2022, college students with SD were recruited from a university in Hubei Province, randomly assigned to Bright Light Therapy (BLT) group (10,000 lx), Dim Light Therapy (DLT) group (200 lx), or Waiting List Control (WLC) group (no intervention). Self-reported questionnaire and facial expressions were assessed for all participants before and after intervention. Repeated measures ANOVA and logistic regression were conducted to compare baseline and post-intervention differences among three groups.

RESULTS

135 participants were enrolled and 121 participants completed the study. Depression symptom and sleep quality scores significantly decreased in both BLT and DLT groups (P < 0.001), while no significant changes were observed in WLC group. BLT (OR, 4.50; 95 % CI, 1.11-18.27; P = 0.035) and DLT group (OR, 4.17; 95 % CI, 1.04-16.79; P = 0.045) had higher efficacy rates than WLC group. For facial expressions, DLT group showed significant increases in two happy-related facial action units (AU) including AU14 values (positive, negative and neutral stimuli) and AU26 values (neutral and negative stimuli). BLT group showed a significant decrease in fear-related AU20 values under negative stimuli (P < 0.001).

CONCLUSION

Light therapy improves depressive symptoms and sleep quality in individuals with SD, and facial expressions can serve as an objective biomarker to support its effectiveness.

Lateral habenula induces cognitive and affective dysfunctions in mice with neuropathic pain via an indirect pathway to the ventral tegmental area

Neuropathic pain, which has become a major public health concern, is frequently accompanied by the deterioration of affective behavior and cognitive function. However, the brain circuitry underlying these changes is poorly understood. Therefore, we aimed to identify in a mouse model the converging circuit that influences the sensory, affective, and cognitive consequences of neuropathic pain. The lateral habenula (LHb) and ventral tegmental area (VTA) have been confirmed to play critical roles in the regulation of pain, cognition, and depression. Given the essential role of the LHb in depression and cognition, we attempted to clarify how neural circuitry involving the LHb integrates pain-related information. Our data confirmed that the VTA receives projections from the LHb, but our results suggest that inhibition of this direct pathway has no effect on the behavior of mice with chronic neuropathic pain. The rostromedial tegmental nucleus (RMTg), a GABAergic structure believed to underlie the transient inhibition of DAergic neurons in the VTA, received glutamatergic inputs from the LHb and projected strongly to the VTA. Furthermore, our data suggest that a projection from LHb glutamatergic neurons to RMTg GABAergic neurons in the VTA, constituting an indirect LHbGlu → RMTgGABA → VTADA pathway, participates in peripheral nerve injury-induced nociceptive hypersensitivity, depressive-like behavior, and cognitive dysfunction. Ex vivo extracellular recordings of LHb neurons showed that the proportion of burst-firing cells in the LHb was significantly increased in indirect projections rather than in direct projections. This may explain the functional discrepancies between direct and indirect projections of the LHb to the VTA. Collectively, our study identifies a pivotal role of the LHbGlu → RMTgGABA → VTADA pathway in processing pain. This pathway may offer new therapeutic targets to treat neuropathic pain and its associated depressive-like and cognitive impairments.

Neural-circuit architecture underlying non-image-forming visual functions

Perceiving and responding to environmental cues underpins survival and cognition. Light, emerging as one of the most ancient and powerful signals, has shaped life on Earth for billions of years. In mammals, light information is primarily detected by retinal photoreceptors: rods, cones, and intrinsically photosensitive retinal ganglion cells. While rods and cones enable image-forming vision, evolution has preserved and extended evolutionarily ancient yet critical non-image-forming visual functions, including circadian photoentrainment, pupillary light reflexes, and light-mediated modulation of metabolism, mood, and neurodevelopment. Although non-image-forming visual functions have been partially characterized in humans and model organisms, our understanding of the neural circuit mechanisms by which light orchestrates diverse behavior remains fragmented. The discovery of ipRGCs, combined with recent advances in systems neuroscience tools, has yielded critical breakthroughs in three domains: (1) light information encoding within photoreceptors, (2) systematic mapping of retinofugal pathways, and (3) central mechanisms of light-regulated physiological functions. These advances have progressively unraveled causal relationships between non-image-forming visual functions and their underlying eye-brain circuitry. This review summarizes groundbreaking progress in the three domains discussed above, highlighting key unresolved questions in the field.

On analogies in vertebrate and insect visual systems

Despite the large evolutionary distance between vertebrates and insects, the visual systems of these two taxa bear remarkable similarities that have been noted repeatedly, including by pioneering neuroanatomists such as Ramón y Cajal. Fuelled by the advent of transgenic approaches in neuroscience, studies of visual system anatomy and function in both vertebrates and insects have made dramatic progress during the past two decades, revealing even deeper analogies between their visual systems than were noted by earlier observers. Such across-taxa comparisons have tended to focus on either elementary motion detection or relatively peripheral layers of the visual systems. By contrast, the aims of this Review are to expand the scope of this comparison to pathways outside visual motion detection, as well as to deeper visual structures. To achieve these aims, we primarily discuss examples from recent work in larval zebrafish (Danio rerio) and the fruitfly (Drosophila melanogaster), a pair of genetically tractable model organisms with comparatively sized, small brains. In particular, we argue that the brains of both vertebrates and insects are equipped with third-order visual structures that specialize in shared behavioural tasks, including postural and course stabilization, approach and avoidance, and some other behaviours. These wider analogies between the two distant taxa highlight shared behavioural goals and associated evolutionary constraints and suggest that studies on vertebrate and insect vision have a lot to inspire each other.

The impact of bright light therapy on Parkinson's disease: A pilot study using vestibular-evoked myogenic potentials

INTRODUCTION

Bright light therapy (BLT) has been proved to have beneficial effects on Parkinson's disease (PD). Brainstem pathways improvements might be crucial to BLT, but the mechanisms remained unclear. The aim of this study is to validate whether BLT improves clinical symptoms in PD and thus explore the possible mechanisms of brainstem pathways evaluated by vestibular-evoked myogenic potentials (VEMPs).

METHODS

A total of 22 PD patients participated were enrolled in this crossover randomized placebo-controlled study. Participants received either one month of BLT or dim light therapy (DLT), separated by a 1-month wash-out period, and underwent clinical scales and VEMPs evaluations before and after each intervention. Mixed-effects regression models were used to determine the effect between BLT and DLT on PD patients by the differentials of clinical scales (Δscales) and VEMPs (ΔVEMPs). Correlations between the improvement of clinical symptoms and VEMPs parameters improvements were analyzed in PD patients receiving BLT.

RESULTS

Excessive daytime sleepiness, anxiety, life quality and autonomic function were improved after BLT. Compared to DLT, the difference was not significant. There were significant differences of cervical VEMPs (cVEMP) and ocular VEMPs (oVEMP) peak latencies after BLT. Compared with DLT, there was significant difference in ΔLp13, ΔRp13 and ΔLp11 peak latencies after BLT.

CONCLUSIONS

BLT may be a valuable non-pharmacological intervention for improving brainstem function, thereby enhancing quality of life and overall health in PD patients.

Lateral habenula astroglia modulate the potentiating antidepressant-like effects of bright light stimulation in intractable depression

Background

Beside image vision, light plays a pivotal role in regulating diverse non-visual functions, including affective behaviors. Recently, bright light stimulation (BLS) was revealed to be beneficial for treating non-seasonal depression, although its mechanism of action is not fully understood.

Methods

We developed a novel mouse model of refractory depression, induced through social isolation and chronic despair during the active (dark) phase of the animal, and we have tested if antidepressant treatments, including BLS, could protect against anxio-depressive-like behavior.

Results

We report that anxiety- and depressive-like behaviors are resistant to BLS as well as to both conventional and new antidepressants, including ketamine. Remarkably, we unveil that BLS potentiates the effect of antidepressants, and this beneficial effect is mediated via rod retinal photoreceptors. Furthermore, we demonstrate that both chemogenetic activation of lateral habenula (LHb) astroglia and serotonin (5-HT) depletion prevent the potentiating effect of BLS on chronic despair.

Conclusion

These results reveal, for the first time, that BLS enhances the efficacy of antidepressants through an unexpectedly circuit involving rods, LHb astroglia and 5-HT.

A cell-type-specific circuit of somatostatin neurons in the habenula encodes antidepressant action in male mice

Major depression is characterized by an array of negative experiences, including hopelessness and anhedonia. We hypothesize that inhibition of negative experiences or aversion may generate antidepressant action. To directly test this hypothesis, we perform multimodal behavioral screenings in male mice and identify somatostatin (SST)-expressing neurons in the region X (HBX) between the lateral and medial habenula as a specific type of antidepressant neuron. SST neuronal activity modulation dynamically regulates antidepressant induction and relief. We also explore the circuit basis for encoding these modulations using single-unit recordings. We find that SST neurons receive inhibitory synaptic inputs directly from cholecystokinin-expressing neurons in the bed nucleus of the stria terminalis and project excitatory axon terminals onto proenkephalin-expressing neurons in the interpeduncular nucleus. This study reveals a cell-type-specific circuit of SST neurons in the HBX that encodes antidepressant action, and the control of the circuit may contribute to improving well-being.

Superior Colliculus Controls the Activity of the Substantia Nigra Pars Compacta and Ventral Tegmental Area in an Asymmetrical Manner

Dopaminergic (DA) neurons of the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) play a crucial role in controlling animals' orienting and approach behaviors toward relevant environmental stimuli. The ventral midbrain receives sensory input from the superior colliculus (SC), a tectal region that processes information from contralateral receptive fields of various modalities. Given the significant influence of dopamine release imbalance in the left and right striatum on animals' movement direction, our study aimed to investigate the lateralization of the connection between the lateral SC and the midbrain DA system in male rats. We explored the circuit's anatomy using transsynaptic viral tract-tracing and its physiology using in vivo single-unit and ex vivo multi-electrode array recordings of SNc and VTA neuronal activity combined with optogenetic stimulation of either the ipsilateral or contralateral SC or its terminals. During the experiments, DA neurons were identified optogenetically (in vivo recordings) or pharmacologically (ex vivo recordings). Anatomical findings revealed a bilateral innervation pattern of the lateral SC to the ventral midbrain, with a significantly stronger ipsilateral connection, particularly evident in the SNc, involving both DA and non-DA neurons. This anatomical asymmetry was also expressed during in vivo and ex vivo recordings, which showed a predominance of ipsilateral connections, especially within the SNc. Ex vivo recordings also confirmed that this lateralized pathway is direct. The described features of the SC→VTA/SNc neuronal circuit, particularly its anatomical and physiological asymmetry, suggest its involvement in orienting and approach behaviors guided by the direction of incoming sensory stimuli.

The activation of the piriform cortex to lateral septum pathway during chronic social defeat stress is crucial for the induction of behavioral disturbance in mice

Chronic stress induces neural dysfunctions and risks mental illnesses. Clinical and preclinical studies have established the roles of brain regions underlying emotional and cognitive functions in stress and depression. However, neural pathways to perceive sensory stimuli as stress to cause behavioral disturbance remain unknown. Using whole-brain imaging of Arc-dVenus neuronal response reporter mice and machine learning analysis, here we unbiasedly demonstrated different patterns of contribution of widely distributed brain regions to neural responses to acute and chronic social defeat stress (SDS). Among these brain regions, multiple sensory cortices, especially the piriform (olfactory) cortex, primarily contributed to classifying neural responses to chronic SDS. Indeed, SDS-induced activation of the piriform cortex was augmented with repetition of SDS, accompanied by impaired odor discrimination. Axonal tracing and chemogenetic manipulation showed that excitatory neurons in the piriform cortex directly project to the lateral septum and activate it in response to chronic SDS, thereby inducing behavioral disturbance. These results pave the way for identifying a spatially defined sequence of neural consequences of stress and the roles of sensory pathways in perceiving chronic stress in mental illness pathology.

Effects of bright light therapy on cingulate cortex dynamic functional connectivity and neurotransmitter activity in young adults with subthreshold depression

BACKGROUND

The neurobiological mechanisms behind the antidepressant effect of bright light therapy (BLT) are unclear. We aimed to explore the dynamic functional connectivity (dFC) changes of the cingulate cortex (CC) in subthreshold depression (StD).

METHODS

The StD participants (38 BLT and 39 placebo) underwent resting-state functional magnetic resonance imaging (rs-fMRI) and mood assessment before and after eight-week BLT. Seed-based whole-brain dFC analysis was conducted and multivariate regression model was adopted to predict Hamilton Depression Rating Scale (HDRS) and Centre for Epidemiologic Studies Depression Scale (CESD) scores changes after BLT. JuSpace toolbox was used to calculate the associations between dFC and neurotransmitter activity in the BLT group.

RESULTS

BLT group showed decreased CESD and HDRS scores. Also, BLT group showed increased dFC of the right supracallosal anterior cingulate cortex (supACC)-right temporal pole (TP), left middle cingulate cortex (MCC)-right insula, and left supACC-pons, and decreased dFC of the right supACC- right middle frontal gyrus (MFG). Changes in dFC of the right supACC-right TP showed positive correlation with changes in CESD and HDRS. Moreover, combining the baseline dFC variability of the CC could predict HDRS changes in BLT. Finally, compared to baseline, the supACC and MCC dFC changes showed significant correlations with the neurotransmitter activities.

CONCLUSIONS

BLT alleviates depressive symptoms and changes the CC dFC variability in StD, and pre-treatment dFC variability of the CC could be used as a biomarker for improved BLT treatment in StD. Furthermore, dFC changes with specific neurotransmitter systems after BLT may underline the antidepressant mechanisms of BLT.

Neural circuits mediating chronic stress: Implications for major depressive disorder

Major depressive disorder (MDD), also known as depression, is a prevalent mental disorder that leads to severe disease burden worldwide. Over the past two decades, significant progress has been made in understanding the pathogenesis and developing novel treatments for MDD. Among the complicated etiologies of MDD, chronic stress is a major risk factor. Exploring the underlying brain circuit mechanisms of chronic stress regulation has been an area of active research for recent years. A growing body of preclinical and clinical research has revealed that abnormalities in the brain circuits are closely associated with failures in coping with stress in depressed individuals. Nevertheless, neural circuit mechanisms underlying chronic stress processing and the onset of depression remain a major puzzle. Here, we review recent literature focusing on circuit- and cell-type-specific dissection of depression-like behaviors in chronic stress-related animal models of MDD and outline the key questions.

Efficacy of bright light therapy for perinatal depression: A meta-analysis of a randomized controlled trial

BACKGROUND

Pharmacological treatments are commonly used in individuals experiencing perinatal depression (PPD); however, a debate regarding the reproductive safety of antidepressants is ongoing. Many pregnant women opt to discontinue antidepressant out of concern about potential negative effects on the developing fetus, while slow and ineffective antidepressant medications hinder improved outcomes in women with PPD. In recent years, bright light therapy (BLT) has gained traction as a treatment option for PPD; however, clinical trials findings examining the efficacy of BLT in this population have been inconclusive.

AIM

To validate the feasibility and safety of BLT for the treatment of PPD.

METHODS

We performed a meta-analysis of randomized controlled trials of patients with PPD treated with BLT vs placebo following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis. We searched PubMed, Embase, the Cochrane Library, and Web of Science for randomized controlled studies published up to December 2023. The results were evaluated using the standardized mean difference of improvement for depression scores and odds ratios (ORs) for remission rate, response rate, incidence of adverse events, and dropout rate.

RESULTS

The BLT group had higher PPD response rate [50.68% vs 33.08%; OR = 2.05; 95% confidence interval (CI): 1.25-3.35; P = 0.004; I^² = 35%] and remission rate (54.10% vs 18.52%; OR = 5.00; 95%CI: 2.09-11.99; P = 0.0003; I^² = 0%) than the placebo group. Improvements in depression scores were higher in the BLT group than the placebo group for the overall efficacy (standardized mean difference = -0.47; 95%CI: -0.80 to -0.13; P = 0.007). No significant differences between the two groups in drop-outs (21.84% vs 29.63%; OR = 0.63; 95%CI: 0.31-1.29; P = 0.21; I^² = 0%) or adverse events (17.89% vs 9.68%; OR = 2.01; 95%CI: 0.95-4.25; P = 0.07; I^² = 0%) were observed.

CONCLUSION

BLT can potentially treat PPD, showing better results than the control group in this study. BLT is effective and safe and could increase the available therapeutic options for PPD.

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.

Optogenetics and chemogenetics: key tools for modulating neural circuits in rodent models of depression

Optogenetics and chemogenetics are emerging neuromodulation techniques that have attracted significant attention in recent years. These techniques enable the precise control of specific neuronal types and neural circuits, allowing researchers to investigate the cellular mechanisms underlying depression. The advancement in these techniques has significantly contributed to the understanding of the neural circuits involved in depression; when combined with other emerging technologies, they provide novel therapeutic targets and diagnostic tools for the clinical treatment of depression. Additionally, these techniques have provided theoretical support for the development of novel antidepressants. This review primarily focuses on the application of optogenetics and chemogenetics in several brain regions closely associated with depressive-like behaviors in rodent models, such as the ventral tegmental area, nucleus accumbens, prefrontal cortex, hippocampus, dorsal raphe nucleus, and lateral habenula and discusses the potential and challenges of optogenetics and chemogenetics in future research. Furthermore, this review discusses the potential and challenges these techniques pose for future research and describes the current state of research on sonogenetics and odourgenetics developed based on optogenetics and chemogenetics. Specifically, this study aimed to provide reliable insights and directions for future research on the role of optogenetics and chemogenetics in the neural circuits of depressive rodent models.

Increased Interleukin-6 Levels in Responders with Treatment-Resistant Depression After Bright Light Therapy

Treatment-resistant depression (TRD) remains a challenge despite the growing number of interventions. Peripheral interleukin-6 (IL-6) levels have repeatedly been associated with both the presence and response to different treatments in TRD. There is currently no information available on the effects of bright light therapy (BLT) on serum IL-6 levels. This study assessed the effects of BLT on serum IL-6 levels in TRD patients. Serum IL-6 was determined at two points in TRD patients-at baseline and after 4 weeks of BLT-and at a single point in the healthy controls. Depression severity was measured by the Hamilton Rating Scale for Depression (HAMD)-17 and the Montgomery-Åsberg Depression Rating Scale (MADRS). The study included 104 females, 54 diagnosed with TRD (median age 52.5) and 50 healthy controls (median age 44.5). At baseline, patients had higher IL-6 levels than the controls. BLT treatment reduced HAMD-17 and MADRS scores. Serum IL-6 levels were not significantly affected by the 4 weeks of BLT. However, when patients were divided according to treatment response, IL-6 levels were increased in responders to BLT. The neuroinflammatory mechanism may be involved in the etiopathogenesis and the treatment of TRD, while changes in serum IL-6 levels may be potential indicators of response to treatment.

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.

The blues and rhythm

Most organisms, including humans, show daily rhythms in many aspects of physiology and behavior, and abnormalities in the rhythms are potential risk factors for various diseases. Mood disorders such as depression are no exception. Accumulating evidence suggests strong associations between circadian disturbances and the development of depression. Numerous studies have shown that interventions to circadian rhythms trigger depression-like phenotypes in human cases and animal models. Conversely, mood changes can affect circadian rhythms as symptoms of depression. Our preliminary data suggest that the phosphorylation signal pathway of the clock protein may act as a common pathway for mood and clock regulation. We hypothesize that mood regulation and circadian rhythms may influence each other and may share a common regulatory mechanism. This review provides an overview of circadian disturbances in animal models and human patients with depression.

Efficacy of bright light therapy improves outcomes of perinatal depression: A systematic review and meta-analysis of randomized controlled trials

The efficacy of bright light therapy (BLT) in the context of perinatal depression remains underexplored. This meta-analysis aimed to systematically assess the effectiveness of BLT among perinatal depression. A comprehensive literature search was performed across several databases, including the Cochrane Central Register of Controlled Trials, PubMed, Embase, CNKI and the clinical trials registry platform, covering the period from the inception of each database up to January 2024. The Cochrane Collaboration's bias assessment tool was employed to evaluate the quality of the included studies. Review Manager 5.3 Software was utilized to conduct the meta-analysis. Six trials, encompassed a total of 167 participants diagnosed with perinatal depression were incorporated quantitative analysis, all of those have been published in English, with no restriction on publication year, and used BLT and dim light therapy (DLT) as intervention. The relative risk (RR) of BLT compared to DLT for perinatal depression is 1.46 (fixed effects model, p = 0.04, 95 % CI = [1.02, 2.10]), indicating a significant improvement in depression outcomes compared to DLT groups. The heterogeneity test yielded an I2 value of 41 % (p = 0.13), indicated a low degree of heterogeneity. Considering the small sample size, we conducted a sensitivity analysis, found RR increased to 2.33 (fixed effects model, p = 0.001, CI = 1.39-3.92). Cochrane Risk of Bias Tool showed only a single study was deemed high quality. This study indicates a beneficial impact of BLT on perinatal depression, subgroup analysis finds no significant mediation effects of different parameters after sensitivity analyses. It is recommended that future studies with larger samples be conducted to explore the effects of BLT on perinatal depression.

High-gamma frequency flash stimulation as a possible cognitive facilitator in rat pups

High-gamma frequency flashes can enhance cognition by synchronizing neural oscillations in mammals. Early flash treatment promotes the development of improved cognitive functions in young children. However, it is unclear whether exposure to high-gamma frequency flashes in preschool-aged individuals affects cognition in preadolescents by regulating neural oscillations in the brain. Here, we aimed to investigate the effects of gamma-frequency flashes on cognitive ability. In this study, the effect of high-frequency flicker on cognitive performance was verified by behavioural experiments such as the open-field test and the water maze, but also proteomics. We found that external 40 Hz and 70 Hz frequency flashes synchronized neural oscillations at the corresponding frequencies in the primary visual cortex (V1) of rats. Rats that underwent 70 Hz flash intervention had better cognitive behavioural performance in the early stages of training. The 70 Hz flash frequency upregulated proteins associated with neuronal growth and differentiation, such as Snapin, FoxO3, Hspa12a, and Penk, and activated the MAPK signalling pathway, signalling pathway regulating stem cell pluripotency, and the neuroactive ligand-receptor interaction pathway. These proteins and pathways play important roles in cognitive functions. Our study revealed that 70 Hz flashes received by young children early in their development substantially promote the growth of cognitive capabilities in the brain. Exposure to 70 Hz flashes may be a new intervention method and a new strategy for improving cognition.

Structural connectivity of thalamic subnuclei in major depressive disorder: An ultra-high resolution diffusion MRI study at 7-Tesla

BACKGROUND

The thalamus serves as a central relay station within the brain, and thalamic connectional anomalies are increasingly thought to be present in major depressive disorder (MDD). However, the use of conventional MRI scanners and acquisition techniques has prevented a thorough examination of the thalamus and its subnuclear connectional profile. We combined ultra-high field diffusion MRI acquired at 7.0 Tesla to map the white matter connectivity of thalamic subnuclei.

METHODS

Fifty-three MDD patients and 12 healthy controls (HCs) were involved in the final analysis. FreeSurfer was used to segment the thalamic subnuclei, and MRtrix was used to perform the preprocessing and tractography. Fractional anisotropy, axial diffusivity, mean diffusivity, radial diffusivity, and streamline count of thalamic subnuclear tracts were measured as proxies of white matter microstructure. Bayesian multilevel model was used to assess group differences in white matter metrics for each thalamic subnuclear tract and the association between these white matter metrics and clinical features in MDD.

RESULTS

Evidence was found for reduced whiter matter metrics of the tracts spanning from all thalamic subnuclei among MDD versus HC participants. Moreover, evidence was found that white matter in various thalamic subnuclear tracts is related to medication status, age of onset and recurrence in MDD.

CONCLUSIONS

Structural connectivity was generally reduced in thalamic subnuclei in MDD participants. Several clinical characteristics are related to perturbed subnuclear thalamic connectivity with cortical and subcortical circuits that govern sensory processing, emotional function, and goal-directed behavior.

Mood variation under dual regulation of circadian clock and light

The intricate relationship between circadian rhythms and mood is well-established. Disturbances in circadian rhythms and sleep often precede the development of mood disorders, such as major depressive disorder (MDD), bipolar disorder (BD), and seasonal affective disorder (SAD). Two primary factors, intrinsic circadian clocks and light, drive the natural fluctuations in mood throughout the day, mirroring the patterns of sleepiness and wakefulness. Nearly all organisms possess intrinsic circadian clocks that coordinate daily rhythms, with light serving as the primary environmental cue to synchronize these internal timekeepers with the 24-hour cycle. Additionally, light directly influences mood states. Disruptions to circadian rhythms, such as those caused by jet lag, shift work, or reduced daylight hours, can trigger or exacerbate mood symptoms. The complex and often subtle connections between circadian disruptions and mood dysregulation suggest that focusing solely on individual clock genes is insufficient to fully understand their etiology and progression. Instead, mood instability may arise from systemic misalignments between external cycles and the internal synchronization of circadian clocks. Here, we synthesize past research on the independent contributions of circadian clocks and light to mood regulation, drawing particularly on insights from animal studies that illuminate fundamental mechanisms relevant to human health.

Modulation of glymphatic system by visual circuit activation alleviates memory impairment and apathy in a mouse model of Alzheimer's disease

Alzheimer's disease is characterized by progressive amyloid deposition and cognitive decline, yet the pathological mechanisms and treatments remain elusive. Here we report the therapeutic potential of low-intensity 40 hertz blue light exposure in a 5xFAD mouse model of Alzheimer's disease. Our findings reveal that light treatment prevents memory decline in 4-month-old 5xFAD mice and motivation loss in 14-month-old 5xFAD mice, accompanied by restoration of glial water channel aquaporin-4 polarity, improved brain drainage efficiency, and a reduction in hippocampal lipid accumulation. We further demonstrate the beneficial effects of 40 hertz blue light are mediated through the activation of the vLGN/IGL-Re visual circuit. Notably, concomitant use of anti-Aβ antibody with 40 hertz blue light demonstrates improved soluble Aβ clearance and cognitive performance in 5xFAD mice. These findings offer functional evidence on the therapeutic effects of 40 hertz blue light in Aβ-related pathologies and suggest its potential as a supplementary strategy to augment the efficacy of antibody-based therapy.

Exercise-Activated mPFC Tri-Synaptic Pathway Ameliorates Depression-Like Behaviors in Mouse

Exercise is considered as playing a pivotal role in the modulation of emotional responses. However, a precise circuit that mediates the effects of exercise on depression have yet to be elucidated. Here, a molecularly defined tri-synaptic pathway circuit is identified that correlates motor inputs with antidepressant effects. With this pathway, initial inputs from neurons within the dorsal root ganglia (DRG) project to excitatory neurons in the gracile nucleus (GR), which in turn connect with 5-HTergic neurons in the dorsal raphe nucleus (DRN), eventually coursing to excitatory pyramidal neurons within the medial prefrontal cortex (mPFC). Exercise activates this pathway, with the result that depressive- and anxiety-like behaviors in mice are significantly reduced. In addition, it is found that exercise may exert antidepressant effects through regulating synaptic plasticity within this tri-synaptic pathway. These findings reveal a hindbrain-to-forebrain neuronal circuit that specifically modulates depression and provides a potential mechanism for the antidepressant effects of exercise.

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.

Chronobiologic treatments for mood disorders

Chronotherapeutics are nonpharmacologic interventions whose development stems from investigations into sleep and circadian rhythm abnormalities associated with mood disorder. These therapies utilize controlled exposure to environmental cues (light, darkness) to regulate biologic rhythms. They encompass sleep-wake manipulations (partial/total sleep deprivation, sleep phase adjustment) and light therapy approaches. Growing evidence supports the safety and efficacy of chronotherapeutics in clinical settings. Indeed, they target core depressive symptoms, including suicidality and may represent a novel therapeutic approach for treatment-resistant depression. This makes them a viable treatment option, both as a monotherapy and in combination with existing psychopharmacologic medications and paves the way for their potential inclusion as first-line treatments for mood disorders.

The disappointment centre of the brain gets exciting: a systematic review of habenula dysfunction in depression

BACKGROUND

The habenula is an epithalamic brain structure that acts as a neuroanatomical hub connecting the limbic forebrain to the major monoamine centres. Abnormal habenula activity is increasingly implicated in depression, with a surge in publications on this topic in the last 5 years. Direct activation of the habenula is sufficient to induce a depressive phenotype in rodents, suggesting a causative role in depression. However, the molecular basis of habenula dysfunction in depression remains elusive and it is unclear how the preclinical advancements translate to the clinical field.

METHODS

A systematic literature search was conducted following the PRISMA guidelines. The two search terms depress* and habenula* were applied across Scopus, Web of Science and PubMed databases. Studies eligible for inclusion must have examined the habenula in clinical cases of depression or preclinical models of depression and compared their measures to an appropriate control.

RESULTS

Preclinical studies (n = 63) measured markers of habenula activity (n = 16) and neuronal firing (n = 22), largely implicating habenula hyperactivity in depression. Neurotransmission was briefly explored (n = 15), suggesting imbalances within excitatory and inhibitory habenula signalling. Additional preclinical studies reported neuroconnectivity (n = 1), inflammatory (n = 3), genomic (n = 3) and circadian rhythm (n = 3) abnormalities. Seven preclinical studies (11%) included both males and females. From these, 5 studies (71%) reported a significant difference between the sexes in at least one habenula measure taken. Clinical studies (n = 24) reported abnormalities in habenula connectivity (n = 15), volume (n = 6) and molecular markers (n = 3). Clinical studies generally included male and female subjects (n = 16), however, few of these studies examined sex as a biological variable (n = 6).

CONCLUSIONS

Both preclinical and clinical evidence suggest the habenula is disrupted in depression. However, there are opportunities for sex-specific analyses across both areas. Preclinical evidence consistently suggests habenula hyperactivity as a primary driver for the development of depressive symptoms. Clinical studies support gross habenula abnormalities such as altered activation, connectivity, and volume, with emerging evidence of blood brain barrier dysfunction, however, progress is limited by a lack of detailed molecular analyses and limited imaging resolution.

Periaqueductal gray passes over disappointment and signals continuity of remaining reward expectancy

Disappointment is a vital factor in the learning and adjustment of strategies in reward-seeking behaviors. It helps them conserve energy in environments where rewards are scarce, while also increasing their chances of maximizing rewards by prompting them to escape to environments where richer rewards are anticipated (e.g., migration). However, another key factor in obtaining the reward is the ability to monitor the remaining possibilities of obtaining the outcome and to tolerate the disappointment in order to continue with subsequent actions. The periaqueductal gray (PAG) has been reported as one of the key brain regions in regulating negative emotions and escape behaviors in animals. The present study suggests that the PAG could also play a critical role in inhibiting escape behaviors and facilitating ongoing motivated behaviors to overcome disappointing events. We found that PAG activity is tonically suppressed by reward expectancy as animals engage in a task to acquire a reward outcome. This tonic suppression of PAG activity was sustained during a series of sequential task procedures as long as the expectancy of reward outcomes persisted. Notably, the tonic suppression of PAG activity showed a significant correlation with the persistence of animals' reward-seeking behavior while overcoming intermittent disappointing events. This finding highlights that the balance between distinct tonic signaling in the PAG, which signals remaining reward expectancy, and phasic signaling in the LHb, which signals disappointment, could play a crucial role in determining whether animals continue or discontinue reward-seeking behaviors when they encounter an unexpected negative event. This mechanism would be essential for animals to efficiently navigate complex environments with various reward volatilities and ultimately contributes to maximizing their reward acquisition.

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.

A small population of stress-responsive neurons in the hypothalamus-habenula circuit mediates development of depression-like behavior in mice

Accumulating evidence has shown that various brain functions are associated with experience-activated neuronal ensembles. However, whether such neuronal ensembles are engaged in the pathogenesis of stress-induced depression remains elusive. Utilizing activity-dependent viral strategies in mice, we identified a small population of stress-responsive neurons, primarily located in the middle part of the lateral hypothalamus (mLH) and the medial part of the lateral habenula (LHbM). These neurons serve as "starter cells" to transmit stress-related information and mediate the development of depression-like behaviors during chronic stress. Starter cells in the mLH and LHbM form dominant connections, which are selectively potentiated by chronic stress. Silencing these connections during chronic stress prevents the development of depression-like behaviors, whereas activating these connections directly elicits depression-like behaviors without stress experience. Collectively, our findings dissect a core functional unit within the LH-LHb circuit that mediates the development of depression-like behaviors in mice.

A prefrontal-habenular circuitry regulates social fear behaviour

The medial prefrontal cortex (mPFC) has been implicated in the pathophysiology of social impairments, including social fear. However, the precise subcortical partners that mediate mPFC dysfunction on social fear behaviour have not been identified. Using a social fear conditioning paradigm, we induced robust social fear in mice and found that the lateral habenula (LHb) neurons and LHb-projecting mPFC neurons are activated synchronously during social fear expression. Moreover, optogenetic inhibition of the mPFC-LHb projection significantly reduced social fear responses. Importantly, consistent with animal studies, we observed an elevated prefrontal-habenular functional connectivity in subclinical individuals with higher social anxiety characterized by heightened social fear. These results unravel a crucial role of the prefrontal-habenular circuitry in social fear regulation and suggest that this pathway could serve as a potential target for the treatment of social fear symptoms often observed in many psychiatric disorders.

GABAergic Retinal Ganglion Cells Projecting to the Superior Colliculus Mediate the Looming-Evoked Flight Response

The looming stimulus-evoked flight response to approaching predators is a defensive behavior in most animals. However, how looming stimuli are detected in the retina and transmitted to the brain remains unclear. Here, we report that a group of GABAergic retinal ganglion cells (RGCs) projecting to the superior colliculus (SC) transmit looming signals from the retina to the brain, mediating the looming-evoked flight behavior by releasing GABA. GAD2-Cre and vGAT-Cre transgenic mice were used in combination with Cre-activated anterograde or retrograde tracer viruses to map the inputs to specific GABAergic RGC circuits. Optogenetic technology was used to assess the function of SC-projecting GABAergic RGCs (scpgRGCs) in the SC. FDIO-DTA (Flp-dependent Double-Floxed Inverted Open reading frame-Diphtheria toxin) combined with the FLP (Florfenicol, Lincomycin & Prednisolone) approach was used to ablate or silence scpgRGCs. In the mouse retina, GABAergic RGCs project to different brain areas, including the SC. ScpgRGCs are monosynaptically connected to parvalbumin-positive SC neurons known to be required for the looming-evoked flight response. Optogenetic activation of scpgRGCs triggers GABA-mediated inhibition in SC neurons. Ablation or silencing of scpgRGCs compromises looming-evoked flight responses without affecting image-forming functions. Our study reveals that scpgRGCs control the looming-evoked flight response by regulating SC neurons via GABA, providing novel insight into the regulation of innate defensive behaviors.

Differential modulation of pain and associated anxiety by GABAergic neuronal circuits in the lateral habenula

Persistent pain frequently precipitates the development of anxiety disorders, yet the underlying mechanisms are not fully understood. In this study, we employed a mouse model that simulates trigeminal neuralgia and observed a marked reduction in the activity of GABAergic neurons in the lateral habenula (LHb), a critical region for modulating pain and anxiety. We utilized precise optogenetic and chemogenetic techniques to modulate these neurons, which significantly alleviated behaviors associated with pain and anxiety. Our investigations revealed an inhibitory pathway from the LHb GABAergic neurons to the posterior paraventricular thalamus. Activation of this pathway primarily mitigated pain-related behaviors, with minimal effects on anxiety. Conversely, interactions between GABAergic and glutamatergic neurons within the LHb were essential in alleviating both pain and anxiety following trigeminal nerve damage. Additionally, we identified that β-sitosterol interacts directly with LHb GABAergic neurons via the estrogen receptor α, providing dual therapeutic effects for both pain and anxiety. These findings highlight the critical role of reduced GABAergic neuronal activity in the LHb in the intersection of pain and anxiety, pointing to promising therapeutic possibilities.

Neuronal TCF7L2 in Lateral Habenula Is Involved in Stress-Induced Depression

Depression is a complex psychiatric disorder that has substantial implications for public health. The lateral habenula (LHb), a vital brain structure involved in mood regulation, and the N-methyl-D-aspartate receptor (NMDAR) within this structure are known to be associated with depressive behaviors. Recent research has identified transcription factor 7-like 2 (TCF7L2) as a crucial transcription factor in the Wnt signaling pathway, influencing diverse neuropsychiatric processes. In this study, we explore the role of TCF7L2 in the LHb and its effect on depressive-like behaviors in mice. By using behavioral tests, AAV-mediated gene knockdown or overexpression, and pharmacological interventions, we investigated the effects of alterations in TCF7L2 expression in the LHb. Our results indicate that TCF7L2 expression is reduced in neurons within the LHb of male ICR mice exposed to chronic mild stress (CMS), and neuron-specific knockdown of TCF7L2 in LHb neurons leads to notable antidepressant activity, as evidenced by reduced immobility time in the tail suspension test (TST) and forced swimming test (FST). Conversely, the overexpression of TCF7L2 in LHb neurons induces depressive behaviors. Furthermore, the administration of the NMDAR agonist NMDA reversed the antidepressant activity of TCF7L2 knockdown, and the NMDAR antagonist memantine alleviated the depressive behaviors induced by TCF7L2 overexpression, indicating the involvement of NMDAR. These findings offer novel insights into the molecular mechanisms of depression, highlighting the potential of TCF7L2 as both a biomarker and a therapeutic target for depression. Exploring the relationship between TCF7L2 signaling and LHb function may lead to innovative therapeutic approaches for alleviating depressive symptoms.

Thalamic Volumes and Functional Networks Linked With Self-Regulation Dysfunction in Major Depressive Disorder

AIMS

Self-regulation (SR) dysfunction is a crucial risk factor for major depressive disorder (MDD). However, neural substrates of SR linking MDD remain unclear.

METHODS

Sixty-eight healthy controls and 75 MDD patients were recruited to complete regulatory orientation assessments with the Regulatory Focus Questionnaire (RFQ) and Regulatory Mode Questionnaire (RMQ). Nodal intra and inter-network functional connectivity (FC) was defined as FC sum within networks of 46 thalamic subnuclei (TS) or 88 AAL brain regions, and between the two networks separately. Group-level volumetric and functional difference were compared by two sample t-tests. Pearson's correlation analysis and mediation analysis were utilized to investigate the relationship among imaging parameters and the two behaviors. Canonical correlation analysis (CCA) was conducted to explore the inter-network FC mode of TS related to behavioral subscales. Network-based Statistics with machine learning combining powerful brain imaging features was applied to predict individual behavioral subscales.

RESULTS

MDD patients showed no group-level volumetric difference in 46 TS but represented significant correlation of TS volume and nodal FC with behavioral subscales. Specially, inter-network FC of the orbital part of the right superior frontal gyrus and the left supplementary motor area mediated the correlation between RFQ/RMQ subscales and depressive severity. Furthermore, CCA identified how the two behaviors are linked via the inter-network FC mode of TS. More crucially, thalamic functional subnetworks could predict RFQ/RMQ subscales and psychomotor retardation for MDD individuals.

CONCLUSION

These findings provided neurological evidence for SR affecting depressive severity in the MDD patients and proposed potential biomarkers to identify the SR-based risk phenotype of MDD individuals.

Rhythmic gamma frequency light flickering ameliorates stress-related behaviors and cognitive deficits by modulating neuroinflammatory response through IL-12-Mediated cytokines production in chronic stress-induced mice

Chronic stress enhances the risk for psychiatric disorders and induces depression and cognitive impairment. Gamma oscillations are essential for neurocircuit function, emotion, and cognition. However, the influence of gamma entrainment by sensory stimuli on specific aspects of chronic stress-induced responses remains unclear. Mice were subjected to corticosterone (CORT) administration and chronic restraint stress (CRS) for weeks, followed by rhythmic gamma frequency light flickering exposure. Local field potentials (LFPs) were recorded from the V1, CA1, and PFC regions to verify the light flicker on gamma oscillations. Behavioral tests were used to examine stress-related and memory-related behaviors. Golgi staining was performed to observe changes in spine morphology. Synaptosomes were isolated to determine the expression of synapse-related proteins through immunoblotting. RNA sequencing (RNA-seq) was applied to explore specific changes in the transcriptome. Immunofluorescence staining, real-time quantitative polymerase chain reaction (qPCR), and ELISA were used to evaluate microglial activation and cytokine levels. In this study, we demonstrated that rhythmic 40 Hz LF attenuated stress-related behavior and cognitive impairments by ameliorating the microstructural alterations in spine morphology and increasing the expression of GluN2A and GluA1 in chronically stressed mice. Transcriptome analysis revealed that significantly downregulated genes in LF-exposed CRS mice were enriched in neuroimmune-related signaling pathways. Rhythmic 40 Hz LF exposure significantly decreased the number of Iba1-positive microglia in the PFC and hippocampus, and the expression levels of the M1 markers of microglia iNOS and CD68 were reduced significantly in CRS mice. In addition, 40 Hz LF exposure suppressed the secretion of cytokines IL-12, which could regulate the production of IFN-γ and IL-10 in stressed mice. Our results demonstrate that exposure to rhythmic 40 Hz LF induces the neuroimmune response and downregulation of neuroinflammation with attenuated stress-related behaviors and cognitive function in CRS-induced mice. Our findings highlight the importance of sensory-evoked gamma entrainment as a potential therapeutic strategy for stress-related disorders treatment. Abbreviations: CORT, Chronic corticosterone treatment; CRS, Chronic restraint stress; IACUC, Institutional Animal Care and Use Committee; LF, light flickers; FST, Forced swim test; NSFT, Novelty-suppressed feeding test; SPT, Sucrose preference test; NSFT, Novelty-suppressed feeding; qPCR, Quantitative real-time polymerase chain reaction; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; PVDF, polyvinylidene fluoride; PBS, phosphate-buffered saline; PBS-T, phosphate-buffered saline plus 0.1% Tween 20; PVDF, polyvinylidene fluoride; GFAP, Glial fibrillary acidic protein; DAPI, 4',6-Diamid- ino-2-phenylindole; Iba1, Ionized calcium-binding adaptor molecule 1; iNOS, Inducible nitric oxide synthase; IL-10, Interleukin-10; IL6, Interleukin 6; IL-1β, Interleukin 1β; IL-12, Interleukin 12; TNF-α, Tumor necrosis factor alpha; IFN-γ, Interferon-gamma; TLR6 and 9, Toll-like Receptor 6 and 9.

Photobiomodulation therapy mitigates depressive-like behaviors by remodeling synaptic links and mitochondrial function

Depression, a multifactorial mental disorder, characterized by cognitive slowing, anxiety, and impaired cognitive function, imposes a significant burden on public health. Photobiomodulation (PBM), involving exposure to sunlight or artificial light at a specific intensity and wavelength for a determined duration, influences brain activity, functional connectivity, and plasticity. It is recognized for its therapeutic efficacy in treating depression, yet its molecular and cellular underpinnings remain obscure. Here, we investigated the impact of PBM with 468 nm light on depression-like behavior and neuronal damage in the chronic unpredictable mild stress (CUMS) murine model, a commonly employed animal model for studying depression. Our results demonstrate that PBM treatment ameliorated behavioral deficits, inhibited neuroinflammation and apoptosis, and notably rejuvenates the hippocampal synaptic function in depressed mice, which may be mainly attributed to the up-regulation of brain-derived neurotrophic factor signaling pathways. In addition, in vitro experiments with a corticosterone-induced hippocampal neuron injury model demonstrate reduced oxidative stress and improved mitochondrial function, further validating the therapeutic potential of PBM. In summary, these findings suggest PBM as a promising, non-invasive treatment for depression, offering insights into its biological mechanisms and potential for clinical application.

The behavioral relevance of a modular organization in the lateral habenula

Behavioral strategies for survival rely on the updates the brain continuously makes based on the surrounding environment. External stimuli-neutral, positive, and negative-relay core information to the brain, where a complex anatomical network rapidly organizes actions, including approach or escape, and regulates emotions. Human neuroimaging and physiology in nonhuman primates, rodents, and teleosts suggest a pivotal role of the lateral habenula in translating external information into survival behaviors. Here, we review the literature describing how discrete habenular modules-reflecting the molecular signatures, anatomical connectivity, and functional components-are recruited by environmental stimuli and cooperate to prompt specific behavioral outcomes. We argue that integration of these findings in the context of valence processing for reinforcing or discouraging behaviors is necessary, offering a compelling model to guide future work.

A potentiation of REM sleep-active neurons in the lateral habenula may be responsible for the sleep disturbance in depression

Psychiatric disorders with dysfunction of the lateral habenula (LHb) show sleep disturbance, especially a disinhibition of rapid eye movement (REM) sleep in major depression. However, the role of LHb in physiological sleep control and how LHb contributes to sleep disturbance in major depression remain elusive. Here, we found that functional manipulations of LHb glutamatergic neurons bidirectionally modulated both non-REM (NREM) sleep and REM sleep. Activity recording revealed heterogeneous activity patterns of LHb neurons across sleep/wakefulness cycles, but LHb neurons were preferentially active during REM sleep. Using an activity-dependent tagging method, we selectively labeled a population of REM sleep-active LHb neurons and demonstrated that these neurons specifically promoted REM sleep. Neural circuit studies showed that LHb neurons regulated REM sleep via projections to the ventral tegmental area but not to the rostromedial tegmental nucleus. Furthermore, we found that the increased REM sleep in a depression mouse model was associated with a potentiation of REM sleep-active LHb neurons, including an increased proportion, elevated spike firing, and altered activity mode. Importantly, inhibition of REM sleep-active LHb neurons not only attenuated the increased REM sleep but also alleviated depressive-like behaviors in a depression mouse model. Thus, our results demonstrated that REM sleep-active LHb neurons selectively promoted REM sleep, and a potentiation of these neurons contributed to depression-associated sleep disturbance.

Elevated dorsal medial prefrontal cortex to lateral habenula pathway activity mediates chronic stress-induced depressive and anxiety-like behaviors

The medial prefrontal cortex (mPFC) sends projections to numerous brain regions and is believed to play a significant role in depression and anxiety. One of the key downstream targets of the mPFC, the lateral habenula (LHb), is essential for chronic stress (CS)-induced depressive and anxiety-like behaviors. Nevertheless, whether the mPFC-LHb pathway mediates the co-occurrence of depression and anxiety and the underlying mechanism remain incompletely understood. Here, using chemogenetics, we first determined that activation of LHb-projecting mPFC neurons is essential for the development of depressive and anxiety-like behaviors induced by CS. Subsequently, we identify the extent and distribution of LHb-projecting neurons originating from the mPFC subregion. Through circuit-specific in vivo fiber photometry, we found that Ca2+ activity in dorsal mPFC (dmPFC) axon terminals within the LHb was increased during exposure to stressful and anxiety-related stimuli, highlighting the potential role of LHb-projecting dmPFC neurons in conveying stressful and anxiety-related information to the LHb. Finally, we observed that activation of both LHb-projecting dmPFC neurons and their postsynaptic counterparts in the LHb was necessary for CS-induced depressive and anxiety-like behaviors. Overall, this study provides multiple lines of evidence demonstrating that activation of the dmPFC-LHb pathway is a crucial neural circuitry for CS-induced depressive and anxiety-like behaviors.

Burst firing in Output-Defined Parallel Habenula Circuit Underlies the Antidepressant Effects of Bright Light Treatment

Research highlights the significance of increased bursting in lateral habenula (LHb) neurons in depression and as a focal point for bright light treatment (BLT). However, the precise spike patterns of LHb neurons projecting to different brain regions during depression, their roles in depression development, and BLT's therapeutic action remain elusive. Here, LHb neurons are found projecting to the dorsal raphe nucleus (DRN), ventral tegmental area (VTA), and median raphe nucleus (MnR) exhibit increased bursting following aversive stimuli exposure, correlating with distinct depressive symptoms. Enhanced bursting in DRN-projecting LHb neurons is pivotal for anhedonia and anxiety, while concurrent bursting in LHb neurons projecting to the DRN, VTA, and MnR is essential for despair. Remarkably, reducing bursting in distinct LHb neuron subpopulations underlies the therapeutic effects of BLT on specific depressive behaviors. These findings provide valuable insights into the mechanisms of depression and the antidepressant action of BLT.

A Light-Responsive Neural Circuit Suppresses Feeding

Light plays an essential role in a variety of physiological processes, including vision, mood, and glucose homeostasis. However, the intricate relationship between light and an animal's feeding behavior has remained elusive. Here, we found that light exposure suppresses food intake, whereas darkness amplifies it in male mice. Interestingly, this phenomenon extends its reach to diurnal male Nile grass rats and healthy humans. We further show that lateral habenula (LHb) neurons in mice respond to light exposure, which in turn activates 5-HT neurons in the dorsal Raphe nucleus (DRN). Activation of the LHb→5-HTDRN circuit in mice blunts darkness-induced hyperphagia, while inhibition of the circuit prevents light-induced anorexia. Together, we discovered a light-responsive neural circuit that relays the environmental light signals to regulate feeding behavior in mice.

Current role of magnetic resonance imaging on assessing and monitoring the efficacy of phototherapy

Phototherapy, also known as photobiological therapy, is a non-invasive and highly effective physical treatment method. Its broad use in clinics has led to significant therapeutic results. Phototherapy parameters, such as intensity, wavelength, and duration, can be adjusted to create specific therapeutic effects for various medical conditions. Meanwhile, Magnetic Resonance Imaging (MRI), with its diverse imaging sequences and excellent soft-tissue contrast, provides a valuable tool to understand the therapeutic effects and mechanisms of phototherapy. This review explores the clinical applications of commonly used phototherapy techniques, gives a brief overview of how phototherapy impacts different diseases, and examines MRI's role in various phototherapeutic scenarios. We argue that MRI is crucial for precise targeting, treatment monitoring, and prognosis assessment in phototherapy. Future research and applications will focus on personalized diagnosis and monitoring of phototherapy, expanding its applications in treatment and exploring multimodal imaging technology to enhance diagnostic and therapeutic precision and effectiveness.

Mediodorsal thalamus projection to medial prefrontal cortical mediates social defeat stress-induced depression-like behaviors

Clinical studies have shown that the mediodorsal thalamus (MD) may play an important role in the development of depression. However, the molecular and circuit mechanisms by which the mediodorsal thalamus (MD) participates in the pathological processes of depression remain unclear. Here, we show that in male chronic social defeat stress (CSDS) mice, the calcium signaling activity of glutamatergic neurons in MD is reduced. By combining conventional neurotracer and transneuronal virus tracing techniques, we identify a synaptic circuit connecting MD and medial prefrontal cortex (mPFC) in the mouse. Brain slice electrophysiology and fiber optic recordings reveal that the reduced activity of MD glutamatergic neurons leads to an excitatory-inhibitory imbalance of pyramidal neurons in mPFC. Furthermore, activation of MD glutamatergic neurons restores the electrophysiological properties abnormal in mPFC. Optogenetic activation of the MD-mPFC circuit ameliorates anxiety and depression-like behaviors in CSDS mice. Taken together, these data support the critical role of MD-mPFC circuit on CSDS-induced depression-like behavior and provide a potential mechanistic explanation for depression.

HCN channels in the lateral habenula regulate pain and comorbid depressive-like behaviors in mice

AIMS

Comorbid anxiodepressive-like symptoms (CADS) in chronic pain are closely related to the overactivation of the lateral habenula (LHb). Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have been implicated to play a key role in regulating neuronal excitability. However, the role of HCN channels in the LHb during CADS has not yet been characterized. This study aimed to investigate the effect of HCN channels in the LHb on CADS during chronic pain.

METHODS

After chronic neuropathic pain induction by spared nerve injury (SNI), mice underwent a sucrose preference test, forced swimming test, tail suspension test, open-field test, and elevated plus maze test to evaluate their anxiodepressive-like behaviors. Electrophysiological recordings, immunohistochemistry, Western blotting, pharmacological experiments, and virus knockdown strategies were used to investigate the underlying mechanisms.

RESULTS

Evident anxiodepressive-like behaviors were observed 6w after the SNI surgery, accompanied by increased neuronal excitability, enhanced HCN channel function, and increased expression of HCN2 isoforms in the LHb. Either pharmacological inhibition or virus knockdown of HCN2 channels significantly reduced LHb neuronal excitability and ameliorated both pain and depressive-like behaviors.

CONCLUSION

Our results indicated that the LHb neurons were hyperactive under CADS in chronic pain, and this hyperactivation possibly resulted from the enhanced function of HCN channels and up-regulation of HCN2 isoforms.

A visual circuit related to the parabrachial nucleus for the antipruritic effects of bright light treatment

In addition to its role in vision, light also serves non-image-forming visual functions. Despite clinical evidence suggesting the antipruritic effects of bright light treatment, the circuit mechanisms underlying the effects of light on itch-related behaviors remain poorly understood. In this study, we demonstrate that bright light treatment reduces itch-related behaviors in mice through a visual circuit related to the lateral parabrachial nucleus (LPBN). Specifically, a subset of retinal ganglion cells (RGCs) innervates GABAergic neurons in the ventral lateral geniculate nucleus and intergeniculate leaflet (vLGN/IGL), which subsequently inhibit CaMKIIα+ neurons in the LPBN. Activation of both the vLGN/IGL-projecting RGCs and the vLGN/IGL-to-LPBN projections is sufficient to reduce itch-related behaviors induced by various pruritogens. Importantly, we demonstrate that the antipruritic effects of bright light treatment rely on the activation of the retina-vLGN/IGL-LPBN pathway. Collectively, our findings elucidate a visual circuit related to the LPBN that underlies the antipruritic effects of bright light treatment.

Visual environment in schools and student depressive symptoms: Insights from a prospective study across multiple cities in eastern China

OBJECTIVE

To investigate the effects of the school visual environment on depressive symptoms in children and adolescents based on cohort study in eastern China. The school visual environment-related indicators included in this study comprise personal factors (visual impairment) and school-related factors (classroom lighting, school green spaces and school air quality).

METHOD

The follow-up cohort comprises 15,348 students from 283 primary and secondary schools in eastern China. This represents the one-year outcomes of a school-based myopia-mental health cohort study. Data collection includes basic demographics (age, gender, region, etc.), physical examination indicators, behavioral indicators, and school visual environment-related indicators.

RESULT

After a one-year follow-up, we found that compared to the more severe vision impairment group (≤4.0), healthy vision group (≥5.0) had a positive effect against the occurrence of depressive symptoms during consecutive follow-ups, with an RR value of 0.61 (95% CI: 0.57-0.66). Higher values of blackboard illumination appear to be associated with greater positive effects, with an RR (Q75%∼Q100% range) value of 0.87(95% CI: 0.81-0.93). School green spaces seem to exhibit relatively good positive effects when in the Q25%∼Q75% range. The combination of physical activity (Weekly high-intensity exercise) with school air quality(PM2.5≤50%)showed a better positive effect, with an RR value of 0.51(95%CI:0.48-0.55).

CONCLUSION

When addressing students' depressive symptoms, it is crucial to improve the visual environment both at the school level and in students' personal level. Paying appropriate attention to modifiable behaviors, like regular participation in high-intensity exercise sessions, can help alleviate students' depressive symptoms.

Circadian-independent light regulation of mammalian metabolism

The daily light-dark cycle is a key zeitgeber (time cue) for entraining an organism's biological clock, whereby light sensing by retinal photoreceptors, particularly intrinsically photosensitive retinal ganglion cells, stimulates the suprachiasmatic nucleus of the hypothalamus, a central pacemaker that in turn orchestrates the rhythm of peripheral metabolic activities. Non-rhythmic effects of light on metabolism have also been long known, and their transduction mechanisms are only beginning to unfold. Here, we summarize emerging evidence that, in mammals, light exposure or deprivation profoundly affects glucose homeostasis, thermogenesis and other metabolic activities in a clock-independent manner. Such light regulation could involve melanopsin-based, intrinsically photosensitive retinal ganglion cell-initiated brain circuits via the suprachiasmatic nucleus of the hypothalamus and other nuclei, or direct stimulation of opsins expressed in the hypothalamus, adipose tissue, blood vessels and skin to regulate sympathetic tone, lipolysis, glucose uptake, mitochondrial activation, thermogenesis, food intake, blood pressure and melanogenesis. These photic signalling events may coordinate with circadian-based mechanisms to maintain metabolic homeostasis, with dysregulation of this system underlying metabolic diseases caused by aberrant light exposure, such as environmental night light and shift work.

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.

The lateral habenula: A hub for value-guided behavior

The habenula is an evolutionarily highly conserved diencephalic brain region divided into two major parts, medial and lateral. Over the past two decades, studies of the lateral habenula (LHb), in particular, have identified key functions in value-guided behavior in health and disease. In this review, we focus on recent insights into LHb connectivity and its functional relevance for different types of aversive and appetitive value-guided behavior. First, we give an overview of the anatomical organization of the LHb and its main cellular composition. Next, we elaborate on how distinct LHb neuronal subpopulations encode aversive and appetitive stimuli and on their involvement in more complex decision-making processes. Finally, we scrutinize the afferent and efferent connections of the LHb and discuss their functional implications for LHb-dependent behavior. A deepened understanding of distinct LHb circuit components will substantially contribute to our knowledge of value-guided behavior.

Association of Retinal Neurovascular Impairment with Disease Severity in Patients with Major Depressive Disorder: An Optical Coherence Tomography Angiography Study

Background

Identifying the fundus objective biomarkers for the major depressive disorders (MDD) may help promote mental health. The aim of this study was to evaluate retinal neurovascular changes and further investigate their association with disease severity in MDD.

Methods

This cross-sectional study conducted in the hospital enrolled patients with MDD and healthy controls.The retinal neurovascular parameters for all subjects, including vessel density (VD), thickness of ganglion cell complex (GCC) and retinal nerve fiber layer (RNFL), and optic nerve head (ONH) eg are automatically calculated by the software in optical coherence tomography angiography (OCTA). The severity of MDD including depressive symptoms, anxiety, cognition, and insomnia was assessed by Hamilton Depression Rating Scale (HAMD), Hamilton Anxiety Scale (HAMA), Montreal Cognitive Assessment (MoCA), and Insomnia Severity Index (ISI) respectively.

Results

This study included 74 MDD patients (n=74 eyes) and 60 healthy controls (HCs) (n=60 eyes). MDD patients showed significantly decreased VD of superficial and deep capillary plexus, thickness of GCC and RNFL, and volume of ONH (all p<0.05) and increased vertical cup-to-disc ratio and global loss volume (GLV) (all p<0.05) compared to HCs. Positive associations were found between HAMD scores and cup area (r=0.30, p=0.035), cup volume (r=0.31, p=0.029), and disc area (r=0.33, p=0.020) as well as ISI scores and RNFL thickness (r=0.34, p=0.047).

Conclusion

We found the retinal neurovascular impairment and its association with disease severity in MDD patients. OCTA showed promise as a potential complementary assessment tool for MDD.