Dopamine: A Modulator of Circadian Rhythms in the Central Nervous System

Repetitive Transcranial Magnetic Stimulation Alleviates MPTP-Induced Parkinson's Disease Symptoms by Regulating CaMKII-CREB-BMAL1 Pathway in Mice Model

Background

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive neuromodulation technique that shows promise for the treatment of Parkinson's disease (PD). However, there is still limited understanding of the optimal stimulation frequencies and whether rTMS can alleviate PD symptoms by regulating the CaMKII-CREB-BMAL1 pathway.

Methods

A PD mouse model was induced intraperitoneally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and treated with 1 Hz, 5 Hz, and 10 Hz rTMS. The neurological function, survival of dopaminergic neurons, and protein levels of Tyrosine hydroxylase (TH), α-synuclein(α-syn), and brain-derived neurotrophic factor (BDNF) in the striatum were measured to determine the optimal stimulation frequencies of rTMS treatment in PD mice. The levels of melatonin, cortisol, and the circadian rhythm of Brain and muscle ARNT-like 1 (BMAL1) in PD model mice were detected after optimal frequency rTMS treatment. Additionally, KN-93 and Bmal1siRNA interventions were used to verify that rTMS could alleviate PD symptoms by regulating the CaMKII-CREB-BMAL1 pathway.

Results

Administration of 10 Hz rTMS significantly improved neurological function, increased the protein levels of TH and BDNF, and inhibited abnormal aggregation of a-syn. Furthermore, administration of 10 Hz rTMS regulated the secretion profile of cortisol and melatonin and reversed the circadian arrhythmia of BMAL1 expression. After the KN-93 intervention, the MPTP+rTMS+KN-93 group exhibited decreased levels of P- Ca2+/calmodulin-dependent protein kinase II (CaMKII)/CaMKII, P-cAMP-response-element-binding protein (CREB)/CREB, BMALI, and TH. After Bmal1siRNA intervention, the protein levels of BMAL1 and TH were significantly reduced in the MPTP+10 Hz+ Bmal1siRNA group. At the same time, there were no significant changes in the proportions of P-CaMKIIα/CaMKIIα and P-CREB/CREB expression levels. Finally, immunohistochemical analysis showed that the number of TH-positive neurons was high in the MPTP+10 Hz group, but decreased significantly after KN-93 and Bmal1siRNA interventions.

Conclusion

Treatment with 10 Hz rTMS alleviated MPTP-induced PD symptoms by regulating the CaMKII-CREB-BMAL1 pathway. This study provides a comprehensive perspective of the therapeutic mechanisms of rTMS in PD.

Disrupted Circadian Rhythms and Substance Use Disorders: A Narrative Review

Substance use disorder is a major global health concern, with a high prevalence among adolescents and young adults. The most common substances of abuse include alcohol, marijuana, cocaine, nicotine, and opiates. Evidence suggests that a mismatch between contemporary lifestyle and environmental demands leads to disrupted circadian rhythms that impair optimal physiological and behavioral function, which can increase the vulnerability to develop substance use disorder and related problems. The circadian system plays an important role in regulating the sleep-wake cycle and reward processing, both of which directly affect substance abuse. Distorted substance use can have a reciprocal effect on the circadian system by influencing circadian clock gene expression. Considering the detrimental health consequences and profound societal impact of substance use disorder, it is crucial to comprehend its complex association with circadian rhythms, which can pave the way for the generation of novel chronotherapeutic treatment approaches. In this narrative review, we have explored the potential contributions of disrupted circadian rhythms and sleep on use and relapse of different substances of abuse. The involvement of circadian clock genes with drug reward pathways is discussed, along with the potential research areas that can be explored to minimize disordered substance use by improving circadian hygiene.

PEDOT/CNT Flexible MEAs Reveal New Insights into the Clock Gene's Role in Dopamine Dynamics

Substantial evidence has shown that the Circadian Locomotor Output Cycles Kaput (Clock) gene is a core transcription factor of circadian rhythms that regulates dopamine (DA) synthesis. To shed light on the mechanism of this interaction, flexible multielectrode arrays (MEAs) are developed that can measure both DA concentrations and electrophysiology chronically. The dual functionality is enabled by conducting polymer PEDOT doped with acid-functionalized carbon nanotubes (CNT). The PEDOT/CNT microelectrode coating maintained stable electrochemical impedance and DA detection by square wave voltammetry for 4 weeks in vitro. When implanted in wild-type (WT) and Clock mutation (MU) mice, MEAs measured tonic DA concentration and extracellular neural activity with high spatial and temporal resolution for 4 weeks. A diurnal change of DA concentration in WT is observed, but not in MU, and a higher basal DA concentration and stronger cocaine-induced DA increase in MU. Meanwhile, striatal neuronal firing rate is found to be positively correlated with DA concentration in both animal groups. These findings offer new insights into DA dynamics in the context of circadian rhythm regulation, and the chronically reliable performance and dual measurement capability of this technology hold great potential for a broad range of neuroscience research.

A mathematical model for the role of dopamine-D2 self-regulation in the production of ultradian rhythms

Many self-motivated and goal-directed behaviours display highly flexible, approximately 4 hour ultradian (shorter than a day) oscillations. Despite lacking direct correspondence to physical cycles in the environment, these ultradian rhythms may be involved in optimizing functional interactions with the environment and reflect intrinsic neural dynamics. Current evidence supports a role of mesostriatal dopamine (DA) in the expression and propagation of ultradian rhythmicity, however, the biochemical processes underpinning these oscillations remain to be identified. Here, we use a mathematical model to investigate D2 autoreceptor-dependent DA self-regulation as the source of ultradian behavioural rhythms. DA concentration at the midbrain-striatal synapses is governed through a dual-negative feedback-loop structure, which naturally gives rise to rhythmicity. This model shows the propensity of striatal DA to produce an ultradian oscillation characterized by a flexible period that is highly sensitive to parameter variations. Circadian (approximately 24 hour) regulation consolidates the ultradian oscillations and alters their response to the phase-dependent, rapid-resetting effect of a transient excitatory stimulus. Within a circadian framework, the ultradian rhythm orchestrates behavioural activity and enhances responsiveness to an external stimulus. This suggests a role for the circadian-ultradian timekeeping hierarchy in governing organized behaviour and shaping daily experience through coordinating the motivation to engage in recurring, albeit not highly predictable events, such as social interactions.

The neurobiological effects of senescence on dopaminergic system: A comprehensive review

Over time, the body undergoes a natural, multifactorial, and ongoing process named senescence, which induces changes at the molecular, cellular, and micro-anatomical levels in many body systems. The brain, being a highly complex organ, is particularly affected by this process, potentially impairing its numerous functions. The brain relies on chemical messengers known as neurotransmitters to function properly, with dopamine being one of the most crucial. This catecholamine is responsible for a broad range of critical roles in the central nervous system, including movement, learning, cognition, motivation, emotion, reward, hormonal release, memory consolidation, visual performance, sexual drive, modulation of circadian rhythms, and brain development. In the present review, we thoroughly examine the impact of senescence on the dopaminergic system, with a primary focus on the classic delimitations of the dopaminergic nuclei from A8 to A17. We provide in-depth information about their anatomy and function, particularly addressing how senescence affects each of these nuclei.

Impaired Glymphatic and Meningeal Lymphatic Functions in Patients with Chronic Migraine

OBJECTIVE

This study was undertaken to investigate migraine glymphatic and meningeal lymphatic vessel (mLV) functions.

METHODS

Migraine patients and healthy controls (HCs) were prospectively recruited between 2020 and 2023. Diffusion tensor image analysis along the perivascular space (DTI-ALPS) index for glymphatics and dynamic contrast-enhanced magnetic resonance imaging parameters (time to peak [TTP]/enhancement integral [EI]/mean time to enhance [MTE]) for para-superior sagittal (paraSSS)-mLV or paratransverse sinus (paraTS)-mLV in episodic migraine (EM), chronic migraine (CM), and CM with and without medication-overuse headache (MOH) were analyzed. DTI-ALPS correlations with clinical parameters (migraine severity [numeric rating scale]/disability [Migraine Disability Assessment (MIDAS)]/bodily pain [Widespread Pain Index]/sleep quality [Pittsburgh Sleep Quality Index (PSQI)]) were examined.

RESULTS

In total, 175 subjects (112 migraine + 63 HCs) were investigated. DTI-ALPS values were lower in CM (median [interquartile range] = 0.64 [0.12]) than in EM (0.71 [0.13], p = 0.005) and HCs (0.71 [0.09], p = 0.004). CM with MOH (0.63 [0.07]) had lower DTI-ALPS values than CM without MOH (0.73 [0.12], p < 0.001). Furthermore, CM had longer TTP (paraSSS-mLV: 55.8 [12.9] vs 40.0 [7.6], p < 0.001; paraTS-mLV: 51.2 [8.1] vs 44.0 [3.3], p = 0.002), EI (paraSSS-mLV: 45.5 [42.0] vs 16.1 [9.2], p < 0.001), and MTE (paraSSS-mLV: 253.7 [6.7] vs 248.4 [13.8], p < 0.001; paraTS-mLV: 252.0 [6.2] vs 249.7 [1.2], p < 0.001) than EM patients. The MIDAS (p = 0.002) and PSQI (p = 0.002) were negatively correlated with DTI-ALPS index after Bonferroni corrections (p < q = 0.01).

INTERPRETATION

CM patients, particularly those with MOH, have glymphatic and meningeal lymphatic dysfunctions, which are highly clinically relevant and may implicate pathogenesis for migraine chronification. ANN NEUROL 2024;95:583-595.

Retinal dysfunction in Huntington's disease mouse models concurs with local gliosis and microglia activation

Huntington's disease (HD) is caused by an aberrant expansion of CAG repeats in the HTT gene that mainly affects basal ganglia. Although striatal dysfunction has been widely studied in HD mouse models, other brain areas can also be relevant to the pathology. In this sense, we have special interest on the retina as this is the most exposed part of the central nervous system that enable health monitoring of patients using noninvasive techniques. To establish the retina as an appropriate tissue for HD studies, we need to correlate the retinal alterations with those in the inner brain, i.e., striatum. We confirmed the malfunction of the transgenic R6/1 retinas, which underwent a rearrangement of their transcriptome as extensive as in the striatum. Although tissue-enriched genes were downregulated in both areas, a neuroinflammation signature was only clearly induced in the R6/1 retina in which the observed glial activation was reminiscent of the situation in HD patient's brains. The retinal neuroinflammation was confirmed in the slow progressive knock-in zQ175 strain. Overall, these results demonstrated the suitability of the mouse retina as a research model for HD and its associated glial activation.

Unraveling the Interplay of Dopamine, Carbon Monoxide, and Heme Oxygenase in Neuromodulation and Cognition

The dopaminergic system plays important roles in neuromodulation, including prominent roles in complex neurological functions such as cognition, reward, motivation, and memory. Understandably, the highly complex nature of such physiological functions means that their regulation is intertwined with other signaling pathways, as has been demonstrated by numerous studies. Contrary to its public perception of being poisonous at all concentrations, carbon monoxide (CO) is produced endogenously from heme degradation by heme oxygenase (HO) as part of the physiological process of red blood cell turnover. Physiological concentrations of CO can reach high micromolar ranges in the hemoglobin bound form. Low-dose CO has shown therapeutic effects in numerous animal models, including traumatic brain injury via engaging various hemoprotein targets. As such, the HO-CO axis has been shown to offer beneficial effects in organ protection, anti-inflammation, and neuroprotection, among many others. Further, a large number of publications have shown the interactions among CO, HO, and the dopaminergic system. In this review, we critically examine such experimental evidence in a holistic fashion and in the context of a possible dopamine-HO-CO signaling axis. We hope that this Perspective will stimulate additional investigations into the molecular connectivity related to this possible axis and open doors to the development of novel therapeutics that impact the dopaminergic system.

Circadian neurogenetics and its implications in neurophysiology, behavior, and chronomedicine

The circadian rhythm affects multiple physiological processes, and disruption of the circadian system can be involved in a range of disease-related pathways. The genetic underpinnings of the circadian rhythm have been well-studied in model organisms. Significant progress has been made in understanding how clock genes affect the physiological functions of the nervous system. In addition, circadian timing is becoming a key factor in improving drug efficacy and reducing drug toxicity. The circadian biology of the target cell determines how the organ responds to the drug at a specific time of day, thus regulating pharmacodynamics. The current review brings together recent advances that have begun to unravel the molecular mechanisms of how the circadian clock affects neurophysiological and behavioral processes associated with human brain diseases. We start with a brief description of how the ubiquitous circadian rhythms are regulated at the genetic, cellular, and neural circuit levels, based on knowledge derived from extensive research on model organisms. We then summarize the latest findings from genetic studies of human brain disorders, focusing on the role of human clock gene variants in these diseases. Lastly, we discuss the impact of common dietary factors and medications on human circadian rhythms and advocate for a broader application of the concept of chronomedicine.

Schizophrenia and disruption of circadian rhythms: An overview of genetic, metabolic and clinical signs

A molecular clock in the suprachiasmatic nucleus of the anterior hypothalamus, which is entrained by the dark-light cycle and controls the sleep-wake cycle, regulates circadian rhythms. The risk of developing mental disorders, such as schizophrenia, has long been linked to sleep abnormalities. Additionally, a common aspect of mental disorders is sleep disturbance, which has a direct impact on the intensity of the symptoms and the quality of life of the patient. This relationship can be explained by gene alterations such as CLOCK in schizophrenia which are also important components of the physiological circadian rhythm. The function of dopamine and adenosine in circadian rhythm should also be noted, as these hypotheses are considered to be the most popular theories explaining schizophrenia pathogenesis. Therefore, determining the presence of a causal link between the two can be key to identifying new potential targets in schizophrenia therapy, which can open new avenues for clinical research as well as psychiatric care. We review circadian disruption in schizophrenia at the genetic, metabolic, and clinical levels. We summarize data about clock and clock-controlled genes' alterations, neurotransmitter systems' impairments, and association with chronotype in schizophrenia patients. Our findings demonstrate that in schizophrenia either homeostatic or circadian processes of sleep regulation are disturbed. Also, we found an insufficient number of studies aimed at studying the relationship between known biological phenomena of circadian disorders and clinical signs of schizophrenia.

Levodopa Rescues Retinal Function in the Transgenic A53T Alpha-Synuclein Model of Parkinson's Disease

BACKGROUND

Loss of substantia nigra dopaminergic cells and alpha-synuclein (α-syn)-rich intraneuronal deposits within the central nervous system are key hallmarks of Parkinson's disease (PD). Levodopa (L-DOPA) is the current gold-standard treatment for PD. This study aimed to evaluate in vivo retinal changes in a transgenic PD model of α-syn overexpression and the effect of acute levodopa (L-DOPA) treatment.

METHODS

Anaesthetised 6-month-old mice expressing human A53T alpha-synuclein (HOM) and wildtype (WT) control littermates were intraperitoneally given 20 mg/kg L-DOPA (50 mg levodopa, 2.5 mg benserazide) or vehicle saline (n = 11-18 per group). In vivo retinal function (dark-adapted full-field ERG) and structure (optical coherence tomography, OCT) were recorded before and after drug treatment for 30 min. Ex vivo immunohistochemistry (IHC) on flat-mounted retina was conducted to assess tyrosine hydroxylase (TH) positive cell counts (n = 7-8 per group).

RESULTS

We found that photoreceptor (a-wave) and bipolar cell (b-wave) ERG responses (p < 0.01) in A53T HOM mice treated with L-DOPA grew in amplitude more (47 ± 9%) than WT mice (16 ± 9%) treated with L-DOPA, which was similar to the vehicle group (A53T HOM 25 ± 9%; WT 19 ± 7%). While outer retinal thinning (outer nuclear layer, ONL, and outer plexiform layer, OPL) was confirmed in A53T HOM mice (p < 0.01), L-DOPA did not have an ameliorative effect on retinal layer thickness. These findings were observed in the absence of changes to the number of TH-positive amacrine cells across experiment groups. Acute L-DOPA treatment transiently improves visual dysfunction caused by abnormal alpha-synuclein accumulation.

CONCLUSIONS

These findings deepen our understanding of dopamine and alpha-synuclein interactions in the retina and provide a high-throughput preclinical framework, primed for translation, through which novel therapeutic compounds can be objectively screened and assessed for fast-tracking PD drug discovery.

Fighting Against the Clock: Circadian Disruption and Parkinson's Disease

Circadian disruption is being increasingly recognized as a critical factor in the development and progression of Parkinson's disease (PD). This review aims to provide an in-depth overview of the relationship between circadian disruption and PD by exploring the molecular, cellular, and behavioral aspects of this interaction. This review will include a comprehensive understanding of how the clock gene system and transcription-translation feedback loops function and how they are diminished in PD. The article also discusses the role of clock genes in the regulation of circadian rhythms, as well as the impact of clock gene dysregulation on mitochondrial function, oxidative stress, and neuroinflammation, including the microbiota-gut-brain axis, which have all been proposed as being crucial mechanisms in the pathophysiology of PD. Finally, this review highlights potential therapeutic strategies targeting the clock gene system and circadian rhythm for the treatment of PD.

Integrative Lighting Aimed at Patients with Psychiatric and Neurological Disorders

The purpose of this paper is to investigate the impact of circadian lighting-induced melatonin suppression on patients with psychiatric and neurological disorders in hospital wards by using an ad-hoc metrology framework and the subsequent metrics formalized by the CIE in 2018. A measurement scheme was conducted in hospital ward rooms in the Department of Neurology, Zealand University Hospital, at Roskilde in Denmark, to evaluate the photometric and colorimetric characteristics of the lighting system, as well as its influence on the circadian rhythm of the occupants. The measurement scheme included point measurements and data logging, using a spectrophotometer mounted on a tripod with adjustable height to assess the newly installed circadian lighting system. The measured spectra were uploaded to the Luox platform to calculate illuminance, CCT, MEDI, etc., in accordance with the CIE S026 standard. Furthermore, the MLIT based on MEDI data logging results was calculated. In addition to CIE S026, we have investigated the usefulness of melatonin suppression models for the assessment of circadian performance regarding measured light. From the results, the lighting conditions in the patient room for both minimal and abundant daylight access were evaluated and compared; we found that access to daylight is essential for both illumination and circadian entrainment. It can be concluded that the measurement scheme, together with the use of the Luox platform and Canva template, is suitable for the accurate and satisfactory measurement of integrative lighting that aligns with CIE requirements and recommendations.

Stress-related cellular pathophysiology as a crosstalk risk factor for neurocognitive and psychiatric disorders

In this narrative review, we examine biological processes linking psychological stress and cognition, with a focus on how psychological stress can activate multiple neurobiological mechanisms that drive cognitive decline and behavioral change. First, we describe the general neurobiology of the stress response to define neurocognitive stress reactivity. Second, we review aspects of epigenetic regulation, synaptic transmission, sex hormones, photoperiodic plasticity, and psychoneuroimmunological processes that can contribute to cognitive decline and neuropsychiatric conditions. Third, we explain mechanistic processes linking the stress response and neuropathology. Fourth, we discuss molecular nuances such as an interplay between kinases and proteins, as well as differential role of sex hormones, that can increase vulnerability to cognitive and emotional dysregulation following stress. Finally, we explicate several testable hypotheses for stress, neurocognitive, and neuropsychiatric research. Together, this work highlights how stress processes alter neurophysiology on multiple levels to increase individuals' risk for neurocognitive and psychiatric disorders, and points toward novel therapeutic targets for mitigating these effects. The resulting models can thus advance dementia and mental health research, and translational neuroscience, with an eye toward clinical application in cognitive and behavioral neurology, and psychiatry.

The Dopaminergic System Modulates the Electrophysiological Activity of the Suprachiasmatic Nucleus Dependent on the Circadian Cycle

The suprachiasmatic nucleus of the hypothalamus (SCN) controls mammalian circadian rhythms. Circadian rhythms influence the dopaminergic system, and dopaminergic tone impresses the physiology and behavior of the circadian clock. However, little is known about the effect of dopamine and dopamine receptors, especially D1-like dopamine receptors (D1Rs), in regulating the circadian rhythm and the SCN neuron's activity. Therefore, the present study aimed to investigate the role of the D1Rs in SCN neural oscillations during the 24-h light-dark cycle using local field potential (LFP) recording. To this end, two groups of rats were given the SKF-38393 (1 mg/kg; i.p.) as a D1-like receptor agonist in the morning or night. LFP recording was performed for ten minutes before and two hours after the SKF-38393 injection. The obtained results showed that diurnal changes affect LFP oscillations so that delta relative power declined substantially, whereas upper-frequency bands and Lempel-Ziv complexity (LZC) index increased at night, which is consistent with rodents' activity cycles. The D1Rs agonist administration in the morning dramatically altered these intrinsic oscillations, decreasing delta and theta relative power, and most of the higher frequency bands and LZC index were promoted. Some of these effects were reversed at the night after the SKF-38393 injection. In conclusion, findings showed that the SCN's neuronal activities are regulated based on the light-dark cycle in terms of population neural oscillatory activity which could be affected by dopaminergic stimulation in a time-dependent way.

Activation patterns of dopaminergic cell populations reflect different learning scenarios in a cichlid fish, Pseudotropheus zebra

Dopamine is present in all vertebrates and the functional roles of the subsystems are assumed to be similar. Whereas the effect of dopaminergic modulation is well investigated in different target systems, less is known about the factors that are causing the modulation of dopaminergic cells. Using the zebra mbuna, Pseudotropheus zebra, a cichlid fish from Lake Malawi as a model system, we investigated the activation of specific dopaminergic cell populations detected by double-labeling with TH and pS6 antibodies while the animals were solving different learning tasks. Specifically, we compared an intense avoidance learning situation, an instrumental learning task, and a non-learning isolated group and found strong activation of different dopaminergic cell populations. Preoptic-hypothalamic cell populations respond to the stress component in the avoidance task, and the forced movement/locomotion may be responsible for activation in the posterior tubercle. The instrumental learning task had little stress component, but the activation of the raphe superior in this group may be correlated with attention or arousal during the training sessions. At the same time, the weaker activation of the nucleus of the posterior commissure may be related to positive reward acting onto tectal circuits. Finally, we examined the co-activation patterns across all dopaminergic cell populations and recovered robust differences across experimental groups, largely driven by hypothalamic, posterior tubercle, and brain stem regions possibly encoding the valence and salience associated with stressful stimuli. Taken together, our results offer some insights into the different functions of the dopaminergic cell populations in the brain of a non-mammalian vertebrate in correlation with different behavioral conditions, extending our knowledge for a more comprehensive view of the mechanisms of dopaminergic modulation in vertebrates.

Profiling transcriptomic responses of human stem cell-derived medium spiny neuron-like cells to exogenous phasic and tonic neurotransmitters

Transcriptomic responses to neurotransmitters contribute to the complex processes driving memory and addiction. Advances in both measurement methods and experimental models continue to improve our understanding of this regulatory layer. Here we focus on the experimental potential of stem cell derived neurons, currently the only ethical model that can be used in reductionist and experimentally perturbable studies of human cells. Prior work has focused on generating distinct cell types from human stem cells, and has also shown their utility in modeling development and cellular phenotypes related to neurodegeneration. Here we seek an understanding of how stem cell derived neural cultures respond to perturbations experienced during development and disease progression. This work profiles transcriptomic responses of human medium spiny neuron-like cells with three specific goals. We first characterize transcriptomic responses to dopamine and dopamine receptor agonists and antagonists presented in dosing patterns mimicking acute, chronic, and withdrawal regimens. We also assess transcriptomic responses to low and persistent tonic levels of dopamine, acetylcholine, and glutamate to better mimic the in vivo environment. Finally, we identify similar and distinct responses between hMSN-like cells derived from H9 and H1 stem cell lines, providing some context for the extent of variability these types of systems will likely pose for experimentalists. The results here suggest future optimizations of human stem cell derived neurons to increase their in vivo relevance and the biological insights that can be garnered from these models.

Parkinson's Disease: A Narrative Review on Potential Molecular Mechanisms of Sleep Disturbances, REM Behavior Disorder, and Melatonin

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. There is a wide range of sleep disturbances in patients with PD, such as insomnia and rapid eye movement (REM) sleep behavior disorder (or REM behavior disorder (RBD)). RBD is a sleep disorder in which a patient acts out his/her dreams and includes abnormal behaviors during the REM phase of sleep. On the other hand, melatonin is the principal hormone that is secreted by the pineal gland and significantly modulates the circadian clock and mood state. Furthermore, melatonin has a wide range of regulatory effects and is a safe treatment for sleep disturbances such as RBD in PD. However, the molecular mechanisms of melatonin involved in the treatment or control of RBD are unknown. In this study, we reviewed the pathophysiology of PD and sleep disturbances, including RBD. We also discussed the potential molecular mechanisms of melatonin involved in its therapeutic effect. It was concluded that disruption of crucial neurotransmitter systems that mediate sleep, including norepinephrine, serotonin, dopamine, and GABA, and important neurotransmitter systems that mediate the REM phase, including acetylcholine, serotonin, and norepinephrine, are significantly involved in the induction of sleep disturbances, including RBD in PD. It was also concluded that accumulation of α-synuclein in sleep-related brain regions can disrupt sleep processes and the circadian rhythm. We suggested that new treatment strategies for sleep disturbances in PD may focus on the modulation of α-synuclein aggregation or expression.

Exploring the associations between the Morningness-Eveningness-Stability-Scale improved (MESSi) and the higher-order personality factors

Morningness-eveningness refers to individual differences in the sleep-wake cycle. Research indicates that morningness-eveningness is associated with the Big Five (neuroticism, extraversion, openness to experience, agreeableness, conscientiousness) and the Big Two (alpha-stability, beta-plasticity) personality factors. However, the latter has not yet been tested within the multidimensional approach to morningness-eveningness. In the present study, we have adapted the Morningness-Eveningness-Stability-Scale improved (MESSi) to Polish (https://osf.io/rcxb5) to explore the associations between its subscales (morning affect, eveningness, distinctness) and the Big Two personality traits in a sample of 1106 participants (559 women and 547 men) aged 18 to 55 (M = 36.26, SD = 9.90). In bivariate correlations, morning affect was positively related to alpha-stability and beta-plasticity, distinctness was correlated negatively with alpha-stability and beta-plasticity, while eveningness was positively correlated only with beta-plasticity. Furthermore, the confirmatory factor analysis supported the original three-factor structure of the Polish version of MESSi, while the associations with affect and the symptoms of depression and anxiety attested to its validity. Overall, the present study provides the first evidence for the associations between MESSi subscales and the Big Two personality traits, as well as shows a good fit of the three-factor structure of MESSi in the Polish population.

Circadian profile, daytime activity, and the Parkinson's phenotype: A motion sensor pilot study with neurobiological underpinnings

Circadian rhythm impairment may play a role in Parkinson's disease (PD) pathophysiology. Recent literature associated circadian rhythm features to the risk of developing Parkinson and to its progression through stages. The association between the chronotype and the phenotype should be verified on a clinical and biological point of view. Herein we investigate the chronotype of a sample of 50 PD patients with the Morningness Eveningness Questionnaire and monitor their daily activity with a motion sensor embedded in a smartphone. Fibroblasts were collected from PD patients (n = 5) and from sex/age matched controls (n = 3) and tested for the circadian expression of clock genes (CLOCK, BMAL1, PER1, CRY1), and for cell morphology, proliferation, and death. Our results show an association between the chronotype and the PD phenotype. The most representative clinical chronotypes were "moderate morning" (56%), the "intermediate" (24%) and, in a minor part, the "definite morning" (16%). They differed for axial motor impairment, presence of motor fluctuations and quality of life (p < 0.05). Patients with visuospatial dysfunction and patients with a higher PIGD score had a blunted motor daily activity (p = 0.006 and p = 0.001, respectively), independently by the influence of age and other motor scores. Fibroblasts obtained by PD patients (n = 5) had an impaired BMAL1 cycle compared to controls (n = 3, p = 0.01). Moreover, a PD flat BMAL1 profile was associated with the lowest cell proliferation and the largest cell morphology. This study contributes to the growing literature on CR abnormalities in the pathophysiology of Parkinson's disease providing a link between the clinical and biological patient chronotype and the disease phenomenology.

Reliability and validity of the Chinese version of the biological rhythms interview of assessment in neuropsychiatry in patients with major depressive disorder

BACKGROUND

Although disturbances in biological rhythms are closely related to the onset of major depressive disorder (MDD), they are not commonly assessed in Chinese clinical practice. The Biological Rhythms Interview of Assessment in Neuropsychiatry (BRIAN) has been used to evaluate disturbances in biological rhythms in MDD. We aimed to assess and confirm the reliability and validity of the Chinese version of the BRIAN (C-BRIAN) in patients with MDD.

METHODS

A total of 120 patients with MDD and 40 age- and sex-matched controls were recruited consecutively. Reliability was estimated using Cronbach's alpha, the split-half coefficient, and the test-retest coefficient; test-retest reliability was assessed using Spearman's correlation coefficient. A confirmatory factor analysis was used to determine the construct validity of the scale. The Pittsburgh Sleep Quality Index (PSQI) and the Morningness-Eveningness Questionnaire (MEQ) were used to check concurrent validity by evaluating the correlation between the C-BRIAN, PSQI, and MEQ.

RESULTS

The overall Cronbach's α value was 0.898, indicating good internal consistency. The Guttman split-half coefficient was 0.792, indicating good split-half reliability. Moreover, the test-retest reliability for both the total and individual item score was excellent. Confirmatory factor analysis revealed that construct validity was acceptable (χ2/df = 2.117, GFI = 0.80, AGFI = 0.87, CFI = 0.848, and RMSEA = 0.097). Furthermore, total BRIAN scores were found to be negatively correlated with MEQ (r = - 0.517, P < 0.001) and positively correlated with PSQI (r = 0.586, P < 0.001). In addition, patients with MDD had higher BRIAN scores than those in controls.

CONCLUSIONS

This study revealed that the C-BRIAN scale has great validity and reliability in evaluating the disturbance of biological rhythms in patients with MDD.

Early Dysbiosis and Dampened Gut Microbe Oscillation Precede Motor Dysfunction and Neuropathology in Animal Models of Parkinson's Disease

BACKGROUND

Studies have shown different gut microbiomes in patients with Parkinson's disease (PD) compared to unaffected controls. However, when the gut microbiota shift toward dysbiosis in the PD process remains unclear.

OBJECTIVE

We aim to investigate the changes in gut microbiota, locomotor function, and neuropathology longitudinally in PD rodent models.

METHODS

Fecal microbiota were longitudinally assessed by sequencing the V4-V5 region of the 16S ribosomal RNA gene in a human mutant α-synuclein over-expressing mouse model of PD, SNCA p.A53T mice, and the non-transgenic littermate controls. The locomotor function, neuronal integrity, and α-synuclein expression in the different brain regions were compared between groups. Human fecal microbiota communities from 58 patients with PD and 46 unaffected controls were also analyzed using metagenomic sequencing for comparison.

RESULTS

Compared to non-transgenic littermate controls, the altered gut microbiota of the SNCA p.A53T mice can be detected as early as 2 months old, and the diurnal oscillation of the gut microbiome was dampened throughout PD progression starting from 4 months old. However, neuropathology changes and motor deficits were observed starting at 6 months old. Similar changes in altered gut microbiota were also observed in another PD genetic mouse model carrying the LRRK2 p.G2019S mutation at 2 months old. Among the commonly enriched gut microbiota in both PD genetic mouse models, the abundance of Parabateroides Merdae and Ruminococcus torques were also increased in human PD patients compared to controls.

CONCLUSION

These findings revealed the altered gut microbiota communities and oscillations preceding the occurrence of neuropathy and motor dysfunction in the PD process.

Circadian dysregulation and Alzheimer’s disease: A comprehensive review

Alzheimer’s disease (AD), the foremost variant of dementia, has been associated with a menagerie of risk factors, many of which are considered to be modifiable. Among these modifiable risk factors is circadian rhythm, the chronobiological system that regulates sleep‐wake cycles, food consumption timing, hydration timing, and immune responses amongst many other necessary physiological processes. Circadian rhythm at the level of the suprachiasmatic nucleus (SCN), is tightly regulated in the human body by a host of biomolecular substances, principally the hormones melatonin, cortisol, and serotonin. In addition, photic information projected along afferent pathways to the SCN and peripheral oscillators regulates the synthesis of these hormones and mediates the manner in which they act on the SCN and its substructures. Dysregulation of this cycle, whether induced by environmental changes involving irregular exposure to light, or through endogenous pathology, will have a negative impact on immune system optimization and will heighten the deposition of Aβ and the hyperphosphorylation of the tau protein. Given these correlations, it appears that there is a physiologic association between circadian rhythm dysregulation and AD. This review will explore the physiology of circadian dysregulation in the AD brain, and will propose a basic model for its role in AD‐typical pathology, derived from the literature compiled and referenced throughout.

Regulation of the rhythmic diversity of daily photoreceptor outer segment phagocytosis in vivo

Outer segment phagocytosis (OSP) is a highly-regulated, biological process wherein photoreceptor outer segment (OS) tips are cyclically phagocytosed by the adjacent retinal pigment epithelium (RPE) cells. Often an overlooked retinal process, rhythmic OSP ensures the maintenance of healthy photoreceptors and vision. Daily, the photoreceptors renew OS at their base and the most distal, and likely oldest, OS tips, are phagocytosed by the RPE, preventing the accumulation of photo-oxidative compounds by breaking down phagocytosed OS tips and recycling useful components to the photoreceptors. Light changes often coincide with an escalation of OSP and within hours the phagosomes formed in each RPE cell are resolved. In the last two decades, individual molecular regulators were elucidated. Some of the molecular machinery used by RPE cells for OSP is highly similar to mechanisms used by other phagocytic cells for the clearance of apoptotic cells. Consequently, in the RPE, many molecular regulators of retinal phagocytosis have been elucidated. However, there is still a knowledge gap regarding the key regulators of physiological OSP in vivo between endogenous photoreceptors and the RPE. Understanding the regulation of OSP is of significant clinical interest as age-related macular degeneration (AMD) and inherited retinal diseases (IRD) are linked with altered OSP. Here, we review the in vivo timing of OSP peaks in selected species and focus on the reported in vivo environmental and molecular regulators of OSP.

Reversible Photocontrol of Dopaminergic Transmission in Wild-Type Animals

Understanding the dopaminergic system is a priority in neurobiology and neuropharmacology. Dopamine receptors are involved in the modulation of fundamental physiological functions, and dysregulation of dopaminergic transmission is associated with major neurological disorders. However, the available tools to dissect the endogenous dopaminergic circuits have limited specificity, reversibility, resolution, or require genetic manipulation. Here, we introduce azodopa, a novel photoswitchable ligand that enables reversible spatiotemporal control of dopaminergic transmission. We demonstrate that azodopa activates D₁-like receptors in vitro in a light-dependent manner. Moreover, it enables reversibly photocontrolling zebrafish motility on a timescale of seconds and allows separating the retinal component of dopaminergic neurotransmission. Azodopa increases the overall neural activity in the cortex of anesthetized mice and displays illumination-dependent activity in individual cells. Azodopa is the first photoswitchable dopamine agonist with demonstrated efficacy in wild-type animals and opens the way to remotely controlling dopaminergic neurotransmission for fundamental and therapeutic purposes.

NADPH and Mitochondrial Quality Control as Targets for a Circadian-Based Fasting and Exercise Therapy for the Treatment of Parkinson's Disease

Dysfunctional mitochondrial quality control (MQC) is implicated in the pathogenesis of Parkinson's disease (PD). The improper selection of mitochondria for mitophagy increases reactive oxygen species (ROS) levels and lowers ATP levels. The downstream effects include oxidative damage, failure to maintain proteostasis and ion gradients, and decreased NAD⁺ and NADPH levels, resulting in insufficient energy metabolism and neurotransmitter synthesis. A ketosis-based metabolic therapy that increases the levels of (R)-3-hydroxybutyrate (BHB) may reverse the dysfunctional MQC by partially replacing glucose as an energy source, by stimulating mitophagy, and by decreasing inflammation. Fasting can potentially raise cytoplasmic NADPH levels by increasing the mitochondrial export and cytoplasmic metabolism of ketone body-derived citrate that increases flux through isocitrate dehydrogenase 1 (IDH1). NADPH is an essential cofactor for nitric oxide synthase, and the nitric oxide synthesized can diffuse into the mitochondrial matrix and react with electron transport chain-synthesized superoxide to form peroxynitrite. Excessive superoxide and peroxynitrite production can cause the opening of the mitochondrial permeability transition pore (mPTP) to depolarize the mitochondria and activate PINK1-dependent mitophagy. Both fasting and exercise increase ketogenesis and increase the cellular NAD⁺/NADH ratio, both of which are beneficial for neuronal metabolism. In addition, both fasting and exercise engage the adaptive cellular stress response signaling pathways that protect neurons against the oxidative and proteotoxic stress implicated in PD. Here, we discuss how intermittent fasting from the evening meal through to the next-day lunch together with morning exercise, when circadian NAD⁺/NADH is most oxidized, circadian NADP⁺/NADPH is most reduced, and circadian mitophagy gene expression is high, may slow the progression of PD.

Ontogenetic rules for the molecular diversification of hypothalamic neurons

The hypothalamus is an evolutionarily conserved endocrine interface that, among other roles, links central homeostatic control to adaptive bodily responses by releasing hormones and neuropeptides from its many neuronal subtypes. In its preoptic, anterior, tuberal and mammillary subdivisions, a kaleidoscope of magnocellular and parvocellular neuroendocrine command neurons, local-circuit neurons, and neurons that project to extrahypothalamic areas are intermingled in partially overlapping patches of nuclei. Molecular fingerprinting has produced data of unprecedented mass and depth to distinguish and even to predict the synaptic and endocrine competences, connectivity and stimulus selectivity of many neuronal modalities. These new insights support eminent studies from the past century but challenge others on the molecular rules that shape the developmental segregation of hypothalamic neuronal subtypes and their use of morphogenic cues for terminal differentiation. Here, we integrate single-cell RNA sequencing studies with those of mouse genetics and endocrinology to describe key stages of hypothalamus development, including local neurogenesis, the direct terminal differentiation of glutamatergic neurons, transition cascades for GABAergic and GABAergic cell-derived dopamine cells, waves of local neuronal migration, and sequential enrichment in neuropeptides and hormones. We particularly emphasize how transcription factors determine neuronal identity and, consequently, circuit architecture, and whether their deviations triggered by environmental factors and hormones provoke neuroendocrine illnesses.

Dopamine systems and biological rhythms: Let's get a move on

How dopamine signaling regulates biological rhythms is an area of emerging interest. Here we review experiments focused on delineating dopamine signaling in the suprachiasmatic nucleus, nucleus accumbens, and dorsal striatum to mediate a range of biological rhythms including photoentrainment, activity cycles, rest phase eating of palatable food, diet-induced obesity, and food anticipatory activity. Enthusiasm for causal roles for dopamine in the regulation of circadian rhythms, particularly those associated with food and other rewarding events, is warranted. However, determining that there is rhythmic gene expression in dopamine neurons and target structures does not mean that they are bona fide circadian pacemakers. Given that dopamine has such a profound role in promoting voluntary movements, interpretation of circadian phenotypes associated with locomotor activity must be differentiated at the molecular and behavioral levels. Here we review our current understanding of dopamine signaling in relation to biological rhythms and suggest future experiments that are aimed at teasing apart the roles of dopamine subpopulations and dopamine receptor expressing neurons in causally mediating biological rhythms, particularly in relation to feeding, reward, and activity.

The dopaminergic control of Cushing's syndrome

Cushing's Syndrome (CS), or chronic endogenous hypercortisolism, is a rare and serious disease due to corticotroph pituitary (Cushing's disease, CD) and extra-pituitary (ectopic CS) tumours overproducing ACTH, or cortisol-secreting adrenal tumours or lesions (adrenal CS). The first-line treatment for CS is represented by the surgical removal of the responsible tumour, but surgery might be unfeasible or ineffective and medical treatment can be required in a relevant percentage of patients with CS, especially CD and ectopic CS. Corticotroph pituitary and extra-pituitary tumours, as well as adrenal tumours and lesions responsible for CS express dopamine receptors (DRs), which have been found to mediate inhibition of hormone secretion and/or cell proliferation in experimental setting, suggesting that dopaminergic system, particularly DRs, might represent a target for the treatment of CS. Dopamine agonists (DAs), particularly cabergoline (CAB), are currently used as off-label treatment for CD, the most common form of CS, demonstrating efficacy in controlling hormone secretion and tumour growth in a relevant number of cases, with the improvement of clinical picture, and displaying good safety profile. Therefore, CAB may be considered a reasonable alternative treatment for persistent or recurrent CD after pituitary surgery failure, but occasionally also before pituitary surgery, as adjuvant treatment, or even instead of pituitary surgery as first-line treatment in case of surgery contraindications or refusal. A certain beneficial effect of CAB has been also reported in ectopic CS. However, the role of DAs in the clinical management of the different types of CS requires further evaluations.

The Circadian Molecular Machinery in CNS Cells: A Fine Tuner of Neuronal and Glial Activity With Space/Time Resolution

The circadian molecular machinery is a fine timekeeper with the capacity to harmonize physiological and behavioral processes with the external environment. This tight-knit regulation is coordinated by multiple cellular clocks across the body. In this review, we focus our attention on the molecular mechanisms regulated by the clock in different brain areas and within different cells of the central nervous system. Further, we discuss evidence regarding the role of circadian rhythms in the regulation of neuronal activity and neurotransmitter systems. Not only neurons, but also astrocytes and microglia actively participate in the maintenance of timekeeping within the brain, and the diffusion of circadian information among these cells is fine-tuned by neurotransmitters (e.g., dopamine, serotonin, and γ-aminobutyric acid), thus impacting on the core clock machinery. The bidirectional interplay between neurotransmitters and the circadian clockwork is fundamental in maintaining accuracy and precision in daily timekeeping throughout different brain areas. Deepening the knowledge of these correlations allows us to define the basis of drug interventions to restore circadian rhythms, as well as to predict the onset of drug treatment/side effects that might promote daily desynchronization. Furthermore, it may lead to a deeper understanding of the potential impacts of modulations in rhythmic activities on the pace of aging and provide an insight in to the pathogenesis of psychiatric diseases and neurodegenerative disorders.

Characterization of retinal function and structure in the MPTP murine model of Parkinson’s disease

In addition to well characterized motor symptoms, visual disturbances are increasingly recognized as an early manifestation in Parkinson’s disease (PD). A better understanding of the mechanisms underlying these changes would facilitate the development of vision tests which can be used as preclinical biomarkers to support the development of novel therapeutics for PD. This study aims to characterize the retinal phenotype of a mouse model of dopaminergic dysfunction and to examine whether these changes are reversible with levodopa treatment. We use a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD to characterize the neurotoxic effects of MPTP on in vivo retinal function (electroretinography, ERG), retinal structure (optical coherence tomography, OCT) and retinal dopaminergic cell number (tyrosine hydroxylase immunohistochemistry, IHC) at two time points (21 and 45 days) post MPTP model induction. We also investigate the effect of levodopa (L-DOPA) as a proof-of-principle chronic intervention against MPTP-induced changes in the retina. We show that MPTP decreases dopaminergic amacrine cell number (9%, p < 0.05) and that a component of the ERG that involves these cells, in particular oscillatory potential (OP) peak timing, was significantly delayed at Day 45 (7–13%, p < 0.01). This functional deficit was paralleled by outer plexiform layer (OPL) thinning (p < 0.05). L-DOPA treatment ameliorated oscillatory potential deficits (7–13%, p < 0.001) in MPTP animals. Our data suggest that the MPTP toxin slows the timing of inner retinal feedback circuits related to retinal dopaminergic pathways which mirrors findings from humans with PD. It also indicates that the MPTP model causes structural thinning of the outer retinal layer on OCT imaging that is not ameliorated with L-DOPA treatment. Together, these non-invasive measures serve as effective biomarkers for PD diagnosis as well as for quantifying the effect of therapy.

Early-stage visual perception impairment in schizophrenia, bottom-up and back again

Visual perception is one of the basic tools for exploring the world. However, in schizophrenia, this modality is disrupted. So far, there has been no clear answer as to whether the disruption occurs primarily within the brain or in the precortical areas of visual perception (the retina, visual pathways, and lateral geniculate nucleus [LGN]). A web-based comprehensive search of peer-reviewed journals was conducted based on various keyword combinations including schizophrenia, saliency, visual cognition, visual pathways, retina, and LGN. Articles were chosen with respect to topic relevance. Searched databases included Google Scholar, PubMed, and Web of Science. This review describes the precortical circuit and the key changes in biochemistry and pathophysiology that affect the creation and characteristics of the retinal signal as well as its subsequent modulation and processing in other parts of this circuit. Changes in the characteristics of the signal and the misinterpretation of visual stimuli associated with them may, as a result, contribute to the development of schizophrenic disease.

Circadian and Immunity Cycle Talk in Cancer Destination: From Biological Aspects to In Silico Analysis

Simple Summary

The circadian cycle is a natural cycle of the body repeated every 24 h, based on a day and night rhythm, and it affects many body processes. The present article reviews the importance and role of the circadian cycle in cancer and its association with the immune system and immunotherapy drugs at the cellular and molecular levels. It also examines the genes and cellular pathways involved in both circadian and immune systems. It offers possible computational solutions to increase the effectiveness of cancer treatment concerning the circadian cycle.

Abstract

Cancer is the leading cause of death and a major problem to increasing life expectancy worldwide. In recent years, various approaches such as surgery, chemotherapy, radiation, targeted therapies, and the newest pillar, immunotherapy, have been developed to treat cancer. Among key factors impacting the effectiveness of treatment, the administration of drugs based on the circadian rhythm in a person and within individuals can significantly elevate drug efficacy, reduce adverse effects, and prevent drug resistance. Circadian clocks also affect various physiological processes such as the sleep cycle, body temperature cycle, digestive and cardiovascular processes, and endocrine and immune systems. In recent years, to achieve precision patterns for drug administration using computational methods, the interaction of the effects of drugs and their cellular pathways has been considered more seriously. Integrated data-derived pathological images and genomics, transcriptomics, and proteomics analyses have provided an understanding of the molecular basis of cancer and dramatically revealed interactions between circadian and immunity cycles. Here, we describe crosstalk between the circadian cycle signaling pathway and immunity cycle in cancer and discuss how tumor microenvironment affects the influence on treatment process based on individuals’ genetic differences. Moreover, we highlight recent advances in computational modeling that pave the way for personalized immune chronotherapy.

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

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

Roles of clock genes in the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a common motor disorder that has become increasingly prevalent in the ageing population. Recent works have suggested that circadian rhythms disruption is a common event in PD patients. Clock genes regulate the circadian rhythm of biological processes in eukaryotic organisms, but their roles in PD remain unclear. Despite this, several lines of evidence point to the possibility that clock genes may have a significant impact on the development and progression of the disease. This review aims to consolidate recent understanding of the roles of clock genes in PD. We first summarized the findings of clock gene expression and epigenetic analyses in PD patients and animal models. We also discussed the potential contributory role of clock gene variants in the development of PD and/or its symptoms. We further reviewed the mechanisms by which clock genes affect mitochondrial dynamics as well as the rhythmic synthesis and secretion of endocrine hormones, the impairment of which may contribute to the development of PD. Finally, we discussed the limitations of the currently available studies, and suggested future potential studies to deepen our understanding of the roles of clock genes in PD pathogenesis.

Narcolepsy in Parkinson's disease with insulin resistance

Background: Parkinson’s disease (PD) is characterized by its progression of motor-related symptoms such as tremors, rigidity, slowness of movement, and difficulty with walking and balance. Comorbid conditions in PD individuals include insulin resistance (IR) and narcolepsy-like sleep patterns. The intersecting sleep symptoms of both conditions include excessive daytime sleepiness, hallucinations, insomnia, and falling into REM sleep more quickly than an average person. Understanding of the biological basis and relationship of these comorbid disorders with PD may help with early detection and intervention strategies to improve quality of life. Methods: In this study, an integrative genomics and systems biology approach was used to analyze gene expression patterns associated with PD, IR, and narcolepsy in order to identify genes and pathways that may shed light on how these disorders are interrelated. A correlation analysis with known genes associated with these disorders (LRRK2, HLA-DQB1, and HCRT) was used to query microarray data corresponding to brain regions known to be involved in PD and narcolepsy. This includes the hypothalamus, dorsal thalamus, pons, and subcoeruleus nucleus. Risk factor genes for PD, IR, and narcolepsy were also incorporated into the analysis. Results: The PD and narcolepsy signaling networks are connected through insulin and immune system pathways. Important genes and pathways that link PD, narcolepsy, and IR are CACNA1C, CAMK1D, BHLHE41, HMGB1, and AGE-RAGE. Conclusions: We have identified the genetic signatures that link PD with its comorbid disorders, narcolepsy and insulin resistance, from the convergence and intersection of dopaminergic, insulin, and immune system related signaling pathways. These findings may aid in the design of early intervention strategies and treatment regimes for non-motor symptoms in PD patients as well as individuals with diabetes and narcolepsy.

Sleep and circadian rhythms in Parkinson's disease and preclinical models

The use of animals as models of human physiology is, and has been for many years, an indispensable tool for understanding the mechanisms of human disease. In Parkinson's disease, various mouse models form the cornerstone of these investigations. Early models were developed to reflect the traditional histological features and motor symptoms of Parkinson's disease. However, it is important that models accurately encompass important facets of the disease to allow for comprehensive mechanistic understanding and translational significance. Circadian rhythm and sleep issues are tightly correlated to Parkinson's disease, and often arise prior to the presentation of typical motor deficits. It is essential that models used to understand Parkinson's disease reflect these dysfunctions in circadian rhythms and sleep, both to facilitate investigations into mechanistic interplay between sleep and disease, and to assist in the development of circadian rhythm-facing therapeutic treatments. This review describes the extent to which various genetically- and neurotoxically-induced murine models of Parkinson's reflect the sleep and circadian abnormalities of Parkinson's disease observed in the clinic.

Photoperiodic light pulse induces ovarian development in the catfish, Mystus cavasius: Possible roles of dopamine and melatonin in the brain

In the freshwater catfish, Mystus cavasius, locally known as gulsha, ovarian maturation is triggered by long-day conditions. Using dopaminergic neuronal activity in the brain, the purpose of this study was to identify the brain's detection of a nocturnal light pulse that induced ovarian development. Since direct inhibition of pituitary gonadotropin release is exerted by dopamine (DA), it may serve as a neuromodulator of photoperiodic stimulation in teleosts. We studied functional effects of photoperiodicity on dopaminergic rhythmicity in gulsha brain. Nocturnal illumination and Nanda-Hamner photocycles revealed that ovarian development is induced by a 1 h light pulse between zeitgeber time (ZT) 12 and 13. Daily fluctuations in DA, 3, 4-dihydroxyphenylacetic acid (DOPAC) and DOPAC/DA were observed under a 12L:12D photoperiod. Fish exhibited increased levels during the daytime and decreased levels at night. Rhythmic patterns of dopaminergic activity also showed clear circadian oscillations under constant light, but not constant dark conditions. After 7 days of exposure to long photoperiod (14L:10D), DA, DOPAC and DOPAC/DA in the brain at ZT12 and ZT16 were significantly higher than during a short photoperiod (10L:14D). Melatonin-containing water inhibited the release of DA and DOPAC 6 h and 24 h after treatment, respectively, and DOPAC/DA 6 h after treatment. This inhibition was blocked by the melatonin receptor antagonist, luzindole. These results suggest that a 1 h nocturnal light pulse induces ovarian development through alteration of dopaminergic neuronal excitability in the brain, via oscillation in melatonin triggered by photic stimuli, which may interfere with the reproductive endocrine axis in gulsha.

Actigraphy-Derived Sleep Profiles of Children with and without Attention-Deficit/Hyperactivity Disorder (ADHD) over Two Weeks-Comparison, Precursor Symptoms, and the Chronotype

Although sleep problems are common in children with ADHD, their extent, preceding risk factors, and the association between neurocognitive performance and neurobiological processes in sleep and ADHD, are still largely unknown. We examined sleep variables in school-aged children with ADHD, addressing their intra-individual variability (IIV) and considering potential precursor symptoms as well as the chronotype. Additionally, in a subgroup of our sample, we investigated associations with neurobehavioral functioning (n = 44). A total of 57 children (6-12 years) with (n = 24) and without ADHD (n = 33) were recruited in one center of the large ESCAlife study to wear actigraphs for two weeks. Actigraphy-derived dependent variables, including IIV, were analyzed using linear mixed models in order to find differences between the groups. A stepwise regression model was used to investigate neuropsychological function. Overall, children with ADHD showed longer sleep onset latency (SOL), higher IIV in SOL, more movements during sleep, lower sleep efficiency, and a slightly larger sleep deficit on school days compared with free days. No group differences were observed for chronotype or sleep onset time. Sleep problems in infancy predicted later SOL and the total number of movements during sleep in children with and without ADHD. No additional effect of sleep problems, beyond ADHD symptom severity, on neuropsychological functioning was found. This study highlights the importance of screening children with ADHD for current and early childhood sleep disturbances in order to prevent long-term sleep problems and offer individualized treatments. Future studies with larger sample sizes should examine possible biological markers to improve our understanding of the underlying mechanisms.

Circadian rhythms in neurodegenerative disorders

Endogenous biological clocks, orchestrated by the suprachiasmatic nucleus, time the circadian rhythms that synchronize physiological and behavioural functions in humans. The circadian system influences most physiological processes, including sleep, alertness and cognitive performance. Disruption of circadian homeostasis has deleterious effects on human health. Neurodegenerative disorders involve a wide range of symptoms, many of which exhibit diurnal variations in frequency and intensity. These disorders also disrupt circadian homeostasis, which in turn has negative effects on symptoms and quality of life. Emerging evidence points to a bidirectional relationship between circadian homeostasis and neurodegeneration, suggesting that circadian function might have an important role in the progression of neurodegenerative disorders. Therefore, the circadian system has become an attractive target for research and clinical care innovations. Studying circadian disruption in neurodegenerative disorders could expand our understanding of the pathophysiology of neurodegeneration and facilitate the development of novel, circadian-based interventions for these disabling disorders. In this Review, we discuss the alterations to the circadian system that occur in movement (Parkinson disease and Huntington disease) and cognitive (Alzheimer disease and frontotemporal dementia) neurodegenerative disorders and provide directions for future investigations in this field.

Peripheral Clock System Abnormalities in Patients With Parkinson's Disease

Objective: To evaluate the altered expression of peripheral clock genes, circulating melatonin levels, and their correlations with sleep-wake phenotypes including probable rapid eye movement sleep behavior disorder (pRBD) symptoms in a relatively large population of Parkinson’s disease (PD) patients.

Methods: We determined the expression profiles of five principal clock genes, BMAL1, CLOCK, CRY1, PER1, and PER2, in the peripheral blood mononuclear cells (PBMCs) of PD patients (n = 326), and healthy controls (HC, n = 314) using quantitative real-time PCR. Melatonin concentration in the plasma of two groups was evaluated by enzyme-linked immunosorbent assay. Then we performed comprehensive association analyses on the PBMCs clock gene expression, plasma melatonin levels and sleep characteristics.

Results: Our data showed that the expression levels of BMAL1, CLOCK, CRY1, PER1, and PER2 were significantly decreased in the PBMCs of PD as compared with that of HC (P < 0.05). PD patients had reduced plasma melatonin levels compared with HC (P < 0.0001). pRBD and excessive daytime sleepiness are common in these PD patients and are associated with the expression levels of all five clock genes (r = −0.344∼−0.789, P < 0.01) and melatonin concentration (r = −0.509∼−0.753, P < 0.01). Statistical analyses also revealed that a combination of five clock genes and melatonin could reach a high diagnostic performance (areas under the curves, 97%) for PD comorbid pRBD.

Conclusion: This case-control study demonstrates that peripheral BMAL1, CLOCK, CRY1, PER1, PER2, and melatonin levels are altered in PD patients and may serve as endogenous markers for sleep and wakefulness disturbances of PD.

[Visual hallucinations in Parkinson's disease]

Visual hallucinations have a negative effect on the course of Parkinson's disease (PD), being a source of stress for the patients themselves and caregivers. The article discusses the basic theories and pathogenetic mechanisms of the development of visual hallucinations in PD consisting of the following components: impairment of the visual information received from the retina with subsequent disruption of its processing in the central parts of the visual system; lack of suppression of internally generated images through the ponto-geniculo-occipital system; the invasion of REM sleep patterns in wakefulness; decreased ability of the brain stem structures to implement appropriate information filtering as well as excessive drug-induced activation of the mesolimbic system. Particular attention is paid to visual impairment and changes in the transmission of information along the retino-hypothalamic tract. In this connection, dysfunction in the «retina - hypothalamus» system can also be considered as one of the factors that determines the time and rhythm of occurrence or exacerbation of visual hallucinations in PD. Attracting attention to this aspect opens new therapeutic possibilities where the circadian system can be positioned as a target of additional exposure in the treatment of visual hallucinations in PD.

Day-Night Variations in the Concentration of Neurotransmitters in the Rat Lumbar Spinal Cord

The purpose of this study was to analyze the light-dark variations in the concentrations of several neurotransmitters in the lumbar spinal cord of rats. Six groups of male Wistar rats were exposed to a 12 h light-12 h dark cycle for 70 days. At different time points of the experimental day (8, 12, 16, 20, 24 and 4 h), one of the groups of rats was randomly selected to be sacrificed, and the spinal cords were removed. The gamma-aminobutyric acid (GABA), glutamate (GLU), dopamine, serotonin, epinephrine (E), and norepinephrine (NE) levels in each extracted spinal cord were measured with high-pressure liquid chromatography (HPLC)-EQ and HPLC-fluorescence systems. Our results indicate that the spinal concentrations of GABA and GLU showed sinusoidal variation in a 24 h cycle, with the highest peak in the dark period (~20 h). Dopamine and serotonin also fluctuated in concentration but peaked in the light period (between 8 and 12 h), while E and NE concentrations showed no significant fluctuations. The possible relationship between neurotransmitter spinal concentration and sensitivity to pain and locomotor activity is discussed. It was concluded that most of the neurotransmitter levels in the lumbar spinal cord showed circadian fluctuations coupled to a light-dark cycle.

Circadian rhythm influences naloxone induced morphine withdrawal and neuronal activity of lateral paragigantocellularis nucleus

Investigations have shown that the circadian rhythm can affect the mechanisms associated with drug dependence. In this regard, we sought to assess the negative consequence of morphine withdrawal syndrome on conditioned place aversion (CPA) and lateral paragigantocellularis (LPGi) neuronal activity in morphine-dependent rats during light (8:00-12:00) and dark (20:00-24:00) cycles. Male Wistar rats (250-300 g) were received 10 mg/kg morphine or its vehicle (Saline, 2 mL/kg/12 h, s.c.) in 13 consecutive days for behavioral assessment tests. Then, naloxone-induced conditioned place aversion and physical signs of withdrawal syndrome were evaluated during light and dark cycles. In contrast to the behavioral part, we performed in vivo extracellular single-unit recording for investigating the neural response of LPGi to naloxone in morphine-dependent rats on day 10 of morphine/saline exposure. Results showed that naloxone induced conditioned place aversion in both light and dark cycles, but the CPA score during the light cycle was larger. Moreover, the intensity of physical signs of morphine withdrawal syndrome was more severe during the light cycle (rest phase) compare to the dark one. In electrophysiological experiments, results indicated that naloxone evoked both excitatory and inhibitory responses in LPGi neurons and the incremental effect of naloxone on LPGi activity was stronger in the light cycle. Also, the neurons with the excitatory response exhibited higher baseline activity in the dark cycle, but the neurons with the inhibitory response showed higher baseline activity in the light cycle. Interestingly, the baseline firing rate of neurons recorded in the light cycle was significantly different in response (excitatory/inhibitory) -dependent manner. We concluded that naloxone-induced changes in LPGi cellular activity and behaviors of morphine-dependent rats can be affected by circadian rhythm and the internal clock.

The impact of chronotype on circadian rest-activity rhythm and sleep characteristics across the week

Circadian rhythms are maintained by a complex "system of systems" that continuously coordinates biological processes with each other and the environment. Although humans predominantly entrain to solar time, individual persons vary in their precise behavioral timing due to endogenous and exogenous factors. Endogenous differences in the timing of individual circadian rhythms relative to a common environmental cue are known as chronotypes, ranging from earlier than average (Morningness) to later than average (Eveningness). Furthermore, individual behavior is often constrained by social constructs such as the 7-day week, and the "sociogenic" impact our social calendar has on our behavioral rhythms is likely modified by chronotype. Our aim in this study was to identify and characterize differences in sleep and rest-activity rhythms (RAR) between weekends and weekdays and between-chronotypes. Male volunteers (n = 24, mean age = 23.46 y) were actigraphically monitored for 4 weeks to derive objective behavioral measures of sleep and RARs. Chronotype was assessed through self-report on the Morningness-Eveningness Questionnaire. Sleep characteristics were derived using Actiware; daily rest-activity rhythms were modeled using a basic 3-parameter cosinor function. We observed that both Eveningness and Morningness Chronotypes were more active and slept later on the weekends than on weekdays. Significant between-chronotype differences in sleep timing and duration were observed within individual days of the week, especially during transitions between weekends and the workweek. Moreover, chronotypes significantly varied in their weekly rhythms: e.g. Morningness Chronotypes generally shifted their sleep duration, timing and quality across work/rest transitions quicker than Eveningness Chronotypes. Although our results should be interpreted with caution due to the limitations of our cosinor model and a homogenous cohort, they reinforce a growing body of evidence that day of the week, chronotype and their interactions must be accounted for in observational studies of human behavior, especially when circadian rhythms are of interest.

Recent Progress in Non-motor Features of Parkinson's Disease with a Focus on Circadian Rhythm Dysregulation

Parkinson's disease (PD) is the second most common neurodegenerative disease, which manifests with both motor and non-motor symptoms. Circadian rhythm dysregulation, as one of the most challenging non-motor features of PD, usually appears long before obvious motor symptoms. Moreover, the dysregulated circadian rhythm has recently been reported to play pivotal roles in PD pathogenesis, and it has emerged as a hot topic in PD research. In this review, we briefly introduce the circadian rhythm and circadian rhythm-related genes, and then summarize recent research progress on the altered circadian rhythm in PD, ranging from clinical features to the possible causes of PD-related circadian disorders. We believe that future comprehensive studies on the topic may not only help us to explore the mechanisms of PD, but also shed light on the better management of PD.