Effect of dopaminergic substances on sleep/wakefulness in saline- and MPTP-treated mice

Clinical Manifestations of Subjective Sleep Disorders in Chinese Patients with Parkinson's Disease and Their Relationship with Dopaminergic Drugs

INTRODUCTION

Sleep disorders are common in Parkinson's disease (PD) and significantly impact quality of life. Herein, we surveyed the incidence and severity of sleep disorders in Chinese PD patients and observed their relationship with dopaminergic drugs.

METHODS

We collected the demographic and disease information of 232 PD patients. The incidence and severity of sleep disorders were surveyed with the Parkinson's disease sleep scale (PDSS) Chinese version. Data on dopaminergic drug intake were collected and converted to levodopa equivalent doses (LED).

RESULTS

The average total score of PDSS in 232 patients was 119.3 ± 19.7. There was a significant difference in PDSS scores between groups classified by the Hoehn-Yahr (H&Y) stage, but not between the groups classified by the type of dopaminergic drugs. Stepwise regression analysis revealed that the LED of dopaminergic drugs taken before bedtime (p < 0.00), LED of dopaminergic drugs taken over a 24-h period (p < 0.00), and scores of the Hamilton Rating Scale for Depression (HAMD) (p = 0.01) were determinants of PDSS.

CONCLUSION

Sleep disorders in PD patients may be multifactorial. High dosage of dopaminergic drugs taken prior to sleep, daily total high dosage of dopaminergic drugs, and depression exert negative effects on subjective sleep. The timing and dosage of dopaminergic drugs taken before bedtime should be considered in PD management.

An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease

Sleep disorders are among the most common nonmotor symptoms in Parkinson's disease and are associated with reduced cognition and health-related quality of life. Disturbed sleep can often present in the prodromal or early stages of this neurodegenerative disease, rendering it crucial to manage and treat these symptoms. Levodopa and dopaminergic agonists are frequently prescribed to treat motor symptoms in Parkinson's disease, and there is increasing interest in how these pharmacological agents affect sleep and their effect on concomitant sleep disturbances and disorders. In this review, we discuss the role of dopamine in regulating the sleep-wake state and the impact of neurodegeneration on sleep. We provide an overview of the effects of levodopa and dopaminergic agonists on sleep architecture, insomnia, excessive daytime sleepiness, sleep-disordered breathing, rapid eye movement sleep behavior disorder, and restless legs syndrome in Parkinson's disease. Levodopa and dopaminergic drugs may have different effects, beneficial or adverse, depending on dosing, method of administration, and differential effects on the different dopamine receptors. Future research in this area should focus on elucidating the specific mechanisms by which these drugs affect sleep in order to better understand the pathophysiology of sleep disorders in Parkinson's disease and aid in developing suitable therapies and treatment regimens.

CITATION

Scanga A, Lafontaine A-L, Kaminska M. An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease. J Clin Sleep Med. 2023;19(6):1133-1144.

Validation of STOP, STOP-BANG, STOP-BAG, STOP-B28, and GOAL screening tools for identification of obstructive sleep apnea in patients with Parkinson disease

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is common in Parkinson disease (PD). Questionnaires can be used as screening tools and have been used as a surrogate definition of OSA in large-scale research. This study aimed to validate the performance of STOP, STOP-BANG, STOP-BAG, STOP-B28, and GOAL and OSA predictors as tools to identify OSA in PD.

METHODS

Data were analyzed from a PD cohort study in which OSA was diagnosed using laboratory polysomnography. We calculated sensitivity and specificity of each questionnaire for OSA using different definitions and performed receiver operating characteristics curve analysis. Linear regression was used to assess adjusted associations between questionnaires and outcomes: Montreal Cognitive Assessment, Epworth Sleepiness Scale, and Movement Disorder Society revision of the Unified Parkinson Disease Rating Scale.

RESULTS

Questionnaire data were available for 68 PD patients (61.8% male, mean age 64.5 [standard deviation 9.9] years, and Hoehn and Yahr score 2.1 [0.8]). OSA (apnea-hypopnea index ≥ 15 events/h) occurred in 69.4% of participants. STOP-B28 ≥ 2 presented a higher sensitivity for OSA than STOP ≥ 2 (0.76 vs 0.65, respectively) and slightly lower specificity (0.65 vs 0.70, respectively). GOAL ≥ 2 had the highest sensitivity but poor specificity. Loud snoring had sensitivity 0.63 and specificity 0.65. STOP and snoring were significantly associated with Montreal Cognitive Assessment, Epworth Sleepiness Scale, and Movement Disorder Society revision of the Unified Parkinson Disease Rating Scale (total, motor, and nonmotor); STOP-BANG, STOP-BAG, and STOP-B28 showed associations with most outcomes, but the GOAL showed none.

CONCLUSIONS

The STOP-B28 followed by STOP and presence of loud snoring alone seem to have the best overall properties to identify PD patients with OSA, whose clinical characteristics differ from the general population with OSA.

CITATION

Gomes T, Benedetti A, Lafontaine A-L, Kimoff RJ Robinson A, Kaminska M. Validation of STOP, STOP-BANG, STOP-BAG, STOP-B28, and GOAL screening tools for identification of obstructive sleep apnea in patients with Parkinson disease. J Clin Sleep Med. 2023;19(1):45-54.

Sinapic Acid Ameliorates REV-ERB α Modulated Mitochondrial Fission against MPTP-Induced Parkinson's Disease Model

Parkinson’s disease (PD) is the second most common neurodegenerative disease worldwide, and accumulating evidence indicates that mitochondrial dysfunction is associated with progressive deterioration in PD patients. Previous studies have shown that sinapic acid has a neuroprotective effect, but its mechanisms of action remain unclear. The neuroprotective effect of sinapic acid was assayed in a PD mouse model generated by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as well as in SH-SY5Y cells. Target protein expression was detected by western blotting. Sinapic acid treatment attenuated the behavioral defects and loss of dopaminergic neurons in the PD models. Sinapic acid also improved mitochondrial function in the PD models. MPTP treatment increased the abundance of mitochondrial fission proteins such as dynamin-related protein 1 (Drp1) and phospho-Drp1 Ser616. In addition, MPTP decreased the expression of the REV-ERB α protein. These changes were attenuated by sinapic acid treatment. We used the pharmacological REV-ERB α inhibitor SR8278 to confirmation of protective effect of sinapic acid. Treatment of SR8278 with sinapic acid reversed the protein expression of phospho-Drp1 Ser616 and REV-ERB α on MPTP-treated mice. Our findings demonstrated that sinapic acid protects against MPTP-induced PD and these effects might be related to the inhibiting abnormal mitochondrial fission through REV-ERB α.

Using Caenorhabditis elegans to Model Therapeutic Interventions of Neurodegenerative Diseases Targeting Microbe-Host Interactions

Emerging evidence from both clinical studies and animal models indicates the importance of the interaction between the gut microbiome and the brain in the pathogenesis of neurodegenerative diseases (NDs). Although how microbes modulate neurodegeneration is still mostly unclear, recent studies have started to probe into the mechanisms for the communication between microbes and hosts in NDs. In this review, we highlight the advantages of using Caenorhabditis elegans (C. elegans) to disentangle the microbe-host interaction that regulates neurodegeneration. We summarize the microbial pro- and anti-neurodegenerative factors identified using the C. elegans ND models and the effects of many are confirmed in mouse models. Specifically, we focused on the role of bacterial amyloid proteins, such as curli, in promoting proteotoxicity and neurodegeneration by cross-seeding the aggregation of endogenous ND-related proteins, such as α-synuclein. Targeting bacterial amyloid production may serve as a novel therapeutic strategy for treating NDs, and several compounds, such as epigallocatechin-3-gallate (EGCG), were shown to suppress neurodegeneration at least partly by inhibiting curli production. Because bacterial amyloid fibrils contribute to biofilm formation, inhibition of amyloid production often leads to the disruption of biofilms. Interestingly, from a list of 59 compounds that showed neuroprotective effects in C. elegans and mouse ND models, we found that about half of them are known to inhibit bacterial growth or biofilm formation, suggesting a strong correlation between the neuroprotective and antibiofilm activities. Whether these potential therapeutics indeed protect neurons from proteotoxicity by inhibiting the cross-seeding between bacterial and human amyloid proteins awaits further investigations. Finally, we propose to screen the long list of antibiofilm agents, both FDA-approved drugs and novel compounds, for their neuroprotective effects and develop new pharmaceuticals that target the gut microbiome for the treatment of NDs. To this end, the C. elegans ND models can serve as a platform for fast, high-throughput, and low-cost drug screens that target the microbe-host interaction in NDs.

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.

Impaired wakefulness and rapid eye movement sleep in dopamine-deficient mice

Despite the established roles of the dopaminergic system in promoting arousal, the effects of loss of dopamine on the patterns of sleep and wakefulness remain elusive. Here, we examined the sleep architecture of dopamine-deficient (DD) mice, which were previously developed by global knockout of tyrosine hydroxylase and its specific rescue in noradrenergic and adrenergic neurons. We found that DD mice have reduced time spent in wakefulness. Unexpectedly, DD mice also exhibited a marked reduction in the time spent in rapid eye movement (REM) sleep. The electroencephalogram power spectrum of all vigilance states in DD mice were also affected. These results support the current understanding of the critical roles of the dopaminergic system in maintaining wakefulness and also implicate its previously unknown effects on REM sleep.

A Comprehensive Phenotype of Non-motor Impairments and Distribution of Alpha-Synuclein Deposition in Parkinsonism-Induced Mice by a Combination Injection of MPTP and Probenecid

Parkinson's disease (PD) is characterized by non-motor symptoms as well as motor deficits. The non-motor symptoms rarely appear individually and occur simultaneously with motor deficits or independently. However, a comprehensive research on the non-motor symptoms using an experimental model of PD remains poorly understood. The aim of the current study is to establish a chronic mouse model of PD mimicking the comprehensive non-motor symptoms of human PD by injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and probenecid (MPTP/p). The non-motor and motor symptoms were evaluated by performing buried food, short-term olfactory memory, hot plate, open field, tail suspension, Y maze, novel object recognition, bead expulsion, one-h stool collection, rotarod, rearing, catalepsy, and akinesia tests after 10 injections of MPTP/p into mice. The expression levels of α-synuclein, glial fibrillary acidic protein (GFAP), tyrosine hydroxylase (TH) or DJ-1 were analyzed by Western blotting or immunostaining. MPTP/p-treated mice achieved to reproduce the key features of non-motor symptoms including olfactory deficit, thermal hyperalgesia, anxiety, depression, cognitive decline, and gastrointestinal dysfunction in addition to motor deficits. The MPTP/p-treated mice also showed the high levels of α-synuclein and low levels of TH and DJ-1 in striatum, substantia nigra, olfactory bulb, hippocampus, amygdala, prefrontal cortex, locus coeruleus, or colon. In addition, the expression levels of phosphorylated-α-synuclein and GFAP were elevated in the striatum and substantia nigra in the MPTP/p-treated mice. Taken together, our study clarifies that the chronic MPTP/p-treated mice have a variety of non-motor dysfunctions as well as motor abnormalities by α-synuclein overexpression and dopaminergic depletion. Therefore, the study of comprehensive phenotypes of non-motor symptoms in one PD model would advance in-depth understandings of neuropathological alternations and contribute to future strategies for PD treatment.

Disrupted Sleep and Circadian Rhythms in Schizophrenia and Their Interaction With Dopamine Signaling

Sleep and circadian rhythm disruption (SCRD) is a common feature of schizophrenia, and is associated with symptom severity and patient quality of life. It is commonly manifested as disturbances to the sleep/wake cycle, with sleep abnormalities occurring in up to 80% of patients, making it one of the most common symptoms of this disorder. Severe circadian misalignment has also been reported, including non-24 h periods and phase advances and delays. In parallel, there are alterations to physiological circadian parameters such as body temperature and rhythmic hormone production. At the molecular level, alterations in the rhythmic expression of core clock genes indicate a dysfunctional circadian clock. Furthermore, genetic association studies have demonstrated that mutations in several clock genes are associated with a higher risk of schizophrenia. Collectively, the evidence strongly suggests that sleep and circadian disruption is not only a symptom of schizophrenia but also plays an important causal role in this disorder. The alterations in dopamine signaling that occur in schizophrenia are likely to be central to this role. Dopamine is well-documented to be involved in the regulation of the sleep/wake cycle, in which it acts to promote wakefulness, such that elevated dopamine levels can disturb sleep. There is also evidence for the influence of dopamine on the circadian clock, such as through entrainment of the master clock in the suprachiasmatic nuclei (SCN), and dopamine signaling itself is under circadian control. Therefore dopamine is closely linked with sleep and the circadian system; it appears that they have a complex, bidirectional relationship in the pathogenesis of schizophrenia, such that disturbances to one exacerbate abnormalities in the other. This review will provide an overview of the evidence for a role of SCRD in schizophrenia, and examine the interplay of this with altered dopamine signaling. We will assess the evidence to suggest common underlying mechanisms in the regulation of sleep/circadian rhythms and the pathophysiology of schizophrenia. Improvements in sleep are associated with improvements in symptoms, along with quality of life measures such as cognitive ability and employability. Therefore the circadian system holds valuable potential as a new therapeutic target for this disorder.

Nigrostriatal and mesolimbic control of sleep-wake behavior in rat

The midbrain dopamine system via the dorsal and ventral striatum regulates a wide range of behaviors. To dissect the role of dopaminergic projections to the dorsal striatum (nigrostriatal projection) and ventral striatum (mesolimbic projection) in sleep-wake behavior, we selectively chemogenetically stimulated nigrostriatal or mesolimbic projections and examined the resulting effects on sleep in rats. Stimulation of nigrostriatal pathways increased sleep and EEG delta power, while stimulation of mesolimbic pathways decreased sleep and reduced cortical EEG power. These results indicate that midbrain dopamine signaling in the dorsal or ventral striatum promotes sleep or wake, respectively.

Modafinil alleviates levodopa-induced excessive nighttime sleepiness and restores monoaminergic systems in a nocturnal animal model of Parkinson's disease

Treatment with dopaminergic agents result excessive daytime sleepiness (EDS) and some studies have shown the benefit of using modafinil for treating excessive daytime sleepiness of Parkinson's disease (PD) patient. We investigated whether modafinil have ameliorative properties against levodopa induced excessive nighttime sleepiness (ENS) in MPTP-treated murine nocturnal PD model. Our EEG analyses of whole day recordings revealed that modafinil reduce ENS of this nocturnal PD models with levodopa medications. Therefore, we investigated whether, modafinil post-treatment followed by MPTP shows any effect on monoamine contents of brain and found to robustly increased noradrenaline (NA) concentration of MPTP treated mice. Modafinil post-treatment, in neurorestorative context (5 days post-lesion) led to increased striatal dopamine (DA) concentrations of MPTP-treated mice. Here, we first confirmed that modafinil ameliorates levodopa induced excessive sleepiness and restores monoaminergic systems. The arousal and anti-parkinsonian effects displayed by modafinil indicate that in combination with dopaminergic agents, modafinil co-administration may be worthwhile in trying to suppress the excessive daytime sleepiness and progressive dopaminergic neuron loss in PD.

Are rodent models of Parkinson's disease behaving as they should?

In recent years our understanding of Parkinson's disease has expanded both in terms of pathological hallmarks as well as relevant genetic influences. In parallel with the aetiological discoveries a multitude of PD animal models have been established. The vast majority of these are rodent models based on environmental, genetic and mechanistic insight. A major challenge in many of these models is their ability to only recapitulate some of the complex disease features seen in humans. Although symptom alleviation and clinical signs are of utmost importance in therapeutic research many of these models lack comprehensive behavioural testing. While non-motor symptoms become increasingly important as early diagnostic markers in PD, they are poorly characterized in rodents. In this review we look at well-established and more recent animal models of PD in terms of behavioural characterization and discuss how they can best contribute to progression in Parkinson's research.

Circadian Dysregulation in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder that affects over one million individuals in the US alone. PD is characterized by a plethora of motor and non-motor manifestations, resulting from a progressive degeneration of dopaminergic neurons and disbalance of several other neurotransmitters. A growing body of evidence points to significant alterations of the circadian system in PD. This is not surprising given the pivotal role that dopamine plays in circadian regulation as well as the role of circadian influences in dopamine metabolism. In this review we present basic and clinical investigations that examined the function of the circadian system in PD.

Nigrostriatal Dopamine Acting on Globus Pallidus Regulates Sleep

Lesions of the globus pallidus externa (GPe) produce a profound sleep loss (∼45%) in rats, suggesting that GPe neurons promote sleep. As GPe neuronal activity is enhanced by dopamine (DA) from the substantia nigra pars compacta (SNc), we hypothesized that SNc DA via the GPe promotes sleep. To test this hypothesis, we selectively destroyed the DA afferents to the caudoputamen (CPu) using 6-hydroxydopamine and examined changes in sleep-wake profiles in rats. Rats with 80-90% loss of SNc neurons displayed a significant 33.7% increase in wakefulness (or sleep reduction). This increase significantly correlated with the extent of SNc DA neuron loss. Furthermore, these animals exhibited sleep-wake fragmentation and reduced diurnal variability of sleep. We then optogenetic-stimulated SNc DA terminals in the CPu and found that 20-Hz stimulation from 9 to 10 PM increased total sleep by 69% with high electroencephalograph (EEG) delta power. We finally directly optogenetic-stimulated GPe neurons and found that 20-Hz stimulation of the GPe from 9 to 10 PM increased total sleep by 66% and significantly increased EEG delta power. These findings elucidate a novel circuit for DA control of sleep and the mechanisms of abnormal sleep in BG disorders such as Parkinson's disease and Huntington's disease.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Inflaming the diseased brain: a role for tainted melanins

Inflammation plays a crucial role in neurodegenerative diseases, but the irritants responsible for this response remain largely unknown. This report addressed the hypothesis that hypochlorous acid reacts with dopamine to produce melanic precipitates that promote cerebral inflammation. Spectrophotometric studies demonstrated that nM amounts of HOCl and dopamine react within seconds. A second-order rate constant for the reaction of HOCl and dopamine of 2.5 × 10(4)M(-1)s(-1) was obtained by measuring loss of dopaminergic fluorescence due to HOCl. Gravimetric measurements, electron microscopy, elemental analysis, and a novel use of flow cytometry confirmed that the major product of this reaction is a precipitate with an average diameter of 1.5 μm. Flow cytometry was also used to demonstrate the preferential reaction of HOCl with dopamine rather than albumin. Engulfment of the chlorodopamine particulates by phagocytes in vitro caused these cells to release TNFα and die. Intrastriatal administration of 10(6) particles also increased the content of TNFα in the brain and led to a 50% loss of the dopaminergic neurons in the nigra. These studies indicate that HOCl and dopamine react quickly and preferentially with each other to produce particles that promote inflammation and neuronal death in the brain.

D1 receptor agonist improves sleep-wake parameters in experimental parkinsonism

Both excessive daytime sleepiness (EDS) and rapid eye movement (REM) sleep deregulation are part of Parkinson's disease (PD) non-motor symptoms and may complicate dopamine replacement therapy. We report here that dopamine agonists act differentially on sleep architecture in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine macaque monkey. Continuous sleep and wake electroencephalographic monitoring revealed no effect of the selective dopamine D2 receptor agonist quinpirole on EDS, whereas the selective dopamine D1 receptor agonist SKF38393 efficiently alleviated EDS and restored REM sleep to baseline values. The present results question the relevance of abandoning D1 receptor agonist treatment in PD as it might actually improve sleep-related disorders.

Association between dopaminergic medications and nocturnal sleep in early-stage Parkinson's disease

BACKGROUND

Poor nocturnal sleep is common in Parkinson's disease (PD) and negatively impacts quality of life. There is little data on how dopaminergic drugs influence nocturnal sleep in PD, particularly in relation to medication timing. We examined the association between dopaminergic medications and subjective and objective nocturnal sleep in PD.

METHODS

Individuals with PD were recruited from the outpatient clinic. Demographics and disease information were collected. Patients underwent one-night polysomnography and responded to SCOPA-SLEEP, a self-administered questionnaire which includes a section on nighttime sleep and an overall measure of sleep quality; higher scores indicate worse sleep. Medication intake, including medication timing in relation to bedtime, was obtained and converted to levodopa equivalents.

RESULTS

41 Males and 21 females, median age 63.9 years, participated. Median disease duration was 5 years. After adjusting for age, sex, disease severity, and disease duration, greater total levodopa equivalent intake within 4 h of sleep was associated with higher total SCOPA-nighttime score (p = 0.009) and greater wake time after sleep onset (p = 0.049). Greater dopaminergic medication intake prior to sleep was also associated with less rapid eye movement (REM) sleep as a percent of total sleep time (p = 0.004).

CONCLUSIONS

Higher amounts of dopaminergic medications taken prior to sleep were associated with poor sleep quality and less REM sleep. Although poor nocturnal sleep in PD is likely multi-factorial in etiology, our findings suggest that timing and dose of medications prior to sleep need to be considered in its management.

Cul3 and the BTB adaptor insomniac are key regulators of sleep homeostasis and a dopamine arousal pathway in Drosophila

Sleep is homeostatically regulated, such that sleep drive reflects the duration of prior wakefulness. However, despite the discovery of genes important for sleep, a coherent molecular model for sleep homeostasis has yet to emerge. To better understand the function and regulation of sleep, we employed a reverse-genetics approach in Drosophila. An insertion in the BTB domain protein CG32810/insomniac (inc) exhibited one of the strongest baseline sleep phenotypes thus far observed, a ∼10 h sleep reduction. Importantly, this is coupled to a reduced homeostatic response to sleep deprivation, consistent with a disrupted sleep homeostat. Knockdown of the INC-interacting protein, the E3 ubiquitin ligase Cul3, results in reduced sleep duration, consolidation, and homeostasis, suggesting an important role for protein turnover in mediating INC effects. Interestingly, inc and Cul3 expression in post-mitotic neurons during development contributes to their adult sleep functions. Similar to flies with increased dopaminergic signaling, loss of inc and Cul3 result in hyper-arousability to a mechanical stimulus in adult flies. Furthermore, the inc sleep duration phenotype can be rescued by pharmacological inhibition of tyrosine hydroxylase, the rate-limiting enzyme for dopamine biosynthesis. Taken together, these results establish inc and Cul3 as important new players in setting the sleep homeostat and a dopaminergic arousal pathway in Drosophila.

Sleep is an essential behavior that encompasses roughly a third of our lives; however, the underlying function remains a mystery. The fruit fly has emerged as an important model system for understanding sleep behavior, exhibiting several behavioral and genetic similarities with mammalian sleep, including consolidated immobility, an elevation of arousal threshold to a range of stimuli, homeostatic drive, and manipulation by proven stimulants and sedatives. We tested disruptions of candidate sleep genes and identified a gene called insomniac that exhibits one of the strongest and most robust sleep phenotypes to date, including a suppressed homeostatic response to sleep deprivation. We find similar phenotypes for a gene previously shown to interact with inc and a known regulator of protein degradation, Cul3, linking sleep homeostasis to protein turnover. Importantly, we find that insomniac functions in a known arousal system in the brain, as defined by the neurotransmitter dopamine. This work provides an important insight into the genetic basis of sleep homeostasis with the discovery of a new molecular component of a dopaminergic arousal pathway. Given the conservation of fly and mammalian systems, these studies may lead to new insights into the molecules that mediate sleep homeostasis and arousal in humans.

Sleep disturbances in Alzheimer's and Parkinson's diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative disorders and exact a burden on our society greater than cardiovascular disease and cancer combined. While cognitive and motor symptoms are used to define AD and PD, respectively, patients with both disorders exhibit sleep disturbances including insomnia, hypersomnia and excessive daytime napping. The molecular basis of perturbed sleep in AD and PD may involve damage to hypothalamic and brainstem nuclei that control sleep-wake cycles. Perturbations in neurotransmitter and hormone signaling (e.g., serotonin, norepinephrine and melatonin) and the neurotrophic factor BDNF likely contribute to the disease process. Abnormal accumulations of neurotoxic forms of amyloid β-peptide, tau and α-synuclein occur in brain regions involved in the regulation of sleep in AD and PD patients, and are sufficient to cause sleep disturbances in animal models of these neurodegenerative disorders. Disturbed regulation of sleep often occurs early in the course of AD and PD, and may contribute to the cognitive and motor symptoms. Treatments that target signaling pathways that control sleep have been shown to retard the disease process in animal models of AD and PD, suggesting a potential for such interventions in humans at risk for or in the early stages of these disorders.

Circadian and sleep disorders in Parkinson's disease

Impaired sleep and alertness, initially recognized by James Parkinson in his famous monograph "An Essay on the Shaking Palsy" in 1817, is one of the most common and disabling nonmotor symptoms of Parkinson's disease (PD). It is only recently, however, that sleep disturbances in PD have received the attention of medical and research community. Dopamine, the major neurotransmitter implicated in the pathogenesis of PD, plays a pivotal role in the regulation of sleep and circadian homeostasis. Sleep dysfunction affects up to 90% of patients with PD, and may precede the onset of the disease by decades. Sleep dysfunction in PD may be categorized into disturbances of overnight sleep and daytime alertness. Etiology of impaired sleep and alertness in PD is multifactorial. Co-existent primary sleep disorders, medication side effects, overnight re-emergence of motor symptoms, and primary neurodegeneration itself, are main causes of sleep disruption and excessive daytime sleepiness among patients with PD. Increasing body of evidence suggests that the circadian system becomes dysregulated in PD, which may lead to poor sleep and alertness. Treatment options are limited and frequently associated with unwanted side effects. Further studies that will examine pathophysiology of sleep dysfunction in PD, and focus on novel treatment approaches are therefore very much needed. In this article we review the role of dopamine in regulation of sleep and alertness and discuss main sleep and circadian disturbances associated with PD.

Dual motor response to l-dopa and nociceptin/orphanin FQ receptor antagonists in 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) treated mice: Paradoxical inhibition is relieved by D(2)/D(3) receptor blockade

Motor activity of mice acutely treated with the parkinsonian toxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) was monitored for 6 days using behavioral tests which provide complementary information on motor function: the bar, reaction time, drag, stair climbing, grip, rotarod and footprinting tests. These tests consistently disclosed a prolonged motor impairment characterized by akinesia, bradykinesia, speed reduction, loss of coordination and gait patterns. This impairment was associated with approximately 60% loss of striatal dopamine terminals, as revealed by tyrosine hydroxylase immunohistochemistry, and was attenuated by dopaminergic drugs. Indeed, the dopamine precursor, l-dopa (1-10 mg/kg), and the D(3)/D(2) receptor agonist pramipexole (0.0001-0.001 mg/kg) promoted stepping activity in the drag test (a test for akinesia/bradykinesia). The novel nociceptin/orphanin FQ receptor (NOP) antagonist 1-[1-(cyclooctylmethyl)-1,2,3,6-tetrahydro-5-(hydroxymethyl)-4-pyridinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (Trap-101, 0.001-0.1 mg/kg), an analogue of 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397), also promoted stepping and synergistically or additively (depending on test) attenuated parkinsonism when combined to dopamine agonists. High doses of l-dopa (100 mg/kg), pramipexole (0.1 mg/kg), Trap-101 and J-113397 (1 mg/kg), however, failed to modulate stepping, worsening immobility time and/or rotarod performance. Low doses of amisulpride (0.1 mg/kg) reversed motor inhibition induced by l-dopa and J-113397, suggesting involvement of D(2)/D(3) receptors. This study brings further evidence for a dopamine-dependent motor phenotype in MPTP-treated mice reinforcing the view that this model can be predictive of symptomatic antiparkinsonian activity provided the appropriate test is used. Moreover, it offers mechanistic interpretation to clinical reports of paradoxical worsening of parkinsonism following l-dopa. Finally, it confirms that NOP receptor antagonists may be proven effective in reversing parkinsonism when administered alone or in combination with dopamine agonists.

Behavioral phenotyping of mouse models of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative movement disorder afflicting millions of people in the United States. The advent of transgenic technologies has contributed to the development of several new mouse models, many of which recapitulate some aspects of the disease; however, no model has been demonstrated to faithfully reproduce the full constellation of symptoms seen in human PD. This may be due in part to the narrow focus on the dopamine-mediated motor deficits. As current research continues to unmask PD as a multi-system disorder, animal models should similarly evolve to include the non-motor features of the disease. This requires that typically cited behavioral test batteries be expanded. The major non-motor symptoms observed in PD patients include hyposmia, sleep disturbances, gastrointestinal dysfunction, autonomic dysfunction, anxiety, depression, and cognitive decline. Mouse behavioral tests exist for all of these symptoms and while some models have begun to be reassessed for the prevalence of this broader behavioral phenotype, the majority has not. Moreover, all behavioral paradigms should be tested for their responsiveness to L-DOPA so these data can be compared to patient response and help elucidate which symptoms are likely not dopamine-mediated. Here, we suggest an extensive, yet feasible, battery of behavioral tests for mouse models of PD aimed to better assess both non-motor and motor deficits associated with the disease.

MPTP-treated mice: long-lasting loss of nigral TH-ir neurons but not paradoxical sleep alterations

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse model is widely used for studying Parkinson's disease. A previous study in our laboratory showed that MPTP-treated mice presented an increase in paradoxical sleep (PS) throughout the sleep/wakefulness cycle. However, many researchers have reported a behavioural and dopaminergic neuron recovery process which appears some time after MPTP treatment. Hence, in a first step, we decided to study tyrosine hydroxylase-immunoreactive (TH-ir) neuron loss in the nigrostriatal pathway 7, 15, 40 and 60 days after MPTP injection. We then studied S/W in MPTP-treated mice 20 days and 40 days after MPTP injection. Our results showed that MPTP-treated mice presented a 30% reduction in the number of TH-ir neurons in the substantia nigra and a 50% decrease in striatal TH staining, compared with saline-treated mice. These nigrostriatal pathway alterations are stable until 60 days post-MPTP treatment. The PS increase observed in our previous study was also observed in the present work 20 days after MPTP treatment but not after 40 days. The present results demonstrated that TH-ir neuronal loss in MPTP mice is quite stable until 60 days, whereas PS alterations are not. This finding suggests that there is no correlation between the dopaminergic neuronal loss and PS alteration in MPTP-treated mice. Hence, other neurotransmission systems may be involved in PS amount variations in MPTP mice and it is possible that the PS increase is accounted for by a homeostatic process, following a hypothetical reduction in this sleep state.