Alteration of the striatal dopaminergic system in human narcolepsy

The Genetic Landscape of Sleep Disorders in Parkinson's Disease

Parknson's disease (PD) is the second most common neurodegenerative disease, affecting 1% of people aged over 60. PD is characterized by a wide range of motor symptoms, however the clinical spectrum of PD covers a wide range of non-motor symptoms, as well. Sleep disorders are among the most common non-motor symptoms of PD, can occur at any stage of the disease and significantly affect quality of life. These include rapid eye movement sleep behavior disorder (RBD), restless legs syndrome (RLS), excessive daytime sleepiness (EDS), insomnia, obstructive sleep apnea (OSA) and circadian rhythm disturbances. One of the main challenges in PD research is identifying individuals during the prodromal phase of the disease. Combining genetic and prodromal data may aid the early identification of individuals susceptible to PD. This review highlights current data regarding the genetic component of sleep disorders in PD patients, focusing on genes that have currently been associated with this PD co-morbidity.

The Park Sleep subtype in Parkinson's disease: from concept to clinic

INTRODUCTION

The heterogeneity of Parkinson's disease (PD) is evident from descriptions of non-motor (NMS) subtypes and Park Sleep, originally identified by Sauerbier et al. 2016, is one such clinical subtype associated with the predominant clinical presentation of sleep dysfunctions including excessive daytime sleepiness (EDS), along with insomnia.

AREAS COVERED

A literature search was conducted using the PubMed, Medline, Embase, and Web of Science databases, accessed between 1 February 2023 and 28 March 2023. In this review, we describe the clinical subtype of Park Sleep and related 'tests' ranging from polysomnography to investigational neuromelanin MRI brain scans and some tissue-based biological markers.

EXPERT OPINION

Cholinergic, noradrenergic, and serotonergic systems are dominantly affected in PD. Park Sleep subtype is hypothesized to be associated primarily with serotonergic deficit, clinically manifesting as somnolence and narcoleptic events (sleep attacks), with or without rapid eye movement behavior disorder (RBD). In clinic, Park Sleep recognition may drive lifestyle changes (e.g. driving) along with therapy adjustments as Park Sleep patients may be sensitive to dopamine D3 active agonists, such as ropinirole and pramipexole. Specific dashboard scores based personalized management options need to be implemented and include pharmacological, non-pharmacological, and lifestyle linked advice.

Sleep, Narcolepsy, and Sodium Oxybate

Sodium oxybate (SO) has been in use for many decades to treat narcolepsy with cataplexy. It functions as a weak GABAB agonist but also as an energy source for the brain as a result of its metabolism to succinate and as a powerful antioxidant because of its capacity to induce the formation of NADPH. Its actions at thalamic GABAB receptors can induce slow-wave activity, while its actions at GABAB receptors on monoaminergic neurons can induce or delay REM sleep. By altering the balance between monoaminergic and cholinergic neuronal activity, SO uniquely can induce and prevent cataplexy. The formation of NADPH may enhance sleep’s restorative process by accelerating the removal of the reactive oxygen species (ROS), which accumulate during wakefulness. SO improves alertness in normal subjects and in patients with narcolepsy. SO may allay severe psychological stress - an inflammatory state triggered by increased levels of ROS and characterized by cholinergic supersensitivity and monoaminergic deficiency. SO may be able to eliminate the inflammatory state and correct the cholinergic/ monoaminergic imbalance.

CSF and serum ferritin levels in narcolepsy type 1 comorbid with restless legs syndrome

OBJECTIVES

To investigate whether cerebrospinal fluid (CSF) and serum ferritin levels differ between patients with narcolepsy type 1 (NT1) comorbid with restless legs syndrome (RLS) or periodic leg movements during sleep (PLMS), and patients with NT1 or controls without comorbid RLS or PLMS.

METHODS

Sixty-six drug-free patients with NT1 (44 males, age 38.5 years [14-81]) were enrolled, including 20 with RLS, 18 with PLMS index ≥15/h (six with both RLS and PLMS). Thirty-eight drug-free patients (12 males, age 22.5 years [12-61]) referred for sleepiness complaint, but without central hypersomnia, RLS, PLMS were included as controls. Clinical, electrophysiological and biological (CSF/serum ferritin, orexin [ORX]) data were quantified.

RESULTS

NT1 patients with and without RLS did not differ for age, gender, and body mass index (BMI). No between-group differences were found for CSF ferritin, ORX, and serum ferritin levels. No CSF ferritin, ORX, and serum ferritin level differences were found between NT1 patients with and without PLMS, or with RLS or PLMS versus not. CSF-ferritin levels were not different between NT1 and controls in adjusted analyses. CSF-ferritin levels in the whole population correlated positively with age, serum-ferritin, BMI, negatively with ORX, but not with PLMS index. In NT1, CSF-ferritin levels correlated with age and serum-ferritin but not with PLMS.

CONCLUSION

The absence of CSF ferritin deficiency in NT1 with comorbid RLS or PLMS indicates normal brain iron levels in that condition. This result suggests that the frequent association between RLS, PLMS, and NT1 is not based on alterations in brain iron metabolism, a pathophysiological mechanism involved in primary RLS.

Neuroimaging of Narcolepsy and Primary Hypersomnias

Advances in neuroimaging open up the possibility for new powerful tools to be developed that potentially can be applied to clinical populations to improve the diagnosis of neurological disorders, including sleep disorders. At present, the diagnosis of narcolepsy and primary hypersomnias is largely limited to subjective assessments and objective measurements of behavior and sleep physiology. In this review, we focus on recent neuroimaging findings that provide insight into the neural basis of narcolepsy and the primary hypersomnias Kleine-Levin syndrome and idiopathic hypersomnia. We describe the role of neuroimaging in confirming previous genetic, neurochemical, and neurophysiological findings and highlight studies that permit a greater understanding of the symptoms of these sleep disorders. We conclude by considering some of the remaining challenges to overcome, the existing knowledge gaps, and the potential role for neuroimaging in understanding the pathogenesis and clinical features of narcolepsy and primary hypersomnias.

Orexin-A Exerts Neuroprotective Effects via OX1R in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by progressive and selective death of dopaminergic neurons. Orexin-A is involved in many biological effects of the body. It has been reported that orexin-A has protective effects in cellular models of PD. However, little is known about the protective effects of orexin-A in animal parkinsonian models and the cellular mechanism has not yet been fully clarified. The aim of this study was to evaluate the effects of orexin-A in MPTP mice model of PD as well as the possible neuroprotective mechanisms of orexin-A on dopaminergic neurons. The results from animal experiments demonstrated that orexin-A attenuated the loss of dopaminergic neurons and the decrease of tyrosine hydroxylase (TH) expression in the substantia nigra, normalized the striatal dopaminergic fibers, and prevented the depletion of dopamine and its metabolites in the striatum. MPTP-treated mice showed cognitive impairments accompanied with significant motor deficiency. Orexin-A improved MPTP-induced impairments in both motor activity and spatial memory. Importantly, orexin-A increased the protein level of brain-derived neurotrophic factor (BDNF) in dopaminergic neurons of the substantia nigra. Furthermore, the protective effects of orexin-A on MPTP parkinsonian mice could be blocked by orexinergic receptor 1 (OX1R) antagonist, SB334867. In another set of experiments with SH-SY5Y dopaminergic cells, orexin-A significantly induced the expression of BDNF in a dose and time-dependent manner. The upregulation of BDNF is mainly concerned with PI3K and PKC signaling pathways via OX1R. The present study demonstrated that orexin-A exerted neuroprotective effects on MPTP parkinsonian mice, which may imply orexin-A as a potential therapeutic target for PD.

Orexin-A Exerts Neuroprotective Effects via OX1R in Parkinson's Disease

Parkinson’s disease (PD) is a common neurodegenerative disorder characterized by progressive and selective death of dopaminergic neurons. Orexin-A is involved in many biological effects of the body. It has been reported that orexin-A has protective effects in cellular models of PD. However, little is known about the protective effects of orexin-A in animal parkinsonian models and the cellular mechanism has not yet been fully clarified. The aim of this study was to evaluate the effects of orexin-A in MPTP mice model of PD as well as the possible neuroprotective mechanisms of orexin-A on dopaminergic neurons. The results from animal experiments demonstrated that orexin-A attenuated the loss of dopaminergic neurons and the decrease of tyrosine hydroxylase (TH) expression in the substantia nigra, normalized the striatal dopaminergic fibers, and prevented the depletion of dopamine and its metabolites in the striatum. MPTP-treated mice showed cognitive impairments accompanied with significant motor deficiency. Orexin-A improved MPTP-induced impairments in both motor activity and spatial memory. Importantly, orexin-A increased the protein level of brain-derived neurotrophic factor (BDNF) in dopaminergic neurons of the substantia nigra. Furthermore, the protective effects of orexin-A on MPTP parkinsonian mice could be blocked by orexinergic receptor 1 (OX1R) antagonist, SB334867. In another set of experiments with SH-SY5Y dopaminergic cells, orexin-A significantly induced the expression of BDNF in a dose and time-dependent manner. The upregulation of BDNF is mainly concerned with PI3K and PKC signaling pathways via OX1R. The present study demonstrated that orexin-A exerted neuroprotective effects on MPTP parkinsonian mice, which may imply orexin-A as a potential therapeutic target for PD.

Neuroimaging correlates of narcolepsy with cataplexy: A systematic review

Recent developments in neuroimaging techniques have advanced our understanding of biological mechanisms underpinning narcolepsy. We used MEDLINE to retrieve neuroimaging studies to compare patients with narcolepsy and healthy controls. Thirty-seven studies were identified and demonstrated several replicated abnormalities: (1) gray matter reductions in superior frontal, superior and inferior temporal, and middle occipital gyri, hypothalamus, amygdala, insula, hippocampus, cingulate cortex, thalamus, and nucleus accumbens, (2) decreased fractional anisotropy in white matter of fronto-orbital and cingulate area, (3) reduced brain metabolism or cerebral blood flow in middle and superior frontal, and cingulate cortex (4) increased activity in inferior frontal gyri, insula, amygdala, and nucleus accumbens, and (5) N-acetylaspartate/creatine-phosphocreatine level reduction in hypothalamus. In conclusion, all the replicated findings are still controversial due to the limitations such as heterogeneity or size of the samples and lack of multimodal imaging or follow-up. Thus, future neuroimaging studies should employ multimodal imaging methods in a large sample size of patients with narcolepsy and consider age, duration of disease, age at onset, severity, human leukocyte antigen type, cerebrospinal fluid hypocretin levels, and medication intake in order to elucidate possible neuroimaging characteristic of narcolepsy and identify therapeutic targets.

REM Sleep at its Core - Circuits, Neurotransmitters, and Pathophysiology

Rapid eye movement (REM) sleep is generated and maintained by the interaction of a variety of neurotransmitter systems in the brainstem, forebrain, and hypothalamus. Within these circuits lies a core region that is active during REM sleep, known as the subcoeruleus nucleus (SubC) or sublaterodorsal nucleus. It is hypothesized that glutamatergic SubC neurons regulate REM sleep and its defining features such as muscle paralysis and cortical activation. REM sleep paralysis is initiated when glutamatergic SubC cells activate neurons in the ventral medial medulla, which causes release of GABA and glycine onto skeletal motoneurons. REM sleep timing is controlled by activity of GABAergic neurons in the ventrolateral periaqueductal gray and dorsal paragigantocellular reticular nucleus as well as melanin-concentrating hormone neurons in the hypothalamus and cholinergic cells in the laterodorsal and pedunculo-pontine tegmentum in the brainstem. Determining how these circuits interact with the SubC is important because breakdown in their communication is hypothesized to underlie narcolepsy/cataplexy and REM sleep behavior disorder (RBD). This review synthesizes our current understanding of mechanisms generating healthy REM sleep and how dysfunction of these circuits contributes to common REM sleep disorders such as cataplexy/narcolepsy and RBD.

Polysomnographic and actigraphic characteristics of patients with H1N1-vaccine-related and sporadic narcolepsy

OBJECTIVE

After the pandemic H1N1 influenza ASO3-adjuvanted vaccine, Pandemrix©, was used in late 2009 and early 2010, the incidence of narcolepsy increased in many European countries. This incidence mainly increased in children and adolescents and, to a lesser degree, in adults.

PATIENTS/METHODS

125 unmedicated patients, aged 4 to 61 years, were included in this case-series study. Of these, 69 were diagnosed to have an H1N1-vaccine-related narcolepsy and 57 had sporadic narcolepsy. Most of these patients had: an actigraphy recording of 1-2 weeks, polysomnography, a Multiple Sleep Latency Test (MSLT), and cerebrospinal fluid hypocretin-1 concentration analysis.

RESULTS

Patients with H1N1-vaccine-related narcolepsy had shorter diagnostic delays, lower periodic leg movement index during sleep, earlier sleep-wake rhythm, and were younger in age at diagnosis, compared with sporadic cases. They also had shorter sleep latency and more sleep onset REM periods in MSLT, but these results were strongly age-dependent. Actigraphy showed quantitatively less sleep and more sleep fragmentation than polysomnography.

CONCLUSION

Regarding polysomnographic and actigraphic characteristics, there were no dramatic deviations between H1N1-vaccine-related and sporadic narcolepsy. Circadian rhythms indicated some interesting new findings with respect to the H1N1-vaccine-related disease. An actigraphy recording of 1-2 weeks is useful when studying the nocturnal aspects of narcolepsy and sleep-wake rhythms of narcoleptic patients.

Rapid eye movement sleep behavior disorder and rapid eye movement sleep without atonia in narcolepsy

Narcolepsy is a rare disabling hypersomnia disorder that may include cataplexy, sleep paralysis, hypnagogic hallucinations, and sleep-onset rapid eye movement (REM) periods, but also disrupted nighttime sleep by nocturnal awakenings, and REM sleep behavior disorder (RBD). RBD is characterized by dream-enacting behavior and impaired motor inhibition during REM sleep (REM sleep without atonia, RSWA). RBD is commonly associated with neurodegenerative disorders including Parkinsonisms, but is also reported in narcolepsy in up to 60% of patients. RBD in patients with narcolepsy is, however, a distinct phenotype with respect to other RBD patients and characterized also by absence of gender predominance, elementary rather than complex movements, less violent behavior and earlier age at onset of motor events, and strong association to narcolepsy with cataplexy/hypocretin deficiency. Patients with narcolepsy often present dissociated sleep features including RSWA, increased density of phasic chin EMG and frequent shift from REM to NREM sleep, with or without associated clinical RBD. Most patients with narcolepsy with cataplexy lack the hypocretin neurons in the lateral hypothalamus. Tonic and phasic motor activities in REM sleep and dream-enacting behavior are mostly reported in presence of cataplexy. Narcolepsy without cataplexy is a condition rarely associated with hypocretin deficiency. We proposed that hypocretin neurons are centrally involved in motor control during wakefulness and sleep in humans, and that hypocretin deficiency causes a functional defect in the motor control involved in the development of cataplexy during wakefulness and RBD/RSWA/phasic motor activity during REM sleep.

Complex movement disorders at disease onset in childhood narcolepsy with cataplexy

Narcolepsy with cataplexy is characterized by daytime sleepiness, cataplexy (sudden loss of bilateral muscle tone triggered by emotions), sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep. Narcolepsy with cataplexy is most often associated with human leucocyte antigen-DQB1*0602 and is caused by the loss of hypocretin-producing neurons in the hypothalamus of likely autoimmune aetiology. Noting that children with narcolepsy often display complex abnormal motor behaviours close to disease onset that do not meet the classical definition of cataplexy, we systematically analysed motor features in 39 children with narcolepsy with cataplexy in comparison with 25 age- and sex-matched healthy controls. We found that patients with narcolepsy with cataplexy displayed a complex array of ‘negative’ (hypotonia) and ‘active’ (ranging from perioral movements to dyskinetic–dystonic movements or stereotypies) motor disturbances. ‘Active’ and ‘negative’ motor scores correlated positively with the presence of hypotonic features at neurological examination and negatively with disease duration, whereas ‘negative’ motor scores also correlated negatively with age at disease onset. These observations suggest that paediatric narcolepsy with cataplexy often co-occurs with a complex movement disorder at disease onset, a phenomenon that may vanish later in the course of the disease. Further studies are warranted to assess clinical course and whether the associated movement disorder is also caused by hypocretin deficiency or by additional neurochemical abnormalities.

Dopaminergic regulation of sleep and cataplexy in a murine model of narcolepsy

STUDY OBJECTIVES

To determine if the dopaminergic system modulates cataplexy, sleep attacks and sleep-wake behavior in narcoleptic mice.

DESIGN

Hypocretin/orexin knockout (i.e., narcoleptic) and wild-type mice were administered amphetamine and specific dopamine receptor modulators to determine their effects on sleep, cataplexy and sleep attacks.

PATIENTS OR PARTICIPANTS

Hypocretin knockout (n = 17) and wild-type mice (n = 21).

INTERVENTIONS

Cataplexy, sleep attacks and sleep-wake behavior were identified using electroencephalogram, electromyogram and videography. These behaviors were monitored for 4 hours after an i.p. injection of saline, amphetamine and specific dopamine receptor modulators (D1- and D2-like receptor modulators).

MEASUREMENTS AND RESULTS

Amphetamine (2 mg/kg), which increases brain dopamine levels, decreased sleep attacks and cataplexy by 61% and 67%, suggesting that dopamine transmission modulates such behaviors. Dopamine receptor modulation also had powerful effects on sleep attacks and cataplexy. Activation (SKF 38393; 20 mg/kg) and blockade (SCH 23390; 1 mg/kg) of D1-like receptors decreased and increased sleep attacks by 77% and 88%, without affecting cataplexy. Pharmacological activation of D2-like receptors (quinpirole; 0.5 mg/kg) increased cataplectic attacks by 172% and blockade of these receptors (eticlopride; 1 mg/kg) potently suppressed them by 97%. Manipulation of D2-like receptors did not affect sleep attacks.

CONCLUSIONS

We show that the dopaminergic system plays a role in regulating both cataplexy and sleep attacks in narcoleptic mice. We found that cataplexy is modulated by a D2-like receptor mechanism, whereas dopamine modulates sleep attacks by a D1-like receptor mechanism. These results support a role for the dopamine system in regulating sleep attacks and cataplexy in a murine model of narcolepsy.

Restless legs syndrome is frequent in narcolepsy with cataplexy patients

STUDY OBJECTIVES

To investigate the occurrence of restless legs syndrome (RLS) in narcolepsy with cataplexy (NC).

DESIGN

A case-control study assessing the frequency of comorbidity of RLS and NC in three European sleep disorder centers.

PATIENTS

Three sleep research centers recruited 184 NC patients and 235 age-matched controls.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

NC patients and controls underwent a face-to-face interview investigating demographics, medical and drug history, sleep habits, and sleep disorders, in particular RLS based on the 4 international criteria and on a frequency > or =2 times/week, with a detailed description of RLS symptoms when present. RLS was significantly more prevalent among NC patients (14.7%) than in controls (3.0%). The age at onset of RLS in NC patients fits with the age at onset in idiopathic RLS, and RLS appeared more than 10 years after NC onset. Unlike idiopathic RLS, RLS in NC subjects was not more prevalent in women and was less familial (15.4% of cases). Lastly, NC patients with RLS showed a moderate disease severity and an almost daily occurrence of symptoms, which were also diurnal in 35% of cases. Older age, higher blood ferritin levels, and sleep paralysis seem to have a predictive value for RLS in NC. The higher ferritin levels indicate that different pathophysiological mechanisms underlie secondary RLS associated with NC.

CONCLUSIONS

This study highlights the association between RLS and NC. The nature of this association is still investigational, but it does indicate that RLS must be addressed in the evaluation and management of nocturnal sleep impairment in NC patients.

Degenerative pontine lesions in patients with familial narcolepsy

BACKGROUND AND PURPOSE

Narcolepsy is characterized by chronic excessive daytime sleepiness with episodic sleep attacks. There are several associated symptoms of narcolepsy: cataplexy (bilateral muscle weakness without loss of consciousness provoked by an emotional trigger, e.g. laughter), sleep paralysis and hypnagogic-hypnopompic hallucinations. Most cases are sporadic; familial narcolepsy contributes to only 1-5% of all cases. While most cases of narcolepsy are idiopathic and are not associated with clinical or radiographic evidence of brain pathology, symptomatic or secondary narcolepsy may occur occasionally in association with lesions caused by tumours, demyelination or strokes of the diencephalon, midbrain, and pons. There are some examples of non-specific brainstem lesions found in magnetic resonance imaging (MRI) in patients with idiopathic narcolepsy.

MATERIAL AND METHODS

The authors present eleven patients from a five-generation family with many members who suffer from episodic excessive daytime sleepiness. Narcolepsy was diagnosed in 9 patients. Sleepiness was frequently associated with cataplexy, hypnagogic-hypnopompic hallucinations and sleep paralysis. Improvement in their clinical state was observed during the treatment with modafinil. All probands had MRI of the brain, routine blood tests, EEG, polysomnography, examination of the level of hypocretin in cerebrospinal fluid and evaluation by means of Epworth and Stanford Sleepiness Scales.

RESULTS

In 9 patients with narcolepsy, decreased thickness of the substantia nigra was found and in six of them degenerative lesions in the pontine substantia nigra were also noticed.

CONCLUSIONS

The significance of these changes remains unclear. No data have been published until now concerning the presence of any brain lesions in patients with familial narcolepsy.

Narcolepsy and depression and the neurobiology of gammahydroxybutyrate

A voluminous literature describes the relationship between disturbed sleep and depression. The breakdown of sleep is one of the cardinal features of depression and often also heralds its onset. Frequent arousals, periods of wakefulness and a short sleep onset REM latency are typical polysomnographic features of depression. The short latency to REM sleep has been attributed to the combination of a monoaminergic deficiency and cholinergic supersensitivity and these irregularities have been proposed to form the biological basis of the disorder. A similar imbalance between monoaminergic and cholinergic neurotransmission has been found in narcolepsy, a condition in which frequent awakenings, periods of wakefulness and short sleep onset REM latencies are also characteristic findings during sleep. In many cases of narcolepsy, this imbalance appears to result from a deficiency of hypocretin but once established, whether in depression or narcolepsy, this disequilibrium sets the stage for the dissociation or premature appearance of REM sleep and for the dissociation of the motor inhibitory component of REM sleep or cataplexy. In the presence of this monoaminergic/cholinergic imbalance, gammahydroxybutyrate (GHB) may acutely further reduce the latency of REM sleep and induce cataplexy, in both patients with narcolepsy or depression. On the other hand, the repeated nocturnal application of GHB in patients with narcolepsy improves the continuity of sleep, prolongs the latency to REM sleep and prevents cataplexy. Evidence to date suggests that GHB may restore the normal balance between monoaminergic and cholinergic neurotransmission. As such, the repeated use of GHB at night and the stabilization of sleep over time makes GHB an effective treatment for narcolepsy and a potentially effective treatment for depression.

Neuroimaging insights into the pathophysiology of sleep disorders

Neuroimaging methods can be used to investigate whether sleep disorders are associated with specific changes in brain structure or regional activity. However, it is still unclear how these new data might improve our understanding of the pathophysiology underlying adult sleep disorders. Here we review functional brain imaging findings in major intrinsic sleep disorders (i.e., idiopathic insomnia, narcolepsy, and obstructive sleep apnea) and in abnormal motor behavior during sleep (i.e., periodic limb movement disorder and REM sleep behavior disorder). The studies reviewed include neuroanatomical assessments (voxel-based morphometry, magnetic resonance spectroscopy), metabolic/functional investigations (positron emission tomography, single photon emission computed tomography, functional magnetic resonance imaging), and ligand marker measurements. Based on the current state of the research, we suggest that brain imaging is a useful approach to assess the structural and functional correlates of sleep impairments as well as better understand the cerebral consequences of various therapeutic approaches. Modem neuroimaging techniques therefore provide a valuable tool to gain insight into possible pathophysiological mechanisms of sleep disorders in adult humans.

Periodic leg movements during sleep and wakefulness in narcolepsy

The objectives of the study were to measure the prevalence of periodic leg movements during NREM and REM sleep (PLMS) and while awake (PLMW) and to assess the impact of PLMS on nocturnal sleep and daytime functioning in patients with narcolepsy. One hundred and sixty-nine patients with narcolepsy and 116 normal controls matched for age and gender were included. Narcoleptics with high and low PLMS indices were compared to assess the impact of PLMS on sleep and Multiple Sleep Latency Test (MSLT) variables. More narcoleptics than controls had a PLMS index greater than 5 per hour of sleep (67% versus 37%) and an index greater than 10 (53% versus 21%). PLMS indices were higher both in NREM and REM sleep in narcoleptic patients, but the between-group difference was greater for REM sleep. A significant increase of PLMS index was also found with aging in both narcoleptic patients and controls. PLMW indices were also significantly higher in narcoleptic patients. Patients with an elevated index of PLMS had a higher percentage of stage 1 sleep, a lower percentage of REM sleep, a lower REM efficiency and a shorter MSLT latency. The present study demonstrates a high frequency of PLMS and PLMW in narcolepsy, an association between the presence of PLMS and measures of REM sleep and daytime functioning disruption. These results suggest that PLMS represent an intrinsic feature of narcolepsy.

Neuroimaging in sleep medicine

The development of neuroimaging techniques has made possible the characterization of cerebral function throughout the sleep-wake cycle in normal human subjects. Indeed, human brain activity during sleep is segregated within specific cortical and subcortical areas in relation to the sleep stage, sleep physiological events and previous waking activity. This approach has allowed sleep physiological theories developed from animal data to be confirmed, but has also introduced original concepts about the neurobiological mechanisms of sleep, dreams and memory in humans. In contrast, at present, few neuroimaging studies have been dedicated to human sleep disorders. The available work has brought interesting data that describe some aspects of the pathophysiology and neural consequences of disorders such as insomnia, sleep apnea and narcolepsy. However, the interpretation of many of these results is restricted by limited sample size and spatial/temporal resolution of the employed technique. The use of neuroimaging in sleep medicine is actually restrained by concerns resulting from the technical experimental settings and the characteristics of the diseases. Nevertheless, we predict that future studies, conducted with state of the art techniques on larger numbers of patients, will be able to address these issues and contribute significantly to the understanding of the neural basis of sleep pathologies. This may finally offer the opportunity to use neuroimaging, in addition to the clinical and electrophysiological assessments, as a helpful tool in the diagnosis, classification, treatment and monitoring of sleep disorders in humans.

[The neurology of REM sleep. A synoptic tour de force]

REM or dreaming sleep is one of three states of consciousness. It is characterized by rapid eye movements, muscle atonia, desynchronized EEG, and autonomic dysregulation. A dysfunction of one of these four cardinal traits explains the primary disorders of REM sleep, including REM sleep behavior disorder and narcolepsy. Although seen in other stages, sleep apnea syndrome, coronary syndromes, and stroke are strongly triggered by the autonomic dysregulation of REM sleep. REM sleep has an antiepileptic effect, which has not yet been used in clinical practice. It favors procedural memory, but not declarative memory. While present neurophysiologic theories, backed up by new neuroimaging techniques, preferentially explore the genesis of REM sleep, psychodynamic theories have searched for its raison d'être by focusing on mentally stabilizing or purifying effects of dreaming. The exploding interest in dreaming sleep, images, and imaging may also yield a harvest for clinical medicine, and further perplexing findings, such as RBD as harbinger of parkinsonism should be expected.

Restless legs syndrome in narcolepsy: a side effect of sodium oxybate?

Gamma-hydroxybutyrate (GHB) has re-emerged as a major treatment for narcolepsy. As dopaminergic transmission is clearly involved in the pathophysiology of restless legs syndrome (RLS), and GHB reduces dopamine release, one may hypothesize that RLS may occur in narcolepsy in the presence of GHB. We report a case of narcolepsy with a severe occurrence of typical RLS with GHB, symptoms never previously experienced by the subject and reversible after withdrawal.

Periodic leg movements in sleep and periodic limb movement disorder: prevalence, clinical significance and treatment

Periodic leg movements in sleep (PLMS) are a frequent finding in polysomnography. The prevalence of PLMS is estimated to be 4-11% in adults. In childhood, PLMS rarely occur although medical conditions like sleep apnea syndrome or neuropsychiatric disorders can lead to high rates of PLMS. In the elderly, PLMS are also common in subjects without sleep disturbances. In sleep studies, PLMS are found most frequently in restless legs syndrome (RLS) and often occur in narcolepsy, sleep apnea syndrome and REM sleep behavior disorder. Some patients with otherwise unexplained insomnia or hypersomnia reveal an elevated number of PLMS, a condition defined as periodic limb movement disorder (PLMD). PLMS were found also in various medical and neurological disorders that do not primarily affect sleep. A summary of these is presented. In sleep disorders related to dopaminergic dysfunction such as RLS, PLMS are considered to be a symptom of the disease. In other disorders like primary insomnia, the clinical relevance of PLMS is still being controversially discussed. Studies with findings both pro and contra are referred. To date, only a few studies have evaluated the efficacy of therapeutic substances in reducing PLMS in PLMD patients. Their results need to be confirmed in controlled randomized trials.

Sleep and COMT polymorphism in ADHD children: preliminary actigraphic data

OBJECTIVE

To examine whether COMT (catechol-O-methyltransferase) polymorphism modulates aspects of sleep in children diagnosed with attention-deficit/hyperactivity disorder (ADHD).

METHOD

Nightly sleep actigraphic recordings during a double-blind, placebo-controlled, crossover clinical study (1 week of 0.5 mg/kg MPH; 1 week of placebo) were obtained for 34 children, 7.4 to 12 years old, diagnosed with ADHD (DSM-IV). Diagnosis was generated by the Diagnostic Interview Schedule for Children and was confirmed by multidisciplinary consensus.

RESULTS

Children who were Val allele carriers had poorer sleep continuity compared with children with the Met-Met genotype while receiving a placebo and while receiving methylphenidate.

CONCLUSIONS

The findings of the present study support the hypothesis that sleep disturbances in children with ADHD are related to the underlying pathophysiology of the disorder.

Neuroimaging of sleep and sleep disorders

Herein are presented the results of research in the area of sleep neuroimaging over the past year. Significant work has been performed to clarify the basic mechanisms of sleep in humans. New studies also extend prior observations regarding altered brain activation in response to sleep deprivation by adding information regarding vulnerability to sleep deprivation and regarding the influence of task difficulty on aberrant responses. Studies in sleep disorder medicine have yielded significant findings in insomnia, depression, and restless legs syndrome. Extensive advances have been made in the area of sleep apnea where physiologic challenges have been used to probe brain activity in the pathophysiology of sleep apnea syndrome.

Cerebral perfusion abnormality in narcolepsy with cataplexy

To investigate abnormal cerebral perfusion in narcoleptics with cataplexy, 25 narcoleptics with cataplexy and 25 normal controls were enrolled in this study. Cerebral perfusion was measured by brain single photon emission computed tomography (SPECT) using 99mTc-ethylcysteinate dimer. Patients and normal controls had not received any medication prior to the SPECT scan. Differences in cerebral perfusion between narcoleptics and normal controls were subjected to statistical parametric mapping (SPM) analysis. Overnight polysomnography and multiple sleep latency test (MSLT) were performed in all patients. Brain SPECT was carried out on all patients and normal controls during the waking state. Clinical symptoms and MSLT results of all patients are in accord with the International Classification of Sleep Disorders criteria for narcolepsy. MSLT showed a short mean sleep latency (1.69 +/- 1.0 min) and 2-5 sleep onset REM periods in individual patient. SPM analysis of brain SPECT showed hypoperfusion of the bilateral anterior hypothalami, caudate nuclei, and pulvinar nuclei of thalami, parts of the dorsolateral/ventromedial prefrontal cortices, parahippocampal gyri, and cingulate gyri in narcoleptics [P < 0.05 by Student's t test with false discovery rate (FDR) correction]. Significant hypoperfusion in the white matter of frontal and parietal lobes was also noted in narcoleptics. This study shows reduced cerebral perfusion in subcortical structures and cortical areas in narcoleptics. The distribution of abnormal cerebral perfusion is concordant with the pathway of the cerebral hypocretin system and may explain the characteristic features of narcolepsy, i.e., cataplexy, emotional lability, and attention deficit.

Orexinergic projections to the cat midbrain mediate alternation of emotional behavioural states from locomotion to cataplexy

Orexinergic neurones in the perifornical lateral hypothalamus project to structures of the midbrain, including the substantia nigra and the mesopontine tegmentum. These areas contain the mesencephalic locomotor region (MLR), and the pedunculopontine and laterodorsal tegmental nuclei (PPN/LDT), which regulate atonia during rapid eye movement (REM) sleep. Deficiencies of the orexinergic system result in narcolepsy, suggesting that these projections are concerned with switching between locomotor movements and muscular atonia. The present study characterizes the role of these orexinergic projections to the midbrain. In decerebrate cats, injecting orexin-A (60 microm to 1.0 mm, 0.20-0.25 microl) into the MLR reduced the intensity of the electrical stimulation required to induce locomotion on a treadmill (4 cats) or even elicit locomotor movements without electrical stimulation (2 cats). On the other hand, when orexin was injected into either the PPN (8 cats) or the substantia nigra pars reticulata (SNr, 4 cats), an increased stimulus intensity at the PPN was required to induce muscle atonia. The effects of orexin on the PPN and the SNr were reversed by subsequently injecting bicuculline (5 mm, 0.20-0.25 microl), a GABA(A) receptor antagonist, into the PPN. These findings indicate that excitatory orexinergic drive could maintain a higher level of locomotor activity by increasing the excitability of neurones in the MLR, while enhancing GABAergic effects on presumably cholinergic PPN neurones, to suppress muscle atonia. We conclude that orexinergic projections from the hypothalamus to the midbrain play an important role in regulating motor behaviour and controlling postural muscle tone and locomotor movements when awake and during sleep. Furthermore, as the excitability is attenuated in the absence of orexin, signals to the midbrain may induce locomotor behaviour when the orexinergic system functions normally but elicit atonia or narcolepsy when the orexinergic function is disturbed.

Pediatric Sleep Disorders

Pediatric sleep disorders represent a heterogeneous collection of disturbances that require varied intervention strategies. The diagnosis of some sleep disorders (eg, OSAS, narcolepsy, PLMD) require PSG, whereas others can be diagnosed during an office visit with a thorough medical,psychiatric, and sleep history. Sleep disorders place children at risk for school failure, accidents, and social problems, and can place a significant burden on families and the parent-child relationship.

Is Schizophrenia Associated with Narcolepsy?

OBJECTIVE

To determine the nature of the relationship between schizophrenia-like psychosis and narcolepsy.

BACKGROUND

A relationship between schizophrenia and narcolepsy has long been postulated due to the association of schizophrenia-like psychosis with narcolepsy and its treatment.

METHOD

We report two patients who presented with schizophrenia-like psychosis of narcolepsy and review the literature regarding possible shared neurobiology between the two disorders that might explain their co-occurrence.

RESULTS

There appears to be little in the way of common pathology between these two conditions when symptoms, human leukocyte antigen associations, rapid eye movement sleep architecture, D2-dopamine receptor changes, and hypocretinergic function are examined.

CONCLUSIONS

The available literature suggests that schizophrenia-like psychosis in narcolepsy is most commonly medication related or a chance co-occurrence, with limited evidence for a separate psychosis of narcolepsy.

Altered setting of the pituitary-thyroid ensemble in hypocretin-deficient narcoleptic men

Narcolepsy is a sleep disorder caused by disruption of hypocretin (orexin) neurotransmission. Injection of hypocretin-1 acutely suppresses TRH and TSH release in rats. In contrast, subchronic administration does not appear to affect the hypothalamo-pituitary-thyroid ensemble in animals. We explored (in 7 patients and 7 controls) whether hypocretin deficiency impacts circulating TSH levels and circadian timing of TSH release in narcoleptic humans. Plasma TSH concentration profiles (blood samples taken at 10-min intervals during 24 h) and TSH levels in response to TRH injection were analyzed by Cluster, robust regression, approximate entropy (ApEn), and deconvolution. Circulating TSH levels were lower in patients, which was primarily attributable to lower pulse amplitude and nadir concentrations. TSH secretion correlated positively with mean 24-h leptin levels (R2 = 0.46, P = 0.02) and negatively with amount of sleep (R2 = 0.29, P = 0.048). Pattern-synchrony between 24-h leptin and TSH concentrations was demonstrated by significant cross-correlation and cross-ApEn analyses with no differences between controls and patients. Sleep onset was closely associated with a fall in circulating TSH. Features of diurnal rhythmicity of circulating TSH fluctuations were similar in patients and controls, with the acrophase occurring shortly after midnight. Thyroxine and triiodothyronine concentrations were similar in patients and controls and did not display a diurnal rhythm. The response of plasma TSH levels to TRH was also similar in both groups. Sleep patterns in narcoleptics were significantly disorderly compared with controls, as measured by ApEn (P = 0.006). In summary, circulating TSH concentrations are low in hypocretin-deficient narcoleptic men, which could be attributable to their low plasma leptin levels and/or their abnormal sleep-wake cycle.

Bupropion is effective in depression in narcolepsy

Narcolepsy is a rare disorder characterised by sleep disturbances, cataplexy, sleep paralysis and hypnagogic, hypnopompic hallucinations. Although several treatment modalities, such as tricyclic antidepressants or selective serotonin reuptake inhibitors, have been used to treat different symptoms, there is no definite treatment for narcolepsy. Modafinil or amphetamine-like stimulants, such as dexamphetamine or methylphenidate, are used to treat sleepiness. Our case was a 58-year-old woman who was diagnosed as narcolepsy cataplexy syndrome. Her Epworth Sleepiness Scale (ESS) score was 14 and Beck Depression Inventory (BDI) score was 29 in the first evaluation. Imipramine and modafinil were begun for the treatment, but there was no improvement in her symptoms. Subsequently, bupropion was started at 150 mg/day and then dosage was increased to 300 mg/day. She was asymptomatic at the end of 3 months. To our knowledge, this is the second depressive narcoleptic patient who has responded to 300 mg/day of bupropion.

Screening for candidate gene regions in narcolepsy using a microsatellite based approach and pooled DNA

Narcolepsy is a complex sleep disorder characterized by excessive daytime sleepiness and cataplexy. Mutations in genes of the hypocretin (orexin) neurotransmitter system cause narcoleptic symptoms in animal models. The absence of hypocretin in the cerebrospinal fluid of human patients is hypothesized to originate from destruction of hypocretinergic cells in the hypothalamus, the cause of which remains unknown. Due to strong HLA association autoimmune models of narcolepsy pathogenesis are still mostly favored. Genetic predisposition factors other than HLA are likely to play a role in causing the disorder. We screened three sets of gene regions ( n=254) for association with narcolepsy using a microsatellite based approach and pooled DNA: genes related to immunity, particularly apoptosis; genes related to regulation of circadian rhythmicity; genes coding for several factors of neurotransmission. In relation to apoptosis an association was found for the BAG1 gene region. Interestingly, microsatellites representing four genomic regions related to neurotransmission revealed association with narcolepsy: COMT, DRD2, GABBR1, and HTR2A. These results, although exploratory and still to be confirmed in independent samples, support a complex pathogenetic model for narcolepsy, including disturbances of neurotransmission rather than involvement of autoimmunity.