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Drugs to interfere with orexins (hypocretins).

Orexins (hypocretins) are bioactive peptides linking arousal, appetite and neuroendocrine-autonomic control. Dysfunction of the orexin system is associated with narcolepsy-cataplexy. Here, we review drugs interfering with orexins directly such as novel selective orexin receptor agonists and antagonists, as well as drugs interfering with orexins indirectly such as those used for the treatment of narcolepsy-cataplexy, and pharmacological targets within the complex network of endogenous neurohumoral signals integrated and relayed by the orexin system. These include amines, acetylcholine, purines, GABA and glutamate, as well as nutritional-metabolic, circadian-photic, immunological and neuroendocrine-peptidergic influences. Basic and clinical evaluation of drugs interfering with the orexin system will lead to a better understanding of the molecular prerequisites that control behavioral state, stress responses, energy homeo- stasis and survival, and yield therapeutic advances for the treatment of narcolepsy and other disorders of sleep, eating, mood and memory.

Animals↗

Sodium oxybate for the treatment of narcolepsy.

Narcolepsy, a lifelong disease with diverse symptoms, poses a therapeutic challenge to physicians. Psychomotor stimulants are used to provide some relief from excessive sleepiness, whereas a variety of other medications have traditionally been used to treat the other symptoms of this disorder. Cataplexy, consisting of sudden episodes of bilateral skeletal muscle weakness, has long been treated with tricyclic antidepressants or selective serotonin re-uptake inhibitors. Although these drugs have brought relief to some patients, they cause intolerable adverse effects in others, whereas still others become tolerant to their beneficial effects. In July of 2002, sodium oxybate was approved by the US FDA for the treatment of cataplexy, representing a significant advance in the treatment of this unusual disease. The following drug evaluation summarises the role of this novel medication in the practice of sleep medicine.

Cataplexy↗

Emerging drugs for narcolepsy.

Narcolepsy is characterised by excessive daytime sleepiness, usually associated with cataplexy, hypnagogic hallucinations, sleep paralysis and fragmented nocturnal sleep. Although uncommon, it results in significant disability. Most cases occur sporadically, but genetic factors probably form a susceptibility background on which unknown environmental triggers act. The hypocretin system is strongly implicated in the development of narcolepsy. Cerebrospinal fluid levels of hypocretin-1 are significantly reduced in narcoleptic subjects with cataplexy. Despite the advances in our understanding of narcolepsy, current therapy is primarily symptomatic. Stimulants (standard and novel) combat excessive daytime sleepiness. Antidepressants (tricyclics, dual-action or selective serotonin re-uptake inhibitors) and sodium oxybate are anticataplexy agents. Hypnagogic hallucinations and sleep paralysis respond to antidepressants. Sodium oxybate consolidates sleep. Novel and experimental treatments include histamine antagonists, hypocretin agonists, slow-wave sleep enhancers, intravenous gamma-globulin, tramadol and corticosteroids.

Antidepressive Agents, Tricyclic↗

Stimulus-induced drop episodes in Coffin-Lowry syndrome.

OBJECTIVE: Coffin-Lowry syndrome (CLS) is a rare disorder characterized by moderate to severe mental retardation, facial dysmorphism, tapering digits, and skeletal deformity. Paroxysmal drop attacks occur in patients with CLS, characterized by sudden loss of muscle tone induced by unexpected tactile or auditory stimuli. Our objective is to characterize these attacks better using neurophysiologic studies. METHODS: We report 2 teenage boys with CLS and stimulus-induced drop episodes (SIDEs). Simultaneous surface electromyogram (EMG) and video electroencephalogram were performed during SIDEs on our 2 patients. RESULTS: Both patients had SIDEs stimulated by a loud noise, unexpected light touch stimulation, or visual threat that were characterized by abrupt episodes of complete or partial loss of lower extremity tone. These events were not associated with impairment of consciousness, and immediate recovery was noted. Simultaneous surface EMG and video electroencephalogram revealed no epileptiform discharges in either patient. In the first patient, after unexpected tactile or auditory stimulation, tonic EMG activity in paraspinal muscles was lost briefly, similar to that seen in cataplexy. In the second patient, at 6 years of age, sudden nonepileptic drop episodes were induced by an unexpected tactile, auditory, or visual stimulation. At 11 years of age, his episodes had changed to brief myoclonic jerk and tonic spasm that were triggered by unexpected tactile and auditory stimuli. An increase in tonic EMG activity occurred during the attacks, consistent with hyperekplexia. CONCLUSIONS: Our data suggest that SIDEs in CLS are a heterogeneous group of nonepileptic events that may manifest features of both cataplexy and hyperekplexia, even in the same patient.

Acoustic Stimulation↗

[Current aspects in the diagnosis and therapy of narcolepsy].

Narcolepsy is a potentially invalidating disorder of the sleep and wakefulness structure, characterized by attacks of sleepiness, cataplexy, hypnagogic hallucinations, sleep paralysis and disturbed night sleep. The diagnosis is mainly based on the history. Additional sophisticated examinations, such as nocturnal polysomnography, are primarily indicated to rule out other causes of excessive daytime somnolence. The recently detected high correlation between a certain HLA status and cataplexy has led to new pathogenetic concepts. The primary aim of the therapy is to keep the patient at work rather than attempting a symptom free state. Measures to organize his day with planned naps should precede the use of medication. Besides stimulants against daytime somnolence and tricyclic antidepressants to suppress cataplectic attacks, some new drugs have been administered successfully against the various symptoms of narcolepsy in recent years.

Antidepressive Agents, Tricyclic↗

[Neurodegenerative, autoimmune and genetic processes of human and animal narcolepsy].

Narcolepsy is a rare disabling sleep disorder whose main features are excessive daytime sleepiness and cataplexy. Human narcolepsy is most frequently a sporadic disorder with both genetic and environmental factors playing a role in its pathophysiology. Implication of the hypocretin system is well-established: as mutations in both canine and murine narcolepsies and as a consistent reduction in hypocretin neuron in human narcolepsy. The cause of human narcolepsy remains unknown. However degenerative, autoimmune and/or genetic processes are the most probable causes of the hypocretin neurons loss. Acting on a specific genetic background, an autoimmune process with hypocretin neuron degeneration, in response to environmental factors, is the most probable hypothesis for most cases of human narcolepsy with cataplexy. Although narcolepsy presents one of the tightest association with a specific HLA antigen (DQB1*0602), there is strong evidence that non-HLA genes also confer susceptibility. Monoaminergic, immune (TNF alpha) and hypocretinergic systems seem to be involved and may interfere with the phenotype. Treatment has not evolved significantly over the last few years. However, new drugs, such as hypocretin agonists, are currently being developed.

Animals↗

Depresssion in narcolepsy and hypersommia.

The authors studied the occurrence of depression in 100 randomly selected patients with narcolepsy and in 30 patients with hypersomnia. In the isolated form of idiopathic narcolepsy (without signs of cataplexy, sleep paralysis or hypnagogic hallucinations) depression occurred 28.6 per cent of cases. In idiopathic narcolepsy with cataplexy or other symptoms of sleep dissociation, depression was found in 17.2 per cent of cases. In idiopathic hypersomnia the occurrence of depression was 26.1 per cent. In the majority of cases the endogenous form of depression was observed. In the symptomatic form of narcolepsy and hypersomnia the occurence of depression has not been noted in any case. In most cases a parallel clincial course has been observed between the manifestation of depression and narcolepsy or hypersomnia. During a remission of the depressive state the hypersomniac symptoms decreased or disappeared totally. The authors furter discuss the possible pathophysiological mechanisms of the above mentioned symptoms. They are of the opinion that an important role is played by the secretion and metabolism of the cerebral monamines.

Cataplexy↗

Characteristics of narcolepsy in preteenaged children.

Narcolepsy is rarely diagnosed in preteenaged children. Its clinical and polysomnographic manifestations, some of which are unusual, are described in four children who were observed prospectively. The mean age at onset of hypersomnia was 10.2 years (range 8.4 to 11.2 years). Daytime naps among these children were lengthy, ranging from 20 to 120 minutes, and generally were considered unrefreshing. Cataplexy was present at the onset in all four children. Three of the four children were obese, with the concurrent nocturnal snoring prompting a misleading concern about obstructive sleep apnea syndrome in two children. The histocompatibility DR2 antigen was present in all four children. Significant behavioral manifestations appeared in all of them. The response to stimulant medications was, at best, modest. Narcolepsy may be difficult to diagnose in this age group. However, a careful history eliciting sleep/wake dysfunction (including cataplexy), leukocyte assays for the histocompatibility DR2 antigen, and serial polysomnographic studies may enable early recognition and treatment of this disease.

Cataplexy↗

Parkinson's disease and sleep.

There are many reasons for patients with idiopathic Parkinson's disease to develop sleep disorders and subsequent daytime sleepiness. Important causes are reduction of total sleep duration and sleep efficiency, and an increase in respiratory and motor arousals. This daytime sleepiness at first glance seems different from the "sleep attacks" which caused motot vehicle mishaps reported recently in persons taking pramipexole and ropinirole. There is, however, only little evidence that we deal with a new phenomenon in a new clinical situation, i. e. cataplexy-like attacks after high doses of new non-ergot dopamine-agonists. Until now there is no single case of a proven cataplexy on one hand, and older dopamine agonists like pergolide as well as L-Dopa + carbidopa have been reported to induce sudden onsets of sleep, too.

Dopamine Agents↗

Narcolepsy.

Narcolepsy is a disabling, chronic sleep-wake disorder that typically starts in a patient's second or third decade of life. Its key features are hypersomnia and cataplexy. Sleep paralysis, hallucinations, and disrupted sleep are nonspecific symptoms and are not always present. Disability relates primarily to sleepiness- related cognitive impairment, accidents, and psychosocial problems. Treatment, which includes counseling, scheduled napping, and pharmacologic intervention, is effective for most patients. Hypersomnia is best treated with such indirect sympathomimetics as mazindol, pemoline, methylphenidate, and amphetamine. Modafinil may become the drug of choice because it has fewer side effects. Cataplexy, sleep paralysis, and hallucinations may be ameliorated by compounds, including clomipramine and imipramine, that suppress rapid eye movement (REM) sleep. Regular follow-up visits enable the clinician to recognize uncommon but serious side effects (tolerance, substance abuse, psychosis, and hypertension) and additional sleep disturbances (sleep apnea, periodic limb movements in sleep, REM sleep behavior disorder), which can be specifically treated.

Journal Article↗

Sleep studies on a 90-minute day.

After 2 adaptation and 2 baseline all-night sleep recordings, 5 normal young adult subjects (3 males) were placed on a schedule alternating 60 min of wakefulness and 30 min of sleep for 5 1/3 24-h periods. A 2-day recovery period followed. One male subject (MA15) was later placed on the identical protocol with the exception that he was allotted periods of 75 min of wakefulness and 15 min of sleep during the experimental period. One male narcolepsy-cataplexy patient was placed on the 60-30 schedule for 48 h. All subjects showed REM sleep during the schedule manipulation. REMM sleep occurred within 10 min of sleep onset (SOREMP) on 79 of 110 REM sleep occasions in the normals, on all 29 REM episodes in MA15, and on 16 of 17 REM periods in the narcoleptic. In the normals, REM sleep showed a tendency to recur on alternate 90-min cycles, while in the narcoleptic REM recurred on consecutive periods. Compared to baseline, REM sleep 24 h was decreased in the normals and increased in the narcoleptic. Time spent in slow wave sleep and stage 2 was also reduced in the normal subjects on the 90-min schedule, and stage 1 sleep time was increased. Peak sleep times for the 5 normals occurred between 09.00 and 12.30 and lowest sleep times from 21.00 to 02.00. During the first recovery night, sleep times ranged from 11.5 to 18.5 h, including significant increases of slow wave sleep and REM sleep. Except for SOREMPs, no signs of the narcolepsy-cataplexy syndrome were seen in any of the normal subjects.

Adaptation, Physiological↗

Narcolepsy and the hypocretins.

Narcolepsy is a chronic neurologic disease characterized by excessive daytime sleepiness and one or more of three additional symptoms (cataplexy, or sudden loss of muscle tone; vivid hallucinations; and brief periods of total paralysis) related to the occurrence of rapid eye movement (REM) sleep at inappropriate times. The daytime sleepiness typically presents as a sudden overwhelming urge to sleep, followed by periods of sleep that last for seconds or minutes, or even longer. During daytime sleep episodes, patients may exhibit "automatic behavior," performing conventionalized functions (eg, taking notes), but not remembering having done so once they are awake. About 10% of narcoleptics are members of familial clusters; however, genetic factors alone are apparently insufficient to cause the disease, inasmuch as the most common genetic disorder, a mutation in chromosome 6 controlling the HLA antigen immune complex, although seen in 90% to 100% of patients, also occurs in as many as 50% of people without narcolepsy. A dog model of narcolepsy exhibits a mutation on chromosome 12 that disrupts the processing of the peptide neurotransmitter hypocretin. No such mutation characterizes human narcolepsy; however, cerebrospinal fluid (CSF) hypocretin levels are profoundly depressed in narcoleptic patients, and a specific reduction in hypocretin-containing neurons has been described. One hypothesis concerning the pathophysiology of narcolepsy proposes that the HLA subtype resulting from the mutation on chromosome 6 increases the susceptibility of hypocretin-containing brain neurons to immune attack. Because hypocretin may normally participate in the maintenance of wakefulness, the loss of neurons that release this peptide might allow REM sleep to occur at inappropriate times, ie, while the patient is awake, in contrast to its normal cyclic appearance after a period of slow-wave sleep. The cataplexy, hallucinations, and/or paralysis associated with REM episodes normally are unnoticed-or, at least, not remembered-when the transition to REM follows slow wave sleep, as is normally the case; however, they are remembered when, in people with narcolepsy, the REM episode starts during a period of wakefulness. The association of narcolepsy with a deficiency in a specific neurotransmitter, in this case, hypocretin, is reminiscent of the associations between Parkinson disease and dopamine, or early Alzheimer disease and acetylcholine.

Animals↗

Modafinil more effectively induces wakefulness in orexin-null mice than in wild-type littermates.

Narcolepsy-cataplexy, a disorder of excessive sleepiness and abnormalities of rapid eye movement (REM) sleep, results from deficiency of the hypothalamic orexin (hypocretin) neuropeptides. Modafinil, an atypical wakefulness-promoting agent with an unknown mechanism of action, is used to treat hypersomnolence in these patients. Fos protein immunohistochemistry has previously demonstrated that orexin neurons are activated after modafinil administration, and it has been hypothesized that the wakefulness-promoting properties of modafinil might therefore be mediated by the neuropeptide. Here we tested this hypothesis by immunohistochemical, electroencephalographic, and behavioral methods using modafinil at doses of 0, 10, 30 and 100 mg/kg i.p. in orexin-/- mice and their wild-type littermates. We found that modafinil produced similar patterns of neuronal activation, as indicated by Fos immunohistochemistry, in both genotypes. Surprisingly, modafinil more effectively increased wakefulness time in orexin-/- mice than in the wild-type mice. This may reflect compensatory facilitation of components of central arousal in the absence of orexin in the null mice. In contrast, the compound did not suppress direct transitions from wakefulness to REM sleep, a sign of narcolepsy-cataplexy in mice. Spectral analysis of the electroencephalogram in awake orexin-/- mice under baseline conditions revealed reduced power in the theta; band frequencies (8-9 Hz), an index of alertness or attention during wakefulness in the rodent. Modafinil administration only partly compensated for this attention deficit in the orexin null mice. We conclude that the presence of orexin is not required for the wakefulness-prolonging action of modafinil, but orexin may mediate some of the alerting effects of the compound.

Animals↗

The association between narcolepsy and REM behavior disorder (RBD).

BACKGROUND AND PURPOSE: Rapid eye movement (REM) sleep Behavior Disorder (RBD) is a movement disorder associated with loss of REM-related muscle atonia and is characterized by complex, vigorous and frequently violent dream-enacting behavior during REM sleep. RBD is usually idiopathic or secondary to neurological problems such as Parkinson's disease. This study looked at the association of RBD with another sleep disorder, narcolepsy. PATIENTS AND METHODS: Seventy-eight questionnaires were sent to known narcoleptics chosen at random from those with contact details available at the center. The questionnaire addressed current narcolepsy symptoms, medication use and symptoms of RBD. Positive questionnaire results were followed up with a telephone interview. Limited polysomnography (PSG) data was also analyzed. RESULTS: Fifty-five patients responded (response rate 71%). Of these, 20 (36%) had symptoms suggestive of RBD. The typical RBD patient is an older male (mean age of onset 60.9 years, 87% male); however, in this study, females were as likely to have RBD as males, and the mean age was 41 years. Sixty-eight percent of patients who regularly experienced cataplexy and the associated symptoms of narcolepsy (sleep paralysis, hypnogogic hallucinations and automatic behavior) had RBD, compared to 14% of those who never or rarely experienced these symptoms. CONCLUSION: This study implies a stronger relationship between these disorders than a previously published figure of 7-12% This is clinically significant as RBD is a potentially distressing but readily treatable disorder. It follows that narcoleptics, especially those with cataplexy and other associated symptoms, should be questioned about symptoms of RBD and treated accordingly. Similarly, anyone presenting with RBD should be assessed for symptoms of narcolepsy, particularly if female or of a younger age group than would otherwise be expected.

Adolescent↗

Monozygotic twins incompletely concordant for narcolepsy.

BACKGROUND: Among 15 monozygotic twin pairs described in the literature, only four pairs were considered to be concordant. There is no detailed report of HLA-DRB1*1501/DQB1*0602 positive monozygotic twins concordant for narcolepsy, with marked difference in the age of onset. METHODS: We compared a pair of female narcoleptic twins clinically. RESULTS: Diagnosis of narcolepsy and monozygosity of the twins were confirmed. The second-born twin demonstrated a typical course of narcolepsy, whereas the first-born twin had a very late onset of recurrent daytime sleep episodes at age 45 and cataplexy at age 50 years, which was apparently triggered by chronic emotional stresses and sleep insufficiency. CONCLUSIONS: The atypical course of narcolepsy in the first-born twin supports the multifactorial model for the development of narcolepsy. It was noted that cataplexy was preceded by sustained polyphasic sleep conditions. Our observation implies that the unaffected co-twins in discordant pairs could develop narcolepsy in stressful situations later in their lives.

Cytochrome P-450 Enzyme System↗

Narcolepsy update.

Narcolepsy, a disorder of excessive daytime sleepiness that affects more than 125,000 people in the United States, is technically defined as a daytime mean sleep latency (time elapsed before falling asleep) of less than 5 minutes in conjunction with verification of rapid eye movement sleep in at least two of five daytime nap periods. Cataplexy, hypnagogic hallucinations, and sleep paralysis are frequently associated with narcolepsy. Currently, overnight polysomnography and multiple sleep latency testing in a sleep disorders laboratory are used to diagnose narcolepsy. Standard pharmacologic therapy consists of the judicious use of stimulants to improve alertness and the administration of tricyclic and other antidepressant drugs to suppress cataplexy. In addition, good sleep hygiene (a regular sleep-wake schedule, an adequate amount of sleep at night, and scheduled daytime naps) is essential for optimal management of this disorder. Patient and family education about narcolepsy and its treatment is also important. Even with use of the best available treatment regimens, many patients with narcolepsy have substantial vocational and social impairments.

Animals↗

Selective excitation of GABAergic neurons in the substantia nigra of the rat by orexin/hypocretin in vitro.

Dysfunction of the orexin/hypocretin neurotransmitter system leads to the sleep disorder narcolepsy. Narcolepsy is characterized by excessive daytime sleepiness and the occurrence of cataplexy--a sudden loss of muscle tone triggered by emotionally arousing events. Both symptoms can be treated with drugs that act on dopaminergic systems. Here we have investigated the effect of orexins on the firing of dopaminergic and GABAergic neurons of the substantia nigra (SN) in brain slices. Surprisingly, dopaminergic neurons in pars compacta were unaffected by orexins. In contrast, bath application of orexin A (100 nM) or orexin B (5-300 nM) greatly increased the firing rate of GABAergic neurons in pars reticulata. The orexin B-mediated excitation was unaffected by blocking synaptic transmission (using low-Ca2+/high-Mg2+ solution). However, the effect of orexin B was reduced significantly by thapsigargin (1 microM) and inhibitors of protein kinase A. The presence of orexinergic fibres in the SN pars reticulata was demonstrated by immunohistochemical methods with the fibre density increasing in the rostrocaudal direction. The orexin excitation of SN reticulata cells may help to maintain their high firing rate during waking. Furthermore, the absence of orexin effects in narcolepsy may predispose affected individuals to attacks of cataplexy.

Animals↗

Narcolepsy and idiopathic hypersomnolence.

Narcolepsy is among the leading causes of excessive daytime sleepiness. Its classic form associates daytime sleepiness with cataplexy, sleep paralysis, hypnopompic hallucinations, and nocturnal disrupted sleep. This form is associated with HLA DQ betal-0602 in about 85% to 90% of affected subjects, independently of their ethnicity. But the definition of the variants of narcolepsy remains controversial, despite the fact that, in some cases, narcolepsy may be limited to daytime sleepiness. In its classic form, it is associated with two or more sleep onset rapid eye movement periods at the Multiple Sleep Latency Test. This test, performed after nocturnal polysomnography, can be helpful in diagnosing narcolepsy, in the absence of a convincing history of partial or complete attacks of cataplexy--a pathognomonic symptom. Investigation of narcoleptic Dobermans has indicated that a muscarinic cholinergic hypersensitivity exists in the brain of affected animals and abnormalities involve also the dopaminergic system. Despite its prevalence of 0.03% to 0.05%, it is still a neurologic entity often missed. Investigations of families of narcoleptics, including monozygotic twins, indicate that this syndrome is polygenic in nature with association of environmental factors. As the peak of onset of disabling symptoms occurs between 15 and 25 years of age, it is important to improve the treatment of this lifelong, disabling illness. Stimulants medications, independently of their mode of action, are prescribed to help daytime sleepiness, and tricyclic antidepressant drugs or serotonergic reuptake blockers are used on the other symptoms. But these medications have a limited efficacy. Short naps at regular intervals during the day are a strong therapeutic adjuvent.

Animals↗