Role of catecholamines in the modafinil and amphetamine induced wakefulness, a comparative pharmacological study in the cat

Weak with sex: sexual intercourse as a trigger for cataplexy

INTRODUCTION

Sudden, often positive emotions are typical triggers for cataplexy in patients with narcolepsy-cataplexy (NC). Cataplexy during sexual intercourse and orgasm (orgasmolepsy) has been previously reported, but its frequency and characteristics are poorly known.

AIM

To assess frequency and features of loss of muscle tone during sexual intercourse in a series of patients with NC, other sleep-wake disorders, and healthy controls.

METHODS

Review of sleep questionnaires (including the Stanford Cataplexy Questionnaire) of 75 subjects (29 with NC, 26 with other sleep-wake disorders, and 20 healthy controls), followed by an interview with specific focus on muscle loss during sexual activity in suspicious cases.

MAIN OUTCOME MEASURES

Cataplexy during sexual intercourse and orgasm (orgasmolepsy).

RESULTS

Orgasmolepsy was reported by three NC patients (two female, one male), one male patient with behaviorally induced insufficient sleep syndrome (BIISS) and cataplexy-like symptoms, and none of the healthy controls. In the two female NC patients, orgasmolepsy occurred by each sexual intercourse, and the male patient reported orgasmolepsy only when in a relationship involving emotional commitment and trust. In the patient with BIISS and orgasmolepsy, cataplexy-like symptoms involved unilaterally upper or lower limbs in association with negative emotions or sports activities.

CONCLUSIONS

Cataplexy during sexual intercourse is a distinct feature of NC, which can, however, be reported rarely also by patients with other sleep-wake disorders. Insufficient arousal may favor the occurrence of cataplexy and cataplexy-like symptoms, including orgasmolepsy. Hypocretin deficiency and reward dysregulation in narcolepsy may further facilitate this phenomenon and contribute to its repetitive occurrence.

Armodafinil promotes wakefulness and activates Fos in rat brain

Modafinil increases waking and labeling of Fos, a marker of neuronal activation. In the present study, armodafinil, the R-enantiomer of racemic modafinil, was administered to rats at 30 or 100 mg/kg i.p. about 5 h after lights on (circadian time 5 and near the midpoint of the sleep phase of the sleep:wake cycle) to assess its effects on sleep/wake activity and Fos activation. Armodafinil at 100 mg/kg increased wakefulness for 2 h, while 30 mg/kg armodafinil only briefly increased wakefulness. Armodafinil (30 and 100 mg/kg) also increased latencies to the onset of sleep and motor activity. Armodafinil had differential effects in increasing neuronal Fos immunolabeling 2 h after administration. Armodafinil at 100 mg/kg increased numbers of Fos-labeled neurons in striatum and anterior cingulate cortex, without affecting nucleus accumbens. Armodafinil at 30 mg/kg only increased numbers of light Fos-labeled neurons in the anterior cingulate cortex. In brainstem arousal centers, 100 mg/kg armodafinil increased numbers of Fos-labeled neurons in the tuberomammillary nucleus, pedunculopontine tegmentum, laterodorsal tegmentum, locus coeruleus, and dorsal raphe nucleus. Fos activation of these brainstem arousal centers, as well as of the cortex and striatum, is consistent with the observed arousal effects of armodafinil.

Modafinil in the treatment of excessive sleepiness

The wake-promoting agent modafinil is approved for the treatment of excessive sleepiness associated with obstructive sleep apnea (OSA), shift work disorder (SWD), and narcolepsy. In OSA, modafinil is recommended for use as an adjunct to standard therapies that treat the underlying airway obstruction. This article reviews the literature on modafinil (pharmacology, pharmacokinetics, efficacy, tolerability, and abuse potential), with emphasis on use of modafinil in the treatment of excessive sleepiness in patients with OSA, SWD, and narcolepsy. In large-scale, double-blind, placebo-controlled studies, modafinil improved objectively determined sleep latency, improved overall clinical condition related to severity of sleepiness, and reduced patient-reported sleepiness. Improvements in wakefulness were accompanied by improvements in behavioral alertness, functional status, and health-related quality of life. In patients with SWD, diary data showed modafinil reduced the maximum level of sleepiness during night shift work, level of sleepiness during the commute home, and incidence of accidents or near-accidents during the commute home when compared with placebo. Modafinil was well tolerated, without adversely affecting cardiovascular parameters or scheduled sleep. These findings and those of extension studies which reported improvements were maintained suggest modafinil has a beneficial effect on daily life and well-being in patients with excessive sleepiness associated with OSA, SWD, or narcolepsy.

Approved and investigational uses of modafinil : an evidence-based review

Modafinil is a wake-promoting agent that is pharmacologically different from other stimulants. It has been investigated in healthy volunteers, and in individuals with clinical disorders associated with excessive sleepiness, fatigue, impaired cognition and other symptoms. This review examines the use of modafinil in clinical practice based on the results of randomized, double-blind, placebo-controlled clinical trials available in the English language in the MEDLINE database. In sleep-deprived individuals, modafinil improves mood, fatigue, sleepiness and cognition to a similar extent as caffeine but has a longer duration of action. Evidence for improved cognition in non-sleep-deprived healthy volunteers is controversial.Modafinil improves excessive sleepiness and illness severity in all three disorders for which it has been approved by the US FDA, i.e. narcolepsy, shift-work sleep disorder and obstructive sleep apnoea with residual excessive sleepiness despite optimal use of continuous positive airway pressure (CPAP). However, its effects on safety on the job and on morbidities associated with these disorders have not been ascertained. Continued use of CPAP in obstructive sleep apnoea is essential. Modafinil does not benefit cataplexy.In very small, short-term trials, modafinil improved excessive sleepiness in patients with myotonic dystrophy. It was efficacious in fairly large studies of attention deficit hyperactivity disorder (ADHD) in children and adolescents, and was as efficacious as methylphenidate in a small trial, but has not been approved by the FDA, in part because of its serious dermatological toxicity. In a trial of 21 non-concurrent subjects, with 2-week treatment periods, modafinil was as effective as dexamfetamine in adult ADHD. Modafinil was helpful for depressive symptoms in bipolar disorder in a trial that excluded patients with stimulant-induced mania. A single dose of modafinil may hasten recovery from general anaesthesia after day surgery. A single dose of modafinil improved the ability of emergency room physicians to attend didactic lectures after a night shift, but did not improve their ability to drive home and caused sleep disturbances subsequently.Modafinil had a substantial placebo effect on outcomes such as fatigue, excessive sleepiness and depression in patients with traumatic brain injury, major depressive disorder, schizophrenia, post-polio fatigue and multiple sclerosis; however, it did not provide any benefit greater than placebo.Trials of modafinil for excessive sleepiness in Parkinson's disease, cocaine addiction and cognition in chronic fatigue syndrome provided inconsistent results; all studies had extremely small sample sizes. Modafinil cannot be recommended for these conditions until definitive data become available.Modafinil induces and inhibits several cytochrome P450 isoenzymes and has the potential for interacting with drugs from all classes. The modafinil dose should be reduced in the elderly and in patients with hepatic disease. Caution is needed in patients with severe renal insufficiency because of substantial increases in levels of modafinil acid. Common adverse events with modafinil include insomnia, headache, nausea, nervousness and hypertension. Decreased appetite, weight loss and serious dermatological have been reported with greater frequency in children and adolescents, probably due to the higher doses (based on bodyweight) used. Modafinil may have some abuse/addictive potential although no cases have been reported to date.

Pharmacotherapy to enhance arousal: what is known and what is not

Severe brain injury results in a disturbance among a wide range of critical neurotransmitter systems. Each neurotransmitter system places its own functional role while being interconnected to a multitude of other systems and functions. This chapter seeks to review the major neurotransmitter systems involved after severe acquired brain injury. While limited in their construct, animal models of brain injury have demonstrated agents that may assist in the recovery process and those that may further slow recovery. We review further the issue of laboratory evidence and what is transferable to the clinic. Lastly, this chapter reviews published clinical pharmacotherapy studies or trials in the arena of arousal for those with clinical severe brain injury. We discuss limitations as well as findings and present the available evidence in a table-based format. While no clear evidence exists to suggest a defined and rigid pharmacotherapeutic approach, interesting data does suggest that several medications have been associated with enhanced arousal. Several studies are underway or about to begin that will shed more light on the utility of such agents in improving function after severe brain injury. For now, clinicians must employ their own judgment and what has been learned from the limited literature to the care of a challenging group of persons.

Modafinil decreases food intake in humans subjected to simulated shift work

In a limited number of studies modafinil has been shown to decrease food intake by laboratory animals and humans. The present study represents a secondary data analysis, in which the effects of modafinil on several measures of food intake were determined in humans living in a residential laboratory during simulated shift work. During this 23-day study, a wide selection of food items and beverages were freely available. During this double-blind, within-participant study, volunteers (N = 11) received oral modafinil dose (0, 200, or 400 mg) 1 h after waking for three consecutive days under two shift conditions: day shift and night shift. Shifts alternated three times during the study, and shift conditions were separated by an "off" day. Modafinil (200, 400 mg) dose-dependently decreased total caloric intake by approximately 18% and approximately 38%, respectively, regardless of shift condition, without selectively altering the proportion of total calories derived from carbohydrate, fat and protein. Ratings of "Hungry" were also significantly decreased by both active doses, but only immediately before the lunch break period. In addition, tolerance to the anorexic effects of modafinil was not apparent, as these effects remained stable across the three days of modafinil dosing. These findings show that modafinil produced clear reductions in food intake and suggest that future prospective studies should examine the drug in obese participants.

Dopaminergic D1 and D2 receptors are essential for the arousal effect of modafinil

Modafinil is a wake-promoting compound with low abuse potential used in the treatment of narcolepsy. Although the compound is reported to affect multiple neurotransmitter systems such as catecholamines, serotonin, glutamate, GABA, orexin, and histamine, however, the molecular mechanism by which modafinil increases wakefulness is debated. Herein we used dopamine (DA) D(2) receptor (D(2)R)-deficient mice combined with D(1)R- and D(2)R-specific antagonists to clarify the role of DA receptors in the arousal effects of modafinil. In wild-type mice, intraperitoneal modafinil induced wakefulness in a dose-dependent manner. Pretreatment with either D(1)R antagonist SCH23390 [R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine] at 30 microg/kg or D(2)R antagonist raclopride at 2 mg/kg blocked the arousal effects of low-dose modafinil at 22.5 and 45 mg/kg. When modafinil was given at 90 and 180 mg/kg, pretreatment of D(1)R antagonist did not affect the wakefulness at all, whereas D(2)R antagonist significantly attenuated the wakefulness to the half level compared with vehicle control. Similarly, D(2)R knock-out (KO) mice exhibited attenuated modafinil-induced wakefulness. However, pretreatment of D(2)R KO mice with D(1)R antagonist completely abolished arousal effects of modafinil. These findings strongly indicate that dopaminergic D(1)R and D(2)R are essential for the wakefulness induced by modafinil.

Management of narcolepsy

BACKGROUND

Narcolepsy is a rare chronic sleep disorder classically characterized by excessive daytime sleepiness. Other symptoms of the disease, including cataplexy, sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep, may follow later. The disease can be incapacitating and frequently results in impaired psychosocial interaction. In the absence of a cure for narcolepsy, medical therapy is directed at symptom control.

OBJECTIVES

The aim of this study was to review the current approach to the treatment of narcolepsy.

METHODS

A search of three bibliographic databases (MEDLINE/PubMed, EMBASE and the Cochrane Library Database) was conducted from 1966 to January 2008 using the National Library of Medicine MeSH search terms narcolepsy and cataplexy. Relevant studies, case reports, review articles, editorials, short communications and chapters from selected textbooks were then extracted and manually cross-referenced.

RESULTS/CONCLUSIONS

Traditionally, stimulants have been used to improve the symptoms of excessive daytime sleepiness. However, the treatment of narcolepsy has evolved recently with the widespread use of newer drugs, including modafinil for daytime sleepiness, newer antidepressants for cataplexy and gamma-hydroxybutyrate (sodium oxybate) for both excessive daytime sleepiness and cataplexy.

Behavioral responses of dopamine beta-hydroxylase knockout mice to modafinil suggest a dual noradrenergic-dopaminergic mechanism of action

Modafinil is approved for use in the treatment of excessive daytime sleepiness. The precise mechanism of modafinil action has not been elucidated, although both dopamine (DA) and norepinephrine (NE) systems have been implicated. To explore the roles of DA and NE in the mechanism of modafinil-induced arousal, dopamine beta-hydroxylase knockout (Dbh -/-) mice were examined in behavioral paradigms of arousal (photobeam breaks and behavioral scoring of sleep latency). Dbh -/- mice completely lack NE but have hypersensitive DA signaling. It was hypothesized that Dbh -/- mice would be unresponsive to modafinil if the compound acts primarily via NE, but would be hypersensitive to modafinil if it acts primarily via DA. Dbh -/- mice had increased sensitivity to the locomotor-activating and wake-promoting effects of modafinil. Paradoxically, the alpha1-adrenergic receptor antagonist, prazosin, attenuated the effects of modafinil in control mice, but not in Dbh -/- mice. Blockade of DA receptors with flupenthixol decreased modafinil-induced locomotion and wake in both control and Dbh -/- mice. These results suggest that both NE and DA are involved in the behavioral effects of modafinil in control mice, but the requirement for NE can be bypassed by hypersensitive DA signaling.

Modafinil: a review of neurochemical actions and effects on cognition

Modafinil (2-[(Diphenylmethyl) sulfinyl] acetamide, Provigil) is an FDA-approved medication with wake-promoting properties. Pre-clinical studies of modafinil suggest a complex profile of neurochemical and behavioral effects, distinct from those of amphetamine. In addition, modafinil shows initial promise for a variety of off-label indications in psychiatry, including treatment-resistant depression, attention-deficit/hyperactivity disorder, and schizophrenia. Cognitive dysfunction may be a particularly important emerging treatment target for modafinil, across these and other neuropsychiatric disorders. We aimed to comprehensively review the empirical literature on neurochemical actions of modafinil, and effects on cognition in animal models, healthy adult humans, and clinical populations. We searched PubMed with the search term 'modafinil' and reviewed all English-language articles for neurochemical, neurophysiological, cognitive, or information-processing experimental measures. We additionally summarized the pharmacokinetic profile of modafinil and clinical efficacy in psychiatric patients. Modafinil exhibits robust effects on catecholamines, serotonin, glutamate, gamma amino-butyric acid, orexin, and histamine systems in the brain. Many of these effects may be secondary to catecholamine effects, with some selectivity for cortical over subcortical sites of action. In addition, modafinil (at well-tolerated doses) improves function in several cognitive domains, including working memory and episodic memory, and other processes dependent on prefrontal cortex and cognitive control. These effects are observed in rodents, healthy adults, and across several psychiatric disorders. Furthermore, modafinil appears to be well-tolerated, with a low rate of adverse events and a low liability to abuse. Modafinil has a number of neurochemical actions in the brain, which may be related to primary effects on catecholaminergic systems. These effects are in general advantageous for cognitive processes. Overall, modafinil is an excellent candidate agent for remediation of cognitive dysfunction in neuropsychiatric disorders.

Promoting of wakefulness by administrations of modafinil into anterior hypothalamus and into the pedunculopontine tegmental nucleus in rats

We investigated whether administration of MOD in rats during the lights-on period into wake-promoting areas, such as anterior hypothalamus (AH) or into the pedunculopontine tegmental nucleus (PPTg) would enhance waking. Results showed that microinjections of 1 microL of MOD (10, 20, or 30 microg) into both brain areas increased the total time of alertness and decreased sleep. Additionally, MOD-treated rats showed an enhancement in alpha power spectra but delta power spectra was diminished. Finally, c-Fos expression was found increased into either AH or the PPTg. Collectively, these results suggest that MOD induces waking via the activity of two wake-related brain areas such as AH and the PPTg.

Smoked cocaine self-administration is decreased by modafinil

Modafinil has been reported to reduce cocaine use in a clinical sample of infrequent users (2 days/week), but the effects of modafinil on cocaine self-administration in the laboratory have not been studied. The present study investigated the effects of modafinil maintenance on cocaine self-administration by frequent users (4 days/week) under controlled laboratory conditions. During this 48-day double-blind, crossover design study, the effects of modafinil maintenance (0, 200, and 400 mg/day) on response to smoked cocaine (0, 12, 25, and 50 mg) were examined in nontreatment-seeking cocaine-dependent individuals (n=8). Cocaine significantly increased self-administration, subjective-effect ratings, and cardiovascular measures; modafinil at both doses (200 and 400 mg/day) markedly attenuated these effects. These findings agree with data from previous human laboratory and clinical investigations of modafinil as a potential cocaine abuse treatment medication. Thus, our data support the potential of modafinil as a pharmacotherapy for cocaine dependence.

Noradrenergic modulation of arousal

Through a highly divergent efferent projection system, the locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. State-dependent neuronal discharge activity of locus coeruleus neurons has long-suggested a role of this system in the induction of an alert waking state. More recent work supports this hypothesis, demonstrating robust wake-promoting actions of the locus coeruleus-noradrenergic system. Norepinephrine enhances arousal, in part, via actions of beta- and alpha1-receptors located within multiple subcortical structures, including the general regions of the medial septal area and the medial preoptic areas. Recent anatomical studies suggest that arousal-enhancing actions of norepinephrine are not limited to the locus coeruleus system and likely include the A1 and A2 noradrenergic cell groups. Thus, noradrenergic modulation of arousal state involves multiple noradrenergic systems acting within multiple subcortical regions. Pharmacological studies indicate that the combined actions of these systems are necessary for the sustained maintenance of arousal levels associated with spontaneous waking. Enhanced arousal state is a prominent aspect of both stress and psychostimulant drug action and evidence indicates that noradrenergic systems likely play an important role in both stress-related and psychostimulant-induced arousal. These and other observations suggest that the dysregulation of noradrenergic neurotransmission could well contribute to the dysregulation of arousal associated with a variety of behavioral disorders including insomnia and stress-related disorders.

Non-cholinergic modulation of antisaccade performance: a modafinil-nicotine comparison

INTRODUCTION

The antisaccade task provides a powerful tool with which to investigate the cognitive and neural systems underlying goal-directed behaviour, particularly in situations when the correct behavioural response requires the suppression of a prepotent response. Antisaccade errors (failures to suppress reflexive prosaccades towards sudden-onset targets) are increased in patients with damage to the dorsolateral prefrontal cortex, and in patients with schizophrenia. Nicotine has been found to improve antisaccade performance in patients with schizophrenia and healthy controls. This performance enhancing effect may be due to direct effects on the cholinergic system, but there has been no test of this hypothesis.

MATERIALS AND METHODS

In a double blind, double dummy, placebo-controlled design, we compared the effect of nicotine and modafinil, a putative indirect noradrenergic agonist, on antisaccade performance in healthy non-smokers.

RESULTS AND DISCUSSION

Both compounds reduced latency for correct antisaccades, although neither reduced antisaccade errors. These findings are discussed with reference to the pharmacological route of performance enhancement on the antisaccade task and current models of antisaccade performance.

A review of the effects of modafinil on cognition in schizophrenia

Modafinil, a wake-promoting agent believed to operate via the hypocretin/orexin system, has a similar clinical profile to that of conventional, dopaminergic stimulants but different biochemical and pharmacological properties. There is increasing interest in the use of modafinil to improve cognition in schizophrenia as well as in other disorders such as attention-deficit/hyperactivity disorder. Recent research has focused on enhancing cognition in patients with schizophrenia because of the association between cognitive performance and functional outcome. Initial findings indicate that modafinil may lead to better executive functioning and attentional performance in patients with schizophrenia. The results further suggest that patient characteristics such as overall current cognitive functioning levels, genetic polymorphisms, and medication status may be important mediators for the effectiveness of modafinil, allowing for future treatment to be targeted to those most likely to benefit. Currently, further research is required to address the potential benefits and risks of chronic administration of modafinil to patients with schizophrenia.

Involvement of central histaminergic systems in modafinil-induced but not methylphenidate-induced increases in locomotor activity in rats

Modafinil is a novel wake-promoting drug used for the treatment of narcolepsy, the mechanism of action of which remains unclear. Previous studies have shown that modafinil produces a different pattern of c-Fos activation in the brain to the classical stimulants amphetamine and methylphenidate. Modafinil, given i.p. to urethane-anesthetized rats, is associated with an increase in histamine release from the anterior hypothalamus, indicating that its behavioral actions may involve histaminergic systems. In the present study, the effects of modafinil on histamine release using in vivo microdialysis and locomotor activity in freely moving rats were examined, and compared with those of the classical psychostimulant methylphenidate. Modafinil (75 and 150 mg/kg, i.p.) increased both histamine release and locomotor activity, significantly. Methylphenidate (3 mg/kg, i.p.) also increased locomotor activity to the same extent as modafinil (150 mg/kg, i.p.) without stimulating histamine release. Depletion of neuronal histamine using alpha-fluoromethylhistidine abolished the effect of modafinil on locomotor activity in mice but had no effect on methylphenidate-induced locomotion. Examination of the effects of modafinil and methylphenidate on locomotor activity in the dark phase at doses that produced comparable effects in the light phase showed that the effect of modafinil in the dark phase was less than that of methylphenidate, a possible indication that modafinil-induced locomotor activity may be partly related to its wake-promoting actions. These findings suggest that the locomotor effects of modafinil but not of methylphenidate, involve the central histaminergic systems.

Paradoxical (REM) sleep genesis: the switch from an aminergic-cholinergic to a GABAergic-glutamatergic hypothesis

In the middle of the last century, Michel Jouvet discovered paradoxical sleep (PS), a sleep phase paradoxically characterized by cortical activation and rapid eye movements and a muscle atonia. Soon after, he showed that it was still present in "pontine cats" in which all structures rostral to the brainstem have been removed. Later on, it was demonstrated that the pontine peri-locus coeruleus alpha (peri-LCalpha in cats, corresponding to the sublaterodorsal nucleus, SLD, in rats) is responsible for PS onset. It was then proposed that the onset and maintenance of PS is due to a reciprocal inhibitory interaction between neurons presumably cholinergic specifically active during PS localized in this region and monoaminergic neurons. In the last decade, we have tested this hypothesis with our model of head-restrained rats and functional neuroanatomical studies. Our results confirmed that the SLD in rats contains the neurons responsible for the onset and maintenance of PS. They further indicate that (1) these neurons are non-cholinergic possibly glutamatergic neurons, (2) they directly project to the glycinergic premotoneurons localized in the medullary ventral gigantocellular reticular nucleus (GiV), (3) the main neurotransmitter responsible for their inhibition during waking (W) and slow wave sleep (SWS) is GABA rather than monoamines, (4) they are constantly and tonically excited by glutamate and (5) the GABAergic neurons responsible for their tonic inhibition during W and SWS are localized in the deep mesencephalic reticular nucleus (DPMe). We also showed that the tonic inhibition of locus coeruleus (LC) noradrenergic and dorsal raphe (DRN) serotonergic neurons during sleep is due to a tonic GABAergic inhibition by neurons localized in the dorsal paragigantocellular reticular nucleus (DPGi) and the ventrolateral periaqueductal gray (vlPAG). We propose that these GABAergic neurons also inhibit the GABAergic neurons of the DPMe at the onset and during PS and are therefore responsible for the onset and maintenance of PS.

Differential effects of modafinil and methylphenidate on stop-signal reaction time task performance in the rat, and interactions with the dopamine receptor antagonist cis-flupenthixol

RATIONALE

The stop-signal reaction time (SSRT) task measures inhibition of a response that has already been initiated, i.e. the ability to stop. 'Impulsive' human subjects, e.g. with attention deficit and hyperactivity disorder (ADHD), have longer SSRTs. Both SSRT and go-trial reaction time (GoRT) may be sensitive to drugs such as d-amphetamine, methylphenidate and modafinil, both in normal subjects and those with ADHD.

OBJECTIVES

To investigate the effects of modafinil (3, 10, 30 and 100 mg/kg) and methylphenidate (0.3, 1.0 and 3.0 mg/kg) on SSRT task performance in the rat. To investigate the possible contribution of dopamine receptors in the action of these drugs using the mixed D1/D2 dopamine receptor antagonist cis-flupenthixol.

RESULTS

Modafinil significantly decreased SSRT with little effect on GoRT but only in rats with slow baseline SSRTs. Fast SSRTs were not changed by modafinil. Methylphenidate decreased GoRTs of all rats. However, methylphenidate had baseline-dependent effects on SSRT, decreasing SSRT in slow responders but increasing SSRT in fast responders. Cis-flupenthixol (0.01, 0.04 and 0.125 mg/kg) had no effects on SSRT but increased GoRT at higher doses. At the lowest dose (0.01 mg/kg), cis-flupenthixol failed to disrupt the SSRT-decreasing effects of either modafinil or methylphenidate, whereas at 0.04 mg/kg, the cis-flupenthixol-dependent increase in GoRT was antagonised by methylphenidate but not by modafinil.

CONCLUSIONS

This evidence supports a hypothesis that stop and go processes are under control of distinct neurochemical mechanisms.

Brain structures and mechanisms involved in the control of cortical activation and wakefulness, with emphasis on the posterior hypothalamus and histaminergic neurons

Wakefulness is a functional brain state that allows the performance of several "high brain functions", such as diverse behavioural, cognitive and emotional activities. Present knowledge at the whole animal or cellular level suggests that the maintenance of the cerebral cortex in this highly complex state necessitates the convergent and divergent activity of an ascending network within a large reticular zone, extending from the medulla to the forebrain and involving four major subcortical structures (the thalamus, basal forebrain, posterior hypothalamus and brainstem monoaminergic nuclei), their integral interconnections and several neurotransmitters, such as glutamate, acetylcholine, histamine and noradrenaline. In this mini-review, the importance of the thalamus, basal forebrain and brainstem monoaminergic neurons in wake control is briefly summarized, before turning our attention to the posterior hypothalamus and histaminergic neurons, which have been far less studied. Classical and recent experimental data are summarized, supporting the hypothesis that (1) the posterior hypothalamus constitutes one of the brain ascending activating systems and plays an important role in waking; (2) this function is mediated, in part, by histaminergic neurons, which constitute one of the excitatory sources for cortical activation during waking; (3) the mechanisms of histaminergic arousal involve both the ascending and descending projections of histaminergic neurons and their interactions with diverse neuronal populations, such as neurons in the pre-optic area and cholinergic neurons; and (4) other widespread-projecting neurons in the posterior hypothalamus also contribute to the tonic cortical activation during wakefulness and/or paradoxical sleep.

The brain H3-receptor as a novel therapeutic target for vigilance and sleep–wake disorders

Brain histaminergic neurons play a prominent role in arousal and maintenance of wakefulness (W). H(3)-receptors control the activity of histaminergic neurons through presynaptic autoinhibition. The role of H(3)-receptor antagonists/inverse agonists (H(3)R-antagonists) in the potential therapy of vigilance deficiency and sleep-wake disorders were studied by assessing their effects on the mouse cortical EEG and sleep-wake cycle in comparison to modafinil and classical psychostimulants. The H(3)R-antagonists, thioperamide and ciproxifan increased W and cortical EEG fast rhythms and, like modafinil, but unlike amphetamine and caffeine, their waking effects were not accompanied by sleep rebound. Conversely, imetit (H(3)R-agonist) enhanced slow wave sleep and dose-dependently attenuated ciproxifan-induced W, indicating that the effects of both ligands involve H(3)-receptor mechanisms. Additional studies using knockout (KO) mice confirmed the essential role of H(3)-receptors and histamine-mediated transmission in the wake properties of H(3)R-antagonists. Thus ciproxifan produced no increase in W in either histidine-decarboxylase (HDC, histamine-synthesizing enzyme) or H(1)- or H(3)-receptor KO-mice whereas its waking effects persisted in H(2)-receptor KO-mice. These data validate the hypothesis that H(3)R-antagonists, through disinhibition of H(3)-autoreceptors, enhancing synaptic histamine that in turn activates postsynaptic H(1)-receptors promoting W. Interestingly amphetamine and modafinil, despite their potent arousal effects, appear unlikely to depend on histaminergic mechanism as their effects still occurred in HDC KO-mice. The present study thus distinguishes two classes of wake-improving agents: the first acting through non-histaminergic mechanisms and the second acting via histamine and supports brain H(3)-receptors as potentially novel therapeutic targets for vigilance and sleep-wake disorders.

Narcolepsy with cataplexy

Narcolepsy with cataplexy is a disabling sleep disorder affecting 0.02% of adults worldwide. It is characterised by severe, irresistible daytime sleepiness and sudden loss of muscle tone (cataplexy), and can be associated with sleep-onset or sleep-offset paralysis and hallucinations, frequent movement and awakening during sleep, and weight gain. Sleep monitoring during night and day shows rapid sleep onset and abnormal, shortened rapid-eye-movement sleep latencies. The onset of narcolepsy with cataplexy is usually during teenage and young adulthood and persists throughout the lifetime. Pathophysiological studies have shown that the disease is caused by the early loss of neurons in the hypothalamus that produce hypocretin, a wakefulness-associated neurotransmitter present in cerebrospinal fluid. The cause of neural loss could be autoimmune since most patients have the HLA DQB1*0602 allele that predisposes individuals to the disorder. Treatment is with stimulant drugs to suppress daytime sleepiness, antidepressants for cataplexy, and gamma hydroxybutyrate for both symptoms. Because narcolepsy is an under-recognised disease, it is important that general practitioners and other primary health-care workers identify abnormal daytime sleepiness early.

Modafinil improves attention, inhibitory control, and reaction time in healthy, middle-aged rats

This study examined the effect of the novel psychostimulant modafinil (Provigil) on a variety of cognitive and behavioral measures including associative learning, sustained attention, inhibitory control, and reaction time. Middle-aged female rats (18-20 months old) were administered oral doses of modafinil (0, 8, 32, and 64 mg/kg) and tested in a 3-choice visual discrimination and sustained attention task. Modafinil produced a dose-dependent pattern of improved response accuracy and impulse control (fewer premature responses) and shorter response latencies, without affecting omission errors, motivation or motor control. Although the biochemical mechanism of modafinil is unknown, these results suggest a profile differing from typical psychostimulants (e.g., amphetamine). The implications of these findings for treatment of narcolepsy, ADHD, and various arousal-related disorders are considered. Further research is needed to examine the relative safety, effectiveness, and addictive potential of modafinil, as well as, its effects in comparison with other performance-enhancing drugs (e.g., caffeine, nicotine, and amphetamines).

Modafinil inhibits rat midbrain dopaminergic neurons through D2-like receptors

Modafinil is a well-tolerated medication for excessive sleepiness, attention-deficit disorder, cocaine dependence and as an adjunct to antidepressants with low propensity for abuse. We investigated the modafinil action on identified dopaminergic and GABAergic neurons in the ventral tegmental area (VTA) and substantia nigra (SN) of rat brain slices. Modafinil (20 microM) inhibited the firing of dopaminergic, but not GABAergic neurons. This inhibition was maintained in the presence of tetrodotoxin and was accompanied by hyperpolarization. Sulpiride (10 microM), a D2-receptor antagonist, but not prazosine (20 microM, an alpha1-adrenoreceptor blocker) abolished the modafinil action. Inhibition of dopamine reuptake with a low dose of nomifensine (1 microM) reduced the firing of DA neurons in a sulpiride-dependent manner and blunted the effect of modafinil. On acutely isolated neurons, modafinil evoked D2-receptor-mediated outward currents in tyrosine-hydroxylase positive cells, identified by single-cell RT-PCR, which reversed polarity near the K(+) equilibrium potential and were unchanged in the presence of nomifensine. Thus modafinil directly inhibits DA neurons through D2 receptors.

EFNS guidelines on management of narcolepsy

Management of narcolepsy with or without cataplexy relies on several classes of drugs, namely stimulants for excessive daytime sleepiness and irresistible episodes of sleep, antidepressants for cataplexy and hypnosedative drugs for disturbed nocturnal sleep. In addition, behavioral measures can be of notable value. Guidelines on the management of narcolepsy have already been published. However contemporary guidelines are necessary given the growing use of modafinil to treat excessive daytime sleepiness in Europe within the last 5-10 years, and the decreasing need for amphetamines and amphetamine-like stimulants; the extensive use of new antidepressants in the treatment of cataplexy, apart from consistent randomized placebo-controlled clinical trials; and the present re-emergence of gamma-hydroxybutyrate under the name sodium oxybate, as a treatment of all major symptoms of narcolepsy. A task force composed of the leading specialists of narcolepsy in Europe has been appointed. This task force conducted an extensive review of pharmacological and behavioral trials available in the literature. All trials were analyzed according to their class evidence. Recommendations concerning the treatment of each single symptom of narcolepsy as well as general recommendations were made. Modafinil is the first-line pharmacological treatment of excessive daytime sleepiness and irresistible episodes of sleep in association with behavioral measures. However, based on several large randomized controlled trials showing the activity of sodium oxybate, not only on cataplexy but also on excessive daytime sleepiness and irresistible episodes of sleep, there is a growing practice in the USA to use it for the later indications. Given the availability of modafinil and methylphenidate, and the forseen registration of sodium oxybate for narcolepsy (including excessive daytime sleepiness, cataplexy, disturbed nocturnal sleep) in Europe, the place of other compounds will become fairly limited. Since its recent registration cataplexy sodium oxybate has now become the first-line treatment of cataplexy. Second-line treatments are antidepressants, either tricyclics or newer antidepressants, the later being increasingly used these past years despite few or no randomized placebo-controlled clinical trials. As for disturbed nocturnal sleep the best option is still hypnotics until sodium oxybate is registered for narcolepsy. The treatments used for narcolepsy, either pharmacological or behavioral, are diverse. However the quality of the published clinical evidences supporting them varies widely and studies comparing the efficacy of different substances are lacking. Several treatments are used on an empirical basis, specially antidepressants for cataplexy, due to the fact that these medications are already used widely in depressed patients, leaving little motivation from the manufacturers to investigate efficacy in relatively rare indications. Others, in particular the more recently developed substances, such as modafinil or sodium oxybate, are evaluated in large randomized placebo-controlled trials. Our objective was to reinforce the use of those drugs evaluated in randomized placebo-controlled trials and to reach a consensus, as much as possible, on the use of other available medications.

Dog EEG for wake-promotion studies

Described in this unit is a protocol for investigating the wake-promoting activity of new chemical entities (NCEs) in dog. The experimental approach is based on scoring of sleep/wake stages in animals implanted with a telemetry device for recording EMG and cortical EEG signals. A major advantage of this procedure is that it is conducted in nontethered animals, limiting possible bias and complications encountered with conventional recording systems. In this procedure, polygraphic recording is conducted using four implanted beagles. Results of studies with modafinil, a wake-promoting agent, are described to demonstrate the utility of this test procedure.

A review of the use of modafinil for attention-deficit hyperactivity disorder

Modafinil (Provigil) is a novel wakefulness-promoting agent that has been shown to have greater efficacy than placebo in the treatment of attention-deficit hyperactivity disorder (ADHD) in children and adults. In particular, three large, drug-company sponsored trials of a film-coated formulation of modafinil (modafinil-ADHD; Sparlon) in children and adolescents with ADHD demonstrated consistent improvements in ADHD symptoms compared with placebo. Mean reductions in symptom ratings (measured using the ADHD-Rating Scale-IV school version questionnaire) ranged from 15.0 to 19.7 (7.3 to 10.1 for placebo). The most common adverse events were insomnia, headache and decreased appetite. Modafinil was generally well tolerated with most side effects considered mild to moderate in severity. Modafinil may have advantages over current therapies for ADHD in that it can be administered once daily and has fewer reinforcing properties than traditional stimulants. Modafinil could potentially be a valuable new treatment option for patients with ADHD. However, rigorous comparative studies with current first-line treatments for ADHD and longer-term independent studies are necessary before modafinil's role in the treatment of ADHD can be fully established.

Modafinil attenuates disruptions in cognitive performance during simulated night-shift work

Common complaints among shift workers are sleep disruptions and increased sleepiness while working, which may contribute to shift workers being more susceptible to diminished performance and work-related accidents. The purpose of this double-blind, within-participant study was to examine the effects of the alerting agent modafinil on cognitive/psychomotor performance, mood, and measures of sleep during simulated shift work. In all, 11 participants completed this 23-day residential laboratory study. They received a single oral modafinil dose (0, 200, 400 mg) 1 h after waking for three consecutive days under two shift conditions: day shift and night shift. Shifts alternated three times during the study, and shift conditions were separated by an 'off' day. When participants received placebo, cognitive performance and subjective ratings of mood were disrupted during the night shift, relative to the day shift. Objective and subjective measures of sleep were also disrupted, but to a lesser extent. Modafinil reversed disruptions in cognitive performance and mood during the night shift. While modafinil produced few effects on sleep measures during the night shift, the largest dose produced several sleep alterations during the day shift. These data demonstrate that abrupt shift changes produced cognitive performance impairments and mood disruptions during night shift work. Therapeutic doses of modafinil attenuated night-shift-associated disruptions, but the larger dose produced some sleep impairments when administered during day-shift work.

A randomized, double-blind, placebo-controlled study of modafinil film-coated tablets in children and adolescents with attention-deficit/hyperactivity disorder

OBJECTIVE

To evaluate the efficacy and tolerability of modafinil in children and adolescents, ages 7 to 17, with attention-deficit/hyperactivity disorder (ADHD).

METHOD

In this 9-week, double-blind, flexible-dose study, patients were randomized to once-daily modafinil (170-425 mg) or placebo. Assessments included ADHD Rating Scale-IV (ADHD-RS-IV) School and Home Versions and Clinical Global Impression of Improvement (CGI-I) scale.

RESULTS

Two hundred patients were randomized. Modafinil produced significant reductions in ADHD-RS-IV total scores at school (n = 128; mean change +/- SD: -17.5 +/- 13.1 points) compared with placebo (n = 66; -9.7 +/- 10.3 points; p < .0001). Similarly, modafinil reduced ADHD-RS-IV total scores at home compared with placebo (-17.6 +/- 13.3 versus -7.5 +/- 11.8 points; p < .0001). Fifty-two percent of patients randomized to modafinil and 18% of those randomized to placebo met prestudy criteria for responder on the CGI-I (p < .0001). Randomization to modafinil was associated with significantly more insomnia, headache, decreased appetite, and weight loss than randomization to placebo, but discontinuation attributed to adverse events did not differ statistically between treatment groups (modafinil, 5%; placebo, 6%).

CONCLUSION

Modafinil was well tolerated and reduced ADHD symptoms at school and home compared with placebo.

Modafinil: new indications for wake promotion

In January 2004, the wake-promoting agent, modafinil, was approved in the US for the treatment of excessive sleepiness (ES) associated with obstructive sleep apnoea/hypopnoea syndrome (OSAHS) and shift-work sleep disorder (SWSD), representing an expansion of its labelling from the initial indication for ES associated with narcolepsy. A total of five randomised, placebo-controlled studies in these three disorders showed statistically significant benefits on various objective measures and subjective estimates of ES, including the Multiple Sleep Latency Test, Maintenance of Wakefulness Test, Epworth Sleepiness Scale and Karolinska Sleepiness Scale. Significant improvement was also seen in overall clinical condition (on the Clinical Global Impression of Change) and measures of sustained attention and reaction time (on the Psychomotor Vigilance Task). The clinical efficacy of modafinil, combined with improved safety over CNS stimulants, has made it the most prescribed medication for the treatment of ES associated with narcolepsy. Modafinil is the only medication approved for ES associated with OSAHS and SWSD (for OSAHS, it is indicated as an adjunct to standard treatments for the under-lying obstruction). Unlike many other medications used for ES, modafinil is not known to be abused. The most common adverse event reported in clinical studies was headaches; most were transient and mild-to-moderate in severity. Modafinil also has the potential for interactions with other drugs metabolised via cytochrome P450 enzyme pathways. Potential obstacles to the use of modafinil include an under-recognition of ES and its consequences. Increased education, both of the public and the medical community, should improve the recognition and therapy of ES.

Molecular genetics and treatment of narcolepsy

Narcolepsy is a neurological disorder characterized by excessive daytime sleepiness and cataplexy. The hypocretin/orexin deficiency is likely to be the key to its pathophysiology in most of cases although the cause of human narcolepsy remains elusive. Acting on a specific genetic background, an autoimmune process targeting hypocretin neurons in response to yet unknown environmental factors is the most probable hypothesis in most cases of human narcolepsy with cataplexy. Although narcolepsy presents one of the tightest associations with a specific human leukocyte antigen (HLA) (DQB1*0602), there is strong evidence that non-HLA genes also confer susceptibility. In addition to a point mutation in the prepro-hypocretin gene discovered in an atypical case, a few polymorphisms in monoaminergic and immune-related genes have been reported associated with narcolepsy. The treatment of narcolepsy has evolved significantly over the last few years. Available treatments include stimulants for hypersomnia with the quite recent widespread use of modafinil, antidepressants for cataplexy, and gamma-hydroxybutyrate for both symptoms. Recent pilot open trials with intravenous immunoglobulins appear an effective treatment of cataplexy if applied at early stages of narcolepsy. Finally, the discovery of hypocretin deficiency might open up new treatment perspectives.

Sleep disturbances, psychiatric disorders, and psychotropic drugs

Brain neurotransmitter dysfunctions involved in the pathophysiological processes of psychiatric disorders are likely to be reflected by concomitant alterations in sleep continuity and architecture. Since the corrective effects of psychotropic drugs on dysfunctional neurotransmission systems can be evidenced through polysomnographic recordings, one may consider sleep as a kind of “window” on the neurobiology of psychiatric disorders. During the last 10 years, major breakthroughs in our understanding of sleep-wake mechanisms have provided some indications on how psychotropic drugs could influence the sleep-wake cycle. In this review, recent inroads into the understanding of sleep regulatory neural mechanisms are introduced and discussed in terms of the effects of psychotropic drugs. The relationship between the patho-physiological process of a disease, its consequence on sleep, and the corrective effect of a psychotropic drug are exemplified by two psychopathological states: substance withdrawal and major depression. One may conclude that polysomnographic recordings are a unique noninvasive tool to analyze brain functioning, and are particularly well suited to evaluating the objective effects of new psychotropic drugs.

Modafinil : a review of its use in excessive sleepiness associated with obstructive sleep apnoea/hypopnoea syndrome and shift work sleep disorder

Modafinil (Provigil is a wake-promoting agent that is pharmacologically distinct from CNS stimulants, such as amfetamine, dexamfetamine and methylphenidate. Modafinil is approved for use in the US and certain European countries for use in patients with excessive sleepiness associated with narcolepsy, obstructive sleep apnoea/hypopnoea syndrome (OSA/HS) or shift work sleep disorder (SWSD). Oral modafinil promotes wakefulness in patients with OSA/HS and SWSD. It is an effective adjunctive therapy in patients with residual excessive sleepiness associated with OSA/HS who are receiving nasal continuous positive airway pressure (nCPAP) therapy. In SWSD, the drug improves night-time wakefulness without disrupting daytime sleep. Modafinil is generally well tolerated in patients with OSA/HS or SWSD and has a low abuse potential. Thus, modafinil is a valuable new treatment option for use in patients with excessive sleepiness associated with OSA/HS (as an adjunct to nCPAP) or SWSD.

Dopaminergic modulation of arousal in Drosophila

BACKGROUND

Arousal levels in the brain set thresholds for behavior, from simple to complex. The mechanistic underpinnings of the various phenomena comprising arousal, however, are still poorly understood. Drosophila behaviors have been studied that span different levels of arousal, from sleep to visual perception to psychostimulant responses.

RESULTS

We have investigated neurobiological mechanisms of arousal in the Drosophila brain by a combined behavioral, genetic, pharmacological, and electrophysiological approach. Administration of methamphetamine (METH) suppresses sleep and promotes active wakefulness, whereas an inhibitor of dopamine synthesis promotes sleep. METH affects courtship behavior by increasing sexual arousal while decreasing successful sexual performance. Electrophysiological recordings from the medial protocerebrum of wild-type flies showed that METH ingestion has rapid and detrimental effects on a brain response associated with perception of visual stimuli. Recordings in genetically manipulated animals show that dopaminergic transmission is required for these responses and that visual-processing deficits caused by attenuated dopaminergic transmission can be rescued by METH.

CONCLUSIONS

We show that changes in dopamine levels differentially affect arousal for behaviors of varying complexity. Complex behaviors, such as visual perception, degenerate when dopamine levels are either too high or too low, in accordance with the inverted-U hypothesis of dopamine action in the mammalian brain. Simpler behaviors, such as sleep and locomotion, show graded responses that follow changes in dopamine level.

From waking to sleeping: neuronal and chemical substrates

Multiple arousal systems maintain waking through the actions of chemical neurotransmitters that are released from broadly distributed nerve terminals when the neurons fire. Among these, noradrenaline-, histamine- and orexin-containing neurons fire during waking with behavioral arousal, decrease firing during slow-wave sleep (SWS) and cease firing during paradoxical sleep (PS), which is also known as rapid-eye-movement sleep. By contrast, acetylcholine (ACh)-containing neurons discharge during waking, decrease firing during SWS and fire at high rates during PS in association with fast cortical activity. Neurons that do not contain ACh, including GABA-containing neurons in the basal forebrain and preoptic area, are active in a reciprocal manner to the neurons of the arousal systems: one group discharges with slow cortical activity during SWS, and another discharges with behavioral quiescence and loss of postural muscle tone during SWS and PS. The reciprocal activities and interactions of these wake-active and sleep-active cell groups determine the alternation between waking and sleeping. Selective enhancement and attenuation of their discharge, transmitter release and postsynaptic actions comprise the substrates for the major stimulant and hypnotic drugs.

Does modafinil activate the locus coeruleus in man? Comparison of modafinil and clonidine on arousal and autonomic functions in human volunteers

RATIONALE

Modafinil is a wakefulness-promoting drug which is likely to activate some wakefulness-promoting and/or inhibit sleep-promoting neurones in the brain. The locus coeruleus (LC) is a wakefulness-promoting noradrenergic nucleus whose activity can be "switched off" by the alpha2-adrenoceptor agonist clonidine, leading to sedative and sympatholytic effects.

OBJECTIVE

The aim of the study is to compare the effects of single doses of modafinil and clonidine on arousal and autonomic functions in human volunteers.

METHODS

Sixteen healthy male volunteers participated in four experimental sessions (modafinil 200 mg; clonidine 0.2 mg; modafinil 200 mg + clonidine 0.2 mg; placebo) at weekly intervals, according to a balanced double-blind protocol. Arousal [pupillary "fatigue waves" (PFW), critical flicker fusion frequency, self-ratings of alertness] and autonomic functions (pupil diameter, pupillary light and darkness reflex responses, blood pressure, heart rate, salivation) were recorded. Data were analyzed with ANOVA, with multiple comparisons.

RESULTS

Clonidine reduced subjective alertness, pupil diameter, the initial velocity and amplitude of the darkness reflex response, systolic and diastolic blood pressure and salivation, prolonged the recovery time of the light reflex response and increased PFW. Modafinil reduced PFW, increased pupil diameter and the initial velocity of the darkness reflex response and tended to reduce the effect of clonidine on pupil diameter and PFW. Modafinil had no effect on non-pupillary autonomic functions.

CONCLUSIONS

Clonidine exerted sympatholytic and sedative effects, whereas modafinil had sympathomimetic and some alerting effects. Modafinil may activate noradrenergic neurones in the LC involved in arousal and pupillary control, without affecting extracoerulear noradrenergic neurones involved in cardiovascular and salivary regulation.

Dopaminergic-adrenergic interactions in the wake promoting mechanism of modafinil

Adrenergic signaling regulates the timing of sleep states and sleep state-dependent changes in muscle tone. Recent studies indicate a possible role for noradrenergic transmission in the wake-promoting action of modafinil, a widely used agent for the treatment of excessive sleepiness. We now report that noradrenergic projections from the locus coeruleus to the forebrain are not necessary for the wake-promoting action of modafinil. The efficacy of modafinil was maintained after treatment of C57BL/6 mice with N-(2-chloroethyl)-N-ethyl 2-bromobenzylamine (DSP-4), which eliminates all noradrenaline transporter-bearing forebrain noradrenergic projections. However, the necessity for adrenergic receptors in the wake-promoting action of modafinil was demonstrated by the observation that the adrenergic antagonist terazosin suppressed the response to modafinil in DSP-4 treated mice. The wake-promoting efficacy of modafinil was also blunted by the dopamine autoreceptor agonist quinpirole. These findings implicate non-noradrenergic, dopamine-dependent adrenergic signaling in the wake-promoting mechanism of modafinil. The anatomical specificity of these dopaminergic-adrenergic interactions, which are present in forebrain areas that regulate sleep timing but not in brain stem areas that regulate sleep state-dependent changes in muscle tone, may explain why modafinil effectively treats excessive daytime sleepiness in narcolepsy but fails to prevent the loss of muscle tone that occurs in narcoleptic patients during cataplexy.

Modafinil: a novel stimulant for the treatment of narcolepsy

Excessive daytime sleepiness (EDS) is a common and debilitating symptom of narcolepsy and other sleep disorders. Modafinil is a novel stimulant which effectively treats EDS, yet lacks many of the undesirable side-effects commonly encountered with currently available compounds. The specific mode of action of modafinil is not well understood, but it may promote sleep by indirectly influencing adrenergic or GABAergic neurotransmission. Modafinil-induced wakefulness is not associated with rebound hypersomnolence or the potential for abuse as is often encountered with other stimulants such as amphetamines. At typical therapeutic doses, modafinil may produce dry mouth but generally has a low incidence of minor side-effects. Many preclinical and clinical studies have demonstrated the effectiveness of modafinil in promoting wakefulness and vigilance in normal subjects and in those with EDS. Modafinil significantly improves the EDS of narcolepsy and also may improve the EDS of idiopathic hypersomnia and obstructive sleep apnoea. Modafinil's low prevalence of side-effects, minimal potential for abuse, and lack of rebound hypersomnia indicate that it has potential to become a widely prescribed drug for the treatment of narcolepsy.

Narcolepsy and Disorders of Excessive Somnolence

Recent studies provide valid criteria that help differentiate idiopathic narcolepsy from other disorders of excessive daytime somnolence [3]. Research to date suggests that idiopathic narcolepsy might properly be considered a disorder of excessive sleepiness with dysfunctional REM-sleep mechanisms, clinically evidenced as cataplexy and electrophysiologically recognized as SOREMPs. Given these criteria, a diagnosis can generally be made using a combination of history, PSG, and MSLT. Traditionally, the medical treatment of idiopathic narcolepsy has centered on a two-drug regimen (stimulants for sleepiness and TCAs for cataplexy and auxiliary symptoms). Some newer medications are proving efficacious for sleepiness with minimal adverse effects, whereas others may provide a single-drug regimen that simultaneously addresses sleepiness and cataplexy [18]. New research has allowed some experts to hypothesize that idiopathic narcolepsy may be the result of a genetic predisposition to autoimmune disease [176]. It is possible that aberrant genetic coding of elements in the hypocretin/orexin systems allows a sensitivity to inducible and possibly virally mediated changes, which leave cells in the lateral hypothalamus susceptible to autoimmune attack [96]. As such, genetic screening of high-risk individuals might eventually rationalize the prophylactic use of immunosuppressants in some instances. In the future, for atypical cases(poorly responsive to therapy), genetic, CSF, and brain imaging studies, and possibly even neuronal transplantation may prove beneficial in the assessment and treatment of idiopathic narcolepsy.

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.

Effects of modafinil on working memory processes in humans

RATIONALE

Modafinil is a well-tolerated psychostimulant drug with low addictive potential that is used to treat patients with narcolepsy or attention deficit disorders and to enhance vigilance in sleep-deprived military personal. So far, understanding of the cognitive enhancing effects of modafinil and the relevant neurobiological mechanisms are incomplete.

OBJECTIVES

The aim of this study was to investigate the effects of modafinil on working memory processes in humans and how they are related to noradrenergic stimulation of the prefrontal cortex.

METHODS

Sixteen healthy volunteers (aged 20-29 years) received either modafinil 200 mg or placebo using a double blind crossover design. Two computerized working memory tasks were administered, a numeric manipulation task that requires short-term maintenance of digit-sequences and different degrees of manipulation as well as delayed matching task that assesses maintenance of visuo-spatial information over varying delay lengths. The battery was supplemented by standardized paper pencil tasks of attentional functions.

RESULTS

Modafinil significantly reduced error rates in the long delay condition of the visuo-spatial task and in the manipulation conditions, but not in the maintenance condition of the numeric task. Analyses of reaction times showed no speed-accuracy trade-off. Attentional control tasks (letter cancellation, trail-making, catch trials) were not affected by modafinil.

CONCLUSIONS

In healthy volunteers without sleep deprivation modafinil has subtle stimulating effects on maintenance and manipulation processes in relatively difficult and monotonous working memory tasks, especially in lower performing subjects. Overlapping attentional and working memory processes have to be considered when studying the noradrenergic modulation of the prefrontal cortex.

The effect of modafinil on counter-regulatory and cognitive responses to hypoglycaemia

AIMS/HYPOTHESIS

Our hypothesis is that reducing release of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) with modafinil will enhance symptomatic and hormonal responses to hypoglycaemia.

METHODS

Nine healthy men received, in random order, two 100-mg doses of modafinil or placebo, followed by an insulin clamp in which plasma glucose was either reduced stepwise to 2.4 mmol/l or was sustained at euglycaemia (four studies). Catecholamines, symptom scores and cognitive function were measured.

RESULTS

Modafinil had no effect on the measured parameters during euglycaemia. During hypoglycaemia, autonomic symptom scores were significantly higher with modafinil (increase at lowest plasma glucose concentration 271.3+/-118.9 vs 211.2+/-80.4/40 min, p=0.019), and the heart rate response was increased (12,928+/-184 vs 6773+/-148 bpm/140 min, p=0.016). Deterioration in performance of two cognitive tasks was reduced: Stroop colour-word test (613+/-204 vs 2375+/-161/65 min, p=0.009) and accuracy of a simple reaction task (11.3+/-1.8 vs 9.4+/-3.7, p=0.039).

CONCLUSIONS/INTERPRETATION

We conclude that modafinil improves adrenergic sensitivity and some aspects of cognitive function at hypoglycaemia, possibly by reducing neuronal central GABA concentrations.

Pharmacotherapy for excessive daytime sleepiness

Excessive daytime sleepiness (EDS) has recognized detrimental consequences such as road traffic accidents, impaired psychological functioning and reduced work performance. EDS can result from multiple causes such as sleep deprivation, sleep fragmentation, neurological, psychiatric and circadian rhythm disorders. Treating the underlying cause of EDS remains the mainstay of therapy but in those who continue to be excessively sleepy, further treatment may be warranted. Traditionally, the amphetamine derivatives, methylphenidate and pemoline (collectively sympathomimetic) psychostimulants were the commonest form of therapy for EDS, particularly in conditions such as narcolepsy. More recently, the advent of modafinil has broadened the range of therapeutic options. Modafinil has a safer side-effect profile and as a result, interest in this drug for the management of EDS in other disorders, as well as narcolepsy, has increased considerably. There is a growing school of thought that modafinil may have a role to play in other indications such as obstructive sleep apnea/hypopnea syndrome already treated by nasal continuous positive airway pressure but persisting EDS, shift work sleep disorders, neurological causes of sleepiness, and healthy adults performing sustained operations, particularly those in the military. However, until adequately powered randomised-controlled trials confirm long-term efficacy and safety, the recommendation of wakefulness promoters in healthy adults cannot be justified.

Enhancement of learning processes following an acute modafinil injection in mice

Modafinil is a wakeness-promoting drug, which is effective in the treatment of narcolepsy; its effects on learning processes are however little studied. Thus, the present study was aimed at determining the effects of an acute modafinil injection on a serial reversal discrimination task performed in a T-maze in mice. Independent groups of mice varying by the level of pretest training (either 1 or 4 days of training) were used. Mice were injected each day with a gum arabic solution before each session began. On the second or the fifth day of training, a single dose of modafinil was injected before testing. Modafinil at 64 mg/kg but not at 32 mg/kg dramatically improved performance as compared to controls in subjects being trained 4 days, but not in subjects being trained 1 day. This improvement of learning was due to the more rapid emergence of a win-stay strategy in modafinil-treated subjects as compare to controls. Thus, our data show that an acute modafinil injection enhances learning processes.

Modafinil improves cognition and attentional set shifting in patients with chronic schizophrenia

Modafinil, a novel cognitive enhancer, selectively improves neuropsychological task performance in healthy volunteers and adult patients with attention deficit hyperactivity disorder (ADHD). It has been argued that persistent cognitive deficits in patients with schizophrenia are responsible for the failure of many patients to rehabilitate socially even when psychotic symptoms are in remission. The present study examined the potential of modafinil as a cognitive enhancer in schizophrenia. Twenty chronic patients with a diagnosis of schizophrenia were entered into a double-blind, randomized, placebo-controlled crossover study using a 200 mg dose of modafinil. Modafinil had some cognitive enhancing properties in schizophrenia similar to those observed in healthy adults and adult patients with ADHD. Improvement was seen on short-term verbal memory span, with trends towards improved visual memory and spatial planning. This was accompanied by slowed response latency on the spatial planning task. No effect on stop-signal performance was seen. Importantly, significant improvement in attentional set shifting was seen, despite no effect of modafinil on this task being seen in healthy volunteers or ADHD patients. Modafinil may have potential as an important therapy for cognitive impairment in patients with schizophrenia, particularly because of its beneficial effects on attentional set shifting.

Brain inhibitory mechanisms involved in basic and higher integrated sleep processes

Brain function is supported by central activating processes that are significant during waking, decrease during slow wave sleep following waking and increase again during paradoxical sleep during which brain activation is as high as, or higher than, during waking in nearly all structures. However, inhibitory mechanisms are crucial for sleep onset. They were first identified by behavioral, neuroanatomical and electrophysiological criteria, then by pharmacological and neurochemical ones. During slow wave sleep, they are supported by GABAergic mechanisms located at midbrain, mesopontine and pontine levels but are induced and sustained by forebrain and hindbrain influences. GABAergic processes are also responsible for paradoxical sleep occurrence, particularly by suppression of noradrenaline and serotonin (5-HT) inhibition of paradoxical sleep-generating structures. Hindbrain and forebrain modulate these structures situated at the mesopontine level. For sleep mentation, the noradrenergic and serotonergic silence is thought, today, to be directly, or indirectly, responsible for dopamine predominance and glutamate decrease in the nucleus accumbens, which could be the background of the well-known psychotic-like mental activity of dreaming.

Modafinil improves cognition and response inhibition in adult attention-deficit/hyperactivity disorder

BACKGROUND

Modafinil, a novel cognitive enhancer, has a clinical profile similar to conventional stimulants such as methylphenidate, despite a seemingly different mechanism of action. Modafinil selectively improves neuropsychological task performance in healthy volunteers, possibly through improved inhibitory control. We examined whether modafinil induced similar improvements in adults with attention-deficit/hyperactivity disorder.

METHODS

Twenty patients with a DSM-IV diagnosis of attention-deficit/hyperactivity disorder were entered into a double-blind, randomized, placebo-controlled crossover study using a single 200 mg dose of modafinil.

RESULTS

Modafinil produced a similar pattern of cognitive enhancement to that observed in healthy adults, with improvements on tests of short-term memory span, visual memory, spatial planning, and stop-signal motor inhibition. On several measures, increased accuracy was accompanied by slowed response latency. This alteration in the speed-accuracy trade-off may indicate that modafinil increases the ability to "reflect" on problems coupled with decreased impulsive responding. Improvements were also seen in sustained attention, which was unaffected in healthy subjects.

CONCLUSIONS

If these benefits are shown to be maintained with chronic administration, modafinil may have potential as an important therapy for attention-deficit/hyperactivity disorder with a similar effect to stimulants such as methylphenidate in improving stop-signal response inhibition but without the side effects commonly experienced with amphetamine-like drugs.