Modafinil enhances extracellular levels of dopamine in the nucleus accumbens and increases wakefulness in rats

Pitolisant-supported bridging during drug holidays to deal with tolerance to modafinil in patients with narcolepsy

STUDY OBJECTIVES

Modafinil is a common treatment for excessive daytime sleepiness (EDS) in narcolepsy. The long-term use of modafinil can lead to tolerance with the loss of efficacy and the continuous increase of its dose. Pharmacological strategies to deal with the tolerance to modafinil are lacking. We investigated the efficacy and safety of pitolisant-supported bridging during drug holidays in patients with tolerance to modafinil.

METHODS

Narcolepsy patients on monotherapy with modafinil who developed symptoms of tolerance were eligible. The following alternating therapy regimen was established: Monday to Friday patients continued on modafinil whereas Saturday and Sunday they switched to pitolisant to "bridge" the EDS symptoms. Patients were assessed at baseline and after three months with the Epworth Sleepiness Scale (ESS) and the Ullanlinna Narcolepsy Scale (UNS). Health-related quality of life (HrQol) was evaluated by EuroQol5D. Adverse events were documented in the patients' diaries.

RESULTS

41 patients aged 30.9 ± 5.6 years were included. After three months of the alternating therapy regimen, the symptoms of tolerance decreased and the modafinil dose could be reduced by 41% (p < 0.01) resulting in better safety. The EDS improved on ESS (baseline: 18.2 ± 4.2, follow-up: 12.6 ± 4.0, p < 0.0001) and UNS (baseline: 25.8 ± 7.9, follow-up: 18.9 ± 5.9, p < 0.0001). The HrQol increased significantly.

CONCLUSION

Patients with tolerance to modafinil could benefit from pitolisant-supported bridging during drug holidays. This alternating pharmacological strategy proved to be safe and helped to reduce EDS and to decrease the modafinil dose. Further randomized controlled studies are required to evaluate the different strategies to deal with the tolerance to modafinil.

CLINICAL TRIAL REGISTRATION NUMBER

Clinical Trials.gov Identifier NCT05321355.

Modafinil, an atypical CNS stimulant?

Modafinil is a central nervous system stimulant approved for the treatment of narcolepsy and sleep disorders. Due to its wide range of biochemical actions, modafinil has been explored for other potential therapeutic uses. Indeed, it has shown promise as a therapy for cognitive disfunction resulting from neurologic disorders like ADHD, and as a smart drug in non-medical settings. The mechanism(s) of actions underlying the therapeutic efficacy of this agent remains largely elusive. Modafinil is known to inhibit the dopamine transporter, thus decreasing dopamine reuptake following neuronal release, an effect shared by addictive psychostimulants. However, modafinil is unique in that only a few cases of dependence on this drug have been reported, as compared to other psychostimulants. Moreover, modafinil has been tested, with some success, as a potential therapeutic agent to combat psychostimulant and other substance use disorders. Modafinil has additional, but less understood, actions on other neurotransmitter systems (GABA, glutamate, serotonin, norepinephrine, etc.). These interactions, together with its ability to activate selected brain regions, are likely one of the keys to understand its unique pharmacology and therapeutic activity as a CNS stimulant. In this chapter, we outline the pharmacokinetics and pharmacodynamics of modafinil that suggest it has an "atypical" CNS stimulant profile. We also highlight the current approved and off label uses of modafinil, including its beneficial effects as a treatment for sleep disorders, cognitive functions, and substance use disorders.

Atomoxetine promotes incentive value of modafinil and sensitizes exploratory behavior

Substance dependence is a disorder that alters the functioning of the nervous system due to frequent abuse of drugs. The role of dopamine in the addictive effect of psychostimulants is well known; however, the involvement of the noradrenergic system is still unclear and poorly understood, though drugs like cocaine and amphetamines are known to exert significant activity on this system. The drug modafinil (MOD) has no proven addictive effect. It promotes wakefulness by acting mainly on the dopaminergic system and, to a lesser degree, the noradrenergic (NOR) system. Atomoxetine (ATX) is a non-stimulant drug that acts only on the NOR system, enhancing its activity. The aims of the present study were to analyze the effect of co-activating the DA and NOR systems (with MOD and ATX, respectively) on motor activity and exploratory behavior, and to examine the possible emergence of rewarding properties of MOD and an MOD+ATX mixture. Male Wistar rats at postnatal day 60 were treated chronically (16 days) with either monotherapy with 2ATX, 4ATX, or 60MOD mg/kg, two combinations of these substances -60MOD + 2ATX and 60MOD + 4ATX- or a vehicle. The rats co-administered with 60MOD + 4ATX reduced the rearing behavior frequency induced by MOD, but this behavior was sensitized by self-administration of the MOD+ATX mixture after chronic treatment. The rats pre-treated with 60MOD + 4ATX showed higher self-administration of MOD and greater activity on an operant task to obtain the MOD+ATX mixture. In addition, the 60MOD, 2ATX, and 60MOD + 2ATX groups showed sensitization of exploratory behavior after ingesting the mixture. Results suggest that the noradrenergic system enhances the incentive value of MOD and a MOD+ATX mixture, while also playing an important role in the sensitization of exploratory behavior.

A multi-pronged investigation of option generation using depression, PET and modafinil

Option generation is a critical process in decision making, but previous studies have largely focused on choices between options given by a researcher. Consequently, how we self-generate options for behaviour remain poorly understood. Here, we investigated option generation in major depressive disorder and how dopamine might modulate this process, as well as the effects of modafinil (a putative cognitive enhancer) on option generation in healthy individuals. We first compared differences in self-generated options between healthy non-depressed adults [n = 44, age = 26.3 years (SD 5.9)] and patients with major depressive disorder [n = 54, age = 24.8 years (SD 7.4)]. In the second study, a subset of depressed individuals [n = 22, age = 25.6 years (SD 7.8)] underwent PET scans with 11C-raclopride to examine the relationships between dopamine D2/D3 receptor availability and individual differences in option generation. Finally, a randomized, double-blind, placebo-controlled, three-way crossover study of modafinil (100 mg and 200 mg), was conducted in an independent sample of healthy people [n = 19, age = 23.2 years (SD 4.8)] to compare option generation under different doses of this drug. The first study revealed that patients with major depressive disorder produced significantly fewer options [t(96) = 2.68, P = 0.009, Cohen's d = 0.54], albeit with greater uniqueness [t(96) = -2.54, P = 0.01, Cohen's d = 0.52], on the option generation task compared to healthy controls. In the second study, we found that 11C-raclopride binding potential in the putamen was negatively correlated with fluency (r = -0.69, P = 0.001) but positively associated with uniqueness (r = 0.59, P = 0.007). Hence, depressed individuals with higher densities of unoccupied putamen D2/D3 receptors in the putamen generated fewer but more unique options, whereas patients with lower D2/D3 receptor availability were likely to produce a larger number of similar options. Finally, healthy participants were less unique [F(2,36) = 3.32, P = 0.048, partial η2 = 0.16] and diverse [F(2,36) = 4.31, P = 0.021, partial η2 = 0.19] after taking 200 mg versus 100 mg and 0 mg of modafinil, while fluency increased linearly with dosage at a trend level [F(1,18) = 4.11, P = 0.058, partial η2 = 0.19]. Our results show, for the first time, that option generation is affected in clinical depression and that dopaminergic activity in the putamen of patients with major depressive disorder may play a key role in the self-generation of options. Modafinil was also found to influence option generation in healthy people by reducing the creativity of options produced.

Treatment of multiple sclerosis fatigue with the synthetic psychoactive drug modafinil

Multiple sclerosis (MS) is a complex disorder characterized by a broad spectrum of symptoms that evolve throughout the disease. Symptoms can be categorized as visible and invisible based on external sight recognition. However, although others poorly recognize it, invisible symptoms such as mood dysfunction, neuropathic pain, or fatigue can significantly affect activities of daily living and the quality of life of people with MS (PwMS). PwMS frequently complain of fatigue, which has physical or cognitive manifestations. Fatigue in MS does not improve or resolve with rest, and it is disproportionate with respect to the exerted effort. Fatigue management in MS is challenging, and a few pharmacological approaches have been successfully proposed. Among them, the drug modafinil has attracted attention because of its properties as a synthetic psychoactive drug. In this review, we focus on the evidence available to date, supporting the use of modafinil in MS fatigue. However, despite the availability of some trials evaluating the effects of modafinil on fatigue, their contrasting results failed to support its usefulness in fatigue management in MS.

Psychostimulant Use Disorder, an Unmet Therapeutic Goal: Can Modafinil Narrow the Gap?

The number of individuals affected by psychostimulant use disorder (PSUD) has increased rapidly over the last few decades resulting in economic, emotional, and physical burdens on our society. Further compounding this issue is the current lack of clinically approved medications to treat this disorder. The dopamine transporter (DAT) is a common target of psychostimulant actions related to their use and dependence, and the recent availability of atypical DAT inhibitors as a potential therapeutic option has garnered popularity in this research field. Modafinil (MOD), which is approved for clinical use for the treatment of narcolepsy and sleep disorders, blocks DAT just like commonly abused psychostimulants. However, preclinical and clinical studies have shown that it lacks the addictive properties (in both behavioral and neurochemical studies) associated with other abused DAT inhibitors. Clinical availability of MOD has facilitated its off-label use for several psychiatric disorders related to alteration of brain dopamine (DA) systems, including PSUD. In this review, we highlight clinical and preclinical research on MOD and its R-enantiomer, R-MOD, as potential medications for PSUD. Given the complexity of PSUD, we have also reported the effects of MOD on psychostimulant-induced appearance of several symptoms that could intensify the severity of the disease (i.e., sleep disorders and impairment of cognitive functions), besides the potential therapeutic effects of MOD on PSUD.

Modulating the immune response with the wake-promoting drug modafinil: A potential therapeutic approach for inflammatory disorders

Modafinil is a psychostimulant drug approved by the FDA primarily for the treatment of sleep disorders such as narcolepsy, excessive daytime sleepiness and sleep apnea. Several documented but not yet approved uses for modafinil have been described over the last 30 years, including alleviating fatigue in neurological and neurodegenerative disorders. Recent evidence has suggested that modafinil may have an immunomodulatory effect. Here, we review the different effects of modafinil treatment in animal models of brain inflammation and peripheral immune function. We conclude that there is unequivocal evidence of an anti-inflammatory effect of modafinil in experimental animal models of brain inflammation and neurodegenerative disorders, including systemic inflammation and methamphetamine-induced neuroinflammation, Parkinson's disease, brain ischemia, and multiple sclerosis. Modafinil acts on resident glial cells and infiltrating immune cells, negatively affecting both innate and adaptive immune responses in the brain. We also review the outcomes of modafinil treatment on peripheral immune function. The results of studies on this subject are still controversial and far from conclusive, but point to a new avenue of research in relation to peripheral inflammation. The data reviewed here raise the possibility of modafinil being used as adjuvant treatment for neurological disorders in which inflammation plays an important role.

Distinct effects of (R)-modafinil and its (R)- and (S)-fluoro-analogs on mesolimbic extracellular dopamine assessed by voltammetry and microdialysis in rats

Psychostimulant use disorders remain an unabated public health concern worldwide, but no FDA approved medications are currently available for treatment. Modafinil (MOD), like cocaine, is a dopamine reuptake inhibitor and one of the few drugs evaluated in clinical trials that has shown promise for the treatment of cocaine or methamphetamine use disorders in some patient subpopulations. Recent structure-activity relationship and preclinical studies on a series of MOD analogs have provided insight into modifications of its chemical structure that may lead to advancements in clinical efficacy. Here, we have tested the effects of the clinically available (R)-enantiomer of MOD on extracellular dopamine levels in the nucleus accumbens shell, a mesolimbic dopaminergic projection field that plays significant roles in various aspects of psychostimulant use disorders, measured in vivo by fast-scan cyclic voltammetry and by microdialysis in Sprague-Dawley rats. We have compared these results with those obtained under identical experimental conditions with two novel and enantiopure bis(F) analogs of MOD, JBG1-048 and JBG1-049. The results show that (R)-modafinil (R-MOD), JBG1-048, and JBG1-049, when administered intravenously with cumulative drug-doses, will block the dopamine transporter and reduce the clearance rate of dopamine, increasing its extracellular levels. Differences among the compounds in their maximum stimulation of dopamine levels, and in their time course of effects were also observed. These data highlight the mechanistic underpinnings of R-MOD and its bis(F) analogs as pharmacological tools to guide the discovery of novel medications to treat psychostimulant use disorders.

Dorsal Striatum Dopamine Levels Fluctuate Across the Sleep-Wake Cycle and Respond to Salient Stimuli in Mice

Dopamine is involved in numerous neurological processes, and its deficiency has been implicated in Parkinson’s disease, whose patients suffer from severe sleep disorders. Destruction of nigrostriatal dopaminergic neurons or dorsal striatum disrupts the sleep–wake cycle. However, whether striatal dopamine levels correlate with vigilance states still remains to be elucidated. Here, we employed an intensity-based genetically encoded dopamine indicator, dLight1.1, to track striatal dopamine levels across the spontaneous sleep–wake cycle and the dopaminergic response to external stimuli. We found that the striatal dLight1.1 signal was at its highest during wakefulness, lower during non-rapid eye movement (non-REM or NREM) sleep, and lowest during REM sleep. Moreover, the striatal dLight1.1 signal increased significantly during NREM sleep-to-wake transitions, while it decreased during wake-to-NREM sleep transitions. Furthermore, different external stimuli, such as sudden door-opening of the home cage or cage-change to a new environment, caused striatal dopamine release, whereas an unexpected auditory tone did not. Finally, despite both modafinil and caffeine being wake-promoting agents that increased wakefulness, modafinil increased striatal dopamine levels while caffeine did not. Taken together, our findings demonstrated that striatal dopamine levels correlated with the spontaneous sleep–wake cycle and responded to specific external stimuli as well as the stimulant modafinil.

Dopamine and Wakefulness: Pharmacology, Genetics, and Circuitry

Over the period of decades in the mid to late twentieth century, arousal-promoting functions were attributed to neuromodulators including serotonin, hypocretin, histamine, and noradrenaline. For some time, a relatively minor role in regulating sleep and wake states was ascribed to dopamine and the dopamine-producing cells of the ventral tegmental area, despite the fact that dopaminergic signaling is a major target, if not the primary target, for wake-promoting agents. In recent years, due to observations from human genetic studies, pharmacogenetic studies in animal models, and the increasingly sophisticated methods used to manipulate the nervous systems of experimental animals, it has become clear that dopaminergic signaling is central to the regulation of arousal. This chapter reviews this central role of dopaminergic signaling, and in particular its antagonistic interaction with adenosinergic signaling, in maintaining vigilance and in the response to wake-promoting therapeutics.

Characterization of the Neurochemical and Behavioral Effects of Solriamfetol (JZP-110), a Selective Dopamine and Norepinephrine Reuptake Inhibitor

Excessive sleepiness (ES) is associated with several sleep disorders, including narcolepsy and obstructive sleep apnea (OSA). A role for monoaminergic systems in treating these conditions is highlighted by the clinical use of US Food and Drug Administration-approved drugs that act on these systems, such as dextroamphetamine, methylphenidate, modafinil, and armodafinil. Solriamfetol (JZP-110) is a wake-promoting agent that is currently being evaluated to treat ES in patients with narcolepsy or OSA. Clinical and preclinical data suggest that the wake-promoting effects of solriamfetol differ from medications such as modafinil and amphetamine. The goal of the current studies was to characterize the mechanism of action of solriamfetol at monoamine transporters using in vitro and in vivo assays. Results indicate that solriamfetol has dual reuptake inhibition activity at dopamine (DA; IC₅₀ = 2.9 μM) and norepinephrine (NE; IC₅₀ = 4.4 μM) transporters, and this activity is associated in vivo with increased extracellular concentration of DA and NE as measured by microdialysis. Solriamfetol has negligible functional activity at the serotonin transporter (IC₅₀ > 100 μM). Moreover, the wake-promoting effects of solriamfetol are probably owing to activity at DA and NE transporters rather than other neurotransmitter systems, such as histamine or orexin. The dual activity of solriamfetol at DA and NE transporters and the lack of significant monoamine-releasing properties of solriamfetol might explain the differences in the in vivo effects of solriamfetol compared with modafinil or amphetamine. Taken together, these data suggest that solriamfetol may offer an important advancement in the treatment of ES in patients with narcolepsy or OSA.

Pleasure: The missing link in the regulation of sleep

Although largely unrecognized by sleep scholars, sleeping is a pleasure. This report aims first, to fill the gap: sleep, like food, water and sex, is a primary reinforcer. The levels of extracellular mesolimbic dopamine show circadian oscillations and mark the "wanting" for pro-homeostatic stimuli. Further, the dopamine levels decrease during waking and are replenished during sleep, in opposition to sleep propensity. The wanting of sleep, therefore, may explain the homeostatic and circadian regulation of sleep. Accordingly, sleep onset occurs when the displeasure of excessive waking is maximal, coinciding with the minimal levels of mesolimbic dopamine. Reciprocally, sleep ends after having replenished the limbic dopamine levels. Given the direct relation between waking and mesolimbic dopamine, sleep must serve primarily to gain an efficient waking. Pleasant sleep (i.e. emotional sleep), can only exist in animals capable of feeling emotions. Therefore, although sleep-like states have been described in invertebrates and primitive vertebrates, the association sleep-pleasure clearly marks a difference between the sleep of homeothermic vertebrates and cool blooded animals.

Excessive daytime sleepiness may be associated with caudate denervation in Parkinson disease

Excessive daytime sleepiness (EDS) is one of the earliest and most common non-motor symptoms of PD, substantially impacting on patient's quality of life. Using the Parkinson's Progression Markers Initiative database, we performed a case-control study to investigate whether dopaminergic deficit is associated with the development of EDS using dopaminergic specific single photon emission computed tomography (SPECT) molecular imaging of dopamine transporters (DAT). We enrolled 84 early de novo PD patients with EDS and 84 without EDS, who were matched for age, gender, age of diagnosis, years of education and disease duration. We assessed and compared semi-quantified [¹²³I]FP-CIT SPECT, and motor and non-motor features among these two groups, alongside exploring the clinical and imaging correlates of EDS and the predictive significance of these markers in the development of EDS. PD patients with EDS had worse non-motor (MDS-UPDRS Part-I, P < 0.001) and motor (MDS-UPRDS Part-II, P = 0.005) experiences of daily living, as well as worse autonomic (SCOPA-AUT, P < 0.0001) and cognitive (MoCA P = 0.05) function, depression (GDS, P = 0.002), and reduced caudate DAT ([¹²³I]FP-CIT, P = 0.024) compared to PD patients without EDS. Lower caudate [¹²³I]FP-CIT values correlated with higher EDS scores (r = -0.192, P = 0.013). Among patients without EDS, 47 PD patients (56%) developed EDS over a median follow-up of 36 months. Cox multivariate analysis, including all clinical and imaging data available, revealed that abnormal caudate [¹²³I]FP-CIT uptake (P = 0.030) and disease duration (P = 0.018) were predictors for the development of EDS. Although our findings indicate that dopaminergic deficits in the caudate may be associated to EDS in patients with PD, the pathophysiological causality is debateable, given that dopamine caudate denervation may covary with dopaminergic involvement at other targets and with non-dopaminergic involvement.

Modafinil enhances alerting-related brain activity in attention networks

RATIONALE

Modafinil is a wake-promoting agent and has been reported to be effective in improving attention in patients with attentional disturbance. However, neural substrates underlying the modafinil effects on attention are not fully understood.

OBJECTIVES

We employed a functional magnetic resonance imaging (fMRI) study with the attention network test (ANT) task in healthy adults and examined which networks of attention are mainly affected by modafinil and which neural substrates are responsible for the drug effects.

METHODS

We used a randomized placebo-controlled within-subjects cross-over design. Twenty-three healthy adults participated in two series of an fMRI study, taking either a placebo or modafinil. The participants performed the ANT task, which is designed to measure three distinct attentional networks, alerting, orienting, and executive control, during the fMRI scanning. The effects of modafinil on behavioral performance and regional brain activity were analyzed.

RESULTS

We found that modafinil enhanced alerting performance and showed greater alerting network activity in the left middle and inferior occipital gyri as compared with the placebo. The brain activations in the occipital regions were positively correlated with alerting performance.

CONCLUSIONS

Modafinil enhanced alerting performance and increased activation in the occipital lobe in the alerting network possibly relevant to noradrenergic activity during the ANT task. The present study may provide a rationale for the treatment of patients with distinct symptoms of impaired attention.

R-Modafinil exerts weak effects on spatial memory acquisition and dentate gyrus synaptic plasticity

Modafinil is a wake promoting drug approved for clinical use and also has cognitive enhancing properties. Its enantiomer R-Modafinil (R-MO) is not well studied in regard to cognitive enhancing properties. Hence we studied its effect in a spatial memory paradigm and its possible effects on dentate gyrus long-term potentiation (DG-LTP). Clinically relevant doses of R-MO, vehicle dimethyl sulfoxide (DMSO) or saline were administered for three days during the hole-board test and in in vivo DG-LTP. Synaptic levels of dopamine receptors D1R, D2R, dopamine transporter (DAT), and its phosphorylated form (ph-DAT) in DG tissue 4 h after LTP induction were quantified by western blot analysis. Monoamine reuptake and release assays were performed by using transfected HEK-293 cells. Possible neurotoxic side effects on general behaviour were also studied. R-MO at both doses significantly enhanced spatial reference memory during the last training session and during memory retrieval compared to DMSO vehicle but not when compared to saline treated rats. Similarly, R-MO rescues DG-LTP from impairing effects of DMSO. DMSO reduced memory performance and LTP magnitude when compared to saline treated groups. The synaptic DR1 levels in R-MO groups were significantly decreased compared to DMSO group but were comparable with saline treated animals. We found no effect of R-MO in neurotoxicity tests. Thus, our results support the notion that LTP-like synaptic plasticity processes could be one of the factors contributing to the cognitive enhancing effects of spatial memory traces. D1R may play an important regulatory role in these processes.

Sleep loss and recovery after administration of drugs related to different arousal systems in rats

Sleep is homeostatically regulated suggesting a restorative function. Sleep deprivation is compensated by an increase in length and intensity of sleep. In this study, suppression of sleep was induced pharmacologically by drugs related to different arousal systems. All drugs caused non-rapid eye movement (NREM) sleep loss followed by different compensatory processes. Apomorphine caused a strong suppression of sleep followed by an intense recovery. In the case of fluoxetine and eserine, recovery of NREM sleep was completed by the end of the light phase due to the biphasic pattern demonstrated for these drugs first in the present experiments. Yohimbine caused a long-lasting suppression of NREM sleep, indicating that either the noradrenergic system has the utmost strength among the examined systems, or that restorative functions occurring normally during NREM sleep were not blocked. Arousal systems are involved in the regulation of various wakefulness-related functions, such as locomotion and food intake. Therefore, it can be hypothesized that activation of the different systems results in qualitatively different waking states which might affect subsequent sleep differently. These differences might give some insight into the homeostatic function of sleep in which the dopaminergic and noradrenergic systems may play a more important role than previously suggested.

Role of N-Arachidonoyl-Serotonin (AA-5-HT) in Sleep-Wake Cycle Architecture, Sleep Homeostasis, and Neurotransmitters Regulation

The endocannabinoid system comprises several molecular entities such as endogenous ligands [anandamide (AEA) and 2-arachidonoylglycerol (2-AG)], receptors (CB₁ and CB₂), enzymes such as [fatty acid amide hydrolase (FAHH) and monoacylglycerol lipase (MAGL)], as well as the anandamide membrane transporter. Although the role of this complex neurobiological system in the sleep–wake cycle modulation has been studied, the contribution of the blocker of FAAH/transient receptor potential cation channel subfamily V member 1 (TRPV1), N-arachidonoyl-serotonin (AA-5-HT) in sleep has not been investigated. Thus, in the present study, varying doses of AA-5-HT (5, 10, or 20 mg/Kg, i.p.) injected at the beginning of the lights-on period of rats, caused no statistical changes in sleep patterns. However, similar pharmacological treatment given to animals at the beginning of the dark period decreased wakefulness (W) and increased slow wave sleep (SWS) as well as rapid eye movement sleep (REMS). Power spectra analysis of states of vigilance showed that injection of AA-5-HT during the lights-off period diminished alpha spectrum across alertness in a dose-dependent fashion. In opposition, delta power spectra was enhanced as well as theta spectrum, during SWS and REMS, respectively. Moreover, the highest dose of AA-5-HT decreased wake-related contents of neurotransmitters such as dopamine (DA), norepinephrine (NE), epinephrine (EP), serotonin (5-HT) whereas the levels of adenosine (AD) were enhanced. In addition, the sleep-inducing properties of AA-5-HT were confirmed since this compound blocked the increase in W caused by stimulants such as cannabidiol (CBD) or modafinil (MOD) during the lights-on period. Additionally, administration of AA-5-HT also prevented the enhancement in contents of DA, NE, EP, 5-HT and AD after CBD of MOD injection. Lastly, the role of AA-5-HT in sleep homeostasis was tested in animals that received either CBD or MOD after total sleep deprivation (TSD). The injection of CBD or MOD increased alertness during sleep rebound period after TSD. However, AA-5-HT blocked this effect by allowing animals to display an enhancement in sleep across sleep rebound period. Overall, our findings provide evidence that AA-5-HT is an important modulator of sleep, sleep homeostasis and neurotransmitter contents.

Modafinil decreases anxiety-like behaviour in zebrafish

Modafinil (2-((diphenylmethyl)sulfinyl)acetamide), a selective dopamine and norepinephrine transporter inhibitor, is most commonly prescribed for narcolepsy but has gained recent interest for treating a variety of disorders. Zebrafish (Danio rerio) are becoming a model of choice for pharmacological and behavioural research. To investigate the behavioural effects of modafinil on anxiety, we administered doses of 0, 2, 20, and 200 mg/L for 30 minutes then tested zebrafish in the novel approach test. In this test, the fish was placed into a circular arena with a novel object in the center and motion-tracking software was used to quantify the time the fish spent in the outer area of the arena (thigmotaxis zone), middle third of the arena (transition zone) and center of the arena, as well as total distance traveled, immobility and meandering. Modafinil caused a decrease in time spent in the thigmotaxis zone and increased time spent in the transition zone across all doses. Modafinil did not significantly alter the time spent in the center zone (near the novel object), the distance moved, meandering, or the duration of time spent immobile. We also validated this test as a measure of anxiety with the administration of ethanol (1%) which decreased time spent in the thigmotaxis zone and increased time spent in the transition zone. These results suggest that modafinil decreases anxiety-like behaviour in zebrafish.

Duration of activity and mode of action of modafinil: Studies on sleep and wakefulness in humans

The duration of activity of modafinil was investigated in healthy male volunteers in two double-blind crossover studies. Mode of action was explored using a statistical model concerned with the relationship between total sleep duration and that of rapid eye movement (REM) sleep. Nocturnal sleep (23:00-07:00) followed by next-day performance (09:00-17:00) was studied in 12 subjects administered 100, 200, 300 mg modafinil and placebo, 0.5 h before bedtime. Performance overnight (19:00-08:45) followed by sleep (09:15-15:15) was studied in nine subjects administered 100, 200, 300, 400 mg modafinil, 300 mg caffeine and placebo at 22:15. Modafinil dose-dependently reduced sleep duration (nocturnal: 200 mg, p<0.05; 300 mg, p<0.001; morning: 300 and 400 mg, p<0.05) and REM sleep (nocturnal: 300 mg; morning: 400 mg; p<0.05). The statistical model revealed that reduced REM sleep was due to alerting activity, with no evidence of direct suppression of REM sleep, suggesting dopaminergic activity. Enhanced performance with modafinil during overnight work varied with dose (200 mg>100 mg; 300, 400 mg>200, 100 mg, caffeine). However, in the study of next-day performance, the enhancement was attenuated at the highest dose (300 mg) by the greater disturbance of prior sleep. These findings indicate that modafinil has a long duration of action, with alerting properties arising predominantly from dopaminergic activity.

Drugs currently in Phase II clinical trials for cocaine addiction

INTRODUCTION

There are no FDA-approved pharmacotherapies for treating cocaine addiction; thus, developing drugs to treat cocaine dependence is an unmet critical need. Fortunately, there are a number of drugs that are currently in Phase II clinical trial/s. This is due in part to the advances from in vivo imaging in humans which provided a roadmap of the neurochemistry of the cocaine-dependent brain. Most drugs currently in Phase II clinical trials attempt to modulate the disturbed neurochemistry in cocaine dependents to resemble those of healthy individuals. These predominantly modulate dopamine, serotonin, glutamate, GABA or noradrenaline signalling.

AREAS COVERED

This review summarizes the therapeutic potential of each drug as evidenced by clinical and preclinical studies. It also discusses their utility in terms of bioavailability and half-life.

EXPERT OPINION

Amphetamine salts and topiramate clearly stand out in terms of their potential efficacy in treating cocaine addiction. The efficacy of topiramate was closely associated with regular cognitive-behavioural therapy (CBT), which highlights the importance of a combined effort to promote abstinence and enhance retention via CBT. Cognitive/psychological screening appears necessary for a more symptom-based approach with more reasonable outcomes other than abstinence (e.g., improved quality of life) in treating cocaine addiction.

Differences in the neurochemical and behavioural profiles of lisdexamfetamine methylphenidate and modafinil revealed by simultaneous dual-probe microdialysis and locomotor activity measurements in freely-moving rats

Lisdexamfetamine dimesylate is a novel prodrug approved in North America, Europe and Brazil for treating attention deficit hyperactivity disorder (ADHD). It undergoes rate-limited hydrolysis by red blood cells to yield d-amphetamine. Following our previous work comparing lisdexamfetamine with d-amphetamine, the neurochemical and behavioural profiles of lisdexamfetamine, methylphenidate and modafinil were compared by dual-probe microdialysis in the prefrontal cortex (PFC) and striatum of conscious rats with simultaneous locomotor activity measurement. We employed pharmacologically equivalent doses of all compounds and those that spanned the therapeutically relevant and psychostimulant range. Lisdexamfetamine (0.5, 1.5, 4.5 mg/kg d-amphetamine base, per os (po)), methylphenidate (3, 10, 30 mg/kg base, po) and modafinil (100, 300, 600 mg/kg base, po) increased efflux of dopamine and noradrenaline in PFC, and dopamine in striatum. Only lisdexamfetamine increased 5-hydroxytryptamine (5-HT) efflux in PFC and striatum. Lisdexamfetamine had larger and more sustained effects on catecholaminergic neurotransmission than methylphenidate or modafinil. Linear correlations were observed between striatal dopamine efflux and locomotor activity for lisdexamfetamine and methylphenidate, but not modafinil. Regression slopes revealed greater increases in extracellular dopamine could be elicited without producing locomotor activation by lisdexamfetamine than methylphenidate. These results are consistent with clinical findings showing that lisdexamfetamine is an effective ADHD medication with prolonged duration of action and good separation between its therapeutic actions and stimulant side-effects.

The neurobiology of modafinil as an enhancer of cognitive performance and a potential treatment for substance use disorders

RATIONALE AND OBJECTIVES

Modafinil (MOD) and its R-enantiomer (R-MOD) are approved medications for narcolepsy and other sleep disorders. They have also been used, off-label, as cognitive enhancers in populations of patients with mental disorders, including substance abusers that demonstrate impaired cognitive function. A debated nonmedical use of MOD in healthy individuals to improve intellectual performance is raising questions about its potential abuse liability in this population.

RESULTS AND CONCLUSIONS

MOD has low micromolar affinity for the dopamine transporter (DAT). Inhibition of dopamine (DA) reuptake via the DAT explains the enhancement of DA levels in several brain areas, an effect shared with psychostimulants like cocaine, methylphenidate, and the amphetamines. However, its neurochemical effects and anatomical pattern of brain area activation differ from typical psychostimulants and are consistent with its beneficial effects on cognitive performance processes such as attention, learning, and memory. At variance with typical psychostimulants, MOD shows very low, if any, abuse liability, in spite of its use as a cognitive enhancer by otherwise healthy individuals. Finally, recent clinical studies have focused on the potential use of MOD as a medication for treatment of drug abuse, but have not shown consistent outcomes. However, positive trends in several result measures suggest that medications that improve cognitive function, like MOD or R-MOD, may be beneficial for the treatment of substance use disorders in certain patient populations.

Effect of psychostimulants on impulsivity and risk taking in narcolepsy with cataplexy

OBJECTIVE

To investigate the effect of psychostimulants on impulsivity, depressive symptoms, addiction, pathological gambling, and risk-taking using objective sensitivity tests in narcolepsy with cataplexy (NC). Drug-free patients with NC present alterations in reward processing, but changes with psychostimulants remain unknown.

DESIGN

Prospective case-control study.

SETTING

Academic sleep disorders center.

PARTICIPANTS

There were 120 participants: 41 drug-free patients with NC, 37 patients with NC taking psychostimulants, and 42 matched healthy controls.

INTERVENTIONS

All participants underwent a semistructured clinical interview for impulse control and addictive behaviors and completed questionnaires for depression and impulsivity. Risk taking was analyzed through performance on a decision-making task under ambiguity (Iowa Gambling Task [IGT]) and under risk (Game of Dice Task [GDT]). All patients with NC underwent 1 night of polysomnography followed by a multiple sleep latency test for drug-free patients and a maintenance wakefulness test for treated patients.

RESULTS

Depressive symptoms were higher in drug-free patients than in treated patients and controls, with no difference between controls and treated patients. No between-group differences were found for impulsivity, substance addiction, or pathological gambling. Drug-free and treated patients showed selective reduced performance on the IGT and normal performance on the GDT compared with controls, with no differences between patients taking medication and those who did not. No clinical or polysomnographic characteristics or medication type was associated with IGT scores.

CONCLUSIONS

Our results demonstrated that, whether taking psychostimulants or not, patients with narcolepsy with cataplexy preferred risky choices on a decision-making task under ambiguity. However, the lack of association with impulsivity, pathological gambling, or substance addiction remains of major clinical interest in narcolepsy with cataplexy.

Role of the basal ganglia in the control of sleep and wakefulness

The basal ganglia (BG) act as a cohesive functional unit that regulates motor function, habit formation, and reward/addictive behaviors, but the debate has only recently started on how the BG maintain wakefulness and suppress sleep to achieve all these fundamental functions of the BG. Neurotoxic lesioning, pharmacological approaches, and the behavioral analyses of genetically modified animals revealed that the striatum and globus pallidus are important for the control of sleep and wakefulness. Here, we discuss anatomical and molecular mechanisms for sleep-wake regulation in the BG and propose a plausible model in which the nucleus accumbens integrates behavioral processes with wakefulness through adenosine and dopamine receptors.

The role of nucleus accumbens core/shell in sleep-wake regulation and their involvement in modafinil-induced arousal

Background

We have previously shown that modafinil promotes wakefulness via dopamine receptor D₁ and D₂ receptors; however, the locus where dopamine acts has not been identified. We proposed that the nucleus accumbens (NAc) that receives the ventral tegmental area dopamine inputs play an important role not only in reward and addiction but also in sleep-wake cycle and in mediating modafinil-induced arousal.

Methodology/Principal Findings

In the present study, we further explored the role of NAc in sleep-wake cycle and sleep homeostasis by ablating the NAc core and shell, respectively, and examined arousal response following modafinil administration. We found that discrete NAc core and shell lesions produced 26.5% and 17.4% increase in total wakefulness per day, respectively, with sleep fragmentation and a reduced sleep rebound after a 6-hr sleep deprivation compared to control. Finally, NAc core but not shell lesions eliminated arousal effects of modafinil.

Conclusions/Significance

These results indicate that the NAc regulates sleep-wake behavior and mediates arousal effects of the midbrain dopamine system and stimulant modafinil.

Interactions between modafinil and cocaine during the induction of conditioned place preference and locomotor sensitization in mice: implications for addiction

Modafinil is a wake-promoting drug effective at enhancing alertness and attention with a variety of approved and off-label applications. The mechanism of modafinil is not well understood but initial studies indicated a limited abuse potential. A number of recent publications, however, have shown that modafinil can be rewarding under certain conditions. The present study assessed the reinforcing properties of modafinil using conditioned place preference and locomotor sensitization in mice. Experiment 1 examined a high dose of modafinil (75 mg/kg) as well as its interactions with cocaine (15 mg/kg). Cocaine alone and modafinil co-administered with cocaine induced sensitization of locomotor activity; modafinil alone showed little or no locomotor sensitization. Animals given modafinil alone, cocaine alone, and modafinil plus cocaine exhibited a strong and roughly equivalent place preference. When tested for sensitization using a low challenge dose of modafinil, cross-sensitization was observed in all cocaine-pretreated mice. Experiment 2 examined a low dose of modafinil that is similar to the dose administered to humans and has been shown to produce cognitive enhancements in mice. Low dose modafinil (0.75 mg/kg) did not produce conditioned place preference or locomotor sensitization. Together, these results suggest that modafinil has the potential to produce reward, particularly in cocaine addicts, and should be used with caution. However, the typical low dose administered likely moderates these effects and may account for lack of addiction seen in humans.

Modafinil effects on cognition and emotion in schizophrenia and its neurochemical modulation in the brain

Modafinil is a central nervous system wake promoting agent used for the treatment of excessive daytime sleeping. Its vigilance promoting properties and low abuse potential has intrigued the scientific community and has led to use it as a cognitive enhancer, before its neural functions were understood. Here, we review the effects of modafinil in human cognition and emotion and its specific actions on symptoms in patients with schizophrenia and whether these are consistently effective throughout the literature. We also performed a systematic review on the effects of modafinil on neurotransmitter signalling in different areas of the brain in order to better understand the neuromechanisms of its cognitive and emotional enhancing properties. A review of its effects in schizophrenia suggests that modafinil facilitates cognitive functions, with pro-mnemonic effects and problem solving improvements. Emotional processing also appears to be enhanced by the drug, although to date there are only a limited number of studies. The systematic review on the neurochemical modulation of the modafinil suggests that its mnemonic enhancing properties might be the result of glutamatergic and dopaminergic increased neuronal activation in the hippocampus and in the prefrontal cortex respectively. Other neurotransmitters were also activated by modafinil in various limbic brain areas, suggesting that the drug acts on these brain regions to influence emotional responses. These reviews seek to delineate the neuronal mechanisms by which modafinil affects cognitive and emotional function. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Individual differences are critical in determining modafinil-induced behavioral sensitization and cross-sensitization with methamphetamine in mice

Modafinil is a non-amphetaminic psychostimulant used therapeutically for sleep and psychiatric disorders. However, some studies indicate that modafinil can have addictive properties. The present study examined whether modafinil can produce behavioral sensitization in mice, an experience and drug-dependent behavioral adaptation, and if individual differences play a role in this process. We further tested context-related factors and cross-sensitization between modafinil and methamphetamine. Important individual differences in the behavioral sensitization of Swiss Albino mice were observed after repeated administration of 50 mg/kg modafinil (Experiment 1), or 1 mg/kg methamphetamine (Experiment 2). Only mice classified as sensitized subgroup developed clear behavioral sensitization to the drugs. After a withdrawal period, mice received challenges of modafinil (Experiment 1), or methamphetamine (Experiment 2) and locomotor activity was evaluated in the activity cages (previous context) and in the open field arena (new context) in order to evaluate the context dependency of behavioral sensitization. The expression of sensitization to modafinil, but not to methamphetamine, was affected by contextual testing conditions, since modafinil-sensitized mice only expressed sensitization in the activity cage, but not in the open field. Subsequently, locomotor cross-sensitization between methamphetamine and modafinil was assessed by challenging modafinil-pretreated mice with 1mg/kg methamphetamine (Experiment 1), and methamphetamine-pretreated mice with 50mg/kg modafinil (Experiment 2). We observed a symmetrical cross-sensitization between the drugs only in those mice that were classified as sensitized subgroup. Our findings indicate that repeated exposure to modafinil induces behavioral sensitization only in some animals by similar neurobiological, but not contextual, mechanisms to those of methamphetamine.

Modulation of fronto-cortical activity by modafinil: a functional imaging and fos study in the rat

Modafinil (MOD) is a wake-promoting drug with pro-cognitive properties. Despite its increasing use, the neuronal substrates of MOD action remain elusive. In particular, animal studies have highlighted a putative role of diencephalic areas as primary neuronal substrate of MOD action, with inconsistent evidence of recruitment of fronto-cortical areas despite the established pro-cognitive effects of the drug. Moreover, most animal studies have employed doses of MOD of limited clinical relevance. We used pharmacological magnetic resonance imaging (phMRI) in the anesthetized rat to map the circuitry activated by a MOD dose producing clinically relevant plasma exposure, as here ascertained by pharmacokinetic measurements. We observed prominent and sustained activation of the prefrontal and cingulate cortex, together with weaker but significant activation of the somatosensory cortex, medial thalamic domains, hippocampus, ventral striatum and dorsal raphe. Correlation analysis of phMRI data highlighted enhanced connectivity within a neural network including dopamine projections from the ventral tegmental area to the nucleus accumbens. The pro-arousing effect of MOD was assessed using electroencephalographic recording under anesthetic conditions comparable to those used for phMRI, together with the corresponding Fos immunoreactivity distribution. MOD produced electroencephalogram desynchronization, resulting in reduced delta and increased theta frequency bands, and a pattern of Fos induction largely consistent with the phMRI study. Altogether, these findings show that clinically relevant MOD doses can robustly activate fronto-cortical areas involved in higher cognitive functions and a network of pro-arousing areas, which provide a plausible substrate for the wake-promoting and pro-cognitive effects of the drug.

Practical use and risk of modafinil, a novel waking drug

OBJECTIVES

Modafinil is a waking drug prescribed to narcolepsy patients, but its usage among healthy individuals is increasing to enhance their alertness or to mitigate fatigue. This study was conducted to investigate practical use and toxic effects on neuro-immune interaction of modafinil.

METHODS

This study reviewed the significance of psychoactive drugs, and discussed the benefits and risks of the application of modafinil, which seems to be ideal as an anti-psychotic or anti-fatigue agent.

RESULTS

Modafinil is known to have less or no adverse effects than those found in traditional psychostimulants such as amphetamine, methylphenidate or cocaine. It can be applied as an anti-psychotic or anti-fatigue agent. However, the waking mechanism of modafinil is yet to be fully revealed. Recent studies reported that modafinil may be subject to abuse and addiction. In addition prolonged sleeplessness induces stress responses and impairs immune function.

CONCLUSIONS

Modafinil can be used by anyone, who wishes to work late, stay awake, enhance their cognitive reactions, or brighten their moods. Users may already be under a great level of stress, i.e. cancer patients or soldiers in a battle field. A psychoneuroimmunological approach is thus needed to investigate the multi-functional effects of modafinil.

ADHD: current and future therapeutics

The stimulants, amphetamine and methylphenidate, have long been the mainstay of attention-deficit hyperactivity disorder (ADHD) therapy. They are rapidly effective and are generally the first medications selected by physicians. In the development of alternative pharmacological approaches, drug candidates have been evaluated with a wide diversity of mechanisms. All of these developments have contributed real progress in the field, but there is still much room for improvement and unmet clinical need in ADHD pharmacotherapy. The availability of a wide range of compounds with a high degree of specificity for individual monoamines (dopamine and noradrenaline) and/or different pharmacological mechanisms has refined our understanding of the essential elements for optimum pharmacological effect in managing ADHD. In this chapter, we review the pharmacology of the different classes of drug used to treat ADHD and provide a neurochemical rationale, predominantly from the use of in vivo microdialysis experiments, to explain their relative efficacy and potential to elicit side effects. In addition, we will consider how predictions based on results from animal models translate into clinical outcomes. The treatment of ADHD is also described from the perspective of the physician. Finally, the new research development for drugs to treat ADHD is discussed.

Addictive potential of modafinil and cross-sensitization with cocaine: a pre-clinical study

Repeated or even a single exposure to drugs of abuse can lead to persistent locomotor sensitization, which is the result of an abundance of neuroplastic changes occurring within the circuitry involved in motivational behavior and is thought to play a key role in certain aspects of drug addiction. There is substantial controversy about the addictive potential of modafinil, a wake-promoting drug used to treat narcolepsy that is increasingly being used as a cognitive enhancer and has been proposed as a pharmacotherapy for cocaine dependence. Male mice were used to investigate the ability of modafinil to induce locomotor sensitization after repeated or single administration in mice. Bidirectional cross-sensitization with cocaine and modafinil-induced conditioned place preference were also evaluated. Both repeated and single exposure to moderate and high doses of modafinil produced a pronounced locomotor sensitization that cross-sensitized in a bidirectional way with cocaine. Remarkably, when cocaine and modafinil were repeatedly administered sequentially, their behavioral sensitization was additive. Supporting these behavioral sensitization data, modafinil produced a pronounced conditioned place preference in the mouse. Taken together, the present findings provide pre-clinical evidence for the addictive potential of modafinil. Our data also strongly suggest that similar neural substrates are involved in the psychomotor/rewarding effects of modafinil and cocaine.

Complex movement disorders at disease onset in childhood narcolepsy with cataplexy

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

Infusion of modafinil into anterior hypothalamus or pedunculopontine tegmental nucleus at different time-points enhances waking and blocks the expression of recovery sleep in rats after sleep deprivation

Clinical studies have indicated that the primary pharmacological activity of modafinil (MOD) is inducing wakefulness; however, the brain targets that underlie its wake-promoting activity have not been described. In the present study, we show that MOD injected into sleep-wake related brain areas promoted alertness. If administered (10, 20, or 30 μg/1 μL) into either anterior hypothalamus (AH) or pedunculopontine tegmental nucleus (PPTg) at 08:00, 12:00 or 16:00 h, MOD enhanced wakefulness whereas diminished slow wave sleep as well as rapid eye movement sleep. In addition, microinjection of MOD (10, 20, or 30 μg/1 μL) either into AH or PPTg after total sleep deprivation prevented the sleep rebound. Taken together, these observations suggest that AH and PPTg play a key role in the wake-inducing effects of MOD and encourage further experimentation to draw a possible mechanism of action.

Effects of modafinil on emotional processing in first episode psychosis

BACKGROUND

Emotional impairments are important determinants of functional outcome in psychosis, and current treatments are not particularly effective. Modafinil is a wake-promoting drug that has been shown to improve emotion discrimination in healthy individuals and attention and executive function in schizophrenia. We aimed to establish whether modafinil might have a role in the adjuvant treatment of emotional impairments in the first episode of psychosis, when therapeutic endeavor is arguably most vital.

METHODS

Forty patients with a first episode of psychosis participated in a randomized, double-blind, placebo-controlled crossover design study testing the effects of a single dose of 200 mg modafinil on neuropsychological performance. Emotional functions were evaluated with the emotional face recognition test, the affective go-no go task, and the reward and punishment learning test. Visual analogue scales were used throughout the study to assess subjective mood changes.

RESULTS

Modafinil significantly improved the recognition of sad facial expressions (z = 2.98, p = .003). In contrast, there was no effect of modafinil on subjective mood ratings, on tasks measuring emotional sensitivity to reward or punishment, or on interference of emotional valence on cognitive function, as measured by the affective go-no go task.

CONCLUSIONS

Modafinil improves the analysis of emotional face expressions. This might enhance social function in people with a first episode of psychosis.

The safety of modafinil in combination with oral ∆9-tetrahydrocannabinol in humans

Marijuana (cannabis) is the most widely used illicit substance globally, and cannabis use is associated with a range of adverse consequences. Currently, no medications have been proven to be effective for the treatment of cannabis addiction. The goals of this study were to examine the safety and efficacy of a potential treatment medication, modafinil, in combination with oral ∆9-tetrahydrocannabinol (THC). Twelve male and female occasional cannabis users participated in an outpatient double-blind, placebo-controlled, crossover study. Across four sessions, participants were randomly assigned to a sequence of four oral treatments: (1) 400 mg modafinil+placebo, (2) 15 mg THC+placebo, (3) 400 mg modafinil+15 mg THC, or (4) placebo+placebo. Outcome measures included heart rate, blood pressure, performance on the Rapid Visual Information Processing (RVIP), and the Hopkins Verbal Learning Test (HVLT), and subjective measures. Oral THC increased heart rate, and produced increased subjective ratings of feeling "high" and "sedated," as well as increased ratings of euphoria. Modafinil alone increased the Profiles of Mood States (POMS) subscales of vigor and tension. These findings support the safety of modafinil in combination with THC. The effects of modafinil in combination with a range of doses of THC need to be determined in future studies.

Modafinil reduces microsleep during partial sleep deprivation in depressed patients

OBJECTIVE

Sleep deprivation (SD) can induce a prompt decrease in depressive symptoms within 24h. Following the recovery night, however, a relapse into depression occurs in most patients. Recovery sleep, naps and even very short episodes of sleep (microsleep; MS) during SD have been shown to provoke a rapid relapse into depression. This study tested the hypothesis that modafinil reduces MS during SD and stabilizes the treatment response to PSD compared to placebo.

METHODS

A total of 28 patients (13 men, 15 women; age 45.1+/-12.1 years) with a major depressive episode and a cumulative daytime microsleep of five or more minutes were investigated using a double-blind placebo-controlled study design. All patients were treated with a stable mirtazapine monotherapy. A partial SD (PSD) was performed after one week. Additional morning treatment with modafinil vs. placebo started during PSD and was maintained over two weeks. Sleep-EEG and MS episodes were recorded with a portable EEG. Depression severity was assessed using the Hamilton Depression Rating Scale before, during and after PSD and at follow-ups after one and two weeks.

RESULTS

Patients treated with modafinil showed significantly reduced microsleep during PSD (11.63+/-15.99 min) compared to the placebo group (47.77+/-65.31 min). This suppression of MS was not associated with the antidepressive effect of PSD.

CONCLUSIONS

Compared to placebo, modafinil was efficient in reducing daytime microsleep following partial sleep deprivation but did not enhance the antidepressive effects of PSD and did not stabilize antidepressive effects over two weeks.

Modanifil activates the histaminergic system through the orexinergic neurons

Modafinil is a drug used to treat hypersomnolence of narcolepsy. We previously reported that modafinil increases hypothalamic histamine release in rats but did not increase locomotor activity in histamine-depleted mice, suggesting that modafinil-induced locomotor activity involves the histaminergic system. Modafinil is also thought to express its effect through the orexinergic neurons, and orexin increases hypothalamic histamine release. These findings led us to investigate whether modafinil activates the histaminergic system via the orexinergic system. In the present study, we performed in vivo microdialysis and c-Fos immunohistochemistry to investigate whether the orexinergic system mediates the activation of the histaminergic system by modafinil using orexin neuron-deficient mice. Two hours after the injection, modafinil (150 mg/kg) caused a significant increase of histamine release compared to the basal release in wild type mice. However, modafinil had no effect on the histamine release in orexin neuron-deficient mice. By immunohistochemical study, we found that there was no neuronal activation in the tuberomammillary nucleus where the cell bodies of the histaminergic neurons exclusively exist in orexin neuron-deficient mice. These findings indicate that modafinil-induced increment of histamine release requires intact orexinergic neurons.

Essential role of dopamine D2 receptor in the maintenance of wakefulness, but not in homeostatic regulation of sleep, in mice

Dopamine (DA) and its D(2) receptor (R) are involved in cognition, reward processing, and drug addiction. However, their roles in sleep-wake regulation remain unclear. Herein we investigated the role of D(2)R in sleep-wake regulation by using D(2)R knock-out (KO) mice and pharmacological manipulation. Compared with WT mice, D(2)R KO mice exhibited a significant decrease in wakefulness, with a concomitant increase in non-rapid eye movement (non-REM, NREM) and REM sleep and a drastic decrease in the low-frequency (0.75-2 Hz) electroencephalogram delta power of NREM sleep, especially during the first 4 h after lights off. The KO mice had decreased mean episode duration and increased episode numbers of wake and NREM sleep, many stage transitions between wakefulness and NREM sleep during the dark period, suggesting the instability of the wake stage in these D(2)R KO mice. When the KO mice were subjected to a cage change or an intraperitoneal saline injection, the latency to sleep in the KO mice decreased to half of the level for WT mice. The D(2)R antagonist raclopride mimicked these effects in WT mice. When GBR12909, a dopamine transport inhibitor, was administered intraperitoneally, it induced wakefulness in WT mice in a dose-dependent manner, but its arousal effect was attenuated to one-third in the D(2)R KO mice. However, these 2 genotypes showed an identical response in terms of sleep rebound after 2, 4, and 6 h of sleep deprivation. These results indicate that D(2)R plays an essential role in the maintenance of wakefulness, but not in homeostatic regulation of NREM sleep.

Receptor-Based Discovery of a Plasmalemmal Monoamine Transporter Inhibitor via High Throughput Docking and Pharmacophore Modeling

Recognition of psychostimulants such as cocaine and the amphetamines by the dopamine transporter (DAT) protein is principally responsible for the euphoria and addiction associated with these drugs. Using as a template the crystal structure of a distantly related bacterial leucine transporter, 3-D DAT computer molecular models have been generated. Ligand docking to such models has revealed potential substrate and inhibitor binding pockets, subsequently confirmed by in vitro pharmacology. An inhibitor pocket defined by the DAT model to be within the "extracellular vestibule", just to the extracellular side of the external gate of the primary substrate pocket, was used for virtual screening of a structural library of compounds. High-throughput docking and application of pharmacophore constraints within this vestibular inhibitor pocket identified a compound structurally dissimilar to the classic monoamine (dopamine, norepinephrine and serotonin) transporter (MAT) inhibitors. The compound displaced binding of radiolabeled cocaine analogs at all three MATs, usually with nanomolar K(i) values and within two fold of cocaine's affinity at the norepinephrine transporter. Although a very weak dopamine uptake inhibitor itself, this compound reduced by three fold the potency of cocaine in inhibiting DAT-mediated cellular uptake of dopamine. To our knowledge, the present findings are the first to successfully employ "receptor-based" computer modeling to identify moderate-to-high affinity MAT ligands. In silico ligand screening using MAT models provides a rapid, low cost discovery process that should accelerate identification of novel ligand scaffolds and provide lead compounds in combating psychostimulant addiction and in treating other monoamine-related CNS diseases.