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

The Issue of "Smart Drugs" on the Example of Modafinil: Toxicological Analysis of Evidences and Biological Samples

Cognitive enhancement through stimulants such as modafinil is becoming increasingly popular, with many individuals using prescription stimulants for non-medical purposes to improve alertness, attention, and mood. The misuse of such substances has raised concerns, particularly in forensic toxicology. The UHPLC-QqQ-MS/MS method was developed to quantify modafinil in evidentiary samples and biological materials. Additionally, the authors noted the presence of sodium adducts during the analysis of samples with high concentrations of modafinil. The method was validated for accuracy, precision, and linearity, with a concentration range of 0.1-10.0 µg/mL for the evidences and 1.0-100.0 ng/mL for blood. The method successfully detected modafinil as the sole substance in all evidences, with concentrations ranging from 90.7 to 120.8 mg, corresponding to 45.5% to 80.5% of the labeled dose. The method was applied to real post-mortem human cases, where, among others, the concentration of modafinil in blood was 110 ng/mL, whereas, in another case, the concentration of modafinil in the putrefaction fluid exceeded 1000 ng/mL. The developed UHPLC-QqQ-MS/MS method is effective for the quantification of modafinil in evidentiary samples and biological materials, offering a reliable tool for forensic toxicology applications. This method can be used to evaluate modafinil use in both legal and illicit contexts, including cases of overdose or misuse.

Contrasting the reinforcing effects of the novel dopamine transport inhibitors JJC8-088 and JJC8-091 in monkeys: Potential translation to medication assisted treatment

Despite considerable efforts, there remains no Food and Drug Administration-approved medications for cocaine use disorder. One strategy to mitigate cocaine craving and relapse is to elevate dopamine. The dopamine transport inhibitor and releaser d-amphetamine has been shown to decrease cocaine self-administration (SA), although it has abuse liability. Recently, several modafinil analogs reduced cocaine SA in rats and monkeys, including JJC8-088, characterized as "cocaine-like" in rats, and JJC8-091, characterized as "atypical" and not SA by rats. The present study evaluated the reinforcing effects of both compounds in monkeys under several conditions. For experiment 1, 4 male cocaine-experienced rhesus monkeys self-administered cocaine (0.001-0.3 mg/kg per injection), JJC8-088 (0.001-0.3 mg/kg per injection), and JJC8-091 (0.1-3.0 mg/kg per injection) under a progressive-ratio schedule of reinforcement. Both JJC compounds functioned as reinforcers with equal reinforcing strength to cocaine. Although JJC8-091 was less potent than cocaine, JJC8-088 and cocaine had similar potencies. For experiment 2, 1 male and 2 female drug-naïve cynomolgus monkeys responded on a fixed-ratio schedule of food reinforcement. JJC8-091 was self-administered at rates higher than saline in all 3 monkeys. In experiment 3, monkeys from experiment 2 responded under a concurrent drug versus food choice paradigm and given access to cocaine or JJC8-091 under these conditions. At doses equal to or one-half log-units higher than doses used in experiment 2, cocaine, but not JJC8-091, was chosen over food. Together, these results demonstrate that although JJC8-091 may be reinforcing under some conditions, its reinforcing strength, in the presence of an alternative reinforcer, is substantially less than cocaine. SIGNIFICANCE STATEMENT: JJC8-088 and JJC8-091 have shown efficacy is reducing cocaine self-administration (SA) in rats and in nonhuman primates. This study found that both compounds maintained SA in monkeys responding under several conditions. However, when given access to an alternative reinforcer during the SA session, JJC8-091 was not reinforcing, suggesting that JJC8-091 may have lower abuse liability than cocaine and may be a viable candidate for cocaine use disorder because, in the human population, alternatives to drug use are often available.

Armodafinil as Monotherapy in Treating Narcolepsy with Cataplexy

In narcolepsy with cataplexy, sodium oxybate and the recently FDA-approved drug pitolisant are preferred medications. Armodafinil, a longer-acting, non-amphetamine stimulant, is often used in patients who have narcolepsy without cataplexy. It enhances alertness by increasing presynaptic dopamine transmission presynaptically, amplifying serotonin in the cerebral cortex, activating glutamatergic circuits, which may contribute to its vigilance-enhancing properties, and stimulating orexin activity. Armodafinil alone is approved for excessive daytime sleepiness (EDS) symptoms. We report this case of narcolepsy with cataplexy, where armodafinil alone improved the symptoms of not only EDS but also cataplexy. It is known that sodium oxybate, through its gamma-aminobutyric acid type B (GABA-B) receptor agonist activity, helps in cataplexy and EDS. However, in some instances, like this patient, armodafinil alone improves the symptoms of cataplexy and maintains wakefulness.

Modulation of Cerebellar-Cortical Connectivity Induced by Modafinil and Its Relationship With Receptor and Transporter Expression

BACKGROUND

Modafinil is primarily used to treat narcolepsy but is also used as an off-label cognitive enhancer. Functional magnetic resonance imaging studies indicate that modafinil modulates the connectivity of neocortical networks primarily involved in attention and executive functions. However, much less is known about the drug's effects on subcortical structures. Following preliminary findings, we evaluated modafinil's activity on the connectivity of distinct cerebellar regions with the neocortex. We assessed the spatial relationship of these effects with the expression of neurotransmitter receptors/transporters.

METHODS

Patterns of resting-state functional magnetic resonance imaging connectivity were estimated in 50 participants from scans acquired pre- and postadministration of a single (100 mg) dose of modafinil (n = 25) or placebo (n = 25). Using specific cerebellar regions as seeds for voxelwise analyses, we examined modafinil's modulation of cerebellar-neocortical connectivity. Next, we conducted a quantitative evaluation of the spatial overlap between the modulation of cerebellar-neocortical connectivity and the expression of neurotransmitter receptors/transporters obtained by publicly available databases.

RESULTS

Modafinil increased the connectivity of crus I and vermis IX with prefrontal regions. Crus I connectivity changes were associated with the expression of dopaminergic D2 receptors. The vermis I-II showed enhanced coupling with the dorsal anterior cingulate cortex and matched the expression of histaminergic H3 receptors. The vermis VII-VIII displayed increased connectivity with the visual cortex, an activity associated with dopaminergic and histaminergic neurotransmission.

CONCLUSIONS

Our study reveals modafinil's modulatory effects on cerebellar-neocortical connectivity. The modulation mainly involves crus I and the vermis and spatially overlaps the distribution of dopaminergic and histaminergic receptors.

Effects of chronic stress on cognitive function - From neurobiology to intervention

Exposure to chronic stress contributes considerably to the development of cognitive impairments in psychiatric disorders such as depression, generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and addictive behavior. Unfortunately, unlike mood-related symptoms, cognitive impairments are not effectively treated by available therapies, a situation in part resulting from a still incomplete knowledge of the neurobiological substrates that underly cognitive domains and the difficulty in generating interventions that are both efficacious and safe. In this review, we will present an overview of the cognitive domains affected by stress with a specific focus on cognitive flexibility, behavioral inhibition, and working memory. We will then consider the effects of stress on neuronal correlates of cognitive function and the factors which may modulate the interaction of stress and cognition. Finally, we will discuss intervention strategies for treatment of stress-related disorders and gaps in knowledge with emerging new treatments under development. Understanding how cognitive impairment occurs during exposure to chronic stress is crucial to make progress towards the development of new and effective therapeutic approaches.

Series of (([1,1'-Biphenyl]-2-yl)methyl)sulfinylalkyl Alicyclic Amines as Novel and High Affinity Atypical Dopamine Transporter Inhibitors with Reduced hERG Activity

Currently, there are no FDA-approved medications for the treatment of psychostimulant use disorders (PSUD). We have previously discovered "atypical" dopamine transporter (DAT) inhibitors that do not display psychostimulant-like behaviors and may be useful as medications to treat PSUD. Lead candidates (e.g., JJC8-091, 1) have shown promising in vivo profiles in rodents; however, reducing hERG (human ether-à-go-go-related gene) activity, a predictor of cardiotoxicity, has remained a challenge. Herein, a series of 30 (([1,1'-biphenyl]-2-yl)methyl)sulfinylalkyl alicyclic amines was synthesized and evaluated for DAT and serotonin transporter (SERT) binding affinities. A subset of analogues was tested for hERG activity, and the IC50 values were compared to those predicted by our hERG QSAR models, which showed robust predictive power. Multiparameter optimization scores (MPO > 3) indicated central nervous system (CNS) penetrability. Finally, comparison of affinities in human DAT and its Y156F and Y335A mutants suggested that several compounds prefer an inward facing conformation indicating an atypical DAT inhibitor profile.

Prescription psychostimulants for the treatment of amphetamine-type stimulant use disorder: A systematic review and meta-analysis of randomized placebo-controlled trials

BACKGROUND AND AIMS

There is currently no standard of care for pharmacological treatment of amphetamine-type stimulant (ATS) use disorder (ATSUD). This systematic review with meta-analysis (PROSPERO CRD42022354492) aimed to pool results from randomized placebo-controlled trials (RCTs) to evaluate efficacy and safety of prescription psychostimulants (PPs) for ATSUD.

METHODS

Major indexing sources and trial registries were searched to include records published before 29 August 2022. Eligible studies were RCTs evaluating efficacy and safety of PPs for ATSUD. Risk of bias (RoB) was assessed using the Cochrane RoB 2 tool. Risk ratio (RR) and risk difference were calculated for random-effect meta-analysis of dichotomous variables. Mean difference and standardized mean difference (SMD) were calculated for random-effect meta-analysis of continuous variables.

RESULTS

Ten RCTs (n = 561 participants) were included in the meta-analysis. Trials studied methylphenidate (n = 7), with daily doses of 54-180 mg, and dextroamphetamine (n = 3), with daily doses of 60-110 mg, for 2-24 weeks. PPs significantly decreased end-point craving [SMD  -0.29; 95% confidence interval (CI) = -0.55, -0.03], while such a decrease did not reach statistical significance for ATS use, as evaluated by urine analysis (UA) (RR = 0.93; 95% CI = 0.85-1.01). No effect was observed for self-reported ATS use, retention in treatment, dropout following adverse events, early-stage craving, withdrawal and depressive symptoms. In a sensitivity analysis, treatment was associated with a significant reduction in UA positive for ATS (RR = 0.89; 95% CI = 0.79-0.99) after removing studies with a high risk of bias. In subgroup analyses, methylphenidate and high doses of PPs were negatively associated with ATS use by UA, while higher doses of PPs and treatment duration (≥ 20 weeks) were positively associated with longer retention.

CONCLUSIONS

Among individuals with amphetamine-type stimulant use disorder, treatment with prescription psychostimulants may decrease ATS use and craving. While effect size is limited, it may increase with a higher dosage of medications.

Modifications to 1-(4-(2-Bis(4-fluorophenyl)methyl)sulfinyl)alkyl Alicyclic Amines That Improve Metabolic Stability and Retain an Atypical DAT Inhibitor Profile

Atypical dopamine transporter (DAT) inhibitors have shown therapeutic potential in the preclinical models of psychostimulant use disorders (PSUD). In rats, 1-(4-(2-((bis(4-fluorophenyl)methyl)sulfinyl)ethyl)-piperazin-1-yl)-propan-2-ol (JJC8-091, 3b) was effective in reducing the reinforcing effects of both cocaine and methamphetamine but did not exhibit psychostimulant behaviors itself. Improvements in DAT affinity and metabolic stability were desirable for discovering pipeline drug candidates. Thus, a series of 1-(4-(2-bis(4-fluorophenyl)methyl)sulfinyl)alkyl alicyclic amines were synthesized and evaluated for binding affinities at DAT and the serotonin transporter (SERT). Replacement of the piperazine with either a homopiperazine or a piperidine ring system was well tolerated at DAT (Ki range = 3-382 nM). However, only the piperidine analogues (20a-d) showed improved metabolic stability in rat liver microsomes as compared to the previously reported analogues. Compounds 12b and 20a appeared to retain an atypical DAT inhibitor profile, based on negligible locomotor activity in mice and molecular modeling that predicts binding to an inward-facing conformation of DAT.

Selenium alleviates modafinil-induced neurobehavioral toxicity in rat via PI3K/Akt/mTOR/GSK3B signaling pathway and suppression of oxidative stress and apoptosis: in vivo and in silico study

Nonmedical use of modafinil (MOD) led to increased rates of overdose toxicity, road accidents, addiction, withdrawal, suicide, and mental illnesses. The current study aims to determine the probable MOD brain toxicity and elucidate the possible role of selenium (Se) in ameliorating the neurotoxicity in rat models. Fifty-four male Albino rats were randomly assigned into nine groups. The groups were G1 (control negative), G2 (Se0.1), G3 (Se0.2), G4 (MOD300), G5 (MOD600), G6 (Se0.1 + MOD300), G7 (Se0.2 + MOD300), G8 (Se0.1 + MOD600), and G9 (Se0.2 + MOD600). After finishing the experiment, blood and brain tissue were harvested for biochemical and histological investigation. Neurobehavior parameters were assessed. Tissue neurotransmitter levels and oxidative stress markers were assessed. Gene expression of PI3K/Akt/mTOR-GSK3B, orexin, and orexin receptor2 was measured by qRT-PCR. Histological and immunohistochemistry assessments, as well as molecular docking, were carried out. MOD-induced neurobehavioral toxicity exhibited by behavioral and cognitive function impairments, which are associated with decreased antioxidant activities, increased MDA levels, and decreases in neurotransmitter levels. Brain levels of mRNA expression of PI3K, Akt, and mTOR were decreased, while GS3K, orexin, and orexin receptors were significantly elevated. These disturbances were confirmed by histopathological brain changes with increased silver and Bax immunostaining and decreased crystal violet levels. MOD induced neurotoxic effects in a dose-dependent manner. Compared with the MOD groups, SE coadministration significantly attenuates MOD-induced toxic changes. Docking study shows the protective role of Se as an apoptosis inhibitor and inflammation inhibitor. In conclusion, Se could be used as a biologically effective antioxidant compound to protect from MOD neurobehavioral toxicity in Wistar rats by reversing behavioral alterations, inflammation, apoptosis, and oxidative injury.

The Atypical Dopamine Transporter Inhibitor CE-158 Enhances Dopamine Neurotransmission in the Prefrontal Cortex of Male Rats: A Behavioral, Electrophysiological, and Microdialysis Study

BACKGROUND

Dopamine plays a key role in several physiological functions such as motor control, learning and memory, and motivation and reward. The atypical dopamine transporter inhibitor S,S stereoisomer of 5-(((S)-((S)-(3-bromophenyl)(phenyl)methyl)sulfinyl)methyl)thiazole (CE-158) has been recently reported to promote behavioral flexibility and restore learning and memory in aged rats.

METHODS

Adult male rats were i.p. administered for 1 or 10 days with CE-158 at the dose of 1 or 10 mg/kg and tested for extracellular dopamine in the medial prefrontal cortex by means of intracerebral microdialysis and single unit cell recording in the same brain area. Moreover, the effects of acute and chronic CE-158 on exploratory behavior, locomotor activity, prepulse inhibition, working memory, and behavioral flexibility were also investigated.

RESULTS

CE-158 dose-dependently potentiated dopamine neurotransmission in the medial prefrontal cortex as assessed by intracerebral microdialysis. Moreover, repeated exposure to CE-158 at 1 mg/kg was sufficient to increase the number of active pyramidal neurons and their firing frequency in the same brain area. In addition, CE-158 at the dose of 10 mg/kg stimulates exploratory behavior to the same extent after acute or chronic treatment. Noteworthy, the chronic treatment at both doses did not induce any behavioral alterations suggestive of abuse potential (e.g., motor behavioral sensitization) or pro-psychotic-like effects such as disruption of sensorimotor gating or impairments in working memory and behavioral flexibility as measured by prepulse inhibition and Y maze.

CONCLUSIONS

Altogether, these findings confirm CE-158 as a promising pro-cognitive agent and contribute to assessing its preclinical safety profile in a chronic administration regimen for further translational testing.

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.

Are There Prevalent Sex Differences in Psychostimulant Use Disorder? A Focus on the Potential Therapeutic Efficacy of Atypical Dopamine Uptake Inhibitors

Psychostimulant use disorders (PSUD) affect a growing number of men and women and exert sizable public health and economic burdens on our global society. Notably, there are some sex differences in the onset of dependence, relapse rates, and treatment success with PSUD observed in preclinical and clinical studies. The subtle sex differences observed in the behavioral aspects of PSUD may be associated with differences in the neurochemistry of the dopaminergic system between sexes. Preclinically, psychostimulants have been shown to increase synaptic dopamine (DA) levels and may downregulate the dopamine transporter (DAT). This effect is greatest in females during the high estradiol phase of the estrous cycle. Interestingly, women have been shown to be more likely to begin drug use at younger ages and report higher levels of desire to use cocaine than males. Even though there is currently no FDA-approved medication, modafinil, a DAT inhibitor approved for use in the treatment of narcolepsy and sleep disorders, has shown promise in the treatment of PSUD among specific populations of affected individuals. In this review, we highlight the therapeutic potential of modafinil and other atypical DAT inhibitors focusing on the lack of sex differences in the actions of these agents.

The Effects of the Dopamine Transporter Ligands JJC8-088 and JJC8-091 on Cocaine versus Food Choice in Rhesus Monkeys

Although there are no Food and Drug Administration-approved treatments for cocaine use disorder, several modafinil analogs have demonstrated promise in reducing cocaine self-administration and reinstatement in rats. Furthermore, the range of dopamine transporter (DAT) compounds provides an opportunity to develop pharmacotherapeutics without abuse liability. This study extended the comparison of JJC8-088 and JJC8-091, the former compound having higher DAT affinity and predicted abuse liability, to rhesus monkeys using a concurrent cocaine versus food schedule of reinforcement. First, binding to striatal DAT was examined in cocaine-naïve monkey tissue. Next, intravenous pharmacokinetics of both JJC compounds were evaluated in cocaine-experienced male monkeys (n = 3/drug). In behavioral studies, acute and chronic administration of both compounds were evaluated in these same monkeys responding under a concurrent food versus cocaine (0 and 0.003-0.1 mg/kg per injection) schedule of reinforcement. In nonhuman primate striatum, JJC8-088 had higher DAT affinity compared with JJC8-091 (14.4 ± 9 versus 2730 ± 1270 nM, respectively). Both JJC compounds had favorable plasma pharmacokinetics for behavioral assessments, with half-lives of 1.1 hours and 3.5 hours for JJC8-088 (0.7 mg/kg, i.v.) and JJC8-091 (1.9 mg/kg, i.v.), respectively. Acute treatment with both compounds shifted the cocaine dose-response curve to the left. Chronic treatment with JJC8-088 decreased cocaine choice in two of the three monkeys, whereas JJC8-091 only modestly reduced cocaine allocation in one monkey. Differences in affinities of JJC8-091 DAT binding in monkeys compared with rats may account for the poor rodent-to-monkey translation. Future studies should evaluate atypical DAT blockers in combination with behavioral interventions that may further decrease cocaine choice. SIGNIFICANCE STATEMENT: Cocaine use disorder (CUD) remains a significant public health problem with no Food and Drug Administration-approved treatments. The ability of drugs that act in the brain in a similar manner to cocaine, but with lower abuse liability, has clinical implications for a treatment of CUD.

A Novel and Selective Dopamine Transporter Inhibitor, (S)-MK-26, Promotes Hippocampal Synaptic Plasticity and Restores Effort-Related Motivational Dysfunctions

Dopamine (DA), the most abundant human brain catecholaminergic neurotransmitter, modulates key behavioral and neurological processes in young and senescent brains, including motricity, sleep, attention, emotion, learning and memory, and social and reward-seeking behaviors. The DA transporter (DAT) regulates transsynaptic DA levels, influencing all these processes. Compounds targeting DAT (e.g., cocaine and amphetamines) were historically used to shape mood and cognition, but these substances typically lead to severe negative side effects (tolerance, abuse, addiction, and dependence). DA/DAT signaling dysfunctions are associated with neuropsychiatric and progressive brain disorders, including Parkinson’s and Alzheimer diseases, drug addiction and dementia, resulting in devastating personal and familial concerns and high socioeconomic costs worldwide. The development of low-side-effect, new/selective medicaments with reduced abuse-liability and which ameliorate DA/DAT-related dysfunctions is therefore crucial in the fields of medicine and healthcare. Using the rat as experimental animal model, the present work describes the synthesis and pharmacological profile of (S)-MK-26, a new modafinil analogue with markedly improved potency and selectivity for DAT over parent drug. Ex vivo electrophysiology revealed significantly augmented hippocampal long-term synaptic potentiation upon acute, intraperitoneally delivered (S)-MK-26 treatment, whereas in vivo experiments in the hole-board test showed only lesser effects on reference memory performance in aged rats. However, in effort-related FR5/chow and PROG/chow feeding choice experiments, (S)-MK-26 treatment reversed the depression-like behavior induced by the dopamine-depleting drug tetrabenazine (TBZ) and increased the selection of high-effort alternatives. Moreover, in in vivo microdialysis experiments, (S)-MK-26 significantly increased extracellular DA levels in the prefrontal cortex and in nucleus accumbens core and shell. These studies highlight (S)-MK-26 as a potent enhancer of transsynaptic DA and promoter of synaptic plasticity, with predominant beneficial effects on effort-related behaviors, thus proposing therapeutic potentials for (S)-MK-26 in the treatment of low-effort exertion and motivational dysfunctions characteristic of depression and aging-related disorders.

Modafinil Administration to Preadolescent Rat Impairs Non-Selective Attention, Frontal Cortex D2 Expression and Mesolimbic GABA Levels

The misuse of psychostimulants is an increasing behavior among young people, highlighting in some countries the abuse of modafinil (MOD) as a neuropotentiator. However, several clinical trials are investigating MOD as an alternative pharmacological treatment for attentional deficit and hyperactivity disorder (ADHD) in children and adolescents. On the other hand, the early use of psychostimulants and the misdiagnosis rates in ADHD make it crucial to investigate the brain effects of this type of drug in young healthy individuals. The aim of this work was to evaluate the effects of chronic MOD treatment on neurochemicals (γ-aminobutyric acid and glutamate), dopamine receptor 2 (D₂) expression and behavior (non-selective attention "NSA") in the mesocorticolimbic system of young healthy Sprague-Dawley rats. Preadolescent male rats were injected with MOD (75 mg/kg, i.p.) or a vehicle for 14 days (from postnatal day 22 to 35). At postnatal day 36, we measured the GLU and GABA contents and their extracellular levels in the nucleus accumbens (NAc). In addition, the GLU and GABA contents were measured in the ventral tegmental area (VTA) and D₂ protein levels in the prefrontal cortex (PFC). Chronic use of MOD during adolescence induces behavioral and neurochemical changes associated with the mesocorticolimbic system, such as a reduction in PFC D₂ expression, VTA GABA levels and NSA. These results contribute to the understanding of the neurological effects of chronic MOD use on a young healthy brain.

Benefits and Harms of 'Smart Drugs' (Nootropics) in Healthy Individuals

'Smart drugs' (also known as 'nootropics' and 'cognitive enhancers' [CEs]) are being used by healthy subjects (i.e. students and workers) typically to improve memory, attention, learning, executive functions and vigilance, hence the reference to a 'pharmaceutical cognitive doping behaviour'. While the efficacy of known CEs in individuals with memory or learning deficits is well known, their effect on non-impaired brains is still to be fully assessed. This paper aims to provide an overview on the prevalence of use; putative neuroenhancement benefits and possible harms relating to the intake of the most popular CEs (e.g. amphetamine-type stimulants, methylphenidate, donepezil, selegiline, modafinil, piracetam, benzodiazepine inverse agonists, and unifiram analogues) in healthy individuals. CEs are generally perceived by the users as effective, with related enthusiastic anecdotal reports; however, their efficacy in healthy individuals is uncertain and any reported improvement temporary. Conversely, since most CEs are stimulants, the related modulation of central noradrenaline, glutamate, and dopamine levels may lead to cardiovascular, neurological and psychopathological complications. Furthermore, use of CEs can be associated with paradoxical short- and long-term cognitive decline; decreased potential for plastic learning; and addictive behaviour. Finally, the non-medical use of any potent psychotropic raises serious ethical and legal issues, with nootropics having the potential to become a major public health concern. Further studies investigating CE-associated social, psychological, and biological outcomes are urgently needed to allow firm conclusions to be drawn on the appropriateness of CE use in healthy individuals.

Modafinil Does Not Reduce Cocaine Use in Methadone-Maintained Individuals

Introduction

There are no approved medications for the treatment of cocaine use disorder (CUD). Modafinil, a cognitive-enhancer with weak stimulant-like effects, has shown promise in initial studies as a treatment for CUD. Its potential efficacy has not been examined in individuals dually dependent on cocaine and opioids.

Methods

This study examined the efficacy of modafinil, in combination with contingency management (CM), for reducing cocaine and opioid use and improving cognitive function in methadone-stabilized individuals with opioid and cocaine dependence. We conducted a 17-week, double-blind, randomized controlled trial in which participants were randomized to one of four conditions: 1) modafinil + CM; 2) modafinil + yoked-control (YC); 3) placebo +CM; or 4) placebo + YC. Additionally, all subjects received platform treatments of cognitive behavioral therapy (CBT) and methadone. While the original planned sample size was N=160, a total of 91 participants were randomized. The two primary cocaine use outcomes were percentage of urine specimens positive for cocaine and percent of days of self-reported abstinence from cocaine during treatment. Cognitive function, opioid use, and secondary cocaine use outcomes were also considered.

Results

Modafinil was well-tolerated with minimal reports of adverse effects. Modafinil was no more effective than placebo in reducing cocaine or opioid use or improving cognitive performance.

Conclusions

In the context of a trial with robust control conditions and platform treatments, findings did not provide support for the efficacy of modafinil treatment for the treatment of CUD in methadone-stabilized individuals with dual opioid and cocaine dependence.

Modafinil rescues repeated morphine-induced synaptic and behavioural impairments via activation of D1R-ERK-CREB pathway in medial prefrontal cortex

Long-term opioid abuse causes a variety of long-lasting cognitive impairments such as attention, impulsivity and working memory. These cognitive impairments undermine behavioural treatment for drug abuse and lead to poor treatment retention and outcomes. Modafinil is a wake-promoting drug that shows potential in improving attention and memory in humans and animals. However, modafinil's effect on opioid-induced cognitive impairments remains unclear, and the underlying mechanism is poorly understood. This study showed that repeated morphine administration significantly impairs attention, increases impulsivity and reduces motivation to natural rewards in mice. Systemic modafinil treatment at low dose efficiently ameliorates morphine-induced attention dysfunction and improves motivation and working memory in mice. High dose of modafinil has adverse effects on impulsive action and attention. Local infusion of D1R antagonist SCH-23390 reverses the morphine-induced synaptic abnormalities and activation of the D1R-ERK-CREB pathway in medial prefrontal cortex (mPFC). This study demonstrated a protective effect of modafinil in mPFC neurons and offered a therapeutic potential for cognitive deficits in opioid abuse.

Analgesic and anti-inflammatory effects of modafinil in a mouse model of neuropathic pain: A role for nitrergic and serotonergic pathways

OBJECTIVES

To evaluate the effects of modafinil on neuropathic pain induced by sciatic nerve cuffing in mice, and possible contribution of nitrergic/inflammatory and serotonergic systems.

METHODS

Neuropathic pain was induced by applying a polyethylene cuff around the left sciatic nerve. Seven days later, mice received modafinil (50, 100, and 200 mg/kg; intraperitoneal [i.p.]) and morphine (10 mg/kg, i.p.) as control. Mice also received pretreatments of the nonselective nitric oxide (NO) synthase (NOS) inhibitor L-NAME, the selective neuronal NOS inhibitor 7-nitroindazole, the selective inducible NOS inhibitor aminoguanidine, and the selective serotonin reuptake inhibitor citalopram before modafinil (100 mg/kg). von Frey test was used to evaluate mechanical allodynia. Additionally, sciatic nerves were collected for histopathological analysis. Tissue levels of NO metabolites, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 were assessed.

RESULTS

Animals whose sciatic nerves were cuffed had a significantly (P<0.001) decreased paw withdrawal threshold (PWT) compared with the sham-operated group. Modafinil (100 mg/kg) and morphine significantly reversed PWT (P<0.001). Pretreatments with L-NAME, 7-nitroindazole, aminoguanidine, and citalopram in different groups markedly reversed analgesic effects of modafinil. Tissue homogenates of Cuffed sciatic nerves showed significantly higher levels of NO metabolites, TNF-α and IL-6 (P<0.001). Modafinil lowered NO metabolites, TNF-α, and IL-6 levels (P<0.001). Histopathology illustrated marked axonal degeneration and shrinkage in the cuffed sciatic nerve, which were improved in the modafinil-treated group.

CONCLUSIONS

Modafinil exerts analgesic and neuroprotective effects in cuff-induced neuropathic mice via possible involvement of the nitrergic/inflammatory and serotonergic systems.

Combined electrochemistry and mass spectrometry imaging to interrogate the mechanism of action of modafinil, a cognition-enhancing drug, at the cellular and sub-cellular level

Modafinil is a mild psychostimulant-like drug enhancing wakefulness, improving attention and developing performance in various cognitive tasks, but its mechanism of action is not completely understood. This is the first combination of amperometry, electrochemical cytometry and mass spectrometry to interrogate the mechanism of action of a drug, here modafinil, at cellular and sub-cellular level. We employed single-cell amperometry (SCA) and intracellular vesicle impact electrochemical cytometry (IVIEC) to investigate the alterations in exocytotic release and vesicular catecholamine storage following modafinil treatment. The SCA results reveal that modafinil slows down the exocytosis process so that, the number of catecholamines released per exocytotic event is enhanced in the modafinil-treated cells. Also, IVIEC results offer an upregulation effect of modafinil on the vesicular catecholamine storage. Mass spectrometry imaging by time-of-flight secondary ion mass spectrometry (ToF-SIMS) illustrates that treatment with modafinil reduces the cylindrical-shaped phosphatidylcholine at the cellular membrane, while the high curvature lipids with conical structures such as phosphatidylethanolamine and phosphatidylinositol are elevated after modafinil treatment. Combining the results obtained by SCA, IVIEC and ToF-SIMS suggests that modafinil-treated cells release a larger portion of their vesicular content at least in part by changing the lipid composition of the cell membrane, suggesting regulation of cognition.

Drug Repurposing: A Network-based Approach to Amyotrophic Lateral Sclerosis

The continuous adherence to the conventional "one target, one drug" paradigm has failed so far to provide effective therapeutic solutions for heterogeneous and multifactorial diseases as amyotrophic lateral sclerosis (ALS), a rare progressive and chronic, debilitating neurological disease for which no cure is available. The present study is aimed at finding innovative solutions and paradigms for therapy in ALS pathogenesis, by exploiting new insights from Network Medicine and drug repurposing strategies. To identify new drug-ALS disease associations, we exploited SAveRUNNER, a recently developed network-based algorithm for drug repurposing, which quantifies the proximity of disease-associated genes to drug targets in the human interactome. We prioritized 403 SAveRUNNER-predicted drugs according to decreasing values of network similarity with ALS. Among catecholamine, dopamine, serotonin, histamine, and GABA receptor modulators, as well as angiotensin-converting enzymes, cyclooxygenase isozymes, and serotonin transporter inhibitors, we found some interesting no customary ALS drugs, including amoxapine, clomipramine, mianserin, and modafinil. Furthermore, we strengthened the SAveRUNNER predictions by a gene set enrichment analysis that confirmed modafinil as a drug with the highest score among the 121 identified drugs with a score > 0. Our results contribute to gathering further proofs of innovative solutions for therapy in ALS pathogenesis.

Nicotine and modafinil combination protects against the neurotoxicity induced by 3,4-Methylenedioxymethamphetamine in hippocampal neurons of male rats

MDMA (3,4-Methylenedioxymethamphetamine) is a common recreational drug of abuse which causes neurodegeneration. Nicotine and modafinil provide antioxidant and neuroprotective properties and may be beneficial in the management of MDMA-induced neurotoxicity. The purpose of this study was to characterize how acute and chronic administration of nicotine and/or modafinil exert protective effects against the MDMA-induced impaired cognitive performance, oxidative stress, and neuronal loss. Adult male rats were divided into three groups, namely control, MDMA and treatment (modafinil and/or nicotine). MDMA (10 mg/kg) was administered intraperitoneally during a three-week schedule (two times/day for two consecutive days/week). The treated-groups were classified based on the acute or chronic status of treatment. In the groups which underwent acute treatments, nicotine (0.5 mg/kg) and/or modafinil (100 mg/kg) were injected just prior to the MDMA administration (acute nicotine (NA), acute modafinil (MA), and acute nicotine and modafinil (NMA)). In the rats which received chronic treatments, nicotine (0.5 mg/kg) and/or modafinil (100 mg/kg) were injected every day during the three week-schedule administration of MDMA (chronic nicotine (NC), chronic modafinil (MC), and chronic nicotine and modafinil (NMC)). Learning and memory performance, as well as avoidance response, were assessed by Morris water maze and Shuttle box, respectively. Our findings indicate enhanced learning and memory and avoidance response in the NMC group. By TUNEL test and Cresyl Violet staining we evaluated neuronal loss and apoptosis in the hippocampal CA1 and found increased neuronal viability in the NMC group. On the other hand, chronic administration of modafinil and nicotine significantly down-regulated the caspase 3 and up-regulated both BDNF and TrkB levels in the MDMA-received rats. The serum levels of glutathione peroxidase (GPx) and total antioxidant capacity (TAC) were evaluated and we found that the alterations of serum levels of GPx and TAC were considerably prevented in the NMC group. The overall results indicate that nicotine and modafinil co-administration rescued brain from MDMA-induced neurotoxicity. We suggest that nicotine and modafinil combination therapy could be considered as a possible treatment to reduce the neurological disorders induced by MDMA.

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.

Excessive Daytime Sleepiness in Obstructive Sleep Apnea. Mechanisms and Clinical Management

Many patients with obstructive sleep apnea (OSA) experience excessive daytime sleepiness (EDS), which can negatively affect daily functioning, cognition, mood, and other aspects of well-being. Although EDS can be reduced with primary OSA treatment, such as continuous positive airway pressure (CPAP) therapy, a significant proportion of patients continue to experience EDS despite receiving optimized therapy for OSA. This article reviews the pathophysiology and clinical evaluation and management of EDS in patients with OSA. The mechanisms underlying EDS in CPAP-treated patients remain unclear. Experimental risk factors include chronic intermittent hypoxia and sleep fragmentation, which lead to oxidative injury and changes in neurons and brain circuit connectedness involving noradrenergic and dopaminergic neurotransmission in wake-promoting regions of the brain. In addition, neuroimaging studies have shown alterations in the brain's white matter and gray matter in patients with OSA and EDS. Clinical management of EDS begins with ruling out other potential causes of EDS and evaluating its severity. Tools to evaluate EDS include objective and self-reported assessments of sleepiness, as well as cognitive assessments. Patients who experience residual EDS despite primary OSA therapy may benefit from wake-promoting pharmacotherapy. Agents that inhibit reuptake of dopamine or of dopamine and norepinephrine (modafinil/armodafinil and solriamfetol, respectively) have demonstrated efficacy in reducing EDS and improving quality of life in patients with OSA. Additional research is needed on the effects of wake-promoting treatments on cognition in these patients and to identify individual or disorder-specific responses.

New Drugs, Old Targets: Tweaking the Dopamine System to Treat Psychostimulant Use Disorders

The abuse of illicit psychostimulants such as cocaine and methamphetamine continues to pose significant health and societal challenges. Despite considerable efforts to develop medications to treat psychostimulant use disorders, none have proven effective, leaving an underserved patient population and unanswered questions about what mechanism(s) of action should be targeted for developing pharmacotherapies. As both cocaine and methamphetamine rapidly increase dopamine (DA) levels in mesolimbic brain regions, leading to euphoria that in some can lead to addiction, targets in which this increased dopaminergic tone may be mitigated have been explored. Further, understanding and targeting mechanisms underlying relapse are fundamental to the success of discovering medications that reduce the reinforcing effects of the drug of abuse, decrease the negative reinforcement or withdrawal/negative affect that occurs during abstinence, or both. Atypical inhibitors of the DA transporter and partial agonists/antagonists at DA D3 receptors are described as two promising targets for future drug development.

Chronic modafinil administration to preadolescent rats impairs social play behavior and dopaminergic system

Some clinical trials are investigating modafinil (Mod) as a treatment for attentional deficit and hyperactivity disorder (ADHD) in children and adolescents. Mod increases dopamine (DA) levels in the reward system by blocking dopamine transporter (DAT). Social interactions are rewarding behaviors and evidence reveals the importance of reward circuitry in social interactions. Chronic psychostimulant treatments alter DA neurotransmission and associated behaviors. The aim of this work was to evaluate the effects of chronic Mod treatment during preadolescence on social play behavior, locomotor activity, and DA in nucleus accumbens (NAc). Preadolescent male Sprague-Dawley rats were injected with Mod (75 mg/kg i.p.) or vehicle for 14 days (PND22 to PND35). After that, we measured social play behavior, content and DA release in NAc by HPLC coupled to electrochemical detection, protein levels of DA type 2 receptor (D₂) by Western blot and DA kinetic by fast-scan cyclic voltammetry (FSCV) in NAc. Regarding social play, the total number of pinning events decreased in the Mod group compared with the vehicle. The K⁺-stimulated DA release in NAc was significantly lower in Mod-treated rats compared with vehicle group. Also, Mod increases locomotor activity at the first injection, but this effect is almost completely lost at day 14 of Mod treatment. Chronic Mod treatment during preadolescence in rats impairs dopaminergic neurotransmission in NAc and decreases the capacity of rats to perceive rewarding effects of social play. Importantly, as Mod is being evaluated to treat ADHD in children and adolescents, potential effects on social behavior should be considered since this kind of behavior in this particular stage is crucial for neurodevelopment.

Behavioral and dopamine transporter binding properties of the modafinil analog (S, S)-CE-158: reversal of the motivational effects of tetrabenazine and enhancement of progressive ratio responding

RATIONALE

Atypical dopamine (DA) transport blockers such as modafinil and its analogs may be useful for treating motivational symptoms of depression and other disorders. Previous research has shown that the DA depleting agent tetrabenazine can reliably induce motivational deficits in rats, as evidenced by a shift towards a low-effort bias in effort-based choice tasks. This is consistent with human studies showing that people with major depression show a bias towards low-effort activities.

OBJECTIVES

Recent studies demonstrated that the atypical DA transport (DAT) inhibitor (S)-CE-123 reversed tetrabenazine-induced motivational deficits, increased progressive ratio (PROG) lever pressing, and increased extracellular DA in the nucleus accumbens. In the present studies, a recently synthesized modafinil analog, (S, S)-CE-158, was assessed in a series of neurochemical and behavioral studies in rats.

RESULTS

(S, S)-CE-158 demonstrated the ability to reverse the effort-related effects of tetrabenazine and increase selection of high-effort PROG lever pressing in rats tested on PROG/chow feeding choice task. (S, S)-CE-158 showed a high selectivity for inhibiting DAT compared with other monoamine transporters, and systemic administration of (S, S)-CE-158 increased extracellular DA in the nucleus accumbens during the behaviorally active time course, which is consistent with the effects of (S)-CE-123 and other DAT inhibitors that enhance high-effort responding.

CONCLUSIONS

These studies provide an initial neurochemical characterization of a novel atypical DAT inhibitor, and demonstrate that this compound is active in models of effort-related choice. This research could contribute to the development of novel compounds for the treatment of motivational dysfunctions in humans.

Modafinil and its structural analogs as atypical dopamine uptake inhibitors and potential medications for psychostimulant use disorder

Pharmacotherapeutics for treatment of psychostimulant use disorder are still an unmet medical goal. Recently, off label use of modafinil (MOD), an approved medication for treatment of sleep disturbances, has been tested as a therapeutic for cocaine and methamphetamine use disorder. Positive results have been found in subjects dependent on psychostimulants without concurrent abuse of other substances. Novel structural analogs of MOD have been synthesized in the search for compounds with potentially broader therapeutic efficacy than the parent drug. In the present report we review their potential efficacy as treatments for psychostimulant abuse and dependence assessed in preclinical tests. Results from these preclinical proof of concept studies reveal that some modafinil analogs do not possess typical cocaine-like neurochemical and behavioral effects. Further, they might blunt the reinforcing effects of psychostimulants in animal models, suggesting their potential efficacy as pharmacotherapeutics for treatment of psychostimulant use disorders.

Modafinil potentiates cocaine self-administration by a dopamine-independent mechanism: possible involvement of gap junctions

Modafinil and methylphenidate are medications that inhibit the neuronal reuptake of dopamine, a mechanism shared with cocaine. Their use as "smart drugs" by healthy subjects poses health concerns and requires investigation. We show that methylphenidate, but not modafinil, maintained intravenous self-administration in Sprague-Dawley rats similar to cocaine. Both modafinil and methylphenidate pretreatments potentiated cocaine self-administration. Cocaine, at self-administered doses, stimulated mesolimbic dopamine levels. This effect was potentiated by methylphenidate, but not by modafinil pretreatments, indicating dopamine-dependent actions for methylphenidate, but not modafinil. Modafinil is known to facilitate electrotonic neuronal coupling by actions on gap junctions. Carbenoxolone, a gap junction inhibitor, antagonized modafinil, but not methylphenidate potentiation of cocaine self-administration. Our results indicate that modafinil shares mechanisms with cocaine and methylphenidate but has a unique pharmacological profile that includes facilitation of electrotonic coupling and lower abuse liability, which may be exploited in future therapeutic drug design for cocaine use disorder.

Cognition and addiction

In this targeted review, we summarize current knowledge on substance-use disorder (SUD)-related cognitive deficits, the link between these deficits and clinical outcomes, and the cognitive training, remediation, and pharmacological approaches that have the potential to rescue cognition. We conclude that: (i) people with SUDs have moderate deficits in memory, attention, executive functions, and decision-making (including reward expectancy, valuation, and learning); (ii) deficits in higher-order executive functions and decision-making are significant predictors of relapse; (iii) cognitive training programs targeting reward-related appetitive biases, cognitive remediation strategies targeting goal-based decision-making, and pharmacotherapies targeting memory, attention, and impulsivity have potential to rescue SUD-related cognitive deficits. We suggest avenues for future research, including developing brief, clinically oriented harmonized cognitive testing suites to improve individualized prediction of treatment outcomes; computational modeling that can achieve deep phenotyping of cognitive subtypes likely to respond to different interventions; and phenotype-targeted cognitive, pharmacological, and combined interventions. We conclude with a tentative model of neuroscience-informed precision medicine.


Neurophysiological and Neurochemical Effects of the Putative Cognitive Enhancer (S)-CE-123 on Mesocorticolimbic Dopamine System

Treatments for cognitive impairments associated with neuropsychiatric disorders, such as attention deficit hyperactivity disorder or narcolepsy, aim at modulating extracellular dopamine levels in the brain. CE-123 (5-((benzhydrylsulfinyl)methyl) thiazole) is a novel modafinil analog with improved specificity and efficacy for dopamine transporter inhibition that improves cognitive and motivational processes in experimental animals. We studied the neuropharmacological and behavioral effects of the S-enantiomer of CE-123 ((S)-CE-123) and R-modafinil in cognitive- and reward-related brain areas of adult male rats. In vivo single unit recordings in anesthetized animals showed that (S)-CE-123, but not R-modafinil, dose-dependently (1.25 to 10 mg/kg i.v.) reduced firing of pyramidal neurons in the infralimbic/prelimbic (IL/PrL) cortex. Neither compound the affected firing activity of ventral tegmental area dopamine cells. In freely moving animals, (S)-CE-123 (10 mg/kg i.p.) increased extracellular dopamine levels in the IL/PrL, with different patterns when compared to R-modafinil (10 mg/kg i.p.); in the nucleus accumbens shell, a low and transitory increase of dopamine was observed only after (S)-CE-123. Neither (S)-CE-123 nor R-modafinil initiated the emission of 50-kHz ultrasonic vocalizations, a behavioral marker of positive affect and drug-mediated reward. Our data support previous reports of the procognitive effects of (S)-CE-123, and show a minor impact on reward-related dopaminergic areas.

Acute Regulation of the Arousal-Enhancing Drugs Caffeine and Modafinil on Class IIa HDACs In Vivo and In Vitro: Focus on HDAC7

Psychostimulant drugs, such as modafinil and caffeine, induce transcriptional alterations through the dysregulation of epigenetic mechanisms. We have previously demonstrated that acute modafinil administration is accompanied by multiple changes in the expression of histone deacetylases (HDACs) within the mouse medial prefrontal cortex (mPFC). Herein, we compared alterations in class IIa HDACs in the mouse mPFC and dorsal striatum (DS) after a single exposure to each psychostimulant. We treated male C57BL/6 mice with modafinil (90 mg/kg, i.p.), caffeine (10 mg/kg, i.p.), or vehicle and evaluated locomotor activity. Following, we examined hdac4, hdac5, and hdac7 mRNA expression using qRT-PCR and HDAC7, pHDAC7, and pHDACs4/5/7 using Western blot. Last, we explored generalized effects in N2a cell line using modafinil (100 μM and 1 mM) or caffeine (80 μM and 800 μM). Our results indicate that modafinil had greater effects on locomotor activity compared with caffeine. qRT-PCR experiments revealed that modafinil decreased hdac5 and hdac7 mRNA expression in the DS, while caffeine had no effects. In the mPFC, modafinil increased hdac7 mRNA expression, with no effects observed for caffeine. Western blot revealed that within the DS, modafinil induced increases in HDAC7, pHDAC7, and pHDACs4/5/7 protein expression, while, in the mPFC, caffeine induced decreases in HDAC7, pHDAC7, and pHDACs4/5/7 protein levels. In vitro studies revealed that modafinil increased hdac4, hdac5, and hdac7 mRNA levels in N2a, while caffeine only increased hdac5 at a higher dose. These findings support the notion that modafinil and caffeine exert distinct regulation of class IIa HDAC family members and that these transcriptional and translational consequences are region-specific.

Involvement of orexinergic system in psychiatric and neurodegenerative disorders: A scoping review

Orexin is a neuropeptide secreted from lateral hypothalamus and pre-frontal cortex concerned in the wakefulness and excitement. This study aimed to review the possible neurobiological effect of orexin. A diversity of search strategies was adopted and assumed which included electronic database searches of Medline and PubMed using MeSH terms, keywords, and title words during the search. Orexin plays a vital role in activation of learning, memory acquisition, and consolidation through activation of monoaminergic system, which affect cognitive flexibility and cognitive function. Orexin stimulates adrenocorticotropin and corticosteroid secretions via activation of central corticotropin-releasing hormone. Cerebrospinal fluid (CSF) and serum orexin serum levels are reduced in depression, schizophrenia, and narcolepsy. However, high orexin serum levels are revealed in drug addictions. Regarding neurodegenerative brain diseases, CSF and serum orexin serum levels are reduced Parkinson disease, Alzheimer dementia, Huntington's disease, amyotrphic lateral sclerosis, and multiple sclerosis. Orexin antagonist leads to significant reduction of sympathetic over-activity during withdrawal syndrome. As well, orexin antagonist improves sleep pattern. Orexinergic system is involved in the different psychiatric and neurological disorders; therefore, targeting of this system could be possible novel pathway in the management of these disorders. In addition, measurement of CSF and serum orexin levels might predict the relapse and withdrawal of addict patients.

Structure-Activity Relationships for a Series of (Bis(4-fluorophenyl)methyl)sulfinyl Alkyl Alicyclic Amines at the Dopamine Transporter: Functionalizing the Terminal Nitrogen Affects Affinity, Selectivity, and Metabolic Stability

Atypical dopamine transporter (DAT) inhibitors have shown therapeutic potential in preclinical models of psychostimulant abuse. In rats, 1-(4-(2-((bis(4-fluorophenyl)methyl)sulfinyl)ethyl)-piperazin-1-yl)-propan-2-ol (3b) was effective in reducing the reinforcing effects of both cocaine and methamphetamine but did not exhibit psychostimulant behaviors itself. While further development of 3b is ongoing, diastereomeric separation, as well as improvements in potency and pharmacokinetics were desirable for discovering pipeline drug candidates. Thus, a series of bis(4-fluorophenyl)methyl)sulfinyl)alkyl alicyclic amines, where the piperazine-2-propanol scaffold was modified, were designed, synthesized, and evaluated for binding affinities at DAT, as well as the serotonin transporter and σ1 receptors. Within the series, 14a showed improved DAT affinity (Ki = 23 nM) over 3b (Ki = 230 nM), moderate metabolic stability in human liver microsomes, and a hERG/DAT affinity ratio = 28. While 14a increased locomotor activity relative to vehicle, it was significantly lower than activity produced by cocaine. These results support further investigation of 14a as a potential treatment for psychostimulant use disorders.

Memory improvement by modafinil at cost of metabolic hazards? A study to decipher the benefits and risks of modafinil in rats

BACKGROUND

Modafinil is approved for narcolepsy and achieved high success in off-label indications in memory-related disorders. However, chronic indiscriminate use of modafinil imposes several health hazards like hyperglycaemia, obesity and metabolic syndrome, owing to impairment of sleep-wake cycle, circadian-rhythm, and neurotransmission. The present protocol elucidates the effects of modafinil per se and diabetic complications apropos.

METHODS

Modafinil (100 and 200 mg/kg) was administered in rats from day 5-26. To induce type-2 diabetes, streptozotocin (STZ) was given on day 1, and blood glucose assessed on day 5. CPP (combination propranolol and phentolamine) was administered to antagonize sympathetic activity. After evaluation of cognitive functions, serum lipid profile, and biomarkers of oxidative stress and acetylcholinesterase (AChE) activity were assessed.

RESULTS

Subacute dosing of modafinil significantly elevated blood glucose levels, albeit considerably less than diabetic group, and attenuated brain oxidative stress and AChE activity. Modafinil caused significant dyslipidaemia, increased body weight, whereas modestly altered abdominal circumference (AC) and thoracic circumference (TC) in rats. Significant hyperglycaemia, derangement of serum lipid-profile, brain lipid peroxidation, cholinergic hypofunction, and decrease in body weight and ACTC was noted in diabetic rats. Modafinil (100 mg/kg) significantly potentiated the hyperglycaemia and dyslipidaemia, however, attenuated oxidative stress and AChE activity in diabetic rats. Modafinil increased short-term (working) memory but not long-term spatial memory in normal and diabetic rats. CPP infusion attenuated these effects of modafinil.

CONCLUSION

Subacute dosing of modafinil differentially modulates long-term and short-term memory subtypes, and also predisposes towards metabolic derangements.

Pharmacokinetic and pharmacodynamic of the cognitive enhancer modafinil: Relevant clinical and forensic aspects

Modafinil is a nonamphetamine nootropic drug with an increasingly therapeutic interest due to its different sites of action and behavioral effects in comparison to cocaine or amphetamine. A review of modafinil (and of its prodrug adrafinil and its R-enantiomer armodafinil) chemical, pharmacokinetic, pharmacodynamic, toxicological, clinical and forensic aspects was performed, aiming to better understand possible health problems associated to its unconscious and unruled use. Modafinil is a racemate metabolized mainly in the liver into its inactive acid and sulfone metabolites, which undergo primarily renal excretion. Although not fully clarified, major effects seem to be associated to inhibition of dopamine reuptake and modulation of several other neurochemical pathways, namely noradrenergic, serotoninergic, orexinergic, histaminergic, glutamatergic and GABAergic. Due its wake-promoting effects, modafinil is used for the treatment of daily sleepiness associated to narcolepsy, obstructive sleep apnea and shift work sleep disorder. Its psychotropic and cognitive effects are also attractive in several other pathologies and conditions that affect sleep structure, induce fatigue and lethargy, and impair cognitive abilities. Additionally, in health subjects, including students, modafinil is being used off-label to overcome sleepiness, increase concentration and improve cognitive potential. The most common adverse effects associated to modafinil intake are headache, insomnia, anxiety, diarrhea, dry mouth and raise in blood pressure and heart rate. Infrequently, severe dermatologic effects in children, including maculopapular and morbilliform rash, erythema multiforme and Stevens-Johnson Syndrome have been reported. Intoxication and dependence associated to modafinil are uncommon. Further research on effects and health implications of modafinil and its analogs is steel needed to create evidence-based policies.

Effects of the monoamine stabilizer (-)OSU6162 on cognitive function in alcohol dependence

INTRODUCTION

Alcohol dependence (AD) is associated with a dysregulated mesolimbocortical dopamine system-a pathway which is also implicated in both reward and cognition. The monoamine stabilizer (-)-OSU6162 (OSU) is a novel pharmacological compound with the ability to reduce ethanol intake and ethanol seeking in long-term drinking rats as well as reducing alcohol craving in AD patients. Dopaminergic drugs can both impair and improve cognitive functions, and the aim of the current study was to investigate the effect of OSU treatment on cognitive functioning in AD patients.

METHOD

In a randomized double-blind placebo-controlled study, 56 individuals with AD received 14 days of OSU or placebo treatment. Neuropsychological tasks from the Cambridge Automated Neuropsychological Test Battery (CANTAB®) and other tasks were used to evaluate treatment effect on executive function/impulsivity, working memory, attention, emotional recognition, and divergent thinking.

RESULTS

Treatment with OSU did not impair neuropsychological function in any of the cognitive domains investigated (all p > 0.1). In fact, OSU treatment did, compared to placebo, improve future planning ability (F_(1,46) = 6.9; p = 0.012; Cohen's d = 0.54), verbal divergent thinking (F_(1,44) = 10.1; p = 0.003; d = 0.96), and response time for emotional recognition (F_(1,47) = 6.7; p = 0.013; d = 0.44).

CONCLUSION

OSU treatment did not cause short-term cognitive side effects, further supporting the potential of OSU as a clinically feasible pharmacological treatment in AD patients. OSU treatment might improve future planning, verbal divergent thinking, and emotional recognition latency, which in turn may have a beneficial impact on alcohol use outcomes. Future studies are needed to confirm these preliminary findings.

Progress in agonist therapy for substance use disorders: Lessons learned from methadone and buprenorphine

Substance use disorders (SUD) are serious public health problems worldwide. Although significant progress has been made in understanding the neurobiology of drug reward and the transition to addiction, effective pharmacotherapies for SUD remain limited and a majority of drug users relapse even after a period of treatment. The United States Food and Drug Administration (FDA) has approved several medications for opioid, nicotine, and alcohol use disorders, whereas none are approved for the treatment of cocaine or other psychostimulant use disorders. The medications approved by the FDA for the treatment of SUD can be divided into two major classes - agonist replacement therapies, such as methadone and buprenorphine for opioid use disorders (OUD), nicotine replacement therapy (NRT) and varenicline for nicotine use disorders (NUD), and antagonist therapies, such as naloxone for opioid overdose and naltrexone for promoting abstinence. In the present review, we primarily focus on the pharmacological rationale of agonist replacement strategies in treatment of opioid dependence, and the potential translation of this rationale to new therapies for cocaine use disorders. We begin by describing the neural mechanisms underlying opioid reward, followed by preclinical and clinical findings supporting the utility of agonist therapies in the treatment of OUD. We then discuss recent progress of agonist therapies for cocaine use disorders based on lessons learned from methadone and buprenorphine. We contend that future studies should identify agonist pharmacotherapies that can facilitate abstinence in patients who are motivated to quit their illicit drug use. Focusing on those that are able to achieve abstinence from cocaine will provide a platform to broaden the effectiveness of medication and psychosocial treatment strategies for this underserved population. This article is part of the Special Issue entitled 'New Vistas in Opioid Pharmacology'.

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.

Translating the atypical dopamine uptake inhibitor hypothesis toward therapeutics for treatment of psychostimulant use disorders

Medication-assisted treatments are unavailable to patients with cocaine use disorders. Efforts to develop potential pharmacotherapies have led to the identification of a promising lead molecule, JJC8-091, that demonstrates a novel binding mode at the dopamine transporter (DAT). Here, JJC8-091 and a structural analogue, JJC8-088, were extensively and comparatively assessed to elucidate neurochemical correlates to their divergent behavioral profiles. Despite sharing significant structural similarity, JJC8-088 was more cocaine-like, increasing extracellular DA concentrations in the nucleus accumbens shell (NAS) efficaciously and more potently than JJC8-091. In contrast, JJC8-091 was not self-administered and was effective in blocking cocaine-induced reinstatement to drug seeking. Electrophysiology experiments confirmed that JJC8-091 was more effective than JJC8-088 at inhibiting cocaine-mediated enhancement of DA neurotransmission. Further, when VTA DA neurons in DAT-cre mice were optically stimulated, JJC8-088 produced a significant leftward shift in the stimulation-response curve, similar to cocaine, while JJC8-091 shifted the curve downward, suggesting attenuation of DA-mediated brain reward. Computational models predicted that JJC8-088 binds in an outward facing conformation of DAT, similar to cocaine. Conversely, JJC8-091 steers DAT towards a more occluded conformation. Collectively, these data reveal the underlying molecular mechanism at DAT that may be leveraged to rationally optimize leads for the treatment of cocaine use disorders, with JJC8-091 representing a compelling candidate for development.

The Novel Atypical Dopamine Uptake Inhibitor (S)-CE-123 Partially Reverses the Effort-Related Effects of the Dopamine Depleting Agent Tetrabenazine and Increases Progressive Ratio Responding

Animal studies of effort-based choice behavior are being used to model effort-related motivational dysfunctions in humans. With these procedures, animals are offered a choice between high-effort instrumental actions leading to highly valued reinforcers vs. low effort/low reward options. Several previous studies have shown that dopamine (DA) uptake inhibitors, including GBR12909, lisdexamfetamine, methylphenidate, and PRX-14040, can reverse the effort-related effects of the vesicular monoamine transport blocker tetrabenazine, which inhibits DA storage. Because many drugs that block DA transport act as major stimulants that also release DA, and produce a number of undesirable side effects, there is a need to develop and characterize novel atypical DA transport inhibitors. (S)-CE-123 ((S)-5-((benzhydrylsulfinyl) methyl)thiazole) is a recently developed analog of modafinil with the biochemical characteristics of an atypical DA transport blocker. The present paper describes the enantioselective synthesis and initial chemical characterization of (S)-CE-123, as well as behavioral experiments involving effort-based choice and microdialysis studies of extracellular DA. Rats were assessed using the fixed ratio 5/chow feeding choice test. Tetrabenazine (1.0 mg/kg) shifted choice behavior, decreasing lever pressing and increasing chow intake. (S)-CE-123 was coadministered at doses ranging from 6.0 to 24.0 mg/kg, and the highest dose partially but significantly reversed the effects of tetrabenazine, although this dose had no effect on fixed ratio responding when administered alone. Additional experiments showed that (S)-CE-123 significantly increased lever pressing on a progressive ratio/chow feeding choice task and that the effective dose (24.0 mg/kg) increased extracellular DA in nucleus accumbens core. In summary, (S)-CE-123 has the behavioral and neurochemical profile of a compound that can block DA transport, reverse the effort-related effects of tetrabenazine, and increase selection of high-effort progressive ratio responding. This suggests that (S)-CE-123 or a similar compound could be useful as a treatment for effort-related motivational dysfunction in humans.

How to rescue misfolded SERT, DAT and NET: targeting conformational intermediates with atypical inhibitors and partial releasers

Point mutations in the coding sequence for solute carrier 6 (SLC6) family members result in clinically relevant disorders, which are often accounted for by a loss-of-function phenotype. In many instances, the mutated transporter is not delivered to the cell surface because it is retained in the endoplasmic reticulum (ER). The underlying defect is improper folding of the transporter and is the case for many of the known dopamine transporter mutants. The monoamine transporters, i.e. the transporters for norepinephrine (NET/SLC6A2), dopamine (DAT/SLC6A3) and serotonin (SERT/SLC6A4), have a rich pharmacology; hence, their folding-deficient mutants lend themselves to explore the concept of pharmacological chaperoning. Pharmacochaperones are small molecules, which bind to folding intermediates with exquisite specificity and scaffold them to a folded state, which is exported from the ER and delivered to the cell surface. Pharmacochaperoning of mutant monoamine transporters, however, is not straightforward: ionic conditions within the ER are not conducive to binding of most typical monoamine transporter ligands. A collection of compounds exists, which are classified as atypical ligands because they trap monoamine transporters in unique conformational states. The atypical binding mode of some DAT inhibitors has been linked to their anti-addictive action. Here, we propose that atypical ligands and also compounds recently classified as partial releasers can serve as pharmacochaperones.

Effects of ( R)-Modafinil and Modafinil Analogues on Dopamine Dynamics Assessed by Voltammetry and Microdialysis in the Mouse Nucleus Accumbens Shell

Recent discoveries have improved our understanding of the physiological and pathological roles of the dopamine transporter (DAT); however, only a few drugs are clinically available for DAT-implicated disorders. Among those drugs, modafinil (MOD) and its ( R)-enantiomer (R-MOD) have been used off-label as therapies for psychostimulant use disorders, but they have shown limited effectiveness in clinical trials. Recent preclinical studies on MOD and R-MOD have led to chemically modified structures aimed toward improving their neurobiological properties that might lead to more effective therapeutics for stimulant use disorders. This study examines three MOD analogues (JJC8-016, JJC8-088, and JJC8-091) with improved DAT affinities compared to their parent compound. These compounds were investigated for their effects on the neurochemistry (brain microdialysis and FSCV) and behavior (ambulatory activity) of male Swiss-Webster mice. Our data indicate that these compounds have dissimilar effects on tonic and phasic dopamine in the nucleus accumbens shell and variability in producing ambulatory activity. These results suggest that small changes in the chemical structure of a DAT inhibitor can cause compounds such as JJC8-088 to produce effects similar to abused psychostimulants like cocaine. In contrast, other compounds like JJC8-091 do not share cocaine-like effects and have a more atypical DAT-inhibitor profile, which may prove to be an advancement in the treatment of psychostimulant use disorders.

Participation of Dopamine D1 and D2 Receptors in the Rapid-Onset Behavioral Sensitization to Modafinil

Studies on the abuse potential of modafinil, a psychostimulant-like drug used to treat narcolepsy, are still controversial. While some studies claim no potential for abuse, increasing evidence suggests that modafinil induces abuse-related effects, including rapid-onset behavioral sensitization (i.e., a type of sensitization that develops within hours from the drug priming administration). The rapid-onset sensitization paradigm is a valuable tool to study the neuroplastic changes that occur quickly after drug administration, and shares neuroadaptations with drug abuse in humans. However, the mechanisms involved in the rapid-onset behavioral sensitization induced by modafinil are uncertain. Our aim was to investigate the possible involvement of dopamine D1 and D2 receptors on acute modafinil-induced hyperlocomotion and on the induction and expression of rapid-onset behavioral sensitization induced by modafinil in male Swiss mice. Treatment with the D1 receptor antagonist SCH 23390 or the D2 receptor antagonist sulpiride attenuated the acute modafinil-induced hyperlocomotion in a dose-dependent manner. Pretreatment with either antagonist before the priming injection of modafinil prevented the development of sensitization in response to a modafinil challenge 4 h later. However, only SCH 23390 decreased the expression of modafinil-induced rapid-onset behavioral sensitization. Taken together, the present findings provide evidence of the participation of D1 and D2 receptors on the development of rapid-onset behavioral sensitization to modafinil, and point to a prominent role of D1 receptors on the expression of this phenomenon.

The effects of single-dose injections of modafinil and methamphetamine on epigenetic and functional markers in the mouse medial prefrontal cortex: potential role of dopamine receptors

METH use causes neuroadaptations that negatively impact the prefrontal cortex (PFC) leading to addiction and associated cognitive decline in animals and humans. In contrast, modafinil enhances cognition by increasing PFC function. Accumulated evidence indicates that psychostimulant drugs, including modafinil and METH, regulate gene expression via epigenetic modifications. In this study, we measured the effects of single-dose injections of modafinil and METH on the protein levels of acetylated histone H3 (H3ac) and H4ac, deacetylases HDAC1 and HDAC2, and of the NMDA subunit GluN1 in the medial PFC (mPFC) of mice euthanized 1 h after drug administration. To test if dopamine (DA) receptors (DRs) participate in the biochemical effects of the two drugs, we injected the D1Rs antagonist, SCH23390, or the D2Rs antagonist, raclopride, 30 min before administration of METH and modafinil. We evaluated each drug effect on glutamate synaptic transmission in D1R-expressing layer V pyramidal neurons. We also measured the enrichment of H3ac and H4ac at the promoters of several genes including DA, NE, orexin, histamine, and glutamate receptors, and their mRNA expression, since they are responsive to chronic modafinil and METH treatment. Acute modafinil and METH injections caused similar effects on total histone acetylation, increasing H3ac and decreasing H4ac, and they also increased HDAC1, HDAC2 and GluN1 protein levels in the mouse mPFC. In addition, the effects of the drugs were prevented by pre-treatment with D1Rs and D2Rs antagonists. Specifically, the changes in H4ac, HDAC2, and GluN1 were responsive to SCH23390, whereas those of H3ac and GluN1 were responsive to raclopride. Whole-cell patch clamp in transgenic BAC-Drd1a-tdTomato mice showed that METH, but not modafinil, induced paired-pulse facilitation of EPSCs, suggesting reduced presynaptic probability of glutamate release onto layer V pyramidal neurons. Analysis of histone 3/4 enrichment at specific promoters revealed: i) distinct effects of the drugs on histone 3 acetylation, with modafinil increasing H3ac at Drd1 and Adra1b promoters, but METH increasing H3ac at Adra1a; ii) distinct effects on histone 4 acetylation enrichment, with modafinil increasing H4ac at the Drd2 promoter and decreasing it at Hrh1, but METH increasing H4ac at Drd1; iii) comparable effects of both psychostimulants, increasing H3ac at Drd2, Hcrtr1, and Hrh1 promoters, decreasing H3ac at Hrh3, increasing H4ac at Hcrtr1, and decreasing H4ac at Hcrtr2, Hrh3, and Grin1 promoters. Interestingly, only METH altered mRNA levels of genes with altered histone acetylation status, inducing increased expression of Drd1a, Adra1a, Hcrtr1, and Hrh1, and decreasing Grin1. Our study suggests that although acute METH and modafinil can both increase DA neurotransmission in the mPFC, there are similar and contrasting epigenetic and transcriptional consequences that may account for their divergent clinical effects.

Pharmacological classification of centrally acting drugs using EEG in freely moving rats: an old tool to identify new atypical dopamine uptake inhibitors

Atypical dopamine uptake inhibitors (DUIs) bind to the dopamine transporter and inhibit the reuptake of dopamine but have lower abuse potential than psychostimulants. Several atypical DUIs can block abuse-related effects of cocaine and methamphetamine, thus making them potential medication candidates for psychostimulant use disorders. The aim of the current study is to establish an in-vivo assay using EEG for the rapid identification of atypical DUIs with potential for medication development. The typical DUIs cocaine and methylphenidate dose-dependently decreased the power of the alpha, beta, and gamma bands. The atypical DUI modafinil and its F-analog, JBG1-049, decreased the power of beta, but in contrast to cocaine, none of the other frequency bands, while JHW007 did not significantly alter the EEG spectrum. The mu-opioid receptor agonists heroin and morphine dose-dependently decreased the power of gamma and increased power of the other bands. The effect of morphine on EEG power bands was antagonized by naltrexone. The NMDA receptor antagonist ketamine increased the power of all frequency bands. Therefore, typical and atypical DUIs and drugs of other classes differentially affected EEG spectra, showing distinctive features in the magnitude and direction of their effects on EEG. Comparative analysis of the effects of test drugs on EEG indicates a potential atypical profile of JBG1-049 with similar potency and effectiveness to its parent compound modafinil. These data suggest that EEG can be used to rapidly screen compounds for potential activity at specific pharmacological targets and provide valuable information for guiding the early stages of drug development. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Effects of circadian misalignment on sleep in mice

Circadian rhythms and sleep-wake history determine sleep duration and intensity, and influence subsequent waking. Previous studies have shown that T cycles - light-dark (LD) cycles differing from 24 h - lead to acute changes in the daily amount and distribution of waking and sleep. However, little is known about the long-term effects of T cycles. Here we performed continuous 10 day recording of electroencephalography (EEG), locomotor activity and core body temperature in C57BL/6 mice under a T20 cycle, to investigate spontaneous sleep and waking at baseline compared with when the circadian clock was misaligned and then re-aligned with respect to the external LD cycle. We found that the rhythmic distribution of sleep was abolished during misalignment, while the time course of EEG slow wave activity (1–4 Hz) was inverted compared to baseline. Although the typical light-dark distribution of NREM sleep was re-instated when animals were re-aligned, slow wave activity during NREM sleep showed an atypical increase in the dark phase, suggesting a long-term effect of T cycles on sleep intensity. Our data show that circadian misalignment results in previously uncharacterised long-term effects on sleep, which may have important consequences for behaviour.