Modafinil treatment of amphetamine abuse in adult ADHD

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.

Investigational drug therapies in phase I and phase II clinical trials for alcohol use disorders

INTRODUCTION

Alcohol use disorder (AUD) is a complex psychiatric condition characterized by craving, compulsive seeking, loss of control of alcohol consumption as well as the emergence of negative emotional states during withdrawal. Despite the large socioeconomic burden of AUD, therapeutic treatment options lag behind.

AREAS COVERED

This review covers pharmacotherapies currently in phase I/II clinical trials for the treatment of AUDs listed on clinicaltrials.gov. We discuss drug therapies that modulate monoamine, GABA/Glutamate, neuropeptide and neuroimmune systems. We examine in depth preclinical and clinical evidence of a select range of these compounds and consider their utility in treating AUDs.

EXPERT OPINION

Current therapeutic options to treat AUD are inadequate at a population level. Currently there are 30 different compounds and one compound combination in phase I/II clinical trials for AUD. These compounds target various aspects of neurotransmitter signaling, neuroimmune modulation, and alcohol metabolism. Almost 75% of these compounds under trial are Food and Drug Administration (FDA) approved for other indications, which may save time and costs in treatment development. Further, development of therapeutics focused on genetic biomarkers and behavioral screening may improve how treatment decisions are made in the future on a case-by-case basis.

Adult ADHD: A new disease?

OBJECTIVES

Until recently, it was believed that attention deficit and hyperactivity disorder (ADHD) are outgrown by the end of adolescence and the beginning of adulthood. The purpose of this review is to describe the characteristics of the disease in adults, depict comorbidities that accompany it, and expand the scope over methods of diagnosis and treatment of these ages.

METHODS

A search was conducted in the PubMed/MEDLINE database for relevant key words 'ADHD', 'attention deficit', 'hyperactivity' and 'adult'. Secondary search parameters were 'comorbid', 'prevalence', 'epidemiology', 'therapy' and 'drug therapy'. Search was limited to 'English' and 'Humans'.

RESULTS

Over the years, the persistent nature of the disorder has been clarified, elucidating prevalence rate, gender differences and subtype shifts among adult ADHD population. Nevertheless, even today, there is only limited awareness of the existence of the disorder across one's lifespan, its consequences and the appropriate treatment.

CONCLUSIONS

Our results emphasise the growing awareness of adult psychosocial impairments due to ADHD symptoms and comorbidities, as well as the need for further collaboration among practitioners and mental health-care professionals to better identify the condition and allow for effective treatment.

Dopaminergic mediation of the discriminative stimulus functions of modafinil in rats

RATIONALE

Modafinil is a wake-promoting drug with FDA approval for the treatment of excessive daytime sleepiness that has been prescribed for ADHD and recently assessed as a potential treatment for psychostimulant dependence. Previous research indicates that modafinil modestly increases locomotor activity and produces similar discriminative stimulus effects to psychostimulants in rodents, although the subjective effects of modafinil are reportedly distinct from those of cocaine or amphetamine in humans with a history of psychostimulant abuse.

OBJECTIVES

The current study employed drug discrimination procedures in rats to examine the pharmacological actions contributing to modafinil's discriminative stimulus functions.

METHODS

Eight male Sprague-Dawley rats were trained to discriminate intragastric administration of 256 mg/kg modafinil from vehicle (5% arabic gum) under a FR 20 schedule of food reinforcement. Substitution tests were conducted with various dopaminergic agents (d-amphetamine, cocaine, PNU-91356A, GBR 12909, methylphenidate) and nondopaminergic agents (nicotine, ethanol). Antagonist tests were conducted with the selective D1 antagonist, SCH 39166, and the nonselective D2 antagonist, haloperidol.

RESULTS

Rats trained to discriminate modafinil displayed complete stimulus generalization to cocaine, methylphenidate, and GBR 12909 and the discrimination was completely blocked by both SCH 39166 and haloperidol. Evidence for significant partial substitution was obtained with d-amphetamine, PNU-91356A, and nicotine.

CONCLUSIONS

Results strongly support the role of dopaminergic mechanisms in the discriminative stimulus functions of modafinil, although further evaluation regarding the contribution of other neurotransmitter systems to these effects should be continued. The findings are discussed in light of clinical research efforts with modafinil as a treatment for psychostimulant dependence.

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.

Combined effects of modafinil and d-amphetamine in male Sprague-Dawley rats trained to discriminate d-amphetamine

Modafinil is a novel wake-promoting drug with FDA approval for the treatment of sleep-related disorders that has recently been investigated as a potential agonist replacement therapy for psychostimulant dependence. Previous research in animals and humans indicates modafinil has a lower abuse liability than traditional psychostimulants, although few studies have carefully assessed modafinil's stimulus properties in combination with other psychostimulants. The current study trained male Sprague-Dawley rats to discriminate subcutaneous injections of 0.3 mg/kg (n=8) or 1.0 mg/kg d-amphetamine (n=8) from saline under an FR 20 schedule of food reinforcement and substitution tests were administered with d-amphetamine (0.03-1.0 mg/kg, s.c.), modafinil (32-256 mg/kg, i.g.), and a low modafinil dose (32 mg/kg, i.g.) in combination with d-amphetamine (0.03-1.0 mg/kg, s.c.) to determine if these drugs have additive effects. The selective D2 dopamine agonist, PNU-91356A, was also tested as a positive control and ethanol and morphine were tested as negative controls. Results indicate that modafinil produced dose-dependent and statistically significant d-amphetamine-lever responding in both groups and nearly complete substitution in animals trained to discriminate 1.0 mg/kg d-amphetamine. Modafinil pretreatment slightly increased the discrimination of low d-amphetamine doses in animals trained to discriminate 0.3 mg/kg d-amphetamine. These results support previous findings that modafinil and d-amphetamine may have additive effects. In consideration of recent interests in modafinil as an agonist treatment for psychostimulant dependence, additional preclinical investigations utilizing other methodologies to examine modafinil in combination with other stimulants, such as behavioral sensitization paradigms or drug self-administration, may be of interest.

Psychostimulant-like discriminative stimulus and locomotor sensitization properties of the wake-promoting agent modafinil in rodents

The present studies assessed the potential abuse liability and likely mechanism(s) of action of the wake-promoting agent modafinil.

METHODS

Experiments assessed the locomotor sensitization (LS) and discriminative stimulus (DS) properties of modafinil in mouse and rat, respectively. Comparative data were generated with a range of psychostimulants and monoamine reuptake inhibitors.

RESULTS

Repeated administration of d-amphetamine and cocaine, psychostimulants with high abuse liability, resulted in the induction and expression of LS in mice. Bupropion and caffeine, two psychostimulants not abused in humans, were not associated with LS. GBR12909 induced LS during repeated exposure, but there was no evidence of expression of LS after acute challenge following withdrawal. In contrast, repeated administration of modafinil resulted in the expression, but not induction, of LS. d-amphetamine, but not the mu-opioid agonist morphine or the nAChR agonist nicotine, fully substituted for the cocaine DS in rats. The selective dopamine transporter (DAT) inhibitor GBR12909 fully substituted, the preferential norepinephrine transporter (NET) inhibitor desipramine partially substituted, and the selective serotonin reuptake inhibitor citalopram failed to substitute for cocaine. Modafinil fully substituted for cocaine, similar to the mixed DAT/NET inhibitor bupropion.

CONCLUSIONS

Two preclinical assays indicated potential abuse liability of modafinil; drug discrimination studies suggest DAT blockade by modafinil is a likely mechanism of action in vivo.