Modafinil facilitates performance on a delayed nonmatching to position swim task in rats

Solriamfetol improves chronic sleep fragmentation-induced increases in sleep propensity and ameliorates explicit memory in male mice

Obstructive sleep apnea (OSA) is a highly prevalent condition characterized by episodes of partial or complete breath cessation during sleep that induces sleep fragmentation (SF). One of the frequent manifestations of OSA is the presence of excessive daytime sleepiness (EDS) associated with cognitive deficits. Solriamfetol (SOL) and modafinil (MOD) are wake-promoting agents commonly prescribed to improve wakefulness in OSA patients with EDS. This study aimed to assess the effects of SOL and MOD in a murine model of OSA characterized by periodic SF. Male C57Bl/6J mice were exposed to either control sleep (SC) or SF (mimicking OSA) during the light period (06:00 h to 18:00 h) for 4 weeks, which consistently induces sustained excessive sleepiness during the dark phase. Both groups were then randomly assigned to receive once-daily intraperitoneal injections of SOL (200 mg/kg), MOD (200 mg/kg), or vehicle for 1 week while continuing exposures to SF or SC. Sleep/wake activity and sleep propensity were assessed during the dark phase. Novel Object Recognition test, Elevated-Plus Maze Test, and Forced Swim Test were performed before and after treatment. SOL or MOD decreased sleep propensity in SF, but only SOL induced improvements in explicit memory, while MOD exhibited increased anxiety behaviors. Chronic SF, a major hallmark of OSA, induces EDS in young adult mice that is mitigated by both SOL and MOD. SOL, but not MOD, significantly improves SF-induced cognitive deficits. Increased anxiety behaviors are apparent in MOD-treated mice. Further studies aiming to elucidate the beneficial cognitive effects of SOL are warranted.

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

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

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.

Modafinil reduces choice impulsivity while increasing motor activity in preadolescent rats treated prenatally with alcohol

Rats exposed prenatally to alcohol show a reduction in the spontaneous activity of dopaminergic neurons of the ventral tegmental area (VTA), as well as greater impulsive behavior and motor activity, behavioral alterations that have been related to dopaminergic dysfunction. Modafinil (MOD) is a dopamine (DA) reuptake blocker prescribed to treat sleep disorders; however, in recent years it has been used for the treatment of ADHD with positive results. Also, studies in humans and rodents show beneficial effects on learning and attention; however, studies evaluating MOD effects on impulsivity are few and show contradictory results. The purpose of this work was to evaluate the effect of a daily dose of MOD (60 mg/kg i.g.) on cognitive (or choice) impulsivity and motor activity in male preadolescent rats exposed prenatally to alcohol or sucrose (isocaloric control). MOD reduced the impulsive responses in a delay discounting task (DDT) at the same time that increased the motor activity, in both healthy and prenatal alcohol treated rats; however, MOD reduced the response latency in DDT only in prenatal alcohol treated rats. This differential effect of DA activation on impulsivity and motor activity show that the MOD dose that improves the impulse control, does not necessarily decrease motor activity, and suggests a possible differential neural mechanism underlying the expression of these behaviors. On the other hand, the changes in the response latency, only in prenatal alcohol treated groups, suggest that decision-making in animals with a dopaminergic dysfunction is more susceptible to be affected by MOD action.

Modafinil Activates Phasic Dopamine Signaling in Dorsal and Ventral Striata

Modafinil (MOD) exhibits therapeutic efficacy for treating sleep and psychiatric disorders; however, its mechanism is not completely understood. Compared with other psychostimulants inhibiting dopamine (DA) uptake, MOD weakly interacts with the dopamine transporter (DAT) and modestly elevates striatal dialysate DA, suggesting additional targets besides DAT. However, the ability of MOD to induce wakefulness is abolished with DAT knockout, conversely suggesting that DAT is necessary for MOD action. Another psychostimulant target, but one not established for MOD, is activation of phasic DA signaling. This communication mode during which burst firing of DA neurons generates rapid changes in extracellular DA, the so-called DA transients, is critically implicated in reward learning. Here, we investigate MOD effects on phasic DA signaling in the striatum of urethane-anesthetized rats with fast-scan cyclic voltammetry. We found that MOD (30-300 mg/kg i.p.) robustly increases the amplitude of electrically evoked phasic-like DA signals in a time- and dose-dependent fashion, with greater effects in dorsal versus ventral striata. MOD-induced enhancement of these electrically evoked amplitudes was mediated preferentially by increased DA release compared with decreased DA uptake. Principal component regression of nonelectrically evoked recordings revealed negligible changes in basal DA with high-dose MOD (300 mg/kg i.p.). Finally, in the presence of the D2 DA antagonist, raclopride, low-dose MOD (30 mg/kg i.p.) robustly elicited DA transients in dorsal and ventral striata. Taken together, these results suggest that activation of phasic DA signaling is an important mechanism underlying the clinical efficacy of MOD.

A Novel Heterocyclic Compound CE-104 Enhances Spatial Working Memory in the Radial Arm Maze in Rats and Modulates the Dopaminergic System

Various psychostimulants targeting monoamine neurotransmitter transporters (MATs) have been shown to rescue cognition in patients with neurological disorders and improve cognitive abilities in healthy subjects at low doses. Here, we examined the effects upon cognition of a chemically synthesized novel MAT inhibiting compound 2-(benzhydrylsulfinylmethyl)-4-methylthiazole (named as CE-104). The efficacy of CE-104 in blocking MAT [dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter] was determined using in vitro neurotransmitter uptake assay. The effect of the drug at low doses (1 and 10 mg/kg) on spatial memory was studied in male rats in the radial arm maze (RAM). Furthermore, the dopamine receptor and transporter complex levels of frontal cortex (FC) tissue of trained and untrained animals treated either with the drug or vehicle were quantified on blue native PAGE (BN-PAGE). The drug inhibited dopamine (IC₅₀: 27.88 μM) and norepinephrine uptake (IC₅₀: 160.40 μM), but had a negligible effect on SERT. In the RAM, both drug-dose groups improved spatial working memory during the performance phase of RAM as compared to vehicle. BN-PAGE Western blot quantification of dopamine receptor and transporter complexes revealed that D1, D2, D3, and DAT complexes were modulated due to training and by drug effects. The drug’s ability to block DAT and its influence on DAT and receptor complex levels in the FC is proposed as a possible mechanism for the observed learning and memory enhancement in the RAM.

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.

Differential effects of wake promoting drug modafinil in aversive learning paradigms

Modafinil (MO) an inhibitor of the dopamine transporter was initially approved to treat narcolepsy, a sleep related disorder in humans. One interesting “side-effect” of this drug, which emerged from preclinical and clinical studies, is the facilitation of cognitive performance. So far, this was primarily shown in appetitive learning paradigms, but it is yet unclear whether MO exerts a more general cognitive enhancement effect. Thus, the aim of the present study in rats was to extend these findings by testing the effects of MO in two aversive paradigms, Pavlovian fear conditioning (FC) and the operant two-way active avoidance (TWA) learning paradigms. We discovered a differential, task-dependent effect of MO. In the FC paradigm MO treated rats showed a dose-dependent enhancement of fear memory compared to vehicle treated rats, indicated by increased context-related freezing. Cue related fear memory remained unaffected. In the TWA paradigm MO induced a significant decrease of avoidance responses compared to vehicle treated animals, while the number of escape reactions during the acquisition of the TWA task remained unaffected. These findings expand the knowledge in the regulation of cognitive abilities and may contribute to the understanding of the contraindicative effects of MO in anxiety related mental disorders.

Modafinil combined with cognitive training: pharmacological augmentation of cognitive training in schizophrenia

Several efforts to develop pharmacological treatments with a beneficial effect on cognition in schizophrenia are underway, while cognitive remediation has shown modest effects on cognitive performance. Our goal was to test if pharmacological augmentation of cognitive training would result in enhancement of training-induced learning. We chose modafinil as the pharmacological augmenting agent, as it is known to have beneficial effects on learning and cognition. 49 participants with chronic schizophrenia were enroled in a double-blind, placebo-controlled study across two sites and were randomised to either modafinil (200mg/day) or placebo. All participants engaged in a cognitive training program for 10 consecutive weekdays. The primary outcome measure was the performance on the trained tasks and secondary outcome measures included MATRICS cognitive battery, proxy measures of everyday functioning and symptom measures. 84% of the participants completed all study visits. Both groups showed significant improvement in the performance of the trained tasks suggesting potential for further learning. Modafinil did not induce differential enhancement on the performance of the trained tasks or any differential enhancement of the neuropsychological and functional measures compared to placebo. Modafinil showed no significant effects on symptom severity. Our study demonstrated that combining pharmacological compounds with cognitive training is acceptable to patients and can be implemented in large double-blind randomised controlled trials. The lack of differential enhancement of training-induced learning raises questions, such as choice and optimal dose of drug, cognitive domains to be trained, type of cognitive training, intervention duration and chronicity of illness that require systematic investigation in future studies.

Modafinil effects on behavior and oxidative damage parameters in brain of wistar rats

The effects of modafinil (MD) on behavioral and oxidative damage to protein and lipid in the brain of rats were evaluated. Wistar rats were given a single administration by gavage of water or MD (75, 150, or 300 mg/kg). Behavioral parameters were evaluated in open-field apparatus 1, 2, and 3 h after drug administration. Thiobarbituric acid reactive substances (TBARS) and protein carbonyl formation were measured in the brain. MD increased locomotor activity at the highest dose 1 and 3 h after administration. MD administration at the dose of 300 mg/kg increased visits to the center of open-field 1 h after administration; however, 3 h after administration, all administered doses of MD increased visits to the open-field center. MD 300 mg/kg increased lipid damage in the amygdala, hippocampus, and striatum. Besides, MD increased protein damage in the prefrontal cortex, amygdala, and hippocampus; however, this effect varies depending on the dose administered. In contrast, the administration of MD 75 and 300 mg/kg decreased the protein damage in the striatum. This study demonstrated that the MD administration induces behavioral changes, which was depending on the dose used. In addition, the effects of MD on oxidative damage parameters seemed to be in specific brain region and doses.

Psychostimulants and cognition: a continuum of behavioral and cognitive activation

Psychostimulants such as cocaine have been used as performance enhancers throughout recorded history. Although psychostimulants are commonly prescribed to improve attention and cognition, a great deal of literature has described their ability to induce cognitive deficits, as well as addiction. How can a single drug class be known to produce both cognitive enhancement and impairment? Properties of the particular stimulant drug itself and individual differences between users have both been suggested to dictate the outcome of stimulant use. A more parsimonious alternative, which we endorse, is that dose is the critical determining factor in cognitive effects of stimulant drugs. Herein, we review several popular stimulants (cocaine, amphetamine, methylphenidate, modafinil, and caffeine), outlining their history of use, mechanism of action, and use and abuse today. One common graphic depiction of the cognitive effects of psychostimulants is an inverted U-shaped dose-effect curve. Moderate arousal is beneficial to cognition, whereas too much activation leads to cognitive impairment. In parallel to this schematic, we propose a continuum of psychostimulant activation that covers the transition from one drug effect to another as stimulant intake is increased. Low doses of stimulants effect increased arousal, attention, and cognitive enhancement; moderate doses can lead to feelings of euphoria and power, as well as addiction and cognitive impairment; and very high doses lead to psychosis and circulatory collapse. This continuum helps account for the seemingly disparate effects of stimulant drugs, with the same drug being associated with cognitive enhancement and impairment.

A Match Made by Modafinil: Probability Matching in Choice Decisions and Spatial Attention

When predicting where a target or reward will be, participants tend to choose each location commensurate with the true underlying probability (i.e., probability match). The strategy of probability matching involves independent sampling of high and low probability locations on separate trials. In contrast, models of probabilistic spatial attention hypothesize that on any given trial attention will either be weighted toward the high probability location or be distributed equally across all locations. Thus, the strategies of probabilistic sampling by choice decisions and spatial attention appear to differ with regard to low-probability events. This distinction is somewhat surprising because similar brain mechanisms (e.g., pFC-mediated cognitive control) are thought to be important in both functions. Thus, the goal of the current study was to examine the relationship between choice decisions and attentional selection within single trials to test for any strategic differences, then to determine whether that relationship is malleable to manipulations of catecholamine-modulated cognitive control with the drug modafinil. Our results demonstrate that spatial attention and choice decisions followed different strategies of probabilistic information selection on placebo, but that modafinil brought the pattern of spatial attention into alignment with that of predictive choices. Modafinil also produced earlier learning of the probability distribution. Together, these results suggest that enhancing cognitive control mechanisms (e.g., through prefrontal cortical function) leads spatial attention to follow choice decisions in selecting information according to rule-based expectations.

Inhibitory effects of modafinil on emotional memory in mice

Modafinil (MOD), a psychostimulant used to treat narcolepsy, excessive daytime sleepiness, and sleepiness due to obstructive sleep apnea, appears to promote a possible facilitatory effect on cognitive function. In the present study, we investigated the effects of the acute administration of MOD on the different steps of emotional memory formation and usage (acquisition, consolidation and retrieval) as well as the possible participation of the state-dependency phenomenon on the cognitive effects of this compound. Mice were acutely treated with 32, 64 or 128 mg/kg MOD before training or testing or immediately after training and were subjected to the plus-maze discriminative avoidance task. The results showed that although pre-training MOD administration did not exert any effects on learning, the doses of 32 or 64 mg/kg induced emotional memory deficits during testing. Still, the post-training acute administration of the higher doses of MOD (64 and 128 mg/kg) impaired associative memory consolidation. When the drug was administered pre-test, only the 32 mg/kg dose impaired the task retrieval. Importantly, the cognitive impairing effects induced by 32 mg/kg MOD were not related to the phenomenon of state-dependency. In all, our findings provide pre-clinical evidence of potential emotional memory amnesia induced by MOD. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

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

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

The likelihood of cognitive enhancement

Whether drugs that enhance cognition in healthy individuals will appear in the near future has become a topic of considerable interest. We address this possibility using a three variable system (psychological effect, neurobiological mechanism, and efficiency vs. capabilities) for classifying candidates. Ritalin and modafinil, two currently available compounds, operate on primary psychological states that in turn affect cognitive operations (attention and memory), but there is little evidence that these effects translate into improvements in complex cognitive processing. A second category of potential enhancers includes agents that improve memory encoding, generally without large changes in primary psychological states. Unfortunately, there is little information on how these compounds affect cognitive performance in standard psychological tests. Recent experiments have identified a number of sites at which memory drugs could, in principle, manipulate the cell biological systems underlying the learning-related long-term potentiation (LTP) effect; this may explain the remarkable diversity of memory promoting compounds. Indeed, many of these agents are known to have positive effects on LTP. A possible third category of enhancement drugs directed specifically at integrated cognitive operations is nearly empty. From a neurobiological perspective, two plausible candidate classes have emerged that both target the fast excitatory transmission responsible for communication within cortical networks. One acts on nicotinic receptors (alpha7 and alpha4) that regulate release of the neurotransmitter glutamate while the other ('ampakines') allosterically modulates the glutamate receptors mediating the post-synaptic response (EPSCs). Brain imaging in primates has shown that ampakines expand cortical networks engaged by a complex task; coupled with behavioral data, these findings provide evidence for the possibility of generating new cognitive capabilities. Finally, we suggest that continuing advances in behavioral sciences provide new opportunities for translational work, and that discussions of the social impact of cognitive enhancers have failed to consider the distinction between effects on efficiency vs. new capabilities.

Modafinil prevents inhibitory avoidance memory deficit induced by sleep deprivation in rats

STUDY OBJECTIVES

Evaluation of modafinil effects on the inhibitory avoidance task (IA).

DESIGN

Rats were trained on a multiple trial IA task after receiving modafinil or vehicle injections. In experiment 1 they were trained with a weak protocol under baseline condition and in experiment 2, with a stronger protocol under sleep-deprivation condition.

RESULTS

In experiment 1 modafinil improved rats' acquisition whereas the retention test remained unaffected. In Experiment 2 modafinil did not interfere with training performance, but the lower dose prevented the retention impairment in sleep-deprived animals.

CONCLUSIONS

Modafinil is able to improve acquisition in normal rats and reverse the long-term memory impairment induced by sleep-deprivation.

Modafinil effects on reinstatement of methamphetamine seeking in a rat model of relapse

RATIONALE

Modafinil (Provigil) is a wake-promoting drug characterized by cognitive enhancing abilities. Recent clinical data have supported the use of modafinil for treatment of chronic psychostimulant addiction and relapse prevention.

MATERIALS AND METHODS

We used an intravenous methamphetamine (meth) self-administration procedure to assess the dose-dependent effects of modafinil on reinstatement following abstinence and after extinction on conditioned-cue and meth-primed reinstatement of meth seeking.

RESULTS

Modafinil attenuated active lever responding in multiple reinstatement conditions-context-induced, conditioned cue, and meth prime. The most pronounced and consistent effect was on meth-primed reinstatement, and modafinil did not reinstate meth seeking when tested alone.

DISCUSSION

These findings support clinical findings in humans that modafinil may be an effective therapeutic agent for the prevention of relapse in abstinent meth users.

Age-dependent effects of modafinil on acoustic startle and prepulse inhibition in rats

Modafinil is a psychostimulant approved for treating excessive sleepiness in adults; off-label uses (e.g., treatment of cognitive impairment in schizophrenia, ADHD and age-related dementias) are currently being explored. The effects and mechanisms of action of modafinil have not been fully established. In the present study, the effects of modafinil were examined in young adult (7-month-old) and middle-aged (21-22-month-old) rats, using the acoustic startle response (ASR) and prepulse inhibition (PPI). In the control condition, middle-aged rats showed lower activity levels, significantly lower ASR amplitudes and significantly longer ASR latencies compared to young adult rats. The effects of modafinil differed by age: activity levels and ASR amplitudes were significantly increased in middle-aged rats, whereas activity levels were lower and ASR amplitude was significantly decreased in young adult rats. Modafinil did not significantly alter PPI or startle latencies relative to the control condition. Amphetamine, used as a positive control, significantly decreased ASR amplitude in young adult rats and significantly impaired PPI for both age groups. Amphetamine-induced PPI impairment was greater for young adult rats (34% reduction in ASR amplitude) than for middle-aged rats (24% reduction). The results offer new insights into the effects of modafinil and its mechanism of action, and are consistent with the idea that modafinil enhances vigilance and cognitive functioning in individuals with deficits but not in normal, healthy individuals.

Asenapine effects in animal models of psychosis and cognitive function

RATIONALE

Asenapine, a novel psychopharmacologic agent in the development for schizophrenia and bipolar disorder, has high affinity for serotonergic, alpha-adrenergic, and dopaminergic receptors, suggesting potential for antipsychotic and cognitive-enhancing properties.

OBJECTIVES

The effects of asenapine in rat models of antipsychotic efficacy and cognition were examined and compared with those of olanzapine and risperidone.

MATERIALS AND METHODS

Amphetamine-stimulated locomotor activity (Amp-LMA; 1.0 or 3.0 mg/kg s.c.) and apomorphine-disrupted prepulse inhibition (Apo-PPI; 0.5 mg/kg s.c.) were used as tests for antipsychotic activity. Delayed non-match to place (DNMTP) and five-choice serial reaction (5-CSR) tasks were used to assess short-term spatial memory and attention, respectively. Asenapine doses varied across tasks: Amp-LMA (0.01-0.3 mg/kg s.c.), Apo-PPI (0.001-0.3 mg/kg s.c.), DNMTP (0.01-0.1 mg/kg s.c.), and 5-CSR (0.003-0.3 mg/kg s.c.).

RESULTS

Asenapine was highly potent (active at 0.03 mg/kg) in the Amp-LMA and Apo-PPI assays. DNMTP or 5-CSR performance was not improved by asenapine, olanzapine, or risperidone. All agents (P < 0.01) reduced DNMTP accuracy at short delays; post hoc analyses revealed that only 0.1 mg/kg asenapine and 0.3 mg/kg risperidone differed from vehicle. All active agents (asenapine, 0.3 mg/kg; olanzapine, 0.03-0.3 mg/kg; and risperidone, 0.01-0.1 mg/kg) significantly impaired 5-CSR accuracy (P < 0.05).

CONCLUSIONS

Asenapine has potent antidopaminergic properties that are predictive of antipsychotic efficacy. Asenapine, like risperidone and olanzapine, did not improve cognition in normal rats. Rather, at doses greater than those required for antipsychotic activity, asenapine impaired cognitive performance due to disturbance of motor function, an effect also observed with olanzapine and risperidone.

How to keep the brain awake? The complex molecular pharmacogenetics of wake promotion

Wake-promoting drugs are widely used to treat excessive daytime sleepiness. The neuronal pathways involved in wake promotion are multiple and often not well characterized. We tested d-amphetamine, modafinil, and YKP10A, a novel wake-promoting compound, in three inbred strains of mice. The wake duration induced by YKP10A and d-amphetamine depended similarly on genotype, whereas opposite strain differences were observed after modafinil. Electroencephalogram (EEG) analysis during drug-induced wakefulness revealed a transient approximately 2 Hz slowing of theta oscillations and an increase in beta-2 (20-35 Hz) activity only after YKP10A. Gamma activity (35-60 Hz) was induced by all drugs in a drug- and genotype-dependent manner. Brain transcriptome and clustering analyses indicated that the three drugs have both common and specific molecular signatures. The correlation between specific EEG and gene-expression signatures suggests that the neuronal pathways activated to stay awake vary among drugs and genetic background.

Modafinil and memory: effects of modafinil on Morris water maze learning and Pavlovian fear conditioning

Modafinil has been shown to promote wakefulness and some studies suggest the drug can improve cognitive function. Because of many similarities, the mechanism of action may be comparable to classical psychostimulants, although the exact mechanisms of modafinil's actions in wakefulness and cognitive enhancement are unknown. The current study aims to further examine the effects of modafinil as a cognitive enhancer on hippocampus-dependent memory in mice. A high dose of modafinil (75 mg/kg ip) given before training improved acquisition on a Morris water maze. When given only before testing, modafinil did not affect water maze performance. We also examined modafinil (0.075 to 75 mg/kg) on Pavlovian fear conditioning. A low dose of pretraining modafinil (0.75 mg/kg) enhanced memory of contextual fear conditioning (tested off-drug 1 week later) whereas a high dose (75 mg/kg) disrupted memory. Pretraining modafinil did not affect cued conditioning at any dose tested, and immediate posttraining modafinil had no effect on either cued or contextual fear. These results suggest that modafinil's effects of memory are more selective than amphetamine or cocaine and specific to hippocampus-dependent memory.

Modafinil: a review of neurochemical actions and effects on cognition

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

Therapeutic effects of Delta9-THC and modafinil in a marmoset Parkinson model

Current therapies for Parkinson's disease (PD) like l-dopa and dopamine (DA) agonists have declined efficacy after long term use. Therefore, research towards supplementary or alternative medication is needed. The implementation in PD can be expedited by application of compounds already used in the clinic. In this study the therapeutic effects of the psychoactive compounds Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and modafinil were tested in the 1-methyl-1,2,3,6-tetrahydropyridine (MPTP)-marmoset model for PD. The anti-parkinson effects of Delta(9)-THC (4 mg/kg) and modafinil (100 mg/kg) in parkinsonian marmosets were assessed with two behavioral rating scales covering parkinsonian symptoms and involuntary movements and two test systems assessing the locomotor activity and hand-eye coordination. Delta(9)-THC improved activity and hand-eye coordination, but induced compound-related side-effects. Modafinil improved activity and observed parkinsonian symptoms but not hand-eye coordination. It can be concluded that both compounds have therapeutic values and could supplement existing therapies for PD.

Efficacy of caffeine and modafinil in counteracting sleep deprivation in the marmoset monkey

BACKGROUND AND PURPOSE

The effects of sleep deprivation are a burden in our 24-h society. The use of wake-promoting compounds could improve the performance in situations where sleep cannot be allowed. In this study, the efficacy of the wake-promoting compounds, modafinil and caffeine, in counteracting the effects of 24-h sleep deprivation in the marmoset monkey were tested. As caffeine is habitually used, the efficacy of both compounds after short- and long-term use was investigated.

MATERIALS AND METHODS

After a normal active day, the animals were kept awake and received wake-promoting compounds during the whole night. Three times during the sleep-deprived night, putative fatigue was assessed with an activity test and the vigilance and ability to execute a task was assessed with a hand-eye coordination (HEC) task.

RESULTS

Both compounds were able to counteract to some extent the decline in performance. Modafinil was able to keep the activity at baseline performance, but performance on the HEC task was not improved. Caffeine was able to keep performance in the HEC task at a level just below daytime level but was not able to keep activity at daytime levels during the last part of the night. Caffeine and modafinil administration for 2 weeks showed a comparable effect on activity as acute use. The performance on the HEC task was similar after chronic caffeine and improved after chronic modafinil.

CONCLUSION

It is therefore concluded that modafinil and caffeine were both able to postpone or prevent the decline in vigilance and psychomotor performance and increase in fatigue induced by sleep deprivation.

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

RATIONALE

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

OBJECTIVES

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

RESULTS

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

CONCLUSIONS

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

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

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

Behavioral effects of modafinil in marmoset monkeys

RATIONALE

Modafinil is increasingly used in sleep disturbances in general and in neurodegenerative diseases and is recently being used in healthy people for attention control. However, the application of modafinil is possibly not only restricted to alertness enhancing effects. More insight in this compound may lead to new applications. Not all behavioral aspects have been studied sufficiently; therefore, more detailed investigations on modafinil's positive and aversive behavioral effects are addressed in this paper.

OBJECTIVES

Determination of effects of modafinil in marmoset monkeys with observational methods and with behavioral tests measuring locomotor activity, hand-eye coordination, response to a threat situation and startle response.

MATERIALS AND METHODS

Two hours after oral administration of modafinil in doses of 50, 100, 150, and 225 mg/kg, animals were observed and tested in the behavioral test systems.

RESULTS

Locomotor activity was increased after 100 mg/kg modafinil in the Bungalow test and after 100, 150, and 225 mg/kg, as found in the movement parameters of the human threat test. Moreover, modafinil showed anxiolytic-like effects in the human threat test. No other side effects were observed, nor were the hand-eye coordination and startle response affected.

CONCLUSIONS

Besides psychostimulation, modafinil has no aversive effects in the doses used in the domains measured. The potential anxiolytic-like effects of modafinil may create new possibilities for the therapeutic use of modafinil.

Modafinil-induced modulation of working memory and plasma corticosterone in chronically-stressed mice

The original aims of our study were to investigate the dose-effect relationship of modafinil administration on working memory performance, in parallel with the measurement of plasma corticosterone in chronically-stressed mice, as compared to control mice. Memory performance was evaluated by spontaneous alternation in a T-maze. Vehicle or modafinil (8, 16 or 32 mg/kg) were administered after or without chronic stress (immobilization and exposure to light) for 15 min/day over a period of consecutive 14 days. Immediately after behavioral testing, blood was sampled to measure plasma corticosterone levels. Under non-stress conditions, corticosterone significantly increased with 16 and 32 mg/kg modafinil administration. Interestingly, optimal working memory performance was revealed at the 16 mg/kg dose. Moreover, no correlation was evidenced between working memory performance and plasma corticosterone level in modafinil-treated animals. Under stress conditions, corticosterone level was lowered at 8 mg/kg and remained unchanged at 16 and 32 mg/kg modafinil. An optimal working memory performance was evidenced at 8 mg/kg, which indicated a decrease in the efficiency threshold of modafinil under stress. Furthermore, an inverse correlation emerged between working memory performance and corticosterone level. Our study evidenced for the first time the interaction between stress and memory, in the emotional modulation of working memory performance, as a function of the administered dose of modafinil.