Modafinil: a review of neurochemical actions and effects on cognition

Effect of modafinil on learning and task-related brain activity in methamphetamine-dependent and healthy individuals

Methamphetamine (MA)-dependent individuals exhibit deficits in cognition and prefrontal cortical function. Therefore, medications that improve cognition in these subjects may improve the success of therapy for their addiction, especially when cognitive behavioral therapies are used. Modafinil has been shown to improve cognitive performance in neuropsychiatric patients and healthy volunteers. We therefore conducted a randomized, double-blind, placebo-controlled, cross-over study, using functional magnetic resonance imaging, to examine the effects of modafinil on learning and neural activity related to cognitive function in abstinent, MA-dependent, and healthy control participants. Modafinil (200 mg) and placebo were administered orally (one single dose each), in counterbalanced fashion, 2 h before each of two testing sessions. Under placebo conditions, MA-dependent participants showed worse learning performance than control participants. Modafinil boosted learning in MA-dependent participants, bringing them to the same performance level as control subjects; the control group did not show changes in performance with modafinil. After controlling for performance differences, MA-dependent participants showed a greater effect of modafinil on brain activation in bilateral insula/ventrolateral prefrontal cortex and anterior cingulate cortices than control participants. The findings suggest that modafinil improves learning in MA-dependent participants, possibly by enhancing neural function in regions important for learning and cognitive control. These results suggest that modafinil may be a suitable pharmacological adjunct for enhancing the efficiency of cognitive-based therapies for MA dependence.

If at first you don't succeed: a review of the evidence for antidepressant augmentation, combination and switching strategies

Major depressive disorder is a common and disabling illness that leads to significant reductions in quality of life and considerable cost to society. Despite numerous advances in the pharmacological treatment of depression, many patients remain ill despite initial treatment. Beyond first-line treatment, current guidelines recommend either augmentation or switching of the initial antidepressant. In this narrative review, we summarize the data from randomized controlled trials and meta-analyses in order to concisely discuss how the impact of current research can be translated into clinical practice and, ultimately, into lasting improvements in patient outcomes. The augmentation strategies reviewed are lithium, thyroid hormone, pindolol, psychostimulants and second-generation antipsychotics. The data on switching from first-line antidepressants to other antidepressants are also reviewed, and include switching within the same class, switching to other first-line antidepressant classes and switching to less commonly prescribed antidepressants. Finally, the strategy of antidepressant combinations is examined. Overall, the strength of evidence supporting a trial of augmentation or a switch to a new agent is very similar, with remission rates between 25% and 50% in both cases. Our review of the evidence suggests several conclusions. First, although it is true that adjunctive lithium and thyroid hormone have established efficacy, we can only be confident that this is true for use in combination with tricyclic antidepressants (TCAs), and the trials were done in less treatment-resistant patients than those who typically receive TCAs today. Of these two options, triiodothyronine augmentation seems to offer the best benefit/risk ratio for augmentation of modern antidepressants. After failure of a first-line selective serotonin reuptake inhibitor (SSRI), neither a switch within class nor a switch to a different class of antidepressant is unequivocally supported by the data, although switching from an SSRI to venlafaxine or mirtazapine may potentially offer greater benefits. Interestingly, switching from a newer antidepressant to a TCA after a poor response to the former is not supported by strong evidence. Of all strategies to augment response to new-generation antidepressants, quetiapine and aripiprazole are best supported by the evidence, although neither the cost effectiveness nor the longer-term benefit of these strategies has been established. The data to guide later steps in the treatment of resistant depression are sparse. Given the wide variety of options for the treatment of major depressive disorder, and the demonstrated importance of truly adequate treatment to the long-term outcomes of patients facing this illness, it is clear that further well conducted studies are needed.

Modafinil-induced conditioned place preference via dopaminergic system in mice

Modafinil, a psychostimulant, is used in the treatment of narcolepsy, shift work sleep disorder, and excessive daytime sleepiness associated with obstructive sleep apnea. Preclinical and clinical studies suggest that modafinil may have reinforcing effects. However, a possible rewarding property of modafinil has not been fully investigated. In this study, we assessed the potential rewarding property of modafinil using the conditioned place preference (CPP) paradigm in mice. Using radiolabeled ligands, we observed changes in dopamine, glutamate, and GABA receptor binding in the brains of mice after treatment with modafinil. Modafinil produced significant CPP in mice at an intraperitoneal (i.p.) dose of 125 mg kg⁻¹ and prevented normal body weight gain of mice in a dose-dependent manner. A significant reduction in normal body weight gain was observed when mice were administrated 125 mg kg⁻¹ modafinil. In addition, there were widespread changes in receptor binding in the brains of modafinil-treated mice; Dopamine D₁ binding was increased in the caudate putamen, the accumbens, and the substantia nigra, while dopamine D₂ binding was decreased in the caudate putamen and the accumbens. Dopamine transporter (DAT) binding was increased in the prefrontal cortex, the caudate putamen, and the nucleus accumbens. No changes were observed in NMDA and GABA(A) receptor binding. These data indicate that modafinil had a significant rewarding property and could be abused as a recreational drug. Dopamine systems may play a key role in the rewarding property of modafinil.

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

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

Neuroethical issues in cognitive enhancement

Neuroethics is a developing field, concerned with addressing present and future applied ethical issues brought about directly and indirectly by neuroscience advancements. One domain where neuroscience has begun to have far-reaching ethical implications is in the research and development of pharmaceutical cognitive enhancers. Though such drugs are typically developed to treat cognitive disabilities and improve the quality of life for patients with neuropsychiatric disorders and brain injury, research has found that such drugs can improve performance on cognitive tasks in healthy individuals. In line with such findings is the growing use of these drugs by students and others for cognitive-enhancing purposes. The present paper reviews some of the evidence in both neuropsychiatric and healthy individuals and discusses the implications such research can have for society.

[Pharmacological neuroenhancement and brain doping : Chances and risks]

Pharmacological neuroenhancement refers to the use of psychoactive substances by healthy subjects with the purpose of cognitive enhancement, e.g., vigilance, concentration, memory, or mood. "Brain doping", however, refers to the illicit use of a subcategory of these substances such as prescription drugs. This subcategory includes psychostimulants (e.g., amphetamines, methylphenidate), modafinil, antidementia drugs (acetylcholine-esterase inhibitors, memantine), and antidepressants (selective serotonin reuptake inhibitors) which are being prescribed for the treatment of ADHD (attention deficit/hyperactivity disorder), Alzheimer's disease, and depression. Only psychostimulants and modafinil show significant effects on concentration, attentiveness, and vigilance in healthy subjects. However, a general use by healthy persons can not be justified because of relevant side effects and safety risks. Caffeine for pharmacological neuroenhancement can be seen as an equally effective alternative. "Brain doping" raises numerous ethical and social concerns that require a continued discussion. Demands of liberalization should be critically questioned.

Central serous chorioretinopathy associated with narcolepsy

PURPOSE

The purpose of this study was to describe a case of central serous chorioretinopathy (CSC) associated with narcolepsy.

METHODS

Case report.

RESULTS

A 34-year-old man was followed for persistent CSC in his left eye for more than 11 months. He did not have any known risk factors for CSC, including obstructive sleep apnea. However, he experienced disrupted sleep because of narcolepsy, which was inadequately treated. After 2 weeks of adequate treatment for his narcolepsy, fundus examination and optic coherence tomography demonstrated complete resolution of his CSC.

CONCLUSION

As this case report suggests, overactivation of the hypothalamic-pituitary-adrenal axis and sympathetic nervous system, seen with disrupted and poor quality sleep, may contribute to the development of CSC. Risk factors for CSC should include sleep disorders that can lead to chronic sleep deprivation.

Cognitive control deficits in schizophrenia: mechanisms and meaning

Although schizophrenia is an illness that has been historically characterized by the presence of positive symptomatology, decades of research highlight the importance of cognitive deficits in this disorder. This review proposes that the theoretical model of cognitive control, which is based on contemporary cognitive neuroscience, provides a unifying theory for the cognitive and neural abnormalities underlying higher cognitive dysfunction in schizophrenia. To support this model, we outline converging evidence from multiple modalities (eg, structural and functional neuroimaging, pharmacological data, and animal models) and samples (eg, clinical high risk, genetic high risk, first episode, and chronic subjects) to emphasize how dysfunction in cognitive control mechanisms supported by the prefrontal cortex contribute to the pathophysiology of higher cognitive deficits in schizophrenia. Our model provides a theoretical link between cellular abnormalities (eg, reductions in dentritic spines, interneuronal dysfunction), functional disturbances in local circuit function (eg, gamma abnormalities), altered inter-regional cortical connectivity, a range of higher cognitive deficits, and symptom presentation (eg, disorganization) in the disorder. Finally, we discuss recent advances in the neuropharmacology of cognition and how they can inform a targeted approach to the development of effective therapies for this disabling aspect of schizophrenia.

Wind-up of stretch reflexes as a measure of spasticity in chronic spinalized rats: The effects of passive exercise and modafinil

Spasticity is a common disorder following spinal cord injury that can impair function and quality of life. While a number of mechanisms are thought to play a role in spasticity, the role of motoneuron persistent inward currents (PICs) is emerging as pivotal. The presence of PICs can be evidenced by temporal summation or wind-up of reflex responses to brief afferent inputs. In this study, a combined neurophysiological and novel biomechanical approach was used to assess the effects of passive exercise and modafinil administration on hyper-reflexia and spasticity following complete T-10 transection in the rat. Animals were divided into 3 groups (n=8) and provided daily passive cycling exercise, oral modafinil, or no intervention. After 6weeks, animals were tested for wind-up of the stretch reflex (SR) during repeated dorsiflexion stretches of the ankle. H-reflexes were tested in a subset of animals. Both torque and gastrocnemius electromyography showed evidence of SR wind-up in the transection only group that was significantly different from both treatment groups (p<0.05). H-reflex frequency dependent depression was also restored to normal levels in both treatment groups. The results provide support for the use of passive cycling exercise and modafinil in the treatment of spasticity and provide insight into the possible contribution of PICs.

Modafinil modulation of the default mode network

RATIONALE

The default mode network (DMN) is a functional network which is implicated in a range of cognitive processes. This network is proposed to consist of hubs located in the ventromedial prefrontal cortex (vmPFC), posterior cingulate/retrosplenial cortex (PCC/rSpl), and inferior parietal lobule (IPL), with other midline cortical and temporal lobe nodes connected to these hubs. How this network is modulated by neurochemical systems during functional brain activity is not yet understood.

OBJECTIVES

In the present study, we used the norepinephrine/dopamine transporter inhibitor modafinil to test the hypothesis that this drug modulates the DMN.

METHODS

Eighteen healthy right-handed adults participated in a double-blind, placebo-controlled study of single oral dose modafinil 200 mg. They performed a simple visual sensorimotor task during slow event-related fMRI. Drug effects were interrogated within the DMN defined by task-induced deactivation (TID) on placebo.

RESULTS

There was a trend toward faster reaction time (RT) on modafinil (Cohen's d = 0.38). Brain regions within the DMN which exhibited significant modafinil-induced augmentation of TID included vmPFC, PCC/rSpl, and left IPL. Across subjects, the modafinil effect on TID in the vmPFC was significantly and specifically associated with drug effects on RT speeding.

CONCLUSIONS

Modafinil augments TID in the DMN to facilitate sensorimotor processing speed, an effect which may be particularly dependent on changes in vmPFC activity. This is consistent with the gain control function of catecholamine systems and may represent an important aspect of the pro-cognitive effects of modafinil.

Cognitive enhancement by drugs in health and disease

Attempts to improve cognitive function in patients with brain disorders have become the focus of intensive research efforts. A recent emerging trend is the use of so-called cognitive enhancers by healthy individuals. Here, we consider some of the effects - positive and negative - that current drugs have in neurological conditions and healthy people. We conclude that, to date, experimental and clinical studies have demonstrated relatively modest overall effects, most probably because of substantial variability in response both across and within individuals. We discuss biological factors that might account for such variability and highlight the need to improve testing methods and to extend our understanding of how drugs modulate specific cognitive processes at the systems or network level.

Neuropharmacology of Sleep and Wakefulness

The development of sedative/hypnotic molecules has been empiric rather than rational. The empiric approach has produced clinically useful drugs but for no drug is the mechanism of action completely understood. All available sedative/hypnotic medications have unwanted side effects and none of these medications creates a sleep architecture that is identical to the architecture of naturally occurring sleep. This chapter reviews recent advances in research aiming to elucidate the neurochemical mechanisms regulating sleep and wakefulness. One promise of rational drug design is that understanding the mechanisms of sedative/hypnotic action will significantly enhance drug safety and efficacy.

Effects of acute modafinil on cognition in trichotillomania

RATIONALE

Individuals with trichotillomania often report significant difficulty resisting the urges and drive to pull hair.

OBJECTIVES

The aim of this study is to examine whether modafinil improves motor inhibitory control, and other cognitive functions, in trichotillomania.

METHODS

Eighteen subjects with trichotillomania (mean age 33.4 ± 12.8 years; 78% female) received a single dose of modafinil (200 mg) and placebo in a crossover double-blind design. Neurocognitive performance was assessed using the stop-signal, pattern recognition, rapid visual information processing and Tower of London tasks.

RESULTS

No effects of modafinil on cognition approached statistical significance on the test measures examined (all p > 0.10).

CONCLUSIONS

These results suggest that modafinil may not be useful for targeting impulse dyscontrol in trichotillomania. However, it remains possible that relatively small effects of modafinil on cognition could exert larger downstream effects on overt behaviour. Further trials using modafinil and other pro-cognitive agents are warranted.

A positron emission tomography study examining the dopaminergic activity of armodafinil in adults using [¹¹C]altropane and [¹¹C]raclopride

BACKGROUND

Armodafinil, prescribed principally to treat narcolepsy, is undergoing assessment of therapeutic potential for other neuropsychiatric disorders and medical conditions. The neurochemical substrates and mechanisms of armodafinil are unresolved. We investigated the hypothesis that armodafinil enhances wakefulness by modulating the activities of the dopamine transporter (DAT). With positron emission tomography imaging, we determined DAT occupancy and changes in extracellular dopamine by armodafinil in vivo.

METHODS

Twelve subjects were enrolled. Plasma armodafinil levels were obtained. In vivo armodafinil occupancy of the DAT in striatum was detected by [¹¹C]altropane and changes in extracellular dopamine were detected by indirect displacement of [¹¹C]raclopride in human subjects at different times after drug administration.

RESULTS

Armodafinil (100 mg by mouth [PO]) occupied striatal DAT (34.0 ± 9.0% at 1 hour, 40.4 ± 9.5% at 2.5 hours, n = 6) and 250 mg occupied striatal DAT (60.5 ± 7.4% at 1 hour, 65.2 ± 6.1% at 2.5 hours, n = 6). In addition, armodafinil was associated with changes in extracellular dopamine (17.8 ± 30.1% [100 mg PO] and 7.0 ± 8.6% [250 mg PO] at 2.5 hours, n = 6).

CONCLUSIONS

Occupancy of the DAT and changes in extracellular dopamine in vivo further implicates the actions of armodafinil on DAT as a potential candidate for its therapeutic improvement of wakefulness and other conditions.

A retrospective review of supratherapeutic modafinil exposures

Modafinil is a non-amphetamine wakefulness-promoting agent used for the treatment of various sleep disorders characterized by excessive daytime sleepiness. There is little information in the medical literature with respect to supratherapeutic doses of this medication. We performed a retrospective review of the California Poison Control System database for all cases of single-substance ingestion of modafinil with follow-up to a known outcome for the time period 1998–2008. Data collected included age, gender, dose ingested, clinical effects, and medical outcome. There were a total of 87 patients, 53 (61%) of which were female. Patient ages ranged from 1.25 to 72 years with a mean of 30 years; 17 (20%) patients were aged 6 years or less. Thirty-three (38%) were intentional overdoses. Most commonly reported effects were tachycardia (n = 23), agitation (n = 14), anxiety (n = 11), headache (n = 8), hypertension (n = 6), dystonia/tremor (n = 6), and dizziness (n = 5). Forty-nine patients (56%) were managed at home, and 38 (44%) were managed in a healthcare setting. Therapies administered included activated charcoal (n = 8), benzodiazepines (n = 7), antihistamines (n = 2), intravenous fluids (n = 2), haloperidol (n = 2), and beta-blockers (n = 1). Effects were classified as none (n = 22), minor (n = 54), and moderate (n = 11). No major effects and no deaths occurred. Effects of modafinil overdose appear to be mild in most cases, with tachycardia and CNS symptoms predominating. Clinically significant effects requiring treatment occurred in a small number of patients.

Effects of modafinil and prazosin on cognitive and physiological functions in healthy volunteers

Previous research has demonstrated cognitive-enhancing effects of modafinil in humans and generated evidence for its therapeutic potential in psychiatric disorders. The neurochemical basis of these effects remains unresolved although a role for α1-adrenoceptors has been hypothesised. In this within-subject, double-blind, placebo-controlled study, 12 healthy male adults received modafinil (300 mg), the α1-adrenoceptor antagonist prazosin (3 mg), both together and placebo on separate occasions at least 5 days apart. Cognitive effects were assessed using a well-validated testing battery focusing on executive and working memory functions. Blood pressure, heart rate and salivary α-amylase (sAA) were measured at hourly intervals. Cognitive effects of modafinil and prazosin were identified at the difficult levels of the One-Touch Stockings of Cambridge (OTSOC) planning task. Prazosin antagonized the error-reducing effect of modafinil when the agents were given together. In contrast, the combined agents acted synergistically to increase time taken to complete OTSOC problems compared with placebo. The tachycardic and sAA-elevating effects of prazosin were also potentiated by concurrent modafinil administration. The current data suggest that the cognitive effects of modafinil on performance accuracy and latency are dissociable in terms of their neurochemical mechanisms. Our findings support the hypothesised involvement of α1-adrenoceptors in some of the cognitive-enhancing effects of modafinil and warrant further investigation.

Structure-Activity Relationships at the Monoamine Transporters for a Novel Series of Modafinil (2-[(diphenylmethyl)sulfinyl]acetamide) Analogues

A series of modafinil (1) analogues was synthesized wherein 1) para-halo-substitutents were added to the aryl rings, 2) the sulfoxide function was removed, and 3) the primary amide group was replaced with secondary and tertiary amides and amines to investigate the effects of these chemical modifications on DAT, SERT and NET binding. In addition, the locomotor-stimulant effects in mice of (±)-modafinil (1), its R- and S-enantiomers and its para-chloro sulfinylacetamide analogue (5c) were compared to those of cocaine.

Modafinil reduces microsleep during partial sleep deprivation in depressed patients

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Modafinil blocks reinstatement of extinguished opiate-seeking in rats: mediation by a glutamate mechanism

Opiate addiction is characterized by high rates of relapse even after long periods of abstinence, requiring new relapse-prevention treatments that do not have abuse potential. Recently, clinical studies suggested that the wake-promoting drug modafinil might decrease relapse in cocaine addicts. In addition, group II metabotropic glutamate receptors (mGlu2/3R) have been suggested as a new therapeutic target for drug addiction. Here, we investigated the ability of modafinil to prevent the acute morphine to promote reinstatement of extinguished preference for morphine, and the involvement of mGlu2/3Rs in this effect. Conditioned place preference (CPP) for morphine was induced in Sprague-Dawley rats, followed by extinction training. Preference for the morphine-paired side was reinstated following extinction by a morphine-priming injection. The results of our study showed that modafinil (300 mg/kg, i.p., but not 100 mg/kg) 30 min before the morphine-priming injection blocked reinstatement of extinguished CPP. The anti-reinstatement effect of modafinil was completely prevented by pretreatment with the selective mGlu2/3 antagonist LY341495. Additional experiments indicated that modafinil alone did not produce a preference, and that modafinil did not alter the expression of morphine CPP or the cueing properties of morphine either 1 or 14 days after morphine CPP conditioning. These data reveal a novel mechanism for modafinil actions, a role for mGlu2/3 receptors in reinstatement of opiate-seeking, and a new therapeutic option to treat relapse in opiate addiction.

Modulatory effects of modafinil on neural circuits regulating emotion and cognition

Modafinil differs from other arousal-enhancing agents in chemical structure, neurochemical profile, and behavioral effects. Most functional neuroimaging studies to date examined the effect of modafinil only on information processing underlying executive cognition, but cognitive enhancers in general have been shown to have pronounced effects on emotional behavior, too. We examined the effect of modafinil on neural circuits underlying affective processing and cognitive functions. Healthy volunteers were enrolled in this double-blinded placebo-controlled trial (100 mg/day for 7 days). They underwent BOLD fMRI while performing an emotion information-processing task that activates the amygdala and two prefrontally dependent cognitive tasks-a working memory (WM) task and a variable attentional control (VAC) task. A clinical assessment that included measurement of blood pressure, heart rate, the Hamilton anxiety scale, and the profile of mood state (POMS) questionnaire was also performed on each test day. BOLD fMRI revealed significantly decreased amygdala reactivity to fearful stimuli on modafinil compared with the placebo condition. During executive cognition tasks, a WM task and a VAC task, modafinil reduced BOLD signal in the prefrontal cortex and anterior cingulate. Although not statistically significant, there were trends for reduced anxiety, for decreased fatigue-inertia and increased vigor-activity, as well as decreased anger-hostility on modafinil. Modafinil in low doses has a unique physiologic profile compared with stimulant drugs: it enhances the efficiency of prefrontal cortical cognitive information processing, while dampening reactivity to threatening stimuli in the amygdala, a brain region implicated in anxiety.

Effect of modafinil on learning performance and neocortical long-term potentiation in rats

Modafinil is a novel wake-promoting agent whose effects on cognitive performance have begun to be addressed at both preclinical and clinical level. The present study was designed to investigate in rats the effects of chronic modafinil administration on cognitive performance by evaluating: (i) working and reference memories in an Olton 4×4 maze, and (ii) learning of a complex operant conditioning task in a Skinner box. In addition, the effect of modafinil on the ability of the rat frontal cortex to develop long-term potentiation (LTP) was also studied. Chronic modafinil did not significantly modify working memory errors but decreased long-term memory errors on the Olton 4×4 maze, meaning that the drug may have a favourable profile on performance of visuo-spatial tasks (typically, a hippocampus-dependent task) when chronically administered. On the other hand, chronic modafinil resulted in a marked decrease of successful responses in a complex operant conditioning learning, which means that repeated administration of the drug influences negatively problem-solving abilities when confronting the rat to a sequencing task (typically, a prefrontal cortex-dependent task). In addition, in vivo electrophysiology showed that modafinil resulted in impaired capacity of the rat prefrontal cortex to develop LTP following tetanization. It is concluded that modafinil can improve the performance of spatial tasks that depend almost exclusively on hippocampal functioning, but not the performance in tasks including a temporal factor where the prefrontal cortex plays an important role. The fact that modafinil together with preventing operant conditioning learning was also able to block LTP induction in the prefrontal cortex, suggests that the drug could interfere some critical component required for LTP can be developed, thereby altering neuroplastic capabilities of the prefrontal cortex.

Opposite roles of dopamine and orexin in quinpirole-induced excessive drinking: a rat model of psychotic polydipsia

RATIONALE

Repeated administration of the dopamine D2/D3 agonist quinpirole (QNP) progressively increases non-regulatory water intake. This effect may model psychotic polydipsia, a potentially fatal but poorly understood condition.

OBJECTIVES

The growing evidence for a role of orexin in mediating arousal and cognition has linked this peptide to schizophrenia, hence we examined whether manipulations of dopaminergic and orexinergic systems, as well as of setting, would further characterize the model.

METHODS

Water intake was measured in rats sequentially tested in home and then operant conditioning setting, with chronic administration of D2 antagonist haloperidol (Hal) prior to QNP treatment. A group of rats similarly treated was also assessed for orexin A (OxA) expression in the cortex. Finally, the effect of the orexin-1 receptor antagonist SB-334867 on QNP-induced polydipsia was evaluated.

RESULTS

In rats made polydipsic by QNP the amount of water drank during the first 4 h was strongly correlated with the degree of dissociation between appetitive and consummatory components of drinking behavior in the following hour of operant access to water. Hal 0.2 mg/kg prevented both polydipsia and the dissociation, while 0.1 mg/kg only blocked the dissociation. Chronic QNP treatment increased, in a Hal-reversible way, OxA expression in the somatosensory cortex (SI). Moreover, pretreatment with SB-334867 sped up and potentiated QNP-induced polydipsia.

CONCLUSIONS

Results disclose compulsive components in QNP-induced polydipsia that are mediated by dopamine D2 receptors. QNP also regulates OxA expression in the SI, while the block of orexin-1 receptors enhances QNP-induced polydipsia. We suggest that dopamine and OxA play opposite roles in QNP-induced polydipsia.

Effects of modafinil on the sleep EEG depend on Val158Met genotype of COMT

STUDY OBJECTIVES

Modafinil may promote wakefulness by increasing cerebral dopaminergic neurotransmission, which importantly depends on activity of catechol-O-methyltransferase (COMT) in prefrontal cortex. The effects of modafinil on sleep homeostasis in humans are unknown. Employing a novel sleep-pharmacogenetic approach, we investigated the interaction of modafinil with sleep deprivation to study dopaminergic mechanisms of sleep homeostasis.

DESIGN

Placebo-controlled, double-blind, randomized crossover study.

SETTING

Sleep laboratory in temporal isolation unit.

PARTICIPANTS

22 healthy young men (23.4 +/- 0.5 years) prospectively enrolled based on genotype of the functional Val158Met polymorphism of COMT(10 Val/Val and 12 Met/Met homozygotes).

INTERVENTIONS

2 x 100 mg modafinil and placebo administered at 11 and 23 hours during 40 hours prolonged wakefulness.

MEASUREMENTS AND RESULTS

Subjective sleepiness and EEG markers of sleep homeostasis in wakefulness and sleep were equally affected by sleep deprivation in Val/Val and Met/Met allele carriers (placebo condition). Modafinil attenuated the evolution of sleepiness and EEG 5-8 Hz activity during sleep deprivation in both genotypes. In contrast to caffeine, modafinil did not reduce EEG slow wave activity (0.75-4.5 Hz) in recovery sleep, yet specifically increased 3.0-6.75 Hz and > 16.75 Hz activity in NREM sleep in the Val/Val genotype of COMT.

CONCLUSIONS

The Val158Met polymorphism of COMT modulates the effects of modafinil on the NREM sleep EEG in recovery sleep after prolonged wakefulness. The sleep EEG changes induced by modafinil markedly differ from those of caffeine, showing that pharmacological interference with dopaminergic and adenosinergic neurotransmission during sleep deprivation differently affects sleep homeostasis.

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.

Healthy brain aging: what has sleep got to do with it?

Sleep plays an important role in learning, memory encoding, and cognition. Insufficient quantity or quality of sleep leads not only to short-term neurocognitive dysfunction but also to permanent changes to the central nervous system. Sleep disorders are common in the geriatric population. The hypoxemia and sleep fragmentation resulting from obstructive sleep apnea are the most likely pathophysiology responsible for damage to the brain. Because treatment of these sleep disorders can lead to improved cognitive function, it is becoming increasingly important for physicians to be able to correctly recognize and treat these disorders in patients presenting with memory or cognitive complaints.

Modafinil administration improves working memory in methamphetamine-dependent individuals who demonstrate baseline impairment

Modafinil improves working memory in healthy subjects and individuals diagnosed with schizophrenia and Attention Deficit/Hyperactivity Disorder, though the effects of modafinil have not been evaluated on working memory in methamphetamine-dependent subjects. This double-blind, placebo-controlled study evaluated whether a daily dose of 400 mg of modafinil, administered over three consecutive days, would enhance performance on a measure of working memory relative to test performance at baseline and following 3 days of placebo administration in 11 methamphetamine addicted, nontreatment-seeking volunteers. The results revealed that participants demonstrating relatively poor performance on the third day of a 3-day washout period (ie, at baseline), showed significant improvement on measures of working memory, but not on measures of episodic memory or information processing speed. In contrast, for participants demonstrating relatively high performance at baseline, modafinil administration did not affect test scores. The findings provide an initial indication that modafinil can reverse methamphetamine-associated impairments in working memory.

[Using psychostimulants in end-of-life patients with hypoactive delirium and cognitive disorders: A literature review]

OBJECTIVE

To review the research about psychostimulant effects on cognitive functions in end-of-life patients diagnosed with hypoactive delirium or cognitive disorders.

METHOD

The MEDLINE (1966-March 2008), Embase (1974-March 2008), PsycINFO (1806-March 2008), IPA (1970-March 2008), CINAHL (1982-March 2008), ISI Web of Science (1945-March 2008), Current Contents (March 2007-March 2008), Access Medicine (2001-March 2008), and ProQuest Dissertations & Theses (1980-March 2008) databases were searched with keywords related to delirium, cognition, psychostimulants, and palliative care for French or English articles in a dementia-free and hyperactive delirium-free end-of-life population. Cognitive functions had to be assessed before and after initiation of the psychostimulant treatment. Moreover, treatment had to be initiated after the onset of cognitive impairments.

RESULTS

A total of 173 studies were screened. Five studies on methylphenidate and 1 study on caffeine met inclusion criteria and were included in this review. Two studies were case reports, 2 were open-label trials, and 2 were double-blind, crossover randomized placebo-controlled trials. Three studies were conducted with hypoactive delirium patients and all studies were conducted in an advanced cancer patient population.

CONCLUSIONS

The reviewed studies support the use of methylphenidate to improve end-of-life patient cognitive functions, particularly in the case of hypoactive delirium. Caffeine seems to have beneficial effects on psychomotor activity. Further well-designed studies are needed to consolidate these findings.

Modafinil treatment for fatigue in HIV/AIDS: a randomized placebo-controlled study

OBJECTIVE

To evaluate the efficacy and safety of modafinil in the treatment of fatigue in patients with human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) and to assess effect on depressive symptoms.

METHOD

Patients who were HIV+ and had clinically significant fatigue (according to the Fatigue Severity Scale [FSS]) were included in a 4-week randomized, placebo-controlled, double-blind trial. This was followed by an additional 8 weeks of open-label treatment for modafinil responders and 12 weeks for placebo nonresponders. The primary outcome measure for fatigue and depression was the Clinical Global Impressions-Improvement scale, supplemented by the FSS, Hamilton Depression Rating Scale, and Beck Depression Inventory. Safety was assessed with assays of CD4 cell count and HIV ribonucleic acid (RNA) viral load. Visits were weekly for 4 weeks, then biweekly, with a follow-up visit at 6 months. Maximum trial dose of modafinil was 200 mg/d. Data for this study were collected between December 2004 and December 2008.

RESULTS

115 patients were randomly assigned. In intention-to-treat analyses, fatigue response rate to modafinil was 73% and to placebo, 28%. Attrition was 9%. Modafinil did not have an effect on mood alone in the absence of improved energy. At week 4, CD4 cell counts did not change significantly; HIV RNA viral load showed a trend decline for patients taking modafinil but not for those taking placebo. At 6 months, those still taking modafinil had more energy and fewer depressive symptoms than patients who were not taking modafinil, and only those still taking modafinil showed a significant decline from baseline in their HIV RNA viral load.

CONCLUSIONS

Modafinil appears to be effective and well tolerated in treating fatigue in HIV+ patients. Consideration of its use is warranted considering the high prevalence of fatigue in the HIV community, its minimal side effects, and overall patient acceptance.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00118378.

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.

Effects of modafinil and methylphenidate on visual attention capacity: a TVA-based study

INTRODUCTION

Theory of visual attention (TVA; Bundesen 1990) whole report tasks allow the independent measurement of visual perceptual processing speed and visual short-term memory (vSTM) storage capacity, unconfounded by motor speed. This study investigates how cognitive enhancing effects of psychostimulants depend on baseline performance and individual plasma levels.

MATERIALS AND METHODS

Eighteen healthy volunteers (aged 20-35 years) received single oral doses of either 40 mg methylphenidate, 400 mg modafinil or placebo in a counterbalanced, double-blind crossover design. A whole report of visually presented letter arrays was performed 2.5-3.5 h after drug administration, and blood samples for plasma level analysis were taken.

RESULTS

Methylphenidate and modafinil both enhanced perceptual processing speed in participants with low baseline (placebo) performance. These improvements correlated with subjective alertness. Furthermore, we observed differential plasma level-dependent effects of methylphenidate in lower and higher performing participants: higher plasma levels led to a greater improvement in low-performing participants and to decreasing improvement in high-performing participants. Modafinil enhanced visual short-term memory storage capacity in low-performing participants.

CONCLUSIONS

This is the first pharmacological investigation demonstrating the usefulness of a TVA task for high-resolution and repeated cognitive parameter estimation after cognitive-enhancing medication. Our results confirm previous findings of attentional capacity improvements in low performers and extend the baseline dependency model to methylphenidate. Plasma level-dependent effects of psychostimulants can be modelled on an inverted U-shaped dose-response relationship, which is highly relevant to predict cognitive enhancing and detrimental effects of psychostimulants in patients with cognitive deficits (e.g., attention deficit hyperactivity disorder) and healthy volunteers (e.g., self-medicating academics).

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.

Temperament and Character Correlates of Neuropsychological Performance

We investigate the association between temperament and character dimensions, on the one hand, and computerised neuropsychological test performance, on the other hand. Temperament and character dimensions were operationalised as scores on the subscales of the Temperament and Character Inventory (TCI), a 240-item measure that is based on the psychobiological theory of personality. Neuropsychological outcomes were measured on six computerised tests of executive functioning and abstract reasoning from the University of Pennsylvania Computerised Neuropsychological Test Battery (PennCNP). The executive and abstract reasoning tasks included a test of Motor Praxis (MPRAXIS), the Penn Abstraction, Inhibition and Working Memory Task (AIM), the Letter-N-Back (LNB2), the Penn Conditional Exclusion Task (PCET), the Penn Short Logical Reasoning Task (SPVRT) and the Short Raven's Progressive Matrices (SRAVEN). Results from this exploratory study yielded significant associations between neuropsychological performance and temperament and character traits. The temperament traits of Harm Avoidance and Reward Dependence were positively correlated with reaction time on the AIM and the SPVRT. The character dimension of Self-Transcendence was significantly associated with performance accuracy on the AIM and the temperament dimension of Novelty Seeking was inversely related to performance accuracy on the LNB2. These results confirm the importance of addressing the temperament and character correlates of neuropsychological performance in both clinical and non-clinical studies.

Randomized, double-blind, placebo-controlled trial of modafinil for the treatment of methamphetamine dependence

OBJECTIVE

To compare modafinil to placebo for reducing methamphetamine (MA) use, improving retention, and reducing depressive symptoms and MA cravings. Rates of adverse events and cigarette smoking with modafinil versus placebo were also compared.

METHODS

Following a 2-week, non-medication lead-in period, 71 treatment-seeking MA-dependent participants were randomly assigned to modafinil (400mg once daily; N=34) or placebo (once daily; N=37) for 12 weeks under double-blind conditions. Participants attended clinic thrice-weekly to provide urine samples analyzed for MA-metabolite, to complete research assessments, and to receive contingency management and weekly cognitive behavioral therapy (CBT) sessions.

RESULTS

There were no statistically significant effects for modafinil on MA use, retention, depressive symptoms, or MA cravings in pre-planned analyses. Outcomes for retention and MA use favored modafinil in a post hoc analysis among participants with low CBT attendance and among participants with baseline high-frequency of MA use (MA use on >18 of past 30 days), but did not reach statistical significance in these small subgroups. Modafinil was safe and well tolerated and did not increase cigarette smoking.

CONCLUSIONS

Modafinil was no more effective than placebo at 400mg daily in a general sample of MA users. A post hoc analysis showing a trend favoring modafinil among subgroups with baseline high-frequency MA use and low CBT attendance suggests that further evaluation of modafinil in MA users is warranted.

Wake promoting effects of cocaine and amphetamine-regulated transcript (CART)

Cocaine- and amphetamine-regulated transcript (CART) peptides modulate anxiety, food intake, endocrine function, and mesolimbic dopamine related reward and reinforcement. Each of these disparate behaviors takes place during the state of wakefulness. Here, we identify a potential wake promoting role of CART by characterizing its effects upon sleep/wake architecture in rats. Dose-dependent increases in wake were documented following intracerebroventricular CART 55-102 administered at the beginning of the rat's major sleep period. Sustained wake was observed for up to 4h following delivery of 2.0 microg of CART peptide. The wake promoting effect was specific to active CART 55-102 because no effect on sleep/wake was observed with the inactive form of the peptide. Increased wake was followed by robust rebound in NREM and REM sleep that extended well into the subsequent lights-off, or typical wake period, of the rat. These findings point to a potential novel role for CART in regulating wakefulness.

Dopamine transporter-related effects of modafinil in rhesus monkeys

RATIONALE

Modafinil is currently used as a treatment for daytime sleepiness.

OBJECTIVES

The objectives of this study were to explore the dopamine transporter (DAT)-related effects of modafinil on behavior and in vivo neurochemistry in rhesus monkeys (Macaca mulatta).

METHODS

The effects of modafinil (3.0-10 mg/kg, i.v.) were evaluated on locomotor activity, reinstatement of cocaine-maintained behavior, extracellular dopamine levels in the caudate nucleus, and DAT occupancy in the dorsal striatum. Eight subjects were fitted with a collar-mounted activity monitor to evaluate sleep-activity cycles, with 4 days of baseline recording preceding an injection of saline or modafinil (3.0-10 mg/kg). The effects of modafinil (3.0-10 mg/kg) and cocaine (0.3 mg/kg) on reinstatement of behavior that was previously maintained under a second-order schedule of i.v. cocaine delivery were tested in a separate group of subjects (n = 6). Finally, the effects of modafinil (3.0-10 mg/kg) on extracellular dopamine levels and DAT occupancy in vivo were characterized using microdialysis and positron emission tomography, respectively, in a within-subjects design (n = 4).

RESULTS

Modafinil significantly increased nighttime locomotor activity and reinstated cocaine-maintained behavior but did not affect daytime locomotor activity. Modafinil significantly increased striatal extracellular dopamine levels at a dose that resulted in DAT occupancy of 64.4% (putamen) and 60.2% (caudate).

CONCLUSION

The behavioral and in vivo dopaminergic effects of modafinil are consistent with the profile of a low potency DAT inhibitor and may indicate potential for abuse at high doses.

Action of modafinil--increased motivation via the dopamine transporter inhibition and D1 receptors?

BACKGROUND

Modafinil is prescribed for the treatment of narcolepsy. It has been postulated that modafinil might treat cognitive disruption in neuropsychiatric disorders. The mechanisms underlying such modafinil-induced improvements in performance have yet to be delineated however. Recent evidence suggests that modafinil might block the dopamine transporter (DAT) and that the dopamine D1 receptor (D1R) might contribute to modafinil effects.

METHODS

Dopamine D1R wildtype (WT), heterozygous (HT), and knockout (KO) mice received vehicle, modafinil, or the selective DAT blocker GBR12909 in a progressive ratio breakpoint study.

RESULTS

Both modafinil and GBR12909 increased motivation in the task as measured by an increase in breakpoint in WT and HT mice. These drug-induced increases in motivation were reduced in dopamine D1R HT mice relative to their WT littermates. The D1R KO mice did not respond in the task.

CONCLUSIONS

These data support the hypothesis that modafinil increases motivation. Moreover, given the similarity of effects with GBR12909, the data corroborate evidence that the behavioral effects of modafinil might be due to DAT inhibition. Furthermore, the dopamine D1R might play a downstream role in mediating modafinil-induced increases in motivation. Thus, studies reporting cognition-enhancing effects of modafinil might have been influenced by its ability to increase motivation.

Modafinil effects during acute continuous positive airway pressure withdrawal: a randomized crossover double-blind placebo-controlled trial

RATIONALE

Continuous positive airway pressure (CPAP) use is associated with reduced motor vehicle accidents in patients with obstructive sleep apnea (OSA). However, interruption of CPAP therapy is common and is associated with a decline in daytime function.

OBJECTIVES

We hypothesized that the wakefulness promoter, modafinil, would ameliorate this decline.

METHODS

Patients were admitted to the laboratory for three consecutive nights. CPAP was used for the first night, followed by a baseline day, and was then withdrawn for the two subsequent nights (nasal airflow monitored). On each of the mornings after the two CPAP withdrawal nights, patients received 200 mg modafinil or placebo (n = 21) in a randomized, double-blind, crossover design. Treatment periods were separated by a 5-week washout. Driving simulator performance, neurocognitive performance, and subjective alertness were measured by the AusEd driving simulator, psychomotor vigilance task, and Karolinska Sleepiness Scale, respectively.

MEASUREMENTS AND MAIN RESULTS

During CPAP withdrawal, severe sleep-disordered breathing was evident and administration of modafinil improved simulated driving performance (steering variability, P < 0.0001; mean reaction time, P

CONCLUSIONS

Modafinil prevented the decline in simulated driving performance, neurocognitive performance, and subjective sleepiness in patients with OSA with acutely interrupted CPAP therapy. Clinical trial registered with the Australian New Zealand Clinical Trials Registry at www.anzctr.org.au (ACTRN12606000027516).

Collapse

Key Words Collapse

MESH Headings

• Accidents, Traffic/prevention & control
• Accidents, Traffic/statistics & numerical data
• Automobile Driving
• Benzhydryl Compounds/therapeutic use
• Central Nervous System Stimulants/therapeutic use
• Continuous Positive Airway Pressure/methods
• Cross-Over Studies
• Double-Blind Method
• Humans
• Male
• Middle Aged
• Modafinil
• Psychomotor Performance/drug effects
• Reaction Time/drug effects
• Sleep Apnea Syndromes/therapy
• Ventilator Weaning/methods
• Wakefulness/drug effects

Collapse

Grants Collapse

Affiliation(s)

Shaun C Williams Sleep and Circadian Research Group/NHMRC Centre for Sleep Medicine, Woolcock Institute, University of Sydney and Royal Prince Alfred Hospital, Sydney, Australia.
Nathaniel S Marshall
Marina Kennerson
Naomi L Rogers
Peter Y Liu
Ronald R Grunstein

Collapse

Collaborators Collapse

Cocaine-induced neuroadaptations in glutamate transmission: potential therapeutic targets for craving and addiction

A growing body of evidence indicates that repeated exposure to cocaine leads to profound changes in glutamate transmission in limbic nuclei, particularly the nucleus accumbens. This review focuses on preclinical studies of cocaine-induced behavioral plasticity, including behavioral sensitization, self-administration, and the reinstatement of cocaine seeking. Behavioral, pharmacological, neurochemical, electrophysiological, biochemical, and molecular biological changes associated with cocaine-induced plasticity in glutamate systems are reviewed. The ultimate goal of these lines of research is to identify novel targets for the development of therapies for cocaine craving and addiction. Therefore, we also outline the progress and prospects of glutamate modulators for the treatment of cocaine addiction.

Brain imaging studies in pathological gambling

This article reviews the neuroimaging research on pathological gambling (PG). Because of the similarities between substance dependence and PG, PG research has used paradigms similar to those used in substance use disorder research, focusing on reward and punishment sensitivity, cue reactivity, impulsivity, and decision making. This review shows that PG is consistently associated with blunted mesolimbic-prefrontal cortex activation to nonspecific rewards, whereas these areas show increased activation when exposed to gambling-related stimuli in cue exposure paradigms. Very little is known, and hence more research is needed regarding the neural underpinnings of impulsivity and decision making in PG. This review concludes with a discussion regarding the challenges and new developments in the field of neurobiological gambling research and comments on their implications for the treatment of PG.

Pharmacological strategies for enhancing cognition in schizophrenia

Researchers have long recognized that individuals with schizophrenia experience challenges in a wide range of cognitive domains, and research on cognitive impairment in schizophrenia is not a recent phenomena. However, the past 10-20 years have seen an increasing recognition of the central importance of cognition to understanding function and outcome in this illness (Green et al. in Schizophr Bull 26:119-136, 2000), an awareness that has shifted the emphasis of at least some work on schizophrenia. More specifically, there has been a rapidly growing body of work on methods of enhancing cognition in schizophrenia, as a means to potentially facilitate improved outcome and quality of life for individuals with this debilitating illness. The current chapter reviews the results of a range of studies examining adjunctive pharmacological treatments to enhance cognition in schizophrenia using a range of designs, including single-dose studies, open-label repeated dosing studies, and double-blind parallel group and crossover designs with repeated dosing. Although many of the single-dose and open-label studies have suggested positive cognitive effects from a range of agents, few of the larger-scale double-blind studies have generated positive results. The current state of results may reflect the need to identify alternative molecular mechanisms for enhancing cognition in schizophrenia or the need to reconceptualize the ways in which pharmacological agents may improve cognition in this illness, with a concomitant change in the traditional clinical trial study design used in prior studies of cognitive enhancement in schizophrenia.

Translational Aspects of the Novel Object Recognition Task in Rats Abstinent Following Sub-Chronic Treatment with Phencyclidine (PCP): Effects of Modafinil and Relevance to Cognitive Deficits in Schizophrenia

Phencyclidine (PCP) induces a behavioral syndrome in rodents that bears remarkable similarities to some of the core symptoms observed in schizophrenic patients, among those cognitive deficits. The successful alleviation of cognitive impairments associated with schizophrenia (CIAS) has become a major focus of research efforts as they remain largely untreated. The aim of the present study was to investigate the effects of selected antipsychotic and cognition enhancing drugs, namely haloperidol, risperidone, donepezil, and modafinil in an animal model widely used in preclinical schizophrenia research. To this end, the novel object recognition (NOR) task was applied to rats abstinent following sub-chronic treatment with PCP. Rats were administered either PCP (5 mg/kg, i.p.) or vehicle twice a day for 7 days, followed by a 7-day washout period, before testing in NOR. Upon testing, vehicle-treated rats successfully discriminated between novel and familiar objects, an effect abolished in rats that had previously been exposed to PCP treatment. Acute treatment with modafinil (64 mg/kg, p.o.) ameliorated the PCP-induced deficit in novel object exploration, whereas haloperidol (0.1 mg/kg, s.c.), risperidone (0.2 mg/kg, i.p.), and donepezil (3 mg/kg, p.o.) were without significant effect. Given the negligible efficacy of haloperidol and risperidone, and the contradictory data with donepezil to treat CIAS in the clinic, together with the promising preliminary pro-cognitive effects of modafinil in certain subsets of schizophrenic patients, the sub-chronic PCP-NOR abstinence paradigm may represent an attractive option for the identification of potential novel treatments for CIAS.