Profile of executive and memory function associated with amphetamine and opiate dependence

Cognitive function and treatment response in a randomized clinical trial of computer-based training in cognitive-behavioral therapy

Cognitive-behavioral therapy (CBT), because of its comparatively high level of cognitive demand, is likely to be challenging for substance users with limitations in cognitive function. However, it is not known whether computer-assisted versions of CBT will be particularly helpful (e.g., allowing individualized pace and repetition) or difficult (e.g., via complexity of computerized delivery) for such patients. In this secondary analysis of data collected from a randomized clinical trial evaluating computer-assisted CBT, four aspects of cognitive functioning were evaluated among 77 participants. Those with higher levels of risk taking completed fewer sessions and homework assignments and had poorer substance use outcomes.

Pharmacological enhancement of drug cue extinction learning: translational challenges

Augmentation of cue exposure (extinction) therapy with cognitive-enhancing pharmacotherapy may constitute a rational strategy for the clinical management of drug relapse. While certain success has been reported for this form of therapy in anxiety disorders, in this paper we highlight several obstacles that may undermine the efficacy of exposure therapy for substance use disorders. We also review translational studies that have evaluated the facilitative effects of the cognitive enhancer D-cycloserine on extinction targeting drug-related cues. Finally, important considerations for the design and implementation of future studies evaluating exposure therapy combined with pharmacotherapy for substance use disorders are discussed.

Peripheral biomarkers of cognitive response to dopamine receptor agonist treatment

RATIONALE

Using biological markers to objectively measure addiction severity or to identify individuals who might benefit most from pro-cognitive treatment could potentially revolutionize neuropsychopharmacology. We investigated the use of dopamine receptor mRNA levels in circulating blood cells as predictors of cognitive response following dopamine agonist treatment, and as biomarkers of the severity of stimulant drug dependence.

METHODOLOGY

We employed a double-blind, placebo-controlled cross-over design, administering a single dose of the selective dopamine D(2/3) receptor agonist pramipexole (0.5 mg) to increase dopamine transmission in one session and a placebo treatment in another session in 36 volunteers. Half the volunteers had a formal diagnosis of stimulant dependence, while half had no psychiatric history. Participants performed neurocognitive tests from the CANTAB battery on both occasions, and stimulant-dependent individuals rated drug craving using visual analog scales. Whole-blood mRNA levels were measured for three dopamine-related genes: DRD3 and DRD4 (dopamine receptors), and catechol-O-methyltransferase (COMT; a dopamine catabolic enzyme).

RESULTS

Stimulant users performed worse than healthy volunteers on the cognitive tests. The variation in peripheral dopamine D(3) receptor mRNA expression explained over one quarter of the variation in response to pramipexole on the spatial working memory test across all participants. The severity of stimulant dependence was also significantly associated with peripheral COMT mRNA expression in stimulant users.

CONCLUSIONS

Peripheral expression of dopamine-related genes may be useful as a biomarker of cognitive response to dopamine agonist drugs and of severity of addiction to dopamine-releasing stimulant drugs.

Khat use and neurobehavioral functions: suggestions for future studies

Although there is a rich body of research available regarding the effect of acute and chronic khat dosing in animal models, research on the behavioral and cognitive effects of khat in human subjects is not extensive and several of the available studies have been done only in the context of observational and single-case studies. In light of the absence of a substantial literature on the neurobehavioral deficits associated with khat use and to provide a context that could be used to identify themes for future research we review previous research that has focused on other stimulant drugs. This review highlights multiple areas of neurocognitive deficit that have been identified in previous studies of individuals who have been chronic users of stimulants, such as amphetamines and methamphetamines. The review highlights a substantial body of evidence demonstrating a wide range of learning and memory impairments including deficits that persist during abstinence from active drug use. This review does not imply a similar khat effect, but due to some similarities pharmacologically between the active components of khat (cathinone and cathine) and amphetamines, future studies examining these same domains of cognitive functioning in chronic khat users and abstinent khat users appears to be warranted, if possible using some of the same or similar laboratory measures.

Sequential Learning Models for the Wisconsin Card Sort Task: Assessing Processes in Substance Dependent Individuals

The Wisconsin Card Sort Task (WCST) is a commonly used neuropsychological test of executive or frontal lobe functioning. Traditional behavioral measures from the task (e.g., perseverative errors) distinguish healthy controls from clinical populations, but such measures can be difficult to interpret. In an attempt to supplement traditional measures, we developed and tested a family of sequential learning models that allowed for estimation of processes at the individual subject level in the WCST. Testing the model with substance dependent individuals and healthy controls, the model parameters significantly predicted group membership even when controlling for traditional behavioral measures from the task. Substance dependence was associated with a) slower attention shifting following punished trials and b) reduced decision consistency. Results suggest that model parameters may offer both incremental content validity and incremental predictive validity.

The role of the somatotrophic axis in neuroprotection and neuroregeneration of the addictive brain

Early studies have shown that the abuse of alcohol, central stimulants, and opiates such as heroin destroys brain cells, reducing attention span and memory. However, new research has suggested that there may be a way to regain some of the lost attention and recall. It has recently been shown that brain cells targeted for early death by continued opiate use can be salvaged by injections of synthetic human growth hormone (GH). GH is a polypeptide hormone, normally secreted by the anterior pituitary gland, which stimulates cell growth and controls body metabolism. Recombinant human GH is currently used in replacement therapy to alleviate the symptoms of adults and children with GH deficiency syndrome. The recent observation that GH can reverse morphine-induced cell damage could open the door to new ways of treating and preventing damage from the abuse of opiates in addicts and also of treating cell damage induced by alcohol and central stimulants. This article reviews current knowledge of the somatotrophic axis, including GH and insulin-like growth factor-1 (IGF-1), in the brain and also discusses the potential use of GH/IGF-1 as agents for treatment of brain pathology in addictive diseases.

Cognitive enhancement as a pharmacotherapy target for stimulant addiction

BACKGROUND

No medications have been proven to be effective for cocaine and methamphetamine addiction. Attenuation of drug reward has been the main strategy for medications development, but this approach has not led to effective treatments. Thus, there is a need to identify novel treatment targets in addition to the brain reward system.

AIM

To propose a novel treatment strategy for stimulant addiction that will focus on medications enhancing cognitive function and attenuating drug reward.

METHODS

Pre-clinical and clinical literature on potential use of cognitive enhancers for stimulant addiction pharmacotherapy was reviewed.

RESULTS AND CONCLUSIONS

Cocaine and methamphetamine users show significant cognitive impairments, especially in attention, working memory and response inhibition functions. The cognitive impairments seem to be predictive of poor treatment retention and outcome. Medications targeting acetylcholine and norepinephrine are particularly well suited for enhancing cognitive function in stimulant users. Many cholinergic and noradrenergic medications are on the market and have a good safety profile and low abuse potential. These include galantamine, donepezil and rivastigmine (cholinesterase inhibitors), varenicline (partial nicotine agonist), guanfacine (alpha(2)-adrenergic agonist) and atomoxetine (norepinephrine transporter inhibitor). Future clinical studies designed optimally to measure cognitive function as well as drug use behavior would be needed to test the efficacy of these cognitive enhancers for stimulant addiction.

A cannabinoid CB(1) receptor antagonist ameliorates impairment of recognition memory on withdrawal from MDMA (Ecstasy)

(+/-)-3,4-Methylenedioxymethamphetamine (MDMA, 'Ecstasy') abusers have persistent neuropsychiatric deficits including memory impairments after the cessation of abuse. On the other hand, cannabinoid CB(1) receptors have been implicated in learning/memory, and are highly expressed in the hippocampus, a region of the brain believed to have an important function in certain forms of learning and memory. In this study, we clarified the mechanism underlying the cognitive impairment that develops during MDMA withdrawal from the standpoint of the cannabinoid CB(1) receptors. Mice were administered MDMA (10 mg/kg, i.p.) once a day for 7 days. On the 7th day of withdrawal, a novel object recognition task was performed and the amount of cannabinoid CB(1) receptor protein was measured with western blotting. Recognition performance was impaired on the 7th day of withdrawal. This impairment was blocked by AM251, a cannabinoid CB(1) receptor antagonist, administered 30 min before the training trial or co-administered with MDMA. At this time, the level of cannabinoid CB(1) receptor protein increased significantly in the hippocampus but not the prefrontal cortex or striatum. This increase of CB(1) receptor protein in the hippocampus was also blocked by the co-administration of AM251. Furthermore, CB(1) receptor knockout mice showed no impairment of recognition performance on the withdrawal from MDMA. The impairment of recognition memory during withdrawal from MDMA may result from the activation of cannabinoid CB(1) receptors in the hippocampus.

The impacts of substance abuse and dependence on neuropsychological functions in a sample of patients from Saudi Arabia

BACKGROUND

A lot of studies were directed to explore the relation between drug abuse and neuropsychological functions. Some studies reported that even after a long duration of disappearance of withdrawal or intoxication symptoms, many patients have obvious deterioration of cognitive functions. The aim of this study was to explore the relationship between the substance use disorders and the executive functions.

METHODS

Two groups were selected for this study. An experimental group consisted of 154 patients and further subdivided according to the substance used into three different subgroups: opioid, amphetamine and alcohol groups which included 49, 56 and 49 patients respectively. The control group was selected matching the experimental group in the demographic characteristics and included 100 healthy persons. Tools used were: Benton visual retention tests, color trail making test, Stroop colors-word test, symbol digit modalities test, the five dots cognitive flexibility test, and TAM verbal flexibility test. All the data were subjected to statistical analysis

RESULTS

The study showed that the group of drug-dependent subjects performed significantly worse than the comparison group on all measures Also, there were significant differences among the subgroups as the alcoholic group was much worse followed by the amphetamine then the opioids groups. Patients with longer duration of dependence and multiple hospital readmissions were much worse in comparison to patients with shorter duration of dependence and less readmission.

CONCLUSION

The study confirmed that the functions of specific brain regions underlying cognitive control are significantly impaired in patients of drug addiction. This impairment was significantly related to type of substance, duration of use and number of hospitalization and may contribute to most of behavioral disturbances found in addicts and need much attention during tailoring of treatment programs.

Cholinergic functioning in stimulant addiction: implications for medications development

Acetylcholine, the first neurotransmitter discovered, participates in many CNS functions, including sensory and motor processing, sleep, nociception, mood, stress response, attention, arousal, memory, motivation and reward. These diverse cholinergic effects are mediated by nicotinic- and muscarinic-type cholinergic receptors (nAChR and mAChR, respectively). The goal of this review is to synthesize a growing literature that supports the potential role of acetylcholine as a treatment target for stimulant addiction. Acetylcholine interacts with the dopaminergic reward system in the ventral tegmental area, nucleus accumbens and prefrontal cortex. In the ventral tegmental area, both nAChR and mAChR stimulate the dopaminergic system. In the nucleus accumbens, cholinergic interneurons integrate cortical and subcortical information related to reward. In the prefrontal cortex, the cholinergic system contributes to the cognitive aspects of addiction. Preclinical studies support a facilitative role of nicotinic receptor agonists in the development of stimulant addiction. In contrast, nonselective muscarinic receptor agonists seem to have an inhibitory role. In human studies, acetylcholinesterase inhibitors, which increase synaptic acetylcholine levels, have shown promise for the treatment of stimulant addiction. Further studies testing the efficacy of cholinergic medications for stimulant addiction are warranted.

The amphetamine sensitization model of schizophrenia: relevance beyond psychotic symptoms?

RATIONALE

A sensitized dopamine system may be linked to the genesis of psychotic symptoms in schizophrenia. Following withdrawal from amphetamine exposures, psychotic-like traits have been robustly demonstrated, but the presence of cognitive/mnemonic deficits remains uncertain.

METHODS

Adult male Lewis and Fischer rats, differing in cognitive performance, were exposed intermittently to escalating doses of amphetamine over 5 weeks. This was effective in producing behavioral sensitization to a subsequent amphetamine challenge. Following 27 days of drug withdrawal, the animals were assessed in Pavlovian conditioning, object recognition, and spatial working memory. In addition, prepulse inhibition (PPI), spontaneous motor activity, and anxiety-like behavior were measured.

RESULTS

Amphetamine pretreatment induced behavioral sensitization in both rat strains similarly. Working memory was enhanced in Fischer but not Lewis rats following withdrawal. Spontaneous novel object preference was enhanced in sensitized Fischer rats, but was impaired in sensitized Lewis rats, thus effectively reversing the strain difference in non-sensitized controls. In contrast, Pavlovian fear conditioning remained unaffected and so were anxiety-like behavior, open field activity, and PPI.

CONCLUSION

The face validity of the amphetamine withdrawal model for cognitive deficits was limited to the object recognition memory impairment observed in sensitized Lewis rats. Yet, the possibility that enhancing dopaminergic neurotransmission may facilitate object recognition and spatial working memory performance was demonstrated in sensitized Fischer rats. Identification of the mechanisms underlying such strain-dependent effects would be instrumental in the further specifications of the construct validity, and therefore the limitations and potential of the amphetamine sensitization model of schizophrenia.

Sustained attention in patients receiving and abstinent following methadone maintenance treatment for opiate dependence: performance and neuroimaging results

OBJECTIVE

Impairments in the function of attention exacerbate the course of opiate dependence and may play a role in the relapsing nature of the disorder. This study used clinical measures and positron emission tomography (PET) to assess the functioning of sustained attention in subjects with a history of opiate dependence.

METHODS

A test of auditory sustained attention was administered to 10 subjects receiving methadone maintenance treatment, 13 formerly opiate-dependent subjects in protracted abstinence, and 14 healthy Comparison subjects. Simultaneous measurement of regional glucose metabolism was made by [(18)F] flourodeoxyglucose PET. Subjects groups were compared on the measures of sustained attention and regional cerebral glucose metabolism.

RESULTS

Healthy Comparison subjects scored significantly better than either methadone-maintained or abstinent former opiate addicts on measures of sustained attention. Formerly opiate-dependent subjects in protracted abstinence scored better than methadone-maintained subjects on sustained attention. Methadone-maintained subjects demonstrated a relative reduction in regional cerebral glucose metabolism in the right supramarginal gyrus, and the thalamus bilaterally. The Comparison subjects without a history of opiate dependence demonstrated a relative increase in regional cerebral glucose metabolism in the right anterior cingulate gyrus, the right medial superior frontal gyrus and the thalamus bilaterally.

CONCLUSIONS

Subjects with a history of opiate dependence have impairments in the functioning of sustained attention, and abnormalities in brain regions identified as important in attention processing. Impairments in attention performance persist in subjects who enjoy prolonged abstinence from opiates.

Bidirectional effects of fentanyl on dendritic spines and AMPA receptors depend upon the internalization of mu opioid receptors

Fentanyl is a frequently used and abused opioid analgesic and can cause internalization of mu opioid receptors (MORs). Receptor internalization modulates the signaling pathways of opioid receptors. As changes in dendritic spines and synaptic AMPA receptors play important roles in addiction and memory loss, we investigated how fentanyl affects dendritic spines and synaptic AMPA receptors in cultured hippocampal neurons. Fentanyl at low concentrations (0.01 and 0.1 microM) caused the collapse of dendritic spines and decreased the number of AMPA receptor clusters. In contrast, fentanyl at high concentrations (1 and 10 microM) had opposite effects, inducing the emergence of new spines and increasing the number of AMPA receptor clusters. These dose-dependent bidirectional effects of fentanyl were blocked by a selective MOR antagonist CTOP at 5 microM. In neurons that had been transfected with HA-tagged or GFP-tagged MORs, fentanyl at high concentrations induced persistent and robust internalization of MORs, whereas fentanyl at lower concentrations induced little or transient receptor internalization. The blockade of receptor internalization with the expression of dominant-negative Dynamin I (the K44E mutant) reversed the effect of fentanyl at high concentrations, supporting a role of receptor internalization in modulating the dose-dependent effects of fentanyl. In contrast to morphine, the effects of fentanyl on dendritic spines are distinctively bidirectional and concentration dependent, probably due to its ability to induce robust internalization of MORs at high concentrations. The characterization of the effects of fentanyl on spines and AMPA receptors may help us understand the roles of MOR internalization in addiction and cognitive deficits.

A novel touchscreen-automated paired-associate learning (PAL) task sensitive to pharmacological manipulation of the hippocampus: a translational rodent model of cognitive impairments in neurodegenerative disease

RATIONALE

Paired-associate learning (PAL), as part of the Cambridge Neuropsychological Test Automated Battery, is able to predict who from an at-risk population will develop Alzheimer's disease. Schizophrenic patients are also impaired on this same task. An automated rodent model of PAL would be extremely beneficial in further research into Alzheimer's disease and schizophrenia.

OBJECTIVE

The objective of this study was to develop a PAL task using touchscreen-equipped operant boxes and test its sensitivity to manipulations of the hippocampus, a brain region of interest in both Alzheimer's disease and schizophrenia.

MATERIALS AND METHODS

Previous work has shown that spatial and non-spatial memory can be tested in touchscreen-equipped operant boxes. Using this same apparatus, rats were trained on two variants of a PAL task differing only in the nature of the S- (the unrewarded stimuli, a combination of image and location upon the screen). Rats underwent cannulation of the dorsal hippocampus, and after recovery were tested under the influence of intra-hippocampally administered glutamatergic and cholinergic antagonists while performing the PAL task.

RESULTS

Impairments were seen after the administration of glutamatergic antagonists, but not cholinergic antagonists, in one of the two versions of PAL.

CONCLUSIONS

De-activation of the hippocampus caused impairments in a PAL task. The selective nature of this effect (only one of the two tasks was impaired), suggests the effect is specific to cognition and cannot be attributed to gross impairments (changes in visual learning). The pattern of results suggests that rodent PAL may be suitable as a translational model of PAL in humans.

Features of men with anabolic-androgenic steroid dependence: A comparison with nondependent AAS users and with AAS nonusers

BACKGROUND

Anabolic-androgenic steroid (AAS) dependence has been a recognized syndrome for some 20 years, but remains poorly understood.

METHODS

We evaluated three groups of experienced male weightlifters: (1) men reporting no history of AAS use (N=72); (2) nondependent AAS users reporting no history of AAS dependence (N=42); and (3) men meeting adapted DSM-IV criteria for current or past AAS dependence (N=20). We assessed demographic indices, lifetime history of psychiatric disorders by the Structured Clinical Interview for DSM-IV, variables related to AAS use, and results from drug tests of urine and hair.

RESULTS

Nondependent AAS users showed no significant differences from AAS nonusers on any variable assessed. Dependent AAS users, however, differed substantially from both other groups on many measures. Notably, they reported a more frequent history of conduct disorder than nondependent AAS users (odds ratio [95% CI]: 8.0 [1.7, 38.0]) or AAS nonusers (13.1 [2.8, 60.4]) and a much higher lifetime prevalence of opioid abuse and dependence than either comparison group (odds ratios 6.3 [1.2, 34.5] and 18.6 [3.0, 116.8], respectively).

CONCLUSIONS

Men with AAS dependence, unlike nondependent AAS users or AAS nonusers, showed a distinctive pattern of comorbid psychopathology, overlapping with that of individuals with other forms of substance dependence. AAS dependence showed a particularly strong association with opioid dependence - an observation that recalls recent animal data suggesting similarities in AAS and opioid brain reward mechanisms. Individuals with AAS dependence and individuals with "classical" substance dependence may possibly harbor similar underlying biological and neuropsychological vulnerabilities.

Tumor necrosis factor-alpha levels in HIV-1 seropositive injecting drug users

TNF-alpha is a highly pleiotropic cytokine and plays an important role in regulating HIV-1 replication. It may compromise the integrity of the blood-brain-barrier and, thus, may contribute to the neurotoxicity of HIV-1-infection. Both intravenous drug abuse (IDU) and HIV infection can increase TNF-alpha activity, but little information is available on the effects of a combination of these factors on TNF-alpha. We investigated plasma TNF-alpha levels and mRNA in the peripheral monocytes of 166 men and women in three groups: HIV-1-positive IDUs, HIV-1-negative IDUs, and HIV-negative non-IDU control participants. HIV-1-positive IDUs had higher TNF-alpha levels than HIV-1-negative IDUs who, in turn, had higher levels than controls. TNF-alpha mRNA expression in peripheral monocytes was significantly increased in both HIV-1-positive and negative IDUs compared to controls. These findings show that the effects of HIV infection and intravenous drug use may be additive in increasing TNF-alpha levels. Given the multiple effects of TNF-alpha in HIV infection, additional investigation of its role is needed.

Modeling stress and drug craving in the laboratory: implications for addiction treatment development

Addition is a chronic relapsing illness affected by multiple social, individual and biological factors that significantly impact course and recovery of the illness. Stress interacts with these factors and increases addiction vulnerability and relapse risk, thereby playing a significant role in the course of the illness. This paper reviews our efforts in developing and validating laboratory models of stress and drug cue-related provocation to assess stress responses and stress-related adaptation in addicted individuals compared with healthy controls. Empirical findings from human laboratory and brain imaging studies are presented to show the specific stress-related dysregulation that accompanies the drug-craving state in addicted individuals. In order to adequately validate our laboratory model, we have also carefully examined relapse susceptibility in the addicted individuals and these data are reviewed. The overarching goal of these efforts is to develop a valid laboratory model to identify the stress-related pathophysiology in addiction with specific regard to persistent craving and compulsive seeking. Finally, the significant implications of these findings for the development of novel treatment interventions that target stress processes and drug craving to improve addiction relapse outcomes are discussed.

Disrupted 'reflection' impulsivity in cannabis users but not current or former ecstasy users

Evidence for serotonin involvement in impulsivity has generated interest in the measurement of impulsivity in regular ecstasy users, who are thought to display serotonergic dysfunction. However, current findings are inconsistent. Here, we used a recently developed Information Sampling Test to measure 'reflection' impulsivity in 46 current ecstasy users, 14 subjects who used ecstasy in the past, 15 current cannabis users and 19 drug-naïve controls. Despite elevated scores on the Impulsivity subscale of the Eysenck Impulsiveness-Venturesomeness-Empathy questionnaire, the current and previous ecstasy users did not differ significantly from the drug-naive controls on the Information Sampling Test. In contrast, the cannabis users sampled significantly less information on the task, and tolerated a lower level of certainty in their decision-making, in comparison to the drug-naive controls. The effect in cannabis users extends our earlier observations in amphetamine- and opiate-dependent individuals (Clark, et al., 2006, Biological Psychiatry 60: 515-522), and suggests that reduced reflection may be a common cognitive style across regular users of a variety of substances. However, the lack of effects in the two ecstasy groups suggests that the relationship between serotonin function, ecstasy use and impulsivity is more complex.

Drug addiction and the memory systems of the brain

We review drug addiction from the perspective of the hypothesis that drugs of abuse interact with distinct brain memory systems. We focus on emotional and procedural forms of memory, encompassing Pavlovian and instrumental conditioning, both for action-outcome and for stimulus-response associations. Neural structures encompassed by these systems include the amygdala, hippocampus, nucleus accumbens, and dorsal striatum. Additional influences emanate from the anterior cingulate and prefrontal cortex, which are implicated in the encoding and retrieval of drug-related memories that lead to drug craving and drug use. Finally, we consider the ancillary point that chronic abuse of many drugs may impact directly on neural memory systems via neuroadaptive and neurotoxic effects that lead to cognitive impairments in which memory dysfunction is prominent.

Chronic stress, drug use, and vulnerability to addiction

Stress is a well-known risk factor in the development of addiction and in addiction relapse vulnerability. A series of population-based and epidemiological studies have identified specific stressors and individual-level variables that are predictive of substance use and abuse. Preclinical research also shows that stress exposure enhances drug self-administration and reinstates drug seeking in drug-experienced animals. The deleterious effects of early life stress, child maltreatment, and accumulated adversity on alterations in the corticotropin releasing factor and hypothalamic-pituitary-adrenal axis (CRF/HPA), the extrahypothalamic CRF, the autonomic arousal, and the central noradrenergic systems are also presented. The effects of these alterations on the corticostriatal-limbic motivational, learning, and adaptation systems that include mesolimbic dopamine, glutamate, and gamma-amino-butyric acid (GABA) pathways are discussed as the underlying pathophysiology associated with stress-related risk of addiction. The effects of regular and chronic drug use on alterations in these stress and motivational systems are also reviewed, with specific attention to the impact of these adaptations on stress regulation, impulse control, and perpetuation of compulsive drug seeking and relapse susceptibility. Finally, research gaps in furthering our understanding of the association between stress and addiction are presented, with the hope that addressing these unanswered questions will significantly influence new prevention and treatment strategies to address vulnerability to addiction.

Character pathology and neuropsychological test performance in remitted opiate dependence

Background

Cognitive deficits and personality pathology are prevalent in opiate dependence, even during periods of remission, and likely contribute to relapse. Understanding the relationship between the two in vulnerable, opiate-addicted patients may contribute to the design of better treatment and relapse prevention strategies.

Methods

The Millon Multiaxial Clinical Inventory (MCMI) and a series of neuropsychological tests were administered to three subject groups: 29 subjects receiving methadone maintenance treatment (MM), 27 subjects in protracted abstinence from methadone maintenance treatment (PA), and 29 healthy non-dependent comparison subjects. Relationships between MCMI scores, neuropsychological test results, and measures of substance use and treatment were examined using bivariate correlation and regression analysis.

Results

MCMI scores were greater in subjects with a history of opiate dependence than in comparison subjects. A significant negative correlation between MCMI scores and neuropsychological test performance was identified in all subjects. MCMI scores were stronger predictors of neuropsychological test performance than measures of drug use.

Conclusion

Formerly methadone-treated opiate dependent individuals in protracted opiate abstinence demonstrate a strong relationship between personality pathology and cognitive deficits. The cause of these deficits is unclear and most likely multi-factorial. This finding may be important in understanding and interpreting neuropsychological testing deficiencies in opiate-dependent subjects.

A touch screen based Stop Signal Response Task in rhesus monkeys for studying impulsivity associated with chronic cocaine self-administration

Among a range of cognitive deficits, human cocaine addicts display increased impulsivity and decreased performance monitoring. In order to establish an animal model that can be used to study the underlying neurobiology of these deficits associated with addiction, we have developed a touch screen based Stop Signal Response Task for rhesus monkeys. This task is essentially identical to the clinically used Stop Signal Task employed for diagnostic and research purposes. In this task, impulsivity is reflected in the amount of time needed to inhibit a response after it has been initiated, the Stop Signal Response Time (SSRT). Performance monitoring is reflected by the slowing of response times following Stop trials (Post-Stop Slowing, PSS). Herein we report on the task structure, the staged methods for training animals to perform the task, and a comparison of performance values for control and cocaine experienced animals. Relative to controls, monkeys that had self-administered cocaine, followed by 18 months abstinence, displayed increased impulsivity (increased SSRT values), and decreased performance monitoring (decreased PSS values). Our results are consistent with human data, and thereby establish an ideal animal model for studying the etiology and underlying neurobiology of cocaine-induced impulse control and performance monitoring deficits.

Dissociation between long-lasting behavioral sensitization to amphetamine and impulsive choice in rats performing a delay-discounting task

RATIONALE

Repeated amphetamine (AMPH) exposure is known to cause long-term changes in AMPH-induced locomotor behavior (i.e., sensitization) that are associated with similarly long-lasting changes in brain function. It is not clear, however, if such exposure produces long-lasting changes in a cognitive behavior that, in humans, is hypothesized to contribute to addiction.

OBJECTIVES

To examine whether repeated AMPH exposure induces both locomotor sensitization and alters impulsive choice in a delay-discounting task.

MATERIALS AND METHODS

Adult, male Sprague-Dawley rats (n = 29) were pretreated with 3.0 mg/kg AMPH or saline every other day for 20 days and were then trained to lever press for small, immediately delivered food reinforcement or larger reinforcements delivered after delays. We subsequently assessed the effects of acute AMPH (0.1-2.0 mg/kg) on delay-discounting. Lastly, we tested for long-lasting effects of pretreatment by giving an AMPH challenge (3.0 mg/kg) 1 week after the final delay-discounting session.

RESULTS

Repeated AMPH produced sensitization to the drug's stereotypy-inducing effects but did not alter acquisition or baseline behavior in the delay-discounting task. Following acute AMPH, impulsive choice and other measures of delay-discounting were altered, but to a similar extent in both saline- and AMPH-pretreated groups. The AMPH challenge, given approximately 3 months after the last pretreatment injection, revealed that sensitization was still evident.

CONCLUSIONS

Our results suggest that one behavioral consequence of repeated AMPH exposure-sensitization-does not overlap with another potential outcome-increased impulsivity. Furthermore, the neuroadaptations known to be associated with sensitization may be somewhat distinct from those that lead to changes in impulsive choice.

Dysregulation of emotional response in current and abstinent heroin users: negative heightening and positive blunting

OBJECTIVE

Evidence suggests that abstinent opioid users have abnormal emotional response to natural reinforcing stimuli, but little is known about the emotional response of subjects currently using heroin. Abnormal emotional experience could underlie poor sensitivity to negative events related to heroin use and reduced ability to consider alternative reinforcers to help overcome addiction. In this paper, we will assess the subjective response of current and abstinent heroin users exposed to emotionally competent positive and negative stimuli.

MATERIALS AND METHODS

We administered the "Clinical Instrument for Emotional Response Evaluation" (including neutral, pleasant, and unpleasant images from the International Affective Picture System) to 22 current opioid users enrolled in a clinical trial using controlled prescribed heroin and 41 abstinent opioid users enrolled in residential treatment. The dependent variable was their subjective response to the images measured with the Self-Assessment Manikin, a scale designed to rate the International Affective Picture System (IAPS) images in the three dimensions of emotion: valence, arousal, and dominance. We compared these ratings with IAPS normative values for healthy participants.

RESULTS

Significant group x emotional condition interactions were found in the arousal dimension. Post-hoc tests showed that compared to healthy participants, both current and abstinent heroin users had greater emotional response to neutral images and lower response to pleasant images. Furthermore, current opioid users had higher emotional response to unpleasant images when compared to healthy participants and lower response to pleasant images when compared to abstinent users.

CONCLUSIONS

Current opioid users have abnormal emotional experience, characterized by heightened response to unpleasant stimuli and blunted response to pleasant stimuli.

Cannabis use and adult ADHD symptoms

BACKGROUND

The present study examined the associations between cannabis use in adolescence and young adulthood and self-reported adult attention deficit/hyperactivity disorder (ADHD) symptoms in adulthood.

METHODS

A 25-year prospective longitudinal study of the health, development, and adjustment of a birth cohort of 1265 New Zealand children. Measures included assessments of adolescent and young adult cannabis use and ADHD symptoms at age 25, measures of childhood socioeconomic disadvantage, family adversity, childhood and early adolescent behavioural adjustment and cognitive ability, and adolescent and young adult other drug use.

RESULTS

Cannabis use by age 25 was significantly (p<.0001) associated with increasing self-reported adult ADHD symptoms at age 25. Adjustment of the association for potentially confounding factors from childhood and early adolescence reduced the magnitude of the association, but it remained statistically significant (p<.0001). However, control for the mediating effects of other drug use in adolescence and early adulthood reduced the association between cannabis use and adult ADHD symptoms to statistical non-significance (p>.20).

CONCLUSIONS

The current study suggested that the association between cannabis use and adult ADHD symptoms was mediated by other substance use that was associated with cannabis use. The results suggest that cannabis use leads to other drug use, which in turn leads to increased ADHD symptoms. However, it should be noted that the potential influence of such factors as genetic predispositions may still be unaccounted for.

Neuropsychological predictors of clinical outcome in opiate addiction

A growing literature supports a role for neurocognitive deficits such as impaired decision-making in the development and maintenance of addictive behaviour. On the basis of these findings, it has been suggested that measures of neurocognitive functioning may be applied to the task of predicting clinical outcome in drug addiction. This in turn may have relevance for differentiating treatment based on individual patient needs. To explore this hypothesis we obtained neurocognitive measures of planning, impulsivity and decision-making from 37 opiate dependent individuals within 6 weeks of starting a community drug treatment programme and we followed them up 3 months into the programme. Performance on two tests of decision-making, but not on tests of planning, motor inhibition, reflection impulsivity or delay discounting, was found to predict abstinence from illicit drugs at 3 months with high specificity and moderate sensitivity. In particular, two thirds of the participants performing normally on the Cambridge Gamble Task and the Iowa Gambling Task, but none of those impaired on both, were abstinent from illicit drugs at follow up. Other neuropsychological, psychiatric or psychosocial factors measured in this sample did not explain this finding. The results are discussed in terms of the brain circuitry involved and the potential implications for the planning of treatment services for opiate dependence.

Cellular and molecular mechanisms involved in the neurotoxicity of opioid and psychostimulant drugs

Substance abuse and addiction are the most costly of all the neuropsychiatric disorders. In the last decades, much progress has been achieved in understanding the effects of the drugs of abuse in the brain. However, efficient treatments that prevent relapse have not been developed. Drug addiction is now considered a brain disease, because the abuse of drugs affects several brain functions. Neurological impairments observed in drug addicts may reflect drug-induced neuronal dysfunction and neurotoxicity. The drugs of abuse directly or indirectly affect neurotransmitter systems, particularly dopaminergic and glutamatergic neurons. This review explores the literature reporting cellular and molecular alterations reflecting the cytotoxicity induced by amphetamines, cocaine and opiates in neuronal systems. The neurotoxic effects of drugs of abuse are often associated with oxidative stress, mitochondrial dysfunction, apoptosis and inhibition of neurogenesis, among other mechanisms. Understanding the mechanisms that underlie brain dysfunction observed in drug-addicted individuals may contribute to improve the treatment of drug addiction, which may have social and economic consequences.

Impulsivity as a vulnerability marker for substance-use disorders: review of findings from high-risk research, problem gamblers and genetic association studies

There is a longstanding association between substance-use disorders (SUDs) and the psychological construct of impulsivity. In the first section of this review, personality and neurocognitive data pertaining to impulsivity will be summarised in regular users of four classes of substance: stimulants, opiates, alcohol and 3,4-methylenedioxymethamphetamine (MDMA). Impulsivity in these groups may arise via two alternative mechanisms, which are not mutually exclusive. By one account, impulsivity may occur as a consequence of chronic exposure to substances causing harmful effects on the brain. By the alternative account, impulsivity pre-dates SUDs and is associated with the vulnerability to addiction. We will review the evidence that impulsivity is associated with addiction vulnerability by considering three lines of evidence: (i) studies of groups at high-risk for development of SUDs; (ii) studies of pathological gamblers, where the harmful consequences of the addiction on brain structure are minimised, and (iii) genetic association studies linking impulsivity to genetic risk factors for addiction. Within each of these three lines of enquiry, there is accumulating evidence that impulsivity is a pre-existing vulnerability marker for SUDs.

Evidence of temporal cortical dysfunction in rhesus monkeys following chronic cocaine self-administration

Cocaine abusers show impaired performance on cognitive tasks that engage prefrontal cortex. These deficits may contribute to impaired control and relapse in abusers. Understanding the neuronal substrates that lead to these deficits requires animal models that are relevant to the human condition. However, to date, models have mostly focused on behaviors mediated by subcortical systems. Here we evaluated the impact of long-term self-administration of cocaine in the rhesus monkey on cognitive performance. Tests included stimulus discrimination (SD)/reversal and delayed alternation tasks. The chronic cocaine animals showed marked deficits in ability to organize their behavior for maximal reward. This was demonstrated by an increased time needed to acquire SDs. Deficits were also indicated by an increased time to initially learn the delayed alternation task, and to adapt strategies for bypassing a reliance on working memory to respond accurately. Working memory per se (delay dependent performance) was not affected by chronic self-administration. This pattern of cognitive deficits suggests dysfunction that extends beyond localized prefrontal cortical areas. In particular, it appears that temporal cortical function is also compromised. This agrees with other recent clinical and preclinical findings, and suggests further study into addiction related dysfunction across more widespread cortical networks is warranted.

Understanding drug addiction: a neuropsychological perspective

The purpose of the present review is to describe the neuropsychological correlates of long-term substance abuse and to discuss the findings within the context of premorbid vulnerabilities, comorbidity and adolescent neurodevelopment. The authors critically review key findings from the neuropsychological literature related to the long-term sequelae of alcohol, cannabis, inhalant, opiates, psychostimulants and ecstasy use. Leading electronic databases such as PubMed were searched to identify relevant studies published in the past 20 years. References identified from bibliographies of pertinent articles and books in the field were also collected and selectively reviewed. Across substances, individuals with long-term abuse consistently demonstrate neuropsychological impairments of executive (inhibitory) control, working memory and decision making, together with neurobiological abnormalities involving frontotemporal and basal ganglia circuits. In some instances these deficits are dose dependent, implying that they are a direct consequence of prolonged drug exposure. However, comorbid behavioural, personality and mental health problems are common among drug-using populations and are associated with similar neuropsychological deficits. Presented herein is a neuropsychological model of addictive behaviour that highlights the complex interplay between cognition, brain maturation, psychopathology and drug exposure.

Cocaine exposure causes long-term increases in impulsive choice

In this study, the authors examined the long-term effects of prior exposure to cocaine on a delay-discounting task commonly used to measure impulsive choice. Male Long-Evans rats received daily intraperitoneal injections of 30 mg/kg cocaine HCl or saline for 14 days. Following 3 weeks of withdrawal, rats began training. On each trial, rats were given a choice between 2 levers. A press on 1 lever resulted in immediate delivery of a single 45-mg food pellet, and a press on the other resulted in delivery of 4 pellets after a delay period. Impulsive choice was defined as preference for the small immediate over the large delayed reward. Three months after treatment, cocaine-exposed rats displayed increased impulsive choice behavior. They also showed less anticipatory responding (entries into the food trough) during the delays prior to reward delivery, indicating that the enhanced impulsive choice in these rats may be related to deficits in bridging the delay between response and reward. These data demonstrate that cocaine exposure can cause enduring increases in impulsive choice behavior, consistent with observations in human subjects with drug addictions.

Long-term effects of prior cocaine exposure on Morris water maze performance

Cocaine addiction is associated with long-term cognitive alterations including deficits on tests of declarative/spatial learning and memory. To determine the extent to which cocaine exposure plays a causative role in these deficits, adult male Long-Evans rats were given daily injections of cocaine (30 mg/kg/day x 14 days) or saline vehicle. Three months later, rats were trained for 6 sessions on a Morris water maze protocol adapted from Gallagher, Burwell, and Burchinal [Gallagher, M., Burwell, R., & Burchinal, M. (1993). Severity of spatial learning impairment in aging: development of a learning index for performance in the Morris water maze. Behavioral Neuroscience, 107, 618-626]. Rats given prior cocaine exposure performed similarly to controls on training trials, but searched farther from the platform location on probe trials interpolated throughout the training sessions and showed increased thigmotaxis. The results demonstrate that a regimen of cocaine exposure can impair Morris water maze performance as long as 3 months after exposure. Although the impairments were not consistent with major deficits in spatial learning and memory, they may have resulted from cocaine-induced increases in stress responsiveness and/or anxiety. Increased stress and anxiety would be expected to increase thigmotaxis as well as cause impairments in searching for the platform location, possibly through actions on ventral striatal dopamine signaling.

Neurocognitive characterizations of Russian heroin addicts without a significant history of other drug use

Research on the neurocognitive characteristics of heroin addiction is sparse and studies that do exist include polydrug abusers; thus, they are unable to distinguish neurocognitive effects of heroin from those of other drugs. To identify neurocognitive correlates specific to heroin addiction, the present study was conducted in St. Petersburg, Russia where individuals typically abuse and/or become addicted to only one substance, generally alcohol or heroin. Heroin addicts were recruited from an inpatient treatment facility in St. Petersburg. Three comparison groups included alcoholics, addicts who used both alcohol and heroin, and non-abusers. Psychiatric, background, and drug history evaluations were administered after detoxification to screen for exclusion criteria and characterize the sample. Executive Cognitive Functions (ECF) that largely activate areas of the prefrontal cortex and its circuitry measured include complex visual pattern recognition (Paired Associates Learning), working memory (Delayed Matching to Sample), problem solving (Stockings of Cambridge), executive decision making (Cambridge Decision Making Task), cognitive flexibility (Stroop Color-Word Task) and response shifting (Stop Change Task). In many respects, the heroin addicts were similar to alcohol and alcohol+heroin dependent groups in neurocognitive deficits relative to controls. The primary finding was that heroin addicts exhibited significantly more disadvantageous decision making and longer deliberation times while making risky decisions than the other groups. Because the nature and degree of recovery from drug abuse are likely a function of the type or pattern of neurocognitive impairment, differential drug effects must be considered.

The differential relationship between cocaine use and marijuana use on decision-making performance over repeat testing with the Iowa Gambling Task

Decision-making deficits are a robust cognitive correlate of substance abuse, but few studies have addressed the long-term differential associations of cocaine use and marijuana (MJ) use on decision-making. This study utilized the Iowa Gambling Task (IGT), a widely used measure of decision-making, to investigate the relationship between cocaine and MJ use and IGT learning. We analyzed between and within group differences across two consecutive testing sessions in abstinent users of either MJ or cocaine. We assessed long-term correlates of the use of these drugs by evaluating users after 25 days of enforced abstinence. Results showed that both cocaine users and MJ users performed worse than controls on the total IGT net score. All groups showed learning between Session 1 and Session 2, but the cocaine users showed the smallest increase in performance. The pattern of learning from the beginning to the end (block x block) of the IGT (Session 2) was different for the drug groups, with the cocaine group showing more learning than the MJ group. Dose-related measures of cocaine use (g/week) and MJ use (joints/week) predicted IGT performance (the heavier the drug use the lower the performance). Differential correlates of cocaine use and MJ use on decision-making learning may have important implications for the development of novel treatment interventions.

Ecological assessment of executive functions in substance dependent individuals

Substance dependence is associated with executive function deficits. However, most available studies have examined the performance of substance dependent individuals (SDI) on traditional laboratory measures of executive functions, whereas few studies have used ecologically valid assessments with SDI. Our aim was to examine the performance of 37 SDI (poly-substance users) and 37 matched controls on an ecologically valid measure of executive function (the Behavioural Assessment of the Dysexecutive Syndrome - BADS). We also administered the Wisconsin Card Sorting Test (WCST) to investigate whether ecological measures were more discriminative than traditional tests in detecting SDI deficits. A related aim was to examine the ability of the BADS (and the WCST) to predict everyday executive problems. Results showed that SDI had widespread deficits on ecological measures of executive function. Conversely, we found no differences between groups on the WCST. Furthermore, the BADS (but not the WCST) predicted everyday problems related to apathy, disinhibition, and executive dysfunction.

The neuropsychology of amphetamine and opiate dependence: implications for treatment

Chronic use of amphetamines and/or opiates has been associated with a wide range of cognitive deficits, involving domains of attention, inhibitory control, planning, decision-making, learning and memory. Although both amphetamine and opiate users show marked impairment in various aspects of cognitive function, the impairment profile is distinctly different according to the substance of abuse. In light of evidence showing that cognitive impairment in drug users has a negative impact on treatment engagement and efficacy, we review substance-specific deficits on executive and memory function, and discuss possibilities to address these during treatment intervention.

Neuropsychological Consequences of Opiate Use

Approximately 3.7 million individuals have used heroin and other opiate substances in their lifetime. Despite increasing knowledge of the effects of heroin, it remains the most abused opiate and use among adults has recently increased. The empirical literature examining the neurocognitive effects of acute and chronic opioid use remains limited; however, findings to date suggest that the use of opiates has both acute and long-term effects on cognitive performance. Neuropsychological data indicate deficits in attention, concentration, recall, visuospatial skills and psychomotor speed with both acute and chronic opioid use. The long-term effects of opiate use appear to have the greatest impact on executive functions, including the ability to shift cognitive set and inhibit inappropriate response tendencies. Factors that contribute to addiction and recovery are also discussed, as it is difficult to disentangle the effects of opiate use on cognitive performance from other factors that may affect neurobehavioral measures.

Cognitive impulsivity in cocaine and heroin polysubstance abusers

RATIONALE

Chronic abuse of psychoactive substances produces significant deficits in executive control functions (ECF). These deficits are prominent in different domains associated with cognitive impulsivity, including response inhibition and decision-making. The extent and nature of these deficits may depend on the principal substance of abuse.

OBJECTIVES

To analyse response inhibition and decision-making performance in abstinent polysubstance abusers (PSA) of cocaine and heroin, and healthy participants.

METHODS

We used univariate and multivariate analyses of variance to compare the performances of cocaine and heroin PSA and healthy controls on several well-validated measures of response inhibition (Stroop, 5-Digit Test and Go/No Go Task) and decision-making (Iowa Gambling Task). Post-hoc exploratory analyses of the results from the Go/No Go task were conducted to examine specific effects of task switching on the pattern of omission/commission errors in the PSA groups.

RESULTS

Cocaine but not heroin PSA showed significant deficits on several measures of response inhibition, when compared to controls. Reversal of task contingencies in the Go/No Go task primarily altered the commission error rate in cocaine PSA, and the omission error rate in heroin PSA. In contrast, both cocaine and heroin PSA showed poorer performance on decision-making compared to controls.

CONCLUSIONS

Assuming the relevance of polysubstance involvement, cocaine abuse seems to differentially correlate with motor impulsivity skills, while both substances seem to be equally linked to the inability to decide advantageously in complex decision-making tasks. Possible discrepancies in the neurological and psychological effects of these drugs are discussed.

Profile of executive deficits in cocaine and heroin polysubstance users: common and differential effects on separate executive components

OBJECTIVES

Structure of executive function was examined and we contrasted performance of substance dependent individuals (polysubstance users) and control participants on neuropsychological measures assessing the different executive components obtained. Additionally, we contrasted performance of polysubstance users with preference for cocaine vs heroin and controls to explore possible differential effects of the main substance abused on executive impairment.

METHODS

Two groups of participants were recruited: abstinent polysubstance users and controls. Polysubstance users were further subdivided based on their drug of choice (cocaine vs heroin). We administered to all participants a comprehensive protocol of executive measures, including tests of fluency, working memory, reasoning, inhibitory control, flexibility, and decision making.

RESULTS

Consistent with previous models, the principal component analysis showed that executive functions are organized into four separate components, three of them previously described: updating, inhibition, and shifting; and a fourth component of decision making. Abstinent polysubstance users had clinically significant impairments on measures assessing these four executive components (with effect sizes ranging from 0.5 to 2.2). Cocaine polysubstance users had more severe impairments than heroin users and controls on measures of inhibition (Stroop) and shifting (go/no go and category test). Greater severity of drug use predicted poorer performance on updating measures.

CONCLUSION

Executive functions can be fractionated into four relatively independent components. Chronic drug use is associated with widespread impairment of these four executive components, with cocaine use inducing more severe deficits on inhibition and shifting. These findings show both common and differential effects of two widely used drugs on different executive components.

Reflection impulsivity in current and former substance users

BACKGROUND

Chronic drug use is associated with increased impulsivity, risky decision making, and impaired behavioral control, but the underlying mechanisms of this neurocognitive profile remain unclear. We investigated impulsive responding in the context of decision making, using a novel behavioral measure of reflection impulsivity: the tendency to gather and evaluate information before making a decision.

METHODS

The Information Sampling Task was administered to current substance users dependent on amphetamines (n = 24) or opiates (n = 40), former users of amphetamines or opiates abstinent for at least 1 year (n = 24), and non-drug-using control subjects (n = 26).

RESULTS

Current users of amphetamines and opiates sampled less information than control subjects and responded at a lower probability of making a correct response. Amphetamine- and opiate-dependent subjects did not differ. Reduced reflection was also apparent in the former substance users, who did not differ from the current users. Questionnaire ratings of impulsivity (on the Barratt Impulsivity Scale, version 11) were also inflated in three groups of substance users but were not significantly correlated with performance on the behavioral task.

CONCLUSIONS

Reduced reflection is suggested to represent a cognitive marker for substance dependence that does not recover with prolonged abstinence and is associated with multiple drugs of abuse.