Profiles of cognitive dysfunction in chronic amphetamine and heroin abusers

Work aversion and associated changes in dopamine and serotonin transporter after methamphetamine exposure in rats

RATIONALE

Methamphetamine (mAMPH) administration in animals can lead to a variety of cognitive and behavioral deficits. We previously reported non-acute reversal learning impairments after a single-day administration of mAMPH, providing evidence of this drug's selective effects on inhibitory control. Effortful decision-making (i.e., how much effort to invest in rewards) is an aspect of cognition that has not yet been explored after mAMPH.

OBJECTIVES

Given that frontostriatal circuitry mediating this type of choice is vulnerable to the effects of mAMPH, we tested the hypothesis that mAMPH may also affect decision-making involving effort, another form of cognitive flexibility.

METHODS

We examined the non-acute effects of an experimenter-administered single day of mAMPH on effort discounting. In this task, rats previously treated with mAMPH or saline (SAL) could select a high reward at the cost of climbing over a tall barrier or a low reward with no barrier impeding its procurement.

RESULTS

Following treatment, mAMPH rats were more work-averse than SAL rats. A control task showed there were no treatment group differences when the high and low rewards involved equal work: all rats chose the high reward preferentially. There were no significant treatment group differences in [(125)I]RTI-55 binding to dopamine and serotonin transporters (DAT, SERT) in any of the regions assayed; however, there were significant correlations of accumbens DAT and cingulate SERT with post-treatment performance.

CONCLUSIONS

These findings suggest that even modest dose mAMPH exposure has long-lasting effects on effortful decision-making and may do so through influences on forebrain monoaminergic systems.

Factors affecting cognitive function of opiate-dependent patients

BACKGROUND

A wide range of studies found that opiate-dependent patients suffer from cognitive impairment due to a number of different factors. However, this issue has never been examined systematically. Thus, the aim of the present study is to provide a comprehensive analysis of factors that might contribute to cognitive impairment of opiate-dependent patients and specifically differentiates between various cognitive abilities as these might be impacted differently.

METHODS

Based on a comprehensive review of the literature with regard to previous findings and suggestions about which factors might affect cognitive functioning, we assessed a wide variety of variables related to substance use and opiate-dependence as well as demographic and socioeconomic variables. Cognitive functioning was assessed through a neuropsychological test-battery.

RESULTS

We found that the duration of opiate dependence and maintenance treatment, as well as additional substance consumption (alcohol, amphetamines, and cocaine) are the main variables contributing to cognitive impairment in the domains of attention and executive function. Comorbid depressive symptoms negatively affected reaction times. There was no evidence for the role of demographic variables like age and education on cognitive functioning.

CONCLUSIONS

Our findings suggest that it might be important in the treatment of opiate dependence to address the consumption of additional substances and to closely monitor the negative effects of maintenance treatment on cognitive functioning.

Rodent models of adaptive decision making

Adaptive decision making affords the animal the ability to respond quickly to changes in a dynamic environment: one in which attentional demands, cost or effort to procure the reward, and reward contingencies change frequently. The more flexible the organism is in adapting choice behavior, the more command and success the organism has in navigating its environment. Maladaptive decision making is at the heart of much neuropsychiatric disease, including addiction. Thus, a better understanding of the mechanisms that underlie normal, adaptive decision making helps achieve a better understanding of certain diseases that incorporate maladaptive decision making as a core feature. This chapter presents three general domains of methods that the experimenter can manipulate in animal decision-making tasks: attention, effort, and reward contingency. Here, we present detailed methods of rodent tasks frequently employed within these domains: the Attentional Set-Shift Task, Effortful T-maze Task, and Visual Discrimination Reversal Learning. These tasks all recruit regions within the frontal cortex and the striatum, and performance is heavily modulated by the neurotransmitter dopamine, making these assays highly valid measures in the study of psychostimulant addiction.

Linking ADHD, impulsivity, and drug abuse: a neuropsychological perspective

In this chapter, we consider the relevance of impulsivity as both a psychological construct and endophenotype underlying attention-deficit/hyperactivity disorder (ADHD) and drug addiction. The case for executive dysfunction in ADHD and drug addiction is critically reviewed in the context of dissociable cognitive control processes mediated by the dorsolateral prefrontal cortex (DLPFC), the orbital and ventral medial prefrontal cortex (VMPFC). We argue that such neuroanatomical divisions within the prefrontal cortex are likely to account for the multidimensional basis of impulsivity conceptually categorized in terms of "motoric" and "choice" impulsivity. The relevance of this distinction for the etiology of ADHD and drug addiction is integrated within a novel theoretical framework. This scheme embraces animal learning theory to help explain the heterogeneity of impulse control disorders, which are exemplified by ADHD as a vulnerability disorder for drug addiction.

Oscillatory power and synchrony in the rat forebrain are altered by a sensitizing regime of D-amphetamine

Repeated injections of psychostimulants, such as D-amphetamine (D-AMPH), provide a well-validated model of progressive cellular and systems-level alterations in brain function and behavior associated with addiction. The present study employed quantitative measures of both power spectral density and synchrony from local field potentials (LFPs) recorded simultaneously from the prefrontal cortex (PFC), parietal cortex (PAR), and hippocampus (HPC) in awake, behaving rats to assess changes in oscillations during different stages of D-AMPH-induced sensitization. The induction and development of sensitization altered the power of multiple frequency bands in a brain region-specific manner, whereas no changes were observed in animals treated with chronic saline. Specifically, the induction of sensitization to D-AMPH was accompanied by alterations in delta (2-5 Hz) and theta (5-11 Hz) oscillations similar to those observed in EEG recordings from addicted individuals describing craving and hedonic experience of the drug. Sensitization was also related to increased theta coherence between the PFC and HPC, along with suppression of cross-frequency correlations between theta and fast-gamma (65-100 Hz) in both the HPC and the PFC. Collectively, the present findings indicated the induction of a state in which the timing and synchronizing effects of oscillations are altered by sensitization to D-AMPH and are especially pronounced in the PFC. Furthermore, numerous LFP-derived measures were characterized that may serve as objective physiological correlates of pathological states observed in addiction.

Oxytocin directly administered into the nucleus accumbens core or subthalamic nucleus attenuates methamphetamine-induced conditioned place preference

Accumulating evidence indicates that the neuropeptide oxytocin (OXY) may modulate reward-related behavioural responses to methamphetamine (METH) administration. Limited research has examined the effect of OXY on METH-induced conditioned place preference (CPP) and little is known about the neural mechanisms involved. A Fos immunohistochemistry study recently demonstrated that peripheral OXY administration reduced METH-induced Fos expression within the nucleus accumbens (NAc) core and subthalamic nucleus (STh) in rats. The current study aimed to (i) investigate the effect of systemically administered OXY on METH-induced CPP, (ii) determine the effectiveness of a single-trial CPP procedure with METH, in order to (iii) evaluate whether pretreatment with OXY injected directly into the NAc core or the STh attenuates METH-induced CPP. Results showed that male Sprague Dawley rats learned to associate unique compartmental cues with METH (1 mg/kg, i.p.) such that they spent more time in the METH-paired compartment and less time in the saline-paired compartment. Pretreatment with systemic OXY (0.6 mg, i.p.), or OXY (0.6 ng, i.c.) microinjected into the NAc core or the STh prior to METH administration attenuated the formation of a CPP to METH. This provides further evidence that OXY acts within either the NAc core or the STh to reduce the rewarding effects of METH administration.

PHENOMENOLOGICAL ARCHITECTURE OF A MIND AND OPERATIONAL ARCHITECTONICS OF THE BRAIN: THE UNIFIED METASTABLE CONTINUUM

In our contribution we will observe phenomenal architecture of a mind and operational architectonics of the brain and will show their intimate connectedness within a single integrated metastable continuum. The notion of operation of different complexity is the fundamental and central one in bridging the gap between brain and mind: it is precisely by means of this notion that it is possible to identify what at the same time belongs to the phenomenal conscious level and to the neurophysiological level of brain activity organization, and what mediates between them. Implications for linguistic semantics, self-organized distributed computing algorithms, artificial machine consciousness, and diagnosis of dynamic brain diseases will be discussed briefly.

Opiate versus psychostimulant addiction: the differences do matter

The publication of the psychomotor stimulant theory of addiction in 1987 and the finding that addictive drugs increase dopamine concentrations in the rat mesolimbic system in 1988 have led to a predominance of psychobiological theories that consider addiction to opiates and addiction to psychostimulants as essentially identical phenomena. Indeed, current theories of addiction - hedonic allostasis, incentive sensitization, aberrant learning and frontostriatal dysfunction - all argue for a unitary account of drug addiction. This view is challenged by behavioural, cognitive and neurobiological findings in laboratory animals and humans. Here, we argue that opiate addiction and psychostimulant addiction are behaviourally and neurobiologically distinct and that the differences have important implications for addiction treatment, addiction theories and future research.

Low dose, short-term rivastigmine administration does not affect neurocognition in methamphetamine dependent individuals

Neurocognitive impairment is a well-documented consequence of methamphetamine addiction. Not surprising, methamphetamine-associated neurocognitive impairment has been identified as an important target of treatment. Thus, this study sought to determine whether rivastigmine, an acetylcholinesterase inhibitor and cognition enhancing agent, could improve neurocognitive performance in a sample of long-term, high-dose methamphetamine addicts who were not seeking treatment at the time of enrollment in the study. This double-blind, placebo-controlled study evaluated whether a daily dose 0, 3, or 6 mg of rivastigmine, administered over six consecutive days, would enhance performance on measures of attention/information processing speed, episodic memory, and executive/frontal lobe functioning relative to test performance at baseline. The results revealed that rivastigmine did not alter neurocognition in this cohort. There are a number of factors that may have mitigated the effects of rivastigmine in this particular study, including especially the short-term, low-dose treatment regimen utilized. The negative findings notwithstanding, the study serves as a springboard for future investigations that will examine whether other medications can alter neurocognition in methamphetamine dependent study participants.

[Reaction time in relation to duration of heroin abuse]

INTRODUCTION

Consequences of heroin abuse include organic damage of cerebral structures. The level of impairments is in a direct and positive relation with the length of heroin abuse.

OBJECTIVE

The aim of this research was the evaluation of the reaction time with heroin addicts with different length of substance abuse.

METHODS

RESEARCH METHOD

90 examinees were divided into three groups with relation to the length of heroin abuse. Data collection included a questionnaire referring to socio-demographic and addictive characteristics. A specially designed programme was used for the evaluation of reaction time to audio/ visual signal.

RESULTS

In relation to the reaction time as overall model, the difference between examinees with different length of heroin abuse can be found on the marginal level of significance (F = 1.69; df = 12; p = 0.07). In visual modality, with the increase of length of heroin abuse leads to a significant prolongation of simple (the first visual sign: F = 3.29; df = 2; p = 0.04) and choice reaction time (the second visual sign: F = 4.97; df = 2; p = 0.00; the third visual sign: F = 3.08; df = 2; p = 0.05). Longer heroin consumption also leads to the prolongation of the simple (the first auditory task: F = 3.41; df = 2; p = 0.04) and the complex auditory reaction time (the second auditory task: F = 5.67; df = 2; p = 0.01; the third auditory task: F = 6.42; df = 2; p = 0.00).

CONCLUSION

Heroin abuse leads to the prolongation of both simple and choice reaction time in visual as well as auditory modality. The average daily dose of opiates was the most important predictor of the abovementioned cognitive dysfunction.

Degree of dependence influences the effect of smoking on cognitive flexibility

Pre-frontal cortical (PFC) dysfunction has been put forward as the basis for development and maintenance of addiction. To explore this relationship, the present study investigated the effects of smoking on PFC-mediated cognitive flexibility and subjective states in low- (LD) and high-dependent (HD) smokers. Twenty-four LD and 24 HD smokers (Fagerström dependence scores ≤ 4 and ≥ 5, respectively) were randomly allocated to non-smoking or smoking condition (12 LD and 12 HD participants per condition). After abstaining from smoking for a minimum of two hours volunteers completed a battery of questionnaires [nicotine-specific Visual Analogue Scales (Nic-VAS), Questionnaire of Smoking Urges (QSU) and Profile of Mood States (POMS)] at baseline [T1] and again after smoking one cigarette or remaining abstinent [T2]. Cognitive flexibility was evaluated at T2 using the Intra-Extra Dimensional Set-Shift test. The Rapid Visual Information Processing test was performed as a control nicotine-sensitive task at several time points during the experiment. Compared to LD smokers, HD smokers had higher salivary cotinine and breath CO levels at baseline and reported more craving (QSU) and felt less stimulated (Nic-VAS), vigorous, friendly and elated (POMS) throughout the experiment. Smoking increased Nic-VAS ratings of 'Buzzed' and 'Dizzy' and decreased craving in all participants. Smoking selectively impaired cognitive flexibility in HD smokers since HD smokers allocated to the smoking condition made significantly more errors with the intra-dimensional set-shift than their counterparts in the abstinent condition. No effect of smoking on RVIP test was observed, most likely due to the practice effect which was significant in both groups of smokers. The practice effect, however, was more pronounced in LD smokers. This study demonstrates that PFC-mediated cognitive effects of smoking as well as subjective reports vary according to the degree of nicotine dependence.

Potential vulnerabilities of neuronal reward, risk, and decision mechanisms to addictive drugs

How do addictive drugs hijack the brain's reward system? This review speculates how normal, physiological reward processes may be affected by addictive drugs. Addictive drugs affect acute responses and plasticity in dopamine neurons and postsynaptic structures. These effects reduce reward discrimination, increase the effects of reward prediction error signals, and enhance neuronal responses to reward-predicting stimuli, which may contribute to compulsion. Addictive drugs steepen neuronal temporal reward discounting and create temporal myopia that impairs the control of drug taking. Tonically enhanced dopamine levels may disturb working memory mechanisms necessary for assessing background rewards and thus may generate inaccurate neuronal reward predictions. Drug-induced working memory deficits may impair neuronal risk signaling, promote risky behaviors, and facilitate preaddictive drug use. Malfunctioning adaptive reward coding may lead to overvaluation of drug rewards. Many of these malfunctions may result in inadequate neuronal decision mechanisms and lead to choices biased toward drug rewards.

Methamphetamine self-administration produces attentional set-shifting deficits and alters prefrontal cortical neurophysiology in rats

BACKGROUND

Chronic methamphetamine abusers exhibit deficits in tasks requiring intact prefrontal cortex function, and prefrontal cortex dysfunction has been implicated in the loss of control over drug use. This study used a combination of behavioral and electrophysiologic assessments in rats with a history of long access methamphetamine self-administration to determine methamphetamine-induced changes in prefrontal cortex-dependent attentional set-shifting performance, drug-seeking, and prefrontal cortex neuronal activity.

METHODS

Male Long-Evans rats self-administered methamphetamine (.02 mg/infusion, intravenous) or received yoked saline infusions for 6 hours a day for 14 days. Cognitive flexibility was assessed using an attentional set-shifting task before 2 weeks of self-administration and 1 day after self-administration. Animals then underwent 11 days of abstinence, followed by three subsequent tests for context-induced drug seeking. Finally, animals were anesthetized, and single-unit in vivo extracellular recordings were performed in the dorsomedial prefrontal cortex.

RESULTS

Methamphetamine-experienced rats showed escalated drug intake and context-induced drug-seeking following abstinence. During the extradimensional set-shift component, meth-experienced rats showed selective impairments that were identical to deficits produced by excitotoxic lesions of the prefrontal cortex. Rats with a history of chronic methamphetamine intake also exhibited higher basal firing frequency and a significantly greater proportion of burst-firing cells in the prefrontal cortex compared with yoked-saline controls.

CONCLUSIONS

Prefrontal cortex-specific alterations in neuronal function may play a key role in methamphetamine-induced attentional deficits and drug-seeking. These data support the possibility that targeting prefrontal cortex pathology may improve treatment outcome in methamphetamine addiction.

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.

Trait-like impulsivity does not predict escalation of heroin self-administration in the rat

RATIONALE

The neural and psychological mechanisms underlying vulnerability to drug addiction are poorly understood. Although a number of animal models have been developed to investigate vulnerability to stimulant addiction, few have considered how vulnerability traits such as impulsivity predict hallmark features of heroin addiction including the escalation of drug intake and increased propensity for relapse following protracted abstinence.

OBJECTIVE

The aim of this study was to investigate whether high impulsivity in rats predicts the propensity to escalate intravenous heroin self-administration and to relapse following an extended withdrawal period from heroin.

METHODS

High (HI)- and low (LI)-impulsive rats, defined by the extent of premature responding on the 5-choice serial reaction time test (5-CSRTT), were catheterized and allowed to self-administer heroin (40 μg/100 μl/infusion). After 5 days of short access (1 h/day) to heroin, rats were then given extended (6 h/day) access to heroin for 18 consecutive days.

RESULTS

High impulsivity predicted neither a greater tendency to acquire heroin SA nor an increased escalation of heroin self-administration. Moreover, high impulsivity was not associated with an increased propensity to relapse after protracted withdrawal from heroin. Nevertheless, marked inter-individual differences in the escalation of heroin self-administration were observed.

CONCLUSIONS

Although high impulsivity on the 5-CSRTT has been shown to predict loss of control over cocaine intake, this does not generalize to a loss of control over heroin self-administration. These findings suggest important distinctions in vulnerability mechanisms underlying cocaine and heroin addiction with trait-like impulsivity playing a role in stimulant but not opiate addiction.

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.

Medial prefrontal gray matter volume reductions in users of amphetamine-type stimulants revealed by combined tract-based spatial statistics and voxel-based morphometry

Amphetamine-type stimulants (ATS) refer to a group of drugs whose principal members include amphetamine, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA). Worldwide, ATS are among the most common illicit drugs. Therefore, understanding whether and to what extent ATS exposure affects brain structure and functioning in recreational users has become a critical public health issue. We studied gray and white matter densities in 20 experienced users of ATS (more than 100 units MDMA and/or 50 g of amphetamine lifetime dose), 42 low exposure users with very limited ATS experience (less than 5 units lifetime dose) and 16 drug-naive controls. A tract-based spatial statistics (TBSS) analysis of fractional anisotropy images was applied to diffusion magnetic resonance imaging (MRI) data. Furthermore, alignment invariant white matter tract representations acquired from the TBSS analysis were used as a reference for inter-subject brain registrations in a voxel-based morphometry (VBM) analysis of gray matter volume, reducing characteristic alignment inaccuracies associated with this voxel-wise gray matter investigation approach. Between-group white matter comparison revealed no significant results. However, compared to low exposure users, experienced users showed several regions of lower gray matter volume in medial frontal regions, in particular the orbital and medial frontal cortex. Differences are likely to reflect effects of repeated ATS exposure even in recreational users. However, differences in pre-existing or confounding factors might also account for between-group differences.

Neuropsychological consequences of alcohol and drug abuse on different components of executive functions

Several studies have shown alterations in different components of executive functioning in users of different drugs, including cannabis, cocaine and heroin. However, it is difficult to establish a specific association between the use of each of these drugs and executive alterations, since most drug abusers are polysubstance abusers, and alcohol is a ubiquitous confounding factor. Moreover, in order to study the association between consumption of different drugs and executive functioning, the patterns of quantity and duration of drugs used must be considered, given the association between these parameters and the executive functioning alteration degree. Based on the multicomponent approach to executive functions, the aims of the present study were: (i) to analyse the differential contribution of alcohol versus cocaine, heroin and cannabis use on executive functions performance; and (ii) to analyse the contribution made by the severity of the different drugs used (quantity and duration patterns) on these functions in a sample of polysubstance abusers that requested treatment for cannabis-, cocaine- or heroin-related problems. We administered measures of fluency, working memory, analogical reasoning, interference, cognitive flexibility, decision-making and self-regulation to two groups: 60 substance-dependent individuals (SDIs) and 30 healthy control individuals (HCIs). SDIs had significantly poorer performance than HCIs across all of the executive domains assessed. Results from hierarchical regression models showed the existence of common correlates of the use of alcohol, cannabis and cocaine on verbal fluency and decision-making; common correlates of quantity of cannabis and cocaine use on verbal working memory and analogical reasoning; common correlates of duration of cocaine and heroin use on shifting; and specific effects of duration of cocaine use on inhibition measures. These findings indicate that alcohol abuse is negatively associated with fluency and decision-making deficits, whereas the different drugs motivating treatment have both generalized and specific deleterious effects on different executive components.

Effects of methamphetamine on sexual performance and compulsive sex behavior in male rats

RATIONALE

Methamphetamine (Meth) is a highly addictive psychostimulant associated with enhanced sexual desire, arousal, and sexual pleasure. Moreover, Meth abuse is frequently linked with the practice of sexual risk behavior and increased prevalence of human immunodeficiency virus. Currently, there is a lack of studies investigating the effects of Meth on maladaptive sexual behavior under controlled experimental settings in animal studies.

OBJECTIVE

The overall objective of the current study was to examine the effects of Meth on various aspects of male sexual behavior including maladaptive sex-seeking behavior.

METHODS

First, a dose-response curve of the effects of Meth (0, 1, 2, and 4 mg/kg; s.c.) on sexual motivation and performance was conducted in sexually naïve and experienced male rats. Next, the effects of Meth (1 mg/kg; s.c.) on inhibition of maladaptive sexual behavior was tested using a sex aversion conditioning paradigm, in which visceral illness induced by lithium chloride (LiCl) was paired with sexual behavior.

RESULTS

Meth administration inhibited sexual performance in a dose-dependent matter as evidenced by the decreased percentages of males that mated and increased latencies to initiate sexual behavior when injected with 2 or 4 mg/kg Meth. Moreover, an acute dose of Meth prior to or following sex aversion conditioning resulted in disrupted conditioned inhibition of sexual behavior.

CONCLUSIONS

These data suggest that Meth administration in male rats impairs sexual motivation and performance. In addition, low doses of Meth that do not disrupt sexual function may result in maladaptive seeking of sexual behavior.

Substance use in adolescence and psychosis: clarifying the relationship

Adolescence is a time of exploration of the self, and this exploration may involve the use of alcohol and drugs. Sadly, for some, adolescence also marks the first signs of a psychosis. The temporal proximity between the onset of substance use and of psychosis has been the cause of much debate. Here we review the association of alcohol, cannabis, stimulants, and other drugs with psychosis, and we conclude that the use of cannabis and the amphetamines significantly contributes to the risk of psychosis.

Substance use and women's health

Scientific findings show that substance abuse in women yields a higher risk of a variety of health problems than substance abuse in men. Research suggests that women experience addiction telescoping when they abuse alcohol, tobacco, specific stimulants, and possibly opioids. Medical side effects also develop more rapidly in women than men when they abuse many substances. Cancer and cardiac complications, specifically, pose a significant threat for women who abuse almost all types of substances. However, the physical consequences are not the only ones women suffer when they engage in substance abuse. Research on substance abuse in women ties opioids to mood and anxiety disorders, heroin to neurological deficiencies, cocaine to immune system suppression, and alcohol to intimate partner abuse. Additionally, female substance abusers, on average, have a lower level of education and lower rates of employment. In light of these gender-specific concerns, physicians should give particular consideration to detecting substance abuse in women.

Deterioration of intelligence in methamphetamine-induced psychosis: comparison with alcohol dependence on WAIS-III

AIMS

Long-term use of methamphetamine could induce psychosis, but consequences with regards to intelligence have seldom been investigated. Long-term use of alcohol could also result in intellectual deterioration.

METHODS

The IQ of 34 methamphetamine-induced psychosis (MIP) patients (age, 28.7 +/- 6.1 years) and 34 alcohol-dependent (AD) patients (age, 40.7 +/- 7.3 years) was compared using the Chinese version of the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III).

RESULTS

The average full-scale IQ, verbal IQ, performance IQ, verbal comprehension index, working memory index, perceptual organization index, and processing speed index was 82.3 +/- 10.8, 84.3 +/- 11.9, 81.9 +/- 12.1, 85.5 +/- 11.9, 84.7 +/- 12.5, 85.4 +/- 13.6, and 78.5 +/- 12.7 in MIP patients and 90.5 +/- 12.0, 95.2 +/- 11.3, 86.0 +/- 13.7, 95.5 +/- 11.0, 87.1 +/- 14.5, 96.2 +/- 13.1, and 84.5 +/- 15.0 in AD patients, respectively. There were six MIP patients (17.6%) whose full-scale IQ was <70 and 13 (38.2%) whose full-scale IQ was <85 and >70, while one AD patient had a full-scale IQ <70 (2.9%) and 10 (22%) had full-scale IQ <85 and >70.

CONCLUSIONS

Long-term use of methamphetamine can result not only in psychosis, but also in mentality deterioration. Intelligence deterioration is more severe in clinical MIP patients than AD patients. Assessment of the mentality of MIP patients is suggested to help with the implementation of rehabilitative programs for these patients.

Reversal-specific learning impairments after a binge regimen of methamphetamine in rats: possible involvement of striatal dopamine

A growing body of evidence indicates that protracted use of methamphetamine (mAMPH) causes long-term impairments in cognitive function in humans. Aside from the widely reported problems with attention, mAMPH users exhibit learning and memory deficits, particularly on tasks requiring response control. Although binge mAMPH administration to animals results in cognitive deficits, few studies have attempted to test behavioral flexibility in animals after mAMPH exposure. The aim of this study was to evaluate whether mAMPH would produce impairments in two tasks assessing flexible responding in rats: a touchscreen-based discrimination-reversal learning task and an attentional set shift task (ASST) based on a hallmark test of executive function in humans, the Wisconsin Card Sort. We treated male Long-Evans rats with a regimen of four injections of 2 mg/kg mAMPH (or vehicle) within a single day, a dosing regimen shown earlier to produce object recognition impairments. We then tested them on (1) reversal learning after pretreatment discrimination learning or (2) the ASST. Early reversal learning accuracy was impaired in mAMPH-treated rats. MAMPH pretreatment also selectively impaired reversal performance during ASST testing, leaving set-shifting performance intact. Postmortem analysis of [(125)I]RTI-55 binding revealed small (10-20%) but significant reductions in striatal dopamine transporters produced by this mAMPH regimen. Together, these results lend new information to the growing field documenting impaired cognition after mAMPH exposure, and constitute a rat model of the widely reported decision-making deficits resulting from mAMPH abuse seen in humans.

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.

Imaging cognitive deficits in drug abuse

The neuropsychological network is a complex structure. To identify processes location and network capacity the brain imaging techniques together and in combination with other neuropsychological techniques and the expanding of well elaborated designs provide us with a multidimensional understanding, and contributes to the understanding of each illicit drug's character, which is of importance in designing of new treatment programs and clinical practice. Cannabis, MDMA, amphetamine, cocaine, and heroin abusers display both acute effects and chronic effects, deficits in attention, memory, and executive functioning. These deficits may last beyond the period of intoxication and cumulate with years of use. Cannabis users may recruit an alternative neural network as a compensatory mechanism during performance of tasks of attention. There is some evidence indicating the detrimental effects of cannabis on the maturing adolescent brain. Stimulant dependence is characterized by a distributed alteration of functional activation. Attenuated anterior and posterior cingulate activation, reduced inferior frontal and dorsolateral prefrontal cortex activation, and altered posterior parietal activation point towards an inadequate demand-specific processing of information. On an individual level they exhibit process-related brain activation differences that are consistent with a shift from context-specific, effortful processing to more stereotyped, habitual response generation. Finally, opiate use appears to decrease the ability to shift cognitive set and inhibit inappropriate response tendencies.

Is moderate substance use associated with altered executive functioning in a population-based sample of young adults?

BACKGROUND

Substance use (SU) has been linked with impaired cognitive functioning. Evidence comes mainly from clinical studies or studies examining heavy users. Though, the majority of users are not involved in heavy use. This study investigates the association between moderate use and cognition in a population-based sample.

METHODS

A total of 284 young adults with ecstasy, cannabis or alcohol use and a control group were sampled from the EDSP database for participation in the Munich Assessment of Young Adults (MAYA) study. Subjects completed a comprehensive battery of neuropsychological tests (executive functions, working memory and impulsivity). Multiple linear regression models were conducted to examine the relationship between use and cognitive performance.

RESULTS

Increased ecstasy consumption was associated with increased error-proneness (Stroop task, CANTAB ID/ED-shift, spatial working memory). More frequent cannabis use and more extensive alcohol consumption were associated with a higher degree of impulsiveness.

CONCLUSIONS

Based on mild to moderate SU, little indication of differences in executive functioning was found. For ecstasy use, an increased error-proneness was revealed. The subtle differences in relatively young individuals warrant further investigation in prospective long-term studies to identify subjects at risk, and to examine effects of prolonged patterns of use on executive functioning.

Neurotoxicity of drugs of abuse--the case of methylenedioxyamphetamines (MDMA, ecstasy), and amphetamines

Ecstasy (MDMA, 3,4-methylendioxymethamphetamine) and the stimulants methamphetamine (METH, speed) and amphetamine are popular drugs among young people, particularly in the dance scene. When given in high doses both MDMA and the stimulant amphetamines are clearly neurotoxic in laboratory animals. MDMA causes selective and persistent lesions of central serotonergic nerve terminals, whereas amphetamines damage both the serotonergic and dopaminergic systems. In recent years, the question of ecstasy-induced neurotoxicity and possible functional sequelae has been addressed in several studies in drug users. Despite large methodological problems, the bulk of evidence suggests residual alterations of serotonergic transmission in MDMA users, although at least partial recovery may occur after long-term abstinence. However, functional sequelae may persist even after longer periods of abstinence. To date, the most consistent findings associate subtle cognitive impairments with ecstasy use, particularly with memory. In contrast, studies on possible long-term neurotoxic effects of stimulant use have been relatively scarce. Preliminary evidence suggests that alterations of the dopaminergic system may persist even after years of abstinence from METH, and may be associated with deficits in motor and cognitive performance. In this paper, we will review the literature focusing on human studies.

Gray matter density negatively correlates with duration of heroin use in young lifetime heroin-dependent individuals

Numerous studies have documented cognitive impairments and hypoactivity in the prefrontal and anterior cingulate cortices in drug users. However, the relationships between opiate dependence and brain structure changes in heroin users are largely unknown. In the present study, we measured the density of gray matter (DGM) with voxel-based morphometry in 30 lifetime heroin-dependent individuals who had abstained from drug use for 5 months, and 34 healthy participants. The DGM of the prefrontal, temporal and cingulate cortices significantly decreased in heroin addicts relative to the healthy group. Critically, partial correlation analysis, which controlled for age, education and gender factors as well as nicotine use and heroin abstinence duration, showed that the duration of heroin use negatively correlated with the DGM in heroin-dependent individuals. These results provide compelling evidence for structural abnormality in heroin-dependent individuals and further suggest that duration of heroin use is a critical factor leading to brain damage.

A review of the clinical pharmacology of methamphetamine

AIMS

To examine the literature regarding clinical pharmacokinetics, direct effects and adverse clinical outcomes associated with methamphetamine use.

METHODS

Relevant literature was identified through a PubMed search. Additional literature was obtained from relevant books and monographs.

FINDINGS AND CONCLUSIONS

The mean elimination half-life for methamphetamine is approximately 10 hours, with considerable inter-individual variability in pharmacokinetics. Direct effects at low-to-moderate methamphetamine doses (5-30 mg) include arousal, positive mood, cardiac stimulation and acute improvement in cognitive domains such as attention and psychomotor coordination. At higher doses used typically by illicit users (> or =50 mg), methamphetamine can produce psychosis. Its hypertensive effect can produce a number of acute and chronic cardiovascular complications. Repeated use may induce neurotoxicity, associated with prolonged psychiatric symptoms, cognitive impairment and an increased risk of developing Parkinson's disease. Abrupt cessation of repeated methamphetamine use leads to a withdrawal syndrome consisting of depressed mood, anxiety and sleep disturbance. Acute withdrawal lasts typically for 7-10 days, and residual symptoms associated with neurotoxicity may persist for several months.

Reduced memory and attention performance in a population-based sample of young adults with a moderate lifetime use of cannabis, ecstasy and alcohol

Regular use of illegal drugs is suspected to cause cognitive impairments. Two substances have received heightened attention: 3,4-methylenedioxymethamphetamine (MDMA or 'ecstasy') and delta-9-tetrahydrocannabinol (THC or 'cannabis'). Preclinical evidence, as well as human studies examining regular ecstasy consumers, indicated that ecstasy use may have negative effects on learning, verbal memory and complex attentional functions. Cannabis has also been linked to symptoms of inattention and deficits in learning and memory. Most of the published studies in this field of research recruited participants by means of newspaper advertisements or by using word-of-mouth strategies. Because participants were usually aware that their drug use was critical to the research design, this awareness may have caused selection bias or created expectation effects. Focussing on attention and memory, this study aimed to assess cognitive functioning in a community-based representative sample that was derived from a large-scale epidemiological study. Available data concerning drug use history allowed sampling of subjects with varying degrees of lifetime drug experiences. Cognitive functioning was examined in 284 young participants, between 22 and 34 years. In general, their lifetime drug experience was moderate. Participants completed a neuropsychological test battery, including measures for verbal learning, memory and various attentional functions. Linear regression analysis was performed to investigate the relationship between cognitive functioning and lifetime experience of drug use. Ecstasy and cannabis use were significantly related to poorer episodic memory function in a dose-related manner. For attentional measures, decrements of small effect sizes were found. Error measures in tonic and phasic alertness tasks, selective attention task and vigilance showed small but significant effects, suggesting a stronger tendency to experience lapses of attention. No indication for differences in reaction time was found. The results are consistent with decrements of memory and attentional performance described in previous studies. These effects are relatively small; however, it must be kept in mind that this study focussed on assessing young adults with moderate drug use from a population-based study.

Long-term changes in dopamine-stimulated gene expression after single-day methamphetamine exposure

Methamphetamine (mAMPH) is a highly addictive psychostimulant drug that injures monoaminergic neurons and results in behavioral impairments in humans and animals. Although evidence exists for changes in cortical volume, metabolism, and blood oxygenation levels in human mAMPH abusers, animal models have instead emphasized this drug's long-lasting influence on ascending monoaminergic (dopamine, serotonin) projections. The aim of this study was to investigate cortical and subcortical function in rats long after administration of a single-day mAMPH regimen known to damage monoaminergic systems, at a time point when behavioral impairments are still evident. Rats were given either saline or a neurotoxic (4 x 4 mg/kg, sc) mAMPH regimen. Five weeks later, they were given pharmacological treatments that stimulate cortical gene expression: either the dopaminergic agonist apomorphine (3 mg/kg, sc) or the muscarinic acetylcholine agonist pilocarpine (25 mg/kg, ip). Cortical and subcortical immediate early gene (IEG) responses were measured by immunocytochemical analysis of Fos or JunB, protein products of the IEGs, c-fos and junB. Compared with saline-pretreated controls, mAMPH-pretreated animals had about 50-70% fewer Fos- and JunB-immunoreactive cells in anterior cingulate, infralimbic, orbital, somatosensory, and rhinal cortices as well as caudate-putamen and nucleus accumbens, 90 min after apomorphine challenge. By contrast, mAMPH-pretreated rats had no reductions in the numbers of Fos or JunB-positive cells following pilocarpine challenge. This study demonstrates the profound and enduring effects of mAMPH administration on dopamine-stimulated cortical function in animals.

Neurocognitive and neuroimaging evidence of behavioural dysregulation in human drug addiction: implications for diagnosis, treatment and prevention

Neuropsychological and neuroimaging studies have generated a wealth of data demonstrating structural and functional brain changes, as well as cognitive deficits in drug addicted populations. Despite this, it is often difficult to make generalisations or conclusive statements about the neuropsychological and neurobiological correlates of chronic drug use given variations in the nature or extent of deficits observed within or across different classes of drugs. In this review, we focus specifically on the evidence for impairments in prefrontally-mediated cognitive functions that underlie behavioural regulation, namely decision making and inhibitory control. We argue that impairments in these specific domains, which are often compounded by an earlier initiation of drug use, polydrug abuse, comorbid psychiatric conditions, previous head injury, and acute withdrawal effects can serve to increase the risk for making decisions that are impulsive, focussed on short-terms gains and lack inhibitory control. We further argue that these impairments of prefrontal functioning may underpin the compulsive and 'loss-of-control' pattern of drug-seeking and drug-taking that is characteristic of drug addiction. Finally, we consider the implications of these findings for diagnosis, treatment and prevention, suggesting that a comprehensive understanding of the nature and extent of these cognitive deficits should form a core part of the conceptualization and focus of effective treatment.

Persistent alterations in cognitive function and prefrontal dopamine D2 receptors following extended, but not limited, access to self-administered cocaine

Drug addicts have deficits in frontocortical function and cognition even long after the discontinuation of drug use. It is not clear, however, whether the cognitive deficits are a consequence of drug use, or are present prior to drug use, and thus are a potential predisposing factor for addiction. To determine if self-administration of cocaine is capable of producing long-lasting alterations in cognition, rats were allowed access to cocaine for either 1 h/day (short access, ShA) or 6 h/day (long access, LgA) for 3 weeks. Between 1 and 30 days after the last self-administration session, we examined performance on a cognitively demanding test of sustained attention that requires an intact medial prefrontal cortex. The expression levels of dopamine D1 and D2 receptor mRNA and D2 protein in the prefrontal cortex were also examined. Early after discontinuation of drug use, LgA (but not ShA) animals were markedly impaired on the sustained attention task. Although the LgA animals improved over time, they continued to show a persistent pattern of performance deficits indicative of a disruption of cognitive flexibility up to 30 days after the discontinuation of drug use. This was accompanied by a significant decrease in DA D2 (but not D1) mRNA in the medial and orbital prefrontal cortex, and D2 receptor protein in the medial prefrontal cortex of LgA (but not ShA) animals. These findings establish that repeated cocaine use is capable of producing persistent alterations in the prefrontal cortex and in cognitive function, and illustrate the usefulness of extended access self-administration procedures for studying the neurobiology of addiction.

A Comparison of Methamphetamine-Dependent Inpatients With and Without Childhood Attention Deficit Hyperactivity Disorder Symptomatology

Methamphetamine-dependent inpatients (N = 51) were screened for childhood attention deficit hyperactivity disorder (ADHD) using the Wender Utah Rating Scale upon admission to 30-day inpatient treatment. Baseline assessments included neuropsychological tests of executive function, memory, information processing, verbal fluency, attention, motor skills, and the Brief Symptom Inventory (BSI), a measure of psychiatric symptomatology. The thirty-six participants (70.6%) screening positive for ADHD reported significantly more frequent methamphetamine use prior to baseline. Baseline cognitive functioning was similar between groups, but the presumptive ADHD participants exhibited significantly worse psychiatric symptomatology. At three-week follow- up, 41 participants (80.4%) repeated the neuropsychological battery and BSI. All 10 non-completers screened positive for ADHD. The entire sample improved with abstinence in most neuropsychological domains except memory. The presumptive ADHD group failed to improve on tests of attention. All participants demonstrated significant reductions in psychiatric symptoms with abstinence. Methamphetamine-dependent individuals with ADHD symptoms are common and pose a significant treatment challenge.

Verbal working memory deficits in abstinent heroin abusers

BACKGROUND

A prevailing belief is that opioids tend not to impair cognitive performance in opioid-dependent users. However, the impact of heroin abuse on verbal memory, especially on working memory, is not well studied and the results available are inconsistent.

OBJECTIVE

This study was carried out to test the hypothesis that abstinent heroin abusers have intact working memory capacity.

METHODS

N-back task and backward digit span task were used to measure the verbal working memory capacity in 28 abstinent heroin abusers and 25 controls matched for age, education level and gender. Forward digit span task was used as a control task to measure short-term memory capacity.

RESULTS

Compared with the control subjects, heroin abusers showed normal backward/forward digit spans but significant performance impairment in the n-back task.

CONCLUSION

Abstinent heroin abusers have intact short-term memory capacity but impaired verbal working memory capacity.

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.

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.

Sensorimotor gating and attentional set-shifting are improved by the mu-opioid receptor agonist morphine in healthy human volunteers

Prepulse inhibition (PPI) of the acoustic startle response (ASR) has been established as an operational measure of sensorimotor gating. Animal and human studies have shown that PPI can be modulated by dopaminergic, serotonergic, and glutamatergic drugs and consequently it was proposed that impaired sensorimotor gating in schizophrenia parallels a central abnormality within the corresponding neurotransmitter systems. Recent animal studies suggest that the opioid system may also play a role in the modulation of sensorimotor gating. Thus, the present study investigated the influence of the mu-opioid receptor agonist morphine on PPI in healthy human volunteers. Eighteen male, non-smoking healthy volunteers each received placebo or 10 mg morphine sulphate (p.o.) at a 2-wk interval in a double-blind, randomized, and counterbalanced order. PPI was measured 75 min after drug/placebo intake. The effects of morphine on mood were measured by the Adjective Mood Rating Scale and side-effects were assessed by the List of Complaints. Additionally, we administered a comprehensive neuropsychological test battery consisting of tests of the Cambridge Neuropsychological Test Automated Battery and the Rey Auditory Verbal Learning Test. Morphine significantly increased PPI without affecting startle reactivity or habituation. Furthermore, morphine selectively improved the error rate in an attentional set-shifting task but did not influence vigilance, memory, or executive functions. These results imply that the opioid system is involved in the modulation of PPI and attentional set-shifting in humans and they raise the question whether the opioid system plays a crucial role also in the regulation of PPI and attentional set-shifting in schizophrenia.

Amphetamine causes dopamine depletion and cell death in the mouse olfactory bulb

Amphetamine is a neurotoxic psychostimulant that causes dopamine depletion and neuronal death in the rodent striatum. In the present study, we sought to determine if toxic doses of the drug can also induce pathological changes in the mouse olfactory bulb. We found that injections of amphetamine (10 mg/kg x 4, given 2 h apart) caused significant decreases in dopamine levels in that structure. This dose of the drug also induced substantial increases in the number of terminal deoxynucleotidyl transferase-mediated deoxyribonucleotide triphosphate (dNTP) nick end labeling (TUNEL)-positive cells in the olfactory bulb indicative of elevated DNA fragmentation. These results show that the toxic effects of amphetamine involve the olfactory bulb in addition to the striatum. These observations need to be taken into consideration when discussing the clinical course of amphetamine addiction.

Methamphetamine influences on recognition memory: comparison of escalating and single-day dosing regimens

Methamphetamine (mAMPH) is an addictive drug that produces memory and recall impairments in humans. Animals subjected to a binge mAMPH dosing regimen that damages brain dopamine and serotonin terminals show impairments in an object recognition (OR) task. Earlier research demonstrated that preceding a single-day mAMPH binge regimen with several days of increasing mAMPH doses greatly attenuates its neurotoxicity in rats. The escalating dose (ED) paradigm appears to mimic the human pattern of escalating drug intake. The current aim was to test whether an ED plus binge mAMPH regimen produces OR impairments. In addition to its translational value, this experiment helps address whether monoaminergic neurotoxicity accounts for OR impairments seen after mAMPH administration. To further address this issue, a separate experiment investigated both OR impairments and monoamine transporter integrity in groups of rats treated with a range of mAMPH doses during a single day. An ED mAMPH regimen attenuated the acute hyperthermic response to the subsequent mAMPH binge and prevented the OR impairments and reductions in [125 I]RTI-55 binding to monoamine transporters in striatum, hippocampus (HC), and perirhinal cortex (pRh) that otherwise occur 1 week after the mAMPH binge. Single-day mAMPH regimens (4 x 1mg/kg to 4 x 4 mg/kg, s.c.) dose-dependently produced acute hyperthermia and, 1 week post-mAMPH, produced dose-dependent impairments in OR and reductions in monoamine transporter binding. The OR impairments of single-day mAMPH-treated rats correlated with monoaminergic transporter loss in ventral caudate-putamen, HC, and pRh. In aggregate, these findings suggest a correspondence between mAMPH-induced monoaminergic injury and the resulting OR deficits.

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.

Chronic cocaine but not chronic amphetamine use is associated with perseverative responding in humans

RATIONALE

Chronic drug use has been associated with increased impulsivity and maladaptive behaviour, but the underlying mechanisms of this impairment remain unclear. We investigated the ability to adapt behaviour according to changes in reward contingencies, using a probabilistic reversal-learning task, in chronic drug users and controls.

MATERIALS AND METHODS

Five groups were compared: chronic amphetamine users (n = 30); chronic cocaine users (n = 27); chronic opiate users (n = 42); former drug users of psychostimulants and opiates (n = 26); and healthy non-drug-taking control volunteers (n = 25). Participants had to make a forced choice between two alternative stimuli on each trial to acquire a stimulus-reward association on the basis of degraded feedback and subsequently to reverse their responses when the reward contingencies changed.

RESULTS

Chronic cocaine users demonstrated little behavioural change in response to the change in reward contingencies, as reflected by perseverative responding to the previously rewarded stimulus. Perseverative responding was observed in cocaine users regardless of whether they completed the reversal stage successfully. Task performance in chronic users of amphetamines and opiates, as well as in former drug users, was not measurably impaired.

CONCLUSION

Our findings provide convincing evidence for response perseveration in cocaine users during probabilistic reversal-learning. Pharmacological differences between amphetamine and cocaine, in particular their respective effects on the 5-HT system, may account for the divergent task performance between the two psychostimulant user groups. The inability to reverse responses according to changes in reinforcement contingencies may underlie the maladaptive behaviour patterns observed in chronic cocaine users but not in chronic users of amphetamines or opiates.

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.