The biological, social and clinical bases of drug addiction: commentary and debate

Dopaminergic systems create reward seeking despite adverse consequences

Resource-seeking behaviours are ordinarily constrained by physiological needs and threats of danger, and the loss of these controls is associated with pathological reward seeking1. Although dysfunction of the dopaminergic valuation system of the brain is known to contribute towards unconstrained reward seeking2,3, the underlying reasons for this behaviour are unclear. Here we describe dopaminergic neural mechanisms that produce reward seeking despite adverse consequences in Drosophila melanogaster. Odours paired with optogenetic activation of a defined subset of reward-encoding dopaminergic neurons become cues that starved flies seek while neglecting food and enduring electric shock punishment. Unconstrained seeking of reward is not observed after learning with sugar or synthetic engagement of other dopaminergic neuron populations. Antagonism between reward-encoding and punishment-encoding dopaminergic neurons accounts for the perseverance of reward seeking despite punishment, whereas synthetic engagement of the reward-encoding dopaminergic neurons also impairs the ordinary need-dependent dopaminergic valuation of available food. Connectome analyses reveal that the population of reward-encoding dopaminergic neurons receives highly heterogeneous input, consistent with parallel representation of diverse rewards, and recordings demonstrate state-specific gating and satiety-related signals. We propose that a similar dopaminergic valuation system dysfunction is likely to contribute to maladaptive seeking of rewards by mammals.

Associations of the P300 Event-Related Potentials and Self-Reported Craving in Substance Use Disorders: A Systematic Review

INTRODUCTION

The phenomenon of craving and attention bias towards drug cues is theorized to operate cooperatively, owing to the principles of associative learning. In this context, the conditioned response to drug-related stimuli activates reward mechanisms within the brain, consequently inducing craving and fostering the underlying mechanisms that contribute to relapse in individuals with substance use disorders. Multiple studies have assessed the relationship between attention to substance-related cues and subjective craving through electroencephalography (EEG), but their findings have yet to be synthesized and examined. This review summarizes the association between the amplitude of the P300 event-related potential (ERP) and substance use craving, compares discrepancies in results by type of substance, and discusses gaps in the literature to inform future research.

METHODS

A systematic search was conducted on Embase, Web of Science, CINAHL, and PsychINFO databases. Studies were published in English and included peer-reviewed human research investigating the relationship between EEG P300 ERP and self-reported substance use craving. The included study samples comprised of in treatment or non-treatment-seeking participants who use substances. The primary outcomes of interest were those derived from inferential statistics assessing P300 amplitude and substance use craving.

RESULTS

Ten studies were included in the final search and were organized by substance type: three alcohol, three cocaine, two tobacco, one heroin, and one cannabis. Results were mixed for alcohol and cocaine. Studies on tobacco, heroin, and cannabis use were congruent for associations between the P300 amplitude and craving.

CONCLUSIONS

Overall findings are mixed between studies addressing the association of the EEG P300 amplitude and craving. These results should be considered in the context of the limited sample size, underpowered analyses, and methodological differences that potentially contribute to discrepancies in outcomes. Further research is required to assess the role of craving assessment, EEG methodology, and substance-related factors on the association between P300 amplitude and self-reported craving.

Impact of spaceflight stressors on behavior and cognition: A molecular, neurochemical, and neurobiological perspective

The response of the human body to multiple spaceflight stressors is complex, but mounting evidence implicate risks to CNS functionality as significant, able to threaten metrics of mission success and longer-term behavioral and neurocognitive health. Prolonged exposure to microgravity, sleep disruption, social isolation, fluid shifts, and ionizing radiation have been shown to disrupt mechanisms of homeostasis and neurobiological well-being. The overarching goal of this review is to document the existing evidence of how the major spaceflight stressors, including radiation, microgravity, isolation/confinement, and sleep deprivation, alone or in combination alter molecular, neurochemical, neurobiological, and plasma metabolite/lipid signatures that may be linked to operationally-relevant behavioral and cognitive performance. While certain brain region-specific and/or systemic alterations titrated in part with neurobiological outcome, variations across model systems, study design, and the conspicuous absence of targeted studies implementing combinations of spaceflight stressors, confounded the identification of specific signatures having direct relevance to human activities in space. Summaries are provided for formulating new research directives and more predictive readouts of portending change in neurobiological function.

Nonhuman primate models in the study of spaceflight stressors: Past contributions and future directions

Studies in rodents suggest that exposure to distinct spaceflight stressors (e.g., space radiation, isolation/confinement, microgravity) may have a profound impact on an astronaut's ability to perform both simple and complex tasks related to neurocognitive performance, central nervous system (CNS) and vestibular/sensorimotor function. However, limited information is currently available on how combined exposure to the spaceflight stressors will impact CNS-related neurocognitive and neurobiological function in-flight and, as well, terrestrial risk of manifesting neurodegenerative conditions when astronauts return to earth. This information gap has significantly hindered our ability to realistically estimate spaceflight hazard risk to the CNS associated with deep space exploration. Notwithstanding a significant body of work with rodents, there have been very few direct investigations of the impact of these spaceflight stressors in combination and, to our knowledge, no such investigations using nonhuman primate (NHP) animal models. In view of the widely-recognized translational value of NHP data in advancing biomedical discoveries, this research deficiency limits our understanding regarding the impact of individual and combined spaceflight stressors on CNS-related neurobiological function. In this review, we address this knowledge gap by conducting a systematic and comprehensive evaluation of existing research on the impact of exposure to spaceflight stressors on NHP CNS-related function. This review is structured to: a) provide an overarching view of the past contributions of NHPs to spaceflight research as well as the strengths, limitations, and translational value of NHP research in its own right and within the existing context of NASA-relevant rodent research; b) highlight specific conclusions based on the published literature and areas needed for future endeavors; c) describe critical research gaps and priorities in NHP research to facilitate NASA's efforts to bridge the key knowledge gaps that currently exist in translating rodent data to humans; and d) provide a roadmap of recommendations for NASA regarding the availability, validity, strengths, and limitations of various NHP models for future targeted research.

Deciphering Human Leukocyte Antigen Susceptibility Maps From Immunopeptidomics Characterization in Oncology and Infections

Genetic variability across the three major histocompatibility complex (MHC) class I genes (human leukocyte antigen [HLA] A, B, and C) may affect susceptibility to many diseases such as cancer, auto-immune or infectious diseases. Individual genetic variation may help to explain different immune responses to microorganisms across a population. HLA typing can be fast and inexpensive; however, deciphering peptides loaded on MHC-I and II which are presented to T cells, require the design and development of high-sensitivity methodological approaches and subsequently databases. Hence, these novel strategies and databases could help in the generation of vaccines using these potential immunogenic peptides and in identifying high-risk HLA types to be prioritized for vaccination programs. Herein, the recent developments and approaches, in this field, focusing on the identification of immunogenic peptides have been reviewed and the next steps to promote their translation into biomedical and clinical practice are discussed.

Plasticity in the Hippocampus, Neurogenesis and Drugs of Abuse

Synaptic plasticity in the hippocampus assists with consolidation and storage of long-lasting memories. Decades of research has provided substantial information on the cellular and molecular mechanisms underlying synaptic plasticity in the hippocampus, and this review discusses these mechanisms in brief. Addiction is a chronic relapsing disorder with loss of control over drug taking and drug seeking that is caused by long-lasting memories of drug experience. Relapse to drug use is caused by exposure to context and cues associated with the drug experience, and is a major clinical problem that contributes to the persistence of addiction. This review also briefly discusses some evidence that drugs of abuse alter plasticity in the hippocampus, and that development of novel treatment strategies that reverse or prevent drug-induced synaptic alterations in the hippocampus may reduce relapse behaviors associated with addiction.

The dopamine D2 receptor gene TaqI A polymorphism is not associated with Novelty Seeking, Harm Avoidance and Reward Dependence in healthy subjects

Allele A1 of the TaqI A restriction fragment length polymorphism (RFLP) of the dopamine D2 receptor gene has been found to be associated with substance abuse and alcoholism. The personality trait of Novelty Seeking (NS) is also associated with substance abuse and dependence. We hypothesised, on the basis of involvement of dopaminergic mechanisms in substance abuse, that the presence of allele A1 of the dopamine D2 receptor gene may represent a genetic predisposition for the NS personality trait. We investigated, therefore, whether the allele A1 of the TaqI A RFLP of the dopamine D2 receptor gene is associated with the NS dimension of the Tridimensional Personality Questionnaire (TPQ) in healthy Caucasian subjects with no history of alcohol or substance abuse or dependence. We genotyped 204 subjects aged 18 to 30 years. There was no association between any of the alleles of the D2 receptor genes and any of the TPQ scores (NS, Harm Avoidance, Reward Dependence). We conclude that allele A1 of the TaqI A RFLP of the dopamine D2 receptor is not associated with NS personality trait in healthy Caucasian subjects.

An association between latent toxoplasmosis and substance abuse: an Egyptian Center Study

Infection of toxoplasma gondii (TG), an intracellular neurotropic parasitic protozoon, has been associated with various neuropsychiatric disorders. TG is usually diagnosed from serological sample in which a positive test for Anti-TG immunoglobulin G (IgG) indicates TG infection (toxoplasmosis). The research was conducted to test the hypothesis that TG infection may be associated with substance abuse. Anti-TG (IgG) was screened in 444 participants (350 abusers and 94 controls) who attended the Psychiatry Department of Mansoura University Hospitals. All participants were screened for different class of abused substances (tramadol, cannabis, opiates, barbiturates and benzodiazepines) using enzyme multiplied immunoassay technique and positive cases were confirmed using gas chromatography-mass spectroscopy (GC-MS). Substance users were also diagnosed according to DSM IV criteria. GC-MS assays revealed that 116 cases (33.1% of users) had documented use of more than one substance. Tramadol was the most common abused substance [86 cases (24.6%)]. About 56% of the participants were sero-positive for anti-TG IgG. Toxoplasmosis sero-positivity was significantly higher among substance abusers (P < 0.0001) irrespective of the class of substance used. There was a significant relationship between toxoplasma sero-positivity and occurrence of convulsions among tramadol users (P = 0.0007) and those relapsing (P < 0.0001) following short periods of abstinence. The data collected suggest that TG infection is significantly associated with the high incidence of substance use, irrespective of the drug class. These preliminary findings warrant further larger multicenter clinical studies to test the robustness of this association.

Role of boyfriends and intimate sexual partners in the initiation and maintenance of injecting drug use among women in coastal Kenya

INTRODUCTION

Gender dynamics and interpersonal relations within intimate partnerships are known to determine health behaviors, including substance use, within couples. In addition, influence from intimate partners may occur in the context of wider social ecological determinants of health behavior. The aim of this study was to document the role of intimate partners in influencing injecting drug use among women in Kenya, where injecting drug use is on the rise.

METHODS

We performed secondary data analysis of an existing dataset from a 2015 qualitative study involving 45 women who inject drugs and 5 key stakeholders in coastal Kenya. Primary data had been collected via a combination of in-depth interviews and focus group discussions exploring sexual, reproductive, drug use, and other social contexts of women who inject drugs. The process by which intimate partners influenced women's initiation of drug use, transition to injecting practices, and maintenance of injecting drug use were identified using thematic analysis.

RESULTS

Boyfriends and intimate either facilitated or restrained women's drug-injecting. On the one hand, young women's entry into drug use was prompted by relationship problems, or a need to acquiesce with their drug-using boyfriends. Once women started injecting, intimate partners facilitated ongoing drug-injecting by financing the acquisition of drugs, peddling drugs to their women, or sharing their drugs with their women. The social capital that peddlers held insulated women from police arrests, and encouraged women to seek and sustain intimate relations with well-connected peddlers. Men's influences over women were driven by an underlying patriarchal drug acquisition and economic power. On the other hand, boyfriends and intimate partners who were non-injectors or non-drug users sought to moderate women's injecting drug use by encouraging them to inject less, to smoke or snort instead of injecting, or to enroll into rehabilitation. These moderating influences were most prominent when couples were pregnant. Despite men being a source of practical and emotional support, women were frequently unable limit or alter their injecting drug use, due to its addictive nature. Men's disagreement with women's ongoing injecting strained relationships, and occasionally led to separation.

CONCLUSIONS

Some boyfriends facilitated women's injecting drug use, while others moderated it, supporting assertions that intimate relationships can both be a site of injecting risks or protection. At the micro-level, these findings highlight an opportunity for couple-based interventions, leveraging on non-drug injecting males as a resource to support women adopt safer injecting practices. At a macro level, incorporating livelihood interventions into harm reduction programs is required in order to mitigate economic-based influence of male intimate partners on women's injecting drug use. At both levels, gender transformative approaches are essential. To gain a comprehensive understanding of women's injecting drug use, future studies drug use should explore women's contexts beyond micro influences and consider their wider macro-structural determinants.

Picosecond self-diffusion in ethanol-water mixtures

We report the self-diffusion in ethanol-water mixtures as a function of the water-ethanol ratio measured at different temperatures using quasi-elastic neutron spectroscopy (QENS). For our protiated samples, QENS is mainly sensitive to the dominant ensemble-averaged incoherent scattering from the hydrogen atoms of the liquid mixtures. The energy range and resolution render our experiment sensitive to the picosecond time scale and nanometer length scale. These observation scales complement different scales accessible by nuclear magnetic resonance techniques. Subsequent to testing different models, we find that a simple jump-diffusion model averaging over both types of molecules, water and ethanol, best fits our data.

Anatomic Review of the Ventral Capsule/Ventral Striatum and the Nucleus Accumbens to Guide Target Selection for Deep Brain Stimulation for Obsessive-Compulsive Disorder

BACKGROUND

Disturbances in the reward network of the brain underlie addiction, depression, and obsessive-compulsive disorder. The ventral capsule/ventral striatum and nucleus accumbens (NAc) region is a clinically approved target for deep brain stimulation for obsessive-compulsive disorder.

METHODS

We performed a comprehensive literature review to define clinically relevant anatomy and connectivity of the ventral capsule/ventral striatum and NAc region to guide target selection for deep brain stimulation.

RESULTS

Architecturally and functionally, the NAc is divided into the core and the shell, with each area having different connections. The shell primarily receives limbic information, and the core typically receives information from the motor system. In general, afferents from the prefrontal cortex, hippocampus, and amygdala are excitatory. The dopaminergic projections to the NAc from the ventral tegmental area modulate the balance of these excitatory inputs. Several important inputs to the NAc converge at the junction of the internal capsule (IC) and the anterior commissure (AC): the ventral amygdalofugal pathways that run parallel to and underneath the AC, the precommissural fornical fibers that run anterior to the AC, axons from the ventral prefrontal cortex and medial orbitofrontal cortex that occupy the most ventral part of the IC and embedding within the NAc and AC, and the superolateral branch of the medial forebrain bundle located parallel to the anterior thalamic radiation in the IC.

CONCLUSIONS

The caudal part of the NAc passing through the IC-AC junction may be an effective target for deep brain stimulation to improve behavioral symptoms associated with obsessive-compulsive disorder.

Impulsivity and compulsivity in Internet gaming disorder: A comparison with obsessive-compulsive disorder and alcohol use disorder

Background and aims Internet gaming disorder (IGD) is characterized by a loss of control and a preoccupation with Internet games leading to repetitive behavior. We aimed to compare the baseline neuropsychological profiles in IGD, alcohol use disorder (AUD), and obsessive-compulsive disorder (OCD) in the spectrum of impulsivity and compulsivity. Methods A total of 225 subjects (IGD, N = 86; AUD, N = 39; OCD, N = 23; healthy controls, N = 77) were administered traditional neuropsychological tests including Korean version of the Stroop Color-Word test and computerized neuropsychological tests, including the stop signal test (SST) and the intra-extra dimensional set shift test (IED). Results Within the domain of impulsivity, the IGD and OCD groups made significantly more direction errors in SST (p = .003, p = .001) and showed significantly delayed reaction times in the color-word reading condition of the Stroop test (p = .049, p = .001). The OCD group showed the slowest reading time in the color-word condition among the four groups. Within the domain of compulsivity, IGD patients showed the worst performance in IED total trials measuring attentional set shifting ability among the groups. Conclusions Both the IGD and OCD groups shared impairment in inhibitory control functions as well as cognitive inflexibility. Neurocognitive dysfunction in IGD is linked to feature of impulsivity and compulsivity of behavioral addiction rather than impulse dyscontrol by itself.

Food and drug addictions: Similarities and differences

This review examines the merits of 'food addiction' as an explanation of excessive eating (i.e., eating in excess of what is required to maintain a healthy body weight). It describes various apparent similarities in appetites for foods and drugs. For example, conditioned environmental cues can arouse food and drug-seeking behaviour, 'craving' is an experience reported to precede eating and drug taking, 'bingeing' is associated with both eating and drug use, and conditioned and unconditioned tolerance occurs to food and drug ingestion. This is to be expected, as addictive drugs tap into the same processes and systems that evolved to motivate and control adaptive behaviours, including eating. The evidence, however, shows that drugs of abuse have more potent effects than foods, particularly in respect of their neuroadaptive effects that make them 'wanted.' While binge eating has been conceptualised as form of addictive behaviour, it is not a major cause of excessive eating, because binge eating has a far lower prevalence than obesity. Rather, it is proposed that obesity results from recurrent overconsumption of energy dense foods. Such foods are, relatedly, both attractive and (calorie for calorie) weakly satiating. Limiting their availability could partially decrease excessive eating and consequently decrease obesity. Arguably, persuading policy makers that these foods are addictive could support such action. However, blaming excessive eating on food addiction could be counterproductive, because it risks trivialising serious addictions, and because the attribution of excessive eating to food addiction implies an inability to control one's eating. Therefore, attributing everyday excessive eating to food addiction may neither explain nor significantly help reduce this problem.

Interaction of the Dopaminergic System With Mechanisms of Associative Learning and Cognition: Implications for Drug Abuse

The possible role of mechanisms of associative learning in drug abuse and addiction is considered with respect to psychomotor stimulant drugs such as cocaine and amphetamine. Although the initial sites of the reinforcing effects of these drugs are associated with the mesolimbic dopamine projection to the nucleus accumbens, other important neuromodulatory influences are identified. These include the amygdala, which appears to mediate the associative processes by which environmental stimuli come to control drug-seeking behavior. Possible parallel mechanisms by which stimulant drugs enhance effects of aversive as well as rewarding stimuli are discussed. The importance of attribution and context in determining relative rewarding and aversive effects is pointed out. These attributional and contextual factors may be a function of cortical regions that may themselves be impaired by chronic drug abuse, leading to further dysexecutive control over cognition and behavior.

Alterations of neuronal precursor cells in stages of human adult neurogenesis in heroin addicts

BACKGROUND

Adult neurogenesis has been shown to occur throughout life and different brain pathologies were demonstrated to be associated with altered neurogenesis. Here, an impact of heroin addiction on neurogenesis in humans is hypothesised.

METHODS

Post mortem hippocampal specimens of drug addicts with known heroin abuse and a group of non-addictive control subjects were analysed, using antibodies indicating different stages of neurogenesis. The subgranular zone of the dentate gyrus was examined qualitatively and quantitatively.

RESULTS

The data indicate (i) a decreased number of neural precursor cells, (ii) accompanied by low rates of proliferation and (iii) a marked loss of dendritic trees in targeting cells in heroin fatalities. (iv) The age-dependent increase of differentiating cells in the healthy controls was not observed in the addicts. Additionally, double immunofluorescence labelling indicated the precursor nature of Musashi-1 positive cells in the human subgranular zone of the dentate gyrus.

CONCLUSIONS

Present data firstly demonstrate the influence of drug addiction with known heroin abuse on different developmental stages of progenitors in the dentate gyrus. The patterns of antibody staining suggest a distinct inhibition of neurogenesis at the stage of neural precursor cells and revealed morphological changes in targeting cells in cases of heroin addicts as compared to healthy controls. These alterations could be considerable for memory and cognitive deficits as well as addictive behaviour in chronic drug abusers and may give rise to specific pro-neurogenic therapies.

Alcohol craving in relation to coping with stress and satisfaction with life in the addicted

<b>Background</b><br /> The present study aimed at finding any relation between alcohol craving and strategies of coping with stress and satisfaction with life in the addicted. Until now, studies have shown that generalized deficits in coping with stress, and the dominance of avoidance strategies, are significantly related to the increase of the risk of addiction and the course of this disease. This relation, which could link strategies of coping with stress and quality of life with experiencing alcohol craving, has only been explained to a small extent. Also, the role of gender in explaining these relations is ambiguous.<br /> <br /> <b>Participants and procedure</b><br /> The study was conducted in a group of 550 addicted subjects in out-patient or in-patient treatment (396 men and 114 women). In the present study the following instruments were used: the Craving Typology Questionnaire by Marinotti et al., the Yale-Brown Obsessive-Compulsive Drinking Scale by Modell et al., the Mini-Cope by Carver et al., SADD by Reistrick et al., and the Satisfaction with Life Scale by Diener et al. Statistical correlational analysis and structural equations were applied, namely partial least squares path modelling (PLS-PM).<br /> <br /> <b>Results</b><br /> There are two types of links between craving and strategies of coping with stress among the addicted. The first dominating type is pointing at casual link between ineffective strategies of coping with stress and craving. The other weaker type indicates the diminishing influence of effective strategies of coping with stress on alcohol craving. Life satisfaction lowers alcohol craving.<br /> <br /> <b>Conclusions</b><br /> Effective strategies of reacting to stress, together with life satisfaction, protect against increase of alcohol craving. Severity of dependence is an important factor which moderates the influence of strategies of coping with stress on alcohol craving.

Serotonin-2C and -2a receptor co-expression on cells in the rat medial prefrontal cortex

Neural function within the medial prefrontal cortex (mPFC) regulates normal cognition, attention and impulse control, implicating neuroregulatory abnormalities within this region in mental dysfunction related to schizophrenia, depression and drug abuse. Both serotonin-2A (5-HT2A) and -2C (5-HT2C) receptors are known to be important in neuropsychiatric drug action and are distributed throughout the mPFC. However, their interactive role in serotonergic cortical regulation is poorly understood. While the main signal transduction mechanism for both receptors is stimulation of phosphoinositide production, they can have opposite effects downstream. 5-HT2A versus 5-HT2C receptor activation oppositely regulates behavior and can oppositely affect neurochemical release within the mPFC. These distinct receptor effects could be caused by their differential cellular distribution within the cortex and/or other areas. It is known that both receptors are located on GABAergic and pyramidal cells within the mPFC, but it is not clear whether they are expressed on the same or different cells. The present work employed immunofluorescence with confocal microscopy to examine this in layers V-VI of the prelimbic mPFC. The majority of GABA cells in the deep prelimbic mPFC expressed 5-HT2C receptor immunoreactivity. Furthermore, most cells expressing 5-HT2C receptor immunoreactivity notably co-expressed 5-HT2A receptors. However, 27% of 5-HT2C receptor immunoreactive cells were not GABAergic, indicating that a population of prelimbic pyramidal projection cells could express the 5-HT2C receptor. Indeed, some cells with 5-HT2C and 5-HT2A receptor co-labeling had a pyramidal shape and were expressed in the typical layered fashion of pyramidal cells. This indirectly demonstrates that 5-HT2C and 5-HT2A receptors may be commonly co-expressed on GABAergic cells within the deep layers of the prelimbic mPFC and perhaps co-localized on a small population of local pyramidal projection cells. Thus a complex interplay of cortical 5-HT2A and 5-HT2C receptor mechanisms exists, which if altered, could modulate efferent brain systems implicated in mental illness.

A comparison of attentional bias towards drug cues in addicts and non-addicts

Background:

According to recent theories on addiction, attentional bias towards drug-related stimuli plays a pivotal role in the initiation of drug abuse.

Objectives:

The present study attempted to investigate attentional bias towards drug-related words in addicts and non-addicts.

Patients and Methods:

To attain the objectives, following a causal-comparative study, a number of 15 addicts under treatment in anonymous groups, and 15 non-addicts from among students at Isfahan University were selected through available sampling. Both groups were evaluated through Stroop test, and the results were analyzed adopting independent t-test. Findings: as indicated by the findings, a significant difference was observed in the two groups concerning color-naming accuracy (P < 0.05, X² (1) = 3.896) as well as reaction time (P < 0.0001, X² (1) = 17.404). The calculated difference between accuracy and reaction time for congruent and incongruent stimuli was significant.

Results:

The results showed that there was a significant difference between the average reaction time of the two groups. In terms of the number of errors, however, no significant difference was observed.

Conclusions:

The attentional bias of drug addicts is associated with drug-related cues or the temptation for drug abuse.

Rapid tolerance development to the NREM sleep promoting effect of alcohol

STUDY OBJECTIVES

Alcohol tolerance is a major contributor towards the development of alcohol dependence. Does alcohol intake result in rapid tolerance development to alcohol induced NREM sleep promotion? This has never been examined. Our objective was to examine whether two bouts of alcohol consumption on consecutive days results in rapid tolerance development to alcohol-induced NREM sleep promotion.

DESIGN

N/A.

SETTING

N/A.

PATIENTS OR PARTICIPANTS

C57BL/6J mice.

INTERVENTIONS

Mice (N = 5) were implanted with sleep electrodes using standard surgical conditions. Following postoperative recovery and habituation, the experiment was begun. On baseline day, water bottle changes were performed at 10:00 (3 h after dark onset) and 14:00 to mimic conditions during alcohol consumption days. On next 2 days, (Days 1 and 2) mice were allowed to self-administer alcohol (20% v/v) for 4 h beginning at 10:00 and ending at 14:00. Sleep-wakefulness was continuously recorded from 10:00 to 18:00 (8 h; 4 h during alcohol + 4 h post-alcohol) on all 3 days.

MEASUREMENTS AND RESULTS

Although mice consumed comparable amounts of alcohol on Days 1 and 2, NREM sleep and wakefulness were significantly and differentially affected during 4 h post-alcohol period. A robust alcohol-induced NREM sleep promotion was observed on Day 1. However, no such sleep promotion was observed on Day 2, suggesting rapid tolerance development.

CONCLUSIONS

Our study is the first to demonstrate that alcohol consumption for two consecutive days results in development of rapid tolerance to alcohol-induced sleep promotion.

On the interaction between drugs of abuse and adolescent social behavior

RATIONALE

Social factors influence drug abuse. Conversely, drugs of abuse alter social behavior. This is especially pertinent during post-weaning development, when there are profound changes in the social repertoire, and the sensitivity to the positive and negative effects of drugs of abuse is altered.

OBJECTIVES

This study aimed to provide an overview of our current understanding of the interaction between drugs of abuse and juvenile/adolescent social behavior.

METHODS

We first provide evidence that a characteristic form of juvenile and adolescent social behavior, i.e., social play behavior, has reinforcing properties and is affected by drugs of abuse. Next, social risk factors for drug use and addiction are described, including antisocial personality traits and early social insults. Last, we discuss research that investigates social influences on drug use, as well as the consequences of perinatal drug exposure on later social interactions.

RESULTS

Social play behavior is highly rewarding in laboratory animals, and it is affected by low doses of opioids, cannabinoids, ethanol, nicotine, and psychostimulants. In humans, antisocial personality traits, most prominently in the form of conduct disorder, are a prominent risk factor for drug addiction. Preclinical studies have consistently shown altered sensitivity to drugs as a result of social isolation during post-weaning development. The social environment of an individual has a profound, but complex, influence on drug use, and perinatal drug exposure markedly alters later social interactions.

CONCLUSIONS

The studies reviewed here provide a framework to understand the interaction between drugs of abuse and adolescent social interaction, at the preclinical and the clinical level.

An integrative analysis of ethanol tolerance and withdrawal in zebrafish (Danio rerio)

The zebrafish is emerging as a popular animal model for alcohol (ethanol or EtOH) addiction due to its simplicity and practical advantages. Two phenomena associated with ethanol addiction are the development of tolerance and withdrawal. Using a multi-level approach in the current study, we characterise ethanol tolerance and withdrawal in zebrafish. We first investigate the temporal trajectory of ethanol concentration in the zebrafish brain in response to an acute exposure and during withdrawal. We report that ethanol concentrations approach a steady state within 60 min of exposure to 0.50% and 1.00% v/v ethanol and rapidly decline and return to zero within 60 min following withdrawal from chronic ethanol exposure (0.50% v/v). We characterise the changes associated with ethanol tolerance and withdrawal in zebrafish by focusing on three domains relevant to ethanol addiction: motor patterns, physiological responses (i.e. cortisol levels), and neurochemical alterations. The use of multiple domains of investigation allowed an in-depth analysis of ethanol induced changes in zebrafish.

Decision-making deficits are still present in heroin abusers after short- to long-term abstinence

BACKGROUND

Substance dependent individuals (SDIs) consistently show deficits in decision making with biased choices toward immediate rewards, even at the expense of future consequences. However, relatively little evidence has been reported concerning the population of drug abusers who are exclusively addicted to heroin.

METHODS

The present study tested 124 male abstinent "pure" heroin (AH) abusers (divided into short-term, mid-term, and long-term groups based on their length of abstinence) and 43 healthy controls (HC) intending to address this issue. Two decision-making tasks, the Delay Discounting Task (DDT) and the Iowa Gambling Task (IGT) were employed to measure their decision-making performance.

RESULTS

Compared to HC participants, AH participants made significantly poorer choices on both the DDT and the IGT and the poor decision-making performances were not influenced by their lengths of abstinence. It is suggested that heroin-abuse-related decision-making deficits that are demonstrated by rapidly discounting future rewards; preferring incentives with large short-term gains while ignoring accompanying potential risks; and being inflexible in adjusting decision-making behaviors in accordance with outcome feedback, may not be compensated for even after a long period of abstinence from heroin abuse.

CONCLUSION

Hence, this inability to recover should be taken into consideration in the evaluation, prevention and intervention of heroin abuse and relapse.

Nicotine derived from the electronic cigarette improves time-based prospective memory in abstinent smokers

RATIONALE

It is well established that nicotine improves, and deprivation impairs, cognitive performance and mood in smokers. Prospective memory (PM), remembering to execute a delayed intention at a given time point, is under-explored in smokers. Whilst a handful of studies have shown improved PM with nicotine, the effects of nicotine delivered via the electronic cigarette (e-cigarette) have not been investigated.

OBJECTIVE

This study explores whether, by comparison with placebo, nicotine delivered via the e-cigarette can improve PM, tobacco withdrawal symptoms and desire to smoke in abstinent smokers.

METHODS

Twenty smokers, abstinent for 8-10 h, each completed two experimental sessions under nicotine (18 mg) and placebo (0 mg) e-cigarette conditions. Participants completed a single-item desire-to-smoke scale and the Mood and Physical Symptoms Scale. PM was measured using the Cambridge Prospective Memory Test.

RESULTS

Compared with placebo, the nicotine e-cigarette reduced the desire to smoke and tobacco withdrawal symptoms, and improved time-based but not event-based PM. There was a moderate, marginally significant negative correlation between PM performance during abstinence and nicotine dependence.

CONCLUSIONS

This is the first study to show that nicotine derived via e-cigarette can improve PM in abstinent smokers, suggesting efficient nicotine delivery. The finding that the effect of nicotine was restricted to time-based rather than event-based PM is consistent with the view that nicotine acts to improve performance on strategic (effortful) rather than automatic processing. These findings add to the growing body of evidence that the e-cigarette can replace some of the effects of nicotine derived from tobacco smoking, thus highlighting its potential for smoking cessation.

Associative learning mechanisms underpinning the transition from recreational drug use to addiction

Learning theory proposes that drug seeking is a synthesis of multiple controllers. Whereas goal-directed drug seeking is determined by the anticipated incentive value of the drug, habitual drug seeking is elicited by stimuli that have formed a direct association with the response. Moreover, drug-paired stimuli can transfer control over separately trained drug seeking responses by retrieving an expectation of the drug's identity (specific transfer) or incentive value (general transfer). This review covers outcome devaluation and transfer of stimulus-control procedures in humans and animals, which isolate the differential governance of drug seeking by these four controllers following various degrees of contingent and noncontingent drug exposure. The neural mechanisms underpinning these four controllers are also reviewed. These studies suggest that although initial drug seeking is goal-directed, chronic drug exposure confers a progressive loss of control over action selection by specific outcome representations (impaired outcome devaluation and specific transfer), and a concomitant increase in control over action selection by antecedent stimuli (enhanced habit and general transfer). The prefrontal cortex and mediodorsal thalamus may play a role in this drug-induced transition to behavioral autonomy.

Emotional valence and context of social influences on drug abuse-related behavior in animal models of social stress and prosocial interaction

RATIONALE

Social factors are important determinants of drug dependence and relapse.

OBJECTIVES

We reviewed pre-clinical literature examining the role of social experiences from early life through the development of drug dependence and relapse, emphasizing two aspects of these experiences: (1) whether the social interaction is appetitive or aversive and (2) whether the social interaction occurs within or outside of the drug-taking context.

METHODS

The models reviewed include neonatal care, isolation, social defeat, chronic subordination, and prosocial interactions. We review results from these models in regard to effects on self-administration and conditioned place preference established with alcohol, psychostimulants, and opiates.

RESULTS

We suggest that in general, when the interactions occur outside of the drug-taking context, prosocial interactions are protective against drug abuse-related behaviors, whereas social stressors facilitate these behaviors. By contrast, positive or negative social interactions occurring within the drug-taking context may interact with other risk factors to enhance or inhibit these behaviors.

CONCLUSIONS

Despite differences in the nature and complexity of human social behavior compared to other species, the evolving animal literature provides useful models for understanding social influences on drug abuse-related behavior that will allow for research on the behavioral and biological mechanisms involved. The models have contributed to understanding social influences on initiation and maintenance of drug use, but more research is needed to understand social influences on drug relapse.

Considering gender in cannabinoid research: a step towards personalized treatment of marijuana addicts

Addiction is a complex disorder with interacting factors, including environmental factors, drug-induced neurobiological changes, comorbidity, personality traits and stress responsivity. Numerous genetic variants that affect these factors may work in concert to affect vulnerability and severity of addiction. Traditionally, abuse of illicit drugs, including cannabis, was considered to be primarily a problem specific to men but the recent focus on drug addiction in women has brought attention to numerous sex differences in the central effects of these drugs, epidemiology of abuse-related disorders, etiologic considerations and psychiatric comorbidity. Gender is now recognised as a major factor in the modulation of the pharmacological effects of drugs of abuse, and sex differences have been reported in various phases of the addiction cycle in both humans and animals. Recently, important gender-dependent differences have been detected in the rates of initiation of marijuana smoking and in the frequency of use. Several animal studies, and in particular self-administration studies, confirmed the crucial role played by sex and gonadal hormones in determining higher sensitivity to marijuana's rewarding properties and vulnerability to cannabis addiction in females than in males. In general, women also show higher rate of relapse to drug use than men, likely due to divergent withdrawal experiences and increased reactivity to internal (emotional) and external (drug-associated) cues. According with this, craving for marijuana smoking and propensity to re-use cannabis after abstinence may also develop differently between the sexes and require distinct treatment approaches, thus highlighting the urgent need for gender-tailored prevention strategies and detoxification treatments.

Distinct contributions of dopamine in the dorsolateral striatum and nucleus accumbens shell to the reinforcing properties of cocaine

Dopaminergic neurotransmission in the dorsal and ventral striatum is thought to be involved in distinct aspects of cocaine addiction. Ventral striatal dopamine mediates the acute reinforcing properties of cocaine, whereas dopamine in the dorsolateral striatum (DLS) is thought to become involved in later stages of the addiction process to mediate well-established cue-controlled drug seeking. However, it is unclear whether the DLS also has a role in the reinforcing properties of cocaine itself. Therefore, we systematically investigated the involvement of dopamine in dorsal and ventral striatal regions in cocaine self-administration, using various schedules of reinforcement in animals with limited drug taking experience. Intra-DLS infusion of the dopamine receptor antagonist α-flupenthixol did not affect the acquisition of cocaine self-administration, increased cocaine self-administration under a fixed ratio-1 (FR-1) schedule of reinforcement, caused a rightward and downward shift of the dose-response curve of cocaine under an FR-1 schedule of reinforcement and decreased responding for cocaine under a progressive ratio (PR) schedule of reinforcement. Infusion of α-flupenthixol into the ventral nucleus accumbens (NAcc) shell inhibited the acquisition of cocaine self-administration, reduced responding for the drug under FR-1 and PR schedules of reinforcement, and caused a downward shift of the dose-response curve of cocaine self-administration under an FR-1 schedule of reinforcement. These data show that dopamine in both the DLS and NAcc shell is involved in cocaine reinforcement. We suggest that the DLS and the NAcc shell mediate somewhat distinct facets of the reinforcing properties of cocaine, related to its rewarding and motivational aspects, respectively.

Effects of nicotine and alcohol on affective responses to emotionally toned film clips

RATIONALE

Smoking abstinence can result in decreased affective reactions to positively valenced stimuli, and this can be reversed via smoking. Given their shared ability to trigger nucleus accumbens dopamine release, a priming dose of alcohol may likewise augment positive affective responses during abstinence.

OBJECTIVES

The purpose of this study is to replicate our previous finding that compared to satiation, abstinence from smoking will be associated with decreased 'happiness' responses to positively valenced film clips (Study 1) and to explore whether a priming dose of alcohol can substitute for nicotine by concomitantly enhancing such responses (Study 2). In both studies, 'sadness' responses to negatively valenced clips were also included.

METHODS

Thirty-two and 77 smokers, respectively, in Studies 1 and 2 were randomly allocated to abstain from smoking for 10 h (abstinent smokers) or smoke as usual (satiated smokers). Participants then rated the extent to which they felt a list of emotions in response to each of 16 film clips. In Study 2, participants were additionally allocated to an alcohol manipulation in which they received either alcohol or placebo.

RESULTS

In Study 1, nicotine administration increased abstinent smokers' ratings of happiness and sadness to the corresponding film clips. In Study 2, nicotine and alcohol both enhanced positive reactivity to happy clips, and their effects were not additive. Alcohol but not nicotine likewise enhanced sadness responses to sad clips.

CONCLUSIONS

Abstinence from smoking can result in blunting of affective responses to positively toned stimuli, an effect that can be ameliorated by both nicotine and alcohol. The impact of nicotine on negative reactivity appears to be less robust.

Drug wanting: behavioral sensitization and relapse to drug-seeking behavior

Repeated exposure to drugs of abuse enhances the motor-stimulant response to these drugs, a phenomenon termed behavioral sensitization. Animals that are extinguished from self-administration training readily relapse to drug, conditioned cue, or stress priming. The involvement of sensitization in reinstated drug-seeking behavior remains controversial. This review describes sensitization and reinstated drug seeking as behavioral events, and the neural circuitry, neurochemistry, and neuropharmacology underlying both behavioral models will be described, compared, and contrasted. It seems that although sensitization and reinstatement involve overlapping circuitry and neurotransmitter and receptor systems, the role of sensitization in reinstatement remains ill-defined. Nevertheless, it is argued that sensitization remains a useful model for determining the neural basis of addiction, and an example is provided in which data from sensitization studies led to potential pharmacotherapies that have been tested in animal models of relapse and in human addicts.

Relapse to smoking during unaided cessation: clinical, cognitive and motivational predictors

RATIONALE

Neurobiological models of addiction suggest that abnormalities of brain reward circuitry distort salience attribution and inhibitory control processes, which in turn contribute to high relapse rates.

OBJECTIVES

The aim of this study is to determine whether impairments of salience attribution and inhibitory control predict relapse in a pharmacologically unaided attempt at smoking cessation.

METHODS

One hundred forty one smokers were assessed on indices of nicotine consumption/dependence (e.g. The Fagerström Test of Nicotine Dependence, cigarettes per day, salivary cotinine) and three trait impulsivity measures. After overnight abstinence, they completed experimental tests of cue reactivity, attentional bias to smoking cues, response to financial reward, motor impulsiveness and response inhibition (antisaccades). They then started a quit attempt with follow-up after 7 days, 1 month and 3 months; abstinence was verified via salivary cotinine levels ≤20 ng/ml.

RESULTS

Relapse rates at each point were 52.5%, 64% and 76.3%. The strongest predictor was pre-cessation salivary cotinine; other smoking/dependence indices did not explain additional outcome variance and neither did trait impulsivity. All experimental indices except responsivity to financial reward significantly predicted a 1-week outcome. Salivary cotinine, attentional bias to smoking cues and antisaccade errors explained unique as well as shared variance. At 1 and 3 months, salivary cotinine, motor impulsiveness and cue reactivity were all individually predictive; the effects of salivary cotinine and motor impulsiveness were additive.

CONCLUSIONS

These data provide some support for the involvement of abnormal cognitive and motivational processes in sustaining smoking dependence and suggest that they might be a focus of interventions, especially in the early stages of cessation.

Is ecstasy a drug of dependence?

This paper examines the evidence for an MDMA or "ecstasy" dependence syndrome. Animal evidence suggests that MDMA may be a less potent reinforcer than other drugs, but that it does have dependence potential. This suggests that (a) ecstasy dependence might be less likely than dependence upon other drugs; and (b) factors related to the behavioural and psychological aspects of reward and dependence may make a relatively greater contribution for ecstasy than for other drugs, where physically centred (and better understood) features of dependence may be more salient. Human evidence supports this proposition. Some people report problems with their use, but the literature suggests that physical features play a more limited role than psychological ones. Tolerance is apparent, and withdrawal is self-reported, but it is unclear whether these reports distinguish sub-acute effects of ecstasy intoxication from symptoms reflective of neuroadaptive processes underlying a "true" withdrawal syndrome. Studies examining the structure of dependence upon ecstasy suggest it may be different from drugs such as alcohol, methamphetamine and opioids. Consistent with studies of hallucinogens, a two-factor structure has been identified with factors suggestive of "compulsive use" and "escalating use". Regardless of the nature of any dependence syndrome, however, there is evidence to suggest that a minority of ecstasy users become concerned about their use and seek treatment. Further controlled studies are required to investigate this phenomenon.

Selective mu- and kappa-opioid receptor antagonists administered into the nucleus accumbens interfere with rapid tolerance to ethanol in rats

BACKGROUND

Previous findings have shown that intra-accumbens injection of naltrexone, a non-selective opioid antagonist, blocks the acquisition of rapid tolerance to ethanol in rats. This study investigates the effects of intra-accumbens injection of the selective mu-, delta-, and kappa-opioid antagonists, respectively, naloxonazine, naltrindole, and nor-binaltorphimine, on rapid tolerance to ethanol.

METHODS

Male Wistar rats with guide cannulae directed to the shell or the core portions of the nucleus accumbens received a microinjection of naloxonazine (2-4 microg), naltrindole (2-4 microg), nor-binaltorphimine (2.5-5 microg), or vehicle. After 5 min, each group was divided in two groups that received ethanol (2.7 g/kg i.p.) or saline. Rats were then tested for motor coordination on the tilting plane apparatus. Twenty four hours later, all rats received a challenge dose of ethanol (2.7 g/kg i.p.) and were tested on the tilt plane again.

RESULTS

Repeated injections of ethanol caused a reduction in motor impairment suggesting the development of tolerance. However, rats injected with 4 microg naloxonazine into either core or shell portions of the nucleus accumbens did not exhibit tolerance when challenged with ethanol on day 2. Rats treated with 5 microg nor-binaltorphimine into accumbens core plus intraperitoneal saline on day 1 showed reduced motor impairment when challenged with ethanol on day 2, suggesting cross-tolerance to ethanol.

CONCLUSIONS

Taken together, our results suggests that mu-opioid receptors in both shell and core portions of the nucleus accumbens, and possibly kappa-opioid in the core, participate in the modulation of rapid tolerance to ethanol.

Treatment for amphetamine psychosis

BACKGROUND

Chronic amphetamine users may have experience of paranoia and hallucination. It has long been believed that dopamine antagonists, such as chlorpromazine, haloperidol, and thioridazine, are effective for the treatment of amphetamine psychosis.

OBJECTIVES

To evaluate risks, benefits, costs of treatments for amphetamine psychosis.

SEARCH STRATEGY

MEDLINE (1966-2007), EMBASE (1980-2007), CINAHL (1982-2007), PsychINFO (1806-2007), CENTRAL (Cochrane Library 2008 issue 1), references of obtained articles.

SELECTION CRITERIA

All randomised controlled and clinical trials (RCTs, CCTs) evaluating treatments (alone or combined) for people with amphetamine psychosis

DATA COLLECTION AND ANALYSIS

Two authors evaluated and extracted the data independently. Dichotomous data were extracted on an intention-to-treat basis in which the dropouts were assigned as participants with the worst outcomes. The Relative Risk (RR) with the 95% confidence interval (95% CI) was used to assess the dichotomous data. The Weighted Mean Difference (WMD) with 95% CI was used to assess the continuous data.

MAIN RESULTS

The comprehensive searches found one randomised controlled trial of treatment for amphetamine psychosis meeting the criteria for considering studies. The study involved 58 participants and compared the efficacy and tolerability of two antipsychotic drugs, olanzapine (a newer antipsychotic) and haloperidol (a commonly used antipsychotic medication used as a control condition), in treating amphetamine-induced psychosis. The results show that both olanzapine and haloperidol at clinically relevant doses were efficacious in resolving psychotic symptoms, with the olanzapine condition showing significantly greater safety and tolerability than the haloperidol control as measured by frequency and severity of extrapyramidal symptoms.

AUTHORS' CONCLUSIONS

Only one RCT of treatment for amphetamine psychosis has been published. Outcomes from this trial indicate that antipsychotic medications effectively reduce symptoms of amphetamine psychosis, the newer generation and more expensive antipsychotic medication, olanzapine, demonstrates significantly better tolerability than the more affordable and commonly used medication, haloperidol.There are other two studies that did not meet the inclusion criteria for this review. The results of these two studies show that agitation and some psychotic symptoms may be abated within an hour after antipsychotic injection.Whether this limited evidence can be applied for amphetamine psychotic patients is not yet known.The medications that should be further investigate are conventional antipsychotics, newer antipsychotics and benzodiazepines. However, naturalistic studies of amphetamine psychotic symptoms and the prevalence of relapse to psychosis in the presence of amphetamine, are also crucial for advising the development of study designs appropriate for further treatment studies of amphetamine psychosis.

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.

Electrophysiological evidence that drug cues have greater salience than other affective stimuli in opiate addiction

Previous research has demonstrated that drug cues are able to capture attentional resources in addicted populations. However, few studies have controlled for the possibility that drug users find all motivationally significant (i.e., affective) stimuli particularly salient. We examined this issue in opiate addiction, by exploring the impact of drug-related and affective stimuli on central attentional processes. Sixteen male heroin addicts (seven on opiate pharmacotherapy and nine recently detoxified subjects) and 12 matched controls were studied. Subjects were fitted with a 32-channel electrode cap and were instructed to passively view a series of neutral, affective and opiate-related images. The P300 elicited by drug-related stimuli was significantly larger than that elicited by affective and neutral stimuli in opiate users but not controls. Baseline ratings of craving were also found to predict the degree of P300 facilitation to the drug-related stimuli in the addicted group. Further, the opiate group demonstrated an absence of the typical enhancement of ERP responses to non-drug affective stimuli. These results suggest that opiate addicts demonstrate greater cortical processing of drug cues than other types of affective stimuli. Further research is required to assess whether addiction is specifically associated with reduced sensitivity to natural rewards, aversive stimuli or affective cues in general.

Aniracetam and DNQX affect the acquisition of rapid tolerance to ethanol in mice

Several studies have emphasized the role of learning in the development of rapid tolerance and have shown that glutamate-mediated neurotransmission plays an important role in this phenomenon. Since the AMPA/kainate receptor system is directly involved in plasticity mechanisms, the influence of this receptor system on rapid tolerance induced by ethanol was studied using the rotarod. In the first experiment, mice were pretreated with aniracetam, an agonist of AMPA/kainate receptors, 30 min before ethanol (2.75 g/kg; IP) treatment, and tested on the rotarod. After 24 h, the groups were tested on the rotarod under ethanol treatment. Aniracetam facilitated the acquisition of rapid tolerance to ethanol. In the second experiment, mice received DNQX, a competitive antagonist of the AMPA receptor, 30 min before ethanol treatment (3 g/kg) and submitted to the rotarod. This dose of ethanol produced tolerance per se. Groups were tested under ethanol treatment (1.75 g/kg) after 24 h. DNQX blocked rapid tolerance to ethanol. Using a similar protocol, the third experiment showed that DNQX blocked the aniracetam-induced facilitation of rapid tolerance to ethanol. Our results show that aniracetam facilitates whereas DNQX blocks ethanol tolerance, suggesting that the non-NMDA receptors are involved in this phenomenon.

Treatment for amphetamine psychosis

BACKGROUND

Chronic amphetamine users may have experience of paranoia and hallucination. It has long been believed that dopamine antagonists, such as chlorpromazine, haloperidol, and thioridazine, are effective for the treatment of amphetamine psychosis.

OBJECTIVES

To evaluate risks, benefits, costs of treatments for amphetamine psychosis.

SEARCH STRATEGY

MEDLINE (1966-2007), EMBASE (1980-2007), CINAHL (1982-2007), PsychINFO (1806-2007), CENTRAL (Cochrane Library 2008 issue 1), references of obtained articles.

SELECTION CRITERIA

All randomised controlled and clinical trials (RCTs, CCTs) evaluating treatments (alone or combined) for people with amphetamine psychosis

DATA COLLECTION AND ANALYSIS

Two authors evaluated and extracted the data independently. Dichotomous data were extracted on an intention-to-treat basis in which the dropouts were assigned as participants with the worst outcomes. The Relative Risk (RR) with the 95% confidence interval (95% CI) was used to assess the dichotomous data. The Weighted Mean Difference (WMD) with 95% CI was used to assess the continuous data.

MAIN RESULTS

The comprehensive searches found one randomised controlled trial of treatment for amphetamine psychosis meeting the criteria for considering studies. The study involved 58 participants and compared the efficacy and tolerability of two antipsychotic drugs, olanzapine (a newer antipsychotic) and haloperidol (a commonly used antipsychotic medication used as a control condition), in treating amphetamine-induced psychosis. The results show that both olanzapine and haloperidol at clinically relevant doses were efficacious in resolving psychotic symptoms, with the olanzapine condition showing significantly greater safety and tolerability than the haloperidol control as measured by frequency and severity of extrapyramidal symptoms.

AUTHORS' CONCLUSIONS

Only one RCT of treatment for amphetamine psychosis has been published. Outcomes from this trial indicate that antipsychotic medications effectively reduce symptoms of amphetamine psychosis, the newer generation and more expensive antipsychotic medication, olanzapine, demonstrates significantly better tolerability than the more affordable and commonly used medication, haloperidol.There are other two studies that did not meet the inclusion criteria for this review. The results of these two studies show that agitation and some psychotic symptoms may be abated within an hour after antipsychotic injection. Whether this limited evidence can be applied for amphetamine psychotic patients is not yet known.The medications that should be further investigate are conventional antipsychotics, newer antipsychotics and benzodiazepines. However, naturalistic studies of amphetamine psychotic symptoms and the prevalence of relapse to psychosis in the presence of amphetamine, are also crucial for advising the development of study designs appropriate for further treatment studies of amphetamine psychosis.

Parallel and interactive learning processes within the basal ganglia: relevance for the understanding of addiction

In this review we discuss the evidence that drug addiction, defined as a maladaptive compulsive habit, results from the progressive subversion by addictive drugs of striatum-dependent operant and Pavlovian learning mechanisms that are usually involved in the control over behaviour by stimuli associated with natural reinforcement. Although mainly organized through segregated parallel cortico-striato-pallido-thalamo-cortical loops involved in motor or emotional functions, the basal ganglia, and especially the striatum, are key mediators of the modulation of behavioural responses, under the control of both action-outcome and stimulus-response mechanisms, by incentive motivational processes and Pavlovian associations. Here we suggest that protracted exposure to addictive drugs recruits serial and dopamine-dependent, striato-nigro-striatal ascending spirals from the nucleus accumbens to more dorsal regions of the striatum that underlie a shift from action-outcome to stimulus-response mechanisms in the control over drug seeking. When this progressive ventral to dorsal striatum shift is combined with drug-associated Pavlovian influences from limbic structures such as the amygdala and the orbitofrontal cortex, drug seeking behaviour becomes established as an incentive habit. This instantiation of implicit sub-cortical processing of drug-associated stimuli and instrumental responding might be a key mechanism underlying the development of compulsive drug seeking and the high vulnerability to relapse which are hallmarks of drug addiction.

A unified framework for addiction: vulnerabilities in the decision process

The understanding of decision-making systems has come together in recent years to form a unified theory of decision-making in the mammalian brain as arising from multiple, interacting systems (a planning system, a habit system, and a situation-recognition system). This unified decision-making system has multiple potential access points through which it can be driven to make maladaptive choices, particularly choices that entail seeking of certain drugs or behaviors. We identify 10 key vulnerabilities in the system: (1) moving away from homeostasis, (2) changing allostatic set points, (3) euphorigenic "reward-like" signals, (4) overvaluation in the planning system, (5) incorrect search of situation-action-outcome relationships, (6) misclassification of situations, (7) overvaluation in the habit system, (8) a mismatch in the balance of the two decision systems, (9) over-fast discounting processes, and (10) changed learning rates. These vulnerabilities provide a taxonomy of potential problems with decision-making systems. Although each vulnerability can drive an agent to return to the addictive choice, each vulnerability also implies a characteristic symptomology. Different drugs, different behaviors, and different individuals are likely to access different vulnerabilities. This has implications for an individual's susceptibility to addiction and the transition to addiction, for the potential for relapse, and for the potential for treatment.

Adult neurogenesis and the memories of drug addiction

Evidence accumulated in the last decade indicating that psychoactive substances negatively influence neurogenesis in the adult hippocampus has provided new insights into the neurobiology of drug addiction. Using a variety of experimental approaches and treatments, drugs such as psychomotor stimulants, opioids, alcohol and psychedelic compounds have been shown to alter one or several aspects of adult neurogenesis, including the rate of progenitor proliferation, the survival of newly generated cells, and the maturation and acquisition of cellular phenotype. This evidence, though critical from a neurotoxicological standpoint, cannot be linked unambiguously to the process of drug dependence at this stage of research. Drug addiction is a complex recurrent process involving the acquisition and maintenance of drug taking, followed by detoxification, abstinence and eventual relapse to drug seeking. The specific contribution of adult hippocampal neurogenesis to each of these processes is yet to be determined. This notwithstanding, the suggested role of the hippocampus in the storage and retrieval of declarative and contextual memories on the one hand, and in the regulation of mood and affect on the other, provides a fertile ground for further exploring the mutual relationships between postnatal hippocampal neurogenesis and addictive behaviours.

A computational model of craving and obsession

If addictions and problematic behaviors arise from interactions between drugs, reward sequences, and natural learning sytems, then an explanation of clinically problematic conditions (such as the self-administration of drugs or problem gambling) requires an understanding of the neural systems that have evolved to allow an agent to make decisions. We hypothesize a unified decision-making system consisting of three components-a situation recognition system, a flexible, planning-capable system, and an inflexible, habit-like system. In this article, we present a model of the planning-capable system based on a planning process arising from experimentally observed look-ahead dynamics in the hippocampus enabling a forward search of possibilities and an evaluation process in the nucleus accumbens. Based on evidence that opioid signaling can provide hedonic evalutation of an achieved outcome, we hypothesize that similar opioid-signaling processes evaluate the value of expected outcomes. This leads to a model of craving, based on the recognition of a path to a high-value outcome, and obsession, based on a value-induced limitation of the search process. This theory can explain why opioid antagonists reduce both hedonic responses and craving.

Omega-3 fatty acid ethyl-eicosapentaenoate attenuates IL-1beta-induced changes in dopamine and metabolites in the shell of the nucleus accumbens: involved with PLA2 activity and corticosterone secretion

Previously, we have reported that interleukin-1 beta (IL-1) induces changes in dopaminergic (DA) and serotonergic systems in the core of the [corrected] nucleus accumbens (NAc). We have also demonstrated that n-3 fatty acid ethyl-eicosapentaenoate (EPA) can significantly reduce stress and anxiety-like behaviors, corticosterone concentrations [corrected] and peripheral inflammatory response induced by IL-1 administration. Compared to the core, the shell is involved more in emotion, stress and psychiatric diseases. However, the relationship between inflammation and the functions of DA system in the shell has not been studied. Since phospholipase (PL) A2 is a key enzyme in the [corrected] arachidonic acid-eicosanoids-prostaglandin [corrected] (PG)E2 pathway, and the change in NAc DA [corrected] system has been associated with glucocorticoid stimulation; [corrected] therefore, the hypotheses of this study are (1) that IL-1 induced changes in DA neurotransmission in the shell may be through PLA2-PGE2-corticosterone pathway; (2) EPA may attenuate IL-1 effects via inhibiting PLA2 activities, which blocks PGE2 stimulation of corticosterone. Using an in vivo microdialysis method, the present study showed that IL-1 administration significantly increased extracellular levels of DA, and its metabolites 3,4-dihydroxyphenylacetic acid, [corrected] and homovanillic acid [corrected] in the shell of the NAc. IL-1 also increased blood concentration of corticosterone and PGE2, and increased the activities of cytosolic and secretory [corrected] PLA2. IL-1-induced changes were significantly attenuated by EPA treatment. Furthermore, glucocorticoid [corrected] receptor antagonist mifepristone (RU486) pretreatment significantly blocked IL-1-induced changes in DA and metabolites. Quinacrine, [corrected] a PLA2 antagonist significantly blocked IL-1-induced [corrected] increase in PGE2 and corticosterone concentrations. These results demonstrated the hypotheses that IL-1 effects may be via PLA2-PGE2-corticosterone pathway and EPA attenuated IL-1 effects may be through the suppression of PLA2 expression, which then reduced PGE2 synthesis and corticosterone secretion.