Addiction: beyond dopamine reward circuitry

Do reward-processing deficits in schizophrenia-spectrum disorders promote cannabis use? An investigation of physiological response to natural rewards and drug cues

BACKGROUND

Dysfunctional reward processing is present in individuals with schizophrenia-spectrum disorders (SSD) and may confer vulnerability to addiction. Our objective was to identify a deficit in patients with SSD on response to rewarding stimuli and determine whether this deficit predicts cannabis use.

METHODS

We divided a group of patients with SSD and nonpsychotic controls into cannabis users and nonusers. Response to emotional and cannabis-associated visual stimuli was assessed using self-report, event-related potentials (using the late positive potential [LPP]), facial electromyography and skin-conductance response.

RESULTS

Our sample comprised 35 patients with SSD and 35 nonpsychotic controls. Compared with controls, the patients with SSD showed blunted LPP response to pleasant stimuli (p = 0.003). Across measures, cannabis-using controls showed greater response to pleasant stimuli than to cannabis stimuli whereas cannabis-using patients showed little bias toward pleasant stimuli. Reduced LPP response to pleasant stimuli was predictive of more frequent subsequent cannabis use (β = -0.24, p = 0.034).

LIMITATIONS

It is not clear if the deficit associated with cannabis use is specific to rewarding stimuli or nonspecific to any kind of emotionally salient stimuli.

CONCLUSION

The LPP captures a reward-processing deficit in patients with SSD and shows potential as a biomarker for identifying patients at risk of heavy cannabis use.

Medications development for substance-use disorders: contextual influences (dis)incentivizing pharmaceutical-industry positioning

INTRODUCTION

The significant contribution of substance-use disorders (SUDs) to the global-disease burden and associated unmet medical needs has not engendered a commensurate level of pharma-industry research and development (R&D) for novel SUD therapeutics invention. Analysis of contextual factors shaping this position suggests potential routes toward incentivizing R&D commitment for that purpose.

AREAS COVERED

This article considers multiple primary factors that have consorted to disincentivize pharma industry's operating in the SUD space: ill-understood pathology; variegated treatments and patient profiles; involved clinical trials; and - with particular reference to SUDs-negative cultural/business stigmas and shallow commercial precedent. Industry incentivization for SUD drug innovation requires progress on several fronts, including: translational experimental data and systems; personalized, holistic SUD treatment approaches; interactions among pharma, nonindustry constituencies, and the medical profession with vested interests in countering negative stereotypes and expanding SUD treatment options; and public-private alliances focused on improving SUD pharmacotherapy.

EXPERT OPINION

Given the well-entrenched business stance whereby the prospect of future profits in major markets largely determines drug-company R&D investment trajectory, strategic initiatives offering substantial reductions in the risks and opportunity (i.e., time and money) costs associated with SUD drug discovery are likely to be the most potent drivers for encouraging mainstream industry positioning in this therapeutic area. Such initiatives could originate from front-loaded R&D operational and back-loaded patent, regulatory, marketing and health-care policy reforms. These may be too involved and protracted for the turbulent pharmaceutical industry to entertain amid its recent retrenchment from psychiatric/CNS diseases and intense pressures to increase productivity and shareholder value.

Overlapping patterns of brain activation to food and cocaine cues in cocaine abusers: association to striatal D2/D3 receptors

Cocaine, through its activation of dopamine (DA) signaling, usurps pathways that process natural rewards. However, the extent to which there is overlap between the networks that process natural and drug rewards and whether DA signaling associated with cocaine abuse influences these networks have not been investigated in humans. We measured brain activation responses to food and cocaine cues with fMRI, and D2/D3 receptors in the striatum with [11C]raclopride and Positron emission tomography in 20 active cocaine abusers. Compared to neutral cues, food and cocaine cues increasingly engaged cerebellum, orbitofrontal, inferior frontal, and premotor cortices and insula and disengaged cuneus and default mode network (DMN). These fMRI signals were proportional to striatal D2/D3 receptors. Surprisingly cocaine and food cues also deactivated ventral striatum and hypothalamus. Compared to food cues, cocaine cues produced lower activation in insula and postcentral gyrus, and less deactivation in hypothalamus and DMN regions. Activation in cortical regions and cerebellum increased in proportion to the valence of the cues, and activation to food cues in somatosensory and orbitofrontal cortices also increased in proportion to body mass. Longer exposure to cocaine was associated with lower activation to both cues in occipital cortex and cerebellum, which could reflect the decreases in D2/D3 receptors associated with chronicity. These findings show that cocaine cues activate similar, though not identical, pathways to those activated by food cues and that striatal D2/D3 receptors modulate these responses, suggesting that chronic cocaine exposure might influence brain sensitivity not just to drugs but also to food cues.

A molecular profile of cocaine abuse includes the differential expression of genes that regulate transcription, chromatin, and dopamine cell phenotype

Chronic drug abuse, craving, and relapse are thought to be linked to long-lasting changes in neural gene expression arising through transcriptional and chromatin-related mechanisms. The key contributions of midbrain dopamine (DA)-synthesizing neurons throughout the addiction process provide a compelling rationale for determining the drug-induced molecular changes that occur in these cells. Yet our understanding of these processes remains rudimentary. The postmortem human brain constitutes a unique resource that can be exploited to gain insights into the pathophysiology of complex disorders such as drug addiction. In this study, we analyzed the profiles of midbrain gene expression in chronic cocaine abusers and well-matched drug-free control subjects using microarray and quantitative PCR. A small number of genes exhibited robust differential expression; many of these are involved in the regulation of transcription, chromatin, or DA cell phenotype. Transcript abundances for approximately half of these differentially expressed genes were diagnostic for assigning subjects to the cocaine-abusing vs control cohort. Identification of a molecular signature associated with pathophysiological changes occurring in cocaine abusers' midbrains should contribute to the development of biomarkers and novel therapeutic targets for drug addiction.

New perspectives on using brain imaging to study CNS stimulants

While the recent application of brain imaging to study CNS stimulants has offered new insights into the fundamental factors that contribute to their use and abuse, many gaps remain. Brain circuits that mediate pleasure, dependence, craving and relapse are anatomically, neurophysiologically and neurochemically distinct from one another, which has guided the search for correlates of stimulant-seeking and taking behavior. However, unlike other drugs of abuse, metrics for tolerance and physical dependence on stimulants are not obvious. The dopamine theory of stimulant abuse does not sufficiently explain this disorder as serotonergic, GABAergic and glutamagergic circuits are clearly involved in stimulant pharmacology and so tracking the source of the "addictive" processes must adopt a more multimodal, multidisciplinary approach. To this end, both anatomical and functional magnetic resonance imaging (MRI), MR spectroscopy (MRS) and positron emission tomography (PET) are complementary and have equally contributed to our understanding of how stimulants affect the brain and behavior. New vistas in this area include nanotechnology approaches to deliver small molecules to receptors and use MRI to resolve receptor dynamics. Anatomical and blood flow imaging has yielded data showing that cognitive enhancers might be useful adjuncts in treating CNS stimulant dependence, while MRS has opened opportunities to examine the brain's readiness to accept treatment as GABA tone normalizes after detoxification. A desired outcome of the above approaches is being able to offer evidence-based rationales for treatment approaches that can be implemented in a more broad geographic area, where access to brain imaging facilities may be limited. This article is part of the Special Issue entitled 'CNS Stimulants'.

Transcranial magnetic stimulation in the treatment of substance addiction

Transcranial magnetic stimulation (TMS) is a noninvasive method of brain stimulation used to treat a variety of neuropsychiatric disorders, but is still in the early stages of study as addiction treatment. We identified 19 human studies using repetitive TMS (rTMS) to manipulate drug craving or use, which exposed a total of 316 adults to active rTMS. Nine studies involved tobacco, six alcohol, three cocaine, and one methamphetamine. The majority of studies targeted high-frequency (5-20 Hz; expected to stimulate neuronal activity) rTMS pulses to the dorsolateral prefrontal cortex. Only five studies were controlled clinical trials: two of four nicotine trials found decreased cigarette smoking; the cocaine trial found decreased cocaine use. Many aspects of optimal treatment remain unknown, including rTMS parameters, duration of treatment, relationship to cue-induced craving, and concomitant treatment. The mechanisms of rTMS potential therapeutic action in treating addictions are poorly understood, but may involve increased dopamine and glutamate function in corticomesolimbic brain circuits and modulation of neural activity in brain circuits that mediate cognitive processes relevant to addiction, such as response inhibition, selective attention, and reactivity to drug-associated cues. rTMS treatment of addiction must be considered experimental at this time, but appears to have a promising future.

Rated and measured impulsivity in children is associated with diminished cardiac reactions to acute psychological stress

This study examined the association between impulsivity and heart rate reactions to a brief psychological stress in pre-adolescent children. Impulsivity was assessed by two response inhibition tasks and maternal self-report. Heart rate was measured at rest and in response to a mental arithmetic challenge. Children high in impulsivity showed blunted cardiac stress reactions. This result resonates with previous findings that blunted stress reactivity is characteristic of a range of problematic behaviours often associated with impulsivity.

Sex differences in adolescent methylphenidate sensitization: effects on glial cell-derived neurotrophic factor and brain-derived neurotrophic factor

This study analyzed sex differences in methylphenidate (MPH) sensitization and corresponding changes in glial cell-derived neurotrophic factor (GDNF) and brain-derived neurotprhic factor protein (BDNF) in adolescent male and female rats. After habituation to a locomotor arena, animals were sensitized to MPH (5mg/kg) or saline from postnatal day (P) 33-49, tested every second day. On P50, one group of animals were injected with saline and behavior assessed for conditioned hyperactivity. Brain tissue was harvested on P51 and analyzed for GDNF protein. A second group of animals was also sensitized to MPH from P33 to 49, and expression of behavioral sensitization was analyzed on a challenge given at P60, and BDNF protein analyzed at P61. Females demonstrated more robust sensitization to MPH than males, but only females given MPH during sensitization demonstrated conditioned hyperactivity. Interestingly, MPH resulted in a significant increase in striatal and accumbal GDNF with no sex differences revealed. Results of the challenge revealed that females sensitized and challenged with MPH demonstrated increased activity compared to all other groups. Regarding BDNF, only males given MPH demonstrated an increase in dorsal striatum, whereas MPH increased accumbal BDNF with no sex differences revealed. A hierarchical regression analysis revealed that behavioral sensitization and the conditioned hyperactivity test were reliable predictors of striatal and accumbal GDNF, whereas sensitization and activity on the challenge were reliable predictors of accumbal BDNF, but had no relationship to striatal BDNF. These data have implications for the role of MPH in addiction and dopamine system plasticity.

[Diagnosis and management of alcohol-use disorders]

With the publication of the DSM-5, the alcoholic disease becomes Alcohol-use disorders taking into account dependence and damages according to a gradient of severity. This conceptual evolution should improve the screening of people affected by this chronic and progressive disease associated with a heavy impact on morbidity and mortality. This identification is provided by the clinical interview and examination. Its sensitivity can be improved by questionnaires and biological markers. Damage and related pathologies have to be systematically revealed. In this context, the MoCA test allows the early detection of cognitive disorders. Care management aims for a change in consumption and consists in supporting the patient in his/her approach. Care management should be personalized, appropriated to the patient's informed choice and graded according to disorders' severity. This includes a psychosocial intervention which can be associated with drugs. Abstinence is no longer the only alternative: decreasing consumption with the aim of regulation has been shown interesting in the reduction of harmful consumption. When therapeutic withdrawal turns out to be necessary, use of a treatment should not be systematic. If necessary, benzodiazepines remain the first-line treatment with a limited duration of prescription. According to his/her profile, the patient can receive a long-term treatment to help to maintain abstinence, prevent relapse or reduce consumption. There is evidence that identifying and involving patients in their care significantly improve their health. Effective treatments are available for treating alcohol-use disorders. However, only a relatively small number of patients receive specific management appropriated to their needs and according to concrete goals.

Treating chronic pain: the need for non-opioid options

Chronic pain is a prevalent problem that exacts a significant toll on society. The medical system has responded to this issue by implementing pain management services centered on opioid pharmacotherapy. However, for many chronic pain patients, the analgesic efficacy of long-term opioids is limited. Moreover, chronic exposure to opioids can result in opioid misuse, addiction, and risk of overdose. As such, non-opioid treatment options are needed. This article first provides a selective review of cognitive, affective, and psychophysiological mechanisms implicated in chronic pain to be targeted by novel non-opioid treatments. Next, it briefly details one such treatment approach, Mindfulness-Oriented Recovery Enhancement, and describes evidence suggesting that this intervention can disrupt the risk chain linking chronic pain to prescription opioid misuse.

Systems-level view of cocaine addiction: the interconnection of the immune and nervous systems

The human body is a complex assembly of physiological systems designed to manage the multidirectional transport of both information and nutrients. An intricate interplay between the nervous, circulatory, and secretory systems is therefore necessary to sustain life, allow delivery of nutrients and therapeutic drugs, and eliminate metabolic waste products and toxins. These systems also provide vulnerable routes for modification by substances of abuse. Addictive substances are, by definition, neurologically active, but as they and their metabolites are spread throughout the body via the nervous, circulatory, respiratory and digestive systems, there is abundant opportunity for interaction with numerous cell and tissue types. Cocaine is one such substance that exerts a broad physiological effect. While a great deal of the research concerning addiction has addressed the neurological effects of cocaine use, only a few studies have been aimed at delineating the role that cocaine plays in various body systems. In this paper, we probe the current research regarding cocaine and the immune system, and map a systems-level view to outline a broader perspective of the biological response to cocaine. Specifically, our overview of the neurological and immunomodulatory effects of the drug will allow a broader perspective of the biological response to cocaine. The focus of this review is on the connection between the nervous and immune systems and the role this connection plays in the long-term complications of cocaine use. By describing the multiplicity of these connections, we hope to inspire detailed investigations into the immunological interplay in cocaine addiction.

Aripiprazole effects on self-administration and pharmacodynamics of intravenous cocaine and cigarette smoking in humans

Aripiprazole is a partial agonist at dopamine (D2) and serotonin (5-HT1a) receptors and 5-HT2 antagonist. Because cocaine affects dopamine and serotonin, this study assessed whether aripiprazole could diminish the reinforcing efficacy of cocaine. Secondary aims evaluated aripiprazole on ad lib cigarette smoking and with a novel 40-hr smoking abstinence procedure. Adults with regular cocaine and cigarette use completed this inpatient double blind, randomized, placebo-controlled mixed-design study. A placebo lead-in was followed by randomization to aripiprazole (0, 2 or 10 mg/day/p.o.; n = 7 completed/group). Three sets of test sessions, each consisting of 3 cocaine sample-choice (i.e., self-administration) sessions and 1 dose-response session, were conducted (once during the lead-in and twice after randomization). Sample sessions tested each cocaine dose (0, 20 and 40 mg/70 kg, i.v.) in random order; subjective, observer-rated and physiologic outcomes were collected. Later that day, participants chose between the morning's sample dose or descending amounts of money over 7 trials. In dose response sessions, all doses were given 1 hr apart in ascending order for pharmacodynamic and pharmacokinetic assessment. Two sets of smoking topography sessions were conducted during the lead-in and after randomization; 1 with and 1 without 40 hr of smoking abstinence. Number of ad lib cigarettes smoked during non-session days was collected. Cocaine produced prototypic effects, but aripiprazole did not significantly alter these effects or smoking outcomes. The smoking abstinence procedure reliably produced nicotine withdrawal and craving and increased smoking modestly. These data do not support further investigation of aripiprazole for cocaine or tobacco use disorder treatment.

Ventral frontal satiation-mediated responses to food aromas in obese and normal-weight women

BACKGROUND

Sensory properties of foods promote and guide consumption in hunger states, whereas satiation should dampen the sensory activation of ingestive behaviors. Such activation may be disordered in obese individuals.

OBJECTIVE

Using functional magnetic resonance imaging (fMRI), we studied regional brain responses to food odor stimulation in the sated state in obese and normal-weight individuals targeting ventral frontal regions known to be involved in coding for stimulus reward value.

DESIGN

Forty-eight women (25 normal weight; 23 obese) participated in a 2-day (fed compared with fasting) fMRI study while smelling odors of 2 foods and an inedible, nonfood object. Analyses were conducted to permit an examination of both general and sensory-specific satiation (satiation effects specific to a given food).

RESULTS

Normal-weight subjects showed significant blood oxygen level-dependent responses in the ventromedial prefrontal cortex (vmPFC) to food aromas compared with responses induced by the odor of an inedible object. Normal-weight subjects also showed general (but not sensory-specific) satiation effects in both the vmPFC and orbitofrontal cortex. Obese subjects showed no differential response to the aromas of food and the inedible object when fasting. Within- and between-group differences in satiation were driven largely by changes in the response to the odor of the inedible stimulus. Responses to food aromas in the obese correlated with trait negative urgency, the tendency toward negative affect-provoked impulsivity.

CONCLUSIONS

Ventral frontal signaling of reward value may be disordered in obesity, with negative urgency heightening responses to food aromas. The observed nature of responses to food and nonfood stimuli suggests that future research should independently quantify each to fully understand brain reward signaling in obesity.

New perspectives on catecholaminergic regulation of executive circuits: evidence for independent modulation of prefrontal functions by midbrain dopaminergic and noradrenergic neurons

Cognitive functions associated with prefrontal cortex (PFC), such as working memory and attention, are strongly influenced by catecholamine [dopamine (DA) and norepinephrine (NE)] release. Midbrain dopaminergic neurons in the ventral tegmental area and noradrenergic neurons in the locus coeruleus are major sources of DA and NE to the PFC. It is traditionally believed that DA and NE neurons are homogeneous with highly divergent axons innervating multiple terminal fields and once released, DA and NE individually or complementarily modulate the prefrontal functions and other brain regions. However, recent studies indicate that both DA and NE neurons in the mammalian brain are heterogeneous with a great degree of diversity, including their developmental lineages, molecular phenotypes, projection targets, afferent inputs, synaptic connectivity, physiological properties, and behavioral functions. These diverse characteristics could potentially endow DA and NE neurons with distinct roles in executive function, and alterations in their responses to genetic and epigenetic risk factors during development may contribute to distinct phenotypic and functional changes in disease states. In this review of recent literature, we discuss how these advances in DA and NE neurons change our thinking of catecholamine influences in cognitive functions in the brain, especially functions related to PFC. We review how the projection-target specific populations of neurons in these two systems execute their functions in both normal and abnormal conditions. Additionally, we explore what open questions remain and suggest where future research needs to move in order to provide a novel insight into the cause of neuropsychiatric disorders related to DA and NE systems.

Dopaminergic modulation of impulsive decision making in the rat insular cortex

Neuroimaging studies have implicated the insular cortex in cognitive processes including decision making. Nonetheless, little is known about the mechanisms by which the insula contributes to impulsive decision making. In this regard, the dopamine system is known to be importantly involved in decision making processes, including impulsive decision making. The aim of the current set of experiments was to further elucidate the importance of dopamine signaling in the agranular insular cortex in impulsive decision making. This compartment of the insular cortex is highly interconnected with brain areas such as the medial prefrontal cortex, amygdala and ventral striatum which are implicated in decision making processes. Male rats were trained in a delay-discounting task and upon stable baseline performance implanted with bilateral cannulae in the agranular insular cortex. Intracranial infusions of the dopamine D1 receptor antagonist SCH23390 and dopamine D2 receptor antagonist eticlopride revealed that particularly blocking dopamine D1 receptors centered on the insular cortex promoted impulsive decision making. Together, the present results demonstrate an important role of the agranular insular cortex in impulsive decision making and, more specifically, highlight the contribution of dopamine D1-like receptors.

Drug abuse relapse rates linked to level of education: can we repair hypodopaminergic-induced cognitive decline with nutrient therapy?

It is well known that athletes and other individuals who have suffered painful injuries are at increased risk for all reward deficiency syndrome (RDS) behaviors, including substance use disorder (SUD). Comparing patient demographics and relapse rates in chemical dependence programs is pertinent because demographics may affect outcomes. Increased risk for relapse and lower academic achievement were found to have a significant association in recent outcome data from a holistic treatment center (HTC) located in North Miami Beach, FL. Relapse outcomes from the Drug Addiction Treatment Outcome Study (DATOS; n = 1738) and HTC (n = 224) were compared for a 12-month period. Post-discharge relapse was reported by 26% of HTC patients and 58% of patients in DATOS. When broken out by education level-less than high school, high school diploma, college degree, and graduate degree-HTC patient relapse was 50%, 36%, 33%, and 16%, respectively, and demonstrated an inverse linear association (F = 5.702; P = 0.017). Looking at DATOS patient relapse rates broken down by educational grades/years completed, patients who attended school between 7th grade and 4 years of college also demonstrated an inverse linear association (F = 5.563; P = 0.018). Additionally, the lowest performers, patients who reported their academic performance as "not so good," had the highest relapse (F = 4.226; P = 0.04). Albeit certain limitations, compared with DATOS patients, HTC patients produced significantly larger net differences in relapse rates (X 2 = 84.09; P = 0.0001), suggesting that other variables, such as the treatment model may also affect patient relapse. Our results implicate the use of vitamin and mineral supplements coupled with a well-researched natural dopamine agonist nutrient therapy; both have been shown to improve cognition and behavior, and thus academic achievement. That relapse is highest among addicts who have less education and who report lower grades is a factor that can be useful when considering treatment type and controlled for when comparing treatment outcomes.

Circadian rhythms and addiction: mechanistic insights and future directions

Circadian rhythms are prominent in many physiological and behavioral functions. Circadian disruptions either by environmental or molecular perturbation can have profound health consequences, including the development and progression of addiction. Both animal and humans studies indicate extensive bidirectional relationships between the circadian system and drugs of abuse. Addicted individuals display disrupted rhythms, and chronic disruption or particular chronotypes may increase the risk for substance abuse and relapse. Moreover, polymorphisms in circadian genes and an evening chronotype have been linked to mood and addiction disorders, and recent efforts suggest an association with the function of reward neurocircuitry. Animal studies are beginning to determine how altered circadian gene function results in drug-induced neuroplasticity and behaviors. Many studies suggest a critical role for circadian rhythms in reward-related pathways in the brain and indicate that drugs of abuse directly affect the central circadian pacemaker. In this review, we highlight key findings demonstrating the importance of circadian rhythms in addiction and how future studies will reveal important mechanistic insights into the involvement of circadian rhythms in drug addiction.

A new window to understanding individual differences in reward sensitivity from attentional networks

Existing evidence suggests that the presence of reward cues modifies the activity in attentional networks, however, the nature of these influences remains poorly understood. Here, we performed independent component analysis (ICA) in two fMRI datasets corresponding to two incentive delay tasks, which compared the response to reward (money and erotic pictures) and neutral cues, and yielded activations in the ventral striatum using a general linear model approach. Across both experiments, ICA revealed that both the right frontoparietal network and default mode network time courses were positively and negatively modulated by reward cues, respectively. Moreover, this dual neural response pattern was enhanced in individuals with strong reward sensitivity. Therefore, ICA may be a complementary tool to investigate the relevant role of attentional networks on reward processing, and to investigate reward sensitivity in normal and pathological populations.

Functional magnetic resonance imaging (fMRI) response to alcohol pictures predicts subsequent transition to heavy drinking in college students

BACKGROUND AND AIMS

Young adults show the highest rates of escalating drinking, yet the neural risk mechanisms remain unclear. Heavy drinkers show variant functional magnetic resonance imaging (fMRI) blood oxygen level-dependent (BOLD) response to alcohol cues, which may presage increasing drinking. In this longitudinal study, we ascertained whether BOLD response to alcohol pictures predicted subsequent heavy drinking among college students.

METHODS

Participants were 43 18-21-year-olds in the United States who underwent BOLD scanning and completed monthly substance use surveys over the following year. Participants were categorized according to baseline and follow-up drinking into 13 continuously moderate drinkers, 16 continuously heavy drinkers and 14 transitioners who drank moderately at baseline but heavily by follow-up. During fMRI scanning at baseline, participants viewed alcohol and matched non-alcohol beverage images.

RESULTS

We observed group differences in alcohol cue-elicited BOLD response in bilateral caudate, orbitofrontal cortex, medial frontal cortex/anterior cingulate and left insula (clusters > 2619 ml, voxelwise F(2,40)  > 3.23, P < 0.05, whole-brain corrected P < 0.05), where transitioners hyperactivated compared with moderate and heavy drinkers (all Tukey P < 0.05). Exploratory factor analysis revealed a single brain network differentiating those who subsequently increased drinking. Exploratory regressions showed that, compared with other risk factors (e.g., alcoholism family history, impulsivity), BOLD response best predicted escalating drinking amount and alcohol-related problems.

CONCLUSIONS

Neural response to pictures of alcohol is substantially enhanced among United States college students who subsequently escalate drinking. Greater cue-reactivity is associated with larger increases in drinking and alcohol-related problems, regardless of other baseline factors. Thus, neural cue-reactivity could uniquely facilitate identifying individuals at greatest risk for future problematic drinking.

Prescribing controlled substances during a prescription drug epidemic

We are currently in the midst of an epidemic of deaths caused by the misuse of prescription medications. Opioids, benzodiazepines, and stimulants are among the most frequently misused controlled substances and are integral to the neurologist's armamentarium. Thus, the decision to prescribe a controlled substance and how to mitigate the associated risks of their misuse is often vexing to the clinician. This installment in the "Clinical Challenge" series provides a basic narrative overview of the epidemiology of prescription drug misuse, a summary of each of the major classes of misused drugs, and clinical recommendations regarding screening for misuse and reducing the risks associated with prescribing controlled substances.

Cognitive and affective mechanisms linking trait mindfulness to craving among individuals in addiction recovery

The present study aimed to identify affective, cognitive, and conative mediators of the relation between trait mindfulness and craving in data culled from an urban sample of 165 persons (in abstinence verified by urinalysis) entering into residential treatment for substance use disorders between 2010 and 2012. Multivariate path analysis adjusting for age, gender, education level, employment status, and substance use frequency indicated that the association between the total trait mindfulness score on the Five Facet Mindfulness Questionnaire and alcohol/drug craving was statistically mediated by negative affect (measured by the PANAS, beta = -.13) and cognitive reappraisal (measured by the CERQ, beta = -.08), but not by readiness to change (measured by the URICA, beta = -.001). Implications for mindfulness-oriented treatment of persons with substance use disorders are discussed. The study's limitations are noted.

Dopaminergic function in cannabis users and its relationship to cannabis-induced psychotic symptoms

BACKGROUND

Cannabis is the most widely used illicit drug globally, and users are at increased risk of mental illnesses including psychotic disorders such as schizophrenia. Substance dependence and schizophrenia are both associated with dopaminergic dysfunction. It has been proposed, although never directly tested, that the link between cannabis use and schizophrenia is mediated by altered dopaminergic function.

METHODS

We compared dopamine synthesis capacity in 19 regular cannabis users who experienced psychotic-like symptoms when they consumed cannabis with 19 nonuser sex- and age-matched control subjects. Dopamine synthesis capacity (indexed as the influx rate constant [Formula: see text] ) was measured with positron emission tomography and 3,4-dihydroxy-6-[(18)F]-fluoro-l-phenylalanine ([(18)F]-DOPA).

RESULTS

Cannabis users had reduced dopamine synthesis capacity in the striatum (effect size: .85; t36 = 2.54, p = .016) and its associative (effect size: .85; t36 = 2.54, p = .015) and limbic subdivisions (effect size: .74; t36 = 2.23, p = .032) compared with control subjects. The group difference in dopamine synthesis capacity in cannabis users compared with control subjects was driven by those users meeting cannabis abuse or dependence criteria. Dopamine synthesis capacity was negatively associated with higher levels of cannabis use (r = -.77, p < .001) and positively associated with age of onset of cannabis use (r = .51, p = .027) but was not associated with cannabis-induced psychotic-like symptoms (r = .32, p = .19).

CONCLUSIONS

These findings indicate that chronic cannabis use is associated with reduced dopamine synthesis capacity and question the hypothesis that cannabis increases the risk of psychotic disorders by inducing the same dopaminergic alterations seen in schizophrenia.

Personality traits and vulnerability or resilience to substance use disorders

Clear evidence supports a genetic basis for substance use disorders (SUD). Yet, the search to identify individual gene contributions to SUD has been unsuccessful. Here, we argue for the study of endophenotypes within the frame of individual differences, and identify three high-order personality traits that are tied to specific brain systems and genes, and that offer a tractable approach to studying SUD. These personality traits, and the genes that moderate them, interact dynamically with the environment and with the drugs themselves to determine ultimately an individual's vulnerability or resilience to developing SUD.

Anhedonia in Parkinson's disease patients with and without pathological gambling: a case-control study

Anhedonia is present in Parkinson's Disease (PD) as well as in addictive behaviors. Pathological Gambling (PG) and other Impulse Control Disorders (ICDs) have emerged as iatrogenic complications associated with dopamine replacement therapy. We studied 154 PD patients, divided into three groups: 11 with PG, 23 with other ICDs (compulsive buying, hypersexuality, binge eating), 120 without ICDs. All patients underwent a thorough clinical, neuropsychological and psychiatric evaluation. The PG-group, compared to the ICDs-group and PD-controls, reported a significantly higher incidence of anhedonia (45% vs. 9% vs. 14% respectively), higher Snaith-Hamilton Pleasure Scale (SHAPS) scores (2.0±1.3 vs. 1.0±1.1 vs. 1.0±1.2), higher levels of impulsivity traits as measured by the Barratt Impulsiveness Scale (70.0±10.6 vs. 64.8±11 vs. 60.9±9.3) and more severe frontal dysfunctions (Frontal Assessment Battery, FAB: 12.4±4.9 vs. 15.5±1.6 vs. 14.4±3). A model for PG (incorporating anhedonia, impulsivity levels and frontal impairment) is discussed in the context of the pathophysiology of addictive behaviors. The impairment of hedonic capacity, possibly resulting from an underlying neuropsychological dysfunction, might facilitate loss of control over reward-related behavior, thus favoring the shift towards predominantly habit-based compulsive behaviors.

Dopamine D(2/3) receptor availability and human cognitive impulsivity: a high-resolution positron emission tomography imaging study with [¹¹C]raclopride

OBJECTIVE

Human impulsivity is a complex multidimensional construct encompassing cognitive, emotional, and behavioural aspects. Previous animal studies have suggested that striatal dopamine receptors play a critical role in impulsivity. In this study, we investigated the relationship between self-reported impulsiveness and dopamine D(2/3) receptor availability in striatal subdivisions in healthy subjects using high-resolution positron emission tomography (PET) with [11C]raclopride.

METHODS

Twenty-one participants completed 3-T magnetic resonance imaging and high-resolution PET scans with [11C]raclopride. The trait of impulsiveness was measured using the Barratt Impulsiveness Scale (BIS-11). Partial correlation analysis was performed between BIS-11 scores and D(2/3) receptor availability in striatal subregions, controlling for the confounding effects of temperament characteristics that are conceptually or empirically related to dopamine, which were measured by the Temperament and Character Inventory.

RESULTS

The analysis revealed that the non-planning (p = 0.004) and attentional (p = 0.007) impulsiveness subscale scores on the BIS-11 had significant positive correlations with D(2/3) receptor availability in the pre-commissural dorsal caudate. There was a tendency towards positive correlation between non-planning impulsiveness score and D(2/3) receptor availability in the post-commissural caudate.

CONCLUSION

These results suggest that cognitive subtrait of impulsivity is associated with D(2/3) receptor availability in the associative striatum that plays a critical role in cognitive processes involving attention to detail, judgement of alternative outcomes, and inhibitory control.

Segregation and crosstalk of D1 receptor-mediated activation of ERK in striatal medium spiny neurons upon acute administration of psychostimulants

The convergence of corticostriatal glutamate and dopamine from the midbrain in the striatal medium spiny neurons (MSN) triggers synaptic plasticity that underlies reinforcement learning and pathological conditions such as psychostimulant addiction. The increase in striatal dopamine produced by the acute administration of psychostimulants has been found to activate not only effectors of the AC5/cAMP/PKA signaling cascade such as GluR1, but also effectors of the NMDAR/Ca(2+)/RAS cascade such as ERK. The dopamine-triggered effects on both these cascades are mediated by D1R coupled to Golf but while the phosphorylation of GluR1 is affected by reductions in the available amount of Golf but not of D1R, the activation of ERK follows the opposite pattern. This segregation is puzzling considering that D1R-induced Golf activation monotonically increases with DA and that there is crosstalk from the AC5/cAMP/PKA cascade to the NMDAR/Ca(2+)/RAS cascade via a STEP (a tyrosine phosphatase). In this work, we developed a signaling model which accounts for this segregation based on the assumption that a common pool of D1R and Golf is distributed in two D1R/Golf signaling compartments. This model integrates a relatively large amount of experimental data for neurons in vivo and in vitro. We used it to explore the crosstalk topologies under which the sensitivities of the AC5/cAMP/PKA signaling cascade to reductions in D1R or Golf are transferred or not to the activation of ERK. We found that the sequestration of STEP by its substrate ERK together with the insensitivity of STEP activity on targets upstream of ERK (i.e. Fyn and NR2B) to PKA phosphorylation are able to explain the experimentally observed segregation. This model provides a quantitative framework for simulation based experiments to study signaling required for long term potentiation in MSNs.

Brain proton magnetic resonance spectroscopy of alcohol use disorders

This chapter critically reviews brain proton magnetic resonance spectroscopy ((1)H MRS) studies performed since 1994 in individuals with alcohol use disorders (AUD). We describe the neurochemicals that can be measured in vivo at the most common magnetic field strengths, summarize our knowledge about their general brain functions, and briefly explain some basic human (1)H MRS methods. Both cross-sectional and longitudinal research of individuals in treatment and of treatment-naïve individuals with AUD are discussed and interpreted on the basis of reported neuropathology. As AUDs are highly comorbid with chronic cigarette smoking and illicit substance abuse, we also summarize reports on their respective influences on regional proton metabolite levels. After reviewing research on neurobiologic correlates of relapse and genetic influences on brain metabolite levels, we finish with suggestions on future directions for (1)H MRS studies in AUDs. The review demonstrates that brain metabolic alterations associated with AUDs as well as their cognitive correlates are not simply a consequence of chronic alcohol consumption. Future MR research of AUDs in general has to be better prepared - and supported - to study clinically complex relationships between personality characteristics, comorbidities, neurogenetics, lifestyle, and living environment, as all these factors critically affect an individual's neurometabolic profile. (1)H MRS is uniquely positioned to tackle these complexities by contributing to a comprehensive biopsychosocial profile of individuals with AUD: it can provide non-invasive biochemical information on select regions of the brain at comparatively low overall cost for the ultimate purpose of informing more efficient treatments of AUDs.

Increase in brain-derived neurotrophic factor expression in early crack cocaine withdrawal

Recent reports suggest that brain-derived neurotrophic factor (BDNF) could be a biomarker for relapse, drug craving and withdrawal severity. In particular, elevated BDNF levels among former cocaine users have been associated with higher rates of relapse in 90 d. However, no data are available on BDNF levels at baseline and during crack cocaine withdrawal. This study evaluated BDNF among crack cocaine users during inpatient treatment, before and after withdrawal, vs. healthy controls. Clinical correlates with changes in BDNF levels were also assessed. Serum BDNF was evaluated in 49 male crack users on the first and last days of hospitalization and in 97 healthy controls. Serum BDNF was assayed using a sandwich ELISA kit. BDNF levels were significantly lower upon admission when compared to controls, even after adjustment for age, length of inpatient treatment, number of crack rocks used in the last 30 d, years of crack use and interaction between the latter two variables. At discharge, BDNF levels between patients and controls were similar. Number of crack rocks used in the last 30 d and years of crack use were inversely correlated with the outcome. Our findings show that BDNF levels increase during early crack cocaine withdrawal, at an inverse correlation with number of crack rocks used in the last 30 d and years of crack use.

The effects of methylphenidate on cognitive control in active methamphetamine dependence using functional magnetic resonance imaging

Methamphetamine (MA) dependence is associated with cognitive deficits. Methylphenidate (MPH) has been shown to improve inhibitory control in healthy and cocaine-dependent subjects. This study aimed to understand the neurophysiological effects before and after acute MPH administration in active MA-dependent and control subjects. Fifteen MA-dependent and 18 control subjects aged 18-46 years were scanned using functional magnetic resonance imaging before and after either a single oral dose of MPH (18 mg) or placebo while performing a color-word Stroop task. Baseline accuracy was lower (p = 0.026) and response time (RT) was longer (p < 0.0001) for the incongruent compared to congruent condition, demonstrating the task probed cognitive control. Increased activation of the dorsolateral prefrontal cortex (DLPFC) and parietal cortex during the incongruent and Stroop effect conditions, respectively was observed in MA-dependent compared to control subjects (p < 0.05), suggesting the need to recruit neural resources within these regions for conflict resolution. Post- compared to pre-MPH treatment, increased RT and DLPFC activation for the Stroop effect were observed in MA-dependent subjects (p < 0.05). In comparison to MPH-treated controls and placebo-treated MA-dependent subjects, MPH-treated MA-dependent subjects showed decreased activation of parietal and occipital regions during the incongruent and Stroop effect conditions (p < 0.05). These findings suggest that in MA-dependent subjects, MPH facilitated increased recruitment of the DLPFC for Stroop conflict resolution, and a decreased need for recruitment of neural resources in parietal and occipital regions compared to the other groups, while maintaining a comparable level of task performance to that achieved pre-drug administration. Due to the small sample size, the results from this study are preliminary; however, they inform us about the effects of MPH on the neural correlates of cognitive control in active MA-dependent subjects.

Modeling intracellular signaling underlying striatal function in health and disease

Striatum, which is the input nucleus of the basal ganglia, integrates cortical and thalamic glutamatergic inputs with dopaminergic afferents from the substantia nigra pars compacta. The combination of dopamine and glutamate strongly modulates molecular and cellular properties of striatal neurons and the strength of corticostriatal synapses. These actions are performed via intracellular signaling networks, containing several intertwined feedback loops. Understanding the role of dopamine and other neuromodulators requires the development of quantitative dynamical models for describing the intracellular signaling, in order to provide precise unambiguous descriptions and quantitative predictions. Building such models requires integration of data from multiple data sources containing information regarding the molecular interactions, the strength of these interactions, and the subcellular localization of the molecules. Due to the uncertainty, variability, and sparseness of these data, parameter estimation techniques are critical for inferring or constraining the unknown parameters, and sensitivity analysis evaluates which parameters are most critical for a given observed macroscopic behavior. Here, we briefly review the modeling approaches and tools that have been used to investigate biochemical signaling in the striatum, along with some of the models built around striatum. We also suggest a future direction for the development of such models from the, now becoming abundant, high-throughput data.

Interactive effects of chronic cigarette smoking and age on brain volumes in controls and alcohol-dependent individuals in early abstinence

Chronic alcohol-use disorders (AUDs) have been shown to interact with normal age-related volume loss to exacerbate brain atrophy with increasing age. However, chronic cigarette smoking, a highly co-morbid condition in AUD and its influence on age-related brain atrophy have not been evaluated. We performed 1.5 T quantitative magnetic resonance imaging in non-smoking controls [non-smoking light drinking controls (nsCONs); n = 54], smoking light drinking controls (sCONs, n = 34), and one-week abstinent, treatment-seeking alcohol-dependent (ALC) non-smokers (nsALCs, n = 35) and smokers (sALCs, n = 43), to evaluate the independent and interactive effects of alcohol dependence and chronic smoking on regional cortical and subcortical brain volumes, emphasizing the brain reward/executive oversight system (BREOS). The nsCONs and sALCs showed greater age-related volume losses than the nsALCs in the dorsal prefrontal cortex (DPFC), total cortical BREOS, superior parietal lobule and putamen. The nsALCs and sALCs demonstrated smaller volumes than the nsCONs in most cortical region of interests (ROIs). The sCONs had smaller volumes than the nsCONs in the DPFC, insula, inferior parietal lobule, temporal pole/parahippocampal region and all global cortical measures. The nsALCs and sALCs had smaller volumes than the sCONs in the DPFC, superior temporal gyrus, inferior and superior parietal lobules, precuneus and all global cortical measures. Volume differences between the nsALCs and sALCs were observed only in the putamen. Alcohol consumption measures were not related to volumes in any ROI for ALC; smoking severity measures were related to corpus callosum volume in the sCONs and sALCs. The findings indicate that consideration of smoking status is necessary for a better understanding of the factors contributing to regional brain atrophy in AUD.

Addiction science: Uncovering neurobiological complexity

Until very recently addiction-research was limited by existing tools and strategies that were inadequate for studying the inherent complexity at each of the different phenomenological levels. However, powerful new tools (e.g., optogenetics and designer drug receptors) and high throughput protocols are starting to give researchers the potential to systematically interrogate "all" genes, epigenetic marks, and neuronal circuits. These advances, combined with imaging technologies (both for preclinical and clinical studies) and a paradigm shift toward open access have spurred an unlimited growth of datasets transforming the way we investigate the neurobiology of substance use disorders (SUD) and the factors that modulate risk and resilience. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Hypothalamic proteoglycan syndecan-3 is a novel cocaine addiction resilience factor

Proteoglycans like syndecan-3 have complex signaling roles in addition to their function as structural components of the extracellular matrix. Here, we show that syndecan-3 in the lateral hypothalamus has an unexpected new role in limiting compulsive cocaine intake. In particular, we observe that syndecan-3 null mice self-administer greater amounts of cocaine than wild-type mice. This effect can be rescued by re-expression of syndecan-3 in the lateral hypothalamus with an adeno-associated viral vector. Adeno-associated viral vector delivery of syndecan-3 to the lateral hypothalamus also reduces motivation for cocaine in normal mice. Syndecan-3 limits cocaine intake by modulating the effects of glial-cell-line-derived neurotrophic factor, which uses syndecan-3 as an alternative receptor. Our findings indicate syndecan-3-dependent signaling as a novel therapeutic target for the treatment of cocaine addiction.

Chronic cocaine dampens dopamine signaling during cocaine intoxication and unbalances D1 over D2 receptor signaling

Dopamine increases triggered by cocaine and consequent stimulation of dopamine receptors (including D1 and D2) are associated with its rewarding effects. However, while facilitation of D1 receptor (D1R) signaling enhances the rewarding effects of cocaine, facilitation of D2R signaling decreases it, which indicates that for cocaine to be rewarding it must result in a predominance of D1R over D2R signaling. Moreover, the transition to compulsive cocaine intake might result from an imbalance between D1R and D2R signaling. To test the hypothesis that chronic cocaine use unbalances D1R over D2R signaling during cocaine intoxication, we used microprobe optical imaging to compare dynamic changes in intracellular calcium ([Ca(2+)]i, marker of neuronal activation) to acute cocaine in striatal D1R-EGFP and D2R-EGFP-expressing neurons between control and chronically treated mice. Chronic cocaine attenuated responses to acute cocaine in D1R (blunting Ca(2+) increases by 67 ± 16%) and D2R (blunting Ca(2+) decrease by 72 ± 17%) neurons in most D1R and D2R neurons (~75%). However, the dynamics of this attenuation during cocaine intoxication was longer lasting for D2R than for D1R. Thus, whereas control mice showed a fast but short-lasting predominance of D1R over D2R signaling (peaking at ~8 min) during acute cocaine intoxication, in chronically treated mice D1R predominance was sustained for >30 min (throughout the measurement period). Thus, chronic cocaine use dramatically reduced cocaine-induced DA signaling, shifting the balance between D1R and D2R signaling during intoxication to a predominance of D1R (stimulatory) over D2R (inhibitory) signaling, which might facilitate compulsive intake in addiction.

Reduced neural tracking of prediction error in substance-dependent individuals

OBJECTIVE

Substance-dependent individuals make poor decisions on the Iowa Gambling Task, a reward-related decision-making task that involves risk and uncertainty. Task performance depends on several factors, including how sensitive individuals are to feedback and how well they learn based on such feedback. A physiological signal that guides decision making based on feedback is prediction error. The authors investigated whether disruptions in the neural systems underlying prediction error processing in substance-dependent individuals could account for decision-making performance on a modified Iowa Gambling Task.

METHODS

Thirty-two substance-dependent individuals and 30 healthy comparison subjects played a modified version of the Iowa Gambling Task during MR scanning. Trial-to-trial behavior and functional MRI (fMRI) blood-oxygen-level-dependent (BOLD) signal were analyzed using a computational model of prediction error based on internal expectancies. The authors investigated how well BOLD signal tracked prediction error in the striatum and the orbitofrontal cortex as well as over the whole brain in patients relative to comparison subjects.

RESULTS

Compared with healthy subjects, substance-dependent patients were less sensitive to loss compared with gain, made less consistent choices, and performed worse on the modified Iowa Gambling Task. The ventral striatum and medial orbitofrontal cortex did not track prediction error as strongly in patients as in healthy subjects.

CONCLUSIONS

Weaker tracking of prediction error in substance-dependent relative to healthy individuals suggests that altered frontal-striatal error learning signals may underlie decision-making impairments in drug abusers. Computational fMRI may help bridge the knowledge gap between physiology and behavior to inform research aimed at substance abuse treatment.

Basal regulation of HPA and dopamine systems is altered differentially in males and females by prenatal alcohol exposure and chronic variable stress

Effects of prenatal alcohol exposure (PAE) on central nervous system function include an increased prevalence of mental health problems, including substance use disorders (SUD). The hypothalamic-pituitary-adrenal (HPA) and dopamine (DA) systems have overlapping neurocircuitries and are both implicated in SUD. PAE alters both HPA and dopaminergic activity and regulation, resulting in increased HPA tone and an overall reduction in tonic DA activity. However, effects of PAE on the interaction between HPA and DA systems have not been investigated. The present study examined PAE effects on basal regulation of central stress and DA systems in key brain regions where these systems intersect. Adult Sprague-Dawley male and female offspring from prenatal alcohol-exposed (PAE), pairfed (PF), and ad libitum-fed control (C) groups were subjected to chronic variable stress (CVS) or remained as a no stress (non-CVS) control group. Corticotropin releasing hormone (CRH) mRNA, as well as glucocorticoid and DA receptor (DA-R) expression were measured under basal conditions 24h following the end of CVS. We show, for the first time, that regulation of basal HPA and DA systems, and likely, HPA-DA interactions, are altered differentially in males and females by PAE and CVS. PAE augmented the typical attenuation in weight gain during CVS in males and caused increased weight loss in females. Increased basal corticosterone levels in control, but not PAE, females suggest that PAE alters the profile of basal hormone secretion throughout CVS. CVS downregulated basal CRH mRNA in the prefrontal cortex and throughout the bed nucleus of the stria terminalis (BNST) in PAE females but only in the posterior BNST of control females. PAE males and females exposed to CVS exhibited more widespread upregulation of basal mineralocorticoid receptor mRNA throughout the hippocampus, and an attenuated decrease in DA-R expression throughout the nucleus accumbens and striatum compared to CVS-exposed control males and females. Overall, these findings enhance our understanding of PAE effects on the cross-talk between HPA and DA systems, and provide insight into possible mechanisms underlying mental health problems that are related to stress and DA signaling, including SUD, which have a high prevalence among individuals with FASD.

Childhood maltreatment and psychopathology: A case for ecophenotypic variants as clinically and neurobiologically distinct subtypes

OBJECTIVE

Childhood maltreatment increases risk for psychopathology. For some highly prevalent disorders (major depression, substance abuse, anxiety disorders, and posttraumatic stress disorder) a substantial subset of individuals have a history of maltreatment and a substantial subset do not. The authors examined the evidence to assess whether those with a history of maltreatment represent a clinically and biologically distinct subtype.

METHOD

The authors reviewed the literature on maltreatment as a risk factor for these disorders and on the clinical differences between individuals with and without a history of maltreatment who share the same diagnoses. Neurobiological findings in maltreated individuals were reviewed and compared with findings reported for these disorders.

RESULTS

Maltreated individuals with depressive, anxiety, and substance use disorders have an earlier age at onset, greater symptom severity, more comorbidity, a greater risk for suicide, and poorer treatment response than nonmaltreated individuals with the same diagnoses. Imaging findings associated with these disorders, such as reduced hippocampal volume and amygdala hyperreactivity, are more consistently observed in maltreated individuals and may represent a maltreatment-related risk factor. Maltreated individuals also differ from others as a result of epigenetic modifications and genetic polymorphisms that interact with experience to increase risk for psychopathology.

CONCLUSIONS

Phenotypic expression of psychopathology may be strongly influenced by exposure to maltreatment, leading to a constellation of ecophenotypes. While these ecophenotypes fit within conventional diagnostic boundaries, they likely represent distinct subtypes. Recognition of this distinction may be essential in determining the biological bases of these disorders. Treatment guidelines and algorithms may be enhanced if maltreated and nonmaltreated individuals with the same diagnostic labels are differentiated.

Pain and suicidality: insights from reward and addiction neuroscience

Suicidality is exceedingly prevalent in pain patients. Although the pathophysiology of this link remains unclear, it may be potentially related to the partial congruence of physical and emotional pain systems. The latter system's role in suicide is also conspicuous during setbacks and losses sustained in the context of social attachments. Here we propose a model based on the neural pathways mediating reward and anti-reward (i.e., allostatic adjustment to recurrent activation of the reward circuitry); both are relevant etiologic factors in pain, suicide and social attachments. A comprehensive literature search on neurobiology of pain and suicidality was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) physical and emotional pain, (2) emotional pain and social attachments, (3) pain- and suicide-related alterations of the reward and anti-reward circuits as compared to addiction, which is the premier probe for dysfunction of these circuits and (4) mechanistically informed treatments of co-occurring pain and suicidality. Pain-, stress- and analgesic drugs-induced opponent and proponent states of the mesolimbic dopaminergic pathways may render reward and anti-reward systems vulnerable to sensitization, cross-sensitization and aberrant learning of contents and contexts associated with suicidal acts and behaviors. These findings suggest that pain patients exhibit alterations in the brain circuits mediating reward (depressed function) and anti-reward (sensitized function) that may affect their proclivity for suicide and support pain and suicidality classification among other "reward deficiency syndromes" and a new proposal for "enhanced anti-reward syndromes". We suggest that interventions aimed at restoring the balance between the reward and anti-reward networks in patients with chronic pain may help decreasing their suicide risk.

Individual differences underlying susceptibility to addiction: Role for the endogenous oxytocin system

Recent research shows that the effects of oxytocin are more diverse than initially thought and that in some cases oxytocin can directly influence the response to drugs and alcohol. Large individual differences in basal oxytocin levels and reactivity of the oxytocin system exist. This paper will review the literature to explore how individual differences in the oxytocin system arise and examine the hypothesis that this may mediate some of the individual differences in susceptibility to addiction and relapse. Differences in the oxytocin system can be based on individual factors, e.g. genetic variation especially in the oxytocin receptor, age or gender, or be the result of early environmental influences such as social experiences, stress or trauma. The paper addresses the factors that cause individual differences in the oxytocin system and the environmental factors that have been identified to induce long-term changes in the developing oxytocin system during different life phases. Individual differences in the oxytocin system can influence effects of drugs and alcohol directly or indirectly. The oxytocin system has bidirectional interactions with the stress-axis, autonomic nervous system, neurotransmitter systems (e.g. dopamine, serotonin and GABA/glutamate) and the immune system. These systems are all important, even vital, in different phases of addiction. It is suggested that early life adversity can change the development of the oxytocin system and the way it modulates other systems. This in turn could minimise the negative feedback loops that would normally exist. Individuals may show only minor differences in behaviour and function unless subsequent stressors or drug use challenges the system. It is postulated that at that time individual differences in oxytocin levels, reactivity of the system or interactions with other systems can influence general resilience, drug effects and the susceptibility to develop problematic drug and alcohol use.

No correlation between body mass index and striatal dopamine transporter availability in healthy volunteers using SPECT and [123I]PE2I

OBJECTIVE

Dopamine plays an important role in both the rewarding and conditioning effects of food. These effects involve mesolimbic, mesocortical, and nigrostriatal pathways. In humans, the most consistent finding has been reduced striatal dopamine D2/3 receptor availability. In striatum, dopamine is inactivated by reuptake via the dopamine transporter (DAT). The aim of the study was to test the hypothesis of lower DAT availability in obese healthy subjects using a selective DAT radiotracer in a sample of subjects with a wide range of BMI values.

DESIGN AND METHODS

Thirty-three healthy subjects with a mean age of 48.4 ± 13.3 (range, 21-71) years and a mean BMI of 29.6 ± 7.8 kg/m2 (range, 21.0-49.5) were included in the study. We used [123I]PE2I and SPECT to measure DAT availability.

RESULTS

Using multiple linear regression analyses with striatal DAT as the dependent variable and BMI, age and gender as predictors was performed. We found no correlation between BMI and striatal DAT availability in striatum (P = 0.99), caudate nucleus (P = 0.61), and putamen (P = 0.30). Furthermore, we found no group difference between obese/severely obese (BMI > 30 kg/m2) and normal weight controls (BMI ≤ 25 kg/m2).

CONCLUSIONS

We did not find any correlation between BMI and DAT availability in healthy volunteers.

Methylphenidate reduces functional connectivity of nucleus accumbens in brain reward circuit

Release of dopamine in the nucleus accumbens (NAcc) is essential for acute drug reward. The present study was designed to trace the reinforcing effect of dopamine release by measuring the functional connectivity (FC) between the NAcc and brain regions involved in a limbic cortical-subcortical circuit during a dopaminergic challenge. Twenty healthy volunteers received single doses of methylphenidate (40 mg) and placebo on separate test days according to a double-blind, cross-over study design. Resting state functional magnetic resonance imaging (fMRI) was measured between 1.5 and 2 h postdosing. FC between regions of interest (ROI) in the NAcc, the medial dorsal nucleus (MDN) of the thalamus and remote areas within the limbic circuit was explored. Methylphenidate significantly reduced FC between the NAcc and the basal ganglia (i.e., subthalamic nucleus and ventral pallidum (VP)), relative to placebo. Methylphenidate also decreased FC between the NAcc and the medial prefrontal cortex (mPFC) as well as the temporal cortex. Methylphenidate did not affect FC between MDN and the limbic circuit. It is concluded that methylphenidate directly affects the limbic reward circuit. Drug-induced changes in FC of the NAcc may serve as a useful marker of drug activity in in the brain reward circuit.