Blunted Endogenous Opioid Release Following an Oral Amphetamine Challenge in Pathological Gamblers

A brainstem circuit amplifies aversion

Dynamic gain control of aversive signals enables adaptive behavioral responses. Although the role of amygdalar circuits in aversive processing is well established, the neural pathway for amplifying aversion remains elusive. Here, we show that the brainstem circuit linking the interpeduncular nucleus (IPN) with the nucleus incertus (NI) amplifies aversion and promotes avoidant behaviors. IPN GABA neurons are activated by aversive stimuli and their predicting cues, with their response intensity closely tracking aversive values. Activating these neurons does not trigger aversive behavior on its own but rather amplifies responses to aversive stimuli, whereas their ablation or inhibition suppresses such responses. Detailed circuit dissection revealed anatomically distinct subgroups within the IPN GABA neuron population, highlighting the NI-projecting subgroup as the modulator of aversiveness related to fear and opioid withdrawal. These findings unveil the IPN-NI circuit as an aversion amplifier and suggest potential targets for interventions against affective disorders and opioid relapse.

Endogenous mu-opioid modulation of social connection in humans: a systematic review and meta-analysis

Social bonding, essential for health and survival in all social species, depends on mu-opioid signalling in non-human mammals. A growing neuroimaging and psychopharmacology literature also implicates mu-opioids in human social connectedness. To determine the role of mu-opioids for social connectedness in healthy humans, we conducted a preregistered ( https://osf.io/x5wmq ) multilevel random-effects meta-analysis of randomised double-blind placebo-controlled opioid antagonist studies. We included data from 8 publications and 2 unpublished projects, totalling 17 outcomes (N = 455) sourced from a final literature search in Web of Science, Scopus, PubMed and EMBASE on October 12, 2023, and through community contributions. All studies used naltrexone (25-100 mg) to block the mu-opioid system and measured social connectedness by self-report. Opioid antagonism slightly reduced feelings of social connectedness (Hedges' g [95% CI) = -0.20] [-0.32, -0.07]. Results were highly consistent within and between studies (I2 = 23%). However, there was some indication of bias in favour of larger effects among smaller studies (Egger's test: B = -2.16, SE = 0.93, z = -2.33, p = 0.02), and publication bias analysis indicated that the effect of naltrexone might be overestimated. The results clearly demonstrate that intact mu-opioid signalling is not essential for experiencing social connectedness, as robust feelings of connectedness are evident even during full pharmacological mu-opioid blockade. Nevertheless, antagonism reduced measures of social connection, consistent with a modulatory role of mu-opioids for human social connectedness. The modest effect size relative to findings in non-human animals, could be related to differences in measurement (subjective human responses versus behavioural/motivation indices in animals), species specific neural mechanisms, or naltrexone effects on other opioid receptor subtypes. In sum, these results help explain how mu-opioid dysregulation and social disconnection can contribute to disability, and conversely-how social connection can buffer risk of ill health.

Exploratory study of associations between monetary reward anticipation brain responses and mu-opioid signalling in alcohol dependence, gambling disorder and healthy controls

Alcohol dependence (AD) and gambling disorder (GD) are common addiction disorders with significant physical and mental health consequences. AD and GD are associated with dysregulated responses to reward which could be due to a common mechanism of dysregulated endogenous opioid signalling. We explored associations between reward anticipation responses, using the Monetary Incentive Delay (MID) functional magnetic resonance imaging (fMRI) task, and mu-opioid receptor (MOR) availability and endogenous opioid release capacity using [11C]carfentanil positron emission tomography (PET), in 13 AD, 15 GD and 14 heathy control (HC) participants. We also examined differences in MID task reward anticipation responses between AD, GD and HC participants. These were secondary exploratory analysis of data collected to examine differences in MOR PET in addiction. We did not find significant differences in MID win > neutral anticipation BOLD responses compared between participant groups in a priori ROIs (ventral striatum, putamen, caudate) or whole brain analyses. We found no significant correlations between MID win > neutral anticipation BOLD responses and [11C]carfentanil PET measures, except for limited negative correlations between putamen MOR availability and MID win > neutral anticipation BOLD response in AD participants. Previous research has suggested a limited role of endogenous opioid signalling on MID task reward anticipation responses in AD and HCs as these responses are not modulated by opioid receptor blockade and this may explain our lack of significant correlations in HC and AD or GD participants. Our results, particularly the lack of differences in MID win > neutral anticipation BOLD responses across participants groups, may be limited due to only including AD or GD participants who are abstinent or in active treatment.

Effects of bariatric surgery and dietary interventions for obesity on brain neurotransmitter systems and metabolism: A systematic review of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies

This systematic review collates studies of dietary or bariatric surgery interventions for obesity using positron emission tomography and single-photon emission computed tomography. Of 604 publications identified, 22 met inclusion criteria. Twelve studies assessed bariatric surgery (seven gastric bypass, five gastric bypass/sleeve gastrectomy), and ten dietary interventions (six low-calorie diet, three very low-calorie diet, one prolonged fasting). Thirteen studies examined neurotransmitter systems (six used tracers for dopamine DRD2/3 receptors: two each for 11 C-raclopride, 18 F-fallypride, 123 I-IBZM; one for dopamine transporter, 123 I-FP-CIT; one used tracer for serotonin 5-HT2A receptor, 18 F-altanserin; two used tracers for serotonin transporter, 11 C-DASB or 123 I-FP-CIT; two used tracer for μ-opioid receptor, 11 C-carfentanil; one used tracer for noradrenaline transporter, 11 C-MRB); seven studies assessed glucose uptake using 18 F-fluorodeoxyglucose; four studies assessed regional cerebral blood flow using 15 O-H2 O (one study also used arterial spin labeling); and two studies measured fatty acid uptake using 18 F-FTHA and one using 11 C-palmitate. The review summarizes findings and correlations with clinical outcomes, eating behavior, and mechanistic mediators. The small number of studies using each tracer and intervention, lack of dietary intervention control groups in any surgical studies, heterogeneity in time since intervention and degree of weight loss, and small sample sizes hindered the drawing of robust conclusions across studies.

Dopaminergic dysfunction: Role for genetic & epigenetic testing in the new psychiatry

Reward Deficiency Syndrome (RDS), particularly linked to addictive disorders, costs billions of dollars globally and has resulted in over one million deaths in the United States (US). Illicit substance use has been steadily rising and in 2021 approximately 21.9% (61.2 million) of individuals living in the US aged 12 or older had used illicit drugs in the past year. However, only 1.5% (4.1 million) of these individuals had received any substance use treatment. This increase in use and failure to adequately treat or provide treatment to these individuals resulted in 106,699 overdose deaths in 2021 and increased in 2022. This article presents an alternative non-pharmaceutical treatment approach tied to gene-guided therapy, the subject of many decades of research. The cornerstone of this paradigm shift is the brain reward circuitry, brain stem physiology, and neurotransmitter deficits due to the effects of genetic and epigenetic insults on the interrelated cascade of neurotransmission and the net release of dopamine at the Ventral Tegmental Area -Nucleus Accumbens (VTA-NAc) reward site. The Genetic Addiction Risk Severity (GARS) test and pro-dopamine regulator nutraceutical KB220 were combined to induce "dopamine homeostasis" across the brain reward circuitry. This article aims to encourage four future actionable items: 1) the neurophysiologically accurate designation of, for example, "Hyperdopameism /Hyperdopameism" to replace the blaming nomenclature like alcoholism; 2) encouraging continued research into the nature of dysfunctional brainstem neurotransmitters across the brain reward circuitry; 3) early identification of people at risk for all RDS behaviors as a brain check (cognitive testing); 4) induction of dopamine homeostasis using "precision behavioral management" along with the coupling of GARS and precision Kb220 variants; 5) utilization of promising potential treatments include neuromodulating modalities such as Transmagnetic stimulation (TMS) and Deep Brain Stimulation(DBS), which target different areas of the neural circuitry involved in addiction and even neuroimmune agents like N-acetyl-cysteine.

Reward processing in schizophrenia and its relation to Mu opioid receptor availability and negative symptoms: A [11C]-carfentanil PET and fMRI study

BACKGROUND

Reward processing deficits are a core feature of schizophrenia and are thought to underlie negative symptoms. Pre-clinical evidence suggests that opioid neurotransmission is linked to reward processing. However, the contribution of Mu Opioid Receptor (MOR) signalling to the reward processing abnormalities in schizophrenia is unknown. Here, we examined the association between MOR availability and the neural processes underlying reward anticipation in patients with schizophrenia using multimodal neuroimaging.

METHOD

37 subjects (18 with Schizophrenia with moderate severity negative symptoms and 19 age and sex-matched healthy controls) underwent a functional MRI scan while performing the Monetary Incentive Delay (MID) task to measure the neural response to reward anticipation. Participants also had a [11C]-carfentanil PET scan to measure MOR availability.

RESULTS

Reward anticipation was associated with increased neural activation in a widespread network of brain regions including the striatum. Patients with schizophrenia had both significantly lower MOR availability in the striatum as well as striatal hypoactivation during reward anticipation. However, there was no association between MOR availability and striatal neural activity during reward anticipation in either patient or controls (Pearson's Correlation, controls df = 17, r = 0.321, p = 0.18, patients df = 16, r = 0.295, p = 0.24). There was no association between anticipation-related neural activation and negative symptoms (r = -0.120, p = 0.14) or anhedonia severity (social r = -0.365, p = 0.14 physical r = -0.120, p = 0.63).

CONCLUSIONS

Our data suggest reduced MOR availability in schizophrenia might not underlie striatal hypoactivation during reward anticipation in patients with established illness. Therefore, other mechanisms, such as dopamine dysfunction, warrant further investigation as treatment targets for this aspect of the disorder.

Psychedelic therapy in the treatment of addiction: the past, present and future

Psychedelic therapy has witnessed a resurgence in interest in the last decade from the scientific and medical communities with evidence now building for its safety and efficacy in treating a range of psychiatric disorders including addiction. In this review we will chart the research investigating the role of these interventions in individuals with addiction beginning with an overview of the current socioeconomic impact of addiction, treatment options, and outcomes. We will start by examining historical studies from the first psychedelic research era of the mid-late 1900s, followed by an overview of the available real-world evidence gathered from naturalistic, observational, and survey-based studies. We will then cover modern-day clinical trials of psychedelic therapies in addiction from first-in-human to phase II clinical trials. Finally, we will provide an overview of the different translational human neuropsychopharmacology techniques, including functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), that can be applied to foster a mechanistic understanding of therapeutic mechanisms. A more granular understanding of the treatment effects of psychedelics will facilitate the optimisation of the psychedelic therapy drug development landscape, and ultimately improve patient outcomes.

The pharmacological management of gambling disorder: if, when, and how

INTRODUCTION

Gambling disorder (GD) consists of a persistent, recurrent pattern of gambling that is associated with substantial distress or impairment. The etiology is multifactorial. GD frequently co-occurs with other psychiatric disorders and is often untreated. Different psychosocial interventions, particularly cognitive-behavioral therapy, are useful in the treatment of GD. Pharmacological therapy may also be helpful . No formal guidelines exist, and the management of the disease is often guided by few clinical elements.

AREAS COVERED

A literature search was performed using PubMed, Scopus, and Web of Science databases about treatment options for GD, considering both psychosocial treatments and available pharmacological ones.

EXPERT OPINION

The authors address whether and when it is appropriate to initiate pharmacological treatment for GD. They focus on providing clinicians with guidance on how to approach patients with GD in those situations where pharmacological therapy may be necessary. The reasons for the clinician to start thinking about a medication are examined. As specific traits in the psychopathology of GD may be managed with a strategic choice of the pharmacologic agent, the different available options are analyzed on the basis of their potential usefulness in GD. Issues that remain open about the pharmacological management of GD are summarized.

Contribution of the μ-opioid receptor system to affective disorders in temporal lobe epilepsy: A bidirectional relationship?

OBJECTIVE

Affective disorders are frequent comorbidities of temporal lobe epilepsy (TLE). The endogenous opioid system has been implicated in both epilepsy and affective disorders, and may play a significant role in their bidirectional relationship. In this cross-sectional study, we investigated the association between μ-opioid receptor binding and affective disorders in patients with TLE.

METHODS

Nine patients with TLE and depression/anxiety underwent ¹¹ C-carfentanil positron emission tomography (CFN PET) and neuropsychiatric assessment, including the Hospital Anxiety and Depression Scale and the Positive and Negative Affect Schedule. The normalized CFN PET scans were compared with those of 26 age-matched healthy controls. Correlation analyses with affective symptoms were performed by region of interest-based analysis focusing on the limbic circuit and orbitofrontal cortex.

RESULTS

We observed widely reduced CFN binding potential (BP) in bilateral frontal lobes and striata in patients with TLE compared to healthy controls. In the TLE group, more severe anxiety and negative affect were associated with decreased CFN BP in the posterior cingulate gyrus.

SIGNIFICANCE

In patients with TLE, interictally reduced binding in the opioid system was associated with higher levels of anxiety and negative affect. We speculate that seizure-related agonist-driven desensitization and downregulation of opioid receptors could be a potential underlying pathomechanism.

Opioid use disorder and the brain: a clinical perspective

Opioid use disorder (OUD) has gained increasing publicity and interest during recent years, with many countries describing problems of epidemic proportions with regard to opioid use and deaths related to opioids. While opioids are not themselves acutely neurotoxic, the chronic relapsing and remitting nature of this disorder means that individuals are often exposed to exogenous opioids for lengthy periods of time (either illicit or prescribed as treatment). We are increasingly characterizing the effect of such long-term opioid exposure on the brain. This narrative review aims to summarize the literature regarding OUD and the brain from a clinical perspective. Alterations of brain structure and function are discussed, as well as neurological and psychiatric disorders in OUD. Finally, we review current and new directions for assessment and treatment.

Risk for opioid misuse in chronic pain patients is associated with endogenous opioid system dysregulation

µ-Opioid receptors (MOR) are a major target of endogenous and exogenous opioids, including opioid pain medications. The µ-opioid neurotransmitter system is heavily implicated in the pathophysiology of chronic pain and opioid use disorder and, as such, central measures of µ-opioid system functioning are increasingly being considered as putative biomarkers for risk to misuse opioids. To explore the relationship between MOR system function and risk for opioid misuse, 28 subjects with chronic nonspecific back pain completed a clinically validated measure of opioid misuse risk, the Pain Medication Questionnaire (PMQ), and were subsequently separated into high (PMQ > 21) and low (PMQ ≤ 21) opioid misuse risk groups. Chronic pain patients along with 15 control participants underwent two separate [¹¹C]-carfentanil positron emission tomography scans to explore MOR functional measures: one at baseline and one during a sustained pain-stress challenge, with the difference between the two providing an indirect measure of stress-induced endogenous opioid release. We found that chronic pain participants at high risk for opioid misuse displayed higher baseline MOR availability within the right amygdala relative to those at low risk. By contrast, patients at low risk for opioid misuse showed less pain-induced activation of MOR-mediated, endogenous opioid neurotransmission in the nucleus accumbens. This study links human in vivo MOR system functional measures to the development of addictive disorders and provides novel evidence that MORs and µ-opioid system responsivity may underlie risk to misuse opioids among chronic pain patients.

Acute acetate administration increases endogenous opioid levels in the human brain: A [11C]carfentanil molecular imaging study

INTRODUCTION

A recent study has shown that acetate administration leads to a fourfold increase in the transcription of proopiomelanocortin (POMC) mRNA in the hypothalamus. POMC is cleaved to peptides, including β-endorphin, an endogenous opioid (EO) agonist that binds preferentially to the µ-opioid receptor (MOR). We hypothesised that an acetate challenge would increase the levels of EO in the human brain. We have previously demonstrated that increased EO release in the human brain can be detected using positron emission tomography (PET) with the selective MOR radioligand [¹¹C]carfentanil. We used this approach to evaluate the effects of an acute acetate challenge on EO levels in the brain of healthy human volunteers.

METHODS

Seven volunteers each completed a baseline [¹¹C]carfentanil PET scan followed by an administration of sodium acetate before a second [¹¹C]carfentanil PET scan. Dynamic PET data were acquired over 90 minutes, and corrected for attenuation, scatter and subject motion. Regional [¹¹C] carfentanil BP_ND values were then calculated using the simplified reference tissue model (with the occipital grey matter as the reference region). Change in regional EO concentration was evaluated as the change in [¹¹C]carfentanil BP_ND following acetate administration.

RESULTS

Following sodium acetate administration, 2.5-6.5% reductions in [¹¹C]carfentanil regional BP_ND were seen, with statistical significance reached in the cerebellum, temporal lobe, orbitofrontal cortex, striatum and thalamus.

CONCLUSIONS

We have demonstrated that an acute acetate challenge has the potential to increase EO release in the human brain, providing a plausible mechanism of the central effects of acetate on appetite in humans.

Addressing unmet needs in opiate dependence: supporting detoxification and advances in relapse prevention

Despite record-breaking numbers of opiate related deaths in the UK in 2019, pharmacological management of opiate dependence has evolved little since the advent of methadone in 1965. Along with harm minimisation and psychosocial interventions, the mainstay of pharmacological treatment remains opioid substitution therapy (OST) using methadone or buprenorphine, with many patients receiving OST for many years. Even with these treatments, opiate users continue to face mortality risks 12 times higher than the general population, and emerging evidence suggests that individuals who remain on long-term OST present with a range of physical and cognitive impairments. Therefore, with a growing ageing opiate dependent population who would benefit from detoxification from OST, this article provides an overview of the current state of opiate dependence in clinical practice, explores the reasons why availability and acceptability of detoxification pathways are declining, and discusses emerging pharmacological therapies that could provide benefit in relapse prevention.

Blunted endogenous opioid release following an oral dexamphetamine challenge in abstinent alcohol-dependent individuals

Addiction has been proposed as a 'reward deficient' state, which is compensated for with substance use. There is growing evidence of dysregulation in the opioid system, which plays a key role in reward, underpinning addiction. Low levels of endogenous opioids are implicated in vulnerability for developing alcohol dependence (AD) and high mu-opioid receptor (MOR) availability in early abstinence is associated with greater craving. This high MOR availability is proposed to be the target of opioid antagonist medication to prevent relapse. However, changes in endogenous opioid tone in AD are poorly characterised and are important to understand as opioid antagonists do not help everyone with AD. We used [11C]carfentanil, a selective MOR agonist positron emission tomography (PET) radioligand, to investigate endogenous opioid tone in AD for the first time. We recruited 13 abstinent male AD and 15 control participants who underwent two [11C]carfentanil PET scans, one before and one 3 h following a 0.5 mg/kg oral dose of dexamphetamine to measure baseline MOR availability and endogenous opioid release. We found significantly blunted dexamphetamine-induced opioid release in 5 out of 10 regions-of-interest including insula, frontal lobe and putamen in AD compared with controls, but no significantly higher MOR availability AD participants compared with HC in any region. This study is comparable to our previous results of blunted dexamphetamine-induced opioid release in gambling disorder, suggesting that this dysregulation in opioid tone is common to both behavioural and substance addictions.

Advances in simultaneous PET/MR for imaging neuroreceptor function

Hybrid imaging using PET/MRI has emerged as a platform for elucidating novel neurobiology, molecular and functional changes in disease, and responses to physiological or pharmacological interventions. For the central nervous system, PET/MRI has provided insights into biochemical processes, linking selective molecular targets and distributed brain function. This review highlights several examples that leverage the strengths of simultaneous PET/MRI, which includes measuring the perturbation of multi-modal imaging signals on dynamic timescales during pharmacological challenges, physiological interventions or behavioral tasks. We discuss important considerations for the experimental design of dynamic PET/MRI studies and data analysis approaches for comparing and quantifying simultaneous PET/MRI data. The primary focus of this review is on functional PET/MRI studies of neurotransmitter and receptor systems, with an emphasis on the dopamine, opioid, serotonin and glutamate systems as molecular neuromodulators. In this context, we provide an overview of studies that employ interventions to alter the activity of neuroreceptors or the release of neurotransmitters. Overall, we emphasize how the synergistic use of simultaneous PET/MRI with appropriate study design and interventions has the potential to expand our knowledge about the molecular and functional dynamics of the living human brain. Finally, we give an outlook on the future opportunities for simultaneous PET/MRI.

Gambling Dual Disorder: A Dual Disorder and Clinical Neuroscience Perspective

Several behaviors, including compulsive gambling, have been considered non-substance-related addictive disorders. Categorical mental disorders (e.g., DSM-5) are usually accompanied by very different symptomatic expressions (affective, behavioral, cognitive, substance abuse, personality traits). When these mental disorders occur with addictive disorders, either concomitantly or sequentially over the life span, this clinical condition is called a dual disorder. Gambling disorder (GD) has been associated with other categorical psychiatric diagnoses: attention deficit hyperactivity disorder, depression, bipolar disorder, social anxiety, schizophrenia, substance use disorder, antisocial personality disorder; and dimensional symptoms including higher impulsivity, poorer emotional wellbeing, cognitive distortion, psychosis, deficient self-regulation, suicide, poorer family environment, and greater mental distress. We are calling this clinical condition Gambling Dual Disorder. From a clinical perspective, it is clear that Gambling Dual Disorder is not the exception but rather the expectation, and this holds true not just for GD, but also for other mental disorders including other addictions. Mental disorders are viewed as biological disorders that involve brain circuits that implicate specific domains of cognition, emotion, and behavior. This narrative review presents the state of the art with respect to GD in order to address current matters from a dual disorder, precision psychiatry, and clinical neuroscience perspective, rather than the more subjective approach of symptomatology and clinical presentation. This review also presents Gambling Dual Disorder as a brain and neurodevelopmental disorder, including from the perspectives of evolutionary psychiatry, genetics, impulsivity as an endophenotype, the self-medication hypothesis, and sexual biological differences. The wide vision of the disease advances a paradigm shift, highlighting how GD and dual disorders should be conceptualized, diagnosed, and treated. Rethinking GD as part of a dual disorder is crucial for its appropriate conceptualization from the perspective of clinical neuroscience and precision psychiatry.

A Survey of Molecular Imaging of Opioid Receptors

The discovery of endogenous peptide ligands for morphine binding sites occurred in parallel with the identification of three subclasses of opioid receptor (OR), traditionally designated as μ, δ, and κ, along with the more recently defined opioid-receptor-like (ORL1) receptor. Early efforts in opioid receptor radiochemistry focused on the structure of the prototype agonist ligand, morphine, although N-[methyl-¹¹C]morphine, -codeine and -heroin did not show significant binding in vivo. [¹¹C]Diprenorphine ([¹¹C]DPN), an orvinol type, non-selective OR antagonist ligand, was among the first successful PET tracers for molecular brain imaging, but has been largely supplanted in research studies by the μ-preferring agonist [¹¹C]carfentanil ([¹¹C]Caf). These two tracers have the property of being displaceable by endogenous opioid peptides in living brain, thus potentially serving in a competition-binding model. Indeed, many clinical PET studies with [¹¹C]DPN or [¹¹C]Caf affirm the release of endogenous opioids in response to painful stimuli. Numerous other PET studies implicate μ-OR signaling in aspects of human personality and vulnerability to drug dependence, but there have been very few clinical PET studies of μORs in neurological disorders. Tracers based on naltrindole, a non-peptide antagonist of the δ-preferring endogenous opioid enkephalin, have been used in PET studies of δORs, and [¹¹C]GR103545 is validated for studies of κORs. Structures such as [¹¹C]NOP-1A show selective binding at ORL-1 receptors in living brain. However, there is scant documentation of δ-, κ-, or ORL1 receptors in healthy human brain or in neurological and psychiatric disorders; here, clinical PET research must catch up with recent progress in radiopharmaceutical chemistry.

Is There a Role for GPCR Agonist Radiotracers in PET Neuroimaging?

Positron emission tomography (PET) is a molecular imaging modality that enables in vivo exploration of metabolic processes and especially the pharmacology of neuroreceptors. G protein-coupled receptors (GPCRs) play an important role in numerous pathophysiologic disorders of the central nervous system. Thus, they are targets of choice in PET imaging to bring proof concept of change in density in pathological conditions or in pharmacological challenge. At present, most radiotracers are antagonist ligands. In vitro data suggest that properties differ between GPCR agonists and antagonists: antagonists bind to receptors with a single affinity, whereas agonists are characterized by two different affinities: high affinity for receptors that undergo functional coupling to G-proteins, and low affinity for those that are not coupled. In this context, agonist radiotracers may be useful tools to give functional images of GPCRs in the brain, with high sensitivity to neurotransmitter release. Here, we review all existing PET radiotracers used from animals to humans and their role for understanding the ligand-receptor paradigm of GPCR in comparison with corresponding antagonist radiotracers.

Reduced mu opioid receptor availability in schizophrenia revealed with [11C]-carfentanil positron emission tomographic Imaging

Negative symptoms, such as amotivation and anhedonia, are a major cause of functional impairment in schizophrenia. There are currently no licensed treatments for negative symptoms, highlighting the need to understand the molecular mechanisms underlying them. Mu-opioid receptors (MOR) in the striatum play a key role in hedonic processing and reward function and are reduced post-mortem in schizophrenia. However, it is unknown if mu-opioid receptor availability is altered in-vivo or related to negative symptoms in schizophrenia. Using [11 C]-carfentanil positron emission tomography (PET) scans in 19 schizophrenia patients and 20 age-matched healthy controls, here we show a significantly lower MOR availability in patients with schizophrenia in the striatum (Cohen's d = 0.7), and the hedonic network. In addition, we report a marked global increase in inter-regional covariance of MOR availability in schizophrenia, largely due to increased cortical-subcortical covariance.

Opioid receptors: drivers to addiction?

Drug addiction is a worldwide societal problem and public health burden, and results from recreational drug use that develops into a complex brain disorder. The opioid system, one of the first discovered neuropeptide systems in the history of neuroscience, is central to addiction. Recently, opioid receptors have been propelled back on stage by the rising opioid epidemics, revolutions in G protein-coupled receptor research and fascinating developments in basic neuroscience. This Review discusses rapidly advancing research into the role of opioid receptors in addiction, and addresses the key questions of whether we can kill pain without addiction using mu-opioid-receptor-targeting opiates, how mu- and kappa-opioid receptors operate within the neurocircuitry of addiction and whether we can bridge human and animal opioid research in the field of drug abuse.

Intranasal naloxone rapidly occupies brain mu-opioid receptors in human subjects

Nasal spray formulations of naloxone, a mu-opioid receptor (MOR) antagonist, are currently used for the treatment of opioid overdose. They may have additional therapeutic utility also in the absence of opioid agonist drugs, but the onset and duration of action at brain MORs have been inadequately characterized to allow such projections. This study provides initial characterization of brain MOR availability at high temporal resolution following intranasal (IN) naloxone administration to healthy volunteers in the absence of a competing opioid agonist. Fourteen participants were scanned twice using positron emission tomography (PET) and [¹¹C]carfentanil, a selective MOR agonist radioligand. Concentrations of naloxone in plasma and MOR availability (relative to placebo) were monitored from 0 to 60 min and at 300-360 min post naloxone. Naloxone plasma concentrations peaked at ~20 min post naloxone, associated with slightly delayed development of brain MOR occupancy (half of peak occupancy reached at ~10 min). Estimated peak occupancies were 67 and 85% following 2 and 4 mg IN doses, respectively. The estimated half-life of occupancy disappearance was ~100 min. The rapid onset of brain MOR occupancy by IN naloxone, evidenced by the rapid onset of its action in opioid overdose victims, was directly documented in humans for the first time. The employed high temporal-resolution PET method establishes a model that can be used to predict brain MOR occupancy from plasma naloxone concentrations. IN naloxone may have therapeutic utility in various addictions where brain opioid receptors are implicated, such as gambling disorder and alcohol use disorder.

Gambling disorder

Gambling disorder is characterized by a persistent, recurrent pattern of gambling that is associated with substantial distress or impairment. The prevalence of gambling disorder has been estimated at 0.5% of the adult population in the United States, with comparable or slightly higher estimates in other countries. The aetiology of gambling disorder is complex, with implicated genetic and environmental factors. Neurobiological studies have implicated cortico-striato-limbic structures and circuits in the pathophysiology of this disorder. Individuals with gambling disorder often go unrecognized and untreated, including within clinical settings. Gambling disorder frequently co-occurs with other conditions, particularly other psychiatric disorders. Behavioural interventions, particularly cognitive-behavioural therapy but also motivational interviewing and Gamblers Anonymous, are supported in the treatment of gambling disorder. No pharmacological therapy has a formal indication for the treatment of gambling disorder, although placebo-controlled trials suggest that some medications, such as opioid-receptor antagonists, may be helpful. Given the associations with poor quality of life and suicide, improved identification, prevention, policy and treatment efforts are needed to help people with gambling disorder.

The role of the opioid system in decision making and cognitive control: A review

The opioid system regulates affective processing, including pain, pleasure, and reward. Restricting the role of this system to hedonic modulation may be an underestimation, however. Opioid receptors are distributed widely in the human brain, including the more "cognitive" regions in the frontal and parietal lobes. Nonhuman animal research points to opioid modulation of cognitive and decision-making processes. We review emerging evidence on whether acute opioid drug modulation in healthy humans can influence cognitive function, such as how we choose between actions of different values and how we control our behavior in the face of distracting information. Specifically, we review studies employing opioid agonists or antagonists together with experimental paradigms of reward-based decision making, impulsivity, executive functioning, attention, inhibition, and effort. Although this field is still in its infancy, the emerging picture suggests that the mu-opioid system can influence higher-level cognitive function via modulation of valuation, motivation, and control circuits dense in mu-opioid receptors, including orbitofrontal cortex, basal ganglia, amygdalae, anterior cingulate cortex, and prefrontal cortex. The framework that we put forward proposes that opioids influence decision making and cognitive control by increasing the subjective value of reward and reducing aversive arousal. We highlight potential mechanisms that might underlie the effects of mu-opioid signaling on decision making and cognitive control and provide directions for future research.

Cued for risk: Evidence for an incentive sensitization framework to explain the interplay between stress and anxiety, substance abuse, and reward uncertainty in disordered gambling behavior

Gambling disorder is an impairing condition confounded by psychiatric co-morbidity, particularly with substance use and anxiety disorders. Yet, our knowledge of the mechanisms that cause these disorders to coalesce remains limited. The Incentive Sensitization Theory suggests that sensitization of neural "wanting" pathways, which attribute incentive salience to rewards and their cues, is responsible for the excessive desire for drugs and cue-triggered craving. The resulting hyper-reactivity of the "wanting' system is believed to heavily influence compulsive drug use and relapse. Notably, evidence for sensitization of the mesolimbic dopamine pathway has been seen across gambling and substance use, as well as anxiety and stress-related pathology, with stress playing a major role in relapse. Together, this evidence highlights a phenomenon known as cross-sensitization, whereby sensitization to stress, drugs, or gambling behaviors enhance the sensitivity and dopaminergic response to any of those stimuli. Here, we review the literature on how cue attraction and reward uncertainty may underlie gambling pathology, and examine how this framework may advance our understanding of co-mordidity with substance-use disorders (e.g., alcohol, nicotine) and anxiety disorders. We argue that reward uncertainty, as seen in slot machines and games of chance, increases dopaminergic activity in the mesolimbic pathway and enhances the incentive value of reward cues. We propose that incentive sensitization by reward uncertainty may interact with and predispose individuals to drug abuse and stress, creating a mechanism through which co-mordidity of these disorders may emerge.

Neuroimaging of reward mechanisms in Gambling disorder: an integrative review

Gambling disorder (GD) was reclassified as a behavioral addiction in the DSM-5 and shares clinical and behavioral features with substance use disorders (SUDs). Neuroimaging studies of GD hold promise in isolating core features of the addiction syndrome, avoiding confounding effects of drug neurotoxicity. At the same time, a neurobiologically-grounded theory of how behaviors like gambling can become addictive remains lacking, posing a significant hurdle for ongoing decisions in addiction nosology. This article integrates research on reward-related brain activity (functional MRI) and neurotransmitter function (PET) in GD, alongside the consideration of structural MRI data as to whether these signals more likely reflect pre-existing vulnerability or neuroadaptive change. Where possible, we point to qualitative similarities and differences with established markers for SUDs. Structural MRI studies indicate modest changes in regional gray matter volume and diffuse reductions in white matter integrity in GD, contrasting with clear structural deterioration in SUDs. Functional MRI studies consistently identify dysregulation in reward-related circuitry (primarily ventral striatum and medial prefrontal cortex), but evidence is mixed as to the direction of these effects. The need for further parsing of reward sub-processes is emphasized, including anticipation vs outcome, gains vs. losses, and disorder-relevant cues vs natural rewards. Neurotransmitter PET studies indicate amplified dopamine (DA) release in GD, in the context of minimal differences in baseline DA D2 receptor binding, highlighting a distinct profile from SUDs. Preliminary work has investigated further contributions of opioids, GABA and serotonin. Neuroimaging data increasingly highlight divergent profiles in GD vs. SUDs. The ability of gambling to perpetually activate DA (via maximal uncertainty) may contribute to neuroimaging similarities between GD and SUDs, whereas the supra-physiological DA effects of drugs may partly explain differences in the neuroimaging profile of the two syndromes. Coupled with consistent observations of correlations with gambling severity and related clinical variables within GD samples, the overall pattern of effects is interpreted as a likely combination of shared vulnerability markers across GD and SUDs, but with further experience-dependent neuroadaptive processes in GD.

Brain and Cognition for Addiction Medicine: From Prevention to Recovery Neural Substrates for Treatment of Psychostimulant-Induced Cognitive Deficits

Addiction to psychostimulants like cocaine, methamphetamine, and nicotine poses a continuing medical and social challenge both in the United States and all over the world. Despite a desire to quit drug use, return to drug use after a period of abstinence is a common problem among individuals dependent on psychostimulants. Recovery for psychostimulant drug-dependent individuals is particularly challenging because psychostimulant drugs induce significant changes in brain regions associated with cognitive functions leading to cognitive deficits. These cognitive deficits include impairments in learning/memory, poor decision making, and impaired control of behavioral output. Importantly, these drug-induced cognitive deficits often impact adherence to addiction treatment programs and predispose abstinent addicts to drug use relapse. Additionally, these cognitive deficits impact effective social and professional rehabilitation of abstinent addicts. The goal of this paper is to review neural substrates based on animal studies that could be pharmacologically targeted to reverse psychostimulant-induced cognitive deficits such as impulsivity and impairment in learning and memory. Further, the review will discuss neural substrates that could be used to facilitate extinction learning and thus reduce emotional and behavioral responses to drug-associated cues. Moreover, the review will discuss some non-pharmacological approaches that could be used either alone or in combination with pharmacological compounds to treat the above-mentioned cognitive deficits. Psychostimulant addiction treatment, which includes treatment for cognitive deficits, will help promote abstinence and allow for better rehabilitation and integration of abstinent individuals into society.

Suggestive association between OPRM1 and impulse control disorders in Parkinson's disease

BACKGROUND

Impulse control disorders are frequently associated with dopaminergic therapy in Parkinson's disease. Genetic studies have suggested a high heritability of impulse control disorders in the general population and in PD. The aim of this study was to identify candidate gene variants associated with impulse control disorders and related behaviors in PD.

METHODS

We performed a multicenter case-control study in PD patients with (cases) or without impulse control disorders and related behaviors despite significant dopamine agonist exposure of >300 mg levodopa-equivalent daily dose during 12 months (controls). Behavioral disorders were assessed using the Ardouin scale. We investigated 50 variants in 24 candidate genes by a multivariate logistic regression analysis adjusted for sex and age at PD onset.

RESULTS

The analysis was performed on 172 cases and 132 controls. Cases were younger (60 ± 8 vs 63 ± 8 years; P < 0.001) and had a higher family history of pathological gambling (12% vs 5%, P = 0.03). No variant was significantly associated with impulse control disorders or related behaviors after correction for multiple testing, although the 2 top variants were close to significant (OPRM1 rs179991, OR, 0.49; 95%CI, 0.32-0.76; P = 0.0013; Bonferroni adjusted P = 0.065; DAT1 40-base pair variable number tandem repeat, OR, 1.82; 95%CI, 1.24-2.68; P = 0.0021; Bonferroni adjusted P = 0.105).

CONCLUSIONS

Our results are suggestive of a novel association of the opioid receptor gene OPRM1 with impulse control disorders and related behaviors in PD and confirm a previous association with DAT1. Although replication in independent studies is needed, our results bring potential new insights to the understanding of molecular mechanisms of impulse control disorders. © 2018 International Parkinson and Movement Disorder Society.

Clinical neuropsychiatric considerations regarding nonsubstance or behavioral addictions

Over the past several decades, non-substance-use behaviors like gambling, gaming, and sex have received greater consideration as possible foci of addictions. In this article, I will review the recent history and current status of non-substance or behavioral addictions. A main focus will involve gambling and gambling disorder, given that the latter is currently the sole non-substance addictive disorder described in the main text of the current (fifth) edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Internet gaming disorder, currently in the DSM-5 section addressing conditions that may need additional research, will also be considered, as will the concept of Internet addiction. Compulsive sexual behaviors (including problematic pornography use) will be considered, particularly with respect to how behavioral addictions may be considered in the forthcoming 11th edition of the International Classification of Diseases (ICD-11).

Dopamine synthesis capacity correlates with µ-opioid receptor availability in the human basal ganglia: A triple-tracer PET study

Animal studies have suggested that dopamine and opioid neurotransmitter systems interact in brain regions that are relevant for reward functions, but data in humans are very limited. The interaction is potentially important in disorders affecting these neurotransmitter systems, such as addiction. Here, we investigated whether subcortical μ-opioid receptor (MOR) availability and presynaptic dopamine synthesis capacity are correlated in the healthy human brain or in pathological gamblers (PGs) using positron emission tomography with 6-[¹⁸F]fluoro-l-dopa and [¹¹C]carfentanil. The specificity of the findings was further investigated by including a serotonin transporter ligand, [¹¹C]MADAM, as a negative control. Thirteen PG patients and 15 age-, sex- and weight-matched controls underwent the scans. In both groups, presynaptic dopamine synthesis capacity was associated with MOR availability in the putamen, caudate nucleus and globus pallidus. No similar associations were observed between dopamine synthesis capacity and [¹¹C]MADAM binding, supporting a specific interplay between presynaptic dopamine neurotransmission and opioid receptor function in the basal ganglia. Correlations were similar between the groups, suggesting that the dopamine-opioid link is general and unaffected by behavioral addiction. The results provide in vivo human evidence of a connection between endogenous opioid and dopamine signaling in the brain.

Binge eating disorder and morbid obesity are associated with lowered mu-opioid receptor availability in the brain

Both morbid obesity and binge eating disorder (BED) have previously been linked with aberrant brain opioid function. Behaviorally these two conditions are however different suggesting also differences in neurotransmitter function. Here we directly compared mu-opioid receptor (MOR) availability between morbidly obese and BED subjects. Seven BED and nineteen morbidly obese (non-BED) patients, and thirty matched control subjects underwent positron emission tomography (PET) with MOR-specific ligand [¹¹C]carfentanil. Both subjects with morbid obesity and BED had widespread reduction in [¹¹C]carfentanil binding compared to control subjects. However, there was no significant difference in brain MOR binding between subjects with morbid obesity and BED. Thus, our results indicate that there is common brain opioid abnormality in behaviorally different eating disorders involving obesity.

Aerobic exercise modulates anticipatory reward processing via the μ-opioid receptor system

Physical exercise modulates food reward and helps control body weight. The endogenous µ-opioid receptor (MOR) system is involved in rewarding aspects of both food and physical exercise, yet interaction between endogenous opioid release following exercise and anticipatory food reward remains unresolved. Here we tested whether exercise-induced opioid release correlates with increased anticipatory reward processing in humans. We scanned 24 healthy lean men after rest and after a 1 h session of aerobic exercise with positron emission tomography (PET) using MOR-selective radioligand [¹¹ C]carfentanil. After both PET scans, the subjects underwent a functional magnetic resonance imaging (fMRI) experiment where they viewed pictures of palatable versus nonpalatable foods to trigger anticipatory food reward responses. Exercise-induced changes in MOR binding in key regions of reward circuit (amygdala, thalamus, ventral and dorsal striatum, and orbitofrontal and cingulate cortices) were used to predict the changes in anticipatory reward responses in fMRI. Exercise-induced changes in MOR binding correlated negatively with the exercise-induced changes in neural anticipatory food reward responses in orbitofrontal and cingulate cortices, insula, ventral striatum, amygdala, and thalamus: higher exercise-induced opioid release predicted higher brain responses to palatable versus nonpalatable foods. We conclude that MOR activation following exercise may contribute to the considerable interindividual variation in food craving and consumption after exercise, which might promote compensatory eating and compromise weight control.

Endogenous Opiates and Behavior: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Focusing on the Opioid System for Addiction Biomarker Discovery

Substance use disorders (SUD) and behavioral addictions are devastating conditions that impose a severe burden on all societies, and represent difficult challenges for clinicians. Therefore, biomarkers are urgently needed to help predict vulnerability, clinical course, and response to treatment. Here, we elaborate on the potential for addiction biomarker discovery of the opioid system, particularly within the emerging framework aiming to probe opioid function in peripheral tissues. Mu, delta, and kappa opioid receptors all critically regulate neurobiological and behavioral processes that define addiction, and are also targeted by major pharmacotherapies used in the management of patients with SUD. We propose that opioid biomarkers may have the potential to improve and guide diagnosis and therapeutic decisions in the addiction field.

Opioid Release after High-Intensity Interval Training in Healthy Human Subjects

Central opioidergic mechanisms may modulate the positive effects of physical exercise such as mood elevation and stress reduction. How exercise intensity and concomitant effective changes affect central opioidergic responses is unknown. We studied the effects of acute physical exercise on the cerebral μ-opioid receptors (MOR) of 22 healthy recreationally active males using positron emission tomography (PET) and the MOR-selective radioligand [¹¹C]carfentanil. MOR binding was measured in three conditions on separate days: after a 60-min aerobic moderate-intensity exercise session, after a high-intensity interval training (HIIT) session, and after rest. Mood was measured repeatedly throughout the experiment. HIIT significantly decreased MOR binding selectively in the frontolimbic regions involved in pain, reward, and emotional processing (thalamus, insula, orbitofrontal cortex, hippocampus, and anterior cingulate cortex). Decreased binding correlated with increased negative emotionality. Moderate-intensity exercise did not change MOR binding, although increased euphoria correlated with decreased receptor binding. These observations, consistent with endogenous opioid release, highlight the role of the μ-opioid system in mediating affective responses to high-intensity training as opposed to recreational moderate physical exercise.

Evidence for GABA-A receptor dysregulation in gambling disorder: correlation with impulsivity

As a behavioural addiction, gambling disorder (GD) provides an opportunity to characterize addictive processes without the potentially confounding effects of chronic excessive drug and alcohol exposure. Impulsivity is an established precursor to such addictive behaviours, and GD is associated with greater impulsivity. There is also evidence of GABAergic dysregulation in substance addiction and in impulsivity. This study therefore investigated GABA_A receptor availability in 15 individuals with GD and 19 healthy volunteers (HV) using [¹¹C]Ro15‐4513, a relatively selective α5 benzodiazepine receptor PET tracer and its relationship with impulsivity. We found significantly higher [¹¹C]Ro15‐4513 total distribution volume (V_T) in the right hippocampus in the GD group compared with HV. We found higher levels of the ‘Negative Urgency’ construct of impulsivity in GD, and these were positively associated with higher [¹¹C]Ro15‐4513 V_T in the amygdala in the GD group; no such significant correlations were evident in the HV group. These results contrast with reduced binding of GABAergic PET ligands described previously in alcohol and opiate addiction and add to growing evidence for distinctions in the neuropharmacology between substance and behavioural addictions. These results provide the first characterization of GABA_A receptors in GD with [¹¹C]Ro15‐4513 PET and show greater α5 receptor availability and positive correlations with trait impulsivity. This GABAergic dysregulation is potential target for treatment.

Clinical neuropsychiatric considerations regarding nonsubstance or behavioral addictions

Over the past several decades, non-substance-use behaviors like gambling, gaming, and sex have received greater consideration as possible foci of addictions. In this article, I will review the recent history and current status of non-substance or behavioral addictions. A main focus will involve gambling and gambling disorder, given that the latter is currently the sole non-substance addictive disorder described in the main text of the current (fifth) edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Internet gaming disorder, currently in the DSM-5 section addressing conditions that may need additional research, will also be considered, as will the concept of Internet addiction. Compulsive sexual behaviors (including problematic pornography use) will be considered, particularly with respect to how behavioral addictions may be considered in the forthcoming 11th edition of the International Classification of Diseases (ICD-11).

Fentanyls continue to replace heroin in the drug arena: the cases of ocfentanil and carfentanil

Purpose

Ocfentanil and carfentanil are two potent synthetic opioids that are analogues of fentanyl and are actively involved in the recent fentanyl crisis. The aim of this review is to provide all the available information on these two fentanyl analogues.

Methods

All reviewed information was gathered through a detailed search of PubMed and the World Wide Web using relevant keywords.

Results

Like most of the members of the family of fentanyls, they are either sold as heroin to unsuspecting users or used extensively to lace heroin street samples. Despite the fact that ocfentanil was studied clinically in the early 1990s, it did not manage to find its place in clinical practice. On the other hand, carfentanil is mainly used today as an anesthetic agent in large animals. Ocfentanil and carfentanil are used and abused extensively, mainly in Europe and in the United States. As a result, they are the cause of some verified intoxication cases and deaths worldwide. This review provides information concerning chemistry, synthesis, prevalence, pharmacology, and toxicology, as well as the current legal status of these two fentanyl analogues. Analytical methods developed for the determination of ocfentanil and carfentanil in biological specimens and seized materials, as well as related intoxication and lethal cases are also presented.

Conclusions

Ocfentanil and carfentanil are undeniably very dangerous opioid drugs and a very serious matter of concern for public safety. The authorities should take the appropriate actions to avoid the expansion of this threat by taking proper and prompt measures.

Opioid Modulation of Value-Based Decision-Making in Healthy Humans

Modifying behavior to maximize reward is integral to adaptive decision-making. In rodents, the μ-opioid receptor (MOR) system encodes motivation and preference for high-value rewards. Yet it remains unclear whether and how human MORs contribute to value-based decision-making. We reasoned that if the human MOR system modulates value-based choice, this would be reflected by opposite effects of agonist and antagonist drugs. In a double-blind pharmacological cross-over study, 30 healthy men received morphine (10 mg), placebo, and the opioid antagonist naltrexone (50 mg). They completed a two-alternative decision-making task known to induce a considerable bias towards the most frequently rewarded response option. To quantify MOR involvement in this bias, we fitted accuracy and reaction time data with the drift-diffusion model (DDM) of decision-making. The DDM analysis revealed the expected bidirectional drug effects for two decision subprocesses. MOR stimulation with morphine increased the preference for the stimulus with high-reward probability (shift in starting point). Compared to placebo, morphine also increased, and naltrexone reduced, the efficiency of evidence accumulation. Since neither drug affected motor-coordination, speed-accuracy trade-off, or subjective state (indeed participants were still blinded after the third session), we interpret the MOR effects on evidence accumulation efficiency as a consequence of changes in effort exerted in the task. Together, these findings support a role for the human MOR system in value-based choice by tuning decision-making towards high-value rewards across stimulus domains.

Dopamine and Opioid Neurotransmission in Behavioral Addictions: A Comparative PET Study in Pathological Gambling and Binge Eating

Although behavioral addictions share many clinical features with drug addictions, they show strikingly large variation in their behavioral phenotypes (such as in uncontrollable gambling or eating). Neurotransmitter function in behavioral addictions is poorly understood, but has important implications in understanding its relationship with substance use disorders and underlying mechanisms of therapeutic efficacy. Here, we compare opioid and dopamine function between two behavioral addiction phenotypes: pathological gambling (PG) and binge eating disorder (BED). Thirty-nine participants (15 PG, 7 BED, and 17 controls) were scanned with [¹¹C]carfentanil and [¹⁸F]fluorodopa positron emission tomography using a high-resolution scanner. Binding potentials relative to non-displaceable binding (BP_ND) for [¹¹C]carfentanil and influx rate constant (K_i) values for [¹⁸F]fluorodopa were analyzed with region-of-interest and whole-brain voxel-by-voxel analyses. BED subjects showed widespread reductions in [¹¹C]carfentanil BP_ND in multiple subcortical and cortical brain regions and in striatal [¹⁸F]fluorodopa K_i compared with controls. In PG patients, [¹¹C]carfentanil BP_ND was reduced in the anterior cingulate with no differences in [¹⁸F]fluorodopa K_i compared with controls. In the nucleus accumbens, a key region involved in reward processing, [¹¹C]Carfentanil BP_ND was 30-34% lower and [¹⁸F]fluorodopa K_i was 20% lower in BED compared with PG and controls (p<0.002). BED and PG are thus dissociable as a function of dopaminergic and opioidergic neurotransmission. Compared with PG, BED patients show widespread losses of mu-opioid receptor availability together with presynaptic dopaminergic defects. These findings highlight the heterogeneity underlying the subtypes of addiction and indicate differential mechanisms in the expression of pathological behaviors and responses to treatment.

Naltrexone in the Treatment of Broadly Defined Behavioral Addictions: A Review and Meta-Analysis of Randomized Controlled Trials

INTRODUCTION

Broadly defined behavioral addiction is a conceptual framework including behaviors characterized by loss of control and continuation despite significant negative consequences. Broadly defined behavioral addictions share many similarities with substance use disorders. As naltrexone is one of the most studied treatment for substance use disorders, we conducted a meta-analysis of randomized placebo-controlled trials (RCT) assessing the effectiveness of naltrexone in the treatment of broadly defined behavioral addictions.

METHOD

We conducted a literature search and selection, up to January 1, 2017, according to previously set inclusion criteria. The selected trials underwent a quality assessment before data extraction and statistical analysis, which used fixed and random effects models. Standardized mean differences (SMD) were calculated using Hedge's adjusted g.

RESULTS

A total of 6 RCTs (n = 356) were included. Of these, 3 assessed naltrexone effectiveness in the treatment of pathological gambling, and 3 tested its benefits in broadly defined behavioral addictions other than pathological gambling (kleptomania, trichotillomania, and impulsive compulsive disorders). The meta-analysis of the whole sample resulted in a statistically significant score improvement under naltrexone versus placebo (fixed effect model: SMD = -0.27, 95% CI [-0.51 to -0.03], z = 2.23; p = 0.025).

CONCLUSION

The results of our meta-analysis suggest a beneficial effect of naltrexone in the treatment of broadly defined behavioral addictions.

Neural substrates of cue reactivity and craving in gambling disorder

Cue reactivity is an established procedure in addictions research for examining the subjective experience and neural basis of craving. This experiment sought to quantify cue-related brain responses in gambling disorder using personally tailored cues in conjunction with subjective craving, as well as a comparison with appetitive non-gambling stimuli. Participants with gambling disorder (n=19) attending treatment and 19 controls viewed personally tailored blocks of gambling-related cues, as well as neutral cues and highly appetitive (food) images during a functional magnetic resonance imaging (fMRI) scan performed ~2-3 h after a usual meal. fMRI analysis examined cue-related brain activity, cue-related changes in connectivity and associations with block-by-block craving ratings. Craving ratings in the participants with gambling disorder increased following gambling cues compared with non-gambling cues. fMRI analysis revealed group differences in left insula and anterior cingulate cortex, with the gambling disorder group showing greater reactivity to the gambling cues, but no differences to the food cues. In participants with gambling disorder, craving to gamble correlated positively with gambling cue-related activity in the bilateral insula and ventral striatum, and negatively with functional connectivity between the ventral striatum and the medial prefrontal cortex. Gambling cues, but not food cues, elicit increased brain responses in reward-related circuitry in individuals with gambling disorder (compared with controls), providing support for the incentive sensitization theory of addiction. Activity in the insula co-varied with craving intensity, and may be a target for interventions.

Parallel role for the dopamine D1 receptor in gambling and amphetamine reinforcement in healthy volunteers

This study investigated the role of dopamine, and specifically the D1 receptor (D1R), in the reinforcing effects of a slot-machine game in healthy volunteers ( n=30). To compare gambling and drug effects, subjects received the prototypic psychostimulant drug d-amphetamine (AMPH; 20 mg) in a multi-session, placebo-controlled design. To isolate D1R, half the subjects were pretreated with the preferential D2 receptor antagonist haloperidol (HAL; 3 mg), and the other half with the mixed D1-D2 antagonist fluphenazine (FLU; 3 mg) before the game (Phase I) and AMPH (Phase II). HAL decreased and FLU increased the post-game desire to gamble and post-AMPH desire to take AMPH again, as well as amphetamine scale ratings on the Addiction Research Center Inventory after gambling and AMPH. The effects of the antagonists on desire to gamble and to take AMPH again were significantly intercorrelated. HAL increased and FLU decreased the salience of negative affective words on a rapid reading task after both reinforcers. HAL also decreased the salience of gambling words after AMPH. Both reinforcers increased diastolic blood pressure equally under antagonists and placebo. Results indicate that D1R plays a parallel role in the psychostimulant-like, incentive-motivational, and salience-enhancing effects of gambling and AMPH. Moderate D1R activation appears to optimize these effects in healthy subjects.

Imaging in Central Nervous System Drug Discovery

The discovery and development of central nervous system (CNS) drugs is an extremely challenging process requiring large resources, timelines, and associated costs. The high risk of failure leads to high levels of risk. Over the past couple of decades PET imaging has become a central component of the CNS drug-development process, enabling decision-making in phase I studies, where early discharge of risk provides increased confidence to progress a candidate to more costly later phase testing at the right dose level or alternatively to kill a compound through failure to meet key criteria. The so called "3 pillars" of drug survival, namely; tissue exposure, target engagement, and pharmacologic activity, are particularly well suited for evaluation by PET imaging. This review introduces the process of CNS drug development before considering how PET imaging of the "3 pillars" has advanced to provide valuable tools for decision-making on the critical path of CNS drug development. Finally, we review the advances in PET science of biomarker development and analysis that enable sophisticated drug-development studies in man.

Naltrexone: A Pan-Addiction Treatment?

Addiction is a major public health problem with few efficacious and safe treatments. The goal of this review is to provide an evidence-based assessment of the therapeutic role of the opioid antagonist naltrexone across the addiction spectrum-substance-based and behavioral. The PubMed database was searched for randomized, placebo-controlled clinical trials that investigated the oral or intramuscular long-acting formulation of naltrexone in substance use disorders or behavioral addictions such as pathological gambling, kleptomania, and trichotillomania. Thirty-nine efficacy studies were retrieved, covering alcohol use disorder (n = 22), opioid use disorder (n = 6), nicotine use disorder (n = 5), stimulant use disorder (n = 2), gambling disorder (n = 2), trichotillomania (n = 1), and kleptomania (n = 1). Despite the very different presentations within and between both addiction categories, the data, as a whole, show consistency in favor of naltrexone's relative efficacy and safety. Given the potential benefit and good tolerability revealed in the studies, the high morbidity associated with addiction, and the dearth of alternate treatments, naltrexone would seem like an underutilized treatment option. Further, naltrexone's seemingly broad anti-addiction efficacy supports a shared role for brain opioid pathways in the pathophysiology of addiction, broadly defined. More studies investigating the efficacy and tolerability of naltrexone and other opioid modulators are warranted. Studies should also further examine the effect of combining psychotherapy with naltrexone, as well as the potential role of naltrexone in treating comorbid addictions.