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Application of metabolic magnetic resonance imaging measures such as cerebral blood flow in translational medicine is limited by the unknown link of observed alterations to specific neurophysiological processes. In particular, the sensitivity of cerebral blood flow to activity changes in specific neurotransmitter systems remains unclear. We address this question by probing cerebral blood flow in healthy volunteers using seven established drugs with known dopaminergic, serotonergic, glutamatergic and GABAergic mechanisms of action. We use a novel framework aimed at disentangling the observed effects to contribution from underlying neurotransmitter systems. We find for all evaluated compounds a reliable spatial link of respective cerebral blood flow changes with underlying neurotransmitter receptor densities corresponding to their primary mechanisms of action. The strength of these associations with receptor density is mediated by respective drug affinities. These findings suggest that cerebral blood flow is a sensitive brain-wide in-vivo assay of metabolic demands across a variety of neurotransmitter systems in humans.

Most addiction research has focused on reward- and impulsivity-related neurocircuitry. However, the impact of the withdrawal/negative affect stage in the addiction cycle has been somewhat overlooked, despite it being commonly evident in the clinic. This stage crucially drives negative reinforcement of repeated drug use and relapse, yet less is known about its neural underpinnings. How negative emotional processing is dysregulated in substance dependence is incompletely understood and may manifest differentially across the types of substances. In turn, the regions involved in negative emotional processing may show different patterns of dysregulation. Understanding how neurocircuitry involved in negative states differs across various substances may help inform new targets for treatments. Following a comprehensive literature search of studies examining negative emotional processing in substance dependence, a quantitative approach was deemed inappropriate. Instead, we employed a narrative approach to exploring neural responses to tasks involving emotional processing in alcohol, cocaine, opioid and cannabis dependence. Regions that were found to be dysregulated included the amygdala, insula, anterior cingulate, and medial prefrontal cortex. However, patterns of reactivity differed across alcohol, cocaine, opioid and cannabis dependence. Brain activation in alcohol dependence broadly appeared blunted in response to negative affective stimuli and emotional faces, whilst conversely appeared heightened in cocaine dependence. In opioid dependence, the amygdala was consistently implicated, whilst the insula, anterior cingulate, and medial prefrontal cortex were implicated in cannabis dependence. However, there was wide variability amongst the studies, with very few studies investigating opioid and cannabis dependence. These findings suggest emotional dysregulation varies according to the type of substance dependence. However, the variability in findings and lack of studies highlights the need for more research in this area. Further characterisation of emotional dysregulation in substance dependence will enable identification of treatment targets. More targeted treatments that modulate negative emotional processing could substantially improve outcomes by aiding relapse prevention.

Background People with substance use disorders may be at a greater risk of contracting COVID-19 infection and developing medical complications. Several institutional and governmental health agencies across the world developed ad hoc guidance for substance use disorder services and care of individuals misusing substances. We aimed to synthesise the best available recommendations on management and care of people with or at risk of substance use disorders during the COVID-19 pandemic from existing guidelines published in UK, USA, Australia, Canada, New Zealand, and Singapore. Methods We systematically searched existing guidelines and websites from 28 international institutions and governmental bodies in the context of the COVID-19 pandemic (May 4 th 2021). We summarized the extracted data as answers to specific clinical questions. Results We organised the available recommendations from 19 sources in three sections. First, we focused on general advice and recommendations for people who misuse alcohol or drugs during the COVID-19 pandemic, the design of contingency plans, safeguarding issues for children and families of service users and advice to the public, patients, and carers. Then, we summarised specific guidelines for people who use illicit drugs and related services, such as opioid substitution treatment and needle and syringe programmes. Finally, we provided a synthesis on specific recommendations for services supporting people who misuse alcohol and key topics in the field, such as management of alcohol detoxification and safe transition between supervised and unsupervised consumption. Conclusions Available guidance reflected different approaches, ranging from being extremely cautious in providing recommendations other than generic statements to proposing adaptation of previously available guidelines to confront the challenges of the COVID-19 pandemic. After the early phase, guidance focused on reduction of infection transmission and service delivery. Guidance did not provide advice on infection prevention via vaccination programmes and service access strategies tailored to individuals with substance use disorders.

Pathological gambling (PG) is a behavioural addiction associated with elevated impulsivity and suspected dopamine dysregulation. Reduced striatal dopamine D2/D3 receptor availability has been reported in drug addiction, and may constitute a premorbid vulnerability marker for addictive disorders. The aim of the present study was to assess striatal dopamine D2/D3 receptor availability in PG, and its association with trait impulsivity. Males with PG (n=9) and male healthy controls (n=9) underwent [11C]-raclopride positron emission tomography imaging and completed the UPPS-P impulsivity scale. There was no significant difference between groups in striatal dopamine D2/D3 receptor availability, in contrast to previous reports in drug addiction. However, mood-related impulsivity (‘Urgency’) was negatively correlated with [11C]-raclopride binding potentials in the PG group. The absence of a group difference in striatal dopamine binding implies a distinction between behavioural addictions and drug addictions. Nevertheless, our data indicate heterogeneity in dopamine receptor availability in disordered gambling, such that individuals with high mood-related impulsivity may show differential benefits from dopamine-based medications. ► Assessed 11C-raclopride binding in pathological gambling, a putative behavioral addiction. ► No group difference in striatal dopamine binding from healthy controls. ► Dopamine binding negatively correlated with mood-related impulsivity (‘Urgency’).

Pathological gambling is a psychiatric disorder and the first recognized behavioral addiction, with similarities to substance use disorders but without the confounding effects of drug-related brain changes. Pathophysiology within the opioid receptor system is increasingly recognized in substance dependence, with higher mu-opioid receptor (MOR) availability reported in alcohol, cocaine and opiate addiction. Impulsivity, a risk factor across the addictions, has also been found to be associated with higher MOR availability. The aim of this study was to characterize baseline MOR availability and endogenous opioid release in pathological gamblers (PG) using [(11)C]carfentanil PET with an oral amphetamine challenge. Fourteen PG and 15 healthy volunteers (HV) underwent two [(11)C]carfentanil PET scans, before and after an oral administration of 0.5 mg/kg of d-amphetamine. The change in [(11)C]carfentanil binding between baseline and post-amphetamine scans (ΔBPND) was assessed in 10 regions of interest (ROI). MOR availability did not differ between PG and HV groups. As seen previously, oral amphetamine challenge led to significant reductions in [(11)C]carfentanil BPND in 8/10 ROI in HV. PG demonstrated significant blunting of opioid release compared with HV. PG also showed blunted amphetamine-induced euphoria and alertness compared with HV. Exploratory analysis revealed that impulsivity positively correlated with caudate baseline BPND in PG only. This study provides the first evidence of blunted endogenous opioid release in PG. Our findings are consistent with growing evidence that dysregulation of endogenous opioids may have an important role in the pathophysiology of addictions.

The treatment of depression remains suboptimal, highlighting the need for more effective antidepressants. Traditional drug discovery and development is time-consuming and costly, prompting the need for faster translation of novel therapies into practice. But clinical expediency comes at a cost against which potential benefits need to be considered judiciously.

The inhibitory γ-aminobutyric acid (GABA) neurotransmitter system is associated with the regulation of normal cognitive functions and dysregulation has been reported in a number of neuropsychiatric disorders including anxiety disorders, schizophrenia and addictions. Investigating the role of GABA in both health and disease has been constrained by difficulties in measuring acute changes in synaptic GABA using neurochemical imaging. The aim of this study was to investigate whether acute increases in synaptic GABA are detectable in the living human brain using the inverse agonist GABA-benzodiazepine receptor (GABA-BZR) positron emission tomography (PET) tracer, [11C]Ro15-4513. We examined the effect of 15mg oral tiagabine, which increases synaptic GABA by inhibiting the GAT1 GABA uptake transporter, on [11C]Ro15-4513 binding in 12 male participants using a paired, double blind, placebo-controlled protocol. Spectral analysis was used to examine synaptic α1 and extrasynaptic α5 GABA-BZR subtype availability in brain regions with high levels of [11C]Ro15-4513 binding. We also examined the test–retest reliability of α1 and a5-specific [11C]Ro15-4513 binding in a separate cohort of 4 participants using the same spectral analysis protocol. Tiagabine administration produced significant reductions in hippocampal, parahippocampal, amygdala and anterior cingulate synaptic α1 [11C]Ro15-4513 binding, and a trend significance reduction in the nucleus accumbens. These reductions were greater than test–retest reliability, indicating that they are not the result of chance observations. Our results suggest that acute increases in endogenous synaptic GABA are detectable in the living human brain using [11C]Ro15-4513 PET. These findings have potentially major implications for the investigation of GABA function in brain disorders and in the development of new treatments targeting this neurotransmitter system. •Increases in synaptic GABA investigated using [11C]Ro15-4513 PET.•Synaptic α1 [11C]Ro15-4513 binding reduced by increased GABA.•α1 [11C]Ro15-4513 binding reductions were greater than test–retest reliability.•Suggests [11C]Ro15-4513 PET can measure increased synaptic GABA in the human brain.•Findings have important implications for examining the human in vivo GABA system.

Rationale Dependence on drugs and alcohol is associated with impaired impulse control, but deficits are rarely compared across individuals dependent on different substances using several measures within a single study. Objectives We investigated impulsivity in abstinent substance-dependent individuals (AbD) using three complementary techniques: self-report, neuropsychological and neuroimaging. We hypothesised that AbDs would show increased impulsivity across modalities, and that this would depend on length of abstinence. Methods Data were collected from the ICCAM study: 57 control and 86 AbDs, comprising a group with a history of dependence on alcohol only ( n  = 27) and a group with history of dependence on multiple substances (“polydrug”, n  = 59). All participants completed self-report measures of impulsivity: Barratt Impulsiveness Scale, UPPS Impulsive Behaviour Scale, Behaviour Inhibition/Activation System and Obsessive-Compulsive Inventory. They also performed three behavioural tasks: Stop Signal, Intra-Extra Dimensional Set-Shift and Kirby Delay Discounting; and completed a Go/NoGo task during fMRI. Results AbDs scored significantly higher than controls on self-report measures, but alcohol and polydrug dependent groups did not differ significantly from each other. Polydrug participants had significantly higher discounting scores than both controls and alcohol participants. There were no group differences on the other behavioural measures or on the fMRI measure. Conclusions The results suggest that the current set of self-report measures of impulsivity is more sensitive in abstinent individuals than the behavioural or fMRI measures of neuronal activity. This highlights the importance of developing behavioural measures to assess different, more relevant, aspects of impulsivity alongside corresponding cognitive challenges for fMRI.

This study aimed to replicate a previous study which showed that endogenous opioid release, following an oral dose of amphetamine, can be detected in the living human brain using [11C]carfentanil positron emission tomography (PET) imaging. Nine healthy volunteers underwent two [11C]carfentanil PET scans, one before and one 3 h following oral amphetamine administration (0.5 mg/kg). Regional changes in [11C]carfentanil BPND from pre- to post-amphetamine were assessed. The amphetamine challenge led to significant reductions in [11C]carfentanil BPND in the putamen, thalamus, frontal lobe, nucleus accumbens, anterior cingulate, cerebellum and insula cortices, replicating our earlier findings. None of the participants experienced significant euphoria/‘high’, supporting the use of oral amphetamine to characterize in vivo endogenous opioid release following a pharmacological challenge. [11C]carfentanil PET is able to detect changes in binding following an oral amphetamine challenge that reflects endogenous opioid release and is suitable to characterize the opioid system in neuropsychiatric disorders.

Cigarette smoking presents a significant worldwide healthcare challenge. Preclinical, genetic association and clinical trials studies provide considerable evidence for the involvement of the human γ-aminobutyric acid (GABA) system in the neurobiology of nicotine addiction. However there are few human GABA neurochemical imaging studies of nicotine addiction. We investigated limbic GABAA receptor availability in volunteers with a history of cigarette smoking using [11C]Ro15 4513 positron emission tomography (PET). Eight [11C]Ro15 4513 PET scans from volunteers with a history of cigarette smoking were compared to twelve scans from volunteers who were non-smokers. Total, α1 and α5 GABAA receptor subtype [11C]Ro15 4513 VT values were quantified using spectral analysis of limbic regions implicated in nicotine addiction. Spectral analysis allows quantification of the overall [11C]Ro15 4513 spectral frequency as well as α1 and α5 GABAA receptor subtype specific spectral frequency components. Volunteers with a history of cigarette smoking showed significantly higher total [11C]Ro15 4513 VT values in the presubgenual cingulate and parahippocampal gyrus, and at a trend level in the insula, nucleus accumbens and subgenual cingulate. In six abstinent previous smokers (‘ex-smokers’), total [11C]Ro15 4513 binding was significantly higher in all limbic regions studied, with higher α5 availability in the amygdala, anterior cingulate, nucleus accumbens and presubgenual cingulate. These results suggest that limbic GABAA receptor availability is higher in volunteers with a history of cigarette smoking which may reflect either higher expression of GABAA receptors or lower endogenous GABA levels. The findings in ex-smokers suggest that higher GABAA receptor availability continues with abstinence indicating that this may be a trait marker for nicotine addiction or that alterations in GABA function associated with cigarette smoking persist. ► We examined human [11C]Ro15 4513 PET binding in nicotine addiction. ► Higher limbic GABAA availability in volunteers with a history of cigarette smoking. ► Higher limbic GABAA receptor availability continues with abstinence. ► Suggests that limbic GABAA receptor system is dysregulated in nicotine addiction. ► Higher GABAA receptor availability may be a trait marker for nicotine addiction.