Midbrain functional connectivity and ventral striatal dopamine D2-type receptors: link to impulsivity in methamphetamine users

VTA glutamatergic projections to the nucleus accumbens suppress psychostimulant-seeking behavior

Converging evidence indicates that both dopamine and glutamate neurotransmission within the nucleus accumbens (NAc) play a role in psychostimulant self-administration and relapse in rodent models. Increased NAc dopamine release from ventral tegmental area (VTA) inputs is critical to psychostimulant self-administration and NAc glutamate release from prelimbic prefrontal cortex (PFC) inputs synapsing on medium spiny neurons (MSNs) is critical to reinstatement of psychostimulant-seeking after extinction. The regulation of the activity of MSNs by VTA dopamine inputs has been extensively studied, and recent findings have demonstrated that VTA glutamate neurons target the NAc medial shell. Here, we determined whether the mesoaccumbal glutamatergic pathway plays a role in psychostimulant conditioned place preference and self-administration in mice. We used optogenetics to induce NAc release of glutamate from VTA inputs during the acquisition, expression, and reinstatement phases of cocaine- or methamphetamine-induced conditioned place preference (CPP), and during priming-induced reinstatement of cocaine-seeking behavior. We found that NAc medial shell release of glutamate resulting from the activation of VTA glutamatergic fibers did not affect the acquisition of cocaine-induced CPP, but it blocked the expression, stress- and priming-induced reinstatement of cocaine- and methamphetamine CPP, as well as it blocked the priming-induced reinstatement of cocaine-seeking behavior after extinction. These findings indicate that in contrast to the well-recognized mesoaccumbal dopamine system that is critical to psychostimulant reward and relapse, there is a parallel mesoaccumbal glutamatergic system that suppresses reward and psychostimulant-seeking behavior.

Effects of exercise interventions on negative emotions, cognitive performance and drug craving in methamphetamine addiction

Introduction

Methamphetamine is currently one of the most commonly used addictive substances with strong addiction and a high relapse rate. This systematic review aims to examine the effectiveness of physical activity in improving negative emotions, cognitive impairment, and drug craving in people with methamphetamine use disorder (MUD).

Methods

A total of 17 studies out of 133 found from Embase and PubMed were identified, reporting results from 1836 participants from MUD populations. Original research using clearly described physical activity as interventions and reporting quantifiable outcomes of negative mood, cognitive function and drug craving level in people with MUD were eligible for inclusion. We included prospective studies, randomized controlled trials, or intervention studies, focusing on the neurological effects of physical activity on MUD.

Results

Taken together, the available clinical evidence showed that physical activity-based interventions may be effective in managing MUD-related withdrawal symptoms.

Discussion

Physical exercise may improve drug rehabilitation efficiency by improving negative emotions, cognitive behaviors, and drug cravings.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42024530359.

Brain connectivity changes to fast versus slow dopamine increases

The rewarding effects of stimulant drugs such as methylphenidate (MP) depend crucially on how fast they raise dopamine in the brain. Yet how the rate of drug-induced dopamine increases impacts brain network communication remains unresolved. We manipulated route of MP administration to generate fast versus slow dopamine increases. We hypothesized that fast versus slow dopamine increases would result in a differential pattern of global brain connectivity (GBC) in association with regional levels of dopamine D1 receptors, which are critical for drug reward. Twenty healthy adults received MP intravenously (0.5 mg/kg; fast dopamine increases) and orally (60 mg; slow dopamine increases) during simultaneous [11C]raclopride PET-fMRI scans (double-blind, placebo-controlled). We tested how GBC was temporally associated with slow and fast dopamine increases on a minute-to-minute basis. Connectivity patterns were strikingly different for slow versus fast dopamine increases, and whole-brain spatial patterns were negatively correlated with one another (rho = -0.54, pspin < 0.001). GBC showed "fast>slow" associations in dorsal prefrontal cortex, insula, posterior thalamus and brainstem, caudate and precuneus; and "slow>fast" associations in ventral striatum, orbitofrontal cortex, and frontopolar cortex (pFDR < 0.05). "Fast>slow" GBC patterns showed significant spatial correspondence with D1 receptor availability (estimated via normative maps of [11C]SCH23390 binding; rho = 0.22, pspin < 0.05). Further, hippocampal GBC to fast dopamine increases was significantly negatively correlated with self-reported 'high' ratings to intravenous MP across individuals (r(19) = -0.68, pbonferroni = 0.015). Different routes of MP administration produce divergent patterns of brain connectivity. Fast dopamine increases are uniquely associated with connectivity patterns that have relevance for the subjective experience of drug reward.

Associations between impulsivity and fecal microbiota in individuals abstaining from methamphetamine

INTRODUCTION

Methamphetamine (MA) abuse is a major public problem, and impulsivity is both a prominent risk factor and a consequence of addiction. Hence, clarifying the biological mechanism of impulsivity may facilitate the understanding of addiction to MA. The microbiota-gut-brain axis was suggested to underlie a biological mechanism of impulsivity induced by MA.

METHODS

We therefore recruited 62 MA addicts and 50 healthy controls (HCs) to investigate the alterations in impulsivity and fecal microbiota and the associations between them in the MA group. Thereafter, 25 MA abusers who abstained from MA for less than 3 months were followed up for 2 months to investigate the relationship between impulsivity and microbiota as abstinence became longer. 16S rRNA sequencing was conducted for microbiota identification.

RESULTS

Elevated impulsivity and dysbiosis characterized by an increase in opportunistic pathogens and a decrease in probiotics were identified in MA abusers, and both the increased impulsivity and disrupted microbiota tended to recover after longer abstinence from MA. Impulsivity was related to microbiota, and the effect of MA abuse on impulsivity was mediated by microbiota.

CONCLUSION

Our findings potentially highlighted the importance of abstention and implicated the significant role of the microbiota-gut-brain axis in the interrelationship between microbiota and behaviors, as well as the potential of microbiota as a target for intervention of impulsivity.

Polygenic contributions to performance on the Balloon Analogue Risk Task

Risky decision-making is a common, heritable endophenotype seen across many psychiatric disorders. Its underlying genetic architecture is incompletely explored. We examined behavior in the Balloon Analogue Risk Task (BART), which tests risky decision-making, in two independent samples of European ancestry. One sample (n = 1138) comprised healthy participants and some psychiatric patients (53 schizophrenia, 42 bipolar disorder, 47 ADHD); the other (n = 911) excluded for recent treatment of various psychiatric disorders but not ADHD. Participants provided DNA and performed the BART, indexed by mean adjusted pumps. We constructed a polygenic risk score (PRS) for discovery in each dataset and tested it in the other as replication. Subsequently, a genome-wide MEGA-analysis, combining both samples, tested genetic correlation with risk-taking self-report in the UK Biobank sample and psychiatric phenotypes characterized by risk-taking (ADHD, Bipolar Disorder, Alcohol Use Disorder, prior cannabis use) in the Psychiatric Genomics Consortium. The PRS for BART performance in one dataset predicted task performance in the replication sample (r = 0.13, p = 0.000012, pFDR = 0.000052), as did the reciprocal analysis (r = 0.09, p = 0.0083, pFDR=0.04). Excluding participants with psychiatric diagnoses produced similar results. The MEGA-GWAS identified a single SNP (rs12023073; p = 3.24 × 10-8) near IGSF21, a protein involved in inhibitory brain synapses; replication samples are needed to validate this result. A PRS for self-reported cannabis use (p = 0.00047, pFDR = 0.0053), but not self-reported risk-taking or psychiatric disorder status, predicted behavior on the BART in our MEGA-GWAS sample. The findings reveal polygenic architecture of risky decision-making as measured by the BART and highlight its overlap with cannabis use.

The evolution of Big Data in neuroscience and neurology

Neurological diseases are on the rise worldwide, leading to increased healthcare costs and diminished quality of life in patients. In recent years, Big Data has started to transform the fields of Neuroscience and Neurology. Scientists and clinicians are collaborating in global alliances, combining diverse datasets on a massive scale, and solving complex computational problems that demand the utilization of increasingly powerful computational resources. This Big Data revolution is opening new avenues for developing innovative treatments for neurological diseases. Our paper surveys Big Data's impact on neurological patient care, as exemplified through work done in a comprehensive selection of areas, including Connectomics, Alzheimer's Disease, Stroke, Depression, Parkinson's Disease, Pain, and Addiction (e.g., Opioid Use Disorder). We present an overview of research and the methodologies utilizing Big Data in each area, as well as their current limitations and technical challenges. Despite the potential benefits, the full potential of Big Data in these fields currently remains unrealized. We close with recommendations for future research aimed at optimizing the use of Big Data in Neuroscience and Neurology for improved patient outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40537-023-00751-2.

Abnormal resting-state functional connectome in methamphetamine-dependent patients and its application in machine-learning-based classification

Brain resting-state functional connectivity (rsFC) has been widely analyzed in substance use disorders (SUDs), including methamphetamine (MA) dependence. Most of these studies utilized Pearson correlation analysis to assess rsFC, which cannot determine whether two brain regions are connected by direct or indirect pathways. Moreover, few studies have reported the application of rsFC-based graph theory in MA dependence. We evaluated alterations in Tikhonov regularization-based rsFC and rsFC-based topological attributes in 46 MA-dependent patients, as well as the correlations between topological attributes and clinical variables. Moreover, the topological attributes selected by least absolute shrinkage and selection operator (LASSO) were used to construct a support vector machine (SVM)-based classifier for MA dependence. The MA group presented a subnetwork with increased rsFC, indicating overactivation of the reward circuit that makes patients very sensitive to drug-related visual cues, and a subnetwork with decreased rsFC suggesting aberrant synchronized spontaneous activity in subregions within the orbitofrontal cortex (OFC) system. The MA group demonstrated a significantly decreased area under the curve (AUC) for the clustering coefficient (Cp) (Pperm &lt; 0.001), shortest path length (Lp) (Pperm = 0.007), modularity (Pperm = 0.006), and small-worldness (σ, Pperm = 0.004), as well as an increased AUC for global efficiency (E.glob) (Pperm = 0.009), network strength (Sp) (Pperm = 0.009), and small-worldness (ω, Pperm &lt; 0.001), implying a shift toward random networks. MA-related increased nodal efficiency (E.nodal) and altered betweenness centrality were also discovered in several brain regions. The AUC for ω was significantly positively associated with psychiatric symptoms. An SVM classifier trained by 36 features selected by LASSO from all topological attributes achieved excellent performance, cross-validated prediction area under the receiver operating characteristics curve, accuracy, sensitivity, specificity, and kappa of 99.03 ± 1.79, 94.00 ± 5.78, 93.46 ± 8.82, 94.52 ± 8.11, and 87.99 ± 11.57%, respectively (Pperm &lt; 0.001), indicating that rsFC-based topological attributes can provide promising features for constructing a high-efficacy classifier for MA dependence.

The effects of early life stress on impulsivity

Elevated impulsivity is a symptom shared by various psychiatric disorders such as substance use disorder, bipolar disorder, and attention-deficit/hyperactivity disorder. However, impulsivity is not a unitary construct and impulsive behaviors fall into two subcategories: impulsive action and impulsive choice. Impulsive choice refers to the tendency to prefer immediate, small rewards over delayed, large rewards, whereas impulsive action involves difficulty inhibiting rash, premature, or mistimed behaviors. These behaviors are mediated by the mesocorticolimbic dopamine (DA) system, which consists of projections from the ventral tegmental area to the nucleus accumbens and prefrontal cortex. Early life stress (ELS) alters both impulsive choice and impulsive action in rodents. ELS also changes DA receptor expression, transmission, and activity within the mesocorticolimbic system. This review integrates the dopamine, impulsivity, and ELS literature to provide evidence that ELS alters impulsivity via inducing changes in the mesocorticolimbic DA system. Understanding how ELS affects brain circuits associated with impulsivity can help advance treatments aimed towards reducing impulsivity symptoms in a variety of psychiatric disorders.

Ginsenoside Rb1 attenuates methamphetamine (METH)-induced neurotoxicity through the NR2B/ERK/CREB/BDNF signalings in vitro and in vivo models

Aim

This study investigates the effects of ginsenoside Rb1 (GsRb1) on methamphetamine (METH)-induced toxicity in SH-SY5Y neuroblastoma cells and METH-induced conditioned place preference (CPP) in adult Sprague-Dawley rats. It also examines whether GsRb1 can regulate these effects through the NR2B/ERK/CREB/BDNF signaling pathways.

Methods

SH-SY5Y cells were pretreated with GsRb1 (20 μM and 40 μM) for 1 h, followed by METH treatment (2 mM) for 24 h. Rats were treated with METH (2 mg/kg) or saline on alternating days for 10 days to allow CPP to be examined. GsRb1 (5, 10, and 20 mg/kg) was injected intraperitoneally 1 h before METH or saline. Western blot was used to examine the protein expression of NR2B, ERK, P-ERK, CREB, P-CREB, and BDNF in the SH-SY5Y cells and the rats' hippocampus, nucleus accumbens (NAc), and prefrontal cortex (PFC).

Results

METH dose-dependently reduced the viability of SH-SY5Y cells. Pretreatment of cells with 40 μM of GsRb1 increased cell viability and reduced the expression of METH-induced NR2B, p-ERK, p-CREB and BDNF. GsRb1 also attenuated the expression of METH CPP in a dose-dependent manner in rats. Further, GsRb1 dose-dependently reduced the expression of METH-induced NR2B, p-ERK, p-CREB, and BDNF in the PFC, hippocampus, and NAc of rats.

Conclusion

GsRb1 regulated METH-induced neurotoxicity in vitro and METH-induced CPP through the NR2B/ERK/CREB/BDNF regulatory pathway. GsRb1 could be a therapeutic target for treating METH-induced neurotoxicity or METH addiction.

Exploratory examination of the effects of d-amphetamine on active-state functional connectivity: Influence of impulsivity and sensation-seeking status

Recent advances in diagnostic research identified that individuals with higher impulsivity and sensation-seeking scores tend to report more positive subjective responses to stimulant drugs such as amphetamine. The current exploratory study hypothesized that differences in underlying mesocorticolimbic circuitry may mediate the relationship between personality and responses to stimulants due to its previously established implication in reward processes as well as the overlap between its dopaminergic projections and the pharmacodynamics of many stimulants. Forty participants (20 female) were recruited with relatively high- and low-impulsivity and sensation-seeking scores as defined by the Zuckerman-Kuhlman Personality Questionnaire (Form IIIR; Zuckerman, Kuhlman, Joireman, Teta, & Kraft, 1993) for a double-blind, placebo-controlled, intranasal amphetamine administration study conducted within an MRI scanner. Active state seed-to-voxel connectivity analyses assessed the effects of amphetamine, personality, subjective responses to amphetamine, and their interactions with mesocorticolimbic seeds on data collected during monetary incentive delay and go/no-go task performance. Results indicated that amphetamine administration largely disrupted brain activity as evidenced by connectivity values shifting toward no correlation among brain stem, striatal, and frontal cortex regions. Additionally, associations of impulsivity and connectivity between ventral tegmental and medial orbitofrontal as well as lateral orbitofrontal and putamen regions were inverted from negative to positive during the placebo and amphetamine conditions, respectively. Personality was unrelated to subjective responses to amphetamine. Results are interpreted as providing evidence of underlying differences in mesocorticolimbic circuitry being a potential target for requisite diagnostic and treatment strategies implicated with stimulant use disorders, but further research is needed. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Brain network dysfunctions in addiction: a meta-analysis of resting-state functional connectivity

Resting-state functional connectivity (rsFC) provides novel insights into variabilities in neural networks associated with the use of addictive drugs or with addictive behavioral repertoire. However, given the broad mix of inconsistent findings across studies, identifying specific consistent patterns of network abnormalities is warranted. Here we aimed at integrating rsFC abnormalities and systematically searching for large-scale functional brain networks in substance use disorder (SUD) and behavioral addictions (BA), through a coordinate-based meta-analysis of seed-based rsFC studies. A total of fifty-two studies are eligible in the meta-analysis, including 1911 SUD and BA patients and 1580 healthy controls. In addition, we performed multilevel kernel density analysis (MKDA) for the brain regions reliably involved in hyperconnectivity and hypoconnectivity in SUD and BA. Data from fifty-two studies showed that SUD was associated with putamen, caudate and middle frontal gyrus hyperconnectivity relative to healthy controls. Eight BA studies showed hyperconnectivity clusters within the putamen and medio-temporal lobe relative to healthy controls. Altered connectivity in salience or emotion-processing areas may be related to dysregulated affective and cognitive control-related networks, such as deficits in regulating elevated sensitivity to drug-related stimuli. These findings confirm that SUD and BA might be characterized by dysfunctions in specific brain networks, particularly those implicated in the core cognitive and affective functions. These findings might provide insight into the development of neural mechanistic biomarkers for SUD and BA.

Magnetic resonance imaging of the dopamine system in schizophrenia - A scoping review

For decades, aberrant dopamine transmission has been proposed to play a central role in schizophrenia pathophysiology. These theories are supported by human in vivo molecular imaging studies of dopamine transmission, particularly positron emission tomography. However, there are several downsides to such approaches, for example limited spatial resolution or restriction of the measurement to synaptic processes of dopaminergic neurons. To overcome these limitations and to measure complementary aspects of dopamine transmission, magnetic resonance imaging (MRI)-based approaches investigating the macrostructure, metabolism, and connectivity of dopaminergic nuclei, i.e., substantia nigra pars compacta and ventral tegmental area, can be employed. In this scoping review, we focus on four dopamine MRI methods that have been employed in patients with schizophrenia so far: neuromelanin MRI, which is thought to measure long-term dopamine function in dopaminergic nuclei; morphometric MRI, which is assumed to measure the volume of dopaminergic nuclei; diffusion MRI, which is assumed to measure fiber-based structural connectivity of dopaminergic nuclei; and resting-state blood-oxygenation-level-dependent functional MRI, which is thought to measure functional connectivity of dopaminergic nuclei based on correlated blood oxygenation fluctuations. For each method, we describe the underlying signal, outcome measures, and downsides. We present the current state of research in schizophrenia and compare it to other disorders with either similar (psychotic) symptoms, i.e., bipolar disorder and major depressive disorder, or dopaminergic abnormalities, i.e., substance use disorder and Parkinson's disease. Finally, we discuss overarching issues and outline future research questions.

Neurophysiological correlate of incubation of craving in individuals with methamphetamine use disorder

Previous studies both in laboratory animals and humans have reported that abstinence induces incubation of cue-induced drug craving for nicotine, alcohol, cocaine, and methamphetamine. However, current experimental procedures utilized to study incubation of methamphetamine craving do not incorporate the temporal dynamics of neuropsychological measures and electrophysiological activities associated with this incubation process. This study utilized the high-density electroencephalogram (EEG) signals as a rapid, inexpensive, and noninvasive measure of cue-induced craving potential. A total of 156 male individuals with methamphetamine use disorder (MUD) enrolled in this multisite, cross-sectional study. Structured clinical interview data, self-report questionnaires (cued craving, quality of sleep, impulsivity, anxiety, and depression) and resting-state, eye-closed 128 high-density channel EEG signals were collected at 5 abstinence duration time points (<1, 1-3, 3-6, 6-12, and 12-24 months) to track the neuropsychological and neurophysiological signatures. Cue-induced craving was higher after 1-3 months than after the other time points. This incubation effect was also observed for sleep quality but not for anxiety, depression, and impulsivity symptoms, along with exhibited decreased power spectrum for theta (5.5-8 Hz) and alpha (8-13 Hz), and increased in beta (16.5-26.5 Hz) frequency band. Source reconstructed resting-state EEG analysis showed increased synchronization of medial prefrontal cortex (MPFC) for the beta frequency band in 1-3 months abstinent MUD group, and associated with the incubation of craving. Remarkably, the robust incubation-related abnormalities may be driven by beta-band source space connectivity between MPFC and bilateral orbital gyrus (ORB). Our findings suggest the enhancement of beta activity in the incubation period most likely originates from a dysfunction involving frontal brain regions. This neurophysiological signature of incubation of craving can be used to identify individuals who might be most susceptible to relapse, providing a potential insight into future therapeutic interventions for MUD via neuromodulation of beta activity.

Prefrontal and striatal dopamine D2/D3 receptors correlate with fMRI BOLD activation during stopping

D₂-like dopamine receptors in animals and humans have been shown to be linked to impulsive behaviors that are highly relevant for several psychiatric disorders. Here, we investigate the relationship between the fronto-striatal D₂/D₃ dopamine receptor availability and response inhibition in a selected population of healthy OPRM1 G-allele carriers. Twenty-two participants successively underwent blood-oxygen level dependent functional magnetic resonance imaging (fMRI) while performing a stop-signal task and a separate positron emission tomography (PET) scan. Striatal and extrastriatal D₂/D₃ dopamine receptor availability was measured using the radiotracer [¹⁸F]fallypride. Caudate D₂/D₃ dopamine receptor availability positively correlated with stopping-related fronto-striatal fMRI activation. In addition, right prefrontal D₂/D₃ dopamine receptor availability correlated positively with stopping-related striatal fMRI BOLD signal. Our study partially replicates previous findings on correlations between striatal D₂/D₃ dopamine receptor availability and response inhibition in a population selected for its genetic determination of dopamine response to alcohol and as a modulator of impulse control via the endogenous opioid system. We confirm the important role of D₂/D₃ dopamine receptor availability in the fronto-striatal neural circuit for response inhibition. Moreover, we extend previous findings suggesting that dopamine receptor availability in the right inferior frontal cortex, a crucial region of the stopping network, is also strongly associated with stopping-related striatal fMRI activity in healthy OPRM1 G-allele carriers.

Long-term effects of intermittent early life stress on primate prefrontal-subcortical functional connectivity

Correlational studies of humans suggest that exposure to early life stress has long-term effects on neural circuits involved in vulnerability and resilience to mental health disorders. Stress-related mental health disorders are more prevalent in women than in men. Here, female squirrel monkeys are randomized to intermittently stressful (IS) social separations or a non-separated (NS) control condition conducted from 17 to 27 weeks of age. Nine years later in mid-life adulthood, resting-state functional magnetic resonance imaging was employed to parcellate prefrontal cortex (PFC). Resulting subdivisions were then used to characterize functional connectivity within PFC, and between PFC subdivisions and subcortical regions that are known to be altered by stress. Extensive hyper-connectivity of medial and orbitofrontal PFC with amygdala, hippocampus, and striatum was observed in IS compared to NS monkeys. Functional hyper-connectivity in IS monkeys was associated with previously reported indications of diminished anxiety-like behavior induced by prepubertal stress. Hyper-connectivity of PFC with amygdala and with hippocampus was also associated with increased ventral striatal dopamine D2 and/or D3 receptor (DRD2/3) availability assessed with positron emission tomography (PET) of [¹¹C]raclopride binding in adulthood. Ventral striatal DRD2/3 availability has been linked to cognitive control, which plays a key role in stress coping as an aspect of emotion regulation. These findings provide causal support for enduring neurobiological effects of early life stress and suggest novel targets for new treatments of stress-related mental health disorders.

The Potential Regulatory Network of Glutamate Metabolic Pathway Disturbance in Chinese Han Withdrawal Methamphetamine Abusers

Objects

To explore the long-term influence of methamphetamine abuse on metabolomics character, with gas chromatography-mass spectrometry (GS-MS) technology, and the potential regulatory network using the bioinformatics method.

Methods

Forty withdrawal methamphetamine abusers (WMA) were recruited from Shanghai Gaojing Forced Isolation Detoxification Institute. Forty healthy controls (HC) were recruited from society. GS-MS technology was used to detect metabolic products in serum. A bioinformatics method was used to build a regulatory network. Q-PCR was used to detect the candidate gene expressions, and ELISA was used to detect the regulatory enzyme expressions.

Results

Four pathways were significantly changed in the MA compared to the HC: (1) the arginine synthesis pathway, (2) alanine, aspartic acid and glutamate metabolic pathway, (3) cysteine and methionine metabolic pathway, and (4) the ascorbate and aldarate pathway (enrichment analysis p < 0.05, Impactor factor > 0.2). When focusing on the ‘Alanine, aspartate, and glutamate metabolism’ pathway, a regulatory network was established, and the expression of candidate regulatory genes and enzymes was verified. It was found that the expression of DLG2 (Discs large MAGUK scaffold protein 2), PLA2G4 (Phospholipase A2 group IVE), PDE4D (Phosphodiesterase 4D), PDE4B (Phosphodiesterase 4B), and EPHB2 (Ephrin type-B receptor 2) were significantly different between the two groups (p < 0.05), However, after adjusting for age and BMI, only DLG2, PLA2G4, and EPHB2 remained significant (p < 0.05). The expression of enzymes was not significantly different (p > 0.05).

Conclusion

Methamphetamine abuse influences the metabolic process in the long term, and DLG2, PLA2G4, and EPHB2 may regulate the glutamate metabolism pathway.

Lack of longitudinal changes in cognition in individuals with methamphetamine use disorder during the first 6 weeks after commencing treatment

Background: Methamphetamine use disorder (MUD) associates with cognitive impulsivity deficits. However, few studies have examined longitudinal changes in cognition, and it remains unclear if deficits resolve during early recovery.Objectives: To compare: (1) cognitive function of individuals with MUD at treatment onset and six-weeks later with controls tested over the same period; (2) cognitive changes in MUD-individuals who remained abstinent versus relapsed.Method: We recruited 108 participants meeting DSM-IV-TR criteria for methamphetamine dependence (81 males) and 50 demographically matched controls (38 males); 77 methamphetamine- dependent participants (59 males) and 48 controls (36 males) were retained at follow-up. We administered response inhibition, delay discounting and uncertainty-based decision-making tests at both endpoints. Relapse was defined as methamphetamine concentrations >0.4 ng/mg at follow-up in hair toxicology.Results: We found a significant time-by-group interaction on uncertainty-based decision-making (effect size: η² = .05), although post-hoc tests to disentangle this interaction yielded inconclusive results (p-range = .14-.40; BF₁₀-range = 0.43-1.67). There were no significant time-by-group interactions on response inhibition or delay discounting, with the former likely a null effect (η²-interaction = .003 and .02; BF_incl = 0.23 and 0.71). There were no significant differences in cognitive recovery between individuals who maintained abstinence (n = 12) versus relapsed (n = 65) (η²-range = .003-.04), although evidence was inconclusive toward whether findings reflected true null effects (BF_incl-range = 0.33-0.75).Conclusion: We did not find evidence that MUD-related cognitive impulsivity deficits improve beyond practice effects over 6 weeks. Findings do not support previous, albeit conflicting, evidence of early recovery of cognitive deficits in MUD.

Treatment Response Prediction and Individualized Identification of Short-Term Abstinence Methamphetamine Dependence Using Brain Graph Metrics

Background: The abuse of methamphetamine (MA) worldwide has gained international attention as the most rapidly growing illicit drug problem. The classification and treatment response prediction of MA addicts are thereby paramount, in order for effective treatments to be more targeted to individuals. However, there has been limited progress. Methods: In the present study, 43 MA-dependent participants and 38 age- and gender-matched healthy controls were enrolled, and their resting-state functional magnetic resonance imaging data were collected. MA-dependent participants who showed 50% reduction in craving were defined as responders to treatment. The present study used the machine learning method, which is a support vector machine (SVM), to detect the most relevant features for discriminating and predicting the treatment response for MA-dependent participants based on the features extracted from the functional graph metrics. Results: A classifier was able to differentiate MA-dependent subjects from normal controls, with a cross-validated prediction accuracy, sensitivity, and specificity of 73.2% [95% confidence interval (CI) = 71.23-74.17%), 66.05% (95% CI = 63.06-69.04%), and 80.35% (95% CI = 77.77-82.93%), respectively, at the individual level. The most accurate combination of classifier features included the nodal efficiency in the right middle temporal gyrus and the community index in the left precentral gyrus and cuneus. Between these two, the community index in the left precentral gyrus had the highest importance. In addition, the classification performance of the other classifier used to predict the treatment response of MA-dependent subjects had an accuracy, sensitivity, and specificity of 71.2% (95% CI = 69.28-73.12%), 86.75% (95% CI = 84.48-88.92%), and 55.65% (95% CI = 52.61-58.79%), respectively, at the individual level. Furthermore, the most accurate combination of classifier features included the nodal clustering coefficient in the right orbital part of the superior frontal gyrus, the nodal local efficiency in the right orbital part of the superior frontal gyrus, and the right triangular part of the inferior frontal gyrus and right temporal pole of middle temporal gyrus. Among these, the nodal local efficiency in the right temporal pole of the middle temporal gyrus had the highest feature importance. Conclusion: The present study identified the most relevant features of MA addiction and treatment based on SVMs and the features extracted from the graph metrics and provided possible biomarkers to differentiate and predict the treatment response for MA-dependent patients. The brain regions involved in the best combinations should be given close attention during the treatment of MA.

Differences in Functional Connectivity Networks Related to the Midbrain Dopaminergic System-Related Area in Various Psychiatric Disorders

OBJECTIVE

Disruptions in the dopamine system have been observed in psychiatric disorders. Since dopamine is mainly produced in the ventral tegmental area (VTA), elucidating the differences in the VTA neural network across psychiatric disorders would facilitate a greater understanding of the pathophysiological mechanisms underlying these disorders. However, no study has compared VTA-seed-based functional connectivity across psychiatric disorders. Therefore, we conducted a resting-state functional magnetic resonance imaging (rs-fMRI) study to perform a seed-based fMRI analysis, using the VTA as a seed.

METHODS

We included participants with major depressive disorder (MDD; n = 45), schizophrenia (n = 32), and bipolar disorder (BPD; n = 30), along with healthy control participants (n = 46) who were matched for age, gender, and handedness.

RESULTS

The results showed that patients with MDD and BPD had altered VTA-related connectivity in the superior frontal gyrus, frontal pole regions, hippocampus, cerebellum, and posterior cingulate cortex. Some of these differences in connectivity were also found between affective disorders and schizophrenia; however, there were no differences between the schizophrenia and control groups. Connectivity between the VTA and the hippocampus was correlated with positive symptoms in the schizophrenia group. The connectivity was not associated with medication dose, and the results remained significant after controlling for dose.

CONCLUSIONS

The results suggest that altered brain functional connectivity related to VTA networks could be associated with the distinctive pathophysiologies of psychiatric disorders, especially affective disorders.

Medial forebrain bundle structure is linked to human impulsivity

Comparative research indicates that projections from midbrain dopamine nuclei [including the ventral tegmental area (VTA)] to the ventral striatum [including the nucleus accumbens (NAcc)] critically support motivated behavior. Using diffusion-weighted imaging and probabilistic tractography in humans, we characterized the trajectory and structure of two tracts connecting the VTA and NAcc, as well as others connecting the substantia nigra and dorsal striatum. Decreased structural coherence of an inferior VTA-NAcc tract was primarily and replicably associated with increased trait impulsivity and also distinguished individuals with a stimulant use disorder from healthy controls. These findings suggest that decreased coherence of the inferior VTA-NAcc tract is associated with increased impulsivity in humans and identify a previously uncharacterized structural target for diagnosing disorders marked by impulsivity.

Dopamine Receptor DRD2 Gene rs1076560, Personality Traits and Anxiety in the Polysubstance Use Disorder

Development of an addiction is conditioned by many factors. The dopaminergic system has been shown to be the key element in this process. In this paper, we analyzed the influence of dopamine receptor 2 polymorphism rs1076560 in two groups—polysubstance-dependent male patients (n = 299) and the controls matched for age (n = 301). In both groups, we applied the same questionnaires for testing—Mini-international neuropsychiatric interview, the NEO Five-Factor Inventory, and the State–Trait Anxiety Inventory. The real-time PCR method was used for genotyping. When we compared the controls with the case group subjects, we observed significantly higher scores in the second group on both the state and trait scales of anxiety, as well as on the Neuroticism and Openness scales of the NEO-FFI; and lower scores on the scales of Extraversion and Agreeability of the NEO-FFI. The model 2 × 3 factorial ANOVA of the addicted subjects and controls was performed, and the DRD2 rs1076560 variant interaction was found for the anxiety state and trait scales, and for the NEO-FFI Neuroticism scale. The observed associations allow noticing that analysis of psychological factors in combination with genetic data opens new possibilities in addiction research.

Cognitive deficits in methamphetamine addiction: Independent contributions of dependence and intelligence

BACKGROUND

Methamphetamine's effects on brain function have been associated with cognitive deficits, which have a negative impact on clinical outcomes. However, it remains unclear if cognitive deficits relate to methamphetamine dependence (potentially amenable to abstinence and retraining) or background characteristics, mental health and other drug use. We tested the association between methamphetamine dependence and cognitive performance, while factoring in the impact of background characteristics, depressive symptoms and tobacco, alcohol and cannabis use.

METHOD

The sample comprised 108 treatment-seeking participants who met the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV TR) criteria for methamphetamine dependence and 50 socio-demographically matched controls. We administered a comprehensive neuropsychological test battery (delay discounting, decision making, disinhibition, episodic and working memory) and examined cognitive deficits in methamphetamine users after taking into account socio-demographic characteristics, tobacco, alcohol and cannabis use, and depressive symptoms.

RESULTS

Hierarchical multiple regression analyses showed that methamphetamine dependence was associated with poorer performance in decision-making and disinhibition over and above other predictors, while IQ better explained performance in episodic and working memory. Although duration of methamphetamine use was linked to disinhibition, other patterns of methamphetamine use (including dose and frequency) were not consistently related to performance.

CONCLUSIONS

Methamphetamine dependence impacts inhibitory control and decision-making, whereas lower IQ associates with memory/working memory deficits among methamphetamine users. Findings suggest the need to target disinhibition and impulsive decision-making as part of methamphetamine dependence treatment, while buffering the impact of IQ on memory systems.

Effect of Low-Frequency Repetitive Transcranial Magnetic Stimulation on Impulse Inhibition in Abstinent Patients With Methamphetamine Addiction: A Randomized Clinical Trial

IMPORTANCE

Impulsivity during periods of abstinence is a critical symptom of patients who use methamphetamine (MA).

OBJECTIVE

To evaluate changes in impulse inhibition elicited by repetitive transcranial magnetic stimulation (rTMS) in patients with MA addiction.

DESIGN, SETTING, AND PARTICIPANTS

This randomized clinical trial was conducted in Da Lian Shan Addiction Rehabilitation Center, Nanjing, China, from December 1, 2018, to April 20, 2019. Effects of the intervention were examined at 3 time points: after a single session (day 1), 24 hours after 10 repeated sessions (day 11), and at 3 weeks of follow-up (day 31). Men with MA addiction and healthy male control participants were recruited for this study. Data analysis was performed from March 2019 to October 2019.

INTERVENTIONS

Patients who use MA were randomized to undergo sham rTMS (36 patients) and or 1-Hz rTMS (37 patients) to the left prefrontal cortex, receiving daily TMS treatments for 10 consecutive days.

MAIN OUTCOMES AND MEASURES

The primary outcome was impulse inhibition, which is primarily embodied by accuracy reduction (ie, accuracy cost) from standard to deviant trials in a 2-choice oddball task (80% standard and 20% deviant trials).

RESULT

The study included 73 men with MA addiction (mean [SD] age, 38.49 [7.69] years) and 33 male healthy control participants without MA addiction (mean [SD] age, 35.15 [9.68] years). The mean (SD) duration of abstinence for the men with MA addiction was 9.27 (4.61) months. Compared with the control group, patients with MA addiction exhibited greater impulsivity (accuracy cost, 3.3% vs 6.2%). The single session of 1-Hz rTMS over the left prefrontal cortex significantly increased accuracy from 91.4% to 95.7% (F1,36 = 9.58; P < .001) and reaction time delay from 50 milliseconds to 77 milliseconds (F1,36 = 22.66; P < .001) in deviant trials. These effects were seen consistently after 10 sessions of 1-Hz rTMS treatment (day 11 vs day 1, t26 = 1.59; P = .12), and the behavioral improvement was maintained at least for 3 weeks after treatment (day 31 vs day 1, t26 = 0.26; P = .80). These improvement effects of impulse inhibition were coupled with a reduction in addictive symptoms as measured by cue-induced craving. The pretest accuracy cost was positively correlated with the change in impulse inhibition (r = 0.615; P < .001) and change in craving (r = 0.334; P = .01), suggesting that these 2 behaviors may be modified simultaneously.

CONCLUSIONS AND RELEVANCE

These findings suggest that repeated rTMS sessions have sustained effects on impulse inhibition in patients with MA addiction and provide novel data on impulsivity management strategies for addiction rehabilitation.

TRIAL REGISTRATION

ChiCTR-ROC-16008541.

Personality Traits or Genetic Determinants-Which Strongly Influences E-Cigarette Users?

Presently, a growing popularity of electronic cigarettes may be observed. Used as a means of obtaining nicotine they allow to substitute traditional cigarettes. The origins of substance use disorders are conditioned by dopaminergic signaling which influences motivational processes being elementary factors conditioning the process of learning and exhibiting goal-directed behaviors. The study concentrated on analysis of three polymorphisms located in the dopamine receptor 2 (DRD2) gene—rs1076560, rs1799732 and rs1079597 using the PCR method, personality traits determined with the Big Five Questionnaire, and anxiety measured with the State Trait Anxiety Inventory. The study was conducted on a group of 394 volunteers, consisting e-cigarette users (n = 144) and controls (n = 250). Compared to the controls the case group subjects achieved significantly higher scores in regard to the STAI state and the trait scale, as well as the NEO-FFI Neuroticism and Openness scale. Likewise, in the case of the STAI state for DRD2 rs1076560 significant differences were found. Furthermore, while comparing the groups (e-cigarette users vs. controls) we noticed interactions for the NEO FFI Neuroticism and DRD2 rs1076560. The same was observed in the case of interactions significance while comparing groups (e-cigarette users vs. controls) for the STAI trait/scale and DRD2 rs1799732. Findings from this study demonstrate that psychological factors and genetic determinants should be analyzed simultaneously and comprehensively while considering groups of addicted patients. Since the use, and rapid increase in popularity, of electronic cigarettes has implications for public health, e-cigarette users should be studied holistically, especially younger groups of addicted and experimenting users.

Human Brain Imaging Links Dopaminergic Systems to Impulsivity

Molecular and functional imaging techniques have been used and combined with pharmacological probes to evaluate the role of dopamine in impulsivity. Overall, strong evidence links striatal dopaminergic function with impulsivity, measured by self-reports and laboratory tests of cognitive control and reward-based decision-making. The combination of molecular imaging using positron emission tomography (PET) with functional magnetic resonance imaging (fMRI) specifically implicates striatal D2-type dopamine receptors (i.e., D2 and D3) and corticostriatal connectivity in cognitive control. Low levels of striatal and midbrain D2-type receptor availability correlate with self-reported impulsivity, whereas striatal D2-type receptor availability shows positive correlation with motor response inhibition and cognitive flexibility. Impulsive choice on reward-based decision-making tasks also is related to deficits in striatal D2-type dopamine receptor availability, and there is evidence for an inverted U-shaped function in this relationship, reflecting an optimum of striatal dopaminergic activity. Findings from studies of clinical populations that present striatal dopamine D2-type receptor deficits as well as healthy control research participants identify D2-type receptors as therapeutic targets to improve cognitive control.

Psychopathy and Corticostriatal Connectivity: The Link to Criminal Behavior in Methamphetamine Dependence

Methamphetamine use and psychopathy are associated with criminal behavior; however, it is unclear how methamphetamine use and psychopathy interact to promote violent, economic and drug offenses. Abnormalities in corticostriatal functional connectivity are exhibited in both psychopathic and methamphetamine dependent individuals, which may contribute to criminal behavior through maladaptive and impulsive decision-making processes. This study shows that psychopathic traits contribute to weaker corticostriatal connectivity in methamphetamine dependence and contributes to an increase in criminal behavior. As the propensity to engage in criminal activity is dependent on a number of factors, a hierarchical regression identifies the contribution of the impulsive antisocial domain of psychopathy, anxiety, years of methamphetamine use and corticostriatal connectivity on different types of criminal offenses. Methamphetamine use and psychopathic traits reduce treatment responsiveness and increase the likelihood of recidivism, and it is therefore important to understand the factors underlying the propensity to engage in criminal behavior.

White Matter Abnormalities Based on TBSS and Its Correlation With Impulsivity Behavior of Methamphetamine Addicts

BACKGROUND

Methamphetamine (MA) abuse is one of the most rapidly growing illicit drug problems worldwide. Impulsivity has been considered as a core impairment underpinning addictive behavior. Studies have demonstrated that MA addicts have white matter abnormalities based on ROIs. There are few studies on whole brain, and the association between whole brain tracts and impulsivity in MA dependence remain unclear. Tract-based spatial statistics (TBSS) was used to detect four DTI measures, and these were correlated with the Barratt Impulsivity Scale (BIS) to verify and expand the previous results.

METHODS

A total of 28 MA addicts and 22 healthy controls were recruited. MRI was performed to evaluate the brain structural changes, the BIS was used to evaluate impulsivity behavior, white matter differences were compared between MA addicts and healthy controls, and then determine correlation between diffusion parameters and BIS scores.

RESULTS

MA addicts had significantly lower FA, and higher AD, RD, and MD in a wide range of white matter, which mainly included: corona radiata, internal capsule, superior longitudinal fasciculus, external capsule, inferior fronto-occipital fascicules, posterior thalamic radiation, sagittal stratum, fornix and stria terminalis, cerebral peduncle, superior cerebellar peduncle, corpus callosum, and corticolspinal tract compared with controls. The MA group had significantly higher total score, attention and motor scores compared to healthy controls. Higher MD in the right corticospinal tract was significantly associated with higher total scores.

CONCLUSION

MA addicts exhibit a globally diminished white matter integrity. furthermore, they present with high levels of impulsivity, and this dysfunction is associated with MD in corticospinal tracts. Future studies on larger sample sizes, gender effects and longitudinal studies are needed.

Dopamine D1 and D2 Receptors Differentially Regulate Rac1 and Cdc42 Signaling in the Nucleus Accumbens to Modulate Behavioral and Structural Plasticity After Repeated Methamphetamine Treatment

BACKGROUND

Methamphetamine (METH) is a highly addictive psychostimulant that strongly activates dopamine receptor signaling in the nucleus accumbens (NAc). However, how dopamine D₁ and D₂ receptors (D₁Rs and D₂Rs, respectively) as well as downstream signaling pathways, such as those involving Rac1 and Cdc42, modulate METH-induced behavioral and structural plasticity is largely unknown.

METHODS

Using NAc conditional D₁R and D₂R deletion mice, Rac1 and Cdc42 mutant viruses, and a series of behavioral and morphological methods, we assessed the effects of D₁Rs and D₂Rs on Rac1 and Cdc42 in modulating METH-induced behavioral and structural plasticity in the NAc.

RESULTS

D₁Rs and D₂Rs in the NAc consistently regulated METH-induced conditioned place preference, locomotor activation, and dendritic and spine remodeling of medium spiny neurons but differentially regulated METH withdrawal-induced spatial learning and memory impairment and anxiety. Interestingly, Rac1 and Cdc42 signaling were oppositely modulated by METH, and suppression of Rac1 signaling and activation of Cdc42 signaling were crucial to METH-induced conditioned place preference and structural plasticity but not to locomotor activation. D₁Rs activated Rac1 and Cdc42 signaling, while D₂Rs inhibited Rac1 signaling but activated Cdc42 signaling to mediate METH-induced conditioned place preference and structural plasticity but not locomotor activation. In addition, NAc D₁R deletion aggravated METH withdrawal-induced spatial learning and memory impairment by suppressing Rac1 signaling but not Cdc42 signaling, while NAc D₂R deletion aggravated METH withdrawal-induced anxiety without affecting Rac1 or Cdc42 signaling.

CONCLUSIONS

D₁Rs and D₂Rs differentially regulate Rac1 and Cdc42 signaling to modulate METH-induced behavioral plasticity and the structural remodeling of medium spiny neurons in the NAc.

Dopamine manipulations drive changes in information sampling in healthy volunteers

BACKGROUND

Information sampling is the cognitive process of accumulating information before committing to a decision. Patients across numerous disorders show decreased information sampling relative to controls.

AIMS

Here, we used the Beads and the Best Choice Tasks to study the role of dopamine signaling in information sampling.

METHODS

Participants were given placebo, amisulpride, or ropinirole in each session, in a double-blind cross-over design.

RESULTS

We found that ropinirole (agonist) increased the number of beads drawn in the Beads Task specifically when participants faced a loss, and decreased the rank of the chosen option in the Best Choice Task.

CONCLUSIONS

These effects are likely driven by a combination of effects at presynaptic D₂ receptors, which affect dopamine release, and post-synaptic D₂ receptors. Increased D₂ relative to D₁ receptor activation in the striatum leads to increased sampling in the loss condition in the Beads Task. It also leads to choice of a poorer ranked option in the Best Choice Task. Decreased D₂ relative to D₁ receptor activation leads to decreased sampling in the Beads Task in the loss condition.

Alterations in resting-state functional connectivity in substance use disorders and treatment implications

Substance use disorders (SUD) are diseases of the brain, characterized by aberrant functioning in the neural circuitry of the brain. Resting state functional connectivity (rsFC) can illuminate these functional changes by measuring the temporal coherence of low-frequency fluctuations of the blood oxygenation level-dependent magnetic resonance imaging signal in contiguous or non-contiguous regions of the brain. Because this data is easy to obtain and analyze, and therefore fairly inexpensive, it holds promise for defining biological treatment targets in SUD, which could help maximize the efficacy of existing clinical interventions and develop new ones. In an effort to identify the most likely "treatment targets" obtainable with rsFC we summarize existing research in SUD focused on 1) the relationships between rsFC and functionality within important psychological domains which are believed to underlie relapse vulnerability 2) changes in rsFC from satiety to deprived or abstinent states 3) baseline rsFC correlates of treatment outcome and 4) changes in rsFC induced by treatment interventions which improve clinical outcomes and reduce relapse risk. Converging evidence indicates that likely "treatment target" candidates, emerging consistently in all four sections, are reduced connectivity within executive control network (ECN) and between ECN and salience network (SN). Other potential treatment targets also show promise, but the literature is sparse and more research is needed. Future research directions include data-driven prediction analyses and rsFC analyses with longitudinal datasets that incorporate time since last use into analysis to account for drug withdrawal. Once the most reliable biological markers are identified, they can be used for treatment matching, during preliminary testing of new pharmacological compounds to establish clinical potential ("target engagement") prior to carrying out costly clinical trials, and for generating hypotheses for medication repurposing.

Mesolimbic Dopamine Function Is Related to Salience Network Connectivity: An Integrative Positron Emission Tomography and Magnetic Resonance Study

BACKGROUND

A wide range of neuropsychiatric disorders, from schizophrenia to drug addiction, involve abnormalities in both the mesolimbic dopamine system and the cortical salience network. Both systems play a key role in the detection of behaviorally relevant environmental stimuli. Although anatomical overlap exists, the functional relationship between these systems remains unknown. Preclinical research has suggested that the firing of mesolimbic dopamine neurons may activate nodes of the salience network, but in vivo human research is required given the species-specific nature of this network.

METHODS

We employed positron emission tomography to measure both dopamine release capacity (using the D2/3 receptor ligand 11C-PHNO, n = 23) and dopamine synthesis capacity (using 18F-DOPA, n = 21) within the ventral striatum. Resting-state functional magnetic resonance imaging was also undertaken in the same individuals to investigate salience network functional connectivity. A graph theoretical approach was used to characterize the relationship between dopamine measures and network connectivity.

RESULTS

Dopamine synthesis capacity was associated with greater salience network connectivity, and this relationship was particularly apparent for brain regions that act as information-processing hubs. In contrast, dopamine release capacity was associated with weaker salience network connectivity. There was no relationship between dopamine measures and visual and sensorimotor networks, indicating specificity of the findings.

CONCLUSIONS

Our findings demonstrate a close relationship between the salience network and mesolimbic dopamine system, and they are relevant to neuropsychiatric illnesses in which aberrant functioning of both systems has been observed.

Neuroinflammation in addiction: A review of neuroimaging studies and potential immunotherapies

Addiction is a worldwide public health problem and this article reviews scientific advances in identifying the role of neuroinflammation in the genesis, maintenance, and treatment of substance use disorders. With an emphasis on neuroimaging techniques, this review examines human studies of addiction using positron emission tomography to identify binding of translocator protein (TSPO), which is upregulated in reactive glial cells and activated microglia during pathological states. High TSPO levels have been shown in methamphetamine use but exhibits variable patterns in cocaine use. Alcohol and nicotine use, however, are associated with lower TSPO levels. We discuss how mechanistic differences at the neurotransmitter and circuit level in the neural effects of these agents and subsequent immune response may explain these observations. Finally, we review the potential of anti-inflammatory drugs, including ibudilast, minocycline, and pioglitazone, to ameliorate the behavioral and cognitive consequences of addiction.

Methamphetamine use and cognitive function: A systematic review of neuroimaging research

BACKGROUND

Long-term use of MA has been associated with cognitive dysfunction in several domains. Neuroimaging studies have also reported structural, metabolic, and functional changes in MA users. However, no systematic review has been conducted on those studies in MA users that combined neuroimaging and cognitive tasks.

METHODS

This article systematically reviews correlation between brain imaging measures and cognitive performance in subjects with current and previous history of MA use. Findings are categorized based on cognitive domain.

RESULTS

MA users performed more poorly than controls in all cognitive domains (psychomotor, working memory, attention, cognitive control, and decision- making) and a positive correlation has been repeatedly observed between performance and brain measures (regional volume/density, blood flow, glucose metabolism, FA value, NAA level, and activation) in MA users. Performance in cognitive control was consistently reported to show relationship with brain measures in the PFC and ACC, while decision- making consistently showed correlation with brain measures in the PFC, ACC, and striatum.

CONCLUSIONS

There is solid evidence for brain- behavior relationship in cognitive functioning in MA users, particularly in cognitive control and decision-making. More research with correlation analysis between brain-behavior and MA use parameters is strongly encouraged.

A preliminary randomized clinical trial of naltrexone reduces striatal resting state functional connectivity in people with methamphetamine use disorder

OBJECTIVE

Naltrexone has been shown to attenuate craving and the subjective effects of methamphetamine. Although naltrexone has modulatory effects on neural activity at dopaminergic synapses, the effect on striatal connectivity is unclear. As methamphetamine use is associated with greater resting-state functional connectivity (RSFC) in the dopaminergic system, we examined whether extended-release naltrexone (XR-NTX) can normalize striatal connectivity and whether changes in RSFC are associated with changes in craving and methamphetamine use.

METHODS

Thirty-seven participants in or seeking treatment for methamphetamine use disorder took part in this clinical trial at a university-based research clinic between May 2013 and March 2015 (Clinicaltrials.gov NCT01822132). Participants were randomized by a random number generator to a single four-week injection of XR-NTX or placebo. Functional magnetic resonance imaging (fMRI) and self-reported measures of craving and methamphetamine use were conducted before and after double-blinded randomization.

FINDINGS

There was a significant reduction in methamphetamine use in the naltrexone group and a significant treatment-by-time interaction on RSFC between the ventral striatum, amygdala, hippocampus, and midbrain. Connectivity was significantly reduced over time in participants randomized to naltrexone but unchanged in those randomized to placebo (p < 0.05, whole-brain corrected). Interactions between treatment and changes in connectivity show that significant reductions in connectivity were associated with reductions in methamphetamine use.

CONCLUSIONS

Neurobiological deficits associated with methamphetamine use may undermine the efficacy of pharmacotherapies that directly target the dopamine reward system. Naltrexone, via antagonism of indirect mu-opioid effects on dopamine neurons, may attenuate reward system connectivity and aid in methamphetamine use treatment.

The neurobiology of impulsivity and substance use disorders: implications for treatment

Impulsivity is strongly associated with substance use disorders (SUDs). Our review discusses impulsivity as an underlying vulnerability marker for SUDs, and treatment of co-occurring impulsivity in SUDs. Three factors should be considered for the complex relationship between impulsivity and a SUD: (1) the trait effect of impulsivity, centering on decreased cognitive and response inhibition, (2) the state effect resulting from either acute or chronic substance use on brain structure and function, and (3) the genetic and environmental factors (e.g., age and sex) may influence impulsive behavior associated with SUDs. Both subjective and objective measures are used to assess impulsivity. Together, treatment developments (pharmacological, behavioral, and neurophysiological) should consider these clinically relevant dimensions assessed by a variety of measures, which have implications for treatment matching in individuals with SUD. Despite its heterogeneity, impulsivity is a marker associated with SUDs and may be understood as an imbalance of bottom-up and top-down neural systems. Further investigation of these relationships may lead to more effective SUD treatments.

Altered functional connectivity of the default mode network by glucose loading in young, healthy participants

Background

The functional connectivity of the default mode network (DMN) decreases in patients with Alzheimer’s disease (AD) as well as in patients with type 2 diabetes mellitus (T2DM). Altered functional connectivity of the DMN is associated with cognitive impairment. T2DM is a known cause of cognitive dysfunction and dementia in the elderly, and studies have established that T2DM is a risk factor for AD. In addition, recent studies with positron emission tomography demonstrated that increased plasma glucose levels decrease neuronal activity, especially in the precuneus/posterior cingulate cortex (PC/PCC), which is the functional core of the DMN. These findings prompt the question of how increased plasma glucose levels decrease neuronal activity in the PC/PCC. Given the association among DMN, AD, and T2DM, we hypothesized that increased plasma glucose levels decrease the DMN functional connectivity, thus possibly reducing PC/PCC neuronal activity. We conducted this study to test this hypothesis.

Results

Twelve young, healthy participants without T2DM and insulin resistance were enrolled in this study. Each participant underwent resting-state functional magnetic resonance imaging in both fasting and glucose loading conditions to evaluate the DMN functional connectivity. The results showed that the DMN functional connectivity in the PC/PCC was significantly lower in the glucose loading condition than in the fasting condition (P = 0.014).

Conclusions

Together with previous findings, the present results suggest that decreased functional connectivity of the DMN is possibly responsible for reduced PC/PCC neuronal activity in healthy individuals with increased plasma glucose levels.

The relationship between interleukin-6 and functional connectivity in methamphetamine users

Methamphetamine (MA) causes an increase in pro-inflammatory cytokines in animal models and in humans. Resulting activation of microglia and neuro-inflammation could, via effects on reward networks, mediate behavioral characteristics of addiction. We examined the relationship between interleukin-6 (IL-6) and corticolimbic and striatolimbic resting-state functional connectivity (RSFC). Thirty adults diagnosed with MA dependence and 20 control subjects underwent a resting-state functional magnetic resonance imaging (fMRI) scan and gave a blood sample for determination of plasma IL-6 levels. Seed-based RSFC analyses were performed to examine the interactive effect of group and IL-6 on ventral striatal and prefrontal connectivity. Within the MA group, IL-6 levels were positively related to striatolimbic RSFC but negatively related to corticostriatal RSFC. Our findings with IL-6 support the idea that inflammation may at least partly mediate the link among MA use disorder, RSFC, and behavior, possibly via effects on mesolimbic and mesocortical dopaminergic systems.

Brain Renin-Angiotensin System Blockade Attenuates Methamphetamine-Induced Hyperlocomotion and Neurotoxicity

Methamphetamine (METH) abuse has become a major public health concern worldwide without approved pharmacotherapies. The brain renin-angiotensin system (RAS) is involved in the regulation of neuronal function as well as neurological disorders. Angiotensin II (Ang II), which interacts with Ang II type 1 receptor (AT1-R) in the brain, plays an important role as a neuromodulator in dopaminergic transmission. However, the role of brain RAS in METH-induced behavior is largely unknown. Here, we revealed that repeated METH administration significantly upregulated the expression of AT1-R in the striatum of mice, but downregulated dopamine D3 receptor (D3R) expression. A specific AT1-R blocker telmisartan, which can penetrate the brain-blood barrier (BBB), or genetic deletion of AT1-R was sufficient to attenuate METH-triggered hyperlocomotion in mice. However, intraperitoneal injection of AT1-R blocker losartan, which cannot penetrate BBB, failed to attenuate METH-induced behavior. Moreover, intra-striatum re-expression of AT1 with lentiviral virus expressing AT1 reversed the weakened locomotor activity of AT1-/- mice treated with METH. Losartan alleviated METH-induced cytotoxicity in SH-SY5Y cells in vitro, which was accompanied by upregulated expressions of D3R and dopamine transporter. In addition, intraperitoneal injection of perindopril, which is a specific ACE inhibitor and can penetrate BBB, significantly attenuated METH-induced hyperlocomotor activity. Collectively, our results show that blockade of brain RAS attenuates METH-induced hyperlocomotion and neurotoxicity possibly through modulation of D3R expression. Our findings reveal a novel role of Ang II-AT1-R in METH-induced hyperlocomotion.

Abstinence to chronic methamphetamine switches connectivity between striatal, hippocampal and sensorimotor regions and increases cerebral blood volume response

Methamphetamine (meth), and other psychostimulants such as cocaine, present a persistent problem for society with chronic users being highly prone to relapse. We show, in a chronic methamphetamine administration model, that discontinuation of drug for more than a week produces much larger changes in overall meth-induced brain connectivity and cerebral blood volume (CBV) response than changes that occur immediately following meth administration. Areas showing the largest changes were hippocampal, limbic striatum and sensorimotor cortical regions as well as brain stem areas including the pedunculopontine tegmentum (PPTg) and pontine nuclei - regions known to be important in mediating reinstatement of drug-taking after abstinence. These changes occur concomitantly with behavioral sensitization and appear to be mediated through increases in dopamine D1 and D3 and decreases in D2 receptor protein and mRNA expression. We further identify a novel region of dorsal caudate/putamen, with a low density of calbindin neurons, that has an opposite hemodynamic response to meth than the rest of the caudate/putamen and accumbens and shows very strong correlation with dorsal CA1 and CA3 hippocampus. This correlation switches following meth abstinence from CA1/CA3 to strong connections with ventral hippocampus (ventral subiculum) and nucleus accumbens. These data provide novel evidence for temporal alterations in brain connectivity where chronic meth can subvert hippocampal - striatal interactions from cognitive control regions to regions that mediate drug reinstatement. Our results also demonstrate that the signs and magnitudes of the induced CBV changes following challenge with meth or a D3-preferring agonist are a complementary read out of the relative changes that occur in D1, D2 and D3 receptors using protein or mRNA levels.

Steep effort discounting of a preferred reward over a freely-available option in prolonged methamphetamine withdrawal in male rats

RATIONALE

Drug addiction can be described as aberrant allocation of effort toward acquiring drug, despite associated costs. It is unclear if this behavioral pattern results from an overvaluation of reward or to an altered sensitivity to costs.

OBJECTIVE

Present experiments assessed reward sensitivity and effortful choice in rats following 1 week of withdrawal from methamphetamine (mAMPH).

METHODS

Rats were treated with either saline or an escalating dose mAMPH regimen, then tested after a week without the drug. In experiment 1, rats were given a free choice between water and various concentrations of sucrose solution to assess general reward sensitivity. In experiment 2, rats were presented with a choice between lever-pressing for sucrose pellets on a progressive ratio schedule or consuming freely-available chow.

RESULTS

In experiment 1, we found no differences in sucrose preference between mAMPH- and saline-pretreated rats. In experiment 2, when selecting between two options, mAMPH-pretreated rats engaged in less lever-pressing for sucrose pellets (p < 0.01) and switched from this preferred reward to the chow sooner than saline-pretreated rats (p < 0.05). This effect was not consistent with general reward devaluation or loss of motivation.

CONCLUSIONS

These findings demonstrate that mAMPH exposure and withdrawal lead to steeper discounting of reward value by effort, an effect that is consistent with the effect of mAMPH on discounting by delay, and which may reflect an underlying shared mechanism.

Abnormal fronto-limbic engagement in incarcerated stimulant users during moral processing

RATIONALE

Stimulant use is a significant and prevalent problem, particularly in criminal populations. Previous studies found that cocaine and methamphetamine use is related to impairment in identifying emotions and empathy. Stimulant users also have abnormal neural structure and function of the ventromedial prefrontal cortex (vmPFC), amygdala, and anterior (ACC) and posterior cingulate (PCC), regions implicated in moral decision-making. However, no research has studied the neural correlates of stimulant use and explicit moral processing in an incarcerated population.

OBJECTIVES

Here, we examine how stimulant use affects sociomoral processing that might contribute to antisocial behavior. We predicted that vmPFC, amygdala, PCC, and ACC would show abnormal neural response during a moral processing task in incarcerated methamphetamine and cocaine users.

METHODS

Incarcerated adult males (N = 211) were scanned with a mobile MRI system while completing a moral decision-making task. Lifetime drug use was assessed. Neural responses during moral processing were compared between users and non-users. The relationship between duration of use and neural function was also examined.

RESULTS

Incarcerated stimulant users showed less amygdala engagement than non-users during moral processing. Duration of stimulant use was negatively associated with activity in ACC and positively associated with vmPFC response during moral processing.

CONCLUSIONS

These results suggest a dynamic pattern of fronto-limbic moral processing related to stimulant use with deficits in both central motive and cognitive integration elements of biological moral processes theory. This increases our understanding of how drug use relates to moral processing in the brain in an ultra-high-risk population.