Lower Fractional Anisotropy in the Gray Matter of Amygdala-Hippocampus-Nucleus Accumbens Circuit in Methamphetamine Users: an In Vivo Diffusion Tensor Imaging Study

Imaging neuroinflammation in individuals with substance use disorders

Increasing evidence suggests a role of neuroinflammation in substance use disorders (SUDs). This Review presents findings from neuroimaging studies assessing brain markers of inflammation in vivo in individuals with SUDs. Most studies investigated the translocator protein 18 kDa (TSPO) using PET; neuroimmune markers myo-inositol, choline-containing compounds, and N-acetyl aspartate using magnetic resonance spectroscopy; and fractional anisotropy using MRI. Study findings have contributed to a greater understanding of neuroimmune function in the pathophysiology of SUDs, including its temporal dynamics (i.e., acute versus chronic substance use) and new targets for SUD treatment.

Adolescent substance use initiation and long-term neurobiological outcomes: insights, challenges and opportunities

The increased frequency of risk taking behavior combined with marked neuromaturation has positioned adolescence as a focal point of research into the neural causes and consequences of substance use. However, little work has provided a summary of the links between adolescent initiated substance use and longer-term brain outcomes. Here we review studies exploring the long-term effects of adolescent-initiated substance use with structural and microstructural neuroimaging. A quarter of all studies reviewed conducted repeated neuroimaging assessments. Long-term alcohol use, as well as tobacco use were consistently associated with smaller frontal cortices and altered white matter microstructure. This association was mostly observed in the ACC, insula and subcortical regions in alcohol users, and for the OFC in tobacco users. Long-term cannabis use was mostly related to altered frontal cortices and hippocampal volumes. Interestingly, cannabis users scanned more years after use initiation tended to show smaller measures of these regions, whereas those with fewer years since initiation showed larger measures. Long-term stimulant use tended to show a similar trend as cannabis in terms of years since initiation in measures of the putamen, insula and frontal cortex. Long-term opioid use was mostly associated with smaller subcortical and insular volumes. Of note, null findings were reported in all substance use categories, most often in cannabis use studies. In the context of the large variety in study designs, substance use assessment, methods, and sample characteristics, we provide recommendations on how to interpret these findings, and considerations for future studies.

Hyperconnectivity of the lateral amygdala in long-term methamphetamine abstainers negatively correlated with withdrawal duration

Introduction: Several studies have reported structural and functional abnormalities of the amygdala caused by methamphetamine addiction. However, it is unknown whether abnormalities in amygdala function persist in long-term methamphetamine abstainers. Methods: In this study, 38 long-term male methamphetamine abstainers (>12 months) and 40 demographically matched male healthy controls (HCs) were recruited. Considering the heterogeneous nature of the amygdala structure and function, we chose 4 amygdala subregions (i.e., left lateral, left medial, right lateral, and right medial) as regions of interest (ROI) and compared the ROI-based resting-state functional connectivity (FC) at the whole-brain voxel-wise between the two groups. We explored the relationship between the detected abnormal connectivity, methamphetamine use factors, and the duration of withdrawal using correlation analyses. We also examined the effect of methamphetamine use factors, months of withdrawal, and sociodemographic data on detected abnormal connectivity through multiple linear regressions. Results: Compared with HCs, long-term methamphetamine abstainers showed significant hyperconnectivity between the left lateral amygdala and a continuous area extending to the left inferior/middle occipital gyrus and left middle/superior temporal gyrus. Abnormal connections negatively correlated with methamphetamine withdrawal time (r = -0.85, p < 0.001). The linear regression model further demonstrated that the months of withdrawal could identify the abnormal connectivity (βadj = -0.86, 95%CI: -1.06 to -0.65, p < 0.001). Discussion: The use of methamphetamine can impair the neural sensory system, including the visual and auditory systems, but this abnormal connectivity can gradually recover after prolonged withdrawal of methamphetamine. From a neuroimaging perspective, our results suggest that withdrawal is an effective treatment for methamphetamine.

Aberrant topology of white matter networks in patients with methamphetamine dependence and its application in support vector machine-based classification

Brain white matter (WM) networks have been widely studied in neuropsychiatric disorders. However, few studies have evaluated alterations in WM network topological organization in patients with methamphetamine (MA) dependence. Therefore, using machine learning classification methods to analyze WM network topological attributes may give new insights into patients with MA dependence. In the study, diffusion tensor imaging-based probabilistic tractography was used to map the weighted WM networks in 46 MA-dependent patients and 46 control subjects. Using graph-theoretical analyses, the global and regional topological attributes of WM networks for both groups were calculated and compared to determine inter-group differences using a permutation-based general linear model. In addition, the study used a support vector machine (SVM) learning approach to construct a classifier for discriminating subjects with MA dependence from control subjects. Relative to the control group, the MA-dependent group exhibited abnormal topological organization, as evidenced by decreased small-worldness and modularity, and increased nodal efficiency in the right medial superior temporal gyrus, right pallidum, and right ventromedial putamen; the MA-dependent group had the higher hubness scores in 25 regions, which were mainly located in the default mode network. An SVM trained with topological attributes achieved classification accuracy, sensitivity, specificity, and kappa values of 98.09% ± 2.59%, 98.24% ± 4.00%, 97.94% ± 4.26%, and 96.18% ± 5.19% for patients with MA dependence. Our results may suggest altered global WM structural networks in MA-dependent patients. Furthermore, the abnormal WM network topological attributes may provide promising features for the construction of high-efficacy classification models.

Nucleus accumbens: a systematic review of neural circuitry and clinical studies in healthy and pathological states

OBJECTIVE

The nucleus accumbens (NAcc) of the ventral striatum is critically involved in goal- and reward-based behavior. Structural and functional abnormalities of the NAcc or its associated neural systems are involved in neurological and psychiatric disorders. Studies of neural circuitry have shed light on the subtleties of the structural and functional derangements of the NAcc across various diseases. In this systematic review, the authors sought to identify human studies involving the NAcc and provide a synthesis of the literature on the known circuity of the NAcc in healthy and diseased states, as well as the clinical outcomes following neuromodulation.

METHODS

A systematic review was conducted using the PubMed, Embase, and Scopus databases. Neuroimaging studies that reported on neural circuitry related to the human NAcc with sample sizes greater than 5 patients were included. Demographic data, aim, design and duration, participants, and clinical and neurocircuitry details and outcomes of the studies were extracted.

RESULTS

Of 3591 resultant articles, 123 were included. The NAcc and its corticolimbic connections to other brain regions, such as the prefrontal cortex, are largely involved in reward and pain processes, with distinct functional circuitry between the shell and core in healthy patients. There is heterogeneity between clinical studies with regard to the NAcc indirect targeting coordinates, methods for postoperative confirmation, and blinded trial design. Neuromodulation studies provided promising clinical results in the context of addiction and substance misuse, obsessive-compulsive disorder, and mood disorders. The most common complications were impaired memory or concentration, and a notable serious complication was hypomania.

CONCLUSIONS

The functional diversity of the NAcc highlights the importance of studying the NAcc in healthy and pathological states. The results of this review suggest that NAcc neuromodulation has been attempted in the management of diverse psychiatric indications. There is promising, emerging evidence that the NAcc may be an effective target for specific reward- or pain-based pathologies with a reasonable risk profile.

Amygdala Structural Connectivity Is Associated With Impulsive Choice and Difficulty Quitting Smoking

Introduction: The amygdala is known to play a role in mediating emotion and possibly addiction. We used probabilistic tractography (PT) to evaluate whether structural connectivity of the amygdala to the brain reward network is associated with impulsive choice and tobacco smoking.

Methods: Diffusion and structural MRI scans were obtained from 197 healthy subjects (45 with a history of tobacco smoking) randomly sampled from the Human Connectome database. PT was performed to assess amygdala connectivity with several brain regions. Seed masks were generated, and statistical maps of amygdala connectivity were derived. Connectivity results were correlated with a subject performance both on a delayed discounting task and whether they met specified criteria for difficulty quitting smoking.

Results: Amygdala connectivity was spatially segregated, with the strongest connectivity to the hippocampus, orbitofrontal cortex (OFC), and brainstem. Connectivity with the hippocampus was associated with preference for larger delayed rewards, whereas connectivity with the OFC, rostral anterior cingulate cortex (rACC), and insula were associated with preference for smaller immediate rewards. Greater nicotine dependence with difficulty quitting was associated with less hippocampal and greater brainstem connectivity. Scores on the Fagerstrom Test for Nicotine Dependence (FTND) correlated with rACC connectivity.

Discussion: These findings highlight the importance of the amygdala-hippocampal-ACC network in the valuation of future rewards and substance dependence. These results will help to identify potential targets for neuromodulatory therapies for addiction and related disorders.

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.

Short communication: Diffusion tensor anisotropy in the cingulate in borderline and schizotypal personality disorder

Despite considerable phenomentological differences between borderline personality disorder (BPD) and schizotypal personality disorder (SPD), research increasingly provides evidence that some BPD symptoms overlap with SPD symptoms (e.g., disturbed cognitions). We examined the cingulate, a brain region implicated in the pathophysiology of both disorders, to determine similarities/differences between the groups, and similarities/differences from healthy controls (HC's). 3T structural and diffusion tensor magnetic resonance imaging scans were acquired in BPD (n = 27), SPD (n = 32), HC's (n = 34). Results revealed that BPD patients exhibited significantly lower FA in posterior cingulate white matter compared to HC's (p = 0.04), but SPD patients did not.

Methamphetamine-associated psychosis: Clinical presentation, biological basis, and treatment options

INTRODUCTION

Methamphetamine associated psychosis (MAP) represents a mental disorder induced by chronic methamphetamine use in a subset of users. The prevalence of the disorder has increased in several countries in Europe and Asia where methamphetamine use has increased. MAP remains difficult to distinguish from primary psychiatric disorders, especially schizophrenia, creating complications in prescribing treatment plans to patients.

DESIGN

This narrative review sought to summarize difficulties related to MAP diagnosis and highlight the need for a better treatment model. Current best practices are described and potential novel therapies and future research suggested.

RESULTS

Results suggest that clear biological and clinical differences appear between patients presenting with MAP and schizophrenia and that there may exist distinct subgroups within MAP itself. MAP-specific treatment studies have been few and have focused on the use of antipsychotic medication. Antipsychotic treatment has been shown to alleviate the psychotic symptoms of MAP but produce debilitating adverse effects and fail to adequately address methamphetamine use in patients.

CONCLUSIONS

Continued identification of subgroups within the heterogenous MAP population may lead to better diagnosis, treatment, and outcomes for patients. Psychosocial therapies should be explored in addressing the cooccurring substance use and psychosis in the treatment of MAP.

Effects of low-level sarin and cyclosarin exposure on hippocampal microstructure in Gulf War Veterans

In early March 1991, shortly after the end of the Gulf War (GW), a munitions dump was destroyed at Khamisiyah, Iraq. Later, in 1996, the dump was found to have contained the organophosphorus (OP) nerve agents sarin and cyclosarin. We previously reported evidence of smaller hippocampal volumes in GW veterans with predicted exposure to the Khamisiyah plume compared to unexposed GW veterans. To investigate whether these macroscopic hippocampal volume changes are accompanied by microstructural alterations in the hippocampus, the current study acquired diffusion-tensor imaging (DTI), T1-, and T2-weighted images from 170 GW veterans (mean age: 53 ± 7 years), 81 of whom had predicted exposure to the Khamisiyah plume according to Department of Defense (DOD) plume modeling. We examined fractional anisotropy (FA), mean diffusivity (MD), and grey matter (GM) density from a hippocampal region of interest (ROI). Results indicate that, even after accounting for total hippocampal GM density (or hippocampal volume), age, sex, apolipoprotein ε4 genotype, and potential confounding OP pesticide exposures, hippocampal MD significantly predicted Khamisiyah exposure status (model p = 0.005, R² = 0.215, standardized coefficient β = 0.26, t = 2.85). Hippocampal MD was also inversely correlated with verbal memory learning performance in the entire study sample (p = 0.001). There were no differences in hippocampal FA or GM density; however, veterans with predicted Khamisiyah exposure had smaller hippocampal volumes compared to unexposed veterans. Because MD is sensitive to general microstructural disruptions that lead to increased extracellular spaces due to neuronal death, inflammation and gliosis, and/or to axonal loss or demyelination, these findings suggest that low-level exposure to the Khamisiyah plume has a detrimental, lasting effects on both macro- and micro-structure of the hippocampus.