White-matter crossing-fiber microstructure in adolescents prenatally exposed to cocaine

White matter microstructure alterations in idiopathic restless legs syndrome: a study combining crossing fiber-based and tensor-based approaches

Introduction

Restless legs syndrome (RLS) is a common sensorimotor disorder characterized by an irrepressible urge to move the legs and frequently accompanied by unpleasant sensations in the legs. The pathophysiological mechanisms underlying RLS remain unclear, and RLS is hypothesized to be associated with alterations in white matter tracts.

Methods

Diffusion MRI is a unique noninvasive method widely used to study white matter tracts in the human brain. Thus, diffusion-weighted images were acquired from 18 idiopathic RLS patients and 31 age- and sex-matched healthy controls (HCs). Whole brain tract-based spatial statistics (TBSS) and atlas-based analyzes combining crossing fiber-based metrics and tensor-based metrics were performed to investigate the white matter patterns in individuals with RLS.

Results

TBSS analysis revealed significantly higher fractional anisotropy (FA) and partial volume fraction of primary (F1) fiber populations in multiple tracts associated with the sensorimotor network in patients with RLS than in HCs. In the atlas based analysis, the bilateral anterior thalamus radiation, bilateral corticospinal tract, bilateral inferior fronto-occipital fasciculus, left hippocampal cingulum, left inferior longitudinal fasciculus, and left uncinate fasciculus showed significantl increased F1, but only the left hippocampal cingulum showed significantly higher FA.

Discussion

The results demonstrated that F1 identified extensive alterations in white matter tracts compared with FA and confirmed the hypothesis that crossing fiber-based metrics are more sensitive than tensor-based metrics in detecting white matter abnormalities in RLS. The present findings provide evidence that the increased F1 metric observed in sensorimotor tracts may be a critical neural substrate of RLS, enhancing our understanding of the underlying pathological changes.

Neurite orientation dispersion and density imaging in cocaine use disorder

Cocaine use disorder (CUD) is characterized by a compulsive search for cocaine. Several studies have shown that cocaine users exhibit cognitive deficits, including lack of inhibition and decision-making as well as brain volume and diffusion-based white-matter alterations in a wide variety of brain regions. However, the non-specificity of standard volumetric and diffusion-tensor methods to detect structural micropathology may lead to wrong conclusions. To better understand microstructural pathology in CUD, we analyzed 60 CUD participants (3 female) and 43 non-CUD controls (HC; 2 female) retrospectively from our cross-sectional Mexican SUD neuroimaging dataset (SUDMEX-CONN), using multi-shell diffusion-weighted imaging and the neurite orientation dispersion and density imaging (NODDI) analysis, which aims to more accurately model microstructural pathology. We used Viso values of NODDI that employ a three-compartment model in white (WM) and gray-matter (GM). These values were also correlated with clinical measures, including psychiatric severity status, impulsive behavior and pattern of cocaine and tobacco use in the CUD group. We found higher whole-brain microstructural pathology in WM and GM in CUD patients than controls. ROI analysis revealed higher Viso-NODDI values in superior longitudinal fasciculus, cingulum, hippocampus cingulum, forceps minor and Uncinate fasciculus, as well as in frontal and parieto-temporal GM structures. We also found correlations between significant ROI and impulsivity, onset age of cocaine use and weekly dosage with Viso-NODDI. However, we did not find correlations with psychopathology measures. Overall, although their clinical relevance remains questionable, microstructural pathology seems to be present in CUD both in gray and white matter.

Brain microstructural changes support cognitive deficits in HIV uninfected children born to HIV infected mothers

Introduction

Antiretroviral therapy (ART) is considered the most effective way to prevent perinatal transmission of human immunodeficiency virus (HIV). However, there is little knowledge about the effect of ART on the brain of HIV uninfected children born to HIV infected mothers (HUC). The current study evaluated the brain's microstructural integrity, and cognitive function in HUC compared to healthy children born to normal mothers (CHNM) and HIV infected children born to HIV infected mothers (HIC) to investigate the effect of in-utero exposure of ART on cerebral gray and white matter.

Materials and methods

Forty nine HIC, 12 HUC and 18 CHNM underwent neuropsychological (NP) assessment and a brain MRI. Diffusion tensor imaging (DTI) data was used to generate fractional anisotropy (FA) and mean diffusivity (MD) maps. Voxel wise comparison for FA and MD was performed between three groups using an analysis of covariance (ANCOVA) including age and sex as covariates, and correction for multiple comparisons (false discovery rate (FDR), p ​< ​0.05 with minimum extended cluster size, 150 voxels). NP test scores were also compared between three groups using ANOVA with Post Hoc Bonferroni multiple comparison corrections (p ​< ​0.05). Significantly changed FA and MD values in different brain regions in HIC and HUC compared to CHNM were used for correlation analysis with NP test scores using Pearson's correlation.

Results

HIC and HUC groups showed significantly decreased NP test scores in various domain compared to CHNM. Significantly lower NP test scores was observed in HIC than those of HUC. HIC showed decreased FA and increased MD in multiple brain sites as compared to both CHNM and HUC. Decreased FA along with both increased and decreased MD in different brain regions was present in HUC compared to CHNM. Both positive and negative correlation of altered FA and MD values from different brain regions in HIC and HUC with NP test scores was observed.

Conclusion

The presence of brain tissue changes and neurocognitive function deficit in absence of HIV infection in HUC indicates that ART may have a detrimental impact on the developing brain. The findings of the current study underscore the need for screening of ART exposed children for neurodevelopment and cognitive abnormalities at an early stage and call for access to early interventions, and nutritional and care programs.

Prenatal drug exposure from infancy through emerging adulthood: Results from neuroimaging

Prenatal drug exposure may have important repercussions across the lifespan for cognition and behavior. While alcohol is a recognized teratogen, the influences of other substances may also be substantial. The neural underpinnings of the influences of prenatal drug exposure have been examined using longitudinal approaches and multiple imaging techniques. Here we review the existing literature on the neural correlates of prenatal drug exposure. We focused the review on studies that have employed functional neuroimaging and electroencephalography and on substances other than alcohol. We also framed the review through the lens of four developmental life stages (infancy, childhood, adolescence and emerging adulthood). We included papers that have examined any drug use, including tobacco, opiates, cocaine, marijuana, methamphetamines, or polysubstance use. Data suggest that prenatal drug exposure has long-lasting, deleterious influences on cognition and reward processing in infancy and childhood that persist into adolescence and emerging adulthood and may underlie some behavioral tendencies, such as increased externalizing and risk-taking behaviors, seen in these groups.

Substance abuse and white matter: Findings, limitations, and future of diffusion tensor imaging research

Individuals who abuse substances often differ from nonusers in their brain structure. Substance abuse and addiction is often associated with atrophy and pathology of grey matter, but much less is known about the role of white matter, which constitutes over half of human brain volume. Diffusion tensor imaging (DTI), a method for non-invasively estimating white matter, is increasingly being used to study addiction and substance abuse. Here we review recent DTI studies of major substances of abuse (alcohol, opiates, cocaine, cannabis, and nicotine substance abuse) to examine the relationship, specificity, causality, and permanence of substance-related differences in white matter microstructure. Across substance, users tended to exhibit differences in the microstructure of major fiber pathways, such as the corpus callosum. The direction of these differences, however, appeared substance-dependent. The subsample of longitudinal studies reviewed suggests that substance abuse may cause changes in white matter, though it is unclear to what extent such alterations are permanent. While collectively informative, some studies reviewed were limited by methodological and technical approach. We therefore also provide methodological guidance for future research using DTI to study substance abuse.

Measures of possible allostatic load in comorbid cocaine and alcohol use disorder: Brain white matter integrity, telomere length, and anti-saccade performance

Chronic cocaine and alcohol use impart significant stress on biological and cognitive systems, resulting in changes consistent with an allostatic load model of neurocognitive impairment. The present study measured potential markers of allostatic load in individuals with comorbid cocaine/alcohol use disorders (CUD/AUD) and control subjects. Measures of brain white matter (WM), telomere length, and impulsivity/attentional bias were obtained. WM (CUD/AUD only) was indexed by diffusion tensor imaging metrics, including radial diffusivity (RD) and fractional anisotropy (FA). Telomere length was indexed by the telomere to single copy gene (T/S) ratio. Impulsivity and attentional bias to drug cues were measured via eye-tracking, and were also modeled using the Hierarchical Diffusion Drift Model (HDDM). Average whole-brain RD and FA were associated with years of cocaine use (R2 = 0.56 and 0.51, both p < .005) but not years of alcohol use. CUD/AUD subjects showed more anti-saccade errors (p < .01), greater attentional bias scores (p < .001), and higher HDDM drift rates on cocaine-cue trials (Bayesian probability CUD/AUD > control = p > 0.99). Telomere length was shorter in CUD/AUD, but the difference was not statistically significant. Within the CUD/AUD group, exploratory regression using an elastic-net model determined that more years of cocaine use, older age, larger HDDM drift rate differences and shorter telomere length were all predictive of WM as measured by RD (model R2 = 0.79). Collectively, the results provide modest support linking CUD/AUD to putative markers of allostatic load.

Substance-use initiation moderates the effect of stress on white-matter microstructure in adolescents

BACKGROUND

While childhood stress may contribute risk to substance-use initiation and differences in brain white-matter development, understanding of the potential impact of substance-use initiation on the relationship between experienced stress and white-matter microstructure remains limited.

OBJECTIVES

This study examined whether substance-use initiation moderated the effect of perceived stress on white-matter differences using measures of primary white-matter fiber anisotropy.

METHODS

Forty adolescents (age 14.75 ± .87 years) were assessed on the Perceived Stress Scale, and 50% were determined to have presence of substance-use initiation. White-matter microstructure was examined using primary-fiber orientations anisotropy, which may reflect white-matter integrity, modeled separately from other fiber orientations in the same voxels. Analyses were conducted on regions of interest previously associated with childhood stress and substance use.

RESULTS

Lower perceived stress and presence of substance-use initiation were related to greater right cingulum primary-fiber measures. Substance-use-initiation status moderated the association between perceived stress and right cingulum primary-fiber measures, such that higher perceived stress was associated with lower right cingulum primary-fiber anisotropy in adolescents without substance-use initiation, but not in those with substance-use initiation.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Findings in primary-fiber anisotropy suggest differences in right cingulum white-matter integrity is associated with substance-use initiation in higher-stress adolescents. This reflects a possible pre-existing risk factor, an impact of early substance use, or a combination thereof. Examination of potential markers associated with substance-use initiation in white-matter microstructure among stress-exposed youth warrant additional investigation as such biomarkers may inform efforts relating to tailored interventions. (Am J Addict 2018;27:217-224).

All Wrapped Up: Environmental Effects on Myelination

To date, studies have demonstrated the dynamic influence of exogenous environmental stimuli on multiple regions of the brain. This environmental influence positively and negatively impacts programs governing myelination, and acts on myelinating oligodendrocyte (OL) cells across the human lifespan. Developmentally, environmental manipulation of OL progenitor cells (OPCs) has profound effects on the establishment of functional cognitive, sensory, and motor programs. Furthermore, central nervous system (CNS) myelin remains an adaptive entity in adulthood, sensitive to environmentally induced structural changes. Here, we discuss the role of environmental stimuli on mechanisms governing programs of CNS myelination under normal and pathological conditions. Importantly, we highlight how these extrinsic cues can influence the intrinsic power of myelin plasticity to promote functional recovery.