Poorer frontolimbic white matter integrity is associated with chronic cannabis use, FAAH genotype, and increased depressive and apathy symptoms in adolescents and young adults

Acute effects of different types of cannabis on young adult and adolescent resting-state brain networks

Adolescence is a time of rapid neurodevelopment and the endocannabinoid system is particularly prone to change during this time. Cannabis is a commonly used drug with a particularly high prevalence of use among adolescents. The two predominant phytocannabinoids are Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), which affect the endocannabinoid system. It is unknown whether this period of rapid development makes adolescents more or less vulnerable to the effects of cannabis on brain-network connectivity, and whether CBD may attenuate the effects of THC. Using fMRI, we explored the impact of vaporized cannabis (placebo, THC: 8 mg/75 kg, THC + CBD: 8 mg/75 kg THC & 24 mg/75 kg CBD) on resting-state networks in groups of semi-regular cannabis users (usage frequency between 0.5 and 3 days/week), consisting of 22 adolescents (16-17 years) and 24 young adults (26-29 years) matched for cannabis use frequency. Cannabis caused reductions in within-network connectivity in the default mode (F[2,88] = 3.97, P = 0.022, η² = 0.018), executive control (F[2,88] = 18.62, P < 0.001, η² = 0.123), salience (F[2,88] = 12.12, P < 0.001, η² = 0.076), hippocampal (F[2,88] = 14.65, P < 0.001, η² = 0.087), and limbic striatal (F[2,88] = 16.19, P < 0.001, η² = 0.102) networks compared to placebo. Whole-brain analysis showed cannabis significantly disrupted functional connectivity with cortical regions and the executive control, salience, hippocampal, and limbic striatal networks compared to placebo. CBD did not counteract THC's effects and further reduced connectivity both within networks and the whole brain. While age-related differences were observed, there were no interactions between age group and cannabis treatment in any brain network. Overall, these results challenge the assumption that CBD can make cannabis safer, as CBD did not attenuate THC effects (and in some cases potentiated them); furthermore, they show that cannabis causes similar disruption to resting-state connectivity in the adolescent and adult brain.

Investigating sex differences and age of onset in emotion regulation, executive functioning, and cannabis use in adolescents and young adults

BACKGROUND

Young adults have historically high levels of cannabis use at a time which coincides with emotional and cognitive development. Age of regular onset of cannabis use and sex at birth are hypothesized to influence the relationship between cannabis use and cognition. Here we investigated past 6-month cannabis use in relation to emotional and executive functioning. We further considered age of onset and sex in subgroup analyses.

METHOD

Young adults (N = 225; ages 16-22) completed a substance use interview and cognitive battery, including the Emotional Word-Emotional Face Stroop and NIH toolbox executive functioning tasks. Linear regressions examined relationships between past 6-month cannabis use episodes and performance. Subgroup analyses investigated whether age of onset or sex impacted relationships.

RESULTS

After correcting for multiple comparisons, greater past 6-month cannabis use episodes were related to poorer Emotional Stroop Congruent Accuracy (p = .0004, FDR-p = .002) and List Sorting Working Memory (p = .02, FDR-p = .10) performance. Younger age of regular use onset marginally related to lower Emotional Stroop Congruent Accuracy performance (p = .03, FDR-p = .13). There were no cannabis use by sex interactions on cognition.

CONCLUSIONS

Consistent with prior findings, results suggest small reductions in cannabis-related performance in processing speed during emotional Stroop and working memory tasks. Age of onset was modestly related to Stroop performance, but not sex. Longitudinal studies which detail patterns of cannabis and other substance use are needed to better assess brain-behavior relationships and other factors (e.g., age of onset of regular use, sex) which could influence cannabis-related impairments in cognitive functioning.

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.

Sex Differences in Response-Contingent Cannabis Vapor Administration During Adolescence Mediate Enduring Effects on Behavioral Flexibility and Prefrontal Microglia Activation in Rats

Introduction: Cannabis is the most used illicit drug in the United States. With many states passing legislation to permit its recreational use, there is concern that cannabis use among adolescents could increase dramatically in the coming years. Historically, it has been difficult to model real-world cannabis use to investigate the causal relationship between cannabis use in adolescence and behavioral and neurobiological effects in adulthood. Materials and Methods: We used a response-contingent vapor administration model to investigate long-term effects of cannabis use during adolescence on the medial prefrontal cortex (mPFC) and mPFC-dependent behaviors in male and female rats. Results: Adolescent (35- to 55-day-old) female rats had significantly higher rates of responding for vaporized Δ9-tetrahydrocannabinol (THC)-dominant cannabis extract (CANTHC) compared with adolescent males. In adulthood (70-110 days old), female, but not male, CANTHC rats also took more trials to reach criterion and made more regressive errors in an automated attentional set-shifting task compared with vehicle rats, thereby indicating sex differences in behavioral flexibility impairments. Notably, sex-treatment interactions were not observed when rats of each sex were exposed to a noncontingent CANTHC vapor dosing regimen that approximated CANTHC vapor deliveries earned by females. No differences were observed in effort-based decision making in either sex. In the mPFC, female (but not male) CANTHC rats displayed more reactive microglia with no changes in myelin basic protein expression or dendritic spine density. Conclusion: Altogether, these data reveal important sex differences in rates of responding for CANTHC vapor in adolescence that may confer enduring alterations to mPFC structure and function and suggest that there may be subtle differences in the effects of response-contingent versus noncontingent cannabis exposure that should be systematically examined in future studies.

The First "Hit" to the Endocannabinoid System? Associations Between Prenatal Cannabis Exposure and Frontolimbic White Matter Pathways in Children

Background

Cannabis is the most used federally illicit substance among pregnant people in the United States. However, emerging preclinical data show that a significant portion of cannabis constituents, such as Δ9-tetrahydrocannabinol and its bioactive metabolites, readily cross the placenta and accumulate in the fetal brain, disrupting neurodevelopment. Recent research using the Adolescent Brain Cognitive Development (ABCD) Study cohort has linked prenatal cannabis exposure (PCE) to greater neurobehavioral problems and lower total gray and white matter volume in children. Here, we examined the impact of PCE on frontolimbic white matter pathways that are critical for cognitive- and emotion-related functioning, show a high density of cannabinoid receptors, and are susceptible to cannabis exposure during other periods of rapid neurodevelopment (e.g., adolescence).

Methods

This study included 11,530 children (mean ± SD age = 118.99 ± 7.49 months; 47% female) from the ABCD Study cohort. Linear mixed-effects models were used to examine the effects of caregiver-reported PCE on fractional anisotropy of 10 frontolimbic pathways (5 per hemisphere).

Results

PCE was associated with lower fractional anisotropy of the right (β = -0.005, p < .001) and left (β = -0.003, p = .007) fornix, and these results remained significant after adjusting for a variety of covariates, multiple comparisons, fractional anisotropy of all fibers, and using a quality-control cohort only.

Conclusions

In sum, we demonstrated small, yet reliable, effects of PCE on white matter integrity during childhood, particularly in the fornix, which plays a crucial role in emotion- and memory-related processes. Future studies are needed to understand the impacts of small changes in brain structure or function on neurodevelopment and risk of neurobehavioral problems.

FAAH rs324420 Polymorphism: Biological Pathways, Impact on Elite Athletic Performance and Insights for Sport Medicine

Gene variation linked to physiological functions is recognised to affect elite athletic performance by modulating training and competition-enabling behaviour. The fatty acid amide hydrolase (FAAH) has been investigated as a good candidate for drug targeting, and recently, its single-nucleotide polymorphism (SNP) rs324420 was reported to be associated with athletic performance. Given the implications, the biological pathways of this genetic polymorphism linked to elite athletic performance, considering sport type, psychological traits and sports injuries, need to be dissected. Thus, a narrative review of the literature concerning the biological mechanisms of this SNP was undertaken. In addition to its role in athletic performance, FAAH rs324420 is also involved in important mechanisms underlying human psychopathologies, including substance abuse and neural dysfunctions. However, cumulative evidence concerning the C385A variant is inconsistent. Therefore, validation studies considering homogeneous sports modalities are required to better define the role of this SNP in elite athletic performance and its impact on stress coping, pain regulation and inflammation control.

The long-term effects of adolescent Δ9-tetrahydrocannabinol on brain structure and function assessed through neuroimaging techniques in male and female rats

Several studies performed on human subjects have examined the effects of adolescent cannabis consumption on brain structure or function using brain imaging techniques. However, the evidence from these studies is usually heterogenous and affected by several confounding variables. Animal models of adolescent cannabinoid exposure may help to overcome these difficulties. In this exploratory study, we aim to increase our understanding of the protracted effects of adolescent Δ9-tetrahydrocannabinol (THC) in rats of both sexes using magnetic resonance (MR) to obtain volumetric data, assess grey and white matter microstructure with diffusion tensor imaging (DTI) and measure brain metabolites with 1H-MR spectroscopy (MRS); in addition, we studied brain function using positron emission tomography (PET) with 2-deoxy-2-[18F]fluoro-d-glucose as the tracer. THC-exposed rats exhibited volumetric and microstructural alterations in the striatum, globus pallidus, lateral ventricles, thalamus, and septal nuclei in a sex-specific manner. THC administration also reduced fractional anisotropy in several white matter tracts, prominently in rostral sections, while in vivo MRS identified lower levels of cortical choline compounds. THC-treated males had increased metabolism in the cerebellum and olfactory bulb and decreased metabolism in the cingulate cortex. By contrast, THC-treated females showed hypermetabolism in a cluster of voxels comprising the entorhinal piriform cortices and in the cingulate cortex. These results indicate that mild THC exposure during adolescence leaves a lingering mark on brain structure and function in a sex-dependant manner. Some of the changes found here resemble those observed in human studies and highlight the importance of studying sex-specific effects in cannabinoid research.

Combined exposure to alcohol and cannabis during development: Mechanisms and outcomes

Exposure to substances of abuse during pregnancy can have long-lasting effects on offspring. Alcohol is one of the most widely used substances of abuse that leads to the most severe consequences. Recent studies in the United States, Canada, and the United Kingdom showed that between 1% and 7% of all children exhibit signs and symptoms of fetal alcohol spectrum disorder (FASD). Despite preventive campaigns, the rate of children with FASD has not decreased during recent decades. Alcohol consumption often accompanies exposure to such drugs as tobacco, cocaine, opioids, and cannabis. These interactions can be synergistic and exacerbate the deleterious consequences of developmental alcohol exposure. The present review focuses on interactions between alcohol and cannabis exposure and the potential consequences of these interactions.

Measuring white matter microstructure in 1,457 cannabis users and 1,441 controls: A systematic review of diffusion-weighted MRI studies

INTRODUCTION

Cannabis is the most widely used regulated substance by youth and adults. Cannabis use has been associated with psychosocial problems, which have been partly ascribed to neurobiological changes. Emerging evidence to date from diffusion-MRI studies shows that cannabis users compared to controls show poorer integrity of white matter fibre tracts, which structurally connect distinct brain regions to facilitate neural communication. However, the most recent evidence from diffusion-MRI studies thus far has yet to be integrated. Therefore, it is unclear if white matter differences in cannabis users are evident consistently in selected locations, in specific diffusion-MRI metrics, and whether these differences in metrics are associated with cannabis exposure levels.

METHODS

We systematically reviewed the results from diffusion-MRI imaging studies that compared white matter differences between cannabis users and controls. We also examined the associations between cannabis exposure and other behavioral variables due to changes in white matter. Our review was pre-registered in PROSPERO (ID: 258250; https://www.crd.york.ac.uk/prospero/).

RESULTS

We identified 30 diffusion-MRI studies including 1,457 cannabis users and 1,441 controls aged 16-to-45 years. All but 6 studies reported group differences in white matter integrity. The most consistent differences between cannabis users and controls were lower fractional anisotropy within the arcuate/superior longitudinal fasciculus (7 studies), and lower fractional anisotropy of the corpus callosum (6 studies) as well as higher mean diffusivity and trace (4 studies). Differences in fractional anisotropy were associated with cannabis use onset (4 studies), especially in the corpus callosum (3 studies).

DISCUSSION

The mechanisms underscoring white matter differences are unclear, and they may include effects of cannabis use onset during youth, neurotoxic effects or neuro adaptations from regular exposure to tetrahydrocannabinol (THC), which exerts its effects by binding to brain receptors, or a neurobiological vulnerability predating the onset of cannabis use. Future multimodal neuroimaging studies, including recently developed advanced diffusion-MRI metrics, can be used to track cannabis users over time and to define with precision when and which region of the brain the white matter changes commence in youth cannabis users, and whether cessation of use recovers white matter differences.

SYSTEMATIC REVIEW REGISTRATION

www.crd.york.ac.uk/prospero/, identifier: 258250.

Sex differences in adolescent cannabis vapor self-administration mediate enduring effects on behavioral flexibility and prefrontal microglia activation in rats

Cannabis is the most used illicit drug in the United States. With many states passing legislation to permit its recreational use, there is concern that cannabis use among adolescents could increase dramatically in the coming years. Historically, it has been difficult to model real-world cannabis use to investigate the causal relationship between cannabis use in adolescence and behavioral and neurobiological effects in adulthood. To this end, we used a novel volitional vapor administration model to investigate long-term effects of cannabis use during adolescence on the medial prefrontal cortex (mPFC) and mPFC-dependent behaviors in male and female rats. Adolescent (35-55 day old) female rats had significantly higher rates of responding for vaporized Δ9-tetrahydrocannabinol (THC)-dominant cannabis extract (CANTHC) compared to adolescent males. In adulthood (70-110 day old), female, but not male, CANTHC rats also took more trials to reach criterion and made more regressive errors in an automated attentional set-shifting task compared to vehicle rats. Similar set-shifting deficits were observed in males when they were exposed to a non-contingent CANTHC vapor dosing regimen that approximated CANTHC self-administration rates in females. No differences were observed in effort-based decision making in either sex. In the mPFC, female (but not male) CANTHC rats displayed more reactive microglia with no significant changes in myelin basic protein expression or dendritic spine density. Together, these data reveal important sex differences in rates of cannabis vapor self-administration in adolescence that confer enduring alterations to mPFC structure and function. Importantly, female-specific deficits in behavioral flexibility appear to be driven by elevated rates of CANTHC self-administration as opposed to a sex difference in the effects of CANTHC vapor per se.

Enhancing axonal myelination in seniors: A review exploring the potential impact cannabis has on myelination in the aged brain

Consumption of cannabis is on the rise as public opinion trends toward acceptance and its consequent legalization. Specifically, the senior population is one of the demographics increasing their use of cannabis the fastest, but research aimed at understanding cannabis' impact on the aged brain is still scarce. Aging is characterized by many brain changes that slowly alter cognitive ability. One process that is greatly impacted during aging is axonal myelination. The slow degradation and loss of myelin (i.e., demyelination) in the brain with age has been shown to associate with cognitive decline and, furthermore, is a common characteristic of numerous neurological diseases experienced in aging. It is currently not known what causes this age-dependent degradation, but it is likely due to numerous confounding factors (i.e., heightened inflammation, reduced blood flow, cellular senescence) that impact the many cells responsible for maintaining overall homeostasis and myelin integrity. Importantly, animal studies using non-human primates and rodents have also revealed demyelination with age, providing a reliable model for researchers to try and understand the cellular mechanisms at play. In rodents, cannabis was recently shown to modulate the myelination process. Furthermore, studies looking at the direct modulatory impact cannabis has on microglia, astrocytes and oligodendrocyte lineage cells hint at potential mechanisms to prevent some of the more damaging activities performed by these cells that contribute to demyelination in aging. However, research focusing on how cannabis impacts myelination in the aged brain is lacking. Therefore, this review will explore the evidence thus far accumulated to show how cannabis impacts myelination and will extrapolate what this knowledge may mean for the aged brain.

Fatty acid amide hydrolase C385A polymorphism affects susceptibility to various diseases

The endocannabinoid (eCB) system is an important neuromodulatory system with its extensive network of receptors throughout the human body that has complex actions in the nervous system, immune system, and all of the body's other organs. Fatty acid amide hydrolase (FAAH) is an important membrane-bound homodimeric degrading enzyme that controls the biological activity of N-arachidonoylethanolamide (AEA) in the eCB system and other relevant bioactive lipids. It has been shown that several single nucleotide polymorphisms (SNPs) of FAAH are associated with various phenotypes and diseases including cardiovascular, endocrine, drug abuse, and neuropsychiatric disorders. A common functional and most studied polymorphism of this gene is C385A (rs324420), which results in the replacement of a conserved proline to threonine in the FAAH enzyme structure, leads to a reduction of the activity and expression of FAAH, compromises the inactivation of AEA and causes higher synaptic concentrations of AEA that can be associated with several various phenotypes. The focus of this review is on evidence-based studies on the associations of the FAAH C385A polymorphism and the various diseases or traits. Although there was variability in the results of these reports, the overall consensus is that the FAAH C385A genotype can affect susceptibility to some multifactorial disorders and can be considered a potential therapeutic target.

Increased White Matter Coherence Following Three and Six Months of Medical Cannabis Treatment

Background: Previous studies have demonstrated abnormal white matter (WM) microstructure in recreational cannabis consumers; however, the long-term impact of medical cannabis (MC) use on WM coherence is unknown. Accordingly, this study assessed the longitudinal impact of MC treatment on WM coherence. Given results from preclinical studies, we hypothesized that MC treatment would be associated with increased fractional anisotropy (FA) and reduced mean diffusivity (MD). Methods: As part of a larger, longitudinal investigation, patients interested in treating at least one medical condition with commercially available MC products of their choosing were assessed before initiating MC use (baseline n=37; female=25, male=12) and following three (n=31) and six (n=22) months of treatment. WM coherence was assessed via diffusion tensor imaging for bilateral regions of interest including the genu of the corpus callosum, anterior limb of the internal capsule, external capsule, and anterior corona radiata, as well as an occipital control region not expected to change over time. Results: In MC patients, FA values significantly increased bilaterally in several callosal regions relative to baseline following both 3 and 6 months of treatment; MD values significantly decreased in all callosal regions but only following 6 months of treatment. No significant changes in WM coherence were observed in the control region or in a pilot sample of treatment-as-usual patients (baseline n=14), suggesting that increased WM coherence observed in MC patients may be attributed to MC treatment as opposed to confounding factors. Interestingly, significant reductions in MD values correlated with higher cannabidiol (CBD) exposure but not Δ-9-tetrahydrocannabinol exposure. Conclusions: Overall, MC treatment was associated with increased WM coherence, which contrasts with prior research examining recreational cannabis consumers, likely related to inherent differences between recreational consumers and MC patients (e.g., product choice, age of onset). In addition, increased CBD exposure was associated with reduced MD following 6 months of treatment, extending evidence from preclinical research indicating that CBD may be neuroprotective against demyelination. However, additional research is needed to elucidate the clinical efficacy of MC treatment and the risks and benefits of long-term MC use.

Cannabis, connectivity, and coming of age: Associations between cannabis use and anterior cingulate cortex connectivity during the transition to adulthood

Cannabis use is common among adolescents and emerging adults and is associated with significant adverse consequences for a subset of users. Rates of use peak between the ages of 18-25, yet the neurobiological consequences for neural systems that are actively developing during this time remain poorly understood. In particular, cannabis exposure may interfere with adaptive development of white matter pathways underlying connectivity of the anterior cingulate cortex, including the cingulum and anterior thalamic radiations (ATR). The current study examined the association between cannabis use during adolescence and emerging adulthood and white matter microstructure of the cingulum and ATR among 158 male subjects enrolled in the Pitt Mother and Child Project, a prospective, longitudinal study of risk and resilience among men of low socioeconomic status. Participants were recruited in infancy, completed follow-up assessments throughout childhood and adolescence, and underwent diffusion imaging at ages 20 and 22. At age 20, moderate cannabis use across adolescence (age 12-19) was associated with higher fractional anisotropy (FA) of the cingulum and ATR, relative to both minimal and heavy adolescent use. Longitudinally, moderate and heavy extended cannabis use (age 12-21) was associated with reduced positive change in FA in the cingulum from age 20 to 22, relative to minimal use. These longitudinal results suggest that cannabis exposure may delay cingulum maturation during the transition to adulthood and potentially impact individuals' functioning later in development.

Systematic review of structural and functional neuroimaging studies of cannabis use in adolescence and emerging adulthood: evidence from 90 studies and 9441 participants

Cannabis use peaks in adolescence, and adolescents may be more vulnerable to the neural effects of cannabis and cannabis-related harms due to ongoing brain development during this period. In light of ongoing cannabis policy changes, increased availability, reduced perceptions of harm, heightened interest in medicinal applications of cannabis, and drastic increases in cannabis potency, it is essential to establish an understanding of cannabis effects on the developing adolescent brain. This systematic review aims to: (1) synthesize extant literature on functional and structural neural alterations associated with cannabis use during adolescence and emerging adulthood; (2) identify gaps in the literature that critically impede our ability to accurately assess the effect of cannabis on adolescent brain function and development; and (3) provide recommendations for future research to bridge these gaps and elucidate the mechanisms underlying cannabis-related harms in adolescence and emerging adulthood, with the long-term goal of facilitating the development of improved prevention, early intervention, and treatment approaches targeting adolescent cannabis users (CU). Based on a systematic search of Medline and PsycInfo and other non-systematic sources, we identified 90 studies including 9441 adolescents and emerging adults (n = 3924 CU, n = 5517 non-CU), which provide preliminary evidence for functional and structural alterations in frontoparietal, frontolimbic, frontostriatal, and cerebellar regions among adolescent cannabis users. Larger, more rigorous studies are essential to reconcile divergent results, assess potential moderators of cannabis effects on the developing brain, disentangle risk factors for use from consequences of exposure, and elucidate the extent to which cannabis effects are reversible with abstinence. Guidelines for conducting this work are provided.

The relation between cannabis use, dependence severity and white matter microstructure: A diffusion tensor imaging study

Despite the significant societal and personal burden of cannabis use, the impact of long‐term use and Cannabis Use Disorder (CUD) on white matter microstructure is still unclear. Previous studies show inconsistent findings, in part due to heterogeneity in methodology, variable severity of cannabis use, and potential confounding effects of other mental health issues and substance use. The goal of this diffusion tensor imaging (DTI) study was to compare whole‐brain white matter microstructure between 39 near daily cannabis users and 28 controls closely matched on age, sex, alcohol use, cigarette use and mental health. Within the group of cannabis users, associations between white matter microstructure and recent cannabis use, dependence severity, and age of onset and duration of weekly use were investigated. White matter microstructure did not differ between cannabis users and controls and did not covary with recent cannabis use, dependence severity, or duration of use. Earlier onset of weekly cannabis use was related to lower fractional anisotropy (FA) in various sections of the right inferior longitudinal fasciculus and uncinate fasciculus. These findings suggest that long‐term near‐daily cannabis use does not necessarily affect white matter microstructure, but vulnerability may be higher during adolescence. These findings underscore the importance of sample composition and warrant further studies that investigate the moderating role of age of onset in the impact of cannabis on the brain.

Cannabis Use and Brain Volume in Adolescent and Young Adult Cannabis Users: Effects Moderated by Sex and Aerobic Fitness

OBJECTIVES

Studies examining the impact of adolescent and young adult cannabis use on structural outcomes have been heterogeneous. One already-identified moderator is sex, while a novel potential moderator is extent of aerobic fitness. Here, we sought to investigate the associations of cannabis use, sex, and aerobic fitness levels on brain volume. Second, we explored brain-behavior relationships to interpret these findings.

METHODS

Seventy-four adolescents and young adults (36 cannabis users and 38 controls) underwent 3 weeks of monitored cannabis abstinence, aerobic fitness testing, structural neuroimaging, and neuropsychological testing. Linear regressions examined cannabis use and its interaction with sex and aerobic fitness on whole-brain cortical volume and subcortical regions of interests.

RESULTS

No main-effect differences between cannabis users and nonusers were observed; however, cannabis-by-sex interactions identified differences in frontal, temporal, and paracentral volumes. Female cannabis users generally exhibited greater volume while male users exhibited less volume compared to same-sex controls. Positive associations between aerobic fitness and frontal, parietal, cerebellum, and caudate volumes were observed. Cannabis-by-fitness interaction was linked with left superior temporal volume. Preliminary brain-behavior correlations revealed that abnormal volumes were not advantageous in either male or female cannabis users.

CONCLUSIONS

Aerobic fitness was linked with greater brain volume and sex moderated the effect of cannabis use on volume; preliminary brain-behavior correlations revealed that differences in cannabis users were not linked with advantageous cognitive performance. Implications of sex-specific subtleties and mechanisms of aerobic fitness require large-scale investigation. Furthermore, present findings and prior literature on aerobic exercise warrant examinations of aerobic fitness interventions that aimed at improving neurocognitive health in substance-using youth.

Associations of cannabis use disorder with cognition, brain structure, and brain function in African Americans

Although previous studies have highlighted associations of cannabis use with cognition and brain morphometry, critical questions remain with regard to the association between cannabis use and brain structural and functional connectivity. In a cross-sectional community sample of 205 African Americans (age 18-70) we tested for associations of cannabis use disorder (CUD, n = 57) with multi-domain cognitive measures and structural, diffusion, and resting state brain-imaging phenotypes. Post hoc model evidence was computed with Bayes factors (BF) and posterior probabilities of association (PPA) to account for multiple testing. General cognitive functioning, verbal intelligence, verbal memory, working memory, and motor speed were lower in the CUD group compared with non-users (p < .011; 1.9 < BF < 3,217). CUD was associated with altered functional connectivity in a network comprising the motor-hand region in the superior parietal gyri and the anterior insula (p < .04). These differences were not explained by alcohol, other drug use, or education. No associations with CUD were observed in cortical thickness, cortical surface area, subcortical or cerebellar volumes (0.12 < BF < 1.5), or graph-theoretical metrics of resting state connectivity (PPA < 0.01). In a large sample collected irrespective of cannabis used to minimize recruitment bias, we confirm the literature on poorer cognitive functioning in CUD, and an absence of volumetric brain differences between CUD and non-CUD. We did not find evidence for or against a disruption of structural connectivity, whereas we did find localized resting state functional dysconnectivity in CUD. There was sufficient proof, however, that organization of functional connectivity as determined via graph metrics does not differ between CUD and non-user group.

White matter integrity after cannabidiol administration for treatment resistant epilepsy

OBJECTIVE

The effects of individual cannabinoids on white matter integrity are unclear. Human studies have shown white matter maturation alterations in regular recreational cannabis users with the magnitude of these effects dependent on the age of exposure. However, studies have yet to determine which phytocannabinoids are most responsible for these changes. In the current study, we analyzed the effects of pharmaceutical grade cannabidiol oral solution (CBD; Epidiolex® in the U.S.; Epidyolex® in the EU; 100 mg/mL oral solution) on white matter integrity using diffusion MRI in patients with treatment resistant epilepsy (TRE).

METHODS

15 patients with TRE underwent 3 T diffusion MRI prior to receiving CBD and then again approximately 12 weeks later while on a stable dose of CBD for at least two weeks. DTI analyzes were conducted using DSI Studio and tract-based spatial statistics (TBSS).

RESULTS

DTI analysis using DSI Studio showed significant increases in fractional anisotropy (FA) in the right medial lemniscus (p = 0.03), right superior cerebellar peduncle (p = 0.03) and the pontine crossing tract (p = 0.04); decreased mean diffusivity (MD) in the left uncinate fasciculus (p = 0.02) and the middle cerebellar peduncle (p = 0.04); decreased axial diffusivity (AD) in the left superior cerebellar peduncle (p = 0.05), right anterior limb of the internal capsule (p = 0.03), and right posterior limb of the internal capsule (p = 0.02); and decreased radial diffusivity (RD) in the middle cerebellar peduncle (p = 0.03) and left uncinate fasiculus (p = 0.01). The follow-up ANCOVA also yielded significant results when controlling for covariates of CBD dosage, age, sex, change in seizure frequency, and scanner type: FA increased in the pontine crossing tract (p = 0.03); RD decreased in the middle cerebellar peduncle (p = 0.04) and left uncinate fasciculus (p = 0.04). Subsequent TBSS analysis controlling for the same variables yielded no significant white matter differences between groups.

CONCLUSION

These findings indicate relatively minor short-term effects of highly-purified plant-derived CBD on white matter structural integrity in patients with TRE.

High genes: Genetic underpinnings of cannabis use phenotypes

Cannabis is one of the most widely used substances across the globe and its use has a substantial heritable component. However, the heritability of cannabis use varies according to substance use phenotype, suggesting that a unique profile of gene variants may contribute to the different stages of use, such as age of use onset, lifetime use, cannabis use disorder, and withdrawal and craving during abstinence. Herein, we review a subset of genes identified by candidate gene, family-based linkage, and genome-wide association studies related to these cannabis use phenotypes. We also describe their relationships with other substances, and their functions at the neurobiological, cognitive, and behavioral levels to hypothesize the role of these genes in cannabis use risk. Delineating genetic risk factors in the various stages of cannabis use will provide insight into the biological mechanisms related to cannabis use and highlight points of intervention prior to and following the development of dependence, as well as identify targets to aid drug development for treating problematic cannabis use.

Fatty acid amide hydrolase is lower in young cannabis users

We have recently shown that levels of fatty acid amide hydrolase (FAAH), the enzyme that metabolizes the endocannabinoid anandamide, are lower in the brains of adult cannabis users (CUs) (34 ± 11 years of age), tested during early abstinence. Here, we examine replication of the lower FAAH levels in a separate, younger cohort (23 ± 5 years of age). Eighteen healthy volunteers (HVs) and fourteen CUs underwent a positron emission tomography scan using the FAAH radioligand [¹¹ C]CURB. Regional [¹¹ C]CURB binding was calculated using an irreversible two-tissue compartment model with a metabolite-corrected arterial plasma input function. The FAAH C385A genetic polymorphism (rs324420) was included as a covariate. All CUs underwent a urine screen to confirm recent cannabis use and had serum cannabinoids measured. One CU screened negative for cannabinoids via serum and was removed from analysis. All HVs reported less than five lifetime cannabis exposures more than a month prior to study initiation. There was a significant effect of group (F_1,26 = 4.31; P = .048) when two A/A (rs324420) HVs were removed from analysis to match the genotype of the CU group (n = 16 HVs, n = 13 CUs). Overall, [¹¹ C]CURB λk₃ was 12% lower in CU compared with HV. Exploratory correlations showed that lower brain [¹¹ C]CURB binding was related to greater use of cannabis throughout the past year. We confirmed our previous report and extended these findings by detecting lower [¹¹ C]CURB binding in a younger cohort with less cumulative cannabis exposure.

Cognition and Cortical Thickness in Heavy Cannabis Users

INTRODUCTION

Acute and long-term adverse effects of heavy cannabis use (HCU) on neurocognitive function have been suggested, as much as regional changes of brain volume. However, little is known about the relationship between impaired cognition and brain structure in individuals with HCU.

OBJECTIVE

Here, we investigated associations between cognition and cortical thickness (CT) in males with HCU and male controls.

METHODS

Twenty-six individuals with HCU and 20 controls were examined using a comprehensive neuropsychological test battery and high-resolution structural MRI at 3T. CT was calculated using the Computational Anatomy Toolbox (CAT12).

RESULTS

Individuals with HCU differed from controls with respect to verbal learning performance and verbal working memory only. Individuals with HCU showed reduced CT in medial temporal, orbitofrontal, and cingulate regions, as well as in areas of the middle temporal and fusiform cortex (peak voxel family-wise error-corrected p < 0.001, followed by empirically determined correction for spatial extent) compared to HC. Verbal learning performance was associated with right entorhinal and left orbitofrontal CT reductions. Entorhinal CT was also significantly associated with amount and frequency of current weekly cannabis use.

CONCLUSIONS

The data support the notion of domain-specific cognitive impairment in individuals with HCU and provide a neuromechanistic understanding of such deficits, particularly with respect to abnormal CT in brain areas associated with long-term memory processing.

Impact of 2 Weeks of Monitored Abstinence on Cognition in Adolescent and Young Adult Cannabis Users

OBJECTIVES

Previous research suggests recovery from cannabis-related deficits in verbal learning and memory functioning after periods of cannabis abstinence in adolescents. Here, we examine how cannabis cessation affects cognitive performance over 2 weeks of monitored abstinence compared to controls in adolescents and young adults.

METHODS

Seventy-four participants (35 cannabis users) aged 16-26 ceased all cannabis, alcohol, and other illicit substance consumption for a 2-week period; abstinence was monitored via weekly urinalysis, breath, and sweat patch testing. Starting at baseline, participants completed weekly abbreviated neuropsychological batteries. Measures included tests of attention, inhibition, verbal working memory, and learning. Repeated measures assessed within and between subject effects for time and group status, while controlling for past year alcohol and nicotine use.

RESULTS

Cannabis users showed increased performance compared to controls on sustained attention tasks after 2 weeks of cannabis use.

CONCLUSIONS

Deficits in attention, but not verbal learning and memory, recovered after 2 weeks of monitored abstinence. This differs from previous literature, suggesting that other cognitive domains may show signs of recovery after periods of cannabis cessation in adolescents and young adults.

Microstructural brain abnormalities in HIV+ individuals with or without chronic marijuana use

OBJECTIVE

Cognitive deficits and microstructural brain abnormalities are well documented in HIV-positive individuals (HIV+). This study evaluated whether chronic marijuana (MJ) use contributes to additional cognitive deficits or brain microstructural abnormalities that may reflect neuroinflammation or neuronal injury in HIV+.

METHOD

Using a 2 × 2 design, 44 HIV+ participants [23 minimal/no MJ users (HIV+), 21 chronic active MJ users (HIV + MJ)] were compared to 46 seronegative participants [24 minimal/no MJ users (SN) and 22 chronic MJ users (SN + MJ)] on neuropsychological performance (7 cognitive domains) and diffusion tensor imaging metrics, using an automated atlas to assess fractional anisotropy (FA), axial (AD), radial (RD), and mean (MD) diffusivities, in 18 cortical and 4 subcortical brain regions.

RESULTS

Compared to SN and regardless of MJ use, the HIV+ group had lower FA and higher diffusivities in multiple white matter and subcortical structures (p < 0.001-0.050), as well as poorer cognition in Fluency (p = 0.039), Attention/Working Memory (p = 0.009), Learning (p = 0.014), and Memory (p = 0.028). Regardless of HIV serostatus, MJ users had lower AD in uncinate fasciculus (p = 0.024) but similar cognition as nonusers. HIV serostatus and MJ use showed an interactive effect on mean diffusivity in the right globus pallidus but not on cognitive function. Furthermore, lower FA in left anterior internal capsule predicted poorer Fluency across all participants and worse Attention/Working Memory in all except SN subjects, while higher diffusivities in several white matter tracts also predicted lower cognitive domain Z-scores. Lastly, MJ users with or without HIV infection showed greater than normal age-dependent FA declines in superior longitudinal fasciculus, external capsule, and globus pallidus.

CONCLUSIONS

Our findings suggest that, except in the globus pallidus, chronic MJ use had no additional negative influence on brain microstructure or neurocognitive deficits in HIV+ individuals. However, lower AD in the uncinate fasciculus of MJ users suggests axonal loss in this white matter tract that connects to cannabinoid receptor rich brain regions that are involved in verbal memory and emotion. Furthermore, the greater than normal age-dependent FA declines in the white matter tracts and globus pallidus in MJ users suggest that older chronic MJ users may eventually have lesser neuronal integrity in these brain regions.

Cannabis Use as a Risk Factor for Depression, Anxiety, and Suicidality: Epidemiological Associations and Implications for Nurses

Psychiatric disorders and substance use disorders commonly co-occur and are major public health concerns given the morbidity and mortality associated with them. Globally, cannabis is among the most commonly used drugs, and cannabis use frequently begins in adolescence or emerging adulthood, both important periods of development and periods in which psychiatric symptoms and disorders frequently emerge. Thus, the relationships between cannabis use and mental illnesses are essential for nurses and other healthcare professionals and researchers to explore and understand. This literature review examines the relationships between cannabis use and depression, anxiety, and suicide. It includes a primer on the neurobiology of cannabis effects; an overview on the epidemiological evidence on the associations between cannabis use and depression, anxiety, and suicide; and a discussion of implications for nurses, particularly important given changes in the medical and recreational cannabis legislation in North America. Overall, this review found consistent evidence showing a cross-sectional association between recreational cannabis use and depression, anxiety, and suicide, despite some limitations and conflicts in the literature. In addition, most evidence from longitudinal or case control studies suggested cannabis use preceded the development of depressive symptoms and suicidal behaviors, although the quality of this evidence was mixed. Implications for future research and nursing practice are discussed.

Depression Onset in Long-term Adolescent Cannabinoid Use: A Neurobiological Review

Escalating cannabis use may be linked to decreased motivation and anhedonia, which are symptoms of depression. Adolescent cannabis users with subthreshold depressive symptoms such as reduced motivation may be susceptible to the development of significant anhedonia in addition to impaired emotional development. The main issue regarding depression within the context of cannabis use is whether or not there is a neurobiological basis linking the two variables.

A Medical Subject Headings (MeSH) function PubMed search using the keywords “cannabis, depression, adolescence, endocannabinoid, and temperament” returned 1,109 articles. Data were included from studies that satisfied the following criteria: (i) published within the last 10 years (older studies were included based on relevance), (ii) on adolescent subjects (animal or human), (iii) published in English, (iv) journal articles, systematic reviews, meta-analyses, clinical trials, observational studies (animal or human), (v) on subjects who had unipolar depression with no comorbidities, and (vi) on subjects who used cannabis [with no confounding variables such as the use of ethanol, nicotine, cocaine, lysergic acid diethylamide (LSD), and heroin; and no medical conditions such as comorbid psychosis, mania, or autism].

Depressive symptoms in cannabinoid users were a common co-occurrence partly explained by pleiotropic linkage of genetic locus identified on chromosome 11q23.1-q23.2 and comprises the gene sequence nuclear cell adhesion molecule 1-tetratricopeptide repeat domain 12-ankyrin repeat and kinase domain containing 1-dopamine receptor D2 (NCAM1-TTC12-ANKK1-DRD2). The relationship between the two is not invariant and is influenced by polymorphic DRD, endocannabinoid receptor (CNR), and 5-HT genes. Anhedonia seemed to be the most important symptom. Cannabinoid-induced long-term neuroplastic changes, particularly in the dorsal striatum, is a possible mechanism resulting in anhedonia and long-term effects on motivation.

Binge and Cannabis Co-Use Episodes in Relation to White Matter Integrity in Emerging Adults

Background: Growing evidence suggests that cannabis and alcohol (and especially binge alcohol drinking) use independently alters neural structure and functioning, particularly during sensitive developmental time periods (e.g., emerging adulthood). However, few studies have investigated the effects of same-day use of these two substances. Here, white matter (WM) integrity was investigated in relation to binge alcohol drinking, cannabis, and same-day binge and cannabis co-use in adolescents and emerging adults. Methods: FreeSurfer's TRACULA was used to assess WM in emerging adults (n=75; 16-26 years old). Timeline Followback calculated past month cannabis use, binge episodes, and same-day cannabis and binge drinking co-use. Multiple regressions investigated WM by past month cannabis, binge, and co-use. Results: Results revealed co-use episodes were related to lower fractional anisotropy (FA), an overall measure of neuronal integrity, in three tracts (left inferior longitudinal fasciculus [ILF], p=0.02; right anterior thalamic radiation [ATR], p=0.01; and left cingulum cingulate gyrus [CCG], p=0.01); and lower axial diffusivity in left ILF (p=0.03). Cannabis use was significantly related to greater FA in left ILF (p=0.005), left ATR (p=0.02), right ATR (p=0.05), left CCG (p=0.006), right CCG (p=0.03), and right superior longitudinal fasciculus parietal (p=0.03). Binge episodes related to greater FA in right ATR (p=0.03). Conclusions: These findings suggest that co-use was associated with lower WM integrity across frontolimbic tracts. In addition, greater FA was related to greater cannabis use across several tracts and binge alcohol use in one tract. Co-users also appeared to be more severe substance users. Future research should investigate the potential independent and interactive effects of these substances on pre-clinical and clinical levels.

Assessing the Role of Cannabis Use on Cortical Surface Structure in Adolescents and Young Adults: Exploring Gender and Aerobic Fitness as Potential Moderators

Cannabis use in adolescents and young adults is linked with aberrant brain structure, although findings to date are inconsistent. We examined whether aerobic fitness moderated the effects of cannabis on cortical surface structure and whether gender may play a moderating role. Seventy-four adolescents and young adults completed three-weeks of monitored abstinence, aerobic fitness testing, and structural magnetic resonance imaging (sMRI). Whole-sample linear regressions examined the effects of gender, VO2 max, cannabis use, and their interactions on the surface area (SA) and local gyrification index (LGI). Cannabis use was associated with greater cuneus SA. Gender-by-cannabis predicted precuneus and frontal SA, and precentral, supramarginal, and frontal LGI; female cannabis users demonstrated greater LGI, whereas male cannabis users demonstrated decreased LGI compared to non-users. Aerobic fitness was positively associated with various SA and LGI regions. Cannabis-by-aerobic fitness predicted cuneus SA and occipital LGI. These findings demonstrate that aerobic fitness moderates the impact of cannabis on cortical surface structure, and gender differences are evident. These moderating factors may help explain inconsistencies in the literature and warrant further investigation. Present findings and aerobic fitness literature jointly suggest aerobic intervention may be a low-cost avenue for improving cortical surface structure, although the impact may be gender-specific.

Cannabis Use and Consequences

As an increasing number of states legalize cannabis use for recreational and/or medical purposes, it is increasingly important to understand the neural and cognitive consequences of recreational cannabis use in adolescent consumers. Adolescence is marked by ongoing neuromaturational processes, making this a particularly vulnerable period, particularly regarding exposure to drugs, including cannabis. This review highlights evidence from studies documenting the neural impact of cannabis use in adolescence and explores mediating factors related to cannabis use.

Intrinsic Frontolimbic Connectivity and Mood Symptoms in Young Adult Cannabis Users

Objective: The endocannbinoid system and cannabis exposure has been implicated in emotional processing. The current study examined whether regular cannabis users demonstrated abnormal intrinsic (a.k.a. resting state) frontolimbic connectivity compared to non-users. A secondary aim examined the relationship between cannabis group connectivity differences and self-reported mood and affect symptoms.

Method: Participants included 79 cannabis-using and 80 non-using control emerging adults (ages of 18–30), balanced for gender, reading ability, and age. Standard multiple regressions were used to predict if cannabis group status was associated with frontolimbic connectivity after controlling for site, past month alcohol and nicotine use, and days of abstinence from cannabis.

Results: After controlling for research site, past month alcohol and nicotine use, and days of abstinence from cannabis, cannabis users demonstrated significantly greater connectivity between left rACC and the following: right rACC (p = 0.001; corrected p = 0.05; f² = 0.55), left amygdala (p = 0.03; corrected p = 0.47; f² = 0.17), and left insula (p = 0.03; corrected p = 0.47; f² = 0.16). Among cannabis users, greater bilateral rACC connectivity was significantly associated with greater subthreshold depressive symptoms (p = 0.02).

Conclusions: Cannabis using young adults demonstrated greater connectivity within frontolimbic regions compared to controls. In cannabis users, greater bilateral rACC intrinsic connectivity was associated with greater levels of subthreshold depression symptoms. Current findings suggest that regular cannabis use during adolescence is associated with abnormal frontolimbic connectivity, especially in cognitive control and emotion regulation regions.

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.

Individuals with psychosis and a lifetime history of cannabis use show greater deficits in emotional experience compared to non-using peers

Background: While previous research suggests that active cannabis use is a barrier to the emotional experiences of anticipating pleasure and expressing emotion in early psychosis, the relationship between lifetime cannabis use, emotional experience and social function over time has been understudied.Aims: This study sought to characterize the influence of lifetime cannabis use on emotional experience in prolonged psychosis and the influence of the interaction of cannabis use and emotional expression on social function.Methods: Emotional expression, experience of pleasure in the moment, anticipatory anhedonia and social functioning were measured concurrently using the Emotional Expressivity Scale (EES), Temporal Experience of Pleasure Scale (TEPS) and Social Functioning Scale (SFS), respectively. Participants were adults with schizophrenia either with (n = 35) or without (n = 36) a lifetime history of cannabis use.Results: Compared to non-using participants, individuals with a history of cannabis use expressed lesser abilities to express emotion, were less likely to expect pleasure and had poorer social function. Cannabis use moderated the relationship between anticipatory pleasure and prosocial activities.Conclusions: Lifetime cannabis use in schizophrenia may be associated with greater deficits in emotional expressivity, anticipation of pleasure and social function. Cannabis use may disrupt the relationship between anticipatory pleasure and social functioning.

FAAH variant Pro129Thr modulates subjective effects produced by cocaine administration

BACKGROUND AND OBJECTIVES

The endogenous cannabinoid anandamide (AEA), an agonist at type-1 cannabinoid (CB1) receptors, is metabolized by fatty acid amide hydrolase (FAAH). The common variant rs324420 C->A within the FAAH gene on chromosome 1 codes for a missense substitution (Pro129Thr), resulting in decreased FAAH activity and increased endocannabinoid potentiation. This FAAH variant has been linked to alterations in mood and stress reactivity, as well as being independently linked to increased risk for addiction. We hypothesized that cocaine use disordered (CUD) participants with the FAAH Pro129 Thr variant would exhibit a distinct profile of cocaine-induced subjective effects in the laboratory.

METHODS

A total of 70 CUD participants received intravenous doses of saline (placebo, 0 mg) and cocaine (20, 40 mg) in a lab-controlled setting and rated 10 subjective effect measures prior to and following saline and cocaine administration, using a Visual Analog Scale (VAS).

RESULTS

The variant allele was associated with increased cocaine-induced subjective ratings for "Drug Effect," "High," and "Depressed." The prevalence of the variant allele A and the AA genotypes were greater in our CUD group than in the general population (A allele: 47% vs. 34%; AA genotype: 30% vs. 13%; p < .05). Finally, the reported amount and frequency of tobacco and cocaine use was higher in subjects with the AC/AA allele.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

These results add to existing evidence that this variant of the FAAH genotype may be over-represented among those who have CUD, and this over-representation may result from greater subjective responses to cocaine administration. (Am J Addict 2018;27:567-573).

Verbal Memory Performance and Reduced Cortical Thickness of Brain Regions Along the Uncinate Fasciculus in Young Adult Cannabis Users

Introduction: Memory impairment is one of the most commonly reported effects of cannabis use, especially among those who initiate use earlier, perhaps due to the effects of delta-9- tetrahydrocannabinol on cannabinoid (CB1) receptors in the brain. Studies have increasingly investigated whether cannabis use is associated with impairments in verbal memory, and with alterations in brain structures underlying verbal memory. The uncinate fasciculus (UF), a long-range white matter tract, connects regions with densely localized CB1 receptors that are important in verbal memory. This study investigated the impact of cannabis use on UF structures and its association with memory performance in young adult cannabis users (CU) and non-using controls (CON).

Materials and Methods: Nineteen CU and 22 CON completed a verbal memory task and a neuroimaging protocol, in which diffusion tensor imaging and structural scans were collected. We compared memory performance, diffusion and tractography measures of the UF, and cortical thickness of regions connected by the UF, between CU and CON. In regions showing a significant group effect, we also examined associations between verbal memory performance, cortical thickness, and age of onset of cannabis use.

Results: Compared to non-users, CU had worse memory performance, decreased fiber bundle length in the UF, and decreased cortical thickness of brain regions along the UF such as the entorhinal cortex and fusiform gyrus. Verbal memory performance was significantly associated with age of onset of cannabis use, indicating that those who initiated cannabis use at an earlier age performed worse. Cortical thickness of the entorhinal cortex was significantly correlated with age of first use and memory performance.

Conclusion: This study provides evidence that cannabis use, especially when initiated at a young age, may be associated with worse verbal memory and altered neural development along the UF. Reductions in cortical thickness in regions implicated in memory processes may underlie weaknesses in verbal memory performance.

Structural neuroimaging correlates of alcohol and cannabis use in adolescents and adults

BACKGROUND AND AIMS

Chronic alcohol use is associated with lower gray matter volume, and we reported recently that alcohol use showed negative associations with widespread gray matter (GM) volume even among young adults. The current study aimed to test the strength of association between (1) alcohol use and GM volume; (2) alcohol use and white matter (WM) integrity; (3) cannabis use and GM volume; and (4) cannabis use and WM integrity among adults and adolescents.

DESIGN AND SETTING

General linear models within large pooled cross-sectional samples of adolescents and adults who had participated in studies collecting substance use and neuroimaging data in the southwestern United States.

PARTICIPANTS

The current analysis included adults aged 18-55 years (n = 853) and adolescents aged 14-18 years (n = 439) with a range of alcohol and cannabis use.

MEASUREMENTS

The dependent variable was GM volume or WM integrity, with key predictors of alcohol use [Alcohol Use Disorders Identification Test (AUDIT) score] and cannabis use (past 30-day use).

FINDINGS

Alcohol use showed large clusters of negative associations (η_p²  = 0.028-0.145, P < 0.001) with GM volume among adults and to a lesser extent (one cluster; η_p²  = 0.070, P < 0.05) among adolescents. Large clusters showed significant associations (η_p²  = 0.050-0.124, P < 0.001) of higher alcohol use with poorer WM integrity, whereas adolescents showed no significant associations between alcohol use and WM. No associations were observed between structural measures and past 30-day cannabis use in adults or adolescents.

CONCLUSIONS

Alcohol use severity is associated with widespread lower gray matter volume and white matter integrity in adults, and with lower gray matter volume in adolescents.

Prefrontal mechanisms of comorbidity from a transdiagnostic and ontogenic perspective

Accumulating behavioral and genetic research suggests that most forms of psychopathology share common genetic and neural vulnerabilities and are manifestations of a relatively few core underlying processes. These findings support the view that comorbidity mostly arises, not from true co-occurrence of distinct disorders, but from the behavioral expression of shared vulnerability processes across the life span. The purpose of this review is to examine the role of the prefrontal cortex (PFC) in the shared vulnerability mechanisms underlying the clinical phenomena of comorbidity from a transdiagnostic and ontogenic perspective. In adopting this perspective, we suggest complex transactions between neurobiologically rooted vulnerabilities inherent in PFC circuitry and environmental factors (e.g., parenting, peers, stress, and substance use) across development converge on three key PFC-mediated processes: executive functioning, emotion regulation, and reward processing. We propose that individual differences and impairments in these PFC-mediated functions provide intermediate mechanisms for transdiagnostic symptoms and underlie behavioral tendencies that evoke and interact with environmental risk factors to further potentiate vulnerability.

Cannabis-associated psychosis: Neural substrate and clinical impact

Prospective epidemiological studies have consistently demonstrated that cannabis use is associated with an increased subsequent risk of both psychotic symptoms and schizophrenia-like psychoses. Early onset of use, daily use of high-potency cannabis, and synthetic cannabinoids carry the greatest risk. The risk-increasing effects are not explained by shared genetic predisposition between schizophrenia and cannabis use. Experimental studies in healthy humans show that cannabis and its active ingredient, delta-9-tetrahydrocannabinol (THC), can produce transient, dose-dependent, psychotic symptoms, as well as an array of psychosis-relevant behavioral, cognitive and psychophysiological effects; the psychotogenic effects can be ameliorated by cannabidiol (CBD). Findings from structural imaging studies in cannabis users have been inconsistent but functional MRI studies have linked the psychotomimetic and cognitive effects of THC to activation in brain regions implicated in psychosis. Human PET studies have shown that acute administration of THC weakly releases dopamine in the striatum but that chronic users are characterised by low striatal dopamine. We are beginning to understand how cannabis use impacts on the endocannabinoid system but there is much still to learn about the biological mechanisms underlying how cannabis increases risk of psychosis. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Pros and Cons of Medical Cannabis use by People with Chronic Brain Disorders

BACKGROUND

Cannabis is the most widely used illicit drug in the world and there is growing concern about the mental health effects of cannabis use. These concerns are at least partly due to the strong increase in recreational and medical cannabis use and the rise in tetrahydrocannabinol (THC) levels. Cannabis is widely used to self-medicate by older people and people with brain disorders such as amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), bipolar disorder, and schizophrenia.

OBJECTIVE

This review provides an overview of the perceived benefits and adverse mental health effects of cannabis use in people with ALS, MS, AD, PD, bipolar disorder, and schizophrenia.

RESULTS

The reviewed studies indicate that cannabis use diminishes some symptoms associated with these disorders. Cannabis use decreases pain and spasticity in people with MS, decreases tremor, rigidity, and pain in people with PD, and improves the quality of life of ALS patients by improving appetite, and decreasing pain and spasticity. Cannabis use is more common among people with schizophrenia than healthy controls. Cannabis use is a risk factor for schizophrenia which increases positive symptoms in schizophrenia patients and diminishes negative symptoms. Cannabis use worsens bipolar disorder and there is no evidence that bipolar patients derive any benefit from cannabis. In late stage Alzheimer's patients, cannabis products may improve food intake, sleep quality, and diminish agitation.

CONCLUSION

Cannabis use diminishes some of the adverse effects of neurological and psychiatric disorders. However, chronic cannabis use may lead to cognitive impairments and dependence.

Marijuana Use Is Associated with Behavioral Approach and Depressive Symptoms in Adolescents and Emerging Adults

BACKGROUND

Repeated CB1 binding due to THC results in downregulation of the endocannabinoid system in cortex and limbic regions, perhaps disrupting frontolimbic functioning. This is particularly a concern in young adults who are still undergoing neurodevelopment in frontal and limbic regions. Such disruptions may be linked to increased depressive symptoms, anxiety symptoms, and executive dysfunction, and decreased behavioral approach.

OBJECTIVES

Here we examine the influence of young adult marijuana use on anxiety, depressive symptoms, behavioral approach, and executive dysfunction. The influence of alcohol and gender were also assessed.

METHODS

84 participants (42 MJ, 42 controls) aged 18-25 were balanced for gender (39 F). Exclusion criteria included: MRI contraindications, left handed, comorbid Axis-I disorders, major medical or neurologic disorders, prenatal issues, or prenatal alcohol/illicit drug exposure, or excessive other drug use. Participants completed the FrsBE, BIS/BAS, State-Trait Anxiety Inventory (State), and BDI-II. Multiple regressions were run to predict anxiety, depressive symptoms, behavioral approach, and executive dysfunction from MJ group status, past year alcohol use, gender, and MJ*gender interactions, controlling for cotinine and ecstasy.

RESULTS

MJ group predicted increased depressive symptoms (p =.049). Decreased fun-seeking (p =.04), reward response (p =.01), and BAS total (p =.01) were predicted by MJ group. Gender predicted decreased reward responsiveness in females (p =.049) and decreased BIS in females (p =.03). Female marijuana users had increased anxiety symptoms (p =.04) and increased disinhibition (p =.04). Increased cotinine predicted increased drive (p =.046), reward responsiveness (p =.008) and BAS Total (p =.02). Apathy and Executive Dysfunction were not predicted by any measures. All results had small effect sizes.

CONCLUSIONS/IMPORTANCE

Depressive symptoms were greater in MJ users, while behavioral approach was decreased. Cotinine levels predicted increased behavioral approach. Female MJ users also had greater anxiety and disinhibition. In sum, these findings suggest sub-clinical threshold deficits related to regular marijuana use that are indicative of a need to prevent marijuana use in adolescents and young adults.

Fatty Acid Amide Hydrolase Binding in Brain of Cannabis Users: Imaging With the Novel Radiotracer [11C]CURB

BACKGROUND

One of the major mechanisms for terminating the actions of the endocannabinoid anandamide is hydrolysis by fatty acid amide hydrolase (FAAH), and inhibitors of the enzyme were suggested as potential treatment for human cannabis dependence. However, the status of brain FAAH in cannabis use disorder is unknown.

METHODS

Brain FAAH binding was measured with positron emission tomography and [¹¹C]CURB in 22 healthy control subjects and ten chronic cannabis users during early abstinence. The FAAH genetic polymorphism (rs324420) and blood, urine, and hair levels of cannabinoids and metabolites were determined.

RESULTS

In cannabis users, FAAH binding was significantly lower by 14%-20% across the brain regions examined than in matched control subjects (overall Cohen's d = 0.96). Lower binding was negatively correlated with cannabinoid concentrations in blood and urine and was associated with higher trait impulsiveness.

CONCLUSIONS

Lower FAAH binding levels in the brain may be a consequence of chronic and recent cannabis exposure and could contribute to cannabis withdrawal. This effect should be considered in the development of novel treatment strategies for cannabis use disorder that target FAAH and endocannabinoids. Further studies are needed to examine possible changes in FAAH binding during prolonged cannabis abstinence and whether lower FAAH binding predates drug use.

An MRI study of white matter tract integrity in regular cannabis users: effects of cannabis use and age

RATIONALE

Conflicting evidence exists on the effects of cannabis use on brain white matter integrity. The extant literature has exclusively focused on younger cannabis users, with no studies sampling older cannabis users.

OBJECTIVES

We recruited a sample with a broad age range to examine the integrity of major white matter tracts in association with cannabis use parameters and neurodevelopmental stage.

METHODS

Regular cannabis users (n = 56) and non-users (n = 20) with a mean age of 32 (range 18-55 years) underwent structural and diffusion MRI scans. White matter was examined using voxel-based statistics and via probabilistic tract reconstruction. The integrity of tracts was assessed using average fractional anisotropy, axial diffusivity and radial diffusivity. Diffusion measures were compared between users and non-users and as group-by-age interactions. Correlations between diffusion measures and age of onset, duration, frequency and dose of current cannabis use were examined.

RESULTS

Cannabis users overall had lower fractional anisotropy than healthy non-users in the forceps minor tract only (p = .015, partial eta = 0.07), with no voxel-wise differences observed. Younger users showed predominantly reduced axial diffusivity, whereas older users had higher radial diffusivity in widespread tracts. Higher axial diffusivity was associated with duration of cannabis use in the cingulum angular bundle (beta = 5.00 × 10(-5), p = .003). Isolated higher AD in older cannabis users was also observed.

CONCLUSIONS

The findings suggest that exogenous cannabinoids alter normal brain maturation, with differing effects at various neurodevelopmental stages of life. These age-related differences are posited to account for the disparate results described in the literature.

Genetic and Environmental Factors Associated with Cannabis Involvement

Approximately 50-70% of the variation in cannabis use and use disorders can be attributed to heritable factors. For cannabis use, the remaining variance can be parsed in to familial and person-specific environmental factors while for use disorders, only the latter contribute. While numerous candidate gene studies have identified the role of common variation influencing liability to cannabis involvement, replication has been elusive. To date, no genomewide association study has been sufficiently powered to identify significant loci. Despite this, studies adopting polygenic techniques and integrating genetic variation with neural phenotypes and measures of environmental risk, such as childhood adversity, are providing promising new leads. It is likely that the small effect sizes associated with variants related to cannabis involvement will only be robustly identified in substantially larger samples. Results of such large-scale efforts will provide valuable single variant targets for translational research in neurogenetic, pharmacogenetic and non-human animal models as well as polygenic risk indices that can be used to explore a host of other genetic hypotheses related to cannabis use and misuse.

Alcohol and Drug Use and the Developing Brain

Adolescence is an important neurodevelopmental period marked by rapidly escalating rates of alcohol and drug use. Over the past decade, research has attempted to disentangle pre- and post-substance use effects on brain development by using sophisticated longitudinal designs. This review focuses on recent, prospective studies and addresses the following important questions: (1) what neuropsychological and neural features predate adolescent substance use, making youth more vulnerable to engage in heavy alcohol or drug use, and (2) how does heavy alcohol and drug use affect normal neural development and cognitive functioning? Findings suggest that pre-existing neural features that relate to increased substance use during adolescence include poorer neuropsychological functioning on tests of inhibition and working memory, smaller gray and white matter volume, changes in white matter integrity, and altered brain activation during inhibition, working memory, reward, and resting state. After substance use is initiated, alcohol and marijuana use are associated with poorer cognitive functioning on tests of verbal memory, visuospatial functioning, psychomotor speed, working memory, attention, cognitive control, and overall IQ. Heavy alcohol use during adolescence is related to accelerated decreases in gray matter and attenuated increases in white matter volume, as well as increased brain activation during tasks of inhibition and working memory, relative to controls. Larger longitudinal studies with more diverse samples are needed to better understand the interactive effects of alcohol, marijuana, and other substances, as well as the role of sex, co-occurring psychopathology, genetics, sleep, and age of initiation on substance use.

Concurrent white and gray matter degeneration of disease-specific networks in early-stage Alzheimer's disease and behavioral variant frontotemporal dementia

This study investigates regional coherence between white matter (WM) microstructure and gray matter (GM) volume and perfusion measures in Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) using a correlational approach. WM-GM coherence, compared with controls, was stronger between cingulum WM and frontotemporal GM in AD, and temporoparietal GM in bvFTD. In addition, in AD compared with controls, coherence was stronger between inferior fronto-occipital fasciculus WM microstructure and occipital GM perfusion. In this first study assessing regional WM-GM coherence in AD and bvFTD, we show that WM microstructure and GM volume and perfusion measures are coherent, particularly in regions implicated in AD and bvFTD pathology. This indicates concurrent degeneration in disease-specific networks. Our methodology allows for the detection of incipient abnormalities that go undetected in conventional between-group analyses.

Longitudinal changes in white matter microstructure after heavy cannabis use

Diffusion tensor imaging (DTI) studies of cannabis users report alterations in brain white matter microstructure, primarily based on cross-sectional research, and etiology of the alterations remains unclear. We report findings from longitudinal voxelwise analyses of DTI data collected at baseline and at a 2-year follow-up on 23 young adult (18-20 years old at baseline) regular cannabis users and 23 age-, sex-, and IQ-matched non-using controls with limited substance use histories. Onset of cannabis use was prior to age 17. Cannabis users displayed reduced longitudinal growth in fractional anisotropy in the central and parietal regions of the right and left superior longitudinal fasciculus, in white matter adjacent to the left superior frontal gyrus, in the left corticospinal tract, and in the right anterior thalamic radiation lateral to the genu of the corpus callosum, along with less longitudinal reduction of radial diffusion in the right central/posterior superior longitudinal fasciculus, corticospinal tract, and posterior cingulum. Greater amounts of cannabis use were correlated with reduced longitudinal growth in FA as was relatively impaired performance on a measure of verbal learning. These findings suggest that continued heavy cannabis use during adolescence and young adulthood alters ongoing development of white matter microstructure, contributing to functional impairment.