Associations between cannabinoid receptor-1 (CNR1) variation and hippocampus and amygdala volumes in heavy cannabis users

Abnormal developmental of hippocampal subfields and amygdalar subnuclei volumes in young adults with heavy cannabis use: A three-year longitudinal study

BACKGROUND

Differences in the volumes of the hippocampus and amygdala have consistently been observed between young adults with heavy cannabis use relative to their non-using counterparts. However, it remains unclear whether the subfields of these functionally and structurally heterogenous regions exhibit similar patterns of change in young adults with long-term heavy cannabis use disorder (CUD).

OBJECTIVES

This study aims to investigate the effects of long-term heavy cannabis use in young adults on the subregional structures of the hippocampus and amygdala, as well as their longitudinal alterations.

METHODS

The study sample comprised 20 young adults with heavy cannabis use and 22 matched non-cannabis using healthy volunteers. All participants completed the Cannabis Use Disorder Identification Test (CUDIT) and underwent two T1-structural magnetic resonance imaging (MRI) scans, one at baseline and another at follow-up 3 years later. The amygdala, hippocampus, and their subregions were segmented on T1-weighted anatomical MRI scans, using a previously validated procedure.

RESULTS

At baseline, young adults with heavy CUD exhibited significantly larger volumes in several hippocampal (bilateral presubiculum, subiculum, Cornu Ammonis (CA) regions CA1, CA2-CA3, and right CA4-Dentate Gyrus (DG)) and amygdala (bilateral paralaminar nuclei, right medial nucleus, and right lateral nucleus) subregions compared to healthy controls, but these differences were attenuated at follow-up. Longitudinal analysis revealed an accelerated volumetric decrease in these subregions in young adults with heavy CUD relative to controls. Particularly, compared to healthy controls, significant accelerated volume decreases were observed in the right hippocampal subfields of the parasubiculum, subiculum, and CA4-DG. In the amygdala, similar trends of accelerated volumetric decreases were observed in the left central nucleus, right paralaminar nucleus, right basal nucleus, and right accessory basal nucleus.

CONCLUSIONS

The current findings suggest that long-term heavy cannabis use impacts maturational process of the amygdala and hippocampus, especially in subregions with high concentrations of cannabinoid type 1 receptors (CB1Rs) and involvement in adult neurogenesis.

G protein-coupled receptor (GPCR) pharmacogenomics

The field of pharmacogenetics, the investigation of the influence of one or more sequence variants on drug response phenotypes, is a special case of pharmacogenomics, a discipline that takes a genome-wide approach. Massively parallel, next generation sequencing (NGS), has allowed pharmacogenetics to be subsumed by pharmacogenomics with respect to the identification of variants associated with responders and non-responders, optimal drug response, and adverse drug reactions. A plethora of rare and common naturally-occurring GPCR variants must be considered in the context of signals from across the genome. Many fundamentals of pharmacogenetics were established for G protein-coupled receptor (GPCR) genes because they are primary targets for a large number of therapeutic drugs. Functional studies, demonstrating likely-pathogenic and pathogenic GPCR variants, have been integral to establishing models used for in silico analysis. Variants in GPCR genes include both coding and non-coding single nucleotide variants and insertion or deletions (indels) that affect cell surface expression (trafficking, dimerization, and desensitization/downregulation), ligand binding and G protein coupling, and variants that result in alternate splicing encoding isoforms/variable expression. As the breadth of data on the GPCR genome increases, we may expect an increase in the use of drug labels that note variants that significantly impact the clinical use of GPCR-targeting agents. We discuss the implications of GPCR pharmacogenomic data derived from the genomes available from individuals who have been well-phenotyped for receptor structure and function and receptor-ligand interactions, and the potential benefits to patients of optimized drug selection. Examples discussed include the renin-angiotensin system in SARS-CoV-2 (COVID-19) infection, the probable role of chemokine receptors in the cytokine storm, and potential protease activating receptor (PAR) interventions. Resources dedicated to GPCRs, including publicly available computational tools, are also discussed.

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.

The Naturalistic Cannabis Administration Protocol (NCAP): A Proof-of-Concept Study

Lab-based studies examining the effects of cannabis administration on human behavior compromise ecological validity due to the influence of set and setting. Contextual factors of clinical settings have long been recognized as producing measurable changes in physiology, emotionality, and cognition. Among people who use drugs, these settings may be associated with higher levels of perceived stigma and stereotype threat which may meaningfully confound the effects of cannabis on outcomes of interest. Recent liberalization of cannabis regulation may allow novel and more ecologically valid approaches to assessing the acute effects of cannabis. The Naturalistic Cannabis Administration Protocol (NCAP) is a novel paradigm for the study of acute cannabis effects in an ecologically valid manner. Two independent studies demonstrated the safety and feasibility of the NCAP. Participants (N= 79; Mage = 25.44, SD = 5.67) self-administered the cannabis of their choice in their home and then (Study 1; n= 47) engaged in a leisure activity or (Study 2; n= 32) underwent cognitive assessment remotely via videoconference following cannabis administration. The NCAP was well tolerated across samples with no reported adverse events. These findings provide a rationale for the adoption of the NCAP to reduce research barriers and develop our research capabilities to fit the landscape of cannabis use today.

Cannabis Use and Endocannabinoid Receptor Genes: A Pilot Study on Their Interaction on Brain Activity in First-Episode Psychosis

The role of both cannabis use and genetic background has been shown in the risk for psychosis. However, the effect of the interplay between cannabis and variability at the endocannabinoid receptor genes on the neurobiological underpinnings of psychosis remains inconclusive. Through a case-only design, including patients with a first-episode of psychosis (n = 40) classified as cannabis users (50%) and non-users (50%), we aimed to evaluate the interaction between cannabis use and common genetic variants at the endocannabinoid receptor genes on brain activity. Genetic variability was assessed by genotyping two Single Nucleotide Polymorphisms (SNP) at the cannabinoid receptor type 1 gene (CNR1; rs1049353) and cannabinoid receptor type 2 gene (CNR2; rs2501431). Functional Magnetic Resonance Imaging (fMRI) data were obtained while performing the n-back task. Gene × cannabis interaction models evidenced a combined effect of CNR1 and CNR2 genotypes and cannabis use on brain activity in different brain areas, such as the caudate nucleus, the cingulate cortex and the orbitofrontal cortex. These findings suggest a joint role of cannabis use and cannabinoid receptor genetic background on brain function in first-episode psychosis, possibly through the impact on brain areas relevant to the reward circuit.

Cannabis Pharmacogenomics: A Path to Personalized Medicine

Cannabis and related compounds have created significant research interest as a promising therapy in many disorders. However, the individual therapeutic effects of cannabinoids and the incidence of side effects are still difficult to determine. Pharmacogenomics may provide the answers to many questions and concerns regarding the cannabis/cannabinoid treatment and help us to understand the variability in individual responses and associated risks. Pharmacogenomics research has made meaningful progress in identifying genetic variations that play a critical role in interpatient variability in response to cannabis. This review classifies the current knowledge of pharmacogenomics associated with medical marijuana and related compounds and can assist in improving the outcomes of cannabinoid therapy and to minimize the adverse effects of cannabis use. Specific examples of pharmacogenomics informing pharmacotherapy as a path to personalized medicine are discussed.

An Individuality of Response to Cannabinoids: Challenges in Safety and Efficacy of Cannabis Products

Since legalization, cannabis/marijuana has been gaining considerable attention as a functional ingredient in food. ∆-9 tetrahydrocannabinol (THC), cannabidiol (CBD), and other cannabinoids are key bioactive compounds with health benefits. The oral consumption of cannabis transports much less hazardous chemicals than smoking. Nevertheless, the response to cannabis is biphasically dose-dependent (hormesis; a low-dose stimulation and a high-dose inhibition) with wide individuality in responses. Thus, the exact same dose and preparation of cannabis may be beneficial for some but toxic to others. The purpose of this review is to highlight the concept of individual variations in response to cannabinoids, which leads to the challenge of establishing standard safe doses of cannabis products for the general population. The mechanisms of actions, acute and chronic toxicities, and factors affecting responses to cannabis products are updated. Based on the literature review, we found that the response to cannabis products depends on exposure factors (delivery route, duration, frequency, and interactions with food and drugs), individual factors (age, sex), and susceptibility factors (genetic polymorphisms of cannabinoid receptor gene, N-acylethanolamine-hydrolyzing enzymes, THC-metabolizing enzymes, and epigenetic regulations). Owing to the individuality of responses, the safest way to use cannabis-containing food products is to start low, go slow, and stay low.

Recent Advances in Endocannabinoid System Targeting for Improved Specificity: Strategic Approaches to Targeted Drug Delivery

Opportunities for developing innovative and intelligent drug delivery technologies by targeting the endocannabinoid system are becoming more apparent. This review provides an overview of strategies to develop targeted drug delivery using the endocannabinoid system (ECS). Recent advances in endocannabinoid system targeting showcase enhanced pharmaceutical therapy specificity while minimizing undesirable side effects and overcoming formulation challenges associated with cannabinoids. This review identifies advances in targeted drug delivery technologies that may permit access to the full pharmacotherapeutic potential of the ECS. The design of optimized nanocarriers that target specific tissues can be improved by understanding the nature of the signaling pathways, distribution in the mammalian body, receptor structure, and enzymatic degradation of the ECS. A closer look at ligand-receptor complexes, endocannabinoid tone, tissue distribution, and G-protein activity leads to a better understanding of the potential of the ECS toolkit for therapeutics. The signal transduction pathways examine the modulation of downstream effector proteins, desensitization, signaling cascades, and biased signaling. An in-depth and overall view of the targeted system is achieved through homology modeling where mutagenesis and ligand binding examine the binding site and allow sequence analysis and the formation of libraries for molecular docking and molecular dynamic simulations. Internalization routes exploring receptor-mediated endocytosis and lipid rafts are also considered for explicit signaling. Furthermore, the review highlights nanotechnology and surface modification aspects as a possible future approach for specific targeting.

Changes in brain structure and function following chronic exposure to inhaled vaporised cannabis during periadolescence in female and male mice: A multimodal MRI study

BACKGROUND AND AIMS

Social norms and legality surrounding the use of medical and recreational cannabis are changing rapidly. The prevalence of cannabis use in adolescence is increasing. The aim of this study was to assess any sex-based neurobiological effects of chronically inhaled, vaporised cannabis on adolescent female and male mice.

METHODS

Female and male mice were exposed daily to vaporised cannabis (10.3% Δ-9-tetrahydrocannabinol [THC] and 0.05% cannabidiol [CBD]) or placebo from postnatal day 23 to day 51. Following cessation of treatment, mice were examined for changes in brain structure and function using noninvasive multimodal magnetic resonance imaging (MRI). Data from voxel-based morphometry, diffusion weighted imaging and rest state functional connectivity were registered to and analysed with a 3D mouse atlas with 139 brain areas. Following imaging, mice were tested for their preference for a novel object.

RESULTS

The effects were sexually dimorphic with females showing a unique distribution and inverse correlation between measures of fractional anisotropy and apparent diffusion coefficient localised to the forebrain and hindbrain. In contrast males displayed significant increased functional coupling with the thalamus, hypothalamus and brainstem reticular activating system as compared with controls. Cannabis males also presented with altered hippocampal coupling and deficits in cognitive function.

CONCLUSION

Chronic exposure to inhaled vaporised cannabis had significant effects on brain structure and function in early adulthood corroborating much of the literature. Females presented with changes in grey matter microarchitecture, while males showed altered functional connectivity in hippocampal circuitry and deficits in object recognition.

Molecular Alterations of the Endocannabinoid System in Psychiatric Disorders

The therapeutic benefits of the current medications for patients with psychiatric disorders contrast with a great variety of adverse effects. The endocannabinoid system (ECS) components have gained high interest as potential new targets for treating psychiatry diseases because of their neuromodulator role, which is essential to understanding the regulation of many brain functions. This article reviewed the molecular alterations in ECS occurring in different psychiatric conditions. The methods used to identify alterations in the ECS were also described. We used a translational approach. The animal models reproducing some behavioral and/or neurochemical aspects of psychiatric disorders and the molecular alterations in clinical studies in post-mortem brain tissue or peripheral tissues were analyzed. This article reviewed the most relevant ECS changes in prevalent psychiatric diseases such as mood disorders, schizophrenia, autism, attentional deficit, eating disorders (ED), and addiction. The review concludes that clinical research studies are urgently needed for two different purposes: (1) To identify alterations of the ECS components potentially useful as new biomarkers relating to a specific disease or condition, and (2) to design new therapeutic targets based on the specific alterations found to improve the pharmacological treatment in psychiatry.

The cannabinoid receptor-1 gene interacts with stressful life events to increase the risk for problematic alcohol use

Problematic alcohol use is a major contributor to the global burden of death and disabilities, and it represents a public health concern that has grown substantially following the COVID-19 pandemic. The available treatment options remain limited and to develop better pharmacotherapies for alcohol misuse we need to identify suitable biological targets. Previous research has implicated the brain’s endocannabinoid system (ECS) in psychiatric and stress-related outcomes, including substance use and habituation to repeated stress. Moreover, genetic variants in the cannabinoid-1 receptor gene (CNR1; CB1R) have been associated with personality traits, which are in turn predictors of substance use disorders. To date, however, no human genome-wide association study has provided evidence for an involvement of the ECS in substance use outcomes. One reason for this ECS-related “missing heritability” may be unexamined gene-environment interactions. To explore this possibility, we conducted cross-sectional analyses using DNA samples and stress-exposure data from a longitudinal Swedish population-based study (N = 2,915). Specifically, we genotyped rs2023239, a functional C/T single nucleotide polymorphism in CNR1, previously reported to be associated with CNR1 binding in the brain, subjective reward following alcohol intake, and alcohol cue-elicited brain activation. Our two outcomes of interest were (i) problematic alcohol use based on the Alcohol Use Disorders Identification Test (AUDIT), and (ii) personality trait scores based on the Five Factor Model. We found no baseline association between rs2023239 and problematic alcohol use or personality traits. However, there was a clear trend for interaction between rs2023239’s risk allele (C) and stressful life events (SLEs) in both childhood and adulthood, which predicted problematic alcohol use. Although not significant, there was also some indication that the risk allele interacted with child SLEs to increase scores on neuroticism. Our study supports the notion that the ECS can affect alcohol intake behaviors by interacting with life adversities and is—to the best of our knowledge—the first to focus on the interaction between CNR1 and stressors in both childhood and adulthood in humans. Further studies are warranted to confirm these findings.

Biomarkers of the Endocannabinoid System in Substance Use Disorders

Despite substance use disorders (SUD) being one of the leading causes of disability and mortality globally, available therapeutic approaches remain ineffective. The difficulty in accurately characterizing the neurobiological mechanisms involved with a purely qualitative diagnosis is an obstacle to improving the classification and treatment of SUD. In this regard, identifying central and peripheral biomarkers is essential to diagnosing the severity of drug dependence, monitoring therapeutic efficacy, predicting treatment response, and enhancing the development of safer and more effective pharmacological tools. In recent years, the crucial role that the endocannabinoid system (ECS) plays in regulating the reinforcing and motivational properties of drugs of abuse has been described. This has led to studies characterizing ECS alterations after exposure to various substances to identify biomarkers with potential diagnostic, prognostic, or therapeutic utility. This review aims to compile the primary evidence available from rodent and clinical studies on how the ECS components are modified in the context of different substance-related disorders, gathering data from genetic, molecular, functional, and neuroimaging experimental approaches. Finally, this report concludes that additional translational research is needed to further characterize the modifications of the ECS in the context of SUD, and their potential usefulness in the necessary search for biomarkers.

The Effects of Nicotine and Cannabis Co-Use During Late Adolescence on White Matter Fiber Tract Microstructure

OBJECTIVE

Co-use of cannabis and nicotine and tobacco products (NTPs) in adolescence/young adulthood is common and associated with worse outcomes than the use of either substance in isolation. Despite this, little is known about the unique contributions of co-use to neurostructural microstructure during this neurodevelopmentally important period. This study sought to investigate the interactive effects of nicotine and cannabis co-use on white matter fiber tract microstructure in emerging adulthood.

METHOD

A total of 111 late adolescent (16-22 years old) nicotine (NTP; n = 55, all past-year cannabis users) and non-nicotine users (non-NTP; n = 56, 61% reporting cannabis use in the past year) completed demographic and clinical interviews and a neuroimaging session comprising anatomical and diffusion-weighted imaging scans. Group connectometry analysis identified white matter tracts significantly associated with the interaction between nicotine group and past-year cannabis use according to generalized fractional anisotropy (GFA).

RESULTS

Nicotine Group × Cannabis Use interactions were observed in the right and left cingulum and left fornix tracts (false discovery rate = 0.053), where greater cannabis use was associated with increased GFA in the cingulum and left fornix, but only when co-used with nicotine.

CONCLUSIONS

This report represents the first group connectometry analysis in late adolescent/young adult cannabis and/or NTP users. Results suggest that co-use of cannabis and NTPs results in a structurally distinct white matter phenotype as compared with cannabis use only, although to what extent this may change over time with more chronic nicotine and cannabis use remains to be examined in future work.

The Effects of Nicotine and Cannabis Co-Use During Late Adolescence on White Matter Fiber Tract Microstructure

OBJECTIVE

Co-use of cannabis and nicotine and tobacco products (NTPs) in adolescence/young adulthood is common and associated with worse outcomes than the use of either substance in isolation. Despite this, little is known about the unique contributions of co-use to neurostructural microstructure during this neurodevelopmentally important period. This study sought to investigate the interactive effects of nicotine and cannabis co-use on white matter fiber tract microstructure in emerging adulthood.

METHOD

A total of 111 late adolescent (16-22 years old) nicotine (NTP; n = 55, all past-year cannabis users) and non-nicotine users (non-NTP; n = 56, 61% reporting cannabis use in the past year) completed demographic and clinical interviews and a neuroimaging session comprising anatomical and diffusion-weighted imaging scans. Group connectometry analysis identified white matter tracts significantly associated with the interaction between nicotine group and past-year cannabis use according to generalized fractional anisotropy (GFA).

RESULTS

Nicotine Group × Cannabis Use interactions were observed in the right and left cingulum and left fornix tracts (false discovery rate = 0.053), where greater cannabis use was associated with increased GFA in the cingulum and left fornix, but only when co-used with nicotine.

CONCLUSIONS

This report represents the first group connectometry analysis in late adolescent/young adult cannabis and/or NTP users. Results suggest that co-use of cannabis and NTPs results in a structurally distinct white matter phenotype as compared with cannabis use only, although to what extent this may change over time with more chronic nicotine and cannabis use remains to be examined in future work.

Network-Based Pharmacology Study Reveals Protein Targets for Medical Benefits and Harms of Cannabinoids in Humans

This network-based pharmacology study intends to uncover the underlying mechanisms of cannabis leading to a therapeutic benefit and the pathogenesis for a wide range of diseases claimed to benefit from or be caused by the use of the cannabis plant. Cannabis contains more than 600 chemical components. Among these components, cannabinoids are well-known to have multifarious pharmacological activities. In this work, twelve cannabinoids were selected as active compounds through text mining and drug-like properties screening and used for initial protein-target prediction. The disease-associated biological functions and pathways were enriched through GO and KEGG databases. Various biological networks [i.e., protein-protein interaction, target-pathway, pathway-disease, and target-(pathway)-target interaction] were constructed, and the functional modules and essential protein targets were elucidated through the topological analyses of the networks. Our study revealed that eighteen proteins (CAT, COMT, CYP17A1, GSTA2, GSTM3, GSTP1, HMOX1, AKT1, CASP9, PLCG1, PRKCA, PRKCB, CYCS, TNF, CNR1, CNR2, CREB1, GRIN2B) are essential targets of eight cannabinoids (CBD, CBDA, Δ9-THC, CBN, CBC, CBGA, CBG, Δ8-THC), which involve in a variety of pathways resulting in beneficial and adverse effects on the human body. The molecular docking simulation confirmed that these eight cannabinoids bind to their corresponding protein targets with high binding affinities. This study generates a verifiable hypothesis of medical benefits and harms of key cannabinoids with a model which consists of multiple components, multiple targets, and multiple pathways, which provides an important foundation for further deployment of preclinical and clinical studies of cannabis.

Genetic basis of cannabis use: a systematic review

BACKGROUND

With the increase in cannabis use rates, cannabis use disorder is being reported as one of the most common drug use disorders globally. Cannabis use has several known physical, psychological, and social adverse events, such as altered judgement, poor educational outcomes, and respiratory symptoms. The propensity for taking cannabis and the development of a cannabis use disorder may be genetically influenced for some individuals. Heritability estimates suggest a genetic basis for cannabis use, and several genome-wide association studies (GWASs) have identified possible regions of association, albeit with inconsistent findings. This systematic review aims to summarize the findings from GWASs investigating cannabis use and cannabis use disorder.

METHODS

This systematic review incorporates articles that have performed a GWAS investigating cannabis use or cannabis use disorder. MEDLINE, Web of Science, EMBASE, CINAHL, GWAS Catalog, GWAS Central, and NIH Database of Genotype and Phenotype were searched using a comprehensive search strategy. All studies were screened in duplicate, and the quality of evidence was assessed using the quality of genetic association studies (Q-Genie) tool. All studies underwent qualitative synthesis; however, quantitative analysis was not feasible.

RESULTS

Our search identified 5984 articles. Six studies met our eligibility criteria and were included in this review. All six studies reported results that met our significance threshold of p ≤ 1.0 × 10-7. In total 96 genetic variants were identified. While meta-analysis was not possible, this review identified the following genes, ANKFN1, INTS7, PI4K2B, CSMD1, CST7, ACSS1, and SCN9A, to be associated with cannabis use. These regions were previously reported in different mental health conditions, however not in relation to cannabis use.

CONCLUSION

This systematic review summarized GWAS findings within the field of cannabis research. While a meta-analysis was not possible, the summary of findings serves to inform future candidate gene studies and replication efforts. Systematic Review Registration PROSPERO CRD42020176016.

Cannabis Affects Cerebellar Volume and Sleep Differently in Men and Women

Background: There are known sex differences in behavioral and clinical outcomes associated with drugs of abuse, including cannabis. However, little is known about how chronic cannabis use and sex interact to affect brain structure, particularly in regions with high cannabinoid receptor expression, such as the cerebellum, amygdala, and hippocampus. Based on behavioral data suggesting that females may be particularly vulnerable to the effects of chronic cannabis use, we hypothesized lower volumes in these regions in female cannabis users. We also hypothesized poorer sleep quality among female cannabis users, given recent findings highlighting the importance of sleep for many outcomes related to cannabis use disorder. Methods: Using data from the Human Connectome Project, we examined 170 chronic cannabis users (>100 lifetime uses and/or a lifetime diagnosis of cannabis dependence) and 170 controls that we attempted to match on age, sex, BMI, race, tobacco use, and alcohol use. We performed group-by-sex ANOVAs, testing for an interaction in subcortical volumes, and in self-reported sleep quality (Pittsburgh Sleep Questionnaire Inventory). Results: After controlling for total intracranial volume and past/current tobacco usage, we found that cannabis users relative to controls had smaller cerebellum volume and poorer sleep quality, and these effects were driven by the female cannabis users (i.e., a group-by-sex interaction). Among cannabis users, there was an age of first use-by-sex interaction in sleep quality, such that females with earlier age of first cannabis use tended to have more self-reported sleep issues, whereas this trend was not present among male cannabis users. The amygdala volume was smaller in cannabis users than in non-users but the group by sex interaction was not significant. Conclusions: These data corroborate prior findings that females may be more sensitive to the neural and behavioral effects of chronic cannabis use than males. Further work is needed to determine if reduced cerebellar and amygdala volumes contribute to sleep impairments in cannabis users.

Sex and dependence related neuroanatomical differences in regular cannabis users: findings from the ENIGMA Addiction Working Group

Males and females show different patterns of cannabis use and related psychosocial outcomes. However, the neuroanatomical substrates underlying such differences are poorly understood. The aim of this study was to map sex differences in the neurobiology (as indexed by brain volumes) of dependent and recreational cannabis use. We compared the volume of a priori regions of interest (i.e., amygdala, hippocampus, nucleus accumbens, insula, orbitofrontal cortex (OFC), anterior cingulate cortex and cerebellum) between 129 regular cannabis users (of whom 70 were recreational users and 59 cannabis dependent) and 114 controls recruited from the ENIGMA Addiction Working Group, accounting for intracranial volume, age, IQ, and alcohol and tobacco use. Dependent cannabis users, particularly females, had (marginally significant) smaller volumes of the lateral OFC and cerebellar white matter than recreational users and controls. In dependent (but not recreational) cannabis users, there was a significant association between female sex and smaller volumes of the cerebellar white matter and OFC. Volume of the OFC was also predicted by monthly standard drinks. No significant effects emerged the other brain regions of interest. Our findings warrant future multimodal studies that examine if sex and cannabis dependence are specific key drivers of neurobiological alterations in cannabis users. This, in turn, could help to identify neural pathways specifically involved in vulnerable cannabis users (e.g., females with cannabis dependence) and inform individually tailored neurobiological targets for treatment.

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.

Recent cannabis use is associated with smaller hippocampus volume: High-resolution segmentation of structural subfields in a large non-clinical sample

There is mixed evidence that individuals who use cannabis have reduced hippocampal and amygdalar gray matter volume, potentially because of small sample sizes and imprecise morphological characterization. New automated segmentation procedures have improved the measurement of these structures and allow better examination of their subfields, which have been linked to distinct aspects of memory and emotion. The current study applies this new segmentation procedure to the Human Connectome Project Young Adult dataset (N = 1080) to investigate associations of cannabis use with gray matter volume in the hippocampus and amygdala. Results revealed significant bilateral inverse associations of hippocampal volume with recent cannabis use (THC+ urine drug screen; P < .005). Hippocampal subfield analyses indicated these associations were primarily driven by the head of the hippocampus, the first section of the cornu amonis (CA1), the subicular complex, and the molecular layer of the hippocampus. No associations were detected for age of cannabis initiation, the frequency of cannabis use across the lifespan, or the lifetime presence of cannabis use disorder. In one of the largest studies to date, these results support the hypothesis that recent cannabis use is linked to reduced hippocampal volume, but that this effect may dissipate following prolonged abstinence. Furthermore, these results clarify the specific subfields which may be most associated with recent cannabis use.

BOLD responses to inhibition in cannabis-using adolescents and emerging adults after 2 weeks of monitored cannabis abstinence

RATIONALE

Previous studies have suggested that chronic cannabis use has been associated with increased blood oxygen level-dependent (BOLD) response during a response inhibition task; however, these studies primarily included males.

OBJECTIVES

We investigated whether gender moderated the effects of cannabis use on BOLD response and behavioral performance during a Go-NoGo task in adolescents and young adults following 2 weeks of monitored abstinence.

METHODS

Participants included 77 16-26-year olds (MJ = 36, controls = 41). An emotion-based Go-NoGo task required participants to inhibit their response during a calm face. A whole-brain analysis looked at differences between cannabis group, gender, and their interaction.

RESULTS

Significant greater BOLD responses were observed in cannabis users compared with that in controls in the left frontal cortex, left cingulate cortex, and the left thalamus during correct response inhibitions; gender did not moderate these effects.

CONCLUSION

Supporting previous research, cannabis users showed greater BOLD responses in core areas associated with response inhibition during a Go-NoGo task, even after a minimum of 2 weeks of abstinence.

Marijuana use and major depressive disorder are additively associated with reduced verbal learning and altered cortical thickness

Marijuana (MJ) use and major depressive disorder (MDD) have both been associated with deficits in verbal learning and memory as well as structural brain abnormalities. It is not known if MJ use by those with MDD confers additional impairment. The goal of this study was to examine unique and combined effects of MDD and MJ use on verbal memory and brain structure. Young adults (n=141) aged 18-25 years with MJ use and no lifetime MDD (MJ, n=46), MDD and no MJ use (MDD, n=23), MJ use and lifetime MDD (MDD+MJ, n=24), and healthy controls without MDD or MJ use (CON, n=48) were enrolled. Participants completed the California Verbal Learning Test, Second Edition (CVLT-II), a measure of verbal learning and memory. A sub-sample of 82 participants also underwent a structural magnetic resonance imaging (MRI) scan. Group differences in CVLT-II performance, cortical thickness, and hippocampal volume were assessed. We found an additive effect of MDD and MJ on memory recall. Only MDD, but not MJ, was associated with poorer initial learning, fewer words recalled, more intrusion errors, and lower percent retention. There was also an additive effect of MDD and MJ use on reduced cortical thickness in the middle temporal gyrus. Findings indicate that MJ use and MDD have additive adverse associations with verbal recall and cortical thickness in the middle temporal gyrus, suggesting that MJ use among those with MDD may be contraindicated. Prospective studies are warranted to determine whether this association may be causal.

Impact of Cannabis Use on Brain Structure and Function in Suppressed HIV Infection

BACKGROUND

Brain atrophy and cognitive deficits persist among individuals with suppressed HIV disease. The impact of cannabis use is unknown.

METHODS

HIV+ and HIV- participants underwent cross-sectional magnetic resonance imaging and neuropsychological testing. Lifetime frequency, duration (years), and recency of cannabis use were self-reported. Relationships of cannabis use to resting-state functional connectivity (RSFC) and to 9 regional brain volumes were assessed with corrections for multiple comparisons. Peripheral blood cytokines and monocyte subsets were measured in the HIV+ group and examined in relation to cannabis exposure.

RESULTS

We evaluated 52 HIV+ [50.8 ± 7.1 years old; 100% on antiretroviral therapy ≥ 3 months; 83% with plasma viral load < 50 copies/mL] and 55 HIV- [54.0 ± 7.5 years old] individuals. Among HIV+ participants, recent cannabis use (within 12 months) was associated with diminished RSFC, including of occipital cortex, controlling for age. Duration of use correlated negatively with volumes of all regions (most strikingly the nucleus accumbens) independently of recent use and intracranial volume. Recent use was associated with larger caudate and white matter volumes and lower soluble vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1 concentrations. Duration of use correlated positively with psychomotor speed. Use > 10 times/lifetime was linked to more somatic symptoms, better executive function, and lower CD14⁺CD16⁺⁺ monocyte count.

CONCLUSION

HIV+ individuals demonstrated opposing associations with cannabis. Recent use may weaken RSFC and prolonged consumption may exacerbate atrophy of the accumbens and other brain regions. More frequent or recent cannabis use may reduce the inflammation and CD14⁺CD16⁺⁺ monocytes that facilitate HIV neuroinvasion. HIV-specific cannabis studies are necessary.

Emerging Promise of Cannabinoids for the Management of Pain and Associated Neuropathological Alterations in Alzheimer's Disease

Alzheimer's disease (AD) is an irreversible chronic neurodegenerative disorder that occurs when neurons in the brain degenerate and die. Pain frequently arises in older patients with neurodegenerative diseases including AD. However, the presence of pain in older people is usually overlooked with cognitive dysfunctions. Most of the times dementia patients experience moderate to severe pain but the development of severe cognitive dysfunctions tremendously affects their capability to express the presence of pain. Currently, there are no effective treatments against AD that emphasize the necessity for increasing research to develop novel drugs for treating or preventing the disease process. Furthermore, the prospective therapeutic use of cannabinoids in AD has been studied for the past few years. In this regard, targeting the endocannabinoid system has considered as a probable therapeutic strategy to control several associated pathological pathways, such as mitochondrial dysfunction, excitotoxicity, oxidative stress, and neuroinflammation for the management of AD. In this review, we focus on recent studies about the role of cannabinoids for the treatment of pain and related neuropathological changes in AD.

Cannabis, Cannabinoids, and Brain Morphology: A Review of the Evidence

Cannabis and cannabinoid-based products are increasingly being accepted and commodified globally. Yet there is currently limited understanding of the effect of the varied cannabinoid compounds on the brain. Exogenous cannabinoids interact with the endogenous cannabinoid system that underpins vital functions in the brain and body, and they are thought to perturb key brain and cognitive function. However, much neuroimaging research has been confined to observational studies of cannabis users, without examining the specific role of the various cannabinoids (Δ⁹-tetrahydrocannabinol, cannabidiol, etc.). This review summarizes the brain structural imaging evidence to date associated with cannabis use, its major cannabinoids (e.g., Δ⁹-tetrahydrocannabinol, cannabidiol), and synthetic cannabinoid products that have emerged as recreational drugs. In doing so, we seek to highlight some of the key issues to consider in understanding cannabinoid-related brain effects, emphasizing the dual neurotoxic and neuroprotective role of cannabinoids, and the need to consider the distinct role of the varied cannabinoids in establishing their effect on the brain.

Acute Hippocampal Encephalopathy in Heavy Cannabis Users: About 2 Cases

BACKGROUND

Cannabis use is increasing worldwide despite the various health effects of this substance.

METHODS

We report 2 cases of acute hippocampal encephalopathy in heavy cannabis users (>10 joints/d).

RESULTS

In both male patients, acute encephalitis was suspected. Brain magnetic resonance imaging (MRI) diffusion-weighted sequences showed bilateral high signal abnormalities in hippocampal regions. Patients had renal dysfunction, rhabdomyolysis, and inflammatory syndrome. Investigations showed no evidence of infectious or autoimmune encephalitides. Repeated electroencephalograms revealed no epileptic activity. Clinical, biological, and magnetic resonance imaging acute abnormalities improved within weeks. New exposure to cannabis yielded a new episode of encephalopathy. In both patients, severe long-lasting episodic memory impairment associated with hippocampal atrophy were observed several months later.

CONCLUSIONS

Health professionals should be aware of this cannabis-related syndrome given its severe and long-lasting effects.

Deconstructing the neurobiology of cannabis use disorder

There have been dramatic changes worldwide in the attitudes toward and consumption of recreational and medical cannabis. Cannabinoid receptors, which mediate the actions of cannabis, are abundantly expressed in brain regions known to mediate neural processes underlying reward, cognition, emotional regulation and stress responsivity relevant to addiction vulnerability. Despite debates regarding potential pathological consequences of cannabis use, cannabis use disorder is a clinical diagnosis with high prevalence in the general population and that often has its genesis in adolescence and in vulnerable individuals associated with psychiatric comorbidity, genetic and environmental factors. Integrated information from human and animal studies is beginning to expand insights regarding neurobiological systems associated with cannabis use disorder, which often share common neural characteristics with other substance use disorders, that could inform prevention and treatment strategies.

Disease-associated polymorphisms within the conserved ECR1 enhancer differentially regulate the tissue-specific activity of the cannabinoid-1 receptor gene promoter; implications for cannabinoid pharmacogenetics

Cannabinoid receptor‐1 (CB1) represents a potential drug target against conditions that include obesity and substance abuse. However, drug trials targeting CB1 (encoded by the CNR1 gene) have been compromised by differences in patient response. Toward addressing the hypothesis that genetic changes within the regulatory regions controlling CNR1 expression contribute to these differences, we characterized the effects of disease‐associated allelic variation within a conserved regulatory sequence (ECR1) in CNR1 intron 2 that had previously been shown to modulate cannabinoid response, alcohol intake, and anxiety‐like behavior. We used primary cell analysis of reporters carrying different allelic variants of the human ECR1 and found that human‐specific C‐allele variants of ECR1 (ECR1(C)) drove higher levels of CNR1prom activity in primary hippocampal cells than did the ancestral T‐allele and demonstrated a differential response to CB1 agonism. We further demonstrate a role for the AP‐1 transcription factor in driving higher ECR1(C) activity and evidence that the ancestral t‐allele variant of ECR1 interacted with higher affinity with the insulator binding factor CTCF. The cell‐specific approaches used in our study represent an important step in gaining a mechanistic understanding of the roles of noncoding polymorphic variation in disease and in the increasingly important field of cannabinoid pharmacogenetics.

Disruption of an enhancer associated with addictive behaviour within the cannabinoid receptor-1 gene suggests a possible role in alcohol intake, cannabinoid response and anxiety-related behaviour

The cannabinoid-1 receptor (CB₁) plays a critical role in a number of biological processes including nutrient intake, addiction and anxiety-related behaviour. Numerous studies have shown that expression of the gene encoding CB1 (CNR1) is highly dynamic with changes in the tissue specific expression of CNR1 associated with brain homeostasis and disease progression. However, little is known of the mechanisms regulating this dynamic expression. To gain a better understanding of the genomic mechanisms modulating the expression of CNR1 in health and disease we characterised the role of a highly conserved regulatory sequence (ECR1) in CNR1 intron 2 that contained a polymorphism in linkage disequilibrium with disease associated SNPs. We used CRISPR/CAS9 technology to disrupt ECR1 within the mouse genome. Disruption of ECR1 significantly reduced CNR1 expression in the hippocampus but not in the hypothalamus. These mice also displayed an altered sex-specific anxiety-related behavioural profile (open field test), reduced ethanol intake and a reduced hypothermic response following CB₁ agonism. However, no significant changes in feeding patterns were detected. These data suggest that, whilst not all of the expression of CNR1 is modulated by ECR1, this highly conserved enhancer is required for appropriate physiological responses to a number of stimuli. The combination of comparative genomics and CRISPR/CAS9 disruption used in our study to determine the functional effects of genetic and epigenetic changes on the activity of tissue-specific regulatory elements at the CNR1 locus represent an important first step in gaining a mechanistic understanding of cannabinoid regulatory pharmacogenetics.

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.

Cortical Thickness and Subcortical Volumes in Adolescent Synthetic Cannabinoid Users with or Without ADHD: a Preliminary Study

Introduction

Synthetic cannabinoids (SCs) have become increasingly popular in the last few years, especially among adolescents. Given Attention deficit/hyperactivity disorder (ADHD) is over represented in patients with substance use across adolescents compared to the general population, the current study aims were two-fold: i) examine cortical thickness, surface area and subcortical volumes in SC users compared to controls, ii) examine the influence of ADHD on cortical thickness, surface area and subcortical volumes in SC users.

Methods

Structural magnetic resonance imaging scans were acquired from 28 SC users (15 without ADHD and 13 with ADHD combined type) and 13 controls.

Results

We found that SC users both with and without ADHD groups have significantly reduced cortical thickness compared to controls in areas of the left caudal middle frontal and left superior frontal. In addition, SC users with ADHD also showed reduced cortical thickness in the right precentral and postcentral gyruses. We also found increased right nucleus accumbens volume in SC users without ADHD, but not with ADHD, compared to controls.

Conclusion

These results suggest that similar to cannabis use, SC use has also negative effects on brain morphology and comorbidity of ADHD and substance dependence may show different cortical thickness and subcortical volume alterations than substance use alone.

Brain-behavior relations and effects of aging and common comorbidities in alcohol use disorder: A review

OBJECTIVE

Alcohol use disorder (AUD) is a complex, dynamic condition that waxes and wanes with unhealthy drinking episodes and varies in drinking patterns and effects on brain structure and function with age. Its excessive use renders chronically heavy drinkers vulnerable to direct alcohol toxicity and a variety of comorbidities attributable to nonalcohol drug misuse, viral infections, and accelerated or premature aging. AUD affects widespread brain systems, commonly, frontolimbic, frontostriatal, and frontocerebellar networks.

METHOD AND RESULTS

Multimodal assessment using selective neuropsychological testing and whole-brain neuroimaging provides evidence for AUD-related specific brain structure-function relations established with double dissociations. Longitudinal study using noninvasive imaging provides evidence for brain structural and functional improvement with sustained sobriety and further decline with relapse. Functional imaging suggests the possibility that some alcoholics in recovery can compensate for impairment by invoking brain systems typically not used for a target task but that can enable normal-level performance.

CONCLUSIONS

Evidence for AUD-aging interactions, indicative of accelerated aging, together with increasing alcohol consumption in middle-age and older adults, put aging drinkers at special risk for developing cognitive decline and possibly dementia. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Associations between adolescent cannabis use frequency and adult brain structure: A prospective study of boys followed to adulthood

BACKGROUND

Few studies have tested the hypothesis that adolescent cannabis users show structural brain alterations in adulthood. The present study tested associations between prospectively-assessed trajectories of adolescent cannabis use and adult brain structure in a sample of boys followed to adulthood.

METHODS

Data came from the Pittsburgh Youth Study - a longitudinal study of ˜1000 boys. Boys completed self-reports of cannabis use annually from age 13-19, and latent class growth analysis was used to identify different trajectories of adolescent cannabis use. Once adolescent cannabis trajectories were identified, boys were classified into their most likely cannabis trajectory. A subset of boys (n = 181) subsequently underwent structural neuroimaging in adulthood, when they were between 30-36 years old on average. For this subset, we grouped participants according to their classified adolescent cannabis trajectory and tested whether these groups showed differences in adult brain structure in 14 a priori regions of interest, including six subcortical (volume only: amygdala, hippocampus, nucleus accumbens, caudate, putamen, and pallidum) and eight cortical regions (volume and thickness: superior frontal gyrus; caudal and rostral middle frontal gyrus; inferior frontal gyrus, separated into pars opercularis, pars triangularis, and pars orbitalis; lateral and medial orbitofrontal gyrus).

RESULTS

We identified four adolescent cannabis trajectories: non-users/infrequent users, desisters, escalators, and chronic-relatively frequent users. Boys in different trajectory subgroups did not differ on adult brain structure in any subcortical or cortical region of interest.

CONCLUSIONS

Adolescent cannabis use is not associated with structural brain differences in adulthood.

CNR1 and FAAH variation and affective states induced by marijuana smoking

Background: Polymorphisms in cannabinoid receptor type 1 (encoded by CNR1) and fatty acid amide hydrolase (encoded by FAAH) have been associated with cannabis dependence, but it remains unknown whether variation within these genes influences cannabis' acute effects on affect. Objective: Conduct a secondary data analysis study to determine whether previously observed acute effects of tetrahydrocannabinol (THC) on mood was dependent upon variation in CNR1 and FAAH. Methods: A balanced placebo design was used crossing marijuana administration (i.e., 0% THC vs. 2.8% THC) with stimulus expectancy. Participants (N = 118; 64% male) provided DNA and completed the Profile of Mood States questionnaire prior to and after smoking. Haplotypes were constructed from genotyped single nucleotide polymorphisms for CNR1 (rs1049353 and rs806368) and FAAH (rs4141964, rs324420, and rs11576941); rs2023239 (CNR1) and rs6703669 (FAAH) were not part of a phased haplotype block. Analyses tested both main and interaction effects for genotype across CNR1 and FAAH, and drug, and expectancy effects. Results: THC increased levels of POMS Tension-Anxiety and Confusion-Bewilderment over and above the effects of variation in CNR1 and FAAH. Significant drug X genotype/haplotype and expectancy X genotype/haplotype interaction effects were observed for some but not all mood states [e.g., 'C' allele carriers of rs2023239 who received THC had higher levels of Anger-Hostility (β= 0.29 (0.12), p= .02) compared to those who received placebo]. Conclusion: These preliminary findings suggest individual differences in mood states after using marijuana depend on genetic variation. Such information might be useful in understanding either motivation for use of marijuana and/or risk for associated behaviors.

Distal Functional Connectivity of Known and Emerging Cortical Targets for Therapeutic Noninvasive Stimulation

Noninvasive stimulation is an emerging modality for the treatment of psychiatric disorders, including addiction. A crucial element in effective cortical target selection is its distal influence. We approached this question by examining resting-state functional connectivity patterns in known and potential stimulation targets in 145 healthy adults. We compared connectivity patterns with distant regions of particular relevance in the development and maintenance of addiction. We used stringent Bonferroni-correction for multiple comparisons. We show how the anterior insula, dorsal anterior cingulate, and ventromedial prefrontal cortex had opposing functional connectivity with striatum compared to the dorsomedial prefrontal cortex. However, the dorsolateral prefrontal cortex, the currently preferred target, and the presupplementary motor area had strongest negative connections to amygdala and hippocampus. Our findings highlight differential and opposing influences as a function of cortical site, underscoring the relevance of careful cortical target selection dependent on the desired effect on subcortical structures. We show the relevance of dorsal anterior cingulate and ventromedial prefrontal cortex as emerging cortical targets, and further emphasize the anterior insula as a potential promising target in addiction treatment, given its strong connections to ventral striatum, putamen, and substantia nigra.

Grey Matter Volume Differences Associated with Extremely Low Levels of Cannabis Use in Adolescence

Rates of cannabis use among adolescents are high, and are increasing concurrent with changes in the legal status of marijuana and societal attitudes regarding its use. Recreational cannabis use is understudied, especially in the adolescent period when neural maturation may make users particularly vulnerable to the effects of Δ-9-tetrahydrocannabinol (THC) on brain structure. In the current study, we used voxel-based morphometry to compare gray matter volume (GMV) in forty-six 14-year-old human adolescents (males and females) with just one or two instances of cannabis use and carefully matched THC-naive controls. We identified extensive regions in the bilateral medial temporal lobes as well as the bilateral posterior cingulate, lingual gyri, and cerebellum that showed greater GMV in the cannabis users. Analysis of longitudinal data confirmed that GMV differences were unlikely to precede cannabis use. GMV in the temporal regions was associated with contemporaneous performance on the Perceptual Reasoning Index and with future generalized anxiety symptoms in the cannabis users. The distribution of GMV effects mapped onto biomarkers of the endogenous cannabinoid system providing insight into possible mechanisms for these effects.SIGNIFICANCE STATEMENT Almost 35% of American 10th graders have reported using cannabis and existing research suggests that initiation of cannabis use in adolescence is associated with long-term neurocognitive effects. We understand very little about the earliest effects of cannabis use, however, because most research is conducted in adults with a heavy pattern of lifetime use. This study presents evidence suggesting structural brain and cognitive effects of just one or two instances of cannabis use in adolescence. Converging evidence suggests a role for the endocannabinoid system in these effects. This research is particularly timely as the legal status of cannabis is changing in many jurisdictions and the perceived risk by youth associated with smoking cannabis has declined in recent years.

Does regular cannabis use affect neuroanatomy? An updated systematic review and meta-analysis of structural neuroimaging studies

Regular cannabis use is associated with adverse cognitive and mental health outcomes that have been ascribed to aberrant neuroanatomy in brain regions densely innervated with cannabinoid receptors. Neuroanatomical differences between cannabis users and controls have been assessed in multiple structural magnetic resonance imaging (sMRI) studies. However, there is heterogeneity in the results leading to cautious interpretation of the data so far. We examined the sMRI evidence to date in human cannabis users, to establish more definitely whether neuroanatomical alterations are associated with regular cannabis use. The regional specificity and association with cannabis use indices (i.e. cumulative dosage, duration) were also explored. We systematically reviewed and meta-analysed published sMRI studies investigating regional brain volumes (cortical, subcortical and global) in cannabis users and non-user controls. Three electronic databases were searched (PubMed, Scopus, and PsycINFO). A total of 17 meta-analyses were conducted (one for each cortical, subcortical and global volume) using the generic inverse variance method, whereby standardised mean difference in volume was calculated between users and non-users. Exploratory meta-regressions were conducted to investigate the association between cannabis use indices and regional brain volumes. A total of 30 articles were eligible for inclusion, contributing 106 effect sizes across 17 meta-analyses. Regular cannabis users had significantly smaller volumes of the hippocampus (SMD = 0.14, 95% CIs [0.02, 0.27]; Z = 2.29, p = 0.02, I² = 74%) and orbitofrontal cortex {medial (SMD = 0.30, 95% CIs [0.15, 0.45]; Z = 3.89, p = 0.0001, I² = 51%), lateral (SMD = 0.19, 95% CIs [0.07, 0.32]; Z = 3.10, p = 0.002, I² = 26%)} relative to controls. The volumes of the hippocampus and orbitofrontal cortex were not significantly associated with cannabis duration and dosage. Our findings are consistent with evidence of aberrance in brain regions involved in reward, learning and memory, and motivation circuits in the regular use of substances other than cannabis, pointing to commonality in neurobiological abnormalities between regular users of cannabis and of other substances.

Tempering aversive/traumatic memories with cannabinoids: a review of evidence from animal and human studies

RATIONALE

Aversive learning and memory are essential to cope with dangerous and stressful stimuli present in an ever-changing environment. When this process is dysfunctional, however, it is associated with posttraumatic stress disorder (PTSD). The endocannabinoid (eCB) system has been implicated in synaptic plasticity associated with physiological and pathological aversive learning and memory.

OBJECTIVE AND METHODS

The objective of this study was to review and discuss evidence on how and where in the brain genetic or pharmacological interventions targeting the eCB system would attenuate aversive/traumatic memories through extinction facilitation in laboratory animals and humans. The effect size of the experimental intervention under investigation was also calculated.

RESULTS

Currently available data indicate that direct or indirect activation of cannabinoid type-1 (CB1) receptor facilitates the extinction of aversive/traumatic memories. Activating CB1 receptors around the formation of aversive/traumatic memories or their reminders can potentiate their subsequent extinction. In most cases, the effect size has been large (Cohen's d ≥ 1.0). The brain areas responsible for the abovementioned effects include the medial prefrontal cortex, amygdala, and/or hippocampus. The potential role of cannabinoid type-2 (CB2) receptors in extinction learning is now under investigation.

CONCLUSION

Drugs augmenting the brain eCB activity can temper the impact of aversive/traumatic experiences by diverse mechanisms depending on the moment of their administration. Considering the pivotal role the extinction process plays in PTSD, the therapeutic potential of these drugs is evident. The sparse number of clinical trials testing these compounds in stress-related disorders is a gap in the literature that needs to be addressed.

Synaptic Plasticity in the Nucleus Accumbens: Lessons Learned from Experience

Synaptic plasticity contributes to behavioral adaptations. As a key node in the reward pathway, the nucleus accumbens (NAc) is important for determining motivation-to-action outcomes. Across animal models of motivation including addiction, depression, anxiety, and hedonic feeding, selective recruitment of neuromodulatory signals and plasticity mechanisms have been a focus of physiologists and behaviorists alike. Experience-dependent plasticity mechanisms within the NAc vary depending on the distinct afferents and cell-types over time. A greater understanding of molecular mechanisms determining how these changes in synaptic strength track with behavioral adaptations will provide insight into the process of learning and memory along with identifying maladaptations underlying pathological behavior. Here, we summarize recent findings detailing how changes in NAc synaptic strength and mechanisms of plasticity manifest in various models of motivational disorders.

Overweight adolescents' brain response to sweetened beverages mirrors addiction pathways

Many adolescents struggle with overweight/obesity, which exponentially increases in the transition to adulthood. Overweight/obesity places youth at risk for serious health conditions, including type 2 diabetes. In adults, neural substrates implicated in addiction (e.g., orbitofrontal cortex (OFC), striatum, amygdala, and ventral tegmental area) have been found to be relevant to risk for overweight/obesity. In this study, we examined three hypotheses to disentangle the potential overlap between addiction and overweight/obesity processing by examining (1) brain response to high vs. low calorie beverages, (2) the strength of correspondence between biometrics, including body mass index (BMI) and insulin resistance, and brain response and (3) the relationship between a measure of food addiction and brain response using an established fMRI gustatory cue exposure task with a sample of overweight/obese youth (M age = 16.46; M BMI = 33.1). Greater BOLD response was observed across the OFC, inferior frontal gyrus (IFG), nucleus accumbens, right amygdala, and additional frontoparietal and temporal regions in neural processing of high vs. low calorie beverages. Further, BMI scores positively correlated with BOLD activation in the high calorie > low calorie contrast in the right postcentral gyrus and central operculum. Insulin resistance positively correlated with BOLD activation across the bilateral middle/superior temporal gyrus, left OFC, and superior parietal lobe. No relationships were observed between measures of food addiction and brain response. These findings support the activation of parallel addiction-related neural pathways in adolescents' high calorie processing, while also suggesting the importance of refining conceptual and neurocognitive models to fit this developmental period.

Cannabinoid Receptors and the Endocannabinoid System: Signaling and Function in the Central Nervous System

The biological effects of cannabinoids, the major constituents of the ancient medicinal plant Cannabis sativa (marijuana) are mediated by two members of the G-protein coupled receptor family, cannabinoid receptors 1 (CB1R) and 2. The CB1R is the prominent subtype in the central nervous system (CNS) and has drawn great attention as a potential therapeutic avenue in several pathological conditions, including neuropsychological disorders and neurodegenerative diseases. Furthermore, cannabinoids also modulate signal transduction pathways and exert profound effects at peripheral sites. Although cannabinoids have therapeutic potential, their psychoactive effects have largely limited their use in clinical practice. In this review, we briefly summarized our knowledge of cannabinoids and the endocannabinoid system, focusing on the CB1R and the CNS, with emphasis on recent breakthroughs in the field. We aim to define several potential roles of cannabinoid receptors in the modulation of signaling pathways and in association with several pathophysiological conditions. We believe that the therapeutic significance of cannabinoids is masked by the adverse effects and here alternative strategies are discussed to take therapeutic advantage of cannabinoids.

The Influence of DAT1, COMT, and BDNF Genetic Polymorphisms on Total and Subregional Hippocampal Volumes in Early Onset Heavy Cannabis Users

Introduction: Hippocampal neuroanatomy is affected by genetic variations in dopaminergic candidate genes and environmental insults, such as early onset of chronic cannabis exposure. Here, we examine how hippocampal total and subregional volumes are affected by cannabis use and functional polymorphisms of dopamine-relevant genes, including the catechol-O-methyltransferase (COMT), dopamine transporter (DAT1), and the brain-derived neurotrophic factor (BDNF) genes.

Material and Methods: We manually traced total hippocampal volumes and automatically segmented hippocampal subregions using high-resolution MRI images, and performed COMT, DAT1, and BDNF genotyping in 59 male Caucasian young adults aged 18–30 years. These included 30 chronic cannabis users with early-onset (regular use at <16 years) and 29 age-, education-, and intelligence-matched controls.

Results: Cannabis use and dopaminergic gene polymorphism had both distinct and interactive effects on the hippocampus. We found emerging alterations of hippocampal total and specific subregional volumes in cannabis users relative to controls (i.e., CA1, CA2/3, and CA4), and associations between cannabis use levels and total and specific subregional volumes. Furthermore, total hippocampal volume and the fissure subregion were affected by cannabis×DAT1 polymorphism (i.e., 9/9R and in 10/10R alleles), reflecting high and low levels of dopamine availability.

Conclusion: These findings suggest that cannabis exposure alters the normal relationship between DAT1 polymorphism and the anatomy of total and subregional hippocampal volumes, and that specific hippocampal subregions may be particularly affected.

Developmentally Specific Associations Between CNR1 Genotype and Cannabis Use Across Emerging Adulthood

OBJECTIVE

Previous studies have found preliminary evidence for associations between common single-nucleotide polymorphisms (SNPs) in the cannabinoid receptor gene CNR1 and cannabis use and dependence. The present study examined a set of eight independent SNPs in or near CNR1 in relation to cannabis use measured longitudinally across emerging adulthood.

METHOD

Using latent growth curve modeling of 10 waves of longitudinal data spanning mean ages 18.4-23.8 years in a sample of non-Hispanic White individuals (n = 334), we tested if genotype at each CNR1 SNP was associated with both level and growth of cannabis use over time. Peer group drug use, a known correlate of individual use, was evaluated as a time-varying predictor of cannabis use and as a moderator of the relationship between SNPs and individual use.

RESULTS

After correction for multiple comparisons, one SNP, rs806374, was significantly associated with individual differences in level-but not growth-of cannabis use over time, such that C carriers were more likely to use cannabis more frequently at study onset (around age 18). Peer drug use was a predictor of individual cannabis use that grew in terms of effect size with time, but did not significantly moderate the effect of rs806374 genotype.

CONCLUSIONS

C carriers at rs806374 may be at specific risk for increased odds of use during the transition out of high school (around age 18). Future studies should investigate potential mechanisms at this developmental stage, including individual differences in subjective response, innate tolerance, reinforcement mechanisms, or general liability for substance misuse.

Cannabinoid Receptor 1 Gene by Cannabis Use Interaction on CB1 Receptor Density

Background: Because delta-9-tetrahydrocannabinol (THC), the primary psychoactive ingredient in cannabis, binds to cannabinoid 1 (CB1) receptors, levels of CB1 protein could serve as a potential biomarker for response to THC. To date, available techniques to characterize CB1 expression and function in vivo are limited. In this study, we developed an assay to quantify CB1 in lymphocytes to determine how it relates to cannabis use in 58 daily cannabis users compared with 47 nonusers. Furthermore, we tested whether CB1 levels are associated with mutations in a single nucleotide polymorphism known to regulate CB1 functioning (i.e., rs2023239).

Methods: Total protein concentration was analyzed through the Pierce BCA Protein assay kit. CB1 protein was quantified through CNR1 enzyme-linked immunosorbent assay (ELISA) kit from MyBioSource. CB1 concentration and total protein concentration were quantified and used to calculate a ratio of CB1 to total protein.

Results: Inherent levels of peripheral lymphocyte CB1 were sufficient for quantification through ELISA without protein amplification. We found a group×genotype interaction such that users with the G allele had greater CB1 concentration than users with the A/A genotype, and a trend-level difference between genotypes in nonusers.

Conclusions: This study demonstrates a minimally invasive technique of CB1 quantification that holds promise for the use of CB1 protein concentration, along with rs2023239 genotype, as a potential biomarker for susceptibility to cannabis use. These results suggest a gene (rs2023239 G)×environment (cannabis use) effect on CB1 density.

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".