Functional imaging studies in cannabis users

Chronic exposure to a synthetic cannabinoid alters cerebral brain metabolism and causes long-lasting behavioral deficits in adult mice

In recent years, there has been growing evidence that cannabinoids have promising medicinal and pharmacological effects. However, the growing interest in medical cannabis highlights the need to better understand brain alterations linking phytocannabinoids or synthetic cannabinoids to clinical and behavioral phenotypes. Therefore, the aim of this study was to investigate the effects of long-term WIN 55,212-2 treatment-with and without prolonged abstinence-on cerebral metabolism and memory function in healthy wildtype mice. Adult C57BI/6J mice were divided into two treatment groups to study the acute effects of WIN 55,212-2 treatment as well the effects of WIN 55,212-2 treatment after an extended washout phase. We could demonstrate that 3 mg/kg WIN 55,212-2 treatment in early adulthood leads to a hypometabolism in several brain regions including the hippocampus, cerebellum, amygdala and midbrain, even after prolonged abstinence. Furthermore, prolonged acute WIN 55,212-2 treatment in 6-months-old mice reduced the glucose metabolism in the hippocampus and midbrain. In addition, Win 55,212-2 treatment during adulthood lead to spatial memory and recognition memory deficits without affecting anxiety behavior. Overall we could demonstrate that treatment with the synthetic CB1/CB2 receptor aganist Win 55,212-2 during adulthood causes persistent memory deficits, especially when mice were treated in early adulthood. Our findings highlight the risks of prolonged WIN 55,212-2 use and provide new insights into the mechanisms underlying the effects of chronic cannabinoid exposure on the brain and behavior.

Reciprocal Influences of HIV and Cannabinoids on the Brain and Cognitive Function

Globally, cannabis is the most commonly used illicit drug, with disproportionately high use among persons with HIV. Despite advances in HIV care, nearly half of persons living with HIV continue to experience neurocognitive deficits or impairments that may have negative impacts on their daily function. Chronic cannabis use may play a role in the development or exacerbation of these impairments. Here we present a review summarizing existing research detailing the effect of cannabis use associated with the neuropathogenesis of HIV. We examine evidence for possible additive or synergistic effects of HIV infection and cannabis use on neuroHIV in both the preclinical and adult human literatures, including in vitro studies, animal models, clinical neuroimaging research, and studies examining the cognitive effects of cannabis. We discuss the limitations of existing research, including methodological challenges involved with clinical research with human subjects. We identify gaps in the field and propose critical research questions to advance our understanding of how cannabis use affects neuroHIV. Graphical Abstract.

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.

Acute and chronic effects of Δ9-tetrahydrocannabinol (THC) on cerebral blood flow: A systematic review

Acute and chronic exposure to cannabis and its main psychoactive component, Δ⁹-tetrahydrocannabinol (THC), is associated with changes in brain function and cerebral blood flow (CBF). We therefore sought to systematically review the literature on the effects of THC on CBF following PRISMA guidelines. Studies assessing the acute and chronic effects of THC on CBF, perfusion and volume were searched in the PubMed database between January 1972 and June 2019. We included thirty-four studies, which altogether investigated 1259 humans and 28 animals. Acute and chronic THC exposure have contrasting and regionally specific effects on CBF. While acute THC causes an overall increase in CBF in the anterior cingulate cortex, frontal cortex and insula, in a dose-dependent manner, chronic cannabis use results in an overall reduction in CBF, especially in the prefrontal cortex, which may be reversed upon prolonged abstinence from the drug. Future studies should focus on standardised methodology and longitudinal assessment to strengthen our understanding of the region-specific effects of THC on CBF and its clinical and functional significance.

Cannabis and the Developing Brain: Insights into Its Long-Lasting Effects

The recent shift in sociopolitical debates and growing liberalization of cannabis use across the globe has raised concern regarding its impact on vulnerable populations, such as pregnant women and adolescents. Epidemiological studies have long demonstrated a relationship between developmental cannabis exposure and later mental health symptoms. This relationship is especially strong in people with particular genetic polymorphisms, suggesting that cannabis use interacts with genotype to increase mental health risk. Seminal animal research directly linked prenatal and adolescent exposure to delta-9-tetrahydrocannabinol, the major psychoactive component of cannabis, with protracted effects on adult neural systems relevant to psychiatric and substance use disorders. In this article, we discuss some recent advances in understanding the long-term molecular, epigenetic, electrophysiological, and behavioral consequences of prenatal, perinatal, and adolescent exposure to cannabis/delta-9-tetrahydrocannabinol. Insights are provided from both animal and human studies, including in vivo neuroimaging strategies.

Cannabis effects on brain structure, function, and cognition: considerations for medical uses of cannabis and its derivatives

Background: Cannabis is the most widely used illicit substance worldwide, and legalization for recreational and medical purposes has substantially increased its availability and use in the United States.Objectives: Decades of research have suggested that recreational cannabis use confers risk for cognitive impairment across various domains, and structural and functional differences in the brain have been linked to early and heavy cannabis use.Methods: With substantial evidence for the role of the endocannabinoid system in neural development and understanding that brain development continues into early adulthood, the rising use of cannabis in adolescents and young adults raises major concerns. Yet some formulations of cannabinoid compounds are FDA-approved for medical uses, including applications in children.Results: Potential effects on the trajectory of brain morphology and cognition, therefore, should be considered. The goal of this review is to update and consolidate relevant findings in order to inform attitudes and public policy regarding the recreational and medical use of cannabis and cannabinoid compounds.Conclusions: The findings point to considerations for age limits and guidelines for use.

Multiple Sclerosis, Cannabis Use, and Clinical Disability: A Preliminary [18F]-Fluorodeoxyglucose Positron Emission Tomography Study

Introduction: Long-term consequences of medicinal cannabis use in people with multiple sclerosis (PwMS) are unknown. This study investigated whether PwMS using cannabis had lower resting brain glucose uptake (GU) and worse clinical test results compared with nonusers. Methods: Sixteen PwMS, eight users, underwent clinical testing followed by [¹⁸F]-Fluorodeoxyglucose positron emission tomography/computed tomography imaging. Results: Users had lower cognitive function test scores, but performed similarly on the other clinical evaluations. Accounting for disease duration, resting brain GU was similar between the groups. Conclusions: Lower cognitive function was not associated with resting brain GU. Cognitive dysfunction may be a contraindication or consequence of cannabis use in PwMS.

Residual effects of cannabis use in adolescent and adult brains - A meta-analysis of fMRI studies

While numerous studies have investigated the residual effects of cannabis use on human brain function, results of these studies have been inconsistent. Using meta-analytic approaches we summarize the effects of prolonged cannabis exposure on human brain function as measured using task-based functional MRI (fMRI) across studies employing a range of cognitive activation tasks comparing regular cannabis users with non-users. Separate meta-analyses were carried out for studies investigating adult and adolescent cannabis users. Systematic literature search identified 20 manuscripts (13 adult and 7 adolescent studies) meeting study inclusion criteria. Adult analyses compared 530 cannabis users to 580 healthy controls while adolescent analyses compared 219 cannabis users to 224 healthy controls. In adult cannabis users brain activation was increased in the superior and posterior transverse temporal and inferior frontal gyri and decreased in the striate area, insula and middle temporal gyrus. In adolescent cannabis users, activation was increased in the inferior parietal gyrus and putamen compared to healthy controls. Functional alteration in these areas may reflect compensatory neuroadaptive changes in cannabis users.

Neuroimaging meta-analysis of cannabis use studies reveals convergent functional alterations in brain regions supporting cognitive control and reward processing

Lagging behind rapid changes to state laws, societal views, and medical practice is the scientific investigation of cannabis's impact on the human brain. While several brain imaging studies have contributed important insight into neurobiological alterations linked with cannabis use, our understanding remains limited. Here, we sought to delineate those brain regions that consistently demonstrate functional alterations among cannabis users versus non-users across neuroimaging studies using the activation likelihood estimation meta-analysis framework. In ancillary analyses, we characterized task-related brain networks that co-activate with cannabis-affected regions using data archived in a large neuroimaging repository, and then determined which psychological processes may be disrupted via functional decoding techniques. When considering convergent alterations among users, decreased activation was observed in the anterior cingulate cortex, which co-activated with frontal, parietal, and limbic areas and was linked with cognitive control processes. Similarly, decreased activation was observed in the dorsolateral prefrontal cortex, which co-activated with frontal and occipital areas and linked with attention-related processes. Conversely, increased activation among users was observed in the striatum, which co-activated with frontal, parietal, and other limbic areas and linked with reward processing. These meta-analytic outcomes indicate that cannabis use is linked with differential, region-specific effects across the brain.

Cannabis use in people with Parkinson's disease and Multiple Sclerosis: A web-based investigation

OBJECTIVES

Cannabis has been used for medicinal purpose for thousands of years; however the positive and negative effects of cannabis use in Parkinson's disease (PD) and Multiple Sclerosis (MS) are mostly unknown. Our aim was to assess cannabis use in PD and MS and compare results of self-reported assessments of neurological disability between current cannabis users and non-users.

METHODS

An anonymous web-based survey was hosted on the Michael J. Fox Foundation and the National Multiple Sclerosis Society webpages from 15 February to 15 October 2016. The survey collected demographic and cannabis use information, and used standardized questionnaires to assess neurological function, fatigue, balance, and physical activity participation. Analysis of variance and chi-square tests were used for the analysis.

RESULTS

The survey was viewed 801 times, and 595 participants were in the final data set. Seventy-six percent and 24% of the respondents reported PD and MS respectively. Current users reported high efficacy of cannabis, 6.4 (SD 1.8) on a scale from 0 to 7 and 59% reported reducing prescription medication since beginning cannabis use. Current cannabis users were younger and less likely to be classified as obese (P < 0.035). Cannabis users reported lower levels of disability, specifically in domains of mood, memory, and fatigue (P<0.040).

CONCLUSIONS

Cannabis may have positive impacts on mood, memory, fatigue, and obesity status in people with PD and MS. Further studies using clinically and longitudinally assessed measurements of these domains are needed to establish if these associations are causal and determine the long-term benefits and consequences of cannabis use in people with PD and MS.

Cannabis and alcohol use, and the developing brain

Sex hormones and white (and grey) matter in the limbic system, cortex and other brain regions undergo changes during adolescence. Some of these changes include ongoing white matter myelination and sexually dimorphic features in grey and white matter. Adolescence is also a period of vulnerability when many are first exposed to alcohol and cannabis, which appear to influence the developing brain. Neuropsychological studies have provided considerable understanding of the effects of alcohol and cannabis on the brain. Advances in neuroimaging have allowed examination of neuroanatomic changes, metabolic and neurotransmitter activity, and neuronal activation during adolescent brain development and substance use. In this review, we examine major differences in brain development between users and non-users, and recent findings on the influence of cannabis and alcohol on the adolescent brain. We also discuss associations that appear to resolve following short-term abstinence, and attentional deficits that appear to persist. These findings can be useful in guiding earlier educational interventions for adolescents, and clarifying the neural sequelae of early alcohol and cannabis use to the general public.

Brain metabolism in substance-induced psychosis and schizophrenia: a preliminary PET study

INTRODUCTION

The relation between schizophrenia and cannabis abuse has been widely discussed from etiopathogenetic, psychopathological and neurometabolic points of view. Relatively little has been written about the differences between schizophrenia with co-occurrent cannabis abuse and substance-induced psychotic disorder (SIPD). Given these premises, our study aims to investigate the psychopathological and neurometabolic features of these clinical entities.

METHODS

We enrolled patients experiencing an acute psychotic episode, affected either by schizophrenia with or without cannabis abuse (SCZ +/- CA; n = 5 and n = 5, respectively) with recent onset (<5 years of illness) or by SIPD (n = 6), as diagnosed by the Structured Clinical Interview for DSM-IV Axis I. Patients affected by SIPD were all cannabis abusers. All patients were assessed with the PANSS (Positive and Negative Scale for Schizophrenia), urinary toxicological tests and brain 18-FDG-PET scanning in resting condition. Statistical analysis (ANOVA) was performed with Statistical Parametric Mapping SPM8 and Scenium software.

RESULTS

Bilateral hypermetabolism in the posterior cingulum and the precuneus (p < 0.001) was observed in SIPD patients compared to patients with schizophrenia, with or without cannabis abuse.

CONCLUSIONS

Our preliminary PET findings suggest that substance abuse may cause increased brain metabolism in patients with induced psychosis but not in those with schizophrenia. These differences in brain metabolism were found in the posterior cingulum and precuneus, which are two core regions of the default mode network in humans.

Effects of cannabis on impulsivity: a systematic review of neuroimaging findings

We conducted a systematic review to assess the evidence for specific effects of cannabis on impulsivity, disinhibition and motor control. The review had a specific focus on neuroimaging findings associated with acute and chronic use of the drug and covers literature published up until May 2012. Seventeen studies were identified, of which 13 met the inclusion criteria; three studies investigated acute effects of cannabis (1 fMRI, 2 PET), while six studies investigated non-acute functional effects (4 fMRI, 2 PET), and four studies investigated structural alterations. Functional imaging studies of impulsivity studies suggest that prefrontal blood flow is lower in chronic cannabis users than in controls. Studies of acute administration of THC or marijuana report increased brain metabolism in several brain regions during impulsivity tasks. Structural imaging studies of cannabis users found differences in reduced prefrontal volumes and white matter integrity that might mediate the abnormal impulsivity and mood observed in marijuana users. To address the question whether impulsivity as a trait precedes cannabis consumption or whether cannabis aggravates impulsivity and discontinuation of usage more longitudinal study designs are warranted.

Functional imaging of implicit marijuana associations during performance on an Implicit Association Test (IAT)

This research evaluated the neural correlates of implicit associative memory processes (habit-based processes) through the imaging (fMRI) of a marijuana Implicit Association Test. Drug-related associative memory effects have been shown to consistently predict level of drug use. To observe differences in neural activity of associative memory effects, this study compared 13 heavy marijuana users and 15 non-using controls, ranging in age from 18 to 25, during performance of a marijuana Implicit Association Test (IAT). Group by condition interactions in the putamen, caudate, and right inferior frontal gyrus were observed. Relative to non-users, marijuana users showed greater bilateral activity in the dorsal striatum (caudate and putamen) during compatible trials focused on perceived positive outcomes of use. Alternatively, relative to the marijuana-using group, the non-users showed greater activity in the right inferior frontal gyrus during incompatible trials, which require more effortful processing of information. Further, relative to fixation, heavy users showed bilateral activity in the caudate and putamen, hippocampus and some frontal regions during compatible trials and no significant activity during incompatible trials. The non-using group showed greater activity in frontal regions during incompatible trials relative to fixation and no significant activity during compatible trials. These findings are consistent with a dual process framework of appetitive behaviors proposing that (1) implicit associations underlying habit are mediated through neural circuitry dependent on the striatum, and (2) deliberative/controlled behaviors are mediated through circuitry more dependent on the prefrontal cortex.

Unbalanced neuronal circuits in addiction

Through sequential waves of drug-induced neurochemical stimulation, addiction co-opts the brain's neuronal circuits that mediate reward, motivation to behavioral inflexibility and a severe disruption of self-control and compulsive drug intake. Brain imaging technologies have allowed neuroscientists to map out the neural landscape of addiction in the human brain and to understand how drugs modify it.

Structural and functional imaging studies in chronic cannabis users: a systematic review of adolescent and adult findings

Background

The growing concern about cannabis use, the most commonly used illicit drug worldwide, has led to a significant increase in the number of human studies using neuroimaging techniques to determine the effect of cannabis on brain structure and function. We conducted a systematic review to assess the evidence of the impact of chronic cannabis use on brain structure and function in adults and adolescents.

Methods

Papers published until August 2012 were included from EMBASE, Medline, PubMed and LILACS databases following a comprehensive search strategy and pre-determined set of criteria for article selection. Only neuroimaging studies involving chronic cannabis users with a matched control group were considered.

Results

One hundred and forty-two studies were identified, of which 43 met the established criteria. Eight studies were in adolescent population. Neuroimaging studies provide evidence of morphological brain alterations in both population groups, particularly in the medial temporal and frontal cortices, as well as the cerebellum. These effects may be related to the amount of cannabis exposure. Functional neuroimaging studies suggest different patterns of resting global and brain activity during the performance of several cognitive tasks both in adolescents and adults, which may indicate compensatory effects in response to chronic cannabis exposure.

Limitations

However, the results pointed out methodological limitations of the work conducted to date and considerable heterogeneity in the findings.

Conclusion

Chronic cannabis use may alter brain structure and function in adult and adolescent population. Further studies should consider the use of convergent methodology, prospective large samples involving adolescent to adulthood subjects, and data-sharing initiatives.

Weed or wheel! FMRI, behavioural, and toxicological investigations of how cannabis smoking affects skills necessary for driving

Marijuana is the most widely used illicit drug, however its effects on cognitive functions underlying safe driving remain mostly unexplored. Our goal was to evaluate the impact of cannabis on the driving ability of occasional smokers, by investigating changes in the brain network involved in a tracking task. The subject characteristics, the percentage of Δ(9)-Tetrahydrocannabinol in the joint, and the inhaled dose were in accordance with real-life conditions. Thirty-one male volunteers were enrolled in this study that includes clinical and toxicological aspects together with functional magnetic resonance imaging of the brain and measurements of psychomotor skills. The fMRI paradigm was based on a visuo-motor tracking task, alternating active tracking blocks with passive tracking viewing and rest condition. We show that cannabis smoking, even at low Δ(9)-Tetrahydrocannabinol blood concentrations, decreases psychomotor skills and alters the activity of the brain networks involved in cognition. The relative decrease of Blood Oxygen Level Dependent response (BOLD) after cannabis smoking in the anterior insula, dorsomedial thalamus, and striatum compared to placebo smoking suggests an alteration of the network involved in saliency detection. In addition, the decrease of BOLD response in the right superior parietal cortex and in the dorsolateral prefrontal cortex indicates the involvement of the Control Executive network known to operate once the saliencies are identified. Furthermore, cannabis increases activity in the rostral anterior cingulate cortex and ventromedial prefrontal cortices, suggesting an increase in self-oriented mental activity. Subjects are more attracted by intrapersonal stimuli ("self") and fail to attend to task performance, leading to an insufficient allocation of task-oriented resources and to sub-optimal performance. These effects correlate with the subjective feeling of confusion rather than with the blood level of Δ(9)-Tetrahydrocannabinol. These findings bolster the zero-tolerance policy adopted in several countries that prohibits the presence of any amount of drugs in blood while driving.

Structural network topology revealed by white matter tractography in cannabis users: a graph theoretical analysis

Endocannabinoid receptors modulate synaptic plasticity in the brain and may therefore impact cortical connectivity not only during development but also in response to substance abuse in later life. Such alterations may not be evident in volumetric measures utilized in brain imaging, but could affect the local and global organization of brain networks. To test this hypothesis, we used a novel computational approach to estimate network measures of structural brain connectivity derived from diffusion tensor imaging (DTI) and white matter tractography. Twelve adult cannabis (CB) users and 13 healthy subjects were evaluated using a graph theoretic analysis of both global and local brain network properties. Structural brain networks in both CB subjects and controls exhibited robust small-world network attributes in both groups. However, CB subjects showed significantly decreased global network efficiency and significantly increased clustering coefficients (degree to which nodes tend to cluster around individual nodes). CB subjects also exhibited altered patterns of local network organization in the cingulate region. Among all subjects, schizotypal and impulsive personality characteristics correlated with global efficiency but not with the clustering coefficient. Our data indicate that structural brain networks in CB subjects are less efficiently integrated and exhibit altered regional connectivity. These differences in network properties may reflect physiological processes secondary to substance abuse-induced synaptic plasticity, or differences in brain organization that increase vulnerability to substance use.

Altered brain activation during visuomotor integration in chronic active cannabis users: relationship to cortisol levels

Cannabis is the most abused illegal substance in the United States. Alterations in brain function and motor behavior have been reported in chronic cannabis users, but the results have been variable. The current study aimed to determine whether chronic active cannabis use in humans may alter psychomotor function, brain activation, and hypothalamic-pituitary-axis (HPA) function in men and women. Thirty cannabis users (16 men, 14 women, 18-45 years old) and 30 nondrug user controls (16 men, 14 women, 19-44 years old) were evaluated with neuropsychological tests designed to assess motor behavior and with fMRI using a 3 Tesla scanner during a visually paced finger-sequencing task, cued by a flashing checkerboard (at 2 or 4 Hz). Salivary cortisol was measured to assess HPA function. Male, but not female, cannabis users had significantly slower performance on psychomotor speed tests. As a group, cannabis users had greater activation in BA 6 than controls, while controls had greater activation in the visual area BA 17 than cannabis users. Cannabis users also had higher salivary cortisol levels than controls (p = 0.002). Chronic active cannabis use is associated with slower and less efficient psychomotor function, especially in male users, as indicated by a shift from regions involved with automated visually guided responses to more executive or attentional control areas. The greater but altered brain activities may be mediated by the higher cortisol levels in the cannabis users, which in turn may lead to less efficient visual-motor function.

Increased brain metabolism after acute administration of the synthetic cannabinoid HU210: a small animal PET imaging study with 18F-FDG

Cannabis use has been shown to alter brain metabolism in both rat models and humans although the observations between both species are conflicting. In the present study, we examined the short term effects of a single-dose injection of the synthetic cannabinoid agonist HU210 on glucose metabolism in the rat brain using small animal (18)F-2-fluoro-deoxyglucose (FDG) Positron Emission Tomography (PET) 15 min (Day 1) and 24h (Day 2) post-injection of the agonist in the same animal. Young adult male Wistar rats received an intra-peritoneal injection of HU210 (100 μg/kg, n=7) or vehicle (n=5) on Day 1. Approximately 1mCi of (18)F-FDG was injected intravenously into each animal at 15 min (Day 1) and 24h (Day 2) post-injection of HU210. A 5-min Computer Tomography (CT) scan followed by a 20-min PET scan was performed 40 min after each (18)F-FDG injection. Standardised Uptake Values (SUVs) were calculated for 10 brain regions of interest (ROIs). Global increased SUVs in the whole brain, hence global brain metabolism, were observed following HU210 treatment on Day 1 compared to the controls (21%, P<0.0001), but not in individual brain regions. On Day 2, however, no statistically significant differences were observed between the treated and control groups. At the 24h time point (Day 2), SUVs in the HU210 treated group returned to control levels (21-30% decrease compared to Day 1), in all ROIs investigated (P<0.0001). In the control group, SUVs did not differ between the two acquisition days in all brain regions. The present results suggest that high-dose HU210 increases brain glucose metabolism in the rat brain shortly after administration, in line with normalised human in vivo studies, an effect that was no longer apparent 24 h later.

Evidence for involvement of the insula in the psychotropic effects of THC in humans: a double-blind, randomized pharmacological MRI study

The main reason for recreational use of cannabis is the 'high', the primary psychotropic effect of Δ9-tetrahydrocannabinol (THC). This psychoactive compound of cannabis induces a range of subjective, physical and mental reactions. The effect on heart rate is pronounced and complicates bloodflow-based neuroimaging of psychotropic effects of THC. In this study we investigated the effects of THC on baseline brain perfusion and activity in association with the induction of 'feeling high'. Twenty-three subjects participated in a pharmacological MRI study, where we applied arterial spin labelling (ASL) to measure perfusion, and resting-state functional MRI to assess blood oxygen level-dependent signal fluctuation as a measure of baseline brain activity. Feeling high was assessed with a visual analogue scale and was compared to the imaging measures. THC increased perfusion in the anterior cingulate cortex, superior frontal cortex, and insula, and reduced perfusion in the post-central and occipital gyrus. Baseline brain activity was altered, indicated by increased amplitude of fluctuations in resting-state functional MRI signal after THC administration in the insula, substantia nigra and cerebellum. Perfusion changes in frontal cortex were negatively correlated with ratings of feeling high, suggesting an interaction between cognitive control and subjective effects of THC. In conclusion, an acute THC challenge altered baseline brain perfusion and activity, especially in frontal brain areas involved in cognitive and emotional processes, and the insula, associated with interoceptive awareness. These changes may represent the THC-induced neurophysiological correlates of feeling high. The alterations in baseline brain perfusion and activity also have relevance for studies on task-related effects of THC on brain function.

Preliminary evidence for white matter metabolite differences in marijuana-dependent young men using 2D J-resolved magnetic resonance spectroscopic imaging at 4 Tesla

Chronic marijuana (MRJ) use is associated with altered cognition and mood state, altered brain metabolites, and functional and structural brain changes. The objective of this study was to apply proton magnetic resonance spectroscopic imaging (MRSI) to compare proton metabolite levels in 15 young men with MRJ dependence and 11 healthy non-using (NU) young men. Spectra were acquired at 4.0 Tesla using 2D J-resolved MRSI to resolve coupled resonances in J-space and to quantify the entire J-coupled spectral surface of metabolites from voxels containing basal ganglia and thalamus, temporal and parietal lobes, and occipital white and gray matter. This method permitted investigation of high-quality spectra for regression analyses to examine metabolites relative to tissue type. Distribution of myo-inositol (mI)/creatine (Cr) was altered in the MRJ group whereas the NU group exhibited higher mI/Cr in WM than GM, this pattern was not observed in MRJ subjects. Significant relationships observed between global mI/Cr and distribution in WM, and self-reported impulsivity and mood symptoms were also unique between MRJ and NU groups. These preliminary findings suggest that mI, and distribution of this glial metabolite in WM, is altered by MRJ use and is associated with behavioral and affective features reported by young MRJ-dependent men.

Poor decision-making by chronic marijuana users is associated with decreased functional responsiveness to negative consequences

Chronic marijuana users (MJ Users) perform poorly on the Iowa Gambling Task (IGT), a complex decision-making task in which monetary wins and losses guide strategy development. This functional magnetic resonance imaging (MRI) study sought to determine if the poor performance of MJ Users was related to differences in brain activity while evaluating wins and losses during the strategy development phase of the IGT. MJ Users (16) and Controls (16) performed a modified IGT in an MRI scanner. Performance was tracked and functional activity in response to early wins and losses was examined. While the MJ Users continued to perform poorly at the end of the task, there was no difference in group performance during the initial strategy development phase. During this phase, before the emergence of behavioral differences, Controls exhibited significantly greater activity in response to losses in the anterior cingulate cortex, medial frontal cortex, precuneus, superior parietal lobe, occipital lobe and cerebellum as compared to MJ Users. Furthermore, in Controls, but not MJ Users, the functional response to losses in the anterior cingulate cortex, ventral medial prefrontal cortex and rostral prefrontal cortex positively correlated with performance over time. These data suggest MJ Users are less sensitive to negative feedback during strategy development.

Associations of marijuana use and sex-related marijuana expectancies with HIV/STD risk behavior in high-risk adolescents

Multiple studies suggest an association of marijuana use with increased rates of sexual risk behavior and sexually transmitted diseases (STDs). Most studies have focused on global associations of marijuana use with sexual risk outcomes and few have examined relevant cognitive variables. Adolescents in the juvenile justice system are at elevated risk for HIV/STDs and preliminary evidence suggests that marijuana is a potentially important cofactor for sexual risk behavior in this population. This study evaluated global, situational and event-level associations of marijuana use and sex-related marijuana expectancies with sexual risk outcomes in a large, racially diverse sample of adjudicated youth (n = 656, 66% male, mean age = 16.7 years). Cross-sectional and prospective analyses identified associations of marijuana use and dependence symptoms with sexual risk outcomes, including lower frequency of condom use and higher STD incidence. Stronger sex-related marijuana expectancies predicted greater intentions for and frequency of marijuana use in sexual situations. In event-level analyses that controlled for alcohol, marijuana use predicted a significantly decreased likelihood of condom use; this association was moderated by sex-related marijuana expectancies. Mediation analyses suggested that behavioral intentions partly accounted for the prospective association of expectancies with marijuana use before sex. These results provide further evidence that marijuana use is a potentially important cofactor for HIV/STD transmission in high-risk adolescents and suggest that cognitive factors could be important for characterizing this association.

Are the effects of cannabis dependence on glucose metabolism similar to schizophrenia? An FDG PET understanding

BACKGROUND

Cannabis has been associated with transient psychotic states; however, the causal relationship between cannabis and schizophrenia continues to remain a matter of debate. Epidemiological and some biological studies hint at cannabis being an independent risk factor for schizophrenia; this has not been definitively proved.

AIMS

We aimed to understand the patterns of glucose uptake in important brain regions among individuals with cannabis dependence and schizophrenia. Furthermore, we compared the interregional metabolic rates in pertinent neural circuits among individuals with cannabis dependence, schizophrenia and normal controls.

SETTING AND DESIGN

This is a case-control cross-sectional study that was carried out by a general psychiatry department in collaboration with a nuclear diagnosis unit.

MATERIALS AND METHODS

Male volunteers with cannabis dependence, schizophrenia and normal controls underwent FDG PET scanning. Glucose uptakes in pre-selected regions of interest were compared using MANOVA. Finally, Chow tests were used to compare interregional metabolic relationships in the mesocortical and cortical-subcortical-cerebellum circuits.

RESULTS

Significant differences (P<0.05) were noted among individuals with cannabis dependence and schizophrenia in the medial and lateral temporal regions. When the neural circuits were compared, significant interregional differences (P<0.05) were noted between individuals with cannabis dependence and normal controls. However, among individuals with cannabis dependence and schizophrenia, no significant differences (P>0.05) were noted in these patterns.

CONCLUSIONS

Our findings suggest that cannabis dependence can alter interregional relationships in a manner similar to schizophrenia. This indicates that cannabis could potentially play a role in the development of psychosis by altering neural circuits.

Structural MRI findings in long-term cannabis users: what do we know?

In animal studies, tetrahydrocannabinol (THC) has been found to affect brain morphology, particularly within areas rich in cannabinoid receptors (e.g., hippocampus, cerebral cortex). While cannabis remains the most widely used illicit drug worldwide, there has been limited work investigating its effects on human brain tissue. In this paper, we conducted a systematic review of existing structural magnetic resonance imaging studies to examine whether cannabis use is associated with significant changes in brain anatomy. We identified only 13 structural neuroimaging studies, which were diverse in terms of sample characteristics (e.g., age of participants, duration and frequency of use) and methodology (e.g., image analysis). No study found global structural changes in cannabis users, although six studies reported regional alterations. While changes in the hippocampus and parahippocampus were frequently identified, the findings were inconsistent across studies. The available literature also provides some evidence that regional structural changes are associated with cannabis use patterns (particularly cumulative dosage and frequency of use), as well as measures of psychopathology (e.g., measures of depressive and psychotic symptoms). Together, these structural imaging findings suggest that THC exposure does affect brain morphology, especially in medial-temporal regions. Given the small literature available and the limitations of studies to date, further research is clearly required, particularly given the prevalence of cannabis use worldwide.

Cannabis dependence: Effects of cannabis consumption on inter-regional cerebral metabolic relationships in an Indian population

BACKGROUND

The effects of cannabis consumption on neurophysiological function have been a matter of considerable debate. With the legalization of medical marijuana, understanding the consequences of cannabis dependence has become extremely important.

AIM

We attempted to understand the influence of cannabis on cerebral glucose metabolism in certain predetermined regions of interest (ROIs). Furthermore, we also explored inter-regional metabolic relationships between ROIs forming the "addiction" and "cognitive dysmetria" circuit.

MATERIALS AND METHODS

2-fluoro, 2-deoxy-glucose positron emission tomography (FDG PET) scans were carried out in 16 male patients (age: 25.3±10.38 years) with cannabis dependence, 8-12 hours after the last cannabis consumption. Resting glucose uptake in 14 pre-determined ROIs was compared with glucose uptake in 16 non-drug using volunteers (age: 29.2±8.39 years).

RESULTS

The two groups differed in their lateral and medial temporal glucose uptakes by approximately 16-24%. The relationships between inter-regional glucose uptakes in the two circuits were compared using the Chow Test. Significant differences in inter-regional correlations in the medial temporo-frontal and parieto-thalamic were noted between the two groups.

CONCLUSION

The altered metabolic relationships among various brain regions can have potentially important implications for understanding cannabis dependence and cannabis-induced psychopathology.

Effects of marijuana on visuospatial working memory: an fMRI study in young adults

OBJECTIVES

The effects of marijuana use on visuospatial working memory were investigated in 19-21-year-olds using functional magnetic resonance imaging (fMRI).

METHODS

Participants were members of the Ottawa Prenatal Prospective Study, a longitudinal study that collected a unique body of information on participants from infancy to young adulthood including: prenatal drug history, detailed cognitive/behavioral performance, and current and past drug usage. This information allowed for the measurement of an unprecedented number of potentially confounding drug exposure variables including: prenatal marijuana, nicotine, alcohol, and caffeine exposure and offspring alcohol, marijuana, and nicotine use. Ten marijuana users and 14 nonusing controls performed a visuospatial 2-back task while fMRI blood oxygen level-dependent response was examined.

RESULTS

Despite similar task performance, marijuana users had significantly greater activation in the inferior and middle frontal gyri, regions of the brain normally associated with visuospatial working memory. Marijuana users also had greater activation in the right superior temporal gyrus, a region of the brain not typically associated with visuospatial working memory tasks.

CONCLUSIONS

These results suggest that marijuana use leads to altered neural functioning during visuospatial working memory after controlling for other prenatal and current drug use. This alteration appears to be compensated for by the recruitment of blood flow in additional brain regions. It is possible that this compensation may not be sufficient in more real-life situations where this type of processing is required and thus deficits may be observed. Awareness of these neural physiological effects of marijuana in youth is critical.

Abnormal cerebellar morphometry in abstinent adolescent marijuana users

Functional neuroimaging data from adults have, in general, revealed frontocerebellar dysfunction associated with acute and chronic marijuana (MJ) use. The goal of this study was to characterize cerebellar volume in adolescent chronic MJ users following 1 month of monitored abstinence. Participants were MJ users (n=16) and controls (n=16) aged 16-18 years. Extensive exclusionary criteria included history of psychiatric or neurologic disorders. Drug use history, neuropsychological data, and structural brain scans were collected after 28 days of monitored abstinence. Trained research staff defined cerebellar volumes (including three cerebellar vermis lobes and both cerebellar hemispheres) on high-resolution T1-weighted magnetic resonance images. Adolescent MJ users demonstrated significantly larger inferior posterior (lobules VIII-X) vermis volume than controls, above and beyond effects of lifetime alcohol and other drug use, gender, and intracranial volume. Larger vermis volumes were associated with poorer executive functioning. Following 1 month of abstinence, adolescent MJ users had significantly larger posterior cerebellar vermis volumes than non-using controls. These greater volumes are suggested to be pathological based on linkage to poorer executive functioning. Longitudinal studies are needed to examine typical cerebellar development during adolescence and the influence of marijuana use.

Neuroimaging in cannabis use: a systematic review of the literature

BACKGROUND

We conducted a systematic review to assess the evidence for specific effects of cannabis on brain structure and function. The review focuses on the cognitive changes associated with acute and chronic use of the drug.

METHOD

We reviewed literature reporting neuroimaging studies of chronic or acute cannabis use published up until January 2009. The search was conducted using Medline, EMBASE, LILACS and PsycLIT indexing services using the following key words: cannabis, marijuana, delta-9-tetrahydrocannabinol, THC, cannabidiol, CBD, neuroimaging, brain imaging, computerized tomography, CT, magnetic resonance, MRI, single photon emission tomography, SPECT, functional magnetic resonance, fMRI, positron emission tomography, PET, diffusion tensor MRI, DTI-MRI, MRS and spectroscopy.

RESULTS

Sixty-six studies were identified, of which 41 met the inclusion criteria. Thirty-three were functional (SPECT/PET/fMRI) and eight structural (volumetric/DTI) imaging studies. The high degree of heterogeneity across studies precluded a meta-analysis. The functional studies suggest that resting global and prefrontal blood flow are lower in cannabis users than in controls. The results from the activation studies using a cognitive task are inconsistent because of the heterogeneity of the methods used. Studies of acute administration of THC or marijuana report increased resting activity and activation of the frontal and anterior cingulate cortex during cognitive tasks. Only three of the structural imaging studies found differences between users and controls.

CONCLUSIONS

Functional neuroimaging studies suggest a modulation of global and prefrontal metabolism both during the resting state and after the administration of THC/marijuana cigarettes. Minimal evidence of major effects of cannabis on brain structure has been reported.

Neurocognitive correlates of white matter quality in adolescent substance users

BACKGROUND

Progressive myelination during adolescence implicates an increased vulnerability to neurotoxic substances and enduring neurocognitive consequences. This study examined the cognitive manifestations of altered white matter microstructure in chronic marijuana and alcohol-using (MJ+ALC) adolescents.

METHODS

Thirty-six MJ+ALC adolescents (ages 16-19) and 36 demographically similar controls were evaluated with diffusion tensor imaging (Bava et al., 2009) and neurocognitive tests. Regions of group difference in fractional anisotropy (FA) and mean diffusivity (MD) were analyzed in relation to cognitive performance.

RESULTS

In users, lower FA in temporal areas related to poorer performance on attention, working memory, and speeded processing tasks. Among regions where users had higher FA than controls, occipital FA was positively associated with working memory and complex visuomotor sequencing, whereas FA in anterior regions was negatively associated with verbal memory performance.

CONCLUSIONS

Findings suggest differential influences of white matter development on cognition in MJ+ALC using adolescents than in non-using peers. Neuroadaptation may reflect additive and subtractive responses to substance use that are complicated by competing maturational processes.

White matter integrity in adolescents with histories of marijuana use and binge drinking

Structural brain abnormalities have been observed in adolescents with alcohol use disorders but less is known about neuropathological brain characteristics of teens with sub-diagnostic binge drinking or the common pattern of binge drinking combined with marijuana use. The goal of this study was to examine white matter integrity in adolescents with histories of binge drinking and marijuana use. Diffusion tensor imaging (DTI) was conducted with 42 adolescents (ages 16-19) classified as controls, binge drinkers, or binge drinkers who are also heavy marijuana users. Tract based spatial analysis identified shared fiber structure across individuals and facilitated voxelwise comparisons of fractional anisotropy (FA) and mean diffusivity (MD) between groups. Significant between group differences were found in FA in eight white matter regions (ps < or = .016) between the binge drink-only group and controls, including superior corona radiata, inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and superior longitudinal fasciculus. Interestingly, in 4 of these same regions, binge drinkers who are also heavy marijuana users had higher FA than binge drinkers who did not use marijuana (ps<.05). MD did not differ between groups. Findings are largely consistent with research suggesting less neuropathology in adolescents without histories of substance use. However, binge drinkers who also use marijuana did not show as consistent a divergence from non-users as did the binge drink-only group. Detection of white matter alterations may have implications in identifying early cognitive dysfunction in substance using adolescents.

The endocannabinoid system as a target for modelling psychosis

INTRODUCTION

Model psychosis is characterised by experimentally induced symptoms of withdrawal from reality, frequently accompanied by perceptual disturbances, thought disorders, delusional ideas and sometimes by hallucinations. These "altered states of consciousness" provide a long-standing and valid approach to enhance our understanding of certain aspects of schizophrenia.

DISCUSSION

Targeting the endocannabinoid system to investigate its involvement in the pathophysiology of schizophrenia became increasingly relevant with the discovery of this system and amounting epidemiological evidence for a deleterious influence of cannabis use on both manifestation and course of the disease. The majority of studies in the field are targeted to investigate drug effect of cannabis and cannabinoids not immediately related to psychosis.

CONCLUSION

In this review, we summarise studies relevant for or designed as model psychosis experiments. Based on the data available, we examine the contribution of these studies to an improved neurobiological assessment of endocannabinoid functioning in psychosis and schizophrenia. An outline for future studies in the field and cross-links to other approaches to model psychosis is provided.

Addictive illegal drugs: structural neuroimaging

Illegal addictive drugs can lead to functional or structural impairment of the central nervous system. This review provides an overview of the structural imaging findings on CT, MR imaging, and conventional angiography related to chronic and acute abuse of the most commonly abused illegal drugs, including cannabis, organic solvents, and amphetamines and opioids and their respective derivatives. Pathomechanisms include excitotoxicity, which may lead to an acute or subacute leukoencephalopathy, and vascular complications, including vasoconstriction, vasculitis, or hypertension, which may lead to intracranial hemorrhage or ischemia. Because clinical findings alone are often nonspecific, and afflicted patients are unlikely to admit to the substance abuse, the neuroradiologist may play an important role in establishing the diagnosis and, thereby, initiating treatment.

Adverse health effects of non-medical cannabis use

For over two decades, cannabis, commonly known as marijuana, has been the most widely used illicit drug by young people in high-income countries, and has recently become popular on a global scale. Epidemiological research during the past 10 years suggests that regular use of cannabis during adolescence and into adulthood can have adverse effects. Epidemiological, clinical, and laboratory studies have established an association between cannabis use and adverse outcomes. We focus on adverse health effects of greatest potential public health interest-that is, those that are most likely to occur and to affect a large number of cannabis users. The most probable adverse effects include a dependence syndrome, increased risk of motor vehicle crashes, impaired respiratory function, cardiovascular disease, and adverse effects of regular use on adolescent psychosocial development and mental health.

Neuroimaging of children following prenatal drug exposure

Recent advances in MR-based brain imaging methods have provided unprecedented capabilities to visualize the brain. Application of these methods has allowed identification of brain structures and patterns of functional activation altered in offspring of mothers who used licit (e.g., alcohol and tobacco) and illicit (e.g., cocaine, methamphetamine, and marijuana) drugs during pregnancy. Here we review that literature, which though somewhat limited by the complexities of separating the specific effects of each drug from other confounding variables, points to sets of interconnected brain structures as being altered following prenatal exposure to drugs of abuse. In particular, dopamine-rich cortical (e.g., frontal cortex) and subcortical (e.g., basal ganglia) fetal brain structures show evidence of vulnerability to intrauterine drug exposure suggesting that during brain development drugs of abuse share a specific profile of developmental neurotoxicity. Such brain malformations may shed light on mechanisms underlying prenatal drug-induced brain injury, may serve as bio-markers of significant intrauterine drug exposure, and may additionally be predictors of subsequent neuro-developmental compromise. Wider clinical use of these research-based non-invasive methods will allow for improved diagnosis and allocation of therapeutic resources for affected infants, children, and young adults.

Central side-effects of therapies based on CB1 cannabinoid receptor agonists and antagonists: focus on anxiety and depression

Both agonists (e.g. Delta(9)-tetrahydrocannabinol, nabilone) and antagonists (e.g. rimonabant, taranabant) of the cannabinoid type-1 (CB(1)) receptor have been explored as therapeutic agents in diverse fields of medicine such as pain management and obesity with associated metabolic dysregulation, respectively. CB(1) receptors are widely distributed in the central nervous system and are involved in the modulation of emotion, stress and habituation responses, behaviours that are thought to be dysregulated in human psychiatric disorders. Accordingly, CB(1) receptor activation may, in some cases, precipitate episodes of psychosis and panic, while its inhibition may lead to behaviours reminiscent of depression and anxiety-related disorders. The present review discusses these side-effects, which have to be taken into account in the therapeutic exploitation of the endocannabinoid system.

The role of the cerebellum in the pathophysiology and treatment of neuropsychiatric disorders: a review

The cerebellum has traditionally been looked upon as a brain area primarily involved in motor behaviour. The last decade has however heralded the cerebellum as a brain region of renewed interest for neuropsychiatric disorders. This renewed interest is fuelled by new insights obtained from neuroanatomical research, modern functional neuroimaging and transcranial magnetic stimulation studies. In this review, evidence in support of cerebellar involvement in neuropsychiatric disorders will be presented. In addition, transcranial magnetic stimulation will be introduced as a novel way to study cerebellar contributions to the pathophysiology of psychiatric disorders. In conclusion, a new functional concept of the cerebellum as more than simply a brain area regulating motor control appears mandatory and the involvement of the cerebellum should be considered when studying the neurological basis of neuropsychiatric disorders.

The effect of cannabis on the brain: can it cause brain anomalies that lead to increased risk for schizophrenia?

PURPOSE OF REVIEW

This review explores what is known about the association of cannabis with schizophrenia, its effects on the brain, and whether the brain changes known to be present in schizophrenia could be caused by cannabis and thus lead to a psychosis.

RECENT FINDINGS

The heavy use of cannabis is known to be associated with some adverse consequences, such as the occurrence of acute psychotic episodes and the development of chronic schizophrenia in some people even after its use has terminated. Recent studies have produced controversy about whether cannabis in heavy use can cause irreversible brain damage, particularly to adolescents, and thus whether a chronic psychosis could be a result of brain changes caused by cannabis.

SUMMARY

From the evidence that exists, it appears that the above view is unlikely and that cannabis may even have benign effects on brain structure, not producing deleterious damage. Its neurochemical interactions with the dopaminergic pathway, however, may, particularly in genetically vulnerable individuals, have adverse consequences.