The neuropsychopharmacology of cannabis: A review of human imaging studies

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

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

New insights into the involvement of serotonin and BDNF-TrkB signalling in cannabidiol's antidepressant effect

Cannabidiol (CBD) is a phytocannabinoid devoid of psychostimulant properties and is currently under investigation as a potential antidepressant drug. However, the mechanisms underlying CBD's antidepressant effects are not yet well understood. CBD targets include a variety of receptors, enzymes, and transporters, with different binding-affinities. Neurochemical and pharmacological evidence indicates that both serotonin and BDNF-TrkB signalling in the prefrontal cortex are necessary for the antidepressant effects induced by CBD in animal models. Herein, we reviewed the current literature to dissect if these are independent mechanisms or if CBD-induced modulation of the serotonergic neurotransmission could mediate its neuroplastic effects through subsequent regulation of BDNF-TrkB signalling, thus culminating in rapid neuroplastic changes. It is hypothesized that: a) CBD interaction with serotonin receptors on neurons of the dorsal raphe nuclei and the resulting disinhibition of serotonergic neurons would promote rapid serotonin release in the PFC and hence its neuroplastic and antidepressant effects; b) CBD facilitates BDNF-TRKB signalling, especially in the PFC, which rapidly triggers neurochemical and neuroplastic effects. These hypotheses are discussed with perspectives for new drug development and clinical applications.

Exploring causal mechanisms of psychosis risk

Robust epidemiological evidence of risk and protective factors for psychosis is essential to inform preventive interventions. Previous evidence syntheses have classified these risk and protective factors according to their strength of association with psychosis. In this critical review we appraise the distinct and overlapping mechanisms of 25 key environmental risk factors for psychosis, and link these to mechanistic pathways that may contribute to neurochemical alterations hypothesised to underlie psychotic symptoms. We then discuss the implications of our findings for future research, specifically considering interactions between factors, exploring universal and subgroup-specific factors, improving understanding of temporality and risk dynamics, standardising operationalisation and measurement of risk and protective factors, and developing preventive interventions targeting risk and protective factors.

The neural oscillations serving task switching are altered in cannabis users

BACKGROUND

Regular cannabis is known to impact higher-order cognitive processes such as attention, but far less is known regarding cognitive flexibility, a component of executive function. Moreover, whether such changes are related to aberrations in the neural oscillatory dynamics serving flexibility remains poorly understood.

AIMS

Quantify the neural oscillatory dynamics serving cognitive flexibility by having participants complete a task-switching paradigm during magnetoencephalography (MEG). Probe whole-brain maps to identify alterations in chronic cannabis users relative to nonusers and determine how these alterations relate to the degree of cannabis use involvement.

METHODS

In all, 25 chronic cannabis users and 30 demographically matched nonuser controls completed neuropsychological testing, an interview regarding their substance use, a urinalysis, and a task switch paradigm during MEG. Time-frequency windows of interest were identified using a data-driven statistical approach and these were imaged using a beamformer. Whole-brain neural switch cost maps were computed by subtracting the oscillatory maps of the no-switch condition from the switch condition per participant. These were examined for group differences.

RESULTS

Cannabis users had weaker theta switch cost responses in the dorsolateral and dorsomedial prefrontal cortices, while nonusers showed the typical pattern of greater recruitment during switch relative to no switch trials. In addition, theta activity in the dorsomedial prefrontal cortex was significantly correlated with cannabis use involvement.

CONCLUSIONS

Cannabis users exhibited altered theta switch cost activity compared to nonusers in prefrontal cortical regions, which are critical for cognitive flexibility. This activity scaled with cannabis use involvement, indicating a link between cannabis use and aberrant oscillatory activity underlying cognitive flexibility.

The association between cannabis use and neuroimaging measures in older adults: findings from the UK biobank

BACKGROUND

Cannabis use has increased in recent years. However, the long-term implications of cannabis use on brain health remain unknown. We explored the associations of cannabis use with volumetric brain magnetic resonance imaging (MRI) measures in dementia-free older adults.

METHODS

This cross-sectional and longitudinal study included dementia-free participants of the UK Biobank aged ≥60 years. Linear regression models were used to evaluate the association of cannabis use and patterns of use with volumetric brain MRI measures. The association between cannabis use and change in brain MRI measures over time was also tested. All models were adjusted for potential confounders.

RESULTS

The sample included 19,932 participants (mean age 68 ± 5 years, 48% men), 3,800 (19%) reported lifetime use of cannabis. Cannabis use was associated with smaller total, white, grey and peripheral cortical grey matter volumes (B = -6,690 ± 1,157; P < 0.001, B = -4,396 ± 766; P < 0.001, B = -2,140 ± 690; P = 0.002 and B = -2,451 ± 606; P < 0.001, respectively). Among cannabis users, longer duration of use was associated with smaller total brain, grey and cortical grey matter volumes (B = -7,878 ± 2,396; P = 0.001, B = -5,411 ± 1,430; P < 0.001, B = -5,396 ± 1,254; P < 0.001, respectively), and with increased white matter hyperintensity volume (B = 0.09 ± 0.03; P = 0.008). Additionally, current vs. former users (B = -10,432 ± 4,395; P = 0.020) and frequent versus non-frequent users (B = -2,274 ± 1,125; P = 0.043) had smaller grey and cortical grey matter volumes, respectively. No significant associations were observed between cannabis use and change in brain MRI measures.

DISCUSSION

Our findings suggest that cannabis use, particularly longer duration and frequent use, may be related to smaller grey and white matter volumes in older ages, but not to late-life changes in these measures over time.

Nabilone Impairs Spatial and Verbal Working Memory in Healthy Volunteers

Background: Memory impairments and psychosis-like experiences can be adverse effects of cannabis use. However, reports on the cognitive impact of cannabis use are not consistent. There are also limited studies on the psychotomimetic effects of cannabinoid compounds to reveal the association between cannabis and psychosis. Therefore, we investigated the effect of acute cannabinoid intoxication on verbal working memory (VWM) and spatial working memory (SWM) following oral doses of the synthetic cannabinoid agonist, nabilone (1-2 mg, oral). We further investigated the effect of nabilone on psychosis-like experiences (schizotypy scores) and associations of schizotypy with VWM and SWM. Methods: Healthy participants (n=28) completed spatial and digit span tasks across different delay conditions (0, 6, 12, and 18 sec) after receiving nabilone (1-2 mg, PO) or placebo in a randomized, double-blind, counterbalanced, crossover manner. A subset of participants completed a short battery of schizotypy measures (n=25). Results: Nabilone impaired VWM (p=0.03, weak effect size η2=0.02) and SWM (p=0.00016, η2=0.08). Nabilone did not significantly change overall schizotypy scores. Schizotypy scores were negatively correlated with working memory (WM) averaged across all delays and both modalities, under placebo (ρ=-0.41, p=0.04). In addition, there were significant negative correlations between occasions of cannabis use and overall WM averaged scores across drug treatments (ρ=-0.49, p=0.007) and under placebo (ρ=-0.45, p=0.004). The results showed that the drug effect in the less frequent cannabis users was more pronounced on the SWM (p<0.01) and VWM (p<0.01), whereas there appeared to be little drug effect in the frequent cannabis users. Conclusion: Low doses of synthetic cannabinoid impaired SWM and VWM, indicating that exogenous activation of the cannabinoid system influences cognitive performance. Further, the results replicated previous findings that schizotypy is correlated with deficits in WM. Clinical Trial Registry Name: Nabilone and caffeine effects on the perceptions of visually, auditory, tactile and multimodal illusions in healthy volunteers. Clinical Trial Registration Number: CT-2018-CTN-02561 (Therapeutic Goods Administration Clinical Trial Registry) and ACTRN12618001292268 (The Australian New Zealand Clinical Trials Registry).

Cannabidiol, but Not Δ9-Tetrahydrocannabinol, Has Strain- and Genotype-Specific Effects in Models of Psychosis

Introduction: Cannabis use has been associated with an increased incidence of psychiatric disorders, yet the underlying neurobiological processes mediating these associations are poorly understood. Whereas exposure to Δ9-tetrahydrocannabinol (THC) has been associated with the development or exacerbation of psychosis, treatment with cannabidiol (CBD) has been associated with amelioration of psychosis. In this study, we demonstrate a complex effect of CBD in mouse models of psychosis, based on factors, including dose, strain, and genotype. Methods: Adult GluN1 knockdown (GluN1KD) and dopamine transporter knockout (DATKO) mice (almost equally balanced for male/female) were acutely treated with vehicle, THC (4 mg/kg), CBD (60, 120 mg/kg), or THC:CBD (1:15, 4:60 mg/kg) and tested in behavioral assays. Results: GluN1KD and DATKO mice displayed hyperactivity, impaired habituation, and sensorimotor gating, along with increased stereotypy and vertical activity. THC, alone and in combination with CBD, produced a robust "dampening" effect on the exploratory behavior regardless of strain or genotype. CBD exhibited a more complex profile. At 60 mg/kg, CBD had minimal effects on horizontal activity, but the effects varied in terms of directionality (increase vs. decrease) in other parameters; effects on stereotypic behaviors differ by genotype, while effects on vertical exploration differ by strain×genotype. CBD at 120 mg/kg had a "dampening" effect on exploration overall, except in GluN1KD mice, where no effect was observed. In terms of sensorimotor gating, both THC and CBD had minimal effects, except for 120 mg/kg CBD, which exacerbated the acoustic startle response. Conclusions: Here, we present a study that highlights the complex mechanism of phytocannabinoids, particularly CBD, in models of psychosis-like behavior. These data require careful interpretation, as agonism of the cannabinoid receptor 1 (CB1) resulting in a decrease in locomotion can be misinterpreted as "antipsychotic-like" activity in murine behavioral outputs of psychosis. Importantly, the THC-mediated decrease in hyperexploratory behavior observed in our models (alone or in combination) was not specific to the genetic mutants, but rather was observed regardless of strain or genotype. Furthermore, CBD treatment, when comparing mutants with their wild-type littermate controls, showed little to no "antipsychotic-like" activity in our models. Therefore, it is not only important to consider dose when designing/interpreting therapeutically driven phytocannabinoid studies, but also effects of strain or genetic vulnerability respective to the general population.

The psychedelic effects of cannabis: A review of the literature

Cannabis and classic psychedelics are controlled substances with emerging evidence of efficacy in the treatment of a variety of psychiatric illnesses. Cannabis has largely not been regarded as having psychedelic effects in contemporary literature, despite many examples of historical use along with classic psychedelics to attain altered states of consciousness. Research into the "psychedelic" effects of cannabis, and delta-9-tetrahydrocannabinol (THC) in particular, could prove helpful for assessing potential therapeutic indications and elucidating the mechanism of action of both cannabis and classic psychedelics. This review aggregates and evaluates the literature assessing the capacity of cannabis to yield the perceptual changes, aversiveness, and mystical experiences more typically associated with classic psychedelics such as psilocybin. This review also provides a brief contrast of neuroimaging findings associated with the acute effects of cannabis and psychedelics. The available evidence suggests that high-THC cannabis may be able to elicit psychedelic effects, but that these effects may not have been observed in recent controlled research studies due to the doses, set, and settings commonly used. Research is needed to investigate the effects of high doses of THC in the context utilized in therapeutic studies of psychedelics aimed to occasion psychedelic and/or therapeutic experiences. If cannabis can reliably generate psychedelic experiences under these conditions, high-THC dose cannabis treatments should be explored as potential adjunctive treatments for psychiatric disorders and be considered as an active comparator in clinical trials involving traditional psychedelic medications.

Cigarette Smoking, Risky Alcohol Consumption, and Marijuana Smoking among University Students in Germany: Identification of Potential Sociodemographic and Study-Related Risk Groups and Predictors of Consumption

(1) Background: Cigarette smoking, risky alcohol consumption, and marijuana smoking are the most common behaviors related to legal and illicit drug use worldwide, including among university students. To plan effective evidence-based programs to prevent the risky consumption of these substances among university students, the present study aimed to identify potential sociodemographic and study-related risk groups and predictors of consumption. (2) Methods: A cross-sectional online health survey with approximately 270 health-related items was conducted among students at the University of Mainz, Germany. Cigarette smoking, risky alcohol consumption (AUDIT-C score: female ≥ 4, male ≥ 5), and marijuana smoking were chosen as dependent variables. Of the 270 health-related items, 56 were chosen as independent variables and collated into five groups (sociodemographic, psychological, study-related psychosocial, general psychosocial and health behavior). The prevalence of cigarette smoking, risky alcohol consumption, and marijuana smoking was assessed using established and validated instruments. Pearson's chi-square test was used to analyze the differences in prevalence between the sociodemographic and study-related groups, and binary logistic regression was used for analyses with stepwise inclusion of the five variable groups. (3) Results: Of the 3991 university students who entered the analyses, 14.9% reported smoking cigarettes, 38.6% reported risky alcohol consumption, and 10.9% reported smoking marijuana. The prevalence of these differed between genders, fields of study, and aspired degree level, among other factors. Binary logistic regression analyses revealed nine significant predictors (p ≤ 0.05) of cigarette smoking (Nagelkerke R2 = 0.314), 18 significant predictors of risky alcohol consumption (Nagelkerke R2 = 0.270), and 16 significant predictors of marijuana smoking (Nagelkerke R2 = 0.239). (4) Conclusions: This study showed cigarette smoking, risky alcohol consumption, and marijuana smoking among university students in Germany to be associated with multiple factors, especially health behaviors. Furthermore, each of the substances was highly associated with each of the two other substances we examined. Other variable groups, such as psychological or psychosocial variables, seemed to play a rather minor role. Therefore, our recommendation for future prevention programs is that substance use among university students should be addressed as a whole, not just in terms of specific substances.

Association between non-medical cannabis legalization and emergency department visits for cannabis-induced psychosis

A major public health concern of cannabis legalization is that it may result in an increase in psychotic disorders. We examined changes in emergency department (ED) visits for cannabis-induced psychosis following the legalization and subsequent commercialization (removal of restrictions on retail stores and product types) of non-medical cannabis in Ontario, Canada (population of 14.3 million). We used health administrative data containing the cause of all ED visits to examine changes over three periods; 1) pre-legalization (January 2014-September 2018); 2) legalization with restrictions (October 2018 - February 2020); and 3) commercialization (March 2020 - September 2021). We considered subgroups stratified by age and sex and examined cocaine- and methamphetamine-induced psychosis ED visits as controls. During our study, there were 6300 ED visits for cannabis-induced psychosis. The restricted legalization period was not associated with changes in rates of ED visits for cannabis-induced psychosis relative to pre-legalization. The commercialization period was associated with an immediate increase in rates of ED visits for cannabis-induced psychosis (IRR 1.30, 95% CI 1.02-1.66) and no gradual monthly change; immediate increases were seen only for youth above (IRR 1.63, 1.27-2.08, ages 19-24) but not below (IRR 0.73 95%CI 0.42-1.28 ages, 15-18) the legal age of purchase, and similar for men and women. Commercialization was not associated with changes in rates of ED visits for cocaine- or methamphetamine-induced psychosis. This suggests that legalization with store and product restrictions does not increase ED visits for cannabis-induced psychosis. In contrast, cannabis commercialization may increase cannabis-induced psychosis presentations highlighting the importance of preventive measures in regions considering legalization.

Acute effects of Δ9-tetrahydrocannabinol (THC) on resting state connectivity networks and impact of COMT genotype: A multi-site pharmacological fMRI study

BACKGROUND

Cannabis produces various acute psychotropic effects, with marked individual differences. Cannabis use is a risk factor for developing psychotic disorders. The main component responsible for these effects is Δ9-tetrahydrocannabinol (THC). Here we investigated the neural basis of acute THC effects and its modulation by catechol-methyl-transferase (COMT) Val158Met genotype.

METHODS

Resting state functional MRI data of healthy occasional cannabis users were combined and re-analyzed from three double-blind, placebo-controlled, within-subject pharmacological functional magnetic resonance imaging studies (total N=87). Functional connectivity after placebo and THC was compared in three functional networks (salience, executive and default mode network) and a network implicated in psychosis (the hippocampus-midbrain-striatum network). COMT genotype modulation of subjective effects and connectivity was examined.

RESULTS

THC reduced connectivity in the salience network, specifically from the right insula to both the left insula and anterior cingulate cortex. We found a trend towards decreased connectivity in the hippocampus-midbrain-striatum network after THC. COMT genotype modulated subjective effects of THC, with strongest dysphoric reactions in Met/Met individuals. In addition, reduced connectivity after THC was demonstrated in the hippocampus-midbrain-striatum network of Met/Met individuals only.

CONCLUSIONS

In this large multisite study we found that THC robustly decreases connectivity in the salience network, involved in processing awareness and salient information. Connectivity changes in the hippocampus-midbrain-striatum network may reflect the acute psychotic-like effects of THC. COMT genotype modulation of THC's impact on subjective effects and functional connectivity provides further evidence for involvement of prefrontal dopamine levels in the acute effects of cannabis.

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

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

Molecular brain differences and cannabis involvement: A systematic review of positron emission tomography studies

BACKGROUND

An increasing number of studies have used positron emission tomography (PET) to investigate molecular neurobiological differences in individuals who use cannabis. This study aimed to systematically review PET imaging research in individuals who use cannabis or have cannabis use disorder (CUD).

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria, a comprehensive systematic review was undertaken using the PubMed, Scopus, PsycINFO and Web of Science databases.

RESULTS

In total, 20 studies were identified and grouped into three themes: (1) studies of the dopamine system primarily found that cannabis use was associated with abnormal striatal dopamine synthesis capacity, which was in turn correlated with clinical symptoms; (2) studies of the endocannabinoid system found that cannabis use and CUD are associated with lower cannabinoid receptor type 1 availability and global reductions in fatty acid amide hydrolase binding; (3) studies of brain metabolism found that individuals who use cannabis exhibit lower normalized glucose metabolism in both cortical and subcortical brain regions, and reduced cerebral blood flow in the lateral prefrontal cortex during experimental tasks. Heterogeneity across studies prevented meta-analysis.

CONCLUSION

Existing PET imaging research reveals substantive molecular differences in cannabis users in the dopamine and endocannabinoid systems, and in global brain metabolism, although the heterogeneity of designs and approaches is very high, and whether these differences are causal versus consequential is largely unclear.

Altered brain structural and functional connectivity in cannabis users

Cannabis is one of the most used and commodified illicit substances worldwide, especially among young adults. The neurobiology mechanism of cannabis is yet to be identified particularly in youth. The purpose of this study was to concurrently measure alterations in brain structural and functional connectivity in cannabis users using resting-state functional magnetic resonance images (rs-fMRI) and diffusion-weighted images (DWI) from a group of 73 cannabis users (age 22-36, 19 female) in comparison with 73 healthy controls (age 22-36, 14 female) from Human Connectome Project (HCP). Several significant differences were observed in local structural/functional network measures (e.g. degree and clustering coefficient), being prominent in the insular and frontal opercular cortex and lateral/medial temporal cortex. The rich-club organization of structural networks revealed a normal trend, distributed within bilateral frontal, temporal and occipital regions. However, minor differences were found between the two groups in the superior and inferior temporal gyri. Functional rich-club nodes were mostly located within parietal and posterior areas, with minor differences between the groups found mainly in the centro-temporal and parietal regions. Regional network measures of structural/functional networks were associated with times used cannabis (TUC) in several regions. Although the structural/functional network in both groups showed small-world property, no differences between cannabis users and healthy controls were found regarding the global network measures, showing no association with cannabis use. After FDR correction, all of the significant associations between network measures and TUC were found to be insignificant, except for the association between degree and TUC within the presubiculum region. To recap, our findings revealed alterations in local topological properties of structural and functional networks in cannabis users, although their global brain network organization remained intact.

Cannabis-Induced Acute Encephalopathy in a 94-Year-Old Woman Due to Family Administration of Cannabidiol (CBD) Products: A Case Report

In the United States, cannabis use is rising, including among older adults, as is unintentional ingestion. We describe the case of a 94-year-old woman admitted with altered mental status, diarrhea, and hallucinations. She lived with her family, who had noticed recent confusion with weakness, poor oral intake, and loose bowel movements. In the emergency room, her vital signs revealed mild tachycardia and hypotension. She was lethargic, disoriented, confused, and anxious but could answer simple questions. The attending hospitalist administered the Mini-Cog dementia screening and found that the patient was oriented to herself only and was unable to perform word recall tests or complete a clock drawing. The rest of her physical exam was within normal limits for her age. Despite a workup including urine culture, chest X-ray, and computed tomography scan of her head, no organic source for her mental change was found. After five days of admission, a close relative confessed that they had given the patient cannabis oil (marketed as "pure CBD," i.e., cannabidiol, a nonpsychoactive cannabis derivative widely touted as a remedy for pain, anxiety, and anorexia) in the form of edible brownies to help her with her persistent back pain and poor appetite. We performed a urine drug screen for tetrahydrocannabinol (THC), the psychoactive component of cannabis, which verified cannabis use, as well as exposure to THC. The patient recovered to baseline with supportive care. Currently, there is no governing body or framework for the regulation of cannabis products in the United States. Nonprescription CBD products are not regulated by the US Food and Drug Administration, and these products are not tested for safety, efficacy, or quality. Some producers voluntarily conduct such testing, but there is no regulatory oversight, and consumers may be unaware of the need for testing and/or which testing bodies are credible. Given the rapidly increasing proportion of older adults who are cannabis users, physicians should inquire about outpatient use of cannabis in general and CBD in particular during discussions with patients, even the most elderly.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

DISCUSSION

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

SYSTEMATIC REVIEW REGISTRATION

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

Regular recreational Cannabis users exhibit altered neural oscillatory dynamics during attention reorientation

BACKGROUND

Cannabis is the most widely used illicit drug in the United States and is often associated with changes in attention function, which may ultimately impact numerous other cognitive faculties (e.g. memory, executive function). Importantly, despite the increasing rates of cannabis use and widespread legalization in the United States, the neural mechanisms underlying attentional dysfunction in chronic users are poorly understood.

METHODS

We used magnetoencephalography (MEG) and a modified Posner cueing task in 21 regular cannabis users and 32 demographically matched non-user controls. MEG data were imaged in the time-frequency domain using a beamformer and peak voxel time series were extracted to quantify the oscillatory dynamics underlying use-related aberrations in attentional reorienting, as well as the impact on spontaneous neural activity immediately preceding stimulus onset.

RESULTS

Behavioral performance on the task (e.g. reaction time) was similar between regular cannabis users and non-user controls. However, the neural data indicated robust theta-band synchronizations across a distributed network during attentional reorienting, with activity in the bilateral inferior frontal gyri being markedly stronger in users relative to controls (p's < 0.036). Additionally, we observed significantly reduced spontaneous theta activity across this distributed network during the pre-stimulus baseline in cannabis users relative to controls (p's < 0.020).

CONCLUSIONS

Despite similar performance on the task, we observed specific alterations in the neural dynamics serving attentional reorienting in regular cannabis users compared to controls. These data suggest that regular cannabis users may employ compensatory processing in the prefrontal cortices to efficiently reorient their attention relative to non-user controls.

The effect of tetrahydrocannabinol:cannabidiol oromucosal spray on cognition: a systematic review

PURPOSE

Previous studies have shown that tetrahydrocannabinol (THC), the main psychoactive component of cannabis, can impair cognitive abilities. There is also some evidence that cannabidiol (CBD), the most abundant non-intoxicating constituent of cannabis, can attenuate these effects. The purpose of this study was to investigate the effects of THC:CBD oromucosal spray (with equal parts THC and CBD) on cognition compared with control conditions in human studies.

METHODS

A systematic literature search was performed on four major bibliographic databases. Studies were included in the present review if they evaluated the cognitive effects of THC:CBD oromucosal spray compared with a control condition.

RESULTS

Ten studies were identified (7 on patients with multiple sclerosis, 1 on those with Huntington, and 2 on healthy volunteers) with 510 participants in total. There was considerable heterogeneity among the studies in terms of dose and duration of administration. All studies have used an equal or nearly equal dose of THC and CBD.

CONCLUSIONS

Although the results across studies were somewhat inconsistent, most evidence revealed that there is no significant difference between THC:CBD oromucosal spray and control treatments in terms of cognitive outcomes. However, more trials are needed with longer follow-up periods, and dose considerations, particularly comparing lower and higher doses of the spray.

Effects of cannabinoids on resting state functional brain connectivity: A systematic review

Cannabis products are widely used for medical and non-medical reasons worldwide and vary in content of cannabinoids such as delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Resting state functional connectivity offers a powerful tool to investigate the effects of cannabinoids on the human brain. We systematically reviewed functional neuroimaging evidence of connectivity during acute cannabinoid administration. A pre-registered (PROSPERO ID: CRD42020184264) systematic review of 13 studies comprising 318 participants (mean age of 25 years) was conducted and reported using the PRISMA checklist. During THC and THCv exposure vs placebo reduced connectivity with the NAcc was widely reported. Limited evidence shows that such effects are offset by co-administration of CBD. NAcc-frontal region connectivity was associated with intoxication levels. Cannabis intoxication vs placebo was associated with lower striatal-ACC connectivity. CBD and CBDv vs placebo were associated with both higher and lower connectivity between striatal-prefrontal/other regions. Overall, cannabis and cannabinoids change functional connectivity in the human brain during resting state as a function of the type of cannabinoid examined.

Smoked cannabis reduces peak cocaine plasma levels and subjective effects in a controlled drug administration study of polysubstance use in men

BACKGROUND

Despite the high prevalence of polysubstance use, outcomes and potential risks associated with common drug combinations are not well characterized. Many individuals who use cocaine also use cannabis, yet little is known about how interactions between the two drugs might contribute to continued co-use.

METHODS

The aim of this double-blind, placebo-controlled study was to determine the physiological and subjective effects of smoked cannabis with smoked cocaine, to identify variables that may contribute to the continued use of this drug combination. Healthy, non-treatment seeking volunteers who reported smoking both cocaine and cannabis (N = 9, all males) completed a 13-day inpatient protocol. On session days, cannabis [0.0 or 5.6 % tetrahydrocannabinol (THC)] was administered 28 min prior to cocaine (0, 12, or 25 mg). Dependent measures included pharmacokinetic assessment of THC and cocaine and their respective metabolites, in addition to subjective and cardiovascular effects.

RESULTS

Active cannabis (5.6 % THC) increased plasma levels of THC and the metabolite 11-nor-9-carboxy-Δ9-THC (THCCOOH), as well as subjective ratings of cannabis effects and heart rate relative to inactive cannabis. Cocaine dose-dependently increased plasma cocaine and metabolites and subjective ratings of cocaine effects. Active cannabis pre-treatment decreased plasma levels of cocaine and metabolites. Furthermore, active cannabis attenuated cocaine-related reductions in 'Hunger' and 'Calm.'

CONCLUSIONS

Cannabis pre-treatment altered the subjective experience of smoked cocaine and reduced peak plasma levels of cocaine. Future studies should explore additional doses of each drug and whether these changes also impact cocaine's reinforcing effects.

Cannabis in Adolescence: Lasting Cognitive Alterations and Underlying Mechanisms

Cannabis consumption during adolescence is an area of particular concern, owing to changes in the social and political perception of the drug, and presents a scientific, medical, and economic challenge. Major social and economic interests continue to push toward cannabis legalization as well as pharmaceutical development. As a result, shifting perceptions of both legal and illicit cannabis use across the population have changed the collective evaluation of the potential dangers of the product. The wave of cannabis legalization therefore comes with new responsibility to educate the public on potential risks and known dangers associated with both recreational and medical cannabis. Among these is the risk of long-term cognitive and psychological consequences, particularly following early-life initiation of use, compounded by high-potency and/or synthetic cannabis, and heavy/frequent use of the drug. Underlying these cognitive and psychiatric consequences are lasting aberrations in the development of synaptic function, often secondary to epigenetic changes. Additional factors such as genetic risk and environmental influences or nondrug toxic insults during development are also profound contributors to these long-term functional alterations following adolescent cannabis use. Preclinical studies indicate that exposure to cannabinoids during specific windows of vulnerability (e.g., adolescence) impacts neurodevelopmental processes and behavior by durably changing dendritic structure and synaptic functions, including those normally mediated by endogenous cannabinoids and neuronal circuits.

Effects of inhaled cannabis high in Δ9-THC or CBD on the aging brain: A translational MRI and behavioral study

With the recent legalization of inhaled cannabis for medicinal and recreational use, the elderly represents one of the newest, rapidly growing cohorts of cannabis users. To understand the neurobiological effects of cannabis on the aging brain, 19-20 months old mice were divided into three groups exposed to vaporized cannabis containing ~10% Δ9-THC, ~10% CBD, or placebo for 30 min each day. Voxel based morphometry, diffusion weighted imaging, and resting state functional connectivity data were gathered after 28 days of exposure and following a two-week washout period. Tail-flick, open field, and novel object preference tests were conducted to explore analgesic, anxiolytic, and cognitive effects of cannabis, respectively. Vaporized cannabis high in Δ9-THC and CBD achieved blood levels reported in human users. Mice showed antinociceptive effects to chronic Δ9-THC without tolerance while the anxiolytic and cognitive effects of Δ9-THC waned with treatment. CBD had no effect on any of the behavioral measures. Voxel based morphometry showed a decrease in midbrain dopaminergic volume to chronic Δ9-THC followed but an increase after a two-week washout. Fractional anisotropy values were reduced in the same area by chronic Δ9-THC, suggesting a reduction in gray matter volume. Cannabis high in CBD but not THC increased network strength and efficiency, an effect that persisted after washout. These data would indicate chronic use of inhaled cannabis high in Δ9-THC can be an effective analgesic but not for treatment of anxiety or cognitive decline. The dopaminergic midbrain system was sensitive to chronic Δ9-THC but not CBD showing robust plasticity in volume and water diffusivity prior to and following drug cessation an effect possibly related to the abuse liability of Δ9-THC. Chronic inhaled CBD resulted in enhanced global network connectivity that persisted after drug cessation. The behavioral consequences of this sustained change in brain connectivity remain to be determined.

The Effects of Acute Cannabis With and Without Cannabidiol on Neural Reward Anticipation in Adults and Adolescents

BACKGROUND

Adolescents may respond differently to cannabis than adults, yet no previous functional magnetic resonance imaging study has examined acute cannabis effects in this age group. In this study, we investigated the neural correlates of reward anticipation after acute exposure to cannabis in adolescents and adults.

METHODS

This was a double-blind, placebo-controlled, randomized, crossover experiment. Forty-seven adolescents (n = 24, 12 females, ages 16-17 years) and adults (n = 23, 11 females, ages 26-29 years) matched on cannabis use frequency (0.5-3 days/week) completed the Monetary Incentive Delay task during functional magnetic resonance imaging after inhaling cannabis with 0.107 mg/kg Δ⁹-tetrahydrocannabinol ("THC") (8 mg THC for a 75-kg person) or with THC plus 0.320 mg/kg cannabidiol ("THC+CBD") (24 mg CBD for a 75-kg person), or placebo cannabis. We investigated reward anticipation activity with whole-brain analyses and region of interest analyses in the right and left ventral striatum, right and left anterior cingulate cortex, and right insula.

RESULTS

THC reduced anticipation activity compared with placebo in the right (p = .005, d= 0.49) and left (p = .003, d = 0.50) ventral striatum and the right insula (p = .01, d = 0.42). THC+CBD reduced activity compared with placebo in the right ventral striatum (p = .01, d = 0.41) and right insula (p = .002, d = 0.49). There were no differences between "THC" and "THC+CBD" conditions and no significant drug by age group interaction effect, supported by Bayesian analyses. There were no significant effects in the whole-brain analyses.

CONCLUSIONS

In weekly cannabis users, cannabis suppresses the brain's anticipatory reward response to money, and CBD does not modulate this effect. Furthermore, the adolescent reward circuitry is not differentially sensitive to acute effects of cannabis on reward anticipation.

Investigating the "two-hit hypothesis": Effects of prenatal maternal immune activation and adolescent cannabis use on neurodevelopment in mice

Prenatal exposure to maternal immune activation (MIA) and chronic adolescent cannabis use are both risk factors for neuropsychiatric disorders. However, exposure to a single risk factor may not result in major mental illness, indicating that multiple exposures may be required for illness onset. Here, we examine whether combined exposure to prenatal MIA and adolescent delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, lead to enduring neuroanatomical and behavioural changes in adulthood. Mice were prenatally exposed to viral mimetic, poly I:C (5 mg/kg), or vehicle at gestational day (GD) 9, and postnatally exposed to chronic THC (5 mg/kg, intraperitoneal) or vehicle during adolescence (postnatal day [PND]28-45). Longitudinal magnetic resonance imaging (MRI) was performed pre-treatment, PND 25, post-treatment, PND 50, and in adulthood, PND85, followed by behavioural tests for anxiety-like, social, and sensorimotor gating. Post-mortem assessment of cannabinoid (CB)1 and 2 receptor expressing cells was performed in altered regions identified by MRI (anterior cingulate and somatosensory cortices, striatum, and hippocampus). Subtle deviations in neurodevelopmental trajectory and subthreshold anxiety-like behaviours were observed in mice exposed to both risk factors. Sex-dependent effects were observed in patterns of shared brain-behaviour covariation, indicative of potential sex differences in response to MIA and THC. Density of CB1 and CB2 receptor positive cells was significantly decreased in all mice exposed to MIA, THC, or both. These findings suggest that there may be a cumulative effect of risk factor exposure on gross neuroanatomical development, and that the endocannabinoid system may be sensitive to both prenatal MIA, adolescent THC, or the combination.

Blockade of endocannabinoid system by oxytocin attenuates memory deficits in oxycodone-treated rats

Oxycodone is a highly prescribed opioid and its abuse has been rampant. Accumulating evidence shows that the cannabinoid CB1 receptor (CB1R) plays a key role in mediating rewarding effects to opioids. However, the downstream signalling of CB1R induced by oxycodone remains unclear. The neuropeptide oxytocin is well known as a potential remedy for drug addiction. Thus, our study aims to explore the mechanism of oxycodone-induced learning and memory deficits underlying the endocannabinoid system (ECS) and the effect of oxytocin. Rats were intraperitoneally injected with oxycodone once a day for eight consecutive day. Novel object recognition, resident-intruder and Morris Water Maze tests were employed to assess the cognitive, social and spatial memory of the rats after oxycodone withdrawal. The (co-)expression of CB1R, cyclin-dependent kinase 5 (Cdk5), regulatory protein p25, tau and phosphorylated tau was measured 1 day after the last behavioural test. The histopathological staining and synaptic density in the hippocampus were observed as well. We found that oxycodone upregulated the expression of p-GSK3β, co-expression of p-Cdk5 and p25 through CB1R. This finding was accompanied by elevation of pSer396, pSer404 in the tau, and reduction of the number of neurons, dendritic spines and synaptic density in the hippocampus. Furthermore, i.c.v. treatment with oxytocin ameliorates memory deficits in oxycodone-treated rats through inhibition of the ECS. We propose further studies on the clinical use of this neuropeptide, which may potentially cure drug addiction.

The C4EB study-Transvamix (10% THC / 5% CBD) to treat chronic pain in epidermolysis bullosa: A protocol for an explorative randomized, placebo controlled, and double blind intervention crossover study

Patients with the genetic blistering skin condition epidermolysis bullosa (EB) report severe pain as a consequence of skin and mucous membrane lesions including blisters, wounds, and scars. Adequate symptom alleviation is not often achieved using conventional pharmacologic interventions. Finding novel approaches to pain care in EB is imperative to improve the quality of life of patients living with EB. There are several anecdotal reports on the use of cannabinoid-based medicines (CBMs) by EB patients to reduce the burden of symptoms. However, controlled clinical investigations assessing these reported effects are lacking. As the pain quality "unpleasantness" delineates EB pain, we hypothesize the modulation of affective pain processing in the brain by way of intervention with CBMs comprising the cannabinoids Δ-9-tetrahydrocannabinol and cannabidiol-objectified by functional magnetic resonance imaging (fMRI). The C4EB study is an investigator-initiated, single-centre, randomized, double-blind, placebo-controlled and crossover trial. Adult patients with the diagnosis epidermolysis bullosa, reporting chronic pain will be eligible to participate. Following baseline measurements, participants will be randomized to receive the sublingually administered interventions placebo and Transvamix® in forward or reversed orders, each for two weeks and separated by a washout. The primary outcome is the difference in numeric rating scale pain scores between grouped interventions, using affective descriptors within the Short-form McGill Pain Questionnaire-2. Secondary outcomes include pain self-efficacy, concomitant analgesic medication-use and adverse events. Additionally, fMRI will be employed to assess brain connectivity related to neuroanatomic pain circuits at baseline, placebo and Transvamix® interventions. The study was approved by the ethical committee at the University Medical Center of Groningen in the Netherlands. Results will be submitted for publication in a peer-reviewed journal. Trial registration number: Netherlands Trial Register: NL9347 (Acronym: C4EB).

In utero exposure to cannabidiol disrupts select early-life behaviors in a sex-specific manner

Cannabidiol (CBD), one of the main components of cannabis, is generally considered safe. CBD crosses the placenta and its use during pregnancy is steadily increasing, the impact of gestational CBD's effects on prenatal life and neurodevelopment are poorly understood. Here, we combined behavioral approaches and deep learning analysis to assess the sex-dependent neonatal behavior of CBD exposed progeny. Gestating C57BL6/J dams were exposed daily with vehicle or CBD (3 mg/Kg, s.c.), from gestational day 5 to 18. Body weight, pup ultrasound vocalizations (USVs, PND 10) and homing behavior (PND 13) were quantified in the progeny. Thus, male (but not female) pups from CBD-treated dams gained more weight than sham. There were sex-dependent differences in the coarse characteristics of ultrasonic vocalizations. Prenatally-CBD exposed male pups emitted shorter calls, whereas CBD females made more high frequency calls when compared with their control counterparts. There were significant qualitative changes in the syllabic USV repertoire reflected in call typologies and communication patterns. Finally, the homing behavior test showed that CBD-exposed females presented a greater vulnerability to gestational CBD than males. Only CBD-exposed female pups showed reduced motor and discriminatory abilities. Together the results suggest a sexual divergence in the consequences of in utero CBD exposure on neonates at early developmental ages, which may be predictive of adult psychopathology. Given the extent of cannabis and CBD use worldwide, these findings challenge the idea that CBD is a universally safe compound and reveal the need for additional studies on the effect of perinatal CBD exposure.

Regular cannabis use modulates the impact of HIV on the neural dynamics serving cognitive control

BACKGROUND

Cannabis use and HIV are independently associated with decrements in cognitive control. However, the combined effects of HIV and regular cannabis use on the brain circuitry serving higher-order cognition are unclear.

AIMS

Investigate the interaction between cannabis and HIV on neural interference effects during the flanker task and spontaneous activity in regions underlying higher-order cognition.

METHODS

The sample consisted of 100 participants, including people with HIV (PWH) who use cannabis, PWH who do not use cannabis, uninfected cannabis users, and uninfected nonusers. Participants underwent an interview regarding their substance use history and completed the Eriksen flanker task during magnetoencephalography (MEG). MEG data were imaged in the time-frequency domain and oscillatory maps depicting the neural flanker interference effect were probed for group differences. Voxel time series were then assessed for group-level differences in spontaneous activity.

RESULTS

Group differences in behavioral performance were identified along with group differences in theta and alpha neural interference responses in higher-order regions across the cortex, with nonusers with HIV generally exhibiting the most aberrant responses. Likewise, time series analyses indicated that nonusers with HIV also had significantly elevated spontaneous alpha activity in the left inferior frontal and dorsolateral prefrontal cortices (dlPFC). Finally, we found that spontaneous and oscillatory alpha activity were significantly coupled in the inferior frontal cortex and dlPFC among cannabis users, but not nonusers.

CONCLUSIONS

Regular cannabis use appears to suppress the impact of HIV on spontaneous and oscillatory alpha deficits in the left inferior frontal cortex and dlPFC.

Diminished Structural Brain Integrity in Long-term Cannabis Users Reflects a History of Polysubstance Use

BACKGROUND

Cannabis legalization and use are outpacing our understanding of its long-term effects on brain and behavior, which is fundamental for effective policy and health practices. Existing studies are limited by small samples, cross-sectional measures, failure to separate long-term from recreational use, and inadequate control for other substance use. Here, we address these limitations by determining the structural brain integrity of long-term cannabis users in the Dunedin Study, a longitudinal investigation of a population-representative birth cohort followed to midlife.

METHODS

We leveraged prospective measures of cannabis, alcohol, tobacco, and other illicit drug use in addition to structural neuroimaging in 875 study members at age 45 to test for differences in both global and regional gray and white matter integrity between long-term cannabis users and lifelong nonusers. We additionally tested for dose-response associations between continuous measures of cannabis use and brain structure, including careful adjustments for use of other substances.

RESULTS

Long-term cannabis users had a thinner cortex, smaller subcortical gray matter volumes, and higher machine learning-predicted brain age than nonusers. However, these differences in structural brain integrity were explained by the propensity of long-term cannabis users to engage in polysubstance use, especially with alcohol and tobacco.

CONCLUSIONS

These findings suggest that diminished midlife structural brain integrity in long-term cannabis users reflects a broader pattern of polysubstance use, underlining the importance of understanding comorbid substance use in efforts to curb the negative effects of cannabis on brain and behavior as well as establish more effective policy and health practices.

Substance Abuse Amongst Adolescents: An Issue of Public Health Significance

Adolescence is a crucial time for biological, psychological, and social development. It is also a time when substance addiction and its adverse effects are more likely to occur. Adolescents are particularly susceptible to the negative long-term effects of substance use, including mental health illnesses, sub-par academic performance, substance use disorders, and higher chances of getting addicted to alcohol and marijuana. Over the past few decades, there have been substantial changes in the types of illegal narcotics people consume. The present article deals with the review of substance abuse as a public health problem, its determinants, and implications seen among adolescents. A systematic literature search using databases such as PubMed and Google Scholar was undertaken to search all relevant literature on teenage stimulant use. The findings have been organized into categories to cover essential aspects like epidemiology, neurobiology, prevention, and treatment. The review showed that substance addiction among adolescents between 12 to 19 years is widespread, though national initiatives exist to support young employment and their development. Research on psychological risk factors for teenage substance abuse is vast, wherein conduct disorders, including aggression, impulsivity, and attention deficit hyperactivity disorder, have been mentioned as risk factors for substance use. Parents' attitudes toward drugs, alcohol, academic and peer pressure, stress, and physical outlook are key determinants. Teenage drug usage has a significant negative impact on users, families, and society as a whole. It was found that a lot has been done to provide correct intervention to those in need with the constant development of programs and rehabilitative centers to safeguard the delicate minds of youths and prevent them from using intoxicants. Still, there is much need for stringent policy and program guidelines to curb this societal menace.

Neutral CB1 Receptor Antagonists as Pharmacotherapies for Substance Use Disorders: Rationale, Evidence, and Challenge

Cannabinoid receptor 1 (CB1R) has been one of the major targets in medication development for treating substance use disorders (SUDs). Early studies indicated that rimonabant, a selective CB1R antagonist with an inverse agonist profile, was highly promising as a therapeutic for SUDs. However, its adverse side effects, such as depression and suicidality, led to its withdrawal from clinical trials worldwide in 2008. Consequently, much research interest shifted to developing neutral CB1R antagonists based on the recognition that rimonabant’s side effects may be related to its inverse agonist profile. In this article, we first review rimonabant’s research background as a potential pharmacotherapy for SUDs. Then, we discuss the possible mechanisms underlying its therapeutic anti-addictive effects versus its adverse effects. Lastly, we discuss the rationale for developing neutral CB1R antagonists as potential treatments for SUDs, the supporting evidence in recent research, and the challenges of this strategy. We conclude that developing neutral CB1R antagonists without inverse agonist profile may represent attractive strategies for the treatment of SUDs.

Cognitive functioning and cannabis use in first-episode psychosis

AIM

Cannabis use is common in people with psychotic disorders. However, the effect of cannabis on cognition in psychosis remains unclear. Our study investigates relationships between the history of cannabis use and cognitive performance in patients with first-episode psychosis (FEP) during a one-year follow-up.

METHODS

The present study included FEP (N = 91) and control (N = 61) groups. Cannabis use was evaluated with a self-report questionnaire, clinical assessment, and medical records during a lifetime and 12 months prior to the treatment onset (recent). Symptoms of psychosis and anxiety were evaluated on the brief psychiatric rating scale. Negative symptoms were assessed using the scale for the assessment of negative symptoms. Cognitive tests were used to evaluate neurocognition (summarized in the g factor) and social cognition. Crude regression analyses for the g factor included variables of cannabis use as independent variables. Full regression models were controlled for gender, education, and clinical symptoms.

RESULTS

In the FEP group, men used cannabis more frequently than women. In the crude regression model for FEP patients, never having used cannabis was associated with a better neurocognitive profile at 12 months. In the full model, more severe anxiety symptoms were associated with better neurocognition at two months, and less severe negative symptoms were associated with better neurocognition at 12 months. Cannabis use was not associated with social cognition. No associations between cognitive performance and cannabis use emerged in the controls.

CONCLUSION

Negative and affective symptom severity in FEP was associated with cognitive performance to a greater degree than a lifetime history of cannabis use.

Neural responses to reward anticipation and feedback in adult and adolescent cannabis users and controls

Chronic use of drugs may alter the brain's reward system, though the extant literature concerning long-term cannabis use and neural correlates of reward processing has shown mixed results. Adolescents may be more vulnerable to the adverse effects of cannabis than adults; however, this has not been investigated for reward processing. As part of the 'CannTeen' study, in the largest functional magnetic resonance imaging study of reward processing and cannabis use to date, we investigated reward anticipation and feedback in 125 adult (26-29 years) and adolescent (16-17 years) cannabis users (1-7 days/week cannabis use) and gender- and age-matched controls, using the Monetary Incentive Delay task. Blood-oxygen-level-dependent responses were examined using region of interest (ROI) analyses in the bilateral ventral striatum for reward anticipation and right ventral striatum and left ventromedial prefrontal cortex for feedback, and exploratory whole-brain analyses. Results showed no User-Group or User-Group × Age-Group effects during reward anticipation or feedback in pre-defined ROIs. These null findings were supported by post hoc Bayesian analyses. However, in the whole-brain analysis, cannabis users had greater feedback activity in the prefrontal and inferior parietal cortex compared to controls. In conclusion, cannabis users and controls had similar neural responses during reward anticipation and in hypothesised reward-related regions during reward feedback. The whole-brain analysis revealed tentative evidence of greater fronto-parietal activity in cannabis users during feedback. Adolescents showed no increased vulnerability compared with adults. Overall, reward anticipation and feedback processing appear spared in adolescent and adult cannabis users, but future longitudinal studies are needed to corroborate this.

Δ9-THC reduces reward-related brain activity in healthy adults

RATIONALE

Greater availability of cannabis in the USA has raised concerns about adverse effects of the drug, including possible amotivational states. Lack of motivation may be assessed by examining acute effects of cannabinoids on reward processing.

OBJECTIVES

This study examined single doses of delta-9-tetrahydrocannabinol (∆9-THC; 7.5, 15 mg oral) in healthy adults using a version of the monetary incentive delay (MID) task adapted for electroencephalography (EEG; e-MID) in a within-subjects, double blind design.

METHODS

Two phases of reward processing were examined: anticipation, which occurs with presentation of cues that indicate upcoming reward, punishment, or neutral conditions, and outcome, which occurs with feedback indicating hits or misses. During anticipation, we measured two event-related potential (ERP) components: the P300, which measures attention and motivation, and the LPP, which measures affective processing. During outcome processing, we measured P300 and LPP, as well as the RewP, which measures outcome evaluation.

RESULTS

We found that ∆9-THC modulated outcome processing, but not reward anticipation. Specifically, both doses of ∆9-THC (7.5 and 15 mg) reduced RewP amplitudes after outcome feedback (hits and misses) relative to placebo. ∆9-THC (15 mg) also reduced P300 and LPP amplitudes following hits compared to misses, relative to both placebo and 7.5 mg ∆9-THC.

CONCLUSIONS

These findings suggest that ∆9-THC dampens responses to both reward and loss feedback, which may reflect an "amotivational" state. Future studies are needed to determine generalizability of this effect, such as its pharmacological specificity and its specificity to monetary vs other types of reward.

Is early exposure to cannabis associated with bipolar disorder? Results from a Finnish birth cohort study

BACKGROUND AND AIMS

There are few longitudinal studies assessing the association of cannabis use and subsequent onset of bipolar disorder. We aimed to measure the association between early cannabis exposure and subsequent bipolar disorder.

DESIGN, SETTING AND PARTICIPANTS

Observational study linking a sample from the northern Finland birth cohort 1986 (n = 6325) to nation-wide register data to examine the association of life-time cannabis exposure at age 15/16 years and subsequent bipolar disorder until age 33 (until the end of 2018); 6325 individuals (48.8% males) were included in the analysis.

MEASUREMENTS

Cannabis exposure was measured via self-report. Bipolar disorder was measured via bipolar disorder-related diagnostic codes (ICD-10: F30.xx, F31.xx) collected from the Care Register for Health Care 2001-18, the Register of Primary Health Care Visits 2011-18, the medication reimbursement register of the Social Insurance Institution of Finland 2001-05 and the disability pensions of the Finnish Center for Pensions 2001-16. Potential confounders included demographic characteristics, parental psychiatric disorders, emotional and behavioral problems and other substance use.

FINDINGS

Three hundred and fifty-two adolescents (5.6%) reported any cannabis use until the age of 15-16 years. Of the whole sample, 66 (1.0%) were diagnosed with bipolar disorder. Adolescent cannabis use was associated with bipolar disorder [hazard ratio (HR) = 3.46; 95% confidence interval (CI) = 1.81-6.61]. This association remained statistically significant after adjusting for sex, family structure and parental psychiatric disorders (HR = 3.00; 95% CI = 1.47-6.13) and after further adjusting for adolescent emotional and behavioral problems (HR = 2.34; 95% CI = 1.11-4.94). Further adjustments for frequent alcohol intoxications, daily smoking and lifetime illicit drug use attenuated the associations to statistically non-significant.

CONCLUSIONS

In Finland, the positive association between early cannabis exposure and subsequent development of bipolar disorder appears to be confounded by other substance use.

Trajectories of adolescent psychotic-like experiences and early cannabis exposure: Results from a Finnish Birth Cohort Study

BACKGROUND

Longitudinal studies examining the effect of cannabis exposure (CE) on the prognosis of adolescents with psychotic-like experiences (PLEs) are scarce. We examined trajectories of mental health in adolescents with PLEs and cannabis exposure.

METHODS

The Northern Finland Birth Cohort 1986 (n = 6552) with linkage to nationwide register data was used. Information on lifetime cannabis exposure was collected when participants were aged 15/16. Register-based outcome data on diagnoses made in clinical practice were obtained until age 33. Logistic regression was used to study the association of PLE/CE patterns and subsequent psychiatric disorders. The group with neither PLEs nor CE was utilized as the reference group. Parental psychiatric disorders, family structure, sex, frequent alcohol intoxications, daily smoking and illicit substance use other than cannabis were adjusted for.

RESULTS

In all, 6552 subjects (49.2 % males) were included in analysis. PLEs with cannabis exposure were associated with any psychiatric disorder (OR = 2.59; 95 % CI 1.82-3.68), psychotic disorders (OR = 3.86; 95 % CI 1.83-8.11), mood disorders (OR 4.07; 95 % CI 2.74-6.04), depressive disorders (OR = 4.35; 95 % CI 2.93-6.48), anxiety disorders (OR = 2.06; 95 % CI 1.34-3.17) and substance use disorders (OR = 2.26; 95 % CI 1.13-4.50) compared to reference group. Effect sizes were greater for group with both PLEs and cannabis use than for group with PLEs only.

CONCLUSIONS

Early-onset cannabis use is an adverse prognostic marker for adolescents with PLEs after extensive confounder control including other substance use.

Curcumin, Resveratrol and Cannabidiol as Natural Key Prototypes in Drug Design for Neuroprotective Agents

Nowadays, neurodegenerative diseases (NDs), such as Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS), represent a great challenge in different scientific fields, such as neuropharmacology, medicinal chemistry, molecular biology and medicine, as all these pathologies remain incurable, with high socioeconomic impacts and high costs for governmental health services. Due to their severity and multifactorial pathophysiological complexity, the available approved drugs for clinic have not yet shown adequate effectiveness and exhibited very restricted options in the therapeutic arsenal; this highlights the need for continued drug discovery efforts in the academia and industry. In this context, natural products, such as curcumin (1), resveratrol (2) and cannabidiol (CBD, 3) have been recognized as important sources, with promising chemical entities, prototype models and starting materials for medicinal organic chemistry, as their molecular architecture, multifunctional properties and single chemical diversity could facilitate the discovery, optimization and development of innovative drug candidates with improved pharmacodynamics and pharmacokinetics compared to the known drugs and, perhaps, provide a chance for discovering novel effective drugs to combat NDs. In this review, we report the most recent efforts of medicinal chemists worldwide devoted to the exploration of curcumin (1), resveratrol (2) and cannabidiol (CBD, 3) as starting materials or privileged scaffolds in the design of multi-target directed ligands (MTDLs) with potential therapeutic properties against NDs, which have been published in the scientific literature during the last 10 years of research and are available in PubMed, SCOPUS and Web of Science databases.

Evidence on the acute and residual neurocognitive effects of cannabis use in adolescents and adults: a systematic meta-review of meta-analyses

BACKGROUND

Cannabis is among the most consumed psychoactive substances world-wide. Considering changing policy trends regarding the substance, it is crucial to understand more clearly its potential acute and residual adverse effects from a public health viewpoint. Cognitive function is one of the targeted areas with conflicting findings. This meta-review measured the magnitude of acute and residual effects of cannabis on cognition in adolescents and adults provided by meta-analyses and evaluated quality of evidence.

METHODS

A systematic search was performed in PubMed, PsycINFO, Web of Science and Google Scholar. Meta-analyses were included if they quantitatively examined the performances of users from the general population on cognitive tasks.

RESULTS

The search retrieved 10 eligible meta-analyses (71 effects sizes, n = 43 761) with evidence ranging from low to moderate quality, which were categorized into domains of cognitive functions: executive functions (k = 7), learning and memory (k = 5), attention (k = 4), processing speed (k = 5), perceptual motor function (k = 2) and language (k = 2). Verbal learning and memory displayed the most robust evidence and were most impaired by acute cannabis intoxication that persisted after intoxication passed. Small-to-moderate acute and residual   adverse effects were reported for executive functioning. Cannabis use led to small deficits in inhibitory processes and flexibility, whereas small-to-moderate deficits were reported for working memory and decision-making. Evidence regarding processing speed and attention has shown that cannabis administration induced small-to-moderate adverse effects and residual neurocognitive deficits were observed in heavy cannabis-using youths. Results showed no significant difference between cannabis users and non-users on language, and small-to-moderate effects for simple motor skills.

CONCLUSION

Meta-analytical data on the acute effects of cannabis use on neurocognitive function have shown that cannabis intoxication leads to small to moderate deficits in several cognitive domains. These acute impairments accord with documented residual effects, suggesting that the detrimental effects of cannabis persist beyond acute intake.

Substance Use Disorders and Psychoactive Drug Poisoning in Medically Authorized Cannabis Patients: Longitudinal Cohort Study

OBJECTIVES

Poisoning from psychoactive drugs and substance use disorders (SUD) have been reported among non-medical cannabis users. However, little is known about medical cannabis users and their risk for poisoning and/or development of SUD. This study assessed the risk of emergency department (ED) visits or hospitalization for 1) poisoning by psychoactive drugs and 2) mental/behavioural disorders due to the use of psychoactive drugs and other substances, in medically authorized cannabis patients in Ontario, Canada from 2014-2017.

METHODS

A cohort study of adult patients authorized for medical cannabis that were matched to population-based controls. ED visit/hospitalization were assessed with a main diagnostic code for: 1) poisoning by psychoactive drugs; 2) mental and behavioural disorder due to psychoactive drugs or other substance use. Conditional Cox proportional hazards regressions were conducted.

RESULTS

18,653 cannabis patients were matched to 51,243 controls. During a median follow-up of 243 days, the incidence rate for poisoning was 4.71 per 1,000 person-years (95%CI: 3.71-5.99) for cases and 1.73 per 1,000 person-years (95% CI: 1.36-2.19) for controls. The adjusted hazard ratio (aHR) was 2.45 (95%CI: 1.56-3.84). For mental/behavioural disorders, the incident rates were 8.89 (95% CI: 7.47-10.57) and 5.01 (95% CI: 4.36-5.76) in the cannabis and the controls group. The aHR was 2.27 (95%CI: 1.66-3.11). No difference was observed between males and females (P-value for interaction > 0.05).

CONCLUSIONS

Our study observed a short-term increased risk of ED visit/hospitalization for poisoning or for mental/behavioural disorders (from use of psychoactive drugs and other substances)- in medically authorized cannabis patients.

Differences in Inhibitory Control and Resting Brain Metabolism between Older Chronic Users of Tetrahydrocannabinol (THC) or Cannabidiol (CBD)—A Pilot Study

Δ9-Tetrahydrocannabinol is the main psychoactive component of cannabis and cannabidiol is purportedly responsible for many of the medicinal benefits. The effects of Δ9-tetrahydrocannabinol and cannabidiol in younger populations have been well studied; however, motor function, cognitive function, and cerebral glucose metabolism in older adults have not been extensively researched. The purpose of this study was to assess differences in cognitive function, motor function, and cerebral glucose metabolism (assessed via [¹⁸F]-fluorodeoxyglucose positron emission tomography) in older adults chronically using Δ9-tetrahydrocannabinol, cannabidiol, and non-using controls. Eight Δ9-tetrahydrocannabinol users (59.3 ± 5.7 years), five cannabidiol users (54.6 ± 2.1 years), and 16 non-users (58.2 ± 16.9 years) participated. Subjects underwent resting scans and performed cognitive testing (reaction time, Flanker Inhibitory Control and Attention Test), motor testing (hand/arm function, gait), and balance testing. Δ9-tetrahydrocannabinol users performed worse than both cannabidiol users and non-users on the Flanker Test but were similar on all other cognitive and motor tasks. Δ9-tetrahydrocannabinol users also had lower global metabolism and relative hypermetabolism in the bilateral amygdala, cerebellum, and brainstem. Chronic use of Δ9-tetrahydrocannabinol in older adults might negatively influence inhibitory control and alter brain activity. Future longitudinal studies with larger sample sizes investigating multiple Δ9-tetrahydrocannabinol:cannabidiol ratios on functional outcomes and cerebral glucose metabolism in older adults are necessary.

Individual and combined effects of cannabidiol and Δ9-tetrahydrocannabinol on striato-cortical connectivity in the human brain

BACKGROUND

Cannabidiol (CBD) and Δ⁹-tetrahydrocannabinol (THC) are the two major constituents of cannabis with contrasting mechanisms of action. THC is the major psychoactive, addiction-promoting, and psychotomimetic compound, while CBD may have opposite effects. The brain effects of these drugs alone and in combination are poorly understood. In particular, the striatum is implicated in the pathophysiology of several psychiatric disorders, but it is unclear how THC and CBD influence striato-cortical connectivity.

AIMS

To examine effects of THC, CBD, and THC + CBD on functional connectivity of striatal sub-divisions (associative, limbic and sensorimotor).

METHOD

Resting-state functional Magnetic Resonance Imaging (fMRI) was used across two within-subjects, placebo-controlled, double-blind studies, with a unified analysis approach.

RESULTS

Study 1 (N = 17; inhaled cannabis containing 8 mg THC, 8 mg THC + 10 mg CBD or placebo) showed strong disruptive effects of both THC and THC + CBD on connectivity in the associative and sensorimotor networks, but a specific effect of THC in the limbic striatum network which was not present in the THC + CBD condition. In Study 2 (N = 23, oral 600 mg CBD, placebo), CBD increased connectivity in the associative network, but produced only relatively minor disruptions in the limbic and sensorimotor networks.

OUTCOMES

THC strongly disrupts striato-cortical networks, but this effect is mitigated by co-administration of CBD in the limbic striatum network. Oral CBD administered has a more complex effect profile of relative increases and decreases in connectivity. The insula emerges as a key region affected by cannabinoid-induced changes in functional connectivity, with potential implications for understanding cannabis-related disorders, and the development of cannabinoid therapeutics.

Long-Term Cannabis Use and Cognitive Reserves and Hippocampal Volume in Midlife

OBJECTIVE

Cannabis use is increasing among midlife and older adults. This study tested the hypotheses that long-term cannabis use is associated with cognitive deficits and smaller hippocampal volume in midlife, which is important because midlife cognitive deficits and smaller hippocampal volume are risk factors for dementia.

METHODS

Participants are members of a representative cohort of 1,037 individuals born in Dunedin, New Zealand, in 1972-1973 and followed to age 45, with 94% retention. Cannabis use and dependence were assessed at ages 18, 21, 26, 32, 38, and 45. IQ was assessed at ages 7, 9, 11, and 45. Specific neuropsychological functions and hippocampal volume were assessed at age 45.

RESULTS

Long-term cannabis users showed IQ decline from childhood to midlife (mean=-5.5 IQ points), poorer learning and processing speed relative to their childhood IQ, and informant-reported memory and attention problems. These deficits were specific to long-term cannabis users because they were either not present or were smaller among long-term tobacco users, long-term alcohol users, midlife recreational cannabis users, and cannabis quitters. Cognitive deficits among long-term cannabis users could not be explained by persistent tobacco, alcohol, or other illicit drug use, childhood socioeconomic status, low childhood self-control, or family history of substance dependence. Long-term cannabis users showed smaller hippocampal volume, but smaller hippocampal volume did not statistically mediate cannabis-related cognitive deficits.

CONCLUSIONS

Long-term cannabis users showed cognitive deficits and smaller hippocampal volume in midlife. Research is needed to ascertain whether long-term cannabis users show elevated rates of dementia in later life.

Acute effects of Δ9-tetrahydrocannabinol and cannabidiol on auditory mismatch negativity

RATIONALE

Mismatch negativity (MMN) is a candidate endophenotype for schizophrenia subserved by N-methyl-D-aspartate receptor (NMDAR) function and there is increasing evidence that prolonged cannabis use adversely affects MMN generation. Few human studies have investigated the acute effects of cannabinoids on brain-based biomarkers of NMDAR function and synaptic plasticity.

OBJECTIVES

The current study investigated the acute effects of Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD) alone and in combination on the mismatch negativity (MMN).

METHODS

In a randomised, double-blind, crossover placebo-controlled study, 18 frequent and 18 less-frequent cannabis users underwent 5 randomised drug sessions administered via vaporiser: (1) placebo; (2) THC 8 mg; (3) CBD 400 mg; (4) THC 8 mg + CBD 4 mg [THC + CBD_low]; (5) THC 12 mg + CBD 400 mg [THC + CBD_high]. Participants completed a multifeature MMN auditory oddball paradigm with duration, frequency and intensity deviants (6% each).

RESULTS

Relative to placebo, both THC and CBD were observed to increase duration and intensity MMN amplitude in less-frequent users, and THC also increased frequency MMN in this group. The addition of low-dose CBD added to THC attenuated the effect of THC on duration and intensity MMN amplitude in less-frequent users. The same pattern of effects was observed following high-dose CBD added to THC on duration and frequency MMN in frequent users.

CONCLUSIONS

The pattern of effects following CBD combined with THC on MMN may be subserved by different underlying neurobiological interactions within the endocannabinoid system that vary as a function of prior cannabis exposure. These results highlight the complex interplay between the acute effects of exogenous cannabinoids and NMDAR function. Further research is needed to determine how this process normalises after the acute effects dissipate and following repeated acute exposure.

Is resting-state functional connectivity altered in regular cannabis users? A systematic review of the literature

RATIONALE

Regular cannabis use has been associated with brain functional alterations within frontal, temporal, and striatal pathways assessed during various cognitive tasks. Whether such alterations are consistently reported in the absence of overt task performance needs to be elucidated to uncover the core neurobiological mechanisms of regular cannabis use.

OBJECTIVES

We aim to systematically review findings from studies that examine spontaneous fluctuations of brain function using functional Magnetic Resonance Imaging (fMRI) resting-state functional connectivity (rsFC) in cannabis users versus controls, and the association between rsFC and cannabis use chronicity, mental health symptoms, and cognitive performance.

METHODS

We conducted a PROSPERO registered systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and searched eight databases.

RESULTS

Twenty-one studies were included for review. Samples comprised 1396 participants aged 16 to 42 years, of which 737 were cannabis users and 659 were controls. Most studies found greater positive rsFC in cannabis users compared to controls between frontal-frontal, fronto-striatal, and fronto-temporal region pairings. The same region pairings were found to be preliminarily associated with varying measures of cannabis exposure.

CONCLUSIONS

The evidence to date shows that regular cannabis exposure is consistently associated with alteration of spontaneous changes in Blood Oxygenation Level-Dependent signal without any explicit cognitive input or output. These findings have implications for interpreting results from task-based fMRI studies of cannabis users, which may additionally tax overlapping networks. Future longitudinal rsFC fMRI studies are required to determine the clinical relevance of the findings and their link to the chronicity of use, mental health, and cognitive performance.

How do cannabis users mentally travel in time? Evidence from an fMRI study of episodic future thinking

RATIONALE

Episodic future thinking (EFT) is a cognitive function that allows individuals to imagine novel experiences that may happen in the future. Prior studies show that EFT is impaired in different groups of substance users. However, there is no evidence regarding the neurobiological mechanisms of EFT in cannabis users.

OBJECTIVES

We aimed to compare brain activations of regular cannabis users and non-using controls during an EFT fMRI task. Exploratory analyses were also conducted to investigate the association between EFT and cannabis use variables (e.g., duration of use, age onset, frequency of use).

METHODS

Twenty current cannabis users and 22 drug-naïve controls underwent an fMRI scanning session while completing a task involving envisioning future-related events and retrieval of past memories as a control condition. The EFT fMRI task was adapted from the autobiographical interview and composed of 20 auditory cue sentences (10 cues for past and 10 cues for future events). Participants were asked to recall a past or generate a future event, in response to the cues, and then rate their vividness after each response.

RESULTS

We found that cannabis users compared to non-user controls had lower activation within the cerebellum, medial and superior temporal gyrus, lateral occipital cortex, and occipital fusiform gyrus while envisioning future events. Cannabis users rated the vividness of past events significantly lower than non-users (P < 0.005). There were marginal group differences for rating the vividness of future events (P = 0.052). Significant correlations were also found between the medial and superior temporal gyrus activities and behavioral measures of EFT and episodic memory.

CONCLUSIONS

Cannabis users, compared to drug-naïve controls, have lower brain activation in EFT relevant regions. Thus, any attempts to improve aberrant EFT performance in cannabis users may benefit from EFT training.

Cannabis suppresses antitumor immunity by inhibiting JAK/STAT signaling in T cells through CNR2

The combination of immune checkpoint blockade (ICB) with chemotherapy significantly improves clinical benefit of cancer treatment. Since chemotherapy is often associated with adverse events, concomitant treatment with drugs managing side effects of chemotherapy is frequently used in the combination therapy. However, whether these ancillary drugs could impede immunotherapy remains unknown. Here, we showed that ^∆9-tetrahydrocannabinol (THC), the key ingredient of drugs approved for the treatment of chemotherapy-caused nausea, reduced the therapeutic effect of PD-1 blockade. The endogenous cannabinoid anandamide (AEA) also impeded antitumor immunity, indicating an immunosuppressive role of the endogenous cannabinoid system (ECS). Consistently, high levels of AEA in the sera were associated with poor overall survival in cancer patients. We further found that cannabinoids impaired the function of tumor-specific T cells through CNR2. Using a knock-in mouse model expressing a FLAG-tagged Cnr2 gene, we discovered that CNR2 binds to JAK1 and inhibits the downstream STAT signaling in T cells. Taken together, our results unveiled a novel mechanism of the ECS-mediated suppression on T-cell immunity against cancer, and suggest that cannabis and cannabinoid drugs should be avoided during immunotherapy.

Translational models of cannabinoid vapor exposure in laboratory animals

Cannabis is one of the most frequently used psychoactive substances in the world. The most common route of administration for cannabis and cannabinoid constituents such as Δ-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) is via smoking or vapor inhalation. Preclinical vapor models have been developed, although the vaporization devices and delivery methods vary widely across laboratories. This review examines the emerging field of preclinical vapor models with a focus on cannabinoid exposure in order to (1) summarize vapor exposure parameters and other methodological details across studies; (2) discuss the pharmacological and behavioral effects produced by exposure to vaporized cannabinoids; and (3) compare behavioral effects of cannabinoid vapor administration with those of other routes of administration. This review will serve as a guide for past and current vapor delivery methods in animals, synergize findings across studies, and propose future directions for this area of research.

Examination of gamma-aminobutyric acid and glutamate-glutamine levels in association with impulsive behavior in adolescent marijuana users

BACKGROUND

Adolescent marijuana (MJ) use has been associated with alterations in brain structure and function as well as behavior. Examination of neurochemical correlates such as GABA (gamma-aminobutyric acid) and Glx (glutamate + glutamine) in MJ users remains limited. Impulsivity, identified as a risk factor and consequence of MJ use, has been associated with GABA and Glx levels in healthy and clinical populations. However, this relationship has not been investigated in MJ users. In this study, we examined levels of GABA and Glx in the anterior cingulate cortex (ACC) and its relationship with impulsive behavior in MJ-using adolescents and healthy controls.

METHODS

Healthy control subjects (HC; N = 21) and MJ-using adolescents (N = 18) completed a metabolite-edited ¹H MRS exam to measure ACC GABA and Glx levels, a structured clinical interview to assess MJ use, and the Barratt Impulsivity Scale (BIS-11) to evaluate impulsive behavior.

RESULTS

Adolescent MJ users had significantly lower tissue-corrected GABA (with macromolecules; GABA+) levels (p = 0.029) compared to HC's. No significant between-group differences were observed in ACC Glx levels. Assessment of impulsive behavior demonstrated no significant between-group differences in motor, non-planning, attention, and total impulsivity scores. Additionally, impulsivity measures and tissue-corrected GABA+ or Glx levels were not significantly correlated in either group.

CONCLUSION

Lower GABA levels in MJ users may indicate alterations in excitatory-inhibitory mechanisms critical for neurodevelopment. Although no significant relationships were observed between impulsive measures and GABA or Glx levels in both groups, further investigations are needed examining the relationship between neurochemical correlates, behavior, and adolescent MJ use.

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

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