Long-Term Outcomes of Adolescent THC Exposure on Translational Cognitive Measures in Adulthood in an Animal Model and Computational Assessment of Human Data

Astrocytic transcriptional and epigenetic mechanisms of drug addiction

Addiction is a leading cause of disease burden worldwide and remains a challenge in current neuroscience research. Drug-induced lasting changes in gene expression are mediated by transcriptional and epigenetic regulation in the brain and are thought to underlie behavioral adaptations. Emerging evidence implicates astrocytes in regulating drug-seeking behaviors and demonstrates robust transcriptional response to several substances of abuse. This review focuses on the astrocytic transcriptional and epigenetic mechanisms of drug action.

Differential associations of adolescent versus young adult cannabis initiation with longitudinal brain change and behavior

Leveraging ~10 years of prospective longitudinal data on 704 participants, we examined the effects of adolescent versus young adult cannabis initiation on MRI-assessed cortical thickness development and behavior. Data were obtained from the IMAGEN study conducted across eight European sites. We identified IMAGEN participants who reported being cannabis-naïve at baseline and had data available at baseline, 5-year, and 9-year follow-up visits. Cannabis use was assessed with the European School Survey Project on Alcohol and Drugs. T1-weighted MR images were processed through the CIVET pipeline. Cannabis initiation occurring during adolescence (14-19 years) and young adulthood (19-22 years) was associated with differing patterns of longitudinal cortical thickness change. Associations between adolescent cannabis initiation and cortical thickness change were observed primarily in dorso- and ventrolateral portions of the prefrontal cortex. In contrast, cannabis initiation occurring between 19 and 22 years of age was associated with thickness change in temporal and cortical midline areas. Follow-up analysis revealed that longitudinal brain change related to adolescent initiation persisted into young adulthood and partially mediated the association between adolescent cannabis use and past-month cocaine, ecstasy, and cannabis use at age 22. Extent of cannabis initiation during young adulthood (from 19 to 22 years) had an indirect effect on psychotic symptoms at age 22 through thickness change in temporal areas. Results suggest that developmental timing of cannabis exposure may have a marked effect on neuroanatomical correlates of cannabis use as well as associated behavioral sequelae. Critically, this work provides a foundation for neurodevelopmentally informed models of cannabis exposure in humans.

Propensity for risky choices despite lower cue reactivity in adolescent rats

Adolescence is a time of heightened risk-taking across species. Salient audiovisual cues associated with rewards are a common feature of gambling environments and have been connected to increased risky decision-making. We have previously shown that, in adult male rats, sign tracking - a behavioral measure of cue reactivity - predicts an individual's propensity for suboptimal risky choices in a rodent gambling task (rGT) with win-paired cues. However, adolescents perform less sign tracking than adult animals, suggesting that they are less cue-reactive than adults in some circumstances. Therefore, we investigated the performance of adolescent male rats on the rGT with win cues and examined its relationship with their sign-tracking behavior. We found that adolescents make more risky choices and fewer optimal choices on the rGT compared with adults, evidence of the validity of the rGT as a model of adolescent gambling behavior. We also confirmed that adolescents perform less sign tracking than adults, and we found that, unlike in adults, adolescents' sign tracking was unrelated to their risk-taking in the rGT. This implies that adolescent risk-taking is less likely than that of adults to be driven by reward-related cues. Finally, we found that adults trained on the rGT as adolescents retained an adolescent-like propensity toward risky choices, suggesting that early exposure to a gambling environment may have a long-lasting impact on risk-taking behavior.

THC exposure during adolescence increases impulsivity-like behavior in adulthood in a WIN 55,212-2 self-administration mouse model

Background

Cannabis addiction is a chronically relapsing disorder lacking effective treatment. Regular cannabis consumption typically begins during adolescence, and this early cannabinoid exposure may increase the risk for drug addiction in adulthood.

Objective

This study investigates the development of cannabis addiction-like behavior in adult mice after adolescent exposure to the main psychoactive component of cannabis, Δ⁹-tetrahydrocannabinol (THC).

Methods

Adolescent male mice were exposed to 5 mg/kg of THC from postnatal days 37 to 57. Operant self-administration sessions of WIN 55,212-2 (12.5 μg/kg/infusion) were conducted for 10 days. Mice were tested for three addiction-like criteria (persistence of response, motivation, and compulsivity), two parameters related to craving (resistance to extinction and drug-seeking behavior), and two phenotypic vulnerability traits related to substance use disorders (impulsivity and reward sensitivity). Additionally, qPCR assays were performed to detect differentially expressed genes in medial prefrontal cortex (mPFC), nucleus accumbens (NAc), dorsal striatum, and hippocampus (HPC) of "addicted" and "non-addicted" mice.

Results

Adolescent THC exposure did not modify WIN 55,212-2 reinforcement nor the development of cannabis addiction-like behavior. Inversely, THC pre-exposed mice displayed impulsive-like behavior in adulthood, which was more pronounced in mice that developed the addiction-like criteria. Moreover, downregulated drd2 and adora2a gene expression in NAc and HPC was revealed in THC pre-exposed mice, as well as a downregulation of drd2 expression in mPFC of vehicle pre-treated mice that developed addiction-like behaviors.

Discussion

These findings suggest that adolescent THC exposure may promote impulsivity-like behavior in adulthood, associated with downregulated drd2 and adora2a expression in NAc and HPC.

Nondisordered Cannabis Use Among US Adolescents

Importance

Cannabis use is increasingly viewed by adolescents as not harmful. Youths with cannabis use disorder (CUD) are recognized by clinicians as being at risk for adverse outcomes, yet little is known about the associations between subclinical cannabis use (ie, nondisordered cannabis use [NDCU]) and adverse psychosocial events.

Objective

To describe the prevalence and demographics of NDCU and to compare associations of cannabis use with adverse psychosocial events among adolescents with no cannabis use, NDCU, and CUD.

Design, Setting, and Participants

This cross-sectional study used a nationally representative sample derived from the 2015 to 2019 National Survey on Drug Use and Health. Participants were adolescents aged 12 to 17 years, separated into 3 distinct groups: nonuse (no recent cannabis use), NDCU (recent cannabis use below diagnostic threshold), and CUD. Analysis was conducted from January to May 2022.

Exposures

CUD, NDCU, or cannabis nonuse. NDCU was defined as endorsing recent cannabis use but not meeting the Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition) (DSM-5) CUD criteria. CUD was defined using DSM-5 criteria.

Main Outcomes and Measures

The main outcomes were prevalence of adolescents meeting criteria for NDCU and associations between adverse psychosocial events and NDCU, adjusted for sociodemographic characteristics.

Results

The 68 263 respondents (mean [SD] age, 14.5 [1.7] years; 34 773 [50.9%] males) included in the analysis represented an estimated yearly mean of 25 million US adolescents during 2015 to 2019. Among respondents, 1675 adolescents (2.5%) had CUD, 6971 adolescents (10.2%) had NDCU, and 59 617 adolescents (87.3%) reported nonuse. Compared with nonusers, individuals with NDCU had approximately 2 to 4 times greater odds of all adverse psychosocial events examined, including major depression (adjusted odds ratio [aOR], 1.86; 95% CI, 1.67-2.08), suicidal ideation (aOR, 2.08; 95% CI, 1.88-2.29), slower thoughts (aOR, 1.76; 95% CI, 1.58-1.96), difficulty concentrating (aOR, 1.81; 95% CI, 1.65-2.00), truancy (aOR, 1.90; 95% CI, 1.67-2.16), low grade point average (aOR, 1.80; 95% CI, 1.62-2.00), arrest (aOR, 4.15; 95% CI, 3.17-5.43), fighting (aOR, 2.04; 95% CI, 1.80-2.31), and aggression (aOR, 2.16; 95% CI, 1.79-2.62). Prevalence of adverse psychosocial events was greatest for adolescents with CUD (range, 12.6% to 41.9%), followed by NDCU (range, 5.2% to 30.4%), then nonuse (range, 0.8% to 17.3%).

Conclusions and Relevance

In this cross-sectional study of US adolescents, past-year NDCU was approximately 4 times as prevalent as past-year CUD. A stepwise gradient association was observed for odds of adverse psychosocial events between adolescent NDCU and CUD. In the context of US normalization of cannabis use, prospective research into NDCU is necessary.