Prior exposure to THC increases the addictive effects of nicotine in rats

Control of motivation for sucrose in the paraventricular hypothalamic nucleus by dynorphin peptides and the kappa opioid receptor

The dynorphin peptides are the endogenous ligands for the kappa opioid receptor (KOR) and regulate food intake. Administration of dynorphin-A1-13 (DYN) in the paraventricular hypothalamic nucleus (PVN) increases palatable food intake, and this effect is blocked by co-administration of the orexin-A neuropeptide, which is co-released with DYN in PVN from neurons located in the lateral hypothalamus. While PVN administration of DYN increases palatable food intake, whether it increases food-seeking behaviors has yet to be examined. We tested the effects of DYN and norBNI (a KOR antagonist) on the seeking and consumption of sucrose using a progressive ratio (PR) and demand curve (DC) tasks. In PVN, DYN did not alter the sucrose breaking point in the PR task nor the elasticity or intensity of demand for sucrose in the DC task. Still, DYN reduced the delay in obtaining sucrose and increased licks during sucrose intake in the PR task, irrespective of the co-administration of orexin-A. In PVN, norBNI increased the delay in obtaining sucrose and reduced licks during sucrose intake in the PR task while reducing elasticity but not intensity of demand in the DC task. However, subcutaneous norBNI reduced the breaking point for sucrose and increased the delay in obtaining sucrose in the PR task while reducing the elasticity of demand. Together, these data show different effects of systemic and PVN blockade of KOR on food-seeking, consummatory behaviors, and incentive motivation for sucrose and suggest that KOR activity in PVN is necessary but not sufficient to drive seeking behaviors for palatable food.

Neural circuit basis of adolescent THC-induced potentiation of opioid responses in adult mice

Use of one drug of abuse typically influences the behavioral response to other drugs, either administered at the same time or a subsequent time point. The nature of the drugs being used, as well as the timing and dosing, also influence how these drugs interact. Here, we tested the effects of adolescent THC exposure on the development of morphine-induced behavioral adaptations following repeated morphine exposure during adulthood. We found that adolescent THC administration impacted morphine-induced behaviors across several dimensions, including potentiating reward and paradoxically impairing the development of morphine reward. We then mapped the whole-brain response to a reinstatement dose of morphine, finding that adolescent THC administration led to increased activity in the basal ganglia and increased functional connectivity between frontal cortical regions and the ventral tegmental area. Last, we show using rabies virus-based circuit mapping that adolescent THC exposure triggers a long-lasting elevation in connectivity from the frontal cortex regions onto ventral tegmental dopamine cells that has the potential to influence dopaminergic response to morphine administration during adulthood. Our study adds to the rich literature on the interaction between drugs of abuse and provides potential circuit substates by which adolescent THC exposure influences responses to morphine later in life.

Experimenter administered Δ9-THC decreases nicotine self-administration in a rat model

BACKGROUND

The co-use of nicotine and cannabis has been steadily rising in the United States. Rodent studies suggest that delta-9-tetrahydrocannabinol (THC) could increase addictive qualities of nicotine, but whether repeated THC exposure alters self-administration of nicotine has not been tested. We hypothesized that THC would increase the reinforcing effects of nicotine and alter nicotine intake.

METHODS

Adult male and female Sprague-Dawley rats were treated with THC (0, 3, 30 mg/kg) daily for 14 days prior to and during training for intravenous self-administration of nicotine. Rats were allowed to self-administer nicotine for several weeks, then tested for sensitivity to nicotine dose through multiple determinations of a nicotine dose-effect curve with or without THC pretreatment. A separate set of rats were trained on fixed ratio responding for sucrose and assessed for THC effects on behavior.

RESULTS

Post-session THC decreased nicotine self-administration in male and female rats throughout acquisition and maintenance and increased the latency to stable rates of nicotine intake during acquisition. Post-session THC shifted nicotine dose-effect curves downward, and pre-session THC suppressed responding at higher nicotine doses. Unlike nicotine, responding for sucrose was not affected by post-session THC. Pre-session THC decreased responding for sucrose, particularly for THC-naïve rats.

CONCLUSIONS

Repeated post-session THC decreased nicotine-taking behaviors but did not alter sucrose responding. Thus, post-session THC may alter sensitivity to nicotine. Pre-session THC treatment decreased lever pressing in both sucrose and nicotine studies, indicating this effect was nonspecific. These studies show that THC modulates patterns of nicotine intake in rat models.

Nicotine Enhances Intravenous Self-administration of Cannabinoids in Adult Rats

INTRODUCTION

Nicotine and cannabis are commonly used together, yet few studies have investigated the effects of concurrent administration. Nicotine exhibits reinforcement enhancing effects by promoting the reinforcing properties of stimuli including other drugs. As many studies of this effect used non-contingent nicotine, we implemented a dual-self-administration model where rats have simultaneous access to two drugs and choose which to self-administer throughout a session. Here, we investigated the effect of self-administered or non-contingently delivered nicotine on cannabinoid self-administration.

METHODS

Adult male rats were allowed to self-administer the synthetic cannabinoid WIN 55,212-2 (WIN) intravenously, with or without subcutaneous nicotine injections before each session. A separate group of animals were allowed to self-administer WIN, nicotine, or saline using a dual-catheter procedure, where each solution was infused independently and associated with a separate operant response. A third group of male and female rats were allowed to self-administer delta-9-tetrahydrocannabinol (THC) with or without pre-session injections of nicotine.

RESULTS

Nicotine injections increased self-administration of WIN and THC. During dual self-administration, nicotine availability increased saline and WIN infusions but nicotine intake was not changed by WIN or saline availability. Rats preferred nicotine over saline, but preferred nicotine and WIN equally when both were available. The effect of nicotine on cannabinoid self-administration was acute and reversible when nicotine was no longer present.

CONCLUSIONS

These results expand our understanding of the ability of nicotine to enhance reinforcement of other drugs and suggest that co-use of nicotine and cannabinoids promotes cannabinoid use beyond what would be taken alone.

IMPLICATIONS

This study utilizes a dual intravenous self-administration model to investigate the ability of nicotine to enhance cannabinoid intake. Our results demonstrate that the reinforcement enhancing properties of nicotine on drug use extend to include cannabinoids, but that this effect occurs specifically when nicotine is administered alongside the cannabinoid. Interestingly, cannabinoid use did not promote nicotine intake, suggesting this mechanism of reinforcement is specific to nicotine.

Youth tobacco use before and after flavoured tobacco sales restrictions in Oakland, California and San Francisco, California

The tobacco industry has used recent findings from the Youth Risk Behavior Surveillance System Survey (YRBSS) to claim that a sales restriction on flavoured tobacco products might increase youth combustible cigarette use. In this special communication, we examined YRBSS data and reached the opposite conclusion. We observed the patterns in youth cigarette smoking in Oakland, California following its 2017 convenience store flavoured tobacco sales restriction. We also found that 2019 YRBSS data from San Francisco, California cannot be used to evaluate the effect of the sales restriction on all flavoured tobacco products in San Francisco as the YRBSS data for this city were collected prior to enforcement of the sales restriction. For future studies, we suggest triangulating with corroborating sales, behavioural and qualitative data over time to assess the effects of tobacco control policies on youth tobacco use. We recommend that policy enactment and enforcement dates, as well as the exact data collection periods for population health surveys, be published to facilitate more rigorous policy evaluation.

Direct Effects of Cannabis Intoxication on Motivations for Softer and Harder Drug Use: An Experimental Approach to the Gateway Hypothesis

Aims: This study experimentally tested whether there is a gateway-type effect of cannabis administration on tobacco and cocaine motivation and whether motivational responses predicted use 6 months later. Methods: A 2 (condition: active cannabis vs. placebo joint)×3 (substance stimulus type: tobacco, cannabis, and cocaine) factor within-subjects design for both implicit and explicit motivation. Both experimental sessions were conducted in a cannabis dispensary ("coffeeshop") in Amsterdam and were separated by ∼1 week, followed by a 6-month online follow-up. Eighty-five participants between 18 and 27 years of age (57% male), who used cannabis, tobacco, and cocaine <15 times per month, participated in session 1 (session 2: N=79 and follow-up: N=81). Counterbalanced over sessions, participants smoked an active and a placebo joint following a paced puffing procedure. Before and after smoking, craving and avoidance (explicit motivation) were assessed using visual analog scales, and after smoking, the stimulus response compatibility test was completed to assess approach biases (implicit motivation). Self-reported intoxication and similarity to their usual smoking experience were assessed at the end of both sessions. Self-reported frequency/quantity and dependence symptoms for tobacco, cannabis, and cocaine were assessed at all time points. A linear mixed model approach was used to assess the effects of condition, substance stimulus type, and their interactions on explicit and implicit motivation. Results: In the active condition, participants reported higher levels of intoxication and an experience more similar to their usual smoking experience than in the placebo condition. There was no significant effect of condition, substance type, or their interaction on approach bias. Participants exhibited increased cannabis craving during the placebo condition only and increased explicit cannabis avoidance during the active condition only. Explicit tobacco avoidance decreased during both conditions. Baseline measures did not predict use at 6-month follow-up. Conclusions: In light users, cannabis intoxication did not affect implicit and explicit tobacco or cocaine motivations. Tobacco avoidance decreased regardless of condition, indicating that the cannabis cue-rich setting-rather than tetrahydrocannabinol itself-may momentarily increase the likelihood to smoke tobacco. However, motivation at baseline did not predict use 6 months later, deeming any gateway-like function unlikely.

State Marijuana Laws and Marijuana Use Among Sexual and Gender Minority Youth in the United States

Purpose: The purpose of this study was to explore the association between state-level marijuana policies and marijuana use among sexual and gender minority (SGM) adolescents. Methods: A secondary analysis was conducted using a nonprobability sample, the 2017 LGBTQ National Teen Survey, based on 10,027 youth who reported their marijuana use behaviors and state of residence. Random intercept multilevel models were estimated to account for between- and within-state variability. Results: State marijuana possession laws were not associated with lifetime use; however, the odds of current marijuana use were 50% greater among youth living in states with legalized marijuana possession for recreational use (adjusted odds ratio [aOR] = 1.50; 95% confidence interval [CI]: 1.21-1.86) compared with states that prohibit any possession. Lesbian, gay, bisexual, transgender, and queer victimization was associated with greater odds of lifetime (aOR = 1.98; 95% CI: 1.78-2.20) and current (aOR = 1.99; 95% CI: 1.74-2.27) marijuana use. Conclusions: State-level policies governing recreational marijuana possession are associated with current marijuana use among SGM youth. Public health approaches to control underage access to legal marijuana and mitigate substance use-related health disparities are needed.

Impact of cannabis legalization in the United States on trends in cannabis use and daily cannabis use among individuals who smoke cigarettes

BACKGROUND

Cannabis legalization and increases in cannabis use are occurring rapidly in the United States (US). Cannabis and tobacco are often used together, but it is unclear whether cannabis legalization will differentially affect cannabis use among those using cigarettes. This study estimated changes from 2004 to 2017 in the prevalence of cannabis use and daily cannabis use by cigarette use status and examined whether state-level cannabis policy modified these trends.

METHODS

Public and restricted-use data from the 2004-2017 National Survey on Drug Use and Health were analyzed. Weighted logistic regressions were used to examine time trends in past-30-day cannabis use and daily caunabis use by cigarette use and cannabis law status from 2004 to 2017.

RESULTS

Cannabis use and daily use increased significantly among those with and without cigarette smoking. Cannabis use and daily cannabis use were consistently 2-10x more common throughout this time among those with, versus without, cigarette smoking. In 2017, cannabis use and daily cannabis use were substantially more common among individuals who use cigarettes, and even greater among those who live in states where cannabis was legal for medical or recreational (i.e., non-medical) use.

CONCLUSIONS

Cannabis use and daily cannabis use are increasing among US individuals who both smoke and do not smoke cigarettes. Cannabis and daily cannabis use are more common among those who smoke cigarettes and elevated even further among those residing in states that have legalized cannabis for recreational (i.e., non-medical) use. Tobacco control efforts should be adjusted to address increases in cannabis use among Americans who smoke cigarettes.

A difference-in-difference approach to examining the impact of cannabis legalization on disparities in the use of cigarettes and cannabis in the United States, 2004-17

AIMS

To estimate the impact of recreational and medical cannabis laws (RCL, MCL) on the use of cannabis and cigarettes in the United States.

DESIGN

A difference-in-difference approach was applied to data from the 2004-17 National Survey on Drug Use and Health (NSDUH).

SETTING

United States.

PARTICIPANTS

Nationally representative cross-sectional survey of Americans aged 12 years and older (combined analytical sample for 2004-17, n = 783 663).

MEASUREMENTS

Data on past-month use of (1) cigarettes and (2) cannabis were used to classify respondents into four groups: cigarette and cannabis co-use, cigarette-only use, cannabis-only use or no cigarette or cannabis use. State of residence was measured by self-report. MCL/RCL status came from state government websites.

FINDINGS

Difference-in-difference analyses suggest that MCL was associated with an increase in cigarette-cannabis co-use overall [adjusted odds ratio (aOR) = 1.09; 95% confidence interval (CI) = 1.02-1.16], with the greatest increases among those aged 50 years and above (aOR = 1.60; CI = 1.39-1.84), married (aOR = 1.19; CI = 1.07-1.31), non-Hispanic (NH) black (aOR = 1.14; CI = 1.02-1.07) and with a college degree or above (aOR = 1.15; CI = 1.06-1.24). MCL was associated with increases in cigarette-only use among those aged 50 years and above (aOR = 1.07; CI = 1.01-1.14) and NH black (aOR = 1.16; CI = 1.06-1.27) and increases in cannabis-only use among those aged 50 years and above (aOR = 1.24; CI = 1.07-1.44) and widowed/divorced/separated (aOR = 1.18; CI = 1.01-1.37). RCL was associated with an increase in cannabis-only use overall (aOR = 1.21; 95% CI = 1.09-1.34), a decline in cigarette-only use overall (aOR = 0.89; 95% CI = 0.81-0.97) and increases in co-use among those who were married (aOR = 1.24; CI = 1.02-1.50) and aged 50 years and above (aOR = 1.37; CI = 1.03-1.84).

CONCLUSIONS

Recreational and medical cannabis legalization have had a varying impact on the use, and co-use, of cannabis and cigarettes in the United States.

HCV cure: an appropriate moment to reduce cannabis use in people living with HIV? (ANRS CO13 HEPAVIH data)

BACKGROUND

Thanks to direct-acting antivirals, hepatitis C virus (HCV) infection can be cured, with similar rates in HCV-infected and HIV-HCV co-infected patients. HCV cure is likely to foster behavioral changes in psychoactive substance use, which is highly prevalent in people living with HIV (PLWH). Cannabis is one substance that is very commonly used by PLWH, sometimes for therapeutic purposes. We aimed to identify correlates of cannabis use reduction following HCV cure in HIV-HCV co-infected cannabis users and to characterize persons who reduced their use.

METHODS

We used data collected on HCV-cured cannabis users in a cross-sectional survey nested in the ANRS CO13 HEPAVIH cohort of HIV-HCV co-infected patients, to perform logistic regression, with post-HCV cure cannabis reduction as the outcome, and socio-behavioral characteristics as potential correlates. We also characterized the study sample by comparing post-cure substance use behaviors between those who reduced their cannabis use and those who did not.

RESULTS

Among 140 HIV-infected cannabis users, 50 and 5 had reduced and increased their use, respectively, while 85 had not changed their use since HCV cure. Cannabis use reduction was significantly associated with tobacco use reduction, a decrease in fatigue level, paying more attention to one's dietary habits since HCV cure, and pre-HCV cure alcohol abstinence (p = 0.063 for alcohol use reduction).

CONCLUSIONS

Among PLWH using cannabis, post-HCV cure cannabis reduction was associated with tobacco use reduction, improved well-being, and adoption of healthy behaviors. The management of addictive behaviors should therefore be encouraged during HCV treatment.

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

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

Increased elasticity of sucrose demand during hyperdopaminergic states in rats

RATIONALE

Deficits in cost-benefit decision-making are a core feature of several psychiatric disorders, including substance addiction, eating disorders and bipolar disorder. Mesocorticolimbic dopamine signalling has been implicated in various processes related to cognition and reward, but its precise role in reward valuation and cost-benefit trade-off decisions remains incompletely understood.

OBJECTIVES

We assessed the role of mesocorticolimbic dopamine signalling in the relationship between price and consumption of sucrose, to better understand its role in cost-benefit decisions.

METHODS

Dopamine neurons in the ventral tegmental area (VTA) were chemogenetically activated in rats, and a behavioural economics approach was used to quantify the relationship between price and consumption of sucrose. Motivation for sucrose was also assessed under a progressive ratio (PR) schedule of reinforcement. To further gauge the role of dopamine in cost-benefit trade-offs for sucrose, the effects of treatment with D-amphetamine and the dopamine receptor antagonist alpha-flupentixol were assessed.

RESULTS

Chemogenetic activation of VTA dopamine neurons increased demand elasticity, while responding for sucrose under a PR schedule of reinforcement was augmented upon stimulation of VTA dopamine neurons. Treatment with amphetamine partially replicated the effects of chemogenetic dopamine neuron activation, whereas treatment with alpha-flupentixol reduced free consumption of sucrose and had mixed effects on demand elasticity.

CONCLUSIONS

Stimulation of mesocorticolimbic dopaminergic neurotransmission altered cost-benefit trade-offs in a complex manner. It reduced the essential value of palatable food, increased incentive motivation and left free consumption unaltered. Together, these findings imply that mesocorticolimbic dopamine signalling differentially influences distinct components of cost expenditure processes aimed at obtaining rewards.

Chronic ∆-9-tetrahydrocannabinol administration delays acquisition of schedule-induced drinking in rats and retains long-lasting effects

RATIONALE

Schedule-induced drinking (SID) is a behavioural phenomenon characterized by an excessive and repetitive drinking pattern with a distinctive temporal distribution that has been proposed as a robust and replicable animal model of compulsivity. Despite cannabis currently being the most widely consumed illicit drug, with growing interest in its clinical applications, little is known about the effects of ∆-9-tetrahydrocannabinol (THC) on SID.

OBJECTIVES

The effects of chronic and acute THC administration on SID acquisition, maintenance and extinction were studied, as were the effects of such administrations on the distinctive temporal distribution pattern of SID.

METHODS

THC (5 mg/kg i.p.), or the corresponding vehicle, was administered to adult Wistar rats for 14 days in a row. Subsequently, THC effects on SID acquisition were tested during 21 sessions using a 1-h fixed-time 60-s food delivery schedule. Acute effects of THC were also evaluated after SID development. Finally, two extinction sessions were conducted to assess behavioural persistence.

RESULTS

The results showed that previous chronic THC treatment delayed SID acquisition and altered the distinctive behavioural temporal distribution pattern during sessions. Moreover, acute THC administration after SID development decreased SID performance in animals chronically pre-treated with the drug. No great persistence effects were observed during extinction in animals pre-treated with THC.

CONCLUSIONS

These results suggest that chronic THC affects SID development, confirming that it can disrupt learning, possibly causing alterations in time estimation, and also leads to animals being sensitized when they are re-exposed to the drug after long periods without drug exposure.

New Insights in the Involvement of the Endocannabinoid System and Natural Cannabinoids in Nicotine Dependence

Nicotine, the main psychoactive component in tobacco smoke, plays a major role in tobacco addiction, producing a high morbidity and mortality in the world. A great amount of research has been developed to elucidate the neural pathways and neurotransmitter systems involved in such a complex addictive behavior. The endocannabinoid system, which has been reported to participate in the addictive properties of most of the prototypical drugs of abuse, is also implicated in nicotine dependence. This review summarizes and updates the main behavioral and biochemical data involving the endocannabinoid system in the rewarding properties of nicotine as well as in nicotine withdrawal and relapse to nicotine-seeking behavior. Promising results from preclinical studies suggest that manipulation of the endocannabinoid system could be a potential therapeutic strategy for treating nicotine addiction.

Cannabinoid Receptor Type 1 Regulates Drug Reward Behavior via Glutamate Decarboxylase 67 Transcription

Interaction of cannabinoid receptor type 1 (CB1) and GABAergic neuronal activity is involved in drug abuse-related behavior. However, its role in drug-dependent Pavlovian conditioning is not well understood. In this study, we aimed to evaluate the effects of a CB1 agonist, JWH-210, on the development of conditioned place preference (CPP)-induced by methamphetamine (METH). Pretreatment with a synthetic cannabinoid, JWH-210 (CB1 agonist), increased METH-induced CPP score and METH-induced dopamine release in acute striatal slices. Interestingly, CB1 was expressed in glutamate decarboxylase 67 (GAD67) positive cells, and overexpression of CB1 increased GAD67 expression, while CB1 knockdown reduced GAD67 expression in vivo and in vitro. GAD67 is known as an enzyme involved in the synthesis of GABA. CB1 knockdown in the mice striatum increased METH-induced CPP. When GAD67 decreased in the mice striatum, mRNA level of CB1 did not change, suggesting that CB1 can regulate GAD67 expression. GAD67 knockdown in the mouse striatum augmented apomorphine (dopamine receptor D2 agonist)–induced climbing behavior and METH-induced CPP score. Moreover, in the human brain, mRNA level of GAD67 was found to be decreased in drug users. Therefore, we suggest that CB1 potentiates METH-induced CPP through inhibitory GABAergic regulation of dopaminergic neuronal activity.

Pharmacokinetic, behavioral, and brain activity effects of Δ9-tetrahydrocannabinol in adolescent male and female rats

Δ⁹-tetrahydrocannabinol (THC) is the intoxicating constituent of cannabis and is responsible for the drug's reinforcing effects. Retrospective human studies suggest that cannabis use during adolescence is linked to long-term negative psychological outcomes, but in such studies it is difficult to distinguish the effects of THC from those of coexisting factors. Therefore, translationally relevant animal models are required to properly investigate THC effects in adolescents. However, though the relevance of these studies depends upon human-relevant dosing, surprisingly little is known about THC pharmacology and its effects on behavior and brain activity in adolescent rodents-especially in females. Here, we conducted a systematic investigation of THC pharmacokinetics, metabolism and distribution in blood and brain, and of THC effects upon behavior and neural activity in adolescent Long Evans rats of both sexes. We administered THC during an early-middle adolescent window (postnatal days 27-45) in which the brain may be particularly sensitive to developmental perturbation by THC. We determined the pharmacokinetic profile of THC and its main first-pass metabolites (11-hydroxy-THC and 11-nor-9-carboxy-THC) in blood and brain following acute injection (0.5 or 5 mg/kg, intraperitoneal). We also evaluated THC effects on behavioral assays of anxiety, locomotion, and place conditioning, as well as c-Fos expression in 14 brain regions. Confirming previous work, we find marked sex differences in THC metabolism, including a female-specific elevation in the bioactive metabolite 11-hydroxy-THC. Furthermore, we find dose-dependent and sex-dependent effects on behavior, neural activity, and functional connectivity across multiple nodes of brain stress and reward networks. Our findings are relevant for interpreting results of rat adolescent THC exposure studies, and may lend new insights into how THC impacts the brain in a sex-dependent manner.

Marijuana Use and Sexual Risk Behavior Among Young Black Men Who Have Sex with Men in California

Young black men who have sex with men (YBMSM) are disproportionately affected by HIV and continue to experience higher rates of new HIV infections when compared to other population groups. As part of the Peer Promotion of Wellness and Enhanced Linkage to Resources Project, we examined problem marijuana use and the overall sexual risk profile of 250 YBMSM. Eighty percent reported prior use of marijuana in their lifetime (n = 200). Among those, problem marijuana use was correlated with problem use of alcohol (r = 0.51, p < 0.001) and other drugs (r = 0.29, p < 0.001); lower household income (r = - .22, p < .01); homelessness (r = 0.15, p < 0.05); incarceration (r = 0.16, p < 0.05); exchanging sex for money, drugs, or shelter (r = 0.18, p < 0.05); having sex with someone known or suspected of having HIV and/or an STI (r = 0.20, p < 0.01); having sex with someone known or suspected of being an injector (r = 0.24, p < 0.01); and having unprotected sex while under the influence of alcohol or drugs (r = 0.32, p < 0.001). The complex relationship between marijuana and sexual risk behavior was examined while accounting for the possible moderating effects of alcohol or other drugs. Problem marijuana, alcohol, and other drug use each made unique contributions to predicting risky sex behavior. A significant marijuana and other drug interaction was found to predict sexual risk behaviors. Future efforts should include holistic intervention approaches for YBMSM that consider factors facilitating high-risk sexual behaviors.

Changes in the Order of Cigarette and Marijuana Initiation and Associations with Cigarette Use, Nicotine Vaping, and Marijuana Use: U.S. 12th Grade Students, 2000-2019

This study (a) examined changes in marijuana and cigarette initiation sequencing and (b) considered implications of such changes for prevention efforts by examining associations between initiation sequencing and current adolescent substance use. Analyses used 2000-2019 cross-sectional data from the national Monitoring the Future (MTF) study (78,252 U.S. 12th grade students). Models examined trends in six distinct patterns of initiation order, and multivariable associations between order of initiation and 30-day cigarette and marijuana use prevalence, cigarette and marijuana use frequency among users, and nicotine and marijuana vaping prevalence. While the percentage of students initiating neither cigarettes nor marijuana increased, increases also were observed in marijuana-only initiation (the fastest-growing pattern) and initiation of marijuana before cigarettes; these increases were accompanied by a significant decrease in cigarette-only initiation. Cigarette use prevalence and frequency were highest among students initiating cigarettes before marijuana; marijuana use prevalence and frequency were highest among students initiating marijuana before cigarettes. Cigarette and marijuana prevalence, as well as marijuana frequency, were lowest among students initiating only a single substance. Nicotine vaping was less prevalent among students initiating a single substance versus both substances, but no significant differences were observed in nicotine vaping prevalence between those initiating only cigarettes versus only marijuana. Implications of these findings for prevention efforts are discussed in the frameworks of both the common liability model and route of administration model.

Pre-conception exposure to THC fails to impact nicotine reward in adult offspring

Exposure to environmental stimuli in one generation can produce altered behavioral and neurobiological phenotypes in descendants. Recent work has shown that parental exposure to cannabinoids alters the rewarding properties of other abused drugs in the subsequent generation. However, whether preconception Δ⁹-tetrahydrocannabinol (THC) administration modifies the affective properties of nicotine in offspring is unknown. To address this question, male and female rats (F0) received THC (0 or 1.5 mg/kg) throughout the adolescent window and were bred on PND 65. In Experiment 1, adult F1-THC and F1-Veh progeny (males and females) underwent nicotine locomotor sensitization procedures during which nicotine (0 or 0.4 mg/kg) was administered every other day for five exposures, and locomotor activity was recorded on each exposure followed by a final nicotine challenge. There was no cross-generational effect of THC on nicotine locomotor sensitization, although acute exposure to nicotine produced greater activity in females relative to males independent of THC history. In Experiment 2, adult F1-THC and F1-Veh progeny (males and females) were implanted with jugular catheters and trained to self-administer nicotine (0.03 mg/kg/infusion). Following acquisition, all subjects were allowed to self-administer nicotine on a number of reinforcement schedules, e.g., FR2, FR5 and PR, followed by dose response and extinction procedures. Across all indices, F1-THC and F1-Veh subjects displayed similar IVSA of nicotine with no sex differences. The fact that there was no evidence of cross-generational effects of THC on nicotine suggests that such effects are drug-specific.

One Is Not Enough: Understanding and Modeling Polysubstance Use

Substance use disorder (SUD) is a chronic, relapsing disease with a highly multifaceted pathology that includes (but is not limited to) sensitivity to drug-associated cues, negative affect, and motivation to maintain drug consumption. SUDs are highly prevalent, with 35 million people meeting criteria for SUD. While drug use and addiction are highly studied, most investigations of SUDs examine drug use in isolation, rather than in the more prevalent context of comorbid substance histories. Indeed, 11.3% of individuals diagnosed with a SUD have concurrent alcohol and illicit drug use disorders. Furthermore, having a SUD with one substance increases susceptibility to developing dependence on additional substances. For example, the increased risk of developing heroin dependence is twofold for alcohol misusers, threefold for cannabis users, 15-fold for cocaine users, and 40-fold for prescription misusers. Given the prevalence and risk associated with polysubstance use and current public health crises, examining these disorders through the lens of co-use is essential for translatability and improved treatment efficacy. The escalating economic and social costs and continued rise in drug use has spurred interest in developing preclinical models that effectively model this phenomenon. Here, we review the current state of the field in understanding the behavioral and neural circuitry in the context of co-use with common pairings of alcohol, nicotine, cannabis, and other addictive substances. Moreover, we outline key considerations when developing polysubstance models, including challenges to developing preclinical models to provide insights and improve treatment outcomes.

Deconstructing the neurobiology of cannabis use disorder

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

THC exposure during adolescence does not modify nicotine reinforcing effects and relapse in adult male mice

RATIONALE

Cannabis use is typically initiated during adolescence, and different studies suggest that adolescent cannabinoid exposure may increase the risk for drug addiction in adulthood.

OBJECTIVES

This study investigated the effects of adolescent exposure to the main psychoactive component of cannabis, ∆⁹-tetrahydrocannabinol (THC), in the reinforcing properties of nicotine in adult male mice. Possible alterations in relapse to nicotine-seeking behaviour in adult animals due to THC adolescent exposure were also evaluated.

METHODS

Adolescent mice were exposed to escalating doses of THC from PND35 to PND49. When mice reached adulthood (PND70), surgical procedures were applied for further behavioural evaluation. Nicotine self-administration sessions were conducted consecutively for 10 days. Following extinction, mice were tested for cue- and stress-induced reinstatement of nicotine-seeking behaviour.

RESULTS

Adolescent THC treatment did not modify acquisition and extinction of nicotine self-administration in adulthood. Moreover, THC exposure did not alter relapse to nicotine seeking induced by stress or nicotine-associated cues.

CONCLUSIONS

These results suggest that a history of exposure to THC during adolescence under these particular conditions does not modify the reinforcing effects and seeking behaviour of nicotine in the adult period.

A behavioral economic analysis of the effects of rimcazole on reinforcing effects of cocaine injection and food presentation in rats

RATIONALE AND OBJECTIVES

Rimcazole, a σ-receptor antagonist with affinity for the dopamine transporter (DAT), decreases rates of cocaine self-administration at doses lower than those that affect food-reinforced responding. As response rates are multiply determined, behavioral-economic analyses were used to provide measures of the reinforcing effectiveness of cocaine and food after rimcazole treatment. Further, effects of combinations of the DAT inhibitor, methylphenidate, and σ-receptor antagonists (BD1008, BD1063) were compared to those of rimcazole to assess mechanism of rimcazole effects.

METHODS

Male Sprague-Dawley rats were trained to lever press with food reinforcement (one or three 20-mg sucrose pellets) or cocaine injection (0.1 or 0.32 mg/kg) under fixed-ratio (FR) 5-response schedules. Drugs or vehicle were administered (i.p.) 5-min before sessions in which FR value was increased from 5 to 80. Economic demand functions were generated from effects of FR value (price) on intake (consumption), with the parameters of demand, consumption at no cost (Q₀) and sensitivity to price (essential value, EV), derived.

RESULTS

Rimcazole dose-dependently decreased Q₀ and EV at both cocaine doses/injection. In contrast, rimcazole had no effect on these parameters at either food amount. Combinations of methylphenidate and the σ-receptor antagonists decreased Q₀ at the lower cocaine dose/injection but had no effect on EV; these treatments were ineffective on both economic parameters at the higher cocaine dose/injection and at either food amount.

CONCLUSIONS

Though the drug combinations only replicated rimcazole's effects incompletely, the present results suggest a specific decrease in the reinforcing effects of cocaine due to dual DAT σ-receptor blockade.

Cannabis and tobacco use and co-use: Trajectories and correlates from early adolescence to emerging adulthood

BACKGROUND

Cannabis and tobacco co-use is a growing concern, yet little is known about its developmental course or associated outcomes during emerging adulthood. This study examines developmental trajectories of cannabis and tobacco co-use from adolescence to emerging adulthood, associations of co-use trajectories with four domains of functioning, and differences across racial/ethnic groups.

METHODS

Survey data come from a racially/ethnically diverse and predominantly California-based cohort that completed 10 surveys from 2008 (wave 1: mean age 11.5; n = 6,509) to 2018 (wave 10: mean age 20.7; n = 2,429). Co-use was defined as use of both cannabis and tobacco (cigarettes or smokeless tobacco) in the past 30 days. Trajectories of use were examined using latent growth modeling in a structural equation modeling framework.

RESULTS

Prevalence of cannabis and tobacco co-use increased from 0.3% at wave 1 to 9.5% at wave 10, with average probabilities of co-use higher among non-Hispanic white versus Hispanic or Asian participants. Higher average probability of co-use was associated with greater delinquency, more mental health symptoms, and poorer physical health during emerging adulthood. Higher rate of change in the probability of co-use over time was associated with greater delinquency, but better social functioning and less physical ailments. There was some evidence of racial/ethnic disparities in functioning, even at similar levels of co-use.

CONCLUSIONS

Cannabis and tobacco co-use deserves greater attention, especially regarding its effects on functioning during emerging adulthood. Results also emphasize the need for future research to focus on racial/ethnic disparities related to co-use and associated outcomes.

The Effects of Marijuana Use on Transitions through Stages of Alcohol Involvement for Men and Women in the NESARC I and II

Background: With the changing context of marijuana use, it is critical to identify effects of use. We extend previous work by examining whether marijuana use influences progression and remission through alcohol involvement stages for men and women. Methods: Data come from Waves I and II of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC, n = 34,432). We assess the potential influence of marijuana use at Wave 1 on transitions across three latent statuses of alcohol involvement between waves. We apply propensity score weighting to account for shared risk factors. Results: Marijuana use was associated cross-sectionally and longitudinally with alcohol involvement statuses for both sexes. After propensity score adjustment, men with marijuana histories were 3.50 times as likely as men without such histories to transition from no to severe problems across waves relative to staying in the same status (p < .001). Women with marijuana histories were 1.74 times as likely as women without such histories to transition from no problems at Wave 1 to moderate problems at Wave 2 (p = .030) and 0.13 times as likely as women without such histories to transition from severe problems to no problems (p = .006). Conclusions: Results suggest that marijuana use impacts progression to more serious stages of alcohol involvement for both men and women, as well as hinders remission among women. Findings point to the importance of screening those with marijuana histories for alcohol problems, as well as the need to understand the mechanism of why marijuana use may increase the risk of alcohol problems.

Varenicline and nabilone in tobacco and cannabis co-users: effects on tobacco abstinence, withdrawal and a laboratory model of cannabis relapse

Tobacco and cannabis co-users (T+CUs) have poor cannabis cessation outcomes, but the mechanisms underlying this are not well understood. This laboratory study examined the effects of (1) the partial nicotinic agonist, varenicline, on tobacco cessation among T+CUs, and (2) varenicline, alone, and when combined with the cannabinoid agonist nabilone, on cannabis withdrawal and a laboratory model of cannabis relapse. Non-treatment-seeking T+CUs were randomized to active-varenicline or placebo-varenicline, and completed a 15-day outpatient phase; varenicline was titrated to 1 mg BID during days 1-8, and participants were instructed to abstain from tobacco during days 9-15. Participants then moved inpatient for 16 days, where they continued their outpatient medication and tobacco abstinence. Inpatient testing included two, 8-day medication periods, where active-nabilone and placebo-nabilone were administered in counterbalanced order, and measures of acute cannabis effects (days 1-2), withdrawal (days 4-5) and 'relapse' (days 6-8) were collected. Participants in the active-varenicline group were more likely to achieve cotinine-verified tobacco abstinence during the outpatient period versus placebo-varenicline group (46 percent versus 24 percent, respectively), and also reported less mood disturbance and cigarette craving while inpatient. Active-nabilone attenuated cannabis withdrawal in both groups but did not affect cannabis relapse. Regression analyses revealed that two tobacco-related variables, i.e. age of first cigarette use, and cigarette craving while inpatient, were independent predictors of cannabis relapse outcomes. Thus, varenicline holds promise in this population, as a tool to examine the effects of tobacco abstinence on cannabis use outcomes, and as a component of smoking cessation treatments targeting T+CUs.

Alcohol, tobacco, and marijuana consumption is associated with increased odds of same-day substance co- and tri-use

BACKGROUND

Little is known about event-level patterns of marijuana co- or tri-use with alcohol and tobacco. Thus, the study goal was to examine patterns of same-day alcohol, cigarette, and marijuana co- and tri-use at the individual level in non-treatment-seeking alcohol users.

METHODS

Participants (N = 551) completed an in-person interview for alcohol, cigarette, and marijuana use over the previous 30 days, and the event-level substance use patterns of n = 179 participants who reported using each of these substances at least once per month were analyzed.

RESULTS

The use of alcohol, marijuana, or cigarettes independently increased the probability of subsequent, simultaneous co-use of one of the two remaining substances. The co-use of alcohol with cigarettes and marijuana with cigarettes produced generally additive effects on the odds of same day tri-use of marijuana and alcohol, respectively. Conversely, the co-use of alcohol and marijuana produced sub-additive effects on likelihood of cigarette use. Sex moderated several of the observed patterns of co- and tri-use: the relationship between alcohol or cigarette use predicting marijuana co-use was stronger in men, whereas the observed additive relationships between drug co-use leading to tri-use was stronger in women.

CONCLUSIONS

The presented results may aid in the understanding of how simultaneous co-use of marijuana with alcohol and/or tobacco relates to the etiology, maintenance, and treatment of comorbid and trimorbid substance use disorder. Replication and extension of the results in treatment seeking populations using more fine-grained analysis approaches, e.g. ecological momentary assessment, is needed.

Legalized Cannabis in Colorado Emergency Departments: A Cautionary Review of Negative Health and Safety Effects

Cannabis legalization has led to significant health consequences, particularly to patients in emergency departments and hospitals in Colorado. The most concerning include psychosis, suicide, and other substance abuse. Deleterious effects on the brain include decrements in complex decision-making, which may not be reversible with abstinence. Increases in fatal motor vehicle collisions, adverse effects on cardiovascular and pulmonary systems, inadvertent pediatric exposures, cannabis contaminants exposing users to infectious agents, heavy metals, and pesticides, and hash-oil burn injuries in preparation of drug concentrates have been documented. Cannabis dispensary workers (“budtenders”) without medical training are giving medical advice that may be harmful to patients. Cannabis research may offer novel treatment of seizures, spasticity from multiple sclerosis, nausea and vomiting from chemotherapy, chronic pain, improvements in cardiovascular outcomes, and sleep disorders. Progress has been slow due to absent standards for chemical composition of cannabis products and limitations on research imposed by federal classification of cannabis as illegal. Given these factors and the Colorado experience, other states should carefully evaluate whether and how to decriminalize or legalize non-medical cannabis use.

The effect of nicotine pre-exposure on demand for cocaine and sucrose in male rats

The aim of the present study was to determine how nicotine pre-exposure affects the elasticity of demand for intravenous cocaine and for sucrose pellets in adult male rats. In Experiment 1, demand for cocaine was assessed in rats that had nicotine in their drinking water. Nicotine pre-exposure significantly decreased rats' willingness to defend cocaine consumption as the price (measured as the number of responses per cocaine infusion) increased compared with a control group with no nicotine pre-exposure. That is, nicotine increased the elasticity of demand for cocaine infusions. Experiment 2 repeated the first experiment, but with rats working for sucrose pellets instead of cocaine. Nicotine pre-exposure had no effect on the elasticity of demand for sucrose. This pattern of results suggests that nicotine pre-exposure can reduce the reinforcing effects of cocaine, but not sucrose, in adult male rats.

GatewayNet: a form of sequential rule mining

Background

The gateway hypothesis (and particularly the prediction of developmental stages in drug abuse) has been a subject of protracted debate since the 1970s. Extensive research has gone into this subject, but has yielded contradictory findings. We propose an algorithm for detecting both association and causation relationships given a discrete sequence of events, which we believe will be useful in addressing the validity of the gateway hypothesis.

To assess the gateway hypothesis, we developed the GatewayNet algorithm, a refinement of sequential rule mining called initiation rule mining. After a brief mathematical definition, we describe how to perform initiation rule mining and how to infer causal relationships from its rules (“gateway rules”).

We tested GatewayNet against data for which relationships were known. After constructing a transaction database using a first-order Markov chain, we mined it to produce a gateway network. We then discuss various incarnations of the gateway network.

We then evaluated the performance of GatewayNet on urine drug screening data collected from the emergency department at LSU Health Sciences Center in Shreveport. A de-identified database of urine drug screenings ordered by the department between August 1998 and June 2011 was collected and then restricted to patients having at least one screening succeeding their first positive drug screening result.

Results

In the synthetic data, a chain of gateway rules was found in the network which demonstrated causation. We did not find any evidence of gateway rules in the empirical data, but we were able to isolate two documented transitions into benzodiazepine use.

Conclusions

We conclude that GatewayNet may show promise not only for substance use data, but other data involving sequences of events. We also express future goals for GatewayNet, including optimizing it for speed.

Electronic supplementary material

The online version of this article (10.1186/s12911-019-0810-3) contains supplementary material, which is available to authorized users.

When Marijuana Is Used before Cigarettes or Alcohol: Demographic Predictors and Associations with Heavy Use, Cannabis Use Disorder, and Other Drug-related Outcomes

Recent loosening of state and federal policy restrictions on marijuana, along with changes in social norms regarding marijuana use and decreases in prevalence of other types of substance use, may lead to increases in youth initiating marijuana before other types of substances such as alcohol and tobacco. We investigated predictors and potential consequences of initiating marijuana before other drugs for youth aged 12-21-years in the USA. Nationally representative, cross-sectional survey data from the US National Survey on Drug Use and Health supplied self-reported age of first marijuana, cigarettes, alcohol, other tobacco, and other illegal drug use among 12-21-year-old samples from 2004 to 2014 (n = 275,559). We first examined the degree to which initiating marijuana use first was associated with sex, age, race/ethnicity, and survey year. Then, we examined whether using marijuana first predicted heavy marijuana use, cannabis use disorder (CUD), alcohol use disorder (AUD), nicotine dependence (ND), or lifetime use of other illegal drugs. Among all survey youth (substance users and non-users), the proportion using marijuana first increased from 4.8 to 8.8% from 2004 to 2014. Those using marijuana first (vs. alcohol or cigarettes first) were more likely to be male and older and Black, American Indian/Alaskan Native, multiracial, or Hispanic than White or Asian. Among substance users and adjusting for age of onset and the number of substances used, using marijuana first was associated higher odds of heavy current marijuana use and CUD. In recent years, youth have been increasingly likely to use marijuana as their first drug and sequence of initiation is associated with race/ethnicity, gender, and age. Using marijuana first might increase the chance of heavy use and CUD.

The Relationship Between Tobacco and Cannabis Use: A Review

BACKGROUND

Based on the prevalence and health implications of tobacco and cannabis use, aiming to reduce their use, especially among youth, is a sound objective at both the individual and public health level. A proper understanding of the relationships between tobacco and cannabis use may help to achieve this goal.

OBJECTIVES

To review the relationships between tobacco and cannabis use.

METHODS

A selective review of the literature.

RESULTS

We present an overview of the motivations for tobacco and cannabis use, and their perceived harmfulness. The article then reviews the gateway theory, reverse gateway theory, route of administration theory, and common liability theory. We describe the link between co-use and dependence symptoms, and the substitution phenomenon between tobacco and cannabis use. Three forms of simultaneous use-mulling, blunt smoking, and chasing-and their impacts are explained. We summarize the impact of tobacco use on cannabis (and vice versa) treatment outcomes, and, finally, review new treatments that simultaneously target tobacco and cannabis dependence. Most of the literature reviewed here relates to substance use among adolescents and young adults.

CONCLUSIONS

The use of tobacco and cannabis-two of the most widely used substances around the world-are strongly intertwined in several respects. Both health professionals and researchers should have well-informed views on this issue to better evaluate, understand, inform, and provide care to their patients.

Historical trends in the grade of onset and sequence of cigarette, alcohol, and marijuana use among adolescents from 1976-2016: Implications for "Gateway" patterns in adolescence

INTRODUCTION

In the past decade, marijuana use prevalence among adolescents has remained relatively steady while cigarette and alcohol prevalence has declined. We examined historical trends in: average grade of onset of marijuana, alcohol, and cigarette use by 12^th grade; proportion who try alcohol/cigarettes before first marijuana use, among those who use by 12^th grade; and conditional probability of marijuana use by 12^th grade after trying alcohol/cigarettes.

METHODS

Data were drawn from 40 yearly, cross-sectional surveys of 12^th grade US adolescents. A subset of students (N = 246,050) were asked when they first used each substance. We reconstructed cohorts of substance use from grade-of-onset to determine sequence of drug use, as well as probability of marijuana use in the same or later grade.

RESULTS

Average grade of first alcohol and cigarette use by 12^th grade increased across time; e.g., first cigarette increased from grade 7.9 in 1986 to 9.0 by 2016 (β=0.04, SE = 0.001, p < 0.01). The proportion of 12^th grade adolescents who smoke cigarettes before marijuana fell below 50% in 2006. Each one-year increase was associated with 1.11 times increased odds of first cigarette in a grade after first marijuana (95% C.I. 1.11-1.12). Among those who initiate alcohol/cigarettes prior to marijuana by 12^th grade, the probability of subsequent marijuana use is increasing.

CONCLUSION

Marijuana is increasingly the first substance in the sequence of adolescent drug use. Reducing adolescent smoking has been a remarkable achievement of the past 20 years; those who continue to smoke are at higher risk for progression to marijuana use.

Transition to drug co-use among adolescent cannabis users: The role of decision-making and mental health

BACKGROUND

Co-use of cannabis and drugs other than cannabis (DOTC) influences the risk of experiencing cannabis disorders. Accordingly, we explored whether speed of transition to drug co-use, the number of DOTC used, and/or being an experimental cannabis-only user, a regular cannabis-only user, or a regular cannabis user who co-uses DOTC (i.e., cannabis-plus user) were associated with decision-making (DM), mental health disorder symptoms, or cannabis use-related characteristics.

METHODS

We analyzed baseline data from a sub-sample of 266 adolescent (ages 14 to 16) cannabis users (CU) participating in an ongoing longitudinal study. Assessments included semi-structured interviews, self-report questionnaires, and measures of drug use, DM (measured via the Iowa Gambling Task), mental health disorders, and cannabis use-related problems.

RESULTS

Endorsing a larger number of mood disorders symptoms was associated with being a regular cannabis-plus user rather than a regular cannabis-only user (AOR = 1.08, C.I.95% 1.01, 1.15). Poorer DM was associated with a faster transition to co-use, such that for each one unit increase in DM performance, the years to onset of drug co-use increased by 1% (p = 0.032). Endorsing a larger number of cannabis use-related problems was positively associated with endorsing a larger number of DOTC used (p = 0.001).

CONCLUSIONS

This study provides new evidence on the process of drug co-use among CU. Specifically, mood disorder symptoms were associated with use of DOTC among regular CU. Furthermore, poorer DM was associated with a faster transition to drug co-use. Poorer DM and mood disorder symptoms may aggravate or accelerate the onset of adverse consequences among adolescent CU.

Adolescent THC exposure does not sensitize conditioned place preferences to subthreshold d-amphetamine in male and female rats

The acute effects of marijuana consumption on brain physiology and behaviour are well documented, but the long-term effects of its chronic use are less well known. Chronic marijuana use during adolescence is of increased interest, given that the majority of individuals first use marijuana during this developmental stage , and  adolescent marijuana use is thought to increase the susceptibility to abusing other drugs when exposed later in life. It is possible that marijuana use during critical periods in adolescence could lead to increased sensitivity to other drugs of abuse later on. To test this, we chronically administered ∆ 9-tetrahydrocannabinol (THC) to male and female Long-Evans (LER) and Wistar (WR) rats directly after puberty onset. Rats matured to postnatal day 90 before being exposed to a conditioned place preference task (CPP). A subthreshold dose of d-amphetamine, found not to induce place preference in drug naïve rats, was used as the unconditioned stimulus. The effect of d-amphetamine on neural activity was inferred by quantifying cfos expression in the nucleus accumbens and dorsal hippocampus following CPP training. Chronic exposure to THC post-puberty had no potentiating effect on a subthreshold dose of d-amphetamine to induce CPP. No differences in cfos expression were observed. These results show that chronic exposure to THC during puberty did not increase sensitivity to a sub-threshold dose of d-amphetamine in adult LER and WR rats. This supports the concept that THC may not sensitize the response to all drugs of abuse.

Adolescent THC exposure does not sensitize conditioned place preferences to subthreshold d-amphetamine in male and female rats

The acute effects of marijuana consumption on brain physiology and behaviour are well documented, but the long-term effects of its chronic use are less well known. Chronic marijuana use during adolescence is of increased interest, given that the majority of individuals first use marijuana during this developmental stage , and  adolescent marijuana use is thought to increase the susceptibility to abusing other drugs when exposed later in life. It is possible that marijuana use during critical periods in adolescence could lead to increased sensitivity to other drugs of abuse later on. To test this, we chronically administered ∆ 9-tetrahydrocannabinol (THC) to male and female Long-Evans (LER) and Wistar (WR) rats directly after puberty onset. Rats matured to postnatal day 90 before being exposed to a conditioned place preference task (CPP). A subthreshold dose of d-amphetamine, found not to induce place preference in drug naïve rats, was used as the unconditioned stimulus. The effect of d-amphetamine on neural activity was inferred by quantifying cfos expression in the nucleus accumbens and dorsal hippocampus following CPP training. Chronic exposure to THC post-puberty had no potentiating effect on a subthreshold dose of d-amphetamine to induce CPP. No differences in cfos expression were observed. These results show that chronic exposure to THC during puberty did not increase sensitivity to d-amphetamine in adult LER and WR rats. This supports the concept that THC may not sensitize the response to all drugs of abuse.

Behavioral economic analysis of the effects of N-substituted benztropine analogs on cocaine self-administration in rats

RATIONALE AND OBJECTIVES

Benztropine (BZT) analogs and other atypical dopamine uptake inhibitors selectively decrease cocaine self-administration at doses that do not affect responding maintained by other reinforcers. Those effects were further characterized in the current study using a behavioral economic assessment of how response requirement (price) affects reinforcers obtained (consumption) in rats.

METHODS

Two groups of rats were trained to press levers with food (45-mg pellet) or cocaine (0.32 mg/kg/injection) reinforcement under fixed-ratio (FR) 5-response schedules. In selected sessions, the FR requirement was increased (5-80) during successive 20-min components to determine demand curves, which plot consumption against price. An exponential function was fitted to the data to derive the consumption at zero price (Q ₀) and the rate of decrease in consumption (essential value, EV) with increased price. The BZT analogs, AHN1-055, AHN2-005, JHW007 (3.2-10 or 17.8 mg/kg, each), vehicle, or comparison drugs (methylphenidate, ketamine), were administered i.p. before selected demand-curve determinations.

RESULTS

Consumption of cocaine or food decreased with increased FR requirement. Each drug shifted the demand curve rightward at the lowest doses and leftward/downward at higher doses. The effects on EV and Q ₀ were greater for cocaine than for food-reinforced responding. Additionally, the effects of the BZT analogs on EV and Q ₀ were greater than those obtained with a standard dopamine transport inhibitor, methylphenidate, and the NMDA antagonist, ketamine (1.0-10.0 mg/kg, each). With these latter drugs, the demand-curve parameters were affected similarly with cocaine and food-maintained responding.

CONCLUSIONS

The current findings, obtained using a behavioral economic assessment, suggest that BZT analogs selectively decrease the reinforcing effectiveness of cocaine.

Preclinical Studies of Cannabinoid Reward, Treatments for Cannabis Use Disorder, and Addiction-Related Effects of Cannabinoid Exposure

Cannabis use has become increasingly accepted socially and legally, for both recreational and medicinal purposes. Without reliable information about the effects of cannabis, people cannot make informed decisions regarding its use. Like alcohol and tobacco, cannabis can have serious adverse effects on health, and some people have difficulty discontinuing their use of the drug. Many cannabis users progress to using and becoming addicted to other drugs, but the reasons for this progression are unclear. The natural cannabinoid system of the brain is complex and involved in many functions, including brain development, reward, emotion, and cognition. Animal research provides an objective and controlled means of obtaining information about: (1) how cannabis affects the brain and behavior, (2) whether medications can be developed to treat cannabis use disorder, and (3) whether cannabis might produce lasting changes in the brain that increase the likelihood of becoming addicted to other drugs. This review explains the tactics used to address these issues, evaluates the progress that has been made, and offers some directions for future research.

Trends in Daily Cannabis Use Among Cigarette Smokers: United States, 2002-2014

OBJECTIVES

To estimate changes in the prevalence of daily cannabis use among current, former, and never cigarette smokers from 2002 to 2014 in the United States.

METHODS

The National Survey on Drug Use and Health is a nationally representative cross-sectional study conducted annually among persons aged 12 years and older in the United States.

RESULTS

Daily cannabis use occurs nearly exclusively among nondaily and daily cigarette smokers compared with former and never smokers (8.03%, 9.01%, 2.79%, 1.05%, respectively). Daily cannabis use increased over the past decade among both nondaily (8.03% [2014] vs 2.85% [2002]; linear trend P < .001) and daily smokers (9.01% [2014]; 4.92% [2002]; linear trend P < .001). Daily cannabis use increased most rapidly among former cigarette smokers (2.79% [2014] vs 0.98% [2002]; linear trend P < .001).

CONCLUSIONS

Daily cannabis use occurs predominantly among cigarette smokers in the United States. Daily cannabis use increased among current, former, and never smokers over the past decade, with particularly rapid increases among youth and female cigarette smokers. Future research is needed to monitor the observed increase in daily cannabis use, especially among youths and adults who smoke cigarettes.

Essential values of cocaine and non-drug alternatives predict the choice between them

This study investigated the relationship between reinforcer value and choice between cocaine and two non-drug alternative reinforcers in rats. The essential value (EV, a behavioral economic measure based on elasticity of demand) of intravenous cocaine and food (Experiment 1) or saccharin (Experiment 2) was determined in the first phase of each experiment. Food had higher EV than cocaine, whereas the EVs of cocaine and saccharin did not differ. In the second phase of each experiment, rats were allowed to make mutually exclusive choices between cocaine and the non-drug alternative reinforcer. The main findings were that the EV of cocaine was a positive predictor of cocaine preference and the EV of food or saccharin was a negative predictor of cocaine preference. An analysis of within-session patterns of choice behavior revealed sequential dependencies, whereby rats were more likely to choose cocaine on a particular trial after having chosen the non-drug alternative on previous trials. When the time between choices was increased, these sequential dependencies disappeared. The results of these experiments are consistent with the suggestion that addiction-like behavior involves both overvaluation of drug reinforcers and undervaluation of non-drug reinforcers.

Marijuana Use and Organ Transplantation: a Review and Implications for Clinical Practice

PURPOSE OF REVIEW

Physicians of all disciplines must rapidly adjust their clinical practices following the expansion of marijuana legalization across the country. Organ transplantation teams are uniquely struggling in this gray zone with eight states having passed laws explicitly banning the denial of transplant listing based on a patient's use of medical marijuana. In this review, we examine the clinical evidence of marijuana use in transplant patients to enable psychiatric providers to meaningfully contribute to the relevant medical and psychiatric aspects of this issue in a unique patient population.

RECENT FINDINGS

There is no consensus among experts regarding marijuana use in transplantation patients. There are extant case reports of post-transplant complications attributed to marijuana use including membranous glomerulonephritis, ventricular tachycardia, and tacrolimus toxicity. However, recent studies suggest that the overall survival rates in kidney, liver, lung, and heart transplant patients using marijuana are equivalent to non-users. Transplant teams should not de facto exclude marijuana users from transplant listing but instead holistically evaluate a patient's candidacy, integrating meaningful medical, psychiatric, and social variables into the complex decision-making process. Psychiatric providers can play a key role in this process. Appropriate stewardship over donor organs, a limited and precious resource, will require a balance of high-clinical standards with inclusive efforts to treat as many patients as possible.

Youth use of electronic vapor products and blunts for administering cannabis

BACKGROUND

The positive association between youth use of cannabis and tobacco is well-established, and reports show that some youth are using electronic vapor products (EVPs) to administer cannabis. This study examines the prevalence and correlates of youth consumption of cannabis via EVP and how this compares with co-use of cannabis with cigars (blunts) among a large statewide sample of youth.

METHODS

We used data from the Florida Youth Tobacco Survey (FYTS), a school-based, pencil-and-paper questionnaire given to Florida middle and high school students (N=12,320). We conducted weighted descriptive analyses and logistic regressions examining prevalence and correlates of EVP/cannabis and blunt use.

RESULTS

Ever EVP/cannabis use was lower among middle school students (3.4%) than high school students (11.5%). Blunt use was reported by 6.0% of middle school and 24.1% of high school students. Approximately one-third of youth who had ever administered cannabis via either mode reported using both EVP/cannabis and blunts. EVP/cannabis and blunt use were both associated with lower school performance and use of other tobacco products. EVP/cannabis use did not vary by race/ethnicity, but blunt use was higher among black and Hispanic youth than white, non-Hispanic youth.

DISCUSSION

A substantial percentage of youth in a statewide sample are using EVPs and blunts to administer cannabis, and overlap between these use patterns is common. Differences in the demographic risk profile for EVP/cannabis and blunt use suggest that EVPs may provide a novel route of administration for delivering cannabis that appeals to groups not otherwise susceptible to using cannabis via blunts.

Young adults report increased pleasure from smoking cigarettes when drinking alcohol but not when using marijuana

BACKGROUND

Among young adults, cigarette smoking is strongly associated with alcohol and marijuana use. The present study compared self-reported co-use of cigarettes and alcohol versus cigarettes and marijuana among young adults using cross-sectional survey data.

METHODS

Participants were young adult cigarette smokers (age 18 to 25) who also reported past month alcohol or marijuana use enrolled in a randomized trial testing a smoking cessation intervention on Facebook. Participants self-reported extent of cigarette smoking under the influence of alcohol or marijuana and differences in perceived pleasure from cigarette smoking when drinking alcohol compared to using marijuana.

RESULTS

Among cigarette smokers who drank alcohol and used marijuana in the past month (n=200), a similar percentage of cigarettes were smoked under the influence of alcohol (42.4%±31.2%) and marijuana (43.1% ±30.0%). Among alcohol + marijuana users, perceived pleasure from smoking cigarettes was significantly greater when drinking alcohol versus when using marijuana (t₍₁₉₉₎=7.05, p<0.001). There was, on average, an increase in perceived pleasure from smoking cigarettes when drinking alcohol, though perceived pleasure did not differ by binge drinking frequency. In contrast, there was on average no change in perceived pleasure from smoking cigarettes when using marijuana. Results from the cigarette smokers who used alcohol + marijuana were similar to cigarette smokers who only used alcohol (n=158) or only used marijuana (n=54).

CONCLUSION

Findings highlight greater perceived reward from smoking cigarettes when drinking alcohol compared to when using marijuana, informing smoking cessation interventions that target users of multiple substances.

Individual and combined effects of cannabis and tobacco on drug reward processing in non-dependent users

RATIONALE

Cannabis and tobacco are often smoked simultaneously in joints, and this practice may increase the risks of developing tobacco and/or cannabis use disorders. Currently, there is no human experimental research on how these drugs interact on addiction-related measures.

OBJECTIVES

This study aimed to investigate how cannabis and tobacco, each alone and combined together in joints, affected individuals' demand for cannabis puffs and cigarettes, explicit liking of drug and non-drug-related stimuli and craving.

METHOD

A double-blind, 2 (active cannabis, placebo cannabis) × 2 (active tobacco, placebo tobacco) crossover design was used with 24 non-dependent cannabis and tobacco smokers. They completed a pleasantness rating task (PRT), a marijuana purchase task (MPT) and a cigarette purchase task (CPT) alongside measures of craving pre- and post-drug administration.

RESULTS

Relative to placebo cannabis, active cannabis reduced liking of cannabis-associated stimuli and increased response time to all stimuli except cigarette-related stimuli. Relative to placebo cannabis, active cannabis decreased demand for cannabis puffs (trends for breakpoint and elasticity) and cigarettes (breakpoint, P _max, O _max) on several characteristics of the purchase tasks. We found no evidence that active tobacco, both alone or combined with cannabis, had an effect on liking, demand or craving.

CONCLUSIONS

Acutely, cannabis reduced liking of cannabis-related stimuli and demand for cannabis itself. Acute cannabis also reduced demand for cigarettes on the CPT. Acute tobacco administration did not affect demand or pleasantness ratings for cigarettes themselves or cannabis. In non-dependent cannabis and tobacco co-users, tobacco did not influence the rewarding effects of cannabis.

Dose and elasticity of demand for self-administered cocaine in rats

The present experiment tested whether the elasticity of demand for self-administered cocaine in rats is dose-dependent. Subjects lever pressed for three different doses of intravenous cocaine - 0.11, 0.33, and 1.0 mg/kg/infusion - on a demand procedure where the number of lever presses required per infusion increased within a session. The main finding was that demand for the 0.11 mg/kg dose was more elastic than it was for the two larger doses. There was no difference in demand elasticity between the 0.33 and 1.0 mg/kg doses. These results parallel findings previously reported in monkeys. The present study also demonstrated that a within-session procedure can be used to generate reliable demand curves.

Nicotine self-administration research: the legacy of Steven R. Goldberg and implications for regulation, health policy, and research

BACKGROUND AND RATIONALE

Steven R. Goldberg was a pioneering behavioral pharmacologist whose intravenous drug self-administration studies advanced the understanding of conditioned stimuli and schedules of reinforcement as determinants of pattern and persistence of drug-seeking behavior, and in particular, the importance of nicotine in tobacco use. His passing in 2014 led to invitations to contribute articles to psychopharmacology dedicated to his work.

OBJECTIVES

The objectives of this review are to summarize and put into historical perspective Goldberg's contributions to elucidate the reinforcing effects of nicotine and to summarize the implications of his research for medication development, tobacco regulation, and potential tobacco control policy options. This includes a review of intravenous nicotine self-administration research from the 1960s to 2016.

RESULTS

Goldberg's application of behavioral pharmacology methods to investigate nicotine reinforcement and the influence of schedule of reinforcement and conditioned stimuli on nicotine administration contributed to the conclusions of the US National Institute on Drug Abuse, and the Surgeon General, that nicotine met the criteria as a dependence-producing drug and cigarette smoking as a prototypic drug dependency or "addiction." Equally important, this work has been systematically extended to other species and applied to address a range of factors relevant to tobacco use, medication development, regulation, and public health policy.

CONCLUSIONS

Steven R. Goldberg was a pioneering scientist whose systematic application of the science of behavioral pharmacology advanced the understanding of tobacco and nicotine use and contributed to the scientific foundation for tobacco product regulation and potential public health tobacco control policy development.

Interactions between nicotine and drugs of abuse: a review of preclinical findings

Polysubstance abuse is common among substance-use disorder patients, and nicotine is one of the most commonly co-used substances. Epidemiological and clinical laboratory studies suggest that nicotine, when combined with other drugs of abuse, increases intake of one or both substances. This review focuses on the preclinical literature regarding nicotine's interaction with alcohol, stimulants (i.e., cocaine, amphetamines), opioids (i.e., morphine, heroin), and Δ⁹-tetrahydrocannabinol (THC). The current understanding of how these various classes of abused drugs may interact with nicotine on behavioral, physiological, and pharmacological indices that may be important in maintaining co-use of one or both substances in human populations are highlighted. Suggestions as to future areas of research and gaps in knowledge are offered.