Cannabis and Driving in Older Adults

Importance

Epidemiological studies have found that cannabis increases the risk of a motor vehicle collision. Cannabis use is increasing in older adults, but laboratory studies of the association between cannabis and driving in people aged older than 65 years are lacking.

Objective

To investigate the association between cannabis, simulated driving, and concurrent blood tetrahydrocannabinol (THC) levels in older adults.

Design, Setting, and Participants

Using an ecologically valid counterbalanced design, in this cohort study, regular cannabis users operated a driving simulator before, 30 minutes after, and 180 minutes after smoking their preferred legal cannabis or after resting. This study was conducted in Toronto, Canada, between March and November 2022 with no follow-up period. Data were analyzed from December 2022 to February 2023.

Exposures

Most participants chose THC-dominant cannabis with a mean (SD) content of 18.74% (6.12%) THC and 1.46% (3.37%) cannabidiol (CBD).

Main outcomes and measures

The primary end point was SD of lateral position (SDLP, or weaving). Secondary outcomes were mean speed (MS), maximum speed, SD of speed, and reaction time. Driving was assessed under both single-task and dual-task (distracted) conditions. Blood THC and metabolites of THC and CBD were also measured at the time of the drives.

Results

A total of 31 participants (21 male [68%]; 29 White [94%], 1 Latin American [3%], and 1 mixed race [3%]; mean [SD] age, 68.7 [3.5] years), completed all study procedures. SDLP was increased and MS was decreased at 30 but not 180 minutes after smoking cannabis compared with the control condition in both the single-task (SDLP effect size [ES], 0.30; b = 1.65; 95% CI, 0.37 to 2.93; MS ES, -0.58; b = -2.46; 95% CI, -3.56 to -1.36) and dual-task (SDLP ES, 0.27; b = 1.75; 95% CI, 0.21 to 3.28; MS ES, -0.47; b = -3.15; 95% CI, -5.05 to -1.24) conditions. Blood THC levels were significantly increased at 30 minutes but not 180 minutes. Blood THC was not correlated with SDLP or MS at 30 minutes, and SDLP was not correlated with MS. Subjective ratings remained elevated for 5 hours and participants reported that they were less willing to drive at 3 hours after smoking.

Conclusions and relevance

In this cohort study, the findings suggested that older drivers should exercise caution after smoking cannabis.

Use of cannabidiol (CBD) for the treatment of cognitive impairment in psychiatric and neurological illness: A narrative review

Cannabidiol (CBD) is one of the major phytocannabinoids present in the cannabis plant, with no acute psychotropic effects and a favorable safety and abuse liability profile. Animal and limited controlled human studies have demonstrated CBD to have analgesic, anxiolytic, anti-inflammatory, antipsychotic, and anticonvulsant effects, to name a few possible indications. There is growing evidence for the use of CBD to treat neurological disorders such as epilepsy, multiple sclerosis, Parkinson's disease, and Alzheimer's disease. It has been suggested that CBD improves cognition and neurogenesis. Cognitive impairment is associated with numerous disorders and can involve deficits in learning, memory, executive functioning, and attention. The purpose of this review will be to evaluate the available preclinical and clinical data on CBD for the treatment of the cognitive impairment associated with several disorders including schizophrenia, epilepsy, Alzheimer's disease, and others. Preclinical, but not clinical, studies found evidence for an improvement in cognitive performance after treatment with CBD. More research is needed to determine whether CBD can be effectively used as a monotherapy to treat cognitive dysfunction. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

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.

The Utility of THC Cutoff Levels in Blood and Saliva for Detection of Impaired Driving

Background: Δ9-Tetrahydrocannabinol (THC) is the psychoactive component in cannabis and a relationship of THC to driving impairment is expected. Despite this, there are discrepant findings with respect to the relationship of blood THC to driving. This study investigated the relationship of blood, urine, and saliva THC/THC-COOH levels to "weaving," as measured by a driving simulator. Methods: Participants smoked cannabis alone or with alcohol. THC/THC-COOH levels in blood, urine, and saliva were correlated with standard deviation of lateral position (SDLP), measuring "weaving." In addition, SDLP after cannabis and/or alcohol were compared with SDLP after placebo when THC/THC-COOH levels were above or below specified thresholds in blood (5 ng/mL), urine (50 ng/mL), or saliva (25 ng/mL). Results: A clear linear relationship between blood THC concentration and SDLP was not observed based on calculation of Spearman coefficients. When compared with placebo, SDLP was significantly increased after cannabis and cannabis combined with alcohol when THC in the blood was above the legal limit. SDLP was increased in drug conditions when saliva cutoffs were above the legal limit. Conclusions: The findings of this study suggest that specified thresholds for THC in blood and saliva may be able to detect driving impairment, but future studies are needed. ClinicalTrials.gov ID: NCT03106363.

On offer to Ontario consumers three years after legalization: A profile of cannabis products, cannabinoid content, plant type, and prices

INTRODUCTION

Cannabis was legalized in Canada in October 2018, regulating the production, distribution, sale, and possession of dried cannabis and cannabis oils. Additional products were legalized 1 year later, including edibles, concentrates, and topicals, with new lines of commercial products coming to market. Ontario is the most populous province in Canada and has the largest cannabis market with the highest number of in-person retail stores and the most cannabis products available online. This study aims to create a profile of products available to consumers three years after legalization by summarizing types of products, THC and CBD potency, plant type, and prices of product sub-categories.

METHODS

We extracted data from the website of the Ontario Cannabis Store (OCS)-the public agency overseeing the only online store and sole wholesaler to all authorized in-person stores-in the first quarter of 2022 (January 19-March 23). We used descriptive analyses to summarize the data. A total of 1,771 available products were mapped by route of administration into inhalation (smoking, vaping, and concentrates), ingestible (edibles, beverages, oils, and capsules) and topical.

RESULTS

Most inhalation products included ≥20%/g THC (dried flower: 94%; cartridges: 96%; resin: 100%) while ingestible products had similar proportions of THC and CBD content. Indica-dominant products tend to be more prominent in inhalation products while sativa-dominant products tend to be more prominent in ingestible products. The average sale price of cannabis was 9.30 $/g for dried flower, 5.79 $/0.1g for cartridges, 54.82 $/g for resin, 3.21 $/unit for soft chews, 1.37 $/ml for drops, 1.52 $/unit for capsules, and 39.94 $/product for topicals.

DISCUSSION

In summary, a wide variety of cannabis products were available to Ontarians for different routes of administration and provides numerous indica-dominant, sativa-dominant, and hybrid/blend options. The current market for inhalation products however is geared towards the commercialization of high-THC products.

Effects of combining alcohol and cannabis on driving, breath alcohol level, blood THC, cognition, and subjective effects: A narrative review

Alcohol and cannabis are the two most commonly found intoxicating substances in fatally injured drivers. Epidemiological studies have demonstrated that the use of alcohol or cannabis can lead to an increase in the risk of a motor vehicle collision. Reducing the risks associated with driving under the influence of alcohol or cannabis is achieved partly through roadside detection of breath alcohol concentrations (BrAC) or blood delta-9-tetrahydrocannabinol (THC) levels. The purpose of the present review is to compile the laboratory studies on the combined effects of alcohol and cannabis on simulated driving as well as those evaluating combinations of these drugs on BrAC or blood THC. Given that driving can be affected by a number of cognitive processes, the literature on the cognitive effects of combinations of alcohol and cannabis is also reviewed, along with a discussion of a potential additive effect on the subjective qualities of these drugs. In sum, it is concluded that alcohol and cannabis have additive effects on driving skills, cognition and subjective effects. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Influence of personality on acute smoked cannabis effects on simulated driving

A recent study of the impact of smoked cannabis on simulated driver behavior demonstrated a reduction in mean speed after smoked cannabis. Previous research identified an association between personality and individual differences and acute drug effects. The present study examined the impact of personality on the reduction in mean speed after smoking cannabis under single- and dual-task driving conditions originally reported by Brands et al. (2019). Sixty-one participants randomly assigned to the active drug condition completed a battery of self-report questionnaires measuring various personality constructs and subsequently operated a driving simulator before and 30 min after smoking a 12.5% Δ9-tetrahydrocannabinol (THC) cigarette. Linear regression modeling tested the influence of self-reported driving errors, lapses, and violations, driver vengeance, psychological distress, impulsivity, and sensation seeking on the reduction in speed after smoking cannabis. After adjusting for the influence of sex, blood THC concentration, and predrug mean speed, impulsivity was a significant predictor of change in speed under both single- (β = -.45, t = -3.94, p < .001) and dual- (β = -.35, t = -2.74, p = .008) task driving conditions after cannabis. Higher trait impulsivity was significantly associated with greater reductions in driving speed after cannabis use, which may reflect greater sensitivity to drug effects and a stronger compensatory response. Further multidisciplinary study, including neurochemical, genetic, and psychological components, would be beneficial in helping to better understand how impulsivity and other personality or individual differences may impact the effects of cannabis on driver behavior and performance. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Combined effect of alcohol and cannabis on simulated driving

RATIONALE

With alcohol and cannabis remaining the most commonly detected drugs in seriously and fatally injured drivers, there is a need to understand their combined effects on driving.

OBJECTIVES

The present study examined the effects of combinations of smoked cannabis (12.5% THC) and alcohol (target BrAC 0.08%) on simulated driving performance, subjective drug effects, cardiovascular measures, and self-reported perception of driving ability.

METHODS

In this within-subjects, double-blind, double-dummy, placebo-controlled, randomized clinical trial, cannabis users (1-7 days/week) aged 19-29 years attended four drug administration sessions in which simulated driving, subjective effects, cardiovascular measures, and whole blood THC and metabolite concentrations were assessed following placebo alcohol and placebo cannabis (<0.1% THC), alcohol and placebo cannabis, placebo alcohol and active cannabis, and alcohol and active cannabis.

RESULTS

Standard deviation of lateral position in the combined condition was significantly different from the placebo condition (p < 0.001). Standard deviation of lateral position was also significantly different from alcohol and cannabis alone conditions in the single task overall drive (p = 0.029 and p = 0.032, respectively), from the alcohol alone condition in the dual task overall drive (p = 0.022) and the cannabis alone condition in the dual task straightaway drive (p = 0.002). Compared to the placebo condition, the combined and alcohol conditions significantly increased reaction time. Subjective effects in the combined condition were significantly greater than with either of the drugs alone at some time points, particularly later in the session. A driving ability questionnaire showed that participants seemed unaware of their level of impairment.

CONCLUSION

Combinations of alcohol and cannabis increased weaving and reaction time, and tended to produce greater subjective effects compared to placebo and the single drug conditions suggesting a potential additive effect. The fact that participants were unaware of this increased effect has important implications for driving safety.

Therapeutic Potential of Histamine H3 Receptors in Substance Use Disorders

Substance use disorders are a leading cause of morbidity and mortality, and available pharmacological treatments are of modest efficacy. Histamine is a biogenic amine with four types of receptors. The histamine H₃ receptor (H₃R) is an autoreceptor and also an heteroreceptor. H₃Rs are highly expressed in the basal ganglia, hippocampus and cortex, and regulate a number of neurotransmitters including acetylcholine, norepinephrine, GABA and dopamine. Its function and localization suggest that the H₃R may be relevant to a number of psychiatric disorders and could represent a potential therapeutic target for substance use disorders. The purpose of the present review is to summarize preclinical studies investigating the effects of H₃R agonists and antagonists on animal models of alcohol, nicotine and psychostimulant use. At present, the effects of H₃R antagonists such as thioperamide, pitolisant or ciproxifan have been investigated in drug-induced locomotion, conditioned place preference, drug self-administration, reinstatement, sensitization and drug discrimination. For alcohol and nicotine, the effects of H₃R ligands on two-bottle choice and memory tasks, respectively, have also been investigated. The results of these studies are inconsistent. For alcohol, H₃R antagonists generally decreased the reward-related properties of ethanol, which suggests that H₃R antagonists may be effective as a treatment option for alcohol use disorder. However, the effects of H₃R antagonists on nicotine and psychostimulant motivation and reward are less clear. H₃R antagonists potentiated the abuse-related properties of nicotine, but only a handful of studies have been conducted. For psychostimulants, evidence is mixed and suggests that more research is needed to establish whether H₃R antagonists are a viable therapeutic option. The fact that different drugs of abuse have different brain targets may explain the differential effects of H₃R ligands.

Are vaporizers a lower-risk alternative to smoking cannabis?

Cannabis use is associated with various adverse physical and mental health outcomes as well as increased risk of motor vehicle collision. Many organizations and the "Lower-Risk Cannabis Use Guidelines" have recommended to use cannabis vaporizers instead of smoking to reduce the associated health risk. This commentary draws attention to the present evidence regarding harm reduction potential of cannabis vaping. Cannabis vaporizer use can reduce the emission of carbon monoxide, chronic respiratory symptoms, and exposure to several toxins while producing similar subjective effects and blood THC concentration compared with smoking cannabis, holding potential for harm reduction among habitual cannabis smokers. However, new cannabis users, regardless of method of administration of cannabis, may experience intense subjective effects and cognitive impairment with increased susceptibility to dependence. Hence, policy makers should consider limiting access to cannabis among young people and adopting strategies to reduce impaired driving under influence of cannabis. Future research should focus on impact of switching from cannabis smoking to dried herb vaping using cannabis vaporizers among chronic cannabis smokers, and long-term outcomes of medical cannabis vaping, and further explore association of vaping-associated lung injury with THC-containing e-liquids.

Preliminary Eye-Tracking Data as a Nonintrusive Marker for Blood Δ-9-Tetrahydrocannabinol Concentration and Drugged Driving

Background: Cannabis is one of the drugs most often found in drivers involved in serious motor vehicle collisions. Validity and reliability of roadside cannabis detection strategies are questioned. This pilot study aimed to investigate the relationship between eye characteristics and cannabis effects in simulated driving to inform potential development of an alternative detection strategy. Materials and Methods: Multimodal data, including blood samples, eye-tracking recordings, and driving performance data, were acquired from 10 participants during a prolonged single-session driving simulator experiment. The study session included a baseline driving trial before cannabis exposure and seven trials at various times over ∼5 h after exposure. The multidimensional eye-tracking recording from each driving trial for each participant was segmented into nonoverlapping epochs (time windows); 34 features were extracted from each epoch. Blood Δ-9-tetrahydrocannabinol (THC) concentration, standard deviation of lateral position (SDLP), and mean vehicle speed were target variables. The cross-correlation between the temporal profile of each eye-tracking feature and target variable was assessed and a nonlinear regression analysis evaluated temporal trend of features following cannabis exposure. Results: Mean pupil diameter (r=0.81-0.86) and gaze pitch angle standard deviation (r=0.79-0.87) were significantly correlated with blood THC concentration (p<0.01) for all epoch lengths. For driving performance variables, saccade-related features were among those showing the most significant correlation (r=0.61-0.83, p<0.05). Epoch length significantly affected correlations between eye-tracking features and speed (p<0.05), but not SDLP or blood THC concentration (p>0.1). Temporal trend analysis of eye-tracking features after cannabis also showed a significant increasing trend (p<0.01) in saccade-related features, including velocity, scanpath, and duration, as the influence of cannabis decreased by time. A decreasing trend was observed for fixation percentage and mean pupil diameter. Due to the lack of placebo control in this study, these results are considered preliminary. Conclusion: Specific eye characteristics could potentially be used as nonintrusive markers of THC presence and driving-related effects of cannabis. clinicaltrials.gov (NCT03813602).

Sex differences in the acute pharmacological and subjective effects of smoked cannabis combined with alcohol in young adults

Objective: The prevalence of co-use of alcohol and cannabis is increasing, particularly among young adults. Sex differences in the effects of alcohol alone and cannabis alone have been observed in animals and humans. However, sex differences in the acute pharmacological effects of cannabis combined with alcohol have not yet been studied. In young adults, aged 19-29 years, we aimed to examine sex differences following an intoxicating dose of alcohol (target 0.08% breath alcohol content) combined with a moderate dose of cannabis (12.5% Δ⁹-tetrahydrocannabinol; THC) using an ad libitum smoking procedure. Method: Using a within-subjects design, 28 regular cannabis users (16 males; 12 females) received in random order: (a) placebo alcohol and placebo cannabis, (b) active alcohol and placebo cannabis, (c) placebo alcohol and active cannabis, and (d) active alcohol and active cannabis. Blood samples for THC were collected and measures of vital signs, subjective drug effects, and cognition were collected. Results: In the alcohol-cannabis combined condition, females smoked significantly less of the cannabis cigarette compared to males (p < .001), although both sexes smoked similar amounts in the other conditions. There was minimal evidence that females and males differed in THC blood concentrations, vitals, subjective effects, or cognitive measures. Conclusions: In the alcohol-cannabis combined condition, females experienced the same acute pharmacological and subjective effects of alcohol and cannabis as males, after smoking less cannabis, which has potential implications for informing education and policy. Further research is warranted on sex differences in cannabis pharmacology, as well as the combined effects of alcohol and cannabis. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Cannabis, Impaired Driving, and Road Safety: An Overview of Key Questions and Issues

The road safety impact of cannabis has been a topic of much discussion and debate over the years. These discussions have been revitalized in recent years by initiatives in several jurisdictions to legalize non-medical cannabis. Canada became the second country to legalize non-medical cannabis use in October, 2018, preceded by Uruguay in December 2013. Road safety concerns were key issues in the Canadian government's deliberations on the issue. In this paper, we identify several key questions related to the impact of cannabis on road safety, and provide a consideration of the relevant literature on these questions. These questions cover several perspectives. From an epidemiological perspective, perhaps the central question is whether cannabis use contributes to the chances of being involved in a collision. The answer to this question has evolved in recent years as the ability to conduct the relevant studies has evolved. A related question is the extent to which cannabis plays an important role in road safety, and recent research has made progress in estimating the collisions, injuries, and deaths that may be attributed to cannabis use. Several questions relate to the behavioral and pharmacological effects of cannabis. One central question is whether cannabis affects driving skills in ways that can increase the chances of being involved in a collision. Another important question is whether the effects of the drug on the driving behavior of medical users is similar to, or different from, the effects on non-medical users and whether there are sex differences in the pharmacological and behavioral effects of cannabis. Other important questions are the impact of tolerance to the effects of cannabis on road safety as well as different routes of administration (e.g., edibles, vaped). It remains unclear if there is a dose-response relationship of cannabis to changes in driving. These and other key questions and issues are identified and discussed in this paper.

Use of Cannabidiol for the Treatment of Anxiety: A Short Synthesis of Pre-Clinical and Clinical Evidence

Anxiety disorders have the highest lifetime prevalence of any mental illness worldwide, leading to high societal costs and economic burden. Current pharmacotherapies for anxiety disorders are associated with adverse effects and low efficacy. Cannabidiol (CBD) is a constituent of the Cannabis plant, which has potential therapeutic properties for various indications. After the recent legalization of cannabis, CBD has drawn increased attention as a potential treatment, as the majority of existing data suggest it is safe, well tolerated, has few adverse effects, and demonstrates no potential for abuse or dependence in humans. Pre-clinical research using animal models of innate fear and anxiety-like behaviors have found anxiolytic, antistress, anticompulsive, and panicolytic-like effects of CBD. Preliminary evidence from human trials using both healthy volunteers and individuals with social anxiety disorder, suggests that CBD may have anxiolytic effects. Although these findings are promising, future research is warranted to determine the efficacy of CBD in other anxiety disorders, establish appropriate doses, and determine its long-term efficacy. The majority of pre-clinical and clinical research has been conducted using males only. Among individuals with anxiety disorders, the prevalence rates, symptomology, and treatment response differ between males and females. Thus, future research should focus on this area due to the lack of research in females and the knowledge gap on sex and gender differences in the effectiveness of CBD as a potential treatment for anxiety.

Exploring occupancy of the histamine H3 receptor by pitolisant in humans using PET

BACKGROUND AND PURPOSE

BF2.649 (pitolisant, Wakix®) is a novel histamine H₃ receptor inverse agonist/antagonist recently approved for the treatment of narcolepsy disorder. The objective of the study was to investigate in vivo occupancy of H₃ receptors by BF2.649 using PET brain imaging with the H₃ receptor antagonist radioligand [¹¹ C]GSK189254.

EXPERIMENTAL APPROACH

Six healthy adult participants were scanned with [¹¹ C]GSK189254. Participants underwent a total of two PET scans on separate days, 3 h after oral administration of placebo or after pitolisant hydrochloride (40 mg). [¹¹ C]GSK189254 regional total distribution volumes were estimated in nine brain regions of interest with the two tissue-compartment model with arterial input function using a common V_ND across the regions. Brain receptor occupancies were calculated with the Lassen plot.

KEY RESULTS

Pitolisant, at the dose administered, provided high (84 ± 7%; mean ± SD) occupancy of H₃ receptors. The drug was well-tolerated, and participants experienced few adverse events.

CONCLUSION AND IMPLICATIONS

The administration of pitolisant (40 mg) produces a high occupancy of H₃ receptors and may be a new tool for the treatment of a variety of CNS disorders that are associated with mechanisms involving H₃ receptors.

Exploring the role of the Ser9Gly (rs6280) Dopamine D3 receptor polymorphism in nicotine reinforcement and cue-elicited craving

Preclinical studies show that the dopamine D3 receptor (D3R) is involved in the reinstatement of drug seeking and motivation for drugs of abuse. A D3R gene variant, Ser9Gly (rs6280) has been linked to nicotine dependence, yet the mechanisms underlying its involvement in nicotine dependence is unclear. This study investigated the relationship between the Ser9Gly variant and measures of both nicotine reinforcement and cue-elicited craving. Phenotypes of smoking behaviors were assessed in genetically grouped (Glycine vs. No Glycine carriers) current smokers (n = 104, ≥ 10 cigarettes per day). Laboratory measures included a forced choice session (to measure reinforcement of nicotine containing vs. denicotinized cigarettes), and a cue-reactivity session (to measure smoking cues vs. neutral cues elicited craving). The forced choice procedure revealed that subjective ratings were significantly higher in response to nicotinized compared to denicotinized cigarettes; however the Ser9Gly variant did not influence this effect. By comparison, smoking cues elicited greater craving over time compared to neutral cues, and Glycine carriers of the Ser9Gly D3R variant seem to experience a significant blunted cue-elicited craving effect. Results support D3R involvement in nicotine cue reactivity. However, more research is needed to reveal how this gene variant modulates various aspects of nicotine dependence.

Sex differences in the acute effects of smoked cannabis: evidence from a human laboratory study of young adults

RATIONALE

Animal studies have found robust sex differences in the pharmacokinetics and pharmacodynamics of Δ⁹-tetrahydrocannabinol (THC). However, the human evidence remains equivocal, despite findings that women may experience more severe consequences of cannabis use than men.

OBJECTIVES

The objective of this secondary analysis was to examine sex differences in THC pharmacokinetics and in acute subjective, physiological, and cognitive effects of smoked cannabis in a sample of regular cannabis users (use 1-4 days per week) aged 19-25 years.

METHODS

Ninety-one healthy young adults were randomized to receive active (12.5% THC; 17 females, 43 males) or placebo (< 0.1% THC; 9 females, 21 males) cannabis using a 2:1 allocation ratio. Blood samples to quantify concentrations of THC, 11-OH-THC, and 11-Nor-carboxy-THC (THC-COOH), as well as measures of subjective drug effects, vital signs, and cognition were collected over a period of 6 h following ad libitum smoking of a 750-mg cannabis cigarette.

RESULTS

Females smoked less of the cannabis cigarette than males (p = 0.008) and had a lower peak concentration of THC and THC-COOH than males (p ≤ 0.01). Blood THC concentrations remained lower in females even when adjusting for differences in estimated dose of THC inhaled. There was very little evidence of sex differences in visual analog scale (VAS) ratings of subjective drug effects, mood, heart rate, blood pressure, or cognitive effects of cannabis.

CONCLUSIONS

Females experienced the same acute effects of smoked cannabis as males at a lower observed dose, highlighting the need for more research on sex differences in the pharmacology of THC, especially when administered by routes in which titrating to the desired effect is more difficult (e.g., cannabis edibles).

Occupancy of dopamine D2 and D3 receptors by a novel D3 partial agonist BP1.4979: a [11C]-(+)-PHNO PET study in humans

There has been considerable interest in the development of dopamine D3 receptor (DRD₃) partial agonists and antagonists for the treatment of substance use disorders. Pre-clinical evidence overwhelmingly supports the use of these drugs, but translation to humans has remained elusive due to the lack of selective compounds that are suitable for use in humans. Although it has been established for full antagonists, little in vivo occupancy data are available with DRD₃ partial agonists. Here we investigate for the first time in healthy controls, the in vivo occupancy of a novel D3 partial agonist (BP1.4979) at the DRD₃ and DRD₂. Participants received either a single dose (1, 3, 10 or 30 mg) or a subchronic regimen (5-7 days, q.d. or b.i.d) of BP1.4979, with the last dose given at 1, 12 or 24 h prior to scanning with [¹¹C]-(+)-PHNO. Single and subchronic administration of BP1.4979 dose-dependently occupied the DRD₃ and DRD₂, and this occupancy was preferential for the DRD₃, notably at longer time points after administration of BP1.4979. Also consistent with preference for the DRD₃, prolactin levels were minimally increased, and no subjective effects of BP1.4979 were reported. Serum levels of BP1.4979 were higher than its active metabolite, BP1.6239, while no notable increases in the inactive metabolite, BP1.6197, were found. These findings indicate the range of doses that can be used to occupy selectively the DRD₃ over the DRD₂ with BP1.4979 and speak to the use of in vivo imaging approaches in dose finding studies.

Testing the PPAR hypothesis of tobacco use disorder in humans: A randomized trial of the impact of gemfibrozil (a partial PPARα agonist) in smokers

Previous pre-clinical studies demonstrated a promising role of alpha-type peroxisome proliferator-activated receptors (PPARα) agonists in decreasing nicotine self-administration and nicotine-seeking behavior in animals. Our goal was to investigate the potential of gemfibrozil, a PPARα agonist, on reducing tobacco smoking in humans. Methods: This was a double-blind, placebo-controlled, crossover study evaluating the effects of gemfibrozil (1200 mg/day) on smoking in 27 treatment-seeking smokers. The study had two 2-week phases separated by a washout period of at least 1 week. In each phase and after 1 week on medication, participants underwent a lab session where cue reactivity and forced choice paradigms were conducted. Physiological responses and self-reported craving were monitored during the presentation of smoking and neutral cues. In addition, two types of cigarettes were used in the forced choice paradigms: the Nicotinized cigarettes (Nic) and the Denicotinized cigarettes (Denic). The goal of the forced choice was to calculate the percentage of choice of Nic cigarettes while taking gemfibrozil or placebo. The number of quit days was calculated during the two quit attempts weeks (one while taking gemfibrozil and one while taking placebo) of the study. Results: There were no significant differences between gemfibrozil and placebo groups in the percentage of choice of Nic cigarettes, the cue-reactivity (both physiological and subjective measures), or in the number of days of abstinence. Conclusions: Although preclinical studies with PPAR α agonists showed promising results, this preliminary study did not demonstrate positive effect of gemfibrozil on tobacco use and cessation indices.

Influence of Nicotine Metabolism Ratio on [11C]-(+)-PHNO PET Binding in Tobacco Smokers

BACKGROUND

Identifying the biological basis of smoking cessation success is of growing interest. The rate of nicotine metabolism, measured by the nicotine metabolite ratio, affects multiple aspects of nicotine dependence. Fast nicotine metabolizers tend to smoke more, experience more withdrawal and craving, and have lower cessation rates compared with slow metabolizers. The nicotine metabolite ratio predicts treatment response, and differences in brain activation between fast metabolizers and slow metabolizers have been reported in fMRI studies. As reinforcing/rewarding effects of tobacco are associated with dopamine transmission, the purpose of the present study was to study the dopaminergic system in human smokers based on their nicotine metabolite ratio.

METHODS

The first aim of the study was to explore if there were differences in D2 and D3 receptor binding between fast metabolizers and slow metabolizers during abstinence. The second aim was to explore smoking-induced dopamine release in both groups. Participants underwent 2 [11C]-(+)-PHNO PET scans: one scan during abstinence and the other after smoking a tobacco cigarette. Subjective measures were recorded and blood was drawn for measurement of nicotine and cotinine levels.

RESULTS

During abstinence, slow metabolizers (n = 13) had lower [11C]-(+)-PHNO binding potential than fast metabolizers (n = 15) restricted to the D2 regions of the associative striatum and sensorimotor striatum. After smoking a cigarette, [11C]-(+)-PHNO binding potential was decreased in the limbic striatum and ventral pallidum, suggestive of increases in dopamine, but there were no nicotine metabolite ratio differences.

CONCLUSIONS

Further studies are required to delineate if differences in [11C]-(+)-PHNO binding between slow metabolizers and fast metabolizers at abstinence baseline are preexisting traits or induced by prolonged tobacco use.

The effects of buspirone on occupancy of dopamine receptors and the rat gambling task

BACKGROUND

The dopamine D3 receptor (DRD₃) has been proposed as a target for drug development for the treatment of addictive disorders. Recently, the anxiolytic buspirone has been shown to have affinity for DRD₃ and DRD₄, and interest in repurposing it for addictive disorders has grown.

METHODS

Binding of [³H]-(+)-PHNO in the rat cerebellum and striatum was used to measure occupancy by buspirone of DRD₃ or DRD₂, respectively. Effects of buspirone in the rat gambling task (rGT) and the five-choice serial reaction time task (5-CSRTT) were examined.

RESULTS

Buspirone occupied both the DRD₂ and DRD₃ at high doses and the DRD₃, but not the DRD₂, in the narrow dose range of 3 mg/kg. At 10 mg/kg, a disruption of performance on rGT was observed. All measures of performance on the rGT, except for perseverations, were affected at 3 mg/kg. On the 5-CSRTT, omissions were increased. Impairments in the rGT were not mimicked by the effects induced by satiation. Further, buspirone did not impair food-maintained responding under a progressive ratio schedule of reinforcement at any dose, suggesting that the effects of buspirone on the rGT cannot be explained by non-selective actions.

CONCLUSIONS

Although buspirone had effects on the rGT at the dose that selectively occupied the DRD₃, the effects found do not parallel those found in previous studies of the effects of selective DRD₃ antagonists on the rGT. Thus, buspirone may impair performance on the rGT through actions at multiple receptor sites.

Investigating the effects of norepinephrine α1 receptor blockade on dopamine levels: A pilot PET study with [11 C]-(+)-PHNO in controls

Interest in a role for norepinephrine (NE) in substance use disorders has increased over recent years. In particular, its interaction with dopamine (DA) is of importance. In this study, positron emission tomography (PET) was used to explore the impact of prazosin (an alpha 1 NE antagonist) on DA levels. Healthy volunteers were administered prazosin for approximately 4 weeks at the daily dose of 15 mg to reach steady state. Participants were scanned with PET imaging and the [¹¹ C]-(+)-PHNO tracer at baseline (before prazosin), at steady state, and after a wash out period. Prazosin administration was associated with an increase of [¹¹ C]-(+)-PHNO binding potential in the dorsal caudate relative to baseline, which corresponds to a decrease in DA levels. This study is the first to demonstrate interactions between DA and NE in healthy humans.

Evaluating the Impact of Naltrexone on the Rat Gambling Task to Test Its Predictive Validity for Gambling Disorder

Gambling Disorder has serious consequences and no medications are currently approved for the treatment of this disorder. One factor that may make medication development difficult is the lack of animal models of gambling that would allow for the pre-clinical screening of efficacy. Despite this, there is evidence from clinical trials that opiate antagonists, in particular naltrexone, may be useful in treating gambling disorder. To-date, the effects of naltrexone on pre-clinical models of gambling have not been evaluated. The purpose of the present study was to evaluate the effects of naltrexone in an animal model of gambling, the rat gambling task (rGT), to determine whether this model has some predictive validity. The rGT is a model in which rats are given a choice of making either a response that produces a large reward or a small reward. The larger the reward, the greater the punishment, and thus this task requires that the animal inhibit the ‘tempting’ choice, as the smaller reward option produces overall the most number of rewards per session. People with gambling disorder chose the tempting option more, thus the rGT may provide a model of problem gambling. It was found that naltrexone improved performance on this task in a subset of animals that chose the ‘tempting’, disadvantageous choice, more at baseline. Thus, the results of this study suggest that the rGT should be further investigated as a pre-clinical model of gambling disorder and that further investigation into whether opioid antagonists are effective in treating Gambling Disorder may be warranted.

Varenicline-Induced Elevation of Dopamine in Smokers: A Preliminary [(11)C]-(+)-PHNO PET Study

Varenicline, a nicotinic partial agonist, is the most effective treatment for tobacco use disorder. However, its mechanism of action is still unclear and may involve stimulating dopaminergic transmission. Here we used PET imaging with [(11)C]-(+)-PHNO to explore for the first time the impact of varenicline on dopamine transmission in the D2-rich striatum and D3-rich extra-striatal regions and its relationship with craving, withdrawal and smoking. Eleven treatment-seeking smokers underwent two PET scans with [(11)C]-(+)-PHNO, each following 12-h overnight smoking abstinence both prior to receiving varenicline and following 10-11 days of varenicline treatment (ie, at steady-state drug levels). Subjective measures of craving and urges to smoke were also assessed on the days of the PET scans. Varenicline treatment significantly reduced [(11)C]-(+)-PHNO binding in the dorsal caudate (p=0.008) and reduced some craving measures. These findings provide the first evidence that varenicline is able to increase DA levels in the human brain, a factor that may contribute to its therapeutic efficacy.

Effect of a D3 receptor antagonist on context-induced reinstatement of nicotine seeking

Despite the existence of several treatment options for smoking cessation, the rate of relapse after treatment is very high. We and others have proposed that targeting the dopamine D3 receptor (DRD3) may be a good strategy for treatment of nicotine dependence. In human participants, reintroduction to an environment previously associated with drug-taking may induce relapse. In animals, such phenomenon can be studied using the context-induced reinstatement paradigm. As the role of DRD3 in context-induced reinstatement of nicotine-seeking has not yet been explored, we investigated the effects of different doses of the selective DRD3 antagonist SB-277011-A on this reinstatement. Sprague-Dawley adult rats were first trained to self-administer nicotine and subsequently underwent extinction in a second context for 5-7 days. We evaluated the effect of 1, 3 or 10mg/kg of SB-277011-A administered prior to the reintroduction to the training context. We used two different designs: 1) a between-subjects design with a unique reinstatement test; and 2) a counterbalanced within-subjects design, with 4 reinstatement tests. Our findings indicate that, in the within-subjects design, the magnitude of responding induced by the context-induced reinstatement of nicotine seeking was robust during the first reinstatement test, but significantly decreased with repeated testing. SB-277011-A (10mg/kg) blocked context-induced reinstatement of nicotine-seeking at first exposure to the context (between-subjects design), but not after repeated context exposure which produced weaker reinstatement over days. Our results support a role for DRD3 mediating context-induced reinstatement of nicotine seeking, but these effects may not be sustained over time. Further studies should explore this in human participants for validation.

The Impact of Selective Dopamine D2, D3 and D4 Ligands on the Rat Gambling Task

Gambling is an addictive disorder with serious societal and personal costs. To-date, there are no approved pharmacological treatments for gambling disorder. Evidence suggests a role for dopamine in gambling disorder and thus may provide a therapeutic target. The present study therefore aimed to investigate the effects of selective antagonists and agonists of D2, D3 and D4 receptors in a rodent analogue of the Iowa gambling task used clinically. In this rat gambling task (rGT), animals are trained to associate different response holes with different magnitudes and probabilities of food pellet rewards and punishing time-out periods. As in the Iowa gambling task, the optimal strategy is to avoid the tempting high-risk high-reward options, and instead favor those linked to smaller per-trial rewards but also lower punishments, thereby maximizing the amount of reward earned over time. Administration of those selective ligands did not affect decision making under the rGT. Only the D4 drug had modest effects on latency measures suggesting that D4 may contribute in some ways to decision making under this task.

Neuronal circuitry underlying the impact of D3 receptor ligands in drug addiction

Since the cloning of the D3 receptor in the early 1990s, there has been a great deal of interest in this receptor as a possible therapeutic target for drug addiction. The development of a D3 ligand suitable for use in humans has remained elusive, so the study of the function of the D3 receptor and its possible therapeutic efficacy has largely been restricted to animals. Pre-clinical studies have established that systemic administration of D3 ligands, particularly antagonists and partial agonists, can alter drug-seeking in animals. Despite over a decade of research, few studies have investigated the effects of intra-cerebral infusion of D3 ligands on drug-seeking. In the present review, these studies are summarized, which have largely focused on stimulus-controlled behaviors. Converging evidence from studies of D3 receptor expression, Fos and pharmacological Magnetic Resonance Imaging (phMRI) is also provided to delineate some of the D3 brain systems involved in drug-seeking and taking. The data so far indicate that different brain systems may be involved in different types of stimulus control as well as drug taking.

Psychiatric disorders as vulnerability factors for nicotine addiction: what have we learned from animal models?

Epidemiological studies indicate a high prevalence of tobacco smoking in subjects with psychiatric disorders. Notably, there is a high prevalence of smoking among those with dependence to other substances, schizophrenia, mood, or anxiety disorders. It has been difficult to understand how these phenomena interact with clinical populations as it is unclear what preceded what in most of the studies. These comorbidities may be best understood by using experimental approaches in well-controlled conditions. Notably, animal models represent advantageous approaches as the parameters under study can be controlled perfectly. This review will focus on evidence collected so far exploring how behavioral effects of nicotine are modified in animal models of psychiatric conditions. Notably, we will focus on behavioral responses induced by nicotine that are relevant for its addictive potential. Despite the clinical relevance and frequency of the comorbidity between psychiatric issues and tobacco smoking, very few studies have been done to explore this issue in animals. The available data suggest that the behavioral and reinforcing effects of nicotine are enhanced in animal models of these comorbidities, although much more experimental work would be required to provide certainty in this domain.

Recent methods for measuring dopamine D3 receptor occupancy in vivo: importance for drug development

There is considerable interest in developing highly selective dopamine (DA) D3 receptor ligands for a variety of mental health disorders. DA D3 receptors have been implicated in Parkinson's disease, schizophrenia, anxiety, depression, and substance use disorders. The most concrete evidence suggests a role for the D3 receptor in drug-seeking behaviors. D3 receptors are a subtype of D2 receptors, and traditionally the functional role of these two receptors has been difficult to differentiate. Over the past 10-15 years a number of compounds selective for D3 over D2 receptors have been developed. However, translating these findings into clinical research has been difficult as many of these compounds cannot be used in humans. Therefore, the functional data involving the D3 receptor in drug addiction mostly comes from pre-clinical studies. Recently, with the advent of [(11)C]-(+)-PHNO, it has become possible to image D3 receptors in the human brain with increased selectivity and sensitivity. This is a significant innovation over traditional methods such as [(11)C]-raclopride that cannot differentiate between D2 and D3 receptors. The use of [(11)C]-(+)-PHNO will allow for further delineation of the role of D3 receptors. Here, we review recent evidence that the role of the D3 receptor has functional importance and is distinct from the role of the D2 receptor. We then introduce the utility of analyzing [(11)C]-(+)-PHNO binding by region of interest. This novel methodology can be used in pre-clinical and clinical approaches for the measurement of occupancy of both D3 and D2 receptors. Evidence that [(11)C]-(+)-PHNO can provide insights into the function of D3 receptors in addiction is also presented.

Dopamine D4 receptors in psychostimulant addiction

Since the cloning of the D4 receptor in the 1990s, interest has been building in the role of this receptor in drug addiction, given the importance of dopamine in addiction. Like the D3 receptor, the D4 receptor has limited distribution within the brain, suggesting it may have a unique role in drug abuse. However, compared to the D3 receptor, few studies have evaluated the importance of the D4 receptor. This may be due, in part, to the relative lack of compounds selective for the D4 receptor; the early studies were mainly conducted in mice lacking the D4 receptor. In this review, we summarize the literature on the structure and localization of the D4 receptor before reviewing the data from D4 knockout mice that used behavioral models relevant to the understanding of stimulant use. We also present evidence from more recent pharmacological studies using selective D4 agonists and antagonists and animal models of drug-seeking and drug-taking. The data summarized here suggest a role for D4 receptors in relapse to stimulant use. Therefore, treatments based on antagonism of the D4 receptor may be useful treatments for relapse to nicotine, cocaine, and amphetamine use.

Peroxisome proliferator-activated receptor (PPAR) agonists as promising new medications for drug addiction: preclinical evidence

This review examines the growing literature on the role of peroxisome proliferator-activated receptors (PPARs) in addiction. There are two subtypes of PPAR receptors that have been studied in addiction: PPAR-α and PPAR-γ. The role of each PPAR subtype in common models of addictive behavior, mainly pre-clinical models, is summarized. In particular, studies are reviewed that investigated the effects of PPAR-α agonists on relapse, sensitization, conditioned place preference, withdrawal and drug intake, and effects of PPAR-γ agonists on relapse, withdrawal and drug intake. Finally, studies that investigated the effects of PPAR agonists on neural pathways of addiction are reviewed. Taken together these preclinical data indicate that PPAR agonists are promising new medications for drug addiction treatment.

Differential effects of nucleus accumbens core, shell, or dorsal striatal inactivations on the persistence, reacquisition, or reinstatement of responding for a drug-paired conditioned reinforcer

Drug-paired conditioned reinforcers can maintain persistent instrumental responding, thus providing a model of some aspects of long-term drug addiction. The purpose of the present study was to investigate the effects of inactivating the dorsal striatum (DStr), nucleus accumbens (NAcc) core, or NAcc shell on different types of responding, each maintained by drug-paired conditioned reinforcers. Inactivations were achieved by infusing a combination of baclofen and muscimol prior to (1) persistent responding for a drug-paired conditioned reinforcer, (2) reacquisition of this instrumental response after extinction by omission of the contingent conditioned stimulus (CS), or (3) CS (cue)-induced reinstatement of the original (and different) instrumental response that had previously delivered cocaine. Inactivation of the DStr attenuated persistent responding for a cocaine-paired conditioned reinforcer, as well as its reacquisition after extinction of this response, while the only effect of inactivation of the NAcc shell was to increase CS (cue)-induced reinstatement of the extinguished instrumental response that had previously delivered cocaine. Inactivation of the NAcc core affected all measures of responding maintained by drug-paired conditioned reinforcers. These results are discussed with reference to the neural systems involved in different aspects of responding maintained by drug-paired conditioned reinforcers.

Facilitated acquisition but not persistence of responding for a cocaine-paired conditioned reinforcer following sensitization with cocaine

Sensitization has been hypothesized to increase the incentive salience of drug-paired conditioned stimuli and in the present study the ability of a sensitizing pretreatment with cocaine to increase responding for a drug-paired conditioned reinforcer was tested. In support of the incentive-sensitization hypothesis, sensitized rats earned more presentations of a drug-paired conditioned reinforcer during acquisition of a new response for this stimulus. By comparison, sensitization had no effect on the number of CSs earned during reversal of the contingency or following pretreatment with d-amphetamine. During reversal learning, however, sensitized rats were impaired in the extinction of the inappropriate response once the contingent CS was no longer available following presses on that lever. The results are discussed with reference to a possible role of increased incentive salience of a drug-paired CS to the formation of a habit.

Involvement of the dorsal striatum in cue-controlled cocaine seeking

Through association with the interoceptive effects of drugs of abuse, neutral environmental stimuli can gain motivational properties themselves, becoming conditioned reinforcers that can evoke craving and relapse to drug seeking. Nucleus accumbens dopamine (DA) neurotransmission plays an important role in the reinforcing effect of cocaine itself, but, unlike nucleus accumbens glutamate, it seems not to mediate the conditioned reinforcing properties of cocaine-paired stimuli. Dorsal striatal DA transmission, in contrast, has been shown to be enhanced during cocaine seeking under a second-order schedule of reinforcement, which depends on the conditioned reinforcing properties of cocaine-associated stimuli. Therefore, the aim of the present study was to evaluate the role of DA and glutamate transmission in the dorsal striatum in cue-controlled cocaine seeking. Infusion of the DA receptor antagonist alpha-flupenthixol into the dorsal striatum decreased cocaine seeking under a second-order schedule of reinforcement. In addition, intradorsal striatal infusion of the AMPA/kainate (KA) receptor antagonist LY293558 (3SR, 4aRS, 6RS, 8aRS-6-[2-(iH-tetrazol-5-yl)ethyl]-1,2,3,4,4a,5,6,7,8,8a-decahydroiso-quinoline-3-carboxylic acid), but not the NMDA receptor antagonist AP-5, also decreased cue-controlled cocaine seeking. These data show that stimulation of DA and AMPA/KA receptors in the dorsal striatum is critical for well established drug seeking that depends on the reinforcing effects of cocaine-associated stimuli. In addition, given the importance of the dorsal striatum in stimulus-response habit learning, these data suggest that the habitual or compulsive quality of persistent drug seeking depends on dorsal striatal mechanisms.

Disrupting reconsolidation of drug memories reduces cocaine-seeking behavior

Maladaptive memories that associate environmental stimuli with the effects of drugs of abuse are known to be a major cause of relapse to, and persistence of, a drug addictive habit. However, memories may be disrupted after their acquisition and consolidation by impairing their reconsolidation. Here, we show that infusion of Zif268 antisense oligodeoxynucleotides into the basolateral amygdala, prior to the reactivation of a well-learned memory for a conditioned stimulus (CS)-cocaine association, abolishes the acquired conditioned reinforcing properties of the drug-associated stimulus and thus its impact on the learning of a new cocaine-seeking response. Furthermore, we show that reconsolidation of CS-fear memories also requires Zif268 in the amygdala. These results demonstrate that appetitive CS-drug memories undergo reconsolidation in a manner similar to aversive memories and that this amygdala-dependent reconsolidation can be disrupted to reduce the impact of drug cues on drug seeking.

Neuropsychopharmacology of drug seeking: Insights from studies with second-order schedules of drug reinforcement

Second-order schedules of reinforcement model complex chains of responding for rewards such as food or drugs. Derived from studies of conditioned reinforcement, an important feature of these schedules is that responding is maintained by the response-dependent presentation of conditioned stimuli. They are thus well-suited to the study of the influences over drug seeking exerted by drug-associated stimuli. In the present review, we summarise studies investigating the neurobiology and neuropsychopharmacology of responding for cocaine under a second-order schedule of reinforcement. We conclude that limbic-striatal circuitries underlie drug seeking measured in this way. Emphasis is placed on potential interactions between structures within these subsystems by reviewing neuropsychopharmacological studies in which antagonists selective for either glutamate or dopamine receptors have been infused directly into limbic, cortical and striatal areas.

Direct interactions between the basolateral amygdala and nucleus accumbens core underlie cocaine-seeking behavior by rats

An insidious feature of drug craving and drug seeking in humans is that it can be induced and maintained by conditioned stimuli after a prolonged drug-free period. Understanding the neural basis of this control over addictive behavior may aid in the development of treatments targeting drug seeking and thereby be beneficial in preventing drug use. In the present study, we used a well established animal model to investigate the functional importance of amygdala-nucleus accumbens interactions in cocaine seeking under the control of drug-associated conditioned reinforcers. To probe the direct neuroanatomical relationship between these structures within a functional corticostriatal loop, we used a neuropharmacological disconnection procedure. Thus, infusing a dopamine receptor antagonist unilaterally into the basolateral amygdala (which had no effect on its own) and an AMPA-kainate (KA) receptor antagonist into the contralateral nucleus accumbens core (which also had no effect on its own) greatly reduced cocaine seeking. We also show that bilateral infusions of the DA receptor antagonist into the amygdala, but not nucleus accumbens, or of the AMPA-KA receptor antagonist in the nucleus accumbens, but not the amygdala, also greatly reduced cocaine seeking. The results of this study demonstrate an amygdala-nucleus accumbens system that critically underlies stimulus-controlled cocaine seeking and indicate possible neurochemical targets for relapse-prevention medication.

Contribution of the ventral tegmental area to cocaine-seeking maintained by a drug-paired conditioned stimulus in rats

Stimuli paired with cocaine can maintain cocaine-seeking as conditioned reinforcers. Although converging evidence implicates a role for the ventral tegmental area (VTA) in the primary reinforcing effects of drugs of abuse, the role of the VTA in mediating associative influences over drug-seeking remains to be determined. The present study therefore investigated the contribution to CS-maintained cocaine-seeking under a second-order schedule of reinforcement of the VTA, and its terminal regions, the nucleus accumbens (NAcc) core and basolateral amygdala (BLA), previously shown to be critical for the acquisition of this behaviour. Inactivation of the VTA or NAcc core by direct infusion of a mixture of the GABA(A) and GABA(B) receptor agonists, baclofen and muscimol, decreased cocaine-seeking when rats were drug-free, while drug-seeking after self-administered cocaine was increased only when they were infused into the NAcc core. Inactivation of the BLA had no effect on drug-seeking. These results are discussed with reference to critical and distinct contributions of the VTA, NAcc core and BLA to drug-seeking maintained by conditioned reinforcers

Conditioned reinforcing properties of stimuli paired with self-administered cocaine, heroin or sucrose: implications for the persistence of addictive behaviour

Conditioned environmental stimuli are known to be important determinants of drug seeking. Traditional models of drug seeking under the control of conditioned stimuli have focused on the ability of conditioned reinforcers either to reinstate extinguished responding or to maintain prolonged chains of drug seeking under second-order schedules. These models have consistently suggested that it is the conditioned reinforcing, rather than other, effects of Pavlovian drug stimuli that most profoundly influence drug seeking. However, the impact of drug-associated conditioned reinforcers has not been studied directly and in isolation, not least because the instrumental seeking response is invariably the same as that which was previously reinforced with the drug itself. The purpose of the present study was, therefore, to investigate the conditioned reinforcing properties of drug-paired CSs using an acquisition of a new response procedure in which an animal learns to make a new instrumental response reinforced solely by the CS. It was found that CSs paired with either cocaine, heroin or sucrose supported the rapid acquisition of lever pressing for the CS that persisted over months of repeated, intermittent testing. Furthermore, rats did not acquire the lever press response when the CS was not paired with drug, suggesting that for this stimulus to acquire conditioned reinforcing properties, it must be predictively associated with the drug's effect. Moreover, lever pressing for the CS could not be explained as coincidental to an over-riding Pavlovian approach response to the location of the lever, since animals also acquired discriminated lever pressing when the CS was above the opposite, inactive lever. Extinction decreased responding with conditioned reinforcement, but only when the CS-US association was devalued prior to, and not after, acquisition of the lever press response, providing evidence for the establishment of habitual CS-maintained responding that may explain the persistence of drug-seeking responses in animal models of addiction and relapse.

The GABA(B) receptor agonist baclofen attenuates cocaine- and heroin-seeking behavior by rats

Conditioned stimuli paired with drugs of abuse can acquire motivational properties, and are capable of inducing drug-seeking behavior and relapse to cocaine use. Converging evidence implicates the mesolimbic dopamine (DA) system, through interactions with limbic afferents to the nucleus accumbens, in behavior controlled by conditioned stimuli. The GABA(B) receptor agonist baclofen has been shown to decrease break points in rats responding for cocaine under progressive ratio schedules and also to attenuate activation of limbic cortical areas in human cocaine addicts. The purpose of the present study was therefore to investigate the effects of baclofen on drug-associated cue-controlled cocaine- or heroin-seeking behavior by rats. Under the second-order schedule of reinforcement used in the present study, cocaine or heroin were available after a fixed time interval, while high rates of responding during the interdrug intervals were maintained by the response-contingent presentations of drug-associated conditioned reinforcers. Baclofen decreased stimulus-maintained responding for either heroin or cocaine, but decreased only cocaine intake under an FR1 schedule. These results therefore support preliminary clinical findings and suggest that drugs with GABA(B) receptor agonist properties may aid abstinence in human drug addicts by decreasing the propensity to cue-induced drug-seeking and relapse.

Attenuation of cue-controlled cocaine-seeking by a selective D3 dopamine receptor antagonist SB-277011-A

Conditioned stimuli (CS) previously paired with drugs of abuse can elicit cravings in humans, relapse to drug use, and can also reinforce drug-seeking behavior in both humans and animals, events that are believed to be subserved in part by activation of the mesolimbic dopamine system. Converging anatomical, pharmacological, and behavioral evidence implicates dopamine D(3) receptors in the mechanisms underlying cue-controlled behaviors. The purpose of the present study was therefore to investigate the effects on cocaine-seeking behavior of a novel D(3) receptor antagonist, SB-277011-A, which is 100-fold more selective for D(3) over D(2) dopamine receptors. We have established previously that second-order schedules of reinforcement provide an animal model of cue-controlled drug-seeking both prior to and after cocaine has been self-administered. SB-277011-A dose-dependently decreased cocaine-seeking maintained by a cocaine-associated conditioned reinforcer in both the first, drug-free interval and also following self-administration of cocaine. At higher doses, SB-277011-A also increased the latency to receive the first CS presentation and cocaine infusion, thereby decreasing the number of cocaine infusions self-administered under the second-order schedule of reinforcement. SB-277011-A had no effect on cocaine intake under an FR-1 schedule of reinforcement, or on responding for sucrose under a second-order schedule of reinforcement, at any dose tested. These results therefore suggest that D(3) dopamine receptors may be critically involved in cue-controlled drug-seeking behavior independently of any interaction with the reinforcing effects of cocaine itself, and may therefore provide a therapeutic target in the treatment of relapse to cocaine use induced by CSs.

Differential control over drug-seeking behavior by drug-associated conditioned reinforcers and discriminative stimuli predictive of drug availability

Conditioned stimuli (CSs) can control behavior either by activating responses when presented noncontingently or through their ability to maintain responding when presented contingently, that is, as conditioned reinforcers. In the present study, the extent to which drug-seeking behavior could be subject to these different types of stimulus control was studied by presenting to rats CSs that were either paired with each drug infusion or presented as discriminative stimuli (DSs) signaling the availability of drug. It was found that stimuli paired with either cocaine or heroin infusions increased drug seeking when presented contingent on responding, but not when presented noncontingently. By contrast, DSs that signaled cocaine availability increased drug seeking when presented either noncontingently or contingently. These results suggest that drug-seeking behavior can be influenced differentially by CSs and that conditioned reinforcers are especially important for maintaining prolonged sequences of drug-seeking behavior.

Inhibition of dopamine efflux in the rat nucleus accumbens during abstinence after free access to d-amphetamine

Abstinence following 'binge' use of psychostimulants is hypothesized to be related to a depletion of synaptic dopamine (DA) in the nucleus accumbens. The present study, therefore, tested the pharmacological responsiveness of the mesolimbic DA system to d-amphetamine injections, measured by in vivo chronoamperometry with stearate-modified graphite paste electrodes, during voluntary abstinence when rats were given prolonged free availability to d-amphetamine. Rats self-administered i.v. d-amphetamine (FR-1 time out 30 s; 0.25 mg/kg per inf) in three sessions, each separated by approximately 24 h, (1) to a criterion of 12 infusions; (2) for 24 h and (3) for 48 h. During the third session, when self-administration had ceased for at least 1.5 h (abstinence), and DA levels were near, or below, pre-drug baseline values, rats received passive i.v. injections of d-amphetamine or vehicle in a pattern that mimicked self-administration patterns during the first hour of the 48 h session. In contrast to the significant increases in DA efflux observed during the first hour of self-administration, d-amphetamine injections during abstinence did not increase DA oxidation currents. Furthermore, the length of the abstinence period was correlated with the time required for DA to return to pre-abstinence values. Together, these results suggest that the mesolimbic DA system is pharmacologically unresponsive to the actions of d-amphetamine during abstinence, and that resumption of drug use is associated with 'recovery of function' in the mesolimbic DA system.