A brain on cannabinoids: the role of dopamine release in reward seeking

Brain region specific regulation of anandamide (down) and sphingosine-1-phosphate (up) in association with anxiety (AEA) and resilience (S1P) in a mouse model of chronic unpredictable mild stress

Chronic unpredictable and unavoidable stress is associated with mental health problems such as depression and anxiety, whereas cycles of stress and stress relief strengthen resilience. It has been suggested that increased breakdown of brain endocannabinoids (eCB) promotes a feeling of adversity. To assess the impact of stress on bioactive lipid homeostasis, we analyzed eCB, sphingolipids, and ceramides in seven brain regions and plasma in a mouse model of chronic unpredictable mild stress. Chronic unpredictable mild stress (CUMS) was associated with low levels of anandamide in hippocampus and prefrontal cortex in association with indicators of anxiety (elevated plus maze). Oppositely, CUMS caused elevated levels of sphingosine-1-phosphate (S1P d18:1) and sphinganine-1-phosphate (S1P d18:0) in the midbrain and thalamus, which was associated with readouts of increased stress resilience, i.e., marble burying and struggling in the tail suspension tests. In the periphery, elevated plasma levels of ceramides revealed similarities with human major depression and suggested unfavorable effects of stress on metabolism, but plasma lipids were not associated with body weight, sucrose consumption, or behavioral features of depression or anxiety. The observed brain site-specific lipid changes suggest that the forebrain succumbs to adverse stress effects while the midbrain takes up defensive adjustments.

Smoking affects symptom improvement in schizophrenia: a prospective longitudinal study of male patients with first-episode schizophrenia

Patients with schizophrenia (SCZ) smoke up to three times more than general people. However, there are conflicting results regarding the relationship between tobacco smoke and clinical symptom severity in SCZ. The aim of this study was to assess the impact of smoking on clinical symptoms after antipsychotic treatment in a 12-week cohort study after controlling for confounding factors. One hundred and forty-five male patients with drug-naïve first-episode (DNFE) SCZ received antipsychotic monotherapy for 12 weeks. Symptom severity was assessed at baseline and at week 12 by the Positive and Negative Syndrome Scale (PANSS). We found no differences in clinical symptoms among male smokers with SCZ compared with male nonsmokers. However, male smokers showed greater improvement in negative symptoms after 12 weeks of treatment, controlling for age, years of education, onset age, and baseline body mass index (BMI). Our study showed that after 12 weeks of treatment with antipsychotics, male smokers showed greater improvement in negative symptoms than male nonsmokers.

Brain reward function in people who use cannabis: a systematic review

Rationale

Cannabis is one of the most widely used psychoactive substances globally. Cannabis use can be associated with alterations of reward processing, including affective flattening, apathy, anhedonia, and lower sensitivity to natural rewards in conjunction with higher sensitivity to cannabis-related rewards. Such alterations have been posited to be driven by changes in underlying brain reward pathways, as per prominent neuroscientific theories of addiction. Functional neuroimaging (fMRI) studies have examined brain reward function in cannabis users via the monetary incentive delay (MID) fMRI task; however, this evidence is yet to be systematically synthesised.

Objectives

We aimed to systematically integrate the evidence on brain reward function in cannabis users examined by the MID fMRI task; and in relation to metrics of cannabis exposure (e.g., dosage, frequency) and other behavioural variables.

Method

We pre-registered the review in PROSPERO and reported it using PRISMA guidelines. Literature searches were conducted in PsycINFO, PubMed, Medline, CINAHL, and Scopus.

Results

Nine studies were included, comprising 534 people with mean ages 16-to-28 years, of which 255 were people who use cannabis daily or almost daily, and 279 were controls. The fMRI literature to date led to largely non-significant group differences. A few studies reported group differences in the ventral striatum while participants anticipated rewards and losses; and in the caudate while participants received neutral outcomes. A few studies examined correlations between brain function and withdrawal, dosage, and age of onset; and reported inconsistent findings.

Conclusions

There is emerging but inconsistent evidence of altered brain reward function in cannabis users examined with the MID fMRI task. Future fMRI studies are required to confirm if the brain reward system is altered in vulnerable cannabis users who experience a Cannabis Use Disorder, as postulated by prominent neuroscientific theories of addiction.

Cannabis use disorder contributes to cognitive dysfunction in Veterans with traumatic brain injury

Background

While emerging evidence supports a link between traumatic brain injury (TBI) and progressive cognitive dysfunction in Veterans, there is insufficient information on the impact of cannabis use disorder (CUD) on long-term cognitive disorders. This study aimed to examine the incidences of cognitive disorders in Veterans with TBI and CUD and to evaluate their relationship.

Methods

This retrospective cohort study used the US Department of Veterans Affairs and Department of Defense administrative data from the Long-term Impact of Military-Relevant Brain Injury Consortium-Chronic Effects of Neurotrauma Consortium Phenotype study. Diagnoses suggesting cognitive disorders after a TBI index date were identified using inpatient and outpatient data from 2003 to 2022. We compared the differential cognitive disorders incidence in Veterans who had the following: (1) no CUD or TBI (control group), (2) CUD only, (3) TBI only, and (4) comorbid CUD+TBI. Kaplan-Meier analyses were used to estimate the overall cognitive disorders incidence in the above study groups. The crude and adjusted Cox proportional hazards models were used to estimate crude and adjusted hazard ratios (HRs) for cognitive disorders.

Results

A total of 1,560,556 Veterans [82.32% male, median (IQR) age at the time of TBI, 34.51 (11.29) years, and 61.35% white] were evaluated. The cognitive disorder incidence rates were estimated as 0.68 (95% CI, 0.62, 0.75) for CUD only and 1.03 (95% CI, 1.00, 1.06) for TBI only per 10,000 person-months of observations, with the highest estimated cognitive disorder incidence observed in participants with both TBI and CUD [1.83 (95% CI, 1.72, 1.95)]. Relative to the control group, the highest hazard of cognitive disorders was observed in Veterans with CUD+TBI [hazard ratio (HR), 3.26; 95% CI, 2.91, 3.65], followed by those with TBI only (2.32; 95 CI%, 2.13, 2.53) and with CUD (1.79; 95 CI%, 1.60, 2.00). Of note, in the CUD only subgroup, we also observed the highest risk of an early onset cognitive disorder other than Alzheimer's disease and Frontotemporal dementia.

Discussion

The results of this analysis suggest that individuals with comorbid TBI and CUD may be at increased risk for early onset cognitive disorders, including dementia.

Perceptions of Orthopaedic Sports Medicine Surgeons About Medical Cannabidiol Use: A Survey Study

INTRODUCTION

Multiple studies exist identifying cannabidiol (CBD) as an effective part of an orthopaedic patient's pain regimen; however, there is a paucity of studies elucidating orthopaedic surgeons' perception of the use and prescription of CBD in the medical setting. This study surveys orthopaedic sports medicine surgeons about their previous education on and current perceptions and usage of CBD in their medical practice.

METHODS

Between April 2023 and July 2023, orthopaedic sports medicine surgeons from across the country were surveyed. This survey was designed in hopes of identifying physician perceptions and current use of CBD as well as their previous education and training on its use.

RESULTS

Overall, 75 orthopaedic surgeons responded. More than three-fourths of responders had not received formal education on medical CBD use, nor did they have partners or colleagues who used CBD in their practice. More than half of all surgeons believed that there is a stigma associated with CBD use. A higher proportion of surgeons from CBD legal states recommended CBD to help patients control their pain (53.7% vs. 37.5%). Less than 15% of responders believed that CBD can adversely affect surgical outcomes. Finally, four-fifths of all responders believed that CBD is easy to legally access and affordable to buy by patients who desire it.

DISCUSSION

The relative novelty of CBD inclusion in medicine has led to a lack of early education and overall experience with its use among orthopaedic sports medicine surgeons. Still, surgeons believe that CBD is a safe and effective option to control pain. As surgeons continue to gain more familiarity and trust with CBD's medical uses over time, it has the potential to be a mainstay in orthopaedic multimodal pain regimens.

Mobilization of endocannabinoids by midbrain dopamine neurons is required for the encoding of reward prediction

Brain levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) shape motivated behavior and nucleus accumbens (NAc) dopamine release. However, it is not clear whether mobilization of 2-AG specifically from midbrain dopamine neurons is necessary for dopaminergic responses to external stimuli predicting forthcoming reward. Here, we use a viral-genetic strategy to prevent the expression of the 2-AG-synthesizing enzyme diacylglycerol lipase α (DGLα) from ventral tegmental area (VTA) dopamine cells in adult mice. We find that DGLα deletion from VTA dopamine neurons prevents depolarization-induced suppression of excitation (DSE), a form of 2-AG-mediated synaptic plasticity, in dopamine neurons. DGLα deletion also decreases effortful, cue-driven reward-seeking but has no effect on non-cued or low-effort operant tasks and other behaviors. Moreover, dopamine recording in the NAc reveals that deletion of DGLα impairs the transfer of accumbal dopamine signaling from a reward to its earliest predictors. These results demonstrate that 2-AG mobilization from VTA dopamine neurons is a necessary step for the generation of dopamine-based predictive associations that are required to direct and energize reward-oriented behavior.

Functional Variation in the FAAH Gene Is Directly Associated with Subjective Well-Being and Indirectly Associated with Problematic Alcohol Use

Fatty acid amide hydrolase (FAAH) is an enzyme that degrades anandamide, an endocannabinoid that modulates mesolimbic dopamine release and, consequently, influences states of well-being. Despite these known interactions, the specific role of FAAH in subjective well-being remains underexplored. Since well-being is a dynamic trait that can fluctuate over time, we hypothesized that we could provide deeper insights into the link between FAAH and well-being using longitudinal data. To this end, we analyzed well-being data collected three years apart using the WHO (Ten) Well-Being Index and genotyped a functional polymorphism in the FAAH gene (rs324420, Pro129Thr) in a sample of 2822 individuals. We found that the A-allele of rs324420, which results in reduced FAAH activity and elevated anandamide levels, was associated with lower well-being scores at both time points (Wave I, B: -0.52, p = 0.007; Wave II, B: -0.41, p = 0.03, adjusted for age and sex). A subsequent phenome-wide association study (PheWAS) affirmed our well-being findings in the UK Biobank (N = 126,132, alternative C-allele associated with elevated happiness, p = 0.008) and revealed an additional association with alcohol dependence. In our cohort, using lagged longitudinal mediation analyses, we uncovered evidence of an indirect association between rs324420 and problematic alcohol use (AUDIT-P) through the pathway of lower well-being (indirect effect Boot: 0.015, 95% CI [0.003, 0.030], adjusted for AUDIT in Wave I). We propose that chronically elevated anandamide levels might influence disruptions in the endocannabinoid system-a biological contributor to well-being-which could, in turn, contribute to increased alcohol intake, though multiple factors may be at play. Further genetic studies and mediation analyses are needed to validate and extend these findings.

Women are Taking the Hit: Examining the Unique Consequences of Cannabis Use Across the Female Lifespan

Cannabis use has risen dramatically in recent years due to global decriminalization and a resurgence in the interest of potential therapeutic benefits. While emerging research is shaping our understanding of the benefits and harms of cannabis, there remains a paucity of data specifically focused on how cannabis affects the female population. The female experience of cannabis use is unique, both in the societal context and because of the biological ramifications. This is increasingly important given the rise in cannabis potency, as well as the implications this has for the prevalence of Cannabis Use Disorder (CUD). Therefore, this scoping review aims to discuss the prevalence of cannabis use and CUD in women throughout their lifespan and provide a balanced prospective on the positive and negative consequences of cannabis use. In doing so, this review will highlight the necessity for continued research that goes beyond sex differences.

Peroral Exposure to Cannabis Sativa Ethanol Extract Caused Neuronal Degeneration and Astrogliosis in Wistar Rats' Prefrontal Cortex

Background

Despite widespread concerns about its possible side effects, notably on the prefrontal cortex (PFC), which mediates cognitive processes, the use of Cannabis sativa as a medicinal and recreational drug is expanding exponentially. This study evaluated possible behavioral alterations, neurotransmitter levels, histological, and immunohistochemical changes in the PFC of Wistar rats exposed to Cannabis sativa.

Purpose

To evaluate the effect of graded doses of Cannabis sativa on the PFC using behavioural, histological, and immunohistochemical approaches.

Methods

Twenty-eight juvenile male Wistar rats weighing between 70 g and 100 g were procured and assigned into groups A-D (n = 7 each). Group A served as control which received distilled water only as a placebo; rats in groups B, C, and D which were the treatment groups were orally exposed to graded doses of Cannabis sativa (10 mg/kg, 50 mg/kg, and 100 mg/kg, respectively). Rats in all experimental groups were exposed to Cannabis sativa for 21 days, followed by behavioral tests using the open field test for locomotor, anxiety, and exploratory activities, while the Y-maze test was for spatial memory assessment. Rats for biochemical analysis were cervically dislocated and rats for tissue processing were intracardially perfused following neurobehavioral tests. Sequel to sacrifice, brain tissues were excised and prefrontal cortices were obtained for the neurotransmitter (glutamate, acetylcholine, and dopamine) and enzymatic assay (Cytochrome C oxidase (CcO) and Glucose 6- Phosphate Dehydrogenase-G-6-PDH). Brain tissues were fixed in 10% Neutral Buffered Formalin (NBF) for histological demonstration of the PFC cytoarchitecture using H&E and glial fibrillary acidic protein (GFAP) for astrocyte evaluation.

Results

Glutamate and dopamine levels were significantly increased (F = 24.44, P = .0132) in groups D, and B, C, and D, respectively, compared to control; likewise, the activities of CcO and G-6-PDH were also significantly elevated (F = 96.28, P = .0001) (F = 167.5, P = .0001) in groups C and D compared to the control. Cannabis sativa impaired locomotor activity and spatial memory in B and D and D, respectively. All Cannabis sativa exposed groups demonstrated evidence of neurodegeneration in the exposed groups; GFAP immunoexpression was evident in all groups with a marked increase in group D.

Conclusion

Cannabis sativa altered neurotransmitter levels, energy metabolism, locomotor, and exploratory activity, and spatial working memory, with neuronal degeneration as well as reactive astrogliosis in the PFC.

Crosstalk between the endocannabinoid and mid-brain dopaminergic systems: Implication in dopamine dysregulation

Endocannabinoids (eCBs) and the expanded endocannabinoid system (ECS)-"endocannabinoidome", consists of the endogenous ligands, eCBs, their canonical and non-canonical receptor subtypes, and their synthesizing and metabolizing enzymes. This system modulates a wide range of body functions and acts as a retrograde signaling system within the central nervous system (CNS) by inhibition of classical transmitters, and plays a vital modulatory function on dopamine, a major neurotransmitter in the CNS. Dopamine is involved in different behavioral processes and contributes to different brain disorders-including Parkinson's disease, schizophrenia, and drug addiction. After synthesis in the neuronal cytosol, dopamine is packaged into synaptic vesicles until released by extracellular signals. Calcium dependent neuronal activation results in the vesicular release of dopamine and interacts with different neurotransmitter systems. The ECS, among others, is involved in the regulation of dopamine release and the interaction occurs either through direct or indirect mechanisms. The cross-talk between the ECS and the dopaminergic system has important influence in various dopamine-related neurobiological and pathologic conditions and investigating this interaction might help identify therapeutic targets and options in disorders of the CNS associated with dopamine dysregulation.

Endocannabinoids regulate cocaine-associated memory through brain AEA-CB1R signalling activation

Objective

Contextual drug-associated memory precipitates craving and relapse in substance users, and the risk of relapse is a major challenge in the treatment of substance use disorders. Thus, understanding the neurobiological underpinnings of how this association memory is formed and maintained will inform future advances in the treatment of drug addiction. Brain endocannabinoids (eCBs) signalling has been associated with drug-induced neuroadaptations, but the role of lipases that mediate small lipid ligand biosynthesis and metabolism in regulating drug-associated memory has not been examined. Here, we explored how manipulation of the lipase fatty acid amide hydrolase (FAAH), which is involved in mediating the level of the lipid ligand anandamide (AEA), affects cocaine-associated memory formation.

Methods

We applied behavioural, pharmacological and biochemical methods to detect cocaine-associated memory formation, eCBs in the dorsal dentate gyrus (dDG), and the activity of related enzymes. We further examined the roles of abnormal FAAH activity and AEA–CB1R signalling in the regulation of cocaine-associated memory formation and granule neuron dendritic structure alterations in the dDG through Western blotting, electron microscopy and immunofluorescence.

Results

In the present study, we found that cocaine induced a decrease in the level of FAAH in the dDG and increased the level of AEA. A high level of AEA activated cannabinoid type 1 receptors (CB1Rs) and further triggered CB1R signalling activation and granule neuron dendritic remodelling, and these effects were reversed by blockade of CB1Rs in the brain. Furthermore, inhibition of FAAH in the dDG markedly increased AEA levels and promoted cocaine-associated memory formation through CB1R signalling activation.

Conclusions

Together, our findings demonstrate that the lipase FAAH influences CB1R signalling activation and granule neuron dendritic structure alteration in the dDG by regulating AEA levels and that AEA and AEA metabolism play a key role in cocaine-associated memory formation. Manipulation of AEA production may serve as a potential therapeutic strategy for drug addiction and relapse prevention.

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AEA plays an important role in the cocaine-associated memory formation through triggering CB1Rs.

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Cocaine decreases FAAH level and leads to AEA increasing, which activate CB1R signaling and remodel dendritic spines structure of granule neurons.

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Regulating AEA degradation through manipulation of FAAH, governs the cocaine-associated memory formation.

Anxiety and cognitive-related effects of Δ 9-tetrahydrocannabinol (THC) are differentially mediated through distinct GSK-3 vs. Akt-mTOR pathways in the nucleus accumbens of male rats

RATIONALE

Δ⁹-tetrahydrocannabinol (THC) is the primary psychoactive compound in cannabis and is responsible for cannabis-related neuropsychiatric side effects, including abnormal affective processing, cognitive and sensory filtering deficits and memory impairments. A critical neural region linked to the psychotropic effects of THC is the nucleus accumbens shell (NASh), an integrative mesocorticolimbic structure that sends and receives inputs from multiple brain areas known to be dysregulated in various disorders, including schizophrenia and anxiety-related disorders. Considerable evidence demonstrates functional differences between posterior vs. anterior NASh sub-regions in the processing of affective and cognitive behaviours influenced by THC. Nevertheless, the neuroanatomical regions and local molecular pathways responsible for these psychotropic effects are not currently understood.

OBJECTIVES

The objectives of this study were to characterize the effects of intra-accumbens THC in the anterior vs. posterior regions of the NASh during emotional memory formation, sensorimotor gating and anxiety-related behaviours.

METHODS

We performed an integrative series of translational behavioural pharmacological studies examining anxiety, sensorimotor gating and fear-related associative memory formation combined with regionally specific molecular signalling analyses in male Sprague Dawley rats.

RESULTS

We report that THC in the posterior NASh causes distortions in emotional salience attribution, impaired sensory filtering and memory retention and heightened anxiety, through a glycogen-synthase-kinase-3 (GSK-3)-β-catenin dependent signalling pathway. In contrast, THC in the anterior NASh produces anxiolytic effects via modulation of protein kinase B (Akt) phosphorylation states.

CONCLUSIONS

These findings reveal critical new insights into the neuroanatomical and molecular mechanisms associated with the differential neuropsychiatric side effects of THC in dissociable nucleus accumbens sub-regions.

Drug Use in Night Owls May Increase the Risk for Mental Health Problems

Drugs of abuse are widely known to worsen mental health problems, but this relationship may not be a simple causational one. Whether or not a person is susceptible to the negative effects of drugs of abuse may not only be determined by their addictive properties, but also the users’ chronotype, which determines their daily activity patterns. The present study investigates the relationship between chronotype, drug use and mental health problems in a cross-sectional community sample. Participants (n = 209) completed a selection of questionnaires online, including the Munich Chronotype Questionnaire, the Depression Anxiety Stress Scale, the Alcohol Use Disorder Identification Test, the Cannabis Use Disorder Identification Test and the Fagerström Test for Nicotine Dependence. We conducted multiple regression models to determine relationships between participants’ chronotype and their reported mental health symptoms and then estimated mediation models to investigate the extent to which their drug consumption accounted for the identified associations. Chronotype was significantly associated with participants’ overall mental health (β = 0.16, p = 0.022) and their anxiety levels (β = 0.18, p = 0.009) but not with levels of depression or stress. However, both relationships were fully mediated by participants’ overall drug consumption. Thus, late chronotypes, so-called “night owls”, not only use more drugs but consequently have an increased risk for developing anxiety and deteriorating mental health status. This group may be particularly vulnerable to the negative psychological effects of drugs. Our results point toward the importance of considering chronotype in designing preventative and therapeutic innovations, specifically for anxiety, which at present has been largely neglected.

Cannabinoids, reward processing, and psychosis

BACKGROUND

Evidence suggests that an overlap exists between the neurobiology of psychotic disorders and the effects of cannabinoids on neurocognitive and neurochemical substrates involved in reward processing.

AIMS

We investigate whether the psychotomimetic effects of delta-9-tetrahydrocannabinol (THC) and the antipsychotic potential of cannabidiol (CBD) are underpinned by their effects on the reward system and dopamine.

METHODS

This narrative review focuses on the overlap between altered dopamine signalling and reward processing induced by cannabinoids, pre-clinically and in humans. A systematic search was conducted of acute cannabinoid drug-challenge studies using neuroimaging in healthy subjects and those with psychosis RESULTS: There is evidence of increased striatal presynaptic dopamine synthesis and release in psychosis, as well as abnormal engagement of the striatum during reward processing. Although, acute THC challenges have elicited a modest effect on striatal dopamine, cannabis users generally indicate impaired presynaptic dopaminergic function. Functional MRI studies have identified that a single dose of THC may modulate regions involved in reward and salience processing such as the striatum, midbrain, insular, and anterior cingulate, with some effects correlating with the severity of THC-induced psychotic symptoms. CBD may modulate brain regions involved in reward/salience processing in an opposite direction to that of THC.

CONCLUSIONS

There is evidence to suggest modulation of reward processing and its neural substrates by THC and CBD. Whether such effects underlie the psychotomimetic/antipsychotic effects of these cannabinoids remains unclear. Future research should address these unanswered questions to understand the relationship between endocannabinoid dysfunction, reward processing abnormalities, and psychosis.

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.

Cannabidiol microinjection into the nucleus accumbens attenuated nociceptive behaviors in an animal model of tonic pain

Cannabidiol, the major non-psychoactive constituent of Cannabis, has attracted much attention as a therapeutic agent for intractable chronic pain in many conditions. Nucleus accumbens (NAc) as a major site of action of cannabinoids is one of the main mediators of several analgesic agents especially in the persistent pain condition. The present study aimed to investigate the effect of cannabidiol microinjection into the NAc on the modulation of nociception induced by formalin injection into the rat's paw. Adult male Wistar rats weighing 220-250 g were underwent stereotaxic surgery for unilateral (right or left side) cannula placement into the NAc. After one week recovery period, intra-NAc administration of the cannabidiol or its vehicle, DMSO was performed in a volume of 0.5 µl, five minutes before the formalin test. The formalin test was performed using 50 µl injection of formalin (2.5%) into the plantar surface of the rat's hind paw. Intra-accumbal administration of cannabidiol attenuated the nociceptive responses during the early and late phases of the formalin test in a dose-dependent manner. However, the antinociceptive effect of cannabidiol was significantly higher in the late phase of the formalin test than that in the early phase. Therefore, a non-psychoactive cannabinoid, cannabidiol may be developed as therapeutic agents in conditions, such as persistent inflammatory pain for which primary treatments are insufficient or not possible.

Residual Effects of Cannabis Use on Effort-Based Decision-Making

OBJECTIVE

Acute Δ9-tetrahydrocannabinol (THC) administration in humans (Lawn etal., 2016) and rats (Silveira, Adams, Morena, Hill, & Winstanley, 2016) has been associated with decreased effort allocation that may explain amotivation during acute cannabis intoxication. To date, however, whether residual effects of cannabis use on effort-based decision-making are present and observable in humans have not yet been determined. The goal of this study was to test whether prolonged cannabis use has residual effects on effort-based decision-making in 24-hr abstinent cannabis using adults.

METHOD

We evaluated performance on the Effort Expenditure for Reward Task (EEfRT) in 41 adult cannabis users (mean age = 24.63 years, 21 males) and 45 nonusers (mean age = 23.90 years, 19 males). A mixed 2x3x3 ANOVA with age as a covariate was performed to examine the effect of group, probability of winning, and reward amount on EEfRT performance. EEfRT performance was operationalized as % of trials for which the hard (vs. easy) condition was chosen. Pearson's correlations were conducted to test the relationship between EEfRT performance and measures of cannabis use, anhedonia and motivation.

RESULTS

We found that cannabis users selected hard trials significantly more than nonusers regardless of win probability or reward level. Frequency of cannabis use was positively correlated with amount of % hard trials chosen. There were no significant correlations between % hard trials chosen, self-reported anhedonia, or motivation.

CONCLUSIONS

These results suggest that unlike acute effects, residual effects of cannabis following 24 hrs of abstinence are associated with greater effort allocation during effort-based decision-making.

The Yin and Yang of Cannabis: A Systematic Review of Human Neuroimaging Evidence of the Differential Effects of Δ9-Tetrahydrocannabinol and Cannabidiol

Cannabidiol (CBD) and Δ9-tetrahydrocannabinol (THC) have been the most investigated cannabinoids at the human and preclinical levels, although the neurobiological mechanisms underlying their effects remain unclear. Human experimental evidence complemented by observational studies suggests that THC may have psychotogenic effects while CBD may have antipsychotic effects. However, whether their effects on brain function are consistent with their opposing behavioral effects remains unclear. To address this, here we synthesize neuroimaging evidence investigating the acute effects of THC and CBD on human brain function using a range of neuroimaging techniques, with an aim to identify the key brain substrates where THC and CBD have opposing effects. After a systematic search, a review of the available studies indicated marked heterogeneity. However, an overall pattern of opposite effect profiles of the two cannabinoids was evident with some degree of consistency, primarily attributed to the head-to-head challenge studies of THC and CBD. While head-to-head comparisons are relatively few, collectively the evidence suggests that opposite effects of THC and CBD may be present in the striatum, parahippocampus, anterior cingulate/medial prefrontal cortex, and amygdala, with opposite effects less consistently identified in other regions. Broadly, THC seems to increase brain activation and blood flow, whereas CBD seems to decrease brain activation and blood flow. Given the sparse evidence, there is a particular need to understand the mechanisms underlying their opposite behavioral effects because it may not only offer insights into the underlying pathophysiological mechanisms of psychotic disorders but also suggest potentially novel targets and biomarkers for drug discovery.

The why behind the high: determinants of neurocognition during acute cannabis exposure

Acute cannabis intoxication may induce neurocognitive impairment and is a possible cause of human error, injury and psychological distress. One of the major concerns raised about increasing cannabis legalization and the therapeutic use of cannabis is that it will increase cannabis-related harm. However, the impairing effect of cannabis during intoxication varies among individuals and may not occur in all users. There is evidence that the neurocognitive response to acute cannabis exposure is driven by changes in the activity of the mesocorticolimbic and salience networks, can be exacerbated or mitigated by biological and pharmacological factors, varies with product formulations and frequency of use and can differ between recreational and therapeutic use. It is argued that these determinants of the cannabis-induced neurocognitive state should be taken into account when defining and evaluating levels of cannabis impairment in the legal arena, when prescribing cannabis in therapeutic settings and when informing society about the safe and responsible use of cannabis.

Endocannabinoid and dopaminergic system: the pas de deux underlying human motivation and behaviors

Endocannabinoid system (ECS) has been identified ever since cannabinoid, an active substance of Cannabis, was known to interact with endogenous cannabinoid (endocannabinoid/eCB) receptors. It later turned out that eCB was more intricate than previously thought. It has a pervasive role and exerts a multitude of cellular signaling mechanisms, regulating various physiological neurotransmission pathways in the human brain, including the dopaminergic (DA) system. eCB roles toward DA system were robust, clearly delineated, and reproducible with respect to physiological as well as pathological neurochemical and neurobehavioral manifestations of DA system, particularly those involving the nigrostriatal and mesocorticolimbic pathways. The eCB–DA system regulates the basics in the Maslow’s pyramid of hierarchy of needs required for individual survival such as food and sexual activity for reproductive purpose to those of higher needs in the pyramid, including self-actualization behaviors leading to achievement and reward (e.g., academic- and/or work-related performance and achievements). It is, thus, interesting to specifically discuss the eCB–DA system, not only on the molecular level, but also its tremendous potential to be developed as a future therapeutic strategy for various neuropsychiatric problems, including obesity, drug addiction and withdrawal, pathological hypersexuality, or low motivation behaviors.

The association between reinforcement sensitivity and substance use is mediated by individual differences in dispositional affectivity in adolescents

BACKGROUND

Adolescence marks the onset of substance use experimentation and adolescents are particularly vulnerable to certain negative effects of substances. Some evidence indicates reinforcement sensitivity is associated with substance use, though little is known about mechanisms underlying such association.

AIMS

in the current study were to examine, (1) associations between behavioral activation (BAS) and behavioral inhibition (BIS) system sensitivity, positive (PA) and negative affectivity (NA), and alcohol use and alcohol problems as well as tobacco, and marijuana use, and whether (2) associations are mediated by PA or NA.

METHODS

Participants were a community sample of N = 125 adolescents (M_age = 15.67 years; SD = 0.93; 52% boys) who completed self-report measures.

RESULTS

evinced associations, generally as expected, across variables (all ps < 0.05). In mediation analyses, an association emerged between BIS sensitivity and alcohol use, mediated by NA (95%CIs [0.034; 0.390]); greater BIS sensitivity was associated with greater NA and greater NA was associated with greater alcohol use. These findings were replicated with alcohol problems. An association also emerged between BAS sensitivity and marijuana use, mediated by PA (95%CIs [-0.296; -0.027]); greater BAS sensitivity was associated with greater PA and greater PA was associated with lower marijuana use. Finally, BIS sensitivity was associated with tobacco use through NA (95%CIs [0.023; 0.325]) and PA (95%CIs [0.004; 0.116]), with NA linked to greater, but PA linked to lower tobacco use. BAS sensitivity was also associated with tobacco use through PA (95%CIs [-0.395; -0.049]), with PA linked again to lower tobacco use.

CONCLUSIONS

There are unique and shared effects of domains of reinforcement sensitivity on adolescent substance use and these vary with index of dispositional affectivity and type of substance considered.

Perceived reward from using cigarettes with alcohol or cannabis and concurrent use: A smartphone-based daily diary study

INTRODUCTION

Smoking cigarettes under the influence of alcohol or cannabis is associated with perceived pleasure. However, it is unclear whether these changes in perceived reward impact the extent of concurrent use of cigarettes with alcohol or cannabis. The current study investigated if self-reported changes in perceived reward from concurrent use of cigarettes with alcohol or cannabis are related to the extent of concurrent use in real-world contexts using a smartphone-based Ecological Momentary Assessment (EMA) study.

METHODS

The sample included 126 diverse young adult smokers in the San Francisco Bay Area who reported current alcohol or cannabis use at baseline (M = 22.8 years, 50.8% male, 40.5% sexual minority, 39.7% Non-Hispanic White). Participants completed an online baseline survey and 30 days of smartphone-based daily EMA surveys of cigarette, alcohol, and cannabis use. The baseline assessed self-reported changes in perceived pleasure of smoking cigarettes while using alcohol or cannabis separately. EMA surveys included detailed questions about concurrent use (i.e., the extent of smoking while using another substance) covering the previous day. A total of 2,600 daily assessments were analyzed using mixed models.

RESULTS

Higher perceived pleasure from smoking cigarettes while drinking alcohol or using cannabis at baseline were both associated with a greater extent of concurrent use of cigarettes with alcohol (b = 0.140; SE = 0.066; t = 2.1; p = .035) and cannabis (b = 0.136; SE = 0.058; t = 2.4; p = .019) on a given day.

CONCLUSIONS

Results suggest that perceived reward from concurrently using cigarettes with alcohol or cannabis is associated with the extent of concurrent use. Findings can inform tailored smoking cessation interventions.

Orexin-A/Hypocretin-1 Controls the VTA-NAc Mesolimbic Pathway via Endocannabinoid-Mediated Disinhibition of Dopaminergic Neurons in Obese Mice

Disinhibition of orexin-A/hypocretin-1 (OX-A) release occurs to several output areas of the lateral hypothalamus (LH) in the brain of leptin knockout obese ob/ob mice. In this study, we have investigated whether a similar increase of OX-A release occurs to the ventral tegmental area (VTA), an orexinergic LH output area with functional effects on dopaminergic signaling at the mesolimbic circuit. By confocal and correlative light and electron microscopy (CLEM) morphological studies coupled to molecular, biochemical, and pharmacological approaches, we investigated OX-A-mediated dopaminergic signaling at the LH-VTA-nucleus accumbens (NAc) pathway in obese ob/ob mice compared to wild-type (wt) lean littermates. We found an elevation of OX-A trafficking and release to the VTA of ob/ob mice and consequent orexin receptor-1 (OX1R)-mediated over-activation of dopaminergic (DA) neurons via phospholipase C (PLC)/diacylglycerol lipase (DAGL-α)-induced biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG). In fact, by retrograde signaling to cannabinoid receptor type 1 (CB1R) at inhibitory inputs to DA neurons, 2-AG inhibited GABA release thus inducing an increase in DA concentration in the VTA and NAc of ob/ob mice. This effect was prevented by the OX1R antagonist SB-334867 (30 mg/Kg, i.p.), or the CB1R antagonist AM251 (10 mg/Kg, i.p.) and mimicked by OX-A injection (40 μg/Kg, i.p.) in wt lean mice. Enhanced DA signaling to the NAc in ob/ob mice, or in OX-A-injected wt mice, was accompanied by β-arrestin2-mediated desensitization of dopamine D2 receptor (D2R) in a manner prevented by SB-334867 or the D2R antagonist L741 (1.5 mg/Kg, i.p.). These results further support the role of OX-A signaling in the control of neuroadaptive responses, such as compulsive reward-seeking behavior or binge-like consumption of high palatable food, and suggest that aberrant OX-A trafficking to the DA neurons in the VTA of ob/ob mice influences the D2R response at NAc, a main target area of the mesolimbic pathway, via 2-AG/CB1-mediated retrograde signaling.

Elevated Brain Fatty Acid Amide Hydrolase Induces Depressive-Like Phenotypes in Rodent Models: A Review

Altered activity of fatty acid amide hydrolase (FAAH), an enzyme of the endocannabinoid system, has been implicated in several neuropsychiatric disorders, including major depressive disorder (MDD). It is speculated that increased brain FAAH expression is correlated with increased depressive symptoms. The aim of this scoping review was to establish the role of FAAH expression in animal models of depression to determine the translational potential of targeting FAAH in clinical studies. A literature search employing multiple databases was performed; all original articles that assessed FAAH expression in animal models of depression were considered. Of the 216 articles that were screened for eligibility, 24 articles met inclusion criteria and were included in this review. Three key findings emerged: (1) FAAH expression is significantly increased in depressive-like phenotypes; (2) genetic knockout or pharmacological inhibition of FAAH effectively reduces depressive-like behavior, with a dose-dependent effect; and (3) differences in FAAH expression in depressive-like phenotypes were largely localized to animal prefrontal cortex, hippocampus and striatum. We conclude, based on the animal literature, that a positive relationship can be established between brain FAAH level and expression of depressive symptoms. In summary, we suggest that FAAH is a tractable target for developing novel pharmacotherapies for MDD.

Addiction and the kynurenine pathway: A new dancing couple?

Drug use poses a serious threat to health systems throughout the world and the number of consumers rises relentlessly every year. The kynurenine pathway, main pathway of tryptophan degradation, has drawn interest in this field due to its relationship with addictive behaviour. Recently it has been confirmed that modulation of kynurenine metabolism at certain stages of the pathway can reduce, prevent or abolish drug seeking-like behaviours in studies with several different drugs. In this review, we present an up-to-date summary of the evidences of a relationship between drug use and the kynurenine pathway, both the alterations of the pathway due to drug use as well as modulation of the pathway as a potential approach to treat drug addiction. The review discusses ethanol, nicotine, cannabis, amphetamines, cocaine and opioids and new prospects in the drug research field are proposed.

Cannabinoids in the Treatment of Back Pain

Marijuana is increasingly utilized for the treatment of multiple medical problems, including back pain, in the United States. Although there is strong preclinical evidence supporting the promise of cannabinoids in the treatment of back pain, there is a paucity of clinical data supporting their use in clinical practice. Opioids are an important medication for the treatment of acute and chronic back pain, but utilization of opioid-based regimens have likely contributed to the growing opioid epidemic. The significant risk of morbidity, mortality, and dependence secondary to opioid medications have increased the interest in nonopioid medications, including cannabinoid-based pain regimens, in treating back pain. This review will provide an overview on the pharmacology, drug delivery methods, clinical evidence, and safety considerations critical to understanding the potential role of cannabinoids in the treatment of back pain.

Chronic cannabinoid exposure produces tolerance to the dopamine releasing effects of WIN 55,212-2 and heroin in adult male rats

Synthetic cannabinoids were introduced into recreational drug culture in 2008 and quickly became one of the most commonly abused drugs in the United States. The neurobiological consequences resulting from synthetic cannabinoid repeated exposure remain poorly understood. It is possible that a blunted dopamine (DA) response may lead drug users to consume larger quantities to compensate for this form of neurochemical tolerance. Because the endogenous cannabinoid and opioid systems exhibit considerable cross-talk and cross-tolerance frequently develops following repeated exposure to either opioids or cannabinoids, there is interest in investigating whether a history of synthetic cannabinoid exposure influences the ability of heroin to increase DA release. To test the effects of chronic cannabinoid exposure on cannabinoid- and heroin-evoked DA release, male adult rats were treated with either vehicle or a synthetic cannabinoid (WIN55-212-2; WIN) using an intravenous (IV) dose escalation regimen (0.2-0.8 mg/kg IV over 9 treatments). As predicted, WIN-treated rats showed a rightward shift in the dose-response relationship across all behavioral/physiological measures when compared to vehicle-treated controls. Then, using fast-scan cyclic voltammetry to measure changes in the frequency of transient DA events in the nucleus accumbens shell of awake and freely-moving rats, it was observed that the DA releasing effects of both WIN and heroin were significantly reduced in male rats with a pharmacological history of cannabinoid exposure. These results demonstrate that repeated exposure to the synthetic cannabinoid WIN can produce tolerance to its DA releasing effects and cross-tolerance to the DA releasing effects of heroin.

How do stupendous cannabinoids modulate memory processing via affecting neurotransmitter systems?

In the present study, we wanted to review the role of cannabinoids in learning and memory in animal models, with respect to their interaction effects with six principal neurotransmitters involved in learning and memory including dopamine, glutamate, GABA (γ-aminobutyric acid), serotonin, acetylcholine, and noradrenaline. Cannabinoids induce a wide-range of unpredictable effects on cognitive functions, while their mechanisms are not fully understood. Cannabinoids in different brain regions and in interaction with different neurotransmitters, show diverse responses. Previous findings have shown that cannabinoids agonists and antagonists induce various unpredictable effects such as similar effect, paradoxical effect, or dualistic effect. It should not be forgotten that brain neurotransmitter systems can also play unpredictable roles in mediating cognitive functions. Thus, we aimed to review and discuss the effect of cannabinoids in interaction with neurotransmitters on learning and memory. In addition, we mentioned to the type of interactions between cannabinoids and neurotransmitter systems. We suggested that investigating the type of interactions is a critical neuropharmacological issue that should be considered in future studies.

Dopamine and Addiction

Addiction is commonly identified with habitual nonmedical self-administration of drugs. It is usually defined by characteristics of intoxication or by characteristics of withdrawal symptoms. Such addictions can also be defined in terms of the brain mechanisms they activate; most addictive drugs cause elevations in extracellular levels of the neurotransmitter dopamine. Animals unable to synthesize or use dopamine lack the conditioned reflexes discussed by Pavlov or the appetitive behavior discussed by Craig; they have only unconditioned consummatory reflexes. Burst discharges (phasic firing) of dopamine-containing neurons are necessary to establish long-term memories associating predictive stimuli with rewards and punishers. Independent discharges of dopamine neurons (tonic or pacemaker firing) determine the motivation to respond to such cues. As a result of habitual intake of addictive drugs, dopamine receptors expressed in the brain are decreased, thereby reducing interest in activities not already stamped in by habitual rewards.

Selective breeding for high alcohol preference is associated with increased sensitivity to cannabinoid reward within the nucleus accumbens shell

RATIONALE

The rate of cannabinoid intake by those with alcohol use disorder (AUD) exceeds that of the general public. The high prevalence of co-abuse of alcohol and cannabis has been postulated to be predicated upon both a common predisposing genetic factor and the interaction of the drugs within the organism. The current experiments examined the effects of cannabinoids in an animal model of AUD.

OBJECTIVES

The present study assessed the reinforcing properties of a cannabinoid receptor 1 (CB1) agonist self-administered directly into the nucleus accumbens shell (AcbSh) in female Wistar and alcohol-preferring (P) rats.

METHODS

Following guide cannulae surgery aimed at AcbSh, subjects were placed in an operant box equipped with an 'active lever' (fixed ratio 1; FR1) that caused the delivery of the infusate and an 'inactive lever' that did not. Subjects were arbitrarily assigned to one of seven groups that self-administered either artificial cerebrospinal fluid (aCSF), or 3.125, 6.25, 12.5, or 25 pmol/100 nl of O-1057, a water-soluble CB1 agonist, dissolved in aCSF. The first four sessions of acquisition are followed by aCSF only infusates in sessions 5 and 6 during extinction, and finally the acquisition dose of infusate during session 7 as reinstatement.

RESULTS

The CB1 agonist was self-administered directly into the AcbSh. P rats self-administered the CB1 agonist at lower concentrations and at higher rates compared to Wistar rats.

CONCLUSIONS

Overall, the data indicate selective breeding for high alcohol preference has produced rats divergent in response to cannabinoids within the brain reward pathway. The data support the hypothesis that there can be common genetic factors influencing drug addiction.

The Cannabinoid CB1 Receptor in Schizophrenia

Converging lines of evidence from epidemiological, preclinical, and experimental studies indicate that the endocannabinoid system may be involved in the pathophysiology of schizophrenia and suggest that the cannabinoid CB₁ receptor may be a potential therapeutic target. In view of this, we first provide an overview of the endocannabinoid system and systematically review the evidence for CB₁ receptor alterations in animal models of schizophrenia and clinical studies in schizophrenia. MEDLINE, EMBASE, PsycArticles, and PsycINFO were systematically searched from inception until January 7, 2020. Of 1187 articles, 24 were included in the systematic review, including 8 preclinical studies measuring the CB₁ receptor in the context of an established animal model of schizophrenia and 16 clinical studies investigating the CB₁ receptor in schizophrenia. The majority of preclinical studies (6 of 8) have shown that the CB₁ receptor is reduced in the context of animal models of schizophrenia. Moreover, the majority of in vivo clinical imaging studies that used arterial blood sampling to quantify the radiotracer kinetics (3 of 4) have shown reduced CB₁ receptor availability in schizophrenia. However, mixed findings have been reported in ex vivo literature, including reports of no change in receptor levels (5 of 11), increased receptor levels (4 of 11), and decreased receptor levels (2 of 11). We review methodological reasons for these discrepancies and review how CB₁ receptor dysfunction may contribute to the pathophysiology of schizophrenia, drawing on the role of the receptor in regulating synaptic transmission and synaptic plasticity. We also discuss how the CB₁ receptor may be a potential therapeutic target.

D3 dopamine receptors and a missense mutation of fatty acid amide hydrolase linked in mouse and men: implication for addiction

The endocannabinoid and dopaminergic systems have independently been implicated in substance use disorder and obesity. We investigated a potential interaction between genetically inherited variation in fatty acid amide hydrolase (FAAH, C385A), which metabolizes the cannabis-like endocannabinoid anandamide, and dopaminergic system, measured by dopamine receptor levels and mRNA. Binding of the dopamine D3 preferring probe [C-11]-(+)-PHNO was measured with positron emission tomography (PET) in 79 human subjects genotyped for the FAAH C385A polymorphism (36/79 AC + AA). Autoradiography with [H-3]-(+)-PHNO and in situ hybridization with a D3-specific S-35 riboprobe were carried out in 30 knock-in mice with the FAAH C385A polymorphism (20/30 AC + AA). We found that the FAAH genetic variant C385A was associated with significantly higher (+)-PHNO binding in both humans and in knock-in mice, and this effect was restricted to D3 selective brain regions (limbic striatum, globus pallidus, and ventral pallidum (9-14%; p < 0.04) in humans and Islands of Calleja (28%; p = 0.036) in mice). In situ hybridization with a D3-specific S-35 riboprobe in FAAH knock-in C385A mice confirmed significantly increased D3 receptor mRNA across examined regions (7-44%; p < 0.02). The association of reduced FAAH function with higher dopamine D3 receptors in human and mouse brain provide a mechanistic link between two brain systems that have been implicated in addiction-risk. This may explain the greater vulnerability for addiction and obesity in individuals with C385A genetic variant and by extension, suggest that a D3 antagonism strategy in substance use disorders should consider FAAH C385A polymorphism.

Endocannabinoid genetic variation enhances vulnerability to THC reward in adolescent female mice

Adolescence represents a developmental period with the highest risk for initiating cannabis use. Little is known about whether genetic variation in the endocannabinoid system alters mesolimbic reward circuitry to produce vulnerability to the rewarding properties of the exogenous cannabinoid Δ9-tetrahydrocannabinol (THC). Using a genetic knock-in mouse model (FAAHC/A) that biologically recapitulates the human polymorphism associated with problematic drug use, we find that in adolescent female mice, but not male mice, this FAAH polymorphism enhances the mesolimbic dopamine circuitry projecting from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and alters cannabinoid receptor 1 (CB1R) levels at inhibitory and excitatory terminals in the VTA. These developmental changes collectively increase vulnerability of adolescent female FAAHC/A mice to THC preference that persists into adulthood. Together, these findings suggest that this endocannabinoid genetic variant is a contributing factor for increased susceptibility to cannabis dependence in adolescent females.

Interaction of Cannabis Use Disorder and Striatal Connectivity in Antipsychotic Treatment Response

Antipsychotic (AP) medications are the mainstay for the treatment of schizophrenia spectrum disorders (SSD), but their efficacy is unpredictable and widely variable. Substantial efforts have been made to identify prognostic biomarkers that can be used to guide optimal prescription strategies for individual patients. Striatal regions involved in salience and reward processing are disrupted as a result of both SSD and cannabis use, and research demonstrates that striatal circuitry may be integral to response to AP drugs. In the present study, we used functional magnetic resonance imaging (fMRI) to investigate the relationship between a history of cannabis use disorder (CUD) and a striatal connectivity index (SCI), a previously developed neural biomarker for AP treatment response in SSD. Patients were part of a 12-week randomized, double-blind controlled treatment study of AP drugs. A sample of 48 first-episode SSD patients with no more than 2 weeks of lifetime exposure to AP medications, underwent a resting-state fMRI scan pretreatment. Treatment response was defined a priori as a binary (response/nonresponse) variable, and a SCI was calculated in each patient. We examined whether there was an interaction between lifetime CUD history and the SCI in relation to treatment response. We found that CUD history moderated the relationship between SCI and treatment response, such that it had little predictive value in SSD patients with a CUD history. In sum, our findings highlight that biomarker development can be critically impacted by patient behaviors that influence neurobiology, such as a history of CUD.

The novel MAGL inhibitor MJN110 enhances responding to reward-predictive incentive cues by activation of CB1 receptors

CB1 receptor antagonists disrupt operant responding for food and drug reinforcers, and cue-induced reinstatement of cocaine and heroin seeking. Conversely, enhancing endocannabinoid signaling, particularly 2-arachidonyl glycerol (2-AG), by inhibition of monoacyl glycerol lipase (MAGL), may facilitate some aspects of reward seeking. To determine how endocannabinoid signaling affects responding to reward-predictive cues, we employed an operant task that allows us to parse the incentive motivational properties of cues. Rats were required to nosepoke during an intermittent audiovisual incentive cue (IC) to obtain a 10% sucrose reward. The CB1 receptor antagonist, rimonabant, dose-dependently decreased the response ratio (rewarded ICs/total presented) and active nosepokes per IC, while it increased the latency to respond to the cue and obtain the reward, indicating an overall decrease in both the choice and vigor of responding. Yet rats persisted in entering the reward cup. Using a modified version of the task, the novel MAGL inhibitor MJN110 increased the response ratio, decreased the latencies to respond to the IC and enhanced active nosepokes per IC, indicating a facilitation of cue-induced reward seeking. These effects were blocked by a subthreshold dose of rimonabant. Finally, MJN110 did not alter consumption of freely available sucrose within volumes obtained in the operant task. Together these data demonstrate blocking endocannabinoid tone at the CB1 receptor attenuates the ability of cues to induce reward seeking, while some aspects of motivation for the reward are retained. Conversely, enhancing 2-AG signaling at CB1 receptors facilitates IC responding and increases the motivational properties of the IC.

Delta-9-tetrahydrocannabinol potentiates fear memory salience through functional modulation of mesolimbic dopaminergic activity states

Chronic or acute exposure to delta-9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, has been associated with numerous neuropsychiatric side-effects, including dysregulation of emotional processing and associative memory formation. Clinical and preclinical evidence suggests that the effects of THC are due to the ability to modulate mesolimbic dopamine (DA) activity states in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Nevertheless, the mechanisms by which THC modulates mesolimbic DA function and emotional processing are not well understood. Using an olfactory associative fear memory procedure combined with in vivo neuronal electrophysiology, we examined the effects of direct THC microinfusions targeting the shell region of the NAc (NASh) and examined how THC may modulate the processing of fear-related emotional memory and concomitant activity states of the mesolimbic DA system. We report that intra-NASh THC dose-dependently potentiates the emotional salience of normally subthreshold fear conditioning cues. These effects were dependent upon intra-VTA transmission through GABAergic receptor mechanisms and intra-NASh DAergic transmission. Furthermore, doses of intra-NASh THC that potentiated fear memory salience were found to modulate intra-VTA neuronal network activity by increasing the spontaneous firing and bursting frequency of DAergic neurones whilst decreasing the activity levels of a subpopulation of putative GABAergic VTA neurones. These findings demonstrate that THC can act directly in the NASh to modulate mesolimbic activity states and induce disturbances in emotional salience and memory formation through modulation of VTA DAergic transmission.

Endocannabinoids Interact With the Dopaminergic System to Increase Sexual Motivation: Lessons From the Sexual Satiety Phenomenon

In male rats, copulation to satiety induces a long-lasting sexual inhibitory state, considered to rely on a decreased sexual motivation. Dopaminergic transmission at the mesolimbic system plays a central role in the regulation of male sexual motivation. Endocannabinoids (eCBs) modulate the activity of the mesolimbic system and both dopamine (DA) and cannabinoid receptor activation reverses the sexual inhibition that characterizes sexually satiated rats. The eCB anandamide reverses sexual satiety when systemically administered or infused into the ventral tegmental area (VTA), the region where the activity of mesolimbic dopaminergic neurons is regulated. Thus, it could be thought that sexual motivation is diminished during the long-lasting sexual inhibition of sexually satiated rats and that eCBs reverse that inhibition through the modulation of the dopaminergic system. To test this hypothesis, we assessed the motivational state of sexually satiated male rats and determined if 2-arachidonoylglycerol (2-AG), the most abundant eCB and a full cannabinoid receptor agonist, also reversed the sexual inhibitory state. To establish the possible interaction between 2-AG and anandamide with the dopaminergic system for the reversal of sexual satiety, we analyzed the effects of the co-administration of each eCB and DA receptor agonists or antagonists. Results showed that 24-h after copulation to satiety, when the sexual inhibition is well established, the males’ sexual motivation is diminished as measured in the sexual incentive motivation test. 2-AG, similarly to anandamide, reverses sexual satiety through the activation of CB1 receptors and both eCBs interact with the dopaminergic system to reverse the sexual inhibitory state. 2-AG effects are mediated by the modulation of the D2-like DA receptor family, whereas anandamide’s effects are clearly mediated by the modulation of the D1-like DA receptor family and the activation of D2-like DA receptors. Present results evidence that a reduced sexual motivation underlies the sexual inhibitory state of sexually satiated rats and support the notion that eCBs reverse sexual satiety by modulating dopaminergic transmission, presumably at the mesolimbic system. Anandamide and 2-AG have a different interaction with D1-like and D2-like DA receptor families. Altogether present data endorse the association of the eCB system with the regulation of the motivational tone at the mesolimbic system.

The Bivalent Rewarding and Aversive properties of Δ9-tetrahydrocannabinol are Mediated Through Dissociable Opioid Receptor Substrates and Neuronal Modulation Mechanisms in Distinct Striatal Sub-Regions

The primary psychoactive compound in cannabis, Δ9-tetrahydrocannabinol (THC), is capable of producing bivalent rewarding and aversive affective states through interactions with the mesolimbic system. However, the precise mechanisms underlying the dissociable effects of THC are not currently understood. In the present study, we identify anatomically dissociable effects of THC within the rat nucleus accumbens (NAc), using an integrative combination of behavioral pharmacology and in vivo neuronal electrophysiology. We report that the rewarding vs. aversive stimulus properties of THC are both anatomically and pharmacologically dissociable within distinct anterior vs. posterior sub-regions of the NAc. While the rewarding effects of THC were dependent upon local μ-opioid receptor signaling, the aversive effects of THC were processed via a κ-opioid receptor substrate. Behaviorally, THC in the posterior NASh induced deficits in social reward and cognition whereas THC in the anterior NAc, potentiated opioid-related reward salience. In vivo neuronal recordings demonstrated that THC decreased medium spiny neuron (MSN) activity in the anterior NAc and increased the power of gamma (γ) oscillations. In contrast, THC increased MSN activity states in the posterior NASh and decreased γ-oscillation power. These findings reveal critical new insights into the bi-directional neuronal and pharmacological mechanisms controlling the dissociable effects of THC in mesolimbic-mediated affective processing.

Cannabis Addiction and the Brain: a Review

(©Zehra A, Liuck, Manza P, Wiers CE, Volkow ND Wergh J, 2018. Reprinted with permission from Journal of Neuroimmune Pharmacology (2018) 13:438-452).

Alcohol Interaction with Cocaine, Methamphetamine, Opioids, Nicotine, Cannabis, and γ-Hydroxybutyric Acid

Millions of people around the world drink alcoholic beverages to cope with the stress of modern lifestyle. Although moderate alcohol drinking may have some relaxing and euphoric effects, uncontrolled drinking exacerbates the problems associated with alcohol abuse that are exploding in quantity and intensity in the United States and around the world. Recently, mixing of alcohol with other drugs of abuse (such as opioids, cocaine, methamphetamine, nicotine, cannabis, and γ-hydroxybutyric acid) and medications has become an emerging trend, exacerbating the public health concerns. Mixing of alcohol with other drugs may additively or synergistically augment the seriousness of the adverse effects such as the withdrawal symptoms, cardiovascular disorders, liver damage, reproductive abnormalities, and behavioral abnormalities. Despite the seriousness of the situation, possible mechanisms underlying the interactions is not yet understood. This has been one of the key hindrances in developing effective treatments. Therefore, the aim of this article is to review the consequences of alcohol's interaction with other drugs and decipher the underlying mechanisms.

Cannabinoid CB1 receptor neutral antagonist AM4113 inhibits heroin self-administration without depressive side effects in rats

Cannabinoid CB₁ receptors (CB₁Rs) have been shown to be a promising target in medication development for the treatment of addiction. However, clinical trials with SR141716A (rimonabant, a selective CB₁R antagonist/inverse agonist) for the treatment of obesity and smoking cessation failed due to unwanted side effects, such as depression, anxiety, and suicidal tendencies. Recent preclinical studies suggest that the neutral CB₁R antagonist AM4113 may retain the therapeutic anti-addictive effects of SR141716A in nicotine self-administration models and possibly has fewer unwanted side effects. However, little is known about whether AM4113 is also effective for other drugs of abuse, such as opioids and psychostimulants, and whether it produces depressive side effects similar to SR141716A in experimental animals. In this study, we demonstrated that systemic administration of AM4113 (3 and 10 mg/kg) dose-dependently inhibited the self-administration of intravenous heroin but not cocaine or methamphetamine, whereas SR141716A (3 and 10 mg/kg) dose-dependently inhibited the self-administration of heroin and methamphetamine but not cocaine. In the electrical brain-stimulation reward (BSR) paradigm, SR141716A (3 and 10 mg/kg) dose-dependently increased the BSR stimulation threshold (i.e., decreased the stimulation reward), but AM4113 had no effect on BSR at the same doses, suggesting that SR141716A may produce aversive effects while AM4113 may not. Together, these findings show that neutral CB₁R antagonists such as AM4113 deserve further research as a new class of CB₁R-based medications for the treatment of opioid addiction without SR141716A-like aversive effects.

The power of price compels you: Behavioral economic insights into dopamine-based valuation of rewarding and aversively motivated behavior

The mesocorticolimbic dopamine pathway is generally considered to be a reward pathway. While shortsighted, there is a strong basis for this view of dopamine function. Here, we first describe the role of phasic dopamine release events in reward seeking. We then explain why these release events are being reconsidered as value signals and how we applied behavioral economics to confirm they play a causal role in the valuation of reward. Just because dopamine release can function as a dopamine reward value signal however, does not imply that dopamine is solely a reward molecule. Rather, mesocorticolimbic dopamine appears to mediate many adaptive behaviors, including: reward seeking, avoidance, escape and fear-associated conditioned freezing. While more studies are needed before a consensus is reached on when, where and how dopamine mediates aversively-motivated behavior, its involvement is almost irrefutable. Thus, we next describe the role dopamine plays in these ethologically-relevant defensive behaviors. We conclude by describing our recent behavioral economics results that reveal a causal role for dopamine in the valuation of avoidance.

Cannabis Addiction and the Brain: a Review

Cannabis is the most commonly used substance of abuse in the United States after alcohol and tobacco. With a recent increase in the rates of cannabis use disorder (CUD) and a decrease in the perceived risk of cannabis use, it is imperative to assess the addictive potential of cannabis. Here we evaluate cannabis use through the neurobiological model of addiction proposed by Koob and Volkow. The model proposes that repeated substance abuse drives neurobiological changes in the brain that can be separated into three distinct stages, each of which perpetuates the cycle of addiction. Here we review previous research on the acute and long-term effects of cannabis use on the brain and behavior, and find that the three-stage framework of addiction applies to CUD in a manner similar to other drugs of abuse, albeit with some slight differences. These findings highlight the urgent need to conduct research that elucidates specific neurobiological changes associated with CUD in humans.

Broad and Region-Specific Impacts of the Synthetic Cannabinoid CP 55,940 in Adolescent and Adult Female Mouse Brains

Relative to Δ⁹-tetrahydrocannabinol (THC), the synthetic cannabinoid CP 55,940 (CP) is significantly more potent and efficacious at cannabinoid receptors, the primary targets for endogenous cannabinoids (eCBs). eCBs belong to a large, interconnected lipidome of bioactive signaling molecules with a myriad of effects in optimal and pathological function. Recreational use of highly potent and efficacious synthetic cannabinoids is common amongst adolescents, potentially impacting brain development. Knowledge of the molecular outcomes of synthetic cannabinoid use will be important to develop more targeted therapies for synthetic cannabinoid intoxication and to prevent long-term disruption to the CNS. Here, we test the hypothesis that CP has age and region-dependent effects on the brain lipidome. Adolescent [post-natal day (PND) 35 and PND 50] and young adult female mice were given either an acute dose of CP or vehicle and brains were collected 2 h later. Eight brain regions were dissected and levels of ∼80 lipids were screened from each region using HPLC/MS/MS. CP had widespread effects on the brain lipidome in all age groups. Interestingly, more changes were observed in the PND 35 mice and more were reductions in a lipid’s concentration, including region-dependent lowering of eCB levels. CP levels were highest in the cortex at PND 35, the hippocampus at PND 50, and in the cerebellum in the adult. These data provide novel insights into how high-potency, synthetic cannabinoids drive different, age-dependent, cellular signaling effects in the brain.

Zebrafish models relevant to studying central opioid and endocannabinoid systems

The endocannabinoid and opioid systems are two interplaying neurotransmitter systems that modulate drug abuse, anxiety, pain, cognition, neurogenesis and immune activity. Although they are involved in such critical functions, our understanding of endocannabinoid and opioid physiology remains limited, necessitating further studies, novel models and new model organisms in this field. Zebrafish (Danio rerio) is rapidly emerging as one of the most effective translational models in neuroscience and biological psychiatry. Due to their high physiological and genetic homology to humans, zebrafish may be effectively used to study the endocannabinoid and opioid systems. Here, we discuss current models used to target the endocannabinoid and opioid systems in zebrafish, and their potential use in future translational research and high-throughput drug screening. Emphasizing the high degree of conservation of the endocannabinoid and opioid systems in zebrafish and mammals, we suggest zebrafish as an excellent model organism to study these systems and to search for the new drugs and therapies targeting their evolutionarily conserved mechanisms.

The ongoing challenge of novel psychoactive drugs of abuse. Part I. Synthetic cannabinoids (IUPAC Technical Report)

In the past decade, the world has experienced a large increase in the number of novel compounds appearing on the illicit drug market for recreational purposes. Such substances are designed to circumvent governmental regulations; the illegal drug manufacturers take a known psychoactive compound reported in the scientific literature and slightly modify its chemical structure in order to produce analogues that will mimic the pharmacological activity of the original substance. Many of these novel substances are sold via the Internet. Among the various chemical classes, synthetic cannabinoid receptor modulators, commonly referred to as “synthetic cannabinoids” have been at the forefront, as demonstrated by the frequency of drug seizures, numerous severe toxic effects, and fatalities associated with some of these substances. This review presents the chemical structures of relevant synthetic cannabinoids and describes their mechanism of action, pharmacological features, metabolic pathways, and structure-activity relationships. It illustrates the approaches used in forensic testing, both for bulk analysis (drug seizures) and for analytical toxicology (biological matrices) and discusses aspects of regulation surrounding this drug class. This report is intended to provide pertinent information for the purposes of informing scientific, medical, social, and governmental bodies about this ever-evolving recreational drug class and the challenges it poses worldwide.

Cannabinoid disruption of learning mechanisms involved in reward processing

The increasing use of cannabis, its derivatives, and synthetic cannabinoids for medicinal and recreational purposes has led to burgeoning interest in understanding the addictive potential of this class of molecules. It is estimated that ∼10% of marijuana users will eventually show signs of dependence on the drug, and the diagnosis of cannabis use disorder (CUD) is increasing in the United States. The molecule that sustains the use of cannabis is Δ⁹-tetrahydrocannabinol (Δ⁹-THC), and our knowledge of its effects, and those of other cannabinoids on brain function has expanded rapidly in the past two decades. Additionally, the identification of endogenous cannabinoid (endocannabinoid) systems in brain and their roles in physiology and behavior, demonstrate extensive involvement of these lipid signaling molecules in regulating CNS function. Here, we examine roles for endogenous cannabinoids in shaping synaptic activity in cortical and subcortical brain circuits, and we discuss mechanisms in which exogenous cannabinoids, such as Δ⁹-THC, interact with endocannabinoid systems to disrupt neuronal network oscillations. We then explore how perturbation of the interaction of this activity within brain reward circuits may lead to impaired learning. Finally, we propose that disruption of cellular plasticity mechanisms by exogenous cannabinoids in cortical and subcortical circuits may explain the difficulty in establishing viable cannabinoid self-administration models in animals.

Cannabidiol regulates behavioural alterations and gene expression changes induced by spontaneous cannabinoid withdrawal

BACKGROUND AND PURPOSE

Cannabidiol (CBD) represents a promising therapeutic tool for treating cannabis use disorder (CUD). This study aimed to evaluate the effects of CBD on the behavioural and gene expression alterations induced by spontaneous cannabinoid withdrawal.

EXPERIMENTAL APPROACH

Spontaneous cannabinoid withdrawal was evaluated 12 h after cessation of CP-55,940 treatment (0.5 mg·kg^-1 every 12 h, i.p.; 7 days) in C57BL/6J mice. The effects of CBD (5, 10 and 20 mg·kg^-1 , i.p.) on withdrawal-related behavioural signs were evaluated by measuring motor activity, somatic signs and anxiety-like behaviour. Furthermore, gene expression changes in TH in the ventral tegmental area, and in the opioid μ receptor (Oprm1), cannabinoid CB₁ receptor (Cnr1) and CB₂ receptor (Cnr2) in the nucleus accumbens, were also evaluated using the real-time PCR technique.

KEY RESULTS

The administration of CBD significantly blocked the increase in motor activity and the increased number of rearings, rubbings and jumpings associated with cannabinoid withdrawal, and it normalized the decrease in the number of groomings. However, CBD did not change somatic signs in vehicle-treated animals. In addition, the anxiogenic-like effect observed in abstinent mice disappeared with CBD administration, whereas CBD induced an anxiolytic-like effect in non-abstinent animals. Moreover, CBD normalized gene expression changes induced by CP-55,940-mediated spontaneous withdrawal.

CONCLUSIONS AND IMPLICATIONS

The results suggest that CBD alleviates spontaneous cannabinoid withdrawal and normalizes associated gene expression changes. Future studies are needed to determine the relevance of CBD as a potential therapeutic tool for treating CUD.