Potential of Cannabinoid Receptor Ligands as Treatment for Substance Use Disorders

Effects of cannabidiol on reward contextual memories induced by cocaine in male and female mice

OBJECTIVE

Preclinical studies suggest that cannabidiol (CBD), a non-intoxicating phytocannabinoid, may reduce addiction-related behaviours for various drug classes in rodents, including ethanol, opiates, and psychostimulants. CBD modulates contextual memories and responses to reward stimuli. Nonetheless, research on the impact of CBD on cocaine addiction-like behaviors is limited and requires further clarification. This study tested the hypothesis that CBD administration inhibits the acquisition and retrieval of cocaine-induced conditioned place preference (CPP) in adult male and female C57BL6/J mice. We also ought to characterise a 5-day CPP protocol in these animals.

METHODS

Male and female C57BL/6J mice were administered CBD (3, 10, and 30 mg/kg) 30 minutes before cocaine (15 mg/kg) acquisition of expression of CPP.

RESULTS

Cocaine induces a CPP in both female and male mice in the 5-day CPP protocol. CBD failed to prevent the acquisition or retrieval of place preference induced by cocaine. CBD did not decrease the time spent on the side paired with cocaine at any of the doses tested in male and female mice, in either acquisition or expression of contextual memory.

CONCLUSION

This study found no support for the hypothesis that CBD decreases reward memory involved in the formation of cocaine addiction. Further research is necessary to investigate the involvement of CBD in other behavioural responses to cocaine and other psychostimulant drugs. This study, however, characterised a 5-day CPP protocol for both female and male C57BL/6J mice.

AM6527, a neutral CB1 receptor antagonist, suppresses opioid taking and seeking, as well as cocaine seeking in rodents without aversive effects

Preclinical research has demonstrated the efficacy of CB1 receptor (CB1R) antagonists in reducing drug-taking behavior. However, clinical trials with rimonabant, a CB1R antagonist with inverse agonist profile, failed due to severe adverse effects, such as depression and suicidality. As a result, efforts have shifted towards developing novel neutral CB1R antagonists without an inverse agonist profile for treating substance use disorders. Here, we assessed AM6527, a CB1R neutral antagonist, in addiction animal models. Our findings revealed that AM6527 did not affect cocaine self-administration under fixed-ratio reinforcement schedules but dose-dependently inhibited it under progressive-ratio reinforcement schedules. Additionally, AM6527 dose-dependently inhibited heroin self-administration under both fixed-ratio and progressive-ratio reinforcement schedules and oral sucrose self-administration under a fixed-ratio reinforcement schedule, as well as cocaine- or heroin-triggered reinstatement of drug-seeking behavior in rats. However, chronic AM6527 administration for five consecutive days significantly inhibited heroin self-administration only during the initial two days, indicating tolerance development. Notably, AM6527 did not produce rewarding or aversive effects by itself in classical electrical intracranial self-stimulation and conditioned place preference tests. However, in optical intracranial self-stimulation (oICSS) maintained by optogenetic stimulation of midbrain dopamine neurons in DAT-cre mice, both AM6527 and rimonabant dose-dependently inhibited dopamine-dependent oICSS behavior. Together, these findings suggest that AM6527 effectively reduces drug-taking and seeking behaviors without rimonabant-like adverse effects. Thus, AM6527 warrants further investigation as a potential pharmacotherapy for opioid and cocaine use disorders.

Peripheral endocannabinoids in major depressive disorder and alcohol use disorder: a systematic review

BACKGROUND

Major Depressive Disorder (MDD) and Alcohol Use Disorder (AUD) are two high-prevalent conditions where the Endocannabinoid system (ECS) is believed to play an important role. The ECS regulates how different neurotransmitters interact in both disorders, which is crucial for controlling emotions and responses to stress and reward stimuli. Measuring peripheral endocannabinoids (eCBs) in human serum and plasma can help overcome the limitations of detecting endocannabinoid levels in the brain. This systematic review aims to identify levels of peripheral eCBs in patients with MDD and/or AUD and find eCBs to use as diagnostic, prognostic biomarkers, and potential therapeutic targets.

METHODS

We conducted a systematic literature search according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines from the earliest manuscript until October 22, 2023, in three electronic databases. We included studies of human adults who had a current diagnosis of AUD and/or MDD and evaluated plasma or serum endocannabinoids. We carefully considered known variables that may affect endocannabinoid levels.

RESULTS

We included 17 articles in this systematic review, which measured peripheral eCBs in 170 AUD and 359 MDD patients. Stressors increase peripheral 2-arachidonyl-glycerol (2-AG) concentrations, and 2-AG may be a particular feature of depression severity and chronicity. Anxiety symptoms are negatively correlated with anandamide (AEA) concentrations, and AEA significantly increases during early abstinence in AUD. Studies suggest a negative correlation between Oleoylethanolamide (OEA) and length of abstinence in AUD patients. They also show a significant negative correlation between peripheral levels of AEA and OEA and fatty acid amide hydrolase (FAAH) activity. Eicosapentaenoylethanolamide (EPEA) is correlated to clinical remission rates in depression. Included studies show known variables such as gender, chronicity, symptom severity, comorbid psychiatric symptoms, length of abstinence in the case of AUD, and stress-inducibility that can affect peripheral eCBs.

CONCLUSIONS

This systematic review highlights the important role that the ECS plays in MDD and AUD. Peripheral eCBs appear to be useful biomarkers for these disorders, and further research may identify potential therapeutic targets. Using accessible biological samples such as blood in well-designed clinical studies is crucial to develop novel therapies for these disorders.

β-caryophyllene inhibits heroin self-administration, but does not alter opioid-induced antinociception in rodents

A growing body of research indicates that β-caryophyllene (BCP), a constituent present in a large number of plants, possesses significant therapeutic properties against CNS disorders, including alcohol and psychostimulant use disorders. However, it is unknown whether BCP has similar therapeutic potential for opioid use disorders. In this study, we found that systemic administration of BCP dose-dependently reduced heroin self-administration in rats under an FR2 schedule of reinforcement and partially blocked heroin-enhanced brain stimulation reward in DAT-cre mice, maintained by optical stimulation of midbrain dopamine neurons at high frequencies. Acute administration of BCP failed to block heroin conditioned place preference (CPP) in male mice, but attenuated heroin-induced CPP in females. Furthermore, repeated dosing with BCP for 5 days facilitated the extinction of CPP in female but not male mice. In the hot plate assay, pretreatment with the same doses of BCP failed to enhance or prolong opioid antinociception. Lastly, in a substitution test, BCP replacement for heroin failed to maintain intravenous BCP self-administration, suggesting that BCP itself has no reinforcing properties. These findings suggest that BCP may have certain therapeutic effects against opioid use disorders with fewer unwanted side-effects by itself.

Endocannabinoid agonist 2-arachidonoylglycerol differentially alters diurnal activity and sleep during fentanyl withdrawal in male and female mice

Fentanyl has become the leading driver of opioid overdoses in the United States. Cessation of opioid use represents a challenge as the experience of withdrawal drives subsequent relapse. One of the most prominent withdrawal symptoms that can contribute to opioid craving and vulnerability to relapse is sleep disruption. The endocannabinoid agonist, 2-Arachidonoylglycerol (2-AG), may promote sleep and reduce withdrawal severity; however, the effects of 2-AG on sleep disruption during opioid withdrawal have yet to be assessed. Here, we investigated the effects of 2-AG administration on sleep-wake behavior and diurnal activity in mice during withdrawal from fentanyl. Sleep-wake activity measured via actigraphy was continuously recorded before and after chronic fentanyl administration in both male and female C57BL/6J mice. Immediately following cessation of fentanyl administration, 2-AG was administered intraperitoneally to investigate the impact of endocannabinoid agonism on opioid-induced sleep disruption. We found that female mice maintained higher activity levels in response to chronic fentanyl than male mice. Furthermore, fentanyl administration increased wake and decreased sleep during the light period and inversely increased sleep and decreased wake in the dark period in both sexes. 2-AG treatment increased arousal and decreased sleep in both sexes during first 24-h of withdrawal. On withdrawal day 2, only females showed increased wakefulness with no changes in males, but by withdrawal day 3 male mice displayed decreased rapid-eye movement sleep during the dark period with no changes in female mice. Overall, repeated administration of fentanyl altered sleep and diurnal activity and administration of the endocannabinoid agonist, 2-AG, had sex-specific effects on fentanyl-induced sleep and diurnal changes.

The Role of Medicinal Cannabis as an Emerging Therapy for Opioid Use Disorder

This narrative review explores current insights into the potential use of medicinal cannabis-related products as an emerging therapy for opioid use disorder in the landscape of increasing knowledge about medicinal cannabis-based products, commercialisation and global legalisation. Preclinical studies have provided preliminary insight into the putative neurobiological mechanisms that underpin the potential for medicinal cannabis to be considered a therapeutic in opioid use disorder and addiction. With the progressive legalisation of cannabis in many jurisdictions worldwide, contemporary research has highlighted further evidence that medicinal cannabis may have efficacy in reducing cravings and withdrawal effects, and therefore may be considered as an adjunct or standalone to current medications for opioid use disorder. Despite this potential, the landscape of research in this space draws from a large number of observational studies, with a paucity of rigorous randomised controlled trials to ascertain a true understanding of effect size and safety profile. With current challenges in implementation that arise from political and legal qualms about adopting medicinal cannabis on the background of associated social stigma, significant hurdles remain to be addressed by government, policy-makers, healthcare providers and researchers before medical cannabis can be introduced globally for the treatment of opioid use disorder.

Effectiveness of cannabis use and cannabis use disorder interventions: a European and international data synthesis

This data synthesis examined the effectiveness of behavioural and pharmacological approaches for cannabis treatment. We integrated findings from high level evidence studies and prioritised data from Europe when available. The synthesis found that only a relatively small number of published behavioural and pharmacological studies on cannabis interventions have been conducted in Europe. Applying both European and non-European data, it was found that Cognitive Behavioural Therapy (CBT) and/or Motivational Enhancement Therapy (MET) improved short-term outcomes in the frequency of cannabis use and dependency severity, although abstinence outcomes were less consistent. These improvements were typically not maintained nine months after treatment. CBT and MET (or combined CBT + MET) treatments that extend beyond four sessions were more effective than fewer sessions over a shorter duration. Combining CBT or MET (or combined CBT + MET) with adjunctive Contingency Management (CM) improved therapeutic outcomes. No pharmacotherapies have been approved for the management of cannabis use, cannabis use disorders or cannabis withdrawal. Despite only weak evidence to support the use of pharmacological agents, some are used 'off-label' to manage withdrawal symptoms outside clinical trials.

The contribution of childhood maltreatment to the incidence of heavy cannabis use in Iran (IRNS-CCI): A multicenter, matched-pairs, nested, case-control study

BACKGROUND

Previous studies have shown the role of the interaction between the endocannabinoid system (ECS) and life's adversities in the formation of addiction, including alcohol abuse.

OBJECTIVE

Our objective was to identify childhood maltreatment (CM) patterns with the strongest impact on the probability of heavy cannabis use (THCCOOH concentrations ≥150 ng/mL) in Iran.

PARTICIPANTS AND SETTING

Using survivor sampling, 350 adult participants were selected, and they were then allocated to three categories based on an optimal algorithm: 1) Sexual abuse, 2) Physical abuse, and 3) Physical neglect.

METHODS

From 1 September 2019 to 1 May 2023, we implemented a multicenter, matched-pairs, nested, case-control study based on the wave 3-wave 6 data of a longitudinal, multicenter, cohort study. The cases and controls (n = 350 men) were defined according to the severity of CM. The THC potency was evaluated with the delta-9 carboxy tetrahydrocannabinol (THC-COOH) levels in urine using gas chromatography/mass spectrometry (GC/MS). We calculated the population attributable fractions (PAFs) to identify the patterns of maltreatment associated with the highest odds of high-potency cannabis use.

RESULTS

Accumulating CM, including sexual abuse, physical abuse, and physical neglect, carried more than three times the risk of heavy cannabis use (OR 3.4 95 % CI 2.9-4.1), and the combination of the three indicators of maltreatment and a high BMI (25-29.9) carried more than four times the risk of heavy cannabis use (OR 4.7 95 % CI 2.7-4.1) compared to the controls. We estimated that in the case of zero CM for each of the three indicators, over 20 % of new cases of heavy cannabis use can be prevented.

CONCLUSIONS

The findings show the significance of CM as a predicator of heavy cannabis use in adulthood and in the abstinence phase.

GPR55 is expressed in glutamate neurons and functionally modulates drug taking and seeking in rats and mice

G protein-coupled receptor 55 (GPR55) has been thought to be a putative cannabinoid receptor. However, little is known about its functional role in cannabinoid action and substance use disorders. Here we report that GPR55 is predominantly found in glutamate neurons in the brain, and its activation reduces self-administration of cocaine and nicotine in rats and mice. Using RNAscope in situ hybridization, GPR55 mRNA was identified in cortical vesicular glutamate transporter 1 (VgluT1)-positive and subcortical VgluT2-positive glutamate neurons, with no detection in midbrain dopamine (DA) neurons. Immunohistochemistry detected a GPR55-like signal in both wildtype and GPR55-knockout mice, suggesting non-specific staining. However, analysis using a fluorescent CB1/GPR55 ligand (T1117) in CB1-knockout mice confirmed GPR55 binding in glutamate neurons, not in midbrain DA neurons. Systemic administration of the GPR55 agonist O-1602 didnt impact ∆9-THC-induced analgesia, hypothermia and catalepsy, but significantly mitigated cocaine-enhanced brain-stimulation reward caused by optogenetic activation of midbrain DA neurons. O-1602 alone failed to alter extracellar DA, but elevated extracellular glutamate, in the nucleus accumbens. In addition, O-1602 also demonstrated inhibitory effects on cocaine or nicotine self-administration under low fixed-ratio and/or progressive-ratio reinforcement schedules in rats and wildtype mice, with no such effects observed in GPR55-knockout mice. Together, these findings suggest that GPR55 activation may functionally modulate drug-taking and drug-seeking behavior possibly via a glutamate-dependent mechanism, and therefore, GPR55 deserves further study as a new therapeutic target for treating substance use disorders.

Sex-specific Effects of the Endocannabinoid Agonist 2-Arachidonoylglycerol on Sleep and Circadian Disruptions during Fentanyl Withdrawal

Fentanyl has become the leading driver of opioid overdoses. Cessation of opioid use represents a challenge as the experience of withdrawal drives subsequent relapse. One of the most prominent withdrawal symptoms that can contribute to opioid craving and vulnerability to relapse is sleep disruption. The endocannabinoid agonist, 2-Arachidonoylglycerol (2-AG), may promote sleep and reduce withdrawal severity; however, the effects of 2-AG on sleep disruption during opioid withdrawal have yet to be assessed. Here, we investigate the effects of 2-AG administration on sleep-wake behavior and diurnal activity in mice during withdrawal from fentanyl. Sleep-wake activity was continuously recorded before and after chronic fentanyl administration in both male and female C57BL/6J mice. Immediately following cessation of fentanyl administration, 2-AG was administered intraperitoneally to investigate the impact of endocannabinoid agonism on opioid-induced sleep disruption. Female mice maintained higher activity levels in response to chronic fentanyl than male mice. Furthermore, fentanyl increased wake and decreased sleep during the light period and inversely increased sleep and decreased wake in the dark period in both sexes. 2-AG treatment increased arousal and decreased sleep in both sexes during first 24 hrs of withdrawal. On withdrawal day 2, only female showed increased wakefulness with no changes in males, but by withdrawal day 3 male mice displayed decreased rapid-eye movement sleep during the dark period with no changes in female mice. Overall, repeated administration of fentanyl altered sleep and diurnal activity and administration of the endocannabinoid agonist, 2-AG, had sex-specific effects on fentanyl-induced sleep and diurnal changes.

The endocannabinoid system as a putative target for the development of novel drugs for the treatment of psychiatric illnesses

Cannabis is well established to impact affective states, emotion and perceptual processing, primarily through its interactions with the endocannabinoid system. While cannabis use is quite prevalent in many individuals afflicted with psychiatric illnesses, there is considerable controversy as to whether cannabis may worsen these conditions or provide some form of therapeutic benefit. The development of pharmacological agents which interact with components of the endocannabinoid system in more localized and discrete ways then via phytocannabinoids found in cannabis, has allowed the investigation if direct targeting of the endocannabinoid system itself may represent a novel approach to treat psychiatric illness without the potential untoward side effects associated with cannabis. Herein we review the current body of literature regarding the various pharmacological tools that have been developed to target the endocannabinoid system, their impact in preclinical models of psychiatric illness and the recent data emerging of their utilization in clinical trials for psychiatric illnesses, with a specific focus on substance use disorders, trauma-related disorders, and autism. We highlight several candidate drugs which target endocannabinoid function, particularly inhibitors of endocannabinoid metabolism or modulators of cannabinoid receptor signaling, which have emerged as potential candidates for the treatment of psychiatric conditions, particularly substance use disorder, anxiety and trauma-related disorders and autism spectrum disorders. Although there needs to be ongoing clinical work to establish the potential utility of endocannabinoid-based drugs for the treatment of psychiatric illnesses, the current data available is quite promising and shows indications of several potential candidate diseases which may benefit from this approach.

GPR55 is expressed in glutamate neurons and functionally modulates nicotine taking and seeking in rats and mice

Cannabis legalization continues to progress in the USA for medical and recreational purposes. G protein-coupled receptor 55 (GPR55) is a putative "CB3" receptor. However, its functional role in cannabinoid action and drug abuse is not explored. Here we report that GPR55 is mainly expressed in cortical and subcortical glutamate neurons and its activation attenuates nicotine taking and seeking in rats and mice. RNAscope in situ hybridization detected GPR55 mRNA in cortical vesicular glutamate transporter 1 (VgluT1)-positive and subcortical VgluT2-positive glutamate neurons in wildtype, but not GPR55-knockout, mice. GPR55 mRNA was not detected in midbrain dopamine (DA) neurons in either genotype. Immunohistochemistry assays detected GPR55-like staining, but the signal is not GPR55-specific as the immunostaining was still detectable in GPR55-knockout mice. We then used a fluorescent CB1-GPR55 ligand (T1117) and detected GPR55 binding in cortical and subcortical glutamate neurons, but not in midbrain DA neurons, in CB1-knockout mice. Systemic administration of O-1602, a GPR55 agonist, dose-dependently increased extracellular glutamate, not DA, in the nucleus accumbens. Pretreatment with O-1602 failed to alter Δ9-tetrahydrocannabinol (D9-THC)-induced triad effects or intravenous cocaine self-administration, but it dose-dependently inhibited nicotine self-administration under fixed-ratio and progressive-ratio reinforcement schedules in rats and wildtype mice, not in GPR55-knockout mice. O-1602 itself is not rewarding or aversive as assessed by optical intracranial self-stimulation (oICSS) in DAT-Cre mice. These findings suggest that GPR55 is functionally involved in nicotine reward process possibly by a glutamate-dependent mechanism, and therefore, GPR55 deserves further research as a new therapeutic target for treating nicotine use disorder.

PPARα and PPARγ are expressed in midbrain dopamine neurons and modulate dopamine- and cannabinoid-mediated behavior in mice

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors that regulate gene expression. Δ9-tetrahydrocannabinol (Δ9-THC) is a PPARγ agonist and some endocannabinoids are natural activators of PPARα and PPARγ. However, little is known regarding their cellular distributions in the brain and functional roles in cannabinoid action. Here, we first used RNAscope in situ hybridization and immunohistochemistry assays to examine the cellular distributions of PPARα and PPARγ expression in the mouse brain. We found that PPARα and PPARγ are expressed in ~70% of midbrain dopamine (DA) neurons. In the amygdala, PPARα is expressed in ~60% of glutamatergic neurons, while PPARγ is expressed in ~60%  of GABA neurons. However, no PPARα/γ signal was detected in GABA neurons in the nucleus accumbens. We then used a series of behavioral assays to determine the functional roles of PPARα/γ in the CNS effects of Δ9-THC. We found that optogenetic stimulation of midbrain DA neurons was rewarding as assessed by optical intracranial self-stimulation (oICSS) in DAT-cre mice. Δ9-THC and a PPARγ (but not PPARα) agonist dose-dependently inhibited oICSS. Pretreatment with PPARα or PPARγ antagonists attenuated the Δ9-THC-induced reduction in oICSS and Δ9-THC-induced anxiogenic effects. In addition, a PPARγ agonist increased, while PPARα or PPARγ antagonists decreased open-field locomotion. Pretreatment with PPARα or PPARγ antagonists potentiated Δ9-THC-induced hypoactivity and catalepsy but failed to alter Δ9-THC-induced analgesia, hypothermia and immobility. These findings provide the first anatomical and functional evidence supporting an important role of PPARα/γ in DA-dependent behavior and cannabinoid action.

Anorectic effect of COR659 in a rat model of overeating

COR659 is a new compound, the action of which is exerted via a dual mechanism: positive allosteric modulation of the GABAB receptor; antagonism or inverse agonism at the cannabinoid CB1 receptor. Recent lines of experimental evidence have indicated that COR659 potently and effectively reduced operant self-administration of and reinstatement of seeking behaviour for a chocolate-flavoured beverage. The present study was designed to assess whether the ability of COR659 to diminish these addictive-like, food-motivated behaviours extended to a rat model of overeating palatable food. To this end, rats were habituated to feed on a standard rat chow for 3 h/day; every 4 days, the 3-hour chow-feeding session was followed by a 1-hour feeding session with highly palatable, calorie-rich Danish butter cookies. Even though satiated, rats overconsumed cookies. COR659 (0, 2.5, 5, and 10 mg/kg, i.p.) was administered before the start of the cookie-feeding session. Treatment with all 3 doses of COR659 produced a substantial decrease in intake of cookies and calories from cookies. These results extend the anorectic profile of COR659 to overconsumption of a highly palatable food and intake of large amounts of unnecessary calories.

Targeting corticostriatal transmission for the treatment of cannabinoid use disorder

It is generally assumed that the rewarding effects of cannabinoids are mediated by cannabinoid CB1 receptors (CB1Rs) the activation of which disinhibits dopaminergic neurons in the ventral tegmental area (VTA). However, this mechanism cannot fully explain novel results indicating that dopaminergic neurons also mediate the aversive effects of cannabinoids in rodents, and previous results showing that preferentially presynaptic adenosine A2A receptor (A2AR) antagonists counteract self-administration of Δ-9-tetrahydrocannabinol (THC) in nonhuman primates (NHPs). Based on recent experiments in rodents and imaging studies in humans, we propose that the activation of frontal corticostriatal glutamatergic transmission constitutes an additional and necessary mechanism. Here, we review evidence supporting the involvement of cortical astrocytic CB1Rs in the activation of corticostriatal neurons and that A2AR receptor heteromers localized in striatal glutamatergic terminals mediate the counteracting effects of the presynaptic A2AR antagonists, constituting potential targets for the treatment of cannabinoid use disorder (CUD).

Exploring the Therapeutic Potential of Cannabinoid Receptor Antagonists in Inflammation, Diabetes Mellitus, and Obesity

Recently, research has greatly expanded the knowledge of the endocannabinoid system (ECS) and its involvement in several therapeutic applications. Cannabinoid receptors (CBRs) are present in nearly every mammalian tissue, performing a vital role in different physiological processes (neuronal development, immune modulation, energy homeostasis). The ECS has an essential role in metabolic control and lipid signaling, making it a potential target for managing conditions such as obesity and diabetes. Its malfunction is closely linked to these pathological conditions. Additionally, the immunomodulatory function of the ECS presents a promising avenue for developing new treatments for various types of acute and chronic inflammatory conditions. Preclinical investigations using peripherally restricted CBR antagonists that do not cross the BBB have shown promise for the treatment of obesity and metabolic diseases, highlighting the importance of continuing efforts to discover novel molecules with superior safety profiles. The purpose of this review is to examine the roles of CB1R and CB2Rs, as well as their antagonists, in relation to the above-mentioned disorders.

Endocannabinoid system as a therapeutic target for psychostimulants relapse: A systematic review of preclinical studies

The mechanism behind the reinstament of psychostimulant, as a major obstacle in addiction treatment is not fully understood. Controversial data are available in the literature concerning the role of the endocannabinoid (eCB) system in regulating the relapse to psychostimulant addiction in preclinical studies. The current systematic review aims to evaluate eCB modulators' effect in the reinstatement of commonly abused psychostimulants, including cocaine, amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine. By searching the PubMed, Web of Science, and Scopus databases, studies were selected. Then the studies^, quality was evaluated by the SYRCLE risk of bias tool. The results have still been limited to preclinical studies. Thirty-nine articles that employed self-administration and CPP as the most prevalent animal models of addiction were selected. This data indicates that cannabinoid receptor 1 antagonists and some cannabinoid receptor 2 agonists could suppress the reinstatement of cocaine and methamphetamine addiction in a dose-dependent manner. However, only AM251 was efficient to block the reinstatement of 3,4-methylenedioxymethamphetamine. In conclusion, cannabinoid receptor 1 antagonists and some cannabinoid receptor 2 agonists may have curative potential in the relapse of psychostimulant abuse. However, time, dose, and route of administration are crucial factors in their inhibitory impacts.

PPARα and PPARγ are expressed in midbrain dopamine neurons and modulate dopamine- and cannabinoid-mediated behavior in mice

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors that regulate gene expression. Δ 9 -tetrahydrocannabinol (Δ 9 -THC) is a PPARg agonist and some endocannabinoids are natural activators of PPAR a and PPARg. Therefore, both the receptors are putative cannabinoid receptors. However, little is known regarding their cellular distributions in the brain and functional roles in cannabinoid action. Here we first used RNAscope in situ hybridization and immunohistochemistry assays to examine the cellular distributions of PPARα and PPARγ expression in the mouse brain. We found that PPARα and PPARγ are highly expressed in ~70% midbrain dopamine (DA) neurons and in ~50% GABAergic and ~50% glutamatergic neurons in the amygdala. However, no PPARα/γ signal was detected in GABAergic neurons in the nucleus accumbens. We then used a series of behavioral assays to determine the functional roles of PPARα/γ in the CNS effects of Δ 9 -THC. We found that optogenetic stimulation of midbrain DA neurons was rewarding as assessed by optical intracranial self-stimulation (oICSS) in DAT-cre mice. Δ 9 -THC and a PPARγ (but not PPARα) agonist dose-dependently inhibited oICSS, suggesting that dopaminergic PPARγ modulates DA-dependent behavior. Surprisingly, pretreatment with PPARα or PPARγ antagonists dose-dependently attenuated the Δ 9 -THC-induced reduction in oICSS and anxiogenic effects. In addition, a PPARγ agonist increased, while PPARa or PPARγ antagonists decreased open-field locomotion. Pretreatment with PPARa or PPARγ antagonists potentiated Δ 9 -THC-induced hypoactivity and catalepsy but failed to alter Δ 9 -THC-induced analgesia, hypothermia and immobility. These findings provide the first anatomical and functional evidence supporting an important role of PPARa/g in DA-dependent behavior and cannabinoid action.

Evidence from Human Studies for Utilising Cannabinoids for the Treatment of Substance-Use Disorders: A Scoping Review with a Systematic Approach

Substance-use disorders are pervasive, comorbid with a plethora of disease and possess limited treatment options. Medicinal cannabinoids have been proposed as a novel potential treatment based on preclinical/animal trials. The objective of this study was to examine the efficacy and safety of potential therapeutics targeting the endocannabinoid system in the treatment of substance-use disorders. We performed a scoping review using a systematic approach of systematic reviews, narrative reviews, and randomised control trials that utilised cannabinoids as treatment for substance-use disorders. For this scoping review we used the PRISMA guidelines, a framework for systematic reviews and meta-analyses, to inform our methodology. We conducted a manual search of Medline, Embase, and Scopus databases in July 2022. Of the 253 results returned by the databases, 25 studies including reviews were identified as relevant, from which 29 randomised controlled trials were derived and analysed via a primary study decomposition. This review captured a small volume of highly heterogenous primary literature investing the therapeutic effect of cannabinoids for substance-use disorders. The most promising findings appeared to be for cannabis-use disorder. Cannabidiol appeared to be the cannabinoid showing the most promise for the treatment of multiple-substance-use disorders.

Pharmacovigilance on cannabidiol as an antiepileptic agent

Introduction: Cannabidiol (CBD) is an active chemical contained in the plant Cannabis sativa. It is a resorcinol-based compound that crosses the blood-brain barrier without causing euphoric effects. CBD has a plethora of pharmacological effects of therapeutic interest. CBD has been authorized in the European Union as an anticonvulsant against serious infantile epileptic syndromes, but its safety profile is still not sufficiently described. Methods: With the goal of expanding information on the safety of CBD use as an antiepileptic agent beyond the most common side effects known through clinical studies, an analysis of serious case reports on suspected adverse reactions (SARs) to CBD licensed as an anti-epileptic drug found in the EudraVigilance database is reported in this article. EudraVigilance is a system purchased by the European Medicines Agency (EMA) for monitoring the safety of medicinal products marketed in Europe. Results: The most frequent serious SARs to CBD in EudraVigilance were epilepsy aggravation, hepatic disorders, lack of efficacy, and somnolence. Discussion: Based on our analysis, the following precautions should be adopted for appropriate monitoring of potential adverse effects, more attention towards possible CBD medical use as an antiepileptic: awareness of interactions with other drugs, epilepsy aggravation, and drug effectiveness.

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

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

Therapeutic potential of PIMSR, a novel CB1 receptor neutral antagonist, for cocaine use disorder: evidence from preclinical research

Cannabinoid CB1 receptors (CB1Rs) have been major targets in medication development for the treatment of substance use disorders. However, clinical trials with rimonabant, a CB1R antagonist/inverse agonist, failed due to severe side effects. Here, we evaluated the therapeutic potential of PIMSR, a neutral CB1R antagonist lacking an inverse agonist profile, against cocaine's behavioral effects in experimental animals. We found that systemic administration of PIMSR dose-dependently inhibited cocaine self-administration under fixed-ratio (FR5), but not FR1, reinforcement, shifted the cocaine self-administration dose-response curve downward, decreased incentive motivation to seek cocaine under progressive-ratio reinforcement, and reduced cue-induced reinstatement of cocaine seeking. PIMSR also inhibited oral sucrose self-administration. Importantly, PIMSR alone is neither rewarding nor aversive as assessed by place conditioning. We then used intracranial self-stimulation (ICSS) to explore the possible involvement of the mesolimbic dopamine system in PIMSR's action. We found that PIMSR dose-dependently attenuated cocaine-enhanced ICSS maintained by electrical stimulation of the medial forebrain bundle in rats. PIMSR itself failed to alter electrical ICSS, but dose-dependently inhibited ICSS maintained by optical stimulation of midbrain dopamine neurons in transgenic DAT-Cre mice, suggesting the involvement of dopamine-dependent mechanisms. Lastly, we examined the CB1R mechanisms underlying PIMSR's action. We found that PIMSR pretreatment attenuated Δ⁹-tetrahydrocannabinol (Δ⁹-THC)- or ACEA (a selective CB1R agonist)-induced reduction in optical ICSS. Together, our findings suggest that the neutral CB1R antagonist PIMSR deserves further research as a promising pharmacotherapeutic for cocaine use disorder.

Molecular Alterations of the Endocannabinoid System in Psychiatric Disorders

The therapeutic benefits of the current medications for patients with psychiatric disorders contrast with a great variety of adverse effects. The endocannabinoid system (ECS) components have gained high interest as potential new targets for treating psychiatry diseases because of their neuromodulator role, which is essential to understanding the regulation of many brain functions. This article reviewed the molecular alterations in ECS occurring in different psychiatric conditions. The methods used to identify alterations in the ECS were also described. We used a translational approach. The animal models reproducing some behavioral and/or neurochemical aspects of psychiatric disorders and the molecular alterations in clinical studies in post-mortem brain tissue or peripheral tissues were analyzed. This article reviewed the most relevant ECS changes in prevalent psychiatric diseases such as mood disorders, schizophrenia, autism, attentional deficit, eating disorders (ED), and addiction. The review concludes that clinical research studies are urgently needed for two different purposes: (1) To identify alterations of the ECS components potentially useful as new biomarkers relating to a specific disease or condition, and (2) to design new therapeutic targets based on the specific alterations found to improve the pharmacological treatment in psychiatry.

Exploring Pharmacological Mechanisms of Essential Oils on the Central Nervous System

Essential oils (EOs) have been traditionally used as ancient remedies to treat many health disorders due to their enormous biological activities. As mainstream allopathic medication currently used for CNS disorders is associated with adverse effects, the search to obtain safer alternatives as compared to the currently marketed therapies is of tremendous significance. Research conducted suggests that concurrent utilization of allopathic medicines and EOs is synergistically beneficial. Due to their inability to show untoward effects, various scientists have tried to elucidate the pharmacological mechanisms by which these oils exert beneficial effects on the CNS. In this regard, our review aims to improve the understanding of EOs' biological activity on the CNS and to highlight the significance of the utilization of EOs in neuronal disorders, thereby improving patient acceptability of EOs as therapeutic agents. Through data compilation from library searches and electronic databases such as PubMed, Google Scholar, etc., recent preclinical and clinical data, routes of administration, and the required or maximal dosage for the observation of beneficial effects are addressed. We have also highlighted the challenges that require attention for further improving patient compliance, research gaps, and the development of EO-based nanomedicine for targeted therapy and pharmacotherapy.

Receptor mechanisms underlying the CNS effects of cannabinoids: CB1 receptor and beyond

Cannabis legalization continues to progress in many US states and other countries. Δ9-tetrahydrocannabinol (Δ9-THC) is the major psychoactive constituent in cannabis underlying both its abuse potential and the majority of therapeutic applications. However, the neural mechanisms underlying cannabis action are not fully understood. In this chapter, we first review recent progress in cannabinoid receptor research, and then examine the acute CNS effects of Δ9-THC or other cannabinoids (WIN55212-2) with a focus on their receptor mechanisms. In experimental animals, Δ9-THC or WIN55212-2 produces classical pharmacological effects (analgesia, catalepsy, hypothermia, hypolocomotion), biphasic changes in affect (reward vs. aversion, anxiety vs. anxiety relief), and cognitive deficits (spatial learning and memory, short-term memory). Accumulating evidence indicates that activation of CB1Rs underlies the majority of Δ9-THC or WIN55121-2's pharmacological and behavioral effects. Unexpectedly, glutamatergic CB1Rs preferentially underlie cannabis action relative to GABAergic CB1Rs. Functional roles for CB1Rs expressed on astrocytes and mitochondria have also been uncovered. In addition, Δ9-THC or WIN55212-2 is an agonist at CB2R, GPR55 and PPARγ receptors and recent studies implicate these receptors in a number of their CNS effects. Other receptors (such as serotonin, opioid, and adenosine receptors) also modulate Δ9-THC's actions and their contributions are detailed. This chapter describes the neural mechanisms underlying cannabis action, which may lead to new discoveries in cannabis-based medication development for the treatment of cannabis use disorder and other human diseases.

β-caryophyllene, an FDA-Approved Food Additive, Inhibits Methamphetamine-Taking and Methamphetamine-Seeking Behaviors Possibly via CB2 and Non-CB2 Receptor Mechanisms

Recent research indicates that brain cannabinoid CB2 receptors are involved in drug reward and addiction. However, it is unclear whether β-caryophyllene (BCP), a natural product with a CB2 receptor agonist profile, has therapeutic effects on methamphetamine (METH) abuse and dependence. In this study, we used animal models of self-administration, electrical brain-stimulation reward (BSR) and in vivo microdialysis to explore the effects of BCP on METH-taking and METH-seeking behavior. We found that systemic administration of BCP dose-dependently inhibited METH self-administration under both fixed-ratio and progressive-ratio reinforcement schedules in rats, indicating that BCP reduces METH reward, METH intake, and incentive motivation to seek and take METH. The attenuating effects of BCP were partially blocked by AM 630, a selective CB2 receptor antagonist. Genetic deletion of CB2 receptors in CB2-knockout (CB2-KO) mice also blocked low dose BCP-induced reduction in METH self-administration, suggesting possible involvement of a CB2 receptor mechanism. However, at high doses, BCP produced a reduction in METH self-administration in CB2-KO mice in a manner similar as in WT mice, suggesting that non-CB2 receptor mechanisms underlie high dose BCP-produced effects. In addition, BCP dose-dependently attenuated METH-enhanced electrical BSR and inhibited METH-primed and cue-induced reinstatement of drug-seeking in rats. In vivo microdialysis assays indicated that BCP alone did not produce a significant reduction in extracellular dopamine (DA) in the nucleus accumbens (NAc), while BCP pretreatment significantly reduced METH-induced increases in extracellular NAc DA in a dose-dependent manner, suggesting a DA-dependent mechanism involved in BCP action. Together, the present findings suggest that BCP might be a promising therapeutic candidate for the treatment of METH use disorder.

Discordant Effects of Cannabinoid 2 Receptor Antagonism/Inverse Agonism During Adolescence on Pavlovian and Instrumental Reward Learning in Adult Male Rats

The endocannabinoid system is responsible for regulating a spectrum of physiological activities and plays a critical role in the developing brain. During adolescence, the endocannabinoid system is particularly sensitive to external insults that may change the brain’s developmental trajectory. Cannabinoid receptor type 2 (CB2R) was initially thought to predominantly function in the peripheral nervous system, but more recent studies have implicated its role in the mesolimbic pathway, a network largely attributed to reward circuitry and reward motivated behavior, which undergoes extensive changes during adolescence. It is therefore important to understand how CB2R modulation during adolescence can impact reward-related behaviors in adulthood. In this study, adolescent male rats (postnatal days 28–41) were exposed to a low or high dose of the CB2R antagonist/inverse agonist SR144528 and Pavlovian autoshaping and instrumental conditional behavioral outcomes were measured in adulthood. SR144528-treated rats had significantly slower acquisition of the autoshaping task, seen by less lever pressing behavior over time [F_{(2, 19)} = 5.964, p = 0.010]. Conversely, there was no effect of adolescent SR144528 exposure on instrumental conditioning. These results suggest that modulation of the CB2R in adolescence differentially impacts reward-learning behaviors in adulthood.

CaMKII Modulates Diacylglycerol Lipase-α Activity in the Rat Nucleus Accumbens after Incubation of Cocaine Craving

Relapse is a major challenge to the treatment of substance use disorders. A progressive increase in cue-induced drug craving, termed incubation of craving, is observed after withdrawal from multiple drugs of abuse in humans and rodents. Incubation of cocaine craving involves the strengthening of excitatory synapses onto nucleus accumbens (NAc) medium spiny neurons via postsynaptic accumulation of high-conductance Ca2+-permeable AMPA receptors. This enhances reactivity to drug-associated cues and is required for the expression of incubation. Additionally, incubation of cocaine craving is associated with loss of the synaptic depression normally triggered by stimulation of metabotropic glutamate receptor 5 (mGlu5), leading to endocannabinoid production, and expressed presynaptically via cannabinoid receptor 1 activation. Previous studies have found alterations in mGlu5 and Homer proteins associated with the loss of this synaptic depression. Here we conducted coimmunoprecipitation studies to investigate associations of diacylglycerol lipase-α (DGL), which catalyzes formation of the endocannabinoid 2-arachidonylglycerol (2-AG), with mGlu5 and Homer proteins. Although these interactions were unchanged in the NAc core at incubation-relevant withdrawal times, the association of DGL with total and phosphorylated Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) and CaMKIIβ was increased. This would be predicted, based on other studies, to inhibit DGL activity and therefore 2-AG production. This was confirmed by measuring DGL enzymatic activity. However, the magnitude of DGL inhibition did not correlate with the magnitude of incubation of craving for individual rats. These results suggest that CaMKII contributes to the loss of mGlu5-dependent synaptic depression after incubation, but the functional significance of this loss remains unclear.

Optogenetic brain-stimulation reward: A new procedure to re-evaluate the rewarding versus aversive effects of cannabinoids in dopamine transporter-Cre mice

Despite extensive research, the rewarding effects of cannabinoids are still debated. Here, we used a newly established animal procedure called optogenetic intracranial self-stimulation (ICSS) (oICSS) to re-examine the abuse potential of cannabinoids in mice. A specific adeno-associated viral vector carrying a channelrhodopsin gene was microinjected into the ventral tegmental area (VTA) to express light-sensitive channelrhodopsin in dopamine (DA) neurons of transgenic dopamine transporter (DAT)-Cre mice. Optogenetic stimulation of VTA DA neurons was highly reinforcing and produced a classical "sigmoidal"-shaped stimulation-response curve dependent upon the laser pulse frequency. Systemic administration of cocaine dose-dependently enhanced oICSS and shifted stimulation-response curves upward, in a way similar to previously observed effects of cocaine on electrical ICSS. In contrast, Δ⁹ -tetrahydrocannabinol (Δ⁹ -THC), but not cannabidiol, dose-dependently decreased oICSS responding and shifted oICSS curves downward. WIN55,212-2 and ACEA, two synthetic cannabinoids often used in laboratory settings, also produced dose-dependent reductions in oICSS. We then examined several new synthetic cannabinoids, which are used recreationally. XLR-11 produced a cocaine-like increase, AM-2201 produced a Δ⁹ -THC-like reduction, while 5F-AMB had no effect on oICSS responding. Immunohistochemistry and RNAscope in situ hybridization assays indicated that CB₁ Rs are expressed mainly in VTA GABA and glutamate neurons, while CB₂ Rs are expressed mainly in VTA DA neurons. Together, these findings suggest that most cannabinoids are not reward enhancing, but rather reward attenuating or aversive in mice. Activation of CB₁ R and/or CB₂ R in different populations of neurons in the brain may underlie the observed actions.

Converging vulnerability factors for compulsive food and drug use

Highly palatable foods and substance of abuse have intersecting neurobiological, metabolic and behavioral effects relevant for understanding vulnerability to conditions related to food (e.g., obesity, binge eating disorder) and drug (e.g., substance use disorder) misuse. Here, we review data from animal models, clinical populations and epidemiological evidence in behavioral, genetic, pathophysiologic and therapeutic domains. Results suggest that consumption of highly palatable food and drugs of abuse both impact and conversely are regulated by metabolic hormones and metabolic status. Palatable foods high in fat and/or sugar can elicit adaptation in brain reward and withdrawal circuitry akin to substances of abuse. Intake of or withdrawal from palatable food can impact behavioral sensitivity to drugs of abuse and vice versa. A robust literature suggests common substrates and roles for negative reinforcement, negative affect, negative urgency, and impulse control deficits, with both highly palatable foods and substances of abuse. Candidate genetic risk loci shared by obesity and alcohol use disorders have been identified in molecules classically associated with both metabolic and motivational functions. Finally, certain drugs may have overlapping therapeutic potential to treat obesity, diabetes, binge-related eating disorders and substance use disorders. Taken together, data are consistent with the hypotheses that compulsive food and substance use share overlapping, interacting substrates at neurobiological and metabolic levels and that motivated behavior associated with feeding or substance use might constitute vulnerability factors for one another. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Beta-caryophyllene inhibits cocaine addiction-related behavior by activation of PPARα and PPARγ: repurposing a FDA-approved food additive for cocaine use disorder

Cocaine abuse continues to be a serious health problem worldwide. Despite intense research, there is still no FDA-approved medication to treat cocaine use disorder (CUD). In this report, we explored the potential utility of beta-caryophyllene (BCP), an FDA-approved food additive for the treatment of CUD. We found that BCP, when administered intraperitoneally or intragastrically, dose-dependently attenuated cocaine self-administration, cocaine-conditioned place preference, and cocaine-primed reinstatement of drug seeking in rats. In contrast, BCP failed to alter food self-administration or cocaine-induced hyperactivity. It also failed to maintain self-administration in a drug substitution test, suggesting that BCP has no abuse potential. BCP was previously reported to be a selective CB2 receptor agonist. Unexpectedly, pharmacological blockade or genetic deletion of CB1, CB2, or GPR55 receptors in gene-knockout mice failed to alter BCP's action against cocaine self-administration, suggesting the involvement of non-CB1, non-CB2, and non-GPR55 receptor mechanisms. Furthermore, pharmacological blockade of μ opioid receptor or Toll-like receptors complex failed to alter, while blockade of peroxisome proliferator-activated receptors (PPARα, PPARγ) reversed BCP-induced reduction in cocaine self-administration, suggesting the involvement of PPARα and PPARγ in BCP's action. Finally, we used electrical and optogenetic intracranial self-stimulation (eICSS, oICSS) paradigms to study the underlying neural substrate mechanisms. We found that BCP is more effective in attenuation of cocaine-enhanced oICSS than eICSS, the former driven by optical activation of midbrain dopamine neurons in DAT-cre mice. These findings indicate that BCP may be useful for the treatment of CUD, likely by stimulation of PPARα and PPARγ in the mesolimbic system.

Dissecting the role of CB1 and CB2 receptors in cannabinoid reward versus aversion using transgenic CB1- and CB2-knockout mice

Cannabinoids produce both rewarding and aversive effects in humans and experimental animals. However, the mechanisms underlying these conflicting findings are unclear. Here we examined the potential involvement of CB1 and CB2 receptors in cannabinoid action using transgenic CB1-knockout (CB1-KO) and CB2-knockout (CB2-KO) mice. We found that Δ9-tetrahydrocannabinol (Δ9-THC) induced conditioned place preference at a low dose (1 mg/kg) in WT mice that was attenuated by deletion of the CB1 receptor. At 5 mg/kg, no subjective effects of Δ9-THC were detected in WT mice, but CB1-KO mice exhibited a trend towards place aversion and CB2-KO mice developed significant place preferences. This data suggests that activation of the CB1 receptor is rewarding, while CB2R activation is aversive. We then examined the nucleus accumbens (NAc) dopamine (DA) response to Δ9-THC using in vivo microdialysis. Unexpectedly, Δ9-THC produced a dose-dependent decrease in extracellular DA in WT mice, that was potentiated in CB1-KO mice. However, in CB2-KO mice Δ9-THC produced a dose-dependent increase in extracellular DA, suggesting that activation of the CB2R inhibits DA release in the NAc. In contrast, Δ9-THC, when administered systemically or locally into the NAc, failed to alter extracellular DA in rats. Lastly, we examined the locomotor response to Δ9-THC. Both CB1 and CB2 receptor mechanisms were shown to underlie Δ9-THC-induced hypolocomotion. These findings indicate that Δ9-THC's variable subjective effects reflect differential activation of cannabinoid receptors. Specifically, the opposing actions of CB1 and CB2 receptors regulate cannabis reward and aversion, with CB2-mediated effects predominant in mice.

Possible Receptor Mechanisms Underlying Cannabidiol Effects on Addictive-like Behaviors in Experimental Animals

Substance use disorder (SUD) is a serious public health problem worldwide for which available treatments show limited effectiveness. Since the legalization of cannabis and the approval of cannabidiol (CBD) by the US Food and Drug Administration, therapeutic potential of CBD for the treatment of SUDs and other diseases has been widely explored. In this mini-review article, we first review the history and evidence supporting CBD as a potential pharmacotherapeutic. We then focus on recent progress in preclinical research regarding the pharmacological efficacy of CBD and the underlying receptor mechanisms on addictive-like behavior. Growing evidence indicates that CBD has therapeutic potential in reducing drug reward, as assessed in intravenous drug self-administration, conditioned place preference and intracranial brain-stimulation reward paradigms. In addition, CBD is effective in reducing relapse in experimental animals. Both in vivo and in vitro receptor mechanism studies indicate that CBD may act as a negative allosteric modulator of type 1 cannabinoid (CB1) receptor and an agonist of type 2 cannabinoid (CB2), transient receptor potential vanilloid 1 (TRPV1), and serotonin 5-HT_1A receptors. Through these multiple-receptor mechanisms, CBD is believed to modulate brain dopamine in response to drugs of abuse, leading to attenuation of drug-taking and drug-seeking behavior. While these findings suggest that CBD is a promising therapeutic candidate, further investigation is required to verify its safety, pharmacological efficacy and the underlying receptor mechanisms in both experimental animals and humans.

Further evidence of anxiety- and depression-like behavior for total genetic ablation of cannabinoid receptor type 1

Cannabinoid receptor type 1 (CB1R) is the most abundant cannabinoid receptor in central nervous system. Clinical studies and animal models have shown that the attenuation of endocannabinoid system signaling correlates with the development of psychiatric disorders such as anxiety, depression and schizophrenia. In the present work, multiple behavioral tests were performed to evaluate behaviors related to anxiety and depression in CB1R^+/- and CB1R^-/-. CB1R^+/- mice had anxiety-related behavior similar to wild type (CB1R^+/+) mice, whereas CB1R^-/- mice displayed an anxious-like phenotype, which indicates that lower expression of CB1R is sufficient to maintain the neural circuits modulating anxiety. In addition, CB1R^-/- mice exhibited alterations in risk assessment and less exploration, locomotion, grooming, body weight and appetite. These phenotypic characteristics observed in CB1R^-/- mice could be associated with symptoms observed in human psychiatric disorders such as depression. A better knowledge of the neuromodulatory role of CB1R may contribute to understand scope and limitations of the development of medical treatments.

Xie2-64, a novel CB2 receptor inverse agonist, reduces cocaine abuse-related behaviors in rodents

Cocaine abuse remains a public health threat around the world. There are no pharmacological treatments approved for cocaine use disorder. Cannabis has received growing attention as a treatment for many conditions, including addiction. Most cannabis-based medication development has focused on cannabinoid CB₁ receptor (CB₁R) antagonists (and also inverse agonists) such as rimonabant, but clinical trials with rimonabant have failed due to its significant side-effects. Here we sought to determine whether a novel and selective CB₂R inverse agonist, Xie2-64, has similar therapeutic potential for cocaine use disorder. Computational modeling indicated that Xie2-64 binds to CB₂R in a way similar to SR144528, another well-characterized but less selective CB2R antagonist/inverse agonist, suggesting that Xie2-64 may also have CB2R antagonist profiles. Unexpectedly, systemic administration of Xie2-64 or SR144528 dose-dependently inhibited intravenous cocaine self-administration and shifted cocaine dose-response curves downward in rats and wild-type, but not in CB2R-knockout, mice. Xie2-64 also dose-dependently attenuated cocaine-enhanced brain-stimulation reward maintained by optical stimulation of ventral tegmental area dopamine (DA) neurons in DAT-Cre mice, while Xie2-64 or SR144528 alone inhibited optical brain-stimulation reward. In vivo microdialysis revealed that systemic or local administration of Xie2-64 into the nucleus accumbens reduced extracellular dopamine levels in a dose-dependent manner in rats. Together, these results suggest that Xie2-64 has significant anti-cocaine reward effects likely through a dopamine-dependent mechanism, and therefore, deserves further study as a new pharmacotherapy for cocaine use disorder.

PSNCBAM-1 analogs: Structural evolutions and allosteric properties at cannabinoid CB1 receptor

Allosteric modulation of the CB1Rs could represent an alternative strategy for the treatment of diseases in which these receptors are involved, without the undesirable effects associated with their orthosteric stimulation. PSNCBAM-1 is a reference diaryl urea derivative that positively affects the binding affinity of orthosteric ligands (PAM) and negatively affects the functional activity of orthosteric ligands (NAM) at CB1Rs. In this work we reported the design, synthesis and biological evaluation of three different series of compounds, derived from structural modifications of PSNCBAM-1 and its analogs reported in the recent literature. Almost all the new compounds increased the percentage of binding affinity of CP55940 at CB1Rs, showing a PAM profile. When tested alone in the [³⁵S]GTPγS functional assay, only a few derivatives lacked detectable activity, so were tested in the same functional assay in the presence of CP55940. Among these, compounds 11 and 18 proved to be functional NAMs at CB1Rs, dampening the orthosteric agonist-induced receptor functionality by approximately 30%. The structural features presented in this work provide new CB1R-allosteric modulators (with a profile similar to the reference compound PSNCBAM-1) and an extension of the structure-activity relationships for this type of molecule at CB1Rs.

Metabolic and psychiatric effects of acyl coenzyme A binding protein (ACBP)/diazepam binding inhibitor (DBI)

Acyl coenzyme A binding protein (ACBP), also known as diazepam binding inhibitor (DBI) is a multifunctional protein with an intracellular action (as ACBP), as well as with an extracellular role (as DBI). The plasma levels of soluble ACBP/DBI are elevated in human obesity and reduced in anorexia nervosa. Accumulating evidence indicates that genetic or antibody-mediated neutralization of ACBP/DBI has anorexigenic effects, thus inhibiting food intake and inducing lipo-catabolic reactions in mice. A number of anorexiants have been withdrawn from clinical development because of their side effects including an increase in depression and suicide. For this reason, we investigated the psychiatric impact of ACBP/DBI in mouse models and patient cohorts. Intravenously (i.v.) injected ACBP/DBI protein conserved its orexigenic function when the protein was mutated to abolish acyl coenzyme A binding, but lost its appetite-stimulatory effect in mice bearing a mutation in the γ2 subunit of the γ-aminobutyric acid (GABA) A receptor (GABA_AR). ACBP/DBI neutralization by intraperitoneal (i.p.) injection of a specific mAb blunted excessive food intake in starved and leptin-deficient mice, but not in ghrelin-treated animals. Neither i.v. nor i.p. injected anti-ACBP/DBI antibody affected the behavior of mice in the dark–light box and open-field test. In contrast, ACBP/DBI increased immobility in the forced swim test, while anti-ACBP/DBI antibody counteracted this sign of depression. In patients diagnosed with therapy-resistant bipolar disorder or schizophrenia, ACBP/DBI similarly correlated with body mass index (BMI), not with the psychiatric diagnosis. Patients with high levels of ACBP/DBI were at risk of dyslipidemia and this effect was independent from BMI, as indicated by multivariate analysis. In summary, it appears that ACBP/DBI neutralization has no negative impact on mood and that human depression is not associated with alterations in ACBP/DBI concentrations.

Possible therapeutic applications of cannabis in the neuropsychopharmacology field

Cannabis use induces a plethora of actions on the CNS via its active chemical ingredients, the so-called phytocannabinoids. These compounds have been frequently associated with the intoxicating properties of cannabis preparations. However, not all phytocannabinoids are psychotropic, and, irrespective of whether they are psychotropic or not, they have also shown numerous therapeutic properties. These properties are mostly associated with their ability to modulate the activity of an intercellular communication system, the so-called endocannabinoid system, which is highly active in the CNS and has been found altered in many neurological disorders. Specifically, this includes the neuropsychopharmacology field, with diseases such as schizophrenia and related psychoses, anxiety-related disorders, mood disorders, addiction, sleep disorders, post-traumatic stress disorder, anorexia nervosa and other feeding-related disorders, dementia, epileptic syndromes, as well as autism, fragile X syndrome and other neurodevelopment-related disorders. Here, we gather, from a pharmacological and biochemical standpoint, the recent advances in the study of the therapeutic relevance of the endocannabinoid system in the CNS, with especial emphasis on the neuropsychopharmacology field. We also illustrate the efforts that are currently being made to investigate at the clinical level the potential therapeutic benefits derived from elevating or inhibiting endocannabinoid signaling in animal models of neuropsychiatric disorders.

Herbal Preparations of Medical Cannabis: A Vademecum for Prescribing Doctors

Cannabis has been used for centuries for therapeutic purposes. In the last century, the plant was demonized due to its high abuse liability and supposedly insufficient health benefits. However, recent decriminalization policies and new scientific evidence have increased the interest in cannabis therapeutic potential of cannabis and paved the way for the release of marketing authorizations for cannabis-based products. Although several synthetic and standardized products are currently available on the market, patients’ preferences lean towards herbal preparations, because they are easy to handle and self-administer. A literature search was conducted on multidisciplinary research databases and international agencies or institutional websites. Despite the growing popularity of medical cannabis, little data is available on the chemical composition and preparation methods of medical cannabis extracts. The authors hereby report the most common cannabis preparations, presenting their medical indications, routes of administration and recommended dosages. A practical and helpful guide for prescribing doctors is provided, including suggested posology, titration strategies and cannabinoid amounts in herbal preparations obtained from different sources of medical cannabis.

A Systematic Review of Essential Oils and the Endocannabinoid System: A Connection Worthy of Further Exploration

Aromatic compounds have a long history of use as medicines in most recorded cultures. An increasing interest in these therapeutic volatile molecules in both scientific and lay communities has led to the advancement of essential oils as phytomedicines. Recent discoveries suggest essential oils augment the endocannabinoid system in a positive manner to mitigate various pathologies. However, the exact mechanisms whereby essential oils influence endocannabinoid system activity are not fully known, these studies provide a glimpse into their involvement and warrant further evaluation. Additional study of the interaction between essential oils and the endocannabinoid system may lead to promising phytomedicines for the treatment of diseases and conditions involving dysregulation or activation of the endocannabinoid system.

β-Caryophyllene, a dietary terpenoid, inhibits nicotine taking and nicotine seeking in rodents

BACKGROUND AND PURPOSE

β-Caryophyllene (BCP) is a plant-derived terpenoid used as a food additive for many decades. Recent studies indicate that BCP is a cannabinoid CB₂ receptor agonist with medical benefits for a number of human diseases. However, little is known about its therapeutic potential for drug abuse and addiction.

EXPERIMENT APPROACH

We used pharmacological, transgenic, and optogenetic approaches to systematically evaluate the effects of BCP on nicotine-taking and nicotine-seeking behaviour in animal models of drug self-administration, electrical, and optical brain-stimulation reward.

KEY RESULTS

Systemic administration of BCP dose-dependently inhibited nicotine self-administration and motivation for nicotine seeking in rats and mice. The reduction in nicotine self-administration was blocked by AM630, a selective CB₂ receptor antagonist, but not by AM251, a selective CB₁ receptor antagonist, suggesting involvement of a CB₂ receptor mechanism. Genetic deletion of CB₂ receptors in mice blocked the reduction in nicotine self-administration produced only by low doses, but not by high doses, of BCP, suggesting involvement of both CB₂ and non-CB₂ receptor mechanisms. Furthermore, in the intracranial self-stimulation paradigm, BCP attenuated electrical brain-stimulation reward and nicotine-enhanced brain-stimulation reward in rats. Lastly, BCP also attenuated brain-stimulation reward maintained by optogenetic stimulation of dopaminergic neurons in the ventral tegmental area in DAT-cre mice, suggesting the involvement of a dopamine-dependent mechanism in BCP's action.

CONCLUSIONS AND IMPLICATIONS

The present findings suggest that BCP has significant anti-nicotine effects via both CB₂ and non-CB₂ receptor mechanisms and, therefore, deserves further study as a potential new pharmacotherapy for cigarette smoking cessation.

Pharmacokinetic and pharmacodynamic considerations in developing a response to the opioid epidemic

Introduction: Opioids continue to be used widely for pain management. Widespread availability of prescription opioids has led to opioid abuse and addiction. Besides steps to reduce inappropriate prescribing, exploiting opioid pharmacology to make their use safer is important.Areas covered: This article discusses the pathology and factors underlying opioid abuse. Pharmacokinetic and pharmacodynamic properties affecting abuse liability of commonly abused opioids have been highlighted. These properties inform the development of ideal abuse deterrent products. Mechanisms and cost-effectiveness of available abuse deterrent products have been reviewed in addition to the pharmacology of medications used to treat addiction.Expert opinion: The opioid crisis presents unique challenges to managing pain effectively given the limited repertoire of strong analgesics. The 5-point strategy to combat the opioid crisis calls for better preventive, treatment, and recovery services, better data, better pain management, better availability of overdose-reversing drugs and better research. There is an urgent need to decrease the cost of abuse deterrent opioids which deters their cost-effectiveness. In addition, discovery of novel analgesics, further insight into central and peripheral pain mechanisms, understanding genomic risk profiles for efficient targeted efforts, and education will be key to winning this fight against the opioid crisis.