Different receptor mechanisms underlying phytocannabinoid- versus synthetic cannabinoid-induced tetrad effects: Opposite roles of CB1 /CB2 versus GPR55 receptors

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.

The Impact of Cannabis Use on Cognition in People with HIV: Evidence of Function-Dependent Effects and Mechanisms from Clinical and Preclinical Studies

PURPOSE OF REVIEW

Cannabis may have beneficial anti-inflammatory effects in people with HIV (PWH); however, given this population's high burden of persisting neurocognitive impairment (NCI), clinicians are concerned they may be particularly vulnerable to the deleterious effects of cannabis on cognition. Here, we present a systematic scoping review of clinical and preclinical studies evaluating the effects of cannabinoid exposure on cognition in HIV.

RECENT FINDINGS

Results revealed little evidence to support a harmful impact of cannabis use on cognition in HIV, with few eligible preclinical data existing. Furthermore, the beneficial/harmful effects of cannabis use observed on cognition were function-dependent and confounded by several factors (e.g., age, frequency of use). Results are discussed alongside potential mechanisms of cannabis effects on cognition in HIV (e.g., anti-inflammatory), and considerations are outlined for screening PWH that may benefit from cannabis interventions. We further highlight the value of accelerating research discoveries in this area by utilizing translatable cross-species tasks to facilitate comparisons across human and animal work.

Comparative pharmacokinetic and intracerebral distribution of MDMB-4F-BICA in mice following inhalation ('vapor') and subcutaneous injection

MDMB-4F-BICA, also known as 4F-MDMB-BICA, is a new psychoactive substance that emerged in 2020. It is often illegally added to electronic cigarette oil for inhalation abuse, leading to serious adverse symptoms and even death. There are significant differences in pharmacokinetics between inhalation administration and conventional drug delivery methods. Inhalation administration can pass through the blood-brain barrier to enter the brain directly. However, the specific distribution of the drug in the brain following inhalation has not been well investigated. In order to scientifically compare the absorption and distribution of MDMB-4F-BICA after two administration methods (inhalation and subcutaneous injection), this study analyzed the drug concentration in mice blood and brain by LC-MS/MS after systemic exposure inhalation in the form of electronic cigarettes. The aim was to conduct the pharmacokinetics study of MDMB-4F-BICA after inhalation('vapor') administration. Pharmacokinetics and distribution of the compound revealed that the maximum concentrations in blood of this compound were reached at 0.5 min and 15 min, respectively, and the concentration in the brain reached the maximum at the same time after two modes of administration. The drug concentration in the brain was higher than that of subcutaneous injection, and the drug remained at a low concentration in the brain for a long period (20 ng/g brain tissue) with a significant distribution in several olfactory primary cortex brain regions. Taken together, the pharmacokinetics of the synthetic cannabinoid MDMB-4F-BICA after single systemic exposure inhalation were investigated for the first time in this study. A basis for subsequent evaluation research of inhalation-related harmfulness is provided by comparing the distribution of drugs in the brain after the two administration modes.

Characterization of binding kinetics and intracellular signaling of new psychoactive substances targeting cannabinoid receptor using transition-based reweighting method

New psychoactive substances (NPS) targeting cannabinoid receptor 1 pose a significant threat to society as recreational abusive drugs that have pronounced physiological side effects. These greater adverse effects compared to classical cannabinoids have been linked to the higher downstream β-arrestin signaling. Thus, understanding the mechanism of differential signaling will reveal important structure-activity relationship essential for identifying and potentially regulating NPS molecules. In this study, we simulate the slow (un)binding process of NPS MDMB-Fubinaca and classical cannabinoid HU-210 from CB1 using multi-ensemble simulation to decipher the effects of ligand binding dynamics on downstream signaling. The transition-based reweighing method is used for the estimation of transition rates and underlying thermodynamics of (un)binding processes of ligands with nanomolar affinities. Our analyses reveal major interaction differences with transmembrane TM7 between NPS and classical cannabinoids. A variational autoencoder-based approach, neural relational inference (NRI), is applied to assess the allosteric effects on intracellular regions attributable to variations in binding pocket interactions. NRI analysis indicate a heightened level of allosteric control of NPxxY motif for NPS-bound receptors, which contributes to the higher probability of formation of a crucial triad interaction (Y7.53-Y5.58-T3.46) necessary for stronger β-arrestin signaling. Hence, in this work, MD simulation, data-driven statistical methods, and deep learning point out the structural basis for the heightened physiological side effects associated with NPS, contributing to efforts aimed at mitigating their public health impact.

The progress of small molecules against cannabinoid 2 receptor (CB2R)

The two subtypes of cannabinoid receptors (CBR), namely CB1R and CB2R, belong to the G protein-coupled receptor (GPCR) superfamily and are confirmed as potential therapeutic targets for a variety of diseases such as inflammation, neuropathic pain, and immune-related disorders. Since CB1R is mainly distributed in the central nervous system (CNS), it could produce severe psychiatric adverse reactions and addiction. In contrast, CB2R are predominantly distributed in the peripheral immune system with minimal CNS-related side effects. Therefore, more attention has been devoted to the discovery of CB2R ligands. In view of the favorable profile of CB2R, many high-binding affinity and selectivity CB2R ligands have been developed recently. This paper reviews recent research progress on CB2R ligands, including endogenous CB2R ligands, natural compounds, and novel small molecules, in order to provide a reference for subsequent CB2R ligand development.

Large library docking for cannabinoid-1 receptor agonists with reduced side effects

Large library docking can reveal unexpected chemotypes that complement the structures of biological targets. Seeking new agonists for the cannabinoid-1 receptor (CB1R), we docked 74 million tangible molecules, prioritizing 46 high ranking ones for de novo synthesis and testing. Nine were active by radioligand competition, a 20% hit-rate. Structure-based optimization of one of the most potent of these (Ki = 0.7 uM) led to '4042, a 1.9 nM ligand and a full CB1R agonist. A cryo-EM structure of the purified enantiomer of '4042 ('1350) in complex with CB1R-Gi1 confirmed its docked pose. The new agonist was strongly analgesic, with generally a 5-10-fold therapeutic window over sedation and catalepsy and no observable conditioned place preference. These findings suggest that new cannabinoid chemotypes may disentangle characteristic cannabinoid side-effects from their analgesia, supporting the further development of cannabinoids as pain therapeutics.

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.

Effects of cannabinoid agonists and antagonists in male rats discriminating the synthetic cannabinoid AM2201

The synthetic forms of delta-9-tetrahydrocannabinol (Δ9-THC), dronabinol or nabilone, have been approved to treat several indications. However, due to safety concerns their clinical utility remains limited. Consequently, there is a need for developing cannabinoid (CB) ligands that display better behavioral pharmacological profiles than Δ9-THC. Here, we utilized drug discrimination methods to compare the interoceptive effects of CB ligands that vary in potency, efficacy, and selectivity at the CB receptors, including two ligands, AM411 and AM4089, that show CB1 partial agonist-like actions in vitro. Male rats were trained to discriminate 0.1 mg/kg AM2201 from saline under a fixed-ratio (FR) 10 response schedule of food reinforcement. After establishing AM2201's discriminative-stimulus effects, pretreatment tests with the CB1 antagonist/inverse agonist rimonabant blocked AM2201's effects, whereas the peripherally-restricted antagonist AM6545 had no effect. Next, the generalization profiles of AM411 and AM4089 with CB1 full agonists (JWH-018, CP-55,940, AM8936), partial agonist (Δ9-THC), and non-cannabinoids (fentanyl, atropine) were compared. The CBs either fully (AM2201, CP-55,940, JWH-018, AM8936, Δ9-THC) or partially (AM411, AM4089) substituted for AM2201, whereas fentanyl and atropine did not produce AM2201-like effects. All CB drugs were more potent than Δ9-THC and correlation analysis confirmed that the relative behavioral potencies of CBs corresponded strongly with their relative affinities at the CB1 but not CB2 receptors. Together, our results further demonstrate that AM411 and AM4089 exhibit better pharmacological profiles compared to Δ9-THC, in that they are more potent and display in vivo partial agonist-like actions that are centrally mediated via CB1 receptors.

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.

Cannabis constituents for chronic neuropathic pain; reconciling the clinical and animal evidence

Chronic neuropathic pain is a debilitating pain syndrome caused by damage to the nervous system that is poorly served by current medications. Given these problems, clinical studies have pursued extracts of the plant Cannabis sativa as alternative treatments for this condition. The vast majority of these studies have examined cannabinoids which contain the psychoactive constituent delta-9-tetrahydrocannabinol (THC). While there have been some positive findings, meta-analyses of this clinical work indicates that this effectiveness is limited and hampered by side-effects. This review focuses on how recent preclinical studies have predicted the clinical limitations of THC-containing cannabis extracts, and importantly, point to how they might be improved. This work highlights the importance of targeting channels and receptors other than cannabinoid CB1 receptors which mediate many of the side-effects of cannabis.

Analgesia by intrathecal delta-9-tetrahydrocannabinol is dependent on Cav3.2 calcium channels

Delta-9-tetrahydrocannabinol (Δ⁹-THC) is known to produce systemic analgesia that involves CB₁ and CB₂ cannabinoid receptors. However, there is compelling evidence that Δ⁹-THC can potently inhibit Cav3.2T-type calcium channels which are highly expressed in dorsal root ganglion neurons and in the dorsal horn of the spinal cord. Here, we investigated whether spinal analgesia produced by Δ⁹-THC involves Cav3.2 channels vis a vis cannabinoid receptors. We show that spinally delivered Δ⁹-THC produced dose-dependent and long-lasting mechanical anti-hyperalgesia in neuropathic mice, and showed potent analgesic effects in models of inflammatory pain induced by formalin or Complete Freund's Adjuvant (CFA) injection into the hind paw, with the latter showing no overt sex differences. The Δ⁹-THC mediated reversal of thermal hyperalgesia in the CFA model was abolished in Cav3.2 null mice, but was unaltered in CB₁ and CB₂ null animals. Hence, the analgesic effects of spinally delivered Δ⁹-THC are due to an action on T-type calcium channels, rather than activation of spinal cannabinoid receptors.

High-CBD Cannabis Vapor Attenuates Opioid Reward and Partially Modulates Nociception in Female Rats

Chronic pain patients report analgesic effects when using cannabidiol (CBD), a phytocannabinoid found in whole-plant cannabis extract (WPE). Several studies suggest that cannabis-derived products may serve as an analgesic adjunct or alternative to opioids, and importantly, CBD may also attenuate the abuse potential of opioids. Vaping is a popular route of administration among people who use cannabis, however both the therapeutic and hazardous effects of vaping are poorly characterized. Despite the fact that chronic pain is more prevalent in women, the ability of inhaled high-CBD WPE to relieve pain and reduce opioid reward has not been studied in females. Here, we present a comprehensive analysis of high-CBD WPE vapor inhalation in female rats. We found that WPE was modestly efficacious in reversing neuropathy-induced cold allodynia in rats with spared nerve injury (SNI). Chronic exposure to WPE did not affect lung cytoarchitecture or estrous cycle, and it did not induce cognitive impairment, social withdrawal or anxiolytic effects. WPE inhalation prevented morphine-induced conditioned place preference and reinstatement. Similarly, WPE exposure reduced fentanyl self-administration in rats with and without neuropathic pain. We also found that WPE vapor lacks of reinforcing effects compared to the standard excipient used in most vapor administration research. Combined, these results suggest that although high-CBD vapor has modest analgesic effects, it has a robust safety profile, no abuse potential, and it significantly reduces opioid reward in females. Clinical studies examining high-CBD WPE as an adjunct treatment during opioid use disorder are highly warranted.

Cannabinoid CB1 Receptors Are Expressed in a Subset of Dopamine Neurons and Underlie Cannabinoid-Induced Aversion, Hypoactivity, and Anxiolytic Effects in Mice

Cannabinoids modulate dopamine (DA) transmission and DA-related behavior, which has been thought to be mediated initially by activation of cannabinoid CB1 receptors (CB1Rs) on GABA neurons. However, there is no behavioral evidence supporting it. In contrast, here we report that CB1Rs are also expressed in a subset of DA neurons and functionally underlie cannabinoid action in male and female mice. RNAscope in situ hybridization (ISH) assays demonstrated CB1 mRNA in tyrosine hydroxylase (TH)-positive DA neurons in the ventral tegmental area (VTA) and glutamate decarboxylase 1 (GAD1)-positive GABA neurons. The CB1R-expressing DA neurons were located mainly in the middle portion of the VTA with the number of CB1-TH colocalization progressively decreasing from the medial to the lateral VTA. Triple-staining assays indicated CB1R mRNA colocalization with both TH and vesicular glutamate transporter 2 (VgluT2, a glutamate neuronal marker) in the medial VTA close to the midline of the brain. Optogenetic activation of this population of DA neurons was rewarding as assessed by optical intracranial self-stimulation. Δ⁹-tetrahydrocannabinol (Δ⁹-THC) or ACEA (a selective CB1R agonist) dose-dependently inhibited optical intracranial self-stimulation in DAT-Cre control mice, but not in conditional knockout mice with the CB1R gene absent in DA neurons. In addition, deletion of CB1Rs from DA neurons attenuated Δ⁹-THC-induced reduction in DA release in the NAc, locomotion, and anxiety. Together, these findings indicate that CB1Rs are expressed in a subset of DA neurons that corelease DA and glutamate, and functionally underlie cannabinoid modulation of DA release and DA-related behavior.SIGNIFICANCE STATEMENT Cannabinoids produce a series of psychoactive effects, such as aversion, anxiety, and locomotor inhibition in rodents. However, the cellular and receptor mechanisms underlying these actions are not fully understood. Here we report that CB1 receptors are expressed not only in GABA neurons but also in a subset of dopamine neurons, which are located mainly in the medial VTA close to the midline of the midbrain and corelease dopamine and glutamate. Optogenetic activation of these dopamine neurons is rewarding, which is dose-dependently inhibited by cannabinoids. Selective deletion of CB1 receptor from dopamine neurons blocked cannabinoid-induced aversion, hypoactivity, and anxiolytic effects. These findings demonstrate that dopaminergic CB1 receptors play an important role in mediating cannabinoid action.

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.

Hepatic circadian and differentiation factors control liver susceptibility for fatty liver disease and tumorigenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths, and the most common primary liver malignancy to present in the clinic. With the exception of liver transplant, treatment options for advanced HCC are limited, but improved tumor stratification could open the door to new treatment options. Previously, we demonstrated that the circadian regulator Aryl Hydrocarbon-Like Receptor Like 1 (ARNTL, or Bmal1) and the liver-enriched nuclear factor 4 alpha (HNF4α) are robustly co-expressed in healthy liver but incompatible in the context of HCC. Faulty circadian expression of HNF4α- either by isoform switching, or loss of expression- results in an increased risk for HCC, while BMAL1 gain-of-function in HNF4α-positive HCC results in apoptosis and tumor regression. We hypothesize that the transcriptional programs of HNF4α and BMAL1 are antagonistic in liver disease and HCC. Here, we study this antagonism by generating a mouse model with inducible loss of hepatic HNF4α and BMAL1 expression. The results reveal that simultaneous loss of HNF4α and BMAL1 is protective against fatty liver and HCC in carcinogen-induced liver injury and in the "STAM" model of liver disease. Furthermore, our results suggest that targeting Bmal1 expression in the absence of HNF4α inhibits HCC growth and progression. Specifically, pharmacological suppression of Bmal1 in HNF4α-deficient, BMAL1-positive HCC with REV-ERB agonist SR9009 impairs tumor cell proliferation and migration in a REV-ERB-dependent manner, while having no effect on healthy hepatocytes. Collectively, our results suggest that stratification of HCC based on HNF4α and BMAL1 expression may provide a new perspective on HCC properties and potential targeted therapeutics.

Review of delta-8-tetrahydrocannabinol (Δ8 -THC): Comparative pharmacology with Δ9 -THC

The use of the intoxicating cannabinoid delta-8-tetrahydrocannabinol (Δ⁸ -THC) has grown rapidly over the last several years. There have been dozens of Δ⁸ -THC studies dating back over many decades, yet no review articles have comprehensively covered these findings. In this review, we summarize the pharmacological studies of Δ⁸ -THC, including receptor binding, cell signalling, in vivo cannabimimetic activity, clinical activity and pharmacokinetics. We give special focus to studies that directly compared Δ⁸ -THC to its more commonly studied isomer, Δ⁹ -THC. Overall, the pharmacokinetics and pharmacodynamics of Δ⁸ -THC and Δ⁹ -THC are very similar. Δ⁸ -THC is a partial agonist of the cannabinoid CB₁ receptor and has cannabimimetic activity in both animals and humans. The reduced potency of Δ⁸ -THC in clinical studies compared with Δ⁹ -THC can be explained by weaker cannabinoid CB₁ receptor affinity, although there are other plausible mechanisms that may contribute. We highlight the gaps in our knowledge of Δ⁸ -THC pharmacology where further studies are needed, particularly in humans.

In Vivo Bio-Activation of JWH-175 to JWH-018: Pharmacodynamic and Pharmacokinetic Studies in Mice

3-(1-Naphthalenylmethyl)-1-pentyl-1H-indole (JWH-175) is a synthetic cannabinoid illegally marketed for its psychoactive cannabis-like effects. This study aimed to investigate and compare in vitro and in vivo pharmacodynamic activity of JWH-175 with that of 1-naphthalenyl (1-pentyl-1H-indol-3-yl)-methanone (JWH-018), as well as evaluate the in vitro (human liver microsomes) and in vivo (urine and plasma of CD-1 male mice) metabolic profile of JWH-175. In vitro binding studies showed that JWH-175 is a cannabinoid receptor agonist less potent than JWH-018 on mouse and human CB1 and CB2 receptors. In agreement with in vitro data, JWH-175 reduced the fESPS in brain hippocampal slices of mice less effectively than JWH-018. Similarly, in vivo behavioral studies showed that JWH-175 impaired sensorimotor responses, reduced breath rate and motor activity, and increased pain threshold to mechanical stimuli less potently than JWH-018. Metabolic studies demonstrated that JWH-175 is rapidly bioactivated to JWH-018 in mice blood, suggesting that in vivo effects of JWH-175 are also due to JWH-018 formation. The pharmaco-toxicological profile of JWH-175 was characterized for the first time, proving its in vivo bio-activation to the more potent agonist JWH-018. Thus, it highlighted the great importance of investigating the in vivo metabolism of synthetic cannabinoids for both clinical toxicology and forensic purposes.

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.

Mepirapim, a Novel Synthetic Cannabinoid, Induces Addiction-Related Behaviors through Neurochemical Maladaptation in the Brain of Rodents

Mepirapim is a synthetic cannabinoid that has recently been abused for recreational purposes. Although serious side effects have been reported from users, the dangerous pharmacological effects of Mepirapim have not been scientifically demonstrated. In this study, we investigated the addictive potential of Mepirapim through an intravenous self-administration test and a conditioned place preference test in rodents. Moreover, to determine whether the pharmacological effects of Mepirapim are mediated by cannabinoid receptors, we investigated whether Mepirapim treatment induces cannabinoid tetrad symptoms in mice. Lastly, to identify Mepirapim induced neurochemical maladaptation in the brains of mice, we performed microdialysis, western blots and neurotransmitter enzyme-linked immunosorbent assays. In the results, Mepirapim supported the maintenance of intravenous self-administration and the development of conditioned place preference. As a molecular mechanism of Mepirapim addiction, we identified a decrease in GABAeric signalling and an increase in dopaminergic signalling in the brain reward circuit. Finally, by confirming the Mepirapim-induced expression of cannabinoid tetrad symptoms, we confirmed that Mepirapim acts pharmacologically through cannabinoid receptor one. Taken together, we found that Mepirapim induces addiction-related behaviours through neurochemical maladaptation in the brain. On the basis of these findings, we propose the strict regulation of recreational abuse of Mepirapim.

Delta-9-tetrahydrocannabinol increases vascular endothelial growth factor (VEGF) secretion through a cyclooxygenase-dependent mechanism in rat granulosa cells

While the effects of delta-9-tetrahydrocannabinol (THC), the psychoactive component of cannabis, have been studied extensively in the central nervous system, there is limited knowledge about its effects on the female reproductive system. The aim of this study was to assess the effect of THC on the expression and secretion of the angiogenic factor vascular endothelial growth factor (VEGF) in the ovary, and to determine if these effects were mediated by prostaglandins. Spontaneously immortalized rat granulosa cells (SIGCs) were exposed to THC for 24hours. Gene expression, proliferation and TNFα-induced apoptosis were evaluated in the cells and concentrations of VEGF and prostaglandin E2 (PGE₂), a known regulator of VEGF production, were determined in the media. To evaluate the role of the prostanoid pathway, cells were pre-treated with cyclooxygenase (COX) inhibitors prior to THC exposure. THC-exposed SIGCs had a significant increase in VEGF and PGE₂ secretion, along with an increase in proliferation and cell survival when challenged with an apoptosis-inducing factor. Pre-treatment with COX inhibitors reversed the THC-induced increase in both PGE₂ and VEGF secretion. Alterations in granulosa cell function, such as the ones observed after THC exposure, may impact essential ovarian processes including folliculogenesis and ovulation, which could in turn affect female reproductive health and fertility. With the ongoing increase in cannabis use and potency, further study on the impact of cannabis and its constituents on female reproductive health is required.

Analyzing the Impact of Cannabinoids on the Treatment of Spinal Disorders

PURPOSE OF REVIEW

Cannabis is among the most used illicit substances globally, with medical applications, increased legalization, and shifting social attitudes leading to increased use in recent years. Cannabinoids are a group of psychoactive substances found within the cannabis plant, with the most common being Δ9-tetrahydrocannabinol and cannabidiol. Due to the high prevalence of use, it is increasingly important to evaluate the effects of cannabis and cannabinoids on spine patients, in both operative and nonoperative settings.

RECENT FINDINGS

Cannabis and cannabinoids may be effective in treating patients with chronic conditions such as back pain and spinal cord injuries. Longitudinal effects and implications on surgical outcomes and complications are poorly understood. High-quality, outcomes-focused research can inform approaches for clinicians to approach cannabis and cannabinoid use. Studies to elucidate the standardization of cannabis regimens can help develop guidelines for potential therapeutic applications. Cannabis and cannabinoids may be useful alternatives or additions for many spine patients, but future research is needed for recommendations to be determined. Our manuscript reviews the available literature regarding cannabis use and various spinal conditions, organizing our findings into the following narrative themes: (1) the management of chronic lower back pain, (2) perioperative outcomes, (3) cannabis use in general orthopaedic procedures, and (4) spinal cord injuries.

Structure-activity relationships for 5F-MDMB-PICA and its 5F-pentylindole analogs to induce cannabinoid-like effects in mice

Synthetic cannabinoid receptor agonists (SCRAs) are an evolving class of new psychoactive substances found on recreational drug markets worldwide. The indole-containing compound, 5F-MDMB-PICA, is a popular SCRA associated with serious medical consequences, including overdose and hospitalizations. In vitro studies reveal that 5F-MDMB-PICA is a potent agonist at cannabinoid type 1 receptors (CB₁), but little information exists regarding in vivo pharmacology of the drug. To this end, we examined the in vitro and in vivo cannabinoid-like effects produced by 5F-MDMB-PICA and related 5F-pentylindole analogs with differing composition of the head group moiety (i.e., 5F-NNEI, 5F-SDB-006, 5F-CUMYL-PICA, 5F-MMB-PICA). In mouse brain membranes, 5F-MDMB-PICA and its analogs inhibited binding to [³H]rimonabant-labeled CB₁ and displayed agonist actions in [³⁵S]GTPγS functional assays. 5F-MDMB-PICA exhibited the highest CB₁ affinity (K_i = 1.24 nM) and functional potency (EC₅₀ = 1.46 nM), but head group composition markedly influenced activity in both assays. For example, the 3,3-dimethylbutanoate (5F-MDMB-PICA) and cumyl (5F-CUMYL-PICA) head groups engendered high CB₁ affinity and potency, whereas a benzyl (5F-SDB-006) head group did not. In C57BL/6J mice, all 5F-pentylindole SCRAs produced dose- and time-dependent hypothermia, catalepsy, and analgesia that were reversed by rimonabant, indicating CB₁ involvement. In vitro K_i and EC₅₀ values were positively correlated with in vivo ED₅₀ potency estimates. Our findings demonstrate that 5F-MDMB-PICA is a potent SCRA, and subtle alterations to head group composition can have profound influence on pharmacological effects at CB₁. Importantly, measures of CB₁ binding and efficacy in mouse brain tissue seem to accurately predict in vivo drug potency in this species.

Effects of synthetic cannabinoids on psychomotor, sensory and cognitive functions relevant for safe driving

Recreational use of Synthetic Cannabinoids (SCs), one of the largest groups of New Psychoactive Substances (NPS), has increased globally over the past few years. Driving is a structured process requiring the cooperation of several cognitive and psychomotor functions, organized in different levels of complexity. Each of these functions can be affected when Driving Under the Influence (DUI) of SCs. In order to reduce the likelihood of SC-related road accidents, it is essential to understand which areas of psychomotor performance are most affected by these substances, as well as the severity of impairment. For this purpose, a multiple database- literature review of recent experimental studies in humans and animals regarding the psychomotor effects of SCs has been performed. Despite the many limitations connected to experimental studies on humans, results showed a consistency between animal and human data. SCs appear to impair psychomotor performance in humans, affecting different domains related to safe driving even at low doses. Cases of DUI of SC have been repeatedly reported, although the exact prevalence is likely to be underestimated due to current analytical and interpretative issues. For this reason, an accurate physical examination performed by trained and experienced personnel has a primary role in recognizing signs of impairment in case of strong suspicion of SC consumption. The identification of a suspected case should be followed by reliable laboratory examination.

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.

Cannabinoid CB2 receptors are expressed in glutamate neurons in the red nucleus and functionally modulate motor behavior in mice

Cannabinoids produce a number of central nervous system effects via the CB2 receptor (CB2R), including analgesia, antianxiety, anti-reward, hypoactivity and attenuation of opioid-induced respiratory depression. However, the cellular distributions of the CB2Rs in the brain remain unclear. We have reported that CB2Rs are expressed in midbrain dopamine (DA) neurons and functionally regulate DA-mediated behavior(s). Unexpectedly, high densities of CB2-like signaling were also found in a neighboring motor structure - the red nucleus (RN) of the midbrain. In the present study, we systematically explored CB2R expression and function in the RN. Immunohistochemistry and in situ hybridization assays showed high densities of CB2R-immunostaining and mRNA signal in RN magnocellular glutamate neurons in wildtype and CB1-knockout, but not CB2-knockout, mice. Ex vivo electrophysiological recordings in midbrain slices demonstrated that CB2R activation by JWH133 dose-dependently inhibited firing rates of RN magnocellular neurons in wildtype, but not CB2-knockout, mice, while having no effect on RN GABA neurons in transgenic GAD67-GFP reporter mice, suggesting CB2-mediated effects on glutamatergic neurons. In addition, microinjection of JWH133 into the RN produced robust ipsilateral rotations in wildtype, but not CB2-knockout mice, which was blocked by pretreatment with either a CB2 or DA D1 or D2 receptor antagonist, suggesting a DA-dependent effect. Finally, fluorescent tract tracing revealed glutamatergic projections from the RN to multiple brain areas including the ventral tegmental area, thalamus, and cerebellum. These findings suggest that CB2Rs in RN glutamate neurons functionally modulate motor activity, and therefore, constitute a new target in cannabis-based medication development for motor disorders.

Oral efficacy of Δ(9)-tetrahydrocannabinol and cannabidiol in a mouse neuropathic pain model

The psychoactive and non-psychoactive constituents of cannabis, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), have synergistic analgesic efficacy in animal models of neuropathic pain when injected systemically. However, the relevance of this preclinical synergy to clinical neuropathic pain studies is unclear because many of the latter use oral administration. We therefore examined the oral effectiveness of these phytocannabinoids and their interactions in a mouse chronic constriction injury (CCI) model of neuropathic pain. THC produced a dose-dependent reduction in mechanical and cold allodynia, but also induced side-effects with similar potency. CBD also reduced allodynia, albeit with lower potency than THC, but did not produce cannabinoid-like side-effects at any dose tested. Combination THC:CBD produced a dose-dependent reduction in allodynia, however, it displayed little to no synergy. Combination THC:CBD produced substantial, synergistic side-effects which increased with the proportion of CBD. These findings demonstrate that oral THC and CBD, alone and in combination, have analgesic efficacy in an animal neuropathic pain model. Unlike prior systemic injection studies, combination THC:CBD lacks analgesic synergy when delivered orally. Furthermore, both THC and combination THC:CBD display a relatively poor therapeutic window when delivered orally. This suggests that CBD provides a safer, albeit lower efficacy, oral treatment for nerve injury induced neuropathic pain than THC-containing preparations. This article is part of the special issue on 'Cannabinoids'.

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.

The effect of intra-striatal administration of GPR55 agonist (LPI) and antagonist (ML193) on sensorimotor and motor functions in a Parkinson's disease rat model

OBJECTIVE

G protein-coupled receptor 55 (GPR55) is an orphan G protein-coupled receptor with various physiological functions. Recent evidence suggests that this receptor may be involved in the control of motor functions. Therefore, in the present study, we evaluated the effects of intra-striatal administration of GPR55 selective ligands in a rat model of Parkinson's disease.

METHODS

Experimental Parkinson was induced by unilateral intra-striatal administration of 6-hydroxydopamine (6-OHDA, 10 µg/rat). L-α-lysophosphatidylinositol (LPI, 1 and 5 µg/rat), an endogenous GPR55 agonist, and ML193 (1 and 5 µg/rat), a selective GPR55 antagonist, were injected into the striatum of 6-OHDA-lesioned rats. Motor performance and balance skills were evaluated using the accelerating rotating rod and the ledged beam tests. The sensorimotor function of the forelimbs and locomotor activity were assessed by the adhesive removal and open field tests, respectively.

RESULTS

6-OHDA-lesioned rats had impaired behaviours in all tests. Intra-striatal administration of LPI in 6-OHDA-lesioned rats increased time on the rotarod, decreased latency to remove the label, with no significant effect on slip steps, and locomotor activity. Intra-striatal administration of ML193 also increased time on the rotarod, decreased latency to remove the label and slip steps in 6-OHDA-lesioned rats mostly at the dose of 1 µg/rat.

CONCLUSIONS

This study suggests that the striatal GPR55 is involved in the control of motor functions. However, considering the similar effects of GPR55 agonist and antagonist, it may be concluded that this receptor has a modulatory role in the control of motor deficits in an experimental model of Parkinson.

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.

Explication of CB1 receptor contributions to the hypothermic effects of Δ9-tetrahydrocannabinol (THC) when delivered by vapor inhalation or parenteral injection in rats

The use of Δ⁹-tetrahydrocannabinol (THC) by inhalation using e-cigarette technology grows increasingly popular for medical and recreational purposes. This has led to development of e-cigarette based techniques to study the delivery of THC by inhalation in laboratory rodents. Inhaled THC reliably produces hypothermic and antinociceptive effects in rats, similar to effects of parenteral injection of THC. This study was conducted to determine the extent to which the hypothermic response depends on interactions with the CB₁ receptor, using pharmacological antagonist (SR141716, AM-251) approaches. Groups of rats were implanted with radiotelemetry devices capable of reporting activity and body temperature, which were assessed after THC inhalation or injection. SR141716 (4 mg/kg, i.p.) blocked or attenuated antinociceptive effects of acute THC inhalation in male and female rats. SR141716 was unable to block the initial hypothermia caused by THC inhalation, but temperature was restored to normal more quickly. Alterations in antagonist pre-treatment time, dose and the use of a rat strain with less sensitivity to THC-induced hypothermia did not change this pattern. Pre-treatment with SR141716 (4 mg/kg, i.p.) blocked hypothermia induced by i.v. THC and reversed hypothermia when administered 45 or 90 min after THC (i.p.). SR141716 and AM-251 (4 mg/kg, i.p.) sped recovery from, but did not block, hypothermia caused by vapor THC in female rats made tolerant by prior repeated THC vapor inhalation. The CB₂ antagonist AM-630, had no effect. These results suggest that hypothermia consequent to THC inhalation is induced by other mechanisms in addition to CB₁ receptor activation.

Cannabinoid Use in Musculoskeletal Illness: a Review of the Current Evidence

PURPOSE OF REVIEW

The use of cannabinoids has increased since legalization of recreational and medical use in the USA. It is likely that many orthopaedic patients consume cannabinoid products during the traumatic or perioperative period. The purpose of this study was to investigate the pre-clinical data evaluating the mechanism of action of cannabidiol (CBD) and Δ9-Tetrahydrocannabinol (Δ9-THC) and to evaluate the current clinical data on the use of cannabinoids in musculoskeletal illness.

RECENT FINDINGS

Recent pre-clinical studies have demonstrated that cannabinoid use and the endocannabinoid system (ECS) has an important role in bone healing and bone homeostasis. There is data that suggests that the use of cannabidiol (CBD) may increase bone healing, whereas the use of Δ9-Tetrahydrocannabinol (Δ9-THC), the major psychoactive ingredient in marijuana, likely inhibits bone metabolism and repair. The clinical implications and consumption of marijuana by orthopaedic patients have not been thoroughly evaluated. Studies have demonstrated concern for negative cardiovascular and psychiatric effects caused by marijuana use, but have not yet elucidated outcomes in the orthopaedic literature. With the recent increase in advertising of CBD products and legalization of marijuana, it is likely that many orthopaedic patients are consuming cannabinoid products. The clinical implications and consumption of these products are unclear. We need more robust and well-designed clinical studies prior to making further recommendations to our patients on the consumption of these products.

Different receptor mechanisms underlying phytocannabinoid- versus synthetic cannabinoid-induced tetrad effects: Opposite roles of CB1 /CB2 versus GPR55 receptors

BACKGROUND AND PURPOSE

Cannabis or cannabinoids produce characteristic tetrad effects-analgesia, hypothermia, catalepsy and suppressed locomotion, which are believed to be mediated by the activation of cannabinoid CB₁ receptors. Given recent findings of CB₂ and GPR55 receptors in the brain, we examined whether these receptors are also involved in cannabinoid action.

EXPERIMENTAL APPROACH

We compared Δ⁹ -tetrahydrocannabinol (Δ⁹ -THC)-, WIN55212-2-, or XLR11-induced tetrad effects between wild-type (WT) and each genotype of CB₁ -, CB₂ - or GPR55-knockout (KO) mice and then observed the effects of antagonists of these receptors on these tetrad effects in WT mice.

KEY RESULTS

Systemic administration of Δ⁹ -THC, WIN55212-2 or XLR11 produced dose-dependent tetrad effects in WT mice. Genetic deletion or pharmacological blockade of CB₁ receptors abolished the tetrad effects produced by all three cannabinoids. Unexpectedly, genetic deletion of CB₂ receptor abolished analgesia and catalepsy produced by Δ⁹ -THC or WIN55212-2, but not by XLR11. Microinjections of Δ⁹ -THC into the lateral ventricles also produced tetrad effects in WT, but not in CB₁ -KO mice. CB₂ -KO mice displayed a reduction in intraventricular Δ⁹ -THC-induced analgesia and catalepsy. In contrast to CB₁ and CB₂ receptors, genetic deletion of GPR55 receptors caused enhanced responses to Δ⁹ -THC or WIN55212-2. Antagonisim of CB₁ , CB₂ or GPR55 receptors produced alterations similar to those observed in each genotype mouse line.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that in addition to CB₁ , both CB₂ and GPR55 receptors are also involved in some pharmacological effects produced by cannabinoids. CB₁ /CB₂ , in contrast to GPR55, receptors appears to play opposite roles in cannabinoid action.