Cannabinoids modulate pain by multiple mechanisms of action

Alcohol and cannabis use for pain management: Translational findings of relative risks, benefits, and interactions

Chronic pain affects over 20% of the global population and contributes to the vast burden of psychiatric illness. While effective treatments for chronic pain remain limited, both alcohol and cannabis have been used for centuries to manage pain and closely associated negative affective symptoms. However, persistent misuse of alcohol and/or cannabis in such a negative reinforcement fashion is hypothesized to increase the risk of severity of substance use disorders (SUDs). The current review describes neurobiological evidence for the analgesic efficacy of alcohol and primary cannabis constituents and how use or co-use of these substances may influence SUD risk.

Kynurenine amplifies tetrahydrocannabinol-induced sensorimotor impairment and classic "tetrad" effects in mice

BACKGROUND

L-kynurenine (KYN), a kynurenine pathway (KP) metabolite, is the main precursor for the neuroactive metabolite kynurenic acid (KYNA). Several studies suggest a patho-physiologically relevant association between increased brain KYNA levels and cognitive dysfunctions in individuals with schizophrenia. Δ9-tetrahydrocannabinol (Δ9-THC; i.e. the main psychoactive compound of cannabis) can worse schizophrenia-related psychosis, often leads to the development of cannabis use disorder in individuals with schizophrenia, and increases the risk of earlier onset of schizophrenia symptoms in those with a genetic predisposition. A role of KP alterations and, specifically, increased brain KYNA levels in Δ9-THC-induced psychotic symptoms has been previously proposed. The aim of the study was to investigate on the possible involvement of KP alterations in Δ9-THC-induced sensorimotor and "tetrad" responses in mice.

METHODS

Adult male CD-1 mice were treated with Δ9-THC (30 mg/ kg; i.p.) and KYN (20 mg/kg; i.p.), alone or in combination, and body temperature, acute mechanical and thermal analgesia, motor activity and sensorimotor responses were evaluated. Furthermore, brain KYNA levels as well as plasma Δ9-THC and its metabolites concentrations after the treatments were also evaluated.

RESULTS

Brain KYNA levels were significantly increased 1 h, but not 4 h, after KYN and KYN + Δ9-THC administration. KYN administration amplified the Δ9-THC-induced impairment of sensorimotor responses (visual placing, acoustic and tactile responses). Furthermore, KYN significantly increased Δ9-THC-induced motor activity impairment (bar test, drag test and rotarod test) and hypothermia (core and surface body temperature), but not Δ9-THC-induced analgesia. Finally, 1 h after Δ9-THC administration, Δ9-THC and its psychoactive metabolite 11-OH-THC plasma levels were higher in mice pretreated with KYN than in control mice.

CONCLUSIONS

The present data indicate for the first time that KYN amplifies the THC-induced sensorimotor impairment and classic "tetrad" response possibly through a pharmacokinetic interaction.

Changes in peripheral endocannabinoid levels in substance use disorders: a review of clinical evidence

Background: The endocannabinoid (eCB) system is a key modulator of stress and reward and is impacted by alcohol and drug use. Recently, the eCB system has been highlighted as a potential novel target in the treatment of substance use disorders (SUDs).Objectives: Understanding how chronic substance use impacts the function of the eCB system can provide a mechanistic rationale for targeting this system in the treatment of SUDs.Methods: A comprehensive review of studies assessing concentrations of eCB ligands N-arachidonoyl ethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG) in individuals with a SUD diagnosis was performed using all EBSCO databases, PubMed, and Google Scholar. Methods and results related to eCB concentrations, diagnosis, and other factors (e.g. treatment status) were extracted from papers written in English and published in peer-reviewed journals before May 22, 2024.Results: Fifteen studies were reviewed; three in alcohol use disorder (AUD), three in cannabis use disorder (CUD), four in cocaine use disorder, one in opioid use disorder (OUD) and four across SUDs. Generally, AEA concentrations were usually, but not always, increased in AUD, CUD, OUD, and cocaine use disorder. 2-AG concentrations were measured less often but were increased in CUD and decreased in cocaine use disorder.Conclusions: Studies generally support the hypothesis that chronic substance use can impact eCB levels, most often with increased AEA and decreased (or not quantified) 2-AG concentrations, though results were often conflicting. Variability in methodology and study design may limit generalizability across studies.

An early economic analysis of medical cannabis for the treatment of chronic pain

BACKGROUND

Cannabis-based medicinal products (CBMPs) are increasingly demonstrating effectiveness in treating a wide range of conditions, with a relatively high safety profile in clinical usage compared to other prescription pain medications and few contraindications. Consultation and other prescription-related costs are, at present, higher for CBMPs than for some other treatment options, leading to some concern around wider prescribing.

RESEARCH DESIGN AND METHODS

An early cost-effectiveness model was developed to estimate the impact of prescribing CBMPs alone and/or in addition to analgesics, physiotherapy, and cognitive behavioral therapy for chronic pain in the UK for 1 year.

RESULTS

Due to their comparative effectiveness, CBMPs were found to be cost saving. Various scenarios were model tested; in all scenarios where CBMPs decrease pain-level states, less resource use is required. Increased efficacy of 5% was conservatively assumed based on current Real-World Evidence. In this scenario, CBMPs were significantly more cost-effective, and as costs relating to the prescribing of these continue to fall, relative savings are predicted to increase.

CONCLUSION

These findings highlight the substantial cost saving that CBMPs may represent for the treatment of chronic pain patients, and the benefits for healthcare providers as a treatment for this often hard-to-treat population.

Cannabinoid Analgesia in Postoperative Pain Management: From Molecular Mechanisms to Clinical Reality

Postoperative pain (POP) is a challenging clinical phenomenon that affects the majority of surgical patients and demands effective management to mitigate adverse outcomes such as persistent pain. The primary goal of POP management is to alleviate suffering and facilitate a seamless return to normal function for the patient. Despite compelling evidence of its drawbacks, opioid analgesia remains the basis of POP treatment. Novel therapeutic approaches rely on multimodal analgesia, integrating different pharmacological strategies to optimize efficacy while minimizing adverse effects. The recognition of the imperative role of the endocannabinoid system in pain regulation has prompted the investigation of cannabinoid compounds as a new therapeutic avenue. Cannabinoids may serve as adjuvants, enhancing the analgesic effects of other drugs and potentially replacing or at least reducing the dependence on other long-term analgesics in pain management. This narrative review succinctly summarizes pertinent information on the molecular mechanisms, clinical therapeutic benefits, and considerations associated with the plausible use of various cannabinoid compounds in treating POP. According to the available evidence, cannabinoid compounds modulate specific molecular mechanisms intimately involved in POP. However, only two of the eleven clinical trials that evaluated the efficacy of different cannabinoid interventions showed positive results.

Medical Cannabis Prescription Practices and Quality of Life in Thai Patients: A Nationwide Prospective Observational Cohort Study

Introduction

The legalization of cannabis in Thailand has renewed interest in its traditional medical use. This study aimed to explore the prescribing patterns of traditional practitioners and assess the impact of cannabis oil on patients' quality of life, with a specific focus on comparing outcomes between cancer and non-cancer patients.

Methods

We conducted a prospective observational cohort study across 30 sites in 21 Thai provinces to analyze the use of "Ganja Oil," a cannabis extract in 10% coconut oil, prescribed for symptoms like pain, anorexia, and insomnia across a diverse patient group, including cancer and migraines. Quality of life was assessed using the Edmonton Symptom Assessment Scale (ESAS) and EQ-5D-5L at baseline, 1, 2, and 3 months. The study included a predefined subgroup analysis to compare the effects on cancer versus non-cancer patients. Data management was facilitated through Research Electronic Data Capture (REDCap), with statistical analysis performed using Stata/MP.

Results

Among 21,284 participants, the mean age was 54.10 ± 15.32 years, with 52.49% being male. The baseline EQ-5D-5L index was 0.85 ± 0.24. Significant differences in EQ-5D-5L indices were seen between cancer patients (0.79 ± 0.32) and non-cancer patients (0.85 ± 0.23; p < 0.001). ESAS scores also differed significantly between these groups for all symptoms, except anxiety. The most frequent prescription of Ganja Oil was oral administration at bedtime (88.26%), with the predominant dosage being three drops daily, approximately 0.204 mg of tetrahydrocannabinol in total. Posttreatment, significant improvements were noted: the EQ-5D-5L index increased by 0.11 points (95% CI: 0.11, 0.11; p < 0.001) overall, 0.13 points (95% CI: 0.12, 0.14; p < 0.001) for cancer patients, and 0.11 points (95% CI: 0.10, 0.11; p < 0.001) for non-cancer patients. ESAS pain scores improved by -2.66 points (95% CI: -2.71, -2.61; p < 0.001) overall, -2.01 points (95% CI: -2.16, -1.87; p < 0.001) for cancer patients, and -2.75 points (95% CI: -2.80, -2.70; p < 0.001) for non-cancer patients, with similar significant improvements in other symptoms.

Conclusion

Our study indicates potential benefits of Ganja Oil for improving quality of life among Thai patients, as a complementary treatment. These findings must be viewed in light of the study's design limitations. Further controlled studies are essential to ascertain its efficacy and inform dosing guidelines.

Pharmacokinetics, efficacy, and safety of cannabidiol in dogs: an update of current knowledge

In the last 5 years, interest has grown in using phytocannabinoids, particularly cannabidiol (CBD), in veterinary medicine to treat several pathologies, including pain, epilepsy, anxiety, nausea, anorexia, skin lesions, and even some types of cancer, among others. Indeed, due to a positive perception of CBD use, many pet owners are increasingly requesting this option to relieve their pets, and many veterinarians are exploring this possibility for their patients. Besides the widespread empiric use of CBD in pets, the research is trying to obtain proof of its efficacy and lack of adverse effects and to know its pharmacokinetics to define an appropriate posology. This review summarizes all data published so far about the canine pharmacokinetics, efficacy, and tolerability of CBD and cannabidiolic acid (CBDA). Despite a certain number of available pharmacokinetic studies, the kinetic profile of CBD has yet to be fully known, probably because of the very different experimental conditions. In terms of efficacy, most studies have tested CBD' ability to relieve osteoarthritic pain. In contrast, few studies have evaluated its role in epilepsy, behavioral disorders, and skin lesions. From obtained results, some evidence exists supporting the beneficial role of CBD. Nevertheless, the limited number of published studies and the occurrence of bias in almost all require caution in interpreting findings. From tolerability studies, CBD' side effects can be classified as mild or unremarkable. However, studies were prevalently focused on short- to medium-term treatment, while CBD is usually employed for long-term treatment. Further studies are warranted to define better whether CBD could be a valid adjunct in canine treatment.

[Exercise for the promotion of mental health II: Putative mechanisms, recommendations, and scientific challenges]

The idea of applying various forms of physical activity for the betterment of physical health and the reduction of chronic medical conditions is ubiquitous. Despite evidence of successful applications of physical activity for improvement of mental health dating back to antiquity, it has until recent years remained unconventional to consider exercise as an intervention strategy for various mental health conditions. The past two decades, however, have seen a relative explosion of interest in understanding and applying various programs and forms of exercise to improve mental health. Here, our purpose is to provide a comprehensive and updated overview of the application of exercise as a strategy for improving mental health. In the present paper we first summarize contemporary research regarding short- and long-term impacts of exercise on mental health. Then an overview of the putative mechanisms and neurobiological bases underpinning the beneficial effects of exercise is provided. Finally, we suggest directions for future research as well as a series of concrete recommendations for clinicians who wish to prescribe physical activity as part of patient mental health management.

Mice from lines selectively bred for voluntary exercise are not more resistant to muscle injury caused by either contusion or wheel running

Muscle injury can be caused by strenuous exercise, repetitive tasks or external forces. Populations that have experienced selection for high locomotor activity may have evolutionary adaptations that resist exercise-induced injury and/or enhance the ability to cope with injury. We tested this hypothesis with an experiment in which mice are bred for high voluntary wheel running. Mice from four high runner lines run ~three times more daily distance than those from four non-selected control lines. To test recovery from injury by external forces, mice experienced contusion via weight drop on the calf. After injury, running distance and speed were reduced in high runner but not control lines, suggesting that the ability of control mice to run exceeds their motivation. To test effects of injury from exercise, mice were housed with/without wheels for six days, then trunk blood was collected and muscles evaluated for injury and regeneration. Both high runner and control mice with wheels had increased histological indicators of injury in the soleus, and increased indicators of regeneration in the plantaris. High runner mice had relatively more central nuclei (regeneration indicator) than control in the soleus, regardless of wheel access. The subset of high runner mice with the mini-muscle phenotype (characterized by greatly reduced muscle mass and type IIb fibers) had lower plasma creatine kinase (indicator of muscle injury), more markers of injury in the deep gastrocnemius, and more markers of regeneration in the deep and superficial gastrocnemius than normal-muscled individuals. Contrary to our expectations, high runner mice were not more resistant to either type of injury.

Advances in the pharmaceutical treatment options for canine osteoarthritis

Canine osteoarthritis is a significant cause of pain in many dogs and can therefore compromise animal welfare. As the understanding of the biology and pain mechanisms underpinning osteoarthritis grows, so do the number of treatments available to manage it. Over the last decade, there have been a number of advances in the pharmaceutical treatment options available for dogs with osteoarthritis, as well as an increasing number of clinical trials investigating the efficacy of pre-existing treatments. This review aims to examine the current evidence behind pharmaceutical treatment options for canine osteoarthritis, including non-steroidal anti-inflammatory drugs, piprants, monoclonal antibodies, adjunctive analgesics, structure modifying osteoarthritis drugs and regenerative therapies.

Effect of Exercises on Central and Endocrine System for Pain Modulation in Primary Dysmenorrhea

Dysmenorrhea is the term for describing complex menstrual flow and painful spasmodic cramps during menstruation, and pain without any pathology is considered Primary Dysmenorrhea (PD). It is the most frequent ailment among women of all ages and races. The pain is dull and throbbing in character and occurs in the lower back and abdomen. Symptoms commonly appear 6 to 12 months after menarche, with the most significant incidence in the late teen and early twenties. Physical exercise is nearly a new non-medical intervention to relieve PD associated pain. Aerobics, stretching and Resistive exercises for 8-12 weeks, either supervised or unsupervised, relieves pain. Exercises are believed to cause hormonal changes in the uterine lining, which reduces PD symptoms. Researchers have presumed different pain-relieving methods, ranging from non-opioids to opioids to hormonal for variations in pain sensitivity. Exercise-induced analgesia provides the central pathway as the primary mechanism for pain reduction while, another way to reducing pain in PD may be a hormonal interaction. The hormonal changes causing exercise-induced pain modulation during the menstruation cycle is not clearly understood and the interaction and activation of all the central and endocrine components, which is a complex mechanism, is also not explained clearly. This study briefly reviews the physiological mechanism of Exercise-induced analgesia and its potent roles in controlling the pathogenesis of PD for pain relief.

Noncanonical Activity of Endocannabinoids and Their Receptors in Central and Peripheral Synapses

This review focuses on new aspects of endocannabinoid functions and mechanisms of activity in central and peripheral synapses, different from the general viewpoint that endocannabinoids are retrograde signaling molecules, which inhibit neurotransmitter release by activating specific presynaptic endocannabinoid receptors CB1 and CB2. Biased agonism of the endogenous and synthetic cannabinoids as well as ability of the CB-receptors to couple not only with classical G_i-proteins, but also with G_s- and G_q-proteins and, moreover, with β-arrestins (thereby triggering additional signaling pathways in synapses) are described here in detail. Examples of noncanonical tonic activity of endocannabinoids and their receptors and their role in synaptic function are also presented. The role of endocannabinoids in short-term and long-term potentiation of neurotransmitter release in central synapses and their facilitating effect on quantal size and other parameters of acetylcholine release in mammalian neuromuscular junctions are highlighted in this review. In conclusion, it is stated that the endocannabinoid system has a wider range of various multidirectional modulating effects (both potentiating and inhibiting) on neurotransmitter release than initially recognized. Re-evaluation of the functions of endocannabinoid system with consideration of its noncanonical features will lead to better understanding of its role in the normal and pathological functioning of the nervous system and other systems of the body, which has an enormous practical value.

Cannabinoids in the Treatment of Back Pain

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

Cannabinoid Receptors and Their Relationship With Chronic Pain: A Narrative Review

The burden of chronic pain has affected many individuals leading to distress and discomfort, alongside numerous side effects with conventional therapeutic approaches. Cannabinoid receptors are naturally found in the human body and have long been an interest in antinociception. These include CB1 and CB2 receptors, which are promising candidates for the treatment of chronic inflammatory pain. The mechanism of action of the receptors and how they approach pain control in inflammatory conditions show that it can be an adjunctive approach towards controlling these symptoms. Numerous studies have shown how the targeted approach towards these receptors has activated them promoting a release in cytokines, all leading to anti-inflammatory effects and immune system regulation. Cannabinoid activation of glycine and gamma-aminobutyric acid (GABA) models also showed efficacy in pain management. Chronic conditions such as osteoarthritis were shown to also benefit from this considerable treatment. However, it is unclear how the cannabinoid system works in relation with the pain pathway. Therefore, in this review we aim to analyse the role of the cannabinoid system in chronic inflammatory pain.

Neuropathic Pain and Sickle Cell Disease: a Review of Pharmacologic Management

PURPOSE OF REVIEW

Sickle cell disease (SCD) remains among the most common and severe monogenic disorders present in the world today. Although sickle cell pain has been traditionally characterized as nociceptive, a significant portion of sickle cell patients has reported neuropathic pain symptoms. Our review article will discuss clinical aspects of SCD-related neuropathic pain, epidemiology of neuropathic pain among individuals with SCD, pain mechanisms, and current and future potential pharmacological interventions.

RECENT FINDINGS

Neuropathic pain in SCD is a complicated condition that often has a lifelong and significant negative impact on life; therefore, improved pain management is considered a significant and unmet need. Neuropathic pain mechanisms are heterogeneous, and the difficulty in determining their individual contribution to specific pain types may contribute to poor treatment outcomes in this population. Our review article outlines several pharmacological modalities which may be employed to treat neuropathic pain in SCD patients.

Physical Pain as Pleasure: A Theoretical Perspective

Physical pain represents a common feature of Bondage and Discipline/Dominance and Submission/Sadism and Machochism (BDSM) activity. This article explores the literature accounting for how painful stimuli may be experienced as pleasurable among practitioners of BDSM, and contrasting this with how it is experienced as painful among non-BDSM individuals. We reviewed the available literature on pain and on BDSM, and used the findings to postulate a theory accounting for how painful stimuli are experienced as pleasurable. Our theory was then checked with BDSM practitioners. The emotional, physiological, and psychological elements of pain interact to facilitate the experience of pain as pleasure in BDSM. A multitude of interconnected factors was theorized to alter the experience of BDSM pain, including: neural networks, neurotransmitters, endogenous opioids and endocannabinoids, visual stimuli, environmental context, emotional state, volition and control, interpersonal connection, sexual arousal, and memories. The experience of pain in this context can bring about altered states of consciousness that may be similar to what occurs during mindfulness meditation. Through understanding the mechanisms by which pain may be experienced as pleasure, the role of pain in BDSM is demystified and, it is hoped, destigmatized.

The Endogenous Cannabinoid System: A Budding Source of Targets for Treating Inflammatory and Neuropathic Pain

A great need exists for the development of new medications to treat pain resulting from various disease states and types of injury. Given that the endogenous cannabinoid (that is, endocannabinoid) system modulates neuronal and immune cell function, both of which play key roles in pain, therapeutics targeting this system hold promise as novel analgesics. Potential therapeutic targets include the cannabinoid receptors, type 1 and 2, as well as biosynthetic and catabolic enzymes of the endocannabinoids N-arachidonoylethanolamine and 2-arachidonoylglycerol. Notably, cannabinoid receptor agonists as well as inhibitors of endocannabinoid-regulating enzymes fatty acid amide hydrolase and monoacylglycerol lipase produce reliable antinociceptive effects, and offer opioid-sparing antinociceptive effects in myriad preclinical inflammatory and neuropathic pain models. Emerging clinical studies show that 'medicinal' cannabis or cannabinoid-based medications relieve pain in human diseases such as cancer, multiple sclerosis, and fibromyalgia. However, clinical data have yet to demonstrate the analgesic efficacy of inhibitors of endocannabinoid-regulating enzymes. Likewise, the question of whether pharmacotherapies aimed at the endocannabinoid system promote opioid-sparing effects in the treatment of pain reflects an important area of research. Here we examine the preclinical and clinical evidence of various endocannabinoid system targets as potential therapeutic strategies for inflammatory and neuropathic pain conditions.

Cannabinoids and Pain: Sites and Mechanisms of Action

The endocannabinoid system, consisting of the cannabinoid₁ receptor (CB₁R) and cannabinoid₂ receptor (CB₂R), endogenous cannabinoid ligands (endocannabinoids), and metabolizing enzymes, is present throughout the pain pathways. Endocannabinoids, phytocannabinoids, and synthetic cannabinoid receptor agonists have antinociceptive effects in animal models of acute, inflammatory, and neuropathic pain. CB₁R and CB₂R located at peripheral, spinal, or supraspinal sites are important targets mediating these antinociceptive effects. The mechanisms underlying the analgesic effects of cannabinoids likely include inhibition of presynaptic neurotransmitter and neuropeptide release, modulation of postsynaptic neuronal excitability, activation of the descending inhibitory pain pathway, and reductions in neuroinflammatory signaling. Strategies to dissociate the psychoactive effects of cannabinoids from their analgesic effects have focused on peripherally restricted CB₁R agonists, CB₂R agonists, inhibitors of endocannabinoid catabolism or uptake, and modulation of other non-CB₁R/non-CB₂R targets of cannabinoids including TRPV1, GPR55, and PPARs. The large body of preclinical evidence in support of cannabinoids as potential analgesic agents is supported by clinical studies demonstrating their efficacy across a variety of pain disorders.

Pharmacological characterization of rat VD-hemopressin(α), an α-hemoglobin-derived peptide exhibiting cannabinoid agonist-like effects in mice

Hemopressin and related peptides have shown to function as the endogenous ligands or the regulator of cannabinoid receptors. Moreover, hemopressin and its truncated peptides were also reported to produce a slight modulatory effect on opioid system. In the present work, based on the amino acid sequence analyses of hemoglobin subunit α, rat VD-hemopressin(α) [(r)VD-Hpα] was predicted as a cannabinoid peptide derived from rat α-hemoglobin. Furthermore, (r)VD-Hpα was synthesized and characterized in a series of in vitro and in vivo assays. Our results demonstrated that (r)VD-Hpα induced neurite outgrowth in Neuro 2A cells via CB₁ receptor. In the tail-flick assay, (r)VD-Hpα dose-dependently exerted central antinociception through CB₁ receptor, but not CB₂ and opioid receptors. In mice, supraspinal administration of (r)VD-Hpα produced dose-dependent hypothermia, which was partially reduced by the CB₁ receptor antagonist AM251, but not by the antagonists of CB₂ and opioid receptors. In addition, (r)VD-Hpα caused hypoactivity after intracerebroventricular injection, and this effect was insensitive to the antagonists of cannabinoid and opioid receptors. Further assessment of the side-effects demonstrated that (r)VD-Hpα evoked the limited effects on gastrointestinal transit at antinociceptive doses, but repeated i.c.v. injection of (r)VD-Hpα induced development of antinociceptive tolerance. Taken together, these data suggest that the predicted peptide (r)VD-Hpα produces antinociception, hypothermia and hypoactivity via different pharmacological mechanisms, at least partially, which may offer an attractive strategy for separating cannabinoid analgesia from hypoactivity. Moreover, it implies that (r)VD-Hpα has therapeutic potential in pain management with limited side-effects.

The endocannabinoid system, a novel and key participant in acupuncture's multiple beneficial effects

Acupuncture and its modified forms have been used to treat multiple medical conditions, but whether the diverse effects of acupuncture are intrinsically linked at the cellular and molecular level and how they might be connected have yet to be determined. Recently, an emerging role for the endocannabinoid system (ECS) in the regulation of a variety of physiological/pathological conditions has been identified. Overlap between the biological and therapeutic effects induced by ECS activation and acupuncture has facilitated investigations into the participation of ECS in the acupuncture-induced beneficial effects, which have shed light on the idea that the ECS may be a primary mediator and regulatory factor of acupuncture's beneficial effects. This review seeks to provide a comprehensive summary of the existing literature concerning the role of endocannabinoid signaling in the various effects of acupuncture, and suggests a novel notion that acupuncture may restore homeostasis under different pathological conditions by regulating similar networks of signaling pathways, resulting in the activation of different reaction cascades in specific tissues in response to pathological insults.

Survey of cannabis use in patients with amyotrophic lateral sclerosis

Cannabis (marijuana) has been proposed as treatment for a widening spectrum of medical conditions and has many properties that may be applicable to the management of amyotrophic lateral sclerosis (ALS). This study is the first, anonymous survey of persons with ALS regarding the use of cannabis. There were 131 respondents, 13 of whom reported using cannabis in the last 12 months. Although the small number of people with ALS that reported using cannabis limits the interpretation of the survey findings, the results indicate that cannabis may be moderately effective at reducing symptoms of appetite loss, depression, pain, spasticity, and drooling. Cannabis was reported ineffective in reducing difficulties with speech and swallowing, and sexual dysfunction. The longest relief was reported for depression (approximately two to three hours).

Intranasal Oxytocin Administration is Associated With Enhanced Endogenous Pain Inhibition and Reduced Negative Mood States

OBJECTIVES

This study examined whether the administration of intranasal oxytocin was associated with pain sensitivity, endogenous pain inhibitory capacity, and negative mood states.

MATERIALS AND METHODS

A total of 30 pain-free, young adults each completed 3 laboratory sessions on consecutive days. The first session (baseline) assessed ischemic pain sensitivity, endogenous pain inhibition via conditioned pain modulation (CPM), and negative mood using the Profile of Mood States. CPM was tested on the dominant forearm and ipsilateral masseter muscle using algometry (test stimulus) and the cold pressor task (conditioning stimulus; nondominant hand). For the second and third sessions, participants initially completed the State-Trait Anxiety Inventory and then self-administered a single (40 IU/1 mL) dose of intranasal oxytocin or placebo in a randomized counterbalanced order. Thirty minutes postadministration, participants again completed the State-Trait Anxiety Inventory and repeated assessments of ischemic pain sensitivity and CPM followed by the Profile of Mood States.

RESULTS

Findings demonstrated that ischemic pain sensitivity did not significantly differ across the 3 study sessions. CPM at the masseter, but not the forearm, was significantly greater following administration of oxytocin compared to placebo. Negative mood was also significantly lower following administration of oxytocin compared to placebo. Similarly, anxiety significantly decreased following administration of oxytocin but not placebo.

DISCUSSION

This study incorporated a placebo-controlled, double-blind, within-subjects crossover design with randomized administration of intranasal oxytocin and placebo. The data suggest that the administration of intranasal oxytocin may augment endogenous pain inhibitory capacity and reduce negative mood states including anxiety.

Antinociceptive effects of central administration of the endogenous cannabinoid receptor type 1 agonist VDPVNFKLLSH-OH [(m)VD-hemopressin(α)], an N-terminally extended hemopressin peptide

The cannabinoid system has been demonstrated to modulate the acute and chronic pain of multiple origins. Mouse VD-hemopressin(α) [(m)VD-Hpα], an 11-residue α-hemoglobin-derived peptide, was recently reported to function as a selective agonist of the cannabinoid receptor type 1 (CB₁) in vitro. To characterize its behavioral and physiological properties, we investigated the in vivo effects of (m)VD-Hpα in mice. In the mouse tail-flick test, (m)VD-Hpα dose-dependently induced antinociception after supraspinal (EC₅₀ = 6.69 nmol) and spinal (EC₅₀ = 2.88 nmol) administration. The antinociceptive effects of (m)VD-Hpα (intracerebroventricularly and intrathecally) were completely blocked by N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3- carboxamide (AM251; CB₁ antagonist), but not by 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl(4-methoxyphenyl)-methanone (AM630; CB₂ antagonist) or naloxone (opioid antagonist), showing its selectivity to the CB₁ receptor. Furthermore, the central nervous system (CNS) effects of (m)VD-Hpα were evaluated in body temperature, locomotor activity, tolerance development, reward, and food intake assays. At the highly antinociceptive dose (3 × EC₅₀), (m)VD-Hpα markedly exerted hypothermia and hypoactivity after supraspinal administration. Repeated intracerebroventricular injection of (m)VD-Hpα resulted in both development of tolerance to antinociception and conditioned place aversion. In addition, central injection of (m)VD-Hpα dose-dependently stimulated food consumption. These findings demonstrate that this novel cannabinoid peptide agonist induces CB₁-mediated central antinociception with some CNS effects, which further supports a CB₁ agonist character of (m)VD-Hpα. Moreover, the current study will be helpful to understand the in vivo properties of the endogenous peptide agonist of the cannabinoid CB₁ receptor.

Cannabinergic pain medicine: a concise clinical primer and survey of randomized-controlled trial results

OBJECTIVES

This article attempts to cover pragmatic clinical considerations involved in the use of cannabinergic medicines in pain practice, including geographical and historical considerations, pharmacokinetics, pharmacodynamics, adverse effects, drug interactions, indications, and contraindications. Topics include molecular considerations such as the 10-fold greater abundance of cannabinoid type 1 receptors compared to µ-opioid receptors in the central nervous system and anatomic distributions of cannabinoid receptors in pain circuits.

METHODS

The article uses a narrative review methodology drawing from authoritative textbooks and journals of cannabinoid medicine, Food and Drug Administration-approved cannabinoid drug labels, and current and historical pain medicine literature to address core clinical considerations. To survey the current evidence base for pain management with cannabinergic medicines, a targeted PubMed search was performed to survey the percentage of positive and negative published randomized-controlled trial (RCT) results with this class of pain medicines, using appropriate search limit parameters and the keyword search string "cannabinoid OR cannabis-based AND pain."

RESULTS

Of the 56 hits generated, 38 published RCTs met the survey criteria. Of these, 71% (27) concluded that cannabinoids had empirically demonstrable and statistically significant pain-relieving effects, whereas 29% (11) did not.

DISCUSSION

Cannabis and other cannabinergic medicines' efficacies for relieving pain have been studied in RCTs, most of which have demonstrated a beneficial effect for this indication, although most trials are short-term. Adverse effects are generally nonserious and well tolerated. Incorporating cannabinergic medicine topics into pain medicine education seems warranted and continuing clinical research and empiric treatment trials are appropriate.

Cannabinoids and muscular pain. Effectiveness of the local administration in rat

BACKGROUND

Pain associated with musculoskeletal disorders can be difficult to control and the incorporation of new approaches for its treatment is an interesting challenge. Activation of cannabinoid (CB) receptors decreases nociceptive transmission in acute, inflammatory and neuropathic pain states; however, although the use of cannabis derivatives has been recently accepted as a useful alternative for the treatment of spasticity and pain in patients with multiple sclerosis, the effects of CB receptor agonists in muscular pain have hardly been studied.

METHODS

Here, we characterized the antinociceptive effect of non selective and selective CB agonists by systemic and local administration, in two muscular models of pain, masseter and gastrocnemius, induced by hypertonic saline (HS) injection. Drugs used were: the non-selective agonist WIN 55,212-2 and two selective agonists, ACEA (CB 1) and JWH 015 (CB 2); AM 251 (CB 1) and AM 630 (CB 2) were used as selective antagonists.

RESULTS

In the masseter pain model, both systemic (intraperitoneal) and local (intramuscular) administration of CB 1 and CB 2 agonists reduced the nociceptive behaviour induced by HS, whereas in the gastrocnemius model the local administration was more effective than systemic.

CONCLUSIONS

Our results provide evidence that both, CB 1 and CB 2 receptors can contribute to muscular antinociception and, interestingly, suggest that the local administration of CB agonists could be a new and useful pharmacological strategy in the treatment of muscular pain, avoiding adverse effects induced by systemic administration.

Fat to treat fat: emerging relationship between dietary PUFA, endocannabinoids, and obesity

Obesity incidence continues to escalate as a global nutrition and health problem. Scientists and clinicians are engaged in numerous research approaches that include behavior, education, applied nutrition studies and clinical therapies to prevent, control and reverse obesity. The common goal is to identify areas of basic and clinical research to understand aspects of human biology that contribute to obesity. In these approaches recent discoveries in biology and advancing technologies are tools employed to prevent and reverse obesity. The purpose of this review article is to present the current knowledge of key components of the endocannabinoid system that contribute to eating, influence systemic energy metabolism, and dietary factors that alter the responses of ligand binding and activation of cannabinoid receptors. Herein the objectives are to (1) describe the relationship between dietary polyunsaturated fatty acids (PUFA) and obesity, (2) explain the role of this signaling system in obesity, and (3) present areas of consequential future research with dietary long chain PUFA. There are several gaps in the knowledge of the role dietary PUFA play in the tone of the endocannabinoid signaling system involving ligands and receptors. Elucidating the PUFA relationship to signaling tone may explain the presumed overstimulation of signaling believed to contribute to over eating, fat accretion and inflammation. Future research in this endeavor must be hypothesis driven utilizing appropriate models for investigations on dietary PUFA, endocannabinoids and obesity.

Cannabinoid CB(2) receptor attenuates morphine-induced inflammatory responses in activated microglial cells

BACKGROUND AND PURPOSE

Among several pharmacological properties, analgesia is the most common feature shared by either opioid or cannabinoid systems. Cannabinoids and opioids are distinct drug classes that have been historically used separately or in combination to treat different pain states. In the present study, we characterized the signal transduction pathways mediated by cannabinoid CB(2) and µ-opioid receptors in quiescent and LPS-stimulated murine microglial cells.

EXPERIMENTAL APPROACH

We examined the effects of µ-opioid and CB(2) receptor stimulation on phosphorylation of MAPKs and Akt and on IL-1β, TNF-α, IL-6 and NO production in primary mouse microglial cells.

KEY RESULTS

Morphine enhanced release of the proinflammatory cytokines, IL-1β, TNF-α, IL-6, and of NO via µ-opioid receptor in activated microglial cells. In contrast, CB(2) receptor stimulation attenuated morphine-induced microglial proinflammatory mediator increases, interfering with morphine action by acting on the Akt-ERK1/2 signalling pathway.

CONCLUSIONS AND IMPLICATIONS

Because glial activation opposes opioid analgesia and enhances opioid tolerance and dependence, we suggest that CB(2) receptors, by inhibiting microglial activity, may be potential targets to increase clinical efficacy of opioids.

Linoleoyl ethanolamide reduces lipopolysaccharide-induced inflammation in macrophages and ameliorates 2,4-dinitrofluorobenzene-induced contact dermatitis in mice

In our previous study, it was found that linoleoyl ethanolamide (LE) is present in sake lees, which are produced as a byproduct during the making of Japanese sake. LE is a fatty acid ethanolamide, which have been demonstrated to exert a variety of biological functions, and in this study, the anti-inflammatory effects of LE were examined using in vitro cell culture and in vivo animal experiments. In mouse RAW264.7 macrophages, LE suppressed the lipopolysaccharide (LPS)-induced expression of pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6. In addition, LE inhibited LPS-induced increases in the levels of cyclooxygenase enzyme-2 and prostaglandin E(2), which are indicators of inflammation. The inhibitory effect of LE on the release of TNF-α was stronger than that of dipotassium glycyrrhizinate, which is widely used in external human skin care treatments. LE also suppressed the LPS-induced activation of Toll-like receptor 4 signaling and nuclear translocation of nuclear factor-κB (NF-κB) p65. In a contact dermatitis animal model, applying LE to affected ear skin ameliorated 2,4-dinitrofluorobenzene-induced contact dermatitis and pro-inflammatory cytokine expression at inflamed sites. These results indicate that LE exerts anti-inflammatory effects by inhibiting NF-κB signaling, and LE is proposed to be a useful therapeutic agent against contact dermatitis.

Exercise-induced endocannabinoid signaling is modulated by intensity

Endocannabinoids (eCB) are endogenous ligands for cannabinoid receptors that are densely expressed in brain networks responsible for reward. Recent work shows that exercise activates the eCB system in humans and other mammals, suggesting eCBs are partly responsible for the reported improvements in mood and affect following aerobic exercise in humans. However, exercise-induced psychological changes reported by runners are known to be dependent on exercise intensity, suggesting that any underlying molecular mechanism should also change with varying levels of exercise intensity. Here, we examine circulating levels of eCBs following aerobic exercise (treadmill running) in recreationally fit human runners at four different intensities. We show that eCB signaling is indeed intensity dependent, with significant changes in circulating eCBs observed following moderate intensities only (very high and very low intensity exercises do not significantly alter circulating eCB levels). Our results are consistent with intensity-dependent psychological state changes with exercise and therefore support the hypothesis that eCB activity is related to neurobiological effects of exercise. Thus, future studies examining the role of exercise-induced eCB signaling on neurobiology or physiology must take exercise intensity into account.

Treating pain in multiple sclerosis

INTRODUCTION

Multiple sclerosis (MS) is an inflammatory, demyelinating, central nervous system disease that frequently causes pain.

AREAS COVERED

This article reviews the current literature and describes the therapeutic options for treating MS-related pain. The reader will be provided with current, evidence-based knowledge about the treatment of MS-related pain, and the review will take a practical approach to the various drugs for treating pain, including starting dose, titration and side effects.

EXPERT OPINION

Only cannabinoids have been assessed in randomized, controlled trials. Because of the concern regarding the risk of abuse and psychiatric adverse events, published guidelines as well as expert recommendations suggest using them as second-line therapy only. Hence, current treatment should be based on the general principles for treating peripheral neuropathic pain, taking into account drug-induced adverse effects.

The effect of chronic opioid vs. cannabinoid exposure on the expression of tolerance to morphine- or WIN-55,212-2-induced analgesia and hypothermia in the guinea pig

Earlier studies using the guinea pig longitudinal muscle/myenteric plexus (LM/MP) demonstrated that chronic morphine treatment in vivo leads to the development of heterologous tolerance while chronic treatment with WIN 55,212-2 induces homologous tolerance. Few studies have evaluated whether a similar difference in tolerance development exists to the analgesic or hypothermic effects of these agents. Tolerance produced following chronic morphine (7 days) or WIN-55,212-2 (5 days) injection was assessed by determining the alteration in hypothermic response (using a rectal thermometer) or mechanical (paw pressure) or thermal (hot plate) analgesic threshold to challenge doses of WIN-55,212-2 and morphine. The tolerance observed in the hot plate test corresponded closely to that observed in the LM/MP studies where morphine pretreatment produced heterologous tolerance and WIN-55,212-2 pretreatment induced homologous tolerance. In contrast, chronic WIN-55,212-2 pretreatment precipitated tolerance to the analgesic effect of morphine in the paw pressure model despite the absence of an analgesic effect to this agent. Unlike chronic treatment with WIN-55,212-2, no tolerance to the hypothermic effect of WIN-55,212-2 was observed following morphine treatment. However, the hypothermic response observed to morphine challenge was modest suggesting that tolerance to this effect may be difficult to assess or not biologically relevant. The non-uniform character of tolerance observed in different models further suggests that the analysis of tolerance using in vivo test systems involves complex neuronal interactions in which altered responsiveness at one site may produce cascading cellular effects within a neuronal circuit that may differentially impact on tolerance expression.

Contemporary and emergent pharmacological therapies for chronic pain: nonopioid analgesia

The American Pain Society estimates that 50 million Americans are partially or totally disabled by pain. This striking statistic is certain to increase as our population continues to age. In order to combat this growing problem, healthcare professionals must arm themselves with information. By developing the appropriate pain assessment skills and by staying abreast of the rapidly-changing therapies used in pain management, clinicians can dramatically impact the quality of life of those living with pain.

Cannabis and Amyotrophic Lateral Sclerosis: Hypothetical and Practical Applications, and a Call for Clinical Trials

Significant advances have increased our understanding of the molecular mechanisms of amyotrophic lateral sclerosis (ALS), yet this has not translated into any greatly effective therapies. It appears that a number of abnormal physiological processes occur simultaneously in this devastating disease. Ideally, a multidrug regimen, including glutamate antagonists, antioxidants, a centrally acting anti-inflammatory agent, microglial cell modulators (including tumor necrosis factor alpha [TNF-α] inhibitors), an antiapoptotic agent, 1 or more neurotrophic growth factors, and a mitochondrial function-enhancing agent would be required to comprehensively address the known pathophysiology of ALS. Remarkably, cannabis appears to have activity in all of those areas. Preclinical data indicate that cannabis has powerful antioxidative, anti-inflammatory, and neuroprotective effects. In the G93A-SOD1 ALS mouse, this has translated to prolonged neuronal cell survival, delayed onset, and slower progression of the disease. Cannabis also has properties applicable to symptom management of ALS, including analgesia, muscle relaxation, bronchodilation, saliva reduction, appetite stimulation, and sleep induction. With respect to the treatment of ALS, from both a disease modifying and symptom management viewpoint, clinical trials with cannabis are the next logical step. Based on the currently available scientific data, it is reasonable to think that cannabis might significantly slow the progression of ALS, potentially extending life expectancy and substantially reducing the overall burden of the disease.

Opioid receptor and NO/cGMP pathway as a mechanism of peripheral antinociceptive action of the cannabinoid receptor agonist anandamide

AIMS

In this study, we investigated whether the opioid system and the nitric oxide pathway were involved in the peripheral antinociception induced by a cannabinoid receptor agonist anandamide.

MAIN METHODS

Hyperalgesia was induced by a subcutaneous injection of carrageenan (250 microg) into the plantar surface of the rat's hindpaw and measured by the paw pressure test 3h after injection. The weight in grams (g) required to elicit a nociceptive response, paw flexion, was determined as the nociceptive threshold.

KEY FINDINGS

Anandamide elicited a dose-dependent (50, 75, and 100 ng per paw) antinociceptive effect. The highest dose of anandamide did not produce antihyperalgesia in the contralateral paw, indicating a peripheral site of action. The CB(1) receptor antagonist AM251 (20, 40, 80 and 160mug per paw) antagonized peripheral antihyperalgesia induced by anandamide (100 ng), in a dose-dependent manner, suggesting CB(1) receptor activation. Anandamide-induced peripheral antihyperalgesia was reverted by blockers of the l-arginine/NO/cGMP pathway N(G)-nitro-l-arginine (NOARG; 24, 36 and 48 microg per paw) and 1H-[1,2,4] Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 25, 50 and 100 microg per paw), in a dose-dependent manner. Furthermore, opioid receptor antagonist naloxone (12.5, 25 and 50 microg per paw) antagonized the peripheral antihyperalgesia induced by anandamide.

SIGNIFICANCE

This study provides evidence that the peripheral antinociceptive effect of the cannabinoid receptor agonist anandamide may result from l-arginine/NO/cGMP pathway activation and that the opioid system is also involved.

Differential response to a selective cannabinoid receptor antagonist (SR141716: rimonabant) in female mice from lines selectively bred for high voluntary wheel-running behaviour

Exercise is a naturally rewarding behaviour in human beings and can be associated with feelings of euphoria and analgesia. The endocannabinoid system may play a role in the perception of neurobiological rewards during and after prolonged exercise. Mice from lines that have been selectively bred for high voluntary wheel running (high runner or HR lines) may have evolved neurobiological mechanisms that increase the incentive salience of endurance-type exercise. Here, we test the hypothesis that endocannabinoid signalling has been altered in the four replicate HR lines as compared with four nonselected control lines. After 18 days of acclimation to cages with attached wheels, we injected mice with rimonabant (SR141716), a selective cannabinoid CB1 receptor antagonist. During the time of normal peak running, each mouse received, in a randomized order, intraperitoneal injection of rimonabant (0.1 or 3.0 mg/kg) or vehicle, over 9 days. Drug response was quantified as wheel revolutions, time and speed 10-70 min postinjection. Rimonabant decreased running in all mice; however, female HR mice differentially decreased running speed and distance (but not time) as compared with control females. We conclude that altered endocannabinoid signalling plays a role in the high wheel running of female HR mice.

The mu-opioid receptor agonist morphine, but not agonists at delta- or kappa-opioid receptors, induces peripheral antinociception mediated by cannabinoid receptors

BACKGROUND AND PURPOSE

Although participation of opioids in antinociception induced by cannabinoids has been documented, there is little information regarding the participation of cannabinoids in the antinociceptive mechanisms of opioids. The aim of the present study was to determine whether endocannabinoids could be involved in peripheral antinociception induced by activation of mu-, delta- and kappa-opioid receptors.

EXPERIMENTAL APPROACH

Nociceptive thresholds to mechanical stimulation of rat paws treated with intraplantar prostaglandin E2 (PGE2, 2 microg) to induce hyperalgesia were measured 3 h after injection using an algesimetric apparatus. Opioid agonists morphine (200 microg), (+)-4-[(alphaR)-alpha-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80) (80 microg), bremazocine (50 microg); cannabinoid receptor antagonists N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) (20-80 microg), 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl(4-methoxyphenyl) methanone (AM630) (12.5-100 microg); and an inhibitor of methyl arachidonyl fluorophosphonate (MAFP) (1-4 microg) were also injected in the paw.

KEY RESULTS

The CB1-selective cannabinoid receptor antagonist AM251 completely reversed the peripheral antinociception induced by morphine in a dose-dependent manner. In contrast, the CB2-selective cannabinoid receptor antagonist AM630 elicited partial antagonism of this effect. In addition, the administration of the fatty acid amide hydrolase inhibitor, MAFP, enhanced the antinociception induced by morphine. The cannabinoid receptor antagonists AM251 and AM630 did not modify the antinociceptive effect of SNC80 or bremazocine. The antagonists alone did not cause any hyperalgesic or antinociceptive effect.

CONCLUSIONS AND IMPLICATIONS

Our results provide evidence for the involvement of endocannabinoids, in the peripheral antinociception induced by the mu-opioid receptor agonist morphine. The release of cannabinoids appears not to be involved in the peripheral antinociceptive effect induced by kappa- and delta-opioid receptor agonists.

Adjuvant analgesics

Adjuvant analgesics represent a diverse group of drugs that were originally developed for a primary indication other than pain. Many of these medications are currently used to enhance analgesia under specific circumstances. The proper use of adjuvant drugs is one of the keys to success in effective pain management. Since adjuvant analgesics are typically administered to patients who take multiple medications, decisions regarding administration and dosage must be made with a clear understanding of the stage of the disease and the goals of care. The article discusses major classes of adjuvant analgesics, with the focus on the mechanism of action, clinical application, and risks and benefits associated with each particular class of adjuvants.

New 1,2,3,4-tetrahydropyrrolo[3,4-b]indole derivatives as selective CB2 receptor agonists

The preparation and evaluation of a novel class of CB2 agonists based on a 1,2,3,4-tetrahydropyrrolo[3,4-b]indole moiety are reported. They showed binding affinities up to 4.2 nM toward CB2 with sub-nanomolar EC(50) values. They also showed moderate to good (>350-fold) selectivity over the CB1 receptor.

The antinociceptive effect of Delta9-tetrahydrocannabinol in the arthritic rat involves the CB(2) cannabinoid receptor

Cannabinoid CB(2) receptors have been implicated in antinociception in animal models of both acute and chronic pain. We evaluated the role both cannabinoid CB(1) and CB(2) receptors in mechanonociception in non-arthritic and arthritic rats. The antinociceptive effect of Delta(9)-tetrahydrocannabinol (Delta(9)THC) was determined in rats following administration of the cannabinoid CB(1) receptor-selective antagonist, SR141716A, the cannabinoid CB(2) receptor-selective antagonist, SR144528, or vehicle. Male Sprague-Dawley rats were rendered arthritic using Freund's complete adjuvant and tested for mechanical hyperalgesia in the paw-pressure test. Arthritic rats had a baseline paw-pressure of 83 +/- 3.6 g versus a paw-pressure of 177 +/- 6.42 g in non-arthritic rats. SR144528 or SR141716A (various doses mg/kg; i.p.) or 1:1:18 (ethanol:emulphor:saline) vehicle were injected 1 h prior to Delta(9)THC (4 mg/kg; i.p) or 1:1:18 vehicle and antinociception determined 30min post Delta(9)THC. AD(50)'s for both antagonists were calculated with 95% confidence limits. In addition, midbrain and spinal cord were removed for determination of cannabinoid CB(1) and CB(2) receptor protein density in the rats. SR144528 significantly attenuated the antinociceptive effect of Delta(9)THC in the arthritic rats [AD(50) = 3.3 (2.7-4) mg/kg], but not in the non-arthritic rats at a dose of 10/mg/kg. SR141716A significantly attenuated Delta(9)THC-induced antinociception in both the non-arthritic [AD(50) = 1.4 (0.8-2) mg/kg] and arthritic rat [AD(50) = 2.6 (1.8-3.1) mg/kg]. SR141716A or SR144528 alone did not result in a hyperalgesic effect as compared to vehicle. Our results indicate that the cannabinoid CB(2) receptor plays a critical role in cannabinoid-mediated antinociception, particularly in models of chronic inflammatory pain.