Epicutaneous Sensitization to the Phytocannabinoid ß-Caryophyllene Induces Pruritic Inflammation.

In recent years, there has been increased accessibility to cannabis for recreational and medicinal use. Incidentally, there has been an increase in reports describing allergic reactions to cannabis including exacerbation of underlying asthma. Recently, multiple protein allergens were discovered in cannabis, yet these fail to explain allergic sensitization in many patients, particularly urticaria and angioedema. Cannabis has a rich chemical profile including cannabinoids and terpenes that possess immunomodulatory potential. We examined whether major cannabinoids of cannabis such as cannabidiol (CBD) and the bicyclic sesquiterpene beta-caryophyllene (ß-CP) act as contact sensitizers. The repeated topical application of mice skin with ß-CP at 10 mg/mL (50 µL) induced an itch response and dermatitis at 2 weeks in mice, which were sustained for the period of study. Histopathological analysis of skin tissues revealed significant edema and desquamation for ß-CP at 10 mg/mL. For CBD and ß-CP, we observed a dose-dependent increase in epidermal thickening with profound thickening observed for ß-CP at 10 mg/mL. Significant trafficking of CD11b cells was observed in various compartments of the skin in response to treatment with ß-CP in a concentration-dependent manner. Mast cell trafficking was restricted to ß-CP (10 mg/mL). Mouse proteome profiler cytokine/chemokine array revealed upregulation of complement C5/5a (anaphylatoxin), soluble intracellular adhesion molecule-1 (sICAM-1) and IL-1 receptor antagonist (IL-1RA) in animals dosed with ß-CP (10 mg/mL). Moreover, we observed a dose-dependent increase in serum IgE in animals dosed with ß-CP. Treatment with ß-CP (10 mg/mL) significantly reduced filaggrin expression, an indicator of barrier disruption. In contrast, treatment with CBD at all concentrations failed to evoke scratching and dermatitis in mice and did not result in increased serum IgE. Further, skin tissues were devoid of any remarkable features, although at 10 mg/mL CBD we did observe the accumulation of dermal CD11b cells in skin tissue sections. We also observed increased filaggrin staining in mice repeatedly dosed with CBD (10 mg/mL). Collectively, our studies indicate that repeated exposure to high concentrations of ß-CP can induce dermatitis-like pathological outcomes in mice.

Mitragynine, bioactive alkaloid of kratom, reduces chemotherapy-induced neuropathic pain in rats through α-adrenoceptor mechanism.

BACKGROUND AND PURPOSE: Kratom is a coffee-like plant containing compounds that cause opioid and stimulant effects. The most prevalent bioactive alkaloid of kratom is mitragynine (MG). Opioid effects of MG are apparent (e.g. antinociception and nanomolar affinity for µ, κ and δ opioid receptors), but effects encompassing interactions with additional systems, such as adrenergic and dopaminergic, remain undefined. Given that enhanced adrenergic transmission is a mechanism common to most first-line neuropathic pain medications, we tested the hypothesis that MG reduces chemotherapy-induced neuropathic pain through a mechanism involving α-adrenoceptor activation. METHODS: Rats were injected once with oxaliplatin (6 mg/kg IP) to induce allodynia and then treated with MG (0, 1, 5, 10 mg/kg IP) for 5-7 days. To investigate receptor mechanisms, a fixed dose of MG (5 mg/kg IP) was injected with yohimbine (5 mg/kg IP, α2-adrenoceptor antagonist), prazosin (5 mg/kg IP, α1-adrenoceptor antagonist), or naltrexone (5 mg/kg IP, opioid antagonist). KEY RESULTS: MG (5, 10 mg/kg) dose-dependently reduced mechanical sensitivity in oxaliplatin-injected rats. Anti-allodynic effects of MG were completely inhibited by yohimbine, and significantly reduced by prazosin and naltrexone. MG produced modest hyperlocomotion but only at a dose (30 mg/kg) higher than those required to reduce allodynia. CONCLUSION AND IMPLICATION: The finding that MG reduced neuropathic pain through a mechanism requiring active α-adrenoceptors indicates that the pharmacological profile of MG includes activation of adrenergic, as well as opioid, systems.

Understanding the endocannabinoid system as a modulator of the trigeminal pain response to concussion.

Post-traumatic headache is the most common symptom of postconcussion syndrome and becomes a chronic neurological disorder in a substantial proportion of patients. This review provides a brief overview of the epidemiology of postconcussion headache, research models used to study this disorder, as well as the proposed mechanisms. An objective of this review is to enhance the understanding of how the endogenous cannabinoid system is essential for maintaining the balance of the CNS and regulating inflammation after injury, and in turn making the endocannabinoid system a potential modulator of the trigeminal response to concussion. The review describes the role of endocannabinoid modulation of pain and the potential for use of phytocannabinoids to treat pain, migraine and concussion.

Anhedonia, Reduced Cocaine Reward, and Dopamine Dysfunction in a Rat Model of Posttraumatic Stress Disorder.

BACKGROUND: Posttraumatic stress disorder (PTSD) co-occurs with substance use disorders at high rates, but the neurobiological basis of this relationship is largely unknown. PTSD and drug addiction each involve dysregulation of brain reward circuitry; therefore, the identification of pathology of the mesolimbic dopamine system may aid in understanding their functional relationship. Dopamine reward dysfunction also may be relevant to the mechanisms underlying the PTSD symptoms of anhedonia and emotional numbing. METHODS: Single-prolonged stress (SPS) was used as a rat model of PTSD, and a series of behavioral and neuropharmacologic assays were applied to assess the impact of SPS on reward, cocaine intake, and components of the striatal dopamine system. RESULTS: Exposure to SPS increased anhedonia-like behaviors and decreased the rewarding properties of cocaine compared with control handling. Altered cocaine intake during extended access self-administration sessions was observed in rats exposed to SPS, further suggesting a difference in the reinforcing properties of cocaine following severe stress. SPS reduced tissue content of dopamine and its metabolites in the striatum, as well as altered striatal dopamine transporter and D2, but not D1, receptor densities. CONCLUSIONS: These results support a role for altered dopaminergic transmission in reduced reward function in PTSD. Pathology of the dopamine system and the degradation of reward processes may contribute to PTSD symptomology and have implications for co-occurring psychiatric disorders such as substance abuse or depression.

Distinct interactions of cannabidiol and morphine in three nociceptive behavioral models in mice.

Cannabinoid and opioid agonists can display overlapping behavioral effects and the combination of these agonists is known to produce enhanced antinociception in several rodent models of acute and chronic pain. The present study investigated the antinociceptive effects of the nonpsychoactive cannabinoid, cannabidiol (CBD) and the µ-opioid agonist morphine, both alone and in combination, using three behavioral models in mice, to test the hypothesis that combinations of morphine and CBD would produce synergistic effects. The effects of morphine, CBD, and morphine/CBD combinations were assessed in the following assays: (a) acetic acid-stimulated stretching; (b) acetic acid-decreased operant responding for palatable food; and (c) hot plate thermal nociception. Morphine alone produced antinociceptive effects in all three models of acute nociception, whereas CBD alone produced antinociception only in the acetic acid-stimulated stretching assay. The nature of the interactions between morphine and CBD combinations were assessed quantitatively based on the principle of dose equivalence. Combinations of CBD and morphine produced synergistic effects in reversing acetic acid-stimulated stretching behavior, but subadditive effects in the hot plate thermal nociceptive assay and the acetic acid-decreased operant responding for palatable food assay. These results suggest that distinct mechanisms of action underlie the interactions between CBD and morphine in the three different behavioral assays and that the choice of appropriate combination therapies for the treatment of acute pain conditions may depend on the underlying pain type and stimulus modality.

Attenuation of morphine antinociceptive tolerance by a CB(1) receptor agonist and an NMDA receptor antagonist: Interactive effects.

CB(1) cannabinoid (CB(1)) receptor agonists and N-Methyl-d-Aspartate (NMDA) receptor antagonists attenuate the development of morphine antinociceptive tolerance. The present study used dose-addition analysis to evaluate CB(1)/NMDA receptor interactions on this endpoint. Chronic morphine administration (5 days, 100 mg/kg, twice daily) resulted in a 2.8-fold rightward shift in the morphine dose-effect curve. Co-administration of either the CB(1) receptor agonist CP-55940 (5-(1,1-Dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]phenol; 0.32-1.0 mg/kg) or the NMDA receptor antagonist (-)-6-phosphonomethyl-deca-hydroisoquinoline-3-carboxylic acid (LY235959; 1.0-3.2 mg/kg) with morphine dose-dependently attenuated morphine tolerance. The relative potency of each drug alone was quantified using a defined level of effect (one-quarter log shift in the morphine dose-effect curve), resulting in equieffective doses of 0.42 mg/kg and 1.1 mg/kg for CP-55940 and LY235959, respectively. Subsequent experiments assessed CP-55940/LY235959 interactions using a fixed-proportion design. Co-administration of CP-55940/LY235959 mixtures (1:1, 1:3.2, or 1:10 CP-55940/LY235959) with morphine dose-dependently attenuated morphine tolerance. Isobolographic and dose-addition analysis were used to statistically compare the experimentally determined potency for each mixture (z(mix)) with predicted additive potency (z(add)). Mixtures of 1:1 and 1:3.2 CP-55940/LY235959 produced additive effects (z(add) = z(mix)), while the mixture of 1:10 CP-55940/LY235959 produced a supra-additive effect (z(add) > z(mix)). These results suggest that CP-55940 and LY235959 produce additive or supra-additive attenuation of morphine antinociceptive tolerance after repeated morphine administration, depending on their relative concentrations.

Chronic unpredictable stress enhances cocaine-conditioned place preference in type 1 cannabinoid receptor knockout mice.

Cannabinoid signaling via the type 1 cannabinoid (CB1) receptor modulates the effects of drugs of abuse and the response to exposure to stressors. In addition, exposure to stressors can alter the effects of drugs of abuse. This study examined the effects of exposure to chronic unpredictable stress (CUS) in CB1 receptor knockout (CB1 KO) mice and their wild-type (WT) littermates, using cocaine-conditioned place preference (CPP) to compare their response to cocaine. Mice were untreated or exposed to 2 weeks of CUS. After this period, the acquisition of a cocaine CPP was examined with one of three doses (3.2, 10.0, or 17.0 mg/kg) of cocaine. Untreated CB1 KO and WT mice both acquired the cocaine CPP; however, exposure to CUS enhanced the acquisition of the cocaine CPP in CB1 KO mice, but did not significantly alter the effects of cocaine in WT mice. Taken together, these findings support earlier evidence suggesting a role for the CB1 receptor in the response to stress as well as in the effects of cocaine.

Lesions of the dorsomedial frontal cortex block sensitization to the positive-reinforcing effects of cocaine.

Previous studies have reported that rats exposed to a binge-abstinence history of cocaine self-administration exhibit sensitization to the positive-reinforcing effects of cocaine on a progressive ratio (PR) schedule of reinforcement. The purpose of the present study was to determine whether lesions of the dorsomedial frontal cortex block sensitization to the reinforcing effects of cocaine in rats with a history of binge-abstinence self-administration. Separate groups of male rats received bilateral infusions of either ibotenic acid (lesion) or sterile saline (sham) into the dorsomedial frontal cortex, or were left undisturbed (intact). All rats were then implanted with jugular catheters and trained to self-administer cocaine. Following acquisition, cocaine was made available on a PR schedule of reinforcement and breakpoints were determined in each group. Rats were then exposed to a discrete-trials (DT) procedure in which cocaine was made available during 10-min discrete-trials that occurred every 15 min (i.e., 4 times per hr) during daily, 24-hr sessions. This procedure elicited a "binge" in all groups, during which high rates of responding were maintained over a period of 1-2 days. After 10 days, the DT procedure was terminated, and no cocaine was available for the next 7 days. Following 7 days of forced "abstinence", cocaine-reinforced breakpoints were redetermined on the PR schedule. Prior to the DT procedure, no differences were observed in breakpoints across the three groups. Following the 7-day abstinence period, breakpoints on the PR schedule increased significantly in intact and sham rats, indicating an increase in the reinforcing efficacy of cocaine. In contrast, breakpoints did not increase in lesion rats, and were similar to those obtained prior to the binge-abstinence history. These data suggest that lesions of the dorsomedial frontal cortex block sensitization to the positive-reinforcing effects of cocaine in rats with a history of binge-abstinence self-administration.

Discrete-trials heroin self-administration produces sensitization to the reinforcing effects of cocaine in rats.

RATIONALE: The prevalence of cocaine use in opioid-dependent individuals is reportedly high, and the associated negative health and social consequences are severe and well documented. Sensitization of the reinforcing effects of cocaine has been demonstrated following noncontingent opioid exposure in animals; however, no preclinical studies have investigated the impact of opioid self-administration on cocaine's reinforcing effects. OBJECTIVE: Experiments were designed to investigate whether access to heroin self-administration altered the subsequent reinforcing effects of cocaine. METHODS: Baseline responding for cocaine under a progressive ratio schedule was first established. Heroin was then self-administered under a 24-h discrete-trials procedure (DT5; access to heroin five times per hour). Subsequently, cocaine-maintained responding was reassessed. RESULTS: Here we demonstrate that 10 days of DT5 heroin self-administration (50 microg/kg per infusion) resulted in an increase in cocaine's reinforcing effects at several doses across the cocaine dose-effect curve (0.38-3.0 mg/kg per infusion). These increases were relatively long lasting, exceeding the time course of a mild withdrawal syndrome. CONCLUSIONS: The DT5x10-day history of heroin self-administration resulted in an upward shift in the cocaine dose-effect curve, suggesting that DT5 heroin self-administration produced an increase in potency and sensitization of the maximal effectiveness with which cocaine functions as a reinforcer. The present experiments contribute to a growing amount of preclinical evidence suggesting an impact of opioid exposure on the reinforcing effects of cocaine, which may partially explain the high incidence of cocaine use in opioid-dependent individuals.