Effect of Fatty Acid Amide Hydrolase Inhibitor URB597 on Orofacial Pain Perception in Rats

Endocannabinoids act as analgesic agents in a number of headache models. However, their effectiveness varies with the route of administration and the type of pain. In this study, we assessed the role of the fatty acid amide hydrolase inhibitor URB597 in an animal model of orofacial pain based on tooth pulp stimulation. More specifically, we assessed the effects of intracerbroventricular (i.c.v.) and intraperitoneal (i.p.) administration of URB597 on the amplitude of evoked tongue jerks (ETJ) in rats. The levels of the investigated mediators anandamide (AEA), 2-arachidonyl glycerol (2-AG), Substance P (SP), calcitonin-gene-related peptide (CGRP), endomorphin-2 (EM-2) and fatty acid amide hydrolase (FAAH) inhibitor by URB597 and receptors cannabinoid type-1 receptors (CB1R), cannabinoid type-2 receptors (CB2R) and µ-opioid receptors (MOR) were determined in the mesencephalon, thalamus and hypothalamus tissues. We have shown that increasing endocannabinoid AEA levels by both central and peripheral inhibition of FAAH inhibitor by URB597 has an antinociceptive effect on the trigemino-hypoglossal reflex mediated by CB1R and influences the activation of the brain areas studied. On the other hand, URB597 had no effect on the concentration of 2-AG in the examined brain structures and caused a significant decrease in CB2R mRNA expression in the hypothalamus only. Tooth pulp stimulation caused in a significant increase in SP, CGRP and EM-2 gene expression in the midbrain, thalamus and hypothalamus. In contrast, URB597 administered peripherally one hour before stimulation decreased the mRNA level of these endogenous neuropeptides in comparison with the control and stimulation in all examined brain structures. Our results show that centrally and peripherally administered URB597 is effective at preventing orofacial pain by inhibiting AEA catabolism and reducing the level of CGRP, SP and EM-2 gene expression and that AEA and 2-AG have different species and model-specific regulatory mechanisms. The data presented in this study may represent a new promising therapeutic target in the treatment of orofacial pain.

Brain imaging of cannabinoid type I (CB1 ) receptors in women with cannabis use disorder and male and female healthy controls

Cannabis effects are predominantly mediated by pharmacological actions on cannabinoid type 1 (CB1 ) receptors. Prior positron emission tomography (PET) studies in individuals who use cannabis included almost exclusively males. PET studies in females are needed because there are sex differences in cannabis effects, progression to cannabis use disorder (CUD), and withdrawal symptom severity. Females with CUD (N = 10) completed two double-blind cannabis smoking sessions (Session 1: placebo; Session 2: active), and acute cannabis effects were assessed. After Session 2, participants underwent 3 days of monitored cannabis abstinence; mood, craving, and withdrawal symptoms were assessed and a PET scan (radiotracer: [11 C]OMAR) followed. [11 C]OMAR Distribution volume (VT ) from these participants was compared with VT of age/BMI-similar female non-users of cannabis ("healthy controls"; N = 10). VT was also compared between female and male healthy controls (N = 7). Females with CUD displayed significantly lower VT than female healthy controls in specific brain regions (hippocampus, amygdala, cingulate, and insula). Amygdala VT was negatively correlated with mood changes (anger/hostility) during abstinence, but VT was not correlated with other withdrawal symptoms or cannabis effects. Among healthy controls, females had significantly higher VT than males in all brain regions examined. Chronic cannabis use appears to foster downregulation of CB1 receptors in women, as observed previously in men, and there are inherent sex differences in CB1 availability. Future studies should elucidate the time course of CB1 downregulation among females who use cannabis and examine the relation between CB1 availability and cannabis effects among other populations (e.g., infrequent users; medicinal users).

Cannabinoid type 1 receptors in A2a neurons contribute to cocaine-environment association

RATIONALE

Cannabinoid type 1 receptors (CB1Rs) are widely expressed within the brain's reward circuits and are implicated in regulating drug induced behavioral adaptations. Understanding how CB1R signaling in discrete circuits and cell types contributes to drug-related behavior provides further insight into the pathology of substance use disorders.

OBJECTIVE AND METHODS

We sought to determine how cell type-specific expression of CB1Rs within striatal circuits contributes to cocaine-induced behavioral plasticity, hypothesizing that CB1R function in distinct striatal neuron populations would differentially impact behavioral outcomes. We crossed conditional Cnr1^fl/fl mice and striatal output pathway cre lines (Drd1a -cre; D1, Adora2a -cre; A2a) to generate cell type-specific CB1R knockout mice and assessed their performance in cocaine locomotor and associative behavioral assays.

RESULTS

Both knockout lines retained typical locomotor activity at baseline. D1-Cre x Cnr1^fl/fl mice did not display hyperlocomotion in response to acute cocaine dosing, and both knockout lines exhibited blunted locomotor activity across repeated cocaine doses. A2a-cre Cnr1^fl/fl, mice did not express a preference for cocaine paired environments in a two-choice place preference task.

CONCLUSIONS

This study aids in mapping CB1R-dependent cocaine-induced behavioral adaptations onto distinct striatal neuron subtypes. A reduction of cocaine-induced locomotor activation in the D1- and A2a-Cnr1 knockout mice supports a role for CB1R function in the motor circuit. Furthermore, a lack of preference for cocaine-associated context in A2a-Cnr1 mice suggests that CB1Rs on A2a-neuron inhibitory terminals are necessary for either reward perception, memory consolidation, or recall. These results direct future investigations into CB1R-dependent adaptations underlying the development and persistence of substance use disorders.

A Cannabinoid-1 Receptor Antagonist MJ08 with Different Effects in Stomach and Small Intestine

Background: To investigate the inverse agonistic effect of a novel type 1 cannabinoid (CB₁) receptor antagonist, MJ08, on the gastrointestinal tract (GIT). Methods: In vivo, carbon propulsion within the stomach of mice was undertaken to investigate the effects of MJ08. In vitro, the effects of MJ08 were investigated on the contraction of smooth muscle on the isolated gastric fundus, gastric body, duodenum, jejunum, and ileum. Results: Western blotting results showed that MJ08 (0.62 mg/kg body weight) reversed WIN55,212-2 (1.0 mg/kg)-induced reduction of carbon transit. MJ08 (1.25, 2.5 mg/kg) stimulated carbon transit dose dependently, demonstrating an inverse agonistic effect. In vitro experiments showed that the expression of MJ08 increased the contraction of small intestine, and that its inverse agonistic effect was significantly stronger than that of SR141716A, but no effect was noted on the gastric body. Western blotting showed that the MJ08 increased the expression of CB₁ receptor in different GIT segments. Conclusion: MJ08 is not only an antagonist but also an inverse agonist of the CB₁ receptor. MJ08 and SR141716A can enhance motility in the small intestine and increase the expression of CB₁ receptor in the small intestine.

Endocannabinoid signaling regulates the reinforcing and psychostimulant effects of ketamine in mice

The abuse potential of ketamine limits its clinical application, but the precise mechanism remains largely unclear. Here we discovered that ketamine significantly remodels the endocannabinoid-related lipidome and activates 2-arachidonoylglycerol (2-AG) signaling in the dorsal striatum (caudate nucleus and putamen, CPu) of mice. Elevated 2-AG in the CPu is essential for the psychostimulant and reinforcing effects of ketamine, whereas blockade of the cannabinoid CB1 receptor, a predominant 2-AG receptor, attenuates ketamine-induced remodeling of neuronal dendrite structure and neurobehaviors. Ketamine represses the transcription of the monoacylglycerol lipase (MAGL) gene by promoting the expression of PRDM5, a negative transcription factor of the MAGL gene, leading to increased 2-AG production. Genetic overexpression of MAGL or silencing of PRDM5 expression in the CPu robustly reduces 2-AG production and ketamine effects. Collectively, endocannabinoid signaling plays a critical role in mediating the psychostimulant and reinforcing properties of ketamine.

Anandamide in the anterior hypothalamus diminishes defensive responses elicited in mice threatened by Epicrates cenchria constrictor serpents

The purpose of this study was to investigate whether the panicolytic‑like effect of different doses of anandamide microinjected into the anterior hypothalamus (AH) follows the same pattern of a bell‑shaped dose‑response curve observed with the same dose treatment in dorsomedial and ventromedial hypothalamus. We investigated this assumption by administering the cannabinoid and vanilloid receptor agonist anandamide into the anterior hypothalamus of mice and exposing them to the real threatening situation by using our experimental model based on confrontations between rodents and wild snakes. Our findings showed a gradual decay of response, with a significant attenuation of the panic attack‑like responses with anandamide at the highest dose but no effect was found after anandamide at the lowest or intermediate doses. An immunohistochemical procedure showed a lower degree of TRPV1 receptor and moderate to higher degree of Cb1 receptors in anterior hypothalamus. In conclusion, the pattern of dose‑response curve of anandamide microinjected in the AH does not seem to be the same classical pattern compared with other hypothalamic nuclei.

Cannabidiol affects circadian clock core complex and its regulation in microglia cells

Cannabis is often used by consumers for sleep disorders. Studies show that circadian rhythm could be affected by a misuse of cannabis. Recent research has connected the role of microglial cells with psychiatric disorders such as substance abuse. The aim was to show the effect of two major components of cannabis on circadian genes regulation in microglial cells. In BV-2 microglial cells, cannabidiol (CBD) induces a deregulation of circadian genes with (P-value = 0.039) or without (P-value = 0.0015) lipopolisaccharides stimulation. CBD up regulated Arntl (P = 9.72E-5) and down regulated Clock (P = 0.0034) in BV-2 cells. Temporal expression of Arntl (light and dark P = 0.0054) and Clock (light and dark P = 0.047) was confirmed to have 24 hours light and dark rhythmic regulation in dissected suprachiasmatic nucleus as well as of Cb1 cannabinoid receptor (light and dark P = 0.019). In BV-2 microglia cells, CBD also up regulated CRY2 (P = 0.0473) and PER1 (P = 0.0131). Other nuclear molecules show a deregulation of circadian rhythm in microglial cells by CBD, such as RORA, RevErbα, RORB, CREBBP, AFT4, AFT5 and NFIL3. Our study suggests that circadian rhythm in microglial cells is deregulated by CBD but not by THC. It is consistent with clinical observations of the use of therapeutic cannabis to treat insomnia.

Opposing actions of CRF-R1 and CB1 receptors on VTA-GABAergic plasticity following chronic exposure to ethanol

Dopamine neurons in the ventral tegmental area (VTA) influence learned behaviors and neuropsychiatric diseases including addiction. The stress peptide corticotrophin-releasing factor (CRF) contributes to relapse to drug and alcohol seeking following withdrawal, although the cellular actions are poorly understood. In this study, we show that presynaptic CRF type 1 receptors (CRF-R1) potentiate GABA release onto mouse VTA dopamine neurons via a PKC-Ca2+ signaling mechanism. In naive animals, activation of CRF-R1 by bath application of CRF or ethanol enhanced GABAA inhibitory postsynaptic currents (IPSCs). Following 3 days of withdrawal from four weekly cycles of chronic intermittent ethanol (CIE) vapor exposure, spontaneous IPSC frequency was enhanced while CRF and ethanol potentiation of IPSCs was intact. However, withdrawal for 3 weeks or more was associated with reduced spontaneous IPSC frequency and diminished CRF and ethanol responses. Long-term withdrawal was also accompanied by decreased sensitivity to the CB1 receptor agonist WIN55212 as well as greatly enhanced sensitivity to the CB1 antagonist AM251. Inclusion of BAPTA in the internal recording solution restored the responsiveness to CRF or ethanol and reduced the potentiating actions of AM251. Together, these data suggest that GABAA inhibition of VTA dopamine neurons is regulated by presynaptic actions of CRF and endocannabinoids and that long-term withdrawal from CIE treatment enhances endocannabinoid-mediated inhibition, thereby suppressing CRF facilitation of GABA release. Such findings have implications for understanding the impact of chronic alcohol on stress-related, dopamine-mediated alcohol-seeking behaviors.

Endocannabinoids in the Islets of Langerhans: the ugly, the bad, and the good facts

The endocannabinoid system (ECS) regulates cellular homeostasis and whole-body metabolism. There is an autonomous ECS in the endocrine pancreas, including the cannabinoid 1 receptor (CB₁R) that is present in β-cells. Here, we discuss conflicts that have arisen with regard to the function(s) of the ECs in the endocrine pancreas and that have caused confusion when defining the role of the ECS in islets of Langerhans, especially the role(s) of CB₁R in β-cells. We also discuss the latest data published concerning the ECS in islets. CB₁R in particular is not simply a negative modulator of insulin secretion as it is also involved in intra-islet inflammation during high fat-high sugar intake and it is a negative regulator of β-cell viability and turnover. We also discuss the feasibility of using CB₁R as a target for the treatment of diabetes.

The tamoxifen derivative ridaifen-B is a high affinity selective CB2 receptor inverse agonist exhibiting anti-inflammatory and anti-osteoclastogenic effects

Selective estrogen receptor modulators (SERMs) target estrogen receptors (ERs) to treat breast cancer and osteoporosis. Several SERMs exhibit anti-cancer activity not related to ERs. To discover novel anti-cancer drugs acting via ER-independent mechanisms, derivatives of the SERM tamoxifen, known as the "ridaifen" compounds, have been developed that exhibit reduced or no ER affinity, while maintaining cytotoxicity. Tamoxifen and other SERMs bind to cannabinoid receptors with moderate affinity. Therefore, ER-independent effects of SERMs might be mediated via cannabinoid receptors. This study determined whether RID-B, a first generation ridaifen compound, exhibits affinity and/or activity at CB₁ and/or CB₂ cannabinoid receptors. RID-B binds with high affinity (K_i = 43.7 nM) and 17-fold selectivity to CB₂ over CB₁ receptors. RID-B acts as an inverse agonist at CB₂ receptors, modulating G-protein and adenylyl cyclase activity with potency values predicted by CB₂ affinity. Characteristic of an antagonist, RID-B co-incubation produces a parallel-rightward shift in the concentration-effect curve of CB₂ agonist WIN-55,212-2 to inhibit adenylyl cyclase activity. CB₂ inverse agonists are reported to exhibit anti-inflammatory and anti-ostoeclastogenic effects. In LPS-activated macrophages, RID-B exhibits anti-inflammatory effects by reducing levels of nitric oxide (NO), IL-6 and IL-1α, but not TNFα. Only reduction of NO concentration by RID-B is mediated by cannabinoid receptors. RID-B also exhibits pronounced anti-osteoclastogenic effects, reducing the number of osteoclasts differentiating from primary bone marrow macrophages in a cannabinoid receptor-dependent manner. In summary, the tamoxifen derivative RID-B, developed with reduced affinity for ERs, is a high affinity selective CB₂ inverse agonist with anti-inflammatory and anti-osteoclastogenic properties.

Anticonvulsive effects of endocannabinoids; an investigation to determine the role of regulatory components of endocannabinoid metabolism in the Pentylenetetrazol induced tonic- clonic seizures

2-Arachidonoylglycerol (2-AG) and anandamide are two major endocannabinoids produced, released and eliminated by metabolic pathways. Anticonvulsive effect of 2-AG and CB1 receptor is well-established. Herein, we designed to investigate the anticonvulsive influence of key components of the 2-AG and anandamide metabolism. Tonic-clonic seizures were induced by an injection of Pentylenetetrazol (80 mg/kg, i.p.) in adult male Wistar rats. Delay and duration for the seizure stages were considered for analysis. Monoacylglycerol lipase blocker (JJKK048; 1 mg/kg) or alpha/beta hydroxylase domain 6 blocker (WWL70; 5 mg/kg) were administrated alone or with 2-AG to evaluate the anticonvulsive potential of these enzymes. To determine the CB1 receptor involvement, its blocker (MJ15; 3 mg/kg) was administrated associated with JJKK048 or WWL70. To assess anandamide anticonvulsive effect, anandamide membrane transporter blocker (LY21813240; 2.5 mg/kg) was used alone or associated with MJ15. Also, fatty acid amide hydrolase blocker (URB597; 1 mg/kg; to prevent intracellular anandamide hydrolysis) were used alone or with AMG21629 (transient receptor potential vanilloid; TRPV1 antagonist; 3 mg/kg). All compounds were dissolved in DMSO and injected i.p., before the Pentylenetetrazol. Both JJKK048 and WWL70 revealed anticonvulsive effect. Anticonvulsive effect of JJKK048 but not WWL70 was CB1 receptor dependent. LY2183240 showed CB1 receptor dependent anticonvulsive effect. However, URB597 revealed a TRPV1 dependent proconvulsive effect. It seems extracellular accumulation of 2-AG or anandamide has anticonvulsive effect through the CB1 receptor, while intracellular anandamide accumulation is proconvulsive through TRPV1.

Sacred Maya incense, copal (Protium copal - Burseraceae), has antianxiety effects in animal models

ETHNOPHARMACOLOGICAL RELEVANCE

The Maya have traditionally used copal, Protium copal, as incense during ceremonies since pre-Columbian times. Anecdotally, copal (when burned as incense), is thought to elicit mentally uplifting and calming effects. The main objective of this study was to determine whether the incense elicits anxiolytic-like behavior in animal models using rats. A second objective was to characterize active constituents and discern potential mechanism(s) of action, specifically the involvement of the GABAergic and endocannabinoid (eCB) systems. Despite the extensive Central American use of this resin, there are currently no known scientific behavioral or pharmacological studies done with the incense.

MATERIALS AND METHODS

Quantification of the triterpenes in the copal resin and cold trapped incense was achieved by HPLC MS. Behavioral effects in rats were assessed using the elevated plus maze (EPM), social interaction (SI) test, conditioned emotion response (CER) and Novel object recognition (NOR) paradigms. Rats were exposed to burning copal (200 mg) over 5 min in a smoking chamber apparatus and then immediately tested in each behavioral paradigm. Follow-up SI tests were done using two antagonists flumazenil (1 mg/kg) and AM251 (1 mg/kg) administered systemically. Inhibition of MAGL (monoacylglycerol lipase) was measured by microplate assay with recombinant human enzyme and probe substrate.

RESULTS

Phytochemical analysis revealed that copal resin and incense had high α- and β-amyrins and low lupeol triterpene content. Exposure to Protium copal incense significantly reduced anxiety-like behavior in the SI and CER tests. In contrast, no anxiolytic effects were observed in the EPM. The CER effect was time dependent. Both flumazenil and AM251 blocked the anxiolytic activity of copal revealing the involvement of GABAergic and endocannabinoid systems. Copal, as well as the identified triterpenes, potently inhibited monoacylglycerol lipase (MAGL) activity in vitro (IC₅₀ ≤ 811 ng/mL).

CONCLUSIONS

This is the first study to show that copal incense from Protium copal elicits anxiolytic-like effects in fear and social interaction models as evidenced by a reduced learned fear behavior and an increase in active social interaction. It's high α and β-amyrin content suggests behavioral effects may be mediated, in part, by the known action of these terpenes at the benzodiazepine receptor. Furthermore, P. copal's observed activity through the eCB system via MAGL offers a new potential mechanism underlying the anxiolytic activity.

The role of the endocannabinoid system in the antihyperalgesic effect of Cedrus atlantica essential oil inhalation in a mouse model of postoperative pain

ETHNOPHARMACOLOGICAL RELEVANCE

Cedar is part of the phylum of conifers, and it's essential oil has been used for therapeutic purposes since ancient times. In our previous study, we have demonstrated that the inhalation of the Cedrus atlantica essential oil (CaEO) induces an antihyperalgesic effect in a model of postoperative pain. But the mechanism that underlies this effect is not yet fully known.

AIM OF THE STUDY

This study investigates the involvement of the endocannabinoid system in the antihyperalgesic effect produced by the inhalation of CaEO in a post operative pain model.

MATERIALS AND METHODS

Male Swiss mice (25-35±2g) were subjected to plantar incision. To assess the involvement of the endocannabinoid system, two different approaches were made: (1) by administering antagonists to the CB₁ and CB₂ receptors in different sites (intraperitoneal [i.p.], intraplantar [i.pl.] and intrathecal [i.t.]) and (2) by assessing the synergic effect of the inhalation of sub-effective doses of CaEO, Fatty acid hydrolase (FAAH) and Monoacylglycerol lipase (MAGL), and endocannabinoid degradation inhibitors (URB937 and JZL184, respectively).

RESULTS

The antihyperalgesic effect of CaEO inhalation was prevented by pretreatment with AM281 or AM630 given by i.p. and i.t., but not i.pl. Additionally, in mice pretreated with FAAH or the MAGL inhibitors, the antihyperalgesic effect of CaEO inhalation was significantly longer, which demonstrates the involvement of the endocannabinoid system in the antihyperalgesic effect of CaEO inhalation in a preclinical model of postoperative pain.

CONCLUSIONS

The present study shows that CaEO inhalation exerts an antihyperalgesic effect, possibly by the activation of the endocannabinoid system in a preclinical model of postoperative pain. It could be a new alternative to treat pain in a clinical environment.

Antidote to cannabinoid intoxication: the CB1 receptor inverse agonist, AM251, reverses hypothermic effects of the CB1 receptor agonist, CB-13, in mice

BACKGROUND AND PURPOSE

Cannabis is a recreational drug leading to intoxication, following stimulation of cannabinoid CB1 receptors. However, more recently, herbs mixed with synthetic cannabinoids sometimes known as 'Spice' and 'Black Mamba' have been increasingly used, and their high CB1 receptor affinity has led not only to marked intoxication but also life-threatening complications and an increasing number of deaths. Although many studies have indicated that prophylactic treatment with CB1 receptor antagonists can block cannabimimetic effects in animals and humans, the aim of this study was to determine whether CB1 receptor antagonism could reverse physical cannabimimetic effects.

EXPERIMENTAL APPROACH

Cannabimimetic effects, measured by the hypothermic response following sedation and hypomotility, were induced by the synthetic CB1 receptor agonist CB-13 (1-naphthalenyl[4-(pentyloxy)-1-naphthalenyl]methanone) in Biozzi Antibody High mice. The CB1 receptor antagonist/inverse agonist AM251 (N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) was administered 20 min after the injection of CB-13 and its effects on the cannabimimetic responses were assessed.

KEY RESULTS

In this study, the CNS-related cannabimimetic effects, as measured by the hypothermic effect, induced by the CB1 receptor agonist were therapeutically treated and were rapidly reversed by the CB1 receptor antagonist/inverse agonist. There was also a subjective reversal of visually evident sedation.

CONCLUSIONS AND IMPLICATIONS

Cannabinoid receptor antagonists have been widely used and so may provide an acceptable single-dose antidote to cannabinoid intoxication. This use may save human life, where the life-threatening effects are mediated by cannabinoid receptors and not off-target influences of the synthetic cannabinoids or non-cannabinoids within the recreational drug mixture.

Dose-Specific Effects of Di-Isononyl Phthalate on the Endocannabinoid System and on Liver of Female Zebrafish

Phthalates, used as plasticizers, have become a ubiquitous contaminant and have been reported for their potential to induce toxicity in living organisms. Among them, di-isononyl phthalate (DiNP) has been recently used to replace di(2-ethylhexyl) phthalate (DEHP). Nowadays, there is evidence that DiNP is an endocrine-disrupting chemical; however, little is known about its effects on the endocannabinoid system (ECS) and lipid metabolism. Hence, the aim of our study was to investigate the effects of DiNP on the ECS in zebrafish liver and brain and on hepatic lipid storage. To do so, adult female zebrafish were exposed to three concentrations (0.42 µg/L, 4.2 µg/L, and 42 µg/L) of DiNP via water for 3 weeks. Afterwards, we investigated transcript levels for genes involved in the ECS of the brain and liver as well as liver histology and image analysis, Fourier-transform infrared spectroscopy imaging, and measurement of endocannabinoid levels. Our results demonstrate that DiNP upregulates orexigenic signals and causes hepatosteatosis together with deregulation of the peripheral ECS and lipid metabolism. A decrease in the levels of ECS components at the central level was observed after exposure to the highest DiNP concentration tested. These findings suggest that replacement of DEHP with DiNP should be considered with caution because of observed adverse DiNP effects on aquatic organisms.

The cannabinoid system and pain

Chronic pain states are highly prevalent and yet poorly controlled by currently available analgesics, representing an enormous clinical, societal, and economic burden. Existing pain medications have significant limitations and adverse effects including tolerance, dependence, gastrointestinal dysfunction, cognitive impairment, and a narrow therapeutic window, making the search for novel analgesics ever more important. In this article, we review the role of an important endogenous pain control system, the endocannabinoid (EC) system, in the sensory, emotional, and cognitive aspects of pain. Herein, we briefly cover the discovery of the EC system and its role in pain processing pathways, before concentrating on three areas of current major interest in EC pain research; 1. Pharmacological enhancement of endocannabinoid activity (via blockade of EC metabolism or allosteric modulation of CB1receptors); 2. The EC System and stress-induced modulation of pain; and 3. The EC system & medial prefrontal cortex (mPFC) dysfunction in pain states. Whilst we focus predominantly on the preclinical data, we also include extensive discussion of recent clinical failures of endocannabinoid-related therapies, the future potential of these approaches, and important directions for future research on the EC system and pain. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Discovery and characterization of two novel CB1 receptor splice variants with modified N-termini in mouse

Numerous studies have been carried out in the mouse model, investigating the role of the cannabinoid receptor type 1 (CB1). However, mouse CB1 (mCB1) receptor differs from human CB1 (hCB1) receptor in 13 amino acid residues. Two splice variants, hCB1a and hCB1b, diverging in their amino-termini, have been reported to be unique for hCB1 and, via different signaling properties, contribute to CB1 receptor physiology and pathophysiology. We hypothesized that splice variants also exist for the mCB1 receptor and have different signaling properties. On murine hippocampal cDNA, we identified two novel mCB1 receptor splice variants generated by splicing of introns with 117 bp and 186 bp in the N-terminal domain, corresponding to deletions of 39 or 62 amino acids, respectively. The mRNAs for the splice variants mCB1a and mCB1b are expressed at low levels in different brain regions. Western blot analysis of protein extracts from stably transfected HEK293 cells indicates a strongly reduced glycosylation because of the absence of two glycosylation sites in mCB1b. On-cell western analysis in these stable lines revealed increased internalization of mCB1a and mCB1b upon stimulation with the agonist WIN55,212-2 as compared to mCB1. Results also point toward an increased affinity to SR141716 for mCB1a, as well as slightly enhanced inhibition of neurotransmission compared to mCB1. In mCB1b, agonist-induced MAPK phosphorylation was decreased compared to mCB1 and mCB1a. Identification of mouse CB1 receptor splice variants may help to explain differences found between human and mouse endocannabinoid systems and improve the understanding of CB1 receptor signaling and trafficking in different species.

Pyrimidinyl Biphenylureas: Identification of New Lead Compounds as Allosteric Modulators of the Cannabinoid Receptor CB1

The allosteric modulator 1-(4-chlorophenyl)-3-(3-(6-(pyrrolidin-1-yl)pyridin-2-yl)phenyl)urea (PSNCBAM-1, 2) bound the cannabinoid receptor 1 (CB1) and antagonized G protein coupling. This compound demonstrated potent anorectic effects similar to the CB1 antagonist rimonabant that once was marketed for the treatment of obesity, suggesting a new chemical entity for the discovery of antiobesity drugs. To increase structural diversity of this class of CB1 ligands, we designed and synthesized two classes of novel analogues, in which the pyridine ring of 2 was replaced by a pyrimidine ring. These positively modulate the binding of the CB1 orthosteric agonist CP55,940 while exhibiting an antagonism of G-protein coupling activity. Interestingly, compounds 7d and 8d demonstrated ERK1/2 phosphorylation mediated via β-arrestin unlike the orthosteric CP55,940 that does so in a G protein-dependent manner. These can serve as new lead compounds for the future development of CB1 allosteric modulators that show biased agonism and potentially antiobesity behavior via a new mechanism.

Combination Chemistry: Structure-Activity Relationships of Novel Psychoactive Cannabinoids

Originally developed as research tools for use in structure-activity relationship studies, synthetic cannabinoids contributed to significant scientific advances in the cannabinoid field. Unfortunately, a subset of these compounds was diverted for recreational use beginning in the early 2000s. As these compounds were banned, they were replaced with additional synthetic cannabinoids with increasingly diverse chemical structures. This chapter focuses on integration of recent results with those covered in previous reviews. Whereas most of the early compounds were derived from the prototypic naphthoylindole JWH-018, currently popular synthetic cannabinoids include tetramethylcyclopropyl ketones and indazole-derived cannabinoids (e.g., AB-PINACA, AB-CHMINACA). Despite their structural differences, psychoactive synthetic cannabinoids bind with high affinity to CB1 receptors in the brain and, when tested, have been shown to activate these receptors and to produce a characteristic profile of effects, including suppression of locomotor activity, antinociception, hypothermia, and catalepsy, as well as Δ9-tetrahydrocannabinol (THC)-like discriminative stimulus effects in mice. When they have been tested, synthetic cannabinoids are often found to be more efficacious at activation of the CB1 receptor and more potent in vivo. Further, their chemical alteration by thermolysis during use and their uncertain stability and purity may result in exposure to degradants that differ from the parent compound contained in the original product. Consequently, while their intoxicant effects may be similar to those of THC, use of synthetic cannabinoids may be accompanied by unpredicted, and sometimes harmful, effects.

Pharmacological and Toxicological Effects of Synthetic Cannabinoids and Their Metabolites

Commercial preparations containing synthetic cannabinoids (SCBs) are rapidly emerging as drugs of abuse. Although often assumed to be "safe" and "legal" alternatives to cannabis, reports indicate that SCBs induce toxicity not often associated with the primary psychoactive component of marijuana, Δ9-tetrahydrocannabinol (Δ9-THC). This chapter will summarize the evidence that use of SCBs poses greater health risks relative to marijuana and suggest that distinct pharmacological properties and metabolism of SCBs relative to Δ9-THC may contribute to this increased toxicity. Studies reviewed will indicate that in contrast to partial agonist properties of Δ9-THC typically observed in vitro, SCBs act as full CB1 and CB2 receptor agonists both in cellular assays and animal studies. Furthermore, unlike Δ9-THC metabolism, several SCB metabolites retain high affinity for and exhibit a range of intrinsic activities at CB1 and CB2 receptors. Finally, the potential for SCBs to cause adverse drug-drug interactions with other drugs of abuse, as well as with common therapeutic agents, will be discussed. Collectively, the evidence provided in this chapter indicates that SCBs should not be considered safe and legal alternatives to marijuana. Instead, the enhanced toxicity of SCBs relative to marijuana, perhaps resulting from the combined actions of a complex mixture of different SCBs present and their active metabolites that retain high affinity for CB1 and CB2 receptors, highlights the inherent danger that may accompany use of these substances.

Endocannabinoids and Synaptic Function in the CNS

Marijuana affects neural functions through the binding of its active component (Δ9-THC) to cannabinoid receptors in the CNS. Recent studies have elucidated that endogenous ligands for cannabinoid receptors, endocannabinoids, serve as retrograde messengers at central synapses. Endocannabinoids are produced on demand in activity-dependent manners and released from postsynaptic neurons. The released endocannabinoids travel backward across the synapse, activate presynaptic CB1 cannabinoid receptors, and modulate presynaptic functions. Retrograde endocannabinoid signaling is crucial for certain forms of short-term and long-term synaptic plasticity at excitatory or inhibitory synapses in many brain regions, and thereby contributes to various aspects of brain function including learning and memory. Molecular identities of the CB1 receptor and enzymes involved in production and degradation of endocannabinoids have been elucidated. Anatomical studies have demonstrated unique distributions of these molecules around synapses, which provide morphological bases for the roles of endocannabinoids as retrograde messengers. CB1-knockout mice exhibit various behavioral abnormalities and multiple defects in synaptic plasticity, supporting the notion that endocannabinoid signaling is involved in various aspects of neural function. In this review article, the authors describe molecular mechanisms of the endocannabinoid-mediated synaptic modulation and its possible physiological significance. NEUROSCIENTIST 13(2):127—137, 2007.

Cannabinoid and Vanilloid Effects of R(+)-Methanandamide in the Hemisected Meningeal Preparation

The endogenous cannabinoid R(+)-methanandamide (mAEA) exerts differential anti- and pronociceptive effects by activating both cannabinoid (CB1) and vanilloid (TRPV1) receptors of nociceptive primary afferents. The significance of these effects in meningeal nociception was evaluated by modulation of calcitonin gene-related peptide (CGRP) release from meningeal afferents measured in an in vitro preparation of the hemisected rat skull. Temperature steps to 39°C and 45°C caused heat-dependent increases in CGRP release. One micromolar mAEA inhibited CGRP release at 32°C but facilitated it at 45°C. This effect was abolished in the presence of the TRPV1 receptor antagonist capsazepine. Lower doses of mAEA had no effect on basal or heat-evoked release. In the presence of the CB1 receptor antagonist SR141716 (0.2 μM) heat-stimulated increase in CGRP release was facilitated. CGRP release in the presence of SR141716 (0.2 μM) was further increased by adding mAEA at a concentration which had no effect on its own. These results confirm an opposing functional role for anandamide at CB1 and TRPV1 receptors on meningeal afferents.

Chronic Δ9-Tetrahydrocannabinol during Adolescence Differentially Modulates Striatal CB1 Receptor Expression and the Acute and Chronic Effects on Learning in Adult Rats

The purpose of this study was to determine whether chronic administration of Δ(9)-tetrahydrocannabinol (THC) during adolescence would (1) modify any sex-specific effects of THC on learning and (2) affect the development of tolerance to THC as an adult. Male and female rats received daily injections of saline or 5.6 mg/kg of THC from postnatal day 35-75, yielding four groups (female/saline, female/THC, male/saline, and male/THC). Rats were then trained on a procedure that assayed both learning and performance behavior and administered 0.32-18 mg/kg of THC acutely as adults (experiment 1). THC produced rate-decreasing and error-increasing effects in both sexes; however, female rats were more sensitive than male rats were to the rate-decreasing effects. Rats were then chronically administered 10 mg/kg of THC (experiment 2). Rats that received THC during adolescence developed tolerance to the rate-decreasing effects more slowly and less completely than did rats that received saline; in addition, females developed tolerance to the error-increasing effects of THC slower than males did. Western blot analysis of brain tissue indicated long-term changes in hippocampal and striatal cannabinoid type-1 receptor (CB1R) levels despite levels that were indistinguishable immediately after chronic treatment during adolescence. Striatal CB1R levels were increased in adult rats that received THC during adolescence; hippocampal CB1R levels varied by sex. In summary, female rats were more sensitive than male rats were to the acute and chronic effects of THC, and chronic administration of THC during adolescence produced long-term changes in CB1R levels that correlated with decreased tolerance development to the rate-decreasing effects of THC.

DNA methyltransferase expressions in Japanese rice fish (Oryzias latipes) embryogenesis is developmentally regulated and modulated by ethanol and 5-azacytidine

We aimed to investigate the impact of the epigenome in inducting fetal alcohol spectrum disorder (FASD) phenotypes in Japanese rice fish embryogenesis. One of the significant events in epigenome is DNA methylation which is catalyzed by DNA methyltransferase (DNMT) enzymes. We analyzed DNMT enzyme mRNA expressions in Japanese rice fish development starting from fertilized eggs to hatching and also in embryos exposed for first 48h of development either to ethanol (300mM) or to 5-azacytidine (5-azaC; 2mM), an inhibitor of DNMT enzyme activity. As observed in FASD phenotypes, 5-azaC exposure was able to induce microcephaly and craniofacial cartilage deformities in Japanese rice fish. Moreover, we have observed that expression of DNMTs (dnmt1, dnmt3aa, and dnmt3bb.1) are developmentally regulated; high mRNA copies were found in early stages (1-2day-post-fertilization, dpf), followed by gradual reduction until hatched. In ethanol-treated embryos, compared to controls, dnmt1 mRNA is in reduced level in 2dpf and in enhanced level in 6dpf embryos. While dnmt3aa and 3bb.1 remained unaltered. In contrast, embryos exposed to 5-azaC have an enhanced level of dnmt1 and dnmt3bb.1 mRNAs both in 2 and 6dpf embryos while dnmt3aa is enhanced only in 6dpf embryos. Moreover, endocannabinoid receptor 1a (cnr1a) mRNA which was found to be reduced by ethanol remained unaltered and cnr1b and cnr2 mRNAs, which were remained unaltered by ethanol, were increased significantly by 5-azaC in 6dpf embryos. This study indicates that the craniofacial defects observed in FASD phenotypes are the results of dysregulations in DNMT expressions.

Lack of presynaptic interaction between glucocorticoid and CB1 cannabinoid receptors in GABA- and glutamatergic terminals in the frontal cortex of laboratory rodents

Corticosteroid and endocannabinoid actions converge on prefrontocortical circuits associated with neuropsychiatric illnesses. Corticosteroids can also modulate forebrain synapses by using endocannabinoid effector systems. Here, we determined whether corticosteroids can modulate transmitter release directly in the frontal cortex and, in doing so, whether they affect presynaptic CB1 cannabinoid receptor- (CB1R) mediated neuromodulation. By Western blotting of purified subcellular fractions of the rat frontal cortex, we found glucocorticoid receptors (GcRs) and CB1Rs enriched in isolated frontocortical nerve terminals (synaptosomes). CB1Rs were predominantly presynaptically located while GcRs showed preference for the post-synaptic fraction. Additional confocal microscopy analysis of cortical and hippocampal regions revealed vesicular GABA transporter-positive and vesicular glutamate transporter 1-positive nerve terminals endowed with CB1R immunoreactivity, apposing GcR-positive post-synaptic compartments. In functional transmitter release assay, corticosteroids, corticosterone (0.1-10 microM) and dexamethasone (0.1-10 microM) did not significantly affect the evoked release of [(3)H]GABA and [(14)C]glutamate in superfused synaptosomes, isolated from both rats and mice. In contrast, the synthetic cannabinoid, WIN55212-2 (1 microM) diminished the release of both [(3)H]GABA and [(14)C]glutamate, evoked with various depolarization paradigms. This effect of WIN55212-2 was abolished by the CB1R neutral antagonist, O-2050 (1 microM), and was absent in the CB1R KO mice. CB2R-selective agonists did not affect the release of either neurotransmitter. The lack of robust presynaptic neuromodulation by corticosteroids was unchanged upon either CB1R activation or genetic inactivation. Altogether, corticosteroids are unlikely to exert direct non-genomic presynaptic neuromodulation in the frontal cortex, but they may do so indirectly, via the stimulation of trans-synaptic endocannabinoid signaling.

Cognitive Impairment Induced by Delta9-tetrahydrocannabinol Occurs through Heteromers between Cannabinoid CB1 and Serotonin 5-HT2A Receptors

Activation of cannabinoid CB1 receptors (CB1R) by delta9-tetrahydrocannabinol (THC) produces a variety of negative effects with major consequences in cannabis users that constitute important drawbacks for the use of cannabinoids as therapeutic agents. For this reason, there is a tremendous medical interest in harnessing the beneficial effects of THC. Behavioral studies carried out in mice lacking 5-HT2A receptors (5-HT2AR) revealed a remarkable 5-HT2AR-dependent dissociation in the beneficial antinociceptive effects of THC and its detrimental amnesic properties. We found that specific effects of THC such as memory deficits, anxiolytic-like effects, and social interaction are under the control of 5-HT2AR, but its acute hypolocomotor, hypothermic, anxiogenic, and antinociceptive effects are not. In biochemical studies, we show that CB1R and 5-HT2AR form heteromers that are expressed and functionally active in specific brain regions involved in memory impairment. Remarkably, our functional data shows that costimulation of both receptors by agonists reduces cell signaling, antagonist binding to one receptor blocks signaling of the interacting receptor, and heteromer formation leads to a switch in G-protein coupling for 5-HT2AR from Gq to Gi proteins. Synthetic peptides with the sequence of transmembrane helices 5 and 6 of CB1R, fused to a cell-penetrating peptide, were able to disrupt receptor heteromerization in vivo, leading to a selective abrogation of memory impairments caused by exposure to THC. These data reveal a novel molecular mechanism for the functional interaction between CB1R and 5-HT2AR mediating cognitive impairment. CB1R-5-HT2AR heteromers are thus good targets to dissociate the cognitive deficits induced by THC from its beneficial antinociceptive properties.

Proapoptotic effect of endocannabinoids in prostate cancer cells

In the early stages, prostate cancer is androgen‑ dependent; therefore, medical castration has shown significant results during the initial stages of this pathology. Despite this early effect, advanced prostate cancer is resilient to such treatment. Recent evidence shows that derivatives of Cannabis sativa and its analogs may exert a protective effect against different types of oncologic pathologies. The purpose of the present study was to detect the presence of cannabinoid receptors (CB1 and CB2) on cancer cells with a prostatic origin and to evaluate the effect of the in vitro use of synthetic analogs. In order to do this, we used a commercial cell line and primary cultures derived from prostate cancer and benign prostatic hyperplasia. The presence of the CB1 and CB2 receptors was determined by immunohistochemistry where we showed a higher expression of these receptors in later stages of the disease (samples with a high Gleason score). Later, treatments were conducted using anandamide, 2-arachidonoyl glycerol and a synthetic analog of anandamide, methanandamide. Using the MTT assay, we proved that the treatments produced a cell growth inhibitory effect on all the different prostate cancer cultures. This effect was demonstrated to be dose-dependent. The use of a specific CB1 receptor blocker (SR141716) confirmed that this effect was produced primarily from the activation of the CB1 receptor. In order to understand the MTT assay results, we determined cell cycle distribution by flow cytometry, which showed no variation at the different cell cycle stages in all the cultures after treatment. Treatment with endocannabinoids resulted in an increase in the percentage of apoptotic cells as determined by Annexin V assays and caused an increase in the levels of activated caspase-3 and a reduction in the levels of Bcl-2 confirming that the reduction in cell viability noted in the MTT assay was caused by the activation of the apoptotic pathway. Finally, we observed that endocannabinoid treatment activated the Erk pathway and at the same time, produced a decrease in the activation levels of the Akt pathway. Based on these results, we suggest that endocannabinoids may be a beneficial option for the treatment of prostate cancer that has become nonresponsive to common therapies.

Ethanol exposure induces neonatal neurodegeneration by enhancing CB1R Exon1 histone H4K8 acetylation and up-regulating CB1R function causing neurobehavioral abnormalities in adult mice

BACKGROUND

Ethanol exposure to rodents during postnatal day 7 (P7), which is comparable to the third trimester of human pregnancy, induces long-term potentiation and memory deficits. However, the molecular mechanisms underlying these deficits are still poorly understood.

METHODS

In the present study, we explored the potential role of epigenetic changes at cannabinoid type 1 (CB1R) exon1 and additional CB1R functions, which could promote memory deficits in animal models of fetal alcohol spectrum disorder.

RESULTS

We found that ethanol treatment of P7 mice enhances acetylation of H4 on lysine 8 (H4K8ace) at CB1R exon1, CB1R binding as well as the CB1R agonist-stimulated GTPγS binding in the hippocampus and neocortex, two brain regions that are vulnerable to ethanol at P7 and are important for memory formation and storage, respectively. We also found that ethanol inhibits cyclic adenosine monophosphate response element-binding protein (CREB) phosphorylation and activity-regulated cytoskeleton-associated protein (Arc) expression in neonatal and adult mice. The blockade or genetic deletion of CB1Rs prior to ethanol treatment at P7 rescued CREB phosphorylation and Arc expression. CB1R knockout mice exhibited neither ethanol-induced neurodegeneration nor inhibition of CREB phosphorylation or Arc expression. However, both neonatal and adult mice did exhibit enhanced CREB phosphorylation and Arc protein expression. P7 ethanol-treated adult mice exhibited impaired spatial and social recognition memory, which were prevented by the pharmacological blockade or deletion of CB1Rs at P7.

CONCLUSIONS

Together, these findings suggest that P7 ethanol treatment induces CB1R expression through epigenetic modification of the CB1R gene, and that the enhanced CB1R function induces pCREB, Arc, spatial, and social memory deficits in adult mice.

The endocannabinoid system and the neuroendocrine control of hydromineral balance

Endocannabinoids (ECBs) are ubiquitous lipophilic agents, and this characteristic is consistent with the wide range of homeostatic functions attributed to the ECB system. There is an increasing number of studies showing that the ECB system affects neurotransmission within the hypothalamic neurohypophyseal system. We provide an overview of the primary roles of ECBs in the modulation of neuroendocrine function and, specifically, in the control of hydromineral homeostasis. Accordingly, the general aspects of ECB-mediated signalling, as well as the specific contributions of the central component of the ECB system to the integration of behavioural and endocrine responses that control body fluid homeostasis, are discussed.

Prenatal poly I:C age-dependently alters cannabinoid type 1 receptors in offspring: a longitudinal small animal PET study using [(18)F]MK-9470

Evidence suggests that there is a link between the endocannabinoid system (ECS) and neuropsychiatric illnesses, including schizophrenia. Whilst the ECS has been shown to be involved in immune system regulation in various ways, it is known that infections during pregnancy can modulate the immune system of the mother and increase the risk for schizophrenia in offspring. In animal studies, maternal immune activation following administration of viral or bacterial mimics has been shown to reproduce many key structural, behavioural, and pharmacological abnormalities in offspring that resemble schizophrenia. In the present study, we used Positron Emission Tomography (PET) and [(18)F]MK-9470, a selective high-affinity inverse agonist radioligand for cannabinoid type 1 receptors (CB1R), to longitudinally assess CB1R expression in the progeny of female rats exposed to the viral mimic polyriboinosinic-polyribocytidilic acid (poly I:C) (4mg/kg i.v.) or vehicle at gestational day 15 (GD 15). PET scans were performed in offspring at postnatal days (PND) 32-42 (adolescence) and in the same animals again at PNDs 75-79 (adulthood). Sixteen regions of interest were assessed, encompassing the whole rat brain. At adolescence, offspring exposed prenatally to poly I:C had significantly lower CB1R relative Standard Uptake Values (rSUV) compared to controls in the globus pallidus (p=0.046). In adulthood, however, poly I:C exposed offspring had higher levels of CB1R rSUV in sensory cortex (p=0.034) and hypothalamus (p=0.032) compared to controls. Our results suggest that prenatal poly I:C leads to long term alterations in the integrity of the ECS that are age and region-specific. The increased CB1R expression in adulthood following poly I:C mirrors the increased CB1R observed in patients with schizophrenia in post-mortem and in vivo PET studies.

[Neurobiology of endocannabinoids and central effects of tetrahydrocannabinol contained in indian hemp]

Tetrahydrocannabinol, the main psychotropic component of Cannabis indica, is an addictive drug with multiple effects including both peripheral and central damages. All these effects are due to interference with endocannabinoidergic transmission. This endocannabinoid system subtly regulates many physiologicalfunctions. This regulation involves various ligands derived from arachidonic acid (anandamide, di-arachidonoylglycerol, virodhamin, noladin ether, N arachidonoyl dopamine, etc.) which stimulate two main types of receptor CB1 in the central nervous system and CB2 in the periphery. CB1 receptors are very numerous and ubiquitous in the brain. They influence various important functions (awakening, attention, delirium, hallucinations, memory, cognition, anxiety, humor stability, motor coordination, brain maturation, etc.). Far from mimicking endocannabinoids, THC caricatures their effects. It affects all brain structures, simultaneously, intensely and durably, inducing down-regulation of CB1 receptors and thereby reducing the effects of their physiological ligands. On account of its exceptional lipophilia, THC accumulates for days and even weeks in the brain. It is not a soft drug but rather a slow drug: its abuse induces long-lasting modifications and deterioration of brain function, potentially leading to various mental and psychiatric disorders.

β-arrestins: regulatory role and therapeutic potential in opioid and cannabinoid receptor-mediated analgesia

Pain is a complex disorder with neurochemical and psychological components contributing to the severity, the persistence, and the difficulty in adequately treating the condition. Opioid and cannabinoids are two classes of analgesics that have been used to treat pain for centuries and are arguably the oldest of "pharmacological" interventions used by man. Unfortunately, they also produce several adverse side effects that can complicate pain management. Opioids and cannabinoids act at G protein-coupled receptors (GPCRs), and much of their effects are mediated by the mu-opioid receptor (MOR) and cannabinoid CB1 receptor (CB1R), respectively. These receptors couple to intracellular second messengers and regulatory proteins to impart their biological effects. In this chapter, we review the role of the intracellular regulatory proteins, β-arrestins, in modulating MOR and CB1R and how they influence the analgesic and side-effect profiles of opioid and cannabinoid drugs in vivo. This review of the literature suggests that the development of opioid and cannabinoid agonists that bias MOR and CB1R toward G protein signaling cascades and away from β-arrestin interactions may provide a novel mechanism by which to produce analgesia with less severe adverse effects.

[Short-and long-term effects of cannabinoids on memory, cognition and mental illness]

Marijuana is considered the most commonly used drug in the world, with estimated millions of users. There is dissent in the medical world about the positive and negative effects of marijuana, and recently, a large research effort has been directed to that domain. The main influencing drug ingredient is THC, which acts on the cannabinoid system and binds to the CB1 receptor. The discovery of the receptor led to the finding of an endogenous ligand, anandamide, and another receptor-CB2. The researchers also discovered that cannabinoids have extensive biological activity, and its short and long-term effects may cause cognitive and emotional deficiencies. Findings show that the short-term effects, such as shortterm memory and verbal Learning, are reversible. However, despite the accumulation of evidence about long-term cognitive damage due to cannabis use, it is difficult to find unequivocal results, arising from the existence of many variables such as large differences between cannabis users, frequency of use, dosage and endogenous brain compensation. Apart from cognitive damage, current studies investigate how marijuana affects mental illness: a high correlation between cannabis use and schizophrenia was found and a high risk to undergo a psychotic attack. Furthermore, patients with schizophrenia who used cannabis showed a selective neuro-psychological disruption, and similar cognitive deficiencies and brain morphological changes were found among healthy cannabis users and schizophrenia patients. In contrast to the negative effects of marijuana including addiction, there are the medical uses: reducing pain, anxiety and nausea, increasing appetite and an anti-inflammatory activity. Medicalization of marijuana encourages frequent use, which may elevate depression.

Cannabinoids and traumatic stress modulation of contextual fear extinction and GR expression in the amygdala-hippocampal-prefrontal circuit

Considerable evidence suggests that cannabinoids modulate the behavioral and physiological response to stressful events. We have recently shown that activating the cannabinoid system using the CB1/CB2 receptor agonist WIN55,212-2 (WIN) in proximity to exposure to single-prolonged stress (SPS), a rat model of emotional trauma, prevented the stress-induced enhancement of acoustic startle response, the impairment in avoidance extinction and the enhanced negative feedback on the hypothalamic-pituitary-adrenal (HPA) axis (Ganon-Elazar and Akirav, 2012). Some of the effects were found to be mediated by CB1 receptors in the basolateral amygdala (BLA). Here we examined whether cannabinoid receptor activation in a putative brain circuit that includes the BLA, hippocampus and prefrontal cortex (PFC), could prevent the effects of traumatic stress on contextual fear extinction and alterations in glucocorticoid receptor (GR) protein levels. We found that: (i) SPS impaired contextual fear extinction tested one week after trauma exposure and that WIN prevented the stress-induced impairment of extinction when microinjected immediately after trauma exposure into the BLA or hippocampus (5 μg), but not when microinjected into the PFC, (ii) the ameliorating effects of WIN on contextual extinction were prevented by blocking GRs in the BLA and hippocampus, and (iii) SPS up regulated GRs in the BLA, PFC and hippocampus and systemic WIN administration (0.5 mg/kg) after trauma exposure normalized GR levels in the BLA and hippocampus, but not in the PFC. Cannabinoid receptor activation in the aftermath of trauma exposure may regulate the emotional response to the trauma and prevent stress-induced impairment of extinction and GR up regulation through the mediation of CB1 receptors in the BLA and hippocampus. Taken together, the findings suggest that the interaction between the cannabinoid and glucocorticoid systems is crucial in the modulation of emotional trauma.

Driving under the influence of synthetic cannabinoids ("Spice"): a case series

Recreational use of synthetic cannabinoid receptor agonists-so-called "Spice" products-became very popular during the last few years. Several reports on clinical symptoms and poisonings were published. Unfortunately, most of these reports do not contain any analytical data on synthetic cannabinoids in body fluids, and no or only a limited number of cases were reported concerning driving under the influence (DUI) of this kind of drugs. In this article, several cases of DUI of synthetic cannabinoids (AM-2201, JWH-018, JWH-019, JWH-122, JWH-210, JWH-307, MAM-2201 (JWH-122 5-fluoropentyl derivative), and UR-144) are presented, focusing on analytical results and signs of impairment documented by the police or the physicians who had taken the blood sample from the suspects. Consumption of synthetic cannabinoids can lead to impairment similar to typical performance deficits caused by cannabis use which are not compatible with safe driving. These deficits include centrally sedating effects and impairment of fine motor skills necessary for keeping the vehicle on track. Police as well as forensic toxicologists and other groups should become familiar with the effects of synthetic cannabinoid use, and be aware of the fact that drug users may shift to these "legal" alternatives due to their nondetectability by commonly used drug screening tests based on antibodies. Sophisticated screening procedures covering the complete range of available compounds or their metabolites have to be developed for both blood/serum and urine testing.

WIN55, 212-2 promotes differentiation of oligodendrocyte precursor cells and improve remyelination through regulation of the phosphorylation level of the ERK 1/2 via cannabinoid receptor 1 after stroke-induced demyelination

In stroke, a common cause of neurological disability in adults is that the myelin sheaths are lost through the injury or death of mature oligodendrocytes, and the failure of remyelination may be often due to insufficient proliferation and differentiation of oligodendroglial progenitors. In the current study, we used middle cerebral artery occlusion (MCAO) to induced transient focal cerebral ischemia, and found that WIN55, 212-2 augmented actively proliferating oligodendrocytes measured by CC1 immunoreactive cells within the peri-infarct areas. To establish whether these effects were associated with changes in myelin formation, we analyzed the expression of myelin basic protein (MBP) and myelin ultrastructure. We found that WIN55, 212-2 showed more extensive remyelination than vehicle at 14 days post injection (dpi). The extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling pathway may be involved in OPCs differentiation. To determine the regulatory effect of WIN55, 212-2 post-treatment on phospho-ERK 1/2 (p-ERK 1/2) after ischemia/reperfusion, Western blot analysis was performed. We found that WIN55, 212-2 regulated the phosphorylation level of the ERK 1/2 to promote OPCs survival and differentiation. Notably, cannabinoid receptor 1 is coupled to the activation of the ERK cascade. Following rimonabant combined treatment, the effect of WIN55, 212-2 on regulating the phosphorylation level of the ERK 1/2 was reversed, and the effect of accelerated myelin formation was partially inhibited. Together, we first found that WIN55, 212-2 promoted OPCs differentiation and remyelination through regulation of the level of the p-ERK 1/2 via cannabinoid receptor 1.

Triphasic blood pressure responses to cannabinoids: do we understand the mechanism?

The cannabinoids comprise three major classes of substances, including compounds derived from the cannabis plant (e.g. Δ(9) -tetrahydrocannabinol and the chemically related substances CP55940 and HU210), endogenously formed (e.g. anandamide) and synthetic compounds (e.g. WIN55212-2). Beyond their psychotropic effects, cannabinoids have complex effects on blood pressure, including biphasic changes of Δ(9) -tetrahydrocannabinol and WIN55212-2 and an even triphasic effect of anandamide. The differing pattern of blood pressure changes displayed by the three types of compounds is not really surprising since, although they share an agonistic effect at cannabinoid CB(1) and CB(2) receptors, some compounds have additional effects. In particular, anandamide is known for its pleiotropic effects, and there is overwhelming evidence that anandamide influences blood pressure via (i) CB(1) receptors, (ii) TRPV1 receptors, (iii) endothelial cannabinoid receptors and (iv) degradation products. This review is dedicated to the description of the effects of externally added cannabinoids on cardiovascular parameters in vivo. First, the cardiovascular effects of cannabinoids in anaesthetized animals will be highlighted since most data have been generated in experiments of that type. The text will follow the three phases of anandamide on blood pressure, and we will check to which extent cardiovascular changes elicited by other cannabinoids show overlap with those effects or differ. The second part will be dedicated to the cardiovascular effects of the cannabinoids in conscious animals. In the third part, cardiovascular effects in humans will be discussed, and similarities and differences with respect to the data from animals will be examined.

Presynaptic CB(1) cannabinoid receptors control frontocortical serotonin and glutamate release--species differences

Both the serotonergic and endocannabinoid systems modulate frontocortical glutamate release; thus they are well positioned to participate in the pathogenesis of psychiatric disorders. With the help of fluorescent and confocal microscopy, we localized the CB(1) cannabinoid receptor (CB(1)R) in VGLUT1- and 2- (i.e. glutamatergic) and serotonin transporter- (i.e. serotonergic) -positive fibers and nerve terminals in the mouse and rat frontal cortex. CB(1)R activation by the synthetic agonists, WIN55212-2 (1 μM) and R-methanandamide (1 μM) inhibited the simultaneously measured evoked Ca(2+)-dependent release of [(14)C]glutamate and [(3)H]serotonin from frontocortical nerve terminals of Wistar rats, in a fashion sensitive to the CB(1)R antagonists, O-2050 (1 μM) and LY320135 (5 μM). CB(1)R agonists also inhibited the evoked release of [(14)C]glutamate in C57BL/6J mice in a reversible fashion upon washout. Interestingly, the evoked release of [(14)C]glutamate and [(3)H]serotonin was significantly greater in the CB(1)R knockout CD-1 mice. Furthermore, CB(1)R binding experiments revealed similar frontocortical CB(1)R density in the rat and the CD-1 mouse. Still, the evoked release of [(3)H]serotonin was modulated by neither CB(1)R agonists nor antagonists in wild-type CD-1 or C57BL/6J mice. Altogether, this is the first study to demonstrate functional presynaptic CB(1)Rs in frontocortical glutamatergic and serotonergic terminals, revealing species differences.

Innate difference in the endocannabinoid signaling and its modulation by alcohol consumption in alcohol-preferring sP rats

The present study was undertaken to examine whether genetically predetermined differences in components of the endocannabinoid system were present in the brain of Sardinian alcohol-preferring (sP) and Sardinian alcohol-non-preferring (sNP) rats, a pair of rat lines selectively bred for opposite alcohol preference. The effects of acquisition and maintenance of alcohol drinking, alcohol withdrawal, and alcohol re-exposure on the endocannabinoid system was also assessed in the striatum of sP rats. The findings revealed significantly higher density of the CB1 receptors and levels of CB1 receptor mRNA, CB1 receptor-mediated G-protein coupling, and endocannabinoids in the cerebral cortex, hippocampus and striatum of alcohol-naive sP rats than sNP rats. A significantly lower expression of mFAAH enzyme was evident in the hippocampus of alcohol-naive sP rats. Alcohol drinking (during both acquisition and maintenance phases) in sP rats resulted in a significant reduction in striatal CB1 receptor-mediated G-protein coupling whereas alcohol withdrawal attenuated this effect. Alcohol consumption was also associated with markedly increased levels of endocannabinoids in the striatum. Co-administration of the CB1 receptor antagonist, rimonabant (SR141716A) reduced alcohol intake, and reversed alcohol-induced changes in CB1 receptor-mediated G-protein activation. These findings provided a new insight into a potential genetic basis of excessive alcohol consumption, suggesting innate differences in the endocannabinoid system might be associated with higher alcohol preference in sP rats. The data also indicate a modulation of CB1 receptor-mediated signaling following alcohol consumption, and further strengthen the potential of the endocannabinoid system as a target for the treatment of alcohol related behaviors.

Regulation of opioid and cannabinoid receptor genes in human neuroblastoma and T cells by the epigenetic modifiers trichostatin A and 5-aza-2'-deoxycytidine

OBJECTIVE

The aim of this study was to investigate the effect of the epigenetic modifiers trichostatin A and 5-aza-2'-deoxycytidine on the expression of the cannabinoid receptors CB1 and CB2 and μ-opioid receptors in human SH SY5Y neuroblastoma cells and human Jurkat T lymphocytes.

METHODS

Using quantitative real-time RT-PCR, mRNA specific for the aforementioned receptors was determined. The functionality of the induced receptors was determined by analyzing the effect of the ligands to regulate intracellular cAMP.

RESULTS

We demonstrated that treatment of SH SY5Y cells, which endogenously express μ-opioid receptors and CB1, but not CB2, resulted in de novo induction of CB2, while mRNA levels of CB1 and μ-opioid receptors were not significantly altered. In contrast, treatment of Jurkat lymphocytes, which endogenously express CB2, but not CB1 and μ-opioid receptors, resulted in de novo induction of CB1 and μ-opioid receptors, while mRNA levels of CB2 were not significantly altered. Furthermore, the functionality of the induced μ-opioid receptors and CB1 in the Jurkat cells was demonstrated.

CONCLUSIONS

Our data suggest an epigenetically regulated expression of cannabinoid receptors and μ-opioid receptors. Their induction by epigenetic modifiers in distinct cells of the nervous and immune system might result in increased effects of the cognate drugs on neuronal and immune functions. Such modifications might be useful for novel therapies for various disorders, e.g. multiple sclerosis, where the elevated transmission of cannabinoid or opioid signals is beneficial.

Bioactive prenylogous cannabinoid from fiber hemp (Cannabis sativa)

The waxy fraction from the variety Carma of fiber hemp (Cannabis sativa) afforded the unusual cannabinoid 4, identified as the farnesyl prenylogue of cannabigerol (CBG, 1) on the basis of its spectroscopic properties. A comparative study of the profile of 4 and 1 toward metabotropic (CB1, CB2) and ionotropic (TRPV1, TRPV2, TRPM8, TRPA1) targets of phytocannabinoids showed that prenylogation increased potency toward CB2 by ca. 5-fold, with no substantial difference toward the other end-points, except for a decreased affinity for TRPM8. The isolation of 4 suggests that C. sativa could contain yet-to-be-discovered prenylogous versions of medicinally relevant cannabinoids, for which their biological profiles could offer interesting opportunities for biomedical exploitation.

Attenuation of food intake in chicks by an inverse agonist of cannabinoid receptor 1 administered by either injection or ingestion in hydrocolloid carriers

The cannabinoid receptor (CB(1)) was studied primarily in mammals where it was found to comprise a link between reward processes and addictive behavior such as food consumption. The purpose of this study was twofold: first to characterize the effect of the chicken CB(1) receptor inverse agonist AM251 on food intake, and second, to establish a stress-free approach for application of AM251 to birds using hydrocolloid carriers, which can be mixed with food. A single administration of AM251 by intravenous injection (at 0.85 or 5 mg kg(-1)BW) or by ingestion of hydrocolloid carriers entrapping AM251 at a concentration of 5 mg kg(-1)BW led to a transient attenuation of food intake. The consequent reduced cumulative food intake and BW were observed in the treated chicks for at least 7h post-administration, with no gender differences. Circulating levels of AM251, assessed by LC-MS following 48 h of continuous feeding with hydrocolloid carriers containing 50mg AM 251 kg(-1) BW day(-1), were physiologically significant at 186 ± 73 pmol ml(-1). It is concluded that unlike some other factors, which act differently in birds compared to mammals such as ghrelin, CB(1) inverse agonists attenuate food intake in chicks similar to its effect in mammals. In addition, the new approach for administration of AM251 to birds in hydrocolloid carriers could provide a simple and stress-free tool for prolonged studies of this control mechanism in birds.

Long-term behavioral and pharmacodynamic effects of delta-9-tetrahydrocannabinol in female rats depend on ovarian hormone status

Abuse of Δ⁹-THC by females during adolescence may produce long-term deficits in complex behavioral processes such as learning, and these deficits may be affected by the presence of ovarian hormones. To assess this possibility, 40 injections of saline or 5.6 mg/kg of Δ⁹-THC were administered i.p. daily during adolescence to gonadally intact or ovariectomized (OVX) female rats, yielding four treatment groups (intact/saline, intact/THC, OVX/saline, and OVX/ THC). Δ⁹-THC (0.56-10 mg/kg) was then re-administered to each of the four groups during adulthood to examine their sensitivity to its disruptive effects. The behavioral task required adult subjects to both learn (acquisition component) different response sequences and repeat a known response sequence (performance component) daily. During baseline (no injection) and control (saline injection) sessions, OVX subjects had significantly higher response rates and lower percentages of error in both behavioral components than the intact groups irrespective of saline or Δ⁹-THC administration during adolescence; the intact group that received Δ⁹-THC had the lowest response rates in each component. Upon re-administration of Δ⁹-THC, the groups that received adolescent ovariectomy alone, adolescent Δ⁹-THC administration alone, or both treatments were found to be less sensitive to the rate-decreasing effects, and more sensitive to the error-increasing effects of Δ⁹-THC than the control group (i.e. intact subjects that received saline during adolescence). Neurochemical analyses of the brains from each adolescent-treated group indicated that there were also persistent effects on cannabinoid type-1 (CB-1) receptor levels in the hippocampus and striatum that depended on the brain region and the presence of ovarian hormones. In addition, autoradiographic analyses of the brains from adolescent-treated, but behaviorally naïve, subjects indicated that ovariectomy and Δ⁹-THC administration produced effects on receptor coupling in some of the same brain regions. In summary, chronic administration of Δ⁹-THC during adolescence in female rats produced long-term effects on operant learning and performance tasks and on the cannabinoid system that were mediated by the presence of ovarian hormones, and that altered their sensitivity to Δ⁹-THC as adults.

A second-order schedule of food reinforcement in rats to examine the role of CB1 receptors in the reinforcement-enhancing effects of nicotine

Nicotine is believed to enhance the motivational value of reinforcers. Although endogenous cannabinoids acting on CB1 receptors have been implicated in the motivational effects of nicotine, their role in the 'reinforcement-enhancing' properties of nicotine is unknown. This study compared the effect of acute and chronic non-contingent nicotine administration on responding for an unconditioned reinforcing stimulus (UCS) and a visual conditioned stimulus (CS) and the role of CB1 receptors was examined. Male hooded Lister rats were trained on a second-order schedule [FI 15' (FR5: S)] under which presentation of the CS (5s/5Hz light oscillation) was intermittently reinforced by the UCS (food). The rats were treated with daily saline or nicotine (0.4 mg/kg, subcutaneous [s.c.]) throughout the study. The effect of the acute nicotine challenge (0.05, 0.1 and 0.2 mg/kg, s.c.) and the CB1 receptor antagonist AM251 (0.1, 0.3 and 1 mg/kg, intraperitoneal [i.p.]) on responding for the CS and/or UCS was examined. The acute nicotine challenge increased responding for both the UCS and CS in the rats chronically treated with nicotine, an effect which was less robust in the nicotine-naive rats. AM251 significantly reduced responding for the UCS and CS, and an interaction with the nicotine challenge was found. These data support and extend the hypothesis that nicotine can enhance the motivational value of reinforcing stimuli and suggest the increases in responding produced by nicotine involve CB1 receptors. Furthermore, this study highlights the utility of second-order schedules of reinforcement for investigation of the neural circuits underlying the reinforcement-enhancing effects of nicotine.

[Analgesic effect of Corydalis yanhusuo in a rat model of trigeminal neuropathic pain]

OBJECTIVE

To evaluate the analgesic effect of Corydalis yanhusuo on trigeminal neuropathic pain.in a rat model.

METHOD

Rat model of trigeminal neuralgia pain were established by inducing chronic constriction injury (CCI) of the infraorbital branch of the trigeminal nerve (ION). The effect of Corydalis yanhusuo, a traditional Chinese medicine, in ameliorating the pain was tested. Western blotting was performed to investigate the change of cannabinoid CB1 receptors in the Vc the injury of the infraorbital branch of the trigeminal nerve (ION-CCI). CB1 receptor antagonist AM 251 was applied to observe its effect on the analgesic effect of Yanhusuo.

RESULT

Administration of dl-THP (2 mg/kg) intraperitoneally increased the response threshold and the cut-off threshold to the mechanical stimulation in ION-CCI rat models. ION-CCI induced an upregulation of cannabinoid CB1 receptors within the ipsilateral of Vc. The effect of Yanhusuo was antagonized by the application of AM 251.

CONCLUSION

The analgesic effect of Yanhusuo involves the participation of CB1 receptors, suggesting that Yanhusuo may offer a useful therapeutic approach for trigeminal neuropathic pain.

Effects of caffeine on striatal neurotransmission: focus on cannabinoid CB1 receptors

Caffeine is the most commonly self-administered psychoactive substance worldwide. At usual doses, the effects of caffeine on vigilance, attention, mood and arousal largely depend on the modulation of central adenosine receptors. The present review article describes the action of caffeine within the striatum, to provide a possible molecular mechanism at the basis of the psychomotor and reinforcing properties of this pharmacological agent. The striatum is in fact a subcortical area involved in sensorimotor, cognitive, and emotional processes, and recent experimental findings showed that chronic caffeine consumption enhances the sensitivity of striatal GABAergic synapses to the stimulation of cannabinoid CB1 receptors. The endocannabinoid system is involved in the psychoactive effects of many compounds, and adenosine A2A receptors (the main receptor target of caffeine) elicit a permissive effect towards CB1 receptors, thus suggesting that A2A-CB1 receptor interaction plays a major role in the generation and maintenance of caffeine reinforcing behavior. Aim of this review is to describe the effects of caffeine on striatal neurotransmission with special reference to the modulation of the endocannabinoid system.

Altered architecture and functional consequences of the mesolimbic dopamine system in cannabis dependence

Cannabinoid withdrawal produces a hypofunction of mesencephalic dopamine neurons that impinge upon medium spiny neurons (MSN) of the forebrain. After chronic treatment with two structurally different cannabinoid agonists, Delta(9)-tetrahydrocannabinol and CP55 940 (CP) rats were withdrawn spontaneously and pharmacologically with the CB1 antagonist SR141716A (SR). In these two conditions, evaluation of tyrosine hydroxylase (TH)-positive neurons revealed significant morphometrical reductions in the ventrotegmental area but not substantia nigra pars compacta of withdrawn rats. Similarly, confocal analysis of Golgi-Cox-stained sections of the nucleus accumbens revealed a decrease in the shell, but not the core, of the spines' density of withdrawn rats. Administration of the CB1 antagonist SR to control rats, provoked structural abnormalities reminiscent of those observed in withdrawal conditions and support the regulatory role of cannabinoids in neurogenesis, axonal growth and synaptogenesis by acting as eu-proliferative signals through the CB1 receptors. Further, these measures were incorporated into a realistic computational model that predicts a strong reduction in the excitability of morphologically altered MSN, yielding a significant reduction in action potential output. These pieces of evidence support the tenet that withdrawal from addictive compounds alters functioning of the mesolimbic system and provide direct morphological evidence for functional abnormalities associated with cannabinoid dependence at the level of dopaminergic neurons and their postsynaptic counterpart and are coherent with recent hypothesis underscoring a hypodopaminergic state as a distinctive feature of the 'addicted brain'.

Dopaminergic augmentation of delta-9-tetrahydrocannabinol (THC) discrimination: possible involvement of D(2)-induced formation of anandamide

RATIONAL

Although delta-9-tetreahydrocannabinol (THC)-induced elevations in accumbal dopamine levels are believed to play an important role in the abuse-related effects of cannabis, little direct evidence has been provided that the dopaminergic system is involved in the psychotropic effects of THC.

OBJECTIVE

The objective of this study is to investigate whether drugs activating or blocking the dopaminergic system modulate the discriminative effects of THC.

METHODS AND RESULTS

In rats that had learned to discriminate 3 mg/kg of THC from vehicle injections, the indirect dopaminergic agonists cocaine and amphetamine, the D(1)-receptor agonist SKF-38393, and the D(2)-receptor agonists quinpirole and apomorphine did not produce significant THC-like discriminative effects. However, both cocaine and amphetamine and D(2)-, but not the D(1)-, receptor agonists, augmented THC discrimination. Neither the D(1)-receptor antagonist SCH-23390 nor the D(2)-receptor antagonist raclopride reduced the discriminative effects of THC, even at doses that significantly depressed baseline operant responding. However, the D(2)-, but not the D(1)-, antagonist counteracted the augmentation of THC's discriminative effects produced by cocaine and amphetamine. We hypothesized that release of anandamide by activation of D(2) receptors was responsible for the observed augmentation of THC discrimination. This hypothesis was supported by two findings. First, the cannabinoid CB(1)-receptor antagonist rimonabant blocked quinpirole-induced augmentation of THC discrimination. Second, inhibition of anandamide degradation by blockade of fatty acid amide hydrolase augmented the THC-like effects of quinpirole.

CONCLUSIONS

Dopamine does not play a major role in THC discrimination. However, activation of the dopaminergic system positively modulates the discriminative effects of THC, possibly through D(2)-induced elevations in brain levels of anandamide.

FAAH and MAGL inhibitors: therapeutic opportunities from regulating endocannabinoid levels

Apart from their widespread recreational abuse, the psychoactive preparations of the plant Cannabis sativa and its major psychotropic component, Delta9-tetrahydrocannabinol (THC), are also known for their medicinal properties. Following the identification of receptors for THC - the cannabinoid CB1 and CB2 receptors - in mammals, various pharmaceutical strategies have attempted to exploit the properties of the cannabinoid system while minimizing psychotropic side effects. The cloning of the cannabinoid CB1 and CB2 receptors enabled the discovery of the endogenous agonists of the receptors, the endocannabinoids, and eventually led to the identification of enzymes that catalyze endocannabinoid inactivation. Unlike exogenously administered THC and synthetic CB1 and CB2 agonists, the endocannabinoids that are produced endogenously following the onset of several pathologies may act in a site- and time-specific manner to minimize the consequences of such conditions. This observation has suggested the possibility of targeting endocannabinoid-degrading enzymes to prolong the precisely regulated pro-homeostatic action of endocannabinoids. Two major enzymes have been cloned and investigated thoroughly: fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). Inhibitors of these enzymes have demonstrated therapeutic benefit in animal models of several disorders, including neuropathic pain, anxiety and inflammatory bowel diseases, as well as against the proliferation and migration of cancer cells. This review describes the major biochemical properties of FAAH and MAGL, and the design and pharmacological properties of inhibitors of these enzymes.