Endocannabinoids and cannabinoid receptor genetics

Crosstalk between the endocannabinoid and mid-brain dopaminergic systems: Implication in dopamine dysregulation

Endocannabinoids (eCBs) and the expanded endocannabinoid system (ECS)-"endocannabinoidome", consists of the endogenous ligands, eCBs, their canonical and non-canonical receptor subtypes, and their synthesizing and metabolizing enzymes. This system modulates a wide range of body functions and acts as a retrograde signaling system within the central nervous system (CNS) by inhibition of classical transmitters, and plays a vital modulatory function on dopamine, a major neurotransmitter in the CNS. Dopamine is involved in different behavioral processes and contributes to different brain disorders-including Parkinson's disease, schizophrenia, and drug addiction. After synthesis in the neuronal cytosol, dopamine is packaged into synaptic vesicles until released by extracellular signals. Calcium dependent neuronal activation results in the vesicular release of dopamine and interacts with different neurotransmitter systems. The ECS, among others, is involved in the regulation of dopamine release and the interaction occurs either through direct or indirect mechanisms. The cross-talk between the ECS and the dopaminergic system has important influence in various dopamine-related neurobiological and pathologic conditions and investigating this interaction might help identify therapeutic targets and options in disorders of the CNS associated with dopamine dysregulation.

Effects of Prenatal Cannabinoids Exposure upon Placenta and Development of Respiratory Neural Circuits

Cannabis use has risen dangerously during pregnancy in the face of incipient therapeutic use and a growing perception of safety. The main psychoactive compound of the Cannabis sativa plant is the phytocannabinoid delta-9-tetrahydrocannabinol (A-9 THC), and its status as a teratogen is controversial. THC and its endogenous analogues, anandamide (AEA) and 2-AG, exert their actions through specific receptors (eCBr) that activate intracellular signaling pathways. CB1r and CB2r, also called classic cannabinoid receptors, together with their endogenous ligands and the enzymes that synthesize and degrade them, constitute the endocannabinoid system. This system is distributed ubiquitously in various central and peripheral tissues. Although the endocannabinoid system's most studied role is controlling the release of neurotransmitters in the central nervous system, the study of long-term exposure to cannabinoids on fetal development is not well known and is vital for understanding environmental or pathological embryo-fetal or postnatal conditions. Prenatal exposure to cannabinoids in animal models has induced changes in placental and embryo-fetal organs. Particularly, cannabinoids could influence both neural and nonneural tissues and induce embryo-fetal pathological conditions in critical processes such as neural respiratory control. This review aims at the acute and chronic effects of prenatal exposure to cannabinoids on placental function and the embryo-fetal neurodevelopment of the respiratory pattern. The information provided here will serve as a theoretical framework to critically evaluate the teratogen effects of the consumption of cannabis during pregnancy.

Molecular Insights into Epigenetics and Cannabinoid Receptors

The actions of cannabis are mediated by G protein-coupled receptors that are part of an endogenous cannabinoid system (ECS). ECS consists of the naturally occurring ligands N-arachidonylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), their biosynthetic and degradative enzymes, and the CB1 and CB2 cannabinoid receptors. Epigenetics are heritable changes that affect gene expression without changing the DNA sequence, transducing external stimuli in stable alterations of the DNA or chromatin structure. Cannabinoid receptors are crucial candidates for exploring their functions through epigenetic approaches due to their significant roles in health and diseases. Epigenetic changes usually promote alterations in the expression of genes and proteins that can be evaluated by various transcriptomic and proteomic analyses. Despite the exponential growth of new evidence on the critical functions of cannabinoid receptors, much is still unknown regarding the contribution of various genetic and epigenetic factors that regulate cannabinoid receptor gene expression. Recent studies have identified several immediate and long-lasting epigenetic changes, such as DNA methylation, DNA-associated histone proteins, and RNA regulatory networks, in cannabinoid receptor function. Thus, they can offer solutions to many cellular, molecular, and behavioral impairments found after modulation of cannabinoid receptor activities. In this review, we discuss the significant research advances in different epigenetic factors contributing to the regulation of cannabinoid receptors and their functions under both physiological and pathological conditions. Increasing our understanding of the epigenetics of cannabinoid receptors will significantly advance our knowledge and could lead to the identification of novel therapeutic targets and innovative treatment strategies for diseases associated with altered cannabinoid receptor functions.

Potential Role of Cannabinoid Type 2 Receptors in Neuropsychiatric and Neurodegenerative Disorders

The endocannabinoid system (ECS) is composed of the two canonical receptor subtypes; type-1 cannabinoid (CB1R) and type 2 receptor (CB2R), endocannabinoids (eCBs) and enzymes responsible for the synthesis and degradation of eCBs. Recently, with the identification of additional lipid mediators, enzymes and receptors, the expanded ECS called the endocannabinoidome (eCBome) has been identified and recognized. Activation of CB1R is associated with a plethora of physiological effects and some central nervous system (CNS) side effects, whereas, CB2R activation is devoid of such effects and hence CB2Rs might be utilized as potential new targets for the treatment of different disorders including neuropsychiatric disorders. Previous studies suggested that CB2Rs were absent in the brain and they were considered as peripheral receptors, however, recent studies confirmed the presence of CB2Rs in different brain regions. Several studies have now focused on the characterization of its physiological and pathological roles. Studies done on the role of CB2Rs as a therapeutic target for treating different disorders revealed important putative role of CB2R in neuropsychiatric disorders that requires further clinical validation. Here we provide current insights and knowledge on the potential role of targeting CB2Rs in neuropsychiatric and neurodegenerative disorders. Its non-psychoactive effect makes the CB2R a potential target for treating CNS disorders; however, a better understanding of the fundamental pharmacology of CB2R activation is essential for the design of novel therapeutic strategies.

New Insights and Potential Therapeutic Targeting of CB2 Cannabinoid Receptors in CNS Disorders

The endocannabinoid system (ECS) is ubiquitous in most human tissues, and involved in the regulation of mental health. Consequently, its dysregulation is associated with neuropsychiatric and neurodegenerative disorders. Together, the ECS and the expanded endocannabinoidome (eCBome) are composed of genes coding for CB1 and CB2 cannabinoid receptors (CB1R, CB2R), endocannabinoids (eCBs), and the metabolic enzyme machinery for their synthesis and catabolism. The activation of CB1R is associated with adverse effects on the central nervous system (CNS), which has limited the therapeutic use of drugs that bind this receptor. The discovery of the functional neuronal CB2R raised new possibilities for the potential and safe targeting of the ECS for the treatment of CNS disorders. Previous studies were not able to detect CB2R mRNA transcripts in brain tissue and suggested that CB2Rs were absent in the brain and were considered peripheral receptors. Studies done on the role of CB2Rs as a potential therapeutic target for treating different disorders revealed the important putative role of CB2Rs in certain CNS disorders, which requires further clinical validation. This review addresses recent advances on the role of CB2Rs in neuropsychiatric and neurodegenerative disorders, including, but not limited to, anxiety, depression, schizophrenia, Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD) and addiction.

Early Consumption of Cannabinoids: From Adult Neurogenesis to Behavior

The endocannabinoid system (ECS) is a crucial modulatory system in which interest has been increasing, particularly regarding the regulation of behavior and neuroplasticity. The adolescent-young adulthood phase of development comprises a critical period in the maturation of the nervous system and the ECS. Neurogenesis occurs in discrete regions of the adult brain, and this process is linked to the modulation of some behaviors. Since marijuana (cannabis) is the most consumed illegal drug globally and the highest consumption rate is observed during adolescence, it is of particular importance to understand the effects of ECS modulation in these early stages of adulthood. Thus, in this article, we sought to summarize recent evidence demonstrating the role of the ECS and exogenous cannabinoid consumption in the adolescent-young adulthood period; elucidate the effects of exogenous cannabinoid consumption on adult neurogenesis; and describe some essential and adaptive behaviors, such as stress, anxiety, learning, and memory. The data summarized in this work highlight the relevance of maintaining balance in the endocannabinoid modulatory system in the early and adult stages of life. Any ECS disturbance may induce significant modifications in the genesis of new neurons and may consequently modify behavioral outcomes.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

Prenatal cannabinoid exposure and altered neurotransmission

Marijuana is one of the most commonly used illicit drugs worldwide. In addition, use of synthetic cannabinoids is increasing, especially among adolescents and young adults. Although human studies have shown that the use of marijuana during pregnancy leads to adverse behavioral effects, such as deficiencies in attention and executive function in affected offspring, the rate of marijuana use among pregnant women is steadily increasing. Various aspects of human behavior including emotion, learning, and memory are dependent on complex interactions between multiple neurotransmitter systems that are especially vulnerable to alterations during the developmental period. Thus, exploration of neurotransmitter changes in response to prenatal cannabinoid exposure is crucial to develop an understanding of how homeostatic imbalance and various long-term neurobehavioral deficits manifest following the abuse of marijuana or other synthetic cannabinoids during pregnancy. Current literature confirms that vast alterations to neurotransmitter systems are present following prenatal cannabinoid exposure, and many of these alterations within the brain are region specific, time-dependent, and sexually dimorphic. In this review, we aim to provide a summary of observed changes to various neurotransmitter systems following cannabinoid exposure during pregnancy and to draw possible correlations to reported behavioral alterations in affected offspring.

Modulation of Endocannabinoid-Binding Receptors in Human Neuroblastoma Cells by Tunicamycin

Endocannabinoid (eCB)-binding receptors can be modulated by several ligands and membrane environment, yet the effect of glycosylation remains to be assessed. In this study, we used human neuroblastoma SH-SY5Y cells to interrogate whether expression, cellular localization, and activity of eCB-binding receptors may depend on N-linked glycosylation. Following treatment with tunicamycin (a specific inhibitor of N-linked glycosylation) at the non-cytotoxic dose of 1 µg/mL, mRNA, protein levels and localization of eCB-binding receptors, as well as N-acetylglucosamine (GlcNAc) residues, were evaluated in SH-SY5Y cells by means of quantitative real-time reverse transcriptase-polymerase chain reaction (qRT-PCR), fluorescence-activated cell sorting (FACS), and confocal microscopy, respectively. In addition, the activity of type-1 and type-2 cannabinoid receptors (CB₁ and CB₂) was assessed by means of rapid binding assays. Significant changes in gene and protein expression were found upon tunicamycin treatment for CB₁ and CB₂, as well as for GPR55 receptors, but not for transient receptor potential vanilloid 1 (TRPV1). Deglycosylation experiments with N-glycosidase-F and immunoblot of cell membranes derived from SH-SY5Y cells confirmed the presence of one glycosylated form in CB₁ (70 kDa), that was reduced by tunicamycin. Morphological studies demonstrated the co-localization of CB₁ with GlcNAc residues, and showed that tunicamycin reduced CB₁ membrane expression with a marked nuclear localization, as confirmed by immunoblotting. Cleavage of the carbohydrate side chain did not modify CB receptor binding affinity. Overall, these results support N-linked glycosylation as an unprecedented post-translational modification that may modulate eCB-binding receptors’ expression and localization, in particular for CB₁.

Mechanisms Underlying Sex Differences in Cannabis Use

Purpose of the Review

Cannabis is the most commonly used illicit substance worldwide. In recent decades, highly concentrated products have flooded the market, and prevalence rates have increased. Gender differences exist in cannabis use, as men have higher prevalence of both cannabis use and cannabis use disorder (CUD), while women progress more rapidly from first use to CUD. This paper reviews findings from preclinical and human studies examining the sex-specific neurobiological underpinnings of cannabis use and CUD, and associations with psychiatric symptoms.

Recent Findings

Sex differences exist in the endocannabinoid system, in cannabis exposure effects on brain structure and function, and in the co-occurrence of cannabis use with symptoms of anxiety, depression and schizophrenia. In female cannabis users, anxiety symptoms correlate with larger amygdala volume and social anxiety disorder symptoms correlate with CUD symptoms. Female cannabis users are reported to be especially vulnerable to earlier onset of schizophrenia, and mixed trends emerge in the correlation of depressive symptoms with cannabis exposure in females and males.

Summary

As prevalence of cannabis use may continue to increase given the shifting policy landscape regarding marijuana laws, understanding the neurobiological mechanisms of cannabis exposure in females and males is key. Examining these mechanisms may help inform future research on sex-specific pharmacological and behavioral interventions for women and men with high-risk cannabis use, comorbid psychiatric disease, and CUD.

The endocannabinoid system in the baboon (Papio spp.) as a complex framework for developmental pharmacology

INTRODUCTION

The consumption of marijuana (exogenous cannabinoid) almost doubled in adults during last decade. Consumption of exogenous cannabinoids interferes with the endogenous cannabinoid (or "endocannabinoid" (eCB)) system (ECS), which comprises N-arachidonylethanolamide (anandamide, AEA), 2-arachidonoyl glycerol (2-AG), endocannabinoid receptors (cannabinoid receptors 1 and 2 (CB1R and CB2R), encoded by CNR1 and CNR2, respectively), and synthesizing/degrading enzymes (FAAH, fatty-acid amide hydrolase; MAGL, monoacylglycerol lipase; DAGL-α, diacylglycerol lipase-alpha). Reports regarding the toxic and therapeutic effects of pharmacological compounds targeting the ECS are sometimes contradictory. This may be caused by the fact that structure of the eCBs varies in the species studied.

OBJECTIVES

First: to clone and characterize the cDNAs of selected members of ECS in a non-human primate (baboon, Papio spp.), and second: to compare those cDNA sequences to known human structural variants (single nucleotide polymorphisms and haplotypes).

MATERIALS AND METHODS

Polymerase chain reaction-amplified gene products from baboon tissues were transformed into Escherichia coli. Amplicon-positive clones were sequenced, and the obtained sequences were conceptually translated into amino-acid sequences using the genetic code.

RESULTS

Among the ECS members, CNR1 was the best conserved gene between humans and baboons. The phenotypes associated with mutations in the untranslated regions of this gene in humans have not been described in baboons. One difference in the structure of CNR2 between humans and baboons was detected in the region with the only known clinically relevant polymorphism in a human receptor. All of the differences in the amino-acid structure of DAGL-α between humans and baboons were located in the hydroxylase domain, close to phosphorylation sites. None of the differences in the amino-acid structure of MAGL observed between baboons and humans were located in the area critical for enzyme function.

CONCLUSION

The evaluation of the data, obtained in non-human primate model of cannabis-related developmental exposure should take into consideration possible evolutionary-determined species-specific differences in the CB1R expression, CB2R transduction pathway, and FAAH and DAGLα substrate-enzyme interactions.

Cnr2 deficiency confers resistance to inflammation-induced preterm birth in mice

Infection-induced inflammation, frequently associated with increased production of proinflammatory cytokines, is considered a significant contributor to preterm birth. A G protein-coupled cannabinoid receptor 2 (CB2), encoded by Cnr2, is expressed in various immune cells and was shown to modulate immune responses. We show here that Cnr2, but not Cnr1, deficient mice are resistant to lipopolysaccharide (LPS)-driven preterm birth and suppression of serum progesterone levels. After LPS challenge, Cnr2(-/-) mice exhibited increased serum levels of IL-10 with decreased IL-6 levels. These changes were associated with reduced LPS-induced Ptgs2 expression at the maternal-conceptus interface on day 16 of pregnancy. LPS stimulation of Cnr2(-/-) dendritic cells in vitro resulted in increased IL-10 with reduced IL-6 production and correlated with increased cAMP accumulation. Collectively, our results suggest that increased IL-10 production occurring via augmented cAMP accumulation represents a potential mechanism for the resistance of Cnr2(-/-) mice to LPS-induced preterm birth. These results may have clinical relevance, because currently, there are limited options to prevent preterm birth.

Association of polymorphisms in the endocannabinoid system genes with myocardial infarction and plasma cholesterol levels

AIMS

The aim of this study was to investigate the relationship between selected symptoms of chronic heart failure (myocardial infarction, plasma cholesterol level) and single nucleotide polymorphisms (SNPs) in the FAAH and CNR1 genes.

METHODS

A case - control study involving 155 patients with chronic heart failure and 169 age- and sex-matched healthy subjects. We detected SNPs 385 C/A (rs324420) in the FAAH and 1359 G/A (rs1049353) in the CNR1 genes using the polymerase chain reaction and restriction analysis. Genotype and allele frequencies were compared between patients and controls as well as between patients with and without myocardial infarction.

RESULTS

No significant differences in genotype or allelic frequencies between patients and controls were found (P > 0.05). Carriers of the FAAH A allele had a 2.37-fold increase in the risk of myocardial infarction (odds ratio 2.37, 95% confidence interval 1.36-6.93, P = 0.01). Homozygous carriers of genotype AA of CNR1 SNP 1359 had significantly higher plasma cholesterol levels than carriers of GG and GA genotypes in patients (P = 0.04).

CONCLUSIONS

The study results suggest a role for allele A of the FAAH 385 variant as a risk factor for myocardial infarction. Genotype AA of CNR1 1359 variant probably affects plasma cholesterol levels. Pharmacological intervention in this system could modify the therapeutic approach to certain cardiovascular disorders.

Changes in endocannabinoid and N-acylethanolamine levels in rat brain structures following cocaine self-administration and extinction training

Preclinical investigations have demonstrated that drugs of abuse alter the levels of lipid-based signalling molecules, including endocannabinoids (eCBs) and N-acylethanolamines (NAEs), in the rodent brain. In addition, several drugs targeting eCBs and/or NAEs are implicated in reward and/or seeking behaviours related to the stimulation of dopamine systems in the brain. In our study, the brain levels of eCBs (anandamide (AEA) and 2-arachidonoylglycerol (2-AG)) and NAEs (oleoylethanolamide (OEA) and palmitoylethanolamide (PEA)) were analyzed via an LC-MS/MS method in selected brain structures of rats during cocaine self-administration and after extinction training according to the "yoked" control procedure. Repeated (14days) cocaine (0.5mg/kg/infusion) self-administration and yoked drug delivery resulted in a significant decrease (ca. 52%) in AEA levels in the cerebellum, whereas levels of 2-AG increased in the frontal cortex, the hippocampus and the cerebellum and decreased in the hippocampus and the dorsal striatum. In addition, we detected increases (>150%) in the levels of OEA and PEA in the limbic areas in both cocaine treated groups, as well as an increase in the tissue levels of OEA in the dorsal striatum in only the yoked cocaine group and increases in the tissue levels of PEA in the dorsal striatum (both cocaine groups) and the nucleus accumbens (yoked cocaine group only). Compared to the yoked saline control group, extinction training (10days) resulted in a potent reduction in AEA levels in the frontal cortex, the hippocampus and the nucleus accumbens and in 2-AG levels in the hippocampus, the dorsal striatum and the cerebellum. The decreases in the limbic and subcortical areas were more apparent for rats that self-administered cocaine. Following extinction, there was a region-specific change in the levels of NAEs in rats previously injected with cocaine; a potent increase (ca. 100%) in the levels of OEA and PEA was detected in the prefrontal cortex and the hippocampus, whilst a drop was noted in the striatal areas versus yoked saline yoked animals. Our findings support the previous pharmacological evidence that the eCB system and NAEs are involved in reinforcement and extinction of positively reinforced behaviours and that these lipid-derived molecules may represent promising targets for the development of new treatments for drug addiction.

Toward a mechanistic understanding of how variability in neurobiology shapes individual differences in behavior

Research has begun to identify how variability in brain function contributes to individual differences in complex behavioral traits. Examining variability in molecular signaling pathways with emerging and established methodologies such as pharmacologic fMRI, multimodal PET/fMRI, and hormonal assays are beginning to provide a mechanistic understanding of how individual differences in brain function arise. Against this background, functional genetic polymorphisms are being utilized to understand the origins of variability in signaling pathways as well as to efficiently model how such emergent variability impacts behaviorally relevant brain function and health outcomes. This chapter provides an overview of a research strategy that integrates these complimentary levels of analysis; existing empirical data is used to illustrate the effectiveness of this approach in illuminating the mechanistic neurobiology of individual differences in complex behavioral traits. This chapter also discusses how such efforts can contribute to the identification of predictive risk markers that interact with unique environmental factors to precipitate psychopathology.

The genetic basis of the endocannabinoid system and drug addiction in humans

The cannabinoid receptor (CNR1) and the fatty acid amide hydrolase (FAAH) genes are located on chromosomes 6 and 1 in the 6q15 and 1p33 cytogenetic bands, respectively. CNR1 encodes a seven-transmembrane domain protein of 472 amino acids, whereas FAAH encodes one transmembrane domain of 579 amino acids. Several mutations found in these genes lead to altered mRNA stability and transcription rate or a reduction of the activity of the encoded protein. Increasing evidence shows that these functional mutations are related to dependence upon cocaine, alcohol, marijuana, heroin, nicotine and other drugs. One of the most compelling associations is with the C385A single nucleotide polymorphism (SNP), which is found in the FAAH gene. For all of the genetic polymorphisms reviewed here, it is difficult to form overall conclusions due to the high diversity of population samples being studied, ethnicity, the use of volunteers, heterogeneity of the recruitment criteria and the drug addiction phenotype studied. Care should be taken when generalizing the results from different studies. However, many works have repeatedly associated polymorphisms in the CNR1 and FAAH genes with drug-related behaviours; this suggests that these genes should be examined in further genetic studies focusing on drug addiction and other psychiatric disorders.

Understanding the Global Problem of Drug Addiction is a Challenge for IDARS Scientists

IDARS is an acronym for the International Drug Abuse Research Society. Apart from our scientific and educational purposes, we communicate information to the general and scientific community about substance abuse and addiction science and treatment potential. Members of IDARS are research scientists and clinicians from around the world, with scheduled meetings across the globe. IDARS is developing a vibrant and exciting international mechanism not only for scientific interactions in the domain of addiction between countries but also ultimately as a resource for informing public policy across nations. Nonetheless, a lot more research needs to be done to better understand the neurobiological basis of drug addiction - A challenge for IDARS scientists.

Cannabis sativa and the endogenous cannabinoid system: therapeutic potential for appetite regulation

The herb Cannabis sativa (C. sativa) has been used in China and on the Indian subcontinent for thousands of years as a medicine. However, since it was brought to the UK and then the rest of the western world in the late 19th century, its use has been a source of controversy. Indeed, its psychotropic side effects are well reported but only relatively recently has scientific endeavour begun to find valuable uses for either the whole plant or its individual components. Here, we discuss evidence describing the endocannabinoid system, its endogenous and exogenous ligands and their varied effects on feeding cycles and meal patterns. Furthermore we also critically consider the mounting evidence which suggests non-Δ(9) tetrahydrocannabinol phytocannabinoids play a vital role in C. sativa-induced feeding pattern changes. Indeed, given the wide range of phytocannabinoids present in C. sativa and their equally wide range of intra-, inter- and extra-cellular mechanisms of action, we demonstrate that non-Δ(9) tetrahydrocannabinol phytocannabinoids retain an important and, as yet, untapped clinical potential.

Endocannabinoid signaling directs differentiation of trophoblast cell lineages and placentation

In most mammals, placentation is critical for fetal development and pregnancy success. Exposure to marijuana during pregnancy has adverse effects, but whether the placenta is a target of cannabinoid/endocannabinoid signaling is not known. Using mice as a model system, we found that the endocannabinoid system is present in the ectoplacental cone and spongiotrophoblast cells. We also observed that aberrant endocannabinoid signaling confers premature trophoblast stem cell differentiation, and defective trophoblast development and invasion. These defects are reflected in retarded fetal development and compromised pregnancy outcome. Because the endocannabinoid system is conserved in mice and humans, our study suggests that endocannabinoid signaling is critical to placentation and pregnancy success in humans and implicates its potential significance in stem cell biology.

Cannabinoid system in the skin - a possible target for future therapies in dermatology

Cannabinoids and their derivatives are group of more than 60 biologically active chemical agents, which have been used in natural medicine for centuries. The major agent of exogenous cannabinoids is Delta(9)-tetrahydrocannabinol (Delta(9)-THC), natural psychoactive ingredient of marijuana. However, psychoactive properties of these substances limited their use as approved medicines. Recent discoveries of endogenous cannabinoids (e.g. arachidonoylethanolamide, 2-arachidonoylglycerol or palmithyloethanolamide) and their receptors initiated discussion on the role of cannabinoid system in physiological conditions as well as in various diseases. Based on the current knowledge, it could be stated that cannabinoids are important mediators in the skin, however their role have not been well elucidated yet. In our review, we summarized the current knowledge about the significant role of the cannabinoid system in the cutaneous physiology and pathology, pointing out possible future therapeutic targets.

The neurobiology of individual differences in complex behavioral traits

Neuroimaging, especially BOLD fMRI, has begun to identify how variability in brain function contributes to individual differences in complex behavioral traits. In parallel, pharmacological fMRI and multimodal PET/fMRI are identifying how variability in molecular signaling pathways influences individual differences in brain function. Against this background, functional genetic polymorphisms are being utilized to understand the origins of variability in signaling pathways as well as to model efficiently how such emergent variability impacts behaviorally relevant brain function. This article provides an overview of a research strategy seeking to integrate these complementary technologies and utilizes existing empirical data to illustrate its effectiveness in illuminating the neurobiology of individual differences in complex behavioral traits. The article also discusses how such efforts can contribute to the identification of predictive markers that interact with environmental factors to precipitate disease and to develop more effective and individually tailored treatment regimes.

The association between cannabinoid receptor 1 gene (CNR1) and cannabis dependence symptoms in adolescents and young adults

OBJECTIVE

This study examined the genetic association between variation in the cannabinoid receptor 1 (CNR1) gene and cannabis dependence symptoms.

METHOD

Adolescent and young adult subjects were recruited from three settings: a treatment program for youth with substance use disorders, the criminal justice system, and the community. A case-control sample consisted of 224 cases who endorsed at least one dependence symptom and 108 controls who tried cannabis but endorsed no symptoms. A family-based sample of 219 families was also analyzed.

RESULTS

Case-control analysis identified a nominal association between SNP rs1049353 and having one or more cannabis dependence symptoms (p=.029), but the association did not hold up in a combined sample. Family-based analysis found a trend for the same SNP (p=.07). We did not replicate a previous report that SNP rs806380 was associated with the development of cannabis dependence.

CONCLUSION

These results provide inconclusive evidence of association between rs1049353/rs806380 and the development of cannabis dependence, and underscore the importance of replicating results of genetic association studies. Additional family-based studies are needed to clarify the role of the CNR1 gene, and its various SNPs, in the development of cannabis use disorders.

Evidence for association between polymorphisms in the cannabinoid receptor 1 (CNR1) gene and cannabis dependence

Genomic studies of cannabis use disorders have been limited. The cannabinoid receptor 1 gene (CNR1) on chromosome 6q14-15 is an excellent candidate gene for cannabis dependence due to the important role of the G-protein coupled receptor encoded by this gene in the rewarding effects of Delta9-tetrahydrocannabinol. Previous studies have found equivocal evidence for an association between SNPs in CNR1 and a general vulnerability to substance use disorders. We investigate the association between 9 SNPs spanning CNR1 and cannabis dependence in 1,923 individuals. Two SNPs that were previously associated with cannabis dependence in other studies were also significant with this phenotype in our analyses [rs806368 (P = 0.05) and rs806380 (P = 0.009)]. Haplotype analyses revealed the association to be largely driven by the SNP rs806380. These results suggest a role for the cannabinoid receptor 1 gene in cannabis dependence.

Divergent effects of genetic variation in endocannabinoid signaling on human threat- and reward-related brain function

BACKGROUND

Fatty acid amide hydrolase (FAAH) is a key enzyme in regulating endocannabinoid (eCB) signaling. A common single nucleotide polymorphism (C385A) in the human FAAH gene has been associated with increased risk for addiction and obesity.

METHODS

Using imaging genetics in 82 healthy adult volunteers, we examined the effects of FAAH C385A on threat- and reward-related human brain function.

RESULTS

Carriers of FAAH 385A, associated with reduced enzyme and possibly increased eCB signaling, had decreased threat-related amygdala reactivity but increased reward-related ventral striatal reactivity in comparison with C385 homozygotes. Similarly divergent effects of FAAH C385A genotype were manifest at the level of brain-behavior relationships. The 385A carriers showed decreased correlation between amygdala reactivity and trait anxiety but increased correlation between ventral striatal reactivity and delay discounting, an index of impulsivity.

CONCLUSIONS

Our results parallel pharmacologic and genetic dissection of eCB signaling, are consistent with the psychotropic effects of Delta(9)-tetrahydrocannabinol, and highlight specific neural mechanisms through which variability in eCB signaling impacts complex behavioral processes related to risk for addiction and obesity.

Endocannabinoid system: emerging role from neurodevelopment to neurodegeneration

The endocannabinoid system, including endogenous ligands ('endocannabinoids' ECs), their receptors, synthesizing and degrading enzymes, as well as transporter molecules, has been detected from the earliest stages of embryonic development and throughout pre- and postnatal development. ECs are bioactive lipids, which comprise amides, esters and ethers of long chain polyunsaturated fatty acids. Anandamide (N-arachidonoylethanolamine; AEA) and 2-arachidonoylglycerol (2-AG) are the best studied ECs, and act as agonists of cannabinoid receptors. Thus, AEA and 2-AG mimic several pharmacological effects of the exogenous cannabinoid delta9-tetrahydrocannabinol (Delta(9)-THC), the psychoactive principle of cannabis sativa preparations like hashish and marijuana. Recently, however, several lines of evidence have suggested that the EC system may play an important role in early neuronal development as well as a widespread role in neurodegeneration disorders. Many of the effects of cannabinoids and ECs are mediated by two G protein-coupled receptors (GPCRs), CB1 and CB2, although additional receptors may be implicated. Both CB1 and CB2 couple primarily to inhibitory G proteins and are subject to the same pharmacological influences as other GPCRs. This new system is briefly presented in this review, in order to put in a better perspective the role of the EC pathway from neurodevelopment to neurodegenerative disorders, like Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In addition, the potential exploitation of antagonists of CB1 receptors, or of inhibitors of EC metabolism, as next-generation therapeutics is discussed.

Candidate genes for cannabis use disorders: findings, challenges and directions

AIM

Twin studies have shown that cannabis use disorders (abuse/dependence) are highly heritable. This review aims to: (i) review existing linkage studies of cannabis use disorders and (ii) review gene association studies, to identify potential candidate genes, including those that have been tested for composite substance use disorders and (iii) to highlight challenges in the genomic study of cannabis use disorders.

METHODS

Peer-reviewed linkage and candidate gene association studies are reviewed.

RESULTS

Four linkage studies are reviewed: results from these have homed in on regions on chromosomes 1, 3, 4, 9, 14, 17 and 18, which harbor candidates of predicted biological relevance, such as monoglyceride lipase (MGLL) on chromosome 3, but also novel genes, including ELTD1[epidermal growth factor (EGF), latrophilin and seven transmembrane domain containing 1] on chromosome 1. Gene association studies are presented for (a) genes posited to have specific influences on cannabis use disorders: CNR1, CB2, FAAH, MGLL, TRPV1 and GPR55 and (b) genes from various neurotransmitter systems that are likely to exert a non-specific influence on risk of cannabis use disorders, e.g. GABRA2, DRD2 and OPRM1.

CONCLUSIONS

There are challenges associated with (i) understanding biological complexity underlying cannabis use disorders (including the need to study gene-gene and gene-environment interactions), (ii) using diagnostic versus quantitative phenotypes, (iii) delineating which stage of cannabis involvement (e.g. use versus misuse) genes influence and (iv) problems of sample ascertainment.

Comparison of hypertension and its risk factors between the Guangxi Bai Ku Yao and Han populations

OBJECTIVE

Little is known about the prevalence of hypertension in Bai Ku Yao, an isolated subgroup of the Yao minority in China. The aim of this study was to compare the difference in the prevalence of hypertension and its risk factors between the Guangxi Bai Ku Yao and Han populations.

METHODS

A cross-sectional study of hypertension in 1170 subjects of Bai Ku Yao and 1173 participants of Han Chinese aged 15-89 was conducted by a stratified randomized cluster sampling. Information on diet and lifestyle was collected with standardized questionnaires. Blood pressure, serum lipids and several anthropometric parameters were obtained in all subjects.

RESULTS

Systolic, diastolic and pulse pressure levels and hypertension prevalence (10.85% vs 16.45%, p<0.001) were lower in Bai Ku Yao than in Han. Hypertension was positively correlated with male, age, physical activity, body mass index, waist circumference, total energy, total fat and sodium intakes, and negatively associated with education level and total dietary fibre intake in both ethnic groups (p<0.05-0.001). Hypertension was also positively associated with alcohol consumption in Han. The rates of awareness, treatment and control were lower in Bai Ku Yao than in Han (p<0.05 for all).

CONCLUSIONS

The difference in the hypertension prevalence between the two ethnic groups might result from different diet, lifestyle, physical activity level, sodium intake and genetic factors.

Cannabinoid receptors in brain: pharmacogenetics, neuropharmacology, neurotoxicology, and potential therapeutic applications

Much progress has been achieved in cannabinoid research. A major breakthrough in marijuana-cannabinoid research has been the discovery of a previously unknown but elaborate endogenous endocannabinoid system (ECS), complete with endocannabinoids and enzymes for their biosynthesis and degradation with genes encoding two distinct cannabinoid (CB1 and CB2) receptors (CBRs) that are activated by endocannabinoids, cannabinoids, and marijuana use. Physical and genetic localization of the CBR genes CNR1 and CNR2 have been mapped to chromosome 6 and 1, respectively. A number of variations in CBR genes have been associated with human disorders including osteoporosis, attention deficit hyperactivity disorder (ADHD), posttraumatic stress disorder (PTSD), drug dependency, obesity, and depression. Other family of lipid receptors including vanilloid (VR1) and lysophosphatidic acid (LPA) receptors appear to be related to the CBRs at the phylogenetic level. The ubiquitous abundance and differential distribution of the ECS in the human body and brain along with the coupling to many signal transduction pathways may explain the effects in most biological system and the myriad behavioral effects associated with smoking marijuana. The neuropharmacological and neuroprotective features of phytocannabinoids and endocannabinoid associated neurogenesis have revealed roles for the use of cannabinoids in neurodegenerative pathologies with less neurotoxicity. The remarkable progress in understanding the biological actions of marijuana and cannabinoids have provided much richer results than previously appreciated cannabinoid genomics and raised a number of critical issues on the molecular mechanisms of cannabinoid induced behavioral and biochemical alterations. These advances will allow specific therapeutic targeting of the different components of the ECS in health and disease. This review focuses on these recent advances in cannabinoid genomics and the surprising new fundamental roles that the ECS plays in the retrograde signaling associated with cannabinoid inhibition of neurotransmitter release to the genetic basis of the effects of marijuana use and pharmacotherpeutic applications and limitations. Much evidence is provided for the complex CNR1 and CNR2 gene structures and their associated regulatory elements. Thus, understanding the ECS in the human body and brain will contribute to elucidating this natural regulatory mechanism in health and disease.

Ultrastructural localization of neuronal brain CB2 cannabinoid receptors

The functional expression of neuronal CB2 cannabinoid receptors (CB2-Rs) in the brain has been controversial. We and others have now demonstrated that CB2-Rs are expressed in neurons and glial cells in the brain. However, the subcellular localization of these receptors has not been characterized. In this study we used immunohistochemical electron microscopy to determine the subcellular distribution of CB2-Rs in two brain regions. Brain sections from the CA1 hippocampal area and substantia nigra were immunostained for CB2-Rs and analyzed by electron microscopy. In each region immunoperoxidase labeling for CB2-Rs was detected in neurons as well as in glial and endothelial cells. In neuronal cells, CB2-R immunoreactivity was observed in somata and large and medium-sized dendrites. In the soma, the CB2-R labeling was mainly associated with the rough endoplasmic reticulum and Golgi apparatus, suggesting its endogenous synthesis. In the dendrites, the CB2-R labeling was observed in the cytoplasm and was associated with the plasma membrane near the area of synaptic contact with axon terminals, indicating a postsynaptic distribution of these receptors. In CB2-Rs in immunoreactive glial and endothelial cells, the labeling was also found to be associated with the plasma membrane. In the substantia nigra, some unmyelinated axons were immunoreactive for CB2-Rs, but we rarely found CB2-R-labeled axon terminals. These results extend our previous detection of postsynaptic cortical CB2-Rs and provide additional ultrastructural evidence that CB2-Rs are mainly postsynaptic in the CA1 area of the hippocampus and substantia nigra. The functional implication of pre- and/or postsynaptic localization of CB2-Rs remains to be determined.

Marijuana withdrawal and craving: influence of the cannabinoid receptor 1 (CNR1) and fatty acid amide hydrolase (FAAH) genes

AIM

To examine whether withdrawal after abstinence and cue-elicited craving were associated with polymorphisms within two genes involved in regulating the endocannabinoid system, cannabinoid receptor 1 (CNR1) and fatty acid amide hydrolase (FAAH). Two single nucleotide polymorphisms (SNPs) in the CNR1 (rs2023239) and FAAH (rs324420) genes, associated previously with substance abuse and functional changes in cannabinoid regulation, were examined in a sample of daily marijuana smokers.

PARTICIPANTS

Participants were 105 students at the University of Colorado, Boulder between the ages of 18 and 25 years who reported smoking marijuana daily.

MEASUREMENTS

Participants were assessed once at baseline and again after 5 days of abstinence, during which they were exposed to a cue-elicited craving paradigm. Outcome measures were withdrawal and craving collected using self-reported questionnaires. In addition, urine samples were collected at baseline and on day 5 for the purposes of 11-nor-9-carboxy-Delta9-tetrahydrocannabinol (THC-COOH) metabolite analysis.

FINDINGS

Between the two sessions, THC-COOH metabolite levels decreased significantly, while measures of withdrawal and craving increased significantly. The CNR1 SNP displayed a significant abstinence x genotype interaction on withdrawal, as well as a main effect on overall levels of craving, while the FAAH SNP displayed a significant abstinence x genotype interaction on craving.

CONCLUSIONS

These genetic findings may have both etiological and treatment implications. However, longitudinal studies will be needed to clarify whether these genetic variations influence the trajectory of marijuana use/dependence. The identification of underlying genetic differences in phenotypes such as craving and withdrawal may aid genetically targeted approaches to the treatment of cannabis dependence.

Diet, lifestyle, and blood pressure of the middle-aged and elderly in the Guangxi Bai Ku Yao and Han populations

BACKGROUND

Bai Ku Yao is an isolated subgroup of the Yao minority in China. Little is known about the association of diet and lifestyle with the prevalence of hypertension in this population.

METHODS

A total of 485 subjects of Bai Ku Yao and 501 participants of Han Chinese aged 40-89 were surveyed using stratified randomized cluster sampling. Information on diet and lifestyle was collected by using standard questionnaires. Blood pressure (BP) and serum lipid levels were measured.

RESULTS

Physical activity levels, carbohydrate, vegetal protein, and dietary fiber intake were higher in Bai Ku Yao than in Han, whereas educational level, height, weight, body mass index (BMI), waist circumference, and total energy, fat, protein, dietary cholesterol, and salt intake were higher in Han than in Bai Ku Yao. Systolic, diastolic, and pulse pressure (PP) levels and the prevalence of hypertension (21.9% vs. 28.9%, P < 0.05)were lower in Bai Ku Yao than in Han. Hypertension was positively correlated with age, physical activity,BMI, and waist circumference, as well as with total energy, fat, and salt intake, and negatively associated with educational levels and dietary fiber intake in both ethnic groups (P < 0.05 for all). Hypertension was also positively correlated with triglycerides (TGs) in Bai Ku Yao and alcohol consumption in Han (P < 0.05 for each).

CONCLUSIONS

The differences in BP levels and the prevalence of hypertension among the middle-aged and elderly between Bai Ku Yao and Han might result from different dietary patterns, lifestyle choices, physical activity levels, sodium intake, and even genetic factors.

Association between single nucleotide polymorphisms in the cannabinoid receptor gene (CNR1) and impulsivity in southwest California Indians

Impulsivity is a personality trait characterized by acting suddenly in an unplanned manner in order to satisfy a desire without consideration for the consequences of such behavior. There are several psychiatric disorders that include the term impulsivity as a criterion and, therefore, it has been suggested that impulsivity may be an important phenotype that may link a number of different behavioral disorders, including substance abuse. This study's aims were to determine if a significant association could be detected between the (AAT)n triplet repeat polymorphism as well as 5 single nucleotide polymorphisms (SNPs) in or near the CNR1 receptor gene and impulsivity in Southwest California 'Mission' Indians (SWC). Impulsivity was assessed using a scale derived from the Maudsley personality inventory, and blood samples were collected for DNA analyses from 251 individuals recruited from local Indian reservations. The estimated heritability (h(2)) for the impulsivity phenotype was 0.20 + 0.12 (p < .004). Impulsivity was significantly associated with the 6-repeat allele of the triplet repeat polymorphism (AATn/A6; p < .0001), as well as four SNPs in or near the CNR1 receptor gene: rs1535255 (p = .001), rs2023239 (p = .004), rs1049353 (p < .001) and rs806368 (p < .0006). These studies provide data to suggest that the CNR1 receptor gene may be significantly associated with impulsivity in SWC Indians.

The CNR1 gene as a pharmacogenetic factor for antipsychotics rather than a susceptibility gene for schizophrenia

Neurobiological research suggests a significant role of the endocannabinoid system in schizophrenia vulnerability and also in the quality of response to antipsychotics. Genetics offer an opportunity to disentangle its involvement in the disease vulnerability vs an influence on antipsychotics' effects. The possible role of a tag SNP (the 1359G/A polymorphism) of the gene encoding the cannabinoid receptor type 1 (CNR1) in schizophrenia and/or therapeutic response to atypical antipsychotics was assessed in a cohort of 133 French schizophrenic patients compared to 141 normal control subjects. No difference in 1359G/A polymorphism was observed between patients and control subjects, and no relationships were noted between this polymorphism and any clinical parameter considered as potential intermediate factor. However, the G allele frequency was significantly higher among non-responsive vs responsive patients, with a dose effect of the G allele. In contrast, no association was found for three other genetic polymorphisms of the CNR1 gene. The G allele of the CNR1 gene polymorphisms could be a psychopharmacogenetic rather than a vulnerability factor regarding schizophrenia and its treatment.

The complex etiology of multiple sclerosis

Multiple sclerosis is a demyelinating disease which is presumed to be a consequence of infiltrating lymphocytes autoreactive to myelin proteins. This is substantiated by several lines of clinical evidence and supported by correlative studies in preclinical models. The development of new therapeutics for MS has been guided by this perspective; however, the pathogenesis of MS has proven to be quite complex as observations exist which question the role of autoreactive lymphocytes in the etiology of MS. In addition the current immunomodulatory therapeutics do not prevent most patients from progressing into more serious forms of the disease. The development of truly transformational therapeutics for MS will likely require a broad assault that expands beyond the concept of MS being an autoimmune disease.

The role of the cannabinoid type 1 receptor and down-stream cAMP/DARPP-32 signal in the nucleus accumbens of methamphetamine-sensitized rats

Blockade of the cannabinoid type 1 (CB(1)) receptor could suppress methamphetamine self-administration; however, the cellular mechanism remains unclear. In this study, we intended to investigate the significance of brain CB(1) receptors on the development of behavioral sensitization to methamphetamine. Male Sprague-Dawley rats treated with chronic methamphetamine (4 mg/kg, i.p.) for either 7 or 14 days developed behavioral sensitization to methamphetamine (1 mg/kg) at withdrawal day 7. A progressive decrease in numbers of CB(1) receptor (both Bmax and mRNA) but increase in binding affinity (Kd) was noticed during withdrawal days 3 to 7. Microinjection of CB(1) antagonist [5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-4-ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide] into the nucleus accumbens (NAc) at withdrawal day 7, significantly suppressed the behavioral sensitization to methamphetamine. In NAc brain slices preparation, acute incubation with CB(1) agonist (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP 55940) dose-dependently enhanced cAMP accumulation in sensitized rats; no change was noticed in control groups. Consequently, treatment of CP 55940 induced a dose-dependent (10 nmol/L-10 micromol/L) phosphorylation on down-stream dopamine and cAMP-regulated phosphoprotein of Mr 32 000 (DARPP-32)/Thr34 in sensitized rats, while only 10 micromol/L CP 55940 was able to enhance the phosphoDARPP-32/T34 in control groups. Alternatively, both basal activity of calcineurin (PP-2B) and CP 55940-induced changes in the amount of PP-2B in the NAc were both decreased in sensitized rats, but not in controls. Overall, we demonstrated that brain CB(1) receptor and its down-stream cAMP/DARPP-32/T34/PP-2B signaling are profoundly altered in methamphetamine-sensitized animals.

Integrated physiology and pathophysiology of CB1-mediated effects of the endocannabinoid system

The discovery of the endocannabinoid system (ECS) has raised a large interest in the scientific community providing us with a strikingly long list of apparently independent multi organ effects. As a result, in most reviews on this issue the main function of the ECS is considered as modulatory. Unfortunately, this vision does not add much to our understanding of the specific biological function of the ECS. Thus, modulatory is what in general all biological systems are or should be. In this review we will show that the apparent inconsistent puzzle of the very different tissue specific effects of endocannabinoids (ECs) can be reconstructed in one unitary picture. This picture clearly shows that all the different CB1-mediated effects of ECs sub-serve one major physiological function: to facilitate and increase energy storage. We will also analyze the implications of this unitary vision of the ECS in different contexts. First, in the context of the systems that regulate energy balance, introducing a new systematization based on two homeostatic systems: an endostatic and an exostatic system. Second, in the context of evolution, showing how the function of the ECS has shifted from essential to survival to almost pathological in current times. Finally, in a pathophysiological context, introducing the new concept of "proactive evolution diseases", which can explain the current obesity epidemic and the role the ECS plays in it.

Association in alcoholic patients between Psychopathic Traits and the additive effect of allelic forms of theCNR1 andFAAH endocannabinoid genes, and the 3′ Region of theDRD2 Gene

Little is known about the genetic factors that underlie the comorbidity between alcohol use disorder and antisocial personality disorder. Previous studies have associated both, dopaminergic and endocannabinoid systems to severe alcoholism with non-adaptive disrupted behaviours. In this work we have examined some gene variants involved in such systems in a sample of alcoholic patients to test whether there is a relationship with antisocial traits. The genetic analysis involved the genotyping of the single nucleotide polymorphism (SNP) TaqIA located nearby the DRD2 gene, the 10-repeat allele of a variable number tandem repeats (VNTR) of the SLC6A3 gene, the C385A FAAH SNP and the 3'-UTR microsatellite of CNR1 gene. The clinical study was performed in 137 Spanish alcohol dependent males. Antisocial Personality Disorder (DSM-IV) diagnosis was made by applying the International Personality Disorder Examination, and psychopathic traits were evaluated by the Hare's Psychopathy Checklist revised (PCL-R). The genotype distribution indicates there is a relationship between the TaqIA SNP, CNR1 and FAAH genes and PCL-R's Factor 1 in alcoholic patients. This relationship seems to be additive and independent and might be responsible for 11.4% of the variance in this PCL-R subscale. Our results suggest the implication of the dopaminergic and endocannabinoid systems in those processes leading to the comorbidity of alcoholism and antisocial behaviour.

Neuropharmacology of the endocannabinoid signaling system-molecular mechanisms, biological actions and synaptic plasticity

The endocannabinoid signaling system is composed of the cannabinoid receptors; their endogenous ligands, the endocannabinoids; the enzymes that produce and inactivate the endocannabinoids; and the endocannabinoid transporters. The endocannabinoids are a new family of lipidic signal mediators, which includes amides, esters, and ethers of long-chain polyunsaturated fatty acids. Endocannabinoids signal through the same cell surface receptors that are targeted by Delta(9)-tetrahydrocannabinol (Delta(9)THC), the active principles of cannabis sativa preparations like hashish and marijuana. The biosynthetic pathways for the synthesis and release of endocannabinoids are still rather uncertain. Unlike neurotransmitter molecules that are typically held in vesicles before synaptic release, endocannabinoids are synthesized on demand within the plasma membrane. Once released, they travel in a retrograde direction and transiently suppress presynaptic neurotransmitter release through activation of cannabinoid receptors. The endocannabinoid signaling system is being found to be involved in an increasing number of pathological conditions. In the brain, endocannabinoid signaling is mostly inhibitory and suggests a role for cannabinoids as therapeutic agents in central nervous system (CNS) disease. Their ability to modulate synaptic efficacy has a wide range of functional consequences and provides unique therapeutic possibilities. The present review is focused on new information regarding the endocannabinoid signaling system in the brain. First, the structure, anatomical distribution, and signal transduction mechanisms of cannabinoid receptors are described. Second, the synthetic pathways of endocannabinoids are discussed, along with the putative mechanisms of their release, uptake, and degradation. Finally, the role of the endocannabinoid signaling system in the CNS and its potential as a therapeutic target in various CNS disease conditions, including alcoholism, are discussed.

Distinctive pattern of cannabinoid receptor type II (CB2) expression in adult and pediatric brain tumors

The efficacy of cannabinoids against high-grade glioma in animal models, mediated by two specific receptors, CB1 and CB2, raised promises for targeted treatment of the most frequent and malignant primary brain tumors. Unlike the abundantly expressed CB1, the CB2 receptor shows a restricted distribution in normal brain. Although brain tumors constitute the second most common malignancy in children and the prevalence of histological types of brain tumors vary significantly between the adult and pediatric populations, cannabinoid receptor expression in pediatric tumors remains unknown. In the present study, we compared the expression of the CB2 receptor in paraffin-embedded sections from primary brain tumors of adult and pediatric patients. Most glioblastomas expressed very high levels of CB2 receptors and the expression correlated with tumor grade. Interestingly, some benign pediatric astrocytic tumors, such as subependymal giant cell astrocytoma (SEGA), which may occasionally cause mortality owing to progressive growth, also displayed high CB2 immunoreactivity. The high levels of CB2 expression would predestine those tumors to be vulnerable to cannabinoid treatment. In contrast, all examined cases of embryonal tumors (medulloblastoma and S-PNET), the most frequently diagnosed malignant brain tumors in childhood, showed no or trace CB2 immunoreactivity. Our results suggest that the CB2 receptor expression depends primarily on the histopathological origin of the brain tumor cells and differentiation state, reflecting the tumor grade.

Cannabis receptor haplotype associated with fewer cannabis dependence symptoms in adolescents

Cannabis is a major substance of abuse, and the gene encoding for the central cannabinoid receptor (CNR1) is a logical candidate gene for vulnerability toward developing symptoms of cannabis dependence. We studied four single-nucleotide polymorphisms (SNPs) in the CNR1 gene for association with having one or more symptoms of cannabis dependence in 541 adolescent subjects who had all tried cannabis five or more times. Cases (327) were defined as those who had tried marijuana and developed one or more symptoms, and controls (214) as those who had tried marijuana but developed no dependence symptoms. Cannabis dependence symptoms were assessed in these youth when they were 17 or older with the Composite International Diagnostic Interview--Substance Abuse Module. Univariate (single-marker) association tests demonstrated that SNP rs806380, located in intron 2 of the CNR1 gene, was significantly associated with developing one or more cannabis dependence symptoms, with the G allele having a protective effect (P < 0.02). This was consistent with the results of the global haplotype test (P < 0.01). One of the common haplotypes examined (present in 21% of the subjects) was significantly associated with a lower rate of having one or more cannabis dependence symptoms. Our findings provide evidence suggesting that a common CNR1 haplotype is associated with developing fewer cannabis dependence symptoms among adolescents who have experimented with cannabis.