Endogenous cannabinoids in the brain and peripheral tissues: regulation of their levels and control of food intake

Central mechanisms mediating the hypophagic effects of oleoylethanolamide and N-acylphosphatidylethanolamines: different lipid signals?

The spread of “obesity epidemic” and the poor efficacy of many anti-obesity therapies in the long-term highlight the need to develop novel efficacious therapy. This necessity stimulates a large research effort to find novel mechanisms controlling feeding and energy balance. Among these mechanisms a great deal of attention has been attracted by a family of phospholipid-derived signaling molecules that play an important role in the regulation of food-intake. They include N-acylethanolamines (NAEs) and N-acylphosphatidylethanolamines (NAPEs). NAPEs have been considered for a long time simply as phospholipid precursors of the lipid mediator NAEs, but increasing body of evidence suggest a role in many physiological processes including the regulation of feeding behavior. Several observations demonstrated that among NAEs, oleoylethanolamide (OEA) acts as a satiety signal, which is generated in the intestine, upon the ingestion of fat, and signals to the central nervous system. At this level different neuronal pathways, including oxytocinergic, noradrenergic, and histaminergic neurons, seem to mediate its hypophagic action. Similarly to NAEs, NAPE (with particular reference to the N16:0 species) levels were shown to be regulated by the fed state and this finding was initially interpreted as fluctuations of NAE precursors. However, the observation that exogenously administered NAPEs are able to inhibit food intake, not only in normal rats and mice but also in mice lacking the enzyme that converts NAPEs into NAEs, supported the hypothesis of a role of NAPE in the regulation of feeding behavior. Indirect observations suggest that the hypophagic action of NAPEs might involve central mechanisms, although the molecular target remains unknown. The present paper reviews the role that OEA and NAPEs play in the mechanisms that control food intake, further supporting this group of phospholipids as optimal candidate for the development of novel anti-obesity treatments.

Effects of mood inductions by meal ambiance and moderate alcohol consumption on endocannabinoids and N-acylethanolamines in humans: a randomized crossover trial

Background

The endocannabinoid system is suggested to play a regulatory role in mood. However, the response of circulating endocannabinoids (ECs) to mood changes has never been tested in humans. In the present study, we examined the effects of mood changes induced by ambiance and moderate alcohol consumption on plasma ECs 2-arachidonoylglycerol (2-AG), anandamide (AEA), and some N-acylethanolamine (NAE) congeners in humans.

Methods

Healthy women (n = 28) participated in a randomized cross-over study. They consumed sparkling white wine (340 mL; 30 g alcohol) or alcohol-free sparkling white wine (340 mL; <2 g alcohol) as part of a standard evening meal in a room with either a pleasant or an unpleasant ambiance.

Results

Plasma concentrations of palmitoylethanolamide (PEA) and stearoylethanolamide (SEA) increased after 30 min in the unpleasant ambiance, while they decreased in the pleasant ambiance. Changes in ECs and their NAE congeners correlated with mood states, such as happiness and fatigue, but in the pleasant ambiance without alcohol only. ECs and their NAE congeners were correlated with serum free fatty acids and cortisol.

Conclusion

This is the first human study to demonstrate that plasma NAEs are responsive to an unpleasant meal ambiance. Furthermore, associations between mood states and ECs and their NAE congeners were observed.

Trial Registration

Clinicaltrials.gov NCT01426022

The inverse agonist of CB1 receptor SR141716 blocks compulsive eating of palatable food

Dieting and the increased availability of highly palatable food are considered major contributing factors to the large incidence of eating disorders and obesity. This study was aimed at investigating the role of the cannabinoid (CB) system in a novel animal model of compulsive eating, based on a rapid palatable diet cycling protocol. Male Wistar rats were fed either continuously a regular chow diet (Chow/Chow, control group) or intermittently a regular chow diet for 2 days and a palatable, high-sucrose diet for 1 day (Chow/Palatable). Chow/Palatable rats showed spontaneous and progressively increasing hypophagia and body weight loss when fed the regular chow diet, and excessive food intake and body weight gain when fed the palatable diet. Diet-cycled rats dramatically escalated the intake of the palatable diet during the first hour of renewed access (7.5-fold compared to controls), and after withdrawal, they showed compulsive eating and heightened risk-taking behavior. The inverse agonist of the CB1 receptor, SR141716 reduced the excessive intake of palatable food with higher potency and the body weight with greater efficacy in Chow/Palatable rats, compared to controls. Moreover, SR141716 reduced compulsive eating and risk-taking behavior in Chow/Palatable rats. Finally, consistent with the behavioral and pharmacological observations, withdrawal from the palatable diet decreased the gene expression of the enzyme fatty acid amide hydrolase in the ventromedial hypothalamus while increasing that of CB1 receptors in the dorsal striatum in Chow/Palatable rats, compared to controls. These findings will help understand the role of the CB system in compulsive eating.

Factors associated with substance use in adolescents with eating disorders

PURPOSE

To examine the prevalence and potential risk factors associated with substance use in adolescents with eating disorders (EDs).

METHODS

This cross-sectional study included 290 adolescents, aged 12-18 years, who presented for an initial ED evaluation at The Eating Disorders Program at the University of Chicago Medicine between 2001 and 2012. Several factors including DSM-5 diagnosis, diagnostic scores, and demographic characteristics were examined. Multinomial logistic regression was used to test associations between several factors and patterns of drug use for alcohol, cannabis, tobacco, and any other substance.

RESULTS

Lifetime prevalence of any substance use was found to be 24.6% in those with anorexia nervosa, 48.7% in bulimia nervosa (BN), and 28.6% in ED not otherwise specified. Regular substance use (monthly, daily, and bingeing behaviors) or a substance use disorder was found in 27.9% of all patients. Older age was the only factor associated with regular use of any substance in the final multinomial model. Older age and non-white race was associated with greater alcohol and cannabis use. Although binge-purge frequency and bulimia nervosa diagnosis were associated with regular substance use in bivariate analyses, gender, race, and age were more robustly associated with substance use in the final multinomial models.

CONCLUSIONS

Co-morbid substance use in adolescents with EDs is an important issue. Interventions targeting high-risk groups reporting regular substance use or substance use disorders are needed.

The endocannabinoid system and appetite: relevance for food reward

Mounting evidence substantiates the central role of the endocannabinoid system (ECS) in the modulation of both homeostatic and hedonic elements of appetite and food intake. Conversely, feeding status and dietary patterns directly influence activity of the ECS. Following a general introduction on the functioning of the ECS, the present review specifically addresses its role in the modulation of hedonic eating. Humans possess strong motivational systems triggered by rewarding aspects of food. Food reward is comprised of two components: one appetitive (orienting towards food); the other consummatory (hedonic evaluation), also referred to as 'wanting' and 'liking', respectively. Endocannabinoid tone seems to influence both the motivation to feed and the hedonic value of foods, probably by modifying palatability. Human physiology underlying hedonic eating is still not fully understood. A better understanding of the role of the ECS in the rewarding value of specific foods or diets could offer new possibilities to optimise the balance between energy and nutrient intake for different target groups. These groups include the obese and overweight, and potentially individuals suffering from malnutrition. Examples for the latter group are patients with disease-related anorexia, as well as the growing population of frail elderly suffering from persistent loss of food enjoyment and appetite resulting in malnutrition and involuntary weight loss. It has become clear that the psychobiology of food hedonics is extremely complex and the clinical failure of CB1 inverse agonists including rimonabant (Accomplia®) has shown that 'quick wins' in this field are unlikely.

Oleoylethanolamide: a novel potential pharmacological alternative to cannabinoid antagonists for the control of appetite

The initial pharmaceutical interest for the endocannabinoid system as a target for antiobesity therapies has been restricted by the severe adverse effects of the CB1 antagonist rimonabant. This study points at oleoylethanolamide (OEA), a monounsaturated analogue, and functional antagonist of anandamide, as a potential and safer antiobesity alternative to CB1 antagonism. Mice treated with equal doses (5 or 10 mg/kg, i.p.) of OEA or rimonabant were analyzed for the progressive expression of spontaneous behaviors (eating, grooming, rearing, locomotion, and resting) occurring during the development of satiety, according to the paradigm called behavioral satiety sequence (BSS). Both drugs reduced food (wet mash) intake to a similar extent. OEA treatment decreased eating activity within the first 30 min and caused a temporary increase of resting time that was not accompanied by any decline of horizontal, vertical and total motor activity. Besides decreasing eating activity, rimonabant caused a marked increase of the time spent grooming and decreased horizontal motor activity, alterations that might be indicative of aversive nonmotivational effects on feeding. These results support the idea that OEA suppresses appetite by stimulating satiety and that its profile of action might be predictive of safer effects in humans as a novel antiobesity treatment.

Biomarkers in the field of obesity and its related comorbidities

INTRODUCTION

The prevalence of obesity has increased dramatically in the last decades both in children and adults and is now considered a major health problem. It is associated with numerous comorbidities such as hypertension, dyslipidemia, diabetes and subsequent cardiovascular disease (CVD). One of the mechanisms that connect obesity with these comorbidities is the secretion of so-called adipocytokines or adipokines by the adipose tissue itself. Most adipokines with pro-inflammatory properties are overproduced with increasing adiposity, whereas some adipokines with anti-inflammatory or insulin-sensitizing properties, like adiponectin, are decreased. This dysregulation of adipokines production may promote obesity-linked metabolic disorders and CVD. Except adipokines a wide complex network of chemicals balances pro-inflammatory and anti-inflammatory effects.

AREAS COVERED

In this review, we summarize the role of various adipokines and other chemicals associated with obesity and its related cardiometabolic comorbidities, with a special focus on recent evidence showing their potential role as biomarkers whose expression are indicative of obesity and its complications.

EXPERT OPINION

Biomarkers associated with obesity, type 2 diabetes (T2D) and CVD could prove beneficial for early identification, proper treatment and good life assurance. Unfortunately, the complexity of biological pathways interactions is such that further research is necessary before any of these markers could reach an accurate diagnostic value.

Long-chain polyunsaturated fatty acids may mutually benefit both obesity and osteoporosis

The overconsumption of n-6 polyunsaturated fatty acids (PUFA), resulting in a high ratio of n-6 to n-3 PUFA, may contribute to the increased pathogenesis of obesity and osteoporosis by promoting low-grade chronic inflammation (LGCI). As evidence suggests, both obesity and osteoporosis are linked on a cellular and systemic basis. This review will analyze if a relationship exists between LGCI, fat, bone, and n-3 PUFA. During the life cycle, inflammation increases, fat mass accumulates, and bone mass declines, thus suggesting that a connection exists. This review will begin by examining how the current American diet and dietary guidelines may fall short of providing an anti-inflammatory dose of the n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It will then define LGCI and outline the evidence for a relationship between fat and bone. Inflammation as it pertains to obesity and osteoporosis and how EPA and DHA can alleviate the associated inflammation will be discussed, followed by some preliminary evidence to show how mesenchymal stem cell (MSC) lineage commitment may be altered by inflammation to favor adipogenesis. Our hypothesis is that n-3 PUFA positively influence obesity and osteoporosis by reducing LGCI, ultimately leading to a beneficial shift in MSC lineage commitment. This hypothesis essentially relates the need for more focused research in several areas such as determining age and lifestyle factors that promote the shift in MSC commitment and if current intakes of EPA and DHA are optimal for fat and bone.

Spinal administration of the monoacylglycerol lipase inhibitor JZL184 produces robust inhibitory effects on nociceptive processing and the development of central sensitization in the rat

BACKGROUND AND PURPOSE

The cannabinoid receptor-mediated analgesic effects of 2-arachidonoylglycerol (2-AG) are limited by monoacylglycerol lipase (MAGL). 4-nitrophenyl 4-[bis (1,3-benzodioxol-5-yl) (hydroxy) methyl] piperidine-1-carboxylate (JZL184) is a potent inhibitor of MAGL in the mouse, though potency is reportedly reduced in the rat. Here we have assessed the effects of spinal inhibition of MAGL with JZL184 on nociceptive processing in rats.

EXPERIMENTAL APPROACH

In vivo spinal electrophysiological assays in anaesthetized rats were used to determine the effects of spinal administration of JZL184 on spinal nociceptive processing in the presence and absence of hindpaw inflammation. Contributions of CB(1) receptors to these effects was assessed with AM251. Inhibition of 2-oleoylglycerol hydrolytic activity and alterations of 2-AG in the spinal cord after JZL 184 were also assessed.

KEY RESULTS

Spinal JZL184 dose-dependently inhibited mechanically evoked responses of wide dynamic range (WDR) neurones in naïve anaesthetized rats, in part via the CB(1) receptor. A single spinal administration of JZL184 abolished inflammation-induced expansion of the receptive fields of spinal WDR neurones. However, neither spinal nor systemic JZL184 altered levels of 2-AG, or 2-oleoylglycerol hydrolytic activity in the spinal cord, although JZL184 displayed robust inhibition of MAGL when incubated with spinal cord tissue in vitro.

CONCLUSIONS AND IMPLICATIONS

JZL184 exerted robust anti-nociceptive effects at the level of the spinal cord in vivo and inhibited rat spinal cord MAGL activity in vitro. The discordance between in vivo and in vitro assays suggests that localized sites of action of JZL184 produce these profound functional inhibitory effects.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8.

Marine cyanobacterial fatty acid amides acting on cannabinoid receptors

Striking cAMP: certain fatty acid amides from marine cyanobacteria can mimic the endocannabinoids. Serinolamide B, a new analogue identified from a Guamanian sample, and malyngamide B, a representative member of a large class of cyanobacterial metabolites, can decrease forskolin-induced cAMP accumulation through the cannabinoid receptors.

Differences in the endocannabinoid system of sperm from fertile and infertile men

Male infertility is a major cause of problems for many couples in conceiving a child. Recently, lifestyle pastimes such as alcohol, tobacco and marijuana have been shown to have further negative effects on male reproduction. The endocannabinoid system (ECS), mainly through the action of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) at cannabinoid (CB₁, CB₂) and vanilloid (TRPV1) receptors, plays a crucial role in controlling functionality of sperm, with a clear impact on male reproductive potential. Here, sperm from fertile and infertile men were used to investigate content (through LC-ESI-MS), mRNA (through quantitative RT-PCR), protein (through Western Blotting and ELISA) expression, and functionality (through activity and binding assays) of the main metabolic enzymes of AEA and 2-AG (NAPE-PLD and FAAH, for AEA; DAGL and MAGL for 2-AG), as well as of their binding receptors CB₁, CB₂ and TRPV1. Our findings show a marked reduction of AEA and 2-AG content in infertile seminal plasma, paralleled by increased degradation: biosynthesis ratios of both substances in sperm from infertile versus fertile men. In addition, TRPV1 binding was detected in fertile sperm but was undetectable in infertile sperm, whereas that of CB₁ and CB₂ receptors was not statistically different in the two groups. In conclusion, this study identified unprecedented alterations of the ECS in infertile sperm, that might impact on capacitation and acrosome reaction, and hence fertilization outcomes. These alterations might also point to new biomarkers to determine male reproductive defects, and identify distinct ECS elements as novel targets for therapeutic exploitation of ECS-oriented drugs to treat male fertility problems.

A potential role for GPR55 in gastrointestinal functions

Despite sharing little homology (10–15%) with cannabinoid-1 (CB₁) and cannabinoid-2 (CB₂) receptors, the G protein-coupled receptor 55 (GPR55) was initially thought to be a new member of the cannabinoid receptor family. Apart from being activated by various exogenous cannabinoids, GPR55 is also activated by endocannabinoids like anandamide, which is found in organs with high GPR55 expression such as the brain and the gastrointestinal (GI) tract. The phylogenetic distance to the classical CB receptors and its pharmacological responsiveness to certain cannabinoids suggests that GPR55 may constitute a novel class of cannabinoid receptors. GPR55 influences mechanisms in the nervous system, vasculature, kidney and bone. Recent research revealed that GPR55 is also involved in cancer development and inflammatory pain. Because of its presence in the GI tract, several studies have started to focus on the involvement of GPR55 in the physiology and pathophysiology of the gut. The following article intends to discuss the potential role of GPR55 in GI functions.

Endocannabinoids measurement in human saliva as potential biomarker of obesity

Background

The discovery of the endocannabinoid system and of its role in the regulation of energy balance has significantly advanced our understanding of the physiopathological mechanisms leading to obesity and type 2 diabetes. New knowledge on the role of this system in humans has been acquired by measuring blood endocannabinoids. Here we explored endocannabinoids and related N-acylethanolamines in saliva and verified their changes in relation to body weight status and in response to a meal or to body weight loss.

Methodology/Principal Findings

Fasting plasma and salivary endocannabinoids and N-acylethanolamines were measured through liquid mass spectrometry in 12 normal weight and 12 obese, insulin-resistant subjects. Salivary endocannabinoids and N-acylethanolamines were evaluated in the same cohort before and after the consumption of a meal. Changes in salivary endocannabinoids and N-acylethanolamines after body weight loss were investigated in a second group of 12 obese subjects following a 12-weeks lifestyle intervention program. The levels of mRNAs coding for enzymes regulating the metabolism of endocannabinoids, N-acylethanolamines and of cannabinoid type 1 (CB₁) receptor, alongside endocannabinoids and N-acylethanolamines content, were assessed in human salivary glands.

The endocannabinoids 2-arachidonoylglycerol (2-AG), N-arachidonoylethanolamide (anandamide, AEA), and the N-acylethanolamines (oleoylethanolamide, OEA and palmitoylethanolamide, PEA) were quantifiable in saliva and their levels were significantly higher in obese than in normal weight subjects. Fasting salivary AEA and OEA directly correlated with BMI, waist circumference and fasting insulin. Salivary endocannabinoids and N-acylethanolamines did not change in response to a meal. CB₁ receptors, ligands and enzymes were expressed in the salivary glands. Finally, a body weight loss of 5.3% obtained after a 12-weeks lifestyle program significantly decreased salivary AEA levels.

Conclusions/Significance

Endocannabinoids and N-acylethanolamines are quantifiable in saliva and their levels correlate with obesity but not with feeding status. Body weight loss significantly decreases salivary AEA, which might represent a useful biomarker in obesity.

Intense exercise increases circulating endocannabinoid and BDNF levels in humans--possible implications for reward and depression

The endocannabinoid system is known to have positive effects on depression partly through its actions on neurotrophins, such as Brain-Derived Neurotrophic Factor (BDNF). As BDNF is also considered the major candidate molecule for exercise-induced brain plasticity, we hypothesized that the endocannabinoid system represents a crucial signaling system mediating the beneficial antidepressant effects of exercise. Here we investigated, in 11 healthy trained male cyclists, the effects of an intense exercise (60 min at 55% followed by 30 min at 75% W(max)) on plasma levels of endocannabinoids (anandamide, AEA and 2-arachidonoylglycerol, 2-AG) and their possible link with serum BDNF. AEA levels increased during exercise and the 15 min recovery (P<0.001), whereas 2-AG concentrations remained stable. BDNF levels increased significantly during exercise and then decreased during the 15 min of recovery (P<0.01). Noteworthy, AEA and BDNF concentrations were positively correlated at the end of exercise and after the 15 min recovery (r>0.66, P<0.05), suggesting that AEA increment during exercise might be one of the factors involved in exercise-induced increase in peripheral BDNF levels and that AEA high levels during recovery might delay the return of BDNF to basal levels. AEA production during exercise might be triggered by cortisol since we found positive correlations between these two compounds and because corticosteroids are known to stimulate endocannabinoid biosynthesis. These findings provide evidence in humans that acute exercise represents a physiological stressor able to increase peripheral levels of AEA and that BDNF might be a mechanism by which AEA influences the neuroplastic and antidepressant effects of exercise.

Peripheral effects of FAAH deficiency on fuel and energy homeostasis: role of dysregulated lysine acetylation

Background

FAAH (fatty acid amide hydrolase), primarily expressed in the liver, hydrolyzes the endocannabinoids fatty acid ethanolamides (FAA). Human FAAH gene mutations are associated with increased body weight and obesity. In our present study, using targeted metabolite and lipid profiling, and new global acetylome profiling methodologies, we examined the role of the liver on fuel and energy homeostasis in whole body FAAH^−/− mice.

Methodology/Principal Findings

FAAH^−/− mice exhibit altered energy homeostasis demonstrated by decreased oxygen consumption (Indirect calorimetry). FAAH^−/− mice are hyperinsulinemic and have adipose, skeletal and hepatic insulin resistance as indicated by stable isotope phenotyping (SIPHEN). Fed state skeletal muscle and liver triglyceride levels was increased 2–3 fold, while glycogen was decreased 42% and 57% respectively. Hepatic cholesterol synthesis was decreased 22% in FAAH^−/− mice. Dysregulated hepatic FAAH^−/− lysine acetylation was consistent with their metabolite profiling. Fasted to fed increases in hepatic FAAH^−/− acetyl-CoA (85%, p<0.01) corresponded to similar increases in citrate levels (45%). Altered FAAH^−/− mitochondrial malate dehydrogenase (MDH2) acetylation, which can affect the malate aspartate shuttle, was consistent with our observation of a 25% decrease in fed malate and aspartate levels. Decreased fasted but not fed dihydroxyacetone-P and glycerol-3-P levels in FAAH^−/− mice was consistent with a compensating contribution from decreased acetylation of fed FAAH^−/− aldolase B. Fed FAAH^−/− alcohol dehydrogenase (ADH) acetylation was also decreased.

Conclusions/Significance

Whole body FAAH deletion contributes to a pre-diabetic phenotype by mechanisms resulting in impairment of hepatic glucose and lipid metabolism. FAAH^−/− mice had altered hepatic lysine acetylation, the pattern sharing similarities with acetylation changes reported with chronic alcohol treatment. Dysregulated hepatic lysine acetylation seen with impaired FAA hydrolysis could support the liver's role in fostering the pre-diabetic state, and may reflect part of the mechanism underlying the hepatic effects of endocannabinoids in alcoholic liver disease mouse models.

Antagonism of peripheral hepatic cannabinoid receptor-1 improves liver lipid metabolism in mice: evidence from cultured explants

It is well established that inactivation of the central endocannabinoid system (ECS) through antagonism of cannabinoid receptor 1 (CB1R) reduces food intake and improves several pathological features associated with obesity, such as dyslipidemia and liver steatosis. Nevertheless, recent data indicate that inactivation of peripheral CB1R could also be directly involved in the control of lipid metabolism independently of central CB1R. To further investigate this notion, we tested the direct effect of the specific CB1R antagonist, SR141716, on hepatic carbohydrate and lipid metabolism using cultured liver slices. CB1R messenger RNA expression was strongly decreased by SR141716, whereas it was increased by the CB1R agonist, arachidonic acid N-hydroxyethylamide (AEA), indicating the effectiveness of treatments in modulating ECS activity in liver explants both from lean or ob/ob mice. The measurement of O(2) consumption revealed that SR141716 increased carbohydrate or fatty acid utilization, according to the cellular hormonal environment. In line with this, SR141716 stimulated ß-oxidation activity, and the role of CB1R in regulating this pathway was particularly emphasized when ECS was hyperactivated by AEA and in ob/ob tissue. SR141716 also improved carbohydrate and lipid metabolism, blunting the AEA-induced increase in gene expression of proteins related to lipogenesis. In addition, we showed that SR141716 induced cholesterol de novo synthesis and high-density lipoprotein uptake, revealing a relationship between CB1R and cholesterol metabolism.

CONCLUSION

These data suggest that blocking hepatic CB1R improves both carbohydrate and lipid metabolism and confirm that peripheral CB1R should be considered as a promising target to reduce cardiometabolic risk in obesity.

Adolescent exposure to cannabis as a risk factor for psychiatric disorders

Adolescence represents a critical period for brain development and the endocannabinoid system plays a crucial role in the regulation of neuronal refinement during this period. Cannabis is the most consumed drug among adolescent people and its heavy use may affect maturational refinement by disrupting the regulatory role of the endocannabinoid system. In animals, adolescent cannabinoid exposure has been reported to cause long-term impairment in specific components of learning and memory and to differentially affect emotional reactivity with milder effects on anxiety behaviour and more pronounced effects on depression-like behaviour. Moreover, adolescent exposure to cannabinoids might represent a risk factor for developing psychotic-like symptoms at adulthood. Also epidemiological studies suggest that heavy adolescent cannabis use may increase the risk of cognitive abnormalities, psychotic illness, mood disorders and other illicit substance use later in life. In conclusion, the available data point to the hypothesis that heavy cannabis use in adolescence could increase the risk of developing psychiatric disorders, especially in people who already have a vulnerability to develop a psychiatric syndrome. Only few papers have investigated the neurobiological substrates of this vulnerability, thus further studies are needed to clarify the molecular mechanisms underlying the effect of cannabis on the adolescent brain.

Cannabinoids and bone: friend or foe?

The endocannabinoid system is recognized to play an important role in regulating a variety of physiological processes, including appetite control and energy balance, pain perception, and immune responses. The endocannabinoid system has also recently been implicated in the regulation of bone metabolism. Endogenously produced cannabinoids are hydrophobic molecules derived from hydrolysis of membrane phospholipids. These substances, along with plant-derived and synthetic cannabinoids, interact with the type 1 (CB(1)) and 2 (CB(2)) cannabinoid receptors and the GPR55 receptor to regulate cellular function through a variety of signaling pathways. Endocannabinoids are produced in bone, but the mechanisms that regulate their production are unclear. Skeletal phenotyping of mice with targeted inactivation of cannabinoid receptors and pharmacological studies have shown that cannabinoids play a key role in the regulation of bone metabolism. Mice with CB(1) deficiency have high peak bone mass as a result of an osteoclast defect but develop age-related osteoporosis as a result of impaired bone formation and accumulation of bone marrow fat. Mice with CB(2) deficiency have relatively normal peak bone mass but develop age-related osteoporosis as a result of increased bone turnover with uncoupling of bone resorption from bone formation. Mice with GPR55 deficiency have increased bone mass as a result of a defect in the resorptive activity of osteoclasts, but bone formation is unaffected. Cannabinoids are also produced within synovial tissues, and preclinical studies have shown that cannabinoid receptor ligands are effective in the treatment of inflammatory arthritis. These data indicate that cannabinoid receptors and the enzymes responsible for ligand synthesis and breakdown play important roles in bone remodeling and in the pathogenesis of joint disease.

Molecular mechanisms involved in the antitumor activity of cannabinoids on gliomas: role for oxidative stress

Cannabinoids, the active components of Cannabis sativa, have been shown to exert antiproliferative and proapoptotic effects on a wide spectrum of tumor cells and tissues. Of interest, cannabinoids have displayed great potency in reducing the growth of glioma tumors, one of the most aggressive CNS tumors, either in vitro or in animal experimental models curbing the growth of xenografts generated by subcutaneous or intrathecal injection of glioma cells in immune-deficient mice. Cannabinoids appear to be selective antitumoral agents as they kill glioma cells without affecting the viability of non-transformed cells. This review will summarize the anti-cancer properties that cannabinoids exert on gliomas and discuss their potential action mechanisms that appear complex, involving modulation of multiple key cell signaling pathways and induction of oxidative stress in glioma cells.

Latest advances in cannabinoid receptor agonists

BACKGROUND

Since the discovery of cannabinoid receptors and their endogenous ligands in early 1990s, the endocannabinoid system has been shown to play a vital role in several pathophysiological processes. It has been targeted for the treatment of several diseases including neurodegenerative diseases (Parkinson's disease, Alzheimer's disease, Huntington's disease and MS), cancer, obesity, inflammatory bowel disease, neuropathic and inflammatory pain. The last decade has witnessed remarkable advances in the development of cannabinergic ligands displaying high selectivity and potency towards two subtypes of cannabinoid receptors, namely CB1 and CB2.

OBJECTIVE

In this review, we highlight the latest advances made in the development of cannabinoid agonists and summarize recently disclosed, novel chemical scaffolds as CB-selective agonists in patents that appeared during January 2008 - June 2009.

METHODS

Data presented here are obtained through the search of PubMed for research articles and reviews, and the website of European patents (http://ep.espacenet.com), SciFinder Scholar and US patents (www.uspto.gov).

CONCLUSIONS

Our analysis reveals prolific patenting activity mainly in the CB2 selective agonist area. Limiting the BBB penetrability, thereby, leading to peripherally restricted CB1/CB2 agonists and enhancing CB2-selectivity emerge as likely prerequisites for avoidance of adverse central CB1 mediated side effects.

Fructose affects enzymes involved in the synthesis and degradation of hypothalamic endocannabinoids

Endocannabinoids have been implicated in the regulation of consumption of palatable food, sugar in particular. In this study, we investigated how palatable solutions would affect the hypothalamic mRNA expression of enzymes involved in the synthesis and degradation of the two main endocannabinoids, anandamide and 2-arachidonoyl-glycerol. Rats were offered sugar solutions to drink for one week, during which daily food and drink intake, and body weight gain was monitored. Rats offered sugar solutions to drink consumed less solid food but drank more of their respective sugar solution than did water-drinking control rats, resulting in increased total calorie intake. However, this increase in caloric intake did not result in increased body weight or adiposity in the rats. The mRNA expression of fatty acid amid hydrolase was up-regulated by sucrose and fructose. N-acyl phospatidyl ethanolamine phospholipase D mRNA was up-regulated by sucrose, whereas phospholipase C was down-regulated by all forms of sugar tested. The mRNA expression of monoglyceride lipase was down-regulated by all three forms of sugar. Also, the mRNA expression of diacylglycerol lipase 1alpha was down-regulated by sucrose and fructose, whereas the mRNA expression of diacylglycerol lipase 1beta was up-regulated by fructose. In this study, we show that sugars in liquid form affect enzymes involved in the degradation and synthesis of endocannabinoids in the hypothalamus and that this effect predates obesity.

FAAH deficiency promotes energy storage and enhances the motivation for food

RATIONALE

Fatty acid amide hydrolase (FAAH) is the main degrading enzyme of the fatty acid ethanolamides anandamide (AEA) and oleoylethanolamide (OEA), which have opposite effects on food intake and energy balance. AEA, an endogenous ligand of CB(1) cannabinoid receptors, enhances food intake and energy storage, whereas OEA binds to peroxisome proliferator-activated receptors-alpha to reduce food intake and promoting lipolysis. To elucidate the role of FAAH in food intake and energy balance, we have evaluated different metabolic and behavioral responses related to feeding in FAAH-deficient (FAAH(-/-)) mice and their wild-type littermates.

METHODOLOGY AND RESULTS

Total daily food intake was similar in both genotypes, but high-fat food consumption was enhanced during the dark hours and decreased during the light hours in FAAH(-/-) mice. The reinforcing and motivational effects of food were also enhanced in FAAH(-/-) mice as revealed by operant behavioral paradigms. These behavioral responses were reversed by the administration of the selective CB(1) cannabinoid antagonist rimonabant. Furthermore, body weight, total amount of adipose tissue, plasma-free fatty acids and triglyceride content in plasma, liver, skeletal muscle and adipose tissue, were increased in FAAH(-/-) mice. Accordingly, leptin levels were increased and adiponectin levels decreased in these mutants, FAAH(-/-) mice also showed enhanced plasma insulin and blood glucose levels revealing an insulin resistance. As expected, both AEA and OEA levels were increased in hypothalamus, small intestine and liver of FAAH(-/-) mice.

CONCLUSION

These results indicate that the lack of FAAH predominantly promotes energy storage by food intake-independent mechanisms, through the enhancement of AEA levels rather than promoting the anorexic effects of OEA.

Evaluation of prevalent phytocannabinoids in the acetic acid model of visceral nociception

Considerable preclinical research has demonstrated the efficacy of Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the primary psychoactive constituent of Cannabis sativa, in a wide variety of animal models of pain, but few studies have examined other phytocannabinoids. Indeed, other plant-derived cannabinoids, including cannabidiol (CBD), cannabinol (CBN), and cannabichromene (CBC) elicit antinociceptive effects in some assays. In contrast, tetrahydrocannabivarin (THCV), another component of cannabis, antagonizes the pharmacological effects of Delta(9)-THC. These results suggest that various constituents of this plant may interact in a complex manner to modulate pain. The primary purpose of the present study was to assess the antinociceptive effects of these other prevalent phytocannabinoids in the acetic acid stretching test, a rodent visceral pain model. Of the cannabinoid compounds tested, Delta(9)-THC and CBN bound to the CB(1) receptor and produced antinociceptive effects. The CB(1) receptor antagonist, rimonabant, but not the CB(2) receptor antagonist, SR144528, blocked the antinociceptive effects of both compounds. Although THCV bound to the CB(1) receptor with similar affinity as Delta(9)-THC, it had no effects when administered alone, but antagonized the antinociceptive effects of Delta(9)-THC when both drugs were given in combination. Importantly, the antinociceptive effects of Delta(9)-THC and CBN occurred at lower doses than those necessary to produce locomotor suppression, suggesting motor dysfunction did not account for the decreases in acetic acid-induced abdominal stretching. These data raise the intriguing possibility that other constituents of cannabis can be used to modify the pharmacological effects of Delta(9)-THC by either eliciting antinociceptive effects (i.e., CBN) or antagonizing (i.e., THCV) the actions of Delta(9)-THC.

Genetical genomic determinants of alcohol consumption in rats and humans

BACKGROUND

We have used a genetical genomic approach, in conjunction with phenotypic analysis of alcohol consumption, to identify candidate genes that predispose to varying levels of alcohol intake by HXB/BXH recombinant inbred rat strains. In addition, in two populations of humans, we assessed genetic polymorphisms associated with alcohol consumption using a custom genotyping array for 1,350 single nucleotide polymorphisms (SNPs). Our goal was to ascertain whether our approach, which relies on statistical and informatics techniques, and non-human animal models of alcohol drinking behavior, could inform interpretation of genetic association studies with human populations.

RESULTS

In the HXB/BXH recombinant inbred (RI) rats, correlation analysis of brain gene expression levels with alcohol consumption in a two-bottle choice paradigm, and filtering based on behavioral and gene expression quantitative trait locus (QTL) analyses, generated a list of candidate genes. A literature-based, functional analysis of the interactions of the products of these candidate genes defined pathways linked to presynaptic GABA release, activation of dopamine neurons, and postsynaptic GABA receptor trafficking, in brain regions including the hypothalamus, ventral tegmentum and amygdala. The analysis also implicated energy metabolism and caloric intake control as potential influences on alcohol consumption by the recombinant inbred rats. In the human populations, polymorphisms in genes associated with GABA synthesis and GABA receptors, as well as genes related to dopaminergic transmission, were associated with alcohol consumption.

CONCLUSION

Our results emphasize the importance of the signaling pathways identified using the non-human animal models, rather than single gene products, in identifying factors responsible for complex traits such as alcohol consumption. The results suggest cross-species similarities in pathways that influence predisposition to consume alcohol by rats and humans. The importance of a well-defined phenotype is also illustrated. Our results also suggest that different genetic factors predispose alcohol dependence versus the phenotype of alcohol consumption.

Circulating endocannabinoids and N-acyl ethanolamines are differentially regulated in major depression and following exposure to social stress

Central endocannabinoid signaling is known to be responsive to stressful stimuli; however, there is no research to date characterizing the effects of stress on peripheral endocannabinoid content. The current study examined serum content of the endocannabinoid ligands N-arachidonylethanolamide (anandamide; AEA) and 2-arachidonoylglycerol (2-AG), and the non-cannabinoid N-acyl ethanolamine (NAE) molecules palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) under basal conditions, immediately following the Trier Social Stress Test (TSST), and 30 min thereafter, in 15 medication-free women diagnosed with major depression, and 15 healthy matched controls. Basal serum concentrations of AEA and 2-AG, but not PEA or OEA, were significantly reduced in women with major depression relative to matched controls, indicating a deficit in peripheral endocannabinoid activity. Immediately following the TSST, serum 2-AG concentrations were increased compared to baseline; serum AEA concentration was unchanged at this time point. Serum concentrations of PEA and OEA were significantly lower than baseline 30 min following the cessation of the TSST. The magnitude of these responses did not differ between depressed and control subjects. These are the first data to demonstrate that the peripheral endocannabinoid/NAE system is responsive to exposure to stress.

Beta-arrestin-based Bret2 screening assay for the "non"-beta-arrestin binding CB1 receptor

CB1 receptor (CB1R) antagonists have been demonstrated to be effective in treating obesity and related disorders. This study has been focused on establishing a beta-arrestin 2-based screening assay for the CB1R using BRET2 technology. When the existing BRET2 screening platform was applied to the CB1R, the authors discovered that the receptor interacted weakly with beta-arrestin 2, resulting in unsatisfactory assay performance. To enhance the beta-arrestin binding capacity, they replaced the C-terminal tail of the CB1R with tails from either the V2 or BRS3 receptors, both of which interact strongly with beta-arrestin 2. Using this chimeric approach, the authors screened a small compound library and identified 21 antagonist and inverse agonist hits with IC50 and EC50 values ranging from 0.3 nM to 7.5 microM. Both primary and secondary screening were performed with Z'>0.5, suggesting that the assay is a robust and cost-effective alternative to existing cell-based assays.

Weight regain after Roux-en-Y: a significant 20% complication related to PYY

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) produces rapid and dramatic weight loss in very heavy obese patients. Up to 20% cannot sustain their weight loss beyond 2 to 3 y after surgery.

METHODS

To identify putative etiologic factors producing post-RYGB weight regain, a literature survey of metabolic changes in very obese and a review of our diet-induced obese RYGB rat model data was done.

RESULTS

Weight regain suggests an imbalance in physiologic mechanisms regulating appetite and metabolic rate. Weight regain occurred in 25% of our rats, produced by return to presurgical energy intake levels. The 75% of rats that sustained weight loss secreted a significantly larger amount of peptide YY (PYY) while suppressing leptin secretion; those that failed were unable to develop or sustain a sufficiently large plasma PYY:leptin ratio. Metabolic consequences of this failure included reversal of initial postsurgical increases in peripheral fatty acid oxidation, anorexigenic activity in the hypothalamic arcuate nucleus and paraventricular nucleus, and the expression of uncoupling protein-2 in adipose tissues, and decreases in hepatic lipogenesis, free tri-iodothyronine secretion, expression of orexigenic activity in the arcuate nucleus and paraventricular nucleus, expression of adenosine monophosphate kinase in adipose tissues, skeletal muscle mitochondrial mass, and endocannabinoid content and appetite.

CONCLUSION

Weight regain after RYGB occurs in approximately 20% of patients and constitutes a serious complication. Weight regain-promoting consequences are attributed to a failure to sustain elevated plasma PYY concentrations, indicating that combining RYGB with pharmacologic stimulation of PYY secretion in patients after RYGB who exhibit inadequate PYY concentration may increase long-term success of surgical weight reduction in morbidly obese adults.

Glycerolipid metabolism and signaling in health and disease

Maintenance of body temperature is achieved partly by modulating lipolysis by a network of complex regulatory mechanisms. Lipolysis is an integral part of the glycerolipid/free fatty acid (GL/FFA) cycle, which is the focus of this review, and we discuss the significance of this pathway in the regulation of many physiological processes besides thermogenesis. GL/FFA cycle is referred to as a "futile" cycle because it involves continuous formation and hydrolysis of GL with the release of heat, at the expense of ATP. However, we present evidence underscoring the "vital" cellular signaling roles of the GL/FFA cycle for many biological processes. Probably because of its importance in many cellular functions, GL/FFA cycling is under stringent control and is organized as several composite short substrate/product cycles where forward and backward reactions are catalyzed by separate enzymes. We believe that the renaissance of the GL/FFA cycle is timely, considering the emerging view that many of the neutral lipids are in fact key signaling molecules whose production is closely linked to GL/FFA cycling processes. The evidence supporting the view that alterations in GL/FFA cycling are involved in the pathogenesis of "fatal" conditions such as obesity, type 2 diabetes, and cancer is discussed. We also review the different enzymatic and transport steps that encompass the GL/FFA cycle leading to the generation of several metabolic signals possibly implicated in the regulation of biological processes ranging from energy homeostasis, insulin secretion and appetite control to aging and longevity. Finally, we present a perspective of the possible therapeutic implications of targeting this cycling.

The CB1 endocannabinoid system modulates adipocyte insulin sensitivity

Mounting evidence suggests that the endocannabinoid system regulates energy metabolism through direct effects on peripheral tissues as well as central effects that regulate appetite. Here we examined the effect of cannabinoid receptor 1 (CB1) signaling on insulin action in fat cells. We examined effects of the natural CB1 agonist, 2-Arachidonoylglycerol (2-AG), and the synthetic CB1 antagonist, SR141716, on insulin action in cultured adipocytes. We used translocation of glucose transporter GLUT4 to plasma membrane (PM) as a measure of insulin action. 2-AG activation of the CB1 receptor promoted insulin sensitivity whereas antagonism by SR141716 reduced insulin sensitivity. Neither drug affected GLUT4 translocation in the absence of insulin or with high doses of insulin. Consistent with these results we found that insulin-stimulated phosphorylation of the protein kinase Akt was increased by 2-AG, attenuated by SR141716, and unaffected in the absence of insulin or by addition of high-dose insulin. These data provide a functional and molecular link between the CB1 receptor and insulin sensitivity, because insulin-stimulated phosphorylation of Akt is required for GLUT4 translocation to the PM. The sensitizing effects of 2-AG were abrogated by SR141716 and Pertussis toxin, indicating that the effects are mediated by CB1 receptor. Importantly, neither 2-AG nor SR141716 alone or in combination with maximal dose of insulin had effects on GLUT4 translocation and Akt phosphorylation. These data are consistent with a model in which the endocannabinoid system sets the sensitivity of the insulin response in adipocytes rather than directly regulating the redistribution of GLUT4 or Akt phosphorylation.

Sustained weight loss after Roux-en-Y gastric bypass is characterized by down regulation of endocannabinoids and mitochondrial function

OBJECTIVE

To determine the physiologic importance of endocannabinoids and mitochondrial function in the long-term outcome using a rat model of Roux-en-Y gastric bypass (RYGB) surgery.

BACKGROUND

Sixteen million people are morbidly obese and RYGB surgery is the most effective treatment. Endocannabinoids are implicated in appetite stimulation and regulation of peripheral energy metabolism. We hypothesize that down-regulation of endocannabinoids and alterations in mitochondrial function and hormones favoring catabolism contribute to sustained RYGB-induced weight loss.

METHODS

Diet-induced obese Sprague-Dawley rats were randomized to sham-operated obese controls, RYGB, and sham-operated obese pair-fed rats. Body weight and food intake were recorded, and food efficiency was calculated. Endocannabinoid levels in skeletal muscle and liver, muscle mitochondrial respiratory complex I-V content, and hormones concentrations were determined 14 and 28 days postsurgery, reflecting rapid and sustained weight loss periods after RYGB, respectively.

RESULTS

Compared with pair-fed controls, RYGB rats had significant reduction in body weight and food efficiency (P < 0.001). Increased cholecystokinin, reduced insulin, leptin, adiponectin, T3, and down-regulation of mitochondrial complex I were evident on day 14 postsurgery. On day 28, leptin, insulin, and T3 remained low, whereas adiponectin and cholecystokinin were normal. Along with complex I, the endocannabinoids anandamide in muscle (P = 0.003) and 2-arachidonoylglycerol in liver were significantly down-regulated (P < 0.001).

CONCLUSIONS

The attenuated caloric intake, reduced food efficiency, and normalization of hormonal levels on day 28 post-RYGB were associated with significant down-regulation of endocannabinoids anandamide and 2-arachidonoylglycerol in muscle and liver, respectively. These results suggest a role for endocannabinoids in the mechanism of sustained weight loss and RYGB success, and may have implications for treatment of morbid obesity.

Activation of the endocannabinoid system by organophosphorus nerve agents

Delta(9)-tetrahydrocannabinol (THC), the psychoactive ingredient of marijuana, has useful medicinal properties but also undesirable side effects. The brain receptor for THC, CB(1), is also activated by the endogenous cannabinoids anandamide and 2-arachidonylglycerol (2-AG). Augmentation of endocannabinoid signaling by blockade of their metabolism may offer a more selective pharmacological approach compared with CB(1) agonists. Consistent with this premise, inhibitors of the anandamide-degrading enzyme fatty acid amide hydrolase (FAAH) produce analgesic and anxiolytic effects without cognitive defects. In contrast, we show that dual blockade of the endocannabinoid-degrading enzymes monoacylglycerol lipase (MAGL) and FAAH by selected organophosphorus agents leads to greater than ten-fold elevations in brain levels of both 2-AG and anandamide and to robust CB(1)-dependent behavioral effects that mirror those observed with CB(1) agonists. Arachidonic acid levels are decreased by the organophosphorus agents in amounts equivalent to elevations in 2-AG, which indicates that endocannabinoid and eicosanoid signaling pathways may be coordinately regulated in the brain.

The endocannabinoid system and gut–brain signalling

The endocannabinoid system (ECS) consists of cannabinoid receptors, endogenous ligands and the biosynthetic and metabolic enzymes for their formation and degradation. Within the gastrointestinal (GI) tract, the ECS is involved in the regulation of motility, secretion, sensation, emesis, satiety and inflammation. Recent studies examining the ECS in the gut-brain axis have shed new light on this system and reveal many facets of regulation that are amenable to targeting by pharmacological interventions that may prove valuable for the treatment of GI disorders. In particular, it has been shown that endocannabinoid levels in the brain and gut vary according to states of satiety, and in conditions of diarrhea, emesis and inflammation. The expression of cannabinoid (CB)(1) receptors on vagal afferents is controlled by the states of satiety and by gut peptides such as cholecystokinin and ghrelin. Vagal control of gut motor function and emesis is regulated by endocannabinoids in the brainstem acting on CB(1), CB(2) and transient receptor potential vanilloid (TRPV)-1 receptors. The ECS is involved in the modulation of visceral sensation and likely contributes to effects of stress on GI function. This review examines recent developments in our understanding of the ECS in gut-brain signalling.

Endocannabinoid regulation of matrix metalloproteinases: implications in ischemic stroke

Stroke is a major cause of morbidity and mortality and follows heart disease and cancer as the third leading cause of death in Western societies [1]. Despite many advances in stroke research and pharmacotherapy, clinical treatment of this debilitating disorder is still inadequate. Recent findings from several laboratories have identified the endocannabinoid signaling pathway, comprised of the endocannabinoid agonist anandamide and its pharmacological targets, CB1 and CB2 cannabinoid receptors and associated anandamide receptors, as a physiological system with capacity to mitigate cardiovascular and cerebrovascular disorders through neuronal and endothelial actions. Variability in experimental stroke models and modes of outcome evaluation, however, have provoked controversy regarding the precise roles of endocannabinoid signals in mediating neural and/or vascular protection versus neurovascular damage. Clinical trials of the CB1 antagonist rimonabant demonstrate that modulation of endocannabinoid signaling during metabolic regulation of vascular disorders can significantly impact clinical outcomes, thus providing strong argument for therapeutic utility of endocannabinoids and/or cannabinoid receptors as targets for therapeutic intervention in cases of stroke and associated vascular disorders. The purpose of this review is to provide updated information from basic science and clinical perspectives on endocannabinoid ligands and their effects in the pathophysiologic genesis of stroke. Particular emphasis will be placed on the endocannabinoids anandamide and 2-arachidonylglycerol and CB1 receptor-mediated mechanisms in the neurovascular unit during stroke pathogenesis. Deficiencies in our knowledge of endocannabinoids in the etiology and pathogenesis of stroke, caveats and limitations of existing studies, and future directions for investigation will be addressed.

The endocannabinoid system and rimonabant: a new drug with a novel mechanism of action involving cannabinoid CB1 receptor antagonism--or inverse agonism--as potential obesity treatment and other therapeutic use

There is considerable evidence that the endocannabinoid (endogenous cannabinoid) system plays a significant role in appetitive drive and associated behaviours. It is therefore reasonable to hypothesize that the attenuation of the activity of this system would have therapeutic benefit in treating disorders that might have a component of excess appetitive drive or over-activity of the endocannabinoid system, such as obesity, ethanol and other drug abuse, and a variety of central nervous system and other disorders. Towards this end, antagonists of cannabinoid receptors have been designed through rational drug discovery efforts. Devoid of the abuse concerns that confound and impede the use of cannabinoid receptor agonists for legitimate medical purposes, investigation of the use of cannabinoid receptor antagonists as possible pharmacotherapeutic agents is currently being actively investigated. The compound furthest along this pathway is rimonabant, a selective CB(1) (cannabinoid receptor subtype 1) antagonist, or inverse agonist, approved in the European Union and under regulatory review in the United States for the treatment of obesity. This article summarizes the basic science of the endocannabinoid system and the therapeutic potential of cannabinoid receptor antagonists, with emphasis on the treatment of obesity.

Endocannabinoid system involvement in brain reward processes related to drug abuse

Cannabis is the most commonly abused illegal drug in the world and its main psychoactive ingredient, delta-9-tetrahydrocannabinol (THC), produces rewarding effects in humans and non-human primates. Over the last several decades, an endogenous system comprised of cannabinoid receptors, endogenous ligands for these receptors and enzymes responsible for the synthesis and degradation of these endogenous cannabinoid ligands has been discovered and partly characterized. Experimental findings strongly suggest a major involvement of the endocannabinoid system in general brain reward functions and drug abuse. First, natural and synthetic cannabinoids and endocannabinoids can produce rewarding effects in humans and laboratory animals. Second, activation or blockade of the endogenous cannabinoid system has been shown to modulate the rewarding effects of non-cannabinoid psychoactive drugs. Third, most abused drugs alter brain levels of endocannabinoids in the brain. In addition to reward functions, the endocannabinoid cannabinoid system appears to be involved in the ability of drugs and drug-related cues to reinstate drug-seeking behavior in animal models of relapse. Altogether, evidence points to the endocannadinoid system as a promising target for the development of medications for the treatment of drug abuse.

Histamine in the brain: Beyond sleep and memory

A few decades elapsed between the attribution of unwanted side effects of classic antihistamine compounds to the blockade of central H(1) receptors, and the acceptance of the concept that the histaminergic system commands general states of metabolism and consciousness. In the early 80s, two laboratories discovered independently that histaminergic neurons are located in the posterior hypothalamus and project to the whole CNS [Panula P, Yang HY, Costa E. Histamine-containing neurons in the rat hypothalamus. Proc Natl Acad Sci 1984;81:2572-76, Watanabe T, Taguchi Y, Hayashi H, Tanaka J, Shiosaka S, Tohyama M, Kubota H, Terano Y, Wada H. Evidence for the presence of a histaminergic neuron system in the rat brain: an immunohistochemical analysis. Neurosci Lett 1983;39:249-54], suggesting a global nature of histamine regulatory effects. Recently, functional studies demonstrated that activation of the central histaminergic system alters CNS functions in both behavioral and homeostatic contexts, which include sleep and wakefulness, learning and memory, anxiety, locomotion, feeding and drinking, and neuroendocrine regulation. These actions are achieved through interactions with other neurotransmitter systems, and the interplay between histaminergic neurons and other neurotransmitter systems are becoming clear. Hence, numerous laboratories are pursuing novel compounds targeting the three known histamine receptors found in the brain for various therapeutic indications. Preclinical studies are focusing on three major areas of interest and intense research is mainly oriented towards providing drugs for the treatment of sleep, cognitive and feeding disorders. This commentary is intended to summarize some of the latest findings that suggest functional roles for the interplay between histamine and other neurotransmitter systems, and to propose novel interactions as physiological substrates that may partially underlie some of the behavioral changes observed following manipulation of the histaminergic system.

Effects of the cannabinoid antagonist SR141716 (rimonabant) and d-amphetamine on palatable food and food pellet intake in non-human primates

The purpose of this study was to determine if a cannabinoid CB(1) receptor antagonist would selectively decrease consumption of highly palatable food in non-human primates. The CB(1) receptor antagonist SR141716 (rimonabant; 0.12-1.0 mg/kg, i.m.) and the stimulant anorectic drug d-amphetamine (0.12-1.0 mg/kg, i.m.) were administered to non-food deprived baboons for the purpose of measuring the effect of each drug on consumption of the normal diet, and a large single meal of a high-carbohydrate candy. Four male and four female baboons had access to food 24 h each day, but they had to complete a two phase operant procedure in order to eat. Responding on one lever during a 30-min appetitive phase was required before animals could start a consumption phase, where responding on another lever led to food delivery, i.e., a meal. Three days a week baboons received a jelly sugar-coated candy (Skittles) during the first meal and then pellets were available in subsequent meals. All baboons ate as many individual candies in one meal as they did pellets throughout the entire day. Acute d-amphetamine and, to a lesser extent, SR141716 decreased both candy intake in a single meal and pellet intake in a single meal and over 24 h. d-Amphetamine, but not SR141716, increased latency to the candy meal and the first pellet meal indicating that the two drugs differentially altered feeding topography. Although males ate more food pellets than females, few other sex differences were observed. Thus, although effective in decreasing food intake, there was no evidence of a specific effect of CB(1) receptor antagonism on consumption of a large meal or a palatable food.