Leptin-regulated endocannabinoids are involved in maintaining food intake

Adipose tissue and adipokines--energy regulation from the human perspective

There has been a rapid rise in the incidence of obesity, primarily as a result of changes in lifestyle (diet and activity levels). Obesity has provided considerable impetus for the investigation of the fundamental mechanisms involved in the regulation of energy balance. Important developments include the identification of novel factors involved in the control of appetite, such as ghrelin, orexin A, and the endogenous cannabinoids, and the emergence of the concept of "nonexercise activity thermogenesis" (NEAT) provided new perspectives on energy expenditure. Studies on white adipose tissue have led to the recognition that it is an important endocrine organ, communicating with the brain and peripheral tissues through the secretion of leptin and other adipokines. There is a rapidly expanding list of protein factors released by white adipose tissue, including the key hormone, adiponectin. Of particular note is the range of cytokines, chemokines, and other inflammation-related proteins secreted by white fat as tissue mass rises; indeed, obesity is characterized by chronic mild inflammation. The adipokines provide an extensive network of communication both within adipose tissue and with other organs, and some are implicated directly in the pathologies associated with obesity, particularly the metabolic syndrome. Although the focus remains very much on obesity in humans, the disorder and its sequelae are also a growing concern in companion animals.

Endocannabinoid system and its role in energy regulation

Endocannabinoids are endogenous agonists for the two types of cannabinoid receptors identified to date, the CB₁ and CB₂ receptors. CB₁ receptors and tissue concentrations of endocannabinoids sufficient to activate them are present in the brain structures controlling energy intake (i.e., the hypothalamus, nucleus accumbens and nodose ganglion), as well as in all peripheral organs mostly involved in the regulation of energy homeostasis (i.e., the duodenum, small and large intestine, adipose tissue, skeletal muscle, pancreas and liver). Several peripheral neuropeptides and hormones involved in energy balance, and type of diet, regulate endocannabinoid levels, whereas endocannabinoids, in turn, regulate the expression and release of hypothalamic mediators involved in nutrient intake. Dysregulation of the endocannabinoid system might contribute to the development of eating disorders and explain why CB₁ receptor blockers are efficacious at reducing not only food intake but also the metabolic consequences of visceral adiposity and obesity.

The cannabinoid CB1 receptor inverse agonist, rimonabant, modifies body weight and adiponectin function in diet-induced obese rats as a consequence of reduced food intake

The cannabinoid CB1 receptor inverse agonist rimonabant induces hypophagia and body weight loss. Reduced body weight may potentially be due to decreased food intake or to direct metabolic effects of drug administration on energy expenditure. This study uses a paired-feeding protocol to quantify the contributions of energy intake to rimonabant-induced body weight loss. Diet-induced obese (DIO) rats were dosed with rimonabant (3, 10 mg/kg PO once daily) and matched with pair-fed controls. Food intake and body weight were measured daily. Blood samples and adipose tissue were collected on day 15 for measurement of plasma adiponectin and adiponectin mRNA levels. DIO rats treated with rimonabant and pair-fed controls showed very similar changes in body weight. Although tolerance developed to the anorectic effect of rimonabant, total food intake was significantly decreased over the 14-day study period and fully accounted for the observed reductions in body weight. Adiponectin mRNA and plasma adiponectin were elevated in vehicle-treated chow-fed animals compared to obese controls, and did not differ between rimonabant-treated and pair-fed animals. The similarities between rimonabant-treated and pair-fed animals in body weight loss and the absence of differences in measures of adiponectin activity between drug-treated and pair-fed animals suggest that the outcomes of this experiment were solely mediated by the drug-induced reduction in food intake.

Involvement of Neuronal Cannabinoid Receptor CB1 in Regulation of Bone Mass and Bone Remodeling

The CB1 cannabinoid receptor has been implicated in the regulation of bone remodeling and bone mass. A high bone mass (HBM) phenotype was reported in CB1-null mice generated on a CD1 background (CD1(CB1-/-) mice). By contrast, our preliminary studies in cb1-/- mice, backcrossed to C57BL/6J mice (C57(CB1-/-) mice), revealed low bone mass (LBM). We therefore analyzed CB1 expression in bone and compared the skeletons of sexually mature C57(CB1-/-) and CD1(CB1-/-) mice in the same experimental setting. CB1 mRNA is weakly expressed in osteoclasts and immunoreactive CB1 is present in sympathetic neurons, close to osteoblasts. In addition to their LBM, male and female C57(CB1-/-) mice exhibit decreased bone formation rate and increased osteoclast number. The skeletal phenotype of the CD1(CB1-/-) mice shows a gender disparity. Female mice have normal trabecular bone with a slight cortical expansion, whereas male CD1(CB1-/-) animals display an HBM phenotype. We were surprised to find that bone formation and resorption are within normal limits. These findings, at least the consistent set of data obtained in the C57(CB1-/-) line, suggest an important role for CB1 signaling in the regulation of bone remodeling and bone mass. Because sympathetic CB1 signaling inhibits norepinephrine (NE) release in peripheral tissues, part of the endocannabinoid activity in bone may be attributed to the regulation of NE release from sympathetic nerve fibers. Several phenotypic discrepancies have been reported between C57(CB1-/-) and CD1(CB1-/-) mice that could result from genetic differences between the background strains. Unraveling these differences can provide useful information on the physiologic functional milieu of CB1 in bone.

Rimonabant: A Cannabinoid Receptor Type 1 Blocker for Management of Multiple Cardiometabolic Risk Factors

Rimonabant is a first selective blocker of the cannabinoid receptor type 1 (CB1) being developed for the treatment of multiple cardiometabolic risk factors, including abdominal obesity and smoking. In four large trials, after one year of treatment, rimonabant 20 mg led to greater weight loss and reduction in waist circumference compared with placebo. Therapy with rimonabant is also associated with favorable changes in serum lipid levels and an improvement in glycemic control in prediabetes patients and in type 2 diabetic patients. At the same dose, rimonabant significantly increased cigarette smoking quit rates as compared with placebo. Rimonabant seems to be well tolerated, with a primary side effect of mild nausea. As an agent with a novel mechanism of action, rimonabant has a potential to be a useful adjunct to lifestyle and behavior modification in treatment of multiple cardiometabolic risk factors, including abdominal obesity and smoking.

Rimonabant: a selective blocker of the cannabinoid CB1 receptors for the management of obesity, smoking cessation and cardiometabolic risk factors

Rimonabant is the first selective blocker of the cannabinoid CB1 receptors being developed for the treatment of obesity, tobacco smoking and cardiometabolic risk factors. Following 1 year of treatment, rimonabant 20 mg/day leads to greater weight loss compared with placebo. Therapy with rimonabant is also associated with favourable changes in serum lipids and an improvement in glycaemic control in Type 2 diabetics. At the same dose, rimonabant significantly increases the cigarette smoking quit rates compared with placebo. Rimonabant appears to be generally well tolerated, with primary side effects of mild nausea, diarrhoea, anxiety and depression. As an agent with a novel mechanism of action, rimonabant has the potential to be a useful adjunct to lifestyle modification in the treatment of obesity, metabolic syndrome and cigarette smoking.

[Endogenous cannabinoid receptor ligands--anandamide and 2-arachidonoylglycerol]

Marijuana has been used as a traditional medicine and a pleasure-inducing drug for thousands of years around the world, especially in Asia. Delta(9)-tetrahydrocannabinol, major psychoactive component of marijuana, has been shown to interact with specific cannabinoid receptors, thereby eliciting a variety of pharmacological responses in experimental animals and human. In 1990, the gene encoding a cannabinoid receptor (CB1) was cloned. This prompted the search for endogenous ligands. In 1992, N-arachidonoylethanolamine (anandamide) was isolated from pig brain as an endogenous ligand, and in 1995, 2-arachidonoylglycerol was isolated from rat brain and canine gut as another endogenous ligand. Both anandamide and 2-arachidonoylglycerol exhibit various cannabimimetic activities. The results of structure-activity relationship experiments, however, revealed that 2-arachidonoylglycerol, but not anandamide, is the intrinsic natural ligand for the cannabinoid receptor. 2-arachidonoylglycerol is a degradation product of inositol phospholipids that links the function of the cannabinoid receptors with the enhanced inositol phospholipid turnover in stimulated tissues and cells. The possible physiological roles of cannabinoid receptors and 2-arachidonoylglycerol in various mammalian tissues such as those of the nervous and inflammatory cells are demonstrated. Furthermore, the future development of therapeutic drugs coming from this endocannabinoid system are discussed.

Emerging drugs for obesity: linking novel biological mechanisms to pharmaceutical pipelines

Obesity is associated with hypertension, diabetes, dyslipidaemias and metabolic syndrome, and causes substantial morbidity and mortality from cardiovascular and other diseases. The cost to treat obesity and its complications in the US has increased steeply and is currently estimated to be USD 100 billion. Current therapy for obesity is mainly based on changes in lifestyle that often fail. Existing pharmacological treatment is marginally efficient and poorly tolerated. The discovery of leptin and related neural mechanisms of energy metabolism regulation has opened the doors to potential targets for new antiobesity drugs. In this review, new pharmacological targets are discussed and an update on the development of emerging antiobesity drugs is provided. Despite intense investigation, the pipelines for antiobesity drugs in late stages of development are relatively empty. Breakthrough treatments for obesity may take some years to emerge. Clinical trials will be necessary to clarify the impact of new antiobesity drugs on hard cardiovascular and metabolic end points.

O sistema endocanabinóide: novo paradigma no tratamento da síndrome metabólica

O balanço energético é um dos mais importantes mecanismos de homeostase e de sobrevivência das espécies. O sistema endocanabinóide é um novo e importante componente entre estes mecanismos. Os seus receptores e agonistas endógenos se expressam no sistema nervoso central (SNC) e perifericamente, em vários sítios, estabelecendo uma rede de comunicação periferiaSNC. Um aspecto marcante é a sua expressão no tecido adiposo, onde regula a lipogênese e aumenta a expressão de genes influentes no metabolismo dos lipídeos e dos carboidratos. Estes aspectos são importantes para o controle do peso corporal e da Síndrome Metabólica (SM). O sistema é ativado sob demanda e desativado rapidamente, atuando autócrina e paracrinamente, e as evidências sugerem que mantém-se hiperativado em estados de obesidade. Um antagonista específico do seu principal receptor (CB1), o Rimonabant, tem se mostrado importante ferramenta no controle do peso em modelos animais de obesidade e de SM. Da mesma forma, grandes estudos em humanos confirmam sua eficácia no controle do peso e das variáveis metabólicas, sugerindo um papel importante deste medicamento para o controle do risco cardiovascular associado à SM.

Cannabinoid receptors regulate Ca(2+) signals and insulin secretion in pancreatic beta-cell

Insulin is the main hormone involved in the regulation of glycaemia, its impaired secretion is a hallmark of type I and type II diabetic individuals. Additionally, insulin is involved in lipogenesis and weight gain, provoking an anorexigenic action. The endocannabinoid system contributes to the physiological regulation of energy balance, food intake and lipid and glucose metabolisms. Despite that, an experimental link between the endocannabinoid system and the endocrine pancreas has not yet been described. Using quantitative real-time PCR and immunocytochemistry, we have demonstrated the existence of both CB1 and CB2 receptors in the endocrine pancreas. While the CB1 receptor is mainly expressed in non-beta-cells, the CB2 type exists in beta- and non-beta-cells within the islet. The endocannabinoid 2-arachidonylglycerol (2-AG) through CB2 receptors regulates [Ca(2+)](i) signals in beta-cells and as a consequence, it decreases insulin secretion. This effect may be a new component involved in the orexigenic effect of endocannabinoids and constitutes a potential target for pharmacologic manipulation of the energy balance.

Differential regulation of synaptic inputs by constitutively released endocannabinoids and exogenous cannabinoids

Endocannabinoid release from a single neuron has been shown to cause presynaptic inhibition of transmitter release at many different sites. Here, we demonstrate that hypothalamic proopiomelanocortin (POMC) neurons release endocannabinoids continuously under basal conditions, unlike other release sites at which endocannabinoid production must be stimulated. The basal endocannabinoid release selectively inhibited GABA release onto POMC neurons, although exogenous administration of cannabinoid agonists also inhibited glutamate release. The CB1 cannabinoid receptor antagonist AM 251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] blocked endocannabinoid-mediated inhibition of GABA release without affecting excitatory synaptic currents, whereas the CB1 receptor agonist WIN 55,212-2 [R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol [1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl) methanone monomethanesulfonate] inhibited both inhibitory and excitatory synaptic currents in POMC neurons. These data demonstrate that endogenously released cannabinoids and exogenously applied CB1 receptor agonists can have markedly different effects on synaptic inputs. Furthermore, the data suggest a novel form of endocannabinoid-mediated retrograde inhibition, whereby the regulation of a subset of inputs requires either the removal of tonic presynaptic inhibition caused by endocannabinoids or the engagement of a mechanism that actively inhibits endocannabinoid production.

Endocannabinoids activate transient receptor potential vanilloid 1 receptors to reduce hyperdopaminergia-related hyperactivity: therapeutic implications

BACKGROUND

Knockout (KO) mice invalidated for the dopamine transporter (DAT) constitute a powerful animal model of neurobiological alterations associated with hyperdopaminergia relevant to schizophrenia and attention-deficit/hyperactivity disorder (ADHD).

METHODS

Because of continuously increasing evidence for a neuromodulatory role of endocannabinoids in dopamine-related pathophysiological responses, we assessed endocannabinoid signaling in DAT KO mice and evaluated the ability of endocannabinoid ligands to normalize behavioral deficits, namely spontaneous hyperlocomotion in these mice.

RESULTS

In DAT KO mice, we found markedly reduced anandamide levels, specifically in striatum, the dopamine nerve terminal region. Furthermore, three distinct indirect endocannabinoid agonists, the selective anandamide reuptake inhibitors AM404 and VDM11 and the fatty acid amidohydrolase inhibitor AA5HT, attenuated spontaneous hyperlocomotion in DAT KO mice. The hypolocomotor effects of AM404, VDM11, and AA5HT were significantly attenuated by co-administration of the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine but not the selective cannabinoid type 1 (CB1)receptor antagonist AM251. Interestingly, TRPV1 binding was increased in the striatum of DAT KO mice, while CB1 receptor binding was unaffected.

CONCLUSIONS

These data indicate a dysregulated striatal endocannabinoid neurotransmission associated with hyperdopaminergic state. Restoring endocannabinoid homeostasis in active synapses might constitute an alternative therapeutic strategy for disorders associated with hyperdopaminergia. In this process, TRPV1 receptors seem to play a key role and represent a novel promising pharmacological target.

Rimonabant: a cannabinoid receptor blocker for the treatment of metabolic and cardiovascular risk factors

AIMS

The endocannabinoid system modulates synaptic neurotransmission centrally and peripherally and is involved in the brain pathways concerned with addiction, central regulation of body weight and adipose tissue function. The system is overactivated in animal models of obesity and nicotine use. This review discusses the role of rimonabant, a cannabinoid receptor 1 blocker, which has undergone Phase III clinical testing, in the treatment of obesity and tobacco dependence.

DATA SYNTHESIS

Results of Phase III clinical trials have shown that rimonabant has promising efficacy in the treatment of obesity, dyslipidaemia and diabetes associated with obesity, in preventing weight gain following smoking cessation, and possibly in smoking cessation. No critical problems with the tolerance and safety of the compound have appeared in studies to date.

CONCLUSION

Rimonabant may prove to be a useful aid in the treatment of the most widespread cardiometabolic risk factors.

Integration of endocannabinoid and leptin signaling in an appetite-related neural circuit

Recently developed therapeutics for obesity, targeted against cannabinoid receptors, result in decreased appetite and sustained weight loss. Prior studies have demonstrated CB1 receptors (CB1Rs) and leptin modulation of cannabinoid synthesis in hypothalamic neurons. Here, we show that depolarization of perifornical lateral hypothalamus (LH) neurons elicits a CB1R-mediated suppression of inhibition in local circuits thought to be involved in appetite and "natural reward." The depolarization-induced decrease in inhibitory tone to LH neurons is blocked by leptin. Leptin inhibits voltage-gated calcium channels in LH neurons via the activation of janus kinase 2 (JAK2) and of mitogen-activated protein kinase (MAPK). Leptin-deficient mice are characterized by both an increase in steady-state voltage-gated calcium currents in LH neurons and a CB1R-mediated depolarization-induced suppression of inhibition that is 6-fold longer than that in littermate controls. Our data provide direct electrophysiological support for the involvement of endocannabinoids and leptin as modulators of hypothalamic circuits underlying motivational aspects of feeding behavior.

A brief history of cannabinoid and endocannabinoid pharmacology as inspired by the work of British scientists

British scientists have played a leading role in the long history of cannabinoid and endocannabinoid research. Such research has progressed from the first crucial evaluation of the medicinal properties of Cannabis sativa in the Western world to pioneering studies of the chemical constituents of this plant, the development of in vitro biological assays to study cannabinoids, the identification of the mechanism of action of cannabinoids, the discovery of endocannabinoids and the assessment of their therapeutic implications. Stemming from the many innovative ideas and achievements of these researchers, I provide a personal view of where these studies have led us thus far and where they are likely to take us in the future.

The emerging role of the endocannabinoid system in endocrine regulation and energy balance

During the last few years, the endocannabinoid system has emerged as a highly relevant topic in the scientific community. Many different regulatory actions have been attributed to endocannabinoids, and their involvement in several pathophysiological conditions is under intense scrutiny. Cannabinoid receptors, named CB1 receptor and CB2 receptor, first discovered as the molecular targets of the psychotropic component of the plant Cannabis sativa, participate in the physiological modulation of many central and peripheral functions. CB2 receptor is mainly expressed in immune cells, whereas CB1 receptor is the most abundant G protein-coupled receptor expressed in the brain. CB1 receptor is expressed in the hypothalamus and the pituitary gland, and its activation is known to modulate all the endocrine hypothalamic-peripheral endocrine axes. An increasing amount of data highlights the role of the system in the stress response by influencing the hypothalamic-pituitary-adrenal axis and in the control of reproduction by modifying gonadotropin release, fertility, and sexual behavior. The ability of the endocannabinoid system to control appetite, food intake, and energy balance has recently received great attention, particularly in the light of the different modes of action underlying these functions. The endocannabinoid system modulates rewarding properties of food by acting at specific mesolimbic areas in the brain. In the hypothalamus, CB1 receptor and endocannabinoids are integrated components of the networks controlling appetite and food intake. Interestingly, the endocannabinoid system was recently shown to control metabolic functions by acting on peripheral tissues, such as adipocytes, hepatocytes, the gastrointestinal tract, and, possibly, skeletal muscle. The relevance of the system is further strenghtened by the notion that drugs interfering with the activity of the endocannabinoid system are considered as promising candidates for the treatment of various diseases, including obesity.

Plant, Synthetic, and Endogenous Cannabinoids in Medicine

Although used for more than 4000 years for recreational and medicinal purposes, Cannabis and its best-known pharmacologically active constituents, the cannabinoids, became a protagonist in medical research only recently. This revival of interest is explained by the finding in the 1990s of the mechanism of action of the main psychotropic cannabinoid, Delta9-tetrahydrocannabinol (THC), which acts through specific membrane receptors, the cannabinoid receptors. The molecular characterization of these receptors allowed the development of synthetic molecules with cannabinoid and noncannabinoid structure and with higher selectivity, metabolic stability, and efficacy than THC, as well as the development of antagonists that have already found pharmaceutical application. The finding of endogenous agonists at these receptors, the endocannabinoids, opened new therapeutic possibilities through the modulation of the activity of cannabinoid receptors by targeting the biochemical mechanisms controlling endocannabinoid tissue levels.

CANNABINOID RECEPTORS AS THERAPEUTIC TARGETS

CB1 and CB2 cannabinoid receptors are the primary targets of endogenous cannabinoids (endocannabinoids). These G protein-coupled receptors play an important role in many processes, including metabolic regulation, craving, pain, anxiety, bone growth, and immune function. Cannabinoid receptors can be engaged directly by agonists or antagonists, or indirectly by manipulating endocannabinoid metabolism. In the past several years, it has become apparent from preclinical studies that therapies either directly or indirectly influencing cannabinoid receptors might be clinically useful. This review considers the components of the endocannabinoid system and discusses some of the most promising endocannabinoid-based therapies.

Hypothalamic regulatory pathways and potential obesity treatment targets

With an ever-growing population of obese people as well as comorbidities associated with obesity, finding effective weight loss strategies is more imperative than ever. One of the challenges in curbing the obesity crisis is designing successful strategies for long-term weight loss and weight-loss maintenance. Currently, weight-loss strategies include promotion of therapeutic lifestyle changes (diet and exercise), pharmacological therapy, and bariatric surgery. This review focuses on several pharmacological targets that activate central nervous system pathways that normally limit food intake and body weight. Though it is likely that no single therapy will prove effective for everyone, this review considers several recent pre-clinical targets, and several compounds that have been in human clinical trials.

Intestinal levels of anandamide and oleoylethanolamide in food-deprived rats are regulated through their precursors

The anorectic lipid oleoylethanolamide and the orexigenic lipid anandamide both belong to the group of N-acylethanolamines that are generated by the enzyme N-acylphosphatidylethanolamine-hydrolyzing phospholipase D. The levels of the two bioactive lipids were investigated in rat intestines after 24 h of starvation as well as after 1 and 4 h of re-feeding. Total levels of precursor phospholipids and N-acylethanolamines were decreased upon food-deprivation whereas the level of the anandamide precursor molecule was significantly increased. The level of 2-arachidonoyl-glycerol was unchanged as was the activity of N-acyltransferase, N-acylphosphatidylethanolamine-hydrolyzing phospholipase D, and fatty acid amide hydrolase upon starvation and re-feeding. It is concluded that remodeling of the amide-linked fatty acids of N-acylphosphatidylethanolamine is responsible for the opposite effects on levels of anandamide and oleoylethanolamide in intestines of food-deprived rats and not an alternative biochemical route for anandamide synthesis. Furthermore, linoleoylethanolamide, which accounted for more than 50 mol% of the endogenous pool of N-acylethanolamines, was found not to have the same inhibitory effect on food intake, as did oleoylethanolamide following oral administration.

CB1 cannabinoid receptor-mediated modulation of food intake in mice

1 Marijuana's appetite-increasing effects have long been known. Recent research suggests that the CB(1) cannabinoid receptor antagonist SR141716A may suppress appetite. This study represents a further, systematic investigation of the role of CB(1) cannabinoid receptors in the pharmacological effects of cannabinoids on food intake. 2 Mice were food-restricted for 24 h and then allowed access to their regular rodent chow for 1 h. Whereas the CB(1) antagonist SR141716A dose-dependently decreased food consumption at doses that did not affect motor activity, Delta(9)-tetrahydrocannabinol (Delta(9)-THC) increased food consumption at doses that had no effect on motor activity. O-3259 and O-3257, structural analogs of SR141716A, produced effects similar to those of the parent compound. 3 Amphetamine (a known anorectic) and diazepam (a benzodiazepine and CNS depressant) decreased food consumption, but only at doses that also increased or decreased motor activity, respectively. The CB(2) cannabinoid receptor antagonist SR144528 and the nonpsychoactive cannabinoid cannabidiol did not affect food intake nor activity. 4 SR141716A decreased feeding in wild-type mice, but lacked pharmacological activity in CB(1) knockout mice; however, basal food intake was lower in CB(1) knockout mice. Amphetamine decreased feeding in both mouse genotypes. 5 These results suggest that SR141716A may affect the actions of endogenous cannabinoids in regulating appetite or that it may have effects of its own aside from antagonism of cannabinoid effects (e.g., decreased feeding behavior and locomotor stimulation). In either case, these results strongly suggest that CB(1) receptors may play a role in regulation of feeding behavior.

Up-regulation of anandamide levels as an endogenous mechanism and a pharmacological strategy to limit colon inflammation

Direct stimulation of cannabinoid CB1 receptors exerts a protective function in animal models of inflammatory bowel diseases (IBDs). However, it is not known whether endocannabinoids are up-regulated during IBDs in animals or humans, nor whether pharmacological elevation of endocannabinoid levels can be exploited therapeutically in these disorders. In this study we addressed these questions. Colon inflammation was induced in mice and rats with 2,4-dinitrobenzene- and 2,4,6-trinitrobenzene sulfonic acids (DNBS and TNBS), respectively. DNBS-treated mice were treated chronically (for 3 or 7 days) with inhibitors of anandamide enzymatic hydrolysis (N-arachidonoyl-serotonin, AA-5-HT) or reuptake (VDM11), 10 or 5 mg/kg, s.c., or with 5-amino-salicilic acid (5-ASA, 1.4 mg/kg, i.r.). Endocannabinoids (anandamide and 2-arachidonoylglycerol, 2-AG) were quantified in mouse colon, or in rat colon mucosa and submucosa, and in bioptic samples from the colon of patients with untreated ulcerative colitis, by liquid chromatography-mass spectrometry. A strong elevation of anandamide, but not 2-AG, levels was found in the colon of DNBS-treated mice, in the colon submucosa of TNBS-treated rats, and in the biopsies of patients with ulcerative colitis. VDM-11 significantly elevated anandamide levels in the colon of DNBS-treated mice and concomitantly abolished inflammation, whereas AA-5-HT did not affect endocannabinoid levels and was significantly less efficacious at attenuating colitis. 5-ASA also increased anandamide levels and abolished colitis. Thus, anandamide is elevated in the inflamed colon of patients with ulcerative colitis, as well as in animal models of IBDs, to control inflammation, and elevation of its levels with inhibitors of its cellular reuptake might be used in the treatment of IBDs.

Endocannabinoids in the regulation of appetite and body weight

The discovery of cannabinoid receptors, together with the development of selective cannabinoid receptor antagonists, has encouraged a resurgence of cannabinoid pharmacology. With the identification of endogenous agonists, such as anandamide, scientists have sought to uncover the biological role of endocannabinoid systems; initially guided by the long-established actions of cannabis and exogenous cannabinoids such as delta9-tetrahydrocannabinol (THC). In particular, considerable research has examined endocannabinoid involvement in appetite, eating behaviour and body weight regulation. It is now confirmed that endocannabinoids, acting at brain CB1 cannabinoid receptors, stimulate appetite and ingestive behaviours, partly through interactions with more established orexigenic and anorexigenic signals. Key structures such as the nucleus accumbens and hypothalamic nuclei are sensitive sites for the hyperphagic actions of these substances, and endocannabinoid activity in these regions varies in relation to nutritional status and feeding expression. Behavioural studies indicate that endocannabinoids increase eating motivation by enhancing the incentive salience and hedonic evaluation of ingesta. Moreover, there is strong evidence of an endocannabinoid role in energy metabolism and fuel storage. Recent developments point to potential clinical benefits of cannabinoid receptor antagonists in the management of obesity, and of agonists in the treatment of other disorders of eating and body weight regulation.

Peripheral cannabinoid receptor, CB2, regulates bone mass

The endogenous cannabinoids bind to and activate two G protein-coupled receptors, the predominantly central cannabinoid receptor type 1 (CB1) and peripheral cannabinoid receptor type 2 (CB2). Whereas CB1 mediates the cannabinoid psychotropic, analgesic, and orectic effects, CB2 has been implicated recently in the regulation of liver fibrosis and atherosclerosis. Here we show that CB2-deficient mice have a markedly accelerated age-related trabecular bone loss and cortical expansion, although cortical thickness remains unaltered. These changes are reminiscent of human osteoporosis and may result from differential regulation of trabecular and cortical bone remodeling. The CB2(-/-) phenotype is also characterized by increased activity of trabecular osteoblasts (bone-forming cells), increased osteoclast (the bone-resorbing cell) number, and a markedly decreased number of diaphyseal osteoblast precursors. CB2 is expressed in osteoblasts, osteocytes, and osteoclasts. A CB2-specific agonist that does not have any psychotropic effects enhances endocortical osteoblast number and activity and restrains trabecular osteoclastogenesis, apparently by inhibiting proliferation of osteoclast precursors and receptor activator of NF-kappaB ligand expression in bone marrow-derived osteoblasts/stromal cells. The same agonist attenuates ovariectomy-induced bone loss and markedly stimulates cortical thickness through the respective suppression of osteoclast number and stimulation of endocortical bone formation. These results demonstrate that the endocannabinoid system is essential for the maintenance of normal bone mass by osteoblastic and osteoclastic CB2 signaling. Hence, CB2 offers a molecular target for the diagnosis and treatment of osteoporosis, the most prevalent degenerative disease in developed countries.

Delta9-THC induced hyperphagia and tolerance assessment: interactions between the CB1 receptor agonist delta9-THC and the CB1 receptor antagonist SR-141716 (rimonabant) in rats

This study examined effects of the CB1 receptor antagonist/inverse agonist SR-141716 and the CB1 receptor agonist delta9-tetrahydrocannabinol (delta9-THC) on feeding behavior in male Sprague-Dawley rats. Rats were housed individually with free access to regular pelletized laboratory chow [after a 2 weeks handling phase, animals had access to regular chow for 21 h (Study 1) or 22 h (Study 2); high-fat powder food for 3 h in Study 1 and 2 h in Study 2, respectively], and free access to water. Animals were maintained on a reversed 12-h light/dark cycle (dark beginning at noon). Rats were habituated to this type of feeding and light/dark schedule for 3 weeks until a stable baseline for food intake was achieved. In Study 1, animals were examined after administration of delta9-THC alone (dose range 0.1-1.8 mg/kg), SR-141716 alone (dose range 0.03-0.3 mg/kg), and the two drugs combined; injections were given i.p. at the beginning of the second hour after presenting the high-fat diet and drugs were given twice weekly. There was a dose-related increase in high-fat diet intake, peaking at 0.56-1 mg/kg delta9-THC. SR-141716 alone suppressed the high-fat diet intake below control levels. A combination of 0.3 mg/kg SR-141716 and 0.56 mg/kg delta9-THC counteracted the effects on consumption of either drug alone. In Study 2, experimental rats were treated initially with 0.56 mg/kg delta9-THC for six consecutive days; controls received vehicle. Attenuation of the hyperphagia (high-fat diet) was evident after the second injection. Increasing doses of delta9-THC (1 and 1.8 mg/kg, for two and three consecutive days, respectively) did not reinstate the initial hyperphagia. In conclusion, low-to-moderate doses of delta9-THC produced hyperphagia (to a high-fat food source), which was antagonized by SR-141716. SR-141716 singly suppressed intake of the high-fat diet. Delta9-THC-induced hyperphagia dissipated rapidly upon chronic treatment; however, it is unclear whether this reflects pharmacological tolerance or the emergence of a conditioned taste aversion in Study 2.

Suppression of feeding, drinking, and locomotion by a putative cannabinoid receptor ‘silent antagonist’

This study compared the effects of the putative cannabinoid receptor 'silent antagonist' O-2050 with the cannabinoid receptor inverse agonist SR 141716 on food and water consumption, and locomotor activity. Non-deprived male Wistar rats were habituated to the apparatus and testing procedures, then injected intraperitoneally with vehicle, O-2050 (0.03-3.0 mg/kg), or SR 141716 (3.0 mg/kg) prior to 4-h test sessions. Food consumption was significantly reduced by both drugs. Water intake and locomotor activity were significantly reduced only by O-2050. Results support the notion that cannabinoid receptor antagonists suppress feeding behaviour by blocking an endogenous cannabinoid orexigenic signal, rather than by inverse agonism at cannabinoid receptors. However, further studies are needed to confirm the status of O-2050 as a cannabinoid CB(1) receptor antagonist devoid of inverse agonist properties.

Rimonabant

Rimonabant is the first of a new class of selective cannabinoid receptor-1 blockers. It reduces the overactivity of the endocannabinoid system, improving lipid and glucose metabolism and regulating food intake and energy balance. In four randomised, double-blind clinical trials in overweight or obese adults with or without type 2 diabetes and/or dyslipidaemia, oral rimonabant 20mg once daily reduced weight and waist circumference to a significantly greater extent than placebo. A significantly greater proportion of rimonabant than placebo recipients achieved the clinically significant weight-loss target of > or =5% or > or =10% of initial weight. Rimonabant was associated with significant improvements in glycaemic control relative to placebo, with approximately equal to 57% of the reduction in glycosylated haemoglobin being independent of the effects of weight loss in one trial. Improvements in other cardiometabolic risk factors (i.e. increases in high-density lipoprotein-cholesterol [HDL-C] and decreases in triglyceride [TG] levels) were significantly greater with rimonabant than with placebo. The improvement in lipid profile also demonstrated a weight-independent effect, with approximately equal to 47-58% of the improvement in HDL-C and TG being beyond that expected through weight loss alone. Rimonabant was generally well tolerated, with most adverse events considered mild to moderate in severity.

Intracellular signalling pathways activated by leptin

Leptin is a versatile 16 kDa peptide hormone, with a tertiary structure resembling that of members of the long-chain helical cytokine family. It is mainly produced by adipocytes in proportion to fat size stores, and was originally thought to act only as a satiety factor. However, the ubiquitous distribution of OB-R leptin receptors in almost all tissues underlies the pleiotropism of leptin. OB-Rs belong to the class I cytokine receptor family, which is known to act through JAKs (Janus kinases) and STATs (signal transducers and activators of transcription). The OB-R gene is alternatively spliced to produce at least five isoforms. The full-length isoform, OB-Rb, contains intracellular motifs required for activation of the JAK/STAT signal transduction pathway, and is considered to be the functional receptor. Considerable evidence for systemic effects of leptin on body mass control, reproduction, angiogenesis, immunity, wound healing, bone remodelling and cardiovascular function, as well as on specific metabolic pathways, indicates that leptin operates both directly and indirectly to orchestrate complex pathophysiological processes. Consistent with leptin's pleiotropic role, its participation in and crosstalk with some of the main signalling pathways, including those involving insulin receptor substrates, phosphoinositide 3-kinase, protein kinase B, protein kinase C, extracellular-signal-regulated kinase, mitogen-activated protein kinases, phosphodiesterase, phospholipase C and nitric oxide, has been observed. The impact of leptin on several equally relevant signalling pathways extends also to Rho family GTPases in relation to the actin cytoskeleton, production of reactive oxygen species, stimulation of prostaglandins, binding to diacylglycerol kinase and catecholamine secretion, among others.

Estrogen differentially modulates the cannabinoid- induced presynaptic inhibition of amino acid neurotransmission in proopiomelanocortin neurons of the arcuate nucleus

The present study sought to determine whether cannabinoids inhibit glutamatergic and GABAergic synaptic input onto neurons of the hypothalamic arcuate nucleus (ARC), and whether estrogen modulates this process. Whole-cell patch clamp recordings were performed in hypothalamic slices prepared from ovariectomized female guinea pigs. CB1 receptor activation reduced the amplitude of excitatory postsynaptic currents (EPSCs) evoked by electrical stimulation that were sensitive to ionotropic glutamate receptor antagonists. The CB1 receptor antagonist AM251 increased evoked EPSC (eEPSC) amplitude, and reversed the agonist-induced decrease. CB1 receptor activation similarly decreased the amplitude of evoked inhibitory postsynaptic currents (eIPSCs). The cannabinoid-induced reduction in eEPSC and eIPSC amplitude correlated with a decrease in the frequency of miniature EPSCs (mEPSCs) and IPSCs (mIPSCs) that were abolished by ionotropic glutamate and GABA(A) receptor antagonists, respectively. AM251 increased mEPSC frequency, and antagonized the agonist-induced decrease. Compared to neurons obtained from vehicle-treated controls, estradiol benzoate (25 mug; s.c.) given 24 h prior to experimentation increased mEPSC frequency, and markedly decreased the potency of CB1 receptor agonists to decrease mEPSC frequency. Conversely, the steroid potentiated the cannabinoid-induced decrease in mIPSC frequency. These effects were observed in neurons subsequently identified as proopiomelanocortin (POMC) neurons. These data reveal that ARC neurons, including POMC neurons, receive glutamatergic and GABAergic synaptic inputs that are presynaptically inhibited by cannabinoids, and differentially modulated by estrogen. These opposing effects of estrogen on the cannabinoid regulation of amino acid neurotransmission excite POMC neurons, and lend additional insight into the mechanisms underlying estrogen-induced anorexia and negative feedback of the reproductive axis.

The relationship of in vivo central CB1 receptor occupancy to changes in cortical monoamine release and feeding elicited by CB1 receptor antagonists in rats

RATIONALE

Cannabinoid type 1 (CB(1)) receptor antagonists are reportedly effective in reducing food intake both preclinically and clinically. This may be due in part to their effects on monoamine release in the brain. The level of central CB(1) receptor occupancy underlying these neurobiological effects is unclear.

OBJECTIVES

We explored the relationship between in vivo CB(1) receptor occupancy in the frontal cortex and changes in both monoamine release in the medial prefrontal cortex (mPFC) and feeding behavior in rats in response to two orally administered CB(1) receptor antagonists presently in clinical trials, SR141716A (rimonabant) and SLV319.

METHODS

CB(1) receptor occupancy was measured using [(3)H] SR141716A, and these occupancies were related to potencies to mediate increases in dopamine (DA) and norepinephrine (NE) release measured with microdialysis and decreases in consumption of a highly palatable diet (HP).

RESULTS

High receptor occupancy levels (>65%) were required to detect increases in monoamine release that were achieved with 3 and 10 mg/kg of SR141716A and 10 mg/kg of SLV319 for DA and 10 mg/kg of SR141716A for NE. Decreases in HP consumption were seen at occupancies higher than 65% for SR141716A that were achieved with 3 and 10 mg/kg. In contrast, decreases in HP consumption were seen at relatively low CB(1) receptor occupancies (11%) for SLV319.

CONCLUSIONS

The occupancy method described here is an effective tool for interrelating central CB(1) receptor occupancy with neurobiological actions of CB(1) receptor antagonists and for furthering our understanding of the role of CB(1) receptors in central nervous system physiology and pathology.

Analysis of the endocannabinoid system by using CB1 cannabinoid receptor knockout mice

The endocannabinoid system has been involved in the control of several neurophysiological and behavioural responses. To date, three lines of CB1 knockout mice have been established independently in different laboratories. This chapter reviews the main results obtained with these lines of CB1 knockout mice in several physiological responses that have been previously related to the activity of the endocannabinoid system. Studies using CB1 knockout mice have demonstrated that this receptor participates in the control of several behavioural responses including locomotion, anxiety- and depressive-like states, cognitive functions such as memory and learning processes, cardiovascular responses and feeding. Furthermore, the CB1 cannabinoid receptor is involved in the control of pain by acting at peripheral, spinal and supraspinal levels. The involvement of the CB1 cannabinoid receptor in the behavioural and biochemical processes underlying drug addiction has also been investigated. These CB1 knockouts have provided new findings to clarify the interactions between cannabinoids and the other drugs of abuse such as opioids, psychostimulants, nicotine and ethanol. Recent studies have demonstrated that endocannabinoids can function as retrograde messengers, modulating the release of different neurotransmitters, including opioids, gamma-aminobutyric acid (GABA), and cholecystokinin (CCK), which could explain some of the responses observed after the stimulation of the CB1 cannabinoid receptor. This review provides an update of the apparently controversial data reported in the literature using the three different lines of CB1 knockout mice, which seem to be mainly due to the use of different experimental procedures rather than any constitutive alteration in these lines of knockouts.

Effects of cannabinoids on hypothalamic and reproductive function

Marijuana and cannabinoids have been shown to exert profound effects on hypothalamic regulatory functions and reproduction in both experimental animals and humans. Here we review the role of (endo)cannabinoids in the regulation of appetite and food intake. There is converging evidence that the hypothalamic endocannabinoid system changes after leptin treatment. Cannabinoid administration decreases heat production by altering hypothalamic neurotransmitter production. Experimental and human data have also shown that the endocannabinoid system is involved in the regulation of reproductive function at both central and peripheral levels. We discuss also the role of fatty acid amide hydrolase (FAAH) in gestation, and in particular the regulation of the activity of FAAH by progesterone and leptin. We show that endocannabinoids inhibit the release of leukaemia inhibitory factor (LIF) from peripheral T lymphocytes. Taken together, endocannabinoids not only help to maintain neuroendocrine homeostasis, but also take part in immunological changes occurring during early pregnancy.

Cannabinoids, opioids and eating behavior: the molecular face of hedonism?

Obesity represents nowadays one of the most devastating health threats. Published reports even project a decline in life expectancy of US citizens due to the rapidly increasing prevalence of obesity. This alarming increase is intimately linked with recent changes of environment and lifestyle in western countries. In this context, the rewarding or even addictive properties of popular food may represent one of the most serious obstacles to overcome for an effective anti-obesity therapy. Therefore, in addition to molecular networks controlling energy homeostasis, now researchers are starting to define central nervous mechanisms governing hedonic and addictive components of food intake. A recently emerging body of data suggests that the endogenous cannabinoid and opioid systems both represent key circuits responding to the rewarding value of food. This review focuses on the role of these two systems for the homeostatic and hedonic aspects of eating behavior and includes their anatomical and functional interactions. Independent from the degree to which eating can be considered an addiction, cannabinoid and opioid receptor antagonists are promising anti-obesity drugs, since they are targeting both hedonic and homeostatic components of energy balance control.

Fatty acid amide hydrolase (-/-) mice exhibit an increased sensitivity to the disruptive effects of anandamide or oleamide in a working memory water maze task

Although recent evidence suggests that fatty acid amide hydrolase (FAAH) may represent a potential therapeutic target, few published studies have investigated FAAH or its fatty acid amide substrates (FAAs) in animal models of learning and memory. Therefore, our primary goal was to determine whether FAAH (-/-) mice, which possess elevated levels of anandamide and other FAAs, would display altered performance in four Morris water maze tasks: acquisition of a hidden fixed platform, reversal learning, working memory, and probe trials. FAAH (-/-) mice failed to exhibit deficits in any task; in fact, they initially acquired the working memory task more rapidly than FAAH (+/+) mice. The second goal of this study was to investigate whether the FAAH inhibitor OL-135 (1-oxo-1[5-(2-pyridyl)-2-yl]-7-phenylheptane), anandamide, other FAAs, and methanandamide would affect working memory in both genotypes. FAAH (-/-), but not (+/+), mice displayed working memory impairments following exogenous administration of anandamide (ED(50) = 6 mg/kg) or oleamide (50 mg/kg). However, the central cannabinoid receptor (CB(1)) receptor antagonist SR141716 [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl] only blocked the disruptive effects of anandamide. Methanandamide, which is not metabolized by FAAH, disrupted working memory performance in both genotypes (ED(50) = 10 mg/kg), suggesting that CB(1) receptor signaling is unaltered by FAAH deletion. In contrast, OL-135 and other FAAs failed to affect working memory in either genotype. These results suggest that FAAH deletion does not impair spatial learning but may enhance acquisition under certain conditions. More generally, FAAH may represent a novel therapeutic target that circumvents the undesirable cognitive side effects commonly associated with direct-acting cannabinoid agonists.

Paraventricular hypothalamic CB1 cannabinoid receptors are involved in the feeding stimulatory effects of Δ9-tetrahydrocannabinol

BACKGROUND/AIMS

The paraventricular nucleus of the hypothalamus (PVN) is the target of converging orexigenic and anorexigenic pathways originating from various hypothalamic sites and is, therefore, considered to be the chief site mediating hypothalamic regulation of energy homeostasis. Although a large body of evidence suggests that central CB(1) cannabinoid receptors mediate food intake, it is not clear whether PVN CB(1) receptors are involved in the control of feeding behaviour. The present study therefore examined the effects of intra-PVN administration of Delta(9)-tetrahydrocannabinol (THC) and the cannabinoid receptor antagonist SR 141716 on feeding.

METHODS

After being habituated to the test environment and injection procedure, sated rats were injected with SR 141716 (0.03-3.0 microg, Experiment 1) alone or in combination with THC (5.0 microg, Experiment 2) into the PVN. Food intake and locomotor activity then were recorded for 120 min.

RESULTS

Intra-PVN administration of THC produced a significant increase in food intake that was attenuated by SR 141716. Administration of SR 141716 alone did not affect feeding. Locomotor activity was not significantly affected by any drug treatments, suggesting that effects on feeding were not due to a non-specific reduction in motivated behaviour. These findings suggest an important role for PVN cannabinoid signalling in mediating THC-induced feeding behaviour. These results also demonstrate that the blockade of PVN CB(1) receptors alone is insufficient to reduce baseline feeding behaviour under these conditions.

Effects of rimonabant on metabolic risk factors in overweight patients with dyslipidemia

BACKGROUND

Rimonabant, a selective cannabinoid-1 receptor (CB1) blocker, has been shown to reduce body weight and improve cardiovascular risk factors in obese patients. The Rimonabant in Obesity-Lipids (RIO-Lipids) study examined the effects of rimonabant on metabolic risk factors, including adiponectin levels, in high-risk patients who are overweight or obese and have dyslipidemia.

METHODS

We randomly assigned 1036 overweight or obese patients (body-mass index [the weight in kilograms divided by the square of the height in meters], 27 to 40) with untreated dyslipidemia (triglyceride levels >1.69 to 7.90 mmol per liter, or a ratio of cholesterol to high-density lipoprotein [HDL] cholesterol of >4.5 among women and >5 among men) to double-blinded therapy with either placebo or rimonabant at a dose of 5 mg or 20 mg daily for 12 months in addition to a hypocaloric diet.

RESULTS

The rates of completion of the study were 62.6 percent, 60.3 percent, and 63.9 percent in the placebo group, the group receiving 5 mg of rimonabant, and the group receiving 20 mg of rimonabant, respectively. The most frequent adverse events resulting in discontinuation of the drug were depression, anxiety, and nausea. As compared with placebo, rimonabant at a dose of 20 mg was associated with a significant (P<0.001) mean weight loss (repeated-measures method, -6.7+/-0.5 kg, and last-observation-carried-forward analyses, -5.4+/-0.4 kg), reduction in waist circumference (repeated-measures method, -5.8+/-0.5 cm, and last-observation-carried-forward analyses, -4.7+/-0.5 cm), increase in HDL cholesterol (repeated-measures method, +10.0+/-1.6 percent, and last-observation-carried-forward analyses, +8.1+/-1.5 percent), and reduction in triglycerides (repeated-measures method, -13.0+/-3.5 percent, and last-observation-carried-forward analyses, -12.4+/-3.2 percent). Rimonabant at a dose of 20 mg also resulted in an increase in plasma adiponectin levels (repeated-measures method, 57.7 percent, and last-observation-carried-forward analyses, 46.2 percent; P<0.001), for a change that was partly independent of weight loss alone.

CONCLUSIONS

Selective CB1-receptor blockade with rimonabant significantly reduces body weight and waist circumference and improves the profile of several metabolic risk factors in high-risk patients who are overweight or obese and have an atherogenic dyslipidemia.

The cannabinoid CB1 receptor antagonist rimonabant (SR141716) inhibits cell proliferation and increases markers of adipocyte maturation in cultured mouse 3T3 F442A preadipocytes

Adipocyte cell proliferation is an important process in body fat mass development in obesity. Adiponectin or Acrp30 is an adipocytokine exclusively expressed and secreted by adipose tissue that regulates lipid and glucose metabolism and plays a key role in body weight regulation and homeostasis. Adiponectin mRNA expression in adipose tissue and plasma level of adiponectin are decreased in obesity and type 2 diabetes. In obese rodents, the selective CB(1) receptor antagonist rimonabant reduces food intake and body weight and improves lipid and glucose parameters. We have reported previously that rimonabant stimulated adiponectin mRNA expression in adipose tissue of obese fa/fa rats, by a direct effect on adipocytes. We report here that rimonabant (10-400 nM) inhibits cell proliferation of cultured mouse 3T3 F442A preadipocytes in a concentration-dependent manner. In parallel to this inhibitory effect on preadipocyte cell proliferation, rimonabant (25-100 nM) stimulates mRNA expression and protein levels of two late markers of adipocyte differentiation (adiponectin and glyceraldehyde-3-phosphate dehydrogenase) with a maximal effect at 100 nM, without inducing the accumulation of lipid droplets. Furthermore, treatment of mouse 3T3 F442A preadipocytes with rimonabant (100 nM) inhibits basal and serum-induced p42/44 mitogen-activated protein (MAP) kinase activity. These results suggest that inhibition of MAP kinase activity by rimonabant may be one of mechanisms involved in the inhibition of 3T3 F442A preadipocyte cell proliferation and stimulation of adiponectin and GAPDH expression. The inhibition of preadipocyte cell proliferation and the induction of adipocyte late "maturation" may participate in rimonabant-induced antiobesity effects, particularly the reduction of body fat mass.

Motivational effects of cannabinoids and opioids on food reinforcement depend on simultaneous activation of cannabinoid and opioid systems

Strong functional interactions exist between endogenous cannabinoid and opioid systems. Here, we investigated whether cannabinoid-opioid interactions modulate motivational effects of food reinforcement. In rats responding for food under a progressive-ratio schedule, the maximal effort (break point) expended to obtain 45 mg pellets depended on the level of food deprivation, with free-feeding reducing break points and food-deprivation increasing break points. Delta-9-tetrahydrocannabinol (THC; 0.3-5.6 mg/kg intrapeitoneally (i.p.)) and morphine (1-10 mg/kg i.p.) dose-dependently increased break points for food reinforcement, while the cannabinoid CB1 receptor antagonist rimonabant (SR-141716A; 0.3-3 mg/kg i.p.) and the preferential mu-opioid receptor antagonist naloxone (0.3-3 mg/kg i.p.) dose-dependently decreased break points. THC and morphine only increased break points when food was delivered during testing, suggesting that these treatments directly influenced reinforcing effects of food, rather than increasing behavior in a nonspecific manner. Effects of THC were blocked by rimonabant and effects of morphine were blocked by naloxone, demonstrating that THC's effects depended on cannabinoid CB1 receptor activation and morphine's effects depended on opioid-receptor activation. Furthermore, THC's effects were blocked by naloxone and morphine's effects were blocked by rimonabant, demonstrating that mu-opioid receptors were involved in the effects of THC and cannabinoid CB1 receptors were involved in the effects of morphine on food-reinforced behavior. Thus, activation of both endogenous cannabinoid and opioid systems appears to jointly facilitate motivational effects of food measured under progressive-ratio schedules of reinforcement and this facilitatory modulation appears to critically depend on interactions between these two systems. These findings support the proposed therapeutic utility of cannabinoid agonists and antagonists in eating disorders.

The therapeutic potential of drugs that target cannabinoid receptors or modulate the tissue levels or actions of endocannabinoids

There are at least 2 types of cannabinoid receptor, CB(1) and CB(2), both G protein coupled. CB(1) receptors are expressed predominantly at nerve terminals and mediate inhibition of transmitter release, whereas CB(2) receptors are found mainly on immune cells, their roles including the modulation of cytokine release and of immune cell migration. Endogenous agonists for cannabinoid receptors also exist. These "endocannabinoids" are synthesized on demand and removed from their sites of action by cellular uptake and intracellular enzymic hydrolysis. Endocannabinoids and their receptors together constitute the endocannabinoid system. This review summarizes evidence that there are certain central and peripheral disorders in which increases take place in the release of endocannabinoids onto their receptors and/or in the density or coupling efficiency of these receptors and that this upregulation is protective in some disorders but can have undesirable consequences in others. It also considers therapeutic strategies by which this upregulation might be modulated to clinical advantage. These strategies include the administration of (1) a CB(1) and/or CB(2) receptor agonist or antagonist that does or does not readily cross the blood brain barrier; (2) a CB(1) and/or CB(2) receptor agonist intrathecally or directly to some other site outside the brain; (3) a partial CB(1) and/or CB(2) receptor agonist rather than a full agonist; (4) a CB(1) and/or CB(2) receptor agonist together with a noncannabinoid, for example, morphine or codeine; (5) an inhibitor or activator of endocannabinoid biosynthesis, cellular uptake, or metabolism; (6) an allosteric modulator of the CB(1) receptor; and (7) a CB(2) receptor inverse agonist.

Hormonal regulation of food intake

Our knowledge of the physiological systems controlling energy homeostasis has increased dramatically over the last decade. The roles of peripheral signals from adipose tissue, pancreas, and the gastrointestinal tract reflecting short- and long-term nutritional status are now being described. Such signals influence central circuits in the hypothalamus, brain stem, and limbic system to modulate neuropeptide release and hence food intake and energy expenditure. This review discusses the peripheral hormones and central neuronal pathways that contribute to control of appetite.

Early age-related cognitive impairment in mice lacking cannabinoid CB1 receptors

The molecular mechanisms contributing to the normal age-related decline of cognitive functions or to pathological learning and memory impairment are largely unknown. We demonstrate here that young mice (6-7 weeks) with a genetic deletion of the cannabinoid CB1 receptor performed as well as WT mice, or often better, in a number of learning and memory paradigms, including animal models of skill-learning, partner recognition, and operant conditioning. In contrast, the performance of mature mice (3-5 months) lacking CB1 receptors was much worse than that of age-matched WT animals. In most tests, these mice performed at the same level as old animals (14-17 months), suggesting that the decline in cognitive functions is accelerated in the absence of CB1 receptors. This rapid decline in CB1-deficient animals is accompanied by a loss of neurons in the CA1 and CA3 regions of the hippocampus.

Endocannabinoids and their implications for epilepsy

This review covers the main features of a newly discovered intercellular signaling system in which endogenous ligands of the brain's cannabinoid receptors, or endocannabinoids, serve as retrograde messengers that enable a cell to control the strength of its own synaptic inputs. Endocannabinoids are released by bursts of action potentials, including events resembling interictal spikes, and probably by seizures as well. Activation of cannabinoid receptors has been implicated in neuroprotection against excitotoxicity and can help explain the anticonvulsant properties of cannabinoids that have been known since antiquity.