Endocannabinoid levels in rat limbic forebrain and hypothalamus in relation to fasting, feeding and satiation: stimulation of eating by 2-arachidonoyl glycerol

The endocannabinoid system and its therapeutic exploitation

The term 'endocannabinoid' - originally coined in the mid-1990s after the discovery of membrane receptors for the psychoactive principle in Cannabis, Delta9-tetrahydrocannabinol and their endogenous ligands - now indicates a whole signalling system that comprises cannabinoid receptors, endogenous ligands and enzymes for ligand biosynthesis and inactivation. This system seems to be involved in an ever-increasing number of pathological conditions. With novel products already being aimed at the pharmaceutical market little more than a decade since the discovery of cannabinoid receptors, the endocannabinoid system seems to hold even more promise for the future development of therapeutic drugs. We explore the conditions under which the potential of targeting the endocannabinoid system might be realized in the years to come.

Overlapping and Interactive Pathways Regulating Appetite and Craving

Multidisciplinary research in recent years has delineated the hypothalamic hardcore wiring that encodes appetitive drive. The appetite regulating network (ARN) consisting of distinct orexigenic and anorexigenic circuitries operates in the arcuate nucleus-paraventricular nucleus axis of the hypothalamus to propagate and relay the appetitive drive, and is subject to modulation by excitatory and inhibitory messages from the lateral hypothalamus and ventromedial nucleus, respectively. Reciprocal afferent humoral signals, comprised of anorexigenic leptin from white adipose tissue and orexigenic ghrelin from stomach, to the ARN integrate the moment-to-moment regulation of energy homeostasis. Various loci in the ARN and afferent hormonal feedback circuitry in the rodent brain are important for food craving elicited by drugs of abuse. This convergence of neurochemical and hormonal signaling has now paved the way to address the fundamental question of whether cellular and molecular events that underlie the appetitive drive in response to diminished energy stores in the body are akin to drug craving during withdrawal in humans.

CB1 cannabinoid receptor knockout in mice leads to leanness, resistance to diet-induced obesity and enhanced leptin sensitivity

OBJECTIVE

There is growing evidence for an implication of the CB1 receptor subtype of the endocannabinoid system in the regulation of eating and fat deposition. To further define the physiological role of these receptors in the control of energy balance, we characterized the phenotype of CB1 receptor knockout (CB1(-/-)) mice maintained on an obesity-prone regimen or on a standard chow.

DESIGN

CB1(-/-) male mice were compared to wild-type animals (CB1(+/+) male mice) in two feeding paradigms: (1) with a standard laboratory regimen (3.5 kcal/g, 14.5% of energy as fat) and (2) on a free-choice paradigm consisting of offering both the standard laboratory chow and a high-fat diet (HFD) (4.9 kcal/g, 49% of energy as fat).

RESULTS

When maintained on the standard diet, CB1(-/-) mice are lean. At the age of 20 weeks, their body weight and adiposity are, respectively, 24 and 60% lower than that of CB1(+/+) mice. They are slightly hypophagic, but when expressed as percent of body weight, their relative energy intake is similar to that of the wild-type animals. Furthermore, inactivation of CB1 receptors reduces plasma insulin and leptin levels, and enhances the response to intracerebroventricular leptin injection. The free-choice paradigm shows that the preference for a high-fat highly palatable chow is slightly delayed in onset but maintained in CB1(-/-) mice. However, loading CB1(-/-) mice with this obesity-prone diet does not result in development of obesity. Knockout mice do not display hyperphagia or reduction of their relative energy intake in contrast to CB1(+/+) mice, and their feeding efficiency remains low. These data suggest an improved energetic metabolism with the high-fat regimen. Furthermore, the insulin resistance normally occurring in HFD-fed mice is not present in CB1(-/-) mice.

CONCLUSION

These results provide evidence that the stimulation of CB1 receptors is a key component in the development of diet-induced obesity, and that these receptors and their endogenous ligands are implicated not only in feeding control but also in peripheral metabolic regulations. The lack of effect of SR141716, a selective CB1 receptor antagonist, in CB1(-/-) mice further supports this hypothesis, as this compound was previously shown to display potent anti-obesity properties in diet-induced obese C57BL/6 mice.

Voluntary exercise augments acute effects of CB1-receptor inverse agonist on body weight loss in obese and lean mice

Cannabinoid CB1 receptor (CB1R) inverse agonists reduce appetite and body weight (BW) gain in various species. Exercise is thought to be a natural reward process and the cannabinoid system is also believed to influence reward. We tested the hypothesis that voluntary exercise would augment the effects of AM251, a CB1R inverse agonist, on food intake (FI) and BW loss in murine genetic models of obesity. ob/ob, agouti yellow (A(y)), and lean C57BL/6J mice were treated via oral gavage with vehicle or AM251 (1, 3, or 10 mg/kg) 1 h before the dark cycle. The suppressive effects of 3 and 10 mg/kg AM251 on overnight FI, BW gain, and water intake (WI) were significant in ob/ob mice. In contrast, in A(y) mice, 10 mg/kg AM251 decreased FI and BW gain while it did not influence WI. Food consumption of ob/ob and A(y) mice, as evidenced by feeding frequency (FF) and feeding duration (FD), was reduced by AM251 for 4-6 h. AM251 at these doses had no impact on the appetitive behavior or BW gain of lean mice. After a 1-week wash-out period, mice were given running wheels in their home cages. With running wheel exercise, lean and obese mice exhibited increased sensitivity to AM251. Low voluntary wheel running activity of ob/ob mice precluded detection of combined effects of AM251 and exercise in this genetic model of obesity. Lean and agouti mice given AM251 combined with exercise lost a greater amount of BW than with AM251 alone. Our data suggest that voluntary exercise can enhance CB1R inverse agonist effects on appetite and BW loss in both lean and agouti obese mice.

Endocannabinoid Receptor Antagonists

Obesity has been described as a global epidemic. Its increasing prevalence is matched by growing costs, not only to the health of the individual, but also to the medical services required to treat a range of obesity-related diseases. In most instances, obesity is a product of progressively less energetic lifestyles and the over-consumption of readily available, palatable, and highly caloric foods. Past decades have seen massive investment in the search for effective anti-obesity therapies, so far with limited success. An important part of the process of developing new pharmacologic treatments for obesity lies in improving our understanding of the psychologic and physiologic processes that govern appetite and bodyweight regulation. Recent discoveries concerning the endogenous cannabinoids are beginning to give greater insight into these processes. Current research indicates that endocannabinoids may be key to the appetitive and consummatory aspects of eating motivation, possibly mediating the craving for and enjoyment of the most desired, most fattening foods. Additionally, endocannabinoids appear to modulate central and peripheral processes associated with fat and glucose metabolism. Selective cannabinoid receptor antagonists have been shown to suppress the motivation to eat, and preferentially reduce the consumption of palatable, energy-dense foods. Additionally, these agents act to reduce adiposity through metabolic mechanisms that are independent of changes in food intake. Given the current state of evidence, we conclude that the endocannabinoids represent an exciting target for new anti-obesity therapies.

Antidepressant-like and anorectic effects of the cannabinoid CB1 receptor inverse agonist AM251 in mice

Psychopathological disorders, and depression in particular, are strongly linked to eating attitude in obese patients. The identification of cannabinoid CB1 receptors (CB1Rs) in areas of the central nervous system (CNS) that have been implicated in regulation of mood and food intake suggests that these receptors may mediate such a behavioral link. The goal of this study was to evaluate CB1R modulation of antidepressant-like effects and food intake. For this purpose, 129/SVE and C57BL/6 male mice were acutely dosed intraperitoneally (i.p.) with the CB1R inverse agonist AM251 (3-30 mg/kg) and tested, respectively, in the tail-suspension test (TST) and in the forced-swim test (FST), which have been used widely as tests sensitive to antidepressant compounds. Like the antidepressant desipramine (DMI, 16 mg/kg), AM251 significantly reduced immobility at 10 mg/kg in the TST and at 1 and 10 mg/kg in the FST. Such a decrease of immobility was not accompanied by an increase in motor activity in the open field, suggesting that occupancy of CB1R by AM251 induced antidepressant-like effects. This was supported by two additional experiments. First, the co-administration of the CB1R agonist CP55940, at a dose that did not induce motor impairment or profound hypothermia (0.01 mg/kg), reversed effects of AM251 in the TST. Secondly, effects of AM251 in the FST were absent in CB1R knockout (KO) mice. In addition to an antidepressant-like effect, AM251 reduced fasting-induced hyperphagia over a comparable dose range. Taken together, these data suggest that regulation of mood and food intake might be obtained through inverse agonism of CB1R.

The endocannabinoid system in the basal ganglia and in the mesolimbic reward system: implications for neurological and psychiatric disorders

To date, N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol are the best studied endocannabinoids and are thought to act as retrograde messengers in the central nervous system (CNS). By activating presynaptic cannabinoid CB1 receptors, they can reduce glutamate release in dorsal and ventral striatum (nucleus accumbens) and alter synaptic plasticity, thereby modulating neurotransmission in the basal ganglia and in the mesolimbic reward system. In this review, we will focus on the role of the endocannabinoid system within these neuronal pathways and describe its effect on dopaminergic transmission and vice versa. The endocannabinoid system is unlikely to directly affect dopamine release, but can modify dopamine transmission trough trans-synaptic mechanisms, involving gamma-aminobutyric acid (GABA)-ergic and glutamatergic synapses, as well as by converging signal transduction cascades of the cannabinoid and dopamine receptors. The dopamine and endocannabinoid systems exert a mutual control on each other. Cannabinergic signalling may lead to release of dopamine, which can act via dopamine D1-like receptors as a negative feedback mechanism to counteract the effects of activation of the cannabinoid CB1 receptor. On the other hand, dopaminergic signalling via dopamine D2-like receptors may lead to up-regulation of cannabinergic signalling, which is likely to represent a negative feedback on dopaminergic signalling. The consequences of these interactions become evident in pathological conditions in which one of the two systems is likely to be malfunctioning. We will discuss neurological and psychiatric disorders such as Parkinson's and Huntington's disease, drug addiction and schizophrenia. Furthermore, the possible role of the endocannabinoid system in disorders not necessarily depending on the dopaminergic system, such as eating disorders and anxiety, will be described.

The cannabinoid system: a role in both the homeostatic and hedonic control of eating?

Knowledge of the cannabinoid system and its components has expanded greatly over the past decade. There is increasing evidence for its role in the regulation of food intake and appetite. Cannabinoid system activity in the hypothalamus is thought to contribute to the homeostatic regulation of energy balance, under the control of the hormone leptin. A second component of cannabinoid-mediated food intake appears to involve reward pathways and the hedonic aspect of eating. With the cannabinoid system contributing to both regulatory pathways, it presents an attractive therapeutic target for the treatment of both obesity and eating disorders.

Short-term fasting and prolonged semistarvation have opposite effects on 2-AG levels in mouse brain

2-Arachidonoyl glycerol (2-AG) levels in whole mouse brain and two of its regions-hippocampus and hypothalamus-were determined after diet restriction (between 60 and 40%) lasting 12 days. The diet restriction lowered the level of 2-AG, which in the hypothalamus depended on the severity of the diet restriction, while the level in the hippocampus was not dependent on the diet regimen. As these observations differ from previously published data showing elevation of 2-AG levels in rat brain after 24 h of severe food restriction, we measured 2-AG levels in whole mouse brain after a comparable period of full starvation (fasting). We confirmed the elevation of 2-AG levels. It seems possible that these time-dependent variations of 2-AG levels may be of importance as a general coping strategy by animals during periods of starvation.

Nongenomic glucocorticoid inhibition via endocannabinoid release in the hypothalamus: a fast feedback mechanism

Glucocorticoid negative feedback in the brain controls stress, feeding, and neural-immune interactions by regulating the hypothalamic-pituitary-adrenal axis, but the mechanisms of inhibition of hypothalamic neurosecretory cells have never been elucidated. Using whole-cell patch-clamp recordings in an acute hypothalamic slice preparation, we demonstrate a rapid suppression of excitatory glutamatergic synaptic inputs to parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVN) by the glucocorticoids dexamethasone and corticosterone. The effect was maintained with dexamethasone conjugated to bovine serum albumin and was not seen with direct intracellular glucocorticoid perfusion via the patch pipette, suggesting actions at a membrane receptor. The presynaptic inhibition of glutamate release by glucocorticoids was blocked by postsynaptic inhibition of G-protein activity with intracellular GDP-beta-S application, implicating a postsynaptic G-protein-coupled receptor and the release of a retrograde messenger. The glucocorticoid effect was not blocked by the nitric oxide synthesis antagonist N(G)-nitro-L-arginine methyl ester hydrochloride or by hemoglobin but was blocked completely by the CB1 cannabinoid receptor antagonists AM251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] and AM281 [1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide] and mimicked and occluded by the cannabinoid receptor agonist WIN55,212-2 [(beta)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate], indicating that it was mediated by retrograde endocannabinoid release. Several peptidergic subtypes of parvocellular neuron, identified by single-cell reverse transcripton-PCR analysis, were subject to rapid inhibitory glucocorticoid regulation, including corticotropin-releasing hormone-, thyrotropin-releasing hormone-, vasopressin-, and oxytocin-expressing neurons. Therefore, our findings reveal a mechanism of rapid glucocorticoid feedback inhibition of hypothalamic hormone secretion via endocannabinoid release in the PVN and provide a link between the actions of glucocorticoids and cannabinoids in the hypothalamus that regulate stress and energy homeostasis.

n-3 Polyunsaturated fatty acid (PUFA) deficiency elevates and n-3 PUFA enrichment reduces brain 2-arachidonoylglycerol level in mice

2-arachidonoylglycerol (2-AG) is a putative endogenous ligand for cannabinoid receptors and was suggested to play an important role in both physiological and pathological events in the central nervous system (CNS) as well as in peripheral organs. The sequential hydrolysis of arachidonic acid (20:4n-6, AA)-containing phospholipids has been proposed as a major biosynthetic route of 2-AG. On the other hand, the manipulation of the dietary n-3 polyunsaturated fatty acid (PUFA) status changes the AA level in tissue phospholipids. We, therefore, conducted two separate experiments to confirm whether the dietary n-3 PUFA status influences the 2-AG level in the mouse brain. In the first experiment, we fed mice with n-3 PUFA-deficient diet, which resulted in a marked decrease in the docosahexaenoic acid (22:6n-3, DHA) levels without a change in the AA level in brain phospholipids as compared with the mice fed with an n-3 PUFA-sufficient diet. The brain 2-AG level in the n-3 PUFA-deficient group was significantly higher than in the n-3 PUFA sufficient group. In the second experiment, we found that short-term supplementation of DHA-rich fish oil reduced brain 2-AG level as compared with the supplementation with low n-3 PUFA. The decrease in the AA level and the increase in the DHA level in the major phospholipids occurred in the brains of the mice fed the fish oil diet compared with those fed the low n-3 PUFA diet. Our results indicate that the n-3 PUFA deficiency elevates and n-3 PUFA enrichment reduces the brain 2-AG level in mice, suggesting that physiological and pathological events mediated by 2-AG through cannabinoid receptor in the CNS could be modified by the manipulation of the dietary n-3 PUFA status.

Hypersensitization of the Orexin 1 receptor by the CB1 receptor: evidence for cross-talk blocked by the specific CB1 antagonist, SR141716

In the present study, we observed evidence of cross-talk between the cannabinoid receptor CB1 and the orexin 1 receptor (OX1R) using a heterologous system. When the two receptors are co-expressed, we observed a major CB1-dependent enhancement of the orexin A potency to activate the mitogen-activated protein kinase pathway; dose-responses curves indicated a 100-fold increase in the potency of orexin-mediated mitogen-activated protein kinase activation. This effect required a functional CB1 receptor as evidenced by the blockade of the orexin response by the specific CB1 antagonist, N-(piperidino-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-pyrazole-3-carboxamide (SR141716), but also by pertussis toxin, suggesting that this potentiation is Gi-mediated. In contrast to OX1R, the potency of direct activation of CB1 was not affected by co-expression with OX1R. In addition, electron microscopy experiments revealed that CB1 and OX1R are closely apposed at the plasma membrane level; they are close enough to form hetero-oligomers. Altogether, for the first time our data provide evidence that CB1 is able to potentiate an orexigenic receptor. Considering the antiobesity effect of SR141716, these results open new avenues to understand the mechanism by which the molecule may prevent weight gain through functional interaction between CB1 and other receptors involved in the control of appetite.

Nongenomic glucocorticoid inhibition via endocannabinoid release in the hypothalamus: a fast feedback mechanism

Glucocorticoid negative feedback in the brain controls stress, feeding, and neural-immune interactions by regulating the hypothalamic-pituitary-adrenal axis, but the mechanisms of inhibition of hypothalamic neurosecretory cells have never been elucidated. Using whole-cell patch-clamp recordings in an acute hypothalamic slice preparation, we demonstrate a rapid suppression of excitatory glutamatergic synaptic inputs to parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVN) by the glucocorticoids dexamethasone and corticosterone. The effect was maintained with dexamethasone conjugated to bovine serum albumin and was not seen with direct intracellular glucocorticoid perfusion via the patch pipette, suggesting actions at a membrane receptor. The presynaptic inhibition of glutamate release by glucocorticoids was blocked by postsynaptic inhibition of G-protein activity with intracellular GDP-beta-S application, implicating a postsynaptic G-protein-coupled receptor and the release of a retrograde messenger. The glucocorticoid effect was not blocked by the nitric oxide synthesis antagonist N(G)-nitro-L-arginine methyl ester hydrochloride or by hemoglobin but was blocked completely by the CB1 cannabinoid receptor antagonists AM251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] and AM281 [1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide] and mimicked and occluded by the cannabinoid receptor agonist WIN55,212-2 [(beta)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate], indicating that it was mediated by retrograde endocannabinoid release. Several peptidergic subtypes of parvocellular neuron, identified by single-cell reverse transcripton-PCR analysis, were subject to rapid inhibitory glucocorticoid regulation, including corticotropin-releasing hormone-, thyrotropin-releasing hormone-, vasopressin-, and oxytocin-expressing neurons. Therefore, our findings reveal a mechanism of rapid glucocorticoid feedback inhibition of hypothalamic hormone secretion via endocannabinoid release in the PVN and provide a link between the actions of glucocorticoids and cannabinoids in the hypothalamus that regulate stress and energy homeostasis.

Leptin activates the anandamide hydrolase promoter in human T lymphocytes through STAT3

Physiological concentrations of leptin stimulate the activity of the endocannabinoid-degrading enzyme anandamide hydrolase (fatty acid amide hydrolase, FAAH) in human T lymphocytes up to approximately 300% over the untreated controls. Stimulation of FAAH occurred through up-regulation of gene expression at transcriptional and translational levels and involved binding of leptin to its receptor with an apparent dissociation constant (K(d)) of 1.95 +/- 0.14 nm and maximum binding (B(max)) of 392 +/- 8 fmol x mg protein(-1). Leptin binding to the receptor triggered activation of STAT3 but not STAT1 or STAT5 or the mitogen-activated protein kinases p38, p42, and p44. Peripheral lymphocytes of leptin knock-out (ob/ob) mice showed decreased FAAH activity and expression (approximately 25% of the wild-type littermates), which were reversed to control levels by exogenous leptin. Analysis of the FAAH promoter showed a cAMP-response element-like site, which is a transcriptional target of STAT3. Consistently, mutation of this site prevented FAAH activation by leptin in transient expression assays. Electrophoretic mobility shift and supershift assays further corroborated the promoter activity data. Taken together, these results suggest that leptin, by up-regulating the FAAH promoter through STAT3, enhances FAAH expression, thus tuning the immunomodulatory effects of anandamide. These findings might also have critical implications for human fertility.

Preferential effects of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight gain of obese (fa/fa) compared to lean Zucker rats

RATIONALE

The selective CB(1) receptor antagonist, SR 141716, has been demonstrated to reduce food consumption in a range of animal species.

OBJECTIVE

To assess the effect of chronic administration of SR 141716 on body weight and ingestive behaviour of lean and obese (fa/fa) Zucker rats.

METHODS

Lean and obese Zucker rats were orally dosed with SR 141716 (3, 10, 30 mg/kg PO), sibutramine (5 mg/kg PO) or vehicle for one week. Pair-fed controls provided insight as to whether the effect of SR 141716 on body weight was attributable to drug-induced hypophagia. Subsequently, the effect of chronic oral administration of SR 141716 (1, 3, 10 mg/kg) was assessed for 28 days. At the end of this period, all animals were given vehicle for 14 days. The incidence of wet-dog shakes, yawning, scratching, and grooming behaviours, was assessed after acute administration and at weekly intervals thereafter for 4 weeks.

RESULTS

SR 141716 dose-dependently decreased food intake and body weight gain in both lean and obese animals. The inhibition of food intake and body weight gain was greater in obese Zuckers than in lean Zucker controls. Changes in the body weights of pair-fed controls closely paralleled those of their drug-treated counterparts. Chronic 28-day treatment led to a maintained reduction of body weight gain. Withdrawal of SR 141716 on day 28 resulted in rebound hyperphagia and a significant weight gain. On acute administration, SR 141716 dose-dependently induced motor behaviours that showed tolerance upon repeated administration.

CONCLUSION

These data indicate that chronic oral treatment with SR 141716 significantly reduces the food intake and body weight gain of obese and lean Zucker rats, an effect that is greater in obese animals and reversible upon drug withdrawal.

Antiobesity effects of chronic cannabinoid CB1 receptor antagonist treatment in diet-induced obese mice

We determined the effect of a cannabinoid CB1 receptor antagonist (AM-251; N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) on food intake, body weight and adipose tissue mass in Western diet-induced obese (DIO) mice using a chronic, interrupted, oral dosing paradigm. The dosing paradigm was 2 weeks on treatment (treatment 1), 2 weeks off-treatment, followed by 2 weeks on treatment (treatment 2). During treatment 1 and treatment 2, food intake and body weight were reduced after a single dose. At 30 mg/kg/day, anorectic efficacy was maintained through 12 days (treatment 1) and 7 days (treatment 2). Body weight of AM-251-treated mice remained less than vehicle-treated mice throughout treatment 1 and treatment 2. Administration of AM-251 reduced inguinal subcutaneous, retroperitoneal and mesenteric adipose tissue mass. Antiobesity effects of AM-251 were lost during the off-treatment period, and hyperphagia was observed in treated animals. With re-initiation of AM-251 treatment, mice again responded to the effects of the compound. These results support the hypothesis that chronic treatment of obese individuals with cannabinoid CB1 receptor antagonists is a viable pharmacologic approach to sustained weight loss.

Anti-obesity effect of SR141716, a CB1 receptor antagonist, in diet-induced obese mice

Because the CB1 receptor antagonist SR141716 was previously reported to modulate food intake in rodents, we studied its efficacy in reducing obesity in a diet-induced obesity (DIO) model widely used for research on the human obesity syndrome. During a 5-wk treatment, SR141716 (10 mg. kg(-1). day(-1) orally) induced a transient reduction of food intake (-48% on week 1) and a marked but sustained reduction of body weight (-20%) and adiposity (-50%) of DIO mice. Furthermore, SR141716 corrected the insulin resistance and lowered plasma leptin, insulin, and free fatty acid levels. Most of these effects were present, but less pronounced at 3 mg. kg(-1). day(-1). In addition to its hypophagic action, SR141716 may influence metabolic processes as the body weight loss of SR141716-treated mice was significantly higher during 24-h fasting compared with vehicle-treated animals, and when a 3-day treatment was compared with a pair feeding. SR141716 had no effect in CB1 receptor knockout mice, which confirmed the implication of CB1 receptors in the activity of the compound. These findings suggest that SR141716 has a potential as a novel anti-obesity treatment.