CRF–CRF1 Receptor System in the Central and Basolateral Nuclei of the Amygdala Differentially Mediates Excessive Eating of Palatable Food

Highly palatable foods and dieting are major contributing factors for the development of compulsive eating in obesity and eating disorders. We previously demonstrated that intermittent access to palatable food results in corticotropin-releasing factor-1 (CRF₁) receptor antagonist-reversible behaviors, which include excessive palatable food intake, hypophagia of regular chow, and anxiety-like behavior. However, the brain areas mediating these effects are still unknown. Male Wistar rats were either fed chow continuously for 7 days/week (Chow/Chow group), or fed chow intermittently 5 days/week, followed by a sucrose, palatable diet 2 days/week (Chow/Palatable group). Following chronic diet alternation, the effects of microinfusing the CRF₁ receptor antagonist R121919 (0, 0.5, 1.5 μg/side) in the central nucleus of the amygdala (CeA), the basolateral nucleus of the amygdala (BlA), or the bed nucleus of the stria terminalis (BNST) were evaluated on excessive intake of the palatable diet, chow hypophagia, and anxiety-like behavior. Furthermore, CRF immunostaining was evaluated in the brain of diet cycled rats. Intra-CeA R121919 blocked both excessive palatable food intake and anxiety-like behavior in Chow/Palatable rats, without affecting chow hypophagia. Conversely, intra-BlA R121919 reduced the chow hypophagia in Chow/Palatable rats, without affecting excessive palatable food intake or anxiety-like behavior. Intra-BNST treatment had no effect. The treatments did not modify the behavior of Chow/Chow rats. Immunohistochemistry revealed an increased number of CRF-positive cells in CeA—but not in BlA or BNST—of Chow/Palatable rats, during both withdrawal and renewed access to the palatable diet, compared with controls. These results provide functional evidence that the CRF–CRF₁ receptor system in CeA and BlA has a differential role in mediating maladaptive behaviors resulting from palatable diet cycling.     

Dissociable effects of CB1 receptor blockade on anxiety-like and consummatory behaviors in the novelty-induced hypophagia test in mice

Rationale

Central CB1 cannabinoid receptors regulate anxiety-like and appetitive consummatory behaviors. Pharmacological antagonism/inverse-agonism of CB1 receptors increases anxiety and decreases appetitive behaviors; however, neither well-defined dose nor context dependence of these effects has been simultaneously assessed in one behavioral assay.

Objectives

We sought to determine the context and dose dependence of the effects of CB1 receptor blockade on anxiety-like and consummatory behaviors in a model that allowed for simultaneous detection of anxiety-like and consummatory-related behaviors.

Methods

We determined the effects of the CB1 receptor antagonist/inverse-agonist, rimonabant, in the novelty-induced hypophagia (NIH) assay in juvenile male ICR mice.

Results

Rimonabant dose-dependently decreased consumption of a palatable reward solution completely independent of contextual novelty. Grooming and scratching behavior was also increased by rimonabant in a context-independent manner. In contrast, rimonabant increased feeding latency, a measure of anxiety-like behaviors, only in a novel, mildly anxiogenic context. The effects of rimonabant were specific since no effects of rimonabant on despair-like behavior were observed in the tail suspension assay. Blockade of CB2 receptors had no effect on novelty-induced increases in feeding latency or palatable food consumption.

Conclusions

Our findings indicate that CB1 receptor blockade decreases the hedonic value of palatable food irrespective of environmental novelty, whereas the anxiogenic-like effects are highly context-dependent. Blockade of CB2 receptors does not regulate either anxiety-like or consummatory behaviors in the NIH assay. These findings suggest that rimonabant modulates distinct and dissociable neural processes regulating anxiety and consummatory behavior to sculpt complex and context-dependent behavioral repertories.     

Inhibition of endocannabinoid catabolic enzymes elicits anxiolytic-like effects in the marble burying assay

Cannabinoids have long been shown to have a range of potential therapeutic effects, including antiemetic actions, analgesia, and anxiolysis. However, psychomimetic and memory disruptive side effects, as well as the potential for abuse and dependence, have restricted their clinical development. Endogenous cannabinoids (i.e., endocannabinoids; eCBs), such as anandamide (AEA) and 2-arachidonoylglycerol (2-AG), are produced throughout the limbic system and other brain regions associated with emotionality and are believed to modulate behavioral responses to stress-related conditions. AEA and 2-AG are rapidly metabolized by the respective enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). Accordingly, inhibition of each enzyme increases brain levels of the appropriate eCB. Although FAAH inhibition has been established to decrease anxiety-like behavior, the role of 2-AG has been difficult to ascertain until the recent synthesis of JZL184, a potent and selective MAGL inhibitor. In the present study, we investigated the effects of inhibiting FAAH or MAGL on anxiety-like behavior in marble burying, a model of repetitive, compulsive behaviors germane to anxiety disorders such as obsessive-compulsive disorder. The FAAH inhibitor PF-3845, the MAGL inhibitor JZL184, and the benzodiazepine diazepam decreased marble burying at doses that did not affect locomotor activity. In contrast, Δ⁹-tetrahydrocannabinol (THC), the primary psychoactive constituent of marijuana, did not consistently reduce marble burying without also eliciting profound decreases in locomotor behavior. The CB₁ cannabinoid receptor antagonist rimonabant blocked the reduction in marble burying caused by FAAH and MAGL inhibitors, but not by diazepam, indicating a CB₁ receptor mechanism of action. These data indicate that elevation of AEA or 2-AG reduces marble burying behavior and suggest that their catabolic enzymes represent potential targets for the development of new classes of pharmacotherapeutics to treat anxiety-related disorders.     

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 (CB₁) 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 CB₁ receptor occupancy underlying these neurobiological effects is unclear. Objectives We explored the relationship between in vivo CB₁ 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 CB₁ receptor antagonists presently in clinical trials, SR141716A (rimonabant) and SLV319. Methods CB₁ receptor occupancy was measured using [³H] 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 CB₁ receptor occupancies (11%) for SLV319. Conclusions The occupancy method described here is an effective tool for interrelating central CB₁ receptor occupancy with neurobiological actions of CB₁ receptor antagonists and for furthering our understanding of the role of CB₁ receptors in central nervous system physiology and pathology.     

AM 251 differentially effects food-maintained responding depending on food palatability

Ligands functioning as antagonists and inverse agonists at the cannabinoid CB₁-receptor (e.g., AM 251, AM 281, and rimonabant (previously identified as SR141716)) have been demonstrated to have effects on satiety, consumption of, and the motivation to work for, or obtain food. These represent behavioral effects that may also be linked to characteristics such as food palatability or motivation to obtain food. Given the recent removal of rimonabant from clinical trials, a thorough characterization of ingestive behaviors that are associated with other likely candidate drugs is warranted. In the present study, normal weight male Long Evans rats were trained to respond for grain or chocolate-flavored food pellets under progressive-ratio schedules of reinforcement. Rats received acute injections of the CB₁ receptor antagonist AM 251 (0.3-3.0 mg/kg) or vehicle prior to daily testing sessions. Administration of AM 251 produced significant dose-dependent reductions in responding for, deliveries of, and break points (BP) associated with chocolate-flavored but not grain pellets. These data add to the literature demonstrating the ability of CB₁ antagonists to selectively reduce motivation to obtain highly palatable reinforcers.     

Operant behavior to obtain palatable food modifies neuronal plasticity in the brain reward circuit

Palatability enhances food intake by hedonic mechanisms that prevail over caloric necessities. Different studies have demonstrated the role of endogenous cannabinoids in the mesocorticolimbic system in controlling food hedonic value and consumption. We hypothesize that the endogenous cannabinoid system could also be involved in the development of food-induced behavioral alterations, such as food-seeking and binge-eating, by a mechanism that requires neuroplastic changes in the brain reward pathway. For this purpose, we evaluated the role of the CB₁ cannabinoid receptor (CB₁-R) in the behavioral and neuroplastic changes induced by operant training for standard, highly caloric or highly palatable isocaloric food using different genetics, viral and pharmacological approaches. Neuroplasticity was evaluated by measuring changes in dendritic spine density in neurons previously labeled with the dye DiI. Only operant training to obtain highly palatable isocaloric food induced neuroplastic changes in neurons of the nucleus accumbens shell and prefrontal cortex that were associated to changes in food-seeking behavior. These behavioral and neuroplastic modifications induced by highly palatable isocaloric food were dependent on the activity of the CB₁-R. Neuroplastic changes induced by highly palatable isocaloric food are similar to those produced by some drugs of abuse and may be crucial in the alteration of food-seeking behavior leading to overweight and obesity.     

Operant behavior to obtain palatable food modifies ERK activity in the brain reward circuit

Food palatability produces behavioral modifications that resemble those induced by drugs of abuse. Palatability-induced behavioral changes require both, the activation of the endogenous cannabinoid system, and changes in structural plasticity in neurons of the brain reward pathway. The ERK intracellular pathway is activated by CB₁ receptors (CB₁-R) and plays a crucial role in neuroplasticity. We investigated the activation of the ERK signaling cascade in the mesocorticolimbic system induced by operant training to obtain highly palatable isocaloric food and the involvement of the CB₁-R in these responses. Using immunofluorescence techniques, we analyzed changes in ERK intracellular pathway activation in the mesocorticolimbic system of wild-type and CB₁ knockout mice (CB₁?/?) trained on an operant paradigm to obtain standard, highly caloric or highly palatable isocaloric food. Operant training for highly palatable isocaloric food, but not for standard or highly caloric food, produced a robust activation of the ERK signaling cascade in the same brain areas where this training modified structural plasticity. These changes induced by the operant training were absent in CB₁?/?. We can conclude that the activation of the ERK pathway is associated to the neuroplasticity induced by operant training for highly palatable isocaloric food and might be involved in CB₁-R mediated alterations in behavior and structural plasticity.     

Stimulatory and Inhibitory Roles of Brain 2-Arachidonoylglycerol in Bombesin-Induced Central Activation of Adrenomedullary Outflow in Rats

2-Arachidonoylglycerol (2-AG) is recognized as a potent endocannabinoid, which reduces synaptic transmission through cannabinoid CB₁ receptors, and is hydrolyzed by monoacylglycerol lipase (MGL) to arachidonic acid (AA), a cyclooxygenase substrate. We already reported that centrally administered MGL and cyclooxygenase inhibitors each reduced the intracerebroventricularly (i.c.v.) administered bombesin-induced secretion of adrenal catecholamines, while a centrally administered CB₁-antagonist potentiated the response, indirectly suggesting bidirectional roles of brain 2-AG (stimulatory and inhibitory roles) in the bombesin-induced response. In the present study, we separately examined these bidirectional roles using 2-AG and 2-AG ether (2-AG-E) (stable 2-AG analog for MGL) in rats. 2-AG (0.5 μmol/animal, i.c.v.), but not 2-AG-E (0.5 μmol/animal, i.c.v.), elevated basal plasma catecholamines with JZL184 (MGL inhibitor)- and indomethacin (cyclooxygenase inhibitor)-sensitive brain mechanisms. 2-AG-E (0.1 μmol/animal, i.c.v.) effectively reduced the bombesin (1 nmol/animal, i.c.v.)-induced elevation of plasma catecholamines with rimonabant (CB₁ antagonist)-sensitive brain mechanisms. Immunohistochemical studies demonstrated the bombesin-induced activation of diacylglycerol lipase α (2-AG-producing enzyme)-positive spinally projecting neurons in the hypothalamic paraventricular nucleus, a control center of central adrenomedullary outflow. These results directly indicate bidirectional roles of brain 2-AG, a stimulatory role as an AA precursor and an inhibitory role as an endocannabinoid, in the bombesin-induced central adrenomedullary outflow in rats.     

Epigenetic and Proteomic Expression Changes Promoted by Eating Addictive-Like Behavior

An increasing perspective conceptualizes obesity and overeating as disorders related to addictive-like processes that could share common neurobiological mechanisms. In the present study, we aimed at validating an animal model of eating addictive-like behavior in mice, based on the DSM-5 substance use disorder criteria, using operant conditioning maintained by highly palatable chocolate-flavored pellets. For this purpose, we evaluated persistence of food-seeking during a period of non-availability of food, motivation for food, and perseverance of responding when the reward was associated with a punishment. This model has allowed identifying extreme subpopulations of mice related to addictive-like behavior. We investigated in these subpopulations the epigenetic and proteomic changes. A significant decrease in DNA methylation of CNR1 gene promoter was revealed in the prefrontal cortex of addict-like mice, which was associated with an upregulation of CB₁ protein expression in the same brain area. The pharmacological blockade (rimonabant 3 mg/kg; i.p.) of CB₁ receptor during the late training period reduced the percentage of mice that accomplished addiction criteria, which is in agreement with the reduced performance of CB₁ knockout mice in this operant training. Proteomic studies have identified proteins differentially expressed in mice vulnerable or not to addictive-like behavior in the hippocampus, striatum, and prefrontal cortex. These changes included proteins involved in impulsivity-like behavior, synaptic plasticity, and cannabinoid signaling modulation, such as alpha-synuclein, phosphatase 1-alpha, doublecortin-like kinase 2, and diacylglycerol kinase zeta, and were validated by immunoblotting. This model provides an excellent tool to investigate the neurobiological substrate underlying the vulnerability to develop eating addictive-like behavior.     

Effects of chronic nicotine on food intake and anxiety-like behaviour in CB1 knockout mice

We have evaluated the effects of chronic nicotine administration and withdrawal in food intake and preference, metabolic parameters and anxiety-like behaviour in CB₁ knockout mice and wild-type littermates. Mutant mice showed lower levels of glucose, insulin and cholesterol after two weeks of high fat diet and reduced preference for saccharine solution when compared with wild-type mice. Nicotine reduced body weight and induced anxiogenic-like effects in wild-type, but not in CB₁ knockout mice. Our results suggest a modulatory role of the endocannabinoid system on the effects induced by nicotine on metabolic parameters and anxiety-like responses.     

Central mediation and differential blockade by cannabinergics of the discriminative stimulus effects of the cannabinoid CB<Subscript>1</Subscript> receptor antagonist rimonabant in rats

Rationale  

Discovery of an endocannabinoid signaling system launched the development of the blocker rimonabant, a cannabinoid CB1 receptor (CB₁R) antagonist/inverse agonist. Due to untoward effects, this medication was withdrawn and efforts have been directed towards discovering chemicals with more benign profiles.     

O-2050 facilitates noradrenaline release and increases the CB1 receptor inverse agonistic effect of rimonabant in the guinea pig hippocampus

The cannabinoid CB₁ receptors on the noradrenergic neurons in guinea pig hippocampal slices show an endogenous endocannabinoid tone. This conclusion is based on rimonabant, the facilitatory effect of which on noradrenaline release might be due to its inverse CB₁ receptor agonism and/or the interruption of a tonic inhibition elicited by endocannabinoids. To examine the latter mechanism, a neutral antagonist would be suitable. Therefore, we studied whether O-2050 is a neutral CB₁ receptor antagonist in the guinea pig hippocampus and whether it mimics the facilitatory effect of rimonabant. CB₁ receptor affinity of O-2050 was quantified in cerebrocortical membranes, using ³H-rimonabant binding. Its CB₁ receptor potency and effect on ³H-noradrenaline release were determined in superfused hippocampal slices. Its intrinsic activity at CB₁ receptors was studied in hippocampal membranes, using ³⁵S-GTPγS binding. Endocannabinoid levels in hippocampus were determined by liquid chromatography-multiple reaction monitoring. O-2050 was about ten times less potent than rimonabant in its CB₁ receptor affinity, potency and facilitatory effect on noradrenaline release. Although not affecting ³⁵S-GTPγS binding by itself, O-2050 shifted the concentration-response curve of a CB₁ receptor agonist to the right but that of rimonabant to the left. Levels of anandamide and 2-arachidonoyl glycerol in guinea pig hippocampus closely resembled those in mouse hippocampus. In conclusion, our results with O-2050 confirm that the CB₁ receptors on noradrenergic neurons of the guinea pig hippocampus show an endogenous tone. To differentiate between the two mechanisms leading to an endogenous tone, O-2050 is not superior to rimonabant since O-2050 may increase the inverse agonistic effect of endocannabinoids.     

Lack of tolerance to the suppressing effect of rimonabant on chocolate intake in rats

Rationale and objectives Previous work indicated that tolerance to the anorectic effect of the cannabinoid CB₁ receptor antagonist/inverse agonist, rimonabant, developed rather rapidly in rats and mice given access to a standard rodent chow. The present study was designed to investigate whether the reducing effect of rimonabant on intake of a highly palatable food such as a chocolate-flavoured beverage underwent a development of tolerance as rapid as that manifested on intake of a standard rodent chow. Materials and methods To this aim, Wistar rats were concurrently exposed, with unlimited access for 24 h/day, to the chocolate-flavoured beverage, regular food pellets and water. Rimonabant (0, 1.25, 2.5 and 5 mg/kg; i.p.) was administered once a day for 21 consecutive days. Results Rimonabant administration resulted in a dose-dependent suppression of the high, daily intake of the chocolate-flavoured beverage; this effect lasted for the entire 21-day treatment period, without any apparent development of tolerance. Conversely, rimonabant-induced reduction in daily intake of regular food pellets was of a smaller magnitude and was limited to the first 3–4 days of treatment. Conclusions Together, these results indicate that chronically administered rimonabant was more effective and longer-lasting in reducing the intake of a highly palatable food than that of regular food pellets in rats. These results also suggest that rimonabant may be more active on the hedonic rather than nutritive properties of diets.     

The disruptive effects of the CB<Subscript>1</Subscript> receptor antagonist rimonabant on extinction learning in mice are task-specific

Rationale Disruption of CB₁ receptor signaling through the use of CB₁ (−/−) mice or the CB₁ receptor antagonist rimonabant (SR141716) has been demonstrated to impair extinction of learned responses in conditioned fear and Morris water maze tasks. In contrast, CB₁ (−/−) mice exhibited normal extinction rates in an appetitively motivated operant conditioning task. Objectives The purpose of this study was to test whether rimonabant would differentially disrupt extinction learning between fear-motivated and food-motivated tasks. Materials and methods Separate groups of C57BL/6J mice were trained in two aversively motivated tasks, conditioned freezing and passive avoidance, and an appetitively motivated operant conditioning task at a fixed ratio (FR-5) schedule of food reinforcement. After acquisition, the respective reinforcers in each task were withheld, and an intraperitoneal injection of vehicle or rimonabant was given 30 min before each extinction session. Results Rimonabant (3 mg/kg) treatment significantly disrupted extinction in both the conditioned freezing and passive avoidance tasks but failed to affect extinction rates in the operant conditioning task, whether using daily or weekly extinction sessions. Interestingly, rimonabant (3 mg/kg) prevented the significant increases in lever pressing (i.e., extinction burst) that occurred during the first extinction session of the operant conditioning task. Conclusions These results support the hypothesis that the CB₁ receptor plays a vital role in the extinction of aversive memories but is not essential for extinction of learned responses in appetitively motivated tasks.     

Are cannabidiol and Δ9-tetrahydrocannabivarin negative modulators of the endocannabinoid system? A systematic review

Based upon evidence that the therapeutic properties of Cannabis preparations are not solely dependent upon the presence of Δ⁹-tetrahydrocannabinol (THC), pharmacological studies have been recently carried out with other plant cannabinoids (phytocannabinoids), particularly cannabidiol (CBD) and Δ⁹-tetrahydrocannabivarin (THCV). Results from some of these studies have fostered the view that CBD and THCV modulate the effects of THC via direct blockade of cannabinoid CB₁ receptors, thus behaving like first-generation CB₁ receptor inverse agonists, such as rimonabant. Here, we review in vitro and ex vivo mechanistic studies of CBD and THCV, and synthesize data from these studies in a meta-analysis. Synthesized data regarding mechanisms are then used to interpret results from recent pre-clinical animal studies and clinical trials. The evidence indicates that CBD and THCV are not rimonabant-like in their action and thus appear very unlikely to produce unwanted CNS effects. They exhibit markedly disparate pharmacological profiles particularly at CB₁ receptors: CBD is a very low-affinity CB₁ ligand that can nevertheless affect CB₁ receptor activity in vivo in an indirect manner, while THCV is a high-affinity CB₁ receptor ligand and potent antagonist in vitro and yet only occasionally produces effects in vivo resulting from CB₁ receptor antagonism. THCV has also high affinity for CB₂ receptors and signals as a partial agonist, differing from both CBD and rimonabant. These cannabinoids illustrate how in vitro mechanistic studies do not always predict in vivo pharmacology and underlie the necessity of testing compounds in vivo before drawing any conclusion on their functional activity at a given target.     

2-arachidonyl glycerol activates platelets via conversion to arachidonic acid and not by direct activation of cannabinoid receptors

AIMS

Cannabinoid receptor-1 (CB₁) antagonists suppress appetite and induce weight loss. Direct antagonism of CB₁ receptors on platelets might be an additional benefit for CB₁ antagonists, but the role of CB₁ receptors in platelets is controversial. We tested the hypothesis that the endocannabinoid, 2-arachidonyl glycerol (2-AG), induces platelet aggregation by a COX-mediated mechanism rather than through CB₁ receptor activation, in blood obtained from healthy volunteers and patients with coronary artery disease receiving low dose aspirin.

METHODS

Aggregatory responses to the cannabinoids 2-AG and Δ⁹-THC were examined in blood sampled from healthy volunteers (n= 8) and patients (n= 12) with coronary artery disease receiving aspirin using whole blood aggregometry. The effects of CB₁ (AM251) and CB₂ (AM630) antagonists, as well as fatty acid amide hydrolase (FAAH) and monoacyl glycerol lipase (MAGL) inhibitors and aspirin on 2-AG-induced aggregation were also assessed.

RESULTS

AM251 (100 nm–30 µm) had no effect on platelet aggregation induced by either ADP (P= 0.90) or thrombin (P= 0.86). 2-AG, but not Δ⁹-THC, induced aggregation. 2-AG-induced aggregation was unaffected by AM251 and AM630 but was abolished by aspirin (P < 0.001) and by the MAGL inhibitor, URB602 (P < 0.001). Moreover, the aggregatory response to 2-AG was depressed (by >75%, P < 0.001) in blood from patients with coronary artery disease receiving aspirin compared with that from healthy volunteers.

CONCLUSIONS

2-AG-mediated activation of platelets is via metabolism to arachidonic acid by MAGL, and not through direct action on CB₁ or CB₂ receptors, at least in the acute phase.     

Pituitary Adenylate Cyclase-Activating Peptide in the Central Amygdala Causes Anorexia and Body Weight Loss via the Melanocortin and the TrkB Systems

Growing evidence suggests that the pituitary adenylate cyclase-activating polypeptide (PACAP)/PAC1 receptor system represents one of the main regulators of the behavioral, endocrine, and autonomic responses to stress. Although induction of anorexia is a well-documented effect of PACAP, the central sites underlying this phenomenon are poorly understood. The present studies addressed this question by examining the neuroanatomical, behavioral, and pharmacological mechanisms mediating the anorexia produced by PACAP in the central nucleus of the amygdala (CeA), a limbic structure implicated in the emotional components of ingestive behavior. Male rats were microinfused with PACAP (0–1 μg per rat) into the CeA and home-cage food intake, body weight change, microstructural analysis of food intake, and locomotor activity were assessed. Intra-CeA (but not intra-basolateral amygdala) PACAP dose-dependently induced anorexia and body weight loss without affecting locomotor activity. PACAP-treated rats ate smaller meals of normal duration, revealing that PACAP slowed feeding within meals by decreasing the regularity and maintenance of feeding from pellet-to-pellet; postprandial satiety was unaffected. Intra-CeA PACAP-induced anorexia was blocked by coinfusion of either the melanocortin receptor 3/4 antagonist SHU 9119 or the tyrosine kinase B (TrKB) inhibitor k-252a, but not the CRF receptor antagonist D-Phe-CRF(12–41). These results indicate that the CeA is one of the brain areas through which the PACAP system promotes anorexia and that PACAP preferentially lessens the maintenance of feeding in rats, effects opposite to those of palatable food. We also demonstrate that PACAP in the CeA exerts its anorectic effects via local melanocortin and the TrKB systems, and independently from CRF.     

Fatty acid amide hydrolase blockade attenuates the development of collagen-induced arthritis and related thermal hyperalgesia in mice

Fatty acid amide hydrolase (FAAH) is the primary degradative enzyme of the endocannabinoid anandamide (N-arachidonoylethanolamine), which activates cannabinoid CB₁ and CB₂ receptors. FAAH disruption reduces nociception in a variety of acute rodent models of inflammatory pain. The present study investigated whether these actions extend to the chronic, collagen-induced arthritis (CIA) model. We investigated the anti-arthritic and anti-hyperalgesic effects of genetic deletion or pharmacological inhibition of FAAH in the CIA model. FAAH (−/−) mice, and FAAH-NS mice that express FAAH exclusively in nervous tissue, displayed decreased severity of CIA and associated hyperalgesia. These phenotypic anti-arthritic effects were prevented by repeated daily injections of the CB₂ receptor antagonist, SR144528, but not the CB₁ receptor antagonist rimonabant. Similarly, repeated administration of the FAAH inhibitor URB597 reduced CIA severity, and acute administration of rimonabant, but not SR144528, blocked the anti-hyperalgesic effects of prolonged FAAH inhibition, suggesting that prolonged CB₂ receptor activation reduces the severity of CIA, whereas acute CB₁ receptor activation reduces CIA-induced hyperalgesia. In contrast, acute administration of URB597 elicited a CB₁ receptor-dependent anti-hyperalgesic effect. The observed anti-arthritic and anti-hyperalgesic properties of FAAH inhibition, coupled with a lack of apparent behavioral alterations, suggest that endocannabinoid modulating enzymes offer a promising therapeutic target for the development of novel pharmacological approaches to treat rheumatoid arthritis and associated hyperalgesia.     

An endocannabinoid signaling system modulates anxiety-like behavior in male Syrian hamsters

Rationale  An endocannabinoid signaling system has not been identified in hamsters. Objective  We examined the existence of an endocannabinoid signaling system in Syrian hamsters using neuroanatomical, biochemical, and behavioral pharmacological approaches. Materials and methods  The distribution of cannabinoid receptors was mapped, and membrane fatty-acid amide hydrolase (FAAH) activity and levels of fatty-acid amides were measured in hamster brain. The impact of cannabinoid CB₁ receptor blockade and inhibition of FAAH was evaluated in the elevated plus maze, rota-rod test, and models of unconditioned and conditioned social defeat. Results  A characteristic heterogeneous distribution of cannabinoid receptors was detected in hamster brain using [³H]CP55,940 binding and autoradiography. The FAAH inhibitor URB597 inhibited FAAH activity (IC₅₀ = 12.8 nM) and elevated levels of fatty-acid amides (N-palmitoyl ethanolamine and N-oleoyl ethanolamine) in hamster brain. Anandamide levels were not reliably altered. The cannabinoid agonist WIN55,212-2 (1– 10 mg/kg i.p.) induced CB₁-mediated motor ataxia. Blockade of CB₁ with rimonabant (5 mg/kg i.p.) induced anxiogenic-like behavior in the elevated plus maze. URB597 (0.1–0.3 mg/kg i.p.) induced CB₁-mediated anxiolytic-like effects in the elevated plus maze, similar to the benzodiazepine diazepam (2 mg/kg i.p.). Diazepam (2–6 mg/kg i.p.) suppressed the expression, but not the acquisition, of conditioned defeat. By contrast, neither URB597 (0.3–3.0 mg/kg i.p.) nor rimonabant (5 mg/kg i.p.) altered unconditioned or conditioned social defeat or rota-rod performance. Conclusions  Endocannabinoids engage functional CB₁ receptors in hamster brain to suppress anxiety-like behavior and undergo enzymatic hydrolysis catalyzed by FAAH. Our results further suggest that neither unconditioned nor conditioned social defeat in the Syrian hamster is dependent upon cannabinoid CB₁ receptor activation.