The cannabinoid CB1 antagonists SR 141716A and AM 251 suppress food intake and food-reinforced behavior in a variety of tasks in rats

Distinct antinociceptive and conditioned behavioral effects are produced by individual cannabinoids and a cannabis-derived mixture

Cannabinoids have been proposed as therapeutics for pain mitigation. Therefore, the antihyperalgesic effects of a proprietary cannabis-derived mixture, Non-Euphoric Phytocannabinoid Elixir #14 (NEPE14), were examined in a persistent Complete Freund's Adjuvant (CFA)-induced model of inflammatory pain. The acute antinociceptive and operant behavioral effects of NEPE14 were then compared with single cannabinoid preparations of Δ9-tetrahydrocannabinol (Δ9-THC), Δ8-THC, the synthetic cannabinoid (-)-CP 55,940 (CP), and cannabidiol (CBD). The THC isomers and CP were also administered with cannabinoid-type-1 receptor (CB1R) antagonist, AM251, and NEPE14 was administered in combination with THC or CP. To induce inflammation, CFA or saline was administered into the paw of male and female Wistar rats. After injections, mechanical hypersensitivity was assessed with Von Frey filaments, and thermal hyperalgesia with a thermal probe. Nine Sprague Dawley rats were also trained to respond under a fixed-ratio 30 schedule for food reinforcers during a 60-min session. Response rates were recorded during the session and warm-water tail-withdrawal latency post session. In CFA-administered rats, mechanical and thermal paw-withdrawal thresholds significantly decreased compared to vehicle, indicating hyperalgesia. Both i.p. (6.6-20.7 ml/kg) and o.m. (30-300 μL) NEPE14 significantly reduced the mechanical and thermal hyperalgesia. In contrast, neither NEPE14 (3.7-20.7 mL/kg i.p., 100-1000 μL o.m.) nor CBD (10-100 mg/kg) significantly decreased response rates or increased tail-withdrawal latency. Acute Δ9-THC, Δ8-THC (1-5.6 mg/kg), and CP (0.032-0.18 mg/kg) significantly and dose-dependently decreased overall response rate and increased tail-withdrawal latency compared to vehicle. AM251 significantly antagonized the rate-decreasing effects of THC, and CP, as well as the antinociceptive effects of CP. Combinations of NEPE14 with Δ9-THC or CP were not significantly different from these cannabinoids alone. In summary, while NEPE14 significantly reduced CFA-induced hyperalgesia, it was more similar to CBD than Δ9-THC, Δ8-THC, and CP for significantly reducing thermal nociception and disrupting conditioned behavior.

Decreased Ventral Tegmental Area CB1R Signaling Reduces Sign Tracking and Shifts Cue-Outcome Dynamics in Rat Nucleus Accumbens

Sign-tracking (ST) rats show enhanced cue sensitivity before drug experience that predicts greater discrete cue-induced drug seeking compared with goal-tracking or intermediate rats. Cue-evoked dopamine in the nucleus accumbens (NAc) is a neurobiological signature of sign-tracking behaviors. Here, we examine a critical regulator of the dopamine system, endocannabinoids, which bind the cannabinoid receptor-1 (CB1R) in the ventral tegmental area (VTA) to control cue-evoked striatal dopamine levels. We use cell type-specific optogenetics, intra-VTA pharmacology, and fiber photometry to test the hypothesis that VTA CB1R receptor signaling regulates NAc dopamine levels to control sign tracking. We trained male and female rats in a Pavlovian lever autoshaping (PLA) task to determine their tracking groups before testing the effect of VTA → NAc dopamine inhibition. We found that this circuit is critical for mediating the vigor of the ST response. Upstream of this circuit, intra-VTA infusions of rimonabant, a CB1R inverse agonist, during PLA decrease lever and increase food cup approach in sign-trackers. Using fiber photometry to measure fluorescent signals from a dopamine sensor, GRABDA (AAV9-hSyn-DA2m), we tested the effects of intra-VTA rimonabant on NAc dopamine dynamics during autoshaping in female rats. We found that intra-VTA rimonabant decreased sign-tracking behaviors, which was associated with increases in NAc shell, but not core, dopamine levels during reward delivery [unconditioned stimulus (US)]. Our results suggest that CB1R signaling in the VTA influences the balance between the conditioned stimulus-evoked and US-evoked dopamine responses in the NAc shell and biases behavioral responding to cues in sign-tracking rats.SIGNIFICANCE STATEMENT Substance use disorder (SUD) is a chronically relapsing psychological disorder that affects a subset of individuals who engage in drug use. Recent research suggests that there are individual behavioral and neurobiological differences before drug experience that predict SUD and relapse vulnerabilities. Here, we investigate how midbrain endocannabinoids regulate a brain pathway that is exclusively involved in driving cue-motivated behaviors of sign-tracking rats. This work contributes to our mechanistic understanding of individual vulnerabilities to cue-triggered natural reward seeking that have relevance for drug-motivated behaviors.

Exploring the Therapeutic Potential of Cannabinoid Receptor Antagonists in Inflammation, Diabetes Mellitus, and Obesity

Recently, research has greatly expanded the knowledge of the endocannabinoid system (ECS) and its involvement in several therapeutic applications. Cannabinoid receptors (CBRs) are present in nearly every mammalian tissue, performing a vital role in different physiological processes (neuronal development, immune modulation, energy homeostasis). The ECS has an essential role in metabolic control and lipid signaling, making it a potential target for managing conditions such as obesity and diabetes. Its malfunction is closely linked to these pathological conditions. Additionally, the immunomodulatory function of the ECS presents a promising avenue for developing new treatments for various types of acute and chronic inflammatory conditions. Preclinical investigations using peripherally restricted CBR antagonists that do not cross the BBB have shown promise for the treatment of obesity and metabolic diseases, highlighting the importance of continuing efforts to discover novel molecules with superior safety profiles. The purpose of this review is to examine the roles of CB1R and CB2Rs, as well as their antagonists, in relation to the above-mentioned disorders.

The Role of the Endocannabinoid System in Binge Eating Disorder

Eating disorders are multifactorial disorders that involve maladaptive feeding behaviors. Binge eating disorder (BED), the most prevalent of these in both men and women, is characterized by recurrent episodes of eating large amounts of food in a short period of time, with a subjective loss of control over eating behavior. BED modulates the brain reward circuit in humans and animal models, which involves the dynamic regulation of the dopamine circuitry. The endocannabinoid system plays a major role in the regulation of food intake, both centrally and in the periphery. Pharmacological approaches together with research using genetically modified animals have strongly highlighted a predominant role of the endocannabinoid system in feeding behaviors, with the specific modulation of addictive-like eating behaviors. The purpose of the present review is to summarize our current knowledge on the neurobiology of BED in humans and animal models and to highlight the specific role of the endocannabinoid system in the development and maintenance of BED. A proposed model for a better understanding of the underlying mechanisms involving the endocannabinoid system is discussed. Future research will be necessary to develop more specific treatment strategies to reduce BED symptoms.

The conserved endocannabinoid anandamide modulates olfactory sensitivity to induce hedonic feeding in C. elegans

The ability of cannabis to increase food consumption has been known for centuries. In addition to producing hyperphagia, cannabinoids can amplify existing preferences for calorically dense, palatable food sources, a phenomenon called hedonic amplification of feeding. These effects result from the action of plant-derived cannabinoids that mimic endogenous ligands called endocannabinoids. The high degree of conservation of cannabinoid signaling at the molecular level across the animal kingdom suggests hedonic feeding may also be widely conserved. Here, we show that exposure of Caenorhabditis elegans to anandamide, an endocannabinoid common to nematodes and mammals, shifts both appetitive and consummatory responses toward nutritionally superior food, an effect analogous to hedonic feeding. We find that anandamide's effect on feeding requires the C. elegans cannabinoid receptor NPR-19 but can also be mediated by the human CB1 cannabinoid receptor, indicating functional conservation between the nematode and mammalian endocannabinoid systems for the regulation of food preferences. Furthermore, anandamide has reciprocal effects on appetitive and consummatory responses to food, increasing and decreasing responses to inferior and superior foods, respectively. Anandamide's behavioral effects require the AWC chemosensory neurons, and anandamide renders these neurons more sensitive to superior foods and less sensitive to inferior foods, mirroring the reciprocal effects seen at the behavioral level. Our findings reveal a surprising degree of functional conservation in the effects of endocannabinoids on hedonic feeding across species and establish a new system to investigate the cellular and molecular basis of endocannabinoid system function in the regulation of food choice.

Gene variants in eating disorders. Focus on anorexia nervosa, bulimia nervosa, and binge-eating disorder

Eating disorders such as anorexia nervosa, bulimia nervosa and binge-eating disorder, have a deep social impact, concluding with death in cases of severe disease. Eating disorders affect up to 5% of the population in the industrialized countries, but probably the phenomenon is under-detection and under-diagnosis. Eating disorders are multifactorial disorders, resulting from the interaction between environmental triggers, psychological factors, but there is also a strong genetic component. In fact, genetic factors predispose for approximately 33-84% to anorexia nervosa, 28-83% to bulimia nervosa, and 41-57% to binge eating disorder. Twins and family studies have provided an unassailable proof on the heritability of these disorders. Other types of genetic studies, including genome-wide association studies, whole genome sequencing and linkage analysis, allowed to identify the genes and their variants associated with eating disorders and moreover global collaborative efforts have led to delineate the etiology of these disorders. Next Generation Sequencing technologies can be considered as an ideal diagnostic approach to identify not only the common variants, such as single nucleotide polymorphism, but also rare variants. Here we summarize the present knowledge on the molecular etiology and genetic determinants of eating disorders including serotonergic genes, dopaminergic genes, opioid genes, appetite regulation genes, endocannabinoid genes and vitamin D3.

Comparative effects of cannabinoid CB1 receptor agonist and antagonist on timing impulsivity induced by d-amphetamine in a differential reinforcement of low-rate response task in male rats

RATIONALE

In human beings and experimental animals, maladaptive impulsivity is manifested by the acute injection of psychostimulants, such as amphetamine. Cannabinoid CB1 receptors have been implicated in the regulation of stimulant-induced impulsive action, but the role of CB1 receptors in timing-related impulsive action by amphetamine remains unknown.

METHODS

Male rats were used in evaluating the effects of CB1 receptor antagonist and agonist (SR141716A and WIN55,212-2, respectively) systemically administered individually and combined with d-amphetamine on a differential reinforcement of low-rate response (DRL) task, an operant behavioral test of timing and behavioral inhibition characterized as a type of timing impulsive action.

RESULTS

A distinct pattern of DRL behavioral changes was produced by acute d-amphetamine (0, 0.5, 1.0, and 1.5 mg/kg) treatment in a dose-dependent fashion, whereas no significant dose effect was detected for acute SR141716A (0, 0.3, 1, and 3 mg/kg) or WIN55,212-2 (0, 0.5, 1, and 2 mg/kg) treatment. Furthermore, DRL behavior altered by 1.5 mg/kg d-amphetamine was reversed by a noneffective dose of SR141716A (3 mg/kg) pretreatment. The minimally influenced DRL behavior by 0.5 mg/kg d-amphetamine was affected by pretreatment with a noneffective dose of WIN55,212-2 (1 mg/kg).

CONCLUSION

These findings reveal that the activation and blockade of CB1 receptors can differentially modulate the timing impulsive action of DRL behavior induced by acute amphetamine treatment. Characterizing how CB1 receptors modulate impulsive behavior will deepen our understanding of the cannabinoid psychopharmacology of impulsivity and may be helpful in developing an optimal pharmacotherapy for reducing maladaptive impulsivity in patients with some psychiatric disorders.

Translational models of cannabinoid vapor exposure in laboratory animals

Cannabis is one of the most frequently used psychoactive substances in the world. The most common route of administration for cannabis and cannabinoid constituents such as Δ-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) is via smoking or vapor inhalation. Preclinical vapor models have been developed, although the vaporization devices and delivery methods vary widely across laboratories. This review examines the emerging field of preclinical vapor models with a focus on cannabinoid exposure in order to (1) summarize vapor exposure parameters and other methodological details across studies; (2) discuss the pharmacological and behavioral effects produced by exposure to vaporized cannabinoids; and (3) compare behavioral effects of cannabinoid vapor administration with those of other routes of administration. This review will serve as a guide for past and current vapor delivery methods in animals, synergize findings across studies, and propose future directions for this area of research.

The Endocannabinoid System and Eating Behaviours: a Review of the Current State of the Evidence

PURPOSE OF THE REVIEW

The endocannabinoid system (ENS) has emerged as an important factor in food intake and may have implications for nutrition research. The objective of the current report is to summarise the available evidence on the ENS and eating behaviour from both animal and human studies.

RECENT FINDINGS

The literature reviewed demonstrates a clear link between the ENS and eating behaviours. Overall, studies indicate that 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA) via cannabinoid receptor-1 (CNR1) binding may stimulate hunger and food intake while oleylethanolamide (OEA) may inhibit hunger. Mechanisms of these associations are not yet well understood, although the evidence suggests that there may be interactions with other physiological systems to consider. Most studies have been conducted in animal models, with few human studies available. Additional research is warranted among human populations into the ENS and eating behaviour. Evaluation of relationships between variation in ENS genes and dietary outcomes is an important area for investigation.

Locus coeruleus anchors a trisynaptic circuit controlling fear-induced suppression of feeding

The circuit mechanisms underlying fear-induced suppression of feeding are poorly understood. To help fill this gap, mice were fear conditioned, and the resulting changes in synaptic connectivity among the locus coeruleus (LC), the parabrachial nucleus (PBN), and the central nucleus of amygdala (CeA)-all of which are implicated in fear and feeding-were studied. LC neurons co-released noradrenaline and glutamate to excite PBN neurons and suppress feeding. LC neurons also suppressed inhibitory input to PBN neurons by inducing heterosynaptic, endocannabinoid-dependent, long-term depression of CeA synapses. Blocking or knocking down endocannabinoid receptors in CeA neurons prevented fear-induced depression of CeA synaptic transmission and fear-induced suppression of feeding. Altogether, these studies demonstrate that LC neurons play a pivotal role in modulating the circuitry that underlies fear-induced suppression of feeding, pointing to new ways of alleviating stress-induced eating disorders.

The effects of fatty acid amide hydrolase inhibition and monoacylglycerol lipase inhibition on habit formation in mice

Emerging data indicate that endocannabinoid signaling is critical to the formation of habitual behavior. Previous work demonstrated that antagonism of cannabinoid receptor type 1 (CB1R) with AM251 during operant training impairs habit formation, but it is not known if this behavioral effect is specific to disrupted signaling of the endocannabinoid ligands anandamide or 2-arachidonoyl glycerol (2-AG). Here, we used selective pharmacological compounds during operant training to determine the impact of fatty acid amide hydrolase (FAAH) inhibition to increase anandamide (and other n-acylethanolamines) or monoacylglycerol lipase (MAGL) inhibition to increase 2-AG levels on the formation of habitual behaviors in mice using a food-reinforced contingency degradation procedure. We found, contrary to our hypothesis, that inhibition of FAAH and of MAGL disrupted the formation of habits. Next, AM251 was administered during training to verify that impaired habit formation could be assessed using contingency degradation. AM251-exposed mice responded at lower rates during training and at higher rates in the test. To understand the inconsistency with published data, we performed a proof-of-principle dose-response experiment to compare AM251 in our vehicle-solution to the published vehicle-suspension on response rates. We found consistent reductions in response rate with increasing doses of AM251 in solution and an inconsistent dose-response relationship with AM251 in suspension. Together, our data suggest that further characterization of the role of CB1R signaling in the formation of habitual responding is warranted and that augmenting endocannabinoids may have clinical utility for prophylactically preventing aberrant habit formation such as that hypothesized to occur in substance use disorders.

The Neurobiology of Binge-eating Disorder Compared with Obesity: Implications for Differential Therapeutics

PURPOSE

Emerging work indicates divergence in the neurobiologies of binge-eating disorder (BED) and obesity despite their frequent co-occurrence. This review highlights specific distinguishing aspects of BED, including elevated impulsivity and compulsivity possibly involving the mesocorticolimbic dopamine system, and discusses implications for differential therapeutics for BED.

METHODS

This narrative review describes epidemiologic, clinical, genetic, and preclinical differences between BED and obesity. Subsequently, this review discusses human neuroimaging work reporting differences in executive functioning, reward processing, and emotion reactivity in BED compared with obesity. Finally, on the basis of the neurobiology of BED, this review identifies existing and new therapeutic agents that may be most promising given their specific targets based on putative mechanisms of action relevant specifically to BED.

FINDINGS

BED is characterized by elevated impulsivity and compulsivity compared with obesity, which is reflected in divergent neurobiological characteristics and effective pharmacotherapies. Therapeutic agents that influence both reward and executive function systems may be especially effective for BED.

IMPLICATIONS

Greater attention to impulsivity/compulsivity-related, reward-related, and emotion reactivity-related processes may enhance conceptualization and treatment approaches for patients with BED. Consideration of these distinguishing characteristics and processes could have implications for more targeted pharmacologic treatment research and interventions.

CB1 Receptor Signaling Modulates Amygdalar Plasticity during Context-Cocaine Memory Reconsolidation to Promote Subsequent Cocaine Seeking

Contextual drug-associated memories precipitate craving and relapse in cocaine users. Such associative memories can be weakened through interference with memory reconsolidation, a process by which memories are maintained following memory retrieval-induced destabilization. We hypothesized that cocaine-memory reconsolidation requires cannabinoid type 1 receptor (CB1R) signaling based on the fundamental role of the endocannabinoid system in synaptic plasticity and emotional memory processing. Using an instrumental model of cocaine relapse, we evaluated whether systemic CB1R antagonism (AM251; 3 mg/kg, i.p.) during memory reconsolidation altered (1) subsequent drug context-induced cocaine-seeking behavior as well as (2) cellular adaptations and (3) excitatory synaptic physiology in the basolateral amygdala (BLA) in male Sprague Dawley rats. Systemic CB1R antagonism, during, but not after, cocaine-memory reconsolidation reduced drug context-induced cocaine-seeking behavior 3 d, but not three weeks, later. CB1R antagonism also inhibited memory retrieval-associated increases in BLA zinc finger 268 (zif268) and activity regulated cytoskeletal-associated protein (Arc) immediate-early gene (IEG) expression and changes in BLA AMPA receptor (AMPAR) and NMDA receptor (NMDAR) subunit phosphorylation that likely contribute to increased receptor membrane trafficking and synaptic plasticity during memory reconsolidation. Furthermore, CB1R antagonism increased memory reconsolidation-associated spontaneous EPSC (sEPSC) frequency in BLA principal neurons during memory reconsolidation. Together, these findings suggest that CB1R signaling modulates cellular and synaptic mechanisms in the BLA that may facilitate cocaine-memory strength by enhancing reconsolidation or synaptic reentry reinforcement, or by inhibiting extinction-memory consolidation. These findings identify the CB1R as a potential therapeutic target for relapse prevention.SIGNIFICANCE STATEMENT Drug relapse can be triggered by the retrieval of context-drug memories on re-exposure to a drug-associated environment. Context-drug associative memories become destabilized on retrieval and must be reconsolidated into long-term memory stores to persist. Hence, targeted interference with memory reconsolidation can weaken maladaptive context-drug memories and reduce the propensity for drug relapse. Our findings indicate that cannabinoid type 1 receptor (CB1R) signaling is critical for context-cocaine memory reconsolidation and subsequent drug context-induced reinstatement of cocaine-seeking behavior. Furthermore, cocaine-memory reconsolidation is associated with CB1R-dependent immediate-early gene (IEG) expression and changes in excitatory synaptic proteins and physiology in the basolateral amygdala (BLA). Together, our findings provide initial support for CB1R as a potential therapeutic target for relapse prevention.

Cannabinoid CB1 Receptors in the Intestinal Epithelium Are Required for Acute Western-Diet Preferences in Mice

The endocannabinoid system plays an important role in the intake of palatable food. For example, endocannabinoid signaling in the upper small-intestinal epithelium is increased (i) in rats after tasting dietary fats, which promotes intake of fats, and (ii) in a mouse model of diet-induced obesity, which promotes overeating via impaired nutrient-induced gut-brain satiation signaling. We now utilized a combination of genetic, pharmacological, and behavioral approaches to identify roles for cannabinoid CB₁Rs in upper small-intestinal epithelium in preferences for a western-style diet (WD, high-fat/sucrose) versus a standard rodent diet (SD, low-fat/no sucrose). Mice were maintained on SD in automated feeding chambers. During testing, mice were given simultaneous access to SD and WD, and intakes were recorded. Mice displayed large preferences for the WD, which were inhibited by systemic pretreatment with the cannabinoid CB₁R antagonist/inverse agonist, AM251, for up to 3 h. We next used our novel intestinal epithelium-specific conditional cannabinoid CB₁R-deficient mice (IntCB₁-/-) to investigate if intestinal CB₁Rs are necessary for WD preferences. Similar to AM251 treatment, preferences for WD were largely absent in IntCB₁-/- mice when compared to control mice for up to 6 h. Together, these data suggest that CB₁Rs in the murine intestinal epithelium are required for acute WD preferences.

Cannabidiol inhibits sucrose self-administration by CB1 and CB2 receptor mechanisms in rodents

A growing number of studies suggest therapeutic applications of cannabidiol (CBD), a recently U.S. Food and Drug Administration (FDA)-approved medication for epilepsy, in treatment of many other neuropsychological disorders. However, pharmacological action and the mechanisms by which CBD exerts its effects are not fully understood. Here, we examined the effects of CBD on oral sucrose self-administration in rodents and explored the receptor mechanisms underlying CBD-induced behavioral effects using pharmacological and transgenic approaches. Systemic administration of CBD (10, 20, and 40 mg/kg, ip) produced a dose-dependent reduction in sucrose self-administration in rats and in wild-type (WT) and CB1-/- mice but not in CB2-/- mice. CBD appeared to be more efficacious in CB1-/- mice than in WT mice. Similarly, pretreatment with AM251, a CB1R antagonist, potentiated, while AM630, a selective CB2R antagonist, blocked CBD-induced reduction in sucrose self-administration, suggesting the involvement of CB1 and CB2 receptors. Furthermore, systemic administration of JWH133, a selective CB2R agonist, also produced a dose-dependent reduction in sucrose self-administration in WT and CB1-/- mice, but not in CB2-/- mice. Pretreatment with AM251 enhanced, while AM630 blocked JWH133-induced reduction in sucrose self-administration in WT mice, suggesting that CBD inhibits sucrose self-administration likely by CB1 receptor antagonism and CB2 receptor agonism. Taken together, the present findings suggest that CBD may have therapeutic potential in reducing binge eating and the development of obesity.

Adolescent CB1 receptor antagonism influences subsequent social interactions and neural activity in female rats

We previously demonstrated that repeated exposure to the CB1 receptor antagonist/inverse agonist AM251 in adolescence (PND 30-44) increased social interactions in female rats when tested 48 h after the final exposure to the antagonist. Here, we investigated whether the increased sociality would be present after a longer drug washout period (5 days) in both male and female rats (experiment 1), and sought to identify candidate brain regions that may explain the observed differences in social behaviours between AM251 and vehicle-treated female rats (experiment 2). While drug-free, adolescent AM251 treatment increased social interactions in females and not in males. AM251 female rats had increased neural activity (as measured by the expression of early growth response protein-1; EGR-1) in the nucleus accumbens shell and cingulate gyrus of the medial prefrontal cortex, with no observed differences in EGR-1 expression in the dorsal hippocampus, nucleus accumbens core, or prelimbic and infralimbic subdivisions of the medial prefrontal cortex relative to vehicle rats. Together, these results demonstrate a sex-specific role of adolescent endocannabinoid signalling in the normative development of social behaviours and provide further support for adolescence as a vulnerable period for the effects of altered endocannabinoid signalling.

Cannabinoids, Chemical Senses, and Regulation of Feeding Behavior

The herb Cannabis sativa has been traditionally used in many cultures and all over the world for thousands of years as medicine and recreation. However, because it was brought to the Western world in the late 19th century, its use has been a source of controversy with respect to its physiological effects as well as the generation of specific behaviors. In this regard, the CB1 receptor represents the most relevant target molecule of cannabinoid components on nervous system and whole-body energy homeostasis. Thus, the promotion of CB1 signaling can increase appetite and stimulate feeding, whereas blockade of CB1 suppresses hunger and induces hypophagia. Taste and flavor are sensory experiences involving the oral perception of food-derived chemicals and drive a primal sense of acceptable or unacceptable for what is sampled. Therefore, research within the last decades focused on deciphering the effect of cannabinoids on the chemical senses involved in food perception and consequently in the pattern of feeding. In this review, we summarize the data on the effect of cannabinoids on chemical senses and their influences on food intake control and feeding behavior.

Disrupting the endocannabinoid system in early adolescence negatively impacts sociability

Animal models suggest that the endocannabinoid system (eCS) helps regulate various aspects of social behavior, including play behavior and social reward, during adolescence. Properly tuned endocannabinoid signaling may be a critical developmental component in the emergence of normal adult sociability. In the current experiment, we attempted to pharmacologically disrupt endocannabinoid tone during early adolescence, and then measure the behavioral effects at two subsequent time points. 36 male and 36 female Long Evans rats received daily injections of one of three treatments between post-natal day (PND) 25-39: 1) vehicle treatment, 2) 0.4 mg/kg CP55,940 (a potent CB1/CB2 receptor agonist), or 3) 0.5 mg/kg AM251 (a CB1 receptor antagonist/inverse agonist). Both soon after treatment (PND 40-44) and several weeks later (PND 66-70), subjects were tested in an elevated plus maze (EPM) for anxiety and in a three-chambered apparatus for sociability. For the latter test, the number of entries into each chamber and the amount of time spent investigating each target were measured. Analyses revealed significant main effects of both sex and age on sociability: males expressed greater sociability compared to females, and sociability was higher in adolescence than adulthood. Most importantly, drug treatment (both CP55,940 and AM251) attenuated sociability in adolescence without having a significant effect on anxiety in the EPM. However, this effect did not persist into adulthood. These results indicate that pharmacological disruption of endocannabinoid tone - through either chronic agonism or antagonism of cannabinoid receptors - during early adolescence has a detrimental effect on sociability. This effect may be caused by transient, compensatory alterations in the eCS.

Effect of acute Δ9-tetrahydrocannabinol administration on subjective and metabolic hormone responses to food stimuli and food intake in healthy humans: a randomized, placebo-controlled study

BACKGROUND

The endocannabinoid system (ECS) is considered a key player in the neurophysiology of food reward. Animal studies suggest that the ECS stimulates the sensory perception of food, thereby increasing its incentive-motivational and/or hedonic properties and driving consumption, possibly via interactions with metabolic hormones. However, it remains unclear to what extent this can be extrapolated to humans.

OBJECTIVE

We aimed to investigate the effect of oral Δ9-tetrahydrocannabinol (THC) on subjective and metabolic hormone responses to visual food stimuli and food intake.

METHODS

Seventeen healthy subjects participated in a single-blinded, placebo-controlled, 2 × 2 crossover trial. In each of the 4 visits, subjective "liking" and "wanting" ratings of high- and low-calorie food images were acquired after oral THC or placebo administration. The effect on food intake was quantified in 2 ways: via ad libitum oral intake (half of the visits) and intragastric infusion (other half) of chocolate milkshake. Appetite-related sensations and metabolic hormones were measured at set time points throughout each visit.

RESULTS

THC increased "liking" (P = 0.031) and "wanting" ratings (P = 0.0096) of the high-calorie, but not the low-calorie images, compared with placebo. Participants consumed significantly more milkshake after THC than after placebo during oral intake (P = 0.0005), but not intragastric infusion, of milkshake. Prospective food consumption ratings during the food image paradigm were higher after THC than after placebo (P = 0.0039). THC also increased plasma motilin (P = 0.0021) and decreased octanoylated ghrelin (P = 0.023) concentrations before milkshake consumption (i.e., in both oral intake and intragastric infusion test sessions), whereas glucagon-like peptide 1 responses to milkshake intake were attenuated by THC during both oral (P = 0.0002) and intragastric (P = 0.0055) administration.

CONCLUSIONS

These findings suggest that the ECS drives food intake by interfering with anticipatory, cephalic phase, and metabolic hormone responses. This trial was registered at clinicaltrials.gov as NCT02310347.

Cannabinoids for the treatment of neuropsychiatric symptoms, pain and weight loss in dementia

PURPOSE OF REVIEW

Efficacious treatment for neuropsychiatric symptoms (NPS), pain and weight loss for dementia patients is desperately needed. This review presents an up-to-date look at the literature investigating the use of cannabinoid for these symptoms in dementia.

RECENT FINDINGS

We searched electronically for publications regarding cannabinoid use in dementia, with a focus on Alzheimer's disease. Seven studies and one case report have been conducted to examine the use of cannabinoids for the treatment of NPS of dementia, and three of these trials reported on the effect of cannabinoids on weight. Five studies reported decreased agitation or improvements in sleep with cannabinoid use. One crossover trial found that cannabinoids positively impacted weight, whereas a chart review study found no impact on weight with cannabinoids, but an increase in food intake. There were no trials examining the use of cannabinoids for pain in dementia.

SUMMARY

Findings from trials with small sample sizes and various clinical populations suggest that cannabinoid use may be well tolerated and effective for treatment of NPS such as agitation as well as weight and pain management in patients with dementia. Additional studies are necessary to further elucidate the relative risks and benefits of this treatment.

Cannabinoid-1 receptor neutral antagonist reduces binge-like alcohol consumption and alcohol-induced accumbal dopaminergic signaling

Binge alcohol (ethanol) drinking is associated with profound adverse effects on our health and society. Rimonabant (SR141716A), a CB1 receptor inverse agonist, was previously shown to be effective for nicotine cessation and obesity. However, studies using rimonabant were discontinued as it was associated with an increased risk of depression and anxiety. In the present study, we examined the pharmacokinetics and effects of AM4113, a novel CB1 receptor neutral antagonist on binge-like ethanol drinking in C57BL/6J mice using a two-bottle choice drinking-in-dark (DID) paradigm. The results indicated a slower elimination of AM4113 in the brain than in plasma. AM4113 suppressed ethanol consumption and preference without having significant effects on body weight, ambulatory activity, preference for tastants (saccharin and quinine) and ethanol metabolism. AM4113 pretreatment reduced ethanol-induced increase in dopamine release in nucleus accumbens. Collectively, these data suggest an important role of CB1 receptor-mediated regulation of binge-like ethanol consumption and mesolimbic dopaminergic signaling, and further points to the potential utility of CB1 neutral antagonists for the treatment of binge ethanol drinking.

Effects of CB1 receptor antagonism and stress exposures in adolescence on socioemotional behaviours, neuroendocrine stress responses, and expression of relevant proteins in the hippocampus and prefrontal cortex in rats

Little is known about the consequences of altered endocannabinoid signalling in adolescence. We hypothesized that CB1 receptor antagonism (AM251, 1 mg/kg) and stress exposures (1 h confinement stress) in adolescence (daily, postnatal days 30-44) would interact to increase neuroendocrine stress responses and anxiety when investigated a minimum of 24 h after drug and stress treatments; these treatment effects were independent of each other. Changes in homecage behaviour and in weight gain confirmed that both males and females were sensitive to the treatments. Nevertheless, in males, repeated AM251 administration was without effect on any of the measures investigated in days post-treatment. Males had reduced corticosterone release to the repeated stress and had increased GAD67 expression in the ventral hippocampus under baseline conditions. In females, AM251 also reduced weight gain and increased stereotypic behaviours in the homecage; these same females showed increased sociality, reduced CB1 receptor expression in the dorsal hippocampus, and increased GAD67 expression in the prefrontal cortex. Further, females exposed to repeated stress had enhanced recovery to baseline corticosterone concentrations after stress. The inclusion of a non-injected comparison group also revealed stress of injection effects in both sexes that otherwise would have been masked. Together, the findings demonstrate effects of CB1 receptor antagonism and stress that were more evident in females than males, suggesting that females may be more vulnerable to the consequences of disrupted endocannabinoid signalling during adolescence.

The CB1 Receptor as the Cornerstone of Exostasis

The type-1 cannabinoid receptor (CB1) is the main effector of the endocannabinoid system (ECS), which is involved in most brain and body functions. In this Perspective, we provide evidence indicating that CB1 receptor functions are key determinants of bodily coordinated exostatic processes. First, we will introduce the concepts of endostasis and exostasis as compensation or accumulation for immediate or future energy needs and discuss how exostasis has been necessary for the survival of species during evolution. Then, we will argue how different specific biological functions of the CB1 receptor in the body converge to provide physiological exostatic processes. Finally, we will introduce the concept of proactive evolution-induced diseases (PEIDs), which helps explain the seeming paradox that an evolutionary-selected physiological function can become the cause of epidemic pathological conditions, such as obesity. We propose here a possible unifying theory of CB1 receptor functions that can be tested by future experimental studies.

Binge-eating disorder: Clinical and therapeutic advances

Binge-eating disorder (BED) is the most prevalent eating disorder with estimates of 2-5% of the general adult population. Nonetheless, its pathophysiology is poorly understood. Furthermore, there exist few therapeutic options for its effective treatment. Here we review the current state of binge-eating neurobiology and pharmacology, drawing from clinical therapeutic, neuroimaging, cognitive, human genetic and animal model studies. These studies, which are still in their infancy, indicate that while there are many gaps in our knowledge, several key neural substrates appear to underpin binge-eating and may be conserved between human and animals. This observation suggests that behavioral intermediate phenotypes or endophenotypes relevant to BED may be modeled in animals, facilitating the identification and testing of novel pharmacological targets. The development of novel, safe and effective pharmacological therapies for the treatment of BED will enhance the ability of clinicians to provide optimal care for people with BED.

Analysis of natural product regulation of cannabinoid receptors in the treatment of human disease

The organized, tightly regulated signaling relays engaged by the cannabinoid receptors (CBs) and their ligands, G proteins and other effectors, together constitute the endocannabinoid system (ECS). This system governs many biological functions including cell proliferation, regulation of ion transport and neuronal messaging. This review will firstly examine the physiology of the ECS, briefly discussing some anomalies in the relay of the ECS signaling as these are consequently linked to maladies of global concern including neurological disorders, cardiovascular disease and cancer. While endogenous ligands are crucial for dispatching messages through the ECS, there are also commonalities in binding affinities with copious exogenous ligands, both natural and synthetic. Therefore, this review provides a comparative analysis of both types of exogenous ligands with emphasis on natural products given their putative safer efficacy and the role of Δ9-tetrahydrocannabinol (Δ9-THC) in uncovering the ECS. Efficacy is congruent to both types of compounds but noteworthy is the effect of a combination therapy to achieve efficacy without unideal side-effects. An example is Sativex that displayed promise in treating Huntington's disease (HD) in preclinical models allowing for its transition to current clinical investigation. Despite the in vitro and preclinical efficacy of Δ9-THC to treat neurodegenerative ailments, its psychotropic effects limit its clinical applicability to treating feeding disorders. We therefore propose further investigation of other compounds and their combinations such as the triterpene, α,β-amyrin that exhibited greater binding affinity to CB₁ than CB₂ and was more potent than Δ9-THC and the N-alkylamides that exhibited CB₂ selective affinity; the latter can be explored towards peripherally exclusive ECS modulation. The synthetic CB₁ antagonist, Rimonabant was pulled from commercial markets for the treatment of diabetes, however its analogue SR144528 maybe an ideal lead molecule towards this end and HU-210 and Org27569 are also promising synthetic small molecules.

Differential effects of cannabinoid CB1 inverse agonists and antagonists on impulsivity in male Sprague Dawley rats: identification of a possibly clinically relevant vulnerability involving the serotonin 5HT1A receptor

RATIONALE

Cannabinoid CB1 inverse agonists hold therapeutic promise as appetite suppressants but have produced suicidal behaviors among a small subpopulation in clinical trials. Anatomical and pharmacological evidence implicate the 5HT_1A serotonin receptor in suicide in humans and impulsivity in humans and animals.

OBJECTIVE

The objective of the study is to assess whether 5HT_1A blockade is necessary for CB1 ligands to produce impulsivity.

METHODS

Sprague Dawley rats were administered the CB1 inverse agonist AM 251, the CB1 antagonist AM 6527, or the peripherally restricted antagonist AM 6545, with or without pretreatment with the 5HT_1A antagonist WAY 100,635 (WAY) on the paced fixed consecutive number (FCN) task, which measures choice to terminate a chain of responses prematurely. As FCN is sensitive to changes in time perception, which have been demonstrated with CB1 blockade, a novel variable consecutive number task with discriminative stimulus (VCN-S _D ) was also performed and proposed to be less sensitive to changes in timing.

RESULTS

Pretreatment with WAY enabled mild but significant reductions in FCN accuracy for AM 251 and AM 6527. No effects were found for AM 6545. On the VCN-S _D task, substantial impairments were found for the combination of WAY and AM 251.

CONCLUSIONS

AM 251, but not the antagonists AM 6527 or AM 6545, produced impulsivity only following systemic 5HT_1A blockade. Although preliminary, the results may indicate that disrupted serotonin signaling produces a vulnerability to undesirable effects of CB1 inverse agonists, which is not evident in the general population. Furthermore, neutral CB1 antagonists do not produce this effect and therefore may have greater safety.

The utility of behavioral economics in expanding the free-feed model of obesity

Animal models of obesity are numerous and diverse in terms of identifying specific neural and peripheral mechanisms related to obesity; however, they are limited when it comes to behavior. The standard behavioral measure of food intake in most animal models occurs in a free-feeding environment. While easy and cost-effective for the researcher, the free-feeding environment omits some of the most important features of obesity-related food consumption-namely, properties of food availability, such as effort and delay to obtaining food. Behavior economics expands behavioral measures of obesity animal models by identifying such behavioral mechanisms. First, economic demand analysis allows researchers to understand the role of effort in food procurement, and how physiological and neural mechanisms are related. Second, studies on delay discounting contribute to a growing literature that shows that sensitivity to delayed food- and food-related outcomes is likely a fundamental process of obesity. Together, these data expand the animal model in a manner that better characterizes how environmental factors influence food consumption.

CB1 antagonism produces behaviors more consistent with satiety than reduced reward value in food-maintained responding in rats

Cannabinoid CB1 antagonists are widely known to reduce motivation for food, but it is not known whether they induce satiety or reduce reward value of food. It may therefore be necessary to compare effects of altered satiety and reward food value in the same appetitive task, and determine whether CB1 antagonism produces a behavior pattern similar to either, both, or neither. A fine-grained analysis of fixed-ratio 10 (FR10) responding for palatable food initially included number and duration of, and between, all lever presses and food tray entries in order to differentiate the pattern of suppression of prefeeding from that caused by reducing the reward value of the pellets with quinine. Discriminant function analysis then determined that these manipulations were best differentiated by effects on tray entries, pellet retrieval latencies, and time of the first response. At 0.5 mg/kg, AM 6527 produced similar effects to reducing reward value, but at 1.0 and 4.0 mg/kg, effects were more similar to those when animals were satiated. We conclude that AM 6527 both reduced reward value and enhanced satiety, but as dose increased, effects on satiety became much more prominent. These findings contribute to knowledge about the behavioral processes affected by CB1 antagonism.

A runner's high depends on cannabinoid receptors in mice

Exercise is rewarding, and long-distance runners have described a runner's high as a sudden pleasant feeling of euphoria, anxiolysis, sedation, and analgesia. A popular belief has been that endogenous endorphins mediate these beneficial effects. However, running exercise increases blood levels of both β-endorphin (an opioid) and anandamide (an endocannabinoid). Using a combination of pharmacologic, molecular genetic, and behavioral studies in mice, we demonstrate that cannabinoid receptors mediate acute anxiolysis and analgesia after running. We show that anxiolysis depends on intact cannabinoid receptor 1 (CB1) receptors on forebrain GABAergic neurons and pain reduction on activation of peripheral CB1 and CB2 receptors. We thus demonstrate that the endocannabinoid system is crucial for two main aspects of a runner's high. Sedation, in contrast, was not influenced by cannabinoid or opioid receptor blockage, and euphoria cannot be studied in mouse models.

Pharmacological modulation of the endocannabinoid signalling alters binge-type eating behaviour in female rats

BACKGROUND AND PURPOSE

Binge eating disorder (BED) is characterized by excessive food intake during short periods of time. Recent evidence suggests that alterations in the endocannabinoid signalling could be involved in the pathophysiology of BED. In this study, we investigated whether pharmacological manipulation of endocannabinoid transmission may be effective in modulating the aberrant eating behaviour present in a validated rat model of BED.

EXPERIMENTAL APPROACH

Binge-type eating was induced in female rats by providing limited access to an optional source of dietary fat (margarine). Rats were divided into three groups, all with ad libitum access to chow and water: control (C), with no access to margarine; low restriction (LR), with 2 h margarine access 7 days a week; high restriction (HR), with 2 h margarine access 3 days a week.

KEY RESULTS

Compared with the LR group, the HR group consumed more margarine and this was accompanied by an increase in body weight. The cannabinoid CB₁/CB₂ receptor agonist Δ⁹-tetrahydrocannabinol significantly increased margarine intake selectively in LR rats, while the fatty acid amide hydrolase inhibitor URB597 showed no effect. The CB₁ receptor inverse agonist/antagonist rimonabant dose-dependently reduced margarine intake in HR rats. Notably, in HR rats, chronic treatment with a low dose of rimonabant induced a selective long-lasting reduction in margarine intake that did not develop tolerance, and a significant and persistent reduction in body weight.

CONCLUSIONS AND IMPLICATIONS

Chronic pharmacological blockade of CB₁ receptors reduces binge eating behaviour in female rats and may prove effective in treating BED, with an associated significant reduction in body weight.

Blockade of CB1 receptors prevents retention of extinction but does not increase low preincubated conditioned fear in the fear incubation procedure

We recently developed a procedure to study fear incubation, in which rats given 100 tone-shock pairings over 10 days show low fear 2 days after conditioned fear training and high fear after 30 days. Notably, fear 2 days after 10 sessions of fear conditioning is lower than fear seen 2 days after a single session of fear conditioning, suggesting that fear is suppressed. Here, we investigate the potential role of CB1 receptor activation by endocannabinoids in this fear suppression. We subjected rats to 10 days of fear conditioning and then administered systemic injections of the CB1 receptor antagonist SR141716 before a conditioned fear test was conducted 2 days later under extinction conditions. A second test was conducted without any injections on the following day (3 days after training) to examine retention of fear extinction. SR141716 injections did not increase fear expression 2 days after extended fear conditioning or affect within-session extinction; however, it impaired retention of between-session fear extinction in the day 3 test. These data suggest that CB1 receptor activation does not suppress fear soon after extended fear conditioning in the fear incubation task. The data also add to the existing literature on the role of CB1 receptors in extinction of conditioned fear.

Translational strategies for therapeutic development in nicotine addiction: rethinking the conventional bench to bedside approach

Tobacco produces an impressive burden of disease resulting in premature death in half of users. Despite effective smoking cessation medications (nicotine replacement therapies, bupropion and varenicline), there is a very high rate of relapse following quit attempts. The use of efficient strategies for the development of novel treatments is a necessity. A 'bench to bedside strategy' was initially used to develop cannabinoid CB1 receptor antagonists for the treatment of nicotine addiction. Unfortunately, after being tested on experimental animals, what seemed to be an interesting approach for the treatment of nicotine addiction resulted in serious unwanted side effects when tested in humans. Current research is focusing again on pre-clinical models in an effort to eliminate unwanted side effects while preserving the initially observed efficacy. A 'bed side to bench strategy' was used to study the role of the insula (part of the frontal cortex) in nicotine addiction. This line of research started based on clinical observations that patients suffering stroke-induced lesions to the insula showed a greater likelihood to report immediate smoking cessation without craving or relapse. Subsequently, animal models of addiction are used to explore the role of insula in addiction. Due to the inherent limitations existing in clinical versus preclinical studies, the possibility of close interaction between both models seems to be critical for the successful development of novel therapeutic strategies for nicotine dependence.

Overlap of food addiction and substance use disorders definitions: analysis of animal and human studies

Food has both homeostatic and hedonic components, which makes it a potent natural reward. Food related reward could therefore promote an escalation of intake and trigger symptoms associated to withdrawal, suggesting a behavioral parallel with substance abuse. Animal and human theoretical models of food reward and addiction have emerged, raising further interrogations on the validity of a bond between Substance Use Disorders, as clinically categorized in the DSM 5, and food reward. These models propose that highly palatable food items, rich in sugar and/or fat, are overly stimulating to the brain's reward pathways. Moreover, studies have also investigated the possibility of causal link between food reward and the contemporary obesity epidemic, with obesity being potentiated and maintained due to this overwhelming food reward. Although natural rewards are a hot topic in the definition and categorization of Substance Use Disorders, proofs of concept and definite evidence are still inconclusive. This review focuses on available results from experimental studies in animal and human models exploring the concept of food addiction, in an effort to determine if it depicts a specific phenotype and if there is truly a neurobiological similarity between food addiction and Substance Use Disorders. It describes results from sugar, fat and sweet-fat bingeing in rodent models, and behavioral and neurobiological assessments in different human populations. Although pieces of behavioral and neurobiological evidence supporting a food addiction phenotype in animals and humans are interesting, it seems premature to conclude on its validity.

Involvement of the cannabinoid CB1 receptor in modulation of dopamine output in the prefrontal cortex associated with food restriction in rats

Increase in dopamine output on corticolimbic structures, such as medial prefrontal cortex (mPFC) and nucleus accumbens, has been related to reward effects associated with palatable food or food presentation after a fasting period. The endocannabinoid system regulates feeding behavior through a modulatory action on different neurotransmitter systems, including the dopaminergic system. To elucidate the involvement of type 1 cannabinoid receptors in the regulation of dopamine output in the mPFC associated with feeding in hungry rats, we restricted the food availability to a 2-h period daily for 3 weeks. In food-restricted rats the extracellular dopamine concentration in the mPFC increased starting 80 min before food presentation and returned to baseline after food removal. These changes were attenuated in animals treated with the CB1 receptor antagonist SR141716. To better understand how food restriction can change the response of mesocortical dopaminergic neurons, we studied several components of the neuronal circuit that regulates dopamine output in the mPFC. Patch-clamp experiments revealed that the inhibitory effect of the CB1 receptor agonist WIN 55,212-2 on GABAergic sIPSC frequency was diminished in mPFC neurons of FR compared to fed ad libitum rats. The basal sIPSC frequency resulted reduced in mPFC neurons of food-restricted rats, suggestive of an altered regulation of presynaptic GABA release; these changes were accompanied by an enhanced excitability of mPFC and ventral tegmental area neurons. Finally, type 1 cannabinoid receptor expression in the mPFC was reduced in food-restricted rats. Together, our data support an involvement of the endocannabinoid system in regulation of dopamine release in the mPFC through changes in GABA inhibitory synapses and suggest that the emphasized feeding-associated increase in dopamine output in the mPFC of food-restricted rats might be correlated with an altered expression and function of type 1 cannabinoid receptor in this brain region.

Endocannabinoid 2-Arachidonoylglycerol Self-Administration by Sprague-Dawley Rats and Stimulation of in vivo Dopamine Transmission in the Nucleus Accumbens Shell

2-Arachidonoylglycerol (2-AG) is the most potent endogenous ligand of brain cannabinoid CB1 receptors and is synthesized on demand from 2-arachidonate-containing phosphoinositides by the action of diacylglycerol lipase in response to increased intracellular calcium. Several studies indicate that the endocannabinoid (eCB) system is involved in the mechanism of reward and that diverse drugs of abuse increase brain eCB levels. In addition, eCB are self-administered (SA) by squirrel monkeys, and anandamide increases nucleus accumbens (NAc) shell dopamine (DA) in rats. To date, there is no evidence on the reinforcing effects of 2-AG and its effects on DA transmission in rodents. In order to fill this gap, we studied intravenous 2-AG SA and monitored the effect of 2-AG on extracellular DA in the NAc shell and core via microdialysis in male Sprague-Dawley rats. Rats were implanted with jugular catheters and trained to self-administer 2-AG [25 mg/kg/inf intravenously (iv)] in single daily 1 h sessions for 5 weeks under initial fixed ratio (FR) 1 schedule. The ratio was subsequently increased to FR2. Active nose poking increased from the 6th SA session (acquisition phase) but no significant increase of nose pokes was observed after FR2. When 2-AG was substituted for vehicle (25th SA session, extinction phase), rate responding as well as number of injections slowly decreased. When vehicle was replaced with 2-AG, SA behavior immediately recovered (reacquisition phase). The reinforcing effects of 2-AG in SA behavior were fully blocked by the CB1 receptor inverse agonist/antagonist rimonabant (1 mg/kg intraperitoneally, 30 min before SA session). In the microdialysis studies, we observed that 2-AG (0.1-1.0 mg/kg iv) preferentially stimulates NAc shell as compared to the NAc core. NAc shell DA increased by about 25% over basal value at the highest doses tested (0.5 and 1.0 mg/kg iv). The results obtained suggest that the eCB system, via 2-AG, plays an important role in reward.

Neutral antagonism at the cannabinoid 1 receptor: a safer treatment for obesity

Obesity is a global problem with often strong neurobiological underpinnings. The cannabinoid 1 receptor (CB1R) was put forward as a promising drug target for antiobesity medication. However, the first marketed CB1R antagonist/inverse agonist rimonabant was discontinued, as its use was occasionally associated with negative affect and suicidality. In artificial cell systems, CB1Rs can become constitutively active in the absence of ligands. Here, we show that such constitutive CB1R activity also regulates GABAergic and glutamatergic neurotransmission in the ventral tegmental area and basolateral amygdala, regions which regulate motivation and emotions. We show that CB1R inverse agonists like rimonabant suppress the constitutive CB1R activity in such regions, and cause anxiety and reduced motivation for reward. The neutral CB1R antagonist NESS0327 does not suppress constitutive activity and lacks these negative effects. Importantly, however, both rimonabant and NESS0327 equally reduce weight gain and food intake. Together, these findings suggest that neutral CB1R antagonists can treat obesity efficiently and more safely than inverse agonists.

Small animal PET imaging of the type 1 cannabinoid receptor in a rodent model for anorexia nervosa

PURPOSE

Several lines of evidence strongly implicate a dysfunctional endocannabinoid system (ECS) in eating disorders. Using [(18)F]MK-9470 and small animal positron emission tomography (PET), we investigated for the first time cerebral changes in type 1 cannabinoid (CB1) receptor binding in vivo in the activity-based rat model of anorexia (ABA), in comparison to distinct motor- and food-related control conditions and in relation to gender and behavioural variables.

METHODS

In total, experiments were conducted on 80 Wistar rats (23 male and 57 female). Male rats were assigned to the cross-sectional conditions: ABA (n = 12) and CONTROL (n = 11), whereas female rats were divided between two settings: (1) a cross-sectional design using ABA (n = 13), CONTROL (n = 9), and two extra control conditions for each of the variables manipulated in ABA, i.e. DIET (n = 8) and WHEEL (n = 9), and (2) a longitudinal one using ABA (n = 10) and CONTROL (n = 8) studied at baseline, during the model and upon recovery. The ABA group was subjected to food restriction in the presence of a running wheel, the DIET group to food restriction without wheel, the WHEEL group to a normal diet with wheel and CONTROL animals had a normal diet and no running wheel. Parametric CB1 receptor images of each group were spatially normalized to Paxinos space and analysed voxel-wise.

RESULTS

In the ABA model, absolute [(18)F]MK-9470 binding was significantly increased in all cortical and subcortical brain areas as compared to control conditions (male +67 %; female >51%, all p cluster < 6.3×10(-6)) that normalized towards baseline values after weight gain. Additionally, relative [(18)F]MK-9470 binding was increased in the hippocampus, inferior colliculus and entorhinal cortex of female ABA (+4.6%; p cluster < 1.3×10(-6)), whereas no regional differences were observed in male subjects. Again, relative [(18)F]MK-9470 binding values normalized upon weight gain.

CONCLUSION

These data point to a widespread transient disturbance of the endocannabinoid transmission, specifically for CB1 receptors in the ABA model. Our data also suggest (1) gender effects on regional CB1 receptor binding in the hippocampus and (2) add further proof to the validity of the ABA model to mimic aspects of human disease.

Low dose naloxone attenuates the pruritic but not anorectic response to rimonabant in male rats

RATIONALE

Previous research suggests that the acute anorectic effect of cannabinoid CB1 receptor antagonist/inverse agonists may be secondary to response competition from the compulsive scratching and grooming syndrome characteristic of these agents.

OBJECTIVES

As the pruritic effect of rimonabant can be attenuated by the opioid receptor antagonist naloxone, these studies test the prediction that naloxone co-treatment should prevent acute rimonabant anorexia.

METHODS

Two experiments comprehensively profiled the behavioural effects of an anorectic dose of rimonabant (1.5 mg/kg) in the absence or presence of naloxone (experiment 1: 0.01 or 0.1 mg/kg; experiment 2: 0.05 mg/kg).

RESULTS

In both experiments, rimonabant not only significantly suppressed food intake and time spent eating but also induced compulsive scratching and grooming. In experiment 1, although the lower dose of naloxone seemed to weakly attenuate the effects of rimonabant both on ingestive and compulsive behaviours, the higher dose more strongly suppressed the compulsive elements but did not significantly affect the anorectic response. The results of experiment 2 showed that naloxone at a dose which markedly attenuated rimonabant-induced grooming and scratching did not alter the effects of the compound on food intake or time spent feeding. The apparent independence of the ingestive and compulsive effects of rimonabant was confirmed by the observation that despite a 'normalising' effect of naloxone co-treatment on behavioural structure (BSS), the opioid antagonist did not impact the suppressant effect of rimonabant on peak feeding.

CONCLUSION

The acute anorectic response to rimonabant would not appear to be secondary to compulsive scratching and grooming.

Changes in cannabinoid CB(1) receptor functionality in the female rat prefrontal cortex following a high fat diet

AIMS

A high fat diet (HFD) has been found to affect neurotransmission in the prefrontal cortex, but the effects of this dietary regime upon the endocannabinoid system has not been studied in this brain region. In consequence, in the present study, we have investigated the effect of HFD for up to 20 weeks upon the endocannabinoid system in the prefrontal cortex of female rats.

MAIN METHODS

CB1 receptor functionality was measured using CP55,940-stimulated [(35)S]GTPγS autoradiography. Fatty acid amide hydrolase and monoacylglycerol lipase activities were analysed in brain regions by assessing rates of [(3)H]anandamide and JZL184-sensitive [(3)H]2-oleoylglycerol hydrolysis, respectively.

KEY FINDINGS

In the prefrontal cortex, a significantly greater stimulation of [(35)S]GTPγS binding by CP55,940 was seen following 4-12, but not 16-20 weeks of HFD. No significant changes were seen for the caudate-putamen, CA1-CA3 region of the hippocampus or the dentate gyrus. The increased response for the 12 week animals was not accompanied by a significant change in the receptor density, measured with [(3)H]CP55,940 autoradiography. No significant changes in the activity of the endocannabinoid hydrolytic enzymes fatty acid amide or monoacylglycerol lipase were seen in the prefrontal cortex, hippocampus, amygdala or hypothalamus following either 12 or 20 weeks of HFD.

SIGNIFICANCE

It is concluded that HFD produces an increased CB1 receptor functionality in the prefrontal cortex of female rats. Given that the endocannabinoid system regulates neurotransmission in the prefrontal cortex, the present data would implicate this system in the disturbed prefrontal cortical activity in this region following a high fat diet.

Cannabis and Δ9-tetrahydrocannabinol (THC) for weight loss?

Obesity is one of the highest preventable causes of morbidity and mortality in the developed world [1]. It has been well known for a long time that exposure to cannabis produces an increase of appetite (a phenomenon referred to as the 'munchies'). This phenomenon led to an exploration of the role of the endocannabinoid system in the regulation of obesity and associated metabolic syndrome. This effort subsequently led to the development of a successful therapeutic approach for obesity that consisted of blocking the cannabinoid CB1 receptors using ligands such as Rimonabant in order to produce weight loss and improve metabolic profile [2]. Despite being efficacious, Rimonabant was associated with increased rates of depression and anxiety and therefore removed from the market. We recently discovered that the prevalence of obesity is paradoxically much lower in cannabis users as compared to non-users and that this difference is not accounted for by tobacco smoking status and is still present after adjusting for variables such as sex and age. Here, we propose that this effect is directly related to exposure to the Δ(9)-tetrahydrocannabinol (THC) present in cannabis smoke. We therefore propose the seemingly paradoxical hypothesis that THC or a THC/cannabidiol combination drug may produce weight loss and may be a useful therapeutic for the treatment of obesity and its complications.

Inhibition of FAAH and activation of PPAR: new approaches to the treatment of cognitive dysfunction and drug addiction

Enhancing the effects of endogenously-released cannabinoid ligands in the brain might provide therapeutic effects more safely and effectively than administering drugs that act directly at the cannabinoid receptor. Inhibitors of fatty acid amide hydrolase (FAAH) prevent the breakdown of endogenous ligands for cannabinoid receptors and peroxisome proliferator-activated receptors (PPAR), prolonging and enhancing the effects of these ligands when they are naturally released. This review considers recent research on the effects of FAAH inhibitors and PPAR activators in animal models of addiction and cognition (specifically learning and memory). These studies show that FAAH inhibitors can produce potentially therapeutic effects, some through cannabinoid receptors and some through PPAR. These effects include enhancing certain forms of learning, counteracting the rewarding effects of nicotine and alcohol, relieving symptoms of withdrawal from cannabis and other drugs, and protecting against relapse-like reinstatement of drug self-administration. Since FAAH inhibition might have a wide range of therapeutic actions but might also share some of the adverse effects of cannabis, it is noteworthy that at least one FAAH-inhibiting drug (URB597) has been found to have potentially beneficial effects but no indication of liability for abuse or dependence. Although these areas of research are new, the preliminary evidence indicates that they might lead to improved therapeutic interventions and a better understanding of the brain mechanisms underlying addiction and memory.

Role of endocannabinoids and cannabinoid-1 receptors in cerebrocortical blood flow regulation

Background

Endocannabinoids are among the most intensively studied lipid mediators of cardiovascular functions. In the present study the effects of decreased and increased activity of the endocannabinoid system (achieved by cannabinoid-1 (CB1) receptor blockade and inhibition of cannabinoid reuptake, respectively) on the systemic and cerebral circulation were analyzed under steady-state physiological conditions and during hypoxia and hypercapnia (H/H).

Methodology/Principal Findings

In anesthetized spontaneously ventilating rats the CB1-receptor antagonist/inverse agonist AM-251 (10 mg/kg, i.v.) failed to influence blood pressure (BP), cerebrocortical blood flow (CoBF, measured by laser-Doppler flowmetry) or arterial blood gas levels. In contrast, the putative cannabinoid reuptake inhibitor AM-404 (10 mg/kg, i.v.) induced triphasic responses, some of which could be blocked by AM-251. Hypertension during phase I was resistant to AM-251, whereas the concomitant CoBF-increase was attenuated. In contrast, hypotension during phase III was sensitive to AM-251, whereas the concomitant CoBF-decrease was not. Therefore, CoBF autoregulation appeared to shift towards higher BP levels after CB1-blockade. During phase II H/H developed due to respiratory depression, which could be inhibited by AM-251. Interestingly, however, the concomitant rise in CoBF remained unchanged after AM-251, indicating that CB1-blockade potentially enhanced the reactivity of the CoBF to H/H. In accordance with this hypothesis, AM-251 induced a significant enhancement of the CoBF responses during controlled stepwise H/H.

Conclusion/Significance

Under resting physiological conditions CB1-receptor mediated mechanisms appear to have limited influence on systemic or cerebral circulation. Enhancement of endocannabinoid levels, however, induces transient CB1-independent hypertension and sustained CB1-mediated hypotension. Furthermore, enhanced endocannabinoid activity results in respiratory depression in a CB1-dependent manner. Finally, our data indicate for the first time the involvement of the endocannabinoid system and CB1-receptors in the regulation of the cerebral circulation during H/H and also raise the possibility of their contribution to the autoregulation of CoBF.

Impulsive-choice patterns for food in genetically lean and obese Zucker rats

Behavioral-economic studies have shown that differences between lean and obese Zuckers in food consumption depend on the response requirement for food. Since a response requirement inherently increases the delay to reinforcement, differences in sensitivity to delay may also be a relevant mechanism of food consumption in the obese Zucker rat. Furthermore, the endocannabinoid neurotransmitter system has been implicated in impulsivity, but studies that attempt to characterize the effects of cannabinoid drugs (e.g., rimonabant) on impulsive choice may be limited by floor effects. The present study aimed to characterize impulsive-choice patterns for sucrose using an adjusting-delay procedure in genetically lean and obese Zuckers. Ten lean and ten obese Zucker rats chose between one lever that resulted in one pellet after a standard delay (either 1 s or 5 s) and a second lever that resulted in two or three pellets after an adjusting delay. After behavior stabilized under baseline, rimonabant (0-10 mg/kg) was administered prior to some choice sessions in the two-pellet condition. Under baseline, obese Zuckers made more impulsive choices than leans in three of the four standard-delay/pellet conditions. Additionally, in the 2-pellet condition, rimonabant increased impulsive choice in lean rats in the 1-s standard-delay condition; however, rimonabant decreased impulsive choice in obese rats in the 1-s and 5-s standard-delay conditions. These data suggest that genetic factors that influence impulsive choice are stronger in some choice conditions than others, and that the endocannabinoid system may be a relevant neuromechanism.

Somatostatin receptor 5 and cannabinoid receptor 1 activation inhibit secretion of glucose-dependent insulinotropic polypeptide from intestinal K cells in rodents

AIMS/HYPOTHESIS

Glucose-dependent insulinotropic polypeptide (GIP) is an enteroendocrine hormone that promotes storage of glucose and fat. Its secretion from intestinal K cells is triggered by nutrient ingestion and is modulated by intracellular cAMP. In view of the proadipogenic actions of GIP, this study aimed to identify pathways in K cells that lower cAMP levels and GIP secretion.

METHODS

Murine K cells purified by flow cytometry were analysed for expression of G(αi)-coupled receptors by transcriptomic microarrays. Somatostatin and cannabinoid receptor expression was confirmed by quantitative RT-PCR. Hormone secretion in vitro was measured in GLUTag and primary murine intestinal cultures. cAMP was monitored in GLUTag cells using the genetically encoded sensor Epac2-camps. In vivo tolerance tests were performed in cannulated rats.

RESULTS

Purified murine K cells expressed high mRNA levels for somatostatin receptors (Sstrs) Sstr2, Sstr3 and Sstr5, and cannabinoid receptor type 1 (Cnr1, CB1). Somatostatin inhibited GIP and glucagon-like peptide-1 (GLP-1) secretion from primary small intestinal cultures, in part through SSTR5, and reduced cAMP generation in GLUTag cells. Although the CB1 agonist methanandamide (mAEA) inhibited GIP secretion, no significant effect was observed on GLP-1 secretion from primary cultures. In cannulated rats, treatment with mAEA prior to an oral glucose tolerance test suppressed plasma GIP but not GLP-1 levels, whereas the CB1 antagonist AM251 elevated basal GIP concentrations.

CONCLUSIONS/INTERPRETATION

GIP release is inhibited by somatostatin and CB1 agonists. The differential effects of CB1 ligands on GIP and GLP-1 release may provide a new tool to dissociate secretion of these incretin hormones and lower GIP but not GLP-1 levels in vivo.

Anorexic effects of intra-VTA leptin are similar in low-fat and high-fat-fed rats but attenuated in a subgroup of high-fat-fed obese rats

Leptin is an adiposity hormone that plays an important role in regulating food intake and energy homeostasis. This study investigated the effects of a high-fat (HF) and a low-fat, high-carbohydrate/sugar (LF) diet on leptin sensitivity in the ventral tegmental area (VTA) in rats. The animals were exposed to a HF or LF diet for 16 weeks. Then the effects of intra-VTA leptin (150 and 500 ng/side, unilateral dose) on food intake and body weights were investigated while the animals were maintained on the HF or LF diet. Long-term exposure to the HF or LF diet led to similar body weight gain in these groups. The HF-fed animals consumed a smaller amount of food by weight than the LF-fed animals but both groups consumed the same amount of calories. The bilateral administration of leptin into the VTA decreased food intake (72 h) and body weights (48 h) to a similar degree in the HF and LF-fed animals. When the HF-fed animals were ranked by body weight gain it was shown that the diet-induced obese rats (HF-fed DIO, upper quartile for weight gain) were less sensitive to the effects of leptin on food intake and body weights than the diet-resistant rats (HF-fed DR, lower quartile for weight gain). A control experiment with fluorescent Cy3-labeled leptin showed that leptin did not spread beyond the borders of the VTA. This study indicates that leptin sensitivity in the VTA is the same in animals that are exposed to a HF or LF diet. However, HF-fed DIO rats are less sensitive to the effects of leptin in the VTA than HF-fed DR rats. Leptin resistance in the VTA might contribute to overeating and weight gain when exposed to a HF diet.

Dopaminergic modulation of effort-related choice behavior as assessed by a progressive ratio chow feeding choice task: pharmacological studies and the role of individual differences

Mesolimbic dopamine (DA) is involved in behavioral activation and effort-related processes. Rats with impaired DA transmission reallocate their instrumental behavior away from food-reinforced tasks with high response requirements, and instead select less effortful food-seeking behaviors. In the present study, the effects of several drug treatments were assessed using a progressive ratio (PROG)/chow feeding concurrent choice task. With this task, rats can lever press on a PROG schedule reinforced by a preferred high-carbohydrate food pellet, or alternatively approach and consume the less-preferred but concurrently available laboratory chow. Rats pass through each ratio level 15 times, after which the ratio requirement is incremented by one additional response. The DA D₂ antagonist haloperidol (0.025–0.1 mg/kg) reduced number of lever presses and highest ratio achieved but did not reduce chow intake. In contrast, the adenosine A_2A antagonist MSX-3 increased lever presses and highest ratio achieved, but decreased chow consumption. The cannabinoid CB1 inverse agonist and putative appetite suppressant AM251 decreased lever presses, highest ratio achieved, and chow intake; this effect was similar to that produced by pre-feeding. Furthermore, DA-related signal transduction activity (pDARPP-32(Thr34) expression) was greater in nucleus accumbens core of high responders (rats with high lever pressing output) compared to low responders. Thus, the effects of DA antagonism differed greatly from those produced by pre-feeding or reduced CB1 transmission, and it appears unlikely that haloperidol reduces PROG responding because of a general reduction in primary food motivation or the unconditioned reinforcing properties of food. Furthermore, accumbens core signal transduction activity is related to individual differences in work output.