Anxiogenic profile of AM-251, a selective cannabinoid CB1 receptor antagonist, in plus-maze-na??ve and plus-maze-experienced mice

Role of endocannabinoid neurotransmission in the insular cortex on cardiovascular, autonomic and behavioral responses evoked by acute restraint stress in rats

This study aimed to investigate the role of endocannabinoid mechanisms present within the insular cortex (IC) on cardiovascular, autonomic and anxiogenic-like responses evoked by an acute session of restraint in rats. For this, bilateral guide cannulas directed to the IC were implanted in male Wistar rats for intrabrain microinjection of the selective CB1 receptor antagonist AM251, the selective TRPV1 receptor antagonist capsazepine, the fatty acid amide hydrolase (FAAH) inhibitor URB597 or the monoacylglycerol lipase (MAGL) inhibitor JZL184. The effects of pharmacological treatments were evaluated on restraint-evoked increases in blood pressure and heart rate, sympathetically-mediated cutaneous vasoconstriction and in delayed anxiogenic-like effect assessed 24h after stress exposure in the elevated plus maze (EPM) and open field (OF). We observed that acute restraint stress decreased the exploration of both EPM open arms and OF center region in animals treated with vehicle into the IC, thus indicating an anxiogenic-like effect. Inhibition of MAGL within the IC evoked by local treatment with JZL184 avoided the restraint-evoked anxiogenic effect. IC treatment with JZL184 also attenuated the tachycardia during restraint. The other pharmacological treatments did not modify the cardiovascular, autonomic and behavioral responses evoked by restraint. Taken together, these findings suggest that endocannabinoid neurotransmission in the IC, potentially acting through the endocannabinoid 2-arachidonoylglycerol, plays an inhibitory role in both tachycardia and anxiogenic-like effect evoked by stressful events.

Bridging the gap: The endocannabinoid system as a functional fulcrum for benzodiazepines in a novel frontier of anxiety pharmacotherapy

While benzodiazepines have been a mainstay of the pharmacotherapy of anxiety disorders, their short-term efficacy and risk of abuse have driven the exploration of alternative treatment approaches. The endocannabinoid (eCB) system has emerged as a key modulator of anxiety-related processes, with evidence suggesting dynamic interactions between the eCB system and the GABAergic system, the primary target of benzodiazepines. According to the existing literature, the activation of the cannabinoid receptors has been shown to exert anxiolytic effects, while their blockade or genetic deletion results in heightened anxiety-like responses. Moreover, studies have provided evidence of interactions between the eCB system and benzodiazepines in anxiety modulation. For instance, the attenuation of benzodiazepine-induced anxiolysis by cannabinoid receptor antagonism or genetic variations in the eCB system components in animal studies, have been associated with variations in benzodiazepine response and susceptibility to anxiety disorders. The combined use of cannabinoid-based medications, such as cannabinoid receptor agonists and benzodiazepine co-administration, has shown promise in augmenting anxiolytic effects and reducing benzodiazepine dosage requirements. This article aims to comprehensively review and discuss the current evidence on the involvement of the eCB system as a key modulator of benzodiazepine-related anxiolytic effects, and further, the possible mechanisms by which the region-specific eCB system-GABAergic connectivity modulates the neuro-endocrine/behavioral stress response, providing an inclusive understanding of the complex interplay between the eCB system and benzodiazepines in the context of anxiety regulation, to inform future research and clinical practice.

The Effects of Indirect and Direct Modulation of Endocannabinoid System Function on Anxiety-Related Behavior in Mice Assessed in the Elevated Plus Maze Test

BACKGROUND

The endocannabinoid system (ECS) is one of the most important systems modulating functions in the body. The ECS, via cannabinoid (CB: CB1 and CB2) receptors, endocannabinoids occurring in the brain (e.g., anandamide (AEA) and 2-arachidonoylglycerol (2-AG)) and enzymes degrading endocannabinoids in the brain (fatty-acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL)), plays a key role in the regulation of mood and anxiety. However, the effects of cannabinoid compounds on anxiety-related responses are complex and yield mixed results depending on the type of pharmacological manipulation (direct or indirect) of functions of the ECS, as well as the kinds of cannabinoids, dosage and procedure.

METHODS

The aim of this study was to determine and compare the influence of the direct (via CB receptors ligands) and indirect (via inhibition of enzymes degrading endocannabinoids in the brain) pharmacological modulation of ECS function on anxiety-like responses in mice in the elevated plus maze (EPM) test. For this purpose, in the first step of the experiments, we used selected ligands of CB1, CB1/CB2 and CB2 receptors to assess which types of CB receptors are involved in anxiety-related responses in mice. Next, we used inhibitors of FAAH (which breaks down AEA) or MAGL (which breaks down 2-AG) to assess which endocannabinoid is more responsible for anxiety-related behavior in mice.

RESULTS

The results of our presented research showed that an acute administration of CB1 receptor agonist oleamide (5-20 mg/kg) had no influence on anxiety-related responses and CB1 receptor antagonist AM 251 (0.25-3 mg/kg) had anxiogenic effects in the EPM test in mice. In turn, an acute administration of mixed CB1/CB2 receptor agonist WIN55,212-2 used at a dose of 1 mg/kg had an anxiolytic effect observed in mice in the EPM test. What is of interest is that both the acute administration of a CB2 receptor agonist (JWH 133 at the doses of 1 and 2 mg/kg) and antagonist (AM 630 at the doses of 0.5-2 mg/kg) had anxiogenic effects in this procedure. Moreover, we revealed that an acute administration of only FAAH inhibitor URB 597 (0.3 mg/kg) had an anxiolytic effect, while MAGL inhibitor JZL 184 (at any used doses (2-40 mg/kg)) after an acute injection had no influence on anxiety behavior in mice, as observed in the EPM test.

CONCLUSIONS

In our experiments, we confirmed the clearly significant involvement of the ECS in anxiety-related responses. In particular, the pharmacological indirect manipulation of ECS functions is able to elicit promising anxiolytic effects. Therefore, the ECS could be a potential target for novel anxiolytic drugs; however, further studies are needed.

Interactions between metabotropic glutamate and CB1 receptors: implications for mood, cognition, and synaptic signaling based on data from mGluR and CB1R-targeting drugs

Metabotropic glutamate receptors (mGluRs) are part of the G protein-coupled receptors (GPCRs) family. They are coupled to Gαq (group I) or Gi/o (groups II and III) proteins, which result in the generation of diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3) or the inhibition of adenylyl cyclase, respectively. mGluRs have been implicated in anxiety, depression, learning, and synaptic plasticity. Similarly, CB1 cannabinoid receptors (CB1Rs), also GPCRs, play roles in cognitive function and mood regulation through Gαi/o-mediated inhibition of adenylyl cyclase. Both mGluRs and CB1Rs exhibit surface labeling and undergo endocytosis. Given the similar cellular distribution and mechanisms of action, this review complies with fundamental data on the potential interactions and mutual regulation of mGluRs and CB1Rs in the context of depression, anxiety, and cognition, providing pioneering insights into their interplay.

Putative Activation of Cannabinoid Receptor Type 1 Prevents Brain Oxidative Stress and Inhibits Aggressive-Like Behavior in Zebrafish

Background: Aggression is a set of complex behaviors commonly described in different neurological disorders, such as schizophrenia, autistim spectrum disorder, and anxiety. Previous studies have described that some changes in the redox status of the brain are closely associated with aggressive behavior in different species. In addition, the endocannabinoid system acts as a neuromodulator of the central nervous system, however, its participation in aggressive behavior needs to be elucidated. Danio rerio (zebrafish) is an important model in the study of aggression, in this context, the present study investigated whether the activation of type 1 cannabinoid receptors (CB1r) alters the cerebral redox state and aggressive behavior in zebrafish. Materials and Methods: We performed pharmacological manipulations with the CB1r agonist (ACEA) and antagonist (AM-251) to assess the role of this receptor in aggressive behavior. Individuals were isolated in pairs, without physical contact for 24 h, treated with the drugs of interest, and after 30 minutes of pharmacokinetics, the fights were filmed for 30 min, and the individuals were identified as dominant or subordinate. Results: A consistent decrease in the strike and bite aggressive behavior was observed in the group treated with the ACEA agonist compared with that in the control and AM-251 groups. When evaluating the cerebral redox state, we observed that treatment with the ACEA agonist reduced malondialdehyde (MDA) levels and increased the levels of sulfhydryl groups compared with those in the control group. These results indicate that the activation of CB1r by the ACEA agonist inhibited aggressiveness and attenuated the levels of oxidative stress in both subjects (dominant or subordinate) in the treated group. Conclusion: Thus, we suggest that zebrafish is an alternative model to study common aggressive behavior disorders among species and that CB1r represent a potential target for the development of treatments for aggressive disorders.

Prenatal ethanol exposure causes anxiety-like phenotype and alters synaptic nitric oxide and endocannabinoid signaling in dorsal raphe nucleus of adult male rats

Mood disorders, including anxiety and depression caused by prenatal ethanol exposure (PE) are prevalent conditions in fetal alcohol spectrum disorders (FASDs). Prenatal ethanol exposure is associated with persistent dysfunctions of several neurotransmitter systems, including the serotonin (5-HT) system, which plays a major role in mood regulation and stress homeostasis. While PE is known to disrupt the development of the 5-HT system, the cellular mechanisms by which it alters the function of dorsal raphe nucleus (DRn) 5-HT neurons and their synaptic inputs remain unknown. Here, we used a second-trimester binge-drinking pattern PE (two daily gavages of 15% w/v ethanol at 3 g/kg, 5-6 h apart) during gestational days 8 - 20 and measured anxiety-like behaviors of adult male rats using the elevated plus (EPM) and zero (ZM) mazes. We also employed ex-vivo electrophysiological and pharmacological approaches to unravel the mechanisms by which PE alters the excitability and synaptic transmission onto DRn 5-HT neurons. We found that PE enhanced anxiety-like behaviors in adult male rats and induced a persistent activation of DRn 5-HT neurons. The PE-induced activation of DRn 5-HT neurons was largely mediated by potentiation of DRn glutamate synapses, which was caused by activation of the nitrergic system and impaired endocannabinoid signaling. As such, the present study reveals "push-pull" effects of PE on nitrergic and eCB signaling, respectively, which mediate the enhanced activity of DRn 5-HT neurons and could contribute to anxiety-like behaviors observed in animal model of FASD.

Reviewing the Role of the Endocannabinoid System in the Pathophysiology of Depression

Major depressive disorder is a high-impact, debilitating disease and it is currently considered the most prevalent mental illness. It is associated with disability, as well as increased morbidity and mortality. Despite its significant repercussions in our society, its exact pathophysiology remains unclear and therefore, available antidepressant treatment options are limited and, in some cases, ineffective. In the past years, research has focused on the development of a multifactorial theory of depression. Simultaneously, evidence supporting the role of the endocannabinoid system in the neurobiology of neuropsychiatric diseases has emerged. Studies have shown that the endocannabinoid system strongly impacts neurotransmission, and the neuroendocrine and neuroimmune systems, which are known to be dysfunctional in depressive patients. Accordingly, common antidepressants were shown to have a direct impact on the expression of cannabinoid receptors throughout the brain. Therefore, the relationship between the endocannabinoid system and major depressive disorder is worth consideration. Nevertheless, most studies focus on smaller pieces of what is undoubtedly a larger mosaic of interdependent processes. Therefore, the present review summarizes the existing literature regarding the role of the endocannabinoid system in depression aiming to integrate this information into a holistic picture for a better understanding of the relationship between the two.

Cannabinoids: Revealing their complexity and role in central networks of fear and anxiety

The first aim of the present review is to provide an in-depth description of the cannabinoids and their known effects at various neuronal receptors. It reveals that cannabinoids are highly diverse, and recent work has highlighted that their effects on the central nervous system (CNS) are surprisingly more complex than previously recognized. Cannabinoid-sensitive receptors are widely distributed throughout the CNS where they act as primary modulators of neurotransmission. Secondly, we examine the role of cannabinoid receptors at key brain sites in the control of fear and anxiety. While our understanding of how cannabinoids specifically modulate these networks is mired by their complex interactions and diversity, a plausible framework(s) for their effects is proposed. Finally, we highlight some important knowledge gaps in our understanding of the mechanism(s) responsible for their effects on fear and anxiety in animal models and their use as therapeutic targets in humans. This is particularly important for our understanding of the phytocannabinoids used as novel clinical interventions.

The Cannabinoid Receptor 1 Reverse Agonist AM251 Ameliorates Radiation-Induced Cognitive Decrements

Despite advancements in the radiotherapeutic management of brain malignancies, resultant sequelae include persistent cognitive dysfunction in the majority of survivors. Defining the precise causes of normal tissue toxicity has proven challenging, but the use of preclinical rodent models has suggested that reductions in neurogenesis and microvascular integrity, impaired synaptic plasticity, increased inflammation, and alterations in neuronal structure are contributory if not causal. As such, strategies to reverse these persistent radiotherapy-induced neurological disorders represent an unmet medical need. AM251, a cannabinoid receptor 1 reverse agonist known to facilitate adult neurogenesis and synaptic plasticity, may help to ameliorate radiation-induced CNS impairments. To test this hypothesis, three treatment paradigms were used to evaluate the efficacy of AM251 to ameliorate radiation-induced learning and memory deficits along with disruptions in mood at 4 and 12 weeks postirradiation. Results demonstrated that acute (four weekly injections) and chronic (16 weekly injections) AM251 treatments (1 mg/kg) effectively alleviated cognitive and mood dysfunction in cranially irradiated mice. The beneficial effects of AM251 were exemplified by improved hippocampal- and cortical-dependent memory function on the novel object recognition and object in place tasks, while similar benefits on mood were shown by reductions in depressive- and anxiety-like behaviors on the forced swim test and elevated plus maze. The foregoing neurocognitive benefits were associated with significant increases in newly born (doublecortin+) neurons (1.7-fold), hippocampal neurogenesis (BrdU+/NeuN+mature neurons, 2.5-fold), and reduced expression of the inflammatory mediator HMGB (1.2-fold) in the hippocampus of irradiated mice. Collectively, these findings indicate that AM251 ameliorates the effects of clinically relevant cranial irradiation where overall neurological benefits in memory and mood coincided with increased hippocampal cell proliferation, neurogenesis, and reduced expression of proinflammatory markers.

Endocannabinoids, cannabinoids and the regulation of anxiety

Cannabis has been used for hundreds of years, with its ability to dampen feelings of anxiety often reported as a primary reason for use. Only recently has the specific role cannabinoids play in anxiety been thoroughly investigated. Here we discuss the body of evidence describing how endocannabinoids and exogenous cannabinoids are capable of regulating the generation and termination of anxiety states. Disruption of the endogenous cannabinoid (eCB) system following genetic manipulation, pharmacological intervention or stress exposure reliably leads to the generation of an anxiety state. On the other hand, upregulation of eCB signaling is capable of alleviating anxiety-like behaviors in multiple paradigms. When considering exogenous cannabinoid administration, cannabinoid receptor 1 (CB1) agonists have a biphasic, dose-dependent effect on anxiety such that low doses are anxiolytic while high doses are anxiogenic, a phenomenon that is evident in both rodent models and humans. Translational studies investigating a loss of function mutation in the gene for fatty acid amide hydrolase, the enzyme responsible for metabolizing AEA, have also shown that AEA signaling regulates anxiety in humans. Taken together, evidence reviewed here has outlined a convincing argument for cannabinoids being powerful regulators of both the manifestation and amelioration of anxiety symptoms, and highlights the therapeutic potential of targeting the eCB system for the development of novel classes of anxiolytics. This article is part of the special issue on 'Cannabinoids'.

Deletion of muscarinic acetylcholine receptor 3 in microglia impacts brain ischemic injury

Microglia are the immune cells of the brain and become activated during any type of brain injury. In the middle cerebral artery occlusion (MCAo) model, a mouse model for ischemic stroke, we have previously shown that microglia and invaded monocytes upregulate the expression of the muscarinic acetylcholine receptor 3 (M3R) in the ischemic lesion. Here we tested whether this upregulation has an impact on the pathogenesis of MCAo. We depleted the m3R receptor in microglia, but not in circulating monocytes by giving tamoxifen to CX3CR1-CreERT^+/+M3R^flox/flox (M3RKO^mi) animals 3 weeks prior to MCAo. We found that M3RKO^mi male mice had bigger lesions, more pronounced motor deficits after one week and cognitive deficits after about one month compared to control males. The density of Iba1⁺ cells was lower in the lesions of M3RKO male mice in the early, but not in the late disease phase. In females, these differences were not significant. By giving tamoxifen 1 week prior to MCAo, we depleted m3R in microglia and in circulating monocytes (M3RKO^mi/mo). Male M3RKO^mi/mo did not differ in lesion size, but had a lower survival rate, showed motor deficits and a reduced accumulation of Iba1⁺ positive cells into the lesion site. In conclusion, our data suggest that the upregulation of m3R in microglia and monocytes in stroke has a beneficial effect on the clinical outcome in male mice.

Cannabinoid receptor type 1 antagonist inhibits progression of obesity-associated nonalcoholic steatohepatitis in a mouse model by remodulating immune system disturbances

SCOPE

This study investigated whether AM251, a cannabinoid receptor type 1 (CB1) antagonist, ameliorates hepatic levels of metabolic abnormalities and inflammatory responses in a murine nonalcoholic steatohepatitis (NASH) model via reversal of disturbances in the immune system.

METHODS AND RESULTS

Fifteen-week-old male obese db/db mice were randomly assigned to the following two groups: no treatment and treatment with AM251 at 5 mg/kg for 15 days. C57BL/6J-Lean mice were utilized as the control group. Plasma parameters, liver histopathology, and hepatic status were measured. For the in vitro study, macrophage-derived RAW264.7 cells were cultured with AM251 or CB1 small interfering RNA (siRNA) before challenge with arachidonyl-2'-chloroethylamide (ACEA) or a high concentration of fatty acids (HFFAs). The db/db mice exhibited an increase in CB1 levels, lipid droplet accumulation, mitogen-activated protein kinase-related inflammatory responses, and macrophage and neutrophil infiltration in the liver tissues. Flow cytometry analysis revealed an elevation in macrophages and T helper cells, plus a decrease in natural killer T cells and regulatory T cells in the liver tissues of the db/db mice; treatment with 5 mg/kg AM251 reversed these changes. Moreover, in vitro experiments revealed that administration of 3.3 μM AM251 or CB1 siRNA prevented 1 mM HFFA- and 1 μΜ ACEA-induced inflammatory cytokine protein expression in the RAW264.7 cells.

CONCLUSION

These findings suggested that a blockade caused by CB1 reduced obesity-associated NASH progression via correction of immune system dysregulations and elevated inflammatory responses in the liver tissues.

Further evidence of anxiety- and depression-like behavior for total genetic ablation of cannabinoid receptor type 1

Cannabinoid receptor type 1 (CB1R) is the most abundant cannabinoid receptor in central nervous system. Clinical studies and animal models have shown that the attenuation of endocannabinoid system signaling correlates with the development of psychiatric disorders such as anxiety, depression and schizophrenia. In the present work, multiple behavioral tests were performed to evaluate behaviors related to anxiety and depression in CB1R^+/- and CB1R^-/-. CB1R^+/- mice had anxiety-related behavior similar to wild type (CB1R^+/+) mice, whereas CB1R^-/- mice displayed an anxious-like phenotype, which indicates that lower expression of CB1R is sufficient to maintain the neural circuits modulating anxiety. In addition, CB1R^-/- mice exhibited alterations in risk assessment and less exploration, locomotion, grooming, body weight and appetite. These phenotypic characteristics observed in CB1R^-/- mice could be associated with symptoms observed in human psychiatric disorders such as depression. A better knowledge of the neuromodulatory role of CB1R may contribute to understand scope and limitations of the development of medical treatments.

Blockade of the endovanilloid receptor, TRPV1, and of the endocannabinoid enzyme, FAAH, within the nucleus accumbens shell elicits anxiolytic-like effects in male rats

RATIONALE

The functional role of the endocannabinoid system (ECS) and Transient Receptor Potential Vanilloid type-1 (TRPV1) within the Nucleus Accumbens shell (NAc shell) remains unknown. Preclinical studies in rodents have reported that the ECS modulates emotional responses such as anxiety. The NAc shell has a high density of synaptically co-localized cannabinoid receptor type-1 (CB1R) and TRPV1, suggesting a potential involvement in the modulation of anxiety.

OBJECTIVES

The present study aims to establish the role of ECS-TRPV1 interactions within the NAc shell and its effects on anxiety. It is hypothesized that the neurochemical regulation elicited by ECS within the NAc shell mediates anxiety-like behaviors in rodents.

METHODS

In this study, male Sprague Dawley rats were implanted with bilateral brain cannula targeting the NAc shell. Following recovery from surgery, animals received microinfusion pretreatments (0, 0.125, 0.5 nmol/0.4 μl) of N-arachidonoyl-serotonin (AA-5-HT), a dual blocker of the endocannabinoid-inactivating enzyme, fatty acid amide hydrolase (FAAH) and a TRPV1 antagonist in the NAc shell. Following treatment, animals were tested in an elevated plus maze (EPM) paradigm for a period of 5 minutes. At the end of the experiment, animals were sacrificed and their brains collected for histological and biochemical analysis.

RESULTS

Results showed that animals treated with AA-5-HT in a dose dependent manner spent significantly more time in the open arms than vehicle-treated animals. In addition, AA-5-HT administration induced a significant downregulation of CB1R expression in the NAc shell.

CONCLUSIONS

The present findings suggest that the ECS within the NAc shell modulates anxiety-like behaviors via FAAH and CB1R activity.

Endocannabinoid System Components as Potential Biomarkers in Psychiatry

The high heterogeneity of psychiatric disorders leads to a lack of diagnostic precision. Therefore, the search of biomarkers is a fundamental aspect in psychiatry to reach a more personalized medicine. The endocannabinoid system (ECS) has gained increasing interest due to its involvement in many different functional processes in the brain, including the regulation of emotions, motivation, and cognition. This article reviews the role of the main components of the ECS as biomarkers in certain psychiatric disorders. Studies carried out in rodents evaluating the effects of pharmacological and genetic manipulation of cannabinoid receptors or endocannabinoids (eCBs) degrading enzymes were included. Likewise, the ECS-related alterations occurring at the molecular level in animal models reproducing some behavioral and/or neuropathological aspects of psychiatric disorders were reviewed. Furthermore, clinical studies evaluating gene or protein alterations in post-mortem brain tissue or in vivo blood, plasma, and cerebrospinal fluid (CSF) samples were analyzed. Also, the results from neuroimaging studies using positron emission tomography (PET) or functional magnetic resonance (fMRI) were included. This review shows the close involvement of cannabinoid receptor 1 (CB1r) in stress regulation and the development of mood disorders [anxiety, depression, bipolar disorder (BD)], in post-traumatic stress disorder (PTSD), as well as in the etiopathogenesis of schizophrenia, attention deficit hyperactivity disorder (ADHD), or eating disorders (i.e. anorexia and bulimia nervosa). On the other hand, recent results reveal the potential therapeutic action of the endocannabinoid tone manipulation by inhibition of eCBs degrading enzymes, as well as by the modulation of cannabinoid receptor 2 (CB2r) activity on anxiolytic, antidepressive, or antipsychotic associated effects. Further clinical research studies are needed; however, current evidence suggests that the components of the ECS may become promising biomarkers in psychiatry to improve, at least in part, the diagnosis and pharmacological treatment of psychiatric disorders.

Endocannabinoid and N-acylethanolamide levels in rat brain and spinal cord following systemic dipyrone and paracetamol administration

The cannabinoid system has been suspected to play a role in the mechanisms of action of dipyrone and paracetamol. Our purpose was to measure the local endocannabinoid and N-acylethanolamide levels in the brain and spinal cord of rats following dipyrone and paracetamol administration. Nociception was assessed 1, 5, and 12 h following drug injections in Wistar rats, using tail-flick and hot-plate tests. The antinociceptive effects of dipyrone (150, 300, and 600 mg/kg, i.p.) and paracetamol (30, 100, and 300 mg/kg, i.p.) were observed. After administration of the highest doses of dipyrone and paracetamol, endocannabinoid (N-arachidonoylethanolamide (AEA), 2-arachidonoylglycerol (2-AG)) and N-acylethanolamide (palmitoylethanolamide (PEA), oleoylethanolamide (OEA)) levels were measured in the periaqueductal gray (PAG), rostral ventromedial medulla (RVM), and spinal cords of rats using tandem mass spectrometry with liquid chromatography. Increased 2-AG levels were observed in the PAG and the RVM 12 h after paracetamol injection; dipyrone exerted no action on 2-AG levels. Analgesic administrations led to a reduction in AEA levels in the RVM and spinal cord; similar decreases in PEA and OEA levels were observed in the RVM and the spinal cord. Dipyrone and paracetamol administrations appear to exert complicated effects on endocannabinoid and N-acylethanolamide levels in rats.

The Lateral Habenula Directs Coping Styles Under Conditions of Stress via Recruitment of the Endocannabinoid System

BACKGROUND

The ability to effectively cope with stress is a critical determinant of disease susceptibility. The lateral habenula (LHb) and the endocannabinoid (ECB) system have independently been shown to be involved in the selection of stress coping strategies, yet the role of ECB signaling in the LHb remains unknown.

METHODS

Using a battery of complementary techniques in rats, we examined the localization of type-1 cannabinoid receptors (CB1Rs) and assessed the behavioral and neuroendocrine effects of intra-LHb CB1R manipulations. We further tested the extent to which the ECB system in the LHb is impacted following chronic unpredictable stress or social defeat stress, and whether manipulation of LHb CB1Rs can bias coping strategies in rats with a history of chronic stress.

RESULTS

Electron microscopy studies revealed CB1R expression on presynaptic axon terminals, postsynaptic membranes, mitochondria, and glial processes in the rat LHb. In vivo microdialysis experiments indicated that acute stress increased the amount of 2-arachidonoylglycerol in the LHb, while intra-LHb CB1R blockade increased basal corticosterone, augmented proactive coping strategies, and reduced anxiety-like behavior. Basal LHb 2-arachidonoylglycerol content was similarly elevated in rats that were subjected to chronic unpredictable stress or social defeat stress and positively correlated with adrenal weight. Finally, intra-LHb CB1R blockade increased proactive behaviors in response to a novel conspecific, increasing approach behaviors irrespective of stress history and decreasing the latency to be attacked during an agonistic encounter.

CONCLUSIONS

Alterations in LHb ECB signaling may be relevant for development of stress-related pathologies in which LHb dysfunction and stress-coping impairments are hallmark symptoms.

The anxiolytic effects of cannabidiol in chronically stressed mice are mediated by the endocannabinoid system: Role of neurogenesis and dendritic remodeling

Repeated injections of cannabidiol (CBD), the major non-psychotomimetic compound present in the Cannabis sativa plant, attenuate the anxiogenic effects induced by Chronic Unpredictable Stress (CUS). The specific mechanisms remain to be fully understood but seem to involve adult hippocampal neurogenesis and recruitment of endocannabinoids. Here we investigated for the first time if the behavioral and pro-neurogenic effects of CBD administered concomitant the CUS procedure (14 days) are mediated by CB₁, CB₂ or 5HT_1A receptors, as well as CBD effects on dendritic remodeling and on intracellular/synaptic signaling (fatty acid amide hydrolase - FAAH, Akt, GSK3β and the synaptic proteins Synapsin Ia/b, mGluR1 and PSD95). After 14 days, CBD injections (30 mg/kg) induced anxiolytic responses in stressed animals in the elevated plus-maze and novelty suppressed feeding tests, that were blocked by pre-treatment with a CB₁ (AM251, 0.3 mg/kg) or CB₂ (AM630, 0.3 mg/kg), but not by a 5HT_1A (WAY100635, 0.05 mg/kg) receptor antagonist. Golgi staining and immunofluorescence revealed that these effects were associated with an increase in hippocampal neurogenesis and spine density in the dentate gyrus of the hippocampus. AM251 and AM630 abolished the effects of CBD on spines density. However, AM630 was more effective in attenuating the pro-neurogenic effects of CBD. CBD decreased FAAH and increased p-GSK3β expression in stressed animals, which was also attenuated by AM630. These results indicate that CBD prevents the behavioral effects caused by CUS probably due to a facilitation of endocannabinoid neurotransmission and consequent CB₁/CB₂ receptors activation, which could recruit intracellular/synaptic proteins involved in neurogenesis and dendritic remodeling.

Integrating Endocannabinoid Signaling and Cannabinoids into the Biology and Treatment of Posttraumatic Stress Disorder

Exposure to stress is an undeniable, but in most cases surmountable, part of life. However, in certain individuals, exposure to severe or cumulative stressors can lead to an array of pathological conditions including posttraumatic stress disorder (PTSD), characterized by debilitating trauma-related intrusive thoughts, avoidance behaviors, hyperarousal, as well as depressed mood and anxiety. In the context of the rapidly changing political and legal landscape surrounding use of cannabis products in the USA, there has been a surge of public and research interest in the role of cannabinoids in the regulation of stress-related biological processes and in their potential therapeutic application for stress-related psychopathology. Here we review the current state of knowledge regarding the effects of cannabis and cannabinoids in PTSD and the preclinical and clinical literature on the effects of cannabinoids and endogenous cannabinoid signaling systems in the regulation of biological processes related to the pathogenesis of PTSD. Potential therapeutic implications of the reviewed literature are also discussed. Finally, we propose that a state of endocannabinoid deficiency could represent a stress susceptibility endophenotype predisposing to the development of trauma-related psychopathology and provide biologically plausible support for the self-medication hypotheses used to explain high rates of cannabis use in patients with trauma-related disorders.

Endocannabinoids and Mental Disorders

Preclinical and clinical data fully support the involvement of the endocannabinoid system in the etiopathogenesis of several mental diseases. In this review we will briefly summarize the most common alterations in the endocannabinoid system, in terms of cannabinoid receptors and endocannabinoid levels, present in mood disorders (anxiety, posttraumatic stress disorder, depression, bipolar disorder, and suicidality) as well as psychosis (schizophrenia) and autism. The arising picture for each pathology is not always straightforward; however, both animal and human studies seem to suggest that pharmacological modulation of this system might represent a novel approach for treatment.

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.

Translational evidence for the involvement of the endocannabinoid system in stress-related psychiatric illnesses

Accumulating evidence over the past decade has highlighted an important role of the endocannabinoid (eCB) system in the regulation of stress and emotional behavior across divergent species, from rodents to humans. The general findings from this work indicate that the eCB system plays an important role in gating and buffering the stress response, dampening anxiety and regulating mood. Work in rodents has allowed researchers to determine the neural mechanisms mediating this relationship while work in human populations has demonstrated the possible importance of this system in stress-related psychiatric diseases, such as post-traumatic stress disorder, generalized anxiety and major depression. These stress-protective effects of eCB signaling appear to be primarily mediated by their actions within corticolimbic structures, particularly the amygdala and the prefrontal cortex. The aim of this review is to provide an up-to-date discussion of the current level of knowledge in this field, as well as address the current gaps in knowledge and specific areas of research that require attention.

Nicotine-induced anxiety-like behavior in a rat model of the novelty-seeking phenotype is associated with long-lasting neuropeptidergic and neuroplastic adaptations in the amygdala: effects of the cannabinoid receptor 1 antagonist AM251

A rat model of the novelty-seeking phenotype predicts vulnerability to the expression of behavioral sensitization to nicotine, where locomotor reactivity to novelty is used to screen experimentally-naïve rats for high (HR) versus low (LR) responders. The present study examines the long-term neuropeptidergic and neuroplastic adaptations associated with the expression of locomotor sensitization to a low dose nicotine challenge and social anxiety-like behavior following chronic intermittent nicotine exposure during adolescence in the LRHR phenotype. Our data show that the expression of behavioral sensitization to nicotine and abstinence-related anxiety are detected in nicotine pre-exposed HRs even across a long (3 wks) abstinence. Moreover, these behavioral effects of nicotine are accompanied by a persistent imbalance between neuropeptide Y and corticotrophin releasing factor systems, and a persistent increase in brain-derived neurotrophic factor (BDNF) and spinophilin mRNA levels in the amygdala. Furthermore, treatment with the cannabinoid receptor 1 antagonist, AM251 (5 mg/kg) during a short (1 wk) abstinence is ineffective in reversing nicotine-induced anxiety, fluctuations in BDNF and spinophilin mRNAs, and the neuropeptidergic dysregulations in the amygdala; although this treatment is effective in reversing the expression of locomotor sensitization to challenge nicotine even after a long abstinence. Interestingly, the identical AM251 treatment administered during the late phase of a long abstinence further augments anxiety and associated changes in BDNF and spinophilin mRNA in the basolateral nucleus of the amygdala in nicotine pre-exposed HRs. These findings implicate long-lasting neuropeptidergic and neuroplastic changes in the amygdala in vulnerability to the behavioral effects of nicotine in the novelty-seeking phenotype.

Nutritional n-3 polyunsaturated fatty acids deficiency alters cannabinoid receptor signaling pathway in the brain and associated anxiety-like behavior in mice

N-3 polyunsaturated fatty acids (PUFAs) cannot be synthesized de novo in mammals and need to be provided by dietary means. In the brain, the main n-3 PUFA is docosahexaenoic acid (DHA), which is a key component of neuronal membranes. A low dietary level of DHA has been associated with increased risk of developing neuropsychiatric diseases; however, the mechanisms involved remain to be determined. In this study, we found that long-term exposure to an n-3 deficient diet decreases the level of DHA in the brain and impairs the cannabinoid receptor signaling pathway in mood-controlling structures. In n-3 deficient mice, the effect of the cannabinoid agonist WIN55,212-2 in an anxiety-like behavior test was abolished. In addition, the cannabinoid receptor signaling pathways were altered in the prefrontal cortex and the hypothalamus. Consequently, our data suggest that behavioral changes linked to an n-3 dietary deficiency are due to an alteration in the endocannabinoid system in specific brain areas.

The cannabinoid receptor inverse agonist AM251 regulates the expression of the EGF receptor and its ligands via destabilization of oestrogen-related receptor α protein

BACKGROUND AND PURPOSE

AM251 is an inverse agonist of the cannabinoid 1 receptor (CB(1)R) that can exert 'off-target' effects in vitro and in CB(1)R knock-out mice. AM251 is also potent at modulating tumour cell growth, suggesting that growth factor-mediated oncogenic signalling could be regulated by AM251. Since dysregulation of the EGF receptor has been associated with carcinogenesis, we examined AM251 regulation of EGF receptor (EGFR) expression and function.

EXPERIMENTAL APPROACH

The various biological functions of AM251 were measured in CB(1)R-negative human cancer cells. Pharmacological and genetic approaches were used to validate the data.

KEY RESULTS

The mRNA levels for EGFR and its associated ligands, including HB-EGF, were induced several fold in PANC-1 and HCT116 cells in response to AM251. This event was associated with enhanced expression of EGFR on the cell surface with concomitant increase in EGF-induced cellular responses in AM251-treated cells. Exposure to XCT790, a synthetic inverse agonist of the orphan nuclear oestrogen-related receptor α (ERRα), also induced EGFR and HB-EGF expression to the same extent as AM251, whereas pretreatment with the ERRα-selective agonist, biochanin A, blunted AM251 actions. AM251 promoted the degradation of ERRα protein without loss of the corresponding mRNA. Knock-down of ERRα by siRNA-based approach led to constitutive induction of EGFR and HB-EGF levels, and eliminated the biological responses of AM251 and XCT790. Finally, AM251 displaced diethylstilbestrol prebound to the ligand-binding domain of ERRα.

CONCLUSIONS AND IMPLICATIONS

AM251 up-regulates EGFR expression and signalling via a novel non-CB(1)R-mediated pathway involving destabilization of ERRα protein in selected cancer cell lines.

Enhancement of endocannabinoid signaling with JZL184, an inhibitor of the 2-arachidonoylglycerol hydrolyzing enzyme monoacylglycerol lipase, produces anxiolytic effects under conditions of high environmental aversiveness in rats

Dysregulation in signaling of the endocannabinoid 2-arachidonoylglycerol (2-AG) is implicated in hyperresponsiveness to stress. We hypothesized that blockade of monoacylglycerol lipase (MGL), the primary enzyme responsible for 2-AG deactivation in vivo, would produce context-dependent anxiolytic effects in rats. Environmental aversiveness was manipulated by varying illumination of an elevated plus maze. Percentage open arm time and numbers of open and closed arm entries were measured in rats receiving a single intraperitoneal (i.p.) injection of either vehicle, the MGL inhibitor JZL184 (1-8mg/kg), the benzodiazepine diazepam (1mg/kg), the cannabinoid CB(1) receptor antagonist rimonabant (1mg/kg), or JZL184 (8mg/kg) coadministered with rimonabant (1mg/kg). JZL184 (8mg/kg) produced anxiolytic-like effects (i.e., increased percentage open arm time and number of open arm entries) under high, but not low, levels of environmental aversiveness. Diazepam produced anxiolytic effects in either context. Rimonabant blocked the anxiolytic-like effects of JZL184, consistent with mediation by CB(1). Anxiolytic effects of JZL184 were preserved following chronic (8mg/kg per day×6 days) administration. Chronic and acute JZL184 treatment similarly enhanced behavioral sensitivity to an exogenous cannabinoid (WIN55,212-2; 2.5mg/kg i.p.) 24 or 72h following the terminal injection, suggesting a pervasive effect of MGL inhibition on the endocannabinoid system. We attribute our results to alterations in emotion rather than locomotor activity as JZL184 did not alter the number of closed arm entries in the plus maze or produce motor ataxia in the bar test. Our results demonstrate that JZL184 has beneficial, context-dependent effects on anxiety in rats, presumably via inhibition of MGL-mediated hydrolysis of 2-AG. These data warrant further testing of MGL inhibitors to elucidate the functional role of 2-AG in controlling anxiety and stress responsiveness. Our data further implicate a role for 2-AG in the regulation of emotion and validate MGL as a therapeutic target.

Alterations in corticolimbic dendritic morphology and emotional behavior in cannabinoid CB1 receptor-deficient mice parallel the effects of chronic stress

Many changes produced by chronic stress are similar to those seen in cannabinoid CB(1) receptor-deficient mice. In the current study, we examined both anxiety-like behavior and dendritic complexity within the prefrontal cortex and basolateral amygdala (BLA) in wild-type and CB(1) receptor-deficient mice, under basal conditions and following exposure to 21 days of protracted restraint stress. CB(1) receptor-deficient mice exhibited increased indices of anxiety in the elevated plus maze under basal conditions that were similar in magnitude to changes seen in wild-type mice exposed to chronic stress. Chronic stress or deletion of the CB(1) receptor also produced a reduction in both apical dendritic length and branch points of neurons within layer II/III of the prelimbic region of the prefrontal cortex. Pyramidal neurons in the (BLA) of CB(1) receptor-deficient mice were found to have increased dendritic length compared with wild type. Chronic stress increased dendritic length of these amygdalar neurons in both wild-type and CB(1) receptor-deficient mice. Collectively, these data demonstrate that loss of cannabinoid CB(1) receptor signaling produces a chronic stress-like phenotype under basal conditions and provide a putative neural substrate that may subserve the changes in emotional behavior seen following disruption of CB(1) receptor signaling.

Deficiency in endocannabinoid signaling in the nucleus accumbens induced by chronic unpredictable stress

The nucleus accumbens (NAc) is a critical component of the reward circuitry, and dysfunction of the NAc may account for anhedonia and other symptoms of depression. Here, we investigated whether alterations in endocannabinoid (eCB) signaling in the NAc contribute to depression-like behaviors induced by chronic unpredictable stress (CUS) in mice. We compared three types of eCB/CB1 receptor-mediated synaptic plasticity in slices prepared from the NAc core of control and stress-exposed mice: depolarization-induced suppression of excitation, long-term depression, and the depression of field excitatory postsynaptic potentials (fEPSPs) induced by group I metabotropic glutamate receptor agonist DHPG. CUS (5-6-week exposure to stressors), but not sub-CUS (1 week exposure to stressors), induces depression-like behaviors and impairs these forms of eCB/CB1 receptor-mediated plasticity examined in the NAc core. Neither sub-CUS nor CUS altered the tissue contents of the eCBs, anandamide and 2-arachidonoylglycerol in the striatum. However, exposure to CUS, but not to sub-CUS, attenuated the depression of fEPSPs induced by the CB1 receptor agonist WIN 55 212-2. CUS exposure reduced the maximal effect without affecting the EC(50) of WIN 55 212-2 to induce fEPSP depression. Thus, impaired CB1 receptor function could account for CUS-induced deficiency in eCB signaling in the NAc. Both CUS-induced deficiency in eCB signaling and depression-like behaviors were reversed by in vivo administration of antidepressant fluoxetine. These results suggest that downregulation of eCB signaling in the NAc occurs after CUS and contributes to the pathophysiology of depression.

The novel cannabinoid CB1 antagonist AM6545 suppresses food intake and food-reinforced behavior

Drugs that interfere with cannabinoid CB1 transmission suppress food-motivated behaviors, and may be useful clinically as appetite suppressants. However, there may also be undesirable side effects (e.g., nausea, malaise, anxiety, and depression) that are produced by the current generation of CB1 inverse agonists such as rimonabant and taranabant. For that reason, it is important to continue research on novel cannabinoid antagonists. The present studies examined the effects of the novel compound AM6545, which is a neutral antagonist of CB1 receptors that is thought to have relatively poor penetrability into the central nervous system. Intraperitoneal administration of AM6545 significantly reduced food-reinforced operant responding at doses of 4.0, 8.0 and 16.0 mg/kg. AM6545 also produced a strong suppression of the intake of high-carbohydrate and high-fat diets in the same dose range, but only produced a mild suppression of lab chow intake at the highest dose (16.0 mg/kg). Although AM6545 did not affect food handling, it did reduce time spent feeding and feeding rate. Taken together, these results suggest that AM6545 is a compound that warrants further study as a potential appetite suppressant drug.

Neuropsychiatric adverse effects of centrally acting antiobesity drugs

INTRODUCTION

Central neurochemical systems including the monoamine, opioid, and cannabinoid systems have been promising targets for antiobesity drugs that modify behavioral components of obesity. In addition to modulating eating behavior, centrally acting antiobesity drugs are also likely to alter emotional behavior and cognitive function due to the high expression of receptors for the neurochemical systems targeted by these drugs within the fronto-striatal and limbic circuitry.

METHODS

This paper reviewed the neuropsychiatric adverse effects of past and current antiobesity drugs, with a central mechanism of action, linking the adverse effects to their underlying neural substrates and neurochemistry.

RESULTS

Antiobesity drugs were found to have varying neuropsychiatric adverse event profiles. Insomnia was the most common adverse effect with drugs targeting monoamine systems (sibutramine, bupropion and tesofensine). These drugs had some positive effects on mood and anxiety and may have added therapeutic benefits in obese patients with comorbid depression and anxiety symptoms. Sedation and tiredness were the most common adverse effects reported with drugs targeting the m-opioid receptors (i.e., naltrexone) and combination therapies targeting the opioid and monoamine systems (i.e., Contrave™). Cognitive impairments were most frequently associated with the antiepileptic drugs, topiramate and zonisamide, consistent with their sedative properties. Drugs targeting the cannabinoid system (rimonabant and taranabant) were consistently associated with symptoms of anxiety and depression, including reports of suicidal ideation. Similar adverse events have also been noted for the D₁/D₅ antagonist ecopipam.

CONCLUSION

These findings highlight the need to assess neuropsychiatric adverse events comprehensively using sensitive and validated methods early in the clinical development of candidate antiobesity drugs with a central mechanism of action.

The cannabinoid CB1 receptor is involved in the anxiolytic, sedative and amnesic actions of benzodiazepines

Previous studies in our laboratory showed that cannabinoid CB1 receptor knockout mice (CB1-/-) presented increased anxiety-like behaviours that did not respond to the anxiolytic actions of benzodiazepines. These results suggest that the pharmacological effects of benzodiazepines may involve the participation of cannabinoid CB1 receptors. Therefore, the purpose of this study was to examine the effects of alprazolam and the cannabinoid CB1 receptor antagonist AM251 on behavioural assays (light-dark box test, neurological severity score and step-down inhibitory avoidance test) and on the functional activity of the CB1 receptor (WIN-55,212-stimulated [(35)S] guanosine triphosphate (GTP) gamma binding autoradiography).The administration of alprazolam (40 microg/kg, intraperitoneal (i.p.)) decreased anxiety-like behaviours in the light-dark box test and significantly reduced WIN-55,212-stimulated [(35)S]GTPgamma binding autoradiography in the amygdala and in the CA1 field of the hippocampus, but was without effects on CA2, CA3 and the dentate gyrus (DG) of the hippocampus. The administration of AM251 (3 mg/kg, i.p.) blocked the anxiolytic action of alprazolam (40 microg/kg, i.p.), significantly reduced the sedative (ataxia, neurological severity score in the 0.5 cm bar) and the amnesic actions (short time term memory (1 h after electric shock)) of alprazolam (0.5 mg/kg, i.p.).Taken together, these findings revealed that cannabinoid CB1 receptor plays a pivotal role in the pharmacological actions of benzodiazepines. Furthermore, these results suggest that blockade of cannabinoid CB1 receptors may be useful in the treatment of patients with problems related to the consumption of benzodiazepines. Further clinical trials are needed to test this hypothesis.

Effects of delta9-tetrahydrocannabinol on reward and anxiety in rats exposed to chronic unpredictable stress

Although cannabis derivatives produce clear subjective motivational responses in humans leading to drug-seeking behaviour, the reinforcing attributes of these subjective effects are difficult to define in experimental animals. The aim of this study was to examine how exposure to chronic unpredictable stress (CUS) will affect reward function and anxiety after acute administration of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) in rats. Male rats were exposed to either 10 days of CUS or no stressor. Alterations in brain reward function were assessed with the intracranial self-stimulation (ICSS) paradigm, and anxiety responses were measured with the elevated plus maze. CUS did not affect baseline brain stimulation reward thresholds. Delta(9)-THC did not exhibit reinforcing actions in the ICSS paradigm neither in nonstressed nor in stressed animals. More importantly, in nonstressed animals, both the low and the high dose of Delta(9)-THC exerted anxiolytic-like effects. In stressed animals, however, only the high dose of THC induced an anxiolytic-like response, whereas the low dose induced anxiogenic effects. The present results provide clear evidence for an anxiolytic effect of Delta(9)-THC both in stressed and in nonstressed animals, and indicate that environmental conditions, such as stressful experiences, do not alter the behavioural effects of Delta( 9)-THC in the ICSS paradigm.

Potential anxiogenic effects of cannabinoid CB1 receptor antagonists/inverse agonists in rats: comparisons between AM4113, AM251, and the benzodiazepine inverse agonist FG-7142

Cannabinoid CB1 inverse agonists suppress food-motivated behaviors, but may also induce psychiatric effects such as depression and anxiety. To evaluate behaviors potentially related to anxiety, the present experiments assessed the CB1 inverse agonist AM251 (2.0-8.0mg/kg), the CB1 antagonist AM4113 (3.0-12.0mg/kg), and the benzodiazepine inverse agonist FG-7142 (10.0-20.0mg/kg), using the open field test and the elevated plus maze. Although all three drugs affected open field behavior, these effects were largely due to actions on locomotion. In the elevated plus maze, FG-7142 and AM251 both produced anxiogenic effects. FG-7142 and AM251 also significantly increased c-Fos activity in the amygdala and nucleus accumbens shell. In contrast, AM4113 failed to affect performance in the plus maze, and did not induce c-Fos immunoreactivity. The weak effects of AM4113 are consistent with biochemical data showing that AM4113 induces little or no intrinsic cellular activity. This research may lead to the development of novel appetite suppressants with reduced anxiogenic effects.

Fatty acid amide hydrolase (FAAH) knockout mice exhibit enhanced acquisition of an aversive, but not of an appetitive, Barnes maze task

It is well established that genetic deletion or pharmacological inhibition of the CB(1) receptor disrupts extinction learning in aversive conditioning tasks, but not in appetitive tasks. Consistent with these findings is that genetic deletion or pharmacological inhibition of fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of the endogenous cannabinoid anandamide (AEA), accelerates acquisition as well as extinction in aversive conditioning tasks. However, it is unknown whether FAAH blockade will affect acquisition in an appetitive conditioning task. Therefore, in the present study, we assessed FAAH (-/-) and (+/+) mice in appetitive and aversive Barnes maze conditioning procedures. Here we report that FAAH (-/-) mice displayed accelerated acquisition rates in an aversively-motivated, but not in the appetitively-motivated, Barnes maze task. The CB(1) receptor antagonist, rimonabant attenuated enhanced acquisition in the aversive procedure, consistent with the idea that elevated AEA levels mediate this apparent nootropic effect. These findings support the hypothesis that stimulation of the endocannabinoid system enhances learned behavior in aversive, but not appetitive, conditioning paradigms.

Differential effects of chronic unpredictable stress on hippocampal CB1 receptors in male and female rats

Chronic unpredictable mild stress (CMS), an animal model of depression, downregulates hippocampal CB1 receptors in adult male rats. Given that endocannabinoids are implicated in modulating stress and anxiety and that women are vulnerable to stress-related disorders, we tested the effects of CMS on both female and male rats. Gonadectomized (gndx) and gonadally intact male and female rats were exposed to a three-week chronic stress protocol. Following CMS, CB1 receptor and fatty-acid-amide-hydrolase (FAAH) expression levels in the hippocampus were assessed by western blot analysis. CMS reliably produced a downregulation of CB1 receptors ( approximately 50%) in the hippocampus of both gndx and intact males. This effect was more robust in the dorsal than in the ventral hippocampus. Conversely, CMS produced an upregulation of CB1 receptors ( approximately 150%) in the hippocampus of both gndx and intact females. This upregulation was only observed in the dorsal hippocampus of female animals. CMS produced an upregulation of FAAH levels in both male and female animals. In non-stress control animals, males were observed to have higher CB1 levels than females, but no differences in FAAH were found. These findings suggest that the endocannabinoid (eCB) system is preferentially organized in male and female animals to respond differentially to chronic stress. These sex differences in the eCB system may help development of novel treatments for stress and depression that are designed specifically for women and men.

Central side-effects of therapies based on CB1 cannabinoid receptor agonists and antagonists: focus on anxiety and depression

Both agonists (e.g. Delta(9)-tetrahydrocannabinol, nabilone) and antagonists (e.g. rimonabant, taranabant) of the cannabinoid type-1 (CB(1)) receptor have been explored as therapeutic agents in diverse fields of medicine such as pain management and obesity with associated metabolic dysregulation, respectively. CB(1) receptors are widely distributed in the central nervous system and are involved in the modulation of emotion, stress and habituation responses, behaviours that are thought to be dysregulated in human psychiatric disorders. Accordingly, CB(1) receptor activation may, in some cases, precipitate episodes of psychosis and panic, while its inhibition may lead to behaviours reminiscent of depression and anxiety-related disorders. The present review discusses these side-effects, which have to be taken into account in the therapeutic exploitation of the endocannabinoid system.