2-AG promotes the expression of conditioned fear via cannabinoid receptor type 1 on GABAergic neurons

The Interplay of Exogenous Cannabinoid Use on Anandamide and 2-Arachidonoylglycerol in Anxiety: Results from a Quasi-Experimental Ad Libitum Study

The public is increasingly reporting using cannabis for anxiety relief. Both cannabis use and the endocannabinoid system have been connected with anxiety relief/anxiolytic properties, but these relationships are complex, and the underlying mechanisms for them are unclear. Background/Objectives: Work is needed to understand how the endocannabinoid system, including the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG), may be impacted by the main constituents of cannabis, Δ9-tetrahydrocannabinol (THC), and cannabidiol (CBD). Methods: The current study examined how the ab libitum use of products differing in THC and CBD affected AEA and 2-AG among 292 individuals randomly assigned to THC-dominant use (N = 92), CBD-dominant use (N = 97), THC + CBD use (N = 74), or non-use (N = 29). Results: The findings suggest that AEA levels do not change differently based on 4 weeks of cannabis use or by cannabinoid content, as AEA similarly increased across all conditions from study weeks 2 to 4. In contrast, AEA decreased at an acute administration session with product conditions containing any THC having greater AEA levels on average than the non-use condition. With regard to 2-AG, its levels appeared to primarily be affected by THC-dominant use, both acutely and over 4 weeks, when controlling for baseline cannabis use and examining study product use frequency among use conditions. Conclusions: Overall, the results continue to shed light on the complicated relationship between cannabinoid content and endocannabinoid production, and highlight the need for continued research on their interplay in human subjects.

Interplay between endocannabinoid and endovanilloid mechanisms in fear conditioning

OBJECTIVE

The transient receptor potential cation channel, subfamily V (vanilloid), member 1 (TRPV1) mediates pain perception to thermal and chemical stimuli in peripheral neurons. The cannabinoid receptor type 1 (CB1), on the other hand, promotes analgesia in both the periphery and the brain. TRPV1 and CB1 have also been implicated in learned fear, which involves the association of a previously neutral stimulus with an aversive event. In this review, we elaborate on the interplay between CB1 receptors and TRPV1 channels in learned fear processing.

METHODS

We conducted a PubMed search for a narrative review on endocannabinoid and endovanilloid mechanisms on fear conditioning.

RESULTS

TRPV1 and CB1 receptors are activated by a common endogenous agonist, arachidonoyl ethanolamide (anandamide), Moreover, they are expressed in common neuroanatomical structures and recruit converging cellular pathways, acting in concert to modulate fear learning. However, evidence suggests that TRPV1 exerts a facilitatory role, whereas CB1 restrains fear responses.

CONCLUSION

TRPV1 and CB1 seem to mediate protective and aversive roles of anandamide, respectively. However, more research is needed to achieve a better understanding of how these receptors interact to modulate fear learning.

Investigating Cannabidiol's potential as a supplementary treatment for schizophrenia: A narrative review

Schizophrenia presents a complex mental health challenge, often inadequately addressed by existing antipsychotic treatments, leading to persistent symptoms and adverse effects. Hence, developing alternative therapeutic approaches is crucial. Cannabidiol (CBD), a nonpsychoactive compound in Cannabis sativa, has been extensively explored for its therapeutic potential in treating psychiatric disorders, including schizophrenia. CBD exhibits antipsychotic, anxiolytic, and neuroprotective effects. However, distinguishing the individual effects of CBD and THC remains challenging. Therefore, this review aims to critically analyze the potential role of CBD as an adjunctive therapy in schizophrenia treatment. The therapeutic action of CBD may involve activating the 5-hydroxytryptamine 1A receptors and suppressing the G-protein-coupled receptor 55, thereby affecting various neurotransmitter systems. Additionally, the anti-inflammatory and antioxidative effects of CBD may contribute to alleviating neuroinflammation linked to schizophrenia. Compared to typical antipsychotics, CBD demonstrates a lower incidence of side effects and it exhibited favorable tolerability in clinical trials. A 2012 clinical trial demonstrated the efficacy of CBD in reducing both positive and negative symptoms of schizophrenia, presenting a safer profile than that of traditional antipsychotics. However, further research is needed to fully establish the safety and efficacy of CBD as an adjunctive treatment. Future research directions encompass exploring detailed antipsychotic mechanisms, long-term safety profiles, interactions with current antipsychotics, optimal dosing, and patient-specific factors such as genetic predispositions. Despite these research needs, the potential of CBD to enhance the quality of life and symptom management positions it as a promising candidate for innovative schizophrenia treatment approaches.

Cannabinoids and monoaminergic system: implications for learning and memory

Cannabinoids and the endocannabinoid system (ECS) have been intensively studied for their neuroregulatory roles in the central nervous system (CNS), especially in regulating learning and memory. However, many experimental and clinical studies obtained conflicting results indicating a complex network of interaction underlying the regulation of learning and memory by different cannabinoids and the ECS. The ECS influences neuronal synaptic communications, and therefore may exert different regulation via their different impact on other neurotransmitters. The monoaminergic system includes a variety of neurotransmitters, such as dopamine, norepinephrine, and serotonin, which play important roles in regulating mood, cognition, and reward. The interaction among cannabinoids, ECS and the monoaminergic system has drawn particular attention, especially their contributions to learning and memory. In this review, we summarized the current understanding of how cannabinoids, ECS and the monoaminergic system contribute to the process of learning and memory, and discussed the influences of monoaminergic neurotransmission by cannabinoids and ECS during this process.

Vaporized Δ9-THC in utero results in reduced birthweight, increased locomotion, and altered wake-cycle activity dependent on dose, sex, and diet in the offspring

AIMS

Preclinical studies have found that chronic ∆9-tetrahydrocannabinol (THC) treatment is directly associated with weight gain when introduced during adolescence and adulthood, but the effect of prenatal THC is unclear. Clinical studies have demonstrated prenatal exposure to THC is a prospective predictor of increased health risks associated with obesity. Our study aims to examine prenatal THC impact on obesity risks in males and females throughout adolescence using a clinically relevant inhalation model.

METHODS

Pregnant rats were exposed to one of the following from gestational day 2 through birth: 10 mg THC, 40 mg THC, or air. Daily 10-min inhalations were conducted in each animal from 0900 to 1200. Offspring from each treatment group were given either a high-fat diet (HFD) or a normal diet (ND). Food and bodyweights were collected daily, while circadian activity, locomotion, and exercise were measured periodically (PND 21-60). Pregnancy weight gain and birth weight were collected to determine early-life developmental effects.

RESULTS

Rats prenatally treated with low-dose THC (LDTHC) generally had lower dark-cycle activity compared with control counterparts, but this altered activity was not observed at the higher dose of THC (HDTHC). In terms of open-field activity, THC doses displayed a general increase in locomotion. In addition, the LDTHC male rats in the ND showed significantly greater exploratory behavior. Prenatal THC had dose-dependent effects on maternal weight gain and birth weight.

CONCLUSIONS

Overall, our findings indicate there are some activity-related and developmental effects of prenatal THC, which may be related to obesity risks later in life.

Pharmacological diacylglycerol lipase inhibition impairs contextual fear extinction in mice

Acquisition and extinction of associative fear memories are critical for guiding adaptive behavioral responses to environmental threats, and dysregulation of these processes is thought to represent important neurobehavioral substrates of trauma and stress-related disorders including posttraumatic stress disorder (PTSD). Endogenous cannabinoid (eCB) signaling has been heavily implicated in the extinction of aversive fear memories and we have recently shown that pharmacological inhibition of 2-arachidonoylglycerol (2-AG) synthesis, a major eCB regulating synaptic suppression, impairs fear extinction in an auditory cue conditioning paradigm. Despite these data, the role of 2-AG signaling in contextual fear conditioning is not well understood. Here, we show that systemic pharmacological blockade of diacylglycerol lipase, the rate-limiting enzyme catalyzing in the synthesis of 2-AG, enhances contextual fear learning and impairs within-session extinction. In sham-conditioned mice, 2-AG synthesis inhibition causes a small increase in unconditioned freezing behavior. No effects of 2-AG synthesis inhibition were noted in the Elevated Plus Maze in mice tested after fear extinction. These data provide support for 2-AG signaling in the suppression of contextual fear learning and the expression of within-session extinction of contextual fear memories.

Inhibition of cannabinoid degradation enhances hippocampal contextual fear memory and exhibits anxiolytic effects

Recent studies have demonstrated the pivotal involvement of endocannabinoids in regulating learning and memory, but the conclusions obtained from different paradigms or contexts are somewhat controversial, and the underlying mechanisms remain largely elusive. Here, we show that JZL195, a dual inhibitor of fatty acid amide hydrolase and monoacylglycerol lipase, can enhance the performance of mice in a contextual fear conditioning task and increase the time spent in open arms in the elevated zero maze (EZM). Although the effect of JZL195 on fear memory could not be inhibited by antagonists of cannabinoid receptors, the effect on the EZM seems to be mediated by CB1R. Simultaneously, hippocampal neurons are hyperactive, and theta oscillation power is significantly increased during the critical period of memory consolidation upon treatment with JZL195. These results suggest the feasibility of targeting the endocannabinoid system for the treatment of various mental disorders.

Biobehavioral Interactions between Endocannabinoid and Hypothalamicpituitary- adrenal Systems in Psychosis: A Systematic Review

BACKGROUND

The diathesis-stress paradigm and the cannabinoid-hypothesis have been proposed as possible pathophysiological models of schizophrenia. However, they have historically been studied independently of each other.

OBJECTIVE

This PRISMA 2020-compliant systematic review aimed at reappraising the interplay between the hypothalamic-pituitary-adrenal (HPA) axis and the endocannabinoid (eCB) system in psychosis- spectrum disorder risk and outcome.

METHODS

All pathophysiological and outcome clinical studies, concomitantly evaluating the two systems in psychosis-spectrum disorder risk and different stages of illness, were gathered from electronic databases (Pubmed, Web of Science, and Scopus), and discussed.

RESULTS

41 eligible outputs were extracted, focusing on at least a biological measure (9 HPA-related studies: 4 eCB-interventional, 1 HPA-interventional, 1 both HPA-interventional and non-interventional, 3 non-interventional; 2 eCB-related studies: non-interventional), environmental measures only (29 studies: 1 eCB- interventional, 28 non-interventional), and genetic measures (1 study: non-interventional). Independent contributions of aberrancies in the two systems to the physiopathology and outcome of psychosis were confirmed. Also, concomitant alterations in the two systems, either genetically defined (e.g., CNR1 genetic variation), biologically determined (e.g., dysfunctional HPA axis or endocannabinoid signaling), or behaviorally imputed (e.g., cannabis use, stress exposure, and response), were consistently reported in psychosis. Further, a complex biobehavioral perturbation was revealed not only within each system (e.g., cannabis use affecting the eCB tone, stress exposure affecting the HPA axis), but also across the two systems (e.g., THC affecting the HPA axis, childhood trauma affecting the endocannabinoid signaling).

CONCLUSION

There is a need to concomitantly study the two systems' mechanistic contribution to psychosis in order to establish more refined biological relevance.

The marijuana-schizophrenia multifaceted nexus: Connections and conundrums towards neurophysiology

Delta-9-tetrahydrocannabinol, a component of marijuana, interacts with cannabinoid receptors in brain involved in memory, cognition, and emotional control. However, marijuana use and schizophrenia development is a complicated and contentious topic. As a result, more investigation is needed to understand this relationship. Through the functional enrichment analysis, we report the delta-9-tetrahydrocannabinol to manipulate the homeostatic biological process and molecular function of different macromolecules. Additionally, using molecular docking and subsequent processing for molecular simulations, we assessed the binding ability of delta-9-tetrahydrocannabinol with the estrogen-related protein, dopamine receptor 5, and hyaluronidase. It was found that delta-9-tetrahydrocannabinol may have an impact on the brain's endocannabinoid system and may trigger the schizophrenia progression in vulnerable people. Delta-9-tetrahydrocannabinol may interfere with the biological function of 18 proteins linked to schizophrenia and disrupt the synaptic transmission (dopamine, glutamine, and gamma-aminobutyric acid). It was discovered that it may affect lipid homeostasis, which is closely related to membrane integrity and synaptic plasticity. The negative control of cellular and metabolic processes, fatty acids binding /activity, and the manipulated endocannabinoid system (targeting cannabinoid receptors) were also concerned with delta-9-tetrahydrocannabinol. Hence, this may alter neurotransmitter signaling involved in memory, cognition, and emotional control, showing its direct impact on brain physiological processes. This may be one of the risk factors for schizophrenia development which is also closely tied to some other variables such as frequency, genetic vulnerability, dosage, and individual susceptibility.

Emerging Therapeutic Potential of Cannabidiol (CBD) in Neurological Disorders: A Comprehensive Review

Cannabidiol (CBD), derived from Cannabis sativa, has gained remarkable attention for its potential therapeutic applications. This thorough analysis explores the increasing significance of CBD in treating neurological conditions including epilepsy, multiple sclerosis, Parkinson's disease, and Alzheimer's disease, which present major healthcare concerns on a worldwide scale. Despite the lack of available therapies, CBD has been shown to possess a variety of pharmacological effects in preclinical and clinical studies, making it an intriguing competitor. This review brings together the most recent findings on the endocannabinoid and neurotransmitter systems, as well as anti-inflammatory pathways, that underlie CBD's modes of action. Synthesized efficacy and safety assessments for a range of neurological illnesses are included, covering human trials, in vitro studies, and animal models. The investigation includes how CBD could protect neurons, control neuroinflammation, fend off oxidative stress, and manage neuronal excitability. This study emphasizes existing clinical studies and future possibilities in CBD research, addressing research issues such as regulatory complications and contradicting results, and advocates for further investigation of therapeutic efficacy and ideal dose methodologies. By emphasizing CBD's potential to improve patient well-being, this investigation presents a revised viewpoint on its suitability as a therapeutic intervention for neurological illnesses.

A cortico-amygdala neural substrate for endocannabinoid modulation of fear extinction

Preclinical and clinical studies implicate endocannabinoids (eCBs) in fear extinction, but the underlying neural circuit basis of these actions is unclear. Here, we employed in vivo optogenetics, eCB biosensor imaging, ex vivo electrophysiology, and CRISPR-Cas9 gene editing in mice to examine whether basolateral amygdala (BLA)-projecting medial prefrontal cortex (mPFC) neurons represent a neural substrate for the effects of eCBs on extinction. We found that photoexcitation of mPFC axons in BLA during extinction mobilizes BLA eCBs. eCB biosensor imaging showed that eCBs exhibit a dynamic stimulus-specific pattern of activity at mPFC→BLA neurons that tracks extinction learning. Furthermore, using CRISPR-Cas9-mediated gene editing, we demonstrated that extinction memory formation involves eCB activity at cannabinoid CB1 receptors expressed at vmPFC→BLA synapses. Our findings reveal the temporal characteristics and a neural circuit basis of eCBs' effects on fear extinction and inform efforts to target the eCB system as a therapeutic approach in extinction-deficient neuropsychiatric disorders.

Goods and Bads of the Endocannabinoid System as a Therapeutic Target: Lessons Learned after 30 Years

The cannabis derivative marijuana is the most widely used recreational drug in the Western world and is consumed by an estimated 83 million individuals (∼3% of the world population). In recent years, there has been a marked transformation in society regarding the risk perception of cannabis, driven by its legalization and medical use in many states in the United States and worldwide. Compelling research evidence and the Food and Drug Administration cannabis-derived cannabidiol approval for severe childhood epilepsy have confirmed the large therapeutic potential of cannabidiol itself, Δ9-tetrahydrocannabinol and other plant-derived cannabinoids (phytocannabinoids). Of note, our body has a complex endocannabinoid system (ECS)-made of receptors, metabolic enzymes, and transporters-that is also regulated by phytocannabinoids. The first endocannabinoid to be discovered 30 years ago was anandamide (N-arachidonoyl-ethanolamine); since then, distinct elements of the ECS have been the target of drug design programs aimed at curing (or at least slowing down) a number of human diseases, both in the central nervous system and at the periphery. Here a critical review of our knowledge of the goods and bads of the ECS as a therapeutic target is presented to define the benefits of ECS-active phytocannabinoids and ECS-oriented synthetic drugs for human health. SIGNIFICANCE STATEMENT: The endocannabinoid system plays important roles virtually everywhere in our body and is either involved in mediating key processes of central and peripheral diseases or represents a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of the components of this complex system, and in particular of key receptors (like cannabinoid receptors 1 and 2) and metabolic enzymes (like fatty acid amide hydrolase and monoacylglycerol lipase), will advance our understanding of endocannabinoid signaling and activity at molecular, cellular, and system levels, providing new opportunities to treat patients.

Cannabidiol: Bridge between Antioxidant Effect, Cellular Protection, and Cognitive and Physical Performance

The literature provides scientific evidence for the beneficial effects of cannabidiol (CBD), and these effects extend beyond epilepsy treatment (e.g., Lennox-Gastaut and Dravet syndromes), notably the influence on oxidative status, neurodegeneration, cellular protection, cognitive function, and physical performance. However, products containing CBD are not allowed to be marketed everywhere in the world, which may ultimately have a negative effect on health as a result of the uncontrolled CBD market. After the isolation of CBD follows the discovery of CB1 and CB2 receptors and the main enzymatic components (diacylglycerol lipase (DAG lipase), monoacyl glycerol lipase (MAGL), fatty acid amino hydrolase (FAAH)). At the same time, the antioxidant potential of CBD is due not only to the molecular structure but also to the fact that this compound increases the expression of the main endogenous antioxidant systems, superoxide dismutase (SOD), and glutathione peroxidase (GPx), through the nuclear complex erythroid 2-related factor (Nrf2)/Keep1. Regarding the role in the control of inflammation, this function is exercised by inhibiting (nuclear factor kappa B) NF-κB, and also the genes that encode the expression of molecules with a pro-inflammatory role (cytokines and metalloproteinases). The other effects of CBD on cognitive function and physical performance should not be excluded. In conclusion, the CBD market needs to be regulated more thoroughly, given the previously listed properties, with the mention that the safety profile is a very good one.

Endocannabinoids at the synapse and beyond: implications for neuropsychiatric disease pathophysiology and treatment

Endocannabinoids (eCBs) are lipid neuromodulators that suppress neurotransmitter release, reduce postsynaptic excitability, activate astrocyte signaling, and control cellular respiration. Here, we describe canonical and emerging eCB signaling modes and aim to link adaptations in these signaling systems to pathological states. Adaptations in eCB signaling systems have been identified in a variety of biobehavioral and physiological process relevant to neuropsychiatric disease states including stress-related disorders, epilepsy, developmental disorders, obesity, and substance use disorders. These insights have enhanced our understanding of the pathophysiology of neurological and psychiatric disorders and are contributing to the ongoing development of eCB-targeting therapeutics. We suggest future studies aimed at illuminating how adaptations in canonical as well as emerging cellular and synaptic modes of eCB signaling contribute to disease pathophysiology or resilience could further advance these novel treatment approaches.

Are the epigenetic changes predictive of therapeutic efficacy for psychiatric disorders? A translational approach towards novel drug targets

The etiopathogenesis of mental disorders is not fully understood and accumulating evidence support that clinical symptomatology cannot be assigned to a single gene mutation, but it involves several genetic factors. More specifically, a tight association between genes and environmental risk factors, which could be mediated by epigenetic mechanisms, may play a role in the development of mental disorders. Several data suggest that epigenetic modifications such as DNA methylation, post-translational histone modification and interference of microRNA (miRNA) or long non-coding RNA (lncRNA) may modify the severity of the disease and the outcome of the therapy. Indeed, the study of these mechanisms may help to identify patients particularly vulnerable to mental disorders and may have potential utility as biomarkers to facilitate diagnosis and treatment of psychiatric disorders. This article summarizes the most relevant preclinical and human data showing how epigenetic modifications can be central to the therapeutic efficacy of antidepressant and/or antipsychotic agents, as possible predictor of drugs response.

Ventral hippocampal diacylglycerol lipase-alpha deletion decreases avoidance behaviors and alters excitation-inhibition balance

The endogenous cannabinoid, 2-arachidonoylglycerol (2-AG), plays a key role in the regulation of anxiety- and stress-related behavioral phenotypes and may represent a novel target for the treatment of anxiety disorders. However, recent studies have suggested a more complex role for 2-AG signaling in the regulation of stress responsivity, including increases in acute fear responses after 2-AG augmentation under some conditions. Thus, 2-AG signaling within distinct brain regions and circuits could regulate anxiety-like behavior and stress responsivity in opposing manners. The ventral hippocampus (vHPC) is a critical region for emotional processing, anxiety-like behaviors, and stress responding. Here, we use a conditional knock-out of the 2-AG synthesis enzyme, diacylglycerol lipase α (DAGLα), to study the role of vHPC 2-AG signaling in the regulation of affective behavior. We show that vHPC DAGLα deletion decreases avoidance behaviors both basally and following an acute stress exposure. Genetic deletion of vHPC DAGLα also promotes stress resiliency, with no effect on fear acquisition, expression, or contextual fear generalization. Using slice electrophysiology, we demonstrate that vHPC DAGLα deletion shifts vHPC activity towards enhanced inhibition. Together, these data indicate endogenous 2-AG signaling in the vHPC promotes avoidance and increases stress reactivity, confirming the notion that 2-AG signaling within distinct brain regions may exert divergent effects on anxiety states and stress adaptability.

Endocannabinoid metabolism inhibition has no effect on spontaneous fear recovery or extinction resistance in Lister hooded rats

Endocannabinoid transmission is emerging as a target for treating anxiety-related disorders, given its regulation of fear extinction. Boosting anandamide levels via inhibition of its metabolism by fatty acid amide hydrolase (FAAH) can enhance extinction, whereas inhibiting monoacylglycerol lipase (MAGL) to elevate 2-arachidonoylglycerol levels can impair extinction. However, whether endocannabinoids regulate fear relapse over time or extinction resistance remains unclear. In two experiments using auditory fear conditioned rats, we examined the effects of the FAAH inhibitor URB597 and the MAGL inhibitor JZL184 administered systemically on 1) spontaneous fear recovery after delayed extinction, and 2) extinction resistance resulting from immediate extinction [the immediate extinction deficit (IED)]. In Experiment 1, URB597 or JZL184 was given immediately after delayed extinction occurring 24 h after conditioning. Extinction recall and spontaneous fear recovery were tested drug-free 1 and 21 days later, respectively. We found no effects of either drug on extinction recall or spontaneous fear recovery. In Experiment 2, URB597 or JZL184 was given before immediate extinction occurring 30 min after conditioning and extinction recall was tested drug-free the next day. We also examined the effects of propranolol, a beta-adrenoceptor antagonist that can rescue the IED, as a positive control. JZL184 enhanced fear expression and impaired extinction learning but we found no lasting effects of URB597 or JZL184 on cued extinction recall. Propranolol reduced fear expression but, unexpectedly, had no enduring effect on extinction recall. The results are discussed in relation to various methodological differences between previous studies examining endocannabinoid and adrenergic regulation of fear extinction.

The Endocannabinoid 2-Arachidonoylglycerol Bidirectionally Modulates Acute and Protracted Effects of Predator Odor Exposure

BACKGROUND

Stress-related disorders are among the most prevalent psychiatric disorders, characterized by excess fear and enhanced avoidance of trauma triggers. Elucidating the mechanisms regulating temporally distinct aspects of innate and conditioned fear responses could facilitate novel therapeutic development for stress-related disorders. One potential target that has recently emerged is the endocannabinoid system, which has been reported to mediate the physiological response to stress and represents an important substrate underlying individual differences in stress susceptibility.

METHODS

Here, we exposed male and female CD-1 mice to an innate predator stressor, 2MT (2-methyl-2-thiazoline), to investigate the ability of endocannabinoid signaling to modulate temporally distinct innate and conditioned fear behaviors.

RESULTS

We found that 2MT exposure increased amygdala 2-AG (2-arachidonoylglycerol) content and selectively increased excitability in central, but not basolateral, amygdala neurons. We also found that pharmacological 2-AG augmentation during stress exposure exacerbated both acute freezing responses and central amygdala hyperexcitability via cannabinoid receptor type 1- and type 2-dependent mechanisms. Finally, 2-AG augmentation during stress exposure reduced long-term contextual conditioned freezing, and 2-AG augmentation 24 hours after stress exposure reduced conditioned avoidance behavior.

CONCLUSIONS

Our findings demonstrate a bidirectional effect of 2-AG augmentation on innate and conditioned fear behavior, with enhancement of 2-AG levels during stress promoting innate fear responses but ultimately resulting in long-term conditioned fear reduction. These data could reconcile contradictory data on the role of 2-AG in the regulation of innate and conditioned fear-related behavioral responses.

Potential Role of Cannabinoid Type 2 Receptors in Neuropsychiatric and Neurodegenerative Disorders

The endocannabinoid system (ECS) is composed of the two canonical receptor subtypes; type-1 cannabinoid (CB1R) and type 2 receptor (CB2R), endocannabinoids (eCBs) and enzymes responsible for the synthesis and degradation of eCBs. Recently, with the identification of additional lipid mediators, enzymes and receptors, the expanded ECS called the endocannabinoidome (eCBome) has been identified and recognized. Activation of CB1R is associated with a plethora of physiological effects and some central nervous system (CNS) side effects, whereas, CB2R activation is devoid of such effects and hence CB2Rs might be utilized as potential new targets for the treatment of different disorders including neuropsychiatric disorders. Previous studies suggested that CB2Rs were absent in the brain and they were considered as peripheral receptors, however, recent studies confirmed the presence of CB2Rs in different brain regions. Several studies have now focused on the characterization of its physiological and pathological roles. Studies done on the role of CB2Rs as a therapeutic target for treating different disorders revealed important putative role of CB2R in neuropsychiatric disorders that requires further clinical validation. Here we provide current insights and knowledge on the potential role of targeting CB2Rs in neuropsychiatric and neurodegenerative disorders. Its non-psychoactive effect makes the CB2R a potential target for treating CNS disorders; however, a better understanding of the fundamental pharmacology of CB2R activation is essential for the design of novel therapeutic strategies.

Behavioral Studies of p62 KO Animals with Implications of a Modulated Function of the Endocannabinoid System

Elementary emotional states and memory can be regulated by the homeostasis of the endocannabinoid system (ECS). Links between the ECS and the autophagy receptor p62 have been found at the molecular level and in animal studies. This project aimed to validate the anxiety and memory phenotype of p62 knockout (KO) animals and whether the ECS plays a role in this. We examined the behavior of p62 KO animals and analyzed whether endocannabinoid levels are altered in the responsible brain areas. We discovered in age-dependent obese p62-KO mice decreased anandamide levels in the amygdala, a brain structure important for emotional responses. Against our expectation, p62 KO animals did not exhibit an anxiety phenotype, but showed slightly increased exploratory behavior as evidenced in novel object and further tests. In addition, KO animals exhibited decreased freezing responses in the fear conditioning. Administration of the phytocannabinoid delta9-tetrahydrocannabinol (THC) resulted in lesser effects on locomotion but in comparable hypothermic effects in p62 KO compared with WT littermates. Our results do not confirm previously published results, as our mouse line does not exhibit a drastic behavioral phenotype. Moreover, we identified further indications of a connection to the ECS and hence offer new perspectives for future investigations.

Anti-aversive effect of 2-arachidonoylglycerol in the dorsolateral periaqueductal gray of male rats in contextual fear conditioning and Vogel tests

The endocannabinoid system modulates the stress coping strategies in the dorsolateral periaqueductal grey (dlPAG). The most relevant endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG) exert inhibitory control over defensive reactions mediated by the dlPAG. However, the protective role of anandamide is limited by its lack of effect in higher concentrations. Thus, the 2-AG emerges as a complementary target for developing new anxiolytic compounds. Nevertheless, the role of 2-AG on stress responsivity may vary according to the nature of the stimulus. In this study, we verified whether the dlPAG injection of 2-AG or inhibitors of its hydrolysis induce anxiolytic-like effects in male Wistar rats exposed to behavioral models in which physical stress (mild electric shock) is a critical component, namely the contextual fear conditioning test (CFC) and the Vogel conflict test (VCT). We also investigated the contribution of cannabinoid receptor type 1 (CB1) and type 2 (CB2) in such effects. The facilitation of 2-AG signaling in the dlPAG reduced contextual fear expression and exhibited an anxiolytic-like effect in the VCT in a mechanism dependent on activation of CB1 and CB2. However, the VCT required a higher dose than CFC. Further, the monoacylglycerol inhibitors, which inhibit the hydrolysis of 2-AG, were effective only in the CFC. In conclusion, we confirmed the anti-aversive properties of 2-AG in the dlPAG through CB1 and CB2 mechanisms. However, these effects could vary according to the type of stressor and the anxiety model employed.

Cannabinoid drugs against chemotherapy-induced adverse effects: focus on nausea/vomiting, peripheral neuropathy and chemofog in animal models

Although new drugs are being developed for cancer treatment, classical chemotherapeutic agents are still front-line therapies, despite their frequent association with severe side effects that can hamper their use. Cannabinoids may prevent or palliate some of these side effects. The aim of the present study is to review the basic research which has been conducted evaluating the effects of cannabinoid drugs in the treatment of three important side effects induced by classical chemotherapeutic agents: nausea and vomiting, neuropathic pain and cognitive impairment. Several published studies have demonstrated that cannabinoids are useful in preventing and reducing the nausea, vomits and neuropathy induced by different chemotherapy regimens, though other side effects can occur, such as a reduction of gastrointestinal motility, along with psychotropic effects when using centrally-acting cannabinoids. Thus, peripherally-acting cannabinoids and new pharmacological options are being investigated, such as allosteric or biased agonists. Additionally, due to the increase in the survival of cancer patients, there are emerging data that demonstrate an important cognitive deterioration due to chemotherapy, and because the cannabinoid drugs have a neuroprotective effect, they could be useful in preventing chemotherapy-induced cognitive impairment (as demonstrated through studies in other neurological disorders), but this has not yet been tested. Thus, although cannabinoids seem a promising therapeutic approach in the treatment of different side effects induced by chemotherapeutic agents, future research will be necessary to find pharmacological options with a safer profile. Moreover, a new line of research awaits to be opened to elucidate their possible usefulness in preventing cognitive impairment.

The role of the cannabinoid system in fear memory and extinction in male and female mice

The prevalence of post-traumatic stress disorder (PTSD) is higher in women than in men. Among both humans and mice, females exhibit higher resistance to fear extinction than males, suggesting that differences between sexes in fear-extinction processes are involved in the pathophysiology of such fear-related diseases. Sex differences in molecular mechanisms underlying fear memory and extinction are unclear. The cannabinoid (CB) system is well known to be involved in fear memory and extinction, but this involvement is based mainly on experiments using male rodents. It is not known whether there are sex differences in the role of the CB system in fear memory and extinction. To explore this possibility, we investigated the effects of pharmacological manipulations of the CB system on the retrieval and extinction of contextual fear memory in male and female mice. WIN55,212-2, a CB receptor (CBR) agonist, augmented the retrieval of fear memory in both sexes, but SR141716 (a CB1R antagonist) did not affect it in either sex. An enhancement of 2-arachidonylglycerol (2-AG, one of the two major endocannabinoids) via JZL184 (an inhibitor of the 2-AG hydrolase monoacylglycerol lipase [MAGL]), augmented the retrieval of fear memory through the activation of CB1R but not CB2R in female mice. In contrast, the enhancement of N-arachidonylethanolamine (AEA, the other major endocannabinoid) via URB597, an inhibitor of an AEA hydrolase (fatty acid amide hydrolase-1) did not show any effects on the retrieval of fear memory in either sex. WIN55,212-2, SR141716, and JZL184 inhibited fear extinction irrespective of sex. URB enhanced fear extinction in females that were in diestrus phase at the first extinction session, but not in males. These results suggest that although the role of CB1R in the retrieval and extinction of contextual fear memory is common among males and females, the effects of an increase in endocannabinoid levels on the retrieval or extinction of contextual fear memory differ between the sexes.

TRPV1 blockers as potential new treatments for psychiatric disorders

The transient receptor potential vanilloid-1 channel (TRPV1) is responsible for decoding physical and chemical stimuli. TRPV1 is activated by capsaicin (a compound from chili peppers), heat (above 43°C) and acid environment, playing a major role in pain, inflammation and body temperature. Molecular and histological studies have suggested TRPV1 expression in specific brain regions, where it can be activated primarily by the endocannabinoid anandamide, fostering studies on its potential role in psychiatric disorders. TRPV1 blockers are effective in various animal models predictive of anxiolytic and antipanic activities, in addition to reducing conditioned fear. In models of antidepressant activity, these compounds reduce behavioral despair and promote active stress-coping behavior. TRPV1 blockers also reduce the effects of certain drugs of abuse and revert behavioral changes in animal models of neurodevelopmental disorders. The main limiting factor in developing TRPV1 blockers as therapeutic agents concerns their effects on body temperature, particularly hyperthermia. New compounds, which block specific states of the channel, could represent an alternative. Moreover, compounds blocking both TRPV1 and the anandamide-hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), termed dual TRPV1/FAAH blockers, have been investigated with promising results. Overall, preclinical studies yield favorable results with TRPV1 blockers in animal models of psychiatric disorders.

Targeting the Endocannabinoid System in the Treatment of Posttraumatic Stress Disorder: A Promising Case of Preclinical-Clinical Translation?

The endocannabinoid (eCB) system is one the most ubiquitous signaling systems of the brain and offers a rich pharmacology including multiple druggable targets. Preclinical research shows that eCB activity influences functional connectivity between the prefrontal cortex and amygdala and thereby influences an organism's ability to cope with threats and stressful experiences. Animal studies show that CB1 receptor activation within the amygdala is essential for extinction of fear memories. Failure to extinguish traumatic memories is a core symptom of posttraumatic stress disorder, suggesting that potentiating eCB signaling may have a therapeutic potential in this condition. However, it has been unknown whether animal findings in this domain translate to humans. Data to inform this critical question are now emerging and are the focus of this review. We first briefly summarize the biology of the eCB system and the animal studies that support its role in fear extinction and stress responding. We then discuss the pharmacological eCB-targeting strategies that may be exploited for therapeutic purposes: direct CB1 receptor activation, using Δ9-tetrahydrocannabinol or its synthetic analogs; or indirect potentiation, through inhibition of eCB-degrading enzymes, the anandamide-degrading enzyme fatty acid amide hydrolase; or the 2-AG (2-arachidonoyl glycerol)-degrading enzyme monoacylglycerol lipase. We then review recent human data on direct CB1 receptor activation via Δ9-tetrahydrocannabinol and anandamide potentiation through fatty acid amide hydrolase blockade. The available human data consistently support a translation of animal findings on fear memories and stress reactivity and suggest a potential therapeutic utility in humans.

Polypharmacological Approaches for CNS Diseases: Focus on Endocannabinoid Degradation Inhibition

Polypharmacology breaks up the classical paradigm of “one-drug, one target, one disease” electing multitarget compounds as potential therapeutic tools suitable for the treatment of complex diseases, such as metabolic syndrome, psychiatric or degenerative central nervous system (CNS) disorders, and cancer. These diseases often require a combination therapy which may result in positive but also negative synergistic effects. The endocannabinoid system (ECS) is emerging as a particularly attractive therapeutic target in CNS disorders and neurodegenerative diseases including Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), stroke, traumatic brain injury (TBI), pain, and epilepsy. ECS is an organized neuromodulatory network, composed by endogenous cannabinoids, cannabinoid receptors type 1 and type 2 (CB₁ and CB₂), and the main catabolic enzymes involved in the endocannabinoid inactivation such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The multiple connections of the ECS with other signaling pathways in the CNS allows the consideration of the ECS as an optimal source of inspiration in the development of innovative polypharmacological compounds. In this review, we focused our attention on the reported polypharmacological examples in which FAAH and MAGL inhibitors are involved.

New Insights and Potential Therapeutic Targeting of CB2 Cannabinoid Receptors in CNS Disorders

The endocannabinoid system (ECS) is ubiquitous in most human tissues, and involved in the regulation of mental health. Consequently, its dysregulation is associated with neuropsychiatric and neurodegenerative disorders. Together, the ECS and the expanded endocannabinoidome (eCBome) are composed of genes coding for CB1 and CB2 cannabinoid receptors (CB1R, CB2R), endocannabinoids (eCBs), and the metabolic enzyme machinery for their synthesis and catabolism. The activation of CB1R is associated with adverse effects on the central nervous system (CNS), which has limited the therapeutic use of drugs that bind this receptor. The discovery of the functional neuronal CB2R raised new possibilities for the potential and safe targeting of the ECS for the treatment of CNS disorders. Previous studies were not able to detect CB2R mRNA transcripts in brain tissue and suggested that CB2Rs were absent in the brain and were considered peripheral receptors. Studies done on the role of CB2Rs as a potential therapeutic target for treating different disorders revealed the important putative role of CB2Rs in certain CNS disorders, which requires further clinical validation. This review addresses recent advances on the role of CB2Rs in neuropsychiatric and neurodegenerative disorders, including, but not limited to, anxiety, depression, schizophrenia, Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD) and addiction.

Changes in Expression of DNA-Methyltransferase and Cannabinoid Receptor mRNAs in Blood Lymphocytes After Acute Cannabis Smoking

BACKGROUND

Cannabis use is a component risk factor for the manifestation of schizophrenia. The biological effects of cannabis include effects on epigenetic systems, immunological parameters, in addition to changes in cannabinoid receptors 1 and 2, that may be associated with this risk. However, there has been limited study of the effects of smoked cannabis on these biological effects in human peripheral blood cells. We analyzed the effects of two concentrations of tetrahydrocannabinol (THC) vs. placebo in lymphocytes of a subset of participants who enrolled in a double-blind study of the effects of cannabis on driving performance (outcome not the focus of this study).

METHODS

Twenty four participants who regularly use cannabis participated in an experiment in which they smoked cannabis cigarettes (5.9 or 13.4% THC) or placebo (0.02%) ad libitum. Blood samples were drawn at baseline and several times after smoking. Lymphocytes were separated and stored at -80^°C for further analysis. Samples were analyzed for mRNA content for cannabinoid receptors 1 (CB1) and 2 (CB2), methylation and demethylating enzymes (DNMT, TET), glucocorticoid receptor (NRC3) and immunological markers (IL1B, TNFα) by qPCR using TaqMan probes. The results were correlated with THC whole blood levels during the course of the day, as well as THCCOOH baseline levels. Statistical analyses used analysis of variance and covariance and t-tests, or non-parametric equivalents for those values which were not normally distributed.

RESULTS

There were no differences in background baseline characteristics of the participants except that the higher concentration THC group was older than the low concentration and placebo groups, and the low concentration THC group had higher baseline CB2 mRNA levels. Both the 5.9 and 13.4% THC groups showed increased THC blood levels that then decreased toward baseline within the first hour. However, there were no significant differences between THC blood levels between the 5.9 and 13.4% groups at any time point. At the 4-h time point after drug administration the 13.4% THC group had higher CB2 (P = 0.021) and DNMT3A (P = 0.027) mRNA levels than the placebo group. DNMT1 mRNA levels showed a trend in the same direction (P = 0.056). The higher 13.4% THC group had significantly increased CB2 mRNA levels than the 5.9% concentration group at several post drug administration time points and showed trends for difference in effects for between 5.9 and 13.4% THC groups for other mRNAs. TET3 mRNA levels were higher in the 13.4% THC group at 55 min post-cannabis ingestion. When the high and lower concentration THC groups were combined, none of the differences in mRNA levels from placebo remained statistically significant. Changes in THC blood levels were not related to changes in mRNA levels.

CONCLUSION

Over the time course of this study, CB2 mRNA increased in blood lymphocytes in the high concentration THC group but were not accompanied by changes in immunological markers. The changes in DNMT and TET mRNAs suggest potential epigenetic effects of THC in human lymphocytes. Increases in DNMT methylating enzymes have been linked to some of the pathophysiological processes in schizophrenia and, therefore, should be further explored in a larger sample population, as one of the potential mechanisms linking cannabis use as a trigger for schizophrenia in vulnerable individuals. Since the two THC groups did not differ in post-smoking blood THC concentrations, the relationship between lymphocytic changes and the THC content of the cigarettes remains to be determined.

Sex differences in anxiety and depression: circuits and mechanisms

Epidemiological sex differences in anxiety disorders and major depression are well characterized. Yet the circuits and mechanisms that contribute to these differences are understudied, because preclinical studies have historically excluded female rodents. This oversight is beginning to be addressed, and recent studies that include male and female rodents are identifying sex differences in neurobiological processes that underlie features of these disorders, including conflict anxiety, fear processing, arousal, social avoidance, learned helplessness and anhedonia. These findings allow us to conceptualize various types of sex differences in the brain, which in turn have broader implications for considering sex as a biological variable. Importantly, comparing the sexes could aid in the discovery of novel therapeutics.

Quality of Life and a Surveillant Endocannabinoid System

The endocannabinoid system (ECS) is an important brain modulatory network. ECS regulates brain homeostasis throughout development, from progenitor fate decision to neuro- and gliogenesis, synaptogenesis, brain plasticity and circuit repair, up to learning, memory, fear, protection, and death. It is a major player in the hypothalamic-peripheral system-adipose tissue in the regulation of food intake, energy storage, nutritional status, and adipose tissue mass, consequently affecting obesity. Loss of ECS control might affect mood disorders (anxiety, hyperactivity, psychosis, and depression), lead to drug abuse, and impact neurodegenerative (Alzheimer's, Parkinson, Huntington, Multiple, and Amyotrophic Lateral Sclerosis) and neurodevelopmental (autism spectrum) disorders. Practice of regular physical and/or mind-body mindfulness and meditative activities have been shown to modulate endocannabinoid (eCB) levels, in addition to other players as brain-derived neurotrophic factor (BDNF). ECS is involved in pain, inflammation, metabolic and cardiovascular dysfunctions, general immune responses (asthma, allergy, and arthritis) and tumor expansion, both/either in the brain and/or in the periphery. The reason for such a vast impact is the fact that arachidonic acid, a precursor of eCBs, is present in every membrane cell of the body and on demand eCBs synthesis is regulated by electrical activity and calcium shifts. Novel lipid (lipoxins and resolvins) or peptide (hemopressin) players of the ECS also operate as regulators of physiological allostasis. Indeed, the presence of cannabinoid receptors in intracellular organelles as mitochondria or lysosomes, or in nuclear targets as PPARγ might impact energy consumption, metabolism and cell death. To live a better life implies in a vigilant ECS, through healthy diet selection (based on a balanced omega-3 and -6 polyunsaturated fatty acids), weekly exercises and meditation therapy, all of which regulating eCBs levels, surrounded by a constructive social network. Cannabidiol, a diet supplement has been a major player with anti-inflammatory, anxiolytic, antidepressant, and antioxidant activities. Cognitive challenges and emotional intelligence might strengthen the ECS, which is built on a variety of synapses that modify human behavior. As therapeutically concerned, the ECS is essential for maintaining homeostasis and cannabinoids are promising tools to control innumerous targets.

Phytocannabinoids and schizophrenia: Focus on adolescence as a critical window of enhanced vulnerability and opportunity for treatment

The recent shift in socio-political debates and growing liberalization of Cannabis use across the globe has raised concern regarding its impact on vulnerable populations such as adolescents. Concurrent with declining perception of Cannabis harms, more adolescents are using it daily in several countries and consuming marijuana strains with high content of psychotropic delta (9)-tetrahydrocannabinol (THC). These dual, related trends seem to facilitate the development of compromised social and cognitive performance at adulthood, which are described in preclinical and human studies. Cannabis exerts its effects via altering signalling within the endocannabinoid system (ECS), which modulates the stress circuitry during the neurodevelopment. In this context early interventions appear to circumvent the emergence of adult neurodevelopmental deficits. Accordingly, Cannabis sativa second-most abundant compound, cannabidiol (CBD), emerges as a potential therapeutic agent to treat neuropsychiatric disorders. We first focus on human and preclinical studies on the long-term effects induced by adolescent THC exposure as a "critical window" of enhanced neurophysiological vulnerability, which could be involved in the pathophysiology of schizophrenia and related primary psychotic disorders. Then, we focus on adolescence as a "window of opportunity" for early pharmacological treatment, as novel risk reduction strategy for neurodevelopmental disorders. Thus, we review current preclinical and clinical evidence regarding the efficacy of CBD in terms of positive, negative and cognitive symptoms treatment, safety profile, and molecular targets.

Spontaneous and Naloxone-Precipitated Withdrawal Behaviors From Chronic Opiates are Accompanied by Changes in N-Oleoylglycine and N-Oleoylalanine Levels in the Brain and Ameliorated by Treatment With These Mediators

Rationale: The endocannabinoidome mediators, N-Oleoylglycine (OlGly) and N-Oleoylalanine (OlAla), have been shown to reduce acute naloxone-precipitated morphine withdrawal affective and somatic responses.

Objectives: To determine the role and mechanism of action of OlGly and OlAla in withdrawal responses from chronic exposure to opiates in male Sprague-Dawley rats.

Methods: Opiate withdrawal was produced: 1) spontaneously 24 h following chronic exposure to escalating doses of morphine over 14 days (Experiments 1 and 2) and steady-state exposure to heroin by minipumps for 12 days (Experiment 3), 2) by naloxone injection during steady-state heroin exposure (Experiment 4), 3) by naloxone injection during operant heroin self-administration (Experiment 5).

Results: In Experiment 1, spontaneous morphine withdrawal produced somatic withdrawal reactions. The behavioral withdrawal reactions were accompanied by suppressed endogenous levels of OlGly in the nucleus accumbens, amygdala, and prefrontal cortex, N-Arachidonylglycerol and OlAla in the amygdala, 2-arachidonoylglycerol in the nucleus accumbens, amygdala and interoceptive insular cortex, and by changes in colonic microbiota composition. In Experiment 2, treatment with OlAla, but not OlGly, reduced spontaneous morphine withdrawal responses. In Experiment 3, OlAla attenuated spontaneous steady-state heroin withdrawal responses at both 5 and 20 mg/kg; OlGly only reduced withdrawal responses at the higher dose of 20 mg/kg. Experiment 4 demonstrated that naloxone-precipitated heroin withdrawal from steady-state exposure to heroin (7 mg/kg/day for 12 days) is accompanied by tissue-specific changes in brain or gut endocannabinoidome mediator, including OlGly and OlAla, levels and colonic microbiota composition, and that OlAla (5 mg/kg) attenuated behavioural withdrawal reactions, while also reversing some of the changes in brain and gut endocannabinoidome and gut microbiota induced by naloxone. Experiment 5 demonstrated that although OlAla (5 mg/kg) did not interfere with operant heroin self-administration on its own, it blocked naloxone-precipitated elevation of heroin self-administration behavior.

Conclusion: These results suggest that OlAla and OlGly are two endogenous mediators whose brain concentrations respond to chronic opiate treatment and withdrawal concomitantly with changes in colon microbiota composition, and that OlAla may be more effective than OlGly in suppressing chronic opiate withdrawal responses.

Pharmacological potential of JWH133, a cannabinoid type 2 receptor agonist in neurodegenerative, neurodevelopmental and neuropsychiatric diseases

The pharmacological activation of cannabinoid type 2 receptors (CB2R) gained attention due to its ability to mitigate neuroinflammatory events without eliciting psychotropic actions, a limiting factor for the drugs targeting cannabinoid type 1 receptors (CB1R). Therefore, ligands activating CB2R are receiving enormous importance for therapeutic targeting in numerous neurological diseases including neurodegenerative, neuropsychiatric and neurodevelopmental disorders as well as traumatic injuries and neuropathic pain where neuroinflammation is a common accompaniment. Since the characterization of CB2R, many CB2R selective synthetic ligands have been developed with high selectivity and functional activity. Among numerous ligands, JWH133 has been found one of the compounds with high selectivity for CB2R. JWH133 has been reported to exhibit numerous pharmacological activities including antioxidant, anti-inflammatory, anticancer, cardioprotective, hepatoprotective, gastroprotective, nephroprotective, and immunomodulatory. Recent studies have shown that JWH133 possesses potent neuroprotective properties in several neurological disorders, including neuropathic pain, anxiety, epilepsy, depression, alcoholism, psychosis, stroke, and neurodegeneration. Additionally, JWH133 showed to protect neurons from oxidative damage and inflammation, promote neuronal survival and neurogenesis, and serve as an immunomodulatory agent. The present review comprehensively examined neuropharmacological activities of JWH133 in neurological disorders including neurodegenerative, neurodevelopmental and neuropsychiatric using synoptic tables and elucidated pharmacological mechanisms based on reported observations. Considering the cumulative data, JWH133 appears to be a promising CB2R agonist molecule for further evaluation and it can be a prototype agent in drug discovery and development for a unique class of agents in neurotherapeutics. Further, regulatory toxicology and pharmacokinetic studies are required to determine safety and proceed for clinical evaluation.

Is PTSD-Phenotype Associated with HPA-Axis Sensitivity?: The Endocannabinoid System in Modulating Stress Response in Rats

Endocannabinoids play a role in adaptation to stress and regulate the release of glucocorticoids in stressed and unstressed conditions. We recently found that basal corticosterone pulsatility may significantly impact the vulnerability for developing post-traumatic-stress-disorder (PTSD), suggesting that the endocannabinoid system may contribute to its development. To examine this, we exposed rats to predator scent stress (PSS). Behavioral reactions were recorded seven days post-PSS. Cerebrospinal fluid (CSF) was collected from anesthetized rats shortly after PSS exposure to determine the levels of 2-arachidonoyl glycerol (2-AG) and anandamide (AEA). To correlate between endocannabinoids and corticosterone levels, rats were placed in metabolic cages for urine collection. To assess the levels of endocannabinoids in specific brain regions, rats' brains were harvested one day after behavioral analysis for staining and fluorescence quantification. Moreover, 2-AG was elevated in the CSF of PTSD-phenotype rats as compared with other groups and was inversely correlated with corticosterone urinary secretion. Eight days post-PSS exposure, hippocampal and hypothalamic 2-AG levels and hippocampal AEA levels were significantly more reduced in the PTSD-phenotype group compared to other groups. We posit that maladaptation to stress, which is propagated by an abnormal activation of endocannabinoids, mediates the subsequent stress-induced behavioral disruption, which, later, reduces neuronal the expression of endocannabinoids, contributing to PTSD symptomology.

Cannabinoids and myocardial ischemia: Novel insights, updated mechanisms, and implications for myocardial infarction

Cannabis is the most widely trafficked and abused illicit drug due to its calming psychoactive properties. It has been increasingly recognized as having potential health benefits and relatively less adverse health effects as compared to other illicit drugs; however, growing evidence clearly indicates that cannabis is associated with considerable adverse cardiovascular events. Recent studies have linked cannabis use to myocardial infarction (MI); yet, very little is known about the underlying mechanisms. A MI is a cardiovascular disease characterized by a mismatch in the oxygen supply and demand of the heart, resulting in ischemia and subsequent necrosis of the myocardium. Since cannabis is increasingly being considered a risk factor for MI, there is a growing need for better appreciating its potential health benefits and consequences. Here, we discuss the cellular mechanisms of cannabis that lead to an increased risk of MI. We provide a thorough and critical analysis of cannabinoids' actions, which include modulation of adipocyte biology, regional fat distribution, and atherosclerosis, as well as precipitation of hemodynamic stressors relevant in the setting of a MI. By critically dissecting the modulation of signaling pathways in multiple cell types, this paper highlights the mechanisms through which cannabis may trigger life-threatening cardiovascular events. This then provides a framework for future pharmacological studies which can identify targets or develop drugs that modulate cannabis' effects on the cardiovascular system as well as other organ systems. Cannabis' impact on the autonomic outflow, vascular smooth muscle cells, myocardium, cortisol levels and other hemodynamic changes are also mechanistically reviewed.

The role of endocannabinoids in consolidation, retrieval, reconsolidation, and extinction of fear memory

Endocannabinoids are involved in various physiological functions, including synaptic plasticity and memory, and some psychiatric disorders, such as posttraumatic stress disorder (PTSD), through the activation of cannabinoid (CB) receptors. Patients with PTSD often show excessive fear memory and impairment of fear extinction (FE). It has been reported that the stability of acquired fear memory is altered through multiple memory stages, such as consolidation and reconsolidation. FE also affects the stability of fear memory. Each stage of fear memory formation and FE are regulated by different molecular mechanisms, including the CB system. However, to the best of our knowledge, no review summarizes the role of the CB system during each stage of fear memory formation and FE. In this review, we summarize the roles of endocannabinoids in fear memory formation and FE. Moreover, based on the summary, we propose a new hypothesis for the role of endocannabinoids in fear regulation, and discuss treatment for PTSD using CB system-related drugs.

Linking mPFC circuit maturation to the developmental regulation of emotional memory and cognitive flexibility

The medial prefrontal cortex (mPFC) and its abundant connections with other brain regions play key roles in memory, cognition, decision making, social behaviors, and mood. Dysfunction in mPFC is implicated in psychiatric disorders in which these behaviors go awry. The prolonged maturation of mPFC likely enables complex behaviors to emerge, but also increases their vulnerability to disruption. Many foundational studies have characterized either mPFC synaptic or behavioral development without establishing connections between them. Here, we review this rich body of literature, aligning major events in mPFC development with the maturation of complex behaviors. We focus on emotional memory and cognitive flexibility, and highlight new work linking mPFC circuit disruption to alterations of these behaviors in disease models. We advance new hypotheses about the causal connections between mPFC synaptic development and behavioral maturation and propose research strategies to establish an integrated understanding of neural architecture and behavioral repertoires.

The endocannabinoid system in the amygdala and modulation of fear

Posttraumatic stress disorder (PTSD) is a persistent, trauma induced psychiatric condition characterized by lifelong complex cognitive, emotional and behavioral phenotype. Although many individuals that experience trauma are able to gradually diminish their emotional responding to trauma-related stimuli over time, known as extinction learning, individuals suffering from PTSD are impaired in this capacity. An inability to decline this initially normal and adaptive fear response, can be confronted with exposure-based therapies, often in combination with pharmacological treatments. Due to the complexity of PTSD, currently available pharmacotherapeutics are inadequate in treating the deficient extinction observed in many PTSD patients. To develop novel therapeutics, researchers have exploited the conserved nature of fear and stress-associated behavioral responses and neurocircuits across species in an attempt to translate knowledge gained from preclinical studies into the clinic. There is growing evidence on the endocannabinoid modulation of fear and stress due to their 'on demand' synthesis and degradation. Involvement of the endocannabinoids in fear extinction makes the endocannabinoid system very attractive for finding effective therapeutics for trauma and stress related disorders. In this review, a brief introduction on neuroanatomy and circuitry of fear extinction will be provided as a model to study PTSD. Then, the endocannabinoid system will be discussed as an important component of extinction modulation. In this regard, anandamide degrading enzyme, fatty acid amide hydrolase (FAAH) will be exemplified as a target identified and validated strongly from preclinical to clinical translational studies of enhancing extinction.

Early-life stress exacerbates the effects of WIN55,212-2 and modulates the cannabinoid receptor type 1 expression

Early-life stress induces an abnormal brain development and increases the risk of psychiatric diseases, including depression, anxiety and substance use disorders. We have developed a reliable model for maternal neglect, named maternal separation with early weaning (MSEW) in CD1 mice. In the present study, we evaluated the long-term effects on anxiety-like behaviours, nociception as well as the Iba1-positive microglial cells in this model in comparison to standard nest (SN) mice. Moreover, we investigated whether MSEW alters the cannabinoid agonist WIN55,212-2 effects regarding reward, spatial and emotional memories, tolerance to different cannabinoid responses, and physical dependence. Adult male offspring of MSEW group showed impaired responses on spatial and emotional memories after a repeated WIN55,212-2 treatment. These behavioural impairments were associated with an increase in basolateral amygdala and hippocampal CB1-expressing fibres and higher number of CB1-containing cells in cerebellum. Additionally, MSEW promotes a higher number of Iba1-positive microglial cells in basolateral amygdala and cerebellum. As for the cannabinoid-induced effects, rearing conditions did not influence the rewarding effects of WIN55,212-2 in the conditioned place preference paradigm. However, MSEW mice showed a delay in the development of tolerance to the cannabinoid effects. Moreover, CB1-positive fibres were reduced in limbic areas in MSEW mice after cannabinoid withdrawal precipitated with the CB1 antagonist SR141617A. These findings support that early-life stress promotes behavioural and molecular changes in the sensitivity to cannabinoids, which are mediated by alterations in CB1 signalling in limbic areas and it induces an increased Iba1-microglial marker which could interfere in emotional memories formation.

Sex-dependent effects of endocannabinoid modulation of conditioned fear extinction in rats

BACKGROUND AND PURPOSE

Women are twice as likely as men to develop post-traumatic stress disorder (PTSD) making the search for biological mechanisms underlying these gender disparities especially crucial. One of the hallmark symptoms of PTSD is an alteration in the ability to extinguish fear responses to trauma-associated cues. In male rodents, the endocannabinoid system can modulate fear extinction and has been suggested as a therapeutic target for PTSD. However, whether and how the endocannabinoid system may modulate fear expression and extinction in females remains unknown.

EXPERIMENTAL APPROACH

To answer this question, we pharmacologically manipulated endocannabinoid signalling in male and female rats prior to extinction of auditory conditioned fear and measured both passive (freezing) and active (darting) conditioned responses.

KEY RESULTS

Surprisingly, we found that acute systemic inhibition of the endocannabinoid anandamide (AEA) or 2-arachidonoyl glycerol (2-AG) hydrolysis did not significantly alter fear expression or extinction in males. However, the same manipulations in females produced diverging effects. Increased AEA signalling at vanilloid TRPV1 receptors impaired fear memory extinction. In contrast, inhibition of 2-AG hydrolysis promoted active over passive fear responses acutely via activation of cannabinoid1 (CB1 ) receptors. Measurement of AEA and 2-AG levels after extinction training revealed sex- and brain region-specific changes.

CONCLUSION AND IMPLICATIONS

We provide the first evidence that AEA and 2-AG signalling affect fear expression and extinction in females in opposite directions. These findings are relevant to future research on sex differences in mechanisms of fear extinction and may help develop sex-specific therapeutics to treat trauma-related disorders.

Cannabis use and posttraumatic stress disorder comorbidity: Epidemiology, biology and the potential for novel treatment approaches

Cannabis use is increasing among some demographics in the United States and is tightly linked to anxiety, trauma, and stress reactivity at the epidemiological and biological level. Stress-coping motives are highly cited reasons for cannabis use. However, with increased cannabis use comes the increased susceptibility for cannabis use disorder (CUD). Indeed, CUD is highly comorbid with posttraumatic stress disorder (PTSD). Importantly, endogenous cannabinoid signaling systems play a key role in the regulation of stress reactivity and anxiety regulation, and preclinical data suggest deficiencies in this signaling system could contribute to the development of stress-related psychopathology. Furthermore, endocannabinoid deficiency states, either pre-existing or induced by trauma exposure, could provide explanatory insights into the high rates of comorbid cannabis use in patients with PTSD. Here we review clinical and preclinical literature related to the cannabis use-PTSD comorbidity, the role of endocannabinoids in the regulation of stress reactivity, and potential therapeutic implications of recent work in this area.

Selective inhibition of monoacylglycerol lipase is associated with passive coping behavior and attenuation of stress-induced dopamine release in the medial prefrontal cortex

The endocannabinoid system is involved in the regulation of the stress response, but the relative contribution of N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) and their mechanisms have to be elucidated. In this study, we compared the effects of the pharmacological inhibition of the two major endocannabinoid-degrading enzymes [fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) for AEA and 2-AG, respectively] on stress-coping [forced swim test (FST) and tail suspension test (TST)] and anxiety-like [elevated-plus maze (EPM) and light-dark test (LDT)] behaviors in wild-type and FAAH knockout mice. In vivo microdialysis estimated the effects of FAAH and MAGL inhibition on dopamine (DA) and serotonin (5-HT) levels in the medial prefrontal cortex (mPFC) during an FST. Mice were treated with PF-3845 (FAAH inhibitor), JZL184 (MAGL inhibitor), JZL195 (dual FAAH/MAGL inhibitor) or vehicle. Our data showed that PF-3845 increased latency to immobility and decreased total immobility time in FST, but no effects were observed in TST compared with vehicle-treated wild-type mice. By contrast, JZL184 decreased latency and increased immobility in TST and FST. JZL195 in wild-type mice and JZL184 in FAAH knockout mice reproduced the same passive coping behaviors as JZL184 in wild-type mice in TST and FST. In the microdialysis experiment, FST was associated with increased DA and 5-HT levels in the mPFC. However, JZL184-treated wild-type mice displayed a significant attenuation of forced swim stress-induced DA release compared with vehicle-treated wild-type mice and PF-3845-treated wild-type mice. Finally, FAAH and/or MAGL inhibitors induced robust and consistent anxiolytic-like effects in EPM and LDT. These results suggested differences between FAAH and MAGL inhibition in stress-coping behaviors. Notably, MAGL inhibition induced a consistent avoidant coping behavior and attenuated the stress-induced mPFC DA response in FST. However, more investigation is needed to elucidate the functional association between DA and 2-AG signaling pathways, and the molecular mechanism in the regulation of passive coping strategies during inescapable stress.

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FAAH and/or MAGL inhibition induce opposite changes in stress-coping behaviors.

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MAGL inhibition increases passive stress-coping behaviors in mice.

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Passive stress-coping behaviors are regulated by 2-AG rather than AEA signaling.

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MAGL inhibition attenuates mPFC dopamine increase in the forced swim test.

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FAAH and/or MAGL inhibitors are associated with anxiolytic-like effects.

Cannabidiol and Neurodevelopmental Disorders in Children

Neurodevelopmental and neuropsychiatric disorders (such as autism spectrum disorder) have broad health implications for children, with no definitive cure for the vast majority of them. However, recently medicinal cannabis has been successfully trialled as a treatment to manage many of the patients' symptoms and improve quality of life. The cannabinoid cannabidiol, in particular, has been reported to be safe and well-tolerated with a plethora of anticonvulsant, anxiolytic and anti-inflammatory properties. Lately, the current consensus is that the endocannabinoid system is a crucial factor in neural development and health; research has found evidence that there are a multitude of signalling pathways involving neurotransmitters and the endocannabinoid system by which cannabinoids could potentially exert their therapeutic effects. A better understanding of the cannabinoids' mechanisms of action should lead to improved treatments for neurodevelopmental disorders.

Prospects for the Use of Cannabinoids in Psychiatric Disorders

Increasing evidence suggests an essential role of the endocannabinoid system in modulating cognitive abilities, mood, stress, and sleep. The psychoactive effects of cannabis are described as euphoric, calming, anxiolytic, and sleep-inducing and positively affect the mood, but can also adversely affect therapy. The responses to cannabinoid medications depend on the patient's endocannabinoid system activity, the proportion of phytocannabinoids, the terpenoid composition, and the dose used. There is some evidence for a therapeutic use of phytocannabinoids in psychiatric conditions. THC and CBD may have opposing effects on anxiety. Current guidelines recommend caution in using THC in patients with anxiety or mood disorders. In a small number of clinical trials, cannabinoids used to treat cancer, HIV, multiple sclerosis, hepatitis C, Crohn's disease, and chronic neuropathic pain report decreases in anxiety or depression symptoms and presented sedative and anxiolytic effects. Several studies have investigated the influence of potential genetic factors on psychosis and schizophrenia development after cannabis use. THC may increase the risk of psychosis, especially in young patients with an immature central nervous system. There is limited evidence from clinical trials that cannabinoids are effective therapy for sleep disorders associated with concomitant conditions. There is evidence for a possible role of cannabis as a substitute for alcohol and drugs, also in the context of the risks of opioid use (e.g., opioid-related mortality). In this narrative review of the recent evidence, we discuss the prospects of using the psychoactive effects of cannabinoids in treating mental and psychiatric disorders. However, this evidence is weak for some clinical conditions and well-designed randomized controlled trials are currently lacking. Furthermore, some disorders may be worsened by cannabis use.

2-Arachidonoylglycerol Modulation of Anxiety and Stress Adaptation: From Grass Roots to Novel Therapeutics

Over the past decade there has been a surge of interest in the development of endocannabinoid-based therapeutic approaches for the treatment of diverse neuropsychiatric conditions. Although initial preclinical and clinical development efforts focused on pharmacological inhibition of fatty acid amide hydrolase to elevate levels of the endocannabinoid anandamide, more recent efforts have focused on inhibition of monoacylglycerol lipase (MAGL) to enhance signaling of the most abundant and efficacious endocannabinoid ligand, 2-arachidonoylglycerol (2-AG). We review the biochemistry and physiology of 2-AG signaling and preclinical evidence supporting a role for this system in the regulation of anxiety-related outcomes and stress adaptation. We review preclinical evidence supporting MAGL inhibition for the treatment of affective, trauma-related, and stress-related disorders; describe the current state of MAGL inhibitor drug development; and discuss biological factors that could affect MAGL inhibitor efficacy. Issues related to the clinical advancement of MAGL inhibitors are also discussed. We are cautiously optimistic, as the field of MAGL inhibitor development transitions from preclinical to clinical and theoretical to practical, that pharmacological 2-AG augmentation could represent a mechanistically novel therapeutic approach for the treatment of affective and stress-related neuropsychiatric disorders.

Attenuation of fear-conditioned analgesia in rats by monoacylglycerol lipase inhibition in the anterior cingulate cortex: Potential role for CB2 receptors

BACKGROUND AND PURPOSE

Improved understanding of brain mechanisms regulating endogenous analgesia is important from a fundamental physiological perspective and for identification of novel therapeutic strategies for pain. The endocannabinoid system plays a key role in stress-induced analgesia, including fear-conditioned analgesia (FCA), a potent form of endogenous analgesia. Here, we studied the role of the endocannabinoid 2-arachidonoyl glycerol (2-AG) within the anterior cingulate cortex (ACC; a brain region implicated in the affective component of pain) in FCA in rats.

EXPERIMENTAL APPROACH

FCA was modelled in male Lister-hooded rats by assessing formalin-evoked nociceptive behaviour in an arena previously paired with footshock. The effects of intra-ACC administration of MJN110 (inhibitor of monoacylglycerol lipase [MGL], the primary enzyme catabolizing 2-AG), AM630 (CB2 receptor antagonist), AM251 (CB1 receptor antagonist) or MJN110 + AM630 on FCA were assessed.

KEY RESULTS

MJN110 attenuated FCA when microinjected into the ACC, an effect associated with increased levels of 2-AG in the ACC. This effect of MJN110 on FCA was unaltered by co-administration of AM251 but was blocked by AM630, which alone reduced nociceptive behaviour in non-fear-conditioned rats. RT-qPCR confirmed that mRNA encoding CB1 and CB2 receptors was detectable in the ACC of formalin-injected rats and unchanged in those expressing FCA.

CONCLUSION AND IMPLICATIONS

These results suggest that an MGL substrate in the ACC, likely 2-AG, modulates FCA and that within the ACC, 2-AG-CB2 receptor signalling may suppress this form of endogenous analgesia. These results may facilitate increased understanding and improved treatment of pain- and fear-related disorders and their co-morbidity.

Protective Effects of N-Oleoylglycine in a Mouse Model of Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the main causes of death in young people for which currently no efficacious treatment exists. Recently, we have reported that mice with mild-TBI with a specific injury in the insula showed elevated levels of a little investigated N-acyl amino acid, N-oleoylglycine (OlGly). N-acyl amino acids have recently experienced an increased interest because of their important biological activities. They belong to the endocannabinoidome family of lipids with structural similarities with the endocannabinoids (eCBs). The aim of this study was to test the neuroprotective and antihyperalgesic actions of OlGly in a model of mouse mild-TBI (mTBI) and its effect on levels of eCBs and N-acylethanolamines at the end of treatment. Following mTBI, mice were administered a daily injection of OlGly (10-50-100 mg/kg i.p.) for 14 days. Treatment with OlGly normalized motor impairment and behavior in the light/dark box test, ameliorated TBI-induced thermal hyperalgesia and mechanical allodynia, and normalized aggressiveness and depression. Moreover, levels of eCBs and some N-acylethanolamines underwent significant changes 60 days after TBI, especially in the prefrontal cortex and hypothalamus, and OlGly reversed some of these changes. In conclusion, our findings reveal that OlGly ameliorates the behavioral alterations associated with mTBI in mice, while concomitantly modulating eCB and eCB-like mediator tone.

Monoacylglycerol lipase alpha inhibition alters prefrontal cortex excitability and blunts the consequences of traumatic stress in rat

Neural activity within the ventromedial prefrontal cortex (vmPFC) is a critical determinant of stressor-induced anxiety. Pharmacological activation of the vmPFC during stress protects against stress-induced social anxiety suggesting that altering the excitatory/inhibitory (E/I) tone in the vmPFC may promote stress resilience. E/I balance is maintained, in part, by endogenous cannabinoid (eCB) signaling with the calcium dependent retrograde release of 2-arachidonoylglycerol (2-AG) suppressing presynaptic neurotransmitter release. We hypothesized that raising 2-AG levels, via inhibition of its degradation enzyme monoacylglycerol lipase (MAGL) with KML29, would shift vmPFC E/I balance and promote resilience. In acute slice experiments, bath application of KML29 (100 nM) augmented evoked excitatory neurotransmission as evidenced by a left-shift in fEPSP I/O curve, and decreased sIPSC amplitude. In whole-cell recordings, KML29 increased resting membrane potential but reduced the after depolarization, bursting rate, membrane time constant and slow after hyperpolarization. Intra-vmPFC administration of KML29 (200ng/0.5μL/hemisphere) prior to inescapable stress (IS) exposure (25, 5s tail shocks) prevented stress induced anxiety as measured by juvenile social exploration 24 h after stressor exposure. Conversely, systemic administration of KML29 (40 mg/kg, i.p.) 2 h before IS exacerbated stress induced anxiety. MAGL inhibition in the vmPFC may promote resilience by augmenting the output of neurons that project to brainstem and limbic structures that mediate stress responses.

Early life stress and development of the endocannabinoid system: A bidirectional process in programming future coping

The endocannabinoid system (ECS) critically regulates stress responsivity and emotional behavior throughout development. It regulates anxiety-like behaviors in humans and animal models. In addition, it is sensitive to early life stress at the gene expression level in a sex-dependent and region-dependent manner, and these changes are already evident in the adolescent brain. The ECS modulates the neuroendocrine and behavioral effects of stress, and is also capable of being affected by stress exposure itself. Early life stress interferes with the development of corticolimbic circuits, a major location of endocannabinoid receptors, and increases vulnerability to adult psychopathology. Early life stress alters the ontogeny of the ECS, resulting in a sustained deficit in its function, particularly within the hippocampus. Specifically, exposure to early stress results in bidirectional changes in anandamide and 2-AG tissue levels within the amygdala and hippocampus and reduces hippocampal endocannabinoid function at puberty. CB1 receptor densities across all brain regions are downregulated later in life following exposure to early life stress. Manipulations affecting the glucocorticoid and the endocannabinoid systems persistently adjust individual emotional responses and synaptic plasticity. This review aims to show the bidirectional trajectories of endocannabinoid modulation of emotionality in reaction to early life stress.

Stress-induced modulation of endocannabinoid signaling leads to delayed strengthening of synaptic connectivity in the amygdala

Even a brief exposure to severe stress strengthens synaptic connectivity days later in the amygdala, a brain area implicated in the affective symptoms of stress-related psychiatric disorders. However, little is known about the synaptic signaling mechanisms during stress that eventually culminate in its delayed impact on the amygdala. Hence, we investigated early stress-induced changes in amygdalar synaptic signaling in order to prevent its delayed effects. Whole-cell recordings in basolateral amygdala (BLA) slices from rats revealed higher frequency of miniature excitatory postsynaptic currents (mEPSCs) immediately after 2-h immobilization stress. This was replicated by inhibition of cannabinoid receptors (CB₁R), suggesting a role for endocannabinoid (eCB) signaling. Stress also reduced N-arachidonoylethanolamine (AEA), an endogenous ligand of CB₁R. Since stress-induced activation of fatty acid amide hydrolase (FAAH) reduces AEA, we confirmed that oral administration of an FAAH inhibitor during stress prevents the increase in synaptic excitation in the BLA soon after stress. Although stress also caused an immediate reduction in synaptic inhibition, this was not prevented by FAAH inhibition. Strikingly, FAAH inhibition during the traumatic stressor was also effective 10 d later on the delayed manifestation of synaptic strengthening in BLA neurons, preventing both enhanced mEPSC frequency and increased dendritic spine-density. Thus, oral administration of an FAAH inhibitor during a brief stress prevents the early synaptic changes that eventually build up to hyperexcitability in the amygdala. This framework is of therapeutic relevance because of growing interest in targeting eCB signaling to prevent the gradual development of emotional symptoms and underlying amygdalar dysfunction triggered by traumatic stress.