The role of endogenous cannabinoids in the hypothalamo-pituitary-adrenal axis regulation: in vivo and in vitro studies in CB1 receptor knockout mice

In silico analyses of the involvement of GPR55, CB1R and TRPV1: response to THC, contribution to temporal lobe epilepsy, structural modeling and updated evolution

Introduction

The endocannabinoid (eCB) system is named after the discovery that endogenous cannabinoids bind to the same receptors as the phytochemical compounds found in Cannabis. While endogenous cannabinoids include anandamide (AEA) and 2-arachidonoylglycerol (2-AG), exogenous phytocannabinoids include Δ-9 tetrahydrocannabinol (THC) and cannabidiol (CBD). These compounds finely tune neurotransmission following synapse activation, via retrograde signaling that activates cannabinoid receptor 1 (CB1R) and/or transient receptor potential cation channel subfamily V member 1 (TRPV1). Recently, the eCB system has been linked to several neurological diseases, such as neuro-ocular abnormalities, pain insensitivity, migraine, epilepsy, addiction and neurodevelopmental disorders. In the current study, we aim to: (i) highlight a potential link between the eCB system and neurological disorders, (ii) assess if THC exposure alters the expression of eCB-related genes, and (iii) identify evolutionary-conserved residues in CB1R or TRPV1 in light of their function.

Methods

To address this, we used several bioinformatic approaches, such as transcriptomic (Gene Expression Omnibus), protein-protein (STRING), phylogenic (BLASTP, MEGA) and structural (Phyre2, AutoDock, Vina, PyMol) analyzes.

Results

Using RNA sequencing datasets, we did not observe any dysregulation of eCB-related transcripts in major depressive disorders, bipolar disorder or schizophrenia in the anterior cingulate cortex, nucleus accumbens or dorsolateral striatum. Following in vivo THC exposure in adolescent mice, GPR55 was significantly upregulated in neurons from the ventral tegmental area, while other transcripts involved in the eCB system were not affected by THC exposure. Our results also suggest that THC likely induces neuroinflammation following in vitro application on mice microglia. Significant downregulation of TPRV1 occurred in the hippocampi of mice in which a model of temporal lobe epilepsy was induced, confirming previous observations. In addition, several transcriptomic dysregulations were observed in neurons of both epileptic mice and humans, which included transcripts involved in neuronal death. When scanning known interactions for transcripts involved in the eCB system (n = 12), we observed branching between the eCB system and neurophysiology, including proteins involved in the dopaminergic system. Our protein phylogenic analyzes revealed that CB1R forms a clade with CB2R, which is distinct from related paralogues such as sphingosine-1-phosphate, receptors, lysophosphatidic acid receptors and melanocortin receptors. As expected, several conserved residues were identified, which are crucial for CB1R receptor function. The anandamide-binding pocket seems to have appeared later in evolution. Similar results were observed for TRPV1, with conserved residues involved in receptor activation.

Conclusion

The current study found that GPR55 is upregulated in neurons following THC exposure, while TRPV1 is downregulated in temporal lobe epilepsy. Caution is advised when interpreting the present results, as we have employed secondary analyzes. Common ancestors for CB1R and TRPV1 diverged from jawless vertebrates during the late Ordovician, 450 million years ago. Conserved residues are identified, which mediate crucial receptor functions.

Nicotine exposure during breastfeeding alters the expression of endocannabinoid system biomarkers in female but not in male offspring at adulthood

Early nicotine exposure compromises offspring's phenotype at long-term in both sexes. We hypothesize that offspring exposed to nicotine during breastfeeding show deregulated central and peripheral endocannabinoid system (ECS), compromising several aspects of their metabolism. Lactating rats received nicotine (NIC, 6 mg/Kg/day) or saline from postnatal day (PND) 2 to 16 through implanted osmotic minipumps. Offspring were analyzed at PND180. We evaluated protein expression of N-acylphosphatidylethanolamide-phospholipase D (NAPE-PLD), fatty acid amide hydrolase (FAAH), diacylglycerol lipase (DAGL), monoacylglycerol lipase (MAGL) and cannabinoid receptors (CB1 and/or CB2) in lateral hypothalamus, paraventricular nucleus of the hypothalamus, liver, visceral adipose tissue (VAT), adrenal and thyroid. NIC offspring from both sexes did not show differences in hypothalamic ECS markers. Peripheral ECS markers showed no alterations in NIC males. In contrast, NIC females had lower liver DAGL and CB1, higher VAT DAGL, higher adrenal NAPE-PLD and higher thyroid FAAH. Endocannabinoids biosynthesis was affected by nicotine exposure during breastfeeding only in females; alterations in peripheral tissues suggest lower action in liver and higher action in VAT, adrenal and thyroid. Effects of nicotine exposure during lactation on ECS markers are sex- and tissue-dependent. This characterization helps understanding the phenotype of the adult offspring in this model and may contribute to the development of new pharmacological targets for the treatment of several metabolic diseases that originate during development.

CB1 receptor signalling mediates cannabidiol-induced panicolytic-like effects and defensive antinociception impairment in mice threatened by Bothrops jararaca lancehead pit vipers

BACKGROUND

Cannabis sativa-derived substances such as cannabidiol (CBD) have attracted increasing clinical interest and consist in a new perspective for treating some neurological and psychiatric diseases.

AIMS

The aim of this work was to investigate the effect of acute treatment with CBD on panic-like defensive responses displayed by mice threatened by the venomous snake Bothrops jararaca.

METHODS

Mice were habituated in the enriched polygonal arena for snake panic test. After recording the baseline responses of the tail-flick test, the prey were pretreated with intraperitoneal (i.p.) administrations of the endocannabinoid type 1 receptor (CB₁) antagonist AM251 (selective cannabinoid 1 receptor antagonist with an IC50 of 8 nM) at different doses, which were followed after 10 min by i.p. treatment with CBD (3 mg/kg). Thirty minutes after treatment with CBD, mice were subjected to confrontations by B. jararaca for 5 min, and the following defensive responses were recorded: risk assessment, oriented escape behaviour, inhibitory avoidance and prey-versus-snake interactions. Immediately after the escape behaviour was exhibited, the tail-flick latencies were recorded every 5 min for 30 min.

OUTCOMES

Mice threatened by snakes displayed several anti-predatory defensive and innate fear-induced antinociception responses in comparison to the control. CBD significantly decreased the risk assessment and escape responses, with a consequent decrease in defensive antinociception. The CBD panicolytic effect was reversed by i.p. treatment with AM251.

CONCLUSIONS

These findings suggest that the anti-aversive effect of CBD depends at least in part on the recruitment of CB₁ receptors.

Lipid endocannabinoids in energy metabolism, stress and developmental programming

The endocannabinoid system (ECS) regulates brain development and function, energy metabolism and stress in a sex-, age- and tissue-dependent manner. The ECS comprises mainly the bioactive lipid ligands anandamide (AEA) and 2-aracdonoylglycerol (2-AG), cannabinoid receptors 1 and 2 (CB1 and CB2), and several metabolizing enzymes. The endocannabinoid tonus is increased in obesity, stimulating food intake and a preference for fat, reward, and lipid accumulation in peripheral tissues, as well as favoring a positive energy balance. Energy balance and stress responses share adaptive mechanisms regulated by the ECS that seem to underlie the complex relationship between feeding and emotional behavior. The ECS is also a key regulator of development. Environmental insults (diet, toxicants, and stress) in critical periods of developmental plasticity, such as gestation, lactation and adolescence, alter the ECS and may predispose individuals to the development of chronic diseases and behavioral changes in the long term. This review is focused on the ECS and the developmental origins of health and disease (DOHaD).

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.

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.

HPA Axis in the Pathomechanism of Depression and Schizophrenia: New Therapeutic Strategies Based on Its Participation

The hypothalamic-pituitary-adrenal (HPA) axis is involved in the pathophysiology of many neuropsychiatric disorders. Increased HPA axis activity can be observed during chronic stress, which plays a key role in the pathophysiology of depression. Overactivity of the HPA axis occurs in major depressive disorder (MDD), leading to cognitive dysfunction and reduced mood. There is also a correlation between the HPA axis activation and gut microbiota, which has a significant impact on the development of MDD. It is believed that the gut microbiota can influence the HPA axis function through the activity of cytokines, prostaglandins, or bacterial antigens of various microbial species. The activity of the HPA axis in schizophrenia varies and depends mainly on the severity of the disease. This review summarizes the involvement of the HPA axis in the pathogenesis of neuropsychiatric disorders, focusing on major depression and schizophrenia, and highlights a possible correlation between these conditions. Although many effective antidepressants are available, a large proportion of patients do not respond to initial treatment. This review also discusses new therapeutic strategies that affect the HPA axis, such as glucocorticoid receptor (GR) antagonists, vasopressin V1B receptor antagonists and non-psychoactive CB1 receptor agonists in depression and/or schizophrenia.

Communication and social interaction in the cannabinoid-type 1 receptor null mouse: Implications for autism spectrum disorder

Clinical and preclinical findings have suggested a role of the endocannabinoid system (ECS) in the etiopathology of autism spectrum disorder (ASD). Previous mouse studies have investigated the role of ECS in several behavioral domains; however, none of them has performed an extensive assessment of social and communication behaviors, that is, the main core features of ASD. This study employed a mouse line lacking the primary endocannabinoid receptor (CB1r) and characterized ultrasonic communication and social interaction in CB1^-/- , CB1^+/- , and CB1^+/+ males and females. Quantitative and qualitative alterations in ultrasonic vocalizations (USVs) were observed in CB1 null mice both during early development (i.e., between postnatal days 4 and 10), and at adulthood (i.e., at 3 months of age). Adult mutants also showed marked deficits in social interest in the three-chamber test and social investigation in the direct social interaction test. These behavioral alterations were mostly observed in both sexes and appeared more marked in CB1^-/- than CB1^+/- mutant mice. Importantly, the adult USV alterations could not be attributed to differences in anxiety or sensorimotor abilities, as assessed by the elevated plus maze and auditory startle tests. Our findings demonstrate the role of CB1r in social communication and behavior, supporting the use of the CB1 full knockout mouse in preclinical research on these ASD-relevant core domains. LAY SUMMARY: The endocannabinoid system (ECS) is important for brain development and neural function and is therefore likely to be involved in neurodevelopmental disorders such as Autism Spectrum Disorder (ASD). Here we investigated changes in social behavior and communication, which are core features of ASD, in male and female mice lacking the chief receptor of this system. Our results show that loss of this receptor results in several changes in social behavior and communication both during early development and in adulthood, thus supporting the role of the ECS in these ASD-core behavioral domains.

Endocannabinoid Receptors in the CNS: Potential Drug Targets for the Prevention and Treatment of Neurologic and Psychiatric Disorders

The endocannabinoid system participates in the regulation of CNS homeostasis and functions, including neurotransmission, cell signaling, inflammation and oxidative stress, as well as neuronal and glial cell proliferation, differentiation, migration and survival. Endocannabinoids are produced by multiple cell types within the CNS and their main receptors, CB₁ and CB₂, are expressed in both neurons and glia. Signaling through these receptors is implicated in the modulation of neuronal and glial alterations in neuroinflammatory, neurodegenerative and psychiatric conditions, including Alzheimer’s, Parkinson’s and Huntington’s disease, multiple sclerosis, amyotrophic lateral sclerosis, stroke, epilepsy, anxiety and depression. The therapeutic potential of endocannabinoid receptors in neurological disease has been hindered by unwelcome side effects of current drugs used to target them; however, due to their extensive expression within the CNS and their involvement in physiological and pathological process in nervous tissue, they are attractive targets for drug development. The present review highlights the potential applications of the endocannabinoid system for the prevention and treatment of neurologic and psychiatric disorders.

Chronic Inhibition of FAAH Reduces Depressive-Like Behavior and Improves Dentate Gyrus Proliferation after Chronic Unpredictable Stress Exposure

Symptoms of depressive disorders such as anhedonia and despair can be a product of an aberrant adaptation to stress conditions. Chronic unpredictable stress model (CUS) can generate an increase in the activity of the hypothalamic-pituitary-adrenal axis (HPA) and induce a reduction of neurotrophin signaling and the proliferation of neural progenitors in the adult dentate gyrus, together with increased oxidative stress. Levels of the endocannabinoid anandamide (AEA) seem to affect these depression-by-stress-related features and could be modulated by fatty acid amide hydrolase (FAAH). We aimed to evaluate the effects of FAAH inhibitor, URB597, on depressive-like behavior and neural proliferation of mice subjected to a model of CUS. URB597 was administered intraperitoneally at a dose of 0.2 mg/kg for 14 days after CUS. Depressive-like behaviors, anhedonia, and despair were evaluated in the splash and forced swimming tests, respectively. Alterations at the HPA axis level were analyzed using the relative weight of adrenal glands and serum corticosterone levels. Oxidative stress and brain-derived neurotrophic factor (BDNF) were also evaluated. Fluorescence immunohistochemistry tests were performed for the immunoreactivity of BrdU and Sox2 colabeling for comparison of neural precursors. The administration of URB597 was able to reverse the depressive-like behavior generated in mice after the model. Likewise, other physiological responses associated with CUS were reduced in the treated group, among them, increase in the relative weight of the adrenal glands, increased oxidative stress, and decreased BDNF and number of neural precursors. Most of these auspicious responses to enzyme inhibitor administration were blocked by employing a cannabinoid receptor antagonist. In conclusion, the chronic inhibition of FAAH generated an antidepressant effect, promoting neural progenitor proliferation and BDNF expression, while reducing adrenal gland weight and oxidative stress in mice under the CUS model.

Understanding neurobehavioral effects of acute and chronic stress in zebrafish

Stress is a common cause of neuropsychiatric disorders, evoking multiple behavioral, endocrine and neuro-immune deficits. Animal models have been extensively used to understand the mechanisms of stress-related disorders and to develop novel strategies for their treatment. Complementing rodent and clinical studies, the zebrafish (Danio rerio) is one of the most important model organisms in biomedicine. Rapidly becoming a popular model species in stress neuroscience research, zebrafish are highly sensitive to both acute and chronic stress, and show robust, well-defined behavioral and physiological stress responses. Here, we critically evaluate the utility of zebrafish-based models for studying acute and chronic stress-related CNS pathogenesis, assess the advantages and limitations of these aquatic models, and emphasize their relevance for the development of novel anti-stress therapies. Overall, the zebrafish emerges as a powerful and sensitive model organism for stress research. Although these fish generally display evolutionarily conserved behavioral and physiological responses to stress, zebrafish-specific aspects of neurogenesis, neuroprotection and neuro-immune responses may be particularly interesting to explore further, as they may offer additional insights into stress pathogenesis that complement (rather than merely replicate) rodent findings. Compared to mammals, zebrafish models are also characterized by increased availability of gene-editing tools and higher throughput of drug screening, thus being able to uniquely empower translational research of genetic determinants of stress and resilience, as well as to foster innovative CNS drug discovery and the development of novel anti-stress therapies.

Colonization with the commensal fungus Candida albicans perturbs the gut-brain axis through dysregulation of endocannabinoid signaling

Anxiety disorders are the most prevalent mental health disorder worldwide, with a lifetime prevalence of 5-7 % of the human population. Although the etiology of anxiety disorders is incompletely understood, one aspect of host health that affects anxiety disorders is the gut-brain axis. Adolescence is a key developmental window in which stress and anxiety disorders are a major health concern. We used adolescent female mice in a gastrointestinal (GI) colonization model to demonstrate that the commensal fungus Candida albicans affects host health via the gut-brain axis. In mice, bacterial members of the gut microbiota can influence the host gut-brain axis, affecting anxiety-like behavior and the hypothalamus-pituitary-adrenal (HPA) axis which produces the stress hormone corticosterone (CORT). Here we showed that mice colonized with C. albicans demonstrated increased anxiety-like behavior and increased basal production of CORT as well as dysregulation of CORT production following acute stress. The HPA axis and anxiety-like behavior are negatively regulated by the endocannabinoid N-arachidonoylethanolamide (AEA). We demonstrated that C. albicans-colonized mice exhibited changes in the endocannabinoidome. Further, increasing AEA levels using the well-characterized fatty acid amide hydrolase (FAAH) inhibitor URB597 was sufficient to reverse both neuroendocrine phenotypes in C. albicans-colonized mice. Thus, a commensal fungus that is a common colonizer of humans had widespread effects on the physiology of its host. To our knowledge, this is the first report of microbial manipulation of the endocannabinoid (eCB) system that resulted in neuroendocrine changes contributing to anxiety-like behavior.

Sex differences in the effect of cannabinoid type 1 receptor deletion on locus coeruleus-norepinephrine neurons and corticotropin releasing factor-mediated responses

Cannabinoids are capable of modulating mood, arousal, cognition and behavior, in part via their effects on the noradrenergic nucleus locus coeruleus (LC). Dysregulation of LC signaling and norepinephrine (NE) efflux in the medial prefrontal cortex (mPFC) can lead to the development of psychiatric disorders, and CB1r deletion results in alterations of α2- and β1-adrenoceptors in the mPFC, suggestive of increased LC activity. To determine how CB1r deletion alters LC signaling, whole-cell patch-clamp electrophysiology was conducted in LC-NE neurons of male and female wild type (WT) and CB1r-knock out (KO) mice. CB1r deletion caused a significant increase in LC-NE excitability and input resistance in male but not female mice when compared to WT. CB1r deletion also caused adaptations in several indices of noradrenergic function. CB1r/CB2r-KO male mice had a significant increase in cortical NE levels and tyrosine hydroxylase and CRF levels in the LC compared to WT males. CB1r/CB2r-KO female mice showed a significant increase in LC α2-AR levels compared to WT females. To further probe actions of the endocannabinoid system as an anti-stress neuromediator, the effect of CB1r deletion on CRF-induced responses in the LC was investigated. The increase in LC-NE excitability observed in male and female WT mice following CRF (300 nM) bath application was not observed in CB1r-KO mice. These results indicate that cellular adaptations following CB1r deletion cause a disruption in LC-NE signaling in males but not females, suggesting underlying sex differences in compensatory mechanisms in KO mice as well as basal endocannabinoid regulation of LC-NE activity.

Cell signaling dependence of rapid glucocorticoid-induced endocannabinoid synthesis in hypothalamic neuroendocrine cells

Glucocorticoids induce a rapid synthesis of endocannabinoid in hypothalamic neuroendocrine cells by activation of a putative membrane receptor. Somato-dendritically released endocannabinoid acts as a retrograde messenger to suppress excitatory synaptic inputs to corticotropin-releasing hormone-, oxytocin-, and vasopressin-secreting cells. The non-genomic signaling mechanism responsible for rapid endocannabinoid synthesis by glucocorticoids has yet to be fully characterized. Here we manipulated cell signaling molecules pharmacologically using an intracellular approach to elucidate the signaling pathway activated by the membrane glucocorticoid receptor in hypothalamic neuroendocrine cells. We found that rapid glucocorticoid-induced endocannabinoid synthesis in magnocellular neuroendocrine cells requires the sequential activation of multiple kinases, phospholipase C, and intracellular calcium mobilization. While there remain gaps in our understanding, our findings reveal many of the critical players in the rapid glucocorticoid signaling that culminates in the retrograde endocannabinoid modulation of excitatory synaptic transmission.

Pharmacological augmentation of endocannabinoid signaling reduces the neuroendocrine response to stress

Activation of the hypothalamic-pituitary-adrenal axis (HPA) is critical for survival when the organism is exposed to a stressful stimulus. The endocannabinoid system (ECS) is currently considered an important neuromodulator involved in numerous pathophysiological processes and whose primary function is to maintain homeostasis. In the tissues constituting the HPA axis, all the components of the ECS are present and the activation of this system acts in parallel with changes in the activity of numerous neurotransmitters, including nitric oxide (NO). NO is widely distributed in the brain and adrenal glands and recent studies have shown that free radicals, and in particular NO, may play a crucial role in the regulation of stress response. Our objective was to determine the participation of the endocannabinoid and NOergic systems as probable mediators of the neuroendocrine HPA axis response to a psychophysical acute stress model in the adult male rat. Animals were pre-treated with cannabinoid receptors agonists and antagonists at central and systemic level prior to acute restraint exposure. We also performed in vitro studies incubating adrenal glands in the presence of ACTH and pharmacological compounds that modifies ECS components. Our results showed that the increase in corticosterone observed after acute restraint stress is blocked by anandamide administered at both central and peripheral level. At hypothalamic level both cannabinoid receptors (CB1 and CB2) are involved, while in the adrenal gland, anandamide has a very potent effect in suppressing ACTH-induced corticosterone release that is mainly mediated by vanilloid TRPV1 receptors. We also observed that stress significantly increased hypothalamic mRNA levels of CB1 as well as adrenal mRNA levels of TRPV1 receptor. In addition, anandamide reduced the activity of the nitric oxide synthase enzyme during stress, indicating that the anti-stress action of endocannabinoids may involve a reduction in NO production at hypothalamic and adrenal levels. In conclusion, an endogenous cannabinoid tone maintains the HPA axis in a stable basal state, which is lost with a noxious stimulus. In this case, the ECS dampens the response to stress allowing the recovery of homeostasis. Moreover, our work further contributes to in vitro evidence for a participation of the endocannabinoid system by inhibiting corticosterone release directly at the adrenal gland level.

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: Effectors of glucocorticoid signaling

For decades, there has been speculation regarding the interaction of cannabinoids with glucocorticoid systems. Given the functional redundancy between many of the physiological effects of glucocorticoids and cannabinoids, it was originally speculated that the biological mechanisms of cannabinoids were mediated by direct interactions with glucocorticoid systems. With the discovery of the endocannabinoid system, additional research demonstrated that it was actually the opposite; glucocorticoids recruit endocannabinoid signaling, and that the engagement of endocannabinoid signaling mediated many of the neurobiological and physiological effects of glucocorticoids. With the development of advances in pharmacology and genetics, significant advances in this area have been made, and it is now clear that functional interactions between these systems are critical for a wide array of physiological processes. The current review acts a comprehensive summary of the contemporary state of knowledge regarding the biological interactions between glucocorticoids and endocannabinoids, and their potential role in health and disease.

Learning about stress: neural, endocrine and behavioral adaptations

In this review, nonassociative learning is advanced as an organizing principle to draw together findings from both sympathetic-adrenal medullary and hypothalamic-pituitary-adrenocortical (HPA) axis responses to chronic intermittent exposure to a variety of stressors. Studies of habituation, facilitation and sensitization of stress effector systems are reviewed and linked to an animal's prior experience with a given stressor, the intensity of the stressor and the appraisal by the animal of its ability to mobilize physiological systems to adapt to the stressor. Brain pathways that regulate physiological and behavioral responses to stress are discussed, especially in light of their regulation of nonassociative processes in chronic intermittent stress. These findings may have special relevance to various psychiatric diseases, including depression and post-traumatic stress disorder (PTSD).

Impaired Ethanol-Induced Sensitization and Decreased Cannabinoid Receptor-1 in a Model of Posttraumatic Stress Disorder

Background and Purpose

Impaired striatal neuroplasticity may underlie increased alcoholism documented in those with posttraumatic stress disorder (PTSD). Cannabinoid receptor-1 (CB1) is sensitive to the effects of ethanol (EtOH) and traumatic stress, and is a critical regulator of striatal plasticity. To investigate CB1 involvement in the PTSD-alcohol interaction, this study measured the effects of traumatic stress using a model of PTSD, mouse single-prolonged stress (mSPS), on EtOH-induced locomotor sensitization and striatal CB1 levels.

Methods

Mice were exposed to mSPS, which includes: 2-h restraint, 10-min group forced swim, 15-min exposure to rat bedding odor, and diethyl ether exposure until unconsciousness or control conditions. Seven days following mSPS exposure, the locomotor sensitizing effects of EtOH were assessed. CB1, post-synaptic density-95 (PSD95), and dopamine-2 receptor (D2) protein levels were then quantified in the dorsal striatum using standard immunoblotting techniques.

Results

Mice exposed to mSPS-EtOH demonstrated impaired EtOH-induced locomotor sensitization compared to Control-EtOH mice, which was accompanied by reduced striatal CB1 levels. EtOH increased striatal PSD95 in control and mSPS-exposed mice. Additionally, mSPS-Saline exposure increased striatal PSD95 and decreased D2 protein expression, with mSPS-EtOH exposure alleviating these changes.

Conclusions

These data indicate that the mSPS model of PTSD blunts the behavioral sensitizing effects of EtOH, a response that suggests impaired striatal neuroplasticity. Additionally, this study demonstrates that mice exposed to mSPS and repeated EtOH exposure decreases CB1 in the striatum, providing a mechanism of interest for understanding the effects of EtOH following severe, multimodal stress exposure.

Crosstalk between endocannabinoid and immune systems: a potential dysregulation in depression?

BACKGROUND

The endocannabinoid (eCB) system, an endogenous lipid signaling system, appears to be dysregulated in depression. The role of endocannabinoids (eCBs) as potent immunomodulators, together with the accumulating support for a chronic low-grade inflammatory profile in depression, suggests a compelling hypothesis for a fundamental impairment in their intercommunication, in depression.

OBJECTIVE

We aim to review previous literature on individual associations between the immune and eCB systems and depression. It will focus on peripheral and central mechanisms of crosstalk between the eCB and immune systems. A potential dysregulation in this crosstalk will be discussed in the context of depression.

RESULTS

Investigations largely report a hypoactivity of the eCB system and increased inflammatory markers in individuals with depression. Findings depict a multifaceted communication whereby immunocompetent and eCB-related cells can both influence the suppression and enhancement of the other's activity in both the periphery and central nervous system. A dysregulation of the eCB system, as seen in depression, appears to be associated with central and peripheral concentrations of inflammatory agents implicated in the pathophysiology of this illness.

CONCLUSION

The eCB and immune systems have been individually associated with and implicated in pathogenic mechanisms of depression. Both systems tightly regulate the other's activity. As such, a dysregulation in this crosstalk has potential to influence the onset and maintenance of this neuropsychiatric illness. However, few studies have investigated both systems and depression conjointly. This review highlights the demand to consider joint eCB-immune interactions in the pathoetiology of depression.

Broad impact of deleting endogenous cannabinoid hydrolyzing enzymes and the CB1 cannabinoid receptor on the endogenous cannabinoid-related lipidome in eight regions of the mouse brain

BACKGROUND AND PURPOSE

The enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) hydrolyze endogenous cannabinoids (eCBs), N-arachidonoyl ethanolamine (AEA) and 2-arachidonoyl glycerol (2-AG), respectively. These enzymes also metabolize eCB analogs such as lipoamines and 2-acyl glycerols, most of which are not ligands at CB1. To test the hypothesis that deleting eCB hydrolyzing enzymes and CB1 shifts lipid metabolism more broadly and impacts more families of eCB structural analogs, targeted lipidomics analyses were performed on FAAH KO, MAGL KO, and CB1 KO mice and compared to WT controls in 8 brain regions.

EXPERIMENTAL APPROACH

Methanolic extracts of discrete brain regions (brainstem, cerebellum, cortex, hippocampus, hypothalamus, midbrain, striatum and thalamus) were partially purified on C-18 solid-phase extraction columns. Over 70 lipids per sample were then analyzed with HPLC/MS/MS.

KEY RESULTS

AEA and 2-AG were unaffected throughout the brain in CB1 KO mice; however, there was an increase in the arachidonic acid (AA) metabolite, PGE2 in the majority of brain areas. By contrast, PGE2 and AA levels were significantly reduced throughout the brain in the MAGL KO corresponding to significant increases in 2-AG. No changes in AA or PGE2 were seen throughout in the FAAH KO brain, despite significant increases in AEA, suggesting AA liberated by FAAH does not contribute to steady state levels of AA or PGE2. Changes in the lipidome were not confined to the AA derivatives and showed regional variation in each of the eCB KO models.

CONCLUSIONS AND IMPLICATIONS

AEA and 2-AG hydrolyzing enzymes and the CB1 receptor link the eCB system to broader lipid signaling networks in contrasting ways, potentially altering neurotransmission and behavior independently of cannabinoid receptor signaling.

Hypothalamic-Pituitary--Adrenal Axis-Feedback Control

The hypothalamo-pituitary-adrenal axis (HPA) is responsible for stimulation of adrenal corticosteroids in response to stress. Negative feedback control by corticosteroids limits pituitary secretion of corticotropin, ACTH, and hypothalamic secretion of corticotropin-releasing hormone, CRH, and vasopressin, AVP, resulting in regulation of both basal and stress-induced ACTH secretion. The negative feedback effect of corticosteroids occurs by action of corticosteroids at mineralocorticoid receptors (MR) and/or glucocorticoid receptors (GRs) located in multiple sites in the brain and in the pituitary. The mechanisms of negative feedback vary according to the receptor type and location within the brain-hypothalmo-pituitary axis. A very rapid nongenomic action has been demonstrated for GR action on CRH neurons in the hypothalamus, and somewhat slower nongenomic effects are observed in the pituitary or other brain sites mediated by GR and/or MR. Corticosteroids also have genomic actions, including repression of the pro-opiomelanocortin (POMC) gene in the pituitary and CRH and AVP genes in the hypothalamus. The rapid effect inhibits stimulated secretion, but requires a rapidly rising corticosteroid concentration. The more delayed inhibitory effect on stimulated secretion is dependent on the intensity of the stimulus and the magnitude of the corticosteroid feedback signal, but also the neuroanatomical pathways responsible for activating the HPA. The pathways for activation of some stressors may partially bypass hypothalamic feedback sites at the CRH neuron, whereas others may not involve forebrain sites; therefore, some physiological stressors may override or bypass negative feedback, and other psychological stressors may facilitate responses to subsequent stress.

Developmental regulation of fear learning and anxiety behavior by endocannabinoids

The developing brain undergoes substantial maturation into adulthood and the development of specific neural structures occurs on differing timelines. Transient imbalances between developmental trajectories of corticolimbic structures, which are known to contribute to regulation over fear learning and anxiety, can leave an individual susceptible to mental illness, particularly anxiety disorders. There is a substantial body of literature indicating that the endocannabinoid (eCB) system critically regulates stress responsivity and emotional behavior throughout the life span, making this system a novel therapeutic target for stress- and anxiety-related disorders. During early life and adolescence, corticolimbic eCB signaling changes dynamically and coincides with different sensitive periods of fear learning, suggesting that eCB signaling underlies age-specific fear learning responses. Moreover, perturbations to these normative fluctuations in corticolimbic eCB signaling, such as stress or cannabinoid exposure, could serve as a neural substrate contributing to alterations to the normative developmental trajectory of neural structures governing emotional behavior and fear learning. In this review, we first introduce the components of the eCB system and discuss clinical and rodent models showing eCB regulation of fear learning and anxiety in adulthood. Next, we highlight distinct fear learning and regulation profiles throughout development and discuss the ontogeny of the eCB system in the central nervous system, and models of pharmacological augmentation of eCB signaling during development in the context of fear learning and anxiety.

Evidence for a Role of Adolescent Endocannabinoid Signaling in Regulating HPA Axis Stress Responsivity and Emotional Behavior Development

Adolescence is a period characterized by many distinct physical, behavioral, and neural changes during the transition from child- to adulthood. In particular, adolescent neural changes often confer greater plasticity and flexibility, yet with this comes the potential for heightened vulnerability to external perturbations such as stress exposure or recreational drug use. There is substantial evidence to suggest that factors such as adolescent stress exposure have longer lasting and sometimes more deleterious effects on an organism than stress exposure during adulthood. Moreover, the adolescent neuroendocrine response to stress exposure is different from that of adults, suggesting that further maturation of the adolescent hypothalamic-pituitary-adrenal (HPA) axis is required. The endocannabinoid (eCB) system is a potential candidate underlying these age-dependent differences given that it is an important regulator of the adult HPA axis and neuronal development. Therefore, this review will focus on (1) the functionality of the adolescent HPA axis, (2) eCB regulation of the adult HPA axis, (3) dynamic changes in eCB signaling during the adolescent period, (4) the effects of adolescent stress exposure on the eCB system, and (5) modulation of HPA axis activity and emotional behavior by adolescent cannabinoid treatment. Collectively, the emerging picture suggests that the eCB system mediates interactions between HPA axis stress responsivity, emotionality, and maturational stage. These findings may be particularly relevant to our understanding of the development of affective disorders and the risks of adolescent cannabis consumption on emotional health and stress responsivity.

Cannabinoid-based drugs targeting CB1 and TRPV1, the sympathetic nervous system, and arthritis

Chronic inflammation in rheumatoid arthritis (RA) is accompanied by activation of the sympathetic nervous system, which can support the immune system to perpetuate inflammation. Several animal models of arthritis already demonstrated a profound influence of adrenergic signaling on the course of RA. Peripheral norepinephrine release from sympathetic terminals is controlled by cannabinoid receptor type 1 (CB1), which is activated by two major endocannabinoids (ECs), arachidonylethanolamine (anandamide) and 2-arachidonylglycerol. These ECs also modulate function of transient receptor potential channels (TRPs) located on sensory nerve fibers, which are abundant in arthritic synovial tissue. TRPs not only induce the sensation of pain but also support inflammation via secretion of pro-inflammatory neuropeptides. In addition, many cell types in synovial tissue express CB1 and TRPs. In this review, we focus on CB1 and transient receptor potential vanilloid 1 (TRPV1)-mediated effects on RA since most anti-inflammatory mechanisms induced by cannabinoids are attributed to cannabinoid receptor type 2 (CB2) activation. We demonstrate how CB1 agonism or antagonism can modulate arthritic disease. The concept of functional antagonism with continuous CB1 activation is discussed. Since fatty acid amide hydrolase (FAAH) is a major EC-degrading enzyme, the therapeutic possibility of FAAH inhibition is studied. Finally, the therapeutic potential of ECs is examined since they interact with cannabinoid receptors and TRPs but do not produce central side effects.

High Times for Painful Blues: The Endocannabinoid System in Pain-Depression Comorbidity

Depression and pain are two of the most debilitating disorders worldwide and have an estimated cooccurrence of up to 80%. Comorbidity of these disorders is more difficult to treat, associated with significant disability and impaired health-related quality of life than either condition alone, resulting in enormous social and economic cost. Several neural substrates have been identified as potential mediators in the association between depression and pain, including neuroanatomical reorganization, monoamine and neurotrophin depletion, dysregulation of the hypothalamo-pituitary-adrenal axis, and neuroinflammation. However, the past decade has seen mounting evidence supporting a role for the endogenous cannabinoid (endocannabinoid) system in affective and nociceptive processing, and thus, alterations in this system may play a key role in reciprocal interactions between depression and pain. This review will provide an overview of the preclinical evidence supporting an interaction between depression and pain and the evidence supporting a role for the endocannabinoid system in this interaction.

Disruption of peri-adolescent endocannabinoid signaling modulates adult neuroendocrine and behavioral responses to stress in male rats

The endocannabinoid (eCB) system is known to regulate neural, endocrine and behavioral responses to stress in adults; however there is little knowledge regarding how this system governs the development and maturation of these responses. Previous work has reported dynamic and time-specific changes in CB1 receptor expression, N-arachidonylethanolamine (AEA) content and fatty acid amide hydrolase (FAAH) activity within corticolimbic structures throughout the peri-adolescent period. To examine whether fluctuations in adolescent eCB activity contribute to the development of adult stress responsivity and emotionality, we treated male Sprague-Dawley rats daily with the CB1R antagonist, AM-251 (5 mg/kg), or vehicle between post-natal days (PND) 35-45. Following this treatment, emotional behavior, HPA axis stress reactivity and habituation to repeated restraint stress, as well as corticolimbic eCB content were examined in adulthood (PND 75). Behaviorally, AM-251-treated males exhibited more active stress-coping behavior in the forced swim test, greater risk assessment behavior in the elevated plus maze and no significant differences in general motor activity. Peri-adolescent AM-251 treatment modified corticosterone habituation to repeated restraint exposure compared to vehicle. Peri-adolescent CB1R antagonism induced moderate changes in adult corticolimbic eCB signaling, with a significant decrease in amygdalar AEA, an increase in hypothalamic AEA and an increase in prefrontal cortical CB1R expression. Together, these data indicate that peri-adolescent endocannabinoid signaling contributes to the maturation of adult neurobehavioral responses to stress.

Role of the basolateral amygdala in mediating the effects of the fatty acid amide hydrolase inhibitor URB597 on HPA axis response to stress

The endocannabinoid system is an important regulator of neuroendocrine and behavioral adaptation in stress related disorders thus representing a novel potential therapeutic target. The aim of this study was to determine the effects of the fatty acid amide hydrolase (FAAH) inhibitor URB597 on stress mediators of HPA axis and to study the role of the basolateral amygdala (BLA) in responses to forced swim stress. Systemic administration of URB597 (0.1 and 0.3mg/kg) reduced the forced swim stress-induced activation of HPA axis. More specifically, URB597 decreased stress-induced corticotropin-releasing hormone (CRH) mRNA expression in the paraventricular nucleus (PVN) of the hypothalamus, and pro-opiomelanocortin (POMC) mRNA expression dose-dependently in pituitary gland without affecting plasma corticosterone levels. URB597 treatment also attenuated stress-induced neuronal activation of the amygdala and PVN, and increased neuronal activation in the locus coeruleus (LC) and nucleus of solitary tract (NTS). Injection of the CB1 receptor antagonist AM251 (1ng/side) in the BLA significantly attenuated URB597-mediated effects in the PVN and completely blocked those induced in the BLA. These results suggest that the BLA is a key structure involved in the anti-stress effects of URB597, and support the evidence that enhancement of endogenous cannabinoid signaling by inhibiting FAAH represents a potential therapeutic strategy for the management of stress-related disorders.

A critical role for prefrontocortical endocannabinoid signaling in the regulation of stress and emotional behavior

The prefrontal cortex (PFC) provides executive control of the brain in humans and rodents, coordinating cognitive, emotional, and behavioral responses to threatening stimuli and subsequent feedback inhibition of the hypothalamic-pituitary-adrenal (HPA) axis. The endocannabinoid system has emerged as a fundamental regulator of HPA axis feedback inhibition and an important modulator of emotional behavior. However, the precise role of endocannabinoid signaling within the PFC with respect to stress coping and emotionality has only recently been investigated. This review discusses the current state of knowledge regarding the localization and function of the endocannabinoid system in the PFC, its sensitivity to stress and its role in modulating the neuroendocrine and behavioral responses to aversive stimuli. We propose a model whereby steady-state endocannabinoid signaling in the medial PFC indirectly regulates the outflow of pyramidal neurons by fine-tuning GABAergic inhibition. Local activation of this population of CB1 receptors increases the downstream targets of medial PFC activation, which include inhibitory interneurons in the basolateral amygdala, inhibitory relay neurons in the bed nucleus of the stria terminalis and monoamine cell bodies such as the dorsal raphe nucleus. This ultimately produces beneficial effects on emotionality (active coping responses to stress and reduced anxiety) and assists in constraining activation of the HPA axis. Under conditions of chronic stress, or in individuals suffering from mood disorders, this system may be uniquely recruited to help maintain appropriate function in the face of adversity, while breakdown of the endocannabinoid system in the medial PFC may be, in and of itself, sufficient to produce neuropsychiatric illness. Thus, we suggest that endocannabinoid signaling in the medial PFC may represent an attractive target for the treatment of stress-related disorders.

Impact of stress on prefrontal glutamatergic, monoaminergic and cannabinoid systems

Stress has been shown to have marked and divergent effects on learning and memory which involves specific brain regions, such as spatial and declarative memory involving the hippocampus, memory of emotional arousing experiences and fear involving the amygdala, and executive functions and fear extinction involving the prefrontal cortex or the PFC. Response to stress involves a coordinated activation of a constellation of physiological systems including the activation of the hypothalamic-pituitary-adrenal (HPA) axis and other modulatory neurotransmitters and signaling systems. This paper presents a concise review of the effects of stress and glucocorticoids on the glutamatergic and monoaminergic (including noradrenergic, dopaminergic, and serotonergic systems) neurotransmitter systems as well as endocannabinoid signaling. Because of the breadth of the scope of this topic, the review is limited to the effects of stress on these brain systems on the prefrontal cortex, and where relevant, the hippocampus and the amygdala.

The endocannabinoid system: an emotional buffer in the modulation of memory function

Extensive evidence indicates that endocannabinoids modulate cognitive processes in animal models and human subjects. However, the results of endocannabinoid system manipulations on cognition have been contradictory. As for anxiety behavior, a duality has indeed emerged with regard to cannabinoid effects on memory for emotional experiences. Here we summarize findings describing cannabinoid effects on memory acquisition, consolidation, retrieval and extinction. Additionally, we review findings showing how the endocannabinoid system modulates memory function differentially, depending on the level of stress and arousal associated with the experimental context. Based on the evidence reviewed here, we propose that the endocannabinoid system is an emotional buffer that moderates the effects of environmental context and stress on cognitive processes.

Cannabinoids and glucocorticoids modulate emotional memory after stress

Bidirectional and functional relationships between glucocorticoids and the endocannabinoid system have been demonstrated. Here, I review the interaction between the endocannabinoid and glucocorticoid/stress systems. Specifically, stress is known to produce rapid changes in endocannabinoid signaling in stress-responsive brain regions. In turn, the endocannabinoid system plays an important role in the downregulation and habituation of hypothalamic-pituitary-adrenocortical (HPA) axis activity in response to stress. Glucocorticoids also recruit the endocannabinoid system to exert rapid negative feedback control of the HPA axis during stress. It became increasingly clear, however, that cannabinoid CB1 receptors are also abundantly expressed in the basolateral amygdala (BLA) and other limbic regions where they modulate emotional arousal effects on memory. Enhancing cannabinoids signaling using exogenous CB1 receptor agonists prevent the effects of acute stress on emotional memory. I propose a model suggesting that the ameliorating effects of exogenously administered cannabinoids on emotional learning after acute stress are mediated by the decrease in the activity of the HPA axis via GABAergic mechanisms in the amygdala.

Screening genetic variability at the CNR1 gene in both major depression etiology and clinical response to citalopram treatment

RATIONALE

The endocannabinoid system has been implicated in the pathogenesis of major depression (MD) as well as in the mediation of antidepressant drug effects.

OBJECTIVES

To analyze CNR1 gene variants in MD and clinical response to citalopram (selective serotonin re-uptake inhibitors [SSRI]).

METHODS

The role of CNR1 gene (rs806368, rs1049353, rs806371, rs806377 and rs1535255) was investigated in 319 outpatients with MD and 150 healthy individuals. A subsample of 155 depressive patients were treated with citalopram and evaluated for response (fourth week) and remission (12th week) by the 21-item Hamilton Depression Rating Scale (HDRS).

RESULTS

We observed a higher frequency of rs806371 G carriers in MD patients with both presence of melancholia (p = 0.018) and psychotic symptoms (p = 0.007) than in controls. Haplotype frequency distributions between MD sample and controls showed a significant difference for Block 1 (rs806368-rs1049353-rs806371) (p = 0.008). This haplotype finding was consistent when we compared controls with MD subsample stratified by melancholia (p = 0.0009) and psychotic symptoms (p = 0.014). The TT homozygous of the rs806368 and rs806371 presented more risk of no Remission than the C carriers (p = 0.008 and 0.012, respectively). Haplotype frequency distributions according to Remission status showed a significant difference for Block 1 (p = 0.032). Also, we observed significant effect of time-sex-genotype interaction for the rs806368, showing that the C carrier men presented a better response to antidepressant treatment throughout the follow-up than TT homozygous men and women group (p = 0.026).

CONCLUSIONS

These results suggest an effect of CNR1 gene in the etiology of MD and clinical response to citalopram.

Novelty-induced emotional arousal modulates cannabinoid effects on recognition memory and adrenocortical activity

Although it is well established that cannabinoid drugs can influence cognitive performance, the findings-describing both enhancing and impairing effects-have been ambiguous. Here, we investigated the effects of posttraining systemic administration of the synthetic cannabinoid agonist WIN55,212-2 (0.1, 0.3, or 1.0 mg/kg) on short- and long-term retention of object recognition memory under two conditions that differed in their training-associated arousal level. In male Sprague-Dawley rats that were not previously habituated to the experimental context, WIN55,212-2 administered immediately after a 3-min training trial, biphasically impaired retention performance at a 1-h interval. In contrast, WIN55,212-2 enhanced 1-h retention of rats that had received extensive prior habituation to the experimental context. Interestingly, immediate posttraining administration of WIN55,212-2 to non-habituated rats, in doses that impaired 1-h retention, enhanced object recognition performance at a 24-h interval. Posttraining WIN55,212-2 administration to habituated rats did not significantly affect 24-h retention. In light of intimate interactions between cannabinoids and the hypothalamic-pituitary-adrenal axis, we further investigated whether cannabinoid administration might differently influence training-induced glucocorticoid activity in rats in these two habituation conditions. WIN55,212-2 administered after object recognition training elevated plasma corticosterone levels in non-habituated rats whereas it decreased corticosterone levels in habituated rats. Most importantly, following pretreatment with the corticosterone-synthesis inhibitor metyrapone, WIN55,212-2 effects on 1- and 24-h retention of non-habituated rats became similar to those seen in the low-aroused habituated animals, indicating that cannabinoid-induced regulation of adrenocortical activity contributes to the environmentally sensitive effects of systemically administered cannabinoids on short- and long-term retention of object recognition memory.

Cannabinoid modulation of midbrain urocortin 1 neurones during acute and chronic stress

Neurones in the centrally projecting Edinger-Westphal nucleus (EWcp) are the main site of urocortin 1 (Ucn1) synthesis in the mammalian brain, and are assumed to play a role in the stress response of the animal. Because endocannabinoid signalling has also been strongly implicated in stress, we hypothesised that endocannabinoids may modulate the functioning of the urocortinergic EWcp. First, using in situ hybridisation, we demonstrated cannabinoid receptor 1 (CB1R) mRNA expression in mouse EWcp-neurones that were Ucn1-negative. Dual- and triple-label immunocytochemistry revealed the presence of CB1R in several GABA-immunopositive fibres juxtaposed to EWcp-Ucn1 neurones. To test functional aspects of such an anatomical constellation, we compared acute (1 h of restraint) and chronic (14 days of chronic mild stress) stress-induced changes in wild-type (WT) and CB1R knockout (CB1R-KO) mice. Acute and especially chronic stress resulted in an increase in Ucn1 content of the EWcp, which was attenuated in CB1R-KO mice. CB1R-KO mice had higher basal and chronic stress-induced adrenocorticotrophin and corticosterone levels and were more anxious on the elevated plus-maze versus WT. Collectively, our results show for the first time EWcp-Ucn1 neurones are putatively innervated by endocannabinoid sensitive, inhibitory, GABAergic afferents. In addition, we provide novel evidence that the absence of the CB1 receptor alters the Ucn1 mRNA and peptide levels in EWcp neurones, concomitant with an augmented stress response and increased anxiety-like behaviour.

Opposing local effects of endocannabinoids on the activity of noradrenergic neurons and release of noradrenaline: relevance for their role in depression and in the actions of CB(1) receptor antagonists

There is strong evidence that endocannabinoids modulate signaling of serotonin and noradrenaline, which play key roles in the pathophysiology and treatment of anxiety and depression. Most pharmacological and genetic, human and rodent studies suggest that the presence of under-functioning endocannabinoid type-1 (CB(1)) receptors is associated with increased anxiety and elevated extracellular serotonin concentration. In contrast, noradrenaline is presumably implicated in the mediation of depression-type symptoms of CB(1) receptor antagonists. Evidence shows that most CB(1) receptors located on axons and terminals of GABA-ergic, serotonergic or glutamatergic neurons stimulate the activity of noradrenergic neurons. In contrast, those located on noradrenergic axons and terminals inhibit noradrenaline release efficiently. In this latter process, excitatory ionotropic or G protein-coupled receptors, such as the NMDA, alpha1 and beta1 adrenergic receptors, activate local endocannabinoid synthesis at postsynaptic sites and stimulate retrograde endocannabinoid neurotransmission acting on CB(1) receptors of noradrenergic terminals. The underlying mechanisms include calcium signal generation, which activates enzymes that increase the synthesis of both anandamide and 2-arachidonoylglycerol, while G(q/11) protein activation also increases the formation of 2-arachidonoylglycerol from diacylglycerol during the signaling process. In addition, other non-CB(1) receptor endocannabinoid targets such as CB(2), transient receptor potential vanilloid subtype, peroxisome proliferator-activated receptor-alpha and possibly GPR55 can also mediate some of the endocannabinoid effects. In conclusion, both neuronal activation and neurotransmitter release depend on the in situ synthesized endocannabinoids and thus, local endocannabinoid concentrations in different brain areas may be crucial in the net effect, namely in the regulation of neurons located postsynaptically to the noradrenergic synapse.

A current overview of cannabinoids and glucocorticoids in facilitating extinction of aversive memories: potential extinction enhancers

Emotional learning is extremely important for the survival of an individual. However, once acquired, emotional associations are not always expressed. The regulation of emotional responses under different environmental conditions is essential for mental health. Indeed, pathologic feelings of fear and anxiety are defining features of many serious psychiatric illness, including post-traumatic stress disorder (PTSD) and specific phobias. The simplest form of regulation of emotional responses is extinction, in which the conditioned response to a stimulus decreases when reinforcement (stimulus) is omitted. In addition to modulating basal anxiety states, recent studies suggest an important role for the endocannabinoid (eCB) and glucocorticoid systems in the modulation of emotional states and extinction of aversive memories in animals. The purpose of this review is to briefly outline the animal models of fear extinction and to describe how these have been used to examine the potential of extinction enhancing agents which specifically alter the eCB and glucocorticoid systems. Pharmacological manipulations of these systems by agents such as cannabinoid or glucocorticoid agonists can enhance the extinction process and avoid the retention of memories which have the potential to trigger trauma. A better understanding of these findings through animal models highlights the possibilities of using combined extinction enhancing agents in exposure-based psychotherapies for anxiety disorders related to inappropriate retention of aversive memories. This article is part of a special issue entitled 'Cognitive Enhancers'.

Endogenous cannabinoid system regulates intestinal barrier function in vivo through cannabinoid type 1 receptor activation

The deleterious effects of stress on the gastrointestinal tract seem to be mainly mediated by the induction of intestinal barrier dysfunction and subsequent subtle mucosal inflammation. Cannabinoid 1 receptor (CB1R) is expressed in the mammalian gut under physiological circumstances. The aim of this investigation is to study the possible role of CB1R in the maintenance of mucosal homeostasis after stress exposure. CB1R knockout mice (CB1R(-/-)) and their wild-type (WT) counterparts were exposed to immobilization and acoustic (IA) stress for 2 h per day during 4 consecutive days. Colonic protein expression of the inducible forms of the nitric oxide synthase and cyclooxygenase (NOS2 and COX2), IgA production, permeability to (51)Cr-EDTA, and bacterial translocation to mesenteric lymph nodes were evaluated. Stress exposure induced greater expression of proinflammatory enzymes NOS2 and COX2 in colonic mucosa of CB1R(-/-) mice when compared with WT animals. These changes were related with a greater degree of colonic barrier dysfunction in CB1R(-/-) animals determined by 1) a significantly lower IgA secretion, 2) higher paracellular permeability to (51)Cr-EDTA, and 3) higher bacterial translocation, both under basal conditions and after IA stress exposure. Pharmacological antagonism with rimonabant reproduced stress-induced increase of proinflammatory enzymes in the colon described in CB1R(-/-) mice. In conclusion, CB1R exerts a protective role in the colon in vivo through the regulation of intestinal secretion of IgA and paracellular permeability. Pharmacological modulation of cannabinoid system within the gastrointestinal tract might be therapeutically useful in conditions on which intestinal inflammation and barrier dysfunction takes place after exposure to stress.

Serum contents of endocannabinoids are correlated with blood pressure in depressed women

BACKGROUND

Depression is known to be a risk factor for cardiovascular diseases but the underlying mechanisms remain unclear. Since recent preclinical evidence suggests that endogenous agonists of cannabinoid receptors (endocannabinoids) are involved in both cardiovascular function and depression, we asked whether endocannabinoids correlated with either in humans.

RESULTS

Resting blood pressure and serum content of endocannabinoids in ambulatory, medication-free, female volunteers with depression (n = 28) and their age- and ethnicity-matched controls (n = 27) were measured. In females with depression, both diastolic and mean arterial blood pressures were positively correlated with serum contents of the endocannabinoids, N-arachidonylethanolamine (anandamide) and 2-arachidonoylglycerol. There was no correlation between blood pressure and endocannabinoids in control subjects. Furthermore, depressed women had significantly higher systolic blood pressure than control subjects. A larger body mass index was also found in depressed women, however, it was not significantly correlated with serum endocannabinoid contents.

CONCLUSIONS

This preliminary study raises the possibility that endocannabinoids play a role in blood pressure regulation in depressives with higher blood pressure, and suggests an interrelationship among endocannabinoids, depression and cardiovascular risk factors in women.