Endocannabinoids, stress signaling, and the locus coeruleus-norepinephrine system

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.

Norepinephrine-Activated p38 MAPK Pathway Mediates Stress-Induced Cytotoxic Edema of Basolateral Amygdala Astrocytes

The amygdala is a core region in the limbic system that is highly sensitive to stress. Astrocytes are key players in stress disorders such as anxiety and depression. However, the effects of stress on the morphology and function of amygdala astrocytes and its potential mechanisms remain largely unknown. Hence, we performed in vivo and in vitro experiments using a restraint stress (RS) rat model and stress-induced astrocyte culture, respectively. Our data show that norepinephrine (NE) content increased, cytotoxic edema occurred, and aquaporin-4 (AQP4) expression was up-regulated in the basolateral amygdala (BLA) obtained from RS rats. Additionally, the p38 mitogen-activated protein kinase (MAPK) pathway was also observed to be significantly activated in the BLA of rats subjected to RS. The administration of NE to in vitro astrocytes increased the AQP4 level and induced cell edema. Furthermore, p38 MAPK signaling was activated. The NE inhibitor alpha-methyl-p-tyrosine (AMPT) alleviated cytotoxic edema in astrocytes, inhibited AQP4 expression, and inactivated the p38 MAPK pathway in RS rats. Meanwhile, in the in vitro experiment, the p38 MAPK signaling inhibitor SB203580 reversed NE-induced cytotoxic edema and down-regulated the expression of AQP4 in astrocytes. Briefly, NE-induced activation of the p38 MAPK pathway mediated cytotoxic edema in BLA astrocytes from RS rats. Thus, our data provide novel evidence that NE-induced p38 MAPK pathway activation may be one of the mechanisms leading to cytotoxic edema in BLA under stress conditions, which also could enable the development of an effective therapeutic strategy against cytotoxic edema in BLA under stress and provide new ideas for the treatment of neuropsychiatric diseases.

Crosstalk Between the Neuroendocrine System and Bone Homeostasis

The homeostasis of bone microenvironment is the foundation of bone health and comprises 2 concerted events: bone formation by osteoblasts and bone resorption by osteoclasts. In the early 21st century, leptin, an adipocytes-derived hormone, was found to affect bone homeostasis through hypothalamic relay and the sympathetic nervous system, involving neurotransmitters like serotonin and norepinephrine. This discovery has provided a new perspective regarding the synergistic effects of endocrine and nervous systems on skeletal homeostasis. Since then, more studies have been conducted, gradually uncovering the complex neuroendocrine regulation underlying bone homeostasis. Intriguingly, bone is also considered as an endocrine organ that can produce regulatory factors that in turn exert effects on neuroendocrine activities. After decades of exploration into bone regulation mechanisms, separate bioactive factors have been extensively investigated, whereas few studies have systematically shown a global view of bone homeostasis regulation. Therefore, we summarized the previously studied regulatory patterns from the nervous system and endocrine system to bone. This review will provide readers with a panoramic view of the intimate relationship between the neuroendocrine system and bone, compensating for the current understanding of the regulation patterns of bone homeostasis, and probably developing new therapeutic strategies for its related disorders.

Addictive drugs modify neurogenesis, synaptogenesis and synaptic plasticity to impair memory formation through neurotransmitter imbalances and signaling dysfunction

Drug abuse changes neurophysiological functions at multiple cellular and molecular levels in the addicted brain. Well-supported scientific evidence suggests that drugs negatively affect memory formation, decision-making and inhibition, and emotional and cognitive behaviors. The mesocorticolimbic brain regions are involved in reward-related learning and habitual drug-seeking/taking behaviors to develop physiological and psychological dependence on the drugs. This review highlights the importance of specific drug-induced chemical imbalances resulting in memory impairment through various neurotransmitter receptor-mediated signaling pathways. The mesocorticolimbic modifications in the expression levels of brain-derived neurotrophic factor (BDNF) and the cAMP-response element binding protein (CREB) impair reward-related memory formation following drug abuse. The contributions of protein kinases and microRNAs (miRNAs), along with the transcriptional and epigenetic regulation have also been considered in memory impairment underlying drug addiction. Overall, we integrate the research on various types of drug-induced memory impairment in distinguished brain regions and provide a comprehensive review with clinical implications addressing the upcoming studies.

Cannabinoids and Multiple Sclerosis: A Critical Analysis of Therapeutic Potentials and Safety Concerns

Multiple sclerosis (MS) is a complicated condition in which the immune system attacks myelinated axons in the central nervous system (CNS), destroying both myelin and axons to varying degrees. Several environmental, genetic, and epigenetic factors influence the risk of developing the disease and how well it responds to treatment. Cannabinoids have recently sparked renewed interest in their therapeutic applications, with growing evidence for their role in symptom control in MS. Cannabinoids exert their roles through the endogenous cannabinoid (ECB) system, with some reports shedding light on the molecular biology of this system and lending credence to some anecdotal medical claims. The double nature of cannabinoids, which cause both positive and negative effects, comes from their actions on the same receptor. Several mechanisms have been adopted to evade this effect. However, there are still numerous limitations to using cannabinoids to treat MS patients. In this review, we will explore and discuss the molecular effect of cannabinoids on the ECB system, the various factors that affect the response to cannabinoids in the body, including the role of gene polymorphism and its relation to dosage, assessing the positive over the adverse effects of cannabinoids in MS, and finally, exploring the possible functional mechanism of cannabinoids in MS and the current and future progress of cannabinoid therapeutics.

Transcriptome profiles associated with resilience and susceptibility to single prolonged stress in the locus coeruleus and nucleus accumbens in male sprague-dawley rats

Although most people are subjected to traumatic stress at least once in their lifetime, only a subset develop long-lasting, stress-triggered neuropsychiatric disorders, such as PTSD. Here we examined different transcriptome profiles within the locus coeruleus (LC) and nucleus accumbens (NAc) that may contribute to stress susceptibility. Sprague Dawley male rats were exposed to the single prolonged stress (SPS) model for PTSD. Two weeks later they were tested for their anxiety/avoidance behavior on the Elevated Plus Maze (EPM) and were divided into high and low anxiety-like subgroups. RNA (n = 5 per group) was subsequently isolated from LC and NAc and subjected to RNAseq. Transcriptome analysis was used to identify differentially-expressed genes (DEGs) which differed by at least 50 % with significance of 0.01. The LC had more than six times the number of DEGs than the NAc. Only one DEG was regulated similarly in both locations. Many of the DEGs in the LC were associated with morphological changes, including regulation of actin cytoskeleton, growth factor activity, regulation of cell size, brain development and memory, with KEGG pathway of regulation of actin cytoskeleton. The DEGs in the NAc were primarily related to DNA repair and synthesis, and differential regulation of cytokine production. The analysis identified MTPN (myotrophin) and NR3C1 (glucocorticoid receptor) as important upstream regulators of stress susceptibility in the LC. Overall the study provides new insight into molecular pathways in the LC and NAc that are associated with anxiety-like behavior triggered by stress susceptibility or resilience.

Cannabidiol Prevents Spontaneous Fear Recovery after Extinction and Ameliorates Stress-Induced Extinction Resistance

Cannabidiol, the main non-psychotropic constituent of cannabis, has potential as a treatment for anxiety-related disorders since it reduces learned fear expression and enhances fear extinction. The return of fear over time after successful extinction and stress-induced extinction resistance are potential barriers to the treatment of these disorders with extinction-based psychological therapy. In two experiments using rats subjected to auditory fear conditioning, we determined the effects of systemic cannabidiol treatment on (1) delayed extinction and later spontaneous fear recovery, and (2) extinction resistance caused by immediate extinction (the immediate extinction deficit (IED)). In Experiment 1, cannabidiol was given before delayed extinction occurring 24 h after conditioning, with extinction recall and spontaneous fear recovery tested drug-free 1 and 21 days after extinction, respectively. We found that cannabidiol had no effect on extinction recall but it prevented spontaneous fear recovery. In Experiment 2, the IED procedure was first validated, with immediate extinction occurring 30 min after conditioning. We confirmed that immediate extinction impaired extinction recall, compared to delayed extinction. Next, cannabidiol was given before immediate or no extinction, with extinction recall tested drug-free the next day. We found that cannabidiol rescued the IED, which did not involve effects on fear memory consolidation. In summary, cannabidiol prevented spontaneous fear recovery after delayed extinction and ameliorated extinction resistance caused by immediate extinction. Although the pharmacological mechanisms underlying these effects remain to be determined, our results add to evidence indicating that cannabidiol might prove useful as an adjunct for potentiating the psychological treatment of anxiety-related disorders.

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.

Wonder or evil?: Multifaceted health hazards and health benefits of Cannabis sativa and its phytochemicals

Cannabis sativa, widely known as 'Marijuana' poses a dilemma for being a blend of both good and bad medicinal effects. The historical use of Cannabis for both medicinal and recreational purposes suggests it to be a friendly plant. However, whether the misuse of Cannabis and the cannabinoids derived from it can hamper normal body physiology is a focus of ongoing research. On the one hand, there is enough evidence to suggest that misuse of marijuana can cause deleterious effects on various organs like the lungs, immune system, cardiovascular system, etc. and also influence fertility and cause teratogenic effects. However, on the other hand, marijuana has been found to offer a magical cure for anorexia, chronic pain, muscle spasticity, nausea, and disturbed sleep. Indeed, most recently, the United Nations has given its verdict in favour of Cannabis declaring it as a non-dangerous narcotic. This review provides insights into the various health effects of Cannabis and its specialized metabolites and indicates how wise steps can be taken to promote good use and prevent misuse of the metabolites derived from this plant.

Effects of Fatty Acid Amide Hydroxylase Inhibitor URB597 on the Catecholaminergic Activity of the Adrenal Medulla in Stressed Male and Female Rats

INTRODUCTION

The present study examined the effects of fatty acid amide hydrolase inhibitor URB597 on the level of plasma catecholamine and their content, synthesis, and degradation in the adrenal medulla of male and female rats subjected to chronic unpredictable stress (CUS).

MATERIAL AND METHODS

Male and female Wistar rats were exposed to the 6 weeks of CUS and treated intraperitoneally with either 0.3 mg/kg/day of URB597 or vehicle in the last 2 weeks of stress protocol. Catecholamines' plasma levels and catecholamines' levels in adrenal medulla were examined using Elabscience ELISA kits. Western blot analysis was used to detect the protein in the medulla.

RESULTS

The results of our experiment showed that adrenal weights and catecholamine of unstressed control were higher in females and that CUS induced further enlargement of adrenal glands and catecholamine content and its synthesis compared to male rats. CUS caused an increase of plasma norepinephrine and depletion of norepinephrine content as well as unchanged synthesis and degradation of catecholamine in the adrenal medulla of male rats. URB597 reduced enlarged adrenals and catecholamine content and its synthesis in stressed female rats. URB597 reduces increased plasma norepinephrine and restores its content in the adrenal medulla, unchanging the expression of enzyme synthesis, while reduced protein levels of monoamine oxidase A in male rats are exposed to CUS.

DISCUSSION

Our results support the role of endocannabinoids as an antistress mechanism that inhibits elevated adrenomedullary activation and promotes its recovery to baseline in both male and female stressed rats.

A review of the effects of acute and chronic cannabinoid exposure on the stress response

While cannabis has been used for centuries for its stress-alleviating properties, the effects of acute and chronic cannabinoid exposure on responses to stress remain poorly understood. This review provides an overview of studies that measured stress-related endpoints following acute or chronic cannabinoid exposure in humans and animals. Acute cannabinoid exposure increases basal concentrations of stress hormones in rodents and humans and has dose-dependent effects on stress reactivity in humans and anxiety-like behavior in rodents. Chronic cannabis exposure is associated with dampened stress reactivity, a blunted cortisol awakening response (CAR), and flattened diurnal cortisol slope in humans. Sex differences in these effects remain underexamined, with limited evidence for sex differences in effects of cannabinoids on stress reactivity in rodents. Future research is needed to better understand sex differences in the effects of cannabis on the stress response, as well as downstream impacts on mental health and stress-related disorders.

Cannabinoid control of hippocampal functions: the where matters

In the brain, hippocampal circuits are crucial for cognitive performance (e.g., memory) and deeply affected in pathological conditions (e.g., epilepsy, Alzheimer). Specialized molecular mechanisms regulate different cell types underlying hippocampal circuitries functions. Among them, cannabinoid receptors exhibit various roles depending on the cell type (e.g., neuron, glial cell) or subcellular organelle (e.g., mitochondria). Determining the site of action and precise mechanisms triggered by cannabinoid receptor activation at a local cellular and subcellular level helps us understand hippocampal pathophysiological states. In doing so, past and current research have advanced our knowledge of cannabinoid functions and proposed novel routes for potential therapeutics. By outlining these data in this work, we aim to showcase current findings and highlight the pathophysiological impact of the cannabinoid receptor type 1 (CB1) localization/activation in hippocampal circuits.

Crosstalk between Bone and Nerves within Bone

For the past two decades, the function of intrabony nerves on bone has been a subject of intense research, while the function of bone on intrabony nerves is still hidden in the corner. In the present review, the possible crosstalk between bone and intrabony peripheral nerves will be comprehensively analyzed. Peripheral nerves participate in bone development and repair via a host of signals generated through the secretion of neurotransmitters, neuropeptides, axon guidance factors and neurotrophins, with additional contribution from nerve-resident cells. In return, bone contributes to this microenvironmental rendezvous by housing the nerves within its internal milieu to provide mechanical support and a protective shelf. A large ensemble of chemical, mechanical, and electrical cues works in harmony with bone marrow stromal cells in the regulation of intrabony nerves. The crosstalk between bone and nerves is not limited to the physiological state, but also involved in various bone diseases including osteoporosis, osteoarthritis, heterotopic ossification, psychological stress-related bone abnormalities, and bone related tumors. This crosstalk may be harnessed in the design of tissue engineering scaffolds for repair of bone defects or be targeted for treatment of diseases related to bone and peripheral nerves.

In it together? The case for endocannabinoid-noradrenergic interactions in fear extinction

Anxiety and trauma-related disorders, such as post-traumatic stress disorder (PTSD), are debilitating mental illnesses with great personal and socioeconomic costs. Examining memory formation and relevant behavioural responding associated with aversive stimuli may improve our understanding of the neurobiology underlying fear memory processing and PTSD treatment. The neurocircuitry underpinning learned fear and its inhibition through extinction is complex, involving synergistic interactions between different neurotransmitter systems in inter-connected brain areas. Endocannabinoid and noradrenergic transmission have both been implicated separately in fear memory processing and PTSD, but potential interactions between these systems in relation to fear extinction have received little attention to date. Their receptors are expressed together in brain areas crucial for fear extinction, which is enhanced by both cannabinoid and noradrenergic receptor activation in these areas. Moreover, cannabinoid signalling modulates the activity of locus coeruleus noradrenaline (NA) neurons and the release of NA in the medial prefrontal cortex, a brain area that is crucial for fear extinction. Interestingly, endocannabinoid-noradrenergic system interactions have been shown to regulate the encoding and retrieval of fear memory. Thus, noradrenergic regulation of fear extinction may also be driven indirectly in part via cannabinoid receptor signalling. In this perspective paper, we collate the available relevant literature and propose a synergistic role for the endocannabinoid and noradrenergic systems in regulating fear extinction, the study of which may further our understanding of the neurobiological substrates of PTSD and its treatment.

Meet Your Stress Management Professionals: The Endocannabinoids

The endocannabinoid signaling system (ECSS) is altered by exposure to stress and mediates and modulates the effects of stress on the brain. Considerable preclinical data support critical roles for the endocannabinoids and their target, the CB1 cannabinoid receptor, in the adaptation of the brain to repeated stress exposure. Chronic stress exposure increases vulnerability to mental illness, so the ECSS has attracted attention as a potential therapeutic target for the prevention and treatment of stress-related psychopathology. We discuss human genetic studies indicating that the ECSS contributes to risk for mental illness in those exposed to severe stress and trauma early in life, and we explore the potential difficulties in pharmacological manipulation of the ECSS.

Inhibition of the fatty acid amide hydrolase changes behaviors and brain catecholamines in a sex-specific manner in rats exposed to chronic unpredictable stress

Sex differences in the susceptibility to chronic unpredictable stress (CUS) and the effects of fatty acid amide hydrolase (FAAH) inhibitor URB597 in rats have been investigated in this study. In this context, we investigated the effects of prolonged treatment with URB597 on behavior, pro-inflammatory interleukin-6 (IL-6) and anti-inflammatory interleukin-10 (IL-10), catecholamine content and the expression of its biosynthetic and degrading enzymes in the hippocampus, hypothalamus and medial prefrontal cortex (mPFC) of rats subjected to CUS. The results show that CUS increases anxiety-like and depression-like behaviors but it was more pronounced in females. The data suggests sex differences in brain cytokines, catecholamines and their enzymes of synthesis and degradation expression in response to CUS. Our findings indicate that the FAAH inhibitor URB597 differently regulated catecholamine levels and its enzymes of synthesis and degradation in the examined brain areas of male and female rats. URB treatment failed to reduce anxiety or restore reduced norepinephrine and did not affect enzymes of catecholamine degradation in the mPFC, hippocampus and hypothalamus of CUS female rats. These studies are important because they investigate the neurochemical consequences of stress related mood disorders that might lead to the development of sex specific treatments.

Sex differences in the interactive effects of early life stress and the endocannabinoid system

Sex differences in both the endocannabinoid system and stress responses have been established for decades. While there is ample evidence that the sexes respond differently to stress and that the endocannabinoid system is involved in this response, what is less clear is whether the endocannabinoid system mediates this response to stress differently in both sexes. Also, do the sexes respond similarly to exogenous cannabinoids (CBs) following stress? Can the administration of exogenous CBs normalize the effects of stress and if so, does this happen similarly in male and female subjects? This review will attempt to delineate the stress induced neurochemical alterations in the endocannabinoid system and the resulting behavioral changes across periods of development: prenatal, early neonatal or adolescent in males and females. Within this frame work, we will then examine the neurochemical and behavioral effects of exogenous CBs and illustrate that the response to CBs is determined by the stress history of the animal. The theoretical framework for this endeavor relates to the established effects of adverse childhood experiences (ACE) in increasing substance abuse, depression and anxiety and the possibility that individuals with high ACE scores may consume cannabinoids to "self-medicate". Overall, we see that while there are instances where exogenous cannabinoids "normalize" the adverse effects produced by early stress, this normalization does not occur in all animal models with any sort of consistency. The most compelling report where CB administration appears to normalize behaviors altered by early stress, shows minimal differences between the sexes (Alteba et al., 2016). This is in stark contrast to the majority of studies on early stress and the endocannabinoid system where both sexes are included and show quite divergent, in fact opposite, effects in males and females. Frequently there is a disconnect between neurochemical changes and behavioral changes and often, exogenous CBs have greater effects in stressed animals compared to non-stressed controls. This report as well as others reviewed here do support the concept that the effects of exogenous CBs are different in individuals experiencing early stress and that these differences are not equal in males and females. However, due to the wide variety of stressors used and the range of ages when the stress is applied, additional careful studies are warranted to fully understand the interactive effects of stress and the endocannabinoid system in males and females. In general, the findings do not support the statement that CB self-administration is an effective treatment for the adverse behavioral effects of early maltreatment in either males or females. Certainly this review should draw the attention of clinicians working with children, adolescents and adults exposed to early trauma and provide some perspective on the dysregulation of the endocannabinoid system in the response to trauma, the complex actions of exogenous CBs based on stress history and the unique effects of these factors in men and women.

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.