The endocannabinoid system and the brain

Cannabinoid agonists rearrange synaptic vesicles at excitatory synapses and depress motoneuron activity in vivo

Impairment of motor skills is one of the most common acute adverse effects of cannabis. Related studies have focused mainly on psychomotor alterations, and little is known about the direct impact of cannabinoids (CBs) on motoneuron physiology. As key modulators of synaptic function, CBs regulate multiple neuronal functions and behaviors. Presynaptic CB1 mediates synaptic strength depression by inhibiting neurotransmitter release, via a poorly understood mechanism. The present study examined the effect of CB agonists on excitatory synaptic inputs incoming to hypoglossal motoneurons (HMNs) in vitro and in vivo. The endocannabinoid anandamide (AEA) and the synthetic CB agonist WIN 55,212-2 rapidly and reversibly induced short-term depression (STD) of glutamatergic synapses on motoneurons by a presynaptic mechanism. Presynaptic effects were fully reversed by the CB1-selective antagonist AM281. Electrophysiological and electron microscopy analysis showed that WIN 55,212-2 reduced the number of synaptic vesicles (SVs) docked to active zones in excitatory boutons. Given that AM281 fully abolished depolarization-induced depression of excitation, motoneurons can be feasible sources of CBs, which in turn act as retrograde messengers regulating synaptic function. Finally, microiontophoretic application of the CB agonist O-2545 reversibly depressed, presumably via CB1, glutamatergic inspiratory-related activity of HMNs in vivo. Therefore, evidence support that CBs, via presynaptic CB1, induce excitatory STD by reducing the readily releasable pool of SVs at excitatory synapses, then attenuating motoneuron activity. These outcomes contribute a possible mechanistic basis for cannabis-associated motor performance disturbances such as ataxia, dysarthria and dyscoordination.

The endocannabinoid system: directing eating behavior and macronutrient metabolism

For many years, the brain has been the primary focus for research on eating behavior. More recently, the discovery of the endocannabinoids (EC) and the endocannabinoid system (ECS), as well as the characterization of its actions on appetite and metabolism, has provided greater insight on the brain and food intake. The purpose of this review is to explain the actions of EC in the brain and other organs as well as their precursor polyunsaturated fatty acids (PUFA) that are converted to these endogenous ligands. The binding of the EC to the cannabinoid receptors in the brain stimulates food intake, and the ECS participates in systemic macronutrient metabolism where the gastrointestinal system, liver, muscle, and adipose are involved. The EC are biosynthesized from two distinct families of dietary PUFA, namely the n-6 and n-3. Based on their biochemistry, these PUFA are well known to exert considerable physiological and health-promoting actions. However, little is known about how these different families of PUFA compete as precursor ligands of cannabinoid receptors to stimulate appetite or perhaps down-regulate the ECS to amend food intake and prevent or control obesity. The goal of this review is to assess the current available research on ECS and food intake, suggest research that may improve the complications associated with obesity and diabetes by dietary PUFA intervention, and further reveal mechanisms to elucidate the relationships between substrate for EC synthesis, ligand actions on receptors, and the physiological consequences of the ECS. Dietary PUFA are lifestyle factors that could potentially curb eating behavior, which may translate to changes in macronutrient metabolism, systemically and in muscle, benefiting health overall.

Endocannabinoids and Reproductive Events in Health and Disease

The lasting research on the endocannabinoid system (ECS) has now provided solid and convincing evidence that proves the detrimental effects of recreational drug abuse (a growing habit among teenagers) on fertility. Endocannabinoids (eCBs) affect reproductive events from gametogenesis to fertilization, from embryo implantation to the final outcome of pregnancy and, thus, they have been proposed as suitable biomarkers to predict the reproductive potential of male and female gametes in clinical practice. Novel tools for reproductive medicine are highly sought after, and here we report the latest findings on the impact of the ECS on fertility, demonstrating how basic research can be translated into new medical strategies.

Role of the endogenous cannabinoid system in nicotine addiction: novel insights

Several lines of evidence have shown that the endogenous cannabinoids are implicated in several neuropsychiatric diseases. Notably, preclinical and human clinical studies have shown a pivotal role of the cannabinoid system in nicotine addiction. The CB1 receptor inverse agonist/antagonist rimonabant (also known as SR141716) was effective to decrease nicotine-taking and nicotine-seeking in rodents, as well as the elevation of dopamine induced by nicotine in brain reward area. Rimonabant has been shown to improve the ability of smokers to quit smoking in randomized clinical trials. However, rimonabant was removed from the market due to increased risk of psychiatric side-effects observed in humans. Recently, other components of the endogenous cannabinoid system have been explored. Here, we present the recent advances on the understanding of the role of the different components of the cannabinoid system on nicotine's effects. Those recent findings suggest possible alternative ways of modulating the cannabinoid system that could have implication for nicotine dependence treatment.

The cannabinoid system and visual processing: a review on experimental findings and clinical presumptions

Cannabis is one of the most prevalent drugs used worldwide. Regular cannabis use is associated with impairments in highly integrative cognitive functions such as memory, attention and executive functions. To date, the cerebral mechanisms of these deficits are still poorly understood. Studying the processing of visual information may offer an innovative and relevant approach to evaluate the cerebral impact of exogenous cannabinoids on the human brain. Furthermore, this knowledge is required to understand the impact of cannabis intake in everyday life, and especially in car drivers. Here we review the role of the endocannabinoids in the functioning of the visual system and the potential involvement of cannabis use in visual dysfunctions. This review describes the presence of the endocannabinoids in the critical stages of visual information processing, and their role in the modulation of visual neurotransmission and visual synaptic plasticity, thereby enabling them to alter the transmission of the visual signal. We also review several induced visual changes, together with experimental dysfunctions reported in cannabis users. In the discussion, we consider these results in relation to the existing literature. We argue for more involvement of public health research in the study of visual function in cannabis users, especially because cannabis use is implicated in driving impairments.

Regulatory role of the cannabinoid CB2 receptor in stress-induced neuroinflammation in mice

BACKGROUND AND PURPOSE

Stress exposure produces excitotoxicity and neuroinflammation, contributing to the cellular damage observed in stress-related neuropathologies. The endocannabinoids provide a homeostatic system, present in stress-responsive neural circuits. Here, we have assessed the possible regulatory role of cannabinoid CB2 receptors in stress-induced excitotoxicity and neuroinflammation.

EXPERIMENTAL APPROACH

We used wild type (WT), transgenic overexpressing CB2 receptors (CB2xP) and CB2 receptor knockout (CB2-KO) mice exposed to immobilization and acoustic stress (2 h·day(-1) for 4 days). The CB2 receptor agonist JWH-133 was administered daily (2 mg·kg(-1), i.p.) to WT and CB2-KO animals. Glutamate uptake was measured in synaptosomes from frontal cortex; Western blots and RT-PCR were used to measure proinflammatory cytokines, enzymes and mediators in homogenates of frontal cortex.

KEY RESULTS

Increased plasma corticosterone induced by stress was not modified by manipulating CB2 receptors. JWH-133 treatment or overexpression of CB2 receptors increased control levels of glutamate uptake, which were reduced by stress back to control levels. JWH-133 prevented the stress-induced increase in proinflammatory cytokines (TNF-α and CCL2), in NF-κB, and in NOS-2 and COX-2 and in the consequent cellular oxidative and nitrosative damage (lipid peroxidation). CB2xP mice exhibited anti-inflammatory or neuroprotective actions similar to those in JWH-133 pretreated animals. Conversely, lack of CB2 receptors (CB2-KO mice) exacerbated stress-induced neuroinflammatory responses and confirmed that effects of JWH-133 were mediated through CB2 receptors.

CONCLUSIONS AND IMPLICATIONS

Pharmacological manipulation of CB2 receptors is a potential therapeutic strategy for the treatment of stress-related pathologies with a neuroinflammatory component, such as depression.

Towards a personalized treatment in depression: endocannabinoids, inflammation and stress response

The complex nature of depression is mirrored by difficulties in tailoring its treatment. Key underlying mechanisms of this mental disorder include elevated inflammation and a dysregulated hypothalamic-pituitary-adrenal (HPA) axis. More recently, the endocannabinoid system has been proposed as another important component in the pathogenesis of depression, and strong evidence suggests that all three systems communicate with each other. A growing number of genetic studies have investigated polymorphisms in depression in each of these systems separately. However, no study to date has looked at these genes in conjunction. In this article we will review the crosstalk between the endocannabinoid system, immune system and HPA axis; and discuss the evidence of gene polymorphisms and their relation to the risk of depression and its treatment. We propose future directions where genes of these three systems are considered from a joint perspective to improve prediction of treatment response, taking into account potentially overlooked genetic variations.

Chronic stimulation of the tone of endogenous anandamide reduces cue- and stress-induced relapse in rats

BACKGROUND

The endogenous cannabinoid system plays an important role in motivation, stress, and drug abuse. Pharmacologically, the endocannabinoid system can be stimulated by either agonists of CB1 receptors or inhibition of metabolic degradation of endogenous cannabinoids and consequent increases in their brain levels.

METHODS

Here, we investigated whether chronic administration during a period of withdrawal of the fatty acid amide hydrolase inhibitor URB597, which increases anandamide levels, would decrease the risks of relapse to cocaine seeking. Rats were allowed to self-administer cocaine and then they underwent forced withdrawal for 28 days, during which they were treated with URB597 or vehicle. One day after the last injection, we investigated cocaine seeking in one 6h extinction session and relapse triggered by re-exposure to drug-associated cues or a pharmacological stressor.

RESULTS

We found that administration of URB597 significantly decreases cocaine-seeking behavior and cue- and stress-induced relapse.

CONCLUSION

These results suggest that stimulation of the endocannabinoid system could be helpful to prevent relapse to cocaine addiction.

Comparative biochemical characterization of the monoacylglycerol lipase inhibitor KML29 in brain, spinal cord, liver, spleen, fat and muscle tissue

Monoacylglycerol lipase (MAGL) is part of the endocannabinoid and the prostaglandin signaling system. MAGL degrades the endocannabinoid 2-arachidonoylglycerol (2-AG) into glycerol and arachidonic acid. MAGL-induced arachidonic acid is the primary source for prostaglandin synthesis in the brain. 2-AG mainly induces neuroprotective and anti-inflammatory effects, whereas prostaglandins are related to pro-inflammatory effects inducing neurotoxicity. Therefore, inhibition of MAGL represents a promising target for neurological diseases characterized by inflammation. However, as 2-AG is an agonist for the cannabinoid receptor 1 (CB1), inhibition of MAGL might be associated with unwanted cannabimimetic effects. Here, we show that oral administration of KML29, a highly selective inhibitor of MAGL, induced large and dose-dependent changes in 2-AG levels in vivo in brain and spinal cord of mice. Of note, MAGL inhibition by KML29 induced a decrease in prostaglandin levels in brain and most peripheral tissues but not in the spinal cord. MAGL expression was highest in fat, liver and brain, whereas the cytosolic phospholipase A2 (cPLA2), a further enzyme responsible for arachidonic acid production, was highly expressed in spinal cord, muscle and spleen. In addition, high doses (10 mg/kg) of KML29 induced some cannabimimetic effects in vivo in the tetrad test, including hypothermia, analgesia and hypomotility without induction of cataleptic behavior. In summary, inhibition of MAGL by KML29 represents a promising strategy for targeting the cannabinoid and prostaglandin system of the brain with only a moderate induction of cannabimimetic effects.

Monoacylglycerol lipase inhibitor JZL184 improves behavior and neural properties in Ts65Dn mice, a model of down syndrome

Genetic alterations or pharmacological treatments affecting endocannabinoid signaling have profound effects on synaptic and neuronal properties and, under certain conditions, may improve higher brain functions. Down syndrome (DS), a developmental disorder caused by triplication of chromosome 21, is characterized by deficient cognition and inevitable development of the Alzheimer disease (AD) type pathology during aging. Here we used JZL184, a selective inhibitor of monoacylglycerol lipase (MAGL), to examine the effects of chronic MAGL inhibition on the behavioral, biochemical, and synaptic properties of aged Ts65Dn mice, a genetic model of DS. In both Ts65Dn mice and their normosomic (2N) controls, JZL184-treatment increased brain levels of 2-arachidonoylglycerol (2-AG) and decreased levels of its metabolites such as arachidonic acid, prostaglandins PGD2, PGE2, PGFα, and PGJ2. Enhanced spontaneous locomotor activity of Ts65Dn mice was reduced by the JZL184-treatement to the levels observed in 2N animals. Deficient long-term memory was also improved, while short-term and working types of memory were unaffected. Furthermore, reduced hippocampal long-term potentiation (LTP) was increased in the JZL184-treated Ts65Dn mice to the levels observed in 2N mice. Interestingly, changes in synaptic plasticity and behavior were not observed in the JZL184-treated 2N mice suggesting that the treatment specifically attenuated the defects in the trisomic animals. The JZL184-treatment also reduced the levels of Aβ40 and Aβ42, but had no effect on the levels of full length APP and BACE1 in both Ts65Dn and 2N mice. These data show that chronic MAGL inhibition improves the behavior and brain functions in a DS model suggesting that pharmacological targeting of MAGL may be considered as a perspective new approach for improving cognition in DS.

Endocannabinoid metabolism by cytochrome P450 monooxygenases

The endogenous cannabinoid system was first uncovered following studies of the recreational drug Cannabis sativa. It is now recognized as a vital network of signaling pathways that regulate several physiological processes. Following the initial discovery of the cannabinoid receptors 1 (CB1) and 2 (CB2), activated by Cannabis-derived analogs, many endogenous fatty acids termed "endocannabinoids" are now known to be partial agonists of the CB receptors. At present, the most thoroughly studied endocannabinoid signaling molecules are anandamide (AEA) and 2-arachidonylglycerol (2-AG), which are both derived from arachidonic acid. Both AEA and 2-AG are also substrates for the eicosanoid-synthesizing pathways, namely, certain cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes. In the past, research in the endocannabinoid field focused on the interaction of AEA and 2-AG with the COX and LOX enzymes, but accumulating evidence also points to the involvement of CYPs in modulating endocannabinoid signaling. The focus of this review is to explore the current understanding of CYP-mediated metabolism of endocannabinoids.

N-Acylethanolamine-hydrolyzing acid amidase inhibition increases colon N-palmitoylethanolamine levels and counteracts murine colitis

N-Palmitoylethanolamine or palmitoylethanolamide (PEA) is an anti-inflammatory compound that was recently shown to exert peroxisome proliferator-activated receptor-α-dependent beneficial effects on colon inflammation. The actions of PEA are terminated following hydrolysis by 2 enzymes: fatty acid amide hydrolase (FAAH), and the less-studied N-acylethanolamine-hydrolyzing acid amidase (NAAA). This study aims to investigate the effects of inhibiting the enzymes responsible for PEA hydrolysis in colon inflammation in order to propose a potential therapeutic target for inflammatory bowel diseases (IBDs). Two murine models of IBD were used to assess the effects of NAAA inhibition, FAAH inhibition, and PEA on macroscopic signs of colon inflammation, macrophage/neutrophil infiltration, and the expression of proinflammatory mediators in the colon, as well as on the colitis-related systemic inflammation. NAAA inhibition increases PEA levels in the colon and reduces colon inflammation and systemic inflammation, similarly to PEA. FAAH inhibition, however, does not increase PEA levels in the colon and does not affect the macroscopic signs of colon inflammation or immune cell infiltration. This is the first report of an anti-inflammatory effect of a systemically administered NAAA inhibitor. Because NAAA is the enzyme responsible for the control of PEA levels in the colon, we put forth this enzyme as a potential therapeutic target in chronic inflammation in general and IBD in particular.

Systemic or intra-amygdala infusion of an endocannabinoid CB1 receptor antagonist AM251 blocked propofol-induced anterograde amnesia

Propofol is well-known for its anterograde amnesic actions. However, a recent experiment showed that propofol can also produce retrograde memory enhancement effects via an interaction with the endocannabinoid CB1 system. Therefore, the authors hypothesized that the regulating effect of propofol on the endocannabinoid CB1 system might also decrease the anterograde amnesic effect of propofol under some conditions, which might be a risk factor for intraoperative awareness. Since, the basolateral amygdala (BLA) has been confirmed to mediate propofol-induced anterograde amnesia and the BLA contains a high concentration of CB1 receptors, the authors investigated whether and how the endocannabinoid system, particularly the CB1 receptor within BLA, influences propofol-induced anterograde amnesia. Male Sprague-Dawley rats trained with inhibitory avoidance (IA) were systematically pre-trained using a memory-impairing dose of propofol (25 mg/kg). Before propofol administration, rats received an intraperitoneal injection of a CB1 receptor antagonist AM251 (1 mg/kg or 2 mg/kg) or a bilateral intra-BLA injection of AM251 (0.6 ng or 6 ng per 0.5 μl). Twenty-four hours after IA training, the IA retention latency was tested. It was found that systemic or intra-BLA injection of a non-regulating dose of AM251 (2 mg/kg or 6 ng per 0.5 μl, respectively) blocked the memory-impairing effect of propofol. These results indicate that the anterograde amnesic effect of propofol is mediated, in part, by activation of the CB1 cannabinoid receptors in the BLA.

The endocannabinoid system modulates stress, emotionality, and inflammation

The physiological and behavioral effects of stress are well characterized. Endocannabinoids are produced on demand and function to attenuate many of the physiological effects of the stress response. The endocannabinoid system is made up of cannabinoid receptors, the fatty acid signaling molecules that bind to and activate these receptors, and the enzymes that synthesize and catabolize these endocannabinoid signaling molecules. Cannabinoid research has recently grown substantially, due in no small part to the development of genetic research models as well as highly selective pharmaceutical tools. The purpose of this minireview is to discuss a subset of the many parallels between cannabinoid and behavioral neuroimmunology research, with specific discussion of interactions between the endocannabinoid system and psychological stress, emotionality, and inflammation.

Synthetic cannabinoids: epidemiology, pharmacodynamics, and clinical implications

BACKGROUND

Synthetic cannabinoids (SC) are a heterogeneous group of compounds developed to probe the endogenous cannabinoid system or as potential therapeutics. Clandestine laboratories subsequently utilized published data to develop SC variations marketed as abusable designer drugs. In the early 2000s, SC became popular as "legal highs" under brand names such as Spice and K2, in part due to their ability to escape detection by standard cannabinoid screening tests. The majority of SC detected in herbal products have greater binding affinity to the cannabinoid CB1 receptor than does Δ(9)-tetrahydrocannabinol (THC), the primary psychoactive compound in the cannabis plant, and greater affinity at the CB1 than the CB2 receptor. In vitro and animal in vivo studies show SC pharmacological effects 2-100 times more potent than THC, including analgesic, anti-seizure, weight-loss, anti-inflammatory, and anti-cancer growth effects. SC produce physiological and psychoactive effects similar to THC, but with greater intensity, resulting in medical and psychiatric emergencies. Human adverse effects include nausea and vomiting, shortness of breath or depressed breathing, hypertension, tachycardia, chest pain, muscle twitches, acute renal failure, anxiety, agitation, psychosis, suicidal ideation, and cognitive impairment. Long-term or residual effects are unknown. Due to these public health consequences, many SC are classified as controlled substances. However, frequent structural modification by clandestine laboratories results in a stream of novel SC that may not be legally controlled or detectable by routine laboratory tests.

METHODS

We present here a comprehensive review, based on a systematic electronic literature search, of SC epidemiology and pharmacology and their clinical implications.

Ethanol exposure induces neonatal neurodegeneration by enhancing CB1R Exon1 histone H4K8 acetylation and up-regulating CB1R function causing neurobehavioral abnormalities in adult mice

BACKGROUND

Ethanol exposure to rodents during postnatal day 7 (P7), which is comparable to the third trimester of human pregnancy, induces long-term potentiation and memory deficits. However, the molecular mechanisms underlying these deficits are still poorly understood.

METHODS

In the present study, we explored the potential role of epigenetic changes at cannabinoid type 1 (CB1R) exon1 and additional CB1R functions, which could promote memory deficits in animal models of fetal alcohol spectrum disorder.

RESULTS

We found that ethanol treatment of P7 mice enhances acetylation of H4 on lysine 8 (H4K8ace) at CB1R exon1, CB1R binding as well as the CB1R agonist-stimulated GTPγS binding in the hippocampus and neocortex, two brain regions that are vulnerable to ethanol at P7 and are important for memory formation and storage, respectively. We also found that ethanol inhibits cyclic adenosine monophosphate response element-binding protein (CREB) phosphorylation and activity-regulated cytoskeleton-associated protein (Arc) expression in neonatal and adult mice. The blockade or genetic deletion of CB1Rs prior to ethanol treatment at P7 rescued CREB phosphorylation and Arc expression. CB1R knockout mice exhibited neither ethanol-induced neurodegeneration nor inhibition of CREB phosphorylation or Arc expression. However, both neonatal and adult mice did exhibit enhanced CREB phosphorylation and Arc protein expression. P7 ethanol-treated adult mice exhibited impaired spatial and social recognition memory, which were prevented by the pharmacological blockade or deletion of CB1Rs at P7.

CONCLUSIONS

Together, these findings suggest that P7 ethanol treatment induces CB1R expression through epigenetic modification of the CB1R gene, and that the enhanced CB1R function induces pCREB, Arc, spatial, and social memory deficits in adult mice.

Marijuana: respiratory tract effects

Marijuana is the most commonly used drug of abuse in the USA. It is commonly abused through inhalation and therefore has effects on the lung that are similar to tobacco smoke, including increased cough, sputum production, hyperinflation, and upper lobe emphysematous changes. However, at this time, it does not appear that marijuana smoke contributes to the development of chronic obstructive pulmonary disease. Marijuana can have multiple physiologic effects such as tachycardia, peripheral vasodilatation, behavioral and emotional changes, and possible prolonged cognitive impairment. The carcinogenic effects of marijuana are unclear at this time. Studies are mixed on the ability of marijuana smoke to increase the risk for head and neck squamous cell carcinoma, lung cancer, prostate cancer, and cervical cancer. Some studies show that marijuana is protective for development of malignancy. Marijuana smoke has been shown to have an inhibitory effect on the immune system. Components of cannabis are under investigation as treatment for autoimmune diseases and malignancy. As marijuana becomes legalized in many states for medical and recreational use, other forms of tetrahydrocannabinol (THC) have been developed, such as food products and beverages. As most research on marijuana at this time has been on whole marijuana smoke, rather than THC, it is difficult to determine if the currently available data is applicable to these newer products.

Toxicology and Management of Novel Psychoactive Drugs

Health care providers are seeing an increased number of patients under the influence of several new psychoactive drug classes. Synthetic cannabinoids, cathinones, and piperazines are sought by users for their psychoactive effects, perceived safety profile, minimal legal regulations, and lack of detection on routine urine drug screening. However, these drugs are beginning to be recognized by the medical community for their toxic effects. The neuropsychiatric and cardiovascular toxicities are among the most common reasons for emergency medical treatment, which in some cases, can be severe and even life-threatening. Management strategies are often limited to supportive and symptomatic care due to the limited published data on alternative treatment approaches. The purpose of this article is to offer health care providers, emergency medical personnel in particular, an awareness and understanding of the dangers related to some of the new psychoactive drugs of abuse. The background, pharmacology, toxicity, management, detection, and legal status of each class will be discussed.

Involvement of the endocannabinoid system in osteoarthritis pain

Osteoarthritis is a degenerative joint disease associated with articular cartilage degradation. The major clinical outcome of osteoarthritis is a complex pain state that includes both nociceptive and neuropathic mechanisms. Currently, the therapeutic approaches for osteoarthritis are limited as no drugs are available to control the disease progression and the analgesic treatment has restricted efficacy. Increasing evidence from preclinical studies supports the interest of the endocannabinoid system as an emerging therapeutic target for osteoarthritis pain. Indeed, pharmacological studies have shown the anti-nociceptive effects of cannabinoids in different rodent models of osteoarthritis, and compelling evidence suggests an active participation of the endocannabinoid system in the pathophysiology of this disease. The ubiquitous distribution of cannabinoid receptors, together with the physiological role of the endocannabinoid system in the regulation of pain, inflammation and even joint function further support the therapeutic interest of cannabinoids for osteoarthritis. However, limited clinical evidence has been provided to support this therapeutic use of cannabinoids, despite the promising preclinical data. This review summarizes the promising results that have been recently obtained in support of the therapeutic value of cannabinoids for osteoarthritis management.

When time stands still: an integrative review on the role of chronodisruption in posttraumatic stress disorder

PURPOSE OF REVIEW

The human circadian system creates and maintains cellular and systemic rhythmicity essential to homeostasis. Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune and autonomic system, similar to chronic stress and, thus, may play a central role in the development of stress-related disorders. This article focuses on the role of circadian misalignment in the pathophysiology of posttraumatic stress disorder (PTSD).

RECENT FINDINGS

Sleep disruption is a core feature of PTSD supporting the important supraordinate pathophysiological role of circadian system in PTSD. Furthermore, direct and indirect human and animal PTSD research suggests circadian system linked neuroendocrine, immune, metabolic and autonomic dysregulation with blunted diurnal rhythms, specific sleep pattern pathologies and cognitive deficits, as well as endocannabinoid and neuropeptide Y system alterations and altered circadian gene expression, linking circadian misalignment to PTSD pathophysiology.

SUMMARY

PTSD development is associated with chronodisruption findings. Evaluation and treatment of sleep and circadian disruption should be the first steps in PTSD management. State-of-the-art methods of circadian rhythm assessment should be applied to bridge the gap between clinical significance and limited understanding of the relationship between traumatic stress, sleep and circadian system.

Towards a better cannabis drug

This commentary discusses the importance of a new study entitled 'Cannabidiol attenuates deficits of visuo-spatial associative memory induced by Δ(9) -tetrahydrocannabinol' by Wright et al. from the Scripps Institute in La Jolla, California. The results in this study show that the non-psychoactive cannabis constituent cannabidiol opposes some, but not all, forms of behavioural and memory disruption caused by Δ(9) -tetrahydrocannabinol in male rhesus monkeys.

LINKED ARTICLE

This article is a commentary on the research paper by Wright et al., pp 1365-1373 of this issue. To view this paper visit http://dx.doi.org/10.1111/bph.12199.

Genetic variability in the human cannabinoid receptor 1 is associated with resting state EEG theta power in humans

It has long been postulated that exogenous cannabinoids have a profound effect on human cognitive functioning. These cannabinoid effects are thought to depend, at least in parts, on alterations of phase-locking of local field potential neuronal firing. The latter can be measured as activity in the theta frequency band (4-7Hz) by electroencephalogram. Theta oscillations are supposed to serve as a mechanism in neural representations of behaviorally relevant information. However, it remains unknown whether variability in endogenous cannabinoid activity is involved in theta rhythms and therefore, may serve as an individual differences index of human cognitive functioning. To clarify this issue, we recorded resting state EEG activity in 164 healthy human subjects and extracted EEG power across frequency bands (δ, θ, α, and β). To assess variability in the endocannabinoid system, two genetic polymorphisms (rs1049353, rs2180619) within the cannabinoid receptor 1 (CB1) were determined in all participants. As expected, we observed significant effects of rs1049353 on EEG power in the theta band at frontal, central and parietal electrode regions. Crucially, these effects were specific for the theta band, with no effects on activity in the other frequency bands. Rs2180619 showed no significant associations with theta power after Bonferroni correction. Taken together, we provide novel evidence in humans showing that genetic variability in the cannabinoid receptor 1 is associated with resting state EEG power in the theta frequency band. This extends prior findings of exogenous cannabinoid effects on theta power to the endogenous cannabinoid system.

Prolonged monoacylglycerol lipase blockade causes equivalent cannabinoid receptor type 1 receptor-mediated adaptations in fatty acid amide hydrolase wild-type and knockout mice

Complementary genetic and pharmacological approaches to inhibit monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), the primary hydrolytic enzymes of the respective endogenous cannabinoids 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine, enable the exploration of potential therapeutic applications and physiologic roles of these enzymes. Complete and simultaneous inhibition of both FAAH and MAGL produces greatly enhanced cannabimimetic responses, including increased antinociception, and other cannabimimetic effects, far beyond those seen with inhibition of either enzyme alone. While cannabinoid receptor type 1 (CB1) function is maintained following chronic FAAH inactivation, prolonged excessive elevation of brain 2-AG levels, via MAGL inhibition, elicits both behavioral and molecular signs of cannabinoid tolerance and dependence. Here, we evaluated the consequences of a high dose of the MAGL inhibitor JZL184 [4-nitrophenyl 4-(dibenzo[d][1,3]dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate; 40 mg/kg] given acutely or for 6 days in FAAH(-/-) and (+/+) mice. While acute administration of JZL184 to FAAH(-/-) mice enhanced the magnitude of a subset of cannabimimetic responses, repeated JZL184 treatment led to tolerance to its antinociceptive effects, cross-tolerance to the pharmacological effects of Δ(9)-tetrahydrocannabinol, decreases in CB1 receptor agonist-stimulated guanosine 5'-O-(3-[(35)S]thio)triphosphate binding, and dependence as indicated by rimonabant-precipitated withdrawal behaviors, regardless of genotype. Together, these data suggest that simultaneous elevation of both endocannabinoids elicits enhanced cannabimimetic activity but MAGL inhibition drives CB1 receptor functional tolerance and cannabinoid dependence.

Cannabis use and first manic episode

BACKGROUND

Cannabis is the most commonly abused drug among patients with bipolar disorder. Available data has shown that the risk of psychotic disorders increases with the frequency and intensity of cannabis abuse. The present purpose was to review relevant studies to investigate whether cannabis use can be linked to the onset of mania in bipolar disorder.

METHODS

Articles published between 1972 and December 2013 were searched on Medline and PsychInfo using the following keywords: first manic episode, or onset mania, or bipolar disorder and cannabis. Relevant papers cited in the references of selected articles were further considered for inclusion into the review.

RESULTS

Lifetime use of cannabis among bipolar patients appears to be around 70% and approximately 30% of patients with a bipolar disorder present a comorbidity of cannabis abuse or dependence. Cannabis use is associated with younger age at onset of first mania and with more frequent depressive or manic episodes, although the evidence is somewhat inconsistent. Likewise cannabis consumption is related to poorer outcome and an increased risk of rapid cycling or mixed episodes. In contrast, neuro-cognitive functioning seems to be positively affected in patients with psychiatric comorbidity. While cannabis use often precedes first manic episodes, the causal direction remains to be determined.

LIMITATIONS

Variations in definition of cannabis use/dependence. Lack of controlled studies limiting definite conclusions about a putative causal relationship between cannabis and onset of mania.

CONCLUSIONS

Further investigations are needed to clarify the relationships between cannabis use and first manic episode.

Multifractal analysis of information processing in hippocampal neural ensembles during working memory under Δ⁹-tetrahydrocannabinol administration

BACKGROUND

Multifractal analysis quantifies the time-scale-invariant properties in data by describing the structure of variability over time. By applying this analysis to hippocampal interspike interval sequences recorded during performance of a working memory task, a measure of long-range temporal correlations and multifractal dynamics can reveal single neuron correlates of information processing.

NEW METHOD

Wavelet leaders-based multifractal analysis (WLMA) was applied to hippocampal interspike intervals recorded during a working memory task. WLMA can be used to identify neurons likely to exhibit information processing relevant to operation of brain-computer interfaces and nonlinear neuronal models.

RESULTS

Neurons involved in memory processing ("Functional Cell Types" or FCTs) showed a greater degree of multifractal firing properties than neurons without task-relevant firing characteristics. In addition, previously unidentified FCTs were revealed because multifractal analysis suggested further functional classification. The cannabinoid type-1 receptor (CB1R) partial agonist, tetrahydrocannabinol (THC), selectively reduced multifractal dynamics in FCT neurons compared to non-FCT neurons.

COMPARISON WITH EXISTING METHODS

WLMA is an objective tool for quantifying the memory-correlated complexity represented by FCTs that reveals additional information compared to classification of FCTs using traditional z-scores to identify neuronal correlates of behavioral events.

CONCLUSION

z-Score-based FCT classification provides limited information about the dynamical range of neuronal activity characterized by WLMA. Increased complexity, as measured with multifractal analysis, may be a marker of functional involvement in memory processing. The level of multifractal attributes can be used to differentially emphasize neural signals to improve computational models and algorithms underlying brain-computer interfaces.

CB1 receptor antagonism in the granular insular cortex or somatosensory area facilitates consolidation of object recognition memory

Cannabinoid agonists typically impair memory, whereas CB1 receptor antagonists enhance memory performance under specific conditions. The insular cortex has been implicated in object memory consolidation. Here we show that infusions of the CB1 receptor antagonist SR141716 enhances long-term object recognition memory in rats in a dose-dependent manner (facilitation with 1.5, but not 0.75 or 3 μg/μL) when administered into the granular insular cortex; the SR141716 facilitation was seen with a memory delay of 72 h, but not when the delay was shorter (1 h), consistent with enhancement of memory consolidation. Moreover, a sub-group of rats with cannulas placed in the somatosensory area were also facilitated. These results highlight the robust potential of cannabinoid antagonists to facilitate object memory consolidation, as well as the capacity for insular and somatosensory cortices to contribute to object processing, perhaps through enhancement of tactile representation.

Substrate-selective COX-2 inhibition as a novel strategy for therapeutic endocannabinoid augmentation

Pharmacologic augmentation of endogenous cannabinoid (eCB) signaling is an emerging therapeutic approach for the treatment of a broad range of pathophysiological conditions. Thus far, pharmacological approaches have focused on inhibition of the canonical eCB inactivation pathways - fatty acid amide hydrolase (FAAH) for anandamide and monoacylglycerol lipase (MAGL) for 2-arachidonoylglycerol. We review here the experimental evidence that cyclooxygenase-2 (COX-2)-mediated eCB oxygenation represents a third mechanism for terminating eCB action at cannabinoid receptors. We describe the development, molecular mechanisms, and in vivo validation of 'substrate-selective' COX-2 inhibitors (SSCIs) that prevent eCB inactivation by COX-2 without affecting prostaglandin (PG) generation from arachidonic acid (AA). Lastly, we review recent data on the potential therapeutic applications of SSCIs with a focus on neuropsychiatric disorders.

N-Acyl amino acids and their impact on biological processes

Over the last two decades a large number of N-long-chain acyl amino acids have been identified in the mammalian body. The pharmacological activities of only a few of them have been investigated and some have been found to be of considerable interest. Thus arachidonoyl serine is vasodilatory and neuroprotective, arachidonoyl glycine is antinociceptive, and oleoyl serine rescues bone loss. However, the pathophysiological/biochemical roles of these amides are mostly unknown.

Morphological and behavioral evidence for impaired prefrontal cortical function in female CB1 receptor deficient mice

The medial prefrontal cortex (mPFC) is known to regulate higher order processes like cognitive flexibility. Accumulating behavioral evidence suggests that endocannabinoid (eCB) signaling regulates neuronal architecture within the PFC, as well as certain forms of cognitive flexibility; however, all of these studies have been performed in male rodents and it is currently unknown whether the eCB system performs a similar role in females. To this extent, dendritic morphology of layer II/III neurons in the infra- and prelimbic regions of the mPFC was analyzed and cognitive ability and flexibility in a fixed-platform Morris water maze task was assessed in adult female CB1 receptor knockout (CB1KO) mice. Similar to data generated in male mice, female mice exhibited no difference in acquisition relative to wildtype (WT); however, during reversal learning, CB1KO females spent more time in the original training quadrant and took significantly longer to learn the location of the new platform relative to WT. Within the mPFC, female mice had reduced length and complexity of layer II/III neurons within the prelimbic, but not infralimbic region of the PFC. Taken together, these findings indicate that the role of eCB signaling in cognitive flexibility is independent of sex and disrupted CB1 receptor signaling results in compromised structure and function of the PFC, at least within the prelimbic division.

The microinjection of a cannabinoid agonist into the accumbens shell induces anxiogenesis in the elevated plus-maze

This study investigated the effect of a cannabinoid agonist injected into the shell region of the nucleus accumbens (nAcb shell) on anxiety-related behaviors. The animals (male Wistar rats) were unilaterally microinjected with either ACEA (arachidonyl-2'-chloroethylamide a CB1 receptor agonist) at doses of 0.005, 0.05 or 0.5 pmol, or vehicle (ethanol 0.04% in saline 0.9%) and submitted to the elevated plus-maze (EPM), a pre-clinical test of anxiety. The data showed that rats microinjected with ACEA (0.05 pmol/0.2 μl) into the nAcb shell exhibited decreased % open arm time and open arm entries in comparison with the control group, which is compatible with an anxiogenic-like effect. To rule out the hypothesis that spread of the drug into the ventricle was responsible for the observed anxiogenic effect, 0.05 pmol ACEA was injected into the lateral ventricle and shown not to alter the responses representative of fear/anxiety and locomotion. The locomotor activity was not changed at the dose of 0.05 pmol ACEA microinjected into the nAcb shell. The present data suggest that activation of cannabinoid receptors in the nAcb shell may modulate fear/anxiety in the EPM.

Ghrelin modulates the fMRI BOLD response of homeostatic and hedonic brain centers regulating energy balance in the rat

The orexigenic gut-brain peptide, ghrelin and its G-protein coupled receptor, the growth hormone secretagogue receptor 1a (GHS-R1A) are pivotal regulators of hypothalamic feeding centers and reward processing neuronal circuits of the brain. These systems operate in a cooperative manner and receive a wide array of neuronal hormone/transmitter messages and metabolic signals. Functional magnetic resonance imaging was employed in the current study to map BOLD responses to ghrelin in different brain regions with special reference on homeostatic and hedonic regulatory centers of energy balance. Experimental groups involved male, ovariectomized female and ovariectomized estradiol-replaced rats. Putative modulation of ghrelin signaling by endocannabinoids was also studied. Ghrelin-evoked effects were calculated as mean of the BOLD responses 30 minutes after administration. In the male rat, ghrelin evoked a slowly decreasing BOLD response in all studied regions of interest (ROI) within the limbic system. This effect was antagonized by pretreatment with GHS-R1A antagonist JMV2959. The comparison of ghrelin effects in the presence or absence of JMV2959 in individual ROIs revealed significant changes in the prefrontal cortex, nucleus accumbens of the telencephalon, and also within hypothalamic centers like the lateral hypothalamus, ventromedial nucleus, paraventricular nucleus and suprachiasmatic nucleus. In the female rat, the ghrelin effects were almost identical to those observed in males. Ovariectomy and chronic estradiol replacement had no effect on the BOLD response. Inhibition of the endocannabinoid signaling by rimonabant significantly attenuated the response of the nucleus accumbens and septum. In summary, ghrelin can modulate hypothalamic and mesolimbic structures controlling energy balance in both sexes. The endocannabinoid signaling system contributes to the manifestation of ghrelin's BOLD effect in a region specific manner. In females, the estradiol milieu does not influence the BOLD response to ghrelin.

Prenatal poly I:C age-dependently alters cannabinoid type 1 receptors in offspring: a longitudinal small animal PET study using [(18)F]MK-9470

Evidence suggests that there is a link between the endocannabinoid system (ECS) and neuropsychiatric illnesses, including schizophrenia. Whilst the ECS has been shown to be involved in immune system regulation in various ways, it is known that infections during pregnancy can modulate the immune system of the mother and increase the risk for schizophrenia in offspring. In animal studies, maternal immune activation following administration of viral or bacterial mimics has been shown to reproduce many key structural, behavioural, and pharmacological abnormalities in offspring that resemble schizophrenia. In the present study, we used Positron Emission Tomography (PET) and [(18)F]MK-9470, a selective high-affinity inverse agonist radioligand for cannabinoid type 1 receptors (CB1R), to longitudinally assess CB1R expression in the progeny of female rats exposed to the viral mimic polyriboinosinic-polyribocytidilic acid (poly I:C) (4mg/kg i.v.) or vehicle at gestational day 15 (GD 15). PET scans were performed in offspring at postnatal days (PND) 32-42 (adolescence) and in the same animals again at PNDs 75-79 (adulthood). Sixteen regions of interest were assessed, encompassing the whole rat brain. At adolescence, offspring exposed prenatally to poly I:C had significantly lower CB1R relative Standard Uptake Values (rSUV) compared to controls in the globus pallidus (p=0.046). In adulthood, however, poly I:C exposed offspring had higher levels of CB1R rSUV in sensory cortex (p=0.034) and hypothalamus (p=0.032) compared to controls. Our results suggest that prenatal poly I:C leads to long term alterations in the integrity of the ECS that are age and region-specific. The increased CB1R expression in adulthood following poly I:C mirrors the increased CB1R observed in patients with schizophrenia in post-mortem and in vivo PET studies.

Increased CB2 mRNA and anandamide in human blood after cessation of cannabis abuse

In previous studies, long-term cannabis use led to alterations of the endocannabinoid system including an increase in CB1 and/or CB2 receptor messenger RNA (mRNA) in blood cells and an increase in the serum level of the endocannabinoid 2-arachidonoyl glycerol. However, in those studies, cannabis use was stopped only few days before testing or not interrupted at all. Therefore, one cannot decide whether the alterations are due to long-term cannabis abuse or are confounded by acute effects of cannabis. Blood was sampled from donors that had smoked marijuana ≥20 times in their lives but had abstained from cannabis for ≥6 months (high-frequency users, HFU) and from controls (cannabis use ≤5 times lifetime). CB1 and CB2 mRNA was determined in peripheral mononuclear blood cells using the reverse transcriptase polymerase chain reaction. Serum anandamide level was assayed using electrospray tandem mass spectrometry. CB2 mRNA was increased by 45 % in HFU when compared to controls, whereas CB1 mRNA did not differ. The anandamide level in HFU exceeded that in controls by 90 %. Tobacco smoking could be excluded as a confounding factor. In conclusion, marijuana users that had smoked marijuana ≥20 times in their lives and stopped cannabis use at least 6 months before the study show an increase in CB2 receptor mRNA in the blood and in serum anandamide level. These alterations resemble those obtained for marijuana smokers that had stopped cannabis use only few days before testing and may be implicated in the pathogenesis of disorders associated with long-term cannabis use.

Prior stimulation of the endocannabinoid system prevents methamphetamine-induced dopaminergic neurotoxicity in the striatum through activation of CB2 receptors

Methamphetamine toxicity is associated with cell death and loss of dopamine neuron terminals in the striatum similar to what is found in some neurodegenerative diseases. Conversely, the endocannabinoid system (ECS) has been suggested to be neuroprotective in the brain, and new pharmacological tools have been developed to increase their endogenous tone. In this study, we evaluated whether ECS stimulation could reduce the neurotoxicity of high doses of methamphetamine on the dopamine system. We found that methamphetamine alters the levels of the major endocannabinoids, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in the striatum, suggesting that the ECS participates in the brain responses to methamphetamine. Δ(9)-tetrahydrocannabinol (THC), a cannabis-derived agonist of both CB1 and CB2 cannabinoid receptors, or inhibitors of the main enzymes responsible for the degradation of AEA and 2-AG (URB597 and JZL184, respectively), blunted the decrease in striatal protein levels of tyrosine hydroxylase induced by methamphetamine. In addition, antagonists of CB2, but not of CB1, blocked the preventive effects of URB597 and JZL184, suggesting that only the former receptor subtype is engaged in neuroprotection exerted by ECS stimulation. Finally, we found that methamphetamine increases striatal levels of the cytokine tumor necrosis factor alpha, an effect that was blocked by ECS stimulation. Altogether, our results indicate that stimulation of ECS prior to the administration of an overdose of methamphetamine considerably reduces the neurotoxicity of the drug through CB2 receptor activation and highlight a protective function for the ECS against the toxicity induced by drugs and other external insults to the brain. This article is part of the Special Issue entitled 'CNS Stimulants'.

Fatty acid-binding protein 5 (FABP5) regulates cognitive function both by decreasing anandamide levels and by activating the nuclear receptor peroxisome proliferator-activated receptor β/δ (PPARβ/δ) in the brain

Endocannabinoids modulate multiple behaviors, including learning and memory. We show that the endocannabinoid anandamide (AEA) can alter neuronal cell function both through its established role in activation of the G-protein-coupled receptor CB1, and by serving as a precursor for a potent agonist of the nuclear receptor PPARβ/δ, in turn up-regulating multiple cognition-associated genes. We show further that the fatty acid-binding protein FABP5 controls both of these functions in vivo. FABP5 both promotes the hydrolysis of AEA into arachidonic acid and thus reduces brain endocannabinoid levels, and directly shuttles arachidonic acid to the nucleus where it delivers it to PPARβ/δ, enabling its activation. In accordance, ablation of FABP5 in mice results in excess accumulation of AEA, abolishes PPARβ/δ activation in the brain, and markedly impairs hippocampus-based learning and memory. The data indicate that, by controlling anandamide disposition and activities, FABP5 plays a key role in regulating hippocampal cognitive function.

Multiple sleep alterations in mice lacking cannabinoid type 1 receptors

Cannabinoid type 1 (CB₁) receptors are highly expressed in the brain and play a role in behavior control. Endogenous cannabinoid signaling is modulated by high-fat diet (HFD). We investigated the consequences of congenital lack of CB₁ receptors on sleep in mice fed standard diet (SD) and HFD. CB₁ cannabinoid receptor knock-out (KO) and wild-type (WT) mice were fed SD or HFD for 4 months (n = 9–10 per group). Mice were instrumented with electroencephalographic (EEG) and electromyographic electrodes. Recordings were performed during baseline (48 hours), sleep deprivation (gentle handling, 6 hours), sleep recovery (18 hours), and after cage switch (insomnia model paradigm, 6 hours). We found multiple significant effects of genotype on sleep. In particular, KO spent more time awake and less time in non-rapid-eye-movement sleep (NREMS) and rapid-eye-movement sleep (REMS) than WT during the dark (active) period but not during the light (rest) period, enhancing the day-night variation of wake-sleep amounts. KO had slower EEG theta rhythm during REMS. REMS homeostasis after sleep deprivation was less effective in KO than in WT. Finally, KO habituated more rapidly to the arousing effect of the cage-switch test than WT. We did not find any significant effects of diet or of diet x genotype interaction on sleep. The occurrence of multiple sleep alterations in KO indicates important roles of CB₁ cannabinoid receptors in limiting arousal during the active period of the day, in sleep regulation, and in sleep EEG in mice.

Endocannabinoids as biomarkers of human reproduction

BACKGROUND

Infertility is a condition of the reproductive system that affects ∼10-15% of couples attempting to conceive a baby. More than half of all cases of infertility are a result of female conditions, while the remaining cases can be attributed to male factors, or to a combination of both. The search for suitable biomarkers of pregnancy outcome is a challenging issue in human reproduction, aimed at identifying molecules with predictive significance of the reproductive potential of male and female gametes. Among the various candidates, endocannabinoids (eCBs), and in particular anandamide (AEA), represent potential biomarkers of human fertility disturbances. Any perturbation of the balance between synthesis and degradation of eCBs will result in local changes of their tone in human female and male reproductive tracts, which in turn regulates various pathophysiological processes, oocyte and sperm maturation included.

METHODS

PubMed and Web of Science databases were searched for papers using relevant keywords like 'biomarker', 'endocannabinoid', 'infertility', 'pregnancy' and 'reproduction'.

RESULTS

In this review, we discuss different studies on the measurements of AEA and related eCBs in human reproductive cells, tissues and fluids, where the local contribution of these bioactive lipids could be critical in ensuring normal sperm fertilizing ability and pregnancy.

CONCLUSION

Based on the available data, we suggest that the AEA tone has the potential to be exploited as a novel diagnostic biomarker of infertility, to be used in association with assays of conventional hormones (e.g. progesterone, β-chorionic gonadotrophin) and semen analysis. However further quantitative research of its predictive capacity is required.

Antinociceptive effects of central administration of the endogenous cannabinoid receptor type 1 agonist VDPVNFKLLSH-OH [(m)VD-hemopressin(α)], an N-terminally extended hemopressin peptide

The cannabinoid system has been demonstrated to modulate the acute and chronic pain of multiple origins. Mouse VD-hemopressin(α) [(m)VD-Hpα], an 11-residue α-hemoglobin-derived peptide, was recently reported to function as a selective agonist of the cannabinoid receptor type 1 (CB₁) in vitro. To characterize its behavioral and physiological properties, we investigated the in vivo effects of (m)VD-Hpα in mice. In the mouse tail-flick test, (m)VD-Hpα dose-dependently induced antinociception after supraspinal (EC₅₀ = 6.69 nmol) and spinal (EC₅₀ = 2.88 nmol) administration. The antinociceptive effects of (m)VD-Hpα (intracerebroventricularly and intrathecally) were completely blocked by N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3- carboxamide (AM251; CB₁ antagonist), but not by 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl(4-methoxyphenyl)-methanone (AM630; CB₂ antagonist) or naloxone (opioid antagonist), showing its selectivity to the CB₁ receptor. Furthermore, the central nervous system (CNS) effects of (m)VD-Hpα were evaluated in body temperature, locomotor activity, tolerance development, reward, and food intake assays. At the highly antinociceptive dose (3 × EC₅₀), (m)VD-Hpα markedly exerted hypothermia and hypoactivity after supraspinal administration. Repeated intracerebroventricular injection of (m)VD-Hpα resulted in both development of tolerance to antinociception and conditioned place aversion. In addition, central injection of (m)VD-Hpα dose-dependently stimulated food consumption. These findings demonstrate that this novel cannabinoid peptide agonist induces CB₁-mediated central antinociception with some CNS effects, which further supports a CB₁ agonist character of (m)VD-Hpα. Moreover, the current study will be helpful to understand the in vivo properties of the endogenous peptide agonist of the cannabinoid CB₁ receptor.

Regulation of nausea and vomiting by cannabinoids and the endocannabinoid system

Nausea and vomiting (emesis) are important elements in defensive or protective responses that animals use to avoid ingestion or digestion of potentially harmful substances. However, these neurally-mediated responses are at times manifested as symptoms of disease and they are frequently observed as side-effects of a variety of medications, notably those used to treat cancer. Cannabis has long been known to limit or prevent nausea and vomiting from a variety of causes. This has led to extensive investigations that have revealed an important role for cannabinoids and their receptors in the regulation of nausea and emesis. With the discovery of the endocannabinoid system, novel ways to regulate both nausea and vomiting have been discovered that involve the production of endogenous cannabinoids acting centrally. Here we review recent progress in understanding the regulation of nausea and vomiting by cannabinoids and the endocannabinoid system, and we discuss the potential to utilize the endocannabinoid system in the treatment of these frequently debilitating conditions.

Control of synaptic function by endocannabinoid-mediated retrograde signaling

Since the first reports in 2001, great advances have been made towards the understanding of endocannabinoid-mediated synaptic modulation. Electrophysiological studies have revealed that one of the two major endocannabinoids, 2-arachidonoylglycerol (2-AG), is produced from membrane lipids upon postsynaptic Ca(2+) elevation and/or activation of Gq/11-coupled receptors, and released from postsynaptic neurons. The released 2-AG then acts retrogradely onto presynaptic cannabinoid CB1 receptors and induces suppression of neurotransmitter release either transiently or persistently. These forms of 2-AG-mediated retrograde synaptic modulation are functional throughout the brain. The other major endocannabinoid, anandamide, mediates a certain form of endocannabinoid-mediated long-term depression (LTD). Anandamide also functions as an agonist for transient receptor potential vanilloid receptor type 1 (TRPV1) and mediates endocannabinoid-independent and TRPV1-dependent forms of LTD. It has also been demonstrated that the endocannabinoid system itself is plastic, which can be either up- or down-regulated by experimental or environmental conditions. In this review, I will make an overview of the mechanisms underlying endocannabinoid-mediated synaptic modulation.

Cannabinoid Regulation of Brain Reward Processing with an Emphasis on the Role of CB1 Receptors: A Step Back into the Future

Over the last decades, the endocannabinoid system has been implicated in a large variety of functions, including a crucial modulation of brain-reward circuits and the regulation of motivational processes. Importantly, behavioral studies have shown that cannabinoid compounds activate brain reward mechanisms and circuits in a similar manner to other drugs of abuse, such as nicotine, alcohol, cocaine, and heroin, although the conditions under which cannabinoids exert their rewarding effects may be more limited. Furthermore, there is evidence on the involvement of the endocannabinoid system in the regulation of cue- and drug-induced relapsing phenomena in animal models. The aim of this review is to briefly present the available data obtained using diverse behavioral experimental approaches in experimental animals, namely, the intracranial self-stimulation paradigm, the self-administration procedure, the conditioned place preference procedure, and the reinstatement of drug-seeking behavior procedure, to provide a comprehensive picture of the current status of what is known about the endocannabinoid system mechanisms that underlie modification of brain-reward processes. Emphasis is placed on the effects of cannabinoid 1 (CB1) receptor agonists, antagonists, and endocannabinoid modulators. Further, the role of CB1 receptors in reward processes is investigated through presentation of respective genetic ablation studies in mice. The vast majority of studies in the existing literature suggest that the endocannabinoid system plays a major role in modulating motivation and reward processes. However, much remains to be done before we fully understand these interactions. Further research in the future will shed more light on these processes and, thus, could lead to the development of potential pharmacotherapies designed to treat reward-dysfunction-related disorders.

Endogenous cannabinoid signaling at inhibitory interneurons

Significant progress has been made in our understanding of how endogenous cannabinoids (eCBs) signal at excitatory and inhibitory synapses in the central nervous system (CNS). This review discusses how eCBs regulate inhibitory interneurons, their synapses, and the networks in which they are embedded. eCB signaling plays a pivotal role in brain physiology by means of their synaptic signal transduction, spatiotemporal signaling profile, routing of information through inhibitory microcircuits, and experience-dependent plasticity. Understanding the normal processes underlying eCB signaling is beginning to shed light on how their dysregulation contributes to disease.