Endocannabinoid regulation of homeostatic feeding and stress-induced alterations in food intake in male rats

NAPE-PLD is target of thiazide diuretics

Thiazide and thiazide-like diuretics are among the most efficacious and used drugs for the treatment of hypertension, edema, and major cardiovascular outcomes. Despite more then than six decades of clinical use, the molecular target and mechanism of action by which these drugs cure hypertension after long-term use have remained mysterious. Here we report the discovery and validation of a previously unknown renal and extrarenal target of these antihypertensives, the membrane-associated phospholipase N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD) of the endocannabinoid system. Structural and functional insights, together with preclinical studies in hypertensive rats, disclose the molecular and physiological basis by which thiazides cause acute diuresis and, at the same time, the distinctive chronic reduction of vascular resistance. Our results shed light on the mechanism of treatment of hypertension and will be useful for developing more efficacious medications for the management of vascular risk factors, as well as associated leukoencephalopathies and myelin disorders.

Ghrelin Recruits the Endocannabinoid System to Modulate Food Reward

Ghrelin enhances feeding by activating the growth hormone secretagogue receptor (GHSR). In the brain, GHSRs are expressed in regions responsible for regulating food motivation including the ventral tegmental area (VTA). Endogenous cannabinoids also promote food-seeking behaviors through the cannabinoid receptor-1 (CB-1Rs) in brain regions including the VTA. It is not known, however, if ghrelin and endocannabinoids interact in the VTA to produce these effects. We therefore examined if GHSR and CB-1R interact within the VTA to enhance food motivation. Results show that GHSR and CB-1R mRNA are expressed in the VTA cells in male and female rats and mice, with the GHSR being expressed in dopamine cells and the CB-1R being expressed primarily in nondopaminergic cells with no obvious sex differences. Ghrelin directly activated and increased excitatory tone onto dopamine cells of male and female mice. Male rats lacking fully functional GHSR signaling showed disrupted gene expression of transcripts important for regulating the synthesis, release, and degradation of endocannabinoids and lowered the levels of 2-arachidonoylglycerol (2-AG) within the VTA. Moreover, pharmacological antagonism of VTA CB-1Rs attenuates the orexigenic and appetitive effects of intra-VTA ghrelin in rats and blocks the ability of ghrelin to promote excitatory drive to VTA dopamine neurons. Finally, blocking the breakdown of cannabinoids in the VTA enhances the effects of ghrelin on food motivation. Together, our data show that ghrelin stimulates VTA dopamine cells and ultimately food motivation in part through a mechanism that involves endocannabinoid signaling at the CB-1R.

MAGL blockade alleviates steroid-induced femoral head osteonecrosis by reprogramming BMSC fate in rat

The leading cause of steroid-induced femoral head osteonecrosis (ONFH) is the imbalance of bone homeostasis. Bone marrow-derived mesenchymal stem cell (BMSC) differentiation and fate are closely associated with bone homeostasis imbalance. Blocking monoacylglycerol lipase (MAGL) could effectively ameliorate ONFH by mitigating oxidative stress and apoptosis in BMSCs induced by glucocorticoids (GC). Nevertheless, whether MAGL inhibition can modulate the balance during BMSC differentiation, and therefore improve ONFH, remains elusive. Our study indicates that MAGL inhibition can effectively rescue the enhanced BMSC adipogenic differentiation caused by GC and promote their differentiation toward osteogenic lineages. Cannabinoid receptor 2 (CB2) is the direct downstream target of MAGL in BMSCs, rather than cannabinoid receptor 1(CB1). Using RNA sequencing analyses and a series of in vitro experiments, we confirm that the MAGL blockade-induced enhancement of BMSC osteogenic differentiation is primarily mediated by the phosphoinositide 3-kinases (PI3K)/ the serine/threonine kinase (AKT)/ (glycogen synthase kinase-3 beta) GSK3β pathway. Additionally, MAGL blockade can also reduce GC-induced bone resorption by directly suppressing osteoclastogenesis and indirectly reducing the expression of receptor activator of nuclear factor kappa-Β ligand (RANKL) in BMSCs. Thus, our study proposes that the therapeutic effect of MAGL blockade on ONFH is partly mediated by restoring the balance of bone homeostasis and MAGL may be an effective therapeutic target for ONFH.

The Role of Adipocytes Recruited as Part of Tumor Microenvironment in Promoting Colorectal Cancer Metastases

Adipose tissue dysfunction, which is associated with an increased risk of colorectal cancer (CRC), is a significant factor in the pathophysiology of obesity. Obesity-related inflammation and extracellular matrix (ECM) remodeling promote colorectal cancer metastasis (CRCM) by shaping the tumor microenvironment (TME). When CRC occurs, the metabolic symbiosis of tumor cells recruits adjacent adipocytes into the TME to supply energy. Meanwhile, abundant immune cells, from adipose tissue and blood, are recruited into the TME, which is stimulated by pro-inflammatory factors and triggers a chronic local pro-inflammatory TME. Dysregulated ECM proteins and cell surface adhesion molecules enhance ECM remodeling and further increase contractibility between tumor and stromal cells, which promotes epithelial-mesenchymal transition (EMT). EMT increases tumor migration and invasion into surrounding tissues or vessels and accelerates CRCM. Colorectal symbiotic microbiota also plays an important role in the promotion of CRCM. In this review, we provide adipose tissue and its contributions to CRC, with a special emphasis on the role of adipocytes, macrophages, neutrophils, T cells, ECM, and symbiotic gut microbiota in the progression of CRC and their contributions to the CRC microenvironment. We highlight the interactions between adipocytes and tumor cells, and potential therapeutic approaches to target these interactions.

Effects of prenatal THC vapor exposure on body weight, glucose metabolism, and feeding behaviors in chow and high-fat diet fed rats

BACKGROUND

4-20% of people report using cannabis during pregnancy, thereby it is essential to assess the associated risks. There is some evidence that prenatal cannabis exposure (PCE) may be associated with increased risk for developing of obesity and diabetes later in life, however this has not been well explored under controlled conditions. The aim of this study was to use a translational THC vapor model in rodents to characterize the effects of PCE on adiposity, glucose metabolism, and feeding patterns in adulthood, with focus on potential sex differences.

METHODS

Pregnant Sprague Dawley rats were exposed to vaporized THC (100 mg/ml) or control (polyethylene glycol vehicle) across the entire gestational period. Adult offspring from PCE (n = 24) or control (n = 24) litters were subjected to measures of adiposity, glucose metabolism and feeding behavior. Rats were then placed onto special diets (60% high-fat diet [HFD] or control 10% low fat diet [LFD]) for 4-months, then re-subjected to adiposity, glucose metabolism and feeding behavior measurements.

RESULTS

PCE did not influence maternal weight or food consumption but was associated with transient decreased pup weight. PCE did not initially influence bodyweight or adiposity, but PCE did significantly reduce the rate of bodyweight gain when on HFD/LFD, regardless of which diet. Further, PCE had complex effects on glucose metabolism and feeding behavior that were both sex and diet dependent. No effects of PCE were found on plasma leptin or insulin, or white adipose tissue mass.

CONCLUSIONS

PCE may not promote obesity development but may increase risk for diabetes and abnormal eating habits under certain biological and environmental conditions. Overall, this data enhances current understanding of the potential impacts of PCE.

4,4-Dimethylsterols Reduces Fat Accumulation via Inhibiting Fatty Acid Amide Hydrolase In Vitro and In Vivo

4,4-Dimethylsterols constitute a unique class of phytosterols responsible for regulating endogenous cannabinoid system (ECS) functions. However, precise mechanism through which 4,4-dimethylsterols affect fat metabolism and the linkage to the ECS remain unresolved. In this study, we identified that 4,4-dimethylsterols, distinct from 4-demethseterols, act as inhibitors of fatty acid amide hydrolases (FAAHs) both in vivo and in vitro. Genetic ablation of FAAHs (faah-1) abolishes the effects of 4,4-dimethylsterols on fat accumulation and locomotion behavior in a Caenorhabditis elegans model. We confirmed that dietary intervention with 4,4-dimethylsterols in a high-fat diet (HFD) mouse model leads to a significant reduction in body weight (>11.28%) with improved lipid profiles in the liver and adipose tissues and increased fecal triacylglycerol excretion. Untargeted and targeted metabolomics further verified that 4,4-dimethylsterols influence unsaturated fatty acid biosynthesis and elevate oleoyl ethanolamine levels in the intestine. We propose a potential molecular mechanism in which 4,4-dimethylsterols engage in binding interactions with the catalytic pocket (Ser241) of FAAH-1 protein due to the shielded polarity, arising from the presence of 2 additional methyl groups (CH3). Consequently, 4,4-dimethylsterols represent an unexplored class of beneficial phytosterols that coordinate with FAAH-1 activity to reduce fat accumulation, which offers new insight into intervention strategies for treating diet-induced obesity.

Circadian Influence on Acute Stress-induced Changes in Cortico-limbic Endocannabinoid Levels in Adult Male Rats

The endocannabinoid (eCB) system plays an important role in regulating the stress response, including glucocorticoid release and the generation of avoidance behaviour. Its two major ligands, 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (anandamide; AEA), are dynamically influenced by psychological stress to gate the generation of the stress response and facilitate recovery upon stress termination. Many biological systems exhibit circadian "daily" rhythms, including glucocorticoids and endocannabinoids, and the behavioural and endocrine impact of stress is modulated by the time of day. Nonetheless, most preclinical experiments investigating the interaction between stress and endocannabinoids occur in the light, "inactive" phase. We therefore tested if circadian phase influences stress-induced changes in eCB levels in the hippocampus (HIP), prefrontal cortex (PFC), and amygdala (AMY). Adult male rats were exposed to 15 min swim stress or immediately euthanized, and brains were collected. Testing occurred either early in the light or early in the dark phase of their cycle to compare circadian effects. We found that overall, stress decreased AEA in the AMY and HIP, with an effect in the PFC dependent on the time of day. Conversely, stress increased 2-AG in the AMY, with an effect in the PFC and HIP dependent on the time of day. This suggests that stress has a similar overall impact on eCB levels regardless of circadian phase, but that subtle differences may occur depending on the brain region, especially the PFC.

Disruption of tonic endocannabinoid signalling triggers cellular, behavioural and neuroendocrine responses consistent with a stress response

BACKGROUND AND PURPOSE

Endocannabinoid (eCB) signalling gates many aspects of the stress response, including the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis is controlled by corticotropin releasing hormone (CRH) producing neurons in the paraventricular nucleus of the hypothalamus (PVN). Disruption of eCB signalling increases drive to the HPA axis, but the mechanisms subserving this process are poorly understood.

EXPERIMENTAL APPROACH

Using an array of cellular, endocrine and behavioural readouts associated with activation of CRH neurons in the PVN, we evaluated the contributions of tonic eCB signalling to the generation of a stress response.

KEY RESULTS

The CB1 receptor antagonist/inverse agonist AM251, neutral antagonist NESS243 and NAPE PLD inhibitor LEI401 all uniformly increased Fos in the PVN, unmasked stress-linked behaviours, such as grooming, and increased circulating CORT, recapitulating the effects of stress. Similar effects were also seen after direct administration of AM251 into the PVN, while optogenetic inhibition of PVN CRH neurons ameliorated stress-like behavioural changes produced by disruption of eCB signalling.

CONCLUSIONS AND IMPLICATIONS

These data indicate that under resting conditions, constitutive eCB signalling restricts activation of the HPA axis through local regulation of CRH neurons in the PVN.

The endocannabinoid system as a putative target for the development of novel drugs for the treatment of psychiatric illnesses

Cannabis is well established to impact affective states, emotion and perceptual processing, primarily through its interactions with the endocannabinoid system. While cannabis use is quite prevalent in many individuals afflicted with psychiatric illnesses, there is considerable controversy as to whether cannabis may worsen these conditions or provide some form of therapeutic benefit. The development of pharmacological agents which interact with components of the endocannabinoid system in more localized and discrete ways then via phytocannabinoids found in cannabis, has allowed the investigation if direct targeting of the endocannabinoid system itself may represent a novel approach to treat psychiatric illness without the potential untoward side effects associated with cannabis. Herein we review the current body of literature regarding the various pharmacological tools that have been developed to target the endocannabinoid system, their impact in preclinical models of psychiatric illness and the recent data emerging of their utilization in clinical trials for psychiatric illnesses, with a specific focus on substance use disorders, trauma-related disorders, and autism. We highlight several candidate drugs which target endocannabinoid function, particularly inhibitors of endocannabinoid metabolism or modulators of cannabinoid receptor signaling, which have emerged as potential candidates for the treatment of psychiatric conditions, particularly substance use disorder, anxiety and trauma-related disorders and autism spectrum disorders. Although there needs to be ongoing clinical work to establish the potential utility of endocannabinoid-based drugs for the treatment of psychiatric illnesses, the current data available is quite promising and shows indications of several potential candidate diseases which may benefit from this approach.

Female rats prefer to forage food from males, an effect that is not influenced by stress

As social beings, animals and humans alike make real life decisions that are often influenced by other members. Most current research has focused on the influence of same-sex peers on individual decision-making, with potential opposite sex effect scarcely explored. Here, we developed a behavioral model to observe food foraging decision-making in female rats under various social situations. We found that female rats preferred to forage food from male over female rats or from the no-rat storage side. Female rats were more likely to forage food from familiar males than from unfamiliar. This opposite-sex preference was not altered by the lure of sweet food, or with estrous cycle, nor under stress conditions. These results suggest that the opposite sex influences food foraging decision-making in female rats. The behavioral model established could facilitate future investigation into the underlying neurobiological mechanisms.

Identification and characterization of hypothalamic circular RNAs associated with bovine residual feed intake

Residual feed intake (RFI) is crucial economic indicator used for calculating the feed efficiency of growing beef cattle. circRNA plays an important biological role in gene transcriptional regulation, but little is known about its potential functional regulation underlying RFI phenotypic variation. As the core center of regulation of animal feeding, the hypothalamus is closely associated with RFI. Therefore, the present study aimed to identify the key genes and functional pathways contributing to variance in cattle RFI phenotypes using RNA sequencing from hypothalamic tissue samples, in order to gain insight into the potential regulatory role of circRNAs in bovine RFI phenotypic variation. Differentially expressed genes were detected by RNA sequencing for beef cattle in the high and low RFI groups, followed by GO, KEGG enrichment, and circRNA-miRNA co-expression network analysis. A total of 257 circRNAs were differentially expressed between the two groups, with 128 significantly upregulated and 129 significantly downregulated genes in H group compared to L group. Among them, 9 unique circRNAs were present in group L and 4 unique circRNAs were present in group H. GO and KEGG enrichment analysis of the source genes of the differentially expressed circRNAs revealed that they were mainly involved in metabolic processes, such as cellular metabolic processes, cellular macromolecular metabolic processes, and regulatory pathways related to nutrient metabolism, including protein and amino acid metabolism, as well as vitamin metabolism and pancreatic secretion associated with the animal feeding behavior. The circRNAs detected in this study were mostly novel, and have not been investigated directly to be associated with the RFI phenotype. Interestingly, most miRNAs of differentially expressed circRNAs predicted based on the circRNA-miRNA co-expression network analysis by using top 50 differentially expressed circRNAs and 13 unique circRNAs, have been reported to be related to animal RFIs, implying that circRNAs in bovine hypothalamic tissue may regulate phenotypic variation in RFI through miRNAs. The study results illustrate the complex biological functions of the hypothalamus in regulating feed efficiency and showing the potential role of circRNAs in the feeding behavior regulation of livestock, which would contributing to expanding the understanding of circRNA.

Endocannabinoid 2-Arachidonoylglycerol Levels in the Anterior Cingulate Cortex, Caudate Putamen, Nucleus Accumbens, and Piriform Cortex Were Upregulated by Chronic Restraint Stress

Endocannabinoid 2-arachidonoylglycerol (2-AG) has been implicated in habituation to stress, and its augmentation reduces stress-induced anxiety-like behavior. Chronic restraint stress (CRS) changes the 2-AG levels in some gross brain areas, such as the forebrain. However, the detailed spatial distribution of 2-AG and its changes by CRS in stress processing-related anatomical structures such as the anterior cingulate cortex (ACC), caudate putamen (CP), nucleus accumbens (NAc), and piriform cortex (PIR) are still unclear. In this study, mice were restrained for 30 min in a 50 mL-centrifuge tube for eight consecutive days, followed by imaging of the coronal brain sections of control and stressed mice using desorption electrospray ionization mass spectrometry imaging (DESI-MSI). The results showed that from the forebrain to the cerebellum, 2-AG levels were highest in the hypothalamus and lowest in the hippocampal region. 2-AG levels were significantly (p < 0.05) upregulated and 2-AG precursors levels were significantly (p < 0.05) downregulated in the ACC, CP, NAc, and PIR of stressed mice compared with control mice. This study provided direct evidence of 2-AG expression and changes, suggesting that 2-AG levels are increased in the ACC CP, NAc, and PIR when individuals are under chronic stress.

Targeting the endocannabinoid system for the treatment of abdominal pain in irritable bowel syndrome

The management of visceral pain in patients with disorders of gut-brain interaction, notably irritable bowel syndrome, presents a considerable clinical challenge, with few available treatment options. Patients are increasingly using cannabis and cannabinoids to control abdominal pain. Cannabis acts on receptors of the endocannabinoid system, an endogenous system of lipid mediators that regulates gastrointestinal function and pain processing pathways in health and disease. The endocannabinoid system represents a logical molecular therapeutic target for the treatment of pain in irritable bowel syndrome. Here, we review the physiological and pathophysiological functions of the endocannabinoid system with a focus on the peripheral and central regulation of gastrointestinal function and visceral nociception. We address the use of cannabinoids in pain management, comparing them to other treatment modalities, including opioids and neuromodulators. Finally, we discuss emerging therapeutic candidates targeting the endocannabinoid system for the treatment of pain in irritable bowel syndrome.

On the Biomedical Properties of Endocannabinoid Degradation and Reuptake Inhibitors: Pre-clinical and Clinical Evidence

The endocannabinoid system (ECS) is composed of endogenous cannabinoids; components involved in their synthesis, transport, and degradation; and an expansive variety of cannabinoid receptors. Hypofunction or deregulation of the ECS is related to pathological conditions. Consequently, endogenous enhancement of endocannabinoid levels and/or regulation of their metabolism represent promising therapeutic approaches. Several major strategies have been suggested for the modulation of the ECS: (1) blocking endocannabinoids degradation, (2) inhibition of endocannabinoid cellular uptake, and (3) pharmacological modulation of cannabinoid receptors as potential therapeutic targets. Here, we focused in this review on degradation/reuptake inhibitors over cannabinoid receptor modulators in order to provide an updated synopsis of contemporary evidence advancing mechanisms of endocannabinoids as pharmacological tools with therapeutic properties for the treatment of several disorders. For this purpose, we revisited the available literature and reported the latest advances regarding the biomedical properties of fatty acid amide hydrolase and monoacylglycerol lipase inhibitors in pre-clinical and clinical studies. We also highlighted anandamide and 2-arachidonoylglycerol reuptake inhibitors with promising results in pre-clinical studies using in vitro and animal models as an outlook for future research in clinical trials.

Targeting Monoacylglycerol Lipase in Pursuit of Therapies for Neurological and Neurodegenerative Diseases

Neurological and neurodegenerative diseases are debilitating conditions, and frequently lack an effective treatment. Monoacylglycerol lipase (MAGL) is a key enzyme involved in the metabolism of 2-AG (2-arachidonoylglycerol), a neuroprotective endocannabinoid intimately linked to the generation of pro- and anti-inflammatory molecules. Consequently, synthesizing selective MAGL inhibitors has become a focus point in drug design and development. The purpose of this review was to summarize the diverse synthetic scaffolds of MAGL inhibitors concerning their potency, mechanisms of action and potential therapeutic applications, focusing on the results of studies published in the past five years. The main irreversible inhibitors identified were derivatives of hexafluoroisopropyl alcohol carbamates, glycol carbamates, azetidone triazole ureas and benzisothiazolinone, whereas the most promising reversible inhibitors were derivatives of salicylketoxime, piperidine, pyrrolidone and azetidinyl amides. We reviewed the results of in-depth chemical, mechanistic and computational studies on MAGL inhibitors, in addition to the results of in vitro findings concerning selectivity and potency of inhibitors, using the half maximal inhibitory concentration (IC50) as an indicator of their effect on MAGL. Further, for highlighting the potential usefulness of highly selective and effective inhibitors, we examined the preclinical in vivo reports regarding the promising therapeutic applications of MAGL pharmacological inhibition.

Inhibition of MAGL activates the Keap1/Nrf2 pathway to attenuate glucocorticoid-induced osteonecrosis of the femoral head

Glucocorticoids (GCs) are used in treating viral infections, acute spinal cord injury, autoimmune diseases, and shock. Several patients develop GC-induced osteonecrosis of the femoral head (ONFH). However, the pathogenic mechanisms underlying GC-induced ONFH remain poorly understood. GC-directed bone marrow mesenchymal stem cells (BMSCs) fate is an important factor that determines GC-induced ONFH. At high concentrations, GCs induce BMSC apoptosis by promoting oxidative stress. In the present study, we aimed to elucidate the molecular mechanisms that relieve GC-induced oxidative stress in BMSCs, which would be vital for treating ONFH. The endocannabinoid system regulates oxidative stress in multiple organs. Here, we found that monoacylglycerol lipase (MAGL), a key molecule in the endocannabinoid system, was significantly upregulated during GC treatment in osteoblasts both in vitro and in vivo. MAGL expression was positively correlated with expression of the NADPH oxidase family and apoptosis-related proteins. Functional analysis showed that MAGL inhibition markedly reduced oxidative stress and partially rescued BMSC apoptosis. Additionally, in vivo studies indicated that MAGL inhibition effectively attenuated GC-induced ONFH. Pathway analysis showed that MAGL inhibition regulated oxidative stress in BMSCs via the Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. The expression of Nrf2, a major regulator of intracellular antioxidants, was upregulated by inhibiting MAGL. Nrf2 activation can mimic the effect of MAGL inhibition and significantly reduce GC-induced oxidative damage in BMSCs. The beneficial effects of MAGL inhibition were attenuated after the blockade of the Keap1/Nrf2 antioxidant signaling pathway. Notably, pharmacological blockade of MAGL conferred femoral head protection in GC-induced ONFH, even after oxidative stress responses were initiated. Therefore, MAGL may represent a novel target for the prevention and treatment of GC-induced ONFH.

Untapped endocannabinoid pharmacological targets: Pipe dream or pipeline?

It has been established that the endogenous cannabinoid (endocannabinoid) system plays key modulatory roles in a wide variety of pathological conditions. The endocannabinoid system comprises both cannabinoid receptors, their endogenous ligands including 2-arachidonoylglycerol (2-AG), N-arachidonylethanolamine (anandamide, AEA), and enzymes that regulate the synthesis and degradation of endogenous ligands which include diacylglycerol lipase alpha (DAGL-α), diacylglycerol lipase beta (DAGL-β), fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), α/β hydrolase domain 6 (ABHD6). As the endocannabinoid system exerts considerable involvement in the regulation of homeostasis and disease, much effort has been made towards understanding endocannabinoid-related mechanisms of action at cellular, physiological, and pathological levels as well as harnessing the various components of the endocannabinoid system to produce novel therapeutics. However, drug discovery efforts within the cannabinoid field have been slower than anticipated to reach satisfactory clinical endpoints and raises an important question into the validity of developing novel ligands that therapeutically target the endocannabinoid system. To answer this, we will first examine evidence that supports the existence of an endocannabinoid system role within inflammatory diseases, neurodegeneration, pain, substance use disorders, mood disorders, as well as metabolic diseases. Next, this review will discuss recent clinical studies, within the last 5 years, of cannabinoid compounds in context to these diseases. We will also address some of the challenges and considerations within the cannabinoid field that may be important in the advancement of therapeutics into the clinic.

Comorbid anxiety-like behavior in a rat model of colitis is mediated by an upregulation of corticolimbic fatty acid amide hydrolase

Peripheral inflammatory conditions, including those localized to the gastrointestinal tract, are highly comorbid with psychiatric disorders such as anxiety and depression. These behavioral symptoms are poorly managed by conventional treatments for inflammatory diseases and contribute to quality of life impairments. Peripheral inflammation is associated with sustained elevations in circulating glucocorticoid hormones, which can modulate central processes, including those involved in the regulation of emotional behavior. The endocannabinoid (eCB) system is exquisitely sensitive to these hormonal changes and is a significant regulator of emotional behavior. The impact of peripheral inflammation on central eCB function, and whether this is related to the development of these behavioral comorbidities remains to be determined. To examine this, we employed the trinitrobenzene sulfonic acid-induced model of colonic inflammation (colitis) in adult, male, Sprague Dawley rats to produce sustained peripheral inflammation. Colitis produced increases in behavioral measures of anxiety and elevations in circulating corticosterone. These alterations were accompanied by elevated hydrolytic activity of the enzyme fatty acid amide hydrolase (FAAH), which hydrolyzes the eCB anandamide (AEA), throughout multiple corticolimbic brain regions. This elevation of FAAH activity was associated with broad reductions in the content of AEA, whose decline was driven by central corticotropin releasing factor type 1 receptor signaling. Colitis-induced anxiety was reversed following acute central inhibition of FAAH, suggesting that the reductions in AEA produced by colitis contributed to the generation of anxiety. These data provide a novel perspective for the pharmacological management of psychiatric comorbidities of chronic inflammatory conditions through modulation of eCB signaling.

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

BACKGROUND AND PURPOSE

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

EXPERIMENTAL APPROACH

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

KEY RESULTS

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

CONCLUSION AND IMPLICATIONS

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

Monoacylglycerol lipase reprograms lipid precursors signaling in liver disease

Dietary oversupply of triglycerides represent the hallmark of obesity and connected complications in the liver such as non-alcoholic fatty liver disease and non-alcoholic steatohepatitis, which eventually progress to cirrhosis and hepatocellular carcinoma. Monoacylglycerol lipase is the last enzymatic step in the hydrolysis of triglycerides, generating glycerol and fatty acids (FAs), which are signaling precursors in physiology and disease. Notably, monoacylglycerol lipase (MGL) also hydrolyzes 2-arachidonoylglycerol, which is a potent ligand within the endocannabinoid system, into arachidonic acid - a precursor for prostaglandin synthesis; thus representing a pivotal substrates provider in multiple organs for several intersecting biological pathways ranging from FA metabolism to inflammation, pain and appetite. MGL inhibition has been shown protective in limiting several liver diseases as FAs may drive hepatocyte injury, fibrogenesis and de- activate immune cells, however the complexity of MGL network system still needs further and deeper understanding. The present review will focus on MGL function and FA partitioning in the horizons of liver disease.

The novel MAGL inhibitor MJN110 enhances responding to reward-predictive incentive cues by activation of CB1 receptors

CB1 receptor antagonists disrupt operant responding for food and drug reinforcers, and cue-induced reinstatement of cocaine and heroin seeking. Conversely, enhancing endocannabinoid signaling, particularly 2-arachidonyl glycerol (2-AG), by inhibition of monoacyl glycerol lipase (MAGL), may facilitate some aspects of reward seeking. To determine how endocannabinoid signaling affects responding to reward-predictive cues, we employed an operant task that allows us to parse the incentive motivational properties of cues. Rats were required to nosepoke during an intermittent audiovisual incentive cue (IC) to obtain a 10% sucrose reward. The CB1 receptor antagonist, rimonabant, dose-dependently decreased the response ratio (rewarded ICs/total presented) and active nosepokes per IC, while it increased the latency to respond to the cue and obtain the reward, indicating an overall decrease in both the choice and vigor of responding. Yet rats persisted in entering the reward cup. Using a modified version of the task, the novel MAGL inhibitor MJN110 increased the response ratio, decreased the latencies to respond to the IC and enhanced active nosepokes per IC, indicating a facilitation of cue-induced reward seeking. These effects were blocked by a subthreshold dose of rimonabant. Finally, MJN110 did not alter consumption of freely available sucrose within volumes obtained in the operant task. Together these data demonstrate blocking endocannabinoid tone at the CB1 receptor attenuates the ability of cues to induce reward seeking, while some aspects of motivation for the reward are retained. Conversely, enhancing 2-AG signaling at CB1 receptors facilitates IC responding and increases the motivational properties of the IC.

Cannabinoids and their actions: An update

LINKED ARTICLES

This article is part of a themed section on 8th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Endocannabinoid regulation of homeostatic feeding and stress-induced alterations in food intake in male rats

BACKGROUND AND PURPOSE

Stress is known to reduce food intake. Many aspects of the stress response and feeding are regulated by the endocannabinoid system, but the roles of anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in stress-induced anorexia are unclear.

EXPERIMENTAL APPROACH

Effects of acute restraint stress on endocannabinoids were investigated in male Sprague-Dawley rats. Systemic and central pharmacological inhibition of fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL) was used to assess the effects of elevated AEA and 2-AG on homeostatic feeding and on food consumption after stress. Animals were pretreated with the FAAH inhibitor, PF-04457845, or the MAGL inhibitor, MJN110, before 2 h acute restraint stress or 2 h homecage period without food.

KEY RESULTS

Restraint stress decreased hypothalamic and circulating AEA, with no effect in the gastrointestinal tract, while 2-AG content in the jejunum (but not duodenum) was reduced. PF-04457845 (30 μg), given i.c.v., attenuated stress-induced anorexia via CB₁ receptors, but reduced homeostatic feeding in unstressed animals through an unknown mechanism. On the other hand, systemic administration of MJN110 (10 mg·kg^-1 ) reduced feeding, regardless of stress or feeding status and inhibited basal intestinal transit in unstressed rats. The ability of MAGL inhibition to reduce feeding in combination with stress was independent of CB₁ receptor signalling in the gut as the peripherally restricted CB₁ receptor antagonist, AM6545 did not block this effect.

CONCLUSIONS AND IMPLICATIONS

Our data reveal diverse roles for 2-AG and AEA in homeostatic feeding and changes in energy intake following stress.

LINKED ARTICLES

This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.