Genetic deletion of monoacylglycerol lipase leads to impaired cannabinoid receptor CB₁R signaling and anxiety-like behavior

Unraveling the Molecular Underpinnings: The Therapeutic Impact of Aerobic Exercise on Anxiety Disorders

Anxiety disorders, characterized by persistent apprehension, somatic symptoms and fatigue, are leading causes of disability worldwide. The burgeoning therapeutic potential of aerobic exercise has gained prominence as a leading non-pharmacological strategy, with evidence supporting its effectiveness in alleviating anxiety across diverse conditions. This review synthesizes current research to clarify the molecular mechanisms through which aerobic exercise ameliorates anxiety in terms of the effects of exercise on the hypothalamic-pituitary-adrenal (HPA) axis, the hepatic-brain axis and epigenetics; electroencephalographic alterations; inflammatory pathways; the balance between oxidative and nitrogenous stress; various substances, such as brain-derived neurotrophic factor (BDNF), atrial natriuretic peptide (ANP), and opioid peptides; and the 5-HT2C receptor and cannabinoid receptor type-1 (CB1R), among others, reflecting the positive modulatory effects of aerobic exercise on anxiety. As a non-pharmacological intervention, aerobic exercise has been demonstrated to be useful in a variety of medical applications and has considerable potential for ameliorating symptoms of anxiety.

Differential regulation of pruritic sensation and emotion by cannabinoid type 1 receptors on mPFC glutamatergic and GABAergic neurons

Itch causes a strong urge to scratch and induces negative emotions, such as aversion and anxiety. Antihistamine medications are key in the clinical management of pruritus, but their therapeutic efficacy in controlling moderate and severe itching remains limited. The neural circuits in the brain that process itching and itch-induced aversion and anxiety remain unclear so far. Human brain imaging suggests that the medial prefrontal cortex (mPFC) is involved in processing the emotional and motivational components of itching. In this study, we investigated the mechanisms by which glutamatergic and GABAergic neurons in mPFC differentially regulated pruritic sensation and emotion through cannabinoid type 1 receptors (CB1Rs). Chloroquinoline (CQ)-induced acute and calcipotriol (MC903)-induced chronic itch models were established. Fiberoptic calcium imaging was used to detect the activity of the two types of neurons in response to itching. The CB1R antagonist AM251 (0.5 mg in 200 nL) was microinjected into the mPFC through the implanted cannula. We showed that chemogenetic activation of glutamatergic neurons and inhibition of GABAergic neurons in the mPFC reduced scratching and chronic itch-induced anxiety. GABAergic, but not glutamatergic, neurons were involved in acute itch-induced aversion. CB1Rs on glutamatergic and GABAergic neurons modulated chronic itch-induced scratching and anxiety in divergent manners. However, CB1Rs did not affect acute itch-induced scratching. CB1Rs on GABAergic, but not glutamatergic, neurons regulated acute itch-induced aversion. These results may guide the development of therapeutic strategies targeting CB1Rs to treat itch-induced sensory and emotional responses.

Acute kappa opioid receptor blocking disrupts the pro-cognitive effect of cannabidiol in neuropathic rats

Cannabidiol has been shown to ameliorate neuropathic pain and its affective components. Previous studies highlighted the pharmacological interaction between the CBD and opioid system, particularly the MOR, but the understanding of the interaction between CBD and kappa opioid receptor (KOR), physiologically stimulated by the endogenous opioid dynorphin, remains elusive. We assessed the pharmacological interactions between CBD and nor-BNI, a selective KOR antagonist in a rat neuropathic pain model. We show an increase in dynorphin peptide and its KOR receptors in the hippocampus' dentate gyrus (DG) of neuropathic rats showing allodynia, and memory deficits. Consistent with these findings, neuropathic pain was associated with long-term potentiation (LTP) impairment in the entorhinal cortex-DG, also referred to as the lateral perforant pathway (LPP). Moreover, a downregulation of the endocannabinoid 2-AG and an upregulation of the cannabinoid CB1 receptors in the DG were detected in neuropathic pain animals. Either an acute KOR antagonist administration or one-week CBD treatment normalized dynorphin levels and improved affective symptoms, LTP and receptor expression, whereas only CBD showed an anti-allodynic effect. In addition, CBD normalized the SNI-induced changes in neuroplasticity as well as endocannabinoid and GABA levels in the DG. Noteworthy, the acute blockade of the KOR carried out after CBD repeated administration causes the re-installment of some neuropathic condition symptoms. As a whole, these original results indicate a critical relationship between the adaptive changes in the hippocampus produced by CBD and the need to maintain the recovered physiological dynorphin tone to preserve the therapeutic effect of CBD in neuropathic rats.

The CB1R of mPFC is involved in anxiety-like behavior induced by 0.8/2.65 GHz dual-frequency electromagnetic radiation

As mobile phones and communication base stations become more widespread, concerns have arisen regarding the potential risks of environmental exposure to multi-frequency electromagnetic radiation (EMR) and its effects on mental health. To address these concerns, our study established a dual-frequency EMR mouse model at 0.8/2.65 GHz to explore potential molecular mechanisms and intervention targets. Our results revealed that exposure to this dual-frequency EMR significantly induced anxiety-like behavior in mice. Molecular experiments further showed a significant decrease in cannabinoid receptor type 1 (CB1R) levels in the medial prefrontal cortex (mPFC) of the mice, along with a notable reduction in the endogenous cannabinoids 2-arachidonoylglycerol and anandamide. This led to a downregulation of the entire endocannabinoid system (ECS). Additional confirmation was obtained by overexpressing and knocking down CB1R in the mPFC. We found that increasing mPFC CB1R levels could effectively reduce anxiety-like behavior, while decreasing mPFC CB1R levels exacerbated it. Furthermore, we found dual-frequency EMR induced the change of ECS in the basolateral amygdala (BLA). Notably, female mice exhibited similar behavioral phenotypes and molecular mechanisms in response to dual-frequency EMR. In summary, our study demonstrates that anxiety induced by dual-frequency EMR is closely linked to the function of the ECS in the mPFC and BLA, and that CB1R expression in the mPFC plays a significant role in modulating emotional behavior in mice.

The endocannabinoid system in the brain undergoes long-lasting changes following neuropathic pain

The endocannabinoid system (ECS), which is composed of endocannabinoids (eCBs), cannabinoid receptors (CBRs), and associated signaling molecules, has been identified within the brain. In neuropathic pain animal models and patients, long-lasting alterations in the ECS have been observed. These changes of neurons and glial cells in the ECS contribute to the modulation of neuropathic pain. Intervention strategies such as the activation of CBRs, the enhancement of hydrolytic enzyme function, and the inhibition of synthetizing enzymes typically alleviate neuropathic pain through CBR-dependent mechanisms. Additionally, emotions such as fear, anxiety, and depression are frequently experienced with neuropathic pain. Exogenous cannabinoids can mitigate these mood disorders via CBR signaling pathways. Therefore, the targeting of long-lasting ECS alterations represents a potential therapeutic approach for both neuropathic pain and emotional disorders. In this review, the long-lasting variations in neurons and glial cells in the ECS related to neuropathic pain and the accompanying emotional comorbidities are elucidated. Furthermore, the cellular and molecular mechanisms underlying synaptic plasticity and neural circuit activities in the brain are reviewed.

The Estrous Cycle Influences the Effects of Fatty Acid Amide Hydrolase and Monoacylglycerol Lipase Inhibition in the Anxiety-Like Behavior in Rats

Background: Sex differences in the response to the anxiety-related effects of cannabinoid drugs have been reported, with females being more sensitive than males. Evidence suggests that, according to sex and estrous cycle phase (ECP), the content of the endocannabinoids (eCBs) N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) varies in brain areas involved in the anxiety-like behavior. Methods: Considering the lack of studies evaluating sex and ECP differences in the eCB system in anxiety, using URB597, a fatty acid amide hydrolase inhibitor, or MJN110, a monoacylglycerol lipase inhibitor, we explored the effects of increasing AEA or 2-AG levels, respectively, in cycling and ovariectomized (OVX) female adult Wistar rats, as well as males, subjected to the elevated plus maze. Results: The administration of URB597 (0.1 or 0.3mg/kg; intraperitoneally) either increased or reduced the percentage of open arms time (%OAT) and open arms entries (%OAE), being anxiolytic in diestrus and anxiogenic in estrus. No effects were observed in proestrus or when all ECPs were analyzed together. Both doses produced anxiolytic-like effects in males. In OVX females, the anxiolytic-like effect of URB597 0.1 was associated with low levels of estradiol, whereas the anxiogenic-like effect of URB597 0.3 was spared by estradiol pretreatment. The systemic administration of MJN110 3.0 mg/kg reduced the risk assessment behavior (RAB), suggesting an anxiolytic-like effect independent of the ECP. When considering the ECP, MJN110 3.0 increased the %OAT and reduced the RAB, being anxiolytic in estrus and diestrus. No effects were observed in proestrus. Both doses of MJN110 were anxiogenic in males. In OVX females, the anxiolytic-like effect of MJN110 was dependent on low estradiol levels. Conclusion: Together, our findings support the evidence that females react differently to the effects of cannabinoids in the anxiety-like behavior; in addition, AEA and 2-AG modulation elicits anxiety-like responses that are closely influenced by hormone levels, mainly estradiol.

Endocannabinoid Hydrolase Inhibitors: Potential Novel Anxiolytic Drugs

Over the past decade, the idea of targeting the endocannabinoid system to treat anxiety disorders has received increasing attention. Previous studies focused more on developing cannabinoid receptor agonists or supplementing exogenous cannabinoids, which are prone to various adverse effects due to their strong pharmacological activity and poor receptor selectivity, limiting their application in clinical research. Endocannabinoid hydrolase inhibitors are considered to be the most promising development strategies for the treatment of anxiety disorders. More recent efforts have emphasized that inhibition of two major endogenous cannabinoid hydrolases, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), indirectly activates cannabinoid receptors by increasing endogenous cannabinoid levels in the synaptic gap, circumventing receptor desensitization resulting from direct enhancement of endogenous cannabinoid signaling. In this review, we comprehensively summarize the anxiolytic effects of MAGL and FAAH inhibitors and their potential pharmacological mechanisms, highlight reported novel inhibitors or natural products, and provide an outlook on future directions in this field.

Anandamide Attenuates Neurobehavioral Deficits and EEG Irregularities in the Chronic Sleep Deprivation Rats: The Role of Oxidative Stress and Neuroinflammation

Sleep deprivation increases stress, anxiety, and depression by altering the endocannabinoid system's function. In the present study, we aimed to investigate the anti-anxiety and anti-depressant effects of the endocannabinoid anandamide (AEA) in the chronic sleep deprivation (SD) model in rats. Adult male Wistar rats (200-250 g) were randomly divided into three groups: control + vehicle (Control), chronic sleep deprivation + vehicle (SD), and chronic sleep deprivation + 20 mg/kg AEA (SD + A). The rats were kept in a sleep deprivation device for 18 h (7 to 1 a.m.) daily for 21 days. Open-field (OFT), elevated plus maze, and forced swimming tests (FST) were used to assess anxiety and depression-like behavior. As well as the cortical EEG, CB1R mRNA expression, TNF-α, IL-6, IL-4 levels, and antioxidant activity in the brain were examined following SD induction. AEA administration significantly increased the time spent (p < 0.01), the distance traveled in the central zone (p < 0.001), and the number of climbing (p < 0.05) in the OFT; it also increased the duration and number of entries into the open arms (p < 0.01 and p < 0.05 respectively), and did not reduce immobility time in the FST (p > 0.05), AEA increased CB1R mRNA expression in the anterior and medial parts of the brain (p < 0.01), and IL-4 levels (p < 0.05). AEA also reduced IL-6 and TNF-α (p < 0.05) and modulated cortical EEG. AEA induced anxiolytic-like effects but not anti-depressant effects in the SD model in rats by modulating CB1R mRNA expression, cortical EEG, and inflammatory response.

Patent Highlights June-July 2023

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Research Progress in Estrogen-related Receptor Gamma (ERRγ) Agonists and Inverse Agonists

Estrogen-related receptor gamma (ERRγ), one of three members of the ERR family, is an inducible transcription factor. ERRγ has dual functions in different tissues. The decreased expression of ERRγ in the brain, stomach, prostate, and fat cells can cause neuropsychological dysfunction, gastric cancer, prostate cancer, and obesity. However, when ERRγ is present in the liver, pancreas, and thyroid follicular cells, ERRγ overexpression is related to liver cancer, type II diabetes, oxidative liver injury, and anaplastic thyroid carcinoma. Signaling pathway studies have confirmed that ERRγ agonists or inverse agonists can regulate ERRγ expression to treat related diseases. The collision between residue Phe435 and the modulator is a key factor determining the activation or inhibition of ERRγ. Although more than 20 agonists and inverse agonists of ERRγ have been reported, no clinical studies have been found in the literature. This review summarizes the important relationship between ERRγ-related signaling pathways and diseases, research progress, and the structure-activity relationship of modulators. These findings provide guidance for further study on new ERRγ modulators.

Wistar-Kyoto rats and chronically stressed Wistar rats present similar depression- and anxiety-like behaviors but different corticosterone and endocannabinoid system modulation

The interplay of social, psychological, and biological stresses can trigger mental health conditions such as major depressive disorder (MDD), adjustment disorder, and posttraumatic stress disorder (PTSD). The endocannabinoid system (ECS), comprising endocannabinoids and cannabinoid receptors, is the critical pathway that mediates responses to stress stimuli. This study aimed to investigate the ECS's impact on responding to chronic social instability stress (SIS). Wistar (WIS) rats and an endogenously depressed rat model, Wistar-Kyoto (WKY), were used to evaluate depression- and anxiety-like behavioral responses, cognitive function, hormone levels, and ECS function. The animals in the stress group (WIS-STS and WKY-STS) were exposed to TMT (predator odor) for 10 mins (two exposures in total: one in light cycle and one in dark cycle) and daily roommate changes (30 days in total), while the control group (CTL) rats were exposed to a sham odor stimulus (distilled water) and did not undergo roommate changes. The results in the open field test suggest that WKY rats had significantly lower locomotor activity than WIS rats. In contrast, WKY rats and chronically stressed WIS rats presented similar depression- and anxiety-like behaviors and impaired cognitive function in the elevated plus maze, forced swimming test, and novel objective recognition test. However, chronic SIS did not exacerbate these behavioral changes in WKY rats. ELISA and Western blot analysis indicated that chronic SIS did not induce further upregulation of endocannabinoids and CB1R downregulation in WKY rats compared to WIS rats. In addition, the Luminex assay revealed that WKY rats showed a higher resilience on the HPA-axis modulation towards chronic SIS, distinguished by the hyperactivity of the HPA-axis modulation in WIS rats. Overall, the study revealed that the chronic SIS animal model (stressed WIS rats) and an animal model of endogenous depression (WKY rats) can generate similar behavioral changes in anxious behavior, behavioral despair, and cognitive impairment. Both animal models present hyperactivity of the ACTH modulation and ECS activity, while WKY rats are more resilient on CORT modulation towards chronic SIS.

Monoacylglycerol Lipase Inhibition Prevents Short-Term Mitochondrial Dysfunction and Oxidative Damage in Rat Brain Synaptosomal/Mitochondrial Fractions and Cortical Slices: Role of Cannabinoid Receptors

Inhibition of enzymes responsible for endocannabinoid hydrolysis represents an invaluable emerging tool for the potential treatment of neurodegenerative disorders. Monoacylglycerol lipase (MAGL) is the enzyme responsible for degrading 2-arachydonoylglycerol (2-AG), the most abundant endocannabinoid in the central nervous system (CNS). Here, we tested the effects of the selective MAGL inhibitor JZL184 on the 3-nitropropinic acid (3-NP)-induced short-term loss of mitochondrial reductive capacity/viability and oxidative damage in rat brain synaptosomal/mitochondrial fractions and cortical slices. In synaptosomes, while 3-NP decreased mitochondrial function and increased lipid peroxidation, JZL184 attenuated both markers. The protective effects evoked by JZL184 on the 3-NP-induced mitochondrial dysfunction were primarily mediated by activation of cannabinoid receptor 2 (CB2R), as evidenced by their inhibition by the selective CB2R inverse agonist JTE907. The cannabinoid receptor 1 (CB1R) also participated in this effect in a lesser extent, as evidenced by the CB1R antagonist/inverse agonist AM281. In contrast, activation of CB1R, but not CB2R, was responsible for the protective effects of JZL184 on the 3-NP-iduced lipid peroxidation. Protective effects of JZL184 were confirmed in other toxic models involving excitotoxicity and oxidative damage as internal controls. In cortical slices, JZL184 ameliorated the 3-NP-induced loss of mitochondrial function, the increase in lipid peroxidation, and the inhibition of succinate dehydrogenase (mitochondrial complex II) activity, and these effects were independent on CB1R and CB2R, as evidenced by the lack of effects of AM281 and JTE907, respectively. Our novel results provide experimental evidence that the differential protective effects exerted by JZL184 on the early toxic effects induced by 3-NP in brain synaptosomes and cortical slices involve MAGL inhibition, and possibly the subsequent accumulation of 2-AG. These effects involve pro-energetic and redox modulatory mechanisms that may be either dependent or independent of cannabinoid receptors' activation.

Cross-disorder GWAS meta-analysis of endocannabinoid DNA variations in major depressive disorder, bipolar disorder, attention deficit hyperactivity disorder, autism spectrum disorder, and schizophrenia

The endocannabinoid system (ECS) is implicated in multiple mental disorders. In this study, we explored DNA variations in the ECS across major depressive disorder (MDD), bipolar disorder, attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and schizophrenia by performing a cross-disorder genome-wide association study (GWAS) meta-analysis. We obtained six datasets from the Psychiatric Genomics Consortium containing GWAS summary statistics from European cohorts (284,023 cases and 508,515 controls). Effective sample size weighted meta-analysis was performed for 2241 single nucleotide polymorphisms (SNPs) pertaining to gene bodies of 33 endocannabinoid genes using METAL, where an overall z-statistic is calculated for each marker based on a weighted sum of individual statistics. Heterogeneity was examined with I2 and X2 tests. MAGMA gene-based analysis was also performed. We identified nine SNPs significantly associated with a change in risk of having a mental disorder. The lead SNP was rs12805732 (Gene: Diacylglycerol Lipase Alpha; DAGLA). Four SNPs had substantial heterogeneity (I2>60 %). DAGLA had the strongest association with disease risk in gene-based analysis. Our findings suggest that the ECS may be a shared pathway in mental disorders. Future studies validating these findings would contribute to the identification of biomarkers of disease risk across multiple mental disorders.

Neuronal Nitric Oxide Synthase Critically Regulates the Endocannabinoid Pathway in the Murine Cerebellum During Development

The cerebellum is a major site of endocannabinoid (eCB) production and signaling. The predominant eCB within the cerebellum, 2-arachidonoylglycerol (2-AG), is produced by a metabotropic glutamate receptor type 1 (mGluR1)-initiated signaling cascade within Purkinje neurons (PNs). 2-AG retrogradely stimulates cannabinoid 1 receptors (CB1Rs) located on presynaptic terminals. The activated CB1R decreases neurotransmitter release and leads to the production of nitric oxide (NO), a gaseous molecule. Recently, our group discovered that during development in mice lacking neuronal nitric oxide synthase (nNOS-/-), PNs display an excitotoxic phenotype associated with overactivated mGluR1. Considering the importance of mGluR1 in 2-AG synthesis, the present study explored the role of nNOS-derived NO in regulating the eCB pathway within the cerebella of wildtype (WT) and nNOS-/- mice at postnatal day 7 (PD7), 2 weeks (2 W), and 7 weeks (7 W). Our analysis showed that diacylglycerol lipase α, the enzyme that catalyzes 2-AG production, was elevated at early postnatal ages, and followed by elevated levels of 2-AG in nNOS-/- cerebella compared to WT. CB1R expression in nNOS-/- cerebella was upregulated at PD7 but decreased at 2 W and 7 W when compared to age-matched WT mice cerebella. Importantly, treating organotypic nNOS-/- cerebellar slice cultures with an NO-donor-attenuated CB1R levels after 7 days in vitro. In addition, expression of the eCB hydrolases fatty acid amide hydrolase and monoacylglycerol lipase were significantly downregulated in nNOS-/- cerebella compared to WT cerebella at 7 W. Together, these results reveal a novel role for nNOS/NO in regulating eCB signaling in the cerebellum.

Imaging and Genetic Tools for the Investigation of the Endocannabinoid System in the CNS

As central nervous system (CNS)-related disorders present an increasing cause of global morbidity, mortality, and high pressure on our healthcare system, there is an urgent need for new insights and treatment options. The endocannabinoid system (ECS) is a critical network of endogenous compounds, receptors, and enzymes that contribute to CNS development and regulation. Given its multifaceted involvement in neurobiology and its significance in various CNS disorders, the ECS as a whole is considered a promising therapeutic target. Despite significant advances in our understanding of the ECS's role in the CNS, its complex architecture and extensive crosstalk with other biological systems present challenges for research and clinical advancements. To bridge these knowledge gaps and unlock the full therapeutic potential of ECS interventions in CNS-related disorders, a plethora of molecular-genetic tools have been developed in recent years. Here, we review some of the most impactful tools for investigating the neurological aspects of the ECS. We first provide a brief introduction to the ECS components, including cannabinoid receptors, endocannabinoids, and metabolic enzymes, emphasizing their complexity. This is followed by an exploration of cutting-edge imaging tools and genetic models aimed at elucidating the roles of these principal ECS components. Special emphasis is placed on their relevance in the context of CNS and its associated disorders.

Anxiety Modulation by Cannabinoids-The Role of Stress Responses and Coping

Endocannabinoids were implicated in a variety of pathological conditions including anxiety and are considered promising new targets for anxiolytic drug development. The optimism concerning the potentials of this system for anxiolysis is probably justified. However, the complexity of the mechanisms affected by endocannabinoids, and discrepant findings obtained with various experimental approaches makes the interpretation of research results difficult. Here, we review the anxiety-related effects of the three main interventions used to study the endocannabinoid system: pharmacological agents active at endocannabinoid-binding sites present on both the cell membrane and in the cytoplasm, genetic manipulations targeting cannabinoid receptors, and function-enhancers represented by inhibitors of endocannabinoid degradation and transport. Binding-site ligands provide inconsistent findings probably because they activate a multitude of mechanisms concomitantly. More robust findings were obtained with genetic manipulations and particularly with function enhancers, which heighten ongoing endocannabinoid activation rather than affecting all mechanisms indiscriminately. The enhancement of ongoing activity appears to ameliorate stress-induced anxiety without consistent effects on anxiety in general. Limited evidence suggests that this effect is achieved by promoting active coping styles in critical situations. These findings suggest that the functional enhancement of endocannabinoid signaling is a promising drug development target for stress-related anxiety disorders.

Monoacylglycerol Lipase Protects the Presynaptic Cannabinoid 1 Receptor from Desensitization by Endocannabinoids after Persistent Inflammation

Cannabinoid-targeted pain therapies are increasing with the expansion of cannabis legalization, however, their efficacy may be limited by pain-induced adaptations in the cannabinoid system. Cannabinoid receptor subtype 1 (CB1R) inhibition of spontaneous, GABAergic miniature IPSCs (mIPSCs) and evoked IPSCs (eIPSCs) in the ventrolateral periaqueductal gray (vlPAG) were compared in slices from naive and inflamed male and female Sprague Dawley rats. Complete Freund's Adjuvant (CFA) injections into the hindpaw induced persistent inflammation. In naive rats, exogenous cannabinoid agonists robustly reduce both eIPSCs and mIPSCs. After 5-7 d of inflammation, the effects of exogenous cannabinoids are significantly reduced because of CB1R desensitization via GRK2/3, as function is recovered in the presence of the GRK2/3 inhibitor, Compound 101 (Cmp101). Inhibition of GABA release by presynaptic μ-opioid receptors in the vlPAG does not desensitize with persistent inflammation. Unexpectedly, while CB1R desensitization significantly reduces the inhibition produced by exogenous agonists, depolarization-induced suppression of inhibition protocols that promote 2-arachidonoylglycerol (2-AG) synthesis exhibit prolonged CB1R activation after inflammation. 2-AG tone is detected in slices from CFA-treated rats when GRK2/3 is blocked, suggesting an increase in 2-AG synthesis after persistent inflammation. Inhibiting 2-AG degradation with the monoacylglycerol lipase (MAGL) inhibitor JZL184 during inflammation results in the desensitization of CB1Rs by endocannabinoids that is reversed with Cmp101. Collectively, these data indicate that persistent inflammation primes CB1Rs for desensitization, and MAGL degradation of 2-AG protects CB1Rs from desensitization in inflamed rats. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapeutics targeting MAGL and CB1Rs.SIGNIFICANCE STATEMENT Presynaptic G-protein-coupled receptors are resistant to desensitization. Here we find that persistent inflammation increases endocannabinoid levels, priming presynaptic cannabinoid 1 receptors for desensitization on subsequent addition of exogenous agonists. Despite the reduced efficacy of exogenous agonists, endocannabinoids have prolonged efficacy after persistent inflammation. Endocannabinoids readily induce cannabinoid 1 receptor desensitization if their degradation is blocked, indicating that endocannabinoid concentrations are maintained at subdesensitizing levels and that degradation is critical for maintaining endocannabinoid regulation of presynaptic GABA release in the ventrolateral periaqueductal gray during inflammatory states. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapies.

Anti-nociceptive potential of an isatin-derived dual fatty acid amide hydrolase-monoacylglycerol lipase inhibitor

BACKGROUND

Recently, we have reported an isatin-derived carbohydrazone, 5-chloro-N'-(6-chloro-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (SIH 3) as dual nanomolar FAAH (fatty acid amide hydrolase)-MAGL (monoacylglycerol lipase) inhibitor with good CNS penetration and neuroprotective activity profile. In this study, we further investigated the pharmacological profile of compound SIH 3 in the neuropathic pain model along with acute toxicity and ex vivo studies.

METHODS

Chronic constrictive injury (CCI) was used to induce neuropathic pain in male Sprague-Dawley rats and the anti-nociceptive activity of the compound SIH 3 was investigated at 25, 50, and 100 mg/kg ip. Subsequently, locomotor activity was measured by rotarod and actophotometer experiments. The acute oral toxicity of the compound was assessed as per the OECD guidelines 423.

RESULTS

Compound SIH 3 showed significant anti-nociceptive activity in the CCI-induced neuropathic pain model without altering the locomotor activity. Furthermore, compound SIH 3 showed an excellent safety profile (up to 2000 mg/kg, po) in the acute oral toxicity study and was also non-hepatotoxic. Further, ex vivo studies revealed that the compound SIH 3 produces a significant antioxidant effect in oxidative stress induced by CCI.

CONCLUSION

Our findings suggest that the investigated compound SIH 3 has the potential to be developed as an anti-nociceptive agent.

Inhibiting degradation of 2-arachidonoylglycerol as a therapeutic strategy for neurodegenerative diseases

Endocannabinoids are endogenous lipid signaling mediators that participate in a variety of physiological and pathological processes. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and is a full agonist of G-protein-coupled cannabinoid receptors (CB1R and CB2R), which are targets of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive ingredient in cannabis. While 2-AG has been well recognized as a retrograde messenger modulating synaptic transmission and plasticity at both inhibitory GABAergic and excitatory glutamatergic synapses in the brain, growing evidence suggests that 2-AG also functions as an endogenous terminator of neuroinflammation in response to harmful insults, thus maintaining brain homeostasis. Monoacylglycerol lipase (MAGL) is the key enzyme that degrades 2-AG in the brain. The immediate metabolite of 2-AG is arachidonic acid (AA), a precursor of prostaglandins (PGs) and leukotrienes. Several lines of evidence indicate that pharmacological or genetic inactivation of MAGL, which boosts 2-AG levels and reduces its hydrolytic metabolites, resolves neuroinflammation, mitigates neuropathology, and improves synaptic and cognitive functions in animal models of neurodegenerative diseases, including Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and traumatic brain injury (TBI)-induced neurodegenerative disease. Thus, it has been proposed that MAGL is a potential therapeutic target for treatment of neurodegenerative diseases. As the main enzyme hydrolyzing 2-AG, several MAGL inhibitors have been identified and developed. However, our understanding of the mechanisms by which inactivation of MAGL produces neuroprotective effects in neurodegenerative diseases remains limited. A recent finding that inhibition of 2-AG metabolism in astrocytes, but not in neurons, protects the brain from TBI-induced neuropathology might shed some light on this unsolved issue. This review provides an overview of MAGL as a potential therapeutic target for neurodegenerative diseases and discusses possible mechanisms underlying the neuroprotective effects of restraining degradation of 2-AG in the brain.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A potent and selective inhibitor for the modulation of MAGL activity in the neurovasculature

Chronic inflammation and blood–brain barrier dysfunction are key pathological hallmarks of neurological disorders such as multiple sclerosis, Alzheimer’s disease and Parkinson’s disease. Major drivers of these pathologies include pro-inflammatory stimuli such as prostaglandins, which are produced in the central nervous system by the oxidation of arachidonic acid in a reaction catalyzed by the cyclooxygenases COX1 and COX2. Monoacylglycerol lipase hydrolyzes the endocannabinoid signaling lipid 2-arachidonyl glycerol, enhancing local pools of arachidonic acid in the brain and leading to cyclooxygenase-mediated prostaglandin production and neuroinflammation. Monoacylglycerol lipase inhibitors were recently shown to act as effective anti-inflammatory modulators, increasing 2-arachidonyl glycerol levels while reducing levels of arachidonic acid and prostaglandins, including PGE₂ and PGD₂. In this study, we characterized a novel, highly selective, potent and reversible monoacylglycerol lipase inhibitor (MAGLi 432) in a mouse model of lipopolysaccharide-induced blood–brain barrier permeability and in both human and mouse cells of the neurovascular unit: brain microvascular endothelial cells, pericytes and astrocytes. We confirmed the expression of monoacylglycerol lipase in specific neurovascular unit cells in vitro, with pericytes showing the highest expression level and activity. However, MAGLi 432 did not ameliorate lipopolysaccharide-induced blood–brain barrier permeability in vivo or reduce the production of pro-inflammatory cytokines in the brain. Our data confirm monoacylglycerol lipase expression in mouse and human cells of the neurovascular unit and provide the basis for further cell-specific analysis of MAGLi 432 in the context of blood–brain barrier dysfunction caused by inflammatory insults.

Identification of Endocannabinoid Predictors of Treatment Outcomes in Major Depressive Disorder: A Secondary Analysis of the First Canadian Biomarker Integration Network in Depression (CAN-BIND 1) Study

INTRODUCTION

An increasing number of studies are examining the link between the endocannabinoidome and major depressive disorder (MDD). We conducted an exploratory analysis of this system to identify potential markers of treatment outcomes.

METHODS

The dataset of the Canadian Biomarker Integration Network in Depression-1 study, consisting of 180 patients with MDD treated for eight weeks with escitalopram followed by eight weeks with escitalopram alone or augmented with aripiprazole was analyzed. Association between response Montgomery-Asberg Depression Rating Scale (MADRS; score reduction≥50%) or remission (MADRS score≤10) at weeks 8 and 16 and single nucleotide polymorphisms (SNPs), methylation, and mRNA levels of 33 endocannabinoid markers were examined. A standard genome-wide association studies protocol was used for identifying SNPs, and logistic regression was used to assess methylation and mRNA levels.

RESULTS

Lower methylation of CpG islands of the diacylglycerol lipase alpha gene (DAGLA) was associated with non-remission at week 16 (DAGLA; OR=0.337, p<0.003, q=0.050). Methylation of DAGLA was correlated with improvement in Clinical Global Impression (p=0.026), Quick Inventory of Depressive Symptomatology (p=0.010), and Snaith-Hamilton Pleasure scales (p=0.028). We did not find any association between SNPs or mRNA levels and treatment outcomes.

DISCUSSION

Methylation of DAGLA is a promising candidate as a marker of treatment outcomes for MDD and needs to be explored further.

Imaging the endocannabinoid signaling system

The endocannabinoid (eCB) system is one of the most widespread neuromodulatory systems in the mammalian brain, with a multifaceted role in functions ranging from development to synaptic plasticity. Endocannabinoids are synthesized on demand from membrane lipid precursors, and act primarily on a single G-protein coupled receptor type, CB1, to carry out diverse functions. Despite the importance of the eCB system both in healthy brain function and in disease, critically important details of eCB signaling remained unknown. How eCBs are released from the membrane, how these lipid molecules are transported between cells, and how the distribution of their receptors is controlled, remained elusive. Recent advances in optical microscopy methods and biosensor engineering may open up new avenues for studying eCB signaling. We summarize applications of superresolution microscopy using single molecule localization to reveal distinct patterns of nanoscale CB1 distribution in neuronal axons and axon terminals. We review single particle tracking studies using quantum dots that allowed visualizing CB1 trajectories. We highlight the recent development of fluorescent eCB biosensors, that revealed spatiotemporally specific eCB release in live cells and live animals. Finally, we discuss future directions where method development may help to advance a precise understanding of eCB signaling.

Potentiation of microglial endocannabinoid signaling alleviates neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) isaprogressive neurodegenerative disorder characterized by chronic inflammation due to the presence of neurotoxic Aβ and tau proteins. Increased microglial activation and inflated immune response are the other factors to be considered in AD pathology. Microglial cells own biochemical machinery that synthesizes and release endocannabinoids. The exploitation of therapeutic actions of endocannabinoid system has newly emerged in the field of Alzheimer's disease. The activation of cannabinoid receptors/ cannabinoid system modulates inflammatory responses. This review assesses the association between the microglial endocannabinoid system and neuroinflammation in AD. The data supporting the anti-inflammatory role of pharmacological agents modulating cannabinoid system are also reviewed.

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.

Cannabinoids and Endocannabinoid System Changes in Intestinal Inflammation and Colorectal Cancer

Despite the multiple preventive measures and treatment options, colorectal cancer holds a significant place in the world's disease and mortality rates. The development of novel therapy is in critical need, and based on recent experimental data, cannabinoids could become excellent candidates. This review covered known experimental studies regarding the effects of cannabinoids on intestinal inflammation and colorectal cancer. In our opinion, because colorectal cancer is a heterogeneous disease with different genomic landscapes, the choice of cannabinoids for tumor prevention and treatment depends on the type of the disease, its etiology, driver mutations, and the expression levels of cannabinoid receptors. In this review, we describe the molecular changes of the endocannabinoid system in the pathologies of the large intestine, focusing on inflammation and cancer.

Mechanisms of endocannabinoid control of synaptic plasticity

The endogenous cannabinoid transmitter system regulates synaptic transmission throughout the nervous system. Unlike conventional transmitters, specific stimuli induce synthesis of endocannabinoids (eCBs) in the postsynaptic neuron, and these travel backwards to modulate presynaptic inputs. In doing so, eCBs can induce short-term changes in synaptic strength and longer-term plasticity. While this eCB regulation is near ubiquitous, it displays major regional and synapse specific variations with different synapse specific forms of short-versus long-term plasticity throughout the brain. These differences are due to the plethora of pre- and postsynaptic mechanisms which have been implicated in eCB signalling, the intricacies of which are only just being realised. In this review, we shall describe the current understanding and highlight new advances in this area, with a focus on the retrograde action of eCBs at CB1 receptors (CB₁Rs).

Endocannabinoids, cannabinoids and the regulation of anxiety

Cannabis has been used for hundreds of years, with its ability to dampen feelings of anxiety often reported as a primary reason for use. Only recently has the specific role cannabinoids play in anxiety been thoroughly investigated. Here we discuss the body of evidence describing how endocannabinoids and exogenous cannabinoids are capable of regulating the generation and termination of anxiety states. Disruption of the endogenous cannabinoid (eCB) system following genetic manipulation, pharmacological intervention or stress exposure reliably leads to the generation of an anxiety state. On the other hand, upregulation of eCB signaling is capable of alleviating anxiety-like behaviors in multiple paradigms. When considering exogenous cannabinoid administration, cannabinoid receptor 1 (CB1) agonists have a biphasic, dose-dependent effect on anxiety such that low doses are anxiolytic while high doses are anxiogenic, a phenomenon that is evident in both rodent models and humans. Translational studies investigating a loss of function mutation in the gene for fatty acid amide hydrolase, the enzyme responsible for metabolizing AEA, have also shown that AEA signaling regulates anxiety in humans. Taken together, evidence reviewed here has outlined a convincing argument for cannabinoids being powerful regulators of both the manifestation and amelioration of anxiety symptoms, and highlights the therapeutic potential of targeting the eCB system for the development of novel classes of anxiolytics. This article is part of the special issue on 'Cannabinoids'.

Targeting Endocannabinoid Signaling in the Lateral Habenula as an Intervention to Prevent Mental Illnesses Following Early Life Stress: A Perspective

Adverse events and childhood trauma increase the susceptibility towards developing psychiatric disorders (substance use disorder, anxiety, depression, etc.) in adulthood. Although there are treatment strategies that have utility in combating these psychiatric disorders, little attention is placed on how to therapeutically intervene in children exposed to early life stress (ELS) to prevent the development of later psychopathology. The lateral habenula (LHb) has been a topic of extensive investigation in mental health disorders due to its prominent role in emotion and mood regulation through modulation of brain reward and motivational neural circuits. Importantly, rodent models of ELS have been shown to promote LHb dysfunction. Moreover, one of the potential mechanisms contributing to LHb neuronal and synaptic dysfunction involves endocannabinoid (eCB) signaling, which has been observed to critically regulate emotion/mood and motivation. Many pre-clinical studies targeting eCB signaling suggest that this neuromodulatory system could be exploited as an intervention therapy to halt maladaptive processes that promote dysfunction in reward and motivational neural circuits involving the LHb. In this perspective article, we report what is currently known about the role of eCB signaling in LHb function and discuss our opinions on new research directions to determine whether the eCB system is a potentially attractive therapeutic intervention for the prevention and/or treatment of ELS-associated psychiatric illnesses.

Role of the Endocannabinoid System in the Adipose Tissue with Focus on Energy Metabolism

The endocannabinoid system is involved in a wide range of processes including the control of energy acquisition and expenditure. Endocannabinoids and their receptors are present in the central nervous system but also in peripheral tissues, notably the adipose tissues. The endocannabinoid system interacts with two main hormones regulating appetite, namely leptin and ghrelin. The inhibitory effect of the cannabinoid receptor 1 (CB₁) antagonist rimonabant on fat mass suggested that the endocannabinoid system can also have a peripheral action in addition to its effect on appetite reduction. Thus, several investigations have focused on the peripheral role of the endocannabinoid system in the regulation of metabolism. The white adipose tissue stores energy as triglycerides while the brown adipose tissue helps to dissipate energy as heat. The endocannabinoid system regulates several functions of the adipose tissues to favor energy accumulation. In this review we will describe the presence of the endocannabinoid system in the adipose tissue. We will survey the role of the endocannabinoid system in the regulation of white and brown adipose tissue metabolism and how the eCB system participates in obesity and metabolic diseases.

Putative Activation of the CB1 Cannabinoid Receptors Prevents Anxiety-Like Behavior, Oxidative Stress, and GABA Decrease in the Brain of Zebrafish Submitted to Acute Restraint Stress

Anxiety disorder is a well-recognized condition observed in subjects submitted to acute stress. Although the brain mechanisms underlying this disorder remain unclear, the available evidence indicates that oxidative stress and GABAergic dysfunction mediate the generation of stress-induced anxiety. Cannabinoids are known to be efficient modulators of behavior, given that the activation of the cannabinoid receptors type-1 (CB1 receptors) induces anxiolytic-like effects in animal models. In the present study, we aimed to describe the effects of the stimulation of the CB1 receptors on anxiety-like behavior, oxidative stress, and the GABA content of the brains of zebrafish submitted to acute restraint stress (ARS). The animals submitted to the ARS protocol presented evident anxiety-like behavior with increased lipid peroxidation in the brain tissue. The evaluation of the levels of GABA in the zebrafish telencephalon presented decreased levels of GABA in the ARS group in comparison with the control. Treatment with ACEA, a specific CB1 receptor agonist, prevented ARS-induced anxiety-like behavior and oxidative stress in the zebrafish brain. ACEA treatment also prevented a decrease in GABA in the telencephalon of the animals submitted to the ARS protocol. Overall, these preclinical data strongly suggest that the CB1 receptors represent a potential target for the development of the treatment of anxiety disorders elicited by acute stress.

Monoacylglycerol Lipase Knockdown Inhibits Cell Proliferation and Metastasis in Lung Adenocarcinoma

Abnormal metabolism is one of the hallmarks of cancer cells. Monoacylglycerol lipase (MGLL), a key enzyme in lipid metabolism, has emerged as an important regulator of tumor progression. In this study, we aimed to characterize the role of MGLL in the development of lung adenocarcinoma (LUAD). To this end, we used tissue microarrays to evaluate the expression of MGLL in LUAD tissue and assessed whether the levels of this protein are correlated with clinicopathological characteristics of LUAD. We found that the expression of MGLL is higher in LUAD samples than that in adjacent non-tumor tissues. In addition, elevated MGLL expression was found to be associated with advanced tumor progression and poor prognosis in LUAD patients. Functional studies further demonstrated that stable short hairpin RNA (shRNA)-mediated knockdown of MGLL inhibits tumor proliferation and metastasis, both in vitro and in vivo, and mechanistically, our data indicate that MGLL regulates Cyclin D1 and Cyclin B1 in LUAD cells. Moreover, we found that knockdown of MGLL suppresses the expression of matrix metalloproteinase 14 (MMP14) in A549 and H322 cells, and in clinical samples, expression of MMP14 is significantly correlated with MGLL expression. Taken together, our results indicate that MGLL plays an oncogenic role in LUAD progression and metastasis and may serve as a potential biomarker for disease prognosis and as a target for the development of personalized therapies.

An updated patent review of monoacylglycerol lipase (MAGL) inhibitors (2018-present)

INTRODUCTION

Monoacylglycerol lipase (MAGL) belongs to the endocannabinoid system and is responsible for the inactivation of endocannabinoid 2-arachidonoylglycerol. Importantly, it was found that MAGL degradation of lipids in cancer cells enhances the availability of free fatty acids for new cellular membrane formation and pro-oncogenic lipid modulators. The multifaceted role of MAGL has greatly stimulated the search for MAGL inhibitors, which could be effective to treat diseases, such as inflammation, neurodegeneration and cancer.

AREAS COVERED

This review covers patents published since 2018 up to now, concerning new MAGL inhibitors and their potential therapeutic applications.

EXPERT OPINION

In the years 2018-2020, several well-known chemical scaffolds of MAGL inhibitors have been further optimized and developed and some new chemical classes have also been identified as MAGL inhibitors. Moreover, an increasing number of scientific publications covering MAGL inhibitors is focused on MAGL-specific positron emission tomography (PET) ligands. The numerous efforts of pharmaceutical companies and academic research groups finalized to find new potent MAGL inhibitors confirm that this research area is rapidly growing. Nevertheless, most of the patented compounds still belong to the large group of irreversible MAGL inhibitors, highlighting that the development of reversible MAGL inhibitors is still an unmet pharmaceutical need.

Druggable Targets in Endocannabinoid Signaling

Cannabis and cannabinoid-based extracts have long been utilized for their perceived therapeutic value, and support for the legalization of cannabis for medicinal purposes continues to increase worldwide. Since the discovery of Δ⁹-tetrahydrocannabinol (THC) as the primary psychoactive component of cannabis over 50 years ago, substantial effort has been directed toward detection of endogenous mediators of cannabinoid activity. The discovery of anandamide and 2-arachidonoylglycerol as two endogenous lipid mediators of cannabinoid-like effects (endocannabinoids) has inspired exponential growth in our understanding of this essential pathway, as well as the pathological conditions that result from dysregulated endocannabinoid signaling. This review examines current knowledge of the endocannabinoid system including metabolic enzymes involved in biosynthesis and degradation and their receptors, and evaluates potential druggable targets for therapeutic intervention.

Neurobiology of cannabinoid receptor signaling

The endocannabinoid system (ECS) is a highly versatile signaling system within the nervous system. Despite its widespread localization, its functions within the context of distinct neural processes are very well discernable and specific. This is remarkable, and the question remains as to how such specificity is achieved. One key player in the ECS is the cannabinoid type 1 receptor (CB₁), a G protein-coupled receptor characterized by the complexity of its cell-specific expression, cellular and subcellular localization, and its adaptable regulation of intracellular signaling cascades. CB₁ receptors are involved in different synaptic and cellular plasticity processes and in the brain's bioenergetics in a context-specific manner. CB₂ receptors are also important in several processes in neurons, glial cells, and immune cells of the brain. As polymorphisms in ECS components, as well as external impacts such as stress and metabolic challenges, can both lead to dysregulated ECS activity and subsequently to possible neuropsychiatric disorders, pharmacological intervention targeting the ECS is a promising therapeutic approach. Understanding the neurobiology of cannabinoid receptor signaling in depth will aid optimal design of therapeutic interventions, minimizing unwanted side effects.
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Involvement of the Ventrolateral Periaqueductal Gray Matter-Central Medial Thalamic Nucleus-Basolateral Amygdala Pathway in Neuropathic Pain Regulation of Rats

The central medial nucleus (CM), a prominent cell group of the intralaminar nuclei (ILN) of the thalamus, and the ventrolateral periaqueductal gray matter (vlPAG) are two major components of the medial pain system. Whether vlPAG and CM are input sources of nociceptive information to the basolateral amygdala (BLA) and whether they are involved in neuropathic pain regulation remain unclear. Clarifying the hierarchical organization of these subcortical nuclei (vlPAG, CM, and BLA) can enhance our understanding on the neural circuits for pain regulation. Behavioral test results showed that a CM lesion made by kainic acid (KA) injection could effectively alleviate mechanical hyperalgesia 4, 6, and 8 days after spared nerve injury (SNI) surgery, with the symptoms returning after 10 days. Morphological studies revealed that: (1) the CM received afferents from vlPAG and sent efferents to BLA, indicating that an indirect vlPAG–CM–BLA pathway exists; (2) such CM–BLA projections were primarily excitatory glutamatergic neurons as revealed by fluorescence in situ hybridization; (3) the fibers originated from the CM-formed close contacts with both excitatory and inhibitory neurons in the BLA; and (4) BLA-projecting CM neurons expressed Fos induced by SNI and formed close contacts with fibers from vlPAG, suggesting that the vlPAG–CM–BLA indirect pathway was activated in neuropathic pain conditions. Finally, the vlPAG–CM–BLA indirect pathway was further confirmed using anterograde and monosynaptic virus tracing investigation. In summary, our present results provide behavioral and morphological evidence that the indirect vlPAG–CM–BLA pathway might be a novel pain pathway involved in neuropathic pain regulation.

Cannabinoids in the descending pain modulatory circuit: Role in inflammation

The legalization of cannabis in some states has intensified interest in the potential for cannabis and its constituents to lead to novel therapeutics for pain. Our understanding of the cellular mechanisms underlying cannabinoid actions in the brain have lagged behind opioids; however, the current opioid epidemic has also increased attention on the use of cannabinoids as alternatives to opioids for pain, especially chronic pain that requires long-term use. Endogenous cannabinoids are lipid signaling molecules that have complex roles in modulating neuronal function throughout the brain. In this review, we discuss cannabinoid functions in the descending pain modulatory pathway, a brain circuit that integrates cognitive and emotional processing of pain to modulate incoming sensory inputs. In addition, we highlight areas where further studies are necessary to understand cannabinoid regulation of descending pain modulation.

Endocannabinoid System Components as Potential Biomarkers in Psychiatry

The high heterogeneity of psychiatric disorders leads to a lack of diagnostic precision. Therefore, the search of biomarkers is a fundamental aspect in psychiatry to reach a more personalized medicine. The endocannabinoid system (ECS) has gained increasing interest due to its involvement in many different functional processes in the brain, including the regulation of emotions, motivation, and cognition. This article reviews the role of the main components of the ECS as biomarkers in certain psychiatric disorders. Studies carried out in rodents evaluating the effects of pharmacological and genetic manipulation of cannabinoid receptors or endocannabinoids (eCBs) degrading enzymes were included. Likewise, the ECS-related alterations occurring at the molecular level in animal models reproducing some behavioral and/or neuropathological aspects of psychiatric disorders were reviewed. Furthermore, clinical studies evaluating gene or protein alterations in post-mortem brain tissue or in vivo blood, plasma, and cerebrospinal fluid (CSF) samples were analyzed. Also, the results from neuroimaging studies using positron emission tomography (PET) or functional magnetic resonance (fMRI) were included. This review shows the close involvement of cannabinoid receptor 1 (CB1r) in stress regulation and the development of mood disorders [anxiety, depression, bipolar disorder (BD)], in post-traumatic stress disorder (PTSD), as well as in the etiopathogenesis of schizophrenia, attention deficit hyperactivity disorder (ADHD), or eating disorders (i.e. anorexia and bulimia nervosa). On the other hand, recent results reveal the potential therapeutic action of the endocannabinoid tone manipulation by inhibition of eCBs degrading enzymes, as well as by the modulation of cannabinoid receptor 2 (CB2r) activity on anxiolytic, antidepressive, or antipsychotic associated effects. Further clinical research studies are needed; however, current evidence suggests that the components of the ECS may become promising biomarkers in psychiatry to improve, at least in part, the diagnosis and pharmacological treatment of psychiatric disorders.

Life-long epigenetic programming of cortical architecture by maternal 'Western' diet during pregnancy

The evolution of human diets led to preferences toward polyunsaturated fatty acid (PUFA) content with 'Western' diets enriched in ω-6 PUFAs. Mounting evidence points to ω-6 PUFA excess limiting metabolic and cognitive processes that define longevity in humans. When chosen during pregnancy, ω-6 PUFA-enriched 'Western' diets can reprogram maternal bodily metabolism with maternal nutrient supply precipitating the body-wide imprinting of molecular and cellular adaptations at the level of long-range intercellular signaling networks in the unborn fetus. Even though unfavorable neurological outcomes are amongst the most common complications of intrauterine ω-6 PUFA excess, cellular underpinnings of life-long modifications to brain architecture remain unknown. Here, we show that nutritional ω-6 PUFA-derived endocannabinoids desensitize CB₁ cannabinoid receptors, thus inducing epigenetic repression of transcriptional regulatory networks controlling neuronal differentiation. We found that cortical neurons lose their positional identity and axonal selectivity when mouse fetuses are exposed to excess ω-6 PUFAs in utero. Conversion of ω-6 PUFAs into endocannabinoids disrupted the temporal precision of signaling at neuronal CB₁ cannabinoid receptors, chiefly deregulating Stat3-dependent transcriptional cascades otherwise required to execute neuronal differentiation programs. Global proteomics identified the immunoglobulin family of cell adhesion molecules (IgCAMs) as direct substrates, with DNA methylation and chromatin accessibility profiling uncovering epigenetic reprogramming at >1400 sites in neurons after prolonged cannabinoid exposure. We found anxiety and depression-like behavioral traits to manifest in adult offspring, which is consistent with genetic models of reduced IgCAM expression, to suggest causality for cortical wiring defects. Overall, our data uncover a regulatory mechanism whose disruption by maternal food choices could limit an offspring's brain function for life.

Cannabis Improves Obsessive-Compulsive Disorder-Case Report and Review of the Literature

Although several lines of evidence support the hypothesis of a dysregulation of serotoninergic neurotransmission in the pathophysiology of obsessive-compulsive disorder (OCD), there is also evidence for an involvement of other pathways such as the GABAergic, glutamatergic, and dopaminergic systems. Only recently, data obtained from a small number of animal studies alternatively suggested an involvement of the endocannabinoid system in the pathophysiology of OCD reporting beneficial effects in OCD-like behavior after use of substances that stimulate the endocannabinoid system. In humans, until today, only two case reports are available reporting successful treatment with dronabinol (tetrahydrocannabinol, THC), an agonist at central cannabinoid CB1 receptors, in patients with otherwise treatment refractory OCD. In addition, data obtained from a small open uncontrolled trial using the THC analogue nabilone suggest that the combination of nabilone plus exposure-based psychotherapy is more effective than each treatment alone. These reports are in line with data from a limited number of case studies and small controlled trials in patients with Tourette syndrome (TS), a chronic motor and vocal tic disorder often associated with comorbid obsessive compulsive behavior (OCB), reporting not only an improvement of tics, but also of comorbid OCB after use of different kinds of cannabis-based medicines including THC, cannabis extracts, and flowers. Here we present the case of a 22-year-old male patient, who suffered from severe OCD since childhood and significantly improved after treatment with medicinal cannabis with markedly reduced OCD and depression resulting in a considerable improvement of quality of life. In addition, we give a review of current literature on the effects of cannabinoids in animal models and patients with OCD and suggest a cannabinoid hypothesis of OCD.

Opioid and Endocannabinoid System in Orofacial Pain

Orofacial pain disorders are frequent in the general population and their pharmacological treatment is difficult and controversial. Therefore, the search for novel, safe and efficient analgesics is an important but still elusive goal for contemporary medicine. In the recent years, the antinociceptive potential of endocannabinoids and opioids has been emphasized. However, concerns for the safety of their use limit their clinical applications. the possibility of modulating the activity of endocannabinoids by regulation of their synthesis and/or degradation offers an innovative approach to the treatment of pain. A rat model of trigeminal pain, utilizing tongue jerks evoked by electrical tooth pulp stimulation during perfusion of the cerebral ventricles with various neurotransmitter solutions can be used in the pharmacological studies of nociception in the orofacial area. The aim of this review is to present the effects of pharmacological activity of opioids and endocannabinoids affecting the transmission of the sensory information from the orofacial area on the example of trigemino-hypoglossal reflex in rats.

Regulating membrane lipid levels at the synapse by small-molecule inhibitors of monoacylglycerol lipase: new developments in therapeutic and PET imaging applications

Monoacylglycerol lipase (MAGL) is a major endocannabinoid hydrolyzing enzyme and can be regulated to control endogenous lipid levels in the brain. This review highlights the pharmacological roles and in vivo PET imaging of MAGL in brain.

CB1 and LPA1 Receptors Relationship in the Mouse Central Nervous System

Neurolipids are a class of bioactive lipids that are produced locally through specific biosynthetic pathways in response to extracellular stimuli. Neurolipids are important endogenous regulators of neural cell proliferation, differentiation, oxidative stress, inflammation and apoptosis. Endocannabinoids (eCBs) and lysophosphatidic acid (LPA) are examples of this type of molecule and are involved in neuroprotection. The present study analyzes a possible relationship of the main receptor subtypes for both neurolipid systems that are present in the central nervous system, the CB₁ and LPA₁ receptors, by using brain slices from CB₁ KO mice and LPA₁-null mice. Receptor-mediated G protein activation and glycerophospholipid regulation of potential precursors of their endogenous neurotransmitters were measured by two different in vitro imaging techniques, functional autoradiography and imaging mass spectrometry (IMS), respectively. Possible crosstalk between CB₁ and LPA₁ receptors was identified in specific areas of the brain, such as the amygdala, where LPA₁ receptor activity is upregulated in CB₁ KO mice. More evidence of an interaction between both systems was that the CB₁-mediated activity was clearly increased in the prefrontal cortex and cerebellum of LPA₁-null mice. The eCB system was specifically over-activated in regions where LPA₁ has an important signaling role during embryonic development. The modifications on phospholipids (PLs) observed in these genetically modified mice by using the IMS technique indicated the regulation of some of the PL precursors of both LPA and eCBs in specific brain areas. For example, phosphatidylcholine (PC) (36:1) was detected as a potential LPA precursor, and phosphatidylethanolamine (PE) (40:6) and PE (p18:0/22:6) as potential eCB precursors. The absence of the main cerebral receptors for LPA or eCB systems is able to induce modulation on the other at the levels of both signaling and synthesis of endogenous neurotransmitters, indicating adaptive responses between both systems during prenatal and/or postnatal development.

Cognitive and neurobehavioral benefits of an enriched environment on young adult mice after chronic ethanol consumption during adolescence

Binge drinking (BD) is a common pattern of ethanol (EtOH) consumption by adolescents. The brain effects of the acute EtOH exposure are well-studied; however, the long-lasting cognitive and neurobehavioral consequences of BD during adolescence are only beginning to be elucidated. Environmental enrichment (EE) has long been known for its benefits on the brain and may serve as a potential supportive therapy following EtOH exposure. In this study, we hypothesized that EE may have potential benefits on the cognitive deficits associated with BD EtOH consumption. Four-week-old C57BL/6J male mice were exposed to EtOH following an intermittent 4-day drinking-in-the-dark procedure for 4 weeks. Then they were exposed to EE during EtOH withdrawal for 2 weeks followed by a behavioral battery of tests including novel object recognition, novel location, object-in-place, rotarod, beam walking balance, tail suspension, light-dark box and open field that were run during early adulthood. Young adult mice exposed to EE significantly recovered recognition, spatial and associative memory as well as motor coordination skills and balance that were significantly impaired after adolescent EtOH drinking with respect to controls. No significant permanent anxiety or depressive-like behaviors were observed. Taken together, an EE exerts positive effects on the long-term negative cognitive deficits as a result of EtOH consumption during adolescence.

Endocannabinoid and Muscarinic Signaling Crosstalk in the 3xTg-AD Mouse Model of Alzheimer's Disease

The endocannabinoid system, which modulates emotional learning and memory through CB1 receptors, has been found to be deregulated in Alzheimer's disease (AD). AD is characterized by a progressive decline in memory associated with selective impairment of cholinergic neurotransmission. The functional interplay of endocannabinoid and muscarinic signaling was analyzed in seven-month-old 3xTg-AD mice following the evaluation of learning and memory of an aversive stimulus. Neurochemical correlates were simultaneously studied with both receptor and functional autoradiography for CB1 and muscarinic receptors, and regulations at the cellular level were depicted by immunofluorescence. 3xTg-AD mice exhibited increased acquisition latencies and impaired memory retention compared to age-matched non-transgenic mice. Neurochemical analyses showed changes in CB1 receptor density and functional coupling of CB1 and muscarinic receptors to Gi/o proteins in several brain areas, highlighting that observed in the basolateral amygdala. The subchronic (seven days) stimulation of the endocannabinoid system following repeated WIN55,212-2 (1 mg/kg) or JZL184 (8 mg/kg) administration induced a CB1 receptor downregulation and CB1-mediated signaling desensitization, normalizing acquisition latencies to control levels. However, the observed modulation of cholinergic neurotransmission in limbic areas did not modify learning and memory outcomes. A CB1 receptor-mediated decrease of GABAergic tone in the basolateral amygdala may be controlling the limbic component of learning and memory in 3xTg-AD mice. CB1 receptor desensitization may be a plausible strategy to improve behavior alterations associated with genetic risk factors for developing AD.

The Endocannabinoid System: A New Treatment Target for Obsessive Compulsive Disorder?

Introduction: Obsessive-compulsive disorder (OCD) is a disabling illness that is associated with significant functional impairment. Although evidence-based pharmacotherapies exist, currently available medications are ineffective in some patients and may cause intolerable side effects in others. There is an urgent need for new treatments. Discussion: A growing body of basic and clinical research has showed that the endocannabinoid system (ECS) plays a role in anxiety, fear, and repetitive behaviors. At the same time, some patients with OCD who smoke cannabis anecdotally report that it relieves their symptoms and mitigates anxiety, and several case reports describe patients whose OCD symptoms improved after they were treated with cannabinoids. Taken together, these findings suggest that the ECS could be a potential target for novel medications for OCD. In this study, we review evidence from both animal and human studies that suggests that the ECS may play a role in OCD and related disorders. We also describe findings from studies in which cannabinoid drugs were shown to impact symptoms of these conditions. Conclusions: An emerging body of evidence suggests that the ECS plays a role in OCD symptoms and may be a target for the development of novel medications. Further exploration of this topic through well-designed human trials is warranted.