Anxiolytic effects in mice of a dual blocker of fatty acid amide hydrolase and transient receptor potential vanilloid type-1 channels

Therapeutic potential of transient receptor potential (TRP) channels in psychiatric disorders

Psychiatric disorders such as Bipolar disorder, Anxiety, Major depressive disorder, Schizophrenia, Attention-deficit/hyperactivity disorder, as well as neurological disorders such as Migraine, are linked by the evidence of altered calcium homeostasis. The disturbance of intra-cellular calcium homeostasis disrupts the activity of numerous ion channels including transient receptor potential (TRP) channels. TRP channel families comprise non-selective calcium-permeable channels that have been implicated in variety of physiological processes in the brain, as well as in the pathogenesis of psychiatric disorders. Through a comprehensive review of current research and experimentation, this investigation elucidates the role of TRP channels in psychiatric disorders. Furthermore, this review discusses about the exploration of epigenetics and TRP channels in psychiatric disorders.

Antinociceptive Effect of Dendrobii caulis in Paclitaxel-Induced Neuropathic Pain in Mice

Paclitaxel-induced neuropathic pain (PINP) is a serious adverse effect of chemotherapy. Dendrobii caulis (D. caulis) is a new food source used as herbal medicine in east Asia. We examined the antinociceptive effects of D. caulis extract on PINP and clarified the mechanism of action of transient receptor potential vanilloid 1 receptor (TRPV1) in the spinal cord. PINP was induced in male mice using multiple intraperitoneal injections of paclitaxel (total dose, 8 mg/kg). PINP was maintained from D10 to D21 when assessed for cold and mechanical allodynia. Oral administration of 300 and 500 mg/kg D. caulis relieved cold and mechanical allodynia. In addition, TRPV1 in the paclitaxel group showed increased gene and protein expression, whereas the D. caulis 300 and 500 mg/kg groups showed a significant decrease. Among various substances in D. caulis, vicenin-2 was quantified by high-performance liquid chromatography, and its administration (10 mg/kg, i.p.) showed antinociceptive effects similar to those of D. caulis 500 mg/kg. Administration of the TRPV1 antagonist capsazepine also showed antinociceptive effects similar to those of D. caulis, and D. caulis is thought to exhibit antinociceptive effects on PINP by modulating the spinal TRPV1.

Expression of the Transient Receptor Potential Vanilloid 1 ion channel in the supramammillary nucleus and the antidepressant effects of its antagonist AMG9810 in mice

The Transient Receptor Potential Vanilloid 1 (TRPV1) non-selective cation channel predominantly expressed in primary sensory neurons of the dorsal root and trigeminal ganglia mediates pain and neurogenic inflammation. TRPV1 mRNA and immunoreactivity were described in the central nervous system (CNS), but its precise expression pattern and function have not been clarified. Here we investigated Trpv1 mRNA expression in the mouse brain using ultrasensitive RNAScope in situ hybridization. The role of TRPV1 in anxiety, depression-like behaviors and memory functions was investigated by TRPV1-deficient mice and pharmacological antagonism by AMG9810. Trpv1 mRNA is selectively expressed in the supramammillary nucleus (SuM) co-localized with Vglut2 mRNA, but not with tyrosine hydroxylase immunopositivity demonstrating its presence in glutamatergic, but not dopaminergic neurons. TRPV1-deleted mice exhibited significantly reduced anxiety in the Light-Dark box and depression-like behaviors in the Forced Swim Test, but their performance in the Elevated Plus Maze as well as their spontaneous locomotor activity, memory and learning function in the Radial Arm Maze, Y-maze and Novel Object Recognition test were not different from WTs. AMG9810 (intraperitoneal injection 50 mg/kg) induced anti-depressant, but not anxiolytic effects. It is concluded that TRPV1 in the SuM might have functional relevance in mood regulation and TRPV1 antagonism could be a novel perspective for anti-depressant drugs.

Multiple Chemical Sensitivity: It's time to catch up to the science

Multiple chemical sensitivity (MCS) is a complex medical condition associated with low dose chemical exposures. MCS is characterized by diverse features and common comorbidities, including fibromyalgia, cough hypersensitivity, asthma, and migraine, and stress/anxiety, with which the syndrome shares numerous neurobiological processes and altered functioning within diverse brain regions. Predictive factors linked to MCS comprise genetic influences, gene-environment interactions, oxidative stress, systemic inflammation, cell dysfunction, and psychosocial influences. The development of MCS may be attributed to the sensitization of transient receptor potential (TRP) receptors, notably TRPV1 and TRPA1. Capsaicin inhalation challenge studies demonstrated that TRPV1 sensitization is manifested in MCS, and functional brain imaging studies revealed that TRPV1 and TRPA1 agonists promote brain-region specific neuronal variations. Unfortunately, MCS has often been inappropriately viewed as stemming exclusively from psychological disturbances, which has fostered patients being stigmatized and ostracized, and often being denied accommodation for their disability. Evidence-based education is essential to provide appropriate support and advocacy. Greater recognition of receptor-mediated biological mechanisms should be incorporated in laws, and regulation of environmental exposures.

TRPV1 modulation of contextual fear memory depends on stimulus intensity and endocannabinoid signalling in the dorsal hippocampus

The transient receptor potential vanilloid type-1 (TRPV1) channels have been implicated in the modulation of aversive responses. The endocannabinoid anandamide acts as an endogenous TRPV1 agonist, exerting opposite functions at TRPV1 and type-1 cannabinoid receptors (CB₁R). Here we tested the hypothesis that hippocampal TRPV1 modulates contextual fear memory retrieval and investigated the influence of the aversive stimulus intensity as well as the role of endocannabinoid signaling. Male C57BL/6J mice were tested for contextual fear memory after low-, moderate-, or high-intensity shock protocols. The selective TRPV1 blockers SB366791 (1-10 nmol) and 6-I-NC (2 nmol) were infused via intra-dorsal hippocampus before the retrieval test session. The local levels of endocannabinoids and Arc and Zif268 mRNAs, involved in synaptic plasticity and memory, were quantified. First, both TRPV1 blockers reduced memory retrieval in animals exposed to moderate or high (but not low) intensity training protocols. In the second series of results, the magnitude of the freezing responses positively correlated with the hippocampal anandamide levels; TRPV1 and CB₁R were found co-localized in this brain region; and the CB₁R antagonist, AM251, prevented the effects of SB366791. Thus, endocannabinoid signaling possibly mediates the effects of TRPV1 blockers. Finally, inhibition of memory retrieval by TRPV1 blockers increased Arc and Zif268 mRNAs and impaired fear memory reinstatement. In conclusion, the modulation of fear memories by dorsal hippocampal TRPV1 channels may depend on the aversive stimulus intensity and occur via anandamide/CB₁ signaling. Moreover, TRPV1 blockers promote Arc and Zif268 transcription, with subsequent attenuation of aversive memory reinstatement.

Endocannabinoid Metabolism and Transport as Drug Targets

The wide distribution of the endocannabinoid system (ECS) throughout the body and its pivotal pathophysiological role offer promising opportunities for the development of novel therapeutic drugs for treating several diseases. However, the need for strategies to circumvent the unwanted psychotropic and immunosuppressive effects associated with cannabinoid receptor agonism/antagonism has led to considerable research in the field of molecular alternatives, other than type-1 and type-2 (CB_1/2) receptors, as therapeutic targets to indirectly manipulate this pro-homeostatic system. In this context, the use of selective inhibitors of proteins involved in endocannabinoid (eCB) transport and metabolism allows for an increase or decrease of the levels of N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) in the sites where these major eCBs are indeed needed. This chapter will briefly review some preclinical and clinical evidence for the therapeutic potential of ECS pharmacological manipulation.

Dual effects of anandamide in the antiepileptic activity of diazepam in pentylenetetrazole-induced seizures in mice

The prototype endocannabinoid, anandamide activates both CB 1 and transient receptor potential vanilloid type 1 channels (TRPV1) receptor at different concentrations. At high concentrations, anandamide-mediated TRPV1 effects are opposite to its effects at low concentrations via CB 1 receptor. Thus, synaptic concentrations of anandamide govern the neuronal activity and consequently might affect the response of a drug. This study was undertaken to investigate the influence of high and low doses of anandamide on the anticonvulsant action of diazepam on the subcutaneous dose of pentylenetetrazole (PTZ) in Swiss mice weighing 20-25 g. Results revealed that intracerebroventricular administration of capsazepine (a TRPV1 antagonist: 1, 10, or 100 µg/mouse) and the low doses (10 µg/mouse) of anandamide, AM404 (anandamide transport inhibitor), or URB597 (fatty acid amide hydrolase inhibitor) augmented the anticonvulsant effect of diazepam. Conversely, higher dose of anandamide, AM404, URB597 (100 µg/mouse) as well as capsaicin (a TRPV1 agonist: 1, 10, or 100 µg/mouse) attenuated the protective effect of diazepam against PTZ-induced seizures. Thus, this study demonstrates that the effects of diazepam may be augmented by activating CB 1 receptors or dampened via TRPV1 receptors. The findings of the present study can be extrapolated to understand the use of TRPV1 blockers alone or in combination of benzodiazepines in the treatment of benzodiazepines-refractory status epilepticus, a condition associated with maladaptive trafficking of synaptic gamma-aminobutyric acid and glutamate receptors. However, potential clinical applications are needed to further support such preclinical studies.

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

BACKGROUND

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

AIMS

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

METHODS

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

OUTCOMES

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

CONCLUSIONS

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

The Enteric Glia and Its Modulation by the Endocannabinoid System, a New Target for Cannabinoid-Based Nutraceuticals?

The enteric nervous system (ENS) is a part of the autonomic nervous system that intrinsically innervates the gastrointestinal (GI) tract. Whereas enteric neurons have been deeply studied, the enteric glial cells (EGCs) have received less attention. However, these are immune-competent cells that contribute to the maintenance of the GI tract homeostasis through supporting epithelial integrity, providing neuroprotection, and influencing the GI motor function and sensation. The endogenous cannabinoid system (ECS) includes endogenous classical cannabinoids (anandamide, 2-arachidonoylglycerol), cannabinoid-like ligands (oleoylethanolamide (OEA) and palmitoylethanolamide (PEA)), enzymes involved in their metabolism (FAAH, MAGL, COX-2) and classical (CB1 and CB2) and non-classical (TRPV1, GPR55, PPAR) receptors. The ECS participates in many processes crucial for the proper functioning of the GI tract, in which the EGCs are involved. Thus, the modulation of the EGCs through the ECS might be beneficial to treat some dysfunctions of the GI tract. This review explores the role of EGCs and ECS on the GI tract functions and dysfunctions, and the current knowledge about how EGCs may be modulated by the ECS components, as possible new targets for cannabinoids and cannabinoid-like molecules, particularly those with potential nutraceutical use.

Roles of the Cannabinoid System in the Basal Ganglia in Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease usually caused by neuroinflammation, oxidative stress and other etiologies. Recent studies have found that the cannabinoid system present in the basal ganglia has a strong influence on the progression of PD. Altering the cannabinoid receptor activation status by modulating endogenous cannabinoid (eCB) levels can exert an anti-movement disorder effect. Therefore, the development of drugs that modulate the endocannabinoid system may be a novel strategy for the treatment of PD. However, eCB regulation is complex, with diverse cannabinoid receptor functions and the presence of dopaminergic, glutamatergic, and γ-aminobutyric signals interacting with cannabinoid signaling in the basal ganglia region. Therefore, the study of eCB is challenging. Here, we have described the function of the cannabinoid system in the basal ganglia and its association with PD in three parts (eCBs, cannabinoid receptors, and factors regulating the cannabinoid metabolism) and summarized the mechanisms of action related to the cannabinoid analogs currently aimed at treating PD. The shortcomings identified from previous studies and the directions that should be explored in the future will provide insights into new approaches and ideas for the future development of cannabinoid-based drugs and the treatment of PD.

TRPV1 blockers as potential new treatments for psychiatric disorders

The transient receptor potential vanilloid-1 channel (TRPV1) is responsible for decoding physical and chemical stimuli. TRPV1 is activated by capsaicin (a compound from chili peppers), heat (above 43°C) and acid environment, playing a major role in pain, inflammation and body temperature. Molecular and histological studies have suggested TRPV1 expression in specific brain regions, where it can be activated primarily by the endocannabinoid anandamide, fostering studies on its potential role in psychiatric disorders. TRPV1 blockers are effective in various animal models predictive of anxiolytic and antipanic activities, in addition to reducing conditioned fear. In models of antidepressant activity, these compounds reduce behavioral despair and promote active stress-coping behavior. TRPV1 blockers also reduce the effects of certain drugs of abuse and revert behavioral changes in animal models of neurodevelopmental disorders. The main limiting factor in developing TRPV1 blockers as therapeutic agents concerns their effects on body temperature, particularly hyperthermia. New compounds, which block specific states of the channel, could represent an alternative. Moreover, compounds blocking both TRPV1 and the anandamide-hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), termed dual TRPV1/FAAH blockers, have been investigated with promising results. Overall, preclinical studies yield favorable results with TRPV1 blockers in animal models of psychiatric disorders.

Polypharmacological Approaches for CNS Diseases: Focus on Endocannabinoid Degradation Inhibition

Polypharmacology breaks up the classical paradigm of “one-drug, one target, one disease” electing multitarget compounds as potential therapeutic tools suitable for the treatment of complex diseases, such as metabolic syndrome, psychiatric or degenerative central nervous system (CNS) disorders, and cancer. These diseases often require a combination therapy which may result in positive but also negative synergistic effects. The endocannabinoid system (ECS) is emerging as a particularly attractive therapeutic target in CNS disorders and neurodegenerative diseases including Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), stroke, traumatic brain injury (TBI), pain, and epilepsy. ECS is an organized neuromodulatory network, composed by endogenous cannabinoids, cannabinoid receptors type 1 and type 2 (CB₁ and CB₂), and the main catabolic enzymes involved in the endocannabinoid inactivation such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The multiple connections of the ECS with other signaling pathways in the CNS allows the consideration of the ECS as an optimal source of inspiration in the development of innovative polypharmacological compounds. In this review, we focused our attention on the reported polypharmacological examples in which FAAH and MAGL inhibitors are involved.

Parkinson's disease related alterations in cannabinoid transmission

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic (DAergic) neurons of the substantia nigra pars compacta (SNc) by neurodegeneration. Recent findings in animal models of PD propose tonic inhibition of the remaining DA neurons through GABA release from reactive glial cells. Movement dysfunctions could be ameliorated by promotion of activity in dormant DA cells. The endocannabinoid system (ECS) is extensively present in basal ganglia (BG) and is known as an indirect modulator of DAergic neurotransmission, thus drugs designed to target this system have shown promising therapeutic potential in PD patients. Interestingly, down/up-regulation of cannabinoid receptors (CBRs) varies across the different stages of PD, suggesting that some of the motor/ non-motor deficits may be related to changes in CBRs. Determination of the profile of changes of these receptors across the different stages of PD as well as their neural distribution within the BG could improve understanding of PD and identify pathways important in disease pathobiology. In this review, we focus on temporal and spatial alterations of CBRs during PD in the BG. At present, as inconclusive, but suggestive results have been obtained, future investigations should be conducted to extend preclinical studies examining CBRs changes within each stage in controlled clinical trials in order to determine the potential of targeting CBRs in management of PD.

Spontaneous and Naloxone-Precipitated Withdrawal Behaviors From Chronic Opiates are Accompanied by Changes in N-Oleoylglycine and N-Oleoylalanine Levels in the Brain and Ameliorated by Treatment With These Mediators

Rationale: The endocannabinoidome mediators, N-Oleoylglycine (OlGly) and N-Oleoylalanine (OlAla), have been shown to reduce acute naloxone-precipitated morphine withdrawal affective and somatic responses.

Objectives: To determine the role and mechanism of action of OlGly and OlAla in withdrawal responses from chronic exposure to opiates in male Sprague-Dawley rats.

Methods: Opiate withdrawal was produced: 1) spontaneously 24 h following chronic exposure to escalating doses of morphine over 14 days (Experiments 1 and 2) and steady-state exposure to heroin by minipumps for 12 days (Experiment 3), 2) by naloxone injection during steady-state heroin exposure (Experiment 4), 3) by naloxone injection during operant heroin self-administration (Experiment 5).

Results: In Experiment 1, spontaneous morphine withdrawal produced somatic withdrawal reactions. The behavioral withdrawal reactions were accompanied by suppressed endogenous levels of OlGly in the nucleus accumbens, amygdala, and prefrontal cortex, N-Arachidonylglycerol and OlAla in the amygdala, 2-arachidonoylglycerol in the nucleus accumbens, amygdala and interoceptive insular cortex, and by changes in colonic microbiota composition. In Experiment 2, treatment with OlAla, but not OlGly, reduced spontaneous morphine withdrawal responses. In Experiment 3, OlAla attenuated spontaneous steady-state heroin withdrawal responses at both 5 and 20 mg/kg; OlGly only reduced withdrawal responses at the higher dose of 20 mg/kg. Experiment 4 demonstrated that naloxone-precipitated heroin withdrawal from steady-state exposure to heroin (7 mg/kg/day for 12 days) is accompanied by tissue-specific changes in brain or gut endocannabinoidome mediator, including OlGly and OlAla, levels and colonic microbiota composition, and that OlAla (5 mg/kg) attenuated behavioural withdrawal reactions, while also reversing some of the changes in brain and gut endocannabinoidome and gut microbiota induced by naloxone. Experiment 5 demonstrated that although OlAla (5 mg/kg) did not interfere with operant heroin self-administration on its own, it blocked naloxone-precipitated elevation of heroin self-administration behavior.

Conclusion: These results suggest that OlAla and OlGly are two endogenous mediators whose brain concentrations respond to chronic opiate treatment and withdrawal concomitantly with changes in colon microbiota composition, and that OlAla may be more effective than OlGly in suppressing chronic opiate withdrawal responses.

Selective inhibition of monoacylglycerol lipase is associated with passive coping behavior and attenuation of stress-induced dopamine release in the medial prefrontal cortex

The endocannabinoid system is involved in the regulation of the stress response, but the relative contribution of N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) and their mechanisms have to be elucidated. In this study, we compared the effects of the pharmacological inhibition of the two major endocannabinoid-degrading enzymes [fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) for AEA and 2-AG, respectively] on stress-coping [forced swim test (FST) and tail suspension test (TST)] and anxiety-like [elevated-plus maze (EPM) and light-dark test (LDT)] behaviors in wild-type and FAAH knockout mice. In vivo microdialysis estimated the effects of FAAH and MAGL inhibition on dopamine (DA) and serotonin (5-HT) levels in the medial prefrontal cortex (mPFC) during an FST. Mice were treated with PF-3845 (FAAH inhibitor), JZL184 (MAGL inhibitor), JZL195 (dual FAAH/MAGL inhibitor) or vehicle. Our data showed that PF-3845 increased latency to immobility and decreased total immobility time in FST, but no effects were observed in TST compared with vehicle-treated wild-type mice. By contrast, JZL184 decreased latency and increased immobility in TST and FST. JZL195 in wild-type mice and JZL184 in FAAH knockout mice reproduced the same passive coping behaviors as JZL184 in wild-type mice in TST and FST. In the microdialysis experiment, FST was associated with increased DA and 5-HT levels in the mPFC. However, JZL184-treated wild-type mice displayed a significant attenuation of forced swim stress-induced DA release compared with vehicle-treated wild-type mice and PF-3845-treated wild-type mice. Finally, FAAH and/or MAGL inhibitors induced robust and consistent anxiolytic-like effects in EPM and LDT. These results suggested differences between FAAH and MAGL inhibition in stress-coping behaviors. Notably, MAGL inhibition induced a consistent avoidant coping behavior and attenuated the stress-induced mPFC DA response in FST. However, more investigation is needed to elucidate the functional association between DA and 2-AG signaling pathways, and the molecular mechanism in the regulation of passive coping strategies during inescapable stress.

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FAAH and/or MAGL inhibition induce opposite changes in stress-coping behaviors.

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MAGL inhibition increases passive stress-coping behaviors in mice.

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Passive stress-coping behaviors are regulated by 2-AG rather than AEA signaling.

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MAGL inhibition attenuates mPFC dopamine increase in the forced swim test.

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FAAH and/or MAGL inhibitors are associated with anxiolytic-like effects.

Potential application of endocannabinoid system agents in neuropsychiatric and neurodegenerative diseases-focusing on FAAH/MAGL inhibitors

The endocannabinoid system (ECS) has received extensive attention for its neuroprotective effect on the brain. This system comprises endocannabinoids, endocannabinoid receptors, and the corresponding ligands and proteins. The molecular players involved in their regulation and metabolism are potential therapeutic targets for neuropsychiatric diseases including anxiety, depression and neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). The inhibitors of two endocannabinoid hydrolases, i.e., fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), have the capacity to increase the level of endocannabinoids indirectly, causing fewer side effects than those associated with direct supplementation of cannabinoids. Their antidepressant and anxiolytic mechanisms are considered to modulate the hypothalamic-pituitary-adrenal axis and regulate synaptic and neural plasticity. In terms of AD/PD, treatment with FAAH/MAGL inhibitors leads to reduction in amyloid β-protein deposition and inhibition of the death of dopamine neurons, which are commonly accepted to underlie the pathogenesis of AD and PD, respectively. Inflammation as the cause of depression/anxiety and PD/AD is also the target of FAAH/MAGL inhibitors. In this review, we summarize the application and involvement of FAAH/MAGL inhibitors in related neurological diseases. Focus on the latest research progress using FAAH/MAGL inhibitors is expected to facilitate the development of novel approaches with therapeutic potential.

Endocannabinoid system alterations in Alzheimer's disease: A systematic review of human studies

Studies investigating alterations of the endocannabinoid system (ECS) in Alzheimer's disease (AD) in humans have reported inconsistent findings so far. We performed a systematic review of studies examining alterations of the ECS specifically within humans with AD or mild cognitive impairment (MCI), including neuroimaging studies, studies of serum and cerebrospinal fluid biomarkers, and post-mortem studies. We attempted to identify reported changes in the expression and activity of: cannabinoid receptors 1 and 2; anandamide (AEA); 2-arachidonoylglycerol (2-AG); monoacylglycerol lipase (MAGL); fatty acid amide hydrolase (FAAH); and transient receptor potential cation channel V1 (TRPV1). Twenty-two studies were identified for inclusion. Mixed findings were reported for most aspects of the ECS in AD, making it difficult to identify a particular profile of ECS alterations characterising AD. The included studies tended to be small, methodologically heterogeneous, and frequently did not control for important potential confounders, such as pathological progression of AD. Eight studies correlated ECS alterations with neuropsychometric performance measures, though studies infrequently examined behavioural and neuropsychiatric correlates. PROSPERO database identifier: CRD42018096249.

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

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

The endocannabinoidome as a substrate for noneuphoric phytocannabinoid action and gut microbiome dysfunction in neuropsychiatric disorders

The endocannabinoid (eCB) system encompasses the eCBs anandamide and 2-arachidonoylglycerol, their anabolic/catabolic enzymes, and the cannabinoid CB1 and CB2 receptors. Its expansion to include several eCB-like lipid mediators, their metabolic enzymes, and their molecular targets, forms the endocannabinoidome (eCBome). This complex signaling system is deeply involved in the onset, progress, and symptoms of major neuropsychiatric disorders and provides a substrate for future therapeutic drugs against these diseases. Such drugs may include not only THC, the major psychotropic component of cannabis, but also other, noneuphoric plant cannabinoids. These compounds, unlike THC, possess a wide therapeutic window, possibly due to their capability of hitting several eCBome and non-eCBome receptors. This is particularly true for cannabidiol, which is one of the most studied cannabinoids and shows promise for the treatment of a wide range of mental and mood disorders. The eCBome plays a role also in the microbiota-gut-brain axis, which is emerging as an important actor in the control of affective and cognitive functions and in their pathological alterations.
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Anticonvulsive Properties of Cannabidiol in a Model of Generalized Seizure Are Transient Receptor Potential Vanilloid 1 Dependent

Introduction: Highly purified cannabidiol (CBD) (approved as Epidiolex^® in the United States) has demonstrated efficacy with an acceptable safety profile in patients with Lennox–Gastaut or Dravet syndrome in four randomized controlled trials. CBD possesses affinity for many target classes with functional effects relevant to the pathophysiology of many disease types, including epilepsy. Although the mechanism of action of CBD underlying the reduction of seizures in humans is unknown, transient receptor potential vanilloid 1 (TRPV1) represents a plausible target because (1) CBD activates and then desensitizes TRPV1, (2) TRPV1 is overexpressed in models of temporal lobe epilepsy and patients with epilepsy, (3) and TRPV1 modulates neuronal excitability.

Methods: To investigate a potential role of TRPV1 in the anticonvulsive effects of CBD, the effect of CBD on seizure threshold was assessed using a mouse maximal electroshock threshold model of generalized seizure in TRPV1 knockout and wildtype mice. The dose dependence of the CBD effect was determined and compared with that of the positive comparator diazepam and vehicle.

Results: At 50 and 100 mg/kg, CBD significantly (p<0.0001) increased seizure threshold in wildtype mice compared with TRPV1 knockout and vehicle controls. This effect was observed only at 100 mg/kg in TRPV1 knockout mice compared with knockout vehicle mice, in which gene deletion partially attenuated the CBD-increased seizure threshold. The effect of high-dose CBD in wildtype mice was nevertheless significantly different from vehicle-treated TRPV1 knockout mice (p<0.0001). Bioanalysis confirmed that genotype-specific differential brain exposure to CBD was not responsible for the observed effect on seizure threshold.

Conclusion: These data strongly implicate TRPV1 in the potential mechanisms of action for the anticonvulsive effects of CBD. The partial inhibition of the anticonvulsive effect of high-dose CBD in TRPV1 knockout mice may indicate the involvement of targets other than TRPV1. Further characterization of TRPV1 in the anticonvulsive effect of CBD in validated models of seizure is warranted, as is pharmacological investigation of the molecular interaction between CBD and TRPV1.

Blockade of the endovanilloid receptor, TRPV1, and of the endocannabinoid enzyme, FAAH, within the nucleus accumbens shell elicits anxiolytic-like effects in male rats

RATIONALE

The functional role of the endocannabinoid system (ECS) and Transient Receptor Potential Vanilloid type-1 (TRPV1) within the Nucleus Accumbens shell (NAc shell) remains unknown. Preclinical studies in rodents have reported that the ECS modulates emotional responses such as anxiety. The NAc shell has a high density of synaptically co-localized cannabinoid receptor type-1 (CB1R) and TRPV1, suggesting a potential involvement in the modulation of anxiety.

OBJECTIVES

The present study aims to establish the role of ECS-TRPV1 interactions within the NAc shell and its effects on anxiety. It is hypothesized that the neurochemical regulation elicited by ECS within the NAc shell mediates anxiety-like behaviors in rodents.

METHODS

In this study, male Sprague Dawley rats were implanted with bilateral brain cannula targeting the NAc shell. Following recovery from surgery, animals received microinfusion pretreatments (0, 0.125, 0.5 nmol/0.4 μl) of N-arachidonoyl-serotonin (AA-5-HT), a dual blocker of the endocannabinoid-inactivating enzyme, fatty acid amide hydrolase (FAAH) and a TRPV1 antagonist in the NAc shell. Following treatment, animals were tested in an elevated plus maze (EPM) paradigm for a period of 5 minutes. At the end of the experiment, animals were sacrificed and their brains collected for histological and biochemical analysis.

RESULTS

Results showed that animals treated with AA-5-HT in a dose dependent manner spent significantly more time in the open arms than vehicle-treated animals. In addition, AA-5-HT administration induced a significant downregulation of CB1R expression in the NAc shell.

CONCLUSIONS

The present findings suggest that the ECS within the NAc shell modulates anxiety-like behaviors via FAAH and CB1R activity.

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.

Early life stress and development of the endocannabinoid system: A bidirectional process in programming future coping

The endocannabinoid system (ECS) critically regulates stress responsivity and emotional behavior throughout development. It regulates anxiety-like behaviors in humans and animal models. In addition, it is sensitive to early life stress at the gene expression level in a sex-dependent and region-dependent manner, and these changes are already evident in the adolescent brain. The ECS modulates the neuroendocrine and behavioral effects of stress, and is also capable of being affected by stress exposure itself. Early life stress interferes with the development of corticolimbic circuits, a major location of endocannabinoid receptors, and increases vulnerability to adult psychopathology. Early life stress alters the ontogeny of the ECS, resulting in a sustained deficit in its function, particularly within the hippocampus. Specifically, exposure to early stress results in bidirectional changes in anandamide and 2-AG tissue levels within the amygdala and hippocampus and reduces hippocampal endocannabinoid function at puberty. CB1 receptor densities across all brain regions are downregulated later in life following exposure to early life stress. Manipulations affecting the glucocorticoid and the endocannabinoid systems persistently adjust individual emotional responses and synaptic plasticity. This review aims to show the bidirectional trajectories of endocannabinoid modulation of emotionality in reaction to early life stress.

Cell-Type- and Endocannabinoid-Specific Synapse Connectivity in the Adult Nucleus Accumbens Core

The nucleus accumbens (NAc) is a mesocorticolimbic structure that integrates cognitive, emotional and motor functions. Although its role in psychiatric disorders is widely acknowledged, the understanding of its circuitry is not complete. Here, we combined optogenetic and whole-cell recordings to draw a functional portrait of excitatory disambiguated synapses onto D1 and D2 medium spiny neurons (MSNs) in the adult male mouse NAc core. Comparing synaptic properties of ventral hippocampus (vHipp), basolateral amygdala (BLA) and prefrontal cortex (PFC) inputs revealed a hierarchy of synaptic inputs that depends on the identity of the postsynaptic target MSN. Thus, the BLA is the dominant excitatory pathway onto D1 MSNs (BLA > PFC = vHipp) while PFC inputs dominate D2 MSNs (PFC > vHipp > BLA). We also tested the hypothesis that endocannabinoids endow excitatory circuits with pathway- and cell-specific plasticity. Thus, whereas CB1 receptors (CB1R) uniformly depress excitatory pathways regardless of MSNs identity, TRPV1 receptors (TRPV1R) bidirectionally control inputs onto the NAc core in a pathway-specific manner. Finally, we show that the interplay of TRPV1R/CB1R shapes plasticity at BLA-NAc synapses. Together these data shed new light on synapse and circuit specificity in the adult NAc core and illustrate how endocannabinoids contribute to pathway-specific synaptic plasticity.SIGNIFICANCE STATEMENT We examined the impact of connections from the ventral hippocampus (vHipp,) basolateral amygdala (BLA) and prefrontal cortex (PFC) onto identified medium spiny neurons (MSNs) in the adult accumbens core. We found BLA inputs were strongest at D1 MSNs while PFC inputs dominate D2 MSNs. Pathway- and cell-specific circuit control was also facilitated by endocannabinoids that endow bidirectional synaptic plasticity at identified BLA-NAc synapses. These data provide mechanistic insights on synapse and circuit specificity in the adult NAc core.

Cannabinoids, TRPV and nitric oxide: the three ring circus of neuronal excitability

Endocannabinoid system is considered a relevant player in the regulation of neuronal excitability, since it contributes to maintaining the balance of the synaptic ionic milieu. Perturbations to bioelectric conductances have been implicated in the pathophysiological processes leading to hyperexcitability and epileptic seizures. Cannabinoid influence on neurosignalling is exerted on classic receptor-mediated mechanisms or on further molecular targets. Among these, transient receptor potential vanilloid (TRPV) are ionic channels modulated by cannabinoids that are involved in the transduction of a plethora of stimuli and trigger fundamental downstream pathways in the post-synaptic site. In this review, we aim at providing a brief summary of the most recent data about the cross-talk between cannabinoid system and TRPV channels, drawing attention on their role on neuronal hyperexcitability. Then, we aim to unveil a plausible point of interaction between these neural signalling systems taking into consideration nitric oxide, a gaseous molecule inducing profound modifications to neural performances. From this novel perspective, we struggle to propose innovative cellular mechanisms in the regulation of hyperexcitability phenomena, with the goal of exploring plausible CB-related mechanisms underpinning epileptic seizures.

Impaired brain endocannabinoid tone in the activity-based model of anorexia nervosa

OBJECTIVE

Despite the growing knowledge on the functional relationship between an altered endocannabinoid (eCB) system and development of anorexia nervosa (AN), to date no studies have investigated the central eCB tone in the activity-based anorexia (ABA) model that reproduces key aspects of human AN.

METHOD

We measured levels of two major eCBs, anandamide (AEA) and 2-arachidonoylglycerol (2-AG), those of two eCB-related lipids, oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), and the cannabinoid type-1 receptor (CB1R) density in the brain of female ABA rats, focusing on areas involved in homeostatic and rewarding-related regulation of feeding behavior (i.e., prefrontal cortex, nucleus accumbens, caudato putamen, amygdala, hippocampus and hypothalamus). Analysis was carried out also at the end of recovery from the ABA condition.

RESULTS

At the end of the ABA induction phase, 2-AG was significantly decreased in ABA rats in different brain areas but not in the caudato putamen. No changes were detected in AEA levels in any region, whereas the levels of OEA and PEA were decreased exclusively in the hippocampus and hypothalamus. Furthermore, CB1R density was decreased in the dentate gyrus of hippocampus and in the lateral hypothalamus. After recovery, both 2-AG levels and CB1R density were partially normalized in some areas. In contrast, AEA levels became markedly reduced in all the analyzed areas.

DISCUSSION

These data demonstrate an altered brain eCB tone in ABA rats, further supporting the involvement of an impaired eCB system in AN pathophysiology that may contribute to the maintenance of some symptomatic aspects of the disease.

Cannabinoid interventions for PTSD: Where to next?

Cannabinoids are a promising method for pharmacological treatment of post-traumatic stress disorder (PTSD). Despite considerable research devoted to the effect of cannabinoid modulation on PTSD symptomology, there is not a currently agreed way by which the cannabinoid system should be targeted in humans. In this review, we present an overview of recent research identifying neurological pathways by which different cannabinoid-based treatments may exert their effects on PTSD symptomology. We evaluate the strengths and weaknesses of each of these different approaches, including recent challenges presented to favourable options such as fatty acid amide hydrolase (FAAH) inhibitors. This article makes the strengths and challenges of different potential cannabinoid treatments accessible to psychological researchers interested in cannabinoid therapeutics and aims to aid selection of appropriate tools for future clinical trials.

Opposing roles of dorsomedial hypothalamic CB1 and TRPV1 receptors in anandamide signaling during the panic-like response elicited in mice by Brazilian rainbow Boidae snakes

RATIONALE

The endocannabinoid system plays an important role in the organization of panic-like defensive behavior. Threatening situations stimulate brain areas, such as the dorsomedial hypothalamus (DMH). However, there is a lack of studies addressing the role of the DMH endocannabinoid system in panic-like responses.

OBJECTIVES

We aimed to verify which mechanisms underlie anandamide-mediated responses in the DMH.

METHODS

To test the hypothesis that the anandamide produces panicolytic-like effects, we treated mice with intra-DMH microinjections of vehicle or increasing doses of anandamide (0.5, 5, or 50 pmol) and then performed confrontation with the South American snake Epicrates cenchria assisi.

RESULTS

Intra-DMH anandamide treatment yielded a U-shaped dose-response curve with no effect of the lowest (0.5 pmol) or the highest (50 pmol) dose and significant inhibition of panic-like responses at the intermediate (5 pmol) dose. In addition, this panicolytic-like effect was prevented by pretreatment of the DMH with the CB1 receptor antagonist AM251 (100 pmol). However, pretreatment of the DMH with the TRPV1 receptor antagonist 6-iodo-nordihydrocapsaicin (3 nmol) restored the panicolytic-like effect of the highest dose of anandamide. Immunohistochemistry revealed that CB1 receptors were present primarily on axonal fibers, while TRPV1 receptors were found almost exclusively surrounding the perikarya in DMH.

CONCLUSIONS

The present results suggest that anandamide exerts a panicolytic-like effect in the DMH by activation of CB1 receptors and that TRPV1 receptors are related to the lack of effect of the highest dose of anandamide.

A Novel Bio-Psychosocial-Behavioral Treatment Model of Panic Disorder

To conceptualize a novel bio-psychosocial-behavioral treatment model of panic disorder (PD), it is necessary to completely integrate behavioral, psychophysiological, neurobiological, and genetic data. Molecular genetic research on PD is specifically focused on neurotransmitters, including serotonin, neuropeptides, glucocorticoids, and neurotrophins. Although pharmacological interventions for PD are currently available, the need for more effective, faster-acting, and more tolerable pharmacological interventions is unmet. Thus, glutamatergic receptor modulators, orexin receptor antagonists, corticotrophin-releasing factor 1 receptor antagonists, and other novel mechanism-based anti-panic therapeutics have been proposed. Research on the neural correlates of PD is focused on the dysfunctional "cross-talk" between emotional drive (limbic structure) and cognitive inhibition (prefrontal cortex) and the fear circuit, which includes the amygdala-hippocampus-prefrontal axis. The neural perspective regarding PD supports the idea that cognitive-behavioral therapy normalizes alterations in top-down cognitive processing, including increased threat expectancy and attention to threat. Consistent with the concept of "personalized medicine," it is speculated that Research Domain Criteria can enlighten further treatments targeting dysfunctions underlying PD more precisely and provide us with better definitions of moderators used to identify subgroups according to different responses to treatment. Structuring of the "negative valence systems" domain, which includes fear/anxiety, is required to define PD. Therefore, targeting glutamate- and orexin-related molecular mechanisms associated with the fear circuit, which includes the amygdala-hippocampus-prefrontal cortex axis, is required to define a novel bio-psychosocial-behavioral treatment model of PD.

FAAH inhibition attenuates TLR3-mediated hyperthermia, nociceptive- and anxiety-like behaviour in female rats

Aberrant activation of toll-like receptor (TLR)s results in persistent and prolonged neuroinflammation and has been implicated in the pathogenesis and exacerbation of psychiatric and neurodegenerative disorders. TLR3 coordinates the innate immune response to viral infection and recent data have demonstrated that inhibiting fatty acid amide hydrolase (FAAH), the enzyme that primarily metabolizes anandamide, modulates TLR3-mediated neuroinflammation. However, the physiological and behavioural consequences of such modulation are unknown. The present study examined the effect of URB597, a selective FAAH inhibitor, on neuroinflammation, physiological and behavioural alterations following administration of the TLR3 agonist and viral mimetic poly I:C to female rats. URB597 attenuated TLR3-mediated fever, mechanical and cold allodynia, and anxiety-like behaviour in the elevated plus maze and open field arena. There was no effect of URB597 on TLR3-mediated decreases in body weight and no effect in the sucrose preference or forced swim tests. URB597 attenuated the TLR3-mediated increase in the expression of CD11b and CD68, markers of microglia/macrophage activation. In summary, these data demonstrate that enhancing FAAH substrate levels suppresses TLR3-mediated microglia/macrophage activation and associated changes in fever, nociceptive responding and anxiety-related behaviour. These data provide further support for FAAH as a novel therapeutic target for neuroinflammatory disorders.

Cannabinoid Receptor Type 1 in the Brain Regulates the Affective Component of Visceral Pain in Mice

Endocannabinoids acting through cannabinoid receptor type 1 (CB1) are major modulators of peripheral somatic and visceral nociception. Although only partially studied, some evidence suggests a particular role of CB1 within the brain in nociceptive processes. As the endocannabinoid system regulates affect and emotional behaviors, we hypothesized that cerebral CB1 influences affective processing of visceral pain-related behaviors in laboratory animals. To study nocifensive responses modulated by supraspinal CB1, we used conditional knock-out mice lacking CB1 either in cortical glutamatergic neurons (Glu-CB1-KO), or in forebrain GABAergic neurons (GABA-CB1-KO), or in principal neurons of the forebrain (CaMK-CB1-KO). These mutant mice and mice treated with the CB1 antagonist SR141716 were tested for different pain-related behaviors. In an acetic acid-induced abdominal constriction test, supraspinal CB1 deletions did not affect nocifensive responses. In the cerulein-model of acute pancreatitis, mechanical allodynia or hyperalgesia were not changed, but Glu-CB1- and CaMK-CB1-KO mice showed significantly increased facial grimacing scores indicating increased affective responses to this noxious visceral stimulus. Similarly, these brain-specific CB1 KO mice also showed significantly changed thermal nociception in a hot-plate test. These results reveal a novel, and important role of CB1 expressed by cortical glutamatergic neurons in the affective component of visceral nociception.

Oleoylethanolamide increases the expression of PPAR-Α and reduces appetite and body weight in obese people: A clinical trial

Obesity is a crucial public health problem worldwide and is considered as the main cause of many chronic diseases. The present study evaluated the effects of Oleoylethanolamide (OEA) supplementation on proximal proliferator-activated receptor-α (PPAR-α) gene expression, appetite sensations, and anthropometric measurements in obese people. This randomized, double-blind, placebo-controlled clinical trial was carried out on 60 healthy obese people in Tabriz, Iran, in 2016. The eligible subjects were divided into an intervention group (who received two 125 mg OEA capsules daily) and a placebo group (who received the same amount of starches) and treated for 60 days. Anthropometric measurements and body composition were assessed in a fasting state at baseline and at the end of the study. The visual analogue scales (VAS) were used to assess appetite sensations. Quantitative real-time PCR analysis targeting the 16S rRNA gene of PPAR-α was done. Analysis was done on 56 participants who continued intervention until the end of the study. A significant increase in PPAR-α gene expression was observed in the intervention group (p < 0.001). Weight, body mass index, waist circumference, and fat percent decreased significantly at the end of the study in the intervention group (all p < 0.01). Hunger, the desire to eat, and cravings for sweet foods decreased significantly and fullness increased significantly by the end of study in the intervention group at the end of study (all p < 0.01). The fullness item increased significantly by the end of study in the intervention group (p < 0.001). Use of OEA as a complementary approach could be effective in suppressing appetite and modulating energy balance in obese people.

A dual inhibitor of FAAH and TRPV1 channels shows dose-dependent effect on depression-like behaviour in rats

OBJECTIVE

The cannabinoid receptor 1 (CB1) and transient receptor potential cation channel subfamily V member 1 (TRPV1) are proposed to mediate opposite behavioural responses. Their common denominator is the endocannabinoid ligand anandamide (AEA), which is believed to mediate antidepressant-like effect via CB1-R stimulation and depressive-like effect via TRPV1 activation. This is supposed to explain the bell-shaped dose-response curve for anandamide in preclinical models.

METHODS

We investigated this assumption by administering the dual inhibitor of AEA hydrolysis and TRPV1 activation N-arachidonoyl-serotonin (AA-5HT) into the medial prefrontal cortex of rats. AA-5HT was given in three different doses (0.125, 0.250, 0.500 nmol/0.4 µl/side) and rat behaviour was assessed in the forced swim test.

RESULTS

Our results show significant antidepressant-like effect of AA-5HT (0.250 nmol) but no effects of low or high doses. The effect of 0.250 nmol AA-5HT was partially attenuated when coadministering the inverse CB1-agonist rimonabant (1.6 µg).

CONCLUSION

A 0.250 nmol of AA-5HT administration into the medial prefrontal cortex induced a significant antidepressant-like effect that was partially attenuated by locally blocking CB1-receptor.

Impairment of opiate-mediated behaviors by the selective TRPV1 antagonist SB366791

Transient receptor potential vanilloid type 1 (TRPV1), the archetypal member of the vanilloid TRP family, was initially identified as the receptor for capsaicin, the pungent ingredient in hot chili peppers. We previously demonstrated that TRPV1 in the dorsal striatum significantly contributes to morphine reward by using the conditioned place preference paradigm in mice; however, it is unknown whether TRPV1 has the same effect in other reward models. In this study, we investigated the role of TRPV1 in morphine reward by using a self-administration paradigm in rats. We found that treatment with a selective TRPV1 antagonist, SB366791, significantly decreased morphine self-administration on a fixed-ratio 1 schedule or a progressive ratio schedule of reinforcement. In addition, treatment with another selective TRPV1 antagonist, AMG9810, not only significantly prevented morphine self-administration but also prevented morphine-induced c-fos expression in the nucleus accumbens. Furthermore, administration of SB366791 decreased an anxiolytic-like effect during the morphine abstinence period. Moreover, treatment with SB366791 significantly decreased morphine-priming reinstatement. Taken together, our findings suggest that blockade of TRPV1 receptors could provide an approach to limiting morphine addiction.

Extinction of avoidance behavior by safety learning depends on endocannabinoid signaling in the hippocampus

The development of exaggerated avoidance behavior is largely responsible for the decreased quality of life in patients suffering from anxiety disorders. Studies using animal models have contributed to the understanding of the neural mechanisms underlying the acquisition of avoidance responses. However, much less is known about its extinction. Here we provide evidence in mice that learning about the safety of an environment (i.e., safety learning) rather than repeated execution of the avoided response in absence of negative consequences (i.e., response extinction) allowed the animals to overcome their avoidance behavior in a step-down avoidance task. This process was context-dependent and could be blocked by pharmacological (3 mg/kg, s.c.; SR141716) or genetic (lack of cannabinoid CB1 receptors in neurons expressing dopamine D1 receptors) inactivation of CB1 receptors. In turn, the endocannabinoid reuptake inhibitor AM404 (3 mg/kg, i.p.) facilitated safety learning in a CB1-dependent manner and attenuated the relapse of avoidance behavior 28 days after conditioning. Safety learning crucially depended on endocannabinoid signaling at level of the hippocampus, since intrahippocampal SR141716 treatment impaired, whereas AM404 facilitated safety learning. Other than AM404, treatment with diazepam (1 mg/kg, i.p.) impaired safety learning. Drug effects on behavior were directly mirrored by drug effects on evoked activity propagation through the hippocampal trisynaptic circuit in brain slices: As revealed by voltage-sensitive dye imaging, diazepam impaired whereas AM404 facilitated activity propagation to CA1 in a CB1-dependent manner. In line with this, systemic AM404 enhanced safety learning-induced expression of Egr1 at level of CA1. Together, our data render it likely that AM404 promotes safety learning by enhancing information flow through the trisynaptic circuit to CA1.

2-Arachidonoylglycerol endocannabinoid signaling coupled to metabotropic glutamate receptor type-5 modulates anxiety-like behavior in the rat ventromedial prefrontal cortex

2-Arachidonoylglycerol and anandamide are the main endocannabinoids, which act through cannabinoid type-1 and type-2 receptors. Among its many functions, anandamide modulates anxiety-like behaviors in the ventromedial prefrontal cortex. The role of 2-arachidonoylglycerol in this region, however, has remained unclear. Here, we verified whether intra- ventromedial prefrontal cortex injection of 2-arachidonoylglycerol or URB602, a monoacylglycerol lipase inhibitor (responsible for 2-arachidonoylglycerol hydrolysis), induce anxiolytic-like effects in Wistar rats. Since activation of metabotropic glutamate receptor type 5 promotes diacylglycerol lipase-α-mediated 2-arachidonoylglycerol synthesis, we also verified if the blockade of this receptor impairs the anxiolytic-like effect induced by URB 602. 2-Arachidonoylglycerol reduced anxiety-like response in rats exposed to the Elevated Plus Maze test, an effect mimicked by URB602. Cannabinoid type-1 and type-2 receptor antagonists prevented these effects. The pre-treatment with an ineffective dose of MPEP, a metabotropic glutamate receptor type 5 antagonist, also attenuated the anxiolytic-like effect of URB602. Moreover, immunofluorescence microscopy revealed co-expression of metabotropic glutamate receptor type 5 and diacylglycerol lipase-α in several neurons in slices from the ventromedial prefrontal cortex. Altogether, our results implicate 2-arachidonoylglycerol and both cannabinoid receptors on anxiety-related behaviors mediated by ventromedial prefrontal cortex. Further, these data support a role for the coupling between metabotropic glutamate receptor type 5 activation and 2-arachidonoylglycerol signalling as a mechanism modulating aversive responses.

N-arachidonoyl-serotonin, a dual FAAH and TRPV1 blocker, inhibits the retrieval of contextual fear memory: Role of the cannabinoid CB1 receptor in the dorsal hippocampus

Anandamide, an endocannabinoid, inhibits aversive responses by activating the CB₁ cannabinoid receptor. At high concentrations, however, anandamide may exert pro-aversive activities mediated by the transient receptor potential vanilloid type-1 channel (TRPV1). Accordingly, N-arachidonoyl-serotonin (AA-5-HT), a dual blocker of the anandamide-hydrolysing enzyme fatty acid amide hydrolase (FAAH) and the TRPV1 channel, induces anxiolytic-like effects. Here we tested the hypothesis that AA-5-HT inhibits the expression of contextual fear conditioning by facilitating CB₁ receptor signalling in the dorsal hippocampus of mice. Intraperitoneal injection of AA-5-HT (0.1, 0.3, 1 mg/kg) inhibited the retrieval of contextual fear memory (freezing response). The effect of AA-5-HT (0.3 mg/kg) was prevented by systemic injection of the CB₁ receptor antagonist, AM251 (1.0 mg/kg), and mimicked by simultaneous FAAH inhibition (URB597, 0.3 mg/kg) and TRPV1 blockage (SB366791, 1 mg/kg). Injection of AA-5-HT (0.125, 0.25, 0.5 nmol) into the dorsal hippocampus also reduced freezing. Finally, the effect of systemic AA-5-HT (0.3 mg/kg) was prevented by intra-hippocampal injection of AM251 (1 nmol). In conclusion, dual FAAH and TRPV1 blockage inhibits contextual fear memory by facilitating anandamide-induced CB₁ receptor activation in the dorsal hippocampus. This approach may lead to new pharmacological treatments for traumatic memories and related psychiatric disorders.

Role of N-Arachidonoyl-Serotonin (AA-5-HT) in Sleep-Wake Cycle Architecture, Sleep Homeostasis, and Neurotransmitters Regulation

The endocannabinoid system comprises several molecular entities such as endogenous ligands [anandamide (AEA) and 2-arachidonoylglycerol (2-AG)], receptors (CB₁ and CB₂), enzymes such as [fatty acid amide hydrolase (FAHH) and monoacylglycerol lipase (MAGL)], as well as the anandamide membrane transporter. Although the role of this complex neurobiological system in the sleep–wake cycle modulation has been studied, the contribution of the blocker of FAAH/transient receptor potential cation channel subfamily V member 1 (TRPV1), N-arachidonoyl-serotonin (AA-5-HT) in sleep has not been investigated. Thus, in the present study, varying doses of AA-5-HT (5, 10, or 20 mg/Kg, i.p.) injected at the beginning of the lights-on period of rats, caused no statistical changes in sleep patterns. However, similar pharmacological treatment given to animals at the beginning of the dark period decreased wakefulness (W) and increased slow wave sleep (SWS) as well as rapid eye movement sleep (REMS). Power spectra analysis of states of vigilance showed that injection of AA-5-HT during the lights-off period diminished alpha spectrum across alertness in a dose-dependent fashion. In opposition, delta power spectra was enhanced as well as theta spectrum, during SWS and REMS, respectively. Moreover, the highest dose of AA-5-HT decreased wake-related contents of neurotransmitters such as dopamine (DA), norepinephrine (NE), epinephrine (EP), serotonin (5-HT) whereas the levels of adenosine (AD) were enhanced. In addition, the sleep-inducing properties of AA-5-HT were confirmed since this compound blocked the increase in W caused by stimulants such as cannabidiol (CBD) or modafinil (MOD) during the lights-on period. Additionally, administration of AA-5-HT also prevented the enhancement in contents of DA, NE, EP, 5-HT and AD after CBD of MOD injection. Lastly, the role of AA-5-HT in sleep homeostasis was tested in animals that received either CBD or MOD after total sleep deprivation (TSD). The injection of CBD or MOD increased alertness during sleep rebound period after TSD. However, AA-5-HT blocked this effect by allowing animals to display an enhancement in sleep across sleep rebound period. Overall, our findings provide evidence that AA-5-HT is an important modulator of sleep, sleep homeostasis and neurotransmitter contents.

The endocannabinoid system as a target for novel anxiolytic drugs

The endocannabinoid (eCB) system has attracted attention for its role in various behavioral and brain functions, and as a therapeutic target in neuropsychiatric disease states, including anxiety disorders and other conditions resulting from dysfunctional responses to stress. In this mini-review, we highlight components of the eCB system that offer potential 'druggable' targets for new anxiolytic medications, emphasizing some of the less well-discussed options. We discuss how selectively amplifying eCBs recruitment by interfering with eCB-degradation, via fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), has been linked to reductions in anxiety-like behaviors in rodents and variation in human anxiety symptoms. We also discuss a non-canonical route to regulate eCB degradation that involves interfering with cyclooxygenase-2 (COX-2). Next, we discuss approaches to targeting eCB receptor-signaling in ways that do not involve the cannabinoid receptor subtype 1 (CB1R); by targeting the CB2R subtype and the transient receptor potential vanilloid type 1 (TRPV1). Finally, we review evidence that cannabidiol (CBD), while representing a less specific pharmacological approach, may be another way to modulate eCBs and interacting neurotransmitter systems to alleviate anxiety. Taken together, these various approaches provide a range of plausible paths to developing novel compounds that could prove useful for treating trauma-related and anxiety disorders.

The interactive role of CB1 receptors and L-type calcium channels in hippocampal long-term potentiation in rats

Long-term potentiation (LTP) of synaptic responses is a widely researched model of synaptic plasticity that occurs during learning and memory. The cannabinoid system is an endogenous system that modulate this kind of synaptic plasticity. In addition, voltage dependent calcium channels is essential for induction of LTP at some synapses in the hippocampus. However, there is currently debate over the interaction between L-type calcium channels and cannabinoid system on the synaptic plasticity. In this study, we examined the effects of an acute administration of the cannabinoid antagonist AM251 following a chronic administration of the Ca²⁺ channel blocker verapamil on LTP induction in the hippocampal dentate gyrus(DG) of rats. Male Wistar rats were administered verapamil(10,25,50mg/kg) or saline intraperitoneally(IP) daily for 13days(n=10/group). After this treatment period, animals were anesthetized with an IP injection of urethane; the recording and stimulating electrodes were positioned in the DG and the perforant pathway. After obtaining a steady state baseline response, a single IP injection of saline or AM251(1 or 5mg/kg) was administered. LTP was induced by high-frequency stimulation(HFS). The population spike(PS) amplitude and the slope of excitatory postsynaptic potentials(EPSP) were compared between the experimental groups. The acute administration of the CB1 antagonist AM251 increased LTP induction. The EPSP slopes and PS amplitude in the verapamil and AM251 groups differed after HFS, such that AM251 increased LTP, whereas verapamil decreased LTP induction. These findings suggest that there are functional interactions between the L-type calcium channels and cannabinoid system in this model of synaptic plasticity in the hippocampus.

Effects of cannabinoid and vanilloid receptor agonists and their interaction on learning and memory in rats

Despite previous findings on the effects of cannabinoid and vanilloid systems on learning and memory, the effects of the combined stimulation of these 2 systems on learning and memory have not been studied. Therefore, in this study, we tested the interactive effects of cannabinoid and vanilloid systems on learning and memory in rats by using passive avoidance learning (PAL) tests. Forty male Wistar rats were divided into the following 4 groups: (1) control (DMSO+saline), (2) WIN55,212–2, (3) capsaicin, and (4) WIN55,212–2 + capsaicin. On test day, capsaicin, a vanilloid receptor type 1 (TRPV1) agonist, or WIN55,212–2, a cannabinoid receptor (CB1/CB2) agonist, or both substances were injected intraperitoneally. Compared to the control group, the group treated with capsaicin (TRPV1 agonist) had better scores in the PAL acquisition and retention test, whereas treatment with WIN55,212–2 (CB1/CB2 agonist) decreased the test scores. Capsaicin partly reduced the effects of WIN55,212–2 on PAL and memory. We conclude that the acute administration of a TRPV1 agonist improves the rats’ cognitive performance in PAL tasks and that a vanilloid-related mechanism may underlie the agonistic effect of WIN55,212–2 on learning and memory.