Role of endocannabinoids in the hippocampus and amygdala in emotional memory and plasticity

Targeting dysfunctional endocannabinoid signaling in a mouse model of Gulf War illness

Gulf War Illness (GWI) is a chronic disorder characterized by a heterogeneous set of symptoms that include pain, fatigue, anxiety, and cognitive impairment. These are thought to stem from damage caused by exposure under unpredictable stress to toxic Gulf War (GW) chemicals, which include pesticides, nerve agents, and prophylactic drugs. We hypothesized that GWI pathogenesis might be rooted in long-lasting disruption of the endocannabinoid (ECB) system, a signaling complex that serves important protective functions in the brain. Using a mouse model of GWI, we found that tissue levels of the ECB messenger, anandamide, were significantly reduced in the brain of diseased mice, compared to healthy controls. In addition, transcription of the Faah gene, which encodes for fatty acid amide hydrolase (FAAH), the enzyme that deactivates anandamide, was significant elevated in prefrontal cortex of GWI mice and brain microglia. Behavioral deficits exhibited by these animals, including heightened anxiety-like and depression-like behaviors, and defective extinction of fearful memories, were corrected by administration of the FAAH inhibitor, URB597, which normalized brain anandamide levels. Furthermore, GWI mice displayed unexpected changes in the microglial transcriptome, implying persistent dampening of homeostatic surveillance genes and abnormal expression of pro-inflammatory genes upon immune stimulation. Together, these results suggest that exposure to GW chemicals produce a deficit in brain ECB signaling which is associated with persistent alterations in microglial function. Pharmacological normalization of anandamide-mediated ECB signaling may offer an effective therapeutic strategy for ameliorating GWI symptomology.

Divergent input patterns to the central lateral amygdala play a duet in fear memory formation

Somatostatin (SOM)-expressing neurons in the central lateral amygdala (CeL) are responsible for fear memory learning, but the circuit and molecular mechanisms underlying this biology remain elusive. Here, we found that glutamatergic neurons in the lateral parabrachial nucleus (LPB) directly dominated the activity of CeLSOM neurons, and that selectively inhibiting the LPBGlu→CeLSOM pathway suppressed fear memory acquisition. By contrast, inhibiting CeL-projecting glutamatergic neurons in the paraventricular thalamic nucleus (PVT) interfered with consolidation-related processes. Notably, CeLSOM-innervating neurons in the LPB were modulated by presynaptic cannabinoid receptor 1 (CB1R), and knock down of CB1Rs in LPB glutamatergic neurons enhanced excitatory transmission to the CeL and partially rescued the impairment in fear memory induced by CB1R activation in the CeL. Overall, our study reveals the mechanisms by which CeLSOM neurons mediate the formation of fear memories during fear conditioning in mice, which may provide a new direction for the clinical research of fear-related disorders.

Electrophysiological Phenotypes of Hippocampal Synaptic and Network Functions in Cannabinoid Receptor 2 Knockout Mice

Background: The cannabinoid receptor 2 (CB2R), a cannabinoid receptor primarily expressed in immune cells, has been found in the brain, particularly in the hippocampus, where it plays crucial roles in modulating various neural functions, including synaptic plasticity, neuroprotection, neurogenesis, anxiety and stress responses, and neuroinflammation. Despite this growing understanding, the intricate electrophysiological characteristics of hippocampal neurons in CB2R knockout (CB2R KO) mice remain elusive. Aim and Methods: This study aimed to comprehensively assess the electrophysiological traits of hippocampal synaptic and network functions in CB2R KO mice. The focus was on aspects such as synaptic transmission, short- and long-term synaptic plasticity, and neural network synchrony (theta oscillations). Results: Our findings unveiled multiple functional traits in these CB2R KO mice, notably elevated synaptic transmission in hippocampal CA1 neurons, decreased both synaptic short-term plasticity (paired-pulse facilitation) and long-term potentiation (LTP), and impaired neural network synchronization. Conclusion: In essence, this study yields insightful revelations about the influence of CB2Rs on hippocampal neural functions. By illuminating the electrophysiological modifications in CB2R KO mice, our research enriches the comprehension of CB2R involvement in hippocampal function. Such insights could hold implications for advancing our understanding of the neural mechanisms under the influence of CB2Rs within the brain.

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.

Interactions between physical exercise, associative memory, and genetic risk for Alzheimer's disease

The ε4 allele of the APOE gene heightens the risk of late onset Alzheimer's disease. ε4 carriers, may exhibit cognitive and neural changes early on. Given the known memory-enhancing effects of physical exercise, particularly through hippocampal plasticity via endocannabinoid signaling, here we aimed to test whether a single session of physical exercise may benefit memory and underlying neurophysiological processes in young ε3 carriers (ε3/ε4 heterozygotes, risk group) compared with a matched control group (homozygotes for ε3). Participants underwent fMRI while learning picture sequences, followed by cycling or rest before a memory test. Blood samples measured endocannabinoid levels. At the behavioral level, the risk group exhibited poorer associative memory performance, regardless of the exercising condition. At the brain level, the risk group showed increased medial temporal lobe activity during memory retrieval irrespective of exercise (suggesting neural compensatory effects even at baseline), whereas, in the control group, such increase was only detectable after physical exercise. Critically, an exercise-related endocannabinoid increase correlated with task-related hippocampal activation in the control group only. In conclusion, healthy young individuals carrying the ε4 allele may present suboptimal associative memory performance (when compared with homozygote ε3 carriers), together with reduced plasticity (and functional over-compensation) within medial temporal structures.

Sex-Related and Brain Regional Differences of URB597 Effects on Modulation of MAPK/PI3K Signaling in Chronically Stressed Rats

Gender differences exist in depression incidence and antidepressant efficacy. In addition to the neurotransmission theory of depression, inflammation and disrupted signaling pathways play crucial roles in the pathophysiology of depression. Endocannabinoids offer a novel approach to treat inflammatory and emotional disorders like depression. URB597, a FAAH inhibitor, reduces endocannabinoids breakdown. In this study, URB597 effects were investigated on the pro-inflammatory cytokine interleukin-1β (IL-1β), nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3(NLRP3), and mitogen-activated protein kinase (MAPK)/ phosphatidylinositol 3-hydroxy kinase/ protein kinase B (PI3K) signaling in the hippocampus and the medial prefrontal cortex (mPFC) of male and female rats subjected to chronic unpredictable stress (CUS). The results show that CUS induces depression-like behaviors, and the URB597 exhibited antidepressant-like effects inboth sexes. URB597 reduced the CUS-induced NLRP3 and IL-1β increase in the hippocampus and mPFC of both sexes. URB597 increased the reduced pERK1/2 levels in the mPFC of both sexes and hippocampus of CUS males. URB597 also prevented the increase in p38 phosphorylation after chronic stress in the mPFC of both sexes and in the hippocampus of the females. The CUS suppressed the downstream Akt phosphorylation in the mPFC and hippocampi of both sexes. URB597 produced an up-regulation of the pAkt in the hippocampus of the CUS animals but did not affect the pAkt in the mPFC. These data demonstrated a sexual dimorphism in the neural cell signaling, and in the effects of endocannabinoids, and indicated these dimorphisms are region-specific.

Pharmacological diacylglycerol lipase inhibition impairs contextual fear extinction in mice

Acquisition and extinction of associative fear memories are critical for guiding adaptive behavioral responses to environmental threats, and dysregulation of these processes is thought to represent important neurobehavioral substrates of trauma and stress-related disorders including posttraumatic stress disorder (PTSD). Endogenous cannabinoid (eCB) signaling has been heavily implicated in the extinction of aversive fear memories and we have recently shown that pharmacological inhibition of 2-arachidonoylglycerol (2-AG) synthesis, a major eCB regulating synaptic suppression, impairs fear extinction in an auditory cue conditioning paradigm. Despite these data, the role of 2-AG signaling in contextual fear conditioning is not well understood. Here, we show that systemic pharmacological blockade of diacylglycerol lipase, the rate-limiting enzyme catalyzing in the synthesis of 2-AG, enhances contextual fear learning and impairs within-session extinction. In sham-conditioned mice, 2-AG synthesis inhibition causes a small increase in unconditioned freezing behavior. No effects of 2-AG synthesis inhibition were noted in the Elevated Plus Maze in mice tested after fear extinction. These data provide support for 2-AG signaling in the suppression of contextual fear learning and the expression of within-session extinction of contextual fear memories.

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.

Basolateral Amygdala Cannabinoid CB1 Receptor Controls Formation and Elimination of Social Fear Memory

Patients with post-traumatic stress disorder (PTSD) usually manifest persistence of the traumatic memory for a long time after the event, also known as resistance to extinction learning. Numerous studies have shown that the endocannabinoid system, specifically the cannabinoid type-1 receptor (CB1R), plays an important role in traumatic memory. However, the effect of basolateral amygdala (BLA) CB1R in social fear memory formation and elimination is still unclear. Here, we built a mouse model of social avoidance induced by acute social defeat stress to investigate the role of BLA CB1R in social fear memory formation and anxiety- and depression-like behavior. Anterograde knockout of CB1R in BLA neurons facilitates social fear memory formation and manifests an anxiolytic effect but does not influence sociability and social novelty. Retrograde knockout of CB1R in BLA promotes social fear memory formation and shows an anxiogenic effect but does not affect sociability and social novelty. Moreover, intracerebral injection of the CB1R antagonist AM251 in BLA during the memory reconsolidation time window eliminates social fear memory. Our findings suggest the CB1R of BLA can be used as a novel molecular target in social fear memory formation and elimination and potential PTSD therapy with memory retrieval and AM251.

The association of circulating endocannabinoids with neuroimaging and blood biomarkers of neuro-injury

BACKGROUND

Preclinical studies highlight the importance of endogenous cannabinoids (endocannabinoids; eCBs) in neurodegeneration. Yet, prior observational studies focused on limited outcome measures and assessed only few eCB compounds while largely ignoring the complexity of the eCB system. We examined the associations of multiple circulating eCBs and eCB-like molecules with early markers of neurodegeneration and neuro-injury and tested for effect modification by sex.

METHODS

This exploratory cross-sectional study included a random sample of 237 dementia-free older participants from the Framingham Heart Study Offspring cohort who attended examination cycle 9 (2011-2014), were 65 years or older, and cognitively healthy. Forty-four eCB compounds were quantified in serum, via liquid chromatography high-resolution mass spectrometry. Linear regression models were used to examine the associations of eCB levels with brain MRI measures (i.e., total cerebral brain volume, gray matter volume, hippocampal volume, and white matter hyperintensities volume) and blood biomarkers of Alzheimer's disease and neuro-injury (i.e., total tau, neurofilament light, glial fibrillary acidic protein and Ubiquitin C-terminal hydrolase L1). All models were adjusted for potential confounders and effect modification by sex was examined.

RESULTS

Participants mean age was 73.3 ± 6.2 years, and 40% were men. After adjustment for potential confounders and correction for multiple comparisons, no statistically significant associations were observed between eCB levels and the study outcomes. However, we identified multiple sex-specific associations between eCB levels and the various study outcomes. For example, high linoleoyl ethanolamide (LEA) levels were related to decreased hippocampal volume among men and to increased hippocampal volume among women (β ± SE =  - 0.12 ± 0.06, p = 0.034 and β ± SE = 0.08 ± 0.04, p = 0.026, respectively).

CONCLUSIONS

Circulating eCBs may play a role in neuro-injury and may explain sex differences in susceptibility to accelerated brain aging. Particularly, our results highlight the possible involvement of eCBs from the N-acyl amino acids and fatty acid ethanolamide classes and suggest specific novel fatty acid compounds that may be implicated in brain aging. Furthermore, investigation of the eCBs contribution to neurodegenerative disease such as Alzheimer's disease in humans is warranted, especially with prospective study designs and among diverse populations, including premenopausal women.

Anandamide and 2-arachidonoylglycerol differentially modulate autistic-like traits in a genetic model of autism based on FMR1 deletion in rats

Autism spectrum disorder (ASD) has a multifactorial etiology. Major efforts are underway to understand the neurobiological bases of ASD and to develop efficacious treatment strategies. Recently, the use of cannabinoid compounds in children with neurodevelopmental disorders including ASD has received increasing attention. Beyond anecdotal reports of efficacy, however, there is limited current evidence supporting such an intervention and the clinical studies currently available have intrinsic limitations that make the interpretation of the findings challenging. Furthermore, as the mechanisms underlying the beneficial effects of cannabinoid compounds in neurodevelopmental disorders are still largely unknown, the use of drugs targeting the endocannabinoid system remains controversial. Here, we studied the role of endocannabinoid neurotransmission in the autistic-like traits displayed by the recently validated Fmr1-Δexon 8 rat model of autism. Fmr1-Δexon 8 rats showed reduced anandamide levels in the hippocampus and increased 2-arachidonoylglycerol (2-AG) content in the amygdala. Systemic and intra-hippocampal potentiation of anandamide tone through administration of the anandamide hydrolysis inhibitor URB597 ameliorated the cognitive deficits displayed by Fmr1-Δexon 8 rats along development, as assessed through the novel object and social discrimination tasks. Moreover, blockade of amygdalar 2-AG signaling through intra-amygdala administration of the CB1 receptor antagonist SR141716A prevented the altered sociability displayed by Fmr1-Δexon 8 rats. These findings demonstrate that anandamide and 2-AG differentially modulate specific autistic-like traits in Fmr1-Δexon 8 rats in a brain region-specific manner, suggesting that fine changes in endocannabinoid mechanisms contribute to ASD-related behavioral phenotypes.

Bed nucleus of the stria terminalis CB1 receptors and the FAAH enzyme modulate anxiety behavior depending on previous stress exposure

The endocannabinoid (eCB) anandamide (AEA) is synthesized on-demand in the post-synaptic terminal and can act on presynaptic cannabinoid type 1 (CB1) receptors, decreasing the release of neurotransmitters, including glutamate. AEA action is ended through enzymatic hydrolysis via FAAH (fatty acid amid hydrolase) in the post-synaptic neuron. eCB system molecules are widely expressed in brain areas involved in the modulation of fear and anxiety responses, including the Bed Nucleus of the Stria Terminalis (BNST), which is involved in the integration of autonomic, neuroendocrine, and behavioral regulation. The presence of the CB1 and FAAH was described in the BNST; however, their role in the modulation of defensive reactions is not fully comprehended. In the present work we aimed at investigating the role of AEA and CB1 receptors in the BNST in modulating anxiety-related behaviors. Adult male Wistar rats received local BNST injections of the CB1 receptor antagonist AM251 (0.1-0.6 nmol) and/or the FAAH inhibitor (URB597; 0.001-0.1 nmol) and were evaluated in the elevated plus maze (EPM) test, with or without previous acute restraint stress (2 h) exposure, or in the contextual fear conditioning. We observed that although AM251 and URB597 had no effects on the EPM, they increased and decreased, respectively, the conditioned fear response. Supporting a possible influence of stress in these differences, URB597 was able to prevent the restraint stress-induced anxiogenic effect in the EPM. The present data, therefore, suggest that eCB signaling in the BNST is recruited during more aversive situations to counteract the stress effect.

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.

Persistent representation of the environment in the hippocampus

In the hippocampus, environmental changes elicit rearrangement of active neuronal ensembles or remapping of place cells. However, it remains elusive how the brain ensures a consistent representation of a certain environment itself despite salient events occurring there. Here, we longitudinally tracked calcium dynamics of dorsal hippocampal CA1 neurons in mice subjected to contextual fear conditioning and extinction training. Overall population activities were significantly changed by fear conditioning and were responsive to footshocks and freezing. However, a small subset of neurons, termed environment cells, were consistently active in a specific environment irrespective of experiences. A decoder modeling study showed that these cells, but not place cells, were able to predict the environment to which the mouse was exposed. Environment cells might underlie the constancy of cognition for distinct environments across time and events. Additionally, our study highlights the functional heterogeneity of cells in the hippocampus.

2-AG-Mediated Control of GABAergic Signaling Is Impaired in a Model of Epilepsy

Repeated seizures result in a persistent maladaptation of endocannabinoid (eCB) signaling, mediated part by anandamide signaling deficiency in the basolateral amygdala (BLA) that manifests as aberrant synaptic function and altered emotional behavior. Here, we determined the effect of repeated seizures (kindling) on 2-arachidonoylglycerol (2-AG) signaling on GABA transmission by directly measuring tonic and phasic eCB-mediated retrograde signaling in an in vitro BLA slice preparation from male rats. We report that both activity-dependent and muscarinic acetylcholine receptor (mAChR)-mediated depression of GABA synaptic transmission was reduced following repeated seizure activity. These effects were recapitulated in sham rats by preincubating slices with the 2-AG synthesizing enzyme inhibitor DO34. Conversely, preincubating slices with the 2-AG degrading enzyme inhibitor KML29 rescued activity-dependent 2-AG signaling, but not mAChR-mediated synaptic depression, over GABA transmission in kindled rats. These effects were not attributable to a change in cannabinoid type 1 (CB1) receptor sensitivity or altered 2-AG tonic signaling since the application of the highly selective CB1 receptor agonist CP55,940 provoked a similar reduction in GABA synaptic activity in both sham and kindled rats, while no effect of either DO34 or of the CB1 inverse agonist AM251 was observed on frequency and amplitude of spontaneous IPSCs in either sham or kindled rats. Collectively, these data provide evidence that repeated amygdala seizures persistently alter phasic 2-AG-mediated retrograde signaling at BLA GABAergic synapses, probably by impairing stimulus-dependent 2-AG synthesis/release, which contributes to the enduring aberrant synaptic plasticity associated with seizure activity.SIGNIFICANCE STATEMENT The plastic reorganization of endocannabinoid (eCB) signaling after seizures and during epileptogenesis may contribute to the negative neurobiological consequences associated with seizure activity. Therefore, a deeper understanding of the molecular basis underlying the pathologic long-term eCB signaling remodeling following seizure activity will be crucial to the development of novel therapies for epilepsy that not only target seizure activity, but, most importantly, the epileptogenesis and the comorbid conditions associated with epilepsy.

Endocannabinoid metabolism inhibition has no effect on spontaneous fear recovery or extinction resistance in Lister hooded rats

Endocannabinoid transmission is emerging as a target for treating anxiety-related disorders, given its regulation of fear extinction. Boosting anandamide levels via inhibition of its metabolism by fatty acid amide hydrolase (FAAH) can enhance extinction, whereas inhibiting monoacylglycerol lipase (MAGL) to elevate 2-arachidonoylglycerol levels can impair extinction. However, whether endocannabinoids regulate fear relapse over time or extinction resistance remains unclear. In two experiments using auditory fear conditioned rats, we examined the effects of the FAAH inhibitor URB597 and the MAGL inhibitor JZL184 administered systemically on 1) spontaneous fear recovery after delayed extinction, and 2) extinction resistance resulting from immediate extinction [the immediate extinction deficit (IED)]. In Experiment 1, URB597 or JZL184 was given immediately after delayed extinction occurring 24 h after conditioning. Extinction recall and spontaneous fear recovery were tested drug-free 1 and 21 days later, respectively. We found no effects of either drug on extinction recall or spontaneous fear recovery. In Experiment 2, URB597 or JZL184 was given before immediate extinction occurring 30 min after conditioning and extinction recall was tested drug-free the next day. We also examined the effects of propranolol, a beta-adrenoceptor antagonist that can rescue the IED, as a positive control. JZL184 enhanced fear expression and impaired extinction learning but we found no lasting effects of URB597 or JZL184 on cued extinction recall. Propranolol reduced fear expression but, unexpectedly, had no enduring effect on extinction recall. The results are discussed in relation to various methodological differences between previous studies examining endocannabinoid and adrenergic regulation of fear extinction.

Enhancing Endocannabinoid Signaling via β-Catenin in the Nucleus Accumbens Attenuates PTSD- and Depression-like Behavior of Male Rats

Inhibition of fatty acid amide hydrolase (FAAH), which increases anandamide levels, has been suggested as a potential treatment for stress-related conditions. We examined whether the stress-preventing effects of the FAAH inhibitor URB597 on behavior are mediated via β-catenin in the nucleus accumbens (NAc). Male rats were exposed to the shock and reminders model of PTSD and then treated with URB597 (0.4 mg/kg; i.p.). They were tested for anxiety- (freezing, startle response), depression-like behaviors (despair, social preference, anhedonia), and memory function (T-maze, social recognition). We also tested the involvement of the CB1 receptor (CB1r), β-catenin, and metabotropic glutamate receptor subtype 5 (mGluR5) proteins. URB597 prevented the shock- and reminders-induced increase in anxiety- and depressive-like behaviors, as well as the impaired memory via the CB1r-dependent mechanism. In the NAc, viral-mediated β-catenin overexpression restored the behavior of rats exposed to stress and normalized the alterations in protein levels in the NAc and the prefrontal cortex. Importantly, when NAc β-catenin levels were downregulated by viral-mediated gene transfer, the therapeutic-like effects of URB597 were blocked. We suggest a potentially novel mechanism for the therapeutic-like effects of FAAH inhibition that is dependent on β-catenin activation in the NAc in a PTSD rat model.

Circadian regulation of memory under stress: Endocannabinoids matter

Organisms ranging from plants to higher mammals have developed 24-hour oscillation rhythms to optimize physiology to environmental changes and regulate a plethora of neuroendocrine and behavioral processes, including neurotransmitter and hormone regulation, stress response and learning and memory function. Compelling evidence indicates that a wide array of memory processes is strongly influenced by stress- and emotional arousal-activated neurobiological systems, including the endocannabinoid system which has been extensively shown to play an integral role in mediating stress effects on memory. Here, we review findings showing how circadian rhythms and time-of-day influence stress systems and memory performance. We report evidence of circadian regulation of memory under stress, focusing on the role of the endocannabinoid system and highlighting its circadian rhythmicity. Our discussion illustrates how the endocannabinoid system mediates stress effects on memory in a circadian-dependent fashion. We suggest that endocannabinoids might regulate molecular mechanisms that control memory function under circadian and stress influence, with potential important clinical implications for both neurodevelopmental disorders and psychiatric conditions involving memory impairments.

Diverse therapeutic developments for post-traumatic stress disorder (PTSD) indicate common mechanisms of memory modulation

Post-traumatic stress disorder (PTSD), characterized by abnormally persistent and distressing memories, is a chronic debilitating condition in need of new treatment options. Current treatment guidelines recommend psychotherapy as first line management with only two drugs, sertraline and paroxetine, approved by U.S. Food and Drug Administration (FDA) for treatment of PTSD. These drugs have limited efficacy as they only reduce symptoms related to depression and anxiety without producing permanent remission. PTSD remains a significant public health problem with high morbidity and mortality requiring major advances in therapeutics. Early evidence has emerged for the beneficial effects of psychedelics particularly in combination with psychotherapy for management of PTSD, including psilocybin, MDMA, LSD, cannabinoids, ayahuasca and ketamine. MDMA and psilocybin reduce barrier to therapy by increasing trust between therapist and patient, thus allowing for modification of trauma related memories. Furthermore, research into the memory reconsolidation mechanisms has allowed for identification of various pharmacological targets to disrupt abnormally persistent memories. A number of pre-clinical and clinical studies have investigated novel and re-purposed pharmacological agents to disrupt fear memory in PTSD. Novel therapeutic approaches like neuropeptide Y, oxytocin, cannabinoids and neuroactive steroids have also shown potential for PTSD treatment. Here, we focus on the role of fear memory in the pathophysiology of PTSD and propose that many of these new therapeutic strategies produce benefits through the effect on fear memory. Evaluation of recent research findings suggests that while a number of drugs have shown promising results in preclinical studies and pilot clinical trials, the evidence from large scale clinical trials would be needed for these drugs to be incorporated in clinical practice.

The role of the cannabinoid system in fear memory and extinction in male and female mice

The prevalence of post-traumatic stress disorder (PTSD) is higher in women than in men. Among both humans and mice, females exhibit higher resistance to fear extinction than males, suggesting that differences between sexes in fear-extinction processes are involved in the pathophysiology of such fear-related diseases. Sex differences in molecular mechanisms underlying fear memory and extinction are unclear. The cannabinoid (CB) system is well known to be involved in fear memory and extinction, but this involvement is based mainly on experiments using male rodents. It is not known whether there are sex differences in the role of the CB system in fear memory and extinction. To explore this possibility, we investigated the effects of pharmacological manipulations of the CB system on the retrieval and extinction of contextual fear memory in male and female mice. WIN55,212-2, a CB receptor (CBR) agonist, augmented the retrieval of fear memory in both sexes, but SR141716 (a CB1R antagonist) did not affect it in either sex. An enhancement of 2-arachidonylglycerol (2-AG, one of the two major endocannabinoids) via JZL184 (an inhibitor of the 2-AG hydrolase monoacylglycerol lipase [MAGL]), augmented the retrieval of fear memory through the activation of CB1R but not CB2R in female mice. In contrast, the enhancement of N-arachidonylethanolamine (AEA, the other major endocannabinoid) via URB597, an inhibitor of an AEA hydrolase (fatty acid amide hydrolase-1) did not show any effects on the retrieval of fear memory in either sex. WIN55,212-2, SR141716, and JZL184 inhibited fear extinction irrespective of sex. URB enhanced fear extinction in females that were in diestrus phase at the first extinction session, but not in males. These results suggest that although the role of CB1R in the retrieval and extinction of contextual fear memory is common among males and females, the effects of an increase in endocannabinoid levels on the retrieval or extinction of contextual fear memory differ between the sexes.

Circulating endocannabinoids and genetic polymorphisms as predictors of posttraumatic stress disorder symptom severity: heterogeneity in a community-based cohort

The endocannabinoid signaling system (ECSS) regulates fear and anxiety. While ECSS hypoactivity can contribute to symptoms of established post-traumatic stress disorder (PTSD), the role of the ECSS in PTSD development following trauma is unknown. A prospective, longitudinal cohort study of 170 individuals (47% non-Hispanic Caucasian and 70% male) treated at a level 1 trauma center for traumatic injury was carried out. PTSD symptom assessments and blood were obtained during hospitalization and at follow-up (6-8 months post injury). Serum concentrations of the endocannabinoids N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) were determined at both time points and selected genetic polymorphisms in endocannabinoid genes, including rs324420 in fatty acid amide hydrolase, were assessed. For the entire sample, serum concentrations of AEA at hospitalization were significantly higher in those diagnosed with PTSD at follow-up (p = 0.030). Serum concentrations of 2-AG were significantly, positively correlated with PTSD symptom severity at follow-up only in minorities (p = 0.014). Minority participants (mostly Black/African American) also demonstrated significant, negative correlations between serum AEA concentrations and PTSD symptom severity both measured at hospitalization (p = 0.015). The A/A genotype at rs324420 was associated with significantly higher PTSD symptom severity (p = 0.025) and occurred exclusively in the Black participants. Collectively, these results are contrary to our hypothesis and find positive associations between circulating endocannabinoids and risk for PTSD. Minority status is an important modulator of the association between endocannabinoids and risk for PTSD, suggesting that the ECSS contributes to risk most significantly in these individuals and the contextual factors related to these findings should be further explored.

Translation of animal endocannabinoid models of PTSD mechanisms to humans: Where to next?

The endocannabinoid system is known to be involved in mechanisms relevant to PTSD aetiology and maintenance, though this understanding is mostly based on animal models of the disorder. Here we review how human paradigms can successfully translate animal findings to human subjects, with the view that substantially increased insight into the effect of endocannabinoid signalling on stress responding, emotional and intrusive memories, and fear extinction can be gained using modern paradigms and methods for assessing the state of the endocannabinoid system in PTSD.

Electrophysiological study of the interactive role of the cannabinoid breakdown inhibitors and L-type calcium channels on granular neurons in the hippocampal dentate gyrus in rats

The interaction between L-type voltage-dependent Ca²⁺ channels and the endocannabinoid system (eCs) in synaptic plasticity is controversial. In the present research, the impact of acute administration of URB597, as an endocannabinoid breakdown inhibitor, was evaluated after chronic injection of verapamil, as a Ca²⁺ channels blocker, on inducing long-term potentiation (LTP) in the rat's hippocampal dentate gyrus (DG). Treatment of male Wistar rats was done using intraperitoneal(i.p) injection of verapamil hydrochloride (n = 8) and saline (n = 10), as the solvent of verapamil once a day within 13 days. Anesthetization was done by i.p injection of urethane and the rats were located in the stereotaxic apparatus for surgery, electrode implantation, and field potential recording. After observing a steady-state baseline response, saline or URB597 were injected (n = 9). Measurement of the population spike (PS) amplitude and slope of field excitatory postsynaptic potentials (fEPSPs) in the DG region was performed as a result of perforant pathway (PP) stimulation. Our treatments could inhibit LTP. Our results indicated that the chronic administration of verapamil produced a significant decrease in the slope of fEPSP and PS amplitude. Also, acute URB597 administration decreased the slope of fEPSP and PS amplitude compared to the saline group. Moreover, URB597 administration in combination with chronic administration of verapamil produced a greater decrease in fEPSP slope and PS amplitude than the saline group. These findings indicated that verapamil and URB597 disrupted LTP induction in the DG. Moreover, an interaction was observed between Ca²⁺ channels and eCs. Therefore, the eCs possibly play a selective role in synaptic plasticity.

Early Consumption of Cannabinoids: From Adult Neurogenesis to Behavior

The endocannabinoid system (ECS) is a crucial modulatory system in which interest has been increasing, particularly regarding the regulation of behavior and neuroplasticity. The adolescent-young adulthood phase of development comprises a critical period in the maturation of the nervous system and the ECS. Neurogenesis occurs in discrete regions of the adult brain, and this process is linked to the modulation of some behaviors. Since marijuana (cannabis) is the most consumed illegal drug globally and the highest consumption rate is observed during adolescence, it is of particular importance to understand the effects of ECS modulation in these early stages of adulthood. Thus, in this article, we sought to summarize recent evidence demonstrating the role of the ECS and exogenous cannabinoid consumption in the adolescent-young adulthood period; elucidate the effects of exogenous cannabinoid consumption on adult neurogenesis; and describe some essential and adaptive behaviors, such as stress, anxiety, learning, and memory. The data summarized in this work highlight the relevance of maintaining balance in the endocannabinoid modulatory system in the early and adult stages of life. Any ECS disturbance may induce significant modifications in the genesis of new neurons and may consequently modify behavioral outcomes.

Is PTSD-Phenotype Associated with HPA-Axis Sensitivity?: The Endocannabinoid System in Modulating Stress Response in Rats

Endocannabinoids play a role in adaptation to stress and regulate the release of glucocorticoids in stressed and unstressed conditions. We recently found that basal corticosterone pulsatility may significantly impact the vulnerability for developing post-traumatic-stress-disorder (PTSD), suggesting that the endocannabinoid system may contribute to its development. To examine this, we exposed rats to predator scent stress (PSS). Behavioral reactions were recorded seven days post-PSS. Cerebrospinal fluid (CSF) was collected from anesthetized rats shortly after PSS exposure to determine the levels of 2-arachidonoyl glycerol (2-AG) and anandamide (AEA). To correlate between endocannabinoids and corticosterone levels, rats were placed in metabolic cages for urine collection. To assess the levels of endocannabinoids in specific brain regions, rats' brains were harvested one day after behavioral analysis for staining and fluorescence quantification. Moreover, 2-AG was elevated in the CSF of PTSD-phenotype rats as compared with other groups and was inversely correlated with corticosterone urinary secretion. Eight days post-PSS exposure, hippocampal and hypothalamic 2-AG levels and hippocampal AEA levels were significantly more reduced in the PTSD-phenotype group compared to other groups. We posit that maladaptation to stress, which is propagated by an abnormal activation of endocannabinoids, mediates the subsequent stress-induced behavioral disruption, which, later, reduces neuronal the expression of endocannabinoids, contributing to PTSD symptomology.

Pharmacological Blockade of PPARα Exacerbates Inflammatory Pain-Related Impairment of Spatial Memory in Rats

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors that exist in three isoforms: PPARα, PPARβ/δ and PPARγ. Studies suggest that the PPAR signalling system may modulate pain, anxiety and cognition. The aim of the present study was to investigate whether endogenous signalling via PPARs differentially modulates innate anxiety responses and mnemonic function in the presence and absence of inflammatory pain. We examined the effects of intraperitoneal administration of GW6471 (PPARα antagonist), GSK0660 (PPARβ/δ antagonist), GW9662 (PPARγ antagonist), and N-palmitoylethanolamide (PEA) on rat behaviour in the elevated plus maze (EPM), open field (OF), light-dark box (LDB), and novel object recognition (NOR) tests in the presence or absence of chronic inflammatory pain. Complete Freund’s Adjuvant (CFA)-injected rats exhibited impaired recognition and spatial mnemonic performance in the NOR test and pharmacological blockade of PPARα further impaired spatial memory in CFA-treated rats. N-oleoylethanolamide (OEA) levels were higher in the dorsal hippocampus in CFA-injected animals compared to their counterparts. The results suggest a modulatory effect of CFA-induced chronic inflammatory pain on cognitive processing, but not on innate anxiety-related responses. Increased OEA-PPARα signalling may act as a compensatory mechanism to preserve spatial memory function following CFA injection.

The role of endocannabinoids in consolidation, retrieval, reconsolidation, and extinction of fear memory

Endocannabinoids are involved in various physiological functions, including synaptic plasticity and memory, and some psychiatric disorders, such as posttraumatic stress disorder (PTSD), through the activation of cannabinoid (CB) receptors. Patients with PTSD often show excessive fear memory and impairment of fear extinction (FE). It has been reported that the stability of acquired fear memory is altered through multiple memory stages, such as consolidation and reconsolidation. FE also affects the stability of fear memory. Each stage of fear memory formation and FE are regulated by different molecular mechanisms, including the CB system. However, to the best of our knowledge, no review summarizes the role of the CB system during each stage of fear memory formation and FE. In this review, we summarize the roles of endocannabinoids in fear memory formation and FE. Moreover, based on the summary, we propose a new hypothesis for the role of endocannabinoids in fear regulation, and discuss treatment for PTSD using CB system-related drugs.

Impairment of Synaptic Plasticity by Cannabis, Δ9-THC, and Synthetic Cannabinoids

The ability of neurons to dynamically and flexibly encode synaptic inputs via short- and long-term plasticity is critical to an organism's ability to learn and adapt to the environment. Whereas synaptic plasticity may be encoded by pre- or postsynaptic mechanisms, current evidence suggests that optimization of learning requires both forms of plasticity. Endogenous cannabinoids (eCBs) play critical roles in modulating synaptic transmission via activation of cannabinoid CB1 receptors (CB1Rs) in many central nervous system (CNS) regions, and the eCB system has been implicated, either directly or indirectly, in several forms of synaptic plasticity. Because of this, perturbations within the eCB signaling system can lead to impairments in a variety of learned behaviors. One agent of altered eCB signaling is exposure to "exogenous cannabinoids" such as the primary psychoactive constituent of cannabis, Δ⁹-THC, or illicit synthetic cannabinoids that in many cases have higher potency and efficacy than Δ⁹-THC. Thus, by targeting the eCB system, these agonists can produce widespread impairment of synaptic plasticity by disrupting ongoing eCB function. Here, we review studies in which Δ⁹-THC and synthetic cannabinoids impair synaptic plasticity in a variety of neuronal circuits and examine evidence that this contributes to their well-documented ability to disrupt cognition and behavior.

The effects of FAAH inhibition on the neural basis of anxiety-related processing in healthy male subjects: a randomized clinical trial

Acute pharmacological inhibition of the anandamide-degrading enzyme, fatty acid amide hydrolase (FAAH), prolongs the regulatory effects of endocannabinoids and reverses the stress-induced anxiety state in a cannabinoid receptor-dependent manner. However, the neural systems underlying this modulation are poorly understood. A single site, randomized, double-blind, placebo-controlled, parallel study was conducted with 43 subjects assigned to receive once daily dosing of either placebo (n = 21) or JNJ-42165279 (100 mg) (n = 22) for 4 consecutive days. Pharmacodynamic effects were assessed on the last day of dosing and included evaluation of brain activation patterns using BOLD fMRI during an (1) emotion face-processing task, (2) inspiratory breathing load task, and (3) fear conditioning and extinction task. JNJ-42165279 attenuated activation in the amygdala, bilateral anterior cingulate, and bilateral insula during the emotion face-processing task consistent with effects previously observed with anxiolytic agents. Higher levels of anandamide were associated with greater attenuation in bilateral anterior cingulate and left insula. JNJ-42165279 increased the activation during anticipation of an aversive interoceptive event in the anterior cingulate and bilateral anterior insula and right inferior frontal cortex. JNJ-42165279 did not affect fear conditioning or within-session extinction learning as evidenced by a lack of differences on a subjective and neural circuit level. Taken together, these results support the hypothesis that JNJ-42165279 at this dose shares some effects with existing anxiolytic agents in dampening response to emotional stimuli but not responses to conditioned fear.

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

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

Understanding the dynamic and destiny of memories

Memory formation enables the retention of life experiences overtime. Based on previously acquired information, organisms can anticipate future events and adjust their behaviors to maximize survival. However, in an ever-changing environment, a memory needs to be malleable to maintain its relevance. In fact, substantial evidence suggests that a consolidated memory can become labile and susceptible to modifications after being reactivated, a process termed reconsolidation. When an extinction process takes place, a memory can also be temporarily inhibited by a second memory that carries information with opposite meaning. In addition, a memory can fade and lose its significance in a process known as forgetting. Thus, following retrieval, new life experiences can be integrated with the original memory trace to maintain its predictive value. In this review, we explore the determining factors that regulate the fate of a memory after its reactivation. We focus on three post-retrieval memory destinies (reconsolidation, extinction, and forgetting) and discuss recent rodent studies investigating the biological functions and neural mechanisms underlying each of these processes.

BDNF Protein and BDNF mRNA Expression of the Medial Prefrontal Cortex, Amygdala, and Hippocampus during Situational Reminder in the PTSD Animal Model

Whether BDNF protein and BDNF mRNA expression of the medial prefrontal cortex (mPFC; cingulated cortex area 1 (Cg1), prelimbic cortex (PrL), and infralimbic cortex (IL)), amygdala, and hippocampus (CA1, CA2, CA3, and dentate gyrus (DG)) was involved in fear of posttraumatic stress disorder (PTSD) during the situational reminder of traumatic memory remains uncertain. Footshock rats experienced an inescapable footshock (3 mA, 10 s), and later we have measured fear behavior for 2 min in the footshock environment on the situational reminder phase. In the final retrieval of situational reminder, BDNF protein and mRNA levels were measured. The results showed that higher BDNF expression occurred in the Cg1, PrL, and amygdala. Lower BDNF expression occurred in the IL, CA1, CA2, CA3, and DG. BDNF mRNA levels were higher in the mPFC and amygdala but lower in the hippocampus. The neural connection analysis showed that BDNF protein and BDNF mRNA exhibited weak connections among the mPFC, amygdala, and hippocampus during situational reminders. The present data did not support the previous viewpoint in neuroimaging research that the mPFC and hippocampus revealed hypoactivity and the amygdala exhibited hyperactivity for PTSD symptoms. These findings should be discussed with the previous evidence and provide clinical implications for PTSD.

Investigating the role of CB1 endocannabinoid transmission in the anti-fear and anxiolytic-like effects of ventromedial prefrontal cortex deep brain stimulation

Deep brain stimulation (DBS) delivered to the ventromedial prefrontal cortex (vmPFC) of rats induces anti-fear and anxiolytic-like behaviours, while reducing principal cell firing in the basolateral amygdala (BLA). In parallel, the endocannabinoid system, particularly in the vmPFC and BLA, has emerged as a target for the amelioration of fear and stress-related behaviours. We tested whether DBS-related improvements in fear and anxiety-type behaviour are mediated by endocannabinoid signalling. First, we examined type-1 cannabinoid (CB1) receptor and fatty acid amide hydrolase (FAAH) expression in the vmPFC and BLA and found reduced CB1 expression in both loci in rats treated with DBS. Next, we conducted pharmacological experiments to test whether the inverse CB1 agonist AM251 could mitigate the behavioural effects of stimulation. Chronic vmPFC DBS was delivered to rats following conditioning and extinction. Animals were then tested for extinction recall and anxiety-type behaviour following the systemic administration of AM251 or vehicle. We found that DBS reduced freezing and induced anxiolytic-type effects in defensive burying and novelty supressed feeding paradigms. These responses were not countered by CB1 antagonism, suggesting that other mechanisms may be involved in the anti-fear and anxiolytic effects of DBS.

A systematic, integrative review of the effects of the endocannabinoid system on inflammation and neurogenesis in animal models of affective disorders

The endocannabinoid (eCB) system is considered relevant in the pathophysiology of affective disorders, and a potential therapeutic target, as its hypoactivity is considered an important risk factor of depression. However, the biological mechanisms whereby the eCB system affects mood remain elusive. Through a systematic review, thirty-seven articles were obtained from the PubMed/Medline, Web of Science, Embase, PsychInfo, and CINAHL databases, investigating the role of the eCB system on the immune system and neurogenesis, as well as resulting behavioural effects in rodent models of affective disorders. Overall, activation of the eCB system appears to decrease depressive-like behaviour and to be anti-inflammatory, while promoting neuro- and synaptogenesis in various models. Activation of cannabinoid receptors (CBRs) is shown to be crucial in improving depressive-like and anxiety-like behaviour, although cannabidiol administration suggests a role of additional mechanisms. CB₁R signalling, as well as fatty acid amide hydrolase (FAAH) inhibition, are associated with decreased pro-inflammatory cytokines. Moreover, activation of CBRs is required for neurogenesis, which is also upregulated by FAAH inhibitors. This review is the first to assess the association between the eCB system, immune system and neurogenesis, alongside behavioural outcomes, across rodent models of affective disorders. We confirm the therapeutic potential of eCB system activation in depression and anxiety, highlighting immunoregulation as an important mechanism whereby dysfunctional behaviour and neurogenesis can be improved.

Genetic analyses of the endocannabinoid pathway in association with affective phenotypic variants

BACKGORUND

Increasing experimental data confirm the crucial role of the endocannabinoid (eCB) system in the regulation of stress response and emotional processes. Despite of the fact, that genetically determined vulnerability for stress is a widely accepted concept in the pathomechanism of affective disorders, replicable human genetic results with interaction analyses of early life trauma and eCB genes are rare. The aim of this study is to test the associations between genetic variants of the eCB pathway, childhood trauma and affective phenotypes.

METHODS

We selected 18,897 SNPs in the eCB pathway of a GWAS dataset in two general population cohorts (BP sample N = 837; MN sample N = 988). Association analyses were performed on the anxious and depressive subscales of the Brief Symptom Inventory (BSI-ANX and BSI-DEP, respectively). Childhood trauma was assessed by the Childhood Adversity Questionnaire (CAQ). Association analyses were performed in the R 2.0. statistical program using the SNPassoc package.

REULTS

Genetic effect was more robust in the BP sample than in the MN sample. The most comprehensive results showed that SNPs in the CACNA1C gene associated with depressive phenotype in interaction with CAQ in both BP (p = 1.2 × 10^-4) and MN samples (p = 1.6 × 10^-4). Direct association analyses (without interaction) provided significant associations between SNPs in different genesets of the two study populations. SNPs in KCNJ3 and GNB5 genes on the BSI-DEP (p = 6.1 × 10^-5; p = 7.1 × 10^-4) and GNG12 gene on the BSI-ANX (p = 7.4 × 10^-6) in the BP sample, while GABAergic, ADCY1 and HTR2A gene variants can be outlined from results of MN sample with less strong p-values.

CONCLUSION

Our results confirmed the prominent role of CACNA1C gene in the pathogenic effect of early life stress in the development of affective vulnerability in two different study populations using GxE interaction analysis. CACNA1C gene, as it encodes for L-type voltage-gated calcium channel, contributes to neuronal excitability, plasticity and neurogenesis being a crucial effector of both eCB signaling and the BDNF-CREB pathway as well. Our findings suggest that childhood trauma related depression may have more robust genetically determined basis than without early life stress.

Kaempferol Facilitated Extinction Learning in Contextual Fear Conditioned Rats via Inhibition of Fatty-Acid Amide Hydrolase

Background: Fear, stress, and anxiety-like behaviors originate from traumatic events in life. Stress response is managed by endocannabinoids in the body by limiting the uncontrolled retrieval of aversive memories. Pharmacotherapy-modulating endocannabinoids, especially anandamide, presents a promising tool for treating anxiety disorders. Here, we investigated the effect of kaempferol, a flavonoid, in the extinction of fear related memories and associated anxiety-like behavior. Methods: The ability of kaempferol to inhibit fatty-acid amide hydrolase (FAAH, the enzyme that catabolizes anandamide) was assessed in vitro using an enzyme-linked immunosorbent assay (ELISA) kit. For animal studies (in vivo), the extinction learning was evaluated using contextual fear conditioning (CFC, a behavioral paradigm based on ability to learn and remember aversive stimuli). Furthermore, an elevated plus-maze (EPM) model was used for measuring anxiety-like behavior, while serum corticosterone served as a biochemical indicator of anxiety. Lastly, the interaction of kaempferol with FAAH enzyme was also assessed in silico (computational study). Results: Our data showed that kaempferol inhibited the FAAH enzyme with an IC₅₀ value of 1 µM. In CFC, it reduced freezing behavior in rats. EPM data demonstrated anxiolytic activity as exhibited by enhanced number of entries and time spent in the open arm. No change in blood corticosterone levels was noted. Our computational study showed that Kaempferol interacted with the catalytic amino acids (SER241, PHE192, PHE381, and THR377) of FAAH enzyme Conclusion: Our study demonstrate that kaempferol facilitated the extinction of aversive memories along with a reduction of anxiety. The effect is mediated through the augmentation of endocannabinoids via the inhibition of FAAH enzyme.

Meet Your Stress Management Professionals: The Endocannabinoids

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

The interaction effect of sleep deprivation and cannabinoid type 1 receptor in the CA1 hippocampal region on passive avoidance memory, depressive-like behavior and locomotor activity in rats

Increasing evidence shows the interaction effect of cannabinoids and sleep on cognitive functions. In the present study, we aimed to investigate the interaction effect of cannabinoids type 1 receptor (CB1r) in the CA1 hippocampal region and sleep deprivation (SD) on passive avoidance memory and depressive-like behavior in male Wistar rats. We used water box apparatus to induce total SD (TSD) for 24 h. The shuttle-box was applied to assess passive avoidance memory and locomotion apparatus was applied to assess locomotor activity. Forced swim test (FST) was used to evaluate rat's behavior. ACPA (CB1r agonist) at the doses of 0.01, 0.001 and 0.0001 μg/rat, and AM251 (CB1r antagonist) at the doses of 100, 10 and 1 ng/rat were injected intra-CA1, five minutes after training via stereotaxic surgery. Results showed SD impaired memory. ACPA at the doses of 0.01 and 0.001 μg/rat impaired memory and at all doses did not alter the effect of SD on memory. AM251 by itself did not alter memory, while at lowest dose (1 ng/rat) restored SD-induced memory deficit. Both drugs induced depressive-like behavior in a dose-dependent manner. Furthermore, both drugs decreased swimming at some doses (ACPA at 0.0001 μg/rat, AM251 at 0.001 and 0.01 ng/rat). Also, ACPA at the highest dose increased climbing of SD rats. In conclusion, we suggest CB1r may interact with the effect of SD on memory. Additionally, cannabinoids may show a dose-dependent manner in modulating mood and behavior. Interestingly, CB1r agonists and antagonists may exhibit a similar effect in some behavioral assessments.

Lights on Endocannabinoid-Mediated Synaptic Potentiation

The endocannabinoid (eCB) system is a lipid-based neurotransmitter complex that plays crucial roles in the neural control of learning and memory. The current model of eCB-mediated retrograde signaling is that eCBs released from postsynaptic elements travel retrogradely to presynaptic axon terminals, where they activate cannabinoid type-1 receptors (CB₁Rs) and ultimately decrease neurotransmitter release on a short- or long-term scale. An increasing body of evidence has enlarged this view and shows that eCBs, besides depressing synaptic transmission, are also able to increase neurotransmitter release at multiple synapses of the brain. This indicates that eCBs act as bidirectional regulators of synaptic transmission and plasticity. Recently, studies unveiled links between the expression of eCB-mediated long-term potentiation (eCB-LTP) and learning, and between its dysregulation and several pathologies. In this review article, we first distinguish the various forms of eCB-LTP based on their mechanisms, resulting from homosynaptically or heterosynaptically-mediated processes. Next, we consider the neuromodulation of eCB-LTP, its behavioral impact on learning and memory, and finally, eCB-LTP disruptions in various pathologies and its potential as a therapeutic target in disorders such as stress coping, addiction, Alzheimer’s and Parkinson’s disease, and pain. Cannabis is gaining popularity as a recreational substance as well as a medicine, and multiple eCB-based drugs are under development. In this context, it is critical to understand eCB-mediated signaling in its multi-faceted complexity. Indeed, the bidirectional nature of eCB-based neuromodulation may offer an important key to interpret the functions of the eCB system and how it is impacted by cannabis and other drugs.

Cannabinoids as therapeutics for PTSD

Post-traumatic stress disorder (PTSD) is a complex disorder that involves dysregulation of multiple neurobiological systems. The traumatic stressor plays a causal role in producing psychological dysfunction and the pattern of findings suggests that the hypothalamic-pituitary-adrenal (HPA) axis, which is instrumental for stress adaptation, is critically dysfunctional in PTSD. Given the lack of understanding of the basic mechanisms and underlying pathways that cause the disorder and its heterogeneity, PTSD poses challenges for treatment. Targeting the endocannabinoid (ECB) system to treat mental disorders, and PTSD in particular, has been the focus of research and interest in recent years. The ECB system modulates multiple functions, and drugs enhancing ECB signaling have shown promise as potential therapeutic agents in stress effects and other psychiatric and medical conditions. In this review, we focus on the interaction between the ECB-HPA systems in animal models for PTSD and in patients with PTSD. We summarize evidence supporting the use of cannabinoids in preventing and treating PTSD in preclinical and clinical studies. As the HPA system plays a key role in the mediation of the stress response and the pathophysiology of PTSD, we describe preclinical studies suggesting that enhancing ECB signaling is consistent with decreasing PTSD symptoms and dysfunction of the HPA axis. Overall, we suggest that a pharmacological treatment targeted at one system (e.g., HPA) may not be very effective because of the heterogeneity of the disorder. There are abnormalities across different neurotransmitter systems in the pathophysiology of PTSD and none of these systems function uniformly among all patients with PTSD. Hence, conceptually, enhancing ECB signaling may be a more effective avenue for pharmacological treatment.

The amygdala via the paraventricular nucleus regulates asthma attack in rats

Aims

This study aimed to investigate the functions of the amygdala in rat asthma model.

Main methods

Wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) was used for tracing from the paraventricular nucleus (PVN) to the amygdala, and nuclear lesions were performed to observe changes in respiratory function and airway inflammation.

Results

This study showed that the extracellular neuronal discharged in the medial amygdala (MeA) and central amygdala (CeA), and the expression of Fos significantly increased in asthmatic rat compared to control group. The distribution of Fos‐ and oxytocin (OT)‐positive neurons and Fos/OT dual‐positive neurons evidently increased in the PVN. WGA‐HRP was injected into the PVN for tracing, and Fos/HRP‐dual‐positive neurons were observed to be distributed in the MeA. By using kainic acid (KA) to injure the MeA and CeA in asthmatic rats, expiratory and inspiratory times (TE/TI) and airway resistance (Raw) decreased, and minute ventilation volume (MVV) and dynamic pulmonary compliance (Cdyn) increased accordingly. In the bronchoalveolar lavage fluid (BALF), the number of eosinophils and the concentration of IL‐4 were lower than those of the control group, and the ratio of Th1/Th2 cells was higher than that of the control group. In the PVN, the distribution of Fos‐, OT‐positive cells and Fos/OT double‐positive cells decreased compared with those of the control group. The activities of the MeA and CeA and of OT neurons in the PVN of the rats were correlated with the occurrence of asthma.

Conclusions

Asthma attack could induce neural activities in the MeA and CeA, and OT neurons in the PVN may be involved in the process of asthma attack.

A time-dependent contribution of hippocampal CB1 , CB2 and PPARγ receptors to cannabidiol-induced disruption of fear memory consolidation

BACKGROUND AND PURPOSE

In preclinical studies, cannabidiol (CBD) mitigates fear memories by facilitating their extinction or interfering with their generalization and reconsolidation. The brain regions and mechanisms underlying these effects, and their temporal window, are still poorly understood. Here, we have investigated related questions in the dorsal hippocampus (DH) during contextual fear consolidation.

EXPERIMENTAL APPROACH

Adult male Wistar rats received CBD (10-30 pmol) intra-DH immediately, 1 or 3 hr after fear conditioning. Effects of CBD on consolidation were inferred behaviourally and by analysing expression of the activity-regulated, cytoskeleton-associated (Arc) protein. The contribution of anandamide, CB₁ , CB₂ , 5-HT_1A , A_2A , and PPARγ receptors was also assessed.

KEY RESULTS

CBD impaired memory consolidation when given immediately or 1 hr after fear conditioning, but not after 3 hr. Expression of Arc protein in DH was reduced by systemic CBD treatment in both cases. Immediately after fear conditioning, CBD effects were abolished by CB₁ or CB₂ receptor blockade, partly reduced by 5-HT_1A or A_2A antagonism, and remained unchanged after antagonism of PPARγ receptors. One hour after fear conditioning, CBD effects were prevented only by PPARγ receptor antagonism. Also, inhibition of fatty acid amide hydrolase by URB597, impaired memory consolidation when infused immediately, but not 1 hr after fear conditioning.

CONCLUSIONS AND IMPLICATIONS

CBD disrupts memory consolidation up to 1 hr after fear conditioning, allowing an extended window of opportunity to mitigate aversive memories after their acquisition. Our results suggest time-dependent participation of anandamide, CB₁ , CB₂ and PPARγ receptors in the DH, during this process.

Endocannabinoid modulating drugs improve anxiety but not the expression of conditioned fear in a rodent model of post-traumatic stress disorder

The endocannabinoid (eCB) system is a potential target for the treatment of symptoms of post-traumatic stress disorder (PTSD). Similar to clinical PTSD, approximately 25-30% of rats that undergo cued fear conditioning exhibit impaired extinction learning. In addition to extinction-resistant fear, these "weak extinction" (WE) rats show persistent anxiety-like behaviors. The goal of the present study was to test the hypothesis that behavioural differences between WE animals and those presenting normal extinction patterns (strong extinction; SE) could be mediated by the eCB system. Rats undergoing fear conditioning/extinction and fear recall sessions were initially segregated in weak and strong-extinction groups. Two weeks later, animals underwent a fear recall session followed by a novelty-suppressed feeding (NSF) test. In acute experiments, WE rats were injected with either the fatty acid amide hydrolase (FAAH) inhibitor URB597 or the CB1 agonist WIN55,212-2 1 h prior to long-term recall and NSF testing. SE animals were injected with the inverse CB₁ receptor agonist AM251. In chronic experiments, WE and SE rats were given daily injections of URB597 or AM251 between short and long-term recall sessions. We found that acute administration of WIN55,212-2 but not URB597 reduced anxiety-like behaviour in WE rats. In contrast, AM251 was anxiogenic in SE animals. Neither treatment was effective in altering freezing expression during fear recall. The chronic administration of AM251 to SE or URB597 to WE did not alter fear or anxiety-like behaviour or changed the expression of FAAH and CB₁. Together, these results suggest that systemic manipulations of the eCB system may alter anxiety-like behaviour but not the behavioural expression of an extinction-resistant associative fear memory.

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.

Neuropeptide Y and cannabinoids interaction in the amygdala after exposure to shock and reminders model of PTSD

Modulation of cannabinoid and neuropeptide Y (NPY) receptors may offer therapeutic benefits for post-traumatic stress disorder (PTSD). In this study, we aimed to investigate the functional interaction between these systems in the basolateral amygdala (BLA) in a rat model of PTSD. Rats were exposed to the shock and reminders model of PTSD and tested for hyper arousal/PTSD- and depression-like behaviors 3 weeks later. Immediately after shock exposure rats were microinjected into the BLA with URB597, a selective inhibitor of fatty acid amide hydrolase (FAAH) that increases the levels of the endocannabinoid anandamide or with the NPY1 receptor agonist Leu³¹,Pro³⁴-NPY (Leu). Intra-BLA URB597 prevented the shock/reminders-induced PTSD- behaviors (extinction, startle) and depression-behaviors (despair, social impairments). These preventing effects of URB597 on PTSD- and depression-like behaviors were shown to be mostly mediated by cannabinoid CB1 and NPY1 receptors, as they were blocked when URB597 was co-administered with a low dose of a CB1 or NPY1 receptor antagonist. Similarly, intra-BLA Leu prevented development of all the behaviors. Interestingly, a CB1 antagonist prevented the effects of Leu on despair and social behavior, but not the effects on extinction and startle. Moreover, exposure to shock and reminders upregulated CB1 and NPY1 receptors in the BLA and infralimbic prefrontal cortex and this upregulation was restored to normal with intra-BLA URB597 or Leu. The findings suggest that the functional interaction between the eCB and NPY1 systems is complex and provide a rationale for exploring novel therapeutic strategies that target the cannabinoid and NPY systems for stress-related diseases.

Endocannabinoids and Fear-Related Behavior in Mice Selectively Bred for High or Low Alcohol Preference

Alcohol use disorders (AUDs) have a high incidence of co-morbidity with stress-related psychopathologies, such as post-traumatic stress disorder (PTSD). Genetic and pharmacological studies support a prominent role for the endocannabinoid system (ECS) in modulating stress-related behaviors relevant to AUDs and PTSD. Mouse lines selectively bred for high (HAP) and low (LAP) alcohol preference show reproducible differences in fear-potentiated startle (FPS), a model for PTSD-related behavior. The first experiment in this study assessed levels of the endocannabinoids, anandamide (AEA) and sn-2 arachidonylglycerol (2-AG), in the prefrontal cortex (PFC), amygdala (AMG), and hippocampus (HIP) of male and female HAP1 and LAP1 mice following the expression of FPS to determine whether ECS responses to conditioned-fear stress (FPS) were correlated with genetic propensity toward high or low alcohol preference. The second experiment examined effects of a cannabinoid receptor type 1 agonist (CP55940) and antagonist (rimonabant) on the expression of FPS in HAP1 and LAP1 male and female mice. The estrous cycle of females was monitored throughout the experiments to determine if the expression of FPS differed by stage of the cycle. FPS was greater in male and female HAP1 than LAP1 mice, as previously reported. In both experiments, LAP1 females in diestrus displayed greater FPS than LAP1 females in metestrus and estrus. In the AMG and HIP, AEA levels were greater in male fear-conditioned HAP1 mice than LAP1 mice. There were no line or sex differences in effects of CP55940 or rimonabant on the expression of FPS. However, surprisingly, evidence for anxiogenic effects of prior treatment with CP55940 were seen in all mice during the third drug-free FPS test. These findings suggest that genetic differences in ECS function in response to fear-conditioning stress may underlie differences in FPS expression in HAP1 and LAP1 selected lines.

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.