Selective alterations of the CB1 receptors and the fatty acid amide hydrolase in the ventral striatum of alcoholics and suicides

How depression and antidepressant drugs affect endocannabinoid system?-review of clinical and preclinical studies

As major depressive disorder is becoming a more and more common issue in modern society, it is crucial to discover new possible grip points for its diagnosis and antidepressive therapy. One of them is endocannabinoid system, which has been proposed as a manager of emotional homeostasis, and thus, endocannabinoid alterations have been found in animals undergoing various preclinical models of depression procedures as well as in humans suffering from depressive-like disorders. In this review article, studies regarding those alterations have been summed up and analyzed. Another important issue raised by the researchers is the impact of currently used antidepressive drugs on endocannabinoid system so that it would be possible to predict reversibility of endocannabinoid alterations following stress exposure and, in the future, to be able to design individually personalized therapies. Preclinical studies investigating this topic have been analyzed and described in this article. Unfortunately, too few clinical studies in this field exist, what indicates an urgent need for collecting such data, so that it would be possible to compare them with preclinical outcomes and draw reliable conclusions.

Omega-3 Recovers Cannabinoid 1 Receptor Expression in the Adult Mouse Brain after Adolescent Binge Drinking

Adolescent binge drinking is a social problem with a long-lasting impact on cognitive functions. The cannabinoid type-1 (CB1) receptor of the endocannabinoid system (ECS) is involved in brain synaptic plasticity, cognition and behavior via receptor localization at specific subcellular compartments of the cortical, limbic and motor regions. Alcohol (EtOH) intake affects the ECS, CB1 and their functions. Evidence indicates that binge drinking during adolescence impairs memory via the abrogation of CB1-dependent synaptic plasticity in the hippocampus. However, the impact of EtOH consumption on global CB1 receptor expression in the adult brain is unknown. We studied this using optical density analysis throughout brain regions processed for light microscopy (LM) immunohistotochemistry. CB1 staining decreased significantly in the secondary motor cortex, cerebellum, cingulate cortex, amygdala and nucleus accumbens. Next, as omega-3 (n-3) polyunsaturated fatty acids (PUFAs) rescue synaptic plasticity and improve EtOH-impaired cognition, we investigated whether docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) had any effect on CB1 receptors. N-3 intake during EtOH abstinence restored CB1 immunostaining in the secondary motor cortex, cerebellum and amygdala, and ameliorated receptor density in the cingulate cortex. These results show that n-3 supplementation recovers CB1 receptor expression disrupted by EtOH in distinct brain regions involved in motor functions and cognition.

Molecular Changes Associated with Suicide

Suicide is a serious global public health problem, with a worrying recent increase in suicide rates in both adolescent and adult populations. However, it is essential to recognize that suicide is preventable. A myriad of factors contributes to an individual's vulnerability to suicide. These factors include various potential causes, from psychiatric disorders to genetic and epigenetic alterations. These changes can induce dysfunctions in crucial systems such as the serotonergic, cannabinoid, and hypothalamic-pituitary-adrenal axes. In addition, early life experiences of abuse can profoundly impact an individual's ability to cope with stress, ultimately leading to changes in the inflammatory system, which is a significant risk factor for suicidal behavior. Thus, it is clear that suicidal behavior may result from a confluence of multiple factors. This review examines the primary risk factors associated with suicidal behavior, including psychiatric disorders, early life adversities, and epigenetic modifications. Our goal is to elucidate the molecular changes at the genetic, epigenetic, and molecular levels in the brains of individuals who have taken their own lives and in the plasma and peripheral mononuclear cells of suicide attempters and how these changes may serve as predisposing factors for suicidal tendencies.

Association Between Fatty Acid Amide Hydrolase and Alcohol Response Phenotypes: A Positron Emission Tomography Imaging Study With [11C]CURB in Heavy-Drinking Youth

BACKGROUND

Reductions in fatty acid amide hydrolase (FAAH), the catabolic enzyme for the endocannabinoid anandamide, may play a role in drinking behavior and risk for alcohol use disorder. We tested the hypotheses that lower brain FAAH levels in heavy-drinking youth are related to increased alcohol intake, hazardous drinking, and differential response to alcohol.

METHODS

FAAH levels in the striatum, prefrontal cortex, and whole brain were determined using positron emission tomography imaging of [11C]CURB in heavy-drinking youth (N = 31; 19-25 years of age). C385A FAAH genotype (rs324420) was determined. Behavioral (n = 29) and cardiovascular (n = 22) responses to alcohol were measured during a controlled intravenous alcohol infusion.

RESULTS

Lower [11C]CURB binding was not significantly related to frequency of use but was positively associated with hazardous drinking and reduced sensitivity to the negative effects of alcohol. During alcohol infusion, lower [11C]CURB binding related to greater self-reported stimulation and urges and lower sedation (p < .05). Lower heart rate variability was related to both greater alcohol-induced stimulation and lower [11C]CURB binding (p < .05). Family history of alcohol use disorder (n = 14) did not relate to [11C]CURB binding.

CONCLUSIONS

In line with preclinical studies, lower FAAH in the brain was related to a dampened response to the negative, impairing effects of alcohol, increased drinking urges, and alcohol-induced arousal. Lower FAAH might alter positive or negative effects of alcohol and increase urges to drink, thereby contributing to the addiction process. Determining whether FAAH influences motivation to drink through increased positive/arousing effects of alcohol or greater tolerance should be investigated.

Cannabidiol regulates behavioral and brain alterations induced by spontaneous alcohol withdrawal

The main goal of this study was to evaluate if the administration of cannabidiol (CBD) regulates behavioral and gene expression alterations induced by spontaneous alcohol withdrawal (SAW) in mice. Increasing doses of ethanol were administered to C57BL/6J male mice for 15 days (2.5, 3 and 3.5 g/kg/12 h, p. o.), and SAW was studied at 6, 12, 24, and 72 h after the last ethanol administration. The efficacy of acute CBD (10, 20, and 40 mg/kg, i. p.) to regulate behavioral changes induced by SAW was explored at 6 h. Gene expression analyses of cannabinoid receptors 1 (Cnr1) and 2 (Cnr2), mu-opioid receptor (Opmr1), and proopiomelanocortin (Pomc) in the nucleus accumbens (NAcc), and Pomc and tyrosine hydroxylase (Th) in the ventral tegmental area (VTA), were carried out by real time-PCR. Pearson correlation was used to identify potential associations between the gene expression data and the anxiety-like behaviors. Biostatistical studies suggest associations between gene expression data and the anxiogenic behaviors in mice exposed to the SAW model and treated with VEH and 40 mg/kg of CBD. Mice exposed to the SAW model showed significant somatic withdrawal signs, anxiety-like behaviors, and remarkable changes in the gene expression of all brain targets at 6 h. CBD dose-dependently normalized the behavioral, somatic withdrawal signs and anxiety-like behaviors and modulated gene expression changes in the NAcc, but not in the VTA. The results of this study suggest that CBD may regulate specific alcohol withdrawal-associated alterations. However, further studies are required to explore the possible mechanisms involved.

Genetic variation in fatty acid amide hydrolase (FAAH): Associations with early drinking and smoking behaviors

BACKGROUND

The endocannabinoid system is implicated in psychiatric disorders and drug dependence. Within this system, fatty acid amide hydrolase (FAAH) metabolizes endocannabinoids. Individuals with A-group genotypes (C/A or A/A) of a common FAAH variant (rs324420; C > A; Pro129Thr) have slower enzymatic activity compared to C-group individuals (C/C genotype). Slow FAAH activity is differentially associated with alcohol and nicotine use.

METHODS

Among European-ancestry participants in the NDIT study (n = 249-607), genotype associations with past-year binge drinking in young adults were estimated in logistic regression models. In adolescents, hazard ratios (HR) were estimated from Cox proportional hazards models to assess the FAAH genotype group association with time to drinking initiation and attaining drinking frequency outcomes. HR were also used to assess genotype effect on time to smoking initiation and attaining early smoking milestones (e.g., first inhalation, ICD-10 dependence).

RESULTS

Compared to those in the C-group, those in the A-group had higher odds of binge drinking at ages 20 (Odds ratio (OR) = 2.16, 95 % CI 1.36-3.42) and 30 (OR = 1.61, 95 % CI 1.10-2.36). Time to initiation of drinking and daily drinking was faster in adolescents in the A-group (HR = 1.39, 95 % CI 1.09-1.77 and HR = 2.24, 95 % CI 1.05-4.76, respectively). Time to smoking initiation was faster in the A-group (HR = 1.20, 95 % CI 1.04-1.39); however, time to smoking milestones among adolescent smokers was not consistently different for the A- versus C-groups (HR = 0.43 to 1.13).

CONCLUSIONS

Slow FAAH activity (A-group) was associated with greater risks for binge drinking, drinking initiation and escalation, and cigarette smoking initiation, but had little impact on the escalation in cigarette smoking behaviors.

Endocannabinoids at the synapse and beyond: implications for neuropsychiatric disease pathophysiology and treatment

Endocannabinoids (eCBs) are lipid neuromodulators that suppress neurotransmitter release, reduce postsynaptic excitability, activate astrocyte signaling, and control cellular respiration. Here, we describe canonical and emerging eCB signaling modes and aim to link adaptations in these signaling systems to pathological states. Adaptations in eCB signaling systems have been identified in a variety of biobehavioral and physiological process relevant to neuropsychiatric disease states including stress-related disorders, epilepsy, developmental disorders, obesity, and substance use disorders. These insights have enhanced our understanding of the pathophysiology of neurological and psychiatric disorders and are contributing to the ongoing development of eCB-targeting therapeutics. We suggest future studies aimed at illuminating how adaptations in canonical as well as emerging cellular and synaptic modes of eCB signaling contribute to disease pathophysiology or resilience could further advance these novel treatment approaches.

Acute stress and alcohol exposure during adolescence result in an anxious phenotype in adulthood: Role of altered glutamate/endocannabinoid transmission mechanisms

BACKGROUND

Stressful episodes and high alcohol consumption during adolescence are considered major risk factors for the development of psychiatric disorders in adulthood. Identification of mechanisms underlying these early events, which enhanced vulnerability to mental illness, is essential for both their prevention and treatment.

METHODS

Male Wistar rats were used to investigate the long-term effects of early restraint stress and intermittent alcohol exposure (intragastric administration of 3 g/kg ethanol; 4 days/week for 4 weeks during adolescence) on anxiety-like behavior and the expression of signaling systems associated with emotional behaviors [e.g., corticosterone, fatty acid-derived molecules and endocannabinoid enzymes, glutamate receptor subunits, corticotropin releasing hormone receptors (CRHR1 and CRHR2) and neuropeptide Y receptors (NPY1R and NPYR2)] in the blood and amygdala.

RESULTS

Overall, both stress and alcohol exposure during adolescence induced anxiogenic-like behaviors, increased plasma levels of corticosterone and increases in the amygdalar expression of the cannabinoid CB₂ receptor and certain subunits of glutamate receptors (i.e., mGluR1, mGluR5 and NMDAR1) in young adult rats. In addition, there were specific main effects of alcohol exposure on the expression of the cannabinoid CB₁ receptor, monoacylglycerol lipase (MAGL) and NPY2R in the amygdala, and significant increases were observed in rats exposed to alcohol. Interestingly, there were significant interaction effects between restraint stress and alcohol exposure on the expression of plasma 2-arachidonoyl glycerol (2-AG), and both CRHR1,2 and NPY1R in the amygdala. Thus, the restraint stress was associated with increased 2-AG levels, which was not observed in rats exposed to alcohol. The alcohol exposure was associated with an increased expression of CRHR1,2 but the restraint stress prevented these increases (stress alcohol rats). In contrast, NPY1R was only increased in rats exposed to stress and alcohol. Finally, we did not observe any potentiation of the behavioral and molecular effects by the combination of stress and alcohol, which is concordant with an overall ceiling effect on some of the variables.

CONCLUSION

Separate and combined early stress and alcohol induced a common anxious phenotype with increased corticosterone in adulthood. However, there were differences in the amygdalar expression of signaling systems involved in maladaptive changes in emotional behavior. Therefore, our results suggest the existence of partially different mechanisms for stress and alcohol exposures.

Biomarkers of the Endocannabinoid System in Substance Use Disorders

Despite substance use disorders (SUD) being one of the leading causes of disability and mortality globally, available therapeutic approaches remain ineffective. The difficulty in accurately characterizing the neurobiological mechanisms involved with a purely qualitative diagnosis is an obstacle to improving the classification and treatment of SUD. In this regard, identifying central and peripheral biomarkers is essential to diagnosing the severity of drug dependence, monitoring therapeutic efficacy, predicting treatment response, and enhancing the development of safer and more effective pharmacological tools. In recent years, the crucial role that the endocannabinoid system (ECS) plays in regulating the reinforcing and motivational properties of drugs of abuse has been described. This has led to studies characterizing ECS alterations after exposure to various substances to identify biomarkers with potential diagnostic, prognostic, or therapeutic utility. This review aims to compile the primary evidence available from rodent and clinical studies on how the ECS components are modified in the context of different substance-related disorders, gathering data from genetic, molecular, functional, and neuroimaging experimental approaches. Finally, this report concludes that additional translational research is needed to further characterize the modifications of the ECS in the context of SUD, and their potential usefulness in the necessary search for biomarkers.

The Synaptic Interactions of Alcohol and the Endogenous Cannabinoid System

PURPOSE

A growing body of evidence has implicated the endocannabinoid (eCB) system in the acute, chronic, and withdrawal effects of alcohol/ethanol on synaptic function. These eCB-mediated synaptic effects may contribute to the development of alcohol use disorder (AUD). Alcohol exposure causes neurobiological alterations similar to those elicited by chronic cannabinoid (CB) exposure. Like alcohol, cannabinoids alter many central processes, such as cognition, locomotion, synaptic transmission, and neurotransmitter release. There is a strong need to elucidate the effects of ethanol on the eCB system in different brain regions to understand the role of eCB signaling in AUD.

SEARCH METHODS

For the scope of this review, preclinical studies were identified through queries of the PubMed database.

SEARCH RESULTS

This search yielded 459 articles. Clinical studies and papers irrelevant to the topic of this review were excluded.

DISCUSSION AND CONCLUSIONS

The endocannabinoid system includes, but is not limited to, cannabinoid receptors 1 (CB₁), among the most abundantly expressed neuronal receptors in the brain; cannabinoid receptors 2 (CB₂); and endogenously formed CB₁ ligands, including arachidonoylethanolamide (AEA; anandamide), and 2-arachidonoylglycerol (2-AG). The development of specific CB₁ agonists, such as WIN 55,212-2 (WIN), and antagonists, such as SR 141716A (rimonabant), provide powerful pharmacological tools for eCB research. Alcohol exposure has brain region-specific effects on the eCB system, including altering the synthesis of endocannabinoids (e.g., AEA, 2-AG), the synthesis of their precursors, and the density and coupling efficacy of CB₁. These alcohol-induced alterations of the eCB system have subsequent effects on synaptic function including neuronal excitability and postsynaptic conductance. This review will provide a comprehensive evaluation of the current literature on the synaptic interactions of alcohol exposure and eCB signaling systems, with an emphasis on molecular and physiological synaptic effects of alcohol on the eCB system. A limited volume of studies has focused on the underlying interactions of alcohol and the eCB system at the synaptic level in the brain. Thus, the data on synaptic interactions are sparse, and future research addressing these interactions is much needed.

Higher trait neuroticism is associated with greater fatty acid amide hydrolase binding in borderline and antisocial personality disorders

Borderline personality disorder (BPD) and antisocial personality disorder (ASPD) are the two most frequently diagnosed and researched DSM-5 personality disorders, and both are characterized by high levels of trait neuroticism. Fatty acid amide hydrolase (FAAH), an enzyme of the endocannabinoid system (ECS), has been linked to regulation of mood through modulation of anandamide, an endocannabinoid. We hypothesized that prefrontal cortex (PFC) FAAH binding would relate to trait neuroticism in personality disorders. Thirty-one individuals with personality disorders (20 with BPD and 11 with ASPD) completed the investigation. All participants completed the revised NEO Personality Inventory, which yields standardized scores (e.g., T scores) for the traits of neuroticism, openness, conscientiousness, agreeableness, and extraversion. All participants were medication free and were not utilizing illicit substances as determined by drug urinalysis. Additionally, none of the participants had a comorbid major depressive episode, bipolar disorder, psychotic disorder, or substance use disorder. Each participant underwent one [¹¹C]CURB PET scan. Consistent with our hypothesis, neuroticism was positively correlated with PFC FAAH binding (r = 0.42, p = 0.021), controlling for genotype. Neuroticism was also positively correlated with dorsal putamen FAAH binding (r = 0.53, p = 0.0024), controlling for genotype. Elevated brain FAAH is an endophenotype for high neuroticism in BPD and ASPD. Novel pharmacological therapeutics that inhibit FAAH could emerge as potential new treatments for BPD and ASPD with high neuroticism.

CB1 receptor neutral antagonist treatment epigenetically increases neuropeptide Y expression and decreases alcohol drinking

Alcohol consumption is mediated by several important neuromodulatory systems, including the endocannabinoid and neuropeptide Y (NPY) systems in the limbic brain circuitry. However, molecular mechanisms through which cannabinoid-1 (CB1) receptors regulate alcohol consumption are still unclear. Here, we investigated the role of the CB1 receptor-mediated downstream regulation of NPY via epigenetic mechanisms in the amygdala. Alcohol drinking behavior was measured in adult male C57BL/6J mice treated with a CB1 receptor neutral antagonist AM4113 using a two-bottle choice paradigm while anxiety-like behavior was assessed in the light-dark box (LDB) test. The CB1 receptor-mediated changes in the protein levels of phosphorylated cAMP-responsive element binding protein (pCREB), CREB binding protein (CBP), H3K9ac, H3K14ac and NPY, and the mRNA levels of Creb1, Cbp, and Npy were measured in amygdaloid brain structures. Npy-specific changes in the levels of acetylated histone (H3K9/14ac) and CBP in the amygdala were also measured. We found that the pharmacological blockade of CB1 receptors with AM4113 reduced alcohol consumption and, in an ethanol-naïve cohort, reduced anxiety-like behavior in the LDB test. Treatment with AM4113 also increased the mRNA levels of Creb1 and Cbp in the amygdala as well as the protein levels of pCREB, CBP, H3K9ac and H3K14ac in the central and medial nucleus of amygdala, but not in the basolateral amygdala. Additionally, AM4113 treatment increased occupancy of CBP and H3K9/14ac at the Npy gene promoter, leading to an increase in both mRNA and protein levels of NPY in the amygdala. These novel findings suggest that CB1 receptor-mediated CREB signaling plays an important role in the modulation of NPY function through an epigenetic mechanism and further support the potential use of CB1 receptor neutral antagonists for the treatment of alcohol use disorder.

Endocannabinoid signaling in the lateral habenula regulates pain and alcohol consumption

Hyperalgesia, which often occurs in people suffering from alcohol use disorder, may drive excessive drinking and relapse. Emerging evidence suggests that the lateral habenula (LHb) may play a significant role in this condition. Previous research suggests that endocannabinoid signaling (eCBs) is involved in drug addiction and pain, and that the LHb contains core components of the eCBs machinery. We report here our findings in rats subjected to chronic ethanol vapor exposure. We detected a substantial increase in endocannabinoid-related genes, including Mgll and Daglb mRNA levels, as well as monoacylglycerol lipase (MAGL) protein levels, as well as a decrease in Cnr1 mRNA and type-1 cannabinoid receptor (CB1R) protein levels, in the LHb of ethanol-exposed rats. Also, rats withdrawing from ethanol exposure displayed hypersensitivity to mechanical and thermal nociceptive stimuli. Conversely, intra-LHb injection of the MAGL inhibitor JZL184, the fatty acid amide hydrolase inhibitor URB597, or the CB1R agonist WIN55,212-2 produced an analgesic effect, regardless of ethanol or air exposure history, implying that alcohol exposure does not change eCB pain responses. Intra-LHb infusion of the CB1R inverse agonist rimonabant eliminated the analgesic effect of these chemicals. Rimonabant alone elicited hyperalgesia in the air-, but not ethanol-exposed animals. Moreover, intra-LHb JZL184, URB597, or WIN55,212-2 reduced ethanol consumption in both homecages and operant chambers in rats exposed to ethanol vapor but not air. These findings suggest that LHb eCBs play a pivotal role in nociception and facilitating LHb eCBs may attenuate pain in drinkers.

Contribution of Fatty Acid Amide Hydrolase to Alcohol Use Disorder: A Systematic Review

Purpose: Recent research has suggested that chronic alcohol exposure induces changes in the endocannabinoid system within the central nervous system and therefore could be an attractive target for better understanding and treating alcohol use disorder (AUD). Much of this research has centered around the CB₁ receptor and its endogenous partial agonist, the endocannabinoid anandamide, as the CB₁ receptor is densely expressed in brain regions involved in development and maintenance of addictive behaviors. In addition, recent evidence has suggested that chronic alcohol exposure induces changes in the modulation of endocannabinoid concentration and suggests that these changes may contribute to the motivation to abuse alcohol. Therefore, we performed a systematic literature review to evaluate how fatty acid amide hydrolase (FAAH), an enzyme that degrades anandamide, relates to the characteristics and biology of AUD, as well as how modulating FAAH through pharmacologic inhibition or genetic manipulation affects outcomes related to alcohol use and consumption. Method: A search strategy was developed using the terms "endocannabinoids" or "drug delivery systems" and "alcohol dependence" or "alcohol use disorder" or "alcoholism" and "Fatty Acid Amide Hydrolase" and "FAAH" as text words and Medical Subject Headings (i.e., MeSH and EMTREE). We then used this search strategy on the electronic databases PubMed, Embase, and Web of Science. Results: We found 224 records; after removing repeated records (37%), articles that did not fit the topic question (47%), or were not primary research (4%), we included 26 for qualitative synthesis (12%). Discussion: The literature clearly suggests that FAAH has a role in the biology and characteristics of AUD. FAAH inhibition seems especially promising as a target for alcohol withdrawal as it may lead to a reduction in symptoms, including anxiety and a reduction of alcohol intake reinstatement. However, decreased FAAH may also lead to reduced sensitivity to alcohol along with increased preference and intake. Conclusions: Modulation of FAAH is promising for therapeutic intervention of AUD, but requires more research. Pre-clinical studies have indicated that FAAH inhibition may reduce withdrawal characteristics, but may also exacerbate other characteristics of AUD outside of that period.

Endocannabinoid-mediated neuromodulation in the main olfactory bulb at the interface of environmental stimuli and central neural processing

The olfactory system has become an important functional gateway to understand and analyze neuromodulation since olfactory dysfunction and deficits have emerged as prodromal and, at other times, as first symptoms of many of neurodegenerative, neuropsychiatric and communication disorders. Considering olfactory dysfunction as outcome of altered, damaged and/or inefficient olfactory processing, in the current review, we analyze how olfactory processing interacts with the endocannabinoid signaling system. In the human body, endocannabinoid synthesis is a natural and on-demand response to a wide range of physiological and environmental stimuli. Our current understanding of the response dynamics of the endocannabinoid system is based in large part on research advances in limbic system areas, such as the hippocampus and the amygdala. Functional interactions of this signaling system with olfactory processing and associated pathways are just emerging but appear to grow rapidly with multidimensional approaches. Recent work analyzing the crystal structure of endocannabinoid receptors bound to their agonists in a signaling complex has opened avenues for developing specific therapeutic drugs that could help with neuroinflammation, neurodegeneration, and alleviation/reduction of pain. We discuss the role of endocannabinoids as signaling molecules in the olfactory system and the relevance of the endocannabinoid system for synaptic plasticity.

The Endocannabinoid System and Alcohol Dependence: Will Cannabinoid Receptor 2 Agonism be More Fruitful than Cannabinoid Receptor 1 Antagonism?

Alcohol-use disorder (AUD) remains a major public health concern. In recent years, there has been a heightened interest in components of the endocannabinoid system for the treatment of AUD. Cannabinoid type 1 (CB1) receptors have been shown to modulate the rewarding effects of alcohol, reduce the abuse-related effects of alcohol, improve cognition, exhibit anti-inflammatory, and neuroprotective effects, which are all favorable properties of potential therapeutic candidates for the treatment of AUD. However, CB1 agonists have not been investigated for the treatment of AUD because they stimulate the motivational properties of alcohol, increase alcohol intake, and have the tendency to be abused. Preclinical data suggest significant potential for the use of CB1 antagonists to treat AUD; however, a clinical phase I/II trial with SR14716A (rimonabant), a CB1 receptor antagonist/inverse agonist showed that it produced serious neuropsychiatric adverse events such as anxiety, depression, and even suicidal ideation. This has redirected the field to focus on alternative components of the endocannabinoid system, including cannabinoid type 2 (CB2) receptor agonists as a potential therapeutic target for AUD. CB2 receptor agonists are of particular interest because they can modulate the reward pathway, reduce abuse-related effects of alcohol, reverse neuroinflammation, improve cognition, and exhibit anti-inflammatory and neuroprotective effects, without exhibiting the psychiatric side effects seen with CB1 antagonists. Accordingly, this article presents an overview of the studies reported in the literature that have investigated CB2 receptor agonists with regards to AUD and provides commentary as to whether this receptor is a worthy target for continued investigation.

Circulating endocannabinoids and prospective risk for depression in trauma-injury survivors

Biological mechanisms associated with response to trauma may impact risk for depression. One such mechanism is endocannabinoid signaling (eCB), a neuromodulatory system comprised of the CB1 subtype of cannabinoid receptors (CB1R), encoded by the CNR1 gene, and two primary endogenous ligands: 2-arachidonoylglycerol (2-AG) and N-arachidonylethanolamine (AEA), hydrolyzed by monoacylglycerol lipase (gene name MGLL) and fatty acid amide hydrolase (gene name FAAH). Preclinical data suggest that eCB/CB1R signaling acts as a stress buffer and its loss or suppression increases depression-like behaviors. We examined circulating concentrations of the eCBs (2-AG and AEA) days and six months after a traumatic injury as a marker of eCB/CB1R signaling and as predictors of Center for Epidemiologic Studies of Depression Scale-Revised [CESD-R] scores as a measure of depression severity six months after injury. We also explored associations of CNR1, FAAH, and MGLL genetic variance with depression severity at six months. Results from hierarchical multiple linear regressions showed that higher 2-AG serum concentrations after trauma predicted greater depression at six months (β = 0.23, p = 0.007); neither AEA after trauma, nor 2-AG and AEA at six months were significant predictors (p's > 0.305). Carriers of minor allele for the putative single nucleotide polymorphism in the CNR1 gene rs806371 (β = 0.19, p = 0.024) experienced greater depression at six months. These data suggest that the eCB signaling system is highly activated following trauma and that eCB/CB1R activity contributes to long-term depression risk.

Lower amygdala fatty acid amide hydrolase in violent offenders with antisocial personality disorder: an [11C]CURB positron emission tomography study

Antisocial personality disorder (ASPD) imposes a high societal burden given the repetitive reactive aggression that affected individuals perpetrate. Since the brain endocannabinoid system (ECS) has been implicated in ASPD and aggressive behavior, we utilized [¹¹C]CURB positron emission tomography to investigate fatty acid amide hydrolase (FAAH), an enzyme of the ECS that degrades anandamide, in 16 individuals with ASPD and 16 control participants. We hypothesized that FAAH density would be lower in the amygdala for several reasons. First, decreased FAAH expression is associated with increased cannabinoid receptor 1 stimulation, which may be responsible for amygdala hyper-reactivity in reactive aggression. Second, the amygdala is the seat of the neural circuit mediating reactive aggression. Third, other PET studies of externalizing populations show reduced brain FAAH density. Conversely, we hypothesized that FAAH expression would be greater in the orbitofrontal cortex. Consistent with our hypothesis, we found that amygdala FAAH density was lower in the amygdala of ASPD (p = 0.013). Cerebellar and striatal FAAH expression were inversely related with impulsivity (cerebellum: r = -0.60, p = 0.017; dorsal caudate: r = -0.58, p = 0.023; dorsal putamen: r = -0.55, p = 0.034), while cerebellar FAAH density was also negatively associated with assaultive aggression (r = -0.54, p = 0.035). ASPD presents high levels of disruptive behavior with few, if any, efficacious treatment options. Novel therapeutics that increase FAAH brain levels in a region-specific manner could hold promise for attenuating certain symptom clusters of ASPD, although our results require replication.

Exo- and Endo-cannabinoids in Depressive and Suicidal Behaviors

Cannabis (marijuana) has been known to humans for thousands of years but its neurophysiological effects were sparsely understood until recently. Preclinical and clinical studies in the past two decades have indisputably supported the clinical proposition that the endocannabinoid system plays an important role in the etiopathogeneses of many neuropsychiatric disorders, including mood and addictive disorders. In this review, we discuss the existing knowledge of exo- and endo-cannabinoids, and role of the endocannabinoid system in depressive and suicidal behavior. A dysfunction in this system, located in brain regions such as prefrontal cortex and limbic structures is implicated in mood regulation, impulsivity and decision-making, may increase the risk of negative mood and cognition as well as suicidality. The literature discussed here also suggests that the endocannabinoid system may be a viable target for treatments of these neuropsychiatric conditions.

Elevated fatty acid amide hydrolase in the prefrontal cortex of borderline personality disorder: a [11C]CURB positron emission tomography study

Amygdala-prefrontal cortex (PFC) functional impairments have been linked to emotion dysregulation and aggression in borderline personality disorder (BPD). Fatty acid amide hydrolase (FAAH), the major catabolic enzyme for the endocannabinoid anandamide, has been proposed as a key regulator of the amygdala-PFC circuit that subserves emotion regulation. We tested the hypothesis that FAAH levels measured with [¹¹C]CURB positron emission tomography in amygdala and PFC would be elevated in BPD and would relate to hostility and aggression. Twenty BPD patients and 20 healthy controls underwent FAAH genotyping (rs324420) and scanning with [¹¹C]CURB. BPD patients were medication-free and were not experiencing a current major depressive episode. Regional differences in [¹¹C]CURB binding were assessed using multivariate analysis of covariance with PFC and amygdala [¹¹C]CURB binding as dependent variables, diagnosis as a fixed factor, and sex and genotype as covariates. [¹¹C]CURB binding was marginally elevated across the PFC and amygdala in BPD (p = 0.08). In a priori selected PFC, but not amygdala, [¹¹C]CURB binding was significantly higher in BPD (11.0%, p = 0.035 versus 10.6%, p = 0.29). PFC and amygdala [¹¹C]CURB binding was positively correlated with measures of hostility in BPD (r > 0.4; p < 0.04). This study is the first to provide preliminary evidence of elevated PFC FAAH binding in any psychiatric condition. Findings are consistent with the model that lower endocannabinoid tone could perturb PFC circuitry that regulates emotion and aggression. Replication of these findings could encourage testing of FAAH inhibitors as innovative treatments for BPD.

Selective breeding for high alcohol preference is associated with increased sensitivity to cannabinoid reward within the nucleus accumbens shell

RATIONALE

The rate of cannabinoid intake by those with alcohol use disorder (AUD) exceeds that of the general public. The high prevalence of co-abuse of alcohol and cannabis has been postulated to be predicated upon both a common predisposing genetic factor and the interaction of the drugs within the organism. The current experiments examined the effects of cannabinoids in an animal model of AUD.

OBJECTIVES

The present study assessed the reinforcing properties of a cannabinoid receptor 1 (CB1) agonist self-administered directly into the nucleus accumbens shell (AcbSh) in female Wistar and alcohol-preferring (P) rats.

METHODS

Following guide cannulae surgery aimed at AcbSh, subjects were placed in an operant box equipped with an 'active lever' (fixed ratio 1; FR1) that caused the delivery of the infusate and an 'inactive lever' that did not. Subjects were arbitrarily assigned to one of seven groups that self-administered either artificial cerebrospinal fluid (aCSF), or 3.125, 6.25, 12.5, or 25 pmol/100 nl of O-1057, a water-soluble CB1 agonist, dissolved in aCSF. The first four sessions of acquisition are followed by aCSF only infusates in sessions 5 and 6 during extinction, and finally the acquisition dose of infusate during session 7 as reinstatement.

RESULTS

The CB1 agonist was self-administered directly into the AcbSh. P rats self-administered the CB1 agonist at lower concentrations and at higher rates compared to Wistar rats.

CONCLUSIONS

Overall, the data indicate selective breeding for high alcohol preference has produced rats divergent in response to cannabinoids within the brain reward pathway. The data support the hypothesis that there can be common genetic factors influencing drug addiction.

Lower brain fatty acid amide hydrolase in treatment-seeking patients with alcohol use disorder: a positron emission tomography study with [C-11]CURB

The endocannabinoid enzyme, fatty acid amide hydrolase (FAAH), has been proposed as a therapeutic target for alcohol use disorder (AUD) and co-morbid psychiatric illnesses. Investigating this target in the living human brain and its relationship to clinical outcome is a critical step of informed drug development. Our objective was to establish whether brain FAAH levels are low in individuals with AUD and related to drinking behavior. In this pilot study, treatment-seeking patients with AUD completed two PET scans with the FAAH radiotracer [C-11]CURB after 3-7 days (n = 14) and 2-4 weeks (n = 9) of monitored abstinence. Healthy controls (n = 25) completed one scan. FAAH genetic polymorphism (rs324420) and blood concentrations of anandamide and other N-acylethanolamines metabolized by FAAH were determined and AUD symptoms assessed. In AUD, brain FAAH levels were globally lower than controls during early abstinence (F(1,36) = 5.447; p = 0.025)) and FAAH substrates (anandamide, oleoylethanolamide, and N-docosahexaenoylethanolamide) were significantly elevated (30-67%). No significant differences in FAAH or FAAH substrates were noted after 2-4 weeks abstinence. FAAH levels negatively correlated with drinks per week (r = -0.57, p = 0.032) and plasma concentrations of the three FAAH substrates (r > 0.57; p < 0.04)). Our findings suggest that early abstinence from alcohol in AUD is associated with transiently low brain FAAH levels, which are inversely related to heavier alcohol use and elevated plasma levels of FAAH substrates. Whether low FAAH is an adaptive beneficial response to chronic alcohol is unknown. Therapeutic strategies focusing on FAAH inhibition should consider the possibility that low FAAH during early abstinence may be related to drinking.

Impact of intermittent voluntary ethanol consumption during adolescence on the expression of endocannabinoid system and neuroinflammatory mediators

The adolescent brain displays high vulnerability to the deleterious effects of ethanol, including greater risk of developing alcohol use disorder later in life. Here, we characterized the gene expression of the endocannabinoid system (ECS) and relevant signaling systems associated with neuroinflammation and emotional behaviors in the brain of young adult control and ethanol-exposed (EtOH) rats. We measured mRNA levels of candidate genes using quantitative real time PCR in the medial prefrontal cortex (mPFC), amygdala and hippocampus. EtOH rats were generated by maintenance on an intermittent and voluntary ethanol consumption during adolescence using the two-bottle choice paradigm (4 days/week for 4 weeks) followed by 2 week-withdrawal, a time-point of withdrawal with no physical symptoms. Mean differences and effect sizes were calculated using t-test and Cohen's d values. In the mPFC and hippocampus, EtOH rats had significantly higher mRNA expression of endocannabinoid-signaling (mPFC: Ppara, Dagla, Daglb and Napepld; and hippocampus: Cnr2, Dagla and Mgll) and neuroinflammation-associated genes (mPFC: Gfap; and hippocampus: Aif1) than in controls. Moreover, EtOH rats had significantly higher mRNA expression of neuropeptide Y receptor genes (Npy1r, Npy2r and Npy5r) in the hippocampus. Finally, EtOH rats also displayed higher plasma endocannabinoid levels than controls. In conclusion, these results suggest that adolescent ethanol exposure can lead to long-term alterations in the gene expression of the ECS and other signaling systems involved in neuroinflammation and regulation of emotional behaviors in key brain areas for the development of addiction.

Dual pharmacological inhibitor of endocannabinoid degrading enzymes reduces depressive-like behavior in female rats

Major depressive disorder (MDD) is common, often under-treated and a leading cause of disability and mortality worldwide. The causes of MDD remain unclear, including the role of the endocannabinoid system. Intriguingly, the prevalence of depression is significantly greater in women than men. In this study we examined the role of endocannabinoids in depressive behavior. The levels of endocannabinoids, N-arachidonoyl ethanolamide (AEA) and 2-arachidonoyl glycerol (2-AG) were measured along with brain derived neurotrophic factor (BDNF) in postmortem ventral striata of female patients with MDD and non-psychiatric controls, and in Wistar Kyoto (WKY) rat, a selectively inbred strain of rat widely used for testing the depressive behavior. The effect of pharmacological elevation of endocannabinoids through inhibition of their catabolizing enzymes (fatty acid amide hydrolase [FAAH] and monoacyl glycerol lipase [MAGL]) on depressive-like phenotype was also assessed in WKY rat. The findings showed lower levels of endocannabinoids and BDNF in the ventral striata of MDD patients and WKY rats. A dual inhibitor of FAAH and MAGL, JZL195, elevated the endocannabinoids and BDNF levels in ventral striatum, and reduced the depressive-like phenotype in female WKY rats. Collectively, our study suggests a blunted ventral striatal endocannabinoid and BDNF signaling in depressive behavior and concludes that endocannabinoid enhancing agents may have an antidepressant effect.

Endocannabinoid Signaling in the Central Amygdala and Bed Nucleus of the Stria Terminalis: Implications for the Pathophysiology and Treatment of Alcohol Use Disorder

High rates of relapse are a chronic and debilitating obstacle to effective treatment of alcohol use disorder (AUD); however, no effective treatments are available to treat symptoms induced by protracted abstinence. In the first part of this 2-part review series, we examine the literature supporting the effects of alcohol exposure within the extended amygdala (EA) neural circuitry. In Part 2, we focus on a potential way to combat negative affect associated with AUD, by exploring the therapeutic potential of the endogenous cannabinoid (eCB) system. The eCB system is a potent modulator of neural activity in the brain, and its ability to mitigate stress and negative affect has long been an area of interest for developing novel therapeutics. This review details the recent advances in our understanding of eCB signaling in 2 key regions of the EA, the central nucleus of the amygdala and the bed nucleus of the stria terminalis (BNST), and their role in regulating negative affect. Despite an established role for EA eCB signaling in reducing negative affect, few studies have examined the potential for eCB-based therapies to treat AUD-associated negative affect. In this review, we present an overview of studies focusing on eCB signaling in EA and cannabinoid modulation on EA synaptic activity. We further discuss studies suggesting dysregulation of eCB signaling in models of AUD and propose that pharmacological augmentation of eCB could be a novel approach to treat aspects of AUD. Lastly, future directions are proposed to advance our understanding of the relationship between AUD-associated negative affect and the EA eCB system that could yield new pharmacotherapies targeting negative affective symptoms associated with AUD.

Distinct functions of endogenous cannabinoid system in alcohol abuse disorders

Δ⁹ -tetrahydrocannabinol, the principal active component in Cannabis sativa extracts such as marijuana, participates in cell signalling by binding to cannabinoid CB₁ and CB₂ receptors on the cell surface. The CB₁ receptors are present in both inhibitory and excitatory presynaptic terminals and the CB₂ receptors are found in neuronal subpopulations in addition to microglial cells and astrocytes and are present in both presynaptic and postsynaptic terminals. Subsequent to the discovery of the endocannabinoid (eCB) system, studies have suggested that alcohol alters the eCB system and that this system plays a major role in the motivation to abuse alcohol. Preclinical studies have provided evidence that chronic alcohol consumption modulates eCBs and expression of CB₁ receptors in brain addiction circuits. In addition, studies have further established the distinct function of the eCB system in the development of fetal alcohol spectrum disorders. This review provides a recent and comprehensive assessment of the literature related to the function of the eCB system in alcohol abuse disorders.

Social isolation as a promising animal model of PTSD comorbid suicide: neurosteroids and cannabinoids as possible treatment options

Post-traumatic stress disorder (PTSD) is a psychiatric condition characterized by drastic alterations in mood, emotions, social abilities and cognition. Notably, one aspect of PTSD, particularly in veterans, is its comorbidity with suicide. Elevated aggressiveness predicts high-risk to suicide in humans and despite the difficulty in reproducing a complex human suicidal behavior in rodents, aggressive behavior is a well reproducible behavioral trait of suicide. PTSD animal models are based on a peculiar phenotype, including exaggerated fear memory and impaired fear extinction associated with neurochemical dysregulations in the brain circuitry regulating emotion. The endocannabinoid and the neurosteroid systems regulate emotions and stress responses, and recent evidence shows these two systems are interrelated and critically compromised in neuropsychiatric disorders. For instance, levels of the neurosteroid, allopregnanolone, as well as those of the endocannabinoids, anandamide and its congener, palmitoylethanolamide are decreased in PTSD. Similarly, the endocannabinoid system and neurosteroid biosynthesis are altered in suicidal individuals. Selective serotonin reuptake inhibitors (SSRIs), the only FDA-approved treatments for PTSD, fail to help half of the treatment-seeking patients. This highlights the need for developing biomarker-based efficient therapies. One promising alternative to SSRIs points to stimulation of allopregnanolone biosynthesis as a treatment and a valid end-point to predict treatment response in PTSD patients. This review highlights running findings on the role of the endocannabinoid and neurosteroid systems in PTSD and suicidal behavior both in a preclinical and clinical perspective. A specific focus is given to predictive PTSD/suicide animal models. Ultimately, we discuss the idea that disruption of neurosteroid and endocannabinoid biosynthesis may offer a novel promising biomarker axis to develop new treatments for PTSD and, perhaps, suicidal behavior.

Adolescent ethanol intake alters cannabinoid type-1 receptor localization in astrocytes of the adult mouse hippocampus

Cannabinoid type-1 (CB₁ ) receptors are widely distributed in the brain and play important roles in astrocyte function and the modulation of neuronal synaptic transmission and plasticity. However, it is currently unknown how CB₁ receptor expression in astrocytes is affected by long-term exposure to stressors. Here we examined CB₁ receptors in astrocytes of ethanol (EtOH)-exposed adolescent mice to determine its effect on CB₁ receptor localization and density in adult brain. 4-8-week-old male mice were exposed to 20 percent EtOH over a period of 4 weeks, and receptor localization was examined after 4 weeks in the hippocampal CA1 stratum radiatum by pre-embedding immunoelectron microscopy. Our results revealed a significant reduction in CB₁ receptor immunoparticles in astrocytic processes of EtOH-exposed mice when compared with controls (positive astrocyte elements: 21.50 ± 2.80 percent versus 37.22 ± 3.12 percent, respectively), as well as a reduction in particle density (0.24 ± 0.02 versus 0.35 ± 0.02 particles/μm). The majority of CB₁ receptor metal particles were in the range of 400-1200 nm from synaptic terminals in both control and EtOH. Altogether, the decrease in the CB₁ receptor expression in hippocampal astrocytes of adult mice exposed to EtOH during adolescence reveals a long lasting effect of EtOH on astrocytic CB₁ receptors. This deficiency may also have negative consequences for synaptic function.

Endocannabinoid System and Alcohol Abuse Disorders

Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the primary active component in Cannabis sativa preparations such as hashish and marijuana, signals by binding to cell surface receptors. Two types of receptors have been cloned and characterized as cannabinoid (CB) receptors. CB1 receptors (CB1R) are ubiquitously present in the central nervous system (CNS) and are present in both inhibitory interneurons and excitatory neurons at the presynaptic terminal. CB2 receptors (CB2R) are demonstrated in microglial cells, astrocytes, and several neuron subpopulations and are present in both pre- and postsynaptic terminals. The majority of studies on these receptors have been conducted in the past two and half decades after the identification of the molecular constituents of the endocannabinoid (eCB) system that started with the characterization of CB1R. Subsequently, the seminal discovery was made, which suggested that alcohol (ethanol) alters the eCB system, thus establishing the contribution of the eCB system in the motivation to consume ethanol. Several preclinical studies have provided evidence that CB1R significantly contributes to the motivational and reinforcing properties of ethanol and that the chronic consumption of ethanol alters eCB transmitters and CB1R expression in the brain nuclei associated with addiction pathways. Additionally, recent seminal studies have further established the role of the eCB system in the development of ethanol-induced developmental disorders, such as fetal alcohol spectrum disorders (FASD). These results are augmented by in vitro and ex vivo studies, showing that acute and chronic treatment with ethanol produces physiologically relevant alterations in the function of the eCB system during development and in the adult stage. This chapter provides a current and comprehensive review of the literature concerning the role of the eCB system in alcohol abuse disorders (AUD).

Cannabinoids in depressive disorders

Cannabis sativa is one of the most popular recreational and medicinal plants. Benefits from use of cannabinoid agents in epilepsy, multiple sclerosis, Parkinson's disease, Alzheimer's disease, and others have been suggested. It seems that the endocannabinoid system is also involved in the pathogenesis and treatment of depression, though its role in this mental disease has not been fully understood yet. Both the pro- and antidepressant activity have been reported after cannabis consumption and a number of pre-clinical studies have demonstrated that both agonist and antagonist of the endocannabinoid receptors act similarly to antidepressants. Responses to the cannabinoid agents are relatively fast, and most probably, the noradrenergic, serotoninergic, glutamatergic neurotransmission, neuroprotective activity, as well as modulation of the hypothalamic-pituitary-adrenal axis are implicated in the observed effects. Based on the published data, the endocannabinoid system evidently gives novel ideas and options in the field of antidepressant treatment, however further studies are needed to determine which group of patients could benefit from this type of therapy.

Deficient endocannabinoid signaling in the central amygdala contributes to alcohol dependence-related anxiety-like behavior and excessive alcohol intake

Negative emotional states that are associated with excessive alcohol intake, particularly anxiety-like states, have been linked to opponent processes in the central nucleus of the amygdala (CeA), affecting stress-related transmitters and monoamines. This study extends these observations to include endocannabinoid signaling in alcohol-dependent animals. Rats and mice were exposed to chronic intermittent alcohol with vapor inhalation or liquid diet to induce dependence. In vivo microdialysis was used to estimate interstitial concentrations of endocannabinoids [N-arachidonoylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG)] and amino acids (glutamate and GABA) in rat CeA. Additionally, we evaluated the inhibition of endocannabinoids clearance enzymes [monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase] on anxiety-like behavior and alcohol consumption in alcohol-dependent rats and mice. Results revealed that alcohol dependence produced decreases in baseline 2-AG dialysate levels and increases in baseline levels of glutamate and GABA. Acute alcohol abstinence induced an enhancement of these dependence-induced effects and the levels of 2-AG and GABA were restored upon alcohol re-exposure. Additional studies showed that the increased CeA 2-AG levels induced by restraint stress and alcohol self-administration were blunted in alcohol-dependent rats. Pharmacological studies in rats and mice showed that anxiety-like behavior and alcohol consumption were increased in alcohol-dependent animals, and these behavioral effects were attenuated mainly by MAGL inhibitors [MJN110 (10 and 20 mg/kg) in rats and JZL184 (1 and 3 mg/kg) in mice]. The present results suggest a key role for endocannabinoid signaling in motivational neuroadaptations during alcohol dependence, in which a deficiency in CeA 2-AG signaling in alcohol-dependent animals is linked to stress and excessive alcohol consumption.

The endocannabinoid-alcohol crosstalk: Recent advances on a bi-faceted target

Increasing evidence has focusesed on the endocannabinoid system as a relevant player in the induction of aberrant synaptic plasticity and related addictive phenotype following chronic excessive alcohol drinking. In addition, the endocannabinoid system is implicated in the pathogenesis of alcoholic liver disease. Interestingly, whereas the involvement of CB1 receptors in alcohol rewarding properties is established, the central and peripheral action of CB2 signalling is still to be elucidated. This review aims at giving the input to deepen knowledge on the role of the endocannabinoid system, highlighting the advancing evidence that suggests that CB1 and CB2 receptors may play opposite roles in the regulation of both the reinforcing properties of alcohol in the brain and the mechanisms responsible for cell injury and inflammation in the hepatic tissue. The manipulation of the endocannabinoid system could represent a bi-faceted strategy to counteract alcohol-related dysfunction in central transmission and liver structural and functional disarrangement.

Cannabinoid Receptors, Mental Pain and Suicidal Behavior: a Systematic Review

PURPOSE OF REVIEW

The current serotonin-based biological model of suicidal behavior (SB) may be too simplistic. There is emerging evidence that other biomarkers and biological systems may be involved in SB pathophysiology. The literature on the endocannabinoid (EC) systems and SB is limited. The objective of the present article is to review all available information on the relationship between cannabinoid receptors (CB₁ and CB₂ receptors), and SB and/or psychological pain.

RECENT FINDINGS

Our review is limited by the small number and heterogeneity of studies identified: (1) an autopsy study describing elevated levels of CB₁ receptor activity in the prefrontal cortex and suicide in both depression and alcoholism and (2) studies supporting the involvement of both CB₁ and CB₂ receptors in the regulation of neuropathic pain and stress-induced analgesia. We conclude that cannabinoid receptors, particularly CB₁ receptors, may become promising targets for the development of novel therapeutic tools for the treatment of SB.

CB1 cannabinoid receptor ligands augment the antidepressant-like activity of biometals (magnesium and zinc) in the behavioural tests

OBJECTIVE

During the last few decades, endocannabinoid system has emerged as a novel possible target for antidepressant treatment. Although the medical literature provides information on the mood-changing effects of CB₁ ligands, little is known about the possible interaction between the simultaneous activation or inhibition of the CB₁ receptor and administration of other agents that possess antidepressant potential. The main goal of our study was to evaluate the influence of the CB₁ cannabinoid receptor ligands (oleamide - an endogenous agonist and AM251 - an inverse agonist/antagonist) on the antidepressant-like activity of biometals (i.e. magnesium and zinc).

METHODS

The forced swim test and the tail suspension test in mice were used to determine the antidepressant-like activity.

KEY FINDINGS

Concomitant intraperitoneal administration of per se inactive doses of oleamide (5 mg/kg) or AM251 (0.25 mg/kg) and the tested biometals (i.e. magnesium, 10 mg/kg or zinc, 5 mg/kg) shortened the immobility time of animals in the forced swim test and the tail suspension test. The observed effect was not associated with an increase in spontaneous locomotor activity of mice.

CONCLUSIONS

The simultaneous modulation of the cannabinoid system and supplementation of magnesium or zinc produce at least additive antidepressant-like effect.

Cannabinoid-1 receptor neutral antagonist reduces binge-like alcohol consumption and alcohol-induced accumbal dopaminergic signaling

Binge alcohol (ethanol) drinking is associated with profound adverse effects on our health and society. Rimonabant (SR141716A), a CB1 receptor inverse agonist, was previously shown to be effective for nicotine cessation and obesity. However, studies using rimonabant were discontinued as it was associated with an increased risk of depression and anxiety. In the present study, we examined the pharmacokinetics and effects of AM4113, a novel CB1 receptor neutral antagonist on binge-like ethanol drinking in C57BL/6J mice using a two-bottle choice drinking-in-dark (DID) paradigm. The results indicated a slower elimination of AM4113 in the brain than in plasma. AM4113 suppressed ethanol consumption and preference without having significant effects on body weight, ambulatory activity, preference for tastants (saccharin and quinine) and ethanol metabolism. AM4113 pretreatment reduced ethanol-induced increase in dopamine release in nucleus accumbens. Collectively, these data suggest an important role of CB1 receptor-mediated regulation of binge-like ethanol consumption and mesolimbic dopaminergic signaling, and further points to the potential utility of CB1 neutral antagonists for the treatment of binge ethanol drinking.

Prenatal Ethanol Exposure Persistently Alters Endocannabinoid Signaling and Endocannabinoid-Mediated Excitatory Synaptic Plasticity in Ventral Tegmental Area Dopamine Neurons

Prenatal ethanol exposure (PE) leads to increased addiction risk which could be mediated by enhanced excitatory synaptic strength in ventral tegmental area (VTA) dopamine (DA) neurons. Previous studies have shown that PE enhances excitatory synaptic strength by facilitating an anti-Hebbian form of long-term potentiation (LTP). In this study, we investigated the effect of PE on endocannabinoid-mediated long-term depression (eCB-LTD) in VTA DA neurons. Rats were exposed to moderate (3 g/kg/d) or high (6 g/kg/d) levels of ethanol during gestation. Whole-cell recordings were conducted in male offspring between 4 and 10 weeks old.We found that PE led to increased amphetamine self-administration. Both moderate and high levels of PE persistently reduced low-frequency stimulation-induced eCB-LTD. Furthermore, action potential-independent glutamate release was regulated by tonic eCB signaling in PE animals. Mechanistic studies for impaired eCB-LTD revealed that PE downregulated CB1 receptor function. Interestingly, eCB-LTD in PE animals was rescued by metabotropic glutamate receptor I activation, suggesting that PE did not impair the synthesis/release of eCBs. In contrast, eCB-LTD in PE animals was not rescued by increasing presynaptic activity, which actually led to LTP in PE animals, whereas LTD was still observed in controls. This result shows that the regulation of excitatory synaptic plasticity is fundamentally altered in PE animals. Together, PE leads to impaired eCB-LTD at the excitatory synapses of VTA DA neurons primarily due to CB1 receptor downregulation. This effect could contribute to enhanced LTP and the maintenance of augmented excitatory synaptic strength in VTA DA neurons and increased addiction risk after PE.SIGNIFICANCE STATEMENT Prenatal ethanol exposure (PE) is among many adverse developmental factors known to increase drug addiction risk. Increased excitatory synaptic strength in VTA DA neurons is a critical cellular mechanism for addiction risk. Our results show that PE persistently alters eCB signaling and impairs eCB-LTD at the excitatory synapses, an important synaptic plasticity that weakens synaptic strength. These effects combined with PE-induced anti-Hebbian long-term potentiation reported in a previous study could result in the maintenance of enhanced excitatory synaptic strength in VTA DA neurons, which in turn contributes to PE-induced increase in addiction risk. Our findings also suggest that restoring normal eCB signaling in VTA DA neurons could be a useful strategy for treating behavioral symptoms caused by PE.

The association between cannabis use and suicidality among men and women: A population-based longitudinal study

BACKGROUND

Evidence regarding the role of sex differences in the association between cannabis use and suicidality is lacking. We explored sex differences in the bidirectional association between cannabis use and suicidality in a 3-year longitudinal study.

METHODS

Data were drawn from waves 1 and 2 of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). Bidirectional analyses were conducted separately by sex, exploring incidence of suicidality among cannabis users (n=963 vs. 30,586 non-users) as well as initiation of cannabis use among suicidal individuals (n=1805 vs. 25,729 non-suicidal). Cannabis use was categorized based on frequency of use. Multivariate logistic regression analyses controlling for multiple covariates were conducted.

RESULTS

Cannabis use was significantly associated with increased incidence of suicidality among men (Adjusted Odds Ratio [AOR] for any cannabis use =1.91[1.02-3.56]) but not among women (AOR=1.19[0.64-2.20]). Daily cannabis use was significantly associated with increased incidence of suicidality among men (AOR=4.28[1.32-13.82]) but not among women (AOR=0.75[0.28-2.05]). Conversely, baseline suicidality was associated with initiation of cannabis use among women (AOR=2.34[1.42-3.87]) but not among men (AOR=1.10[0.57-2.15]). Separate analyses of suicidal ideation and suicide attempts demonstrated a significant association between cannabis use and subsequent incidence of suicidal ideation in men, and a significant association between baseline suicidal ideation and subsequent initiation of cannabis use in women. No significant association was found for the bidirectional association between cannabis use and suicide attempts in either sex.

LIMITATIONS

Suicidality was assessed only in individuals reporting depressed mood and/or anhedonia.

CONCLUSIONS

Our findings support a longitudinal association between heavy cannabis use and the incidence of suicidality in men, but not in women. Conversely, baseline suicidality is longitudinally associated with the initiation of cannabis use in women, but not in men. This may have implications on clinical and social aspects of cannabis use and merit further research into the unique effects of sex differences on cannabis induced psychopathology.

FAAH Gene Variation Moderates Stress Response and Symptom Severity in Patients with Posttraumatic Stress Disorder and Comorbid Alcohol Dependence

BACKGROUND

A common single nucleotide polymorphism (C385A) in the human fatty acid amide hydrolase (FAAH) gene has been associated with decreased distress responses in healthy volunteers, but its role in psychiatric disorders remains unknown. Here, we obtained genotypes and carried out a secondary analysis of subjects from a trial of comorbid posttraumatic stress disorder (PTSD) and alcohol dependence (AD). We evaluated the effects of C385A variation on behavioral and biochemical biomarkers of distress responses.

METHODS

Forty-nine patients with PTSD and AD were admitted for 4 weeks to an experimental medicine unit at the National Institutes of Health Clinical Center. Following detoxification, stress reactivity and peripheral endocannabinoid (eCB) levels were assessed in response to a challenge session using personalized auditory guided imagery. Over the course of the study, subjects were also evaluated for changes in PTSD symptom severity.

RESULTS

FAAH C385A allele carriers showed a marked increase in serum anandamide levels at baseline and throughout the stress challenge procedure compared with C allele homozygotes, while levels of eCBs primarily metabolized through other enzymatic activity, such as 2-arachidonoylglycerol, did not differ between genotype groups. FAAH C385A carriers also had decreased subjective anxiety responses to the stress challenge. Similar effects of FAAH C385A genotype were found at the level of clinical PTSD symptom severity, in particular in the arousal domain.

CONCLUSIONS

This is to our knowledge the first study showing that FAAH C385A variation modulates stress responses in subjects with disorders characterized by increased stress reactivity. These findings point to the eCB pathway as a promising target for future antistress therapeutics.

Physiological processes underlying organ injury in alcohol abuse

This review summarizes the American Physiological Society (APS) Presidential Symposium 1 entitled "Physiological Processes Underlying Organ Injury in Alcohol Abuse" at the 2016 Experimental Biology meeting. The symposium was organized by Dr. Patricia Molina, past president of the APS, was held on April 3 at the Convention Center in San Diego, CA, and was funded by the National Institute on Alcohol Abuse and Alcoholism. The "Physiological Processes Underlying Organ Injury in Alcohol Abuse Symposium" assembled experts and leaders in the field and served as a platform to discuss and share knowledge on the latest developments and scientific advances on the mechanisms underlying organ injury in alcohol abuse. This symposium provided unique, interdisciplinary alcohol research, including several organs, liver, muscle, adipose, and brain, affected by excessive alcohol use.

Chronic ethanol exposure decreases CB1 receptor function at GABAergic synapses in the rat central amygdala

The endogenous cannabinoids (eCBs) influence the acute response to ethanol and the development of tolerance, dependence and relapse. Chronic alcohol exposure alters eCB levels and Type 1 cannabinoid receptor (CB1 ) expression and function in brain regions associated with addiction. CB1 inhibits GABA release, and GABAergic dysregulation in the central nucleus of the amygdala (CeA) is critical in the transition to alcohol dependence. We investigated possible disruptions in CB1 signaling of rat CeA GABAergic transmission following intermittent ethanol exposure. In the CeA of alcohol-naive rats, CB1 agonist WIN 55,212-2 (WIN) decreased the frequency of spontaneous and miniature GABAA receptor-mediated inhibitory postsynaptic currents (s/mIPSCs). This effect was prevented by CB1 antagonism, but not Type 2 cannabinoid receptor (CB2 ) antagonism. After 2-3 weeks of intermittent ethanol exposure, these WIN inhibitory effects were attenuated, suggesting ethanol-induced impairments in CB1 function. The CB1 antagonist AM251 revealed a tonic eCB/CB1 control of GABAergic transmission in the alcohol-naive CeA that was occluded by calcium chelation in the postsynaptic cell. Chronic ethanol exposure abolished this tonic CB1 influence on mIPSC, but not sIPSC, frequency. Finally, acute ethanol increased CeA GABA release in both naive and ethanol-exposed rats. Although CB1 activation prevented this effect, the AM251- and ethanol-induced GABA release were additive, ruling out a direct participation of CB1 signaling in the ethanol effect. Collectively, these observations demonstrate an important CB1 influence on CeA GABAergic transmission and indicate that the CeA is particularly sensitive to alcohol-induced disruptions of CB1 signaling.

Impaired Ethanol-Induced Sensitization and Decreased Cannabinoid Receptor-1 in a Model of Posttraumatic Stress Disorder

Background and Purpose

Impaired striatal neuroplasticity may underlie increased alcoholism documented in those with posttraumatic stress disorder (PTSD). Cannabinoid receptor-1 (CB1) is sensitive to the effects of ethanol (EtOH) and traumatic stress, and is a critical regulator of striatal plasticity. To investigate CB1 involvement in the PTSD-alcohol interaction, this study measured the effects of traumatic stress using a model of PTSD, mouse single-prolonged stress (mSPS), on EtOH-induced locomotor sensitization and striatal CB1 levels.

Methods

Mice were exposed to mSPS, which includes: 2-h restraint, 10-min group forced swim, 15-min exposure to rat bedding odor, and diethyl ether exposure until unconsciousness or control conditions. Seven days following mSPS exposure, the locomotor sensitizing effects of EtOH were assessed. CB1, post-synaptic density-95 (PSD95), and dopamine-2 receptor (D2) protein levels were then quantified in the dorsal striatum using standard immunoblotting techniques.

Results

Mice exposed to mSPS-EtOH demonstrated impaired EtOH-induced locomotor sensitization compared to Control-EtOH mice, which was accompanied by reduced striatal CB1 levels. EtOH increased striatal PSD95 in control and mSPS-exposed mice. Additionally, mSPS-Saline exposure increased striatal PSD95 and decreased D2 protein expression, with mSPS-EtOH exposure alleviating these changes.

Conclusions

These data indicate that the mSPS model of PTSD blunts the behavioral sensitizing effects of EtOH, a response that suggests impaired striatal neuroplasticity. Additionally, this study demonstrates that mice exposed to mSPS and repeated EtOH exposure decreases CB1 in the striatum, providing a mechanism of interest for understanding the effects of EtOH following severe, multimodal stress exposure.

Roles for the endocannabinoid system in ethanol-motivated behavior

Alcohol use disorder represents a significant human health problem that leads to substantial loss of human life and financial cost to society. Currently available treatment options do not adequately address this human health problem, and thus, additional therapies are desperately needed. The endocannabinoid system has been shown, using animal models, to modulate ethanol-motivated behavior, and it has also been demonstrated that chronic ethanol exposure can have potentially long-lasting effects on the endocannabinoid system. For example, chronic exposure to ethanol, in either cell culture or preclinical rodent models, causes an increase in endocannabinoid levels that results in down-regulation of the cannabinoid receptor 1 (CB1) and uncoupling of this receptor from downstream G protein signaling pathways. Using positron emission tomography (PET), similar down-regulation of CB1 has been noted in multiple regions of the brain in human alcoholic patients. In rodents, treatment with the CB1 inverse agonist SR141716A (Rimonabant), or genetic deletion of CB1 leads to a reduction in voluntary ethanol drinking, ethanol-stimulated dopamine release in the nucleus accumbens, operant self-administration of ethanol, sensitization to the locomotor effects of ethanol, and reinstatement/relapse of ethanol-motivated behavior. Although the clinical utility of Rimonabant or other antagonists/inverse agonists for CB1 is limited due to negative neuropsychiatric side effects, negative allosteric modulators of CB1 and inhibitors of endocannabinoid catabolism represent therapeutic targets worthy of additional examination.

Acute and chronic ethanol exposure differentially regulate CB1 receptor function at glutamatergic synapses in the rat basolateral amygdala

The endogenous cannabinoid (eCB) system has been suggested to play a key role in ethanol preference and intake, the acute effects of ethanol, and in the development of withdrawal symptoms following ethanol dependence. Ethanol-dependent alterations in glutamatergic signaling within the lateral/basolateral nucleus of the amygdala (BLA) are critical for the development and expression of withdrawal-induced anxiety. Notably, the eCB system significantly regulates both glutamatergic and GABAergic synaptic activity within the BLA. Chronic ethanol exposure significantly alters eCB system expression within regions critical to the expression of emotionality and anxiety-related behavior, including the BLA. Here, we investigated specific interactions between the BLA eCB system and its functional regulation of synaptic activity during acute and chronic ethanol exposure. In tissue from ethanol naïve-rats, a prolonged acute ethanol exposure caused a dose dependent inhibition of glutamatergic synaptic activity via a presynaptic mechanism that was occluded by CB1 antagonist/inverse agonists SR141716a and AM251. Importantly, this acute ethanol inhibition was attenuated following 10 day chronic intermittent ethanol vapor exposure (CIE). CIE exposure also significantly down-regulated CB1-mediated presynaptic inhibition at glutamatergic afferent terminals but spared CB1-inhibition of GABAergic synapses arising from local inhibitory-interneurons. CIE also significantly elevated BLA N-arachidonoylethanolamine (AEA or anandamide) levels and decreased CB1 receptor protein levels. Collectively, these data suggest a dynamic regulation of the BLA eCB system by acute and chronic ethanol.

Altered CB1 receptor coupling to G-proteins in the post-mortem caudate nucleus and cerebellum of alcoholic subjects

Biochemical, pharmacological and genetic evidence suggests the involvement of the endocannabinoid system in alcohol dependence. The aim of the present study was to evaluate the state of CB1 receptors in post-mortem caudate nucleus, hippocampus and cerebellum of alcoholic subjects.CB1 protein levels were measured by Western blot, CB1 receptor density and affinity by [(3)H]WIN55,212-2 saturation assays and CB1 functionality by [(35)S]GTPγS binding assays. Experiments were performed in samples from 24 subjects classified as non-suicidal alcoholics (n = 6), suicidal alcoholics (n = 6), non-alcoholic suicide victims (n = 6) and control subjects (n = 6).Alcoholic subjects presented hyperfunctional CB1 receptors in the caudate nucleus resulting in a higher maximal effect in both alcoholic groups compared to the non-alcoholic groups (p < 0.001). Conversely, in the cerebellum the non-suicidal alcoholic subjects showed hypofunctional receptors with lower maximal effect and potency (p < 0.001). No changes were found in the CB1 protein expression in either region. In the hippocampus of alcoholic subjects, no changes were observed either in the functionality, density or protein levels.Our data support an association between endocannabinoid system activity and alcoholism. The modifications reported here could be either a consequence of high lifetime ethanol consumption or a vulnerability factor to develop alcohol addiction.

Endocannabinoid signalling in reward and addiction

Brain endocannabinoid (eCB) signalling influences the motivation for natural rewards (such as palatable food, sexual activity and social interaction) and modulates the rewarding effects of addictive drugs. Pathological forms of natural and drug-induced reward are associated with dysregulated eCB signalling that may derive from pre-existing genetic factors or from prolonged drug exposure. Impaired eCB signalling contributes to dysregulated synaptic plasticity, increased stress responsivity, negative emotional states and cravings that propel addiction. Understanding the contributions of eCB disruptions to behavioural and physiological traits provides insight into the eCB influence on addiction vulnerability.

Cannabinoid Ligands and Alcohol Addiction: A Promising Therapeutic Tool or a Humbug?

The vast therapeutic potential of cannabinoids of both synthetic and plant-derived origins currently makes these compounds the focus of a growing interest. Although cannabinoids are still illicit drugs, their possible clinical usefulness, including treatment of acute or neuropathic pain, have been suggested by several studies. In addition, some observations indicate that cannabinoid receptor antagonists may be useful for the treatment of alcohol dependence and addiction, which is a major health concern worldwide. While the synergism between alcohol and cannabinoid agonists (in various forms) creates undesirable side effects when the two are consumed together, the administration of CB1 antagonists leads to a significant reduction in alcohol consumption. Furthermore, cannabinoid antagonists also mitigate alcohol withdrawal symptoms. Herein, we present an overview of studies focusing on the effects of cannabinoid ligands (agonists and antagonists) during acute or chronic consumption of ethanol.