Association of the Fatty Acid Amide Hydrolase C385A Polymorphism With Alcohol Use Severity and Coping Motives in Heavy-Drinking Youth.

BACKGROUND: Reduced function of fatty acid amide hydrolase, the catabolic enzyme for the endocannabinoid anandamide, can be inherited through a functional genetic polymorphism (FAAH rs324420, C385A, P129T). The minor (A) allele has been associated with reduced FAAH enzyme activity and increased risk for substance use disorders in adults. Whether this inherited difference in endocannabinoid metabolism relates to alcohol use disorder etiology and patterns of alcohol use in youth is unknown. METHODS: To examine this question, heavy-drinking youth (n = 302; mean age = 19.74 ± 1.18) were genotyped for FAAH C385A. All subjects completed a comprehensive interview assessing alcohol use patterns including the Timeline Follow-back Method, Alcohol Use Disorders Identification Test (AUDIT), and Drinking Motives Questionnaire. Analyses of Covariance (ANCOVAs) were conducted to assess differences in drinking patterns and drinking motives between genotype groups, and mediation analyses investigated whether drinking motives accounted for indirect associations of genotype with alcohol use severity. RESULTS: Youth with the FAAH minor allele (AC or AA genotype) reported significantly more drinking days (p = 0.045), significantly more frequent heavy episodic drinking (p = 0.003), and significantly higher alcohol-related problems and consumption patterns (AUDIT score p = 0.045, AUDIT-C score p = 0.02). Mediation analyses showed that the association of FAAH C385A with drinking outcomes was mediated by coping motives. CONCLUSIONS: These findings extend previous studies by suggesting that reduced endocannabinoid metabolism may be related to heavier use of alcohol in youth, prior to the onset of chronic drinking problems. Furthermore, differences in negative reinforcement-related drinking could account in part for this association.

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.

Effects of endocannabinoid system modulation on social behaviour: A systematic review of animal studies.

There is a clear link between psychiatric disorders and social behaviour, and evidence suggests the involvement of the endocannabinoid system (ECS). A systematic review of preclinical literature was conducted using MEDLINE (PubMed) and PsychINFO databases to examine whether pharmacological and/or genetic manipulations of the ECS alter social behaviours in wildtype (WT) animals or models of social impairment (SIM). Eighty studies were included. Risk of bias (RoB) was assessed using SYRCLE's RoB tool. While some variability was evident, studies most consistently found that direct cannabinoid receptor (CBR) agonism decreased social behaviours in WT animals, while indirect CBR activation via enzyme inhibition or gene-knockout increased social behaviours. Direct and, more consistently, indirect CBR activation reversed social deficits in SIM. These CBR-mediated effects were often sex- and developmental-phase-dependent and blocked by CBR antagonism. Overall, ECS enzyme inhibition may improve social behaviour in SIM, suggesting the potential usefulness of ECS enzyme inhibition as a therapeutic approach for social deficits. Future research should endeavour to elucidate ECS status in neuropsychiatric disorders characterized by social deficits.

Fatty acid amide hydrolase levels in brain linked with threat-related amygdala activation.

Background: Preclinical evidence suggests that increasing levels of the major endocannabinoid anandamide decreases anxiety and fear responses potentially through its effects in the amygdala. Here we used neuroimaging to test the hypothesis that lower fatty acid amide hydrolase (FAAH), the main catabolic enzyme for anandamide, is associated with a blunted amygdala response to threat. Methods: Twenty-eight healthy participants completed a positron emission tomography (PET) scan with the radiotracer for FAAH, [11C]CURB, as well as a block-design functional magnetic resonance imaging session during which angry and fearful faces meant to activate the amygdala were presented. Results: [11C]CURB binding in the amygdala as well as in the medial prefrontal cortex, cingulate and hippocampus correlated positively with blood-oxygen-level-dependent (BOLD) signal during processing of angry and fearful faces (pFWE < 0.05). Conclusion: Our finding that lower levels of FAAH in amygdala, medial prefrontal cortex, cingulate and hippocampus was associated with a dampened amygdala response to a threatening social cue aligns with preclinical and neuroimaging studies in humans and suggests the involvement of FAAH in modulating stress and anxiety in humans. The current neuroimaging study also lends support for the potential use of FAAH inhibitors to control amygdala hyperactivity, which is known to be involved in the pathophysiology of anxiety and trauma-related disorders.

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.

D3 dopamine receptors and a missense mutation of fatty acid amide hydrolase linked in mouse and men: implication for addiction.

The endocannabinoid and dopaminergic systems have independently been implicated in substance use disorder and obesity. We investigated a potential interaction between genetically inherited variation in fatty acid amide hydrolase (FAAH, C385A), which metabolizes the cannabis-like endocannabinoid anandamide, and dopaminergic system, measured by dopamine receptor levels and mRNA. Binding of the dopamine D3 preferring probe [C-11]-(+)-PHNO was measured with positron emission tomography (PET) in 79 human subjects genotyped for the FAAH C385A polymorphism (36/79 AC + AA). Autoradiography with [H-3]-(+)-PHNO and in situ hybridization with a D3-specific S-35 riboprobe were carried out in 30 knock-in mice with the FAAH C385A polymorphism (20/30 AC + AA). We found that the FAAH genetic variant C385A was associated with significantly higher (+)-PHNO binding in both humans and in knock-in mice, and this effect was restricted to D3 selective brain regions (limbic striatum, globus pallidus, and ventral pallidum (9-14%; p < 0.04) in humans and Islands of Calleja (28%; p = 0.036) in mice). In situ hybridization with a D3-specific S-35 riboprobe in FAAH knock-in C385A mice confirmed significantly increased D3 receptor mRNA across examined regions (7-44%; p < 0.02). The association of reduced FAAH function with higher dopamine D3 receptors in human and mouse brain provide a mechanistic link between two brain systems that have been implicated in addiction-risk. This may explain the greater vulnerability for addiction and obesity in individuals with C385A genetic variant and by extension, suggest that a D3 antagonism strategy in substance use disorders should consider FAAH C385A polymorphism.

Effects of anxiogenic drugs on the emission of 22- and 50-kHz ultrasonic vocalizations in adult rats.

RATIONALE: Adult rat 22-kHz vocalizations are often associated with alarm or distress, whereas a subset of 50-kHz calls is preferentially emitted in response to amphetamine and other rewarding stimuli. Whether any 50-kHz calls reflect anxiety is unknown. OBJECTIVE: To determine the effects of anxiogenic drugs on 50-kHz call rate and call subtype profile, in comparison with D-amphetamine. METHODS: Adult male rats received systemic amphetamine (1 mg/kg) three times several days before testing. Ultrasonic vocalizations were then recorded after acute intraperitoneal injection of amphetamine or one of five anxiogenic drugs: yohimbine (2.5 mg/kg), N-methyl-ß-carboline-3-carboxamide (FG 7142, 5 mg/kg), pentylenetetrazol (PTZ, 20 mg/kg), m-chlorophenylpiperazine (mCPP, 1 mg/kg), caffeine (25 mg/kg), or vehicle. RESULTS: The duration of immobility was increased by FG 7142, PTZ, and mCPP; this measure was unchanged by yohimbine and reduced by the locomotor stimulant drugs amphetamine and caffeine. Conversely, the 50-kHz call rate was reduced by FG 7142, PTZ and mCPP, and increased by caffeine and amphetamine. Overall, the most common 50-kHz call subtypes were flat, trill, step-up, and complex. Consistent with previous reports, amphetamine increased the relative prevalence of trill calls while reducing the relative prevalence of flat calls. Yohimbine and caffeine reduced flat call prevalence, whereas mCPP reduced trill call prevalence. No other shifts in the call profile were observed, and no anxiogenic drug induced 22-kHz calls. CONCLUSION: Anxiogenic drugs, as a class, did not uniformly alter the 50-kHz call rate or subtype profile. Amphetamine-induced effects on 50-kHz call rate and profile do not reflect anxiety.

Effects of repeated morphine on ultrasonic vocalizations in adult rats: increased 50-kHz call rate and altered subtype profile.

RATIONALE: Adult rat 50-kHz vocalizations have been proposed to indicate a positive affective state, putatively revealed by a predominance of trill calls over flat calls. However, short-term exposure to non-sedative doses of the euphorigen morphine suppresses calling, with no discernible shift in trill or flat call prevalence. OBJECTIVES: This study aimed to determine whether morphine acutely increases 50-kHz call rates or alters the relative prevalence of trill or flat calls, after long-term morphine exposure or acute pharmacological pretreatment. METHODS: Experiment 1 comprised 10 once-daily tests, alternating between saline and morphine, 1 mg/kg SC, followed by dose-response testing (0, 0.3, 1, and 3 mg/kg). Experiment 2 was similar but included additional testing with morphine in combination with the antinausea drug ondansetron or the peripheral opioid antagonist methylnaltrexone. In experiment 3, morphine was again combined with ondansetron or methylnaltrexone but in rats that were initially drug naïve. RESULTS: In animals that were initially drug naïve, morphine tended to suppress calling and did not alter the 50-kHz call subtype profile. In morphine-experienced rats, morphine acutely increased the 50-kHz call rate and promoted trills over flat calls; short calls were also inhibited. Neither ondansetron nor methylnaltrexone detectably altered any effect of morphine on calling, nor did these two drugs affect 50-kHz calling when given alone. CONCLUSIONS: With chronic exposure, morphine acutely enhances 50-kHz calling and differentially promotes trill calls, mainly at the expense of flat calls. These effects appear consistent with a positive affect interpretation of 50-kHz vocalizations.