Reduced central serotonin transporters in alcoholism

Serotonergic dysfunction may mediate the relationship between alcohol consumption and Alzheimer's disease

The impact of Alzheimer's disease (AD) and its related dementias is rapidly expanding, and its mitigation remains an urgent social and technical challenge. To date there are no effective treatments or interventions for AD, but recent studies suggest that alcohol consumption is correlated with the risk of developing dementia. In this review, we synthesize data from preclinical, clinical, and epidemiological models to evaluate the combined role of alcohol consumption and serotonergic dysfunction in AD, underscoring the need for further research on this topic. We first discuss the limitations inherent to current data-collection methods, and how neuropsychiatric symptoms common among AD, alcohol use disorder, and serotonergic dysfunction may mask their co-occurrence. We additionally describe how excess alcohol consumption may accelerate the development of AD via direct effects on serotonergic function, and we explore the roles of neuroinflammation and proteostasis in mediating the relationship between serotonin, alcohol consumption, and AD. Lastly, we argue for a shift in current research to disentangle the pathogenic effects of alcohol on early-affected brainstem structures in AD.

The role of brain serotonin signaling in excessive alcohol consumption and withdrawal: A call for more research in females

Alcohol Use Disorder (AUD) is a leading cause of death and disability worldwide, but current treatments are insufficient in fully addressing the symptoms that often lead to relapses in alcohol consumption. The brain's serotonin system has been implicated in AUD for decades and is a major regulator of stress-related behaviors associated with increased alcohol consumption. This review will discuss the current literature on the association between neurobiological adaptations in serotonin systems and AUD in humans as well as the effectiveness of serotonin receptor manipulations on alcohol-related behaviors like consumption and withdrawal. We will further discuss how these findings in humans relate to findings in animal models, including a comparison of systemic pharmacological manipulations modulating alcohol consumption. We next provide a detailed overview of brain region-specific roles for serotonin and serotonin receptor signaling in alcohol-related behaviors in preclinical animal models, highlighting the complexity of forming a cohesive model of serotonin function in AUD and providing possible avenues for more effective therapeutic intervention. Throughout the review, we discuss what is known about sex differences in the sequelae of AUD and the role of serotonin in these sequelae. We stress a critical need for additional studies in women and female animals so that we may build a clearer path to elucidating sex-specific serotonergic mechanisms and develop better treatments.

Changes in serotonin neurotransmission as assayed by microdialysis after acute, intermittent or chronic ethanol administration and withdrawal

BACKGROUND

The serotonergic neurotransmitter system is involved in many ethanol-induced changes, including many behavioural alterations, as well as contributing to alcohol dependence and its withdrawal.

AIMS

This review has evaluated microdialysis studies where alterations in the serotonin system, that is, serotonin, 5-HT, or its metabolite 5-hydroxyindoleacetic acid, 5-HIAA, have been reported during different ethanol intoxication states, as well as in animals showing alcohol preference or not. Changes in 5-HT receptors and the 5-HT transporter are briefly reviewed to comprehend the significance of changes in microdialysate 5-HT concentrations.

MATERIALS AND METHODS

Changes in 5-HT content following acute, chronic and during ethanol withdrawal states are evaluated. In addition, the serotoninergic system was assessed in animals that have been genetically selected for alcohol preference to ascertain whether changes in this monoamine microdialysate content may contribute to alcohol preference.

RESULTS AND DISCUSSION

Changes occurred in 5-HT signalling in the limbic brain regions, increasing after acute ethanol administration in specific brain regions, particularly at higher doses, while chronic alcohol exposure essentially decreased serotonergic transmission. Such changes may play a pivotal role in emotion-driven craving and relapse. Depending on the dosage, mode of administration and consumption rate, ethanol affects specific brain regions in different ways, enhancing or reducing 5-HT microdialysate content, thereby inducing behavioural and cognitive functions and enhancing ethanol consumption.

CONCLUSION

Microdialysis studies demonstrated that ethanol induces several alterations in 5-HT content as well as its metabolites, 5-HIAA and 5-HTOL, not only in its release from a specific brain region but also in the modifications of its different receptor subtypes and its transporter.

The Dopamine System in Mediating Alcohol Effects in Humans

Brain-imaging studies show that the development and maintenance of alcohol use disorder (AUD) is determined by a complex interaction of different neurotransmitter systems and multiple psychological factors. In this context, the dopaminergic reinforcement system appears to be of fundamental importance. We focus on the excitatory and depressant effects of acute versus chronic alcohol intake and its impact on dopaminergic neurotransmission. Furthermore, we describe alterations in dopaminergic neurotransmission as associated with symptoms of alcohol dependence. We specifically focus on neuroadaptations to chronic alcohol consumption and their effect on central processing of alcohol-associated and reward-related stimuli. Altered reward processing, complex conditioning processes, impaired reinforcement learning, and increased salience attribution to alcohol-associated stimuli enable alcohol cues to drive alcohol seeking and consumption. Finally, we will discuss how the neurobiological and neurochemical mechanisms of alcohol-associated alterations in reward processing and learning can interact with stress, cognition, and emotion processing.

Molecular Imaging Studies of Alcohol Use Disorder

Alcohol use disorder (AUD) is a serious public health problem in many countries, bringing a gamut of health risks and impairments to individuals and a great burden to society. Despite the prevalence of a disease model of AUD, the current pharmacopeia does not present reliable treatments for AUD; approved treatments are confined to a narrow spectrum of medications engaging inhibitory γ-aminobutyric acid (GABA) neurotransmission and possibly excitatory N-methyl-D-aspartate (NMDA) receptors, and opioid receptor antagonists. Molecular imaging with positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can open a window into the living brain and has provided diverse insights into the pathology of AUD. In this narrative review, we summarize the state of molecular imaging findings on the pharmacological action of ethanol and the neuropathological changes associated with AUD. Laboratory and preclinical imaging results highlight the interactions between ethanol and GABA A-type receptors (GABAAR), but the interpretation of such results is complicated by subtype specificity. An abundance of studies with the glucose metabolism tracer fluorodeoxyglucose (FDG) concur in showing cerebral hypometabolism after ethanol challenge, but there is relatively little data on long-term changes in AUD. Alcohol toxicity evokes neuroinflammation, which can be tracked using PET with ligands for the microglial marker translocator protein (TSPO). Several PET studies show reversible increases in TSPO binding in AUD individuals, and preclinical results suggest that opioid-antagonists can rescue from these inflammatory responses. There are numerous PET/SPECT studies showing changes in dopaminergic markers, generally consistent with an impairment in dopamine synthesis and release among AUD patients, as seen in a number of other addictions; this may reflect the composite of an underlying deficiency in reward mechanisms that predisposes to AUD, in conjunction with acquired alterations in dopamine signaling. There is little evidence for altered serotonin markers in AUD, but studies with opioid receptor ligands suggest a specific up-regulation of the μ-opioid receptor subtype. Considerable heterogeneity in drinking patterns, gender differences, and the variable contributions of genetics and pre-existing vulnerability traits present great challenges for charting the landscape of molecular imaging in AUD.

Neurobiological mechanisms of control in alcohol use disorder - moving towards mechanism-based non-invasive brain stimulation treatments

Alcohol use disorder (AUD) is characterized by excessive habitual drinking and loss of control over alcohol intake despite negative consequences. Both of these aspects foster uncontrolled drinking and high relapse rates in AUD patients. Yet, common interventions mostly focus on the phenomenological level, and prioritize the reduction of craving and withdrawal symptoms. Our review provides a mechanistic understanding of AUD and suggests alternative therapeutic approaches targeting the mechanisms underlying dysfunctional alcohol-related behaviours. Specifically, we explain how repeated drinking fosters the development of rigid drinking habits and is associated with diminished cognitive control. These behavioural and cognitive effects are then functionally related to the neurobiochemical effects of alcohol abuse. We further explain how alterations in fronto-striatal network activity may constitute the neurobiological correlates of these alcohol-related dysfunctions. Finally, we discuss limitations in current pharmacological AUD therapies and suggest non-invasive brain stimulation (like TMS and tDCS interventions) as a potential addition/alternative for modulating the activation of both cortical and subcortical areas to help re-establish the functional balance between controlled and automatic behaviour.

Alcohol-related phenotypes and platelet serotonin concentration

Alcohol dependence is a chronic relapsing mental disorder with heterogeneous and complex underlying biology. It is frequently associated with nicotine dependence, severity of alcohol dependence symptoms, and diverse alcohol-related phenotypes, including the presence of delirium tremens and withdrawal symptoms, early or late onset of alcohol abuse, aggression, suicidal behavior, and anxiety. While searching for peripheral biomarkers of altered serotonergic (5-HT) function in alcohol dependence and alcohol-related behaviors, we determined a peripheral biomarker, i.e., platelet 5-HT concentration in a large group of Caucasian subjects with alcohol dependence subdivided according to the presence of specific alcohol-related phenotypes and smoking status. Individuals with alcohol dependence (n = 661) of both sexes were evaluated using Structural Clinical Interview based on DSM-IV criteria, while platelet 5-HT concentration was determined using the spectrophotofluorimetric method. Smoking is significantly associated, while sex and age are not, with platelet 5-HT concentration. Severe alcohol dependence and lack of withdrawal symptoms were associated with significantly decreased platelet 5-HT concentration in alcohol-dependent non-smokers. In smokers, significantly lower platelet 5-HT concentration was found in patients with the late onset of alcohol abuse. These results suggested that platelet 5-HT concentration might be used as a peripheral marker of different alcohol-related phenotypes, after controlling for the effects of smoking and sex.

Imipramine attenuates anxiety- and depressive-like effects of acute and prolonged ethanol-abstinence in male rats by modulating SERT and GR expression in the dorsal hippocampus

AIMS

Considering that serotoninergic agents attenuate symptoms of anxiety and are used to treat depression, we investigated whether subchronic treatment with imipramine, a serotonin/noradrenaline reuptake inhibitor, would prevent the anxiogenic-like behaviour induced by acute and/or chronic ethanol withdrawal. We also investigated whether those changes were related to the disfunctioning of hypothalamic-pituitary-adrenal (HPA) axis and serotonergic neurotransmission.

MAIN METHODS

264 Male Wistar rats were treated with ethanol 6% (vol./vol.) for 21 days. Acute ethanol withdrawal was induced by abrupt discontinuation of treatment and sustained for 48 h. Protracted abstinence was sustained for an additional period of 21 days. Behavioural tests included the Elevated Plus Maze (EPM) or Light/Dark Box (LDB) after acute abstinence, and the Forced Swim Test (FST) after protracted abstinence. Imipramine (15 mg/kg, i.p.) was administered 24, 19 and 1 h before EPM or LDB tests.

KEY FINDINGS

Acute abstinence decreased exploration of the open arms of the EPM, without changing exploration of LDB. Additionally, chronic abstinent rats displayed more time immobile in the FST, when compared to control animals. These effects were attenuated by imipramine treatment, without changing basal response. Imipramine prevented protracted abstinence -induced decrease in glucocorticoid receptor (GR) and serotonin transporter (SERT) expression in the dorsal hippocampus.

SIGNIFICANCE

Our findings indicate that chronic ethanol withdrawal affects the hippocampal serotonergic system by decreasing serotonin transporter expression. It also disturbs the HPA axis functioning through an imbalance on GR and mineralocorticoid (MR) expression.

The physiological responses to acute stress in alcohol-dependent patients: A systematic review

Dysregulation of physiological stress reactivity plays a key role in the development and relapse risk of alcohol dependence. This article reviews studies investigating physiological responses to experimentally induced acute stress in patients with alcohol dependence. A systematic search from electronic databases resulted in 3641 articles found and after screening 62 articles were included in our review. Studies are analyzed based on stress types (i.e., social stress tasks and nonsocial stress tasks) and physiological markers (i.e., the nervous system, the endocrine system, somatic responses and the immune system). In studies applying nonsocial stress tasks, alcohol-dependent patients were reported to show a blunted stress response compared with healthy controls in the majority of studies applying markers of adrenocorticotropic hormone and cortisol. In studies applying social stress tasks, findings are inconsistent, with less than half of the studies reporting altered physiological stress responses in patients. We discuss the impact of duration of abstinence, comorbidities, baseline physiological arousal and intervention on the discrepancy of study findings. Furthermore, we review evidence for an association between blunted physiological stress responses and the relapse risk among patients with alcohol dependence.

Bioinformatics identification and pharmacological validation of Kcnn3/KCa2 channels as a mediator of negative affective behaviors and excessive alcohol drinking in mice

Mood disorders are often comorbid with alcohol use disorder (AUD) and play a considerable role in the development and maintenance of alcohol dependence and relapse. Because of this high comorbidity, it is necessary to determine shared and unique genetic factors driving heavy drinking and negative affective behaviors. In order to identify novel pharmacogenetic targets, a bioinformatics analysis was used to quantify the expression of amygdala K+ channel genes that covary with anxiety-related phenotypes in the well-phenotyped and fully sequenced family of BXD strains. We used a model of stress-induced escalation of drinking in alcohol-dependent mice to measure negative affective behaviors during abstinence. A pharmacological approach was used to validate the key bioinformatics findings in alcohol-dependent, stressed mice. Amygdalar expression of Kcnn3 correlated significantly with 40 anxiety-associated phenotypes. Further examination of Kcnn3 expression revealed a strong eigentrait for anxiety-like behaviors and negative correlations with binge-like and voluntary alcohol drinking. Mice treated with chronic intermittent alcohol exposure and repeated swim stress consumed more alcohol in their home cages and showed hypophagia on the novelty-suppressed feeding test during abstinence. Pharmacologically targeting Kcnn gene products with the KCa2 (SK) channel-positive modulator 1-EBIO decreased drinking and reduced feeding latency in alcohol-dependent, stressed mice. Collectively, these validation studies provide central nervous system links into the covariance of stress, negative affective behaviors, and AUD in the BXD strains. Further, the bioinformatics discovery tool is effective in identifying promising targets (i.e., KCa2 channels) for treating alcohol dependence exacerbated by comorbid mood disorders.

Alcohol Binge Drinking: Negative and Positive Valence System Abnormalities

BACKGROUND

Each year, 3 million deaths occur owing to alcohol misuse. Translational studies are crucial to translate preclinical findings to patients. Preclinical studies have highlighted abnormalities in specific brain systems, with these forming the basis of allostasis theory. However, few studies have tested predictions in humans using neuroimaging.

METHODS

We used a Research Domain Criteria approach to test allostasis theory predictions of blunted positive valence system (PVS) and abnormally increased negative valence system (NVS) responses in 57 binge alcohol drinking subjects and healthy control subjects who completed an instrumental task during functional magnetic resonance imaging.

RESULTS

As hypothesized, binge alcohol drinkers showed abnormally increased activity in NVS-linked regions, such as the hippocampus and dorsal cingulate, and abnormally blunted activity in PVS-linked regions, such as the striatum, compared with control subjects. Higher measures of problematic alcohol use were associated with more abnormal brain activity only for binge drinkers who had been most recently drinking.

CONCLUSIONS

These results support allostasis theory predictions of abnormally increased NVS and blunted PVS responses in binge alcohol drinkers. Further similar translational neuroimaging studies are indicated, particularly focusing on the NVS.

Tobacco smoke and ethanol during adolescence: Both combined- and single-drug exposures lead to short- and long-term disruption of the serotonergic system in the mouse brain

The impairment of the serotonergic system contributes to nicotine and ethanol effects on mood, suggesting that this system is targeted by each of these drugs and that co-exposure possibly worsens the disruption. Here, we tested this hypothesis in an adolescent mice model of tobacco smoke and/or ethanol exposure. From postnatal day (PN) 30-45, Swiss mice were exposed to one of the following: 1) tobacco smoke (SMK; research cigarettes 2R1F, whole-body exposure, 8 h/daily); 2) ethanol (ETOH; 2 g/kg i.p., every other day); 3) SMK + ETOH; 4) Control (VEH). At PN45 (end-of-exposure), hippocampal serotonin transporter (5 H TT) binding was increased in SMK and decreased in ETOH male mice. At PN50 (short-term deprivation), cortical 5 H TT was reduced in all drug-exposed mice. In the hippocampus, similar deficits were identified in females. In both brain regions, the effects of SMK + ETOH deprivation on 5 H TT were equivalent to the damage caused by either drug. At PN50, hippocampal 5 H T1A receptor binding was reduced in ETOH and SMK + ETOH mice. Similar results were observed in the male cortex. In females, deficits were identified in SMK mice. In both brain regions, SMK + ETOH 5 H T1A deficits reflected the summation of SMK and ETOH outcomes. At PN75 (long-term deprivation), there was a late-emergent increase in cortical 5 H T1A binding in SMK mice, while cortical 5 H T2 receptor binding was similarly increased in SMK and SMK + ETOH groups. Adolescent SMK and/or ETOH serotonergic impairment is sex-dependent and most evident during short-term deprivation. SMK + ETOH deprivation evokes serotonergic disruption that is at least equivalent to that caused by either drug alone.

PET imaging of the mouse brain reveals a dynamic regulation of SERT density in a chronic stress model

The serotonin transporter (SERT, Slc6a4) plays an important role in the regulation of serotonergic neurotransmission and its aberrant expression has been linked to several psychiatric conditions. While SERT density has been proven to be amenable to in vivo quantitative evaluation by positron emission tomography (PET) in humans, this approach is in its infancy for rodents. Here we set out to evaluate the feasibility of using small-animal PET employing [¹¹C]DASB ([¹¹C]-3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile) as a radiotracer to measure SERT density in designated areas of the mouse brain. Using Slc6a4^+/+, Slc6a4^+/-, and Slc6a4^-/- mice as a genetic model of different SERT expression levels, we showed the feasibility of SERT imaging in the mouse brain with [¹¹C]DASB-PET. The PET analysis was complemented by an evaluation of SERT protein expression using western blot, which revealed a highly significant correlation between in vivo and ex vivo measurements. [¹¹C]DASB-PET was then applied to the examination of dynamic changes of SERT levels in different brain areas in the chronic corticosterone mouse model of chronic stress. The observed significant reduction in SERT density in corticosterone-treated mice was independently validated by and correlated with western blot analysis. This is the first demonstration of a quantitative in vivo evaluation of SERT density in subregions of the mouse brain using [¹¹C]DASB-PET. The evidenced decrease in SERT density in response to chronic corticosterone treatment adds a new dimension to the complex involvement of SERT in the pathophysiology of stress-induced mental illnesses.

Ketamine administration during a critical period after forced ethanol abstinence inhibits the development of time-dependent affective disturbances

Forced abstinence from chronic two bottle-choice ethanol drinking produces the development of negative affective states in female C57BL/6J mice. We previously reported that this disrupted behavior is acutely reversed by administration of ketamine 30 min-prior to testing. Here we assessed whether ketamine can be used as an inoculant against the development of abstinence- dependent affective disturbances. In parallel, we examined the impact of ketamine administration on long-term potentiation (LTP) in the bed nucleus of the stria terminalis (BNST), a region implicated in affective disturbances. We administered ketamine (3 mg/kg i.p.) to female C57BL/6J mice with a history of chronic ethanol drinking at either the onset, two, or 6 days- post-abstinence and observed its impact on affective behavior in the elevated plus maze (EPM), the Novelty Suppressed Feeding Test (NSFT), and the Forced Swim Test (FST). In addition, we assessed BNST synaptic plasticity with field potential electrophysiology two to 3 weeks into abstinence. We found that early abstinence was associated with disrupted behavior on the EPM. Ketamine administered at the onset of forced abstinence prevented both the deficit in early EPM behavior, and the delayed deficits in NSFT and FST. However, ketamine administered either two or 6 days post-abstinence failed to prevent the abstinence-induced affective disturbances. To begin to explore potential alterations in neural circuit activity that accompanies these actions of ketamine, we assessed the impact of ketamine administration at the onset of forced abstinence and measured LTP induction in the BNST. We find that early ketamine administration persistently increased the capacity for LTP within the BNST. These findings suggest a critical period at the onset of forced abstinence in which ketamine inoculation can prevent the development of affective disturbances, in part by enhancing plasticity within the BNST.

OPRM1 genotype interacts with serotonin system dysfunction to predict alcohol-heightened aggression in primates

Although the notion that alcohol promotes violence is widespread, not all individuals are aggressive while intoxicated. Genetic variation could be a contributing factor to individual differences in alcohol-heightened aggression. The present study examines the effects of OPRM1C77G genotype on responses to threat in rhesus macaques under normal conditions and following alcohol administration. Prior studies have shown that a low CSF level of 5-HIAA is a trait marker for individuals prone to escalated aggression. We wanted to examine whether the predictive value for this marker on aggression was moderated by OPRM1 genotype. Animals were administered alcohol (BAC 100-200 mg%), were provoked by a human intruder, and aggressive responses were recorded. Factor analysis was performed to generate aggressive response factors, which were then used as dependent variables for ANOVA, with OPRM1 genotype and CSF 5-HIAA as independent variables. Factor analysis generated three factors ('Threatening', 'Distance Decreasing' and 'High Intensity'). We found that High Intensity aggression was increased among carriers of the OPRM1 G allele, especially among individuals with low CSF levels of 5-HIAA. Aggression in the non-intoxicated state was predicted by 5-HIAA, but not by genotype. This study demonstrates that OPRM1 genotype predicts alcohol-heightened aggression in rhesus macaques with low CSF levels of 5-HIAA. Because OPRM1 variation predicts similar effects on alcohol response and behavior in humans and macaques, this study could suggest a role for OPRM1 genotype in alcohol-heightened aggression in humans. If so, it may be that compounds that block this receptor could reduce alcohol-associated violence in selected patient populations.

Deep Transcranial Magnetic Stimulation of the Dorsolateral Prefrontal Cortex in Alcohol Use Disorder Patients: Effects on Dopamine Transporter Availability and Alcohol Intake

Repetitive Transcranial Magnetic Stimulation (rTMS) of the dorsolateral prefrontal cortex may affect neuro-adaptations associated with alcohol use disorder (AUD), potentially influencing craving and alcohol intake. We investigated alcohol intake and dopamine transporter (DAT) availability by Single Photon Emission Computed Tomography (SPECT) in the striatum of AUD patients before and after deep rTMS. Fourteen patients underwent baseline clinical and SPECT assessment. Eleven out of fourteen patients were randomized into two groups for the REAL (n.5) or SHAM (n.6) treatment. Clinical and SPECT evaluations were then carried out after four weeks of rTMS sessions (T1). At baseline, AUD patients showed higher striatal DAT availability than healthy control subjects (HC). Patients receiving the REAL stimulation revealed a reduction in DAT availability at T1, whereas the SHAM-treated group did not. In addition, patients receiving the REAL stimulation had a decrease in alcohol intake. The results of this longitudinal pilot study may suggest a modulatory effect of deep rTMS on dopaminergic terminals and a potential clinical efficacy in reducing alcohol intake in AUD patients. Further investigations are required to confirm these preliminary data.

Ethanol induced antidepressant-like effect in the mouse forced swimming test: modulation by serotonergic system

AIM

The present investigation explored the modulatory role of serotonergic transmission in the acute ethanol-induced effects on immobility time in the mouse forced swim test (FST).

METHODS AND RESULTS

Acute i.p. administration of ethanol (20% w/v, 2 or 2.5 g/kg, i.p.) decreased the immobility time in FST of mice, indicating its antidepressant-like effect while lower doses of ethanol (1, 1.5 g/kg, i.p.) were devoid of any effect in the FST. The mice pre-treated with a sub-effective dose of 5-HT_2A agonist, DOI (10 μg/mouse, i.c.v.) or 5-HT_1A receptor antagonist, WAY 100635 (0.1 μg/mouse, i.c.v.) but not with the 5-HT_2A/2C antagonist, ketanserin (1.5 μg/mouse, i.c.v.) exhibited a synergistic reduction in the immobility time induced by sub-effective dose of ethanol (1.5 g/kg, i.p.). On the other hand, ethanol (2.5 g/kg, i.p.) failed to decrease the immobility time in mice, pre-treated with 5-HT_1A agonist, 8-OH-DPAT (0.1 μg/mouse, i.c.v.) or ketanserin (1.5 μg/mouse, i.c.v.). In addition, pre-treatment with a 5-HT neuronal synthesis inhibitor, p-CPA (300 mg/kg, i.p. × 3 days) attenuated the anti-immobility effect ethanol (2.5 g/kg, i.p.) in mouse FST.

CONCLUSIONS

Thus, the results of the present study points towards the essentiality of the central 5-HT transmission at the synapse for the ethanol-induced antidepressant-like effect in the FST wherein the regulatory role of the 5-HT_1A receptor or contributory role of the 5-HT_2A/2C receptor-mediated mechanism is proposed in the anti-immobility effect of acute ethanol in mouse FST.

Neurochemical and metabolic effects of acute and chronic alcohol in the human brain: Studies with positron emission tomography

The use of Positron emission tomography (PET) to study the effects of acute and chronic alcohol on the human brain has enhanced our understanding of the mechanisms underlying alcohol's rewarding effects, the neuroadaptations from chronic exposure that contribute to tolerance and withdrawal, and the changes in fronto-striatal circuits that lead to loss of control and enhanced motivation to drink that characterize alcohol use disorders (AUD). These include studies showing that alcohol's reinforcing effects may result not only from its enhancement of dopaminergic, GABAergic and opioid signaling but also from its caloric properties. Studies in those suffering from an AUD have revealed significant alterations in dopamine (DA), GABA, cannabinoids, opioid and serotonin neurotransmission and in brain energy utilization (glucose and acetate metabolism) that are likely to contribute to compulsive alcohol taking, dysphoria/depression, and to alcohol-associated neurotoxicity. Studies have also evaluated the effects of abstinence on recovery of brain metabolism and neurotransmitter function and the potential value of some of these measures to predict clinical outcomes. Finally, PET studies have started to provide insights about the neuronal mechanisms by which certain genes contribute to the vulnerability to AUD. These findings have helped identify new strategies for prevention and treatment of AUD. This article is part of the Special Issue entitled "Alcoholism".

Serotonergic Neuroplasticity in Alcohol Addiction

Alcohol addiction is a debilitating disorder producing maladaptive changes in the brain, leading drinkers to become more sensitive to stress and anxiety. These changes are key factors contributing to alcohol craving and maintaining a persistent vulnerability to relapse.

Serotonin (5-Hydroxytryptamine, 5-HT) is a monoamine neurotransmitter widely expressed in the central nervous system where it plays an important role in the regulation of mood. The serotonin system has been extensively implicated in the regulation of stress and anxiety, as well as the reinforcing properties of all of the major classes of drugs of abuse, including alcohol. Dysregulation within the 5-HT system has been postulated to underlie the negative mood states associated with alcohol use disorders.

This review will describe the serotonergic (5-HTergic) neuroplastic changes observed in animal models throughout the alcohol addiction cycle, from prenatal to adulthood exposure. The first section will focus on alcohol-induced 5-HTergic neuroadaptations in offspring prenatally exposed to alcohol and the consequences on the regulation of stress/anxiety. The second section will compare alterations in 5-HT signalling induced by acute or chronic alcohol exposure during adulthood and following alcohol withdrawal, highlighting the impact on the regulation of stress/anxiety signalling pathways. The third section will outline 5-HTergic neuroadaptations observed in various genetically-selected ethanol preferring rat lines. Finally, we will discuss the pharmacological manipulation of the 5-HTergic system on ethanol- and anxiety/stress-related behaviours demonstrated by clinical trials, with an emphasis on current and potential treatments.

Exercise training - A beneficial intervention in the treatment of alcohol use disorders?

BACKGROUND

A growing body of evidence suggests that exercise training may have multiple beneficial effects in individuals with mental health or substance use disorders. Yet, relatively little knowledge exists regarding the benefits of exercise training to augment treatment for alcohol use disorders (AUDs).

PURPOSE

The purpose of this narrative review is to present a summary of the growing body of published literature supporting exercise training as a treatment strategy for individuals with AUDs. We will provide evidence on the myriad of ways in which exercise may exert a positive effect on AUD outcomes including stress, anxiety, impulsivity, and depression. Further, we will explore how these mechanisms share common neurobiological pathways. The role of exercise in enhancing the social environment and increasing individual self-efficacy to reduce excess and/or inappropriate alcohol consumption will also be discussed.

DISCUSSION

We will conclude with a description of completed investigations involving exercise training and provide suggestions for next steps in this innovative field of study.

Probing the Serotonin Transporter Availability Among Male Cigarette Smokers: A SPECT Study With [123I] ADAM

OBJECTIVE

Genetic studies have suggested that the serotonin transporter (SERT) could be associated with cigarette smoking. However, evidence from neuroimaging is scarce. The aim of the present study was to examine the SERT availability among cigarette smokers by using single-photon emission computed tomography (SPECT).

METHODS

Sixteen male smokers and 32 controls were enrolled. The SERT availability was measured by SPECT with a radiotracer, [I] ADAM, which is highly sensitive and specific to SERT.

RESULTS

No significant difference in SERT availability was found between 2 groups in the midbrain (smokers: 2.12 ± 0.70, nonsmokers: 2.13 ± 0.63; P = 0.86), basal ganglia (smokers: 0.83 ± 0.30, nonsmokers:0.90 ± 0.39; P = 0.95), or thalamus (smokers: 1.14 ± 0.41, nonsmokers: 1.20 ± 0.38; P = 0.88). No significant association was found between the SERT availability, and either the breath carbon monoxide level or the score of the Fagerström Test for Nicotine Dependence.

CONCLUSIONS

Whether the SERT availability in the brain is altered in smokers remains unclear.

Nonhuman primate models of neuropsychiatric disorders: influences of early rearing, genetics, and epigenetics

This report reviews the scientific literature from the past several decades that focuses on nonhuman primates (NHPs) as models of neuropsychiatric disorders, including anxiety, and alcoholism. In particular, we highlight the approaches, advantages, and disadvantages of the rearing, genetic, and epigenetic methodologies behind these studies as a means of evaluating the application of these methods in assessing disorders in NHPs as models of human disease. Finally, we describe the contributions the NHP studies have made to neuropsychiatric research and areas for future research.

Serotonin and mental disorders: a concise review on molecular neuroimaging evidence

Serotonin is one of the most important neurotransmitters influencing mental health and, thus, is a potential target for pharmaco-logical treatments. Functional neuroimaging techniques, such as positron-emission tomography (PET) and single photon emission computed tomography (SPECT), could provide persuasive evidence for the association between mental disorders and serotonin. In this concise review, we focus on evidence of the links between serotonin and major depressive disorders, as well as other mood disorders, anxiety disorders, schizophrenia, addiction, attention deficit hyperactivity disorder (ADHD), and autism.

The effects of chronic alcohol self-administration on serotonin-1A receptor binding in nonhuman primates

BACKGROUND

Previous studies have found interrelationships between the serotonin system and alcohol self-administration. The goal of this work was to directly observe in vivo effects of chronic ethanol self-administration on serotonin 5-HT1A receptor binding with [(18)F]mefway PET neuroimaging in rhesus monkeys. Subjects were first imaged alcohol-naïve and again during chronic ethanol self-administration to quantify changes in 5-HT1A receptor binding.

METHODS

Fourteen rhesus monkey subjects (10.7-12.8 years) underwent baseline [(18)F]mefway PET scans prior to alcohol exposure. Subjects then drank gradually increasing ethanol doses over four months as an induction period, immediately followed by at least nine months ad libidum ethanol access. A post [(18)F]mefway PET scan was acquired during the final three months of ad libidum ethanol self-administration. 5-HT1A receptor binding was assayed with binding potential (BPND) using the cerebellum as a reference region. Changes in 5-HT1A binding during chronic ethanol self-administration were examined. Relationships of binding metrics with daily ethanol self-administration were also assessed.

RESULTS

Widespread increases in 5-HT1A binding were observed during chronic ethanol self-administration, independent of the amount of ethanol consumed. A positive correlation between 5-HT1A binding in the raphe nuclei and average daily ethanol self-administration was also observed, indicating that baseline 5-HT1A binding in this region predicted drinking levels.

CONCLUSIONS

The increase in 5-HT1A binding levels during chronic ethanol self-administration demonstrates an important modulation of the serotonin system due to chronic alcohol exposure. Furthermore, the correlation between 5-HT1A binding in the raphe nuclei and daily ethanol self-administration indicates a relationship between the serotonin system and alcohol self-administration.

Alcohol use disorders and current pharmacological therapies: the role of GABA(A) receptors

Alcohol use disorders (AUD) are defined as alcohol abuse and alcohol dependence, which create large problems both for society and for the drinkers themselves. To date, no therapeutic can effectively solve these problems. Understanding the underlying mechanisms leading to AUD is critically important for developing effective and safe pharmacological therapies. Benzodiazepines (BZs) are used to reduce the symptoms of alcohol withdrawal syndrome. However, frequent use of BZs causes cross-tolerance, dependence, and cross-addiction to alcohol. The FDA-approved naltrexone and acamprosate have shown mixed results in clinical trials. Naltrexone is effective to treat alcohol dependence (decreased length and frequency of drinking bouts), but its severe side effects, including withdrawal symptoms, are difficult to overcome. Acamprosate showed efficacy for treating alcohol dependence in European trials, but two large US trials have failed to confirm the efficacy. Another FDA-approved medication, disulfiram, does not diminish craving, and it causes a peripheral neuropathy. Kudzu is the only natural medication mentioned by the National Institute on Alcohol Abuse and Alcoholism, but its mechanisms of action are not yet established. It has been recently shown that dihydromyricetin, a flavonoid purified from Hovenia, has unique effects on GABAA receptors and blocks ethanol intoxication and withdrawal in alcoholic animal models. In this article, we review the role of GABAA receptors in the treatment of AUD and currently available and potentially novel pharmacological agents.

Greater monoamine oxidase a binding in alcohol dependence

BACKGROUND

Alcohol dependence (AD) is a multiorgan disease in which excessive oxidative stress and apoptosis are implicated. Monoamine oxidase A (MAO-A) is an important enzyme on the outer mitochondrial membrane that participates in the cellular response to oxidative stress and mitochondrial toxicity. It is unknown whether MAO-A levels are abnormal in AD. We hypothesized that MAO-A VT, an index of MAO-A level, is elevated in the prefrontal cortex (PFC) during AD, because markers of greater oxidative stress and apoptosis are reported in the brain in AD and a microarray analysis reported greater MAO-A messenger RNA in the PFC of rodents exposed to alcohol vapor.

METHODS

Sixteen participants with alcohol dependence and 16 healthy control subjects underwent [(11)C]-harmine positron emission tomography. All were nonsmoking, medication- and drug-free, and had no other past or present psychiatric or medical illnesses.

RESULTS

MAO-A VT was significantly greater in the PFC (37%, independent samples t test, t₃₀ = 3.93, p < .001), and all brain regions analyzed (mean 32%, multivariate analysis of variance, F₇,₂₄ = 3.67, p = .008). Greater duration of heavy drinking correlated positively with greater MAO-A VT in the PFC (r = .67, p = .005) and all brain regions analyzed (r = .73 to .57, p = .001-.02).

CONCLUSIONS

This finding represents a new pathological marker present in AD that is therapeutically targetable through direct inhibition or by novel treatments toward oxidative/pro-apoptotic processes implicated by MAO-A overexpression.

Extrastriatal binding of [¹²³I]FP-CIT in the thalamus and pons: gender and age dependencies assessed in a European multicentre database of healthy controls

PURPOSE

Apart from binding to the dopamine transporter (DAT), [(123)I]FP-CIT shows moderate affinity for the serotonin transporter (SERT), allowing imaging of both monoamine transporters in a single imaging session in different brain areas. The aim of this study was to systematically evaluate extrastriatal binding (predominantly due to SERT) and its age and gender dependencies in a large cohort of healthy controls.

METHODS

SPECT data from 103 healthy controls with well-defined criteria of normality acquired at 13 different imaging centres were analysed for extrastriatal binding using volumes of interest analysis for the thalamus and the pons. Data were examined for gender and age effects as well as for potential influence of striatal DAT radiotracer binding.

RESULTS

Thalamic binding was significantly higher than pons binding. Partial correlations showed an influence of putaminal DAT binding on measured binding in the thalamus but not on the pons. Data showed high interindividual variation in extrastriatal binding. Significant gender effects with 31 % higher binding in women than in men were observed in the thalamus, but not in the pons. An age dependency with a decline per decade (±standard error) of 8.2 ± 1.3 % for the thalamus and 6.8 ± 2.9 % for the pons was shown.

CONCLUSION

The potential to evaluate extrastriatal predominant SERT binding in addition to the striatal DAT in a single imaging session was shown using a large database of [(123)I]FP-CIT scans in healthy controls. For both the thalamus and the pons, an age-related decline in radiotracer binding was observed. Gender effects were demonstrated for binding in the thalamus only. As a potential clinical application, the data could be used as a reference to estimate SERT occupancy in addition to nigrostriatal integrity when using [(123)I]FP-CIT for DAT imaging in patients treated with selective serotonin reuptake inhibitors.

Molecular imaging in alcohol dependence

The cellular mechanisms of alcohol's effects in the brain are complex, targeting multiple transmitter systems. Molecular imaging has been used to study the effects of alcohol and alcohol use disorders on these various systems. Studies of dopaminergic indices have provided robust evidence for deficits in D2-mediated transmission in the striatum of chronic recently detoxified alcoholics. Their presence in the at-risk state prior to excessive drinking, and their recovery after long-term sobriety, are unclear and represent an active area of current research. Investigations of the GABAergic system have shown generalized deficits in various brain regions in the chronic abstinence phase. Studies of the opiate system have suggested alterations in some subtypes in discrete brain regions, including the ventral striatum, while studies of serotonin have been negative and those of the cannabinoid system have been inconclusive. Future investigations should target the glutamatergic system, which plays an important role both in the acute intoxicating effects of alcohol as well as in the long-term effects associated with dependence.

Change over time in brain serotonin transporter binding in major depression: effects of therapy measured with [(123) I]-ADAM SPECT

Several studies have reported low brain serotonin transporter (SERT) binding in individuals with major depression. We hypothesized that the SERT standardized uptake ratio (SUR) values using [(123) I]-ADAM single photon emission computed tomography would increase in depressed subjects who responded to cognitive behavior therapy (CBT) compared to CBT nonresponders. [(123) I]-ADAM scans were acquired before and after 12 weeks of CBT from 20 depressed subjects and on two occasions 12 weeks apart from 10 nondepressed, healthy volunteers. The primary outcome measure was change over time in SUR values in the midbrain, medial temporal lobe, and basal ganglia regions. Depressed subjects demonstrated low pretreatment mean SUR values that significantly increased over time in the midbrain (P = .011), right medial temporal lobe (P = .008), and left medial temporal lobe (P = .000) regions. Treatment responders showed a significant increase over time in SUR values in left medial temporal lobe (P = .029) and right medial temporal lobe (P = .007) regions. Partial and nonresponder subjects also showed a significant increase over time in SUR values in the left medial temporal region (P = .040) (vs. healthy volunteers), but to a lesser degree. The findings suggest that low pretreatment SERT binding may increase over time in some depressed individuals who experience symptom improvement.

Role of 5-hydroxytryptamine 1B (5-HT1B) receptors in the regulation of ethanol intake in rodents

Evidence indicates that the serotonergic system is important in mediating dependence on and craving for alcohol. Among serotonin receptors, 5-hydroxytryptamine 1B (5-HT1B) receptors have been associated with drug abuse including alcohol. In this review, the neurocircuitry involving 5-HT1B receptors in central reward brain regions related to alcohol intake are discussed in detail. Emphasis has been placed on the pharmacological manipulations of 5-HT1B receptor-mediated alcohol intake. Furthermore, 5-HT1B auto- and hetero-receptors regulate alcohol intake through the regulatory mechanism involving release of 5-HT, gamma-aminobutyric acid (GABA), dopamine, and glutamate is evaluated. Thus, interactions between 5-HT1B receptors and these neurotransmitter systems are suggested to modulate alcohol-drinking behavior. This review on the role of 5-HT1B receptors in neurotransmitter release and consequent alcohol intake provides important information about the potential therapeutic role of 5-HT1B receptors for the treatment of alcohol dependence.

Serotonin transporter genotype by environment: Studies on alcohol use and misuse in non-human and human primates

Much evidence indicates that gene-by-environment interactions (GxE) play a role in alcohol misuse. It has been proposed that interactions between serotonin and stress confer vulnerability for alcohol misuse. The present review examined studies of the interaction between the serotonin transporter linked polymorphic region (5-HTTLPR) genotype and stressful life events and alcohol-related phenotypes, in rhesus monkeys and humans. Ten studies were found that had investigated the interaction of 5-HTTLPR and various measures of stress and alcohol use or misuse, two studies of rhesus monkeys, and eight of humans. The results are contradictory. Important differences were reported in study samples, experimental designs, measures used to assess environmental variables, definitions and measurements of alcohol-related phenotypes, and in the statistical analyses. These differences may explain the contradictory results. Guidelines for future studies are suggested. Results are discussed in light of findings from molecular, non-human animal, and clinical studies. The review highlights the need for future studies examining associations of interactions between the serotonin transporter gene and environmental factors and alcohol misuse, especially in samples followed over time.

Wege aus der Abhängigkeit

Hintergrund: Alkohol-assoziierte Reize lösen bei alkoholabhängigen Patienten konditionierte Reaktionen aus, die zu einer erhöhten Motivation der Alkoholeinnahme führen können. Klassische Konditionierungsprozesse scheinen demnach sowohl zur Aufrechterhaltung der Abhängigkeit als auch zum Rückfallgeschehen nach Entzug beizutragen. Bildgebende Studien weisen darauf hin, dass das dopaminerge Neurotransmittersystem an assoziativen Lernvorgängen beteiligt ist und Veränderungen innerhalb dieses Systems bei entgifteten alkoholabhängigen Patienten zum Rückfall beitragen könnten. Die genauen Mechanismen in diesem Zusammenhang sind bisher jedoch ungeklärt. Zielsetzung: Ziel dieser Arbeit ist die Darstellung von motivationalen Veränderungen und deren (neuroadaptiven) Grundlagen bei Alkoholabhängigkeit. Ein genaueres Verständnis davon, welche neuronalen und motivationalen Prozesse im Rahmen des Rückfallgeschehens eine Rolle spielen, könnte sowohl pharmakologische als auch therapeutische Implikationen für die Behandlung der Alkoholabhängigkeit liefern. Methodik: Diese Arbeit umfasst eine Literaturanalyse über neuroadaptive Veränderungen bei Alkoholabhängigkeit mit besonderem Fokus auf Lernprozesse und deren Rolle beim Rückfallgeschehen. Die Literaturrecherche basiert auf Recherchen der Forschergruppe 1617 der Deutschen Forschungsgesellschaft (DFG; Learning and Habitization in Alcohol Dependence, LeAD). Schlussfolgerung: Bisher existieren keine Untersuchungen, in denen neuroadaptive Veränderungen der Alkoholabhängigkeit mit spezifischen Lerndefiziten in Zusammenhang gebracht werden. Die DFG Forschergruppe LeAD untersucht neuronale Korrelate von lernbezogenen Rückfallprädiktoren. Ein Ziel dieser Untersuchung ist es herauszufinden, warum alkoholabhängige Patienten nach ihrer Entgiftung oft nicht lernen, Alkohol durch alternative belohnende Reize und Situation zu ersetzen und welche neuronalen Grundlagen diesem Defizit zu Grunde liegen.

Stress produces aversion and potentiates cocaine reward by releasing endogenous dynorphins in the ventral striatum to locally stimulate serotonin reuptake

Activation of the dynorphin/κ-opioid receptor (KOR) system by repeated stress exposure or agonist treatment produces place aversion, social avoidance, and reinstatement of extinguished cocaine place preference behaviors by stimulation of p38α MAPK, which subsequently causes the translocation of the serotonin transporter (SERT, SLC6A4) to the synaptic terminals of serotonergic neurons. In the present study we extend those findings by showing that stress-induced potentiation of cocaine conditioned place preference occurred by a similar mechanism. In addition, SERT knock-out mice did not show KOR-mediated aversion, and selective reexpression of SERT by lentiviral injection into the dorsal raphe restored the prodepressive effects of KOR activation. Kinetic analysis of several neurotransporters demonstrated that repeated swim stress exposure selectively increased the V(max) but not K(m) of SERT without affecting dopamine transport or the high-capacity, low-affinity transporters. Although the serotonergic neurons in the dorsal raphe project throughout the forebrain, a significant stress-induced increase in cell-surface SERT expression was only evident in the ventral striatum, and not in the dorsal striatum, hippocampus, prefrontal cortex, amygdala, or dorsal raphe. Stereotaxic microinjections of the long-lasting KOR antagonist norbinaltorphimine demonstrated that local KOR activation in the nucleus accumbens, but not dorsal raphe, mediated this stress-induced increase in ventral striatal surface SERT expression. Together, these results support the hypothesis that stress-induced activation of the dynorphin/KOR system produces a transient increase in serotonin transport locally in the ventral striatum that may underlie some of the adverse consequences of stress exposure, including the potentiation of the rewarding effects of cocaine.

Characterization of serotonin transporter gene (SLC6A4) polymorphisms and its association with drug dependence in a Jordanian Arab population

Drug dependence is a pattern of repeated self-administration of a drug, which can result in tolerance, withdrawal and compulsive drug-taking behaviour. It has been recently suggested that 5-HTTLPR (LL/LS/SS) variants and rs25531 (A/G) polymorphism in the serotonin transporter gene (SLC6A4) may play a role in drug dependence. The current study aimed to (1) identify allelic, haplotypic and genotypic frequencies of the 5-HTTLPR variants and rs25531 polymorphisms of SLC6A4 gene in drug and nondrug-dependent Jordanian Arab population and (2) determine whether there is an association of these variants in a drug-dependent population from the same area. Jordanian drug male addicts of Arab descent (n = 192) meeting the Diagnostic and Statistical Manual of Mental Disorders - Fourth edition criteria for drug dependence and 230 healthy male controls from an ethnically homogenous Jordanian Arab population were examined. Genotyping was performed using the restriction fragment length polymorphism-polymerase chain reaction-based method to genotype the 5-HTTLPR variants and detect the A/G polymorphism at position rs25531. The biallelic analysis revealed that the frequency of 5-HTTLPR (LL/LS/SS) genotypes was statistically significant different between drug-dependent individuals and controls (χ (2) (2, N = 422), p = 0.04). Drug-dependent subjects had a higher frequency of 'L' allele. However, using the triallelic approach, the estimated frequency of haplotypes (SA , SG , LA and LG ) and phased genotypes (LA /LA , LA /SA , LA /LG , SA /SA and SA /SG) did not show significant association with drug dependence (χ (2) (3, N = 422), p = 0.53 and χ (2) (4, N = 422), p = 0.06, respectively). This study suggests a putative role of the 5-HTTLPR for drug dependence in the Jordanian Nationals of Arab ancestry.

Effects of acute combined serotonin and dopamine depletion on cue-induced drinking intention/desire and cognitive function in patients with alcohol dependence

BACKGROUND

Alcohol cues can precipitate the desire to drink and cause relapse in recovering alcohol-dependent patients. Serotonin and dopamine may play a role in alcohol cue-induced craving. Acute combined tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe) depletion (CMD) in the diet attenuates the synthesis of serotonin and dopamine in the human brain. However, no study of the effects of acute CMD has been previously conducted. Therefore, we investigated whether the attenuation of serotonin and dopamine synthesis changes cue-induced alcohol craving in recently abstinent alcoholics.

METHODS

In this double-blind, randomized, placebo-controlled, crossover design, 12 male patients who met the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, criteria for alcohol dependence were divided into two conditions: (1) monoamine depletion (i.e., consumption of a concentrated amino acid beverage that resulted in a rapid and significant decrease in plasma-free Tyr/Phe/Trp) and (2) balanced condition (i.e., consumption of a similar beverage that contained Tyr/Phe/Trp). The participants were scheduled for two experimental sessions, with an interval of ≥7 days. The cue-induced craving test session was conducted 6h after each amino acid beverage administration. Drinking urge, blood pressure, heart rate, working memory, and attention/psychomotor performance were assessed before and after administration.

RESULTS

Compared with the balanced condition, the monoamine depletion condition significantly increased drinking intention/desire and diastolic blood pressure. Cognitive performance was not different between the two conditions.

CONCLUSIONS

Acute combined serotonin and dopamine depletion may increase drinking intention/desire and diastolic blood pressure without influencing cognitive function.

Low brain serotonin transporter binding in major depressive disorder

We examined midbrain, medial temporal lobe, and basal ganglia serotonin transporter (SERT) distribution volume ratio (DVR) values in subjects with major depressive disorder versus healthy volunteers using a selective SERT radioligand and single photon emission computed tomography (SPECT). We hypothesized that the DVR value for SERT binding would be lower in depressed versus non-depressed subjects. [(123)I]-ADAM SPECT scans were acquired from 20 drug free, depressed subjects and 20 drug-free depressed subjects and 10 drug-free healthy volunteers. The primary outcome measure was the DVR value for [(123)I]-ADAM uptake in the midbrain, medial temporal lobe, and basal ganglia regions. Depressed subjects demonstrated significantly lower DVR values in the midbrain, right and left medial temporal lobe, and right and left basal ganglia. There was significant probability that lower DVR values could distinguish between depressed and non-depressed subjects in the midbrain, medial temporal lobe, and the right and left basal ganglia. These findings confirm prior observations of lower SERT binding in depression, and suggest that low SERT binding may represent a putative biomarker of depression. Future studies are needed to confirm these observations.

Deficits in emotion-regulation skills predict alcohol use during and after cognitive-behavioral therapy for alcohol dependence

OBJECTIVE

As emotion regulation is widely considered to be a primary motive in the misuse of alcohol, our aim in the study was to investigate whether deficits in adaptive emotion-regulation skills maintain alcohol dependence (AD).

METHOD

A prospective study investigated whether emotion-regulation skills were associated with AD and whether these skills predicted alcohol use during and after treatment for AD. Participants were 116 individuals treated for AD with cognitive-behavioral therapy. Emotion regulation and severity of AD symptoms were assessed by self-report. Alcohol use during treatment was assessed by Breathalyzer and urine analysis for ethyl glucuronide; alcohol use during the 3-month follow-up interval was assessed by self-report.

RESULTS

Pretreatment emotion-regulation skills predicted alcohol use during treatment, and posttreatment emotion-regulation skills predicted alcohol use at follow-up, even when controlling for other predictors potentially related to emotion regulation. Among a broad range of specific emotion-regulation skills, the ability to tolerate negative emotions was the only skill that negatively predicted subsequent alcohol consumption when controlling for the other skills. Individuals in the AD sample reported significantly larger deficits in emotion-regulation skills than did those in a nonclinical control sample but significantly less than did those in a sample of individuals exclusively meeting criteria for major depressive disorder.

CONCLUSIONS

Enhancement of general emotion-regulation skills, especially the ability to tolerate negative emotions, appears to be an important target in the treatment of AD.

The effects of chronic ethanol self-administration on hippocampal serotonin transporter density in monkeys

Evidence for an interaction between alcohol consumption and the serotonin system has been observed repeatedly in both humans and animal models yet the specific relationship between the two remains unclear. Research has focused primarily on the serotonin transporter (SERT) due in part to its role in regulating extracellular levels of serotonin. The hippocampal formation is heavily innervated by ascending serotonin fibers and is a major component of the neurocircuitry involved in mediating the reinforcing effects of alcohol. The current study investigated the effects of chronic ethanol self-administration on hippocampal SERT in a layer and field specific manner using a monkey model of human alcohol consumption. [(3)H]Citalopram was used to measure hippocampal SERT density in male cynomolgus macaques that voluntarily self-administered ethanol for 18 months. Hippocampal [(3)H]citalopram binding was less dense in ethanol drinkers than in controls, with the greatest effect observed in the molecular layer of the dentate gyrus. SERT density was not correlated with measures of ethanol consumption or blood ethanol concentrations, suggesting the possibility that a threshold level of consumption had been met. The lower hippocampal SERT density observed suggests that chronic ethanol consumption is associated with altered serotonergic modulation of hippocampal neurotransmission.

Alcohol and the human brain: a systematic review of different neuroimaging methods

BACKGROUND

Imaging techniques have been in widespread use in the scientific community for more than 3 decades. They facilitate noninvasive, in vivo studies of the human brain in both healthy and diseased persons. These brain-imaging techniques have contributed significantly to our understanding of the effects of alcohol abuse and dependence on structural and functional changes in the human brain. A systematic review summarizing these contributions has not previously been conducted, and this is the goal of the current paper.

METHODS

The databases PubMed, PsycINFO, and PSYNDEX were searched using central key words. Fulfilling the inclusion criteria were 140 functional and structural imaging studies, together comprising data from more than 7,000 patients and controls. The structural imaging techniques we considered were cranial computerized tomography and various magnetic resonance imaging-based techniques, including voxel-based morphometry, deformation-based morphometry, diffusion tensor magnetic resonance imaging, and diffusion-weighted magnetic resonance imaging. The functional methods considered were magnetic resonance spectroscopy, positron emission tomography, single photon emission computed tomography, and functional magnetic resonance imaging.

RESULTS

Results from studies using structural imaging techniques have revealed that chronic alcohol use is accompanied by volume reductions of gray and white matter, as well as microstructural disruption of various white matter tracts. These changes are partially reversible following abstinence. Results from functional imaging methods have revealed metabolic changes in the brain, lower glucose metabolism, and disruptions of the balance of neurotransmitter systems. Additionally, functional imaging methods have revealed increased brain activity in the mesocorticolimbic system in response to alcohol-themed pictures relative to nondrug-associated stimuli, which might be of predictive value with regard to relapse.

CONCLUSIONS

There has been tremendous progress in the development of imaging technologies. Use of these technologies has clearly demonstrated the structural and functional brain abnormalities that can occur with chronic alcohol use. The study of the alcoholic brain provides an heuristic model which furthers our understanding of neurodegenerative changes in general, as well as their partial reversibility with sustained abstinence. Additionally, functional imaging is poised to become an important tool for generating predictions about individual brain functioning, which can then be used as a basis for personalized medicine.

Genetic influences of dopamine transport gene on alcohol dependence: a pooled analysis of 13 studies with 2483 cases and 1753 controls

Previous genetic association studies have reported a possible role of the dopamine transporter (DAT, gene symbol: SLC6A3) gene in the etiology of alcohol dependence, but the results were conflicting with each other. We conducted a pooled analysis of published population-based case-control genetic studies investigating associations between polymorphisms in SLC6A3 and alcohol dependence. We also explored whether geographic area, ethnicity, gender, and diagnostic criteria moderated any association by using stratified analysis. Through combining 13 studies with 2483 cases and 1753 controls, the 40-base pair variable number tandem repeat (VNTR) in the 3' un-translated region, the well studied polymorphism in SLC6A3, did not show any association with alcohol dependence in general or in stratified analyses according to geographic area, ethnicity, gender, and diagnostic criteria. Due to limited studies focused on polymorphisms in other regions of the SLC6A3 gene, we cannot rule out the role of the SLC6A3 gene in the involvement of the genetic risk of alcohol dependence. Further clarification of the genetic role of SLC6A3 in the susceptibility to alcohol dependence should be centered on other potential functional regions of the SLC6A3 gene.

Cognitive and neurobiological mechanisms of alcohol-related aggression

Alcohol-related violence is a serious and common social problem. Moreover, violent behaviour is much more common in alcohol-dependent individuals. Animal experiments and human studies have provided insights into the acute effect of alcohol on aggressive behaviour and into common factors underlying acute and chronic alcohol intake and aggression. These studies have shown that environmental factors, such as early-life stress, interact with genetic variations in serotonin-related genes that affect serotonergic and GABAergic neurotransmission. This leads to increased amygdala activity and impaired prefrontal function that, together, predispose to both increased alcohol intake and impulsive aggression. In addition, acute and chronic alcohol intake can further impair executive control and thereby facilitate aggressive behaviour.

Fluoxetine, desipramine, and the dual antidepressant milnacipran reduce alcohol self-administration and/or relapse in dependent rats

A few clinical studies have shown that dual antidepressants (serotonergic (5-HT) and noradrenergic (NE) transporter inhibitors, SNRIs) may be effective in alcoholism treatment. We studied the effect of the dual antidepressant milnacipran on ethanol operant self-administration in acutely withdrawn ethanol-dependent and in -non-dependent Wistar rats, and used fluoxetine and desipramine to dissect both 5-HT and NE components, respectively, in the effect of milnacipran. Milnacipran was also tested for relapse after protracted abstinence and on ethanol-induced (1.0 g/kg) conditioned place preference in control rats and ethanol-induced locomotor sensitization in DBA/2J female mice. Milnacipran dose dependently (5-40 mg/kg) attenuated the increased ethanol self-administration observed during early withdrawal and was more potent in preventing reinstatement in dependent rats after protracted abstinence as compared with non-dependent rats. Desipramine and fluoxetine (10 mg/kg) blocked ethanol self-administration during early withdrawal, and recovery was delayed in dependent animals, indicating a potent effect. Ethanol self-administration was also reduced 1 day after treatment with desipramine and fluoxetine but not with milnacipran. Finally, milnacipran prevented ethanol-induced place preference in ethanol-naive rats and reduced the magnitude of ethanol-induced sensitization associated with a delayed induction in mice. Desipramine (20 mg/kg) countered sensitization development and reduced its expression at 1 week after treatment; fluoxetine (10 mg/kg) reduced sensitization expression. Thus, 5-HT and NE transmissions during sensitization expression may mediate the effect of milnacipran on sensitization induction. These results support that SNRIs may have a potential use in alcoholism treatment.

Epigenetic changes of serotonin transporter in the patients with alcohol dependence: methylation of an serotonin transporter promoter CpG island

OBJECTIVE

Psychiatric disorders such as depression, anxiety and alcohol dependence are associated with serotonin metabolism. We assessed the methylation level of the serotonin transporter (5-HTT) promoter region in control and alcohol dependent patients.

METHODS

Twenty seven male patients who met the Diagnostic and Statistical Manual of Mental Disorder IV (DSM-IV) criteria for alcohol dependence were compared with fifteen controls. Polymerase chain reaction (PCR) assays of bisulfate-modified DNA were designed to amplify a part of the CpG island in the 5HTT gene. Pyrosequencing was performed and the methylation level at seven CpG island sites was measured.

RESULTS

We found no differences in the methylation patterns of the serotonin transporter linked promoter region (5-HTTLPR) between alcohol-dependent and control subjects.

CONCLUSION

Our negative finding may be because 5-HTT epigenetic variation may not affect the expression for 5-HTT or there may be other methylation site critical for its expression. To find out more conclusive result, repeating the study in more methylation sites with a larger number of samples in a well-controlled setting is needed.