Convergent evidence from alcohol-dependent humans and rats for a hyperdopaminergic state in protracted abstinence

Different dopamine tone in ethanol high- and low-consuming Wistar rats

Excessive alcohol use causes considerable morbidity and mortality worldwide. Changes in the mesolimbic dopamine system have been postulated as a neurobiological underpinning of excessive alcohol consumption, and recent research also suggests that the amino acid taurine plays a central role in ethanol-induced dopamine elevation. The aim of this study was to further outline the role of dopamine and taurine in regulating alcohol consumption. In this study, a choice between ethanol (20%) and water was administered to Wistar rats in an intermittent manner (three times/week) for seven consecutive weeks. In vivo microdialysis was used to explore baseline levels as well as ethanol-induced increases of extracellular dopamine and taurine, in the nucleus accumbens (nAc) of Wistar rats voluntarily consuming large or small amounts of ethanol. Basal levels of taurine were also measured in cerebrospinal fluid (CSF) and serum in a subset of rats. Ethanol-induced increases in nAc dopamine and taurine did not differ between alcohol-consuming and naïve rats. However, when categorized based on ethanol intake, rats consuming larger amounts of ethanol exhibited a lower dopamine tone in the nucleus accumbens and responded to ethanol with a slower elevation of extracellular taurine levels, as compared with low-consuming animals. Basal levels of taurine in nAc, CSF, or serum did not differ between ethanol high- and low-consuming rats. Our data support previous studies claiming an association between low endogenous dopamine levels and excessive alcohol intake.

Effects of Ethanol Exposure During Adolescence or Adulthood on Locomotor Sensitization and Dopamine Levels in the Reward System

Behavioral sensitization is a process of neuroadaptation characterized by a gradual increase in motor behaviors. The major neural substrates involved in the behavioral sensitization lie on the dopaminergic mesocorticolimbic pathway, which is still under development during adolescence. To investigate age-differences in ethanol behavioral sensitization and dopamine levels in distinct brain regions of the reward system, adolescent and adult mice were repeatedly pretreated with saline or ethanol (2.0 g/kg i.p.) during 15 consecutive days and challenged with saline or ethanol 5 days after pretreatment. Dopamine and its metabolites were measured in tissue samples of the prefrontal cortex (PFC), nucleus accumbens (NAc) and striatum by HPLC analysis. While repeated ethanol administration resulted in the development of locomotor sensitization in both adult and adolescent mice, only the adults expressed sensitization to a subsequent ethanol challenge injection. Neurochemical results showed reduced dopamine levels in adolescents compared to adults. Specifically, mice pretreated with ethanol during adolescence displayed lower dopamine levels in the PFC compared to the respective adult group in response to an ethanol challenge injection, and preadolescent mice exhibited lower dopamine levels in the NAc following an acute ethanol treatment compared to adults. These findings suggest that adolescent mice are not only less sensitive to the expression of ethanol-induced sensitization than adults, but also show lower dopamine content after ethanol exposition in the PFC and NAc.

Interaction between behavioral inhibition and neural alcohol cue-reactivity in ADHD and alcohol use disorder

RATIONALE

Compared to the general population, adult Attention-Deficit / Hyperactivity Disorder (ADHD) is more prevalent in patients with Alcohol Use Disorder (AUD). Impaired behavioral inhibition is a common characteristic in both ADHD and AUD. Relapse risk is increased in patients with AUD and comorbid, untreated ADHD and in AUD patients with increased neural cue-reactivity.

OBJECTIVES

In this study, we examined the interaction between neural correlates of behavioral inhibition and alcohol cue-reactivity with a hybrid imaging task.

METHODS

Out of 69 adult study participants, we included n = 49 in our final analyses: Individuals had a diagnosis of either AUD (n = 13), ADHD (n = 14) or both (n = 5), or were healthy controls (HC; n = 17). The functional magnetic resonance imaging paradigm aimed to examine the combined effects of both an interference-inhibition task ("Simon-task") and an alcohol cue-reactivity task. Instead of segregating by diagnostic group, we pursued a dimensional approach in which we compared measures of AUD and ADHD severity, as well as the interaction of both, using multiple regression analyses.

RESULTS

The four groups did not differ on the behavioral level on either the inhibition task or the alcohol cue-reactivity task. However, brain activation in frontal control and reward-related regions during completion of the combined tasks were related to ADHD and AUD severity (symptom load). During presentation of both alcohol cues and the inhibition task, participants with higher AUD and ADHD symptom load exhibited greater BOLD (blood oxygen level dependent) responses in subcortical reward-related regions.

CONCLUSIONS

Our findings support the hypothesis that ADHD additionally diminishes inhibition ability in individuals with AUD. This may increase relapse risk when confronted with alcohol cues. Further, it is crucial for patients with comorbid AUD and ADHD to take into account not only reduced cognitive control over behavioral inhibition but also simultaneously heightened alcohol cue-reactivity.

Evidence for incentive salience sensitization as a pathway to alcohol use disorder

The incentive salience sensitization (ISS) theory of addiction holds that addictive behavior stems from the ability of drugs to progressively sensitize the brain circuitry that mediates attribution of incentive salience (IS) to reward-predictive cues and its behavioral manifestations. In this article, we establish the plausibility of ISS as an etiological pathway to alcohol use disorder (AUD). We provide a comprehensive and critical review of evidence for: (1) the ability of alcohol to sensitize the brain circuitry of IS attribution and expression; and (2) attribution of IS to alcohol-predictive cues and its sensitization in humans and non-human animals. We point out gaps in the literature and how these might be addressed. We also highlight how individuals with different alcohol subjective response phenotypes may differ in susceptibility to ISS as a pathway to AUD. Finally, we discuss important implications of this neuropsychological mechanism in AUD for psychological and pharmacological interventions attempting to attenuate alcohol craving and cue reactivity.

The selective κ-opioid receptor antagonist JDTic attenuates the alcohol deprivation effect in rats

The mechanisms behind relapse to ethanol intake in recovering alcoholics are still unclear. The negative reinforcing effects contributing to ethanol addiction, including relapse, are considered to be partly driven by the κ-opioidergic system. As the κ-opioidergic system interacts with the mesolimbic reward pathway, the aim of the study was to clarify the role of nucleus accumbens shell κ-opioidergic mechanisms in relapse to ethanol intake by using the alcohol deprivation effect (ADE) paradigm. The ADE is defined as a transient increase in voluntary ethanol intake after a forced period of abstinence. Male Long-Evans rats were trained to voluntarily consume 10% (v/v) ethanol solution. Ethanol access and deprivation cycles were initiated after stable ethanol intake baselines had been reached and bilateral guide cannulas had been implanted above the nucleus accumbens shell. One cycle consisted of 10 days of 90 min access to ethanol followed by 6 days of ethanol deprivation. The ADE was measured in the beginning of a new cycle. Rats received JDTic, a selective κ-antagonist, either subcutaneously (10 mg/kg) or intra-accumbally (15 µg/site) or, as a reference substance, systemic naltrexone (0.3 mg/kg) before ethanol re-access, and the effects on the ADE were evaluated. Systemic and intra-accumbal JDTic significantly attenuated the ADE on the first day of ethanol re-access, as did systemic naltrexone. Additionally, naltrexone decreased ethanol intake levels. These results suggest that nucleus accumbens shell κ-opioidergic mechanisms may have a role in mediating relapse to ethanol intake. Additionally, κ-antagonism could be a valuable adjunct in ethanol relapse prevention.

Inhibition of the rostromedial tegmental nucleus reverses alcohol withdrawal-induced anxiety-like behavior

Acute withdrawal from alcohol is associated with a number of unpleasant symptoms that play an important role in preventing recovery and long-term abstinence. Considerable research has focused on the role that neuropeptide systems and the amygdala play in mediating affective symptoms of acute withdrawal, but promising preclinical findings have not translated successfully into the clinic. The rostromedial tegmental nucleus (RMTg) has been implicated in both fear and anxiety. In addition, RMTg neurons exert inhibitory control over midbrain dopamine neurons, the activity of which are suppressed during acute withdrawal. Thus, we hypothesized that the RMTg may play a role in mediating symptoms of acute withdrawal. Using a chronic ethanol vapor exposure paradigm that renders rats physically dependent on ethanol, we observed significant withdrawal-induced enhancement of cFos expression in the RMTg. This was accompanied by a significant increase in somatic symptoms and a decrease in reward sensitivity as measured by intracranial self-stimulation (ICSS). Both measures followed a similar time course to RMTg cFos expression with peak symptom severity occurring 12 h following cessation of ethanol exposure. Heightened anxiety-like behavior was also observed in withdrawn rats at this same time point. RMTg inhibition had no effect on somatic signs of withdrawal or withdrawal-induced changes in reward sensitivity, but significantly attenuated withdrawal-induced anxiety-like behavior. Together, these data demonstrate that the RMTg plays a distinct role in the negative affective state associated with acute withdrawal and may therefore be critically involved in the neurobiological mechanisms that promote relapse during early stages of recovery.

Concurrent, successful management of bipolar I disorder with comorbid alcohol dependence via aripiprazole long-acting injection: A case report

Alcohol dependence is frequently comorbid with bipolar I disorder. Aripiprazole and its long-acting injection have demonstrated efficacy in the treatment and prevention of bipolar I disorder and its attendant symptoms, especially manic episodes. However, whether aripiprazole can alleviate alcohol dependence remains controversial. We report the case of a 47-year-old woman who had been diagnosed with bipolar I disorder and alcohol dependence, characterized by poor adherence to pharmacological treatment and our hospital's alcoholic treatment program. Consequently, she was repeatedly hospitalized several times per year due to manic episodes and heavy drinking. After treatment with aripiprazole long-acting injection at a dosage of 400 mg/mo intramuscularly, she has been relapse-free for over 2 years. Aripiprazole long-acting injection might therefore be effective for treating patients with bipolar disorder and a comorbid diagnosis of alcohol dependence.

phMRI, neurochemical and behavioral responses to psychostimulants distinguishing genetically selected alcohol-preferring from genetically heterogenous rats

Alcoholism is often associated with other forms of drug abuse, suggesting that innate predisposing factors may confer vulnerability to addiction to diverse substances. However, the neurobiological bases of these factors remain unknown. Here, we have used a combination of imaging, neurochemistry and behavioral techniques to investigate responses to the psychostimulant amphetamine in Marchigian Sardinian (msP) alcohol-preferring rats, a model of vulnerability to alcoholism. Specifically, we employed pharmacological magnetic resonance imaging to investigate the neural circuits engaged by amphetamine challenge, and to relate functional reactivity to neurochemical and behavioral responses. Moreover, we studied self-administration of cocaine in the msP rats. We found stronger functional responses in the extended amygdala, alongside with increased release of dopamine in the nucleus accumbens shell and augmented vertical locomotor activity compared with controls. Wistar and msP rats did not differ in operant cocaine self-administration under short access (2 hours) conditions, but msP rats exhibited a higher propensity to escalate drug intake following long access (6 hours). Our findings suggest that neurobiological and genetic mechanisms that convey vulnerability to excessive alcohol drinking also facilitate the transition from psychostimulants use to abuse.

Increased Ethanol Consumption and Locomotion Develop upon Ethanol Deprivation in Rats Overexpressing the Adenosine (A)2A Receptor

Preclinical data indicate that ethanol produces behavioral effects that can be regulated by many neurotransmitters and neuromodulators like adenosine (A). The most important receptors with respect to the rewarding effects of ethanol seem to be the A_2A receptors. This study used a transgenic strategy, specifically rats overexpressing the A_2A receptor, to characterize the neurobiological mechanisms of ethanol consumption as measured by intermittent access to 20% ethanol in a two-bottle choice paradigm. In this model, no change in ethanol consumption was observed in transgenic animals compared to wild type controls during the acquisition/maintenance phase. Following alcohol deprivation, only transgenic rats overexpressing the A_2A receptor exhibited escalation of ethanol consumption and drank more (by ca. 90%), but not significantly, ethanol than did the wild type rats. During ethanol withdrawal, the immobility time of rats overexpressing the A_2A receptor in the forced swim test was lower than that of wild type rats. Moreover, transgenic rats withdrawn from ethanol, compared to the drug-naive transgenic animals, exhibited an increase above 70% in locomotion. The results indicated that the overexpression of A_2A receptors may be a risk factor for the escalation of ethanol consumption despite the reduction in depression-like signs of ethanol withdrawal.

Nicotine and alcohol: the role of midbrain dopaminergic neurons in drug reinforcement

Nicotine and alcohol addiction are leading causes of preventable death worldwide and continue to constitute a huge socio-economic burden. Both nicotine and alcohol perturb the brain's mesocorticolimbic system. Dopamine (DA) neurons projecting from the ventral tegmental area (VTA) to multiple downstream structures, including the nucleus accumbens, prefrontal cortex, and amygdala, are highly involved in the maintenance of healthy brain function. VTA DA neurons play a crucial role in associative learning and reinforcement. Nicotine and alcohol usurp these functions, promoting reinforcement of drug taking behaviors. In this review, we will first describe how nicotine and alcohol individually affect VTA DA neurons by examining how drug exposure alters the heterogeneous VTA microcircuit and network-wide projections. We will also examine how coadministration or previous exposure to nicotine or alcohol may augment the reinforcing effects of the other. Additionally, this review briefly summarizes the role of VTA DA neurons in nicotine, alcohol, and their synergistic effects in reinforcement and also addresses the remaining questions related to the circuit-function specificity of the dopaminergic system in mediating nicotine/alcohol reinforcement and comorbidity.

Presynaptic Ethanol Actions: Potential Roles in Ethanol Seeking

Ethanol produces intoxication through actions on numerous molecular and cellular targets. Adaptations involving these and other targets contribute to chronic drug actions that underlie continued and problematic drinking. Among the mechanisms involved in these ethanol actions are alterations in presynaptic mechanisms of synaptic transmission, including presynaptic protein function and excitation-secretion coupling. At synapses in the central nervous system (CNS), excitation-secretion coupling involves ion channel activation followed by vesicle fusion and neurotransmitter release. These mechanisms are altered by presynaptic neurotransmitter receptors and prominently by G protein-coupled receptors (GPCRs). Studies over the last 20-25 years have revealed that acute ethanol exposure alters neurotransmitter secretion, with especially robust effects on synapses that use the neurotransmitter gamma-aminobutyric acid (GABA). Intracellular signaling pathways involving second messengers such as cyclic AMP and calcium are implicated in these acute ethanol actions. Ethanol-induced release of neuropeptides and small molecule neurotransmitters that act on presynaptic GPCRs also contribute to presynaptic potentiation at synapses in the amygdala and hippocampus and inhibition of GABA release in the striatum. Prolonged exposure to ethanol alters neurotransmitter release at many CNS GABAergic and glutamatergic synapses, and changes in GPCR function are implicated in many of these neuroadaptations. These presynaptic neuroadaptations appear to involve compensation for acute drug effects at some synapses, but "allostatic" effects that result in long-term resetting of synaptic efficacy occur at others. Current investigations are determining how presynaptic neuroadaptations contribute to behavioral changes at different stages of alcohol drinking, with increasing focus on circuit adaptations underlying these behaviors. This chapter will discuss the acute and chronic presynaptic effects of ethanol in the CNS, as well as some of the consequences of these effects in amygdala and corticostriatal circuits that are related to excessive seeking/drinking and ethanol abuse.

Conditioned Aversion and Neuroplasticity Induced by a Superagonist of Extrasynaptic GABAA Receptors: Correlation With Activation of the Oval BNST Neurons and CRF Mechanisms

THIP (gaboxadol), a superagonist of the δ subunit-containing extrasynaptic GABA_A receptors, produces persistent neuroplasticity in dopamine (DA) neurons of the ventral tegmental area (VTA), similarly to rewarding drugs of abuse. However, unlike them THIP lacks abuse potential and induces conditioned place aversion in mice. The mechanism underlying the aversive effects of THIP remains elusive. Here, we show that mild aversive effects of THIP were detected 2 h after administration likely reflecting an anxiety-like state with increased corticosterone release and with central recruitment of corticotropin-releasing factor corticotropin-releasing factor receptor 1 (CRF₁) receptors. A detailed immunohistochemical c-Fos expression mapping for THIP-activated brain areas revealed a correlation between the activation of CRF-expressing neurons in the oval nucleus of the bed nuclei of stria terminalis and THIP-induced aversive effects. In addition, the neuroplasticity of mesolimbic DA system (24 h after administration) and conditioned place aversion by THIP after four daily acute sessions were dependent on extrasynaptic GABA_A receptors (abolished in δ-GABA_A receptor knockout mice) and activation of the CRF₁ receptors (abolished in wildtype mice by a CRF₁ receptor antagonist). A selective THIP-induced activation of CRF-expressing neurons in the oval part of the bed nucleus of stria terminalis may constitute a novel mechanism for inducing plasticity in a population of VTA DA neurons and aversive behavioral states.

Building better strategies to develop new medications in Alcohol Use Disorder: Learning from past success and failure to shape a brighter future

Alcohol Use Disorder (AUD) is a chronic disease that develops over the years. The complexity of the neurobiological processes contributing to the emergence of AUD and the neuroadaptive changes occurring during disease progression make it difficult to improve treatments. On the other hand, this complexity offers researchers the possibility to explore new targets. Over years of intense research several molecules were tested in AUD; in most cases, despite promising preclinical data, the clinical efficacy appeared insufficient to justify futher development. A prototypical example is that of corticotropin releasing factor type 1 receptor (CRF1R) antagonists that showed significant effectiveness in animal models of AUD but were largely ineffective in humans. The present article attempts to analyze the most recent venues in the development of new medications in AUD with a focus on the most promising drug targets under current exploration. Moreover, we delineate the importance of using a more integrated translational framework approach to correlate preclinical findings and early clinical data to enhance the probability to validate biological targets of interest.

No effect of sex on ethanol intake and preference after dopamine transporter (DAT) knockdown in adult mice

RATIONALE

Dopamine levels are controlled in part by transport across the cell membrane by the dopamine transporter (DAT), and recent evidence showed that a polymorphism in the gene encoding DAT is associated with alcoholism. However, research in animal models using DAT knockout mice has yielded conflicting results.

OBJECTIVES

The present study was planned to evaluate the effects of DAT knockdown in the nucleus accumbens (Nacc) on voluntary ethanol consumption and preference in male and female C57BL/6J mice.

METHODS

For this purpose, animals were stereotaxically injected with DAT siRNA-expressing lentiviral vectors in the Nacc, and using a voluntary, continuous access two-bottle choice model of alcohol, we investigated the importance of accumbal DAT expression in voluntary alcohol intake and preference. We also investigated the effects of DAT knockdown on saccharin and quinine consumption and ethanol metabolism.

RESULTS

We show that females consumed more alcohol than males. Interestingly, DAT knockdown in the Nacc significantly decreased alcohol intake and preference in both groups, but no significant sex by group interaction was observed. Also, DAT knockdown did not alter total fluid consumption, saccharin or quinine consumption, or blood ethanol concentrations. Using Pearson correlation, results indicated a strong positive relationship between DAT mRNA expression and ethanol consumption and preference.

CONCLUSIONS

Taken together, these data provide further evidence that DAT plays an important role in controlling ethanol intake and that accumbal DAT contributes in the modulation of the reinforcing effects of ethanol. Overall, the results suggest that DAT inhibitors may be valuable in the pharmacotherapy of alcoholism.

Effects of Citalopram on Cue-Induced Alcohol Craving and Thalamic D2/3 Dopamine Receptor Availability

BACKGROUND

Selective serotonin reuptake inhibitors are often used in alcohol use disorders. Clinical trials with selective serotonin reuptake inhibitors for alcohol use disorders, however, have yielded mixed results. The goal of this project was to assess whether a single i.v. dose of a selective serotonin reuptake inhibitor reduces craving for alcohol and/or simultaneously increases striatal dopamine concentration in individuals with alcohol dependence.

METHODS

Alcohol-dependent (DSM-IV-TR criteria) volunteers and matched controls (n = 10/group) underwent a double-blind, placebo-controlled, within-subjects study. Participants received i.v. citalopram (40 mg) or saline (counter-balanced) followed by a cue-induced craving assessment and [18F]-fallypride positron emission tomography scanning.

RESULTS

In the alcohol-dependent individuals, the citalopram (compared with saline) resulted in decreased cue-induced craving for alcohol. For the whole study group, cue-induced alcohol craving was inversely correlated with thalamic (but not striatal) dopamine D2/3 receptor availability.

CONCLUSIONS

Acute serotonin reuptake inhibition reduces cue-induced alcohol craving. Furthermore, thalamic dopamine abnormalities and the striatal hyperdopaminergic hypothesis of alcohol use disorder are supported.

Effects of leptin and ghrelin on neural cue-reactivity in alcohol addiction: Two streams merge to one river?

Leptin and ghrelin and a "cross-talk" between both hormones were implicated in the pathophysiology of alcohol dependence, both modulating alcohol craving and drug-seeking. To date, the neurobiological mechanisms underlying those effects are still little-known. We thus investigated the effect of leptin and ghrelin on alcohol cue-induced brain response, alcohol craving and relapse risk in alcohol-dependent subjects. Seventy abstinent alcohol dependent individuals underwent a functional magnetic resonance imaging (fMRI) alcohol cue-reactivity task and patients` alcohol craving was assessed. Plasma levels of leptin, total and acylated, active ghrelin were measured prior to the fMRI session. Additionally, relapse data was collected during a three-month follow-up. Associations between hormone levels, mesolimbic cue-reactivity, alcohol craving and relapse risk were tested. Leptin levels showed a significant negative association to alcohol cue-induced brain response in the striatum and alcohol craving. In addition, there was a significant effect of leptin on time to first heavy relapse in which higher leptin levels predicted longer times to first heavy relapse. Moreover, positive associations between acylated ghrelin and increased cue-reactivity in bilateral insulae as well as increased craving for alcohol during the fMRI task were revealed. Leptin and acylated ghrelin show opposing effects on mesolimbic cue-reactivity and alcohol craving. We suspect that the reduced striatal cue-reactivity might be the neurobiological correlate of leptin's effect on relapse-risk. The reported results further support the relevance of appetite regulating hormones in the pathophysiology of addiction and their potential role as future treatment targets.

Molecular Imaging of Opioid and Dopamine Systems: Insights Into the Pharmacogenetics of Opioid Use Disorders

Opioid use in the United States has steadily risen since the 1990s, along with staggering increases in addiction and overdose fatalities. With this surge in prescription and illicit opioid abuse, it is paramount to understand the genetic risk factors and neuropsychological effects of opioid use disorder (OUD). Polymorphisms disrupting the opioid and dopamine systems have been associated with increased risk for developing substance use disorders. Molecular imaging studies have revealed how these polymorphisms impact the brain and contribute to cognitive and behavioral differences across individuals. Here, we review the current molecular imaging literature to assess how genetic variations in the opioid and dopamine systems affect function in the brain's reward, cognition, and stress pathways, potentially resulting in vulnerabilities to OUD. Continued research of the functional consequences of genetic variants and corresponding alterations in neural mechanisms will inform prevention and treatment of OUD.

Persistent Neuroadaptations in the Expression of Genes Involved in Cholesterol Homeostasis Induced by Chronic, Voluntary Alcohol Intake in Rats

Alcohol use disorder (AUD) is associated with persistent adaptations in the brain that are believed to participate in the long-lasting vulnerability to relapse after abstinence. Cholesterol, the major sterol compound found in the central nervous system (CNS), plays a major role in maintenance of neuronal morphology, synaptogenesis and synaptic communication and may be involved in alcohol-induced neuroadaptations. In this study, we investigated whether alcohol consumption in a two-bottle choice paradigm followed by 3 weeks of abstinence could alter the expression of genes encoding proteins involved in cholesterol homeostasis in brain regions involved in addiction and relapse, namely the prefrontal cortex (PFC), the nucleus accumbens (NAc), the mesencephalon and the amygdala. We found that voluntary alcohol intake followed by 3 weeks of forced abstinence produces changes in the transcription of several genes encoding proteins directly involved in cholesterol synthesis such as 3-hydroxyl-3-methylglutaryl-coenzyme A (HMGCoA) reductase, farnesyl-diphosphate farnesyltransferase 1 (FDFT1) and farnesyl diphosphate synthase (FDPS) and in its regulation such as sterol regulatory element-binding factor-2 (SREBF2), in cholesterol transport such as ATP-binding cassette subfamily A member 1 (ABCA1) and in cholesterol degradation such as CYP46A1. Interestingly, these changes appeared to be region-specific and suggest that previous chronic exposure to alcohol might durably increase cholesterol metabolism in the PFC, the NAc and the mesencephalon and decrease cholesterol metabolism in the amygdala. Altogether, these results suggest that alcohol consumption leads to durable deregulations in cholesterol metabolism in key areas involved in loss of control over drug use and addiction. These long-term neuroadaptations may participate in the changes in brain structure and functioning that are responsible for the long-lasting risks of relapse to alcohol.

Systemic neurotransmitter responses to clinically approved and experimental neuropsychiatric drugs

Neuropsychiatric disorders are the third leading cause of global disease burden. Current pharmacological treatment for these disorders is inadequate, with often insufficient efficacy and undesirable side effects. One reason for this is that the links between molecular drug action and neurobehavioral drug effects are elusive. We use a big data approach from the neurotransmitter response patterns of 258 different neuropsychiatric drugs in rats to address this question. Data from experiments comprising 110,674 rats are presented in the Syphad database [ www.syphad.org ]. Chemoinformatics analyses of the neurotransmitter responses suggest a mismatch between the current classification of neuropsychiatric drugs and spatiotemporal neurostransmitter response patterns at the systems level. In contrast, predicted drug-target interactions reflect more appropriately brain region related neurotransmitter response. In conclusion the neurobiological mechanism of neuropsychiatric drugs are not well reflected by their current classification or their chemical similarity, but can be better captured by molecular drug-target interactions.

Minor Adaptations of Ethanol-Induced Release of Taurine Following Chronic Ethanol Intake in the Rat

Alcohol dependence is a puzzling brain disorder causing enormous suffering and financial costs world-wide. One of the few common denominators of all addictive drugs is activation of the mesolimbic dopamine system resulting in increased dopamine levels in the nucleus accumbens. In order to understand the development of addiction and find new efficient treatment strategies we need to understand how addictive drugs increase dopamine following acute and chronic administration of drugs. In the search for mechanisms underlying ethanol's ability to increase dopamine in the nucleus accumbens we have found taurine to be of major importance, although the complete picture remains to be disclosed. The aim of the present study was to explore whether chronic voluntary ethanol intake influences the ethanol-induced elevation of taurine. By means of in vivo micro-dialysis we found that voluntary intake of large amounts of ethanol for 12 weeks only had a modest influence on ethanol-induced elevations of taurine in the rat.

Animal models of addiction

In recent years, animal models in psychiatric research have been criticized for their limited translational value to the clinical situation. Failures in clinical trials have thus often been attributed to the lack of predictive power of preclinical animal models. Here, I argue that animal models of voluntary drug intake—under nonoperant and operant conditions—and addiction models based on the Diagnostic and Statistical Manual of Mental Disorders are crucial and informative tools for the identification of pathological mechanisms, target identification, and drug development. These models provide excellent face validity, and it is assumed that the neurochemical and neuroanatomical substrates involved in drug-intake behavior are similar in laboratory rodents and humans. Consequently, animal models of drug consumption and addiction provide predictive validity. This predictive power is best illustrated in alcohol research, in which three approved medications—acamprosate, naltrexone, and nalmefene—were developed by means of animal models and then successfully translated into the clinical situation.

Histone Deacetylase Inhibitor Suberanilohydroxamic Acid Treatment Reverses Hyposensitivity to γ-Aminobutyric Acid in the Ventral Tegmental Area During Ethanol Withdrawal

Background

The ventral tegmental area (VTA) is important for alcohol‐related reward and reinforcement. Mouse VTA neurons are hyposensitive to γ‐aminobutyric acid (GABA) during ethanol (EtOH) withdrawal, and GABA responsiveness is normalized by in vitro treatment with histone deacetylase inhibitors (HDACi). The present study examined the effect of a systemically administered HDACi, suberanilohydroxamic acid (SAHA) on GABA sensitivity, and related molecular changes in VTA neurons during withdrawal after chronic EtOH intake in rats.

Methods

Sprague Dawley male adult rats were fed with Lieber‐DeCarli diet (9% EtOH or control diet) for 16 days. Experimental groups included control diet‐fed and EtOH diet‐fed (0‐ or 24‐hour withdrawal) rats treated with either SAHA or vehicle injection. Single‐unit recordings were used to measure the response of VTA neurons to GABA. Immunohistochemistry was performed to examine levels of HDAC2, acetylated histone H3 lysine 9 (acH3K9), and GABA_A receptor α1 and α5 subunits in the VTA; quantitative polymerase chain reaction was performed to examine the mRNA levels of HDAC2 and GABA_A receptor subunits.

Results

VTA neurons from the withdrawal group exhibited GABA hyposensitivity. In vivo SAHA treatment 2 hours before sacrifice normalized the sensitivity of VTA neurons to GABA. EtOH withdrawal was associated with increased HDAC2 and decreased acH3K9 protein levels; SAHA treatment normalized acH3K9 levels. Interestingly, no significant change was observed in the mRNA levels of HDAC2. The mRNA levels, but not protein levels, of GABA_A receptor α1 and α5 subunits were increased during withdrawal.

Conclusions

Withdrawal from chronic EtOH exposure results in a decrease in GABA‐mediated inhibition, and this GABA hyposensitivity is normalized by in vivo SAHA treatment. Disruption of signaling in the VTA produced by alteration of GABA neurotransmission could be 1 neuroadaptive physiological process leading to craving and relapse. These results suggest that HDACi pharmacotherapy with agents like SAHA might be an effective treatment for alcoholism.

Operant over-responding is more sensitive than reversal learning for revealing behavioral changes after withdrawal from alcohol consumption

In humans, prior alcohol use is linked with impulsivity and impaired decision-making, but the nature of this relationship is unclear. In a previous study in rats, we found that prior alcohol access led to over-responding in go/no-go discrimination training, but had no effect on discrimination learning. It was unclear whether this over-responding effect would occur in a reversal learning task, or whether prior alcohol would impair reversal learning in our task. In the present experiments, we determined whether six weeks of chronic intermittent alcohol access would induce over-responding or impair reversal learning in our task. Our task allowed for multiple responses/trial with limited reinforcement, so over-responding could be assessed. In Exp. 1, we gave three days of discrimination training prior to access to 20% alcohol or water, then reversed task contingencies starting 4 days after the end of alcohol access. In Exp. 2, we gave either three or six days of discrimination training prior to the same alcohol access and reversal learning procedures to determine if the original training length would affect alcohol's behavioral effects. We found no reversal learning deficits in either experiment. Across both experiments, we found that the Alcohol group exhibited over-responding to the active lever, but this effect was smaller than in our previous discrimination experiments. Our data suggest that there are behavioral changes after voluntary alcohol access that can be missed by some discrimination/reversal learning assessments, and our over-responding task can detect these transient changes. However, over-responding is more pronounced in discrimination than reversal learning.

Targeted overexpression of CRH receptor subtype 1 in central amygdala neurons: effect on alcohol-seeking behavior

RATIONALE

The corticotropin-releasing hormone (CRH) system is a key mediator of stress-induced responses in alcohol-seeking behavior. Recent research has identified the central nucleus of the amygdala (CeA), a brain region involved in the regulation of fear and stress-induced responses that is especially rich in CRH-positive neurons, as a key player in mediating excessive alcohol seeking. However, detailed characterization of the specific influences that local neuronal populations exert in mediating alcohol responses is hampered by current limitations in pharmacological and immunohistochemical tools for targeting CRH receptor subtype 1 (CRHR1).

OBJECTIVE

In this study, we investigated the effect of cell- and region-specific overexpression of CRHR1 in the CeA using a novel transgenic tool.

METHODS

Co-expression of CRHR1 in calcium-calmodulin-dependent kinase II (αCaMKII) neurons of the amygdala was demonstrated by double immunohistochemistry using a Crhr1-GFP reporter mouse line. A Cre-inducible Crhr1-expressing adeno-associated virus (AAV) was site-specifically injected into the CeA of αCaMKII-Cre^ERT2 transgenic rats to analyze the role of CRHR1 in αCaMKII neurons on alcohol self-administration and reinstatement behavior.

RESULTS

Forty-eight percent of CRHR1-containing cells showed co-expression of αCaMKII in the CeA. AAV-mediated gene transfer in αCaMKII neurons induced a 24-fold increase of Crhr1 mRNA in the CeA which had no effect on locomotor activity, alcohol self-administration, or cue-induced reinstatement. However, rats overexpressing Crhr1 in the CeA increased responding in the stress-induced reinstatement task with yohimbine serving as a pharmacological stressor.

CONCLUSION

We demonstrate that CRHR1 overexpression in CeA-αCaMKII neurons is sufficient to mediate increased vulnerability to stress-triggered relapse into alcohol seeking.

The κ-opioid receptor antagonist JDTic decreases ethanol intake in alcohol-preferring AA rats

RATIONALE

Studies suggest that the κ-opioidergic system becomes overactivated as ethanol use disorders develop. Nalmefene, a currently approved treatment for ethanol use disorders, may also elicit some of its main effects via the κ-opioidergic system. However, the exact role of κ-opioid receptors on regulating ethanol intake and contribution to the development of ethanol addiction remains to be elucidated.

OBJECTIVES

The aim of the present study was to clarify the role of accumbal κ-opioid receptors in controlling ethanol intake in alcohol-preferring Alko Alcohol (AA) rats.

METHODS

Microinfusions of the long-acting and selective κ-opioid receptor antagonist JDTic (1-15 μg/site) were administered bilaterally into the nucleus accumbens shell of AA rats voluntarily consuming 10% ethanol solution in the intermittent, time-restricted two-bottle choice access paradigm. JDTic (10 mg/kg) was also administered subcutaneously. Both the acute and long-term effects of the treatment on ethanol intake were examined. As a reference, nor-BNI (3 μg/site) was administered intra-accumbally.

RESULTS

Systemically administered JDTic decreased ethanol intake significantly 2 days and showed a similar trend 4 days after administration. Furthermore, intra-accumbally administered JDTic showed a weak decreasing effect on ethanol intake long-term but had no acute effects. Intra-accumbal administration of nor-BNI tended to decrease ethanol intake.

CONCLUSIONS

The results provide further evidence that κ-opioid receptors play a role in controlling ethanol intake and that accumbal κ-opioid receptors participate in the modulation of the reinforcing effects of ethanol. Furthermore, the results suggest that κ-opioid receptor antagonists may be a valuable adjunct in the pharmacotherapy of ethanol use disorders.

Oxytocin Reduces Alcohol Cue-Reactivity in Alcohol-Dependent Rats and Humans

Approved pharmacological treatments for alcohol use disorder are limited in their effectiveness, and new drugs that can easily be translated into the clinic are warranted. One of those candidates is oxytocin because of its interaction with several alcohol-induced effects. Alcohol-dependent rats as well as post-mortem brains of human alcoholics and controls were analyzed for the expression of the oxytocin system by qRT-PCR, in situ hybridization, receptor autoradiography ([¹²⁵I]OVTA binding), and immunohistochemistry. Alcohol self-administration and cue-induced reinstatement behavior was measured after intracerebroventricular injection of 10 nM oxytocin in dependent rats. Here we show a pronounced upregulation of oxytocin receptors in brain tissues of alcohol-dependent rats and deceased alcoholics, primarily in frontal and striatal areas. This upregulation stems most likely from reduced oxytocin expression in hypothalamic nuclei. Pharmacological validation showed that oxytocin reduced cue-induced reinstatement response in dependent rats-an effect that was not observed in non-dependent rats. Finally, a clinical pilot study (German clinical trial number DRKS00009253) using functional magnetic resonance imaging in heavy social male drinkers showed that intranasal oxytocin (24 IU) decreased neural cue-reactivity in brain networks similar to those detected in dependent rats and humans with increased oxytocin receptor expression. These studies suggest that oxytocin might be used as an anticraving medication and thus may positively affect treatment outcomes in alcoholics.

Molecular mechanisms underlying striatal synaptic plasticity: relevance to chronic alcohol consumption and seeking

The striatum, the input structure of the basal ganglia, is a major site of learning and memory for goal-directed actions and habit formation. Spiny projection neurons of the striatum integrate cortical, thalamic, and nigral inputs to learn associations, with cortico-striatal synaptic plasticity as a learning mechanism. Signaling molecules implicated in synaptic plasticity are altered in alcohol withdrawal, which may contribute to overly strong learning and increased alcohol seeking and consumption. To understand how interactions among signaling molecules produce synaptic plasticity, we implemented a mechanistic model of signaling pathways activated by dopamine D1 receptors, acetylcholine receptors, and glutamate. We use our novel, computationally efficient simulator, NeuroRD, to simulate stochastic interactions both within and between dendritic spines. Dopamine release during theta burst and 20-Hz stimulation was extrapolated from fast-scan cyclic voltammetry data collected in mouse striatal slices. Our results show that the combined activity of several key plasticity molecules correctly predicts the occurrence of either LTP, LTD, or no plasticity for numerous experimental protocols. To investigate spatial interactions, we stimulate two spines, either adjacent or separated on a 20-μm dendritic segment. Our results show that molecules underlying LTP exhibit spatial specificity, whereas 2-arachidonoylglycerol exhibits a spatially diffuse elevation. We also implement changes in NMDA receptors, adenylyl cyclase, and G protein signaling that have been measured following chronic alcohol treatment. Simulations under these conditions suggest that the molecular changes can predict changes in synaptic plasticity, thereby accounting for some aspects of alcohol use disorder.

Dopamine Transporter and Reward Anticipation in a Dimensional Perspective: A Multimodal Brain Imaging Study

Dopamine function and reward processing are highly interrelated and involve common brain regions afferent to the nucleus accumbens, within the mesolimbic pathway. Although dopamine function and reward system neural activity are impaired in most psychiatric disorders, it is unknown whether alterations in the dopamine system underlie variations in reward processing across a continuum encompassing health and these disorders. We explored the relationship between dopamine function and neural activity during reward anticipation in 27 participants including healthy volunteers and psychiatric patients with schizophrenia, depression, or cocaine addiction, using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) multimodal imaging with a voxel-based statistical approach. Dopamine transporter (DAT) availability was assessed with PET and [11C]PE2I as a marker of presynaptic dopamine function, and reward-related neural response was assessed using fMRI with a modified Monetary Incentive Delay task. Across all the participants, DAT availability in the midbrain correlated positively with the neural response to anticipation of reward in the nucleus accumbens. Moreover, this relationship was conserved in each clinical subgroup, despite the heterogeneity of mental illnesses examined. For the first time, a direct link between DAT availability and reward anticipation was detected within the mesolimbic pathway in healthy and psychiatric participants, and suggests that dopaminergic dysfunction is a common mechanism underlying the alterations of reward processing observed in patients across diagnostic categories. The findings support the use of a dimensional approach in psychiatry, as promoted by the Research Domain Criteria project to identify neurobiological signatures of core dysfunctions underling mental illnesses.

Dynamical state transitions into addictive behaviour and their early-warning signals

The theory of critical transitions in complex systems (ecosystems, climate, etc.), and especially its ability to predict abrupt changes by early-warning signals based on analysis of fluctuations close to tipping points, is seen as a promising avenue to study disease dynamics. However, the biomedical field still lacks a clear demonstration of this concept. Here, we used a well-established animal model in which initial alcohol exposure followed by deprivation and subsequent reintroduction of alcohol induces excessive alcohol drinking as an example of disease onset. Intensive longitudinal data (ILD) of rat drinking behaviour and locomotor activity were acquired by a fully automated drinkometer device over 14 weeks. Dynamical characteristics of ILD were extracted using a multi-scale computational approach. Our analysis shows a transition into addictive behaviour preceded by early-warning signals such as instability of drinking patterns and locomotor circadian rhythms, and a resultant increase in low frequency, ultradian rhythms during the first week of deprivation. We find evidence that during prolonged deprivation, a critical transition takes place pushing the system to excessive alcohol consumption. This study provides an adaptable framework for processing ILD from clinical studies and for examining disease dynamics and early-warning signals in the biomedical field.

Dynorphin and κ-Opioid Receptor Dysregulation in the Dopaminergic Reward System of Human Alcoholics

Molecular changes induced by excessive alcohol consumption may underlie formation of dysphoric state during acute and protracted alcohol withdrawal which leads to craving and relapse. A main molecular addiction hypothesis is that the upregulation of the dynorphin (DYN)/κ-opioid receptor (KOR) system in the nucleus accumbens (NAc) of alcohol-dependent individuals causes the imbalance in activity of D1- and D2 dopamine receptor (DR) expressing neural circuits that results in dysphoria. We here analyzed post-mortem NAc samples of human alcoholics to assess changes in prodynorphin (PDYN) and KOR (OPRK1) gene expression and co-expression (transcriptionally coordinated) patterns. To address alterations in D1- and D2-receptor circuits, we studied the regulatory interactions between these pathways and the DYN/KOR system. No significant differences in PDYN and OPRK1 gene expression levels between alcoholics and controls were evident. However, PDYN and OPRK1 showed transcriptionally coordinated pattern that was significantly different between alcoholics and controls. A downregulation of DRD1 but not DRD2 expression was seen in alcoholics. Expression of DRD1 and DRD2 strongly correlated with that of PDYN and OPRK1 suggesting high levels of transcriptional coordination between these gene clusters. The differences in expression and co-expression patterns were not due to the decline in neuronal proportion in alcoholic brain and thereby represent transcriptional phenomena. Dysregulation of DYN/KOR system and dopamine signaling through both alterations in co-expression patterns of opioid genes and decreased DRD1 gene expression may contribute to imbalance in the activity of D1- and D2-containing pathways which may lead to the negative affective state in human alcoholics.

A Review of the Potential Mechanisms of Action of Baclofen in Alcohol Use Disorder

Baclofen, a GABA-B receptor agonist, is a promising treatment for alcohol use disorder (AUD). Its mechanism of action in this condition is unknown. GABA-B receptors interact with many biological systems potentially involved in AUD, including transduction pathways and neurotransmitter systems. Preclinical studies have shown that GABA-B receptors are involved in memory storage and retrieval, reward, motivation, mood and anxiety; neuroimaging studies in humans show that baclofen produces region-specific alterations in cerebral activity; GABA-B receptor activation may have neuroprotective effects; baclofen also has anti-inflammatory properties that may be of interest in the context of addiction. However, none of these biological effects fully explain the mechanism of action of baclofen in AUD. Data from clinical studies have provided a certain number of elements which may be useful for the comprehension of its mechanism of action: baclofen typically induces a state of indifference toward alcohol; the effective dose of baclofen in AUD is extremely variable from one patient to another; higher treatment doses correlate with the severity of the addiction; many of the side effects of baclofen resemble those of alcohol, raising the possibility that baclofen acts as a substitution drug; usually, however, there is no tolerance to the effects of baclofen during long-term AUD treatment. In the present article, the biological effects of baclofen are reviewed in the light of its clinical effects in AUD, assuming that, in many instances, clinical effects can be reliable indicators of underlying biological processes. In conclusion, it is proposed that baclofen may suppress the Pavlovian association between cues and rewards through an action in a critical part of the dopaminergic network (the amygdala), thereby normalizing the functional connectivity in the reward network. It is also proposed that this action of baclofen is made possible by the fact that baclofen and alcohol act on similar brain systems in certain regions of the brain.

Alcohol and the Brain: Neuronal Molecular Targets, Synapses, and Circuits

Ethanol is one of the most commonly abused drugs. Although environmental and genetic factors contribute to the etiology of alcohol use disorders, it is ethanol's actions in the brain that explain (1) acute ethanol-related behavioral changes, such as stimulant followed by depressant effects, and (2) chronic changes in behavior, including escalated use, tolerance, compulsive seeking, and dependence. Our knowledge of ethanol use and abuse thus relies on understanding its effects on the brain. Scientists have employed both bottom-up and top-down approaches, building from molecular targets to behavioral analyses and vice versa, respectively. This review highlights current progress in the field, focusing on recent and emerging molecular, cellular, and circuit effects of the drug that impact ethanol-related behaviors. The focus of the field is now on pinpointing which molecular effects in specific neurons within a brain region contribute to behavioral changes across the course of acute and chronic ethanol exposure.

Region specific activation of the AKT and mTORC1 pathway in response to excessive alcohol intake in rodents

We previously reported that the kinase AKT is activated in the nucleus accumbens (NAc) of rodents in response to excessive consumption of alcohol. One of the important downstream targets of AKT is the mammalian Target Of Rapamycin in Complex 1 (mTORC1), which was also activated by alcohol intake. mTORC1 controls dendritic protein translation, and we showed that the mTORC1-dependent translational machinery is activated in the NAc in response to alcohol intake. Importantly, systemic or intra-NAc inhibition of the AKT/mTORC1 pathway attenuated alcohol-drinking behaviors. Here, we mapped the activation patterns of AKT and mTORC1 in corticostriatal regions of rodents consuming large amounts of alcohol. We found that the activation of AKT and mTORC1 in response to cycles of binge drinking of 20 percent alcohol was centered in the NAc shell. Both kinases were not activated in the dorsolateral striatum (DLS); however, AKT, but not mTORC1, was activated in the dorsomedial striatum (DMS) of mice but not rats. Interestingly, excessive intake of alcohol produced a selective activation of the AKT/mTORC1 pathway in the orbitofrontal cortex (OFC), which was not observed in medial prefrontal cortex (mPFC). Furthermore, this signaling pathway was not activated in the NAc shell or OFC of rats consuming moderate amounts of alcohol nor was it activated in rats consuming sucrose. Together, our results suggest that excessive alcohol intake produces a brain region selective activation of the AKT/mTORC1 pathway, which is likely to contribute to NAc shell and OFC-dependent mechanisms that underlie the development and maintenance of alcohol drinking behavior.

Junk food diet-induced obesity increases D2 receptor autoinhibition in the ventral tegmental area and reduces ethanol drinking

Similar to drugs of abuse, the hedonic value of food is mediated, at least in part, by the mesostriatal dopamine (DA) system. Prolonged intake of either high calorie diets or drugs of abuse both lead to a blunting of the DA system. Most studies have focused on DAergic alterations in the striatum, but little is known about the effects of high calorie diets on ventral tegmental area (VTA) DA neurons. Since high calorie diets produce addictive-like DAergic adaptations, it is possible these diets may increase addiction susceptibility. However, high calorie diets consistently reduce psychostimulant intake and conditioned place preference in rodents. In contrast, high calorie diets can increase or decrease ethanol drinking, but it is not known how a junk food diet (cafeteria diet) affects ethanol drinking. In the current study, we administered a cafeteria diet consisting of bacon, potato chips, cheesecake, cookies, breakfast cereals, marshmallows, and chocolate candies to male Wistar rats for 3–4 weeks, producing an obese phenotype. Prior cafeteria diet feeding reduced homecage ethanol drinking over 2 weeks of testing, and transiently reduced sucrose and chow intake. Importantly, cafeteria diet had no effect on ethanol metabolism rate or blood ethanol concentrations following 2g/kg ethanol administration. In midbrain slices, we showed that cafeteria diet feeding enhances DA D2 receptor (D2R) autoinhibition in VTA DA neurons. These results show that junk food diet-induced obesity reduces ethanol drinking, and suggest that increased D2R autoinhibition in the VTA may contribute to deficits in DAergic signaling and reward hypofunction observed with obesity.

Addictions Neuroclinical Assessment: A reverse translational approach

Incentive salience, negative emotionality, and executive function are functional domains that are etiologic in the initiation and progression of addictive disorders, having been implicated in humans with addictive disorders and in animal models of addictions. Measures of these three neuroscience-based functional domains can capture much of the effects of inheritance and early exposures that lead to trait vulnerability shared across different addictive disorders. For specific addictive disorders, these measures can be supplemented by agent specific measures such as those that access pharmacodynamic and pharmacokinetic variation attributable to agent-specific gatekeeper molecules including receptors and drug-metabolizing enzymes. Herein, we focus on the translation and reverse translation of knowledge derived from animal models of addiction to the human condition via measures of neurobiological processes that are orthologous in animals and humans, and that are shared in addictions to different agents. Based on preclinical data and human studies, measures of these domains in a general framework of an Addictions Neuroclinical Assessment (ANA) can transform the assessment and nosology of addictive disorders, and can be informative for staging disease progression. We consider next steps and challenges for implementation of ANA in clinical care and research. This article is part of the Special Issue entitled "Alcoholism".

Adaptive dynamics of the 5-HT systems following chronic administration of selective serotonin reuptake inhibitors: a meta-analysis

Selective serotonin reuptake inhibitors (SSRIs) are the most frequently prescribed antidepressants. However, a major concern is their delayed onset of action, which is hypothesized to be associated with the time required for serotonin (5-HT) autoreceptors to desensitize, which should be reflected by actual neurochemical changes. Numerous in vivo microdialysis studies have been published that report on 5-HT levels in different brain sites following SSRI administration. Here, we performed a meta-analysis on dynamic changes of 5-HT neurotransmission during the course of chronic SSRI treatment. We conducted a meta-analysis on research articles of 5-HT neurotransmission measured by in vivo microdialysis in rat brain after subchronic and chronic SSRI administrations. In total, data from 42 microdialysis studies (798 rats) were analyzed. Within the first week of SSRI treatment, extracellular 5-HT concentrations drop in frontal cortex. Over the next 2 weeks of treatment, a linear increase in extracellular 5-HT levels up to 350% of prior treatment baseline is evident (n = 269). However, in hippocampus, prefrontal cortex, nucleus accumbens, and ventral tegmental area we found increased 5-HT levels within the first 3 days of SSRI administration. The time course of 5-HT dynamics in frontal cortex is in line with the hypothesis that 5-HT autoreceptors desensitize over 2-3 weeks of SSRI treatment and thereby enhanced extracellular 5-HT levels ensue. Yet, in other regions we did not find evidence supporting the traditional autoreceptor-mediated feedback loops hypothesis and thus other neurobiological adaptation mechanisms may also play a role in the delayed onset of SSRI action.

Frontostriatal Connectivity During Reward Anticipation

Abstract. Neurobiological research indicates that altered reward processing is among the most promising risk mechanisms in alcohol use disorder and depression. To elucidate differences and similarities between both disorders, we investigated clinical patients and at-risk individuals in two studies using a functional magnetic resonance imaging (fMRI) monetary reward paradigm. In the first study, alcohol use disorder patients compared to depressed and healthy individuals showed increased activation of the ventral striatum during reward anticipation. In contrast, both patient groups showed reduced frontostriatal connectivity compared to controls. In the second study, at-risk comorbid individuals showed decreased activation in the dorsal striatum along with decreased frontostriatal connectivity. While the connectivity results replicate the common pattern found for the patient groups, the activation results indicate a more depression-related pattern in individuals prone to developing both disorders. In conclusion, frontostriatal connectivity might be a promising transdiagnostic marker for depression, alcohol use disorder, and their comorbidity.

Changes in cerebral [18F]-FDG uptake induced by acute alcohol administration in a rat model of alcoholism

Several [¹⁸F]-FDG positron emission tomography (PET) studies in alcoholics have consistently reported decreases in overall brain glucose metabolism at rest and following acute alcohol administration. However, changes in cerebral glucose utilization associated with the transition to addiction are not well understood and require longitudinal translational imaging studies in animal models of alcoholism. Here, we studied brain glucose uptake in alcohol drinking rats in order to provide convergent evidence to what has previously been reported in human studies. Brain glucose metabolism was measured by [¹⁸F]-FDG microPET imaging in different male Wistar rat groups: short-term drinking (three months), long-term drinking (twelve months) and alcohol-naïve. Global and regional cerebral glucose uptake was measured at rest and following acute alcohol administration. We showed that alcohol significantly reduced the whole-brain glucose metabolism. This effect was most pronounced in the parietal cortex and cerebellum. Alcohol-induced decreases in brain [¹⁸F]-FDG uptake was most apparent in alcohol-naïve rats, less intense in short-term drinkers and absent in long-term drinkers. The latter finding indicates the occurrence of tolerance to the intoxicating effects of alcohol in long-term drinking individuals. In contrast, some regions, like the ventral striatum and entorhinal cortex, showed enhanced metabolic activity, an effect that did not undergo tolerance during long-term alcohol consumption. Our findings are comparable to those described in human studies using the same methodology. We conclude that [¹⁸F]-FDG PET studies in rat models of alcoholism provide good translation and can be used for future longitudinal studies investigating alterations in brain function during different stages of the addiction cycle.

Genome-wide analysis of the nucleus accumbens identifies DNA methylation signals differentiating low/binge from heavy alcohol drinking

Alcohol-use disorders encompass a range of drinking levels and behaviors, including low, binge, and heavy drinking. In this regard, investigating the neural state of individuals who chronically self-administer lower doses of alcohol may provide insight into mechanisms that prevent the escalation of alcohol use. DNA methylation is one of the epigenetic mechanisms that stabilizes adaptations in gene expression and has been associated with alcohol use. Thus, we investigated DNA methylation, gene expression, and the predicted neural effects in the nucleus accumbens core (NAcc) of male rhesus macaques categorized as "low" or "binge" drinkers, compared to "alcohol-naïve" and "heavy" drinkers based on drinking patterns during a 12-month alcohol self-administration protocol. Using genome-wide CpG-rich region enrichment and bisulfite sequencing, the methylation levels of 2.6 million CpGs were compared between alcohol-naïve (AN), low/binge (L/BD), and heavy/very heavy (H/VHD) drinking subjects (n = 24). Through regional clustering analysis, we identified nine significant differential methylation regions (DMRs) that specifically distinguished ANs and L/BDs, and then compared those DMRs among H/VHDs. The DMRs mapped to genes encoding ion channels, receptors, cell adhesion molecules, and cAMP, NF-κβ and Wnt signaling pathway proteins. Two of the DMRs, linked to PDE10A and PKD2L2, were also differentially methylated in H/VHDs, suggesting an alcohol-dose independent effect. However, two other DMRs, linked to the CCBE1 and FZD5 genes, had L/BD methylation levels that significantly differed from both ANs and H/VHDs. The remaining five DMRs also differentiated L/BDs and ANs. However, H/VHDs methylation levels were not distinguishable from either of the two groups. Functional validation of two DMRs, linked to FZD5 and PDE10A, support their role in regulating gene expression and exon usage, respectively. In summary, the findings demonstrate that L/BD is associated with unique DNA methylation signatures in the primate NAcc, and that the methylation signatures identify synaptic genes that may play a role in preventing the escalation of alcohol use.

Differential Roles for L-Type Calcium Channel Subtypes in Alcohol Dependence

It has previously been shown that the inhibition of L-type calcium channels (LTCCs) decreases alcohol consumption, although the contribution of the central LTCC subtypes Cav1.2 and Cav1.3 remains unknown. Here, we determined changes in Cav1.2 (Cacna1c) and Cav1.3 (Cacna1d) mRNA and protein expression in alcohol-dependent rats during protracted abstinence and naive controls using in situ hybridization and western blot analysis. Functional validation was obtained by electrophysiological recordings of calcium currents in dissociated hippocampal pyramidal neurons. We then measured alcohol self-administration and cue-induced reinstatement of alcohol seeking in dependent and nondependent rats after intracerebroventricular (i.c.v.) injection of the LTCC antagonist verapamil, as well as in mice with an inducible knockout (KO) of Cav1.2 in Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα)-expressing neurons. Our results show that Cacna1c mRNA concentration was increased in the amygdala and hippocampus of alcohol-dependent rats after 21 days of abstinence, with no changes in Cacna1d mRNA. This was associated with increased Cav1.2 protein concentration and L-type calcium current amplitudes. Further analysis of Cacna1c mRNA in the CA1, basolateral amygdala (BLA), and central amygdala (CeA) revealed a dynamic regulation over time during the development of alcohol dependence. The inhibition of central LTCCs via i.c.v. administration of verapamil prevented cue-induced reinstatement of alcohol seeking in alcohol-dependent rats. Further studies in conditional Cav1.2-KO mice showed a lack of dependence-induced increase of alcohol-seeking behavior. Together, our data indicate that central Cav1.2 channels, rather than Cav1.3, mediate alcohol-seeking behavior. This finding may be of interest for the development of new antirelapse medications.

Hypothesizing That Neuropharmacological and Neuroimaging Studies of Glutaminergic-Dopaminergic Optimization Complex (KB220Z) Are Associated With "Dopamine Homeostasis" in Reward Deficiency Syndrome (RDS)

BACKGROUND

There is need for better treatments of addictive behaviors, both substance and non-substance related, termed Reward Deficiency Syndrome (RDS). While the FDA has approved pharmaceuticals under the umbrella term Medication Assisted Treatment (MAT), these drugs are not optimal.

OBJECTIVES

It is our contention that these drugs work well in the short-term by blocking dopamine function leading to psychological extinction. However, use of buprenorphine/Naloxone over a long period of time results in unwanted addiction liability, reduced emotional affect, and mood changes including suicidal ideation.

METHODS

We are thus proposing a paradigm shift in addiction treatment, with the long-term goal of achieving "Dopamine Homeostasis." While this may be a laudable goal, it is very difficult to achieve. Nevertheless, this commentary briefly reviews past history of developing and subsequently, utilizing a glutaminergic-dopaminergic optimization complex [Kb220Z] shown to be beneficial in at least 20 human clinical trials and in a number of published and unpublished studies.

RESULTS

It is our opinion that, while additional required studies could confirm these findings to date, the cited studies are indicative of achieving enhanced resting state functional connectivity, connectivity volume, and possibly, neuroplasticity. Conclusions/Importance: We are proposing a Reward Deficiency Solution System (RDSS) that includes: Genetic Addiction Risk Score (GARS); Comprehensive Analysis of Reported Drugs (CARD); and a glutaminergic-dopaminergic optimization complex (Kb220Z). Continued investigation of this novel strategy may lead to a better-targeted approach in the long-term, causing dopamine regulation by balancing the glutaminergic-dopaminergic pathways. This may potentially change the landscape of treating all addictions leading us to the promised land.

Towards trans-diagnostic mechanisms in psychiatry: neurobehavioral profile of rats with a loss-of-function point mutation in the dopamine transporter gene

The research domain criteria (RDoC) matrix has been developed to reorient psychiatric research towards measurable behavioral dimensions and underlying mechanisms. Here, we used a new genetic rat model with a loss-of-function point mutation in the dopamine transporter (DAT) gene (Slc6a3_N157K) to systematically study the RDoC matrix. First, we examined the impact of the Slc6a3_N157K mutation on monoaminergic signaling. We then performed behavioral tests representing each of the five RDoC domains: negative and positive valence systems, cognitive, social and arousal/regulatory systems. The use of RDoC may be particularly helpful for drug development. We studied the effects of a novel pharmacological approach metabotropic glutamate receptor mGluR2/3 antagonism, in DAT mutants in a comparative way with standard medications. Loss of DAT functionality in mutant rats not only elevated subcortical extracellular dopamine concentration but also altered the balance of monoaminergic transmission. DAT mutant rats showed deficits in all five RDoC domains. Thus, mutant rats failed to show conditioned fear responses, were anhedonic, were unable to learn stimulus-reward associations, showed impaired cognition and social behavior, and were hyperactive. Hyperactivity in mutant rats was reduced by amphetamine and atomoxetine, which are well-established medications to reduce hyperactivity in humans. The mGluR2/3 antagonist LY341495 also normalized hyperactivity in DAT mutant rats without affecting extracellular dopamine levels. We systematically characterized an altered dopamine system within the context of the RDoC matrix and studied mGluR2/3 antagonism as a new pharmacological strategy to treat mental disorders with underlying subcortical dopaminergic hyperactivity.

Summary: The first systematic RDoc study of a disease mechanism proposes dopamine transporter DAT mutant rats as a model for drug development, targeting a hyperdopaminergic state.

Low μ-Opioid Receptor Status in Alcohol Dependence Identified by Combined Positron Emission Tomography and Post-Mortem Brain Analysis

Blockade of the μ-opioid receptor (MOR) by naltrexone reduces relapse risk in a subpopulation of alcohol-dependent patients. Previous positron-emission-tomography (PET) studies using the MOR ligand [¹¹C]carfentanil have found increased MOR availability in abstinent alcoholics, which may reflect either increased MOR expression or lower endogenous ligand concentration. To differentiate between both effects, we investigated two cohorts of alcoholic subjects using either post-mortem or clinical PET analysis. Post-mortem brain tissue of alcohol-dependent subjects and controls (N=43/group) was quantitatively analyzed for MOR ([³H]DAMGO)-binding sites and OPRM1 mRNA in striatal regions. [¹¹C]carfentanil PET was performed in detoxified, medication free alcohol-dependent patients (N=38), followed by a randomized controlled study of naltrexone versus placebo and follow-up for 1 year (clinical trial number: NCT00317031). Because the functional OPRM1 variant rs1799971:A>G affects the ligand binding, allele carrier status was considered in the analyses. MOR-binding sites were reduced by 23-51% in post-mortem striatal tissue of alcoholics. In the PET study, a significant interaction of OPRM1 genotype, binding potential (BP_ND) for [¹¹C]carfentanil in the ventral striatum, and relapse risk was found. Particularly in G-allele carriers, lower striatal BP_ND was associated with a higher relapse risk. Interestingly, this effect was more pronounced in the naltrexone treatment group. Reduced MOR is interpreted as a neuroadaptation to an alcohol-induced release of endogenous ligands in patients with severe alcoholism. Low MOR availability may explain the ineffectiveness of naltrexone treatment in this subpopulation. Finally, low MOR-binding sites are proposed as a molecular marker for a negative disease course.