Lisuride, a dopamine D2 receptor agonist, and anticraving drug expectancy as modifiers of relapse in alcohol dependence

Indole-containing pharmaceuticals: targets, pharmacological activities, and SAR studies

Indole is a prestigious heterocyclic skeleton widely found in both naturally-occurring and biologically-active compounds. Pharmaceutical agents containing an indole skeleton in their framework possess a wide range of pharmacological properties, including antiviral, antitumor, analgesic, and other therapeutic activities, and many indole-containing drugs have been proven to have excellent pharmacokinetic and pharmacological effects. Over the past few decades, the FDA has approved over 40 indole-containing drugs for the treatment of various clinical conditions, and the development of indole-related drugs has attracted significant attention from medicinal chemists. This review aims to provide an overview of all the approved drugs that contain an indole nucleus, focusing on their targets, pharmacological activities, and SAR studies.

Antidepressant-like effects of psychedelics in a chronic despair mouse model: is the 5-HT2A receptor the unique player?

Major depressive disorder (MDD) is one of the most disabling psychiatric disorders in the world. First-line treatments such as selective serotonin reuptake inhibitors (SSRIs) still have many limitations, including a resistance to treatment in 30% of patients and a delayed clinical benefit that is observed only after several weeks of treatment. Increasing clinical evidence indicates that the acute administration of psychedelic agonists of the serotonin 5-HT2A receptor (5-HT2AR), such as psilocybin, to patients with MDD induce fast antidepressant effects, which persist up to five weeks after the treatment. However, the involvement of the 5-HT2AR in these antidepressant effects remains controversial. Furthermore, whether the hallucinogenic properties of 5-HT2AR agonists are mandatory to their antidepressant activity is still an open question. Here, we addressed these issues by investigating the effect of two psychedelics of different chemical families, DOI and psilocybin, and a non-hallucinogenic 5-HT2AR agonist, lisuride, in a chronic despair mouse model exhibiting a robust depressive-like phenotype. We show that a single injection of each drug to wild type mice induces anxiolytic- and antidepressant-like effects in the novelty-suppressed feeding, sucrose preference and forced swim tests, which last up to 15 days. DOI and lisuride administration did not produce antidepressant-like effects in 5-HT2A-/- mice, whereas psilocybin was still effective. Moreover, neither 5-HT1AR blockade nor dopamine D1 or D2 receptor blockade affected the antidepressant-like effects of psilocybin in 5-HT2A-/- mice. Collectively, these findings indicate that 5-HT2AR agonists can produce antidepressant-like effects independently of hallucinogenic properties through mechanisms involving or not involving the receptor.

Identification of 5-HT2A receptor signaling pathways associated with psychedelic potential

Serotonergic psychedelics possess considerable therapeutic potential. Although 5-HT2A receptor activation mediates psychedelic effects, prototypical psychedelics activate both 5-HT2A-Gq/11 and β-arrestin2 transducers, making their respective roles unclear. To elucidate this, we develop a series of 5-HT2A-selective ligands with varying Gq efficacies, including β-arrestin-biased ligands. We show that 5-HT2A-Gq but not 5-HT2A-β-arrestin2 recruitment efficacy predicts psychedelic potential, assessed using head-twitch response (HTR) magnitude in male mice. We further show that disrupting Gq-PLC signaling attenuates the HTR and a threshold level of Gq activation is required to induce psychedelic-like effects, consistent with the fact that certain 5-HT2A partial agonists (e.g., lisuride) are non-psychedelic. Understanding the role of 5-HT2A Gq-efficacy in psychedelic-like psychopharmacology permits rational development of non-psychedelic 5-HT2A agonists. We also demonstrate that β-arrestin-biased 5-HT2A receptor agonists block psychedelic effects and induce receptor downregulation and tachyphylaxis. Overall, 5-HT2A receptor Gq-signaling can be fine-tuned to generate ligands distinct from classical psychedelics.

Identification of 5-HT2A Receptor Signaling Pathways Responsible for Psychedelic Potential

Serotonergic psychedelics possess considerable therapeutic potential. Although 5-HT2A receptor activation mediates psychedelic effects, prototypical psychedelics activate both 5-HT2A-Gq/11 and β-arrestin2 signaling, making their respective roles unclear. To elucidate this, we developed a series of 5-HT2A-selective ligands with varying Gq efficacies, including β-arrestin-biased ligands. We show that 5-HT2A-Gq but not 5-HT2A-β-arrestin2 efficacy predicts psychedelic potential, assessed using head-twitch response (HTR) magnitude in male mice. We further show that disrupting Gq-PLC signaling attenuates the HTR and a threshold level of Gq activation is required to induce psychedelic-like effects, consistent with the fact that certain 5-HT2A partial agonists (e.g., lisuride) are non-psychedelic. Understanding the role of 5-HT2A-Gq efficacy in psychedelic-like psychopharmacology permits rational development of non-psychedelic 5-HT2A agonists. We also demonstrate that β-arrestin-biased 5-HT2A receptor agonists induce receptor downregulation and tachyphylaxis, and have an anti-psychotic-like behavioral profile. Overall, 5-HT2A receptor signaling can be fine-tuned to generate ligands with properties distinct from classical psychedelics.

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.

Genetic factors associated with empathy in humans and mice

The neurocognitive ability to recognize and share the mental states of others is crucial for our emotional experience and social interaction. Extensive human studies have informed our understanding of the psychobehavioral and neurochemical bases of empathy. Recent evidence shows that simple forms of empathy are conserved from rodents to humans, and rodent models have become particularly useful for understanding the neurobiological correlates of empathy. In this review, we first summarize aspects of empathy at the behavioral and neural circuit levels, and describe recent developments in rodent model behavioral paradigms. We then highlight different neurobiological pathways involved in empathic abilities, with special emphasis on genetic polymorphisms associated with individual differences in empathy. By directly assessing various neurochemical correlates at molecular and neural circuit levels using relevant animal models, we conclude with the suggestion that rodent research can significantly advance our understanding of the neural basis of empathy. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Critical needs in drug discovery for cessation of alcohol and nicotine polysubstance abuse

Polysubstance abuse of alcohol and nicotine has been overlooked in our understanding of the neurobiology of addiction and especially in the development of novel therapeutics for its treatment. Estimates show that as many as 92% of people with alcohol use disorders also smoke tobacco. The health risks associated with both excessive alcohol consumption and tobacco smoking create an urgent biomedical need for the discovery of effective cessation treatments, as opposed to current approaches that attempt to independently treat each abused agent. The lack of treatment approaches for alcohol and nicotine abuse/dependence mirrors a similar lack of research in the neurobiology of polysubstance abuse. This review discusses three critical needs in medications development for alcohol and nicotine co-abuse: (1) the need for a better understanding of the clinical condition (i.e. alcohol and nicotine polysubstance abuse), (2) the need to better understand how these drugs interact in order to identify new targets for therapeutic development and (3) the need for animal models that better mimic this human condition. Current and emerging treatments available for the cessation of each drug and their mechanisms of action are discussed within this context followed by what is known about the pharmacological interactions of alcohol and nicotine. Much has been and will continue to be gained from studying comorbid alcohol and nicotine exposure.

Clinically Combating Reward Deficiency Syndrome (RDS) with Dopamine Agonist Therapy as a Paradigm Shift: Dopamine for Dinner?

Everyday, there are several millions of people that are increasingly unable to combat their frustrating and even fatal romance with getting high and/or experiencing “normal” feelings of well-being. In the USA, the FDA has approved pharmaceuticals for drug and alcohol abuse: tobacco and nicotine replacement therapy. The National Institute on Drug Abuse (NIDA) and the National Institute on Alcohol Abuse and Alcoholism (NIAAA) remarkably continue to provide an increasing understanding of the intricate functions of brain reward circuitry through sophisticated neuroimaging and molecular genetic applied technology. Similar work is intensely investigated on a worldwide basis with enhanced clarity and increased interaction between not only individual scientists but across many disciplines. However, while it is universally agreed that dopamine is a major neurotransmitter in terms of reward dependence, there remains controversy regarding how to modulate its role clinically to treat and prevent relapse for both substance and non-substance-related addictive behaviors. While the existing FDA-approved medications promote blocking dopamine, we argue that a more prudent paradigm shift should be biphasic—short-term blockade and long-term upregulation, enhancing functional connectivity of brain reward circuits.

Emerging pharmacotherapies for alcohol dependence: a systematic review focusing on reduction in consumption

BACKGROUND

European Medicines Agency guidelines recognize two different treatment goals for alcohol dependence: abstinence and reduction in alcohol consumption. All currently approved agents are indicated for abstinence. This systematic review aimed to identify drugs in development for alcohol dependence treatment and to establish, based upon trial design, if any are seeking market authorization for reduction in consumption.

METHODS

We searched PubMed and Embase (December 2001-November 2011) to identify agents in development for alcohol dependence treatment. Additional studies were identified by searching ClinicalTrials.gov and the R&D Insight and Clinical Trials Insight databases. Studies in which the primary focus was treatment of comorbidity, or n≤20, were excluded. Studies were then classified as 'abstinence' if they: described a detoxification/alcohol withdrawal period; enrolled patients who had undergone detoxification previously; or presented relapse/abstinence rates as the primary outcome. Studies in patients actively drinking at baseline were classified as 'reduction in consumption'.

RESULTS

Of 602 abstracts identified, 45 full-text articles were eligible. Five monotherapies were in development for alcohol dependence treatment: topiramate, fluvoxamine, aripiprazole, flupenthixol and nalmefene. Nalmefene was the only agent whose sponsor was clearly seeking definitive approval for reduction in consumption. Development status was unclear for topiramate, fluvoxamine, aripiprazole and flupenthixol. Fifteen agents were examined in published exploratory investigator-initiated trials; the majority focused on abstinence. Ongoing (unpublished) trials tended to focus on reduction in consumption.

CONCLUSIONS

While published studies generally focused on abstinence, ongoing trials focused on reduction in consumption, suggesting a change in emphasis in the approach to treating alcohol dependence.

LSD but not lisuride disrupts prepulse inhibition in rats by activating the 5-HT(2A) receptor

RATIONALE

Compounds that activate the 5-HT(2A) receptor, such as lysergic acid diethylamide (LSD), act as hallucinogens in humans. One notable exception is the LSD congener lisuride, which does not have hallucinogenic effects in humans even though it is a potent 5-HT(2A) agonist. LSD and other hallucinogens have been shown to disrupt prepulse inhibition (PPI), an operational measure of sensorimotor gating, by activating 5-HT(2A) receptors in rats.

OBJECTIVE

We tested whether lisuride disrupts PPI in male Sprague-Dawley rats. Experiments were also conducted to identify the mechanism(s) responsible for the effect of lisuride on PPI and to compare the effects of lisuride to those of LSD.

RESULTS

Confirming a previous report, LSD (0.05, 0.1, and 0.2 mg/kg, s.c.) reduced PPI, and the effect of LSD was blocked by pretreatment with the selective 5-HT(2A) antagonist MDL 11,939. Administration of lisuride (0.0375, 0.075, and 0.15 mg/kg, s.c.) also reduced PPI. However, the PPI disruption induced by lisuride (0.075 mg/kg) was not blocked by pretreatment with MDL 11,939 or the selective 5-HT(1A) antagonist WAY-100635 but was prevented by pretreatment with the selective dopamine D(2)/D(3) receptor antagonist raclopride (0.1 mg/kg, s.c).

CONCLUSIONS

The effect of LSD on PPI is mediated by the 5-HT(2A) receptor, whereas activation of the 5-HT(2A) receptor does not appear to contribute to the effect of lisuride on PPI. These findings demonstrate that lisuride and LSD disrupt PPI via distinct receptor mechanisms and provide additional support for the classification of lisuride as a non-hallucinogenic 5-HT(2A) agonist.

Serotonin transporter promoter polymorphism and dopaminergic sensitivity in alcoholics

The central serotonin (5-HT) system plays an important role in the rewarding and addictive properties of alcohol by a direct activation of the mesolimbic dopamine (DA) system. An insertion/deletion (L/S) promoter polymorphism (5-HTTLPR) of the 5-HT transporter (5-HHT) gene (SLC6A4) has been shown to influence transcriptional activity. It is predicted that reduced transynaptic 5-HT neurotransmission in alcoholics with the L/L genotype of 5-HTTLPR would result in a change in DA function compared to the S/S genotype. Thus the present study has tested whether dopaminergic sensitivity is influenced by the 5-HTTLPR genotype. Dopaminergic sensitivity, 5-HTTLPR genotype and smoking status were assessed in 121 alcoholics. Dopaminergic sensitivity as an indicator of the functional state of the dopaminergic system was measured by the amount of growth hormone (GH) secretion after subcutaneous administration of apomorphine (APO, 0.01 mg/kg). 5-HTTLPR genotype was significantly associated with dopaminergic sensitivity (P = 0.004) explaining 9.2% of the variance of GH response. Subjects homozygous for the L allele (with high 5-HTT expression) showed the lowest GH response, whereas those homozygous for the S allele (with low 5-HTT expression) showed the highest GH response (this was intermediate in heterozygous participants). Furthermore smoking was associated with a significantly reduced GH response (P = 0.006). Our findings indicate that the postsynaptic dopaminergic sensitivity is influenced by the 5-HTTLPR genotype. It is hypothesized that the reduction of sensitivity of the central DA receptors in alcoholics with the L/L genotype might be due to their higher vulnerability to the neurotoxic effects of chronic alcohol consumption than the S carriers.

A quantitative review of the ubiquitous relapse curve

The primary goal of this study is to ascertain whether relapse to drug dependence, in terms of continuous abstinence assessment, exhibits a typical pattern that can be characterized by a common quantitative function. If the relapse curve is indeed ubiquitous, then some underlying mechanism must be operating to shape the curve that transcends variables such as drug class, population, or treatment type. Survival analyses are performed on 20 alcohol and tobacco treatment studies using the proportions of individuals remaining abstinent after a period of initial abstinence. Several parametric models of relapse are compared, and the results demonstrate that a log-logistic distribution is the most accurate reflection of the available data and the basic shape of the relapse curve is uniform. In most reports examined, the rate of relapse decelerates after initial abstinence has been achieved, and therefore, the amount of accumulated time abstinent may be the transcending variable that operates to shape the relapse curve.

Approach to the genetics of alcoholism: A review based on pathophysiology

Alcohol dependence is a common disorder with a heterogenous etiology. The results of family, twin and adoption studies on alcoholism are reviewed. These studies have revealed a heritability of alcoholism of over 50%. After evaluating the results, it was epidemiologically stated that alcoholism is heterogenous complex disorder with a multiple genetic background. Modern molecular genetic techniques allow examining specific genes involved in the pathophysiology of complex diseases such as alcoholism. Strategies for gene identification are introduced to the reader, including family-based and association studies. The susceptibility genes that are in the focus of this article have been chosen because they are known to encode for underlying mechanisms that are linked to the pathophysiology of alcoholism or that are important for the pharmacotherapeutic approaches in the treatment of alcohol dependence. Postulated candidate genes of the metabolism of alcohol and of the involved neurotransmitter systems are introduced. Genetic studies on alcoholism examining the metabolism of alcohol and the dopaminergic, GABAergic, glutamatergic, opioid, cholinergic and serotonergic neurotransmitter systems as well as the neuropeptide Y are presented. The results are critically discussed followed by a discussion of possible consequences.

The efficacy of the dopamine D2/D3 antagonist tiapride in maintaining abstinence: a randomized, double-blind, placebo-controlled trial in 299 alcohol-dependent patients

In this investigation, the hypothesis was tested whether the selective dopamine D2/D3 receptor antagonist tiapride is effective in maintaining abstinence after detoxification in alcohol-dependent patients. The rationale of the study was based on the relevance of the dopaminergic system for addictive behaviour as well as some preliminary studies. A multi-centre, randomized, double-blind, placebo-controlled, parallel-group study was conducted. A total of 299 detoxified alcohol-dependent patients (ICD-10: F10.2) received either tiapride (300 mg/d) or placebo over a 24-wk study period. Subjects with severe comorbid psychiatric disorder such as schizophrenia or Wernicke-Korsakoff syndrome were excluded. Primary outcome variable was the time to first relapse with relapse defined as any alcohol consumption after detoxification. Data analysis was done with Kaplan-Meier estimates with log-rank test (one-sided, p<0.05). Tiapride was not superior to placebo in maintaining abstinence. The time to first relapse was 71 d in the tiapride group and 92 d in the placebo group (log-rank test, p=0.9895). Relapse rate was higher in the intervention group (54.4%) than in the control group (40.7%). Like the dopamine antagonist flupenthixol, tiapride was not effective in maintaining alcohol abstinence. Regarding the high success rate in the placebo group the influence of psychosocial treatment in studies investigating drug effects on the course of alcohol dependence has to be considered.

Preclinical and clinical pharmacology of alcohol dependence

In recent years, advances in neuroscience led to the development of new medications to treat alcohol dependence and especially to prevent alcohol relapse after detoxification. Whereas the earliest medications against alcohol dependence were fortuitously discovered, recently developed drugs are increasingly based on alcohol's neurobiological mechanisms of action. This review discusses the most recent developments in alcohol pharmacotherapy and emphasizes the neurobiological basis of anti-alcohol medications. There are currently three approved drugs for the treatment of alcohol dependence with quite different mechanisms of action. Disulfiram is an inhibitor of the enzyme aldehyde dehydrogenase and acts as an alcohol-deterrent drug. Naltrexone, an opiate antagonist, reduces alcohol craving and relapse in heavy drinking, probably via a modulation of the mesolimbic dopamine activity. Finally, acamprosate helps maintaining alcohol abstinence, probably through a normalization of the chronic alcohol-induced hyperglutamatergic state. In addition to these approved medications, many other drugs have been suggested for preventing alcohol consumption on the basis of preclinical studies. Some of these drugs remain promising, whereas others have produced disappointing results in preliminary clinical studies. These new drugs in the field of alcohol pharmacotherapy are also discussed, together with their mechanisms of action.

Blockade of cue-induced brain activation of abstinent alcoholics by a single administration of amisulpride as measured with fMRI

BACKGROUND

Once alcohol dependence is established, alcohol-associated cues may induce dopamine release in the reward system, which is accompanied by alcohol craving and may lead to relapse. In cocaine addicts, dopamine release in the thalamus was positively correlated with cocaine craving. We tested the effects of the atypical dopamine D(2/3) blocker amisulpride on cue-induced brain activation in a functional magnetic resonance imaging (fMRI) paradigm.

METHODS

Alcohol-associated and neutral pictures were presented in a block design to 10 male abstinent alcoholics (1-3 weeks after detoxification) and 10 healthy men during fMRI. The fMRI scans were acquired before and 2 hours after the oral application of 400 mg amisulpride. Before and after each scan, alcohol craving was measured with visual analogue scales.

RESULTS

Before the application of amisulpride, alcohol versus control cues elicited a higher blood oxygen level-dependent (BOLD) signal in the left frontal and orbitofrontal lobe, left cingulate gyrus, bilateral parietal lobe, and bilateral hippocampus in alcoholics compared with healthy controls. After amisulpride, alcoholics showed a reduced activation in the right thalamus compared with the first scan. Alcoholics no longer showed significant differences in their cue-elicited BOLD response after amisulpride medication compared with medication-free controls. Self-reported craving was not affected by amisulpride medication.

CONCLUSIONS

Amisulpride medication was associated with reduced cue-induced activation of the thalamus, a brain region closely connected with frontostriatal circuits that regulate behavior and may influence relapse risk.

New achievements and pharmacotherapeutic approaches in the treatment of alcohol dependence

The treatment of alcohol dependence mainly consists of psychological, social, and pharmacotherapeutic interventions aiming to reduce physical withdrawal, craving, and alcohol relapse. During the last years, it has become increasingly clear that adjuvant pharmacotherapy is efficacious especially in rehabilitation programs for alcohol dependent patients. The development of alcohol dependence seems to involve adaptive changes in amino acid neurotransmitter systems, stimulation of dopamine and opioid peptide systems, and changes in serotonergic activity. Disulfiram, naltrexone and acamprosate are approved treatments for the management of abstinence maintenance treatment. New compounds are under investigation. This review discusses the neurobiological basis of alcohol addiction, pharmacological targets for relapse prevention treatment and pre-clinical and clinical results with the most promising drugs.

Alcohol-withdrawn animals have a prolonged increase in dopamine D2high receptors, reversed by general anesthesia: relation to relapse?

The biochemical basis for alcohol addiction and relapse is not known. Although ethanol promotes the release of dopamine like other drugs of abuse, many unknown factors remain to be investigated concerning the biochemical abnormalities which persist after ethanol drinking and which contribute to alcohol relapse. Although ethanol withdrawal is associated with enhanced sensitivity to dopamine in animals and humans, only minor changes in the striatal density of dopamine D2 receptors have been found in humans, and animals show a small reduction in striatal D2 receptors. But how can dopamine-related functions be increased in ethanol withdrawal in the face of an unchanged or reduced density of dopamine D2 receptors? Considering that ethanol sensitizes rats to amphetamine, and that the high-affinity state of D2, or D2High, is markedly increased in striata from amphetamine-sensitized rats, we measured the density of D2High in striata from rats withdrawn from ethanol. These sites were elevated by 360% (7.2 pmol/g) for at least 8 days after stopping ethanol and returned to normal levels of 2 pmol/g after 2 weeks of ethanol withdrawal. In addition, 1 h of deep general anesthesia given 5 days into withdrawal resulted in a normal level of D2High within 24 h. Because the D2High states are the functional form of D2, their elevated density in ethanol withdrawal may be related to ethanol relapse in humans. General anesthesia may alleviate aspects of alcohol or amphetamine abuse or psychosis associated with elevated D2High.

The reinstatement model and relapse prevention: a clinical perspective

OBJECTIVES

This commentary assesses the degree to which the reinstatement model is homologous to the human experience of relapse.

RESULTS

A review of the literature suggests that the relationship is less clear than is often assumed, largely due to a lack of prospective data on the precipitants and process of relapse (especially relapse to heroin or cocaine abuse). However, reinstatement does not need to resemble relapse to have immediate clinical value; predictive validity as a medication screen would be sufficient. Whether the model has predictive validity is unknown, because, to date, very few clinical trials have tested medications that are effective in the reinstatement model, and even fewer have used designs comparable to those of reinstatement experiments. A clinical trial comparable to a reinstatement experiment would enroll participants who are already abstinent, and its main outcome measure would be propensity to undergo a specific type of relapse (e.g., relapse induced by stress or cues).

CONCLUSIONS

Until clinical and preclinical work are more comparable, criticisms of the reinstatement model's presumed shortcomings are premature.

Neurodevelopmental liabilities in alcohol dependence: central serotonin and dopamine dysfunction

Alcoholism is a complex disorder with symptoms ranging from abuse to dependence, often comorbid with depression, antisocial personality, or anxiety. Neurodevelopmental causes of the disorder are unknown but inferences are possible from current knowledge. Neurobiological studies implicate multiple brain changes, which may be characterized as premorbid or morbid. These studies have also examined specific aspects of the alcohol dependence syndrome, including alcohol reinforcement and craving. Here, we review the evidence for vulnerability factors in alcohol dependence, with an emphasis on central serotonin (5-HT) and dopamine (DA). Serotonin dysfunction likely contributes to the development of alcoholism since studies of alcohol-preferring rodents show decreased 5-HT function on many measures. We have shown that serotonin-enhancing drugs reduce consumption and craving in mild to moderate alcoholics, yet similar studies in severely dependent individuals remain inconclusive. Studies indicate that serotonin dysfunction may contribute to the development of dependence via impaired impulse control and/or mood regulation. The mesocorticolimbic dopamine pathway represents another important pathophysiological target in alcoholism. Differences in D(2) receptor density, dopamine sensitivity, and gene expression have been linked to consumption, reinforcement, craving, and relapse. However, while DA agonists reduce self-administration in animals, we found no effect in humans with long-acting bromocriptine, a D(2) agonist. Dopamine may contribute differentially to the development of dependence via its effects on alcohol wanting, reinforcement, and reward memory. Although animal experiments show consistent roles for serotonin and dopamine in alcohol dependence, human studies are not always concordant. Such discrepancies highlight the complexity of dependence-related behaviors in humans and of identifying vulnerabilities to alcoholism.