Alcoholism can be defined by a compulsion to seek and take drug, loss of control in limiting intake, and the emergence of a negative emotional state when access to the drug is prevented. Alcoholism impacts multiple motivational mechanisms and can be conceptualized as a disorder that includes a progression from impulsivity (positive reinforcement) to compulsivity (negative reinforcement). The compulsive drug seeking associated with alcoholism can be derived from multiple neuroadaptations, but the thesis argued here is that a key component involves the construct of negative reinforcement. Negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from dysregulation of specific neurochemical elements involved in reward and stress within the basal forebrain structures involving the ventral striatum and extended amygdala, respectively. Specific neurochemical elements in these structures include not only decreases in reward neurotransmission, such as decreased dopamine and γ-aminobutyric acid function in the ventral striatum, but also recruitment of brain stress systems, such as corticotropin-releasing factor (CRF), in the extended amygdala. Acute withdrawal from chronic alcohol, sufficient to produce dependence, increases reward thresholds, increases anxiety-like responses, decreases dopamine system function, and increases extracellular levels of CRF in the central nucleus of the amygdala. CRF receptor antagonists also block excessive drug intake produced by dependence. A brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of alcoholism. Other components of brain stress systems in the extended amygdala that interact with CRF and that may contribute to the negative motivational state of withdrawal include norepinephrine, dynorphin, and neuropeptide Y. The combination of loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for a negative emotional state that is responsible for the negative reinforcement driving, at least partially, the compulsivity of alcoholism.
"This hypothesis presently remains untested. A proposed mechanism underlying the reinforcement from alcohol consumption is activation of brain reward circuitry, particularly the striatum and midbrain dopamine neurons (Volkow et al., 2002; Koob, 2013). Alcohol potentiates the response of nAChRs to acetylcholine (Cardoso et al., 1999; Zuo et al., 2002), and stimulating nAChRs enhances dopamine release in the striatum, amygdala, and prefrontal cortex (Arqueros et al., 1978; Palotai et al., 2013). "
[Show abstract][Hide abstract] ABSTRACT: Preclinical and emerging clinical evidence indicates that varenicline, a nicotinic partial agonist approved for smoking cessation, attenuates alcohol seeking and consumption. Reductions of alcohol craving have been observed under varenicline treatment and suggest effects of the medication on alcohol reward processing, but this hypothesis remains untested.
In this double-blind, placebo-controlled randomized experimental medicine study, 29 heavy drinkers underwent a functional magnetic resonance imaging scan after 2 weeks of varenicline (2mg/d) or placebo administration. During functional magnetic resonance imaging, participants performed the Alcohol-Food Incentive Delay task, where they could earn points for snacks or alcohol. At baseline and after 3 weeks of medication, participants underwent intravenous alcohol self-administration sessions in the laboratory.
During the functional magnetic resonance imaging scan, participants in the varenicline group (N=17) reported lower feelings of happiness and excitement on subjective mood scales when anticipating alcohol reward compared with the placebo group (N=12). Linear mixed effects analysis revealed that anticipation of alcohol reward was associated with significant blood oxygen level dependent activation of the ventral striatum, amygdala, and posterior insula in the placebo group; this activation was attenuated in the varenicline group. The varenicline group showed no difference in intravenous alcohol self-administration relative to the placebo group for either session. Participants with higher insula activation when anticipating alcohol reward showed higher alcohol self-administration behavior across groups.
Our findings suggest that varenicline decreases blood oxygen level dependent activation in striato-cortico-limbic regions associated with motivation and incentive salience of alcohol in heavy drinkers. This mechanism may underlie the clinical effectiveness of varenicline in reducing alcohol intake and indicates its potential utility as a pharmacotherapy for alcohol use disorders.
Published by Oxford University Press on behalf of CINP 2015. This work is written by (a) US Government employee(s) and is in the public domain in the US.
The International Journal of Neuropsychopharmacology 07/2015; DOI:10.1093/ijnp/pyv068 · 4.01 Impact Factor
"Such tests could aid a clinician in providing a patient-specific risk assessment that could be used to objectively communicate risk to the patient or change the course of treatment to reduce risk status. One proposed marker of substance use disorders (SUDs), including methamphetamine dependence (MD; May et al., 2013; Schouw et al., 2013; Stewart et al., 2014), is altered neural response of the limbic reward system (Koob, 2013; Volkow and Fowler, 2000). There are two prominent hypotheses on how the response changes: individuals with SUDs may have hyper-or hypo-activation in response to rewarding stimuli, reflecting either enhanced incentive salience or reward deficiency, respectively. "
[Show abstract][Hide abstract] ABSTRACT: Nearly half of individuals with substance use disorders relapse in the year after treatment. A diagnostic tool to help clinicians make decisions regarding treatment does not exist for psychiatric conditions. Identifying individuals with high risk for relapse to substance use following abstinence has profound clinical consequences. This study aimed to develop neuroimaging as a robust tool to predict relapse.
68 methamphetamine-dependent adults (15 female) were recruited from 28-day inpatient treatment. During treatment, participants completed a functional MRI scan that examined brain activation during reward processing. Patients were followed 1 year later to assess abstinence. We examined brain activation during reward processing between relapsing and abstaining individuals and employed three random forest prediction models (clinical and personality measures, neuroimaging measures, a combined model) to generate predictions for each participant regarding their relapse likelihood.
18 individuals relapsed. There were significant group by reward-size interactions for neural activation in the left insula and right striatum for rewards. Abstaining individuals showed increased activation for large, risky relative to small, safe rewards, whereas relapsing individuals failed to show differential activation between reward types. All three random forest models yielded good test characteristics such that a positive test for relapse yielded a likelihood ratio 2.63, whereas a negative test had a likelihood ratio of 0.48.
These findings suggest that neuroimaging can be developed in combination with other measures as an instrument to predict relapse, advancing tools providers can use to make decisions about individualized treatment of substance use disorders.
Published by Elsevier Ireland Ltd.
Drug and alcohol dependence 04/2015; 152. DOI:10.1016/j.drugalcdep.2015.04.018 · 3.42 Impact Factor
"Alcohol is one of the most abused drugs in the world. Studies of neurobiological mechanisms underlying alcohol abuse have demonstrated the importance of different neurochemical systems that are responsive to ethanol exposure and, in turn, promote intake  . While these studies have been performed mostly in humans and rodents  , zebrafish are being increasingly utilized as an animal model for studying the effects of ethanol on behavior and brain neurotransmitters known to be involved in alcoholism. "
[Show abstract][Hide abstract] ABSTRACT: Recent studies in zebrafish have shown that exposure to ethanol in tank water affects various behaviors, including locomotion, anxiety and aggression, and produces changes in brain neurotransmitters, such as serotonin and dopamine. Building on these investigations, the present study had two goals: first, to develop a method for inducing voluntary ethanol intake in individual zebrafish, which can be used as a model in future studies to examine how this behavior is affected by various manipulations, and second, to characterize the effects of this ethanol intake on different behaviors and the expression of hypothalamic orexigenic peptides, galanin (GAL) and orexin (OX), which are known in rodents to stimulate consumption of ethanol and alter behaviors associated with alcohol abuse. Thus, we first developed a new model of voluntary intake of ethanol in fish by presenting this ethanol mixed with gelatin, which they readily consume. Using this model, we found that individual zebrafish can be trained in a short period to consume stable levels of 10% or 20% ethanol (v/v) mixed with gelatin and that their intake of this ethanol-gelatin mixture leads to pharmacologically relevant blood ethanol concentrations which are strongly, positively correlated with the amount ingested. Intake of this ethanol-gelatin mixture increased locomotion, reduced anxiety, and stimulated aggressive behavior, while increasing expression of GAL and OX in specific hypothalamic areas. These findings, confirming results in rats, provide a method in zebrafish for investigating with forward genetics and pharmacological techniques the role of different brain mechanisms in controlling ethanol intake.
Behavioural Brain Research 09/2014; 278. DOI:10.1016/j.bbr.2014.09.024 · 3.03 Impact Factor
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