- 15 Sep, 2022
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How Does Alcohol Affect Dopamine Levels in the Brain?
Dopamine D2 receptor antagonists have been studied in human laboratory studies involving alcohol administration in dependent individuals and found to be effective in reducing craving. In a laboratory study involving 16 individuals with alcohol abuse and/or dependence, the D2 antagonist haloperidol was compared to placebo. The results of this small study demonstrated that haloperidol significantly decreased measures of craving, reduced impulsivity, and the amounts of alcohol ingested [144]. The dopamine D2 antagonist flupenthixol has also been evaluated in a clinical study of 281 recently detoxified alcohol‐dependent patients [145]. The results demonstrated that treatment with the depot formulation of flupenthixol led to a significant increase in rates of relapse (85.2% on active treatment can alcoholics have food cooked with alcohol compared with 62.5% on placebo).
Based on this clinical finding and the knowledge that olanzapine also has a high affinity for the D4 receptors, it was hypothesized whether the dopamine receptor D4 gene maybe involved in meditating its clinical effects. These data are supported by the findings that olanzapine reduces craving for alcohol at baseline for both individuals with the DRD4 shorter and longer allele, but only reduces craving after exposure to alcohol cues and after a priming dose of alcohol for individuals with the DRD4 longer allele [166]. Overall, the results from studies evaluating olanzapine as a potential medication for alcohol dependence have provided evidence of a marginal effect restricted to a sub population of patients (with the longer dopamine D4 receptor allele). Several studies have shown that changes in the DA system in the CNS can influence drinking behaviors both in animals and in humans. Early animal models have shown that injection of the neurotoxin 6-hydroxydopamine (6-OHDA) in the ventricle or in other brain regions destroys dopaminergic neurons.
- Moreover, data from a randomized clinical trial in alcohol‐dependent individuals show that the smoking cessation agent reduced the weekly percent heavy drinking days drinks, decreased the drinks per drinking day as well as prevented alcohol craving [211].
- Glutamate is the major excitatory neurotransmitter in the brain and it exerts its effects through several receptor subtypes, including one called the N-methyl-D-aspartate (NMDA) receptor.
- Given that treatment-seeking individuals with AUD invariably go through repeated periods of abstinence and relapse, it is important for animal models of AUD to incorporate this element into the experimental design as these abstinence periods may contribute to the neurobiology of AUD.
Presynaptic regulation of dopamine release by dopamine and acetylcholine
Alcohol addiction and dependence of late has been shown to be affected by the influence of genes. The presence of such genes does not confirm whether a person will turn into an alcohol addict, but there is a high correlation amongst carriers of such genes and alcohol addiction. 2Autonomic, or visceral, responses regulate the involuntary bodily functions, such as heart rate, blood pressure, and gastrointestinal activity. 1The term “dopaminergic” refers to both the neurons and the signaling processes that use dopamine. Dopaminergic neurons reach not only the NAc, but also other areas of the extended amygdala as well as parts of the septo-hippocampal system. Consequently, dopamine acts at multiple sites to control the integration of biologically relevant information that determines motivated responding.
Given our findings showing differences in dopamine release, it might be assumed that these effects are attributable to changes in presynaptic dopamine terminals. It should be noted, however, that our study utilized electrical stimulation to induce dopamine release. This stimulation method is nonspecific and activates all axons and neurons near the stimulus electrode, including cholinergic interneurons.
The development of compulsive coping behavior depends on dorsolateral striatum dopamine-dependent mechanisms
A major concern with flupenthixol is results from studies demonstrating an increase in the risk of relapse in rodents as well as humans [146], an effect preferentially observed in males [147]. Overall, the clinical utility of atypical antipsychotics has shown to be of some benefit in patients suffering from alcohol dependence and a concomitant psychiatric diagnosis including schizophrenia [148, 149]. A major challenge, however, with the first‐generation antipsychotic drugs is their severe side effect profile including extrapyramidal symptoms, sedation, cognitive impairment, neuroleptic malignant syndrome, which have limited their use in research and in turn its clinical utility in treating alcohol dependence [150, 151]. In healthy controls, alcohol consumption stimulates dopamine release mediating its reinforcing effects.
More recently, the EMA granted authorization also for nalmefene, a compound intended for the reduction of alcohol consumption in adults with alcohol dependence (EMA 2012). Details regarding the mechanism of action of these compounds are outside the scope of this review. In brief, the pharmacological profile is established for disulfiram (an aldehydedehydrogenase inhibitor), naltrexone (an opioid receptor antagonist) and nalmefene (an opioid receptor modulator), whereas the mechanism of action of the anti‐alcohol relapse drug acamprosate is not fully understood. An indirect activation of mesolimbic dopamine via accumbal glycine receptors and ventral tegmental nicotinic acetylcholine receptors (nAChRs) appears likely [2, 3], but additional targets has been suggested (for review see [4]). Finally, the clinical efficacy of these agents is limited [5], possibly due to the heterogeneous nature of the disorder and the complex neurochemical mechanisms underlying alcohol dependence. These atypical antipsychotics have a significantly improved side effect profile compared to the traditional first generation of dopamine D2 antagonists.
This may be related to varying methodologies, to non-linear dosage effects, to non-transferability of animal results to humans, to different target groups (most previous studies have used samples from Western countries), and to the possible confounding effects what is a roofi of other inter-related neurotransmitter systems. Further research aimed at clarifying the interaction between the DA system, the glutamatergic system and other neurotransmitter systems is needed before it will be possible to improve the effectiveness of interventions for preventing and treating alcohol dependence. The fourth pathway which interests us and is of note for alcohol addiction is the pathway of glutamate.
Two weeks of OSU6162 treatment significantly attenuated priming‐induced craving and induced significantly lower subjective “liking” of the consumed alcohol, compared to placebo. Interestingly, the treatment effects of OSU6162 were driven by those individuals with high level of baseline impulsivity, corroborating previous results with the partial dopamine D2 agonist aripiprazole [185]. These results suggest that pharmacological stabilization of the dopamine system might prove as an effective target for alleviating some of the reward driven behaviours during alcohol dependence. Together with OSU6162’s favourable side effect profile [198, 197, 199], these results render support for a larger placebo‐controlled efficacy trial in alcohol‐dependent patients to evaluate OSU6162’s effect on drinking outcomes.
Furthermore, after 10 months of drinking, a blunted dopamine response following a systemic alcohol challenge has been found in long‐term drinking, compared to alcohol‐naïve rats [29]. These results indicate that long‐term drinking attenuates the responsiveness of the system to external dopamine stimulation, in addition to decreasing baseline levels of dopamine. It should, however, be noted that acute administration of alcohol induces a twofold increase in dopamine output in the NAc shell in high compared to low‐alcohol‐preferring rats [105], indicating that there might be a difference in these aspects between outbred standard laboratory rats and inbred what type of drug is mary jane alcohol‐preferring rats.
Dopamine and Alcohol Dependence: From Bench to Clinic
Furthermore, I would like to state that no financial aid in any form was received for undertaking this work. It is classified as a catecholamine (a class of molecules that serve as neurotransmitters and hormones). It is a monoamine (a compound containing nitrogen formed from ammonia by replacement of one or more of the hydrogen atoms by hydrocarbon radicals).
How — and why — to fit more fiber and fermented food into your meals
The mechanisms underlying this dysregulation of dopamine transmission are not well understood, particularly in a primate brain. Therefore, in the current study, we used fast-scan cyclic voltammetry (FSCV) to study dopamine release dynamics in striatal slices from long-term alcohol drinking and control rhesus macaques. This method allows for examination of dopamine release and its regulation on a subsecond time scale that has seldom been used in NHPs [18,19,20,21,22,23,24]. Furthermore, FSCV allows for the study of dopamine uptake using Michaelis–Menten based kinetic modeling of uptake parameters, allowing researchers to assess dopamine transporter function. Finally, we can pharmacologically probe the contribution of different regulatory systems, including the D2 dopamine autoreceptor and nicotinic acetylcholine receptor (nAChR), to dopamine release. Olanzapine, another example of a second generation of antipsychotics, has been evaluated in a human cue‐craving study, where the compound reduced the urge to drink post‐exposure to alcohol cues, without affecting the rewarding effects of alcohol following the consumption of a priming dose of alcohol [152].
Thus, there has been a renewed interest in evaluating these medications as potential treatment for alcohol dependence with the assumption that the atypical antipsychotics might reduce craving and consumption of alcohol without the substantial adverse effect profile [152]. Furthermore, they are clinically used for alcohol‐dependent patients during the acute detoxification phase to prevent agitation, hallucinations and delirium tremens [153]. Traditional dopamine D2 receptor antagonists (so‐called neuroleptics, first‐generation antipsychotic drugs or typical antipsychotic drugs) are primary used for the treatment of psychosis, schizophrenia and bipolar disorder [11] based on their ability to counteract a heightened dopamine activity in the brain. It should also be mentioned that these typical antipsychotic agents might have effects on other receptors including dopamine D1, 5HT2 and alpha1 receptors. As reviewed above, the acute reinforcing effects of addictive drugs, including alcohol, could be mediated by increased dopamine release in the NAc, activating dopamine D2 receptors [71, 27, 30]. Thus, traditional dopamine D2 receptor antagonists have been evaluated as potential treatment targets for alcohol dependence based on the hypothesis that they are expected to block the rewarding effects of alcohol.
Male and female rhesus macaques (Macaca mulatta; 5.5–8.5 years old at study onset) obtained from the Oregon National Primate Research Center were used in the current studies. All procedures were conducted in accordance with the NIH Guide for the Care and Use of Laboratory Animals and approved by the Oregon National Primate Research Center Institutional Animal Care and Use Committee. These substances usually trigger the release of dopamine, the body’s “feel-good” neurotransmitter. Once a person does something that trips the brain’s reward center, they feel good and are more likely to repeat the activity. Marco Leyton, a professor and addiction researcher at McGill University’s Department of Psychiatry, said in a 2013 press release that participants more at risk for developing alcoholism had “an unusually large brain dopamine response” when they took a drink.