An activated neuron sends chemical signaling molecules called neurotransmitters through the neural circuit which bind to specific molecules called the receptors. Depending upon the circuit involved, the binding of these neurotransmitters may cause excitatory or inhibitory signals to be passed further along the circuit. Recent advances in the study of alcoholism have thrown light on the involvement of various neurotransmitters in the phenomenon of alcohol addiction. Various neurotransmitters have been implicated in alcohol addiction due to their imbalance in the brain, which could be either due to their excess activity or inhibition. This review paper aims to consolidate and to summarize some of the recent papers which have been published in this regard. The review paper will give an overview of the neurobiology of alcohol addiction, followed by detailed reviews of some of the recent papers published in the context of the genetics of alcohol addiction.
P/T depletion effects on frontolimbic FC
Given the relevance of dopamine in the chronic phase of alcohol use and in the development of alcohol dependence, there is considerable interest in evaluating medications that can specifically modify dopamine, thereby serving as potential pharmacotherapies to treat alcohol dependence. Dopamine has also been implicated in schizophrenia and ADHD; the brain systems underlying these conditions (as well as substance abuse disorder) are complex. The activity of the dopamine system depends on the state of one’s dopamine receptors, and in people with these conditions, the chemical interacts with other factors in ways that have yet to be explained. By jacking up dopamine levels in your brain, alcohol tricks you into thinking that it’s actually making you feel great (or maybe just better, if you are drinking to get over something emotionally difficult). The effect is that you keep drinking to get more dopamine release, but at the same time you’re altering other brain chemicals that are enhancing feelings of depression.
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However, in this study, the behavioral tasks were performed after the resting-state scan; future work pairing event-related fMRI AB tasks with the P/T depletion procedure may provide additional insight into the dopamine response to alcohol or non-drug reward cues. A series of experiments in outbred rats show that the dopamine stabilizer OSU6162 attenuates several alcohol‐mediated behaviours including voluntary alcohol intake, alcohol withdrawal symptoms and cue/priming‐induced reinstatement of alcohol seeking in long‐term drinking rats [196]. Furthermore, OSU6162 blunted alcohol‐induced dopamine output in the NAc of alcohol‐naïve rats [196], indicating that OSU6162 has the ability to attenuate the rewarding effects of alcohol.
Alcohol’s Actions as a Reinforcer: Dopamine’s Role
There’s also more of an effect on your brain and its development if you’re younger — one that can have a lasting impact. As BAC ascends, drinkers report increases in elation, excitement, and extroversion, with simultaneous decreases in fatigue, restlessness, depression, and tension. Conversely, a descending BAC corresponds to a decrease in vigor and an increase in fatigue, relaxation, confusion, and depression. I would like to acknowledge https://sober-home.org/ my faculty at Amity Institute of Biotechnology, Dr. Manju Pathak for her unwavering support and encouragement in writing this review paper. She single-handedly inspired me to undertake this task and the work would not have borne fruition without her support and guidance. Thanks are also due to my mother, Dr. Sharmila Banerjee, without whose support and editorial help, I could not have had the will to complete this work.
1. The brain reward system: the mesocorticolimbic dopamine system
For example, different subpopulations of neurons in the striatum carry different dopamine receptors on their surfaces (Le Moine et al. 1990, 1991; Gerfen 1992). Dopamine binding to D1 receptors enhances the excitatory effects that result from glutamate’s interaction with a specific glutamate receptor subtype (i.e., the NMDA receptor4). Conversely, activation of D2 receptors inhibits the effects induced by glutamate’s binding to another glutamate-receptor subtype (i.e., the AMPA receptor5) (Cepeda et al. 1993).
2. Atypical dopamine D2 receptor antagonists
- Furthermore, a genome-wide association study identified PDE4B as a risk factor in elevated alcohol consumption [6,7].
- 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).
- Finally, preclinical and clinical studies evaluating the potential of available dopaminergic agents as well as indirect dopamine modulators as novel medications for alcohol dependence are discussed.
A gatekeeper, the cell membrane’s job is to regulate what goes in and out of a cell. We hear many different things about how alcohol affects the brain and body, most notably that it is a depressant. Alcohol is a depressant, but it’s also an indirect stimulant, and plays a few other roles that might surprise you. Beyond this, by definition, consuming enough alcohol to cause a “brownout,” “blackout,” hangover, or other overt brain symptomatology is evidence that the alcohol you’ve consumed is creating problems in your brain. It has been linked to a higher risk for dementia, especially early-onset dementia in a study of 262,000 adults, as well as to smaller brain size. Alcohol addiction and dependence of late has been shown to be affected by the influence of genes.
Thus, an alcohol-induced increase in adenosine levels might be responsible for part of alcohol’s sedative actions. Studies about the relationship of D1 receptors and affinity for alcohol have had inconsistent results. While drinking initially boosts a person’s dopamine levels, the brain adapts to the dopamine overload with continued alcohol use. It produces less of the neurotransmitter, reducing the number of dopamine receptors in the body and increasing dopamine transporters, which carry away the excess dopamine. Researchers are investigating whether drugs that normalize dopamine levels in the brain might be effective in reducing alcohol cravings and treating alcoholism.
Concomitantly, adaptations in glutamatergic, GABAergic, and dopamine transmission occur [15] and greater or continued amounts of alcohol can result in allostatic changes to preserve normal brain function. This allostasis is characterized by aberrant glutamate, GABA, and opioid signaling, as well as, a dysfunction in nigrostriatal and mesolimbic dopamine transmission [16, 17]. 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.
The following text introduces some of the neural circuits relevant to AD, categorized by neurotransmitter systems. These neural circuits include the dopaminergic, serotoninergic, glutamatergic and GABAergic neural circuits. Dopamine’s effects on neuronal function depend on the specific dopamine-receptor subtype that is activated on the postsynaptic cell.
When alcohol consumption is abruptly reduced or discontinued, a withdrawal syndrome may follow, characterized by seizures, tremor, hallucinations, insomnia, agitation, and confusion (Metten and Crabbe 1995). Scientists postulate that this syndrome represents the hyperactivity of neural adaptive mechanisms no longer balanced by the inhibitory effects of alcohol (see figure). Researchers are focusing much of their attention on other inhibitory neurotransmitters. Alcohol has been shown to increase the function of glycine receptors in laboratory preparations (Valenzuela and Harris 1997). Alcohol’s actions on inhibitory neurotransmission in this lower area of the central nervous system may cause some of alcohol’s behavioral effects.
The effects of SSRI’s and other serotonergic medications on alcohol abuse will be difficult to disentangle from their effects on co-occurring mental disorders. Nevertheless, the information currently available clearly indicates that serotonergic signal transmission plays an important role in alcohol abuse and therefore may yet be a target for therapies to reduce alcohol consumption. More research is needed to determine how and under what drinking conditions alcohol consumption is affected by different serotonin receptor antagonists.
Studies in animal models provide initial hints to possible contributors to these differences. Furthermore, rats undergoing intermittent access to 20% alcohol in 2 bottle choice paradigm exhibit distinct profiles of intake ranging from low alcohol consumers to rats that exhibit slow or rapid escalation of excessive drinking [125]. The kinase mTOR in complex 1 (mTORC1) plays a crucial role in synaptic plasticity, learning and memory by orchestrating the translation of several dendritic proteins [39]. MTORC1 is activated by alcohol in discrete brain regions resulting in the translation of synaptic proteins such as Collapsin response-mediated protein 2 (CRMP2) [40] and ProSap-interacting protein 1 (Prosapip1) [41], as well as Homer1 and PSD-95, GluA2 and Arc [40,42,43]. Through the translation of these transcripts and others, mTORC1 contributes to mechanisms underlying alcohol seeking and drinking as well as reconsolidation of alcohol reward memories and habit [44–46].
Your brain adapts to the sudden increase in the neurotransmitter by producing less dopamine, but because of the link to pleasure, it doesn’t want you to stop after a few drinks — even when your dopamine levels start to deplete. Dopamine levels fall, and the euphoric buzz goes with it, but your brain is looking to regain the feeling caused by the increased level of dopamine. Eventually, you rely fully on alcohol to generate dopamine release, and without it, you experience withdrawal symptoms. Alcohol-induced epigenetic alterations are often mediated by altered expression or activity of epigenetic enzymes, which thus represent a promising new avenue for targeted therapeutic interventions. For example, increased enrichment of DNA methylation in the mPFC was linked to enhanced DNA methyltransferase (Dnmt) activity [23]. Inhibition of Dnmt rescued the methylation and transcriptional changes and prevented the escalation of alcohol intake [23].
These alleles are of 9 base pair repeats, 10 base pair repeats as well as 12 base pair repeats. The 9 base pair repeat is extremely rare and in statistical studies, often clubbed with the 10 base pair repeat. Recently mutations in the SERT gene, commonly known as 5’- hydroxtryptamine transporter linked polymorphic region (5’-HTTLPR), has been implicated in cases of alcoholism.
Opioid peptide antagonists act primarily on a brain area where dopaminergic neurons that extend to the NAc originate. These observations indicate that alcohol stimulates the activity of endogenous opioid peptides, leading indirectly to the activation of dopaminergic neurons. Opioid peptide antagonists would interfere with this process, thereby reducing dopamine release. Dopaminergic neurons that relay information to the NAc shell are extremely sensitive to alcohol.
Inhibitory neurotransmitters transiently decrease the responsiveness of other neurons to further stimuli, whereas excitatory neurotransmitters produce the opposite effect. Some neurotransmitters produce longer lasting changes, contributing to processes such as learning and memory. In addition, https://sober-home.org/family-involvement-in-treatment-and-recovery-for/ one of the latest studies on this pathway found an association between a polymorphism in the promoter of a glutamate receptor subunit gene and alcoholism. The study was conducted by[68] and the study found that short alleles were significantly less frequent among AD subjects.
Here we quantified AB toward alcohol and non-drug, reward-conditioned cues and their neural underpinnings after acute dopamine precursor depletion across a broad spectrum of alcohol users. P/T depletion significantly reduced AB across three different tasks, particularly in individuals who reported heavier drinking. P/T depletion altered FC between prefrontal and subcortical brain regions involved in reward processing and motivation, and these alterations predicted changes in AB. A one-factor ANOVA with Tukey’s post hoc test was used to compare the average lifetime alcohol intake between cohorts. Two-factor ANOVAs (stimulation intensity and treatment group) were used for the input–output curve experiments examining dopamine release. For the dopamine uptake rate (Vmax) data, two-factor ANOVAs (treatment and brain region) were used.
Other drugs that affect serotonergic signal transmission also alter alcohol consumption in animals (LeMarquand et al. 1994b). For example, antagonists of the 5-HT3 and 5-HT1A receptors reduced alcohol ingestion in rodents (Litten et al. 1996; Pettinati 1996; DeVry 1995). However, the 5-HT1A receptor antagonists also altered food and water intake, suggesting that this receptor may modulate general consummatory behavior rather than specifically reduce the desire to drink alcohol. In humans, the 5-HT3 receptor antagonist ondansetron reduced total alcohol consumption and the desire to drink in alcoholics; as with the SSRI’s, however, this effect was relatively modest (Johnson et al. 1993; Pettinati 1996; Sellers et al. 1994).