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Dopamine is a neuromodulator that is used by neurons in several brain regions involved in motivation and reinforcement, most importantly the nucleus accumbens (NAc). Dopamine alters the sensitivity of its target neurons to other neurotransmitters, particularly glutamate.
In addition, dopamine can affect the neurotransmitter release by the target neurons. Dopamine-containing neurons in the NAc are activated by motivational stimuli, which encourage a person to perform or repeat a behavior. Even low alcohol doses can increase dopamine release in part of the NAc. This dopamine release may contribute to the rewarding effects of alcohol and may thereby play a role in promoting alcohol consumption. In contrast to other stimuli, alcohol-related stimuli maintain their motivational signiFicance even after repeated alcohol administration, which may contribute to the craving for alcohol observed in alcoholics. KEY WORDS: dopamine; dopaminergic receptors; cell signaling; neurotransmission; reinforcement; motivation; neurotransmitters; nucleus accumbens; brain; neuron; sensory stimuli; AOD craving; AOD dependence; neurobiological theory; literature review
Many substances that relay signals among neurons (i.e., neurotransmitters) are affected by alcohol. Among these, dopamine has received special attention, because several studies have found that alcohol stimulates the activity of a subset of dopamine-releasing neurons and thus enhances dopamine-mediated (i.e., dopaminergic') signal transmission in a discrete brain area called the nucleus accumbens (NAc) (Di Chiara and Imperato 1985; Imperato and Di Chiara 1986; Gessa et al. 1985). Alcohol shares this property with most substances of abuse (Di Chiara and Imperato 1988), including nicotine, marijuana, heroin, and cocaine (Pontieri et al. 1995, 1996; Tanda et al. 1997). These observations have stimulated many studies on dopamine's role in alcohol abuse and dependence, also with the intent of finding new pharmacological approaches to alcoholism treatment. This review summarizes some of the characteristics of dopaminergic signal transmission as well as dopamine's potential role in alcohol reinforcement.
DOPAMINE PRODUCTION AND DISTRIBUTION IN THE BRAIN
Dopaminergic neurons produce dopamine from the dietary amino acid tyrosine. The neurons then store the dopamine in small compartments (i.e., vesicles) in the terminals of their axons. When the dopaminergic neurons are activated, the resulting change in the electrical charges on both sides of the cell membrane (i.e., depolarization) induces dopamine release into the gap separating the neurons (i.e., the synaptic cleft) through a process called exocytosis. (For more...