Academic journal article Alcohol Research

Biological Processes Underlying Co-Use of Alcohol and Nicotine: Neuronal Mechanisms, Cross-Tolerance, and Genetic Factors

Academic journal article Alcohol Research

Biological Processes Underlying Co-Use of Alcohol and Nicotine: Neuronal Mechanisms, Cross-Tolerance, and Genetic Factors

Article excerpt

Alcohol and nicotine are two of the oldest and most commonly used recreational drugs, and many people use both of them together. Although their ready availability likely contributes to the strong correlation between alcohol and nicotine use, several lines of evidence suggest that biological factors play a role as well. For example, both alcohol and nicotine act on a brain system called the mesolimbic dopamine system, which mediates the rewarding and reinforcing properties of both drugs. Modification of the activities of the mesolimbic dopamine system can interfere with the effects of both alcohol and nicotine. Another mechanism that may contribute to alcohol-nicotine interactions is cross-tolerance to the effects of both drugs. Finally, genetic studies in humans and of selectively bred mouse and rat strains suggest that shared genetic factors help determine a person's liability to use or abuse both alcohol and nicotine. KEY WORDS: Alcohol and tobacco; alcohol and other drug (AOD) use, abuse, and dependence; nicotine dependence; dual addiction; brain; ventral tegmental area; mesolimbic dopamine system; animal models; genetic theory of alcohol and other drug use (AODU); cross-tolerance


Alcohol and nicotine are two of the most commonly used drugs in the world, and many people use both of them, often together. In humans, alcohol and nicotine use are highly correlated. For example, the prevalence of smoking is about three times higher in alcoholics than in the general population (Substance Abuse and Mental Health Services Administration 2005). This relationship between alcohol and nicotine consumption is especially interesting because the two drugs are rather dissimilar in their mechanisms of action and their effects:

* Nicotine acts on the brain by directly binding to and activating a molecule called the nicotinic acetylcholine receptor, which is found on certain brain cells. In contrast, alcohol does not bind directly to any one receptor type.

* Alcohol usually is classified as a depressant, impairs alertness, and can have anticonvulsant effects. Conversely, nicotine primarily has stimulant effects, increases alertness, and can trigger convulsions.

* The withdrawal symptoms induced by the two drugs following chronic administration differ considerably.

The fact that alcohol and tobacco are readily and legally available likely contributes to their co-use. Over the past two decades, however, it has become increasingly clear that biological factors also contribute to the concurrent use of alcohol and nicotine--that is, certain common physiological mechanisms may account for people's liability to use both alcohol and nicotine. Several such mechanisms have been suggested. For example, both alcohol and nicotine may enhance a person's motivation to also consume the other drug by acting on a common target in the brain that is responsible for the reinforcing effects of both drugs. Alternatively, cross-tolerance between the two drugs may reduce the drugs' aversive effects and motivate people to use more of the drugs in order to achieve the same rewarding effects. (The concept of cross-tolerance will be explained in more detail in the section "Tolerance and Cross-Tolerance.") The study of this possible mechanism, however, is complicated by the fact that both alcohol and nicotine can exert different effects on a variety of behavioral and physiological variables, depending on the amount of the drugs consumed (Moore et al. 1993; Nanri et al. 1998; Schaefer and Michael 1986). Finally, several recent studies have suggested that a shared genetic component may predispose people to the use or abuse of both alcohol and nicotine.

This article reviews and evaluates the evidence for these three biological mechanisms that potentially contribute to the co-use of alcohol and nicotine. After reviewing human and animal studies that demonstrate how alcohol and nicotine interact in producing their rewarding effects, the article presents the evidence that a pathway in the brain--the mesolimbic dopamine system--participates in this interaction. …

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