The Interactions of Nicotine and Ethanol in the Brain: Can consuming alcohol cause nicotine cravings in people who have previously used both drugs together?
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Alcohol and nicotine use are both highly prevalent in the United States. It is estimated that over 19% of the population over the age of 18 smokes cigarettes, while over 51% of people over the age of 18 are current, regular drinkers (CDC, 2011; CDC, 2012). Epidemiological evidence appears to show a correlation between the usage of each drug: A longitudinal study of college students has shown that nicotine dependence and alcohol abuse each predict each other over time (Sher et. al., 1996). Additionally, alcoholic smokers have been found to smoke nearly double the number of cigarettes per day when compared to non-alcoholic smokers (Dawson, 2000). MRI studies on alcoholics have found that alcohol cue presentation increases the urge to drink and smoke (Cooney et al., 2003). Such evidence suggests that there may be a common underlying neural mechanism mediating the association between these two drugs. The leading candidate for this association is the mesolimbic dopamine pathway. This pathway, projecting from the ventral tegmental area (VTA) to the nucleus accumbens (NAcc) has been found to mediate drug craving and reward for almost every major drug of abuse (Wise, 1998). In this paper, I will first look at the epidemiological evidence for this association. Then I will look at some important preliminary studies on ethanol and nicotine’s effects on the mesolimbic dopamine pathway. After I have constructed a diagram of the major synaptic connections between these neurotransmitter systems and discussed their roles, I will then explore a large body of literature researching the effects both nicotine and ethanol on the two other major neurotransmitter systems which influence this pathway: GABA and glutamate. After discussing the direct effects of ethanol on nicotinic receptors, I will then summarize the evidence regarding the effects of prolonged exposure to nicotine, ethanol, or both drugs. Finally, I will discuss the current neuroanatomical model for nicotine addiction, and the ability of nicotine to elicit long-term potentiation at certain synapses in the VTA – a change which may both readily sensitize the mesolimbic system and provide a means of associating ethanol intoxication with nicotine consumption.