A study in the May issue of Alcoholism: Clinical & Experimental Research builds on previous research that identified four potential alcohol-sensitive genes in the prefrontal cortex, finding that smoking also influences the expression of these genes.
"Nicotine and alcohol are both addictive drugs," said Traute Flatscher-Bader, BSc(Hons), a postdoctoral research officer at the Alcohol Research Unit of the University of Queensland, Brisbane, Australia, and corresponding author. "They act on the same brain region, the ‘drug reward pathway’ or mesocorticolimbic system (MDS) [sic]. The MDS contains the feel-good neurotransmitter dopamine.
"Acute nicotine and alcohol [use] cause an imbalance within the MDS by artificially increasing dopamine levels through direct and/or indirect modulation of dopaminergic neurons," Ms. Flatscher-Bader continued. "While the long-term effect of alcoholism on the human brain has been investigated, surprisingly little is known about the long-term effect of nicotine on specific regions of the drug reward pathway in the human brain."
The researchers classified 30 postmortem brain samples into four groups: nonsmoker, nonalcoholic; nonsmoker, alcoholic; smoker, alcoholic; and smoker, nonalcoholic. They measured all of the brain tissue samples for messenger RNA expression of four genes or proteins previously identified as potentially alcohol sensitive: apolipoprotein D, involved in the transport of small lipids; metalloproteinase inhibitor, member 3, a secreted protein that associates closely with the extracellular matrix; glial high-affinity glutamate transporter, a membrane protein that is vital for the removal of glutamate from the synaptic cleft, terminating excitatory neurotransmission; and midkine, which generally is neuroprotective.
"Alcoholism and nicotine appear to have a higher number of genetic targets in common than previously expected," said Ms. Flatscher-Bader. "While we know that alcoholism has a drastic effect on the prefrontal cortex, this study indicates that—while not as dramatic—the effect of chronic smoking on the pre-frontal cortex may be stronger than previously expected.
"The study also indicates that the combination of smoking and drinking may aggravate the negative long-term effects of either drug on the human brain," Ms. Flatscher-Bader added.
