Researchers already know that many of the psychological, physiological, and behavioral effects of alcohol are determined by the central nervous system and related neurotransmitter activity, although beliefs about the effects of drinking alcohol are also important.
Symposium proceedings published in the February 2004 issue of Alcoholism: Clinical & Experimental Research present evidence for how genetic variation may influence neurotransmitter activity, thereby having an effect on alcohol sensitivity and subsequent behaviors.
"Activities of neurons, which are specialized cells of the nervous system, influence the release of neurochemicals that cause increases or decreases in brain activity," said Kim Fromme, symposium organizer and associate professor of psychology at The University of Texas at Austin. "Virtually everything we think, feel, sense, and do are determined by activity of these neurochemicals and their related neuronal activity in the brain. Approximately 100 different neurochemicals have been identified, and many of them have been found to be affected by alcohol." Four presentations were given during the symposium at the June 2003 Research Society on Alcoholism meeting in Fort Lauderdale, Florida. Presenters combined human genotyping with laboratory measures of behavior and subjective reports in order to "match" individuals' genetic makeup with the behavioral effects that people experience and exhibit due to alcohol. Some of the key points were:
"Neurotransmitters can be classified in three ways," said Fromme, "excitatory, which means they increase brain activity; inhibitory, which means they decrease brain activity; or modulatory, which means they don't act directly on brain activity but rather influence other neurotransmitters. Dopamine has been classified as both an excitatory and a modulatory neurotransmitter, which means that it tends to increase brain activity, especially when related to pleasure seeking and exploration. As indicated by these findings, dopamine is thought to possibly underlie the stimulant effects of alcohol. GABA, on the other hand, is an inhibitory neurotransmitter. When activated by alcohol, GABA is thought to contribute to the anxiety reduction and relaxation many people experience from alcohol."
"These contradictory findings are perplexing," said Fromme, "but may relate to the populations studied, to variation in the laboratory methods used to assay the genetic material, or to neurotransmitters that interact with SLC6A4 and vary among different people and have yet to be measured."
"Previous studies have shown that aldehyde dehydrogenase and alcohol dehydrogenase contribute to the metabolism of consumed alcohol into its natural and safe components," said Fromme. "If individuals have an impaired ability to metabolize alcohol, via alterations in either of the dehydrogenases, they can have a negative physiological response to alcohol, such as flushing or nausea. This reaction might protect the individual from continuing to drink at a rate that would lead him or her to develop alcohol dependence."
