BACKGROUND: Alcohol interferes with how brain cells communicate with one another, coordination, grogginess, impaired memory and loss of inhibitions associated with drunkenness. Yet researchers have been unable to pinpoint how alcohol causes this disruption in the brain. FINDINGS: Now scientists at the David Geffen School of Medicine at UCLA have deciphered how a naturally occurring gene mutation in rats’ brains lowers the animals’ tolerance to alcohol, leading to rapid and acute intoxication after the equivalent of one drink. The UCLA study is the first to identify how the gene variation alters GABA receptors -- specific sites targeted by chemicals from the brain cells -- making them more responsive to very low levels of alcohol. Alcohol enhances the GABA receptors’ influence on brain cells, slowing the cells’ activity and ability to communicate.