with alcohol addiction had an excess of the neurotransmitter GABA there. That, in turn, was probably due to a lack of a chemical called GAT-3, which normally clears out excess GABA. To see whether a shortage of GAT-3 really could cause addiction, Heilig’s team took rats that showed no addiction-like behaviours and lowered the amount of the chemical in their amygdala to the level found in the “hooked” rats. Suddenly, those rats that had previously chosen the sweet solution now compulsively pressed the lever for alcohol, even when given an electric shock. Turning to brains donated by people who had been addicted to alcohol, the team again looked at GAT-3 levels in the amygdala. “It turns out that the picture in human brains is just unbelievably similar to the rats,” says Heilig. “We were blown away.” This was a pioneering study in pinpointing why some people are more vulnerable to alcoholism than others, but there are still unanswered questions, including how exactly GABA and the amygdala relate to addiction. And explaining this link is likely to be just one part of the puzzle, says Heilig. ROLL OF THE DICE Other factors include genetics and personality. A variant of the DRD2 gene “is implicated in nearly all addictive behaviour I can think of”, says Mark Griffiths at Nottingham Trent University in the UK. “But we also know that people who have this don’t
