Exploring the molecular basis of addiction: drug-induced neuroadaptations

Abuse of a number of psychoactive substances can eventually control an individual's behavior by producing dependence and/or addiction. Recent surveys estimate that there are about 200 million users of illegal drugs worldwide, which represent 3.4 % of the world population. An ever-increasing number of neuroscientists are searching for clues regarding the molecular determinants of addictive behavior. The low-hanging fruit would be to study dopamine receptors and transporters in the nucleus accumbens (NAc); however, scientists are now exploring mechanisms far beyond dopaminergic targets. For example, some scientists have chosen to target molecular mechanisms within the hippocampus because of its role in encoding and retrieving information in the central nervous system. In addition, this brain region sends and receives projections from the mesolimbic dopamine system so often implicated in addiction (Bannerman et al, 2004). Further, the hippocampus has been directly implicated in addiction behavior (Vorel et al, 2001), likely because of the fact that there is increasing evidence suggesting that drug addiction represents a conditioning phenomenon that is largely dependent on associations between drug effects and environmental cues (Berke and Hyman, 2000)