The Temporal Sequence of Changes in Gene Expression by Drugs of Abuse

Addiction is a complex maladaptive behavior produced by repeated exposure to rewarding stimuli (1 ). There are two primary features of addiction to all forms of natural and pharmacological stimuli. First, the rewarding stimulus associated with the addiction is a compelling motivator of behavior at the expense of behaviors leading to the acquisition of other rewarding stimuli. Thus, individuals come to orient increasing amounts of their daily activity around acquisition of the rewarding stimulus to which they are addicted. Second, there is a persistence of craving for the addictive stimulus, combined with an inability to regulate the behaviors associated with obtaining that stimulus. Thus, years after the last exposure to an addictive stimulus, reexposure to that stimulus or environmental cues associated with that stimulus will elicit behavior seeking to obtain the reward.