Undoing cocaine's consequences on behavior and brain

A large body of animal research within the field of drug abuse has established that environmental variables can significantly modulate a range of addiction-related behaviors. Stressful and aversive conditions can enhance sensitization to the locomotor stimulant effects of drugs as well as drug-seeking and drug intake (1, 2). Stress-reducing manipulations and nondrug rewards may have the opposite effect, in that they can reduce such behaviors (2, 3). Some of this latter work has shown that the acquisition of addiction-related behaviors such as sensitization and drug self-administration is attenuated in animals housed in “enriched” environments (containing novel toys, food, and conspecifics with which to interact) compared with those housed in standard laboratory conditions (4, 5), but such findings do not present a practical guide to treating drug-addicted humans, who present for treatment only after drug use is acquired. However, in this issue of PNAS, Solinas et al. (6) suggest that environmental enrichment can still exert its beneficial effects on addiction-related behaviors even after they are established. In the first experiment in this article, mice were subjected to a cocaine sensitization paradigm in which a series of repeated cocaine injections enhanced the locomotor response to a subsequent challenge injection of cocaine (7). This sensitized locomotor response is thought to reflect drug-induced alterations in the neural mechanisms that mediate drug reward and addictive behavior (8). As is typical, mice housed in standard laboratory …