Environmental Modulation of Drug Taking

A variety of animal models have been developed to mimic the interactions between drugs and environment that are thought to play a crucial role in human addiction. A history of exposure to stress, for example, facilitates the development of drug addiction and drug relapse. Furthermore, there is solid evidence that drug-related contextual cues (i.e., environmental stimuli paired with drug taking that have acquired conditioned stimulus properties) can precipitate drug seeking in both humans and animals, indicating the importance of associative learning processes. Finally, there is some evidence (mostly of anecdotal nature) that the circumstances immediately surrounding drug taking can modulate drug intake in ways that are not easily reducible to conditioning or stress. In the past few years some effort has been made to investigate this latter type of drug-environment interaction using animal models. Most importantly, we have recently shown that the context can modulate the reinforcing effects of addictive drugs independently of its physical characteristics. In these studies, some animals were transferred to the test cages immediately before the treatment (Non Resident group), whereas other animals were kept at all times in the test cages (Resident group). Some studies were conducted using a single drug, whereas others employed a polydrug taking procedure. In the present chapter, we will review not only the results obtained using this animal model but also those yielded by translational studies conducted in human addicts. Finally, we will discuss the implications of these findings for the study of drug addiction in humans and animals.