Drug Addiction: Behavioral Pharmacology of Drug Addiction in Rats

The enormous advances made possible by developments in molecular pharmacology, and the availability of refined preparations that provide exquisite control over many variables, make it very tempting to try and reduce the effects of psychoactive drugs to their direct actions on a receptor, following which a fixed series of intracellular reactions is initiated. The thesis of this article, however, is that the behavioral and psychological effects of psychoactive drugs cannot be reduced to the straightforward consequences of ligand–receptor binding, and attempts to do so neglect the complexity of drug actions. This is because, as put forward by Falk and Feingold, nearly two decades ago, ‘‘the behavioral action of a drug [is due to] a cluster of interactions among the pharmacological substance, the individual set of the organism, and the environmental setting’’; that is, the effects of drugs on behavioral and psychological functions are not only a consequence of the pharmacological effects of the drug, but also on the context in which the drug is experienced. Of course, it has long been known that the physical characteristics of the environment (e.g., in laboratory settings, the size and shape of cage, type of bedding, etc.) can have a large effect on the behavioral actions of drugs. However, of particular importance here is the notion that even when the physical characteristics of the environment are held constant, apparently subtle differences in the ‘psychological context’ powerfully modulate both the acute effects of psychoactive drugs on brain and behavior and, with repeated administration, the ability of these drugs to change the brain. This general theme is illustrated here by discussing a series of studies by Aldo Badiani, Terry Robinson, and colleagues concerning how the neurobehavioral effects of psychostimulant and opioid drugs are modulated by the circumstances surrounding their administration.