Historical influences affecting the behavioral actions of abused drugs

The studies summarized briefly in this chapter provide several examples of experiments in which a behavioral or pharmacologic history produced profound changes in the effects of an abused drug. In many instances these changes were qualitative, that is, the direction of the effects that drug usually has on behavior was modified dramatically. AMPH and cocaine--both of which may normally decrease a particular behavior--will, after a suitable history, produce large increases in the behavior under study. If the behavioral effects of a drug are related to the abuse potential of that drug, then any condition that alters the behavioral effects of that drug could be an important component underlying vulnerability to drug abuse. A noteworthy aspect of the studies that have been described is the lasting influence that prior experience can have on behavior and the behavioral effects of drugs in the absence of overt changes in behavior itself. The traces of past experience may not be apparent in ongoing behavior until a drug is administered. This feature makes drugs an important tool for studying behavioral processes and raises several related questions pertaining to the mechanisms responsible for these effects (Barrett 1986). Although at present there is little information available to answer the several questions raised by these experiments, newer techniques available in the neurosciences promise to help reveal the neurobiological correlates of these changes that should be of general importance in understanding both behavioral and pharmacologic processes.