Nonetheless, and putting these issues aside for the time being, these studies have helped to identify the mechanisms of action of drugs of abuse underlying their behavioral and physiological effects, including abuse liability and important adverse consequences, such as toxicity and lethality. These models have also been used to confirm the potential for these genes to contribute to addiction based on nomination from human genetic studies. This literature has been reviewed a number of times recently (e.g. (Moriya, Hall, & Sora, 2013; Sora, Li, Igari, Hall, & Ikeda, 2010)) so we will only briefly describe this work here, in order to illustrate the logic that initiated these studies, and focus primarily upon the KO mice that were developed for the main molecular targets of opiates, cocaine and amphetamine-like drugs. Again, the important point here is that these studies were initiated in the mid-1990s based upon a priori assumptions about the importance of certain genes in addiction, including data from candidate gene studies. These studies thus began in the pre-genomic era, and as the ability to examine the association of all
