Giving drugs to knockout mice: can they do that?

The past ten years have seen an explosion in the number of genetically modified mice created to aid understanding of the basic mechanisms of learning and memory. There are still significant problems associated with this useful technique, mostly involving the lack of temporal or spatial control over the genetic 'lesion'. By combining the application of drugs that are sub-threshold in wild-type mice with heterozygosity for gene mutations that do not produce effects alone, it is now possible to avoid many of the problems of both the genetic and the pharmacological approaches.