Knockout mouse models in pain research

Gene targeting in mice by homologous recombination is a powerful approach to study the role of specific genes in vivo. This technology is now applied to pain-related genes to understand molecular mechanisms of nociceptive behaviors. In this chapter, we provide detailed methodological information for the construction of knockout animals, exemplified by the generation of mice lacking opioid receptor genes. We report our protocols for the production, maintenance, transfection, and selection of embryonic stem (ES) cells, as well as for blastocyst injection, which are generally applicable to any gene-targeting project. We also describe strategies for the construction of targeting vectors, as well as for ES cell and animal genotyping, in the context of mu, delta, and kappa opioid receptor genes. We finally provide a few examples of mouse phenotyping in pain behavioral assays.