The complexity of finding the genes for alcohol dependence derives both from its multigenic and polygenic character but also from the fact that alcohol dependence is co-morbid with other psychiatric disorders and other drug dependencies. Additionally, a host of environmental factors influence the development of alcoholism, and genetic and environmental risk factors may interact substantially (see Schuckit, 1995; Johnson et al., 1998; Goldman et al., 2005). Animal models of alcoholism have an advantage in that they allow for the control of a number of characteristics of the animal's genetic background, prior drug exposure, and to a large extent, the environment (for recent reviews see Rodd et al., 2004; Lovinger and Crabbe, 2005; Bell et al., 2006, Bennett et al 2006; Sanchis-Segura and Spanagel, 2006; Treadwell, 2006). Invertebrates such as C. elegans (Crowder, 2004) and D. melanogaster (Heberlein, 2000) have been used and been found to be informative. Notably, genetic selection studies have established high drinking lines of mice and rats (see McBride and Li, 1998; Bell et al., 2006; Green and Grahame, 2008), and some models have also been developed in non-human primates (see Grant and Bennett, 2003; Barr and Goldman, 2006).
