Another interesting result is GRM3 (metabotropic glutamate 3 receptor gene) on chromosome 7. In animal models of ND, chronic nicotine exposure was associated with increased activity of mGlu3 receptors (Kenny et al., 2003) and administration of an mGlu2/3 agonist was associated with decreased nicotine consumption, and nicotine self-administration was associated with a downregulation of mGlu2/3 receptors (Liechti et al., 2007). In humans, eight studies have found at least nominal associations with SNPs within GRM3 and schizophrenia (Chen et al., 2005; Egan et al., 2004; Fallin et al., 2005; Fujii et al., 2003; Marti et al., 2002; Mossner et al., 2008; Norton et al., 2005; Tochigi et al., 2006), and it is known that rates of smoking are very high (> 90%) in patients with schizophrenia (de Leon et al., 2002).
