Functional brain imaging studies of the DA system (Table 3) corroborate and expand upon these laboratory findings. Striatal DA release in response to a nicotine or cigarette challenge has been demonstrated repeatedly in both nonhuman primates and humans (Brody et al. 2004b, 2006; Dewey et al. 1999; Marenco et al. 2004; Tsukada et al. 2002), with most of these studies using PET and the radiotracer 11C-raclopride (a specific D2/D3 DA receptor binder) to demonstrate DA release through radiotracer displacement. These studies have reported a wide range of DA concentration change. In two studies that examined the question directly (Marenco et al. 2004; Tsukada et al. 2002), nicotine was found to result in less radiotracer displacement than amphetamine, while it has also been reported that nicotine-induced DA release is comparable in magnitude to that induced by other addictive drugs (Pontieri et al. 1996). Also, an association between 11C-raclopride displacement and the hedonic effects of smoking (defined as elation and euphoria) has been demonstrated (Barrett et al. 2004), though this study did not find an overall difference between the smoking and nonsmoking
