Seminal studies by Hernandez & Hoebel (1988) demonstrated that food reward increased DA in the NAc as measured by microdialysis [5], and Radhakishun and colleagues reported a similar result in the same year [44]. A key question that remained to be addressed, however, was whether DA output in the NAc was part of a general stimulus-induced arousal process or, alternatively, did DA play a role in the transduction of ingestive reward valence. To address these issues, Hoebel and colleagues performed two studies that examined the responses of NAc DA to conditioned taste stimuli. In the first experiment, extracellular dopamine in the NAc of rats was measured before and after they had developed a conditioned aversion to the taste of saccharin. In rats that had not developed an aversion, intra-orally applied saccharin increased DA. In contrast, DA decreased in response to saccharin in rats that had developed an aversion [45]. A complementary study was performed in rats with a conditioned taste preference to a normally aversive tastant, using a procedure eloquently developed by Sclafani and colleagues [46]. DA in the NAc
