Additional evidence for greater rewarding effects of ethanol among adolescents than adults was recently obtained through the assessment of ethanol-induced tachycardia, an autonomic measure shown to be positively correlated with DA release in the ventral striatum (Boileau et al., 2003), and with subjective measures of ethanol’s rewarding effects in human studies (Conrod et al., 1998; Holdstock & de Wit, 2001; Holdstock et al., 2000). Ristuccia & Spear (2008) used ethanol-induced tachycardia to index the hedonic value of ethanol in both adolescent and adult male rats during a 2-hr limited-access, oral self-administration session. Under these conditions, adolescent rats not only consumed more ethanol than adults, an age difference in ethanol intake that has been repeatedly observed (Brunell & Spear, 2005; Doremus et al., 2005; Vetter et al., 2007), but they also showed a significantly greater increase in heart rate when drinking the ethanol relative to the saccharin control solution—a difference not observed among adults. To the extent that the tachycardic responses to self-administered ethanol represent a valid index of its rewarding/positive hedonic effects, these results suggest that adolescents are more likely than adults to voluntarily consume sufficient amounts of ethanol to gain its rewarding benefits.
