Re-evaluation of the reward comparison hypothesis for alcohol abuse

This study examined whether various doses of ethanol induced reward or aversion and then evaluated Grigson's reward comparison hypothesis (1997). Rats were given a 0.1% saccharin solution (conditioned stimulus 1 [CS1]) 15 min prior to administration of a 0, 0.05, 0.125, 0.20, 0.35, or 0.50 g/kg dose of ethanol (unconditioned stimulus [US]). The rats were then exposed to a paired compartment (CS2) for 30 min. The low dose of 0.05 g/kg ethanol did not induce conditioned suppression (i.e., conditioned taste aversion [CTA]) or conditioned place preference (CPP). The dose of 0.125 g/kg ethanol induced CPP but not CTA. High doses of ethanol, including 0.35 g/kg and 0.50 g/kg, produced CTA but not CPP. The middle dose of 0.20 g/kg ethanol simultaneously induced CTA and CPP. As a result, the reward comparison hypothesis cannot explain the present finding that the middle dose of ethanol induced CTA and CPP. Meanwhile, the high doses of ethanol induced motivationally aversive CTA but not rewarding CPP. The reward comparison hypothesis should be updated further.