Effects of self-administered alcohol or sucrose preloads on subsequent consumption in the rat

OBJECTIVE: The initial drink of alcohol is often conceptualized as "priming" the individual for the following drinking bout. For the alcoholic, this priming effect has been considered a key for the loss of control that then occurs. Although there have been a few animal studies examining the effects of an investigator-administered ethanol preload on subsequent ethanol self-administration, the effects of a small self-administered oral preload on subsequent consumption have not been examined. METHOD: Adult, male rats, initiated to self-administer ethanol using the sucrose-substitution procedure, were given brief access periods to drink ethanol or water, 5 minutes prior to a second opportunity to press a lever for an additional 20-minute access to a 10% ethanol solution. A second group of rats were trained to press a lever to gain access to a 3% sucrose solution, and the effects of sucrose or water preloads were examined and compared with results in the ethanol group. Results: In the ethanol group, both the ethanol and water preload intakes increased as preload access time increased and were not different from each other. However, ethanol preloads at the longer access times (60 seconds and 120 seconds) decreased subsequent ethanol consumption and at the highest time also affected ethanol-seeking behavior. Equal volumes of water intake at these longer access times had no effects on subsequent ethanol consumption. In the sucrose group, sucrose preload intakes increased as access time increased, but water preload intakes did not. Neither sucrose nor water preloads had any effect on subsequent sucrose consumption. CONCLUSIONS: The data failed to find any priming effect of ethanol preloads in terms of increased subsequent ethanol consumption. It appears that a major factor in the regulation of ethanol intake for the rat in this training procedure is the postingestional effects of ethanol, because taste stimuli did not appear to be important. However, it appears that these ethanol postingestive stimuli are not identical to those involved in the regulation of sucrose consumption.