Voluntary ethanol consumption in rats: the importance of the exposure paradigm in determining final intake outcome

The present investigation examined two methods of ethanol presentation to laboratory rats that have been used to examine the mechanisms mediating voluntary ethanol intake in animals. Experiment I examined whether a restricted access procedure had any significant and meaningful relationship in individual animals to drinking behavior in an unrestricted 24h paradigm. An unselected strain of rats was given free access (unrestricted 24h free choice) to ethanol and water, and later exposed to a restricted 10min access to ethanol. A significant positive relationship between the absolute amount of ethanol consumed in the 24h access paradigm and the amount ingested by the same animals in the restricted access procedure was demonstrated. Experiment 2 examined the extent to which a forced choice preference testing procedure, commonly used in screening ethanol-preferring P rats, was in and of itself sufficient to produce increased levels of ethanol consumption in unselected Long-Evans rats. Results indicated that subjects receiving only 4 days of forced exposure to 10% ethanol consumed, over the next eight ethanol presentations, levels of ethanol exceeding 5g/kg with a 0.60 preference ratio. A microstructural analysis of the pattern of free choice ethanol intake following forced ethanol exposure (Experiment 3) revealed that rats consumed ethanol within short discrete bouts with the largest of these daily bouts consisting of approximately 4ml (0.75g/kg) of 10% ethanol. The amount consumed during the restricted access bout of Experiment 1 was seen to be within the range of the bouts recorded in Experiment 3. These results suggest that consumption of ethanol during the restricted access may simulate an individual bout of ethanol intake during non-restricted access. The results support the notion that many of the different ethanol drinking models used may have a common basis and that the assessment of the amount and pattern of intake across methods and strains may represent different but equally valid approaches to the study of the same underlying mechanisms.