A new assessment of the ability of oral ethanol to function as a reinforcing stimulus

Background: In animal studies, the ability of ethanol to function as a rein forcer has been described as weak to moderate. This is in contrast with the human condition, where the consumption of alcoholic beverages can result i n a variety of unwanted drinking behaviors. However, when the ethanol self- administration pattern is examined, animal studies over the last several ye ars indicate that the ability of ethanol presentation to maintain behavior may be greater than originally assumed. Methods: We reevaluated the ability of ethanol to function as a reinforcing stimulus in two paradigms by using an analysis of drinking bout characteri stics. Data from previous studies that employed two self-administration mod els were analyzed. With the "dipper" model, small amounts of ethanol are pr esented after each completion of a response requirement; with the "sipper" model, the animal is allowed access to a drinking tube that contains ethano l for an extended period after completing a single response requirement. Fo r both models, the consumption pattern could be characterized as occurring in a bout. Each drinking bout was divided into runs within the bout, and ru n rates and size were analyzed. As well, in the "sipper" model, the data on response requirement size were reviewed to demonstrate the ability of etha nol presentation to maintain high levels of responding in this model. Results: From this assessment, we suggest that ethanol presentation in non- food- or non-water-restricted rats is as reinforcing as many other stimuli generally considered to be strong reinforcers (i.e., food in food-restricte d rats). Using run size, we demonstrated that intake control appears to be regulated by shifts in run size during the bout and not run rate. Conclusions: Assessment of the pattern of ethanol consummatory bouts and th e behaviors that precede them is critical in understanding how ethanol func tions as a reinforcer. By using a drinking pattern analysis, the shifts in the momentary salience of the ethanol stimulus can be evaluated in these an imal models. In addition, the separation of responding required to gain acc ess to ethanol from consumption of ethanol demonstrated that ethanol presen tation in this procedure can be a strong reinforcer for rats.