A descriptive analysis of the structure and temporal pattern of voluntary ethanol intake within an acquisition paradigm

Objective: The present experiment examined the microstructure and temporal pattern of consummatory behavior to provide insight into the behavioral processes that regulate the acquisition of voluntary oral ethanol intake. Method: A microcomputer-controlled data acquisition system was used to dynamically monitor food, water and ethanol intake in Long Evans rats across acquisition of ethanol drinking initiated through the presentation of a sequence of increasing concentrations of ethanol solutions in a free choice with water. Results: The results showed a biphasic pattern of ethanol intake as a function of presentation of increasing concentrations of ethanol. Total ethanol intake decreased as the ethanol concentration was increased from 2% to 6%, while, inversely, ethanol intake was significantly increased as the concentration went from 6% to 10%. The initial decrease in ethanol intake, across 2% to 6% ethanol, was a function of decreases in both frequency and size of ethanol bouts. The increase in ethanol intake observed following presentation of higher ethanol presentations was solely a function of increased size of ethanol bouts. The increased size of ethanol bouts was paralleled by an increase in the rate of intake which was not evident across presentation of concentrations below 6%. The pattern of intake across the 23-hour daily sessions exhibited no differences across the dark/light cycle in ethanol or water intake as the concentrations of ethanol were increased. The results indicated, however, that food intake was characterized by increases in consumption during the first hour following the presentation of fluids and the night portion of the dark/light cycle. Conclusions: The present study revealed, for the first time, the involvement of differential, concentration dependent, behavioral processes in the mediation of the acquisition of voluntary ethanol intake.