A three-day exposure to 10% ethanol with 10% sucrose successfully initiates ethanol self-administration

Abstract

The initiation phase of ethanol self-administration is difficult to study using the well-established, sucrose-fading procedure due to the changing concentrations of ethanol in the first few days. The purpose of this experiment was to test whether a modified sucrose-substitution procedure in which rats are initially exposed to high concentrations of ethanol and sucrose for three days would successfully initiate ethanol self-administration. Male Long-Evans rats were trained to lever-press with a 10% sucrose solution in which four or 20 responses allowed 20-min access to the solution. Subsequently, rats were exposed to a 3-day period of operant self-administration of 10% sucrose+10% ethanol. This constant-concentration exposure was followed by the standard procedure in which sucrose is completely faded out. The establishment of ethanol self-administration was determined by ethanol intake, pre- and postprocedure two-bottle choice preference tests, and extinction trials. The mean ethanol intake was 2.2 times higher on day 2 compared with day 1 on the 10% sucrose+10% ethanol solution. After fading out the sucrose, the daily intake of 10% ethanol solution over 5 days was stable at approximately 0.57 g/kg. Ethanol preference was approximately threefold higher after the modified sucrose-fading procedure. Responding during a single session extinction test was dramatically increased from 4 to 61+/-13 or 20 to 112+/-22 responses in 20 min. Similar to the standard sucrose-fading method, we did not observe a significant relationship between extinction responding and ethanol intake. Blood alcohol concentrations were 4.5 mM 20 min after consumption began. We conclude that initiation and establishment of ethanol self-administration will occur using this modified sucrose-fading procedure.