Ethanol reinforced responding in the rat: relation of ethanol introduction to later ethanol responding

Rats, maintained on ad lib food and water, were trained to lever press on a concurrent schedule using water and sucrose (10% w/v) as the fluids presented contingent on responding. Each fluid was associated with a lever and available on a fixed ratio eight (FR8) response requirement. The lever with which each fluid was paired was alternated daily. When stable responding occurred, ethanol was substituted for water, first at low concentrations, and then slowly increased to 5% (v/v). When stable sucrose-ethanol responding was reached, the response requirement for sucrose was altered to fixed ratio requirements of either FR32 or FR64. Moderate, but unstable increments in the number of ethanol responses occurred during the increased sucrose response requirements. Following the sucrose response requirement manipulation, water was substituted for the sucrose. Ethanol responding was found to fall to or below prior baseline levels. Weight reduction by food restriction failed to increase ethanol responding. The levels of ethanol responding resulting from this introduction procedure were always much lower independent of body weight than previously reported levels found in rats trained to respond for ethanol using a different procedure of initial ethanol introduction.