Ethanol reinforced behavior assessed with a concurrent schedule.

Oral ethanol (5% v/v) reinforced responding was studied in three rats using a concurrent fixed ratio (FR) schedule with water available at a second lever. First, concurrent (FR8 FR8) responding on both levers for water presentation was established. Then a concurrent (FR8 FR8) water-ethanol presentation schedule was introduced and a food ration was placed in the chamber at the beginning of the session. Within 12 sessions, ethanol responding developed and within-session feeding was discontinued. When stable concurrent water-ethanol performance was achieved, average ethanol responding was 11 times greater than water responding, even when ethanol availability switched from one level to the other. During the one hour session, in some cases, sufficient ethanol was ingested to produce blood ethanol levels between 30 and 50 mg/100 ml. As the ethanol FR requirement was increased for four sessions each to FR10, 12, 14, 16, 18, 20, 40 and 50, rats continued to respond for ethanol, and in some rats, ethanol preference was maintained even when the ethanol FR was 50 while the water FR remained at 8.