I'h~trma,'~logy Bi~Jchemi.~try& Behavi,,r, Vol. 15, pp. 53%544. 1981. Printed in the U.S.A. Ethanol Reinforced Behavior Assessed with a Concurrent Schedule TIMOTHY A. ROEHRS 1 AND HERMAN H. SAMSON Alcoholism and l)rug Abuse Institute and Department of Psychology, University of Washington Seatth,, WA 98195 Received 17 April 1981 ROEHRS, T. A. AND H. H. SAMSON. Ethanol reinfi~rc'ed behavior asse.~sed with a c'om'urrent schedule. PHARMAC. BIOCHEM. BEHAV. 15(4) 53%544, 1981 .--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 FRS) 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 1 I times greater than water responding, even when ethanol availability switched from one lever 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 FR 10, 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. Ethanol reinforced behavior Concurrent schedules Ethanol drinking Blood ethanol concentrations Rats IN a series of studies, it was demonstrated that rats will press a lever to obtain access to a dipper filled with ethanol solutions in concentrations as high as 32°~ w/v 112, 13, 141. To demonstrate that ethanol per se was maintaining respond- ing, Meisch and Thompson [ 14] showed that the number of ethanol reinforced responses was greater than the number of water reinforced responses. These comparisons were made when water was available in either a previous session or during a two-hour period before the ethanol test, but at no time were both water and ethanol available simultaneously. An alternative demonstration of ethanol as a reinforcer would be to show responding for ethanol when there is simultaneous access to water, the vehicle for ethanol. A concurrent schedule makes two or more schedules of rein- forcement independently and simultaneously available. Re- sponding to each of the two schedules has been used as a measure of choice and is considered a sensitive index of different conditions of reinforcement [5]. A study in rats used a concurrent schedule (CRF CRF) to assess water-reinforced and ethanol-reinforced responding I 11 ]. Ethanol presentation maintained responding at all con- centrations studied (8 to 32c~ w/v), but very few water- reinforced responses were ever made. While this would suggest that oral ethanol can function as a reinforcer and maintain behavior, the exact role of the concurrent schedule requires further assessment using increased behavioral re- quirements. As has been shown for other reinforcers, ethanol rein- forced behavior is subject to control by schedules of rein- forcement. Studies using a single reinforcement schedule have demonstrated an orderly relation between number of ethanol reinforced responses and FR size Ii41, FI size [I], and dipper volumes [6]. All these studies were conducted without the presence of concurrent water presentation, the ethanol vehicle, associated with a second lever. It is not known whether simultaneous access to the ethanol vehicle will alter, for example, the relation between FR size and ethanol reinforced responding. There is evidence showing that the behavioral effect of a drug is altered when a second reinforcer is available 18J. It may be the case that the rein- forcing effect of ethanol is altered in the presence of water, the vehicle for ethanol, depending on the schedule of availa- bility. The present study used a concurrent schedule to assess the relation of ethanol reinforced responding to FR size when concurrent water presentation was available. METHOD A nim a/s Three naive, male Long Evans rats were gradually re- duced to 8~,4 of their free-feeding body weights (at 80cA Rat 6 = 321 g, Rat 7 = 314 g, and Rat 8 -- 309 g) and were main- tained at that level during the water training phase of the experiment (Phase I) by both restricting the daily food sup- ply and allowing only 30 min access to water. During the ethanol testing phase of the experiment (Phase 2), the rats 'Supported by postdoctoral training grant AA07171 from the National Institute on Alcohol Abuse and Alcoholism. Present address: Henry Ford Hospital Sleep Center, 2799 West Grand Boulevard, Detroit. MI 48202. Copyright ' 1981 ANKHO International Inc.--0091-3057/81/100539-06501.10/0