The University of Wisconsin—MilwaukeePhencyclidine and amphetamine have been shown to decrease social interactions in humans andanimals. However, it has not been known whether the drugged animal withdraws from surroundingundrugged conspecifics, the undrugged conspecifics avoid the drugged animal, or a combination ofthese two possibilities. To explore this issue a novel tether paradigm was used that limited themovement of one of the rats to one half of the chamber, such that the freely moving rat had theoption of escaping social interactions. Conditions were included in which both undrugged anddrugged rats were the tethered animal. Results indicated that the social withdrawal induced byphencyclidine and amphetamine is a function of the freely moving drugged animals' voluntaryavoidance of social interactions. Results indicate that the tether paradigm successfully pinpointsthe source of social withdrawal.Phencyclidine and amphetamine are drugs of abuse, whichhave been shown to produce social withdrawal in humans(Griffith, Cavanaugh, Held, & Gates, 1972; Nicholi, 1984) andanimals (Beatty, Costelo, & Berry, 1984; Gambill & Kornetsky,1976; Miczek, 1981,1987; Miczek & Yoshimura, 1982; Schior-ring, 1977; Scraggs & Ridley, 1979; Segal & Janowsky, 1978;Steinpreis, Longyhore, & Salamone, 1990). However, previousresearch with animals has not allowed for the determination ofthe source of social withdrawal produced by amphetamine andphencyclidine. To date, all of the literature on these drugs hasfocused on social interactions in freely moving animals, whichmeans that the subjects have no choice of whether or not tointeract socially. Thus, it is not known whether the drugged ratavoids social interactions because of the effects of the drug orwhether the undrugged rat avoids social interactions becauseof the abnormal behavior of the drugged rat. It is also possiblethat both the drugged rat and the undrugged rat may avoideach other. The purpose of the present study was to determinethe source of social withdrawal produced by amphetamine andphencyclidine in rats.MethodSubjectsThe subjects for this study were 84 male albino Sprague-Dawley rats(Rattus norvegicus), which were obtained from Harlan Sprague Dawley(Indianapolis, IN). Forty-eight rats were included in the study ofphencyclidine, and 36 rats were included in the study of amphetamine.Each rat weighed between 300-350 grams at the beginning of theexperiment. All of the rats were housed individually in a colony roomHeidi E. Kuppinger, Amy Harrington, Helen J. Kaczmerek, John J.Panos, and Rhea E. Steinpreis, Department of Psychology, TheUniversity of Wisconsin—Milwaukee.Correspondence concerning this article should be addressed toRhea E. Steinpreis, Department of Psychology, The University ofWisconsin—Milwaukee, 138 Garland Hall, 2441 East Hartford Ave-nue, Milwaukee, Wisconsin 53211. Electronic mail may be sent viaInternet to rhea@csd.uwm.edu.with an ambient temperature of 70 °F and a 12-hr light-dark cycle(lights on at 0700 hr). All observations were conducted during thelights-on cycle. Standard lab chow and water were available ad libitum.DrugsPhencyclidin e (PCP) an d amphetamin wer obtaine from thNational Institute on Drug Abuse (Rockville, MD) and were dissolvedin a 0.9% saline vehicle. Rats receiving drug were injected once aweek. The phencyclidine rats received four injections, one per weekover a 4-week period. These injections included a saline solution (1.0ml/kg) and three doses of phencyclidine (2.0 mg/kg, 4.0 mg/kg, and6.0 mg/kg). The amphetamine rats were injected according to thesame schedule except they received 2.0 mg/kg, 4.0 mg/kg, and 6.0mg/kg of amphetamine and the saline solution. The drug doses wererandomize d acros s the week according to a computer-generateprogram.ProcedureThe between-subjects aspect of the design consisted of threedifferent conditions: both rats untethered, the drugged rat tethered,and the undrugged rat tethered. The within-subjects aspect of thisdesign was composed of four different drug conditions: a salinesolution and three different doses of drug. Each trial included one pairof rats resulting in eight pairs of rats per drug and tether condition forphencyclidine and six pairs of rats per drug and tether condition foramphetamine.In the untethered condition, the rats were injected and placedimmediately into the observation chamber for data collection. Thetethered rats, however, were placed in the rat jacket and tether andallowed to habituate to the situation 5 min before injection. Onceinjected, the injected rat and an uninjected rat were placed at oppositeends of the observation chamber, and the observations began.The observation chamber consisted of a rectangular box with threewooden walls, one plexiglass wall, and a wire mesh floor. Ononeendofthe box, the tether was attached to the wall with an elastic metal cordthat allowed for movement across one half of the chamber. Thedimensions of the chamber were 46 in. x 13.5 in. x 18.25 in. (116.8cm x