(C/A). All intruder rats from Experiment lb were exposed to a total of twelve social

defeat sessions. Each intruder from the repeatedly stressed groups was placed in the cage

of a different resident each day of his chronic stress routine.

Social Defeat Stress and Porsolt Swim Test: Experiment 2

 Twenty-four naive male LE rats were assigned to three experimental groups (Table

2-3). The unhandled control rats from Group 1 (n = 8) remained in their original cages

throughout the social defeat portion of the experiment. These rats were exposed to no

chronic and no acute social defeat stress (NC/NA). The intruders from Group 2 (n = 8)

were only exposed to social defeat stress on the final day of the social defeat portion of

the experiment. These rats were exposed to no chronic, just acute stress (NC/A). The

intruders from Group 3 (n = 8) were repeatedly exposed to social defeat stress over the

course of five days, once every 24 h. These rats were exposed to chronic and acute stress

(C/A). Each repeatedly stressed intruder was placed in the cage of a different resident

each day of his chronic stress routine. All of the rats from each of the three groups were

then exposed to the Porsolt swim test.

 Twenty-four hours after the final social defeat session, each rat from Experiment

2 was individually removed from its home cage and placed into a plastic cylinder filled

with approximately 25 cm of clean tap water at 24-270C. The depth of water allowed

each rat to reach the bottom of the cylinder with its tail, with enough head room that the

rat was unable to escape from the tank. The water in each cylinder was changed between

trials. Each rat was subjected, one at a time, to a 15-min swim session then carefully

dried and returned to its home cage. Each Porsolt swim session was run between

8:00a.m. and 10:00a.m., and was videotaped for further analysis.