Effects of progesterone and nesting materials on response prevention and extinction of avoidance in rats

Female rats received either progesterone or saline injections prior to learning a simple one-way avoidance response. During a 10-min response prevention procedure half of the animals in each group had nesting material present while the remaining rats did not. The availability of nesting material during response prevention hastened extinction while progesterone injections significantly increased the frequency of nesting activities during response prevention but did not affect rate of extinction. The availability of nesting materials increased the frequency of standing but reduced the frequency of crouching. The results were discussed in terms of the role of ethological displacement activities during response prevention as well as the role of ‘relaxational’ activities as discussed by Baum and Denny.