Locomotor activity and defecation of rats observed alone and in pairs in repeated open-field sessions.

Several experiments with independent groups have shown social effects on open-field defecation and locomotor activity in male rats. In this experiment these social effects were studied with a different methodological approach, namely, with repeated measurements. One group of 8 animals was tested always alone in an open field over 10 trials on successive days. The second group of 16 animals was also tested alone on Days 1 to 4 and on Day 9, while they were placed in the open field with a conspecific on Days 5 to 8 and again on Day 10. There was markedly reduced defecation and enhanced locomotion with the conspecific present, while with the absence of the conspecific on Day 9 the scores again reached the level of the rats always tested alone. Therefore, the social effects on defecation and locomotion are very robust phenomena which can also be shown with dependent measurements.