Short-term isolation increases social interactions of male rats: a parametric analysis.

Frequencies of social interactions were higher in pairs of short-term individually housed male Wistar rats as compared to group-housed animals. This was most pronounced when an individually housed rat and a group-housed conspecific were tested together in the morning under red light conditions. Then, in particular the behavioral elements exploration partner, anogenital investigation, crawl over/mount and social grooming were enhanced. The increases in social interactions was dependent on the duration of the period of individual housing and appeared to be maximal after 4 to 7 days of individual housing. The effect extinguished after repeated testing. The observed behavioral changes were hardly affected by habituation to the test cage and were also present in young animals. The increase in social interactions is apparently not due to a general increase in locomotor or exploratory behavior, since no differences in ambulation between individually- and group-housed animals were observed when they were tested together in the social interaction test, and locomotor activities hardly differed in an open field test procedure.