[Play Fighting in Rats, Selected for the Elimination and the Enhancement of Aggressiveness Towards Human].

As a result of long-term bidirectional selection for aggressiveness towards human, tame and aggres- sive outbred gray rat lines were established. The objective of the current work was to compare play fighting during adolescence in tame, aggressive and unselected rats. It was shown that the selection for the absence of aggression towards human is associated with longer maintenance of some juvenile play features compared to unselected rats. Although, the time of play fighting during different stages of adolescence didn't differ in tame and unselected rats. The selection for enhancement of aggressiveness towards human didn't change the play behavior structure, but caused an increase of play behavior during middle stage of adolescence. It seems that the attenuation of aggression and longer maintenance of some juvenile play features in tame rats is part of fundamental behavioral reorganization during domestication, which is connected with neoteny.