Suckling stimulation induces aggression in virgin female mice

Abstract

THE aggression shown by parturient mammals of various species towards strange conspecifics^1,2, referred to as “maternal aggression”, ostensibly serves to protect the young. Although much is known about the aetiology of other forms of aggressive behaviour, no information is available about the mechanism responsible for maternal aggression. We found recently that suckling stimulation may be important in the initiation of aggressive behaviour in parturient mice³. Animals whose nipples were removed before parturition and that were given foster young each day after delivery did not become aggressive. Moreover, we could not induce aggression in virgin female mice by exposing them continuously to foster young. A reason for this may be that virgin females, because of the lack of nipples, which usually develop during pregnancy, did not receive suckling stimulation from foster young. We hypothesised that if nipple growth were induced in virgin females, they would be able to receive suckling stimulation and thus would exhibit aggressive behaviour comparable with that of parturient animals. The results presented here confirm the hypothesis by showing that suckling stimulation induces aggression.