Mice: suckling stimulation but not lactation important for maternal aggression

Abstract

Two experiments were conducted in order to examine the role of nipple growth, suckling stimulation by young, and lactation in the maternal aggressive behavior displayed by Rockland-Swiss (R-S) Albino mice. Experiment 1 examined the aggressive behavior of parturient animals and separate groups of pregnant animals hysterectomized at various stages of gestation (Days 9, 11, 13, or 15) and fostered young. Aggressive behavior was present in pregnant animals hysterectomized and fostered young at a time when nipple growth was adequate for suckling to take place (i.e., after Gestation Day 11). In contrast, aggression was not evident in animals hysterectomized and fostered young at a time during gestation when nipple growth was inadequate for suckling to take place (i.e., on or before Gestation Day 11). Experiment 2 examined the aggressive behavior of separate groups of parturient animals fostered young for the first time 0, 1, 2, or 3 weeks postpartum. Parturient animals fostered young for the first time 1 to 3 weeks following parturition did not lactate but received suckling stimulation and exhibited aggression identical to that of animals fostered young for the first time immediately following parturition. The growth of nipples and suckling stimulation are necessary conditions for the display of meternal aggression in mice, but suckling-induced changes in lactogenic hormones may not be necessary.