Contributions of olfaction to maternal aggression in laboratory rats (Rattus norvegicus): effects of peripheral deafferentation of the primary olfactory system.

We examined the effects in postpartum female rats (Rattus norvegicus) of olfactory deafferentation by intranasal ZnSO4 on maternal aggression and retention of aggression 24 hr after pups are removed. When females were tested with pups, effects of deafferentation depended on postpartum interval; anosmia failed to reduce aggression on Lactation Day 3 (L3), but anosmia was associated with moderate reductions on L8-L12. We propose that postpartum aggression is stimulated initially by hormonal factors associated with late pregnancy but later is supported by exteroceptive stimulation. After removal of pups, although aggression scores were lower across treatment conditions, anosmic females had shorter latencies to attack and tended to elicit more submissive behavior from intruders. Data suggest that odor cues from conspecifics normally inhibit aggression by females, but this inhibition is reduced during lactation.