The role of progesterone in pregnancy-induced aggression in mice.
A series of six experiments was performed in order to explore the potential involvement of progesterone (P) in pregnancy-induced aggression (PIA) displayed by Rockland-Swiss mice toward adult male intruders. In Experiment 1, circulating levels of P and aggression were low on gestation Days 6 and 10 while both the behavior and the steroid reached peak levels by gestation Day 14. By gestation Day 18 (the day prior to parturition), serum P was at its lowest level yet aggressive behavior was still intense. Also, individual differences in the display of fighting behavior by pregnant females were not related to circulating P. Experiments 2 and 3 showed that supplemental P treatment to early pregnant female mice did not advance the onset of aggression. Experiment 4 showed that P treatment promoted the onset and elevated the incidence of aggression in virgin mice, but only in those females with intact ovaries. Experiment 5 showed that the aggressive behavior of P-stimulated virgin females was qualitatively and quantitatively different from that exhibited by pregnant mice in that the former exhibited fewer attacks and lunges than the latter. Finally, Experiment 6 showed that the removal of P from aggressive, P-stimulated virgins dramatically attenuated levels of the behavior. This contrasts sharply with the continued fighting behavior observed in late pregnant P-deficient mice. Thus, although P augments aggression in female mice it apparently is not a sufficient stimulus for producing pregnancy-like aggressive behavior.
D000374:Aggression / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002369:Castration; D003692:Delayed-Action Preparations; D005260:Female; D007279:Injections, Subcutaneous; D051379:Mice; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology / Q000502:physiology*
D003692:Delayed-Action Preparations; D011374:Progesterone