Abstract: Objective To investigate the effect and protective mechanism of different-dose of oxytocin on maternal aggression in stress model rats during pregnancy period.Methods Female Wistar rats(n=40) were randomly divided into four groups named group A(n=10)，group B(n=10)， group C(n=10) and group D(n=10). During the intervals from 14th day to due day groups(A，B，C) were intraperitoneally injected with 1 mL dilated solution of 0.3， 1.0， 2.0 mg/kg of oxytocin respectively before the forced swimming once a day; meanwhile, group D as control group was given equal volume of normal saline. Some indexes of maternal aggression were tested, such as biting times， keep-down times， attack times， attack duration and latent period, on the 3rd day of parturition .HE staining and immunohistochemical method were used to test changes of oxytocin nuclei injury and oxytocin expression level.Results Regarding biting times group B and C were significantly different from group D(P＜0.01);for attack times group C was different from group D(P＜0.05);as to attack duration group B and C were different from group D (P＜0.05);for attack latent period group B and group C were significantly different from group D（P＜0.01）. HE staining showed that in supraoptic nuclei(SON) the four groups were significantly different in staining， numbers and density（P＜0.01）; in paraventricular nuclei(PVN)，group C was different from group D(P＜0.05）,while there was no difference in group A，B and D（P＞0.05）.Immunohistochemical method showed in SON gray density there was no difference in both group A and D（P＞0.05）; group C was significantly different from group D（P＜0.01）; in PVN gray density， group B was significantly different from group D（P＜0.01）， while there was no difference in group A and D（P＞0.05）.Conclusion Stress would obviously impair maternal aggression of pregnant rats; different doses of oxytocin could regulate such behavior as influenced by stress and meditate rat brain nuclei oxytocin expression level so that swelling and dissolution of nuclei could be attenuated.

Key words: maternal aggression, stress model, oxytocin, HE staining, immunohistochemical method, Wistar rat