Abstract: Objective To study the correlation between neonatal maternal separation (MS) and the FOS expression in hypothalamus paraventricular nucleus(PVN) and anterior cingulated cortex(ACC) in central nervous system in developing rats. Methods According to the factorial design, 32 SD rats were divided into four groups with 8 each. Group A1B1 and group A1B2 were MS group. Group A1B1 were imposed on CRD at 6-week age, yet group A1B2 was not imposed on CRD. Group A2B1 and group A2B2 both as the control groups weren’t accepted MS. Group A2B1 was imposed on CRD at 6-week age, while group A2B2 were untreated. The rats were killed after the group A1B1 and A2B1 were imposed on CRD for 2 hours while the group A1B2 and A1B2 were not imposed on CRD. The semiquantity analysis of the FOS-Like Immunoreactivity(FLI) cell numbers of different sites（including PVN and ACC ） in central nervous system were made by immuno- hisrochemical staining. Results Both neonatal MS and CRD at 6-week age could significantly increase the of FLI cell numbers，not only in PVN (F was 7.033,35.212 respectively, p＜0.01) but also in ACC (F was 22.745,15.106 respectively, p＜0.01).There was no interaction between neonatal MS and infant CRD on the expression of FOS in PVN and ACC. Conclusion The increase of FOS expression in PVN and ACC in central nervous system in developing rats is related with neonatal MS obviously.

Key words: FOS expression, Developing rat , Maternal separation, Hypothalamus paraventricular nucleus, Anterior cingulated cortex