BACKGROUND: Under the normal circumstance, there exist some synapses with inactive functions in central nervous system (CNS), but these functions are activated following nerve injury. At the early stage of brain injury, the abnormal functions of brain are varied, and they have very strong plasticity and are corrected easily.OBJECTTVE: To observe the changes of neuronal morphology in hippocampal CA1 region and memory function in newb rats with hypoxic-ischemic encephalopathy(HIE) from ischemia 6 hours to adult.DESTGN: Completely randomized grouping, controlled experiment.SETTING: Taian Health Center for Women and Children; Taishan Medical College.MATERTALS: Altogether 120 seven-day-old Wistar rats, of clean grade, were provided by the Experimental Animal Center, Shandong University of Traditional Chinese Medicine. Synaptophysin (SYN) polyclonal antibody was provided by Maixin Biological Company, Fuzhou.METHODS: This experiment was carried out in the Laboratory of Morphology, Taishan Medical College between October 2000 and December 2003. ① The newb rats were randomly divided into 2 groups: model group and control group, 60 rats in each group. Five rats were chosen from each group at postoperative 6 hours, 24hours, 72 hours, 7 days, 2 weeks and 3 weeks separately for immunohistochemical staining. Fifteen newb rats were chosen from each group at postoperative 4 weeks and 2 months separately for testing memory ability(After test, 5 rats from each group were sacrificed and used for immunohistochemical staining) ② The right common carotid artery of newb rats of model group was ligated under the sthetized status. After two hours of incubation, the rats were placed for 2 hours in a container filled with nitrogen oxygen atmosphere containing 0.08 volume fraction of oxygen, thus, HIE models were created; As for the newb rats in the control group, only blood vessels were isolated, and they were not ligated and hypoxia-treated. ③Thalamencephal tissue sections of newb rats of two groups were performed DAB developing and haematoxylin slight staining. Cells with normal nucleous in 250 μm-long granular layer which started from hippocampal CA1 region were counted with image analysis system under high-fold optical microscope (×600),and the thickness of granular layer was measured. The absorbance (A) of positive reactant of SYN in immunohistochemically-stained CA1 region was measured. Leing and memory ability were measured with step through test 3 times successively. ④ t test and paired t test were used for omparing intergroup and intragroup difference of measurement data respectively, and Chi-square for comparing the difference of enumeration data..MATN OUTCOME MEASURES: Comparison of cytological changes in ippocampal CA1 region and memory ability at different postoperative time points between two groups.hippocampal CA1 region: In the control group, with aging, perikaryon, nucleus and nucleolus in cortex of parietal lobe were significantly increased, Nissl body was compacted, the amount of neurons was declined, but the A of SYN positive reactant was relatively increased. In the model group, at postoperative each time point,neurons were seriously shrunk and dark-stained, nucleus was contracted, chromatin was condensed, nucleolus was unclear, even cells disappeared, especially the cells in 6 hours and 24 hours groups. The amount of neurons with normal morphology in hippocampal CA1 region and granular layer thickness in the model group at postoperative each time point were significantly less or smaller than those in the control group at postoperative 6 hours respectively (t =3.002-1.254, P ＜ 0.01 ). The A value of SYN positive reactant at postoperative 2, 3 and results of leing and memory ability: In the first test, there was no significant difference in the ratio of rats which kept memory ability between two groups (P ＞ 0.05); In the third test, the ratio of rats which kept memory ability in the model group was significantly lower than that in the control group at postoperative 4 weeks and 2months[53%(8/15), 100%(15/15); 60%(9/15), 93%(14/15), χ 2=2.863,2.901, P ＜ 0.01 ].CONCLUSTON: The destroyed hippocampal structure induces the decrease of leing and memory ability of developmental rats. Early interference can increase the quality of neurons and also promote functional development of the nervous system.