| Object To exploring the relationship of neural protective mechanism with expressiones of p-CREB ,c-Fos , c-Jun and NGF in the hippocampal of neonatal rat after hypoxic-ischemia brain damage and reperfusion of the brain. And in order to offer some theoretical basis for the therapy of HIBD in clinic and the development of some new drugs. METHOD Seven days old Sprague-Dawley rats from seven broods(chosed eight rats from each brood, n=56) were used. Each brood was randomly divided into HIBD group and control group (HIBD groupwas composed of reperfusion for 3h, 6h, 12h, 24h, 48h, 72h, 7d. and the control group was 24h after sham operation). The HIBD model was established by the right common carotid artery temporarily occluded for 3h through a elastic tube circling a thread. HIBD group was exposed to 80ml L-1 oxygen and 920ml I/-1 nitrogen gas mixture for In. After 3h the tube was removed and the common carotid artery was reperfused. The flowing of blood was detected by the Color Doppler. At different reperfused periods rats were perfusion-fixed. The p-CREB and c-Fos were immunohistochemically evaluated at different perfusion period (3h, 6h, I2h, 24h, 48h, 72h, 7d; sham operation in 24h) in different regions of rat'shippocampus. Thionin staining and Hematoxylin-Eosin staining were carried out to observe the apoptosis and survival of neurons. RESULTS The expression of p-CREB reached the peak at 3h and 24h postreperfusion in the right hippocampus of HIBD group, and then decreased to the normal level on the seventh day. On the contralateral hippocampus the immunopositive cells also increased, but less than right side. In the control group the hippocampus' same regions of two sides showed basic immunoreactivity with the specific antibodies, but there were no difference between two sides. In addition the number of immunopositive cells which combinded with the specific antibodies against c-Fos reached the peak at 6h postreperfusion, and the other peak appeared at 48h, then with a gradual decline. On the seven day of reperfusion the number of positive cells were still more than control group (P<0.01). The expression of c-Jun is similar with c-Fos. The expression of NGF markedly increased at 6h, and persisted in the peak at 48h and 72h. After the reperfusion of 7d the expression is still obviously higher than the control group. On the contralateral hippocampus the immunopositive cells also increased, and in the control group the hippocampus' same regions of two sides showed basic and indifferential immunoreactivity. Using the staining we find that the apoptosis of the neurons in CA1 region was marked at 24h postreperfusion. But there were no obvious loss of neurons on the 7d of reperfusion (P>0.05). In addition we count the numbers of survival neurons in the regions of hippocampus at different time of reperfusion, but the neurons had no significant loss on the seventh day of reperfusion campared with the control group. Similarly on the CA3, DG the neuronsremained intact on the morphoplogy. CONCLUSION The persistent activation of CREB in the hippocampus regulates the expression of c-Fos, c-Jun and NGF through the signal transductions and participates in the course of neurons' survival, regeneration, differentiation and repair during the period of post hypoxic-ischemia reperfusion. It is very immportant for the protection of the pyramidal hippocampal neurons on the damaged side, especialy for the sensitive region CA1.
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