BACKGROUND: It has been confirmed that Fas and Bax respectively mediate the exogenous and endogenous pathways of neuronal apoptosis, and then mediate the neuronal injury after status epilepticus.OBJECTIVE: To comparatively observe the injury of mitochondrial ultrastructure and the expressions of fas and bax in hippocampal tissue of rats with status epilepticus of different latency.DESIGN: A randomized control study.SETTING: Department of Anesthesiology and Department of Neurology, Qilu Hospital of Shandong University.MATERIALS: Totally 110 male adult SD rats of 260-300 g were used. Kainic acid was purchased from American Sigma Company.METHODS: The experiment was carried out in the Pathological Laboratory of Shandong Academy of Medical Sciences between March and July 2005.① Totally 100 SD rats were divided into two groups according to the random number table method:intraperitoneal injection group and caudal venous injection group.The rats were given kainic acid injected intraperitoneally(12 mg/kg)and through caudal vein (10 mg/kg) respectively. Each group was observed at 3, 6, 24, 48 and 72 hours after status epilepticus respectively.Ten rats were selected for each time point, including 2 for examination of electron microscope and 8 for the diction of the fas and bax mRNA expressions. The time and manifestations of seizure were observed, and the seizure was lasted for 2 hours, and then it was terminated by intraperitoneal injection of diazepam (10 mg/kg). Another 10 rats were used as the normal control group, and the materials were taken at 24 hours after status epilepticus, 2 of rats for the examination of electron microscope and 8 of them for the reverse transcription-polymerase chain reaction (RT-PCR). ② The ultrastructure of hippocampal neurons and its mitochondria were observed with transmission electron microscope. ③ The fas and bax mRNA expressions were detected with reverse transcription-polymerase chain reaction (RT-PCR).MAIN OUTCOME MEASURES: The complete form of hippocampal neurons, changes of mitochondrial structure, and the expression of fas and bax mRNA after status epilepticus were observed.RESULTS: All the 110 rats were involved in the analysis of results. ① In the intraperitoneal injection group,the average latency of the occurrence of status epilepticus was (97±11) minutes, mitochondrial swelling in hippocampus was observed under electron microscope, neurons showed apoptosis; In the caudal venous injection group, the latency was (48±13) minutes, hippocampal mitochondria swelled and accompanied by the membranous disintegration, and neurons showed necrosis. ② In the caudal venous injection group, no obvious increases of fas and bax mRNA expressions were observed as compared with the control group (P＞ 0.05). In the intraperitoneal injection group, the fas and bax mRNA expressions began to increase at 6hours after status epilepticus (0.13±0.042, 0.29±0.016), reached the peak values at 48 hours (0.78±0.063,1.04±0.061), and lasted to 72 hours (0.64±0.063, 0.97±0.069) (P ＜ 0.05-0.01 ).CONCLUSION: The mitochondrial injury of hippocampal neurons in rats with longer latency of status epilepticus is mainly the manifestation of apoptosis, which is milder than in the rats with shorter latency manifested by necrosis, and the fas and bax mRNA expressions in hippocampus are higher than in those with shorter latency.