Study On The Seizure-induced Mitochondrion-linked Apoptotic Pathways Of Neurons In Hippocampus

Epilepsy is a kind of neurological syndrome characterized by chronic andunpredictable onset of repetitive seizures. Selective neuronal loss was found in thehippocampus of temporal lobe epilepsy or complex partial seizures. Sustainedseizures cause hippocampus sclerosis followed by memory deficits, psychiatric andcognitive impairment and even dementia. Selective neuronal death likely plays animportant role in the process of epileptogenesis in complex partial seizures. Furtherinsight into the mechanisms involved may provide a window of opportunity to findpotential neuroprotective agents, increase the effect of treatment and decrease the rateof disability. Studies in experimental models of temporal lobe epilepsy have suggestedthat apoptosis is an important type of cell death in hippocampus induced by seizures.Seizures induced activation of caspase-9 and caspase-3 in mitochondrion-linkedapoptotic pathways. Recent studies suggest that several proteins regulate caspaseactivity in apoptotic pathways. XIAP, one of the most potent apoptosis inhibitor, canbind and inhibit the processed forms of caspase-9, caspase-3 and caspase-7 directly.Smac/DIABLO can promote caspase activation by eliminating the caspase-inhibitoryactivity of XIAP. Proapoptotic BAD has been shown to dissociate from its chaperoneprotein to promote caspase activation. A few studies demonstrated the role of BAD inmitochondrion-linked apoptotic pathways induced by seizures, and the role of XIAPand Smac/DIABLO in the apoptotic pathways has not been addressed. As previousstudies suggest the seizures induced by intraamygadaloid injection of KA havesufficient similarities to temporal lobe or complex partial epilepsy,we thereforinvestigated the change of the expression of BAD, Smac/DIABLO and XIAPfollowing seizures in a model of limbic seizures evoked by intraamygadaloid injectionof KA , in order to define the mechanisms underlying the mitochondrion-linkedapoptotic pathways induced by seizures and highlight novel targets for treatment ofbrain injury associated with seizures, and further study to demonstrate theneuroprotection of PTD-XIAP(BIR3-RING) against brain injury associated withseizures and explore its possible mechanisms. 4复旦大学博士论文 摘要Part I The model of limbic seizures induced by intraamygdaloidinjection of kainic acid and spatio-temporal profile of neuronalapoptosis in hippocampus following seizures Animals received intraamygdaloid injection of kainic acid (KA) to establish thefocal limbic seizures model under monitoring with continuous electroencephalogram(EEG) and Laser- Doppler Flowmetry for 1 h, after then diazepam (30mg/kg) wasadministered to terminate the seizures. The apoptotic and surviving neurons inhyppocampus were observed by Terminal deoxynucleotidyl transferrase-mediateddUTP nick end labeling (TUNEL) and cresyl violet staining. Results show that theanimals seizured 15～20 min after KA injection. Type Ⅱ EEG activity precededType Ⅲ and Type Ⅳ EEG activity, and no significant difference was found in theduration of Type Ⅳ EEG activity ( seizures activity characterized by bursts of highfrequency polyspike paroxysmal discharges in EEG). TUNEL-positive cells appearedselectively within the ipsilateral CA3 subfield of the hippocampus 8 h followingseizures cessation, reached maximal at 24 h and decreased at 72 h. The longer theduration of polyspike paroxysmal discharges, the more TUNEL-positive cellsappeared in CA3. There was little change in regional cerebral blood flow (r-CBF)after the seizures. Suggesting that KA-induced seizures lead to neuronal apoptosisselectively in CA3 subfield of hippocampus, which may be associated with a specificcomponent of seizures activity electrographically determined, but not related withr-CBF.Part Ⅱ Seizure-induced mitochondrion-linked apoptotic pathways of...