Seizure-Induced Neuronal Necrosis: Implications for Programmed Cell Death Mechanisms

Summary: Purpose : To determine definitively the morphology of neuronal death from lithium-pilocarpine (LPC)-and kainic acid (KA)-induced status epilepticus (SE), and to correlate this with markers of DNA fragmentation that have been associated with cellular apoptosis. Endogenous glutamate release is probably responsible for neuronal death in both seizure models, because neuronal death in both is N -methyl-D-aspartate receptor-mediated.
Methods : SE was induced for 3 hours in adult male Wistar rats with either LPC or KA, and 24 or 72 hours later the rats were killed. One group of rats had brain sections, stained with hematoxylin and eosin and the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) technique, examined by light microscopy and by electron microscopy. A separate group of rats had DNA extracted from the same brain regions examined by electron microscopy in the first group. The extracted DNA was electrophoresed on an agarose gel with ethidium bromide and was examined for the presence or absence of internucleosomal DNA cleavage (DNA "laddering").
Results : Twenty-four and 72 hours after 3 hours of LPC- or KA-induced SE, neuronal death in the hippocampus, amygdala, and piriform, entorhinal, and frontal cortices was morphologically necrotic, in spite of DNA laddering in these regions 24 and 72 hours after SE and positive TUNEL staining in some of the regions 72 hours after SE. Ultrastructurally, necrotic neurons were dark and shrunken, with cytoplasmic vacuoles and pyknotic nuclei with small, irregular, dispersed chromatin clumps.
Conclusions : Our results, together with those of other reports, suggest that programmed cell death-promoting mechanisms are activated by SE in neurons that become necrotic rather than apoptotic and point to the possibility that such mechanisms may contribute to SE-induced neuronal necrosis.     

Lithium-pilocarpine-induced status epilepticus produces necrotic neurons with internucleosomal DNA fragmentation in adult rats

Prolonged and continuous epileptic seizures [status epilepticus (SE)] produce a widespread pattern of neuronal death, primarily in limbic brain regions. Because it has been suggested that seizure-induced neuronal death may be apoptotic in nature, we tested the hypothesis that lithium-pilocarpine-induced status epilepticus (LPCSE) produces apoptotic neurons. LPCSE lasting 3 h was induced in male Wistar rats which were allowed to recover for 24 or 72 h before perfusion-fixation. Neuronal death was assessed by light microscopy with the haematoxylin-and-eosin stain (H&E), with in situ DNA nick-end labelling (TUNEL stain), by electron microscopy, and by agarose gel electrophoresis of DNA extracted from vulnerable brain regions. Ultrastructurally, acidophilic neurons identified with H&E were dark, shrunken and necrotic in appearance, exhibiting pyknotic nuclei, irregular, dispersed chromatin clumps and cytoplasmic vacuolization. No cells with apoptotic features were seen. Acidophilic neurons were found in 21 out of 23 brain regions examined, and comprised 26-45% of the total number of neurons examined. A subset of these neurons (< 10% of the total number of neurons) were TUNEL-positive at 72 h, but not 24 h, after SE. Internucleosomal DNA cleavage (DNA 'laddering') was found in the six brain regions examined ultrastructurally 24 and 72 h after SE. These results indicate that, in adult rats, LPCSE produces neuronal injury with the appearance of necrosis rather than apoptosis. The necrotic neurons show nuclear pyknosis, chromatin condensation and internucleosomal DNA fragmentation, confirming the nonspecificity of these nuclear changes. Internucleosomal DNA cleavage and other programmed cell death mechanisms can be activated by SE in neurons which become necrotic.     

Age-dependent cyclooxygenase-2 induction and neuronal damage after status epilepticus in the postnatal rat hippocampus

PURPOSE: Epileptic seizures lead to age-dependent neuronal damage in the developing brain, particularly in the hippocampus, but the mechanisms involved have remained poorly elucidated. In this study, we investigated the contribution of apoptosis and inflammatory processes to neuronal damage after status epilepticus (SE) in postnatal rats. METHODS: SE was induced by an intraperitoneal injection of kainic acid (KA) in 21- and 9-day-old (P21 and P9) rats. The expression of Bax, Bcl-2 and caspase-3, markers for apoptosis, and cyclooxygenase-2 (COX-2), an indicator for activation of inflammatory processes, were studied from 6 h up to 1 week after SE by Western blotting and immunocytochemistry. Neuronal damage was verified by Fluoro-Jade B staining. RESULTS: In P21 rats, SE resulted in neuronal damage in the CA1 neurons of the hippocampus. COX-2 expression was extensively, but transiently, increased and its immunoreactivity pronouncedly enhanced in several hippocampal subregions, amygdala, and piriform cortex by 24 h after SE. The expression of Bax and caspase-3 remained unchanged, whereas the antiapoptotic factor Bcl-2 transiently decreased by 24 h. Single caspase-3 positive neurons appeared in the CA1 region of both control and KA-treated rats. In P9 rats, no neuronal death was detected, and COX-2 expression and immunoreactivity remained at the control level. DISCUSSION: Our results suggest that SE provokes age-specific effects on COX-2 expression. This together with the activation of putative inflammatory processes may contribute to neuronal cell death in the hippocampus of postnatal rats, whereas caspase-dependent apoptosis seems not to be involved in the death process.     

海人酸致癎大鼠海马CA_3区神经元线粒体与细胞核损伤及caspase-3表达的研究

目的观察海人酸(KA)诱导的癫疒间持续状态(SE)大鼠海马CA3区神经元线粒体与细胞核超微结构的损伤及caspase-3表达的变化。方法用KA诱导大鼠SE 2 h。分别于SE终止后第3 h、12 h、24 h取海马CA3区制作切片,光镜下观察神经元的变化,电镜下观察线粒体和细胞核的超微结构;免疫组化方法检测相同部位caspase-3的表达变化。结果光镜下SE后24 h神经元出现排列散乱、胞体皱缩、胞浆红染以及胞核固缩。电镜下SE后3 h,可见线粒体嵴肿胀及膜的崩解;SE后24 h细胞核染色质明显边聚。Caspase-3平均阳性细胞数及灰度值于SE后12 h较正常对照组显著增加(均P<0.05);24 h出现极显著增加(均P<0.01)。结论SE后早期海马神经元线粒体损伤可能是神经元损伤的关键环节。     

A short episode of seizure activity protects from status epilepticus-induced neuronal damage in rat brain

Kainic acid (KA)-induced status epilepticus (SE) in adult rats results in extensive neuronal damage throughout the limbic system and the loss of selectively vulnerable neuronal populations, particularly CA3 neurons. We investigated the effects of a short episode of seizure activity on neuronal death elicited by a subsequent prolonged SE episode. A short episode of seizure activity was produced by sub-cutaneous (s.c.) injection of KA followed after 1 h by pentobarbital administration. Twenty-four hours later, KA was administered again, and animals were sacrificed 3 days later. Neuronal damage was estimated by visual analysis of neuronal density. Our results show that a short episode of seizure activity did not produce neuronal damage but almost completely protected vulnerable neurons from KA-induced neuronal damage. These results extend to epileptic tolerance the notion of tolerance previously described in the case of ischemia.     

Time-dependent changes in distribution of basic fibroblast growth factor immunoreactive cells in rat hippocampus after status epilepticus

OBJECTIVE: In this study, we aimed to examine time-dependent morphologic changes and quantitative alterations in the density of basic fibroblast growth factor (bFGF)-immunoreactive (ir) astrocytes and CA2 pyramidal neurons in dorsal hippocampus of rats after status epilepticus (SE) induced by kainic acid (KA) injection. METHODS: Wistar albino rats were injected with saline or KA i.p. to investigate time-dependent alterations in morphology and the number of bFGF-ir astrocytes and neurons in the dorsal hippocampus 15, 30 and 90 days after KA injection. RESULTS: Fifteen days after KA injection, gliosis was present throughout the hippocampus and neuronal loss was evident in CA1 and CA3 regions, which was more severe after 30 and 90 days. KA-injected rats demonstrated significantly increased number of both bFGF-ir astrocytes throughout the hippocampus and pyramidal neurons in CA2 after 15 days and decreased number after 30 and 90 days. CONCLUSION: The decrease in the number of bFGF-ir astroglia and neurons in long term after KA injection may indicate a decrease in the production of bFGF and/or number of bFGF-ir cells, suggesting that protective effects of bFGF might be altered during epileptogenesis in the hippocampus.     

Hippocampal programmed cell death after status epilepticus: evidence for NMDA-receptor and ceramide-mediated mechanisms

PURPOSE: Status epilepticus (SE) can result in acute neuronal injury with subsequent long-term age-dependent behavioral and histologic sequelae. To investigate potential mechanisms that may underlie SE-related neuronal injury, we studied the occurrence of programmed cell death (PCD) in the hippocampus in the kainic acid (KA) model. METHODS: In adult rats, KA-induced SE resulted in DNA fragmentation documented at 30 h after KA injection. Ceramide, a known mediator of PCD in multiple neural and nonneural tissues, increased at 2-3 h after KA intraperitoneal injection, and then decreased to control levels before increasing again from 12 to 30 h after injection. MK801 pretreatment prevented KA-induced increases in ceramide levels and DNA fragmentation, whether there was reduction in seizure severity or not (achieved with 5 mg/kg and 1 mg/kg of MK801, respectively). RESULTS: Both ceramide increases and DNA fragmentation were observed after KA-induced SE in adult and in P35 rats. Ceramide did not increase after KA-induced SE in P7 pups, which also did not manifest any DNA fragmentation. Intrahippocampal injection of the active ceramide analogue C2-ceramide produced widespread DNA fragmentation, whereas the inactive ceramide analogue C2-dihydroceramide did not. CONCLUSIONS: Our data support the hypotheses that (a) N-methyl-d-aspartate-receptor activation results in ceramide increases and in DNA fragmentation; (b) ceramide is a mediator of PCD after SE; and (c) there are age-related differences in PCD and in the ceramide response after SE. Differences in the ceramide response could, potentially, be responsible for observed age-related differences in the response to SE.     

Propofol administration reduces hippocampal neuronal damage induced by kainic acid in rats

The goal of this study was to determine whether propofol has protective effect against kainic acid (KA)-induced excitotoxicity. Administration of propofol (25 mg kg-1 i.p.) was done 2 h before KA (10 mg kg-1 i.p.), immediately after, and 2 h, 4 h, 6 h, and 12 h after the KA, and twice daily for an additional three days. Neuronal cell death in CA1 and CA3 subsector of hippocampus was evaluated quantitatively four days after KA. The KA and propofol-injected rats had a greater number of surviving neuronal cells than did KA (and vehicle)-injected rats. Our results suggest that propofol holds potential for the protection of neuronal cells against KA induced excitotoxicity.     

红藻氨酸致痫大鼠海马S100B、CGRP蛋白表达及病理改变

目的 研究红藻氨酸(KA)致痫大鼠海马S100B、降钙素基因相关肽(CGRP)的表达及病理改变.方法 雄性SD大鼠按照完全随机数字表法分成对照组(8只)和模型组(40只),模型组再根据处死时间分为造模后6 h、12 h、24 h、72 h、1周5个亚组,每组8只.模型组采用KA建立颞叶癫痫动物模型,对照组用等体积生理盐水代替KA注射.模型组造模后6 h、12 h、24 h、72 h、1周,对照组注射后24 h取大鼠海马组织行Nissl染色、Timm染色和免疫组化染色,观察S100B、CGRP蛋白的表达情况以及海马神经元和胶质细胞的病理变化.结果 Nissl染色结果显示,模型组大鼠1周后CA3区出现大量固缩的坏死神经元,胞体萎缩,尼氏体消失.Timm染色结果显示,模型组大鼠1周后CA3区始层出现条带状分布的棕色颗粒,齿状回内分子层亦可见少量棕色颗粒.免疫组化染色结果显示,模型组大鼠海马CGRP蛋白大量表达,72 h时达到高峰,同时伴随大量神经元丧失及胶质细胞增生.结论 KA致痫大鼠出现S100B、CGRP蛋白高表达,尼氏体消失,苔藓纤维发芽等一系列病理学改变,推测S100B、CGRP蛋白参与了癫痫发生.

Abstract：

Objective To investigate the expressions of S100B and calcitonin gene related peptide (CGRP) and the pathologic alterations of the hippocampus in kainic acid (KA)-induced epileptic rats. Methods Male SD rats were randomly divided into control group (n=8) and model group (n=40).Animal models of temporal lobe epilepsy were established by intracerebroventricular injection of KA; the same volume of saline was injected into the rats in the control group. Hippocampal tissues within various phases after seizures (6, 12, 24 and 72 h, and 24 h after the success of model making) were performed Nissl staining, Timm staining and immunohistochemical staining. The expressions of S100B and CGRP were observed, and the pathologic alterations of the hippocampal neurons and glial cells were studied.Results All rat models were successfully induced with epileptic seizures. Nissl staining showed that pyknotic neuronal necrosis appeared in the CA3 area of the hippocampus in the model group with cell body atrophy and disappearance of Nissl bodies 1 week after the injection. Timm staining showed that brown particles showed stripped distribution in the CA3 area of the hippocampus and some brown particles in the molecular layer of fascia dentate. Immunohistochemical staining indicated that significant neurons lost and gliosis appeared after seizures with abundant expressions of S100B and CGRP.Conclusion KA-induced epileptic rats express abundant S100B and CGRP and appear such pathological changes as disappearance of Nissl bodies and mossy fiber sprouting, indicating that both S100B and CGRP participate in the onset of epilepsy.     

The temporal evolution of neuronal damage from pilocarpine-induced status epilepticus

The temporal evolution of irreversible neuronal damage from pilocarpine-induced seizures was studied by light microscopy. Neuronal cell death was judged on a 0–3 scale by estimating the percentage of acidophilic neurons in each of 23 brain regions. In addition, in the dorsal dentate hilus (CA4), quantitative cell counts of normal and acidophilic neurons were also performed. A few dead neurons (grade 0.5 damage) appeared in ventral hippocampal CA1 and CA3 regions after 20-min status epilepticus (SE). Slight-to-mild damage (grades 0.5–1.5) occurred in 14 and 12 brain regions after 40-min and 1-h SE respectively, and slight-to-moderate damage (grades 0.5–2.0) was found in 15 regions after 3-h SE. Twenty-four h and 72 h after 3-h SE, there was slight-to-severe damage (grade 0.5–3.0) in 22 and 21 regions respectively. Three-h SE produced more severe damage to 7 brain regions compared to 1-h SE, and 16 regions had more pronounced neuronal injury 24 h after rather than 0–4 h after 3-h SE. Eight brain regions had less damage 72 h compared to 24 h after SE, probably because of progressive neuronal lysis and dropout, but in mediodorsal and lateroposterior thalamic nuclei damage worsened from 24 to 72 h after SE. Neuronal cell counting revealed 20% acidophilic neurons in dorsal dentate hilus after 40-min SE and no difference between the 1-h and 3-h seizure groups (31% vs. 43% acidophilic neurons respectively). Among the 3 groups of rats with 3-h SE and varying recovery periods, the 24-h and 72-h recovery groups had higher percentages of acidophilic neurons (65% and 54% respectively) than the 0–4-h group (43%). Finally, the hippocampal CA2 region and dentate granule cell layer and the caudate-putamen, considered resistant to seizure-induced cell injury, were all damaged from SE lasting 40 min or more.     

Time course changes of estrogen receptor α expression in the adult rat hippocampus after kainic acid-induced status epilepticus

Although estrogens possess neuroprotective and epileptogenic properties, the expression pattern of the estrogen receptor (ER) following status epilepticus (SE) remains unclear. We therefore examined the expression pattern of ER in the adult rat hippocampus after SE. SE was induced in rats by kainic acid (KA; 12 mg/kg, i.p.). ER expression was assessed by immunostaining and Western blotting at various times (24 h, and 7, 14, and 21 days) after SE onset. Immunohistochemistry disclosed ER expression in the CA1 and CA3 pyramidal cells of control rats, whereas, after SE, ER-immunoreactive neurons decreased in number due to neuronal death in the CA1 from days 7 to 21. On the other hand, ER-immunoreactive cells with astrocytic morphology were observed in the CA1 beginning on day 7 after SE. This immunoreactivity increased in proportion to the hypertrophy of astrocytes up to day 21. Western blotting revealed a significant decrease in ER expression on day 7 after SE in comparison with control level. However, ER expression on days 14 and 21 were similar when comparing KA-treated and control rats. These results indicate that reactive astrocytes are important sites of estrogen action in the hippocampal CA1 after SE.     

Programmed cell death in the lithium pilocarpine model: evidence for NMDA receptor and ceramide-mediated mechanisms

Ceramide is known to induce programmed cell death (PCD) in neural and non-neural tissues and to increase after kainic acid (KA) status epilepticus (SE). Ceramide increases have been shown to depend on NMDA receptor activation in the KA model, but these changes have not been studied in the lithium pilocarpine (LiPC) model. Thus, the purpose of this study was to determine if hippocampal ceramide levels increase after LiPC induced SE and if NMDA receptor blockade prevents PCD and any such ceramide increases. We found that LiPC induced SE resulted in ceramide increases and DNA fragmentation in the hippocampus of adult, P21, and P7 rats. The administration of MK-801, the NMDA receptor antagonist, in adults, 15min prior to pilocarpine, prevented ceramide increases, and DNA fragmentation.     

Time-dependent changes in distribution of basic fibroblast growth factor immunoreactive cells in hippocampus after kainic acid injection in rat pups

Five-day-old Wistar albino rats were injected with kainic acid (KA) or saline i.p. to investigate time-dependent alterations in morphology and number of basic fibroblast growth factor (bFGF) immunoreactive (-ir) astrocytes and neurons in hippocampus at 15, 30, and 90 days after the injections. Sections were stained with cresyl violet for morphological evaluation and bFGF immunohistochemistry was used for quantitative evaluation of bFGF-ir cell density. Fifteen days after KA injection, there was gliosis but no neuronal loss although disorganization in CA1, CA3, CA4 pyramidal layers and neuronal loss were evident 30 and 90 days after the injection. KA injected rats demonstrated significantly increased number of bFGF-ir astrocytes throughout the hippocampus and pyramidal neurons in CA2 after 15 days and decreased number of bFGF-ir cells after 30 and 90 days. The decrease in the number of bFGF-ir astroglia and neurons in long term after KA injection may indicate a decrease in the production of bFGF and/or number of bFGF-ir cells suggesting that protective effects of bFGF may be altered during epileptogenesis in hippocampus.     

癫痫持续状态大鼠内质网应激预适应对海马神经元保护作用的实验研究

目的 探讨2-脱氧葡萄糖诱导内质网应激预适应对癫痫持续状态大鼠海马神经元的保护作用及其可能机制。方法 采用2-脱氧葡萄糖连续腹腔注射诱导内质网应激,并在此基础上制备氯化锂-匹罗卡品癫痫持续状态大鼠模型。Nissl染色观察癫痫持续状态后海马神经元损伤情况、计数海马CA1和CA3区存活神经元数目;免疫组织化学检测海马CA3区内质网应激标志物葡萄糖调节蛋白78（GRP78）和X盒结合蛋白1（XBP-1）表达变化。结果 与癫痫持续状态组相比,癫痫持续状态后第7天时内质网应激预适应组大鼠海马存活神经元数目增加,以CA1区显著（t=5.353,P=0.000）。癫痫持续状态组大鼠发作后6 h,海马CA3区GRP78和XBP-1表达水平升高且高于对照组（均P=0.000）,于发作第2天达峰值水平（均P=0.000）;内质网应激预适应组大鼠发作前海马CA3区GRP78和XBP-1表达即高于对照组（均P=0.000）,GRP78在发作后24 h和2 d时维持在峰值水平（均P=0.000）,XBP-1在发作后24 h达峰值水平（P=0.000）;内质网应激预适应组大鼠海马CA3区GRP78和XBP-1表达在癫痫持续状态前,以及癫痫持续状态后6、12、24 h均高于癫痫持续状态组（均P=0.000）,至第2和7天时与癫痫持续状态组之间差异无统计学意义（P〉0.05）。结论 经2-脱氧葡萄糖诱导的内质网应激预适应对癫痫持续状态大鼠海马神经元具有保护作用,而XBP-1-GRP78信号转导通路的活化可能是其机制之一。     

Anticonvulsant and neuroprotective effects of the novel calcium antagonist NP04634 on kainic acid‐induced seizures in rats

Kainic acid (KA)‐induced status epilepticus (SE) is a well‐characterized model of excitotoxic neuronal injury. Excitotoxicity results from activation of specific glutamate receptors, with resultant elevation of intracellular Ca²⁺. The CA1 and CA3 subregions of the hippocampus are especially vulnerable to KA, and this pattern of neuronal injury resembles that occurring in patients with temporal lobe epilepsy. Calcium plays an essential role in excitotoxicity, and accordingly calcium channel inhibitors have been shown to have protective effects in various experimental models of epilepsy and brain injury. Moreover, they also potentiate the antiseizure efficacy of conventional antiepileptic drugs. This study was undertaken to determine whether NP04634, a novel compound, reported as a non‐L‐type voltage‐sensitive calcium channel (VSCC) inhibitor, could prevent the entrance in SE and the neuronal loss evoked by intraperitoneal injection of KA. Our results show that intragastrical administration of NP04634 reduced the percentage of rats that entered SE after KA injection, increased the latency of SE entry, and significantly reduced the mortality of rats that entered SE. Also, NP04634 prevented the loss of hippocampal CA1 and CA3 pyramidal neurons and reduced the gliosis induced by KA. These results point to a potential anticonvulsant and neuroprotective role for NP04634. © 2009 Wiley‐Liss, Inc.     

托吡酯对癫痫大鼠海马神经元超微结构及bcl-2表达的影响

目的观察托吡酯对癫痫大鼠海马神经元超微结构及bcl-2表达的影响,以探讨托吡酯可能的神经保护机制。方法将大鼠随机分为正常对照组、海人酸组(KA)和托吡酯预处理组(TPM)。采用海人酸腹膜腔注射制作癫痫持续状态(SE)模型。在SE模型制作前,TPM组大鼠用TPM(18mg/(kg·d))灌胃15d,同时用等量生理盐水给KA组大鼠灌胃。正常对照组大鼠不作任何处理。在痫性发作终止后6、24、48h取海马,电镜观察神经元的超微结构,免疫组化方法检测bcl-2的表达。结果KA组神经元呈凋亡特征。TPM组神经元结构大致正常,但出现核仁边聚和细胞器增多现象,亦观察到少量凋亡神经元。KA组于SE后6h观察到bcl-2表达增高(与对照组相比,P<0.05),于24h开始减弱,48h仅有微弱表达。TPM组在24h点有bcl-2的强表达(P<0.001),并持续至48h。结论托吡酯预处理能减轻癫痫大鼠神经元的损伤,其神经保护作用可能与bcl-2蛋白的表达上调有关。     

Changes of Cortical Interhemispheric Responses after Status Epilepticus in Immature Rats

Summary:  Purpose: To study cortical excitability after status epilepticus induced in two age groups of immature rats.
Methods: Lithium-pilocarpine status epilepticus was elicited in 12- (SE12) or 25-day-old (SE25) rats. Control siblings received saline instead of pilocarpine. Interhemispheric responses were elicited by stimulation of sensorimotor region of cerebral cortex 3, 6, 9, 13, or 26 days after status. Single biphasic pulses with intensities from 0.2 to 4 mA were used for stimulation; eight responses were always averaged. Amplitude of the first positive and negative waves (i.e., monosynaptic transcallosal responses) was measured and used for construction of input–output (I/O) curves. FluoroJade B was used to visualize degenerating neurons 24 h after status in both age groups.
Results: No significant changes were found at short intervals, but only a tendency to lower amplitudes 3 days after status in SE12 group. Marked changes appeared 26 days after status. The younger group exhibited lower amplitudes than did control rats, whereas SE25 animals generated responses with higher amplitude than did controls (i.e., the I/O curve was steeper. FluoroJade B-positive neurons were scarce in SE12 rats, whereas a substantial number of positive neurons was found in SE25 animals. The positive neurons exhibited characteristics of interneurons, and their distribution in cortical layers differed in the two groups.
Conclusions: Status epilepticus resulted in neuronal death in both SE12 and SE25 animals. Changes in transcallosal evoked potentials were opposite in the two age groups. Augmented amplitude of responses in SE25 rats may indicate an increased cortical excitability.     

Activation of cell death pathway after a brief period of global ischemia in diabetic and non-diabetic animals

Mitochondria play a critical role in the pathogenesis of cerebral ischemia. Acute hyperglycemia has been shown to activate the mitochondria-initiated cell death pathway after an intermediate period of ischemia. The objective of the present study was to determine if diabetic hyperglycemia induced by streptozotocin activates the cell death pathway after a brief period of global ischemia. Five minutes of global ischemia was induced in nondiabetic and diabetic rats. Brain samples were collected after 30 min, 6 h, 1, 3, and 7 days of recirculation as well as from sham-operated controls. Histopathological examination in the hippocampal CA1, CA3, hilus, and dentate gyrus regions, as well as in the cortical and thalamic areas, showed that neuronal death in diabetic animals increased compared to nondiabetic ischemic controls. Neuronal damage maturation occurred after 7 days of recovery in nondiabetic rats, while it was shortened to 3 days of recovery in diabetic animals. Western blot analyses revealed that release of cytochrome c markedly increased after 1 and 3 days of reperfusion in diabetic rats. Caspase-3 activation was evident in the nuclear fraction of the cortex of diabetic rats after 3 days recovery and it was preceded by activation of caspase-9, but not activation of caspase-8. Electron microscopy demonstrated that chromatin condensation and mitochondrial swelling were features of the diabetes-mediated ischemic neuronal damage. However, no apoptotic bodies were observed in any sections examined. These results suggest that a brief period of global ischemia in diabetic animals activates a neuronal cell death pathway involving cytochrome c release, caspase-9 activation, and caspase-3 cleavage, all of which are most likely initiated by early mitochondria damage.     

Mu-calpain mediates hippocampal neuron death in rats after lithium-pilocarpine-induced status epilepticus

Status epilepticus (SE) is a severe clinical manifestation of epilepsy which causes brain damage. The pathological process and underlying mechanisms involved in the programmed cell death (PCD) are still not fully clear. In the current study, rats were induced SE by lithium–pilocarpine administration. Our data showed hippocampal neurons death appeared at 6 h after SE and sustained for 7 days. By blotting the activation of μ-calpain and its specific cleavage of nonerythroid -spectrin (SpII) (145 kDa) was evident at 1 and 3 days after SE, which coincided with Bid activation, apoptosis inducing factor (AIF) translocation and cytochrome c release from mitochondria, whereas, activated caspase-3 and caspase-3-specific fragments of SpII (120 kDa) predominantly appeared at 5 and 7 days after SE. Moreover, MDL-28170, a calpain inhibitor, partially rescued the neuron death and attenuated the expression of activated μ-calpain, cleavage of Bid (15 kDa), AIF translocation and cytochrome c release. Taken together, our study indicated that μ-calpain mediated hippocampal neuron PCD is prior to caspase-3 activation. It functioned via translocation of Bid, AIF and cytochrome c release.