Preservation of mitochondrial integrity and energy metabolism during experimental status epilepticus leads to neuronal apoptotic cell death in the hippocampus of the rat

Status epilepticus results in mitochondrial damage or dysfunction and preferential neuronal cell loss in the hippocampus. Since a critical determinant of the eventual cell death fate resides in intracellular ATP concentration, we investigated whether mitochondrial integrity and level of energy metabolism are related with apoptotic cell death in specific hippocampal neuronal populations. A kainic acid (KA)-induced experimental temporal lobe status epilepticus model was used. Qualitative and quantitative analysis of DNA fragmentation, TUNEL immunohistochemistry, double immunofluorescence staining for activated caspase-3, electron microscopy or measurement of ATP level in the bilateral hippocampus was carried out 1, 3 or 7 days after microinjection unilaterally of a low dose of KA (0.5 nmol) into the CA3 hippocampal subfield. Characteristic biochemical (DNA fragmentation), histochemical (TUNEL or activated caspase-3 staining) or ultrastructural (electron microscopy) features of apoptotic cell death were presented bilaterally in the hippocampus 7 days after the elicitation of sustained hippocampal seizure activity by microinjection of KA into the unilateral CA3 subfield. At the same time, CA3 or CA1 subfield on either side manifested a maintained ATP level; alongside relatively intact mitochondria, rough endoplasmic reticulum, Golgi apparatus or cytoplasmic membrane in hippocampal neurons that exhibited ultrastructural features of apoptotic cell death. Our results demonstrated that preserved mitochondrial ultrastructural integrity and maintained energy metabolism during experimental temporal lobe status epilepticus is associated specifically with apoptotic, not necrotic, cell death in hippocampal CA3 or CA1 neurons.     

Contribution of nitric oxide, superoxide anion, and peroxynitrite to activation of mitochondrial apoptotic signaling in hippocampal CA3 subfield following experimental temporal lobe status epilepticus

Purpose: One cellular consequence of status epilepticus is apoptosis in the hippocampal CA3 subfield. We evaluated the hypothesis that the repertoire of cellular events that underlie such elicited cell death entails mitochondrial dysfunction induced by an excessive production of nitric oxide synthase II (NOS II)‐derived NO, increased superoxide anion (O₂^?) production, and peroxynitrite formation. Methods: In Sprague‐Dawley rats, kainic acid was microinjected unilaterally into the hippocampal CA3 subfield to induce bilateral seizure‐like electroencephalography (EEG) activity. The effects of pretreatments with various test agents on the induced O₂^? production, peroxynitrite formation, mitochondrial respiratory chain enzyme activities, cytochrome c/caspase‐3 signaling, and DNA fragmentation in bilateral CA3 subfields were examined. Results: Significantly and temporally correlated increase in O₂^? and peroxynitrite levels (3 to 24 h), depressed mitochondrial Complex I activity (3 h), enhanced translocation of cytochrome c to cytosol (day 1), and augmented activated caspase‐3 (day 7) and DNA fragmentation (day 7) were detected bilaterally in hippocampal CA3 subfields after the elicitation of sustained seizure. Pretreatment with microinjection into the bilateral hippocampal CA3 subfield of a water‐soluble formulation of coenzyme Q₁₀; a selective NOS II inhibitor, S‐methylisothiourea; a superoxide dismutase mimetic, 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl; an active peroxynitrite decomposition catalyst, 5,10, 15,20‐tetrakis‐(N‐methyl‐4‐pyridyl)‐ porphyrinato iron (III); or a peroxynitrite scavenger, L‐cysteine significantly blunted these cellular events. Discussion: Prolonged seizures prompted NO‐, O₂^?‐, and peroxynitrite‐dependent reduction in mitochondrial respiratory enzyme Complex I activity, leading to cytochrome c/caspase‐3‐dependent apoptotic cell death in the hippocampal CA3 subfield after induction of experimental temporal lobe status epilepticus.     

Seizure-dependent modulation of mitochondrial oxidative phosphorylation in rat hippocampus

Mitochondrial function is a key determinant of both excitability and viability of neurons. Here, we demonstrate seizure-dependent changes in mitochondrial oxidative phosphorylation in the epileptic rat hippocampus. The intense pathological neuronal activity in pilocarpine-treated rats exhibiting spontaneous seizures resulted in a selective decline of the activities of NADH-CoQ oxidoreductase (complex I of the respiratory chain) and cytochrome c oxidase (complex IV of respiratory chain) in the CA3 and CA1 hippocampal pyramidal subfields. In line with these findings, high-resolution respirometry revealed an increased flux control of complex I on respiration in the CA1 and CA3 subfields and decreased maximal respiration rates in the more severely affected CA3 subfield. Imaging of mitochondrial membrane potential using rhodamine 123 showed a lowered mitochondrial membrane potential in both pyramidal subfields. In contrast to the CA1 and CA3 subfields, mitochondrial oxidative phosphorylation was unaltered in the dentate gyrus and the parahippocampal gyrus. The changes of oxidative phosphorylation in the epileptic rat hippocampus cannot be attributed to oxidative enzyme modifications but are very likely related to a decrease in mitochondrial DNA copy number as shown in the more severely affected CA3 subfield and in cultured PC12 cells partially depleted of mitochondrial DNA. Thus, our results demonstrate that seizure activity downregulates the expression of mitochondrial-encoded enzymes of oxidative phosphorylation. This mechanism could be invoked during diverse forms of pathological neuronal activity and could severely affect both excitability and viability of hippocampal pyramidal neurons.     

Mitochondrial complex I inhibition produces selective damage to hippocampal subfield CA1 in organotypic slice cultures

The effects of mitochondrial respiratory chain inhibitors and the excitotoxinN-methyl-D-aspartate (NMDA) on cell death in hippocampal subfields CA1 and CA3 were examined in hippocampal organotypic slice cultures. Slice cultures, 2–3 week old, were exposed for 1 h to either the Complex 1 inhibitors, rotenone or 1-methyl-4-phenylpyridium (MPP⁺), the Complex II inhibitor 3-nitropropionic acid (3-NP), or the excitotoxin NMDA. Cell death was examined 24 and 48 h following treatment, by measuring propidium iodide (PI) fluorescence. Treatment with 1 μM rotenone caused greater cell death in hippocampal subfield CA1 than CA3. Exposure of hippocampal slice cultures to 10 μM rotenone, to MPP⁺ or to NMDA resulted in damage to both CA1 and CA3 subfields. 3-NP produced little damage in either subfield. The data suggest that mitochondrial complex I inhibition can produce selective cell damage in hippocampus and in this regard is similar to that observed following hypoxia/ischemia.     

Transient elevation in plasma prolactin level in rats with temporal lobe status epilepticus.

Microinjection of kainic acid into the CA3 subfield of hippocampus in anesthetized rats elicited seizure-like hippocampal EEG activity that persisted for more than 180 minutes. There was a concomitant rise in plasma prolactin level that peaked at 15 to 20 minutes but endured less than 60 minutes. We conclude that plasma prolactin exhibited only transient elevations during experimental temporal lobe status epilepticus in rats.     

Ketogenic diet reduces Smac/Diablo and cytochrome c release and attenuates neuronal death in a mouse model of limbic epilepsy

The ketogenic diet (KD) is effective in the treatment of refractory epilepsy, yet the molecular mechanisms underlying its antiepileptic effects have not been determined. There is increasing evidence that neuronal cell death induced by seizures via mitochondrial pathway and seizures can lead to mitochondrial release of cytochrome c, and we have shown previously that translocation of Smac/DIABLO into the cytosol play a role in the brain damage in a model of limbic seizure. In the present study, we explored the neuroprotective effect of KD in C57BL/6 mice with seizures induced by kainic acid (KA). Status epilepticus triggered by intra-amygdaloid microinjection of KA lead to neuronal death in the selective ipsilateral CA3 subfield of the hippocampus and mitochondrial release of Smac/DIABLO and cytochrome c. We found that KD significantly decreased neuronal death in the ipsilateral CA3 at 24h after KA-induced seizures. Furthermore, KD reduced Smac/DIABLO and cytochrome c release from mitochondria, attenuated activation of casepase-9 and caspase-3 following seizures. These results demonstrate that the neuroprotective effect of KD against brain injury induced by limbic seizures, at least partially, is associated with inhibition of mitochondrial release of Smac/DIABLO and cytochrome c.     

Resistance of immature hippocampus to morphologic and physiologic alterations following status epilepticus or kindling.

Seizures in adult rats result in long-term deficits in learning and memory, as well as an enhanced susceptibility to further seizures. In contrast, fewer lasting changes have been found following seizures in rats younger than 20 days old. This age-dependency could be due to differing amounts of hippocampal neuronal damage produced by seizures at different ages. To determine if there is an early developmental resistance to seizure-induced hippocampal damage, we compared the effects of kainic acid (KA)-induced status epilepticus and amygdala kindling on hippocampal dentate gyrus anatomy and electrophysiology, in immature (16 day old) and adult rats. In adult rats, KA status epilepticus resulted in numerous silver-stained degenerating dentate hilar neurons, pyramidal cells in fields CA1 and CA3, and marked numerical reductions in CA3c pyramidal neuron counts (-57%) in separate rats. Two weeks following the last kindled seizure, some, but significantly less, CA3c pyramidal cell loss was observed (-26%). Both KA status epilepticus and kindling in duced mossy-fiber sprouting, as evidenced by ectopic Timm staining in supragranular layers of the dentate gyrus. In hippocampal slices from adult rats, paired-pulse stimulation of perforant path axons revealed a persistent enhancement of dentate granule-cell inhibition following KA status epilepticus or kindling. While seizures induced by KA or kindling in 16-day-old rats were typically more severe than in adults, the immature hippocampus exhibited markedly less KA-induced cell loss (-22%), no kindling-induced loss, no detectable synaptic rearrangement, and no change in dentate inhibition. These results demonstrate that, in immature rats, neither severe KA-induced seizures nor repeated kindled seizures produce the kind of hippocampal damage and changes associated with even less severe seizures in adults. The lesser magnitude of seizure-induced hippocampal alterations in immature rats may explain their greater resistance to long-term effects of seizures on neuronal function, as well as future seizure susceptibility. Conversely, hippocampal neuron loss and altered synaptic physiology in adults may contribute to increased sensitivity to epileptogenic stimuli, spontaneous seizures, and behavioral deficits.     

Limbic seizures without brain damage after injection of low doses of kainic acid into the amygdala of freely moving rats

Kainic acid (KA, 8-15 ng) was injected into the amygdala of conscious freely moving rats via chronically implanted fused silica cannulas. At 15-25 min after the injection, most rats suffered a limbic seizure attack of short duration, consisting of mastication, forelimb clonus, and raising on hind limbs, behaviorally indistinguishable from kindled seizures. Typically, the attack was followed by stereotypies, intense exploration, and by 1 or 2 more attacks. About 60 min after the injection, most rats appeared normal again and histopathological changes in their brains did not exceed those seen in vehicle-injected rats. In 3 cases, however, recurrent seizures culminated in behavioral status epilepticus 60-90 min after the injection. The status epilepticus was stopped by i.p. injection of diazepam (10 mg/kg) after a duration of 10 min (1 case) and 30 min (2 cases), respectively. After 10 min status epilepticus, we observed marginal neuronal damage with slight gliosis in both hippocampi (CA3 and CA1); after 30 min, hippocampal histopathology was more pronounced, with additional necrosis of the ipsilateral piriform cortex. After 0.8 microgram KA, a hundredfold higher dose, the incidence of limbic seizures during the first 40 min was not significantly higher (9/12) than after the lower KA doses (13/19). However, a significantly higher proportion of rats exhibited long-lasting seizure activity, associated with confluent destruction of CA3 pyramidal cells and additional seizure-related brain damage. Our results show that limbic motor seizures do not inevitably lead to histopathological changes in the brain, provided they do not culminate in a state of permanent seizure activity.     

Characterization of neuronal death induced by focally evoked limbic seizures in the C57BL/6 mouse

Research into the molecular mechanisms of epileptic brain injury is hampered by the resistance of key mouse strains to seizure-induced neuronal death evoked by systemically administered excitotoxins such as kainic acid. Because C57BL/6 mice are extensively employed as the genetic background for transgenic/knockout modeling in cell death research but are seizure resistant, we sought to develop a seizure model in this strain characterized by injury to the hippocampal CA subfields. Adult male C57BL/6 mice underwent focally evoked seizures induced by intraamygdala microinjection of kainic acid. Kainic acid (KA) effectively elicited ipsilateral CA3 pyramidal neuronal death within a narrow dose range of 0.1-0.3 microg, with mortality < 10%. With employment of the most consistent (0.3 microg) dose, seizures were terminated 15, 30, 60, or 90 min after KA by diazepam. Damage was largely restricted to the ipsilateral CA3 subfield of the hippocampus, but injury was also consistent within CA1, suggesting that this mouse model better reflects the hippocampal neuropathology of human temporal lobe epilepsy than does the rat, in which CA1 is typically spared. Confirming this CA1 injury as seizure specific and not a consequence of ischemia, we used laser-Doppler flowmetry to determine that cerebral perfusion did not significantly change (97% to 118%) over control. Degenerating cells were > 95% neuronal as determined by neuron-specific nuclear protein (NeuN) counterstaining of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeled (TUNEL) brain sections. Furthermore, TUNEL-positive cells often exhibited the morphological features of apoptosis, and small numbers were positive for cleaved caspase-3. These data establish a mouse model of focally evoked seizures in the C57BL/6 strain associated with a restricted pattern of apoptotic neurodegeneration within the hippocampal subfields that may be applied to research into the molecular basis of neuronal death after seizures.     

Activation of calcium/calmodulin‐dependent protein kinase IV and peroxisome proliferator‐activated receptor γ coactivator‐1α signaling pathway protects against neuronal injury and promotes mitochondrial biogenesis in the hippocampal CA1 subfield after transient global ischemia

Delayed neuronal cell death occurs in the vulnerable CA1 subfield of the hippocampus after transient global ischemia (TGI). We demonstrated previously, based on an experimental model of TGI, that the significantly increased content of oxidized proteins in hippocampal CA1 neuron was observed as early as 30 min after TGI, followed by augmentation of PGC‐1α expression at 1 hr, as well as up‐regulation of mitochondrial uncoupling protein 2 (UCP2) and superoxide dismutases 2 (SOD2). Using the same animal model, the present study investigated the role of calcium/calmodulin‐dependent protein kinase IV (CaMKIV) and PGC‐1α in delayed neuronal cell death and mitochondrial biogenesis in the hippocampus. In Sprague‐Dawley rats, significantly increased expression of nuclear CaMKIV was noted in the hippocampal CA1 subfield as early as 15 min after TGI. In addition, the index of mitochondrial biogenesis, including a mitochondrial DNA‐encoded polypeptide, cytochrome c oxidase subunit 1 (COX1), and mitochondrial number significantly increased in the hippocampal CA1 subfield 4 hr after TGI. Application bilaterally into the hippocampal CA1 subfield of an inhibitor of CaMKIV, KN‐93, 30 min before TGI attenuated both CaMKIV and PGC‐1α expression, followed by down‐regulation of UCP2 and SOD2, decrease of COX1 expression and mitochondrial number, heightened protein oxidation, and enhanced hippocampal CA1 neuronal damage. This study provides correlative evidence for the neuroprotective cascade of CaMKIV/PGC‐1α which implicates at least in part the mitochondrial antioxidants UCP2 and SOD2 as well as mitochondrial biogenesis in ischemic brain injury. © 2010 Wiley‐Liss, Inc.     

Nitric oxide synthase immunoreactivity in the rat hippocampus after status epilepticus induced by perforant pathway stimulation

Nitric oxide has recently been implicated in mediation of neuronal excitotoxicity and damage. This study aimed at elucidating the changes in the expression of neuronal isoform of nitric oxide synthase (nNOS) in the hippocampus after status epilepticus induced by perforant pathway stimulation. nNOS-immunoreactivity (nNOS-ir) and neuronal damage, assessed by silver staining, were evaluated separately in different hippocampal subfields 2 weeks after induction of status epilepticus. Perforant pathway stimulation resulted in an increase in the number of nNOS-immunoreactive neurons in the stratum radiatum of the CA1 and CA3 subfields of the hippocampus proper, and the hilus of the dentate gyrus. The morphology and distribution of the nNOS-ir neurons resembled that of interneurons. No correlation of the number of nNOS-ir neurons to the neuronal damage score was observed. Our results suggest that status epilepticus provokes a de novo expression of nNOS protein, and the nNOS expressing neurons may be selectively resistant to epileptic brain injury.     

Glutamic acid decarboxylase-67-positive hippocampal interneurons undergo a permanent reduction in number following kainic acid-induced degeneration of ca3 pyramidal neurons

Kainic acid (KA)-induced degeneration of CA3 pyramidal neurons leads to synaptic reorganization and hyperexcitability in both dentate gyrus and CA1 region of the hippocampus. We hypothesize that the substrate for hippocampal inhibitory circuitry incurs significant and permanent alterations following degeneration of CA3 pyramidal neurons. We quantified changes in interneuron density (N(v)) in all strata of the dentate gyrus and the CA1 and CA3 subfields of adult rats at 1, 4, and 6 months following intracerebroventricular (icv) KA administration, using glutamic acid decarboxylase-67 (GAD-67) immunocytochemistry. At 1 month postlesion, GAD-67-positive interneuron density was significantly reduced in all strata of every hippocampal region except stratum pyramidale of CA1. The reduction in GAD-67-positive interneuron density either persisted or exacerbated at 4 and 6 months postlesion in every stratum of all hippocampal regions. Further, the soma of remaining GAD-67-positive interneurons in dentate gyrus and CA3 subfield showed significant hypertrophy. Thus, both permanent reductions in the density of GAD-67-positive interneurons in all hippocampal regions and somatic hypertrophy of remaining GAD-67-positive interneurons in dentate gyrus and CA3 subfield occur following icv KA. In contrast, the density of interneurons visualized with Nissl in CA1 and CA3 regions was nearly equivalent to that in the intact hippocampus at all postlesion time points. Collectively, these results suggest that persistent reductions in GAD-67-positive interneuron density observed throughout the hippocampus following CA3 lesion are largely due to a permanent loss of GAD-67 expression in a significant fraction of interneurons, rather than widespread degeneration of interneurons. Nevertheless, a persistent decrease in interneuron activity, as evidenced by permanent down-regulation of GAD-67 in a major fraction of interneurons, would likely enhance the degree of hyperexcitability in the CA3-lesioned hippocampus.     

Status epilepticus results in reversible neuronal injury in infant rat hippocampus: novel use of a marker

Despite ready induction of severe limbic status epilepticus by systemic kainic acid (KA) in infant rats, excitotoxic neuronal injury has not been observed. The mechanisms of this resistance of the immature hippocampus to excitotoxicity are unknown. Acid fuchsin stain has been used as a marker of irreversibly injured neurons in the adult brain. We speculated that the dye might map reversibly injured neurons in the infant. Subsequent to KA-induced status epilepticus in 11-day-old rats, acid fuchsin stain was evident in the hippocampal CA3, CA1, dentate gyrus and hilus by 24 h, peaked at 48 h and disappeared by 6 days, without evidence for neuronal loss. Acid fuchsin may be a useful tool for delineating the distribution of reversibly injured immature neurons in experimental seizure paradigms.     

Hippocampal subfields alterations in adolescents with post‐traumatic stress disorder

Reexperiencing symptoms in adolescent Post‐Traumatic Stress Disorder (PTSD) are characterized by the apparition of vivid intrusive images of the traumatic event. The emergence of these intrusions is thought to be related to a deficiency in context processing and could then be related to hippocampal alterations. The hippocampus is a complex structure which can be divided into several subfields, namely, the Cornu Ammonis (CA1, CA2, and CA3), the subiculum, and the dentate gyrus (DG). As each subfield presents different histological characteristics and functions, it appears more relevant to consider hippocampal subfields, instead of only assessing the whole hippocampus, to understand the neurobiology of PTSD. Hence, this study presents the first investigation of structural alterations within hippocampal subfields and their links to reexperiencing symptoms in adolescent PTSD. Hippocampal subfields were manually delineated on high‐resolution MRI images in 15 adolescents (13–18 years old) with PTSD and 24 age‐matched healthy controls. The volume of the region CA2‐3/DG region was significantly smaller in the PTSD group compared to controls in both hemispheres. No other significant difference was found for other subfields. Moreover, the volume of the left CA2‐3/DG was negatively correlated with the intrusion score (as measured by the Impact of Events Scale‐Revised) in the PTSD group. To conclude, an alteration in the hippocampal subregion CA2‐3/DG, known to resolve interferences between new and similar stored memories, could participate in the apparition of intrusive trauma memories in adolescents with PTSD.     

Smaller hippocampal subfield volumes predict verbal associative memory in pediatric brain tumor survivors

The developing hippocampus is highly sensitive to chemotherapy and cranial radiation treatments for pediatric cancers, yet little is known about the effects that cancer treatents have on specific hippocampal subfields. Here, we examined hippocampal subfield volumes in 29 pediatric brain tumor survivors treated with cranial radiation and chemotherapy, and 30 healthy developing children and adolescents. We also examined associations between hippocampal subfield volumes and short‐term verbal memory. Hippocampal subfields (Cornus Ammonis (CA) 1, CA2‐3, dentate gyrus (DG)‐CA4, stratum radiatum—lacunosum—moleculare, and subiculum) were segmented using the Multiple Automatically Generated Templates for Different Brains automated segmentation algorithm. Neuropsychological assessment of short‐term verbal associative memory was performed in a subset of brain tumor survivors (N = 11) and typically developing children (N = 16), using the Children's Memory Scale or Wechsler's Memory Scale—third edition. Repeated measures analysis of variance showed that pediatric brain tumor survivors had significantly smaller DG‐CA4, CA1, CA2‐3, and stratum radiatum‐lacunosum‐moleculare volumes compared with typically developing children. Verbal memory performance was positively related to DG‐CA4, CA1, and stratum radiatum‐lacunosum‐moleculare volumes in pediatric brain tumor survivors. Unlike the brain tumor survivors, there were no associations between subfield volumes and memory in typically developing children and adolescents. These data suggest that specific subfields of the hippocampus may be vulnerable to brain cancer treatments, and may contribute to impaired episodic memory following brain cancer treatment in childhood.     

Age differences in hippocampal subfield volumes from childhood to late adulthood

The hippocampus is composed of distinct subfields: the four cornu ammonis areas (CA1‐CA4), dentate gyrus (DG), and subiculum. The few in vivo studies of human hippocampal subfields suggest that the extent of age differences in volume varies across subfields during healthy childhood development and aging. However, the associations between age and subfield volumes across the entire lifespan are unknown. Here, we used a high‐resolution imaging technique and manually measured hippocampal subfield and entorhinal cortex volumes in a healthy lifespan sample (N = 202), ages 8–82 yrs. The magnitude of age differences in volume varied among the regions. Combined CA1‐2 volume evidenced a negative linear association with age. In contrast, the associations between age and volumes of CA3‐DG and the entorhinal cortex were negative in mid‐childhood and attenuated in later adulthood. Volume of the subiculum was unrelated to age. The different magnitudes and patterns of age differences in subfield volumes may reflect dynamic microstructural factors and have implications for cognitive functions across the lifespan. © 2015 Wiley Periodicals, Inc.     

幼鼠早期癫痫持续状态对海马结构损伤的远期影响

目的　探讨幼鼠早期癫痫持续状态 (status epilepticus,SE)对成鼠后海马结构损伤的远期影响。方法　健康生后 1 5～ 2 0 d Wistar幼鼠 48只 ,随机分为生理盐水对照组和氯化锂 -匹罗卡品腹腔注射诱导的 SE组 ,并持续追踪至成鼠阶段 ,应用常规病理及电镜观察海马结构的形态学改变 ,同时应用 Timm组织化学染色方法进行苔藓纤维发芽研究。结果　约 2 /3 SE幼鼠发育至成鼠阶段后 ,海马结构的神经元仍可发现变性和坏死性改变 ,以 CA1区、CA3区和齿状回为重。 Timm染色见 CA3区有苔藓纤维发芽现象。约 1 /3 SE幼鼠发育至成鼠后未见海马结构损伤性改变。结论　幼鼠早期 SE造成的海马结构损伤性改变可持续至成鼠阶段 ,但存在个体差异 ,可能与个体耐受性有关。     

Chronic temporal lobe epilepsy is associated with severely declined dentate neurogenesis in the adult hippocampus

While it is clear that acute hippocampal injury or status epilepticus increases the production of new neurons in the adult dentate gyrus (DG), the effects of chronic epilepsy on dentate neurogenesis are unknown. We hypothesize that epileptogenic changes and spontaneous recurrent motor seizures (SRMS) that ensue after hippocampal injury or status epilepticus considerably decrease dentate neurogenesis. We addressed this issue by quantifying the number of cells that are positive for doublecortin (DCX, a marker of new neurons) in the DG of adult F344 rats at 16 days and 5 months after an intracerebroventricular kainic acid (ICV KA) administration or after graded intraperitoneal KA (IP KA) injections, models of temporal lobe epilepsy (TLE). At early post-KA administration, the injured hippocampus exhibited increased dentate neurogenesis in both models. Conversely, at 5 months post-KA administration, the chronically epileptic hippocampus demonstrated severely declined neurogenesis, which was associated with considerable SRMS in both KA models. Additionally, stem/progenitor cell proliferation factors, FGF-2 and IGF-1, were decreased in the chronically epileptic hippocampus. Interestingly, the overall decrease in neurogenesis and the extent of SRMS were greater in rats receiving IP KA than rats receiving ICV KA, suggesting that the extent of neurogenesis during chronic TLE exhibits an inverse relationship with SRMS. These results provide novel evidence that chronic TLE is associated with extremely declined dentate neurogenesis. As fraction of newly born neurons become GABA-ergic interneurons, declined neurogenesis may contribute to the increased seizure-susceptibility of the DG in chronic TLE. Likewise, the hippocampal-dependent learning and memory deficits observed in chronic TLE could be linked at least partially to the declined neurogenesis.