Kainic acid dose affects delayed cell death mechanism after status epilepticus

Kainic acid (KA)-induced status epilepticus (SE) produces hippocampal neuronal death, which varies from necrosis to apoptosis or programmed cell death (PCD). We examined whether the type of neuronal death was dependent on KA dose. Adult rats were induced SE by intraperitoneal injection of KA at 9 mg/kg (K9) or 12 mg/kg (K12). Hippocampal neuronal death was assessed by TUNEL staining, electron microscopy, and Western blotting of caspase-3 on days 1, 3 and 7 after SE induction. K12 rats showed higher a mortality rate and shorter latency to the onset of SE when compared with K9 rats. In both groups, acidophilic and pyknotic neurons were evident in CA1 at 24h after SE and neuronal loss developed from day 3. The degenerated neurons became TUNEL-positive on days 3 and 7 in K9 rats but not in K12 rats. Caspase-3 activation was detected on days 3 and 7 in K9 rats but was undetectable in K12 rats. Ultrastructural study revealed shrunken neurons exhibiting pyknotic nuclei containing small and dispersed chromatin clumps 24h after SE in CA1. No cells exhibited apoptosis. On days 3 and 7, the degenerated neurons were necrotic with high electron density and small chromatin clumps. There were no ultrastructural differences between the K9 and K12 groups. These results revealed that differences in KA dose affected the delayed cell death (3 and 7 days after SE); however, no effect was seen on the early cell death (24h after SE). Moderate-dose KA induced necrosis, while low-dose KA induced PCD.     

Adult neurogenesis in the mouse dentate gyrus protects the hippocampus from neuronal injury following severe seizures

Previous studies suggest that reducing the numbers of adult‐born neurons in the dentate gyrus (DG) of the mouse increases susceptibility to severe continuous seizures (status epilepticus; SE) evoked by systemic injection of the convulsant kainic acid (KA). However, it was not clear if the results would be the same for other ways to induce seizures, or if SE‐induced damage would be affected. Therefore, we used pilocarpine, which induces seizures by a different mechanism than KA. Also, we quantified hippocampal damage after SE. In addition, we used both loss‐of‐function and gain‐of‐function methods in adult mice. We hypothesized that after loss‐of‐function, mice would be more susceptible to pilocarpine‐induced SE and SE‐associated hippocampal damage, and after gain‐of‐function, mice would be more protected from SE and hippocampal damage after SE. For loss‐of‐function, adult neurogenesis was suppressed by pharmacogenetic deletion of dividing radial glial precursors. For gain‐of‐function, adult neurogenesis was increased by conditional deletion of pro‐apoptotic gene Bax in Nestin‐expressing progenitors. Fluoro‐Jade C (FJ‐C) was used to quantify neuronal injury and video‐electroencephalography (video‐EEG) was used to quantify SE. Pilocarpine‐induced SE was longer in mice with reduced adult neurogenesis, SE had more power and neuronal damage was greater. Conversely, mice with increased adult‐born neurons had shorter SE, SE had less power, and there was less neuronal damage. The results suggest that adult‐born neurons exert protective effects against SE and SE‐induced neuronal injury.     

Effect of theophylline and trimethobenzamide when given during kainate-induced status epilepticus: an improved histopathologic rat model of human hippocampal sclerosis

PURPOSE: The most common pathology in temporal lobe epilepsy (TLE) is hippocampal sclerosis. It is controversial whether status epilepticus (SE) or prolonged seizures plus secondary cerebral injuries are pathogenic mechanisms of hippocampal sclerosis. This study addressed this question in rat models of TLE. METHODS: Hippocampal neuron densities and supragranular mossy fiber sprouting were determined in adult rats subjected to systemic kainate-induced SE (KA-only) and KA-induced SE followed 75 minutes later by theophylline (KA/Theo) or trimethobenzamide (KA/Tri). These drugs probably decrease seizure-induced cerebral hyperemia or hypertension. RESULTS: Compared with controls and KA-only rats, KA/Tri and KA/Theo rats showed decreased CA3b and CA1 neuron densities (i.e., greater Sommer's sector injury). In addition, KA/Tri rats showed that increased trimethobenzamide dosages were associated with decreased hilar, CA3c, CA3b, CA1, and subiculum neuron densities. There were no significant differences in supragranular mossy fiber sprouting between KA-only, KA/Tri, and KA/Theo rats. CONCLUSIONS: Pharmacologic manipulations during KA-induced SE are associated with differences in hippocampal pathology, especially in Sommer's sector, and the final pattern of damage and axon sprouting shows histopathologic similarities to that in patients with hippocampal sclerosis. Our findings support the hypothesis that secondary physiologic insults during SE that are likely to decrease seizure-induced cerebral hyperemia and hypertension may generate greater hippocampal neuronal injury compared with SE alone, and this may be a pathogenic mechanism of human hippocampal sclerosis in patients with TLE.     

N w‐Propyl‐l‐arginine (L‐NPA) reduces status epilepticus and early epileptogenic events in a mouse model of epilepsy: behavioural,EEG and immunohistochemical analyses

We investigated the anticonvulsant and neurobiological effects of a highly selective neuronal nitric oxide synthase (nNOS) inhibitor, N ^w‐propyl‐l ‐arginine (L‐NPA), on kainic acid (KA)‐induced status epilepticus (SE) and early epileptogenesis in C57BL/6J mice. SE was induced with 20 mg/kg KA (i.p.) and seizures terminated after 2 h with diazepam (10 mg/kg, i.p). L‐NPA (20 mg/kg, i.p.) or vehicle was administered 30 min before KA. Behavioural seizure severity was scored using a modified Racine score and electrographic seizure was recorded using an implantable telemetry device. Neuronal activity, activity‐dependent synaptogenesis and reactive gliosis were quantified immunohistochemically, using c‐Fos, synaptophysin and microglial and astrocytic markers. L‐NPA treatment reduced the severity and duration of convulsive motor seizures, the power of electroencephalogram in the gamma band, and the frequency of epileptiform spikes during SE. It also reduced c‐Fos expression in dentate granule cells at 2 h post‐KA, and reduced the overall rate of epileptiform spiking (by 2‐ to 2.5‐fold) in the first 7 days after KA administration. Furthermore, treatment with L‐NPA suppressed both hippocampal gliosis and activity‐dependent synaptogenesis in the outer and middle molecular layers of the dentate gyrus in the early phase of epileptogenesis (72 h post‐KA). These results suggest that nNOS facilitates seizure generation during SE and may be important for the neurobiological changes associated with the development of chronic epilepsy, especially in the early stages of epileptogenesis. As such, it might represent a novel target for disease modification in epilepsy.     

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.     

Hypothermia reduces brain edema, spontaneous recurrent seizure attack, and learning memory deficits in the kainic acid treated rats

Aims: It is unknown whether hypothermia can disrupt the progress of epileptogenesis. The present study aimed to determine the effect of hypothermia on brain edema and epileptogenesis and to establish whether brain edema is associated with epileptogenesis after severe status epilepticus (SE). Methodology: Rats were injected with a single dose of Kainic acid (KA) to produce either chronic epileptic rats (rats with spontaneous recurrent seizure, SRS) or rats without spontaneous recurrent seizure (no‐SRS rats). A second KA injection was used to induce SE in SRS rats and in no‐SRS rats. The number of SRS was counted and the brain edema induced by SE was assessed by brain water content measurement. The cognitive function was assessed by the radial‐arm maze (RAM) test. Results: A second KA injection resulted in brain edema that was more severe in SRS rats than in no‐SRS rats. After second injection of KA, hypothermia treatment attenuated the KA induced brain edema and reduced the SRS attack in SRS rats. Additionally cognitive function was better in hypothermia‐treated SRS rats than in nomothermia treated SRS rats 1 month after the second KA injection. Conclusions: Hypothermia treatment immediately after SE not only exhibited protective effects against the chronic spontaneous recurrent convulsant seizures but also improved cognitive function. These antiepileptogenic properties of hypothermia may be related to its attenuating effect on brain edema induced by SE. They therefore suggest that brain edema may be involved in the progress of epileptogenesis.     

Extrahippocampal high‐frequency oscillations during epileptogenesis

The current study aimed to investigate the spatial and temporal patterns of high‐frequency oscillations (HFOs) in the intra‐/extrahippocampal areas during epileptogenesis. Local field potentials were bilaterally recorded from hippocampus (CA1), thalamus, motor cortex, and prefrontal cortex in 13 rats before and after intrahippocampal kainic acid (KA) lesions. HFOs in the ripple (100‐200 Hz) and fast ripple (250‐500 Hz) ranges were detected and their rates were computed during different time periods (1‐5 weeks) after KA‐induced status epilepticus (SE). Recurrent spontaneous seizures were observed in 7 rats after SE, and the other 6 rats did not develop epilepsy. During the latent period, the rate of hippocampal HFOs increased at the ipsilateral site of the KA lesion in both groups, and the HFO rate was significantly higher in the animals that later developed epilepsy. Animals that later developed epilepsy also demonstrated widespread appearance of HFOs, in both the ripple and the fast ripple range, whereas animals that did not develop epilepsy only exhibited changes in the ipsilateral intrahippocampal HFO rate. This study demonstrates an association between an increased rate of widespread HFOs and the later development of epilepsy, suggesting the formation of large‐scale distributed pathological networks during epileptogenesis.     

A guinea pig model of mesial temporal lobe epilepsy following nonconvulsive status epilepticus induced by unilateral intrahippocampal injection of kainic acid

Purpose: Models of temporal lobe epilepsy are commonly utilized to study focal epileptogenesis and ictogenesis. The criteria that define animal models representative of human mesial temporal lobe may vary in different laboratories. We describe herein a focal epilepsy model of mesial temporal (hippocampal) origin that relies on the analysis of interictal and ictal electroencephalography (EEG) patterns and on their correlation with seizure symptoms and neuropathologic findings. The study is based on guinea pigs, a species seldom utilized to develop chronic epilepsy models. Methods: Young adult guinea pigs were bilaterally implanted under isoflurane anesthesia with epidural electrodes over somatosensory cortex and depth electrodes in CA1 hippocampal region. A stainless steel guide cannula was positioned unilaterally in the right dorsal hippocampus to inject 1 μl of 0.9% NaCl solution containing 1 μg kainic acid (KA). One week after surgery, continuous 24 h/day video‐EEG monitoring was performed 48 h before and every other week after KA injection, for no <1 month. EEG data were recorded wide‐band at 2 kHz. After video‐EEG monitoring, brains were analyzed for thionine and Timm staining and glial fibrillary acid protein (GFAP) immunostaining. Key Findings: Unilateral injection of KA in dorsal hippocampus of guinea pigs induces an acute nonconvulsive status epilepticus (SE) that terminates within 24 h (n = 22). Chronic seizures with very mild motor signs (undetectable without EEG monitoring) and highly variable recurrence patterns appear in 45.5% (10 of 22) KA‐treated animals, with variable delays from the initial SE. In these animals interictal events, CA1 cell loss, gliosis, and altered Timm staining pattern were observed. The induction of a chronic condition did not correlate with the duration of the nonconvulsive acute SE, but correlated with the extension and quality of neuropathologic damage. Significance: We demonstrate that a model of hippocampal (mesial temporal lobe) epilepsy can be developed in the guinea pig by intrahippocampal injection of KA. Seizure events in this model show little behavioral signs and may be overlooked without extensive video‐EEG monitoring. The establishment of a chronic epileptic condition correlates with the extension of the hippocampal damage (mainly cell loss and gliosis) and not with the intensity of the initial SE.     

Involvement of P2X4 receptors in hippocampal microglial activation after status epilepticus

Within the central nervous system, functions of the ATP‐gated receptor‐channel P2X4 (P2X4R) are still poorly understood, yet P2X4R activation in neurons and microglia coincides with high or pathological neuronal activities. In this study, we investigated the potential involvement of P2X4R in microglial functions in a model of kainate (KA)‐induced status epilepticus (SE). We found that SE was associated with an induction of P2X4R expression in the hippocampus, mostly localized in activated microglial cells. In P2X4R‐deficient mice, behavioral responses during KA‐induced SE were unaltered. However, 48h post SE specific features of microglial activation, such as cell recruitment and upregulation of voltage‐dependent potassium channels were impaired in P2X4R‐deficient mice, whereas the expression and function of other microglial purinergic receptors remained unaffected. Consistent with the role of P2X4R in activity‐dependent degenerative processes, the CA1 area was partially protected from SE‐induced neuronal death in P2X4R‐deficient mice compared with wild‐type animals. Our findings demonstrate that P2X4Rs are brought into play during neuronal hyperexcitability and that they control specific aspects of microglial activation. Our results also suggest that P2X4Rs contribute to excitotoxic damages by regulating microglial activation. GLIA 2013;61:1306–1319     

Upregulated TWIK‐related acid‐sensitive K+ channel‐2 in neurons and perivascular astrocytes in the hippocampus of experimental temporal lobe epilepsy

Purpose: To identify the modulation of Tandem of P‐domains in a weak inwardly rectifying K⁺ channel (TWIK)–related acid‐sensitive K⁺ (TASK)‐2 channel expressions in epilepsy, we conducted a comparative analysis of TASK‐2 channel immunoreactivity in the hippocampus of a pilocarpine‐induced rat epilepsy model. Methods: We performed and immunohistochemical study for TASK‐2 and double immunofluorescent staining for TASK‐2 and glial fibrillary acidic protein (GFAP) in the rat hippocampus of pilocarpine‐induced epilepsy models. Results: In control animals, TASK‐2 immunoreactivity was strongly detected in CA1–3 pyramidal layers and dentate granule cell layer. After status epilepticus (SE), TASK‐2 immunoreactivity was increased in dentate granule cell layer and CA3 pyramidal cell layer, whereas its immunoreactivity was reduced in CA1 pyramidal cell layer. In addition, TASK‐2 immunoreactivity is gradually increased in perivascular regions following SE. Double immunofluorescent study revealed that the enhancement of TASK‐2 immunoreactivity in perivascular regions is caused by increase in the number of TASK‐2 immunoreactive endfeet of perivascular astrocytes. Discussion: Our findings suggest that elevated TASK‐2 immunoreactivity in neurons may contribute to rapid adaptive responses (presumably for extracellular alkalinization), which result in hyperpolarization and regulate seizure activity. In contrast, upregulated TASK‐2 immunoreactivity in perivascular regions may be involved in abnormalities of blood flow regulation or brain‐blood barrier impairment. These changes may contribute to acquisition of the properties of the epileptic hippocampus.     

Long-term cosequences of intrahippocampal kainate injection in the Proechimys guyannensis rodent

The Proechimys guyannensis (PG), a spiny rodent specie living in the Amazonian region has been recently studied as an animal model of anti-convulsant mechanisms. The PG was found to be resistant to the administration of the muscarinic cholinergic agonist pilocarpine or the amygdala kindling development. This study examined the susceptibility of this animal species to the intrahippocampal kainic acid (KA) injection. Electrographic, behavioral and neuropathological changes induced by intrahippocampal KA injections were analyzed. PG showed to be extremely sensitive to the acute effects of the KA injection. Although the EEG findings in PG rodents were similar to those typically obtained in Wistar rats the pattern of electrographic activity in PG animals was longer than in Wistar rats. Neuropathological examinations of PG brains that survived KA-induced SE revealed severe cell loss in CA1/CA3 areas of the hippocampus, an extensive cell dispersion in the hilus of DG at the injected site with mossy fiber sprouting in the dentate gyrus supragranular layer. None of PG animals presented spontaneous seizures during the 120 days of observation. These findings confirm our previous observation on the resistance of this animal specie to experimental models of limbic epilepsy.     

红藻氨酸诱导性癫痫发作大鼠海马cNOS及iNOS的变化及作用

目的研究组成型一氧化氮合酶（ｃＮＯＳ）及诱导型一氧化氮合酶（ｉＮＯＳ）在红藻氨酸（ＫＡ）诱导癫痫发作中的变化及作用。方法采用免疫组织化学方法显示ｃＮＯＳ及ｉＮＯＳ的变化;Ｎｉｓｓｌ染色显示神经元的损害。结果ＫＡ３０分钟ｃＮＯＳ较对照组明显增加（Ｐ＜０．０５）,随后下降至正常水平;ＫＡ诱导２小时ｉＮＯＳ明显升高,以ＣＡ１区为著,至ＫＡ６小时达高峰,然后在高水平缓慢下降;Ｎｉｓｓｌ染色神经元变性坏死ＣＡ３＝齿状回＞ＣＡ１。结论ＫＡ诱导癫痫发作导致海马ｃＮＯＳ及ｉＮＯＳ表达增多,神经元的坏死与ＮＯＳ表达增多无明显关系。     

Seizures in the intrahippocampal kainic acid epilepsy model: characterization using long‐term video‐EEG monitoring in the rat

Objective – Intrahippocampal injection of kainic acid (KA) in rats evokes a status epilepticus (SE) and leads to spontaneous seizures. However to date, precise electroencephalographic (EEG) and clinical characterization of spontaneous seizures in this epilepsy model using long‐term video‐EEG monitoring has not been performed. Materials and Methods – Rats were implanted with bipolar hippocampal depth electrodes and a cannula for the injection of KA (0.4 μg/0.2 μl) in the right hippocampus. Video‐EEG monitoring was used to determine habitual parameters of spontaneous seizures such as seizure frequency, severity, progression and day–night rhythms. Results – Spontaneous seizures were detected in all rats with 13 out of 15 animals displaying seizures during the first eight weeks after SE. A considerable fraction (35%) of the spontaneous seizures did not generalize secondarily. Seizure frequency was quite variable and the majority of the KA‐treated animals had less than one seizure per day. A circadian rhythm was observed in all rats that showed sufficient seizures per day. Conclusions – This study shows that the characteristics of spontaneous seizures in the intrahippocampal KA model display many similarities to other SE models and human temporal lobe epilepsy.     

Dantrolene inhibits the calcium plateau and prevents the development of spontaneous recurrent epileptiform discharges following in vitro status epilepticus

Status epilepticus is a clinical emergency that can lead to the development of acquired epilepsy following neuronal injury. Understanding the pathophysiological changes that occur between the injury itself and the expression of epilepsy is important in the development of new therapeutics to prevent epileptogenesis. Currently, no anti‐epileptogenic agents exist; thus, the ability to treat an individual immediately after status epilepticus to prevent the ultimate development of epilepsy remains an important clinical challenge. In the Sprague–Dawley rat pilocarpine model of status epilepticus‐induced acquired epilepsy, intracellular calcium has been shown to increase in hippocampal neurons during status epilepticus and remain elevated well past the duration of the injury in those animals that develop epilepsy. This study aimed to determine if such changes in calcium dynamics exist in the hippocampal culture model of status epilepticus‐induced acquired epilepsy and, if so, to study whether manipulating the calcium plateau after status epilepticus would prevent epileptogenesis. The in vitro status epilepticus model resembled the in vivo model in terms of elevations in neuronal calcium concentrations that were maintained well past the duration of the injury. When used following in vitro status epilepticus, dantrolene, a ryanodine receptor inhibitor, but not the N‐methyl‐d ‐aspartic acid channel blocker MK‐801 inhibited the elevations in intracellular calcium, decreased neuronal death and prevented the expression of spontaneous recurrent epileptiform discharges, the in vitro correlate of epilepsy. These findings offer potential for a novel treatment to prevent the development of epileptiform discharges following brain injuries.     

Potentiation of kainic acid epileptogenicity and sparing from neuronal damage by an NMDA receptor antagonist

The time course and severity of the excitotoxic syndrome induced in rats by s.c. injection of 10 mg/kg kainic acid (KA) was modified by pretreatment with MK801, a non-competitive inhibitor of the NMDA receptor, at doses of 0.1, 1 and 10 mg/kg. A dose-dependent increase in the severity of the KA-induced electrographic (EEG) manifestations of epilepsy was seen after MK801. This consisted of an earlier appearance and higher number of EEG seizures, longer time spent in seizures, and an earlier onset of status epilepticus. In contrast, behavioral seizures were increased only in the 0.1 mg/kg MK801 group, but abolished by higher doses. On the contrary, wet dog shakes were progressively reduced with increasing doses of MK801. Four of the 9 animals receiving KA-only group and 3 of the 10 animals in the 1 and 10 mg MK801 groups were sacrificed 5 days after KA. The brain of the KA-only rats presented diffuse gross and microscopic evidence of hemorrhagic necrosis and neuronal damage; the MK801 rats showed only minimal neuronal loss in the CA3 hippocampal sector. This study demonstrates that neuronal damage and epileptiform activity can be dissociated. Furthermore, it confirms the protective effect of MK801 against neuronal damage caused by multiple factors. Lastly, it emphasizes the need for EEG monitoring in order to accurately assess any epileptic/antiepileptic effect.     

Consequences of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor blockade during status epilepticus in the developing brain

To investigate if AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor activation contributes to acute manifestations and long term consequences of status epilepticus (SE), we administered the AMPA receptor antagonist NBQX to P35 rats undergoing kainic acid (KA)-induced SE. NBQX (30 mg/kg/dose) given intraperitoneally (i.p.) at 30, 60 and 90 min after i.p. KA injection (12 mg/kg) reduced severity of SE. When tested as adults, rats that had received KA and NBQX were similar to controls with no long term impairment in visuospatial memory (assessed by the water maze test), or histologic damage in the CA1 or CA3 hippocampal subfields. However, both P35 groups, those receiving KA alone and those receiving KA and NBQX, had similar rates of spontaneous recurrent seizures (SRS). In P15 rats, NBQX resulted in increased acute mortality from KA associated SE. These results indicate that the effects of NBQX on KA-induced SE are age dependent, and that non-NMDA receptor activation contributes to the acute manifestations and to the long term sequelae seen after KA-induced SE in the prepubescent rat brain.     

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.