Injection Of Kainic Acid Research Articles

A novel non-transcriptional pathway mediates the proconvulsive effects of interleukin-1

Interleukin-1beta (IL-1beta) is overproduced in human and rodent epileptogenic tissue and it exacerbates seizures upon brain application in rodents. Moreover, pharmacological prevention of IL-1beta endogenous synthesis, or IL-1 receptor blockade, mediates powerful anticonvulsive actions indicating a significant role of this cytokine in ictogenesis. The molecular mechanisms of the proconvulsive actions of IL-1beta are not known. We show here that EEG seizures induced by intrahippocampal injection of kainic acid in C57BL6 adult mice were increased by 2-fold on average by pre-exposure to IL-1beta and this effect was blocked by 3-O-methylsphingomyelin (3-O-MS), a selective inhibitor of the ceramide-producing enzyme sphingomyelinase. C2-ceramide, a cell permeable analog of ceramide, mimicked IL-1beta action suggesting that ceramide may be the second messenger of the proconvulsive effect of IL-1beta. The seizure exacerbating effects of either IL-1beta or C2-ceramide were dependent on activation of the Src family of tyrosine kinases since they were prevented by CGP76030, an inhibitor of this enzyme family. The proconvulsive IL-1beta effect was associated with increased Tyr(418) phosphorylation of Src-family of kinases indicative of its activation, and Tyr(1472) phosphorylation of one of its substrate, the NR2B subunit of the N-methyl-d-aspartate receptor, which were prevented by 3-O-MS and CGP76030. Finally, the proconvulsive effect of IL-1beta was blocked by ifenprodil, a selective NR2B receptor antagonist. These results indicate that the proconvulsive actions of IL-1beta depend on the activation of a sphingomyelinase- and Src-family of kinases-dependent pathway in the hippocampus which leads to the phosphorylation of the NR2B subunit, thus highlighting a novel, non-transcriptional mechanism underlying seizure exacerbation in inflammatory conditions.

Epileptiform activities in slices of hippocampus from mice after intra‐hippocampal injection of kainic acid

Intra-hippocampal kainate injection induces the emergence of recurrent seizures after a delay of 3-4 weeks. We examined the cellular and synaptic basis of this activity in vitro using extracellular and intracellular records from longitudinal hippocampal slices. These slices permitted recordings from the dentate gyrus, the CA3 and CA1 regions and the subiculum of both the injected and the contralateral non-injected hippocampus. A sclerotic zone was evident in dorsal regions of slices from the injected hippocampus, while ventral regions and tissue from the contralateral hippocampus were not sclerotic. Interictal field potentials of duration 50-200 ms were generated spontaneously in both ipsilateral and contralateral hippocampal slices, but not in the sclerotic region, at 3-12 months after injection. They were initiated in the CA1 and CA3 regions and the subiculum. They were blocked by antagonists at glutamatergic receptors and were transformed into prolonged epileptiform events by GABAergic receptor antagonists. The membrane potential and the reversal potential of GABAergic synaptic events were more depolarized in CA1 pyramidal cells from kainate-treated animals than in control animals. Ictal-like events of duration 8-80 s were induced by tetanic stimulation (50 Hz, 0.2-1 s) preferentially in dorsal contralateral and ventral ipsilateral slices. Similar events were initiated by focal application of a combination of high K(+) and GABA. These data show that both interictal and ictal-like activities can be induced in slices of both ipsilateral and contralateral hippocampus from kainate-treated animals and suggest that changes in cellular excitability and inhibitory synaptic signalling may contribute to their generation.

Does kainic acid induce partial brain lesion in an invertebrate model: Sepia officinalis? Comparison with electrolytic lesion

The present study investigates the feasibility of excitotoxic lesions in the cuttlefish in the mapping of brain functions in Cephalopods. Adult animals were injected locally with a neurotoxin, kainic acid. The brain region receiving the neurotoxin was the vertical lobe, a key brain structure for learning and memory processes. Brain damage induced by these injections was evaluated using different histological stainings: hematoxilin–eosin, Fink–Heimer and DAPI. The results were compared with histological changes after electrolytic lesion of the vertical lobe. Neurodegeneration was revealed in and around the injection site: an intense area of proliferative cells, degenerating terminal axon ramifications and cell death. In comparison with electrolytic lesion, excitotoxic lesion displays important advantages, since fibres of passage are not destroyed by kainic acid injection, which induces only a restricted lesion and so is an appropriate method of investigating the role of the vertical lobe or other brain regions in a Cephalopod model, Sepia officinalis.

Changes in sphingomyelinases, ceramide, Bax, Bcl2, and caspase-3 during and after experimental status epilepticus

Status epilepticus (SE) induces a number of events leading to programmed cell death (PCD). The aim of our work is to study the time sequence of activation of different factors in experimental SE (intraperitoneal kainic acid (KA) model). We studied ceramide, a known mediator of apoptosis in multiple models, sphingomyelinases (SMases), enzymes that break down sphingomyelin and increase ceramide thus leading to apoptosis in many models, Bcl(2), Bax, and caspase-3. SE induced a sustained ceramide increase starting 2h after kainic acid injection followed by an increase in Bax protein at 6 and 12h, and the appearance of caspase-3-activated fragment (caspase-3a) immunostaining and TUNEL positivity at 12h. Status epilepticus also induced an increase in acidic and neutral sphingomyelinases that preceded (acidic sphingomyelinase) and parallelled (acidic and neutral sphingomyelinase) the increases in ceramide. These data suggest that, in this model, Bax is activated early in the process and that its increase is sustained till 12h after kainic acid injection which is the time of first appearance of caspase-3 activation and TUNEL positivity, and that SMases contribute to increases in ceramide levels during and after status epilepticus.

COGNITIVE FUNCTION AND VASCULAR EFFECTS ON WHITE MATTER IN SCHIZOPHRENIA

Mesial temporal lobe epilepsy (MTLE) is the most prevalent form of epilepsy, characterized by recurrent complex partial seizures and hippocampal sclerosis. The pathophysiology underlying this disorder remains unidentified. While a loss of benzodiazepine binding sites is a key diagnostic feature of MTLE, experimental studies have shown enhanced inhibitory transmission and increased expression of GABAA-receptors, suggesting that compensatory mechanisms are operative in epileptic hippocampus. In the present study, changes in the expression and cellular distribution of major GABAA-receptor subunits were investigated in the hippocampus of pilocarpine-treated rats during the phase of spontaneous recurrent seizures. A uniform decrease in GABAA-receptor subunit-immunoreactivity was observed in regions of extensive neuronal death (i.e. CA1, CA3, hilus), whereas a prominent increase occurred in the dentate gyrus (DG). Most strikingly, the increase was largest for the α3- and α5-subunits, which are expressed at very low levels in the DG of control rats, suggesting the formation of novel GABAA-receptor subtypes in epileptic tissue. Furthermore, an extensive loss of interneurons expressing the α1-subunit, representing presumptive basket cells, was seen in the DG. These changes were very similar to those reported in a novel mouse model of MTLE, based on the unilateral injection of kainic acid into the dorsal hippocampus (Bouilleret et al., 1999). This indicates that the regulation of GABAA-receptor expression is related to chronic recurrent seizures, and is not due to the extrahippocampal neuronal damage affecting pilocarpine-treated rats. These results allow causal relationships in the induction and maintenance of chronic recurrent seizures to be distinguished. The loss of a critical number of interneurons in the DG is a possible cause of seizure initiation, whereas the long-lasting upregulation of GABAA-receptors in granule cells represents a compensatory response to seizure activity.

ALTERED AGEING IN SCHIZOPHRENIA: META-ANALYSIS OF CELL DENSITY STUDIES IN SCHIZOPHRENIA INDICATES DIRECTION OF CHANGE DEPENDS ON AGE OF SUBJECTS

Mesial temporal lobe epilepsy (MTLE) is the most prevalent form of epilepsy, characterized by recurrent complex partial seizures and hippocampal sclerosis. The pathophysiology underlying this disorder remains unidentified. While a loss of benzodiazepine binding sites is a key diagnostic feature of MTLE, experimental studies have shown enhanced inhibitory transmission and increased expression of GABAA-receptors, suggesting that compensatory mechanisms are operative in epileptic hippocampus. In the present study, changes in the expression and cellular distribution of major GABAA-receptor subunits were investigated in the hippocampus of pilocarpine-treated rats during the phase of spontaneous recurrent seizures. A uniform decrease in GABAA-receptor subunit-immunoreactivity was observed in regions of extensive neuronal death (i.e. CA1, CA3, hilus), whereas a prominent increase occurred in the dentate gyrus (DG). Most strikingly, the increase was largest for the α3- and α5-subunits, which are expressed at very low levels in the DG of control rats, suggesting the formation of novel GABAA-receptor subtypes in epileptic tissue. Furthermore, an extensive loss of interneurons expressing the α1-subunit, representing presumptive basket cells, was seen in the DG. These changes were very similar to those reported in a novel mouse model of MTLE, based on the unilateral injection of kainic acid into the dorsal hippocampus (Bouilleret et al., 1999). This indicates that the regulation of GABAA-receptor expression is related to chronic recurrent seizures, and is not due to the extrahippocampal neuronal damage affecting pilocarpine-treated rats. These results allow causal relationships in the induction and maintenance of chronic recurrent seizures to be distinguished. The loss of a critical number of interneurons in the DG is a possible cause of seizure initiation, whereas the long-lasting upregulation of GABAA-receptors in granule cells represents a compensatory response to seizure activity.

Status epilepticus during old age is not associated with enhanced hippocampal neurogenesis

Increased production of new neurons in the adult dentate gyrus (DG) by neural stem/progenitor cells (NSCs) following acute seizures or status epilepticus (SE) is a well known phenomenon. However, it is unknown whether NSCs in the aged DG have similar ability to upregulate neurogenesis in response to SE. We examined DG neurogenesis after the induction of continuous stages III-V seizures (SE) for over 4 h in both young adult (5-months old) and aged (24-months old) F344 rats. The seizures were induced through 2-4 graded intraperitoneal injections of the excitotoxin kainic acid (KA). Newly born cells in the DG were labeled via daily intraperitoneal injections of the 5'-bromodeoxyuridine (BrdU) for 12 days, which commenced shortly after the induction of SE in KA-treated rats. New cells and neurons in the subgranular zone (SGZ) and the granule cell layer (GCL) were analyzed at 24 h after the last BrdU injection using BrdU and doublecortin (DCX) immunostaining, BrdU-DCX and BrdU-NeuN dual immunofluorescence and confocal microscopy, and stereological cell counting. Status epilepticus enhanced the numbers of newly born cells (BrdU(+) cells) and neurons (DCX(+) neurons) in young adult rats. In contrast, similar seizures in aged rats, though greatly increased the number of newly born cells in the SGZ/GCL, failed to increase neurogenesis due to a greatly declined neuronal fate-choice decision of newly born cells. Only 9% of newly born cells in the SGZ/GCL differentiated into neurons in aged rats that underwent SE, in comparison to the 76% neuronal differentiation observed in age-matched control rats. Moreover, the number of newly born cells that migrate abnormally into the dentate hilus (i.e., ectopic granule cells) after SE in the aged hippocampus is 92% less than that observed in the young adult hippocampus after similar SE. Thus, SE fails to increase the addition of new granule cells to the GCL in the aged DG, despite a considerable upregulation in the production of new cells, and SE during old age leads to much fewer ectopic granule cells. These results have clinical relevance because earlier studies have implied that both increased and abnormal neurogenesis occurring after SE in young animals contributes to chronic epilepsy development.

Grafting of striatal precursor cells into hippocampus shortly after status epilepticus restrains chronic temporal lobe epilepsy

Status epilepticus (SE) typically progresses into temporal lobe epilepsy (TLE) typified by complex partial seizures. Because sizable fraction of patients with TLE exhibit chronic seizures that are resistant to antiepileptic drugs, alternative therapies that are efficient for diminishing SE-induced chronic epilepsy have great significance. We hypothesize that bilateral grafting of appropriately treated striatal precursor cells into hippocampi shortly after SE is efficacious for diminishing SE-induced chronic epilepsy through long-term survival and differentiation into GABA-ergic neurons. We induced SE in adult rats via graded intraperitoneal injections of kainic acid, bilaterally placed grafts of striatal precursors (pre-treated with fibroblast growth factor-2 and caspase inhibitor) into hippocampi at 4 days post-SE, and examined long-term effects of grafting on spontaneous recurrent motor seizures (SRMS). Analyses at 9–12 months post-grafting revealed that, the overall frequency of SRMS was 67–89% less than that observed in SE-rats that underwent sham-grafting surgery and epilepsy-only controls. Graft cell survival was ~ 33% of injected cells and ~ 69% of surviving cells differentiated into GABA-ergic neurons, which comprised subclasses expressing calbindin, parvalbumin, calretinin and neuropeptide Y. Grafting considerably preserved hippocampal calbindin but had no effects on aberrant mossy fiber sprouting. The results provide novel evidence that bilateral grafting of appropriately treated striatal precursor cells into hippocampi shortly after SE is proficient for greatly reducing the frequency of SRMS on a long-term basis in the chronic epilepsy period. Presence of a large number of GABA-ergic neurons in grafts further suggests that strengthening of the inhibitory control in host hippocampi likely underlies the beneficial effects mediated by grafts.

CCAAT/enhancer binding protein β deficiency provides cerebral protection following excitotoxic injury

The CCAAT/enhancer-binding protein beta (C/EBPbeta, also known as CEBPB) was first identified as a regulator of differentiation and inflammatory processes in adipose tissue and liver. Although C/EBPbeta was initially implicated in synaptic plasticity, its function in the brain remains largely unknown. We have previously shown that C/EBPbeta regulates the expression of genes involved in inflammatory processes and brain injury. Here, we have demonstrated that the expression of C/EBPbeta is notably increased in the hippocampus in a murine model of excitotoxicity. Mice lacking C/EBPbeta showed a reduced inflammatory response after kainic acid injection, and exhibited a dramatic reduction in pyramidal cell loss in the CA1 and CA3 subfields of the hippocampus. These data reveal an essential function for C/EBPbeta in the pathways leading to excitotoxicity-mediated damage and suggest that inhibitors of this transcription factor should be evaluated as possible neuroprotective therapeutic agents.

Effect of age on kainate-induced seizure severity and cell death

While the onset and extent of epilepsy increases in the aged population, the reasons for this increased incidence remain unexplored. The present study used two inbred strains of mice (C57BL/6J and FVB/NJ) to address the genetic control of age-dependent neurodegeneration by building upon previous experiments that have identified phenotypic differences in susceptibility to hippocampal seizure-induced cell death. We determined if seizure induction and seizure-induced cell death are affected differentially in young adult, mature, and aged male C57BL/6J and FVB/NJ mice administered the excitotoxin, kainic acid. Dose response testing was performed in three to four groups of male mice from each strain. Following kainate injections, mice were scored for seizure activity and brains from mice in each age group were processed for light microscopic histopathologic evaluation 7 days following kainate administration to evaluate the severity of seizure-induced brain damage. Irrespective of the dose of kainate administered or the age group examined, resistant strains of mice (C57BL/6J) continued to be resistant to seizure-induced cell death. In contrast, aged animals of the FVB/NJ strain were more vulnerable to the induction of behavioral seizures and associated neuropathology after systemic injection of kainic acid than young or middle-aged mice. Results from these studies suggest that the age-related increased susceptibility to the neurotoxic effects of seizure induction and seizure-induced injury is regulated in a strain-dependent manner, similar to previous observations in young adult mice.

Rapid activity‐dependent delivery of the neurotrophic protein CPG15 to the axon surface of neurons in intact Xenopus tadpoles

CPG15 (aka neuritin) is an activity-induced GPI-anchored axonal protein that promotes dendritic and axonal growth, and accelerates synaptic maturation in vivo. Here we show that CPG15 is distributed inside axons and on the axon surface. CPG15 is trafficked to and from the axonal surface by membrane depolarization. To assess CPG15 trafficking in vivo, we expressed an ecliptic pHluorin (EP)-CPG15 fusion protein in optic tectal explants and in retinal ganglion cells of intact Xenopus tadpoles. Depolarization by KCl increased EP-CPG15 fluorescence on axons. Intraocular kainic acid (KA) injection rapidly increased cell-surface EP-CPG15 in retinotectal axons, but coinjection of TTX and KA did not. Consistent with this, we find that intracellular CPG15 is localized to vesicles and endosomes in presynaptic terminals and colocalizes with synaptic vesicle proteins. The results indicate that the delivery of the neurotrophic protein CPG15 to the axon surface can be regulated on a rapid time scale by activity-dependent mechanisms in vivo.

Edaravone prevents kainic acid-induced neuronal death

There is growing evidence that free radical generation may play a key role in the neuronal damage induced by prolonged convulsions. Free radical scavengers are known to inhibit neuronal death induced by exposure to excitotoxins. However, this neuroprotective effect has not been demonstrated with treatment after seizures had been stopped. We investigated whether 3-methyl-1-phenyl-2-pyrazolin-5-one, edaravone (Ed), a newly developed free radical scavenger that has been used clinically to treat cerebral infarction, could prevent neuronal loss when administered after the occurrence of seizures in a kainic acid (KA)-induced seizure model. Compared with KA alone, cell loss was significantly reduced when animals received Ed (10 mg/kg i.v.) just after seizures, and when Ed was administered both 60 min before (30 mg/kg i.p.) and after KA injection. Combined before-and-after treatment with Ed significantly ameliorated the KA-induced decrease of glutathione and blocked the KA-induced increase of 4-hydroxy-2-nonenal (HNE). Because before-and-after treatment with Ed significantly lessened the KA-induced increase of HNE, Ed may exert its neuroprotective effect by inhibiting lipid peroxidation. However, post-treatment with Ed prevented neuronal cell loss, while HNE and glutathione levels did not differ from those in animals without Ed, so a mechanism other than free radical scavenging must be involved in the prevention of cell loss. Patients who develop status epilepticus are unlikely to receive adequate antioxidant therapy before the onset, so it is an advantage that Ed can prevent neuronal death even when administered after seizures.

Reciprocal neuronal projections between arcuate and ventrolateral periaqueductal gray participate in long‐lasting EA inhibition of reflex blood pressure elevation

We have shown the prolonged inhibition of electroacupuncture (EA) on reflex elevations of blood pressure (BP). EA activates the arcuate nucleus (ARC) that sends excitatory projection to ventrolateral periaqueductal gray (vlPAG), in turn, inhibits cardiovascular sympathetic premotor neurons in the medulla. This study investigated the role of a reciprocal neural circuit between the vlPAG and ARC. In alpha‐chloralose anesthetized cats recordings showed that injection of DL‐homocysteic acid (DLH, 4 nM, 50 nl) into vlPAG facilitated the ARC neuronal response to splanchnic nerve stimulation over 40 min. Injection of kainic acid (KA, 1 mM, 50 nl) into the vlPAG blocked the long‐lasting EA (P5‐6 overlying median nerve) excitation on ARC neurons. The EA inhibition on reflex‐induced elevation of BP could be blocked by microinjection of glutamate receptor antagonist, kynurenic acid (KYN) into the ARC. The EA excitation of vlPAG neurons also was blocked by microinjection of glutamate NMDA and non‐NMDA receptor antagonists, CNQX and AP‐5 as well as by atropine. Retrograde morphological studies using colored microspheres (six rats) showed the reciprocal neuronal projections between ARC and vlPAG that contain glutamate. These data demonstrated that the long‐lasting EA inhibition is partly due to the ARC‐vlPAG excitatory neural circuitry involving glutamate and acetylcholine. (Supported by HL‐63313, ‐72125)

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

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. 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. 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. 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.

Experimental Petit Mal-Like Seizure Induced by Microinjection of Kainic Acid Into the Unilateral Mediodorsal Nucleus of the Thalamus

The mediodorsal nucleus (MD) of the thalamus has reciprocal projections with the frontal cortex and limbic system, and may be involved in absence seizures. Kainic acid was injected into the left MD of Wistar rats, and behavior and electroencephalography were monitored for 24 hours, then continued intermittently for 8 weeks. The rat brains were then examined histologically. Brain metabolic changes were also investigated by intravenous injection of 100 microCi/kg of [(14)C]2-deoxyglucose to measure local cerebral glucose metabolism. Bilateral synchronous spike and wave complexes appeared almost 2 hours after kainic acid injection, and the waveforms continued for about 5-7 hours in the bilateral MDs, ipsilateral sensorimotor cortex, and basolateral nucleus of the amygdala. The associated behavioral changes were mainly those of behavioral arrest and staring, associated with occasional limbic seizures. Clear metabolic increases were found in the ipsilateral frontal cortex, hippocampus, and amygdala. The present results suggest that the MD was involved in both the mechanism of spike and wave complexes in the bilateral frontal cortices, and in seizure propagation to the limbic system. Consequently, kainic acid-induced MD seizure is associated with significant cognitive impairment and may explain the mechanism of petit mal seizure.

Acupuncture Inhibits Kainic Acid–Induced Hippocampal Cell Death in Mice

We examined whether acupuncture can reduce both the incidence of seizures and hippocampal cell death using a mouse model of kainic acid (KA)-induced epilepsy. ICR mice were given acupuncture once a day at acupoint HT8 (sobu) bilaterally during 2 days before KA injection. After an intracerebroventricular injection of 0.1 microg of KA, acupuncture treatment was subsequently administered once more (total 3 times), and the degree of seizure was observed for 20 min. Three hours after injection, the survival of neuronal cells and the expressions of c-Fos, c-Jun, and glutamate decarboxylase (GAD)-67 in the CA1 and CA3 were determined using immunohistochemistry and Western blotting techniques. Acupuncture reduced the severity of the KA-induced epileptic seizure and the rate of neural cell death, and it also decreased the expressions of c-Fos and c-Jun induced by KA in the hippocampus. Furthermore, acupuncture increased GAD-67 expressions in the same areas. These results demonstrated that it could inhibit the KA-induced epileptic seizure and hippocampal cell death by increasing GAD-67 expressions.

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.

Botulinum neurotoxin E (BoNT/E) reduces CA1 neuron loss and granule cell dispersion, with no effects on chronic seizures, in a mouse model of temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is often the result of an early insult that induces a reorganization in hippocampal circuitry leading, after a latent period, to chronic epilepsy. Hippocampal rearrangements during the latent phase include neuronal loss, axonal and dendritic plasticity, neurogenesis, and cell repositioning, but the role of these changes in epilepsy development is unclear. Here we have tested whether administration of the synaptic blocker botulinum neurotoxin E (BoNT/E) interferes with development of spontaneous seizures and histopathological changes following an episode of status epilepticus (SE). SE was induced by unilateral intrahippocampal injection of kainic acid in mice and BoNT/E was delivered to the same hippocampus 3 h later. We found that treatment with BoNT/E prolonged the duration of the latent period but did not block the occurrence of spontaneous seizures. At the histopathological level, BoNT/E reduced loss of CA1 pyramidal neurons and dispersion of dentate granule cells. Downregulation of reelin expression along the hippocampal fissure was also suppressed by BoNT/E treatment. Our findings indicate that administration of BoNT/E after SE inhibits specific morphological changes in hippocampal circuitry but not the development of spontaneous seizures. This indicates a dissociation between certain anatomical modifications and establishment of chronic epilepsy in MTLE.

Ablation of p27 enhance kainate-induced seizure and hippocampal degeneration

p27 is a cyclin-dependent kinase inhibitor which arrests cell cycle at G1-S phase. Using RNA interference method, we previously showed that reduction of endogenous p27 expression induces cell death through cell cycle progression in cultured cortical neurons. In this study, we investigated responses to kainate treatment using p27 knockout mice. Injection of kainic acid induced p27 downregulation and retinoblastoma protein phosphorylation in wild-type mouse hippocampus. No change was observed in hippocampal cell viability in untreated adult p27 heterozygous and homozygous mice compared with wild type (+/+). p27 homozygous mice, however, displayed enhanced seizure and hippocampal degeneration after kainic acid treatment. This study first suggests that ablation of p27 enhance kainate-induced seizure and hippocampal cell death in vivo.

Dietary Restriction Enhances Kainate-Induced Increase in NCAM While Blocking the Glial Activation in Adult Rat Brain

In the present study effect of dietary restriction (DR) on neuronal plasticity markers neural cell adhesion molecule (NCAM) and its polysialylated form PSA-NCAM and astrocytic marker glial fibrillary acidic protein (GFAP) was assessed following brain injury by intraperitoneal injection of kainic acid or physiological saline in adult male wistar rats. After 7-day recovery period, rats were sacrificed to study the NCAM-ir, PSA-NCAM-ir, and GFAP-ir in all the groups with immunohistofluorescence and immunoblotting. We noticed increase in NCAM and PSA-NCAM expression after KA excitotoxicity, and DR enhanced this increase in NCAM and PSA-NCAM expression. A marked increase in NCAM and PSA-NCAM-ir was observed in CA3 region of hippocampus, subgranular region and hilus of dentate gyrus, hypothalamus, and piriform cortex in both vehicle treated as well KA-treated DR rats as compared to vehicle and KA-treated AL rats, respectively. Whenever, CNS is damaged it undergoes an injury response called reactive gliosis. Our study confirmed the neuroprotective role of DR as evident from attenuation of GFAP-ir and enhanced levels of neuronal plasticity markers NCAM and PSA-NCAM. The potential beneficial role of DR regimen in attenuating KA-induced reactive astrogliosis and enhancing expression of neuronal plasticity markers may point the way to new strategies of intervention therapy by DR that will facilitate recovery from ageing and disease related neuronal dysfunction and enhance restorative processes by modulating astrogliosis.