Intracerebroventricular Injection Of Kainic Acid Research Articles

Alpha-Pinene Decreases the Elevated Levels of Astrogliosis, Pyroptosis, and Autophagy Markers in the Hippocampus Triggered by Kainate in a Rat Model of Temporal Lobe Epilepsy.

The development and progression of temporal lobe epilepsy (TLE) are heavily influenced by inflammation, excessive activation of glial cells, and neuronal cell death. This study aimed to investigate the effects of treatment with alpha-pinene (APN) on pro-and anti-inflammatory cytokine levels, astrogliosis, pyroptosis, and autophagy markers in the hippocampus in a rat model of TLE induced by kainic acid (KA). Male Wistar rats were employed, and TLE was induced by intracerebroventricular injection of KA. APN (50mg/kg) was intraperitoneally administered for 19days, including two weeks before and five days after the administration of KA. After full recovery from anesthesia and KA injection, the seizure-related behavioral expressions were evaluated. On day 19, the hippocampal levels of IL-1β, TNF-α, progranulin, IL-10, ERK1/2, phospho-ERK1/2, NF-κB, GFAP, S100-B, NLRP1, NLRP3, caspase-1, and becline-1 were examined. The results revealed that treatment with APN significantly diminished the heightened levels of IL-1β, TNF-α, progranulin, ERK1/2, and NF-κB and reversed the reduced levels of the anti-inflammatory cytokine, IL-10, in the hippocampus caused by KA. Furthermore, administration of APN significantly reduced the levels of astrogliosis, pyroptosis, and autophagy markers in the hippocampus that were elevated by KA. It can be concluded that treatment with APN for 19days alleviated neuroinflammation by inhibiting ERK1/2 and NF-κB signaling pathways and prevented increases in astrogliosis, pyroptosis, and autophagy markers in the hippocampus in a rat model of TLE.

Alpha-Pinene Exerts Antiseizure Effects by Preventing Oxidative Stress and Apoptosis in the Hippocampus in a Rat Model of Temporal Lobe Epilepsy Induced by Kainate.

Oxidative stress and apoptosis following seizures play pivotal roles in the consequences of repeated seizures. Beneficial effects of alpha-pinene (APN) have been reported in some experimental models of neurodegenerative diseases. However, its neuroprotective efficacy in a rat model of temporal lobe epilepsy (TLE) induced by kainic acid (KA) has remained unexplored. We aimed to explore the possible antiseizure effects of APN pretreatment and underlying molecular mechanisms in a rat model of TLE induced by KA. TLE was induced in male Wistar rats by intracerebroventricular injection of KA. APN at a dose of 50 mg/kg/day was intraperitoneally injected for 2 weeks before induction of TLE. One day after the induction of TLE, behavioral expressions of seizure were recorded and scored using Racine's scale. Furthermore, the hippocampal levels of oxidative stress markers, B-cell lymphoma 2 (Bcl2), BCL2-associated X protein (BAX), and c-Jun N-terminal kinase (JNK) protein levels were also assessed. Histopathological assessment in the hippocampus was performed with Nissl staining 5 days following induction of TLE. The results revealed that APN pretreatment alleviated epileptic seizures, diminished oxidative stress indicators, blocked the mitochondrial apoptotic pathway via decreasing BAX and raising BCL2 protein levels in the hippocampus at least partly through inhibiting JNK activity, and decreased neuronal death in the CA3 and hilus regions. These findings reveal that APN pretreatment mitigates KA-induced seizures by blocking oxidative stress and neuronal damage factors. It can be concluded that APN has a potent potential to be considered an antiseizure medication, but it needs further investigation.

Altered Expression of Par3, aPKC-λ, and Lgl1 in Hippocampus in Kainic Acid-Induced Status Epilepticus Rat Model

Introduction: Mossy fiber sprouting (MFS) is a frequent histopathological finding in temporal lobe epilepsy (TLE) and is involved in the pathology of TLE. However, molecular signals underlying MFS remain unclear. Partitioning defective 3(Par3), atypical protein kinase C-λ(aPKC-λ), and lethal giant larvae 1(Lgl1) were involved in the neuronal polarity and axon growth. The potential roles of those proteins in MFS and epileptogenesis of TLE were investigated.Material and Methods: The epileptic rat models were established by intracerebroventricular injection of kainic acid (KA). The degree of MFS was measured by using Timm staining, Neuronal loss and the expression aPKC-λ, Par3, and Lgl1 in hippocampus were measured by using immunohistochemistry and western blot analysis.Results: The neuronal loss in CA3 region was observed from 3 days to 8 weeks, while the neuronal loss in the hilar region was observed from 1 to 8 weeks in experimental group. The Timm score in the CA3 region in experimental group was significantly higher than that in the control group from 2 to 8 weeks. Compared with control group, the expressions of Par3 and Lgl1 were upregulated and the expression of aPKC-λ was downregulated in the experimental groups. Positive correlation between the Par3 expression and Timm scores, and the negative correlation between the aPKC-λ expression and Timm scores in CA3 region were discovered in experimental group.Conclusion: The findings of the present study indicated that aPKC-λ, Par3, and Lgl1 may be involved in MFS and in the epileptogenesis of temporal lobe epilepsy.

The complement C3-C3aR pathway mediates microglia-astrocyte interaction following status epilepticus.

Gliosis is a histopathological characteristic of epilepsy that comprises activated microglia and astrocytes. It is unclear whether or how crosstalk occurs between microglia and astrocytes in the evolution of epilepsy. Here, we report in a mouse model of status epilepticus, induced by intracerebroventricular injection of kainic acid (KA), sequential activation of microglia and astrocytes and their close spatial interaction in the hippocampal CA3 region. Microglial ablation reduced astrocyte activation and their upregulation of complement C3. When compared to wild-type mice, both C3-/- and C3aR-/- mice had significantly less microglia-astrocyte interaction in response to KA-induced status epilepticus. Additionally, KA-injected C3-/- mice had significantly less histochemical evidence of neurodegeneration. The results suggest that the C3-C3aR pathway contributes to KA-induced neurodegeneration by mediating microglia-astrocyte communication. The C3-C3aR pathway may prove to be a potential therapeutic target for epilepsy treatment.

TIGAR suppresses seizures induced by kainic acid through inhibiting oxidative stress and neuronal apoptosis

TP53-induced glycolysis and apoptosis regulator (TIGAR) activates the pentose phosphate pathway (PPP), which feeds reduced nicotinamide adenine dinucleotide phosphate (NADPH) to the antioxidant glutathione pathway. Oxidative stress-induced neuronal apoptosis is the pathological basis of several neurological disorders, including epilepsy. To determine the potential anti-epileptic action TIGAR in a rodent kainic acid (KA)-induced seizure model.Seizures were induced by the intra-cerebroventricular injection of KA, followed by injection of empty or TIGAR-expressing lentiviral vectors. Immunofluorescence was used to detect the localization of TIGAR in the cortices and hippocampi, and the expression levels of relevant proteins were determined by Western blotting. Oxidative stress-related markers were detected using commercially available kits. Neuronal apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. TIGAR were mainly expressed in the neurons and rarely located in the astrocytes, and increased in the cortices and hippocampi of KA-treated rats in a time-dependent manner. Lentivirus-mediated TIGAR overexpression significantly decreased the oxidative stress and neuronal apoptosis induced by KA, resulting in prolonged seizure latency and lower Racine scores. Our findings indicate that TIGAR has anti-epileptic, anti-oxidant and anti-apoptotic effects, and is therefore a promising therapeutictarget for epilepsy.

Neuroprotective effects of isoliquiritigenin against cognitive impairment via suppression of synaptic dysfunction, neuronal injury, and neuroinflammation in rats with kainic acid-induced seizures

Epileptogenesis is a dynamic process initiated by insults to brain and commonly accompanied by cognitive impairment. Isoliquiritigenin (ISL), a flavonoid in licorice, has a broad spectrum of biological effects including anti-inflammatory and antioxidant activities. However, the protective effects of ISL against cognitive impairment in epileptic processes and the underlying molecular mechanism are not well understood. To address these questions, we established an reproducible seizure model by intracerebroventricular injection of kainic acid (KA) in 21-day-old rats; ISL was intraperitoneally administered three times prior to KA injection, and changes in cognitive function; synaptic plasticity; neuronal injury; number of glial cells; and expression of pro-inflammatory cytokines and nuclear factor-like (NRF)2 signaling and NACHT, LRR, and PYD domains-containing protein (NLRP)3 inflammasome components in the hippocampus were examined. Rats with KA-induced seizures showed longer average escape latency and decreases in the number of platform crossings and average time spent in the target quadrant in the Morris water maze; ISL pretreatment reversed this decline in cognitive impairment and increased the protein levels of synaptophysin, postsynaptic density-95 and brain-derived neurotrophic factor while reducing the number of Fluoro Jade B-positive cells, microglia, and astrocytes; cleaved-Caspase-3 and -9 protein levels; and tumor necrosis factor-α, interleukin (IL)-1β, and IL-18 production. It also enhanced the nuclear localization of NRF2, hemeoxygenase-1, and NAD(P)H:quinone oxidoreductase (NQO) 1, and reversed the upregulation of NLRP3 inflammasome components NLRP3 and Caspase-1 induced by KA injection. Thus, ISL protects against cognitive impairment in KA-induced epileptic processes possibly through regulation of NRF2 signaling and the NLRP3 inflammasome pathway.

Oriental Medicine Woohwangchungsimwon Attenuates Kainic Acid-Induced Seizures and Neuronal Cell Death in the Hippocampus

Woohwangchungsimwon (WCW) is an oriental medicine that has been extensively prescribed in Asia to patients with apoplexy, high blood pressure, acute/chronic convulsion, and so on. However, the potential therapeutic value of WCW in treating the pathologic brain has not yet been fully investigated. In the present study, we evaluated whether WCW has beneficial effects on kainic acid (KA)-induced excitotoxicity. An intraperitoneal injection of KA (40 mg/kg) and an intracerebroventricular injection of KA (0.2 μg) produced typical seizure behavior and neuronal cell death in the CA1 and CA3 pyramidal layers of the hippocampus, respectively. However, the systemic administration of WCW significantly attenuated the seizure behavior and neuronal cell death. WCW was found to exert the best protective effect when it was administrated 2 hours before a KA injection. Moreover, this WCW-induced neuroprotection was accompanied by a reduction in microglia activation and tumor necrosis factor-alpha, interleukin (IL)-1β, IL-6, inducible nitric oxide synthase, and cyclooxyganase-2 in the hippocampus. These results suggest that WCW has therapeutic potential to suppress KA-induced pathogenesis in the brain by inhibiting inflammation.

Effect of pioglitazone on excitotoxic neuronal damage in the mouse hippocampus.

Pioglitazone (PGZ), a synthetic peroxisome proliferator-activated receptor γ agonist, is known to regulate inflammatory process and to have neuroprotective effects against neurological disorders. In the present study, we examined the effects of 30 mg/kg PGZ on excitotoxic neuronal damage and glial activation in the mouse hippocampus following intracerebroventricular injection of kainic acid (KA). PGZ treatment significantly reduced seizure-like behavior. PGZ had the neuroprotective effect against KA-induced neuronal damage and attenuated the activations of astrocytes and microglia in the hippocampal CA3 region. In addition, MPO and NFκB immunoreactivities in the glial cells were also decreased in the PGZ-treated group. These results indicate that PGZ had anticonvulsant and neuroprotective effects against KA-induced excitotocix injury, and that neuroprotective effect of PGZ might be due to the attenuation of KA-induced activation in astrocytes and microglia as well as KA-induced increases in MPO and NFκB.

Ginseng Rb fraction protects glia, neurons and cognitive function in a rat model of neurodegeneration.

The loss and injury of neurons play an important role in the onset of various neurodegenerative diseases, while both microgliosis and astrocyte loss or dysfunction are significant causes of neuronal degeneration. Previous studies have suggested that an extract enriched panaxadiol saponins from ginseng has more neuroprotective potential than the total saponins of ginseng. The present study investigated whether a fraction of highly purified panaxadiol saponins (termed as Rb fraction) was protective for both glia and neurons, especially GABAergic interneurons, against kainic acid (KA)-induced excitotoxicity in rats. Rats received Rb fraction at 30 mg/kg (ip), 40 mg/kg (ip or saline followed 40 min later by an intracerebroventricular injection of KA. Acute hippocampal injury was determined at 48 h after KA, and impairment of hippocampus-dependent learning and memory as well as delayed neuronal injury was determined 16 to 21 days later. KA injection produced significant acute hippocampal injuries, including GAD67-positive GABAergic interneuron loss in CA1, paralbumin (PV)-positive GABAergic interneuron loss, pyramidal neuron degeneration and astrocyte damage accompanied with reactive microglia in both CA1 and CA3 regions of the hippocampus. There was also a delayed loss of GAD67-positive interneurons in CA1, CA3, hilus and dentate gyrus. Microgliosis also became more severe 21 days later. Accordingly, KA injection resulted in hippocampus-dependent spatial memory impairment. Interestingly, the pretreatment with Rb fraction at 30 or 40 mg/kg significantly protected the pyramidal neurons and GABAergic interneurons against KA-induced acute excitotoxicity and delayed injury. Rb fraction also prevented memory impairments and protected astrocytes from KA-induced acute excitotoxicity. Additionally, microglial activation, especially the delayed microgliosis, was inhibited by Rb fraction. Overall, this study demonstrated that Rb fraction protected both astrocytes and neurons, especially GABAergic interneurons, and maintained microglial homeostasis against KA-induced excitotoxicity. Therefore, Rb fraction has the potential to prevent and treat neurodegenerative diseases.

Midkine, heparin-binding growth factor, blocks kainic acid-induced seizure and neuronal cell death in mouse hippocampus

BackgroundMidkine (MK), a member of the heparin-binding growth factor family, which includes MK and pleiotrophin, is known to possess neurotrophic and neuroprotective properties in the central nervous system. Previous studies have shown that MK is an effective neuroprotective agent in reducing retinal degeneration caused by excessive light and decreasing hippocampal neuronal death in ischemic gerbil brain. The present study was undertaken to investigate whether MK acts as an anticonvulsant in kainic acid (KA)-induced seizure in mouse and blocks KA-mediated neuronal cell death in hippocampus.ResultsIncreased expression of MK was found in hippocampus of mouse following seizures induced by intracerebroventricular injection of KA, and MK expression was found in glial fibrillary acidic protein (GFAP)-positive astrocytes. Concurrent injection of MK and KA attenuated KA-induced seizure activity and cell death of hippocampal neurons including pyramidal cells and glutamic acid decarboxylase 67 (GAD67)-positive GABAergic interneurons in the CA3 and hilar area.ConclusionThe results of the present study indicate that MK functions as an anticonvulsant and neuroprotective agent in hippocampus during KA-induced seizures.

Glial expression of the 90-kDa heat shock protein (HSP90) and the 94-kDa glucose-regulated protein (GRP94) following an excitotoxic lesion in the mouse hippocampus.

Heat shock proteins (HSPs) are immediately expressed in neuronal and glial cells under various stressful conditions and play a protective role through molecular chaperones. Although several studies have been focused on the expression of HSPs, little is known about HSP90s expression in glial cells under neuropathological conditions. In this study, we evaluated the expression pattern of the glial cell-related HSP90 and GRP94 proteins, following the induction of an excitotoxic lesion in the mouse brain. Adult mice received an intracerebroventricular injection of kainic acid; the brain tissue was then analyzed immunohistochemically for HSPs and double labeling using glial markers. HSPs expression was quantified by Western blot analysis. Excitotoxic damage was found to cause pyramidal cell degeneration in the CA3 region of the hippocampus. In the injured hippocampus, reactive microglia/macrophages expressed HSP90 from 12 h until 7 days postlesion (PL), showing maximal levels at day 1. In parallel, hippocampal reactive astrocytes showed the expression of GRP94 from 12 h until 7 days PL. In general, HSPs expression was transient, peaked at 1-3 days PL and reached basal levels by day 7. For the first time, our data demonstrate the injury-induced expression of HSP90 and GRP94 in glial cells, which may contribute to the mechanism of glial cell protection and adaptation in response to damage, thereby playing an important role in the evolution of the glial response and the excitotoxic lesion outcome. HSP90 may provide antioxidant protective mechanisms against microglia/macrophages, whereas GRP94 may stabilize the astroglial cytoskeleton and participate in astroglial antioxidant mechanisms.

Induction of transcription factor c-myb expression in reactive astrocytes following intracerebroventricular kainic acid injection in mouse hippocampus

The transcription factor c-myb is known to play an important role in the regulation of cellular proliferation and differentiation. Recently, the constitutive and aberrant expression of c-myb in the normal and Cu/Zn SOD mutant mouse brain was reported. However, the expression of c-myb in the process of reactive gliosis is not known yet. Here we report the delayed and protracted induction of c-myb in the brain of mice following kainic acid (KA) induced seizure. Our western blot analysis revealed that the amount of c-myb was dramatically increased in the brain 3 days after KA treatment. The induction of c-myb was sustained for more than 7 days after KA treatment. The c-myb immunoreactivity (IR) was restricted to neurons of the hippocampus in control mice. Three days after KA treatment, a strong c-myb IR was found in reactive astrocytes in the whole areas of the CA3 region. Thereafter, c-myb IR astrocytes were gradually concentrated around the CA3 region undergoing selective neuronal loss. A few c-myb IR astrocytes were continuously persisted in the CA3 region 14 days after KA treatment. These findings suggest a role of c-myb signal pathway in reactive gliosis in mice with KA induced seizure.

Increased expression of phosphatase and tensin homolog in reactive astrogliosis following intracerebroventricular kainic acid injection in mouse hippocampus

A phosphatase and tensin homolog (PTEN) has been known to play multiple biological roles. However, role of PTEN in astrocyte activation is not clear yet. In the present study, the expression pattern of PTEN in the process of reactive gliosis was immunohistochemically examined in intracerebroventricular (i.c.v.) injected kainic acid mouse hippocampus. Mice were grouped into three; 30 min, 1 day and 7 days after kainic acid i.c.v. injection. Thirty minutes after kainic acid i.c.v. injection, astrocytes were activated and PTEN was weakly expressed in immature astrocytes. Seven days after kainic acid i.c.v. injection, PTEN expression was decreased in highly activated astrocytes showing extensively spindled shape. Immunofluorescence double labeling experiment showed that PTEN was expressed in glial fibrillary acidic protein-positive astrocytes. These findings suggest that PTEN might have a role in early stage of reactive astrogliosis in vivo.

Endogenous adenosine protects CA1 neurons from kainic acid-induced neuronal cell loss in the rat hippocampus.

CA3 pyramidal neurons in the rat hippocampus show selective vulnerability to the intracerebroventricular injection of kainic acid (KA). However, the mechanism of this selective neuronal vulnerability remains unclear. In this study, we examined the contribution of endogenous adenosine, a potent inhibitory neuromodulator, to the differences in the neuronal vulnerability of the hippocampus, using microtubule-associated protein (MAP)-2, phosphorylated c-Jun, and major histocompatibility complex (MHC) class II immunoreactivities as markers for neuronal cell loss, neuronal apoptosis and glial activation, respectively. Pretreatment with 8-cyclopenthyltheophylline (CPT), an A1 adenosine receptor antagonist, significantly exacerbated KA-induced neuronal cell loss in both the CA1 and CA3. Although c-Jun phosphorylation, a critical step in neuronal apoptosis, was not detected in the vehicle-injected rat hippocampus, c-Jun phosphorylation was induced in the CA3 by the injection of KA alone. Pretreatment with CPT induced c-Jun phosphorylation in both the CA1 and CA3. MHC class II antigen was also detected in the regions of c-Jun phosphorylation. Coadministration of N6-cyclopenthyladenosine (CHA), an A1 adenosine receptor agonist, attenuated the neuronal cell loss in the CA1 and CA3 with or without pretreatment with CPT. These results strongly suggest that endogenous adenosine has neuroprotective effects against excitotoxin-induced neurodegeneration in the CA1 through its A1 receptors.

Expression of heme oxygenase-1 mediated by non-NMDA and metabotropic receptors in glial cells: possible involvement of reactive oxygen species production and protein kinase C activation

Heme oxygenase (HO) produces biliverdin and bilirubin which are physiological antioxidants and potent scavengers of oxygen radicals. Recently, we found that intracerebroventricular injection of kainic acid (KA) induced inducible HO (HO-1) predominantly in glial cells in the rat hippocampus in vivo. In this study, we examined the mechanism of HO-1 expression induced by agonists for glutamate receptors in cultured glial cells in vitro. The HO-1 protein level was significantly enhanced by several agonists for non- N-methyl- d-aspartate (non-NMDA) receptors and metabotropic glutamate receptors (mGluR) such as KA, quisqualic acid (QA), (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propanoic acid (AMPA), and trans-(±)-1-amino-(1 S,3 R)-cyclopentanedicarboxylic acid (ACPD). Among these agonists, QA had the greatest potency. KA-induced HO-1 expression was inhibited by the non-NMDA antagonist NBQX. In addition, KA induced the marked production of reactive oxygen species (ROS), and KA-induced HO-1 expression was also inhibited by the antioxidants allopurinol and ascorbic acid. ACPD-induced HO-1 expression was inhibited by the mGluR antagonist MCPG and the protein kinase C (PKC) inhibitor calphostin C. These results suggest that induction of HO-1 expression by the activation of non-NMDA receptors is mediated by ROS production, and that expression induced by mGluR activation is mediated by PKC activation in rat glial cells.

Kainic acid induction of heme oxygenase in vivo and in vitro

Heme oxygenase, catalyses oxidation of the heme molecule in concert with NADPH-cytochrome P450 reductase and then specifically cleaves heme into biliverdin, carbon monoxide, and iron. Biliverdin and its product, bilirubin, are known to be strong antioxidants. Kainic acid is a potent neurotoxin, and induces selective neuronal loss in the rat hippocampus. Kainic acid acts on the kainate receptors, and kainic acid neurotoxicity may be in part mediated by oxidative stress. In this study, we examined whether or not heme oxygenase was activated in kainic acid-induced neurotoxicity. After intracerebroventricular injection of kainic acid, the heme oxygenase-1 protein level was strongly enhanced, although the constitutive heme oxygenase (heme oxygenase-2) protein level was not changed. One day after treatment, the protein level of heme oxygenase-1 reached a maximum and then gradually decreased over a period of three to seven days. In the rat hippocampus, cells expressing heme oxygenase-1 in vivo were predominately microglia and only a few astrocytes. In addition, heme oxygenase-1 immunoreactivity was predominantly co-localized with major histocompatibility complex class II-, and partly co-localized with class I-immunoreactive microglia. In cultured glial cells in vitro, heme oxygenase-1 protein was expressed in the microglia even with the vehicle treatment, and was strongly induced in astrocytes by kainic acid treatment. These results suggest that ameboid microglia, which express both heme oxygenase-1 and major histocompatibility complex antigens, may play a key role in a delayed episode of kainic acid-induced microglial activation and neurodegeneration.

Kainic acid increases the proliferation of granule cell progenitors in the dentate gyrus of the adult rat

Granule cell progenitors in the dentate gyrus of the hippocampal formation have the unusual capacity to be able to divide in the brains of adult rats and primates. The basal proliferation rate of granule cell progenitors in the adult rat is low compared with development, however, it is possible that this rate may become significantly altered under pathological conditions such as epilepsy. We have investigated whether the proliferation of granule cell progenitors is increased in adult rats in a model of temporal lobe epilepsy, by using systemic bromodeoxyuridine injections to label dividing cells. We report here for the first time that granule cell neurogenesis is increased bilaterally 1 week after a single unilateral intracerebroventricular injection of kainic acid. Bromodeoxyuridine labeled neurons increased at least 6-fold on the side ipsilateral to the kainic acid injection compared to controls, but significantly, were also increased, by at least 3-fold on the side contralateral to the injection. The dividing cells in the subgranular zone were identified as neurons since they expressed Class III beta tubulin but not glial fibrillary acidic protein.

α2 mRNA of Na +K + ATPase is increased in astrocytes of rat hippocampus after treatment with kainic acid

The Na +K + ATPase (Na + pump) plays a central role in regulating cation homeostasis and is thought to have an important role in cell proliferation. The multitude of subunit isoforms comprising the functional Na +K + ATPase has raised the possibility that specific subunit isoform combinations may be involved in different cellular processes. We have investigated the involvement of the specific isoforms in neurons and glia at the site of a CNS lesion. Intracerebroventricular injection of kainic acid was used to induce neuronal cell loss and reactive gliosis in rat hippocampus and levels of Na +K + ATPase subunit isoform mRNA levels were determined in cells of rat hippocampus using in situ hybridization. α2 mRNA levels increased 35–40% in CA1 and CA3 astrocytes between 1–3 weeks after KA injection with no significant change in other subunit isoform mRNA levels. In addition α3 mRNA levels in CA1 pyramidal neurons were decreased by approx. 35%. Small neurons in the CA1 and CA3 region showed no changes in mRNA levels for any of the Na +K + ATPase subunit isoforms. These results may indicate a possible role for α2 subunit isoform in the conversion of glial cells from a normal phenotype to the reactive phenotype characteristic in this model of CNS injury.

Intracerebroventricular kainic acid administration in adult rat alters hippocampal calbindin and non-phosphorylated neurofilament expression.

Calbindin and non-phosphorylated neurofilament proteins were assessed in hippocampus following a unilateral intracerebroventricular kainic acid injection at 4, 26, and 60 days post-lesion, using immunocytochemical expression. The density of calbindin-positive non-pyramidal neurons throughout the hippocampus showed no significant alteration at 4 days post-lesion, a significant decrease at 26 days post-lesion, and a partial recovery at 60 days post-lesion. In addition, calbindin immunoreactivity was dramatically reduced at 26 days post-lesion in the CA1 pyramidal and dentate granule cell layers and the mossy fibers, bilaterally. Although not significant statistically, most of these reductions showed signs of reversal at 60 days post-lesion except the CA1 pyramidal cell layer where the dramatic reductions persisted. Neurofilaments were also altered throughout the post-lesion period, particularly in abnormal expression of non-phosphorylated neurofilament proteins in mossy fibers. The apparent return of calbindin immunoreactivity in non-pyramidal neurons by 60 days post-lesion suggests that recovery from the lesion may involve remaining neuronal elements which either become reactivated with time or have the capability to express normal levels of calbindin with re-innervation. On the other hand, prolonged calbindin reductions in superficial CA1 pyramidal cells suggest sustained down-regulation of calbindin expression owing to persistent reductions in the activity of these neurons. The temporal correlation of the expression of non-phosphorylated neurofilaments in mossy fibers with their sprouting response following target loss suggests a potential role for non-phosphorylated neurofilaments in neuronal plasticity involving axonal sprouting. Alternatively, it may also suggest that injury-induced neurofilament modifications are either conducive or permissive for axonal sprouting.

Plasticity of AMPA and NMDA receptor-mediated epileptiform activity in a chronic model of temporal lobe epilepsy.

We have investigated the consequences of tetanic stimulation on epileptiform activity mediated by NMDA and AMPA receptors in an experimental model of human temporal lobe epilepsy. Recordings were performed in the CA1 area of the hippocampus one week following intracerebroventricular injection of kainic acid. Data presented here show that, after tetanic stimulation, there was a long-term increase in the amplitude of the population spikes associated with the epileptiform burst. This activity was triggered by the simultaneous activation of both NMDA and AMPA receptors. However, whilst the pharmacologically isolated AMPA component of this burst underwent long-term enhancement, the NMDA component underwent a long-term decrease in amplitude. These data suggest that in this chronic model of epileptiform activity, there is long-term potentiation of excitatory mediated events regulated primarily by AMPA receptors. Furthermore, the slow time course of the NMDA receptor-mediated synaptic conductances was responsible for prolonging the duration of the epileptiform bursts. However, the powerful depression of NMDA receptor-mediated events following tetanic stimulation suppressed the normally large potentiation of the overall response. Thus although it has been suggested that the NMDA receptor-mediated synaptic events contribute to the epileptogenic properties of the neocortex and hippocampus, this evoked depression may act as an intrinsic anticonvulsant mechanism.