Widespread patterns of neuronal damage following systemic or intracerebral injections of kainic acid: a histological study

Enhanced cyclooxygenase-2 expression in olfactory-limbic forebrain following kainate-induced seizures

Cyclooxygenase-2 is expressed at low levels in a subset of neurons in CNS and is rapidly induced by a multiplicity of factors including seizure activity. A putative relationship exists between cyclooxygenase-2 induction and glutamatergic neurotransmission. Cyclooxygenase-1 is constitutively expressed in glial cells and has been specifically linked to microglia. In this study we evaluated cyclooxygenase-2 protein immunocytochemically and found markedly enhanced immunostaining primarily in olfactory-limbic regions at 2, 6 and 24 h following kainate-induced status epilepticus. Impressive enhanced cyclooxygenase-2 immunoreactivity was localized in anterior olfactory nucleus, tenia tecta, nucleus of the lateral olfactory tract, piriform cortex, lateral and basolateral amygdala, orbital frontal cortex, nucleus accumbens (shell) and associated areas of ventral striatum, entorhinal cortex, dentate gyrus granule cells and hilar neurons, hippocampal CA subfields and subiculum. Alternate sections were processed for dual immunocytochemical analysis utilizing c-Fos and cyclooxygenase-2 antiserum to examine the possibility that the neuronal induction of cyclooxygenase-2 was associated with seizure activity. Neurons that showed a timeline of cyclooxygenase-2 upregulation were found to possess c-Fos immunopositive nuclei. Additional results from all seizure groups showed cyclooxygenase-1 induction in microglia, which was confirmed by Western blot analysis of hippocampus. Western blot and real-time quantitative RT-PCR analysis showed significant upregulation of cyclooxygenase-2 expression, confirming its induction in neurons. These data indicate that cyclooxygenase-2 induction in a neuronal network can be a useful marker for pathways associated with seizure activity.

Chronic bilateral stimulation of the anterior thalamus of kainate-treated rats increases seizure frequency

PURPOSE

Electrical stimulation of the anterior nucleus of the thalamus (ANT) is receiving increased attention as a novel means of controlling intractable epilepsy, and has entered human clinical trial. Animal data supporting the anticonvulsant benefit of ANT stimulation, however, has been obtained from acute chemoconvulsant models of epilepsy rather than models of chronic epilepsy with spontaneous seizures. It is unknown whether ANT stimulation is effective in models of chronic epilepsy.

METHODS

Bilateral ANT stimulation was evaluated in rats with chronic epilepsy following acute status epilepticus (SE) produced by systemic kainic acid (KA) administration. The evolution of epilepsy following KA SE and the effects of ANT stimulation were monitored by continuous video-EEG.

RESULTS

Following KA SE, most rats have 2-8 seizures per day, and the average seizure rate increases over time, doubling over the course of 14 weeks. Behavioral seizure severity, after the initial development of epilepsy, remains stable. Seizure frequency during ANT stimulation was 2.5 times the baseline seizure frequency. In some cases stimulation triggered seizures were observed. The effects of stimulation were specific to the ANT. Stimulation applied to electrodes placed outside the ANT did not significantly worsen seizure frequency.

CONCLUSIONS

ANT stimulation exacerbated seizure frequency in rats with chronic epilepsy following kainate status epilepticus.

Dopamine in neurotoxicity and neuroprotection: what do D2 receptors have to do with it?

Accurate control of dopamine levels and/or the resulting dopamine-receptor interaction is essential for brain function. Indeed, several human neurological and psychiatric disorders are characterized by dysfunctions of the dopaminergic system. Dopamine has been reported to exert either protective or toxic effects on neurons, yet it is unclear whether these effects are receptor-dependent and, if so, which dopamine receptor could be involved. The D(2) dopamine receptor occupies a privileged position because its signalling might be neuroprotective in human diseases, such as Parkinson's disease, ischaemia and epilepsy. Unravelling the role of D(2) receptors in neuronal death and survival might be central to understanding the mechanisms that underlie several neuropathologies.

Kainic acid-induced recurrent mossy fiber innervation of dentate gyrus inhibitory interneurons: possible anatomical substrate of granule cell hyper-inhibition in chronically epileptic rats

Kainic acid-induced neuron loss in the hippocampal dentate gyrus may cause epileptogenic hyperexcitability by triggering the formation of recurrent excitatory connections among normally unconnected granule cells. We tested this hypothesis by assessing granule cell excitability repeatedly within the same awake rats at different stages of the synaptic reorganization process initiated by kainate-induced status epilepticus (SE). Granule cells were maximally hyperexcitable to afferent stimulation immediately after SE and became gradually less excitable during the first month post-SE. The chronic epileptic state was characterized by granule cell hyper-inhibition, i.e., abnormally increased paired-pulse suppression and an abnormally high resistance to generating epileptiform discharges in response to afferent stimulation. Focal application of the gamma-aminobutyric acid type A (GABA(A)) receptor antagonist bicuculline methiodide within the dentate gyrus abolished the abnormally increased paired-pulse suppression recorded in chronically hyper-inhibited rats. Combined Timm staining and parvalbumin immunocytochemistry revealed dense innervation of dentate inhibitory interneurons by newly formed, Timm-positive, mossy fiber terminals. Ultrastructural analysis by conventional and postembedding GABA immunocytochemical electron microscopy confirmed that abnormal mossy fiber terminals of the dentate inner molecular layer formed frequent asymmetrical synapses with inhibitory interneurons and with GABA-immunopositive dendrites as well as with GABA-immunonegative dendrites of presumed granule cells. These results in chronically epileptic rats demonstrate that dentate granule cells are maximally hyperexcitable immediately after SE, prior to mossy fiber sprouting, and that synaptic reorganization following kainate-induced injury is temporally associated with GABA(A) receptor-dependent granule cell hyper-inhibition rather than a hypothesized progressive hyperexcitability. The anatomical data provide evidence of a possible anatomical substrate for the chronically hyper-inhibited state.

Anticonvulsant and neuroprotective effects of the novel nootropic agent nefiracetam on kainic acid-induced seizures in rats

Nefiracetam is a novel pyrrolidone-type nootropic agent, and it has been reported to possess a potential for antiepileptic therapy as well as cognition-enhancing effects. We investigated the anticonvulsant and neuroprotective effects of nefiracetam in kainic acid-induced seizures of rats, compared with levetiracetam and standard antiepileptic drugs. Subcutaneous injection of kainic acid (10 mg/kg) induced typical behavioral seizures such as wet dog shakes and limbic seizures and histopathological changes in the hippocampus (degeneration and loss of pyramidal cells in CA1 to CA4 areas). Nefiracetam (25, 50 and 100 mg/kg po) had no effect on the behavioral seizures and dose-dependently inhibited the hippocampal damage. In contrast, levetiracetam, a pyrrolidone-type antiepileptic drug, inhibited neither. Valproic acid and ethosuximide prevented the hippocampal damage without attenuating the behavioral seizures as nefiracetam. Zonisamide and phenytoin did not inhibit the behavioral seizures, while zonisamide enhanced the hippocampal damage and phenytoin increased the lethality rate. Carbamazepine inhibited the behavioral seizures at 50 mg/kg and enhanced that at 100 mg/kg, and it completely inhibited the hippocampal damage at both doses. We have previously reported that anticonvulsant spectrum of nefiracetam paralleled that of zonisamide, phenytoin or carbamazepine in standard screening models. However, the pharmacological profile of nefiracetam was closer to valproic acid or ethosuximide than that of zonisamide, phenytoin or carbamazepine in this study. These results suggest that anticonvulsant spectrum and mechanism of nefiracetam are distinct from those of standard antiepileptic drugs, and nefiracetam possesses a neuroprotective effect that is unrelated to seizure inhibition.

Regional neuropathology following kainic acid intoxication in adult and aged C57BL/6J mice

We evaluated regional neuropathological changes in adult and aged male mice treated systemically with kainic acid (KA) in a strain reported to be resistant to excitotoxic neuronal damage, C57BL/6. KA was administered in a single intraperitoneal injection. Adult animals were dosed with 35 mg/kg KA, while aged animals received a dose of 20 mg/kg in order to prevent excessive mortality. At time-points ranging from 12 h to 7 days post-treatment, animals were sacrificed and prepared for histological evaluation utilizing the cupric-silver neurodegeneration stain, immunohistochemistry for GFAP and IgG, and lectin staining. In animals of both ages, KA produced argyrophilia in neurons throughout cortex, hippocampus, thalamus, and amygdala. Semi-quantitative analysis of neuropathology revealed a similar magnitude of damage in animals of both ages, even though aged animals received less toxicant. Additional animals were evaluated for KA-induced reactive gliosis, assayed by an ELISA for GFAP, which revealed a 2-fold elevation in protein levels in adult mice, and a 2.5-fold elevation in aged animals. Histochemical evaluation of GFAP and lectin staining revealed activation of astrocytes and microglia in regions with corresponding argyrophilia. IgG immunostaining revealed a KA-induced breach of the blood-brain barrier in animals of both ages. Our data indicate widespread neurotoxicity following kainic acid treatment in C57BL/6J mice, and reveal increased sensitivity to this excitotoxicant in aged animals.

Pentoxifylline and insulin-like growth factor-I (IGF-I) abrogate kainic acid-induced cognitive impairment in mice

Hippocampal insults involving neuroimmune mechanisms can impair learning and memory in a variety of tasks. The present study was designed to assess the effect of pentoxifylline, an inhibitor of tumor necrosis factor alpha (TNFalpha), and insulin-like growth factor-I (IGF-I) on kainate (KA)-induced impairment in spatial memory. Male mice received a subcutaneous injection of a dose of KA (15 mg/kg) that had no cytotoxic effect on hippocampal neurons as confirmed by Fluorojade B staining. This dose resulted in an impairment of spatial memory in a two-trial recognition task 11 days later. Intraperitoneal administration of pentoxifylline (200 mg/kg) abrogated this effect. Repeated intracerebroventricular injection of IGF-I (2 microg/mouse on day 1 followed by 1 microg/mouse on days 2-5) abrogated KA-induced deficits in spatial memory whereas acute IGF-I (2 microg/mouse on day 1 only) had mixed effects. These findings indicate that endogenous TNFalpha is probably involved in the detrimental effects of kainate on cognition and that exogenous IGF-I can oppose these effects, probably by antagonizing TNFalpha-induced neurotoxicity.

Assessment of the effects of the cyclooxygenase-2 inhibitor rofecoxib on visuospatial learning and hippocampal cell death following kainate-induced seizures in the rat

Kainate-induced seizures result in hippocampal neurodegeneration and spatial learning deficits in rodents. Previous studies show that rofecoxib, a selective cyclooxygenase-2 inhibitor, protects against kainate-induced hippocampal cell death 3 days after seizures. Our aim was to determine whether rofecoxib attenuates visuospatial learning deficits and late neuronal death after kainate-induced seizures. Seizures were induced in Sprague-Dawley rats with kainic acid (10 mg/kg, i.p.). Eight hours later, animals received rofecoxib (10 mg/kg; n = 15) or vehicle (dimethylsulfoxide, n = 11). Animals were then treated daily for additional 2 or 9 days. Visuospatial learning was assessed in the Morris water maze (MWM) on days 5-9 after seizures. Seizure animals learned the MWM task significantly slower than non-seizure controls, but seizure animals showed higher swim speed (P < 0.05). Seizure animals receiving rofecoxib for 2 days showed no significant improvement in acquisition of the task compared to the vehicle group, even though mean latencies in the rofecoxib group were shorter from the third trial day onwards. This tendency was lost when rofecoxib was given for 9 days. TdT-mediated dUTP nick end labelling showed cell death in limbic structures 9 days after seizures. The time course of kainate-induced hippocampal cell death might be delayed by rofecoxib treatment, as the attenuation of cell death observed 3 days after seizures was no longer present after 9 days. We conclude that even though increasing evidence points to an injurious role of cyclooxygenase-2 products in acute brain injury processes, rofecoxib treatment failed to attenuate seizure-induced visuospatial learning deficits and the late phase of hippocampal neurodegeneration.

Stereological analysis of forebrain regions in kainate-treated epileptic rats

Patients and models of temporal lobe epilepsy display neuron loss in the hippocampal formation, but neuropathological changes also occur in other forebrain regions. We sought to evaluate the specificity and extent of volume loss of the major forebrain regions in epileptic rats months after kainate-induced status epilepticus. In systematic series of Nissl-stained sections, the areas of major forebrain regions were measured, and volumes were estimated using the Cavalieri principle. In some regions, the optical fractionator method was used to estimate neuron numbers. Most kainate-treated rats showed significant volume loss in the amygdala, olfactory cortex, and septal region, but others displayed different patterns, with significant loss only in the hippocampus or thalamus, for example. Average volume loss was most severe in the amygdala and olfactory cortex (82-83% of controls), especially the caudal parts of both regions. In the piriform cortex (including the endopiriform nucleus) of epileptic rats, an average of approximately one-third of Nissl-stained neurons and one-third of the GABAergic interneurons labeled by in situ hybridization for GAD67 mRNA were lost, and the extent of neuron loss was correlated with the extent of volume loss. Volumetric analysis of major forebrain regions was insensitive to specific neuron loss in subregions such as layer III of the entorhinal cortex and the hilus of the dentate gyrus. These findings provide quantitative evidence that kainate-treated rats tend to display extensive neuron and volume loss in the amygdala and olfactory cortex, although the patterns and extent of loss in forebrain regions vary considerably among individuals. In this status epilepticus-based model, extrahippocampal damage appears to be more extensive and hippocampal damage appears to be less extensive than that reported for patients with temporal lobe epilepsy.

Susceptibility to seizure-induced injury and acquired microencephaly following intraventricular injection of saporin-conjugated 192 IgG in developing rat brain

To study the role of neurotrophin-responsive neurons in brain growth and developmental resistance to seizure-induced injury, we infused saporin-conjugated 192-IgG (192 IgG-saporin), a monoclonal antibody directed at the P75 neurotrophin receptors (p75(NTR)), into the ventricles of postnatal day 8 (P8) rat pups. 7-10 days after immunotoxin treatment, loss of p75(NTR) immunoreactivity was associated with depletion of basal forebrain cholinergic projection to the neocortex and hippocampus. Kainic acid (KA)-induced seizures on P15 resulted in hippocampal neuronal injury in the majority of toxin-treated animals (13/16), but only rarely in saline-injected controls (2/25) (P < 0.001). In addition, widespread cerebral atrophy and a significant decrease in brain weight with preserved body weight were observed. Volumetric analysis of the hippocampal hilar region revealed a 2-fold reduction in perikaryal size and a 1.7-fold increase in cell packing density after 192 IgG-saporin injection. These observations indicate that neurotrophin-responsive neurons including basal forebrain magnocellular cholinergic neurons may be critical for normal brain growth and play a protective role in preventing excitotoxic neuronal injury during development.

Proechimys guyannensis: an animal model of resistance to epilepsy

PURPOSE

The potential interest of Proechimys guyannensis (PG), a spiny rat species living in the Amazonian region, as an animal model of anticonvulsant mechanisms, prompted the investigation of the susceptibility of this animal species to different epileptogenic treatments.

METHODS

Adult male Wistar and PG animals were submitted to amygdala kindling, the pilocarpine model and the intrahippocampal kainic acid (KA) model. Electrographic, behavioral, and neuropathological changes were compared between Wistar and PG animals.

RESULTS

PG animals demonstrated a striking resistance to reaching stage 5 of kindling. Of the 43 PG rats submitted to the kindling process, only three animals reached stage 5. In the pilocarpine and KA models, doses lower than those used in Wistar rats were able to induce status epilepticus (SE) in PG animals. Pilocarpine-induced SE in PG had a shorter duration, rarely exceeding 2 h, in contrast to the 8- to 12- h long SE in the Wistar rat. Of the 61 PG animals injected with pilocarpine, 48 presented with SE and only two presented with some spontaneous seizures after silent periods of 60 and 66 days. KA elicited self-sustained electrographic SE in PG animals, which lasted for 72 h. None of the surviving animals presented with spontaneous seizures in the long-term observation period (up to 120 days).

CONCLUSIONS

These findings indicate that the PG animal may have natural endogenous anticonvulsant mechanisms and also may be an animal model that is resistant to epileptogenic treatments.

Histamine H(1) and H(3) receptors in the rat thalamus and their modulation after systemic kainic acid administration

In rat thalamus, histamine H(1) receptor and isoforms of H(3) receptor were expressed predominantly in the midline and intralaminar areas. Correspondingly, higher H(1) and H(3) receptor binding was also detected in these areas. All isoforms of H(3) receptor were expressed in several thalamic nuclei, but there were minor differences between their expression patterns. H(1) mRNA expression was high in the ventral thalamus, but the H(1) binding level was low in these areas. Since increased brain histamine appears to have an antiepileptic effect through the H(1) receptor activity, kainic acid (KA)-induced status epilepticus in rat was used to study modulation of H(1) and H(3) receptors in the thalamus following seizures. After systemic KA administration, transient decreases in mRNA expression of H(1) receptor and H(3) receptor isoforms with full-length third intracellular loops were seen in the midline areas and the H(1) receptor mRNA expression also decreased in the ventral thalamus. After 1 week, a robust increase in mRNA expression of H(3) receptor isoforms with a full-length third intracellular loop was found in the ventral posterior, posterior, and geniculate nuclei. The changes indicate a modulatory role of H(3) receptor in the sensory and motor relays, and might be involved in possible neuroprotective and compensatory mechanisms after KA administration. However, short-term increases in the H(3) receptor binding appeared earlier (72 h) than the increases of H(3) mRNA expression (1-4 w). The elevations in H(3) binding were evident in the intralaminar area, laterodorsal, lateral posterior, posterior and geniculate nuclei, and were likely to be related to the cortical and subcortical inputs to thalamus.

Effects of ryanodine receptor activation on neurotransmitter release and neuronal cell death following kainic acid-induced status epilepticus

Dynamic changes in intracellular free Ca(2+) concentration play a crucial role in various neural functions. The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) and the ryanodine (Ry) receptor (RyR) are involved in Ca(2+)-induced Ca(2+)-release (CICR). Recent studies have shown that type 3 IP3R is highly expressed in rat hippocampal neurons after kainic acid (KA)-induced seizures and that dantrolene, a RyR antagonist, reduces KA-induced neuronal cell death. We investigated the RyR-associated effects of CICR agents on basal and K(+)-evoked releases of GABA and glutamate in rat hippocampus and the changes in expression of mRNA for RyRs in mouse brain after KA-induced seizures. The stimulatory effect of Ry on releases of GABA and glutamate was concentration-dependent in a biphasic manner. The inflection point in concentration-response curves for Ry on GABA release was lower than that for glutamate in both basal and K(+)-evoked conditions, suggesting that hyperactivation of RyR-associated CICR produces the imbalance between GABAergic and glutamatergic transmission. Following KA-induced seizures, transient up-regulation of brain-type RyR mRNA was observed in the hippocampal CA3 region and striatum, and signals for c-Fos mRNA increased transiently in the hippocampus, dentate gyrus and deeper layers of the neocortex. Thereafter, some dead neurons with single-stranded DNA (ssDNA) immunoreactive fragmented nuclei appeared in these areas. These findings suggest that intracellular Ca(2+) release via the RyR might be one of the mechanisms involved in KA-induced neuronal cell death.

Advances in the pathophysiology of developmental epilepsies

Pediatric epilepsies display unique characteristics that differ significantly from epilepsy in adults. The immature brain exhibits a decreased seizure threshold and an age-specific response to seizure-induced brain injury. Many idiopathic epilepsy syndromes and symptomatic epilepsies commonly present during childhood. This review highlights recent advances in the pathophysiology of developmental epilepsies. Cortical development involves maturational regulation of multiple cellular and molecular processes, such as neurogenesis, neuronal migration, synaptogenesis, and expression of neurotransmitter receptors and ion channels. These normal developmental changes of the immature brain also contribute to the increased risk for seizures and unique responses to seizure-induced brain injury in pediatric epilepsies. Recent technological advances, especially in genetics and imaging, have yielded exciting discoveries about the pathophysiology of specific pediatric epilepsy syndromes, such as the emergence of channelopathies as the cause of many idiopathic epilepsies and identification of malformations of cortical development as a major source of symptomatic epilepsies in children.

The neurobiology of temporal lobe epilepsy: too much information, not enough knowledge

Although there are many types of epilepsy of both genetic and acquired forms, temporal lobe epilepsy (TLE) with hippocampal sclerosis is probably the single most common human epilepsy, and the one most intensely studied. Despite a wealth of descriptive data obtained from patient histories, imaging techniques, electroencephalographic recording, and histological studies, the epileptogenic process remains poorly understood. Progress toward understanding the etiology of an acquired neurological disorder is largely dependent on the degree to which experimental animal models reflect the human condition. Recent observations suggest that significant disparities exist between the features of human TLE with hippocampal sclerosis and those of animal models that involve prolonged status epilepticus to initiate the epileptogenic process. TLE most commonly involves patients with focal seizures who exhibit limited and often asymmetrical brain damage, did not experience status epilepticus prior to the onset of epilepsy, and who appear relatively normal on neurological examination. Conversely, animals subjected to prolonged status epilepticus exhibit severe brain damage, behavioral abnormalities, and frequent generalized seizures. In addition, although many TLE patients exhibit an atrophic hippocampus that may, or may not, be a source of spontaneous seizures, hippocampal damage in animals subjected to status epilepticus is an inconsistent and often minor part of a much greater constellation of damage to other brain structures. Furthermore, many patients exhibit developmental structural abnormalities that presumably play a role in the clinical etiology, whereas most animal models involve severe insults in initially normal laboratory rats. Although much has been learned using the current animal models, the available data suggest the need for a critical reappraisal of the assumptions underlying their use, and the need to develop experimental preparations that may more closely model the human epileptic state.

Choline acetyltransferase, glutamic acid decarboxylase and somatostatin in the kainic acid model for chronic temporal lobe epilepsy

The aim of the study was to investigate neurochemical changes in a kainic acid (KA; 10 mg/kg, s.c.)-induced spontaneous recurrent seizure model of epilepsy, 6 months after the initial KA-induced seizures. The neuronal markers of cholinergic and gamma-aminobutyric acid (GABA)ergic systems, i.e. choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities, and a marker for neuropeptide, i.e. level of somatostatin, have been investigated. The brain regions investigated were the hippocampus, amygdala/piriform cortex, caudate nucleus, substantia nigra and the frontal, parietal, temporal and occipital cortices. Six months after KA injection, reduced ChAT activity was observed in the amygdala/piriform cortex (47% of control; p<0.001), increased ChAT activity in the hippocampus (119% of control; p<0.01) and normal ChAT activity in the other brain regions. The activity of GAD was significantly increased in all analysed cortical regions (between 146 and 171% of control), in the caudate nucleus (144% of control; p<0.01) and in the substantia nigra (126% of control; p<0.01), whereas in the amygdala/piriform cortex, the GAD activity was moderately lowered. The somatostatin level was significantly increased in all cortical regions (between 162 and 221% of control) as well as in the hippocampus (119% of control), but reduced in the amygdala/piriform cortex (45% of control; p<0.01). Six months after KA injection, the somatostatin:GAD ratio was lowered in the amygdala/piriform cortex (49% of control) and in the caudate nucleus (41% of control), whereas it was normal in the hippocampus and moderately increased in the cortical brain regions. A positive correlation was found between seizure severity and the reduction of both ChAT activities and somatostatin levels in the amygdala/piriform cortex. The results show a specific pattern of changes for cholinergic, GABAergic and somatostatinergic activities in the chronic KA model for epilepsy. The revealed data suggest a functional role for them in the new network that follows spontaneous repetitive seizures.

Degenerative neuronal changes in the rat thalamus induced by status epilepticus at different developmental stages

SE was induced in Wistar rats at post-natal (P) days 12, 15, 18, 21, and 25 to determine distribution and severity of thalamic damage in relation to time after SE. Six different intervals from 4 h up to 1 week were studied using Fluoro-Jade B (FJB) staining. Severity of damage was semi-quantified for every age-and-interval group. Distribution of neuronal damage within various thalamic nuclei was mapped by a computer-aided digitizing system. A consistent neuronal damage occurred in functionally heterogenous thalamic nuclei. Damage was found in all age groups although its extension and time course as well as the number of involved thalamic nuclei varied. Number of injured thalamic nuclei rapidly increased with age on SE-onset. In P12 group, degenerating neurons were consistently seen in the mediodorsal and lateral dorsal thalamic nuclei. Since P15, neurodegeneration was observed additionally in midline, ventral and caudal thalamic nuclei (visual and auditory thalamic nuclei), in the lateral posterior and in the reticular nucleus. In P21 and P25 animals, the majority of thalamic nuclei exhibited marked neuronal damage. Nuclei with a small number (anterior and intralaminar) or no FJB-positive neurons (the ventral nucleus of the lateral geniculate body) were exceptional. The pattern of thalamic damage is age-specific; its extent and severity increases with age.

Serial MRI after experimental febrile seizures: altered T2 signal without neuronal death

Whereas most febrile seizures (FSs) carry a benign outcome, a subpopulation of individuals with prolonged FSs are at risk for later temporal lobe epilepsy. Signal changes on magnetic resonance imaging (MRI) may provide early markers for changes in neuronal integrity that may promote epileptogenesis in such individuals. Here, we used serial MRIs, obtained before and at several time points after experimental prolonged FSs, to determine the prevalence and distribution of signal changes on T2-weighted images and to investigate the pathological substrates leading to these changes. Seventy-five percent of immature rats with experimental prolonged FSs had abnormal T2 signal enhancement at 24 hours, and 87.5% at 8 days after the seizures. The altered T2 values involved the dorsal hippocampus (75%), the piriform cortex (87.5%), and the amygdala (25%). However, these changes were not accompanied by evidence of neuronal injury or death in these regions, as assessed using the Fluoro-Jade method. Thus, experimental prolonged FSs lead to relatively frequent abnormal MRI signal in "temporal lobe" structures. Although these changes do not signify cell death, they may denote pathological cellular processes that promote epileptogenesis. .

Sensitive indicators of injury reveal hippocampal damage in C57BL/6J mice treated with kainic acid in the absence of tonic-clonic seizures

Sensitive indices of neural injury were used to evaluate the time course of kainic acid (KA)-induced hippocampal damage in adult C57BL/6J mice (4 months), a strain previously reported to be resistant to kainate-induced neurotoxicity. Mice were injected systemically with saline or kainate, scored for seizure severity (Racine scale), and allowed to survive 12 h, one, three, or seven days following which they were evaluated for neuropathological changes using histological or biochemical endpoints. Most kainate-treated mice exhibited limited seizure activity (stage 1); however, cupric-silver and Fluoro-Jade B stains revealed significant damage by 12 h post-treatment. Immunohistochemistry and immunoassay of glial fibrillary acidic protein and lectin staining revealed a strong treatment-induced reactive gliosis and microglial activation. Immunostaining for immunoglobulin G revealed a kainate-induced breach in the blood-brain barrier. Nissl and hematoxylin stains provided little information regarding neuronal damage, but revealed the identity of non-resident cells which infiltrated the pyramidal layer. Our data suggest sensitive indicators of neural injury evaluated over a time course, both proximal and distal to treatment, are necessary to reveal the full extent of neuropathological changes which may be underestimated by traditional histological stains. The battery of neuropathological indices reported here reveals the C57BL/6J mouse is sensitive to excitotoxic neural damage caused by kainic acid, in the absence of tonic-clonic seizures.

Ginsenosides inhibit NMDA receptor-mediated epileptic discharges in cultured hippocampal neurons

Epilepsy or the occurrence of spontaneous recurrent epileptiform discharges (SREDs, seizures) is one of the most common neurological disorders. Shift in the balance of brain between excitatory and inhibitory functions due to different types of structural or functional alterations may cause epileptiform discharges. N-Methyl-D-aspartate (NMDA) receptor dysfunctions have been implicated in modulating seizure activities. Seizures and epilepsy are clearly dependent on elevated intracellular calcium concentration ([Ca2+]i) by NMDA receptor activation and can be prevented by NMDA antagonists. This perturbed [Ca2+]i levels is forerunner of neuronal death. However, therapeutic tools of elevated [Ca2+]i level during status epilepticus (SE) and SREDs have not been discovered yet. Our previous study showed fast inhibition of ginseng total saponins and ginsenoside Rg3 on NMDA receptor-mediated [Ca2+]i in cultured hippocampal neurons. We, therefore, examined the direct modulation of ginseng on hippocampal neuronal culture model of epilepsy using fura-2-based digital Ca2+ imaging and neuronal viability assays. We found that ginseng total saponins and ginsenoside Rg3 inhibited Mg2+ free-induced increase of [Ca2+]i and spontaneous [Ca2+]i oscillations in cultured rat hippocampal neurons. These results suggest that ginseng may play a neuroprotective role in perturbed homeostasis of [Ca2+]i and neuronal cell death via the inhibition of NMDA receptor-induced SE or SREDs.

Soluble KDI domain of γ1 laminin protects adult hippocampus from excitotoxicity of kainic acid

Recent data indicate that the soluble KDI domain of gamma1 laminin promotes survival and neurite outgrowth of human central neurons in vitro (Liebkind et al.[2003] J Neurosci Res 73:637-643), and seems to neutralize both glia- and myelin-derived signals that hamper regeneration in the central nervous system (CNS) of adult mammals. We show that damage of adult rat neocortical and hippocampal areas by a stereotaxic injection of kainic acid (KA) is prevented by a preceding injection of the soluble KDI domain. In the presence of the KDI domain, both neocortical and hippocampal areas show extensive gliosis but have viable neurons and glial cells, which are absent and the areas fully destroyed after injection of KA alone. This result indicates that the KDI domain of the gamma1 laminin protects the CNS against excitotoxic insults and promotes survival of both neurons and glial cells. The KDI domain may thus be a potential drug to prevent CNS damage induced by neurodegenerative disorders, mechanical injury, or ischemia.

Mitochondrial Dysfunction and Ultrastructural Damage in the Hippocampus during Kainic Acid-induced Status Epilepticus in the Rat

PURPOSE

Prolonged and continuous epileptic seizure (status epilepticus) results in cellular changes that lead to neuronal damage. We investigated whether these cellular changes entail mitochondrial dysfunction and ultrastructural damage in the hippocampus, by using a kainic acid (KA)-induced experimental status epilepticus model.

METHODS

In Sprague-Dawley rats maintained under chloral hydrate anesthesia, KA (0.5 nmol) was microinjected unilaterally into the CA3 subfield of the hippocampus to induce seizure-like hippocampal EEG activity. The activity of key mitochondrial respiratory chain enzymes in the dentate gyrus (DG), or CA1 or CA3 subfield of the hippocampus was measured 30 or 180 min after application of KA. Ultrastructure of mitochondria in those three hippocampal subfields during KA-induced status epilepticus also was examined with electron microscopy.

RESULTS

Microinjection of KA into the CA3 subfield of the hippocampus elicited progressive build-up of seizure-like hippocampal EEG activity. Enzyme assay revealed significant depression of the activity of nicotinamide adenine dinucleotide cytochrome c reductase (marker for Complexes I+III) in the DG, or CA1 or CA3 subfields 180 min after KA-elicited temporal lobe status epilepticus. Conversely, the activities of succinate cytochrome c reductase (marker for Complexes II+III) and cytochrome c oxidase (marker for Complex IV) remained unaltered. Discernible mitochondrial ultrastructural damage, varying from swelling to disruption of membrane integrity, also was observed in the hippocampus 180 min after hippocampal application of KA.

CONCLUSIONS

Our results demonstrated that dysfunction of Complex I respiratory chain enzyme and mitochondrial ultrastructural damage in the hippocampus are associated with prolonged seizure during experimental temporal lobe status epilepticus.

Hippocampal neurotransplantation evaluated in the rat kainic acid epilepsy model

OBJECTIVE

Neurotransplantation has focused on disorders that involve subcortical brain targets. We evaluated the concepts of epileptic focus repair and changes in animal behavior through replacement of lost hippocampal neurons. The safety of hippocampal neurotransplantation was assessed in the rat kainic acid (KA) epilepsy model.

METHODS

Sixty-three rats were studied and classified into six groups: KA plus 40,000 LBS-Neurons (Layton BioScience, Sunnyvale, CA; n = 13); KA plus 80,000 cells (n = 12); KA plus media (n = 9); no-KA plus 40,000 cells (n = 12); no-KA plus 80,000 cells (n = 12); and no-KA plus media (n = 5). Clinical observation (2 h daily) and electroencephalogram recording (3 h every other week) were performed to check for seizures until Week 11 after KA injection. On Week 12, the Morris water maze test was performed to assess spatial learning and memory.

RESULTS

Four rats were excluded because of intracranial hematoma or abscess. In the clinical observation of seizures, the no-KA plus media group had significantly fewer seizures than rats that received KA followed by injection of 40,000 cells, 80,000 cells, or media (P = 0.001, 0.0004, and 0.004, respectively). On electroencephalographic analysis, there was no significant difference between any of the groups. Transplanted rats with KA-induced epilepsy did not have an increased number of seizures. In the Morris water maze test, the hidden platform task showed that the KA plus 80,000 cell group had significantly longer swim latencies than groups with no-KA plus 40,000 cells (P = 0.035) or no-KA plus 80,000 cells (P = 0.015), demonstrating the behavioral deficits caused by KA injection. The probe trial showed no significant difference for the percentage of time in the target quadrant between any of the groups. Histological studies showed that 26 (59%) of 44 transplanted rats had evidence of graft survival.

CONCLUSION

The safety of cortical neurotransplantation was demonstrated, even in an animal model predisposed to epilepsy. We did not find evidence for cessation of seizures or improvement in behavior using this model.

Latency to onset of status epilepticus determines molecular mechanisms of seizure-induced cell death

The molecular mechanisms mediating degeneration in response to neuronal insults, including damage evoked by prolonged seizure activity, show substantial variability across laboratories and injury models. Here we investigate the extent to which the proportion of cell death occurring by apoptotic vs. necrotic mechanisms may be shifted by changing the temporal parameters of the insult. In initial studies with continuous seizures (status epilepticus, SE), signs of apoptotic degeneration were most clearly observed when SE occurred following a long latency (>86 min) after injection of kainic acid as compared with a short-latency SE (<76 min). Therefore, in this study we directly compared short- with long-latency SE for the expression of molecular markers for apoptosis and necrosis in an especially vulnerable brain region (rhinal cortex). Molecular markers of apoptosis (DNA fragmentation, cleavage of ICAD, an inhibitor of "caspase-activated DNase" (CAD), and prevalence of a caspase-generated fragment of alpha-spectrin) were detected following long-latency SE. Short-latency SE resulted in expression of predominantly necrotic features of cell death, such as "non-ladder" pattern of genomic DNA degradation, prevalence of a calpain-generated alpha-spectrin fragment, and absence of ICAD cleavage. Silver staining revealed no significant difference in the extent and spatial distribution of degeneration between long- or short-latency SE. These data indicate that the latency to onset of SE determines the extent to which apoptotic or necrotic mechanisms contribute to the degeneration following SE. The presence of a long latency period, during which multiple brief seizure episodes may occur, favors the occurrence of apoptotic cell death. It is possible that the absence of such "preconditioning" period in short-latency SE favors predominantly necrotic profile.

Early increase of apoptosis-linked gene-2 interacting protein X in areas of kainate-induced neurodegeneration

Apoptosis-linked gene-2 interacting protein X (Alix) is thought to be involved in both cell death and vesicular trafficking. We examined Alix expression 2 h, 6 h and 24 h after triggering seizure-dependent neuronal death by i.p. kainic acid injection. In the hippocampus, intense, transient immunolabelling was observed in the strata lucidum, oriens and radiatum, areas of high synaptic activity. The similarity of this distribution to those of synaptophysin and endophilin suggests a presynaptic localisation. Alix labelling was increased in neuronal cell bodies in kainate-sensitive regions before or concomitant with the first signs of oedema and/or neuronal eosinophilia. The increase persisted 24 h after kainate-injection in CA3 and the piriform cortex which are areas with massive swelling and numerous pyknotic neurons. This suggests that Alix may play an early role in the mechanisms leading to cell death. Taken together, our results suggest that Alix may be a molecular link between synaptic functioning and neuronal death.

Dietary restriction differentially protects from neurodegeneration in animal models of excitotoxicity

Reduced caloric intake obtained through long-term dietary restriction has been found beneficial in some animal models of neurodegeneration. We report here that rats maintained under dietary restriction from the second to the eighth month of age are fully protected towards degeneration of GABAergic neurons in the hippocampus and the olfactory-entorhinal cortex caused by systemic administration of the convulsant toxin, kainic acid. However, in a different model of excitotoxic neurodegeneration, injection of ibotenic acid in the forebrain magnocellular basal nucleus, the decrease of a cholinergic marker in the target areas of the cortex was only partially protected by dietary restriction. Thus, in different experimental models neurodegeneration can be differentially rescued by dietary restriction. Analysis of alterations in the expression of relevant genes in different experimental conditions, could help in better understanding these differences.

Fiber connections of the hippocampal formation and septum and subdivisions of the hippocampal formation in the pigeon as revealed by tract tracing and kainic acid lesions

The organization of the pigeon hippocampal formation was examined by tract tracing by using biotinylated dextran amine (BDA) and cholera toxin B subunit (CTB) and by injections of kainic acid to produce excitotoxic lesions. The hippocampal formation was divided into seven subdivisions based on Nissl staining and intrinsic and septal connections: dorsomedial (DM), dorsolateral (DL), triangular (Tr), V-shaped layer, magnocellular (Ma), parvocellular, and cell-poor regions. DL was composed of dorsal and ventral portions and sent associational fibers to DM, the V-shaped layer, and Tr. DL had strong reciprocal connections with the densocellular part of the hyperpallium (HD) and projected to the dorsolateral corticoid area. DM had reciprocal fiber connections with the V-shaped layer, Ma, and DL as well as with several subdivisions of the arcopallium. DL and DM, but not the V-shaped layer, projected fibers to the septum where those from DM exceeded in number those from DL. These projections further extended to the hypothalamus, particularly the lateral hypothalamic area. The lateral and medial septal nuclei projected back a very small number of ascending fibers to the hippocampal formation. Intraventricular injections of kainic acid induced neuronal loss widely in the hippocampal formation and subsequently produced gliosis in DM. These results indicate that DL receives its main afferents from HD and in turn sends inputs to an intrinsic circuit composed of hippocampal subdivisions DM, Ma, Tr, and the V-shaped layer; and also that DM is the main exit to the septum and hypothalamus. It is suggested that neurons in the V-shaped layer are intrinsic. Together, the results suggest that the V-shaped layer is comparable to the dentate gyrus of the mammalian hippocampal formation and that DM incorporates components comparable to both Ammon's horn and the subiculum.

Damage to the amygdalo-hippocampal projection in temporal lobe epilepsy: A tract-tracing study in chronic epileptic rats

Both the amygdala and hippocampus are damaged in drug-resistant temporal lobe epilepsy (TLE), suggesting that amygdalo-hippocampal interconnectivity is compromised in TLE. Therefore, we examined one of the major projections from the amygdala to the hippocampus, the projection from the amygdala to the CA1 subfield of the hippocampus/subiculum border region, and assessed whether it is preserved in rats with spontaneous seizures. Male Wistar rats were injected with kainic acid (9 mg/kg, i.p.) to induce chronic epilepsy. The occurrence of spontaneous seizures was monitored 5 or 15 weeks later by video-recording the rats for up to 5 days. Saline-injected animals served as controls. Thereafter, the retrograde tracer Fluoro-gold was injected into the border region of the temporal CA1/subiculum. Rats were perfused for histology 1-2 weeks later and sections were immunohistochemically processed to detect Fluoro-gold-positive cells. Comparison of the labeling in control and epileptic tissue indicated that a large cluster of retrogradely labeled cells in the parvicellular division of the basal nucleus was well preserved in epilepsy, even when the neuronal damage in the amygdala was substantial. Another large cluster of retrogradely labeled cells in the lateral division of the amygdalo-hippocampal area, the posterior cortical nucleus (part of the vomeronasal amygdala), and the periamygdaloid cortex (part of the olfactory amygdala), however, had disappeared in epileptic brain in parallel to severe neuronal loss in these nuclei. These data demonstrate that a projection from the parvicellular division of the basal nucleus to the temporal CA1/subiculum region is resistant to status epilepticus-induced neuronal damage and provides a candidate pathway by which seizure activity can spread and propagate from the amygdala to the hippocampal formation.

Response to kainic acid injections: changes in staining for zinc, FOS, cell death and glial response in the rat forebrain

A pool of zinc is present in synaptic vesicles in a population of glutamatergic neurones. Zinc appears to modulate synaptic transmission and cause neuronal death. The status of vesicular zinc, neuronal death and glial reaction in the rat forebrain was analysed after a systemic injection of kainic acid in order to establish a model for future studies on zinc function. Rats received a systemic injection of kainic acid (10 mg/kg) and were killed 3, 6, 12, 24 and 48 h post-treatment. Timm's method and zinquin staining were used to detect zinc. Immunostaining for Fos-like proteins and staining with Fluoro-Jade B were used to detect cell reaction and degeneration, respectively. Glial fibrillary acidic protein and tomato lectin were used as glial markers. Zinquin staining for zinc rose transitorily in neuronal somata 6 h after injection (not observed at 24-48 h) in the piriform and entorhinal cortices, amygdala and hippocampus. In contrast sulphide/silver staining for zinc showed virtually no rise in cytoplasmic zinc (except in cornus ammonis field 1 of the hippocampus) 6 h after injection, and a decrease (bleaching) in some terminal fields starting 12 h after injection and increasing at 24-48 h. The areas most affected by the zinc bleaching were the olfactory bulb, piriform and entorhinal cortices, endopiriform and amygdaloid nuclei. Transitory Fos immunostaining (within neuronal nuclei) was observed between 3 and 12 h after kainate treatment in many telencephalic areas: olfactory bulb, cortex (piriform, hippocampal and neocortex) and amygdaloid nuclei. This was accompanied by changes in glial markers starting 3 h after injection. Fluoro-Jade B staining in neurones (degeneration) appeared 6 h after treatment and increased later. Degenerating areas generally coincided with those showing Fos immunoreactivity. Zinquin and sulphide/silver methods revealed various pools of zinc after kainate injection: a cytoplasmic pool and a terminal field (or vesicular) pool. Cytoplasmic zinc (zinquin) was coincident, in time and location, with cell degeneration, thus implicating zinc in cell death. This zinc may not have come from presynaptic stores, since no bleaching (sulphide/silver method) was observed 6 h after injection. Future experiments altering zinc pools (e.g. by chelating agents) may elucidate the function of zinc.

Reduced inhibition and increased output of layer II neurons in the medial entorhinal cortex in a model of temporal lobe epilepsy

Temporal lobe epilepsy is the most common type of epilepsy in adults, and its underlying mechanisms are unclear. To investigate how the medial entorhinal cortex might contribute to temporal lobe epilepsy, we evaluated the histology and electrophysiology of slices from rats 3-7 d after an epileptogenic injury (pilocarpine-induced status epilepticus). Nissl staining, NeuN immunocytochemistry, and in situ hybridization for GAD65 mRNA were used to verify the preferential loss of glutamatergic neurons and the relative sparing of GABAergic interneurons in layer III. From slices adjacent to those that were used for anatomy, we obtained whole-cell patch recordings from layer II medial entorhinal cortical neurons. Recordings under current-clamp conditions revealed similar intrinsic electrophysiological properties (resting membrane potential, input resistance, single spike, and repetitive firing properties) to those of controls. Spontaneous IPSCs were less frequent (68% of controls), smaller in amplitude (57%), and transferred less charge (51%) than in controls. However, the frequency, amplitude, and rise time of miniature IPSCs were normal. These findings suggest that after epileptogenic injuries the layer II entorhinal cortical neurons receive less GABA(A) receptor-mediated synaptic input because presynaptic inhibitory interneurons become less active. To investigate the possible consequences of reduced spontaneous inhibitory input to layer II neurons, we recorded field potentials in the dentate gyrus, their major synaptic target. At 5 d after pilocarpine-induced status epilepticus the spontaneous field potentials recorded in vivo were over three times more frequent than in controls. These findings suggest that an epileptogenic injury reduces inhibition of layer II neurons and results in excessive synaptic input to the dentate gyrus.

Quantification and localization of kainic acid-induced neurotoxicity employing a new biomarker of cell death: cleaved microtubule-associated protein-tau (c-tau)

Previous studies of neuronal degeneration induced by the neurotoxin, kainic acid, employed silver stain techniques that are non-quantitative or ELISA measurement of the non-neuronal protein, glial fibrillary acidic protein. As previous studies employed biomarkers that were either non-quantitative or non-neuronal, the present study employed a new neuronally localized biomaker of neuronal damage, cleaved microtubule-associated protein (MAP)-tau (C-tau). The time course of kainate neurotoxicity was quantitatively determined in several brain regions in the present study employing a C-tau specific ELISA. Differences in ELISA determined regional brain levels of C-tau were compared with the density of somatodendritic C-tau labeling qualitatively determined in immunohistochemical anatomical mapping studies of kainic acid-treated animals. Immunoblot studies revealed that the C-tau antibodies employed in the present study were highly specific for proteolytic cleaved C-tau. Immunolabeling of 45 kD-50 kD C-tau proteins was observed only in brain samples from kainic acid-treated but not vehicle-treated rats. Time course studies revealed that C-tau levels determined by ELISA were maximal 3 days after kainic acid with C-tau levels increasing 26-fold in hippocampus, 16-fold in cortex and four-fold in both striatum and hypothalamus. These statistical differences in maximal C-tau levels observed in the ELISA studies were similar to differences qualitatively observed in C-tau immunohistochemical studies. C-tau immunohistochemistry revealed extensive damage in hippocampal regions CA1 and 3, moderate damage in several cortical regions and mild damage in striatum and hypothalamus. Similar cleavage of rat MAP-tau to C-tau has been reported after neuronal degeneration induced by neurotoxic doses of methamphetamine and neuronal degeneration resulting from bacterial meningitis. In humans, C-tau proteolysis has been demonstrated to be a reliable biomarker of neuronal damage in traumatic brain injury and stroke where cerebrospinal C-tau levels are correlated with patient clinical outcome. These data suggest that C-tau proteolysis may prove a reliable species independent biomarker of neuronal degeneration regardless of source of injury.

Protection provided by cyclosporin A against excitotoxic neuronal death is genotype dependent

PURPOSE

Previous studies have shown that the immunosuppressant cyclosporin A (CsA), a specific blocker of the mitochondrial permeability transition (MPT) pore, can dramatically ameliorate the selective neuronal necrosis resulting from ischemia-reperfusion, traumatic brain injury, and N-methyl-d-aspartate (NMDA)-evoked neurotoxicity. The purpose of this study was to determine whether two different immunosuppressants, CsA and FK-506, could ameliorate the neuronal damage observed after kainate-induced seizures in strains that are differentially susceptible to excitotoxin-induced cell death.

METHODS

Excitotoxin-resistant (C57BL/6) or -susceptible (FVB/N) mice were administered kainate alone (30 mg/kg), CsA alone (5, 10, or 20 mg/kg), or one of the immunosuppressants (CsA, 5 mg/kg or 10 mg/kg; FK-506, 0.5 mg/kg) followed by kainate. After drug administration, mice were monitored continuously for the onset and extent of seizure activity. After a survival of 7 days, animals were assessed for hippocampal damage.

RESULTS

Whereas CsA alone induced no epileptogenic effects and both immunosuppressants were without effect on the induction of kainate-induced seizures, administration of CsA to excitotoxin-susceptible mice (FVB/N) virtually eliminated neuronal cell death. In contrast, induction of neuronal cell death was evident when CsA was administered to excitotoxin-resistant mice (C57BL/6). Administration of FK-506, another commonly used immunosuppressant, which lacks an effect on the MPT, had no effect on modification of susceptibility to kainate-induced cell death in either strain.

CONCLUSIONS

As our data show differential protection of hippocampal neurons against excitotoxic cell death by pretreatment with CsA, these results suggest that strain-dependent differences in mitochondrial integrity and function may exist.

Mitochondrial uncoupling protein-2 protects the immature brain from excitotoxic neuronal death

Excitotoxic cell death is the fundamental process responsible for many human neurodegenerative disorders, yet the basic mechanisms involved are not fully understood. Here, we exploited the fact that the immature brain is remarkably resistant to seizure-induced excitotoxic cell death and examined the underlying protective mechanisms. We found that, unlike in the adult, seizures do not increase the formation of reactive oxygen species or result in mitochondrial dysfunction in neonatal brain, because of high levels of the mitochondrial uncoupling protein (UCP2). UCP2 expression and function were basally increased in neonatal brain by the fat-rich diet of maternal milk, and substituting a low-fat diet reduced UCP2, restored mitochondrial coupling, and permitted seizure-induced neuronal injury. Thus, modulation of UCP2 expression and function by dietary fat protects neonatal neurons from excitotoxicity by preventing mitochondrial dysfunction. This mechanism offers novel neuroprotective strategies for individuals, greater than 1% of the world's population, who are affected by seizures.

Anti-epileptic drugs as possible neuroprotectants in cerebral ischemia

Many similarities exist between cerebral ischemia and epilepsy regarding brain-damaging and auto-protective mechanisms that are activated following the injurious insult. Therefore, drugs that are effective in minimizing seizure-induced brain damage may also be useful in minimizing ischemic injury. Use of such drugs in stroke victims may have important clinical and financial advantages. Therefore, the authors conducted a Medline search of studies involving the use of anti-epileptic drugs (AEDs) as possible neuroprotectants and summarize the data. Most AEDs have been tested in animal models of focal or global ischemia and some were already tested in humans, for a possible neuroprotective effect. The existing data is rather scant and insufficient but it appears that only drugs that have multiple mechanisms of action seem to have some potential in conferring a degree of neuroprotection that could be clinically applicable to stroke patients. In conclusion, some of the newer AEDs show promise as possible neuroprotectants in the setup of acute ischemic stroke but more studies are needed before clinical trials in humans could be undertaken.

The neuroprotective effects of heat shock protein 27 overexpression in transgenic animals against kainate-induced seizures and hippocampal cell death

The 27-kDa heat shock protein (HSP27) has a potent ability to increase cell survival in response to a wide range of cellular challenges. In order to investigate the mode of action of HSP27 in vivo, we have developed transgenic lines, which express human HSP27 at high levels throughout the brain, spinal cord, and other tissues. In view of the particular property of HSP27 compared with other HSPs to protect neurons against apoptosis, we have tested these transgenic lines in a well established in vivo model of neurotoxicity produced by kainic acid, where apoptotic cell death occurs. Our results demonstrate for the first time the marked protective effects of HSP27 overexpression in vivo, which significantly reduces kainate-induced seizure severity and mortality rate (>50%) in two independent lines and markedly reduces neuronal cell death in the CA3 region of hippocampus. This reduced seizure severity in HSP27 transgenic animals was associated with a marked attenuation of caspase 3 induction and apoptotic features. These studies clearly demonstrate that HSP27 has a major neuroprotective effect in the central nervous system in keeping with its properties demonstrated in culture and highlight an early stage in the cell death pathway that is affected by HSP27.

Neuronal cell death in a rat model for mesial temporal lobe epilepsy is induced by the initial status epilepticus and not by later repeated spontaneous seizures

PURPOSE

To determine whether repeated seizures contribute to hippocampal sclerosis, we investigated whether cell loss in the (para) hippocampal region was related to the severity of chronic seizure activity in a rat model for temporal lobe epilepsy (TLE).

METHODS

Chronic epilepsy developed after status epilepticus (SE) that was electrically induced 3-5 months before. The presence of neuronal damage was assessed by using Fluoro-Jade and dUTP nick end-labeling (TUNEL) of brain sections counterstained with Nissl.

RESULTS

We found a negative correlation between the numbers of surviving hilar cells and the duration of the SE (r = -0.66; p < 0.01). In the chronic phase, we could discriminate between rats with occasional seizures (0.15 +/- 0.05 seizures per day) without progression and rats with progressive seizure activity (8.9 +/- 2.8 seizures/day). In both groups, the number of TUNEL-positive cells in parahippocampal regions was similar and higher than in controls. In the hippocampal formation, this was not significantly different from controls. Fluoro-Jade staining showed essentially the same pattern at 1 week and no positive neurons in chronic epileptic rats.

CONCLUSIONS

Cell death in this rat model is related to the initial SE rather than to the frequency of spontaneous seizures. These results emphasize that it is of crucial importance to stop the SE as soon as possible to prevent extended cell loss and further progression of the disease. They also suggest that neuroprotectants can be useful during the first week after SE, but will not be very useful in the chronic epileptic phase.

"Dormant basket cell" hypothesis revisited: relative vulnerabilities of dentate gyrus mossy cells and inhibitory interneurons after hippocampal status epilepticus in the rat

The "dormant basket cell" hypothesis suggests that postinjury hippocampal network hyperexcitability results from the loss of vulnerable neurons that normally excite insult-resistant inhibitory basket cells. We have reexamined the experimental basis of this hypothesis in light of reports that excitatory hilar mossy cells are not consistently vulnerable and inhibitory basket cells are not consistently seizure resistant. Prolonged afferent stimulation that reliably evoked granule cell discharges always produced extensive hilar neuron degeneration and immediate granule cell disinhibition. Conversely, kainic acid-induced status epilepticus in chronically implanted animals produced similarly extensive hilar cell loss and immediate granule cell disinhibition, but only when granule cells discharged continuously during status epilepticus. In both preparations, electron microscopy revealed degeneration of presynaptic terminals forming asymmetrical synapses in the mossy cell target zone, including some terminating on gamma-aminobutyric acid-immunoreactive elements, but no evidence of axosomatic or axoaxonic degeneration in the adjacent granule cell layer. Although parvalbumin immunocytochemistry and in situ hybridization revealed decreased staining, this apparently was due to altered parvalbumin expression rather than basket cell death, because substance P receptor-positive interneurons, some of which contained residual parvalbumin immunoreactivity, survived. These results confirm the inherent vulnerability of dendritically projecting hilar mossy cells and interneurons and the relative resistance of dentate inhibitory basket and chandelier cells that target granule cell somata. The variability of hippocampal cell loss after status epilepticus suggests that altered hippocampal structure and function cannot be assumed to cause the spontaneous seizures that develop in these animals and highlights the importance of confirming hippocampal pathology and pathophysiology in vivo in each case.

Differences in ionotropic glutamate receptor subunit expression are not responsible for strain-dependent susceptibility to excitotoxin-induced injury

Systemic administration of kainic acid in C57BL/6 and FVB/N mice induces a comparable level of seizure induction yet results in differential susceptibility to seizure-induced cell death. While kainate administration causes severe hippocampal damage in mice of the FVB/N strain, C57BL/6 mice display no demonstrable cell loss or damage. At present, while the cellular mechanisms underlying strain-dependent differences in susceptibility remain unclear, some of this variation is assumed to have a genetic basis. As glutamate receptors are thought to participate in seizure induction and the subsequent neuronal degeneration that ensues, previous studies have proposed that variation in the precise subunit composition of glutamate receptors may result in differential susceptibility to excitotoxic cell death. Thus, we chose to examine the relationship between the cellular distribution and expression of glutamate receptor subunit proteins and cell loss within the hippocampus in mouse strains resistant and susceptible to kainate-induced excitotoxicity. Using semi-quantitative Western blot techniques and immunohistochemistry with the use of antibodies that recognize subunits of the KA (GluR5,6,7), AMPA (GluR1, GluR2, and GluR4), and NMDA (NMDAR1 and NMDAR2A/2B) receptors, we found no significant strain-dependent differences in the expression or distribution of these glutamate receptor subunits in the intact hippocampus. Following kainate administration, expression changes in ionotropic glutamate receptor subunits paralleled the development of susceptibility to cell death in the FVB/N strain only. Strain differences in hippocampal vulnerability to kainate-induced status epilepticus are not due to glutamate receptor protein expression.

GluR5 kainate receptors, seizures, and the amygdala

The amygdala is a critical brain region for limbic seizure activity, but the mechanisms underlying its epileptic susceptibility are obscure. Several lines of evidence implicate GluR5 (GLU(K5)) kainate receptors, a type of ionotropic glutamate receptor, in the amygdala's vulnerability to seizures and epileptogenesis. GluR5 mRNA is abundant in temporal lobe structures including the amygdala. Brain slice recordings indicate that GluR5 kainate receptors mediate a portion of the synaptic excitation of neurons in the rat basolateral amygdala. Whole-cell voltage-clamp studies demonstrate that GluR5 kainate receptor-mediated synaptic currents are inwardly rectifying and are likely to be calcium permeable. Prolonged activation of basolateral amygdala GluR5 kainate receptors results in enduring synaptic facilitation through a calcium-dependent process. The selective GluR5 kainate receptor agonist ATPA induces spontaneous epileptiform bursting that is sensitive to the GluR5 kainate receptor antagonist LY293558. Intra-amygdala infusion of ATPA in the rat induces limbic status epilepticus; in some animals, recurrent spontaneous seizures occur for months after the ATPA treatment. Together, these observations indicate that GluR5 kainate receptors have a unique role in triggering epileptiform activity in the amygdala and could participate in long-term plasticity mechanisms that underlie some forms of epileptogenesis. Accordingly, GluR5 kainate receptors represent a potential target for antiepileptic and antiepileptogenic drug treatments. Most antiepileptic drugs do not act through effects on glutamate receptors. However, topiramate at low concentrations causes slow inhibition of GluR5 kainate receptor-mediated synaptic currents in the basolateral amygdala, indicating that it may protect against seizures, at least in part, through suppression of GluR5 kainate receptor responses.

Changes on diffusion-weighted MRI with focal motor status epilepticus: case report

Transient imaging abnormalities, including changes on diffusion-weighted imaging (DWI), may be seen in focal status epilepticus. The changes on DWI provide am insight into the pathophysiology. We report a 53-year-old man with focal motor status epilepticus involving the left hand, arm and face with focal slowing on EEG. The apparent diffusion coefficients (ADC) were higher in the affected hemisphere than on the other side. At 10 days and 6 weeks after the end of the seizures, we saw normal ADCs and atrophy of the affected hemisphere. We conclude that the MRI findings indicate both cytotoxic and vasogenic oedema during seizure activity and subsequent loss of brain parenchyma.

Heat shock protein 27 delivered via a herpes simplex virus vector can protect neurons of the hippocampus against kainic-acid-induced cell loss

Heat shock proteins are expressed in response to cellular stress and can protect cells from further stress and facilitate recovery. Heat shock protein 27 is of particular interest because it has been implicated in a range of protective roles including protein chaperoning, stabilising elements of the cytoskeleton and as an active inhibitor of apoptosis. In the present study, we have examined the potential of administration of exogenous HSP27 to confer protection against KA-induced neuronal cell death in vivo. We aimed to exploit the neurotropic specificity of herpes simplex virus-1 based virus vectors, which have been rendered replication-incompetent, to infect neurons of the hippocampus. The systemic administration of kainic acid, an analogue of glutamate, causes seizures resulting in neuronal damage and is an established animal model of epilepsy. Neuron loss is particularly prominent in the hippocampus and the mode of death is at least partly apoptotic in nature. We show that the overexpression of HSP27 in these neurons can significantly augment their survival following kainic acid administration. In contrast, injection of a control virus expressing beta-galactosidase does not confer protection. This is the first time that protection by exogenously expressed HSP27 has been demonstrated in an in vivo model of neuronal cell death.

Vagal afferents are necessary for the establishment but not the maintenance of kainic acid-induced hyperalgesia in mice

Systemic administration of a single, sub-convulsive dose (20mg/kg) of kainic acid (KA) produces long-term hyperalgesia. The robustness and reproducibility of this effect makes this a valuable model of chronic pain. However, the mechanism by which KA produces hyperalgesia remains unknown. We evaluated the role of vagal afferents on KA-induced hyperalgesia in mice by assessing the influence of bilateral subdiaphragmatic vagotomy and of direct application of KA to vagal afferents on the development of hyperalgesia. The hot plate and tail flick tests were used to assess pain behavior. Central nervous system (CNS) activity evoked by acute administration of KA or exposure to a nociceptive stimulus was also determined by the immunocytochemical detection of Fos and of phosphorylated extracellular signal-regulated protein kinases 1 and 2 (pErk). Mice exhibited a persistent hyperalgesia after either systemic application of KA or topical treatment with KA on vagal afferents. Vagotomy performed 2 weeks before the application of KA was able to prevent the establishment of hyperalgesia, but vagotomy performed 2 weeks after the application of KA was unable to reverse the already established hyperalgesia. This result establishes that vagal afferents are pivotal to the onset of hyperalgesia. Consistent with this, KA evoked the expression of Fos in vagal related areas of the brainstem, including the nucleus tractus solitarius (NTS) and area postrema (AP), as well as widespread areas of the forebrain. Vagotomy selectively decreased KA-evoked Fos in the NTS while sparing that in other brain areas. In addition to hyperalgesia, weeks after KA treatment, stimulus induced pErk was increased in spinal nociceptive neurons and the medial hypothalamus, a phenomenon that was prevented by prior vagotomy. No signs of cell death were detected using in situ nick end-labeling (TUNEL) assay and Nissl staining at 1, 5, 24, 36 h and 12 days post-KA. These findings suggest that the mechanism underlying KA-induced hyperalgesia is a long-term dysfunction of CNS areas that are activated by vagal afferents and involved in descending control of spinal nociceptive neurons.

The protective effect of a ketogenic diet on kainic acid-induced hippocampal cell death in the male ICR mice

This study was designed to evaluate the antiapoptotic effects of a ketogenic diet (KD) through histological (cresyl violet staining, TUNEL staining and immunohistochemistry) and behavioral studies using kainic acid (KA, 25mg/kg i.p.)-induced seizures in male ICR mice. KA-induced seizure in rodents is widely used as an experimental model for human temporal lobe epilepsy because of their behavioral and pathological similarities. A KA-induced seizure causes neuronal damage in hippocampal pyramidal neurons and involves a caspase-3-mediated apoptotic pathway. In this study, the seizure onset time of the KD-fed group was delayed compared to that of the group fed a normal diet (ND) after a systemic KA injection. Histological studies revealed that KA caused pyknosis in most of the hippocampal areas in the ND-fed group, however, well-preserved pyramidal neurons were detected in the hippocampus of mice that had been on KD for 1 month, which began on postnatal day 21. The number of TUNEL-positive cells and caspase-3-positive cells in the hippocampus of the KD-fed group was lower than that of the ND-fed group. These findings indicate that KD has an antiepileptic effect via a neuroprotective action that involves the inhibition of caspase-3-mediated apoptosis of hippocampal neurons.

Neural growth, neural damage and neurotrophins in the kindling model of epilepsy

Do seizures change the brain? Studies on the kindling model--a widely used animal model of epilepsy--suggest that they do. Dr. Racine, one of the pioneers in the kindling field, describes the basic phenomena of kindling, and discusses the possible roles of cell growth and cell death in this model.

Early induction of secretoneurin expression following kainic acid administration at convulsant doses in the rat and gerbil hippocampus

The expression of secretogranin-II and its major proteolytic product secretoneurin (SN) is under the control of neuronal excitation, as demonstrated by treating rats with the excitotoxic kainic acid (KA). Differences in the structure and function of the hippocampus in rats and gerbils have been described; these suggest possible differential reactive responses to KA. In the present study, the SN immunostaining pattern in relation with cell damage is analyzed from 6 h to 4 days following KA administration in rats and gerbils. Dramatic differences in the expression of SN were found in the hippocampal complex following KA administration in gerbils and rats. A robust increase in SN immunoreactivity was detected in the pyramidal cell layer of the rat hippocampus, especially in the CA1 area. In the gerbil, however, a strong increase in SN immunostaining was detected in interneurons of the hippocampal formation, as shown by double-labeling immunohistochemistry to SN and the calcium-binding proteins parvalbumin, calbindin, and calretinin. In addition, no damage (in the hippocampal formation) or moderate damage (in the entorhinal cortex) was observed in the gerbil, in contrast to the rat. The administration of KA and the GABA-B receptor inhibitors (CGP56999A or CGP36742) to the gerbil resulted in a strong rise in SN immunoreactitivty in the CA1 pyramidal cell layer of the hippocampus, as in the rat. However, no increased cell damage was observed under these conditions. The present data provide evidence of a species-differential reactive response to KA that might be based, in part, on distinct inhibitory intrahippocampal circuitry.

Dantrolene protects neurons against kainic acid induced apoptosis in vitro and in vivo

Apoptotic cell death induced by kainic acid (KA) in cultures of rat cerebellar granule cells (CGC) and in different brain regions of Wistar rat pups on postnatal day 21 (P21) was studied. In vitro, KA (100-500 microM) induced a concentration-dependent loss of cell viability in MTT assay and cell death had apoptotic morphology as studied by chromatin staining with propidium iodide (PI). In vivo, twenty-four hours after induction of status epilepticus (SE) by an intraperitoneal KA injection (5 mg/kg) we quantified apoptotic cells in hippocampus (CA1 and CA3), parietal cortex and cerebellum using PI staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique. We report that dantrolene, a specific ryanodine receptor antagonist, was able to significantly reduce the apoptotic cell death in CGC cultures and in hyppocampal CA1 and parietal cortex regions. Our finding can be valuable for neuroprotective therapy strategies in patients with repeated generalized seizures or status epilepticus.

Are seizures harmful: what can we learn from animal models?

Epilepsy is a brain disease that requires distributed neuronal networks for its expression. Several characteristics of epilepsy, including its natural history, the latency between an initial insult and the first manifestation of seizures, the complex interaction of seizures with development as a function of developmental stage, the modulating effect of systemic physiological responses, and the fact that seizures are ultimately defined by a combination of electrical and behavioral criteria all suggest that epilepsy should ideally be studied in an intact whole animal preparation. Such preparations offer the ability to study acute and chronic changes in brain structure and function after single or repeated seizures. Animal models have major limitations, however, including strain specificity, difficulty in isolating potentially confounding variables, a relative lack of accessible higher cortical functions, such as language and abstract processing, and shorter lifespans that may be insufficient to allow the complete expression of seizure-related injury. Information we have learned from animal studies includes a broad understanding of the chemical, molecular and anatomic consequences of seizures, including their temporal and spatial relationships to each other, and information on the consequences of seizures as a function of development. Recent studies have cast light on potential mechanisms of resistance to seizure-induced injury in the developing brain. In the future, we can anticipate that animal models will continue to be useful, especially when whole-animal preparations are used to generate material for detailed in vitro examination.

Memory impairment in temporal lobe epilepsy: the role of entorhinal lesions

Temporal lobe epilepsy (TLE) patients are frequently afflicted with deficits in spatial and other forms of declarative memory. This impairment is likely associated with the medial temporal lobe, which suffers widespread damage in the disease. Physiological and lesion studies, as well as examinations of the complex connectivity of the medial temporal lobe in animals and humans, have identified the entorhinal cortex (EC) as a key structure in the function and dysfunction of this brain region. Lesions in EC layer III, which normally provides monosynaptic input to area CA1 of the hippocampus, frequently occur in TLE and may be causally related to the memory impairments seen in the disease. Lesions that are initially largely restricted to EC layer III can be produced in rats by focal intra-entorhinal injections of 'indirect excitotoxins' such as aminooxyacetic acid or gamma-acetylenic GABA. These animals eventually show more extensive neurodegeneration in temporal lobe structures and, after a latent period, exhibit spontaneously recurring seizure activity. These progressive features, which may mimic events that occur in TLE, provide new opportunities to explore the role of the EC in memory deficits associated with TLE. These animals will also be useful for evaluating new treatment strategies that focus on the prevention of pathological events in the EC.

Spontaneous limbic seizures after intrahippocampal infusion of brain-derived neurotrophic factor

The results of several studies have contributed to the hypothesis that BDNF promotes seizure activity, particularly in adult hippocampus. To test this hypothesis, BDNF, vehicle (phosphate-buffered saline, PBS), or albumin was infused directly into the hippocampus for 2 weeks using osmotic minipumps. Rats were examined behaviorally, electrophysiologically, and anatomically. An additional group was tested for sensitivity to the convulsant pilocarpine. Spontaneous behavioral seizures were observed in BDNF-infused rats (8/32; 25%) but not in controls (0/20; 0%). In a subset of six animals (three BDNF, three albumin), blind electrophysiological analysis of scalp recordings contralateral to the infused hippocampus demonstrated abnormalities in all BDNF rats; but not controls. Neuronal loss in BDNF-treated rats was not detected relative to PBS- or albumin-treated animals, but immunocytochemical markers showed a pattern of expression in BDNF-treated rats that was similar to rats with experimentally induced seizures. Thus, BDNF-infused rats had increased expression of NPY in hilar neurons of the dentate gyrus relative to control rats. NPY and BDNF expression was increased in the mossy fiber axons of dentate gyrus granule cells relative to controls. The increase in NPY and BDNF expression in BDNF-treated rats was bilateral and occurred throughout the septotemporal axis of the hippocampus. Mossy fiber sprouting occurred in five BDNF-treated rats but no controls. In another group of infused rats that was tested for seizure sensitivity to the convulsant pilocarpine, BDNF-infused rats had a shorter latency to status epilepticus than PBS-infused rats. In addition, the progression from normal behavior to severe seizures was faster in BDNF-treated rats. These data support the hypothesis that intrahippocampal BDNF infusion can facilitate, and potentially initiate, seizure activity in adult hippocampus.

Gas1 is induced during and participates in excitotoxic neuronal death

We have performed differential screening to identify genes participating in NMDA-induced neuronal death. The gas1 (growth arrest-specific gene 1) gene, whose product is known to inhibit cell cycle progression, was induced in cultured corticohippocampal neurons committed to die after a brief exposure to NMDA. Overexpression of Gas1 in cultured hippocampal neurons and in human neuroblastoma NB69 cells produced a marked reduction in the number of viable cells. Furthermore, gas1 antisense oligodeoxynucleotide or antisense mRNA protected hippocampal neurons or NB69 cells from neuronal death. Importantly, Gas1-induced neuronal death was attenuated by coexpression of the human Bcl-2 protein or the baculoviral caspase inhibitor OpIAP2. While Gas1 does not directly interact with Bcl-2, OpIAP2 coimmunoprecipitates with Gas1. In addition, induction of gas1 also occurred in rat brain in two models of excitotoxicity: delayed neuronal death after intraperitoneal kainate injection and neuronal death in hippocampal slices after ischemia. These results indicate that Gas1 is induced by activation of glutamate receptors and is part of the gene expression program directing neuronal death after mild excitotoxic insults.