Kainic Acid-induced Seizure Activity Research Articles

Induction of the dual specificity phosphatase PAC1 in rat brain following seizure activity.

Recurrent seizure activity leads to delayed neuronal death as well as to inflammatory responses involving microglia in hippocampal subfields CA1, CA3 and CA4. Since mitogen activated protein (MAP) kinases control neuronal apoptosis and trigger generation of inflammatory cytokines, their activation state could determine seizure-related brain damage. PAC1 is a dual specificity protein phosphatase inactivating MAP kinases which we have found to be undetectable in normal brain. Despite this, kainic acid-induced seizure activity lead to rapid (approximately 3 h) but transient appearance of PAC1 mRNA in granule cells of the dentate gyrus as well as in pyramidal CA1 neurons. This pattern changed with time and after 2-3 days PAC1 was induced in dying CA1 and CA3 neurons. At this time PAC1 mRNA was also expressed in white matter microglia as well as in microglia invading the damaged hippocampus. PAC1 may play an important role controlling MAP kinase involvement in both neuronal death and neuro-inflammation following excitotoxic damage.

Anterograde transport of endogenous brain-derived neurotrophic factor in hippocampal mossy fibers.

Neurotrophic factors such as brain-derived neurotrophic factor (BDNF) are assumed to provide trophic support via a target-derived, retrograde mechanism of action. However, recent studies suggest that neurotrophic factors can act in an autocrine fashion and perhaps even in an anterograde direction similar to neurotransmitters. To further explore this hypothesis, we compared the neuroanatomical pattern of BDNF mRNA and protein in response to electroconvulsive seizures (ECS) or kainic acid-induced seizure activity. Using in situ hybridization, we found that chronic ECS induced BDNF mRNA predominantly in the granule neurons of the dentate gyrus. However, immunohistochemistry with an anti-BDNF antibody revealed that ECS increased endogenous BDNF protein in the mossy fibers, which are composed of axons projecting from the granule neurons of the dentate gyrus to the CA3 pyramidal layer of the hippocampus. Kainic acid administration (10 mg/kg, i.p., once) was used to lesion CA3 neurons selectively, as these are a possible retrograde source of BDNF protein in mossy fibers. Three weeks later, a prolonged elevation of BDNF mRNA in granule neurons, but not elsewhere in hippocampus, was accompanied by an increase in BDNF protein in the mossy fibers. These results suggest that BDNF was transcribed and translated in granule neuron cell bodies but transported in an anterograde direction to provide trophic support of CA3 pyramidal neurons.

Fos Induction Following Systemic Kainic Acid: Early Expression in Hippocampus and Later Widespread Expression Correlated With Seizure

We determined the distribution of Fos protein expression in a model of generalised epilepsy caused by excessive neuronal excitation. Fos immunoreactivity was mapped in forebrain in unrestrained rats, previously prepared with an indwelling venous catheter, after the intravenous administration of kainic acid (10 mg/kg). We determined cerebral activation following various periods of exposure to kainic acid by using intravenous administration of pentobarbitone to prevent further activation. Within a few minutes, kainic acid caused episodes of staring, sniffing, wet dog shakes, nodding and chewing. Fos induction occurred initially and simultaneously in hippocampus, subiculum, septum and entorhinal cortex as early as 9.5 min after kainate injection. After up to 40 min of staring, sniffing, wet dog shakes, nodding and chewing, Fos induction was not further increased above levels present within the first 9.5 min. After 56±6 min a motor convulsion occurred, initially affecting the jaw, head and tail and variably extending to the forelimbs, trunk or hindlimbs. Following the convulsive event, additional Fos was expressed in hippocampus, thalamus, caudate–putamen and other subcortical structures and in the cerebral cortex. Fos induction was sometimes asymmetric in entorhinal, visual, piriform, cingulum, parietal and frontal cortices and in amygdala and dorsal endopiriform area. Electroencephalographic recordings after a few minutes exposure to kainic acid revealed an increased amplitude of fast frequencies in hippocampus which appeared to correlate with Fos induction in this structure. The findings are generally consistent with the reported distribution and slow development of kainic acid-induced seizure activity using electrophysiological and deoxyglucose methods. However, the Fos distribution suggests that (i) hippocampal, possibly dentate, activation precedes significant activation elsewhere, (ii) extensive involvement of other cerebral structures and cerebral cortex occurs simultaneously and correlates with motor seizures and (iii) brain structures can be recruited asymmetrically.

Generation of lipid radicals in the hippocampal extracellular space during kainic acid-induced seizures in rats.

We report direct electron spin resonance (ESR) evidence of extracellular free radical formation during kainic acid-induced seizures obtained using in vivo brain microdialysis in freely moving rats. Saline solution containing the spin trap agent alpha-(4-pyridyl-N-oxide)-N-tert-butylnitrone was perfused through the hippocampus. ESR analysis of the dialysate samples revealed a six-line spectra, for which the hyperfine coupling constants corresponded to those of the ESR signal from the lipoxygenase/linoleic acid system, a lipid radical generating system. This result is direct evidence that lipid peroxidation of the neuronal membrane progresses during seizure activity. Increased formation of lipid radicals may participate in the cascade of reactions leading to neuronal damage in the hippocampus following kainic acid-induced seizure activity.

Stimulation of 5-HT1A receptors in the dorsal hippocampus and inhibition of limbic seizures induced by kainic acid in rats.

1. We studied whether the stimulation of 5-HT1A receptors by 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), a specific 5-HT1A receptor agonist, reduced electroencephalographic (EEG) seizures induced by intrahippocampal injection of 0.04 microgram in 0.5 microliter of the glutamate analogue kainic acid in freely-moving rats. 2. Pretreatment with 8-OH-DPAT 15 min earlier at the same site as kainic acid injection, caused a dose-dependent decrease of kainic acid-induced seizure activity. One and 10 micrograms significantly reduced the total time spent in seizures by 72% on average and the total number of seizures by 58% (P < 0.01) and 43% (P < 0.05) respectively. The latency to onset of the first seizure was increased 2.8 times (P < 0.01) only after 1 microgram 8-OH-DPAT; 0.1 microgram was ineffective on all seizure parameters. 3. Systemic administration of 25, 100 and 1000 micrograms kg-1 8-OH-DPAT significantly reduced the total number of seizures and the total time in seizures induced by intrahippocampal kainic acid by 52% and 74% on average. The latency to onset of the first seizure was delayed 1.8 times by 100 and 1000 micrograms kg-1 (P < 0.05). 4. The anticonvulsant action of 8-OH-DPAT given intrahippocampally or systemically was significantly blocked by 5 micrograms, but not 1 microgram WAY 100635, a selective 5-HT1A receptor antagonist, administered in the hippocampus before the agonist. 5. These results indicate that postsynaptic 5-HT1A receptors in the hippocampus mediate the anticonvulsant action of 8-OH-DPAT and that their stimulation has an inhibitory role in the generation of limbic seizures.

Kainic Acid-Induced Focal Cortical Seizure Is Associated with an Increase of Synaptophysin Immunoreactivity in the Cortex

Aberrant neural sprouting of mossy fiber terminals in the supragranular layer of dentate gyrus is consistently observed following seizures in an animal model of epilepsy. It is also observed in hippocampi taken from epileptic patients with hippocampal sclerosis. The aberrant neural sprouting with synaptic reorganization is one of the proposed cellular mechanisms underlying epileptogenesis. It is not known whether aberrant synaptogenesis can be induced in the cortex, as in hippocampus, by seizure activity. In this study, synaptic terminals in the cortex were measured after focal cortical seizures by a semiquantitative image analysis of synaptophysin immunoreactivity. Brief intracortical perfusion of kainic acid induced focal status epilepticus and destructive cortical lesions. Synaptophysin immunoreactivity was significantly increased in the area where kainic acid was perfused. The increase of synaptophysin immunoreactivity, indicating an increase of synaptogenesis, was observed at 2 and 4 weeks after focal cortical seizures. This result suggests that kainic acid-induced seizure activity is associated with long-lasting synaptogenesis in the cortex. Studies centering on the physiological consequences of aberrant synaptogenesis may lead to additional understanding of the mechanisms underlying cortical epileptogenesis.

Potent inhibitory effects of glial derived neurotrophic factor against kainic acid mediated seizures in the rat

Recently messenger RNA (mRNA) for glial derived neurotrophic factor (GDNF), a recently discovered member of the TGF-β superfamily, was shown to increase in the hippocampus after kainic acid-induced seizures. The possibility that exogenous recombinant human (rh) GDNF may have anticonvulsant properties was investigated using a model of temporal lobe epilepsy in the rat. rhGDNF, vehicle or inactive rhGDNF were injected intracerebroventricularly 1 h before peripheral administration of kainic acid. rhGDNF suppressed kainic acid-induced tonic-clonic convulsions when compared to animals treated with vehicle or inactive rhGDNF. The inhibition of kainic acid-induced seizure activity by rhGDNF also prevented the associated neuronal cell loss in hippocampal, thalamic and amygdaloid regions. These results suggest that rhGDNF should be evaluated in other seizure and acute neural disorders that are associated with excitotoxic processes.

Cycloheximide prevents kainate-induced neuronal death and c-fos expression in adult rat brain.

The present study was directed at evaluating the possible involvement of protein synthesis in excitotoxin-induced neuronal damage and prolonged expression of the proto-oncogene, c-fos. Kainic acid-induced seizure activity elicited varying degrees of neuronal damage and cell loss in selectively vulnerable regions of the adult rat limbic system. Pretreatment with cycloheximide, a protein synthesis inhibitor, did not alter behavioral seizure characteristics, but markedly attenuated damage to susceptible neuronal populations. A prolonged increase in c-fos mRNA was observed by in situ hybridization up to 16 h after the onset of seizures in regions exhibiting neuronal death. Pretreatment with cycloheximide did not affect the transient induction of c-fos observed in numerous structures, but significantly reduced the prolonged expression of c-fos mRNA in kainate-vulnerable regions. Despite producing massive seizure activity, systemic kainic acid administration during the early postnatal period did not induce any neuronal death, and did not result in prolonged c-fos expression in any brain structures. The developmental onset of selective neuronal vulnerability coincided with that of prolonged c-fos expression in susceptible neuronal populations. In adult rats, seizure activity induced by pentylenetetrazole did not produce neuronal damage nor did it produce prolonged c-fos expression. These results not only demonstrate that kainate-induced neurotoxicity and the prolonged expression of c-fos are both prevented by cycloheximide, but also strengthen idea that prolonged c-fos expression is a marker of neuronal death.

Effect of seizure activity and calpain inhibitor I on LTP in juvenile hippocampal slices

Kainic acid-induced seizure activity in adult rats produces an impairment of long-term potentiation induction in hippocampal slices. As the consequences of seizure activity are different in adult and juvenile rats, we tested the ability of hippocampal slices prepared from kainate-treated juvenile rats to exhibit long-term potentiation. Long-term potentiation was induced by theta-burst stimulation and was not significantly different in slices prepared from control or kainate-injected juvenile rats (16–18 postnatal days). Short-term potentiation, however, was reduced in the kainate-treated juveniles. Calpain inhibitor I has been shown to prevent long-term potentiation formation in adult hippocampal slices, and we evaluated its effect on long-term potentiation in hippocampal slices from juvenile rats. Calpain inhibitor I produced a significant reduction in the degree of long-term potentiation induced by theta-burst stimulation in hippocampal slices prepared from 14–20 postnatal day-old animals. The results are consistent with the notion that, although similar mechanisms participate in the formation of long-term potentiation in juvenile and adult animals, juvenile animals are much more resistant than adult animals to the consequences of seizure activity.

BDNF mRNA expression in the developing rat brain following kainic acid-induced seizure activity

Brain-derived neurotrophic factor (BDNF) mRNA expression was studied in the hippocampus at various developmental stages in normal rats and following kainic acid (KA)-induced seizure activity. Systemic administration of KA strongly elevated BDNF mRNA levels in all hippocampal subregions after postnatal day 21. In contrast, even though KA induced intense behavioral seizure activity at postnatal day 8, the seizures were not associated with elevations of BDNF mRNA levels, indicating a clear dissociation between behavioral seizures and increases in BDNF mRNA levels and contradicting the view that BDNF mRNA expression is principally regulated by neuronal activity. In the dentate gyrus at postnatal day 13, intense BDNF mRNA expression was limited to a defined area at the border between granule cell and molecular layers, suggesting the possibility that segregation of BDNF mRNA into defined subcellular compartments may play a role in establishing the well-delineated patterns of innervation in the hippocampus.

Regionally specific and rapid increases in brain-derived neurotrophic factor messenger RNA in the adult rat brain following seizures induced by systemic administration of kainic acid

In situ hybridization techniques were used to analyse the spatiotemporal pattern of brainderived neurotrophic factor messenger RNA elevation associated with kainic acid-induced seizure activity in the rat. Pronounced increases in hippocampal brain-derived neurotrophic factor messenger RNA levels were observed as early as 30 min following the onset of behavioral seizures. The greatest increase (10-fold) occurred in the dentate granule cell layer, while pyramidal layers CA1, CA3, and CA4 exhibited increases of two- to six-fold. Peak elevation of brain-derived neurotrophic factor messenger RNA in CA1 hippocampal region was evident at 4 h in CA3, and in the dentate granule layer at 30 min postseizure. Elevations persisted in the dentate and hilar regions to four days, while the increases in CA1 and CA3 returned to control levels by 16 h following seizure. Significant increases in brain-derived neurotrophic factor messenger RNA were also observed in the superficial layers of cortex (II and III) and in the piriform cortex which reached peak elevations by 8 h. No detectable changes were observed in the dorsomedial thalamus. Although histologically defined pyramidal and granule cell layers displayed relatively uniform increases in brain-derived neurotrophic factor messenger RNA in response to kainate, a closer examination of the labeling patterns using emulsion autoradiography revealed discrete areas of high grain densities overlapping uniform, moderate hybridization densities in the dentate granule cell layer and CA3, suggesting that the capacity to upregulate brain-derived neurotrophic factor messenger RNA in these regions may differ among individual neurons. In conclusion, our studies revealed that brain-derived neurotrophic factor messenger RNA induction in response to systemic kainate administration differs in hippocampal and cortical areas, in magnitude, time of onset and duration. The observed temperospatial pattern does not correspond in a simple way to increases in metabolic or electrical activity associated with seizures or neuronal vulnerability coincident with the seizures.

Glucocorticoids potentiate kainic acid-induced seizures and wet dog shakes

Glucocorticoid effects on kainic acid-induced motor seizures and wet dog shakes in rats were investigated by adrenalectomy and dexamethasone treatment. One-day adrenalectomy attenuated kainic acid-induced wet dog shakes and seizure activity. These effects were restored by dexamethasone. Administration of dexamethasone to non-adrenalectomized rats potentiated kainic acid-induced wet dog shakes and severity of seizure activity. These results suggest that glucocorticoids may play an important role in modulating the severity of kainic acid-induced seizures and wet dog shakes.

Attenuation of cerebral glucose use in kainic acid-treated rats by diazepam

Diazepam's impact on kainic acid seizure-induced local cerebral glucose utilization (LCGU) was assessed by a quantitative [ 14C]2-deoxyglucose method. Male rats were injected i.p. with either kainic acid (12 mg/kg) or its vehicle, 3 or 48 h before LCGU determination. Diazepam (3.2 mg/kg) or its vehicle were injected i.m. 15 min before, 1 and 2.5 h after kainic acid. Diazepam blocked kainic acid-induced overt convulsions, attenuated LCGU increases at 3 h and prevented 48 h LCGU decreases in piriform cortex and amygdala. LCGU in (% of vehicle): CA 3 (438%), CA 4 (537%) and CA 1-ventral (340%) of hippocampus, interpeduncular nucleus (200%) and lateral lemniscus (213%) were still significantly above vehicle levels in the 3 h diazepam-kainic acid group. These results suggest that diazepam suppresses the spread of kainic acid-induced seizure activity from the proposed CA 3 epileptogenic focus. In addition, diazepam reduces, but does not abolish, hypermetabolic activity at the foci itself.