Progressive pathology of the caudate nucleus, the substantia nigra pars reticulata and the deeper layers of the colliculus superior: acute behavioural and metabolic effects of intrastriatal kainic acid

The acute behavioural and metabolic consequences of functional changes following unilateral intracaudate kainic acid at the level of the feline caudate nucleus, the substantia nigra pars reticulata and the deeper layers of the colliculus superior were investigated. The present study became possible since it was previously found that unilateral changes in neurotransmission processes in these structures all result in behavioural alterations that can be distinguished from each other. During the first 17 min after kainic acid, all animals displayed contralateral forced staccato head turning; these movements are characteristic for an activation of dopamine receptors and/or inhibition of GABA receptors in the rostromedial caudate nucleus. Between 15 and 50 min, all animals displayed fast, uninterrupted contralateral forced head, torso or body turning; these movements are characteristic for an activation of nigral GABA receptors. From about 48 min, all animals displayed sequences of short contralateral forced ear, head, torso and body turnings; these movements are characteristic for an inhibition of collicular GABA receptors. Furthermore, most cats displayed ipsilateral orofacial dyskinetic movements during the whole 180 min observation period. Metabolism was analysed in three cats that received [14C]2-D-deoxyglucose immediately before, 5 min after, or 70 min after kainic acid. Metabolism was increased in the ipsilateral caudate nucleus; this effect was most pronounced in the cat that received deoxyglucose immediately before kainic acid. Metabolic activity was increased in the ipsilateral substantia nigra pars reticulata; this effect was most pronounced in the cat treated with deoxyglucose 5 min after kainic acid. Metabolism was increased in the ipsilateral deeper layers of the colliculus superior in the cat that received deoxyglucose 70 min after kainic acid. The present behavioural and metabolic data suggest that kainic acid produces an increasing pathology resulting successively in functional changes in the caudate nucleus, its output-station the substantia nigra pars reticulata and the nigral output-station the deeper layers of the colliculus superior. It is suggested that the successive appearance of the latter effects is inherent in the hierarchical order of the brain structures under study. The occurrence of orofacial dyskinetic movements during the whole observation period suggests that the former movements were not mediated via the striato-nigro-collicular pathway. Finally, apomorphine injected in the ipsilateral caudate nucleus 1 week after kainic acid was significantly less effective compared to apomorphine injected 1 week before kainic acid. The c     

Uncoupling of local blood flow and metabolism in the hippocampal CA3 in kainic acid-induced limbic seizure status

Limbic seizure status was induced by microinjection of kainic acid into a unilateral amygdala in rats. Two hours after kainic acid injection, distant neuronal cell damage was produced, especially in the hippocampal CA3 on the kainic acid-injected side. In order to elucidate the mechanism of this neuronal cell damage, local cerebral glucose utilization and local cerebral blood flow were studied by means of an autoradiographic method using [14C]2-deoxyglucose and [14C]iodoantipyrine during kainic acid-induced limbic seizure status. These studies were performed 2 h after kainic acid microinjection into a unilateral amygdala. Both local cerebral glucose utilization and local cerebral blood flow were remarkably increased in the limbic system, ventrobasal complex of the thalamus, septal nucleus, nucleus accumbens, caudate nucleus, substantia nigra and hypothalamus on the kainic acid-injected side. In the hippocampus, local cerebral glucose utilization increased 2.6 times control in CA1 and 4.1 times in CA3, whereas the rates of increase in local cerebral blood flow were similarly low in CA1 and CA3: 1.2 and 1.4 times control, respectively. The results demonstrated that the degree of uncoupling of local cerebral glucose utilization and local cerebral blood flow were higher in CA3 than in CA1, and also suggested that relative hypoxia occurred in CA3 in this high degree of uncoupling, resulting in pyramidal cell damage in CA3 in kainic acid-induced limbic seizure status.     

Effects of microdialysis on brain metabolism in normal and seizure states

The effect of intracranial microdialysis on brain glucose metabolism in control and kainic acid-treated rats was assessed by semi-quantitative [14C]2-deoxyglucose autoradiography. A dialysis fiber loop was implanted into the piriform cortex or a horizontal Vita fiber into the hippocampus, and 24 h later, fibers were perfused with Krebs-Ringer bicarbonate solution before and after injection of kainic acid (16 mg/kg, i.p.) [14C]2-Deoxyglucose was injected i.p. 3 h after the injection of kainic acid. Rats injected with kainic acid were initially lethargic and then proceeded through behavioral phases of staring, "wet-dog shakes", Straub tail, rearing, forepaw clonus, and, in some cases, tonic-clonic convulsions. Three hours after kainic acid, the fiber presence in the piriform cortex enhanced kainic acid-induced metabolic activity in areas adjacent to the fiber assembly, whereas the fiber in hippocampus attenuated kainic acid-induced metabolic activity in areas adjacent to the fiber assembly. The results indicate that intracranial microdialysis alters the already abnormal brain metabolism in a kainic acid-induced seizure state, but has no significant effect in the non-seizure control state.     

A role for astrocyte‐derived amyloid β peptides in the degeneration of neurons in an animal model of temporal lobe epilepsy

Kainic acid, an analogue of the excitatory neurotransmitter glutamate, can trigger seizures and neurotoxicity in the hippocampus and other limbic structures in a manner that mirrors the neuropathology of human temporal lobe epilepsy (TLE). However, the underlying mechanisms associated with the neurotoxicity remain unclear. Since amyloid‐β (Aβ) peptides, which are critical in the development of Alzheimer's disease, can mediate toxicity by activating glutamatergic NMDA receptors, it is likely that the enhanced glutamatergic transmission that renders hippocampal neurons vulnerable to kainic acid treatment may involve Aβ peptides. Thus, we seek to establish what role Aβ plays in kainic acid‐induced toxicity using in vivo and in vitro paradigms. Our results show that systemic injection of kainic acid to adult rats triggers seizures, gliosis and loss of hippocampal neurons, along with increased levels/processing of amyloid precursor protein (APP), resulting in the enhanced production of Aβ‐related peptides. The changes in APP levels/processing were evident primarily in activated astrocytes, implying a role for astrocytic Aβ in kainic acid‐induced toxicity. Accordingly, we showed that treating rat primary cultured astrocytes with kainic acid can lead to increased Aβ production/secretion without any compromise in cell viability. Additionally, we revealed that kainic acid reduces neuronal viability more in neuronal/astrocyte co‐cultures than in pure neuronal culture, and this is attenuated by precluding Aβ production. Collectively, these results indicate that increased production/secretion of Aβ‐related peptides from activated astrocytes can contribute to neurotoxicity in kainic acid‐treated rats. Since kainic acid administration can lead to neuropathological changes resembling TLE, it is likely that APP/Aβ peptides derived from astrocytes may have a role in TLE pathogenesis.     

Intrahippocampal injection of kainic acid produces significant pyramidal cell loss in neonatal rats

Previous reports have indicated that pyramidal cells in the developing rat hippocampal formation are not destroyed by intraventricular or intraperitoneal administration of kainic acid. We examined the neurotoxic properties of kainic acid and ibotenic acid following intrahippocampal injection in neonatal rats and found significant pyramidal cell death following injection of 1.0 microgram kainic acid in 6, 7 and 9-day-old pups. At doses 2.5 or five times this amount, significant pyramidal cell loss was obtained in 5-day-old rats as well. The susceptibility of pyramidal neurons to kainic acid increased as a function of age. The developing hippocampus was considerably more vulnerable to ibotenic acid compared with kainic acid, in contrast to the order of potency reported in adult rats. The increased sensitivity of CA3 pyramidal cells parallels the development of the mossy fiber innervation to the dendrites of these cells supporting the twofold mechanism suggested by Coyle for kainic acid neurotoxicity; that is, a direct cytotoxic action via postsynaptic receptors as well as increased sensitivity due to the presence of excitatory inputs.     

Intrahippocampal kainic acid reduces glutamine synthetase

Kainic acid was injected into the hippocampus of rats and glutamine synthetase was measured to determine whether astrocytes are involved in the early effects of this neurotoxic agent. Glutamine synthetase was reduced by 38%, 24 h after the stereotaxic application of 4 nmol of kainic acid to this region. The reduction in glutamine synthetase by kainic acid was not due to direct inhibition of the brain enzyme. This effect also was not due to seizure activity since rats peripherally injected with a convulsant dose of kainic acid were found to have normal hippocampal glutamine-synthetase activity. Exposure of astrocyte cultures to kainic acid for 24 h produced no evidence of gliotoxicity and no change in glutamine synthetase activity. The effect of intrahippocampal kainic acid on glutamine synthetase appears to be indirect, most likely produced secondarily to its neuronal effects. Several studies have shown that endogenous glutamate is involved in kainate neurotoxicity. A reduction in glutamine synthetase by kainic acid may impair the capacity for astrocytes to metabolize glutamate. Such an impairment could contribute to the glutamate-mediated cell death following kainic acid exposure.     

Kainic acid microinjected into the cat raphe dorsal nucleus modulates the somatosensory evoked potentials and their cycles of excitability

Studies were made on the effect of the neuroexcitatory agent kainic acid, microinjected into raphe dorsal nucleus by glass micropipette and an air pressure system in doses ranging from 0.2 to 24.0 nmol (in volumes from 0.05 microliter to 0.47 microliter), on the somatosensory evoked potentials and their cycles of recovery (excitability) obtained from cortex (primary somatosensory and parietal associative), thalamus (ventral posterolateral nucleus and centre median nucleus), mesencephalic reticular formation and raphe dorsal nucleus. Kainic acid in doses higher than 3 nmol exerted an activating effect on the evoked potentials and their recovery cycles especially in thalamus and mesencephalic reticular formation. The analysis of these electrophysiological parameters revealed that the non-specific structures were involved to a larger extent in the activating effect of kainic acid than the specific ones. The morphological changes were not severe and were limited to a part of the raphe dorsal nucleus neurons. Our data indicate that kainic acid injected into raphe dorsal nucleus modulates (in direction of facilitation) the somatosensory evoked potentials and their cycles of excitability obtained in some brain structures. The results suggest that this nucleus is involved in the somatosensory information processing in a non-specific manner.     

Different sensitivity of hippocampal neurons to kainic acid in the rabbit

The toxic effect of kainic acid, a cyclic analogue of glutamic acid, was investigated in the rabbit hippocampus. Using histological methods it was found that intrahippocampal injection of one or two doses of 5 nm of kainic acid produced cell losses in different cell layers. The cells with the highest sensitivity to kainic acid were the cornu ammonis pyramidal cells, whereas those with the lowest sensitivity were the dentate granular cells.These findings suggest that the sensitivity to kainic acid is different in discrete cell areas of the hippocampus.     

Interleukin-6 deficiency reduces the brain inflammatory response and increases oxidative stress and neurodegeneration after kainic acid-induced seizures

The role of interleukin-6 in hippocampal tissue damage after injection with kainic acid, a rigid glutamate analogue inducing epileptic seizures, has been studied by means of interleukin-6 null mice. At 35mg/kg, kainic acid induced convulsions in both control (75%) and interleukin-6 null (100%) mice, and caused a significant mortality (62%) only in the latter mice, indicating that interleukin-6 deficiency increased the susceptibility to kainic acid-induced brain damage. To compare the histopathological damage caused to the brain, control and interleukin-6 null mice were administered 8.75mg/kg kainic acid and were killed six days later. Morphological damage to the hippocampal field CA1-CA3 was seen after kainic acid treatment. Reactive astrogliosis and microgliosis were prominent in kainic acid-injected normal mice hippocampus, and clear signs of increased oxidative stress were evident. Thus, the immunoreactivity for inducible nitric oxide synthase, peroxynitrite-induced nitration of proteins and byproducts of fatty acid peroxidation were dramatically increased, as was that for metallothionein I+II, Mn-superoxide dismutase and Cu/Zn-superoxide dismutase. In accordance, a significant neuronal apoptosis was caused by kainic acid, as revealed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling and interleukin-1beta converting enzyme/Caspase-1 stainings. In kainic acid-injected interleukin-6 null mice, reactive astrogliosis and microgliosis were reduced, while morphological hippocampal damage, oxidative stress and apoptotic neuronal death were increased. Since metallothionein-I+II levels were lower, and those of inducible nitric oxide synthase higher, these concomitant changes are likely to contribute to the observed increased oxidative stress and neuronal death in the interleukin-6 null mice. The present results demonstrate that interleukin-6 deficiency increases neuronal injury and impairs the inflammatory response after kainic acid-induced seizures.     

Neuroprotective effects of brain-derived neurotrophic factor in seizures during development.

Although the immature brain is highly susceptible to seizures, it is more resistant to seizure-induced neuronal loss than the adult brain. The developing brain contains high levels of neurotrophins which are involved in growth, differentiation and survival of neurons. To test the hypothesis that neurotrophins may protect the developing brain from seizure-induced neuronal loss, brain-derived neurotrophic factor up-regulation was blocked by intracerebroventricular infusion of an 18mer antisense oligodeoxynucleotide sequence to brain-derived neurotrophic factor in 19-day-old rats using micro-osmotic pumps. Control rats were infused with sense or missense oligodeoxynucleotide. Status epilepticus was induced by intraperitoneal administration of kainic acid 24 h after the start of oligodeoxynucleotide infusion. Seizure duration was significantly increased in the antisense oligodeoxynucleotide plus kainic acid group compared to groups that received kainic acid alone or kainic acid plus sense or missense oligodeoxynucleotide. There was no difference between groups in the latency to forelimb clonus. A twofold increase in brain-derived neurotrophic factor levels was observed in the hippocampus 20 h following kainic acid-induced seizures. This kainic acid-induced increase was absent in animals receiving infusion of antisense oligodeoxynucleotide to brain-derived neurotrophic factor at time of seizure induction. Hippocampi of rats in this group (antisense oligodeoxynucleotide plus kainic acid) showed a loss of CA1 and CA3 pyramidal cells and hilar interneurons. This neuronal loss was not dependent upon seizure duration since animals injected with diazepam to control seizure activity in the antisense plus kainic acid group also showed similar neuronal loss. Administration of kainic acid or infusion of antisense alone did not produce any cell loss in these regions. Induction of seizures at postnatal day 20, in the presence or absence of antisense oligonucleotide, did not produce an impairment in learning and memory when tested 15 days later in the Morris water maze. The hippocampi of these animals did not show any synaptic reorganization as assessed by growth-associated protein-43 immunostaining and Timm staining. Our findings confirm prior studies demonstrating that seizures in the immature brain are associated with little, if any, cell loss. However, when seizure-induced increase in brain-derived neurotrophic factor is blocked, seizures do result in neuronal loss in the developing brain. Thus, brain-derived neurotrophic factor appears to provide protection against kainic acid seizure-induced neuronal damage in the developing brain.     

海人藻酸注射大鼠纹状体边缘区后c-fos原癌基因蛋白在脑内的表达

为研究纹状体边缘区与脑内其他和学习记忆等功能有关结构间的关系，将海人藻酸注射于大鼠纹状体边缘区，观察c-fos原癌基因蛋白（FOS）在脑内的表达。海人藻酸注射4h后，脑内有少量FOS表达．海人藻酸注射6h后，脑内FOS表达增至最高峰．在嗅脑、基底前脑、海马、杏仁核，大脑皮质以及丘脑的中线核和网状核中有大量密集的FOS表达。另外，在纹状体、Meynert基底核、脚内核、丘脑底核、黑质外侧都及其背外侧区可见较多FOS表达．在视前区、丘脑下部外侧区、外侧缰核和中脑中央灰质等部位可见少量FOS表达。海人藻酸注射纹状体边缘区后18～24h，上述各部位的阳住表达逐渐减少，齿状回的表达消失．海人藻酸注射后48h，脑内各部位的FOS阳性反应均消失。本研究结果提示：纹状体边缘区和脑内与学习记忆功能有关的结构间有密切的功能联系，但边缘区在脑学习记忆功能中的地位以及与脑中其他学习记忆有关结构间的关系尚待进一步研究．     

Effect of mannitol treatment on brain neurotransmitter markers in kainic acid-induced epilepsy

The effect of mannitol treatment on the behavioural, morphological and neurochemical brain damage induced after subcutaneously applied kainic acid (10 mg/kg) was studied in the rat. Mannitol at a dose of 1.5 g/kg was injected intravenously 10 min, 1.5 h and 3 h respectively after kainic acid administration. A protective effect of mannitol was observed only when mannitol was given 1.5 h after kainic acid application, i.e. within the early phase of kainic acid-induced brain oedema development. At this time period, mannitol prevented the development of kainic acid-induced seizures as well as irreversible brain lesions and neurochemical changes, the latter being reduction of noradrenaline levels in amygdala/pyriform cortex measured 3 h, and reduction of glutamate decarboxylase and choline acetyltransferase activities measured 3 days after kainic acid treatment. Similarly loss of glutamate decarboxylase activity in dorsal hippocampus induced by kainic acid was prevented by mannitol treatment. It is concluded that by washing out brain oedema, mannitol treatment may prevent propagation of seizures and brain damage in the kainic acid model of epilepsy.     

Gonadal hormones affect neuronal vulnerability to excitotoxin-induced degeneration

The role of endogenous gonadal secretions in neuroprotection has been assessed in a model of hippocampal degeneration induced by the systemic administration of kainic acid to adult male and female rats. A low dose of kainic acid (7 mg/Kg b.w.) induced a significant loss of hilar dentate neurons in castrated males and did not affect hilar neurons in intact males. The effect of kainic acid on hilar neurons in female rats was different depending on the day of the estrous cycle in which the neurotoxin was administered; while no significant effect of kainic acid was observed when it was injected in the morning of estrus, there was a significant loss of hilar neurons when it was injected in the morning of proestrus as well as when it was injected into ovariectomized rats. Estradiol or estradiol plus progesterone prevented hilar neuronal loss when injected simultaneously with kainic acid in ovariectomized rat. Progesterone by itself did not prevent neuronal loss induced by kainic acid and estogen was only effective when it was injected either 24 h before or simultaneously with kainic acid and not when it was injected 24 h after the administration of the toxin. These findings indicate that endogenous gonadal hormones protect hippocampal hilar neurons from excitotoxic degeneration. In addition, the timing of exposure to ovarian hormones and the natural fluctuation of ovarian hormones during the estrous cycle may influence the vulnerability of hilar neurons to excitotoxicity. These findings are relevant to possible modifications in neurodegenerative risk in humans as endogenous levels of gonadal hormones change during the menstrual cycle and during aging.     

Synergistic effects of corticosterone and kainic acid on neurite outgrowth in axotomized dorsal root ganglion

Corticosterone is the main adrenal glucocorticoids induced by stress in rats. Therapeutic use of high concentration of synthetic glucocorticoids in clinical treatment of spinal cord injury suggests that pharmacological action of glucocorticoids might be beneficial for nerve repair. In this article we cultured axotomized rat dorsal root ganglion neurons to investigate the effects of corticosterone and a glutamate receptor agonist kainic acid on neurite outgrowth. Our results revealed a synergistic effect of corticosterone and kainic acid in promoting neurite outgrowth when applied as early as one and two days in vitro, but not effective at three and four days in vitro. In addition, applied corticosterone and kainic acid were neurotoxic at three and four days in vitro but not at one and two days in vitro. The minimal concentrations of corticosterone and kainic acid to be effective were 10 microM and 1 mM, respectively. The neurotrophic effect of corticosterone and kainic acid was attenuated by the receptor tyrosine kinase A (TrkA) inhibitor AG-879. Western blot analysis and immunocytochemical studies revealed an increase of expressions of both TrkA and growth-associated protein GAP-43 in dorsal root ganglion neurons with combined treatment of corticosterone and kainic acid. Immunocytochemistry showed that corticosterone+kainic acid increase nerve growth factor immunoreactivity in dorsal root ganglion neurites and enhance GAP-43 immunointensity in dorsal root ganglion neurons. These results suggest that the neurotrophic effect of glucocorticoids on axonal regeneration might require facilitation of excitatory stimulation at an early stage of nerve injury, and nerve growth factor may mediate a growth signaling to accomplish the effect.     

Enhanced but fragile inhibition in the dentate gyrus in vivo in the kainic acid model of temporal lobe epilepsy: a study using current source density analysis

Temporal lobe epilepsy is related to many structural and physiological changes in the brain. We used kainic acid in rats as an animal model of temporal lobe epilepsy, and studied the neural interactions of the dentate gyrus in urethane-anesthetized rats in vivo. Our initial hypothesis was that sprouting of mossy fibers, the axons of the granule cells, increases proximal dendritic excitatory currents in the inner molecular layer of the dentate gyrus. Extracellular currents were detected in vivo using current source density analysis. Backfiring the mossy fibers in CA3 or orthodromic excitation of the granule cells through the medial perforant path induced a current sink at the inner molecular layer. However, the sink or inferred excitation at the inner molecular layer was not increased in kainic acid-treated rats and the sink actually correlated negatively with the degree of mossy fiber sprouting. It is inferred that the latter sink was mediated mainly by association fibers and not by recurrent mossy fibers. After kainic acid treatment, paired-pulse inhibition of the population spikes in the dentate gyrus was increased. In contrast, reverberant activity that involved looping around an entorhinal-hippocampal circuit was increased in kainic acid-treated rats, compared to control rats. The increase of inhibition in kainic acid-treated rats was readily blocked by a small dose of GABA(A) receptor antagonist bicuculline. The latter dose of bicuculline induced paroxsymal spike bursts in kainic acid-treated but not control rats, demonstrating that the increased inhibition in dentate gyrus was fragile.In conclusion, after kainic acid induced seizures, the dentate gyrus in vivo showed an increase in inhibition that appeared to be fragile. The hypothesized increase in proximal dendritic excitation due to mossy fiber sprouting was not detected. However, the fragile inhibition could explain the seizure susceptibility in patients with temporal lobe epilepsy.     

A multidisciplinary study of folic acid neurotoxicity: Interactions with kainate binding sites and relevance to the aetiology of epilepsy

Folic acid has been injected unilaterally into the amygdaloid complex of awake chronically implanted rats, or in rats under anaesthesia. Clinical, electrographic and metabolic changes (estimated by means of the 2-deoxyglucose method) have been studied in relation to subsequently demonstrated neuropathology using Fink-Heimer and Nissl stains. The observations are compared to the corresponding effects of intra-amygdaloid application of kainic acid.Major differences were noted between the folate and the kainate induced seizure/brain damage syndrome. Thus: (a) folate produced essentially stereotypies, alternating with myoclonic unilateral jerks of head and limbs. In contrast, limbic motor seizures which are characteristically produced by kainic acid, were extremely rare, (b) Folate did not produce the preferential and sequential electrographic activation of limbic structures as observed after kainate. (c) 2-Deoxyglucose autoradiography revealed an enhanced metabolic activity in the injected amygdala and in the overlying piriform and entorhinal cortices. The most conspicuous rise in labelling, however, occurred in the entire fronto-parietal cortex (ipsilaterally) up to the cingulate region, as well as in the ventral thalamic complex and the globus pallidus, i.e. in structures which are not labelled after kainate treatment. (d) Some extent of local damage was observed 1–8 days after the injection; distant from the injection site, we found massive anoxic-ischemic type of damage in the superficial layers of the fronto-parietal cortex, a complete necrosis of the piriform lobe and neuronal cell loss in the ventral thalamus and several extrapyramidal structures. The full range of limbic damage associated with kainate was never produced by folate. The CA3 region of the hippocampus, most susceptible to kainate, was only mildly affected by folate.These differences between kainate and folate prompted us to re-evaluate the recently reported high affinity of folates for kainic acid membrane binding sites. We found that folic acid competed only very weakly with [³H]kainic acid for binding sites on striatal, cortical, hippocampal, amygdaloid and cerebellar membranes. It is thus concluded, that folate is not a good candidate for an endogenous kainate-like substance. We propose intracerebral injections of folic acid as a useful tool to study the vulnerability of brain structures to anoxic-ischemic conditions.     

Systemic injection of kainic acid: effect on neurotransmitter markers in piriform cortex, amygdaloid complex and hippocampus and protection by cortical lesioning and anticonvulsants

Systemic injection of kainic acid (12 mg/kg) in rats induces a well established pattern of neuronal lesions in different brain regions. These lesions are accompanied by changes in neurotransmitter markers. In the piriform cortex and amygdaloid complex, the kainic acid lesion was accompanied by a reduction in the high affinity uptake of glutamate and in the activities of glutamate decarboxylase and choline acetyltransferase, whereas in the hippocampus there was a reduction in the high affinity uptake of glutamate and in glutamate decarboxylase activity. Hemidecortication, hemitransection, a caudal knife cut in the cortex, or treatment with diazepam, all protected against the effects of kainic acid in the piriform cortex and amygdaloid complex but not in the hippocampus. Diphenylhydantoin had no effect on the neurotoxicity of kainic acid. The results indicate that the neurotoxic effects of kainic acid in the piriform cortex and amygdala are dependent on an intact cortical structure, probably due to a dependence on specific excitatory circuitry. The neurons involved may be glutamergic/aspartergic.     

The aspirin metabolite sodium salicylate causes focal cerebral hemorrhage and cell death in rats with kainic acid-induced seizures

Aspirin (acetylsalicylic acid), and its main metabolite sodium salicylate, have been shown to protect neurons from excitotoxic cell death in vitro. The objective of our study was to investigate the possible neuroprotective effects of sodium salicylate in vivo in rats with kainic acid-induced seizures, a model for temporal lobe epilepsy in human patients. Male Sprague-Dawley rats received intraperitoneal injections of kainic acid either alone, or with sodium salicylate given before and for 40h after kainic acid injections. The control group received either phosphate-buffered saline or sodium salicylate without co-administration of kainic acid. Animals developed status epilepticus, which was aborted 1.5-2h later with diazepam. On day 3 following kainic acid-induced seizures, animals received bromodeoxyuridine to measure cellular proliferation, and were killed under anesthesia 24h later. Brains were removed, sectioned, and analysed for gross histological changes, evidence of hemorrhage, DNA fragmentation, cellular proliferation, and microglial immunohistochemistry. We report that sodium salicylate did not protect neurons from seizure-induced cell death, and to the contrary, it caused focal hemorrhage and cell death in the hippocampal formation and the entorhinal/piriform cortex of rats with kainic acid-induced seizures. Hemorrhage was never observed in animals that received vehicle, kainic acid or sodium salicylate only, which indicated that sodium salicylate exerted its effect only in animals with seizures, and was confined to select regions of the brain that undergo seizure activity. Large numbers of cells displaying DNA fragmentation were detected in the hippocampal formation, entorhinal/piriform cortex and the dorsomedial thalamic nucleus of rats that received kainic acid or kainic acid in combination with sodium salicylate. Bromodeoxyuridine immunohistochemistry revealed large numbers of proliferating cells in and around the areas with most severe neural injury induced by kainic acid or kainic acid co-administered with sodium salicylate. These same brain regions displayed intense staining with a microglia-specific marker, an indication of microglial activation in response to brain damage. In all cases, the degree of cell death, cell proliferation and microglia staining was more severe in animals that received the combination of kainic acid and sodium salicylate when compared to animals that received kainic acid alone.We hypothesize that our findings are attributable to sodium salicylate-induced blockade of cellular mechanisms that protect cells from calcium-mediated injury. These initial observations may have important clinical implications for patients with epilepsy who take aspirin while affected by these conditions, and should promote further investigation of this relationship.     

Kainic acid-mediated increase of preprotachykinin-A messenger RNA expression in the rat hippocampus and a region-selective attenuation by dexamethasone.

The hippocampus contains the highest number of glucocorticoid-sensitive neurons in the rat brain and excessive exposure to glucocorticoids can cause damage to hippocampal neurons and impair the capacity of the hippocampus to survive neuronal insults. In this study in situ hybridization combined with quantitative image analysis was used to study preprotachykinin-A mRNA levels after administration of a toxic dose of kainic acid in animals pretreated with glucocorticoids. Kainic acid was injected into dorsal hippocampus CA3 region in animals pretreated with the synthetic glucocorticoid receptor agonist dexamethasone and in control animals. Preprotachykinin-A mRNA was not detected in the hippocampus of untreated animals or in animals analysed 30 min after a kainic acid injection. However, 4 h after injection of kainic acid, the level of preprotachykinin-A mRNA increased to 20-times above the detection limit both in the dentate gyrus and the CA3 region of the hippocampus. Treatment of kainic acid-injected animals with dexamethasone 30 min before and 2 h after the injection attenuated the increase in the granule cells of the dentate gyrus by 50%. In contrast, dexamethasone pretreatment had no significant effect on the kainic acid-induced increase of preprotachykinin-A mRNA in pyramidal cells in regions CA3 or CA1. These results show that an excitatory stimulus within the hippocampus causes a substantial increase in the level of preprotachykinin-A mRNA in hippocampal granule and pyramidal cells and suggest that in granule cells of the dentate gyrus this increase can be modulated by glucocorticoids.     

Hippocampal excitatory amino acid receptors in elderly, normal individuals and those with Alzheimer's disease: non-N-methyl-D-aspartate receptors.

Quantitative receptor autoradiography was used to examine the density and distribution of [3H]kainic acid and [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) binding sites in the hippocampal formation and parahippocampal gyrus obtained at autopsy from 10 Alzheimer's disease and eight normal control individuals. In control and Alzheimer's disease individuals, [3H]kainic acid saturation binding analysis in the outer molecular layer of the dentate gyrus fitted a single-site model. Added calcium ions did not alter the density of [3H]kainic acid binding in the human tissues. These results suggest that calcium-sensitive high-affinity kainic acid binding sites are not present in the human brain in contrast to kainic acid receptors in the rat brain. [3H]AMPA binding was also slightly different in the human brain as compared to the rat, being greatest in the inner third as compared to the outer two-thirds of the dentate gyrus molecular layer. In both control and Alzheimer's disease individuals, [3H]kainic acid and [3H]AMPA binding densities were similar at anterior and posterior levels of the hippocampal formation. In Alzheimer's disease patients, there was a significant increase in [3H]AMPA binding in the infragranular layer. In some, but not all Alzheimer's disease patients, there was an increase in [3H]kainic acid binding densities in the outer half of the dentate gyrus molecular layer. The same individuals which exhibited an increase in [3H]kainic acid binding in the outer molecular layer also displayed increased [3H]AMPA binding in the hilar region. Similar alterations in [3H]kainic acid binding have been observed in rats which had received fimbria-fornix lesions, a model of chronic epilepsy and in individuals with temporal lobe epilepsy. Advanced Alzheimer's disease patients are at risk of developing seizures. The results suggest that several factors including cortical and subcortical pathology and seizure activity may contribute to the alterations in [3H]kainic acid and [3H]AMPA binding observed in the hippocampal formation in Alzheimer's disease.