Intracerebroventricular Kainic Acid Research Articles

Benchmarking the proteomic profile of animal models of mesial temporal epilepsy.

ObjectivesWe compared the proteomic signatures of the hippocampal lesion induced in three different animal models of mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE+HS): the systemic pilocarpine model (PILO), the intracerebroventricular kainic acid model (KA), and the perforant pathway stimulation model (PPS).MethodsWe used shotgun proteomics to analyze the proteomes and find enriched biological pathways of the dorsal and ventral dentate gyrus (DG) isolated from the hippocampi of the three animal models. We also compared the proteomes obtained in the animal models to that from the DG of patients with pharmacoresistant MTLE+HS.ResultsWe found that each animal model presents specific profiles of proteomic changes. The PILO model showed responses predominantly related to neuronal excitatory imbalance. The KA model revealed alterations mainly in synaptic activity. The PPS model displayed abnormalities in metabolism and oxidative stress. We also identified common biological pathways enriched in all three models, such as inflammation and immune response, which were also observed in tissue from patients. However, none of the models could recapitulate the profile of molecular changes observed in tissue from patients.SignificanceOur results indicate that each model has its own set of biological responses leading to epilepsy. Thus, it seems that only using a combination of the three models may one replicate more closely the mechanisms underlying MTLE+HS as seen in patients.

Microglial P2Y12 Receptor Regulates Seizure-Induced Neurogenesis and Immature Neuronal Projections.

Seizures are common in humans with various etiologies ranging from congenital aberrations to acute injuries that alter the normal balance of brain excitation and inhibition. A notable consequence of seizures is the induction of aberrant neurogenesis and increased immature neuronal projections. However, regulatory mechanisms governing these features during epilepsy development are not fully understood. Recent studies show that microglia, the brain's resident immune cell, contribute to normal neurogenesis and regulate seizure phenotypes. However, the role of microglia in aberrant neurogenic seizure contexts has not been adequately investigated. To address this question, we coupled the intracerebroventricular kainic acid model with current pharmacogenetic approaches to eliminate microglia in male mice. We show that microglia promote seizure-induced neurogenesis and subsequent seizure-induced immature neuronal projections above and below the pyramidal neurons between the DG and the CA3 regions. Furthermore, we identify microglial P2Y12 receptors (P2Y12R) as a participant in this neurogenic process. Together, our results implicate microglial P2Y12R signaling in epileptogenesis and provide further evidence for targeting microglia in general and microglial P2Y12R in specific to ameliorate proepileptogenic processes.SIGNIFICANCE STATEMENT Epileptogenesis is a process by which the brain develops epilepsy. Several processes have been identified that confer the brain with such epileptic characteristics, including aberrant neurogenesis and increased immature neuronal projections. Understanding the mechanisms that promote such changes is critical in developing therapies to adequately restrain epileptogenesis. We investigated the role of purinergic P2Y12 receptors selectively expressed by microglia, the resident brain immune cells. We report, for the first time, that microglia in general and microglial P2Y12 receptors in specific promote both aberrant neurogenesis and increased immature neuronal projections. These results indicate that microglia enhance epileptogenesis by promoting these processes and suggest that targeting this immune axis could be a novel therapeutic strategy in the clinic.

CXCR4 Antagonist AMD3100 Suppresses the Long-Term Abnormal Structural Changes of Newborn Neurons in the Intraventricular Kainic Acid Model of Epilepsy.

Abnormal hippocampal neurogenesis is a prominent feature of temporal lobe epilepsy (TLE) models, which is thought to contribute to abnormal brain activity. Stromal cell-derived factor-1 (SDF-1) and its specific receptor CXCR4 play important roles in adult neurogenesis. We investigated whether treatment with the CXCR4 antagonist AMD3100 suppressed aberrant hippocampal neurogenesis, as well as the long-term consequences in the intracerebroventricular kainic acid (ICVKA) model of epilepsy. Adult male rats were randomly assigned as control rats, rats subjected to status epilepticus (SE), and post-SE rats treated with AMD3100. Animals in each group were divided into two subgroups (acute stage and chronic stage). We used immunofluorescence staining of BrdU and DCX to analyze the hippocampal neurogenesis on post-SE days 10 or 74. Nissl staining and Timm staining were used to evaluate hippocampal damage and mossy fiber sprouting, respectively. On post-SE day 72, the frequency and mean duration of spontaneous seizures were measured by electroencephalography (EEG). Cognitive function was evaluated by Morris water maze testing on post-SE day 68. The ICVKA model of TLE resulted in aberrant neurogenesis such as altered proliferation, abnormal dendrite development of newborn neurons, as well as spontaneous seizures and spatial learning impairments. More importantly, AMD3100 treatment reversed the aberrant neurogenesis seen after TLE, which was accompanied by decreased long-term seizure activity, though improvement in spatial learning was not seen. AMD3100 could suppress long-term seizure activity and alter adult neurogenesis in the ICVKA model of TLE, which provided morphological evidences that AMD3100 might be beneficial for treating chronic epilepsy.

Neuroprotective effects of anti-high-mobility group box 1 antibody in juvenile rat hippocampus after kainic acid-induced status epilepticus

High-mobility group box 1 (HMGB1) is a potent cytokine that has been proved to participate in diverse neurological diseases including seizures. Blockade of HMGB1 with neutralizing antibody has shown protective effects against different kinds of insults. However, the potential role of anti-HMGB1 antibody in status epilepticus (SE) has not yet been addressed. In the present study, we investigated the effects of anti-HMGB1 antibody on hippocampal damage and inflammatory reaction after SE induced by an intracerebroventricular kainic acid (KA) injection in postnatal day 21 rats. We found that KA-induced SE markedly increased the mRNA expression of interleukin-1β and tumor necrosis factor-α, microglial activation, and neuronal damage in the hippocampus. An intracerebroventricular injection of anti-HMGB1 antibody dose dependently inhibited the synthesis of cytokines, microglial activation, and neuronal losses in the hippocampus after SE. In conclusion, our findings suggest that HMGB1 blocking therapy exerts neuroprotective effects during the early phase of KA-induced SE in juvenile rats.

Characterization of the expression of macrophage inflammatory protein‐1α (MIP‐1α) and C‐C chemokine receptor 5 (CCR5) after kainic acid‐induced status epilepticus (SE) in juvenile rats

To identify the potential role of macrophage inflammatory protein-1α (MIP-1α) with its C-C chemokine receptor 5 (CCR5) in epileptogenic brain injury, we examined their expression in juvenile rat hippocampus and explored the potential link between MIP-1α, CCR5 and neuropathological alterations after status epilepticus (SE) induced by intracerebroventricular (i.c.v.) kainic acid (KA) injection. Based on the determination of the development of spontaneous seizures initiated by SE in developing rat brain, we firstly examined hippocampal neurone damage through Nissl and Fluoro-Jade B staining, and evaluated microglial reaction during the early phase following KA-induced SE in 21-day-old rats. MIP-1α and CCR5 protein were quantified by ELISA and Western blot respectively following mRNA by real-time PCR. We also mapped MIP-1α and CCR5 expression in the hippocampus by immunohistochemistry and identified their cellular sources using double-labelling immunofluorescence. In juvenile rats, KA caused characteristic neurone damage in the hippocampal subfields, with accompanying microglial accumulation. In parallel with mRNA expression, MIP-1α protein in hippocampus was transiently increased after KA treatment, and peaked from 16 to 72 h. Double-labelling immunofluorescence revealed that MIP-1α was localized to microglia. Up-regulated CCR5 remained prominent at 24 and 72 h and was mainly localized to activated microglia. Further immunohistochemistry revealed that MIP-1α and CCR5 expression were closely consistent with microglial accumulation in corresponding hippocampal subfields undergoing degenerative changes. Our data indicated that MIP-1α as a regulator, linking with the CCR5 receptor, may be involved within the early stages of the epileptogenic process following SE by i.c.v. KA injection.

The effect of visnagin administered orally on hippocampal cell death and neuroinflammation induced by intracerebroventricular kainic acid in mice

The effect of visnagin administered orally on hippocampal cell death and neuroinflammation induced by intracerebroventricular kainic acid in mice

Restoration of calbindin after fetal hippocampal CA3 cell grafting into the injured hippocampus in a rat model of temporal lobe epilepsy

Degeneration of the CA3 pyramidal and dentate hilar neurons in the adult rat hippocampus after an intracerebroventricular kainic acid (KA) administration, a model of temporal lobe epilepsy, leads to permanent loss of the calcium binding protein calbindin in major fractions of dentate granule cells and CA1 pyramidal neurons. We hypothesize that the enduring loss of calbindin in the dentate gyrus and the CA1 subfield after CA3-lesion is due to disruption of the hippocampal circuitry leading to hyperexcitability in these regions; therefore, specific cell grafts that are capable of both reconstructing the disrupted circuitry and suppressing hyperexcitability in the injured hippocampus can restore calbindin. We compared the effects of fetal CA3 or CA1 cell grafting into the injured CA3 region of adult rats at 45 days after KA-induced injury on the hippocampal calbindin. The calbindin immunoreactivity in the dentate granule cells and the CA1 pyramidal neurons of grafted animals was evaluated at 6 months after injury (i.e. at 4.5 months post-grafting). Compared with the intact hippocampus, the calbindin in "lesion-only" hippocampus was dramatically reduced at 6 months post-lesion. However, calbindin expression was restored in the lesioned hippocampus receiving CA3 cell grafts. In contrast, in the lesioned hippocampus receiving CA1 cell grafts, calbindin expression remained less than the intact hippocampus. Thus, specific cell grafting restores the injury-induced loss of calbindin in the adult hippocampus, likely via restitution of the disrupted circuitry. Since loss of calbindin after hippocampal injury is linked to hyperexcitability, re-expression of calbindin in both dentate gyrus and CA1 subfield following CA3 cell grafting may suggest that specific cell grafting is efficacious for ameliorating injury-induced hyperexcitability in the adult hippocampus. However, electrophysiological studies of KA-lesioned hippocampus receiving CA3 cell grafts are required in future to validate this possibility.

Chronic temporal lobe epilepsy is associated with severely declined dentate neurogenesis in the adult hippocampus

While it is clear that acute hippocampal injury or status epilepticus increases the production of new neurons in the adult dentate gyrus (DG), the effects of chronic epilepsy on dentate neurogenesis are unknown. We hypothesize that epileptogenic changes and spontaneous recurrent motor seizures (SRMS) that ensue after hippocampal injury or status epilepticus considerably decrease dentate neurogenesis. We addressed this issue by quantifying the number of cells that are positive for doublecortin (DCX, a marker of new neurons) in the DG of adult F344 rats at 16 days and 5 months after an intracerebroventricular kainic acid (ICV KA) administration or after graded intraperitoneal KA (IP KA) injections, models of temporal lobe epilepsy (TLE). At early post-KA administration, the injured hippocampus exhibited increased dentate neurogenesis in both models. Conversely, at 5 months post-KA administration, the chronically epileptic hippocampus demonstrated severely declined neurogenesis, which was associated with considerable SRMS in both KA models. Additionally, stem/progenitor cell proliferation factors, FGF-2 and IGF-1, were decreased in the chronically epileptic hippocampus. Interestingly, the overall decrease in neurogenesis and the extent of SRMS were greater in rats receiving IP KA than rats receiving ICV KA, suggesting that the extent of neurogenesis during chronic TLE exhibits an inverse relationship with SRMS. These results provide novel evidence that chronic TLE is associated with extremely declined dentate neurogenesis. As fraction of newly born neurons become GABA-ergic interneurons, declined neurogenesis may contribute to the increased seizure-susceptibility of the DG in chronic TLE. Likewise, the hippocampal-dependent learning and memory deficits observed in chronic TLE could be linked at least partially to the declined neurogenesis.

Nestin expression in hippocampal astrocytes after injury depends on the age of the hippocampus.

Analysis of the expression of nestin in reactive astrocytes facilitates quantification of the extent of activation of astrocytes after injury in the mature CNS. We hypothesize that the capability of astrocytes for re-expressing nestin in response to CNS injury diminishes as a function of age. We quantified astrocytes positive for S-100beta protein, glial fibrillary acidic protein (GFAP) and nestin in the hippocampus of young adult, middle-aged, and aged Fischer 344 rats after an intracerebroventricular kainic acid (KA) administration. In all age groups, KA administration induced degeneration of CA3 pyramidal neurons, which led to a significant deafferentation in the CA1 region. The KA-induced neurodegeneration and deafferentation resulted in an increased population of astrocytes positive for S-100beta and glial fibrillary acidic protein (GFAP) in all age groups. Interestingly, these increases were highly comparable across the three age groups. However, in areas of both neurodegeneration and deafferentation, the overall numerical density of nestin-positive reactive astrocytes varied depending on the age at the time of injury with noticeably decreased numerical density in the injured middle-aged and aged hippocampus. In contrast, nestin-immunoreactive radial glia framework after lesion is not impaired with aging in the ependymal lining of the CA3 region.

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

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

Increased hippocampal neurogenesis accompanies apoptosis in neonatal rats exposed to intracerebroventricular kainic acid

Increased hippocampal neurogenesis accompanies apoptosis in neonatal rats exposed to intracerebroventricular kainic acid

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

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

Entorhinal axons exhibit sprouting in CA1 subfield of the adult hippocampus in a rat model of temporal lobe epilepsy

Intracerebroventricular kainic acid administration in rat, a model of temporal lobe epilepsy, results in CA3 pyramidal neuron degeneration leading to deafferentation of CA1 pyramidal neurons. Denervation in CA1 shows a near-complete recovery of synaptic density over 2-3 months, but the source of axons participating in the reinnervation is not clear. This study investigated the contribution of the entorhinal cortex in this reinnervation by comparing the distribution of the entorhinal axons in the CA1 subfield between the intact hippocampus and the CA3-lesioned hippocampus at 3 months after administration of kainic acid. Entorhinal axons were visualized by anterograde tracing using injections of the biotinylated dextran amine into the entorhinal cortex. In the CA1 subfield of the intact hippocampus, entorhinal axons were conspicuous in the alveus and the stratum lacunosum moleculare. The distribution in the strata oriens, pyramidale, and radiatum was sparse and was characterized by isolated entorhinal fibers of the alvear pathway crossing these strata to the stratum lacunosum moleculare. However, after kainic acid-induced CA3 lesion, the density of entorhinal axons increased significantly in the CA1 stratum radiatum (375% of the intact hippocampus), as a large number of axons emanating from the entorhinal fiber plexus in the stratum lacunosum moleculare invaded the stratum radiatum. The stratum radiatum also exhibited wavy entorhinal axons filled with boutons and oriented parallel to the stratum pyramidale, suggesting collateral sprouting from entorhinal axons traversing the stratum radiatum. Thus, a significant aberrant sprouting of entorhinal axons occurs into the CA1 stratum radiatum after CA3 lesion. The sprouted fibers appear to come from both entorhinal fiber plexus in the stratum lacunosum moleculare (translaminar sprouting) and entorhinal axons traversing the stratum radiatum (intralaminar sprouting). However, the major contribution appears to be from the entorhinal plexus in the stratum lacunosum moleculare. This aberrant sprouting may lead to altered afferent excitatory connectivity in the CA1 subfield and contribute to the persistent CA1 hyperexcitability that occurs after the CA3 lesion.

Fetal Hippocampal Grafts Containing CA3 Cells Restore Host Hippocampal Glutamate Decarboxylase-Positive Interneuron Numbers in a Rat Model of Temporal Lobe Epilepsy

Degeneration of CA3-pyramidal neurons in hippocampus after intracerebroventricular kainic acid (KA) administration, a model of temporal lobe epilepsy, results in hyperexcitability within both dentate gyrus and the CA1 subfield. It also leads to persistent reductions in hippocampal glutamate decarboxylase (GAD) interneuron numbers without diminution in Nissl-stained interneuron numbers, indicating loss of GAD expression in a majority of interneurons. We hypothesize that enduring loss of GAD expression in hippocampal interneurons after intracerebroventricular KA is attributable to degeneration of their CA3 afferent input; therefore, fetal CA3 grafts can restore GAD interneuron numbers through graft axon reinnervation of the host. We analyzed GAD interneuron density in the adult rat hippocampus at 6 months after KA administration after grafting of fetal mixed hippocampal, CA3 or CA1 cells into the CA3 region at 45 d after lesion, in comparison with "lesion-only" and intact hippocampus. In dentate and CA1 regions of the lesioned hippocampus receiving grafts of either mixed hippocampal or CA3 cells, GAD interneuron density was both significantly greater than lesion-only hippocampus and comparable with the intact hippocampus. In the CA3 region, GAD interneuron density was significantly greater than lesion-only hippocampus but less than the intact hippocampus. Collectively, the overall GAD interneuron density in the lesioned hippocampus receiving either mixed hippocampal or CA3 grafts was restored to that in the intact hippocampus. In contrast, GADinterneuron density in the lesioned hippocampus receiving CA1 grafts remained comparable with lesion-only hippocampus. Thus, grafts containing CA3 cells restore CA3 lesion-induced depletions in hippocampal GAD interneurons, likely by reinnervation of GAD-deficient interneurons. This specific graft-mediated effect is beneficial because reactivation of interneurons could ameliorate both loss of functional inhibition and hyperexcitability in CA3-lesioned hippocampus.

Participation of NMDA and kainate receptors of paraventricular nucleus in cardiovascular responses to glutamate receptor agonist

The nuclei of the hypothalamus have been shown to be involved in central cardiovascular homeostasis. Recent studies suggest that glutamate-containing neurons have an important role in the regulation of central cardiovascular function. We report first on the effects of intracerebrally injected NMDA and non-NMDA receptor ligands on blood pressure and heart rate in conscious Sprague–Dawley rats. In the second part, we describe the effect of blockade of NMDA or kainate receptors in the paraventricular nucleus on glutamate receptor agonist-induced blood pressure responses. Intracerebroventricular injections of l-glutamic acid, NMDA and kainic acid produced increases in mean arterial pressure. Kainic acid produced significant decreases in heart rate. Microinjection of dl-2-amino-5-phosphonopentanoic acid (APV; 25 and 50 nmol), a competitive NMDA receptor antagonist, into the paraventricular nucleus blunted the increases in the mean arterial pressure evoked by intracerebroventricular injections of NMDA (1 nmol), whereas microinjection of dinitroquinoxaline (DNQX; 20, 40 and 80 pmol), which acts as an antagonist at kainate receptors, failed to antagonize the cardiovascular effects of intracerebroventricular kainic acid (10 pmol). Microinjections of NMDA (100 pmol) into the paraventricular nucleus produced pressor responses, but kainic acid (5 and 10 pmol) failed to affect either mean arterial pressure or heart rate. These results suggest participation of the glutamergic system in cardiovascular regulation via NMDA receptors located within the paraventricular nucleus of the hypothalamus in rats.

Aging impairs axonal sprouting response of dentate granule cells following target loss and partial deafferentation.

Compared to other brain regions, the hippocampus shows considerable susceptibility to the aging process. Aging may impair the compensatory plastic response of hippocampal neurons following lesions, target loss, and/or deafferentation. We hypothesize that sprouting of dentate granule cell axons (mossy fibers) in response to target loss and partial deafferentation diminishes with age. We quantified mossy fiber sprouting into the dentate supragranular layer (DSGL) following intracerebroventricular kainic acid administration in young adult, middle-aged, and aged rats, using Timm's histochemical method. Mossy fiber ingrowth into the DSGL was assessed in the septal hippocampus at 2- and 4 months postlesion by measuring both the average width and the relative density of sprouted terminals. Kainic acid lesions produced degeneration of CA3 pyramids with sparing of CA1 and dentate granule cells in all age groups. Although young adults demonstrated robust DSGL mossy fiber sprouting, sprouting was significantly reduced in both middle-aged and aged rats. Compared to the case in young adults, the overall sprouting in middle-aged animals was reduced by 52% at 2 months and 50% at 4 months postlesion, whereas in aged rats the sprouting was reduced by 53% at 2 months and 64% at 4 months postlesion. Aged animals also showed an overall reduction of 28% compared to middle-aged animals at 4 months postlesion. Dramatically reduced sprouting in aged animals may represent a deficit in recognition of target loss and partial deafferentation by aged granule cells and/or an impaired up-regulation of factors that stimulate neurite outgrowth in the aged brain.

Vulnerability of the Dentate Gyrus to Aging and Intracerebroventricular Administration of Kainic Acid

The hippocampal formation is highly vulnerable to the aging process, demonstrating functional alterations in circuitry with aging. Aging may also change the sensitivity of the hippocampal formation to excitotoxic lesions. In this study, using young adult, middle aged, and aged Fischer 344 rats, we evaluated morphometric changes in the dentate gyrus as a function of age and also in response to an administration of an excitotoxin (kainic acid) into the right lateral ventricle. The dentate gyrus was measured for changes in the area of dentate hilus and the dentate granule cell layer, alterations in the width of the dentate granule cell layer, and degree of dentate hilar cell loss. With aging, the hilar area increased in size while the area and width of the dentate granule cell layer remained constant. However, the most striking change with aging was a significant reduction in the number of dentate hilar neurons. Intracerebroventricular kainic acid produced consistent lesions in the entire ipsilateral CA3 region, and the size of CA3 lesion was identical in all three ages of animals. Following the lesion, areas of both the dentate hilus and the granule cell layer were significantly decreased in only young adult and middle aged animals whereas the width of the dentate granule cell layer was significantly increased only in the middle aged group. In contrast, dentate hilar neurons were significantly reduced in all ages of animals with the maximum reductions in neuron number observed in the aged group. Thus, aging in the dentate gyrus is characterized by a significantly decreased number of dentate hilar neurons and also a significantly increased susceptibility of dentate hilar neurons to excitotoxic damage.

Delayed neuronal loss after administration of intracerebroventricular kainic acid to preweanling rats

Excitotoxins, such as kainic acid (KA), have been shown to produce both immediate and delayed neuronal degeneration in adult rat brain. While preweanling rats have been shown to be resistant to the immediate neurotoxicity of KA, the presence of delayed neuronal loss has not been investigated in such animals. To determine whether intracerebroventricular (i.c.v.) administration of KA would produce delayed neuronal loss, preweanling rats were administered 5 nmol or 10 nmol KA i.c.v. on postnatal day 7 (P7) and then examined at P14, P45, and P75. Using three-dimensional, non-biased cell counting, neuronal loss was observed in the CA3 subfield of the hippocampal formation at P45 and P75 in animals administered 10 nmol KA, as compared to animals administered 5 nmol KA or artificial cerebrospinal fluid. Further, the amount of immunoreactivity to jun, the protein product of the immediate early gene, c- jun, adjusted for the number of remaining neurons was increased in the same brain areas. Antibody labeling of inducible heat shock protein and glial fibrillary acidic protein was not similarly increased in animals administered i.c.v. KA. The data suggest that while i.c.v. KA does not produce immediate neuronal loss in preweanling rats, the hippocampus is altered so that neuronal loss occurs after a delay, perhaps through apoptosis. These findings may be relevant to the pathogenesis of neuropsychiatric disorders, such as schizophrenia, that are characterized by early limbic–cortical deficits but onset of illness in young adulthood.

Progressive neurodegeneration after intracerebroventricular kainic acid administration in rats: implications for schizophrenia?

Background: Intracerebroventricular (ICV) administration of kainic acid to rats produces limbic-cortical neuronal damage that has been compared to the neuropathology of schizophrenia. Methods: Groups of adult rats were administered ICV kainic acid and then assessed for neuronal loss and the expression of proteins relevant to mechanisms of neuronal damage after one and fourteen days. Neuronal loss was assessed by two-dimensional cell counting and protein expression was assessed by immunohistochemistry. Results: ICV kainic acid administration was associated with both immediate (day 1) and delayed (day 14) neuronal loss in the dorsal hippocampus. The immediate injury was largely limited to the CA3 hippocampal subfield, while the delayed injury included the CA1 subfield. Multiple mechanisms of cell death appeared to be involved in the delayed neuronal loss, as evidenced by changes in the expression of glutamate receptor subunits, heat shock protein and jun protein. Conclusions: ICV kainic acid administration to adult rats produces progressive damage to limbic-cortical neurons, involving both fast and slow mechanisms of cell death. Given the evidence for clinical deterioration, cognitive deficits and hippocampal neuropathy in some cases of schizophrenia, this animal model may be relevant for hypotheses regarding mechanisms of neurodegeneration in that disorder.

Spread of Excitation in Chronically Lesioned Mouse Hippocampus Determined by Laser Scanning Microscopy

Fast optical recordings by means of laser scanning microscopy in conjunction with a voltage-sensitive dye (RH 414) were performed to monitor the spatio-temporal spread of neuronal activity in CA3/CA4-lesioned C57BL6 mouse hippocampal slices prepared approximately 3 months after intracerebroventricular kainic acid (KA) injection. The aim of our study was to assess the effects of a circumscribed neuronal loss on the propagation of electrical activity along the trisynaptic hippocampal circuit. Both in physiological bathing solution and in bicuculline (10 μM), hilar stimulation failed to activate the downstream pathway, so that, under these conditions, the chronically disinhibited CA1 region appeared to be effectively isolated from burst activity arising upstream; however, epileptiform discharges evoked in zero Mg2+solution were reliably transmitted from the dentate gyrus to the CA1 region. That these bursts were indeed spreading across the lesion, and not along newly formed connections (e.g., between dentate gyrus and CA1), was confirmed by acute transection experiments of the Schaffer collateral/commissural pathway, which completely abolished translesional burst propagation. The fact that the surviving CA3–CA1 connections are unable to trigger epileptiform bursts after suppression of GABAergic inhibition suggests that the lesioned region might serve as a filter that shields hyperexcitable CA1 neurons from epileptic activity arising upstream, in particular from chronically disinhibited granule cells of the dentate gyrus. An impaired GABAergic inhibition will thus only have minor facilitating effects on seizure propagation in the hippocampus of CA3-lesioned animals.