Reactive astrocytes in the kainic acid-damage hippocampus have the phenotypic features of type-2 astrocytes

Lactation reduces glial activation induced by excitotoxicity in the rat hippocampus

Motherhood induces a series of adaptations in the physiology of the female, including an increase of maternal brain plasticity and a reduction of cell damage in the hippocampus caused by kainic acid (KA) excitotoxicity. We analysed the role of lactation in glial activation in the hippocampal fields of virgin and lactating rats after i.c.v. application of 100 ng of KA. Immunohistochemical analysis for glial fibrillary acidic protein (GFAP) and ionised calcium binding adaptor molecule 1 (Iba-1), which are markers for astrocytes and microglial cell-surface proteins, respectively, revealed differential cellular responses to KA in lactating and virgin rats. A significant astrocyte and microglial response in hippocampal areas of virgin rats was observed 24 h and 72 h after KA. By contrast, no increase in either GFAP- or Iba-1-positive cells was observed in response to KA in the hippocampus of lactating rats. Western blot analysis of GFAP showed an initial decrease at 24 h after KA treatment, with an increase at 72 h in the whole hippocampus of virgin but not of lactating rats. The number of GFAP-positive cells was increased by lactation in the dentate gyrus of the hippocampus but not in CA1 and CA3 areas. The present results indicate that lactating rats exhibit diminished responses of astrocyte and microglial cells in the hippocampus to damage induced by KA, supporting the notion that the maternal hippocampus is resistant to excitotoxic insults.

Transcriptome profiling of hippocampal CA1 after early-life seizure-induced preconditioning may elucidate new genetic therapies for epilepsy

Injury of the CA1 subregion induced by a single injection of kainic acid (1 × KA) in juvenile animals (P20) is attenuated in animals with two prior sustained neonatal seizures on P6 and P9. To identify gene candidates involved in the spatially protective effects produced by early-life conditioning seizures we profiled and compared the transcriptomes of CA1 subregions from control, 1 × KA- and 3 × KA-treated animals. More genes were regulated following 3 × KA (9.6%) than after 1 × KA (7.1%). Following 1 × KA, genes supporting oxidative stress, growth, development, inflammation and neurotransmission were upregulated (e.g. Cacng1, Nadsyn1, Kcng1, Aven, S100a4, GFAP, Vim, Hrsp12 and Grik1). After 3 × KA, protective genes were differentially over-expressed [e.g. Cat, Gpx7, Gad1, Hspa12A, Foxn1, adenosine A1 receptor, Ca(2+) adaptor and homeostasis proteins, Cacnb4, Atp2b2, anti-apoptotic Bcl-2 gene members, intracellular trafficking protein, Grasp and suppressor of cytokine signaling (Socs3)]. Distinct anti-inflammatory interleukins (ILs) not observed in adult tissues [e.g. IL-6 transducer, IL-23 and IL-33 or their receptors (IL-F2 )] were also over-expressed. Several transcripts were validated by real-time polymerase chain reaction (QPCR) and immunohistochemistry. QPCR showed that casp 6 was increased after 1 × KA but reduced after 3 × KA; the pro-inflammatory gene Cox1 was either upregulated or unchanged after 1 × KA but reduced by ~70% after 3 × KA. Enhanced GFAP immunostaining following 1 × KA was selectively attenuated in the CA1 subregion after 3 × KA. The observed differential transcriptional responses may contribute to early-life seizure-induced pre-conditioning and neuroprotection by reducing glutamate receptor-mediated Ca(2+) permeability of the hippocampus and redirecting inflammatory and apoptotic pathways. These changes could lead to new genetic therapies for epilepsy.

Water maze experience and prenatal choline supplementation differentially promote long-term hippocampal recovery from seizures in adulthood

Status epilepticus (SE) in adulthood dramatically alters the hippocampus and produces spatial learning and memory deficits. Some factors, like environmental enrichment and exercise, may promote functional recovery from SE. Prenatal choline supplementation (SUP) also protects against spatial memory deficits observed shortly after SE in adulthood, and we have previously reported that SUP attenuates the neuropathological response to SE in the adult hippocampus just 16 days after SE. It is unknown whether SUP can ameliorate longer-term cognitive and neuropathological consequences of SE, whether repeatedly engaging the injured hippocampus in a cognitive task might facilitate recovery from SE, and whether our prophylactic prenatal dietary treatment would enable the injured hippocampus to more effectively benefit from cognitive rehabilitation. To address these issues, adult offspring from rat dams that received either a control (CON) or SUP diet on embryonic days 12-17 first received training on a place learning water maze task (WM) and were then administered saline or kainic acid (KA) to induce SE. Rats then either remained in their home cage, or received three additional WM sessions at 3, 6.5, and 10 weeks after SE to test spatial learning and memory retention. Eleven weeks after SE, the brains were analyzed for several hippocampal markers known to be altered by SE. SUP attenuated SE-induced spatial learning deficits and completely rescued spatial memory retention by 10 weeks post-SE. Repeated WM experience prevented SE-induced declines in glutamic acid decarboxylase (GAD) and dentate gyrus neurogenesis, and attenuated increased glial fibrilary acidic protein (GFAP) levels. Remarkably, SUP alone was similarly protective to an even greater extent, and SUP rats that were water maze trained after SE showed reduced hilar migration of newborn neurons. These findings suggest that prophylactic SUP is protective against the long-term cognitive and neuropathological effects of KA-induced SE, and that rehabilitative cognitive enrichment may be partially beneficial.

Expression of glutamine synthetase and glutamate dehydrogenase in the latent phase and chronic phase in the kainate model of temporal lobe epilepsy

It has been suggested that astrocytic glutamate release or perturbed glutamate metabolism contributes to the proneness to epileptic seizures. Here we investigated whether astrocytic contents of the major glutamate degrading enzymes glutamine synthetase (GS) and glutamate dehydrogenase (GDH) decreases on moving from the latent phase (prior to seizures) to the chronic phase (after onset of seizures) in the kainate (KA) model of temporal lobe epilepsy. Western blotting and immunogold analysis of hippocampal formation indicated similar levels of GDH in the latent and chronic phases of KA injected rats and in corresponding controls. In contrast, the level of GS was increased in the latent phase compared with controls, as assessed by Western blots of whole hippocampal formation and subregions. The increase in GS paralleled that of glial fibrillary acidic protein (GFAP). Compared with the latent phase, the chronic phase revealed a lower level of GS (approaching control levels) but an unchanged GFAP content. The decrease in GS from latent to chronic phase was significant in whole hippocampal formation, dentate gyrus and CA3. It is concluded that kainate treated rats show an initial increase in GS, pari passu with the increase in GFAP, and a secondary decrease in GS that is not accompanied by a similar loss of GFAP. In a situation where glutamate catabolism is in high demand the secondary reduction in GS level may be sufficient to contribute to the seizure proneness that develops between the latent and chronic phases.

Prenatal choline supplementation attenuates neuropathological response to status epilepticus in the adult rat hippocampus

Prenatal choline supplementation (SUP) protects adult rats against spatial memory deficits observed after excitotoxin-induced status epilepticus (SE). To examine the mechanism underlying this neuroprotection, we determined the effects of SUP on a variety of hippocampal markers known to change in response to SE and thought to underlie ensuing cognitive deficits. Adult offspring from rat dams that received either a control or SUP diet on embryonic days 12-17 were administered saline or kainic acid (i.p.) to induce SE and were euthanized 16 days later. SUP markedly attenuated seizure-induced hippocampal neurodegeneration, dentate cell proliferation, and hippocampal GFAP mRNA expression levels, prevented the loss of hippocampal GAD65 protein and mRNA expression, and altered growth factor expression patterns. SUP also enhanced pre-seizure hippocampal levels of BDNF, NGF, and IGF-1, which may confer a neuroprotective hippocampal microenvironment that dampens the neuropathological response to and/or helps facilitate recovery from SE to protect cognitive function.

Dissociation of the immunoreactivity of synaptophysin and GAP-43 during the acute and latent phases of the lithium–pilocarpine model in the immature and adult rat

RATIONALE

Lithium-pilocarpine-induced status epilepticus (SE) generates neuronal lesions in the limbic forebrain, cerebral cortex and thalamus that lead to circuit reorganization and spontaneous recurrent seizures. The process of reorganization in regions with neuronal damage is not fully clarified.

METHODS

In the present study, we evaluated by immunohistochemistry the early reorganization during the latent period with two neuronal markers, synaptophysin and growth-associated protein 43 (GAP-43) in rats subjected to SE at PN21 and as adults.

RESULTS

Synaptophysin immunoreactivity increased between 24 h and 3 weeks post-SE in regions with severe and rapidly occurring neuronal loss, namely thalamus, amygdala, piriform and entorhinal cortices. GAP-43 expression decreased at 1 and 3 weeks in the same regions. The immunoreactivity of synaptophysin and GAP-43 increased in the inner molecular layer of dentate gyrus from 24 h after SE, and decreased in the outer molecular layer from 72 h after SE. These changes likely result from the death of hilar neurons and the reduction of the input from the entorhinal cortex. In 21-day-old rats that experience less SE-induced neuronal loss, increased immunoreactivity of synaptophysin was only found in piriform and entorhinal cortex while no changes occurred in GAP-43 expression.

CONCLUSION

These findings suggest that there is an age-related relation between the extent and rapidity of the process of neuronal death and the expression of these markers. Synaptophysin appears to be a more sensitive marker of plasticity induced by SE than GAP-43.

Differential upregulation of extracellular matrix molecules associated with the appearance of granule cell dispersion and mossy fiber sprouting during epileptogenesis in a murine model of temporal lobe epilepsy

We have investigated changes in the extracellular matrix of the hippocampus associated with the early progression of epileptogenesis in a murine model of temporal lobe epilepsy using immunohistochemistry. In the first week following intrahippocampal injection of the glutamate agonist, domoate, there is a latent period at the end of which begins a sequential upregulation of extracellular matrix (ECM) molecules in the granule cell layer of the dentate gyrus, beginning with neurocan and tenascin-C. This expression precedes the characteristic dispersion of the granule cell layer which is evident at 14 days post-injection when the first recurrent seizures can be recorded. At this stage, an upregulation of the chondroitin sulfate proteoglycan, phosphacan, the DSD-1 chondroitin sulfate motif, and the HNK-1 oligosaccharide are also observed. The expression of these molecules is localized differentially in the epileptogenic dentate gyrus, especially in the sprouting molecular layer, where a strong upregulation of phosphacan, tenascin-C, and HNK-1 is observed but there is no expression of the proteoglycan, neurocan, nor of the DSD-1 chondroitin sulfate motif. Hence, it appears that granule cell layer dispersion is accompanied by a general increase in the ECM, while mossy fiber sprouting in the molecular layer is associated with a more restricted repertoire. In contrast to these changes, the expression of the ECM glycoproteins, laminin and fibronectin, both of which are frequently implicated in tissue remodelling events, showed no changes associated with either granule cell dispersion or mossy fiber sprouting, indicating that the epileptogenic plasticity of the hippocampus is accompanied by ECM interactions that are characteristic of the CNS.

Neuroprotection and epilepsy

During the last years it has become obvious that the current way of treating epilepsy with antiepeileptic drugs is insufficient concerning the modification of the underlying disesease and provides merely a symptomatic treatment, without clear influence on the course of the disease. There is a pressing need to find alternative strategies and to find possibilities to intervene either into the basic processes determining the development of epilepsies or to promote compensatory processes in repairing these dysfunctions. The increasing knowledge about the basic neuronal changes underlying epilepsies allows now to analyse the potential role of neuroprotective agents in in epileptogenesis. In epilepsy the most frequent constellation is the presence of damage and overexcitation together. Increase in excitability may develop after a primary damage as in posttraumatic epilepsy, or outburst of epileptic excitability may cause neuronal damage as in cell loss after status epilepticus or in any case of the so called cytotoxic damage from extensive glutamatergic involvement. Epilepsy in certain forms is a progressive disease. The factors determining the progressive course and the possibe prevention of it is obviously an overlaping field with neuroprotection. Therefore although neuroprotection works only against certain aspects of a complex cascade of pathological events, might be a promising option in several stadiums during the development and course of epilepsy. We provide evidences that some of the new antiepileptic drugs have neuroprotective effect on different animal models of chronic partial epilepsies, and how this effect is fitting to the antiepileptogenic, and seizure supressing effect of the same drugs.

Intrinsic optical signals in the rat optic nerve: role for K(+) uptake via NKCC1 and swelling of astrocytes

Measurements of extracellular space volume and imaging of intrinsic optical signals (IOSs) have shown that neuronal activity increases light transmittance by causing cellular swelling. However, the cellular mechanisms underlying these volume changes and the contribution of astrocyte swelling to the changes in tissue volume are unclear. In this study, we have investigated IOSs in optic nerves to analyze the mechanisms contributing to these signals in a system consisting of only axons and glial cells. We examined both intact optic nerves and enucleated optic nerves, which contained no axons and consisted primarily of astrocytes. Electrical stimulation of intact optic nerves evoked an increase in light transmittance, which was graded with increasing stimulation frequency and was mimicked by raising extracellular K(+) concentration ([K(+)](o)). The stimulation-induced IOS grew in amplitude and had a time course similar to extracellular space shrinkage. Tetrodotoxin (TTX) blocked the electrically induced but not the high K(+)-induced IOS. In enucleated nerves, light transmittance progressively increased in higher [K(+)](o). The high [K(+)](o)-induced IOSs were reversibly depressed by furosemide and bumetanide, antagonists for Na-K-2Cl cotransport, but were unaltered by TTX. We also used a monoclonal antibody to the NKCC1 form of the Na-K-2Cl cotransporter to show that NKCC1 is expressed in optic nerves as shown in Western blotting and is colocalized in GFAP immunopositive astrocytes. In summary, these results indicated that KCl uptake into astrocytes via an Na-K-2Cl cotransporter during raised [K(+)](o) contributes to the generation of cellular swelling and the intrinsic optical signals.

Transient expression of the NG2 proteoglycan by a subpopulation of activated macrophages in an excitotoxic hippocampal lesion

Cells that express the NG2 proteoglycan (NG2+ cells) constitute a large glial population in the normal mature rodent brain. They can differentiate into oligodendrocytes but are distinct from mature oligodendrocytes, astrocytes, microglia, and neurons. Changes in NG2+ cells were examined in kainic acid-induced excitotoxic lesions of the hippocampus, and the relationship between NG2+ cells and reactive astrocytes and microglia was investigated between 1 and 90 days after lesioning. Two types of reactive NG2+ cells with altered morphology and increased NG2 immunoreactivity were observed in the lesion. Early changes, consisting of an increase in NG2 immunoreactivity and the number of processes, were apparent 24 h after lesioning and persisted through 3 months. These cells were distinct from reactive astrocytes or activated microglia/macrophages. A second type of reactive NG2+ cells appeared 2 weeks after injection, following an influx of macrophages. They had large, round cell bodies with short processes and expressed the microglia/macrophage antigens OX42 and ED1. Single cells coexpressing NG2 and macrophage/microglial antigens could be isolated from the lesion. The number of NG2+/OX42+ cells gradually declined and disappeared by 3 months after injection. They did not express glial fibrillary acidic protein or the alpha receptor for platelet-derived growth factor, indicating that they are distinct from astrocytes or oligodendrocyte progenitor cells. Cells that coexpressed NG2 and OX42 were never observed in hippocampal slice cultures treated with kainic acid, suggesting that NG2+/OX42+ cells are not derived from endogenous resident brain cells. These findings demonstrate that NG2 expression is transiently upregulated on activated macrophages/microglia that appear during the chronic stage in an excitotoxic lesion in the adult CNS.

Facial motor neuron regeneration induces a unique spatial and temporal pattern of myristoylated alanine-rich C kinase substrate expression

We have previously shown that the myristoylated alanine-rich C kinase substrate, a primary protein kinase C substrate in brain that binds and cross-links filamentous actin, is enriched in neuronal growth cones and is developmentally regulated in brain. Here we examined myristoylated alanine-rich C kinase substrate expression in the facial motor nucleus during axonal regeneration following facial nerve axotomy or facial nerve resection lesions, which impede regeneration, or following motor neuron degeneration induced by the retrograde neurotoxin ricin. For comparative purposes, the protein kinase C substrates myristoylated alanine-rich C kinase substrate-like protein and growth-associated protein-43 were examined in parallel. Myristoylated alanine-rich C kinase substrate messenger RNA exhibited a robust increase in both neurons and non-neuronal cells in the facial motor nucleus beginning four days after axotomy, peaked at seven days (2.5-fold), and declined back to baseline levels by 40 days. Myristoylated alanine-rich C kinase substrate protein similarly exhibited a twofold elevation in the facial motor nucleus determined four and 14 days post-axotomy. Following nerve resection, myristoylated alanine-rich C kinase substrate messenger RNA levels increased at seven days and returned to baseline levels by 40 days. Unlike myristoylated alanine-rich C kinase substrate messenger RNA, myristoylated alanine-rich C kinase substrate-like messenger RNA levels did not increase in the facial motor nucleus at any time point following nerve axotomy or resection, whereas growth-associated protein-43 messenger RNA exhibited a rapid (one day) and prolonged (40 days) elevation in facial motor nucleus neurons following either nerve axotomy or resection. Ricin-induced degeneration of facial motor neurons elevated myristoylated alanine-rich C kinase substrate and myristoylated alanine-rich C kinase substrate-like messenger RNAs in both microglia (lectin-positive) and astrocytes (glial fibrillary acidic protein-positive).Collectively, these data demonstrate that myristoylated alanine-rich C kinase substrate exhibits a unique expression profile in the facial motor nucleus following facial nerve lesions, and it is proposed that myristoylated alanine-rich C kinase substrate may serve to mediate actin-membrane cytoskeletal plasticity in both neurons and glial cells in response to protein kinaseC-mediated signaling during nerve regeneration and degeneration.

Negative and positive regulation of astrocyte DNA synthesis by ethanol

Ethanol suppression of astrocyte mitogenesis is well recognized but ethanol, under some conditions, has also been shown to stimulate astrocyte proliferation. This study addressed the role of protein kinase C and other mitogenic factors as mechanisms responsible for the bidirectional effects of ethanol on astrocyte DNA synthesis. Ethanol treatment inhibited astrocyte DNA synthesis both at 4 hr (short term) and 24 hr (long term) in serum free medium. In contrast, when the medium contained serum, ethanol was less effective in inhibiting DNA synthesis at 4 hr and treatment with ethanol for 24 hr increased DNA synthesis. Protein kinase C activity was increased in cells treated with ethanol for either 4 or 24 hr. Ethanol inhibition of DNA synthesis in serum free medium was not reversed by down regulating protein kinase C. In contrast, downregulating protein kinase C activity by continuous treatment with phorbol myristic acetate partially reversed the effect ethanol had on DNA synthesis. Also, directly inhibiting protein kinase C with H-7 in cells maintained and treated in the presence of serum abolished the stimulatory effect ethanol had on DNA synthesis. It appears that the negative regulation of astrocyte DNA synthesis by ethanol occurs by protein kinase C and serum independent mechanisms whereas adaptive or stimulatory effects of ethanol on astrocyte DNA synthesis requires the interaction of protein kinase C with other factors present in serum.

Expression of GABA(A) receptors by reactive astrocytes in explant and primary cultures of rat CNS

The presence of GABA(A)-receptors on astrocytes was studied in explant and primary cultures of rat cerebellum, hippocampus and spinal cord by means of immunohistochemistry. For these studies we have used the monoclonal antibody bd 17 against the beta2- and beta3-subunits of GABA(A)-receptor. In explant cultures many neurones were intensely stained with the GABA(A)-receptor antibody whereas adjacent astrocytes revealed little or no immunoreactivity. In the far outgrowth zone of explant culture, however, many immunostained astrocytes were observed. In primary astrocyte cultures, only a few cells were stained by the antibody. Astrocytes which became reactive after producing an artificial scar or after addition of certain compounds such as dibutyryl cyclic AMP, interleukin-6, basic fibroblast growth factor and kainic acid, also revealed GABA(A)-receptor immunoreactivity. Furthermore, these astrocytes were intensely stained for glial fibrillary acidic protein and vimentin. From our studies we conclude that only a sub-population of normal astrocytes are immunopositive for the GABA(A)-receptor antibody whereas astrocytes which become reactive following injury of the tissue or after addition of dibutyryl cyclic AMP, the cytokine interleukin-6, fibroblast growth factor or the neurotoxin kainic acid express GABA(A)-sites.

B-50, the growth associated protein-43: modulation of cell morphology and communication in the nervous system

The growth-associated protein B-50 (GAP-43) is a presynaptic protein. Its expression is largely restricted to the nervous system. B-50 is frequently used as a marker for sprouting, because it is located in growth cones, maximally expressed during nervous system development and re-induced in injured and regenerating neural tissues. The B-50 gene is highly conserved during evolution. The B-50 gene contains two promoters and three exons which specify functional domains of the protein. The first exon encoding the 1-10 sequence, harbors the palmitoylation site for attachment to the axolemma and the minimal domain for interaction with G0 protein. The second exon contains the "GAP module", including the calmodulin binding and the protein kinase C phosphorylation domain which is shared by the family of IQ proteins. Downstream sequences of the second and non-coding sequences in the third exon encode species variability. The third exon also contains a conserved domain for phosphorylation by casein kinase II. Functional interference experiments using antisense oligonucleotides or antibodies, have shown inhibition of neurite outgrowth and neurotransmitter release. Overexpression of B-50 in cells or transgenic mice results in excessive sprouting. The various interactions, specified by the structural domains, are thought to underlie the role of B-50 in synaptic plasticity, participating in membrane extension during neuritogenesis, in neurotransmitter release and long-term potentiation. Apparently, B-50 null-mutant mice do not display gross phenotypic changes of the nervous system, although the B-50 deletion affects neuronal pathfinding and reduces postnatal survival. The experimental evidence suggests that neuronal morphology and communication are critically modulated by, but not absolutely dependent on, (enhanced) B-50 presence.

Systemic administration of kainic acid induces selective time dependent decrease in [125I]insulin-like growth factor I, [125I]insulin-like growth factor II and [125I]insulin receptor binding sites in adult rat hippocampal formation

Administration of kainic acid evokes acute seizure in hippocampal pathways that results in a complex sequence of functional and structural alterations resembling human temporal lobe epilepsy. The structural alterations induced by kainic acid include selective loss of neurones in CA1-CA3 subfields and the hilar region of the dentate gyrus followed by sprouting and permanent reorganization of the synaptic connections of the mossy fibre pathways. Although the neuronal degeneration and process of reactive synaptogenesis have been extensively studied, at present little is known about means to prevent pathological conditions leading to kainate-induced cell death. In the present study, to address the role of insulin-like growth factors I and II, and insulin in neuronal survival as well as synaptic reorganization following kainate-induced seizure, the time course alterations of the corresponding receptors were evaluated. Additionally, using histological preparations, the temporal profile of neuronal degeneration and hypertrophy of resident astroglial cells were also studied. [125I]Insulin-like growth factor I binding was found to be decreased transiently in almost all regions of the hippocampal formation at 12 h following treatment with kainic acid. The dentate hilar region however, exhibited protracted decreases in [125I]insulin-like growth factor I receptor sites throughout (i.e. 30 days) the study. [125I]Insulin-like growth factor II receptor binding sites in the hippocampal formation were found to be differentially altered following systemic administration of kainic acid. A significant decrease in [125I]insulin-like growth factor II receptor sites was observed in CA1 subfield and the pyramidal cell layer of the Ammon's horn at all time points studied whereas the hilar region and the stratum radiatum did not exhibit alteration at any time. A kainate-induced decrease in [125I]insulin receptor binding was noted at all time points in the molecular layer of the dentate gyrus whereas binding in CA1-CA3 subfields and discrete layers of the Ammon's horn was found to be affected only after 12 h of treatment. These results, when analysed with reference to the observed histological changes and established neurotrophic/protective roles of insulin-like growth factors and insulin, suggest possible involvement of these growth factors in the cascade of neurotrophic events that is associated with the reorganization of the hippocampal formation observed following kainate-induced seizures.

Temporal profiles of the in vitro phosphorylation rate and immunocontent of glial fibrillary acidic protein (GFAP) after kainic acid-induced lesions in area CA1 of the rat hippocampus: demonstration of a novel phosphoprotein associated with gliosis

The in vitro phosphorylation rate and immunocontent of glial fibrillary acidic protein was studied in slices of area CA1 of the rat hippocampus after stereotaxic injection of 1 nmol of kainic acid. For controls the contralateral hippocampus was injected with saline. Hippocampal tissue was incubated with [32P]phosphate and analysed by two-dimensional electrophoresis for phosphorylation rate and by immunoblotting for immunocontent. Both these parameters decreased during the first 4 days after injection and then started to increase at 10 days and continued to increase until at least 84 days. Except for a small excess of phosphorylation rate at 28 days, the relationship between immunocontent and in vitro phosphorylation rate of glial fibrillary acidic protein remained constant, indicating that the reactive gliosis was not associated with hypo- or a major hyperphosphorylation of this protein. Histology showed a pronounced loss of CA1 pyramidal cells 1 day after injection. At 28 days after injection the pyramidal cells had disappeared and only a few abnormal neurones were present. In contrast, immunocytochemistry after 28 days showed a marked increase in astrocytes reacting positive to the antibody in the strata radiatum and lacunosum moleculare. Besides glial fibrillary acidic protein the expression of several other proteins was upregulated as a result of the injection of kainic acid. These included phosphovimentin and an unknown phosphoprotein designated pp25 which co-migrated on 2-D gels with a prominent phosphoprotein expressed in primary cultures of astrocytes. Pp25 was expressed in lesioned tissue more frequently than phosphovimentin and with a time course that started earlier. Of particular interest was the expression of pp25 in the contralateral saline-injected hippocampus 1 day after injection of kainic acid. It is possible that pp25 will prove to be a sensitive marker of gliosis.

Effects of tenascin-C in cultured hippocampal astrocytes: NCAM and fibronectin immunoreactivity changes

Tenascin-C is an extracellular matrix glycoprotein with trophic and repulsive properties on neuronal cells, involved in migratory processes of immature neurons. Previous reports demonstrated that this molecule is produced and secreted by astrocytes, in vitro after activation by bFGF or in vivo after CNS lesion. In injured brain the expression of tenascin-C has been correlated with the glial reaction since it was observed in regions suffering a dramatic glial proliferation and hypertrophy. In this report we show that the treatment of cultured hippocampal astrocytes with tenascin-C results in an increased fibronectin and NCAM immunoreactivities. In addition, treated astrocytes form longer extensions than control ones. The number of cells as well as the levels of GFAP mRNA and protein immunoreactivity are not modified after tenascin-C treatment. The present changes may, therefore, be related to the modification of the adhesive properties of astrocytes to the substrate. These observations are compatible with the hypothesis that tenascin-C may contribute to the glial scarring process.

Entactin immunoreactivity in immature and adult rat brain

Entactin (nidogen) is a glycoprotein of 150 kDa mainly found in the basement membranes of peripheral tissues where it is co-localized and forms a very tight complex with the outgrowth-promoting molecule laminin. In the present report we tested by immunoblotting the specificity of polyclonal antibodies to laminin and entactin isolated from Engelbreth-Holm-Swarm (EHS) mouse sarcoma and investigated laminin and entactin immunoreactivities in the hippocampus of newborn, adult control and kainate-injured rats. The three polyclonal antibodies to laminin (two of them commercial) used in the present study stained somas of neurons, blood vessels and reactive glial cells, in agreement with previous reports. Nevertheless, all of them cross-reacted with entactin. The anti-entactin serum, which specifically recognized entactin protein, but not laminin or fibronectin, stained mainly the walls of blood vessels in rat brain slices. We observed a stronger entactin expression in immature than in adult brain, and a dramatic increase of vascular staining in kainate-injured hippocampus, suggesting a contribution of entactin to both development and reactive angiogenesis.

Tenascin-C mRNA and tenascin-C protein immunoreactivity increase in astrocytes after activation by bFGF

Tenascin-C is an extracellular matrix glycoprotein with trophic and repulsive properties, involved in migratory processes in CNS. Previous reports demonstrated that this molecule is produced and secreted by astrocytes. Preliminary data on fibroblasts and astrocytes have suggested that bFGF may modulate tenascin-C expression. bFGF is a mitogenic growth factor, involved in cell differentiation and neovascularization. In the present study, we examined whether bFGF modulates the expression of tenascin-C in hippocampal astrocytes from newborn rats. Our results suggest that bFGF increases the production of tenascin-C by cultured hippocampal astrocytes. We found that both tenascin-C mRNA and protein immunoreactivity were increased after bFGF treatment. Our results also demonstrated that tenascin-C polypeptides were secreted into the extracellular medium. In agreement with previous studies, we suggest that secreted tenascin-C is mainly the high molecular weight form. In addition, our results suggest that a cleavage of the high molecular weight form. In addition, our results suggest that a cleavage of the high molecular weight form may occur in the extracellular medium causing production of proteolytic fragments, that may modify the biological properties of tenascin-C. The present results may be relevant to the understanding of lesion scarring and regeneration process.

Seizures induce tenascin-C mRNA expression in neurons

Tenascin-C, an extracellular matrix glycoprotein that exhibits both growth-promoting and growth-inhibiting properties, is produced in the CNS mainly by astrocytes. In the present study we show that kainate-induced seizures result in an increased expression of tenascin-C in rat brain. Tenascin-C mRNA was increased mainly in the granule cell layer of the hippocampal complex, but tenascin-C mRNA expression was also observed in the pyriform cortex and amygdalo-cortical nucleus. Double labelling experiments using tenascin-C probes and MAP2 (a neuronal microtubule associated protein) antibodies revealed many neurons in these layers that express tenascin-C mRNA. These results support our previous findings of an increased tenascin-C immunoreactivity associated with the axons of granule cells. Tenascin-C expression is rapidly induced by seizures (6 h), preceding any lesion and glial reaction. In this pathological condition tenascin-C appears to be produced by both glia and neurons. The functional repercussions on the scarring and remodelling processes are also discussed.

Reactive glial cells express a vitronectin-like protein in the hippocampus of epileptic rats

Injection of kainic acid into the amygdala induces in addition to a local cell loss a seizure related distal damage of the hippocampal complex, in particular in the CA3 field and hilus. This neuronal lesion is associated with hypertrophy and proliferation of astroglial cells which start around 3 days after kainate and peaks within 20 days of kainate. We now report that reactive astrocytes are labelled with antibodies against vitronectin in the CA3 field and hilus. In the present study we also exclude that the presence of vitronectin into the brain is due to an extravasation from serum throughout a blood brain barrier leakage. The present results constitute the first demonstration for a glial expression of vitronectin in vivo. Vitronectin is an extracellular matrix glycoprotein involved in axonal growth. The glial expression of vitronectin may therefore contribute to the synaptic remodeling of mossy fibers induced in the hippocampus by such treatment.

Expression and distribution of GAP-43 in human astrocytes in culture

By combining mRNA analysis and immunocytochemistry, we investigated the expression of the growth associated protein 43 (GAP-43) in enriched populations of astrocytes, obtained from mixed cultures of human fetal brains. Total cellular RNA was extracted from cell pellets and reverse transcribed into cDNA; cDNA was subjected to PCR amplification using primers specific for GAP-43 and PCR products were separated through polyacrylamide gels. Double immunofluorescence staining was performed on dissociated cell cultures using antibodies to glial fibrillary acidic protein (GFAP) and to GAP-43. Results showed that both transcription and translation for GAP-43 occur in cultured astrocytes. GAP-43 immunoreacting material was detected in the cell processes and diffusely in the cytoplasm of GFAP-positive astrocytes, during early stages of maintenance in vitro. In older cultures, GAP-43 immunoreactivity persisted in a large percentage of cells, with a tendency to accumulate in perinuclear areas. These observations provide evidence that GAP-43 is not restricted to neuronal cells. The close spatial association with cytoskeletal constituents, as observed in astrocytes, suggests a role for this protein in the control of cell shape, motility and adhesion processes.

Gliosis and axonal sprouting in the hippocampus of epileptic rats are associated with an increase of tenascin-C immunoreactivity

Temporal lobe epilepsy is associated with neuronal death, gliosis and sprouting of mossy fibres in the hippocampus of human and rats. In the present study we show that immunoreactivity for tenascin-C (an extracellular matrix glycoprotein) increase in the hippocampus of epileptic rats. However, this increase was only observed in the cases displaying neuronal cell loss and glial reaction (i.e. after kainate treatment but not after kindling). Tenascin-C increase was particularly striking at Ammon's horn, where the antibody labelled both reactive astrocytes (confirmed by double-labelling experiments) and axonal plasma membranes. In the molecular layer tenascin-C immunoreactivity remained unchanged in both kindled or kainate treated rats. It is interesting that increased tenascin-C immunoreactivity was observed within zones in which axonal regeneration did not occur (the CA3 area in kainate-treated animals) whereas zones in which reactive synaptogenesis occurred (such as the CA3 area of kindled rats or the molecular layer of both kindled and kainate-treated rats) were devoid of tenascin-C immunoreactivity. We infer from these results that tenascin-C impedes the terminal sprouting of mossy fibres in CA3 of kainate-treated rats.

Increase in GAP-43 and GFAP immunoreactivity in the rat hippocampus subsequent to perforant path kindling

Kindling is an animal model of epilepsy which is accompanied by morphological and biochemical changes in the brain, including sprouting of fibers and increased transmitter release. Here we have examined the immunocytochemical expression of 1) GAP-43, a growth-associated protein, which is a neuron-specific PKC substrate, particularly expressed in development and regeneration and 2) glial fibrillary acidic protein (GFAP), part of the astrocytic cytoskeleton, after perforant path kindling. Subsequent to kindling, GAP-43 immunoreactivity was increased in CA1 stratum lacunosum-moleculare and the inner and outer molecular layer of the fascia dentata. Other hippocampal subregions showed a lower increase. GFAP immunoreactivity was increased in the entire hippocampus, but especially in stratum lacunosum-moleculare of the CA1 and the hilus of fascia dentata. The difference between the number of GFAP-positive profiles in the hippocampus of control rats and in fully kindled rats was found to be non-significant. We interpret these findings as being related to both plastic neuronal changes and possible neuronal degeneration.

Post-ischemic administration of the acetylcholinesterase inhibitor ENA-713 prevents delayed neuronal death in the gerbil hippocampus

We examined by morphological methodology the effect of (S)-N-ethyl-3-[(1-dimethyl-amino)ethyl]-N-methyl-phenylcarbamate hydrogentartrate (ENA-713), an acetylcholinesterase (AChE) inhibitor, on ischemia-induced neuronal death in the gerbil hippocampus due to a 5-min ligation of bilateral common carotid arteries after light ether anesthesia. Pyramidal cells had been decreased to 27% of sham-operated controls and the number of hypertrophic astrocytes expressing glial fibrillary acidic protein (GFAP) markedly increased in the hippocampal CA1 subfield 14 days after ischemia. However, post-ischemic administration of ENA-713 (three times 0.2 mg/kg, i.p.) significantly ameliorated this ischemia-induced decrease in the number of pyramidal cells by 47% of sham-operated controls, furthermore, it reduced the ischemia-induced accumulation of GFAP-positive astrocyte in the CA1 region. Together with previous results showing that ENA-713 protected against the ischemia-induced cholinergic abnormalities in the gerbil brain and improved cholinergic dysfunctions in the senescent rat brain, our present findings suggest that ENA-713 prove to be useful for treatment with senile dementia such as cerebrovascular dementia.

In vitro glial responses to nerve growth factor

Nerve growth factor (NGF) stimulates expression of the low affinity neurotrophin receptor p75NGFR mRNA in primary cultures of neonatal rat cortical type I astrocytes. Nerve growth factor treatment altered glial morphology in glial fibrillary acidic protein positive (GFAP+) cell cultures derived from newborn (P0) and 3-day-old (P3) rat pups. When P0- or P3-derived primary glial cultures were serum-deprived, in the presence of 200 pM NGF for 5 days, the flat polygonal glia present in culture assumed a fibrous morphology, an effect not seen in the untreated serum-deprived controls. The NGF effect on astrocytic morphology was blocked by continuous serum treatment. Nerve growth factor did not stimulate astrocytic proliferation under these culture conditions, as assayed by cell cycle analysis using 3H thymidine autoradiography. P0-derived primary glial cultures expressed the signal transducing neurotrophin receptors p145trkB and p140trkA as determined by reverse transcription-polymerase chain reaction (RT-PCR). RT-PCR products were identified by sequencing or restriction enzyme analysis. Astrocytes internalized 125I-NGF at 37 degrees C but not at 4 degrees C, consistent with energy requirements for internalization. Also, internalization of 125I-NGF was abolished by the addition of a 300-1,000-fold excess of unlabeled NGF. Thus, astroglial cells in culture internalize NGF through a specific receptor-mediated process, express trkA and full-length trkB mRNAs at low levels, and respond to exogenous NGF by expressing a fibrous morphology under serum-free culture conditions.

Colchicine induces the GAP-43 gene expression in rat hypothalamus

Injection of colchicine, a mitogen inhibitor, in the dorsal third ventricle induced the expression of the growth associated protein-43 (GAP-43) mRNA in some groups of cells of the adult rat brain. These mRNAs were detected by in situ hybridization histochemistry using an alkaline phosphatase labeled oligonucleotide probe. A substantial up-regulation of GAP-43 mRNA was noticed by the increase of both the number of positive cells and the intensity of the hybridization signal. These changes were observed in the hypothalamic nuclei located near the ventral third ventricle, namely the preoptic area, the supraoptic nucleus, the peri- and the paraventricular nuclei of the hypothalamus, the dorsal subnucleus of the ventromedial nucleus, the arcuate nucleus and the posterior part of the peri-mammillary region. Such abundant GAP-43 mRNA positive cells have not been observed in control adult rat hypothalamus. Since the positive cell number and shape initially suggested that these were neurons or astrocytes, double labeling in situ hybridization using both radioactive (for the detection of GFAP mRNA as a marker of astrocyte) and non-radioactive (for the detection of GAP-43 mRNA) probes was carried out. This demonstrated that these GAP-43 mRNA positive cells were not astrocytes. In addition enhanced GAP-43 mRNA expression was also found in some neuronal component, particularly in neurosecretory magnocells of the pareaventricular and the supraoptic nuclei. This up-regulation was further confirmed by the Northern blot analysis. About five fold increase in GAP-43 mRNA in the colchicine-treated hypothalamic tissue was shown.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular correlates between reactive and developmental plasticity in the rat hippocampus

Area CA3 of the hippocampus is the most epileptogenic structure of the brain. Various studies have shown that kainate-induced experimental epilepsy in rats and human cases of epilepsy are associated with sprouting of the mossy fibers of the dentate granule neurons and selective loss of pyramidal neurons, notably in the CA3-CA4 areas of Ammon's horn. In experimental models of epilepsy, brief seizure activity initiates a cascade of molecular alterations that will contribute to changes in the expression of numerous genes, which can last several weeks. The products of some of these genes will contribute to the permanent state of enhanced synaptic efficiency, to the sprouting and formation of novel excitatory synapses, and possibly to neuronal cell loss. The expression of genes encoding transcription factors and numerous growth factors is rapidly altered following seizure episodes. Based on observations in vivo and in vitro in cultured hippocampal neurons, it is hypothesized that an interplay between transcription and growth factors, because of their pleiotropic effects on the regulation of effector genes, may be instrumental in coupling transient extracellular stimuli to irreversible cellular alterations.

Cell death, gliosis, and synaptic remodeling in the hippocampus of epileptic rats

Seizures set in motion complex molecular and morphological changes in vulnerable structures, such as the hippocampal complex. A number of these changes are responsible for neuronal death of CA3 and hilar cells, which involves necrotic and apoptotic mechanisms. In surviving dentate granule cells seizures induce an increased expression of tubulin subunits and microtubule-associated proteins, suggesting that an overproduction of tubulin polymers would lead to a remodeling of mossy fibers (the axons of granule cells). In fact, these fibers sprout in the dentate gyrus to innervate granule cell dendrites, creating recurrent excitatory circuits. In contrast, terminal mossy fibers do not sprout in the CA3 field. Navigation of mossy fiber's growth cones may be facilitated by astrocytes, which would exert differential effects by producing and excreting cell adhesion and substrate molecules. In the light of the results discussed here, we suggest that in adult brain activated-resident astrocytes (nonproliferating, tenascin-negative, neuronal cell-adhesion molecule-positive astrocytes) could contribute to the process of axonal outgrowth and synaptogenesis in the dentate gyrus, while proliferating astrocytes, tenascin-positive, could impede any axonal rearrangement in CA3.

Proliferative astrocytes may express fibronectin-like protein in the hippocampus of epileptic rats

Kainic acid treatment, a model of temporal lobe epilepsy, induces in CA3-CA4 fields of hippocampal complex a neuronal degeneration associated with glial hypertrophy and proliferation. After treatment with kainate, fibronectin (an extracellular matrix protein) immunoreactivity increases in CA3-CA4. Fibronectin antibodies stain proliferative cells (simultaneously labelled by [3H]thymidin) of astrocytic type (double-immunostained by GFAP antibodies). This result constitutes the first direct demonstration of astroglial fibronectin expression in vivo. In the molecular layer of kainate-treated rats there is an axon-terminal degeneration of association-fibers. This is associated with a transient hypertrophy of resident astrocytes but not with any glial proliferation. Reactive astrocytes do not express (or faintly) fibronectin immunoreactivity in this layer. Since fibronectin is involved in astroglial proliferation in vitro, the present observations suggest that astrocytes contribute in vivo to the astroglial proliferation by an autocrin mechanism.

Glial reaction after seizure induced hippocampal lesion: immunohistochemical characterization of proliferating glial cells

Kainic acid treatment (a model of temporal lobe epilepsy) induces Ammon's horn sclerosis, which is characterized by degeneration of CA3 pyramidal neurons and reactive gliosis. In the present study we have combined autoradiographic analysis of 3H-thymidine incorporation and immunocytochemistry to investigate this glial scarring phenomenon. The present results demonstrate that in the fields showing neuronal degeneration (i.e. CA3-CA4 fields of Ammon's horn and dentate hilus) the glial reaction consists of a proliferation and hypertrophy of astrocytes and microglia-macrophages. In the regions showing exclusively terminal axonal degeneration (i.e. the molecular layer of kainate-treated rats), glial cells do not proliferate but astrocytes show a transient hypertrophy. These results also demonstrate that oligodendrocytes do not proliferate in the hippocampus of kainate-treated rats. In agreement with our previous report we find that hippocampal astrocytes from kainate-treated rats express A2B5 immunoreactivity, a marker of type-2 astrocytes. A2B5 immunoreactivity was expressed by astrocytes not only in areas showing glial proliferation such as CA3-CA4 fields, but also in the molecular layer, where astrocytes do not proliferate. This suggests that in the CNS, normal resident astrocytes acquire the phenotypic properties of type-2 astrocytes.

Strategies for the development of drugs for pharmacoresistant epilepsies

Presently, most strategies for development of antiepileptic drugs (AEDs) center around seizure models that are known to respond to presently marketed AEDs. These strategies do not take into account that epilepsy can be a progressive disease. Moreover, region-specific aspects of epileptogenesis are rarely considered when new AEDs are developed. Seizures in the temporal lobe are often difficult to treat. Animal studies on various seizure models in the hippocampus and the entorhinal cortex (EC) suggest that these structures do not a priori produce seizures that are difficult to treat. However, seizure-like events in the EC tend to progress to a state of status epilepticus-like activity that cannot be suppressed by presently marketed AEDs. Loss of gamma-aminobutyric acid (GABA)ergic neurotransmission and increased excitatory synaptic coupling seem to cooperate for induction of this state. Epilepsy induced alterations in the interaction between the EC and the hippocampus may lead to alterations that facilitate precipitation of seizures. Because of the recurrent interaction between the hippocampus and the EC, these seizures may reach an intensity that is no longer controllable by presently available AEDs. Ontogenetic alterations of the circuitry between the EC and the hippocampus, seizure-induced stabilization of synaptic connections overexpressed during ontogenesis, seizure-induced lesions and subsequent rearrangements of internal cell properties, and synaptic arrangements and kindling-like alterations of nerve cell and glial behavior may all be involved in the generation of a neuronal aggregate whose balance between inhibitory and excitatory processes becomes readily disturbed. Strategies for the development of AEDs treating such seizures should suppress hyperactivity and prevent progression of epileptogenesis. AEDs directed against seizures may be effective if they can be given in sufficient concentrations to suppress very intense local seizures.

Correlation between reactive sprouting and microtubule protein expression in epileptic hippocampus

Temporal lobe epilepsy in both human and rats is associated with a collateral sprouting of hippocampal mossy fibers (i.e. the axons of granule cells). This sprouting generates abnormal recurrent synaptic connections. We previously showed that in the experimental model of temporal lobe epilepsy induced by an intra-amygdaloid injection of kainate, the synaptic remodeling of mossy fibers was preceded by a transient increased expression of alpha-tubulin in granule cells. This suggests that an overproduction of tubulin polymers may be responsible, at least in part, for the elongation and side-branching of mossy fibers, which occurs 12-30 days after seizures. In the present study we show that this increased expression of alpha-tubulin is accompanied by an increased expression of the microtubule-associated proteins MAP2 and TAU. Thus, using in situ hybridization, we observe that MAP2 messenger RNA levels increased in granule cell bodies and dendrites from day 3 to two weeks after kainate treatment. This rise is associated with a concomitant transient increase of MAP2 immunoreactivity in the granule cell dendrites. TAU messenger RNA also increases in granule cell bodies, while TAU immunoreactivity increases in their axons, the mossy fibers. The time course of these changes parallels that of alpha-tubulin, and develops before and during the axonal mossy fiber sprouting. Since MAP2 and TAU are important for the initiation, elongation and stabilization of neurites, we suggest that the overexpression of these proteins via the formation of microtubules may play an important role in the sprouting of mossy fibers in epileptic rats.

Trimethyltin-induced expression of GABA and vimentin immunoreactivities in astrocytes of the rat brain

Adult Sprague-Dawley rats were given a single dose of trimethyltin chloride (TMT). Three days following treatment, a neuronal alteration was observed in the CA3c pyramidal cell layer of hippocampus which was not accompanied by any apparent astrocyte reaction. At 1 as well as 2 weeks after treatment, a gliosis in hippocampus, piriform, and entorhinal cortices was detected by glial fibrillary acidic protein (GFAP) immunohistochemistry. Concomitant with the enhanced astrocytic GFAP, astrocytes were swollen and expressed immunoreactivity to vimentin and gamma-aminobutyric acid (GABA). The astrocytic GABA immunoreactivity may reflect a trimethyltin-induced alteration in astrocyte phenotype, or alterations in compartmentalization and/or metabolism of GABA.

Short- and long-term induction of basic fibroblast growth factor gene expression in rat central nervous system following kainate injection

Both RNase protection assay and in situ hybridization were used to investigate the effect of intraperitoneal injection of kainate on the messenger RNA levels for basic fibroblast growth factor in the rat central nervous system. Limbic motor seizures were produced by kainate injection and this event was followed by a significant elevation of basic fibroblast growth factor gene expression in rat hippocampus and striatum 6 h after the convulsant injection. The increase in hippocampus was maximal at 24 h and it was delayed with respect to nerve growth factor induction, which peaked 3 h after kainate injection. Animals that suffered prolonged seizure activity also showed a significant elevation of basic fibroblast growth factor gene expression four and 14 days after kainate, when no changes in nerve growth factor gene expression were observed. We show that, within the hippocampus, the increase of basic fibroblast growth factor messenger RNA was localized in dentate gyrus and the CA1 layer 6 and 24 h after kainate injection. Long-term effects on its gene expression were measurable only in the CA1 hippocampal subfield, where major cell damage and astrocytosis have been reported to occur following kainate-induced seizure activity [Ben-Ari Y. et al. (1981) Neuroscience 7, 1361-1391; Lothman E. W. and Collins R. C. (1981) Brain Res. 218, 299-318; Schwob J. E. et al. (1980) Neuroscience 5, 991-1014]. Indeed, the animals which displayed elevated messenger RNA levels for basic fibroblast growth factor four and 14 days after kainate injection showed a marked induction of messenger RNA expression for the astroglial marker glial fibrillary acidic protein. These results indicate that the glutamate analogue kainate produces short- and long-term increases of basic fibroblast growth factor messenger RNA expression with a specific anatomical pattern. Therefore, the gene expression for this neurotrophic factor is probably regulated by neuronal activity at early points in time, whereas the induction observed at later time points is related to adaptive mechanisms taking place following kainate-induced neuronal degeneration.

NCAM immunoreactivity on mossy fibers and reactive astrocytes in the hippocampus of epileptic rats

Sprouting and synaptogenesis of mossy fibers develop in adult hippocampus after epilepsy. In control conditions, mossy fibers constitute the main afferent pathway to the Ammon's horn, where they mainly innervate CA3 pyramidal cells, but after treatment with the convulsant agent, kainate, mossy fibers also innervate granule cell dendrites generating recurrent excitatory circuits which may contribute to the maintenance of the epileptic condition. In the present study we show an enhanced immunoreactivity to neural cell adhesion molecules (NCAMs), a family of membrane glycoproteins involved in axonal growth. NCAM immunoreactivity is enriched on cytoplasmic membranes of axon shafts that are likely to be mossy fiber collaterals. NCAM immunoreactivity was also observed on the cytoplasmic membranes of reactive astrocytes, at the axon-glial contacts. Our results therefore suggest that there is an interaction of newly developed mossy fibers with other fibers and glial cells. This interaction may be mediated by NCAMs. Taking into account the trophic properties of NCAMs we suggest that they regulate the sprouting, growing and synaptogenesis of mossy fibers in epileptic conditions.