Seizure-associated induction of basic fibroblast growth factor and its receptor in the rat brain

HB-EGF activates EGFR to induce reactive neural stem cells in the mouse hippocampus after seizures

Hippocampal seizures mimicking mesial temporal lobe epilepsy cause a profound disruption of the adult neurogenic niche in mice. Seizures provoke neural stem cells to switch to a reactive phenotype (reactive neural stem cells, React-NSCs) characterized by multibranched hypertrophic morphology, massive activation to enter mitosis, symmetric division, and final differentiation into reactive astrocytes. As a result, neurogenesis is chronically impaired. Here, using a mouse model of mesial temporal lobe epilepsy, we show that the epidermal growth factor receptor (EGFR) signaling pathway is key for the induction of React-NSCs and that its inhibition exerts a beneficial effect on the neurogenic niche. We show that during the initial days after the induction of seizures by a single intrahippocampal injection of kainic acid, a strong release of zinc and heparin-binding epidermal growth factor, both activators of the EGFR signaling pathway in neural stem cells, is produced. Administration of the EGFR inhibitor gefitinib, a chemotherapeutic in clinical phase IV, prevents the induction of React-NSCs and preserves neurogenesis.

Golgi-specific DHHC type zinc finger protein is decreased in neurons of intractable epilepsy patients and pentylenetetrazole-kindled rats

Golgi-specific DHHC type zinc finger protein (GODZ) is a member of the DHHC protein family, and its enzymatic activity is regulated by fibroblast growth factor or Src kinase-mediated tyrosine phosphorylation. In cultured neurons, GODZ affects the numbers of calcium ions channels, α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors, N-methy-D-aspartate receptors, and γ-aminobutyric acid A receptors on postsynaptic membrane by palmitoylation, thus modulating synaptic plasticity. As the change in synaptic plasticity plays a role in epilepsy, GODZ may play roles in epilepsy. However, the expression of GODZ has never been investigated in brain tissues in vivo, and its change during epilepsy is still unclear. In this study, the cellular distribution of GODZ in brain tissues of both patients and rats was determined using double-labeled immunofluorescence and the levels of GODZ protein and mRNA among intractable epilepsy patients, pentylenetetrazole (PTZ)-kindled rats, and controls were measured using immunohistochemistry, Western blot, and real-time quantitative polymerase chain reaction. GODZ expression was identified on cytomembranes and in the cytoplasm of neurons in the temporal neocortex of intractable epilepsy patients and in the hippocampus and the adjacent temporal cortex of PTZ-kindled rats, but not in astrocytes. Decreased GODZ protein and mRNA were identified in brain tissues of intractable epilepsy patients and PTZ-kindled rats compared with the controls. In conclusion, GODZ is expressed in neurons, but not astrocytes, and epilepsy may reduce the protein and mRNA levels of GODZ, indicating a possible role of GODZ in the pathogenesis or the pathophysiology of epilepsy.

The Contradictory Effects of Neuronal Hyperexcitation on Adult Hippocampal Neurogenesis

Adult hippocampal neurogenesis is a highly plastic process that responds swiftly to neuronal activity. Adult hippocampal neurogenesis can be regulated at the level of neural stem cell recruitment and activation, progenitor proliferation, as well as newborn cell survival and differentiation. An "excitation-neurogenesis" rule was proposed after the demonstration of the capability of cultured neural stem and progenitor cells to intrinsically sense neuronal excitatory activity. In vivo, this property has remained elusive although recently the direct response of neural stem cells to GABA in the hippocampus via GABAA receptors has evidenced a mechanism for a direct talk between neurons and neural stem cells. As it is pro-neurogenic, the effect of excitatory neuronal activity has been generally considered beneficial. But what happens in situations of neuronal hyperactivity in which neurogenesis can be dramatically boosted? In animal models, electroconvulsive shock markedly increases neurogenesis. On the contrary, in epilepsy rodent models, seizures induce the generation of misplaced neurons with abnormal morphological and electrophysiological properties, namely aberrant neurogenesis. We will herein discuss what is known about the mechanisms of influence of neurons on neural stem cells, as well as the severe effects of neuronal hyperexcitation on hippocampal neurogenesis.

Impact of the neural cell adhesion molecule-derived peptide FGL on seizure progression and cellular alterations in the mouse kindling model

The neural cell adhesion molecule peptide mimetic fibroblast growth loop (FGL) proved to exert neuroprotective, neurotrophic, and anti-inflammatory effects in different in vitro and in vivo experiments. Based on this beneficial efficacy profile, it is currently in clinical development for neurodegenerative diseases and brain insults. Here, we addressed the hypothesis that the peptide might affect development of seizures in a kindling paradigm, as well as associated behavioral and cellular alterations. Both doses tested, 2 and 10 mg/kg FGL, significantly reduced the number of stimulations necessary to induce a generalized seizure. FGL did not exert relevant effects on the behavioral patterns of kindled animals. As expected, kindling increased the hippocampal cell proliferation rate. Whereas the low dose of FGL did not affect this kindling-associated alteration, 10 mg/kg FGL proved to attenuate the expansion of the doublecortin-positive cell population. These data suggest that FGL administration might have an impact on disease-associated alterations in the hippocampal neuronal progenitor cell population. In conclusion, the effects of the peptide mimetic FGL in the kindling model do not confirm a disease-modifying effect with a beneficial impact on the development or course of epilepsy. The results obtained with FGL rather raise some concern regarding a putative effect, which might promote the formation of a hyperexcitable network. Future studies are required to further assess the risks in models with development of spontaneous seizures.

Implication of fibroblast growth factors in epileptogenesis-associated circuit rearrangements

The transformation of a normal brain in epileptic (epileptogenesis) is associated with extensive morpho-functional alterations, including cell death, axonal and dendritic plasticity, neurogenesis, and others. Neurotrophic factors (NTFs) appear to be very strongly implicated in these phenomena. In this review, we focus on the involvement of fibroblast growth factor (FGF) family members. Available data demonstrate that the FGFs are highly involved in the generation of the morpho-functional alterations in brain circuitries associated with epileptogenesis. For example, data on FGF2, the most studied member, suggest that it may be implicated both in seizure susceptibility and in seizure-induced plasticity, exerting different, and apparently contrasting effects: favoring acute seizures but reducing seizure-induced cell death. Even if many FGF members are still unexplored and very limited information is available on the FGF receptors, a complex and fascinating picture is emerging: multiple FGFs producing synergic or antagonistic effects one with another (and/or with other NTFs) on biological parameters that, in turn, facilitate or oppose transformation of the normal tissue in epileptic. In principle, identifying key elements in these phenomena may lead to effective therapies, but reaching this goal will require confronting a huge complexity. One first step could be to generate a "neurotrophicome" listing the FGFs (and all other NTFs) that are active during epileptogenesis. This should include identification of the extent to which each NTF is active (concentrations at the site of action); how it is active (local representation of receptor subtypes); when in the natural history of disease this occurs; how the NTF at hand will possibly interact with other NTFs. This is extraordinarily challenging, but holds the promise of a better understanding of epileptogenesis and, at large, of brain function.

Fgf-2 in astroglial cells during vertebrate spinal cord recovery

Fibroblast growth factor-2 is a pleiotrophic cytokine with neurotrophic and gliogenic properties. It is known to regulate CNS injury responses, which include transformation of reactive astrocytes, neurogenesis, and promotion of neurotrophic activities. In the brain, it is localized in astrocytes and discrete neuronal populations. Following both central and peripheral nervous system injury, astrocytes become reactive. These activated cells undergo hypertrophy. A key indicator of astrocyte activation is the increased accumulation of intermediate filaments composed of glial fibrillary acidic protein (GFAP). Following physical insult of brain or spinal cord, reactive astrocytes show increased FGF-2 immunoreactivity. Thus, FGF-2 appears to participate in astrocytic differentiation and proliferation and a good candidate for astrocytic function regulation in healthy, injured, or diseased CNS. To further investigate the cellular mechanisms underlying FGF-2 restorative actions and to analyze the changes within astroglial cells, we studied the localization of GFAP and FGF-2 in adult intact and injured Pleurodeles CNS. Our results show that spinal cord injury triggers a significant increase in FGF-2 immunoreactivity in reactive astrocytes at sites of insult. In addition, these results were time-dependent. Increase in FGF-2 immunoreactivity along the CNS axis, starting 1-week post-injury, was long-lasting extending to 6 weeks. This increase was accompanied by an increase in GFAP immunoreactivity in the same spatial pattern except in SC3 where its level was almost similar to sham-operated animals. Therefore, we suggest that FGF-2 may be involved in cell proliferation and/or astroglial cells differentiation after body spinal cord transection, and could thus play an important role in locomotion recovery.

Doublecortin expression in the normal and epileptic adult human brain

Mesial temporal lobe epilepsy (MTLE) is a neurological disorder associated with spontaneous recurrent complex partial seizures and hippocampal sclerosis. Although increased hippocampal neurogenesis has been reported in animal models of MTLE, increased neurogenesis has not been reported in the hippocampus of adult human MTLE cases. Here we showed that cells expressing doublecortin (Dcx), a microtubule-associated protein expressed in migrating neuroblasts, were present in the hippocampus and temporal cortex of the normal and MTLE adult human brain. In particular, increased numbers of Dcx-positive cells were observed in the epileptic compared with the normal temporal cortex. Importantly, 56% of Dcx-expressing cells in the epileptic temporal cortex coexpressed both the proliferative cell marker, proliferating cell nuclear antigen and early neuronal marker, TuJ1, suggesting that they may be newly generated neurons. A subpopulation of Dcx-positive cells in the epileptic temporal cortex also coexpressed the mature neuronal marker, NeuN, suggesting that epilepsy may promote the generation of new neurons in the temporal cortex. This study has identified, for the first time, a novel population of Dcx-positive cells in the adult human temporal cortex that can be upregulated by epilepsy and thus, raises the possibility that these cells may have functional significance in the pathophysiology of epilepsy.

Fgf-2 overexpression increases excitability and seizure susceptibility but decreases seizure-induced cell loss

Fibroblast growth factor 2 (FGF-2) has multiple, pleiotropic effects on the nervous system that include neurogenesis, neuroprotection and neuroplasticity. Thus, alteration in FGF-2 expression patterns may have a profound impact in brain function, both in normal physiology and in pathology. Here, we used FGF-2 transgenic mice (TgFGF2) to study the effects of endogenous FGF-2 overexpression on susceptibility to seizures and to the pathological consequences of seizures. TgFGF2 mice display increased FGF-2 expression in hippocampal pyramidal neurons and dentate granule cells. Increased density of glutamatergic synaptic vesicles was observed in the hippocampus of TgFGF2 mice, and electrophysiological data (input/output curves and patch-clamp recordings in CA1) confirmed an increase in excitatory inputs in CA1, suggesting the presence of a latent hyperexcitability. Indeed, TgFGF2 mice displayed increased susceptibility to kainate-induced seizures compared with wild-type (WT) littermates, in that latency to generalized seizure onset was reduced, whereas behavioral seizure scores and lethality were increased. Finally, WT and TgFGF2 mice with similar seizure scores were used for examining seizure-induced cellular consequences. Neurogenesis and mossy fiber sprouting were not significantly different between the two groups. In contrast, cell damage (assessed with Fluoro-Jade B, silver impregnation and anti-caspase 3 immunohistochemistry) was significantly lower in TgFGF2 mice, especially in the areas of overexpression (CA1 and CA3), indicating reduction of seizure-induced necrosis and apoptosis. These data suggest that FGF-2 may be implicated in seizure susceptibility and in seizure-induced plasticity, exerting different, and apparently contrasting effects: favoring ictogenesis but reducing seizure-induced cell death.

Neurogenesis in the human hippocampus and its relevance to temporal lobe epilepsies

Ample evidence points to the dentate gyrus as anatomical region for persistent neurogenesis in the adult mammalian brain. This has been confirmed in a variety of animal models under physiological as well as pathophysiological conditions. Notwithstanding, similar experiments are difficult to perform in humans. Postmortem studies demonstrated persisting neurogenesis in the elderly human brain. In addition, neural precursor cells can be isolated from surgical specimens obtained from patients with intractable temporal lobe epilepsy (TLE) and propagated or differentiated into neuronal and glial lineages. It remains a controversial issue, whether epileptic seizures have an effect on or even increase hippocampal neurogenesis in humans. Recent data support the notion that seizures induce neurogenesis in young patients, whereas the capacity of neuronal recruitment and proliferation decreases with age. Animal models of TLE further indicate that these newly generated neurons integrate into epileptogenic networks and contribute to increased seizure susceptibility. However, pathomorphological disturbances within the epileptic hippocampus, such as granule cell dispersion (GCD), may not directly result from compromised neurogenesis. Still, the majority of adult TLE patients present with significant dentate granule cell loss at an end stage of the disease, which relates to severe memory and learning disabilities. In conclusion, surgical specimens obtained from TLE patients represent an important tool to study mechanisms of stem cell recruitment, proliferation and differentiation in the human brain. In addition, increasing availability of surgical specimens opens new avenues to systematically explore disease pathomechanisms in chronic epilepsies.

Time-dependent changes in distribution of basic fibroblast growth factor immunoreactive cells in hippocampus after kainic acid injection in rat pups

Five-day-old Wistar albino rats were injected with kainic acid (KA) or saline i.p. to investigate time-dependent alterations in morphology and number of basic fibroblast growth factor (bFGF) immunoreactive (-ir) astrocytes and neurons in hippocampus at 15, 30, and 90 days after the injections. Sections were stained with cresyl violet for morphological evaluation and bFGF immunohistochemistry was used for quantitative evaluation of bFGF-ir cell density. Fifteen days after KA injection, there was gliosis but no neuronal loss although disorganization in CA1, CA3, CA4 pyramidal layers and neuronal loss were evident 30 and 90 days after the injection. KA injected rats demonstrated significantly increased number of bFGF-ir astrocytes throughout the hippocampus and pyramidal neurons in CA2 after 15 days and decreased number of bFGF-ir cells after 30 and 90 days. The decrease in the number of bFGF-ir astroglia and neurons in long term after KA injection may indicate a decrease in the production of bFGF and/or number of bFGF-ir cells suggesting that protective effects of bFGF may be altered during epileptogenesis in hippocampus.

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Cytoarchitecture of fibroblast growth factor receptor 2 (FGFR-2) immunoreactivity in astrocytes of neurogenic and non-neurogenic regions of the young adult and aged rat brain

Fibroblast growth factors (FGFs) are polypeptides that exert diverse biological effects on many cell types and tissues during embryogenesis and adulthood. In the adult brain, FGF-2 is primarily expressed by astrocytes and select groups of neurons. It has been shown that FGF-2 is neuroprotective and can stimulate proliferation of NSCs in neurogenic regions of the adult mammalian brain. Cellular responses to FGFs are mediated through membrane-spanning tyrosine kinase receptors in conjunction with low affinity binding to heparin sulfate proteoglycans. Four FGF receptors (FGFR1-4) have been cloned and characterized to date. In this study, we describe the anatomical distribution of FGFR-2 in young and aged rat brains. We demonstrate that the olfactory bulb, hippocampus, and cerebellum display the most robust FGFR-2 expression and observed age-related decrease in FGFR-2 levels in some but not all brain regions. In addition, we identified astrocytes as the primary source of FGFR-2 expression using immunofluorescence confocal microscopy. The astrocyte populations in the neurogenic areas, the subventricular zone (SVZ) and the subgranular zone (SGZ) of the dentate gyrus, express high levels of FGFR-2 protein, which points to its possible involvement in neurogenesis. We also explored the role of FGFR-2 in response to perforant pathway lesion and observed enhanced FGFR-2 expression by astrocytes surrounding the lesion. Thus, FGF-2 biological effects on astrocytes appear to be mediated through FGFR-2-dependent mechanisms, and this may provide an indirect route by which FGF-2 acts on neuronal populations.

Stem/progenitor cell proliferation factors FGF-2, IGF-1, and VEGF exhibit early decline during the course of aging in the hippocampus: role of astrocytes

Dentate neurogenesis, important for learning and memory, declines dramatically by middle age. Although studies have shown that this age-related decrease can be reversed to some extent by exogenous applications of mitogenic factors, it is unclear whether one or more of these factors exhibits decline by middle age. We hypothesize that multiple stem/progenitor cell proliferation factors exhibit early decline during the course of aging in the hippocampus, and some of these declines are linked to age-related alterations in hippocampal astrocytes. We measured the concentrations of fibroblast growth factor-2 (FGF-2), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF) in the hippocampus of young, middle-aged, and aged F344 rats, using enzyme-linked immunosorbent assay (ELISA). In addition, we quantified the total number of FGF-2 immunopositive (FGF-2+) and glial fibrillary acidic protein immunopositive (GFAP+) cells in the dentate gyrus and the entire hippocampus. Our results provide new evidence that the concentrations of FGF-2, IGF-1, and VEGF decline considerably by middle age but remain steady between middle age and old age. Further, decreased concentrations of FGF-2 during aging are associated with decreased numbers of FGF-2+ astrocytes. Quantification of GFAP+ cells, and GFAP and FGF-2 dual immunostaining analyses, reveal that aging does not decrease the total number of astrocytes but fractions of astrocytes that express FGF-2 decline considerably by middle age. Thus, dramatically decreased dentate neurogenesis by middle age is likely linked to reduced concentrations of FGF-2, IGF-1, and VEGF in the hippocampus, as each of these factors can individually influence the proliferation of stem/progenitor cells in the dentate gyrus. Additionally, the results demonstrate that decreased FGF-2 concentration during aging is a consequence of age-related impairment in FGF-2 synthesis by astrocytes.

Alterations in seizure susceptibility and in seizure-induced plasticity after pharmacologic and genetic manipulation of the fibroblast growth factor-2 system

PURPOSE

The adult brain undergoes activity-dependent plastic modifications during pathologic processes that are reminiscent of those observed during development. For example, seizures induce neuronal loss, neurogenesis, axonal and dendritic sprouting, gliosis, and circuit remodeling. Neurotrophic factors and fibroblast growth factor-2 (FGF-2), in particular, are well-known mediators in each of these cellular events. The aim of this minireview is to summarize and discuss the data supporting the idea that FGF-2 may be involved in seizure generation and in their sequelae.

METHODS

We used epilepsy models of kainate and kindling, with FGF-2 knockout mice and FGF-2 overexpressing mice.

RESULTS

Seizures increase FGF-2 mRNA and protein levels in specific brain areas and upregulate the expression of its receptor FGFR-1. Short-term intrahippocampal injection of FGF-2 cause seizures, whereas long-term i.c.v. infusion of low-dose FGF-2 does not affect kainate seizures but promotes behavioral recovery and reduces hippocampal damage. Kainate seizure severity is not altered in FGF-2 knockout mice, but is increased in FGF-2 overexpressing mice.

CONCLUSIONS

FGF-2 is implicated in seizure susceptibility and in seizure-induced plasticity.

Effects of neurotransmitter agonists on electrocortical activity in the rat kainate model of temporal lobe epilepsy and the modulatory action of basic fibroblast growth factor

We used systemic kainic acid (KA) injection to investigate how the development of temporal lobe epilepsy and the associated network reorganization affect the electrocorticogram (ECoG) responses to various neurotransmitter agonists. Unrestrained rats chronically implanted with electrodes over somatosensory cortex and dorsal hippocampus and a cannula into the right lateral ventricle were used to investigate the ECoG frequency responses of intracerebroventricularly applied agonists (NMDA, clonidine, muscimol, and baclofen) at several types of receptors [NMDA, alpha2-adrenergic (NE), GABAA, and GABAB, respectively] in KA-treated versus naïve animals. The ECoG was analyzed 2, 5, and 9 weeks after intraperitoneal injection of KA alone or in combination with basic fibroblast growth factor (bFGF, intracerebroventricularly). Within the first 5 weeks of KA injection, the ECoG power shifted towards the lower-frequency range. Concurrently, the electrographic responses to NMDA and clonidine were potentiated, whereas the ECoG effects mediated by GABAA and GABAB receptors remained largely unaffected. In control rats, bFGF strongly enhanced the electrographic NMDA responses. In sharp contrast, bFGF potently mitigated the abnormally increased NMDA sensitivity of epileptic rats, if applied 4 weeks post KA injection. These data suggest that upregulation and downregulation of the NMDA receptor-mediated effects on cortical activity might be a prominent feature of bFGF signaling in the intact and the damaged brain, respectively.

Monocyte chemoattractant protein-1 and macrophage inflammatory protein-2 are involved in both excitotoxin-induced neurodegeneration and regeneration

Intrahippocamal injections of kainic acid (KA) significantly increase the expression of monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) in the ipsilateral hippocampus at 2-4 h and 21-45 days post-administration, suggesting the possible involvement of these chemokines in both neurodegenerative and regenerative processes. To examine the possible role of these chemokines on neuronal cell death, hippocampal neurons were incubated with either MCP-1 or MIP-2 in vitro and examined to assess the effects on neuronal cell viability. These treatments resulted in significant neuronal apoptosis that could be abrogated by prior treatment with the caspase-1 inhibitor, Z-VAD-FMK, the caspase-3 inhibitor, Z-DEVD-FMK, the Galphai inhibitor, pertussis toxin, or the MAO-B inhibitor, (-)deprenyl. Furthermore, this chemokine apoptotic effect could also be observed in vivo as intrahippocampal injections of MCP-1 or MIP-2 resulted in the apoptosis of hippocampal neurons, thus supporting a direct role of these chemokines in neuronal death. In contrast, immunohistological analysis of kainic acid lesions on days 21-45 revealed significant expression of MCP-1 and MIP-2 associated with reactive astrocytes and macrophages, respectively, with no apoptotic populations being observed. These results suggested that these chemokines might also mediate distinct biological effects on local microenvironmental cell populations at various stages post truama and during cellular repair. To address this possibility, astrocyte were cultured in the presence or absence of these chemokines and examined by microarray analysis for effects on astrocytes gene expression. A number of genes encoding proteins associated with inflammation, cellular signaling, differentiation, and repair were directly modulated by chemokine treatment. More specifically, the RNA and protein expression of the neurotrophic factor, basic fibroblast growth factor (bFGF), was found to be significantly increased upon culture with MCP-1 and MIP-2. Conditioned media derived from chemokine-stimulated astrocytes also facilitated bFGF-dependent neuronal cell differentiation and promoted survival of H19-7 neurons in vitro, suggesting a possible role for chemokine-activated astrocytes as a source of trophic support. Taken together, these data support possible autocrine and paracrine roles for MCP-1 and MIP-2 in both the "death and life" of hippocampal neurons following CNS injury.

Dopaminergic D2 receptor activation modulates FGF-2 gene expression in rat prefrontal cortex and hippocampus

We have investigated the role of dopaminergic receptors in modulation of basic fibroblast growth factor (FGF-2) expression in rat prefrontal cortex and hippocampus, two brain regions important for cognition. We found that FGF-2 expression is upregulated by quinpirole, a D2 agonist, in prefrontal cortex and to a lesser extent in hippocampus. This modulation was specific for dopamine D2 receptors because no effect was observed when the dopamine D1 and D3 agonists, SKF38393 and 7-OH-DPAT, respectively, were administered. Our findings show that activation of dopaminergic D2 receptors modulates FGF-2 expression in rat prefrontal cortex and hippocampus. Our data highlight the complex modulation of FGF-2 expression in limbic areas pointing to this trophic molecule as a putative target of drugs used against acute and chronic neurodegenerative diseases such as Parkinson's disease.

Fibroblast growth factors and neuroprotection

Several members of the FGF family, in particular FGF2, are intimately involved in neuronal protection and repair after ischemic, metabolic or traumatic brain injury. Expression of Fgf2 mRNA and protein is strongly upregulated after neuronal damage, with glial cells as the predominant source. Given its survival-promoting effects on cultured neurons, exogenous FGF2 was tested in several animal models of stroke and excitotoxic damage, in which it consistently proved protective against neuronal loss. FGF2 affords neuroprotection by interfering with a number of signaling pathways, including expression and gating of NMDA receptors, maintenance of Ca2+ homeostasis and regulation of ROS detoxifying enzymes. FGF2 prevents apoptosis by strengthening anti-apoptotic pathways and promotes neurogenesis in adult hippocampus after injury. The protective action of FGF2 has been linked to its augmenting effect on the lesion-induced upregulation of activin A, a member of the TGF-beta superfamily. Despite the well-documented benefits of FGF2 in animal models of stroke, there is currently no clinical development in stroke, after a phase II/III trial with FGF2 in acute stroke patients was discontinued because of an unfavorable risk-to-benefit ratio. As the molecular targets of FGF2 are going to be unraveled over the next years, new therapeutic strategies will hopefully emerge that enable us to influence the various protective mechanisms of FGF2 in a more specific fashion.

The effects of repeated minimal electroconvulsive shock exposure on levels of mRNA encoding fibroblast growth factor-2 and nerve growth factor in limbic regions

Chronic, but not acute, exposure to minimal electroconvulsive shock (ECS) has been shown to decrease vulnerability to neuronal cell death, without itself causing neuronal damage. One potential mechanism for the neuroprotective effect of ECS is the increase in fibroblast growth factor-2 (FGF-2) which occurs after chronic, but not acute, ECS exposure. This raises the possibility that repeated seizures over a period of several days may alter the transcriptional regulation of FGF-2. To test this hypothesis, the present study compared the effect of acute (1 day) vs. chronic (7 days) ECS treatment on levels of mRNA for FGF-2 in rhinal and frontal cortices, hippocampus, and olfactory bulbs. In addition, mRNA for another prominent neurotrophic factor, nerve growth factor (NGF), was assayed concurrently. At 8 h after acute ECS, mRNA levels increased by 60% for FGF-2 and 136% for NGF in rhinal cortex, 32% for FGF-2 and 36% for NGF in frontal cortex, and by 13% for NGF in hippocampus. After 7 days of ECS treatment the respective increases were 72% and 80%, 53% and 38%, and 28%. No increases were observed in olfactory bulbs after either treatment regimen. The peak increases in FGF-2 mRNA were consistently greater after chronic treatment, but the differences from those seen acutely reached significance in frontal cortex only. However, the duration over which mRNA for FGF-2 was elevated did not differ between the acute and chronic ECS groups. NGF mRNA induction was neither enhanced nor prolonged as a result of chronic ECS as compared to acute ECS treatment. These results suggest that chronic ECS treatment may lead to an enhanced rate of transcription of message for FGF-2 but not for NGF, in selected brain regions. At the same time, the results indicate that chronic ECS treatment induces FGF-2 and NGF mRNA expression in a tissue-specific manner and that this induction is maintained over the 7-day treatment period. The sustained increases in mRNAs for these trophic factors may contribute to the neuroprotective actions of chronic ECS treatment.

FGF-2 regulation of neurogenesis in adult hippocampus after brain injury

Fibroblast growth factor-2 (FGF-2) promotes proliferation of neuroprogenitor cells in culture and is up-regulated within brain after injury. Using mice genetically deficient in FGF-2 (FGF-2(-/-) mice), we addressed the importance of endogenously generated FGF-2 on neurogenesis within the hippocampus, a structure involved in spatial, declarative, and contextual memory, after seizures or ischemic injury. BrdUrd incorporation was used to mark dividing neuroprogenitor cells and NeuN expression to monitor their differentiation into neurons. In the wild-type strain, hippocampal FGF-2 increased after either kainic acid injection or middle cerebral artery occlusion, and the numbers of BrdUrd/NeuN-positive cells significantly increased on days 9 and 16 as compared with the controls. In FGF-2(-/-) mice, BrdUrd labeling was attenuated after kainic acid or middle cerebral artery occlusion, as was the number of neural cells colabeled with both BrdUrd and NeuN. After FGF-2(-/-) mice were injected intraventricularly with a herpes simplex virus-1 amplicon vector carrying FGF-2 gene, the number of BrdUrd-labeled cells increased significantly to values equivalent to wild-type littermates after kainate seizures. These results indicate that endogenously synthesized FGF-2 is necessary and sufficient to stimulate proliferation and differentiation of neuroprogenitor cells in the adult hippocampus after brain insult.

The role of cytokines and growth factors in seizures and their sequelae

Although the neuropathological changes caused by severe or repeated seizures have been well characterized, many questions about the molecular mechanisms involved remain unanswered. Neuronal cell death, reactive gliosis, enhanced neurogenesis, and axonal sprouting are four of the best-studied sequelae of seizures. In vitro, each of these pathological processes can be substantially influenced by soluble protein factors, including neurotrophins, cytokines, and growth factors. Furthermore, many of these proteins and their receptors are expressed in the adult brain and are up-regulated in response to neuronal activity and injury. We review the evidence that these intercellular signaling proteins regulate seizure activity as well as subsequent pathology in vivo. As nerve growth factor and brain derived neurotrophic factor are the best-studied proteins of this class, we begin by discussing the evidence linking these neurotrophins to epilepsy and seizure. More than a dozen additional cytokines, growth factors, and neurotrophins that have been examined in the context of epilepsy models are then considered. We discuss the effect of seizure on expression of cytokines and growth factors, and explore the regulation of seizure development and aftermath by exogenous application or antagonist perturbation of these proteins. The experimental evidence supports a role for these factors in each aspect of seizure and pathology, and suggests potential targets for future therapeutics.

Stimulatory role of dopamine on fibroblast growth factor-2 expression in rat striatum

We have previously shown that systemic injection of (-)nicotine produces a selective up-regulation of fibroblast growth factor (FGF)-2 mRNA levels in rat striatum. Because (-)nicotine can increase striatal release of dopamine and glutamate, in the present study we have investigated the contribution of these neurotransmitters in the modulation of FGF-2 expression. We found that coinjection of dopaminergic D1 (SCH23390) or D2 (haloperidol) receptor antagonists prevents nicotine-induced elevation of FGF-2 expression. However, injection of the NMDA receptor antagonist MK-801 produced a significant increment of FGF-2 mRNA and protein levels in rat striatum similar to the effect produced by (-)nicotine alone. Interestingly this effect of MK-801 could also be prevented by D1 or D2 receptor antagonists, suggesting that an elevation of dopamine levels may be required for the regulation of the trophic molecule. Accordingly we found that the non-selective dopaminergic agonist apomorphine can similarly increase striatal FGF-2 mRNA levels. Despite the observation that both D1 and D2 receptors appear to contribute to the modulation of FGF-2 expression, only a direct activation of D2 receptors, through quinpirole administration, was able to mimic the effect of apomorphine. On the basis of FGF-2 neurotrophic activity, these results suggest that direct or indirect activation of dopaminergic system can be neuroprotective and might reduce cell vulnerability in degenerative disorders.

Differential expression of fibroblast growth factor-2 and fibroblast growth factor receptor 1 in a scarring and nonscarring model of CNS injury in the rat

Injury to the adult brain results in abortive axon regeneration and the deposition of a dense fibrous glial scar. Therapeutic strategies to promote postinjury axon regeneration are likely to require antiscarring strategies. In neonatal brain wounds, scar material is not laid down and axons grow across the lesion site, either by de novo growth or regeneration. To achieve the therapeutic goal of recapitulating the nonscarring neonatal response in the injured adult, an understanding of how ontogenic differences in scarring reflect developmental diversities in the trophic response to injury is required. Fibrobast growth factor-2 (FGF-2) expression is developmentally regulated and has been implicated as a regulator of the wounding response of the adult rat central nervous system. We have investigated the expression of FGF-2 and fibroblast growth factor receptor 1 (FGFR1) after penetrating lesions to the cerebral cortex of 5 days post partum (dpp) (nonscarring) and 16 dpp and adult (scarring) rats. In situ hybridization, immunohistochemistry and Western blotting showed robust and sustained increases in FGF-2 and FGFR1 mRNA and protein in reactive astrocytes around the lesion in scarring rats, a response that was attenuated substantially in the nonscarring neonate. These results demonstrate that changes in astrocyte FGF-2 and FGFR1 expression are coincident with the establishment of a mature pattern of glial scarring after injury in the maturing central nervous system, but it is premature to infer a causal relationship without further experiments.

Different patterns of induction of fibroblast growth factor-2 and brain-derived neurotrophic factor messenger RNAs during kindling epileptogenesis, and development of a herpes simplex vector for fibroblast growth factor-2 gene transfer in vivo

PURPOSE

To investigate the gene expression patterns of brain-derived neurotrophic factor (BDNF) and fibroblast growth factor-2 (FGF-2) in the kindling model, and to construct a replication-defective herpes simplex virus vector to induce expression of FGF-2 in vivo.

METHODS

RNase protection assay and herpes simplex virus vector (TH FGF-2) deleted in the immediate-early genes ICP4, ICP22, and ICP27, with FGF-2 inserted in tk under the control of the human cytomegalovirus immediate-early promoter.

RESULTS

A single kindling stimulation did not modify BDNF gene expression, whereas it increased FGF-2 messenger RNA (mRNA) levels in the hippocampus, the cortex, and the hypothalamus. BDNF and FGF-2 gene expression were not altered in kindled animals left unstimulated for 1 week. In contrast, kindled seizures produced a great increase in hippocampal and cortical BDNF mRNA levels, but FGF-2 mRNA was increased only in the ipsilateral cortex. Infection of Vero cells with TH FGF-2 resulted in a long-lasting increase in FGF-2 levels. Protein extracts of infected cells induced neuronal differentiation of PC12 cells, indicating that the newly synthesized FGF-2 was biologically active. Robust transient transgene expression was observed in the rat hippocampus after inoculation with TH FGF-2 in the absence of significant toxicity.

CONCLUSIONS

BDNF and FGF-2 are recruited at different stages of kindling and, accordingly, may play different roles in the adaptive changes taking place during epileptogenesis. TH FGF-2 is suitable for studies of FGF-2 involvement in kindling epileptogenesis.

Cortical spreading depression increases protein synthesis and upregulates basic fibroblast growth factor

Protective effects of cortical spreading depression (CSD) against ischemic damage have been demonstrated in cortex when elicited at either 24 h or 3 days prior to ischemia. The present study was carried out to investigate possible mechanisms of neuroprotection following CSD. In Sprague-Dawley rats, 5 M KCl, 5 M NaCl, or physiological saline was applied to the cortex for 1 h. Repetitive CSD waves were elicited only in the KCl group. Measurements of cerebral glucose utilization demonstrated a marked reduction in affected cortex and subcortical regions in both the NaCl and the KCl groups, whereas cortical and hippocampal protein synthesis was discretely increased only in the KCl group. Immunohistochemistry of GFAP demonstrated a rapid activation in reactive astrocytes at 3 days in the KCl group whereas only a discrete activation was observed in the NaCl group. Similar changes were observed for basic fibroblast growth factor. Our results suggest that CSD-induced ischemic tolerance is not due to a reduction in energy metabolism but rather is associated with an upregulation of trophic factors and glial cell activation which might provide a mechanism for a long-lasting neuroprotection.

Visual input regulates the expression of basic fibroblast growth factor and its receptor

Emerging evidence indicates that the expression of trophic factors in the brain is regulated in an activity-dependent manner, which suggests an involvement of trophic factors in events controlled by input activity. We have investigated the possibility that visual sensory input impacts the expression of basic fibroblast growth factor and its receptor in the brain. Rats were maintained for seven days in darkness and then re-exposed to normal illumination for 0, 1, 3 or 6 h. We assessed relative levels of basic fibroblast growth factor and fibroblast growth factor receptor messenger RNAs using nuclease protection assays, and examined possible changes in the phenotypic expression of basic fibroblast growth factor and its receptor using immunohistochemistry. There was a significant decrease in levels of basic fibroblast growth factor and fibroblast growth factor receptor messenger RNAs as a result of dark rearing, and levels of messenger RNAs increased progressively with light re-exposure. Changes in messenger RNAs were observed primarily in the cerebral cortex (caudal portion) and were accompanied by alterations in the staining intensity and density of cells exhibiting basic fibroblast growth factor and fibroblast growth factor receptor phenotypes. Regulation of the basic fibroblast growth factor system by sensory input suggests that basic fibroblast growth factor, and perhaps other trophic factors, are mediators of the effects of experience on the structure and function of the CNS.

Localization and regulation of basic fibroblast growth factor (FGF-2) and FGF receptor-1 in rat superior cervical ganglion after axotomy

In response to peripheral nerve lesion, synthesis of basic fibroblast growth factor (FGF-2) increases in sensory ganglia and motoneurons. Here, we investigated the axotomy-induced regulation of FGF-2 and FGF receptor-1 (FGFR-1) expression in the autonomic nervous system using the sympathetic superior cervical ganglion of the adult rat as a model. Transcripts for both proteins were detected by ribonuclease protection assay. Western blotting indicated the presence of all three FGF-2 isoforms (18, 21, and 23 kD) in the superior cervical ganglion. Immunohistochemical analysis revealed FGF-2 localization in nuclei of satellite cells surrounding postganglionic perikarya. After transection of the carotid nerves, the number of FGF-2-immunoreactive glial cells increased. FGF-2 mRNA was up-regulated within 6 h and remained elevated for 3 weeks. The 18-, 21-, and 23-kD isoforms were all increased 7 days after axotomy. FGFR-1 immunoreactivity was observed in neuronal and nonneuronal nuclei in the normal rat superior cervical ganglion. In contrast to FGF-2, expression of FGFR-1 was unchanged in ganglia after axotomy. Taken together, the present results suggest that FGF-2 participates in neuron-glial interactions of sympathetic ganglia and may be involved in sympathetic neuron survival or nerve regeneration after nerve lesion.

Selective inhibition of kindling development by intraventricular administration of TrkB receptor body

Recent work has shown that neurotrophin gene expression is increased after seizures evoked in the kindling model of epilepsy, but whether neurotrophins regulate kindling development is as yet unclear. In this study, we attempted to block selectively the activation of distinct neurotrophin receptors throughout kindling development in the rat via chronic intracerebroventricular administration of trk receptor bodies. The efficacy and selectivity of the trk receptor bodies were established by inhibition of neurotrophin-induced trk receptor phosphorylation in pheochromocytoma (PC12) cells and primary cultures of cortical neurons. The intracerebroventricular infusion of trkB receptor body (trkB-Fc) inhibited development of kindling in comparison with that seen with saline or human IgG controls, trkA-Fc, or trkC-Fc. These results imply that activation of trkB receptors contributes to the development of kindling, a form of activity-dependent behavioral plasticity in the adult mammalian brain.

Fibroblast growth factor receptor-1 expression in the cortex and hippocampus in Alzheimer's disease

Localization of fibroblast growth receptor (FGFR)-1 immunoreactivity was investigated immunochemically in postmortem brain tissue of Alzheimer's disease (AD) and age-matched control cases using a rabbit polyclonal antibody and a mouse monoclonal antibody specific for FGFR-1. In control cases, FGFR-1 immunoreactivity was identified in astrocytes in white matter and in hippocampal pyramidal neurons. In AD cases, the immunoreactivity in reactive astrocytes surrounding senile plaques was increased. The pattern of FGFR-1 immunoreactivity was confirmed in selected cases by in situ hybridization for FGFR-1 mRNA. Immunoreactivity using a monoclonal antibody demonstrated a similar distribution pattern. The localization of FGFR-1 is consistent with previous reports on the involvement of FGF-1 and FGF-2 in AD.

Differential regulation of FGF-2 and FGFR-1 in rat cortical astrocytes by dexamethasone and isoproterenol

We have used rat cortical astrocytes in culture to investigate the signaling pathways involved in the regulation of fibroblast growth factor-2 (FGF-2) and one of its high affinity receptor FGF receptor-1 (FGFR-1). These cells represent a source of different neurotrophic factors and play important roles in physiological and pathological conditions of the central nervous system. FGF-2 mRNA levels are increased by stimulation of beta-adrenergic receptors or exposure to glucocorticoid hormones and these effects are additive to each other. The regulation of FGFR-1, highly expressed in cultured astroglial cells, appears to be different. Isoproterenol produced an elevation of FGFR-1 mRNA levels, whereas dexamethasone decreased its expression alone or in the presence of isoproterenol, suggesting that the glucocorticoid pathway may predominate over the cAMP-induced up-regulation of the receptor. FGF-2 over-expression may produce different cellular responses depending on the concomitant regulation of its receptor and the cell phenotype where these changes do occur. These mechanisms can contribute to adaptive changes taking place in the CNS in different physiological and pathological situations.

Acute intermittent nicotine treatment produces regional increases of basic fibroblast growth factor messenger RNA and protein in the tel- and diencephalon of the rat

Several findings show a neuroprotective effect of nicotine treatment in different experimental models, and a negative correlation has been observed between cigarette smoking and the incidence of Parkinson's disease. It seems possible that nicotine may in part exert its neuroprotective actions by favouring the synthesis of neurotrophic factors. The aim of this study was to determine whether the nicotine treatment could be associated with the induction of a neurotrophic factor in brain regions with nicotinic receptors. Thus, we analysed by in situ hybridization and RNAse protection assay the effects of (-)nicotine on basic fibroblast growth factor messenger RNA and by immunocytochemistry fibroblast growth factor-2 protein in the tel- and diencephalon of rats following single or acute intermittent (-)nicotine treatment. The present results showed that acute intermittent (-)nicotine treatment (four i.p. injections at intervals of 30 min), but not single injections, lead to a substantial and dose-related (0.1-2 mg/kg) up-regulation of fibroblast growth factor-2 messenger RNA levels in the cerebral cortex, in the hippocampus, in the striatum and ventral midbrain. This induction of fibroblast growth factor-2 expression peaked 4 h after the first injection and returned to normal levels within 24 h. The change of fibroblast growth factor-2 messenger RNA levels was associated with increased fibroblast growth factor-2 immunoreactivity mainly localized to nerve cells. The treatment was effective also when repeated in the same animals three or five days after the first injection. The pre-treatment with the non-competitive (-)nicotine receptor antagonist mecamylamine blocked the (-)nicotine effects on fibroblast growth factor-2 messenger RNA levels. In the above areas, no changes were observed in the fibroblast growth factor-1, 2 and 3 receptor messenger RNA levels nor in brain-derived neurotrophic factor messenger RNA levels. The present data indicate an ability of intermittent (-)nicotine to increase fibroblast growth factor-2 in many tel- and diencephalic areas. In view of the trophic function of fibroblast growth factor-2, the previously observed neuroprotective effects of (-)nicotine may at least in part involve an activation of the neuronal fibroblast growth factor-2 signalling, and open up new avenues for treatment of Parkinson's disease and Alzheimer's disease based on the existence of nicotinic receptor subtypes enhancing fibroblast growth factor-2 signalling in many regions of the tel- and diencephalon.

Different patterns of induction of FGF-2, FGF-1 and BDNF mRNAs during kindling epileptogenesis in the rat

Neurotrophic factors (NTF) play important roles in the developing and in the adult brain. NTF involvement in neuronal plasticity is suggested by the modulation of NTF expression patterns in different physiological and pathological situations and by the effects they produce in the adult brain (e.g. axonal sprouting induction and neuroprotection). We used the RNAase protection assay to investigate the expression patterns of some NTFs during amygdala kindling, an animal model of epilepsy in which 'pathological' neuronal plasticity appears to occur. After a single kindling stimulation, fibroblast growth factor-2 (FGF-2) mRNA levels were increased in the hippocampus, the cortex and the hypothalamus, whereas they were not significantly altered in the thalamus and the striatum. A single stimulation did not alter fibroblast growth factor-1 (FGF-1) and brain-derived neurotrophic factor (BDNF) gene expression. Fully kindled animals, left unstimulated for a week, did not exhibit any alteration in the mRNA levels for any of the NTFs examined. However, in contrast with the effect of a single stimulation, amygdala stimulation of kindled animals (evoking a generalized tonic-clonic seizure) produced a great increase in hippocampal and cortical BDNF mRNA levels, but FGF-1 mRNA levels were not altered, and FGF-2 mRNA levels were significantly increased only in the cortex. These results suggest that different NTFs can be recruited at different stages of kindling epileptogenesis and, accordingly, may play different parts in the adaptive changes taking place in this experimental paradigm.

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.

Focal brain injury increases activin betaA mRNA expression in hippocampal neurons

The role of activin in the mammalian brain is of increasing interest as evidence accumulates to suggest a number of different neural functions. Here, we report that activin betaA mRNA is transiently induced in dentate gyrus neurons after unilateral mechanical brain injury by saline injection. Expression is dependent on NMDA receptor activation since pretreatment with MK801 (5 mg/kg, i.p.) largely attenuates the signal. Induction also requires de novo protein synthesis, as cycloheximide (10 mg/kg, i.p.) pretreatment abolishes the expression of activin betaA mRNA 1 h after injury. These results show that activin betaA mRNA expression is regulated by excitatory activity induced by focal brain injury and suggests a possible neuroplastic role in the recovery from such injury.

Physical exercise induces FGF-2 and its mRNA in the hippocampus

Clinical and experimental evidence indicate that physical activity has a positive impact on brain function; however, the molecular bases for how exercise affects the structure and function of the brain are largely unknown. We have investigated the influences of variable periods of voluntary wheel-running on the expression of basic fibroblast growth factor and its mRNA in various brain regions. Nuclease protection assays revealed that the hippocampus was the only region examined exhibiting changes in FGF-2 mRNA as a result of exercise. FGF-2 mRNA increased to reach a peak by the 4th night of wheel-running. FGF-2 immunoreactivity, normally located in the perinuclear area of astrocytes, following exercise became stronger and appeared to spread to the cytoplasm and processes of astrocytes. Quantification of the FGF-2-immunoreactive astrocytes showed an increase in density between 2 and 4 nights of running in discrete regions of the hippocampus. These results demonstrate that exercise regulates FGF-2 expression and suggest that growth factors are likely mediators of the positive effects of exercise on the brain.

mRNAs encoding urokinase-type plasminogen activator and plasminogen activator inhibitor-1 are elevated in the mouse brain following kainate-mediated excitation

Urokinase-type plasminogen activator (uPA) is an inducible extracellular serine protease implicated in fibrinolysis and in tissue remodeling. Recently, we have localized uPA mRNA strictly in limbic structures and the parietal cortex of the adult mouse brain. Here, we tested whether the systemic treatment of mice with kainic acid (KA), an amino acid inducing limbic seizures, could elevate in the brain mRNAs encoding uPA and its specific inhibitor, plasminogen activator inhibitor-1 (PAI-1), a major antifibrinolytic agent. Brain sections encompassing the hippocampus were tested through in situ hybridization using radiolabeled riboprobes specific for the two mRNA species. The results showed that KA greatly enhanced both mRNA species in sites of limbic structures and cortex. However, in the hypothalamus and brain blood vessels only PAI-1 mRNA was elevated. Those were also the only two locations where PAI-1 mRNA was detected in the non-treated control brain, although at a low level. For both mRNAs, KA enhancement was first evident 2-4 h after treatment, and it was most prolonged in the hippocampal area, where prominent hybridization signals persisted for three days. Here, both mRNAs were initially elevated in the hilar region of the dentate gyrus and in the molecular and oriens layers; however, PAI-1 mRNA became evident throughout the area, while uPA mRNA became especially pronounced in the CA3/CA4 subfield. In the cortex both mRNA types were induced, but only uPA mRNA was elevated in the retrosplenial cortex, and also in the subiculum. In the amygdaloid complex, uPA mRNA was restricted to the basolateral nucleus, whereas PAI-1 mRNA was seen throughout the structure, however, excluding this nucleus. These data show that seizure activity enhances the expression of uPA and PAI-1 genes in the brain; the patterns of enhancement suggest that the protease and its inhibitor may act in brain plasticity in synchrony, however, also independently of each other. Furthermore, the results suggest that by elevating PAI-1 mRNA in brain blood vessels, limbic seizures generate a risk for stroke.

Discriminable excitotoxic effects of ibotenic acid, AMPA, NMDA and quinolinic acid in the rat laterodorsal tegmental nucleus

Excitotoxins are valuable tools in neuroscience research as they can help us to discover the extent to which certain neurones are necessary for different types of behaviour. They have distinctive neurotoxic effects depending on where they are infused, and this study was conducted to delineate the neurotoxic profiles of excitotoxins in the laterodorsal tegmental nucleus (LDTg). Two 0.1 microl infusions of 0.1 M ibotenate, 0.1 M quinolinate, 0.04-0.1 M NMDA, or 0.05-0.015 M AMPA, were made unilaterally into the LDTg under either pentobarbitone or Avertin anaesthesia. The injection needle was oriented at an angle of 24 degrees from vertical in the mediolateral plane. After 23-27 days, sections through the mesopontine tegmentum were processed using standard histological procedures for NADPH-diaphorase histochemistry, tyrosine hydroxylase or 5-hydroxytryptamine immunohistochemistry, and Cresyl violet. Lesions were assessed in terms of the size of the damaged area (identified by reactive gliosis), the extent of cholinergic cell loss in the mesopontine tegmentum (by counting NADPH-diaphorase-positive neurones), and neuronal loss induced in the locus coeruleus and dorsal raphe nucleus. Ibotenate induced compact lesions in the LDTg (more than 80% cholinergic loss) and did little damage to the locus coeruleus and dorsal raphe nucleus. Quinolinate and low doses of AMPA and NMDA made very small lesions with less than 35% cholinergic loss, while at higher doses, AMPA and NMDA induced large areas of reactive gliosis but killed only a proportion of the cholinergic neurones. AMPA appeared to have a particular affinity for noradrenergic neurones in the locus coeruleus, with the 0.015 M dose injected into the LDTg typically destroying the majority of these neurones. The results are discussed in the context of what is known about the mechanisms of excitotoxins and the glutamate receptor profile of mesopontine neurones.

bFGF and FGFR-3 immunoreactivity in the rat brain following systemic kainic acid administration at convulsant doses: localization of bFGF and FGFR-3 in reactive astrocytes, and FGFR-3 in reactive microglia

Strong bFGF immunoreactivity was observed in reactive astrocytes, as shown by double-labeling immunohistochemistry of bFGF and GFAP, from days 7 up to 30 (last time point examined) following kainic acid (KA) injection at convulsant doses in the adult rat. bFGF was not found in OX-42-positive reactive microglia. A few reactive glia co-localized FGFR-3 and GFAP, whereas the majority of cells expressing FGFR-3 were OX-42-immunoreactive. This was further supported by the observation that only approximately 10% of reactive glia co-localized bFGF and FGFR-3. These results show that reactive astrocytes are a major source of bFGF during the subacute stages of tissue damage following KA injection and that reactive astrocytes and, most particularly, reactive microglia are putative targets of bFGF through FGFR-3.

Basic fibroblast growth factor is highly neuroprotective against seizure-induced long-term behavioural deficits

Basic fibroblast growth factor has been reported to protect neurons of various structures from excitotoxic damage. To study the effects of basic fibroblast growth factor on seizure-induced brain damage we infused the growth factor into the lateral ventricles of 35-day-old rats receiving convulsant dosages of kainic acid. Artificial cerebrospinal fluid or basic fibroblast growth factor at dosages of 0.5 ng/h or 2.5 ng/h was infused into the lateral ventricle continuously for seven days starting two days before and continuing for five days after the animals had kainic acid-induced status epilepticus. At age 80 days the animals underwent behavioural testing using the water maze, open field, and handling tests and at age 95 days were tested for seizure threshold using flurothyl inhalation. Neither artificial cerebrospinal fluid or basic fibroblast growth factor modified the latency or duration of the acute seizures following kainic acid. However, rats infused with 2.5 ng/h, but not 0.5 ng/h of basic fibroblast growth factor, had fewer spontaneous recurrent seizures, a higher seizure threshold, better performance in the handling, open field and water maze test, and less cell loss in the hippocampus when compared to rats receiving artificial cerebrospinal fluid or 0.5 ng/h of basic fibroblast growth factor. These results show that basic fibroblast growth factor has a dose-related neuroprotective effect against seizure-induced long-term behavioural deficits when administered by osmotic pump prior to seizure onset. This neuroprotective effect is not related to an anticonvulsant effect.

Heparan sulfate potentiates the autocrine action of basic fibroblast growth factor in astrocytes: an in vivo and in vitro study

Increasing evidence indicates that heparan sulfate proteoglycans have a critical role in the regulation of the activity of basic fibroblast growth factor by interacting with it or its receptor. In this study we examined the possibility that heparan sulfate can modulate the basic fibroblast growth factor system at a more fundamental level than activity regulation, by influencing the synthesis of basic fibroblast growth factor and its receptor messenger RNAs. Previous studies in vitro indicate that basic fibroblast growth factor promotes proliferation and differentiation of astrocytes. Accordingly, we examined the possibility that the action of heparan sulfate on the basic fibroblast growth factor system could have a critical role in the modulation of reactivity and/or proliferation of astrocytes in vitro and in vivo. We report that basic fibroblast growth factor applied to pure astrocyte cultures or rat neocortex promoted an increase in the messenger RNA for basic fibroblast growth factor itself and for its receptor. Furthermore, basic fibroblast growth factor applied directly into the brain elicited an increase in messenger RNA for the astrocytic marker glial fibrillary acidic protein. All of these actions, both in vitro and in vivo, were highly potentiated when heparan sulfate was applied in combination with basic fibroblast growth factor. These results suggest that basic fibroblast growth factor regulates astrocytic proliferation or reactivity via an autocrine cascade that involves induction of its own receptor and that this action is modulated by heparan sulfate.

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.

Expression of a phosphorylated isoform of MAP1B is maintained in adult central nervous system areas that retain capacity for structural plasticity

Microtubule-associated protein IB (MAP1B) is the first MAP to be detected in the developing nervous system, and it becomes markedly down-regulated postnatally. Its expression, particularly that of its phosphorylated isoform, is associated with axonal growth. To determine whether adult central nervous system (CNS) areas that retain immunoreactivity for MAP1B are associated with morphological plasticity, we compared the distribution of a phosphorylated MAP1B isoform (MAP1B-P) to the distribution of total MAP1B protein and MAP1B-mRNA. Although they were present only at very low levels, both protein and message were found ubiquitously in almost all adult CNS neurons. The intensity of staining, however, varied markedly among different regions, with only a few nuclei retaining relatively high levels. MAP1B-P was restricted to axons, whereas total MAP1B was present in cell bodies and processes. Relatively to total MAP1B protein and its mRNA, MAP1B-P levels decreased more dramatically with maturation, and they were detectable in only a few specific areas that underwent structural modifications. These included primary afferents and motor neurons, olfactory tubercles, habenular and raphe projections to interpeduncular nuclei, septum, and the hypothalamus. The distribution pattern of MAP1B-P was compared to that of the embryonic N-CAM rich in polysialic acid (PSA-NCAM). We found that the PSA-NCAM immunostaining was largely overlapped with that of MAP1B-P in the adult CNS. These results suggest that, like PSA-NCAM, MAP1B may be one of the molecules expressed during brain development that also plays a role in structural remodeling in the adult.

Antiepileptic effects of acidic fibroblast growth factor examined in kainic acid-mediated seizures in the rat

The possibility that exogenous recombinant human acidic fibroblast growth factor (rhaFGF) may have anticonvulsant properties was investigated in a model of temporal lobe epilepsy in awake rats. We found that after intraperitoneal injection of rhaFGF in kainic acid-treated rats, tonic-clonic convulsions and mortality were decreased by 74% and 77%, respectively. These results are consistent with previous studies showing a neuroprotective effect of FGF against insults to the brain and support a possible therapeutic role for FGF in the treatment of excitotoxic processes.

Selective enhancement of axonal branching of cultured dentate gyrus neurons by neurotrophic factors

Epileptic seizures in the mature nervous system are associated with axonal sprouting of the hippocampal dentate granule cells and pathological synapse formation. The molecular basis of this morphological rearrangement is obscure. Since epileptic seizures induce the transcriptional activation of genes encoding diverse neurotrophic and growth factors in the dentate granule cells and their targets, morphoregulatory effects of these proteins may contribute to this morphological rearrangement. To determine whether neurotrophins or growth factors exert morphoregulatory effects on dentate gyrus neurons, quite homogeneous preparations of these neurons from postnatal rats were established in primary culture at low density in defined media. Dendrites were distinguished from axons by phase contrast appearance together with microtubule-associated protein-2 immunocytochemistry. Multiple factors enhanced branching of axons but not dendrites of these neurons. The rank order of effectiveness was: basic fibroblast growth factor > brain-derived growth factor > neurotrophin-4 > neurotrophin-3; nerve growth factor was ineffective. No additives of synergistic effects were detected. These results are consistent with the idea that activity-driven expression of these genes contributes to the axonal sprouting and pathological synapse formation evident in diverse forms of epilepsy.

A comprehensive analysis of the distribution of FGF-2 and FGFR1 in the rat brain

We have examined the cellular distribution of both FGF-2 and FGFR1 immunoreactivity and their mRNAs throughout the normal adult rat brain in order to reconcile numerous disparate findings in the published literature. The results confirm a widespread distribution of FGF-2 and FGFR1 in the rat brain, and different regions express distinct patterns of FGF-2 and FGFR1 mRNA and protein: neuronal and non-neuronal cells show different subcellular distributions that vary according to the area where they are located. The intensity of the staining and hybridization also varies according to the loci examined and the cell type involved. Astrocytes contain the highest levels of FGF-2 and FGFR1 mRNAs, and characteristically, possess high levels of immunoreactive FGF-2 within the nucleus. Amongst non-neuronal cells, oligodendrocytes do not synthesize or contain significant levels of FGF-2 immunoreactivity however, they do express FGFR1 mRNA. In these cells, immunoreactive FGFR1 is mainly associated with the myelin sheaths of neuronal fibers. In ventricular systems, ependymal cells synthesize and contain immunoreactive FGFR1. In contrast, only cells lining the lateral wall of the IIIrd ventricle express FGF-2 mRNA. Subependymal cells contain high levels of both FGF-2 and FGFR1 immunoreactivity. Neurons express low levels of FGF-2 mRNA and immunoreactive FGF-2 is localized predominantly to the perikaryon. However, selected populations of neurons, such as CA2 field of the hippocampus, show high levels of FGF-2 mRNA, in which the nucleus is strongly immunopositive. Similarly, high levels of FGFR1 mRNA are localized to select populations of neurons (e.g. amygdala). FGFR1 immunoreactivity is mainly associated with myelinated fiber tracts (e.g. striatum), and some neurons show immunoreactivity in the perikaryon (e.g. hippocampus), the nucleus (e.g. mesencephalic trigeminal nucleus), or in axonal projections (e.g. hypothalamus). Remarkably, in many of the areas studied, FGF-2 and FGFR1 mRNA and/or their translated protein do not co-localize in neurons (e.g. neo-cortices) or even in the same regions of the brain (e.g. substantia nigra). In other instances, mRNAs for both FGF-2 and FGFR1 colocalize (e.g. supraoptic nucleus). The brain, in contrast to peripheral tissues, contains high levels of FGF-2 and actively expresses its gene under normal physiological conditions. The highly specific anatomical distribution of immunoreactive FGF-2 in neuronal and non-neuronal brain cells, supports the notion that it plays a multifunctional role in the CNS under normal physiology. By correlating the localization and the synthesis of FGF-2 and one of its high affinity receptors, FGFR1, in the CNS, it should be possible to obtain a better understanding of the roles of FGF-2 in normal and pathological conditions.