Basic fibroblast growth factor and brain-derived neurotrophic factor promote survival and neuronal circuit formation in organotypic hippocampal culture

Polystyrene microplastics induced disturbances in neuronal arborization and dendritic spine density in mice prefrontal cortex

An increasing use of plastics in daily life leads to the accumulation of microplastics (MPs) in the environment, posing a serious threat to the ecosystem, including humans. It has been reported that MPs cause neurotoxicity, but the deleterious effect of polystyrene (PS) MPs on neuronal cytoarchitectural morphology in the prefrontal cortex (PFC) region of mice brain remains to be established. In the present study, Swiss albino male mice were orally exposed to 0.1, 1, and 10 ppm PS-MPs for 28 days. After exposure, we found a significant accumulation of PS-MPs with a decreased number of Nissl bodies in the PFC region of the entire treated group compared to the control. Morphometric analysis in the PFC neurons using Golgi-Cox staining accompanied by Sholl analysis showed a significant reduction in basal dendritic length, dendritic intersections, nodes, and number of intersections at seventh branch order in PFC neurons of 1 ppm treated PS-MPs. In neurons of 0.1 ppm treated mice, we found only decrease in the number of intersections at the seventh branch order. While 10 ppm treated neurons decreased in basal dendritic length, dendritic intersections, followed by the number of intersections at the third and seventh branch order were observed. As well, spine density on the apical secondary branches along with mRNA level of BDNF was significantly reduced in all the PS-MPs treated PFC neurons, mainly at 1 ppm versus control. These results suggest that PS-MPs exposure affects overall basal neuronal arborization, with the highest levels at 1 and 10 ppm, followed by 0.1 ppm treated neurons, which may be related to the down-regulation of BDNF expression in PFC.

Recombinant human fibroblast growth factor-2 promotes nerve regeneration and functional recovery after mental nerve crush injury

Several studies have shown that fibroblast growth factor-2 (FGF2) can directly affect axon regeneration after peripheral nerve damage. In this study, we performed sensory tests and histological analyses to study the effect of recombinant human FGF-2 (rhFGF2) treatment on damaged mental nerves. The mental nerves of 6-week-old male Sprague-Dawley rats were crush-injured for 1 minute and then treated with 10 or 50 μg/mL rhFGF2 or PBS in crush injury area with a mini Osmotic pump. Sensory test using von Frey filaments at 1 week revealed the presence of sensory degeneration based on decreased gap score and increased difference score. However, at 2 weeks, the gap score and difference score were significantly rebounded in the mental nerve crush group treated with 10 μg/mL rhFGF2. Interestingly, treatment with 10 μg/mL rhFGF had a more obviously positive effect on the gap score than treatment with 50 μg/mL rhFGF2. In addition, retrograde neuronal tracing with Dil revealed a significant increase in nerve regeneration in the trigeminal ganglion at 2 and 4 weeks in the rhFGF2 groups (10 μg/mL and 50 μg/mL) than in the PBS group. The 10 μg/mL rhFGF2 group also showed an obviously robust regeneration in axon density in the mental nerve at 4 weeks. Our results demonstrate that 10 μg/mL rhFGF induces mental nerve regeneration and sensory recovery after mental nerve crush injury.

Electroosmotic push-pull perfusion: description and application to qualitative analysis of the hydrolysis of exogenous galanin in organotypic hippocampal slice cultures

We demonstrate here a method that perfuses a small region of an organotypic hippocampal culture with a solution containing an enzyme substrate, a neuropeptide. Perfusate containing hydrolysis products is continually collected and subsequently analyzed for the products of the enzymatic degradation of the peptide substrate. The driving force for perfusion is an electric field. The fused silica capillaries used as "push" and "pull" or "source" and "collection" capillaries have a ζ-potential that is negative and greater in magnitude than the tissue's ζ-potential. Thus, depending on the magnitudes of particular dimensions, the electroosmotic flow in the capillaries augments the fluid velocity in the tissue. The flow rate is not directly measured; however, we determine it using a finite-element approach. We have determined the collection efficiency of the system using an all d-amino acid internal standard. The flow rates are low, in the nL/min range, and adjustable by controlling the current or voltage in the system. The collection efficiency of the d-amino acid peptide internal standard is variable, increasing with increased current and thus electroosmotic flow rate. The collection efficiency can be rationalized in the context of a Peclet number. Electroosmotic push-pull perfusion of the neuropeptide galanin (gal1-29) through the extracellular space of an organotypic hippocampal culture results in its hydrolysis by ectopeptidase reactions occurring in the extracellular space. The products of hydrolysis were identified by MALDI-MS. Experiments at two levels of current (8-12 μA and 19-40 μA) show that the probability of seeing hydrolysis products (apparently from aminopeptidases) is greater in the Cornu Ammonis area 3 (CA3) than in the Cornu Ammonis area 1 (CA1) in the higher current experiments. In the lower current experiments, shorter peptide products of aminopeptidases (gal13-29 to gal20-19) are seen with greater frequency in CA3 than in CA1 but there is no statistically significant difference for longer peptides (gal3-29 to gal12-29).

Bystander effect on brain tissue of mesoangioblasts producing neurotrophins

Neurotrophic factors (NTFs) are involved in the regulation of neuronal survival and function and, thus, may be used to treat neurological diseases associated with neuronal death. A major hurdle for their clinical application is the delivery mode. We describe here a new strategy based on the use of progenitor cells called mesoangioblasts (MABs). MABs can be isolated from postnatal mesoderm tissues and, because of a high adhesin-dependent migratory capacity, can reach perivascular targets especially in damaged areas. We generated genetically modified MABs producing nerve growth factor (MABs-NGF) or brain-derived neurotrophic factor (MABs-BDNF) and assessed their bystander effects in vitro using PC12 cells, primary cultures, and organotypic cultures of adult hippocampal slices. MABs-NGF-conditioned medium induced differentiation of PC12 cells, while MABs-BDNF-conditioned medium increased viability of cultured neurons and slices. Slices cultured with MABs-BDNF medium also better retained their morphology and functional connections, and all these effects were abolished by the TrkB kinase blocker K252a or the BDNF scavenger TrkB-IgG. Interestingly, the amount of BDNF released by MABs-BDNF produced greater effects than an identical amount of recombinant BDNF, suggesting that other NTFs produced by MABs synergize with BDNF. Thus, MABs can be an effective vehicle for NTF delivery, promoting differentiation, survival, and functionality of neurons. In summary, MABs hold distinct advantages over other currently evaluated approaches for NTF delivery in the CNS, including synergy of MAB-produced NTF with the neurotrophins. Since MABs may be capable of homing into damaged brain areas, they represent a conceptually novel, promising therapeutic approach to treat neurodegenerative diseases.

Evaluation of cell damage in organotypic hippocampal slice culture from adult mouse: a potential model system to study neuroprotection

The use of organotypic hippocampal slice culture (OHSC) has become a powerful tool for studying cell damage in different neuropathological states, since it reproduces the basic morphological and functional properties of hippocampal neuronal network. However, the conventional OHSCs are established from postnatal animals rather than adult. Here we reevaluated the features of cell death in adult OHSC in detail and found potential utility for the study of neuroprotection. Organotypic culture of hippocampal slices from adult mice under conventional conditions led to a time-dependent and reproducible cell death. Around 6days in vitro (DIV), slices lost 50% of the cells, based on LDH release assessment. The cell death was greater than 90% after DIV 15. The cell loss was linearly correlated (r=0.944, P<0.01) with the time in culture. The electrophysiological responses to the stimulus in the cultured adult slices were accordingly reduced. The cell degeneration during adult OHSC might be utilized as a tool for studying neuroprotective effects in drug development. To illustrate this potential use, adult OHSCs were challenged with brain-derived neurotrophic factor (BDNF). We found that the continuous supplementation of 300ng/ml BDNF promoted cell survival of adult OHSC. Using immunohistochemistry and Western blot analyses of neuronal markers, we also demonstrated the pro-survival effects of BDNF on neurons in the adult OHSC system. It is suggested that OHSCs from adult mice might provide an alternative model system for neuronal degeneration, suitable for studying physiological factors and pharmacological compounds contributing to neuronal survival.

Fibroblast growth factor-2 deficiency causes defects in adult hippocampal neurogenesis, which are not rescued by exogenous fibroblast growth factor-2

Neurogenesis within the adult brain is restricted to selected areas, one of which is the dentate gyrus (DG). Several growth factors have been reported to affect neurogenesis in the adult DG. However, a role of fibroblast growth factor-2 (FGF-2) in adult hippocampal neurogenesis has not been firmly established. We have analyzed neurogenesis in the DG using in vivo and in vitro approaches. FGF-2(-/-) mice revealed no alterations in the number of proliferating cells but a significant decrease in the numbers of newly generated neurons. Moreover, FGF-2 added to hippocampal slice cultures from FGF-2(-/-) mice was unable to rescue the phenotype. Although an increase in death of neurogenic cells in the FGF-2-deficient DG could not be specifically demonstrated, there was a massive increase in global cell death in FGF-2(-/-) hippocampal slice cultures compared with slices from wild-type mice. Cell death could not be prevented by addition of FGF-2. Neutralization of endogenous FGF-2 in hippocampal slices did not interfere with neurogenesis in a short-term paradigm. Together, our data suggest that FGF-2 is essentially required for maturation of new neurons in adult hippocampal neurogenesis but is likely to operate synergistically in combination with other mechanisms/growth factors.

Stem cell review series: role of neurogenesis in age-related memory disorders

Neuroplasticity is characterized by growth and branching of dendrites, remodeling of synaptic contacts, and neurogenesis, thus allowing the brain to adapt to changes over time. It is maintained in adulthood but strongly repressed during aging. An age-related decline in neurogenesis is particularly pronounced in the two adult neurogenic areas, the subventricular zone and the dentate gyrus. This age-related decline seems to be attributable mainly to limited proliferation, associated with an age-dependent increase in quiescence and/or a lengthening of the cell cycle, and is closely dependent on environmental changes. Indeed, when triggered by appropriate signals, neurogenesis can be reactivated in senescent brains, thus confirming the idea that the age-related decrease in new neuron production is not an irreversible, cell-intrinsic process. The coevolution of neurogenesis and age-related memory deficits--especially regarding spatial memory--during senescence supports the idea that new neurons in the adult brain participate in memory processing, and that a reduction in the ability to generate new neurons contributes to the appearance of memory deficits with advanced age. Furthermore, the age-related changes in hippocampal plasticity and function are under environmental influences that can favor successful or pathological aging. A better understanding of the mechanisms that regulate neurogenesis is necessary to develop new therapeutic tools to cure or prevent the development of memory disorders that may appear during the course of aging in some individuals.

Enhanced production and dendritic growth of new dentate granule cells in the middle-aged hippocampus following intracerebroventricular FGF-2 infusions

Declined production and diminished dendritic growth of new dentate granule cells in the middle-aged and aged hippocampus are correlated with diminished concentration of fibroblast growth factor-2 (FGF-2). This study examined whether increased FGF-2 concentration in the milieu boosts both production and dendritic growth of new dentate granule cells in the middle-aged hippocampus. The FGF-2 or vehicle was infused into the posterior lateral ventricle of middle-aged Fischer (F)344 rats for 2 weeks using osmotic minipumps. New cells born during the first 12 days of infusions were labeled via daily intraperitoneal injections of 5'-bromodeoxyuridine (BrdU) and analysed at 10 days after the last BrdU injection. Measurement of BrdU(+) cells revealed a considerably enhanced number of new cells in the subgranular zone (SGZ) and granule cell layer (GCL) of the dentate gyrus (DG) ipsilateral to FGF-2 infusions. Characterization of beta-III tubulin(+) neurons among newly born cells suggested an increased addition of new neurons to the SGZ/GCL ipsilateral to FGF-2 infusions. Quantification of DG neurogenesis at 8 days post-infusions via doublecortin (DCX) immunostaining also revealed the presence of an enhanced DG neurogenesis ipsilateral to FGF-2 infusions. Furthermore, DCX(+) neurons in FGF-2-infused rats exhibited enhanced dendritic growth compared with their counterparts in vehicle-infused rats. Thus, subchronic infusion of FGF-2 is efficacious for stimulating an enhanced DG neurogenesis from neural stem/progenitor cells in the middle-aged hippocampus. As dentate neurogenesis is important for hippocampal-dependent learning and memory and DG long-term potentiation, strategies that maintain increased FGF-2 concentration during ageing may be beneficial for thwarting some of the age-related cognitive impairments.

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.

Silencing urokinase in the ventral tegmental area in vivo induces changes in cocaine-induced hyperlocomotion

Serine proteases in the nervous system have functional roles in neural plasticity. Among them, urokinase-type plasminogen activator (uPA) exerts a variety of functions during development, and is involved in learning and memory. Furthermore, psychostimulants strongly induce uPA expression in the mesolimbic dopaminergic pathway. In this study, doxycycline-regulatable lentiviruses expressing either uPA, a dominant-negative form of uPA, or non-regulatable lentiviruses expressing small interfering RNAs (siRNAs) targeted against uPA have been prepared and injected into the ventral tegmental area (VTA) of rat brains. Over-expression of uPA in the VTA induces doxycycline-dependent expression of its receptor, uPAR, but not its inhibitor, plasminogen activator inhibitor-1 (PAI-1). uPAR expression in the VTA is repressed upon silencing of uPA with lentiviruses expressing siRNAs. In addition, over-expression of uPA in the VTA promotes a 15-fold increase in locomotion activity upon cocaine delivery. Animals expressing the dominant-negative form of uPA did not display such hyperlocomotor activity. These cocaine-induced behavioural changes, associated with uPA expression, could be suppressed in the presence of doxycycline or uPA-specific siRNAs expressing lentiviruses. These data strongly support the major role of urokinase in cocaine-mediated plasticity changes.

Basic fibroblast growth factor and fibroblast growth factor receptor-1 in the human hippocampal formation

Basic fibroblast growth factor (bFGF) is an important mitogen and neurotrophic factor that binds and signals through the high-affinity receptor, fibroblast growth factor receptor 1 (FGFR1). However, only a limited amount of information is available concerning the molecular forms and anatomical distribution of fibroblast growth factors (FGFs) in the normal human brain. We found multiple bFGF and FGFR1 mRNA transcripts which vary in expression pattern across human brain regions. Using in situ hybridization and immunohistochemistry, we localized bFGF and FGFR1 mRNA and protein to cells in the normal adult human hippocampus and caudal entorhinal cortex (ERC). The majority of pyramidal neurons contained FGFR1 mRNA and protein in the mesial temporal lobe, with neurons in the CA2/CA3 region demonstrating the highest levels of FGFR1 mRNA. In contrast to FGFR1, bFGF mRNA expression was detected at very low levels in a small fraction of the neurons in the human hippocampus and caudal ERC. While bFGF mRNA may be expressed at low levels in neurons, bFGF-immunopositive cells with astrocytic features were detected throughout the mesial temporal lobe in rats, monkeys and humans. bFGF immunoreactive processes are found traversing the dentate gyrus, and bFGF immunoreactive cells are found in the neurogenic subgranular zone in all three mammalian species studied. The anatomical distribution of these two FGF family members suggests that bFGF is endogenously positioned to be involved in ongoing neurogenesis in the adult hippocampus, and that FGF trophic signaling to differentiated neurons could involve the release of astrocytic bFGF acting on neuronal FGFR1 in the normal adult human hippocampus.

Time-dependent increase in basic fibroblast growth factor protein in limbic regions following electroshock seizures

Brief experimentally induced seizures have been shown to increase the expression of mRNA encoding basic fibroblast growth factor (FGF-2) in specific brain regions. However, the extent to which this change in mRNA affects the expression of FGF-2 protein in these brain regions has not been examined. In the present study, we exposed rats to brief non-injurious seizures to determine whether this treatment would lead to an increase in FGF-2 protein expression in selected brain regions. Because initial results indicated that the elevation of FGF-2 protein was not significant following acute seizure exposure, we examined both acute and chronic seizure treatment to determine whether FGF-2 protein expression could be increased under conditions of repeated seizures. Brief limbic seizures were induced by minimal electroconvulsive shock (ECS) given as daily treatments for 1 (acute) or 7 (chronic) days. FGF-2 protein was measured in hippocampus, rhinal cortex, frontal cortex, and olfactory bulb at 20, 48, and 72 h following the last seizure. No significant increases in FGF-2 protein were observed in any region following acute ECS. In the chronic ECS-treated groups, significantly elevated FGF-2-like immunoreactivity was found in the frontal and rhinal cortex as compared with the same regions from both control and acute ECS animals. Increases after chronic ECS were maximal at 20 h, and remained significantly elevated as long as 72 h. These increases were predominantly observed for the 24-kDa and 22/22.5-kDa FGF-2 isoforms. Because chronic ECS, which has been shown to be protective against neuronal cell death, induced significantly more FGF-2 immunoreactivity than did acute ECS, we suggest that FGF-2 expression may be an important substrate for the neuroprotective action of non-injurious seizures. A prolonged induction of the high molecular weight isoforms of FGF-2, as occurs after chronic ECS, may selectively reduce the vulnerability of certain brain regions to a variety of neurodegenerative insults.

Brain-derived neurotrophic factor promotes the maturation of GABAergic mechanisms in cultured hippocampal neurons

Brain-derived neurotrophic factor (BDNF) has been implicated in activity-dependent plasticity of neuronal function and network arrangement. To clarify how BDNF exerts its action, we evaluated the physiological, histological, and biochemical characteristics of cultured hippocampal neurons after long-term treatment with BDNF. Here we show that BDNF facilitates high K(+)-elicited release of GABA but not of glutamate and induces an increase in immunoreactive signals of glutamic acid decarboxylase, a GABA-synthesizing enzyme. The soma size of GABAergic neurons was enlarged in BDNF-treated cultures, whereas the average soma size of all neurons was virtually unchanged. BDNF also upregulated protein levels of GABA(A) receptors but not of glutamate receptors. These data imply that BDNF selectively advances the maturation of GABAergic synapses. However, immunocytochemical analyses revealed that a significant expression of TrkB, a high-affinity receptor for BDNF, was detected in non-GABAergic as well as GABAergic neurons. BDNF also increased to total amount of synaptic vesicle-associated proteins without affecting the number of presynaptic vesicles that can be labeled with FM1-43 after K(+) depolarization. Together, our findings indicate that BDNF principally promotes GABAergic maturation but may also potentially contribute to excitatory synapse development via increasing resting synaptic vesicles.

Polysaccharide Krestin enhances manganese superoxide dismutase activity and mRNA expression in mouse peritoneal macrophages

Manganese superoxide dismutase (MnSOD), an inductive antioxidant enzyme, can protect cells from oxidative injury to the mitochondria. The elevation of MnSOD activity in cells can effectively prevent many diseases associated with oxidative stress. Polysaccharide Krestin (PSK), a kind of protein-bound polysaccharide extracted from Coriolus versicolor, is used as an immune response modifier in anti-tumor therapy. We have previously found that PSK could alleviate the oxidative injury that oxidized low density lipoprotein (Ox-LDL) brought to monocytes/macrophages, and therefore had some preventive or therapeutic effect on atherosclerosis. In order to find out if the effects of PSK were associated with the alteration ofantioxidant enzymes, we investigated its effect on MnSOD activity and gene expression in mouse peritoneal macrophages. The results showed that PSK could enhance SOD activity and increase the contents ofMnSOD mRNA in mouse peritoneal macrophages. Furthermore, the induction of MnSOD by PSK could be blocked by cycloheximide and actinomycin D.

HSV-1 Vector-Delivered FGF2 to the Retina Is Neuroprotective but Does Not Preserve Functional Responses

Fibroblast growth factor 2 (bFGF, FGF2) exhibits mitogenic, angiogenic, wound healing, and neuroprotective properties. Infusion of FGF2 in vivo to treat neurodegenerative disorders in animal models results in increased survival of damaged neurons, but these effects are transient. To test the feasibility of HSV vector-delivered FGF2 for neuroprotection, we inserted the FGF2 gene under the control of the HCMV immediate-early promoter into an attenuated avirulent HSV-1 vector. Transduction with FGF2/HSV-1 virus promoted survival of PC12 cells, induced differentiation of these cells to the neuronal phenotype in vitro, and protected PC12 neuronal cells from death induced by nerve growth factor withdrawal. The attenuated FGF2/HSV-1 virus was able to deliver and direct expression of the FGF2 gene in the eye. Delivery prior to light exposure in a rat model of retinal degeneration resulted in significant protection against photoreceptor loss. However, functional ERG responses were not detected. Treatment of normal eyes with the vector alone suppressed ERGs, which were only partially restored in eyes receiving the FGF2 vector. Thus, although the FGF2-HSV-1 virus induced preservation of cell and tissue structure, this was not sufficient to protect photoreceptor function.

Effects of basic fibroblast growth factor on central nervous system functions

Basic fibroblast growth factor (bFGF), initially identified as mitogens with prominent angiogenic properties, is now recognized as multifunctional growth factors with notable actions on neuronal cells. bFGF promotes the survival and neurite growth of brain neurons in vitro and in vivo, suggesting that it functions as a neurotrophic factor. This effect of bFGF could be beneficial for improving the survival of grafted neurons in transplantation. Furthermore, bFGF acutely modulates synaptic transmission in the hippocampus, suggesting that it has a role like a neurotransmitter or neuromodulator. In this article, we make a brief review of multiple biological activities of bFGF for brain neurons and discuss its potential usefulness for the treatment of neurodegenerative disorders including Alzheimer's disease and Parkinson's disease.

Extracellular ATP reduces optically monitored electrical signals in hippocampal slices through metabolism to adenosine

Electrical signals in rat hippocampal slices were optically monitored using a voltage-sensitive dye to determine whether extracellular ATP exhibits direct effects through its own receptors or indirect effects after its hydrolysis to adenosine. The dentate gyrus was stimulated and electrical signals in the CA1 and the CA3 region were analyzed. The signals were divided into two components: a transient component peaking within 10 ms (fast component) and a subsequent sustained component (slow component). ATP (10 to 100 microM) inhibited both the fast and the slow components in the CA1 region by about 30% and 70%, respectively. ADP, AMP and adenosine also inhibited the fast and the slow components. The inhibition by ATP was antagonized by aminophylline and other adenosine receptor antagonists, and by alpha,beta-methylene ADP, an inhibitor of 5'-nucleotidases. These results suggest that extracellular ATP inhibits neuronal electrical signals in hippocampal slices after its metabolism to adenosine.

Laminin degradation by plasmin regulates long-term potentiation

Plasmin is converted from its zymogen plasminogen by tissue type or urokinase type plasminogen activator (PA) and degrades many components of the extracellular matrix (ECM). To explore the possibility that the PA-plasmin system regulates synaptic plasticity, we investigated the effect of plasmin on degradation of ECM and synaptic plasticity by using organotypic hippocampal cultures. High-frequency stimulation produced long-term potentiation (LTP) in control slices, whereas the potentiation was induced but not maintained in slices pretreated with 100 nM plasmin for 6 hr. The baseline synaptic responses were not affected by pretreatment with plasmin. The impairment of LTP maintenance was not observed in slices pretreated with 100 nM plasmin for 6 hr, washed, and then cultured for 24-48 hr in the absence of plasmin. To identify substrates of plasmin, the expression of three major components of ECM, laminin, fibronectin, and type IV collagen, was investigated by immunofluorescence imaging. The three ECM components were widely distributed in the hippocampus, and only laminin was degraded by plasmin pretreatment. The expression level of laminin returned to normal levels when the slices were cultured for 24-48 hr after washout of plasmin. Furthermore, preincubation with anti-laminin antibodies prevented both the degradation of laminin and the impairment of LTP maintenance by plasmin. These results suggest that the laminin-mediated cell-ECM interaction may be necessary for the maintenance of LTP.

Abnormal targeting of developing hippocampal mossy fibers after epileptiform activities via L-type Ca2+ channel activation in vitro

The hippocampal mossy fibers, which originate from the dentate granule cells, develop mainly in the early postnatal period and are involved in numerous pathological processes. In this study, hippocampal slices prepared from premature rats were cultivated in the presence of convulsants to evaluate the influences of epileptiform activities on mossy fiber ontogeny. Electrophysiological and histochemical analyses revealed that prolonged hyperexcitability inhibited proper growth of the mossy fibers and caused ectopic innervation to the stratum oriens and the dentate molecular layer. These phenomena were prevented by pharmacological blockade of L-type Ca2+ channels, which did not affect convulsant-evoked ictal bursts. After single-pulse stimulation of the stratum granulosum in the slices cultured under paroxysmal conditions, the dentate gyrus displayed excessive excitation, but synaptic transmission to the CA3 region was hypoactive. However, brief repetitive stimulation elicited delayed epileptiform discharges in the CA3 region that were inhibited by an NMDA receptor antagonist. Chronic treatment with an L-type Ca2+ channel blocker ameliorated such aberrant neurotransmissions. These results suggest that ictal neuron activities at the developmental stage of the mossy fibers bring about the errant maturation associated with hippocampal dysfunction, which may form a cellular basis for the sequelae of childhood epilepsy, including chronic epilepsy or cognitive deficits. Thus I propose that L-type Ca2+ channel blockers can ameliorate the aversive prognosis of childhood epilepsy.

Markers for neuronal degeneration in organotypic slice cultures

This protocol describes ways of monitoring spontaneous or induced neuronal degeneration in organotypic brain slice cultures. Hippocampal cultures (4-week-old) are grown in normal serum-free control medium, or exposed to the neurotoxin trimethyltin (TMT) (0.5-100 microM) for 24 h or the excitotoxic glutamate agonist kainic acid (KA) (5-25 microM) for 48 h followed by 24 h or 48 h, respectively, in normal medium. Corticostriatal slice cultures (also 4-week-old) are exposed to KA (6-24 microM) for 48 h and normal medium for control. The resulting neurodegeneration is estimated by (a) propidium iodide (PI) uptake, (b) lactate dehydrogenase (LDH) efflux to the culture medium, (c) ordinary Nissl cell staining, (d) staining by the neurodegenerative marker Fluoro-Jade (FJ), (e) neuronal microtubule degeneration by immunohistochemical staining for microtubule-associated protein 2 (MAP2), and (f) Timm sulphide silver staining for heavy metal alterations. Both hippocampal and corticostriatal slice cultures show a dose- and time-dependent increase in PI uptake and LDH efflux after exposure to TMT and KA. The mean PI uptake and the LDH efflux into the medium correlate well for both types of cultures. Both TMT and KA exposed hippocampal cultures display in vivo patterns of differential neuronal vulnerability as evidenced by PI uptake, FJ staining and MAP2 immunostaining. Corticostriatal slice cultures exposed to a high dose of KA display extensive striatal and cortical degeneration in FJ staining as suggested by a high PI uptake. A change in Timm sulphide silver staining in deep central parts of some control cultures, corresponds to areas with loss of cells in cell staining, loss of MAP2 staining, PI uptake, and FJ staining. We conclude that organotypic brain slice cultures, in combination with appropriate markers in standardized protocols, represent feasible means for studies of excitotoxic and neurotoxic compounds.