Astroglia-neuron interactions that promote long-term neuronal survival

The cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) targets the olfactory bulb region

Olfactory dysfunction is implicated in neurodegenerative disorders and typically manifests years before other symptoms. The cyanobacterial neurotoxin β-N-methylamino-l-alanine (BMAA) is suggested as a risk factor for neurodegenerative disease. Detection of BMAA in air filters has increased the concern that aerosolization may lead to human BMAA exposure through the air. The aim of this study was to determine if BMAA targets the olfactory system. Autoradiographic imaging showed a distinct localization of radioactivity in the right olfactory mucosa and bulb following a unilateral intranasal instillation of ³H-BMAA (0.018 µg) in mice, demonstrating a direct transfer of BMAA via the olfactory pathways to the brain circumventing the blood–brain barrier, which was confirmed by liquid scintillation. Treatment of mouse primary olfactory bulb cells with 100 µM BMAA for 24 h caused a disruption of the neurite network, formation of dendritic varicosities and reduced cell viability. The NMDA receptor antagonist MK-801 and the metabotropic glutamate receptor antagonist MCPG protected against the BMAA-induced alterations, demonstrating the importance of glutamatergic mechanisms. The ionotropic non-NMDA receptor antagonist CNQX prevented the BMAA-induced decrease of cell viability in mixed cultures containing both neuronal and glial cells, but not in cultures with neurons only, suggesting a role of neuron–glial interactions and glial AMPA receptors in the BMAA-induced toxicity. The results show that the olfactory region may be a target for BMAA following inhalation exposure. Further studies on the relations between environmental olfactory toxicants and neurodegenerative disorders are warranted.

Pharmacological Suppression of CNS Scarring by Deferoxamine Reduces Lesion Volume and Increases Regeneration in an In Vitro Model for Astroglial-Fibrotic Scarring and in Rat Spinal Cord Injury In Vivo

Lesion-induced scarring is a major impediment for regeneration of injured axons in the central nervous system (CNS). The collagen-rich glial-fibrous scar contains numerous axon growth inhibitory factors forming a regeneration-barrier for axons. We demonstrated previously that the combination of the iron chelator 2,2’-bipyridine-5,5’-decarboxylic acid (BPY-DCA) and 8-Br-cyclic AMP (cAMP) inhibits scar formation and collagen deposition, leading to enhanced axon regeneration and partial functional recovery after spinal cord injury. While BPY-DCA is not a clinical drug, the clinically approved iron chelator deferoxamine mesylate (DFO) may be a suitable alternative for anti-scarring treatment (AST). In order to prove the scar-suppressing efficacy of DFO we modified a recently published in vitro model for CNS scarring. The model comprises a co-culture system of cerebral astrocytes and meningeal fibroblasts, which form scar-like clusters when stimulated with transforming growth factor-β (TGF-β). We studied the mechanisms of TGF-β-induced CNS scarring and compared the efficiency of different putative pharmacological scar-reducing treatments, including BPY-DCA, DFO and cAMP as well as combinations thereof. We observed modulation of TGF-β-induced scarring at the level of fibroblast proliferation and contraction as well as specific changes in the expression of extracellular matrix molecules and axon growth inhibitory proteins. The individual and combinatorial pharmacological treatments had distinct effects on the cellular and molecular aspects of in vitro scarring. DFO could be identified as a putative anti-scarring treatment for CNS trauma. We subsequently validated this by local application of DFO to a dorsal hemisection in the rat thoracic spinal cord. DFO treatment led to significant reduction of scarring, slightly increased regeneration of corticospinal tract as well as ascending CGRP-positive axons and moderately improved locomotion. We conclude that the in vitro model for CNS scarring is suitable for efficient pre-screening and identification of putative scar-suppressing agents prior to in vivo application and validation, thus saving costs, time and laboratory animals.

Interaction of electrically evoked activity with intrinsic dynamics of cultured cortical networks with and without functional fast GABAergic synaptic transmission

The modulation of neuronal activity by means of electrical stimulation is a successful therapeutic approach for patients suffering from a variety of central nervous system disorders. Prototypic networks formed by cultured cortical neurons represent an important model system to gain general insights in the input–output relationships of neuronal tissue. These networks undergo a multitude of developmental changes during their maturation, such as the excitatory–inhibitory shift of the neurotransmitter GABA. Very few studies have addressed how the output properties to a given stimulus change with ongoing development. Here, we investigate input–output relationships of cultured cortical networks by probing cultures with and without functional GABA_Aergic synaptic transmission with a set of stimulation paradigms at various stages of maturation. On the cellular level, low stimulation rates (<15 Hz) led to reliable neuronal responses; higher rates were increasingly ineffective. Similarly, on the network level, lowest stimulation rates (<0.1 Hz) lead to maximal output rates at all ages, indicating a network wide refractory period after each stimulus. In cultures aged 3 weeks and older, a gradual recovery of the network excitability within tens of milliseconds was in contrast to an abrupt recovery after about 5 s in cultures with absent GABA_Aergic synaptic transmission. In these GABA deficient cultures evoked responses were prolonged and had multiple discharges. Furthermore, the network excitability changed periodically, with a very slow spontaneous change of the overall network activity in the minute range, which was not observed in cultures with absent GABA_Aergic synaptic transmission. The electrically evoked activity of cultured cortical networks, therefore, is governed by at least two potentially interacting mechanisms: A refractory period in the order of a few seconds and a very slow GABA dependent oscillation of the network excitability.

Characterization of Regenerative Phenotype of Unrestricted Somatic Stem Cells (USSC) from Human Umbilical Cord Blood (hUCB) by Functional Secretome Analysis

Stem cell transplantation is a promising therapeutic strategy to enhance axonal regeneration after spinal cord injury. Unrestricted somatic stem cells (USSC) isolated from human umbilical cord blood is an attractive stem cell population available at GMP grade without any ethical concerns. It has been shown that USSC transplantation into acute injured rat spinal cords leads to axonal regrowth and significant locomotor recovery, yet lacking cell replacement. Instead, USSC secrete trophic factors enhancing neurite growth of primary cortical neurons in vitro. Here, we applied a functional secretome approach characterizing proteins secreted by USSC for the first time and validated candidate neurite growth promoting factors using primary cortical neurons in vitro. By mass spectrometric analysis and exhaustive bioinformatic interrogation we identified 1156 proteins representing the secretome of USSC. Using Gene Ontology we revealed that USSC secretome contains proteins involved in a number of relevant biological processes of nerve regeneration such as cell adhesion, cell motion, blood vessel formation, cytoskeleton organization and extracellular matrix organization. We found for instance that 31 well-known neurite growth promoting factors like, e.g. neuronal growth regulator 1, NDNF, SPARC, and PEDF span the whole abundance range of USSC secretome. By the means of primary cortical neurons in vitro assays we verified SPARC and PEDF as significantly involved in USSC mediated neurite growth and therewith underline their role in improved locomotor recovery after transplantation. From our data we are convinced that USSC are a valuable tool in regenerative medicine as USSC's secretome contains a comprehensive network of trophic factors supporting nerve regeneration not only by a single process but also maintained its regenerative phenotype by a multitude of relevant biological processes.

Inhibition of the Jak-STAT pathway prevents CNTF-mediated survival of axotomized oxytocinergic magnocellular neurons in organotypic cultures of the rat supraoptic nucleus

Previous studies have demonstrated that ciliary neurotrophic factor (CNTF) enhances survival and process outgrowth from magnocellular neurons in the paraventricular (PVN) and the supraoptic (SON) nuclei. However, the mechanisms by which CNTF facilitates these processes remain to be determined. Therefore, the aim of this study was to identify the immediate signal transduction events that occur within the rat SON following administration of exogenous rat recombinant CNTF (rrCNTF) and to determine the contribution of those intracellular signaling pathway(s) to neuronal survival and process outgrowth, respectively. Immunohistochemical and Western blot analyses demonstrated that axonal injury and acute unilateral pressure injection of 100 ng/μl of rrCNTF directly over the rat SON resulted in a rapid and transient increase in phosphorylated-STAT3 (pSTAT3) in astrocytes but not neurons in the SON in vivo. Utilizing rat hypothalamic organotypic explant cultures, we then demonstrated that administration of 25 ng/ml rrCNTF for 14days significantly increased the survival and process outgrowth of OT magnocellular neurons. In addition, pharmacological inhibition of the Jak-STAT pathway via AG490 and cucurbitacin I significantly reduced the survival of OT magnocellular neurons in the SON and PVN; however, the contribution of the Jak-STAT pathway to CNTF-mediated process outgrowth remains to be determined. Together, these data indicate that CNTF-induced survival of OT magnocellular neurons is mediated indirectly through astrocytes via the Jak-STAT signaling pathway.

Phenotype, differentiation, and function differ in rat and mouse neocortical astrocytes cultured under the same conditions

The study of slowly progressing brain diseases in which glial cells play a pathogenic role requires astrocytes that have been cultured for several weeks. We characterized neocortical astrocytes, grown for up to 42 days in vitro (DIV), from newborn rats and mice by indirect immunofluorescence technique, Western blot, and real-time RT-PCR analyses. We obtained highly enriched rat and mouse astrocyte cultures, where most cells were positively stained for the astrocyte markers GFAP, vimentin, and S100β, whereas neuronal and oligodendrocyte markers were undetectable. The protein and mRNA levels of GFAP, vimentin, and nestin were higher in rat than in mouse astrocytes. From 28 to 42 DIV, the levels of vimentin and nestin, but not of GFAP, decreased in both species, with an increase in the vimentin-GFAP ratio of 1.7 for rat, and of 0.9 for mouse astrocytes suggesting that the rat cultures were more differentiated than the mouse cultures, although both remained partially immature. The protoplasmic appearance of the cells, the negative A2B5 immunoreactivity, and the expression of the glutamate transporters GLAST and GLT-1 indicate that the rat and mouse cultures contained mainly type I astrocytes. The protein levels of GLAST and GLT-1 decreased from 28 to 42 DIV in the mouse, but not in the rat astrocytes, suggesting that the rat cultures are suitable for functional studies. Thus, under the same culture conditions, astrocyte cultures from rats and mice differ in phenotype, differentiation, and functionality. This finding should be taken into account when long-lasting glial reaction patterns are being studied.

Immunomodulatory influence of bone marrow-derived mesenchymal stem cells on neuroinflammation in astrocyte cultures

The therapeutic benefits associated with mesenchymal stem cells (MSCs) largely result from their immunomodulatory and neurotrophic properties. In this study, we evaluated the effects of MSCs on astrocyte cultures exposed to lipopolysaccharide. In response to this inflammatory trigger, astrocytes showed an increased expression of pro-inflammatory genes (IL-1β, TNFα, IL-6), which was attenuated by pre-exposure to MSC conditioned medium. Furthermore, mediators released by MSCs increased cell proliferation and altered the regulation of intermediate filaments (GFAP, vimentin), pro-inflammatory enzymes (iNOS, COX-2) and receptors (TLR4, CD14, mGluR3, mGluR5). These data demonstrate that MSCs influence diverse cell types participating in the response to neuroinflammation.

Significant clinical, neuropathological and behavioural recovery from acute spinal cord trauma by transplantation of a well-defined somatic stem cell from human umbilical cord blood

Stem cell therapy is a potential treatment for spinal cord injury and different stem cell types have been grafted into animal models and humans suffering from spinal trauma. Due to inconsistent results, it is still an important and clinically relevant question which stem cell type will prove to be therapeutically effective. Thus far, stem cells of human sources grafted into spinal cord mostly included barely defined heterogeneous mesenchymal stem cell populations derived from bone marrow or umbilical cord blood. Here, we have transplanted a well-defined unrestricted somatic stem cell isolated from human umbilical cord blood into an acute traumatic spinal cord injury of adult immune suppressed rat. Grafting of unrestricted somatic stem cells into the vicinity of a dorsal hemisection injury at thoracic level eight resulted in hepatocyte growth factor-directed migration and accumulation within the lesion area, reduction in lesion size and augmented tissue sparing, enhanced axon regrowth and significant functional locomotor improvement as revealed by three behavioural tasks (open field Basso-Beattie-Bresnahan locomotor score, horizontal ladder walking test and CatWalk gait analysis). To accomplish the beneficial effects, neither neural differentiation nor long-lasting persistence of the grafted human stem cells appears to be required. The secretion of neurite outgrowth-promoting factors in vitro further suggests a paracrine function of unrestricted somatic stem cells in spinal cord injury. Given the highly supportive functional characteristics in spinal cord injury, production in virtually unlimited quantities at GMP grade and lack of ethical concerns, unrestricted somatic stem cells appear to be a highly suitable human stem cell source for clinical application in central nervous system injuries.

Slow oscillating population activity in developing cortical networks: models and experimental results

During early development neuronal networks express slow oscillating synchronized activity. The activity can be driven by several, not necessarily mutually exclusive, mechanisms. Each mechanism might have distinctive consequences for the phenomenology, formation, or sustainment of the early activity pattern. Here we study the emergence of the oscillatory activity in three computational models and multisite extracellular recordings that we obtained from developing cortical networks in vitro. The modeled networks consist of leaky integrate-and-fire neurons with adaptation coupled via depressing synapses, which were driven by neurons that are intrinsically bursting, intrinsically random spiking, or driven by spontaneous synaptic activity. The activity of model networks driven by intrinsically bursting cells best matched the phenomenology of 1-wk-old cultures, in which early oscillatory activity has just begun. Intrinsically bursting neurons were present in cortical cultures, but we found them only in those cultures that were younger than 3 wk in vitro. On the other hand, synaptically dependent random spiking was highest after 3 wk in vitro. In conclusion, model networks driven by intrinsically bursting cells show a good approximation of the emergent recurrent population activity in young networks, whereas the activity of more mature networks seems to be better explained by spontaneous synaptic activity. Moreover, similar to previous experimental observations, distributed stimulation in the model was more effective in suppressing population bursts than repeated stimulation of the same neurons. This observation can be explained by an effective depression of a larger fraction of synapses by distributed stimulation.

Contribution of GABAergic interneurons to the development of spontaneous activity patterns in cultured neocortical networks

Periodic synchronized events are a hallmark feature of developing neuronal networks and are assumed to be crucial for the maturation of the neuronal circuitry. In the developing neocortex, the early network oscillations coincide with an excitatory action of the neurotransmitter gamma-aminobutyric acid (GABA). A relationship between the emerging inhibitory action of GABA and the gradual disappearance of early synchronized network activity has been previously suggested. Therefore we investigate the interplay between the action of GABA and spontaneous activity in cultured networks of the lateral or dorsal embryonic rat neocortex, which show considerable difference in the content of GABAergic neurons. Here we present the results of long-term monitoring of spontaneous electrical activity of cultured networks growing on microelectrode arrays and the time course of changes in GABA action using calcium imaging. All cultures studied displayed stereotyped synchronized burst events at the end of the first week in vitro. As the GABA_A depolarizing action decreases, naturally or after bumetanide treatment, network activity in lateral cortex cultures changed from stereotypic bursting to more clustered and asynchronous activity patterns. Dorsal cortex cultures and cultures lacking GABA_A-receptor mediated synaptic transmission, retained an immature synchronous firing pattern, but developed prominent intraburst oscillations (∼3–10 Hz). Large, mostly parvalbumin positive, GABAergic neurons dominate the GABAergic population in lateral cortex cultures. These large interneurons were virtually absent in dorsal cortex cultures. Based on these results, we suggest that the richly interconnected large GABAergic neurons contribute to desynchronize and temporally differentiate the spontaneous activity of cultured cortical networks.

Neurotoxicant-induced inflammatory response in three-dimensional brain cell cultures

Brain inflammatory response is triggered by the activation of microglial cells and astrocytes in response to various types of CNS injury, including neurotoxic insults. Its outcome is determined by cellular interactions, inflammatory mediators, as well as trophic and/or cytotoxic signals, and depends on many additional factors such as the intensity and duration of the insult, the extent of both the primary neuronal damage and glial reactivity and the developmental stage of the brain. Depending on particular circumstances, the brain inflammatory response can promote neuroprotection, regeneration or neurodegeneration. Glial reactivity, regarded as the central phenomenon of brain inflammation, has also been used as an early marker of neurotoxicity. To study the mechanisms underlying the glial reactivity, serum-free aggregating brain cell cultures were used as an in vitro model to test the effects of conventional neurotoxicants such as organophosphate pesticides, heavy metals, excitotoxins and mycotoxins. This approach was found to be relevant and justified by the complex cell-cell interactions involved in the brain inflammatory response, the variability of the glial reactions and the multitude of mediators involved. All these variables need to be considered for the elucidation of the specific cellular and molecular reactions and their consequences caused by a given chemical insult.

Inflammatory cytokines induce protein tyrosine nitration in rat astrocytes

Protein tyrosine nitration may be relevant for the pathogenesis of hepatic encephalopathy (HE). Infections, sepsis, and trauma precipitate HE episodes. Recently, serum levels of tumor necrosis factor (TNF)-alpha were shown to correlate with severity of HE in chronic liver failure. Here the effects of inflammatory cytokines on protein tyrosine nitration in cultured rat astrocytes and rat brain in vivo were studied. In cultured rat astrocytes TNF-alpha (50 pg/ml-10 ng/ml) within 6h increased protein tyrosine nitration. TNF-alpha-induced tyrosine nitration was related to an increased formation of reactive oxygen and nitrogen intermediates, which was downstream from a NMDA-receptor-dependent increase of intracellular [Ca(2+)](i) and nNOS-catalyzed NO production. Astroglial tyrosine nitration was also elevated in brains of rats receiving a non-lethal injection of lipopolysaccharide, as indicated by colocalization of nitrotyrosine immunoreactivity with glial fibrillary acidic protein and glutamine synthetase, and by identification of the glutamine synthetase among the tyrosine-nitrated proteins. It is concluded that reactive oxygen and nitrogen intermediates as well as protein tyrosine nitration by inflammatory cytokines may alter astrocyte function in an NMDA-receptor-, Ca(2+)-, and NOS-dependent fashion. This may be relevant for the pathogenesis of HE and other conditions involving cytokine exposure the brain.

Age-related changes of structures in cerebellar cortex of cat

We studied the structures of the cerebellar cortex of young adult and old cats for age-related changes, which were statistically analysed. Nissl staining was used to visualize the cortical neurons. The immunohistochemical method was used to display glial fibrillary acidic protein (GFAP)-immunoreactive (IR) astrocytes and neurofilament-immunoreactive (NF-IR) neurons. Under the microscope, the thickness of the cerebellar cortex was measured; and the density of neurons in all the layers as well as that of GFAP-IR cells in the granular layer was analysed. Compared with young adult cats, the thickness of the molecular layer and total cerebellar cortex was significantly decreased in old cats, and that of the granular layer increased. The density of neurons in each layer was significantly lower in old cats than in young adult ones. Astrocytes in old cats were significantly denser than in young adult ones, and accom-panied by evident hypertrophy of the cell bodies and enhanced immunoreaction of GFAP substance. Purkinje cells (PCs) in old cats showed much fewer NF-IR dendrites than those in young adults. The above findings indicate a loss of neurons and decrease in the number of dendrites of the PCs in the aged cerebellar cortex, which might underlie the functional decline of afferent efficacy and information integration in the senescent cerebellum. An age-dependent enhancement of activity of the astrocytes may exert a protective effect on neurons in the aged cerebellum.

Neuronal network properties of human teratocarcinoma cell line-derived neurons

Understanding the structural and functional development of neurons in networks has a high impact to estimate the potentials for restorative therapies. Neurons derived from the human NT2 cell line (hNT) formed networks with a clustered neuritic architecture in vitro, whereas primary dissociated embryonic rat cortical neurons (Cx) displayed a more homogenous cell assembly. Spontaneous spikes of both cell types were recorded on microelectrode arrays within 2 weeks after seeding, but hNT showed a mostly uncorrelated firing pattern in contrast to Cx with highly synchronized bursting. hNT neurons were less sensitive to TTX (IC50 = 5.7 +/- 0.1 nM vs. IC50 = 1.1 +/- 0.2 nM), magnesium (IC50 = 1.83 +/- 0.01 mM vs. IC50 = 0.161 +/- 0.023 mM), and APV (IC50 > 100 microM vs. IC50 = 18 microM). We conclude that embryonic cortical neurons and hNT neurons have different network properties. This should be carefully considered before hNT neurons are used in therapeutic approaches, e g., central nervous system (CNS) grafting.

Protective role of melatonin in domoic acid-induced neuronal damage in the hippocampus of adult rats

Domoic acid (DA), a kainite-receptor agonist and potent inducer of neurotoxicity, has been administered intravenously in adult rats in the present study (0.75 mg/kg body weight) to demonstrate neuronal degeneration followed by glial activation and their involvement with inducible nitric oxide synthase (iNOS) in the hippocampus. An equal volume of normal saline was administered in control rats. The pineal hormone melatonin, which protects the neurons efficiently against excitotoxicity mediated by sensitive glutamate receptor, was administered intraperitoneally (10 mg/kg body weight), 20 min before, immediately after, and 1 h and 2 h after the DA administration, to demonstrate its role in therapeutic strategy. Histopathological analysis (Nissl staining) demonstrated extensive neuronal damage in the pyramidal neurons of CA1, CA3 subfields and hilus of the dentate gyrus (DG) in the hippocampus at 5 days after DA administration. Sparsely distributed glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were observed in the hippocampus at 4-24 h after DA administration and in the control rats. Astrogliosis was evidenced by increased GFAP immunoreactivity in the areas of severe neuronal degeneration at 5 days after DA administration. Along with this, microglial cells exhibited an intense immunoreaction with OX-42, indicating upregulation of complement type 3 receptors (CR3). Ultrastructural study revealed swollen or shrunken degenerating neurons in the CA1, CA3 subfields and hilus of the DG and hypertrophied astrocytes showing accumulation of intermediate filament bundles in the cytoplasm were observed after administration of DA. Although no significant change could be observed in the mRNA level of iNOS expression between the DA-treated rats and controls at 4-24 h and at 5-day time intervals, double immunofluorescense revealed co-expression of induced iNOS with GFAP immunoreactive astrocytes, but not in the microglial cells, and iNOS expression in the neurons of the hippocampal subfields at 5 days after DA administration. Expression of iNOS was not observed in the hippocampus of control rats. DA-induced neuronal death, glial activation, and iNOS protein expression were attenuated significantly by melatonin treatment and were comparable to the control groups. The results of the present study suggest that melatonin holds potential for the treatment of pathologies associated with DA-induced brain damage. It is speculated that astrogliosis and induction of iNOS protein expression in the neurons and astrocytes of the hippocampus may be in response to DA-induced neuronal degeneration.

A serum- and antioxidant-free primary culture model of mouse cortical neurons for pharmacological screen and studies of neurotrophic and neuroprotective agents

1. Morphologically developmental properties of fetal mouse cortical neurons in the chemically defined serum- and antioxidant-free culture condition were observed. Also, cellular composition in cultures was identified by immunostaining with anti-NSE and anti-GFAP. 2. Various cell densities ranging from 1 x 10(3) to 1 x 10(6) cells/cm2 were prepared to further assess the effect of cell density on time-course of neuronal survival by counting the number of remaining attached neurons after 3 and 7 days in culture. 3. Neuronal responses to neurotrophic effect of NGF on neurite outgrowth and neuroprotective effect of MK-801 against glutamate-induced excitotoxity were evaluated by image analysis and MTT assay, respectively. 4. Results showed that this culture system was neuronal-enriched with a neuronal lifetime more than 35 days. Neurons survived best when seeded at a density > or =1.5 x 10(5) cells/cm2. Cultured neurons were capable of exhibiting sensitive responses to the effects of NGF and MK-801. 5. These findings suggest that this primary culture system provides a sensitive and powerful in vitro model for pharmacological screen and studies of neurotrophic and neuroprotective agents.

Gene expression of neurotrophins and their high-affinity Trk receptors in cultured human Müller cells

PURPOSE

To investigate the gene expression of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3) and their high-affinity receptors (TrkA, TrkB and TrkC) in cultured human Müller cells.

METHODS

The polymerase chain reaction was performed using specific primers for NGF, BDNF, NT-3, TrkA, TrkB and TrkC with complementary DNAs as the template, which were generated from poly-A+ RNA of cultured human Müller cells.

RESULTS

We detected the precursor mRNA transcripts for NGF, BDNF, NT-3, TrkB and TrkC, but not TrkA.

CONCLUSION

Human Müller cells can direct mRNA expressions of a number of neurotrophins which may have a neurotrophic function in the retina. An autocrine mode of action is suggested, since Müller cells not only synthesize neurotrophic factors, but also express their specific receptors.

Astrocytes attenuate oligodendrocyte death in vitro through an alpha(6) integrin-laminin-dependent mechanism

Oligodendrocyte (OL) death occurs in many disorders of the CNS, including multiple sclerosis and brain trauma. Factors reported to induce OL death include deprivation of growth factors, elevation of cytokines, oxidative stress, and glutamate excitotoxicity. Because astrocytes produce a large amount of growth factors and antioxidants and are a major source of glutamate uptake, we tested the hypothesis that astrocytes may have a protective role for OL survival. We report that when OLs from the adult mouse brain were initiated into tissue culture, DNA fragmentation and chromatin condensation resulted, indicative of apoptosis. OL death was significantly reduced in coculture with astrocytes, but not with fibroblasts, which provided a similar monolayer of cells as astrocytes. The protection of OL demise by astrocytes was not reproduced by its conditioned medium and was not accounted for by several neurotrophic factors. In contrast, interference with the alpha(6) integrin subunit, but not the alpha(1), alpha(2), alpha(3), alpha(4), alpha(5), or alpha(v) integrin chains, negated astrocyte protection of OLs. Furthermore, a function-blocking antibody to alpha(6)beta(1) integrin reduced the ability of astrocytes to promote OL survival. The extracellular matrix ligand for alpha(6)beta(1) is laminin, which is expressed by astrocytes. Significantly, neutralizing antibodies to laminin-2 and laminin-5 inhibited the astrocyte mediation of OL survival. These results implicate astrocytes in promoting OL survival through a mechanism involving the interaction of alpha(6)beta(1) integrin on OLs with laminin on astrocytes. Enhancing this interaction may provide for OL survival in neurological injury.

Cyclic AMP increases the survival of ganglion cells in mixed retinal cell cultures in the absence of exogenous neurotrophic molecules, an effect that involves cholinergic activity

Natural cell death is a well-known degenerative phenomenon occurring during development of the nervous system. The role of trophic molecules produced by target and afferent cells as well as by glial cells has been extensively demonstrated. Literature data demonstrate that cAMP can modulate the survival of neuronal cells. Cultures of mixed retinal cells were treated with forskolin (an activator of the enzyme adenylyl cyclase) for 48 h. The results show that 50 microM forskolin induced a two-fold increase in the survival of retinal ganglion cells (RGCs) in the absence of exogenous trophic factors. This effect was dose dependent and abolished by 1 microM H89 (an inhibitor of protein kinase A), 1.25 microM chelerythrine chloride (an inhibitor of protein kinase C), 50 microM PD 98059 (an inhibitor of MEK), 25 microM Ly 294002 (an inhibitor of phosphatidylinositol-3 kinase), 30 nM brefeldin A (an inhibitor of polypeptide release), and 10 microM genistein or 1 ng/ml herbimycin (inhibitors of tyrosine kinase enzymes). The inhibition of muscarinic receptors by 10 microM atropine or 1 microM telenzepine also blocked the effect of forskolin. When we used 25 microM BAPTA, an intracellular calcium chelator, as well as 20 microM 5-fluoro-2'-deoxyuridine, an inhibitor of cell proliferation, we also abolished the effect. Our results indicate that cAMP plays an important role controlling the survival of RGCs. This effect is directly dependent on M1 receptor activation indicating that cholinergic activity mediates the increase in RGC survival. We propose a model which involves cholinergic amacrine cells and glial cells in the increase of RGC survival elicited by forskolin treatment.

Cellular localization of the disintegrin CRII-7/rMDC15 mRNA in rat PNS and CNS and regulated expression in postnatal development and after nerve injury

Disintegrins perform putative functions in cell adhesion, signaling and fusion. We have isolated a 2815-bp rat cDNA (CRII-7) representing a transcript that is differentially expressed during sciatic nerve regeneration. Nucleotide sequence comparison indicates that CRII-7 is the rat homologue to the recently cloned cDNAs MDC15 (ADAM 15) and metargidin (hMDC15) of mouse and human, respectively. The CRII-7 cDNA (rMDC15) encodes a membrane-anchored glycoprotein of approximately 85 kDa containing a disintegrin and a metalloprotease domain. Cellular metalloprotease disintegrins are a family of proteins (ADAMs or MDC proteins) with important roles, e.g., in cell-cell interactions during fertilization, muscle and nerve development, or tumor necrosis factor-alpha (TNF-alpha) cleavage. Northern blot analysis demonstrated a predominant expression of CRII-7/rMDC15 in the nervous system (PNS and CNS) and lung. Analysis of the CRII-7/rMDC15 transcript levels following peripheral nerve lesions demonstrated regulated mRNA expression during Wallerian degeneration and nerve regeneration. The steady-state levels of CRII-7/rMDC15 transcripts markedly increased within the first day after lesion and then steadily decreased for at least 4 weeks. CRII-7/rMDC15 mRNA expression was further examined during postnatal development and maturation of rat sciatic nerve and brain, as well as in cultured Schwann cells, meningeal fibroblasts, and astrocytes. In situ hybridization on paraffin sections showed the cellular localization of CRII-7/rMDC15 mRNA in Schwann cells and endothelial cells of peripheral nerve and in various neuronal populations in brain and spinal cord.

The effect of PKC activation on the survival of rat retinal ganglion cells in culture

Natural cell death is a degenerative phenomenon occurring during the development of the nervous system. Approximately half the neurons initially generated during this period die. The role of trophic molecules produced by target and afferent neurons as well as by glial cells controlling this regressive event has been extensively demonstrated. The aim of this work was to study the role of activated protein kinase C (PKC), an enzyme involved in apoptosis regulation, on the survival of retinal ganglion cells kept "in vitro" for 48 h. For this purpose, we used the phorbol 12-myristate 13-acetate (PMA), a tumor promoter agent that activates PKC. Our results showed that PMA increases the survival of ganglion cells. The effect was dose-dependent and PMA concentrations of 10 or 100 ng/ml produced the maximal effect (a two-fold increase on ganglion cells survival compared with 48 h control). This effect was totally abolished by 1.25 microM chelerythrine chloride (an inhibitor of PKC) and 30 microM genistein (an inhibitor of tyrosine kinase enzymes). Otherwise, PMA was effective only when it was chronically present in the cultures. On the other hand, treatment with 20 microM 5-fluoro-2'-deoxyuridine, an inhibitor of cell proliferation, or 25 microM BAPTA-AM, an intracellular calcium chelator, did not block PMA effect. Our results suggest that the survival of retinal ganglion cells "in vitro" may be mediated by a mechanism that involves PKC activation.

Astroglia inhibit the proliferation of neocortical cells and prevent the generation of small GABAergic neurons in vitro

We quantitatively studied the dynamics of rat neocortical precursor proliferation in vitro, and additionally examined the effects of neuron-glia interactions on the proliferation and differentiation of neurons, and particularly of gamma-aminobutyric acid (GABA)-containing cells. In cultures grown on glia-free substrate, cellular proliferation was detected at least until the end of the second week in vitro, but most neurons which expressed detectable amounts of microtubule-associated protein at 12 days in vitro were generated early during the first week. Further double-labelling experiments, combining 5'-bromo-2'-deoxyuridine with GABA or beta-tubulin III immunohistochemistry, provided direct evidence that neuronal proliferation continued through the second week in vitro, and that a population of small GABAergic neurons was generated between 3 and 12 days in vitro. Culturing cells on a glial substrate significantly reduced the generation of small GABAergic cells and strongly inhibited the total cell proliferation. Inhibition also occurred if astrocytes were added to the culture after 6 days in vitro, but was significantly decreased if cells were grown on a fixed glial substrate, suggesting that the effect might be at least partially mediated by active interactions between neurons and glia. In conclusion, our results show that the sustained proliferation of precursor cells in neocortical cultures is necessary for the differentiation of small GABAergic neurons, and that mature astroglia effectively inhibit the proliferation of neocortical precursors thereby affecting the appearance of a population of GABAergic cells.

Effects of astrocytes on neuronal attachment and survival shown in a serum-free co-culture system

In order to study the neurosupportive effects of glial cells, we optimized a glial-neuron non-contact co-culture method. Astrocyte conditioned medium (ACM) and an astrocyte feeder layer were used to promote neuronal attachment and neuronal survival respectively. Neuron-enriched cultures were prepared from cortices of E-18 day rat embryos. Instead of plating cells in serum-supplemented medium, as an indispensable first-step procedure for many serum-free culture protocols, we found that coating the coverslips briefly with ACM was sufficient for the healthy attachment and neurite outgrowth of the dissociated neurons in serum-free medium. A high survival rate of the low density (4x10(4) cells/cm(2)) neuronal cultures was achieved by co-culturing primary neurons with an astrocyte feeder layer. This non-contact co-culture method could be easily implemented with ordinary culture dishes. Our serum-free chemically defined medium was MEM supplemented with insulin, transferrin, selenium and pyruvate. In this serum-free medium, glial cells did not proliferate and a neuron-enriched population was obtained without the need for mitotic inhibitors. Our experimental results reveal a critical role for astrocytes in neuronal attachment and growth. This method can be used to study glial-neuron interactions as well as culturing low-density population of pure neurons.

Age-related changes of glial fibrillary acidic protein immunoreactive astrocytes in the rat cerebellar cortex

Age-related changes of glial fibrillary acidic protein (GFAP) immunoreactivity were investigated in the cerebellar cortex of young (3 months), adult (12 months) and old (24 months) rats using immunohistochemical techniques associated with image analysis. In young rats, cell bodies of GFAP-immunoreactive astrocytes were found in the white matter and in the granular layer of cerebellar cortex. Radially-oriented branches of astrocytes which are sited in the granular layer were also observed in the molecular layer. The number of GFAP-immunoreactivity astrocytes of white matter was decreased in adult and old rats in comparison with young cohorts, whereas their size increased progressively from 3 to 24 months old. The number and the size of GFAP-immunoreactive astrocytes of the granular layer was similar in young and adult rats. An increased number and size of GFAP-immunoreactive astrocytes was noticeable in old rats in comparison with younger cohorts. The number of radially oriented branches of the molecular layer was the same in the three age groups investigated. The above results indicate that GFAP-immunoreactive astrocytes of rat cerebellar cortex undergo age-related changes. The not homogeneous sensitivity to aging of cerebellar astrocytes suggests that evaluation of changes of different cell populations of cerebellar cortex should represent an important step of research on aging cerebellum.

Functional synapses are formed between human NTera2 (NT2N, hNT) neurons grown on astrocytes

The formation of functional synapses is a late milestone of neuronal differentiation. The establishment of functional synapses can be used to assess neuronal characteristics of different cell lines. In the present study, we examined the in vitro conditions that influence the ability of human neurons derived from the NT2 cell line (NT2N neurons) to establish synapses. The morphologic, immunologic, and electrophysiologic characteristics of these synapses was examined. In the absence of astrocytes, NT2N neurons rarely formed synapses and their action potentials were weak and uncommon. In contrast, when plated on primary astrocytes, NT2N neurons were able to form both glutamatergic excitatory (71%) and GABAergic inhibitory (29%) functional synapses whose properties (kinetics, ion selectivity, pharmacology, and ultrastructure) were similar to those of synapses of neurons in primary cultures. In addition, coculture of NT2N neurons with astrocytes modified the morphology of the neurons and extended their in vitro viability to more than 1 year. Because astrocyte-conditioned medium did not produce these effects, we infer that direct contact between NT2N neurons and astrocytes is required. These results suggest that NT2N neurons are similar to primary neurons in their synaptogenesis and their requirement for glial support for optimal survival and maturation. This system provides a model for further investigations into the neurobiology of synapses formed by human neurons.

Astrocyte changes in aging cerebral cortex and hippocampus: a quantitative immunohistochemical study

Glial cells are sensitive to aging, but the real extent of age-related quantitative and qualitative changes of these brain cellular elements has not yet been clarified. Brain volume undergoes age-related changes, but several studies on the number of glial cells have not taken this important variable into account. In this study we quantitatively evaluated the number and morphology of glial fibrillary acidic protein (GFAP)-immunoreactive astroglia in the frontal cortex and in the CA1 subfield of the hippocampus of male Sprague-Dawley rats of aged 12 and 24 months, considered adult and aged, respectively. The volume of frontal cortex was unchanged in the two age groups investigated, whereas the volume of hippocampus was higher in aged rats. An increase in the number and size of GFAP-immunoreactive astrocytes was observed in the frontal cortex and in the CA1 subfield of the hippocampus of aged rats. The numeric increase in astrocytes was more pronounced in the hippocampus than in the frontal cortex, whereas age-related hypertrophy of astroglia was more accentuated in the frontal cortex. The possible significance of hyperplasia and hypertrophy of GFAP-immunoreactive astrocytes in the frontal cortex and in the CA1 subfield of the hippocampus of aged rats is discussed.

Glutamine is involved in the dependency of brain neuron survival on cell plating density in culture

The mechanism by which neuronal cell viability in culture is dependent on cell plating density is unclear. To address this question, dissociated cells from the neonatal rat cortex were cultured in a chemically defined medium. Medium conditioned with cortical cells plated at high density (2000 cells/mm2) promoted the survival of neurons grown at low cell density (100 cells/mm2) in a dose-dependent manner. Data obtained from molecular sieving suggested that the molecule(s) promoting the survival of neurons was smaller than 1000 Da. Amino acid analysis of the conditioned medium revealed the release of a mass of glutamine from cortical cells in culture. L-Glutamine mimicked the conditioned medium in action promoting the viability of neurons. These findings suggest that the effect of plating density on neuronal cell viability is mediated at least in part by glutamine released from cultured cells.

Ultrastructural evidence for combined action of noradrenaline and vasoactive intestinal polypeptide upon neurons, astrocytes, and blood vessels of the rat cerebral cortex

The intracortical organization of the noradrenaline (NA) and vasoactive intestinal polypeptide (VIP) systems provides ample opportunity for functional convergence, and accumulated evidence indicates that NA and VIP share certain cellular actions upon both neuronal and nonneuronal cortical elements. In the present study, a double immunolabeling method was combined with a silver-gold intensification procedure to examine the ultrastructural relationships of the NA coeruleocortical afferents and the intrinsic VIP neurons with three main constituents of the cortex: neurons, astrocytes, and blood vessels. Electron microscopy of singly or doubly labeled material indicated that NA and VIP boutons are engaged in a variety of anatomical relationships with both neuronal and nonneuronal elements. Dendritic shafts and perikarya of nonpyramidal neurons, some of which are VIP positive, receive combined NA and VIP synapses. A significant number of cortical microvessels are in intimate contact with NA or VIP profiles. NA axons often form perivascular loops, and VIP dendritic shafts of large diameter are frequently observed to bend around the vessel circumference. Serial section examination demonstrates that some NA boutons are directly apposed to the capillary wall at sites of glial end-feet discontinuities, whereas VIP boutons contact astrocytic sleeves of capillaries but never cross the perivascular astroglial barrier. Some VIP dendrites containing coated vesicles make intimate contact with the capillary basal lamina. Astrocytic perikarya, mainly in the supragranular layers, are also directly apposed to NA and/or VIP elements. These complex anatomical relationships provide a structural basis for the known interactions between NA and VIP in the control of cortical metabolism and function.

Ammonia-induced depolarization of cultured rat cortical astrocytes

Exposure of cultured rat cortical astrocytes to increased concentrations of ammonia has been shown to induce morphological and biochemical changes similar to those found in hyperammonemic (e.g., hepatic) encephalopathy in vivo. Alterations of electrophysiological properties are not well investigated. In this study, we examined the effect of ammonia on the astrocyte membrane potential by means of perforated patch recordings. Exposure to millimolar concentrations of NH4Cl induced a slow dose-dependent and reversible depolarization. At steady state, i.e., after several tens of minutes, the cells were significantly depolarized from a resting membrane potential of -96.2 +/- 0.6 mV (n = 83, S.E.M.) to -89.1 +/- 1.6 mV (n = 7, S.E.M.) at 5 mM NH4Cl, -66.3 +/- 3.6 mV (n = 9, S.E.M.) at 10 mM NH4Cl and -50.4 +/- 2.5 mV (n = 12, S.E.M.) at 20 mM NH4Cl, respectively. In order to examine the underlying depolarizing mechanisms we determined changes in the fractional ion conductances for potassium, chloride and sodium induced by 20 mM NH4Cl. No significant changes were found in the fractional sodium or chloride conductances, but the dominating fractional potassium conductance decreased slightly from a calculated 0.86 +/- 0.04 to 0.77 +/- 0.04 (n = 9, S.E.M.). Correspondingly, we found a significant fractional ammonium ion (NH4+) conductance of 0.23 +/- 0.02 (n = 10, S.E.M.) which was blocked by the potassium channel blocker barium and, hence, most likely mediated by barium-sensitive potassium channels. Our data suggest that the sustained depolarization induced by NH4Cl depended on changes in intracellular ion concentrations rather than changes in ion conductances. Driven by the high membrane potential NH4+ accumulated intracellularly via a barium-sensitive potassium conductance. The concomitant decrease in the intracellular potassium concentration was primarily responsible for the observed slow depolarization.

In vitro differentiation of chick spinal cord neurons in the presence of Reissner's fibre, an ependymal brain secretion

The subcommissural organ (SCO), which belongs to the circumventricular organs, is a specialized ependymal structure of the brain that secretes glycoproteins into the cerebrospinal fluid (CSF) which condense to form a thread-like structure, the Reissner's fibre (RF). Regarding the presence of this ependymal brain secretion all along the central canal of the developing spinal cord, we analysed a putative developmental activity of RF on neuronal spinal cord cells. The effects of RF proper and soluble RF-material were examined in primary cultures of dissociated spinal cord cells from day 6 chicken embryos. In serum-containing mixed glial/neuronal cell cultures, both RF and soluble RF-material promoted neuronal survival. This effect was blocked by addition of specific antibodies raised against bovine RF into the culture medium. In serum-free neuron-enriched cultures, no neuronal survival activity was observed; however, under these conditions RF proper induced neuronal aggregation and neuritic outgrowth of spinal cord cells. Interestingly, neurites extending from the aggregates appeared mainly unfasciculated. Our results suggest a direct modulation of cell-cell interactions by SCO/RF glycoproteins and an indirect survival effect on neurons. These data strengthen the hypothesis of the involvement of SCO/RF complex in the development of the central nervous system (CNS) and are discussed regarding molecular features of SCO-spondin, a novel glycoprotein recently identified in this complex.

Chondroitin/dermatan sulphate promotes the survival of neurons from rat embryonic neocortex

Recently we have shown that biglycan, a small chondroitin sulphate proteoglycan of the extracellular matrix, supports the survival of cultured neurons from the developing neocortex of embryonic day 15 rats. Here we investigate the structure-function relationship of this neurotrophic proteoglycan and show that chondroitin/dermatan sulphate chains are the active moieties supporting survival. Heparin, a highly sulphated glucosaminoglycan, is less active than the galactosaminoglycans (chondroitin-4-sulphate, chondroitin-6-sulphate and dermatan sulphate), whereas hyaluronic acid, an unsulphated glucosaminoglycan, does not support neuron survival. Galactosaminoglycans must be in direct contact with neurons to cause survival. Experiments with elevated potassium concentrations and antagonists of voltage-gated calcium channels exclude the involvement of membrane depolarization. However, genistein and an erbstatin analogue, which are inhibitors of tyrosine kinases with low specificity, abolished neuron survival in the presence of chondroitin/dermatan sulphate, whereas a selective inhibitor of neurotrophin receptor kinases (K252a) had no suppressive effect. Thus, yet unidentified tyrosine kinases are involved in the chondroitin/dermatan sulphate-dependent survival of neocortical neurons. In the embryonic stages of rat neocortical development chondroitin sulphate is mainly located in layers I, V and VI and the subplate. Chondroitin sulphate expression is maintained after birth, extends up to cortical layer IV on postnatal day 7, and is down-regulated until postnatal day 21 concomitant with the period of naturally occurring cell death. The latter observation is consistent with a putative role of chondroitin sulphate in the control of neuron survival during cortical histogenesis.

Selegiline enhances NGF synthesis and protects central nervous system neurons from excitotoxic and ischemic damage

It has been previously demonstrated that selegiline, an irreversible monoamine oxidase B (MAO-B) inhibitor, potentiates glial reaction to injury and possesses some 'trophic-like' activities which do not depend on the inhibition of MAO-B and which are probably associated with the induction of astrocyte-derived neurotrophic substances. Based on these findings, we tried to find out whether selegiline is able to modify the expression of nerve growth factor (NGF) and to protect central nervous system (CNS) neurons from excitotoxic and ischemic damage. Selegiline (10 pM-1 nM) induced NGF messenger RNA (mRNA) expression in cultured rat cortical astrocytes as determined by reverse transcription-polymerase chain reaction (RT-PCR) followed by a corresponding increase in NGF protein content measured by two-site NGF-enzyme-linked immunosorbent assay (ELISA) in astrocyte-conditioned medium. Additionally, exposure of hippocampal cultures containing neuronal and glial cells to this drug at the same concentrations enhanced significantly the content of NGF measured in the culture medium after 6 h of incubation. We hypothesize that selegiline could rescue hippocampal neurons from injury by induction of astrocyte-derived NGF in this cell culture system. To test this hypothesis, an excitotoxic damage was induced in the same type of cells by exposure to 0.5 mM L-glutamate for 1 h. Selegiline (10 pM-1 nM) present in the growth medium 6 h before until 18 h after induction of injury (the point of glutamate-toxicity measurement) protected hippocampal neurons from excitotoxic death. Furthermore, administered intraperitoneally (i.p.) (8 x 15 mg/kg per day) this drug enhanced the expression of NGF message in intact rat cerebral cortex and protected rat cortical tissue from ischemic insult due to permanent occlusion of the middle cerebral artery (MCA). The neuroprotective activity of selegiline (5 x 10 mg/kg per day i.p.) was also demonstrated in a mouse model of focal cerebral ischemia. The present data show that selegiline induced NGF expression in cultured rat cortical astrocytes. In mixed primary cultures of hippocampal neuronal and glial cells, selegiline increased NGF protein content and protected hippocampal neurons from excitotoxic degeneration. In vivo, this drug induced NGF gene expression in cerebral cortex from intact rats and protected rat and mouse cortical tissue from ischemic insult after occlusion of the MCA. Our results indicate that the induction of astrocyte-derived NGF could contribute to the neuroprotective activity of selegiline demonstrated both in vivo and in vitro and can explain, in part, the 'trophic-like' properties of this compound which has been observed by others.

Cultured astrocytes express biglycan, a chondroitin/dermatan sulfate proteoglycan supporting the survival of neocortical neurons

Astrocyte-conditioned medium (ACM) supports the survival of rat E15 neocortical neurons. Using a microtiter assay for neuronal survival, we demonstrated that part of the survival activity is associated with a proteoglycan fraction obtained after two chromatographic steps: (1) preparative Q-Sepharose anion-exchange chromatography under non-denaturating conditions and (2) MonoQ chromatography in the presence of 8 M urea. Analytical SDS-polyacrylamide gradient gel electrophoresis of pooled active MonoQ-fractions (MQ-pool) revealed a broad proteoglycan band migrating with an apparent M(r) in the range of 150-400 kDa. Digestion of the MQ-pool with chondroitin-ABC-lyase yielded a major core protein of 50 kDa. In Western blots the high molecular weight (150-400 kDa) material as well as the 50 kDa core protein band were immunoreactive to chicken polyclonal antibodies raised against purified biglycan from rat meningeal fibroblasts. Northern blot analysis of total RNA prepared from highly enriched astrocyte cultures revealed a single 2.9 kb biglycan transcript. By using in situ hybridization we demonstrated that essentially all cells in these cultures expressed biglycan mRNA. Furthermore, highly purified biglycan from bovine cartilage was shown to markedly enhance survival of rat neocortical neurons. In conclusion, we have shown that astrocytes synthesize and release the small chondroitin/dermatan sulfate proteoglycan (CS/DSPG) biglycan, a molecule that was found to support survival of neocortical neurons in vitro.

Ultrastructural relationships between noradrenergic nerve fibers and non-neuronal elements in the rat cerebral cortex

Pharmacological and biochemical data suggest that noradrenaline (NA)-containing fibers not only regulate the activity of cortical neurons but also influence the functional state of non-neuronal elements. In the present study, immunocytochemistry with an antiserum against NA, followed by silver-gold intensification of the immunoreaction end-product, was employed to examine the ultrastructural relationships between the NA fiber system and the intraparenchymal blood vessels, oligodendrocytes, and astrocytes in the rat visual cortex. Electron microscopy revealed a large number of fine varicose NA fibers to be in intimate contact with cortical capillaries. Examination of single thin sections showed that NA boutons were usually separated from the capillary wall by a fine astroglial sleeve. However, serial section analysis revealed that the continuity of the astrocytic end feet was interrupted at sites, resulting in direct apposition of the perivascular NA fibers to the capillary basal lamina. Noradrenergic fibers were found to contact both types of macroglial cells. Single or clustered oligodendrocytes in intimate contact with NA fibers were observed throughout the cortical depth. Individual contacts could be followed in more than six successive thin sections, and oligodendrocyte plasma membrane frequently exhibited a light thickening at the sites of the NA fiber apposition. NA fiber-astroglial relationships were largely encountered in supragranular layers. In these layers, astrocytic cell bodies were characteristically outlined by fine varicose NA fibers. However, no plasma membrane differentiations were observed at the sites of intimate NA fiber apposition. The present ultrastructural findings provide the anatomical substrate for the control exerted by the NA fiber system over cortical microvasculature and macroglia.

Clenbuterol protects mouse cerebral cortex and rat hippocampus from ischemic damage and attenuates glutamate neurotoxicity in cultured hippocampal neurons by induction of NGF

It has been shown previously that clenbuterol, a beta 2-adrenergic receptor agonist, enhances NGF synthesis in adult rat brain. Since NGF is able to protect neurons against damage, we tried to find out whether clenbuterol can rescue cultured hippocampal neurons from excitotoxic damage by induction of NGF. The neuroprotective activity of clenbuterol on neurons in the vulnerable CA1 subfield of the hippocampus was tested in a rat model of transient forebrain ischemia. Additionally, in the mouse model of focal cerebral ischemia the ability of clenbuterol to reduce the infarct size was examined. Exposure of mixed neuronal/glial hippocampal cultures to clenbuterol (1 to 100 microM) enhanced significantly the content of NGF measured in the culture medium by two-site ELISA. The excitotoxic injury was induced in the same type of cells after 14 days in vitro by exposure to 1 mM L-glutamate for 1 h in serum-free medium. NGF itself (0.15 to 100 ng/ml) added to the growth medium 4 h before until 18 h after induction of injury (the point of glutamate-toxicity measurement), protected hippocampal neurons from excitotoxic damage. Clenbuterol (1 to 100 microM) provided similar neuroprotection as NGF under the same experimental conditions. The neuroprotective activity of clenbuterol (100 microM) against glutamate-induced damage in hippocampal cultures was blocked by anti-NGF monoclonal antibodies (0.5 microgram/ml) added to the medium during the clenbuterol exposure, demonstrating that the neuronal rescue is mediated by NGF. Propranolol, a beta-adrenergic receptor antagonist (10 microM) added 20 min before and kept in the medium during exposure of the cultures to clenbuterol (1 microM) reversed the neuroprotective activity, suggesting that the induction of NGF and neuroprotection caused by clenbuterol are mediated via beta-adrenergic receptor activation. The capacity of clenbuterol to protect hippocampal neurons was also demonstrated in vivo in a rat model of transient forebrain ischemia. Clenbuterol (4 x 1 mg/kg) administered intraperitoneally increased the number of viable neurons in CA1 subfield of the rat hippocampus. Furthermore, clenbuterol (0.3 and 1 mg/kg, i.p. and 1 mg/kg, s.c.) reduced significantly the infarct area on the mouse brain surface after occlusion of the middle cerebral artery. The present data demonstrate that clenbuterol induces NGF synthesis in cultured hippocampal cells and protects hippocampal neurons from excitotoxic damage. The neuroprotective activity of clenbuterol is also demonstrated in vivo in two rodent models of cerebral ischemia. The results offer strong evidence that the neuroprotective activity of clenbuterol is caused by activation of beta-adrenergic receptors and the subsequent increased expression of NGF.

Purification of a meningeal cell-derived chondroitin sulphate proteoglycan with neurotrophic activity for brain neurons and its identification as biglycan

Serum-free cultures of meningeal fibroblasts synthesize and release a chondroitin sulphate proteoglycan (CSPG) that markedly enhances survival but not adhesion of embryonic rat (embryonic day 15) neocortical neurons in vitro. The active molecule was purified from conditioned medium (meningeal cell-conditioned medium, MCM) in three steps by means of fast-performance liquid chromatography fractionation combined with a quantitative microphotometric bioassay: (i) preparative Q-Sepharose anion exchange chromatography under native conditions; (ii) rechromatography of biologically active Q-Sepharose fractions on a MonoQ column in the presence of 8 M urea; and (iii) final gel filtration of active MonoQ fractions on Superose 6 in the presence of 4 M guanidinium hydrochloride. Analytical sodium dodecyl sulphate-polyacrylamide gradient gel electrophoresis of active Superose 6 fractions revealed a single broad glycoprotein band with a molecular mass in the range of 220-340 kDa. Further characterization of the purified molecule with glycosaminoglycan:lyases revealed a core protein of 50 kDa and the nearly complete loss of neurotrophic activity after chondroitinase digestion, whereas heparitinase treatment changed neither electrophoretic mobility nor biological activity. Amino-terminal sequencing of the purified CSPG core protein revealed identity with the amino acid sequence of rat biglycan. Biglycan purified from bovine cartilage supported neuron survival with virtually the same activity as the CSPG purified from MCM (half-maximal activity approximate to 10(-8) M). In conclusion, we isolated a neurotrophic CSPG from meningeal cells with strong survival-enhancing activity for brain neurons that was identified as biglycan, a molecule not previously related to neural functions.

Astrocyte differentiation is enhanced in chick embryos treated with ethanol during early neuroembryogenesis

In this study, we examined the effects of ethanol administered to chick embryos, on the maturation of astrocytes, using glutamine synthetase (GS) activity as an astrocyte marker. Ethanol (50 mM) was administered in ovo via the air sac, embryos were sacrificed at various days of embryonic development and GS activity was determined in cerebral hemispheres and cerebellum. We found that in both cerebral hemispheres and cerebellum, GS activity was higher in the ethanol-treated embryos, as compared to controls, during the embryonic periods, E6 to E10 in the cerebral hemispheres and E10 to E14 in the cerebellum. These periods are characterized by increased neuronal differentiation in these CNS areas. The increase in GS activity in the ethanol-treated embryos is speculated to reflect either a transient reactive gliosis and/or an enhancement in the differentiation of radial glia, immature glia, to more mature astrocytes.

The concept of trophic units in the central nervous system

The present paper proposes that trophic interplay among cells may represent the final common pathway for both genetic and environmental influences, and hence new criteria for the understanding of central nervous system (CNS) connectivity can be suggested. In particular, trophic signals may make up the common "language" through which genetic and epigenetic influences mold the CNS during development and the adult life. Furthermore, it will put forward the hypothesis that the developmental trophic interplay among cells leads to the formation of trophic units in the adult brain. A trophic unit is defined as the smallest set of cells, within the CNS, which act in a complementary way to support each other's trophism. The trophic units consist of neurons, glial cells, blood vessels, extracellular matrix (ECM). In particular, ECM gives support to the thin elongated cell processes and gives rise to selective chemical bridges between cell surfaces or between cell surfaces and the extracellular milieu. The trophic unit is a plastic device that not only assures neuronal survival, but also operates to adapt neuronal networks to new tasks by controlling extension of neuronal processes, synapse turnover and ECM characteristics. These plastic responses depend on the interplay of all the elements that constitute the trophic units. The concept of trophic unit may help to understand some features of neurodegenerative diseases, for example, the clustering of tangles in the neocortex and in the entorhinal cortex of Alzheimer's patients [corrected].

Distribution of glial fibrillary acidic protein (GFAP) in the cochlear nucleus of adult and aged rats

The age-related change in glial fibrillary acidic protein (GFAP) immunoreactivity was analyzed in young (3 months) and old (24 months) adult rat cochlear nuclei (CN). Quantitative analyses show a significant increase with age, in the number of GFAP positive astrocytes and processes in the old adult when compared with the young adult rat. There was also a differential distribution of GFAP immunoreactivity in the young adult CN where it predominates in the granular cell region, whereas in old rats, the GFAP immunoreactivity distribution was homogeneous in all parts of the nucleus. There was no change in the total number of neurons between these two stages in any part of the nucleus except for the antero-ventral CN, where a decrease in neuronal number was observed in the aged rats. The increase in GFAP immunoreactivity was related to an increase of both GFAP positive astrocyte number and processes. The increase of GFAP positive astrocytes may be due either to an alteration of auditory nerve fibers, changing the trophic interactions with post-synaptic cells, or to intrinsic alterations of CN neurons and local circuits reflecting aging of the CN.