CNS glial scar tissue: a source of molecules which inhibit central neurite outgrowth

Nerve implants with bioactive interfaces enhance neurite outgrowth and nerve regeneration in vivo

Nerve implants functionalized with growth factors and stem cells are critical to promote neurite outgrowth, regulate neurodifferentiation, and facilitate nerve regeneration. In this study, human umbilical cord mesenchymal stem cells (hUCMSCs) and 3,4-hydroxyphenalyalanine (DOPA)-containing insulin-like growth factor 1 (DOPA-IGF-1) were simultaneously applied to enhance the bioactivity of poly(lactide-co-glycolide) (PLGA) substrates which will be potentially utilized as nerve implants. In vitro and in vivo evaluations indicated that hUCMSCs and DOPA-IGF-1 could synergistically regulate neurite outgrowth of PC12 cells, improve intravital recovery of motor functions, and promote conduction of nerve electrical signals in vivo. The enhanced functional and structural nerve regeneration of injured spinal cord might be mainly attributable to the synergistically enhanced biofunctionality of hUCMSCs and DOPA-IGF-1/PLGA on the bioactive interfaces. Findings from this study demonstrate the potential of hUCMSC-seeded, DOPA-IGF-1-modified PLGA implants as promising candidates for promoting axonal regeneration and motor functional recovery in spinal cord injury treatment.

AQP4 labels a subpopulation of white matter-dependent glial radial cells affected by pediatric hydrocephalus, and its expression increased in glial microvesicles released to the cerebrospinal fluid in obstructive hydrocephalus

Hydrocephalus is a distension of the ventricular system associated with ventricular zone disruption, reactive astrogliosis, periventricular white matter ischemia, axonal impairment, and corpus callosum alterations. The condition's etiology is typically attributed to a malfunction in classical cerebrospinal fluid (CSF) bulk flow; however, this approach does not consider the unique physiology of CSF in fetal and perinatal patients. The parenchymal fluid contributes to the glymphatic system, and plays a fundamental role in pediatric hydrocephalus, with aquaporin 4 (AQP4) as the primary facilitator of these fluid movements. Despite the importance of AQP4 in the pathophysiology of hydrocephalus, it’s expression in human fetal life is not well-studied. This manuscript systematically defines the brain expression of AQP4 in human brain development under control (n = 13) and hydrocephalic conditions (n = 3). Brains from 8 postconceptional weeks (PCW) onward and perinatal CSF from control (n = 2), obstructive (n = 6) and communicating (n = 6) hydrocephalic samples were analyzed through immunohistochemistry, immunofluorescence, western blot, and flow cytometry. Our results indicate that AQP4 expression is observed first in the archicortex, followed by the ganglionic eminences and then the neocortex. In the neocortex, it is initially at the perisylvian regions, and lastly at the occipital and prefrontal zones. Characteristic astrocyte end-feet labeling surrounding the vascular system was not established until 25 PCW. We also found AQP4 expression in a subpopulation of glial radial cells with processes that do not progress radially but, rather, curve following white matter tracts (corpus callosum and fornix), which were considered as glial stem cells (GSC). Under hydrocephalic conditions, GSC adjacent to characteristic ventricular zone disruption showed signs of early differentiation into astrocytes which may affect normal gliogenesis and contribute to the white matter dysgenesis. Finally, we found that AQP4 is expressed in the microvesicle fraction (p < 0.01) of CSF from patients with obstructive hydrocephalus. These findings suggest the potential use of AQP4 as a diagnostic and prognostic marker of pediatric hydrocephalus and as gliogenesis biomarker.

Gsx1 promotes locomotor functional recovery after spinal cord injury

Promoting residential cells, particularly endogenous neural stem and progenitor cells (NSPCs), for tissue regeneration represents a potential strategy for the treatment of spinal cord injury (SCI). However, adult NSPCs differentiate mainly into glial cells and contribute to glial scar formation at the site of injury. Gsx1 is known to regulate the generation of excitatory and inhibitory interneurons during embryonic development of the spinal cord. In this study, we show that lentivirus-mediated expression of Gsx1 increases the number of NSPCs in a mouse model of lateral hemisection SCI during the acute stage. Subsequently, Gsx1 expression increases the generation of glutamatergic and cholinergic interneurons and decreases the generation of GABAergic interneurons in the chronic stage of SCI. Importantly, Gsx1 reduces reactive astrogliosis and glial scar formation, promotes serotonin (5-HT) neuronal activity, and improves the locomotor function of the injured mice. Moreover, RNA sequencing (RNA-seq) analysis reveals that Gsx1-induced transcriptome regulation correlates with NSPC signaling, NSPC activation, neuronal differentiation, and inhibition of astrogliosis and scar formation. Collectively, our study provides molecular insights for Gsx1-mediated functional recovery and identifies the potential of Gsx1 gene therapy for injuries in the spinal cord and possibly other parts of the central nervous system.

Novel bone repairing scaffold consisting of bone morphogenetic Protein-2 and human Beta Defensin-3

Background

Synthetic biomaterials assist in modulating the vascular response in an injured bone by serving as delivery vehicles of pro-angiogenic molecules to the site of injury or by serving as mimetic platforms which offer support to cell growth and proliferation.

Methods

This study applied natural phospholipid modified protein technologies together with low temperature three-dimensional printing technology to develop a new model of three-dimensional artificial bone scaffold for potential use in repairing body injuries. The focus was to create a porous structure (PS) scaffold of two components, Bone Morphogenetic Protein-2 and Human Beta Defensin-3 (BMP2 and hBD3), which can synchronously realize directional bone induction, angiogenesis and postoperative antibacterial effects. BMP2 induces osteogenesis, whereas hBD3 is antibacterial.

Results

Our data showed that in the BMP2-hBD3-PS or hBD3-PS scaffolds, BMP2 had a slow-release rate of about 40% in 30 days, ensuring that BMP2 could penetrate into stem cells for osteogenic differentiation for a long time. The scaffolds promoted cell growth when in combination with BMP2, thus showing its importance in promoting cell growth. Alkaline Phosphatase (ALP) staining showed that the ALP content of BMP2-hBD3-PS and BMP2-PS had a significant increase in samples that contained BMP2, thus showing that these scaffolds promoted osteogenic differentiation. In all the constructs that had hBD3, they displayed antibacterial properties with hBD3, having a slow release of about 35% in 30 days, thus ensuring they provided protection.

Conclusion

Based on this study, the 3D printed BMP2 scaffolds show a great potential for the development of biodegradable bone implants.

Level of evidence

Level II, experimental comparative design.

The Influence of Neuron-Extrinsic Factors and Aging on Injury Progression and Axonal Repair in the Central Nervous System

In the aging western population, the average age of incidence for spinal cord injury (SCI) has increased, as has the length of survival of SCI patients. This places great importance on understanding SCI in middle-aged and aging patients. Axon regeneration after injury is an area of study that has received substantial attention and made important experimental progress, however, our understanding of how aging affects this process, and any therapeutic effort to modulate repair, is incomplete. The growth and regeneration of axons is mediated by both neuron intrinsic and extrinsic factors. In this review we explore some of the key extrinsic influences on axon regeneration in the literature, focusing on inflammation and astrogliosis, other cellular responses, components of the extracellular matrix, and myelin proteins. We will describe how each element supports the contention that axonal growth after injury in the central nervous system shows an age-dependent decline, and how this may affect outcomes after a SCI.

Molecular and histologic outcomes following spinal cord injury in spiny mice, Acomys cahirinus

The spiny mouse (Acomys cahirinus) appears to be unique among mammals by showing little scarring or fibrosis after skin or muscle injury, but the Acomys response to spinal cord injury (SCI) is unknown. We tested the hypothesis that Acomys would have molecular and immunohistochemical evidence of reduced spinal inflammation and fibrosis following SCI as compared to C57BL/6 mice (Mus), which similar to all mammals studied to date exhibits spinal scarring following SCI. Initial experiments used two pathway-focused RT-PCR gene arrays ("wound healing" and "neurogenesis") to evaluate tissue samples from the C2-C6 spinal cord 3 days after a C3/C4 hemi-crush injury (C3Hc). Based on the gene array results, specific genes were selected for RT-qPCR evaluation using species-specific primers. The results supported our hypothesis by showing increased inflammation and fibrosis related gene expression (Serpine 1, Plau, and Timp1) in Mus as compared to Acomys (p < .05). RT-qPCR also showed enhanced stem cell and axonal guidance related gene expression (Bmp2, GDNF, and Shh) in Acomys compared to Mus (p < .05). Immunohistochemical evaluation of the spinal lesion at 4 weeks postinjury indicated less collagen IV immunostaining in Acomys (p < .05). Glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1(IBA1) immunostaining indicated morphological differences in the appearance of astrocytes and macrophages/microglia in Acomys. Collectively, the molecular and histologic results support the hypothesis that Acomys has reduced spinal inflammation and fibrosis following SCI. We suggest that Acomys may be a useful comparative model to study adaptive responses to SCI.

Evaluating sex hormones and cytokine profile in Egyptian females with relapsing-remitting multiple sclerosis

Background

Sexual dimorphism shown in multiple sclerosis suggests an interaction between immune system and sex hormones. The objective of this study is to determine the hormonal profile and serum cytokine levels in Egyptian female patients with relapsing-remitting MS (RRMS) compared with healthy controls and their associations with disease disability.

Methods

This study was conducted on 40 female patients with RRMS and 20 age-matched controls subjected to measurements of the hormonal profile (estrogen, testosterone) and cytokine levels (interleukin 10 and 4 and tumor necrosis factor alpha) and disability assessment using Expanded Disability Status Scale (EDSS).

Results

Levels of estrogen, testosterone, interleukin 10 and 4 (IL-10 and IL-4), and tumor necrosis factor alpha (TNF-α) were higher in patients compared to control with no statistically significant difference. Estrogen levels were positively correlated with interleukin 10 and interleukin 4 levels and negatively correlated with tumor necrosis factor alpha (TNF-α), but there was no statistically significant correlation between hormonal profile or cytokine profile (IL-10, IL-4, and TNF-α) and EDSS.

Conclusions

It is suggested that estrogen has an anti-inflammatory effect on cytokine milieu; therefore, it can be tried as a treatment option in multiple sclerosis.

Cell therapy for spinal cord injury with olfactory ensheathing glia cells (OECs)

The prospects of achieving regeneration in the central nervous system (CNS) have changed, as most recent findings indicate that several species, including humans, can produce neurons in adulthood. Studies targeting this property may be considered as potential therapeutic strategies to respond to injury or the effects of demyelinating diseases in the CNS. While CNS trauma may interrupt the axonal tracts that connect neurons with their targets, some neurons remain alive, as seen in optic nerve and spinal cord (SC) injuries (SCIs). The devastating consequences of SCIs are due to the immediate and significant disruption of the ascending and descending spinal pathways, which result in varying degrees of motor and sensory impairment. Recent therapeutic studies for SCI have focused on cell transplantation in animal models, using cells capable of inducing axon regeneration like Schwann cells (SchCs), astrocytes, genetically modified fibroblasts and olfactory ensheathing glia cells (OECs). Nevertheless, and despite the improvements in such cell-based therapeutic strategies, there is still little information regarding the mechanisms underlying the success of transplantation and regarding any secondary effects. Therefore, further studies are needed to clarify these issues. In this review, we highlight the properties of OECs that make them suitable to achieve neuroplasticity/neuroregeneration in SCI. OECs can interact with the glial scar, stimulate angiogenesis, axon outgrowth and remyelination, improving functional outcomes following lesion. Furthermore, we present evidence of the utility of cell therapy with OECs to treat SCI, both from animal models and clinical studies performed on SCI patients, providing promising results for future treatments.

Improving the regenerative potential of olfactory ensheathing cells by overexpressing prostacyclin synthetase and its application in spinal cord repair

Background

Olfactory ensheathing cells (OEC), specialized glia that ensheathe bundles of olfactory nerves, have been reported as a favorable substrate for axonal regeneration. Grafting OEC to injured spinal cord appears to facilitate axonal regeneration although the functional recovery is limited. In an attempt to improve the growth-promoting properties of OEC, we transduced prostacyclin synthase (PGIS) to OEC via adenoviral (Ad) gene transfer and examined the effect of OEC with enhanced prostacyclin synthesis in co-culture and in vivo. Prostacyclin is a vasodilator, platelet anti-aggregatory and cytoprotective agent.

Results

Cultured OEC expressed high level of cyclooxygneases, but not PGIS. Infection of AdPGIS to OEC could selectively augument prostacyclin synthesis. When cocultured with either OEC or AdPGIS-OEC, neuronal cells were resistant to OGD-induced damage. The resulted OEC were further transplanted to the transected cavity of thoracic spinal cord injured (SCI) rats. By 6 weeks post-surgery, significant functional recovery in hind limbs occurred in OEC or AdPGIS-OEC transplanted SCI rats compared with nontreated SCI rats. At 10–12 weeks postgraft, AdPGIS-OEC transplanted SCI rats showed significantly better motor restoration than OEC transplanted SCI rats. Futhermore, regenerating fiber tracts in the distal spinal cord stump were found in 40–60% of AdPGIS-OEC transplanted SCI rats.

Conclusions

Enhanced synthesis of prostacyclin in grafted OEC improved fiber tract regeneration and functional restoration in spinal cord injured rats. These results suggest an important potential of prostacyclin in stimulating OEC therapeutic properties that are relevant for neural transplant therapies.

Integrated Stress Response as a Therapeutic Target for CNS Injuries

Central nervous system (CNS) injuries, caused by cerebrovascular pathologies or mechanical contusions (e.g., traumatic brain injury, TBI) comprise a diverse group of disorders that share the activation of the integrated stress response (ISR). This pathway is an innate protective mechanism, with encouraging potential as therapeutic target for CNS injury repair. In this review, we will focus on the progress in understanding the role of the ISR and we will discuss the effects of various small molecules that target the ISR on different animal models of CNS injury.

Neuroprotection and Blood-Brain Barrier Restoration by Salubrinal After a Cortical Stab Injury

Following a central nervous system (CNS) injury, restoration of the blood-brain barrier (BBB) integrity is essential for recovering homeostasis. When this process is delayed or impeded, blood substances and cells enter the CNS parenchyma, initiating an additional inflammatory process that extends the initial injury and causes so-called secondary neuronal loss. Astrocytes and profibrotic mesenchymal cells react to the injury and migrate to the lesion site, creating a new glia limitans that restores the BBB. This process is beneficial for the resolution of the inflammation, neuronal survival, and the initiation of the healing process. Salubrinal is a small molecule with neuroprotective properties in different animal models of stroke and trauma to the CNS. Here, we show that salubrinal increased neuronal survival in the neighbourhood of a cerebral cortex stab injury. Moreover, salubrinal reduced cortical blood leakage into the parenchyma of injured animals compared with injured controls. Adjacent to the site of injury, salubrinal induced immunoreactivity for platelet-derived growth factor subunit B (PDGF-B), a specific mitogenic factor for mesenchymal cells. This effect might be responsible for the increased immunoreactivity for fibronectin and the decreased activation of microglia and macrophages in injured mice treated with salubrinal, compared with injured controls. The immunoreactivity for PDGF-B colocalized with neuronal nuclei (NeuN), suggesting that cortical neurons in the proximity of the injury were the main source of PDGF-B. Our results suggest that after an injury, neurons play an important role in both, the healing process and the restoration of the BBB integrity. J. Cell. Physiol. 232: 1501-1510, 2017. © 2016 Wiley Periodicals, Inc.

Astrocytes: inexplicable cells in neurodegeneration

Astrocytes are the most explored non-neuronal cells in the brain under neurophysiological and neurodegenerative conditions. Extensive research has been done to understand their specific role during neuropathological conditions but still the existing findings could not conclude their mechanism of action and their specific role in neurodegenerative conditions. This review discusses their physiological and pathological roles, their activation, morphological alterations and their probable use in search of new therapeutic targets for the treatment of neurodegenerative diseases.

Salubrinal inhibits the expression of proteoglycans and favors neurite outgrowth from cortical neurons in vitro

After CNS injury, astrocytes and mesenchymal cells attempt to restore the disrupted glia limitans by secreting proteoglycans and extracellular matrix proteins (ECMs), forming the so-called glial scar. Although the glial scar is important in sealing the lesion, it is also a physical and functional barrier that prevents axonal regeneration. The synthesis of secretory proteins in the RER is under the control of the initiation factor of translation eIF2α. Inhibiting the synthesis of secretory proteins by increasing the phosphorylation of eIF2α, might be a pharmacologically efficient way of reducing proteoglycans and other profibrotic proteins present in the glial scar. Salubrinal, a neuroprotective drug, decreased the expression and secretion of proteoglycans and other profibrotic proteins induced by EGF or TGFβ, maintaining eIF2α phosphorylated. Besides, Salubrinal also reduced the transcription of proteoglycans and other profibrotic proteins, suggesting that it induced the degradation of non-translated mRNA. In a model in vitro of the glial scar, cortical neurons grown on cocultures of astrocytes and fibroblasts with TGFβ treated with Salubrinal, showed increased neurite outgrowth compared to untreated cells. Our results suggest that Salubrinal may be considered of therapeutic value facilitating axonal regeneration, by reducing overproduction and secretion of proteoglycans and profibrotic protein inhibitors of axonal growth.

Titania nanotube arrays as interfaces for neural prostheses

Neural prostheses have become ever more acceptable treatments for many different types of neurological damage and disease. Here we investigate the use of two different morphologies of titania nanotube arrays as interfaces to advance the longevity and effectiveness of these prostheses. The nanotube arrays were characterized for their nanotopography, crystallinity, conductivity, wettability, surface mechanical properties and adsorption of key proteins: fibrinogen, albumin and laminin. The loosely packed nanotube arrays fabricated using a diethylene glycol based electrolyte, contained a higher presence of the anatase crystal phase and were subsequently more conductive. These arrays yielded surfaces with higher wettability and lower modulus than the densely packed nanotube arrays fabricated using water based electrolyte. Further the adhesion, proliferation and differentiation of the C17.2 neural stem cell line was investigated on the nanotube arrays. The proliferation ratio of the cells as well as the level of neuronal differentiation was seen to increase on the loosely packed arrays. The results indicate that loosely packed nanotube arrays similar to the ones produced here with a DEG based electrolyte, may provide a favorable template for growth and maintenance of C17.2 neural stem cell line.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

A microfluidic neuronal platform for neuron axotomy and controlled regenerative studies

We have presented here a simple microfluidic approach to model mechanical and synchronized axotomy of a large number of axons to study axonal regeneration, and to facilitate rapid screening and discovery of novel pharmaceutical compounds.

Proteoglycans: road signs for neurite outgrowth

Proteoglycans in the central nervous system play integral roles as "traffic signals" for the direction of neurite outgrowth. This attribute of proteoglycans is a major factor in regeneration of the injured central nervous system. In this review, the structures of proteoglycans and the evidence suggesting their involvement in the response following spinal cord injury are presented. The review further describes the methods routinely used to determine the effect proteoglycans have on neurite outgrowth. The effects of proteoglycans on neurite outgrowth are not completely understood as there is disagreement on what component of the molecule is interacting with growing neurites and this ambiguity is chronicled in an historical context. Finally, the most recent findings suggesting possible receptors, interactions, and sulfation patterns that may be important in eliciting the effect of proteoglycans on neurite outgrowth are discussed. A greater understanding of the proteoglycan-neurite interaction is necessary for successfully promoting regeneration in the injured central nervous system.

Repair of injured spinal cord using biomaterial scaffolds and stem cells

The loss of neurons and degeneration of axons after spinal cord injury result in the loss of sensory and motor functions. A bridging biomaterial construct that allows the axons to grow through has been investigated for the repair of injured spinal cord. Due to the hostility of the microenvironment in the lesion, multiple conditions need to be fulfilled to achieve improved functional recovery. A scaffold has been applied to bridge the gap of the lesion as contact guidance for axonal growth and to act as a vehicle to deliver stem cells in order to modify the microenvironment. Stem cells may improve functional recovery of the injured spinal cord by providing trophic support or directly replacing neurons and their support cells. Neural stem cells and mesenchymal stem cells have been seeded into biomaterial scaffolds and investigated for spinal cord regeneration. Both natural and synthetic biomaterials have increased stem cell survival in vivo by providing the cells with a controlled microenvironment in which cell growth and differentiation are facilitated. This optimal multi‒disciplinary approach of combining biomaterials, stem cells, and biomolecules offers a promising treatment for the injured spinal cord.

The Astroglial Reaction along the Mouse Cochlear Nerve following Inner Ear Damage

Objective

Determine how the astroglial cells of the peripheral and central nervous system transitional zone (PCTZ) react to sensorineural hearing loss using a mouse cochlear nerve model.

Study Design

Prospective, basic science.

Setting

Research laboratory.

Subjects and Methods

Neomycin was injected into the mouse inner ear to cause chemically induced hearing loss. Auditory brainstem responses (ABRs) were used to determine hearing threshold shifts after neomycin treatment. Immunofluorescence was used to detect the expression of proteins specific for hair cells, spiral ganglion neurons, astrocytes, and the myelin components of both oligodendrocytes and Schwann cells.

Results

ABR threshold shifts and immunofluorescence results supported that hair cells and spiral ganglion neurons were damaged in neomycin-treated mice. Immunofluorescence showed the peripheral and central nervous system (PNS and CNS) transitional zone of the cochlear nerve at the interface of the myelin components of the PNS and CNS. In the control mice, the expression of glial fibrillary acidic protein (GFAP) was observed proximally to the PCTZ closer to the CNS, which is their normal location. However, in neomycin-treated animals the expression of GFAP was detected distally to the PCTZ and was found close to the spiral lamina level in the basal cochlear turn, suggesting that GFAP-expressing astrocytes migrated across the PCTZ and reached the PNS.

Conclusion

The GFAP positive astrocyte processes extended across the PCTZ along the mouse cochlear nerve following chemically induced sensorineural hearing loss.

Proliferation of a subpopulation of reactive astrocytes following needle-insertion lesion in rat

It is well known that traumatic injuries of the CNS induce a gliotic reaction, characterized by the presence of reactive astrocytes. Reactive astrocytes exhibit enhanced expression of the astrocyte-specific intermediate filament, glial fibrillary acidic protein (GFAP), hypertrophy, and thickened processes. Recently, we have demonstrated that injuries of the CNS induce a re-expression of an embryonic intermediate filament-associated protein, IFAP-70/280 kDa. Based on IFAP-70/280 kDa immunolabeling, we have shown that reactive astrocytes, activated by stab-wound injury, can be divided into two major groups: 1. persistent IFAP+/GFAP+ cells which are close to the wound in the area of glial scar, and 2. transient IFAP-/GFAP+ cells which are farther from the wound. In this study, we use BrdU incorporation to examine proliferation in these two groups of reactive astrocytes induced by stab injury of the rat cerebrum. Triple/double-label immunofluorescence microscopy was performed using antibodies to IFAP-70/280 kDa, GFAP, and BrdU. The results showed that BrdU+ reactive astrocytes (GFAP+) were always IFAB-70/280 kDa+ as well. However, not all IFAP+ reactive astrocytes are BrdU+. BrdU+ signal was not observed in any IFAP- reactive astrocytes. At five days post-lesion, IFAP+ reactive astrocytes were increasing in the area of the wound (0-50 micrograms from the wound edge), but had reached a peak in the proximal area (50-800 micrograms away from the wound edge). At eight days post-lesion, IFAP+ reactive astrocytes achieved the highest percentage in the wound area. At the same time, BrdU-containing reactive astrocytes occupied an area closer to the wound. By 20 days post-lesion, following the formation of the gliotic scar at the stab-wound, a few IFAP+/GFAP+ cells still persisted. BrdU-containing reactive astrocytes were only observed in the scar. These results indicate that many IFAP+ reactive astrocytes close to the wound, in contrast to the IFAP- ones farther from the wound, appear to regain their proliferative potential to increase in number and participate in the formation of the gliotic scar.

Neurochemical profile of dementia pugilistica

Dementia pugilistica (DP), a suite of neuropathological and cognitive function declines after chronic traumatic brain injury (TBI), is present in approximately 20% of retired boxers. Epidemiological studies indicate TBI is a risk factor for neurodegenerative disorders including Alzheimer disease (AD) and Parkinson disease (PD). Some biochemical alterations observed in AD and PD may be recapitulated in DP and other TBI persons. In this report, we investigate long-term biochemical changes in the brains of former boxers with neuropathologically confirmed DP. Our experiments revealed biochemical and cellular alterations in DP that are complementary to and extend information already provided by histological methods. ELISA and one-dimensional and two dimensional Western blot techniques revealed differential expression of select molecules between three patients with DP and three age-matched non-demented control (NDC) persons without a history of TBI. Structural changes such as disturbances in the expression and processing of glial fibrillary acidic protein, tau, and α-synuclein were evident. The levels of the Aβ-degrading enzyme neprilysin were reduced in the patients with DP. Amyloid-β levels were elevated in the DP participant with the concomitant diagnosis of AD. In addition, the levels of brain-derived neurotrophic factor and the axonal transport proteins kinesin and dynein were substantially decreased in DP relative to NDC participants. Traumatic brain injury is a risk factor for dementia development, and our findings are consistent with permanent structural and functional damage in the cerebral cortex and white matter of boxers. Understanding the precise threshold of damage needed for the induction of pathology in DP and TBI is vital.

Astrocytes acquire morphological and functional characteristics of ependymal cells following disruption of ependyma in hydrocephalus

Hydrocephalic hyh mutant mice undergo a programmed loss of the neuroepithelium/ependyma followed by a reaction of periventricular astrocytes, which form a new cell layer covering the denuded ventricular surface. We present a comparative morphological and functional study of the newly formed layer of astrocytes and the multiciliated ependyma of hyh mice. Transmission electron microscopy, immunocytochemistry for junction proteins (N-cadherin, connexin 43) and proteins involved in permeability (aquaporin 4) and endocytosis (caveolin-1, EEA1) were used. Horseradish peroxidase (HRP) and lanthanum nitrate were used to trace the intracellular and paracellular transport routes. The astrocyte layer shares several cytological features with the normal multiciliated ependyma, such as numerous microvilli projected into the ventricle, extensive cell–cell interdigitations and connexin 43-based gap junctions, suggesting that these astrocytes are coupled to play an unknown function as a cell layer. The ependyma and the astrocyte layers also share transport properties: (1) high expression of aquaporin 4, caveolin-1 and the endosome marker EEA1; (2) internalization into endocytic vesicles and early endosomes of HRP injected into the ventricle; (3) and a similar paracellular route of molecules moving between CSF, the subependymal neuropile and the pericapillary space, as shown by lanthanum nitrate and HRP. A parallel analysis performed in human hydrocephalic foetuses indicated that a similar phenomenon would occur in humans. We suggest that in foetal-onset hydrocephalus, the astrocyte assembly at the denuded ventricular walls functions as a CSF–brain barrier involved in water and solute transport, thus contributing to re-establish lost functions at the brain parenchyma–CSF interphase.

Post-ischemic estradiol treatment reduced glial response and triggers distinct cortical and hippocampal signaling in a rat model of cerebral ischemia

BACKGROUND

Estradiol has been shown to exert neuroprotective effects in several neurodegenerative conditions, including cerebral ischemia. The presence of this hormone prior to ischemia attenuates the damage associated with such events in a rodent model (middle cerebral artery occlusion (MCAO)), although its therapeutic value when administered post-ischemia has not been assessed. Hence, we evaluated the effects of estradiol treatment after permanent MCAO (pMCAO) was induced in rats, studying the PI3K/AKT/GSK3/β-catenin survival pathway and the activation of SAPK-JNK in two brain areas differently affected by pMCAO: the cortex and hippocampus. In addition, we analyzed the effect of estradiol on the glial response to injury.

METHODS

Male rats were subjected to pMCAO and estradiol (0.04 mg/kg) was administered 6, 24, and 48 h after surgery. The animals were sacrificed 6 h after the last treatment, and brain damage was evaluated by immunohistochemical quantification of 'reactive gliosis' using antibodies against GFAP and Iba1. In addition, Akt, phospho-Akt(Ser473), phospho-Akt(Thr308), GSK3, phospho-GSK3(Ser21/9), β-catenin, SAPK-JNK, and pSAPK-JNK(Thr183/Tyr185) levels were determined in western blots of the ipsilateral cerebral cortex and hippocampus, and regional differences in neuronal phospho-Akt expression were determined by immunohistochemistry.

RESULTS

The increases in the percentage of GFAP- (5.25-fold) and Iba1- (1.8-fold) labeled cells in the cortex and hippocampus indicate that pMCAO induced 'reactive gliosis'. This effect was prevented by post-ischemic estradiol treatment; diminished the number of these cells to those comparable with control animals. pMCAO down-regulated the PI3K/AkT/GSK3/β-catenin survival pathway to different extents in the cortex and hippocampus, the activity of which was restored by estradiol treatment more efficiently in the cerebral cortex (the most affected region) than in the hippocampus. No changes in the phosphorylation of SAPK-JNK were observed 54 h after inducing pMCAO, whereas pMCAO did significantly decrease the phospho-Akt(Ser473) in neurons, an effect that was reversed by estradiol.

CONCLUSION

The present study demonstrates that post-pMCAO estradiol treatment attenuates ischemic injury in both neurons and glia, events in which the PI3K/AKT/GSK3/β-catenin pathway is at least partly involved. These findings indicate that estradiol is a potentially useful treatment to enhance recovery after human ischemic stroke.

Transplantation of Olfactory Ensheathing Cells as Adjunct Cell Therapy for Peripheral Nerve Injury

Traumatic events, such as work place trauma or motor vehicle accident violence, result in a significant number of severe peripheral nerve lesions, including nerve crush and nerve disruption defects. Transplantation of myelin-forming cells, such as Schwann cells (SCs) or olfactory ensheathing cells (OECs), may be beneficial to the regenerative process because the applied cells could mediate neurotrophic and neuroprotective effects by secretion of chemokines. Moreover, myelin-forming cells are capable of bridging the repair site by establishing an environment permissive to axonal regeneration. The cell types that are subject to intense investigation include SCs and OECs either derived from the olfactory bulb or the olfactory mucosa, stromal cells from bone marrow (mesenchymal stem cells, MSCs), and adipose tissue-derived cells. OECs reside in the peripheral and central nervous system and have been suggested to display unique regenerative properties. However, so far OECs were mainly used in experimental studies to foster central regeneration and it was not until recently that their regeneration-promoting activity for the peripheral nervous system was recognized. In the present review, we summarize recent experimental evidence regarding the regenerative effects of OECs applied to the peripheral nervous system that may be relevant to design novel autologous cell transplantation therapies.

Chapter 22: Transplantation of olfactory ensheathing cells for peripheral nerve regeneration

Peripheral nerve injury is a common clinical problem, and the development of novel strategies to enhance peripheral nerve regeneration is important. Traumatic events, including motor vehicle accidents, sports-related injuries, violence, and falls, lead to significant numbers of peripheral nerve lesions. Traumatic nerve injuries are often associated with life-threatening injuries, which must be treated first. During the delay in nerve repair, the transected nerves undergo Wallerian degeneration. Therefore, delay before surgical treatment is critical, but care must also be taken to ensure that nerve reapposition is performed in a manner that will result in a therapeutic benefit. Peripheral nerve repair after transection injury combined with transplantation of myelin-forming glia cells, for example, Schwann cells (SCs) or olfactory ensheathing cells (OECs), may facilitate the regenerative process. Cell-based therapies are being considered in clinical trials for a number of neurological diseases, including multiple sclerosis, spinal cord injury, Parkinson's disease, and stroke. The rationale is that transplanted cells may provide neuroprotection by production of chemokines and neurotrophins or could serve as a replacement therapy. A number of cells derived from adult peripheral tissues for cell therapies are also being actively investigated. These cells include SCs from peripheral nerve, olfactory OECs from the olfactory system, and stromal cells from bone marrow (mesenchymal stem cells, MSCs). In principle, these cells could be derived autologously, and used acutely or expanded in culture and used for cell-based therapies. Here, we review experimental work demonstrating the potential of one of these cells, the OEC, as an experimental tool for promoting recovery in peripheral nerve injury.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

Glial and axonal regeneration following spinal cord injury

Spinal cord injury (SCI) has been regarded clinically as an irreversible damage caused by tissue contusion due to a blunt external force. Past research had focused on the analysis of the pathogenesis of secondary injury that extends from the injury epicenter to the periphery, as well as tissue damage and neural cell death associated with secondary injury. Recent studies, however, have proven that neural stem (progenitor) cells are also present in the brain and spinal cord of adult mammals including humans. Analyses using spinal cord injury models have also demonstrated active dynamics of cells expressing several stem cell markers, and methods aiming at functional reconstruction by promoting the potential self-regeneration capacity of the spinal cord are being explored. Furthermore, reconstruction of the neural circuit requires not only replenishment or regeneration of neural cells but also regeneration of axons. Analysis of the tissue microenvironment after spinal cord injury and research aiming to remove axonal regeneration inhibitors have also made progress. SCI is one of the simplest central nervous injuries, but its pathogenesis is associated with diverse factors, and further studies are required to elucidate these complex interactions in order to achieve spinal cord regeneration and functional reconstruction.

Down-regulation of neurocan expression in reactive astrocytes promotes axonal regeneration and facilitates the neurorestorative effects of bone marrow stromal cells in the ischemic rat brain

The glial scar, a primarily astrocytic structure bordering the infarct tissue inhibits axonal regeneration after stroke. Neurocan, an axonal extension inhibitory molecule, is up-regulated in the scar region after stroke. Bone marrow stromal cells (BMSCs) reduce the thickness of glial scar wall and facilitate axonal remodeling in the ischemic boundary zone. To further clarify the role of BMSCs in axonal regeneration and its underlying mechanism, the current study focused on the effect of BMSCs on neurocan expression in the ischemic brain. Thirty-one adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion followed by an injection of 3 x 10(6) rat BMSCs (n = 16) or phosphate-buffered saline (n = 15) into the tail vein 24 h later. Animals were sacrificed at 8 days after stroke. Immunostaining analysis showed that reactive astrocytes were the primary source of neurocan, and BMSC-treated animals had significantly lower neurocan and higher growth associated protein 43 expression in the penumbral region compared with control rats, which was confirmed by Western blot analysis of the brain tissue. To further investigate the effects of BMSCs on astrocyte neurocan expression, single reactive astrocytes were collected from the ischemic boundary zone using laser capture microdissection. Neurocan gene expression was significantly down-regulated in rats receiving BMSC transplantation (n = 4/group). Primary cultured astrocytes showed similar alterations; BMSC coculture during reoxygenation abolished the up-regulation of neurocan gene in astrocytes undergoing oxygen-glucose deprivation (n = 3/group). Our data suggest that BMSCs promote axonal regeneration by reducing neurocan expression in peri-infarct astrocytes.

Transplantation of olfactory ensheathing cells enhances peripheral nerve regeneration after microsurgical nerve repair

While axonal regeneration is more successful in peripheral nerve than in the central nervous system, it is by no means complete and research to enhance peripheral nerve regeneration is clinically important. Olfactory ensheathing cells (OECs) are known to enhance axonal regeneration and to produce myelin after transplantation. In contrast to Schwann cells their migratory potential and ability to penetrate glial scars is higher. This study evaluated the effect of OEC transplantation on microsurgically repaired sciatic nerves. Rat sciatic nerves were transected followed by microsurgical repair and transplantation of OECs or injection of medium without cells. Twenty-one days later the nerves were removed and prepared for either histology or electrophysiological analysis. Footprint analysis was carried out at 7, 14 and 21 days. The OECs survived and integrated into the repaired nerves as indicated by eGFP-expressing cells aligned with neurofilament identified axons bridging the repair site. Moreover, regenerated axons were myelinated by the transplanted OECs and nodes of Ranvier were formed. Conduction velocity in the OEC transplant group was increased in comparison to the microsurgical repair alone, and improved stepping was observed in the transplant group. These results suggest that presentation of OECs at the time of nerve injury enhances regeneration and improves functional outcome. Even a modest improvement in nerve regeneration could have significant clinical implications for reconstructive nerve surgery.

Recording advances for neural prosthetics

An important challenge for neural prosthetics research is to record from populations of neurons over long periods of time, ideally for the lifetime of the patient. Two new advances toward this goal are described, the use of local field potentials (LFPs) and autonomously positioned recording electrodes. LFPs are the composite extracellular potential field from several hundreds of neurons around the electrode tip. LFP recordings can be maintained for longer periods of time than single cell recordings. We find that similar information can be decoded from LFP and spike recordings, with better performance for state decodes with LFPs and, depending on the area, equivalent or slightly less than equivalent performance for signaling the direction of planned movements. Movable electrodes in microdrives can be adjusted in the tissue to optimize recordings, but their movements must be automated to be a practical benefit to patients. We have developed automation algorithms and a meso-scale autonomous electrode testbed, and demonstrated that this system can autonomously isolate and maintain the recorded signal quality of single cells in the cortex of awake, behaving monkeys. These two advances show promise for developing very long term recording for neural prosthetic applications.

Reduction of astrogliosis and microgliosis by cerebrospinal fluid shunting in experimental hydrocephalus

Background

Reactive gliosis has the potential to alter biomechanical properties of the brain, impede neuronal regeneration and affect plasticity. Determining the onset and progression of reactive astrogliosis and microgliosis due to hydrocephalus is important for designing better clinical treatments.

Methods

Reactive astrogliosis and microgliosis were evaluated as the severity of hydrocephalus increased with age in hydrocephalic H-Tx rats and control littermates. Previous studies have suggested that gliosis may persist after short-term drainage (shunt treatment) of the cerebrospinal fluid. Therefore shunts were placed in 15d hydrocephalic rats that were sacrificed after 6d (21d of age) or after 21d (36d of age). Tissue was processed for Western blot procedures and immunohistochemistry, and probed for the astrocytic protein, Glial Fibrillary Acidic Protein (GFAP) and for microglial protein, Isolectin B4 (ILB4).

Results

In the parietal cortex of untreated hydrocephalic animals, GFAP levels increased significantly at 5d and at 12d compared to age-matched control rats. There was a continued increase in GFAP levels over control at 21d and at 36d. Shunting prevented some of the increase in GFAP levels in the parietal cortex. In the occipital cortex of untreated hydrocephalic animals, there was a significant increase over control in levels of GFAP at 5d. This trend continued in the 12d animals, although not significantly. Significant increases in GFAP levels were present in 21d and in 36d animals. Shunting significantly reduced GFAP levels in the 36d shunted group. Quantitative grading of immuno-stained sections showed similar changes in GFAP stained astrocytes.

Immuno-stained microglia were altered in shape in hydrocephalic animals. At 5d and 12d, they appeared to be developmentally delayed with a lack of processes. Older 21d and 36d hydrocephalic animals exhibited the characteristics of activated microglia, with thicker processes and enlarged cell bodies. Following shunting, fewer activated microglia were present.

Histologic examination of the periventricular area and the periaqueductal area showed similar findings with the 21d and 36d animals having increased populations of both astrocytes and microglia which were reduced following shunting with a more dramatic reduction in the long term shunted animals.

Conclusion

Overall, these results suggest that reactive astrocytosis and microgliosis are associated with progressive untreated ventriculomegaly, but that shunt treatment can reduce the gliosis occurring with hydrocephalus.

Astrogliosis is delayed in type 1 interleukin-1 receptor-null mice following a penetrating brain injury

The cytokines IL-1α and IL-1β are induced rapidly after insults to the CNS, and their subsequent signaling through the type 1 IL-1 receptor (IL-1R1) has been regarded as essential for a normal astroglial and microglial/macrophage response. To determine whether abrogating signaling through the IL-1R1 will alter the cardinal astrocytic responses to injury, we analyzed molecules characteristic of activated astrocytes in response to a penetrating stab wound in wild type mice and mice with a targeted deletion of IL-1R1. Here we show that after a stab wound injury, glial fibrillary acidic protein (GFAP) induction on a per cell basis is delayed in the IL-1R1-null mice compared to wild type counterparts. However, the induction of chondroitin sulfate proteoglycans, tenascin, S-100B as well as glutamate transporter proteins, GLAST and GLT-1, and glutamine synthetase are independent of IL-1RI signaling. Cumulatively, our studies on gliosis in the IL-1R1-null mice indicate that abrogating IL-1R1 signaling delays some responses of astroglial activation; however, many of the important neuroprotective adaptations of astrocytes to brain trauma are preserved. These data recommend the continued development of therapeutics to abrogate IL-1R1 signaling to treat traumatic brain injuries. However, astroglial scar related proteins were induced irrespective of blocking IL-1R1 signaling and thus, other therapeutic strategies will be required to inhibit glial scarring.

Collagen matrix in spinal cord injury

The fibrous scar that develops after central nervous system (CNS) injury is considered a major impediment for axonal regeneration. It consists of a dense collagen IV meshwork, which serves as a binding matrix for numerous other extracellular matrix components and inhibitory molecules like proteoglycans and semaphorins, but also growth-promoting factors. Inhibition of collagen matrix formation in brain and spinal cord lesions leads to axonal regeneration and functional recovery, although collagen IV per se is not inhibitory for axonal outgrowth. This review focuses on the molecular properties of the collagen IV matrix and its interactions with various molecules that are expressed after CNS lesion. Moreover, studies on collagen expression and matrix formation after injury of regenerating versus non-regenerating nervous systems are reviewed. Major differences in collagen deposition in the CNS and the peripheral nervous system (PNS) and differences in specific cell responses to extracellular matrix deposition in the lesion area are discussed. Therapeutic treatments aiming at suppression of fibrous scarring have been shown to promote axon regeneration in various lesion paradigms of the mammalian CNS.

Cognitive neural prosthetics

Research on neural prosthetics has focused largely on using activity related to hand trajectories recorded from motor cortical areas. An interesting question revolves around what other signals might be read out from the brain and used for neural prosthetic applications. Recent studies indicate that goals and expected value are among the high-level cognitive signals that can be used and will potentially enhance the ability of paralyzed patients to communicate with the outside world. Other new findings show that local field potentials provide an excellent source of information about the cognitive state of the subject and are much easier to record and maintain than spike activity. Finally, new movable probe technologies will enable recording electrodes to seek out automatically the best signals for decoding cognitive variables.

Expression of neurocan after transient middle cerebral artery occlusion in adult rat brain

Neurocan is one of the major chondroitin sulfate proteoglycans in the nervous tissues. The expression and proteolytic cleavage of neurocan are developmentally regulated in the normal rat brain, and the full-length neurocan is detected in juvenile brains but not in normal adult brains. Recently, some studies showed that the full-length neurocan was detectable even in the adult brain when it was exposed to mechanical incision or epileptic stimulation. In the present study, we demonstrated by Western blot analysis that the full-length neurocan transiently appeared in the peri-ischemic region of transient middle cerebral artery occlusion (tMCAO) in adult rat with a peak level at 4 days after tMCAO. Immunohistochemical analysis showed that a clear positive signal of neurocan was observed 4 days after tMCAO in the peri-ischemic region of cerebral cortex and caudate, where cells strongly positive in GFAP expression were also distributed. These results indicate that accumulation of the full-length neurocan produced by reactive astrocytes may be one of the processes for tissue repair and reconstruction of neural networks after focal brain ischemia as well.

Contact guidance induced organization of extracellular matrix

The scarring response following injury to the central nervous system disrupts the anatomical organization of nervous tissue posing a barrier to the regeneration of axons. In the present study, using materials with nanometer level surface features we examined whether matrix organization could be controlled by engineering meningeal cell asymmetry. Following 5 days in culture, the organization of meningeal cells along with their cytoskeletal elements and extracellular matrix proteins was evaluated. Meningeal cell morphology was markedly affected by nanometer level substrate topography. Cell alignment increased with increasing surface roughness. In addition, linear arrays of extracellular matrix were expressed that appeared related to cellular orientation. When cultured on substrates with topographical features of less than 10 nm neither cells nor their extracellular matrix showed organizational asymmetry. However, as oriented surface roughness increased, cellular and matrix asymmetrical organization became more pronounced reaching a threshold at 345 nm. These results suggest that biomaterial surface topography or other methods of altering the orientation of cells may be used to engineer orientation into the secreted extracellular matrix and as such may be a potential strategy for developing organized cell-derived matrix as a bridging material for nerve repair or other regenerative applications.

Effects of progesterone on the inflammatory response to brain injury in the rat

The effects of progesterone on the cellular inflammatory response to frontal cortex injury were examined on postsurgical days 1, 3, 5, 7 and 9 in male rats treated with progesterone (4 mg/kg) and/or vehicle. Rats with bilateral contusions showed increased levels of edema on days 1, 3 and 5, more reactive astrocytes on days 3, 5, 7 and 9, and more macrophages/activated microglia on days 1, 3, 5 and 9 compared to shams. The number of neurons in the medial dorsal nucleus (MDN) of the thalamus reduced on days 5 and 9 after injury compared to shams. Progesterone reduced edema levels and increased the accumulation of macrophages/activated microglia compared to vehicle controls (p<0.025); however, these changes in the inflammatory response were not related to MDN neuronal survival. Our results confirm the possibility that one way progesterone mediates its neuroprotective effects following injury is through its actions on the inflammatory response.

Central nervous system lesions that can and those that cannot be repaired with the help of olfactory bulb ensheathing cell transplants

Growth-promoting macroglia (aldynoglia) with growth properties and immunological markers similar to Schwann cells, are found in loci of the mammalian CNS where axon regeneration occurs throughout life, like the olfactory sytem, hypothalamus-hypophysis and the pineal gland. Contrary to Schwann cells, aldynoglia mingle freely with astrocytes and can migrate in brain and spinal cord. Transplantation of cultured and immunopurified olfactory ensheathing cells (OECs) in the spinal cord after multiple central rhizotomy, promoted sensory and central axon growth and partial functional restoration, judging by anatomical, electrophysiological and behavioural criteria. OEC transplants suppressed astrocyte reactivity, thus generally favouring axon growth after a lesion. However, the functional repair promoted by OEC transplants was partial in the best cases, depending on lesion type and location. Cyst formation after photochemical cord lesion was partially prevented but neither the corticospinal tract, interrupted by a mild contusion, nor the sectioned medial longitudinal fascicle, did regrow after OEC transplantation in the injured area.

Brain responses to micro-machined silicon devices

Micro-machined neural prosthetic devices can be designed and fabricated to permit recording and stimulation of specific sites in the nervous system. Unfortunately, the long-term use of these devices is compromised by cellular encapsulation. The goals of this study were to determine if device size, surface characteristics, or insertion method affected this response. Devices with two general designs were used. One group had chisel-shaped tips, sharp angular corners, and surface irregularities on the micrometer size scale. The second group had rounded corners, and smooth surfaces. Devices of the first group were inserted using a microprocessor-controlled inserter. Devices of the second group were inserted by hand. Comparisons were made of responses to the larger devices in the first group with devices from the second group. Responses were assessed 1 day and 1, 2, 4, 6, and 12 weeks after insertions. Tissues were immunochemically labeled for glial fibrillary acidic protein (GFAP) or vimentin to identify astrocytes, or for ED1 to identify microglia. For the second comparison devices from the first group with different cross-sectional areas were analyzed. Similar reactive responses were observed following insertion of all devices; however, the volume of tissue involved at early times, <1 week, was proportional to the cross-sectional area of the devices. Responses observed after 4 weeks were similar for all devices. Thus, the continued presence of devices promotes formation of a sheath composed partly of reactive astrocytes and microglia. Both GFAP-positive and -negative cells were adherent to all devices. These data indicate that device insertion promotes two responses-an early response that is proportional to device size and a sustained response that is independent of device size, geometry, and surface roughness. The early response may be associated with the amount of damage generated during insertion. The sustained response is more likely due to tissue-device interactions.

Macroglia distribution in the developing and adult inferior colliculus

Macroglia distribution in the developing and adult gerbil inferior colliculus (IC) was investigated using two oligodendrocytic [myelin-associated-glycoprotein (MAG) and oligodendrocyte-specific molecule (Rip)] and two astrocytic [glial fibrillary acidic protein (GFAP) and S100] markers and immunohistochemistry. There was a spatio-temporal pattern of myelin marker expression starting in the ventral area of the IC and continuing to the dorsal part of the nucleus. Myelination, as revealed by MAG and Rip markers, starts in the IC during the second postnatal week. The intensity of myelination increased between stages P15 and P21 and extended to the whole IC. The appearance of myelin proteins in the IC may suggest a possible axonal outgrowth inhibition by oligodendrocytes in this structure. A differential pattern of staining was obtained with S100 and GFAP antibodies. Astrocytes identified as S100 immunoreactive cells were observed in the IC by birth and the staining was localized to their cell body and processes. S100 positive cells were homogeneously distributed within the IC nucleus. S100 pattern of staining remained the same in stages P7, P15 and P21. In adult IC, S100 positive cell processes were in contact with neuronal cell bodies, other S100 positive cells and blood vessels. Quantitative analysis showed an increase in the density of positive cells during the first postnatal week and a decrease then after through to adulthood. Unlike S100, GFAP immunoreactivity showed a different pattern of staining. At birth GFAP positive astrocytes were observed along the collicular brain midline and around the IC nucleus delimiting its boundaries. The GFAP pattern of labelling remained the same during development and in the adult. This data suggests the presence of two astrocytes subtypes with different locations in the IC nucleus. The GFAP positive astrocytes were located along the edge of the nucleus, while the S100 positive ones displayed a homogeneous distribution across the nucleus.

Oligodendrocyte progenitor migration in response to injury of glial monolayers requires the polysialic neural cell-adhesion molecule

Injury to the nervous system results in reactive astrogliosis that is a critical determinant of neuronal regeneration. To analyze glial responses to mechanical injury and the role of the polysialic neural cell adhesion molecule (PSA-NCAM) in this process, we established primary glia cultures from newborn rat cerebral cortex. Scratching a confluent monolayer of primary glial cells resulted in two major events: rapid migration of oligodendrocyte progenitor-like (O-2A) cells into the wounded area and development of polarized morphology of type 1 astrocytes at the wound edge. Migrating O-2A progenitors had a bipolar morphology and exhibited A2B5 and O4 immunolabeling. Once these cells were established inside the wounded area, they lost A2B5 immunoreactivity and differentiated into glial fibrillary acidic protein-positive astrocytes. Migrating O-2A cells expressed PSA-NCAM, but type 1 astrocytes at the wound edge did not. Treatment of wounded cultures with Endo-N, which specifically removes PSA from the surface of cells, resulted in a significant decrease in O-2A cell migration into the wounded area and completely blocked the wound closure. Video time-lapse analysis showed that, in the presence of Endo-N, O-2A cells remained motile and migrated short distances but did not move away from the monolayer. These results demonstrate that O-2A progenitors contribute to reactive astrogliosis in culture and that PSA-NCAM is involved in this process by regulating cell migration.

Neurite outgrowth is impaired on HSP70-positive astrocytes through a mechanism that requires NF-kappaB activation

In the adult central nervous system (CNS), prominent reactive astrocytosis is seen in acute traumatic brain injury, neurodegenerative diseases and a variety of viral infections. Reactive astrocytes synthesize a number of factors that could play different roles in neuronal regeneration. In this study, the effects of thermal stress were evaluated on nuclear factor-kappaB (NF-kappaB) activation and proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) secretion in primary astrocytic cultures. The ability of HSP70-positive astrocytes to support or inhibit neurite outgrowth was investigated in neuron-astrocyte cocultures. Cultured astrocytes from cerebral cortex of rats were exposed to transient hyperthermia (42 degrees C/30 min) and incubated at 37 degrees C for different periods of recovery. During HSP70 accumulation, astrocytes extended large and thick processes associated to rearrangement of glial fibrillary acidic protein (GFAP) filaments and an increase in protein synthesis and GFAP, suggesting an astrogliosis event. A delay of NF-kappaB activation appeared closely related to TNF-alpha secretion by HSP70-positive astrocytes. These cells demonstrated a functional shift from neurite growth-promoting to non-permissive substrate. We also found that gliotoxin, a specific NF-kappaB inhibitor, partially abrogated the inhibitory ability of reactive astrocytes. These findings may suggest a involvement of NF-kappaB and TNF-alpha in modulating the failure of HSP70-positive astrocytes to provide functional support to neuritic outgrowth.

Transient expression of juvenile-type neurocan by reactive astrocytes in adult rat brains injured by kainate-induced seizures as well as surgical incision

Neurocan is one of the major chondroitin sulfate proteoglycans expressed in nervous tissues. The expression of neurocan is developmentally regulated, and full-length neurocan is detected in juvenile brains but not in adult brains. In the present study, we demonstrated by western blot analysis that full-length neurocan transiently appeared in adult rat hippocampus when it was lesioned by kainate-induced seizures. Immunohistochemical studies showed that neurocan was detected mainly around the CA1 region although the seizure resulted in neuronal cell degeneration in both the CA1 and CA3 regions of the hippocampus. Double-labeling for neurocan mRNA and glial fibrillary acidic protein demonstrated that many reactive astrocytes expressed neurocan mRNA. The re-expression of full-length neurocan was also observed in the surgically injured adult rat brain. In contrast, the expression of other nervous tissue chondroitin sulfate proteoglycans, such as phosphacan and neuroglycan C, was not intensified but rather was either reduced in the kainate-lesioned hippocampus or in the surgically injured cerebral cortex. These observations indicate that induction of neurocan expression by reactive astrocytes is a common phenomenon in the repair process of adult brain injury, and therefore, it can be postulated that juvenile-type neurocan plays some roles in brain repair.