Astrocytes and axon regeneration in the central nervous system

Reduced expression of regeneration associated genes in chronically axotomized facial motoneurons

Chronically axotomized motoneurons progressively fail to regenerate their axons. Since axonal regeneration is associated with the increased expression of tubulin, actin and GAP-43, we examined whether the regenerative failure is due to failure of chronically axotomized motoneurons to express and sustain the expression of these regeneration associated genes (RAGs). Chronically axotomized facial motoneurons were subjected to a second axotomy to mimic the clinical surgical procedure of refreshing the proximal nerve stump prior to nerve repair. Expression of α1-tubulin, actin and GAP-43 was analyzed in axotomized motoneurons using in situ hybridization followed by autoradiography and silver grain quantification. The expression of these RAGs by acutely axotomized motoneurons declined over several months. The chronically injured motoneurons responded to a refreshment axotomy with a re-increase in RAG expression. However, this response to a refreshment axotomy of chronically injured facial motoneurons was less than that seen in acutely axotomized facial motoneurons. These data demonstrate that the neuronal RAG expression can be induced by injury-related signals and does not require acute deprivation of target derived factors. The transient expression is consistent with a transient inflammatory response to the injury. We conclude that transient RAG expression in chronically axotomized motoneurons and the weak response of the chronically axotomized motoneurons to a refreshment axotomy provides a plausible explanation for the progressive decline in regenerative capacity of chronically axotomized motoneurons.

A novel mouse model of penetrating brain injury

Penetrating traumatic brain injury (pTBI) has been difficult to model in small laboratory animals, such as rats or mice. Previously, we have established a non-fatal, rat model for pTBI using a modified air-rifle that accelerates a pellet, which hits a small probe that then penetrates the experimental animal’s brain. Knockout and transgenic strains of mice offer attractive tools to study biological reactions induced by TBI. Hence, in the present study, we adapted and modified our model to be used with mice. The technical characterization of the impact device included depth and speed of impact, as well as dimensions of the temporary cavity formed in a brain surrogate material after impact. Biologically, we have focused on three distinct levels of severity (mild, moderate, and severe), and characterized the acute phase response to injury in terms of tissue destruction, neural degeneration, and gliosis. Functional outcome was assessed by measuring bodyweight and motor performance on rotarod. The results showed that this model is capable of reproducing major morphological and neurological changes of pTBI; as such, we recommend its utilization in research studies aiming to unravel the biological events underlying injury and regeneration after pTBI.

Astrocyte transplantation for spinal cord injury: current status and perspective

Spinal cord injury (SCI) often causes incurable neurological dysfunction because axonal regeneration in adult spinal cord is rare. Astrocytes are gradually recognized as being necessary for the regeneration after SCI as they promote axonal growth under both physiological and pathophysiological conditions. Heterogeneous populations of astrocytes have been explored for structural and functional restoration. The results range from the early variable and modest effects of immature astrocyte transplantation to the later significant, but controversial, outcomes of glial-restricted precursor (GRP)-derived astrocyte (GDA) transplantation. However, the traditional neuron-centric view and the concerns about the inhibitory roles of astrocytes after SCI, along with the sporadic studies and the lack of a comprehensive review, have led to some confusion over the usefulness of astrocytes in SCI. It is the purpose of the review to discuss the current status of astrocyte transplantation for SCI based on a dialectical view of the context-dependent manner of astrocyte behavior and the time-associated characteristics of glial scarring. Critical issues are then analyzed to reveal the potential direction of future research.

Characterization of a novel rat model of penetrating traumatic brain injury

A penetrating traumatic brain injury (pTBI) occurs when an object impacts the head with sufficient force to penetrate the skin, skull, and meninges, and inflict injury directly to the brain parenchyma. This type of injury has been notoriously difficult to model in small laboratory animals such as rats or mice. To this end, we have established a novel non-fatal model for pTBI based on a modified air rifle that accelerates a pellet, which in turn impacts a small probe that then causes the injury to the experimental animal's brain. In the present study, we have focused on the acute phase and characterized the tissue destruction, including increasing cavity formation, white matter degeneration, hemorrhage, edema, and gliosis. We also used a battery of behavioral models to examine the neurological outcome, with the most noteworthy finding being impairment of reference memory function. In conclusion, we have described a number of events taking place after pTBI in our model. We expect this model will prove useful in our efforts to unravel the biological events underlying injury and regeneration after pTBI and possibly serve as a useful animal model in the development of novel therapeutic and diagnostic approaches.

Transient and Widespread Astroglial Activation in the Brain after a Striatal 6-Ohda-Induced Partial Lesion of the Nigrostriatal System

The authors have previously described astroglial activation in the ipsilateral nigrostriatal system and ventral tegmental area following small doses of 6-hydroxydopamine (6-OHDA) injected unilaterally in the striatum. This article further evaluated astroglial reactivity in several brain regions after striatal 6-OHDA-induced punctate lesion in the nigrostriatal pathway. Adult male Wistar rats received a unilateral stereotaxical injection of the 6-OHDA (8 microg/4 microl) in the neostriatum and sacrificed 1 or 3 weeks later. Control animals received only solvent. Immunohistochemistry was employed for visualization of the tyrosine hydroxylase (TH), marker for dopamine cells, and glial fibrillary acidic protein (GFAP), marker for astrocytes. TH immunoreactive terminals disappeared in the striatum close to the injection site and a disappearance of a small number of a defined population of dopamine cell bodies was observed in the ipsilateral pars compacta of the substantia nigra (SNc). No dopamine lesion was detected in the contralateral nigrostriatal pathway. Astroglial reaction was seen close to the lesion in the neostriatum and in the ipsilateral SNc of the 1 week 6-OHDA lesioned rats. Specific stereological tools employing point intercepts and rotator, revealed an increased presence of reactive astrocytes in many forebrain regions like frontal, parietal and piriform cortex, septum, neostriatum and SNc, bilaterally, and also corpus callosum after 1 week of 6-OHDA injection. The astroglial activation was characterized by increases in the size of the cell body and/or processes. Astrocytic reaction was found only in the ipsilateral nigrostriatal pathway by 3 weeks of 6-OHDA, a slight activation also remaining in the ipsilateral septum and piriform cortex. Astrocytic reaction was seen in the solvent-injected rats only in the neostriatum close to the needle track. The transient widespread astroglial reaction observed in many brain regions following a striatal injection of 6-OHDA may represent a global paracrine trophic response in the brain.

ASTROGLIAL AND MICROGLIAL ACTIVATION IN THE WISTAR RAT VENTRAL TEGMENTAL AREA AFTER A SINGLE STRIATAL INJECTION OF 6-HYDROXYDOPAMINE

Astroglial and microglial activation were analyzed in the ventral tegmental area (VTA) in adult male Wistar rats, after an unilateral striatal 6-hydroxydopamine (6-OHDA) injection. Different doses (8, 4, and 1 microg) of 6-OHDA were injected in the left side of the neostriatum; animals were sacrificed 22 days later. Control animals received an injection of the same volume of the solvent. The tyrosine hydroxylase (TH) positive dopamine cells, the glial fibrillary acidic protein (GFAP) immuno -labeled astrocytes, and the OX42 immunoreactive microglia were visualized by means of immunohistochemistry and quantified by stereologic methods employing the optical dissector and the point intercepts. The number and the density of TH immunoreactive cell bodies were decreased by 45% and 46%, respectively, in the sampled field of the ipsilateral VTA of 8 microg 6-OHDA injected rats. The GFAP immunohistochemistry revealed in the ipsilateral VTA increases the number and density of astroglial cells (154% and 166% of control, respectively) in the rats with a higher dose of the 6-OHDA, and also in the volume fraction of the astroglial processes after 8 microg (41% of control) and 4 microg (24% of control) of 6-OHDA. Increased number (76% of control) and density (77% of control) of OX42 microglial labeled profiles and microglial processes (51% of control) were found in the ipsilateral VTA of the 8 microg 6-OHDA injected animals. These results suggest that the retrograde degeneration of the mesostriatal dopamine pathways, induced by a striatal injection of 6-OHDA, leads to astroglial and microglial reactions in the VTA. The interaction between activated glial cells may be involved in the wounding and repair events in the partial lesioned system, and also in the trophic paracrine responses in the surviving VTA dopamine neurons.

Induction of corticospinal regeneration by lentiviral trkB-induced Erk activation

Several experimental manipulations of the CNS environment successfully elicit regeneration of sensory and bulbospinal motor axons but fail to elicit regeneration of corticospinal axons, suggesting that cell-intrinsic mechanisms limit the regeneration of this critical class of motor neurons. We hypothesized that enhancement of intrinsic neuronal growth mechanisms would enable adult corticospinal motor axon regeneration. Lentiviral vectors were used to overexpress the BDNF receptor trkB in layer V corticospinal motor neurons. After subcortical axotomy, trkB transduction induced corticospinal axon regeneration into subcortical lesion sites expressing BDNF. In the absence of trkB overexpression, no regeneration occurred. Selective deletion of canonical, trkB-mediated neurite outgrowth signaling by mutation of the Shc/FRS-2 activation domain prohibited Erk activation and eliminated regeneration. These findings support the hypothesis that the refractory regenerative state of adult corticospinal axons can be attributed at least in part to neuron-intrinsic mechanisms, and that activation of ERK signaling can elicit corticospinal tract regeneration.

Nano neurology and the four P's of central nervous system regeneration: preserve, permit, promote, plasticity

True nanomaterials are delivered as a specific structure, or combination of structures, designed to deliver the therapeutic intact, directly to the site, requiring a much lower dose. These materials use very specific and deliberate molecular structures that can interact with neurons or protein structures inside the cells. Until recently, functional recovery of the central nervous system (CNS) was an unattainable goal and nanotechnology was an invisible science. A well-planned treatment spaced over time will produce functional return in the CNS. The four P's of CNS regeneration is a new framework for approaching CNS injury and evidence shows that nanotechnology is currently being used for stroke rehabilitation and, in several clinical trials, the treatment of scar formation blockade in the spinal cord. The four components are preserve, permit, promote, and plasticity.

Nano neuro knitting: peptide nanofiber scaffold for brain repair and axon regeneration with functional return of vision

Nanotechnology is often associated with materials fabrication, microelectronics, and microfluidics. Until now, the use of nanotechnology and molecular self assembly in biomedicine to repair injured brain structures has not been explored. To achieve axonal regeneration after injury in the CNS, several formidable barriers must be overcome, such as scar tissue formation after tissue injury, gaps in nervous tissue formed during phagocytosis of dying cells after injury, and the failure of many adult neurons to initiate axonal extension. Using the mammalian visual system as a model, we report that a designed self-assembling peptide nanofiber scaffold creates a permissive environment for axons not only to regenerate through the site of an acute injury but also to knit the brain tissue together. In experiments using a severed optic tract in the hamster, we show that regenerated axons reconnect to target tissues with sufficient density to promote functional return of vision, as evidenced by visually elicited orienting behavior. The peptide nanofiber scaffold not only represents a previously undiscovered nanobiomedical technology for tissue repair and restoration but also raises the possibility of effective treatment of CNS and other tissue or organ trauma.

Inhibition of collagen synthesis overrides the age-related failure of regeneration of nigrostriatal dopaminergic axons

To investigate the mechanism of the age-related failure of regeneration of transected axons, nigrostriatal dopaminergic axons were unilaterally transected in the lateral hypothalamus in adult mice and in immature mice aged postnatal days 7, 14, and 21. Ten days after the transection, tyrosine hydroxylase-immunoreactive axons had regenerated from caudally to rostrally across the lesion site in mice transected at postnatal day 7, whereas they stopped and did not extend across the lesion site in mice transected at postnatal day 14 or older. Reactive astrocytes bearing chondroitin sulfate proteoglycans were observed around the lesion in mice transected at all ages. However, a fibrotic scar containing type IV collagen-immunoreactive deposits, which was consistently formed at the lesion site in mice transected at postnatal day 14 or older, was not formed in mice lesioned at postnatal day 7. When 2,2'-dipyridyl, an inhibitor of collagen synthesis, was injected into the lesion site at the time of transection in both postnatal day 14 and adult mice, the deposition of type IV collagen and the formation of a fibrotic scar were completely prevented, and large numbers of tyrosine hydroxylase-immunoreactive axons extended across the lesion and reinnervated the striatum. These results imply that the fibrotic scar formed in the lesion site is a crucial impediment to the regeneration of ascending dopaminergic axons in adult mice and suggest that type IV collagen is required for the development of the fibrotic response to adult brain injury.

Glial bFGF and S100 immunoreactivities increase in ascending dopamine pathways following striatal 6-OHDA-induced partial lesion of the nigrostriatal system: a sterological analysis

S100, a calcium-binding protein, and basic fibroblast growth factor (bFGF, FGF-2) are found predominantly in astrocytes in the central nervous system. Those molecules show trophic properties to neurons and are upregulated after brain lesions. The present study investigated the changes in the S100beta and bFGF immunoreactivities after a partial lesion of the rat midbrain ascending dopamine pathways induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA). Stereological method revealed increases in the estimated total number and density of bFGF immunoreactive astroglial profiles in the ipsilateral pars compacta of the substantia nigra (SNc) and ventral tegmental area (VTA). Increases in the counts of astroglial S100beta immunoreactive profiles were found in the striatum, SNc, and VTA mainly ipsilateral but also in the contralateral nuclei. These results open up the possibility that interactions between astroglial S100beta and bFGF may be relevant to paracrine events related to repair and maintenance of remaining dopamine neurons following striatal 6-OHDA induced partial lesion of ascending midbrain dopamine pathway.

Chondroitinase ABCI improves locomotion and bladder function following contusion injury of the rat spinal cord

Chondroitin sulfate proteoglycans are synthesized and deposited in the spinal cord following injury. These proteoglycans may restrict regeneration and plasticity and contribute to the limited recovery seen after an injury. Chondroitinase, a bacterial enzyme that catalyzes the hydrolysis of the chondroitin chains on proteoglycans, has been shown to improve motor and sensory function following partial transection lesions of the spinal cord. To assess the effects of chondroitinase in a clinically relevant model of spinal cord injury, 128 female Long-Evans rats received either a severe, moderate, or mild contusion injury at the vertebral level T9/T10 with a forceps model and were treated for 2 weeks with chondroitinase ABCI at 0.06 Units per dose, penicillinase, or vehicle control via an intrathecal catheter placed near the injury. Motor behavior was measured by open-field testing of locomotion and bladder function monitored by measuring daily residual urine volumes. Animals treated with chondroitinase showed significant improvements in open-field locomotor activity as measured by the Basso, Beattie and Bresnahan scoring system after both severe and moderate SCI (p<0.05 and 0.01, respectively). No significant locomotor differences were observed in the mild injury group. In the moderate injury group, residual urine volumes were reduced with chondroitinase treatment by 2 weeks after injury (p<0.05) and in the severe injury group, by 6 weeks after injury (NS). These results demonstrate that chondroitinase is effective at promoting both somatic and autonomic motor recovery following a clinically relevant contusion spinal cord injury and is a candidate as a therapeutic for human spinal cord injury.

Striatal injection of 6-hydroxydopamine induces retrograde degeneration and glial activation in the nigrostriatal pathway

PURPOSE: The effect of a highly selective 6-hydroxydopamine (6-OHDA)-induced lesion of the nigrostriatal system on the astroglial and microglial activation was analysed in adult Wistar rats after an unilateral striatal injection of the neurotoxin. METHODS: Male rats received an unilateral stereotaxical injection of the 6-OHDA in the left side of the neostriatum and were sacrificed 22 days later. Control animals received the injection of the solvent. The rotational behaviour was registered by a rotometer just before the sacrifice. Immunohistochemistry was employed for visualization of the tyrosine hydroxylase (TH) positive dopamine cells, glial fibrillary acidic protein (GFAP) immunolabeled astrocytes and OX42 immunoreactive microglia. Stereological method employing the optical disector was used to estimate the degree of the changes. RESULTS: The striatal injection of the 6-OHDA induced a massive disappearance (32% of control) of the TH immunoreactive terminals in a defined area within the striatum surrounding the injection site. A disappearance (54% of control) of dopamine cell bodies was observed in a small region of the ipsilateral pars compacta of the substantia nigra (SNc). The GFAP and OX42immunohistochemistry revealed astroglial and microglial reactions (increases in the number and size of the cells) in the ipsilateral neostriatum and SNc of the 6-OHDA injected rats. CONCLUSIONS: The striatal injection of 6-OHDA leads to retrograde degeneration as well as astroglial and microglial activation in the nigrostriatal dopamine pathway. Modulation of activated glial cells may be related to wound repair and to the trophic paracrine response in the lesioned nigrostriatal dopamine system.

Increased syndecan expression by pleiotrophin and FGF receptor-expressing astrocytes in injured brain tissue

Syndecan-1, -2, -3, and -4 are heparan sulfate proteoglycans that are differentially expressed during development and wound repair. To determine whether syndecans are also involved in brain injury, we examined the expression of syndecan core proteins genes in cryo-injured mouse brain, using in situ hybridization. All syndecan mRNA transcripts were similarly expressed in the region surrounding the necrotic tissue, exhibiting peak levels at day 7 after injury. Comparison with cellular markers showed that reactive astrocytes were the primary source of syndecans. Syndecans serve as co-receptors for fibroblast growth factor (FGF) and as a reservoir for another heparin-binding growth factor, pleiotrophin (PTN, or heparin-binding growth-associated molecule. In our model, FGF receptor1 (FGFR1) and PTN mRNA levels were upregulated in reactive astrocytes. The distribution patterns of FGFR1 and PTN overlapped considerably with those of syndecan-1 and -3 mRNAs, respectively. These results suggest that syndecans are expressed primarily in reactive astrocytes, and may provide a supportive environment for regenerating axons in concert with heparin-binding growth factors (e.g., FGF and PTN) in the injured brain.

Astroglial and microglial reaction after a partial nigrostriatal degeneration induced by the striatal injection of different doses of 6-hydroxydopamine

Astroglial and microglial activation was analyzed in adult male Wistar rats after a unilateral striatal injection of different doses (8, 4 and 1 micrograms) of 6-hydroxydopamine (6-OHDA). Control animals received the injection of the same volume of the solvent. The rotational behavior was registered by a rotometer 24 and 72 hours, 7, 10, 14 and 22 days after lesion. Following, animals were sacrificed and the tyrosine hydroxylase (TH) positive dopamine cells, the glial fibrillary acidic protein (GFAP) immunolabeled astrocytes and the OX42 immunoreactive microglia were visualized by mean of immunohistochemistry and quantified by stereologic method employing the optical disector and the point intercepts. The apomorphine (0.5 mg/kg)-induced circling behavior was seen only after 8 micrograms of 6-OHDA from 72 hours postlesion until sacrifice. Decreases of the TH immunoreactive terminals and cell bodies were found in the sampled fields of the striatum and pars compacta of the substantia nigra (SNc), respectively, after 8 and 4 micrograms of 6-OHDA. The GFAP immunohistochemistry revealed increases in the number/density of astroglial cells in the ipsilateral neostriatum (137% of control) and ipsilateral SNc (83% of control) and also in the volumeal fraction of the astroglial processes in the ipsilateral neostriatum (30% of control) and ipsilateral SNc (38% of control) in the rats with higher dose of the neurotoxin. Increases in the number of OX42 microglial labeled profiles and in the volumeal fraction of microglial processes were found in the ipsilateral neostriatum (67% and 27%, respectively, of control) and ipsilateral SNc (100% and 50%, respectively, of control) in the 8 micrograms 6-OHDA injected rats. These results suggest that the retrograde degeneration induced by a intrastriatal injection of a small dose of the 6-OHDA leads to an astroglial and microglial reaction in the nigrostriatal dopamine pathway. The interaction between activated glial cells may be involved in the wounding and repair events in the partial lesioned nigrostriatal system as well as in the paracrine responses to surviving dopamine neurons.

IL-6-type cytokines enhance epidermal growth factor-stimulated astrocyte proliferation

Proliferating astrocytes are frequently observed in diseased and injured brains. These newly generated astrocytes are necessary to reestablish the barriers that isolate the CNS from the rest of the body; however, they also create a matrix that inhibits regeneration and remyelination. Therefore, it is important to understand the mechanisms that enable a terminally differentiated astrocyte to reenter the cell cycle. Ciliary neurotrophic factor (CNTF), interleukin-6 (IL-6), transforming growth factor-alpha (TGF-alpha), and fibroblastic growth factor-2 (FGF-2) are four cytokines that are rapidly elevated in damaged neural tissue. These cytokines also have been implicated in glial scar formation. We sought to determine whether IL-6 and CNTF stimulate astroglial proliferation alone or in combination with other mitogens. Intraparenchymal CNTF modestly increased the number of proliferating cell nuclear antigen (PCNA) and glial fibrillary acidic protein (GFAP) double positive astrocytes when introduced by stereotactic injection into the adult rat brain. When applied directly to highly enriched rat forebrain astrocyte cultures, neither CNTF nor IL-6-stimulated DNA synthesis. Therefore, they are not astroglial mitogens. However, both cytokines synergized with epidermal growth factor (EGF), increasing its mitogenicity by approximately twofold. Astrocytes that had been "aged" for at least 3 weeks in vitro became refractory to EGF; however, when these "aged" astrocytes were pretreated with either IL-6 or CNTF for as little as 2 h, they became competent to reenter the cell cycle upon exposure to EGF. These data suggest that IL-6 type cytokines, likely by activating STAT family transcription factors, induce the expression of signaling molecules that endow resting astrocytes with the competence to respond to mitogens and to reenter the cell cycle.

Laminins and human disease

The laminin protein family has diverse tissue expression patterns and is involved in the pathology of a number of organs, including skin, muscle, and nerve. In the skin, laminins 5 and 6 contribute to dermal-epidermal cohesion, and mutations in the constituent chains result in the blistering phenotype observed in patients with junctional epidermolysis bullosa (JEB). Allelic heterogeneity is observed in patients with JEB: mutations that results in premature stop codons produce a more severe phenotype than do missense mutations. Gene therapy approaches are currently being studied in the treatment of this disease. A blistering phenotype is also observed in patients with acquired cicatricial pemphigoid (CP). Autoantibodies targeted against laminins 5 and 6 destabilize epithelial adhesion and are pathogenic. In muscle cells, laminin alpha 2 is a component of the bridge that links the actin cytoskeleton to the extracellular matrix. In patients with laminin alpha 2 mutations, the bridge is disrupted and mature muscle cells apoptose. Congenital muscular dystrophy (CMD) results. The role of laminin in diseases of the nervous system is less well defined, but the extracellular protein has been shown to serve an important role in peripheral nerve regeneration. The adhesive molecule influences neurite outgrowth, neural differentiation, and synapse formation. The broad spatial distribution of laminin gene products suggests that laminin may be involved in a number of diseases for which pathogenic mechanisms are still being unraveled.

Enhanced neurotrophin-induced axon growth in myelinated portions of the CNS in mice lacking the p75 neurotrophin receptor

Axonal growth in the adult mammalian CNS is limited because of inhibitory influences of the glial environment and/or a lack of growth-promoting molecules. Here, we investigate whether supplementation of nerve growth factor (NGF) to the CNS during postnatal development and into adulthood can support the growth of sympathetic axons within myelinated portions of the maturing brain. We have also asked whether p75(NTR) plays a role in this NGF-induced axon growth. To address these questions we used two lines of transgenic mice overexpressing NGF centrally, with or without functional expression of p75(NTR) (NGF/p75(+/+) and NGF/p75(-/-) mice, respectively). Sympathetic axons invade the myelinated portions of the cerebellum, beginning shortly before the second week of postnatal life, in both lines of NGF transgenic mice. Despite the presence of central myelin, these sympathetic axons continue to sprout and increase in density between postnatal days 14 and 100, resulting in a dense plexus of sympathetic fibers within this myelinated environment. Surprisingly, the growth response of sympathetic fibers into the cerebellar white matter of NGF/p75(-/-) mice is enhanced, such that both the density and extent of axon ingrowth are increased, compared with age-matched NGF/p75(+/+) mice. These dissimilar growth responses cannot be attributed to differences in cerebellar levels of NGF protein or sympathetic neuron numbers between NGF/p75(+/+) and NGF/p75(-/-) mice. Our data provide evidence demonstrating that growth factors are capable of overcoming the inhibitory influences of central myelin in the adult CNS and that neutralization of the p75(NTR) may further enhance this growth response.

The astroglial response to Wallerian degeneration after spinal cord injury in humans

We describe the changes exhibited by astrocytes in areas of Wallerian degeneration after spinal cord injury in humans using glial fibrillary acidic protein immunohistochemistry correlated to standard histology at time points ranging from 8 days to 23 years after injury. Astrocytes were slow to react; a slight increase in immunoreactivity was observed at 4 months. Over time they began to lose immunoreactivity in both the somata and the processes as the debris from the degenerative process was cleared. By 1 year after injury the staining intensity had decreased to levels which were lower than in normal areas of the cord. This hypointense staining persisted for at least 23 years after injury. These findings are significantly different from those observed in animal studies and emphasize the need for additional pathological studies of human spinal cord injury.

Obtention and characterization of primary astrocyte and microglial cultures from adult monkey brains

Simple methods for obtention of primary cultures of isolated astrocytes and microglia from adult simian brain have been developed. Characterization of these two glial cell populations were performed by morphological observations and by immunocytochemistry. The astroglial cultures were obtained by an indirect method. After L-leucine methyl-ester treatment and trypsinizations, more than 99% of cells expressed glial fibrillary acidic protein (GFAP), whereas no macrophages or microglia could be detected. Likely, the 1% remaining cells were immature astrocytes or cells that lost their GFAP expression. Cultured simian astrocytes expressed vimentin, laminin, and fibronectin. We also found a constitutively low expression of major histocompatibility complex (MHC) class II by cultured astrocytes which was significantly enhanced by lipopolysaccharide (LPS), interferon gamma (IFN-gamma), or tumor necrosis factor alpha (TNF-alpha) treatments. Microglial cultures were obtained by a direct method of isolation using Percoll gradient separations and compared to simian monocyte-derived macrophages or alveolar macrophages. Microglial cells differed from macrophages by their proliferation upon granulocyte-macrophage colony stimulating factor (GM-CSF) treatment and by their typical morphology when observed by scanning electron microscopy. As macrophages, they expressed in vitro CD68, CD64, CD14, CD11b, MHC class II, and fibronectin. However, contrary to macrophages, simian cultured microglia expressed laminin. This observation suggests that microglia represent a new potential source of this extracellular matrix protein in the brain.

Neuronal laminins and their cellular receptors

The laminins are a family of extracellular matrix glycoproteins expressed throughout developing neural tissues. The laminins are potent stimulators of neurite outgrowth in vitro for a variety of cell types, presumably reflecting an in vivo role in stimulating axon outgrowth. In recent years, the laminins have been shown to occur in several distinct isoforms; currently, the precise functional differences between the laminin variants are not well understood. A variety of neuronal surface receptors have been identified for one laminin isoform, laminin-1. These receptors include several members of the integrin family, as well as non-integrin laminin-binding proteins such as LBP-110, the 67 kDa laminin-receptor, alpha-dystroglycan, and beta 1,4 galactosyltransferase. Little is currently known about receptors for other laminin isoforms.

Reconstruction of the glial environment of a photochemically induced lesion in the rat spinal cord by transplantation of mixed glial cells

It is becoming increasingly apparent that the astrocytic environment is critical to the normal development and functioning of the CNS, and that acute injury to the spinal cord causes destruction of glial cells in addition to neurones and axons. The aims of this study were to assess the viability of reconstructing the astrocytic environment of a cystic spinal cord lesion by transplantation of glial cells and to examine the effect of the transplanted cells on meningeal cell invasion and revascularisation of the lesion and on axonal regeneration. Neonatal rat and kitten mixed glial cells and the CG-4 rat O-2A progenitor cell line were transplanted into a lesion produced in the dorsal funiculus of the rat spinal cord by photochemical infarction. The animals were killed 4 weeks after injury, their cords examined with light and electron microscopy and compared with control animals that were injected with medium alone. Transplantation of all three preparations resulted in increased numbers of astrocytes in the area of Wallerian degeneration cranial to the lesion and within the cyst. Mixed glial cell cultures prepared from neonatal rat forebrain contained cells with in vitro characteristics of type-1 astrocytes, and produced dense clusters of astrocytes that were surrounded by meningeal cells, resulting in a fragmented environment in the cyst. In contrast, glial cell cultures prepared from kitten forebrain and the CG-4 cell line produced cells that filled the cyst with a loose network of fine processes and reduced meningeal cell infiltration of the lesion. The CG-4 cell line significantly increased the density of blood vessels in the centre of the lesion and the number of spared axons present dorsal to the lesion, but none of the preparations significantly increased the number of axons regenerating at the caudal end of the lesion. We conclude that O-2A progenitor-derived astrocytes are more suitable for reconstruction of the glial environment of a cystic lesion in the rat spinal cord than 'type-1 like' astrocytes and would therefore be the cell of choice to engineer to produce factors that promote axonal regeneration.

The use of transplanted glial cells to reconstruct glial environments in the CNS

Transplantation studies have demonstrated that glia-depleted areas of the CNS can be reconstituted by the introduction of cultured cells. Thus, the influx of Schwann cells into glia-free areas of demyelination in the spinal cord can be prevented by the combined introduction of astrocytes and cells of the O-2A lineage. Although Schwann cell invasion of areas of demyelination is associated with destruction of astrocytes, the transplantation of rat tissue culture astrocytes ("type-1") alone cannot suppress this invasion, indicating a role for cells of the O-2A lineage in reconstruction of glial environments. By transplanting different glial cell preparations and manipulating lesions so as to prevent meningeal cell and Schwann cell proliferation it is possible to demonstrate that the behaviour of tissue culture astrocytes ("type-1") and astrocytes derived from O-2A progenitor cells ("type-2") is different. In the presence of meningeal cells, tissue culture astrocytes clump together to form cords of cells. In contrast, type-2 astrocytes spread throughout glia-free areas in a manner unaffected by the presence of meningeal cells or Schwann cells. Thus, progenitor-derived astrocytes show a greater ability to fill glia-free areas than tissue culture astrocytes. Similarly, when introduced into infarcted white matter in the spinal cord, progenitor-derived astrocytes fill the malacic area more effectively than tissue culture astrocytes, although axons do not regenerate into the reconstituted area.