Astrocyte activation and fibrous gliosis: glial fibrillary acidic protein immunostaining of astrocytes following intraspinal cord grafting of fetal CNS tissue

Regulation of mitochondrial dynamics in astrocytes: Mechanisms, consequences, and unknowns

Astrocytes are the major glial cell in the central nervous system. These polarized cells possess numerous processes that ensheath the vasculature and contact synapses. Astrocytes play important roles in synaptic signaling, neurotransmitter synthesis and recycling, control of nutrient uptake, and control of local blood flow. Many of these processes depend on local metabolism and/or energy utilization. While astrocytes respond to increases in neuronal activity and metabolic demand by upregulating glycolysis and glycogenolysis, astrocytes also possess significant capacity for oxidative (mitochondrial) metabolism. Mitochondria mediate energy supply and metabolism, cellular survival, ionic homeostasis, and proliferation. These organelles are dynamic structures undergoing extensive fission and fusion, directed movement along cytoskeletal tracts, and degradation. While many of the mechanisms underlying the dynamics of these organelles and their physiologic roles have been characterized in neurons and other cells, the roles that mitochondrial dynamics play in glial physiology is less well understood. Recent work from several laboratories has demonstrated that mitochondria are present within the fine processes of astrocytes, that their movement is regulated, and that they contribute to local Ca²⁺ signaling within the astrocyte. They likely play a role in local ATP production and metabolism, particularly that of glutamate. Here we will review these and other findings describing the mechanism by which mitochondrial dynamics are regulated in astrocytes, how mitochondrial dynamics might influence astrocyte and brain metabolism, and draw parallels to mitochondrial dynamics in neurons. Additionally, we present new analyses of the size, distribution, and dynamics of mitochondria in astrocytes performed using in vivo using 2-photon microscopy.

IKVAV-linked cell membrane-spanning peptide treatment induces neuronal reactivation following spinal cord injury

Spinal cord regeneration following treatment with a novel membrane-spanning peptide (MSP) expressing the isoleucine-lysine-valine-alanine-valine (IKVAV) epitope was assessed in Balb-c mice. After hemilaminectomy and compression injury, mice were treated with IKVAV, IKVAV-MSP, peptide or vehicle control. Functional improvement was assessed using modified Basso, Beattie, and Bresnahan Scale (mBBB) and spinal cord segments were studied histologically 28 days after injury. IKVAV-MSP group scores increased significantly compared with control groups after 4 weeks of observation (p < 0.05). The number of protoplasmic astrocytes, neurons and muscle bundle size in the IKVAV-MSP mice were significantly increased (p < 0.001; p < 0.05 and p < 0.007; respectively). This study demonstrates that it is possible to promote functional recovery after SCI using bioactive IKVAV presenting cell membrane-spanning peptides.

The changeable nervous system: studies on neuroplasticity in cerebellar cultures

Circuit reorganization after injury was studied in a cerebellar culture model. When cerebellar cultures derived from newborn mice were exposed at explantation to a preparation of cytosine arabinoside that destroyed granule cells and oligodendrocytes and compromised astrocytes, Purkinje cells surviving in greater than usual numbers were unensheathed by astrocytic processes and received twice the control number of inhibitory axosomatic synapses. Purkinje cell axon collaterals sprouted and many of their terminals formed heterotypical synapses with other Purkinje cell dendritic spines. The resulting circuit reorganization preserved inhibition in the cerebellar cortex. Following this reorganization, replacement of the missing granule cells and glia was followed by a restitution of the normal circuitry. Most of these developmental and reconstructive changes were not dependent on neuronal activity, the major exception being inhibitory synaptogenesis. The full complement of inhibitory synapses did not develop in the absence of neuronal activity, which could be mitigated by application of exogenous TrkB receptor ligands. Inhibitory synaptogenesis could also be promoted by activity-induced release of endogenous TrkB receptor ligands or by antibody activation of the TrkB receptor.

The total synthesis of a ganglioside Hp-s1 analogue possessing neuritogenic activity by chemoselective activation glycosylation

The total synthesis of ganglioside 2, an analogue of the ganglioside Hp-s1 (1) which displays neuritogenic activity toward the rat pheochromocytoma cell line PC-12 cell in the presence of nerve growth factor (NGF) with an effect (34.0%) greater than that of the mammalian ganglioside GM 1 (25.4%), was accomplished by applying a chemoselective-activation glycosylation strategy. Moreover, we also demonstrate that the synthesized ganglioside 2 exhibited neuritogenic activity toward the human neuroblastoma cell line SH-SY5Y without the presence of NGF.

Astrocytes in multiple sclerosis: a product of their environment

It has long been thought that astrocytes, like other glial cells, simply provide a support mechanism for neuronal function in the healthy and inflamed central nervous system (CNS). However, recent evidence suggests that astrocytes play an active and dual role in CNS inflammatory diseases such as multiple sclerosis (MS). Astrocytes not only have the ability to enhance immune responses and inhibit myelin repair, but they can also be protective and limit CNS inflammation while supporting oligodendrocyte and axonal regeneration. The particular impact of these cells on the pathogenesis and repair of an inflammatory demyelinating process is dependent upon a number of factors, including the stage of the disease, the type and microenvironment of the lesion, and the interactions with other cell types and factors that influence their activation. In this review, we summarize recent data supporting the idea that astrocytes play a complex role in the regulation of CNS autoimmunity.

Toll-like receptor (TLR)-2 and TLR-4 regulate inflammation, gliosis, and myelin sparing after spinal cord injury

Activation of macrophages via toll-like receptors (TLRs) is important for inflammation and host defense against pathogens. Recent data suggest that non-pathogenic molecules released by trauma also can trigger inflammation via TLR2 and TLR4. Here, we tested whether TLRs are regulated after sterile spinal cord injury (SCI) and examined their effects on functional and anatomical recovery. We show that mRNA for TLR1, 2, 4, 5, and 7 are increased after SCI as are molecules associated with TLR signaling (e.g. MyD88, NFkappaB). The significance of in vivo TLR2 and TLR4 signaling was evident in SCI TLR4 mutant (C3H/HeJ) and TLR2 knockout (TLR2-/-) mice. In C3H/HeJ mice, sustained locomotor deficits were observed relative to SCI wild-type control mice and were associated with increased demyelination, astrogliosis, and macrophage activation. These changes were preceded by reduced intraspinal expression of interleukin-1beta mRNA. In TLR2-/- mice, locomotor recovery also was impaired relative to SCI wild-type controls and novel patterns of myelin pathology existed within ventromedial white matter--an area important for overground locomotion. Together, these data suggest that in the absence of pathogens, TLR2 and TLR4 are important for coordinating post-injury sequelae and perhaps in regulating inflammation and gliosis after SCI.

Proinflammatory cytokine synthesis in the injured mouse spinal cord: multiphasic expression pattern and identification of the cell types involved

We have studied the spatial and temporal distribution of six proinflammatory cytokines and identified their cellular source in a clinically relevant model of spinal cord injury (SCI). Our findings show that interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF) are rapidly (<5 and 15 minutes, respectively) and transiently expressed in mice following contusion. At 30-45 minutes post SCI, IL-1beta and TNF-positive cells could already be seen over the entire spinal cord segment analyzed. Multilabeling analyses revealed that microglia and astrocytes were the two major sources of IL-1beta and TNF at these times, suggesting a role for these cytokines in gliosis. Results obtained from SCI mice previously transplanted with green fluorescent protein (GFP)-expressing hematopoietic stem cells confirmed that neural cells were responsible for the production of IL-1beta and TNF for time points preceding 3 hours. From 3 hours up to 24 hours, IL-1beta, TNF, IL-6, and leukemia inhibitory factor (LIF) were strongly upregulated within and immediately around the contused area. Colocalization studies revealed that all populations of central nervous system resident cells, including neurons, synthesized cytokines between 3 and 24 hours post SCI. However, work done with SCI-GFP chimeric mice revealed that at least some infiltrating leukocytes were responsible for cytokine production from 12 hours on. By 2 days post-SCI, mRNA signal for all the above cytokines had nearly disappeared. Notably, we also observed another wave of expression for IL-1beta and TNF at 14 days. Overall, these results indicate that following SCI, all classes of neural cells initially contribute to the organization of inflammation, whereas recruited immune cells mostly contribute to its maintenance at later time points.

Signaling from P2 nucleotide receptors to protein kinase cascades induced by CNS injury: implications for reactive gliosis and neurodegeneration

Gliosis is a hypertrophic and hyperplastic response to many types of central nervous system injury, including trauma, stroke, seizure, as well as neurodegenerative and demyelinating disorders. Reactive astrocytes, a major component of the glial scar, express molecules that can both inhibit and promote axonal regeneration. ATP, which is released upon traumatic injury, hypoxia, and cell death, contributes to the gliotic response by binding to specific cell surface astrocytic P2 nucleotide receptors and evoking characteristic features of gliosis such as increased expression of glial fibrillary acidic protein (GFAP), generation and elongation of astrocytic processes, and cellular proliferation. Here, we review recent studies that demonstrate that (1) metabotropic, P2Y, and ionotropic, P2X, receptors expressed in astrocytes are coupled to protein kinase signaling pathways that regulate cellular proliferation, differentiation, and survival such as ERK and protein kinase B/Akt and (2) these P2 receptor/protein kinase cascades are activated after trauma induced by mechanical strain. We suggest that P2 receptor/protein kinase signaling pathways might provide novel therapeutic targets to regulate the formation of reactive astrocytes and the production of molecules that affect axonal regeneration and neurodegeneration.

Homologous Transplantation of Neural Stem Cells to the Injured Spinal Cord of Mice

OBJECTIVE

Murine neural stem cells (NSCs) were homografted onto the injured spinal cord (SC) to assess their potential to improve motor behavior, to differentiate as neurons, and to establish synapse-like contacts with the descending axonal paths of the host. In addition, we investigated whether transduced NSCs over-expressing vascular endothelial growth factor might exert any angiogenetic effect in the injured SC.

METHODS

NSCs derived from mouse embryos were transduced to express either green fluorescent protein or vascular endothelial growth factor. The cells were engrafted in mice where an extended dorsal funiculotomy had been performed at the T8-T9 level. At intervals from 4 to 12 weeks after grafting, motor behavior was assessed using an open field locomotor scale and footprint analysis. At the same time points, the SC was studied by conventional histology, immunohistochemistry, and fluorescence microscopy. The interactions between the grafted NSCs and descending axonal paths were investigated using anterogradely transported fluorescent axonal tracers.

RESULTS

By the 12-week time point, mice engrafted with NSCs significantly improved both their locomotor score on open field test and their base of support on footprint analysis. Histological studies showed that green fluorescent protein-positive NSCs survived as long as 12 weeks after grafting, migrated from the grafting site with a tropism toward the lesion, and either remained undifferentiated or differentiated into the astrocytic phenotype without neuronal or oligodendrocytic differentiation. Interestingly, the NSC-derived astrocytes expressed vimentin, suggesting that these cells differentiated as immature astrocytes. The tips of severed descending axonal paths came adjacent to grafted NSCs without forming synapse-like structures. When genetically engineered to over-express vascular endothelial growth factor, the grafted NSCs significantly increased vessel density in the injured area.

CONCLUSION

In the traumatically injured mice SC, NSC grafting improves motor recovery. Although differentiation of engrafted NSCs is restricted exclusively toward the astrocytic phenotype, the NSC-derived astrocytes show features that are typical of the early phase after SC injury when the glial scar is still permissive to regenerating axons. The immature phenotype of the NSC-derived astrocytes suggests that these cells might support neurite outgrowth by the host neurons. Thus, modifying the glial scar with NSCs might enhance axonal regeneration in the injured area. The use of genetically engineered NSCs that express trophic factors appears to be an attractive tool in SC transplantation research.

Cytokine changes in the horizontal diagonal band of Broca in the septum after running and stroke: a correlation to glial activation

The relationship between running, glial cell activation and pro-inflammatory cytokines was studied in the context of neuroprotection against ischemic stroke induced by middle cerebral artery occlusion (MCAO). This was investigated in four groups of rats, namely, (1) nonrunner, (2) runner after 12 weeks of treadmill running, (3) nonrunner with MCAO and (4) runner with MCAO. The horizontal diagonal band of Broca (HDB) in the septum was scrutinized for qualitative cum quantitative changes in the microglia and astrocytes. Reverse transcription-polymerase chain reaction and immunoblot work were carried out in the forebrain homogenate to determine, respectively, the gene and protein expression of several pro-inflammatory cytokines. Our results indicated that the runner exhibited less immunoreactivity and reduced numbers of glial cells within the HDB compared with the nonrunner. Interestingly, the mRNA and protein levels of tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6 and interferon-gamma, were significantly downregulated in the runner. Our data also suggest albeit with some inconsistency that the runner/MCAO rats had benefited from running. These observations suggest that running can result in changes to the microenvironment, in which the microglia and astrocytes exist in a state of quiescence concomitant with a reduced expression of pro-inflammatory cytokines, that may lead to beneficial effects seen in ischemic stroke induced by MCAO.

The responses of oligodendrocyte precursor cells, astrocytes and microglia to a cortical stab injury, in the brain

The cortical stab injury has been widely used for biochemical analysis of molecular changes following CNS injury. However, the cellular responses to this injury have not been accurately quantified. In order to provide a baseline for biochemical studies and future experiments on the manipulation of the CNS injury response we have undertaken a quantitative analysis of this injury. The proliferative and reactive responses of oligodendrocyte precursor cells, astrocytes and microglia were measured, using antibodies to NG2, glial fibrillary acidic protein (GFAP) and the cd11-b clone OX-42 to characterise these cell types at 2, 4, 7 and 14 days post-injury. Oligodendrocyte precursors and microglia proliferated rapidly during the first week, mostly within 0.3 mm of the lesion. Of the dividing cells over 60% were oligodendrocyte precursor cells with microglia making up the balance of the dividing cells. Minimal numbers of astrocytes divided in response to the lesion. Large cells with one or two short processes that were both NG2 and OX-42 positive were identified very close to the lesion at 2 and 4 days post-lesion but not thereafter. They are likely to be blood-derived cells that express NG2 or have ingested it. NG2 immunohistochemistry and platelet-derived growth factor alpha receptor (PDGFalpha-R) in situ hybridisation on neighbouring sections was performed. In the lesioned area only 12% of NG2 positive (+ive) cells were PDGFalpha-R +ive (a ratio of 1:8 for PDGFalpha-R +ive cells: NG2 +ive cells) compared with 33% in the unlesioned cortex and an almost 100% overlap in the spinal cord.

Mesial temporal lobe epilepsy: a proton magnetic resonance spectroscopy study and a histopathological analysis

Object. Proton magnetic resonance (MR) spectroscopy imaging of the ratio of N-acetylaspartate (NAA) to creatine (Cr) has proved efficacious as a localizing tool in demonstrating the metabolic changes associated with temporal lobe epilepsy. To analyze the significance of these MR spectroscopy findings further, the authors explored the relationship between regional alterations in the NAA/Cr ratio in hippocampi measured preoperatively and histopathological findings in hippocampi resected in patients with intractable mesial temporal lobe epilepsy (MTLE).

Methods. Twelve patients in whom the diagnosis of MTLE had been made and 12 healthy volunteers with no known history of neurological disease underwent high-resolution 1H MR spectroscopy imaging of NAA and Cr (0.64 cm3 nominal voxel resolution) in five voxels spanning the anteroposterior length of the hippocampus. The authors correlated the NAA/Cr ratio with neuropathological findings in resected hippocampi, specifically glial fibrillary acidic protein (GFAP) immunoreactivity and pyramidal neuronal loss. A linear regression analysis of the ipsilateral NAA/Cr ratio revealed a statistically significant relation to the extent of hippocampal neuronal loss in only the CA2 sector (correlation coefficient [r] = −0.66, p < 0.03). The ipsilateral NAA/Cr ratio displayed significant regressions with GFAP immunoreactivity from all the CA sectors (r values ranged from −0.69 and p < 0.01 for the CA4 sector to −0.88 and p < 0.001 for the CA2 sector) except for the CA1. The extent of neuronal cell loss in every hippocampal subfield (r = 0.71−0.74, p < 0.007), except the CA2 (p = 0.08), correlated to the extent of neuronal cell loss in the dentate gyrus. There was no significant relationship between the duration or frequency of seizures and the mean ipsilateral NAA/Cr ratio; however, the mean density of GFAP-immunopositive cells correlated with seizure frequency (p < 0.03).

Conclusions. The NAA/Cr ratio may not measure the full extent of hippocampal neuronal cell loss. The significant association of the NAA/Cr ratio with the GFAP immunoreactivity of most CA sectors indicates that the NAA/Cr ratio may provide a more accurate measurement of recent neuronal injury caused by epileptic activity. The coupling between neuronal impairment and astroglial GFAP expression may indicate the close association between neuronal and glial dysfunction in patients with epilepsy.

The pathology of human spinal cord injury: defining the problems

This article reviews the pathology of human spinal cord injury (SCI), focusing on potential differences between humans and experimental animals, as well as on aspects that may have mechanistic or therapeutic relevance. Importance is placed on astrocyte and microglial reactions. These cells carry out a myriad of functions and we review the evidence that supports their beneficial or detrimental effects. Likewise, vascular responses and the role of inflammation and demyelination in the mechanism of SCI are reviewed. Lastly, schwannosis is discussed, highlighting its high frequency and potential role when designing therapeutic interventions. We anticipate that a better understanding of the pathological responses in the human will be useful to investigators in their studies on the pathogenesis and therapy of SCI.

Ephrin-B2 and EphB2 regulation of astrocyte-meningeal fibroblast interactions in response to spinal cord lesions in adult rats

The present study provides the first evidence that signaling occurs between B-ephrins and EphB receptors in the adult CNS in response to injury. Specifically, our combined histological and biochemical data indicate that two members of the B-class of ephrins and Eph receptors, ephrin-B2 and EphB2, are expressed by astrocytes and meningeal fibroblasts, respectively, in the adult spinal cord. In response to thoracic spinal cord transection lesions, ephrin-B2 and EphB2 protein levels exhibit an initial decrease (1 d after lesion), followed by a significant increase by day 14. Immunohistochemical data indicate that ephrin-B2 is expressed by reactive CNS astrocytes, and EphB2 is present on fibroblasts invading the lesion site from the adjacent meninges. During the first 3 d after injury, there is intermingling of ephrin-B2-expressing reactive astrocytes at the lesion surface with EphB2-containing fibroblasts that is concurrent with bidirectional activation (phosphorylation) of ephrin-B2 and EphB2. By 7 d, both cell types are establishing restricted cellular domains containing dense networks of cells and interweaving processes. This astroglial-meningeal fibroblast scar is fully developed by day 14 when there is strict segregation of ephrin-B2-expressing astrocytes from EphB2-positive meningeal fibroblasts. These morphological changes are concomitant with a simultaneous decrease in ephrin-B2 and EphB2 activation. These observations provide strong evidence that cell contact-mediated bidirectional signaling between ephrin-B2 on reactive astrocytes and EphB2 on meningeal fibroblasts is an early event in the cellular cascades that result in the development of the glial scar and the exclusion of meningeal fibroblasts from the injured spinal cord.

Piracetam and vinpocetine exert cytoprotective activity and prevent apoptosis of astrocytes in vitro in hypoxia and reoxygenation

The aim of the present study was to establish whether piracetam (2-pyrrolidon-N-acetamide; PIR) and vinpocetine (a vasoactive vinca alkaloid; VINP) are capable of protecting astrocytes against hypoxic injury. Using the model of astrocyte cell culture we observed the cells treated with PIR and VINP during and after in vitro simulated hypoxia. Cell viability was determined by Live/Dead Viability/Cytotoxicity Assay Kit, LDH release assay and MTT conversion test. Apoptotic cell death was distinguished by a method of Hoechst 33342 staining underfluorescence microscope and caspase-3 colorimetric assay. In addition the intracellular levels of ATP and phosphocreatine (PCr) were evaluated by bioluminescence method. Moreover, the effect of the drugs on the DNA synthesis was evaluated by measuring the incorporation of [3H]thymidine into DNA of astrocytes. PIR (0.01 and 1 mM) and VINP (0.1 and 10 microM) were added to the medium both during 24 h normoxia, 24 h hypoxia or 24 h reoxygenation. Administration of 1 mM PIR or 0.1 microM VINP to the cultures during hypoxia significantly decreases the number of dead and apoptotic cells. The antiapoptic effects of drugs in the above mentioned concentrations was also confirmed by their stimulation of mitochondrial function, the increase of intracellular ATP, and the inhibition of the caspase-3 activity. The prevention of apoptosis was accompanied by the increase in ATP and PCr levels and increase in the proliferation of astrocytes exposed to reoxygenation. The higher concentration of VINP (10 microM) was detrimental in hypoxic conditions. Our experiment proved the significant cytoprotective effect of 1 mM PIR and 0.1 microM VINP on astrocytes in vitro.

Enriched environmental conditions reverse age-dependent gliosis and losses of neurofilaments and extracellular matrix components but do not alter lipofuscin accumulation in the hindlimb area of the aging rat brain

We provide a description of a correlation of lipofuscin accumulation and expression of glial fibrillary acidic protein in the cerebral cortex of aged rats. Glial fibrillary acidic protein showed a complementary distribution pattern to perineuronal nets, visualized with Wisteria floribunda agglutinin. With progressing age (12-36 months), a strong increase of lipofuscin and gliosis occurred in functionally characterized cortical areas, whereas a concomitant, area-specific loss of perineuronal nets was found in the cortical somatosensory representation of the hindlimbs. In contrast to lipofuscin accumulation and increased gliosis, the loss of perineuronal nets and the reduction of non-phosphorylated neurofilament H were in part reduced or prevented by housing the animals under enriched environmental conditions between 33 and 36 months of age. Especially the reduction of astrocytosis by 20% which coincided with a reduction in the loss of extracellular matrix components involved in forming the glia-neuron-interface demonstrates, that the aging cortex retains its potential for functional plasticity.

A model for the mechanism of astrogliosis in prion disease

Astrogliosis is a hallmark of prion diseases. Finding ways of inhibiting astrocyte proliferation may be beneficial to treating these diseases. PrP106-126 a peptide fragment of the prion protein induces proliferation of astrocytes. The mechanism of its action was studied in detail. Induction of astrocyte proliferation in culture requires cytokines interleukin-1 and interleukin-6 released from microglia in the presence of PrP106-126. However, the increased release of these cytokines is insufficient without direct effects of PrP106-126 on astrocytes. PrP106-126 induces increased progression through the cell cycle to late G1 and enhances the level of both p53 and phosphorylated ERKs in astrocytes. PrP106-126-induced proliferation of astrocytes in culture can be inhibited by antibodies to cytokines or by MEK inhibitors.

Light and confocal laser-scanning microscopical evidences for complementary patterns of glial fibrillary acidic protein and Wisteria floribunda agglutinin labeled structures in human and rat brain

We investigated the pattern of glial fibrillary acidic protein (GFAP) and Wisteria floribunda agglutinin (WFA) labeled structures in the superior colliculus and in the somatosensory cortex of humans and rats of different age groups using immunohistochemical methods, light and confocal laser-scanning microscopy. We never found a double labeling of WFA and GFAP positive structures neither in the superior colliculus nor in the cortex of both man and rat. The complementary pattern of WFA and GFAP labeling was present both at the macroscopic and microscopic level. We found a clear prevalence of either WFA or GFAP expression in the arborization of the astrocytes as well as in the pattern of lamination.

Nogo-A, a potent inhibitor of neurite outgrowth and regeneration

The lack of regrowth of injured neurons in the adult central nervous system (CNS) of higher vertebrates was accepted as a fact for many decades. In the last few years a very different view emerged; regeneration of lesioned fibre tracts in vivo could be induced experimentally, and molecules that are responsible for inhibition and repulsion of growing neurites have been defined. Mechanisms that link cellular phenomena like growth cone turning or growth cone collapse to intracellular changes in second messenger systems and cytoskeletal dynamics became unveiled. This article reviews recent developments in this field, focusing especially on one of the best characterised neurite out-growth inhibitory molecules found in CNS myelin that was recently cloned: Nogo-A. Nogo-A is a high molecular weight transmembrane protein and an antigen of the monoclonal antibody mAb IN-1 that was shown to promote long-distance regeneration and functional recovery in vivo when applied to spinal cord-injured adult rats. Nogo-A is expressed by oligodendrocytes in white matter of the CNS. With the molecular characterisation of this factor new possibilities open up to achieve structural and functional repair of the injured CNS.

The glial scar and central nervous system repair

Damage to the central nervous system (CNS) results in a glial reaction, leading eventually to the formation of a glial scar. In this environment, axon regeneration fails, and remyelination may also be unsuccessful. The glial reaction to injury recruits microglia, oligodendrocyte precursors, meningeal cells, astrocytes and stem cells. Damaged CNS also contains oligodendrocytes and myelin debris. Most of these cell types produce molecules that have been shown to be inhibitory to axon regeneration. Oligodendrocytes produce NI250, myelin-associated glycoprotein (MAG), and tenascin-R, oligodendrocyte precursors produce NG2 DSD-1/phosphacan and versican, astrocytes produce tenascin, brevican, and neurocan, and can be stimulated to produce NG2, meningeal cells produce NG2 and other proteoglycans, and activated microglia produce free radicals, nitric oxide, and arachidonic acid derivatives. Many of these molecules must participate in rendering the damaged CNS inhibitory for axon regeneration. Demyelinated plaques in multiple sclerosis consists mostly of scar-type astrocytes and naked axons. The extent to which the astrocytosis is responsible for blocking remyelination is not established, but astrocytes inhibit the migration of both oligodendrocyte precursors and Schwann cells which must restrict their access to demyelinated axons.

Carbon filaments direct the growth of postlesional plastic axons after spinal cord injury

The effect of implantation of carbon filaments and fetal tissues on the axonal regeneration following contusion injury in a rat model was investigated by in situ immunofluorescence. Female Sprague-Dawley rats were subjected to severe contusion injury to the spinal cord at T9-T10. All animals were divided into 5 groups (N = 5/group): normal controls. surgical controls, with carbon filament implants, with fetal tissue implants and with implants consisting of fetal tissue cocultured with carbon filaments. After a 10-week survival period, the astroglial response was assessed by immunoreactive glial fibrillary acidic protein and the neuro-axonal profile by immunoreactive phosphorylated and nonphosphorylated neurofilament proteins. The contusion injury resulted in: (a) dramatically increased immunoreactivity of glial fibrillary acidic protein indicating injury-associated reactive astrogliosis, (b) increase in immunoreactive phosphorylated neurofilament protein indicating upregulated phosphorylation of neurofilament protein, (c) with no change in the highly differentiated nonphosphorylated neurofilament protein which normally occur in the nonregenerating mature neurons. Implantation of fetal tissues alone following contusion injury did not show any appreciable change with regard to the immunoreactivities for the glial and neuronal markers studied, compared to the injury controls. However, the implantation of carbon filaments alone or together with fetal tissues directed the growth of glial fibrillary acidic protein-positive astroglia and phosphoneurofilament-positive neurites along the carbon fibers, with no effect on nonphosphoneurofilament protein. In conclusion, implantation of carbon filaments appears to be critical for facilitating the attachment of astroglia forming a substrate and scaffolding that can further support and direct the growth of postlesional plastic axons across the lesion. In addition, carbon filament prostheses in combination with fetal tissue implants provides an improved combinational approach to promote regrowth of injured neurons following injury.

Astrocytic demise precedes delayed neuronal death in focal ischemic rat brain

Active neuronal-glial interaction is important in the maintenance of brain homeostasis and is vital for neuronal survival following brain injury. The time course of post-ischemic astroglial dysfunction and neuronal death was studied in the spontaneously hypertensive rat (SHR) brain following permanent middle cerebral artery occlusion (MCAO). In situ hybridization with 35S-labeled riboprobes for GFAP and GLUT3 was used to monitor mRNA expression in glia and neurons. Astrocytic proteins GFAP, vimentin, S100, Glutathione-S-Transferase Yb (GST Yb) and neuronal protein TG2 were detected by immunofluorescence. Cells were co-stained with in situ end labeling (ISEL) to detect DNA fragmentation, a hallmark of cell death. GFAP mRNA expression declined rapidly in the ischemic region of the cortex and was almost absent by 12 h. Immunohistochemical studies revealed a parallel decline in the corresponding protein: a reduction in GFAP staining was apparent in the infarct after 3 h and by 24 h, there was essentially no remaining GFAP. Three other glial proteins (vimentin, S100 and GST Yb) disappeared from infarct over a similar time course. A few ISEL positive cells were observed in the infarct at 6 h, but maximal detection was not seen until 24-48 h. Most of the ISEL-positive cells were neurons, identified by co-staining with the neuronal marker TG2. Few cells expressing GFAP or other glial markers were positive at any time point. Neuronal GLUT3 mRNA declined more slowly than GFAP mRNA in the ischemic core and disappeared during the period of neuronal death. Concurrent with the loss of GFAP mRNA and protein expression in the infarct, there was a rapid rise in GFAP mRNA in the peri-infarct region of ipsilateral hemisphere and proximal region of the contralateral hemisphere. This was followed by the enhanced GFAP protein expression characteristic of reactive astrocytes, but over a significantly slower time course. These studies show that MCAO leads to a rapid decline of GFAP mRNA and glial proteins, which appears to precede the decline in neuronal mRNA and neuronal death within the infarct. Early astroglial dysfunction may play a critical role in determining the outcome of acute hypoxic-ischemic injury by compromising neuronal-glial interactions.

Alterations in temporal/spatial distribution of GFAP- and vimentin-positive astrocytes after spinal cord contusion with the New York University spinal cord injury device

Astrocytes become reactive as a result of various types of lesions and upregulate 2 intermediate filaments, glial fibrillary acidic protein (GFAP), and the developmentally regulated protein vimentin. Young female Sprague-Dawley rats were subjected to a spinal cord contusion at segment T10 using the New York University injury device. Animals were killed at 1, 2, 7, 14, and 30 days postinjury. Horizontal spinal cord sections spanning segments T7-T13 were assessed with antibodies to both intermediate filament proteins. The number of gray matter GFAP-positive astrocytes increased by 2 days postinjury, with segments adjacent (proximal) to the injury site showing greater responses than areas several segments away (distal). By 30 days following injury, astroglial cell numbers returned to normal levels. Vimentin-positive astrocytes also showed a graded proximal/distal response by 2 days following injury. Proximal regions remained significantly higher at 30 days following injury than control animals. Rostral/caudal changes were also evident, with regions caudal to the injury showing significantly higher numbers of vimentin positive astrocytes than those rostral, indicating that gray matter areas caudal to spinal cord injury may undergo more stress following spinal cord injury.

Induction of IGF-1 mRNA expression following traumatic injury to the postnatal brain

A variety of adult, non-neural tissues respond to injury by increasing expression of the gene which encodes for insulin-like growth factor-1 (IGF-1). This response is thought to be a key component in the regenerative capacity of these tissues. In contrast, the central nervous system (CNS) has relatively little regenerative capacity following injury. Interestingly, compared to many non-neuronal tissues, little IGF-1 mRNA can be detected in the adult CNS, raising the possibility that its lack of regenerative capacity is related its relative lack of IGF-1 expression. However, in the 2-week-old adolescent CNS IGF-1 mRNA can be detected in numerous brain regions. Therefore, the purpose of this study was to determine the responsiveness of the IGF-1 gene to injury in adolescent CNS tissue, a period in which expression of this gene is relatively abundant. Expression of IGF-1 mRNA was measured by means of a sensitive solution hybridization/RNase protection assay in the parieto-occipital lobes of 2-week-old and adult mice following penetrating injury. Levels of IGF-1 transcript in the injured brains were significantly increased above those of controls in both 2-week-old and adult brains 3-day post injury and remained elevated for 1 week after injury. These observations demonstrate that the adult CNS, like other tissues, can respond to injury by increasing expression of IGF-1 mRNA.

A prion protein fragment primes type 1 astrocytes to proliferation signals from microglia

Giliosis is a hallmark of prion disease. A neurotoxic prion peptide (PrP106-126) induces astrocyte proliferation in the presence of microglia. This peptide also directly enhances microglial proliferation in culture. We have investigated this further to understand the method by which factors released by microglia and PrP106-126 work together to enhance astrocyte proliferation. PrP106-126 in the presence of microglia specifically enhanced type 1 astrocyte proliferation but not Type 2. Astrocytes that do not express the prion protein were more sensitive to oxidative stress and the toxicity of cytosine arabinoside. In the presence of cytosine arabinoside, PrP106-126 was toxic to pure astrocyte cultures. Using conditioned medium from microglia we have shown that PrPc-expressing astrocytes proliferate in response to factors released by microglia stimulated by granulocyte/macrophage colony-stimulating factor. This response is enhanced in the presence of PrP106-126. PrPc-deficient astrocytes do not show this response. These results suggest that astrocytes are primed by PrP106-126 to respond more to factors released by proliferating microglia. Astrocytes may proliferate in this system to escape entering the cell suicide pathway.

Neurotoxic effects of fractionated diesel exhausts following microinjections in rat hippocampus and striatum

Exhaust emissions from a heavy-duty diesel vehicle, separated into particulate and semivolatile phases and thereafter fractionated according to polarity, were studied in the adult rat brain after intracranial microinjections using cresyl violet staining and immunohistochemistry. Intrastriatal as well as intrahippocampal injections of particulate fractions III [containing mononitro-polycyclic aromatic hydrocarbon (PAH)], IV (dinitro-PAH and quinones) and V (polar material) and of semivolatile fractions IV and V, in amounts corresponding to a driven length of 19.5 m, caused major lesions with tissue loss and disappearance of immunoreactivity for glial fibrillary acidic protein, tyrosine hydroxylase, and acetylcholine esterase. Particulate fractions I ("light" aliphatic hydrocarbons) and II ("heavy" aliphatic hydrocarbons and PAH) and semivolatile fraction III produced smaller lesions; semivolatile fractions I and II led to lesions equivalent to those of the vehicle dimethyl sulfoxide alone. Microinjected doses of particulate fractions III or IV corresponding to driven lengths of 2.0 and 9.8 m produced a variable lesion. Thus, fractions containing nitro-derivatives of PAH, quinones, and polar material caused the greatest damage after intracranial injections. It is concluded that intracerebral microinjections of fractionated motor vehicle exhausts provide a method for systematic testing of direct neurotoxicity.

Low-level cadmium exposure of lactating rats causes alterations in brain serotonin levels in the offspring

Effects on monoaminergic and cholinergic transmitter systems as well as neurotrophins were characterized in developing Sprague-Dawley rats directly exposed to 5 ppm cadmium in the drinking water or indirectly via exposed dams. Cadmium was given to dams during the lactation period, from parturition to postnatal day 17, and/or to the offspring until postnatal day 42. Cresyl violet staining and glial fibrillary acidic protein immunohistochemistry did not reveal any obvious neuropathology after cadmium exposure. Following high-power microwave fixation, concentrations of acetylcholine (ACh) and monoamines were determined in cerebral cortex, striatum, and hippocampus using HPLC with electro-chemical detection. ACh, dopamine, and noradrenaline levels were not significantly affected after the different cadmium exposures. Cortical levels of serotonin were significantly reduced in rats exposed to cadmium during lactation as well as in rats exposed to cadmium during both lactation and postweaning. A major decrease in 5-hydroxyindoleacetic acid was found in cortex and hippocampus in rats exposed to cadmium during lactation. The regional characteristics of cadmium toxicity as reflected in changes of neurotrophins were studied using in situ hybridization histochemistry with oligonucleotide probes and phosphoimaging evaluation. No significant changes in the mRNA expression of brain-derived neurotrophic factor (BDNF), neurotrophin-3, and the high-affinity tyrosine kinase receptor of BDNF, trkB, were detected. The present results demonstrate that exposure to levels of cadmium as low as 5 ppm in the drinking water leads to neurochemical disturbances of the serotonergic system in the offspring during the lactational period.

Leptomeningeal cells modulate the neurite growth promoting properties of astrocytes in vitro

Leptomeningeal cells migrate into the lesion cavity after stab wounds to the adult mammalian central nervous system (CNS) and interact with astrocytes that form a new glia limitans. However, it is not known if leptomeningeal cells alter the ability of astrocytes near the lesion to support axon growth. In this study, we have used an in vitro approach to assess leptomeningeal cell-astrocyte interactions in a model that resembles the interactions of these cells in vivo. We cultured rat cortical astrocytes on top of monolayers of leptomeningeal cells or astrocytes. Differences in the morphology, neurite growth promoting properties, and expression of various extracellular matrix molecules and beta 1-integrin were assessed. Astrocytes acquired a long slender morphology when plated on leptomeningeal cells. Functionally, astrocytes cultured on top of leptomeningeal monolayers supported less neurite growth. Similar results were also obtained when astrocyte monolayers were treated with leptomeningeal cell-conditioned medium. Quantitative immunofluorescence labeling showed a reduction in cell surface bound laminin on astrocytes plated on leptomeningeal monolayers. Qualitative assessment of the immunofluorescence labeling showed an increase in matrix-like deposits of tenascin-C and chondroitin sulfate proteoglycan under similar culture conditions. This study provides the first direct evidence that leptomeningeal cells reduce the neurite growth promoting properties of astrocytes. These results suggest that interactions with leptomeningeal cells may 1) induce the formation of the slender astrocyte processes that form parallel to the lesion wall after penetrating injuries to the CNS; and 2) contribute along with other factors to alter astrocytes near the site of injury to a state that is less permissive for axon growth and regeneration.

A neurotoxic prion protein fragment enhances proliferation of microglia but not astrocytes in culture

The scrapie isoform of the prion protein (PrPSc) induces pathological changes in the central nervous system including neurodegeneration and gliosis. A synthetic prion protein (PrP) peptide corresponding to amino acid residues 106-126 has been shown to be toxic to neurons that express PrPC, the cellular isoform of PrP. Here we show that in mixed glial cultures PrP106-126 induces astroglial proliferation that is dependent on cellular PrPc expression. In purified cultures of glial subtypes only microglia proliferated in response to PrP106-126. This effect was independent of PrP expression. Destruction of microglia in mixed glial cultures by L-leucine methyl ester (LLME) treatment abolished enhanced proliferation caused by PrP106-126. This proliferative effect can be restored by co-culturing LLME-treated astrocytes with microglia. Microglia therefore seem to mediate the proliferative effect exerted by PrP106-126 on astrocytes.

Astrocyte-astrocytoma cell line interactions in culture

Astrocytomas are the most common brain tumors arising in the CNS and account for 65% of all primary brain tumors. Astrocytes have been shown to have the highest predisposition to malignant transformation compared to any other CNS cell type. The majority of astrocytomas are histologically malignant neoplasm. Previous studies have shown that resident astrocytes are the first cell type to react to tumors and surround them. However, the role of these astrocytes in tumor formation and progression has not been determined. In the present study, we have co-cultured astrocytes with a permanent cell line S635c15 (derived from anaplastic astrocytoma) in order to understand the cellular interactions between astrocytes and astrocytoma cells. Our studies demonstrate that astrocytes in contact with the tumor cells become reactive and fibrous with an increase in glial fibrillary acidic protein (GFAP) immunoreactivity as early as 4 days in culture. By 8 days, astrocytes formed glial boundaries around the tumor cells which grew as round colonies. The astrocytic processes surrounding the tumor cells were also intensely GFAP positive. Since the behavior of these cells observed in culture is very similar to their interaction seen in vivo, this co-culture system may serve as an in vitro model for astrocyte and astrocytoma cell line interaction and aid in our understanding of the molecular and cellular mechanisms during early stages of tumor formation and cell interactions.

Adrenalectomy increases the glial fibrillary acidic immunoreactive-elements in the ventricular ependyma and adjacent neuropil of the rat third ventricle

The reactions of bilateral adrenalectomy (14 days) on the rat glial fibrillary acidic-immunoreactive elements of the third ventricular ependyma and adjacent neuropil were analyzed using histological, immunohistochemical and morphometric methods. Bilateral adrenalectomy led to a drastic increase in the number of immunoreactive elements located in the neuropil adjacent to the third ventricle and the optic chiasm when compared to normal and sham-operated animals (p < 0.05). By contrast, the adrenalectomized animals receiving corticosterone showed the same characteristics and morphometric values as those found in normal and sham-operated animals. The results show that the participation of the adrenal gland in astroglial responses should be taken into account.

Inhibition of growth factor-induced DNA synthesis in astrocytes by ligands of peripheral-type benzodiazepine receptors

The effect of diazepam and specific ligands of peripheral-type benzodiazepine receptors (PBRs) on growth factor-induced DNA synthesis in quiescent cultures of rat astrocytes has been examined. It was found that diazepam inhibited the ability of basic fibroblast growth factor (bFGF) to stimulate [3H]thymidine incorporation; the IC50 was approximately 5 microM. Ro5-4864, a specific agonist of PBRs, also blocked bFGF-induced DNA synthesis. PK11195, which in some cases functions as an antagonist of PBRs, did not prevent the effect of Ro5-4864 on bFGF-induced DNA synthesis; rather, addition of PK11195 also inhibited bFGF-induced DNA synthesis. In addition, diazepam reduced the stimulation of DNA synthesis caused by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF), polypeptide growth factors coupled to receptor tyrosine kinases, as well as thrombin, an activator of G protein-coupled receptors. These data suggest that ligands of PBRs may limit astrocyte mitosis, a phenomenon that occurs following CNS injury.

Altered pattern of immunohistochemical staining for glial fibrillary acidic protein (GFAP) in the forebrain and cerebellum of the mutant spastic rat

The spastic rat is a neurological mutant of the Han-Wistar strain with prominent spasticity, tremor, and ataxia. Neurodegeneration is found in the CA3 sector of the hippocampus and in Purkinje cells of the cerebellum. We examined the forebrain and cerebellum of spastic rats for glial reactions by using immunolabelling for the astrocytic marker, glial fibrillary acidic protein (GFAP). First, a map of the GFAP-distribution was made representing a systematic series of frontal sections in controls. Reactive astrocytes with increased GFAP should occur in the areas with established neuronal degeneration, but they could also demarcate further regions with pathology in this rat strain. Since the baseline levels of GFAP-immunoreactivity differ between brain regions, control rats and clinically normal littermates served as controls to judge relative increases in major structures. In the CA3 sector and hilus of the dorsal hippocampus, a massive gliosis was detected. In the cerebellum, a patchy increase of GFAP labelling in Bergmann glia was found. Further increases of GFAP-labelling in reactive astrocytes occurred in fiber tracts, the ventral thalamic nuclei, medial geniculate nuclei, pontine region and optic layer of the superior colliculus. Inconsistent changes were noted in cortex and pallidum. No defects of glial labelling or malformations in glial architectonics were found. The reactive changes of astroglial cells in hippocampus and cerebellum are in proportion to the neuronal degeneration. The glial reactions in the other brain regions possibly reflect a reaction to fiber degeneration and incipient neuronal degeneration or functional alterations of glial cells in response to neuronal dysfunction.

Loss of immunoreactivity for glial fibrillary acidic protein (GFAP) in astrocytes as a marker for profound tissue damage in substantia nigra and basal cortical areas after status epilepticus induced by pilocarpine in rat

Status epilepticus induced by pilocarpine in rats induces massive tissue damage comprising neurons and astrocytes (incomplete infarction) in substantia nigra pars reticulata (SNR) and in basal cortical areas (BCTX). Immunohistochemistry with a polyclonal antiserum and a monoclonal antibody to GFAP were used here to study the astroglial damage in these regions. Control sections showed a strong labeling for glial fibrillary acidic protein (GFAP) for both antibodies in SNR and BCTX. At 1 day after induction of seizures, labeling with the polyclonal antibodies showed diffuse increase within the lesioned areas and enhanced staining of astrocytes at the border zones. However, staining with the monoclonal antibody was abolished. At 3 days, labeling with both the polyclonal antiserum and the monoclonal antibody was severely reduced within the damaged regions. Reactive astrocytes in the surround of the infarct showed enhanced labeling with both antibodies. This combination of enhanced labeling with polyclonal antibodies and decreased labeling with the specific monoclonal antibody for GFAP can be taken as indicator for acute glial cell damage in seizures and related experimental conditions.

Trimethyltin-induced expression of GABA and vimentin immunoreactivities in astrocytes of the rat brain

Adult Sprague-Dawley rats were given a single dose of trimethyltin chloride (TMT). Three days following treatment, a neuronal alteration was observed in the CA3c pyramidal cell layer of hippocampus which was not accompanied by any apparent astrocyte reaction. At 1 as well as 2 weeks after treatment, a gliosis in hippocampus, piriform, and entorhinal cortices was detected by glial fibrillary acidic protein (GFAP) immunohistochemistry. Concomitant with the enhanced astrocytic GFAP, astrocytes were swollen and expressed immunoreactivity to vimentin and gamma-aminobutyric acid (GABA). The astrocytic GABA immunoreactivity may reflect a trimethyltin-induced alteration in astrocyte phenotype, or alterations in compartmentalization and/or metabolism of GABA.

Persistence of heterotypical synapses in transplanted cerebellar cultures in the absence of functional glia

Neonatal mouse cerebellar cultures depleted of granule cells and functional glia by exposure to cytosine arabinoside were transplanted with either granule cells and glia or with granule cells in the absence of functional glia. Myelination was evident in cultures transplanted with granule cells and glia, excess sprouted cortical neurites were reduced, Purkinje cells acquired astrocytic sheaths and had a near normal complement of axosomatic synapses, and homotypical parallel fiber-Purkinje cell dendritic spine synapses were present in a 2.4:1 ratio to heterotypical recurrent axon collateral-Purkinje cell dendritic spine synapses. Cultures transplanted with granule cells were not myelinated, sprouted cortical neurites were not reduced. Purkinje cells lacked astrocytic sheaths and their somata remained hyperinnervated, and the ratio of homotypical to heterotypical dendritic spine synapses was 1.4:1. In the absence of functional glia there was a greater persistence of heterotypical recurrent axon collateral-Purkinje cell dendritic spine synapses. These results are consistent with a previously described astrocytic role in the regulation of axosomatic synapse density on glially ensheathed neurons, and suggest astrocytic participation in the reduction of heterotypical axospinous synapses. Astrocyte-mediated synapse reduction may be an important mechanism for circuit reorganization after transplantation or during development.

Polarity of processes with Golgi apparatus in a subpopulation of type I astrocytes

The Golgi apparatus-complex (GA), is a key organelle involved in several posttranslational modifications of polypeptides destined for lysosomes, plasma membranes and secretion. As reported from this laboratory, certain astrocytes in rat brain contain cisternae of the GA not only in perikarya, but also in processes. In order to further investigate which type of astrocytes contain GA in processes we conducted the present study using primary cultures of rat astrocytes and organelle specific antibodies against the GA and the rough endoplasmic reticulum (RER). While the perikarya of all cells contained elements of the GA, only a single process of a subset of type I astrocytes, negative to antibodies A2B5 and HNK-1, contained GA. In contrast, elements of the RER were found within perikarya and all processes. In order to confirm that the immunostained structures in processes indeed represent the GA, we exposed cultures to Brefeldin A (BFA), a secretion blocker which disperses the GA and redistributes it to the RER. We observed that BFA disrupted the GA of both perikarya and processes. However, astrocytes were resistant to prolonged incubations with BFA, while a similar treatment killed cultured fibroblasts and PC-12 cells. Furthermore, in astrocytes exposed to BFA for several days, the delicate network of glial fibrillary acidic protein (GFAP), was replaced by large perinuclear masses of the protein. These observations demonstrate that a subset of type I astrocytes have a single process with elements of the GA. We suggest that this specialization of the GA may be related to yet unrecognized secretory or protein processing functions of these cells. The resistance of astrocytes to BFA and the striking changes in their cytoskeleton induced by the drug, may contribute to studies on the mechanism(s) of action of BFA.

Expression of peripherin in solid transplants of foetal spinal cord and dorsal root ganglia grafted to the injured cervical spinal cord of adult rats

The expression of the neuronal type III intermediate filament protein peripherin was studied in E14 spinal cord fragments and E15 dorsal root ganglia 1-30 weeks after their transplantation to the injured cervical spinal cord of the adult rat. In the dorsal root ganglion transplants, the surviving neurons generally appeared as a rather healthy looking population of small strongly immunoreactive cells which are very similar to the small dorsal root ganglion neurons of adult control rats. In the spinal cord transplants, there were only a few peripherin-immunoreactive neurons, morphologically close to the motoneurons or to the preganglionic sympathetic neurons of adult rats. In both types of transplants, peripherin expression of the immunoreactive neurons was apparently correlated with the previously established ability of these transplanted neurons for extensive axonal growth into a co-grafted peripheral nerve.

Tenascin in the injured rat optic nerve and in non-neuronal cells in vitro: potential role in neural repair

The distribution of tenascin was examined in the lesioned adult rat optic nerve and central nervous system (CNS) non-neuronal cells in vitro, by means of a double immunofluorescence technique. Tenascin-like immunoreactivity is localized to the leptomeninges and astrocytes that border the site of optic nerve transection. Anti-tenascin labeling was observed as early as 24 hours after transection, when it appeared as a fine interface between leptomeninges and neural tissue. The anti-tenascin labeling increased in the cells at this border zone during the next 2 weeks, and disappeared 18-21 days after transection. In vitro studies further confirmed that both astrocytes and leptomeningeal cells express tenascin as detected by immunofluorescence labeling with anti-tenascin antibodies. However, the pattern of immunolabeling associated with the two cell types differed. Astrocytes showed exclusively punctate labeling of the cell surface, while leptomeningeal cells showed mainly coarse, fibrillary, matrix-like deposits. Astrocytes and leptomeningeal cells remained segregated when cocultured. In these cultures, an increased amount of the fibrillary, matrix-like deposits of tenascin was also observed in the region of the interface between astrocytes and leptomeningeal cells when these two cell types contact each other. Given the antiadhesive and antispreading properties of tenascin, these in vivo and in vitro results suggest that tenascin might play a role in the initial segregation of leptomeningeal cells from neural tissue at the site of CNS trauma during the first 2 weeks after injury, i.e., prior to the formation of a fully differentiated glia limitans. Therefore, tenascin may influence the early stages in the formation of the glia limitans, and thus prevent the indiscriminate migration of leptomeningeal cells into CNS tissue after injury.

Methamphetamine (METH) causes reactive gliosis in vitro: attenuation by the ADP-ribosylation (ADPR) inhibitor, benzamide

We examined the effects of methamphetamine (METH) in an in vitro model of rat fetal mesencephalic cells. METH causes loss of dopamine (DA) cells and neuronal process degeneration. In addition, the drug causes an increase in reactive gliosis as shown by the number of cells that stain for and by the intensity of staining with a glial fibrillary acidic protein (GFAP) antibody. Co-incubation of METH-treated cells with benzamide, which is a known inhibitor of ADP-ribosylation (ADPR), attenuated METH effects on both DA and glial cells. However, the effects of benzamide were somewhat more prominent on the glial cells. These results suggest that ADP-ribosylation may play a very important role in the development of reactive gliosis after the administration of neurotoxic agents.

Different rates of axonal degeneration in the crossed and uncrossed retinofugal pathways of Monodelphis domestica

The uncrossed retinofugal fibres in the marsupial Monodelphis domestica form a separate bundle as they pass through the optic chiasm. The uncrossed fibres segregate from the crossed fibres a short distance before they reach the chiasm, gathering as an essentially exclusive bundle in the ventral part of the optic nerve. This bundle then passes laterally through the optic chiasm and into the optic tract. The distinctive position of the uncrossed fibres has allowed us to recognise that, surprisingly, the uncrossed fibres degenerate more rapidly than the rest. Seven days after a monocular enucleation approximately 60-80% of the fibres of the crossed component in the main part of the optic nerve near the chiasm have a normal cross sectional appearance in electron micrographs whereas less than 20% of the fibres in the uncrossed bundle look normal. The rapid degeneration of the uncrossed fibres cannot be related to any morphological parameter of the axons. Their fibre diameters are mainly medium to thick, lying within the range of axon diameters found in the rest of the nerve. The axon-myelin ratios of the uncrossed fibres are also no different from those of the crossed optic fibres. There are no structural peculiarities identifiable with light or electron microscopical methods in either the axons or in the glia of the uncrossed bundle that might account for the more rapid degeneration. There is evidence that the degenerative change in the main part of the optic nerve progresses from the lesion towards the chiasm, and that for the crossed fibres it may progress slightly faster for the thicker than for the thinner fibres. The degeneration in the uncrossed bundle does not fit any of the rules that have been proposed for relating rate of degeneration to fibre diameter. We conclude that the rate of Wallerian degeneration is determined by factors that yet remain to be defined.

Invasion of experimental rat brain tumor: early morphological changes following microinjection of C6 glioma cells

We present morphological data of the early stage of tumor invasion in the central nervous system. C6 rat glioma cells were injected into the caudate-putamen of rat brain using glass micropipettes to minimize traumatic reactions. Four days after the inoculation, we examined the tumor-brain interface using light and electron microscopy. Ultrastructurally the tumor processes were attached to the perivascular basement membrane instead of the astroglial end-feet. At the tumor periphery, the vessel walls were in contact with both tumor processes and astroglial end-feet. Astrocytes withdrew their processes from the vascular walls and changed into a reactive phenotype, while the neuronal cells remained virtually intact, even when surrounded by tumor cells. Immunohistochemical study using C6 cells labeled with bromodeoxyuridine showed migration of the cells toward the perivascular space that was distant from the site of injection. These observations represent the earliest morphologically detectable changes of the tumor-brain interface, and suggest that the C6 cells possess the characteristics of high affinity to the endothelial basement membrane and invade along the preexisting blood vessels with brain parenchymal infiltration.

Immunohistochemical staining for glial fibrillary acidic protein (GFAP) after deafferentation or ischemic infarction in rat visual system: features of reactive and damaged astrocytes

Immunohistochemical staining for glial fibrillary acidic protein (GFAP) is standard for visualization of reactive astrocytes in tissue sections, whereas various forms of astrocytic damage remain to be described in detail. In this study we tested differences in GFAP labeling in reactive astrocytes and in glial cells damaged by ischemia and edema. Studies were performed in the anatomically well defined visual system of rat. Basic staining patterns for GFAP were established in subcortical visual nuclei and visual cortex. In the first model, deafferentation of visual centers was performed by unilateral optic nerve lesion, and characteristic changes of GFAP labeling in reactive astrocytes were studied at 0.5, 1, 1.5, 2, 4, 8 and 21 days after lesion. Initial changes were seen in the deafferented superior colliculus at 1 day after deafferentation with a diffuse increase and stellate types of reactive cells formed at 2-8 days. In the second model, small ischemic infarcts were produced in the visual cortex of rats using the method of photochemically-induced thrombosis. GFAP labeling with a polyclonal antiserum was massively enhanced in the infarct at 4 hr. Characteristic morphological changes in damaged astrocytes were seen which were also identified in experiments with simulated global ischemia. In the surround of the infarct, swelling of astrocytes also caused increased labeling. At 3-4 days infarction typical reactive astrocytes surrounded the lesioned area. In conclusion, these immunohistochemical studies on GFAP in rat visual system allow for the following classifications. (a) Normal astrocytes vary in labeling at different anatomical localizations. (b) Reactive astrocytes show enhanced labeling and larger cell-size within an interval of 1-2 days after lesion. (c) Astrocytes damaged by ischemia reveal increased labeling of disintegrating cellular elements within hours after a lesion. (d) Swollen astrocytes undergo enhanced labeling in areas with vasogenic edema.