Synemin is expressed in reactive astrocytes in neurotrauma and interacts differentially with vimentin and GFAP intermediate filament networks

Immature astrocytes and astrocytoma cells contain synemin and three other intermediate filament (IF) proteins: glial fibrillary acidic protein (GFAP), vimentin and nestin. Here, we show that, after neurotrauma, reactive astrocytes produce synemin and thus propose synemin as a new marker of reactive astrocytes. Comparison of synemin mRNA and protein levels in brain tissues and astrocyte cultures from wild-type, Vim-/- and Gfap-/-Vim-/- mice showed that in the absence of vimentin, synemin protein was undetectable although synemin mRNA was present at wild-type levels. By contrast, in Gfap-/- astrocytes, synemin protein and mRNA levels, as well as synemin incorporation into vimentin IFs, were unaltered. Biochemical assays with purified proteins suggested that synemin interacts with GFAP IFs like an IF-associated protein rather than like a polymerization partner, whereas the opposite was true for synemin interaction with vimentin. In transfection experiments, synemin did not incorporate into normal, filamentous GFAP networks, but integrated into vimentin and GFAP heteropolymeric networks. Thus, alongside GFAP, vimentin and nestin, reactive astrocytes contain synemin, whose accumulation is suppressed post-transcriptionally in the absence of a polymerization partner. In astrocytes, this partner is vimentin and not GFAP, which implies a functional difference between these two type III IF proteins.

Enriched environment and astrocytes in central nervous system regeneration

Rehabilitation medicine is entering a new era, based on the knowledge that the central nervous system has a substantial capacity for repair and regeneration. This capacity is used in 3 distinct but overlapping situations: (i) routine housekeeping throughout life (i.e. taking care of normal wear-and-tear); (ii) older age, when functional reserves of various kinds are depleted, resulting in cognitive, motor, and other deficits; and (iii) contexts in which a neurological deficit reflects an acute or chronic pathological process, such as neurotrauma, stroke, or neurodegenerative disease. The positive message here is two-fold. First, some aspects of regeneration occur even in the adult and ageing brain and spinal cord, and we are starting to unravel the underlying molecular mechanisms. Secondly, novel therapeutic approaches and targets are emerging that will substantially increase the efficiency and efficacy of rehabilitation and will transform rehabilitation into a discipline focusing both on its traditional domain and on prevention, ultimately across all the age categories. This review attempts to sum up the present knowledge about an enriched environment, currently the single most efficient plasticity- and regeneration-promoting paradigm. It also summarizes research showing that astrocytes - considered only years ago merely to nurse and support neurones - are a novel and highly interesting target for regenerative strategies in the brain and spinal cord.

The role of astrocytes and complement system in neural plasticity

In neurotrauma, brain ischemia or neurodegenerative diseases, astrocytes become reactive (which is known as reactive gliosis) and this is accompanied by an altered expression of many genes. Two cellular hallmarks of reactive gliosis are hypertrophy of astrocyte processes and the upregulation of the part of the cytoskeleton known as intermediate filaments, which are composed of nestin, vimentin, and GFAP. Our aim has been to better understand the function of reactive astrocytes in CNS diseases. Using mice deficient for astrocyte intermediate filaments (GFAP(-/-)Vim(-/-)), we were able to attenuate reactive gliosis and slow down the healing process after neurotrauma. We demonstrated the key role of reactive astrocytes in neurotrauma-at an early stage after neurotrauma, reactive astrocytes have a neuroprotective effect; at a later stage, they facilitate the formation of posttraumatic glial scars and inhibit CNS regeneration, specifically, they seem to compromise neural graft survival and integration, reduce the extent of synaptic regeneration, inhibit neurogenesis in the old age, and inhibit regeneration of severed CNS axons. We propose that reactive astrocytes are the future target for the therapeutic strategies promoting regeneration and plasticity in the brain and spinal cord in various disease conditions. Through its involvement in inflammation, opsonization, and cytolysis, complement protects against infectious agents. Although most of the complement proteins are synthesized in CNS, the role of the complement system in the normal or ischemic CNS remains unclear. Complement activiation in the CNS has been generally considered as contributing to tissue damage. However, growing body of evidence suggests that complement may be a physiological neuroprotective mechanism as well as it may participate in maintenance and repair of the adult brain.

Redefining the concept of reactive astrocytes as cells that remain within their unique domains upon reaction to injury

Reactive astrocytes in neurotrauma, stroke, or neurodegeneration are thought to undergo cellular hypertrophy, based on their morphological appearance revealed by immunohistochemical detection of glial fibrillary acidic protein, vimentin, or nestin, all of them forming intermediate filaments, a part of the cytoskeleton. Here, we used a recently established dye-filling method to reveal the full three-dimensional shape of astrocytes assessing the morphology of reactive astrocytes in two neurotrauma models. Both in the denervated hippocampal region and the lesioned cerebral cortex, reactive astrocytes increased the thickness of their main cellular processes but did not extend to occupy a greater volume of tissue than nonreactive astrocytes. Despite this hypertrophy of glial fibrillary acidic protein-containing cellular processes, interdigitation between adjacent hippocampal astrocytes remained minimal. This work helps to redefine the century-old concept of hypertrophy of reactive astrocytes.

Cytoskeleton and Vesicle Mobility in Astrocytes

Exocytotic vesicles in astrocytes are increasingly viewed as essential in astrocyte-to-neuron communication in the brain. In neurons and excitable secretory cells, delivery of vesicles to the plasma membrane for exocytosis involves an interaction with the cytoskeleton, in particular microtubules and actin filaments. Whether cytoskeletal elements affect vesicle mobility in astrocytes is unknown. We labeled single vesicles with fluorescent atrial natriuretic peptide and monitored their mobility in rat astrocytes with depolymerized microtubules, actin, and intermediate filaments and in mouse astrocytes deficient in the intermediate filament proteins glial fibrillary acidic protein and vimentin. In astrocytes, as in neurons, microtubules participated in directional vesicle mobility, and actin filaments played an important role in this process. Depolymerization of intermediate filaments strongly affected vesicle trafficking and in their absence the fraction of vesicles with directional mobility was reduced.

Hepatic stellate cells express synemin, a protein bridging intermediate filaments to focal adhesions

BACKGROUND AND AIMS

In the liver, stellate cells play several important (patho)physiological roles. They express a broad but variable spectrum of intermediate filament (IF) proteins. The aim of this study was to investigate the expression and functions of the intermediate filament protein synemin in hepatic stellate cells (HSCs).

METHODS

In isolated and cultured rat HSCs, synemin expression was examined by quantitative reverse transcriptase polymerase chain reaction, western blotting, and immunocytochemistry. Protein-protein interaction between synemin and possible binding partners was investigated by co-immunoprecipitation and confocal microscopy.

RESULTS

Expression of synemin was significantly downregulated with increased culture time. In 1-day cultured HSCs, synemin associated with other IF proteins (GFAP, desmin, and vimentin), and with the focal adhesion proteins vinculin and talin, but not with alpha-actinin or paxillin. Synemin IF and focal adhesion proteins co-localised in long slender processes, but not in the lamellipodia. In human and rat liver tissue, the presence of synemin was investigated by immunohistochemistry. In normal rat and human livers, synemin immunoreactivity was found in HSCs, smooth muscle cells of hepatic arterioles, and nerve bundles in portal tracts, but not in portal fibroblasts. In CCl4-intoxicated rat livers and in human cirrhotic livers, immunoreactivity for synemin in the parenchymal tissue was decreased. Thus synemin was expressed in quiescent HSCs but not in portal fibroblasts; and synemin expression decreased with HSC activation in vivo during chronic liver damage and with HSC activation in culture.

CONCLUSIONS

Synemin forms heteropolymeric filaments with type-III IF proteins and acts as a bridging protein between IFs and a specific type of focal adhesions.

Complement: a novel factor in basal and ischemia-induced neurogenesis

Through its involvement in inflammation, opsonization, and cytolysis, the complement protects against infectious agents. Although most of the complement proteins are synthesized in the central nervous system (CNS), the role of the complement system in the normal or ischemic CNS remains unclear. Here we demonstrate for the first time that neural progenitor cells and immature neurons express receptors for complement fragments C3a and C5a (C3a receptor (C3aR) and C5a receptor). Mice that are deficient in complement factor C3 (C3(-/-)) lack C3a and are unable to generate C5a through proteolytic cleavage of C5 by C5-convertase. Intriguingly, basal neurogenesis is decreased both in C3(-/-) mice and in mice lacking C3aR or mice treated with a C3aR antagonist. The C3(-/-) mice had impaired ischemia-induced neurogenesis both in the subventricular zone, the main source of neural progenitor cells in adult brain, and in the ischemic region, despite normal proliferative response and larger infarct volumes. Thus, in the adult mammalian CNS, complement activation products promote both basal and ischemia-induced neurogenesis.

Re-establishing the regenerative potential of central nervous system axons in postnatal mice

At a certain point in development, axons in the mammalian central nervous system lose their ability to regenerate after injury. Using the optic nerve model, we show that this growth failure coincides with two developmental events: the loss of Bcl-2 expression by neurons and the maturation of astrocytes. Before postnatal day 4, when astrocytes are immature, overexpression of Bcl-2 alone supported robust and rapid optic nerve regeneration over long distances, leading to innervation of brain targets by day 4 in mice. As astrocytes matured after postnatal day 4, axonal regeneration was inhibited in mice overexpressing Bcl-2. Concurrent induction of Bcl-2 and attenuation of reactive gliosis reversed the failure of CNS axonal re-elongation in postnatal mice and led to rapid axonal regeneration over long distances and reinnervation of the brain targets by a majority of severed optic nerve fibers up to 2 weeks of age. These results suggest that an early postnatal downregulation of Bcl-2 and post-traumatic reactive gliosis are two important elements of axon regenerative failure in the CNS.

Astrocyte activation and reactive gliosis

Astrocytes become activated (reactive) in response to many CNS pathologies, such as stroke, trauma, growth of a tumor, or neurodegenerative disease. The process of astrocyte activation remains rather enigmatic and results in so-called "reactive gliosis," a reaction with specific structural and functional characteristics. In stroke or in CNS trauma, the lesion itself, the ischemic environment, disrupted blood-brain barrier, the inflammatory response, as well as in metabolic, excitotoxic, and in some cases oxidative crises--all affect the extent and quality of reactive gliosis. The fact that astrocytes function as a syncytium of interconnected cells both in health and in disease, rather than as individual cells, adds yet another dimension to this picture. This review focuses on several aspects of astrocyte activation and reactive gliosis and discusses its possible roles in the CNS trauma and ischemia. Particular emphasis is placed on the lessons learnt from mouse genetic models in which the absence of intermediate filament proteins in astrocytes leads to attenuation of reactive gliosis with distinct pathophysiological and clinical consequences.

Increased cell proliferation and neurogenesis in the hippocampal dentate gyrus of old GFAP(-/-)Vim(-/-) mice

In response to central nervous system (CNS) injury, and more discretely so also during aging, astrocytes become reactive and increase their expression of the intermediate filament proteins glial fibrillary acidic protein (GFAP) and vimentin. Studies of mice deficient in astrocytic intermediate filaments have provided insights into the function of reactive gliosis. Recently we demonstrated robust integration of retinal transplants (1) and increased posttraumatic synaptic regeneration (2) in GFAP(-/-)Vim(-/-) mice, suggesting that modulation of astrocyte activity affects the permissiveness of the CNS environment for regeneration. Neurogenesis in the adult mammalian CNS is restricted to essentially two regions, the hippocampus and the subventricular zone. Here, we assessed neurogenesis in the hippocampus of 18-month-old GFAP(-/-)Vim(-/-) mice. In the granular layer of the dentate gyrus, cell proliferation/survival was 34% higher and neurogenesis 36% higher in GFAP(-/-)Vim(-/-) mice than in wildtype controls. These findings suggest that the adult hippocampal neurogenesis in healthy old mice can be increased by modulating astrocyte reactivity.

Absence of glial fibrillary acidic protein and vimentin prevents hypertrophy of astrocytic processes and improves post-traumatic regeneration

The regenerative capacity of the CNS is extremely limited. The reason for this is unclear, but glial cell involvement has been suspected, and oligodendrocytes have been implicated as inhibitors of neuroregeneration (Chen et al., 2000, GrandPre et al., 2000; Fournier et al., 2001). The role of astrocytes in this process was proposed but remains incompletely understood (Silver and Miller, 2004). Astrocyte activation (reactive gliosis) accompanies neurotrauma, stroke, neurodegenerative diseases, or tumors. Two prominent hallmarks of reactive gliosis are hypertrophy of astrocytic processes and upregulation of intermediate filaments. Using the entorhinal cortex lesion model in mice, we found that reactive astrocytes devoid of the intermediate filament proteins glial fibrillary acidic protein and vimentin (GFAP-/-Vim-/-), and consequently lacking intermediate filaments (Colucci-Guyon et al., 1994; Pekny et al., 1995; Eliasson et al., 1999), showed only a limited hypertrophy of cell processes. Instead, many processes were shorter and not straight, albeit the volume of neuropil reached by a single astrocyte was the same as in wild-type mice. This was accompanied by remarkable synaptic regeneration in the hippocampus. On a molecular level, GFAP-/-Vim-/- reactive astrocytes could not upregulate endothelin B receptors, suggesting that the upregulation is intermediate filament dependent. These findings show a novel role for intermediate filaments in astrocytes and implicate reactive astrocytes as potent inhibitors of neuroregeneration.

Astrocyte intermediate filaments in CNS pathologies and regeneration

Astroglial cells are the most abundant cells in the mammalian central nervous system (CNS), yet our knowledge about their function in health and disease has been limited. This review focuses on the recent work addressing the function of intermediate filaments in astroglial cells under severe mechanical or osmotic stress, in hypoxia, and in brain and spinal cord injury. Recent data show that when astrocyte intermediate filaments are genetically ablated in mice, reactive gliosis is attenuated and the course of several CNS pathologies is altered, while the signs of CNS regeneration become more prominent. GFAP is the principal astrocyte intermediate filament protein and dominant mutations in the GFAP gene have been shown to lead to Alexander disease, a fatal neurodegenerative condition in humans.

Under stress, the absence of intermediate filaments from Müller cells in the retina has structural and functional consequences

In epithelial and muscle cells, intermediate filaments (IFs) are important for resistance to mechanical stress. The aim of this study was to elucidate whether IFs are also important for providing resistance to mechanical stress in the Müller cells of the retina and whether this has any pathophysiological consequences. We used mice deficient in IF proteins glial fibrillary acidic protein and/or vimentin (GFAP(-/-), Vim(-/-) and GFAP(-/-) Vim(-/-)), and stress on the retina was applied by excision of the eyes immediately post mortem (compared with in situ fixation) or by inducing a neovascular response to oxygen-induced retinopathy (OIR). The structure of unchallenged retinas was normal, but mechanical stress caused local separation of the inner limiting membrane (ILM) and adjacent tissue from the rest of the retina in GFAP(-/-) Vim(-/-) mice and, to a lesser extent, in Vim(-/-) mice. This detachment occurred within the endfeet of Müller cells, structures normally rich in IFs but IF-free in GFAP(-/-) Vim(-/-) mice. Hypoxia-induced neovascularization was comparable in all groups of mice with respect to the retinal surface area occupied by new vessels. However, the vessels traversed the ILM and penetrated the vitreous body less frequently than in wild-type retinas (31-55% in Vim(-/-), 66-79% in GFAP(-/-) Vim(-/-)). We conclude that IFs are important for maintaining the mechanical integrity of Müller-cell endfeet and the inner retinal layers under a mechanical challenge. Furthermore, the absence of IFs in Müller cells leads to an abnormal response of the vascular system to ischemia, specifically decreased ability of newly formed blood vessels to traverse the ILM.

Bfsp2 mutation found in mouse 129 strains causes the loss of CP49' and induces vimentin-dependent changes in the lens fibre cell cytoskeleton

Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.

Bfsp2 mutation found in mouse 129 strains causes the loss of CP49 and induces vimentin-dependent changes in the lens fibre cell cytoskeleton

Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.

Robust neural integration from retinal transplants in mice deficient in GFAP and vimentin

With recent progress in neuroscience and stem-cell research, neural transplantation has emerged as a promising therapy for treating CNS diseases. The success of transplantation has been limited, however, by the restricted ability of neural implants to survive and establish neuronal connections with the host. Little is known about the mechanisms responsible for this failure. Neural implantation triggers reactive gliosis, a process accompanied by upregulation of intermediate filaments in astrocytes and formation of astroglial scar tissue. Here we show that the retinas of adult mice deficient in glial fibrillary acidic protein and vimentin, and consequently lacking intermediate filaments in reactive astrocytes and Müller cells, provide a permissive environment for grafted neurons to migrate and extend neurites. The transplanted cells integrated robustly into the host retina with distinct neuronal identity and appropriate neuronal projections. Our results indicate an essential role for reactive astroglial cells in preventing neural graft integration after transplantation.

Loss of GFAP expression in high-grade astrocytomas does not contribute to tumor development or progression

In astrocytic neoplasms, the number of cells expressing glial fibrillary acidic protein (GFAP) is inversely proportional to the extent of anaplasia. The loss of GFAP expression, the principal marker of astroglial cells, in these tumors has been proposed to constitute a step in their development and progression. To test this hypothesis, we crossed p53-negative (p53(-/-)) mice, which frequently develop astrocytomas after intrauterine exposure to ethylnitrosourea, with GFAP-negative (GFAP(-/-)) mice or GFAP(+/+) controls. Brain tumors of glial origin were found in 12 of 35 GFAP(+/+) p53(-/-) mice (34%) and in 11 of 27 GFAP(-/-) p53(-/-) mice (41%). The two groups did not differ in the age at which tumors were detected or in tumor histology or progression. Thus, the loss of GFAP expression frequently seen in high-grade astrocytomas does not constitute a step in tumor development. Rather, it may represent the undifferentiated state of these cells.

Neuron-specific ablation of PDGF-B is compatible with normal central nervous system development and astroglial response to injury

Members of the PDGF family have multiple roles during embryogenesis and in a variety of pathological situations in the adult. One of the major sites of PDGF-B expression in adult mammals are postmitotic CNS neurons. Combined with reported neurotrophic and neuroprotective effects of exogenously administered PDGFs, this has led to the speculation that PDGF-B may have a role in CNS development, in maintenance, or in response to CNS injury. To test these hypotheses, we developed mice in which PDGF-B was ablated genetically in postmitotic neurons at sites where PDGF-B is normally expressed. We found that these mice develop to adulthood without apparent defects. We demonstrate PDGF-B expression in the postnatal mouse hippocampus and forebrain cortex. We show that neuron-specific knockout of PDGF-B does not influence the astroglial and angiogenic responses to injury in the hippocampus or forebrain cortex. We conclude that the role of neuron-derived PDGF-B remains obscure. A role for neuron-derived PDGF-B, if existing, might be redundant with other CNS growth factors. Alternatively, other and more specific analyses of CNS functions in the normal and injured states will be required to demonstrate such a role.

Mice lacking the adenosine A1 receptor are anxious and aggressive, but are normal learners with reduced muscle strength and survival rate

Behavioural assessment of mice lacking adenosine A1 receptors (A1Rs) showed reduced activity in some phases of the light-dark cycle, reduced exploratory behaviour in the open-field and in the hole-board, increased anxiety in the plus maze and dark-light box and increased aggressiveness in the resident-intruder test. No differences were found in spatial reference and working memory in several Morris water maze tasks. Both mutant mice had reduced muscle strength and survival rate. These results confirm the involvement of adenosine in motor activity, exploratory behaviour, anxiety and aggressiveness. A1Rs also appear to play a critical role in ageing-related deterioration.

Intermediate filaments regulate astrocyte motility

Intermediate filaments (IFs) compose, together with actin filaments and microtubules, the cytoskeleton and they exhibit a remarkable but still enigmatic cell-type specificity. In a number of cell types, IFs seem to be instrumental in the maintenance of the mechanical integrity of cells and tissues. The function of IFs in astrocytes has so far remained elusive. We have recently reported that glial scar formation following brain or spinal cord injury is impaired in mice deficient in glial fibrillary acidic protein and vimentin. These mice lack IFs in reactive astrocytes that are normally pivotal in the wound repair process. Here we show that reactive astrocytes devoid of IFs exhibit clear morphological changes and profound defects in cell motility thereby revealing a novel function for IFs.

Effect of elevated K(+), hypotonic stress, and cortical spreading depression on astrocyte swelling in GFAP-deficient mice

Glial fibrillary acidic protein (GFAP) is the main component of intermediate filaments in astrocytes. To assess its function in astrocyte swelling, we compared astrocyte membrane properties and swelling in spinal cord slices of 8- to 10-day-old wild-type control (GFAP(+/+)) and GFAP-knockout (GFAP(-/-)) mice. Membrane currents and K(+) accumulation around astrocytes after a depolarizing pulse were studied using the whole-cell patch-clamp technique. In vivo cell swelling was studied in the cortex during spreading depression (SD) in 3 to 6-month-old animals. Swelling-induced changes of the extracellular space (ECS) diffusion parameters, i.e., volume fraction alpha and tortuosity lambda, were studied by the real-time iontophoretic tetramethylammonium (TMA(+)) method using TMA(+)-selective microelectrodes. Morphological analysis using confocal microscopy and quantification of xy intensity profiles in a confocal plane revealed a lower density of processes in GFAP(-/-) astrocytes than in GFAP(+/+) astrocytes. K(+) accumulation evoked by membrane depolarization was lower in the vicinity of GFAP(-/-) astrocytes than GFAP(+/+) astrocytes, suggesting the presence of a larger ECS around GFAP(-/-) astrocytes. Astrocyte swelling evoked by application of 50 mM K(+) or by hypotonic solution (HS) produced a larger increase in [K(+)](e) around GFAP(+/+) astrocytes than around GFAP(-/-) astrocytes. No differences in alpha and lambda in the spinal cord or cortex of GFAP(+/+) and GFAP(-/-) mice were found; however, the application of either 50 mM K(+) or HS in spinal cord, or SD in cortex, evoked a large decrease in alpha and an increase in lambda in GFAP(+/+) mice only. Slower swelling in GFAP(-/-) astrocytes indicates that GFAP and intermediate filaments play an important role in cell swelling during pathological states.