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E Syková

Publications and source records attributed to E Syková.

At least 19 recordsLinked to original sources
PubMed2002

Diffusion parameters in the striatum of rats with 6-hydroxydopamine-induced lesions and with fetal mesencephalic grafts.

Functional recovery after transplantation of dopaminergic cells into the lesioned striatum is dependent on widespread diffusion of the transmitter released by the graft. In the present study, we investigated the diffusion parameters of the extracellular space in the striatum of control, 6-hydroxydopamine-lesioned, intrastriatally grafted, and sham-grafted rats in vivo. We used two types of grafts-single macrografts or multiple micrografts. The real-time iontophoretic tetramethylammonium method enabled us to extract three extracellular space diffusion parameters: volume fraction, alpha, tortuosity, lambda, and nonspecific uptake of tetramethylammonium, k'. Compared with controls (alpha = 0.19, lambda = 1.59), in lesioned animals both alpha and lambda were lower (alpha = 0.14, lambda = 1.50). alpha and lambda were increased inside macro-and micrografts, where alpha = 0.24 and lambda = 1.80, and in sham-grafted areas, where alpha = 0.24 and lambda = 1.72. In regions outside the grafts (alpha = 0.15, lambda = 1.51) or in sham grafts (alpha = 0.14, lambda = 1.49), the values of alpha and lambda were similar to the values observed in lesioned striatum. Nonspecific uptake (k') did not differ among the groups. Our results show that, compared with control, alpha and lambda were decreased in dopamine-depleted areas and increased in areas with grafts. Multiple but smaller graft deposits, in contrast to their enlarged capability for dopaminergic reinnervation, impair the conditions for diffusion and extrasynaptic transmission in a larger area of the striatum than do single macrografts, presumably because of more extensive tissue damage, cell loss, and astrogliosis.

Animals↗
PubMed2002

Learning deficits in aged rats related to decrease in extracellular volume and loss of diffusion anisotropy in hippocampus.

The extracellular space (ECS) is the microenvironment of the nerve cells and an important communication channel, allowing for long-distance extrasynaptic communication between cells. Changes in ECS size, geometry, and composition have been reported in diverse (patho)physiological states, including aging. In the present study, real-time tetramethylammonium (TMA+) iontophoresis was used to quantify ECS diffusion parameters in different brain regions of adult and behaviorally characterized aged rats. Prior to ECS diffusion measurement, superior and inferior learners were selected from a large group of aged rats, according to their performance in the open-field water maze. The main finding was that the degree of impaired maze performance of old rats correlates, firstly, with decrease in ECS volume, loss of diffusion anisotropy in hippocampus, and degree of astrogliosis, and secondly, with disorganization of the astrocytic processes and reduction of hippocampal ECS matrix molecules. Importantly, no significant differences were found in the density of neurons in any region of the hippocampus or dentate gyrus. The alterations in hippocampal diffusion parameters evident in aged animals with severe learning deficits could account for the learning impairment, due to their effects on extrasynaptic volume transmission and/or on the "cross-talk" between synapses, which has been suggested to be involved in neural processes associated with learning and memory formation.

Aging↗
PubMed2002

Water ADC, extracellular space volume, and tortuosity in the rat cortex after traumatic injury.

The diffusion parameters in rat cortex were studied 3-35 days following a cortical stab wound, using diffusion-weighted MR to determine the apparent diffusion coefficient of water (ADC(W)) in the tissue, and the real-time iontophoretic tetramethylammonium (TMA) method to measure the extracellular space (ECS) diffusion parameters: ECS volume fraction alpha and the ADC of TMA(+) (ADC(TMA)). Severe astrogliosis was found close to the wound, and mild astrogliosis was found in the ipsilateral but not the contralateral cortex. Chondroitin sulfate proteoglycan (CSPG) expression was increased throughout the ipsilateral cortex. In the hemisphere contralateral to the wound, alpha, ADC(TMA), and ADC(W) were not significantly different from control values. ECS volume fraction was increased only in the vicinity of the wound, in the region of cell death and severe astrogliosis, at 3 and 7 days after injury. However, both ADC(TMA) and ADC(W) were significantly decreased after lesion in the vicinity of the wound as well as in the rest of the ipsilateral hemisphere distant from the wound. Thus, both ADC(W) and ADC(TMA) decreased in regions wherein alpha did not change but CSPG increased. An increase in extracellular matrix expression may therefore impose diffusion barriers for water as well as for TMA molecules.

Animals↗
PubMed2002

Polymer hydrogels usable for nervous tissue repair.

The implantation of non-resorbable biocompatible polymer hydrogels into defects in the central nervous system can reduce glial scar formation, bridge the lesion and lead to tissue regeneration within the hydrogel. We implanted hydrogels based on crosslinked poly hydroxyethyl-methacrylate (pHEMA) and poly N-(2-hydroxypropyl)-methacrylamide (pHPMA) into the rat cortex and evaluated the cellular invasion into the hydrogels by means of immunohistochemical methods and tetramethylammonium diffusion measurements. Astrocytes and NF160-positive axons grew similarly into both types of hydrogels. We found no cell types other than astrocytes in the pHEMA hydrogels. In the pHPMA hydrogels, we found a massive ingrowth of connective tissue elements. These changes were accompanied by corresponding changes in the extracellular space volume fraction and tortuosity of the hydrogels.

Animals↗
PubMed2002

Changes in extracellular space volume and geometry induced by cortical spreading depression in immature and adult rats.

Changes in extracellular space (ECS) diffusion parameters, DC potentials and extracellular potassium concentration were studied during single and repeated cortical spreading depressions (SD) in 13-15 (P13-15), 21 (P21) and 90-day-old (adult) Wistar rats. The real-time iontophoretic method using tetramethylammonium (TMA+)-selective microelectrodes was employed to measure three ECS parameters in the somatosensory cortex: the ECS volume fraction alpha (alpha = ECS volume/total tissue volume), ECS tortuosity lambda (increase in diffusion path length) and the nonspecific TMA+ uptake k'. SD was elicited by needle prick. SD was significantly longer at P13-15 than at P21 and in adults. During SD, alpha in all age groups decreased from 0.21-0.23 to 0.05-0.09; lambda increased from 1.55-1.65 to 1.95-2.07. Ten minutes after SD, alpha (in adults) and lambda (all age groups) increased compared to controls. This increase persisted even 1 hour after SD. When SD was repeated at 1 hour intervals, both alpha and lambda showed a gradual cumulative increase with SD repetition. Our study also shows that cortical SD is, as early as P13, accompanied by severe ECS shrinkage and increased diffusion path length (tortuosity) with values similar to adults, followed by a long-lasting increase in ECS volume and tortuosity when compared to pre-SD values.

Aging↗
PubMed2001

Effect of osmotic stress on potassium accumulation around glial cells and extracellular space volume in rat spinal cord slices.

In rat brain and spinal cord slices, the local extracellular accumulation of K(+), as indicated by K(+) tail currents (I(tail)) after a depolarization step, is greater in the vicinity of oligodendrocytes than that of astrocytes. It has been suggested that this may reflect a smaller extracellular space (ECS) around oligodendrocytes compared to astrocytes [Chvátal et al. [1997] J. Neurosci. Res. 49:98-106; [1999] J. Neurosci. Res. 56:493-505). We therefore compared the effect of osmotic stress in spinal cord slices from 5-11-day-old rats on the changes in reversal potentials (V(rev)) of I(tail) measured by the whole-cell patch-clamp technique and the changes in ECS volume measured by the real-time iontophoretic method. Cell swelling induced by a 20 min perfusion of hypoosmotic solution (200 mmol/kg) decreased the ECS volume fraction from 0.21 +/- 0.01 to 0.15 +/- 0.02, i.e., by 29%. As calculated from V(rev) of I(tail) using the Nernst equation, a depolarizing prepulse increased [K(+)](e) around astrocytes from 11.0 to 44.7 mM, i.e., by 306%, and around oligodendrocytes from 26.1 to 54.9 mM, i.e., by 110%. The ECS volume fraction decrease had the same time course as the changes in V(rev) of I(tail). Cell shrinkage in hyperosmotic solution (400 mmol/kg) increased ECS volume fraction from 0.24 +/- 0.02 to 0.32 +/- 0.02, i.e., by 33%. It had no effect on [K(+)](e) evoked by a depolarizing prepulse in astrocytes, whereas in oligodendrocytes [K(+)](e) rapidly decreased from 52 to 26 mM, i.e., by 50%. The increase in ECS volume was slower than the changes in [K(+)](e). These data demonstrate that hypoosmotic solution has a larger effect on the ECS volume around astrocytes than around oligodendrocytes and that hyperosmotic solution affects the ECS volume around oligodendrocytes only. This indicates that increased K(+) accumulation in the vicinity of oligodendrocytes could be due to a restricted ECS. Oligodendrocytes in the CNS are therefore most likely surrounded by clusters of "compacted" ECS, which may selectively affect the diffusion of neuroactive substances in specific areas and directions and facilitate spatial K(+) buffering.

Animals↗
PubMed2001

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.

Animals↗
PubMed2001

Poly[N-(2-hydroxypropyl)methacrylamide] polymers diffuse in brain extracellular space with same tortuosity as small molecules.

Integrative optical imaging was used to show that long-chain synthetic poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) polymers in a range of molecular weights from 7.8 to 1057 kDa were able to diffuse through the extracellular space in rat neocortical slices. Tortuosity (square root of ratio of diffusion coefficient in aqueous medium to that in brain) measured with such polymers averaged 1.57, a value similar to that obtained previously with tetramethylammonium, a small cation. When PHPMA was conjugated with bovine serum albumin (BSA) to make a bulky polymer with molecular weight 176 kDa, the tortuosity rose to 2.27, a value similar to that obtained previously with BSA alone and with 70-kDa dextran. The method of image analysis was justified with diffusion models involving spherical and nonspherical initial distributions of the molecules.

Animals↗
PubMed2001

Glial diffusion barriers during aging and pathological states.

In conclusion, glial cells control not only ECS ionic composition, but also ECS size and geometry. Since ECS ionic and volume changes have been shown to play an important role in modulating the complex synaptic and extrasynaptic signal transmission in the CNS, glial cells may thus affect neuronal interaction, synchronization and neuron-glia communication. As shown in Fig. 2, a link between ionic and volume changes and signal transmission has been proposed as a model for the non-specific feedback mechanism suppressing neuronal activity (Syková, 1997; Ransom, 2000). First, neuronal activity results in the accumulation of [K+]e, which in turn depolarizes glial cells, and this depolarization induces an alkaline shift in glial pHi. Second, the glial cells extrude acid and the resulting acid shift causes a decrease in the neuronal excitability. Because ionic transmembrane shifts are always accompanied by water, this feedback mechanism is amplified by activity-related glial swelling compensated for by ECS volume shrinkage and by increased tortuosity, presumably by the crowding of molecules of the ECS matrix and/or by the swelling of fine glial processes. This, in turn, results in a larger accumulation of ions and other neuroactive substances in the brain due to increased diffusion hinderance in the ECS. Astrocyte hypertrophy, proliferation and swelling influence the size of the ECS volume and tortuosity around neurons, slowing diffusion in the ECS. Their organization may also affect diffusion anisotropy, which could be an underlying mechanism for the specificity of extrasynaptic transmission, including 'cross-talk' between distinct synapses (Barbour and Hausser, 1997; Kullmann and Asztely, 1998). An increased concentration of transmitter released into a synapse (e.g. repetitive adequate stimuli or during high frequency electrical stimulation which induces LTP) results in a significant activation of high-affinity receptors at neighboring synapses. The efficacy of such synaptic cross-talk would be dependent on the extracellular space surrounding the synapses, i.e. on intersynaptic geometry and diffusion parameters. Other recent studies have also suggested an important role for proteoglycans, known to participate in multiple cellular processes, such as axonal outgrowth, axonal branching and synaptogenesis (Hardington and Fosang, 1992; Margolis and Margolis, 1993) that are important for the formation of memory traces. Recent observation of a decrease of fibronectin and chondroitin sulfate proteoglycan staining in the hippocampus of behaviorally impaired aged rats (Syková et al., 1998a,b) supports this hypothesis. It is reasonable to assume that besides neuronal and glial processes, macromolecules of the extracellular matrix contribute to diffusion barriers in the ECS. It is therefore apparent that glial cells play an important role in the local architecture of the CNS and they may also be involved in the modulation of signal transmission, in plastic changes, LTP, LTD and in changes of behavior and memory formation.

Aging↗
PubMed2001

Membrane currents and morphological properties of neurons and glial cells in the spinal cord and filum terminale of the frog.

Using the patch-clamp technique in the whole-cell configuration combined with intracellular dialysis of the fluorescent dye Lucifer yellow (LY), the membrane properties of cells in slices of the lumbar portion of the frog spinal cord (n=64) and the filum terminale (FT, n=48) have been characterized and correlated with their morphology. Four types of cells were found in lumbar spinal cord and FT with membrane and morphological properties similar to those of cells that were previously identified in the rat spinal cord (Chvátal, A., Pastor, A., Mauch, M., Syková, E., Kettenmann, H., 1995. Distinct populations of identified glial cells in the developing rat spinal cord: Ion channel properties and cell morphology. Eur. J. Neurosci. 7, 129-142). Neurons, in response to a series of symmetrical voltage steps, displayed large repetitive voltage-dependent Na(+) inward currents and K(+) delayed rectifying outward currents. Three distinct types of non-neuronal cells were found. First, cells that exhibited passive symmetrical non-decaying currents were identified as astrocytes. These cells immunostained for GFAP and typically had at least one thick process and a number of fine processes. Second, cells with the characteristic properties of rat spinal cord oligodendrocytes, with passive symmetrical decaying currents and large tail currents after the end of the voltage step. These cells exhibited either long parallel or short hairy processes. Third, cells that expressed small brief inward currents in response to depolarizing steps, delayed rectifier outward currents and small sustained inward currents identical to rat glial precursor cells. Morphologically, they were characterized by round cell bodies with a number of finely branched processes. LY dye-coupling in the frog spinal cord gray matter and FT was observed in neurons and in all glial populations. All four cell types were found in both the spinal cord gray matter and FT. The glia/neuron ratio in the spinal cord was 0.78, while in FT it was 2.0. Moreover, the overall cell density was less in the FT than in the spinal cord. The present study shows that the membrane and morphological properties of glial cells in the frog and rat spinal cords are similar. Such striking phylogenetic similarity suggests a significant contribution from distinct glial cell populations to various spinal cord functions, particularly ionic and volume homeostasis in both mammals and amphibians.

Animals↗
PubMed2001

MR in phenylketonuria-related brain lesions.

PURPOSE: Phenylketonuria (PKU) patients were examined by different MR techniques to explain the pathological changes observed in periventricular white brain matter using conventional MR imaging. MATERIAL AND METHODS: Fifteen patients with treated classical PKU were examined by 1H spectroscopy, relaxometry and diffusion imaging on a whole-body 1.5-T MR imager. RESULTS: Known PKU lesions characterized by T2 enhancement in periventricular white matter were observed in all patients. The MR spectra from the lesioned areas showed a significant decrease in choline concentration. The mean ADC of water decreased and tortuosity increased in PKU lesions compared to control data. CONCLUSION: The results support the following hypothesis: The T2 increase in the PKU lesion reflects a raised concentration of free water molecules (about 15%) that have an increased trajectory between collisions compared to the same region in controls. The increase in water mobility might be explained by changes in extracellular space volume and myelin sheaths, which, presumably, have a different geometry with more hydrophobic sites in PKU patients. The changes result in increased tortuosity and may be confirmed by the loss of anisotropy in PKU lesions.

Adult↗
PubMed2001

Glutamate, NMDA, and AMPA induced changes in extracellular space volume and tortuosity in the rat spinal cord.

Glutamate release, particularly in pathologic conditions, may result in cellular swelling. The authors studied the effects of glutamate, N-methyl-D-aspartate (NMDA), and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) on extracellular pH (pH(e)), extracellular potassium concentration ([K(+)](e)), and changes in extracellular space (ECS) diffusion parameters (volume fraction alpha, tortuosity lambda) resulting from cellular swelling. In the isolated spinal cord of 4-to 12-day-old rats, the application of glutamate receptor agonists induced an increase in [K(+)](e), alkaline-acid shifts, a substantial decrease in alpha, and an increase in lambda. After washout of the glutamate receptor agonists, alpha either returned to or overshot normal values, whereas lambda remained elevated. Pretreatment with 20 mmol/L Mg(++), MK801, or CNQX blocked the changes in diffusion parameters, [K(+)](e) and pH(e) evoked by NMDA or AMPA. However, the changes in diffusion parameters also were blocked in Ca(2+)-free solution, which had no effect on the [K(+)](e) increase or acid shift. The authors conclude that increased glutamate release may produce a large, sustained and [Ca(2+)](e)-dependent decrease in alpha and increase in lambda. Repetitive stimulation and pathologic states resulting in glutamate release therefore may lead to changes in ECS volume and tortuosity, affecting volume transmission and enhancing glutamate neurotoxicity and neuronal damage.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2000

Extracellular diffusion parameters in spinal cord and filum terminale of the frog.

Extracellular space (ECS) diffusion parameters were studied in isolated frog spinal cord grey matter and filum terminale (FT), that is predominantly composed of glial cells and axons. We compared the cell swelling induced by K(+) application, hypotonic stress and tetanic stimulation of afferent input. The ECS diffusion parameters, volume fraction alpha (alpha = ECS volume/total tissue volume), tortuosity lambda (lambda(2) = free/apparent diffusion coefficient in the tissue) and non-specific cellular uptake k', were determined by the real-time iontophoretic method using TMA(+)-selective microelectrodes. Stimulation-evoked changes in extracellular K(+) concentration ([K(+)](e)) were measured by K(+)-selective microelectrodes. Histological analysis revealed that in the central region of the FT, the cell density was lower than in SC, neurons and oligodendrocytes were scarce, GFAP-positive astrocytes were abundant, and they showed thicker and more densely stained processes than in spinal cord. In the FT, alpha was 58% higher and lambda significantly lower than in the spinal cord. In 50 mM K(+), alpha in spinal cord decreased from about 0.19 to 0.09, i.e., by 53%, whereas in FT from about 0.32 to 0.20, i.e., by only 38%; lambda increased significantly more in FT than in spinal cord. Hypotonic solution (175 mmol/kg(-1)) resulted in similar decreases in alpha, and there were no changes in lambda in either spinal cord or FT. Stimulation of VIII or IX dorsal root (DR) by 30 Hz evoked an increase in [K(+)](e) from 3 to 11-12 mM in spinal cord, but to only 4-5 mM in FT. In the spinal cord this stimulation led to a 30% decrease in alpha and a small increase in lambda whereas in the FT the decrease in alpha was only about 10% and no increase in lambda was found. We conclude that in spinal cord, a complex tissue with a higher density of cellular elements than the FT, 50 mM K(+), hypotonic stress as well as DR stimulation evoked a greater decrease in ECS volume than in FT. Nevertheless, the K(+)-induced increase in tortuosity was higher in FT, suggesting that a substantial part of the K(+)-evoked increase in lambda was due to astrocytic swelling.

Animals↗
PubMed2000

Glial cells and volume transmission in the CNS.

Although synaptic transmission is an important means of communication between neurons, neurons themselves and neurons and glia also communicate by extrasynaptic "volume" transmission, which is mediated by diffusion in the extracellular space (ECS). The ECS of the central nervous system (CNS) is the microenvironment of neurons and glial cells. The composition and size of ECS change dynamically during neuronal activity as well as during pathological states. Following their release, a number of neuroactive substances, including ions, mediators, metabolites and neurotransmitters, diffuse via the ECS to targets distant from their release sites. Glial cells affect the composition and volume of the ECS and therefore also extracellular diffusion, particularly during development, aging and pathological states such as ischemia, injury, X-irradiation, gliosis, demyelination and often in grafted tissue. Recent studies also indicate that diffusion in the ECS is affected by ECS volume inhomogeneities, which are the result of a more compacted space in certain regions, e.g. in the vicinity of oligodendrocytes. Besides glial cells, the extracellular matrix also changes ECS geometry and forms diffusion barriers, which may also result in diffusion anisotropy. Glial cells therefore play an important role in extrasynaptic transmission, for example in functions such as vigilance, sleep, depression, chronic pain, LTP, LTD, memory formation and other plastic changes in the CNS. In turn, ECS diffusion parameters affect neuron-glia communication, ionic homeostasis and movement and/or accumulation of neuroactive substances in the brain.

Aging↗