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C Nolte

Publications and source records attributed to C Nolte.

At least 19 recordsLinked to original sources
PubMed2001

GFAP promoter-controlled EGFP-expressing transgenic mice: a tool to visualize astrocytes and astrogliosis in living brain tissue.

We have generated transgenic mice in which astrocytes are labeled by the enhanced green fluorescent protein (EGFP) under the control of the human glial fibrillary acidic protein (GFAP) promoter. In all regions of the CNS, such as cortex, cerebellum, striatum, corpus callosum, hippocampus, retina, and spinal cord, EGFP-positive cells with morphological properties of astrocytes could be readily visualized by direct fluorescence microscopy in living brain slices or whole mounts. Also in the PNS, nonmyelinating Schwann cells from the sciatic nerve could be identified by their bright green fluorescence. Highest EGFP expression was found in the cerebellum. Already in acutely prepared whole brain, the cerebellum appeared green-yellowish under normal daylight. Colabeling with GFAP antibodies revealed an overlap with EGFP in the majority of cells. Some brain areas, however, such as retina or hypothalamus, showed only low levels of EGFP expression, although the astrocytes were rich in GFAP. In contrast, some areas that were poor in immunoreactive GFAP were conspicuous for their EGFP expression. Applying the patch clamp technique in brain slices, EGFP-positive cells exhibited two types of membrane properties, a passive membrane conductance as described for astrocytes and voltage-gated channels as described for glial precursor cells. Electron microscopical investigation of ultrastructural properties revealed EGFP-positive cells enwrapping synapses by their fine membrane processes. EGFP-positive cells were negative for oligodendrocyte (MAG) and neuronal markers (NeuN). As response to injury, i.e., by cortical stab wounds, enhanced levels of EGFP expression delineated the lesion site and could thus be used as a live marker for pathology.

Animals↗
PubMed2000

Extracellular acidification decreases the basal motility of cultured mouse microglia via the rearrangement of the actin cytoskeleton.

The present study was undertaken to examine the effect of extracellular pH (pH(0)) on the locomotor function of murine microglial cells in vitro. We have found that basal motility of microglia, as measured by a computer-assisted video assay, decreased in an acidic, but not in an alkaline environment. Extracellular acidification affected the architecture of F-actin cytoskeleton, inducing bundling of actin and the formation of stress fibers. The change in intracellular pH (pH(i)) resulting from the change in pH(0) seems to be a prerequisite for the motility decrease since other means to decrease pH(i), namely Na(+)-free solution (in the absence of HCO(-)(3)) and nigericin-containing solution, mimicked the extracellular acidification. In contrast to its pronounced effect on basal motility of microglial cells, the motility increase, as induced by the chemoattractant complement 5a (C5a), was not affected by the acidic environment. The relationship of pH(0) to the locomotor function was also studied in a long-term microchemotaxis assay where microglia migrated within a pH gradient. Intracellular acidification induced by lowering pH(0) to 6.0 or removal of Na(+) from the assay medium decreased basal microglial cell migration. The C5a-induced chemotactic migration was moderately decreased by the acidic environment. In conclusion, our results suggest that acidification of the microglial extracellular milieu leads to a decrease in pH(i) and thereby reduces the basal microglial motility and C5a-induced chemotaxis via a rearrangement of the cytoskeleton. We would therefore like to speculate that changes in pH(i) constitute an important control mechanism in regulating the locomotor function of microglia in culture and probably also in the intact tissue.

Acids↗
PubMed2000

Ammonium triggers calcium elevation in cultured mouse microglial cells by initiating Ca(2+) release from thapsigargin-sensitive intracellular stores.

Microglial cells are thought to serve as sensors for pathologic events in the brain. In the present study we demonstrate that these cells respond with an increase in intracellular calcium concentration ([Ca2+]i) to intracellular alkaline shifts induced by either application of NH3/NH4+ or by an extracellular alkaline shift. The cytoplasmic pH (pHi) and [Ca2+]i in cultured mouse microglial cells were studied employing the fluorescent probes BCECF and fura-2, respectively. Application of NH3/NH4+ caused an initial rapid alkalinization followed by a slow recovery towards the resting level, while application of alkaline (pH 8.2) solution triggered a slower rise in pHi. The [Ca2+]i elevation triggered by NH3/NH4+ and extracellular alkaline shift were caused by different mechanisms: extracellular alkalinization induced a transmembrane Ca2+ entry, whereas NH3/NH4+ triggered Ca2+ release from thapsigargin- and ATP-sensitive intracellular pools. The mobilization of intracellular Ca2+ caused by NH3/NH4+ was blocked by a specific inhibitor of phospholipase C, U-73122, but was not affected by an inhibitor of G-protein, pertussis toxin. This implies that NH3/NH4 interacts with phospholipase C and leads to an increase in the intracellular level of inositol 1,4,5-trisphosphate (InsP3). In contrast to a previous study using a microglial cell line, application of NH3/NH4+ did not result in a release of tumor necrosis factor alpha (TNF-alpha), a marker of microglial activation, in the primary microglial cells. This implies that ammonium does not lead to activation of microglia in the culture model.

Adenosine Triphosphate↗
PubMed2000

Electrophysiological properties of microglial cells in normal and pathologic rat brain slices.

UNLABELLED: Microglial cells serve as pathologic sensors of the brain. They are highly abundant in all regions of the central nervous system (CNS) and are characterized by a ramified morphology within the normal tissue. In the present study, we have developed a procedure to study the membrane properties of identified, in situ microglia in acutely isolated brain slices from rat cortex, striatum and facial nucleus. Unlike the well characterized cultured microglial cells, ramified microglia of the slice are characterized by little, if any, voltage-gated membrane currents and a very low membrane potential. They are thus distinct from neurons, other glial cells and nonbrain macrophages. To study the consequences of microglial activation on the membrane channel pattern, we compared cells in the normal facial nucleus and at defined times after facial nerve axotomy. Within 12 h of axotomy, microglial cells expressed a prominent inward rectifier current and thus acquired the physiological properties of cultured microglia. Within 24 h of the lesion, the cells expressed an additional outward current, which is typical for lipopolysaccharide (LPS)-activated microglia in vitro. Seven days after the lesion, at a time of major regenerative processes in the facial nucleus, the physiological properties of microglial cells had reverted to those present prior to the pathological event. IN CONCLUSION: (i) ramified microglial cells represent a physiologically unique population of cells in the brain; (ii) are distinct from their cultured counterparts; and (iii), undergo a defined pattern of physiological states in the course of pathologic events.

Animals↗
PubMed2000

Phagocytic clearance of apoptotic neurons by Microglia/Brain macrophages in vitro: involvement of lectin-, integrin-, and phosphatidylserine-mediated recognition.

Microglia, the tissue macrophages of the brain, play a crucial role in recognition and phagocytic removal of apoptotic neurons. The microglial receptors for recognition of apoptotic neurons are not yet characterized. Here we established a co-culture model of primary microglia and cerebellar granule neurons to examine the receptor systems involved in recognition/uptake of apoptotic neurons. Treatment with 100 microM S-nitrosocysteine induced apoptosis of cerebellar neurons as indicated by nuclear condensation and phosphatidylserine exposure to the exoplasmic leaflet of the plasma membrane. Microglial cells were added to neurons 2 h after apoptosis induction and co-cultured for 6 h in the presence of ligands that inhibit recognition by binding to respective receptors. Binding/phagocytosis was determined after combined 4', 6-diamidino-2-phenylindole/propidium iodide (for apoptotic/necrotic neurons) and lectin staining (for microglia). Uptake of apoptotic neurons was reduced by N-acetylglucosamine or galactose, suggesting that recognition involves asialoglycoprotein-like lectins. Furthermore, the inhibition of microglial binding/uptake of apoptotic neurons by RGDS peptide suggests a role of microglial vitronectin receptor. As microglia selectively bind lipid vesicles enriched in phosphatidylserine and O-phospho-L-serine interfered with the uptake of apoptotic neurons, an involvement of phosphatidylserine receptor is rather likely. Apoptotic neurons do not release soluble signals that serve to attract or activate microglia. Collectively, these results suggest that apoptotic neurons generate a complex surface signal recognized by different receptor systems on microglia.

Animals↗
PubMed1999

[Transesophageal imaging of a coronary fistula in simultaneous endocarditis lenta].

A 61 year old diabetic patient with bacterial endocarditis probably caused by a congenital coronary fistula is presented. The fistula was already detected by transthoracic echocardiography. Transesophageal color-Doppler echocardiography identified the precise localization and course of the fistula. Additionally, in some parts of the fistula echogenic material could be seen that decreased in size after antibiotic treatment. Therefore, it was considered as corresponding to bacterial vegetations. Coronary angiography disclosed an ectopic aneurysmatic and elongated circumflex coronary artery. Thus, even in rare conditions such as coronary fistulas transesophageal echocardiography may be helpful to allow detection of morphological substrate of associated infective endocarditis.

Coronary Thrombosis↗
PubMed1999

Immunolocalization of the neural cell adhesion molecule L1 in epithelia of rodents.

The expression of the neural cell adhesion molecule L1 was analyzed in several non-neural tissues of the mouse using immunohistochemical and immunochemical techniques. In the adult mouse, L1 immunoreactivity was detectable in the basal and intermediate layers of epidermal and lingual epithelia, in the outer sheath of hair roots and in the single-layered endodermal epithelia of lung, small intestine, and colon. Epithelia of salivary glands also showed L1 immunoreactivity, while endothelial cells of blood vessels did not express detectable levels of L1. The epithelia of the kidney showed expression only in the collecting tubule system. In single-layered kidney epithelia and stratified epithelia, L1 expression was confined to lateral cell contacts and basal infoldings of the epithelial cells but was absent from apical and basal cell surface membranes. Also, in cultured keratinocytes L1 was confined to cell-cell contacts. During development of the epidermis, L1 immunoreactivity was first detectable at the onset of keratinization around embryonic day 16. At this age LI was detectable in the kidney on branching tubules of the ureter. Western blot analysis showed that L1 immunoreactivity in epidermis and kidney appeared as two bands of 190-210 and 210-230 kDa. Northern blot analysis of mRNA from the L1-immunopositive HEL-30 keratinocyte cell line revealed a single band with the expected size of 6 kb. The presence of L1 in epithelia indicates that this molecule may be involved in interactions between epithelial cells and thereby may affect differentiation and maintenance of epithelial tissues.

Animals↗
PubMed1998

Characterization of the pulse signal over the human head by near infrared spectroscopy.

In this study we examine and describe the changes in the hemoglobin oxygenation and the Cytochrome-C-Oxidase redox state that are caused by the pulsatile character of the blood flow in the human head. We used near-infrared spectroscopy (NIRS) in combination with simultaneously recorded ECG and Transcranial Doppler sonography of arteries and veins and show that there is a distinct time lag between heart activity, arterial blood flow, hemoglobin concentration as measured by NIRS and venous blood flow. NIRS has intensively been used to measure functional activation of the brain. When measuring cortical activation by functional stimulation, the pulse signal interferes with the acquired activation signal. We demonstrate that a filter algorithm can remove the pulse artifact and therefore improves the data acquired during visual stimulation.

Adult↗
PubMed1998

Tuberculin skin test conversion rates in New York City Emergency Medical Service health care workers.

OBJECTIVE: To determine annual tuberculin skin test conversion (infection) rates for prehospital health care workers (EMTs and paramedics) in an urban environment with a high prevalence of Mycobacterium tuberculosis. METHODS: We conducted a prospective study of prehospital health care workers for the New York City EMS, EMS Employee Health Service, and the Fire Department Bureau of Health Service to determine the tuberculin skin test conversion rates. In 1992, all current and new EMS prehospital health care workers without a known history of a positive tuberculin reaction received a baseline tuberculin purified protein derivative (PPD) skin test. Thereafter, (January 1, 1993-December 31, 1996) all EMS health care workers who had negative PPD skin test results received annual tuberculin PPD skin tests. Tuberculin skin test conversion was defined as induration of 10 mm or greater in a worker with a documented prior negative test result. The PPD skin test reaction was measured by trained professional readers. RESULTS: A total of 7,290 PPD test results were read during this study. Compliance with annual testing was 75%. Annual tuberculin skin test conversion rates were 1.3% in 1993, .7% in 1994, .1% in 1995, and .2% in 1996 (average .5%). In a static subgroup with at least 15 years' seniority, compliance with annual testing was 100% and annual tuberculin skin test conversion rates were .5% in 1993, 0 in 1994, .5% in 1995, and 1.5% in 1996 (average .6%). CONCLUSION: Despite the high prevalence of M tuberculosis infection in New York City and the potential for difficulty in the use of respiratory precautions during emergency response operations, EMS prehospital health care workers have an annual tuberculin conversion rate that is relatively low compared with hospital-based health care workers.

Cohort Studies↗
PubMed1998

Determination of the wavelength dependence of the differential pathlength factor from near-infrared pulse signals.

For the calculation of changes in oxyhaemoglobin, deoxyhaemoglobin and the redox state of cytochrome-c-oxidase from attenuation data via a modified Beer-Lambert equation the wavelength dependence of the differential pathlength factor (DPF(lambda)) has to be taken into account. The DPF, i.e. the ratio of the mean optical pathlength and the physical light source-detector separation at each wavelength, determines the crosstalk between the different concentrations and is therefore essential for a sensitive detection of chromophore changes. Here a simple method is suggested to estimate the wavelength dependence of the DPF(lambda) from pulse-induced attenuation changes measured on the head of adult humans. The essence is that the DPF is the ratio of the attenuation changes over absorption coefficient changes, and that the spectral form of the pulse correlated absorption coefficient change can be assumed to be proportional to the extinction coefficient of blood. Indicators for the validity of the DPF(lambda) derived for wavelengths between 700 and 970 nm are the stability of the calculated haemoglobin and cytochrome signals with variations of the wavelength range included for their calculation and its overall agreement with the data available from the literature.

Adult↗
PubMed1997

Microglial phagocytosis is modulated by pro- and anti-inflammatory cytokines.

Activation of microglial cells in neurological diseases involves proliferation and the induction of phagocytic and cytotoxic properties. We studied the effects of four different cytokines on microglial phagocytosis of latex beads to gain further insights into the signals modulating different aspects of microglial activity. Granulocyte/macrophage colony stimulating factor and tumor necrosis factor-alpha enhanced microglial phagocytic activity as measured by flow cytometry. A phagocytosis inhibiting effect was observed after preincubation with transforming growth factor-beta1 and interleukin-4. In conclusion, the activating and deactivating cytokines differentially regulate microglial phagocytic activity in vitro and might also play an important role in vivo in modulating microglial activation to keep the balance between the protective, defensive and destructive, chronic inflammatory properties of microglia.

Animals↗
PubMed1997

Mouse brain microglia express interleukin-15 and its multimeric receptor complex functionally coupled to Janus kinase activity.

The cytokine, interleukin (IL)-15, and the T cell growth factor, IL-2, exhibit a similar spectrum of immune effects and share the IL-2 receptor (IL-2R) subunits IL-2Rbeta and IL-2Rgamma for signaling in hematopoietic cells. Numerous neuroregulatory activities of IL-2 have been suggested, but its expression in the normal central nervous system (CNS) is apparently very low and regionally restricted. We show by RNA and protein detection that IL-15, its specific receptor molecule, IL-15Ralpha, and the signal-transducing receptor subunits, IL-2Rbeta and IL-2Rgamma, are constitutively present in various regions of the developing and adult mouse brain. We further demonstrate, also at the single-cell level, that IL-15 and the components for IL-15Ralpha/IL-2Rbetagamma receptors are expressed by microglia. Tyrosine phosphorylation data are presented showing that IL-15 signaling in microglia involves Janus kinase 1 activity. At doses of 0.1-10 ng/ml, IL-15 affected functional properties of these cells, such as the production of nitric oxide, and supported their growth in culture, suggestive of a role as an autocrine growth factor. Microglial IL-15 could thus play a pivotal role in the CNS and may participate in certain CNS and neuroendocrine functions previously ascribed to IL-2.

Animals↗
PubMed1997

Mechanisms of C5a and C3a complement fragment-induced [Ca2+]i signaling in mouse microglia.

Microglial cells are activated in response to brain insults; the mechanisms of this process are not yet understood. One of the important signaling mechanisms that might be involved in microglia activation is related to changes in the intracellular calcium concentration ([Ca2+]i). Using fluo-3 microfluorimetry, we have found that external application of the complement fragment C5a (4-10 nM) induced [Ca2+]i elevation in microglial cells in situ in corpus callosum slices. Similarly, application of complement fragments C5a (0.1-10.0 nM) or C3a (100 nM) generates biphasic [Ca2+]i transients composed of an initial peak followed by a plateau in cultured microglia. Incubation of microglial cells for 30 min with pertussis toxin (PTX; 1 microgram/ml) inhibited both C5a- and C3a-triggered [Ca2+]i responses, suggesting the involvement of PTX-sensitive G-proteins in the signal transduction chain. Removal of Ca2+ ions from the extracellular solution eliminated the plateau phase and limited the response to the initial peak. The restoration of the extracellular Ca2+ concentration within 30-60 sec after the beginning of the complement fragment-induced [Ca2+]i elevation led to the recovery of the plateau phase. Inhibition of the endoplasmic reticulum Ca2+ pumps with 500 nM thapsigargin transiently increased the [Ca2+]i and blocked the [Ca2+]i signals in response to subsequent complement fragment application. Our data suggest that complement factors induce [Ca2+]i responses by Ca2+ release from internal pools and subsequent activation of Ca2+ entry controlled by the filling state of the intracellular Ca2+ depots.

Animals↗
PubMed1997

Epidermal growth factor is a motility factor for microglial cells in vitro: evidence for EGF receptor expression.

Epidermal growth factor (EGF) and its receptor are present in the central nervous system and modulate a variety of neural functions. Here we show that microglial cells, the brain-intrinsic macrophages, express the receptor for EGF and migrate in response to EGF. Transcripts encoding the EGF receptor could be detected in purified microglial cultures obtained from newborn mouse cortex. More specifically, cDNA fragments derived from EGF receptor mRNA could be amplified from 21% of electrophysiologically characterized microglial cells by the use of a single-cell reverse transcription-polymerase chain reaction method. Expression of the protein was confirmed on rat microglia by flow cytometry. EGF dose-dependently stimulated chemotactic migration, as revealed with a microchemotaxis assay. The dose-response curve peaked-at 10 ng/ml EGF, reaching a 3-fold increase in migration over the unstimulated control; migration was about half of that induced by complement 5a (10 nM), a previously described microglial chemoattractant. Chequerboard analysis showed that EGF-induced motility was composed of both chemotaxis and chemokinesis. In contrast to its pronounced effect on cell motility, EGF (0.01-10 ng/ml) was not a mitotic signal for microglia, as shown by lack of bromodeoxyuridine incorporation. Acute and chronic pathological processes within the brain stimulate the synthesis and release of immunoregulators and growth factors (including EGF) that play a major role in the brain's response to injury. EGF may serve as a paracrine factor to direct microglial cells to the lesion site. Moreover, since EGF is secreted by activated microglia themselves in vivo, it may act as an autocrine modulator of microglial cell function.

Animals↗