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K Kristensson

Publications and source records attributed to K Kristensson.

At least 19 recordsLinked to original sources
PubMed2005

Influenza A virus infection causes alterations in expression of synaptic regulatory genes combined with changes in cognitive and emotional behaviors in mice.

Epidemiological studies have indicated a link between certain neuropsychiatric diseases and exposure to viral infections. In order to examine long-term effects on behavior and gene expression in the brain of one candidate virus, we have used a model involving olfactory bulb injection of the neuro-adapted influenza A virus strain, WSN/33, in C57Bl/6 mice. Following this olfactory route of invasion, the virus targets neurons in the medial habenular, midline thalamic and hypothalamic nuclei as well as monoaminergic neurons in the brainstem. The mice survive and the viral infection is cleared from the brain within 12 days. When tested 14-20 weeks after infection, the mice displayed decreased anxiety in the elevated plus-maze and impaired spatial learning in the Morris water maze test. Elevated transcriptional activity of two genes encoding synaptic regulatory proteins, regulator of G-protein signaling 4 and calcium/calmodulin-dependent protein kinase IIalpha, was found in the amygdala, hypothalamus and cerebellum. It is of particular interest that the gene encoding RGS4, which has been related to schizophrenia, showed the most pronounced alteration. This study indicates that a transient influenza virus infection can cause persistent changes in emotional and cognitive functions as well as alterations in the expression of genes involved in the regulation of synaptic activities.

Animals↗
PubMed2004

Interferon-gamma mediates neuronal killing of intracellular bacteria.

Neurons can be targets for microbes, which could kill the neurons. Just in reverse, we, in this study, report that bacteria can be killed when entering a neuron. Primary cultures of foetal mouse hippocampal neurons and a neuronal cell line derived from mouse hypothalamus were infected by Listeria monocytogenes. Treatment with interferon-gamma (IFN-gamma) did not affect bacterial uptake, but resulted in increased killing of intracellular bacteria, whereas the neuronal cell remained intact. The IFN-gamma-mediated bacterial killing was mapped to the neuronal cytosol, before listerial actin tail formation. Treatment with IFN-gamma induced phosphorylation of the transcription factor STAT-1 in neurons and IFN-gamma-mediated listerial killing was not observed in STAT-1(-/-) neurons or neurons treated with IFN regulatory factor-1 antisense oligonucleotides. IFN-gamma-treated neuronal cells showed increased levels of inducible nitric oxide synthase (iNOS) mRNA, and antisense iNOS oligonucleotides hampered the bacterial killing by neurons upon IFN-gamma treatment. This novel neuronal function - i.e., that of a microbe killer - could play a crucial role in the control of infections in the immuno-privileged nervous system.

Animals↗
PubMed2002

Priming by muscle inflammation alters the response and vulnerability to axotomy-induced damage of the rat facial motor nucleus.

To ascertain whether signaling due to peripheral inflammation affects motoneuron vulnerability, we examined in adult rats the reaction to axonal injury of facial motoneurons primed by muscle inflammation. In this double-hit paradigm, preconditioning was achieved by injections into the facial muscles of the T cell mitogen phytohemagglutinin, which was found in a previous study ( 11 ) to elicit a retrograde response in motoneurons. Facial nerve transection was used as test lesion. Intramuscular injections of saline prior to axotomy were used as control for lectin pretreatment. In rats pretreated with phytohemagglutinin injection, upregulation of the expression of the antiapoptotic bcl-2 gene, examined with in situ hybridization, was significantly higher in facial motoneurons at 2 days postaxotomy compared with saline-injected control cases. After repeated phytohemagglutinin injections followed by nerve transection, induction in facial motoneurons of nitric oxide synthase, revealed by histochemistry and immunohistochemistry, as well as activation of the surrounding microglia, was enhanced at 14 days postaxotomy with respect to the saline-treated control cases. At the same time point, no significant intergroup difference was detected in the intensity of astrocytic activation. At 1 month postaxotomy, stereological cell counts revealed that motoneuron loss was significantly greater in the cases pretreated with phytohemagglutinin than in the saline-treated cases. The data point out that the response of the facial motor nucleus to axonal damage is altered by previous exposure to peripheral inflammation and that such preconditioning stimulus enhances motoneuron vulnerability to nerve injury.

Animals↗
PubMed2002

Disruption of circadian rhythms in synaptic activity of the suprachiasmatic nuclei by African trypanosomes and cytokines.

Disturbances in biological rhythms pose a major disease problem, not the least in the aging population. Experimental sleeping sickness, caused by Trypanosoma brucei brucei, in rats constitutes a unique and robust chronic model for studying mechanisms of such disturbances. The spontaneous postsynaptic activity was recorded in slice preparations of the suprachiasmatic nuclei (SCN), which contain the master pacemaker for circadian rhythms in mammals, from trypanosome-infected rats. The excitatory synaptic events, which in normal rats show a daily variation, were reduced in frequency, while the inhibitory synaptic events did not significantly differ. This indicates selective disturbances in glutamate receptor-mediated neurotransmission in the SCN. Treatment with interferon-gamma in combination with lipopolysaccharide, which has synergistic actions with cytokines, and tumor necrosis factor-alpha similarly caused a reduction in excitatory synaptic SCN activity. We suggest that changes in the synaptic machinery of SCN neurons play an important pathogenetic role in sleeping sickness, and that proinflammatory cytokines can mimic these changes.

Action Potentials↗
PubMed2001

Sensitization of dorsal horn neurons in a two-compartment cell culture model: wind-up and long-term potentiation-like responses.

One of the main characteristics of central sensitization associated with postinjury pain and chronic pain is increased excitability of the dorsal horn neurons in the spinal cord. Two electrophysiological features associated with the origin and modulation of central sensitization are wind-up of action potential frequency and long-term potentiation (LTP), which have been demonstrated previously in the intact dorsal horn. Here we present evidence for electrically evoked sensitization of dorsal horn neurons in a two-compartment cell culture system of rat dorsal root ganglia (DRGs) and dorsal horn neurons. Whole-cell recordings of dorsal horn neurons showed that repetitive low-frequency stimulation of DRG axons induced a frequency-dependent cumulative depolarization of the membrane potential with a concomitant increase in action potential frequency in a subset of neurons (41%). The characteristics presented here for dissociated cells are in accordance with those ascribed to classical wind-up in the intact dorsal horn. In addition, tetanic stimulation of DRG axons resulted in a significant increase in the number of action potentials in response to test stimuli in 42% of the cells tested. This prolonged potentiation of neuronal excitability in the dorsal horn lasted throughout the recording period (>1 hr) and tended to be voltage dependent in an LTP-like manner. To our knowledge, this is the first time that wind-up and LTP-like responses are reported for dorsal horn neurons in cell culture.

Action Potentials↗
PubMed2001

A two-compartment in vitro model for studies of modulation of nociceptive transmission.

Here we present a two-compartment in vitro model in which embryonic rat dorsal root ganglia (DRG) neurons are cultured separately from their target dorsal horn neurons. Although separated, synaptic contact can be established between the peripheral and central neurons since the system allows the DRG axons to project into the other compartment, which contains a network of dorsal horn neurons. The efficacy of the model was evaluated by immunocytochemical, calcium imaging and electrophysiological experiments. The results showed that a subpopulation of the DRG neurons had nociceptor characteristics and that these made synaptic contact with the dorsal horn network. Application of current pulses, according to the stimulus paradigm used, evoked action potentials in DRG axons selectively. This in turn gave rise to increased postsynaptic activity in the network of dorsal horn neurons. The model offers a high degree of efficiency since large numbers of DRG axons can be stimulated simultaneously, thus permitting recording of strong output responses from the dorsal horn neurons. This in vitro model provides a means for studying the mechanisms by which modulatory factors, such as immunoregulatory molecules, applied at either the PNS or the CNS level, can affect synaptic activity and nociceptive transmission in single neurons or network of neurons in the dorsal horn.

Action Potentials↗
PubMed2001

Changes in calcium currents and GABAergic spontaneous activity in cultured rat hippocampal neurons after a neurotropic influenza A virus infection.

In order to study mechanisms by which a neurotropic strain of influenza A virus (A/WSN/33) may affect neuronal function or cause nerve cell death, hippocampal cultures from embryonic rats were infected with this virus. Approximately 70% of the neurons in the infected cultures became immunopositive for viral antigens and showed reduced voltage-dependent Ca(2+) currents in whole-cell patch clamp recordings, but no changes in other membrane properties or in cytosolic Ca(2+) concentration were seen. These immunopositive neurons underwent apoptosis 3-4 days after infection. Ca(2+) channel inhibitors had no significant effect on neuronal survival. The immunonegative population of neurons survived, but displayed increased frequency of miniature inhibitory postsynaptic currents of gamma-amino-butyric acid origin compared with controls. The frequency of alpha-amino-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide (AMPA) receptor-mediated miniature excitatory postsynaptic currents was not altered. Viral nucleoproteins, overexpressed using the Semliki Forest virus system, were localized to the dendritic spines as shown by double immunolabeling with actinin, but did not by themselves cause neuronal death or changes in synaptic transmission as measured by AMPA-mediated excitatory postsynaptic currents. Our results show that an influenza A virus infection can cause selective neurophysiological changes in hippocampal neurons and that these can persist even after the viral antigens have been cleared.

Animals↗
PubMed2001

Trypanosoma brucei brucei crosses the blood-brain barrier while tight junction proteins are preserved in a rat chronic disease model.

African trypanosomiasis, sleeping sickness in humans, is caused by the systemic infection of the host by the extracellular parasite, the African trypanosome. The pathogenetic mechanisms of the severe symptoms of central nervous system involvement are still not well understood. The present study examined the routes of haematogenous spread of Trypanosoma brucei brucei (Tbb) to the brain, in particular on the question whether parasites can cross the blood-brain barrier, as well as their effect on tight junction proteins. Rats were infected with Tbb and at various times post-infection, the location of the parasite in the central nervous system was examined in relation to the brain vascular endothelium, visualized with an anti-glucose transporter-1 antibody. The tight junction-specific proteins occludin and zonula occludens 1, and the possible activation of the endothelial cell adhesion molecules ICAM-1 and VCAM-1 were also studied. At 12 and 22 days post-infection, the large majority of parasites were confined within blood vessels. At this stage, however, some parasites were also clearly observed in the brain parenchyma. This was accompanied by an upregulation of ICAM-1/VCAM-1. At later stages, 42, 45 and 55 days post-infection, parasites could still be detected within or in association with blood vessels. In addition, the parasite was now frequently found in the brain parenchyma and the extravasation of parasites was more prominent in the white matter than the cerebral cortex. A marked penetration of parasites was seen in the septal nuclei. In spite of this, occludin and zonula occludens 1 staining of the vessels was preserved. The results indicate that the Tbb parasite is able to cross the blood-brain barrier in vivo, without a generalized loss of tight junction proteins.

Animals↗
PubMed2001

Retrograde response of the rat facial motor nucleus to muscle inflammation elicited by phytohaemagglutinin.

To investigate whether motoneurons react to signals deriving from target inflammation, we studied the facial motor nucleus after injections of phytohaemagglutinin in the snout of adult rats. This plant lectin is a tool widely used to induce proliferation and activation of T lymphocytes, and we observed marked lymphocyte infiltration in the injected facial muscles. Retrograde labelling of motoneurons was not detected after peripheral injections of fluorochrome-conjugated phytohaemagglutinin. Nitric oxide synthase, revealed by NADPH-diaphorase histochemistry, OX-42-immunoreactive microglia, and expression of the cell death repressor gene bcl-2, investigated with nonradioactive in situ hybridization and immunohistochemistry, were evaluated in the facial nucleus. Daily phytohaemagglutinin injections for 4 days, mimicking repeated muscle exposure to inflammatory stimuli, resulted after 2-day survival in NADPH-diaphorase induction in motoneurons and marked activation of the surrounding microglia. Quantitative image analysis of NADPH-diaphorase staining, and OX-42 immunoreactivity and microglial cell counts indicated highly significant increases with respect to saline-injected control cases. The occurrence of a neuroprotective retrograde response was evaluated monitoring bcl-2 expression. Following single phytohaemagglutinin administration, bcl-2 mRNA was significantly upregulated at 6 h in facial motoneurons and returned to basal levels at 24 h. Bcl-2 immunoreactivity was markedly upregulated at 24 h and was still significantly higher than in controls at 7 days, when concomitant NADPH-diaphorase induction in motoneurons and microglia activation was also observed. No degenerative features were observed in motoneurons after phytohaemagglutinin injections at the examined time-points. The data point out that local muscle inflammation retrogradely elicits gene activation in motoneurons and their microenvironment.

Animals↗
PubMed2001

Persistence of the influenza A/WSN/33 virus RNA at midbrain levels of immunodefective mice.

Strains of influenza A virus are known to infect specific subpopulations of neurons in the mouse brain. Here we report that all segments of the genome of the neurotropic influenza A virus, strain WSN/33, can persist in the brains of immunodefective transporter associated with Antigen Processing 1 (TAP1) mutant mice. Ten to 17 months after injection of virus into the olfactory bulbs, viral RNA encoding the nonstructural NS1 protein was detected in sections from the brain at midbrain levels by RT-PCR in almost all animals. Both negative-strand genomic RNA (vRNA) and positive-strand RNA, including mRNA, were found. RNA encoding nucleoprotein and polymerases, which form the replicative complex of the virus, were detected in fewer brains. RNA encoding envelope proteins were found only in occasional brains. No viral cDNA could be identified. This observation shows that certain regions of the brain in immunodefective mice may harbor the genome of influenza A virus including the NS1 gene, the products of which may play a regulatory role in host-cell metabolism.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Neural route of cerebral Listeria monocytogenes murine infection: role of immune response mechanisms in controlling bacterial neuroinvasion.

The pathologic features of cerebral Listeria monocytogenes infection strongly suggest that besides hematogenous spread, bacteria might also spread via a neural route. We propose that after snout infection of recombination activating gene 1 (RAG-1)-deficient mice, L. monocytogenes spreads to the brain via a neural route. The neural route of invasion is suggested by (i) the immunostaining of L. monocytogenes in the trigeminal ganglia (TG) and brain stem but not in other areas of the brain; (ii) the kinetics of bacterial loads in snout, TG, and brain; and (iii) the increased resistance of mice infected with a plcB bacterial mutant (unable to spread from cell to cell). Gamma interferon (IFN-gamma) plays a protective role in neuroinvasion; inducible nitric oxide synthase (iNOS) accounts only partially for the protection, as shown by a comparison of the susceptibilities of IFN-gamma receptor (IFN-gamma R)-deficient, iNOS-deficient, and wild-type mice to snout infection with L. monocytogenes. The dramatically enhanced susceptibility of RAG-1-deficient, IFN-gamma R gene-deficient mice indicated the overall importance of innate immune cells in the release of protective levels of IFN-gamma. The source of IFN-gamma appeared to be NK cells, as shown by use of RAG-1-deficient, gamma-chain receptor gene-deficient mice; NK cells played a relevant protective role in neuroinvasion through a perforin-independent mechanism. In vitro evidence indicated that IFN-gamma can directly induce bacteriostatic mechanisms in neural tissue.

Animals↗
PubMed2000

Direct NK cell-mediated lysis of syngenic dorsal root ganglia neurons in vitro.

In contrast to extensive studies on the role of T and B lymphocytes in the pathogenesis of autoimmune diseases of the nervous system, little is known about NK cells and their potential role in the destruction of neural tissue. NK cells have been implicated in the selective death of sympathetic neurons resident in the superior cervical ganglia of rats after exposure to the drug guanethidine. This observation suggests that NK cells may function as principle effectors in immunological diseases of the nervous system. However, the direct mechanism of action of NK cells in this model is not known. In particular, it is not known whether NK cells can kill autologous neurons directly. The aim of the present study was to examine whether NK cells can kill directly dorsal root ganglia neurons cultured in vitro. We demonstrate that C57BL/6 (B6)-derived dorsal root ganglia neurons can be killed directly by syngenic IL-2-activated NK cells, and that this nerve cell lysis is dependent on the expression of perforin in the NK cells. NK cells were less effective in destroying neurons grown in the presence of glial cells. These observations indicate a potential role for NK cells in nerve cell degeneration in inflammatory diseases of the nervous system.

Animals↗
PubMed2000

Inducible nitric oxide synthase expression elicited in the mouse brain by inflammatory mediators circulating in the cerebrospinal fluid.

Expression of inducible nitric oxide synthase (iNOS) protein was studied in the brain after intracerebroventricular injections of interferon (IFN)-gamma, and IFN-gamma combined with lipopolysaccharide (LPS) or tumor necrosis factor (TNF)-alpha, compared to ovalbumin as control. Wild-type mice and mice with targeted deletion of the IFN-gamma receptor gene were used. Findings based on iNOS immunoreactivity were evaluated at 1, 2, 4 and 7 days post-injection, using also quantitative image analysis and double labeling with glial cell markers. IFN-gamma administration induced iNOS immmunostaining in activated microglia and macrophages in the parenchyma surrounding the ventricular system, several cortical fields and fiber tracts. IFN-gamma-elicited iNOS immunoreactivity was down-regulated after 1 day. The number of iNOS-immunopositive cells was significantly enhanced by co-administration of LPS or TNF-alpha; IFN-gamma+TNF-alpha injections also resulted in longer persistence of iNOS immunoreactivity. No immunopositive cells were seen in the brain of IFN-gamma receptor knockout mice after IFN-gamma administration; very few immunostained macrophages were detected in these cases, mostly around the injection needle track, after co-administration of LPS or TNF-alpha. Western blot analysis confirmed a marked iNOS induction in the brain of wild-type mice 24 h after IFN-gamma+LPS injections. The findings show that inflammatory mediators circulating in the cerebrospinal fluid induce in vivo iNOS in the brain with topographical selectivity and temporal regulation. The data also demonstrate that the signaling cascade activated by IFN-gamma binding to its receptor is critical for iNOS induction, and the synergistic action of LPS and TNF-alpha as iNOS inducers in brain cells is largely mediated by the receptor-regulated action of IFN-gamma.

Animals↗
PubMed2000

Interferon-gamma-responsive neuronal sites in the normal rat brain: receptor protein distribution and cell activation revealed by Fos induction.

Constitutive expression of the interferon-gamma receptor protein (IFN-gammaR), and the distribution of cells in which Fos, a marker of cell activation, is induced by intracerebroventricular administration of IFN-gamma, were studied in the rat brain by immunohistochemistry. IFN-gammaR immunopositivity was found in neuronal elements, which exhibited a selective distribution being concentrated in the piriform and entorhinal cortex, midline thalamus and medial hypothalamic structures, brainstem nociceptive relays (including the periaqueductal gray, the parabrachial nuclei and the caudal part of the spinal trigeminal nuclei), and circumventricular organs such as the median eminence and area postrema. IFN-gamma-induced Fos expression mostly corresponded to neuronal sites of receptor distribution. Because of its topographical distribution, it is suggested that activation of the IFN-gammaR in neurons may play a role to limit spread of infections in the brain and, in concert with other proinflammatory cytokines, to modulate adaptive responses to an antigen challenge mediated by the central nervous system.

Animals↗
PubMed2000

The spectral and thermodynamic properties of staphylococcal enterotoxin A, E, and variants suggest that structural modifications are important to control their function.

The superantigens staphylococcal enterotoxin A and E (SEA and SEE) can activate a large number of T-cells. SEA and SEE have approximately 80% sequence identity but show some differences in their biological function. Here, the two superantigens and analogues were characterized biophysically. SEE was shown to have a substantially higher thermal stability than SEA. Both SEA and SEE were thermally stabilized by 0.1 mM Zn(2+) compared with Zn(2+)-reduced conditions achieved using 1 mM EDTA or specific replacements that affect Zn(2+) coordination. The higher stability of SEE was only partly caused by the T-cell receptor (TCR) binding regions, whereas regions in the vicinity of the major histocompatibility complex class II binding sites affected the stability to a greater extent. SEE exhibited a biphasic denaturation between pH 5.0-6.5, influenced by residues in the TCR binding regions. Interestingly, enzyme-linked immunosorbent assay, isoelectric focusing, and circular dichroism analysis indicated that conformational changes had occurred in the SEA/E chimerical constructs relative to SEA and SEE. Thus, it is proposed that the Zn(2+) binding site is very important for the stability and potency of SEA and SEE, whereas residues in the TCR binding site have a substantial influence on the molecular conformation to control specificity and function.

Amino Acid Sequence↗
PubMed2000

Chronic sodium salicylate treatment exacerbates brain neurodegeneration in rats infected with Trypanosoma brucei.

We have reported previously that axonal degeneration in specific brain regions occurs in rats infected with the parasite Trypanosoma brucei. These degenerative changes occur in spatiotemporal association with over-expression of pro-inflammatory cytokine messenger RNAs in the brain. To test how aspirin-like anti-inflammatory drugs might alter the disease process, we fed trypanosome-infected rats with 200mg/kg of sodium salicylate (the first metabolite of aspirin) daily in their drinking water. Sodium salicylate treatment in uninfected rats did not cause any neural damage. However, sodium salicylate treatment greatly exacerbated neurodegeneration in trypanosome-infected rats, resulting in extensive terminal and neuronal cell body degeneration in the cortex, hippocampus, striatum, thalamus, and anterior olfactory nucleus. The exaggerated neurodegeneration, which occurred in late stages of infection, was temporally and somewhat spatially associated with a late-appearing enhancement of messenger RNA expression of interleukin-1beta, interleukin-1beta converting enzyme, tumor necrosis factor-alpha, and inhibitory factor kappaBalpha in the brain parenchyma. Restricted areas showed elevations in messenger RNA expression of interleukin-1 receptor antagonist, interleukin-6, inducible nitric oxide synthase, interferon-gamma, and inducible cyclooxygenase. The association suggests that increased production of pro-inflammatory cytokines in the brain may be an underlying mechanism for neural damage induced by the chronic sodium salicylate treatment. Furthermore, the results reveal a serious complication in using aspirin-like drugs for the treatment of trypanosome infection.

Animals↗