Biomedical subjects

Thomas Hübschle

Publications and source records attributed to Thomas Hübschle.

15 recordsLinked to original sources

PubMed2006

Molecular aspects of fever and hyperthermia.

A rise in core temperature during fever usually results from change in the thermocontroller characteristics, resulting in an elevation of the set point of body temperature. Time course and extent of natural fevers are variable, but an upper limit (41 degrees C in humans), at which core temperature is maintained for some time and reduced when the set point of body temperature returns to its normal level, rarely is exceeded. Although any rise in body temperature may result from fever, those rises that are not accompanied by supportive changes in thermoeffector activities are termed hyperthermia.

Acute-Phase Reaction↗

PubMed2005

Immunohistochemical evidence of functional leptin receptor expression in neuronal and endothelial cells of the rat brain.

Leptin binding to its functional receptor leads to activation of the JAK-STAT-signaling pathway and especially to the activation of the signal transducer and activator of transcription factor 3 (STAT3). The immunohistochemical detection of nuclear STAT3 translocation is used as a neuroanatomical mapping tool to determine leptin-responsive cells in the rat brain. This study neuroanatomically identifies those brain cell phenotypes showing STAT3 activation after intraperitoneal leptin treatment (5 mg/kg) using immunohistochemical colocalization with neuronal and endothelial cell marker proteins. Leptin treatment induced nuclear STAT3 signals with the strongest response observed 90min after the treatment. The caudobasal hypothalamus showed a particularly pronounced STAT3 response. Leptin-induced nuclear STAT3 signals were additionally determined in the solitary tract nucleus, the choroid plexus and in the brain endothelium. The vast majority of STAT3-responsive cells proved to be neurons located in the caudobasal hypothalamus, however, a marked number of brain endothelial cells distributed throughout the entire brain got activated as well. In conclusion, neurons and non-neuronal brain cells, e.g., endothelial or choroid plexus cells, seem to express functional leptin receptors and might thereby mediate leptin-dependent functions in the rat brain.

Animals↗

PubMed2005

Nuclear STAT3 translocation in guinea pig and rat brain endothelium during systemic challenge with lipopolysaccharide and interleukin-6.

During systemic inflammation, cytokines are released by immune-competent cells into the circulation, which in turn signal the brain to mediate brain-controlled signs of illness. Cytokine-responsive brain cells can be mapped by histological analysis of cytokine-induced transcription factors or transcription factor-associated molecules revealing different cell phenotypes that respond to activation of the immune system. Critical sites mediating cytokine-dependent immuneffector functions can be divided into two groups, one group of responding cells situated along a tight blood-brain barrier (BBB), and a second cell group in structures with an open BBB, e.g., the sensory circumventricular organs (CVOs). Previous reports from our group suggest that activation of the signal transducer and activator of transcription factor 3 (STAT3) during lipopolysaccharide (LPS)-induced systemic inflammation is mediated by interleukin-6 (IL-6) and occurs in astrocytes of the rat CVOs. Here we show in the guinea pig a time-dependent marked LPS-induced STAT3 activation within astrocytes and endothelial cells of the CVOs, within astrocytes located in brain structures with a functional BBB and within the brain endothelium of the entire brain. In addition, systemic treatment of rats with either rat recombinant IL-6 or LPS induced STAT3 activation in brain endothelial cells in a similar way as observed in the guinea pig brain, stressing the involvement of IL-6 in this phenomenon in a more generalized way. The STAT3-activated brain cells are located in critical target structures mediating cytokine action during LPS-induced inflammation. STAT3-controlled transcriptional activation with yet unknown cell-specific functional consequences seems to be involved in this process.

Animals↗

PubMed2005

Pyrexia, anorexia, adipsia, and depressed motor activity in rats during systemic inflammation induced by the Toll-like receptors-2 and -6 agonists MALP-2 and FSL-1.

Macrophage-activating lipopeptide-2 (MALP-2) from Mycoplasma fermentans has been identified as a pathogen-associated molecular pattern of Mycoplasmas that causes activation of the innate immune system through the activation of the heterodimeric Toll-like receptors (TLRs)-2 and -6. The aim of this study was to characterize the ability of MALP-2 and a synthetic analog fibroblast-stimulating lipopeptide-1 (FSL-1; represents the NH2-terminal sequence of a lipoprotein from M. salivarium) to act as exogenous pyrogens, to induce formation of cytokines (endogenous pyrogens), and to cause sickness behavior, such as depressed motor activity, anorexia, and adipsia. For this purpose, body temperature, activity, food intake, and water intake were recorded for 3 days by use of telemetry devices in several groups of rats treated with MALP-2/FSL-1 or the respective control solutions. Intraperitoneal injections of FSL-1 caused fever at doses of 10 or 100 microg/kg, which was preceded by a pronounced phase of hypothermia in response to a dose of 1,000 microg/kg. The maximal fever (a peak of 1.5 degrees C above baseline) was caused by the 100 microg/kg dose with almost identical responses to both MALP-2 and FSL-1. Fever was accompanied by pronounced rises of the proinflammatory cytokines TNF and IL-6 in plasma. Treatment with the TLR-2 and -6 agonists further induced a dose-dependent manifestation of anorexia and adipsia, as well as a reduction of motor activity. We could thus demonstrate that activation of TLR-2 and -6 can induce systemic inflammation in rats accompanied by the classical signs of brain-controlled illness responses.

Animals↗

PubMed2005

Localized vs. systemic inflammation in guinea pigs: a role for prostaglandins at distinct points of the fever induction pathways?

In guinea pigs, dose-dependent febrile responses were induced by injection of a high (100 microg/kg) or a low (10 microg/kg) dose of bacterial lipopolysaccharide (LPS) into artificial subcutaneously implanted Teflon chambers. Both LPS doses further induced a pronounced formation of prostaglandin E(2) (PGE(2)) at the site of localized subcutaneous inflammation. Administration of diclofenac, a nonselective cyclooxygenase (COX) inhibitor, at different doses (5, 50, 500, or 5,000 microg/kg) attenuated or abrogated LPS-induced fever and inhibited LPS-induced local PGE(2) formation (5 or 500 microg/kg diclofenac). Even the lowest dose of diclofenac (5 microg/kg) attenuated fever in response to 10 microg/kg LPS, but only when administered directly into the subcutaneous chamber, and not into the site contralateral to the chamber. This observation indicated that a localized formation of PGE(2) at the site of inflammation mediated a portion of the febrile response, which was induced by injection of 10 microg/kg LPS into the subcutaneous chamber. Further support for this hypothesis derived from the observation that we failed to detect elevated amounts of COX-2 mRNA in the brain of guinea pigs injected subcutaneously with 10 microg/kg LPS, whereas subcutaneous injections of 100 microg/kg LPS, as well as systemic injections of LPS (intra-arterial or intraperitoneal routes), readily caused expression of the COX-2 gene in the guinea pig brain, as demonstrated by in situ hybridization. Therefore, fever in response to subcutaneous injection of 10 microg/kg LPS may, in part, have been evoked by a neural, rather than a humoral, pathway from the local site of inflammation to the brain.

Animals↗

PubMed2004

Identification of sympathetic premotor neurons in medullary raphe regions mediating fever and other thermoregulatory functions.

Sympathetic premotor neurons directly control sympathetic preganglionic neurons (SPNs) in the intermediolateral cell column (IML) of the thoracic spinal cord, and many of these premotor neurons are localized in the medulla oblongata. The rostral ventrolateral medulla contains premotor neurons controlling the cardiovascular conditions, whereas rostral medullary raphe regions are a candidate source of sympathetic premotor neurons for thermoregulatory functions. Here, we show that these medullary raphe regions contain putative glutamatergic neurons and that these neurons directly control thermoregulatory SPNs. Neurons expressing vesicular glutamate transporter 3 (VGLUT3) were distributed in the rat medullary raphe regions, including the raphe magnus and rostral raphe pallidus nuclei, and mostly lacked serotonin immunoreactivity. These VGLUT3-positive neurons expressed Fos in response to cold exposure or to central administration of prostaglandin E2, a pyrogenic mediator. Transneuronal retrograde labeling after inoculation of pseudorabies virus into the interscapular brown adipose tissue (BAT) or the tail indicated that those VGLUT3-expressing medullary raphe neurons innervated these thermoregulatory effector organs multisynaptically through SPNs of specific thoracic segments, and microinjection of glutamate into the IML of the BAT-controlling segments produced BAT thermogenesis. An anterograde tracing study further showed a direct projection of those VGLUT3-expressing medullary raphe neurons to the dendrites of SPNs. Furthermore, intra-IML application of glutamate receptor antagonists blocked BAT thermogenesis triggered by disinhibition of the medullary raphe regions. The present results suggest that VGLUT3-expressing neurons in the medullary raphe regions constitute excitatory neurons that could be categorized as a novel group of sympathetic premotor neurons for thermoregulatory functions, including fever.

Adipose Tissue, Brown↗

PubMed2004

Nuclear translocation of the transcription factor STAT3 in the guinea pig brain during systemic or localized inflammation.

The purpose of the present study was to investigate a possible lipopolysaccharide (LPS)-induced activation of brain cells that is mediated by the pleiotropic cytokine interleukin-6 (IL-6) and its transcription factor STAT3 during systemic or localized inflammation. In guinea pigs, intra-arterial (i.a., 10 microg x kg(-1)) or intraperitoneal (i.p., 30 microg x kg(-1)) injections of bacterial LPS cause a systemic inflammatory response which is accompanied by a robust fever. A febrile response can also be induced by administration of LPS into artificial subcutaneously implanted Teflon chambers (s.c. 100 or 10 microg x kg(-1)), which reflects an experimental model that mimics local tissue inflammation. Baseline plasma levels of bioactive IL-6 determined 60 min prior to injections of LPS or vehicle amounted to 35-80 international units (i.u.) ml(-1). Within 90 min of LPS injection, plasma IL-6 rose about 1000-fold in the groups injected i.a. or i.p., about 50-fold in the group injected s.c. with 100 microg x kg(-1) LPS, and only 5-fold in guinea pigs injected with the lower dose of LPS (10 microg x kg(-1)). At this time point, a distinct nuclear translocation pattern of the transcription factor STAT3 became evident in several brain structures. Amongst those, the sensory circumventricular organs known to lack a tight blood-brain barrier such as the area postrema, the vascular organ of the lamina terminalis and the subfornical organ, as well as the hypothalamic supraoptic nucleus showed intense nuclear STAT3 signals in the i.a. or i.p. injected groups. In contrast a moderate (s.c. group, 100 microg x kg(-1)), or even no (s.c. group, 10 microg x kg(-1)), nuclear STAT3 translocation occurred in response to s.c. injections of LPS. These results suggest that STAT3-mediated genomic activation of target gene transcription in brain cells occurred only in those cases in which sufficiently high concentrations of circulating IL-6 were formed during systemic (i.a. and i.p. groups) or localized (s.c. group, 100 microg x kg(-1)) inflammation.

Animals↗

PubMed2004

Signaling the brain in systemic inflammation: role of sensory circumventricular organs.

The sensory circumventricular organs (CVOs) are specialized brain regions that lack a tight blood-brain barrier. A role for these brain structures in signaling the brain during systemic inflammation is based on the following sets of observations. In spite of some conflicting data from literature, lesions of CVOs have been shown to block several components of brain controlled illness responses (i.e. fever or neuroendocrine modifications). Receptors for inflammatory cytokines and for bacterial fragments are constitutively expressed in cells within the sensory CVOs. The expression of most of these receptors is upregulated under conditions of systemic inflammation. Cellular responses in theses brain areas can be recorded and documented after stimulation of these respective receptors. Such responses include changes in electrical activity of neurons, induction of transcription factors leading to modifications in gene expression during inflammation and to a localized release of secondary signal molecules. These molecules may influence or even gain access to neural structures inside the blood-brain barrier, which can normally not directly be reached by circulating cytokines or bacterial fragments.

Animals↗

PubMed2003

Interleukin-6 mediates lipopolysaccharide-induced nuclear STAT3 translocation in astrocytes of rat sensory circumventricular organs.

Pyrogenic treatment with lipopolysaccharide (LPS) or interleukin-6 (IL-6) induces nuclear STAT3 translocation in the vascular organ of the laminae terminalis (OVLT) and the subfornical organ (SFO). STAT3 immunohistochemistry was combined with the detection of marker proteins (glial, neuronal, endothelial) and the nuclear DAPI stain to determine the phenotype of responding cells. At time points with high pyrogen-induced IL-6 plasma levels, nuclear STAT3 signals were co-localized with an astrocytic cell marker. IL-6 might therefore mediate genomic activation of OVLT/SFO astrocytes during LPS-induced fever.

Animals↗

PubMed2003

Neurons of the rat preoptic area and the raphe pallidus nucleus innervating the brown adipose tissue express the prostaglandin E receptor subtype EP3.

The major effector organ for thermogenesis during inflammation or experimental pyrogen-induced fever in rodents is the brown adipose tissue (BAT). Prostaglandin E2 (PGE2) microinjection into the medial preoptic area (POA) of rats leads to hyperthermia through an increase in BAT thermogenesis and induces pyrogenic signal transmission towards the raphe pallidus nucleus (RPa), a brainstem nucleus known to contain sympathetic premotor neurons for BAT control. The medial POA has a high expression of prostaglandin E receptor subtype EP3 (EP3R) on POA neurons, suggesting that these EP3R are main central targets of PGE2 to mediate BAT thermogenesis. To reveal central command neurons that contain EP3R and polysynaptically project to the BAT, we combined EP3R immunohistochemistry with the detection of transneuronally labelled neurons that were infected after injection of pseudorabies virus into the BAT. Neurons double-labelled with EP3R and viral surface antigens were particularly numerous in two brain regions, the medial POA and the RPa. Of all medial POA neurons that became virally infected 71 h after BAT inoculation, about 40% expressed the EP3R. This subpopulation of POA neurons is the origin of a complete neuronal chain that connects potential PGE2-sensitive POA neurons with the BAT. As for the efferent pathway of pyrogenic signal transmission, we hypothesize that neurons of this subpopulation of EP3R expressing POA neurons convey their pyrogenic signals towards the BAT via the RPa. We additionally observed that two-thirds of those RPa neurons that polysynaptically project to the interscapular BAT also expressed the EP3R, suggesting that RPa neurons themselves might possess prostaglandin sensitivity that is able to modulate BAT thermogenesis under febrile conditions.

Adipose Tissue, Brown↗

PubMed2002

Fever induction by localized subcutaneous inflammation in guinea pigs: the role of cytokines and prostaglandins.

In guinea pigs, dose-dependent febrile responses can be induced by injection of a high (100 micro g/kg) or low (10 micro g/kg) dose of bacterial lipopolysaccharide (LPS) into artificial subcutaneously implanted Teflon chambers. In this fever model, LPS does not enter the systemic circulation from the site of localized tissue inflammation in considerable amounts but causes a local induction of the proinflammatory cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6), which can be measured in lavage fluid collected from the chamber area. Only in response to the high LPS dose, small traces of TNF are measurable in blood plasma. A moderate increase of circulating IL-6 occurs in response to administration of both LPS doses. To investigate the putative roles of TNF and prostaglandins in this fever model, a neutralizing TNF binding protein (TNF-bp) or a nonselective inhibitor of cyclooxygenases (diclofenac) was injected along with the high or low dose of LPS into the subcutaneous chamber. In control groups, both doses of LPS were administered into the chamber along with the respective vehicles for the applied drugs. The fever response to the high LPS dose remained unimpaired by treatment with TNF-bp despite an effective neutralization of bioactive TNF in the inflamed tissue area. In response to the low LPS dose, there was an accelerated defervescence under the influence of TNF-bp. Blockade of prostaglandin formation with diclofenac completely abolished fever in response to both LPS doses. In conclusion, prostaglandins seem to be essential components for the manifestation of fever in this model.

Animals↗

PubMed2002

Action of palytoxin on apical H+/K+-ATPase in rat colon.

Palytoxin stimulated a cation-dependent short-circuit current (Isc) in rat distal and proximal colon in a concentration-dependent fashion when applied to the mucosal surface of the tissue. The distal colon exhibited a higher sensitivity to the toxin. The palytoxin-induced Isc was blocked by vanadate but was resistant to ouabain or scilliroside, suggesting the conversion of a vanadate-sensitive H+/K+-ATPase into an electrogenic cation transporter. Cation substitution experiments with basolaterally depolarized tissues suggested an apparent permeability of the palytoxin-induced conductance of Na+>K+>Li+. Immunohistochemical control experiments confirmed the absence of the Na+/K+-ATPase in the apical membrane. Consequently, the pore-forming action of palytoxin is not restricted to Na+/K+-ATPase but is also observed with the colonic H+/K+-ATPase.

Acrylamides↗

PubMed2002

MSG lesions decrease body mass of suckling-age rats by attenuating circadian decreases of energy expenditure.

Suckling-age rats display endogenous circadian rhythmicity of metabolic rate (MR) with energy-saving, torpor-like decreases, which are sympathetically controlled and suppressed by leptin treatment. We investigated whether neonatal monosodium glutamate (MSG) treatment, known to cause arcuate nucleus damage and adult-age obesity, alters energy balance in the first two postnatal weeks. Continuously recorded MR and core temperatures (T(c)) show that MSG treatment disinhibits the periodic, sympathetically controlled, energy-saving drops of T(c) and MR. Increased energy expenditure thus explains reduced body fat at normal lean body mass found in MSG-treated pups artificially nourished identically to controls. In MSG-treated mother-reared pups, lean body mass is additionally reduced, suggesting that MSG also reduces suckling. Plasma leptin levels are similar in controls and MSG-treated pups but higher per unit of fat mass in the latter. We conclude that the postweaning development of MSG obesity and depressed thermogenesis are preceded by an early phase of increased energy expenditure with decreased fat deposition during suckling age and hypothesize cell damage in the arcuate nucleus to be involved in both.

Animal Husbandry↗

PubMed2002

Selected contribution: role of IL-6 in LPS-induced nuclear STAT3 translocation in sensory circumventricular organs during fever in rats.

Interleukin-6 (IL-6) is regarded as an endogenous mediator of lipopolysaccharide (LPS)-induced fever. IL-6 is thought to act on the brain at sites that lack a blood-brain barrier, the circumventricular organs (CVOs). Cells that are activated by IL-6 respond with nuclear translocation of the signal transducer and activator of transcription 3 molecule (STAT3) and can be detected by immunohistochemistry. We investigated whether the LPS-induced release of IL-6 into the systemic circulation was accompanied by a nuclear STAT3 translocation within the sensory CVOs. Treatment with LPS (100 microg/kg) led to a slight (1 h) and then a strong increase (2-8 h) in plasma IL-6 levels, which started to decline at the end of the febrile response. Administration of both pyrogens LPS and IL-6 (45 microg/kg) induced a febrile response with IL-6, causing a rather moderate fever compared with the LPS-induced fever. Nuclear STAT3 translocation in response to LPS was observed within the vascular organ of the lamina terminalis (OVLT) and the subfornical organ (SFO) 2 h after LPS treatment. To investigate whether this effect was mediated by IL-6, the cytokine itself was systemically applied and indeed an identical pattern of nuclear STAT3 translocation was observed. However, nuclear STAT3 translocation already occurred 1 h after IL-6 application and proved to be less effective compared with LPS treatment when analyzing OVLT and SFO cell numbers that showed nuclear STAT3 immunoreactivity after the respective pyrogen treatment. Our observations represent the first molecular evidence for an IL-6-induced STAT3-mediated genomic activation of OVLT and SFO cells and support the proposed role of these brain areas as sensory structures for humoral signals created by the activated immune system and resulting in the generation of fever.

Animals↗

PubMed2001

Influence of systemic treatment with cyclooxygenase inhibitors on lipopolysaccharide-induced fever and circulating levels of cytokines and cortisol in guinea-pigs.

Peripheral inflammatory stimuli result in the modification of a number of vital brain-controlled functions including the thermoregulatory set-point (induction of fever) and the activity of the hypothalamic-pituitary-adrenal (HPA) axis. We addressed the question of whether both of these components of the acute-phase response are induced by a common signal pathway. For this purpose we recorded body temperature (by remote radio-telemetry), HPA axis activity (circulating concentrations of cortisol by radio-immunoassay) and levels of the pro-inflammatory cytokines tumour necrosis factor and interleukin-6 (TNF, IL-6, using specific bioassays) in six groups of guinea-pigs. The animals received intra-arterial injections of either 10 microg/kg lipopolysaccharide (LPS) plus saline, 10 microg/kg LPS plus 5 mg/kg meloxicam (an inhibitor of the inducible form of cyclooxygenase), 10 microg/kg LPS plus 5 mg/kg diclofenac (a non-selective cyclooxygenase inhibitor), saline plus solvent, saline plus 5 mg/kg meloxicam or saline plus 5 mg/kg diclofenac. Injection of the cyclooxygenase inhibitors per se had no influence on the investigated parameters. Injection of LPS alone resulted in a biphasic fever, a more than fivefold increase in circulating cortisol and pronounced induction of TNF and IL-6. Treatment with the cyclooxygenase inhibitors either attenuated (meloxicam) or abolished (diclofenac) LPS-induced fever, but had no effect on the LPS-induced rise of plasma cortisol or IL-6. Circulating levels of TNF, in response to LPS, were enhanced by meloxicam and diclofenac, reflecting the negative feedback control exerted by prostaglandins on cytokine (specifically TNF) formation. These results provide the first evidence that the prostaglandin-dependent inflammatory pathway for fever induction is distinct from the pathway of HPA axis activation since fever, but not circulating cortisol, was attenuated by an inhibition of prostaglandin formation.

Animals↗