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Biomedical subjects

U Herwig

Publications and source records attributed to U Herwig.

12 recordsLinked to original sources
PubMed2006

Extensive training of elementary finger tapping movements changes the pattern of motor cortex excitability.

There is evidence of a strong capacity for functional and structural reorganization in the human motor system. However, past research has focused mainly on complex movement sequences over rather short training durations. In this study we investigated changes in corticospinal excitability associated with longer training of elementary, maximum-speed tapping movements. All participating subjects were consistent right-handers and were trained using either the right (experiment 1) or the left thumb (experiment 2). Transcranial magnetic stimulation was applied to obtain motor evoked potentials (MEPs) from the abductor pollicis brevis (APB) muscle of the right and the left hand before and after training. As a result of training, a significant increase was observed in tapping speed accompanied by increased MEPs, recorded from the trained APB muscle, following contralateral M1 stimulation. In the case of subdominant-hand training we additionally demonstrate increased MEP amplitudes evoked at the right APB (untrained hand) in the first training week. Enhanced corticospinal excitability associated with practice of elementary movements may constitute a necessary precursor for inducing plastic changes within the motor system. The involvement of the ipsilateral left M1 likely reflects the predominant role of the left M1 in the general control (modification) of simple motor parameters in right-handed subjects.

Action Potentials↗
PubMed2003

Verbal storage in a premotor-parietal network: evidence from fMRI-guided magnetic stimulation.

Phonological rehearsal helps to keep selected information consciously in mind for further processing. This part of short-term storage takes place during the delay period of verbal working memory tasks and involves a frontoparietal network as functional magnetic resonance imaging (fMRI) studies have shown. The involved cortical areas can be further investigated by interfering with the local information processing using transcranial magnetic stimulation (TMS). On a single subject level, we identified predominantly left-sided premotor, prefrontal, and parietal areas active during the delay period of a verbal working memory task using event-related fMRI. In a pilot approach, TMS was neuronavigated to the individually active areas by using a stereotaxic device. Then, TMS was applied during the delay period of similar tasks as in fMRI. Error rates increased significantly upon stimulating left premotor cortex, but not upon parietal or prefrontal stimulation. The contribution of the premotor cortex to storage and rehearsal is discussed as an active top-down storage process within the frontoparietal network.

Adult↗
PubMed2002

[Historical review and recent research trends of the antidepressant repetitive transcranial magnetic stimulation (rTMS)].

The antidepressant effect of repetitive transcranial magnetic stimulation (rTMS) has been studied intensively over the last years. Numerous studies worldwide yielded variable results ranging from ineffectivity to an efficacy rate of more than 50 % for the reduction of depressive symptoms. A comparison of the effectiveness of TMS across studies is difficult due to the variety of chosen stimulation parameters, different inclusion criteria, and different designs. The discrepancies in results could be partially in account to these factors. From a pathophysiological point of view, there are no empirically justified parameters published carrying out an antidepressant TMS. Further studies are required to find optimal stimulation parameters using complementary methods like functional imaging techniques or regarding other factors that could interfere with its efficacy. An overview of studies published in the last ten years, a critical analysis of stimulation procedures and protocols, and possible future perspectives of this method are reviewed in this article.

Brain↗
PubMed2001

The navigation of transcranial magnetic stimulation.

Transcranial magnetic stimulation (TMS) is a new method for investigating cortical information processing and for investigating therapeutic applications in psychiatry and neurology. A common problem of most studies in this field regards the localization of the magnetic coil with respect to the cortex. This article reviews the currently used methods and proposes a neuronavigational approach. The method of neuronavigated TMS is described and discussed in detail. It is used to guide the magnetic coil on an individual basis to a structurally or functionally predetermined cortical area while monitoring the location of the coil in relation to the subject's head in real time. Possible applications of TMS in combination with functional neuroimaging in clinical research within a cognitive neuroscience framework are discussed. Future applications of TMS should take individual anatomy into account, and neuronavigation provides the means to do so.

Brain Mapping↗
PubMed2001

Low-level expression of functional foamy virus receptor on hematopoietic progenitor cells.

Foamy viruses have several qualities favorable for vector development: they are not known to cause disease; they can transduce stationary cells; and the foamy virus receptor is expressed on a wide variety of cells. Here, we analyzed the level of virus receptor expression on hematopoietic progenitor cells. Foamy virus binding was measured by a flow cytometric assay and was found to be considerably reduced in hematopoietic progenitors cell lines as well as in primary CD34(+) cells when compared to fibroblasts. Retroviral vectors based on murine leukemia virus (MLV) pseudotyped with a foamy virus envelope transduced hematopoietic cell lines with a more than 10-fold lower efficiency than fibroblasts. Moreover, less than 1% of primary CD34(+) hematopoietic progenitor cells were transduced with the foamy virus pseudotypes, while gene transfer efficiencies of 8-40% were achieved using pseudotypes with amphotropic envelope or the G protein of vesicular stomatitis virus. In conclusion, the expression of functional foamy virus receptors on hematopoietic progenitors cells was found to be insufficient to achieve high levels of gene transfer into CD34(+) hematopoietic progenitor cells with cell-free vector supernatants using current transduction protocols.

Animals↗
PubMed2001

Transcranial magnetic stimulation in therapy studies: examination of the reliability of "standard" coil positioning by neuronavigation.

Transcranial magnetic stimulation is investigated as a new tool in the therapy of depression and other psychiatric disorders. In almost all studies, the dorsolateral prefrontal cortex (DLPFC) has been selected as the target site for stimulation. Usually this region was determined by identifying the patient's motor cortex, and from there the coil was placed 5 cm rostrally. The aim of our study was to test the reliability of this standard procedure. A neuronavigational system was used to relate the final coil position after applying the standard procedure to the individual cortical anatomy. In 7 of 22 subjects, the Brodman area 9 of the DLPFC was targeted correctly in this manner. In 15 subjects, the center of the coil was found to be located more dorsally (e.g., above the premotor cortex). The current method for locating the DLPFC is not precise anatomically and may be improved by navigating procedures taking individual anatomy into account.

Adult↗
PubMed2001

Differential mechanisms of neuroprotection by 17 beta-estradiol in apoptotic versus necrotic neurodegeneration.

The major goal of this study was to compare mechanisms of the neuroprotective potential of 17 beta-estradiol in two models for oxidative stress-independent apoptotic neuronal cell death with that in necrotic neuronal cell death in primary neuronal cultures derived from rat hippocampus, septum, or cortex. Neuronal apoptosis was induced either by staurosporine or ethylcholine aziridinium (AF64A), as models for necrotic cell death glutamate exposure or oxygen-glucose deprivation (OGD) were applied. Long-term (20 hr) pretreatment (0.1 microm 17 beta-estradiol) was neuroprotective in apoptotic neuronal cell death induced by AF64A (40 microm) only in hippocampal and septal neuronal cultures and not in cortical cultures. The neuroprotective effect was blocked by the estrogen antagonists ICI 182,780 and tamoxifen and the phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002. In glutamate and OGD-induced neuronal damage, long-term pretreatment was not effective. In contrast, short-term (1 hr) pretreatment with 17 beta-estradiol in the dose range of 0.5-1.0 microm significantly reduced the release of lactate dehydrogenase and improved morphology of cortical cultures exposed to glutamate or OGD but was not effective in the AF64A model. Staurosporine-induced apoptosis was not prevented by either long- or short-term pretreatment. The strong expression of the estrogen receptor-alpha and the modulation of Bcl proteins by 17 beta-estradiol in hippocampal and septal but not in cortical cultures indicates that the prevention of apoptotic, but not of necrotic, neuronal cell death by 17 beta-estradiol possibly depends on the induction of Bcl proteins and the density of estrogen receptor-alpha.

Animals↗
PubMed2000

Amphotropic and VSV-G-pseudotyped retroviral vectors transduce human hematopoietic progenitor cells with similar efficiency.

One restriction of retroviral gene transfer into hematopoietic stem cells is the low level of amphotropic virus receptor. In the present study, we examined whether retroviral vectors pseudotyped with the G-protein of vesicular stomatitis virus (VSV) can overcome this restriction. Human progenitor cells purified by magnetic beads and cell sorting were transduced with an amphotropic or VSV-G-pseudotyped retroviral vector containing the truncated human nerve growth factor receptor as a marker gene. Cells were prestimulated with flt-3 ligand, stem cell factor, and interleukin-3 and transduced on fibronectin. Marker gene expression was analyzed by flow cytometry. Transduction efficiencies of amphotropic and VSV-G-pseudotyped virus for CD34+ cells did not differ significantly. Gene transfer into CD34+CD38- cells, which are enriched in more immature progenitors, was not restricted and transfer efficiencies for this subset were also similar for both pseudotypes. The addition of fibronectin improved gene transfer with the amphotropic vector considerably (5- to 19.3-fold, mean 12.6), while the effect on the VSV-G-pseudotype was far less pronounced (1- to 3.9-fold, mean 2.1, P = 0.04). In conclusion, high levels of gene transfer to human hematopoietic progenitors were achieved with an optimized transduction protocol, and transduction efficiencies could not be improved further by the use of VSV-G-pseudotypes.

ADP-ribosyl Cyclase↗
PubMed2000

[The study of central nervous information processing with transcranial magnetic stimulation].

In cognitive neuroscience different methods are used to study central nervous information processing. Transcranial magnetic stimulation (TMS) is a non-invasive, well tolerated technique to interfere with cortical neuronal activity with high temporal and fair spatial resolution. In the past 10 years the use of TMS expanded from its application as a diagnostic routine procedure in neurology to the study of various cognitive functions. In this paper the physical and technical aspects of TMS and studies on the effects of single pulse versus repetitive TMS in the motor cortex are reviewed. Then, research on visual perception and attention is presented and studies on higher cognitive functions, such as speech, memory, and emotions are discussed.

Brain↗
PubMed1999

Hyperthyroidism mimicking increased intracranial pressure.

We report a 32-year-old woman presenting with progressive symptoms of increased intracranial pressure and slight enlargement of the ventricles on CT scan. The underlying cause was hyperthyroidism due to Graves' disease. With treatment to correct the hyperthyroid state, all symptoms rapidly disappeared. The rare onset of hyperthyroidism with symptoms indicating intracranial hypertension, and the possible pathophysiologic mechanisms are discussed.

Adult↗
PubMed1981

[Respiratory depression after diazepam-fentanyl anaesthesia (author's transl)].

105 patients were given diazepam-fentanyl anaesthesia and the respiratory values were studied spirometrically before the operation, after intramuscular premedication and postoperatively (i.e. after additional doses of diazepam during induction). The occurrence of respiratory depression which has been reported by some authors was confirmed. Blood gas analyses performed in 79 patients during the recovery period showed a significant improvement after the patients had been made to breathe deeply for five minutes. The results confirm the observations made in more than 12000 patients who had this type of anaesthesia that they must be kept under surveillance during the first 30-40 minutes in the recovery ward, but can then be returned to the ward.

Adolescent↗