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Biomedical subjects

B Köster

Publications and source records attributed to B Köster.

At least 19 recordsLinked to original sources
PubMed2000

Tremor-correlated cortical activity detected by electroencephalography.

OBJECTIVE: In this study we investigated whether cortical activity related to Parkinsonian resting tremor can be detected by electroencephalography (EEG). METHODS: Seven patients with idiopathic Parkinson's disease suffering from unilateral tremor participated in the study. Electromyography (EMG) signals arising from the wrist extensor and flexor muscles as well as a high resolution EEG were recorded simultaneously. Coherencies between EEG and EMG were calculated. RESULTS: In all patients, we found highly significant coherencies at the tremor frequency or its first harmonic between the tremor EMG and contralateral EEG channels. There were no significant coherencies between the tremor EMG and ipsilateral EEG channels. Isocoherency maps illustrating the topography of the coherencies over the scalp showed that the maximum coherencies were situated over the cortical motor areas. In one case, a high coherency was also found over the parietal cortex. CONCLUSIONS: The results show for the first time that tremor-correlated cortical activity can be detected by electroencephalography. The findings underline that motor areas of the cerebral cortex are involved in the neuronal network generating resting tremor in Parkinson's disease.

Aged↗
PubMed1999

Classical conditioning of the electrically elicited blink reflex in humans: a new method of data analysis.

The eyeblink conditioning paradigm is a well-established model to study learning processes in humans and animals. Especially results from animal studies have supplied new insight into physiological pathways and brain structures involved in associative motor learning and memory. An important role of the cerebellum and its afferent fiber systems could be shown. Recent studies in humans have given evidence that results of animal experiments can be applied directly to the human condition. A high variation of baseline EMG activity and/or spontaneous blinks may influence the analysis of classical conditioning of the electrically elicited blink reflex in humans. To optimize differentiation between real conditioned responses and stimulus-independent EMG activity, we developed an algorithm which is fully automated and independent of a possible bias of an examiner. In a first step the algorithm decides whether a subject fulfills the criteria of a successful learning process or not. The second step quantifies the learning process. For quantification of the learning process, the following parameters were calculated: number of conditioned responses, onset of conditioning, time and amount of maximal conditioning, speed of conditioning and speed of habituation. According to our criteria, 80% of the healthy volunteers acquired conditioned responses. There is an age-related decline in eyeblink classical conditioning. Analysis of patient groups with different types of lesions will further improve our knowledge and understanding of pathways involved in learning processes in humans. The proposed new algorithm of data analysis takes less than 10 s on a standard computer, is more sensitive and more specific in detecting conditioned responses and, therefore, may further improve the value and reliability of the eyeblink conditioning paradigm in clinical research.

Adult↗
PubMed1999

Involvement of cranial muscles and high intermuscular coherence in orthostatic tremor.

Electromyographic recordings were conducted from limb, trunk, and cranial muscles in 6 patients with orthostatic tremor. Spectral analysis revealed a high-frequency tremor not only in the muscles of the limbs and trunk, but also in cranial muscles. The cross spectra were analyzed between various pairs of muscles that displayed a high-frequency tremor pattern. The resulting peak correlations were uniformly very high (near one) suggesting a high level of coherence. The involvement of cranial muscles suggests that supraspinal mechanisms are involved in the generation of orthostatic tremor. The high intermuscular coherence between all muscles indicates the existence of either a unique oscillator that generates tremor in all involved muscles on both sides of the body or a linking mechanism probably at a supraspinal level. The high-frequency tremor was only found when the muscles were contracted isometrically, irrespective of body posture. Thus, tremor generation might be more closely linked to mechanisms responsible for isometric force control than to those involved in stance regulation.

Aged↗
PubMed1999

Side-to-side correlation of muscle activity in physiological and pathological human tremors.

OBJECTIVE: Many tremors occur always or often bilaterally. The question arises whether this could be explained by a common source or commonly transmitting pathways or by bilaterally represented, independent structures with the same oscillatory properties. A similar tremor frequency does not provide sufficient information to clarify this question. METHODS: We analyze coherencies between surface electromyographies (EMG) to investigate if bilateral physiologic (PT), essential (ET), Parkinsonian (PD) and orthostatic (OT) tremors originate from a common source for both sides of the body. We show that commonly used techniques to test whether coherencies are significant could lead to false positive results for tremor EMGs. A new estimation procedure is proposed to test EMG tremor time series on their linear independence. We apply this test to bilateral tremors. RESULTS: All measured EMG-pairs in OT (n = 7) were highly coherent between both sides with reproducible coherency values of up to 0.99. All other investigated tremors, i.e. PT and enhanced physiological tremors (EPT, n = 117), ET (n = 76) and PD resting and postural tremors (n = 70) do not show a significant side-to-side correlation. CONCLUSIONS: This finding shows that the pathophysiologies of OT and other pathological tremors are definitely different. Either they have different origins or different kinds of transmitting pathways. The proposed method might also be used to investigate other electrophysiological data and is a helpful, easy to use investigation for a daily clinical routine.

Computer Simulation↗
PubMed1998

Central mechanisms in human enhanced physiological tremor.

The sites of the central nervous structures involved in enhanced physiological tremor (EPT) are still unclear. The syndrome of persistent mirror movements (PMM) is characterized by abnormal bilateral corticospinal projections. If a supraspinal mechanism is involved in EPT, the activity of EPT should be coherent between both sides in subjects with this abnormality. We investigated three PMM subjects and three normal controls. Focal transcranial magnetic stimulation (TMS) resulted in contralateral hand muscle responses in the controls. The PMM subjects, in contrast, had bilateral responses. Similarly, long-latency reflexes (LLR) in PMM could be recorded bilaterally, while the control subjects showed responses only on the stimulated side. EPT was evoked by intravenous salbutamol. EMG time series were recorded bilaterally from the wrist extensor muscles and cross spectra were calculated. If there was a significant right-left-coherence, phase analysis was performed. No control subject showed a significant right-left-coherence of tremor activity. In contrast, a significant coherence was found in PMM between 8 and 12 Hz. When the mechanical tremor frequency of one hand was reduced by loading, coherences and phase spectra of the EMGs remained unchanged. By comparing the results from TMS, LLR and cross spectral analysis we come to the conclusion, that the 8 to 12 Hz component of EPT is transmitted transcortically, most likely originating from two separate generators for both sides.

Adult↗
PubMed1998

Diagnostic and pathophysiological aspects of psychogenic tremors.

Psychogenic tremor has become a rare movement disorder. Twenty-five patients from our movement disorder unit presented either with obviously nonorganic body shaking during stance or with extremity tremors. A sudden onset and a variable but rarely remitting course of the condition was common. The "coactivation sign of psychogenic tremor" and absent finger tremor were the most consistent criteria to separate them from organic tremors. Quantitative analysis of tremor shows decreasing amplitudes in most organic tremors when the extremity is loaded with additional weights. In contrast, we found an increase of tremor amplitude for most of the cases with psychogenic tremor. This might be caused by increased coactivation to maintain the oscillation. These clinical and electrophysiological features suggest a clonus mechanism induced by coactivation as the pathophysiological basis of psychogenic extremity tremor. Psychiatric evaluation did not show overt signs of hysteria for the majority of the patients. However, we found depression and functional somatic or psychosomatic conditions to be frequent among the patients. A reduced ability to cope with stressful situations may play a significant role. The clinical course of the condition is usually far from benign. We conclude that psychogenic tremor can be positively diagnosed by means of neurologic signs in the majority of patients and is not only a diagnosis of exclusion. The poor outcome makes early and serious neuropsychiatric attempts at therapy necessary.

Adaptation, Psychological↗
PubMed1996

[Diagnosis, symptoms and follow-up of psychogenic tremor].

A total of 21 patients with psychogenic tremor (PT) were asked to take part in a neurologic and psychosomatic assessment; for 17 patients follow-up information was also recorded. Women out-numbered men in the sample. In the majority of patients the tremor was associated with a variety of other conversion symptoms. The clinical picture of the tremor varied. After beginning exclusively in the extremities, it tended to spread to other parts of the body. Other psychopathology (depression and histrionic personality disorder) existed in almost a third of the sample. Many patients had retired from professional life, or planned to do so in the near future, because of PT. At follow up the initial diagnosis was confirmed in all patients although in some patients additional physical illness had developed during the follow-up period. When neurological and psychiatric/psychosomatic criteria are applied the diagnosis of PT can be established reliably. Studies that have questioned the validity of the conversion concept on the basis of frequent misdiagnoses may indicate problems in the diagnostic procedure rather than an invalid theoretical construct.

Adult↗
PubMed1994

Schistosoma mansoni: Sm23 is a transmembrane protein that also contains a glycosylphosphatidylinositol anchor.

Sm23, a surface protein of the human parasite Schistosoma mansoni, belongs to the family of "cysteine-rich, hydrophobic proteins," which are expressed on mammalian hematopoietic cells or tumor cells. Sm23 shares the highly conserved hydrophobicity profile of these proteins, which predicts four transmembrane segments, but is in addition linked to the membrane by a glycosylphosphatidylinositol (GPI) anchor. Our results suggest that Sm23 uses both the potential transmembrane domains and the GPI anchor for membrane insertion: (a) Sm23 was not released from the surface after cleavage with phosphatidylinositol-specific phospholipase C (PIPLC). (b) In a Triton X-114 phase-separation system, native [3H]ethanolamine- or [35S]methionine-labeled Sm23 partitioned into the detergent phase. Upon removal of the GPI anchor by PIPLC, the majority of the molecules stayed in the detergent-phase as expected of a transmembrane protein. (c) When full-length recombinant Sm23 was transcribed and translated in vitro, the polypeptide chain was inserted into microsomal membranes: Sm23 stayed associated with the membranes when they were incubated with carbonate buffer at pH 11.5, and membrane bound Sm23 was protected from digestion with proteinase K. (d) Recombinant Sm23, when expressed in the baculovirus expression system, was transported to the surface of infected insect cells, and similarly to the native protein it was not released from these cells after cleavage with PIPLC.

Animals↗
PubMed1994

Schistosoma mansoni: immunolocalization of two different fucose-containing carbohydrate epitopes.

We have used two monoclonal antibodies, 128C3/3 and 504B1, to immunolocalize their carbohydrate epitopes in different developmental stages of Schistosoma mansoni. Both epitopes contain fucose: mAb 128C3/3, as we have shown previously, recognizes fucose in a novel, possibly internal linkage (Levery et al. 1992) while mAb 504B1, as we show here, bound to the Le(x) epitope, which contains fucose alpha 1-->3 linked to N-acetyl-glucosamine. The tissue expression of these epitopes was strikingly different and both elicit an immune response in infected hosts. The mAb 128C3/3-defined epitope was exposed on the surface of all larval stages but not on adult worms; however, it was found in the excretory system of adult worms of both sexes. In contrast, surface expression of the Le(x) epitope was initiated after the transformation of cercariae to schistosomula and was maintained throughout the adult life in both sexes.

Animals↗
PubMed1993

Schistosoma mansoni: immunoreactivity of human sera with the surface antigen Sm23.

Sm23, a surface antigen of Schistosoma mansoni, elicits an immune response in patients infected with the parasite, although to a lesser degree than Sj23, the homologue of Sm23 in Schistosoma japonicum. To characterize the host immune response to Sm23, we have expressed full-length Sm23 using the baculovirus expression system and have also expressed the N-terminal 133 amino acids and the 85 C-terminal amino acids by means of the prokaryotic vector pGEX. A total of 70 sera from patients from Sudan and Egypt were examined for alpha-Sm23 antibodies in an ELISA and in Western blot analysis using both the C-terminal polypeptide and the full-length protein. A subset of these sera was also tested for reactivity with the N-terminal polypeptide. The alpha-Sm23 antibody titers in infected patients varied widely and were not correlated with egg counts or age of the individuals. Most of the seroreactivity was directed against the C-terminal polypeptide.

Age Factors↗
PubMed1993

[Hemoglobin SD disease].

A 7 year old Kurdish girl presented with a cerebral infarction and a resulting hemiparesis following a blood transfusion. Examination of the blood film suggested sickle cell anaemia. However a simultaneously carried out haemoglobin electrophoresis showed haemoglobin S and haemoglobin D. The diagnosis of haemoglobin SD disease was thereby established. This kind of haemoglobin disorder usually shows a mild clinical manifestation. According to our knowledge such serious cases have not been published before. With this disease the main emphasis is on the prevention of recurrent cerebral infarctions bay a long-term transfusion programme whereas the effects of the cerebral infarction are treated in the usual way.

Anemia, Sickle Cell↗
PubMed1990

Preparation of proteosome-based vaccines. Correlation of immunogenicity with physical characteristics.

In order to facilitate the use of proteosome-based vaccines, we have identified and analyzed the parameters that affect their immunogenicity. As a model system we used synthetic peptides (LCF6) containing sequences from the immunodominant (NANP)n tandem repeat region of the P. falciparum circumsporozoite protein, hydrophobically complexed to multimeric protein preparations (proteosomes) of meningococcal outer membrane proteins (OMP), since we have previously shown that high levels of anti-(NANP)n IgG can be elicited in mice by use of this novel adjuvant system (Lowell et al., 1988a). We have now examined these preparations by velocity sedimentation and measured their ability to elicit an IgG response in mice. Velocity sedimentation of freshly mixed OMP and LCF6, without dialysis, produced a limited number of small complexes, whereas dialysis of the mixture for 4 d yielded heterogeneously sized complexes that became more homogeneous when the dialysis was carried out for 7 or 10 days. The most homogeneous of these peptide-proteosome complexes (those dialyzed for 10 days) induced substantial levels of anti-(NANP)n IgG in mice, and shorter periods of dialysis resulted in vaccines that induced proportionately lower titers. Analysis of a series of preparations with varying LCF6: OMP ratios (w/w) showed that the degree of peptide substitution of the proteosomes was inversely proportional to the rate of sedimentation of the complexes and that there exists an optimal degree of lipopeptide complexing to the proteosomes. Our results suggest that the parameters affecting the immunogenicity of the peptide-proteosome complexes are: (i) hapten density, and (ii) size of the complex. Furthermore, sedimentation analysis of peptide-proteosome immunogens may serve as a rapidly performed assay of immunogenic potency.

Adjuvants, Immunologic↗
PubMed1988

Identification and localisation of the products of a putative eggshell precursor gene in the vitellarium of Schistosoma mansoni.

An abundant 0.9 kb female-specific mRNA in Schistosoma mansoni is thought to code for an egg-shell precursor protein [Bobek et al. (1986) Proc. Natl. Acad. Sci. USA 83, 5544-5548]. This gene contains two ORFs. A recombinant plasmid was constructed that expresses a fusion protein containing a glycine- and tyrosine-rich polypeptide coded for by one of these ORFs. Antisera raised against homogenates of female, but not of male, S. mansoni recognise this fusion protein, providing direct evidence that this ORF is used by S. mansoni. In comparative Western blots of S. mansoni homogenates from males and females affinity purified antibodies that react with the fusion protein react exclusively with proteins from females, recognising a 28 kDa polypeptide and a smear of immunoreactive material probably caused by oxidative crosslinking. In immunohistology, the affinity purified antibodies react with mature vitelline cells in female schistosomes. The immunoreactive material is localised in the so-called 'vitelline droplets' that are morphologically very similar to 'shell globules', known to contain egg-shell precursors, that are found in Fasciola hepatica. In situ hybridisation shows that the eggshell precursor gene is only transcribed in immature vitelline cells and has a short half-life. Taken together, these observations provide persuasive evidence that the 0.9 kb mRNA codes for an eggshell precursor.

Animals↗
PubMed1986

[Acute encephalopathy following cranial irradiation of previously treated meningeal leukemia].

The sudden occurrence of an encephalopathic symptomatology within a day following commencement of radiotherapy is demonstrated by a case report of a small child suffering from CNS leukemia. Former intrathecal chemotherapy appears to be a prerequisite for this toxicity. In spite of diuretic therapy the patients condition may worsen initially, but recovery is possible within days. Patient characteristics and disease course identify a new toxicity syndrome, which is not yet familiar.

Antineoplastic Agents↗