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Biomedical subjects

K Maurer

Publications and source records attributed to K Maurer.

At least 145 records · Page 8Linked to original sources
PubMed1989

Synergistic effects of calcium-mobilizing agents and adenosine on histamine release from rat peritoneal mast cells.

1. Adenosine and its metabolically stable analogue N-ethyl-carboxamidoadenosine (NECA) enhance histamine release from rat peritoneal mast cells when these are stimulated by calcium-mobilizing agents. NECA and adenosine shift the concentration-response curve of the calcium ionophore A23187 to lower concentrations. 2. The potencies of NECA or adenosine in enhancing A23187-induced histamine release are dependent on the level of stimulated release in the absence of adenosine analogues. At high levels of release their potencies are up to 20 times higher than at low levels. Consequently, averaged concentration-response curves of adenosine and NECA for enhancing histamine release are shallow. 3. The adenosine transport blocker S-(p-nitrobenzyl)-6-thioinosine (NBTI) has no effect by itself at low levels of stimulated histamine release, but abolishes the enhancing effect of adenosine. At high levels of release, however, NBTI alone enhances the release of histamine. 4. It is concluded that adenosine and calcium reciprocally enhance the sensitivity of the secretory processes to the effects of the other agent. The levels of intracellular adenosine obtained by trapping adenosine inside stimulated mast cells are sufficient to enhance histamine release substantially, suggesting that this effect may play a physiological and pathophysiological role.

Adenosine↗
PubMed1989

Differences between paranoid and nonparanoid schizophrenic patients on the somatosensory P300 event-related potential.

Event-related potentials were recorded from schizophrenic patients (n = 30) and healthy controls (n = 30) using a somatosensory-reaction-time version of the oddball paradigm, by stimulating the right and the left median nerve. Latency, amplitude, duration and area of the P300 were measured. The patient group was subdivided into a paranoid (n = 16) and a nonparanoid (n = 14) subgroup and each was compared to controls. After stimulation of the right median nerve the nonparanoid group had a significantly prolonged P300 latency and a normal amplitude. The paranoid subgroup had a trend toward reduction of the P300 amplitude; its P300 latency was normal. After stimulation of the left median nerve, a prolongation of the P300 latency was observed in the paranoid subgroup. This subgroup had also a reduced P300 amplitude, while the nonparanoid patients had both values comparable to those of the controls. Duration and area were not significantly different between the two subgroups of patients and controls. Paranoid and nonparanoid patients showed a different behavior on reaction time parameters. No relationship was observed between P300 parameters and clinical ratings, neuroleptic dose and demographic data. The P300 parameters did not correlate with the reaction time measures. These results are discussed in terms of a disturbance of CNS inhibitory mechanisms in cognitive processes of paranoid schizophrenic patients and could be a further indication that different subtypes of schizophrenia may have different biological substrates.

Adult↗
PubMed1989

[Normative aspects of somatosensory evoked P300 components].

Using a somatosensory version of the oddball-paradigma the influence of age and gender on the P300-component and the comparison of the potential after stimulation of the right and left median nerve was studied in 30 healthy right handed volunteers (age: 20-35 years). Latency, amplitude, area and duration of the P300-potential were analysed. No relationship between age, gender and the P300-parameters were observed. The amplitude and the area of the potential obtained from the F3 electrode were greater after stimulation of the right median nerve compared to the potential after stimulation of the left median nerve. All other results were not significantly different. Strong positive correlations between the results after stimulation of the right and left median nerve were observed. These results showed that by a young group of volunteers age and gender did not influence the P300-component. Although the P300-Parameters had a between-subject variability, their mean remained constant over the study, their correlation coefficients were strong positive and the side of stimulation did not influence them (except for the electrode F3).

Adult↗
PubMed1988

Physiological regulation of Paracoccus denitrificans methanol dehydrogenase synthesis and activity.

An enzyme-linked immunosorbent assay and a whole-cell activity assay were developed which allowed detection of methanol dehydrogenase (MDH) of Paracoccus denitrificans with increased sensitivity. By these methods, it was shown that MDH was not induced by its natural substrate, methanol. Relief from a catabolite repression-like mechanism seemed responsible for low-level MDH synthesis, while product induction was the hypothesized mechanism for synthesis of high amounts of MDH. In the latter process, formaldehyde may play an important role as effector. For a variety of culture conditions, inconsistencies were observed in the relation between amounts of MDH protein synthesized and enzyme activities measured in vitro. Regulation of pyrrolo-quinoline-quinone biosynthesis or a modulation of its incorporation and stability in MDH may constitute an overriding mechanism to ensure a correct tuning between metabolic rates of methanol consumption and the required methanol oxidation rates.

Alcohol Oxidoreductases↗
PubMed1988

[Topography of P300 in psychiatry--1. Cognitive P300 fields in psychoses].

P300 is known as a wave which enables the evaluation of cognitive function in neuropsychology and psychiatry. The most reliable result in psychoses was an amplitude reduction. Since similar wave alteration occurred not only in psychoses but also in dementia, the P300 reduction was too unspecific to serve as criteria for differential diagnosis. By means of topographical procedures it could be found out that the well defined P300 fields underwent characteristic changes in psychoses which even allowed a differentiation between different subgroups in schizophrenia. In hebephrenics the frontal field was very low whereas the paranoid group showed a lateralized P300-pattern with lower amplitudes in the right parieto-temporal area. In depression the P300-pattern was identical to the fields known in geriatric controls. The results will be discussed regarding other structural and functional imaging procedures. By means of topographical display of P300 the specificity of cognitive waves can be augmented considerably with the possibility to differentiate between different types of psychoses.

Affective Disorders, Psychotic↗
PubMed1988

[Topography of P300 in psychiatry--II. Cognitive P300 fields in dementia].

The P300 wave undergoes alterations during physiological aging showing lower amplitudes and longer latencies in geriatric controls. By means of topographical display of P300-data it could be shown that the topography with maximal positivity at parietal sites is maintained in aging. In patients, however, suffering from senile dementia of Alzheimer's type signs of a frontal elevation and a parietal decrement of P300 amplitudes could be observed. The findings can be interpreted firstly as an indication that the frontal lobe is less effected. On the other side if a hippocampal dipole is assumed a neuronal lesion could lead to a turn of this dipole with the result of a now frontally located positivity.

Adult↗
PubMed1988

[The topography of P300 in neuropsychiatric pharmacotherapy. III. Cognitive P300 fields in an organic psychosyndrome (Wilson's disease) before and during treatment with D-penicillamine].

Beside senile dementia of Alzheimer's type (SDAT) there are also dementive syndromes due to a disturbance in metabolism. In a case with a disturbance of copper metabolism (Wilson's disease) a similar P300-pattern was found as described in SDAT with signs of a frontal amplitude elevation. Under therapy with d-penicillamine the frontal P300-positivity moved from frontal to parietal structures. Combined with this migration was an amelioration in cognitive function. This single-case study underlines the significance of P300-topography in the evaluation of therapy effects in dementive disorders.

Adult↗
PubMed1987

Dual actions of adenosine on rat peritoneal mast cells.

The effects of adenosine and its analogues on cAMP-responses and histamine release of rat peritoneal mast cells were investigated. The adenosine analogue 5'-N-ethylcarboxamidoadenosine (NECA') activates the adenylate cyclase of the mast cell membranes and elevates the cAMP-levels of the intact mast cells. Both effects are antagonized by methylxanthines, suggesting that they are mediated via an A2 adenosine receptor. Adenosine and its analogues enhance the release of histamine from these cells, when the release is stimulated either by the calcium ionophore A 23187 or by concanavalin A. However, this effect is not antagonized by theophylline or 8-phenyltheophylline. In contrast, it is antagonized by the adenosine uptake blockers S-(p-nitrobenzyl)-6-thioinosine (NBTI) and S-(p-nitrobenzyl)-6-thioguanosine (NBTG). It is concluded that adenosine has two different effects on mast cells: it activates adenylate cyclase via an A2 adenosine receptor, and it enhances histamine release via an action at an intracellular site.

Adenosine↗
PubMed1987

Functional imaging of the brain in psychiatry--mapping of EEG and evoked potentials.

Topographic brain mapping of EEG and evoked potentials permits the display of spontaneous and event-related activity of the brain. This new method is superior to conventional polygraphy because of the topographic approach which delineates structural and functional brain lesions. Data from 16 to 20 scalp electrodes were evaluated. Not only spontaneous EEG but also EEG during various testing conditions which activated particular brain regions was measured. For EEG fast Fourier transformation (FFT) was used for mapping. For late evoked potentials (VEP, AEP, SEP and P300) a single value representing the amplitude of EP at each 2-ms poststimulus latency point was used. Statistical techniques (Students'-test, correlation coefficient) were used to render the regions where a clinical population differs from normal subjects. The results show abnormalities of EGG and EP in patients with psychiatric and neurological diseases.

Arousal↗
PubMed1987

Isolation and nucleotide sequence of the methanol dehydrogenase structural gene from Paracoccus denitrificans.

A genomic clone bank of Paracoccus denitrificans DNA has been constructed in the expression vector set pEX1, pEX2, and pEX3. Screening of this clone bank with antibodies raised against P. denitrificans methanol dehydrogenase resulted in the isolation of a clone, pNH3, that synthesized methanol dehydrogenase cross-reactive proteins. The nucleotide sequence of the P. denitrificans DNA fragment inserted in this clone has been determined and shown to contain the full methanol dehydrogenase structural gene. DNA cross-hybridization was found with DNA fragments which have been reported to contain the methanol dehydrogenase structural genes from Methylobacterium sp. strain AM1 and Methylobacterium organophilum.

Alcohol Oxidoreductases↗
PubMed1987

[Brain mapping--topographic demonstration of the EEG and evoked potentials in psychiatry and neurology].

Brain mapping of EEG and evoked potentials permits the topographic display of electrical activity of the brain and is superior to conventional polygraphic procedures. Data from 16 scalp electrodes and two ear reference electrodes were worked up. The spontaneous EEG and the EEG during different testing conditions to activate particular brain regions was measured. 2 s EEG data segments were subjected to spectral analysis by a fast Fourier transformation (FFT). For late evoked potentials (VEP, AEP, SEP and P300) a single value representing the amplitude of EP at each 2-ms poststimulus latency point served for subsequent topographic mapping. Statistical techniques (Student's t-test) have been used in conjunction with EEG and EP data to render visible the regions where a clinical population differ from normal subjects. The results show abnormalities of EEG and EP in patients with psychical und neurological diseases.

Arousal↗
PubMed1986

Prediction of outcome and utilization of medical services in a prospective study of first onset schizophrenics. Results of a prospective 5-year follow-up study.

After an introduction on design and definition of constructs, followed by an overview on case-finding, description of cohort and epidemiological considerations, this paper presents results on (social) disability (course of disability, prediction of disability), reported symptoms (course of symptomatology, prediction of symptomatology), observed (psychological) impairments (course of impairments, prediction of impairments, and value of impairment scores as predictors) and the utilization of medical services (scale of predominant utilization levels, longitudinal pattern of care, proportions of time in and out of hospital, prediction of length of hospitalization and cumulative time in rehabilitation institutions) in an epidemiological cohort of first onset schizophrenics prospectively over 5 years.

Female↗