PubMed Health⌕ Search

Biomedical subjects

M Schiebe

Publications and source records attributed to M Schiebe.

25 records · Page 2Linked to original sources
PubMed1985

A new sensitive method for the quantification of internal carotid stenoses by means of ultrasound Doppler signal processing.

A new way of processing the ultrasound Doppler spectrum is presented. By introducing a Disturbance Index (DI), based on a double Fourier transformation, the quantitative evaluation of blood flow disturbance is possible. The integral value of this index over the whole cardiac cycle can be used to quantify the degree of lower grade internal carotid artery (ICA) stenoses and plaques. In a preliminary study, this new method has been tested in 18 normal and 10 atherosclerotic carotid arteries against Duplex-scan and angiography. The results were compared with 5 alternative methods of processing the Doppler spectrum.

Carotid Arteries↗
PubMed1984

Synaptic and non-synaptic effects of molluscan cardioexcitatory neuropeptides on locust skeletal muscle.

Neurally evoked contractions of the locust jumping muscle are potentiated by the molluscan cardioexcitatory peptide (FMRFamide) and related peptides. This effect is due to a synaptic and a non-synaptic action of the peptides: (1) excitatory synaptic potentials are increased; (2) excitation-contraction coupling becomes more efficient, as indicated by an increased strength of potassium contractures. Octopus heptapeptide (YGGFMRFamide), which contains the entire enkephalin structure (YGGFM), is 100 times more potent than FMRFamide. Structure-activity studies indicate that the observed actions are not mediated by opioid receptors but are dependent on the C-terminal structure of the peptides.

Animals↗
PubMed1984

Dishabituating effects of an ACTH 4-9 analog in a vigilance task.

Ten male adults were tested in a vigilance task after oral administration of either 40 mg ACTH 4-9 analog, ORG 2766, or placebo in a single three hour session. EEG spectra, averaged auditory evoked responses, heart rate and blood pressure, and behavioral performance were measured during a vigilance task. ACTH 4-9 analog treatment led to a decreased inhibition of the central nervous system across the experiment: to less mean power density and faster center frequencies within the alpha band, and to less attenuated amplitudes of the components of the auditory vertex potential (P50, N100, P200). Treatment effects increased towards the end of the session and might indicate a dishabituating effect, probably due to suppression of inhibitory influences of limbic structures on mesencephalic reticular activity.

Adrenocorticotropic Hormone↗
PubMed1983

Continuous registration of membrane input resistances of small plant cells using a double-pulse current clamp technique for single-electrode impalements : comparison with the conventional two-electrode method.

To measure the cell input resistance in Elodea leaf cells, a new single-microelectrode method was explored by comparing the results with conventional two-microelectrode experiments. The new method takes advantage of the difference in the frequency response curves between electrode and cell impedances. By application of electrical stimuli, which contain specific frequency bands, the different impedances can be analyzed separately. To get a distinct separation in the frequency response of cell and electrode, respectively, the electrode capacitance has to be compensated during the impalement. Different time constants of the cell membrane can be accounted for by adjustment of the stimulus length. It is shown that both the single- and the double-electrode method yield the same results, even if the cell input resistances change considerably during the course of the experiment. This demonstrates the usefulness of the new single-electrode method for continuous measurements of cell membrane resistances, especially in cells so small that the double-electrode method is no longer applicable.

Journal Article↗
PubMed1981

Enkephalin-related peptides: direct action on the octopus heart.

Immunocytochemical evidence for the occurrence of "vertebrate" peptides in the neuropil of the vena cava [12, 13] and the structural similarity between enkephalin precursor peptides and the molluscan cardioexcitatory peptide [16], lead us to study the action of enkephalin-related peptides on the octopus heart. Systemic hearts of Octopus vulgaris were perfused with sea wate and test substances and a crude extract of vena cave were added for 1 min; frequency and pressure were monitored continuously. The heptapeptide Leu5-enkephalin-Arg6-Phe7 and the Met5-analogue, both in the amidized form, displayed dose-response relationship with a sensitivity of about 10 nmol. The C-terminal tetrapeptide amides, Phe-Leu/Met-Arg-Phe-NH2, were active at the same doses. Opiate receptors do not seem to be involved in this action on the octopus heart, as naloxone treatment had no effect. Whereas the N-terminal portion of the heptapeptide is known to be crucial for activity as an opioid, the C-terminal NH2 group is essential for cardioexcitatory activity.

Animals↗
PubMed1980

Sampling membrane potential, membrane resistance and electrode resistance with a glass electrode impaled into a single cell.

A method is demonstrated to measure membrane resistances and membrane potentials of single cells during impalement by a single glass microelectrode. The intention was to develop a procedure which would provide data almost continuously. Therefore, a frequency-dependent voltage divider network has been chosen to represent the basic electrical properties of the electrode and cell membrane, and used to explore its voltage response to a current stimulus, consisting of two rectangular pulses of different widths. It can be shown that the resolution of the method can be improved by inverting this stimulus so that each polarization becomes a relaxation and vice versa. In order to generate, analyze and display this signal continuously, a device has been designed which has been called 'Electrophysiological Monitor, (E1M2)'. E1M2 provides a current stimulus as input into a standard bridge network and can analyze the summed response of the electrode and cell by a set of sample-hold amplifiers. It then decodes and displays the data continuously, as membrane potential (Em), input resistance of the cell (Rinp) and the electrode resistance (Re) respectively. From Rinp the membrane resistance (Rm) can be deduced. The validity of the method has been examined by measuring these parameters in frog muscle cells. Technical design considerations, the accuracy and possible pitfalls with the suggested procedure are discussed.

Animals↗