Biomedical subjects

T Kammer

Publications and source records attributed to T Kammer.

23 records · Page 2Linked to original sources

PubMed1995

[Neurofunctional MRI imaging of higher cognitive performance of the human brain].

Functional magnetic resonance imaging (fMRI) offers a powerful experimental tool for mapping activated cortical regions in man. Thereby, the paramagnetic deoxyhemoglobin in the red blood cells acts as an endogenous susceptibility contrast agent, which allows the noninvasive detection of stimulus-induced transient changes in regional cerebral blood flow and volume. Fifteen normal subjects were examined on a conventional 1.5-T MR system to visualize cortical activation during the performance of high-level cognitive tasks. A computer-controlled videoprojector was employed to present psychometrically optimized activation paradigms. Reaction times and error rates of the volunteers were acquired online during stimulus presentation. The time course of cortical activation was measured in a series of strongly T2*-weighted gradient-echo images from three or four adjacent slices. For anatomical correlation, picture elements showing a stimulus-related significant signal increase were color-coded and superimposed on T1-weighted spin-echo images. Analysis of the fMRI data revealed a subtle (range 2-5%), but statistically significant (P < 0.05) increase in signal intensity during the periods of induced cortical activation. Judgment of semantic relatedness of word pairs, for example, activated selectively cortical areas in left frontal and left temporal brain regions. The strength of cortex activation in the semantic task decreased significantly in the course of stimulus presentation and was paralleled by a decrease in the corresponding reaction times. With its move into the area of cognitive neuroscience, fMRI calls both for the careful design of activation schemes and for the acquisition of behavioral data. For example, brain regions involved in language processing could only be identified clearly when psychometrically matched activation paradigms were employed. The reaction time data correlated well with selective learning and thus helped to facilitate interpretation of the fMRI data sets.

Arousal↗

PubMed1994

Proinflammatory cytokines in serum of patients with acute cerebral ischemia: kinetics of secretion and relation to the extent of brain damage and outcome of disease.

The release of the proinflammatory cytokines IL-1 beta, IL-6, TNF-alpha and soluble TNF-receptors p55 and p75 in peripheral blood was serially determined in 19 patients with acute cerebral ischemia. Only patients admitted within 4 h following onset of symptoms were studied. In contrast to serum levels of IL-1 beta, TNF-alpha and TNF-receptors, which did not exhibit a significant response, IL-6 showed a significant increase of serum levels already within the first hours following onset of disease and reached a plateau at 10 h until day 3 and returned to baseline by day 7. The increase of levels of this cytokine was significantly (P < 0.05) correlated with increasing volumes of brain lesion and was also significantly (P < 0.005) associated with poor functional and neurological outcome. The increase of levels of IL-6 despite a considerable dilution in peripheral blood shown in this preliminary study suggests an early inflammatory response in ischemic brain lesion.

Activities of Daily Living↗

PubMed1993

Electrophysiological characterization of class III activity of a verapamil derivative in guinea-pig cardiac tissues.

In isolated guinea-pig papillary muscle ([K+]o: 4.7 mmol/l, stimulation rate: 1 Hz) the verapamil derivative NN-bis-(3,4-dimethoxyphenethyl)-N-methylamine)-HCl (YS035; 0.3-100 mumol/l) increased the action potential duration measured at 90% repolarization level (APD90) up to 132% of control and enhanced the force of contraction (Fc) up to 125% of control while resting potential (RP) and the maximum upstroke velocity (Vmax) remained nearly unchanged. At 300 mumol/l YS 035, the membrane became depolarised and action potentials could no longer be elicited. These effects were reversed during wash-out. The increase of ADP90 was largest at 0.05 Hz, and the drug-induced effect continuously declined with an increase in stimulation frequency to 2 Hz. Control ADP90 was correlated to the absolute increase of ADP90 (r = 0.84). In atrial muscle the effect of YS 035 on APD90 was more pronounced than in papillary muscle. The Vmax of slow responses ([K+]o: 27 mmol/l, [Ba2+]o: 0.5 mmol/l) was not affected by concentrations as high as 30 mumol/l YS 035, whereas APD90 was enhanced. An increase in the stimulation rate (0.05 to 0.33 Hz) induced only a small decrease of Vmax at 100 mumol/l YS 035. According to this electrophysiological characterisation YS 035 shows Class III antiarrhythmic properties.

Action Potentials↗

PubMed1991

Inhibition of potassium outward currents and pacemaker current in sheep cardiac Purkinje fibres by the verapamil derivative YS 035.

The electrophysiologic mode of action and potency of the verapamil derivative YS 035 (N,N-bis-(3,4-dimethoxyphenethyl)-N-methyl amine) were investigated in sheep cardiac Purkinje fibres. Action potential duration measured at a repolarization level of -60 mV (APD-60) and membrane currents recorded with the two-microelectrode voltage-clamp technique were evaluated. At 10 mumols/l YS 035 APD-60 was increased to about 115% of reference. Prolongation measured as percentage of the respective control exhibited on the average no dependence on stimulation frequency (0.17-2 Hz). At 100 mumols/l membrane became depolarized to about -50 mV and action potentials could no longer be elicited. Further study was focussed on effects on outward currents, mostly activated at a frequency of 0.05 Hz. Transient outward current (ito) was completely blocked at 100 mumols/l and half-maximal inhibition occurred at about 14 mumols/l. Inwardly rectifying potassium current (ik1) was reduced to 47% of reference at 100 mumols/l. An initially activating outward current at positive membrane potentials (iinst) was reduced to 73% at 100 mumols/l. Time-dependent (delayed) outward current (iK) was on the average not affected up to 100 mumols/l. Besides inhibition of repolarizing outward currents YS 035 completely blocked pacemaker current (if) at 100 mumols/l and half-maximal reduction was achieved at 5 mumols/l. YS 035 (1-100 mumols/l) did not clearly affect time constants of activation at selected test potentials (IK: +35 mV; if: -90 mV) or inactivation (ito: 0 mV). Voltage-dependent control mechanisms of currents (ito, if) were not influenced by YS 035 but the amount of available current was reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMedDate not supplied

Modulation of action potential duration by inhibition of the transient outward current in sheep cardiac Purkinje fibers.

In sheep cardiac Purkinje fibers concentration-dependent inhibition of transient outward current (ito) by 4-aminopyridine (4-AP, 3-1000 mumol/l) was recorded with the two-microelectrode voltage-clamp technique, and correlated effects on action potential duration measured at -70 mV (APD-70) were investigated. Half-maximal inhibition of ito-amplitude occurred at 15 mumol/l 4-AP. The drug exhibited no major effect on voltage-dependent control of inactivation but reduced the maximally available ito-current. At different activation frequencies (0.05 Hz, 0.25 Hz, 1 Hz) an equal amount of ito-current, measured as percentage of the respective control, was inhibited by 4-AP. The APD-70 was on the average increased by 4-AP (3-500 mumol/l) in a concentration-dependent manner up to 151% of control. The drug-induced prolongation, measured as percentage of the respective control, was independent of stimulation frequency (0.05 Hz, 0.25 Hz, 1 Hz). Prolongation of APD-70 was on the average more pronounced for short action potentials (APD-70 < 150 ms: 169% of reference) than for longer ones (APD-70 150-300 ms: prolongation to 117% of reference; 500 mumol/l 4-AP; 0.25 Hz stimulation rate). Few long control signals (APD-70 > 300 ms) were shortened by 4-AP. These results indicate that inhibition of ito-current by appropriate drugs will result in a reduction of inhomogeneity of action potential duration.

4-Aminopyridine↗