Brain tissue slice thickness monitored by ion-profile measurement.

The thickness of a brain tissue slice preparation governs the amount of time required for substances to diffuse from the bathing solution to preparation. Slice thickness may increase during the experiment, e.g., in cases of hypoxia where osmotic pressure within the tissue changes, enabling water to enter the preparation. With increasing slice thickness diffusion paths from the bath to central layers of the preparation increase possibly resulting in an insufficient O2 supply to central layers. Therefore, the actual slice thickness should be monitored during the experiment especially in cases where osmolarity is changed or during hypoxia. This paper describes a simple method to monitor the actual slice thickness using ion profiles measured by ion selective micro-electrodes driven at a constant rate of approximately 10 microns/s (sample rate ca. 10/s). The method is based on steep changes in the concentration gradients at the upper and lower surfaces of the preparation induced by simple diffusion in the presence of concentration gradients between the non-tortuous bath and the tortuous tissue. The thickness of the preparation is derived from the location of the steep gradient changes as reflected by the registered profile.

Diffusion in slice preparations bathed in unstirred solutions.

A diffusion model is described here, which allows for the estimations of drug concentration changes in porous media, such as in slice tissues of the central nervous system (CNS) bathed in unstirred solutions following abrupt changes of drug concentration. This model may be used for the interpretation of data obtained in neuropharmacological studies if (i) the diffusion coefficient of the molecules under investigation is constant within the excised tissue, (ii) drug molecules are diffusing only in the extracellular space (ECS) and are not bound by the tissue, (iii) drug molecules diffuse mainly within one dimension, (iv) the drug concentration in the bath is changed within 5 s, and (v) the bathing solutions at the surfaces of the slices are stagnant during the period of diffusion. To test this model, estimated tetramethylammonium (TMA) ion concentrations within a tissue slice were compared to actual TMA concentration changes measured at the same depth in the tissue of hippocampal slices by means of TMA-sensitive microelectrodes. A statistically significant correlation (P less than 0.05) was observed between the estimated and measured TMA concentrations which indicates that the model is valid under the defined conditions.

pO2-dependent distribution of potassium in hippocampal slices of the guinea pig.

The distribution of extracellular K+-concentration (cK+s) in 200-1000-micron thick hippocampal slices was studied with ion-selective microelectrodes. In ca. 500-micron thick slices cK+s increased from the surface to the innermost layers by ca. 2 mmol/liter if the pO2 of the bath (pBO2) ranged from 300-600 mm Hg and if the temperature was 28 degrees C. In thicker slices and lowered pO2-values further elevations of cK+s were observed. In vital slices thinner than 500 micron cK+s-values exceeded the potassium-concentration of the bath (cK+B) only when pBO2 was markedly lowered. When pBO2 was reincreased in such thin slices, cK+s rapidly declined and often decreased transiently below ck+B. Similar undershoots of cK+s were observed when cK+B was lowered from high to normal levels. The rapid decline was blocked by hypoxia, ouabain, antimycine and a temperature of 18 degrees C. A stepwise rise of cK+B also caused rapid changes of cK+s in vital thin slices. The rates of changes, however, were hardly affected e.g. by a transient hypoxia. Diffusion did not contribute significantly to these steep changes of cK+s. These rapid distribution modes were widely missing in slices thicker than 500 micron. Therefore in such preparations, the extracellular microenvironment of neurons may markedly differ from the ionic concentrations in the bath.

Model calculations of oxygen supply to tissue slice preparations.

Excised tissue slice preparations are widely used in experimental medicine, pharmacology and physiology. Since slices are separated from the vascular system they have to be supplied with oxygen from the bath solution in which the slices are fixed. Otto Warburg designed a simple model of oxygen diffusion in such a tissue preparation. His model does not utilise some important parameters which may influence the oxygen distribution in the tissue: Unstirred bathing, non-vital superficial layers of tissue slices, damage by the cutting procedure and the influence of volume fraction and tortuosity over the oxygen supply. A compartment model has been designed to test how these parameters affect the oxygen distribution in tissue slices. The calculations have shown that all parameters may considerably affect the oxygen supply to tissue slices. Therefore, they have to be considered in the analysis of oxygen distribution and consumption in tissue slice preparations.

Time courses of lidocaine effects on sodium membrane currents in small and large neurons.

Time courses of effects of lidocaine on sodium currents and sodium dependent action potentials were studied in somata of small and large neurons. Cultured rat sensory spinal ganglion cells (diameter: 30 microns) and neurons of the buccal ganglion of Helix pomatia (diameter: 150 microns) served as the test cells. The latency of the suppressive action of lidocaine was the longer the larger the of the cells was. Maximal blocking effects occurred within 10 min in sensory spinal ganglion cells and within 40 min in snail neurons. Model calculations based on the assumptions (i) that lidocaine is distributed in the extra- and intracellular space by simple diffusion and (ii) that the drug concentration at the outer surface of the cells is elevated stepwisely, revealed a strong dependency of intracellular concentration changes on the size of the cells. From these findings it is concluded that lidocaine blocks sodium channels primarily from the intracellular side.

Graphical visualization of the pattern of muscular weakness in neuromuscular diseases.

A graphical method for the description of the spatial extension and temporal development of muscular weakness in neurological disorders implemented on a personal computer is described. Different degrees of paresis of individual muscle groups are represented by distinct grey tone values or colors in a semi-anatomic scheme. This representation provides a rapid recognition of essential features of the clinical syndrome, such as the pattern of muscular weakness and its temporal development. In parallel to the results of force testing, the results of other investigations in the same muscle groups can also be presented by the graphical method.

[Optimizing histological image data for 3-D reconstruction using an image equalizer]. / Optimierung histologischer Bilddaten für die 3D-Rekonstruktion mit Hilfe eines Image-Equalizers.

Bone cells form a wired network within the extracellular bone matrix. To analyse this complex 3D structure, we employed a confocal fluorescence imaging procedure to visualize live bone cells within their native surrounding. By means of newly developed image processing software, the "Image-Equalizer", we aimed to enhanced the contrast and eliminize artefacts in such a way that cell bodies as well as fine interconnecting processes were visible.

New trends in computer graphics and computer vision to assist functional neurosurgery.

Computer vision (CV), a computerized method to analyze digital images (e.g., CT scans), and computer graphics (CG), a set of computer programs for displaying two, three- or four-dimensional data, are recent computer techniques which are appropriate to assist functional stereotactic surgery. CV and CG are useful for the evaluation of spatial relations between anatomical structures and the sites of spontaneous neuronal noise or of electrophysiological stimulation data gathered during stereotactic interventions for movement disorders. CV and CG can be employed for stereotactic operation planning, during the operation for target point evaluation and for further postoperative data analysis.

Transformation modes in computerized human thalamic brain mapping.

An exact transfer of data intraoperatively gathered in thalamic nuclei to an anatomical atlas requires an efficient mathematical transformation mode. Three different kinds of transformation modes were analyzed: First, the AC PC distance was used as a parameter to correlate data with the atlas coordinate system. Second, the influence of the patients 3rd ventricle widths on the transformation procedure. Third, a transformation mode was performed based on "noise"-data, registered when the electrode penetrated patient's thalamus. This method was also used to combine the atlas and CT images.

Computer-assisted analysis of functional anatomy of human ventrolateral thalamus.

A three-dimensional map was created by a computer-assisted analysis of functional and somatotopic organization of the target area in the human ventrolateral thalamus. Stimulation in the target area mostly elicited increased tone in skeletal muscles, with a concomitant decrease or stop of tremor. Despite averaging of all responses, no clear somatotopic organization could be demonstrated for the tonifying stimulation effects. In addition, somatosensory-evoked potentials were recorded, indicating an afferent projection to the target area.