Uptake of phosphatidylserine-containing liposomes by liver sinusoidal endothelial cells in the serum-free perfused rat liver.

We studied the kinetics of hepatic uptake of liposomes during serum-free recirculating perfusion of rat livers. Liposomes consisted of phosphatidylcholine, cholesterol and phosphatidylserine in a 6:4:0 or a 3:4:3 molar ratio and were radiolabelled with [3H]cholesteryl oleyl ether. The negatively charged liposomes were taken up to a 10-fold higher extent than the neutral ones. Hepatic uptake of fluorescently labelled liposomes was examined by fluorescence microscopy. The neutral liposomes displayed a typical Kupffer cell distribution pattern, in addition to weak diffuse staining of the parenchyma, while the negatively charged liposomes showed a characteristic sinusoidal lining pattern, consistent with an endothelial localization. In addition, scattered Kupffer cell staining was distinguished as well as diffuse parenchymal fluorescence. The mainly endothelial localisation of the negatively charged liposomes was confirmed by determining radioactivity in endothelial and Kupffer cells isolated following a 1-h perfusion. Perfusion in the presence of polyinosinic acid, an inhibitor of scavenger receptor activity, reduced the rate of uptake of the negatively charged liposomes twofold, indicating the involvement of this receptor in the elimination mechanism. These results are compatible with earlier in vitro studies on liposome uptake by isolated endothelial cells and Kupffer cells, which showed that in the absence of serum also endothelial cells in situ are able to take up massive amounts of negatively charged liposomes. The present results emphasize that the high in vitro endothelial cell uptake in the absence of serum from earlier observations was not an artifact induced by the cell isolation procedure.

Power spectra of the natural input to the visual system.

The efficient coding hypothesis posits that sensory systems are adapted to the regularities of their signal input so as to reduce redundancy in the resulting representations. It is therefore important to characterize the regularities of natural signals to gain insight into the processing of natural stimuli. While measurements of statistical regularity in vision have focused on photographic images of natural environments it has been much less investigated, how the specific imaging process embodied by the organism's eye induces statistical dependencies on the natural input to the visual system. This has allowed using the convenient assumption that natural image data are homogeneous across the visual field. Here we give up on this assumption and show how the imaging process in a human model eye influences the local statistics of the natural input to the visual system across the entire visual field. Artificial scenes with three-dimensional edge elements were generated and the influence of the imaging projection onto the back of a spherical model eye were quantified. These distributions show a strong radial influence of the imaging process on the resulting edge statistics with increasing eccentricity from the model fovea. This influence is further quantified through computation of the second order intensity statistics as a function of eccentricity from the center of projection using samples from the dead leaves image model. Using data from a naturalistic virtual environment, which allows generation of correctly projected images onto the model eye across the entire field of view, we quantified the second order dependencies as function of the position in the visual field using a new generalized parameterization of the power spectra. Finally, we compared this analysis with a commonly used natural image database, the van Hateren database, and show good agreement within the small field of view available in these photographic images. We conclude by providing a detailed quantitative analysis of the second order statistical dependencies of the natural input to the visual system across the visual field and demonstrating the importance of considering the influence of the sensory system on the statistical regularities of the input to the visual system.

[Pain specialist in the assessment process]. / Der Schmerztherapeut bei der Begutachtung.

Pain specialists are often involved in assessing social medical aspects of chronic pain patients. A standardized examination in the assessment process is not published. Data and statements on the assessment process between 1993 and 1997 were recorded from 15 experts by questionnaire. Statements to 568 reports were made. The majority of performance impairments were caused by back pain (35.9%) and headache (19.3%). All examiners integrated a psychological assessment. Although the assessment processes were very different, all examiners fulfilled the minimal criteria of the presented process for assessment of chronic pain patients. Verifying the symptoms as well as capturing some aspects of aggravation proved to be problematic. The present assessment practice is discussed with regard to the unequal procedure. On basis of the received data and the own experience in examination the process of structured assessment of chronic pain patients is presented under medical and psychological aspects. It contains a recommendation of a standardized process with minimal criteria and an optional supplement of the standardized process with problematical patients (e.g.demonstration, aggravation, simulation). Minimal demands on a qualified assessment of chronic pain patients should contain the study of the history, the German Pain-Questionnaire, the analysis of all the painful complaints with weighting their importance, the examination and the basic registration of sensational, emotional, cognitive, behavioral and social aspects of the chronic pain syndrome. An appended glossary of the most usable psychological tests with comments on their validation criteria aims to provide a more standard multimodal assessment of chronic pain patients complaints and functionability.