Impairment of endothelium-dependent arterial relaxation by lysolecithin in modified low-density lipoproteins

Atherosclerosis in animals and humans is associated with an unresponsiveness of arteries and arterioles to endothelium-dependent vasodilators--agents acting on smooth muscle indirectly by stimulating the release from endothelial cells of a vasodilator principle (endothelium-derived relaxing factor). Altered vasomotor regulation in atherosclerosis could partly reflect an injurious action of abnormal lipoproteins on endothelium. Recently, 'cell-modified' or 'oxidized' low-density lipoprotein (EC-LDL) has received increasing attention because of its potential cytotoxic and atherogenic properties. We report here that arteries exposed to EC-LDL in vitro show an endothelium-dependent vasoregulatory impairment closely resembling that of atherosclerotic arteries. Our results indicate that transfer of lysolecithin from EC-LDL to endothelial membranes produces a selective unresponsiveness to receptor-regulated endothelium-dependent vasodilators.     

Acetylcholine contributes through muscarinic receptors to attentional modulation in V1

Attention exerts a strong influence over neuronal processing in cortical areas. It selectively increases firing rates and affects tuning properties, including changing receptive field locations and sizes. Although these effects are well studied, their cellular mechanisms are poorly understood. To study the cellular mechanisms, we combined iontophoretic pharmacological analysis of cholinergic receptors with single cell recordings in V1 while rhesus macaque monkeys (Macaca mulatta) performed a task that demanded top-down spatial attention. Attending to the receptive field of the V1 neuron under study caused an increase in firing rates. Here we show that this attentional modulation was enhanced by low doses of acetylcholine. Furthermore, applying the muscarinic antagonist scopolamine reduced attentional modulation, whereas the nicotinic antagonist mecamylamine had no systematic effect. These results demonstrate that muscarinic cholinergic mechanisms play a central part in mediating the effects of attention in V1.     

Modeling distributions of rare plants in the Great Basin, western North America

In this 2-phase study, we developed field-validated site and landscape-level predictive models for identifying potential rare and endemic plant habitat in the Great Basin of western North America. Four species were chosen to include a range of environmental variability and plant communities. Herbarium records of known occurrences were used to identify initial sample sites. The geographic coordinates, environmental attributes, and vegetation data collected at each site were used to develop 2 predictive models for each species: a field key and a probability-of-occurrence or predictor map. The field key was developed using only field data collected at the sites on environmental attributes and associated species. Predictive maps were developed with a geographic information system (GIS) containing slope, elevation, aspect, soils, and geologic data. Classification-tree (CT) software was used to generate dichotomous field keys and maps of occurrence probabilities. Predictions from both models were then field-validated during the 2nd phase of the study, and final models were developed through an iterative process, in which data collected during the field validation were incorporated into subsequent predictive models. Cross-validated models were >96% accurate and generally predicted presence with >60% accuracy. These models identified potential habitat by combining elevation, slope, aspect, rock type, and geologic process into habitat models for each species. ACRONYMS.—CEC—cation exchange capacity, CT—classification tree, DEM—digital elevation model, GAM—generalized additive model, GIS—geographic information system, GLM—generalized linear model, GPS—geographic positioning system, ROC—receiver operating curves, STATSGO—State Soil Geographic Database, USGS—United States Geological Survey, UTM—Universal Transverse Mercator. Nomenclature and distributions: Welsh et al. 2003, Shultz et al. 2005.