Quantitative assessment of tactile allodynia in the rat paw
We applied and validated a quantitative allodynia assessment technique, using a recently developed rat surgical neuropathy model wherein nocifensive behaviors are evoked by light touch to the paw. Employing von Frey hairs from 0.41 to 15.1 g, we first characterized the percent response at each stimulus intensity. A smooth log-linear relationship was observed, with a median 50% threshold at 1.97 g (95% confidence limits, 1.12-3.57 g). Subsequently, we applied a paradigm using stimulus oscillation around the response threshold, which allowed more rapid, efficient measurements. Median 50% threshold by this up-down method was 2.4 g (1.81-2.76). Correlation coefficient between the two methods was 0.91. In neuropathic rats, good intra- and inter-observer reproducibility was found for the up-down paradigm; some variability was seen in normal rats, attributable to extensive testing. Thresholds in a sizable group of neuropathic rats showed insignificant variability over 20 days. After 50 days, 61% still met strict neuropathy criteria, using survival analysis. Threshold measurement using the up-down paradigm, in combination with the neuropathic pain model, represents a powerful tool for analyzing the effects of manipulations of the neuropathic pain state.
A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. Probable benefits of increasing folic acid intakes.
OBJECTIVES To determine the risk of elevated total homocysteine (tHcy) levels for arteriosclerotic vascular disease, estimate the reduction of tHcy by folic acid, and calculate the potential reduction of coronary artery disease (CAD) mortality by increasing folic acid intake. DATA SOURCES MEDLINE search for meta-analysis of 27 studies relating homocysteine to arteriosclerotic vascular disease and 11 studies of folic acid effects on tHcy levels. STUDY SELECTION AND DATA EXTRACTION Studies dealing with CAD, cerebrovascular disease, and peripheral arterial vascular disease were selected. Three prospective and six population-based case-control studies were considered of high quality. Five cross-sectional and 13 other case-control studies were also included. Causality of tHcy's role in the pathogenesis of vascular disease was inferred because of consistency across studies by different investigators using different methods in different populations. DATA SYNTHESIS Elevations in tHcy were considered an independent graded risk factor for arteriosclerotic vascular diseases. The odds ratio (OR) for CAD of a 5-mumol/L tHcy increment is 1.6 (95% confidence interval [CI], 1.4 to 1.7) for men and 1.8 (95% CI, 1.3 to 1.9) for women. A total of 10% of the population's CAD risk appears attributable to tHcy. The OR for cerebrovascular disease (5-mumol/L tHcy increment) is 1.5 (95% CI, 1.3 to 1.9). Peripheral arterial disease also showed a strong association. Increased folic acid intake (approximately 200 micrograms/d) reduces tHcy levels by approximately 4 mumol/L. Assuming that lower tHcy levels decrease CAD mortality, we calculated the effect of (1) increased dietary folate, (2) supplementation by tablets, and (3) grain fortification. Under different assumptions, 13,500 to 50,000 CAD deaths annually could be avoided; fortification of food had the largest impact. CONCLUSIONS A 5-mumol/L tHcy increment elevates CAD risk by as much as cholesterol increases of 0.5 mmol/L (20 mg/dL). Higher folic acid intake by reducing tHcy levels promises to prevent arteriosclerotic vascular disease. Clinical trials are urgently needed. Concerns about masking cobalamin deficiency by folic acid could be lessened by adding 1 mg of cobalamin to folic acid supplements.
Quantitative assessment of antimalarial activity in vitro by a semiautomated microdilution technique
A rapid, semiautomated microdilution method was developed for measuring the activity of potential antimalarial drugs against cultured intraerythrocytic asexual forms of the human malaria parasite Plasmodium falciparum. Microtitration plates were used to prepare serial dilutions of the compounds to be tested. Parasites, obtained from continuous stock cultures, were subcultured in these plates for 42 h. Inhibition of uptake of a radiolabeled nucleic acid precursor by the parasites served as the indicator of antimalarial activity. Results of repeated measurements of activity with chloroquine, quinine, and the investigational new drug mefloquine demonstrated that the method is sensitive and precise. Several additional antimalarial drugs and compounds of interest were tested in vitro, and the results were consistent with available in vivo data. The use of P. falciparum isolates with known susceptibility to antimalarial drugs also permitted evaluation of the cross-resistance potential of each compound tested. The applications and expectations of this new test system within a drug development program are discussed.
Quantitative assessment of atherosclerotic lesions in mice.
The well-defined genetic systems of the mouse are proving useful in experimental studies of atherosclerosis. Inbred mouse strains differ in atherosclerosis susceptibility, and several variants of apolipoproteins have been identified and mapped. This report explores the location and timing of lesion formation in the mouse in an effort to provide a basis for quantitatively comparing groups of mice. After 14 weeks on an atherogenic diet containing 1.25% cholesterol, 15% fat, and 0.5% cholic acid, C57BL/6J female mice had aortic lesions at each of the intercostal arteries, at the junction of the aorta to the heart, and in scattered areas covering 1.1% +/- 0.5 (SD) of the aortic surface. After 9 months on the atherogenic diet, those lesions near the heart and intercostal arteries were extensive, 8% +/- 3 (SD) of the remainder of the aorta was involved in lesions, and lesions were found in the coronary arteries. Results indicated that one suitable location for scoring lesions was in a 300 micron area of the aorta just beyond the aortic sinus. The mean number of lesions/mouse in the selected area after 14 weeks on the atherogenic diet was 1.1 +/- 0.3 (SD). The results were reproducible over 10 separate experiments. The number of lesions per mouse fit a Poisson distribution indicating that the presence of one lesion did not predispose the mouse to acquiring a second lesion. Lesion formation and cholesterol levels did not vary with the season of the year as demonstrated by 9 separate experiments over more than 12 months. Methods of evaluating the number and size of lesions were compared including sizing with a microscope eyepiece grid and computer-assisted planimetry. The resulting data provide reproducible methods of quantitatively comparing lesion formation in various strains or groups of mice, thereby increasing the usefulness of the mouse as an experimental system for atherosclerosis research.
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