Quercetin in association with moderate exercise training attenuates injuries induced by experimental diabetes in sciatic nerves.

Diabetic neuropathy (DN) is a frequent, serious and debilitating chronic complication of diabetes mellitus (DM). Hyperglycemia, oxidative and nitrosative stress are involved in causing nerve damage in several animals, humans and experimental models of diabetes. This study was designed to investigate the synergistic cumulative neuroprotective effect of quercetin administration and moderate exercise training on sciatic nerves injuries in streptozotocin (STZ)-diabetic rats. DM was induced in Wistar rats by intraperitoneal administration of STZ (60 mg/kg). The diabetic rats received quercetin (30 mg/kg body weight/day) and performed an exercise training program (30 minutes/day, 5 days/week) for 5 weeks. Various biochemical parameters of oxidative and nitrosative stress were determined and histopathological evaluations were performed from sciatic nerves. Diabetic rats showed significantly increased oxidative and nitrosative stress parameter levels in the sciatic nerves. Diabetic trained rats treated with quercetin exhibited a significantly reduced hyperglycemia and its metabolic abnormalities induced by intraperitoneal administration of STZ. Histological alterations of the sciatic nerves induced after STZ administration were restored by administration of quercetin. Quercetin administration in association with moderate exercise training not only attenuated the diabetic condition but also restored sciatic nerves injuries by controlling hyperglycemia to down-regulate the generation of free radicals, as well as the elevation of antioxidant enzymes.

Histological changes in the vulva and vagina from ovariectomised rats undergoing oestrogen treatment.

BACKGROUND: The purpose of this study was to assess the histological changes occurring in the vagina and vulva in ovariectomised female rats, as well as the response to the administration of injectable oestrogens. MATERIAL AND METHODS: We used 30 female Wistar white rats, distributed as follows: group 1 - the control group, group 2 - the operated but untreated rats, and groups 3, 4 and 5 - operated rats, to which oestrogenic treatment was administered (Estradiol, Estradurin, Sintofolin) at a dosage of 0.2 mg/rat/day. After 14 days of treatment, all animals were sacrificed and vaginal and vulvar biopsies were taken from all groups. RESULTS: In group 2, we encountered structural changes of the vaginal mucosa, with severe atrophy and alterations in the thickness of the vagina and vulva. In groups 3, 4 and 5 we found marked hyperplasia of the vaginal and vulvar epithelium, eosinophilic and mast cell infiltration in the chorion. CONCLUSIONS: Our study proves that the histopathological changes during anoestrus after administration of oestrogens are cell hyperplasia, thickening of the superficial mucosal layer, eosinophilic and mast cells infiltrations, and chorionic congestion. Furthermore, we demonstrated that Estradiol therapy induces the most evident histological changes when compared to synthetic oestrogens such as Estradurin or Sintofolin.

Protective effects of Quercetin and chronic moderate exercise (training) against oxidative stress in the liver tissue of streptozotocin-induced diabetic rats.

Background To investigate the protective effects of Quercetin administration associated with chronic moderate exercise (training) on oxidative stress in the liver in streptozotocin-induced diabetic rats. Methods Diabetic rats that performed exercise training were subjected to a swimming training program (1 hour/day, 5 days/week, 4 weeks). The diabetic rats received natural antioxidant, Quercetin (20 mg/kg body weight/day) for 4 weeks. At the end of the study, all animals were sacrificed and liver samples were collected for estimation: some oxidative stress markers (malondialdehyde, MDA and protein carbonyls groups, PC), the activity of antioxidant enzymes (superoxide dismutase, SOD and catalase, CAT), reduced glutathione (GSH) level and reduced (GSH) and oxidized (GSSG) glutathione ratio. Results Diabetic rats submitted to exercise training showed significantly increased the oxidative stress markers (MDA and PC) and a reduction of antioxidant enzyme (SOD and CAT) activity, GSH level and GSH/ GSSG ratio in hepatic tissues. A decrease in the levels of oxidative stress markers associated with elevated activity of antioxidant enzymes, the GSH level and GSH/GSSG ratio in the hepatic tissue were observed in Quercetin-treated diabetic trained rats. Conclusions These findings suggest that Quercetin administration in association with chronic moderate exercise exerts a protective effect in diabetes by attenuating hyperglycemia-mediated oxidative stress in hepatic tissue.

Set-size and chromatic uncertainty in an accuracy visual search task.

Thresholds for chromatic differences were measured in a simple visual search task in which the target differed from the distractors in chromaticity only. In Experiment 1, the spatial separation between stimulus elements was varied. Slopes of threshold versus set-size (2-16) for elements in close proximity were somewhat elevated, suggesting non-independence of the stimulus elements. In Experiment 2, chromatic uncertainty was introduced to increase the attentional load beyond that accomplished with the set-size manipulation. The results were accounted for by a model assuming no limit in attention capacity. Furthermore, chromatic uncertainty was successfully modeled as a simple increase in the number of monitored signals.

Uncertainty, attentional capacity and chromatic mechanisms in visual search.

Two general questions were investigated using a visual search task. First, we asked whether effects of target uncertainty on reaction time varied with the discriminability of the target and distractors. Second, a higher order chromatic mechanism model was tested against a flexible model in which the signals in cardinal color-opponent mechanisms are combined through an attentional process. The models were tested by measuring the effects of target uncertainty on search time. A regression analysis indicated that the magnitude of the uncertainty effect was approximately constant in logarithmic units as a function of the chromatic difference between the target and distractors. The constant magnitude of the uncertainty effect suggested that an attentional capacity limit was exceeded when observers were required to monitor several chromatic mechanisms at several locations. The results of experiments 3 and 4 suggested that search for chromatic targets among distractors was mediated by diagonally tuned higher order chromatic mechanisms, rather than by signals in cardinal color-opponent mechanisms that were combined through an attentional mechanism.

The achromatic mechanism and mechanisms tuned to chromaticity and luminance in visual search.

The purpose of the study was to determine whether visual search can be mediated by an achromatic, or luminance, mechanism in which signals are independent of the chromaticity of the stimuli. Experiments were designed to determine whether variability in the chromaticity of distractor stimuli made it more difficult to search for a target that differed from the distractor stimuli in luminance. Variability in the chromaticity of the distractors had little or no effect on search times when the target stimulus was white. Variability in the chromaticity of the distractors increased search times when the target was a reddish or bluish chromaticity. Results obtained with white targets suggest that these searches are mediated by an achromatic mechanism in which the signals are independent of the chromaticity of the stimuli. Results obtained with reddish and bluish targets suggest that searches for those targets may be mediated by mechanisms tuned to both chromaticity and luminance. Further experiments in which observers searched for targets that differed from distractors in both chromaticity and luminance provided additional support for the second conclusion.

Interactions between achromatic and chromatic mechanisms in visual search.

The purpose of this study was to explore the interaction between achromatic information and chromatic information in a visual search task. It is widely accepted that signals in second stage color opponent mechanisms vary with both the luminance and chromaticity of a stimulus. However, detection experiments suggest a large degree of independence between chromatic thresholds and achromatic thresholds. The independence at threshold has led to the proposal of a third processing stage in which achromatic and chromatic information is separated. Experiments were designed to determine if variability in the luminance of distractor stimuli made it more difficult to search for a target that differed in chromaticity. When the chromaticity of the distractors was held constant variability in distractor luminance had little effect on search performance, but when signals in second stage color opponent mechanisms were held constant variability in distractor luminance resulted in poorer performance. The results suggest that search for chromatic targets is mediated by a processing stage that calculates the ratio of chromatic and achromatic signals so that the chromatic signal is independent of stimulus luminance.

Luminance discrimination, color contrast, and multiple mechanisms.

The purpose of this study was to investigate the effect of color contrast on luminance discrimination. Observers were required to indicate the more intense of two stimuli presented briefly in a surround. In some conditions the two stimuli were the same chromaticity as the surround, while in other conditions the stimuli differed in chromaticity from the surround. The luminance of the fixed test stimulus was varied in different conditions over a range from below the surround level to above the surround level. Difference thresholds were proportional to the luminance difference between test and surround over much of the range. However, difference thresholds were higher at low luminance contrasts when the chromatic contrast between the stimuli and the surround was high. Results also indicate that the effects of chromatic contrast may be mediated by local contrast mechanisms, but that the relationship between threshold and luminance contrast is not mediated entirely by these local contrast mechanisms.

Red-green color discrimination as a function of stimulus field size in peripheral vision.

Red-green color-discrimination thresholds were measured at eccentricities of 10 and 25 deg in the nasal retina. Thresholds were measured as a function of stimulus field size both during the cone plateau and after dark adaptation. During the cone plateau, threshold decreased with increasing field size, but the effect of field size was dependent on the color of the test stimulus. The decrease in threshold was greater for yellow and orange test stimuli than for red and green tests. Two factors, summation and opponent-mechanism adaptation, appear to affect the relation between threshold and field size. An equation suggested by Boynton and Kambe in 1980 [Color Res. Appl. 5, 13 (1980)] provides a good description of the variation in thresholds with field size and eccentricity. After dark adaptation, thresholds increased for all test colors, suggesting that rod signals reduce discrimination. The dark-adapted thresholds could be described well by the addition of a rod term to the Boynton-Kambe equation.

Red-green color discrimination in peripheral vision.

Color discrimination thresholds were measured for four colors from the red-green portion of the visible spectrum. Thresholds were measured for a stimulus field 1.5 deg in diameter in the fovea and at three locations on the nasal retina (eccentricities of 5, 20 and 40 deg). Outside the fovea threshold increased exponentially with eccentricity and the slope of the function was similar for all four standard colors. Peripheral thresholds were adequately described by an equation developed for foveal red-green thresholds by Boynton and Kambe [(1980) Color Research and Applications, 5, 13-23] and also by a modified form of this equation containing a rod term. Differences between foveal and peripheral thresholds were characterized by changes in two coefficients in the equations. The CIELUV color difference equation also provided a reasonably good description of peripheral thresholds.

Chromaticity and luminance as coding dimensions in visual search.

Visual search times were measured as a function of chromaticity and luminance differences between a target and distractor stimuli. Results showed that mean search time increased linearly with the number of distractors if the luminance difference between target and distractors was small but was roughly constant if the luminance difference was large. Similar results were previously found for chromaticity differences. With the number of distractor stimuli held constant, the mean search time decreased with increases in the difference between target and distractors, up to some critical difference. Further increases in target-distractor difference had little effect. Results were similar for targets defined by luminance and chromaticity. There was some advantage to combining luminance differences with chromaticity differences when the target was dimmer than the distractors. Generally there was no advantage for combining a chromaticity difference with a luminance difference when the target was brighter than the distractors.

Visual search for color differences with foveal and peripheral vision.

Color differences required for fast parallel searches were measured for small and large display fields. The main purpose of the measurement was to test the hypothesis that serial searches obtained with small color differences in large display fields are due to poor discrimination in the peripheral visual field and to the need for foveal fixation. Results do not support this hypothesis but show that the color differences required for parallel search are just as large in a display confined to an area roughly the size of the fovea as in a large display. However, results also show that the color difference required for a fast, parallel search is dependent on the size of the stimuli in a large display field. This result is consistent with the possibility that poor discrimination in the periphery may contribute to the size of the required differences if the stimuli are small.

Critical color differences determined with a visual search task.

Response times were measured for a visual search task in which the observer was required to find a target that differed from distracting stimuli only in color. In the first experiment the search time was measured as a function of display density for both small and large color differences. With small color differences response time increased with display density, indicating a serial search, but with large color differences response time was constant, indicating a parallel search. In the second experiment the color difference required for parallel search was measured in eight different directions from the distracter chromaticity. These color differences were much larger than threshold color differences and were not well represented by the ellipse used to describe the threshold contour around a point in color space.

Analysis of color-matching ellipses in a cone-excitation space.

Color-discrimination ellipses derived from the variability of color-matching data of six observers are analyzed in a normalized constant-luminance cone-excitation space. The analysis shows that the ellipses do not vary significantly in shape with chromaticity, observer, or experimental conditions. The discrimination contours are predictable from the thresholds on the two cardinal axes of this space; these are used to normalize the data at each chromaticity for each observer. Thresholds on these two axes vary with chromaticities, individuals, and experimental conditions in accordance with simple and familiar laws.

Color discrimination and neural coding in color deficients.

Rayleigh color match ranges obtained from color deficient observers varied considerably as a function of spatial and temporal parameters of stimulus presentation. The results suggest that color discrimination losses in color deficients result from abnormalities in the spatial and temporal properties of neural coding in addition to cone photopigment abnormalities.

Equilibrium hue judgements of dichromats.

It is generally held that protanopes and deuteranopes see only regions of blues and yellows in the visible spectrum, with an achromatic point, called the neutral point, separating these regions. Considerations of a zone model of color vision for the dichromatic observer led us to predict that a reduced form of red/green discrimination would allow equilibrium blue judgements to be made by protanopes. We show that protanopes can make equilibrium blue determinations with as much reliability as they make neutral point settings. Our results indicate that protanopes but not deuteranopes are able to rely on a reduced form of red/green discrimination in the short wavelength part of the spectrum. Protanopes describe wavelengths longer than the neutral point as yellow. Between the neutral point and equilibrium blue, different wavelengths are described as having varying aspects of blue and green; and short of equilibrium blue they appear reddish blue. For dueteranopes, the spectrum longer than the neutral point appears yellow, and short of it, blue. The results of our experiments showing that the protanopic equilibrium blue is invariant with intensity variations, as it is in the trichromat, add support to the idea of a reduced form of red/green discrimination for protanopes. Our results also allow the evaluation of various models of protanopia.

Similarity of normalized discrimination ellipses in the constant-luminance chromaticity plane.

Discrimination steps were measured for three subjects, along oblique axes passing through nine points in a 25 td constant-luminance chromaticity plane. When plotted in a normalized cone-excitation chromaticity diagram, the best-fitting discrimination ellipses for a given subject have approximately the same shape and orientation regardless of the reference chromaticity. Their orientation is consistent with the hypothesis that excitation of B-cones affects the red-green opponent balance, otherwise determined by R- and G-cone excitations, in a manner independent of initial cone-excitation levels. The CIELAB formula predicts an orientation for normalized ellipses in agreement with the data, but it also predicts systematic changes in the ratio of minor to major axes which are not observed experimentally.

Cone mechanisms underlying the color discrimination of deutan color deficients.

An alternation method of color matching was used to obtain a series of extended Rayleigh matches from several deutan color deficients with varying degrees of color discrimination. With large stimulus fields there were differences in the matches made by observers with good color discrimination and the matches made by observers with poor color discrimination. The matches made by observers with poor discrimination could not be modeled with normal cone action spectra. When the field size was reduced the matches of all observers were quite similar and could be modeled with two cone action spectra that were normal in shape and separated by approximately 5 nm. Results suggest that individual differences in ability to discriminate color among deutan observers are not solely related to differences in the cone action spectra.

Additivity of dichromatic color matches to short-wavelength lights.

The additivity of color matches to short-wavelength lights was examined in observers who behaved as red-green dichromats under the stimulus conditions used. Color matches were obtained at several luminance levels and on several different adapting backgrounds. The range of mixtures acceptable as a match and the midpoint of this range varied considerably over different conditions. However, for each observer, a set of mixtures that remained a match under all conditions could always be found. Results suggest that the additivity laws hold for these observers in the sense that there is a color match that remains a match under all conditions.

Homogeneity of large-field color matches in congenital red-green color deficients.

Rayleigh matches obtained from red-green color deficients with conventional methods show large individual differences within diagnostic categories. Similar matches obtained from the same observers with a large-field substitution method show much less variability and suggest that the differences observed among simple anomals, extreme anomals, and dichromats with conventional methods are probably not solely due to the visual pigments contained in the cones. A theory that attributes these differences to the relative number of abnormal cones present in the observer's retina is described.