Biomedical subjects

C Redies

Publications and source records attributed to C Redies.

64 records · Page 4Linked to original sources

PubMed1987

Time-dependent changes of lumped and rate constants in the deoxyglucose method in experimental cerebral ischemia.

Time-dependent changes in the lumped and rate constants in a bilateral middle cerebral artery (MCA) occlusion in cats were evaluated. These variables were measured in 11 cats after a sham operation, in five after a 1-h occlusion, in two after a 2-h occlusion, in five after a 4-h occlusion, and in four after a 16-h occlusion. The time course of the cerebral tissue radioactivity [Ci* (t)] was monitored by external coincidence counting during a programmed infusion of [18F]2-fluorodeoxyglucose (FDG). Arterial plasma concentration [Cp* (t)] of tracer was kept constant during the first 45 min. Comparison of k2* and k3* in the sham-operated group, estimated by external coincidence counting, and by the ratio of extraction fractions of glucose and [18F]2-FDG, demonstrated no significant difference between these rate constants in these two groups of animals. The rate and lumped constants were also estimated from Ci* (t) and Cp* (t), as well as from the ratio of extraction fractions of glucose and [18F]2-FDG, respectively, in the MCA occlusion group. Significant decrease in k3* was observed after 1 h of occlusion (20% lower than in the sham operation, p less than 0.05); in k1* decrease occurred within 4 h of occlusion (21% lower than in the sham operation, p less than 0.05). However, decrease in k2* was observed only after 16 h of occlusion (26% lower than in the sham operation, p less than 0.05). Namely, decrease of rate constants occurred first in k3* then in k1* and k2*.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Estimation of cerebral oxygen utilization rate by single-bolus 15O2 inhalation and dynamic positron emission tomography.

This study shows that regional CMRO2 can be estimated by means of nonlinear regression using dynamic positron emission tomographic data acquired during 1 min following single-bolus inhalation of 15O2. The feasibility of simultaneous estimation of CBF, cerebral blood volume (CBV), oxygen extraction ratio (OER), and CMRO2 was assessed by simulations using the model of Mintun et al. Four oxygen metabolic measurements, each consisting of a CBF, CBV, and 15O2 bolus study, were carried out on three volunteers. Regional values for CBF, CBV, OER, and CMRO2 were derived in two ways: from the fits of the time-activity curves of the dynamic 15O2 bolus study alone [CMRO2(fit)] and from the three separate studies [CMRO2 (control)]. For the 56 regions of interest analyzed, using a fit interval of 60 s, CMRO2(fit) was 93.4 +/- 7.8% of CMRO2(control) (mean +/- SD) with a correlation coefficient of r = 0.95. CMRO2(control) ranged from 87 to 290 mumol/min/100 g. Individual simultaneous estimates of CBF, CBV, and OER were not reliable. Finally, we found that the validity of the model was limited in practice to the first minute after tracer inhalation.

Administration, Inhalation↗

PubMed1987

Alternative approach to estimate lumped constant in the deoxyglucose model: simulation and validation.

An alternative method of estimating the lumped constant (LC) in the deoxyglucose model was developed. The LC was estimated using data obtained during the first 10 min after injection of the tracer by a nonlinear least-squares (NLSQ) method. The method does not require a constant plasma concentration. This approach was evaluated in a computer simulation by adding different levels of noise and considering various input functions. Errors in the estimated LC in this and Sokoloff et al.'s conventional method were compared. We found that the approach proposed here results in more reliable estimates of LC. The study in completed in a shorter experimental period, and any shape of the input function can be used. The new technique was then applied to measure whole brain LC and rate constants in cat brain for 2-[18F]fluoro-2-deoxy-D-glucose (2-[18F]FDG). Measured mean value (+/-s.e.m.) for the whole brain LC = 0.443 +/- 0.012 (N = 7), for the whole brain k2* = 0.124 +/- 0.009 and k3* = 0.024 +/- 0.001 (N = 7).

Animals↗

PubMed1986

Neuronal responses to borders with and without luminance gradients in cat visual cortex and dorsal lateral geniculate nucleus.

We investigated responses of neurones in cortical areas 17 and 18 and in the dorsal lateral geniculate nucleus (dLGN) of the cat to a phase shift in a moving line pattern forming a border without a luminance gradient ("subjective contour"). In both areas 17 and 18, S cells and B cells respond only slightly or not at all along the phase shift while C cells respond strongly. The response of C cells is strongest for line patterns with medium line separation and decreases with smaller and larger separation. In the dLGN the relative magnitude of neuronal responses along a phase shift is similar to that of C cells. However, C cells respond uniformly along the entire phase shift, whereas geniculate cells merely respond to individual line ends along the phase shift. In addition we compared responses along a phase shift and those to a luminance gradient formed by a dotted line whose dots were separated by the same distance as the line ends along the phase shift. S cells and B cells respond preferentially to dotted lines whereas C cells and geniculate cells respond equally well along both phase shifts and dotted lines. Possible explanations for these results in terms of receptive field structure and differences in inhibitory input to the cells are discussed. Differential neurone responses may account for the perceptual distinctness of the contours with and without luminance gradients.

Animals↗

PubMed1986

Effect of vascular activity in the determination of rate constants for the uptake of 18F-labeled 2-fluoro-2-deoxy-D-glucose: error analysis and normal values in older subjects.

Regional cerebral blood volume (CBV) can be calculated using data obtained during the kinetic analysis of 18F-labeled 2-fluoro-2-deoxy-D-glucose (FDG) uptake measured by positron emission tomography (PET). As a result the influence of vascular activity upon the determination of FDG rate constants can be minimized. The method is investigated by simulation experiments and by analysis of PET studies on seven older, healthy human volunteers aged 52-70 years. The accuracy of measured FDG rate constants k1, k2, and k3, obtained either by omitting the early portion of the uptake curve or by explicit inclusion of CBV as a fit parameter, is compared. The root mean square error in measured rate constant for the latter method is equivalent to that obtained by omitting the first 2.5-3 min of tissue data and neglecting the CBV term. Hence, added information about the physiological state of the tissue is obtained without compromising the accuracy of the (FDG) rate constant measurement. In hyperemic tissue the explicit determination of the vascular fraction results in more accurate estimates of the FDG rate constants. The ratio of CBV determined by this method to CBV obtained using C15O in six subjects with CBV in the normal range was 0.92 +/- 0.32. A comparison of the CBV image obtained by this method with that obtained using C15O in an arteriovenous malformation case demonstrates the accuracy of the approach over a wide range of CBV values. The mean value for CBV fraction in gray matter obtained by this method in the older control group was 0.040 +/- 0.014. Average gray matter rate constants obtained were k1 = 0.084 +/- 0.012, k2 = 0.150 +/- 0.071, and k3 = 0.099 +/- 0.045 min-1.

Aging↗

PubMed1984

The neon color effect in the Ehrenstein pattern. Dependence on wavelength and illuminance.

The neon color effect can be described as an illusory spread of color surrounding colored lines embedded in certain line gaps. The effect is seen in the Ehrenstein pattern if colored crosses are added to the central gaps so as to connect the inner tips of the pattern. Experiments were conducted to explore the dependence of this neon color effect on the wavelength and retinal illuminance of the inducing lines. The following results were obtained: neon color effects are strong when the wavelength of the crosses is in the short- (less than 480 nm) or long-wave part of the spectrum (greater than 620 nm) and the wavelength of the Ehrenstein pattern is in the middle-wave part (500-580 nm). Effects are weak or absent when the crosses and the pattern have similar wavelengths. The neon color effect is just detectable when the ratio between the retinal illuminances of the Ehrenstein pattern and the crosses ranges from 0.1 to 0.8. The neon color effect is maximal at illuminance ratios ranging from 0.8 to 8. The strength of the neon color effect is independent of the illuminance level of the crosses if the illuminance ratio to the Ehrenstein pattern is maintained.

Color Perception↗

PubMed1984

Colored neon flanks and line gap enhancement.

When a colored line connects two black (or differently colored) lines across a gap, colored neon flanks are seen on either side of it. These flanks extend over gap sizes of 50 min arc foveally and are not explained by Bezold-type assimilation. They may be elicited by black lines as short as 6 min arc adjoining the colored line at each end. To maximize these flanks, the black and colored lines must appear linearly continuous. Nonaligned junctions weaken the effect and an angular tilt of more than 40 dog destroys it. In this and other respects, (local) neon flanks are similar to van Tuijl's (global) neon color spreading (1975). Both phenomena have analogs in brightness perception. We propose that neon spreading is a lateral extension of neon flanks across the empty space between them, and discuss similarities of these effects with other brightness illusions (Schumann, Prandtl, Ehrenstein). For this group of illusions the term "line gap enhancement" is introduced to imply perceptual enhancement of changes in brightness and/or color along lines. Correspondences between the psychophysical properties and structural prerequisites for line gap enhancement on one hand and neuronal response properties of end-zone inhibited (hypercomplex) cortical cells on the other are discussed.

Color Perception↗

PubMed1982

The neon color effect in the Ehrenstein illusion.

Van Tuijl's neon color effect arises in the Ehrenstein figure if a colored cross is added such as to connect the black arms across the central gap. The effect consists of a circular veil of color in the illusory area and has the same hue as the inducing cross. The neon-like coloration is uniform, or when elicited by two color bipartite; it is strongest on backgrounds resembling the color of the cross. The effect cannot be attributed to chromatic aberration or eye movements. In foveal vision (and for red crosses) neon spreading is limited to gap sizes between 4 and 35 min of arc. Extrafoveally, gap sizes may be larger by a factor of two. Neon perception is enhanced by flicker and weakened if stimuli are oriented obliquely. It does not occur with dichoptic presentation. A maximum illusion requires that the Ehrenstein figure and cross are laterally and angularly aligned for good perceptual continuation. A neuronal origin by spreading and summation, together with cognitive processes, is proposed.

Afterimage↗

PubMed1981

Random-dot motion displaces Ehrenstein illusion.

When a random-dot screen is used as a background for Ehrenstein figures, brightness enhancement is replaced by a change of grain and structure. Dots in the illusory area appear less densely packed and may be perceived as concentrically organized. When the screen is moved with respect to the Ehrenstein figures, the illusory patches seem to move in the same direction and out of the inducing area while maintaining their characteristic organization. It is proposed that neurophysiological mechanisms with different persistencies are involved in producing the observed phenomenon. It is also suggested that random dots moving along the same open path are combined into a figure, whereas dots crossing the lines of the pattern remain unstructured and serve as a ground against which the displacement is seen.

Humans↗

PubMedDate not supplied

Granule cell raphes in the cerebellar cortex of chicken and mouse.

The cerebellar cortex of the chicken embryo contains parasagittal segments of Purkinje cells. At intermediate stages of development, cell-dense ribbons of migrating granule cells ("raphes") are found between the segments. The complementary pattern of granule cell raphes and Purkinje cell segments represents a basic scheme of cerebellar organization that coincides with the expression domains of various genes, such as cadherins, gene regulatory proteins, and ephrins and their receptors. We have recently found the raphe/segment pattern also in a mammalian species, the postnatal mouse. Like in the chicken, the parasagittal raphes of granule cells were observed at the boundaries of Purkinje cell segments that differentially express cadherins. The number and arrangement of the raphes in the different cerebellar lobules is roughly similar in both species. The raphe/segment pattern is thus more widely distributed in vertebrates than previously assumed.

Animals↗