Search PubMed⌕ Search

Biomedical subjects

D Ristanović

Publications and source records attributed to D Ristanović.

At least 19 recordsLinked to original sources
PubMed2005

Fractal analysis of the laminar organization of spinal cord neurons.

Images of Golgi impregnated neurons from different laminae of the human and rat dorsal horns were subjected to a quantitative analysis to support the Rexed's laminar scheme in mammals. Four methods of fractal analysis were performed in the proceedings: box-counting, mass-radius, cumulative intersection, and vectorized intersection. The results show that the box-counting method is more precise than the other fractal methods performed, and offers support for the conclusion that fractal analysis can successfully discriminate the neuron populations among different laminae. The analysis supports the concept of Rexed's cytoarchitectonic lamination of the dorsal horn.

Animals↗
PubMed2002

Fractal and nonfractal analysis of cell images: comparison and application to neuronal dendritic arborization.

Neurons of the rat spinal cord were stained using the Golgi impregnation method. Successfully impregnated neurons from laminae II, III, and VI were subjected to fractal and nonfractal analyses. Fractal analysis was performed using length-related techniques. Since an application of fractal methods to the analysis of dendrite arbor structures requires caution, we adopted as appropriate a nonfractal method proposing a generalized power-law model with two main nonfractal parameters: (i) the anfractuosity, characterizing the degree of dendritic deviation from straight lines; and (ii) an estimate of the total length of arbor dendrites. The anfractuosity can distinguish between two sets of drawings where the fractal methods failed. We also redefine some basic concepts of fractal geometry, present the ruler-counting method, and propose a new definition of fractal dimension.

Animals↗
PubMed1999

Topography of visual EEG reactivity in school-age children.

In order to quantify the visual reactivity of EEG to opening the eyes, the topography of EEG power spectra for a sample of 72 healthy subjects of age ranging from 7 to 15 years was investigated. The EEGs were recorded from 16 scalp sites with eyes open (EOP) and eyes closed (ECL). Ln-transformed absolute EEG powers, acquired under these two states, were tested with Wilcoxon's paired test for differences between the powers. The absolute powers in alpha band and in total, were significantly higher in all derivations, under the ECL, as compared with the EOP, condition. Absolute powers in theta band under the ECL condition were also significantly higher than those under the EOP condition, except for frontal derivations. Changes in delta power were insignificant. Beta 1 band activity, when eyes were closed, was maximal in posterior and minimal in anterior derivations. When the eyes were open, the greatest beta 1 power was found in the frontal derivations. Beta 2 was the only band in which a frequent increase in power took place with eyes opening. Eyes opening appeared to decrease significantly, the beta 1 and beta 2 powers only in posterior derivations. The results showed that the visual blocking of EEG was mostly due to a higher degree of EEG desynchronization for the subjects aged 7-5 years.

Adolescent↗
PubMed1998

The acidophilic nature of neuronal Golgi impregnation.

The mechanisms of Golgi impregnation of neurons has remained enigmatic for decades. Recently, it was suggested that divalent (di)chromate anions play a role in the Golgi impregnation process. Therefore, we incubated slices of (para)formaldehyde-fixed rat brain tissue in solutions of potassium (di)chromate, phosphate, chloride or nitrate at pH 6 or 7. Slices were then immersed in solutions of silver nitrate and processed for light microscopical analysis. At pH 6, dichromate probes resulted in dense and homogeneous impregnation of neuronal cytoplasm (typical impregnation). At pH 7, chromate probes showed solely partial cytoplasmic and heavy nuclear-region neuron impregnation (atypical impregnation). Phosphate probes at pH 6 resulted in typical impregnation, whereas at pH 7 phosphate probes gave atypical impregnation. Both at pH 6 and 7, chloride and nitrate probes did not yield any Golgi impregnation. These findings confirmed the pH-dependence of silver-chromate Golgi impregnation as well as the correctness of corresponding acidic silver-phosphate impregnation. Our study revealed a previously unknown, strong anion-dependence of Golgi impregnation, suggesting that hydrogenated monovalent anions are carriers of the neuron impregnation.

Animals↗
PubMed1998

EEG power spectra of normal preadolescent twins. Gender differences of quantitative EEG maturation.

To determine developmental changes of quantitative EEG maturation, we investigated the electroencephalogram (EEG) power spectra in a sample of 72 pairs of healthy twins (144 subjects, 75 girls and 69 boys) ranging in age from 7-15 years. Main spectral parameters were measured in 16 EEG channels. The statistical significance of differences in the EEG power spectra was compared in relation to age and gender. Gender differences were tested by comparing the EEG parameters of boys and girls in the whole sample and separately in the subgroup of dizygotic twins of the opposite sex (DZO twin pairs). A statistically significant decrease of absolute power occurred with increasing age. A significant redistribution of relative power also appeared in higher age, mainly consisting of a progressive increase of alpha 2 power inversely related to relative alpha 1 and theta power. Polynomial regression models of the relation between alpha 2 and theta relative power with age were best described by a 5-order function. The mean frequency of activity across all spectra also increased with age and was maximal in the eldest subjects (13-15 years), with a significantly higher mean frequency of alpha 2 power in females. Similar age and gender differences were less marked in the subgroup of DZO twin pairs. The topographic distribution of spectral bands in normal subjects suggested an earlier maturation of midparietal or occipital than frontocentral regions, and indicated that the growth spurt does not occur simultaneously over homologous right and left hemisphere regions at the same age.

Adolescent↗
PubMed1998

Dynamics of granule cells migration into the internal granular layer in developing human cerebellum.

The aim of these investigations was to find out the dynamics of migration of granule cells into the internal granular layer in three different parts of cerebellar cortex. The dynamics of changes was followed in vermis, in lateral hemispheres and in flocculus. For that purpose, 25 fetal brains of different postovulatory age (12.5, 15, 17.5, 19.5, 21, 31 week and one brain of 6 days old newborn) were fixed in formalin, embedded in paraffin, than stained with Cresyl violet and cut in 6, 15 and 30 microm. Each fifth slice was analyzed using the light microscope and numerical density of granule cell nuclei was established by point counting method according to Weibel. Results show a steady increase of the granule cell population in the internal granular layer of all regions investigated, being still greater in vermis and in hemispheres. This increase in the cell number lasted during the whole period of intrauterine development. Moreover, according to the trend of the curves, the increase of the cell number continues even after the birth, suggesting that at least some synaptic connections of granule cells are not established yet. For each region the adequate mathematical model of migration dynamics was calculated.

Algorithms↗
PubMed1997

Computerized EEG topography of normal preadolescent twins--correlating similarity of background activity with genetic relatedness.

The influence of genetic relatedness on the similarity degree of topographical EEG parameters was studied in a sample of 26 sets of monozygotic (MZ) and 46 sets of dizygotic (DZ) twins. All 144 subjects were healthy, primary school children, aged 7-15 years, 69 boys and 75 girls. Correlation coefficients were calculated for 50 quantitative EEG parameters of paired values obtained at each of 16 active electrode sites, in four groups of paired tracings: 1. MZ twins, 2. DZ twins, 3. The autocorrelated (A) group formed by correlating the spectral parameters from the same subjects in two different analyzed sequences, 4. The random (R) control group of 1200 unrelated pairs formed from DZ twin pairs. Sets of MZ twins and A group showed the highest degrees of similarity of spectral parameters over all brain areas except for significant differences only for some background features over posterior regions. In contrast, highly significant differences in topographic parameters were evident in comparison of MZ sets with DZ sets, particularly when MZ sets were compared with DZ subsets of opposite sex. Both number and degree of significant differences increased progressively in comparisons with groups 3 vs 2, 1 vs 4, and 3 vs 4. The data gave strong evidence for a complex polygenic determination of normal human EEG topography.

Adolescent↗
PubMed1990

Pattern-reversal visual evoked potentials recorded in children with generalized epilepsy.

Visual potentials evoked by pattern reversal (PRVEPs) were studied in 64 normal subjects (age range 7 to 15 years) and in 15 patients with primary generalized epilepsy (age range 8 to 13 years), 10 of whom were without anticonvulsant medication. Most of them were studied during sodium valproate (VPR) therapy and some during carbamazepine (CBZ) medication. A Quadristim set (Alvar) was used to present checkerboard patterns on a TV monitor, to amplify the EEG signals and to average and plot the evoked potentials. The potentials were elicited by binocular full-field 2/s checkerboard reversals, recorded from an electrode 4 cm above the inion, and analyzed for latency, amplitude and waveform. Our PRVEP measurements examined peak latency of positive P2 (or P100) component and trough-to-peak amplitude on N1P2 wave complex. The degree of similarity between pairs of PRVEP plots were determined by Pearson correlation coefficient r for an analysis time of 150 ms. In most of our patients, no pronounced influence of the disease itself on the parameters and waveform of the normal PRVEP pattern was demonstrated if anticonvulsant drugs were not taken. In patients who were under complete seizure control, the anticonvulsant did not change the PRVEP morphology as well. The PRVEP abnormality was most pronounced in patients who were taking anticonvulsant medication, but whose seizures were poorly controlled. This pattern distortion can be revealed by the correlation coefficient, but not by other PRVEP parameters. Therefore, this coefficient may be useful as a sensitive and objective measure both of PRVEP distortion and PRVEP improvement. Our results give further evidence that nondemyelinating disorders, but with synaptic transmission defects, can produce measurable changes in PRVEP morphology.

Adolescent↗
PubMed1990

Pattern-reversal visual evoked potentials in children with migraine: a correlation analysis.

Visual potentials evoked by pattern reversal (PRVEPs) were studied in 64 normal children (age range 7 to 15 years) and in 20 age-matched patients with common and complicated migraine (age range 6 to 16 years). Most of them were studied before and during prophylactic therapy. A Quadristim set (Alvar) was used to present checkerboard patterns on a TV monitor, to amplify the EEG signals and to average and plot the evoked potentials. The potentials were elicited by binocular full-field 2/s checkerboard reversal, recorded from an electrode 4 cm above the inion, and analyzed for latency, amplitude and waveform morphology. The degree of similarity between pairs of PRVEPs was determined by the correlation coefficient. In all our patients no pronounced influence of the disease itself was demonstrated on the PRVEP latencies and amplitudes, but in most of them the correlation coefficients were significantly different from that showing the measure of normal PRVEP variations. Prophylactic medication influenced non-significant increase of the coefficient. This increase seems to be related to recovery from medication in terms of attack frequency. No significant difference in PRVEP results of common and complicated migraine was noticed. The PRVEP distortion can be revealed by the correlation coefficient but not by other PRVEP parameters. Therefore, this parameter may be useful as a sensitive measure of both PRVEP distortion and PRVEP improvement. Our results give further evidence that non-demyelinating disorders, but with ischemic damage and abnormalities in neurotransmitters, can produce measurable changes in PRVEP morphology.

Adolescent↗
PubMed1989

The relationship between muscle kinetic parameters and kinematic variables in a complex movement.

Kinematic variables of the vertical jump (jumping height, jump phase durations and joint angles) were measured on 39 male physical education students. In addition, kinetic parameters of the hip and knee extensors, and of the plantar flexors (maxima voluntary force and its rate of development) were recorded on the same subjects, in isometric conditions. The results demonstrated significant positive correlations between kinetic parameters of the active muscle groups and jumping height (r = 0.217-0.464). The dominant effect on these correlations was due to the knee extensors. Correlations between these parameters and the duration of the jump phases were much weaker. Correlation coefficients between kinetic parameters and limb angles in the lowest body position showed that fast force production in one muscle group was related to a significant decrease in the joint angles of distant body segments. Multiple correlation coefficients between leg extensor parameters and kinematic variables (ranging between 0.256 for the duration of the counter-movement phase and 0.616 for jump height) suggested that kinetic parameters could explain more than a quarter of the variability of this complex human movement. Therefore, the conclusion was drawn that an extended set of measurements of the relevant musculo-skeletal system parameters could predict a considerable amount of the variability of human movement. However, high correlation coefficients between the same kinetic parameters of different muscle groups suggest that not all active muscle groups have to be included in the measurements.

Adult↗
PubMed1989

Pattern-reversal visual evoked potentials in normal 7- to 15-year-old twins: a correlation analysis.

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 sets of monozygotic (MZ) twins and 22 sets of dizygotic (DZ) twins matched on age, sex and educational level. They ranged in age from 7 to 15 years. The PRVEPs of MZ twins exhibited a significantly greater degree of similarity than those of DZ twins. The peak latencies and amplitudes of PRVEP components obtained from MZ twin pairs were significantly correlated. The correlation coefficients for the peak latencies of the P2 (or P100) component were the only ones to differ significantly between the DZ twins of the same sex and DZ twins of opposite sexes. These coefficients, obtained using PRVEPs, were much greater than those obtained with flash visual evoked potentials.

Adolescent↗
PubMed1989

Some uses of visual evoked potentials in the diagnostics of neurological disorders in developmental period.

The diagnostic value of visual evoked potentials (VEP) was assessed in a sample of 146 patients aged from 4 months to 18 years with a variety of visual disorders, and in 81 healthy controls. The methods of stimulation consisted of 1) a series of pattern reversals (PR) in 105 fully cooperative patients aged 6-18 years, or 2) a series of diffuse flashes in 41 infants, small children and mentally retarded subjects. The ranges of normal VEP parameters were defined by comparison of the subjects' groups with healthy controls of the same age and sex, who were recently tested by the same methods developed in our laboratory. The incidence of various VEP abnormalities was related to clinical findings and other investigations carried out with the scope to establish the localization and/or the disease etiology. The greatest localizing validity of VEP was found in patients with unilateral visual disorders, while the highest frequency of the most different types of VEP abnormalities was found in subjects with multiple sclerosis. Although nonspecific for any etiology, VEP abnormalities represent a sensitive screening method aimed to discover and to follow-up possible progression of visual dysfunction in children and adolescents. Since VEP, particularly of PR type, allow monitoring of subtle influences on the neuronal cortical functions, its full diagnostic value in the developmental neurology should be determined by further studies.

Adolescent↗
PubMed1986

Double and single exponential kinetics of microtubule assembly in vitro.

The kinetics of the microtubule protein assembly were studied in Mes buffer, pH 6.6, at 28 degrees C. The assembly under above conditions follow a kinetic expression containing two exponential terms. The observed two rate constants depend on protein concentration, and are on the order of 10(-2) sec-1 and 10(-3) sec-1. When CaCl2 is added to the system in low concentration, the kinetic expression becomes single exponential. The observed rate constant is independent of protein concentration and its value is 5 X 10(-3) sec-1. It is concluded that the double exponential kinetics correspond to favorable assembly conditions, probably to a high extent of nucleation, whereas the single exponential kinetics correspond to favorable assembly conditions, probably to a high extent of nucleation, whereas the single exponential kinetics is a slower process which occur under hindered assembly conditions.

Animals↗
PubMed1984

A routine fitting of kinetic data to sums of exponentials with a programmable calculator.

The effects of prolonged ingestion of ethyl alcohol on the elimination kinetics of bromsulphalein (BSP) from the plasma and the excretion of the dye into bile after a single intravenous injection into the circulation of the rat were examined by means of the colorimetrical technique. Simple numerical methods for fitting the experimental data to polyexponential and convex upward functions were also proposed. Two multioptional programs written for the Texas Instrument 59 programmable calculator and for the Sharp 1500 pocket computer were developed which provide for fully automated exponential stripping of pharmacokinetic data and which will allow workers to calculate the numerical values of all the coefficients and exponents for the tracer function fitting the monotone sequences of data.

Alcohol Drinking↗
PubMed1983

Bromsulphalein plasma kinetics after obstruction of the common bile duct in rats: curve fitting with a programmable calculator.

Plasma kinetics of bromsulphalein (BSP) after a single injection into the bloodstream of the rat with total obstruction of the common bile duct was examined. The concentrations of BSP were determined colorimetrically. A monoexponential plus a general first-degree function in time with four unknown parameters was fitted. Two programs were developed for the Texas Instruments 59 programmable calculator to estimate the values of all the parameters by an iteration procedure. The programs executed at about twice normal speed.

Animals↗
PubMed1982

A numerical method for biphasic curve fitting with a programmable calculator.

Elimination kinetics of bromsulphalein (BSP) after a single injection into the circulation of rats were examined by means of a four-compartment model. BSP plasma concentrations were measured colorimetrically. A program written for the Texas Instruments TI-59 programmable calculator is presented, which will calculate the fractional blood clearance of BSP using an iteration procedure. A simple method of fitting biphasic decay curves to experimental data is also proposed.

Animals↗
PubMed1981

Effects of spatially structured stimulus fields on pattern reversal visual evoked potentials.

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 healthy individuals. A photic stimulator for pattern production on a TV monitor, an electroencephalograph for EEG signal amplification and a computer for averaging the potentials and displaying the traces were used in the experiments. The peak latencies and both trough-to-peak and baseline-to-peak amplitudes of the main PRVEP components were found to be closely related to both the check size of checkerboard pattern and the bar width of barred pattern. The latencies decreased exponentially and amplitudes varied non-monotonically with check size or bar width. Most of the amplitudes of these components were greatest when checkerboard patterns with check sizes subtending visual angles of 60--70 min of arc, or barred patterns with bar widths subtending angles of 7--15 min of arc, were presented.

Adult↗