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Biomedical subjects

L Rakić

Publications and source records attributed to L Rakić.

At least 19 recordsLinked to original sources
PubMed2000

Modulatory effect of 7-thia-8-oxoguanosine on proliferation of rat thymocytes in vitro stimulated with concanavalin A.

7-thia-8-oxoguanosine (immunosine) is a guanosine analogue showing immunostimulatory activity on different components of the immune system, including B lymphocytes, natural killer cells and macrophages. However, little is known about its effect on T-cell functions. In this work it was demonstrated that immunosine at concentrations between 10 microM and 1 mM stimulated proliferation of rat thymocytes in vitro triggered by suboptimal concentrations of concanavalin A (Con A). The effect correlated with increased interleukin 2 (IL-2) production, upregulation of the IL-2 receptor alpha (IL-2Ralpha) expression and decreased apoptosis of thymocytes in comparison to the effect of Con A alone.

Adjuvants, Immunologic↗
PubMed2000

8-Cl-cAMP and tiazofurin affect vascular endothelial growth factor production and glial fibrillary acidic protein expression in human glioblastoma cells.

Compounds that could block tumor angiogenesis and induce tumor cell differentiation in malignant gliomas represent a very valuable tool in anticancer treatments. In this paper, we demonstrate that more selective drugs, which interfere with specific cellular targets, could treat glioma more effectively. 8-Cl-cAMP and tiazofurin (TR) are site-specific analogs that selectively inhibit PKAI and IMP dehydrogenase, are directly involved in cell proliferation and apoptosis, and mediate the mitogenic effects of different oncogenes and growth factors. In this study, we have examined influence of 8-Cl-cAMP and TR on the production of an angiogenic factor [vascular endothelial growth factor (VEGF)] by human glioblastoma U251 MG cells, as well as their influence on the expression of a differentiating marker [glial fibrillary acidic protein (GFAP)]. Using a cell proliferation assay, VEGF enzyme-linked immunoassay and GFAP immunocytochemistry we demonstrated the effects of these compounds. Our results demonstrate that 8-Cl-cAMP and TR decrease VEGF production by U251 MG cells, and that under the influence of both agents these cells increase GFAP expression and change their morphology, becoming more differentiated. These findings also suggest that 8-Cl-cAMP and TR may have potential for further investigation of their antiangiogenic and differentiational role in malignant disease such as human gliomas.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1999

A nucleoside analogue, 7-thia-8-oxoguanosine stimulates proliferation of thymocytes in vitro.

7-thia-8-oxoguanosine (immunosine) is a nucleoside analogue with immunoenhancing activity. In this work, its effects on proliferation of thymocytes in vitro were studied. It was found that immunosine stimulated proliferation of thymocytes both of mice and rats. The stimulatory effect depended on antigen presenting cells (APC), since thymocytes depleted of accessory cells did not proliferate to immunosine. In addition, pretreatment of APC with immunosine for 24 h significantly increased proliferation of thymocytes. Immunosine stimulated interleukin 2 (IL-2) production and the expression of activation markers (CD25 and CD71). The upregulation of CD25 (alpha subunit of IL-2R) was detected both on thymocytes and thymic dendritic cells. Proliferation of thymocytes in the presence of immunosine was predominantly mediated by IL-2 since blocking IL-2Ralpha by specific monoclonal antibodies inhibited cell proliferation by 65-85%.

Animals↗
PubMed1998

Detection of apoptosis and phagocytosis in vitro in C6 rat glioma cells treated with tiazofurin.

Tiazofurin, an anticancer drug which inhibits IMP dehydrogenase activity and decreases GTP concentration in various malignant cells, induced inhibition of growth and apoptosis in C6 rat glioma in vitro. The effects of tiazofurin were significantly blocked by addition of exogenous guanosine, suggesting the role of decreased GTP in triggering specific signal transduction pathways involved in apoptosis of C6 cells. The most interesting result of this study was the evidence of phagocytosis of apoptotic cells in vitro by neighbouring cells, a phenomenon considered to occur only in apoptosis in vivo. The possibility of observing phagocytosis in C6 glioma cells suggests that this cell system could be a good model for studying mechanisms of phagocytosis in vitro.

Journal Article↗
PubMed1997

Improved polymerase chain reaction conditions for quick diagnostics of Huntington disease.

Huntington disease (HD) belongs to a growing list of neurodegenerative disorders (fragile X syndrome [6], myotonic dystrophy [1], spino-bulbar muscular atrophy [2] etc.) characterized by unstable expanded trinucleotide repeats (so-called 'dynamic mutations'). The dynamic mutation causing HD represents the expansion of CAG triplets in the first exon of a gene IT15 (chromosome 4) coding for huntington. This trinucleotide stretch is varying in the range of 11-34 in normal chromosomes and 39-121 in HD chromosomes. The most direct diagnostic approach is to amplify the proximal region of IT15 gene (from patients genomic DNA) by polymerase chain reaction (PCR) and estimate the number of CAG triplets. All protocols published to date are difficult to reproduce because amplification is inefficient giving additional non-specific products. The strategy of our experiment is shown in Fig. 1. We designed one new primer, primer No. 2 (another primer was primer No. 1) and novel PCR conditions. Primer No. 2 is located closer to CAG triplets and its extension is not including the GC rich region. PCR amplified products, using primer Nos. 1 and 2, thus do not include the GC rich region and, therefore, are much more efficiently amplified (compared to the products of amplification with primer Nos. 1 and 3).

Chromosome Mapping↗
PubMed1997

The connection between absence-like seizures and hypothermia induced by penicillin: possible implication on other animal models of petit mal epilepsy.

In this study we investigated the relationship between penicillin-induced hypothermia and petit mal epilepsy induced by this proconvulsant antibiotic. In order to find a possible dose-dependent relationship, we used two doses: 1500.000 and 1000.000 U/kg b.wt., both known as being sufficient to induce absence-like attacks with subsequent spike and wave discharges (SWD) in electrocorticogram (ECoG). Because of experimental data suggesting penicillin binding to benzodiazepine receptor recognition site, we also studied penicillin-induced changes in body temperature after diazepam pretreatment. Results of this study clearly show that penicillin in doses known to induce petit mal-like epilepsy concomitantly induces statistically significant dose-dependent decrease in body temperature. Pretreatment with diazepam completely prevents both penicillin-induced hypothermia and SWDs. On the other hand, both the diazepam and mixed diazepam + penicillin treatments did not significantly alter body temperature. These results suggest, however, that at least some of the penicillin effects described could be assigned to its binding to the benzodiazepine receptor recognition site at GABA(A) ionophore. This may have an important clinical implication because the inhibitory action of penicillin at the benzodiazepine receptor recognition site could account for the mechanism of penicillin-induced unspecific encephalopathies in humans. The relationship between petit mal epilepsy and hypothermia sheds new light on the action mechanisms of penicillin-induced absence seizures.

Animals↗
PubMed1997

Learning and memory in nucleus basalis magnocellularis-lesioned rats after transplantation of fetal frontal cortex.

The effect of fetal frontal cortex transplantation on behaviour performance was examined in adult male Wistar rats with lesions of the nucleus basalis magnocellularis (NBM). Compared to intact and sham-operated controls, the rats tested ten or twenty days after bilateral electrolytic lesions of NBM exhibited the significant learning and memory impairments (acquisition and performance of two-way active avoidance) whereas spontaneous motor activity was not significantly altered. The animals which received allotransplants of fetal frontal cortex (from 18-day gestational rat fetuses) into NBM, two ("early" transplantation-NBM-ET) or ten ("delayed" transplantation-NBM-DT) days after lesioning, respectively, manifested the complete amelioration of noticed impairments when tested ten days after transplantation procedure. Corresponding sham-transplants groups (NBM-SET and NBM-SDT) showed only slightly improvement of acquisition but not performance of two-way active avoidance. The ability of the transplants to restore learning and memory in the NBM lesioned rats suggests that graft of fetal frontal cortex can functionally influence neuronal activity of the lesioned host brain.

Animals↗
PubMed1997

Humoral and cell-mediated immune responses following lesions of the nucleus basalis magnocellularis in the rat.

The present study was undertaken to elucidate whether electrolytic lesions of nucleus basalis magnocellularis--NBM (an animal model of Alzheimer's disease--AD) may influence humoral and cellular immune responses in adult male Wistar rats. For this purpose intact control (IC), sham-operated (SO) and NBM-lesioned rats were divided into two main groups: (1) rats immunized with sheep red blood cells (SRBC) for plaque-forming cell (PFC) response and anti-SRBC agglutinins, and (2) rats immunized with bovine serum albumin in complete Freund's adjuvant (BSA-CFA) for anti-BSA antibody production, Arthus and delayed hypersensitivity skin reaction to BSA. PFC responses and anti-SRBC agglutinins as well as diameter and expression of edema/induration of Arthus/delayed skin reaction and titer of anti-BSA antibody were significantly lower in NBM lesioned rats (compared to IC and SO). The results showed that in NBM-lesioned rats both the humoral and cellular immune responses were suppressed.

Agglutination Tests↗
PubMed1997

Biochemical characterization of the hippocampal and striatal Na,K-ATPase reveals striking differences in kinetic properties.

The activities and basic enzymatic properties of Na,K-ATPase were examined in synaptosomal plasma membranes (SPM) prepared from rat hippocampus and striatum. A kinetic analysis showed profound differences in apparent affinities for ATP (Km) between hippocampal (1.21 mmol/l) and striatal (0.76 mmol/l) enzyme preparations, as well as in the corresponding Vmax values. However, physiological efficiencies were almost the same. The complex pattern of dose-response curves to ouabain indicated the presence of two high-affinity forms of Na,K-ATPase in the striatum ("very high-": Ki = 3.73 x 10(-8) mol/l and "high-": Ki = 4.21 x 10(-5) mol/l), and one high affinity form in the hippocampus (Ki = 6.6 x 10(-7) mol/l). In addition, both SPM preparations contained one low affinity form with similar Ki. The "very high-affinity" form had positive cooperativity for ouabain inhibition of Na,K-ATPase activity, in contrast to "high" and "low-affinity" forms, which exhibited negative cooperativity. The respective contributions of ouabain-sensitive forms to the total activity were estimated as 22%, 46%, 19% for the striatum and 36%, 45% for the hippocampus. These data clearly demonstrate striking differences in kinetic properties of the hippocampal and striatal Na,K-ATPase that may be due to the isoenzyme diversity and adaptation to specific physiological demands of the examined rat brain regions.

Animals↗
PubMed1996

Ganglioside GM1 and GM3 in early human brain development: an immunocytochemical study.

The distribution of GM1 and GM3 gangliosides in human brain development between gestational week (g.w.) 6 and 15 was demonstrated by an immunocytochemical approach using polyclonal anti-GM1 and anti-GM3 antibodies. The first appearance of GM1- and GM3-positive cells was recorded as early as in g.w.6. Both antibodies labeled the cells in the ventricular zone of the telencephalic wall, with radially oriented fibers toward the pial surface, which represent radial glia cells with glia fibers. The intensive GM3 immunoreactivity was also exhibited in proliferating cells in the ventricular zone between g.w.6 and 12. During the period from g.w. 12 to 15, characterized by a rapid multiplication of neurons and glia cells, an increased number of GM1- and GM3-positive cells was observed. Prominent GM1 ganglioside staining was observed at the surface of the cell bodies in the ventricular zone. Besides surface labeling in migrating cells, GM1 immunoreactivity was identified inside the soma in the regions of cortical plate and subplate. GM1 immunoreactivity was more pronounced on the membrane of neuronal cells migrating along radial glia fibers, especially at the contact site between neuronal and glial cells. The GM3 ganglioside was localized mostly inside the soma, showing a granular immunoreactivity pattern. Our observations confirm the presence of GM1 and GM3 gangliosides in neuronal and glial cells in early human brain development. The involvement, especially of GM1 ganglioside in glia-neuronal contacts during migration of neuroblasts to their final destination, as well as the presence of GM3 ganglioside in proliferative cells in the ventricular zone of the telencephalic wall was also recorded.

Brain Chemistry↗
PubMed1996

Behavioral and adaptive status in an experimental model of Alzheimer's disease in rats.

Ten days after bilateral electrolytic lesions of nucleus basalis magnocellularis (NBM) we tested behavioral (spontaneous motor activity, acquisition and performance of two-way active avoidance, fear-response in open field test, foot shock induced aggression, depression-response in learned helplessness test) and adaptive status (body temperature at standard, hot and cold environment as well as cold restraint-induced gastric lesions) in adult male Wistar rats. Compared to intact control and sham-operated rats, the bilateral NBM-lesioned rats showed the significant impairment of learning behavior and reduced fear, aggression and depression as well as altered body temperature at standard and stressed conditions. Namely, it was established that body temperature in NBM-lesioned rats was significantly lower at standard laboratory conditions, but in these rats body temperature significantly was raised after exposing to cold and hot environment. On the other hand, spontaneous motor activity and number and length of cold restraint-induced gastric lesions (erosions and petechiae) in NBM-lesioned rats were similarly to those in both controls. It could be concluded that NBM plays a significant role in cognitive, emotional and adaptive processes in the rats.

Adaptation, Psychological↗
PubMed1995

Effect of neurotoxin DSP4 on EEG power spectra in the rat acute model of epilepsy.

The effect of the adrenergic neurotoxin N-(chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) on electroencephalographic (EEG) activity was studied in the model of epilepsy induced by systemic application of penicillin (1,000,000 IU/kg, i.p). DSP4 (50 mg/kg, i.p.) was administrated to male Wistar rats, while the control animals were rats from the same litters. EEG activity was recorded in acute and chronic experiments 3 or 4 weeks after DSP4 treatment, before and after penicillin administration. Occasional locus coeruleus (LC) stimulation served as an electrophysiological test of DSP4 toxic effect. EEG power spectra in DSP4 treated animals showed a tendency to be greater in lower frequency bands than in controls before penicillin administration; there was almost no effect of electrical LC stimulation, regardless on penicillin treatment. In the model of epilepsy, the mean total EEG power spectra were greater in the period of 135-330 min after penicillin administration, as well as during 345-540 min, in DSP4 treated animals as compared to the controls. It seems that neurotoxin DSP4 is an optimal tool for studying the removal of LC influence in the acute model of epilepsy. It is also suggested that norepinephrine (NE) may have a modulatory role in the systemic penicillin epilepsy.

Adrenergic Agents↗
PubMed1995

Changes in neuropeptide levels after brain damage in rats.

The physiological and pathophysiological roles of neuropeptides are still not clear. The aim of our study was to detect long lasting changes of vasoactive-intestinal peptide (VIP), somatostatin (SOM) and substance P (SP) contents in the rat cerebral cortex and hippocampus after brain lesion. The experiments were performed on groups of adult male Wistar rats. The first group consisted of animals with unilateral ablation of the sensorimotor cortex performed at the age of 60 days. The second group was a control one (rats of the same age but with an intact brain). Both groups of animals were sacrificed at the age of 90-105 days and radioimmunoassay was used to determine amounts of VIP, SOM and SP. The mean values of VIP levels were decreased significantly only in contralateral cortical areas, while there was an increase of SP in lesioned animals. Our results suggest that descrete changes in neuropeptide levels occur during restorative processes after brain lesion.

Analysis of Variance↗
PubMed1995

Effect of early cortical lesion on the acute model of epilepsy.

The experiments were performed in order to investigate the sparing of function following early postnatal cortical lesion in the acute rat model of epilepsy. Sensorimotor cortex was unilaterally removed at 9 and 10 days of postnatal age in lesioned animals, while control animals were only sham operated (at the same early stage of life) or non-operated (before implantation of the electrodes). Seizure activity was recorded by means of electroencephalograms at adult stage of life induced by parenteral administration of penicillin (1,000,000 I.U./kg, i.p.). Our results showed that when the cortical lesion was performed in infancy (on the contrary to the lesion performed in adulthood) there was no prolongation of seizure activity in an acute model of epilepsy.

Aging↗
PubMed1994

Amphetamine and haloperidol modulatory effects on Purkinje cell activity and on EEG power spectra in the acute rat model of epilepsy.

The modulation of cerebellar Purkinje cell activity and EEG from parietal cortex was studied in the rat model of epilepsy induced by penicillin under acute haloperidol and amphetamine treatment. The discharge pattern of Purkinje cells showed tendency towards inhibition and EEG power spectra increased after parenteral administration of penicillin (1000000 IU/kg, i.p.). Acute haloperidol treatment (1 mg/kg, i.p.), performed after the development of penicillin induced epileptic episodes, elicited a prominent excitation of Purkinje cell discharges associated with parallel increase in mean EEG power spectra. However, acute DL-amphetamine treatment induced marked suppression of Purkinje cell discharges as well as outstanding decrease of the mean EEG power spectra. These results indicate that cerebellar Purkinje cells may be important in the control of seizure activity and that noradrenergic influences are relevant.

Amphetamine↗
PubMed1994

Mechanisms of cardiac risk among professional drivers.

This literature review indicates that professional drivers have excess cardiac risk that is not fully explained by standard risk factors. The contribution of occupation is suggested by two independent methods and by psychophysiological studies during on the job driving. Driving has been conceptualized as a threat-avoidance task. Stimuli encountered in traffic are not inherently aversive but become so by association with driving experience, a formulation corroborated by laboratory studies in which stimuli such as car headlights elicit cardiovascular hyperreactivity and electroencephalographic signs of arousal in professional drivers. More-advanced neurophysiological methods (event-related potentials) show higher cortical electronegativity to imperative signals among professional drivers than among non-driver referents. These data are viewed in light of reports of possible associations between event-related slow potentials and cardiac risk. A clinically and ecologically relevant neurocardiological model is proposed, and preventive strategies, including workplace interventions, are suggested.

Adult↗
PubMed1992

The effect of cortical lesion on systemic penicillin epilepsy in rats.

There is a certain recovery of function following brain damage, due to neuronal plasticity. The experiments were performed in order to investigate the effects of cortical lesion on seizural activity in rats induced by systemic application of penicillin. The sensorimotor cortex was unilaterally removed in the lesioned animals, while the control animals were only sham operated or non-operated (before implantation of the electrodes). Seizural activity was recorded by means of electroencephalograms before and after penicillin treatment (1,000,000 I.U./kg, i.p). Testing of penicillin started at least 30 days after cortical lesion. Seizural activity was characterized by spike and wave complexes accompanied by vigilance reduction and sometimes by mild myoclonic jerks in both control and lesioned animals. The early period (about 2 h after penicillin administration) with appearance of the spike-wave discharges with relative increase of the mean total electroencephalogram powers as well as the succeeding period 2.5-5.5 h after penicillin administration) with maximum number of spike-wave discharges did not differ in the electroencephalogram of the control and lesioned animals. The late period of penicillin effect (from 6-11 h after penicillin administration) with frequent spike-wave discharges and still large mean total electroencephalogram powers was observed only in lesioned animals. It is concluded that a cortical lesion destabilizes the brain function in the rat model of epilepsy induced by parenteral administration of penicillin.

Animals↗