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J Pavlásek

Publications and source records attributed to J Pavlásek.

At least 19 recordsLinked to original sources
PubMed2004

[Significance of determination of intra-acrosomal proteins and sperm antibodies in human reproduction].

OBJECTIVE: Comparison of the positive intra-acrosomal proteins and spermagglutinating antibodies in human semen samples from various groups of patients. DESIGN: Prospective study. SETTING: Department of Gynecology and Obstetrics and Faculty Hospital, Charles University, Pilsen, Institute of Molecular Genetics, Czech Academy of Science, Prague. METHODS: Monoclonal antibodies Hs-8 and Hs-14 (prepared in the Institute of Molecular Genetics, Prague) were used for detection of intra-acrosomal sperm proteins. Microscopic immunofluorescent methods detected the incidence, the character and the percentage of the spermatozoa specified by above-mentioned monoclonal antibodies. Direct mixed anti-immunoglobulin reactions test (MAR-test) for IgG, IgM, IgA, IgE was used for detection of spermagglutinating antibody. We examined 315 infertile patients from Special Consultation for Immunology of Reproduction and from the IVF programme, and sperm healthy donors (January 2002-March 2003). RESULTS: Native donor's sperm cells had excellent positive intra-acrosomal proteins stained with monoclonal antibodies Hs8 and Hs14 and after thawing as well as. No spermagglutinating antibodies were found. In the group with normal sperm count and light microscopic morphology we found the presence of seminal spermagglutinating antibodies in 11% (IgG), in 14.5% (IgA), in 3.6% (IgM), in 5.2% (IgE). Significant positivity of intra-acrosomal protein stained with Hs8 monoclonal antibody was reached in 68.4%, and with Hs14 monoclonal antibody in even 81.3% of men. On the other hand, in oligoasthenospermatic patients we found significant increasing of spermagglutinating antibodies (for IgG 40.5%, for IgA 28.6%, for IgM 9.5%, for IgE 11.9%). Dominant good staining of intra-acrosomal proteins were seen only in 15.5% of men (for Hs8) and in 20.2% (for Hs14). CONCLUSION: The quantitative detection of intra-acrosomal sperm proteins and spermagglutinating antibodies are used as important properties of human semen and serve for evaluation of acrosomal state, and male fertility together.

Acrosome↗
PubMed2001

Neural network comparing two-rate-encoded inputs entering in parallel.

Presented computational model of a neural network is able to compare two regular input frequencies. The comparison is based on detection of inter-spike interval differences of the two frequencies. This detection is continuous and the network dynamically changes its output according to the changes in the input frequencies. The entire network is composed of biologically plausible parts. A combination of such simple comparators might be involved in the information processing in the central nervous system.

Animals↗
PubMed1999

Temporal patterns recognized by a network of coordinated time delays and coincidence detectors.

A computational model of a neuronal network is described which performs a fundamental task of general perception: recognition of temporal patterns in continuous and uncued neuronal spike trains. The presented network is able to recognize each pattern element (100 ms interval composed of sets of 10, 20, 30 and 40 ms interspike intervals combined in linear order) as it arrives. Its operation is based upon biologically plausible filtering mechanisms and population neurodynamics.

Animals↗
PubMed1998

Mannitol derivate used as a marker for voltammetrically monitored transport across the blood-brain barrier under condition of locus coeruleus stimulation.

1-Deoxy-1-nitro-D-mannitol (DN-Man) was used (femoral vein injection, approximate concentration in the blood 30 mmol.l-1) in pentobarbital anaesthetized rats as a promising marker detectable by differential pulse voltammetry (DPV) to study its transport across the blood-brain barrier (BBB) to the extra-cellular space of the frontoparietal cortex. DN-Man detection limit in in vitro calibrations (saline, blood) using DPV and carbon fiber microelectrodes was 0.5 mmol.l-1 with a good linearity (r = = 0.996) over the entire tested range (up to 30 mmol.l-1). The slow time-course of the rise of DN-Man signal (y = 106/(1 + (17.8/t)3)) in the cortex confirmed the functional BBB state. Electrical stimulation of the locus coeruleus (LC) (300 rectangular pulses at a frequency of 100 Hz, 1 mA, pulse duration 0.2 ms) elevated significantly DN-Man current in the cortex (to 168 +/- 59% of the control, mean +/- S.D., n = 8). The evoked permeation increase of the BBB to DN-Man was short-lasting (minutes), and the second LC stimulation (repeated 5 min after the first one) was ineffective. This fact was probably due to the reduction of DN-Man levels in blood and/or an altered response of microvessels to neurotransmitters. It was shown here that, under carefully controlled surgical and experimental conditions, DPV and DN-Man might be useful for the monitoring of the regional dynamics of BBB transport changes. The presented results also support the view that BBB transport can be influenced by LC neuronal activity.

Animals↗
PubMed1998

The binding problem in population neurodynamics: a network model for stimulus-specific coherent oscillations.

A hypothesis is presented that coherent oscillatory discharges of spatially distributed neuronal groups (the supposed binding mechanism) are the result of the convergence of stimulus-dependent activity in modality-specific afferent pathways with oscillatory activity generated in unspecific sensory systems. This view is supported by simulation experiments on model networks.

Computer Simulation↗
PubMed1997

Timing of neural commands: a model study with neuronal networks.

Networks constructed of biologically realistic model neurons (neuroids) were used to study how in a neural assembly using pulse (interval)-coded information slow rhythmical oscillations with possible mode transitions might occur and how the efferent commands might be structured and their phase-shifts created. The simulations show that slow oscillations (in the hertz range) can be derived from reverberatory spiking in relatively short closed loops (fewer than ten neuroids) with the inputs protected against disturbing afferent signals and the outputs coupled by convergence on a common neuroid. Slow oscillations can be modified by a tonic activity entering the network; this activity changes the transmission time in the coupled loops involved. The structuring of the regulatory commands (in the millisecond range) was achieved by simulation of sequential activity propagation in a non-ring neuronal assembly supervised by a tonic activity in a set of inputs. The tonic activity acted as an instructive signal influencing the pattern of the functional connectivity in such a way that a particular efferent command was generated by the instructed network.

Central Nervous System↗
PubMed1997

Neuroprotection by the pyridoindole stobadine: a minireview.

The minireview summarizes data documenting that pyridoindole stobadine (STB) may protect nervous structures against oxidative stress. This was demonstrated by the impairment of synaptic transmission in hippocampal slices and sympathetic ganglia exposed to hypoxia/reoxygenation (H/R) in vitro as well as by survival of rats and dogs exposed to brain ischemia/reperfusion (I/R) in vivo. The STB effect was linked mostly to its free radical scavenging and antioxidant properties. STB seems to act primarily on phospholipids, thus protecting the integrity and function of somatic membranes in neurons as well as those in subcellular organelles, such as mitochondria and endoplasmic reticulum. STB prevented damage to Ca2+ sequestering systems in endoplasmic reticulum and synaptosomes induced by lipid peroxidation initiators. It was found to diminish changes in NMDA and adrenergic alpha1-receptors evoked in the brain by I/R or H/R. The compound prevented total thiols, participating in tissue antioxidative protection, from decreasing in brain under these conditions. It readily penetrates into both the hydrophilic and the hydrophobic compartments of the CNS. Data were obtained indicating that in I/R, protection of structures such as brain-blood vessels, endothelium, and/or erythrocytes may participate in the STB effect, besides the direct protection of nervous tissue. STB may be characterized as a potential protectant of the CNS in diseases in which oxidative injury may play an important role, for example, stroke, neurotrauma, chronic brain ischemia, or some neurodegenerative diseases. Its molecule could provide a useful model in the further search for novel compounds with even more pertinent pharmacological and pharmacokinetic profiles.

Animals↗
PubMed1996

Transport of an antihypoxic drug stobadine across the blood-brain barrier in rat striatum and its influence on catecholamine-oxidative current: a voltammetric study under normal and anoxic/ischaemic conditions.

Differential pulse voltammetry with a carbon fibre microelectrode (ME) was used in pentobarbital-anaesthetized rats for monitoring the stobadine current (STB.C) on both sides of the blood-brain barrier (BBB) in the arterial bloodstream (BS) and in the corpus striatum (CS). The STB.C exhibited a distinct peak at a polarization voltage 540 +/- 30 mV (n = 4). The maximum of STB.C in BS attained 2-3 min after the STB administration (2.8 mg/100 g in 1.0 ml saline solution i.a.) was followed by a rapid decrease to about 20% within next 3 min. The STB readily passed across the BBB: the STB.C peak appeared in the CS in the 3rd minute and continued to rise up to the 30th min. The administration of STB did not prevent a large increase (1347 +/- 326%, n = 3) of the catechol-oxidative current (CA.OC) occurring in the CS between the 4th and 5th minute after cardiac arrest. However, a decrease of ME sensitivity to CA.OC in the presence of STB was observed. This fact leads to the speculation whether a similar "quenching" of dopamine by STB could not participate in the protective effects of STB observed in the brain exposed to hypoxia-reoxygenation.

Animals↗
PubMed1994

Decrease of extracellular catecholamine content in the vicinity of cortical penicillin-induced epileptogenic focus: voltammetric study in the rat.

Differential pulse voltammetry with carbon-fibre microelectrodes was used in chloralhydrate-anaesthetized rats to test the influence of the penicillin-G-Na (PNC)-induced (topical application, approximately 2000 IU) epileptic activity on the catecholamine content (catechol-oxidative current, CA.OC) in the parietal cortex. In the experimental group (n = 4) after PNC a nonlinear CA.OC lowering was observed; this decrease during the first 10 min was faster than in the control group (n = 4). Significantly different values were observed from the 4th min after application. The best fit for this experimental curve gave the logarithmic function (f(t) = a+b.ln(t), a = 105.8, b = -10.6) with regression coefficient r = 0.98. From the 12th min after PNC application until the end of the experiments (54th min) CA.OC values ranged from 78% to 84% of the control group.

Anesthesia↗
PubMed1994

Catecholamine overflow within rat striatum: the influence of microstimulation and electroconvulsive stimulation as observed with voltammetry.

Differential pulse voltammetry with a carbon fibre microelectrode was used in chloral hydrate-anaesthetized rats for testing the influence of microstimulation and of electroconvulsive stimulation on the changes in concentration of electro-oxidizable materials (catechol derivates) in the extracellular space of the corpus striatum. Microstimulation applied in the striatum (8 V anodal pulses, 0.1 ms, 100 Hz for 40 s) caused a significant increase of the catechol-oxidative current (Ico); 5 s after microstimulation was stopped Ico ranged from 117 to 141% of the control (all values means +/- S.D. unless otherwise stated; 124 +/- 11%, n = 4, P < or = 0.01, Student's t test). This effect ceased in the third minute after microstimulation. A comparable result was observed when microstimulation was repeated at intervals of 10 min. Electroconvulsive stimulation with a sinusoidal current (50 Hz, approximately 150 mA, 0.2 s) caused a large increase in Ico; 20 s after stimulation ceased, Ico was 987 +/- 90% (n = 3) of the control and it returned to the baseline 2 min later. The mechanisms inducing transmitter overflow are considered and the influence of electroconvulsive stimulation on the striatum is discussed in the context of its beneficial effects in psychopathic patients.

Animals↗
PubMed1994

Effects of electroconvulsive shock on catecholamine release in the corpus striatum of the rat: a voltammetric study.

A voltammetric technique was used (differential pulse voltammetry with a carbon fibre microelectrode) to investigate dynamics of the changes of catecholamine overflow in the corpus striatum following electroconvulsive stimulation (ECS) of chloral hydrate-anaesthetized rats. Application of "maximal" ECS (50 Hz, AC, sine wave, approximately 150 mA, 0.2 s) caused large enhancement of catechol-oxidative current (CA.OC): In the first minute after its arrest, the CA.OC peak raised to 1032 +/- 405% (n = 5, mean +/- S.D.) of the controls (P < or = 0.001, Student's t-test). This large elevation of the extracellular catecholamine content ceased rapidly--the baseline level was attained in the second minute. CA.OC changes evoked by a "minimal" ECS (50 Hz, AC, sine wave, approximately 30 mA, 0.2 s) were equivocal in the first minute (increase, decrease: 145 +/- 56%, P > 0.05, n = 6). Possible mechanisms of the ECS therapeutic effect are discussed.

Animals↗
PubMed1993

Increase of catecholamine content in the extracellular space of the rat's brain cortex during spreading depression wave as determined by voltammetry.

The effect of chemically initiated (KCl) spreading cortical depression on catecholamine content in the extracellular cortical space was examined using voltammetry technique in chloralhydrate-anaesthetized rats. Correlation between alterations in catechol-oxidative current (CA.OC) and the time-course of the slow potential (SP) change (one of the chief features of the spreading depression) showed that spreading depression wave was accompanied by the significant increase in CA.OC content (up to 158 +/- 43%, mean +/- S.D., P < 0.001). The rise of the negative SP preceded significant CA.OC increase by 20 +/- 8 s. This fact provides the evidence that catecholamine overflow cannot participate in triggering spreading depression wave; nevertheless it can be an important link of the spreading depression mechanism.

Animals↗
PubMed1992

Voltammetrically determined differences in changes evoked by KCl microinjections on catecholamine levels in the reticular formation and corpus striatum of the rat.

Using a microelectrode with carbon filaments and the voltammetric technique, changes evoked in the catechol oxidation current (CA.OC) and multiple unit activity (MUA) by microinjection of 3-5 microliters 0.5 mol.l-1 KCl were studied in the reticular formation (RF) of the medulla oblongata of anaesthetized rats; the effect of KCl stimulation of the RF and corpus striatum (S) on the CA.OC in these structures was compared. The microinjection of KCl in the vicinity of the working electrode in the RF caused depression of MUA which began 2-3 s after administration, persisted for up to 6 min after and then diminished, reaching control values within 9 min. The voltammetric signal was first recorded in the 1st min after microinjection, when there was an evident decrease in the CA.OC value (59% of the control value); this effect reached its maximum 7 min after administration (a mean drop to 23% of the control), while at the end of the experiment (i.e. after 24 min) CA.OC values had risen to 45-80% of the control value. The response in the S had a biphasic character, however. Immediately after the microinjection (1st min), the mean CA.OC value rose to 626% of the control, while in the second phase (3-10 min) it was seen to fall below the control values (means 21-63% of the control). The differences in the changes evoked by K+ depolarization in the concentration of catecholamines in the RF and S microenvironment are discussed from the aspect of the existence of different pools of the transmitter and other regional differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Monitoring of potassium-stimulated catecholamine changes in striatal synaptosomal preparations and in corpus striatum of rats: a comparative voltammetric study.

Voltammetric techniques were used to compare the effects of K(+)-induced depolarization on catecholamine levels in in vitro synaptosomal preparations of the corpus striatum with those in the in vivo corpus striatum of anaesthetized animals. In vitro, the catechol-oxidation currents could be recorded only in dopamine-preloaded synaptosomes. In isolated synaptosomes prepared in the presence of elevated concentrations of Ca2+ (1 mmol.l-1) and Na+ (135 mmol.l-1), K(+)-induced depolarization had variable effects on catechol-oxidation current. The stimulatory effect of K(+)-induced depolarization (a short transient increase of catechol-oxidation current lasting for 30 s) could be observed after the addition of dopamine loaded synaptosomes in EGTA into the medium with elevated K+ concentration (90 mmol.l-1) and decreased concentrations of Na+ (75 mmol.l-1) and Ca2+ (0.75 mmol.l-1). These results suggest that experimental procedures and parameters of ionic composition of incubation media have to be carefully controlled, owing to an enhanced in vitro permeability of membranes of isolated synaptosomes for Ca2+ and Na+. In in vivo experiments, microinjection of KCl (3 microliters of 0.5 mol.l-1 KCl in 10 mmol.l-1 HEPES, pH 7.4) resulted in the appearance of several phases of catechol-oxidation current: the current increased (to severalfold of the control values) followed by a decrease or even total disappearance, with a gradual return to control values. Under conditions of depletion of extracellular calcium by EGTA (5 microliters of 0.5 mol.l-1 KCl + 0.25 mol.l-1 EGTA in 10 mmol.l-1 HEPES, pH 7.4) K(+)-induced depolarization confirmed the key role of calcium in the release of catecholamine transmitters as well as that in processes regulating the uptake and metabolism of these transmitters. The voltammetric techniques used in the present study may be a useful tool in extending of our knowledge about the cellular mechanisms of stimulus-response coupling in nerve cells.

Animals↗
PubMed1989

The startle reaction to an acoustic stimulus in the rat: the effect of noradrenaline administered by microinjection into the pontomedullary reticular formation.

The effect of the local administration of noradrenaline (NA) by microinjection into the pontomedullary reticular formation on the startle reaction (SR) evoked by an acoustic stimulus was studied in waking, non-immobilized rats. NA (10(-6) mol.l-1 in 2.5 microliters artificial cerebrospinal fluid) was administered 21 times to five animals in 13 experiments. In nine cases (43%), a significant change in the mean amplitude of the SR to a series of 30 stimuli (recorded in the third minute after administering NA) was observed; in eight cases (38%) it rose and in only one (5%) it fell. Binomial statistics confirmed the preponderance of results with an increase in SR amplitude. The results indicated that the potentiating effect of NA could actively help to regulate the function of the pontomedullary part of the neuronal circuit for the acoustic SR.

Acoustic Stimulation↗
PubMed1988

The extrasynaptic effect of gamma-aminobutyric acid and pentobarbital and the influence of temperature on the response of parallel fibres of the frog cerebellum in vitro.

The authors studied the effect of two biologically active substances (gamma-aminobutyric acid-GABA, pentobarbital-PB) and a physical factor (temperature-T) on the direct response of parallel fibres of the isolated frog cerebellum to electrical stimulation in vitro. The extrasynaptic action of GABA and PB during superfusion (10(-6), 10(-5), 10(-4) and 10(-3) mol.l-1) significantly reduced the amplitude of the response of parallel fibres. Superfusion with picrotoxin (10(-6) mol.l-1) only partly blocked the effect of GABA (10(-3) mol.l-1), although it abolished the effect of PB (10(-3) mol.l-1). Cooling the cerebellum from the control temperature (T = 16 degrees C) to T = 13 and 10 degrees C significantly augmented the amplitude of the responses, while raising it to 19 and 22 degrees C significantly reduced their amplitude. At T = 13 degrees C, depression of direct responses was significant only in superfusion with GABA (10(-6) and 10(-3) mol.l-1) and not in superfusion with PB (10(-6) and 10(3-) mol.l-1). The results with picrotoxin (PTX) applications, indicated that the extrasynaptic action of GABA and PB took effect by partly different mechanisms. That would account for the difference in the effect of GABA and PB in conjunction with the physical factor.

Animals↗