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Biomedical subjects

J Myslivecek

Publications and source records attributed to J Myslivecek.

At least 37 records · Page 2Linked to original sources
PubMed1996

Biphasic changes in the density of muscarinic and beta-adrenergic receptors in cardiac atria of rats treated with diisopropylfluorophosphate.

Chronic treatment with organophosphate inhibitors of cholinesterases is known to bring about down-regulation of muscarinic acetylcholine receptors in the heart while its effect on the functionally antagonistic beta-adrenergic receptors is not known. We describe experiments in which rats were exposed to daily injections of diisopropylflurophosphate (DFP) and the density of muscarinic and beta-adrenergic binding sites in their cardiac atria was measured according to the binding of (3H)quinuclidinyl benzilate ((3H)QNB) and (-)-4-(3-tert-butylamino-2-hydroxy)-propoxy-(5,7-3H) benzimidazol-2-one ((3H)CGP 12177) as subtype non-specific muscarinic and beta-adrenergic ligands, respectively. Biphasic course of changes was discovered with both ligands. With the dosage scheme applied, the density of beta-adrenoceptors was augmented 24 h after the first dose of DFP and decreased to about one half of control values after 5 days of treatment with DFP. The density of muscarinic receptors was augmented after two days of treatment with DFP and decreased to about one half of control values after 5 days of treatment. Comparatively small changes in the heart rate were observed during the treatment, they reflected changes in the muscarinic and beta-adrenergic receptor density. The finding of DFP-induced changes in the binding of (3H)CGP 12177 suggests that the mechanisms responsible for the control of the density of muscarinic and beta-adrenergic receptors in the heart cells are interconnected but potential roles of other factors involved in in vivo experiments deserve further analysis. The transient increase in the density of muscarinic receptors after two days of DFP treatment appears related to published data on transient stimulation by cholinergic agonists of the transcription of mRNAs for muscarinic receptors.

Animals↗
PubMed1996

Quantitative changes of dendrites in rat dentate gyrus and basal nucleus of Meynert after passive avoidance training in the neonatal period.

Quantitative morphological analysis of the number of granule cell dendritic spines, as well as total dendritic length and dendritic branching of neurons in the dentate gyrus and the nucleus of Meynert was done in 11-day-old rats after passive avoidance training in the neonatal period. Learning improved stepwise and its neuromorphological sequels were characterized by a statistically significant enhanced number of dendritic spines, due to an increase of thin spines, enhanced dendritic branching in both structures, and increased total dendritic length in the dentate gyrus compared with the controls.

Animals↗
PubMed1996

Inhibitory learning and memory in newborn rats influenced by nitric oxide.

The impact of nitric oxide on learning, memory processing and retrieval was studied in the neonatal rats. For comparison, spontaneous motor activity and changes of brain temperature were also studied after nitric oxide manipulations in identical age groups. The nitric oxide availability was either increased by a systemic or intracerebroventricular application of L-arginine, a substrate of nitric-oxide synthase, or decreased by nitro-L-arginine, its inhibitor. L-arginine, 20 mM or nitro-L-arginine, 10 or 5 mM were given intraperitoneally, 1 ml/100 g weight, or in the amounts of 11 into both lateral cerebral ventricles. Intact and saline injected pups were used as controls. Spontaneous motor behavior of newborn pups were not unambiguously affected by nitric oxide, and the same applies to changes of brain and body temperature or heart rate. In no case any correlation with changes of learning and/or memory could be established. Learning was dose dependently impaired relative to controls by intraperitoneal application of nitroarginine. L-arginine only slightly decreased numbers of trials to both criteria and partially abolished the blocking effect of nitroarginine on nitric oxide synthase. With the use of intracerebroventricular injections the positive impact of L-arginine on learning became highly significant. In 24-h memory, intraperitoneal injections of L-arginine enhanced the retention indexes. The impairing effect of nitro-L-arginine significantly increased with delaying after-learning application intervals, being more pronounced at the 3-h than at 0-h interval. Here also, its effect was partially abolished by L-arginine. Effects of nitric-oxide availability in brain after intracerebroventricular application of these substances at 16 various post-learning intervals were assessed on memory processing and retrieval. A general enhancing effect of increased nitric-oxide supply on 24-h retention indexes was found through all studied intervals, which was not, however, monotonous, but several peaks appeared with application at 3, 6, 18 and 23.5 h after learning. On the other hand, the suppressive effect of NArg was not evident relative to saline before the 6-h post-learning injection delay. These results show that nitric oxide exerts a considerable central modulatory effect on learning, memory processing and retrieval at the very early postnatal period of the rat. The efficiency of nitric-oxide manipulations depends on its actual bioavailability in the brain and the stage of memory processing.

Animals↗
PubMed1996

[Receptors--one component of intercellular communication pathways].

Every event, which occurs in the cell, can be an information capable to propagate. The existence of the structures which are capable of transmission (i.e. RECEPTORS) is necessary for the effective signal propagation. In this review the receptors are divided according their localization in the cell, genetic and structural similarity to cytoplasmatic, organelic and membrane receptors. Structure and function (including basic characteristics of intracellular signalization) of the main representatives of the previously mentioned groups are described. The possible interactions between receptors are mentioned too.

Cell Communication↗
PubMed1996

[Regulatory mechanisms of receptor-mediated signal transduction].

The signal activation of the target structure, mediated via receptors, could be also the source of some regulatory events. An intensive signaling brings about desensitization, sequestration and down-regulation of receptors, while in the case of absenting signal the sensitization and the up-regulation occur. Such change in the function of one receptor system could influence the function of the other one (we talk about cross-regulation). This review is focused on mechanisms of the homologous regulation (changes in the pathway activated by the appropriate type of receptor) and possible mechanisms of cross-regulation (changes in pathway activated by other type of receptor).

Arrestins↗
PubMed1991

Ontogeny of ribonucleic acid content in rat cortical neurons influenced by early stimulation.

Developmental changes in the total RNA content were studied in pyramidal cells of the frontal, parietal (somesthetic), temporal (auditory) and occipital (visual) cortical areas in Wistar rats aged 13, 14, 15, 21, 28, 35 and 56 days, and compared with those after complex, visual and acoustic stimulation. In all areas neuronal RNA content reached peak values at the age of 3 weeks, except the parietal cortex, where the values were highest as early as at 15 days (in 21-day pups they were only insignificantly lower). Between the age of 3 and 4 weeks, RNA content of cortical neurons decreased in all three projection areas, whereas in the frontal cortex a significant decline came later--in the 5th week. In the occipital cortex neuronal RNA at 8 weeks reached reliably lower values than in 13-day pups. Neuronal RNA increased at the time of eye-lid opening (13-15 days), highly significantly in the visual cortex. Complex visual and acoustic stimulation raised neuronal RNA content in projection areas of modality involved in stimulation and, moreover, acoustic stimulation did so in the frontal and occipital cortex. On the contrary, complex and visual stimulation decreased RNA contents in the frontal cortex. Developmental dependence, stimulation contingency, and specificity vs. nonspecificity of the observed changes are discussed, and compared with other biochemical, morphological and functional changes that have been found in the period of peaking RNA content, or immediately thereafter.

Acoustic Stimulation↗
PubMed1991

Impact of prenatal low-dose diazepam or chlorpromazine on reflex and motor development and inhibitory-learning.

Long-term behavioral effects of a low dose of diazepam (1 mg/kg body weight) or chlorpromazine (2.5 mg/kg) administered 2-3 times during the last week of pregnancy i.m. were studied in Wistar rats and compared with sequelae of analogously applied saline as well as with normal ontogeny in controls. Inhibitory learning-and-memory ontogeny was assessed by 3 types of passive avoidance (PA) at 3 different life periods: neonatal, 2 months, 4 months. Also were investigated: development of righting, air righting, hanging on a thin horizontal bar, eye-lid opening, somatic development and mortality. Prenatal application of diazepam had adverse effects in all parameters except of eye-lid opening. The reflex and motor development was retarded, and so was body weight. The high mortality in the diazepam treated progeny was due to increased death rate in males. In all PA paradigms investigated no memory was established in rats given diazepam prenatally. Chlorpromazine exhibited a lesser effect. I.m. saline had doubtless a character of prenatal-stress. The impact of diazepam was therefore the result of its proper action and only of a partial, if any, after-effect of prenatal stressful manipulation of the dam.

Animals↗
PubMed1991

Step-down passive avoidance in the rat ontogeny.

Ontogeny of step-down passive avoidance (PA) was studied in 174 Wistar rats at the age of 2, 3, 4, 6, 8 and 13 weeks. Latency to the first descent from the safe bench (DL), number of descents (DN), time to criterion meeting (TC) and time during which animals were shocked (TS), were evaluated within learning (L) and two consecutive retention tests (R1 and R2); R1 took place at short to intermediate intervals (5 min-6 h), R2 24 h after learning. None of 2-week pups mastered the task. The most efficient learning was in 6-week pups, and also three indices of R1 (DN, TC and TS) were best at this age. However, the longest DL (most commonly used memory index in PA) was found in R1 and R2 of 3-week pups, due probably to high fear motivation. In 3-month animals DL was zero in R1. It is emphasized that the development of learning and memory is non-monotonous, which was also seen in our previous studies. There were differences between DL recalled from memory and other three indices (DN, TC and TS) in which further reinforcement within the retention test facilitated the retrieval.

Age Factors↗
PubMed1990

Early inhibitory learning in the rat. I. Learning and memory development.

The present status of knowledge on early inhibitory learning and memory is presented. The inhibitory learning (passive avoidance) can be mastered by rat pups several hours after parturition, provided specific characteristics of the newborn organism and its neurobehavioral capabilities are respected. The curve of numbers of trials to criterion displays, as already reported earlier, a generally decreasing trend which is, however, interrupted by a temporary inversion in both strains studied, but at different time, taking place in Long Evans between postnatal day 1 and 2, which is shifted in Wistar pups one day later. Present data show significant learning differences between strains at postnatal days 1-4; from day 5 onward no significant differences are evidenced up to postnatal day 11. A reliable 24-hour memory shown by positive values of the retention index (RI) is revealed from postnatal day 4, having in Long Evans higher RI values. Moreover, high positive RIs of 24-hour memory are found in animals trained on the day just before the inversion of the learning development. It is conjectured that the indirect development of the early inhibitory learning is due to the developmental reorganization within CNS, and the necessity to find out its underlying mechanisms is emphasized.

Aging↗
PubMed1987

Differential ontogenetic peaks and drops in various conditioned reactions.

A survey of results obtained by the authors was compared with the body of recent data of the literature on the development of learning and memory. The following conclusions were pointed out: The development of learning and memory is not a monotonous process; one or more peaks followed by temporary drops or lasting decay are characteristic for it. There is no coincidence in time between learning and memory peaks, both are greatly dependent on the experimental design and conditions. Learning of more complex reactions and prolonged retention intervals shift the peaks toward later age periods. Early learning and memory that occurs at earlier age periods than thought before may be proved in the very first postnatal days in altricial mammals for inhibitory conditioning as well, if neurobiological and developmental specificities of this age are respected.

Animals↗
PubMed1985

Maze-escape learning and memory during rat ontogeny.

With the method of a simple automatic rectangular maze the development of escape reaction was studied in albino rats aged 3 weeks to 3 months as well as memory retrieval within 24 h and then after one month. Learning of escape improves sharply between the 3rd and 4th postnatal week, and then, with the exception of week 8, remains approximately on the same level. Memory retrieval up to 24 h is not significantly influenced by age or sex, but is best immediately after learning interval of 10 min and the poorest after 24 h, except the age of 5 weeks, where it is best in 3 and 6 h after learning. One-month retention of maze escape improves during development except in animals trained at the age of 6 weeks in which the level is lower than in all other investigated groups. One-month memory retrieval in animals taught at the age of 4 weeks is influenced by the time of the first retention test with the best values in animals tested for the first time after 3 h and poorest in animals tested after 24 h after learning. Animals trained at 5 weeks had a marginally better result after the one-month retention test in females, perhaps due to the influence of sexual maturation on memory traces. This was not observed in the other age groups. Attention is drawn to the different development of learning and memory of various types of conditioned reactions stemming from the difference in their complexity.

Analysis of Variance↗