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Biomedical subjects

J Myslivecek

Publications and source records attributed to J Myslivecek.

At least 19 recordsLinked to original sources
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↗
PubMed1979

Effects of early visual and complex stimulation on learning, brain biochemistry, and electrophysiology.

A complex stimulation regimen (visual, auditory, and somesthetic-kinesthetic with forced movements, 30 times for 30 min each within 14 days) increased significantly the amplitudes of visual cortical evoked potentials (EPs) in adult rats if applied during the second postnatal fortnight. The EP increase after stimulation during the first 14 days after birth was not significant. Visual stimulation alone was compared with complex stimulation (visual plus forced movements) during the 2nd postnatal fortnight. More specific local changes in the visual cortex were revealed in brain biochemistry (lower DNA concentration, more RNA and protein per cell) and cortical electrogenesis (enhanced visual EPs) after visual stimulation alone, whereas complex stimulation induced more diffuse changes and rather profoundly influenced higher nervous functions (viz., memory retrieval - improved 24-h). Involvement of both specific and nonspecific mechanisms in the aftereffects of early stimulation is indicated.

Animals↗
PubMed1979

Ontogeny of active avoidance in the rat: learning and memory.

Ontogenetic development of active avoidance learning, extinction and retention was studied in rats. The learning of a 1-way active avoidance was most rapid between Weeks 4 and 6, although some slight gender-related differences were evident. No such unambiguous development was detected in forced extinction. The 24-hr retention of avoidance peaked at the age of 4 weeks whereas 1-month retention was best in animals trained at the age of 8 weeks. The retrieval of memory trace also had best values at these ages. Retention of forced extinction was found to peak in 6-week animals. The existence of developmental "critical periods" must be considered cautiously as various functions have different time courses depending upon the chosen parameters in assessment.

Animals↗