Ontogenesis In Rats Research Articles

Structural changes of the hippocampus nervous tissue in rat ontogenesis after prenatal hypoxia

Structural changes of the hippocampus nervous tissue in rat ontogenesis after prenatal hypoxia

Change of composition of intermediate filaments in rat telencephalon during early postnatal period of ontogenesis

The goal of the present work was to study composition and spatial-temporal distribution of cells containing various proteins of intermediate filaments (nestin, vimentin, GFAP) in various brain areas at the early postnatal period of rat ontogenesis. By using methods of immunohistochemical determination of proteins of intermediate filaments, it has been found that at the early postnatal period of development, in the course of maturation of the nervous tissue, in the cells of cortex, hippocampus, and subventricular area, there occurred changes of immunohistochemical profile of intermediate filaments (ratio of immunopositive (+) and immunonegative (−) cells): nestin+/vimentin+/GFAP− cells become nestin−/vimentin−/GFAP+.

Action of novocain on cardiac and somatomotor autorhythmical functions in early postnatal ontogenesis in rats

In conscious rat pups aged 2-3, 10-11, and 22-23 postnatal days, it has been shown that intraperitoneal administration of 0.5 % novocain at a dose of 25 mg/kg body mass leads to phasic changes of the level of spontaneous periodic motor activity--from increased at once after the administration to depression and subsequent restoration. They are accompanied by the cardiac rhythm fluctuations that change with age their direction on the background of an increased motor activity from brady--to tachycardia. All the changes are the most pronounced in newborns. At comparison of the results with the afferent impulsation level fluctuations recorded under the same conditions in the peripheral vagus segment, it is suggested that the revealed reactions are associated with changes of the interoceptive afferentation flow. The conclusion is made that at early stages of ontogenesis, interoception plays an important role in regulation of autorhythmical functions and that this role decreases with age.

Prenatal hypoxia affects amyloid metabolism and formation of cognitive functions in postnatal ontogenesis of rats

In medicine, primary prevention constitutes the first level of health care with the goal of preventing onset of a given disease process, whereas secondary prevention represents a second level of postonset early detection and treatment. Because preclinical Alzheimer’s disease (AD) is marked by the asymptomatic onset of AD pathogenesis, preventive measures undertaken at this stage should be regarded as secondary prevention; yet, they are commonly characterized as “primary prevention” or “prevention” in the literature on AD. Certain nontoxic, pleiotropic polyphenolic compounds suitable for long-term use among healthy individuals, derived from the ancient foods identified in the preceding chapter, possess the capability to safely upregulate alpha-secretase activity, decrease beta-secretase and gamma-secretase activity, and enhance clearance of amyloid beta from the brain, thus potentially establishing homeostasis between amyloid beta production and clearance. These pleiotropic capabilities as applied to the preonset “zero stage” of AD may provide a unique primary prevention competence prior to disease-process onset.

Vasopressinergic neurons in rats in ontogenesis: Responses to salt loading and their modulation by noradrenergic afferents

Salt loading in adult mammals leads to increased vasopressin secretion by vasopressinergic neurons in the supraoptic nucleus, which is mediated by the actions of a number of hormones and neurotransmitters, including noradrenaline. The present study addressed identification of the stage of ontogenesis at which vasopressinergic neurons start to respond to salt loading and when the noradrenalinergic regulation of this process begins. Studies were performed on rats at embryonic day 21 (E21), postnatal day 3 (P3), and postnatal day 13 (P13) using immunocytochemical and in situ hybridization. Animals were subjected to salt loading, in some cases on the background of the alpha1-adrenoceptor inhibitor prazosin. Salt loading in rats of all age groups induced increases in the synthesis of vasopressin mRNA, probably accompanied by increased synthesis of vasopressin peptide. At E21 and P3, intraneuronal vasopressin levels were increased; there was no change at P13. In salt loading on the background of prazosin administration, vasopressin mRNA and vasopressin contents at E21 showed no change, while at P3 they were increased, which is evidence of the inhibitory effect of noradrenaline on vasopressin expression in the early postnatal period. Thus, vasopressinergic neurons start to respond to salt loading at the end of the prenatal period with increases in vasopressin expression; noradrenergic afferents have inhibitory influences on vasopressin expression in the early postnatal period.

Structural changes in the neocortex nervous tissue in rat ontogenesis after hypoxia at various terms of embryogenesis

The performed study has shown that in rats submitted to hypoxia (3 h, 7% O2) at the 14th day of embryogenesis (E14) as compared with control animals, density of distribution of cells in the brain cortex decreased for the first month of postnatal ontogenesis (maximally by 40.8% by P20). In dying neurons, swelling of the cell body, lyses of or ganoids, and disturbance of the cytoplasm membrane intactness were observed. Two waves of neuronal death by the mechanism of capsize-dependent apoptosis were revealed; the first involved large pyramidal neurons of the layer V (P10–20), the second-small pyramidal and non-pyramidal neurons of the layers II–III (P20–30). In neurosis of molecular layer, a decrease of the mean amount of labile synaptopodin-positive dendrite spines was observed, as compared with control. In rats exposed to hypoxia at E18, no changes of cell composition and structure of the nervous tissue were found in the studied brain cortex areas. Thus, formation of the cortex nervous tissue in postnatal ontogenesis of rats submitted to hypoxia at the period of neuroblast proliferation-migration is accompanied not only by a change of the cell composition of various cortex layers in early ontogenesis, but also by a decrease of the number of the synaptopodin-positive spines in the molecular layer, the decrease being preserved in adult animals.

Peculiarities of regulation of high-frequency oscillations of cardiac rhythm in rat ontogenesis

Dynamics of high-frequency components of heart periodogram whose main part is respiratory arrhythmia (RA) as well as consequences of vagotomy, block of M-cholinoreceptors by atropine and of beta-adrenoreceptors by propranolol was studied in Wistar white rats in a large age diapason from 2-4 days to adults. It was established that results of the actions in immature rats did not essentially differ from those observed in adult rats and described in animals of other species and in human. In rats of young age, predominant in genesis of RA is peripheral mechanism. Vagotomy produces an elevation of the RA amplitude due to a sharp increase of the inspiration time as well as to deafferentation. Sympathetic nervous system produces restricting action on RA. This role is preserved in animals of all age groups. Participation of parasympathetic innervation in the RA genesis is revealed from the third week and continues increasing to the mature age. However, in adult rats, the peripheral mechanism of the RA formation is preserved, as disturbance of parasympathetic innervation leads not to the disappearance of RA, but only to a decrease of its amplitude.

The brain is one of the most important sources of dopamine in the systemic circulation in the perinatal period of ontogenesis in rats

This study was designed to test the authors' hypothesis that dopamine passes from dopamine-synthesizing cells in the brain to the systemic circulation prior to the formation of the blood-brain barrier during ontogenesis. High-performance liquid chromatography studies demonstrated that peripheral blood dopamine levels before formation of the blood-brain barrier-in rat fetuses and neonates-are significantly higher than after formation of the barrier in adult rats, providing indirect evidence in support of the hypothesis. Furthermore, formation of the blood-brain barrier is accompanied by a significant increase in dopamine levels in the rat brain. Direct evidence for the hypothesis was obtained in the form of a sharp decrease in blood dopamine levels in fetuses after lesioning of dopamine-synthesizing neurons in the brain by encephalectomy.

Formation of cardiomotor interrelations in rat ontogenesis

Age-related transformations and nature of short-term positive and negative oscillations of cardiac contraction rhythm were studied in comparison with periodical spontaneous somatomotor activity bursts in rats for the first 3 weeks after birth. It has been established that both accelerations and decelerations can be independent, precede motor excitation or appear as a consequence of muscle contraction. The main role in genesis of decelerations is played by parasympathetic mechanisms whose action is blocked by atropine. Activation of vagus cardiomotor centers can ether occur spontaneously by producing independent declerations or appear as reaction to motor excitation. Genesis of accelerations is connected with activity of sympathetic nervous system, as they are inhibited under conditions of desympathization or block of adrenoreceptors. The main role in realization of accelerations is played by somatosympathetic reflex, but connection with motor activity can also be effected by the principle of pre-tuning to expected movement.

Formation of the structural and ultrastructural organization of the striatum in early postnatal ontogenesis of rats in altered conditions of embryonic development

Light (Nissl and Golgi methods) and electron microscopy methods were used to study the formation of the structure of the striatum during the first two weeks after birth in rats subjected to acute hypoxia at different times of embryogenesis. The dynamics of the physiological development of the same population of rats were studied in parallel. Hypoxia at day 13.5 of embryogenesis was found to lead to delayed neurogenesis (delayed establishment of elements of the neuropil and differentiation of cells) and abnormalities in the structure of the striatum (degeneration, particularly chromatolysis, of neurons and the appearance of glial nodes). Morphometric analysis demonstrated a decrease in the total number of cells in the striatum; small changes in large neurons were seen. Hypoxia at day 18.5 of embryogenesis produced no significant changes. Structural abnormalities were accompanied by changes in the process of the animals' physiological development. The data obtained here show that changes in the conditions of embryogenesis (hypoxia) during the period of the most intense proliferation of neuroblasts in the forebrain lead to impairment of the process of formation of striatal nervous tissue and the body as a whole in the period of early postnatal ontogenesis.

Expression of tyrosine hydroxylase in vasopressinergic neurons of the supraoptic nucleus in rat ontogenesis and its modulation by noradrenergic afferents

An attempt is made to find out, at what stage of ontogenesis an expression of gene and synthesis of tyrosine hydroxylase (TH) is started, and whether noradrenergic afferents participate in regulation of these processes. The study is carried out on rats at the 21st embryonal day (E21), P3 and P13 with use of quantitative and semi-quantitative immunocytochemistry and hybridization in situ. Animals of all ages were subjected to a salt load, in some cases on the background of introduction of and α1-adrenoreceptor inhibitor, prazozine. According to the obtained data, the TH expression in SON neurons in response to the salt load begins at P3. The number of VP-ergic neurons expressing TH during the salt load is 3-fold reduced from P3 to P13. Taking into account that the innervation of VP-ergic SON neurons is realized for this period of development, we formulated a hypothesis that the TH expression is inhibited by noradrenergic afferents. According to the obtained data, TH is not expressed in osmotically stimulated VP-ergic neurons on the background of prazozine injection at E21; however, this combined effect results in increased TH expression at P3 and P13. At P13, i.e., in animals with a more developed afferent innervation, the amount of TH-immunoreactive neurons is three times lower, than at P3. Thus, in ontogenesis of rats, VP-ergic neurons begin to respond to osmotic stimulation by inclusion of the TH gene expression and its synthesis at the neonatal period, the both processes being under the inhibitory control of noradrenergic afferents mediated through α1-adrenoreceptors.

Peculiarities of Formation of the Wakefulness—Sleep Cycle in Ontogenesis of Rats

Electrophysiological changes in the wakefulness—sleep cycle were studied in early postnatal ontogenesis of rat pups. EEG was recorded and its spectral power was determined, as well as spatial-temporal synchronization between the brain cortex zones (visual and sensomotor) and hippocampus in the process of sleep at various periods of ontogenesis. These data were compared with the literature data on studying of cytoarchitectonics and ultrastructure of rat neocortex as well as on formation of neuronal activity and maturation of transmitter systems at the same periods. Based on time of formation of interneuronal and interstructural connections and of maturation of transmitter systems, 3 stages of functional development of sleep in ontogenesis were identified: the first stage—undifferentiated sleep, the interneuronal connections are absent; the second stage—partially differentiated sleep, interneuronal connections function and control from subcortical structures appears; the third stage—differentiated sleep, clear division into sleep phase, additional control from all three transmitter systems: noradrenergic, cholinergic, and serotoninergic, action of the latter providing inhibitory mechanisms in CNS.

A Population of Neurons Expressing Tyrosine Hydroxylase and Migrating from Olfactory Placodes into Forebrain during Ontogenesis in Rats

Olfactory placodes, that give rise to the olfactory and respiratory epithelia during ontogenesis, are a source of many neurons migrating into forebrain in the direction of growth of the olfactory nerves. The neurons expressing gonadotropin releasing hormone (GnRH) are among the best studied in the population in question. This hormone is responsible for the central regulation of reproduction in adult animals. It was already shown that, in addition to the GnRH-immunoreactive neurons, a small amount of neurons expressing tyrosine hydroxylase (TH), the first enzyme of catecholamine synthesis, migrates into the forebrain. Such a transient population of TH-immunoreactive neurons was shown by means of single and double immmunohistochemical labeling. The TH neurons were first found on branches of the olfactory, terminal, and vomeronasal nerves, along the trajectory of migration of GnRH-immunoreactive neurons on day 15 of embryogenesis, which preceded the appearance of GnRH-immunoreactive neurons. On days 17-21 of embryogenesis, both populations of neurons were found in almost the same areas and on day 21 single neurons contained both GnRH and TH. There were no neurons expressing decarboxylase of aromatic acids (DAA), the second enzyme of catecholamine synthesis, among TH-immunoreactive neurons, thus suggesting noncatecholaminergic nature of these neurons. However, single nonenzymatic DAA-immunoreactive neurons were found in the area of anterior olfactory nuclei in the forebrain, which suggests their involvement in local cooperative synthesis of catecholamines in the area where GnRH-immunoreactive neurons penetrate in the forebrain. Thus, the neurons expressing TH, TH and GnRH, and DAA were found in rats during prenatal period in the nasal part of the head along the nerves projecting into the forebrain and in the rostral part of forebrain. The origin and functional significance of these neurons are discussed.

Secondary Rhythms of Cardiac Activity within Early Ontogenesis: Effects of Blocking of Adreno- and Cholinoreceptors in Rats

The genesis of secondary rhythms in autorhythmic functional systems is analyzed on the example of the spectra of fluctuations of the heart rate observed within early postnatal ontogenesis of rats (from the moment of birth until three weeks old). We studied the effects of blocking of α-adrenoreceptors with phentolamine (5 mg/kg, i.p.), of β-adrenoreceptors with propranolol (1 mg/kg), and of M cholinoreceptors with atropine (1 mg/kg). We concluded that sympathetic influences stabilize the cardiac rhythm in newborn animals, but from the second postnatal week the effects determining generation of secondary rhythms of cardiac activity begin to be mediated by these receptors. Parasympathetic effects on secondary cardiorhythms mediated by M cholinoreceptors are effective even in newborn rats. In rats older than 7 to 8 days, blocking of α-adrenoreceptors and M cholinoreceptors led to the same result, synchronization of the secondary cardiac rhythms. Disorders in the afferent link of the baroreflex arcs after the blockade of α-adrenoreceptors and cessation of transmission in the efferent link of these arcs after blockade of M cholinoreceptors are considered a probable reason for this phenomenon.

Development of Lateralization of Unconditional Motor Reactions in Early Ontogenesis of White Rats

The problem of development of lateralization of motor systems in the course of early ontogenesis is important for understanding regularities of formation of functional characteristics of motor control. To solve these tasks, in the 8–74-day old rat pups the presence of lateralization was studied in two motor tests: the choice of the preferable rotation direction at holding the rat by the tail and the choice of one of the forelimbs in the test of initiation of the limb placement onto a support. It has been shown that in early ontogenesis, until the age of the sexual maturation, no constant lateralization is observed in realization of the unconditional motor reactions in any of the performed tests. The turning point of the establishment of the lateral preference has been revealed to correspond to the three-week age (the 21–23rd days), while the final lateralization both for individual animals and for the entire sample takes place at the age of 1.5–2 months. It is suggested that development of lateralization of the limb placement on a support occurs with the approximately two-week delay as compared with the process of formation of the preference in the choice of the rotation direction.

Activity of Acetylcholinesterase in the Motor-Sensory Cortex in Early Ontogenesis of Rats Exposed to Prenatal Hypoxia

Effects of acute prenatal hypoxia (13–14 days of gestation, 3 h, O2 = 7%) on acetylcholinesterase (AChE, EC 3.1.1.7) activity in homogenates, synaptosomes, and cytosol of the motor-sensory cortex of Wistar rats were studied on the days 1, 5, 10, 19 and 30 after birth. In homogenates of normally developing cortex, the AChE activity did not significantly change with age. Activity of AChE in synaptosomes increased 4 times throughout the entire period of observation, while in the cytosol, 4.3 times to reach maximum at the 19th day. Maximum rise of the AChE activity in synaptosomes was observed at the period from the 5th to the 10th day. Activity of AChE in homogenate and synaptosomes of rats submitted to prenatal hypoxia decreased during the first five days after birth (p < 0.001) but later, starting from the day 10, it increased in all fractions. A statistically significantly higher activity of AChE than in controls was revealed in homogenate of the motor-sensory cortex on day 19 (p < 0.01), while in synaptosomes, on the days 19 and 26 (p < 0.001 and p < 0.05, respectively), and in cytosol, on the days 10, 26, and 30 (p < 0.05, p < 0.05, and p < 0.001). Maximum change in the ratio of AChE activities in cytosol and synaptosomes was found on the day 19 (p < 0.01). At the same period of development, changes in the ratio of AChE activity in synaptosomes and homogenate of the control and hypoxic animals were also observed. Thus, prenatal hypoxia leads to in changes in the activity both of the cytosol and synaptosomal membrane-bound forms of AChE in the motor-sensory cortex of rats, which agrees with our own and literature data on disorder of neuro- and neuritogenesis in the process of formation of CNS and of behavioral reactions in early postnatal ontogenesis under the effect of pathogenic factors at certain days of prenatal ontogenesis.

Function of the hypothalamo-pituitary-adrenocortical system during ontogenesis in rats with inherited stress-induced arterial hypertension.

The functional activity of the hypothalamo-pituitary-adrenocortical system (HPAS) during the development of rats with inherited stress-induced arterial hypertension (HSIAH rats) was compared with that in normotensive Wistar rats. In rats aged 2, 3, 4, 6, 8, 10, 12, and 18 weeks, competitive protein binding assays were used to estimate peripheral blood plasma corticosterone levels at rest and after 1 h of restricted mobility in mesh cylinders. Basal corticosterone levels and HPAS responses to stress were lower during ontogenesis in hypertensive rats than in Wistar rats of the same age. The exception was rats aged four weeks, when HSIAH rats started to develop hypertension and their HPAS was more sensitive to emotional stress than was the case in Wistar rats, this being associated with the greater reaction of the adrenals to ACTH. Decreased reactions of the HPAS to emotional stress in adult HSIAH rats is not associated with loss of adrenal ACTH sensitivity.

Hypothalamo-pituitary system controls the development of humoral immune response during prenatal ontogenesis in rats

We studied the influence of the neuroendocrine system on the development of humoral immune response to sheep erythrocytes in rat fetuses. The removal of brain in utero by decapitation of 18-day fetuses induced a fourfold increase in the number of antibody-forming cells in the liver, as compared to the unoperated fetuses. After the removal of the forebrain, including hypothalamus (encephalectomy), the number of antibody-forming cells was comparable to that in unoperated fetuses. The observed increase in the number of antibody-forming cells in the liver was not due to a disturbed migration of precursors of B-lymphocytes in the spleen, since their content in the spleen was also four times that in the encephalectomized and unoperated fetuses. The increased number of antibody-forming cells in decapitated fetuses could be due to an enhanced proliferative activity of the lymphocytes in the liver of these fetuses. It has been proposed that humoral immunity is controlled by the hypothalamo-pituitary-adrenal system already during prenatal development; the adrenocorticotropic hormone and glucocorticoids appear to be involved in this regulation.

Expression of glucose transporter‐2, glucokinase and mitochondrial glycerolphosphate dehydrogenase in pancreatic islets during rat ontogenesis

To gain better insight into the insulin secretory activity of fetal beta cells in response to glucose, the expression of glucose transporter 2 (GLUT-2), glucokinase and mitochondrial glycerol phosphate dehydrogenase (mGDH) were studied. Expression of GLUT-2 mRNA and protein in pancreatic islets and liver was significantly lower in fetal and suckling rats than in adult rats. The glucokinase content of fetal islets was significantly higher than of suckling and adult rats, and in liver the enzyme appeared for the first time on about day 20 of extrauterine life. The highest content of hexokinase I was found in fetal islets, after which it decreased progressively to the adult values. Glucokinase mRNA was abundantly expressed in the islets of all the experimental groups, whereas in liver it was only present in adults and 20-day-old suckling rats. In fetal islets, GLUT-2 and glucokinase protein and their mRNA increased as a function of increasing glucose concentration, whereas reduced mitochondrial citrate synthase, succinate dehydrogenase and cytochrome c oxidase activities and mGDH expression were observed. These findings, together with those reported by others, may help to explain the decreased insulin secretory activity of fetal beta cells in response to glucose.

Hypothalamo-pituitary-adrenocortical function in the ontogenesis in rats with hereditary stress-induced arterial hypertension

Functional activity of the hypothalamo-pituitary-adrenocortical system (HPAS) was evaluated over time in rats with hereditary stress-induced arterial hypertension (HSIAH) and normotensive Wistar rats. Peripheral blood plasma corticosterone was measured in rats aged 2, 3, 4, 6, 8, 10, 12, and 18 weeks at rest and after 1-h immobilization in perforated cylinders by competitive protein binding. Basal corticosterone level and HPAS reaction to stress were lower in hypertensive rats than in Wistar rats of the same age. The only exclusion was the age of 4 weeks, when hypertension starts to form in HSIAH rats and their HPAS is more sensitive to emotional stress than that of Wistar rate, this sensitivity being associated with increased adrenal reaction to ACTH. Decreased HPAS reaction to emotional stress in adult HSIAH rats was not associated with disorders in adrenal sensitivity to ACTH.