Mechanisms of formation of background activity of cerebral neurons in ontogenesis

Background activity of brain cortex neurons in ontogenesis appears very early, soon after completion of their migration. At the moment of its appearance, the background activity has several peculiarities, the most characteristic of which are its episodic character and synchronous bursts of adjacent neurons forming domains. This paper considers mechanisms determining the appearance and the most characteristic peculiarities of the background activity of cerebral cortex neurons in ontogenesis.     

Development of dendritic spines in the piriform neurons of the cerebellar cortex in human prenatal ontogeny

The submicroscopic investigation on developmental peculiarities of the dendritic spines in the piriform neurons of the cerebellar cortex has been performed during the human prenatal ontogenesis. The process of morphogenesis of the spines of the tertiary dendrites in the piriform neurons is demonstrated to start rather early--on the 24th week of embryogenesis and goes through three successive stages: 1) formation of a long cytoplasmic processes deprived of any membranous specialization; 2) formation of the terminal spinal head, making synapses with parallel fibers of the cerebellar cortex; 3) definitive stage. A suggestion is made that differentiation processes of the spines depend on inductive influence of the parallel fibers of the cerebellar cortex.     

Formation of cortical inhibition in ontogenesis

Analysis of the literature on the development of cortical inhibition suggests that synaptic inhibition of cerebral cortical neurons arises almost simultaneously with the onset of their background activity. All types of cortical inhibition operate simultaneously since the emergence of inhibitory processes. Thus, the basic mechanisms of cortical inhibition in mature cerebral cortex begin to function since cortex activation at the earliest stages of ontogenesis.     

Neuronal Organization of Mammalian Stellate Ganglion in Postnatal Ontogenesis

The paper considers the problem of peculiarities of maturation of the stellate ganglion nerve elements in mammals of different species. This process differs in precocious and altricial animals. It has been shown that in spite of some individual peculiarities, the neurons, fibers, and conducting pathways in altricial animals are not, on the whole, completely formed morphologically and functionally. In the course of postnatal ontogenesis, not only an increase of cell sizes and development of dendrite tree, but also reorganization of nerve connections with target organ occur. The postnatal ontogenesis is also accompanied by an increase of the excitation transmission rate along the fibers and by their myelination. The asymmetry of the right and left stellate ganglia (SG) by their sizes and functional peculiarities, which exists in adult animals appears as soon as at early stages of postnatal development. The neural elements of precocious animals are changed to a lesser extent in postnatal ontogenesis and are, in many aspects, similar to those of adult organisms as early as at birth.     

Electron microscopic and cytointerferometric study of the cortical neurons from the 2d-generation progeny of preneurosensitized female rats

A study was made of the sensorimotor cortex of the brain of the second generation offspring of preneurosensitized female rats. Vacuolization of the neurocyte nuclei, elevated lability of nuclear membranes, appearance of numerous dark neurons were discovered at all times of postnatal ontogenesis (from 2 to 90 days). At the same time ultrastructure of a considerable number of neurons was unchanged. The tendency toward normalization of cellular structures was noted by the 3d month. The one-month-old rats demonstrated a decrease in the content of protein substances in the nucleus and cytoplasm of the neurons as compared to normal. By the 3d month this indicator rose but did not reach the control level. It is concluded that neurosensitization of females before pregnancy affects the morphofunctional state of the neurons of the cerebral cortex in both first and second generation offspring, although the changes seen in the latter offspring are less marked, being compensated for with time.     

The background and evoked neuronal impulse activity of embryonic neurotransplant of somatosensory brain cortex in rats

The investigation was intended for studying the character of the background and evoked impulse activity of embryonic neurotransplant neurons 4 months after homotopical allotransplantation into the barrel field of somatosensory recipient's brain cortex of the rat. It is established, that the current average frequency of background impulse activity of transplant neurons is reduced in comparison with one of the control rats. It is shown that the evoked impulse activity of neurotransplant develops with the long latency than in somatosensory cortex of the control animals. Thus in patterns of the evoked activity of neurotransplant cells reactions, characteristic for the neurons of barrel field somatosensory recipient's cortex of control rats are registered: an increase of frequency of pulses' generating, or alternating of the activation and reduction periods of impulse frequency with its subsequent regeneration up to a pristine level.     

Lesion and regeneration in the medial cerebral cortex of lizards.

The cerebral cortex of Squamate reptiles (lizards and snakes) may be regarded as an archicortex or "reptilian hippocampus". In lizards, one cortical area, the medial cortex, may be considered as a true "fascia dentata" on grounds of its anatomy, connectivity and cyto- chemo-architectonics of its main zinc-rich axonal projection. Moreover, its late ontogenesis and postnatal development support this view. In normal conditions, it shows delayed postnatal neurogenesis and growth during the lizard's life span. Remnant neuroblasts in the medial cortical ependyma of adult lizards seasonally proliferate. The late-produced immature neurocytes migrate to the medial cortex cell layer where they differentiate and give off zinc-containing axons directed to the rest of cortical areas. This results in a continuous growth of the medial cortex and its zinc-rich axonal projection. Perhaps the most important characteristic of the lizard medial cortex is that it can regenerate after having been almost completely destroyed. Recent experiments in our laboratory have shown that chemical lesion of its neurons (up to 95%) results in a cascade of events; first, those related with massive neuronal death and axonal-dendritic retraction and, secondly, those related with a triggered neuroblast proliferation and subsequent neo-histogenesis, and the regeneration of an almost new medial cortex that shows itself undistinguishable from a normal undamaged one. This is the only report to our knowledge that an amniote central nervous centre may regenerate by new neuron production and neo-histogenesis. Perhaps the medial cortex of lizards may be used as a model for neuronal regeneration and/or transplant experiments in mammals or even in primates.     

Reactions of neurons of the parietal associative cortex field 7 to electric stimulation of the latero-dorsal and postero-lateral thalamic nuclei]

Neuronal responses of the parietal associative cortex (PAC) field 7 to the electrical stimulation of laterodorsal (LD) and posterolateral (PL) thalamic nuclei were studied in calypsol-narcotized cats. A correlation between depth, duration of the background activity inhibition and latent periods was determined for distribution of neurons responding to stimulation of associative nuclei by impulses. It is shown that there are functional relations between LD and field 7 of PAC. Common and specific peculiarities of neuronal responses of the associative cortex were found when a volley of impulses came from LD- and PA-nuclei of the thalamus.     

Identification of Cajal-Retzius cells during neocortical ontogenesis in mice with fluorescent carbocyanine

Cajal-Retzius cells, which are present transiently in the first layer of the mammalian neocortex, have been revealed in the mouse by DiI. This lipophilic fluorescent dye, locally applied over the cortex after formaldehyde fixation, allowed the global view of cortical cells. During ontogenesis, Cajal-Retzius cells retained their initial characteristic bipolar shape and orientation parallel to the meningeal surface. The bright fluorescent light emitted by this dye allowed visualization of the labelled cells by "microtomoscopy" using a confocal scanning laser microscope and analysis of the detailed aspect of these neurons and of their connections.     

Postnatal physiological development of rats after acute prenatal hypoxia

The aim of study was to investigate the physiological development of the brain and behaviour in rats subjected to prenatal hypoxia on the 13.5th day of embryogenesis. We have found that such rats manifested a delayed physiological development and a change in nervous tissue of the sensorimotor cortex, as well a disturbed formation of motor responses during the first month of postnatal ontogenesis. During maturation these modifications were in part compensated, however we observed a decrease of the rats' ability to learn new forepaw movements. The destruction of the brain tissue and the modification of neurons composition in the sensorimotor cortex correlated with changes of behaviour at different stages of ontogenesis. Thus, changes of the conditions under which an organism develops during embryogenesis, predetermine a disturbance in ontogenesis and the learning ability.     

THe age-related characteristics of interhemispheric asymmetry during the perception of verbal information by stuttering children]

Age peculiarities of functional brain asymmetry in perception of emotional information of the speech have been revealed. It was shown that the age of 4-7 years is the most important period in ontogenesis for the age dynamics of functional brain asymmetry in perception of emotions. It is in this particular age that functional reorganization of perception in stuttering children is observed. The revealed disturbances in functional brain asymmetry indicate that correction of emotional activity in stutterers should be made during early periods of ontogenesis.     

The development of thalamocortical connections studied by using carbocyanine dyes in the early ontogeny of rats]

We studied the differentiation of neurons and development of their connections in the occipital cortex and thalamic areas of the brain in early ontogenesis of rats: from day 11 of embryogenesis until day 19 of postnatal development. We used the method of staining of brain tissues by carbocyanine dyes after its preliminary fixation in aldehydes. Three carbocyanine dyes were used: DiI, DiO and DiA. We showed the dynamics of structural differentiation of the cortical neurons and lateral geniculate body of the thalamus and the specificity of formation of the axonal pathways between the neocortex and thalamic areas. The results obtained confirmed the hypothesis on ordered spatial-temporal growth of the cortical and thalamic fibers in early embryogenesis and revealed synchronous development of both classes of neurons of the lateral geniculate body. Retrograde and anterograde staining of the nerve cells processes by DiI and DiO showed fine morphological details of their structure. DiI provided for a good staining of the cells until day 19 of postnatal ontogenesis and DiO, until the end of embryogenesis, while DiA was not capable of diffusion in the fixed tissue.     

Neuronal mechanisms of interaction of Deiters nucleus with the cerebral cortex.

The effects of stimulation of the vestibular nerve and five different cerebral cortex areas on the neuronal activity of the lateral vestibular nucleus of Deiters were studied. Stimulation of the cerebral cortex is shown to lead to antidromic and synaptic activation of Deiters neurons. The synaptic potentials of Deiters neurons evoked from the cerebral cortex were of mono- and polysynaptic origin. In particular, stimulation of the cerebral cortex evoked in Deiters neurons mono- and polysynaptic excitatory postsynaptic potentials. Collaterals of vestibulospinal neurons reaching different cortex fields as well as convergence of influences from these cortex fields on Deiters neurons were revealed. Inhibitory effects of the cerebral cortex on Deiters neurons were of polysynaptic origin and occurred rarely. The topical correlation between Deiters nucleus and different areas of the cerebral cortex was found. The peculiarities and functional significance of the effects obtained are discussed.     

Change of 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 disposition 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, lysis of organoids, and disturbance of the cytoplasmic membrane intactness were observed. Two waved of neuronal death by the mechanism of caspase-dependent apoptosis were revealed; the first involved large pyramidal neurons of the V layer (P10-20), the second--small pyramidal and non-pyramidal neurons of the II--III layers (P20-30). In neuropil 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 molecular layer, the decrease being preserved in adult animals.     

Comparative study of effects of cortical nucleus of amygdala and pyriform cortex on activity of bulbar respiratory neurons in cats

Comparative microelectrophysiological study of character and peculiarities of effects of the cortical nucleus of amygdala and of the periamygdalar area of pyriform cortex on impulse activity was performed on the same single functionally identified respiratory medullar neurons. A high reactivity of bulbar respiratory neurons on stimulation is established in both studied limbic structures. There is established the qualitatively different character of their response reactions at stimulation of the cortical amygdala nucleus and the periamygdalar cortex. The cortical amygdala nucleus has been shown to produce on the activity of medullar respiratory neurons both facilitating and inhibitory action with predominance of the activating one (without topographical orderliness). The effect of periamygdalar cortex at stimulation of various parts was characterized by topographic differentiation. The suppressing reactions of neurons in the majority of cases were recorded at stimulation of the rostral area of periamygdalar cortex, whereas the excitatory reactions--at stimulation of its caudal part. Functional organization of respiratory control of the studied limbic system structures is discussed.     

Comparative study of effect of cortical nucleus of amygdala and pyriform cortex on activity of bulbar respiratory neurons in cats

Comparative microelectrophysiological study of character and peculiarities of effects of the cortical nucleus of amygdala and of the periamygdalar area of pyriform cortex on impulse activity was performed on the same single functionally identified respiratory medullar neurons. A high reactivity of bulbar respiratory neurons to stimulation is established in both studied limbic structures. There is established the qualitatively different character of their response reactions at stimulation of the cortical amygdala nucleus and the periamygdalar cortex. The cortical amygdala nucleus has been shown to produce both facilitating and inhibitory effects (with predominance of the activating one) on activity of medullar respiratory neurons (without topographical orderliness). The effect of periamygdalar cortex at stimulation of various parts was characterized by topographic differentiation. The suppressing reactions of neurons in the majority of cases were recorded at stimulation of the rostral area of periamygdalar cortex, whereas the excitatory reactions-at stimulation of its caudal part. Functional organization of respiratory control of the studied limbic system structures is discussed.     

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.     

Main principles of the organization of the microcirculatory bed of the human greater omentum in early ontogenesis

The formation process of the terminal blood bed of the greater omentum has been studied in 42 human fetuses 14--28-week-old. The main peculiarities of the greater omentum blood bed by the 14th week of development are: paired arrangement of the afferent and deferent blood vessels and loop-shaped type of capillary growth, that joining the arteriole and venule, lend the blood stream a maximally centralized character. In 15--16 weeks of the fetal development in the omentum another type of the vascular growth occurs, characterized with appearance of single angioblastic processes that branch off the apex of the capillary loops. As a result new capillaries form; they connect apices of the capillary loops, that in their turn make bases for developing a true capillary network. Together with this, presence in ontogenesis of an autochthonous way of capillary appearance is proved, their connection with the closed blood stream is followed. Distinguishing of the loop-shaped stage in the capillary growth determines certain difference between vasculogenesis in ontogenesis and the vascular growth at reparative regeneration, since the base for the latter is only the capillary growth by means of single angioblastic processes.     

Ultrastructure of sensorimotor cortex neurons in the progeny of rats receiving alcohol during pregnancy

Dynamics of ultrastructural changes in the sensomotor cortex neurons has been studied on the 21st, 30th and 60th days of life in offspring born by the rats given 20% alcohol (2 g/kg) during pregnancy. Moderate antenatal alcoholization produces certain disturbances in the ultrastructure of the cortical neurons and their dendrites. This is manifested as presence of retardation signs in maturation of nervous cell populations, as dystrophic changes in the neurons and their dendrites and display of reparative character with their own dynamics in the postnatal period of ontogenesis. The first two categories of the ultrastructural changes in the cortical neurons are more manifested at early stages of the postnatal development of the offspring, and the reparative processes--at the age of two months. Despite the presence of the reparative shifts, the dystrophic changes of the neurons of hypoxic character are present up to the period of sexual maturation. This demonstrates that the antenatal alcoholic intoxication in the offspring is manifested in the postnatal ontogenesis for a long time.     

Gamma- and UV-induced DNA synthesis in neurons of the rat neocortex

Nuclear DNA synthesis in neocortex neurons of neonatal 14- and 60-day rats after in vitro irradiation of isolated sections was estimated by the incorporation of a labeled precursor into DNA. gamma- and UV-radiation increased the rate of DNA synthesis in the cells of animals of all studied age groups. However, the level of the UV-induced synthesis sharply dropped during the postnatal ontogenesis while gamma-radiation-induced synthesis decreased slightly. The peculiarities revealed in the repair DNA synthesis seem to be influenced by the process of postnatal differentiation of a neuron accompanied by the nucleosome length shortening and the decrease in the DNA-polymerase alpha content.