Mechanisms of formation of brain cortex background activity 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 has several peculiarities, the most characteristic of which are its episodic character and synchronous fires of adjacent neurons forming domains. This paper considers mechanisms determined the appearance and the most characteristic peculiarities of the background of cerebral cortex neurons in ontogenesis.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Effect of the vermian cortex of the anterior lobe of the cerebellum on the background electrical activity of fastigial neurons

The effect of electrical stimulation of the vermian cortex of the anterior lobe of the cerebellum on the activity of neurons of different portions of the fastigial nucleus was studied in acute experiments on cats under light nembutal anesthesia. Inhibitory influences of the cortex (80.6% of the reacting neurons) were manifested in total blocking or decrease in the frequency of the background activity of the neurons and were characterized by a long aftereffect and "rebound." Stimulation of the cortex also had a blocking effect on the inhibitory interaction of adjacent nuclear elements. Facilitatory influences (14.5% of the neurons) were expressed either by an increase of spontaneous discharges of the neurons or by the appearance of activity in rhythm with the stimulation. The effectiveness of cortical stimulation depended on the localization of the stimulating electrodes. Zones of maximum density of projections to a given neuron of the nucleus and convergence and divergence of influences were found in the cerebellar cortex.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziolgiya, Vol. 2, No. 3, pp. 260–268, May–June, 1970.     

Chromatin matrix activity in Purkinje cells and granular cells of the rat cerebellar cortex during postnatal differentiation

Moore's method used for the examination of chromatin template activity in Purkinje and granule cells of 7, 14, 30 days and 3 months old rate cerebellar cortex has shown the age-dependent changes during differentiation period. The histograms for Purkinje cells have demonstrated that all neurons were distributed into 3 groups of activity according to their nuclear labelling. The cell percentage in each group varied during ontogenesis.     

Influence of prenatal stress on free radical oxidation lipids, both proteins and activity of superoxiddismutase in neurones and glial cells of the rat brain cortex

Processes of free radical oxidation of protein, lipids, and activity of superoxiddismutase in neurons and glial cells of the rat brain cortex in ontogenesis and after prenatal stress. Irrespective of age, the level of free radical oxidation of lipids and proteins in neurons is higher in comparison with the glia. The same was found in the study of superoxiddismutase activity. After prenatal stress, the level of free radical oxidation of lipids is reduced both in neurons, and in the glia. On the contrary, the contents of oxidation of proteins rises in neurons on the average fourfold. Activity of superoxiddismutase in animals who had suffered from prenatal stress is considerably reduced in neurons remaining unchanged in glial cells.     

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.     

Cerebellum and organization of behavior: A comparative-physiological aspect

The ontophylogenetic analysis of morphofunctional peculiarities of the cerebellum shows its extremely high adaptability to the requirements for the organization of the nervous activity of the organism corresponding to the level of its evolutionary development and ecological habitat conditions. The changes of the cerebellum in the course of its onto- and phylogenetic development appear to be more pronounced as compared with other cerebral regions. Depending on the level of the development, revealed are different aspects of the cerebellar integrative activity which contributed, if necessary, a quite new directions of the nervous activity, such as learning and cognition, which demonstrates astonishingly wide limits of the adaptability. This explains that the cerebellum in various vertebrates is considerably different by its shape, location of neurons in the cerebellar cortex, and the main peculiarities of afferent, internal, and efferent pathways. There is a reason to suggest that the future study of these aspects of the cerebellar activity will bring us to a clearer understanding of the cerebellar mechanisms of learning.     

Integrative properties of parietal cortex neurons of rabbits during the switching of heterogeneous classical conditioned reflexes

The impulsive activity of parietal cortex neurons of rabbits during the elaboration and specialisation of switching-over of alimentary and defensive conditioned reflexes has been studied. There are changes of parietal cortex neurons activity correlated with the stages of switching-over elaboration. The significant differences of the background neurons activity and neurons response to the conditional signal during alimentary and defensive conditioned reflexes have been established. The dominant motivation influences the neurons activity by modulation of background and conditioned activity of neurons. The integrative properties of neurons investigated in switching-over situation are revealed in their ability to summarize the excitation coming to the same sensory input with excitation from different motivational and reinforcement systems.     

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.     

The modulation of the pulse activity of neocortical neurons during a conditioned reflex]

Spontaneous and evoked activity of neurons in the sensorimotor cortex was recorded in cats with learned conditioned placing reaction before, during, and after the iontophoretic application of synaptically active substances. It was shown that apart from direct excitatory effect on the cortical neurons during its application, glutamate (Glu) exerted some modulatory influence on unit activity in subsequent 20 min. Noradrenaline suppressed the background and evoked activity through beta 1 adrenoreceptors. Activation of beta 2 adrenoreceptors by metaproterenol was accompanied by facilitation of the background and evoked activity during application and 10-20 min after. The joint application of Glu and metaproterenol improved facilitation of neuronal responses evoked by conditioned stimuli. Application of levodopa, like Glu, increased the background and evoked activity of many sensorimotor cortical neurons. The joint effect of Glu and levodopa was not substantially more intensive than the changes produced by the isolated application of any of these substances. A nonselective blocker of DA1 and DA2 receptors haloperidol either increased or did not change the background and evoked activity of some cortical neurons. In contrast to isolated application of Glu, simultaneous application of Glu and haloperidol to neocortex suppressed the neuronal responses associated with conditioned movements. The results suggest that the Glu-induced potentiation is substantially realized through molecular mechanisms common for Glu and dopamine, probably, through Gi-proteins. The conclusion is drawn that the adrenergic and dopaminergic inputs to neocortical neurons are involved in the Glu-mediated plastic changes in the cortex during conditioning.     

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.