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.     

Biochemical characteristics of the synaptosomes and mitochondria of the motor area of the cerebral cortex following switching off of sensory impulsation]

Changes in the specific activity of cytochrome oxidase, monoamine oxidase, acetylcholinesterase and Na,K-ATPase in the light and heavy synaptosomes and mitochondria of neurone bodies fractions in the motor cerebral cortex of rabbits were demonstrated under conditions of light (visual) deprivation. These changes were specific of different metabolic cycles and differed in individual cell ultrastructures. The influence of sensory impulsation on functional neuron activity in different projection regions of the cerebral cortex is discussed.     

Ultrastructural modifications in the hypophyseal-adrenocortical system in rabbits during experimentally induced parodontosis (author's transl)

During parodontosis induced experimentally by irritation of dental pulp with carbolic acid in rabbits, the participation in the pathological process of adenohypophyseal ACTH-producing cells and of adrenocortical fasciculata cells was studied. Ultrastructural alterations suggesting stimulation of ACTH and glycocorticoid synthesis were observed. The data obtained prove that via afferent pathways to the central nervous system, irritation of the dental pulp induces morphofunctional alterations in the hypothalamo-adenohypophyseal neurosecretory system, by means of functional perturbation of the cerebral cortex leads to hypothalamus (CRF) leads to adenohypophysis (ACTH) leads to adrenal cortex (glucocorticoids)axis.     

Postnatal development of the scratch reflex in rabbits]

The development of the scratch reflex was studied in newborn (up to 2 months old) rabbits in norm and after elimination or activation of some parts of their nervous system (reticular formation, cerebellum, caudate nucleus, cerebral cortex, superior cervical sympathetic ganglia). The experiments with the section of the brain stem at the border between the medulla and the midbrain showed that in very young (5-10 days old) rabbits in norm the scratch reflex is controlled by the spinal cord with no influences of structures situated above the section's level. Later on the spinal mechanism of the scratch reflex becomes subject to supraspinal influences, among which in 2-3 weeks old animals facilitatory effects are predominant produced, in particular, by the reticular formation and the cerebellum, whereas in older age prevail inhibitory influences of the cerebral cortex, cerebellum, caudate nucleus and the sympathetic nervous system.     

EEG, ERP in selective attention paradigm and the level of some metabolites in brain prefrontal cortex

The preliminary analysis at the first stage of the research has revealed the statistically significant correlations between electrophysiological parameters and the level of several metabolites (determined by magnetic-resonance spectroscopy) in the left dorsolateral prefrontal cortex. The findings are assumed to be due to the individually specific peculiarities of activation of this brain region and its impact on the information processing. The neurophysiological markers of decreased brain functional state are associated with the lower N-acetyl aspartate and choline and higher level of creatin/phosphocreatin in the tested region of prefrontal cortex.     

Neurophysiologic and biochemical aspects of visual system development in the rabbit under conditions of photic deprivation]

Changes in the functional state of the visual cortex were studied by behavioral and electrophysiological cues and the chemism of its neurones at the cellular and subcellular levels in rabbits raised for one to two months in the dark. It has been shown that visual deprivation leads to retarded dynamics of elaboration and consolidation of the conditioned defensive reflex to light and to changes of opposite signs of the visual cortex surface EPs to specific and non-specific stimuli. Typical of the EPs to photic stimuli is a considerable decrease in amplitude and longer latency as compared with normal, and enhanced amplitude and shorter latency to acoustic stimuli. It has been cytochemically established that about half of the pyramidal neurones of the visual cortex layer V of the experimental animals display features of biochemical underdevelopment (of the size of the cytoplasmatic mass, the protein reserve). Under the same conditions activity depression was revealed in cytochromoxydase, Na, P-ATPhase and ACHE, expressed to a different degree in separate subcellular fractions of the visual cortex. The MAO activity selectively augments in the subfraction of cholinergic synaptosomes. It has been assumed that functional and biochemical changes in different groups of the visual cortex neurones due to deprivation are linked with both the properties of the synaptic structures in regard to perception of impulses of different modalities and the peculiarities of their chemism.     

Causal interactions between the cerebral cortex and the autonomic nervous system

Mental states such as stress and anxiety can cause heart disease.On the other hand,meditation can improve cardiac performance.In this study,the heart rate variability,directed transfer function and corrected conditional entropy were used to investigate the effects of mental tasks on cardiac performance,and the functional coupling between the cerebral cortex and the heart.When subjects tried to decrease their heart rate by volition,the sympathetic nervous system was inhibited and the heart rate decreased.When subjects tried to increase their heart rate by volition,the parasympathetic nervous system was inhibited and the sympathetic nervous system was stimulated,and the heart rate increased.When autonomic nervous system activity was regulated by mental tasks,the information flow from the post-central areas to the pre-central areas of the cerebral cortex increased,and there was greater coupling between the brain and the heart.Use of directed transfer function and corrected conditional entropy techniques enabled analysis of electroencephalographic recordings,and of the information flow causing functional coupling between the brain and the heart.     

"The avoidance" of the direct current application to the sensorimotor cortex (a computer-controlled experiment in rabbits)

In a computer controlled experiment the electric activity of rabbits right sensorimotor cortex was recorded in the area of the excitation focus produced by the direct current (2 mcA) application. The current was switched on at the 5th, 10th and 15th minutes of experiment only in cases when the mean amplitude of the delta waves exceeded the baseline. The current was switched off at the mean amplitude of the delta waves exceeding the baseline level by 50%. After training some experiments (2-4), rabbits learned to change their functional state in such way that they "avoided" the action of the direct current.     

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.     

The structure of the background EEG of the rabbit in the high-frequency portion of the spectrum]

With the purpose of studying the character and structure of high frequency bioelectric activity of rabbits cerebral cortex in the state of calm alertness, the EEG ensembles of different areas of the cortex (sensorimotor, visual, acoustic) and dorsal hippocampus were studied with FFT method. A supposition was made about the presence of systemic organization of the background EEG in rabbits cerebral cortex, reflected, in particular, in the presence of determined components both of chaotic and rhythmic character having different degrees of manifestation. Heterogeneity was revealed in distribution of energies of spectral EEG components in the studied frequency ranges from 14.7 to 100 Hz with predominance of total specific energy value in the band of 14.7-60 Hz. In coherence functions of all the studied pairs of EEG leads rhythmic component, stable in time, was absent. Functions of the mean EEG coherence in the band of 61-100 Hz had significantly greater values in comparison with the values in the band of 14.7-40 Hz.     

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.     

Functional organization of the cortico-reticular system of the brain in response to physical loads

An estimation was carried out by factor analysis method of informative value of alpha-like rhythm, EEG theta-rhythm, local cerebral blood filling and oxygen tension (pO2) in estimation of functional state of cerebral structures under submaximal physical loads. Experiments were carried out on 35 rabbits with electrodes chronically implanted in the sensorimotor cortex and reticular formation. The obtained values were processed by a variant of factor analysis--a method of main components. For interpretation of factor loads matrix an orthogonal turn of factor axes was carried out according to varimax criterion. It has been established that informative value of the parameters depends on the brain structure where the given parameters were defined. Dynamics of pO2 and the theta-rhythm mostly influence the changes in other parameters. The states of structures before and during the period of physical load after-effect are mostly characterized by the brain local blood filling and less by the theta-rhythm amplitude.     

Selective Modulation of Interhemispheric Functional Connectivity by HD-tACS Shapes Perception

Oscillatory neuronal synchronization between cortical areas has been suggested to constitute a flexible mechanism to coordinate information flow in the human cerebral cortex. However, it remains unclear whether synchronized neuronal activity merely represents an epiphenomenon or whether it is causally involved in the selective gating of information. Here, we combined bilateral high-density transcranial alternating current stimulation (HD-tACS) at 40 Hz with simultaneous electroencephalographic (EEG) recordings to study immediate electrophysiological effects during the selective entrainment of oscillatory gamma-band signatures. We found that interhemispheric functional connectivity was modulated in a predictable, phase-specific way: In-phase stimulation enhanced synchronization, anti-phase stimulation impaired functional coupling. Perceptual correlates of these connectivity changes were found in an ambiguous motion task, which strongly support the functional relevance of long-range neuronal coupling. Additionally, our results revealed a decrease in oscillatory alpha power in response to the entrainment of gamma band signatures. This finding provides causal evidence for the antagonistic role of alpha and gamma oscillations in the parieto-occipital cortex and confirms that the observed gamma band modulations were physiological in nature. Our results demonstrate that synchronized cortical network activity across several spatiotemporal scales is essential for conscious perception and cognition.     

Effect of microwave radiation on regional blood flow and tissue oxygenation in the brain

The effect of irradiation of the central nervous system by microwaves (MW) at a frequency of 2450 MHz and power 5-40 W on the regulation of cerebral circulation and oxygen supply to the nervous tissue were studied in rabbits. Local irradiation of the exposed cerebral cortex resulted in hyperemia and hyperoxia in the zone of exposure induced by the hyperthermal effect of MW. When the region of the medulla oblongata was irradiated even with low MW power (not leading to hyperthermia), the local circulation and oxygen tension increased in the whole brain, apparently due to the impairment of the regulation of the cerebral blood flow and oxygen supply to the brain tissue.     

Intracellular progesterone receptors are differentially regulated by sex steroid hormones in the hypothalamus and the cerebral cortex of the rabbit

The aim of this study was to examine the role of sex steroid hormones in the regulation of intracellular progesterone receptors (PR) in the rabbit central nervous system. We determined PR concentration in cytosol preparations from the hypothalamus, the frontal, tempo-parietal and occipital cortex, by using the specific binding of the synthetic progestin [³H]ORG 2058. PR concentration was higher in the hypothalamus of intact adult females than in that of adult males and prepubertal females, whereas no significant differences were observed in the cerebral cortex of these animals. PR concentration was similar in the three cortical regions analyzed, indicating a homogeneous distribution of PR in the cerebral cortex. The administration of estradiol to ovariectomized animals increased PR concentration in the hypothalamus but not in the cortex. The administration of progesterone to ovariectomized rabbits did not modify PR concentration in any region, however when progesterone was administered after estradiol, it induced a significant diminution in hypothalamic PR concentration without effects in the cortex. These findings suggest that in the rabbit, PR are estrogen regulated in the hypothalamus but not in the cerebral cortex. In the latter, PR are not regulated by progesterone, whereas in the former the estrogen-induced PR are down-regulated by progesterone. Interestingly, hypothalamic PR constitutively expressed in ovariectomized animals are progesterone-insensitive.     

Various types of non-synaptic intercellular contacts in the developing brain of the rat

Peculiarities of ultrastructural organization and localization of early forms of avascular nonsynaptic types of junctions formed in 14-18-day-old rat embryos have been studied; cerebral structures different in their phylogenic relations (the sensomotor cortex and nucleus caudatus) are taken as an example. Five main types of nonsynaptic intercellular junctions have been revealed: desmosome-like, gap, symmetric, asymmetric and mixed junctions. They differ by their ultrastructural organization. These types of junctions make the main types of contacts: soma-somatic, dendro-somatic, dendro-dendritic, axo-somatic, axo-dendritic. Desmosomes form the greatest number of the contacts. The earliest and the most primitive are gap junctions; they, evidently, reflect functional activity of desmosome-like junctions. The mixed junctions, perhaps, reflect the developmental stages of the intercellular contacts of transition from one type of junctions into another. Localization peculiarities of the nonsynaptic intercellular contacts are demonstrated: glomerule-like formations, establishment of numerous contacts looking like a successive chain, and so on. For some other indices a longer period of intercellular contact formation in the nucleus caudatus is noted, comparing the sensomotor cortex, though the latter is a newer structural cerebral formation from the phylogenic point of view.     

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.     

The protein of glial intermediate filaments in different areas of the rat brain at experimental neurosis

The content and polypeptide composition of glial fibrillary acidic protein (GFAP) in the rat cerebral cortex, cerebellum, hippocampus, and mesencephalon were studied under conditions of experimental neurosis. Significant changes of the total GFAP content were observed in the hippocampus, mesencephalon, and cerebellum. Both the content and polypeptide composition of soluble GFAP form were markedly modified. These changes of glial filament protein apparently reflect the peculiarities of the reorganization of the astrocyte intermediate filaments at the animal’s long-term neurotization.     

利用连续光声成像监测动物脑部血液动力学变化

基于B型扫描超声诊断仪和线性阵列探测器的快速光声成像系统被搭建,并用于脑部血液动力学的监测研究。实验中,小鼠脑部皮层的全景血管网络分布图像通过光声探测器双扫描采集接收的方式被重建出来。然后,针对小鼠的脑中动脉,利用阵列电子扫描采集方式,光声成像实现了局部连续地监测由静脉注射生理盐水和吲哚菁绿引起的脑部血液动力学反应,成功地利用光声图像记录其光吸收的改变。实验展示了光声快速成像获取脑部功能信号的应用潜力。