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The reactions of forming synapses in rat neocortex to the effect of hypoxia in the early postnatal period (day 2) were studied. Using immunocytochemistry for synaptophysin demonstratoion and electron microscopic methods, the sensorimotor cortex was studied in rats at days 3, 4 and 10 of postnatal development (6 to 10 animals of each age) in both experimental and control groups (intact animals). Immunocytochemical study of the control animals demonstrated significant differences in the quantitative distribution of synaptophysin-positive structures in the different layers of the neocortex in the early postnatal period of development (day 5). It is shown that after exposure to perinatal hypoxia, more than 2-fold decrease of the optical density of the immunocytochemical reaction product took place together with the reduction of synaptophysin-positive granules distribution density in all cortical layers of. At the same time, electron-dense terminals demonstrating early degenerative processes were found. In the neuropil of the neocortex, a sharp decline in the number of growth cones, small processes and forming synapses was accompanied by significant changes of the electron density of synaptic, especially post-synaptic, membranes and densities. In the experimental animals, the number of growth cones and emerging synaptic structures were shown to increase only by postnatal day 10. Thus, the effects of hypoxia in the early postnatal period, causing disturbances of synaptogenesis, persist throughout the whole neonatal period examined.

Electron microscopy and morphometry of neurons in layer V of the somatosensory area in the neocortex and CA3 field in the dorsal hippocampus showed that single and 5-fold intraperitoneal injection of Polidan was followed by ultrastructural and metabolic changes in neurons reflecting activation of protein synthesis. The number of free ribosomes decreased; the number of polysomes and count of ribosomes in polysomes and tubules of the granular endoplasmic reticulum increased. Study of mitochondria and neuropil showed that Polidan activates synthetic processes in the neocortex and hippocampus. It should be emphasized that single treatment with Polidan led to functional activation of synthetic processes, while 5-fold injection of Polidan was followed by hyperactivation of synthetic processes and depletion of ultrastructures in the neocortex and hippocampus.

The paper reviews the current data on the structural peculiarities of the interneurons of hippocampal area CA 3. Special attention is paid to horizontal spiny interneurons located in the stratum lucidum and forming direct contacts with the system of mossy fibers. Their axons terminate at the proximal portions of dendrites and cell body of pyramidal neurons, occasionally they make contacts with the main cells of the hilus and other hippocampal interneurons. Some portion of axon collaterals is in close vicinity to direct and indirect entorhinal-hippocampal connections, indicating their accommodation to selectively suppress mossy fiber input. The latter form the synapses of various types on the principal cells and on various types of interneurons of area CA 3, indicating different mechanisms of transmitter uptake and presynaptic control of their release.

This paper summarizes the author's personal research and the literature data on the sensory innervation of the brain. The following cells were analyzed as presumable primary sensory neurons: ciliated brain neurons, supraependymal plexus and cerebrospinal fluid-contacting intraependymal neurons, Cajal-Retzius neurons of the marginal layer of the cerebral cortex, brain and spinal cord Dolgo-Saburov paravasal neurons, Lugaro cells of the cerebellar cortex, some NO- and synthase-positive cells of the cerebral cortex, asynaptic dendrites of which innervate the precapillary space. Due to the painlessness of the brain and visceral parenchyma, containing local primary sensory neurons, similar to intramural metasympathetic type II Dogiel sensory cells, the hypothesis is formulated on the participation of brain and other intraorgan tissue receptors in the short "autonomic" reflex arcs, which provide only for the local metabolism control, but not for the pain reactions.

Two types of Lugaro cells--fusiform and triangular--were found at different levels of granular layer in the sections of cat cerebellar cortex, stained with silver nitrate using Golgi-Kopsch method. Their processes are oriented horizontally, vertically or obliquely to the folium axis, while their axons never leave the limits of cerebellar cortex, therefore these cells should be considered as interneurons. The processes of Lugaro cells have very large spatial expansion, due to which these cells form numerous axosomatic and axodendritic connections with all the neurons and fibers of the cerebellar cortex. Structural and topographic characteristics of Lugaro cells, as well as the peculiarities of their contacts with the other cells of cerebellar cortex, in combination with the data on their neurotransmitter content, indicate that these cells play the role of inhibitory interneurons.

To investigate the adaptive morphological changes of cellular elements of the spinal cord following the dosed application of physical loads (running in treadmill for 7-35 min), the motor neurons and interneurons of i.v. lumbar spinal cord segment were studied in 38 mongrel male dogs. It was shown that single integrating physical loads contributed to significant increase in the number of functionally active neurons. It is noted that the morphological changes are more pronounced in the motor neurons as compared to interneurons.

This review summarizes the literature data and the results of the authors' own investigations on morphology, neurochemical specialization, and spatial organization of unipolar brush neurons (UBN) in the cerebellar cortex and brainstem cochlear nuclei. UBN represent excitatory interneurons with a single dendrite that forms a compact brush-like branching in its terminal part. They are distributed non-uniformly in the granular layer of the cerebellar cortex and are localized predominantly in its vestibular areas. UBN synthesize glutamate, calretinin, contain metabo- and ionotropic glutamate receptors. Dendritic brush of UBN forms the giant synapses with the rosettes of glutamate- and cholinergic afferent mossy fibers. Axons of UBN form intracortical system of mossy fibers, which, by forming rosettes and glomeruli, make contacts with dendrites of similar cells and those of the granular cells. In the chain of inerneuronal communications, UBN may be regarded as the intermediate link, which amplifies the excitatory effect of the afferent mossy fibers upon granular cells of the cerebellar cortex and brainstem cochlear nuclei.

Topography and structure of rat area postrema were specified using light optic and electron microscope. Disturbance of liquor-encephalic transport (hydrops of ependymocytes), sharp changes of cytoplasmic organelles in neurons, signs of intercellular desintergration (synapse degeneration after "clear" type), death of part of neurons, disorder in secretory processes in neuroendocrine cells were shown to occur following chronic effect of gravitation overloads, in its structural elements. These changes take place on the background of hemomicrocirculatory disturbances, appearance of connective tissue fibres in perivascular space of Virchow-Robin and are probably conditioned by a developing circulatory hypoxia.

Using the electron microscopy immunocytochemistry, the GABA and glycine immunoreactivity was studied in presynaptic axon terminals of the spinal cord central gray in the lamprey Lampetra fluviatilis. All immunopositive presynaptic terminals contacting motoneurones or non-identified post-synaptic profiles were divided into only GABA- (44%), only glycine-immunopositive terminals (26%), and both GABA- and glycine-containing terminals (30%). The glycine-immunopositive axon terminals contained flattened synaptic vesicles. Large dense core vesicles were co-localised with conventional synaptic vesicles in 74% of GABA-containing presynaptic terminals.

Two types of intermedial Lugaro cells are distinguished in the cat cerebellum: fusiform (horizontal, vertical and obliquely oriented at angles 60-70 to longitudinal axis of folia cerebelli at different levels of granular layer) and those with triangular somata, sparsely branching dendrites and small number of spines. Both fusiform and triangular neuron axons do not stretch out beyond the borders of cerebellar cortex and may be thought of as recurrent interneurons as they contain GABA and glycine. Lugaro cells form numerous contacts almost with all cortical nervous elements: piriform (Purkinje) and Golgi cells, granular and basket neurons, parallel and mossy fibres and even unipolar, (brush) cells. At light microscopic level they are represented as axosomatic and axodendritic contacts. Lugaro cells are the only cerebellar cortical interneurons with dendritic arborizarion oriented in horizontal plane in contrast to vertical orientation of the other interneurons of cerebellar cortex.

To understand the mechanisms of brain activity and behaviour alterations in chronic morphine intoxication, it is especially important to analyze the changes occurring in the interneuronal connections. Analyzing cerebral cortical synapses during morphine treatment revealed that some new synapses formed. The newly formed synapses increased the total number of synapses of the cerebral cortex and reorganized synaptic architectonics. The changes in the synaptic architectonics accompanied ultrastructural changes of dendrites. The development of new synapses and changes of dendrites are the basis for the formation of pathological cerebral cortical systems.

Ultrastructural and immunocytochemical results of studies on interneuronal relationship in vegetative ganglia were represented. Age-related changes of synapses (appearance of synaptic type vesicles and smooth endoplasmic reticulum cisterns in postsynaptic terminals), peculiarities of interneuronal links in neurons containing neuropeptide Y and NO-synthase and structural manifestations of non-synaptic interneuronal links were shown. Modern views on interneuronal communications were discussed.

A qualitative and quantitative electron microscopic study was performed. in some postmortem brain structures of the dopaminergic system: the substantia nigra, ventral tegmentum area, prefrontal cortex (area 10), anterior cingulate cortex (area 24), the head of the caudate nucleus in schizophrenia and age-matched controls without mental disorders. The study revealed the heterogeneity of ultrastructural changes in synaptic ultrastructure and organization in schizophrenia as compared to controls. There was an anomalous sprouting of axons and a trend to increase the numerical density of axospinous synapses and to decrease axodendritic synapses in the schizophrenic brains due to disontogenesis or anomalous synaptic plasticity. No correlations with neuroleptic treatment were found. Synaptic plasticity might be involved in the pathophysiology and clinical symptoms of schizophrenic patients.

A comparative analysis of intraneuronal relationship between Purkinje cells and granule cells zones of the cerebellar cortex molecular layer with different extent of expression of destructive and compensatory-adaptive processes was performed in rats in the dynamics of postischemic period. The ischemia was modelled by the 10 minutes long compression of the heart vascular bundle under the ethereal narcosis, Dependence between type and extent of the synaptic profile and functional state of the synapse was shown. Dynamics of changes of the synapse numerical density was demonstrated so as the regularities of the axo-spinous synapses structural organization changes during their dysfunction, destruction and interneuronal contact repair within and outside the nidi of interneuronal interrelations during 30 days of postischemic period.

The influence of sudden systemic hemostasis on the change dynamics of numerical density of perforated (PS) and non-perforated (NS) interneuronal synaptic contacts in cerebral sensomotor cortex layer 1 were studied in albino rats during 30 postischemic days using electron microscopy and morphometric methods of examining the material treated with osmium and contrasted with phosphotungstic acid. Regularities of junction and disjunction mechanisms realization in arising PS from NS in diverse postischemic terms were demonstrated. A significant role of PS appearance in reorganization of neocortical neuronal interrelations is shown.

The correlation between structure and function of synapses is discussed. Identification of 4 types of synapses has been made based on the authors' own evidence provided for the rat sensomotor cortex with the light and electron microscopy: 1--asymmetrical (excitatory, glutamate- or aspartatergic); 2--symmetrical (inhibitory, GABAergic); 3--symmetrical (disinhibitory, GABAergic); 4--symmetrical or asymmetrical (modulatory, monoaminergic). The ultrastructure of some synaptic categories may be equalized with their function. It makes possible to identify not only excitatory and inhibitory synapses, as considered before, but also disinhibitory and modulatory ones.

Data, received in investigation of the small intestine intramural ganglia of 34 suckling rabbits show, that development of experimental cholera induce in the neurons reactive shifts, changed by dystrophic alterations. Prevaluation of cholinergic influences in autonomic ganglia in small intestine promotes enterocytes hypersecretion and accelerating of motor activity.

During prolonged electrical stimulation of the septum (self-stimulation 2-3 h daily for 2.5 months) perikarion of most neurons, situated around the tip of the stimulating electrode undergoes peripheral chromatolysis, less part of the neurons is shrunk, mitochondria are desorganized, invaginations of the nuclear membrane occur more often and deeper. Intercellular clefts are sharply dilated, profiles of altered myelin fibers are observed, presynaptic terminals decrease in their number. Axonal terminals with agglutinated vesicles become more numerous. In other terminals osmiophilic bodies and membranous inclusions are revealed. Under electric stimulation a sharp reaction of glial cells, especially astrocytes is observed. One group of astrocytes participate in phagocytosis of the degenerating structures, while the other--in formation of the glial scar.

Organizational peculiarities of the frontal-parietal area of the sensomotor cortex are: parvicellularity, alveolar-like distribution of neurons, radial striation of the lower zone, distinctly manifested stratification of the higher zone in the cortical plate, the middle zones contain short axonal pyramidal, stellate and granular neurons. Formation of somato-somatic contacts is specific for interneuronal interaction. Peculiarity of the normal ultrastructure of the neuronal cytoplasm is presence of 2-4 subsuperficial cisterns in the section. In neuropil, which is presented mainly as axo-spinal assymetrical contacts of the I type after Grey, transversal profiles of tightly arranged and collected in fasciculi finest axonal collaterals and terminal dendritic ramifications are revealed.

Staining of brain tissue with phosphotungstic acid was used to assay interneuronal contacts in the molecular layer of the cerebral cortex of rats with a history of clinical death because of hemorrhage and asphyxia. Common regularities of reconstruction of neocortical architectonics during the resuscitation period were defined. Marked reduction in the number of synapses was discovered in the neocortex. The main form of destruction of the contacts was the light type of destruction. Hypertrophy of the remaining synapses occurs in the early periods. The processes of neosynaptogenesis get activated on day 7. Both the types of structural recovery of the synaptic pool (hypertrophy and neoformation of the contacts) were fairly marked in the long-term period.

The present state of morphological study of variability in the nervous elements under conditions of adaptive change under the influence of afferent effects, age changes during different periods of ontogenesis, under conditions of de- and regeneration of synapses have been considered. A question on correlation between structure and the function of synapses during the change has been analysed. The tasks of subsequent study of this problem have been outlined.

The sensorimotor cortex of the alcoholized rat progeny showed the signs of the delayed ultrastructural development of neurons and interneuronal connections and their dystrophic changes, particularly in 21-day-old experimental rats. Thirty-day-old animals demonstrated pronounced reparative alterations. But in spite of this fact the ultrastructure of cortical neurons, particularly of dendrites was not completely restored.

Hypoxic effect (a 6 minute asphyxia) on the presynaptic grid structure and on the amount of synapses in the neocortex has been studied in white rats using the method of selective staining of synapses with phosphoric tungsten acid. Neurofilamentous formations of the presynaptic grid appeared to be most labile structures. Dense projections of the presynaptic grid are most sensitive to hypoxia: their height, distinctness of the frame, and the intensity degree of phosphoric tungsten acid staining decrease. The content of intermediate form contacts with low indistict dense projections increases with the increase in the number of light type changed synapses. The principle organization of the presynaptic grid does not change in the posthypoxic period: hexagonal division of dense projections and places of vesicular attachment are kept. The hypertrophy of the presynaptic grid is also kept during that process.

The nerve endings in the intramural ganglia of the rat's heart are connected by synaptic and non-synaptic junctions with the dendrites and neuron bodies. Peri-membrane indurations of synaptic complexes may look relatively symmetrical or asymmetrical depending on the orientation of the section in relation to the elements of the Akert's presynaptic lattice. In non-synaptic junctions the indurations are symmetrical, but the presynaptic one may be more complicated in its structure. The synaptic complexes are disposed in the field of synaptic dilatations of axons and in the sites of interlacing thin "preterminal" parts of axons with dendrites. They connect preganglionic fibres with dendrites, neuron bodies and with the filamentous and fungiform thorns.

Changes in the ultrastructure of neurons and synapses of the paraventricular nucleus of the hypothalamus were studied in old rats. The time-course of the pathomorphological alterations was shown. Dendrites, particularly those of medium size, were found to be especially vulnerable. The first signs of ultrastructural changes in neurons were shown in mitochondria. Although chromatolytic changes predominated in the majority of the hypothalamic neurons, hyperchronic alterations could also be observed. The nucleoli and nucleoliform formations in the cytoplasm proved the most "stable" components of neurons.

Distribution of marked preganglionic neurons over spinal nuclei and segments was studied in cats with the aid of microinjections of the horse-radish peroxidase into the cranial cervical ganglion. The major part of these neurons were revealed in the main part of the intermediolateral nucleus. A somewhat lesser number of the cells were found in the funicular part of the nucleus. In the T1 segment they constituted about 90% of cells containing the peroxidase. Other neurons were localized in the paraependymal and intercalative nuclei. In longitudinal sections of the spinal cord, the preganglionic sympathetic neurons projecting their axons into the cranial cervical ganglion, form a rostro-caudal chain made of small ensembles of cells.

Synaptogenesis in presumptive cerebral cortex was studied in 7-8 week human embryos by electron microscopy. The first synapses in the regions studied appeared in 7-week embryos. These synapses were detected only in the marginal zone of the developing human cerebral cortex, where they were localized on the somas and processes of the young Cajal-Retzius' neurons. A functional role of early embryonic synaptogenesis in the developing human cerebral cortex is suggested.

Using the technique for the cerebral tissue contrasting with phosphoric-tungsten acid, synaptic architectonics of the molecular layer of the rat sensomotor cortex has been studied for 30 days of recirculation after 5 minutes' stop of the systemic circulation resulted from an acute hemorrhage. Gradation of the synapses per groups is performed according to the height of compact projections of the presynaptic network. Dynamics of the synaptic compactness changes with different height is stated to differ essentially during the postischemic period. A conclusion is made that in reconstruction of the synaptic architectonics of the neocortex during the postischemic period a leading role belongs to the change of state of specialized paramembranous microfilamentous compact projections of the presynaptic network. They make a part of the neuronal cytoskeleton and are included into a single integral complex--the system of subcytoskeleton and are included into a single integral complex--the system of subsynaptic units.

Using anterograde labeling by horseradish peroxidase, studies have been made on the formation of axonal projections of cells of the dorsal ganglia in lumbar segments of Xenopus tadpoles at different stages of development of their hindlimbs. It was shown that at the early stages of premetamorphosis, primary afferents grow into the spinal cord and form collaterals directed into the grey matter. During prometamorphosis, the axons reach lateral motor nucleus. At final stages of prometamorphosis, when the hind limbs are used for locomotion, as well as at further stages of development, axons of the 9th and 10th dorsal roots reach motoneurons mainly in the Xth, not the IXth segment. During final stages of metamorphosis, contralateral projections of primary afferents were found in the lumbar segments. In two experiments, labeled interneurons were revealed in the intermediate grey matter. Organization and development of the primary afferent projections in the anuran spinal cord are discussed.

Ultrastructural organization of the lateral hypothalamic area (LHA) has been studied in Wistar rats. Structural peculiarities of neurons and interneuronal connections in the anterior, middle and posterior parts of the LHA have been demonstrated. In the anterior and middle parts, neurons of middle size (17-22 mcm) make the most of the cellular population; large neurons (35-50 mcm) predominate in the posterior part of the LHA. Small cells are diffusely distributed in all the parts. Two types of axons are defined: axons of the I type--with round light, and some of them, with large granular synaptic vesicles; axons of the II type contain smaller and polymorphous light synaptic vesicles. The axons form axodendritic and axosomatic synapses. The former predominate in all parts of the LHA. The axons of the I type form, mainly, asymmetrical, and the axons of the II type--symmetrical contacts. Most of the synapses are formed by the axons of the I type, overwhelmed majority of the synapses are axodendritic. Differences in localization and in distribution of the axodendritic synapses in different parts of the LHA are revealed. In the anterior part of the LHA the axodendritic synapses form synaptic muffs around large and middle dendrites, and more seldom around small and spine-shaped processes of the dendrites. In the middle and posterior parts of the LHA no synaptic muffs are revealed.

The numeral density of the revealed with the help of PTA-plane and twisted asymmetric and symmetric interneuronal contacts of the sensomotor brain cortex of rats after 6 minutes mechanical asphyxia has been studied. It was revealed that in 90 minutes and 6 hours the relative contacts of the concave synapses will be increased progressively. This reaction has the compensatory-adaptive character and ensures the restoration of the integrative activity of the brain during the early postresuscitation period.

Changes in bodies of neurons, their processes and synapses in the lateral hypothalamic area (LHA) in rats at various time (1, 3, 5 and 7 days) of food deprivation have been studied electron microscopically. The changes in the posterior part of the LHA are the first and in the middle part of the LHA are the last to appear. The number of altered bodies of the neurons, their processes, synapses and severity of their injury during all the time of fasting is the greatest in the posterior and the least in the middle part of the LHA. The character of the ultrastructural changes is unitypical everywhere. Dendrites, especially those of middle and large size are the first to be injured. Their changes immediately acquire destructive character (vacuolization of dendroplasm, appearance of complex membranous bodies, swelling and destruction od microtubules and neurofilaments). One of peculiar features of the destructive changes of the neuronal processes and synapses is invagination of adjoining areas of axons and synapses into the dendrite. In the bodies of the neurons the changes appear later than in the dendrites and at first they are of functional character and only beginning from the 5th day of fasting certain signs of destructive disorders are noted. With increasing time of fasting, the injury is growing more severe and a greater and a greater number of the neuronal bodies, processes and synapses are involved into the pathological process.

The electron microscopic method has revealed early maturation of the protein-synthesizing apparatus of some cells, on the one hand, and underdevelopment of neuroblast volumes, appearance of artificial contacts, axonal degeneration and destruction in large trunks, on the other hand. Compensatory-restorative processes in the cell on the 14th and 21st days of the postnatal development result in a complete restoration of morphological organization of neurons and interneuronal connections in the hypothalamus of offspring of the morphine-dependent rats.

Twelve human cervical-thoracic sympathetic ganglia have been studied 3 h after a sudden death. Peculiar osmophilic bodies in the neuronal mitochondria have been revealed electron microscopically. In the preparation successive stages of these bodies formation are seen. Ultrastructure of afferent neural terminals adjoining the sympathetic neuron bodies but divided from them with a gap space is described. The structure of the receptors in the ganglia and that of the sympathetic contacts are compared, the latter are predominantly axodendritic.

The fine structure of upper layer of axodendritic synapses of the cat cerebral cortex was studied during 10, 45 and 90 minute applications of aminazine, and also 2.5 and 5 hours after the cessation of the 90 minute application. During the 10 and 45 minute applications no clear-cut changes are observed in the ultrastructure of the synapses. 90 minutes after the onset of application osmophilic changes are enhanced in the pre- and postsynaptic areas. During the drug application, the number of synaptic vesicles and the area of the axonal terminals decrease. The above morphological changes are reversible: restoration of the number of synaptic vesicles commences, but the area of the terminal is still shrunken.

Electron microscopy was used to study synapse development in the cardiac ganglia of human fetuses ranging from 8 to 27 weeks of ovulation time. Staining with ethanolic phosphotungstic acid was used for analysis of synaptic active zones. Specialization of interneuronal links begins with the appearance of electron dense material on plasmalemmas of nerve cells in the places of simple contacts. First synapses with single synaptic vesicles and short osmiophilic zones were found in cardiac ganglia in 8-week-old fetuses. Large granular vesicles and mitochondria vesicles are formed from cisternae of agranular endoplasmic reticulum in the preterminal parts of axons and moved by axoplasmic transport to the osmiophilic zones of future synapses. Axodendritic synapses appeared earlier in the cardiac ganglia than axosomatic ones, the latter were observed from the middle of gestation. Transient neuroglial synapse-like contacts were found in the cardiac ganglia. Staining with phosphotungstic acid made it possible to distinguish the degree of synapse maturation according to active synaptic zones. The peculiarities of synaptic development in cardiac ganglia in comparison with that in the central nervous system may be accounted for by different origins of the neural tube and of neural crest and by the level of their phylogenic development.

The ultrastructure of intermediate neurons of the ventral horn of the spinal cord of cats was studied. It has been established that interneuronal contacts having different structural organization may be grouped according to the principle of different space distribution of pre- and postsynaptic elements. Contacts of the first type realize convergence of different synaptic effects on one post-synaptic structure. In contacts of the second type the synaptic action of the axon fibre or a terminal diverge to different elements of the neuropile. Several synaptic forms of contacts of the second type were revealed. The role of the above structures in the physiological activity of intermediate neurons of the spinal cord is discussed.

Electron-microscopic investigations of various parts of the CNS in laboratory mammals and man have demonstrated that a single cerebral intercellular space, presenting an immediate internal medium for the nervous tissue elements, has different structure at the border separating the media. Here is a complex of structures, included into composition of the hemato-encephalic and liquor-encephalic barrier. Data of the literature on chemical composition of the intercellular contents and on specific membranous receptors make it possible to suppose a communication role of the intercellular spaces, ensuring nonsynaptic intercellular connections and modulation of the synaptic transmission. At the level of membranes, that make walls of the intercellular clefts by means of certain phylogenetically ancient humoral mechanisms, interaction of systems of synaptic and nonsynaptic interneuronal connections is secured.

In Krushinskiĭ-Molodkina rats sensibilized for 5 days with brain extract antigens (BEA) and/or subjected to repetitive seizures (S), the synaptic architectonics of the molecular layer was studied in the sensorimotor cortex preparations treated with phosphotungstic acid. Unlike the S effect, BEA-sensibilization and BEA+S action sharply reduced the number of interneuronal contacts, especially the symmetric ones, and the structure relations of the subsynaptic units system with the surrounding cytoskeleton with decrease in the number of very small, small and medium-size synapses. In any effects the major compensatory mechanism was the hypertrophy and splitting of the interneuronal contacts. Only S action resulted in the compensatory enhancement of the new synapses formation. Possible mechanisms of the "immune" lesion of the interneuronal contacts are discussed.

Electron microscopy was used to study the process of ingrowth of nerve terminals in the primordia of sympathetic ganglia and the formation of specialized contacts. Nerve terminals appeared first in 12 day old embryos. In the forming ganglia of 13 day old embryos there are many preganglionic nerve terminals and processes of principal neuroblasts. The growth cones of nerve endings are usually distended and with transparent cytoplasm. The plasmalemmas of growth cones are lacking often the trilaminar structure. Synapses were observed first in 16 day old fetuses. They are axo-dendritic and axo-somatic ones. The number of synaptic contacts does not increase much during prenatal period. Presumptive afferent nerve terminals were found in the late fetuses.

Using the technique of contrasting the cerebral tissue with phosphotungstic acid, the authors studied the structural and functional status of interneuronal contacts of the molecular layer of the sensomotor cortex in the brain of Krushinsky-Molodkina rats following convulsive sound stimulation and the subsequent audiogenic convulsive paroxysm. Marked reduction in the general number of synapses 4 h after the attack was attended by transformation of some flat functionally mature contacts into concave ones, which reflects the activation of the synaptic pool. The relative levels of concave and flat mature contacts returned to the initial level 8 to 24 h later.

Structural-functional reconstructions of the frog autonomic interneuronal synapsis have been studied at its activation with endogenic acetylcholine under conditions of acetylcholinesterase suppression. The investigation has been performed with preparations of isolated sympathetic trunk of Rana temporaria treated with armine (5 X 10(-6) M) and subjected to electrostimulation (5 imp/sec) up to a complete block of the synaptic transmission. Certain structural changes are revealed in the axo-somatic synapses, demonstrating an increased adhesive properties of the membranes, ("hatch-like" membranes, numerous submembranous aggregates, aggregates of the intercellular cleft and neuronal-glial contacts). In the terminals changed according to the "light type", with poorly manifested changes, light synaptic vesicles loose their spheric form, their diameter decreases. In the boutons with more intensive changes, the vesicles gradually change into the mass of cluster-floccular material. In the boutons with intensively manifested disorders in the ultrastructure, a complete destruction of the light vesicles is observed. The great part of the ganglionic neuron bodies changes according the "dark type". In their neuroplasm a great amount of subsuperficial cisterns of the endoplasmic reticulum and formation of powerful fasciculi of microfilaments are noted to appear.