GABAergic Mechanism of Anticonvulsive Effect of Chemical Agent RU-1205.

The study examined the effect of 9-(2-morpholinoethyl)-2-(4-fluorophenyl)imidazo[1,2-α] benzimidazole dihydrochloride (RU-1205) on the latency of seizures provoked by corazol, bicuculline, or picrotoxin. This agent (10 and 20 mg/kg) increased the seizure latency in the experimental models of epileptogenesis. The blockers of GABAA and GABA A -ρ receptors picrotoxin and (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid, respectively, were employed to study the effects of RU-1205 on electrical activity of somatosensory cortical neurons and on formation of pathological rhythms in the rat brain. RU-1205 inhibited the focal background rhythm and eliminated the epileptiform activity, which can be mediated by interaction with GABAA receptors.

[STRUCTURAL CHARACTERISTICS AND SPATIAL ORGANIZATION OF THE PARVALBUMIN-CONTAINING NEURONS OF THE SOMATOSENSORY AREA OF THE SI CEREBRAL CORTEX IN RATS].

The aim of the study was laminar morphometric study of immuno-labeled parvalbumin containing (PA+) neurons of cortical somatosensory area SI in outbred albino rats (n = 10). The study of frontal and tangential sections 60 µm and 4 µm thick demonstrated a considerable diversity in cell body shape and size as well as in branching of the processes in PA+ neurons in all the layers of the cortex. The greatest number of PA+ neurons (47.1%) was found in layer IV of the cortex, in the zone of barrel formation. The study of tangential sections has shown that the largest number of PA+ neurons was localized in the barrel septa (43%). In layer IV, their greatest density was detected in the walls of the barrel, making it possible to clearly identify their outlines. Quantitative predominance of PA+ neurons in the septa may be associated with the direction of their dendrite course into the inner part of the barrel and the formation of dendro-dendritic gap junctions that, in turn, could be a morphological basis of individual local pacemaker rhythmogenesis and regulation of the functional state of the cortical columns.

[Influence of GABA(C)-Receptor Antagonist on Formation of Evoked Potentials in Columns of the Rat Somatosensory Cortex].

Microelectrode studies of evoked potentials (EP) in neuronal column of rats barrel cortex show activating action of selective GABA(C)-receptor antagonist 1,2,5,6-tetrahydropyridin-4-yl-methylphosphinic acid (TPMPA) mainly on secondary components of EP of supragranular afferent layers of column compared to the efferent infragranular layers. These data suggest localization of GABA(C)-receptors on pre- synaptic terminals of thalamo-cortical glutamatergic afferents and ascending apical dendrites of pyramidal cells. A blockade of GABA(C)-receptors with the selective antagonist TPM PA leads to dose-dependent afferent depolarization with development of presynaptic inhibition and suppression of primary components of EP GABA(C)-receptors blocker produces different effects on secondary components of EP in supragranular layers of the cortex caused by the development of neuronal after hyperpolarization followed by high-amplitude primary response and afterdepolarization followed by low-amplitude primary responses with subsequent activation of different voltage-gated channels and formation of different level of cortical direct current potential gradients.

[GABAergic receptor system and its role in system activity of the brain].

In the review the analysis of structural and functional features of the main types of GABA-receptors and their distribution in various regions of a brain of vertebrata is carried out. Questions of an involvement of various types of GABA-receptors in various processes of brain activity are investigated. The data concerning tonic GABAergic inhibition in CNS, connected with extrasynaptic receptors, are shown. The physiological importance of mechanisms of tonic inhibition is discussed.

[Analysis of spatial arrangement of gap junctions in respect to chemical synapses in the serial ultrathin sections of rat barrel cortex].

Electron microscopic investigation of gap junctions (GJ) on serial sections of rat barrel cortex has shown that GJ were in contact with one or both processes that formed chemical synapses, however, these connections could not traced in single sections. In the serial sections, it was possible to observe two GJ in the immediate proximity to one another, in a single field of vision, thus, each GJ was traced in two or three successive sections in a series. Considering the described variants of GJ arrangement in the cortex, it is suggested that GJ could be a structural basis for local synchronization of the bioelectrical activity not only at postsynaptic, but also at presynaptic level, and the formation of GJ occurs both before, and after the development of chemical synapses.

[The role of GABAA and GABAB receptors in formation of evoked potentials in the barrel cortex of rats].

By means of local microapplication of GABA, picrotoxin and CGP 52432, different roles of GABAA and GABAB receptors in the geneses of primary and secondary components of evoked potentials in the somatosensory barrel cortex of rats were shown. The authors conclude that the aftereffect rhythmical components of the evoked potentials are caused by the local pacemaker mechanisms based on endogene properties of barrel neurons.

[Research of imidazo[1,2-a]benzimidazole derivatives. XXX. Synthesis and properties of (imidazo[1,2-a]benzimidazolyl-2)acetic acid derivatives].

Ethyl esters of (9-subtituted-imidazo[1,2-a]benzimidazolyl-2)acetic acids were synthesized. The chemical properties of these esters (hydrolysis, decarboxylation, hydrazinolysis) and biological activity (fungicidal, antimicrobial, antiarrhythmic activity, and also affects on the brain rhythmogenesis) of the prepared compounds were studied.

[Structural organization of the barrel cerebral cortex in rat (an immunohistochemical study)].

Immunohistochemical investigation of the regional distribution of neuronal and glial elements in the barrels of somatic cortex was carried out in rats (n=10). High level of synaptophysin protein expression was detected in the in barrel walls together with the accumulation of astroglial cells in their central areas. Ultrastructural investigation of chemical synapse structure showed the predominance of asymmetrical perforated axospinous contacts, presumably of excitatory type. The symmetric inhibitory synapses were more frequently located in the barrel walls in the areas of the denser neuronal perikarya distribution, as well as on the large dendritic processes. The number of vertically oriented myelinated axons within the barrels was found to be significantly greater than the number of the horizontally oriented interneuronal circuits.

Role of gap junctions in local rhythmogenesis in cortical columns.

Complex morphofunctional studies of the barrel cortex of the rat identified and analyzed the ultrastructural characteristics of the dendrodendritic electrical synapses--gap junctions (GJ)--of stellate neurons of barrels D2-D3. The local nature of dendrite branching of barrel cells, limited to the volume of the barrel, suggests that these GJ, which account for 7% of all synapses, may be the structural basis of local intrabarrel electrotonic synchronization of pacemaker potentials of barrel neuron hyperpolarization on development of spindle-type activity in the corresponding column.

[The role of gap junctions in the local rhythmogenesis in the cortical columns].

Ultrastructural characteristics of electrical dendro-dendritic synapses (gap junctions (GJ) of stellate neurons of D2-D3 barrels were detected and analyzed in the complex morpho-functional investigations of rat barrel cortex. Considering the local character of dendritic branching of the barrel cells, which is limited by the borders of a single column, it may be suggested that GJ which account for only 7% of the whole number of synapses, may be the structural base of local intracolumnar electrotonic synchronization of pacemaker hyperpolarisation potentials of barrel neurons during the development of spindle activity in the corresponding column.

Characteristics of the post-tetanic modification of synaptic transmission in the thalamocortical input of the somatosensory cortex in rats.

The development of both long-term post-tetanic potentiation and depression of focal evoked potentials by identified columns in the somatosensory cortex of unanesthetized rats was shown to occur in conditions of stimulation of their thalamocortical afferents. Trains of theta stimulation induced the phase-dependent development of post-tetanic potentiation after tetanization on the negative phase of the theta wave, while depression occurred after stimulation on the positive phase. Continuous tetanization produced potentiation only with stimulation at optimum amplitude and duration; extremely strong tetanization generally induced depression of responses to test stimuli, evidently because of activation of recurrent inhibition.

[Specifics of post-theta modification of synaptic transmission in thalamo-cortical input of the rat's barrel cortex]. / Osobennosti posttetanicheskoi modifikatsii sinapticheskoi peredachi v talamo-kortikal'nom vkhode somaticheskoi kory krys.

The possibility of the development of either the long-term posttetanic potentiation or the depression of focal evoked potentials in identified columns of the barrel somatic cortex of unanaesthetized rats during stimulation of their specific thalamocortical afferent fibers was shown. Phase-dependent potentiation developed after burst tetanization with the frequency of theta rhythm at the negative phase of a theta wave, whereas the stimulation at the positive phase produced the depression. Potentiation after continuous tetanization was observed only at the optimal selection of stimuli amplitude and duration. Excessively intense tetanization more frequently caused the depression of tested responses probably due to the involvement of recurrent inhibition.

[Biotropic effects of electromagnetic fields: benefit or harm?]. / Biotropnoe vliianie élektromagnitnykh polei: pol'za ili vred?

An overview contains the analysis of controversial literary data on possible therapeutic and pathogenic effects of electromagnetic fields on humans. The non-specific character of body shifts induced by electromagnetic fields with a prevalence of adaptive reactions at the onset and an emergence of dysadaptive processes during extremely long exposure was displayed. The leading role in the development of a therapeutic or pathogenic effect is played by the functional characteristics of an individual postulating the interaction of cumulative and adaptive processes in the body during long-term exposure in an electromagnetic field.

[The comparative characteristics of the neuronal responses of the rat somatic cortex during active and passive movements of the vibrissae]. / Sravnitel'naia kharakteristika otvetov neironov somaticheskoi kory krysy pri aktivnykh i passivnykh dvizheniiakh vibriss.

Responses of rat barrel-field cortex neurons were recorded during vibrissae deflection, voluntary movements of whiskers and vibrissae movements produced by stimulation of the motor cortex and facial muscles. Changes in the patterns of responses of the three groups of neurons were revealed during the performance of active vibrissae movements: neurons with short-latency responses, neurons with long-latency responses and neurons with changes in the activity occurred early before the movements onset. It is suggested that somatosensory cortical neurons receive peripheral (from the whiskers' follicles and facial muscles) as well as central (from the motor cortex) inputs that modulate their activity.

[Convergence of projections from various thalamic nuclei on the rat somatosensory cortex columns]. / Konvergentsiia proektsii razlichnykh talamicheskikh iader k kolonkam somatosensornoi kory krysy.

The method of primuline fluorochrome retrograde transport was used to study sources of thalamo-cortical projections on a separate somatic cortical neuronal column connected with C3 vibrissae of albino rat. Labeled cells were found in 8 thalamic nuclei: tv, tvd, tpo, pf, rh, tvm, tvl, tr. The intensity of neuron staining and cell quantity and density varied in different nuclei. Hence their axon branching in the rat cortex was also different. The majority of intensively stained and densely packed cells have been observed in tv nucleus. The observed convergence of different thalamo-cortical inputs on single somatic cortex column explains heterogeneity in functional properties of the same column neurons and makes it possible for the column to form several neuronal assemblies with different functions.

[Electrophysiological and catecholamine mechanisms of negative feedback in regulation of the hypothalamus by male sex glands]. / Elektrofiziologicheskie i katekholaminovye mekhanizymy otritsatel'noi obratnoi sviazi v gipotalamicheskoi reguliatsii muzhskimi polovymi zhelezami.

The immediate response on the part of the sympathoadrenal system (SAS) in mature male rats to testosterone propionate involves an increase in the content of dopamine and lowering of adrenaline and noradrenaline content in the hypothalamus, brain cortex, adrenals and peripheral organs, paralleled by an increase in the amplitude of evoked potentials and reduction in the frequency of induced impulse activity of arcuate neurons of the hypothalamus. This attests to the specificity of the associated response of the SAS and the hypothalamus-pituitary-gonadal system (HPGS) to hyperandrogenization and to the dopaminergic nature of the negative feed-back mechanism in the HPGS.

[Neuronal organization of the central mechanisms of reflexes from vibrissae]. / O neironnoi organizatsii tsentral'nykh mekhanizmov refleksov s vibriss

Functional characteristics (size of receptive fields, directional sensitivity, threshold sensitivity to amplitude, and speed of vibrissae deflection) of neurons in the rat cortical zone of vibrissae representation, were studied. Histological control showed that in the IV cortical layer these neurons form somatotopically structured barrel-shaped cytoarchitectonic clusters. It was found that each "barrel" consisted of several neuronal groups--elementary neuronal ensembles--which selectively detected different stimulus parameters: direction, speed, and amplitude of deflection of the corresponding vibrissa. The data obtained show that temporal and power competition of adjacent ensembles, on the basis of lateral inhibition, is an important mechanism for signal processing and selection of dominant afferent inputs.