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O G Bogdanova

Publications and source records attributed to O G Bogdanova.

17 recordsLinked to original sources
PubMed2005

Studies of the synaptic plasticity of field CA3 of the hippocampus during tetanization of the perforant path.

Studies on living slices of hippocampus-entorhinal cortex formation from adult rats were performed to investigate changes in responses in field CA3 to stimulation of mossy fibers in conditions of perforant path tetanization with different parameters. Tetanization of the perforant path at frequencies of 10 and 100 Hz induced depression of responses in CA3 on testing of this same path. Tetanization of the perforant path at a frequency of 10 Hz and an amplitude subthreshold for potentiating mossy fiber synapses in CA3 became threshold if preceded by tetanization of the perforant path at a frequency of 100 Hz. Tetanization of mossy fibers at 10 Hz resulted in potentiation of the input to CA3, while tetanization at 100 Hz induced depression. High-frequency tetanization of the perforant path (100 Hz) delivered in trains following at the frequency of the theta rhythm, led mainly to depression of field CA3 responses to stimulation of mossy fibers.

Animals↗
PubMed1998

[Effect of high frequency cortical microstimulation on the interhemisphere synchronization in the rat motor cortex].

Long-term posttetanic changes of callosal neurons' synchronisation was studied in the rat motor cortex. Following tetanisation, the synchronisation of previously active cells decreased whereas the cells that became active were mostly synchronised. Ultra "narrow" peaks appeared in callosal interactions and correlated with "intermediate" (30-80 ms) those.

Action Potentials↗
PubMed1998

[Characteristics and mechanisms of the interhemisphere synchronization in the rat motor cortex].

Synchronised activity of the callosal cells was studied in the rat motor cortex. Cross-correlation analysis revealed narrow symmetrical peaks (less than 20 ms) and intermediate ones (30-80 ms). Common neuron(s) located in one hemisphere reciprocally connected callosal cells can play the role of a "common input" that synchronises discharges of the cells in both hemispheres. The narrow and intermediate peaks seem to be mediated by mono- and polysynaptic connections, resp.

Action Potentials↗
PubMedDate not supplied

The effects of high-frequency microstimulation of the cortex on interhemisphere synchronization in the rat motor cortex.

Studies were carried out on long-term changes in the synchronization of neuronal activity in networks including callosal cells of the opposite hemispheres evoked by high-frequency microstimulation in the motor cortex of anesthetized rats. The level of synchronization was assessed in terms of the amplitude and width of peaks located symmetrically on cross-correlograms relative to the coordinate origin. Tetanization predominantly decreased synchronization in a group of initially background-active neurons, while there was a significant number of synchronously firing neurons in a group of cells which became activated. "Super-narrow" peaks appeared in interhemisphere interactions. There was a correlation between the type of modification of "narrow" (<20 msec) and "intermediate" (30-80 msec) peaks and changes in the efficiencies of mono- and polysynaptic connections.

Animals↗
PubMedDate not supplied

The properties and possible mechanisms of interhemisphere synchronization in the motor cortex of the rat.

Cross-correlation analysis was used to observe interhemisphere synchronization of motor cortex neuron activity in anesthetized rats, which was seen on cross-correlograms as peaks located symmetrically relative to the coordinate origin. Peaks included "narrow" peaks (less than 20 msec) and "intermediate" peaks (30-80 msec). The results showed that the "common" source synchronizing the discharges of pairs of neurons located in different hemispheres of the brain might be a neuron (or group of neurons) located in one of the hemispheres and playing this role when there were reciprocal excitatory connections between it and each neuron in a pair. Comparison of the widths of symmetrical peaks with latent periods corresponding to transcallosal connections suggested that mono- and polysynaptic connections underlie the formation of "narrow" and "intermediate" peaks respectively.

Animals↗
PubMedDate not supplied

Background gamma-oscillations in neuronal networks with interhemisphere connections.

Results obtained in studies of the high-frequency components of EEG recordings and in modeling, determining the conditions for the appearance of gamma oscillations in interneuronal interactions, were compared with features of the background gamma oscillations recorded in the activity of interacting neurons located in symmetrical loci of the right and left hemisphere motor areas in anesthetized rats. Similarities in high frequencies extracted from EEG recordings and in the most commonly observed gamma oscillation frequencies suggested that these oscillations may represent one of the mechanisms underlying the high-frequency EEG component. Published modeling data indicating that the formation of these oscillations involves reciprocal inhibitory connections, along with our own data that interhemisphere oscillations are seen 1.5 times more commonly than ipsilateral oscillations, suggested that transcallosal inhibition is more effective than inhibition between neighboring cells. Simultaneously extracted background oscillations in the interacting activity of callosal cells and neighboring cells could be different, as could those characterizing the activity of individual neurons. It is suggested that these differences underlie the functional heterogeneity of local cortical neuronal networks and explain the fact that these networks contain various types of inhibitory neurons.

Animals↗
PubMedDate not supplied

Post-tetanic changes in background gamma oscillations in interhemisphere interactions.

Experiments conducted on the motor cortex of anesthetized rats were performed to study the effects of high-frequency microstimulation of one of the hemispheres on oscillation parameters in neuronal networks containing callosal cells. Before tetanization, there were three modes in the distribution of gamma oscillation periods, corresponding to frequencies of 40-60, 70-100, and 100-200 Hz. In cells active in pre-tetanization background conditions, the three modes were retained after tetanization; there was a relative increase in the number of oscillatory interactions in that part of the gamma range (40-60 Hz) which dominated before tetanization. The distribution of oscillation periods in neurons which became active in background conditions after tetanization contained the same three modes. Tetanization resulted in a relative decrease in the number of oscillatory interactions and the number of neuron pairs in which additional synchronization occurred, along with a reduction in the extent of oscillations, which is evidence of reduced synchronization. Existing modeling data taken together with the present results led to the suggestion that these post-tetanization changes were based on a modification of the efficiency of excitatory and inhibitory inputs to neurons in both hemispheres.

Anesthesia↗
PubMedDate not supplied

Post-tetanic modification of the efficiency of excitatory transmission in neural networks including interhemispheric connections.

This is the first report of modifiable reciprocal transcallosal monosynaptic excitatory connections, detected in in vivo experiments in the rat motor cortex by recording of multineuron activity and cross-correlation analysis. High-frequency microstimulation of a small group of cortical neurons in one hemisphere was shown to alter the efficiency of transcallosal excitatory connections, and also altered the efficiency of ipsilateral connections in both hemispheres. Post-tetanic changes consisted of long-term potentiation and depression. Neurons producing spike trains were found to have better conditions (compared with other neurons) for long-term potentiation of inputs converging on them. Synapses formed by axon collaterals of a given callosal cell on several neurons could simultaneously induce both long-term potentiation and long-term depression, while a given callosal neuron could simultaneously show long-term potentiation in some synapses and long-term depression in others. After microstimulation there were increases in the number of background-active callosal neurons, along with increases in the number and efficiency of transcallosal connections, while the number and efficiency of ipsilateral connections decreased. These data lead to the conclusion that ipsilateral inhibition is more effective than transcallosal inhibition. Microstimulation modified the pattern of initially existing connections between the many elements of ensembles including callosal cells in both hemispheres.

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PubMedDate not supplied

[Post-tetanic modification of the efficacy of excitatory transmission in neuronal networks with interhemispheric connections].

The modifiable reciprocal transcallosal monosynaptic excitatory connections were for the first time detected in vivo experiments in rat motor cortex using multiunit recording and crosscorrelation analysis, It was shown that high-frequency microstimulation (MCS) of a small group of cortical cells of one hemisphere produces long-term changes in the efficacy of transcallosal excitatory connections, and also ipsilateral connections in both hemispheres. The posttetanic changes appear as long-term potentiation (LTP) and long-term depression (LTD). The bursting neurons were found to have more favorable conditions for the induction of LTP of most converging inputs (in contrast to cells with other discharge patterns). Both LTP and LTD could be simultaneously induced in synapses formed by axon collaterals of a callosal cell on several neurons. LTP and LTD could be simultaneously obtained at diverse synapses of the same cell. The number of spontaneously active callosal neurons as well as the number and efficacy of transcallosal connections increased after the MCS, whereas the number and efficacy of ipsilateral connections decreased. Basing on these data we assume that the ipsilateral inhibition is more effective than the transcallosal inhibition. MCS results in the modification of the pattern of initially existing connections between numerous neurons of an ensemble including cells of both hemispheres.

Action Potentials↗
PubMedDate not supplied

[Study of synaptic plasticity of hippocampal CA3 area as a result of tetanization of perforant path].

Evoked responses in CA3 area to the mossy fibers stimulation were studied after low and high frequency tetanizations of the perforant path. Stimulations of perforant path with 10 and 100 Hz frequencies inducted depression testing through the same path. Subthreshold for potentiation of the mossy fibers inputs to the CA3 tetanization of the perforant path with 10 Hz frequency transformed to threshold one after previous tetanization of the perforant path with 100 Hz frequency. Tetanization of the mossy inputs to the CA3 with 10 Hz frequency leaded to potentiation whereas tetanization with frequency 100 Hz depressed the same inputs. High frequency tetanizations (100 Hz) of the perforant path with theta-rithm frequency stimulation basically depressed of the CA3 evoked responces to the mossy fiber stimulation.

Animals↗
PubMedDate not supplied

[The baseline gamma oscillations in neural networks with interhemispheric connections].

The evidence obtained from the studies of EEG high-frequency components and computer simulation which determined the necessary conditions for occurrence of oscillations were compared with some features of spontaneous gamma oscillations, which had been revealed by us in interconnections of neurons located in symmetrical loci of both hemispheres of motor cortex of anaesthetized rats. Based on the similarity of the most expressed high-frequency EEG components and dominant frequencies of gamma oscillations, we proposed that gamma oscillations could underlie the appearance of the high-frequency EEG components. Taking into account the obtained by us results that interhemispheric oscillations occurred 1.5 times more frequently than ipsilateral and the evidence from computer simulation experiments that reciprocal inhibition underlies oscillations in neural networks, we suggested that transcallosal inhibition was more effective than inhibition between the neighbouring cells. Parameters of simultaneously revealed spontaneous oscillations caused by interhemispheric and ipsilateral interactions and in individual cell activity could be different. It was assumed that functional variability of local neocortical networks and participation of different inhibitory neurons underlie distinctions in oscillation parameters.

Animals↗
PubMedDate not supplied

[Posttetanic changes in the background gamma oscillations in interhemispheric interactions].

The influence of high-frequency microstimulation (HFMS) of one of the hemispheres on the parameters of spontaneous gamma-oscillations in the neural network containing callosal cells of the motor cortex of both hemispheres. There were three modes in the background oscillation periods distribution, which corresponded to the frequencies 40-60, 70-100, and 100-200 Hz. These oscillation frequencies were also revealed after the HFMS in neural interactions of the cells, which were active before the HFMS; the frequency 40-60 Hz, which dominated before the HFMS, became even more pronounced. The same three groups of oscillation frequencies were found in the activity of cells which became active after the HFMS. The expression of oscillations, the number of oscillatory interactions, as well as the number of neuronal pairs with additional synchronization decreased after the HFMS, which suggests a decrease in synchronization. Taking into account the results of simulation experiments that the frequency of gamma-oscillations is determined by the strength of inhibitory and excitatory input, we suggest that the long-term posttetanic modifications in the efficacy of synaptic inputs of the neurons of both hemispheres underlie the observed posttetanic changes.

Action Potentials↗