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L L Voronin

Publications and source records attributed to L L Voronin.

At least 19 recordsLinked to original sources
PubMed1992

Reliability of quantal parameter estimates and their changes during long-term potentiation in guinea pig hippocampal slices.

Previously we found increases in quantal content (m) and smaller increases in quantal size (v) during long-term potentiation (LTP) in CA1 of hippocampal slices. However, the validity of the deconvolution technique was questioned recently because v estimates correlated with the noise standard deviation (Sn). In computer simulations we show a double-step dependence of v on Sn/v: correct v estimates (within +/- 20%) for Sn/v < or = 0.5 and overestimates (correlated with Sn) for Sn/v > 0.5. A novel 'noise addition' procedure is proposed for accepting reliable solutions on the basis of the double-step relationship between v and Sn. Quantal analysis of LTP for more reliable solutions confirmed previous conclusions.

Animals↗
PubMed1992

Quantal parameters of "minimal" excitatory postsynaptic potentials in guinea pig hippocampal slices: binomial approach.

Binomial distributions of amplitudes of excitatory postsynaptic potentials (EPSPs) mixed with Gaussian noise were simulated. The objective of Monte Carlo simulations was, firstly, to study influences of sampling size (N) and noise standard deviation (Sn) on estimates of mean quantal content (m), quantal size (v) and binomial parameters (n and p) by four methods of quantal analysis (histogram, variance, failures and combined method) based on the binomial model and, secondly, to modify these methods on the basis of comparison of estimated with simulated parameters. Reliable estimates (within +/- 10% of the simulated values) were obtained for large sample sizes (N = 500-1000) with Sn less than or equal to v by the histogram (deconvolution) method and with Sn less than or equal to 2v by the other three methods. Similar results were obtained by averages from about 10 simulations if smaller samples were used (N = 50-200). In electrophysiological experiments on slices, "minimal" EPSPs were recorded from CA1 pyramidal cells after low-intensity stimuli to stratum radiatum or stratum oriens. Amplitudes of minimal EPSPs fluctuated in a manner predicted by the quantum hypothesis. Amplitude distributions of EPSPs in the non-facilitated state were adequately described either by binomial statistics with an average p equal to about 0.4 (a range of 0.3-0.7) and an average n of about 3 (range 2-6) or by Poisson statistics with m of about 1. The quantal analysis suggests that typical values of m and v for a single activated fibre in stratum radiatum might be about 0.5-1 and 300-400 microV, respectively, with low p (0.1-0.3) and n (2-4). However, the estimates of binomial parameters should be considered as coarse approximations in view of the simulation results and a possible nonuniformity of parameter p. The comparison of results of various methods based on the binomial model, in both simulation and physiological experiments, indicates the reliability of estimates of basic quantal parameters (m and v) under realistic conditions of physiological experiments. The methods are considered to be sufficiently sensitive to make use of them for studies on mechanisms of long-term synaptic plasticity.

Animals↗
PubMed1992

Statistical analysis of long-term potentiation of large excitatory postsynaptic potentials recorded in guinea pig hippocampal slices: binomial model.

Excitatory postsynaptic potentials (EPSPs) were recorded in guinea pig hippocampal slices (area CA1) from 15 neurons after stimulation of stratum radiatum (str. rad.) and stratum oriens. EPSP amplitudes increased in 8 neurones (10 post-tetanic regions) recorded 15 to 45 min after tetanic stimulation of str. rad. The increase was considered to represent long-term potentiation (LTP). Quantal analysis was performed by two methods assuming binomial statistics: the histogram method using deconvolution of noise and the variance method. According to both methods, LTP was associated with an increase in mean quantal content (m) which correlated with LTP magnitude. A statistically significant increase in quantal size (v) was found only by the histogram method and the increase was not correlated with LTP magnitude. A separate analysis of EPSPs with small LTP magnitude demonstrated that with the histogram method only v was increased but not m. A smaller increase in m for the pooled data of both methods did not correlate with LTP magnitude for this EPSP subset. The increase in m for the whole EPSP set corresponds to previous results on the quantal analysis of LTP in in vivo preparations and favours a presynaptic location of major mechanisms underlying LTP maintenance. The increase in v indicates the existence of another mechanism responsible for the maintenance of a small part of LTP. This mechanism might involve either pre- or postsynaptic changes or both.

Algorithms↗
PubMed1992

Quantal analysis of long-term potentiation of "minimal" excitatory postsynaptic potentials in guinea pig hippocampal slices: binomial approach.

"Minimal" excitatory postsynaptic potentials (EPSPs) were recorded from 13 neurones in area CA1 of guinea pig hippocampal slices after double-pulse stimulation of stratum radiatum (str. rad.) and stratum oriens (str. or.). Amplitudes of EPSPs significantly increased in 8 neurones 5 to 55 min after 9 tetanizations in str. rad.. The increase was considered to represent long-term potentiation (LTP). Altogether 26 EPSPs (42 post-tetanic regions) were statistically analysed by four methods of the quantum hypothesis assuming the binomial model of transmitter release: the deconvolution (histogram), the variance, the failures, and the combined (variance-failures) methods. The mean quantal content (m) significantly increased after LTP induction according to all methods used. Quantal size (v) also tended to increase but according to some methods, the increase was not statistically significant and it did not correlate with LTP magnitude. However, for an EPSP subset with a LTP magnitude of less than 1.55, the increase in v correlated with LTP magnitude, whereas the increase in m did not. The relative contribution of the increase in v to LTP magnitude was larger for cases with small LTP than for the whole EPSP set. In general, the increase in m corresponds to previous studies and favours the presynaptic location of major mechanisms of LTP maintenance, i.e. an increase in the average number of transmitter quanta released by each presynaptic volley. The post-tetanic increase in v might reflect some additional mechanisms which presumably include an increase in the amount of transmitter in one quantum.

Animals↗
PubMed1992

Analysis of fluctuations of "minimal" excitatory postsynaptic potentials during long-term potentiation in guinea pig hippocampal slices.

In previous studies, quantal analysis assuming a simple binomial model has shown that long-term potentiation (LTP) is accompanied by an increase in both mean quantal content (m) and quantal size (v), whereby the increase in m predominates. In the present study, "compound" binomial distributions with variable probabilities were convolved with Gaussian distributions in computer experiments to simulate amplitude histograms of intracellular excitatory postsynaptic potentials (EPSPs). A deconvolution procedure assuming equal "quantal" separation (v) between discrete components, but without assuming binomial statistics, was applied to the simulated distributions to determine v. It was found that with a small ratio of standard deviation of noise to v (Sn/v less than 0.4), a reliable estimate of v can be obtained even for small samples (N = 100). When Sn/v was larger (0.4-0.6), approximate v estimates (within +/- 10-20% of the simulated v) could be obtained by averaging estimates from about 10 small samples (N = 100). "Minimal" EPSPs were recorded in area CA1 of guinea pig hippocampal slices. 37 EPSP amplitude samples of 9 neurones were measured before and up to 55 min after 10 tetanizations of stratum radiatum. In accordance with the previous data, the increase in v accounted for only about 10% of the average post-tetanic increase in EPSP amplitude and was not correlated with the latter. However, for an EPSP subset with small LTP magnitude, the increase in v accounted for an essential part of the LTP magnitude while the increase in m did not correlate with it. The results are in agreement with previous data obtained in the context of the simple binomial model and are interpreted as indicating primarily a presynaptic mechanism of LTP maintenance. The results suggest two types of synaptic mechanism of LTP maintenance related to the increases in m and v, respectively. The latter mechanism is saturated at about 10 to 30% increase in post-tetanic amplitude above the pre-tetanic EPSP amplitude.

Animals↗
PubMed1990

[A quantum analysis of the long-term posttetanic changes in the minimal postsynaptic potentials in surviving hippocampal slices].

Excitatory postsynaptic potentials (EPSPs) were recorded in guinea pig hippocampal slices (area CA1) from 13 neurons after single or double-pulse stimulation of stratum radiatum (the Schaffer collaterals) and stratum oriens. Amplitudes of 23 EPSPs (9 neurons, 12 pathways) grew 5 to 55 min after 10 tetanic stimulations of the Schaffer collaterals. This increase has been considered as a long-term potentiation (LTP). A statistical analysis was carried out by four methods of the quantal hypothesis based on the binomial distribution. It revealed an increase in the mean quantal content (m) during LTP. An increase in the quantal size was also observed in the majority of the cases but it showed only a weak correlation with the LTP magnitude and for some methods it was statistically significant only for the periods later than 15 min after tetanic stimulation. A well expressed increase in m demonstrated by various methods corresponds to data of the previous in vivo studies and favours the presynaptic location of mechanisms of the LTP maintenance.

Animals↗
PubMed1990

[Suppression of the "fast" IPSP when superimposed on the "slow" IPSP as a possible cause of priming in the mouse hippocampus].

Extra- and intracellular responses of the mouse hippocampus were recorded at CA1 region after stimulation of two independent inputs from the Schaffer collateral/commissural fibres: conditioning or priming input (C1) and testing or primed one (C2). Duration and amplitude of primed field potentials (FP) and excitatory postsynaptic potentials (EPSP) as well as amplitudes of early (IPSPa) and late (IPSPb) components of inhibitory postsynaptic potentials (IPSP) were measured with variation of C1-C2 intervals from 0 to 1 s. An increase in the FP duration as well as EPSP duration and amplitude and suppression of the IPSP amplitude occurred after conditioning with intervals of 50-500 ms, maximal effect was at 200 ms ("priming" effect). These changes correlated with the amplitude of priming IPSPb. The most prominent effect was observed in cells with hyperpolarizing IPSPa. It is assumed that primed FP and EPSP increase due to suppression of the primed IPSPa, when it is superimposed on the priming IPSPb.

Animals↗
PubMed1990

[A quantal analysis of the long-term potentiation of the total postsynaptic neuronal potentials in surviving hippocampal slices].

Excitatory postsynaptic potentials (EPSPs) from 14 neurons have been recorded in hippocampal slices (area CA1) of guinea pigs after stimulation of stratum radiatum (Schaffer collaterals) and stratum oriens. An increase of EPSP amplitudes observed in 7 neurons (9 pathways) recorded 15-45 min after titanic stimulation of Schaffer collaterals is considered as a long-term potentiation (LTP). A statistical analysis in the frame of two methods of the quantal hypothesis (histogram and variance methods) has shown an increase in the mean quantal content (m) during LTP. An increase in the quantal size found only by the histogram method is considered to be less reliable because comparatively strong dependence of the histogram method on the noise level. An increase in m revealed by two methods corresponds to the previous in vivo studies and favours a presynaptic location of mechanisms responsible for the growth of the synaptic efficacy during LTP.

Animals↗
PubMed1990

[A comparison of statistical methods for quantal analysis in computer and physiological experiments].

Amplitude distributions of postsynaptic potentials were simulated in computer experiments on the basis of binomial statistics. Influences of the sample size (N) and noise standard deviation (Sn) on the determination of the quantal content (m) and quantal size (v) were studied. Four methods of the quantal parameter estimation were modified and used: histogram, variance, failure and combined method. Three last methods gave satisfactory estimations (within +/- 10%) at N = 500-1000 and Sn less than 2v. The histogram method was adequate at Sn less than or equal to v. Similar results were obtained at N = 50-200, when the experiment was repeated about ten times. Applicability of similar methods was confirmed by the analysis of an intracellular record of inhibitory postsynaptic potentials (N = 1333) from the sensorimotor cortex of rabbit.

Action Potentials↗
PubMed1989

[Disordered associative long-term potentiation in the hippocampus after the tetanization of the reinforcing input].

Field potentials (FPs) were recorded from stratum radiatum of CA1 region of mouse hippocampal slices after weak orthodromic stimulation (C2). Associative long-term potentiation (ALTP), induced by simultaneous tetanization of C2 with strong tetanization of another group of fibres (C1) was investigated. Effects of the additional tetanization of C1 delivered 50-300 ms before and 50-300 ms after conjoint tetanization of two inputs were compared. In experiments with intervals 50-200 ms preliminary tetanizations of C1 suppressed ALTP (the FPs amplitude increase was 10.4 +/- 5.2%) in comparison with procedure in which an additional tetanization of C1 follows conjoint tetanization (the FPs increase was 32.4 +/- 5.3%). There was no significant difference between two procedures in experiments with 300 ms intervals. Three mechanisms have been considered to explain the influence of the preliminary strong tetanus on ALTP: inactivation of "fast" calcium channels, afterburst hyperpolarization and synaptic inhibition. It is suggested that mechanisms of this suppression are similar to mechanisms underlying relative inefficacy of the "backward" association procedure in behavioral conditioning.

Animals↗
PubMed1987

Quantal analysis of paired-pulse facilitation in guinea pig hippocampal slices.

Intracellular excitatory postsynaptic potentials (EPSPs) were recorded in area CA1 of hippocampal slices from guinea pigs. With paired-pulse stimulation of stratum radiatum, the second stimulus (interval of 40-50 ms) produced an EPSP with enlarged amplitude. Two methods of quantal analysis showed an increase in quantal content of the facilitated EPSP and a smaller increase in quantal size. The correlation between amplitudes of the first and second EPSP was usually insignificant. The results favour a presynaptic location of the mechanisms of the paired-pulse facilitation and suggest increases in the average of transmitter quanta released by presynaptic volley as well as increases in the amount of transmitter in each quantum.

Animals↗
PubMed1979

[Quantum analysis of postsynaptic potentials].

Basic formulations of the quantum theory for synaptic transmission are listed. Methods for determining the mean quantum content, quantum value and binomial parameters describing the amplitude distributions of the unitary and "minimal" postsynaptic potentials are discussed. Literature and author's determinations of the quantum parameters for the synapses of the central nervous system are described. The comparison is made with similar determinations for more studied peripheral junctions. Some difficulties and perspective of the quantum theory are discussed.

Animals↗
PubMed1979

[Structure of the theoretical distributions of postsynaptic potential amplitudes upon quantum analysis].

It is suggested that formulas commonly used to calculate theoretical amplitude distributions of postsynaptic potentials (PSPs) for their further quantum analysis lead to the overestimation of the quantum value variations (sigma nu) and neglect the variations of a noise level (sigma 2n). A proper formula taking into account both parameters in proposed. The necessity to consider sigma 2n is shown by statistical analysis of "individual" and "minimal" PSPs recorded in the neurons of the central ganglion of the snail and hippocampal neurons of the rabbit. Taking into account sigma 2n resulted in a better agreement between theoretical and experimental distributions and provided an indirect method for sigma nu estimation.

Animals↗
PubMed1977

["Minimal" focal potentials of the hippocampus and their post-tetanic alteration].

The work was aimed at recording in the hippocampus of unanesthetized rabbits changes in the EEG evoked by a single afferent spike. Extracellular focal activity was summarized by a computer triggered by spontaneous single unit discharges from a contralateral homotopic hippocampal point. No stable signal was revealed consistent with characteristics of EEG evoked by a unit discharge. Discharges of presumed Shafter collaterals were recorded at CA1 in two cases. After summation of focal activity recorded by the same microelectrode negative of 40-60 micronV amplitude were seen when the computer was triggered by these discharges. Such waves are supposed to be evoked by single spikes. Evoked potentials were recorded at the level of Shaffer collaterals (CA1) and mossy fibres (CA3) layers. In most cases the dependence of the evoked potential amplitudes on the current strength was not smooth but stepwise at nearthreshold stimulation. "Minimal" evoked potentials corresponding to the first step (40-80 micronV) are supposed to be produced by impulses in a single afferent fibres. No long-lasting posttetanic potentiation of "minimal" evoked potentials produced by the Shaffer collateral synapses was found. "Minimal" evoked potentials after mossy fibres stimulation underwent prominent potentiation. These data are consistent with the hypothesis of synaptic localization of the mechanisms of the long-lasting hippocampal posttetanic potentiation.

Animals↗