Biomedical subjects

M Bykhovskaia

Publications and source records attributed to M Bykhovskaia.

8 recordsLinked to original sources

PubMed2005

Recruitment of synapses in the neurosecretory process during long-term facilitation at the lobster neuromuscular junction.

We investigated long-term facilitation at the lobster neuromuscular synapse employing a combination of FM1-43 staining of synaptic vesicles, electron microscopy analysis, and electrical recordings of synaptic activity. Synaptic terminals were loaded with the fluorescent dye FM1-43 producing clusters of activity-dependent fluorescent spots. Electron microscopy analysis of synaptic ultrastructure suggested that fluorescent spots represent compartments of synaptic terminals filled with vesicles. Excitatory postsynaptic currents were recorded from the stained synaptic terminals using focal macropatch electrodes. Terminals were stained during the nerve stimulation at a low stimulation frequency (2, 5 or 10 Hz) before and after long-term facilitation was elicited by high-frequency stimulation (20 or 30 Hz for 5 min). We found that staining after long-term facilitation results in the appearance of new fluorescent spots, as well as in the increase in fluorescence of the spots that appeared before long-term facilitation. This increase in fluorescence accounted for the increase in quantal release. Activation of individual fluorescent spots was found to be non-uniform. In spite of overall increase in fluorescence, some synaptic compartments decreased their staining after long-term facilitation. Thus, our study demonstrates that long-term facilitation produces non-uniform activation of FM1-43 uptake in synaptic compartments that correlates with the increase in quantal neurosecretion.

Animals↗

PubMed2002

Submillimeter-wave phonon modes in DNA macromolecules.

A detailed investigation of phonon modes in DNA macromolecules is presented. This work presents experimental evidence to confirm the presence of multiple dielectric resonances in the submillimeter-wave spectra (i.e., approximately 0.01-10 THz) obtained from DNA samples. These long-wave (i.e., approximately 1-30 cm(-1)) absorption features are shown to be intrinsic properties of the particular DNA sequence under study. Most importantly, a direct comparison of spectra between different DNA samples reveals a large number of modes and a reasonable level of sequence-specific uniqueness. This work establishes the initial foundation for the future use of submillimeter-wave spectroscopy in the identification and characterization of DNA macromolecules.

Biophysics↗

PubMed2001

Hyperosmolarity reduces facilitation by a Ca(2+)-independent mechanism at the lobster neuromuscular junction: possible depletion of the releasable pool.

1. At the crustacean neuromuscular junction, action potential-evoked neurosecretion increases in proportion to stimulation frequency, a process termed frequency facilitation. In the present study we examined how frequency facilitation is affected by osmotic pressure. 2. Hypertonic solution (HS) was applied by local superfusion of the synaptic area. Quantal release was monitored by focal extracellular recordings of postsynaptic potentials. Several stimulation frequencies (f) in the range from 1 to 10 Hz were employed, and quantal content (m) together with the number of releasable units (n) and release probability (p) was evaluated for each frequency. 3. Osmotic pressure enhanced quantal release at the lowest f tested (1 Hz) but suppressed neurosecretion at higher f (7-10 Hz). Thus, hyperosmolarity enhanced action potential-evoked release but suppressed frequency facilitation. 4. Chelation of intracellular calcium by BAPTA showed that the effect of HS was calcium independent. 5. Binomial analysis of quantal content revealed that HS suppressed the increase in the number of releasable units, which was very pronounced during facilitation under control conditions. Since HS also stimulated asynchronous quantal release, the observed effect of HS on facilitation can be explained by the depletion of the releasable pool of quanta caused by the asynchronous neurosecretion. 6. To test this hypothesis we increased the available pool of vesicles using serotonin and demonstrated that the suppressing effect of HS on facilitation was reversed. 7. The observed effects of HS on facilitated neurosecretion could be described quantitatively using our model for mobilization of vesicles into the releasable pool enhanced by action potentials.

Animals↗

PubMed1999

Evaluation of quantal neurosecretion from evoked and miniature postsynaptic responses by deconvolution method.

A new deconvolution algorithm has been developed for evaluation of quantal content and its variability at high-output synapses. The algorithm derives the distribution of the number of neurosecretory quanta released in a trial (M) from the measured sizes of evoked postsynaptic responses. The deconvolution employs the distribution of quantal sizes obtained by measuring sizes of miniature postsynaptic responses. The distribution of quantal content M is derived by ridge regression method from the distributions of sizes of the responses and of quantal sizes. The deconvolution method was applied to postsynaptic responses from the excitory innervation of lobster dactyl opener muscle obtained by focal extracellular recordings. The obtained solution (distribution of M) had six to eight components and was stable. The method was tested by the analysis of simulated multiquantal responses. For the simulated responses, the ridge regression solution reproduced the imposed distribution of M within the limits of the calculated confidence intervals. To further test the algorithm, the distribution of M at a low-output synapse was obtained both by deconvolution method and by the method of direct quantal counts. The results of these two methods were found to be in a very good agreement.

Action Potentials↗

PubMed1999

Asynchrony of quantal events in evoked multiquantal responses indicates presynaptic quantal interaction.

Asynchrony of quantal events in evoked multiquantal responses indicates presynaptic quantal interaction. We have analyzed the possibility of quantal interactions by inspecting action potential-evoked postsynaptic multiquantal responses recorded extracellularly from the lobster neuromuscular junction. These recorded responses were compared with simulated multiquantal responses constructed from statistically independent quantal events. The simulated multiquantal responses were generated by random superposition of single quantal responses aligned according to the timing of the action potential. The methods of analysis consisted of 1) the comparison of quantal contents obtained from direct counting or by measuring of the size of the responses and 2) the analysis of distributions of quantal latencies. This analysis revealed a large error in the detection of quantal events for responses simulated with no quantal interaction. In contrast, very few errors in quantal detection were made in the analysis of experimental recordings. Latency histograms of recorded responses demonstrate that the proportion of late quantal events (those with latencies of >/=5 ms) increased as a function of quantal content. This shift in latency histograms was not observed for simulated responses. Our interpretation is that quanta interact presynaptically to cause asynchrony of quantal events in evoked responses.

Action Potentials↗

PubMed1997

Facilitation at the lobster neuromuscular junction: a stimulus-dependent mobilization model.

Frequency facilitation is a process whereby neurosecretion increases as a function of stimulation frequency during repetitive synaptic activity. To examine the physiological basis underlying facilitation, we have estimated the frequency dependence of the synaptic parameters n (number of units capable of responding to a nerve impulse) and P (average probability of responding) at the lobster neuromuscular junction. Both n and P increase as a function of frequency, suggesting that the efficiency of quantal docking and quantal fusion is regulated by repetitive synaptic activity. In experiments in which facilitation is strong and quantal content does not saturate over the frequency range tested, the value of P saturates at low frequencies of stimulation, and increases in quantal content at higher frequencies of stimulation are due to an increase in n. Therefore the value of P does not limit facilitation. We propose that transmitter release is limited by the rates of quantal mobilization and demobilization, and that each excitatory stimulus causes additional mobilization of quanta to dock at the presynaptic release sites. In such a model the binomial parameter n will correspond to the number of quanta docked at the release sites and available for release. We have developed and solved kinetic equations that describe how the number of docked quanta changes as a function of time and of stimulation frequency. The stimulus-dependent mobilization model of facilitation predicts that the reciprocal value of the quantal content depends linearly on the reciprocal product of the stimulation frequency and the probability of release. Fits of the experimental data confirm the accuracy of this prediction, showing that the model proposed here quantitatively describes frequency facilitation. The model predicts that high rates of quantal demobilization will produce strong frequency facilitation.

Algorithms↗

PubMed1996

An algorithm for high-resolution detection of postsynaptic quantal events in extracellular records.

A software package has been developed for the detection and measurement of extracellularly recorded postsynaptic quantal events evoked by neural stimulation. The algorithm is based on the identification of monotonic regions of a differentiated current signal and detects the small inflections and peaks of a postsynaptic response that result from the asynchronous presynaptic release of individual packets of neurotransmitter. Recorded and simulated postsynaptic responses have been used to verify the accuracy of the algorithm and to determine its resolution. The algorithm can accurately detect up to six individual quanta in a time period of 20 ms, with a resolution of 0.5-1.0 ms.

Action Potentials↗

PubMedDate not supplied

Stochastic modeling of facilitated neurosecretion.

Two models of neurosecretion were evaluated in terms of their ability to predict the dependency of quantal content (m) on the frequency of repetitive stimulation of a lobster motoneuron. First, the hypothesis that neurosecretion is limited by a fixed number of release sites was tested by the fit of the distribution of m by uniform and nonuniform binomial statistics. The obtained release probabilities suggest that frequency facilitation can be due to activation of a group of sites with high release probabilities. However, the fit obtained using this model is not statistically significant due to a large number of fitting parameters. Second, the hypothesis that neurosecretion is limited by the rates of exchange between the releasable pool and the total store of quanta and that each stimulus enhances quantal mobilization was tested. Monte Carlo simulation was carried out in accordance with this model and reproduced the observed distribution of m with very few fitting parameters and therefore with a high level of significance (>0.1). This result demonstrates that mobilization of extra vesicles with each stimulus is a mechanism that allows a very accurate and parsimonious quantitative description of frequency facilitation.

Action Potentials↗