A. Yu. Malyshev

Effects of serotonin levels on postsynaptically induced potentiation of snail neuron responses.

Studies on identified neurons in the common snail were performed to investigate potentiation of EPSP arising after intracellular tetanization of the post-synaptic neuron. These experiments showed that high-frequency intracellular tetanization of a command neuron leads to biphasic long-term increases in the amplitude of synaptic responses to test stimulation. The role of serotonin in forming potentiation was studied. It was suggested that the presence of particular serotonin concentrations in the intercellular fluid is required for forming the second phase of the increase in synaptic responses, while the first (transient) phase is insensitive to CNS serotonin levels.

Determination of Impurity Arsenic in High-Purity Sulfur by Electrothermal Atomic-Absorption Spectrometry with the Use of Solvent Extraction

A procedure was developed for determining impurity arsenic in high-purity sulfur with a detection limit of 1 × 10–7 wt %. The samples of sulfur to be studied were dissolved in nitric acid in an autoclave, and then the arsenic impurity was extracted with toluene and back-extracted with distilled water. Arsenic was determined in the back-extract by electrothermal atomic-absorption spectrometry.

The formation of convex microstructures on the surface of polymeric materials under laser irradiation

The formation of convex structures on the surface of colored samples of polymethylmethacrylate (PMMA) when they are irradiated by the second-harmonic radiation of a neodymium laser has been experimentally investigated. The dependences of the height and the diameter of the resulting convex microstructures on the energy density of the laser pulse have been investigated. The formation threshold of structures has been determined for various samples, and the optimum structuring regimes have been found. The possibility of obtaining arrays of convex structures (microlenses) and structures in the form of convex fillets has been demonstrated.

Functions of Peptide CNP4, Encoded by the HCS2 Gene, in the Nervous System of Helix Lucorum

The aims of the present work were to study the role of neuropeptide CNP4, encoded by the HCS2 gene (which is expressed mainly in parietal command interneurons), in controlling the activity of the respiratory system, and also to study the effects of this neuropeptide on isolated defensive behavior neurons in prolonged culture. The influence of the command interneuron on the pneumostoma included a direct effect consisting of closure and a delayed effect consisting of intensification of respiratory movements. Application of neuropeptide CNP4 produced a pattern similar to the delayed effects seen on stimulation of the command interneuron, i.e., significant increases in the frequency and intensity of pneumostoma movements and strengthening of the rhythmic activity of the pneumostoma motoneuron. Studies of the effects of neuropeptide CNP4 on isolated neurons after prolonged culture showed that neuron process growth correlated with the presence of the neuropeptide in the medium. Identification of the location of the HCS2 precursor protein and neuropeptide CNP4 in isolated command interneurons after prolonged culture showed that that only those parts of the cell showing active process growth were immunopositive. Thus, neuropeptide CNP4 appears to be a secreted neuropeptide controlling respiratory system activity, which may also be involved in rearrangements of the network controlling defensive behavior in Helix snails

Fine Purification of Sulfur from Carbon by High-Temperature Oxidation

Using high-temperature oxidation, the residual carbon content of high-purity sulfur was reduced to 10–5wt %. The effects of the oxidation temperature and duration on the efficiency of the process were studied. The results are used to elucidate the mechanism for the removal of carboniferous impurities in the course of purification.

Anion-selective channelrhodopsin expressed in neuronal cell culture and in vivo in murine brain: Light-induced inhibition of generation of action potentials.

Anionic channelrhodopsin slow ChloC was expressed in the culture of nerve cells and in vivo in mouse brain. We demonstrated ability of slow ChloC to suppress effectively the activity of the neuron in response to the illumination with the visible light. It has been shown for a first time that slow ChloC works equally efficiently in both neuronal culture and in the whole brain being expressed in vivo. Thus, slow ChloC could be considered as an effective optogenetic tool capable in response to light stimulation to inhibit the generation of action potentials in the neuron.

Ephaptic feedback in identified synapses in mollusk neurons.

The possible existence of intrasynaptic ephaptic feedback in the invertebrate CNS was studied. Intracellular recordings were made of excitatory postsynaptic potentials and currents arising on activation of the recently described monosynaptic connection between identified neurons in the snail CNS. In the presence of ephaptic feedback, tetanization of the postsynaptic neuron with hyperpolarizing impulses should activate presynaptic calcium channels, thus increasing the amplitude of excitatory postsynaptic potential, while sufficiently strong postsynaptic hyperpolarization applied during generation of the excitatory postsynaptic current should induce “supralinear” increases in its amplitude, as has been observed previously in rat hippocampal neurons. The first series of experiments involved delivery of 10 trains of hyperpolarizing postsynaptic impulses (40–50 mV, duration 0.5 sec, frequency 1 Hz, train duration 45 sec); significant changes in the amplitude of excitatory postsynaptic were not seen. In the second series of experiments, changes in the amplitude of the excitatory postsynaptic current were studied during hyperpolarization of the postsynaptic neuron. At a potential of −100 mV, the amplitude of the excitatory postsynaptic current increased significantly more than predicted by its “classical” linear relationship with membrane potential. This “supralinear” increase in the amplitude of the excitatory postsynaptic potential can be explained by the operation of ephaptic feedback and is the first evidence for this phenomenon in CNS synapses of invertebrates.

Effect of crystal growth on the effectiveness of fine purification through counterflow melt crystallization

A method is proposed for calculating the axial impurity profile in a crystallization column and assessing the effectiveness of the purification of a substance via counterflow melt crystallization. The method takes into account the combined effect of diffusion and crystallization processes. An approximate equation for the separation factor is derived. The results obtained for a few systems agree well with experiment.

Physiological Aspects of the Use of the Hodgkin–Huxley Model of Action Potential Generation for Neurons in Invertebrates and Vertebrates

Recent studies have shown that the dynamics of action potential generation in neurons in vertebrates, in contrast to invertebrates, is significantly different from the slow exponential dynamics predicted by the Hodgkin–Huxley equations and is characterized by a sudden kink-like origin in the form of a steep linear increase. In this context, new and important aspects of studies of the links between the dynamics of action potential generation and the frequency coding abilities of neurons and neuronal networks have been found. This review addresses contemporary models describing the kink-type dynamics of action potential generation, including an alternative model of cooperative activation of potential-dependent sodium channels and the effects of the dynamics of action potential generation on the processing abilities of neural networks. The relevance of this direction comes from the fact that despite the rapid development of neuron simulation in recent years, generally accepted models of nerve cells cannot provide a realistic description of the complete dynamics of action potential generation in mammalian neurons or correct assessments of the ability of these cells to encode high-frequency signals. Contemporary experimental and theoretical analyses of action potential generation and neuronal encoding, as summarized in the present work, are highly significant for improving our understanding of nerve cell physiology and assisting the creation of more accurate and correct models of neurons.

An analysis of the effect of the internal ribosome entry site of the encephalomyocarditis virus on the expression of the second gene in the bicistronic matrix in neurons of primary hippocampal cultures

Molecular biological experiments sometimes require expression of two or more genes in a single cell with an accurate ratio between their expression levels. One of the methods to provide this control is the use of the internal ribosome entry site (IRES) from the encephalomyocarditis virus as a separating insert between two target genes in the expression vector. Previously, it was shown that the efficacy of translation of the gene after IRES varies considerably in a range from 6 to 100% depending on the cell type. In neurons, the exact ratio between the expression levels of genes that are located before and after the IRES in the expression vector is unknown. Here, we analyzed the ratio between the amounts of products of the first and second genes located before and after the IRES in a plasmid that was used to transfect neurons in a primary hippocampal culture. We created two plasmid vectors that contain genes of the yellow (Venus) and red (mCherry) fluorescent proteins in different orders, which are separated by the IRES. We found that the unmodified IRES sequence of the encephalomyocarditis virus decreases the expression in the second cistron by a factor of 2.7 in a primary culture of hippocampal neurons. These data will help us to use currently available libraries of mutant IRES sequences for accurate control of the relationships between the expression of different target genes in neurons.