Serotonin Modulates Oscillations of the Membrane Potential in Isolated Spinal Neurons from Lampreys

Studies were performed on spinal neurons from lampreys isolated by an enzymatic/mechanical method using pronase. The effects of 100 µM serotonin (5-HT) on membrane potential oscillations induced by a variety of excitatory amino acids were studied. 5-HT was found to depolarize branched cells (presumptive motoneurons and interneurons) by 2–6 mV without inducing membrane potential oscillations. However, when oscillations were already present because of an excitatory amino acid, 5-HT changed the parameters of these oscillations, increasing the amplitudes of all types of oscillations, increasing the frequency of irregular oscillations, and increasing the duration of the depolarization plateaus accompanied by action potentials. Serotonin modulation of the effects of excitatory amino acids and the electrical activity of cells in the neural locomotor network facilitates motor activity and leads to increases in the contraction of truncal muscles and more intense movements by the animal. The possible mechanisms of receptor coactivation are discussed, along with increases in action potential frequency and changes in the parameters of the locomotor rhythm

The Effects of Serotonin on Functionally Diverse Isolated Lamprey Spinal Cord Neurons

The experiments reported here showed that application of serotonin (5-hydroxytryptamine, 5-HT) (100 µ M) did not induce any significant current through the membranes of any of the spinal neurons studied (n = 62). At the same time, the membranes of most motoneurons and interneurons (15 of 18) underwent slight depolarization (2–6 mV) in the presence of 5-HT, which was not accompanied by any change in the input resistance of the cells. Depolarization to 10–20 mV occurred in some cells (3 of 18) of these functional groups, this being accompanied by 20–60% decreases in input resistance. The same concentration of 5-HT induced transient low-amplitude depolarization of most sensory spinal neurons (dorsal sensory cells), this changing smoothly to long-term hyperpolarization by 2–7 mV. The input resistance of the cell membranes in these cases showed no significant change (n = 8). Data were obtained which provided a better understanding of the mechanism by which 5-HT modulates the activity of spinal neurons. Thus, 5-HT facilitates chemoreceptive currents induced by application of NMDA to motoneurons and interneurons, while the NMDA responses of dorsal sensory cells were decreased by 5-HT. 5-HT affected the post-spike afterresponses of neurons. 5-HT significantly decreased the amplitude of afterhyperpolarization arising at the end of the descending phase of action potentials in motoneurons and interneurons and increased the amplitude of afterdepolarization in these types of cells. In sensory spinal neurons, 5-HT had no great effect on post-spike afterresponses. The results obtained here support the suggestion that 5-HT significantly modulates the activity of spinal neurons of different functional types. 5-HT facilitates excitation induced by subthreshold depolarization in motoneurons and some interneurons, facilitating the generation of rhythmic discharges by decreasing afterhyperpolarization. In sensory cells, 5-HT enhances inhibition due to hyperpolarization, suppressing NMDA currents. The differences in the effects of 5-HT on functionally diverse neurons are presumed to be associated with the combination of different types of 5-HT receptors on the membranes of these types of spinal neurons

Phytoplankton of the delta of the Mekong River during the dry season

Human activity has disturbed the functioning of river ecosystems all around the globe. The current global climatic fluctuations and local anthropogenic impact lead to rearrangement in the structure and functioning of aquatic communities. One of the most important components of aquatic ecosystems is phytoplankton as the main primary producer of the organic matter, the basis for trophic relations and indicator of changes in the environment. This article presents the first results of a study concerning the peculiarities of quantitative distribution of biomass and species composition of phytoplankton in the delta of the Mekong River at the beginning of the dry season (December of 2018). Diatoms dominated according to biomass practically in all the stations of selection of samples. The total biomass of phytoplankton on average accounted for 0.049 ± 0.007 mg/L at the abundance of 40 ± 7 103 ind./L. In practically all the studied plots, according to biomass, the dominating diatoms were first of all Aulacoseira granulata, A. islandica, Cyclotella meneghiniana, Cyclotella spp., and Oxyneis binalis. Among Chlorophyta, most often we found Chlorella sp. and Scenedesmus quadricauda, but their biomass was insignificant. We determined statistically significant correlation relationships between biomass of phytoplankton and hydrological parameters. Based on the Spearman’s rank correlation coefficient, we determined negative relations between the total biomass of phytoplankton with salinity and pH. Positive correlation was seen between the biomass of diatoms and turbidity, and also between the temperature and the biomass of chlorophytes and Dinophyta. The biomass of golden algae (Chrysophyceae) and Dinophyta positively correlated with the mineralization. Quantitative regression analysis confirmed the close relationship between the total biomass of phytoplankton, hydrophysical and hydrochemical parameters. Besides the importance of scientific data on biological diversity and ecology of plankton algae, the results we obtained are necessary for organizing biological monitoring in the delta of the Mekong River in the future

PrBaCo 2 O 6−δ -Ce 0.8 Sm 0.2 O 1.9 composite cathodes for intermediate-temperature solid oxide fuel cells: Stability and cation interdiffusion

The single-phase oxide PrBaCo 2 O 6−δ and composites (100 − y)PrBaCo 2 O 6−δ -yCe 0.8 Sm 0.2 O 1.9 (y = 10–30 wt.%) were investigated as cathode materials for intermediate-temperature solid oxide fuel cells. The chemical compatibility, cation interdiffusion, thermal expansion and dc conductivity were studied. As a result, strong interdiffusion of Pr and Sm was found between PrBaCo 2 O 6−δ and Ce 0.8 Sm 0.2 O 1.9 . This leads to only insignificantly decreasing thermal expansion coefficient of composite with increasing fraction of Ce 0.8 Sm 0.2 O 1.9 and, thus, mixing PrBaCo 2 O 6−δ with Ce 0.8 Sm 0.2 O 1.9 does not improve thermal expansion behavior of the cathode material. Moreover, formation of poorly-conducting BaCeO 3 , caused by chemical interaction between the double perovskite and doped ceria, was shown to lead to pronounced drop in the electrical conductivity of the composite cathode material with increasing Ce 0.8 Sm 0.2 O 1.9 content. © 2019 by the authors

Special features of helminth fauna of Mustelidae in the Polistovsky National Nature Reserve and development factors

The purpose of the research is to study the species composition of helminths of the Mustelidae family taking into account biotopic and trophic factors in the Polistovsky National Nature Reserve.Materials and methods. Faeces of Mustela putorius, Neovison vison, Lutra lutra and Martes martes were studied to determine a helminth fauna composition in the Mustelidae family and the factors affecting its development. Helminth eggs were detected using coproovoscopy. For detection of nematode eggs in the feces, the Forate sugar solution flotation method was used; for detection of trematode and cestode eggs, the successive washing method was used. Sexually mature nematodes of the genus Eucoleus were obtained from the pine marten by the method of B. V. Romashov. Species diagnostics of helminth eggs was carried out according to determinants, monographic and other works. The morphometric study of eggs was carried out using the Screen Meter computer program with an accuracy of 0.001 mm. The final diagnostics was carried out by comparing eggs from the faeces of predators and eggs from mature helminths. To study the trophic factor in helminth fauna development, the faeces composition was studied.Results and discussion. The studied mustelids were infected by nematodes Eucoleus sp., Eucoleus aerophilus and Capillaria putorii, and trematodes Isthmiophora melis and Opisthorchiidae sp. Helminth eggs were found in 42.3% samples. The helminth eggs prevail in the material from the polecat and American mink (60.5%) over that from the otter (30.5%). Stenobionts, stenophagy and morphophysiology determine a low infection rate in the otter versus the mink and polecat. Mixed coniferous-small-leafed forest shows a richer list of helminths than the marsh. The obtained data evidences limited helminth circulation in high moor. It is not possible to differentiate eggs of E. aerophilus and E. trophimenkovi according to the previously proposed shape index due to the high individual variability of eggs. High moor as a specific biotope reduces biodiversity including helminths