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

Calculation of overdamped c-axis charge dynamics and the coupling to polar phonons in cuprate superconductors

In our recent paper we presented empirical evidences suggesting that electrons in cuprate superconductors are strongly coupled to unscreened c-axis polar phonons. In the overdoped regime the c-axis metallizes and we present here simple theoretical arguments demonstrating that the observed effect of the metallic c-axis screening on the polar electron-phonon coupling is consistent with a strongly overdamped c-axis charge dynamics in the optimally doped system, becoming less dissipative in the overdoped regime.Comment: 6 pages, 1 figure. to be published in Phys. Rev.

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

The Reddening-Free Decline Rate Versus Luminosity Relationship for Type Ia Supernovae

We develop a method for estimating the host galaxy dust extinction for type Ia supernovae based on an observational coincidence first noted by Lira (1995), who found that the B-V evolution during the period from 30-90 days after V maximum is remarkably similar for all events, regardless of light curve shape. This fact is used to calibrate the dependence of the B(max)-V(max) and V(max)-I(max) colors on the light curve decline rate parameter delta-m15, which can, in turn, be used to separately estimate the host galaxy extinction. Using these methods to eliminate the effects of reddening, we reexamine the functional form of the decline rate versus luminosity relationship and provide an updated estimate of the Hubble constant of Ho = 63.3 +- 2.2(internal) +- 3.5(external) km/s/Mpc.Comment: 32 pages, 10 figures, AJ 1999 in pres