The mechanism of formation of Liesegang structures around Dictyostelium discoideum

A theoretical study of the phenomenon of Liesegang structure formation induced by the Dictyostelium discoideum population in a medium containing folic acid was carried out. Using a "reaction-diffusion" model proposed in this work, it was shown that the formation of Liesegang structures around the Dictyostelium discoideum population depends on two competing processes: (a) inactivation of folic acid by vegetative amoebae and (b) the chemical reaction of folic acid with the products of amoeba metabolism, which results in the formation of insoluble sediment. The dependence of the model solutions on the geometric and functional parameters was studied. The results are in good agreement with experimental data.     

The three-dimensional structure of presynaptic mitochondria in a factorial experiment involving irradiation of the brain with a low-intensity laser

Parameters of the mitochondrial ultrastructure in the presynaptic terminals of the dorsal horn have been investigated in the control cats and in those exposed to helium-neon laser. Using the factor analysis and stereologic approach changes have been revealed in actual tridimensional parameters of organelles.     

Molecular signals of plasticity at the tetrapartite synapse

The emergence of astroglia as an important participant of the synaptic machinery has led to the 'tripartite synapse' hypothesis. Recent findings suggest that synaptic signaling also involves the surrounding extracellular matrix (ECM). The ECM can incorporate and store molecular traces of both neuronal and glial activities. It can also modulate function of local receptors or ion channels and send diffuse molecular signals using products of its use-dependent proteolytic cleavage. Recent experimental findings implicate the ECM in mechanisms of synaptic plasticity and glial remodeling, thus lending support to the 'tetrapartite synapse' concept. This inclusive view might help to understand better the mechanisms underlying signal integration and novel forms of long-term homeostatic regulation in the brain.     

Localization of point mutations in the coding part of the VHL gene in clear cell renal cancer

VHL gene is often inactivated in sporadic clear cell renal cancer (CCRC) due to somatic mutations, and it's germline mutations cause hereditary CCRC--von Hippel-Lindau syndrome. Localization of mutations in VHL, identification of new mutations and their influence on CCRC progression and sensitivity to targeted therapy are actual problems in modern oncogenetics. We have provided search and characterization of mutations in 248 primary CCRC using SSCP-analysis and sequencing. Somatic mutations were detected in 37.5% of samples, 72% of mutations were identified for the first time. New missense-mutations were analyzed by alignment programs and three-dimensional structure modeling. Mutation frequency was compared in different groups of patients in respect to stage, grade, and metastases. It was demonstrated that 39.1% samples with stage I harbor somatic mutations, however, no association with progression or metastases was found. We also have investigated localization of mutations in the VHL coding part and positions of missense-mutations and inframe deletions/insertions focusing on VHL critical sequences. VHL mutation analysis performed in this study improve the possibilities of laboratory diagnostics of familial and sporadic CCRC.     

d-Serine: A key to synaptic plasticity?

Two discoveries have put d-serine in the spotlight of neuroscience. First, d-serine was detected in brain tissue at high levels. Second, it was found to act on the N-methyl-d-aspartate receptor (NMDAR). This receptor is central to use-dependent synaptic plasticity, the cellular process which is widely believed to underlie learning. The ensuing quest for the mechanisms of d-serine synthesis, release and clearance, as well as for its physiological significance has provided a wealth of experimental evidence implicating d-serine in synaptic plasticity. However some key questions remain unanswered. Which cells release d-serine and upon what stimuli? Is d-serine supply dynamically regulated? What is the fate of released d-serine? Answering these questions appears to be an essential step in our understanding of how NMDARs trigger synaptic plasticity and learning. This review will highlight some recent advances and avenues of enquiry in dynamic d-serine signaling in the mammalian brain with emphasis on neurophysiology.     

Independent Regulation of Basal Neurotransmitter Release Efficacy by Variable Ca2+ Influx and Bouton Size at Small Central Synapses

The efficacy of action potential evoked neurotransmitter release varies widely even among synapses supplied by the same axon, and the number of release-ready vesicles at each synapse is a major determinant of this heterogeneity. Here we identify a second, equally important, mechanism for release heterogeneity at small hippocampal synapses, the inter-synaptic variation of the exocytosis probability of release-ready vesicles. Using concurrent measurements of vesicular pool sizes, vesicular exocytosis rates, and presynaptic Ca²⁺ dynamics, in the same small hippocampal boutons, we show that the average fusion probability of release-ready vesicles varies among synapses supplied by the same axon with the size of the spike-evoked Ca²⁺ concentration transient. We further show that synapses with a high vesicular release probability exhibit a lower Ca²⁺ cooperativity, arguing that this is a direct consequence of increased Ca²⁺ influx at the active zone. We conclude that variability of neurotransmitter release under basal conditions at small central synapses is accounted for not only by the number of release-ready vesicles, but also by their fusion probabilities, which are set independently of bouton size by variable spike-evoked presynaptic Ca²⁺ influx.

Author Summary

Synaptic transmission underlies information transfer among neurons in the brain. The probability that a synapse will release neurotransmitter in response to an action potential varies widely, even among synapses supplied by the same axon. The molecular mechanisms underlying this heterogeneity remain poorly understood. At the level of single synapses, release efficacy is determined largely by two factors: (i) the number of neurotransmitter-containing vesicles ready to be released, and (ii) by the fusion probabilities of these vesicles. By using novel imaging techniques at individual hippocampal presynaptic boutons in culture, we distinguish two independent sources of variability of release probability in small central synapses. First, we find differences in the number of releasable vesicles, and second, we find differences in the exocytosis probability of individual vesicles. To our knowledge, this is the first direct experimental demonstration that the fusion probability of release-ready vesicles is variable among synapses supplied by a single axon, and contributes roughly as much to the overall variability in release probability as does the number of release-ready vesicles.     

Certain biochemical characteristics of an insulin-like substance from the bivalve mollusk Anodonta cygnea

An insulin-like substance (ILS) was isolated from the visceral organs of the bivalve mollusc Anodonta cygnea by chromatography on a sulfocationite CU-23 and purified by reverse phase liquid chromatography. ILS was shown to be made up to several fractions with Mr ranging from 9 to 20 kDa which have identical amino acid composition but different hydrophobicity and N-terminal amino acids. It was supposed that the heterogeneity of ILS fractions is due to its genetical or posttranslational polymorphism. ILS has a low (0.02%) affinity for the mammalian insulin receptor and a low immune affinity for mammalian insulin and possesses a mitogenic activity which is commensurate with that of the epidermal growth factor. The data obtained suggest that Anodonta cygnea ILS represents a separate branch of a relatively ancient family of insulin-like hormones and growth factors responsible for metabolism and proliferation of invertebrate tissues.     

Effect of acute intestinal obstruction on erythrocyte membrane function

The amino acid composition of red blood cell membrane proteins had been studied in different stages of acute intestinal obstruction. Hydrophobic amino acids were revealed to increase and glutamate was found to decrease during the early period of acute intestinal obstruction. Later neutral amino acids and some of the main amino acids were stated to decrease. Shifts in the ratio of protein fractions seen in red blood cell membrane of rats with acute intestinal obstruction could be explained by changes followed in the amino acid composition. The data accumulated had demonstrated that such a significant modification of protein component of the red blood cell membrane could be one of the reasons of the erythrocyte membrane penetrability violation and could play the pathogenetic role in the occurrence of irreversibility changes in cases of the intestinal obstruction. All that was mentioned above had shown the necessity to use membrane protectors and antienzyme drugs in the postoperative period.     

Geometrical characteristics of mitochondria and active presynaptic zones in the dorsal horn of the cat spinal cord

A morphometric electron microscope study was carried out on the ultrastructure of 140 presynaptic terminals (PT) in the dorsal horn of the cat spinal cord. Some spatial characteristics of mitochondria and active zones (AZ) for these PT were examined using statistical stereological analysis techniques. The distribution of 3-dimensional mitochondrial radii was determined, together with average mitochondrial volume, mean area of the external membrane, and average numbers of the test population falling within the PT. Distribution of diameters and estimates of mean area of AZ were obtained, as well as of mean value of synaptic clefts. The relationship between findings from morphometric research and parameters of processes underlying ionic transmembrane diffusion and accumulation is discussed.Dnepopetrovsk State University. A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 741–747, November–December, 1989.