Effect of local surface cooling of the rat cortex on the impulse activity of neurons assumed to be the sources of corticofugal influences

In an experiment on albino rats with electrodermal stimulation of the forepaw evoked potentials (EP) in the neostriatum (NS), the cortical primary response (PR), and impulse reactions of neurons (mainly of layers V and VI of the cortex) were recorded. The zone of leading-off of the potentials in the cortex was subjected to local surface cooling, which led to an increase in the PR amplitude. This facilitation was accompanied by a change in the time parameters of the impulse reactions of the cortical neurons: the latency and duration increased, and a rhythmic organization of activity appeared or intensified (if it was already present). The increase in the PR amplitude and number of spikes in the response of the cortical neurons to stimulus presentation was far less intensive than the sharp increase in EP amplitude in the NS, and did not correspond to it fully in time. The data suggest that the activating influence of the corticofugal signal on EP in the NS is determined not so much by the intensity of the descending signal as by its temporal organization.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 181–189, March–April, 1991.     

Transferase and hydrolytic activities of the laminarinase from rhodothermus marinus and its M133A, M133C, and M133W mutants

Comparative studies of the transglycosylation and hydrolytic activities have been performed on the Rhodothermus marinus β-1,3-glucanase (laminarinase) and its M133A, M133C, and M133W mutants. The M133C mutant demonstrated near 20% greater rate of transglycosylation activity in comparison with the M133A and M133W mutants that was measured by NMR quantitation of nascent β(1-4) and β(1-6) linkages. To obtain kinetic probes for the wild-type enzyme and Met-133 mutants, p-nitrophenyl β-laminarin oligosaccharides of degree of polymerisation 2–8 were synthesized enzymatically. Catalytic efficiency values, k _cat/K _m, of the laminarinase catalysed hydrolysis of these oligosaccharides suggested possibility of four negative and at least three positive binding subsites in the active site. Comparison of action patterns of the wild-type and M133C mutant in the hydrolysis of the p-nitrophenyl-β-D-oligosac- charides indicated that the increased transglycosylation activity of the M133C mutant did not result from altered subsite affinities. The stereospecificity of the transglycosylation reaction also was unchanged in all mutants; the major transglycosylation products in hydrolysis of p-nitrophenyl laminaribioside were β-glucopyranosyl-β-1,3-D-glucopy- ranosyl-β-1,3-D-glucopyranose and β-glucopyranosyl-β-1, 3-D-glucopyranosyl-β-1,3-D-glucpyranosyl-β-1,3-D- glucopyranoxside. In a memoriam of Dr. Kirill N. Neustroev. All we, his friends and colleagues, mourn for his sudden death. He was a bright and talented scientist, brilliant manager and good friend.     

Cryptococcus silvicola nov. sp. from nature reserves of Russia and Portugal

Nitrate-positive strains of a filobasidiaceous anamorphic yeast related to Cryptococcus cylindricus were isolated from forest litter in a Russian nature reserve and from a lichen in Portuguese one. Mycocinotyping and rDNA sequence analysis revealed that the strains represent a novel species, for which the name Cryptococcus silvicola (type strain VKM Y-2939=CBS 10099) is proposed. An erratum to this article can be found at     

Production of Antifungal Cellobiose Lipids by <Emphasis Type="Italic">Trichosporon porosum</Emphasis>

The yeast Trichosporon porosum suppresses growth of ascomycetes and basidiomycetes belonging to 52 genera. It is due to secretion of a thermostable fungicidal agent. The suppression was maximal at pH 3.5–4.0. Fungicidal preparation obtained from the culture broth was shown to be a mixture of cellobiosides of dihydrodecane acid with different degree of acetylation of cellobiose residue. The preparation caused the death of Candida albicans and Filobasidiella neoformans cells in the concentrations of 0.2 and 0.03 mM, respectively.     

ATP leakage from yeast cells treated by extracellular glycolipids of Pseudozyma fusiformata

The ustilaginaceous yeast Pseudozyma fusiformata secreted glycolipids which were lethal to many yeasts and fungi more active at pH of about 4.0, and in the temperature range of 20-30 degrees C. Purified glycolipids enhanced non-specific permeability of the cytoplasmic membrane in sensitive cells, which resulted in ATP leakage and susceptibility of the cells to staining with bromocresol purple. Cells of Saccharomyces cerevisiae lost the ability to acidify the medium. Basidiomycetous yeasts were more sensitive to the glycolipids than ascomycetous ones. The minimal effective glycolipid concentration was 0.13 and 0.26 mg ml(-1) for Cryptococcus terreus and Filobasidiella neoformans, while for Candida albicans and Saccharomyces cerevisiae it was 1.0 and 1.6 mg ml(-1).