Spatio-temporal visual properties in the ascending tectofugal system

Our study compares the spatio-temporal visual receptive field properties of different subcortical stages of the ascending tectofugal visual system. Extracellular single-cell recordings were performed in the superficial (SCs) and intermediate (SCi) layers of the superior colliculus (SC), the suprageniculate nucleus (Sg) of the posterior thalamus and the caudate nucleus (CN) of halothane-anesthetized cats. Neuronal responses to drifting gratings of various spatial and temporal frequencies were recorded. The neurons of each structure responded optimally to low spatial and high temporal frequencies and displayed narrow spatial and temporal frequency tuning. The detailed statistical analysis revealed that according to its stimulus preferences the SCs has markedly different spatio-temporal properties from the homogeneous group formed by the SCi, Sg and CN. The SCs neurons preferred higher spatial and lower temporal frequencies and had broader spatial tuning than the other structures. In contrast to the SCs the visually active SCi, as well as the Sg and the CN neurons possessed consequently similar spatio-temporal preferences. These data support our hypothesis that the visually active SCi, Sg and CN neurons form a homogeneous neuronal population given a similar spatio-temporal frequency preference and a common function in processing of dynamic visual information.     

Geographical and temporal patterns of cyanobacterial assemblages in the Danube Delta lake complexes

Hydrobiologia - Danube Delta shallow lakes experience cyanobacteria blooms that can negatively affect the aquatic ecosystem. Although there are several studies on Danube Delta cyanobacteria, little...     

Claudin 1 Expression Characterizes Human Uterine Cervical Reserve Cells

Stem cells participate in cervical carcinogenesis but their function and exact features are still not clear. One type of stem-like cells are endocervical reserve cells (RCs), and their association with other normal/altered cervical cells is not exactly known. Epithelial cells are attached to each other by tight junctions. Their dominant components are the claudin proteins, which show changed expression in cancer; however, no data are available on their pattern. Expressions of various claudins (1, 2, 3, 4, 7), occludin, cytokeratins 5/6 and 7, and p63 were analyzed in 60 paraffin-embedded cervical samples. Immunohistochemical reactions were evaluated semiquantitatively and statistically. Claudin 1 was as high in RCs as in cervical intraepithelial neoplasia (CIN) and higher than in suprabasal squamous epithelial cells, contrary to the negative glandular and squamous basal cells. Claudin 2 was positive in all cell types except parabasal cells, whereas claudins 4 and 7 were weakly positive and claudin 3 was negative in all cell types. Occludin was positive in RCs, basal/parabasal cells, and CIN, whereas glandular cells were negative. This is a first report that describes the intermediate claudin pattern of RCs, demonstrating that it differs from that of cervical glandular and squamous basal cells, but showing an expression similar to the strong claudin 1 expression detected in cervical neoplastic cells.     

C-Terminal Turn Stability Determines Assembly Differences between Aβ40 and Aβ42

Oligomerization of the amyloid β-protein (Aβ) is a seminal event in Alzheimer's disease. Aβ42, which is only two amino acids longer than Aβ40, is particularly pathogenic. Why this is so has not been elucidated fully. We report here results of computational and experimental studies revealing a C-terminal turn at Val36–Gly37 in Aβ42 that is not present in Aβ40. The dihedral angles of residues 36 and 37 in an Ile31–Ala42 peptide were consistent with β-turns, and a β-hairpin-like structure was indeed observed that was stabilized by hydrogen bonds and by hydrophobic interactions between residues 31–35 and residues 38–42. In contrast, Aβ(31–40) mainly existed as a statistical coil. To study the system experimentally, we chemically synthesized Aβ peptides containing amino acid substitutions designed to stabilize or destabilize the hairpin. The triple substitution Gly33Val–Val36Pro–Gly38Val (“VPV”) facilitated Aβ42 hexamer and nonamer formation, while inhibiting formation of classical amyloid-type fibrils. These assemblies were as toxic as were assemblies from wild-type Aβ42. When substituted into Aβ40, the VPV substitution caused the peptide to oligomerize similarly to Aβ42. The modified Aβ40 was significantly more toxic than Aβ40. The double substitution d-Pro36–l-Pro37 abolished hexamer and dodecamer formation by Aβ42 and produced an oligomer size distribution similar to that of Aβ40. Our data suggest that the Val36–Gly37 turn could be the sine qua non of Aβ42. If true, this structure would be an exceptionally important therapeutic target.