Dendritic Branch Intersections Are Structurally Regulated Targets for Efficient Axonal Wiring and Synaptic Clustering

Synaptic clustering on dendritic branches enhances plasticity, input integration and neuronal firing. However, the mechanisms guiding axons to cluster synapses at appropriate sites along dendritic branches are poorly understood. We searched for such a mechanism by investigating the structural overlap between dendritic branches and axons in a simplified model of neuronal networks - the hippocampal cell culture. Using newly developed software, we converted images of meshes of overlapping axonal and dendrites into topological maps of intersections, enabling quantitative study of overlapping neuritic geometry at the resolution of single dendritic branch-to-branch and axon-to-branch crossings. Among dendro-dendritic crossing configurations, it was revealed that the orientations through which dendritic branches cross is a regulated attribute. While crossing angle distribution among branches thinner than 1 µm appeared to be random, dendritic branches 1 µm or wider showed a preference for crossing each other at angle ranges of either 50°–70° or 80°–90°. It was then found that the dendro-dendritic crossings themselves, as well as their selective angles, both affected the path of axonal growth. Axons displayed 4 fold stronger tendency to traverse within 2 µm of dendro-dendritic intersections than at farther distances, probably to minimize wiring length. Moreover, almost 70% of the 50°–70° dendro-denritic crossings were traversed by axons from the obtuse angle’s zone, whereas only 15% traversed through the acute angle’s zone. By contrast, axons showed no orientation restriction when traversing 80°–90° crossings. When such traverse behavior was repeated by many axons, they converged in the vicinity of dendro-dendritic intersections, thereby clustering their synaptic connections. Thus, the vicinity of dendritic branch-to-branch crossings appears to be a regulated structure used by axons as a target for efficient wiring and as a preferred site for synaptic clustering. This synaptic clustering mechanism may enhance synaptic co-activity and plasticity.     

Monte carlo study of the percolation in two-dimensional polymer systems

The structure of a two-dimensional film formed by adsorbed polymer chains was studied by means of Monte Carlo simulations. The polymer chains were represented by linear sequences of lattice beads and positions of these beads were restricted to vertices of a two-dimensional square lattice. Two different Monte Carlo methods were employed to determine the properties of the model system. The first was the random sequential adsorption (RSA) and the second one was based on Monte Carlo simulations with a Verdier-Stockmayer sampling algorithm. The methodology concerning the determination of the percolation thresholds for an infinite chain system was discussed. The influence of the chain length on both thresholds was presented and discussed. It was shown that the RSA method gave considerably lower thresholds for longer chains. This behavior can be explained by a different pool of chain conformations used in the calculations in both methods under consideration.

Lipid Nanoparticles Vectorized with NFL-TBS.40-63 Peptide Target Oligodendrocytes and Promote Neurotrophin-3 Effects After Demyelination In Vitro

Neurochemical Research - Promoting remyelination in multiple sclerosis is important to prevent axon degeneration, given the lack of curative treatment. Although some growth factors improve this...     

The Influence of Two Lithium Forms on the Growth, l-Ascorbic Acid Content and Lithium Accumulation in Lettuce Plants

Lithium (Li) is a trace element that is essential in the human diet due to its importance for health and proper functioning of an organism. However, the biological activity of this metal in crop plants, which are the primary dietary sources of Li, is still poorly understood. The aim of the presented study was to comparatively analyse two Li chemical forms on the growth, as well as the l-ascorbic acid content, the Li accumulation and translocation in butterhead lettuce (Lactuca sativa L. var. capitata) cv. Justyna. The plants were grown in a nutrient solution enriched with Li in the form of LiCl or LiOH at the following concentrations: 0, 2.5, 20, 50 or 100 mg?Li?dm^?3. The obtained results indicate that the presence of Li⁺ ions in the root environment reduced the yield of edible parts of the lettuce if the Li concentration in a nutrient solution had reached 20 mg?Li?dm^?3. However, a yield reduction under these conditions was found to be significant only for LiOH. In plants exposed to 50 mg?Li?dm^?3, both shoot and root fresh weights (FW) significantly decreased, regardless of the supplied Li chemical form. On the other hand, under the lowest LiOH dose, a significant increase in the root FW was noted, suggesting beneficial effects of Li on the growth of lettuce plants. However, applied Li concentrations and forms did not affect the l-ascorbic acid content in the lettuce leaves. Regardless of which Li form was used, Li accumulated mainly in the root tissues. An exception was the higher concentration of this metal in the shoots than in the roots of plants supplied with 100 mg?Li?dm^?3 in LiCl, and there were almost the same Li concentrations in both examined organs of plants supplied with 100 mg?Li?dm^?3 in LiOH. The effectiveness of Li translocation from roots to shoots rose with increasing Li concentrations in the growth medium, and this suggests a relatively ready translocation of this metal throughout the plant. Moreover, these results suggest that Li toxicity in lettuce plants is related to a high accumulation of this element in the root and shoot tissues, causing a drastic reduction in the yield, in the presence either of LiCl or LiOH, but not affecting the l-ascorbic acid accumulation in the leaves.