Nitric oxide mediates local activity-dependent excitatory synapse development

Learning related paradigms play an important role in shaping the development and specificity of synaptic networks, notably by regulating mechanisms of spine growth and pruning. The molecular events underlying these synaptic rearrangements remain poorly understood. Here we identify NO signaling as a key mediator of activity-dependent excitatory synapse development. We find that chronic blockade of NO production in vitro and in vivo interferes with the development of hippocampal and cortical excitatory spine synapses. The effect results from a selective loss of activity-mediated spine growth mechanisms and is associated with morphological and functional alterations of remaining synapses. These effects of NO are mediated by a cGMP cascade and can be reproduced or prevented by postsynaptic expression of vasodilator-stimulated phosphoprotein phospho-mimetic or phospho-resistant mutants. In vivo analyses show that absence of NO prevents the increase in excitatory synapse density induced by environmental enrichment and interferes with the formation of local clusters of excitatory synapses. We conclude that NO plays an important role in regulating the development of excitatory synapses by promoting local activity-dependent spine-growth mechanisms

Grain shape and size and structural and phase conditions modified by aluminum ion implantation in UFG titanium

The paper presents the transmission electron microscopy investigations of the granular state and the structural and phase conditions of commercially pure ultra-fine grain (UFG) titanium VT1-0 alloyed with aluminum ions. The UFG-titanium is obtained by the multiple uniaxial compaction with intermediate annealing. The ion implantation is carried out on Mevva-V.Ru ion source at ion-implantation dosages of 1·10{17}, 5·10{17} and 1·10{18} ion/cm{2}. The functions are constructed for the grain size distribution in longitudinal and cross sections; the average grain size and the grain anisotropy factor are determined in this paper. It is shown that the grain shape and size of titanium specimens are modified due to the ion implantation. With the increase of the ion-implantation dosage the anisotropy factor decreases three times. At 1·10{18} ion/cm{2} ion-implantation dosage the longitudinal grain size comes to 0.7 [mu]m. The phase composition of the alloy is detected after the ion implantation and its modification induced by the implantation dosage. The quantitative characteristics and locations of secondary [beta]-Ti, TiAl[3], Ti[3] Al, TiC and TiO[2] phases are ascertained during the investigations. It is shown that TiAl[3] and Ti[3] Al are ordered phases formed during the ion implantation on [alpha]-Ti grain boundaries. The volume ratios of these phases are detected and determined by the ion-implantation dosage. The volume ratios of [alpha]-Ti and secondary TiC and TiO[2] phases do not depend on the implantation dosage and range between 0.3-0.9 vol.%

Hardening by ion implantation of VT1-0 alloy having different grain size

The paper presents a transmission electron microscopy (TEM) study of the structural and phase state of commercially pure titanium implanted by aluminum ions. TEM study has been carried out for two types of grains, namely coarse (0.4 µm) and small (0.5 µm). This paper presents details of the yield stress calculations and the analysis of strength components for the both grain types in two areas of the modified layer: at a distance of 0-150 nm (surface area I) and ∼300 nm (central area II) from the irradiated surface. It is shown that the ion implantation results in a considerable hardening of the entire thickness of the implanted layer in the both grain types. The grain size has, however, a different effect on the yield stress in areas I and II. Thus, near the ion-alloyed layer, the yield stress decreases with the increase of the grain size, whilst area II demonstrates its increase. Moreover, the contribution to the general hardening of the alloy made by certain hardening mechanisms differs from contributions made by each of these mechanisms in each certain case

The effect of aluminum ion implantation on the grain size and structure of UFG titanium

Using the transmission electron microscopy technique, we have studied the structural-phase state of UFG titanium with an average grain size ~0.2 μm implanted with aluminum ions. An MEVVA-V.RU source has been used to implant the specimen at room temperature, implantation time 5.25 hours, and irradiation dose 1⋅1018 ion/cm2. To produce the UFG titanium samples, we have employed the combined multiple uniaxial pressing technique (abc-pressing) followed by grooved rolling and subsequent annealing at 573 K for one hour. The samples have been studied in two states: 1) before implantation (initial state) and 2) after implantation at a distance 70-100 nm from the sample surface. We have obtained the aluminum concentration profile of implanted α-Ti. It has been established that the maximum concentration of aluminum is 70 at.% and the thickness of the implanted layer is 200 nm. We have determined the grain distribution functions over the grain size, calculated the grain anisotropy coefficient before and after implantation. It has been established that implantation decreases the average longitudinal and transversal sizes of α-Ti grains, and reduces the anisotropy coefficient by three times. It has been established that aluminum implantation into titanium brings about formation of a whole set of phases with different crystal lattices, namely, β-Ti, TiAl3, Ti3Al, TiC, and TiO2

Modification of structural phase state and mechanical properties of poly-grained titanium alloy implanted by aluminum ions

The paper presents TEM analysis of microstructure, phase composition, and mechanical properties of commercially pure titanium. These properties of two types of grains are compared before and after modification of titanium by aluminum ions, namely: large grains (1.4 μm) and small (0.5μm) grains. The analysis shows that ion implantation results in a considerable improvement of mechanical properties of both large and small grains throughout their implantation depth. However, with increase of the grain size, the stress in the ion-modified surface layer decreases while in the subsurface layer it increases