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.%