The multimodal antidepressant vortioxetine may facilitate pyramidal cell firing by inhibition of 5-HT3 receptor expressing interneurons: An in vitro study in rat hippocampus slices.

The multimodal antidepressant vortioxetine is thought to mediate its pharmacological effects via 5-HT1A receptor agonism, 5-HT1B receptor partial agonism, 5-HT1D, 5-HT3, 5-HT7 receptor antagonism and 5-HT transporter inhibition. Here we studied vortioxetine's functional effects across species (canine, mouse, rat, guinea pig and human) in cellular assays with heterologous expression of 5-HT3A receptors (in Xenopus oocytes and HEK-293 cells) and in mouse neuroblastoma N1E-115 cells with endogenous expression of 5-HT3A receptors. Furthermore, we studied the effects of vortioxetine on activity of CA1 Stratum Radiatum interneurons in rat hippocampus slices using current- and voltage-clamping methods. The patched neurons were subsequently filled with biocytin for confirmation of 5-HT3 receptor mRNA expression by in situ hybridization. Whereas, both vortioxetine and the 5-HT3 receptor antagonist ondansetron potently antagonized 5-HT-induced currents in the cellular assays, vortioxetine had a slower off-rate than ondansetron in oocytes expressing 5-HT3A receptors. Furthermore, vortioxetine's but not ondansetron's 5-HT3 receptor antagonistic potency varied considerably across species. Vortioxetine had the highest potency at rat and the lowest potency at guinea pig 5-HT3A receptors. Finally, in 5-HT3 receptor-expressing GABAergic interneurons from the CA1 stratum radiatum, vortioxetine and ondansetron blocked depolarizations induced by superfusion of either 5-HT or the 5-HT3 receptor agonist mCPBG. Taken together, these data add to a growing literature supporting the idea that vortioxetine may inhibit GABAergic neurotransmission in some brain regions via a 5-HT3 receptor antagonism-dependent mechanism and thereby disinhibit pyramidal neurons and enhance glutamatergic signaling.

Enhanced wetting of Cu on ZnO by migration of subsurface oxygen vacancies.

Metal adhesion on metal oxides is strongly controlled by the oxide surface structure and composition, but lack of control over the surface conditions often limits the possibilities to exploit this in opto- and micro-electronics applications and heterogeneous catalysis where nanostructural control is of utmost importance. The Cu/ZnO system is among the most investigated of such systems in model studies, but the presence of subsurface ZnO defects and their important role for adhesion on ZnO have been unappreciated so far. Here we reveal that the surface-directed migration of subsurface defects affects the Cu adhesion on polar ZnO(0001) in the technologically interesting temperature range up to 550 K. This leads to enhanced adhesion and ultimately complete wetting of ZnO(0001) by a Cu overlayer. On the basis of our experimental and computational results we demonstrate a mechanism which implies that defect concentrations in the bulk are an important, and possibly controllable, parameter for the metal-on-oxide growth.

Correlation between stoichiometry and surface structure of the polar MgAl2O4(100) surface as a function of annealing temperature.

The correlation between surface structure, stoichiometry and atomic occupancy of the polar MgAl2O4(100) surface has been studied with an interplay of noncontact atomic force microscopy, X-ray photoelectron spectroscopy and surface X-ray diffraction under ultrahigh vacuum conditions. The Al/Mg ratio is found to significantly increase as the surface is sputtered and annealed in oxygen at intermediate temperatures ranging from 1073-1273 K. The Al excess is explained by the observed surface structure, where the formation of nanometer-sized pits and elongated patches with Al terminated step edges contribute to stabilizing the structure by compensating surface polarity. Surface X-ray diffraction reveals a reduced occupancy in the top two surface layers for both Mg, Al, and O and, moreover, vacancies are preferably located in octahedral sites, indicating that Al and Mg ions interchange sites. The excess of Al and high concentration of octahedral vacancies, very interestingly, indicates that the top few surface layers of the MgAl2O4(100) adopts a surface structure similar to that of a spinel-like transition Al2O3 film. However, after annealing at a high temperature of 1473 K, the Al/Mg ratio restores to its initial value, the occupancy of all elements increases, and the surface transforms into a well-defined structure with large flat terraces and straight step edges, indicating a restoration of the surface stoichiometry. It is proposed that the tetrahedral vacancies at these high temperatures are filled by Mg from the bulk, due to the increased mobility at high annealing temperatures.

Atomic structure of a spinel-like transition Al2O3(100) surface.

We study a crystalline epitaxial alumina thin film with the characteristics of a spinel-type transition Al2O3(100) surface by using atom-resolved noncontact atomic force microscopy and density functional theory. It is shown that the films are terminated by an Al-O layer rich in Al vacancies, exhibiting a strong preference for surface hydroxyl group formation in two configurations. The transition alumina films are crystalline and perfectly stable in ambient atmospheres, a quality which is expected to open the door to new fundamental studies of the surfaces of transition aluminas.

Quantification of tip-broadening in non-contact atomic force microscopy with carbon nanotube tips.

Carbon nanotube terminated atomic force microscopy (AFM) probes have been used for the imaging of 5 nm wide surface supported Pt nanoclusters by non-contact (dynamic mode) AFM in an ultra-high vacuum. The results are compared to AFM measurements done with conventional Si-tips, as well as with transmission electron microscopy images, which give accurate measures for cluster widths. Despite their ideal aspect ratio, tip-broadening is concluded to be a severe problem even when imaging with carbon nanotube tips, which overestimates the cluster width by several times the nominal width of the nanotube tip. This broadening is attributed to a bending of the carbon nanotubes, and not to pure geometrical factors, which coincidentally results in a significant improvement for relative height measurements of tightly spaced high aspect ratio structures, as compared to what can be achieved with geometrically limited conventional probes. Superior durability also stands out as a defining feature of carbon nanotube terminated probes, allowing them to give results with a greatly enhanced reproducibility.

Al2O3(1120) surface as a template for the ordered growth of Ni and Co nanoclusters.

The morphology and thermal stability of Ni and Co nanoclusters grown by physical vapour deposition on a reconstructed (1120) surface of α-Al(2)O(3) is investigated using non-contact atomic force microscopy (NC-AFM). NC-AFM images reveal that the clean α-Al(2)O(3)(1120) substrate adopts a characteristic (12 × 4) reconstruction when prepared in vacuum at high temperature. Subsequent deposition of Ni and Co onto this substrate at room temperature facilitates the growth of well-ordered metal nanocluster arrays with a preferred inter-cluster distance determined by the (12 × 4) periodicity of the substrate surface. The order in the cluster arrangement remains intact even upon annealing the system to temperatures up to 500 °C indicating a high resistance against sintering. The reconstructed α-Al(2)O(3)(1120) surface can, therefore, serve as an appropriate insulating template for studies of size-dependent magnetic or catalytic effects in a well-defined ensemble of metallic nanoclusters.

Molecular cloning and pharmacological characterization of serotonin 5-HT(3A) receptor subtype in dog.

In order to establish if the canine 5-hydroxytryptamine type 3A (5-HT(3A)) receptors share the pharmacological profile with human 5-HT(3A) receptors, we cloned and performed a molecular pharmacological characterization of the canine 5-HT(3A) receptor. The 5-HT(3A) cDNA was cloned from canine brain by polymerase chain reaction amplification. It encodes a 483 amino acid peptide that exhibits from 80% (mice) to 90% (ferrets) identity to other sequenced mammalian 5-HT(3A) receptors. The receptor agonists 5-hydroxytryptamine (5-HT) and meta-chlorophenylbiguanide (mCPBG) showed little differences between the two species, whereas 2-methyl-5-hydroxytryptamine (2-Me-5-HT) was ten times weaker at canine receptors than at human receptors. The potencies at the canine 5-HT(3) receptors were 9.9 microM (5-HT), 79 microM (2-Me-5-HT) and 0.8 microM (mCPBG). The selective, competitive receptor antagonist ondansetron was ten times more potent at human receptors compared to canine receptors (K(b)=0.9 nM), while (+)-tubocurarine was 1000-fold more potent at canine receptors (K(b)=3.0 nM) than at human receptors. Examination of the presumed ligand binding extracellular domain revealed one residue, where the canine receptor differs from all previously characterized 5-HT(3A) receptors, i.e. other species contain a conserved Trp(195), whereas the canine orthologue contains a Leu(195). To address the differences in potencies at the human and canine 5-HT(3A) receptors seen in this study, we introduced a L195W point mutation in the canine orthologue. Data showed that the 195 residue can affect receptor agonist potency and efficacy as well as antagonist potency, but did produce a pharmacological profile identical to the human orthologue. We therefore conclude that position 195 is strongly involved in the receptor-ligand interaction, but additional residues must contribute to the overall pharmacological profile.