Reentrant surface anisotropy in the antiferromagnetic/ferromagnetic bilayer Mn/Co/Cu(001).

We investigated the magnetic anisotropy energy of monatomic surface-step atoms in antiferromagnetic/ferromagnetic (AF/FM) epitaxial Mn/Co bilayers grown on vicinal Cu(001) surfaces. The step-induced anisotropy of the Co/Cu(001) films was quenched upon submonolayer Mn deposition, but a reentrant uniaxial surface anisotropy was observed for Mn thickness (tMn) between 1 and 2 monolayers, which disappears for Mn thickness above 2 monolayers. In the Mn/Co/Cu(001) system, Mn films undergo a tMn-dependent transition from FM to AF in the 1-2 Mn monolayer thickness range, which entails the coexistence of FM and AF Mn phases in the film. The observation of a sizeable uniaxial anisotropy exclusively in the Mn-thickness range of coexistence of the FM and AF phases points out the crucial role of the boundaries between FM and AF regions within the Mn film. A symmetry-breaking mechanism of a magnetic type, rather than a purely geometric one, is therefore proposed as the origin of the reentrant anisotropy.

Growth dynamics of L-cysteine SAMs on single-crystal gold surfaces: a metastable deexcitation spectroscopy study.

We report on a metastable deexcitation spectroscopy investigation of the growth of L-cysteine layers deposited under UHV conditions on well-defined Au(110)- (1 × 2) and Au(111) surfaces. The interaction of He(*) with molecular orbitals gave rise to well-defined UPS-like Penning spectra which provided information on the SAM assembly dynamics and adsorption configurations. Penning spectra have been interpreted through comparison with molecular orbital DFT calculations of the free molecule and have been compared with XPS results of previous works. Regarding adsorption of first-layer molecules at room temperature (RT), two different growth regimes were observed. On Au(110), the absence of spectral features related to orbitals associated with SH groups indicated the formation of a compact SAM of thiolate molecules. On Au(111), the data demonstrated the simultaneous presence, since the early stages of growth, of strongly and weakly bound molecules, the latter showing intact SH groups. The different growth mode was tentatively assigned to the added rows of the reconstructed Au(110) surface which behave as extended defects effectively promoting the formation of the S-Au bond. The growth of the second molecular layer was instead observed to proceed similarly for both substrates. Second-layer molecules preferably adopt an adsorption configuration in which the SH group protrudes into the vacuum side.

Direct conjugation of antibodies to the ZnS shell of quantum dots for FRET immunoassays with low picomolar detection limits.

Compact and functional nanoparticle-antibody conjugates are of paramount importance for the development of quantum dot (QD)-based immunoassays. Here, we present a simple strategy to directly conjugate IgG, F(ab')2, and Fab antibodies via their endogenous disulfide groups directly to the inorganic ZnS shell of compact penicillamine-coated QDs. The functionality of the conjugates was demonstrated by terbium (Tb)-to-QD FRET immunoassays against prostate specific antigen in serum samples. Detection limits of 2.5 pM (0.080 ng mL-1) were 10 and 25 times lower compared to conjugation via maleimide-terminated ligands and polymer chains, respectively. These more compact, simple, and sensitive QD-antibody conjugates will be highly advantageous for nanocrystal-based biosensing applications.

Phospholipid metabolism and protein phosphorylation in sciatic nerve from genetically diabetic (db/db) mouse.

The incorporation of [32P]orthophosphate into phospholipids and proteins of sciatic nerve from genetically diabetic (db/db) and littermate control (db/m) C57BL/KsJ mice was studied. Nerves from animals of ages 12, 16, 22, 26, and 38 wk were incubated in vitro. Among phospholipids, the uptake of isotope into phosphatidic acid was higher at nearly all ages examined. Phosphorylation of several proteins, including the major myelin glycoprotein, P0, and the small myelin basic proteins Pr + P2, was significantly enhanced in nerves from both 12- and 38-wk-old diabetic mice. The altered pattern of protein phosphorylation, but not that of phospholipid metabolism, was similar to changes observed in sciatic nerve from streptozocin-induced diabetic rats. The relationship of the results to reported levels of myo-inositol, sorbitol, and Na+-K+-ATPase activity and to functional abnormalities in nerves of db/db mice is discussed. The findings suggest that caution should be exercised in reaching conclusions concerning which biochemical alterations observed in different animal models of diabetic neuropathy are invariably associated with the development of this disorder.

Altered protein phosphorylation in sciatic nerve from rats with streptozocin-induced diabetes.

The effect of experimental diabetes on the phosphorylation of proteins in the rat sciatic nerve was studied. Nerves from animals made diabetic with streptozocin were incubated in vitro with [32P]orthophosphate and divided into segments from the proximal to the distal end, and proteins from each segment were then separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The principal labeled species were the major myelin proteins, P0, and the basic proteins. After 6 wk of diabetes, the incorporation of isotope into these proteins rose as a function of distance along the nerve in a proximal to distal direction and was significantly higher at the distal end compared with incorporation into nerves from age-matched controls. The overall level of isotope uptake was similar in nerves from diabetic animals and weight-matched controls. The distribution of 32P among proteins also differed in diabetic nerve compared with both control groups in that P0 and the small basic protein accounted for a greater proportion of total label incorporated along the entire length of nerve. In contrast to intact nerve, there was no significant difference in protein phosphorylation when homogenates from normal and diabetic nerve were incubated with [32P]-gamma-ATP. The results suggest that abnormal protein phosphorylation, particularly of myelin proteins, is a feature of experimental diabetic neuropathy and that the changes are most pronounced in the distal portion of the nerve.

Correction of altered metabolic activities in sciatic nerves of streptozocin-induced diabetic rats. Effect of ganglioside treatment.

The effect of ganglioside administration to nondiabetic and streptozocin-induced diabetic rats on sciatic nerve Na(+)-K(+)-ATPase, polyphosphoinositide (PPI) turnover, and protein phosphorylation was investigated. Gangliosides were injected (10 mg/kg body wt i.p.) for 10 or 30 days beginning 20 days after induction of diabetes. Na(+)-K(+)-ATPase activity was reduced nearly 50% in diabetic nerve and was restored to normal by both ganglioside treatments. The elevated levels of fructose and sorbitol and depressed content of myoinositol in diabetic nerve were unaffected by 30 days of ganglioside treatment, indicating that the restoration of Na(+)-K(+)-ATPase activity is not dependent on normal concentrations of these compounds. In the same nerves, 32P incorporation into phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-phosphate increased 73-76 and 39-53%, respectively, in diabetic compared with nondiabetic tissue. Ganglioside administration abolished the elevated labeling of PPIs after 30 days but was ineffective after only 10 days. Neither ganglioside regimen was able to reverse enhanced phosphorylation of the major peripheral nerve myelin protein P0. The finding that gangliosides can more quickly correct the effects of diabetes on Na(+)-K(+)-ATPase activity than on PPI turnover suggests that the mechanisms underlying these two phenomena are not closely related and are distinct from the sequence of events responsible for altered myelin protein phosphorylation.

Alteration of phosphoinositide metabolism, protein phosphorylation, and carbohydrate levels in sciatic nerve from Wistar fatty diabetic rats.

Sciatic nerve from the Wistar fatty diabetic (FD) rat, a prospective model for non-insulin-dependent diabetes mellitus, was investigated to determine the content of carbohydrates and to measure the incorporation of 32P into phosphoinositides and proteins. This strain has been shown to develop structural abnormalities in nerves and to exhibit reduced conduction velocity. Males became diabetic between the ages of 8 and 10 wk and were maintained together with lean sibling controls until the animals were either 22 or 44 wk old. Throughout this period, FD rats displayed moderate hyperglycemia. The carbohydrate profile of FD rat sciatic nerve exhibited modest increases in glucose, fructose, and sorbitol levels and significantly reduced myo-inositol concentrations, which were comparable at both ages. When nerves from 22-wk-old animals were incubated with [32P]orthophosphate and incorporation of radioactivity into phospholipids was measured, an increase in isotope uptake into phosphatidylinositol-4,5-bisphosphate and phosphatidylinositol-4-phosphate in the distal portions of tissue from the FD rat was observed. This effect was more pronounced in nerves from 44-wk-old rats. Phosphorylation of the major myelin protein P0 was 70% higher in the most distal portion of FD sciatic nerve from 22-wk-old animals. A comparable rise in phosphorylation of P0 as well as the large (P1) and small (Pr) myelin basic proteins occurred in nerves from 44-wk-old rats. In these animals, an approximately 50% decrease in the uptake of 32P into P0 and P1 in the most proximal region of FD nerve was also apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

The human V3 pituitary vasopressin receptor: ligand binding profile and density-dependent signaling pathways.

The vasopressin (AVP) V3 pituitary receptor (V3R) is a G protein-coupled corticotropic phenotypic marker that is overexpressed in ACTH-hypersecreting tumors. Studies of the agonist/antagonist binding profile and signal transduction pathways linked to the human V3R have been limited because of the scarcity of this protein. To define the signals activated by V3Rs and the eventual changes triggered by developmental or pathological receptor regulation, we developed Chinese hamster ovary (CHO)-V3 cells stably expressing low, medium, or high levels of human V3Rs (binding capacity, <10, 10-25, and 25-100 pmol/mg, respectively). The affinity of the V3R for 21 peptide and nonpeptide AVP analogs was clearly distinct from that exhibited by the human V1R and V2R. AVP triggered stimulation of phospholipase C in CHO-V3 cells (partially sensitive to treatment with pertussis toxin) with a potency directly proportional to receptor density. V3R-mediated arachidonic acid release also was also sensitive to pertussis toxin and more efficacious in cells exhibiting medium than in those with high receptor density. AVP also stimulated the pertussis toxin-insensitive uptake of [3H]thymidine in CHO-V3 cells. The concentration-response curves for this effect were monophasic in cells expressing low and medium levels of V3Rs; on the contrary, a biphasic curve was observed in cells with high V3R density. Coupling of V3R to increased production of cAMP was only observed in CHOV3 high cells, suggesting a negative relationship between increased cAMP production and DNA synthesis. Activation of mitogen-activated protein kinases by V3R was pertussis toxin insensitive, but was dependent on activation of phospholipase C and protein kinase C; both the level and duration of activation were a function of the receptor density. Thus, the human V3R has a pharmacological profile clearly distinct from that of the human V1R and V2R and activates several signaling pathways via different G proteins, depending on the level of receptor expression. The increased synthesis of DNA and cAMP levels observed in cells expressing medium and high levels of V3Rs, respectively, may represent important events in the tumorigenesis of corticotroph cells.

Signal transduction pathways of the human V1-vascular, V2-renal, V3-pituitary vasopressin and oxytocin receptors.

Vasopressin (VP) and oxytocin (OT) are cyclic nonapeptides whose actions are mediated by stimulation of specific G protein-coupled receptors (GPCRs) currently classified into V1-vascular (V1R), V2-renal (V2R) and V3-pituitary (V3R) VP receptors and OT receptors (OTR). The recent cloning of the different members of the VP/OT family of receptors now allows the extensive characterization of the molecular determinants involved in ligand binding and signal transduction pathways coupled to a given VP/OT receptor subtype in stably transfected mammalian cell lines. In this article, we review the present knowledge of the signal transduction pathways coupled to the different VP/OT receptor subtypes and we present new observations derived from the study of each human VP or OT receptor subtype stably expressed in CHO cells.

Isolation of oligodendroglial cells from young and adult whole rat brains using an in situ generated percoll density gradient.

A method for the isolation of oligodendroglial cells from young and adult whole rat brains, using a Percoll density gradient is presented. The minced tissue, incubated in a balanced salt solution containing 0.1% trypsin is further dissociated by forcing it through nylon screens to 145 and 74 ?m pore size. The crude suspension is then mixed with an isosmotic Percoll solution and centrifuged for 15 min. An in situ generated density gradient allows the separation of five bands, only one of which (Band C) lying between ?1.050 and ?1.062 contains cellular elements. The isolated cells show the typical morphological characteristics of oligodendroglia. A detailed morphological study of the cells isolated from whole brains of 10-, 30- and 120-day old rats is presented for the first time in the literature and immunocytochemical characterization is carried out using specific (antigalactocerebroside) and non specific (anti-glial fibrillary acidic protein) anti-sera. The method is simple and rapid and isosmotic conditions are maintained throughout, resulting in a better preservation of cell integrity. It represents an improvement over the two previous methods described in the literature and will be useful for studying different developmental events (biochemical and morphological) occurring in oligodendroglial cells at early stages of myelin formation.

An aldose reductase inhibitor but not myo-inositol blocks enhanced polyphosphoinositide turnover in peripheral nerve from diabetic rats.

Experimental diabetic neuropathy, whether chemically induced or present in several spontaneously diabetic animal models, is characterized by sorbitol accumulation and myo-inositol depletion and usually also by enhanced turnover of the monoesterified moieties of polyphosphoinositides, particularly phosphatidylinositol-4,5-bisphosphate (PIP2). This study examined the relationship of these alterations by assessing the effects of myo-inositol and the aldose reductase inhibitor, sorbinil, supplied as dietary supplements, on sorbitol and myo-inositol concentrations and incorporation of 32P into polyphosphoinositides in sciatic nerve from rats killed 8 weeks after induction of diabetes with streptozotocin. Nerves from diabetic rats killed after 8 weeks of disease exhibited 52% to 76% greater PIP2 labeling, markedly elevated sorbitol levels, and 30% less myo-inositol when compared with age-matched normal rats. Incorporation of isotope into PIP2 in nerves from animals fed a myo-inositol supplement, added to either a high-sucrose diet or standard rat chow beginning immediately after induction of diabetes, remained substantially elevated, whereas myo-inositol levels were corrected to normal. Essentially the same results were obtained when rats were fed the myo-inositol-containing diet beginning 4 weeks after streptozotocin injection. In contrast, PIP2 labeling in nerves from diabetic rats that received the sorbinil-supplemented diet for either 4 or 8 weeks was not different from that in controls. myo-Inositol levels in these animals were also restored to normal, whereas sorbitol levels remained elevated, albeit reduced by approximately 30%. These results indicate that myo-inositol administration is unable to completely counteract the impact of diabetes on the turnover of monoesterified phosphate groups in PIP2. In contrast, sorbinil can correct this abnormality, but this beneficial effect is not dependent on the presence of normal sorbitol concentrations.

Hexanedione effects on protein phosphorylation in rat peripheral nerve.

Rats were treated with either 2,5-hexanedione (2,5-HD), 1,6-hexanediol (1,6-HDIOL), or saline for 7, 15 or 24 days. Protein phosphorylation was measured in proximal and distal sciatic nerve segments following incubation with [32P]orthophosphate. In proximal segments, 2,5-HD administration caused selective time-dependent increases in isotope incorporation in a 55 kDa protein, tentatively identified as tubulin, and a 180 kDa protein. Enhanced phosphorylation was highest at 24 days when motor function was most impaired. Administration of 1,6-HDIOL produced no consistent phosphorylation changes. Animals intoxicated with 3,4-dimethyl-2,5-hexanedione for 12 days showed proximal region increases in phosphorylation of the 55 and 180 kDa proteins and the major myelin proteins, Po and Pr.

Molecular pharmacology of human vasopressin receptors.

Vasopressin (AVP) and oxytocin (OT) are cyclic nonapeptides whose actions are mediated by activation of specific G protein-coupled receptors (GPCRs) currently classified into V1-vascular (V1R), V2-renal (V2R) and V3-pituitary (V3R) AVP receptors and OT receptors (OTR). The cloning of the different members of the AVP/OT family of receptors now allows the extensive molecular pharmacological characterization of a single AVP/OT receptor subtype in stably transfected mammalian cell lines. The human V1-vascular (CHO-V1), V2-renal (CHO-V2), V3-pituitary (CHO-V3) and oxytocin (CHO-OT) receptors stably expressed in CHO cells display distinct binding profiles for 18 peptide and 5 nonpeptide AVP/OT analogs. Several peptide and nonpeptide compounds have a greater affinity for the V1R than AVP itself. V2R peptide agonists and antagonists tend to be non-selective ligands whereas nonpeptide V2R antagonists are potent and subtype-selective. None of the 22 AVP/OT analogs tested has a better affinity for the human V3R than AVP itself. Several peptide antagonists do not select well between V1R and OTR. These results underscore the need for developing specific and potent analogs interacting specifically with a given human AVP/OT receptor subtype.

Tuning the magneto-optical response of iron oxide nanocrystals in Au- and Ag-based plasmonic media.

We investigated the magneto-optical response of chemically synthesized iron oxide magnetic nanocrystals, optically coupled with ordered planar arrays of plasmonic nanoparticles. We compare the signals from two classes of systems, featuring either Au or Ag as the plasmonic counterpart. The localized surface plasmon resonance of the Ag and Au nanoparticles arrays were superimposed or detuned, respectively, with respect to the dominant magneto-optical transitions of the magnetic material. Under resonance, a significant enhancement of the magneto-optical signal was observed. In both cases, we could separate the purely plasmonic and the magnetic contributions in the magneto-optical spectrum of the optically coupled composite based on their different magnetic-field dependence.

NF-κB subunits are differentially distributed in cells of lumbar dorsal root ganglia in naïve and diabetic rats.

Previous studies demonstrated that nuclear factor κB (NF-κB) activation is decreased in dorsal root ganglia (DRG) of rats having streptozotocin (STZ)-induced diabetes. DRG contain cell bodies of neurons that convey sensory signals from the periphery. To determine the relationship between diabetes-induced neuropathy and NF-κB expression in DRG, behavioral, immunohistochemical, and biochemical studies were performed on naïve and 3-month diabetic rats. Behavioral studies confirmed that many diabetic rats develop tactile allodynia, or increased sensitivity to light touch, in the hind paws. Immunohistochemical studies on lumbar DRG that receive input from the affected regions revealed that p50 and p65, frequent NF-κB subunit partners, are differentially localized. Intense p65 immunostaining was detected in the cytoplasm of small- and medium-sized neurons as well as in satellite cells. In contrast, p50 was localized in the cytoplasm of virtually all neurons. In many cases, prominent staining was also present in nuclei, a location consistent with transcription factor activation. Immunohistochemical and biochemical studies found that the nuclear to cytoplasmic ratio of p50 expression was significantly reduced in diabetic rats compared to that in naïve animals. Our findings raise the possibility that changes in NF-κB activation in a subset of DRG neurons participates in mediating diabetes-induced sensory neuropathy.