Remodeling of synaptic actin induced by photoconductive stimulation

Use-dependent synapse remodeling is thought to provide a cellular mechanism for encoding durable memories, yet whether activity triggers an actual structural change has remained controversial. We use photoconductive stimulation to demonstrate activity-dependent morphological synaptic plasticity by video imaging of GFP-actin at individual synapses. A single tetanus transiently moves presynaptic actin toward and postsynaptic actin away from the synaptic junction. Repetitive spaced tetani induce glutamate receptor-dependent stable restructuring of synapses. Presynaptic actin redistributes and forms new puncta that label for an active synapse marker FM5-95 within 2 hr. Postsynaptic actin sprouts projections toward the new presynaptic actin puncta, resembling the axon-dendrite interaction during synaptogenesis. Our results indicate that activity-dependent presynaptic structural plasticity facilitates the formation of new active presynaptic terminals.

Glycolipids support E-selectin-specific strong cell tethering under flow

This study provides functional evidence that glycosphingolipids constitute ligands for E-selectin but not P-selectin. Chinese hamster ovary (CHO) cells expressing E-selectin (CHO-E) or P-selectin (CHO-P) were perfused over alpha2,3-sialyl Lewis X (alpha2,3-sLe(x)) presented as the hexaosylceramide glycosphingolipid adsorbed in a monolayer containing phosphatidylcholine and cholesterol. CHO-E cells tethered extensively and formed slow, stable rolling interactions with alpha2,3-sLe(x) glycosphingolipid but not with the comparable alpha2,6-sLe(x) glycosphingolipid. Tethering/rolling varied with wall shear stress, selectin density, and ligand density. In contrast, alpha2,3-sLe(x) glycosphingolipid supported only limited, fast CHO-P cell rolling. As calculated from a stochastic model of cell rolling, the step size between successive bond releases from the alpha2,3-sLe(x) glycosphingolipid was smaller for CHO-E than CHO-P cells, whereas the opposite effect was observed for the waiting time between these events. Detachment assays revealed stronger adhesive interactions of CHO-E than CHO-P cells with alpha2,3-sLe(x) glycosphingolipid. These findings indicate that glycosphingolipids expressing an appropriate oligosaccharide mediate cell tethering/rolling via E-selectin but not P-selectin.

Conversion of cellular sialic acid expression from N-acetyl- to N-glycolylneuraminic acid using a synthetic precursor, N-glycolylmannosamine pentaacetate: inhibition of myelin-associated glycoprotein binding to neural cells

Sialic acids are prominent termini of mammalian glycoconjugates and are key binding determinants for cell-cell recog-nition lectins. Binding of the sialic acid-dependent lectin, myelin-associated glycoprotein (MAG), to nerve cells is implicated in the inhibition of nerve regeneration after injury. Therefore, blocking MAG binding to nerve cell sialoglycoconjugates might enhance nerve regeneration. Previously, we reported that certain sialoglycoconjugates bearing N-acetylneuraminic acid (NeuAc) but not N-glycolylneuraminic acid (NeuGc) support MAG binding (Collins et al., 1997a). We now report highly efficient conversion of sialic acids on living neural cells from exclusively NeuAc to predominantly NeuGc using a novel synthetic metabolic precursor, N-glycolylmannosamine pentaacetate (Man-NGc-PA). When NG108-15 neuroblastoma-glioma hybrid cells, which normally express only NeuAc (and bind to MAG), were cultured in the presence of 1 mM ManNGcPA, they expressed 80-90% of their sialic acid precursor pool as NeuGc within 24 h. Within 5 days, 80% of their ganglioside-associated sialic acids and 70% of their glycoprotein-associated sialic acids were converted to NeuGc. Consistent with this result, treatment of NG108-15 cells with ManNGcPA resulted in nearly complete abrogation of MAG binding. These results demonstrate that ManNGcPA treatment efficiently alters the sialic acid structures on living cells, with a commensurate change in recognition by a physiologically important lectin.

Enhanced binding of the neural siglecs, myelin-associated glycoprotein and Schwann cell myelin protein, to Chol-1 (alpha-series) gangliosides and novel sulfated Chol-1 analogs

Extended glycoconjugate binding specificities of three sialic acid-dependent immunoglobulin-like family member lectins (siglecs), myelin-associated glycoprotein (MAG), Schwann cell myelin protein (SMP), and sialoadhesin, were compared by measuring siglec-mediated cell adhesion to immobilized gangliosides. Synthetic gangliosides bearing the alpha-series determinant (NeuAc alpha2,6-linked to GalNAc on a gangliotetraose core) were tested, including GD1alpha (IV(3)NeuAc, III(6)NeuAc-Gg(4)OseCer), GD1alpha with modified sialic acid residues at the III(6)-position, and the "Chol-1" gangliosides GT1aalpha (IV(3)NeuAc, III(6)NeuAc, II(3)NeuAc-Gg(4)OseCer) and GQ1balpha (IV(3)NeuAc, III(6)NeuAc, II(3)(NeuAc)(2)-Gg(4)OseCer). The alpha-series gangliosides displayed enhanced potency for MAG- and SMP-mediated cell adhesion (GQ1balpha > GT1aalpha, GD1alpha > GT1b, GD1a >> GM1 (nonbinding)), whereas sialoadhesin-mediated adhesion was comparable with alpha-series and non-alpha-series gangliosides. GD1alpha derivatives with modified sialic acids (7-, 8-, or 9-deoxy) or sulfate (instead of sialic acid) at the III(6)-position supported adhesion comparable with that of GD1alpha. Notably, a novel GT1aalpha analog with sulfates at two internal sites of sialylation (NeuAcalpha2,3Galbeta1,4GalNAc-6-sulfatebeta1, 4Gal3-sulfatebeta1,4Glcbeta1,1'ceramide) was the most potent siglec-binding structure tested to date (10-fold more potent than GT1aalpha in supporting MAG and SMP binding). Together with prior studies, these data indicate that MAG and SMP display an extended structural specificity with a requirement for a terminal alpha2, 3-linked NeuAc and great enhancement by nearby precisely spaced anionic charges.

Ganglioside GD1 alpha analogues as high-affinity ligands for myelin-associated glycoprotein (MAG)

The first systematic synthesis of ganglioside GD1 alpha analogues carrying N-acetyldeoxyneuraminic acids linked to C-6 of the GalNAc residue was accomplished. The suitably protected GM1b pentasaccharide derivative was regioselectively glycosylated with the phenyl 2-thioglycosides of 7-deoxy, 8-deoxy, and 9-deoxy-N-acetylneuraminic acid promoted by N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) in acetonitrile, and the resulting hexasaccharides were converted to the target GD1 alpha analogues. All of the analogues retained excellent efficiency in supporting the adhesion to myelin-associated glycoprotein (MAG), raising the possibility that the internal sialic acid linked to the GalNAc residue may be replaced by other anionic substituents, in contrast to the terminal sialic acid, which is essential for MAG binding.

Myelin-associated glycoprotein binding to gangliosides. Structural specificity and functional implications

Myelin-associated glycoprotein (MAG), which mediates certain myelin-neuron cell-cell interactions, is a lectin that binds to sialylated glycoconjugates. Gangliosides, the most abundant sialylated glycoconjugates in the brain, may be the functional neuronal ligands for MAG. Cells engineered to express MAG on their surface adhered specifically to gangliosides bearing an alpha 2,3-linked N-acetylneuraminic acid on a terminal galactose, with the following relative potency: GQ1b alpha >> GD1a, GT1b >> GM3, GM4 (GM1, GD1b, GD3, and GQ1b did not support adhesion). MAG binding was abrogated by modification of the carboxylic acid, any hydroxyl, or the N-acetyl group of the ganglioside's N-acetylneuraminic acid moiety. Related immunoglobulin (Ig) superfamily members either failed to bind gangliosides (CD22) or bound with less stringent specificity (sialoadhesin), whereas a modified form of MAG (bearing three of its five extra-cellular Ig-like domains) bound only GQ1b alpha. Enzymatic removal of sialic acids from the surface of intact nerve cells altered their functional interaction with myelin. These data are consistent with a role for gangliosides in MAG-neuron interactions.

Identification of a ganglioside recognition domain of tetanus toxin using a novel ganglioside photoaffinity ligand

Tetanus toxin entry into vertebrate motorneurons may involve binding of neuronal surface gangliosides containing the "1b" substructure (a NeuAcalpha2,8NeuAc group on an internal galactose residue). The domains of tetanus toxin involved in ganglioside binding are known to reside within the carboxyl-terminal half of the toxin's heavy chain ("C fragment"). We developed a novel photoaffinity reagent based upon the structure of the 1b ganglioside GD1b (125I-azido-GD1b) to define the ganglioside-binding domains of tetanus toxin. Using this ligand, we observed radiolabeling of tetanus toxin C fragment which could be specifically inhibited by a ganglioside of the 1b series (GT1b), but not by a non-1b series ganglioside (GM3). When tetanus toxin C fragment was proteolyzed with clostripain, whether before or after reaction with 125I-azido-GD1b, a radiolabeled band was observed by SDS-polyacrylamide gel electrophoresis autoradiography, which was selectively inhibited by GT1b. Protein sequencing of proteolyzed tetanus toxin C fragment co-migrating with that band revealed the carboxyl-terminal 34 amino acid residues of tetanus toxin. Matrix-assisted laser desorption/ionization mass spectrometry of a photoaffinity labeled synthetic polypeptide representing the 34-amino acid domain revealed modification at a single residue (His1293). We propose that this domain of tetanus toxin is sufficient for ganglioside binding.

Brain neurosteroids during the mouse oestrous cycle

Concentrations of the neuroactive steroid 3alpha,5alpha-tetrahydroprogesterone (TH PROG or allopregnanolone) and its precursors progesterone (PROG) and 5alpha-dihydroprogesterone (DH PROG) have been measured in mouse brain throughout the oestrous cycle. Plasma PROG concentrations were also measured for comparison. At each stage, circadian fluctuations were found in the concentrations of brain PROG and its metabolites. Such fluctuations were greater than those attributable to any particular stage of the oestrous cycle. Over the entire cycle, a significant correlation was found between brain TH PROG (or DH PROG) and PROG concentrations but not between brain TH PROG (or DH PROG) and plasma PROG concentrations. There was also no correlation between endogenous TH PROG (or DH PROG) and activity of the 5alpha-reductase converting 3H-PROG to 3H-DH PROG in whole brain homogenates. Concentrations of another neuroactive steroid, pregnenolone sulphate (PREG S), in the brain during the oestrous cycle were in phase with plasma PROG but not brain PROG concentrations. Our results indicate that circadian and ovarian influences on the concentrations of PROG and its metabolite TH PROG in female whole mouse brain are caused predominantly by changes in the supply of PROG from within the tissue, whatever the contribution of peripheral sources.

Binding specificities of the sialoadhesin family of I-type lectins. Sialic acid linkage and substructure requirements for binding of myelin-associated glycoprotein, Schwann cell myelin protein, and sialoadhesin

The carbohydrate binding specificities of three sialoadhesins, a subgroup of I-type lectins (immunoglobulin superfamily lectins), were compared by measuring lectin-transfected COS cell adhesion to natural and synthetic gangliosides. The neural sialoadhesins, myelin-associated glycoprotein (MAG) and Schwann cell myelin protein (SMP), had similar and stringent binding specificities. Each required an alpha2,3-linked sialic acid on the terminal galactose of a neutral saccharide core, and they shared the following rank-order potency of binding: GQ1balpha >> GD1a = GT1b >> GM3 = GM4 >> GM1, GD1b, GD3, GQ1b (nonbinders). In contrast, sialoadhesin had less exacting specificity, binding to gangliosides that bear either terminal alpha2,3- or alpha2,8-linked sialic acids with the following rank-order potency of binding: GQ1balpha > GD1a = GD1b = GT1b = GM3 = GM4 > GD3 = GQ1b >> GM1 (nonbinder). CD22 did not bind to any ganglioside tested. Binding of MAG, SMP, and sialoadhesin was abrogated by chemical modification of either the sialic acid carboxylic acid group or glycerol side chain on a target ganglioside. Synthetic ganglioside GM3 derivatives further distinguished lectin binding specificities. Deoxy and/or methoxy derivatives of the 4-, 7-, 8-, or 9-position of sialic acid attenuated or eliminated binding of MAG, as did replacement of the sialic acid acetamido group with a hydroxyl. In contrast, the 4- and 7-deoxysialic acid derivatives supported sialoadhesin binding at near control levels (the other derivatives did not support binding). These data are consistent with sialoadhesin binding to one face of the sialic acid moiety, whereas MAG (and SMP) may have more complex binding sites or may bind sialic acids only in the context of more restricted oligosaccharide conformations.

Sialic acid specificity of myelin-associated glycoprotein binding

Myelin-associated glycoprotein (MAG), a nervous system cell adhesion molecule, is an I-type lectin that binds to sialylated glycoconjugates, including gangliosides bearing characteristic structural determinants (Yang, L. J.-S., Zeller, C. B., Shaper, N. L., Kiso, M., Hasegawa, A., Shapiro, R. E., and Schnaar, R. L. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 814-818). Two cell adhesion systems, COS-1 monkey kidney fibroblasts transiently transfected to express MAG and Chinese hamster ovary (CHO) cells stably transfected to express MAG, were used to probe the structural specificity of MAG-ganglioside binding. Both cell types bound to the same gangliosides: GQ1b alpha (IV3NeuAc,III6NeuAc,II3(NeuAc)2Gg4Cer) > GT1b = GD1a > GM3 > GM1, GD1b, and GQ1b (the latter do not support adhesion). Binding was enhanced by pretreatment of MAG-expressing cells with neuraminidase. MAG-expressing Chinese hamster ovary cells bound directly to gangliosides resolved on thin layer chromatograms, allowing detection of MAG binding species in a mixture. The simplest ganglioside ligand for MAG was GM3 bearing N-acetylneuraminic acid, whereas GM3 bearing N-glycolylneuraminic acid did not support adhesion. Chemical modifications of N-acetylneuraminic acid residues (on GD1a) abrogated MAG binding. Mild periodate oxidation of sialic acids to their corresponding seven-carbon (or eight-carbon) sialic acid aldehydes abolished MAG binding, as did further conversion to the corresponding primary alcohols. Eliminating the anionic charge by ethyl esterification, amidation, or reduction also abolished MAG-mediated cell adhesion. These data demonstrate that MAG-ganglioside binding is highly specific and defines key carbohydrate structural determinants for MAG-mediated cell adhesion to gangliosides.

Interdomain interactions in the chimeric protein toxin sCD4(178)-PE40: a differential scanning calorimetry (DSC) study

The thermal denaturation of the chimeric protein toxin known as sCD4(178)-PE40 (sCD4-PE40) was studied using differential scanning calorimetry (DSC). sCD4-PE40 consists of HIV-binding domains of the T-cell membrane protein known as CD4 and the cytotoxic domains of Pseudomonas exotoxin A (PE40). sCD4-PE40 undergoes two DSC transitions. An endothermic transition associated with unfolding of the CD4 and PE40 components occurs at approximately 46 degrees C in buffered saline at pH 6.5. An exothermic transition associated with precipitation of unfolded protein occurs at higher temperatures. Both transitions are irreversible. DSC studies of solutions of pH 5.0 to 9.5 indicate that sCD4-PE40 shows maximal thermal stability at around pH 6.5. Variable pH experiments are also presented on solutions of sCD4(183) and PE40 revealing how these components denature as independent structural entities. sCD4(183) denaturation occurs at significantly higher temperatures than does the CD4 component of sCD4-PE40. PE40 denaturation occurs at the same temperatures as sCD4-PE40. These results suggest that the native CD4 and PE40 components are independent and non-interacting entities in the chimeric sCD4-PE40 molecule and that unfolding of the less-stable PE40 component induces unfolding of the CD4 component. These destabilizing interdomain interactions of sCD4-PE40 are in contrast to the stabilizing interactions which apparently exist in wild-type Pseudomonas exotoxin A between its PE40 domains and the cell binding domain of the native toxin (analogous to the CD4 component in sCD4-PE40). Reasons are discussed why the type of interdomain interactions observed for sCD4-PE40 might be the norm for chimeric proteins.

The UCLA Multidimensional Condom Attitudes Scale: documenting the complex determinants of condom use in college students

This article describes the development and validation of the UCLA Multidimensional Condom Attitudes Scale (MCAS). The relationships between the MCAS and gender, sexual experience, intentions to use a condom, and past condom use were assessed. The MCAS has five distinct factors: (a) Reliability and Effectiveness of condoms, (b) the sexual Pleasure associated with condom use, (c) the stigma attached to persons who use condoms (Identity Stigma), (d) the Embarrassment About Negotiation and Use of condoms, and (e) the Embarrassment About the Purchase of condoms. The results strongly suggest that condom attitudes are multidimensional and thus cannot meaningfully be summed to a single global score. Results further indicate that men and women hold very different attitudes toward condoms. Implications of scale multidimensionality and directions for future research are discussed.

The UCLA Multidimensional Condom Attitudes Scale: documenting the complex determinants of condom use in college students

This article describes the development and validation of the UCLA Multidimensional Condom Attitudes Scale (MCAS). The relationships between the MCAS and gender, sexual experience, intentions to use a condom, and past condom use were assessed. The MCAS has five distinct factors: (a) Reliability and Effectiveness of condoms, (b) the sexual Pleasure associated with condom use, (c) the stigma attached to persons who use condoms (Identity Stigma), (d) the Embarrassment About Negotiation and Use of condoms, and (e) the Embarrassment About the Purchase of condoms. The results strongly suggest that condom attitudes are multidimensional and thus cannot meaningfully be summed to a single global score. Results further indicate that men and women hold very different attitudes toward condoms. Implications of scale multidimensionality and directions for future research are discussed.

Qualitative influence on the perception of movement: an experimental study

One of the most puzzling features of "hyperactivity" in children is the importance of activity itself. Generalized overactivity has not been found to be a valid diagnostic marker. Could some qualitative features of activity be important determinants of the perceived quantity of activity? The analogue study reported here derives from a social-psychological hypothesis that anything that makes a behavior more noticeable or distracting can create an illusion of increased movement. Subjects performed a simple cognitive task while watching short films of adult actors. Two variables were manipulated: (a) The sound level was either loud or quiet, and (b) instructions to subjects were varied so that the behaviors shown were perceived as either appropriate or inappropriate. Results strongly supported the hypothesis. Loudness and contextual inappropriateness made the films more distracting, produced higher ratings of the amount of movement observed, and led to more negative evaluations of the behaviors seen. Implications for assessment and intervention are discussed.

Peer interaction in a structured communication task: comparisons of normal and hyperactive boys and of methylphenidate (Ritalin) and placebo effects

Peer communication patterns were assessed as school-aged boys participated in a dyadic referential communication task. The responses of comparison boys were compared to those of hyperactive boys on methylphenidate (Ritalin) and on placebo in a double-blind crossover design. 2 separate systems for assessing communication were developed, a qualitative system designed to capture the "flavor" of interaction and a quantitative system focused on specific types of communicative content. Task products and completion times were also scored. The results suggest that hyperactive children, regardless of medication status, are less likely than comparison peers to (a) modulate ongoing or habitual behavior patterns in response to externally imposed shifts in role-appropriate behaviors; (b) maintain consistent, uninterrupted goal orientation; and (c) respond to subtle social learning opportunities. In this situation, methylphenidate appeared to have a greater impact on behavioral style than on competence, decreasing perceived intensity without influencing efficiency. A mild medication-induced dysphoria was also documented. Directions for future research and the need for caution in clinical interpretation are discussed.

Double-blind and triple-blind assessments of medication and placebo responses in hyperactive children

Hyperactive boys taking psychostimulant medication were studied using a randomized, placebo-controlled, crossover design. Behavior ratings and medication guesstimates were obtained for the boys when they were given methylphenidate (Ritalin) and when they were given a placebo. The ratings showed positive medication-related changes, and the guesses, done by independent judges, were significantly better than chance. The pattern of ratings for double-blind and triple-blind raters was identical. These results imply that positive psychostimulant effects are not attributable to rater sensitization or expectancy. The medication-placebo differences were highly reliable for the group comparisons and were in the predicted direction for 21 of 22 individuals, but the magnitude of the change for many individuals was not dramatic. Implications for child psychopharmacology research and differences between clinical and experimental significance are discussed.

A social ecology of hyperactive boys: medication effects in structured classroom environments

Hyperactive boys on methylphenidate (Ritalin), hyperactive boys on placebo, and comparison boys were observed in quasi-naturalistic classroom settings. Ambient stimulation (quiet versus noisy conditions) and source of regulation (self-paced versus other-paced activities) were varied in a 2 x 2 design. Compared to their peers, hyperactive boys on placebo showed lower rates of task attention and higher rates of gross motor movement, regular and negative verbalization, noise-making, physical contact, social initiation, disruption, and acts that were perceived as energetic, inappropriate, or unexpected. Self-paced activities resulted in increased rates of verbalization, social initiation, and high-energy episodes. High ambient noise levels reduced task attention and increased the rates of many other behaviors including verbalization, physical contact, gross motor movement, and high-energy acts. Medication-by-situation interactions emerged for both classroom dimensions, with hyperactive boys on placebo being readily distinguishable from their peers under some classroom conditions and indistinguishable under other conditions. Moderate relationships were found between teacher ratings and many individual behavior categories. Discussion focused on (a) the merits and limitations of a social ecological research perspective, and (b) the implications of these findings for the design of intervention strategies.

Studies in forced compliance. X. Attitude change and commitment to maintain publicly a counterattitudinal position

Three variables thought to affect attitude change produced by forced compliance were varied: public-private, true-persuasive and high-low financial inducement. Public Ss signed a statement in which they promised to maintain their counterattitudinal position outside the laboratory. These public Ss had a tendency ( p < .10) to show more attitude change than private Ss. Significantly more Ss refused to comply in the low inducement, public conditions than in the other conditions combined. Analysis of performance measures indicated generally negative results.

A comparison of two multidimensional health locus of control instruments

This study examined the factor structure, internal consistency reliability, and construct validity of the multidimensional health locus of control (MHLC) instruments developed by K.A. Wallston, B.S. Wallston, and DeVellis (1978) and Lau (Lau, 1982; Lau & Ware, 1981). Both measures were administered to a sample of Veterans Administration (VA) medical outpatients (N = 181). Only minimal evidence of convergence was found between corresponding scales of the two MHLC instruments. Low convergent validity appears attributable to the poor internal consistency reliability of the Lau-Ware subscales. Moreover, results of factor analysis largely supported the a priori factor structure of the K.A. Wallston et al. (1978) MHLC instrument but failed to support the factor structure of the Lau-Ware instrument. Health locus of control (HLC) dimensions that emerged from simultaneous factor analysis of both instruments were most consistent with a three-dimensional typology (i.e., Personal Control, Professional Control, and Chance) rather than the four-dimensional typology proposed by Lau (Lau, 1982; Lau & Ware, 1981). Implications for HLC conceptualization and measurement are discussed.