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No abstract available.
A combined criterion involving the regression slopes of pretest-posttest achievement scores and achievement gain scores was used to classify similar types of classrooms. Mathematics achievement differences among 632 fifth graders were analysed in a longitudinal design and explained in a structural equation framework provided by LISREL, separately for four types of classrooms. The results replicated the findings of an earlier study (Schneider & Treiber, 1984) in that the local nature of achievement models could be demonstrated. That is, the structural components of the causal models could not be generalized across the four groups of classrooms. The inclusion of a second grouping criterion (i. e., achievement gainJ proved useful in that a better model fit was always obtained for classrooms with high achievement gains. As a global model test ignoring group and classroom membership did mask the differential validity of the achievement model in the various subgro.ups, the need for multilevel approaches was emphasized.
No abstract available.
No abstract available.
No abstract available.
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No abstract available.
The binding of agonists and antagonists to a2-adrenergic receptors of human platelets was studied. The receptors showed homogeneaus affinities for antagonists but two affinity states for the agonist (-)-epinephrine, which were modulated by guanine nucleotides. Van't Hoffplots of antagonist binding had a break point at about 18° and considerable diversity between 18° and 0°. Agonist binding to both affinity states showed a similar break point; agonist binding to the high affinity state was characterized by a large entropy component compared to the low affinity state. This entropy component was reduced at higher concentrations of sodium, indicating that it may be due to Iiberation of sodium ions. Measurements of the fluorescence of 1-anilin-8-naphthalenesulfonate showed thermotropic phase transitions of theplatelet membranes at about 17°. The transition temperature was decreased to about 12° by addition of 1 0 mM octanoic acid. Octanoic acidalso shifted the break points of the van't Hoffplot of antagonist and low affinity agonist binding from 18° to 12°. High affinity agonist binding, however, remained unchanged. It is concluded that agonist-specific thennodynamic characteristics of ligand binding to a2-receptors of human platelets can only be investigated by regarding differences between high and low affinity agonist binding. These differences include an entropy increase upon Iigand binding, which is in part due to enhanced liberation of sodium ions, and a loss of sensitivity to fluidity changes in the outer layer of the plasma membrane.
The purpose of the experiments reported is to provide an unambiguous demonstration that embryonie skeletal muscle contains factors that act directly on embryonie spinal motor neurons both to support their survival and to stimulate the outgrowth of neurites. Cells of lumbar and brachial ventral spinal cords from 6-day-old chick embryos were separated by centrifugation in a two-step metrizamide gradient, and a motor neuron enriched fraction was obtained. Motor neurons were identified by retrogradely labeling with rhodamine isothiocyanate, and were enriched fourfold in the motor neuron fraction relative to unfractionated cells. In culture, the isolated motor neurons died within 3-4 days unless they were supplemented with embryonie chick skeletal muscle extract. Two functionally distinct entities separable by ammonium sulfate precipitation were responsible for the effects of muscle extracts on motor neurons. The 0-25% ammonium sulfate precipitate contained molecules that alone bad no effect on neuronal survival but when bound to polyornithine-coated culture substrata, stimulated neurite outgrowth and potentiated the survival activity present in muscle. Most of this activity was due to a laminin-like molecule being immunoprecipitated with antisera against laminin, and immunoblotting demonstrated the presence of both the A and B chains of laminin. A long-term survival activity resided in the 25-70% ammonium sulfate fraction, and its apparent total and specific activities were strongly dependent on the culture substrate. In contrast to the motor neurons, the cells from the other metrizamide fraction (including neuronal cells) could be kept in culture for a prolonged time without addition of exogenous factor(s).
E. coli stcains isolated from patients with urinary tcact infecrions (UTn very often possess mannose"sensitive (MS) and mannose-resistant (MR) adherence facmrs (fimbriae). According to their receptor specificity the mannose-resistant adhesins can be divided inm several types, P, S, M and X. We have cloned rhe determinants of rhree groups of UTI E. coli adhesins, MS, p and S, and prepared specific aorisera against the fimbriae antigens. 189 hernagglutination (HA+) -positive stcains, 96 fecal isolates and 93 strains isoJated from UTI . have been tesred with rhese specific antisera and further characterized by receptor specific : HA, HA parteras and further of rhe "common 0 serogroups" 01, 02, 04, 06, 07, 08, 018, ' 025, 075, most prevalenr in UTI, and hemolysin production. · 68 (73 %) of the UTI srrains a.nd 50 (52%) of the fecal isolates showed P-receptor specificiry; 16 (17%) of the uropathogenic bacteria and 33 (34%) of the fecal strains exhibited S, M or X-fimbriae antigens. 24% of rhe P-hemagglutinating (P+) strains reacted wirb P (F8)-specific antiserum. In contrast, more than three quaner of the s+-srrains were agglutinated by S-specific antiserum. HA-pattern VJ and 018 amigen were found to be associared with P-fimbriae strains, wbereas HA-pattern V and VII and the 0 anrigens 02 (M-type), 06 and 018 (5-type) occurred most frequently in p- -strains. A high percentage of P-fimbriated strains showed mannose-sensitive hemagglurination and hemolysin production.
Murine spienie T lymphocytes display maximal cellular myc gene (c-myc) expression already 3 h after concanavalin A timulation and sub equent down-regulation before the onset of DNA syntbesis. Stimulation by leucoagglulinin in the prcsence or absence of interleukin 2 Ieads to only low initiaJ Ievels of c-myc-specific RNA which, however, increase later on. A similar pattero of c-myc expression is shown by the Lyt- 2+ T cell subpopulation stimuiated with eilher concanavalin A or leucoagglutinin in the prescncc of interleukin 2. Although eH]thyn1idine incorporation was identical, the leucoagglutinin-stimulated Lyt-2+ T cells werc void of any demon. trable c-mycspeci. fic RNA at 3 h post-stimulation. Thus, the kinetics of c-myc expression in mause T lymphocytes arenot at all uniform, but depend on the mitogen and the subpopulation. [n contrast, lcvel8 of c-rasH•-spccific R A wcre always low at early times, always increased towards tbe onset ofDNA synthesis and down-regulationwas not observed.
The cardiovascular and endocrine activity of three analogs of thyrotropin releasing hor.mone (TRH), 4-nitro-imidazole TRH (4-nitroTRH), 2-trifluoro-methyl-imidazole TRH (2-TFM-TRH) and 4-trifluoromethyl- imidazole TRH (4-TFM-TRH), was compared to TRH in conscious rats. Injection of TRH or the three analogs (1 mg/kg or 5 mg/kg) into the arterial line induced increases in mean arterial pressure, pulse pressure and heart rate and raised plasma prolactin (PRL). None of the analogs were more potent than TRH in inducing cardiovascular changes. The 4-TFM-TRH was significantly less potent than the 2-TFM-TRH in increasing blood pressure, while the nitro-TRH was more potent than the 2-TFM-TRH in producing tachycardia. TRH induced a two-fold increase in PRL at the 5 mg/kg dose, while both the fluorinated analogs elici ted a 4 to 5 fold increase in PRL at the higher dose. The present results suggest that the receptors for TRH-elicited PRL release differ from TRH-receptors involved in its cardiovascular actions.