Identification of a protein related to tubulin in the postsynaptic density

The postsynaptic density is a unique subcellular organelle associated with the synaptic complex and appears as an electron-dense area immediately subjacent to the postsynaptic plasma membrane. The postsynaptic density was isolated from the synaptosomal fraction and the protein constituents were analyzed by polyacrylamide gel electrophoresis. Polypeptides closely related to tubulin were identified as a major component of the postsynaptic density on the basis of molecular weight, subunit structure, and peptide map criteria.

Antihemophilic factor inhibitors. Management with prothrombin complex concentrates

Prothrombin complex concentrates have been evaluated in the treatment of acute bleeding episodes occurring in 11 hemophilic and two nonhemophilic patients with factor VIII inhibitors. In several of the hemophilic patients, a continued fall in inhibitor levels has been observed coincident with continued use of the concentrate Proplex, and one of these patients is now responsive to factor VIII therapy. The therapeutic effectiveness of prothrombin complex products appears to be related to the presence of small amounts of activated factors or to the continued formation of factor Xa in vivo as a result of the increased levels of prothrombin and factors VII and X. Until high-potency activated products are available, prothrombin concentrates offer an effective means of treating patients with factor VIII inhibitor.

Distribution and mobility of lectin receptors on synaptic membranes of identified neurons in the central nervous system

The distribution and mobility of concanavalin A (Con A) and Ricinus communis agglutinin (RCA) receptors (binding sites) on the external surfaces of Purkinje, hippocampal pyramidal, and granule cells and their attached boutons were studied using ferritin-lectin conjugates. Dendritic fields of these cells were isolated by microdissection and gently homogenized. Cell fragments and pre- and postsynaptic membranes were labeled with the ferritin-lectin conjugates at a variety of temperatures, and the distribution of lectin receptors was determined by electron microscopy. Both classes of these lectin receptors were concentrated at nearly all open and partially open postsynaptic junctional membranes of asymmetric-type synapses on all three neuron types. Con A receptors were most concentrated at the junctional membrane region, indicating that the mature neuron has a specialized nonrandom organization of carbohydrates on its outer surface. Lectin receptors located on postsynaptic junctional membranes appeared to be restricted in their mobility compared to similar classes of receptors on extrajunctional membrane regions. Labeling with ferritin-RCA and -Con A at 37 degrees C produced clustering of lectin receptors on nonjunctional surfaces; however, Con A and RCA receptors retained their nonrandom topographic distribution on the postsynaptic junctional surface. The restricted mobility of lectin receptors was an inherent property of the postsynaptic membrane since the presynaptic membrane was absent. It is proposed that structures in the postsynaptic density may be transmembrane-linked to postsynaptic receptors and thereby determine topographic distribution and limit diffusion of specialized synaptic molecules. Speicalized receptor displays may play an important role in the formation and maintenance of specific synaptic contacts.

Carbohydrate composition of central nervous system synapses. Analysis of isolated synaptic junctional complexes and postsynaptic densities

The composition of specialized structures present at synapses within the central nervous system was elucidated by biochemical analysis of fractions enriched in synaptic junctional complexes and postsynaptic densities. The results indicate that the synaptic junctional complex is primarily protein together with some glycoproteins. The synaptic junctional complex proteins are similar in amino acid composition to synaptic membrane proteins; they are not expecially rich in basic residues, as previously suggested. The major carbohydrates present in the synaptic junctional complex and postsynaptic density glycoproteins are mannose, galactose, and glucosamine, with lesser amounts of fucose, N-acetylneuraminic acid, and galactosamine. Comparison with the synaptic membrane fraction indicates that galactose is more concentrated in the synaptic junctional complex and mannose in the postsynaptic density. Glucose is dramatically enriched in both these fractions. Sucrose binding during isolation may partially account for the glucose enrichment.

Qualitative and quantitative morphological changes in subcellular fractions from mouse cerebral cortex during postnatal development

Discontinuous Ficoll-sucrose gradients were used to prepare subcellular fractions from mouse cerebral cortex at various stages of postnatal development. Representative samples of each subcellular fraction were obtained by sedimentation in an analytical ultracentrifuge and each fraction was examined quantitatively and qualitatively by electron microscopy. The amount of synaptosomal material was determined for each fraction on the basis of volume percentage, obtained from a series of contiguous micrographs, to circumvent any sampling error. This allowed an accurate appraisal of synaptosomal distribution during neural development and a direct comparison of the Ficoll-sucrose gradient fractions to the original crude mitochondrial preparations. The distribution of synaptosomal material was shown to be quantitatively altered during neural development, and maturation-dependent changes, at a qualitative level, were described. In addition, the relationship between neural maturation and the relative proportion and distribution of subcellular particles which contain processes tentatively identified as growth cones were characterized.

Variations of the Spectral Sensitivity of RCA 6217 and 5819 Photomultipliers at Low Temperature

The behavior of various types of photomultipliers (CsAg cathodes and CsSb cathodes) at very low temperatures has been investigated and reported in the literature. No information was found on the behavior of photomultipliers having Ag-Bi-O-Cs photocathodes (S-10 type). A study was therefore made to investigate changes of the spectral sensitivity of two RCA 6217 photomultipliers as a function of temperature. The results show a behavior quite different from that of other types of photomultipliers. Efforts were made to separate dynode effects from cathode effects. No definite explanation as to the origin of this extraordinary behavior has been found.

Friction torque studies of total joint replacements. The use of a simulator

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