Incorporation of intrastriatally injected[3H]fucose into electrophoretically separated synaptosomal glycoproteins. I. Turnover and molecular weight estimations

Effects of the amnesic agent 2-deoxygalactose on incorporation of fucose into chick brain glycoproteins

The interaction of the amnesic agent 2-deoxygalactose with fucose incorporation into glycoproteins in day-old chick forebrain has been studied with the aim of identifying glycoproteins whose synthesis is modified during memory formation. 2-Deoxygalactose inhibited total exogenous [14C]fucose incorporation into the forebrain glycoproteins by 26%. Sodium dodecyl sulphate-polyacrylamide gradient gel analysis revealed that intracerebrally injected 2-[3H]deoxygalactose labelled the same eight major glycoprotein bands as were identified using [14C]fucose labelling. Subsequent investigations focussed on these selected components. Subcellular fractionation showed that between 4 and 24 h after administration of the deoxy-sugar, the incorporated radioactivity was found predominantly at the synaptic sites, some glycoproteins being more abundant in synaptic plasma membranes and others in postsynaptic densities. This distribution pattern varied according to the time after injection. The effect of passive avoidance training, using a methylanthranilate-coated bead, on [14C]fucose incorporation into forebrain was to decrease fucose uptake into components of molecular mass 150-180 kilodaltons but to increase significantly labelling of glycoproteins of molecular mass 33 and 28 kilodaltons. The possible implications of these training-induced changes are discussed.

Long-term memory formation in chicks is blocked by 2-deoxygalactose, a fucose analog

When day-old chicks are trained on a passive avoidance task there is enhanced synthesis of glycoproteins. Bilateral intracerebral injections of 20 mumole of 2-deoxygalactose (2-D-gal), administered just before and just after training on the task, produce amnesia for the avoidance. Amnesia develops slowly over the first hour and persists for at least 24 h subsequently. If 2-D-gal injections are administered 4 h prior to the training or delayed for 3 h after training, no amnesia occurs. Apart from a brief initial suppression of pecking following injection there are no effects of 2-D-gal on other observed behaviors of the birds. Within the first hour this dose of 2-D-gal inhibits [3H]fucose incorporation into acid-insoluble material by 26% (or 68%, calculated relative to free pool fucose). The amnestic effect of 2-D-gal is not shown by galactose, glucose, fucose, or 2-D-glucose. Injecting 40 mumole of galactose simultaneously with the 2-D-gal abolishes the 2-D-gal-induced amnesia; 40 mumole of fucose, however, does not abolish the amnesia. The utility of 2-D-gal as an agent for analyzing the role of glycoproteins in memory formation is discussed.

Induction of expression of the rat G5 nervous system antigen occurs postnatally

G5 is a cell membrane component found in high levels in the adult rat central nervous system and in low levels on some cells of the rat immune system. Binding assays with adult brain particulate protein preparations and monoclonal antibody to G5 (G5-IgG) gave highest activity in cerebral cortex and lowest in the white matter rich regions pons and spinal cord. Three peripheral nervous system components had no G5 activity. Analysis of G5 content in particulate protein preparations from whole rat brain of ages embryonic day 15 to adult indicates that G5 is present in negligible amounts in the newborn rat. It increases in both specific and total activity to reach adult levels by postnatal day 30. A similar induction curve was observed with cerebellum samples. In adult cerebellum, high levels of G5 were found in the molecular layer using both autoradiographic and immunofluorescence techniques. White matter had essentially no activity. The density and uniformity of reaction product in these techniques suggest that G5 is present on a major cellular constituent of the molecular layer. Pharmacologic experiments indicate G5 is not detectable on climbing fibers or adrenergic fibers. Cerebellar samples from juvenile rats also had predominant G5 activity in the forming molecular layer.

Distribution of fucosyl-conjugates in rat cerebellar cells in vitro: binding patterns of Lotus tetragonolobus and Ulex europeus lectins

Light microscope radioautographic procedures were employed to investigate the binding patterns of lectins derived from Lotus tetragonolobus (Lotus A) and Ulex europeus (UEA I) to the surfaces of rat cerebellar cells maintained in dispersed cell culture. Lotus A bound extensively to the surfaces of neuronal cell somata and neuronal processes at all time points investigated; the lectin also bound to nonneuronal cell surfaces, but to an extent much less than that for neurons. Lectin binding was completely inhibited by the presence of 0.1 M alpha-L-fucose in the reaction medium. Conversely, UEA I did not appear to bind to any significant extent to the surfaces of cerebellar cells in vitro at any stage of maintenance. The incorporation of [3H]fucose into fucosyl-conjugates by cerebellar neurons in culture was investigated using light microscope radioautography and polyacrylamide gel electrophoretic methods. Radioautographs indicated that the fucose came to be distributed throughout neuronal cell somata and processes and that, with increasing time, the grain density appeared to be highest over areas of neuropil and fascicles of cellular processes. The electrophoresis data demonstrated that, among others, the label was incorporated into prominent classes of polypeptides having nominal molecular weights of 400,000, 125,000, 91,000 and 46,000 daltons.

Brain pyruvate dehydrogenase: phosphorylation and enzyme activity altered by a training experience

The active portion of the alpha subunit of pyruvate dehydrogenase in rat frontal cortex was elevated after a training experience. No change in total pyruvate dehydrogenase activity was observed. The phosphorylation in vitro of pyruvate dehydrogenase (band F-2) was also elevated after training. Since activation of pyruvate dehydrogenase requires its dephosphorylation, the following sequence is proposed. Training alters frontal cortex and reduces the phosphate content of pyruvate dehydrogenase in vivo; this leads to enzyme activation; and an increase in back-titration of sites available for phosphorylation in vitro.

In vivo phosphorylation following [32P]orthophosphate injection into neostriatum or hippocampus: selective and rapid labeling of electrophoretically separated brain proteins

Intracranial injections of [32P]orthophosphate readily label a number of brain phosphoproteins as resolved by polyacrylamide gel electrophoresis. The majority of these in vivo labeled phosphoproteins co-migrate with phosphoproteins that are labeled in vitro by incubation of brain membranes with [32P]ATP. Two of the major in vitro labeled phosphoproteins with apparent molecular weights of 47,000 (band F1) and 41,000 (band F2) are rapidly labeled in vivo. Since they are rapidly dephosphorylated in vitro, this suggests a high rate of phosphate turnover. The electrophoretic pattern of in vivo labeled phosphoproteins did not appear to be altered by the method of sacrifice (focused microwave irradiation, decapitation or liquid nitrogen immersion) or by the state of the animal at the time of labeling (awake or lightly anesthetized with pentobarbital). The reduction of phosphatase activity during tissue processing at 0 degree C may account for the similarities observed with different sacrifice methods. Removal of phospholipids or polynucleotides had little effect on the in vivo labeled 32P-containing bands. However, alkaline hydrolysis or protease treatment uniformly reduced the radioactivity in the labeled bands. These findings suggest that the 32P-containing bands consist of phosphoester linkages to serine or threonine residues. The present evidence emphasizes that previously characterized in vitro labeled brain phosphoproteins are, in fact, labeled in the awake, freely-moving animal.

Development of synaptic glycoproteins: effect of postnatal age on the synthesis and concentration of synaptic membrane and synaptic junctional fucosyl and sialyl glycoproteins

Synaptic plasma membranes (SPM) and synaptic junctions (SJ) were isolated from the cortices of rats varying in age between 5 and 28 days. Gel electrophoresis of SPM and SJ indicated a marked increase in the concentration of the "PSD protein" (M. W. 52,000) with development. The biosynthesis of glycoproteins was measured following the intracranial injection of [3H]fucose or [3H]N'-acetylmannosamine. The incorporation of [3H]fucose into synaptic fractions decreased two- to threefold between 10 and 28 days whereas little change in the incorporation of [3H]N'-acetylmannosamine occurred over the same period. Gel electrophoretic analyses of labeled synaptic membranes indicated major increases in the relative incorporation of radiolabeled precursors into glycoproteins with apparent molecular weights of 74,000, 65,000, 50,000, and 40,000 with increasing age. Identification of fucosyl and sialyl glycoproteins following reaction with 125I-fucose-binding protein or labeling of sialic acid with NaIO4/NaB[3H4] demonstrated similar increases in the concentrations of these glycoproteins. Synaptic junctions contained three major glycoproteins with apparent molecular weights of 180,000, 130,000 and 110,000. The reaction of these glycoproteins with 125I-fucose-binding protein increased one- to twofold between 10 and 28 days but little variation in their relative distribution or synthesis occurred over this period. The reaction of synaptic junctional glycoproteins GP 180 and GP 110 with 125I-wheat germ agglutinin increased between 10 and 28 days. The results indicate that the molecular composition of the synapse continues to evolve after the initial synaptic contact has been formed.

A new antigen common to the rat nervous and immune systems: II. Molecular characterization

G5-IgG is a monoclonal antibody that binds specifically to some cells and tissues of the adult rat nervous and immune systems. The molecular nature of the G5 antigen from adult rat brain is described in this paper. G5 antigen in adult rat brain membrane fractions was trypsin-sensitive and heat-labile but not chloroform/methanol-soluble. It was solubilized by the nonionic detergent NP40 but not by 3 M KCl. Detergent-soluble rat brain particulate protein inhibited G5-IgG binding to glutaraldehyde-fixed rat brain particulate protein. Inhibitory activity could be removed by prior incubation with concanavalin-A agarose beads. Immunoprecipitates of enzymatically iodinated, detergent-solubilized brain particulate protein gave a single band on polyacrylamide gels of apparent molecular weight 95,000--105,000 daltons. A band of identical molecular weight was visualized in gels of unlabeled immune precipitates by 125I-concanavalin A. These results strongly suggest that G5 is an integral membrane glycoprotein in adult rat brain.

The incorporation of intrastriatally injected [3H]fucose into electrophoretically separated synaptosomal glycoproteins. II. The influence of passive avoidance training

Following intrastriatal injections of [3H]L-fucose, male albino rats served as (a) trained subjects in a step-down passive avoidance task, (b) stress controls receiving inescapable shock or (c) handled controls. At a series of time points after treatment the animals were sacrificed and the P2 fraction of the injected neostriatum was isolated. This tissue was electrophoresed on SDS-polyacrylamide gels and radioactivity profiles were constructed from 1 mm gel slices. The profiles of trained subjects were compared to shocked and handled control subjects from the same time point group. No differences in total [3H]fucose incorporation into neostriatal glycoproteins were detected as a result of the behavioral treatment used, nor was an incorporation into the majority of electrophoresed peaks altered. Three radioactive gel peaks were significantly altered as a function of experience. At the one day time point, trained subjects exhibited a significant increase in the tritium content of a 70,000 dalton fucosyl-glycoprotein peak. At the 5 day time point, increased label was detected in a 180,000 dalton peak in both trained and shocked subjects, while a significant increase in a 140,000 dalton peak was observed only in trained animals. The relation of the present findings to perviously reported training related differences in glycoprotein metabolism are discussed.