Changes in the incorporation of [3H]fucose into rat hippocampus after acquisition of a brightness discrimination reaction. An electrophoretic study

A review on selective l-fucose/d-arabinose isomerases for biocatalytic production of l-fuculose/d-ribulose

L-Fuculose and D-ribulose are kinds of rare sugars used in food, agriculture, and medicine industries. These are pentoses and categorized into the two main groups, aldo pentoses and ketopentoses. There are 8 aldo- and 4 ketopentoses and only fewer are natural, while others are rare sugars found in a very small amount in nature. These sugars have great commercial applications, especially in many kinds of drugs in the medicine industry. The synthesis of these sugars is very expensive, difficult by chemical methods due to its absence in nature, and could not meet industry demands. The pentose izumoring strategy offers a complete enzymatic tactic to link all kinds of pentoses using different enzymes. The enzymatic production of L-fuculose and D-ribulose through L-fucose isomerase (L-FI) and D-arabinose isomerase (D-AI) is the inexpensive and uncomplicated method up till now. Both enzymes have similar kinds of isomerizing mechanisms and each enzyme can catalyze both L-fucose and D-arabinose. In this review article, the enzymatic process of biochemically characterized L-FI & D-AI, their application to produce L-fuculose and D-ribulose and its uses in food, agriculture, and medicine industries are reviewed.

Glycan analysis of the chicken synaptic plasma membrane glycoproteins--a major synaptic N-glycan carries the LewisX determinant

The majority of synaptic plasma membrane components are glycosylated. It is now widely accepted that this post-translational modification is crucial during the establishment, maintenance and function of the nervous system. Despite its significance, structural information about the glycosylation of nervous system specific glycoproteins is very limited. In the present study the major glycan structures of the chicken synaptic plasma membrane (SPM) associated glycoprotein glycans were determined. N-glycans were released by hydrazinolysis, labelled with 2-aminobenzamide, treated with neuraminidase and subsequently fractionated by size exclusion chromatography. Individual fractions were characterized by the combination of high-pressure liquid chromatography, exoglycosidase treatment or reagent array analysis method (RAAM). In addition to oligomannose-type glycans, core-fucosylated complex glycans with biantennary bisecting glycans carrying the LewisX epitope were most abundant. The overall chicken glycan profile was strikingly similar to the rat brain glycan profile. The presence of the LewisX determinant in relatively large proportions suggests a tissue-specific function for these glycans.

Transient prenatal vitamin D deficiency is associated with subtle alterations in learning and memory functions in adult rats

Based on clues from epidemiology, low prenatal vitamin D has been proposed as a candidate risk factor for schizophrenia. Recent animal experiments have demonstrated that transient prenatal vitamin D deficiency is associated with persistent alterations in brain morphology and neurotrophin expression. In order to explore the utility of the vitamin D animal model of schizophrenia, we examined different types of learning and memory in adult rats exposed to transient prenatal vitamin D deficiency. Compared to control animals, the prenatally deplete animals had a significant impairment of latent inhibition, a feature often associated with schizophrenia. In addition, the deplete group was (a) significantly impaired on hole board habituation and (b) significantly better at maintaining previously learnt rules of brightness discrimination in a Y-chamber. In contrast, the prenatally deplete animals showed no impairment on the spatial learning task in the radial maze, nor on two-way active avoidance learning in the shuttle-box. The results indicate that transient prenatal vitamin D depletion in the rat is associated with subtle and discrete alterations in learning and memory. The behavioural phenotype associated with this animal model may provide insights into the neurobiological correlates of the cognitive impairments of schizophrenia.

sgk, a primary glucocorticoid-induced gene, facilitates memory consolidation of spatial learning in rats

By using differential display PCR, we have identified 98 cDNA fragments from the rat dorsal hippocampus that are expressed differentially between the fast learners and slow learners in the water maze learning task. One of these cDNA fragments encodes the rat serum- and glucocorticoid-inducible kinase (sgk) gene. Northern blot analysis revealed that the sgk mRNA level was approximately 4-fold higher in the hippocampus of fast learners than slow learners. In situ hybridization results indicated that sgk mRNA level was increased markedly in CA1, CA3, and dentate gyrus of hippocampus in fast learners. Transient transfection of the sgk mutant DNA to the CA1 area impaired, whereas transfection of the sgk wild-type DNA facilitated water maze performance in rats. These results provide direct evidence that enhanced sgk expression facilitates memory consolidation of spatial learning in rats. These results also elucidate the molecular mechanism of glucocorticoid-induced memory facilitation in mammals.

God's organism? The chick as a model system for memory studies

The young chick is a powerful model system in which to study the biochemical and morphological processes underlying memory formation. Training chicks on a one trial passive avoidance task results in a molecular cascade in a specific brain region, the intermediate medial hyperstriatum ventrale. This cascade is initiated by glutamate release and engages a series of synaptic transients including increased calcium flux, up-regulation of NMDA-glutamate receptors, membrane protein phosphorylations, and the retrograde messenger NO. Expression of immediate early genes c-fos and c-jun precedes the synthesis, glycosylation, and redistribution, >4 hr downstream, of a number of synaptic membrane proteins, notably NCAM and L1. Other membrane proteins required in the early phase of memory formation include the amyloid precursor protein (APP) and apolipoprotein E. There are concomitant increases in dendritic spine number and changes in synaptic structure. Nonsynaptic factors, including corticosterone and BDNF, can modulate retention of the avoidance response, enhancing the salience of otherwise weakly retained memory. These results are discussed in relation to general concepts of memory formation and the spatio-temporal distribution of the putative memory trace.

Sequence-Specific Impairment of Memory Formation by NCAM Antisense Oligonucleotides

The functional role of NCAM gene expression in memory formation was studied in the one-trial passive avoidance task in day-old chicks by pretraining injections of one of three different 18-mer end-protected oligonucleotides corresponding to positions 190-, 207-, and 332- of the NCAM Ig1 domain. Twenty-four-hour-old chicks were trained by pecking at a bitter-tasting bead and tested for avoidance 30 min, 3, 8, or 24 hr later. Memory retention was significantly reduced only in the group of animals injected with the NCAM antisense corresponding to position 207- (AS-ODN-207), and only if given twice, both immediately after hatching and 12 hr before training. This antisense was without effect on the general behavior of the chicks, training or acquisition, and did not produce observable neurotoxic damage. Under such conditions amnesia was evident by 3 hr after training and lasted until at least 24 hr after training. The two other tested oligonucleotides were without behavioral effect. To control for nonsequence-specific effects of AS-ODN-207, brains from injected and trained animals were processed for Western blotting and probed using anti-NCAM, anti-L1, and anti-actin antibodies. NCAM antisense corresponding to position 207- significantly reduced the level of NCAM, whereas the level of L1 and actin remained unchanged. These results confirm our earlier conclusion that NCAM is necessary for longer term memory retention.

Two critical periods of protein and glycoprotein synthesis in memory consolidation for visual categorization learning in chicks

A protein synthesis inhibitor, anisomycin (ANI), and an inhibitor of glycoprotein synthesis, 2-deoxygalactose (2-D-gal), were used to investigate memory consolidation following visual categorization training in 2-day-old chicks. ANI (0.6 micromole/chick) and 2-D-gal (40 micromoles/chick) were injected intracerebrally at different time intervals from 1 hr before to 23 hr after the training. Retention was tested 24 hr post-training. Both ANI and 2-D-gal injections revealed two periods of memory sensitivity to pharmacological intervention. ANI impaired retention when injected from 5 min before to 30 min after the training or from 4 hr to 5 hr post-training, thus demonstrating that consolidation of long-term memory in this task requires two periods of protein synthesis. 2-D-Gal first produced an amnesia when it was injected in the interval from 5 min before to 5 min after the training. Injections made between 5 min and 5 hr post-training were without effect on the retention. The second period of memory impairment by 2-D-gal started at 5 hr post-training and lasted until 21 hr after the training. Administration of 2-D-gal made 23 hr after the training did not influence retention in the test at either 24 hr or 26 hr. These results are consistent with the hypothesis that two waves of protein and glycoprotein synthesis are necessary for the formation of long-term memory. The prolonged duration of performance impairment by 2-D-gal in the present task might reflect an extended memory consolidation period for a categorization form of learning.

Fucose and fucosyllactose enhance in-vitro hippocampal long-term potentiation

Bath application of L-fucose and 2-fucosyllactose (2FI) increases the potentiation of the population spike amplitude (POP-spike) and the field excitatory postsynaptic potential (fEPSP) after tetanization of the Schaffer collaterals of the rat hippocampus. The ineffective isomers D-fucose and 3-fucosyllactose (3-FI) have no such effect. Since not only the maintenance of long-term potentiation LTP is influenced but also its induction is drastically improved, an effect of the sugars via the formation of glycoproteins but also via different actions on induction mechanisms is discussed.

Cell-adhesion molecules, glucocorticoids and long-term-memory formation

The transition from short- to long-term memory requires lasting modulations of synaptic connectivity. In a variety of species and learning tasks, enhanced synthesis of glycoprotein cell-adhesion molecules (CAMs), such as neural CAM (NCAM) and Ll, 5-8 h post-training is a necessary step in this process. If the training event is weak, this phase of glycoprotein synthesis does not occur and memory is not retained. Antibodies or fragments that bind to the extracellular domains of NCAM or Ll at this time produce amnesia for the task. Centrally administered corticosterone enhances retention of weak learning, and steroid-receptor antagonists are amnestic. The effects of corticosterone are mediated through synthesis of 'second-wave' glycoproteins. As 'nootropic' drugs such as piracetam only enhance long-term retention and are ineffective in adrenalectomized animals, the interaction between glucocorticoids and glycoproteins might provide a site for pharmacological intervention in alleviating the losses of memory that occur in neurodegenerative disorders.

Glycoproteins and memory formation

One-trial passive avoidance training in day-old chicks results in a biochemical cascade occurring in two forebrain regions, the intermediate medial hyperstriatum ventrale and the lobus parolfactorius. This cascade, initiated by synaptic transients, results in the activation of immediate early genes and culminates in the de novo synthesis of a family of pre- and post-synaptic membrane glycoproteins, that, inserted into the membrane, serve in the remodelling of synaptic connectivity which is a requirement for the brain representations constituting long-term memory. There are two waves of glycoprotein synthesis consequent on training, the first occurring within an hour of the training experience and the second 5.5-8 h post-training. Blocking synthesis during these time windows results in amnesia for the task. Amongst the glycoproteins involved are two cell adhesion molecules, NCAM and L1. Injection of antibodies to L1 result in amnesia if injected during either time window, but not outside these times; antibodies to NCAM result in amnesia only if injected at the 5.5-h timepoint. I interpret these results as indicating that de novo synthesis of NCAM during the second time window is necessary for producing a persistent memory trace.

2-deoxygalactose interferes with an intermediate processing stage of memory

The effect of 2-deoxygalactose (2-D-gal), an inhibitor of glycoprotein synthesis, on memory formation was investigated with the day-old chick trained on a single-trial passive discrimination task. 2-D-gal (10 mumol/chick) was shown to inhibit memory formation at a time before the emergence of an antibiotic-sensitive long-term memory stage. The amnestic effect of 2-D-gal was successfully prevented by galactose, and more significantly by noradrenaline. In contrast, anisomycin-induced amnesia was resistant to challenge by either galactose or noradrenaline. The results are consistent with the view that some glycoprotein involvement in memory formation occurs prior to the formation of protein synthesis-dependent long-term memory, and this role of glycoproteins may be associated with the triggering of long-term memory formation by noradrenaline.

Fucose and fucose-containing sugar epitopes enhance hippocampal long-term potentiation in the freely moving rat

Male Wistar rats were intrahippocampally injected with L-fucose and the sugar epitope 2'-fucosyl-lactose prior to induction of long-term potentiation (LTP). Both substances had only a minimal and short-lasting depressive effect on the monosynaptically evoked field potential recorded in the dorsal blade of the dentate gyrus of freely moving rats upon stimulation of the perforant pathway. However, LTP induced by fractionated tetanization of the perforant pathway, which declined within 24 h in control animals injected with Lactose, remained at the initial level even 48 h after tetanization (difference to the control group significant with P < 0.01). The results support earlier findings which have indicated a participation of fucosylated macromolecules in the maintenance of LTP. Different molecular mechanisms concerning the effect of both substances and the significance of the data in elucidation of the relationship between LTP and memory formation are discussed.

Characterisation and regional localisation of pre- and postsynaptic glycoproteins of the chick forebrain showing changed fucose incorporation following passive avoidance training

To identify those glycoproteins whose synthesis or modification is necessary for memory formation, we have studied the uptake of radiolabelled fucose into synaptic plasma membranes (SPMs) and postsynaptic densities (PSDs) derived from two specific left and right forebrain loci, at two different times after training of 1-day-old chicks on a one-trial passive avoidance learning task. To increase the reliability of the comparison, a double-labelling method was used. Tissue samples from intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO) were isolated at 6 and 24 h after training. At both times, training resulted in region-specific changes, both increases and decreases, in incorporated radioactivity into pre- and postsynaptic glycoproteins. After 6 h, there was a relative decline in incorporation into both SPMs and PSDs of the right IMHV of trained chicks, a decline that persisted in the PSDs until 24 h. A small decline in incorporation in SPMs from the right LPO of trained chicks at 6 h was reversed by 24 h, by which time there was a 64% increase in incorporation into SPMs and a 24% increase into PSDs of the left LPO. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis of left and right hemisphere samples containing LPO revealed that 6 h after training the main effect was presynaptic, including a reduction of incorporation into high molecular mass glycoproteins, of 150-180 kDa, and an increase in a lower molecular mass (41 kDa) fraction. By 24 h after training, a left hemisphere presynaptic glycoprotein of molecular mass approximately 50 kDa showed the biggest increase in fucosylation. In addition, a wide group of postsynaptic glycoproteins of both hemispheres, in the ranges 150-180, 100-120, and 33 kDa now showed increases in incorporation. Some other fractions showed decreases. These results are in accord with previous data on incorporation obtained using the amnesic agent 2-deoxygalactose. They also support the hypothesis that memory formation involves the strengthening of connections between pre- and postsynaptic neurons of the LPO by growth or modulation of pre- and postsynaptic structures.

Phorbol ester-induced changes in rat hippocampal glycoprotein fucosylation

Studies on glycoprotein fucosylation were carried out using hippocampal slices from rat brain. These slices were incubated in the presence of the protein kinase C (PKC) activating phorbol ester, 4 beta-phorbol-12,13-dibutyrate (PDBu), or an inactive isoform, 4 alpha-phorbol-12,13-didecanoate (PDD), respectively, for 7 min followed by a 60 min pulse of [3H]fucose. PDBu caused an increase in [3H]fucose incorporation into glycoproteins by 29% as well as an activation of the fucokinase enzyme reaction by 21%. The PDBu-induced stimulation of [3H]fucose insertion into hippocampal glycoproteins was abolished by the PKC inhibitors, staurosporine and H7. The importance of a PKC-regulated glycoprotein fucosylation in mechanisms underlying changes in neuronal plasticity is discussed.

The amnesic substance 2-deoxy-D-galactose suppresses the maintenance of hippocampal LTP

Male Wistar rats were intraventricularly injected with 2-deoxy-D-galactose (do-gal), a substance interfering with the fucosylation of glycomacromolecules and impairing memory consolidation in various learning tasks. Do-gal was found to have no influence on the monosynaptically evoked field potential (MEFP) recorded in the dentate gyrus upon stimulation of the perforant pathway. However, hippocampal long-term potentiation (LTP) induced in do-gal-pretreated animals by fractionated tetanization of the perforant pathway declined to control levels 2 h after tetanization, whereas it remained constant for 24 h in saline-treated rats. Similar effects were observed in the CA1 region of hippocampal slices. The results indicate a participation of fucosylated macromolecules in the maintenance of LTP. The possible significance of processes involved in LTP for memory formation is discussed.

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.

Incorporation of [3H]fucose in rat hippocampal structures after conditioning by perforant path stimulation and after LTP-producing tetanization

The contribution of glycoprotein synthesis to functional synaptic changes and to the formation of memory traces was investigated by autoradiographic determination of the incorporation of [3H]fucose into the hippocampal structures of rats. In the first experiment, the fucose incorporation was measured after induction of post-tetanic long-term potentiation (LTP) in granular cell synapses by repeated tetanization (200 cps) of the perforant path, and after stimulation of this hippocampal input by the same number of impulses with very low frequency (0.2 cps) not producing LTP. In the second experiment, the incorporation of fucose was determined after an active avoidance training using the stimulation of the perforant path by impulse trains of 15 cps as conditioning stimuli, and after a session of corresponding unpaired stimulations of the perforant path. Unstimulated animals were used in both experiments to measure the basal glycosylation. LTP-producing tetanization resulted only in a slight increase of incorporation into the ipsilateral hippocampal structures without significant differences to similar changes after the corresponding control stimulation with single impulses. After a session of unpaired stimulation of the perforant path with impulse trains of 15 cps only slight and inconsistent changes of incorporation occurred in the hippocampus too. However, after conditioning by the corresponding perforant path stimulation as conditioned stimulus, considerable increases of incorporation were observed in all structures of the ipsilateral hippocampus, when compared to the unpaired control stimulation. An enhanced labeling occurred also in some structures of the contralateral hippocampus mainly receiving commissural inputs. The results suggest again, that the activation of one single hippocampal afferent, even if producing LTP, would not be sufficient to induce an increased glycosylation of neuronal proteins. The increase of glycoprotein formation seems to require the convergence of several inputs, which can be assumed to occur during learning. Therefore, LTP of a single synaptic population seems not to represent the complete long-lasting memory trace, but only one of its components, or a preceding transient storage mechanism.

Increased fucosylation of chick brain proteins following training: effects of cycloheximide

When chicks are trained to avoid pecking a bead coated with methylanthranilate in a one-trial passive avoidance task there is an increase in fucose incorporation in vivo and in vitro in the right forebrain base of methylanthranilate (M)-trained compared to water (W)-trained chicks. The relation of this increase to de novo protein synthesis in vivo and in vitro has been examined. Cycloheximide (Cx), 1 mM, inhibited in vitro fucosylation of chick brain slices by 60% after 3 h. However, the training-related increase in in vitro fucosylation still persisted. When Cx was injected intraventricularly 10 min before training, the subsequent increase in in vitro fucosylation due to training was still apparent. When Cx was injected and [14C]leucine and [3H]fucose incorporation studied in vivo in M-trained and W-trained chicks, there was no increase in fucosylation due to training in the Cx-treated M-trained over the W-trained chicks. These results are taken to indicate that in vitro fucosylation and its increase subsequent to training is not protein synthesis-dependent, but that both in vivo and in vitro there are interactions between Cx and fucosylation steps that are independent of Cx's effects on protein synthesis.

Impairment of glycoprotein fucosylation in rat hippocampus and the consequences on memory formation

The intraventricular injection of 2-deoxy-D-galactose led to a dose- and time-dependent decrease in the fucosylation of hippocampal glycoproteins in rats whereas the incorporation of 3H-N-acetyl-glucosamine was not influenced. This effect is not related to an interference with fucose activating or transferring enzymes but can be abolished by an application of D-galactose. Thus, it seems likely that also in brain tissue a deoxy-galactose induced decrease in the fucosylation is due to a hindering of a glycosidic linkage of fucose to the deoxy-sugar incorporated into glycoprotein chains. As a consequence of an intrahippocampal injection of the deoxy-sugar the retention performance of the animals in a foot-shock motivated brightness discrimination task was considerably impaired. But deoxy-galactose is effective only when administered before and immediately after training whereas either a pre- or a post-training injection did not influence the retention performance of the rats. Thus, an effective metabolic inhibition of the glycoprotein completion by the deoxy-sugar starting at the time of training seems to be crucial to interfere with such morphofunctional alterations in the neuronal network underlying the formation of a memory trace.

Anisomycin blocks the late phase of long-term potentiation in the dentate gyrus of freely moving rats

Freely moving rats, chronically implanted with stimulation electrodes in the medial entorhinal cortex and recording electrodes in the dentate gyrus, received two 400 micrograms intraventricular injections of anisomycin during a tetanization procedure that induced a long-lasting potentiation (72 hours) of the monosynaptic field potential. Inhibition of protein synthesis during the tetanization procedure did not immediately influence the induction of long-term potentiation (LTP). However, 3-4 hours after the beginning of tetanization the potentiation effect decayed progressively and was abolished totally during the remaining 7 day observation period. In control experiments anisomycin did not affect the slope of field EPSP's and produced a reversible depression of the population spike amplitude. These data indicate a relatively specific effect of the protein synthesis inhibitor on mechanisms involved in a late phase of LTP stabilization.

Changes in activities of fucokinase and fucosyltransferase in rat hippocampus after acquisition of a brightness discrimination reaction

Activities of enzymes involved in utilization of the glycoprotein precursor L-fucose (fucokinase and fucosyltransferase) were studied in rat hippocampal tissue after acquisition of a brightness discrimination reaction. Fucokinase activity was increased immediately after training, while fucosyltransferase revealed decreased values. However, 7 hr after training fucokinase activity showed normal values, while fucosyltransferase activity rose in trained animals over active and passive controls. The results are discussed in the light of a regulatory role that fucokinase and fucosyltransferase may play in fucose utilization under altered functional conditions.

Distribution of hippocampal glycoproteins as demonstrated in rats by lectin binding and autoradiography after intraventricular injections of labelled fucose, N-acetyl-glucosamine and mannose

The present study demonstrates distinct distribution patterns of glycoproteins in rat hippocampus, with respect to synthesis from precursors (autoradiography) and endogenous contents (lectin binding). The autoradiographic analysis performed 1, 2, 8 and 24 h after intraventricular injections of tritium-labelled L-fucose. N-acetyl-D-glucosamine and D-mannose revealed that up to 2 h after application of any of the three precursors, radioactivity occurred in the pyramidal and granular cell layers. Afterwards, however, rapid migration of label proceeded from the cell bodies into the neuropil after application of fucose and acetylglucosamine, while after injection of mannose a considerable amount of radioactivity stayed in the cell body layers, even 24 h after administration of labelled precursor. These findings were consistent with the histochemical visualization of glycoprotein constituents by fluorescent wheat germ lectin (preferentially binding to glucosaminyl residues) and concanavalin A-horseradish peroxidase (preferentially binding to mannosyl residues). These showed a heavy staining predominantly in neuropil and somata, respectively, with concanavalin A-binding giving more distinct patterns than the application of labelled mannose. The usefulness of the three glycoprotein precursors as correlates with functional behavioural changes in discussed.

Mechanisms of dopamine induced changes in hippocampal glycoprotein metabolism

In rat hippocampal slices incubated in the presence of dopamine, a relatively strong correlation was observed between changes in the incorporation of 3H-fucose into total proteins and the formation of GDP-3H-fucose. However, in hippocampal homogenate the incorporation of 14C-fucose from GDP-14C-fucose was not stimulated by dopamine. In contrast, the incorporation of 3H-fucose was stimulated by dopamine to a similar extent observed in hippocampal slices. Furthermore, in hippocampal slices dopamine did not increase the activity of fucosyltransferase. These results, together with our previous findings, suggest that the increased incorporation of fucose induced by dopamine in the hippocampal slices may be due to a receptor-mediated cAMP-dependent regulation, which controls the rate of fucosylation of acceptor-glycoproteins either at the level of fucose phosphorylation or of formation of GDP-fucose rather than the activity of fucosyltransferase.

Apomorphine and glycoprotein synthesis during consolidation

The dopamine agonist, apomorphine, was injected intrahippocampally immediately after acquisition of a brightness discrimination task, which was motivated by footshock in rats. This led to an increase in the incorporation of L-fucose into total proteins which were measured in the hippocampus 7-9 hours later. In behavioral experiments, the same application improved the retention of a learned task. A possible linkage between increased glycoprotein synthesis and improvement of the retention of a new learned behavior due to the action of apomorphine is discussed.

Dopamine induced changes in L-fucose incorporation into proteins of rat hippocampus and corpus striatum during postnatal development

In 60 day old (adult) male Wistar rats dopamine caused a dose-dependent increase of L-fucose incorporation into total proteins of both hippocampus and corpus striatum slices up to +47.8 +/- 6.0% (n=6) and +53.2 +/- 8.5% (n=20), respectively, when compared to corresponding controls. Under these conditions the dopamine concentration leading to a maximum stimulation of fucose incorporation was 5 X 10(-4) M in hippocampus and 1 X 10(-3) M in corpus striatum. In the latter tissue the range of dopamine concentrations causing a significant elevation in incorporation rates was larger than in hippocampal tissue. In the corpus striatum of 9 day old rats dopamine was ineffective, but by 30 days the transmitter stimulated fucose incorporation rate reached the maximum observed for any age studied. This developmental pattern seems to be related to the ontogenesis of dopamine receptor sites or dopamine sensitive adenylate cyclase formation in this brain structure. In the hippocampus the postnatal development of dopamine induced augmentation of glycoprotein synthesis showed a longer latency, but the maximum effect was also seen in 30 day old animals. These results support our assumption that at the end of the postnatal differentiation period the glycoprotein synthesis in brain tissue may be controlled (at least to some extent) by the state of dopaminergic receptors and/or of dopamine sensitive adenylate cyclase.

Effect of L-fucose on brain protein metabolism and retention of a learned behavior in rats

The intraperitoneal or intraventricular application of L-fucose (100 mg/kg or 75 microgram, respectively) prior to training in shuttle box avoidance as well as in shock-motivated brightness discrimination in rats significantly improved the retention of learned behavior 24 hr later. The application of D-fucose was without influence on retention. In naive animals, intraventricularly applied L-fucose (75-200 microgram) caused an increase in the rate of protein synthesis in the hippocampus, resulting in a significant increase in total proteins of this brain structure, mainly attributed to the Tris-insoluble protein fractions. The results are discussed in terms of an activation of glycoprotein formation by increasing supply with L-fucose.

Subcellular localization of increased incorporation of [3H]fucose following passive avoidance learning in the chick

The effect of training on a passive avoidance test on incorporation of [3H]fucose into subcellular fractions of the anterior forebrain roof of 1-day-old chicks was determined. Isotope was injected intraperitoneally, and birds tested and killed after 3 h. There was an increase in incorporation in trained compared with untrained control birds in the synaptic membrane (19% elevation, P less than 0.02) and the mitochondrial (14% elevation, P less than 0.05) fractions. Following intracranial injection, increased incorporation in trained birds was seen only in the synaptic membrane fraction (39% elevation, P less than 0.01); this increase in incorporation was not limited to any particular electrophoretically separated glycopeptides, but occurred in all 9 detected peaks.

The influence of dopamine on the incorporation of different sugars into total proteins of hippocampal slices

Dopamine increases the incorporation of L-fucose and of D-mannose to a similar significant degree, whereas the incorporation of D-galactose as well as of N-acetyl-D-glucosamin into the total proteins of hippocampal slices was only slightly enhanced. The incorporation of N-acetyl-neuraminic acid was not influenced by dopamine. The results suggest that the effect of dopamine on glycoprotein formation seems mainly to depend on the kind of nucleotides necessary for activation of sugars and not on the sugar's final position in the glycan chain.

Two sensitive periods for the amnesic effect of anisomycin

Impairment of retention of a brightness discrimination in rats was obtained when anisomycin (80 microgram bilaterally into both hippocampi) was injected 10 min before and 80 min after training or 240 and 360 min after training. No amnesia was observed when anisomycin was injected 45 and 165 min post training. The two separate sensitive periods for the amnesic effect of the inhibitor obviously correspond to the two phases of increased protein synthesis during the consolidation of the same learning procedure. The results support the previous findings of the two independent and qualitatively different macromolecular processes. They also argue for the inhibition of protein synthesis as an important mechanism in the amnesic effect of anisomycin.