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

Human and Bovine Milk Oligosaccharides Elicit Improved Recognition Memory Concurrent With Alterations in Regional Brain Volumes and Hippocampal mRNA Expression

Human milk contains a unique profile of oligosaccharides (OS) and preliminary evidence suggests they impact brain development. The objective of this study was to assess the impact of bovine and/or human milk oligosaccharides (HMO) (2′-fucosyllactose and Lacto-N-neotetraose) on cognition, brain development, and hippocampal gene expression. Beginning on postnatal day (PND) 2, male pigs received one of four milk replacers containing bovine milk oligosaccharides (BMOS), HMO, both (BMOS + HMO), or neither. Pigs were tested on the novel object recognition task using delays of 1- or 48-h at PND 22. At PND 32–33, magnetic resonance imaging procedures were used to assess structural brain development and hippocampal tissue was collected for analysis of mRNA expression. Pigs consuming only HMO exhibited recognition memory after a 1-h delay and those consuming BMOS + HMO exhibited recognition memory after a 48-h delay. Both absolute and relative volumes of cortical and subcortical brain regions were altered by diet. Hippocampal mRNA expression of GABRB2, SLC1A7, CHRM3, and GLRA4 were most strongly affected by diet. HMO and BMOS had distinct effects on brain structure and cognitive performance. These data suggest different mechanisms underlie their influence on brain development.

Dietary Oligofructose Alone or in Combination with 2'-Fucosyllactose Differentially Improves Recognition Memory and Hippocampal mRNA Expression

Mounting evidence suggests that dietary oligosaccharides promote brain development. This study assessed the capacity of oligofructose (OF) alone or in combination with 2'-fucosyllactose (2'-FL) to alter recognition memory, structural brain development, and hippocampal gene expression. Beginning on postnatal day (PND) 2, male pigs received one of three milk replacers formulated to contain OF, OF + 2'-FL, or no oligosaccharides (CON). Pigs were tested on the novel object recognition task using delays of 1 or 48 h at PND 22. At PND 32-33, magnetic resonance imaging (MRI) procedures were used to assess structural brain development and hippocampal tissue was collected for analysis of mRNA expression. Pigs that consumed the OF diet demonstrated increased recognition memory after a 1 h delay, whereas those consuming diets containing OF + 2'-FL displayed increased recognition memory after a 48 h delay. Pigs fed OF or OF + 2'-FL exhibited a larger relative volume of the olfactory bulbs compared with CON pigs. Provision of OF or OF + 2'-FL altered gene expression related to dopaminergic, GABAergic, cholinergic, cell adhesion, and chromatin remodeling processes. Collectively, these data indicate that dietary OF and OF + 2'-FL differentially improve cognitive performance and affect olfactory bulb structural development and hippocampal gene expression.

Quantitative proteomic analysis of milk fat globule membrane (MFGM) proteins from donkey colostrum and mature milk

The composition and functions of milk fat globule membrane (MFGM) proteins are important indicators of the nutritional quality of milk.

Dietary 2'-Fucosyllactose Enhances Operant Conditioning and Long-Term Potentiation via Gut-Brain Communication through the Vagus Nerve in Rodents

2´-fucosyllactose (2´-FL) is an abundant human milk oligosaccharide (HMO) in human milk with diverse biological effects. We recently reported ingested 2´-FL stimulates central nervous system (CNS) function, such as hippocampal long term potentiation (LTP) and learning and memory in rats. Conceivably the effect of 2´-FL on CNS function may be via the gut-brain axis (GBA), specifically the vagus nerve, and L-fucose (Fuc) may play a role. This study had two aims: (1) determine if the effect of ingested 2´-FL on the modulation of CNS function is dependent on the integrity of the molecule; and (2) confirm if oral 2´-FL modified hippocampal LTP and associative learning related skills in rats submitted to bilateral subdiaphragmatic vagotomy. Results showed that 2´-FL but not Fuc enhanced LTP, and vagotomy inhibited the effects of oral 2´-FL on LTP and associative learning related paradigms. Taken together, the data show that dietary 2´-FL but not its Fuc moiety affects cognitive domains and improves learning and memory in rats. This effect is dependent on vagus nerve integrity, suggesting GBA plays a role in 2´-FL-mediated cognitive benefits.

Proteomics of the Synapse--A Quantitative Approach to Neuronal Plasticity

The advances in mass spectrometry based proteomics in the past 15 years have contributed to a deeper appreciation of protein networks and the composition of functional synaptic protein complexes. However, research on protein dynamics underlying core mechanisms of synaptic plasticity in brain lag far behind. In this review, we provide a synopsis on proteomic research addressing various aspects of synaptic function. We discuss the major topics in the study of protein dynamics of the chemical synapse and the limitations of current methodology. We highlight recent developments and the future importance of multidimensional proteomics and metabolic labeling. Finally, emphasis is given on the conceptual framework of modern proteomics and its current shortcomings in the quest to gain a deeper understanding of synaptic plasticity.

Effects of a human milk oligosaccharide, 2'-fucosyllactose, on hippocampal long-term potentiation and learning capabilities in rodents

Human milk oligosaccharides (HMOs) are unique with regard to their diversity, quantity and complexity, particularly in comparison to bovine milk oligosaccharides. HMOs are associated with functional development during early life, mainly related to immunity and intestinal health. Whether HMOs elicit a positive effect on cognitive capabilities of lactating infants remains an open question. This study evaluated the role of the most abundant HMO, 2'-fucosyllactose (2'-FL), in synaptic plasticity and learning capabilities in rodents. Mice and rats were prepared for the chronic recording of field excitatory postsynaptic potentials evoked at the hippocampal CA3-CA1 synapse. Following chronic oral administration of 2'-FL, both species showed improvements in input/output curves and in long-term potentiation (LTP) evoked experimentally in alert behaving animals. This effect on LTP was related to better performance of animals in various types of learning behavioral tests. Mice were tested for spatial learning, working memory and operant conditioning using the IntelliCage system, while rats were submitted to a fixed-ratio schedule in the Skinner box. In both cases, 2'-FL-treated animals performed significantly better than controls. In addition, chronic administration of 2'-FL increased the expression of different molecules involved in the storage of newly acquired memories, such as the postsynaptic density protein 95, phosphorylated calcium/calmodulin-dependent kinase II and brain-derived neurotrophic factor in cortical and subcortical structures. Taken together, the data show that dietary 2'-FL affects cognitive domains and improves learning and memory in rodents.

Transient prenatal vitamin D deficiency is associated with changes of synaptic plasticity in the dentate gyrus in adult rats

Transient prenatal vitamin D deficiency is considered a neurodevelopmental animal model in schizophrenia research. Vitamin D deficiency in female rats causes morphological, cellular and molecular changes in the brain and alters behaviour and nerve growth factors expression in their offspring. Prenatal depleted animals showed a significant impairment of latent inhibition, a feature often associated with schizophrenia and of hole board habituation. Interestingly, memory consolidation of brightness discrimination was improved. Possible functional effects of altered brain development that results from prenatal vitamin D deficiency were characterized by investigation of potentiation phenomena in the hippocampus in freely moving rats. Transient prenatal vitamin D deficiency induced an enhancement of long-term potentiation (LTP) using either weak tetanic or strong tetanic stimulation, whereas the response to test stimuli was not changed. The classic neuroleptic drug haloperidol (Hal) and the atypical neuroleptic risperidone (Ris) in doses, which normalized behavioural disturbances in prenatal vitamin D-deficient animals without any side effects on the normal behaviour decreased the enhanced LTP in the experimental group to control level. Interestingly, the effect of the substances was different in experimental and control rats. The LTP was enhanced in control animals by the low doses of the drugs effective in our behavioural experiments. It can be suggested, that changes in brain development induced by prenatal vitamin D deficiency lead to specific functional alterations in hippocampal synaptic plasticity. LTP is considered a cellular correlate of learning and memory. The better retention performance in brightness discrimination seems in accordance with enhanced potentiation level.

Metabolic oligosaccharide engineering: perspectives, applications, and future directions

Many adhesion and signaling molecules critical for development, as well as surface markers implicated in diseases ranging from cancer to influenza, contain oligosaccharides that modify their functions. Inside a cell, complex glycosylation pathways assemble these oligosaccharides and attach them to proteins and lipids as they traffic to the cell surface. Until recently, practical technologies to manipulate glycosylation have lagged unlike the molecular biologic and genetic methods available to intervene in nucleic acid and protein biochemistry; now, metabolic oligosaccharide engineering shows promise for manipulating glycosylation. In this methodology, exogenously-supplied non-natural sugars intercept biosynthetic pathways and exploit the remarkable ability of many of the enzymes involved in glycosylation to process metabolites with slightly altered chemical structures. To date, non-natural forms of sialic acid, GalNAc, GlcNAc, and fucose have been incorporated into glycoconjugates that appear on the cell surface; in addition O-GlcNAc protein modification involved in intracellular signaling has been tagged with modified forms of this sugar. Reactive functional groups, including ketones, azides, and thiols, have been incorporated into glycoconjugates and thereby provide chemical 'tags' that can be used for diverse purposes ranging from drug delivery to new modes of carbohydrate-based cell adhesion that can be used to control stem cell destiny. Finally, strategies for further engineering non-natural sugars to improve their pharmacological properties and provide complementary biological activities, such as addition of short chain fatty acids, are discussed in this article.

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.

Glycosylation of proteins during a critical time window is necessary for the maintenance of long-term potentiation in the hippocampal CA1 region

This paper focuses on the role of glycoproteins in activity-dependent synaptic plasticity. The effect of the different inhibitors of protein glycosylation, Tunicamycin, Brefeldin A and Swainsonine, on long-term potentiation was studied in the CA1 region of rat hippocampal slices. Bath application of the inhibitors 60 min before and during tetanization did not interfere with the induction of long-term potentiation of the field excitatory postsynaptic potential. However, the potentiation in inhibitor-treated slices decreased to baseline levels during 90-180 min. Significant differences in the potentiation in non-treated slices were detectable 80 min (Tunicamycin), 60 min (Brefeldin A) and 75 min (Swainsonine) after tetanization, thus indicating the prevention of long-term potentiation maintenance. The application of Swainsonine 120 and 240 min after tetanization did not influence the potentiated field excitatory postsynaptic potential. These data demonstrate the need for undisturbed glycoprotein processing in a time window around long-term potentiation induction to maintain later phases of long-term potentiation and essential functional implications of protein glycosylation in mechanisms underlying synaptic plasticity.

Enhancement of glutamate release by L-fucose changes effects of glutamate receptor antagonists on long-term potentiation in the rat hippocampus

In previous studies L-fucose has been shown to facilitate long-term memory formation and to enhance and prolong long-term potentiation (LTP). To search for possible presynaptic or postsynaptic mechanisms that are affected by L-fucose, we examined the effect of L-fucose on (1) inhibition of LTP induction via glutamate receptors by antagonists, (2) paired-pulse facilitation, and (3) presynaptic transmitter release. Coapplication of 0.2 mM L-fucose with the competitive N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonovalerate (AP5), or coapplication of 0.2 mM L-fucose in the presence of an inhibitor for class I/II metabotropic glutamate receptors, (S)-alpha-methyl-4-carboxyphenylglycine (MCPG), reversed LTP blockade in the CA1-region of hippocampal slices. In contrast, L-fucose had no effect on the LTP blockade by the noncompetitive NMDA ion-channel blocker (5R,10S)-(+)-5-Methyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine hydrogen maleate (MK-801). Paired-pulse facilitation, which is a primarily presynaptic phenomenon of short-term plasticity, was decreased in the presence of 0.2 mM L-fucose. Furthermore, L-fucose enhanced the K(+)-stimulated release of [(3)H]-D-aspartate from preloaded hippocampal slices in a concentration-dependent manner. These observations demonstrate an influence of L-fucose on transmitter release that in turn can increase transmitter availability at postsynaptic glutamate receptors. This effect of L-fucose may contribute to the LTP facilitation seen in vitro and in vivo as well as to improvement in memory formation.

The synaptic glycoprotein neuroplastin is involved in long-term potentiation at hippocampal CA1 synapses

Neuroplastin-65 and -55 (previously known as gp65 and gp55) are glycoproteins of the Ig superfamily that are enriched in rat forebrain synaptic membrane preparations. Whereas the two-Ig domain isoform neuroplastin-55 is expressed in many tissues, the three-Ig domain isoform neuroplastin-65 is brain-specific and enriched in postsynaptic density (PSD) protein preparations. Here, we have assessed the function of neuroplastin in long-term synaptic plasticity. Immunocytochemical studies with neuroplastin-65-specific antibodies differentially stain distinct synaptic neuropil regions of the rat hippocampus with most prominent immunoreactivity in the CA1 region and the proximal molecular layer of the dentate gyrus. Kainate-induced seizures cause a significant enhancement of neuroplastin-65 association with PSDs. Similarly, long-term potentiation (LTP) of CA1 synapses in hippocampal slices enhanced the association of neuroplastin-65 with a detergent-insoluble PSD-enriched protein fraction. Several antibodies against the neuroplastins, including one specific for neuroplastin-65, inhibited the maintenance of LTP. A similar effect was observed when recombinant fusion protein containing the three extracellular Ig domains of neuroplastin-65 was applied to hippocampal slices before LTP induction. Microsphere binding experiments using neuroplastin-F(c) chimeric proteins show that constructs containing Ig1-3 or Ig1 domains, but not Ig2-3 domains mediate homophilic adhesion. These data suggest that neuroplastin plays an essential role in implementing long-term changes in synaptic activity, possibly by means of a homophilic adhesion mechanism.

Synaptic tagging: implications for late maintenance of hippocampal long-term potentiation

A novel property of hippocampal LTP, 'variable persistence', has recently been described that is, we argue, relevant to the role of LTP in information storage. Specifically, new results indicate that a particular pattern of synaptic activation can give rise, either to a relatively short-lasting LTP, or to a longer-lasting LTP as a function of the history of activation of the neuron. This has led to the idea that the induction of LTP is associated with the setting of a'synaptic tag' at activated synapses, whose role is to sequester plasticity-related proteins that then serve to stabilize temporary synaptic changes and so extend their persistence. In this article, we outline the synaptic tag hypothesis, compare predictions it makes with those of other theories about the persistence of LTP, and speculate about the cellular identity of the tag. In addition, we outline the requirement for aminergic activation to induce late LTP and consider the functional implications of the synaptic tag hypothesis with respect to long-term memory.

Identification of fucose alpha(1-2) galactose epitope-containing glycoproteins from rat hippocampus

Fucosylation of terminal galactose residues of brain glycoproteins in the alpha(1-2) position has been shown to be crucial for neuronal plasticity, including phenomena such as long-term potentiation and long-term memory formation. We raised antibodies against the plasticity-relevant fucalpha(1-2)gal epitope and used them to determine the distribution of the epitope in adult rat hippocampus. To identify proteins bearing fucalpha(1-2)gal glycostructures antibodies against known synaptic fucoglycoproteins were used in combination with the fucalpha(1-2)gal antibodies. The NMDA receptor subunit NR1 and fractions of gp65 and cadherin were found to carry the epitope, while fucosylation of NCAM180 and NCAM140 obviously occurs via different linkages to the glycan chains.

Kindling of the dorsal and the ventral hippocampus: effects on learning performance in rats

The hippocampus represents a heterogeneous structure which has been associated with different functions. It has been suggested that it plays an important role in both learning and memory and epileptogenesis. Thus, it is not surprising that seizure activity generated in the hippocampal formation interferes with memory storage. Little is known about the functional differentiation between the dorsal (DH) and ventral hippocampus (VH). To study this functional differentiation, we kindled Wistar rats either in the DH or in the VH by electrical stimulation. Afterwards, learning performance of these rats was tested in three different models, i.e., response to change (short-term memory), shuttle box (two-way active avoidance), and Y-chamber (brightness discrimination reaction). It was found that VH-kindled rats reached higher seizure scores than DH-kindled rats, but there was no difference in seizure duration. Kindling induced in the VH significantly impaired shuttle box learning, whereas DH-kindled rats showed a dramatically worsened acquisition in the brightness discrimination task. Different anatomical projections probably account, in part, for these differences.

2-Deoxy-D-galactose effects on passive avoidance memorization in the rat

2-Deoxy-D-galactose (do-gal) hinders glycoprotein fucosylation. This compound was intracerebroventricularly administered to male adult Wistar rats in order to assess whether it could exert amnesic effects on a passive avoidance response (PAR) to be learned in the light-dark box apparatus. Three experiments were performed. In the first, do-gal was administered immediately after the acquisition trials at three dosages (2, 4, and 8 mumol). It was found that only the 4-mumol dosage was followed by PAR disruption. In the second, do-gal was administered at the adequate dosage (4 mumol) either 30 min before the acquisition trial or 30 min before retrieval testing. It was found that only the preretrieval administration was followed by PAR impairment. In the third, do-gal (4 mumol) was administered in postacquisition, at increasing postacquisition delays (0.25, 1.5, 4, and 6 h). It was found that there was PAR disruption only after do-gal administration at the shortest (0.25 h) delay. The results confirm that in the rat, glycoprotein fucosylation is involved in some of the phases of memory trace processing, and they are discussed in relation to other findings in the rat and the chick.

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.

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.

The maintenance of hippocampal long-term potentiation is paralleled by a dopamine-dependent increase in glycoprotein fucosylation

Induction of long-term potentiation (LTP) in hippocampal slices of rats caused an increase in both protein synthesis and glycoprotein fucosylation by 38 and 34%, respectively. The enhanced incorporation of [3H]fucose into glycoproteins observed 1 h after tetanization was abolished in the presence of the dopamine D1 receptor antagonist SCH23390 during stimulation whereas the LTP-induced increase of protein synthesis was not influenced by this drug. The enhanced insertion of [3H]fucose into hippocampal glycoproteins 1 h after tetanization was paralleled by an increase in the activity of the fucose metabolizing enzyme, fucokinase. In contrast no changes in protein and glycoprotein synthesis were detectable 5 h after tetanization of the slices. The results provide evidence that in addition to an enhanced protein synthesis a dopamine (D1) mediated increase in glycoprotein fucosylation is necessary for the maintenance of the late stage of LTP.

Incorporation of the hexose analogue 2-deoxy-D-galactose into membrane glycoproteins in HepG2 cells

The incorporation of 2-deoxy-D-galactose into the oligosaccharide moieties of glycoproteins and the consequences of 2-deoxy-D-galactose treatment on the fucosylation of glycoproteins were investigated in the human hepatoma cell line HepG2. Using different methods, it was shown that treatment of HepG2 cells with 2-deoxy-D-galactose leads to an incorporation of 2-deoxy-D-galactose and a decrease of L-fucose incorporation into the oligosaccharides of glycoproteins. The extent of labeling by L-[3H]fucose was determined by removing L-[3H]fucose from labeled cells with the aid of a purified alpha 1,2-fucosidase from Aspergillus niger. Using this method, it was shown that 2-deoxy-D-galactose markedly inhibits alpha 1,2-fucosylation. Measurement of the amount of 2-deoxy-D-galactose incorporated, however, showed that replacement of D-galactose by 2-deoxy-D-galactose does not entirely account for the decrease in alpha 1,2-fucosylation. In addition, a hitherto unreported compensatory increase of alpha 1,3/alpha 1,4-fucosylation was found to occur when alpha-1,2-fucosylation was inhibited by treatment with 2-deoxy-D-galactose.

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.

Enhanced development of morphine tolerance in rats treated with 2-deoxy-D-galactose

Rats treated subcutaneously for 6 days with morphine developed a weak tolerance which was characterized by a decrease in the analgesic action of the opioid. Under those experimental conditions a simultaneous intracerebroventricular application of 2-deoxy-D-galactose enhanced development of morphine tolerance, while other deoxy-sugars like 2-deoxy-D-glucose and 6-deoxy-D-galactose were ineffective. In contrast, no influence of 2-deoxy-D-galactose on a more enhanced morphine tolerance after a 11-day pretreatment with morphine was found. The results are discussed in the light of a rather specific interference of 2-deoxy-D-galactose with neuronal glycoprotein processing and related cellular mechanism underlying adaptive processes involved in the development of morphine tolerance.

Increased retention of calcium in the dendrites of long-term potentiated CA1 neurons of the hippocampal slice. A combined electrophysiological and electron histochemical study

In view of the importance of calcium in the induction of long-term potentiation (LTP), experiments were carried out to localize calcium at the electron microscopic level in the CA1 region of guinea pig hippocampal slices, following high-frequency stimulation of the Schaffer collaterals. Apart from the ultrastructural localization, a semi-quantitative method was used to count the calcium-containing deposits in electron micrographs. Significantly more calcium-containing deposits were seen in the dendrites of the stratum radiatum in slices with LTP than in those without it. A moderate increase of the extradendritic deposits was observed, too. The calcium content of the deposits was determined by means of EGTA incubation and X-ray analysis. The presented results, together with the relevant literature data, underline the importance of calcium-activated processes in postsynaptic structures probably involved in the generation of LTP.