Effect of ganglioside (GM1) on memory in senescent rats

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.

The role of gangliosides in neurodevelopment

Gangliosides are important components of neuronal cell membranes and it is widely accepted that they play a critical role in neuronal and brain development. They are functionally involved in neurotransmission and are thought to support the formation and stabilization of functional synapses and neural circuits required as the structural basis of memory and learning. Available evidence, as reviewed herein, suggests that dietary gangliosides may impact positively on cognitive functions, particularly in the early postnatal period when the brain is still growing. Further, new evidence suggests that the mechanism of action may be through an effect on the neuroplasticity of the brain, mediated through enhanced synaptic plasticity in the hippocampus and nigro-striatal dopaminergic pathway.

Acute and chronic ethanol differentially modify the emotional significance of a novel environment: implications for addiction

Using open-field behaviour as an experimental paradigm, we demonstrated a complex interaction between the rewarding/stimulating effects and the anxiogenic/stressful effects of both novelty and acute or chronic amphetamine in mice. As a consequence of this interaction, acute amphetamine-induced hyperlocomotion was inhibited, whereas the expression of its sensitization was facilitated in a novel environment. In the present study, we aimed to investigate the interactions between exposure to a novel environment and the acute and chronic effects of ethanol (Eth), a drug of abuse known to produce anxiolytic-like behaviour in mice. Previously habituated and non-habituated male Swiss mice (3 months old) were tested in an open field after receiving an acute injection of Eth or following repeated treatment with Eth. Acute Eth administration increased locomotion with a greater magnitude in mice exposed to the apparatus for the first time, and this was thought to be related to the attenuation of the stressful effects of novelty produced by the anxiolytic-like effect of acute Eth, leading to a subsequent prevalence of its stimulant effects. However, locomotor sensitization produced by repeated Eth administration was expressed only in the previously explored environment. This result might be related to the well-known tolerance of Eth-induced anxiolytic-like behaviour following repeated treatment, which would restore the anxiogenic effect of novelty. Our data suggest that a complex and plastic interaction between the emotional and motivational properties of novelty and drugs of abuse can critically modify the behavioural expression of addiction-related mechanisms.

Effects of sleep deprivation on memory in mice: role of state-dependent learning

STUDY OBJECTIVES

A considerable amount of experimental evidence suggests that sleep plays a critical role in learning/memory processes. In addition to paradoxical sleep, slow wave sleep is also reported to be involved in the consolidation process of memories. Additionally, sleep deprivation can induce other behavioral modifications, such as emotionality and alternations in locomotor activity in rodents. These sleep deprivation-induced alterations in the behavioral state of animals could produce state-dependent learning and contribute, at least in part, to the amnestic effects of sleep deprivation. The aim of the present study was to examine the participation of state-dependent learning during memory impairment induced by either paradoxical sleep deprivation (PSD) or total sleep deprivation (TSD) in mice submitted to the plus-maze discriminative avoidance or to the passive avoidance task.

DESIGN

Paradoxical sleep deprivation (by the multiple platform method) and total sleep deprivation (by the gentle handling method) were applied to animals before training and/or testing.

CONCLUSIONS

Whereas pre-training or pre-test PSD impaired retrieval in both memory models, pre-training plus pre-test PSD counteracted this impairment. For TSD, pre-training, pre-test, and pre-training plus pre-test TSD impaired retrieval in both models. Our data demonstrate that PSD- (but not TSD-) memory deficits are critically related to state-dependent learning.

Sialic acid is an essential nutrient for brain development and cognition

The rapid growth of infant brains places an exceptionally high demand on the supply of nutrients from the diet, particularly for preterm infants. Sialic acid (Sia) is an essential component of brain gangliosides and the polysialic acid (polySia) chains that modify neural cell adhesion molecules (NCAM). Sia levels are high in human breast milk, predominately as N-acetylneuraminic acid (Neu5Ac). In contrast, infant formulas contain a low level of Sia consisting of both Neu5Ac and N-glycolylneuraminic acid (Neu5Gc). Neu5Gc is implicated in some human inflammatory diseases. Brain gangliosides and polysialylated NCAM play crucial roles in cell-to-cell interactions, neuronal outgrowth, modifying synaptic connectivity, and memory formation. In piglets, a diet rich in Sia increases the level of brain Sia and the expression of two learning-related genes and enhances learning and memory. The purpose of this review is to summarize the evidence showing the importance of dietary Sia as an essential nutrient for brain development and cognition.

GM1 ganglioside induces vasodilation and increases catalase content in the brain

Monosialoganglioside (GM1) is a glycosphingolipid present in most cell membranes that displays antioxidant and neuroprotective properties. GM1 increases catalase activity in cerebral cortices in vivo, but the mechanisms underlying this effect of GM1 are not known. In the current study we investigated the effect of GM1 (50 mg/kg, ip) on the content of hemoglobin and catalase activity of hippocampus, cortex, and striatum of rats. GM1 administration increased catalase activity and hemoglobin content in brain samples after 30 min, but had no effect on blood catalase activity. GM1-induced increase in catalase activity was abolished by brain perfusion with heparinized saline. Brain catalase activity in the absence of blood, estimated by regression analysis of data from perfused and nonperfused animals, was not altered by the systemic injection of GM1. Moreover, the addition of GM1 (30 or 100 microM) did not increase catalase activity in slices of cerebral cortex in situ, further suggesting that blood circulation is required for this effect. The GM1-induced vasodilation was confirmed in vivo, because the systemic injection of GM1 (50 mg/kg, ip) increased (1.2-1.6 times) the width of pial vessels.

Postnatal dietary supplementation with either gangliosides or choline: effects on spatial short-term memory in artificially-reared rats

This study addressed the hypothesis that dietary supplementation with either gangliosides or choline during the brain growth spurt would enhance short-term spatial memory. Male Long-Evans rats were reared artificially from postnatal days (PD) 5-18 and were fed diets containing either (i) choline chloride 1250 mg/l (CHL), (ii) choline chloride 250 mg/l and GD3 24 mg/l (GNG) or (iii) choline chloride 250 mg/l (STD). A fourth group (SCK) was reared normally. Rats were weaned onto AIN 93G diet and on PD 35 were trained on a cued delayed- matching-to-place version of the Morris water maze. All groups learned to swim to the beacon that indicated the platform position on the first trial; similarly, on the second un-cued trial, the distance swam to reach the platform decreased to the same extent in all groups over the five days of training. The groups also responded in the same way to an increase in delay between the first and second trial from 1 min to 1 h, showing an increase in the distance swam, accompanied by a decrease in the number of direct swims to the platform. Thus, all rats were equally proficient at using spatial short-term memory, regardless of the choline or ganglioside content of the preweaning diet.

Effects of 3-nitropropionic acid administration on memory and hippocampal lipid peroxidation in sleep-deprived mice

Numerous studies have described memory deficits following sleep deprivation. There is also evidence that the absence of sleep increases brain oxidative stress. The present study investigates the effects of a pro-oxidant agent--3-nitropropionic acid (3-NP)--on hippocampal oxidative stress and passive avoidance performance of sleep-deprived mice. Mice were repeatedly treated i.p. with saline or 5 or 15 mg/kg 3-NP and sleep-deprived for 24 h by the multiple platform method--groups of 4-5 animals placed in water tanks, containing 12 platforms (3 cm in diameter) surrounded by water up to 1 cm beneath the surface or kept in their home cage (control groups). The results showed that: (1) neither a 24 h sleep deprivation period nor 3-NP repeated treatment alone were able to induce memory deficits and increased hippocampal lipid peroxidation; (2) this same protocol of sleep deprivation, combined with 15 mg/kg 3-NP repeated treatment, induced memory deficits and an increase in hippocampal lipid peroxidation. The results support the involvement of hippocampal oxidative stress in the memory deficits induced by sleep deprivation and the hypothesis that normal sleep would prevent oxidative stress.

A new model of neonatal stress which produces lasting neurobehavioral effects in adult rats

BACKGROUND

During critical care in neonatal intensive care units (NICU), infants experience stressors and treatments that may produce lasting effects on adult health. An animal model simulating the NICU experience is needed to understand the impact of specific neonatal stressors.

OBJECTIVE

We combined approaches to develop a neonatal rat model simulating NICU stressors in order to examine the hypothesis that early stress and morphine sulfate (MS) exposure would affect development and alter adult behavior.

METHODS

Rat pups were exposed to stressors and given twice daily MS injections (2 mg/kg s.c.) for 5 days (postnatal days 3-7). Stress included daily maternal separation (from 08.00 to 16.00 h), hand feedings, a daily hypoxia/hyperoxia episode (100% N(2) for 8 min, then 100% O(2) for 4 min), and cold exposure (4 degrees C for 20 min/day). Five treatment groups were formed: (1) 'control control' (dam reared and untreated); (2) control vehicle; (3) stress vehicle; (4) control morphine, and (5) stress morphine. Early growth and developmental indices were measured. Adult neurobehavioral tests were paw flick, passive avoidance, and forced swimming. Neonatal MS pharmacokinetics, neonatal and adult corticosterone levels, and adult hematocrit and blood pressure values were measured.

RESULTS

Neonatal stress significantly increased the mortality. Neonatal stress and MS treatment slowed early growth. Neonatal MS impaired passive avoidance learning and increased frequency, duration, and distance of forced swimming. There were no differences in corticosterone, hematocrit, or blood pressure values.

CONCLUSIONS

This model simulates NICU stressors and enables measurement of acute physiological and long-term neurobehavioral indices. Neonatal MS treatment impaired the adult cognitive functioning.

Effects of morphine on the plus-maze discriminative avoidance task: role of state-dependent learning

RATIONALE

The amnesic effects of morphine may be related to its action on nociception, anxiety, or locomotion. This effect is also suggested to be related to state dependency.

OBJECTIVES

The aims of this study were to verify the effects of morphine on mice tested in the plus-maze discriminative avoidance task (DAT) that uses light and noise as aversive stimuli and allows the concomitant evaluation of learning, memory, anxiety, and locomotion and also to verify the possible role of state-dependent learning in the effects of morphine.

METHODS AND RESULTS

The DAT was conducted in a modified elevated plus-maze. In the training, the aversive stimuli were applied when mice entered in one of the enclosed arms, whereas in the test, no stimuli were applied. The main results showed that (1) pretraining morphine (5-20 mg/kg i.p.) induced retrieval deficits (evaluated by the time spent in the aversive arm in the test) but not acquisition deficits (evaluated by the decrease in aversive arm exploration along the training); (2) pretest morphine (5-10 but not 20 mg/kg) counteracted this deficit; (3) morphine induced hypolocomotion (decreased number of entries in the arms), irrespective of memory alterations; and (4) morphine did not alter anxiety-like behavior (evaluated by the time spent in the open arms) during the training.

CONCLUSIONS

Morphine given before training induces retrieval deficits in mice tested in the DAT, and these deficits could be related to morphine-induced state-dependent learning. Neither the memory deficit induced by pretraining morphine nor the reversal of this deficit by pretest morphine seems to be related to anxiety levels or locomotor alterations.

Effects of social isolation on aging-induced orofacial movements in rats

World population is becoming older, and aging is a common risk factor for a number of pathologies. In this respect, it is important to study possible factors that could modify alterations implicated in the process of aging. The aim of the present study is to verify the effects of social isolation on the expression of orofacial movements in adult and old rats. Adult and old rats were housed isolated for 5 days or kept in their home cages in groups of six. Before and after this period, orofacial movements and open-field general activity were evaluated. Aging-induced orofacial movements were abolished by isolation. On the other hand, isolated adult rats presented an increase in orofacial movements. General activity was decreased by aging but was not modified by isolation. Our results indicate that social isolation produces different effects in adult and old rats, and these effects are specific for orofacial movements and not related to a decrease in general motor activity.

Behavioral characterization of morphine effects on motor activity in mice

A biphasic effect of morphine on locomotion has been extensively described. Nevertheless, the effects of this opioid on other behavioral parameters have been overlooked. The aim of the present study was to verify the effects of different doses of morphine on motor behaviors observed in an open-field. Adult female mice were injected with saline or morphine (10, 15 and 20 mg/kg, i.p.) and observed in an open-field for quantification of locomotor and rearing frequencies as well as duration of immobility and grooming. The lowest dose of morphine decreased locomotion (and increased immobility duration) while the highest dose increased it. All doses tested decreased rearing and grooming. Thus, the effects of morphine on locomotion do not parallel to its effects on rearing and grooming. Our results indicate that locomotion not always reflects the effect of drugs on motor activity, which can be better investigated when other behavioral parameters are concomitantly taken into account.

Role of hippocampal oxidative stress in memory deficits induced by sleep deprivation in mice

Numerous animal and clinical studies have described memory deficits following sleep deprivation. There is also evidence that the absence of sleep increases brain oxidative stress. The present study investigates the role of hippocampal oxidative stress in memory deficits induced by sleep deprivation in mice. Mice were sleep deprived for 72 h by the multiple platform method-groups of 4-6 animals were placed in water tanks, containing 12 platforms (3 cm in diameter) surrounded by water up to 1 cm beneath the surface. Mice kept in their home cage or placed onto larger platforms were used as control groups. The results showed that hippocampal oxidized/reduced glutathione ratio as well as lipid peroxidation of sleep-deprived mice was significantly increased compared to control groups. The same procedure of sleep deprivation led to a passive avoidance retention deficit. Both passive avoidance retention deficit and increased hippocampal lipid peroxidation were prevented by repeated treatment (15 consecutive days, i.p.) with the antioxidant agents melatonin (5 mg/kg), N-tert-butyl-alpha-phenylnitrone (200 mg/kg) or vitamin E (40 mg/kg). The results indicate an important role of hippocampal oxidative stress in passive avoidance memory deficits induced by sleep deprivation in mice.

The role and potential of sialic acid in human nutrition

Sialic acids are a family of nine-carbon acidic monosaccharides that occur naturally at the end of sugar chains attached to the surfaces of cells and soluble proteins. In the human body, the highest concentration of sialic acid (as N-acetylneuraminic acid) occurs in the brain where it participates as an integral part of ganglioside structure in synaptogenesis and neural transmission. Human milk also contains a high concentration of sialic acid attached to the terminal end of free oligosaccharides, but its metabolic fate and biological role are currently unknown. An important question is whether the sialic acid in human milk is a conditional nutrient and confers developmental advantages on breast-fed infants compared to those fed infant formula. In this review, we critically discuss the current state of knowledge of the biology and role of sialic acid in human milk and nervous tissue, and the link between sialic acid, breastfeeding and learning behaviour.