Open field behaviours and spatial learning performance in C57BL/6 mice: early stage effects of chronic GM1 ganglioside administration

LC-MS/MS quantification of N-acetylneuraminic acid, N-glycolylneuraminic acid and ketodeoxynonulosonic acid levels in the urine and potential relationship with dietary sialic acid intake and disease in 3- to 5-year-old children

Red meat and dairy products contain high sialic acid (Sia) levels, but the metabolic fate and health impact in children remain unknown. The aims of the present study were to quantify the levels of urinary Sia N-acetylneuraminic acid (Neu5Ac), N-glycolylneuraminic acid (Neu5Gc) and ketodeoxynonulosonic acid (KDN) and to determine their relationship with dietary Sia intake. Spot urine samples were collected from 386 healthy children aged 3 (n 108), 4 (n 144) and 5 (n 134) years at 06.30-07.00, 11.30-12.00 and 16.30-17.00 hours. Food intake levels were recorded on the day of urine sample collection. Sia levels were quantified using LC-MS/MS with [13C3]Sia as an internal standard. We found that (1) total urinary Sia levels in healthy pre-school children ranged from 40 to 79 mmol Sia/mol creatinine; (2) urinary Sia levels were independent of age and consisted of conjugated Neu5Ac (approximately 70·8 %), free Neu5Ac (approximately 21·3 %), conjugated KDN (approximately 4·2 %) and free KDN (approximately 3·7 %); Neu5Gc was detected in the urine of only one 4-year-old girl; (3) total urinary Sia levels were highest in the morning and declined over time in 4- and 5-year-old children (P< 0·05), but not in 3-year-old children; (4) Sia intake levels at breakfast and lunch were approximately 2·5 and 0·16 mg Sia/kg body weight; and (5) there was no significant correlation between dietary Sia intake levels and urinary Sia levels. Urinary Sia levels varied with age and time of day, but did not correlate with Sia intake in 3- to 5-year-old children. The difference in urinary Sia levels in children of different age groups suggests that the metabolism and utilisation rates of dietary Sia are age dependent.

Antidepressant-like effect of sildenafil through oxytocin-dependent cyclic AMP response element-binding protein phosphorylation

Oxytocin (OT) levels in plasma increase during sexual response and are significantly lower in patients with depression. A drug for the treatment of sexual dysfunction, sildenafil, enhances the electrically evoked release of OT from the posterior pituitary. In this study, we showed that sildenafil had an antidepressant-like effect through activation of an OT signaling pathway. Application of sildenafil reduced depression-related behavior in male mice. The antidepressant-like effect was blocked by an OT receptor (OTR) antagonist and was absent in OTR knockout (KO) mice. Sildenafil increased the phosphorylation of cAMP response element-binding protein (CREB) in the hippocampus. The OTR antagonist inhibited sildenafil-induced CREB phosphorylation and sildenafil had no effect on CREB phosphorylation in OTR KO mice. These results suggest sildenafil to have an antidepressant-like effect through the activation of OT signaling and to be a promising drug for the treatment of depression.

Long-term swimming in an inescapable stressful environment attenuates the stimulatory effect of endurance swimming on duodenal calcium absorption in rats

Endurance swimming is known to increase duodenal calcium absorption in normal rats and bone strength in estrogen-deficient rats. Because the stress resulting from forced training often attenuates the stimulatory effect of exercise, swimming in an inescapable chamber should reveal both the positive effect of the exercise and the negative effect of stress. In the work reported herein, swimming rats showed no signs of stress during 2 weeks of training. However, stress response gradually developed thereafter and peaked at weeks 6 and 7. In rats swimming for 2 weeks, transcellular duodenal calcium transport was enhanced ~2-fold. In contrast, calcium absorption was reduced in rats swimming for 8 weeks, consistent with the absence of swimming-induced upregulation of calcium transporter genes in the 8-week group. In conclusion, prolonged stress hindered the stimulatory effect of swimming on duodenal calcium absorption, and thus endurance exercise should be performed without forced training or stress to retain its beneficial effect on calcium metabolism.

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.

Beneficial effects of GM1 ganglioside on photochemically-induced microvascular injury in cerebral cortex and hypophysis in rat

Gangliosides, the glycophospholipids which are abundantly present in the central nervous system, have been shown to stimulate neuronal regeneration and counteract the deleterious effects of ischemia on cerebral neurons. The further elucidate the mechanism of action of gangliosides in cerebral ischemia, we investigated the influence of GM1 ganglioside in the model of photochemically-induced microvascular injury in rat brain. The animals were injected with rose Bengal and illuminated through cranium with halogen lamp. This treatment resulted in the development of microthrombi and alterations in endothelial cells in the microvessels. Administration of 20 mg/kg GM1 ganglioside, 1 h before the photochemical reaction, largely reduced subsequent microvascular damage. In conclusion, the GM1 ganglioside is able to prevent microvascular damage in the central nervous system.

Effect of ganglioside (GM1) on memory in senescent rats

Monosialoganglioside GM1 (GM1) has been found to alleviate genetic and lesion-induced memory deficits. The purpose of this study was to investigate the effects of 7-day treatment with GM1 (50 mg/kg IP) on acquisition and retention performance of senescent rats in a passive avoidance situation. Saline-treated old rats showed a decreased performance in acquisition and retention tests as compared to saline-treated adult rats. GM1 improved both acquisition and retention performance of old animals, and there was no significant difference between GM1-treated old rats and saline-treated adult rats. These data suggest that GM1 treatment can improve memory deficits in intact senescent animals.

Dose-dependent effect of GM1 ganglioside during development on inhibitory avoidance behaviour in mice: influence of the period of administration

Groups of C57BL/6 mice were injected intraperitoneally with GM1 monosialoganglioside at different ages during development and subsequently tested for the retention of an inhibitory avoidance task 24 h after training. Results show improvements in inhibitory avoidance retention according to the age of the animals, the doses of GM1 used and the length of treatment. The effective doses ranged from 20 mg/kg for all age groups after 7 days treatment to 280 mg/kg for 6- and 7-week old animals after pre-trial treatment. Six- and 7-week-old mice are more sensitive to GM1 treatment than 5-week-old animals and, with decreasing lengths of treatment, increasing doses of GM1 are needed to improve the performance of the animals. These findings show that short treatment durations can be effective in improving inhibitory avoidance retention as long as the doses of GM1 administered are increased and that animals are more sensitive to the treatment when they are 6 or 7 weeks of age than when they are 5 weeks old.