Glycosphingolipids (GSLs) and their sialic acid-containing derivatives, gangliosides, are important cellular components and are abundant in the nervous system. They are known to undergo dramatic changes during brain development. However, knowledge on the mechanisms underlying their qualitative and qualitative changes is still fragmentary. In this investigation, we have provided a detailed study on the developmental changes of the expression patterns of GSLs, GM3, GM1, GD3, GD1a, GD2, GD1b, GT1b, GQ1b, A2B5 antigens (c-series gangliosides such as GT3 and GQ1c), Chol-1a (GT1aa and GQ1ba), glucosylceramide, galactosylceramide (O1 antigen), sulfatide (O4 antigen), stage-specific embryonic antigen-1 (Lewis x) glycolipids, and human natural killer-1 glycolipid (sulfoglucuronosyl paragloboside) in developing mouse brains [embryonic day 12 (E12) to adult]. In E12-E14 brains, GD3 was a predominant ganglioside. After E16, the concentrations of GD3 and GM3 markedly decreased, and the concentrations of a-series gangliosides, such as GD1a, increased. GT3, glucosylceramide, and stagespecific embryonic antigen-1 were expressed in embryonic brains. Human natural killer-1 glycolipid was expressed transiently in embryonic brains. On the other hand, Chol-1a, galactosylceramide, and sulfatide were exclusively found after birth. To provide a better understanding of the metabolic basis for these changes, we analyzed glycogene expression patterns in the developing brains and found that GSL expression is regulated primarily by glycosyltransferases, and not by glycosidases. In parallel studies using primary neural precursor cells in culture as a tool for studying developmental events, dramatic changes in ganglioside and glycosyltransferase gene expression were also detected in neurons induced to differentiate from neural precursor cells, including the expression of GD3, followed by up-regulation of complex a-and b-series gangliosides. These changes in cell culture systems resemble that occurring in brain. We conclude that the dramatic changes in GSL pattern and content can serve as useful markers in neural development and that these changes are regulated primarily at the level of glycosyltransferase gene expression.

Milk and milk products, such as cheese, have been shown to exhibit anticariogenic properties in human and animal models. CPP-ACP shows an anti-caries effect by suppressing demineralization, enhancing remineralization, or possibly a combination of both. The purpose of this study was to evaluate the effect of CPP-ACP paste on demineralization by observing the treated tooth surface using an FE-SEM. The specimens were prepared by cutting enamel and dentin of bovine teeth into blocks. A few specimens were stored in 0.1 M lactic acid buffer solution for 10 min and then in artificial saliva (negative control). The remaining specimens were stored in a 10 times-diluted solution of CPP-ACP paste or a placebo paste containing no CPP-ACP for 10 min, followed by 10 min immersion in a demineralizing solution (pH = 4.75, Ca) twice a day before storage in artificial saliva. After treatment of the specimens for 3, 7, 21 and 28 days, they were fixed in 2.5% glutaraldehyde in cacodylate buffer solution, dehydrated in ascending grades of tert-butyl alcohol, and then transferred to a critical-point dryer. The surfaces were coated with a thin film of Au in a vacuum evaporator, and were observed under field emission-scanning electron microscopy (FE-SEM). The SEM observations revealed different morphological features brought about by the various storage conditions. Demineralization of the enamel and dentin surfaces was more pronounced with the longer test period in the control and negative control specimens. On the other hand, enamel and dentin specimens treated with CPP-ACP paste revealed slight changes in their morphological features. From the morphological observations of the enamel and dentin surfaces, it could be considered that the CPP-ACP paste might prevent demineralization of the tooth structure.

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Cognitive function as measured by the Hebb-Williams maze task was examined in Fischer 344 male rats that had been exposed to an enriched environment for periods of variable duration and at different starting ages. In one experiment, rats were exposed to environmental enrichment from weaning until the age of 2.5, 15, or 25 months. The results of 12 problems of the Hebb-Williams maze task showed that the enriched rearing condition improved the learning ability in all the age groups; however, factor analysis and ANOVA demonstrated that four of the 12 maze problems were not suitable for detecting the effect of age under different environmental conditions. Reanalysis of the results obtained with the other eight maze problems more clearly revealed both the effects of rearing condition and aging. The latter analysis demonstrated that the learning rate of rats reared under enriched conditions was faster than that of rats reared under standard social conditions. Short-term (3-month) exposure also had positive effects on cognitive function in both adult (11-month-old) and aged (22-month-old) animals. The effect of long-term exposure to an enriched environment starting at weaning was much greater than that of short-term exposure in aged rats, whereas the effects of both long-term and short-term exposure were almost the same in adult rats. These results show that aged animals still have appreciable plasticity in cognitive function, and suggest that environmental stimulation could benefit aging humans as well.

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