Annals of the New York Academy of Sciences
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Ann. N. Y. Acad. Sci. · Nov 1998
Alterations in the neurotrophic factors BDNF, GDNF and CNTF in the regenerating olfactory system.
Neurogenesis, axonal outgrowth and synapse formation are usually restricted to specific stages during central nervous system development, but the mature olfactory system maintains these capacities. The cycle of neuronal turnover can be experimentally induced by surgical ablation of the olfactory bulb (OB). We are interested in the growth factor regulation of these processes and the trophic role played by the target tissue, the OB. ⋯ Expression of CNTF by both the basal cells and the ORNs suggests that it may play an integral role in this neuronal differentiation pathway. Finally, the expression of GDNF exclusively by mature ORNs in the ON, its presence in the target cells in the OB and abolition of expression by bulbectomy, suggests that it may be target-derived. This provides a major mechanism by which the bulb could exert trophic influences on ORNs.
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Psychophysical and electrophysiological studies indicated that the umami substances have no enhancing activity on other primary tastes. Experiments using amiloride clearly show that the umami component of canine chorda tympani nerve response to umami substances is independent of the salt component. Single fiber analysis of the responses of the mouse glossopharyngeal nerve and the monkey primary taste cortex neuron show that the responses to umami substances are independent of other primary tastes. ⋯ The order of intensity of umami taste induced by a mixture of 0.5 mM GMP and 1.5 mM of various agonists for the glutamate receptors was glutamate > ibotenate > DL(+)-2-amino-4-phosphonobutyric acid (DL-AP4)-(+)-1- aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD). Kainate, N-methyl-D-aspartate (NMDA) and (RS)--amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), which are agonists for ionotropic receptors, have no umami taste. It was concluded that the umami receptor is not identical to any of known glutamate receptors, and there seems to be a unique receptor for umami.
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Ann. N. Y. Acad. Sci. · Nov 1998
ReviewOxidative damage and mutation to mitochondrial DNA and age-dependent decline of mitochondrial respiratory function.
Mitochondrial respiration and oxidative phosphorylation are gradually uncoupled, and the activities of the respiratory enzymes are concomitantly decreased in various human tissues upon aging. An immediate consequence of such gradual impairment of the respiratory function is the increase in the production of the reactive oxygen species (ROS) and free radicals in the mitochondria through the increased electron leak of the electron transport chain. Moreover, the intracellular levels of antioxidants and free radical scavenging enzymes are gradually altered. ⋯ The respiratory enzymes containing the mutant mtDNA-encoded defective protein subunits inevitably exhibit impaired respiratory function and thereby increase electron leak and ROS production, which in turn elevates the oxidative stress and oxidative damage of the mitochondria. This vicious cycle operates in different tissue cells at different rates and thereby leads to the differential accumulation of mutation and oxidative damage to mtDNA in human aging. This may also play some role in the pathogenesis of degenerative diseases and the age-dependent progression of the clinical course of mitochondrial diseases.
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Loss of bone is an almost universal accompaniment of aging that proceeds at an average rate of 0.5-1% per annum from midlife onwards. There are at least four nutrients involved in this process: calcium, salt, protein, and vitamin D, at least in women. The pathogenesis of osteoporosis in men is more obscure. ⋯ Low protein intakes in third world countries may partially protect against osteoporosis. Vitamin D (sometimes called a nutrient and sometimes a hormone) is important because age-related vitamin D deficiency leads to malabsorption of calcium, accelerated bone loss, and increased risk of hip fracture. Vitamin D supplementation has been shown to retard bone loss and reduce hip fracture incidence in elderly women.