References: Hair growth and hair loss
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A major reorganization of afferent and efferent nerve terminals, concomitant to significant neuronal cell loss and pruning of superfluous fibers, takes place during the development of the organ of Corti, prior to the onset of hearing. We examined the spatio/temporal distribution of subtype-specific AMPA- and N-methyl-d-aspartate (NMDA)-selective glutamate receptor proteins in postnatal inner ears from rats during this critical period. From the first postnatal day onwards, GluR2/3 receptor subtypes appeared in nerve endings of afferent fibers associated with inner and outer hair cells. During the following 2 weeks, GluR2/3 receptors were downregulated in exchange for GluR4 receptors. In parallel efferents projecting from the medial olivocochlear complex to the outer hair cells underwent synaptogenesis and efferents projecting from the lateral olivocochlear complex to the inner hair cells appeared to change contacts to the dendrites of afferents. Concomitant to these events, NMDA receptor subtypes NR1 and NR2A transiently appeared in hair cells as well as afferent and efferent fibers. Recently, we described a temporary expression of the neurotrophin receptor trkB in hair cells, coincident to the growth (GAP-43) and synaptogenesis (synaptophysin) of efferents. Here, we show that trkB was expressed together with NR1 receptors in hair cells in high spatio/temporal correlation with the rearrangement of afferents and efferents. Cochlea NMDA receptors may, therefore, be a part of the mechanism by which, in addition to neurotrophic activity, the mature phenotype of cochlea neurons is acquired through activity-dependent processes.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9011399&dopt=Abstract
Dev Biol. 1997 Jan 15;181(2):257-67.
Targeted mutation in beta1,4-galactosyltransferase leads to pituitary insufficiency and neonatal lethality.
Lu Q, Hasty P, Shur BD.
Department of Biochemistry and Molecular Biology, M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Despite much attention, the function of oligosaccharide chains on glycoproteins and glycolipids remains largely unknown. Our understanding of oligosaccharide function in vivo has been limited to the use of reagents and targeted mutations that eliminate entire classes of oligosaccharide chains. However, most biological functions for oligosaccharides have been attributed to specific terminal sequences on these glycoside chains; yet, there have been few studies that examine the consequences of modifying terminal oligosaccharide structures in vivo. To address this issue, mice were created bearing a targeted mutation in beta1,4-galactosyltransferase (GalTase), an enzyme responsible for elaboration of many of the proposed biologically active carbohydrate epitopes. Most GalTase-null mice died within the first few weeks after birth and were characterized by stunted growth, thin skin, sparse hair, and dehydration. In addition, spermatogenesis was delayed, the lungs were poorly developed, and the adrenal cortices were poorly stratified. The few surviving adults had puffy skin (myxedema) and difficulty delivering pups at birth (dystocia) and failed to lactate (agalactosis). All of these defects are consistent with endocrine insufficiency, which was confirmed by markedly decreased levels of serum thyroxine. The polyglandular nature of the endocrine insufficiency is indicative of a failure of the anterior pituitary gland to stimulate the target endocrine organs. Previous in vitro studies have suggested that incomplete glycosylation of anterior pituitary hormones leads to the creation of hormone antagonists, which down-regulate subsequent endocrine function, producing polyglandular endocrine insufficiency. In GalTase-null mice, the anterior pituitary acquired a normal secretory phenotype during neonatal development indicative of normal glycoprotein hormone synthesis and secretion. However, as expected, the gland was devoid of GalTase activity. These results support a requirement for terminal oligosaccharide sequences for anterior pituitary hormone function. The fact that approximately 10% of the GalTase-null mice survive the neonatal period indicates the presence of a previously unrecognized compensatory pathway for glycoprotein hormone glycosylation and/or action.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9013935&dopt=Abstract
Ann Hum Biol. 1997 Jan-Feb;24(1):19-31.
Maturity-associated variation in peak oxygen uptake in active adolescent boys and girls.
Malina RM, Beunen G, Lefevre J, Woynarowska B.
Michigan State University, East Lansing, USA.
Maturity-associated variation in peak O2 uptake was considered in a longitudinal sample of 47 boys and 40 girls who were enrolled in sports schools. The children were followed annually from 11 to 14 years of age. O2 uptake and heart rate were measured during a maximal exercise test on a cycle ergometer. For boys, individual velocity curves were used to operationally define maturity groups: early-decreasing velocities from 11 to 14 years, n = 9; average-velocities reaching a peak and then decreasing, n = 7; and late-increasing velocities from 11 to 14 years, n = 31. The distributions of stages of genital and public hair development were consistent with early, average and late maturity status designation based on velocities of stature growth. Prospectively collected ages at menarche were used to define maturity groups in girls: early--< 12.0 years, n = 7, 10.8 +/- 0.6 years; average--12.0.12.9 years, n = 20, 12.4 +/- 0.3 years; and late-- > or = 13.0 years, n = 13, 13.5 +/- 0.4 years. Early maturing boys had a greater O2 uptake at each observation period. Early and average maturing girls did not differ in maximal O2 uptake, but both had greater O2 uptake than late maturers. When expressed per unit body mass, differences among the three maturity groups of boys were reduced and not significant. Late maturing girls tended to have greater maximal O2 uptake per unit body mass than early and average maturing girls, but the differences were not significant at all ages. However, with body mass at the first observation as the covariate in analyses of covariance, the three maturity groups of boys differed significantly in peak VO2 at each observation, while the three maturity groups of girls did not. Thus, removing the confounding effect of body mass on O2 uptake by simply dividing the measured values by mass is of limited utility.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9022903&dopt=Abstract
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