The influence of inorganic silicon (Si) on pituitary-thyroid axis

The influence of silicon-treatment on the levels of TSH and thyroid hormones was studied in rats. Concentrations of thyrotropin (TSH), triiodothyronine (T₃), and thyroxine (T₄) were estimated in sera of rats receiving per os a soluble silicon compound—sodium metasilicate nonahydrate (Na₂SiO₃·9H₂O), dissolved in the animals' drinking water. An increase in the TSH level in the tested group was observed, without statistically significant differences in T₃ and T₄ concentrations between the two groups of animals. The results provide evidence for the influence of silicon on the endocrine balance. They could also prove that this chemical element is capable of modifying the rate of some hormones' synthesis.     

The genus Cabomba (Cabombaceae)–a taxonomic study

The genus Cabomba (Cabombaceae) is revised. Five species and three varieties are recognized: C. aquatica, C. palaeformis, C. furcata, C. haynesii and C. caroliniana including var. caroliniana , var. pulcherrima , and var. flavida var. nov. A basic chromosome number of x = 13 is proposed. Special emphasis has been given to pollen and seed morphology as revealed by SEM studies.     

EFFECT OF LEAF ANGLE AND ORIENTATION ON PHOTOSYNTHESIS AND WATER RELATIONS IN SILPHIUM TEREBINTHINACEUM

Leaf angle and orientation were measured for 217 leaves from two populations of Silphium terebinthinaceum Jacq., a prairie forb with large, unlobed leaves. Seventy-five percent of leaves measured had an angle of deviation from horizontal of more than 60°, and 60% were oriented within 15° of North. Incident Photon Flux Density (PFD), leaf temperature, photosynthesis, stomatal conductance to CO₂, internal CO₂ concentration, transpiration, and water use efficiency (WUE) were measured on 67 pairs of leaves with the axes oriented in either a North-South (N–S) or East–West (E–W) direction. Leaves with axes oriented N–S intercepted higher levels of PFD during morning and afternoon and exhibited higher diurnal rates of photosynthesis and WUE. Leaf temperature was reduced in N–S leaves during midday as compared to E–W leaves, and was lower in vertical leaves than in those in a horizontal position. Therefore, it was concluded that leaf orientation and verticality enhance carbon gain and minimize water loss—characteristics which may have adaptive significance in a hot, stressful prairie environment.     

Does photorespiration protect the photosynthetic apparatus in french bean leaves from photoinhibition during drought stress?

Dithiothreitol (DTT), an inhibitor of violaxanthin de-epoxidation and zeaxanthin formation in chloroplasts, inhibited blue-light-stimulated stomatal opening in epidermal peels of Vicia faba L. in a concentration-dependent fashion. Complete inhibition was observed at 3 mM DTT. The DTT effect was specific for the stomatal response to blue light, and the red-light-stimulated opening, which depends on photosynthetic reactions in the guard cells, was unaffected. Preirradiation of stomata in epidermal peels with increasing photon fluence rates of red light, prior to an incubation in 10 mol·m^-2·s^-1 of blue light and 100 mol·m^-2·s^-1 red light, resulted in a DTT-sensitive, blue-light-stimulated opening that was proportional to the fluence rate of the red light pre-treatment. Guard cells in epidermal peels and guard-cell protoplasts irradiated with red light showed increases in their zeaxanthin content that depended on the fluence rate of red light, or on the incubation time. The increases in zeaxanthin concentration were inhibited by DTT. The obtained results indicate that zeaxanthin could function as a photoreceptor mediating the stomatal responses to blue light.Abbreviation DTT dithiothreitol This work was supported by grants from the National Science Foundation and the US Department of Energy to E.Z.     

Seasonal variation in positional behavior of malagasy lemurs

I describe the positional behavior of four species of Malagasy lemur (Propithecus diadema, Eulemur fulvus rufus, Eulemur rubriventer,and Varecia variegata)at two times of year at Ranomafana National Park,Madagascar. There were significant seasonal differences in locomotor behavior in all species except P. diademaAmong the lemurids, leaping was more frequent and quadrupedism less frequent in the dry season. Only E. rubriventerexhibited seasonal differences in posture, and there were few seasonal differences in support use. The observed differences in positional behavior were not the result of differences in activity budget or in microhabitat use attributable to seasonal variation in resource use.     

Regulation of Phenylethanolamine N-Methyltransferase Gene Expression by Imidazoline Receptors in Adrenal Chromaffin Cells

Abstract: As adrenal medullary chromaffin cells express imidazoline binding sites in the absence of α₂-adrenergic receptors, these cells provide an ideal system in which to determine whether imidazolines can influence catecholamine gene expression through nonadrenergic receptors. This study evaluates the ability of clonidine and related drugs to regulate expression of the gene for the epinephrine-synthesizing enzyme phenylethanolamine N -methyltransferase (PNMT) in the rat adrenal gland and in bovine adrenal chromaffin cell cultures. In vivo, PNMT and tyrosine hydroxylase (TH) mRNA levels increase in rat adrenal medulla after a single injection of clonidine. Clonidine also dose-dependently stimulates PNMT mRNA expression in vitro in primary cultures of bovine chromaffin cells, with a threshold dose of 0.1 μ M . Other putative imidazoline receptor agonists, including cimetidine, rilmenidine, and imidazole-4-acetic acid, likewise enhance PNMT mRNA production showing relative potencies that correlate with their binding affinities at chromaffin cell I₁-imidazoline binding sites. The effects of clonidine on PNMT mRNA appear to be distinct from and additive with those exerted by nicotine. Moreover, neither nicotinic antagonists nor calcium channel blockers, which attenuate nicotine's influence on PNMT mRNA production, diminish clonidine's effects on PNMT mRNA. Although 100 μ M clonidine diminishes nicotine-stimulated release of epinephrine and norepinephrine in chromaffin cells, this effect appears unrelated to stimulation of imidazoline receptor subtypes. This is the first report to link imidazoline receptors to neurotransmitter gene expression.     

Clinical phenotype of nephrogenic diabetes insipidus in females heterozygous for a vasopressin type 2 receptor mutation

Nephrogenic diabetes insipidus (NDI) usually shows an X-linked recessive mode of inheritance caused by mutations in the vasopressin type 2 receptor gene (AVPR2). In the present study, three NDI families are described in which females show clinical features resembling the phenotype in males. Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and the absence of extra-renal responses to 1-desamino-8-d-arginine vasopressin was demonstrated in two of them. All affected females and two asymptomatic female family members were shown to be heterozygous for an AVPR2 mutation. Skewed X-inactivation is the most likely explanation for the clinical manifestation of NDI in female carriers of an AVPR2 mutation. It is concluded that, in female NDI patients, the possibility of heterozygosity for an AVPR2 gene mutation has to be considered in addition to homozygosity for mutations in the aquaporin 2 gene.     

Effect of dibutyryl cyclic AMP and dexamethasone on glutamine synthetase gene expression in rat astrocytes in culture

Astrocytes are the primary site of glutamate conversion to glutamine in the brain. We examined the effects of treatment with either dibutyryl cyclic AMP and/or the synthetic glucocorticoid dexamethasone on glutamine synthetase enzyme activity and steady-state mRNA levels in cultured neonatal rat astrocytes. Treatment of cultures with dibutyryl cyclic AMP alone (0.25 mM–1.0 mM) increased glutamine synthetase activity and steady state mRNA levels in a dose-dependent manner. Similarly, treatment with dexamethasone alone (10^–7–10^–5 M) increased glutamine synthetase mRNA levels and enzyme activity. When astrocytes were treated with both effectors, additive increases in glutamine synthetase activity and mRNA were obtained. However, the additive effects were observed only when the effect of dibutyryl cyclic AMP alone was not maximal. These findings suggest that the actions of these effectors are mediated at the level of mRNA accumulation. The induction of glutamine synthetase mRNA by dibutyryl cyclic AMP was dependent on protein synthesis while the dexamethasone effect was not. Glucocorticoids and cyclic AMP are known to exert their effects on gene expression by different molecular mechanisms. Possible crosstalk between these effector pathways may occur in regulation of astrocyte glutamine synthetase expression.Abbreviations used GS glutamine synthetase - dbcAMP dibutyryl cyclic AMP - MEM minimal essential medium - cyx cycloheximide - GRE glucocorticoid response element - CRE cyclic AMP response element     

Bioprocessing in space: Human cells attach to beads in microgravity

Attachment to a substrate and survival of human embryonic kidney (HEK) cells have been tested in an incubator installed in the flight-deck of the Space Shuttle ‘Challenger’ during its eighth mission.HEK cells are producing the enzyme urokinase and are presently investigated as candidates for electrophoretic separation in an apparatus developed and manufactured by McDonnell Douglas.Attachment of HEK cells to a substrate is mandatory for survival and production of urokinase after electrophoretic separation.Analysis of the samples shows that cells adhere, spread and survive in microgravity (< 10⁻³ ×g) conditions as well as the ground controls at 1 × g. This result represents an important step towards further bioprocessing in space.