A long-term perspective of dissolved organic carbon transport in Sycamore Creek, Arizona, USA

Dissolved organic carbon (DOC) dynamics were examined over five years (1989–1993) in Sycamore Creek, a Sonoran Desert stream, specifically focusing on DOC concentration in surface and hyporheic waters, and rates of export. In 1989 and 1990, the years of lowest stream discharge (0.08 and 0.04 m³ s^–1 annual mean of daily discharge, respectively), DOC was high, averaging 7.37 and 6.22 mgC l^–1 (weighted annual means). In contrast, from 1991 through 1993, a period of increased flow (1.1, 1.2 and 4.3 m³ s^–1), concentration was significantly lower (P<0.001) with annual mean concentrations of 3.54, 3.49 and 3.39 mgC l^–1. Concentration exhibited little spatial variation between two sampling stations located 6 km apart along the mainstem or between surface and hyporheic waters. Annual export of DOC from Sycamore Creek varied 100-fold over the five-year period from a mean rate of only 24 kgC d^–1 in 1990 to 2100 kgC d^–1 in 1993. Ninety percent of DOC was exported by flows greater than 2.8 m³ s^–1, and 50% during flows greater than 27 m³ s^–1; flows of 2.8 and 24 m³ s^–1 occurred only 9 and 1% of the time. The export of organic matter in Sycamore Creek appears to be coupled to El Niño-Southern Oscillation phenomena. The years of highest export, 1991–1993, had El Niño conditions while 1989 and 1990 had medial conditions.     

Evidence for a correlation between ambient cholesterol levels and soluble plasma sialyltransferase enzyme activity

While soluble forms of the sialyltransferase (sialyl-T) enzyme have been detected in significant quantities in serum, the exact source(s) of the enzyme, or the factors controlling its secretion are poorly understood. In this study, we have examined the relationship between ambient plasma cholesterol concentrations and sialyl-T activities and also levels of constituent plasma sialoglycoproteins (SGP). There was an inverse relationship between levels of the 2,6 sialyl-T enzyme and both total plasma cholesterol and HDL, although no such relationship was observed for the 2,3 enzyme. While there was no correlation between total cholesterol and the levels of plasma SGPs, there was an inverse relationship between the HDL component and 2,3 SGPs.     

The Hypothalamic-Pituitary-Adrenal Axis in Obesity

The hypothalamic-pituitary-adrenal (HPA) axis normally maintains the concentration of Cortisol within a narrow range with a diurnal variation characterized by higher Cortisol concentrations in the morning and reduced levels in the evening. Excessive or deficient secretion of Cortisol is associated with pathologic changes. Obesity has been linked with age, sex and racial alterations in the functioning of the HP A axis which are reviewed. The possible relationship of altered HPA axis activity with the long-term complications of obesity are considered.     

Vertical bars on male Xiphophorus multilineatus: a signal that deters rival males and attracts females

We examined the function of the vertical bar pattern on maleswordtails (Xiphophorus multilinneatus) as a signal in bothmale-male competition and female choice. This pattern had previouslybeen described as an aggressive signal because males intensifiedthe bars during male-male encounters in the laboratory. Ourfield observations supported this observation and also showedthat bars intensified when males courted females. The intensityof bars was correlated with access to females in the field.Within the size range of males that have bars, however, neitherbar number nor male size appeared to influence access to females.We used freeze-branding to remove the bars from males in thelaboratory so that we could control for characters correlatedwith bar intensity, and tested males and females separatelyso that we could separate the influence of these two componentsof sexual selection. We compared the responses of males andfemales to males that had their bars removed and control malesfreeze-branded between the bars. Test males responded more aggressivelyto males without bars as compared to control males. In addition,females showed a preference for control males over males thathad their bars removed. These results suggest that the barsmay function as a signal that deters rival males and attractsfemales.     

Taxonomy of Pyramimonas obovata and other observations on the subgenus Vestigifera of Pyramimonas (Prasinophyceae, Chlorophyta)

A vestigiferan species commonly referred to as Pyramimonas obovata N. Carter has been redescribed as P. melkonianii sp, nov. Characters of this species and a further six (P. disomata Butcher ex McFadden, Hill et Wetherbee, P. mantoniae Moestrup et Hill, P. mitra Moestrup et Hill. P. moestrupii McFadden, P. aff. nephroidea McFadden, P. orientalis Butcher ex McFadden, Hill et Wetherbee) isolated from South African waters are used to define further the subgenus Vestigifera McFadden. This includes a unique chloroplast shape and basal hyaline region with stellate or cruciform vacuoles, a transitional plate-like structure in the flagellum, and a different microtubular root system. The proximal set of basal body connectives were found to be remarkably symmetrical and like those of the subgenus Trichocystis McFadden, and a duct fibre was found associated with the Id root in all currently investigated species. The validity of the larger body (box and crown) scales as taxonomic markers at a fine level is also questioned.     

Platelet activating factor (PAF) stimulates release of PGI2 from inflamed rabbit gallbladder cell cultures

This study examines the hypothesis that PAF stimulates release of PGI₂ from inflamed rabbit gallbladder explant cell cultures. New Zealand white rabbits underwent bile duct ligation for 72 h (72 h BDL), or sham operation, Sham and 72 h BDL gallbladder explants were placed in culture, and the cells grown to 75% confluence. The cells were exposed to increasing concentrations of PAF for 60 min. The media analyzed for eicosanoid release by EIA and the cells analyzed for cyclooxygenase and prostacyclin synthase content by immunoblot analysis. PAF increased release of 6-keto-PGF_1α from the 72 h BDL gallbladder cell cultures in a dose-related manner which was inhibited by indomethacin preincubation by 90%. The increased 72 h BDL cell release of 6-keto-PGF_1α was not associated with changes in the content of cyclooxygenase or prostacyclin synthase. PAF did not alter eicosanoid release from sham control cell cultures. These data suggest that PAF can only up-regulate endogenous 6-keto-PGF_1α release from the 72 h BDL cells that had been previously stimulated by inflammation. PAF may thus contribute to gallbladder distention and injury by chronic stimulation of inflamed gallbladder PGI₂ release.     

Polymorphism analysis of the prion gene in BSE-affected and unaffected cattle

Polymerase chain reaction (PCR) primers designed to amplify the octapeptide repeat region of the bovine prion gene were used to test the association of genotypes with bovine spongiform encephalitis (BSE) in 56 BSE-affected and 177 unaffected animals. Three alleles (A, B, C) were detected as single-strand conformation polymorphisms (SSCPs) and two alleles (1,2 representing six or five copies of the octapeptide repeat respectively) were detected as amplified double-strand fragment length polymorphisms (AMFLPs). Observed genotypes of SSCPs and AMFLPs were analysed by x-square. The SSCP genotypes of nuclear family members of animals with BSE and BSE-affected animals were different (P < 0.001, P < 0.01) from unrelated animals of the same breed without BSE. No genotypic differences were found between the BSE-affected animals and their relatives (P > 0.469). No AMFLP genotypic differences were detected between BSE-affected animals, their relatives, unrelated animals of the same breed or animals of different breeds (P > 0.05). These data suggest that BSE-affected animals and their relatives are more likely to have the AA SSCP genotype than unrelated animals of the same breed or animals of different breeds.