FGF-2 and S100beta immunoreactivities increase in reactive astrocytes, but not in microglia, in ascending dopamine pathways following a striatal 6-OHDA-induced partial lesion of the nigrostriatal system

Partial lesions were induced in rat midbrain dopamine ascending pathways by intrastriatal injection of 6-hydroxydopamine (6-OHDA), and after two weeks changes were observed in the immunoreactivities of S100beta, a calcium-binding protein, and basic fibroblast growth factor (FGF-2), which is neurotrophic. Semiquantitative microdensitometric image analysis revealed increased intensities of FGF-2 and S100beta immunostaining in putative glial profiles of the ipsilateral neostriatum, pars compacta (SNc) and reticulata (SNr) of the substantia nigra and ventral tegmental area (VTA). Double immunofluorescence and immunoperoxidase procedures, using antibodies against glial fibrillary acidic protein and OX-42, showed that these increased immunoreactivities were restricted to reactive astrocytes; they were not observed in reactive microglia. These results indicate that reactive astrocytes may exert paracrine trophic actions through S100beta and FGF-2 in the midbrain dopamine ascending pathways after striatal 6-OHDA treatment. Interactions between S100beta and FGF-2 may be relevant to neuronal maintenance and repair following dopamine injury.     

A model of Taura syndrome virus (TSV) epidemics in Litopenaeus vannamei

Taura syndrome virus (TSV) is a highly virulent pathogen of Litopenaeus vannamei, has affected shrimp aquaculture throughout the world, and threatens wild populations. Despite its importance, little work has been done on the pathogen's formal epidemiology. Therefore we developed a compartment model for epidemics of TSV in closed populations of L. vannamei. The model includes five compartments, uninfected susceptible, prepatently infected, acutely infected, chronically infected, and dead infected shrimp. The transmission coefficients, patency coefficient, virulence coefficients, and removal coefficient (disappearance of dead infected shrimp) control the dynamics of the model. We estimated the coefficients in laboratory studies and inserted the estimates in the model to characterize TSV epidemics and to estimate the basic reproduction ratio R(0) and threshold density for TSV epidemics in L. vannamei. Further we examined through computer simulation the effect of varying the coefficients on R(0). Decreases in transmission decrease R(0), decreases in virulence increase R(0), increases in patency do not affect R(0), and increases in recovery most likely increase R(0) but under some conditions might decrease it.     

Inhibitory effect of bFGF on endochondral heterotopic ossification

Basic fibroblast growth factor (bFGF) is reported to stimulate repair of fracture and bony defects in in vivo animal studies. However, most studies performed in vitro demonstrate inhibitory effect of bFGF on cartilage and bone differentiation. To understand the discrepancy observed in in vivo and in vitro studies, we evaluated the effect of bFGF on chondro-osteogenesis initiated by bone matrix powder (MP). MP was implanted in the murine hamstring muscles with or without administration of bFGF. Injection of 1 microg of bFGF markedly reduced the size of heterotopic bone induced by MP, as detected by X-ray. Injection of 10 microg of bFGF completely inhibited ossification and only fibrous tissues were observed at the site of MP implantation. The expressions of alkaline phosphatase and osteocalcin mRNAs, markers for bone differentiation, were completely suppressed by 10 microg of bFGF. These results demonstrate the inhibitory effect of bFGF on endochondral ossification in vivo, implicating a precaution for its use in musculo-skeletal disorders.     

Response of coastal phytoplankton to ammonium and nitrate pulses: seasonal variations of nitrogen uptake and regeneration

Seasonal variation in uptake and regeneration of ammonium and nitrate in a coastal lagoon was studied using ¹⁵N incorporation in particulate matter and by measuring changes in particulate nitrogen. Uptake and regeneration rates were two orders of magnitude lower in winter than in summer. Summer uptake values were 2.8 and 2.2 mol N.l^–1.d^–1 for ammonium and nitrate, respectively. Regeneration rates were 2.9 and 2.1 mol N.l^–1.d^–1 for ammonium and nitrate respectively. Regeneration/uptake ratios were often below one, indicating that water column processes were not sufficient to satisfy the phytoplankton nitrogen demand. This implies a role of other sources of nitrogen, such as macrofauna (oysters and epibionts) and sediment. Phytoplankton was well adapted to the seasonal variations in resources, with mixotrophic dinoflagellates dominant in winter, and fast growing diatoms in summer. In winter and spring, ammonium was clearly preferred to nitrate as a nitrogen source, but nitrate was an important nitrogen source in summer because of high nitrification rates. Despite low nutrient levels, the high rates of nitrogen regeneration in summer as well as the simultaneous uptake of nitrate and ammonium allow high phytoplankton growth rates which in turn enable high oyster production.     

Is xanthine dehydrogenase involved in response of pea plants (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.) to salinity or ammonium treatment?

The effect of salinity and different nitrogen sources on the level of xanthine dehydrogenase (XDH) activity in roots and leaves of pea plants was investigated. Two bands of xanthine dehydrogenase activity (XDH-R2, XDH-R3) were detected in roots after native PAGE and staining with hypoxanthine as substrate. Only one band of XDH activity (XDH-L1) was detected in leaf extracts. Within leaves of three different ages the highest XDH activity was detected in young leaves both under control as well as stress conditions. Salinity did not affect significantly the activity of XDH in pea roots, however, depressed XDH activity in leaves. A significant increase of XDH activity both in roots and leaves was observed only when ammonium was applied as the sole N source. Increased concentration of ureides in the xylem sap of pea plants was observed for both ammonium and high salt treatments, although the higher content of ureides in the xylem sap of 100 mM NaCl treated plants may be rather a result of lower rate of exudation from roots than of increased root ureide biosynthesis. Thus, the changes of root and leaf XDH activity in pea plants seem to be tightly correlated with ureide synthesis that is induced by NH ₄ ⁺ , the product of N fixation, and rather than by salinity. A contribution of pea XDH in increased oxygen species or uric acid production under saline conditions seems to be less than likely.     

Nitrogen use efficiency by a slow-growing species as affected by CO2 levels, root temperature, N source and availability

This study examines the importance of N source and concentration on plant response to distinct CO₂ concentrations and root temperatures. The experimental design of this work was a factorial combination of: CO₂ concentration, nitrogen concentration, nitrogen source and root temperature. Carob (Ceratonia siliqua L.) was assessed as a potential model of a slow growing Mediterranean species.

The results showed that: 1) biomass increment under high CO₂ varied between 13 and 100 percnt; in relation to plants grown under the same conditions but at ambient CO₂ concentrations, depending on the root temperature and nitrogen source; 2) nitrate-fed plants attained a larger increase in biomass production compared to ammonium-fed ones. This performance seems to be linked to the co-ordinated regulation of the activities of glutamine synthetase and sucrose phosphate synthase. The variations in the magnitude and nature of growth responses to elevated CO₂ observed resulted in substantial changes in the chemical composition of the plant material and consequently in plant nitrogen use efficiency.

Although performed with seedlings and under controlled conditions, this work emphasizes the importance of the nitrogen source used by the plants, a factor rarely taken into consideration when forecasting plant responses to global changes. Particularly, the results presented here, highlight the potential for uncoupling biomass accumulation from increment of air CO₂ concentration and show that more than nitrogen availability N source may offset positive plant growth responses under elevated CO₂ and root temperature.     

The specific transport system for lysine is fully inhibited by ammonium in Penicillium chrysogenum: An ammonium-insensitive system allows uptake in carbon-starved cells

The regulation exerted by ammonium and other nitrogen sources on amino acid utilization was studied in swollen spores of Penicillium chrysogenum. Ammonium prevented the L-lysine, L-arginine and L-ornithine utilization by P. chrysogenum swollen spores seeded in complete media, but not in carbon-deficient media. Transport of L-[¹⁴C]lysine into spores incubated in presence of carbon and nitrogen sources was fully inhibited by ammonium ions (35 mM). However, in carbon-derepressed conditions (growth in absence of sugars, with amino acids as the sole carbon source) L-[¹⁴C]lysine transport was only partially inhibited. Competition experiments showed that L-lysine (1 mM) inhibits the utilization of L-arginine, and vice versa, L-arginine inhibits the L-lysine uptake. High concentrations of L-ornithine (100 mM) prevented the L-lysine and L-arginine utilization in P. chrysogenum swollen spores. In summary, ammonium seems to prevent the utilization of basic amino acids in P. chrysogenum spores by inhibiting the transport of these amino acids through their specific transport system(s), but not through the general amino acid transport system that is operative under carbon-derepression conditions.     

In vitro cytotoxicity of Acanthamoeba spp. isolated from contact lens containers in Korea by crystal violet staining and LDH release assay

In order to observe the cytotoxicity of Acanthamoeba spp., which were isolated from contact lens containers as ethiological agents for the probable amoebic keratitis in Korea, the crystal violet staining method and LDH release assay were carried out. In the crystal violet staining method, among eight contact lens container isolates, isolate 3 (Acanthamoeba KA/LS5) showed 83.6% and 81.8% of cytotoxicity, and isolate 7 (Acanthamoeba KA/LS37) showed 28.2% and 25.1% of cytotoxicity, in 1 mg/ml and 0.5 mg/ml lysate treatments, respectively. Acanthamoeba culbertsoni and A. healyi showed 84.0% and 82.8% of cytotoxicity. Similar results were observed in A. castellanii and A. hatchetti which showed 83.6% and 75.5% of cytotoxicity. Acanthamoeba royreba and A. polyphaga showed 9.0% and 1.7% of cytotoxicity. In the LDH release assay, isolate 3 (20.4%) showed higher cytotoxicity than other isolates in 1 mg/ml lysate treatment. The results provide that at least isolate 3 has the cytotoxic effect against CHO cells and seems to be the pathogenic strain.     

Regulation of ectodermal differentiation in Xenopus laevis animal caps treated with TPA and ammonium chloride

Animal caps isolated from Xenopus laevis embryos at the blastula stage were treated sequentially with NH₄Cl, a known cement gland inducer, and with 12-O-tetradecanoyl phorbol-13-acetate (TPA), a known neural inducer. The two artificial inducers were also used in reverse order to see if they can mimic the natural inducers acting during the progressive determination of the ectodermal organ. Immunofluorescence and whole-mount in situ hybridization were used to study the expression of tubulin, taken to indicate an early step on the pathway of cell elongation, and neural cell adhesion molecule (N-CAM) taken to indicate an early step in the determination of the nervous system. The expression of XCG-1, a marker of early specification of the cement gland, was also studied. The results showed that the two artificial inducers can mimic the effects of the natural inducers in animal cap explants. The TPA behaves like a neural inducer, reducing the number and the extension of the cement gland when added to the medium in addition to NH₄Cl, before or after NH₄Cl treatment. In the process of cement gland/neural induction, it is possible to redirect the ectoderm already specified as cement gland to neural tissue, but it does not seem possible to respecify the neural tissue as cement gland. Moreover, the animal caps were also cut into dorsal and ventral parts and the two halves were treated separately. The results were similar to those obtained with treatment of the entire animal cap, suggesting that a dorsal-ventral pattern is not yet established before the gastrula stage, and that in normal embryos there are boundaries between the effects of different inducers.