Modelling production and biomasses of zoobenthos in lakes

This work presents a dynamic model to predict zoobenthos in lakes. The model has been developed within the framework of a more comprehensive lake ecosystem model, LakeWeb, which also accounts for the following functional groups of organisms, phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), macrophytes, prey fish and predatory fish. This work also presents a new data-base for zoobenthos in lakes. Many of the lakes included in this study are situated in the former Soviet Union. They were investigated during the Soviet period and those results have been largely unknown in the West. Using this data-base, this work also presents new empirical models for zoobenthos. The new dynamic model gives seasonal variations (the calculation time, dt, is 1 week using Euler's method and enough iterations to get stable solutions). The basic aim of the dynamic model is that it should capture general functional and structural patterns in lakes. We have demonstrated by several model tests along limnological gradients (total phosphorus concentrations, pH, lake colour, latitude and lake size) that the dynamic model gives predictions that agree well with the values given by the empirical regressions, and also expected and requested divergences from these regressions when they do not provide sufficient resolution. It would have been very difficult indeed to carry out such tests regarding ecosystem responses using traditional methods with extensive field studies in a few lakes. We have given algorithms for (1) production of zoobenthos from eating macrophytes, benthic algae and sediments, (2) elimination (related to the turnover time of zooplankton), and (3) zoobenthos consumption by prey fish, and the factors influencing these processes/rates. The model is driven by data easily accessed from standard monitoring programs or maps a prerequisite for practical utility in contexts of lake management.     

Melting of cross-linked DNA v. cross-linking effect caused by local stabilization of the double helix

DNA interstrand cross-links are usually formed due to bidentate covalent or coordination binding of a cross-linking agent to nucleotides of different strands. However interstrand linkages can be also caused by any type of chemical modification that gives rise to a strong local stabilization of the double helix. These stabilized sites conserve their helical structure and prevent local and total strand separation at temperatures above the melting of ordinary AT and GC base pairs. This local stabilization makes DNA melting fully reversible and independent of strand concentration like ordinary covalent interstrand cross-links. The stabilization can be caused by all the types of chemical modifications (interstrand cross-links, intrastrand cross-links or monofunctional adducts) if they give rise to a strong enough local stabilization of the double helix. Our calculation demonstrates that an increase in stability by 25 to 30 kcal in the free energy of a single base pair of the double helix is sufficient for this "cross-linking effect" (i.e. conserving the helicity of this base pair and preventing strand separation after melting of ordinary base pairs). For the situation where there is more then one stabilized site in a DNA duplex (e.g., 1 stabilized site per 1000 bp), a lower stabilization per site is sufficient for the "cross-linking effect" (18 - 20 kcal). A substantial increase in DNA stability was found in various experimental studies for some metal-based anti-tumor compounds. These compounds may give rise to the effect described above. If ligand induced stabilization is distributed among several neighboring base pairs, a much lower minimum increase per stabilized base pair is sufficient to produce the cross-linking effect (1 bp- 24.4 kcal; 5 bp- 5.3 kcal; 10 bp- 2.9 kcal, 25 bp- 1.4 kcal; 50 bp- 1.0 kcal). The relatively weak non-covalent binding of histones or protamines that cover long regions of DNA (20- 40 bp) can also cause this effect if the salt concentration of the solution is sufficiently low to cause strong local stabilization of the double helix. Stretches of GC pairs more than 25 bp in length inserted into poly(AT) DNA also exhibit properties of stabilizing interstrand cross-links.     

Development of Agrobacterium tumefaciens C58-induced plant tumors and impact on host shoots are controlled by a cascade of jasmonic acid,auxin, cytokinin,ethylene and abscisic acid

The development of Agrobacterium tumefaciens-induced plant tumors primarily depends on the excessive production of auxin and cytokinin by enzymes encoded on T-DNA genes integrated into the plant genome. The aim of the present study was to investigate the involvement of additional phytohormone signals in the vascularization required for rapid tumor proliferation. In stem tumors of Ricinus communis L., free auxin and zeatin riboside concentrations increased within 2 weeks to 15-fold the concentrations in control stem tissue. Auxin and cytokinin immunolocalization revealed the highest concentrations within and around tumor vascular bundles with concentration gradients. The time-course of changes in free auxin concentration in roots was inversely correlated with that in the tumors. The high ethylene emission induced by increased auxin- and cytokinin correlated with a 36-fold accumulation of abscisic acid in tumors. Ethylene emitted from tumors and exogenously applied ethylene caused an increase in abscisic acid concentrations also in the host leaves, with a diminution in leaf water vapor conductance. Jasmonic acid concentration reached a maximum already within the first week of bacterial infection. A wound effect could be excluded. The results demonstrate the concerted interaction of a cascade of transiently induced, non-T-DNA-encoded phytohormones jasmonic acid, ethylene and abscisic acid with T-DNA-encoded auxin and zeatin riboside plus trans-zeatin, all of which are required for successful plant tumor vascularization and development together with inhibition of host plant growth.     

Analysis of multidimensional neural activity via CNN-UM

In this paper we show that the Cellular Nonlinear Network Universal Machine (CNN-UM) is an excellent tool for analyzing time series of multidimensional binary signals. The developed algorithm is dedicated to process electrophysiological multi-neuron recordings: our aim is to find specific multidimensional activity patterns, which may reflect higher order functional cell-assemblies. The analysis consists of two parts: first, the occurrences of different patterns are counted, then the statistical significance of each occurrence frequency is calculated separately.     

TIP,a T-cell factor identified using high-throughput screening increases survival in a graft-versus-host disease model

A coordinated effort combining bioinformatic tools with high-throughput cell-based screening assays was implemented to identify novel factors involved in T-cell biology. We generated a unique library of cDNAs encoding predicted secreted and transmembrane domain-containing proteins generated by analyzing the Human Genome Sciences cDNA database with a combination of two algorithms that predict signal peptides. Supernatants from mammalian cells transiently transfected with this library were incubated with primary T cells and T-cell lines in several high-throughput assays. Here we describe the discovery of a T cell factor, TIP (T cell immunomodulatory protein), which does not show any homology to proteins with known function. Treatment of primary human and murine T cells with TIP in vitro resulted in the secretion of IFN-gamma, TNF-alpha, and IL-10, whereas in vivo TIP had a protective effect in a mouse acute graft-versus-host disease (GVHD) model. Therefore, combining functional genomics with high-throughput cell-based screening is a valuable and efficient approach to identifying immunomodulatory activities for novel proteins.     

CCK-58 is the only detectable endocrine form of cholecystokinin in rat

CCK-58 differs from CCK-8 in patterns of expression of pancreatic secretion of fluid and amylase and gallbladder contraction. These differences have physiological relevance only if CCK-58 release is stimulated by nutrients entering the intestine and if CCK-58 circulates in sizeable amounts. In this study, we report that when radiolabeled CCK-58 is added to rat blood and plasma is formed, there is extensive loss and degradation of the radioactive peptide. Therefore, a new method was developed to minimize loss and degradation of this label. This method recovered >85% of the label with no detectable degradation. Furthermore, the optimized method recovered all unlabeled exogenous cholecystokinin molecular forms in >80% yields. Blood from fasted rats and rats in which cholecystokinin release was stimulated by the trypsin inhibitor camostat contained only CCK-58 (3.5 +/- 0.5 and 17 +/- 1.5 fmol/ml, respectively). Because CCK-58 predominates in the blood, this molecular form should be used in studies on the physiology and pathophysiology of cholecystokinin.     

Melatonin reduces glial reactivity in the hippocampus, cortex, and cerebellum of streptozotocin-induced diabetic rats

Hyperglycemia plays a critical role in the development and progression of diabetic neuropathy. One of the mechanisms by which hyperglycemia causes neural degeneration is via the increased oxidative stress that accompanies diabetes. Metabolic and oxidative insults often cause rapid changes in glial cells. Key indicators of this response are increased synthesis of glial fibrillary acidic protein (GFAP) and S100B, both astrocytic markers. In the present study, we examined glial reactivity in hippocampus, cortex, and cerebellum of streptozotocin (STZ)-induced diabetic rats by determining the expression of GFAP and S-100B and we evaluated the effect of melatonin on the glial response. Western blot measurement of contents in brain regions after 6 weeks of STZ-induced diabetes indicated significant increases in these constituents compared with those in nondiabetic controls. Administration of melatonin prevented the upregulation of GFAP in all brain regions of diabetic rats. Using GFAP immunohistochemistry, we observed an increase in GFAP immunostaining in the hippocampus of STZ-diabetic rats relative to levels in the control brains. Treatment with melatonin resulted in an obvious reduction of GFAP-immunoreactive astrocytes in hippocampus. Like GFAP, S100B levels also were increased in all three brain areas of diabetic rats, an effect also reduced by melatonin treatment. Finally, the levels of lipid peroxidation products were elevated as a consequence of diabetes, with this change also being prevented by melatonin. These results suggest that diabetes causes increased glial reactivity possibly due to elevated oxidative stress, and administration of melatonin represents an achievable adjunct therapy for preventing gliosis.     

In Vitro susceptibility of 137 Candida sp. Isolates from HIV positive patients to several antifungal drugs

Oropharyngeal candidiasis caused by various species of Candida is one of the most common infections in HIV seropositive or AIDS patients. Drug resistance among these yeasts is an increasing problem. We studied the frequency of resistance profile to fluconazole, itraconazole, ketoconazole, amphotericin B and terbinafine of 137 isolates of Candida sp. From HIV positive or AIDS patients with oropharyngeal candidiasis at Instituto de Inmunología, U.C.V. and the Hospital “Jose Ignacio Baldó”, Caracas Venezuela, using the well diffusion susceptibility test (Magaldi et al.). We found that nearly 10% of C. albicans isolates were primarily fluconazole resistant, 45% of C. albicans isolates from patients with previous treatment were resistant to fluconazole, of which 93% showed cross-resistance to itraconazole, and even about 30% of C. tropicalis (n = 13) were resistant to fluconazole and/or itraconazole. To this respect, several recent reports have been described antifungal cross-resistance among azoles. Therefore, we consider that C. tropicalis should be added to the growing list of yeast in which antifungal drug resistance is common. This report could be useful for therapeutic aspect in AIDS patients with oral candidiasis. This revised version was published online in July 2006 with corrections to the Cover Date.     

“In vitro” Antifungal activity of protease inhibitors

In the last five years, as HAART has become standard therapy in HIV seropositive or AIDS patients, changes have been noted in the numbers and types of opportunistic fungal infections in these cohorts of patients. Particularly, oropharyngeal candidiasis have become rare in HIV infected patients since the introduction of new anti-HIV drugs of the protease inhibitors type. At the Immunology Institute of the Universidad Central de Venezuela the most frequent protease inhibitors (PIs) used for the treatment of these patients have been: Nelfinavir (Viracept^TM, Roche),Indinavir (Crixivan^® Merck),Ritonavir (Norvir^®, Abbott),Saquinavir (Fortovase^®, Roche).Recently, we observed that recurrent candidiasis was less frequent and no Candidacould be isolated in our patients. A direct relation to the PIs was suspected. In order to assess the in vitro antifungal activity of the afore mentioned protease inhibitors on Candida sp., we used both the well diffusion test and the NCCLS broth microdilution test to assay 100 Candida sp. isolates from HIV seropositive or AIDS patients with syntomatic oropharyngeal Candida infection. In general, the data obtained with the well diffusion test were in agreement with those obtained by the broth microdilution test. All 100 isolates were susceptible to Saquinavir and 32 were susceptible to Indinavir using the NCCLS microdilution test,while 97 were susceptible to Saquinavir and 52 to Indinavir by the well diffusion test. From 17 C. albicans resistant to fluconazole, all were susceptible to Saquinavir by the NCCLS micro method and 16 by the well diffusion test. Our results showed anticandidal activity in vitro of PIs, mainly Saquinavir.This revised version was published online in October 2005 with corrections to the Cover Date.