Locking,intermittency, and bifurcations in a periodically driven pacemaker neuron: Poincaré maps and biological implications

Slowly adapting stretch receptor (SAO) pacemaker neurons, driven with periodic tugs, were analyzed by way of Poincaré mappings (Appendix). Two behaviors were apparent, i) Intermittency characterized previously unclear situations: discharges shifted irregularly between prolonged epochs where spike phases (relative to tugs) and intervals barely changed (slid), and brief bursts with marked variations (skipped), ii) Locking was well-known: phases and intervals remained almost fixed, regardless of the initiation. Changing frequencies, map domains with locking (ordered according to spikes/tugs ratios), alternated with intermittent ones. The best fit for any experimental map was a curve, not straight but certainly unidimensional, continuous and monotonic; it varied characteristically with frequency. This suggested relations called diffeomorphisms, implying periodicity and quasi-periodicity. Outcomes, expanding previous knowledge and meaningful biologically, were i)a precise, exhaustive behavior list (including between behavior transitions) and ii)a thorough understanding or model. This, in turn, provides norms for more specific models (single-variable ones suffice), constraints upon basic mechanisms (one variable, reflecting several real ones combined, should behave as the phase), and forecasts for future experimentation (e.g., unexamined tug frequencies and amplitudes).Supported by funds from CONACYT (PCEXCNA 040539) to ODM and a donation from Trent J. Wells Inc. to JPS     

Evidence from field nitrogen balance and 15N natural abundance data for the contribution of biological N2 fixation to Brazilian sugarcane varieties

Aims

In Brazil N fertilization of sugarcane (Saccharum spp.) is low compared to most other countries. ¹⁵N-aided studies and the occurrence of many N₂-fixing bacteria associated with cane plants suggest significant contributions from biological N₂ fixation (BNF). The objective of this study was to evaluate BNF contributions to nine cane varieties under field conditions using N balance and ¹⁵N natural abundance techniques.

Methods

The field experiment was planted near Rio de Janeiro in 1989, replanted in 1999 and harvested 13 times until 2004. Soil total N was evaluated at planting and again in 2004. Samples of cane leaves and weeds for the evaluation of ¹⁵N natural abundance were taken in 2000, 2003 and 2004.

Results

N accumulation of the commercial cane varieties and a variety of Saccharum spontaneum were persistently high and N balances (60 to 107?kg?N ha^?1?yr^?1) significantly (p?<?0.05) positive. The δ¹⁵N of leaf samples were lower than any of the weed reference plants and data obtained from a greenhouse study indicated that this was not due to the cane plants tapping into soil of lower ¹⁵N abundance at greater depth.

Conclusion

The results indicate that the Brazilian varieties of sugarcane were able to obtain at least 40?kg?N ha^?1?yr^?1 from BNF.     

Pastoralism in Northern Peru during Pre-Hispanic Times: Insights from the Mochica Period (100–800 AD) Based on Stable Isotopic Analysis of Domestic Camelids

Llama (Lama glama) and alpaca (Vicugna pacos) are the only large domesticated animals indigenous to the Americas. Pastoralism occupies a fundamental economic, social and religious role in Andean life. Today, camelid livestock are confined to the ecozone of the puna (above 3,500 masl), while their presence on the Pacific coast during pre-Hispanic times is attested by archaeological skeletal remains. This study aims to document herding practices on the northern Peruvian coast during the Early Intermediate Period (200 BC-600 AD) by gaining insights into diet, location of breeding and mobility of archaeological camelids from the funerary and ritual contexts of two Mochica sites, Uhle Platform in Huacas de Moche and El Brujo. The three first early years and the long-term life histories of the animals were documented by the combined bulk analysis of bone collagen (δ¹³C_col and δ¹⁵N_col) and bone structural carbonate (δ¹³C_bone and δ¹⁸O_bone) and the serial analysis of structural carbonate of molar tooth enamel (δ¹³C_enamel and δ¹⁸O_enamel). Mochica camelids were bred in the low and/or middle valleys, unlike their modern counterparts, who are restricted to highland puna C₃ pastures. Archaeological camelids had diverse and complex life histories, usually with substantial maize foddering. An ontogenetic switch in diet and possible residential mobility during the course of life were identified for some specimens. Although the inference of geographic origin from δ¹⁸O_bone and δ¹⁸O_enamel values was limited because of the lack of understanding of the influence of environmental and biological factors, tooth enamel analysis has great potential for exploring camelid herding practices and Andean pastoralism. Our study suggested that Mochica herders adapted their practices to the difficult lowland environment and that herding practices were varied and not restricted to breeding at higher altitudes. The role of maize in different aspects of the economic life of the Mochicas is also underlined.     

Oscillating chemiluminescence systems: state of the art

Oscillating chemiluminescence (CL) was reported for the first time about 30 years ago. Since then several systems based on addition of a chemiluminescent reagent to a known oscillator system or based on the light emitting features of one component of the oscillating system, have been described. This information, scattered in the scientific literature, is compiled in the present paper. Several oscillating CL systems, including those based on Belousov–Zhabotinskii and Orban oscillators, or horseradish peroxidase‐catalyzed reactions, among others, are critically presented. The application of this type of oscillatory systems is also discussed, in analytical chemistry and for educational purposes. Copyright © 2010 John Wiley & Sons, Ltd.     

Impact of pre-harvest burning versus trash conservation on soil carbon and nitrogen stocks on a sugarcane plantation in the Brazilian Atlantic forest region

Owing to the increased demand for ethanol biofuel from sugar cane, the area planted to this crop in Brazil has increased from 4.8 to 9.5 Mha since 2000. At the same time there has been pressure from environmental groups and others to cease the pre-harvest burning of cane, and today over 40% of the crop is harvested without burning, thus conserving the trash on the soil surface. While most trash decomposes during the year, it is generally assumed that this transition from burning to trash conservation will have benefits for cane productivity and increase soil carbon stocks. To investigate the possible benefits of this change of practice an experiment was carried out in the state of Espírito Santo, south-eastern Brazil, to investigate the long-term effects of the practice of pre-harvested burning compared to trash conservation on soil fertility and soil C and N stocks. The results showed that over a 14-year period, trash conservation marginally decreased soil acidity and significantly increased soil C and N stocks in 0–10 cm depth interval. Although the trash conservation treatment accumulated 13 Mg C ha^?1 more than the burned treatment, this difference was not statistically different. However, the stocks of N to 100 cm depth were 900 kg ha^?1 higher under the trash conservation treatment and this difference was statistically significant. The ¹³C abundance data suggested that where trash was conserved, more soil C was derived from the sugar cane than from the original native vegetation.     

Expression of ERp5 and GRP78 on the membrane of chronic lymphocytic leukemia cells: association with soluble MICA shedding

MICA is a ligand of the activating receptor NKG2D, expressed by NK and T cells. MICA expression is induced in cancer cells favoring their elimination by the immune system; however, many advanced tumors shed soluble MICA (sMICA), which impairs NKG2D-mediated cytotoxicity. ERp5 and GRP78 are endoplasmic reticulum-resident proteins that are translocated to the surface of epithelial tumor cells where they interact with MICA and are involved in sMICA shedding. In this study, we analyze the role of ERp5 and GRP78 in sMICA shedding in chronic lymphocytic leukemia (CLL). Immunofluorescence and flow cytometry analyses showed that ERp5 and GRP78 were significantly expressed on the surface of B cells and leukemia cells, but they were not expressed on T cells. The expression of ERp5 and GRP78 was significantly higher in leukemia cells than in B cells from controls. ERp5 and GRP78 co-localized with MICA on the surface of leukemia cells and the levels of expression of ERp5 and GRP78 correlated with the level of expression of membrane-bound MICA in CLL patients. Associated with higher expression of membrane-bound ERp5 and GRP78, serum sMICA levels were approximately threefold higher in patients than in controls. Elevated sMICA levels in CLL patients were associated with the down-modulation of NKG2D surface expression on CD8 T cells. Finally, pharmacological inhibition of B cell lines and stimulated leukemia cells showed that ERp5 activity is involved in sMICA shedding in CLL. In conclusion, these results uncover a molecular mechanism which regulates MICA protein shedding and immune evasion in CLL.     

Impact of plant growth-promoting bacteria on grain yield,protein content,and urea-<Superscript>15</Superscript> N recovery by maize in a Cerrado Oxisol

Background and aims

The inoculation of cereal crops with plant growth-promoting bacteria (PGPB) is a potential strategy to improve fertilizer-N acquisition by crops in soils with low capacity to supply N. A study was conducted to assess the impact of three inoculants on grain yield, protein content, and urea-¹⁵ N recovery in maize (Zea mays L.) under Cerrado soil and climate conditions.

Methods

The main treatments included inoculants containing (i) Azospirillum brasilense strain Sp245, (ii) A. brasilense strains AbV5 + AbV6, (iii) Herbaspirillum seropedicae strain ZAE94, and (iv) a non-inoculated control. The subtreatments were (i) urea-N fertilization (100 kg N ha^?1) at 30 days after sowing and (ii) no N addition at the stage. To determine fertilizer-N recovery, ¹⁵N–labelled urea was applied in microplots.

Results

Inoculants carrying A. brasilense improved urea-¹⁵ N acquisition efficiency in maize and also improved grain yield compared to the non-inoculated control, while urea-N fertilization enhanced grain quality by providing higher protein content.

Conclusion

Our results suggest that the inoculation of maize grains with PGPB represents a strategy to improve fertilizer-N recovery and maize yield in Cerrado soil with a low capacity to supply N.

     

Syndromic Management and STI Control in Urban Peru

Background

Syndromic management is an inexpensive and effective method for the treatment of symptomatic sexually transmitted infections (STIs), but its effectiveness as a method of STI control in at-risk populations is questionable. We sought to determine the potential utility of syndromic management as a public health strategy to control STI transmission in high-risk populations in urban Peru.

Methodology

We surveyed 3,285 at-risk men and women from three Peruvian cities from 2003–05. Participants were asked about the presence of genital ulcers, discharge, or dysuria in the preceding six months. Participants reporting symptoms were asked about subsequent health-seeking and partner notification behavior. Urine and vaginal swab samples were tested for Neisseria gonorrhoeae and Chlamydia trachomatis by nucleic acid testing. Serum was tested for syphilis and Herpes Simplex Virus-Type 2 antibodies.

Findings

Recent urogenital discharge or dysuria was reported by 42.1% of participants with gonorrhea or chlamydia versus 28.3% of participants without infection. Genital ulceration was reported by 6.2% of participants with, and 7.4% of participants without, recent syphilis. Many participants reporting symptoms continued sexual activity while symptomatic, and approximately half of all symptomatic participants sought treatment. The positive and negative predictive values of urogenital discharge or genital ulcer disease in detecting STIs that are common in the study population were 14.4% and 81.5% for chlamydia in women and 8.3% and 89.5% for syphilis among gay-identified men.

Conclusions

In our study, STIs among high-risk men and women in urban Peru were frequently asymptomatic and symptomatic participants often remained sexually active without seeking treatment. Additional research is needed to assess the costs and benefits of targeted, laboratory-based STI screening as part of a comprehensive STI control program in developing countries.