Self-organized vegetation patterning as a fingerprint of climate and human impact on semi-arid ecosystems

Spatially periodic vegetation patterns are well known in arid and semi-arid regions around the world. Mathematical models have been developed that attribute this phenomenon to a symmetry-breaking instability. Such models are based on the interplay between competitive and facilitative influences that the vegetation exerts on its own dynamics when it is constrained by arid conditions, but evidence for these predictions is still lacking. Moreover, not all models can account for the development of regularly spaced spots of bare ground in the absence of a soil prepattern. We applied Fourier analysis to high-resolution, remotely sensed data taken at either end of a 40-year interval in southern Niger. Statistical comparisons based on this textural characterization gave us broad-scale evidence that the decrease in rainfall over recent decades in the sub-Saharan Sahel has been accompanied by a detectable shift from homogeneous vegetation cover to spotted patterns marked by a spatial frequency of about 20 cycles km-1. Wood cutting and grazing by domestic animals have led to a much more marked transition in unprotected areas than in a protected reserve. Field measurements demonstrated that the dominant spatial frequency was endogenous rather than reflecting the spatial variation of any pre-existing heterogeneity in soil properties. All these results support the use of models that can account for periodic vegetation patterns without invoking substrate heterogeneity or anisotropy, and provide new elements for further developments, refinements and tests. This study underlines the potential of studying vegetation pattern properties for monitoring climatic and human impacts on the extensive fragile areas bordering hot deserts. Explicit consideration of vegetation self-patterning may also improve our understanding of vegetation and climate interactions in arid areas. © 2006 The Authors.

The impact of chemotherapy dose density and dose intensity on breast cancer outcome: what have we learned?

Optimising chemotherapy dose density and dose intensity are strategies aimed at improving outcomes in adjuvant therapy for patients with breast cancer. There are, in theory, at least five models allowing the delivery of a higher overall drug dose intensity. These are reviewed in this article and vary according to three main variables: the dose per course, the interval between doses and the total cumulative dose. Cyclophosphamide, anthracyclines and taxanes are among the most active agents for the treatment of breast cancer and, as such, they have been or are currently the focus of prospective, randomised clinical trials testing some of these dose-intensity models in the adjuvant setting. The results of recent trials suggest that anthracyclines, but not cyclophosphamide, are associated with better outcomes if used at higher doses per course and at higher cumulative doses. However, care has to be taken with premenopausal women where an increased dose of anthracycline per course but a reduced cumulative dose appears to produce a worse outcome. Moreover, decreasing the interval between doses, for anthracyclines and cyclophosphamide, does not seem to provide, so far, additional benefits for women with locally advanced breast cancer. This approach is not feasible with docetaxel, since an increase in dose density induces unwanted side-effects. These results represent our current state of knowledge, but clinical trials are being performed to evaluate further the effect of dose intensity, dose density and cumulative dose of key therapeutic agents on patient outcomes.

Impact of various endocrine and paracrine factors on in vitro culture of preantral follicles in rodents

Folliculogenesis is a complex process regulated by various paracrine and autocrine factors. In vitro growth systems of primordial and preantral follicles have been developed for future use of immature oocytes, as sources of fertilizable oocytes and for studying follicular growth and oocyte maturation mechanisms. Rodents were often chosen for in vitro follicular culture research and a lot of factors implicated in folliculogenesis have been identified using this model. To date, the mouse is the only species in which the whole process of follicular growth, oocyte maturation, fertilization and embryo transfer into recipient females was successfully performed. However, the efficiency of in vitro culture systems must still be considerably improved. Within the follicle, numerous events affect cell proliferation and the acquisition of oocyte developmental competency in vitro, including interactions between the follicular cells and the oocyte, and the composition of the culture medium. Effects of the acting factors depend on the stage of follicle development, the culture system used and the species. This paper reviews the action of endocrine, paracrine factors and other components of culture medium on in vitro growth of preantral follicles in rodents.

Impact of tumor board recommendations on treatment outcome for locally advanced head and neck cancer

Background/Aims: To identify physician selection factors in the treatment of locally advanced head and neck cancer and how treatment outcome is affected by Tumor Board recommendations. Methods: A retrospective analysis of 213 patients treated for locally advanced head and neck cancer in a single institution was performed. All treatments followed Tumor Board recommendations: 115 patients had chemotherapy and radiation, and 98 patients received postoperative radiation. Patient characteristics, treatment toxicity, locoregional control and survival between these two treat- ment groups were compared. Patient survival was compared with survival data reported in randomized studies of locally advanced head and neck cancer. Results: There were no differences in comorbidity factors, and T or N stages between the two groups. A statistically significant number of patients with oropharyngeal and oral cavity tumors had chemoradiation and postoperative radiation, respectively (p < 0.0001). Grade 3-4 toxicities during treatment were 48 and 87% for the postoperative radiation and chemoradiation groups, respectively (p = 0.0001). There were no differences in survival, locoregional recurrences and distant metastases between the two groups. Patient survival was comparable to survival rates reported by randomized studies of locally advanced head and neck cancer. Conclusion: Disease sites remained the key determining factor for treatment selection. Multidisciplinary approaches provided optimal treatment outcome for locally advanced head and neck cancer, with overall survival in these patients being comparable to that reported in randomized clinical trials. Copyright © 2008 S. Karger AG.