The effect of cell density on the maturation and contractile ability of muscle derived cells in a 3D tissue-engineered skeletal muscle model and determination of the cellular and mechanical stimuli required for the synthesis of a postural phenotype

The successful engineering of a truly biomimetic model of skeletal muscle could have a significant impact on a number of biomedical disciplines. Although a variety of techniques are currently being developed, there is, as of yet, no widely available and easily reproducible culture system for the synthesis of 3D artificial muscle tissues. In attempting to generate such a model it is essential to optimise any protocol in order to generate a tissue that best represents the in vivo environment. Since the maturation of muscle derived cells in culture is critically dependent on density, a major factor to be addressed in the development of these models is the ideal concentration at which to seed cells in order to generate an optimal response. In studying the effect of cell density on the performance of cells in an established 3D collagen based model of skeletal muscle, we demonstrate that an optimum density does exist in terms of peak force generation and myogenic gene expression data. Greater densities however, lead to the formation of a more physiologically relevant tissue with a phenotype characteristic of slow, postural muscle.

Large-scale mapping and predictive modeling of submerged aquatic vegetation in a shallow eutrophic lake

A spatially intensive sampling program was developed for mapping the submerged aquatic vegetation (SAV) over an area of approximately 20,000 ha in a large, shallow lake in Florida, U.S. The sampling program integrates Geographic Information System (GIS) technology with traditional field sampling of SAV and has the capability of producing robust vegetation maps under a wide range of conditions, including high turbidity, variable depth (0 to 2 m), and variable sediment types. Based on sampling carried out in August-September 2000, we measured 1,050 to 4,300 ha of vascular SAV species and approximately 14,000 ha of the macroalga Chara spp. The results were similar to those reported in the early 1990s, when the last large-scale SAV sampling occurred. Occurrence of Chara was strongly associated with peat sediments, and maximal depths of occurrence varied between sediment types (mud, sand, rock, and peat). A simple model of Chara occurrence, based only on water depth, had an accuracy of 55%. It predicted occurrence of Chara over large areas where the plant actually was not found. A model based on sediment type and depth had an accuracy of 75% and produced a spatial map very similar to that based on observations. While this approach needs to be validated with independent data in order to test its general utility, we believe it may have application elsewhere. The simple modeling approach could serve as a coarse-scale tool for evaluating effects of water level management on Chara populations.

Hurricane effects on a shallow lake ecosystem and its response to a controlled manipulation of water level

In order to reverse the damage to aquatic plant communities caused by multiple years of high water levels in Lake Okeechobee, Florida (U.S.), the Governing Board of the South Florida Water Management District (SFWMD) authorized a "managed recession" to substantially lower the surface elevation of the lake in spring 2000. The operation was intended to achieve lower water levels for at least 8 weeks during the summer growing season, and was predicted to result in a large-scale recovery of submerged vascular plants. We treated this operation as a whole ecosystem experiment, and assessed ecological responses using data from an existing network of water quality and submerged plant monitoring sites. As a result of large-scale discharges of water from the lake, coupled with losses to evaporation and to water supply deliveries to agriculture and other regional users, the lake surface elevation receded by approximately 1 m between April and June. Water depths in shoreline areas that historically supported submerged plant communities declined from near 1.5 m to below 0.5 m. Low water levels persisted for the entire summer. Despite shallow depths, the initial response (in June 2000) of submerged plants was very limited and water remained highly turbid (due at first to abiotic seston and later to phytoplankton blooms). Turbidity decreased in July and the biomass of plants increased. However, submerged plant biomass did not exceed levels observed during summer 1999 (when water depths were greater) until August. Furthermore, a vascular plant-dominated assemblage (Vallisneria, Potamogeton, and Hydrilla) that occurred in 1999 was replaced with a community of nearly 98% Chara spp. (a macro-alga) in 2000. Hence, the lake"s submerged plant community appeared to revert to an earlier successional stage despite what appeared to be better conditions for growth. To explain this unexpected response, we evaluated the impacts that Hurricane Irene may have had on the lake in the previous autumn. In mid-October 1999, this category 1 hurricane passed just to the south of the lake, with wind velocities over the lake surface reaching 90 km h(-1) at their peak. Output from a three-dimensional hydrodynamic/sediment transport model indicates that during the storm, current velocities in surface waters of the lake increased from near 5 cm s(-1) to as high as 100 cm s(-1). These strong velocities were associated with large-scale uplifting and horizontal transport of fine- grained sediments from the lake bottom. Water quality data collected after the storm confirmed that the hurricane resulted in lake-wide nutrient and suspended solids concentrations far in excess of those previously documented for a 10-year data set. These conditions persisted through the winter months and may have negatively impacted plants that remained in the lake at the end of the 1999 growing season. The results demonstrate that in shallow lakes, unpredictable external forces, such as hurricanes, can play a major role in ecosystem dynamics. In regions where these events are common (e.g., the tropics and subtropics), consideration should be given to how they might affect long-term lake management programs.

Role delineation study of pediatric nurse practitioners: a national study of practice responsibilities and trends in role functions

INTRODUCTION

This study explored the current practice responsibilities of pediatric nurse practitioners (PNPs) from a national perspective Educational preparation, geographic region of practice, years of employment as a PNP, type of employment setting, and full-time versus part-time employment were examined.

METHOD

From a randomly selected sample (N = 997), a total of 387 respondents returned their questionnaire, resulting in 325 usable questionnaires.

RESULTS

Years of experience as a PNP, setting of employment, geographic region, prescriptive authority, and subspecialty practice were significantly related to various health supervision and illness-focused activities performed by PNPs, as well as level of management responsibility. Anticipatory guidance supervision continues to be an integral part of the PNP role. PNPs report that they assume major responsibility for the health assessment and management of children with common pediatric illnesses as well as chronic illnesses and conditions.

DISCUSSION

The ability to prescribe prescription medications produced the greatest overall effect on PNP role activities and level of management responsibility. Years of experience exerted an interesting effect on role functions related to the overall health supervision and illness-focused activities in which PNPs engaged. Implications for the educational preparation of PNPs, the updating of national certification examinations, and planning for adequate numbers in the workforce to replace the cohort of retiring PNPs in the next 20 years are discussed.

Health issues for aboriginal youth: social and cultural factors associated with resilience

Research into Aboriginal health has tended to focus on the morbidity of babies and young children, or on the chronic illnesses of adults. Adolescent Aborigines are rarely the target of health research. While health services for Aboriginal people, even in remote areas, have improved enormously over the last few years with the provision of Aboriginal-controlled organizations, health services alone do not prevent the major causes of morbidity. In any case, young people, particularly adolescent boys, are poor users of these facilities. The major causes of adolescent Aboriginal morbidity and mortality are preventable: they have to do with ways of living, with the social, cultural and physical environments which surround adolescents. The paper draws on anthropological fieldwork which pays close attention to these issues. The paper examines the concept of 'adolescence' among Aboriginal groups, and explores the reasons for the resilience of some populations to a particular health problem, that of petrol sniffing among the young.

Nonradioactive DNA detection on Southern blots by enzymatically triggered chemiluminescence

A chemiluminescent reaction based on the deprotection of a phosphorylated phenyl dioxetane by alkaline phosphatase has recently been described (Schaap, A.P., 1988, J. Biolumin. Chemilumin. 2, 253). Light output is enhanced by intermolecular energy transfer to a micelle-solubilized fluorophore. This system is applied here to the detection of DNA probes on Southern blots. Enzyme solution assays which give an indication of sensitivity show that using this substrate 100 fg (0.7 amol) alkaline phosphatase can be detected on a luminescence plate reader (200 ms reading time). In a model Southern blotting system 180 fg HindIII digested lambda DNA was detected on film with homologous biotinylated DNA and a streptavidin-alkaline phosphatase complex. The single copy genes mos and raf-1, representing targets of 4.2 and 2.4 pg target DNA respectively, have also been detected in Southern-blotted human genomic DNA. A delay in reaching a plateau level of light output which is dependent on pH is observed but signal continues for at least 7 days. Typically, 12-h exposures to X-ray film were performed but once a steady-state light output had been achieved this time could be reduced to 2 h by preflashing film. This detection system represents a sensitive nonradioactive method, which is applicable not only to Southern blots but also to Northern and Western blots and any assay in which alkaline phosphatase is the label.

Nonradioactive nucleic acid detection by enhanced chemiluminescence using probes directly labeled with horseradish peroxidase

The use of nucleic acid probes directly labeled with horseradish peroxidase for detection of single copy sequences on Southern blots of human genomic DNA by enhanced chemiluminescence is described. Of the target sequences, 6 x 10(5) molecules (1 amol) have been detected on blue sensitive film using exposures of up to 60 min and probes of 0.3-5.1 kb. The chemiluminescent signal quantified using a cooled charge coupled device (CCD) camera is proportional to probe length for DNA probes in the range 50-3571 bases. The enzyme has no significant effect on the stability of a DNA/DNA hybrid formed with a 3571-base probe and target as determined by increasing the stringency of posthybridization washes by decreasing the concentration of a monovalent cation (NaCl) and by a Tm analysis. The kinetics of DNA hybridization have been analyzed by a cooled CCD camera to provide quantitative data. Ten nanograms per milliliter of probe may be used for an overnight hybridization. Southern blots can be reprobed using a DNA probe for the same or a different sequence without the necessity of stripping off the previously bound probe.