Asymmetric interactions and their consequences for vital rates and dynamics: the smaller tea tortrix as a model system.

Asymmetric interactions among conspecifics can have diverse effects on population dynamics including stabilization, generation of cycles, and induction of chaotic fluctuations. A difficult challenge, however, is establishing the link between the impact of asymmetric interactions on life history and the consequences for population dynamics. The smaller tea tortrix, Adoxophyes honmai, is a good example. Larval instars differ dramatically in size and have a tendency for cannibalism, which suggests the potential for strong asymmetric interactions among instars. Yet whether these asymmetries have any role in generating the distinct single-generation cycles observed in the field and laboratory is unclear. Here we report on the development of a new experimental approach to characterize the impact of asymmetric interactions on life history that can be directly embedded into stage-structured population models. The experiments use donor-replacement protocols in which focal individuals are challenged to complete their life cycles in competitive environments where the instar and density of the competitors are held constant. The experimentally derived interaction surface contains all the information about stage-specific interactions and provides a straightforward framework for evaluating alternative ways of abstracting the interactions into traditional models of asymmetric competition. Working with the smaller tea tortrix, we found strong evidence of asymmetric interactions and identified critical "tipping points" in the competitive environment that strongly affected survival but not development. We incorporated the experimentally derived interaction surface into a stage-structured population model and found that despite the strong impact that asymmetric interactions have on tea tortrix life history, they do not scale-up to impact the predicted asymptotic population dynamics. Comparing these dynamics with two abstracted models of stage-structured interactions revealed that while the quantitative details of the emergent dynamics depends on the shape of the interaction surface, the qualitative features, such as the emergence of single-generation cycles and rapid synchronization of development among individuals, are pleasingly robust.

The fitness of drug-resistant malaria parasites in a rodent model: multiplicity of infection.

Malaria infections normally consist of more than one clonally replicating lineage. Within-host interactions between sensitive and resistant parasites can have profound effects on the evolution of drug resistance. Here, using the Plasmodium chabaudi mouse malaria model, we ask whether the costs and benefits of resistance are affected by the number of co-infecting strains competing with a resistant clone. We found strong competitive suppression of resistant parasites in untreated infections and marked competitive release following treatment. The magnitude of competitive suppression depended on competitor identity. However, there was no overall effect of the diversity of susceptible parasites on the extent of competitive suppression or release. If these findings generalize, then transmission intensity will impact on resistance evolution because of its effect on the frequency of mixed infections, not because of its effect on the distribution of clones per host. This would greatly simplify the computational problems of adequately capturing within-host ecology in models of drug resistance evolution in malaria.

Multiple dynamics in a single predator-prey system: experimental effects of food quality.

Recent work with the freshwater zooplankton Daphnia has suggested that the quality of its algal prey can have a significant effect on its demographic rates and life-history patterns. Predator-prey theory linking food quantity and food quality predicts that a single system should be able to display two distinct patterns of population dynamics. One pattern is predicted to have high herbivore and low algal biomass dynamics (high HBD), whereas the other is predicted to have low herbivore and high algal biomass dynamics (low HBD). Despite these predictions and the stoichiometric evidence that many phytoplankton communities may have poor access to food of quality, there have been few tests of whether a dynamic predator-prey system can display both of these distinct patterns. Here we report, to the authors' knowledge, the first evidence for two dynamical patterns, as predicted by theory, in a single predator-prey system. We show that the high HBD is a result of food quantity effects and that the low HBD is a result of food quality effects, which are maintained by phosphorus limitation in the predator. These results provide an important link between the known effects of nutrient limitation in herbivores and the significance of prey quality in predator-prey population dynamics in natural zooplankton communities.

Glucocorticoids regulate Na+ transport in vascular smooth muscle through the glucocorticoid receptor-mediated mechanism.

The incidence of hypertension in conditions of chronic glucocorticoid (GC) excess is very high, though the mechanism whereby GC elevate blood pressure is far from being understood. We have recently found that GC markedly increase influx of Na+ in vascular smooth muscle (VSM) cells. We and other investigators have previously described receptors for GC in arterial tissues, and we have now examined whether the effect of GC on Na+ transport in VSM is mediated through these receptors. Vascular smooth muscle cells were cultured from rabbit aortas. The cells were treated for 48 h with 10(-7) mol/L dexamethasone (DEX), in the presence or absence of RU 486, a competitive inhibitor of DEX binding to its receptor, or progesterone, an allosteric accelerator of DEX dissociation from the receptor. Unidirectional influx of Na+ was measured with 22Na as tracer. Dexamethasone more than doubled the influx rate of Na+, RU 486 completely prevented this increase, and progesterone reduced the DEX-induced increase by approximately 80%. The time of the cell exposure to DEX necessary for the DEX effect to occur was 4 to 6 h, with a maximal effect at 48 h, suggesting a genomic effect. Addition of protein synthesis inhibitors, actinomycin D or cycloheximide, to VSM cells cultured in the presence of DEX prevented the increase of Na+ influx by DEX.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of the effects of glucocorticoids and mineralocorticoids on vascular smooth muscle contractility.

We have previously demonstrated that receptors to both mineralocorticoids (MC) and glucocorticoids (GC) exist in the arterial wall and that treatment with GC markedly increases Na+ and Ca2+ influx in cultured aortic vascular smooth muscle (VSM) cells, whereas treatment with MC increases only Na+ influx. We now report the results of the study aimed at the elucidation of the mechanism(s) of these effects. Unidirectional influx of Na+ and Ca2+ was measured in cultured cells of rabbit aortic media, using 22Na and 45Ca as tracers, in the presence of ouabain. The cells were treated for different periods with dexamethasone (DEX) or aldosterone (ALDO) in physiologic or supraphysiologic concentrations, in the presence or absence of competitive inhibitors of GC-receptor binding, RU 486, or MC-receptor binding, K-prorenoate. DEX in 50 nM concentration increased Na+ influx by 98 +/- 18% and Ca2+ influx by 100 +/- 20%, and the maximum effect was seen after 48 hour cell-treatment. ALDO in 5 nM concentration increased Na+ influx by 90 +/- 12% and had no effect on Ca2+ influx, and the maximum effect was seen after 7-10 days of cell-treatment. The enhancing effect of both DEX and ALDO on the influx rate of Na+ was prevented by actinomycin D and by cycloheximide. RU 486 completely inhibited DEX from exercising its enhancing effect on Na+ influx, but diminished influx rate of Na+ increased by ALDO only by 25%. Prorenoate (PRN) did not have any effect on DEX-increased Na+ influx, but completely inhibited ALDO from exercising its effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Decisions to withhold or terminate treatment.

Decisions to withhold or terminate treatment are common clinical dilemmas in patients dying from diseases of the nervous system. Decision making for such patients must be based upon ethical principles. Under the doctrine of valid consent and refusal, competent patients have the right to refuse life-sustaining therapies. For incompetent patients, this right may be exercised through their previously executed advanced directives or through appointed proxy decision makers. Physicians have the duty to assess the potential benefits and harms of various treatment options and to clearly communicate this information to patients and their proxies in a supportive manner. The authors illustrate the application of ethical principles in neurologists' management of patients in persistent vegetative states, dementia, and end-stage neuromuscular disease.

Moral theory and neurology.

This article presents an outline of a general moral theory and shows its relationship to the concepts of paternalism and that of valid consent and refusal. The authors then show how this theory and these concepts can be usefully applied to the moral problems that neurologists often face in determining how to act when they have distressing information for their patients. Finally, a procedure is provided for determining when it is morally justified to deceive patients by withholding information about their diagnoses, prognoses, or about their prospective treatments.

Fine-needle aspiration of metastatic atrial myxoma.

Atrial myxoma is the most common primary neoplasm of the heart, but "metastatic" or embolic phenomena are rare. The first reported case of "metastatic" atrial myxoma diagnosed by fine-needle aspiration biopsy is presented. It occurred in a 54-yr-old woman with multiple metastatic lesions. The cytologic and histologic findings of the fine-needle aspiration biopsy and subsequent surgical excision are presented as is a discussion of the incidence, origin, and clinical findings of atrial myxoma and the characteristics of its emboli.

Fine-needle biopsy of pediatric lesions: a three-year study in an outpatient biopsy clinic.

Diagnostic Cytology Laboratory, Inc., has an outpatient Fine Needle Biopsy Clinic, which evaluated 7,487 fine-needle biopsies (FNB) from January 1989 to February 1992. Two hundred eighty-eight (3.8%) of these specimens were collected from patients 19 years old or younger and this represents the largest study of this population in the scientific literature. The majority of these specimens were obtained from palpable masses in the head and neck region [lymph nodes (58.3%), thyroid (7.6%), and salivary gland (5.2%)] while a smaller number were collected from miscellaneous soft tissue (18.8%) and breast masses (10.1%). Thirteen (4.5%) (from 12 patients) were diagnosed as malignant by FNB and 275 (95.5%) (264 patients) were benign by FNB. This benign:malignant ratio (22:1) is significantly higher than has been reported from tertiary care institutions and is a reflection of the difference of this outpatient population. Two hundred nine of 276 patients (75.7%) had adequate follow-up, including 137 (49.6%) patients followed by observation, 48 (17.4%) patients followed by surgical biopsy, and 24 (8.7%) patients followed by some other modality: imaging studies, flow cytometry, or treatment. There was a single false positive diagnosis (a pilomatrixoma) and one (1) false negative interpretation (a cystic acinic cell carcinoma) resulting in a diagnostic sensitivity of 92.3% and a specificity of 99.6%. The positive predictive value was 92.3%, the negative predictive value was 99.6%, and the test efficiency was 99.3%. The utility, cost-effectiveness and uniqueness of the clinic population is discussed.

Fine needle aspiration of rhabdomyosarcoma of the heart. Light and electron microscopic findings and histologic correlation.

Fine needle aspiration (FNA) biopsy was performed on a 12-year-old child with intractable cardiac arrhythmias and a mediastinal mass. The cytologic, immunocytochemical and electron microscopic findings on the aspirated material established an initial diagnosis of cardiac rhabdomyosarcoma. Subsequent histologic material confirmed the cytologic diagnosis. The findings are presented, and the use of FNA to definitively establish a preoperative diagnosis of cardiac rhabdomyosarcoma is discussed.

Development of a culturally sensitive rural practicum.

Wanting to increase their students' awareness of and experience with providing culturally sensitive care in a rural setting, the authors developed a nursing elective course. They discuss the structure, goals, and outcomes of the course.