Contrasting Responses of Lizards to Divergent Ecological Stressors Across Biological Levels of Organization

It is frequently hypothesized that animals employ a generalized “stress response,” largely mediated by glucocorticoid (GC) hormones, such as corticosterone, to combat challenging environmental conditions. Under this hypothesis, diverse stressors are predicted to have concordant effects across biological levels of an organism. We tested the generalized stress response hypothesis in two complementary experiments with juvenile and adult male Eastern fence lizards (Sceloporus undulatus). In both experiments, animals were exposed to diverse, ecologically-relevant, acute stressors (high temperature or red imported fire ants, Solenopsis invicta) and we examined their responses at three biological levels: behavioral; physiological (endocrine [plasma corticosterone and blood glucose concentrations] and innate immunity [complement and natural antibodies]); and cellular responses (gene expression of a panel of five heat-shock proteins in blood and liver) at 30 or 90 min post stress initiation. In both experiments, we observed large differences in the cellular response to the two stressors, which contrasts the similar behavioral and endocrine responses. In the adult experiment for which we had innate immune data, the stressors affected immune function independently, and they were correlated with CORT in opposing directions. Taken together, these results challenge the concept of a generalized stress response. Rather, the stress response was context specific, especially at the cellular level. Such context-specificity might explain why attempts to link GC hormones with life history and fitness have proved difficult. Our results emphasize the need for indicators at multiple biological levels and whole-organism examinations of stress.

Bio-electrospraying and aerodynamically assisted bio-jetting the model eukaryotic Dictyostelium discoideum : assessing stress and developmental competency post treatment

Bio-electrospraying (BES) and aerodynamically assisted bio-jetting (AABJ) have recently been established as important novel biospray technologies for directly manipulating living cells. To elucidate their potential in medical and clinical sciences, these bio-aerosol techniques have been subjected to increasingly rigorous investigations. In parallel to these studies, we wish to introduce these unique biotechnologies for use in the basic biological sciences, for handling a wide range of cell types and systems, thus increasing the range and the scope of these techniques for modern research. Here, the authors present the analysis of the new use of these biospray techniques for the direct handling of the simple eukaryotic biomedical model organism Dictyostelium discoideum . These cells are widely used as a model for immune cell chemotaxis and as a simple model for development. We demonstrate that AABJ of these cells did not cause cell stress, as defined by the stress-gene induction, nor affect cell development. Furthermore, although BES induced the increased expression of one stress-related gene ( gapA ), this was not a generalized stress response nor did it affect cell development. These data suggest that these biospray techniques can be used to directly manipulate single cells of this biomedical model without inducing a generalized stress response or perturbing later development.

The Transcriptome of Prematurely Aging Yeast Cells Is Similar to That of Telomerase-deficient Cells

To help define the pathologies associated with yeast cells as they age, we analyzed the transcriptome of young and old cells isolated by elutriation, which allows isolation of biochemical quantities of old cells much further advanced in their life span than old cells prepared by the biotin-streptavidin method. Both 18-generation-old wild-type yeast and 8-generation-old cells from a prematurely aging mutant (dna2-1), with a defect in DNA replication, were evaluated. Genes involved in gluconeogenesis, the glyoxylate cycle, lipid metabolism, and glycogen production are induced in old cells, signifying a shift toward energy storage. We observed a much more extensive generalized stress response known as the environmental stress response (ESR), than observed previously in biotin-streptavidin-isolated cells, perhaps because the elutriated cells were further advanced in their life span. In addition, there was induction of DNA repair genes that fall in the so-called DNA damage “signature” set. In the dna2-1 mutant, energy production genes were also induced. The response in the dna2-1 strain is similar to the telomerase delete response, genes whose expression changes during cellular senescence in telomerase-deficient cells. We propose that these results suggest, albeit indirectly, that old cells are responding to genome instability.

Central vs. peripheral metabolic control of estrous cycles in Syrian hamsters. II. Glucoprivation

Estrous cycles in Syrian hamsters are inhibited by food deprivation or treatment with pharmacological inhibitors of intracellular glucose utilization (glucoprivic treatments). These same metabolic challenges increase neural stimulation in areas of the caudal brain stem thought to be involved in detection of metabolic signals. Experiment 1 was designed to examine whether vagally transmitted signals are important for glucoprivic effects on estrous cycles and on neural stimulation in the caudal brain stem. Vagotomized or sham-operated hamsters were treated with 2-deoxy-D-glucose (2-DG) at a dose known to decrease cellular glucose utilization and inhibit estrous cycles (1,750 mg/kg). Vagotomized and sham-operated hamsters did not differ significantly in incidence of 2-DG-induced anestrus or in neural stimulation in the caudal brain stem, but the effects of 2-DG on estrous cycles and neural stimulation appeared to have been attenuated in vagotomized hamsters. In experiment 2, hamsters were injected intracerebroventricularly with 2-DG or glucose at doses that did not induce anestrus when injected systemically (125 and 250 mg/kg). Groups treated with intracerebroventricular injections of 2-DG showed a significantly higher incidence of anestrus than those treated with glucose. In experiment 3, effects of systemic injections of 2-DG were prevented by prior injection of glucose or fructose at the same concentration, indicating that 2-DG acts via effects on glucose metabolism, rather than via a nonspecific pharmacological effect or generalized stress response. Results of these experiments and those reported elsewhere (J. E. Schneider, A. J. Hall, and G. N. Wade. Am. J. Physiol. 272 (Regulatory Integrative Comp. Physiol, 41) R400-R405, 1997] are consistent with the notion that central glucoprivation is sufficient, whereas peripheral lipoprivation is not critical, for metabolic effects on estrous cycles.