Yeast cell responses and survival during periodic osmotic stress are controlled by glucose availability.

Natural environments of living organisms are often dynamic and multifactorial, with multiple parameters fluctuating over time. To better understand how cells respond to dynamically interacting factors, we quantified the effects of dual fluctuations of osmotic stress and glucose deprivation on yeast cells using microfluidics and time-lapse microscopy. Strikingly, we observed that cell proliferation, survival, and signaling depend on the phasing of the two periodic stresses. Cells divided faster, survived longer, and showed decreased transcriptional response when fluctuations of hyperosmotic stress and glucose deprivation occurred in phase than when the two stresses occurred alternatively. Therefore, glucose availability regulates yeast responses to dynamic osmotic stress, showcasing the key role of metabolic fluctuations in cellular responses to dynamic stress. We also found that mutants with impaired osmotic stress response were better adapted to alternating stresses than wild-type cells, showing that genetic mechanisms of adaptation to a persistent stress factor can be detrimental under dynamically interacting conditions.

Confidence-accuracy relations for faces and scenes: roles of features and familiarity.

Using naturalistic scenes, we recently demonstrated that confidence-accuracy relations differ depending on whether recognition responses are based on memory for a specific feature or instead on general familiarity: When confidence is controlled for, accuracy is higher for familiarity-based than for feature-based responses. In the present experiment, we show that these results generalize to face recognition. Subjects studied photographs of scenes and faces presented for varying brief durations and received a recognition test on which they (1) indicated whether each picture was old or new, (2) rated their confidence in their response, and (3) indicated whether their response was based on memory for a feature or on general familiarity. For both stimulus types, subjects were more accurate and more confident for their feature-based than for their familiarity-based responses. However, when confidence was held constant, accuracy was higher for familiarity-based than for feature-based responses. These results demonstrate an important similarity between face and scene recognition and show that for both types of stimuli, confidence and accuracy are based on different information.

Different confidence-accuracy relationships for feature-based and familiarity-based memories.

Participants studied naturalistic pictures presented for varying brief durations and then received a recognition test on which they indicated whether each picture was old or new and rated their confidence. In 1 experiment they indicated whether each "old"/"new" response was based on memory for a specific feature in the picture or instead on the picture's general familiarity; in another experiment, we defined pictures that tended to elicit feature versus familiarity responses. Thus, feature/familiarity was a dependent variable in 1 experiment and an independent variable in the other. In both experiments feature-based responses were more accurate than those that were familiarity based, and confidence and accuracy increased with duration for both response types. However, when confidence was controlled for, mean accuracy was higher for familiarity-based than for feature-based responses. The theoretical implication is that confidence and accuracy arise from different underlying information. The applied implication is that confidence differences should not be taken as implying accuracy differences when the phenomenal basis of the memory reports differ.

A significant bilateral field advantage for shapes defined by static and motion cues.

Matching performance is better when pairs of visual stimuli are presented in bilateral conditions--in which one stimulus is presented to each side of the visual field--than in unilateral presentations-when both stimuli are presented to one side of the field. This is called the bilateral field advantage (BFA). The processing of visual motion has also been found to be more strongly integrated across the cerebral hemispheres than is processing of static cues. However, in these studies higher-order motion tasks, such as processing motion-defined form, have not been examined. To determine if the BFA generalises to such tasks, we measured the magnitude of the effect using a shape-matching task in which the stimuli were random polygons that were either in motion, motion-defined, or static. The polygon pairs were presented either: (i) bilaterally, one to either side of the vertical meridian; (ii) unilaterally, both to one side of the vertical meridian (left or right visual fields); or (iii) centrally, vertically separated across the horizontal meridian (a control condition). An equal advantage of bilateral conditions over unilateral ones was found for all three types of polygon shape cues, showing that the BFA generalises to conditions where shapes are in motion and where shape is defined by motion. These findings are compatible with the notion that motion processing is strongly integrated across the cerebral hemispheres, and with the idea that this integration manifests itself with simple motion information, rather than with higher-order motion processing such as matching shapes defined by motion.

Proinflammatory cytokines differentially influence adult hippocampal cell proliferation depending upon the route and chronicity of administration.

Disturbances of hippocampal plasticity, including impaired dendritic branching and reductions of neurogenesis, are provoked by stressful insults and may occur in depression. Although corticoids likely contribute to stressor-induced reductions of neurogenesis, other signaling messengers, including pro-inflammatory cytokines might also be involved. Accordingly, the present investigation assessed whether three proinflammatory cytokines, namely interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha) (associated with depression) influenced cellular proliferation within the hippocampus. In this regard, systemic administration of TNF-alpha reduced 5-bromo-2-deoxyuridine (BrdU) labeling within the hippocampus, whereas IL-1beta and IL-6 had no such effect. However, repeated but not a single intra-hippocampal infusion of IL-6 and IL-1beta actually increased cellular proliferation and IL-6 infusion also enhanced microglial staining within the hippocampus. Yet, no changes in doublecortin expression were apparent, suggesting that the cytokine did not influence the birth of cells destined to become neurons. Essentially, the route of administration and chronicity of cytokine administration had a marked influence upon the nature of hippocampal alterations provoked, suggesting that cytokines may differentially regulate hippocampal plasticity in neuropsychiatric conditions.

End-tidal CO2 in some aquatic mammals of large size.

While resting on land or at the water surface, the breathing frequency (f) of aquatic mammals of medium and large size is lower than in terrestrial mammals of similar body weight (W), the difference widening with the increase in W. The allometric function for aquatic mammals is f proportional to W(-0.42) (f, breaths/min, W, kg) and that of terrestrial species is f proportional to W(-0.25). We asked whether or not resting breathing at such low f would entail high values of alveolar CO2. End-tidal alveolar CO2 pressure, taken as representative of alveolar CO2 pressure, PaCO2, was measured from the expired gas during resting breathing in captive specimens of aquatic species trained to rest in proximity of their keepers, either on land (walrus and sea lion) or at the water surface (dolphin, orca, beluga and hippopotamus). Their f during the recordings ranged from less than 1 (orca) to 6 (walrus) breaths/min. The average PaCO2 values ranged from 32 to 42 mm Hg, the peaks being a few mm Hg higher. These values were similar or slightly higher than literature data of many terrestrial species, with no relation to the animal f or W. The quasi-normality of PaCO2 in large aquatic species breathing at rest, despite their exceptionally low f and normal metabolism, can be explained mainly by two factors, their large tidal volume/W, about three times the average terrestrial value, and their peculiar breathing pattern with sustained high lung volume during the expiratory pause. This latter is key in avoiding a substantial rise in PaCO2 during the inter-breath pause.

Genome-wide transcriptional response of an avian pathogenic Escherichia coli (APEC) pst mutant.

BACKGROUND: Avian pathogenic E. coli (APEC) are associated with extraintestinal diseases in poultry. The pstSCAB-phoU operon belongs to the Pho regulon and encodes the phosphate specific transport (Pst) system. A functional Pst system is required for full virulence in APEC and other bacteria and contributes to resistance of APEC to serum, to cationic antimicrobial peptides and acid shock. The global mechanisms contributing to the attenuation and decreased resistance of the APEC pst mutant to environmental stresses have not been investigated at the transcriptional level. To determine the global effect of a pst mutation on gene expression, we compared the transcriptomes of APEC strain chi7122 and its isogenic pst mutant (K3) grown in phosphate-rich medium. RESULTS: Overall, 470 genes were differentially expressed by at least 1.5-fold. Interestingly, the pst mutant not only induced systems involved in phosphate acquisition and metabolism, despite phosphate availability, but also modulated stress response mechanisms. Indeed, transcriptional changes in genes associated with the general stress responses, including the oxidative stress response were among the major differences observed. Accordingly, the K3 strain was less resistant to reactive oxygen species (ROS) than the wild-type strain. In addition, the pst mutant demonstrated reduced expression of genes involved in lipopolysaccharide modifications and coding for cell surface components such as type 1 and F9 fimbriae. Phenotypic tests also established that the pst mutant was impaired in its capacity to produce type 1 fimbriae, as demonstrated by western blotting and agglutination of yeast cells, when compared to wild-type APEC strain chi7122. CONCLUSION: Overall, our data elucidated the effects of a pst mutation on the transcriptional response, and further support the role of the Pho regulon as part of a complex network contributing to phosphate homeostasis, adaptive stress responses, and E. coli virulence.