Time course of air hunger mirrors the biphasic ventilatory response to hypoxia.

Determining response dynamics of hypoxic air hunger may provide information of use in clinical practice and will improve understanding of basic dyspnea mechanisms. It is hypothesized that air hunger arises from projection of reflex brain stem ventilatory drive ("corollary discharge") to forebrain centers. If perceptual response dynamics are unmodified by events between brain stem and cortical awareness, this hypothesis predicts that air hunger will exactly track ventilatory response. Thus, during sustained hypoxia, initial increase in air hunger would be followed by a progressive decline reflecting biphasic reflex ventilatory drive. To test this prediction, we applied a sharp-onset 20-min step of normocapnic hypoxia and compared dynamic response characteristics of air hunger with that of ventilation in 10 healthy subjects. Air hunger was measured during mechanical ventilation (minute ventilation = 9 +/- 1.4 l/min; end-tidal Pco(2) = 37 +/- 2 Torr; end-tidal Po(2) = 45 +/- 7 Torr); ventilatory response was measured during separate free-breathing trials in the same subjects. Discomfort caused by "urge to breathe" was rated every 30 s on a visual analog scale. Both ventilatory and air hunger responses were modeled as delayed double exponentials corresponding to a simple linear first-order response but with a separate first-order adaptation. These models provided adequate fits to both ventilatory and air hunger data (r(2) = 0.88 and 0.66). Mean time constant and time-to-peak response for the average perceptual response (0.36 min(-1) and 3.3 min, respectively) closely matched corresponding values for the average ventilatory response (0.39 min(-1) and 3.1 min). Air hunger response to sustained hypoxia tracked ventilatory drive with a delay of approximately 30 s. Our data provide further support for the corollary discharge hypothesis for air hunger.     

Time dependence of B cell processing and presentation of peptide and native protein antigens

Th cell recognition of globular proteins requires the uptake and intracellular processing of the native Ag by an APC to produce a peptide fragment containing the T cell antigenic determinant, which is recognized in conjunction with Ia. This report describes the time course of the processing and presentation of a soluble globular protein Ag, pigeon cytochrome c (Pc), and of the presentation of a C-terminal peptide fragment of Pc, residues 81 to 104 (Pc 81-104), which does not require processing. Splenic B cells, acting as APC, require 6 to 8 h incubation with native Pc to process and present it to an I-Ek-restricted Pc-specific T cell hybrid, resulting in the secretion of IL-2. Moreover, the time required for B cells to process Pc is the same whether the Ag is taken up by nonspecific fluid phase pinocytosis or by binding to surface Ig. Once processed, Ag is lost from the B cell surface by 8 to 12 h, although when provided with fresh Pc, the same B cells are still capable of processing and presenting. In contrast to native Pc, only 1 to 2 h are required for the peptide fragment Pc 81-104 to become associated with B cells in a stimulatory fashion, and this time is similar for live and paraformaldehyde-fixed B cells, which cannot internalize or process the peptide. Washed free of excess peptide after 2 h, B cells lose their ability to stimulate T cells by 8 to 12 h, with a time course indistinguishable from that for the loss of processed native Pc. Prolonged incubation of B cells with the peptide for 18 to 24 h results in a dramatic loss of the ability to present Pc 81-104. Even when provided with fresh Pc or Pc 81-104, these cells have diminished ability to present these Ag. This loss is selective, inasmuch as these B cells remain equivalent to untreated B cells in the presentation of an unrelated Ag, OVA, to an I-Ak-restricted specific T cell. However, the ability to present another I-Ek-restricted antigenic peptide of the D glycoprotein of HSV to its specific T cell is also diminished. Loss of activity is observed after incubation only with the peptide and not with the native protein and is not due to a depletion of the antigenic peptide from the incubation medium.(ABSTRACT TRUNCATED AT 400 WORDS)     

Smelling on the fly: sensory cues and strategies for olfactory navigation in Drosophila

Navigating toward (or away from) a remote odor source is a challenging problem that requires integrating olfactory information with visual and mechanosensory cues. Drosophila melanogaster is a useful organism for studying the neural mechanisms of these navigation behaviors. There are a wealth of genetic tools in this organism, as well as a history of inventive behavioral experiments. There is also a large and growing literature in Drosophila on the neural coding of olfactory, visual, and mechanosensory stimuli. Here we review recent progress in understanding how these stimulus modalities are encoded in the Drosophila nervous system. We also discuss what strategies a fly might use to navigate in a natural olfactory landscape while making use of all these sources of sensory information. We emphasize that Drosophila are likely to switch between multiple strategies for olfactory navigation, depending on the availability of various sensory cues. Finally, we highlight future research directions that will be important in understanding the neural circuits that underlie these behaviors.     

Time course of bioluminescent signal in orthotopic and heterotopic brain tumors in nude mice

In vivo bioluminescence imaging is becoming increasingly popular. Quantification of bioluminescence signals requires knowledge of the variability and reproducibility of this technique. The objective of this study was to analyze the time course of luminescent signal emitted from firefly luciferase-expressing tumors in two locations, following luciferin injection and at different times after tumor cell implantation. Knowledge of the kinetics of the bioluminescent signals is required for the reliable quantification and comparison of signal during longitudinal studies. The kinetics of bioluminescence was evaluated in orthotopic and heterotopic brain tumors in mice using a human brain tumor cell line constitutively expressing luciferase. Tumor cells were implanted in the brains and flanks of the animals, and whole-body images revealing tumor location were obtained. Tumor burden was monitored over time by the quantitation of photon emission. The magnitude of bioluminescence measured in vivo varied with time after the injection of luciferin, as well as with dose, which necessitated that the comparison of the quantitative results take into consideration the time after injection. Heterotopic and orthotopic tumors exhibited significantly different time courses; however, time after implantation as characterized by kinetic studies performed on days 4 and 14 after cell implantation revealed no significant differences in orthotopic tumors. Future quantitative longitudinal studies must take into account the differences in the kinetics of different models.     

Time course and temperature dependence of the membrane translocation of tetanus and botulinum neurotoxins C and D in neurons

Tetanus and botulinum neurotoxins act inside nerve terminals and, therefore, they have to translocate across a membrane to reach their targets. This translocation is driven by a pH gradient, acidic on the cis side and neutral on the cytosol. Recently, a protocol to induce translocation from the plasma membrane was established. Here, we have used this approach to study the temperature dependence and time course of the entry of the L chain of tetanus neurotoxin and of botulinum neurotoxins type C and D across the plasma membrane of cerebellar granular neurons. The time course of translocation of the L chain varies for the three neurotoxins, but it remains in the range of minutes at 37 °C, whilst it takes much longer at 20 °C. BoNT/C does not enter neurons at 20 °C. Translocation also depends on the dimension of the pH gradient. These data are discussed with respect to the contribution of the membrane translocation step to the total time to paralysis and to the low toxicity of these neurotoxins in cold-blood vertebrates.     

Information processing limits on generating neuroanatomy: global optimization of rat olfactory cortex and amygdala

A pattern of widespread connection optimization in the nervous system has become evident: deployment of some neural interconnections attains optimality, sometimes without detectable limits. New results for optimization of layout of connected areas of rat olfactory cortex and of rat amygdala are reported here. One larger question concerns mechanisms—how such minimization is attained. A next question is why a nervous system would optimize rather than just moderately satisfice. A morphogenic proposal that relates these questions is that the means of organizing neural wiring happens also to yield optimization. Some neuroanatomy is generated via “saving wire,” and this optimizing is via simple physical processes rather than DNA-mediated mechanisms. Such “non-genomic nativism” is thereby a path around fundamental limitations on generating brains, some of the most complex structures in the known universe.     

Homing pigeons only navigate in air with intact environmental odours: a test of the olfactory activation hypothesis with GPS data loggers

A large body of evidence has shown that anosmic pigeons are impaired in their navigation. However, the role of odours in navigation is still subject to debate. While according to the olfactory navigation hypothesis homing pigeons possess a navigational map based on the distribution of environmental odours, the olfactory activation hypothesis proposes that odour perception is only needed to activate a navigational mechanism based on cues of another nature. Here we tested experimentally whether the perception of artificial odours is sufficient to allow pigeons to navigate, as expected from the olfactory activation hypothesis. We transported three groups of pigeons in air-tight containers to release sites 53 and 61 km from home in three different olfactory conditions. The Control group received natural environmental air; both the Pure Air and the Artificial Odour groups received pure air filtered through an active charcoal filter. Only the Artificial Odour group received additional puffs of artificial odours until release. We then released pigeons while recording their tracks with 1 Hz GPS data loggers. We also followed non-homing pigeons using an aerial data readout to a Cessna plane, allowing, for the first time, the tracking of non-homing homing pigeons. Within the first hour after release, the pigeons in both the Artificial Odour and the Pure Air group (receiving no environmental odours) showed impaired navigational performances at each release site. Our data provide evidence against an activation role of odours in navigation, and document that pigeons only navigate well when they perceive environmental odours.     

Survival and growth of hatchling Crocodylus porosus in saltwater without access to fresh drinking water

Summary It has been suggested that C. porosus select nest sites which provide a source of freshwater for hatchlings during the dry season. From a mark-recapture study, we conclude that hatchling C. porosus can survive and grow in hyperosmotic saltwater without drinking freshwater. Hence, the siting of nests is unlikely to be the consequence of a requirement by hatchlings for freshwater. Considered along with other information, our observations imply that hatchling C. porosus have functional salt glands.     

Adaptation to environmental pH: integrating the Rim101 and calcineurin signal transduction pathways

The ability to appropriately respond to environmental conditions is critical for the survival of simple microbes and for development of complex multicellular organisms. Sensing and responding to a given environmental condition requires the integration of numerous signals through one or more signal transduction pathways. This leads to changes in gene expression, and potentially post-translational modifications, that favour growth in the given environment. In the fungus Candida albicans, an important opportunistic pathogen, environmental pH has profound effects on morphology and proper adaptation to extracellular pH is critical for pathogenesis. Here, we demonstrate that the Rim101/PacC pH-sensing pathway acts in parallel to Crz1, via calcineurin, to adapt to alkaline pH. We also show that the Rim101 pathway acts in parallel to Crz2, independent of calcineurin, to adapt to high lithium concentrations and to repress filamentation at acidic pH. Our studies also revealed a novel requirement for Crz1, Crz2 and calcineurin for growth at acidic pH. From these studies, we propose that the Crz1 homologue Crz2 is calcineurin-independent, but like Crz1, acts in parallel to promote specific Rim101-dependent processes. These results establish and begin to dissect the complex interactions between important signal transduction pathways in C. albicans, which are critical for virulence.     

Time course and Ca(2+) dependence of sensitivity modulation in cyclic GMP-gated currents of intact cone photoreceptors

We determined the Ca(2+) dependence and time course of the modulation of ligand sensitivity in cGMP-gated currents of intact cone photoreceptors. In electro-permeabilized single cones isolated from striped bass, we measured outer segment current amplitude as a function of cGMP or 8Br-cGMP concentrations in the presence of various Ca(2+) levels. The dependence of current amplitude on nucleotide concentration is well described by the Hill function with values of K(1/2), the ligand concentration that half-saturates current, that, in turn, depend on Ca(2+). K(1/2) increases as Ca(2+) rises, and this dependence is well described by a modified Michaelis-Menten function, indicating that modulation arises from the interaction of Ca(2+) with a single site without apparent cooperativity. (Ca)K(m), the Michaelis-Menten constant for Ca(2+) concentration is 857 +/- 68 nM for cGMP and 863 +/- 51 for 8Br-cGMP. In single cones under whole-cell voltage clamp, we simultaneously measured changes in membrane current and outer segment free Ca(2+) caused by sudden Ca(2+) sequestration attained by uncaging diazo-2. In the presence of constant 8Br-cGMP, 15 micro, Ca(2+) concentration decrease was complete within 50 ms and membrane conductance was enhanced 2.33 +/- 0.95-fold with a mean time to peak of 1.25 +/- 0.23 s. We developed a model that assumes channel modulation is a pseudo-first-order process kinetically limited by free Ca(2+). Based on the experimentally measured changes in Ca(2+) concentration, model simulations match experimental data well by assigning the pseudo-first-order time constant a mean value of 0.40 +/- 0.14 s. Thus, Ca(2+)-dependent ligand modulation occurs over the concentration range of the normal, dark-adapted cone. Its time course suggests that its functional effects are important in the recovery of the cone photoresponse to a flash of light and during the response to steps of light, when cones adapt.     

昆虫嗅觉受体及其介导的信号转导机制研究进展

高度灵敏的嗅觉系统,能够帮助昆虫准确识别环境中不同来源的挥发性化合物,在昆虫觅食、交配和产卵等生命活动过程中起着至关重要的作用.通过感觉神经元膜上数量巨大且种类繁多的嗅觉受体,昆虫可以识别不同的气味物质,进而调控其行为.已知的昆虫嗅觉受体主要有三种,离子型受体、气味受体和响应二氧化碳及信息素的味觉受体.目前嗅觉受体的分子结构及其介导的信号转导机制仍然没有得到完整的阐释,嗅觉受体配体的鉴定工作也还任重道远.本综述就昆虫嗅觉受体的结构、进化、功能表征方法以及气味受体介导信号转导的机制等方面的研究进展进行了综述,以期对研究昆虫嗅觉编码和调控,以及昆虫与植物间互作提供一定的理论参考.     

Assessing the contributions of multiple interacting traits to plant reproductive success: environmental dependence

The reproductive success of sibling cocklebur plants (Compositae: Xanthium strumarium) was monitored after growth at different levels of availability of water and nutrient resources. Variation in reproductive success among individual plants was related to physiological, structural, and phenological characteristics. Reproductive success increased with increased availability of resources, but the relative contribution of particular traits to reproductive success varied with resource availability. Allocation of biomass to different vegetative tissues, time to seedling emergence, degree of branching, transpiration rates, water use efficiency, the rate of decline in height growth after seedling emergence and final plant size all varied significantly with resource availability. However, the changes in each of these phenotypic traits across three garden environments did not always correlate with reproductive success. The shifts across environments in the apparent importance of somatic traits for reproductive success were attributed to plastic changes in the traits but also to changes in the phenotypic correlations of the traits with reproductive success.