Experimentally elevated corticosterone does not affect bacteria killing ability of breeding female tree swallows (Tachycineta bicolor)

The immune system can be modulated when organisms are exposed to acute or chronic stressors. Glucocorticoids (GCs), the primary hormonal mediators of the physiological stress response, are suspected to play a crucial role in immune modulation. However, most evidence of stress-associated immunomodulation does not separate the effects of glucocorticoid-dependent pathways from those of glucocorticoid-independent mechanisms on immune function. In this study, we experimentally elevated circulating corticosterone, the main avian glucocorticoid, in free-living female tree swallows (Tachycineta bicolor) for one to two weeks to test its effects on immune modulation. Natural variation in bacteria killing ability (BKA), a measure of innate constitutive immunity, was predicted by the interaction between timing of breeding and corticosterone levels. However, experimental elevation of corticosterone had no effect on BKA. Therefore, even when BKA is correlated with natural variation in glucocorticoid levels, this relationship may not be causal. Experiments are necessary to uncover the causal mechanisms of immunomodulation and the consequences of acute and chronic stress on disease vulnerability. Findings in other species indicate that acute increases in GCs can suppress BKA; but our results support the hypothesis that this effect does not persist over longer timescales, during chronic elevations in GCs. Direct comparisons of the effects of acute vs. chronic elevation of GCs on BKA will be important for testing this hypothesis.

Social signal manipulation and environmental challenges have independent effects on physiology, internal microbiome, and reproductive performance in tree swallows (Tachycineta bicolor)

The social environment that individuals experience appears to be a particularly salient mediator of stress resilience, as the nature and valence of social interactions are often related to subsequent health, physiology, microbiota, and overall stress resilience. Relatively few studies have simultaneously manipulated the social environment and ecological challenges under natural conditions. Here, we report the results of experiments in wild tree swallows (Tachycineta bicolor) in which we manipulated both ecological challenges (predator encounters and flight efficiency reduction) and social interactions (by experimental dulling of a social signal). In two experiments conducted in separate years, we reversed the order of these treatments so that females experienced either an altered social signal followed by a challenge or vice-versa. Before, during, and after treatments were applied, we tracked breeding success, morphology and physiology (mass, corticosterone, and glucose), nest box visits via an RFID sensor network, cloacal microbiome diversity, and fledging success. Overall, we found that predator exposure during the nestling period reduced the likelihood of fledging and that signal manipulation sometimes altered nest box visitation patterns, but little evidence that the two categories of treatment interacted with each other. We discuss the implications of our results for understanding what types of challenges and what conditions are most likely to result in interactions between the social environment and ecological challenges.

Cold temperatures induce priming of the glucose stress response in tree swallows

Capricious environments often present wild animals with challenges that coincide or occur in sequence. Conceptual models of the stress response predict that one threat may prime or dampen the response to another. Although evidence has supported this for glucocorticoid responses, much less is known about the effects of previous challenges on energy mobilization. Food limitation may have a particularly important effect, by altering the ability to mobilize energy when faced with a subsequent challenge. We tested the prediction that challenging weather conditions, which reduce food availability, alter the energetic response to a subsequent acute challenge (capture and restraint). Using a three-year dataset from female tree swallows measured during three substages of breeding, we used a model comparison approach to test if weather (temperature, wind speed, and precipitation) over 3- or 72-hour timescales predicted baseline and post-restraint glucose levels, and if so which environmental factors were the strongest predictors. Contrary to our predictions, weather conditions did not affect baseline glucose; however, birds that had experienced lower temperatures over the preceding 72 h tended to have higher stress-induced glucose when faced with an acute stressor. We also saw some support for an effect of rainfall on stress-induced glucose: around the time that eggs hatched, birds that had experienced more rainfall over the preceding 72 h mounted lower responses. Overall, we find support in a wild animal for the idea that the glucose stress response may be primed by exposure to prior challenges.

Timing of Breeding Reveals a Trade-Off between Immune Investment and Life History in Tree Swallows

The allocation of limited resources among life history traits creates trade-offs that constrain the range of possible phenotypes of organisms. In animals, the cost of maintaining an effective immune response may reduce the ability to invest in reproduction, resulting in altered susceptibility to disease. However, not all members of a population face identical constraints because differences in an individual's environmental context or physiological state can influence the degree to which traits are negatively associated. Here, we evaluated how variation in timing of breeding, a correlate of fitness, may result in different patterns of trait associations between immunity and reproduction. We measured constitutive immunity in breeding female tree swallows (Tachycineta bicolor) using a bacteria killing assay with blood plasma to assess the relationships between bacteria killing ability (BKA), reproductive effort, and reproductive success. We found that timing of breeding can influence the association between BKA and reproductive effort, but its effects are not homogeneous among all traits. Late-breeding tree swallows with stronger BKA laid smaller clutches, a pattern that was not apparent in early breeders. Regardless of the timing of breeding, birds with stronger BKA fed their nestlings less. Despite a negative association with reproductive effort, we found no association between immunity and reproductive success. We provide evidence that individual tree swallows do not experience some trade-offs equally, and that timing of breeding likely plays a role in how costs of immunity are weighed. To understand how investment in immunity can limit life history traits, we must consider how a variation among individuals influences the relative costs of immunity.

Individual variation in natural or manipulated corticosterone does not covary with circulating glucose in a wild bird

Animals respond to sudden challenges with a coordinated set of physiological and behavioral responses that enhance the ability to cope with stressors. While general characteristics of the vertebrate stress response are well described, it is not as clear how individual components covary between- or within-individuals. A rapid increase in glucocorticoids coordinates the stress response and one of the primary downstream results is an increase in glucose availability via reduced glucose utilization. Here, we asked whether between- and within-individual variation in corticosterone directly predicted variation in glucose. We collected 2,673 paired glucose and corticosterone measures from 776 tree swallows (Tachycineta bicolor) from four populations spanning the species range. In adults, glucose and corticosterone both increased during a standardized restraint protocol in all four populations. Moreover, in one population experimentally increasing a precursor that stimulates corticosterone release resulted in a further increase in both measures. In contrast, nestlings did not show a robust glucose response to handling or manipulation. Despite this group level variation, there was very little evidence in any population that between-individual variation in corticosterone predicted between-individual variation in glucose regulation. Glucose was moderately repeatable within-individuals, but within-individual variation in glucose and corticosterone were unrelated. Our results highlight the fact that a strong response in one aspect of the coordinated acute stress response (corticosterone) does not necessarily indicate that specific downstream components, such as glucose, will show similarly strong responses. These results have implications for understanding the evolution of integrated stress response systems.

Live imaging of intra-lysosome pH in cell lines and primary neuronal culture using a novel genetically encoded biosensor

Disorders of lysosomal physiology have increasingly been found to underlie the pathology of a rapidly growing cast of neurodevelopmental disorders and sporadic diseases of aging. One cardinal aspect of lysosomal (dys)function is lysosomal acidification in which defects trigger lysosomal stress signaling and defects in proteolytic capacity. We have developed a genetically encoded ratiometric probe to measure lysosomal pH coupled with a purification tag to efficiently purify lysosomes for both proteomic and in vitro evaluation of their function. Using our probe, we showed that lysosomal pH is remarkably stable over a period of days in a variety of cell types. Additionally, this probe can be used to determine that lysosomal stress signaling via TFEB is uncoupled from gross changes in lysosomal pH. Finally, we demonstrated that while overexpression of ARL8B GTPase causes striking alkalinization of peripheral lysosomes in HEK293 T cells, peripheral lysosomes per se are no less acidic than juxtanuclear lysosomes in our cell lines.Abbreviations: ARL8B: ADP ribosylation factor like GTPase 8B; ATP: adenosine triphosphate; ATP5F1B/ATPB: ATP synthase F1 subunit beta; ATP6V1A: ATPase H+ transporting V1 subunit A; Baf: bafilomycin A1; BLOC-1: biogenesis of lysosome-related organelles complex 1; BSA: bovine serum albumin; Cos7: African green monkey kidney fibroblast-like cell line; CQ: chloroquine; CTSB: cathepsin B; CYCS: cytochrome c, somatic; DAPI: 4',6-diamidino -2- phenylindole; DIC: differential interference contrast; DIV: days in vitro; DMEM: Dulbecco's modified Eagle's medium;‎ E8: embryonic day 8; EEA1: early endosome antigen 1; EGTA: ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid; ER: endoplasmic reticulum; FBS: fetal bovine serum; FITC: fluorescein isothiocyanate; GABARAPL2: GABA type A receptor associated protein like 2; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GOLGA2/GM130: golgin A2; GTP: guanosine triphosphate; HEK293T: human embryonic kidney 293 cells, that expresses a mutant version of the SV40 large T antigen; HeLa: Henrietta Lacks-derived cell; HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; HRP: horseradish peroxidase; IGF2R/ciM6PR: insulin like growth factor 2 receptor; LAMP1/2: lysosomal associated membrane protein 1/2; LMAN2/VIP36: lectin, mannose binding 2; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTORC1: mechanistic target of rapamycin kinase complex 1; PCR: polymerase chain reaction; PDL: poly-d-lysine; PGK1p: promotor from human phosphoglycerate kinase 1; PIKFYVE: phosphoinositide kinase, FYVE-type zinc finger containing; PPT1/CLN1: palmitoyl-protein thioesterase 1; RPS6KB1/p70: ribosomal protein S6 kinase B1; STAT3: signal transducer and activator of transcription 3; TAX1BP1: Tax1 binding protein 1; TFEB: transcription factor EB; TGN: trans-Golgi network; TGOLN2/TGN46: trans-Golgi network protein 2; TIRF: total internal reflection fluorescence; TMEM106B: transmembrane protein 106B; TOR: target of rapamycin; TRPM2: transient receptor potential cation channel subfamily M member 2; V-ATPase: vacuolar-type proton-translocating ATPase; VPS35: VPS35 retromer complex component.

Tollip coordinates Parkin-dependent trafficking of mitochondrial-derived vesicles

Multiple mitochondrial quality control pathways exist to maintain the health of mitochondria and ensure cell homeostasis. Here, we investigate the role of the endosomal adaptor Tollip during the mitochondrial stress response and identify its interaction and colocalisation with the Parkinson's disease-associated E3 ubiquitin ligase Parkin. The interaction between Tollip and Parkin is dependent on the ubiquitin-binding CUE domain of Tollip, but independent of Tom1 and mitophagy. Interestingly, this interaction is independent of Parkin mitochondrial recruitment and ligase activity but requires an intact ubiquitin-like (UBL) domain. Importantly, Tollip regulates Parkin-dependent endosomal trafficking of a discrete subset of mitochondrial-derived vesicles (MDVs) to facilitate delivery to lysosomes. Retromer function and an interaction with Tom1 allow Tollip to facilitate late endosome/lysosome trafficking in response to mitochondrial stress. We find that upregulation of TOM20-positive MDVs upon mitochondrial stress requires Tollip interaction with ubiquitin, endosomal membranes and Tom1 to ensure their trafficking to the lysosomes. Thus, we conclude that Tollip, via an association with Parkin, is an essential coordinator to sort damaged mitochondrial-derived cargo to the lysosomes.

Stress Resilience and the Dynamic Regulation of Glucocorticoids

Vertebrates respond to a diversity of stressors by rapidly elevating glucocorticoid (GC) levels. The changes in physiology and behavior triggered by this response can be crucial for surviving a variety of challenges. Yet the same process that is invaluable in coping with immediate threats can also impose substantial damage over time. In addition to the pathological effects of long-term exposure to stress hormones, even relatively brief elevations can impair the expression of a variety of behaviors and physiological processes central to fitness, including sexual behavior, parental behavior, and immune function. Therefore, the ability to rapidly and effectively terminate the short-term response to stress may be fundamental to surviving and reproducing in dynamic environments. Here we review the evidence that variation in the ability to terminate the stress response through negative feedback is an important component of stress coping capacity. We suggest that coping capacity may also be influenced by variation in the dynamic regulation of GCs-specifically, the ability to rapidly turn on and off the stress response. Most tests of the fitness effects of these traits to date have focused on organisms experiencing severe or prolonged stressors. Here we use data collected from a long-term study of tree swallows (Tachycineta bicolor) to test whether variation in negative feedback, or other measures of GC regulation, predict components of fitness in non-chronically stressed populations. We find relatively consistent, but generally weak relationships between different fitness components and the strength of negative feedback. Reproductive success was highest in individuals that both mounted a robust stress response and had strong negative feedback. We did not see consistent evidence of a relationship between negative feedback and adult or nestling survival: negative feedback was retained in the best supported models of nestling and adult survival, but in two of three survival-related analyses the intercept-only model received only slightly less support. Both negative feedback and stress-induced GC levels-but not baseline GCs-were individually repeatable. These measures of GC activity did not consistently covary across ages and life history stages, indicating that they are independently regulated. Overall, the patterns seen here are consistent with the predictions that negative feedback-and the dynamic regulation of GCs-are important components of stress coping capacity, but that the fitness benefits of having strong negative feedback during the reproductive period are likely to manifest primarily in individuals exposed to chronic or repeated stressors.

Optineurin: A Coordinator of Membrane-Associated Cargo Trafficking and Autophagy

Optineurin is a multifunctional adaptor protein intimately involved in various vesicular trafficking pathways. Through interactions with an array of proteins, such as myosin VI, huntingtin, Rab8, and Tank-binding kinase 1, as well as via its oligomerisation, optineurin has the ability to act as an adaptor, scaffold, or signal regulator to coordinate many cellular processes associated with the trafficking of membrane-delivered cargo. Due to its diverse interactions and its distinct functions, optineurin is an essential component in a number of homeostatic pathways, such as protein trafficking and organelle maintenance. Through the binding of polyubiquitinated cargoes via its ubiquitin-binding domain, optineurin also serves as a selective autophagic receptor for the removal of a wide range of substrates. Alternatively, it can act in an ubiquitin-independent manner to mediate the clearance of protein aggregates. Regarding its disease associations, mutations in the optineurin gene are associated with glaucoma and have more recently been found to correlate with Paget’s disease of bone and amyotrophic lateral sclerosis (ALS). Indeed, ALS-associated mutations in optineurin result in defects in neuronal vesicular localisation, autophagosome–lysosome fusion, and secretory pathway function. More recent molecular and functional analysis has shown that it also plays a role in mitophagy, thus linking it to a number of other neurodegenerative conditions, such as Parkinson’s. Here, we review the role of optineurin in intracellular membrane trafficking, with a focus on autophagy, and describe how upstream signalling cascades are critical to its regulation. Current data and contradicting reports would suggest that optineurin is an important and selective autophagy receptor under specific conditions, whereby interplay, synergy, and functional redundancy with other receptors occurs. We will also discuss how dysfunction in optineurin-mediated pathways may lead to perturbation of critical cellular processes, which can drive the pathologies of number of diseases. Therefore, further understanding of optineurin function, its target specificity, and its mechanism of action will be critical in fully delineating its role in human disease.

Role of matrix metalloproteinases 2 and 9, toll-like receptor 4 and platelet-leukocyte aggregate formation in sepsis-associated thrombocytopenia

Background

The development of thrombocytopenia in sepsis is a poor prognostic indicator associated with a significantly increased mortality risk. Mechanisms underlying this phenomenon remain to be clearly elucidated. Matrix metalloproteinases (MMPs) are enzymes that regulate the turnover of the extra-cellular matrix. MMP-2 is recognised as a platelet agonist with MMP-9 proposed as an inhibitor of platelet activation. The existence of MMP-9 in platelets is a subject of debate. There is limited evidence thus far to suggest that toll-like receptor 4 (TLR-4) and platelet-leukocyte aggregate (PLA) formation may be implicated in the development of sepsis-associated thrombocytopenia.

Objectives

To investigate whether MMP -2/-9, toll-like receptor 4 (TLR-4) or platelet-leukocyte aggregate (PLA) formation are implicated in a decline in platelet numbers during septic shock.

Methods

This was an observational study which recruited healthy controls, non-thrombocytopenic septic donors and thrombocytopenic septic donors. MMP-2, MMP-9 and TLR-4 platelet surface expression as well as PLA formation was examined using flow cytometry. In addition MMP-2 and MMP-9 were examined by gelatin zymography and enzyme-linked immunosorbent assay (ELISA) using a 3 compartment model (plasma, intraplatelet and platelet membrane).

Results

There was no difference found in MMP-2, MMP-9 or TLR-4 levels between non-thrombocytopenic and thrombocytopenic septic donors. PLA formation was increased in thrombocytopenic patients. MMP-9 was detected in platelets using flow cytometry, gelatin zymography and ELISA techniques.

Conclusions

Platelet consumption into PLAs may account for the development of thrombocytopenia in septic shock. MMP-9 is found in platelets and it is upregulated during septic shock.

Short-term effects of military fog oil on the fountain darter (Etheostoma fonticola)

Toxicity tests evaluated chronic and sublethal effects of fog oil (FO) on a freshwater endangered fish. FO is released during military training as an obscurant smoke that can drift into aquatic habitats. Fountain darters, Etheostoma fonticola, of four distinct life stages were exposed under laboratory conditions to three forms of FO. FO was vaporized into smoke and allowed to settle onto water, violently agitated with water, and dosed onto water followed by photo-oxidization by ultraviolet irradiation. Single smoke exposures of spawning adult fish did not affect egg production, egg viability, or adult fish survival in 21-day tests. Multiple daily smoke exposures induced mortality after 5 days for larvae fish. Larvae and juvenile fish were more sensitive than eggs in 96-h lethal concentration (LC50) tests with FO–water mixtures and photo-oxidized FO. Water-soluble FO components photo-modified by ultraviolet radiation were the most toxic, thus indicating the value of examining weathering and aging of chemicals for the best determination of environmental impact.

Differences in sexual development in inbred and outbred zebrafish (Danio rerio) and implications for chemical testing

Outbred laboratory animal strains used in ecotoxicology are intended to represent wild populations. However, breeding history may vary considerably between strains, driving differences in genetic variation and phenotypes used for assessing effects of chemical exposure. We compared a range of phenotypic endpoints in zebrafish from four different "breeding treatments" comprising a Wild Indian Karyotype (WIK) zebrafish strain and a WIK/Wild strain with three levels of inbreeding (F(IT)=n, n+0.25, n+0.375) in a new Fish Sexual Development Test (FSDT). There were no differences between treatments in terms of egg viability, hatch success or fry survival. However, compared with WIKs, WIK/Wild hybrids were significantly larger in size, with more advanced gonadal (germ cell) development at the end of the test (63 days post fertilisation). Increasing the levels of inbreeding in the related WIK/Wild lines did not affect body size, but there was a significant male-bias (72%) in the most inbred line (F(IT)=n+0.375). Conversely, in the reference WIK strain there was a significant female-bias in the population (80% females). Overall, our results support the use of outbred zebrafish strains in the FSDT, where one of the core endpoints is sex ratio. Despite increased variance (and reduced statistical power) for some endpoints, WIK/Wild outbreds (F(IT)=n) met all acceptance criteria for controls in this test, whereas WIKs failed to comply with tolerance limits for sex ratio (30-70% females). Sexual development was also more advanced in WIK/Wild outbreds (cf. WIKs), providing greater scope for detection of developmental reproductive toxicity following chemical exposure.

Calcium: an important second messenger in mast cells

Recently there has been considerable controversy over the mechanism(s) by which intracellular Ca2+ is elevated when receptors for IgE on the surface of mast cells are aggregated by antigen. The central role played by calcium in the initiation of secretion from these cells has also been called into question. In a mast cell line which has been widely used to study stimulus-secretion coupling in non-excitable cells it is now clear that calcium is indeed important in the physiological response of the cells but that other intracellular messengers are also involved. In addition it has been shown that while the increase in intracellular Ca2+ probably originates from intracellular stores it can only be sustained by the influx of calcium across the plasma membrane. The nature of the Ca2+ permeability pathway has yet to be elucidated although a number of candidates for the calcium channel in mast cells have been proposed. Significant oscillations and spatial gradients of Ca2+ are often seen when the responses of individual antigen-stimulated cells are measured using digital imaging microscopy. The complexity of these responses highlights the importance of single-cell measurements in elucidating the relationship between IgE receptor activation, Ca2+ movements and exocytosis.

Correction of phenotype in a thalassemia mouse model using a nonmyeloablative marrow transplantation regimen

Gene therapy, the replacement of normal human beta- or gamma-globin genes into the hematopoietic stem cells of patients with homozygous beta-thalassemia, is a promising therapy for the future. High-level lineage-specific stable globin expression in transduced cells reinfused into patients in an autologous transplantation setting could be curative, if successful. Previous studies have shown high-level donor chimerism in nonmyeloablated non-thalassemic hosts. We have now studied the conditions for stable long-term engraftment of normal cells into a thalassemia mouse model that lead to high-level donor chimerism and correction of the abnormal phenotype. Thalassemic female mice treated with 0 to 300 cGy whole-body irradiation received transplantations of donor cells harvested from wild-type males. Engraftment of male cells was quantitated by Y-chromosome polymerase chain reaction analysis of blood and marrow progenitors, and changes in hemoglobin levels, red cell morphology, and spleen size were measured at various times posttransplantation. High-level stable donor cell engraftment was achieved in mice given 200 cGy and receiving transplants of 2 x 10(7) or more donor cells. The anemia, abnormal peripheral blood smears, and splenomegaly improved in the thalassemic mice that had successful engraftment. These studies demonstrate that stable and successful levels of engraftment of normal cells can correct the thalassemic phenotype without fully myeloablating the host. This animal model should allow us to test the amount of cytoreduction required and the level of engraftment and beta-globin expression needed in autologous transplantation of beta-globin gene-transduced cells to correct the abnormal phenotype in thalassemic mice, and it may be relevant to human clinical trials, as well.

NCAM and vesicle cycling: the importance of good glue in the long run

Careful functional dissection of mouse neuromuscular junctions (NMJs) formed in the absence of NCAM reveal that in spite of relatively normal morphology and ultrastructure, the presynaptic terminals have profound alterations in the mechanisms of recycling of synaptic vesicles. These alterations, including the appearance of a brefeldin-sensitive pathway, leave synaptic transmission impaired for certain types of activity. NCAMs thus appear to play a critical role in the molecular organization and function of synaptic terminals.

Synapsin dispersion and reclustering during synaptic activity

Presynaptic modulation of synaptic transmission provides an important basis for control of synaptic function. The synapsins, a family of highly conserved proteins associated with synaptic vesicles, have long been implicated in the regulation of neurotransmitter release. However, direct physiological measurements of the molecular mechanisms have been lacking. Here we show that in living hippocampal terminals, green fluorescent protein (GFP)-labeled synapsin Ia dissociates from synaptic vesicles, disperses into axons during action potential (AP) firing, and reclusters to synapses after the cessation of synaptic activity. Using various mutated forms of synapsin Ia that prevent phosphorylation at specific sites, we performed simultaneous FM 4-64 measurements of vesicle pool mobilization along with synapsin dispersion kinetics. These studies indicate that the rate of synapsin dispersion is controlled by phosphorylation, which in turn controls the kinetics of vesicle pool turnover. Thus synapsin acts as a phosphorylation-state-dependent regulator of synaptic vesicle mobilization, and hence, neurotransmitter release.

Visualizing recycling synaptic vesicles in hippocampal neurons by FM 1-43 photoconversion

Exo-endocytotic turnover of synaptic vesicles (SVs) at synapses between hippocampal neurons in culture was examined by electron microscopy (EM). We carried out photoconversion (PC) of the fluorescent endocytotic marker FM 1-43 by using 3,3'-diaminobenzidine to convert the dye signal into an electron-dense product. Electron-dense products were located almost exclusively in SVs, whose densities were bimodally distributed in two sharply demarcated populations, PC-positive (PC+) and PC-negative (PC-). The median densities of these populations did not vary with the proportion of vesicles stained within a presynaptic terminal (bouton). The proportion of PC+ SVs remained constant across consecutive thin sections of single boutons, but varied greatly from one bouton to another, indicating marked heterogeneity in exo-endocytotic activity. Our experiments indicated that only a minority of SVs were stained in most boutons after stimuli known to cause complete turnover of the functional vesicular pool. A direct spatial correlation was found between FM 1-43 fluorescent spots seen with light microscopy and PC+ boutons by EM. The correlation was clearer in isolated boutons than in clusters of boutons. Photoconversion in combination with FM dyes allows clarification of important aspects of vesicular traffic in central nervous system nerve terminals.

Presynaptic imaging techniques

Understanding the detailed molecular events that support chemical synaptic transmission requires high-resolution methods that provide quantitative information combined with molecular specificity. In recent years, many new technological approaches, including genetically encoded fluorescent indicators, ultra-thin sectioning, and live-cell imaging have been brought to bear on understanding the cell biology and physiology of presynaptic terminals.

Measurements of vesicle recycling in central neurons

Neurotransmitter-containing vesicles in presynaptic nerve terminals are essential for synaptic transmission. The vesicles undergo a cycle that leads to transmitter release by exocytosis followed by endocytosis and refilling of the vesicles. Here we discuss new optical methods that have helped researchers study this cycle at functional and molecular levels, which is essential for our understanding of the regulation of synaptic transmission.

Calcium accelerates endocytosis of vSNAREs at hippocampal synapses

A pH-sensitive form of green-fluorescent protein (GFP) fused to the lumenal domain of VAMP (synapto-pHluorin) provides a sensitive optical probe to track the net balance between exocytosis and endocytosis of this protein at small synaptic terminals of the central nervous system. Here we used a reversible proton-pump blocker that prevents vesicle re-acidification upon endocytosis to trap vesicles in the alkaline state during recycling. In combination with optical measurements of synapto-pHluorin, we used alkaline trapping to examine the kinetic components of exocytosis and endocytosis separately at synaptic terminals. Using this approach, we show that, in addition to controlling exocytosis, intracellular calcium levels tightly regulate the speed of endocytosis, increasing it to a maximal speed of approximately one vesicle per second.

Long-term survival and functional capacity in cardiac surgery patients after prolonged intensive care

OBJECTIVE

To determine whether hospital discharge alone represents a good outcome for patients who had prolonged intensive care after cardiac surgery by studying their postdischarge survival and functional outcome. The secondary objective is to estimate the proportion of intensive care unit (ICU) resources used by the long-stay (> or = 10 initial consecutive ICU days) patients and to identify preoperative patient characteristics that are associated with a prolonged ICU stay and hospital and long-term survival.

DESIGN

Inception cohort study.

SETTING

The Cleveland Clinic Foundation, a tertiary care, academic teaching institution.

PATIENTS

Cardiac surgery patients with an initial ICU stay of 10 or more consecutive days.

INTERVENTIONS

Data were collected daily during hospitalization on every adult who underwent coronary artery bypass graft and/or valve surgery at one institution in 1993. Discharged patients who spent >10 initial consecutive days in the ICU after surgery were contacted by telephone to determine vital status and functional capacity using the Duke Activity Status Index. Total ICU and total hospital direct costs were obtained for each patient.

MEASUREMENTS AND MAIN RESULTS

The primary outcome measurements were ICU length of stay, hospital mortality, after-surgery and postdischarge mortality and functional capacity, and relative resource utilization. Of the 2,618 cardiac surgery patients who met the inclusion criteria, 142 (5.4%) had an initial ICU length of stay of 10 or more consecutive days. Of these, 47 (33.1%) died in the hospital. Ninety-four of the 95 discharged patients were followed up (median follow-up, 30.6 months), and 44 of the 94 (46.8%) died during the follow-up period. The median Duke Activity Status Index for the 50 survivors was 26 out of a possible 58.2. The 142 long-stay patients used 50% of the total ICU days and 48% of the total ICU direct cost for all 2,618 patients.

CONCLUSIONS

Many survivors of prolonged intensive care die soon after hospital discharge and many longer term survivors have a poor functional state. Therefore, hospital discharge is an incomplete measure of outcome for these patients, and longer follow-up is more appropriate. The relatively small number of patients who require prolonged intensive care consumes a disproportionate amount of the total ICU and total hospital direct cost.

The use of pHluorins for optical measurements of presynaptic activity

Genetically encoded reporters for optical measurements of presynaptic activity hold significant promise for measurements of neurotransmission within intact or semi-intact neuronal networks. We have characterized pH-sensitive green fluorescent protein-based sensors (pHluorins) of synaptic vesicle cycling at nerve terminals. pHluorins have a pK approximately 7.1, which make them ideal for tracking synaptic vesicle lumen pH upon cycling through the plasma membrane during action potentials. A theoretical analysis of the expected signals using this approach and guidelines for future reporter development are provided.

Real-time measurements of vesicle-SNARE recycling in synapses of the central nervous system

Following the fusion of synaptic vesicles with the presynaptic plasma membrane of nerve terminals by the process of exocytosis, synaptic-vesicle components are recycled to replenish the vesicle pool. Here we use a pH-sensitive green fluorescent protein to measure the residence time of VAMP, a vesicle-associated SNARE protein important for membrane fusion, on the surfaces of synaptic terminals of hippocampal neurons following exocytosis. The time course of VAMP retrieval depends linearly on the amount of VAMP that is added to the plasma membrane, with retrieval occurring between about 4 seconds and 90 seconds after exocytosis, and newly internalized vesicles are rapidly acidified. These data are well described by a model in which endocytosis appears to be saturable, but proceeds with an initial maximum velocity of about one vesicle per second. We also find that, following exocytosis, a portion of the newly inserted VAMP appears on the surface of the axon.

Inhibitors of myosin light chain kinase block synaptic vesicle pool mobilization during action potential firing

During repetitive action potential firing the maintenance of synaptic transmission relies on a continued supply of synaptic vesicles for fusion with the presynaptic plasma membrane. The mechanism of transport by which vesicles are delivered to the site of fusion from a reserve pool is unknown, as are the biochemical pathways linking intracellular Ca2+ elevation with vesicle mobilization. Here, using the fluorescent tracer FM1-43 in hippocampal synaptic terminals, I show that inhibitors of myosin light chain kinase can block mobilization of the reserve pool and not the immediately releasable pool.

Predictors of outcome in cardiac surgical patients with prolonged intensive care stay

OBJECTIVE

To determine the predictors of outcome in cardiac surgical patients with prolonged ICU stay.

DESIGN

Inception cohort with retrospective chart review.

SETTING

Adult cardiovascular ICU.

PATIENTS

All patients admitted after cardiac surgery who stayed in ICU for at least 14 consecutive days.

INTERVENTIONS

Collection of data, including preoperative demographics, comorbidity, routine laboratory testing, surgical procedure, duration of cardiopulmonary bypass and aortic cross-clamping, postoperative requirement for transfusion and intra-aortic balloon counterpulsation, and postoperative indexes of organ dysfunction 14 and 28 days after surgery. An organ failure score (OFS) was calculated for days 1, 14, and 28.

OUTCOME MEASURES

Hospital mortality.

RESULTS

One hundred forty-one of 324 (43.5%) ICU admissions lasting at least 14 days resulted in hospital mortality. Seventy-four of 166 (45%) ICU admissions lasting at least 28 days resulted in hospital mortality. Preoperative demographics, morbidity, and indexes of organ failure in the first 24 h after surgery were not predictive of hospital mortality. Indexes of organ failure predictive of hospital death at 14 days included requirement for epinephrine infusion, diminished Glasgow coma scale, requirement for dialysis, greater value of BUN, lower value of creatinine, greater value of bilirubin, greater value of arterial PCO2, lower platelet count, and lower value of serum albumin. After a 28-day stay in ICU, the indexes of organ failure predictive of hospital mortality included requirement for dopamine or norepinephrine infusions, diminished Glasgow coma score, greater value of bilirubin, greater value of arterial PCO2, lower value of serum albumin, and advanced age. The area under the receiver operating characteristic curve for the OFS on day 1 was 0.55+/-0.04 (p=0.12), on day 14 it was 0.75+/-0.03 (p<0.0001), and on day 28 it was 0.76+/-0.04 (p<0.0001).

CONCLUSION

Preoperative health status and early organ failure were not predictive of late hospital mortality. The pattern of late organ failure associated with hospital mortality changed with time.

Optical detection of a quantal presynaptic membrane turnover

Exploration of the mechanisms and plasticity of synaptic transmission has been hindered by the lack of a method to measure single vesicle turnover directly in individual presynaptic boutons at isolated nerve terminals. Although postsynaptic electrical recordings have provided a wealth of invaluable basic information about quantal presynaptic processes, this approach has often proved difficult to apply at most central nervous system synapses. Here we describe the direct optical detection of single quantal events in individual presynaptic boutons of cultured hippocampal neurons. Using the fluorescent dye FM 1-43 as a tracer for presynaptic endocytosis, we have characterized both evoked and spontaneous components of presynaptic function at the level of individual quanta. Our results are consistent with quantal interpretations of previous electrophysiological analyses and provide new information about the unitary membrane recycling event and its coupling to individual action potential stimuli, about spontaneous vesicle turnover at individual boutons, and about the numbers of vesicles recycling at individual boutons.

Synaptic vesicle recycling in synapsin I knock-out mice

The synapsins are a family of four neuron-specific phosphoproteins that have been implicated in the regulation of neurotransmitter release. Nevertheless, knock-out mice lacking synapsin Ia and Ib, family members that are major substrates for cAMP and Ca2+/ Calmodulin (CaM)-dependent protein kinases, show limited phenotypic changes when analyzed electrophysiologically (Rosahl, T.W., D. Spillane, M. Missler, J. Herz, D.K. Selig, J.R. Wolff, R.E. Hammer, R.C. Malenka, and T.C. Sudhof. 1995. Nature (Lond.). 375: 488-493; Rosahl, T.W., M. Geppert, D. Spillane, D., J. Herz, R.E. Hammer, R.C. Malenka, and T.C. Sudhof. 1993. Cell. 75:661-670; Li, L., L.S. Chin, O. Shupliakov, L. Brodin, T.S. Sihra, O. Hvalby, V. Jensen, D. Zheng, J.O. McNamara, P. Greengard, and P. Andersen. 1995. Proc. Natl. Acad. Sci. USA. 92:9235-9239; see also Pieribone, V.A., O. Shupliakov, L. Brodin, S. Hilfiker-Rothenfluh, A.J. Czernik, and P. Greengard. 1995. Nature (Lond.). 375:493-497). Here, using the optical tracer FM 1-43, we characterize the details of synaptic vesicle recycling at individual synaptic boutons in hippocampal cell cultures derived from mice lacking synapsin I or wild-type equivalents. These studies show that both the number of vesicles exocytosed during brief action potential trains and the total recycling vesicle pool are significantly reduced in the synapsin I-deficient mice, while the kinetics of endocytosis and synaptic vesicle repriming appear normal.

Potentiation of evoked vesicle turnover at individually resolved synaptic boutons

We have studied synaptic plasticity in hippocampal cell cultures using a new imaging approach that allows unambiguous discrimination of presynaptic function at the level of single synaptic boutons. Employing a protocol designed to test for use-dependent plasticity resembling N-methyl-D-aspartate receptor-dependent long-term potentiation (NMDA-type LTP), we find that brief tetanic stimuli induce a potentiation of evoked synaptic vesicle turnover that lasts for at least 1 hr. Induction of this clearly presynaptic potentiation is blocked by putative postsynaptic glutamate receptor antagonists, suggesting that a retrograde induction signal might be involved. Potentiation appears to occur approximately equally at boutons of low and high initial release probabilities, and evidently does not involve an increase in the size of the total recycling synaptic vesicle pool.

The timing of synaptic vesicle endocytosis

Alternative models to describe the endocytosis phase of synaptic vesicle recycling are associated with time scales of vesicle recovery ranging from milliseconds to tens of seconds. There have been suggestions that one of the major models, envisioned as a slow process that occurs only after complete fusion of the vesicle membrane with the neurolemma, might be applicable only under conditions of heavy, nonphysiological stimulation. Using FM 1-43 and similar fluorescent probes to label recycling synaptic vesicles in rat hippocampal neurons, we have measured the kinetics of endocytosis with a wide range of action-potential-driven exocytotic loads. Our results indicate that when either 5% or 25% of the vesicle pool is used, vesicles are recovered with a half-time on the order of 20 s (24 degrees C). This endocytosis rate was not influenced by operations designed to alter intracellular Ca2+ during membrane retrieval, suggesting that residual Ca2+ after strong stimuli probably does not greatly retard endocytosis. Finally, we have shown that vesicle-destaining kinetics are not strongly influenced by the substantially differing rates at which two marker dyes tested dissociate from membranes. This observation suggests that vesicles remain open long enough for essentially complete dissociation of even the slower dye (a few seconds) or, alternatively, that both dyes readily escape vesicle membrane by lateral diffusion through any exocytotic opening. These data seem most consistent with applicability of the slow-endocytosis, complete-fusion model at low as well as high levels of exocytosis.

Vesicle pool mobilization during action potential firing at hippocampal synapses

Using the fluorescent membrane label FM 1-43, we have measured the release, reuptake, and repriming of synaptic vesicles in response to action potential stimulation of cultured hippocampal neurons. We find that approximately 90% of a recycling vesicle pool is released during 60 s of 10 Hz action potential firing, and that a single action potential releases approximately 0.5% of that pool. Our data also indicate that endocytic reuptake of vesicle membrane externalized by 10 Hz action potentials lags exocytosis, with a half-time on the order of 20 s, and that the minimum time for repriming of an endocytosed vesicle is on the order of 15 s. Finally, we find that once vesicles have undergone this repriming period, they become functionally mixed in the vesicle pool within a few minutes; the probability of release for recently recycled vesicles is indistinguishable from that of vesicles that have resided within the bouton for much longer periods.

Existence of nitric oxide synthase in rat hippocampal pyramidal cells

It has been proposed that nitric oxide (NO) serves as a key retrograde messenger during long-term potentiation at hippocampal synapses, linking induction of long-term potentiation in postsynaptic CA1 pyramidal cells to expression of long-term potentiation in presynaptic nerve terminals. However, nitric oxide synthase (NOS), the proposed NO-generating enzyme, has not yet been detected in the appropriate postsynaptic cells. We here demonstrate specific NOS immunoreactivity in the CA1 region of hippocampal sections by using an antibody specific for NOS type I and relatively gentle methods of fixation. NOS immunoreactivity was found in dendrites and cell bodies of CA1 pyramidal neurons. Cultured hippocampal pyramidal cells also displayed specific immunostaining. Control experiments showed no staining with preimmune serum or immune serum that was blocked with purified NOS. These results demonstrate that CA1 pyramidal cells contain NOS, as required were NO involved in retrograde signaling during hippocampal synaptic plasticity.

The kinetics of synaptic vesicle recycling measured at single presynaptic boutons

We used the fluorescent membrane probe FM 1-43 to label recycling synaptic vesicles within the presynaptic boutons of dissociated hippocampal neurons in culture. Quantitative time-lapse fluorescence imaging was employed in combination with rapid superfusion techniques to study the dynamics of synaptic vesicles within single boutons. This approach enabled us to measure exocytosis and to analyze the kinetics of endocytosis and the preparation of endocytosed vesicles for re-release (repriming). Our measurements indicate that under sustained membrane depolarization, endocytosis persists much longer than exocytosis, with a t1/2 approximately 60 s (approximately 24 degrees C); once internalized, vesicles become reavailable for exocytosis in approximately 30 s. Furthermore, we have shown that endocytosis is not dependent on membrane potential and, unlike exocytosis, that it is independent of extracellular Ca2+.

Ruffles induced by Salmonella and other stimuli direct macropinocytosis of bacteria

Ruffles are specialized plasma membrane ultrastructures of mammalian cells though to be integral to growth, development and locomotion. Induced by growth factors, mitogens or oncogene expression, ruffles are sites of filamentous actin rearrangement and are temporally associated with enhanced pinocytosis. But the function of ruffles, their mechanism of induction and their role in pinocytosis are not understood. We have observed formation of structures resembling ruffles associated with the site of entry of invasive Salmonella typhimurium. Here we report that ruffles elicited by invasive Salmonella directly mediate internalization of non-invasive bacteria in a macropinocytotic fashion, a phenomenon we term 'passive entry'. Furthermore, ruffles induced in the absence of Salmonella also facilitate passive entry. We present evidence that ruffles, common to many signalling events, comprise the macropinocytotic machinery mediating pinocytosis and are subverted by Salmonella so as to enter mammalian cells.

Spatial and temporal dissection of immediate and early events following cadherin-mediated epithelial cell adhesion

Cell-cell adhesion is at the top of a molecular cascade of protein interactions that leads to the remodeling of epithelial cell structure and function. The earliest events that initiate this cascade are poorly understood. Using high resolution differential interference contrast microscopy and retrospective immunohistochemistry, we observed that cell-cell contact in MDCK epithelial cells consists of distinct stages that correlate with specific changes in the interaction of E-cadherin with the cytoskeleton. We show that formation of a stable contact is preceded by numerous, transient contacts. During this time and immediately following formation of a stable contact, there are no detectable changes in the distribution, relative amount, or Triton X-100 insolubility of E-cadherin at the contact. After a lag period of approximately 10 min, there is a rapid acquisition of Triton X-100 insolubility of E-cadherin localized to the stable contact. Significantly, the total amount of E-cadherin at the contact remains unchanged during this time. The increase in the Triton X-100 insoluble pool of E-cadherin does not correlate with changes in the distribution of actin or fodrin, suggesting that the acquisition of the Triton X-100 insolubility is due to changes in E-cadherin itself, or closely associated proteins such as the catenins. The 10 minute lag period, and subsequent prompt and localized nature of E-cadherin reorganization indicate a form of signaling is occurring.

Mechanism for regulating cell surface distribution of Na+,K(+)-ATPase in polarized epithelial cells

Restriction of sodium, potassium adenosine triphosphatase (Na+,K(+)-ATPase) to either the apical or basal-lateral membrane domain of polarized epithelial cells is fundamental to vectorial ion and solute transport in many tissues and organs. A restricted membrane distribution of Na+,K(+)-ATPase in Madin-Darby canine kidney (MDCK) epithelial cells was found experimentally to be generated by preferential retention of active enzyme in the basal-lateral membrane domain and selective inactivation and loss from the apical membrane domain, rather than by vectorial targeting of newly synthesized protein from the Golgi complex to the basal-lateral membrane domain. These results show how different distributions of the same subunits of Na+,K(+)-ATPase may be generated in normal polarized epithelial and in disease states.

Imaging [Ca2+]i dynamics during signal transduction

The elevation of free intracellular Ca2+ activity ([Ca2+]i) is widely recognised as a central event in many signal transduction processes in cellular physiology. Recent advances in optical techniques for measuring [Ca2+]i as well as developments in quantitative low light level fluorescence microscopy have led to the application of these methods to the study of subcellular [Ca2+]i in many biological systems. In the following paper we describe some techniques in our laboratory to provide quantitative high spatio-temporal resolution measurements of [Ca2+]i in individual living cells during the signal transduction of cell surface receptor ligand interactions. In particular, we are studying the changes in [Ca2+]i induced by the micro-aggregation of immunoglobulin E (IgE) receptor complexes on the surface of rat basophilic leukemia (RBL) cells (a tumor mast cell line) by multivalent antigen. We seek to understand the mechanisms which are involved in the detection of these cell surface events which lead to changes in [Ca2+]i as well as the interactions between the various subcellular components which impart the delicate control of [Ca2+]i during cellular stimulation. The limitations and properties of the technology used for these studies will be discussed, and some illustrative examples of the type of [Ca2+]i changes found in this biological system will be given.

Immunoglobulin E receptor cross-linking induces oscillations in intracellular free ionized calcium in individual tumor mast cells

Fura-2 fluorescence in single rat basophilic leukemia cells was monitored to study the rise in intracellular free ionized calcium ([Ca2+]i) produced by aggregation of immunoglobulin E receptors. Repetitive transient increases in [Ca2+]i were induced by antigen stimulation and were measured using digital video imaging microscopy at high time resolution. The [Ca2+]i oscillations were not dependent upon changes in the membrane potential of the cells and were observed in cells stimulated with antigen either with or without extracellular Ca2+. Transient oscillations in [Ca2+]i were also observed when calcium influx was blocked with La3+. These results suggested that during antigen stimulation of cells under normal physiological conditions, release of Ca2+ from intracellular stores makes an important contribution to the initial increase in [Ca2+]i. Oscillations in [Ca2+]i are not induced by elevating [Ca2+]i with the calcium ionophore ionomycin. Mitochondrial calcium buffering is not required for [Ca2+]i oscillations to occur. The results show that rat basophilic leukemia cells have significant stores of calcium and that release of calcium from these stores can participate in both the initial rise and the oscillations in [Ca2+]i.

Memory impairment in schizophrenic patients with tardive dyskinesia

Memory functioning was contrasted in 40 schizophrenic patients with and without tardive dyskinesia (TD). Visual and verbal memory tests were used to investigate specific types of impairments. The presence of TD was ascertained using the Abnormal Involuntary Movement Scale (AIMS). TD patients scored significantly lower than non-TD patients on two measures of visual learning, though no differences were found for verbal learning or immediate recall. These results are consistent with previous reports that schizophrenic patients with TD demonstrate impaired cognitive functioning. They also raise the possibility that the neurochemical and structural changes underlying TD may produce specific deficits in memory for visual materials. In addition, a significant relationship was found between total score on the Brief Psychiatric Rating Scale (BPRS) and performance on all of the test measures included in the cognitive test battery. This demonstrates the importance of attending to the overall level of schizophrenic symptomatology when evaluating results from experimental learning tasks.

Molecular crowding on the cell surface

Strong steric interactions among proteins on crowded living cell surfaces were revealed by measurements of the equilibrium spatial distributions of proteins in applied potential gradients. The fraction of accessible surface occupied by mobile surface proteins can be accurately represented by including steric exclusion in the statistical thermodynamic analysis of the data. The analyses revealed enhanced, concentration-dependent activity coefficients, implying unanticipated thermodynamic activity even at typical cell surface receptor concentrations.