A simple ex vivo model of human renal allograft preservation using the gonadal vein

INTRODUCTION

Hypothermic machine perfusion, an organ preservation modality, involves flow of chilled preservation fluid through an allograft's vasculature. This study describes a simple, reproducible, human model that allows for interrogation of flow effects during ex vivo organ perfusion.

MATERIALS AND METHODS

Gonadal veins from deceased human renal allografts were subjected to either static cold storage or hypothermic machine perfusion for up to 24 hours. Caspase-3, Krüppel-like factor 2 expression and electron microscopic analysis were compared between 'flow' and 'no-flow' conditions, with living donor gonadal vein sections serving as negative controls.

RESULTS

The increase in caspase-3 expression was less pronounced for hypothermic machine-perfused veins compared with static cold storage (median-fold increase 1.2 vs 2.3; P < 0.05). Transmission electron microscopy provided ultrastructural corroboration of endothelial cell apoptosis in static cold storage conditions. For static cold storage preserved veins, Krüppel-like factor 2 expression diminished in a time-dependent manner between baseline and 12 hours (P < 0.05) but was abrogated and reversed by hypothermic machine perfusion (P < 0.05).

CONCLUSIONS

Our methodology is a simple, reproducible and successful model of ex vivo perfusion in the context of human organ preservation. To demonstrate the model's utility, we establish that two widely used markers of endothelial health (caspase-3 and Krüppel-like factor 2) differ between the flow and no-flow conditions of the two predominant kidney preservation modalities. These findings suggest that ex vivo perfusion may mediate the induction of a biochemically favourable endothelial niche which may contribute tohypothermic machine perfusion's association with improved renal transplantation outcomes.

Exploring the role of mononuclear phagocytes in the epididymis

The onslaught of foreign antigens carried by spermatozoa into the epididymis, an organ that has not demonstrated immune privilege, a decade or more after the establishment of central immune tolerance presents a unique biological challenge. Historically, the physical confinement of spermatozoa to the epididymal tubule enforced by a tightly interwoven wall of epithelial cells was considered sufficient enough to prevent cross talk between gametes and the immune system and, ultimately, autoimmune destruction. The discovery of an intricate arrangement of mononuclear phagocytes (MPs) comprising dendritic cells and macrophages in the murine epididymis suggests that we may have underestimated the existence of a sophisticated mucosal immune system in the posttesticular environment. This review consolidates our current knowledge of the physiology of MPs in the steady state epididymis and speculates on possible interactions between auto-antigenic spermatozoa, pathogens and the immune system by drawing on what is known about the immune system in the intestinal mucosa. Ultimately, further investigation will provide valuable information regarding the origins of pathologies arising as a result of autoimmune or inflammatory responses in the epididymis, including epididymitis and infertility.

Oxidative stress and male reproductive health

One of the major causes of defective sperm function is oxidative stress, which not only disrupts the integrity of sperm DNA but also limits the fertilizing potential of these cells as a result of collateral damage to proteins and lipids in the sperm plasma membrane. The origins of such oxidative stress appear to involve the sperm mitochondria, which have a tendency to generate high levels of superoxide anion as a prelude to entering the intrinsic apoptotic cascade. Unfortunately, these cells have very little capacity to respond to such an attack because they only possess the first enzyme in the base excision repair (BER) pathway, 8-oxoguanine glycosylase 1 (OGG1). The latter successfully creates an abasic site, but the spermatozoa cannot process the oxidative lesion further because they lack the downstream proteins (APE1, XRCC1) needed to complete the repair process. It is the responsibility of the oocyte to continue the BER pathway prior to initiation of S-phase of the first mitotic division. If a mistake is made by the oocyte at this stage of development, a mutation will be created that will be represented in every cell in the body. Such mechanisms may explain the increase in childhood cancers and other diseases observed in the offspring of males who have suffered oxidative stress in their germ line as a consequence of age, environmental or lifestyle factors. The high prevalence of oxidative DNA damage in the spermatozoa of male infertility patients may have implications for the health of children conceived in vitro and serves as a driver for current research into the origins of free radical generation in the germ line.

ROS1 signaling regulates epithelial differentiation in the epididymis

The initial segment (IS) of the epididymis plays an essential role in male fertility. The IS epithelium is undifferentiated and nonfunctional at birth. Prior to puberty, the epithelium undergoes differentiation that leads to the formation of a fully functional organ. However, the mechanistic details of this program are not well understood. To explore this further, we used genetic engineering to create a kinase dead allele of the ROS1 receptor tyrosine kinase in mice and studied the effects of ROS1 tyrosine kinase activity on the differentiation of the IS epithelium. We show that the expression and activation of ROS1 coincides with the onset of differentiation and is exclusively located in the IS of the maturing and adult mouse epididymides. Here we demonstrate that the differentiation of the IS is dependent on the kinase activity of ROS1 and its downstream effector MEK1/2-ERK1/2 signaling axis. Using genetic engineering, we show that germ line ablation of ROS1 kinase activity leads to a failure of the IS epithelium to differentiate, and as a consequence sperm maturation and infertility were dramatically perturbed. Pharmacological inhibition of ROS1 kinase activity in the developing epididymis, however, only delayed differentiation transiently and did not result in infertility. Our results demonstrate that ROS1 kinase activity and the ensuing MEK1/2-ERK1/2 signaling are necessary for the postnatal development of the IS epithelium and that a sustained ablation of ROS1 kinase activity within the critical window of terminal differentiation abrogate the function of the epididymis and leads to sterility.

Mononuclear phagocytes rapidly clear apoptotic epithelial cells in the proximal epididymis

We have shown previously that a network of mononuclear phagocytes (MPs) expressing macrophage and dendritic cell markers such as CD11c, F4/80 and CX3CR1, lines the base of the epididymal tubule. However, in the initial segment (IS) and only in that particular segment, epididymal MPs establish extremely close interactions with the epithelium by projecting slender dendrites between most epithelial cells. We undertook the present study to determine how epididymal phagocytes respond to the transient wave of apoptosis initiated by unilateral efferent duct ligation (EDL) in the epididymal epithelium. We show profound morphological and phenotypical changes restricted to the MPs populating the proximal epididymis following EDL. Within 48 h, a large subset of IS epithelial cells had entered an apoptotic state, visualized by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay and CD11c(+) and CX3CR1(+) MPs readily engulfed TUNEL-positive cells and other debris. Despite the high levels of apoptosis and the rapid clearance of apoptotic cells occurring after EDL, the epithelium preserved its overall architecture and maintained tight junctions of the blood-epididymis barrier (BEB). The discovery of a functional population of MPs in the epididymal epithelium responsible for maintaining the integrity of the BEB raises further questions regarding the role of these cells in clearing defective epithelial cells in the steady-state epididymis, as well as pathogens and abnormal spermatozoa in the lumen.

Epithelial basal cells are distinct from dendritic cells and macrophages in the mouse epididymis

The epithelium that lines the epididymal duct establishes the optimal milieu in which spermatozoa mature, acquire motility, and are stored. This finely tuned environment also protects antigenic sperm against pathogens and autoimmunity, which are potential causes of transient or permanent infertility. The epididymal epithelium is pseudostratified and contains basal cells (BCs) that are located beneath other epithelial cells. Previous studies showed that in the mouse epididymis, BCs possess macrophage-like characteristics. However, we previously identified a dense population of cells belonging to the mononuclear phagocyte (MP) system (comprised of macrophages and dendritic cells) in the basal compartment of the mouse epididymis and showed that a subset of MPs express the macrophage marker F4/80. In the present study, we evaluate the distribution of BCs and MPs in the epididymis of transgenic CD11c-EYFP mice, in which EYFP is expressed exclusively in MPs, using antibodies against the BC marker keratin 5 (KRT5) and the macrophage marker F4/80. Immunofluorescence labeling for laminin, a basement membrane marker, showed that BCs and most MPs are located in the basal region of the epithelium. Confocal microscopy showed that in the initial segment, both BCs and MPs project intraepithelial extensions and establish a very intricate network. Flow cytometry experiments demonstrated that epididymal MPs and BCs are phenotypically distinct. BCs do not express F4/80, and MPs do not express KRT5. Therefore, despite their proximity and some morphological similarities with peritubular macrophages and dendritic cells, BCs do not belong to the MP system.

Validation and evaluation of a novel time-resolved laser-induced fluorescence technique

We present a novel technique to measure time-resolved laser-induced fluorescence signals in plasma sources that have a relatively constant Fourier spectrum of oscillations in steady-state operation, but are not periodically pulsed, e.g., Hall thrusters. The technique uses laser modulation of the order of MHz and recovers signal via a combination of band-pass filtering, phase-sensitive detection, and averaging over estimated transfer functions calculated for many different cycles of the oscillation. Periodic discharge current oscillations were imposed on a hollow cathode. Measurements were validated by comparison with independent measurements from a lock-in amplifier and by comparing the results of the transfer function average to an independent analysis technique triggering averaging over many oscillation cycles in the time domain. The performance of the new technique is analyzed and compared to prior techniques, and it is shown that this new technique has a niche in measurements where the analog photomultiplier signal has a nonwhite noise spectral density and cycles of oscillation are not sufficiently repeatable to allow for reliable triggering or a meaningful average waveform in the time domain.

Functional deletion of Txndc2 and Txndc3 increases the susceptibility of spermatozoa to age-related oxidative stress

Oxidative stress in the male germ line is known to be a key factor in both the etiology of male infertility and the high levels of DNA damage encountered in human spermatozoa. Because the latter has been associated with a variety of adverse clinical outcomes, including miscarriage and developmental abnormalities in the offspring, the mechanisms that spermatozoa use to defend themselves against oxidative stress are of great interest. In this context, the male germ line expresses three unique forms of thioredoxin, known as thioredoxin domain-containing proteins (Txndc2, Txndc3, and Txndc8). Two of these proteins, Txndc2 and Txndc3, retain association with the spermatozoa after spermiation and potentially play an important role in regulating the redox status of the mature gamete. To address this area, we have functionally deleted the sperm-specific thioredoxins from the male germ line of mice by either exon deletion (Txndc2) or mutation of the bioactive cysteines (Txndc3). The combined inactivation of these Txndc isoforms did not have an overall impact on spermatogenesis, epididymal sperm maturation, or fertility. However, Txndc deficiency in spermatozoa did lead to age-dependent changes in these cells as reflected by accelerated motility loss, high rates of DNA damage, increases in reactive oxygen species generation, enhanced formation of lipid aldehyde-protein adducts, and impaired protamination of the sperm chromatin. These results suggest that although there is considerable redundancy in the systems employed by spermatozoa to defend themselves against oxidative stress, the sperm-specific thioredoxins, Txndc2 and Txndc3, are critically important in protecting these cells against the increases in oxidative stress associated with paternal age.

The senescence-accelerated mouse prone 8 as a model for oxidative stress and impaired DNA repair in the male germ line

The discovery of a truncated base excision repair pathway in human spermatozoa mediated by OGG1 has raised questions regarding the effect of mutations in critical DNA repair genes on the integrity of the paternal genome. The senescence-accelerated mouse prone 8 (SAMP8) is a mouse model containing a suite of naturally occurring mutations resulting in an accelerated senescence phenotype largely mediated by oxidative stress, which is further enhanced by a mutation in theOgg1gene, greatly reducing the ability of the enzyme to excise 8-hydroxy,2′-deoxyguanosine (8OHdG) adducts. An analysis of the reproductive phenotype of the SAMP8 males revealed a high level of DNA damage in caudal epididymal spermatozoa as measured by the alkaline Comet assay. Furthermore, these lesions were confirmed to be oxidative in nature, as demonstrated by significant increases in 8OHdG adduct formation in the SAMP8 testicular tissue (P<0.05) as well as in mature spermatozoa (P<0.001) relative to a control strain (SAMR1). Despite this high level of oxidative DNA damage in spermatozoa, reactive oxygen species generation was not elevated and motility of spermatozoa was found to be similar to that for the control strain with the exception of progressive motility, which exhibited a slight but significant decline with advancing age (P<0.05). When challenged with Fenton reagents (H2O2and Fe2+), the SAMP8 spermatozoa demonstrated a highly increased susceptibility to formation of 8OHdG adducts compared with the controls (P<0.001). These data highlight the role of oxidative stress and OGG1-dependent base excision repair mechanisms in defining the genetic integrity of mammalian spermatozoa.

The presence of a truncated base excision repair pathway in human spermatozoa that is mediated by OGG1

DNA repair has long been considered impossible in human spermatozoa due to the high level of DNA compaction observed in these cells. However, detailed examination of the base excision repair pathway in human spermatozoa has revealed the presence of an enzyme critical to this pathway, 8-oxoguanine DNA glycosylase 1 (OGG1). This glycosylase was associated with the sperm nucleus and mitochondria and could actively excise 8-hydroxy-2'-deoxyguanosine (8OHdG), releasing this adduct into the extracellular space. This activity was significantly reduced in the presence of cadmium (II), a recognized inhibitor of OGG1, in a time- and dose-dependent manner (P<0.001). Remarkably, spermatozoa do not possess the downstream components of the base excision repair pathway, apurinic endonuclease 1 (APE1) and X-ray repair complementing defective repair in Chinese hamster cells 1 (XRCC1). The absence of these proteins was particularly significant, as APE1 is required to create a 3'-hydroxyl (3'-OH) terminus at the apurinic site created by OGG1, which would be recognized by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. As a result, TUNEL was unable to detect oxidatively induced DNA damage in spermatozoa following exposure to hydrogen peroxide. In the same cells, intracellular and extracellular 8OHdG could be clearly detected in a manner that was highly correlated with the outcome of the sperm chromatin structure assay (SCSA). However, incubation of these cells for 48 hours revealed a time-dependent increase in TUNEL positivity, suggesting the perimortem activation of a nuclease. These results emphasize the limited capacity of mature spermatozoa to mount a DNA repair response to oxidative stress, and highlight the importance of such mechanisms in the oocyte in order to protect the embryo from paternally mediated genetic damage.

On methods for the detection of reactive oxygen species generation by human spermatozoa: analysis of the cellular responses to catechol oestrogen, lipid aldehyde, menadione and arachidonic acid

Oxidative stress is known to have a major impact on human sperm function and, as a result, there is a need to develop sensitive methods for measuring reactive oxygen species (ROS) generation by these cells. A variety of techniques have been developed for this purpose including chemiluminescence (luminol and lucigenin), flow cytometry (MitoSOX Red, dihydroethidium, 4,5-diaminofluorescein diacetate and 2',7'-dichlorodihydrofluorescein diacetate) and spectrophotometry (nitroblue tetrazolium). The relative sensitivity of these assays and their comparative ability to detect ROS generated in different subcellular compartments of human spermatozoa, have not previously been investigated. To address this issue, we have compared the performance of these assays when ROS generation was triggered with a variety of reagents including 2-hydroxyestradiol, menadione, 4-hydroxynonenal and arachidonic acid. The results revealed that menadione predominantly induced release of ROS into the extracellular space where these metabolites could be readily detected by luminol-peroxidase and, to a lesser extent, 2',7'-dichlorodihydrofluorescein. However, such sensitivity to extracellular ROS meant that these assays were particularly vulnerable to interference by leucocytes. The remaining reagents predominantly elicited ROS generation by the sperm mitochondria and could be optimally detected by MitoSOX Red and DHE. Examination of spontaneous ROS generation by defective human spermatozoa revealed that MitoSOX Red was the most effective indicator of oxidative stress, thereby emphasizing the general importance of mitochondrial dysregulation in the aetiology of defective sperm function.

Origin and population history of a recent colonizer, the yellow warbler in Galápagos and Cocos Islands

The faunas associated with oceanic islands provide exceptional examples with which to examine the dispersal abilities of different taxa and test the relative contribution of selective and neutral processes in evolution. We examine the patterns of recent differentiation and the relative roles of gene flow and selection in genetic and morphological variation in the yellow warbler (Dendroica petechia aureola) from the Galápagos and Cocos Islands. Our analyses suggest aureola diverged from Central American lineages colonizing the Galápagos and Cocos Islands recently, likely less than 300 000 years ago. Within the Galápagos, patterns of genetic variation in microsatellite and mitochondrial markers suggest early stages of diversification. No intra-island patterns of morphological variation were found, even across steep ecological gradients, suggesting that either (i) high levels of gene flow may be homogenizing the effects of selection, (ii) populations may not have had enough time to accumulate the differences in morphological traits, or (iii) yellow warblers show lower levels of 'evolvability' than some other Galápagos species. By examining genetic data and morphological variation, our results provide new insight into the microevolutionary processes driving the patterns of variation.

Nonspecific patterns of vector, host and avian malaria parasite associations in a central African rainforest

Malaria parasites use vertebrate hosts for asexual multiplication and Culicidae mosquitoes for sexual and asexual development, yet the literature on avian malaria remains biased towards examining the asexual stages of the life cycle in birds. To fully understand parasite evolution and mechanism of malaria transmission, knowledge of all three components of the vector-host-parasite system is essential. Little is known about avian parasite-vector associations in African rainforests where numerous species of birds are infected with avian haemosporidians of the genera Plasmodium and Haemoproteus. Here we applied high resolution melt qPCR-based techniques and nested PCR to examine the occurrence and diversity of mitochondrial cytochrome b gene sequences of haemosporidian parasites in wild-caught mosquitoes sampled across 12 sites in Cameroon. In all, 3134 mosquitoes representing 27 species were screened. Mosquitoes belonging to four genera (Aedes, Coquillettidia, Culex and Mansonia) were infected with twenty-two parasite lineages (18 Plasmodium spp. and 4 Haemoproteus spp.). Presence of Plasmodium sporozoites in salivary glands of Coquillettidia aurites further established these mosquitoes as likely vectors. Occurrence of parasite lineages differed significantly among genera, as well as their probability of being infected with malaria across species and sites. Approximately one-third of these lineages were previously detected in other avian host species from the region, indicating that vertebrate host sharing is a common feature and that avian Plasmodium spp. vector breadth does not always accompany vertebrate-host breadth. This study suggests extensive invertebrate host shifts in mosquito-parasite interactions and that avian Plasmodium species are most likely not tightly coevolved with vector species.

Spatially explicit predictions of blood parasites in a widely distributed African rainforest bird

Critical to the mitigation of parasitic vector-borne diseases is the development of accurate spatial predictions that integrate environmental conditions conducive to pathogen proliferation. Species of Plasmodium and Trypanosoma readily infect humans, and are also common in birds. Here, we develop predictive spatial models for the prevalence of these blood parasites in the olive sunbird (Cyanomitra olivacea). Since this species exhibits high natural parasite prevalence and occupies diverse habitats in tropical Africa, it represents a distinctive ecological model system for studying vector-borne pathogens. We used PCR and microscopy to screen for haematozoa from 28 sites in Central and West Africa. Species distribution models were constructed to associate ground-based and remotely sensed environmental variables with parasite presence. We then used machine-learning algorithm models to identify relationships between parasite prevalence and environmental predictors. Finally, predictive maps were generated by projecting model outputs to geographically unsampled areas. Results indicate that for Plasmodium spp., the maximum temperature of the warmest month was most important in predicting prevalence. For Trypanosoma spp., seasonal canopy moisture variability was the most important predictor. The models presented here visualize gradients of disease prevalence, identify pathogen hotspots and will be instrumental in studying the effects of ecological change on these and other pathogens.

Assessing coral reef health across onshore to offshore stress gradients in the US Virgin Islands

Managing the effects of anthropogenic disturbance on coral reefs is highly dependant on effective strategies to assess degradation and recovery. We used five years of field data in the US Virgin Islands to investigate coral reef response to a potential gradient of stress. We found that the prevalence of old partial mortality, bleaching, and all forms of coral health impairment (a novel category) increased with nearshore anthropogenic processes, such as a five-fold higher rate of clay and silt sedimentation. Other patterns of coral health, such as recent partial mortality, other diseases, and benthic cover, did not respond to this potential gradient of stress or their response could not be resolved at the frequency or scale of monitoring. We suggest that persistent signs of disturbance are more useful to short-term, non-intensive (annual) coral reef assessments, but more intensive (semi-annual) assessments are necessary to resolve patterns of transient signs of coral health impairment.

Divergence in mating signals correlates with ecological variation in the migratory songbird, Swainson's thrush (Catharus ustulatus)

Song divergence among populations of passerine birds is recognized as a potentially important premating isolation mechanism and may represent the first step in speciation. Because song divergence may be influenced by an array of acoustic, ecological, and genetic factors, the study of its origin requires a multifaceted approach. Here we describe the relationship between acoustic, neutral genetic and ecological variation in five populations of the Swainson's thrush: two from coastal temperate rainforest habitat representing the 'russet-backed' subspecies group, two from inland coniferous forest habitat representing the 'olive-backed' subspecies group, and one mixed locality that resides within a contact zone between the two groups. Song in the five populations is analysed using a multivariate analysis of spectral and temporal measurements, population genetic structure is assessed using an analysis of five microsatellite loci and ecological differences between populations are quantified using an analysis of climatic parameters. Matrix correspondence tests are used to distinguish between the potential for drift and selection in driving song divergence. No significant correlation was found between acoustic and genetic distance suggesting that song divergence cannot be explained by drift alone. A significant correlation between ecological and acoustic distance after accounting for genetic distance, suggests a potential role for ecological selection on divergence in spectral and temporal components of Swainson's thrush song.

Measurement of Parity Violation in np Capture: the NPDGamma Experiment

The NPDGamma experiment will measure the parity-violating directional gamma ray asymmetry A γ in the reaction [Formula: see text]. Ultimately, this will constitute the first measurement in the neutron-proton system that is sensitive enough to challenge modern theories of nuclear parity violation, providing a theoretically clean determination of the weak pion-nucleon coupling. A new beam-line at the Los Alamos Neutron Science Center (LANSCE) delivers pulsed cold neutrons to the apparatus, where they are polarized by transmission through a large volume polarized (3)He spin filter and captured in a liquid para-hydrogen target. The 2.2 MeV gamma rays from the capture reaction are detected in an array of CsI(Tl) scintillators read out by vacuum photodiodes operated in current mode. We will complete commissioning of the apparatus and carry out a first measurement at LANSCE in 2004-05, which would provide a statistics-limited result for A γ accurate to a standard uncertainty of ±5 × 10(-8) level or better, improving on existing measurements in the neutron-proton system by a factor of 4. Plans to move the experiment to a reactor facility, where the greater flux would enable us to make a measurement with a standard uncertainty of ±1 × 10(-8), are actively being pursued for the longer term.

Commissioning of the NPDGamma Detector Array: Counting Statistics in Current Mode Operation and Parity Violation in the Capture of Cold Neutrons on B 4 C and (27) Al

The NPDGamma γ-ray detector has been built to measure, with high accuracy, the size of the small parity-violating asymmetry in the angular distribution of gamma rays from the capture of polarized cold neutrons by protons. The high cold neutron flux at the Los Alamos Neutron Scattering Center (LANSCE) spallation neutron source and control of systematic errors require the use of current mode detection with vacuum photodiodes and low-noise solid-state preamplifiers. We show that the detector array operates at counting statistics and that the asymmetries due to B4C and (27)Al are zero to with- in 2 × 10(-6) and 7 × 10(-7), respectively. Boron and aluminum are used throughout the experiment. The results presented here are preliminary.

Testing alternative mechanisms of evolutionary divergence in an African rain forest passerine bird

Abstract Models of speciation in African rain forests have stressed either the role of isolation or ecological gradients. Here we contrast patterns of morphological and genetic divergence in parapatric and allopatric populations of the Little Greenbul, Andropadus virens, within different and similar habitats. We sampled 263 individuals from 18 sites and four different habitat types in Upper and Lower Guinea. We show that despite relatively high rates of gene flow among populations, A. virens has undergone significant morphological divergence across the savanna-forest ecotone and mountain-forest boundaries. These data support a central component of the divergence-with-gene-flow model of speciation by suggesting that despite large amounts of gene flow, selection is sufficiently intense to cause morphological divergence. Despite evidence of isolation based on neutral genetic markers, we find little evidence of morphological divergence in fitness-related traits between hypothesized refugial areas. Although genetic evidence suggests populations in Upper and Lower Guinea have been isolated for over 2 million years, morphological divergence appears to be driven more by habitat differences than geographic isolation and suggests that selection in parapatry may be more important than geographic isolation in causing adaptive divergence in morphology.

Refugial isolation versus ecological gradients. Testing alternative mechanisms of evolutionary divergence in four rainforest vertebrates

Hypotheses for divergence and speciation in rainforests generally fall into two categories: those emphasizing the role of geographic isolation and those emphasizing the role of divergent selection along gradients. While a majority of studies have attempted to infer mechanisms based on the pattern of species richness and congruence of geographic boundaries, relatively few have tried to simultaneously test alternative hypotheses for diversification. Here we discuss four examples, taken from our work on diversification of tropical rainforest vertebrates, in which we examine patterns of genetic and morphological variation within and between biogeographic regions to address two alternative hypotheses. By estimating morphological divergence between geographically contiguous and isolated populations under similar and different ecological conditions, we attempt to evaluate the relative roles of geographic isolation and natural selection in population divergence. Results suggest that natural selection, even in the presence of appreciable gene flow, can result in morphological divergence that is greater than that found between populations isolated for millions of years and, in some cases, even greater than that found between congeneric, but distinct, species. The relatively small phenotypic divergence that occurs among long-term geographic isolates in similar habitats suggests that morphological divergence via drift may be negligible and/or that selection is acting to produce similar phenotypes in populations occupying similar habitats. Our results demonstrate that significant phenotypic divergence: (1) is not necessarily coupled with divergence in neutral molecular markers; and (2) can occur without geographic isolation in the presence of gene flow.

Phylogeographical approaches to assessing demographic connectivity between breeding and overwintering regions in a Nearctic-Neotropical warbler (Wilsonia pusilla)

We characterized the pattern and magnitude of phylogeographical variation among breeding populations of a long-distance migratory bird, the Wilson's warbler (Wilsonia pusilla), and used this information to assess the utility of mtDNA markers for assaying demographic connectivity between breeding and overwintering regions. We found a complex pattern of population differentiation in mitochondrial DNA (mtDNA) variation among populations across the breeding range. Individuals from eastern North America were differentiated from western individuals and the eastern haplotypes formed a distinct, well-supported cluster. The more diverse western group contained haplotype clusters with significant geographical structuring, but there was also broad mixing of haplotype groups such that no haplotype groups were population specific and the predominance of rare haplotypes limited the utility of frequency-based assignment techniques. Nonetheless, the existence of geographically diagnosable eastern vs. western haplotypes enabled us to characterize the distribution of these two groups across 14 overwintering locations. Western haplotypes were present at much higher frequencies than eastern haplotypes at most overwintering sites. Application of this mtDNA-based method of linking breeding and overwintering populations on a finer geographical scale was precluded by the absence of population-specific markers and by insufficient haplotype sorting among western breeding populations. Our results suggest that because migratory species such as the Wilson's warbler likely experienced extensive gene flow among regional breeding populations, molecular markers will have the greatest utility for characterizing breeding-overwintering connectivity at a broad geographical scale.

Host specificity and incidence of Trypanosoma in some African rainforest birds: a molecular approach

Studies of host-parasite interactions in birds have contributed greatly to our understanding of the evolution and ecology of disease. Here we employ molecular techniques to determine the incidence and study the host-specificity of parasitic trypanosomes in the African avifauna. We developed a polymerase chain reaction (PCR)-based diagnostic test that amplified the small subunit ribosomal RNA gene (SSU rRNA) of Trypanosoma from avian blood samples. This nested PCR assay complements and corroborates information obtained by the traditional method of blood smear analysis. The test was used to describe the incidence of trypanosomes in 479 host individuals representing 71 rainforest bird species from Cameroon, the Ivory Coast and Equatorial Guinea. Forty-two (59%) of these potential host species harboured trypanosomes and 189 individuals (35%) were infected. To examine host and geographical specificity, we examined the morphology and sequenced a portion of the SSU rRNA gene from representative trypanosomes drawn from different hosts and collecting locations. In traditional blood smear analyses we identified two trypanosome morphospecies, T. avium and T. everetti. Our molecular and morphological results were congruent in that these two morphospecies had highly divergent SSU rRNA sequences, but the molecular assay also identified cryptic variation in T. avium, in which we found seven closely allied haplotypes. The pattern of sequence diversity within T. avium provides evidence for widespread trypanosome mixing across avian host taxa and across geographical locations. For example, T. avium lineages with identical haplotypes infected birds from different families, whereas single host species were infected by T. avium lineages with different haplotypes. Furthermore, some conspecific hosts from geographically distant sampling locations were infected with the same trypanosome lineage, but other individuals from those locations harboured different trypanosome lineages. This apparent lack of host or geographical specificity may have important consequences for the evolutionary and ecological interactions between parasitic trypanosomes and their avian hosts.

Seasonal variation in the feeding ecology of the grey-cheeked mangabey (Lophocebus albigena) in Cameroon

Seasonal fluctuations in resource abundance often cause primates to change their feeding behavior and ecology. The objective of this study was to examine the response of a largely frugivorous monkey, the grey-cheeked mangabey (Lophocebus albigena), to seasonal variations in fruit abundance. We used 15-min scan sampling to quantify feeding, activity, and habitat use by monkeys between February and December 1998 in the Dja Reserve, Cameroon. L. albigena were found to have omnivorous feeding habits, consuming the fruits, seeds, leaves, and flowers of 132 plant species. Although monkeys fed from many plant species, only five plant species accounted for 45% of all feeding records. The number of feeding observations on a plant species was significantly correlated with its fruit production. L. albigena responded to fruit-lean periods by shifting from a diet dominated by fruit to one dominated by seeds, flowers, and young leaves. This diet shift coincided with greater use of swamp habitat and higher dietary diversity. L. albigena spent the greatest percentage of scan samples feeding and traveling, but activities varied significantly over the day. Individuals spent a significantly higher percentage of scan samples feeding during the fruit-rich season than in the fruit-lean season. Comparing our results to those of studies in Gabon and Uganda, we found that L. albigena differ across regions in the number of plant species they consume and time spent feeding. These differences may be a result of variations in tree diversity or the strength of seasonal fluctuations in resource abundance among sites.

Parenting stress in families of children with disabilities

Using measures of child and family functioning, this study evaluated levels of parenting stress in 880 families of children with disabilities. Results suggest that factors such as income, time available for interaction with the child, and social support predict parenting stress much better than do aspects of child functioning. Implications for intervention and for future research are discussed.

Ethnic representation in a sample of the literature of applied psychology

A number of authors have raised concerns over the external validity of psychological research. This study examined the extent to which empirical articles include human participants from diverse ethnic backgrounds. Articles published over a 5-year period in 14 selected journals representing 3 applied sub-disciplines of psychology were examined. Of the 2,536 articles coded, only 61% indicated the ethnicity of the participants. For those articles, the ethnic compositions approximated U.S. Census estimates, with the exception of an overrepresentation of African Americans and an underrepresentation of Hispanic Americans. The results imply that although the field is apparently adequately recruiting English speakers, representation of non-English speakers should be increased. To further enhance the external validity of psychological research, ethnicity of participants should be not only specified but also analyzed in relation to the results of a study.

Ethnic representation in a sample of the literature of applied psychology

A number of authors have raised concerns over the external validity of psychological research. This study examined the extent to which empirical articles include human participants from diverse ethnic backgrounds. Articles published over a 5-year period in 14 selected journals representing 3 applied sub-disciplines of psychology were examined. Of the 2,536 articles coded, only 61% indicated the ethnicity of the participants. For those articles, the ethnic compositions approximated U.S. Census estimates, with the exception of an overrepresentation of African Americans and an underrepresentation of Hispanic Americans. The results imply that although the field is apparently adequately recruiting English speakers, representation of non-English speakers should be increased. To further enhance the external validity of psychological research, ethnicity of participants should be not only specified but also analyzed in relation to the results of a study.

Comparative avian phylogeography of Cameroon and equatorial Guinea mountains: implications for conservation

We illustrate the use of Faith's 'Phylogenetic Diversity' measure to compare the phylogeographic structure of two bird species with patterns of avian endemism across six mountains in Cameroon and Equatorial Guinea. The Mountain Greenbul and Cameroon Blue-headed Sunbird showed phylogeographic patterns that together defined three biogeographic regions: Bioko, Mt. Cameroon, and the northern mountains of Cameroon. In contrast, the distributions of endemic species were largely a function of geographical distance, with close mountains sharing more endemic species than distant mountains. Moreover, for both species, populations on Mt. Cameroon were distinctive with respect to the ecologically relevant character bill size. Our results, while preliminary, illustrate the utility of a comparative approach for identifying geographical regions that harbour evolutionarily distinct populations and caution against using only the distributional patterns of endemics to prioritize regions for conservation. Results show that patterns of endemism may not be concordant with patterns of phylogenetic diversity nor morphological variation in a character important in fitness. While incorporation of additional species from unrelated taxa will be necessary to draw definitive conclusions about evolutionarily distinct regions, our preliminary results suggest a conservation approach for the Afromontane region of the Gulf of Guinea that would: (i) emphasize protection of both Bioko and Mt. Cameroon, thereby maximizing preservation of within-species phylogenetic and morphologic diversity; (ii) emphasize protection within the northern mountains to further conserve intraspecific phylogenetic diversity and maximize protection of endemic species.

Effects of mothers' locus of control for child improvement in a developmentally delayed sample

A potentially important variable that has received little attention in the literature is the locus of control (LOC) a caregiver holds for child improvement, including its influence on the caregiver's treatment compliance and on actual child improvement. In this study, 131 mother-child dyads were assessed across 1 year, to evaluate the utility of the LOC construct in a practice setting. Children were approximately 4 years old at the first assessment, and all of them had been diagnosed with a developmental disability. Mothers' compliance with treatment (mothers' attendance at sessions; teachers' ratings of mothers' support and knowledge) was tracked, and measures of child development status and mothers' locus of control were administered. Statistical results indicated that mothers' locus of control was not significantly correlated with children's gains in development over the year. The mothers' beliefs about whether the child or chance would be responsible for improvement were associated with lower compliance with treatment, whereas the mothers' beliefs that child improvement was attributable to professional intervention were associated with enhanced involvement in treatment.

Genetic evidence for the effect of a postglacial population expansion on the phylogeography of a North American songbird

Phylogeographical studies of Nearctic songbirds conducted to date have yielded unexpectedly low levels of genetic differentiation and weak phylogeographical structure in mitochondrial DNA lineages as compared with species studied in Neotropical areas. Factors leading to this pattern may include (i) gene flow, (ii) population expansions from bottlenecked populations, and (iii) selective sweeps. Here we provide evidence for the role played by Pleistocene postglacial population expansions on the phylogeography of MacGillivray's warbler (Oporornis tolmiei), a long-distance migratory bird. Samples from 12 breeding localities in the temperate USA were compared with those from two localities in north-eastern Mexico. The former showed evidence of a Late Pleistocene population expansion as indicated by low haplotype and nucleotide diversity, a star-like phylogeny of alleles, and a mismatch distribution indicating a sudden increase in effective population size. By contrast, the Mexican population showed high levels of genetic diversity and a mismatch distribution as expected for a population unaffected by sudden demographic change. Haplotypes from the two regions formed two distinct phylogroups which separated roughly one million years ago according to a conventional molecular clock for songbirds. This study provides support for the Pleistocene expansion hypothesis in MacGillivray's warbler and suggests that postglacial expansion of bottlenecked populations is responsible for the lack of variation and structure reported for most North American songbird species.

A test of alternative models of diversification in tropical rainforests: ecological gradients vs. rainforest refugia

Comparison of mitochondrial and morphological divergence in eight populations of a widespread leaf-litter skink is used to determine the relative importance of geographic isolation and natural selection in generating phenotypic diversity in the Wet Tropics Rainforest region of Australia. The populations occur in two geographically isolated regions, and within each region, in two different habitats (closed rainforest and tall open forest) that span a well characterized ecological gradient. Morphological differences among ancient geographic isolates (separated for several million years, judging by their mitochondrial DNA sequence divergence) were slight, but morphological and life history differences among habitats were large and occurred despite moderate to high levels of mitochondrial gene flow. A field experiment identified avian predation as one potential agent of natural selection. These results indicate that natural selection operating across ecological gradients can be more important than geographic isolation in similar habitats in generating phenotypic diversity. In addition, our results indicate that selection is sufficiently strong to overcome the homogenizing effects of gene flow, a necessary first step toward speciation in continuously distributed populations. Because ecological gradients may be a source of evolutionary novelty, and perhaps new species, their conservation warrants greater attention. This is particularly true in tropical regions, where most reserves do not include ecological gradients and transitional habitats.

Health and educational outcomes of children who experienced severe neonatal medical complications

To determine the long-term developmental and educational outcomes of a sample of low birthweight infants with intraventricular hemorrhage (IVH), the authors conducted developmental assessments and interviews 8 years after the initiation of an early intervention project. At the time of the follow-up, 62% of the children were experiencing some developmental or behavior problems, with visual impairments, cerebral palsy, and attention deficits occurring most frequently. Grade of IVH and the number of days spent in the neonatal intensive care unit were the best predictors of later developmental delays. The sample also scored below average on school achievement; approximately 30% of those in school were eligible for special education services. These findings corroborate results from investigations with similar populations whose birth characteristics put them at risk for subsequent developmental delay.

Copper deficiency increases cytochrome P450-dependent 7-ethoxyresorufin-O-deethylase activity in rat small intestine

Although impaired heme synthesis during copper deficiency may limit the production and function of hemoproteins, little is known about the effects of copper deficiency on the cytochromes P450, an important family of hemoproteins, in the small intestine. A series of experiments was conducted to examine the effects of copper deficiency on cytochrome P450 content, ethoxyresorufin-O-deethylase (EROD) activity, and NADPH-cytochrome P450 reductase activity in rat small intestine. Sixteen hours after a single oral administration of 5,6-benzoflavone (BF), an inducer of cytochromes P4501A1 and P4501A2, intestinal cytochrome P450 content was elevated as indicated by the CO-difference spectrum of the reduced cytochrome and by immunoblotting using anticytochrome P4501A1/1A2. However, cytochrome P450 content, measured by either method following BF induction, was not affected by copper deficiency. Thus, copper deficiency did not impair the availability of heme for cytochrome P450 synthesis in the small intestine. Even though copper deficiency did not affect intestinal cytochrome P450 content, EROD activity, which is a cytochrome P450-associated monooxygenase activity, was 9-fold higher in copper-deficient rats compared with controls following BF treatment. The finding that copper deficiency has no effect on intestinal cytochrome P450 content suggests that the increased EROD activity results from an effect of copper deficiency on the cytochrome P450 reductase component of the monooxygenase system. Measurement of cytochrome P450 reductase activity showed a 2-fold increase in the small intestines of copper-deficient rats compared with controls. It is possible, therefore, that increased intestinal cytochrome P450 reductase activity during copper deficiency increases EROD activity by facilitating the flow of electrons to cytochrome P450 during the redox cycle that cytochrome P450 undergoes during the O-deethylation of ethoxyresorufin.

In vitro fracture behavior of ceramic and metal-ceramic restorations

PURPOSE

Failed crowns and failure load data were studied to gain insights into the fracture behavior of prostheses under incisal-directed, load-to-failure testing.

MATERIALS AND METHODS

Incisor crowns (n = 68) were fabricated: two all-ceramic groups (feldspathic veneer on high-strength core), differing in core design, and two metal-ceramic groups, differing in metal oxidation time (30 seconds v 3 minutes). Crowns were loaded to failure on their incisal edge. Gross visual, microscopic, and elemental microprobe analyses of failed crowns were coupled with Weibull analysis of the failure load data.

RESULTS

Failure loads were higher for the normal oxidation time (TN) than for the extended oxidation time (TE) metal-ceramic crowns (P < .02), but both groups had indistinguishable Weibull moduli indicating the possibility of a common failure origin. Fracture behavior and Weibull results both implicated the oxide layer as being the origin of failure. The ratio of fracture loads (TE/TN) corresponded well with calculated oxide-volume ratios. Failure loads were lower for the all-ceramic than for the metal-ceramic crowns (P < .001). Fifty percent of the all-ceramic crowns failed by delamination of veneering glass alone, leaving a thin layer of residual glass on the core surface. Scanning electron microscope views showed that delamination occurred 10 to 50 microns away from the core-veneer interface. Electron microprobe elemental analysis of the core-veneer interface showed that residual core infiltration glass was not present on the core surface and that chemical alterations in the veneering glass were apparently limited to less than a 2- to 3-microns thick layer.

CONCLUSIONS

Failure for both restorative systems involved interfacial stresses with crack propagation occurring at or near the core-veneer interface. The weaker interface in the metal-ceramic system probably resulted from an increase in surface oxide volume, irrespective of any change in its adherence or physical properties. For the ceramic crowns, delamination crack fronts appeared to propagate through chemically unaltered veneering porcelain. Both the Weibull moduli and characteristic strengths were indistinguishable between either of the two ceramic core designs or between groups failing from delamination with or without core cracking/failure. This is consistent with delamination being the primary fracture process during failure. Clinical implications should not be drawn from results of this study because no correlation is known to have ever been established between clinical behavior and incisal load-to-failure results.

Respiratory responses of elite oarsmen, former oarsmen, and highly trained non-rowers during rowing, cycling and running

The position of the body and use of the respiratory muscles in the act of rowing may limit ventilation and thereby reduce maximal aerobic power relative to that achieved in cycling or running, in spite of the greater muscle mass involved in rowing. This hypothesis was investigated for three groups of male subjects: nine elite senior oarsmen, eight former senior oarsmen and eight highly trained athletes unskilled in rowing. The subjects performed graded exercise to maximal effort on a rowing ergometer, cycle ergometer and treadmill while respiratory minute volume (VE) and oxygen consumption (VO2) were monitored continuously. The VE at a given VO2 during intense submaximal exercise (greater than 75% of maximal VO2) was not significantly lower in rowing compared with that in cycling and treadmill running for any group, which would suggest that submaximal rowing does not restrict ventilation. At maximal effort, VO2, and VE for rowing were less than those for the other types of exercise in all the groups, although the differences were not statistically significant in the elite oarsmen. These data are consistent with a ventilatory limitation to maximal performance in rowing that may have been partly overcome by training in the elite oarsmen. Alternatively, a lower maximal VE in rowing might have been an effect rather than a cause of a lower maximal VO2, if maximal VO2 was limited by the lower rate of muscle activation in rowing.

Effects of subliminal stimuli on unconscious processing of anxiety: an examination of implicit perception

Researchers in cognitive psychology generally accept that information, including emotions, may be processed outside of awareness. Some have postulated that anxiety may be induced by stimuli presented below the level of detection, a process called implicit perception; however, conflicting findings as to the validity of subliminal stimuli in influencing anxiety have been reported over the past decade. In the present study, 39 subjects were exposed to either positive, negative, or neutral subliminal stimuli, and half the subjects were informed as to the type of stimuli they received. All subjects were monitored for frontalis muscle tension, a physiological indicator of anxiety, on an electromyograph (EMG). No significant effects of the exposure upon EMG recordings were noted. Awareness of the type of stimuli presented had a small but insignificant effect. These results, although tentative, when replicated would question the validity of subliminal visual presentation in altering emotive states.

Depressive symptomatology and interaction behaviors of mothers having a child with disabilities

Previous research has indicated that parents who raise children having disabilities report greater emotional distress than other parents. To investigate the association between symptoms of depression and maternal behaviors, interactions between 48 mothers and children having disabilities were rated. Measures of maternal depression and child functioning were also administered. Analyses indicated that mothers reported a relatively large number of symptoms often associated with depression. However, reports of depressive symptomatology were not meaningfully related to the children's developmental status or parent-child interaction behaviors.

A prospective evaluation of a simplified captopril test for the detection of renovascular hypertension

Renovascular hypertension is potentially curable but of low prevalence. A previous retrospective study has demonstrated the use of a potentiated increase in plasma renin activity after captopril administration as a diagnostic test for renovascular hypertension; this requires two blood samples for plasma renin activity determination and three inclusive criteria for a positive test result. We applied this test prospectively to screen 100 hypertensive patients for renovascular hypertension. We evaluated 29 patients with renovascular hypertension; the remainder were diagnosed as having essential hypertension. In our patient population, a postcaptopril plasma renin activity of 5.7 ng of angiotensin per milliliter per hour (ngAl.mL-1.h-1) or greater had a 100% sensitivity and an 80% specificity for renovascular hypertension. An absolute increase in plasma renin activity with captopril of 4.7 ngAl.mL-1.h-1 or greater had a lower sensitivity of 90% and a specificity of 87%, whereas a fractional increase in plasma renin activity after captopril of 150% or higher had the lowest sensitivity of 69% and a specificity of 86%. A subgroup analysis of 38 patients who were receiving diuretic therapy demonstrated that the test sensitivity was unchanged but the specificity was reduced. In conclusion, a single postcaptopril plasma renin activity value of 5.7 ngAl.mL-1.h-1 or greater is a simplified screening test for renovascular hypertension, with excellent sensitivity and acceptable specificity. This test is well tolerated, inexpensive, and easy to perform.

The captopril glomerular filtration rate renogram in renovascular hypertension

Administration of captopril to animals with two-kidney, one clip, renovascular hypertension (RH) lowers the glomerular filtration rate (GFR) in the clipped kidney. The authors therefore tested the hypothesis that a decrease in GFR after captopril administration would identify patients with RH. Total GFR was measured by the plasma disappearance of Tc-99m-diethylenetriaminepentaacetic acid (DTPA) after bolus injection and single-kidney GFR from renal uptake of DTPA assessed by renography. The authors studied six patients with arteriosclerotic RH who had strongly lateralizing renal vein renin levels and greater than 80% stenosis of the renal artery to that kidney. Results were contrasted with those of six patients with essential hypertension (EH) with a similar mean arterial blood pressure (MABP). Captopril (50 mg orally) increased total GFR (ml/min) in all patients with EH (102 +/- 8 to 120 +/- 12, P less than 0.005). However, GFR decreased in patients with RH (73 +/- 8 to 61 +/- 9, P less than 0.05) after captopril. Although the single-kidney GFR of patients with RH decreased in all six stenotic kidneys (27 +/- 4 to 21 +/- 5, P less than 0.02), it did not change consistently in the contralateral kidneys (45 +/- 8 to 40 +/- 6, N.S.). Clonidine (0.3 mg) also lowered MABP in patients with RH but, unlike captopril, it did not reduce total kidney GFR (75 +/- 10 to 79 +/- 11, N.S.). In conclusion, short-term captopril administration increases GFR in patients with EH, but decreases it in those with RH. This action is unrelated to its depressor response.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood parasites of birds in Cameroon

Birds from south-central Cameroon, western Africa, were surveyed for blood parasites from August to October 1986. Of 331 birds examined, representing 65 species of 15 families and 6 orders (mostly passerines), 55 (17%) were found to be infected with 1 or more genera of hemotropic parasites. These included: Haemoproteus spp. (11% prevalence), Leucocytozoon spp. (3%), Plasmodium spp. (2%), Trypanosoma spp. (1%), and microfilariae of filariid nematodes (1%). Several new host-parasite associations were identified.

Diagnostic uses of angiotensin-converting enzyme inhibitors in renovascular hypertension

The response to angiotensin-converting enzyme inhibitors (ACEIs) can be of considerable help in the diagnosis of human renovascular hypertension (RVH) in three settings. First, a particularly dramatic antihypertensive response or a decline in glomerular filtration rate (GFR), as indexed by a rise in serum creatinine or blood urea nitrogen concentrations, are useful clues to the presence of renovascular hypertension. Second, an exaggerated rise in plasma renin activity (PRA) after short-term captopril administration is a very promising screening test for this condition. Third, ACEI-induced changes in single-kidney hemodynamics (assessed by renography) may be helpful in confirming the diagnosis and offers the prospect of localizing the ischemic kidney.

Hearing loss in pediatric meningitis

Bacterial meningitis is the leading cause of acquired sensorineural hearing loss in children. Acquired hearing loss can have a devastating effect on a child's speech, language and eventual intellectual development, especially when the hearing loss occurs before the child learns to talk. If an immediate referral for audiologic testing is not made, valuable time is lost in obtaining hearing aids and habilitative/rehabilitative services for children during the critical period of language development.

Clinical evaluation of three urine screening tests

Evaluations of screening tests for bacteriuria have traditionally compared the test results with those of quantitative urine cultures. However, many patients with symptomatic urinary tract infections can have less than 10(5) CFU/ml in their urine. Therefore, the results of urine culture and three screening tests (Bac-T-Screen, Chemstrip LN [which tests for leukocyte esterase and nitrate reductase], and Gram stain) were correlated with the clinical classification of urinary tract infection. The Bac-T-Screen test detected 98, 93, and 100% of the infections classified as probable, possible, and asymptomatic, respectively. In contrast, the Gram stain, leukocyte esterase, and nitrate reductase tests were all insensitive screening tests for infection. Additionally, only 45% of the patients with probable infections had greater than or equal to 10(5) CFU/ml. Thus, the majority of infected patients would not have been detected if quantitative urine cultures were used alone.

Health insurance coverage of the unemployed

Of 1,332 unemployed individuals in the Detroit area interviewed in late 1983, 51% did not have health insurance. Lack of insurance was directly related to length of unemployment. Of those unemployed 3 months or less, 31% had no insurance, as compared with 56% of those unemployed more than 3 years. For the most part, these were not the chronically uninsured: 78% of them were insured when they were employed. Three fourths of those without insurance were not covered by Medicaid either. These findings suggest that during the latest economic recession, the problem of health insurance loss due to losing one's job was more severe than had been assumed by most policymakers.