Topsoil porosity prediction across habitats at large scales using environmental variables

Soil porosity and its reciprocal bulk density are important environmental state variables that enable modelers to represent hydraulic function and carbon storage. Biotic effects and their 'dynamic' influence on such state variables remain largely unknown for larger scales and may result in important, yet poorly quantified environmental feedbacks. Existing representation of hydraulic function is often invariant to environmental change and may be poor in some systems, particularly non-arable soils. Here we assess predictors of total porosity across two comprehensive national topsoil (0-15 cm) data sets, covering the full range of soil organic matter (SOM) and habitats (n = 1385 & n = 2570), using generalized additive mixed models and machine learning. Novel aspects of this work include the testing of metrics on aggregate size and livestock density alongside a range of different particle size distribution metrics. We demonstrate that porosity trends in Great Britain are dominated by biotic metrics, soil carbon and land use. Incorporating these variables into porosity prediction improves performance, paving the way for new dynamic calculation of porosity using surrogate measures with remote sensing, which may help improve prediction in data sparse regions of the world. Moreover, dynamic calculation of porosity could support representation of feedbacks in environmental and Earth System Models. Representing the hydrological feedbacks from changes in structural porosity also requires data and models at appropriate spatial scales to capture conditions leading to near-saturated soil conditions. Classification. Environmental Sciences.

Nanoscale electrochemical kinetics & dynamics: the challenges and opportunities of single-entity measurements

The development of nanoscale electrochemistry since the mid-1980s has been predominately coupled with steady-state voltammetric (i-E) methods. This research has been driven by the desire to understand the mechanisms of very fast electrochemical reactions, by electroanalytical measurements in small volumes and unusual media, including in vivo measurements, and by research on correlating electrocatalytic activity, e.g., O2 reduction reaction, with nanoparticle size and structure. Exploration of the behavior of nanoelectrochemical structures (nanoelectrodes, nanoparticles, nanogap cells, etc.) of a characteristic dimension λ using steady-state i-E methods generally relies on the well-known relationship, λ2 ∼ Dt, which relates diffusional lengths to time, t, through the coefficient, D. Decreasing λ, by performing measurements at a nanometric length scales, results in a decrease in the effective timescale of the measurement, and provides a direct means to probe the kinetics of steps associated with very rapid electrochemical reactions. For instance, steady-state voltammetry using a nanogap twin-electrode cell of characteristic width, λ ∼ 10 nm, allows investigations of events occurring at timescales on the order of ∼100 ns. Among many other advantages, decreasing λ also increases spatial resolution in electrochemical imaging, e.g., in scanning electrochemical microscopy, and allows probing of the electric double layer. This Introductory Lecture traces the evolution and driving forces behind the "λ2 ∼ Dt" steady-state approach to nanoscale electrochemistry, beginning in the late 1950s with the introduction of the rotating ring-disk electrode and twin-electrode thin-layer cells, and evolving to current-day investigations using nanoelectrodes, scanning nanocells for imaging, nanopores, and nanoparticles. The recent focus on so-called "single-entity" electrochemistry, in which individual and very short redox events are probed, is a significant departure from the steady-state approach, but provides new opportunities to probe reaction dynamics. The stochastic nature of very fast single-entity events challenges current electrochemical methods and modern electronics, as illustrated using recent experiments from the authors' laboratory.

Household aggregation of Staphylococcus aureus by clonal complex and methicillin resistance profiles in Starr County, Texas

Staphylococcus aureus is one of the most common causes of skin and soft tissue infections in health-care and community settings, but transmission of S. aureus in community-based populations is incompletely understood. S. aureus carriage phenotypes (persistent, intermittent, and non-carriers) were determined for households from Starr County, TX. Nasal swabs were collected from a cohort of 901 residents and screened for the presence of S. aureus. Isolated strains were spa-typed and assigned to clonal complexes. Of the 901 participants there were 134 pairs, 28 trios, 11 quartets, 3 quintets and 1 septet residing in the same household. There was a significant increase in "ever" carriers (persistent and intermittent carriers combined) in these households over that expected based on population frequencies (p = 0.029). There were 42 ever carrier pairs of individuals with 21 concordant for clonal complex type whereas only 4.7 were expected to be so (p = 6.9E-11). These results demonstrated clear aggregation of S. aureus carriage and concordance for strain types within households. As antibiotic-resistant S. aureus strains increase in community settings, it is important to better understand risk factors for colonization, mechanisms of transmission, clonal complexes present, and the role of household concordance/transmission.

Mechanistic aspects of hydrazine-induced Pt colloid instability and monitoring aggregation kinetics with nanoparticle impact electroanalysis

Here we investigate the mechanistic aspects of Pt nanoparticle (NP) aggregation in solutions typically used for detecting NP/electrode impacts by electrocatalytic amplification (ECA). We previously proposed a general mechanism for Pt colloid destabilization that involved the participation of both the hydrazine redox probe and the pH buffer species as coagulants. Herein the Pt NP coagulation and aggregation mechanisms were further investigated with microscopic kinetic NP concentration monitoring and zeta potential measurements using nanoparticle tracking analysis (NTA), as well as open circuit potential experiments with a citrate-treated polycrystalline Pt surface to assess electrical double layer potential. After considering the combined results of these experiments we propose that the colloidal stability of citrate-capped platinum nanoparticles involves much more than the typical physicochemical interactions predicted by DLVO theory. A structure based on intermolecular H-bonding in the citrate capping layer is the most plausible explanation for the exceptional stability of large Pt NPs in high ionic strength buffers. Thus, the mechanism of Pt NP aggregation includes specific reactive contributions from hydrazine. The catalytic decomposition of hydrazine, in particular, is thought to occur to some extent at the citrate-coated Pt surface while the citrate remains adsorbed. Evolved gases such as ammonia and possible surface bound intermediates from Pt-catalyzed decomposition of hydrazine may disrupt the stability of the citrate layer, causing colloidal instability and thus promoting Pt NP coagulation. In the closing section, we demonstrate nanoparticle impact electroanalysis by ECA detection as a method to quantify Pt NP concentration with adequate time resolution for monitoring the kinetics of Pt NP coagulation.

ST2249-MRSA-III: a second major recombinant methicillin-resistant Staphylococcus aureus clone causing healthcare infection in the 1970s

Typing of healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) from Australia in the 1970s revealed a novel clone, ST2249-MRSA-III (CC45), present from 1973 to 1979. This clone was present before the Australian epidemic caused by the recombinant clone, ST239-MRSA-III. This study aimed to characterize the genome of ST2249-MRSA-III to establish its relationship to other MRSA clones. DNA microarray analysis was conducted and a draft genome sequence of ST2249 was obtained. The recombinant structure of the ST2249 genome was revealed by comparisons to publicly available ST239 and ST45 genomes. Microarray analysis of genomic DNA of 13 ST2249 isolates showed gross similarities with the ST239 chromosome in a segment around the origin of replication and with ST45 for the remainder of the chromosome. Recombination breakpoints were precisely determined by the changing pattern of nucleotide polymorphisms in the genome sequence of ST2249 isolate SK1585 compared with ST239 and ST45. One breakpoint was identified to the right of oriC, between sites 1014 and 1065 of the gene D484_00045. Another was identified to the left of oriC, between sites 1185 and 1248 of D484_01632. These results indicate that ST2249 inherited approximately 35.3% of its chromosome from an ST239-like parent and 64.7% from an ST45-like parent. ST2249-MRSA-III resulted from a major recombination between parents that resemble ST239 and ST45. Although only limited Australian archival material is available, the oldest extant isolate of ST2249 predates the oldest Australian isolate of ST239 by 3 years. It is therefore plausible that these two recombinant clones were introduced into Australia separately.

Nitrogen deposition and climate effects on soil nitrogen availability: influences of habitat type and soil characteristics

The amount of plant-available nitrogen (N) in soil is an important indicator of eutrophication of semi-natural habitats, but previous studies have shown contrasting effects of N deposition on mineralisable N in different habitats. The stock of readily mineralisable N (N(rm)) was measured in 665 locations across Britain from a range of intensively and extensively managed habitats, allowing N availability to be studied in relation to soil and vegetation type, and also to variation in climate and in reactive N deposition from the atmosphere. Mineralisable N contents were correlated with deposition in extensively managed habitats but not in intensively managed habitats. The following statements apply only to extensively managed habitats. All habitats showed a similar increase in N(rm) with N deposition. However, soil characteristics affected the relationship, and soil carbon content in particular was a major control on mineralisation. The N(rm) stock increased more with N deposition in organic than in mineral soils. The nitrate proportion of N(rm) also increased with N deposition but, conversely, this increase was greater in mineral than in organic soils. The measurements could be used as indicators of eutrophication, e.g. deposition rates of over 20 kg N ha(-1) y(-1) are associated with nitrate proportions of >41% in a mineral soil (2% carbon), and with N(rm) stocks of over 4.8 kg N ha(-1) in an organic soil (55% carbon). Both N(rm) and nitrate proportion increased with mean annual temperature of the sampling location, despite consistent incubation temperature, suggesting that increasing temperatures are likely to increase the eutrophying effects of N pollution on semi-natural ecosystems.

Treatment of massive rotator-cuff tears with a polyester ligament (Dacron) augmentation: clinical outcome

We describe the clinical outcome of a technique of surgical augmentation of chronic massive tears of the rotator cuff using a polyester ligament (Dacron) in 21 symptomatic patients (14 men, seven women) with a mean age of 66.5 years (55.0 to 85.0). All patients had MRI and arthroscopic evidence of chronic massive tears. The clinical outcome was assessed using the Constant and Murley and patient satisfaction scores at a mean follow-up of 36 months (30 to 46). The polyester ligament (500 mm × 10 mm) was passed into the joint via the portal of Neviaser, medial to the tear through healthy cuff. The two ends of the ligament holding the cuff were passed through tunnels made in the proximal humerus at the footprint of the insertion of the cuff. The ligament was tied with a triple knot over the humeral cortex. All the patients remained free from pain (p < 0.001) with improvement in function (p < 0.001) and range of movement (p < 0.001). The mean pre-operative and post-operative Constant scores were 46.7 (39.0 to 61.0) and 85.4 (52.0 to 96.0), respectively (p < 0.001). The mean patient satisfaction score was 90%. There were two failures, one due to a ruptured ligament after one year and the other due to deep-seated infection. The MR scan at the final follow-up confirmed intact and thickened bands in 15 of 17 patients. This technique of augmentation gives consistent relief from pain with improved shoulder movement in patients with symptomatic massive tears of the rotator cuff.

In vivo expression of myosin essential light chain using plasmid expression vectors in regenerating frog skeletal muscle

It is well established that mutations in specific structural elements of the motor protein myosin are directly linked to debilitating diseases involving malfunctioning striated muscle cells. A potential way to study the relationship between myosin structure and function is to express exogenous myosin in vivo and determine contractile properties of the transgenic muscle cells. However, in vivo expression of functional levels of contractile proteins using transient transgenesis in skeletal muscle has not been demonstrated. Presently, we used in vivo gene transfer to express high levels of full-length myosin light chain (MLC) in skeletal muscle fibers of Rana pipiens. Anterior tibialis (AT) muscles were injected with cardiotoxin to cause degeneration and then injected at various stages of regeneration with plasmid expression vectors encoding full-length MLC1(f). In fibers from the most robustly transfected muscles 3 weeks after plasmid injections, trans-MLC1(f) expression averaged 22-43% of the endogenous MLC1(f). Trans-MLC1(f) expression was the same whether a small epitope tag was placed on the C- or N-terminus and was highly variable along individual fibers. Confocal microscopy of skinned fibers showed correct sarcomeric incorporation of trans-MLC1(f). The expression profile of myosin heavy chain isoforms 21 days after transfection was similar to normal AT muscle. These data demonstrate the feasibility of using in vivo gene transfer to probe the structural basis of contractile protein function in skeletal muscle. Based on these promising results, we discuss how further improvements in the level and consistency of myosin transgene expression may be achieved in future studies, and the therapeutic potential of plasmid gene transfer in regenerating muscle.

Diversity among community isolates of methicillin-resistant Staphylococcus aureus in Australia

Community methicillin-resistant Staphylococcus aureus (CMRSA) strains are being isolated with increasing frequency around the world. In Western Australia CMRSA are endemic in geographically remote communities and have been found to belong to five different contour-clamped homogeneous electric field (CHEF) electrophoretic patterns. Representatives of each of these CHEF patterns have been compared to CMRSA representative of CHEF patterns from other Australian states and New Zealand. With one exception, all of the isolates were nonmultiresistant and were not resistant to many antimicrobial agents other than the beta-lactams. With one exception, which is not believed to be a CMRSA, all of the isolates harbored a beta-lactamase plasmid. Erythromycin resistance was associated with a 2-kb plasmid. One of the beta-lactamase plasmids was found to be able to acquire additional resistance determinants to become a multiple resistance plasmid. There were 10 multilocus sequence types belonging to eight distantly related clonal complexes of S. aureus. One new sequence type was found. Although most of the CMRSA harbored the type IVa SCCmec, a type IV structural variant was found and two new SCCmec types were identified. Protein A gene (spa) typing revealed two new spa types and, with two exceptions, corresponded to multilocus sequence typing. In contrast to other reports on CMRSA, most of the CMRSA strains studied here did not contain the Panton-Valentine leukocidin genes. The results also demonstrate that nonmultiresistant hospital strains such as UK EMRSA-15 may be able to circulate in the community and could be mistaken for CMRSA based on their resistance profiles.

Genetic association between an AACC insertion in the 3'UTR of the stratum corneum chymotryptic enzyme gene and atopic dermatitis

Atopic dermatitis is a disease with an impaired skin barrier that affects 15%-20% of children. In the normal epidermis, the stratum corneum chymotryptic enzyme (SCCE) thought to play a central role in desquamation by cleaving proteins of the stratum corneum (e.g., corneodesmosin and plakoglobin). Genetic variations within the SCCE gene could be associated with dysregulation of SCCE activity leading to an abnormal skin barrier. We screened the SCCE gene for variations and performed a case-control study on 103 atopic dermatitis patients and 261 matched controls. 16 synonymous single nucleotide polymorphisms (SNPs) have been identified and a 4 bp (AACC) insertion has been found in the 3'UTR. We performed an association study of the SCCE AACC insertion in the 3'UTR, and found a significant trend between the AACC allele with the two insertions and disease in the overall data set [odds ratio (OR)=2.31; p=0.0007]. The AACC insertion in the SCCE gene may result in a change to SCCE activity within the skin barrier. These findings suggest that SCCE could have an important role in the development of atopic dermatitis.

Multilocus sequence typing and the evolution of methicillin-resistant Staphylococcus aureus

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in many countries is increasing and, in hospitals in some areas, more than half of all S. aureus disease isolates are MRSA. MRSA strains are becoming increasingly multiresistant, and have recently developed resistance to vancomycin, used successfully to treat MRSA for more than 30 years. This review summarises recent studies that have elucidated the evolutionary history of MRSA. The first MRSA isolate evolved from a sensitive, epidemic strain prevalent in Europe, and its progeny-the first MRSA clone-quickly spread to other continents. Analyses of epidemic MRSA isolates from hospitals in different countries by molecular methods, including multilocus sequence typing (MLST) and DNA microarray analysis, reveal that MRSA strains have evolved separately within five distinct epidemic, sensitive lineages. However, resistance has been transferred to S. aureus on many more than five occasions, as some lineages have acquired different structural types of the element carrying the methicillin resistance gene. The emergence of MRSA as a community pathogen has been noted in several countries, and MLST and SCCmec typing have been used to demonstrate that community-acquired MRSA strains are typically related only distantly to hospital MRSA strains, and thus represent novel acquisitions of SCCmec.

Experiences with the shikimate-pathway enzymes as targets for rational drug design

The background and current context of work on the shikimate-pathway enzymes as potential targets for anti-bacterial, anti-fungal and anti-parasitic drugs is reviewed. Recent work on the third enzyme of the pathway, dehydroquinase, which occurs in two structurally and mechanistically distinct forms, is used to illustrate the present state of studies into rational drug design.

Oxytocin mediates stress-induced analgesia in adult mice

As a neurohormone and as a neurotransmitter, oxytocin has been implicated in the stress response. Descending oxytocin-containing fibres project to the dorsal horn of the spinal cord, an area important for processing nociceptive inputs. Here we tested the hypothesis that oxytocin plays a role in stress-induced analgesia and modulates spinal sensory transmission. Mice lacking oxytocin exhibited significantly reduced stress-induced antinociception following both cold-swim (10 degrees C, 3 min) and restraint stress (30 min). In contrast, the mice exhibited normal behavioural responses to thermal and mechanical noxious stimuli and morphine-induced antinociception. In wild-type mice, intrathecal injection of the oxytocin antagonist dOVT (200 microM in 5 microl) significantly attenuated antinociception induced by cold-swim. Immunocytochemical staining revealed that, in the mouse, oxytocin-containing neurones in the paraventricular nucleus of the hypothalamus are activated by stress. Furthermore, oxytocin-containing fibres were present in the dorsal horn of the spinal cord. To test whether descending oxytocin-containing fibres could alter nociceptive transmission, we performed intracellular recordings of dorsal horn neurones in spinal slices from adult mice. Bath application of oxytocin (1 and 10 microM) inhibited excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation. This effect was reversed by the oxytocin antagonist dOVT (1 microM). Whole-cell recordings of dorsal horn neurones in postnatal rat slices revealed that the effect of oxytocin could be blocked by the addition of GTP-gamma-S to the recording pipette, suggesting activation of postsynaptic oxytocin receptors. We conclude that oxytocin is important for both cold-swim and restraint stress-induced antinociception, acting by inhibiting glutamatergic spinal sensory transmission.

Prominent R wave in lead V1: electrocardiographic differential diagnosis

Tall lead V1 (tall RV1), defined as an R/S ratio equal to or greater than 1, is not an infrequent occurrence in emergency department patients. This electrocardiographic finding exists as a normal variant in only 1% of patients. Physicians should therefore be familiar with the differential diagnosis for this important QRS configuration. The electrocardiographic entities which can present with this finding include right bundle branch block, left ventricular ectopy, right ventricular hypertrophy, acute right ventricular dilation (acute right heart strain), type a Wolff-Parkinson-White syndrome, posterior myocardial infarction, hypertrophic cardiomyopathy, progressive muscular dystrophy, dextrocardia, misplaced precordial leads, and normal variant. Various cases are presented to highlight the different causes of the tall RV1.

Clones of Streptococcus pneumoniae isolated from nasopharyngeal carriage and invasive disease in young children in central Tennessee

To determine whether nasopharyngeal carriage isolates of Streptococcus pneumoniae are of the same genetic background as isolates that caused invasive disease in one community, IS1167 and boxA genotypes were obtained for 182 pneumococcal isolates from children living in central Tennessee. The isolates represented 70 combined IS1167-boxA genotypes. The genotypic diversity of the invasive isolates was significantly less than that of the total population (P=.003). Most of the carriage isolates belonged to genotypes unique to carriage, whereas most of the invasive isolates belonged to genotypes common to carriage and disease (P=.02). Monte Carlo simulations showed a greater number of genotypes unique to carriage than can be explained by chance (P<.05 in all cases). Two genotypes were identified by multilocus sequence typing as members of globally disseminated clones, and one such genotype that was strictly carriage in this sample caused disease in other studies. Thus, clones can have different propensities for carriage and invasion.

Nystagmus induced by pharmacological inactivation of the brainstem ocular motor integrator in monkey

A common cause of pathological nystagmus is malfunction of the mechanism by which the brain integrates eye velocity signals to produce eye position commands. For horizontal gaze, neurons in the nucleus prepositus hypoglossi-medial vestibular nucleus region (NPH-MVN) play a vital role in this neural integrator function. We studied the effects on gaze stability of pharmacological intervention in the NPH-MVN of monkeys by microinjections of eight drugs. Agents with agonist or antagonist actions at gamma-aminobutyric acid (GABA), glutamate, and kainate receptors all caused gaze-evoked nystagmus with centripetal eye drifts; glycine and strychnine had no effect. When the GABAA-agonist muscimol was injected near the center of MVN, the eyes drifted away from the central position with increasing-velocity waveforms, implying an unstable neural integrator. The observed effects of these drugs on gaze stability may be related to inactivation either of neurons within NPH-MVN or the cerebellar projections to them that control the fidelity of neural integration. Drugs that influence GABA or glutamine transmission may have a role in the treatment of nystagmus due to an abnormal neural integrator.

Electrocardiographic manifestations of hyperkalemia

Hyperkalemia is one of the more common acute life-threatening metabolic emergencies seen in the emergency department. Early diagnosis and empiric treatment of hyperkalemia is dependent in many cases on the emergency physician's ability to recognize the electrocardiographic manifestations of hyperkalemia. The electrocardiographic manifestations commonly include peaked T-waves, widening of the QRS-complex, and other abnormalities of altered cardiac conduction. Peaked T-waves in the precordial leads are among the most common and the most frequently recognized findings on the electrocardiogram. Other "classic" electrocardiographic findings in patients with hyperkalemia include prolongation of the PR interval, flattening or absence of the P-wave, widening of the QRS complex, and a "sine-wave" appearance at severely elevated levels. A thorough knowledge of these findings is imperative for rapid diagnosis and treatment of hyperkalemia.

Measurement of vestibular ocular reflex (VOR) time constants with a caloric step stimulus

A protocol is described for measuring responses to a broad-band (1-2 Hz) caloric step stimulus from which the vestibular ocular reflex (VOR) and adaptation time constants can be estimated. This novel stimulation is the caloric equivalent to a rotatory step of head acceleration. In this protocol, the ear is irrigated continuously for 5 min with water at a constant temperature. During the initial 2-min period of irrigation the subject is seated and leaning forward in a nonstimulable position (horizontal canals in a horizontal plane). This irrigation phase establishes a steady-state thermal gradient across the horizontal canal, effectively eliminating thermal dynamic properties of the caloric transmission as a confounding factor. At the end of this phase, the subject is rapidly reclined to a stimulable position (horizontal canals in vertical plane) that elicits the VOR nystagmus response to an on-step of force on the cupula. Consistent with adaptation processes, the VOR response first increases and then declines gradually over the 2-min period that the step of force is maintained. Four minutes after the onset of irrigation, the subject is rapidly returned to the nonstimulable position (off-step), which is then maintained for a final 1 min. The response after the off-step, which releases the force on the cupula, reveals reversed after-nystagmus due to adaptation. Five subjects provided caloric step responses for 26 caloric temperature conditions spanning the range from 28.4 to 43.0 degrees C. The resulting responses were fitted with an adaptation model similar to models applied to rotatory acceleration step responses. Estimates of the model parameters for robust caloric stimulation, including time constants for the VOR (18.3 sec) and for vestibular adaptation (153.2 sec), are considered in relation to corresponding values reported in the literature for rotatory and caloric vestibular stimulation. The results suggest that caloric step stimulation can be used successfully to probe VOR dynamics.

Graft dilatation following abdominal aortic aneurysm resection and grafting

BACKGROUND

It has been suggested that graft dilatation following repair of abdominal aortic aneurysm (AAA) is associated with complications such as anastomotic aneurysm and graft rupture. The purpose of the present study was to document the degree of dilatation observed in grafts after aneurysm repair and to correlate this with any graft-related complications.

METHODS

Between January 1987 and December 1992, 219 patients had elective repair of their AAA at St George Hospital. A follow-up ultrasound scan was available for 154 of these patients. The following factors were examined: age, sex, size of aneurysm, type and size of graft, time of follow-up scan, size of graft at follow-up and any graft-related complications.

RESULTS

The mean graft dilatation observed in knitted grafts (42.6%; 95% CI: 39.1-46.1%) was significantly greater than that observed for woven grafts (25.5%; 95% CI: 19.0-32.1%; P < 0.0001). There were no graft-related complications.

CONCLUSIONS

Graft dilatation is a predictable phenomenon following AAA repair. It is more pronounced in knitted than in woven grafts, but does not necessarily lead to graft-related complications or failure.

Molecular characterization of a globally distributed lineage of serotype 12F Streptococcus pneumoniae causing invasive disease

These studies have identified a major genetic lineage of capsule serotype 12F Streptococcus pneumoniae, which has maintained two different types of the pneumococcal surface protein A (PspA) virulence factor and caused invasive disease in geographically disjoint locations. Twenty outbreak strains from a Texas jail and Maryland day care center and 16 reference strains from Texas, Maryland, Washington, Michigan, Oklahoma, Missouri, Alaska, and Australia were examined. Although the Texas and Maryland outbreak strains were indistinguishable by IS1167 and boxA genotyping procedures, all strains examined were members of a genetically similar lineage. The microevolutionary history of pspA differed from that of the overall genetic background of the strains. Taken together, these findings suggested that the Texas and Maryland outbreaks were caused by different clones of a major genetic lineage of serotype 12F pneumococci, within which at least one PspA has been acquired via localized genetic recombination.

The IS1167 insertion sequence is a phylogenetically informative marker among isolates of serotype 6B Streptococcus pneumoniae

The phylogenetic utility of the IS1167 insertion sequence was examined with restriction fragment length polymorphism (RFLP) analyses of a sample of 50, predominantly invasive, capsular serotype 6B Streptococcus pneumoniae isolates previously characterized by multilocus enzyme electrophoresis (MLEE). The strains represented a genetically diverse assemblage of 34 distinct clonotypes composed of 26 restriction fragment types and 23 multilocus enzyme types. All isolates carried the IS1167 insertion sequence, with an average of 9.5 copies. The cross-classification of isolates based on RFLP and MLEE typing schemes was 81% concordant. Phylogenetic analyses demonstrated a significant (P < 0.0001) association between strains of a given RFLP lineage with those of a given MLEE lineage. A significant correlation (P < 0.00004) was also found between the proportion of restriction fragments shared by any given pair of isolates and their genetic distances estimated from the MLEE data. Parity between the two genetic markers implied that the sampled isolates were in linkage disequilibrium. The existence of nonrandom associations among genetic loci was confirmed by Monte Carlo analyses of the MLEE data. These studies, thus, demonstrated that invasive pneumococcal isolates of a single capsule type recovered on a regional scale can retain a largely clonal population structure over a period of 8 years. The ability to detect linkage disequilibrium and generate relatively congruent dendrograms based on distance and parsimony methods suggested that the restriction fragment data were robust to phylogenetic analysis.

Administration of ATP-MgCl2 after trauma-hemorrhage and resuscitation restores the depressed cardiac performance

Although adenosine triphosphate (ATP)-MgCl2 has been shown to improve cardiac performance under normal and postischemic conditions, it is not known whether this agent has any salutary effects on cardiac performance following trauma-hemorrhage and crystalloid resuscitation. To determine this, rats underwent laparotomy (i.e., trauma induction) and were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of the maximum shed blood volume was returned in the form of Ringer's lactate. The animals were then resuscitated with four times the volume of shed blood using Ringer's lactate over 60 min and received either ATP-MgCl2 (50 mumole/kg body wt) in 1 ml volume or an equivalent volume of normal saline intravenously over 95 min. Maximum dP/dt during contraction as well as relaxation (+/-dP/dtmax) and ventricular peak systolic pressure (VPSP) were determined 15 min prior to the end of resuscitation and every 30 min thereafter for 4 hr after the completion of resuscitation. The results indicate that both -dP/dtmax and +dP/dtmax decreased significantly beginning at 0 and 2 hr after the completion of resuscitation, respectively, and remained depressed throughout the duration of the study in saline-treated animals. In addition, VPSP was significantly depressed at 2-4 hr after resuscitation. Treatment with ATP-MgCl2, however, restored these parameters. Moreover, the depressed heart rate was also restored following ATP-MgCl2 administration. Since ATP-MgCl2 restores various left ventricular performance parameters, this agent appears to be a promising adjunct for improving cardiac function after trauma and hemorrhage, even in the absence of blood resuscitation.

The oculomotor integrator: testing of a neural network model

An important part of the vestibulo-ocular reflex is a group of cells in the caudal pons, known as the neural integrator, that converts eye-velocity commands, from the semicircular canals for example, to eye-position commands for the motoneurons of the extraocular muscles. Previously, a recurrently connected neural network model was developed by us that learns to simulate the signal processing done by the neural integrator, but it uses an unphysiological learning algorithm. We describe here a new network model that can learn the same task by using a local, Hebbian-like learning algorithm that is physiologically plausible. Through the minimization of a retinal slip error signal the model learns, given randomly selected initial synaptic weights, to both integrate simulated push-pull semicircular canal afferent signals and compensate for orbital mechanics as well. Approximately half of the model's 14 neurons are inhibitory, half excitatory. After learning, inhibitory cells tend to project contralaterally, thus forming an inhibitory commissure. The network can, of course, recover from lesions. The mature network is also able to change its gain by simulating abnormal visual-vestibular interactions. When trained with a sine wave at a single frequency, the network changed its gain at and near the training frequency but not at significantly higher or lower frequencies, in agreement with previous experimental observations. Commissural connections are essential to the functioning of this model, as was the case with our previous model. In order to determine whether a commissure plays a similar role in the real neural integrator, a series of electrical perturbations were performed on the midlines of awake, behaving juvenile rhesus monkeys and the effects on the monkeys' eye movements were examined. Eye movements were recorded using the coil system before, during, and after electrical stimulation in the midline of the pons just caudal to the abducens nuclei, which reversibly made the integrator leaky. Eye movements were also recorded from two of the monkeys before and after a midline electrolytic lesion was made at the location where stimulation produced a leaky integrator. This lesion disabled the integrator irreversibly. The eye movements that were produced by the monkeys as a result of these perturbations were then compared with eye movements produced by the model after analogous perturbations. The results are compatible with the hypothesis that integration comes about by positive feedback through lateral inhibition effected by an inhibitory commissure.

A neural network model of the vestibulo-ocular reflex using a local synaptic learning rule

Vertebrates use the vestibulo-ocular reflex to maintain clear vision during head movements. This reflex requires eye-velocity com m ands from the semicircular canals to be integrated (mathematically) to produce eye-position com m ands for the extraocular muscles. This is accomplished by a neural network in the caudal pons. A model of this network is proposed using positive feedback via lateral inhibition. The model has been adapted to a learning network. We have developed a synaptic learning rule using only local information to make the model more physiological.

Pentoxifylline restores the depressed cardiac performance after trauma-hemorrhage and resuscitation

Although studies have shown that pentoxifylline (PTX) improves tissue perfusion and hepatocellular function after trauma-hemorrhage and resuscitation, it is not known whether this agent has any beneficial effects on left ventricular performance under such conditions. To study this, rats underwent laparotomy (i.e., trauma induced) and were bled to and maintained at a blood pressure of 40 mm Hg until 40% of the maximum shed blood volume was returned in the form of Ringer's lactate. The animals were then resuscitated with four times the volume of shed blood with Ringer's lactate over 60 min, following which PTX (50 mg/kg body wt) or an equivalent volume of normal saline was infused intravenously over 100 min. Maximum dP/dt during contraction (+dP/dtmax) and relaxation (-dP/dtmax), maximum rate of a "pressure-normalized" change in ventricular pressure during ventricular contraction (dP/dtmax/P), and ventricular peak systemic pressure (VPSP) were determined at 15 min before the completion of resuscitation and every 30 min up to 4 hr after resuscitation. The results indicated that both +dP/dtmax and -dP/dtmax decreased significantly beginning at 0.5 h after resuscitation and remained depressed throughout the study period in saline-treated animals. In addition, VPSP was significantly depressed at 2.5 to 4 hr after resuscitation. Treatment with PTX, however, significantly improved the above parameters as well as dP/dtmax/P and heart rate. Since PTX restores various left ventricular performance parameters, this agent appears to be a useful adjunct for improving cardiac function after trauma and hemorrhagic shock, even in the absence of blood resuscitation.

Evidence for the simultaneous expression of two PspAs by a clone of capsular serotype 6B Streptococcus pneumoniae

Pneumococcal surface protein A (PspA) has been shown to be a serologically variable virulence factor of Streptococcus pneumoniae. In mice, PspA can elicit antibodies capable of protecting them against otherwise fatal infections with encapsulated pneumococci. In previous studies it has been reported that almost all isolates have two apparently unlinked genomic sequences that are highly homologous to the 5' and 3' halves of Rx1 pspA, although out MAbs to PspA have not detected more than one PspA in any given isolate of S. Pneumoniae. Recently, we have identified four isolates from a clone of capsular serotype 6B pneumococci (MC25-28) that simultaneously express two distinct PspAs. Each of the isolates (MC25-28) exhibited the same two Kpn I fragments (each containing a Hind III site) that hybridized with Rx1 pspA. MAbs specific for PspA detected two PspAs characterized by different molecular weights and different serologic patterns of reactivity (PspA type 6 detected by MAbs XiR278 and 2A4, and PspA type 34 detected only by MAb 7D2) in each of the four isolates. In previous studies XiR278 and 2A4 frequently have been observed to react with PspA epitopes of the same strain. Based on molecular weight data both epitopes were always present on the same molecule. Our present findings raise the possibility that pneumococci make a second serologically variable PspA which is generally not detected by currently available MAbs to PspA.

Synchronous, bilateral mastectomy

Sixty-four patients (mean age, 51 years) had mastectomies which were synchronous and bilateral. Sixty-one premastectomy biopsies (bilateral, 34 and unilateral, 27) demonstrated the following: invasive carcinoma, 17; noninvasive carcinoma, 24; combination of above, 10; and benign disease, 10. Twenty-two patients had bilateral mastectomy because of bilateral positive biopsy. Twenty-nine patients with unilateral carcinoma on biopsy had bilateral mastectomy. Thirteen patients had bilateral mastectomy despite benign disease only on biopsy (10) or no biopsy (3). Ten unexpected carcinomas (34%) were found in the contralateral breast in the 29 patients with carcinoma diagnosed on unilateral biopsy. The biopsy pathology of these 10 specimens was invasive ductal carcinoma in 1 and multifocal, noninvasive carcinoma (ductal, 3 and lobular, 6) in 9. An unexpected carcinoma may be found in the contralateral breast in a significant number of patients who are selected for bilateral mastectomy, particularly if the selection is on the basis of a noninvasive, lobular histology. Bilateral mastectomy may be appropriate for such patients, particularly when complicated by a strong family history and breasts which are difficult to assess by physical or mammographic examination.

Gain changes of the cat's vestibulo-ocular reflex after flocculus deactivation

Motor learning can be demonstrated in the vestibulo-ocular reflex (VOR) by changing its gain (eye velocity/head velocity) with goggles and optokinetic (OK) drums. It is known that the flocculus is essential for this plasticity but there is controversy about whether the modifiable synapses mainly responsible are in the flocculus. To investigate this further we utilized the known reciprocal relationship between complex spikes and simple spikes in Purkinje cell discharges. By stimulating climbing fibers from the olive to the flocculus at 7 Hz, the simple spike rate of almost all recorded floccular cells could be driven to zero. This was termed floccular shutdown and it felt to effect a functional, reversible flocculectomy. Sixty single units in the flocculi of four cats were recorded. Stimulation of the climbing fibers at 7 Hz caused the discharge rate to decrease to zero in 95% of these cells. The gain of the horizontal VOR in three cats was driven repeatedly to twice or half its normal value by rotation within a moving OK drum and also by wearing magnifying or fixed-field goggles; this process required 3 days. If, on the 4th day, the cat was exposed to an OK drum rotating in the opposite direction, the gain was driven back to normal in 30 min. If, however, the climbing fibers were stimulated at 7 Hz during these 30 min, the gain did not return--learning was blocked. This verified that loss of floccular activity by this method abolishes VOR gain plasticity. Moreover, when 7 Hz stimulation first began, after 3 days of adaptation, the adapted gain remained at its adapted value, either half or twice normal, even in the face of floccular shutdown. This result appears incompatible with the hypothesis that the modifiable synapses are in the flocculus.

Visually induced cross-axis postsaccadic eye drift

1. It has been previously shown that, if a visual pattern is transiently moved just after every saccade, it is possible to induce horizontal, postsaccadic, ocular drift after horizontal saccades that persists in the dark. In this study we show that horizontal ocular drift can also be created after vertical saccades. Five human subjects viewed binocularly the interior of a full-field hemisphere filled with a random-dot pattern. They were encouraged to make frequent vertical saccades. During training, eye movements were recorded by the electrooculogram. A computer detected the end of every saccade and immediately moved the pattern to the left after up saccades and right after down saccades. The motion was exponential, its amplitude was 25% of the vertical component of the antecedent saccade, its time constant was 50 ms. Before and after 2-3 h of training, movements of both eyes were measured by the eye-coil/magnetic-field method while subjects were instructed to make vertical saccades in the dark, in the presence of the movable adapting pattern, and between stationary targets for calibration. 2. After training (approximately 20,000 saccades) all subjects developed a zero-latency, exponential ocular drift to the left after up saccades and to the right after down saccades. The amplitude of the horizontal drift, expressed as a percentage of the vertical component of the preceding saccade, was 2.7% in the dark. This rose to 10.2% in the presence of the movable adapting stimulus. The latter rise is not due to visual following systems but to a zero-latency increase in initial drift velocity. 3. The horizontal drifts were usually unequal between the two eyes, indicating the presence of disconjugate movements. We measured intrasaccadic disconjugate horizontal movements of all subjects. In agreement with studies by others of saccades in the light, we measured a divergence during up saccades (1.3 degrees) and a convergence for down (0.4 degrees), but in this case for spontaneous saccades in the dark. After training, these values increased for saccades in the dark but decreased in the light in the presence of the adapting stimulus. These changes were largely idiosyncratic and statistically significant in only a few subjects. 4. The cross-axis postsaccadic drifts were separated into their conjugate and disconjugate components. The disconjugate components were small and idiosyncratic, and the means were small for saccades in the dark. The only consistent trend was in the presence of the adapting stimulus where up saccades were often followed by convergence.(ABSTRACT TRUNCATED AT 400 WORDS)

The natural history of asymptomatic carotid artery disease

PURPOSE

The purpose of this article is to determine the natural history of carotid artery disease among asymptomatic patients with cervical bruits or other risk factors for stroke and to study the value of duplex ultrasonography in predicting future neurologic events.

METHODS

Two hundred forty-two asymptomatic, unoperated patients, referred for evaluation of asymptomatic carotid artery disease, were followed prospectively with duplex ultrasonography.

RESULTS

Fifteen ischemic strokes (6.2%) and 20 transient ischemic attacks (TIA) (8.3%) occurred in 34 patients during a mean follow-up of 27.4 months. Annual stroke, TIA, and combined event rates were 2.7%, 3.6%, and 6.2%, respectively. Although patients with 80% to 99% lesions had a 20.6% annual event rate, most events occurred contralateral to these lesions; the vessel-specific annual event rate for 80% to 99% disease was 5.1%. Only one of 15 strokes occurred ipsilateral to an 80% to 99% stenosis. Echolucent plaques were associated with TIA and stroke (5.7% annual vessel event rate vs 2.4% for echogenic plaques, p = 0.03). Disease progression was highly correlated with TIA and stroke (p < 0.0001), but it usually occurred in association with rather than before ischemic events, thus proving more useful in explaining pathogenesis than in predicting future events. There was no association between aspirin use and TIA, but patients taking aspirin had a threefold higher annual stroke rate (1.6% vs 4.8%, p = 0.027).

CONCLUSIONS

This study, while confirming significant risk for asymptomatic patients with critical stenosis or echolucent plaque, demonstrates the importance of contralateral disease and the absence of orderly progression from minimal disease through high-grade stenosis to symptomatic cerebral ischemia. TIA and stroke commonly occur in association with abrupt, unpredictable, quantum changes in carotid artery disease.

Safety and efficacy of fire ant venom in the diagnosis of fire ant allergy

Thirty-three adult patients who had had systemic allergic reactions to fire ant stings and 33 insect-nonallergic control subjects were skin tested with single lots of Solenopsis invicta (Sol i) fire ant venom (IFAV) and two commercially available imported fire ant whole body extracts (IFA WBEs). All three extracts were analyzed for protein concentration. Sol i II and Sol i III concentrations were each assayed by means of two ELISAs with complementary monoclonal antibodies, one species specific and one cross-reactive. Radioallergosorbent test (RAST) to IFAV and both IFA WBEs was performed on sera from all study subjects. Both IFA WBEs contained high concentrations of fire ant body proteins. Sol i II and III concentrations each varied twofold between the two IFA WBE preparations. Patients were generally more reactive to IFAV than IFA WBE by skin testing and RAST. IFAV RAST appeared to be a more sensitive assay than IFA WBE RAST. No adverse reactions occurred to skin testing with IFAV, but intradermal testing with higher concentrations of IFA WBE caused delayed large local reactions in 16 of 30 (53%) control subjects. These reactions were attributed to the large amounts of extraneous body proteins in IFA WBE. These results (1) demonstrate that skin testing with IFAV is safe, (2) indicate that IFAV is more potent than IFA WBE, and (3) suggest that IFAV may be the superior reagent for diagnosis of fire ant allergy.

Failure of the oculomotor neural integrator from a discrete midline lesion between the abducens nuclei in the monkey

Recent anatomical studies indicate that axons of neurons in the vestibular nuclei, projecting to the contralateral abducens nuclei, cross the midline at the abducens level. These axons then give off collaterals to the contralateral vestibular and prepositus nuclei that may be important for the neural integrator that converts eye-velocity to eye-position signals. We disrupted a subset of these commissural projections by making a small midline lesion between the abducens nuclei in a monkey. The vestibulo-ocular reflex and saccades were still present post-lesion, indicating that premotor drive was intact, but the lesion produced severe post-saccadic drift, indicating failure of the neural integrator. We conclude that commissural projections crossing at the abducens level may be important for oculomotor integration.

Benefits of a multidisciplinary pulmonary rehabilitation program. Improvements are independent of lung function

We evaluated the conditions of 33 patients who completed an outpatient pulmonary rehabilitation program to determine what types of improvements occurred, and whether these changes were related to the baseline degree of ventilatory impairment, to determine whether rehabilitation was beneficial to patients, regardless of the degree of underlying lung dysfunction. Endurance measurements, including sustained submaximal performance on a cycle ergometer and the 12-minute walk distance (1,349 +/- 625 feet to 1,700 +/- 670 feet) increased significantly (p less than 0.01), as did multiple educational and subjective parameters. Maximal exercise performance on a graded cycle test improved very little, with a decline in the ventilatory equivalent for oxygen consumption (VE/VO2) being the only significant change (48.2 +/- 28.3 L/ml to 36.6 +/- 8.7 L/ml). Of the observed changes, only one endurance measurement, the sustained submaximal exercise performance, correlated with FEV1 (r = 0.5, p less than 0.01), but only if it was expressed as an absolute number (liters) and not as percent predicted. Lung function did not correlate with changes in the 12-minute walk distance, in maximal exercise performance on the cycle ergometer or with changes in educational and subjective parameters. We conclude that because the magnitude of change in both physiologic and psychologic parameters was not directly related to lung function, the benefits of rehabilitation can extend to all patients with chronic lung disease, regardless of the severity of preexisting pulmonary dysfunction.

Precision of Larsen grading of radiographs in assessing progression of rheumatoid arthritis in individual patients

A study was designed to evaluate observer variation in the assessment of radiographic deterioration of individual patients using the Larsen grading system. Radiographs of hands and feet of 52 patients were assessed by three observers. Each patient had paired films taken one year apart which were assessed together for change in score. To assess within-observer variation each set of films was read twice by all observers. The average progression was 11.6 (SD 9.0). Analysis of the source of variation showed the single observer replication SD to be 3.7 but that for different observers to be 5.5. This may be interpreted as indicating that to achieve 95% confidence of detecting a true change an increase in Larsen score of 8 is required if the same observer assesses or up to 11 if a different observer assesses.