Actin Disruption by Latrunculin B Causes Turgor-Related Changes in Tip Growth of Saprolegnia ferax Hyphae

Hyphae of Saprolegnia ferax growing under normal or low-turgor conditions were exposed to 0.1-10 &mgr;g/ml latrunculin B, an actin inhibitor. In the first 10 s of addition, hyphae with normal turgor levels accelerated while those with low turgor decelerated, consistent with the suggestion that actin restrains or protrudes tips under these respective turgor conditions. Both sets of hyphae then decelerated and eventually ceased extension within 60 s. These changes were reflected in rhodamine-phalloidin staining patterns, which showed that actin caps were disrupted progressively under both conditions in a time-dependent manner. After 60 s, normal-turgored hyphae started to swell rapidly while low-turgored hyphae showed little or no swelling. Swelling was characteristically subapical, which is best explained by tip growth models which incorporate actin-mediated exocytosis.     

Expression of Ndi1p, an alternative NADH:ubiquinone oxidoreductase, increases mitochondrial membrane potential in a C. elegans model of mitochondrial disease

The NADH:ubiquinone oxidoreductase or complex I of the mitochondrial respiratory chain is an intricate enzyme with a vital role in energy metabolism. Mutations affecting complex I can affect at least three processes; they can impair the oxidation of NADH, reduce the enzyme's ability to pump protons for the generation of a mitochondrial membrane potential and increase the production of damaging reactive oxygen species. We have previously developed a nematode model of complex I-associated mitochondrial dysfunction that features hallmark characteristics of mitochondrial disease, such as lactic acidosis and decreased respiration. We have expressed the Saccharomyces cerevisiae NDI1 gene, which encodes a single subunit NADH dehydrogenase, in a strain of Caenorhabditis elegans with an impaired complex I. Expression of Ndi1p produces marked improvements in animal fitness and reproduction, increases respiration rates and restores mitochondrial membrane potential to wild type levels. Ndi1p functionally integrates into the nematode respiratory chain and mitigates the deleterious effects of a complex I deficit. However, we have also shown that Ndi1p cannot substitute for the absence of complex I. Nevertheless, the yeast Ndi1p should be considered as a candidate for gene therapy in human diseases involving complex I.     

Periodic operation of immobilized cell systems: analysis

The authors' mathematical model of transient immobilized cell growth and product formation is applied here to examine the performance of an immobilized cell system subject to periodic cycling of the rate-limiting substrate supply. The model system consists of a single hydrogel-like (porous) particle entrapping viable microorganisms. Proper nutrient cycling is shown to yield a relaxed periodic system and to virtually eliminate the leakage of biomass from the support that is commonly observed experimentally in steady (continuous nutrient supply) operation of these systems. The use of cyclic operation is evaluated by calculating the average product yield (the ratio of product formed to substrate consumed) and the average product flux from the particle (a measure of the total productivity of the system), for various cycling rates. Cycling increased the average product yield by at least a factor of three in nongrowth-related fermentations, relative to steady operation, without any significant sacrifice in average total productivity. Growth-related fermentations lost significant total productivity under most cycling conditions, while the average product yield was approximately unchanged at all cycling rates. Thus, immobilization in conjunction with periodic operation should be considered as an alternative process design for the production of nongrowth-related products such as penicillin and monoclonal antibodies.     

Reverberation challenges the temporal representation of the pitch of complex sounds

Accurate neural coding of the pitch of complex sounds is an essential part of auditory scene analysis; differences in pitch help segregate concurrent sounds, while similarities in pitch can help group sounds from a common source. In quiet, nonreverberant backgrounds, pitch can be derived from timing information in broadband high-frequency auditory channels and/or from frequency and timing information carried in narrowband low-frequency auditory channels. Recording from single neurons in the cochlear nucleus of anesthetized guinea pigs, we show that the neural representation of pitch based on timing information is severely degraded in the presence of reverberation. This degradation increases with both increasing reverberation strength and channel bandwidth. In a parallel human psychophysical pitch-discrimination task, reverberation impaired the ability to distinguish a high-pass harmonic sound from noise. Together, these findings explain the origin of perceptual difficulties experienced by both normal-hearing and hearing-impaired listeners in reverberant spaces.     

Perceptual organization of sound begins in the auditory periphery

Segmenting the complex acoustic mixture that makes a typical auditory scene into relevant perceptual objects is one of the main challenges of the auditory system [1], for both human and nonhuman species. Several recent studies indicate that perceptual auditory object formation, or "streaming," may be based on neural activity within the auditory cortex and beyond [2, 3]. Here, we find that scene analysis starts much earlier in the auditory pathways. Single units were recorded from a peripheral structure of the mammalian auditory brainstem, the cochlear nucleus. Peripheral responses were similar to cortical responses and displayed all of the functional properties required for streaming, including multisecond adaptation. Behavioral streaming was also measured in human listeners. Neurometric functions derived from the peripheral responses predicted accurately behavioral streaming. This reveals that subcortical structures may already contribute to the analysis of auditory scenes. This finding is consistent with the observation that species lacking a neocortex can still achieve and benefit from behavioral streaming [4]. For humans, we argue that auditory scene analysis of complex scenes is probably based on interactions between subcortical and cortical neural processes, with the relative contribution of each stage depending on the nature of the acoustic cues forming the streams.     

Opportunities for Tuberculosis Diagnosis and Prevention among Persons Living with HIV: A Cross-Sectional Study of Policies and Practices at Four Large Ryan White Program-Funded HIV Clinics

Objective

We describe the frequency and attributes of tuberculosis testing and treatment at four publicly-funded HIV clinics.

Methods

We abstracted medical records from a random sample of 600 HIV-infected patients having at least one clinic visit in 2009 at four clinics in New York and Los Angeles Metropolitan Statistical areas. We described testing and treatment for tuberculosis infection (TBI), 2008–2010, and estimated adjusted odds ratios (aORs). We interviewed key informants and described clinic policies and practices.

Results

Of 600 patients, 500 were eligible for testing, and 393 (79%) were tested 2008–2010; 107 (21%) did not receive at least one tuberculin skin test or interferon gamma release assay. Results were positive in 20 (5%) patients, negative in 357 (91%), and unknown in 16 (4%). Fourteen (70%) of 20 patients with TBI initiated treatment at the clinics; only three were documented to have completed treatment. Three hundred twenty three (54%) patients had chest radiography, 346 (58%) had tuberculosis symptom screening, and three had tuberculosis disease (117 per 100,000 person-years, 95% confidence interval (CI) = 101–165). Adjusting for site, non-Hispanic ethnicity (aOR = 4.9, 95% CI = 2.6–9.5), and employment (aOR = 1.9, 95% CI = 1.0–3.4) were associated with TBI testing; female gender (aOR = 2.0, 95% CI = 1.4–3.3), non-black race (aOR = 1.7, 95% CI = 1.3–2.5), and unemployment (aOR = 1.5, 95% CI = 1.1–2.1) were associated with chest radiography. Clinics evaluated TBI testing performance annually and identified challenges to TB prevention.

Conclusions

Study clinics routinely tested patients for TBI, but did not always document treatment. In a population with a high TB rate, ensuring treatment of TBI may enhance TB prevention.     

Salivary and serum procalcitonin and C-reactive protein as biomarkers of periodontitis in United States veterans with osteoarthritis or rheumatoid arthritis

Serum procalcitonin (ProCT) is elevated in response to bacterial infections, whereas high sensitivity C-reactive protein (hsCRP) is a nonspecific inflammatory marker that is increased by excess adipose tissue. We examined the efficacy of ProCT and hsCRP as biomarkers of periodontitis in the saliva and serum of patients with arthritis, which is characterized by variable levels of systemic inflammation that potentially can confound the interpretation of inflammatory biomarkers. Blood and unstimulated whole saliva were collected from 33 patients with rheumatoid arthritis (RA) and 50 with osteoarthritis (OA). Periodontal status was assessed by full mouth examination and patients were categorized as having no/mild, moderate or severe periodontitis by standard parameters. Salivary and serum ProCT and hsCRP concentrations were compared. BMI, diabetes, anti-inflammatory medications and smoking status were ascertained from the patient records. Differences between OA and RA in proportionate numbers of patients were compared for race, gender, diabetes, adiposity and smoking status. Serum ProCT was significantly higher in arthritis patients with moderate to severe and severe periodontitis compared with no/mild periodontitis patients. There were no significant differences in salivary ProCT or salivary or serum hsCRP in RA patients related to periodontitis category. Most of the OA and RA patients were middle aged or older, 28.9% were diabetic, 78.3% were overweight or obese, and slightly more than half were either current or past smokers. The OA and RA groups differed by race, but not gender; blacks and males were predominant in both groups. The OA and RA groups did not differ in terms of controlled or uncontrolled diabetes, smoking status or BMI. The RA patients had been prescribed more anti-inflammatory medication than the OA patients. Our results demonstrate that circulating ProCT is a more discriminative biomarker for periodontitis than serum hsCRP in patients with underlying arthritis. Any elevation in salivary and serum hsCRP due to periodontitis apparently was overshadowed by differences among these patients in factors that influence CRP, such as the extent of inflammation between RA and OA, the extent of adipose tissue, the use of anti- inflammatory medications and smoking status. Although our study showed no differences in salivary ProCT related to severity of periodontitis, this biomarker also may be useful with further refinement.