bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the Genetic Components of
Streptomyces lividans
Linear Plasmid SLP2 for Replication in Circular and Linear Modes
Authors: Xu Mingxuan , Zhu Yingmin , Zhang Ran , Shen Meijuan , Jiang Weihong , Zhao Guoping , Qin Zhongjun
Published: September 2006

The nucleotide sequence of
Streptomyces lividans
linear plasmid SLP2 consists of 50,410 bp (C. H. Huang, C. Y. Chen, H. H. Tsai, C. Chen, Y. S. Lin, and C. W. Chen, Mol. Microbiol.
47:
1563-1576, 2003). Here we report that the basic SLP2 locus for plasmid replication in circular mode resembles that of
Streptomyces
linear plasmids pSLA2 and SCP1 and comprises iterons
SLP2
and the adjacent
rep

SLP2

gene. More efficient replication additionally required the 47-bp sequence between bp 581 and 628 upstream of the iterons. Replacement of either the iterons or the
rep
gene of SLP2 by the corresponding genes of pSLA2 or SCP1 still allows propagation in
Streptomyces
, although the transformation frequencies were 3 orders of magnitude lower than the original plasmids, suggesting that these plasmids share similar replication mechanisms. To replicate SLP2 in linear mode, additional SLP2 loci—either
mtap

SLP2

/
tpg

SLP2

or
mtap

SLP2

/
ilrA

SLP2

—were required. IlrA
SLP2
protein binds specifically to the iterons
SLP2
in vitro. Interactions were detected between these SLP2-borne replication proteins (Mtap
SLP2
, Tpg
SLP2
, and IlrA
SLP2
) and the telomeric replication proteins (TpgL, TapL, and TpgL) of the
S. lividans
chromosome, respectively, but the SLP2 proteins failed to interact. These results suggest that SLP2 recruits chromosomally encoded replication proteins for its telomere replication.
Characterization of ExsC and ExsD Self-Association and Heterocomplex Formation
Authors: Lykken Guinevere L. , Chen GuoZhou , Brutinel Evan D. , Chen Lingling , Yahr Timothy L.
Published: September 2006

Expression of the
Pseudomonas aeruginosa
type III secretion system (T3SS) is induced by calcium depletion and is positively regulated by the ExsA transcriptional activator and negatively regulated by the ExsD antiactivator. Under conditions permissive for expression of the T3SS, the negative regulatory activity of ExsD is antagonized by a direct binding interaction with ExsC. In the present study, the ExsC-ExsD binding interaction was characterized. Individually, both ExsC and ExsD form self-associated complexes, as judged by bacterial monohybrid and gel filtration experiments. A mixture of purified ExsC and ExsD readily formed a complex that elutes from gel filtration medium as a single included peak. The calculated molecular weight of the ExsC-ExsD complex is consistent with a complex containing multiple copies of ExsC and ExsD. Isothermic titration calorimetry experiments found formation of the ExsC-ExsD complex to be thermodynamically favorable, with a

K
d

of ∼18 nM and a likely binding ratio of 1:1. To identify amino acid residues important for the regulatory activities of ExsC and ExsD, self-association, and complex formation, charged-cluster mutagenesis was performed. Two of the resulting ExsD charged-cluster mutants (DM2 and DM3) demonstrated a hyperrepressive phenotype for expression of the T3SS. By two-hybrid and copurification assays, the DM3 mutant was found to be impaired in its interaction with ExsC. This finding demonstrates that the binding of ExsC to ExsD is required for transcriptional induction of the T3SS under calcium-limiting growth conditions.
ArecANull Mutation May Be Generated inStreptomyces coelicolor
Authors: Huang Tzu-Wen , Chen Carton W.
Published: September 2006

The recombinase RecA plays a crucial role in homologous recombination and the SOS response in bacteria. AlthoughrecAmutants usually are defective in homologous recombination and grow poorly, they nevertheless can be isolated in almost all bacteria. Previously, considerable difficulties were experienced by several laboratories in generatingrecAnull mutations inStreptomyces, and the onlyrecAnull mutants isolated (fromStreptomyces lividans) appeared to be accompanied by a suppressing mutation. Using gene replacement mediated byEscherichia coli-Streptomycesconjugation, we generatedrecAnull mutations in a series ofStreptomyces coelicolorA3(2) strains. TheserecAmutants were very sensitive to mitomycin C but only moderately sensitive to UV irradiation, and the UV survival curves showed wide shoulders, reflecting the presence of arecA-independent repair pathway. The mutants segregated minute colonies with low viability during growth and produced more anucleate spores than the wild type. Some crosses between pairs ofrecAnull mutants generated no detectable recombinants, showing for the first time that conjugal recombination inS. coelicolorisrecAmediated, but other mutants retained the ability to undergo recombination. The nature of this novel recombination activity is unknown.
Rem, a New Transcriptional Activator of Motility and Chemotaxis in
Sinorhizobium meliloti
Authors: Rotter Christine , Mühlbacher Susanne , Salamon Daniel , Schmitt Rüdiger , Scharf Birgit
Published: September 2006

The expression of 51 known genes clustered in the flagellar regulon of
Sinorhizobium meliloti
is organized as a three-class hierarchy: class IA comprises the master regulatory genes,
visN
and
visR
; class II, controlled by VisNR, comprises flagellar assembly and motility genes; and class III comprises flagellin and chemotaxis genes requiring class II for expression. The expression of
visN-visR
is constitutive throughout growth, whereas that of class II and class III genes is limited to exponential growth. A new OmpR-like, 25-kDa transcription factor, Rem, whose synthesis is confined to exponential growth, was shown to positively control swimming motility. No phosphorylation of the receiver domain of Rem was required for its activity. Gene expression in tester strains with known deficiencies placed the
rem
gene (class IB) below
visN-visR
(class IA) and above class II genes in the regulatory cascade. Footprinting analysis demonstrated that the Rem protein binds to class II gene promoters as well as to its own promoter, indicating that this protein is autoregulatory. An alignment of the Rem-protected DNA sequences revealed a conserved binding motif of imperfect tandem repeats overlapping a predicted −35 promoter box by 3 bp. This new promoter was confirmed by mapping the transcription start site of a typical class II gene,
flgB
, 5 nucleotides downstream of the −10 promoter box. The transcription of
rem
is under dual control of an upstream (Rem-activated) class II-type promoter and a downstream (VisNR-activated) σ
70
-like promoter. The central role of Rem as the growth-dependent transcriptional activator intermediate between the master regulator, VisNR, and the flagellar and motility genes is a new distinguishing feature of the
S. meliloti
regulatory cascade.
Interventions for the prevention and management of neck/upper extremity musculoskeletal conditions: a systematic review
Authors: Boocock M G , McNair P J , Larmer P J , Armstrong B , Collier J , Simmonds M , Garrett N
Published: September 2006

Considered from medical, social or economic perspectives, the cost of musculoskeletal injuries experienced in the workplace is substantial, and there is a need to identify the most efficacious interventions for their effective prevention, management and rehabilitation. Previous reviews have highlighted the limited number of studies that focus on upper extremity intervention programmes. The aim of this study was to evaluate the findings of primary, secondary and/or tertiary intervention studies for neck/upper extremity conditions undertaken between 1999 and 2004 and to compare these results with those of previous reviews. Relevant studies were retrieved through the use of a systematic approach to literature searching and evaluated using a standardised tool. Evidence was then classified according to a “pattern of evidence” approach. Studies were categorised into subgroups depending on the type of intervention: mechanical exposure interventions; production systems/organisational culture interventions and modifier interventions. 31 intervention studies met the inclusion criteria. The findings provided evidence to support the use of some mechanical and modifier interventions as approaches for preventing and managing neck/upper extremity musculoskeletal conditions and fibromyalgia. Evidence to support the benefits of production systems/organisational culture interventions was found to be lacking. This review identified no single-dimensional or multi-dimensional strategy for intervention that was considered effective across occupational settings. There is limited information to support the establishment of evidence-based guidelines applicable to a number of industrial sectors.
Potential of ultrasonography for epidemiological study of work-related wrist tenosynovitis
Authors: Violante F S , Bonfiglioli R , Graziosi F , Caso A , Isolani L , Fiorentini C , Mattioli S
Published: September 2006

Objective:To explore the possible role of ultrasonography in case definitions for epidemiological studies of work-related wrist tenosynovitis.

Methods:Clinical and ultrasonography (7.5 MHz linear probe) data systematically collected from meat workers (n = 128) with biomechanical exposure characterisation were analysed. The diagnostic accuracy of different combinations of potentially relevant ultrasonography findings (nonhomogeneity, thickening and anechoic halo) was evaluated using symptomatology as a reference standard. The concordance between ultrasonography findings and symptoms was then analysed.

Results:Analysis of wrist biomechanical exposure was suggestive of increased prevalence of musculoskeletal disorders. Using symptoms as a reference standard, each of the three ultrasonography findings (and their combinations) showed good specificity (⩾85%) accompanied by low sensitivity (<60%); the positive likelihood ratio for at least two findings was 4.1. κ Values (95% confidence intervals) between symptoms and different sets of ultrasonography findings were as follows: for non-homogeneity, κ = 0.31 (0.19 to 0.43); at least one finding, κ = 0.28 (0.16 to 0.40); at least two findings, κ = 0.32 (0.20 to 0.44); all p<0.01.

Conclusion:The use of ultrasonography in symptomatic subjects could contribute to a more specific epidemiological case definition of wrist tenosynovitis. The results of this study could help orient future research in this direction.
Do ambient noise exposure levels predict hearing loss in a modern industrial cohort?
Authors: Rabinowitz P M , Galusha D , Dixon-Ernst C , Slade M D , Cullen M R
Published: September 2006

Background:Much of what is known about the exposure–response relationship between occupational noise exposures and hearing loss comes from cross-sectional studies conducted before the widespread implementation of workplace hearing conservation programmes. Little is known about the current relationship of ambient noise exposure measurements to hearing loss risk.

Aim:To examine the relationship between rates of high frequency hearing loss and measured levels of noise exposure in a modern industrial workforce.

Methods:Ten-year hearing loss rates were determined for 6217 employees of an aluminium manufacturing company. Industrial hygiene and human resources records allowed for reconstruction of individual noise exposures. Hearing loss rates were compared to ANSI 3.44 predictions based on age and noise exposure. Associations between hearing loss, noise exposure, and covariate risk factors were assessed using multivariate regression.

Results:Workers in higher ambient noise jobs tended to experience less high frequency hearing loss than co-workers exposed at lower noise levels. This trend was also seen in stratified analyses of white males and non-hunters. At higher noise exposure levels, the magnitude of hearing loss was less than predicted by ANSI 3.44 formulae. There was no indication that a healthy worker effect could explain these findings. The majority of 10 dB standard threshold shifts (STS) occurred in workers whose calculated ambient noise exposures were less than or equal to 85 dBA.

Conclusions:In this modern industrial cohort, hearing conservation efforts appear to be reducing hearing loss rates, especially at higher ambient noise levels. This could be related to differential use of hearing protection. The greatest burden of preventable occupational hearing loss was found in workers whose noise exposure averaged 85 dBA or less. To further reduce rates of occupational hearing loss, hearing conservation programmes may require innovative approaches targeting workers with noise exposures close to 85 dBA.
Respiratory symptoms and bronchial responsiveness among cleaning and disinfecting workers in the food industry
Authors: Massin N , Hecht G , Ambroise D , Héry M , Toamain J P , Hubert G , Dorotte M , Bianchi B
Published: September 2006

Objectives:To measure the levels of exposure to nitrogen trichloride (NCl3) and aldehydes among cleaning and disinfecting workers in the atmosphere of food industry plants during cleaning and disinfecting operations, and to examine how they relate to irritant and chronic respiratory symptoms—which are indices of pulmonary function—and bronchial hyperresponsiveness (BHR) to methacholine.

Methods:175 exposed workers (M = 149; F = 26) recruited from 17 enterprises of the food industry (8 cattle, pig, and ovine slaughterhouses, 8 fowl slaughterhouses, and 1 catering firm) and 70 non-exposed workers (M = 52; F = 18) were examined. Concentration levels of NCl3and aldhehydes were measured by personal sampling. Symptoms were assessed by means of a questionnaire and the methacholine bronchial challenge (MBC) test using an abbreviated method. Subjects were labelled MBC+ if forced expiratory volume in one second (FEV1) fell by 20% or more. The linear dose-response slope (DRS) was calculated as the percentage fall in FEV1 at last dose divided by the total dose administered.

Results:277 air samples were taken in the 17 food industry plants. For a given plant and in a given workshop, the actual concentrations of chloramines, aldehydes, and quaternary ammonium compounds were measured with personal samplers during the different steps of the procedures. For each cleaner, a total exposure index Σ was calculated. A statistically significant concentration-response relationship was found between eye, nasal, and throat symptoms of irritation—but not chronic respiratory symptoms—and exposure levels or exposure duration. No relation was found between BHR and exposure.

Conclusions:These data show that cleaning and disinfecting workers in the food industry are at risk of developing eye, nasal, and throat irritation symptoms. Although NCl3exposure does not seem to carry a risk of developing permanent BHR, the possibility of transient BHR cannot be ruled out entirely.
Mortality from non-malignant respiratory diseases among people with silicosis in Hong Kong: exposure–response analyses for exposure to silica dust
Authors: Tse L A , Yu I T S , Leung C C , Tam W , Wong T W
Published: September 2006

Objectives:To examine the exposure–response relationships between various indices of exposure to silica dust and the mortality from non-malignant respiratory diseases (NMRDs) or chronic obstructive pulmonary diseases (COPDs) among a cohort of workers with silicosis in Hong Kong.

Methods:The concentrations of respirable silica dust were assigned to each industry and job task according to historical industrial hygiene measurements documented previously in Hong Kong. Exposure indices included cumulative dust exposure (CDE) and mean dust concentration (MDC). Penalised smoothing spline models were used as a preliminary step to detect outliers and guide further analyses. Multiple Cox’s proportional hazard models were used to estimate the dust effects on the risk of mortality from NMRDs or COPDs after truncating the highest exposures.

Results:371 of the 853 (43.49%) deaths occurring among 2789 workers with silicosis during 1981–99 were from NMRDs, and 101 (27.22%) NMRDs were COPDs. Multiple Cox’s proportional hazard models showed that CDE (p = 0.009) and MDC (p<0.001) were significantly associated only with NMRD mortality. Subgroup analysis showed that deaths from NMRDs (p<0.01) and COPDs (p<0.05) were significantly associated with both CDE and MDC among underground caisson workers and among those ever employed in other occupations with high exposure to silica dust. No exposure–response relationship was observed for surface construction workers with low exposures. A clear upward trend for both NMRDs and COPDs mortality was found with increasing severity of radiological silicosis.

Conclusion:This study documented an exposure–response relationship between exposure to silica dust and the risk of death from NMRDs or COPDs among workers with silicosis, except for surface construction workers with low exposures. The risk of mortality from NMRDs increased significantly with the progression of International Labor Organization categories, independent of dust effects.
Transient risk factors for acute traumatic hand injuries: a case-crossover study in Hong Kong
Authors: Chow C Y , Lee H , Lau J , Yu I T S
Published: September 2006

Objectives:To identify the remediable transient risk factors of occupational hand injuries in Hong Kong in order to guide the development of prevention strategies.

Methods:The case-crossover study design was adopted. Study subjects were workers with acute hand injuries presenting to the government Occupational Medicine Unit for compensation claims within 90 days from the date of injury. Detailed information on exposures to specific transient factors during the 60 minutes prior to the occurrence of the injury, during the same time interval on the day prior to the injury, as well as the usual exposure during the past work-month was obtained through telephone interviews. Both matched-pair interval approach and usual frequency approach were adopted to assess the associations between transient exposures in the workplace and the short-term risk of sustaining a hand injury.

Results:A total of 196 injured workers were interviewed. The results of the matched-pair interval analysis matched well with the results obtained using the usual frequency analysis. Seven significant transient risk factors were identified: using malfunctioning equipment/materials, using a different work method, performing an unusual work task, working overtime, feeling ill, being distracted and rushing, with odds ratios ranging from 10.5 to 26.0 in the matched-pair interval analysis and relative risks ranging between 8.0 and 28.3 with the usual frequency analysis. Wearing gloves was found to have an insignificant protective effect on the occurrence of hand injury in both analyses.

Conclusions:Using the case-crossover study design for acute occupational hand injuries, seven transient risk factors that were mostly modifiable were identified. It is suggested that workers and their employers should increase their awareness of these risk factors, and efforts should be made to avoid exposures to these factors by means of engineering and administrative controls supplemented by safety education and training.
Regulation of Receptor Tyrosine Kinase Signaling by GRKs and β-Arrestins
Authors: Hupfeld Christopher J. , Olefsky Jerrold M.
Published: September 2006

Receptor tyrosine kinases (RTKs) are a unique family of cell surface receptors, each containing a common intracellular domain that has tyrosine kinase activity. However, RTKs share many signaling molecules with another unique family of cell surface receptors, the seven-transmembrane receptors (7TMRs), and these receptor families can activate similar signaling cascades. In this review of RTK signaling, we describe the role of cross talk between RTKs and 7TMRs, focusing specifically on the role played in this process by β-arrestins and by G proteins.
The VSL#3 probiotic formula induces mucin gene expression and secretion in colonic epithelial cells
Authors: Caballero-Franco C. , Keller K. , De Simone C. , Chadee K.
Published: September 2006

Several studies have stressed the importance of the microbiota in the maintenance of the gastrointestinal epithelium. Administration of probiotic bacteria, supplements composed of microbiota constituents, was previously shown to diminish symptoms in patients suffering from inflammatory bowel diseases. This raises the possibility that probiotics may play an active role in enhancing the intestinal barrier at the mucosal surface. In this study, we investigated whether the clinically tested VSL#3 probiotic formula and/or its secreted components can augment the protective mucus layer in vivo and in vitro. For in vivo studies, Wistar rats were orally administered the probiotic mixture VSL#3 on a daily basis for seven days. After treatment, basal luminal mucin content increased by 60%. In addition, we exposed isolated rat colonic loops to the VSL#3 probiotic formula, which significantly stimulated colonic mucin (MUC) secretion and MUC2 gene expression; however, MUC1 and MUC3 gene expression were only slightly elevated. The effect of the VSL#3 mucin secretagogue was also tested in vitro by use of LS 174T colonic epithelial cells. In contrast to the animal studies, cultured cells incubated with VSL#3 bacteria did not exhibit increased mucin secretion. However, the bacterial secreted products contained in the conditioned media stimulated a remarkable mucin secretion effect. Among the three bacterial groups ( Lactobacilli, Bifidobacteria, and Streptococci) contained in VSL#3, the Lactobacillus species were the strongest potentiator of mucin secretion in vitro. A preliminary characterization of the putative mucin secretagogue suggested that it was a heat-resistant soluble compound, which is not sensitive to protease and DNase treatment. These findings contribute to a better understanding of the complex and beneficial interaction between colonic epithelial cells and intestinal bacteria.
The peristaltic reflex induced by short-chain fatty acids is mediated by sequential release of 5-HT and neuronal CGRP but not BDNF
Authors: Grider J. R. , Piland B. E.
Published: September 2006

Short-chain fatty acids (SCFAs) accelerate colonic transit. This study examined whether this action was mediated by activation of the peristaltic reflex. SCFAs (acetate, butyrate, or propionate) were applied to the central compartment of a three-compartment flat-sheet preparation of the rat middle to distal colon. The release of serotonin (5-HT), brain-derived neurotrophic factor (BDNF), and CGRP was measured in all three compartments. Ascending contraction and descending relaxation were measured in the orad and caudad compartments. The addition of SCFAs at physiological to supraphysiological concentrations (0.5–100 mM) to the central compartment elicited concentration-dependent ascending contraction and descending relaxation (EC50∼5 mM). At this concentration, SCFAs induced an 8- to 11-fold increase in 5-HT release and a 2- to 3-fold increase in CGRP release in the central compartment only. They had no effect on BDNF release. CGRP release was inhibited by a 5-HT4but not a 5-HT3receptor antagonist. Ascending contraction and descending relaxation were also inhibited by 5-HT4and by CGRP receptor antagonists added to the central compartment. 5-HT and CGRP release, as well as ascending contraction and descending relaxation induced by mechanical stimulation of the mucosa (2–8 strokes), were significantly augmented by 1 mM acetate. Acetate (1 mM) also doubled propulsive velocity in isolated whole segments of the guinea pig colon. In conclusion, chemical stimulation of the mucosa by SCFAs triggers a peristaltic reflex mediated by the release of 5-HT from mucosal cells and activation of 5-HT4receptors on sensory CGRP-containing nerve terminals. This SCFA-induced peristaltic pathway augments the peristaltic reflex elicited by mechanical stimulation of the mucosa.
Transforming growth factor-β1 decreases cardiac muscle L-type Ca2+ current and charge movement by acting on the Cav1.2 mRNA
Authors: Avila Guillermo , Medina Irma M. , Jiménez Esperanza , Elizondo Guillermo , Aguilar Citlalli I.
Published: September 2006

Transforming growth factors-β (TGF-βs) are essential to the structural remodeling seen in cardiac disease and development; however, little is known about potential electrophysiological effects. We hypothesized that chronic exposure (6–48 h) of primary cultured neonatal rat cardiomyocytes to the type 1 TGF-β (TGF-β1, 5 ng/ml) may affect voltage-dependent Ca2+ channels. Thus we investigated T- ( ICaT) and L-type ( ICaL) Ca2+ currents, as well as dihydropyridine-sensitive charge movement using the whole cell patch-clamp technique and quantified CaV1.2 mRNA levels by real-time PCR assay. In ventricular myocytes, TGF-β1 did not exert significant electrophysiological effects. However, in atrial myocytes, TGF-β1 reduced both ICaL and charge movement (55% at 24–48 h) without significantly altering ICaT, cell membrane capacitance, or channel kinetics (voltage dependence of activation and inactivation, as well as the activation and inactivation rates). Reductions of ICaL and charge movement were explained by concomitant effects on the maximal values of L-channels conductance ( Gmax) and charge movement (Qmax). Thus TGF-β1 selectively reduces the number of functional L-channels on the surface of the plasma membrane in atrial but not ventricular myocytes. The TGF-β1-induced ICaL reduction was unaffected by supplementing intracellular recording solutions with okadaic acid (2 μM) or cAMP (100 μM), two compounds that promote L-channel phosphorylation. This suggests that the decreased number of functional L-channels cannot be explained by a possible regulation in the L-channels phosphorylation state. Instead, we found that TGF-β1 decreases the expression levels of atrial CaV1.2 mRNA (70%). Thus TGF-β1 downregulates atrial L-channel expression and may be therefore contributing to the in vivo cardiac electrical remodeling.
ANG II-induced hypertension and the role of the area postrema during normal and increased dietary salt
Authors: Nahey David B. , Collister John P.
Published: September 2006

It has been shown that the area postrema (AP) plays a role in the development of certain types of chronic angiotensin II (ANG II)-induced hypertension in the rat but is not of great importance in the salt sensitivity of arterial pressure. It has recently been proposed, however, that elevated sodium levels may exacerbate the hypertensive effects of ANG II, which by itself dramatically affects salt sensitivity, by acting at sodium-sensing neurons in certain circumventricular organs of the brain. Thus the interactions of ANG II, sodium, and the central nervous system remain to be fully understood. The purpose of this study was to examine the role of the AP in ANG II-induced hypertension during periods of normal and elevated dietary salt. We hypothesized that an intact AP was necessary for the full development of hypertension under chronic ANG II infusion and that its role would be pronounced during periods of increased dietary sodium. To test this, male Sprague-Dawley rats underwent ablation of the area postrema (APx, n = 6) or sham operation (sham, n = 6). After 3 wk of recovery, rats were instrumented with radiotelemetry transducers for constant blood pressure and heart rate monitoring and venous catheters for vehicle infusion. After a 3-day control period of 0.9% saline infusion (7 ml/day) and 0.4% dietary sodium, a 10-day period of ANG II infusion (10 ng·kg−1·min−1) was begun, immediately followed by a second 10-day period during which rats were fed a 4.0% sodium diet. By day 6 of ANG II infusion, mean arterial pressure (MAP) in APx rats had increased to 139 ± 4 mmHg, whereas MAP in sham rats had increased to 126 ± 3 mmHg. This difference was found to be significant and continued through day 1 of the high-salt period, after which MAP of the two groups had risen to similar levels. On day 9 of high salt, MAP was again observed to be significantly higher (162 ± 1 mmHg) in APx rats when compared with sham rats (147 ± 4 mmHg.) These results do not support the hypothesis that the AP is necessary for the full development of ANG II-induced hypertension at normal or elevated levels of dietary sodium.
Combined prenatal and postnatal protein restriction influences adult kidney structure, function, and arterial pressure
Authors: Hoppe Chantal C. , Evans Roger G. , Moritz Karen M. , Cullen-McEwen Luise A. , Fitzgerald Sharyn M. , Dowling John , Bertram John F.
Published: September 2006

The effects of prenatal protein restriction on adult renal and cardiovascular function have been studied in considerable detail. However, little is known about the effects of life-long protein restriction, a common condition in the developing world. Therefore, we determined in rats the effects of combined pre- and postnatal protein restriction on adult arterial pressure and renal function and responses to increased dietary sodium. Nephron number was also determined. Male Sprague-Dawley rats were born to mothers fed a low [8% (wt/wt), LP] or normal [20% (wt/wt), NP] isocaloric protein diet throughout pregnancy and maintained on these diets after birth. At postnatal day 135, nephron number, mean arterial pressure (MAP), and renal function were determined. A high-NaCl [8.0% (wt/wt), high-salt] diet was fed to a subset of rats from weaning. MAP was less in LP than in NP rats (120 ± 2 vs. 128 ± 2 mmHg, P < 0.05) and was not significantly altered by increased salt intake. Nephron number was 31% less in LP than in NP rats ( P < 0.001). The volume of individual glomeruli was also less in LP than in NP rats, as were calculated effective renal plasma flow and glomerular filtration rate. Glomerular filtration rate, but not effective renal plasma flow, appeared to be increased by high salt intake, particularly in LP rats. In conclusion, protein restriction induced a severe nephron deficit, but MAP was lower, rather than higher, in protein-restricted than in control rats in adulthood. These findings indicate that the postnatal environment plays a key role in determining the outcomes of developmental programming.
Regular heartbeat dynamics are associated with cardiac health
Authors: Cysarz Dirk , Lange Silke , Matthiessen Peter F. , Leeuwen Peter van
Published: September 2006

The human heartbeat series is more variable and, hence, more complex in healthy subjects than in congestive heart failure (CHF) patients. However, little is known about the complexity of the heart rate variations on a beat-to-beat basis. We present an analysis based on symbolic dynamics that focuses on the dynamic features of such beat-to-beat variations on a small time scale. The sequence of acceleration and deceleration of eight successive heartbeats is represented by a binary sequence consisting of ones and zeros. The regularity of such binary patterns is quantified using approximate entropy (ApEn). Holter electrocardiograms from 30 healthy subjects, 15 patients with CHF, and their surrogate data were analyzed with respect to the regularity of such binary sequences. The results are compared with spectral analysis and ApEn of heart rate variability. Counterintuitively, healthy subjects show a large amount of regular beat-to-beat patterns in addition to a considerable amount of irregular patterns. CHF patients show a predominance of one regular beat-to-beat pattern (alternation of acceleration and deceleration), as well as some irregular patterns similar to the patterns observed in the surrogate data. In healthy subjects, regular beat-to-beat patterns reflect the physiological adaptation to different activities, i.e., sympathetic modulation, whereas irregular patterns may arise from parasympathetic modulation. The patterns observed in CHF patients indicate a largely reduced influence of the autonomic nervous system. In conclusion, analysis of short beat-to-beat patterns with respect to regularity leads to a considerable increase of information compared with spectral analysis or ApEn of heart-rate variations.
Baroreflex control of renal sympathetic nerve activity during air-jet stress in rats
Authors: Kanbar Roy , Oréa Valérie , Barrès Christian , Julien Claude
Published: September 2006

The effects of acute emotional stress on the sympathetic component of the arterial baroreceptor reflex have not yet been described in conscious animals and humans. Arterial pressure (AP) and renal sympathetic nerve activity (RSNA) were simultaneously recorded in 11 conscious rats before and during exposure to a mild environmental stressor (jet of air). Baroreflex function curves relating AP and RSNA were constructed by fitting a sigmoid function to RSNA and AP measured during sequential nitroprusside and phenylephrine administrations. Stress increased mean AP from 112 ± 2 to 124 ± 2 mmHg, heart rate from 381 ± 10 to 438 ± 18 beats/min, and RSNA from 0.80 ± 0.14 to 1.49 ± 0.23 μV. The RSNA-AP relationship was shifted toward higher AP values, and its maximum gain was significantly ( P < 0.01) increased from 9.0 ± 1.3 to 16.2 ± 2.1 normalized units (NU)/mmHg. The latter effect was secondary to an increase ( P < 0.01) in the range of the RSNA variation from 285 ± 33 to 619 ± 59 NU. In addition, the operating range of the reflex was increased ( P < 0.01) from 34 ± 2 to 41 ± 3 mmHg. The present study indicates that in rats, the baroreflex control of RSNA is sensitized and operates over a larger range during emotional stress, which suggests that renal vascular tone, and possibly AP, are very efficiently controlled by the sympathetic nervous system under this condition.
Transient receptor potential ion channels as participants in thermosensation and thermoregulation
Authors: Caterina Michael J.
Published: September 2006

Living organisms must evaluate changes in environmental and internal temperatures to mount appropriate physiological and behavioral responses conducive to survival. Classical physiology has provided a wealth of information regarding the specialization of thermosensory functions among subclasses of peripheral sensory neurons and intrinsically thermosensitive neurons within the hypothalamus. However, until recently, the molecular mechanisms by which these cells carry out thermometry have remained poorly understood. The demonstration that certain ion channels of the transient receptor potential (TRP) family can be activated by increases or decreases in ambient temperature, along with the recognition of their heterogeneous expression patterns and heterogeneous temperature sensitivities, has led investigators to evaluate these proteins as candidate endogenous thermosensors. Much of this work has involved one specific channel, TRP vanilloid 1 (TRPV1), which is both a receptor for capsaicin and related pungent vanilloid compounds and a “heat receptor,” capable of directly depolarizing neurons in response to temperatures >42°C. Evidence for a contribution of TRPV1 to peripheral thermosensation has come from pharmacological, physiological, and genetic approaches. In contrast, although capsaicin-sensitive mechanisms clearly influence core body temperature regulation, the specific contribution of TRPV1 to this process remains a matter of debate. Besides TRPV1, at least six additional thermally sensitive TRP channels have been identified in mammals, and many of these also appear to participate in thermosensation. Moreover, the identification of invertebrate TRP channels, whose genetic ablation alters thermally driven behaviors, makes it clear that thermosensation represents an evolutionarily conserved role of this ion channel family.
Interaction of epithelium with mesenchyme affects global features of lung architecture: a computer model of development
Authors: Tebockhorst Seth , Lee DongYoub , Wexler Anthony S. , Oldham Michael J.
Published: September 2006

Lung airway morphogenesis is simulated in a simplified diffusing environment that simulates the mesenchyme to explore the role of morphogens in airway architecture development. Simple rules govern local branching morphogenesis. Morphogen gradients are modeled by four pairs of sources and their diffusion through the mesenchyme. Sensitivity to lobar architecture and mesenchymal morphogen are explored. Even if the model accurately represents observed patterns of local development, it could not produce realistic global patterns of lung architecture if interaction with its environment was not taken into account, implying that reciprocal interaction between airway growth and morphogens in the mesenchyme plays a critical role in producing realistic global features of lung architecture.
How much is there really? Why stereology is essential in lung morphometry
Authors: Weibel Ewald R. , Hsia Connie C. W. , Ochs Matthias
Published: September 2006

Quantitative data on lung structure are essential to set up structure-function models for assessing the functional performance of the lung or to make statistically valid comparisons in experimental morphology, physiology, or pathology. The methods of choice for microscopy-based lung morphometry are those of stereology, the science of quantitative characterization of irregular three-dimensional objects on the basis of measurements made on two-dimensional sections. From a practical perspective, stereology is an assumption-free set of methods of unbiased sampling with geometric probes, based on a solid mathematical foundation. Here, we discuss the pitfalls of lung morphometry and present solutions, from specimen preparation to the sampling scheme in multiple stages, for obtaining unbiased estimates of morphometric parameters such as volumes, surfaces, lengths, and numbers. This is demonstrated on various examples. Stereological methods are accurate, efficient, simple, and transparent; the precision of the estimates depends on the size and distribution of the sample. For obtaining quantitative data on lung structure at all microscopic levels, state-of-the-art stereology is the gold standard.
Neural drive to tongue protrudor and retractor muscles following pulmonary C-fiber activation
Authors: Lee Kun-Ze , Fuller David D. , Lu I-Jung , Lin Jin-Tun , Hwang Ji-Chuu
Published: September 2006

Hypoglossal (XII) nerve recordings indicate that pulmonary C-fiber (PCF) receptor activation reduces inspiratory bursting and triggers tonic discharge. We tested three hypotheses related to this observation: 1) PCF receptor activation inhibits inspiratory activity in XII branches innervating both tongue protrudor muscles (medial branch; XIImed) and retractor muscles (lateral branch; XIIlat); 2) reduced XII neurogram amplitude reflects decreased XII motoneuron discharge rate; and 3) tonic XII activity reflects recruitment of previously silent motoneurons. Phrenic, XIImed, and XIIlat neurograms were recorded in anesthetized, paralyzed, and ventilated rats. Capsaicin delivered to the jugular vein reduced phrenic bursting at doses of 0.625 and 1.25 μg/kg but augmented bursting at 5 μg/kg. All doses reduced inspiratory amplitude in XIImed and XIIlat ( P < 0.05), and these effects were eliminated following bilateral vagotomy. Single-fiber recordings indicated that capsaicin causes individual XII motoneurons to either decrease discharge rate ( n = 101/153) or become silent ( n = 39/153). Capsaicin also altered temporal characteristics such that both XIImed and XIIlat inspiratory burst onset occurred after the phrenic burst ( P < 0.05). Increases in tonic discharge after capsaicin were greater in XIImed vs. XIIlat ( P < 0.05); single-fiber recordings indicated that tonic discharge reflected recruitment of previously silent motoneurons. We conclude that PCF receptor activation reduces inspiratory XII motoneuron discharge and transiently attenuates neural drive to both tongue protrudor and retractor muscles. However, tonic discharge appears to be selectively enhanced in tongue protrudor muscles. Accordingly, reductions in upper airway stiffness associated with reduced XII burst amplitude may be offset by enhanced tonic activity in tongue protrudor muscles.
Exercise-dependent IGF-I, IGFBPs, and type I collagen changes in human peritendinous connective tissue determined by microdialysis
Authors: Olesen Jens L. , Heinemeier Katja M. , Gemmer Carsten , Kjær Michael , Flyvbjerg Allan , Langberg Henning
Published: September 2006

Microdialysis studies indicate that mechanical loading of human tendon during exercise elevates type I collagen production in tendon. However, the possibility that the insertion of microdialysis fibers per se may increase the local collagen production due to trauma has not been explored. Insulin-like growth factor I (IGF-I) and its binding proteins (IGFBPs), which are known to stimulate collagen production in animal tendons, may regulate the translation of mechanical loading to collagen synthesis. Systemic and tissue levels of IGF-I, IGFBP, and type I collagen metabolism markers [procollagen I COOH-terminal propeptide (PICP) and COOH-terminal telopeptide of type I collagen] were measured by microdialysis in peritendinous tissue of the human Achilles tendon in an exercise group (performing a 36-km run, n = 6) and a control group (no intervention, n = 6). An increase in local PICP concentration was seen in both groups after 72 h and stayed elevated in the exercise group at 96 h ( P < 0.05). IGFBP-1 in both serum and dialysate increased in the exercise group immediately after exercise ( P < 0.05), whereas IGFBP-3 decreased systemically ( P < 0.05). Elevation of local IGFBP-4 was observed in both the control and exercise groups after 48 h ( P < 0.05). Total IGF-I did not change in locally or systemically in either group. Our results indicate an increased local production of PICP in human peritendinous tissue in response to prolonged mechanical loading with part of the increase due to trauma from the sampling technique. Care must therefore be emphasized to minimize the numbers of insertions with microdialysis. We demonstrated an elevation of IGFBP-1 both systemically and peritendinously in response to prolonged acute exercise. The local increased collagen synthesis was preceded by an elevation of local concentration of IGFBP-4, suggesting that IGFBP-4 may have a key role in the IGF-axis effect on the human collagen synthesis in vivo.
An Original Approach to Aging: An Appreciation of Fritz Verzár’s Contribution in the Light of the Last 50 Years of Gerontological Facts and Thinking
Authors: Robert Ladislas
Published: September 2006

The motivation of this review is the 120th anniversary of the birth of Fritz Verzár, founder of experimental gerontology. His major contributions to aging research are shortly reviewed and re-evaluated in the light of modern gerontological research. Verzár undertook aging research after his retirement from the Chair of Physiology at the Medical Faculty of Basel. His first experiments on aging of the rat tail tendon revealed an important mechanism of aging: an exponential increase of cross-linking of collagen fibres. This observation, correctly interpreted by Verzár as a new age-dependent mechanism, was shown later to be attributed to the Maillard reaction, the non-enzymatic glycosylation of protein (and nucleotide bases) amino groups followed by evolution of the reaction to advanced glycation end products (AGEs) involved in a number of harmful reactions. Many of these reactions were shown to be mediated by receptors recognizing AGE products (RAGEs). This was the first example of a post-synthetic (post-translational) reaction involved in the aging of biological macromolecules, especially those of the extracellular matrix. Verzár extended the research activity of his team to several other aspects of aging research, such as loss of muscular strength, nutritional requirements at high altitude, cell loss with aging, and ultrastructural studies, and started also the first longitudinal clinical study of aging in a Basel population. Modern gerontological research confirmed and extended Verzár’s observations. His work on collagen cross-linking by glycation became of paramount importance in recent times because of the rapid increase of diabetes type II, combined with the metabolic syndrome, one of the major pathologies of modern times.
Cerebral Blood Flow Responses to Severe Orthostatic Stress in Fit and Unfit Young and Older Adults
Authors: Franke Warren D. , Allbee Kelly A. , Spencer Seldon E.
Published: September 2006

Background: Animal models suggest that aging negatively affects the cerebral blood flow (CBF) response to a hypotensive challenge while research with humans suggests that chronic physical activity may positively affect age-associated alterations in CBF. The extent to which chronic exercise affects the CBF responses to orthostatic stress in older subjects is unknown. Objectives: The purpose of this study was to determine the extent to which differences in age and cardiovascular fitness, reflective of differences in chronic exercise training, affect cerebral blood flow responses to severe orthostatic stress. Methods: Subjects were divided into four groups: old fit (OF; 72 ± 2 year-olds; 38.7 ± 1.6 ml·kg–1·min–1), old unfit (OU; 71 ± 1 year-olds; 27.7 ± 2.9 ml·kg–1·min–1), young fit (YF; 23 ± 0.5 year-olds; 56.1 ± 1.8 ml·kg–1·min–1) and young unfit (YU; 23 ± 1 year-olds; 41.1 ± 1.6 ml·kg–1·min–1). Fitness was quantified with maximal graded exercise testing. Middle cerebral artery blood flow velocity (CBF velocity; transcranial Doppler) responses to graded orthostatic stress (lower body negative pressure) to presyncope were assessed. Results: Orthostatic tolerance did not differ between groups (p = 0.633). The groups differed in fitness (YF >YU = OF >OU; p < 0.001) but not in either resting CBF velocity (p = 0.364) or pulsatility index (PI; p = 0.251). CBF velocity decreased below rest in the last completed stage of submaximal LBNP (p < 0.001) but did not differ between groups (p = 0.182). PI did not change with submaximal LBNP within groups. At presyncope, mean CBF velocity decreased below that of the last completed stage of LBNP in all groups (p < 0.001) while the PI increased in the young fit group only (p < 0.001). Conclusion: Marked differences in age and fitness did not affect cerebral blood flow responses to severe orthostatic stress. While severe orthostatic stress can compromise CBF velocity in all age groups, older adults appear to autoregulate CBF as well as much younger subjects.