Sufficiency of Favard's condition for a class of band-dominated operators on the axis

The purpose of this paper is to show that, for a large class of band-dominated operators on $\ell^\infty(Z,U)$, with $U$ being a complex Banach space, the injectivity of all limit operators of $A$ already implies their invertibility and the uniform boundedness of their inverses. The latter property is known to be equivalent to the invertibility at infinity of $A$, which, on the other hand, is often equivalent to the Fredholmness of $A$. As a consequence, for operators $A$ in the Wiener algebra, we can characterize the essential spectrum of $A$ on $\ell^p(Z,U)$, regardless of $p\in[1,\infty]$, as the union of point spectra of its limit operators considered as acting on $\ell^p(Z,U)$.

Pre-pubertal measurements of the somatotrophic axis as predictors of milk production in Holstein-Friesian dairy cows

This study investigated possible relationships between measurements of the somatotrophic axis in pre-pubertal dairy calves and subsequent milk yields. Endogenous growth hormone (GH) release was measured through a fed and fasted period in fifty 6-month-old Holstein-Friesian heifers and they were then challenged with growth hormone-releasing factor (GRF) to assess their GH release pattern. Insulin-like growth factor-I (IGF-I), insulin and glucose concentrations were measured in relation to time of feeding. Cows were subsequently monitored through their first three lactations to record peak and 305-day milk yields. In the first lactation, milk energy output for the first 120 days of lactation was also calculated. The mean 305-day milk yield increased from 7417 +/- 191 kg in the first lactation (n = 37) to 8749 +/- 252 kg in the third (n = 25). There were no significant relationships between any measures of GH secretion and peak or 305-day yield in any lactation. A highly significant positive relationship was established between the GH peak measured 10 min post-GRF challenge and 120-day milk energy values in the first lactation. This relationship was, however, only present in the subpopulation of 12 cows culled after one or two lactations and was absent in the 25 animals remaining for the third lactation. There were no significant relationships between pre-pubertal IGF-I and fed or fasted insulin or glucose concentrations and any subsequent measurement of yield. The usefulness of GH secretagogue challenges in calves as a predictive test for future milk production is thus limited but may have some bearing on nutrient partitioning and longevity. (c) 2005 Elsevier Inc. All rights reserved.

The tissue-specific processing of pro-opiomelanocortin

It is just over 30 years since the definitive identification of the adrenocorticotrophin (ACTH) precursor, pro-opiomelanocotin (POMC). Although first characterised in the anterior and intermediate lobes of the pituitary, POMC is also expressed in a number of both central and peripheral tissues including the skin, central nervous tissue and placenta. Following synthesis, POMC undergoes extensive post-translational processing producing not only ACTH, but also a number of other biologically active peptides. The extent and pattern of this processing is tissue-specific, the end result being the tissue dependent production of different combinations of peptides from the same precursor. These peptides have a diverse range of biological roles ranging from pigmentation to adrenal function to the regulation of feeding. This level of complexity has resulted in POMC becoming the archetypal model for prohormone processing, illustrating how a single protein combined with post-translational modification can have a diverse number of roles.

Role of gamma-MSH peptides in the regulation of adrenal steroidogenesis

Alpha-, beta- and gamma-melanocyte stimulating hormones (MSHs) are peptides derived from the ACTH precursor, pro-opiomelanocortin. All three peptides have been highly conserved throughout evolution but their exact biological function in mammals is still largely obscure. In recent years, there has been a surge of interest in alpha-MSH and its role in the regulation of feeding. Gamma-MSH by contrast has been shown to be involved in the regulation of adrenal steroidogenesis and also has effects on the cardiovascular and renal systems. This review will provide an overview of the role that gamma-MSH peptides play in the regulation of adrenal steroidogenesis. (c) 2005 Elsevier Inc. All rights reserved.

Variation in pituitary expression of mRNAs encoding the putative inhibin co-receptor (betaglycan) and type-I and type-II activin receptors during the chicken ovulatory cycle

Secretion of LH and FSH from the anterior pituitary is regulated primarily by hypothalamic GnRH and ovarian steroid hormones. More recent evidence indicates regulatory roles for certain members of the transforming growth factor beta (TGF beta) superfamily including inhibin and activin. The aim of this study was to identify expression of mRNAs encoding key receptors and ligands of the inhibin/activin system in the hen pituitary gland and to monitor their expression throughout the 24-25-h ovulatory cycle. Hens maintained on long days (16 h light/8 h dark) were killed 20, 12, 6 and 2 h before predicted ovulation of a midsequence egg (n = 8 per group). Anterior pituitary glands were removed, RNA extracted and cDNA synthesized. Plasma concentrations of LH, FSH, progesterone and inhibin A were measured. Real-time quantitative PCR was used to quantify pituitary expression of mRNAs encoding betaglycan, activin receptor (ActR) subtypes (type I, IIA), GnRH receptor (GnP,H-R), LH beta subunit, FSH beta subunit and GAPDH. Levels of mRNA for inhibin/activin beta A and beta B subunits, inhibin alpha subunit, follistatin and ActRIIB mRNA in pituitary were undetectable by quantitative PCR (< 2 amol/reaction). Significant changes in expression (P < 0.05) of ActRIIA and betaglycan mRNA were found, both peaking 6 h before ovulation just prior to the preovulatory LH surge and reaching a nadir 2 h before ovulation, just after the LH surge. There were no significant changes in expression of ActRI mRNA throughout the cycle although values were correlated with mRNA levels for both ActRIIA (r=0.77; P < 0.001) and betaglycan (r=0.45; P < 0.01). Expression of GnRH-R mRNA was lowest 20 h before ovulation and highest (P < 0.05) 6 h before ovulation; values were weakly correlated with betaglycan (r=0.33; P=0.06) and ActRIIA (r=0.34; P=0.06) mRNA levels. Expression of mRNAs encoding LH beta and FSH beta subunit were both lowest (P < 0.05) after the LH surge, 2 h before ovulation. These results are consistent with an endocrine, but not a local intrapituitary, role of inhibin-related proteins in modulating gonadotroph function during the ovulatory cycle of the hen, potentially through interaction with betaglycan and ActRIIA. In contrast to mammals, intrapituitary expression of inhibin/activin subunits and follistatin appears to be extremely low or absent in the domestic fowl.

The adrenal secretory serine protease AsP is a short secretory isoform of the transmembrane airway trypsin-like protease

To further elucidate the role of proteases capable of cleaving N-terminal proopiomelanocortin (N-POMC)-derived peptides, we have cloned two cDNAs encoding isoforms of the airway trypsin-like protease (AT) from mouse (MAT) and rat ( RAT), respectively. The open reading frames comprise 417 amino acids (aa) and 279 aa. The mouse AT gene was located at chromosome 5E1 and contains 10 exons. The longer isoform, which we designated MAT1 and RAT1, has a simple type II transmembrane protein structure, consisting of a short cytoplasmic domain, a transmembrane domain, a SEA (63-kDa sea urchin sperm protein, enteropeptidase, agrin) module, and a serine protease domain. The human homolog of MAT1 and RAT1 is the human AT ( HAT). The shorter isoform, designated MAT2 and RAT2, which contains an alternative N terminus, was formerly described in the rat as adrenal secretory serine protease (AsP) and has been shown to be involved in the processing of N-POMC-derived peptides. In contrast to the long isoform, neither MAT2 and RAT2 ( AsP) contain a transmembrane domain nor a SEA domain but an N-terminal signal peptide to direct the enzyme to the secretory pathway. The C terminus, covering the catalytic triad, is identical in both isoforms. Immunohistochemically, MAT/RAT was predominantly expressed in tissues of the upper gastrointestinal and the respiratory tract - but also in the adrenal gland. Moreover, isoform-specific RT-PCR and quantitative PCR analysis revealed a complex expression pattern of the two isoforms with differences between mice and rats. These findings indicate a multifunctional role of these proteases beyond adrenal proliferation.

The role of the melanocortin 3 receptor in mediating the effects of gamma-MSH peptides on the adrenal

The pro-opiomelanocortin (POMC)-derived peptides, pro-gamma-MSH (16K fragment), and Lys-gamma(3)-MSH, have been shown to potentiate the steroidogenic action of corticotrophin (ACTH) on the adrenal cortex. Using a continuously perfused adrenal cell column system, we have tested the hypothesis that gamma-MSH peptides exert their effect through the Melanocortin 3 Receptor (MC3-R), since this is the only known receptor to have high affinity for gamma-MSH peptides and has been suggested to be expressed in the rat adrenal. To investigate this hypothesis we tested whether the MC3-R agonist MTII and antagonist SHU9119 could mimic or block the actions of pro-gamma-MSH. We found that MTII could not mimic, and SHU9119 could not block pro-gamma-MSH mediated potentiation of ACTH-induced steroidogenesis. These results suggest that the MC3-R is not involved in mediating the potentiation effect, adding further evidence to the argument that another melanocortin receptor exists.

Variation in pituitary expression of mRNAs encoding the putative inhibin co-receptor (betaglycan) and type-I and type-II activin receptors during the chicken ovulatory cycle

Secretion of LH and FSH from the anterior pituitary is regulated primarily by hypothalamic GnRH and ovarian steroid hormones. More recent evidence indicates regulatory roles for certain members of the transforming growth factor beta (TGF beta) superfamily including inhibin and activin. The aim of this study was to identify expression of mRNAs encoding key receptors and ligands of the inhibin/activin system in the hen pituitary gland and to monitor their expression throughout the 24-25-h ovulatory cycle. Hens maintained on long days (16 h light/8 h dark) were killed 20, 12, 6 and 2 h before predicted ovulation of a midsequence egg (n = 8 per group). Anterior pituitary glands were removed, RNA extracted and cDNA synthesized. Plasma concentrations of LH, FSH, progesterone and inhibin A were measured. Real-time quantitative PCR was used to quantify pituitary expression of mRNAs encoding betaglycan, activin receptor (ActR) subtypes (type I, IIA), GnRH receptor (GnP,H-R), LH beta subunit, FSH beta subunit and GAPDH. Levels of mRNA for inhibin/activin beta A and beta B subunits, inhibin alpha subunit, follistatin and ActRIIB mRNA in pituitary were undetectable by quantitative PCR (< 2 amol/reaction). Significant changes in expression (P < 0.05) of ActRIIA and betaglycan mRNA were found, both peaking 6 h before ovulation just prior to the preovulatory LH surge and reaching a nadir 2 h before ovulation, just after the LH surge. There were no significant changes in expression of ActRI mRNA throughout the cycle although values were correlated with mRNA levels for both ActRIIA (r=0.77; P < 0.001) and betaglycan (r=0.45; P < 0.01). Expression of GnRH-R mRNA was lowest 20 h before ovulation and highest (P < 0.05) 6 h before ovulation; values were weakly correlated with betaglycan (r=0.33; P=0.06) and ActRIIA (r=0.34; P=0.06) mRNA levels. Expression of mRNAs encoding LH beta and FSH beta subunit were both lowest (P < 0.05) after the LH surge, 2 h before ovulation. These results are consistent with an endocrine, but not a local intrapituitary, role of inhibin-related proteins in modulating gonadotroph function during the ovulatory cycle of the hen, potentially through interaction with betaglycan and ActRIIA. In contrast to mammals, intrapituitary expression of inhibin/activin subunits and follistatin appears to be extremely low or absent in the domestic fowl.

The ACTH response to dexamethasone in PTSD

Objective: Enhanced negative feedback and reduced adrenal output are two different models that have been put forth to explain the paradoxical observations of increased release of corticotropin-releasing factor in the face of low cortisol levels in posttraumatic stress disorder (PTSID). To discriminate between these models, the authors measured levels of adrenocorticopic hormone (ACTH) and cortisol at baseline and in response to dexamethasone in medically healthy subjects with and without PTSID. Under conditions of enhanced negative feedback inhibition, ACTH levels would not be altered relative to cortisol levels, but the ACTH response to dexamethasone would be augmented, in concert with the enhanced cortisol response to dexamethasone. In contrast, under conditions of reduced adrenal output, ACTH levels would be expected to be higher at baseline relative to cortisol levels, but the ACTH response to dexamethasone would be unchanged in PTSID relative to healthy comparison subjects. Method: The ACTH and cortisol responses to 0.50 mg of dexamethasone were assessed in 19 subjects (15 men and four women) with PTSID and 19 subjects (14 men and five women) without psychiatric disorder. Results: The ACTH-to-cortisol ratio did not differ between groups before or after dexamethasone, but the subjects with PTSD showed greater suppression of ACTH (as well as cortisol) in response to dexamethasone. Conclusions: The data support the hypothesis of enhanced cortisol negative feedback inhibition of ACTH secretion at the level of the pituitary in PTSD. Pituitary glucocorticoid receptor binding, rather than low adrenal output, is implicated as a likely mechanism for this effect.

The role played by the interaction between genetic factors and attachment in the stress response in infancy

Background: The importance of understanding which environmental and biological factors are involved in determining individual differences in physiological response to stress is widely recognized, given the impact that stress has on physical and mental health. Methods: The child-mother attachment relationship and some genetic polymorphisms (5-HTTLPR, COMT and GABRA6) were tested as predictors of salivary cortisol and alpha amylase concentrations, two biomarkers of hypothalamic-pituitary-adrenocortical (HPA) axis and sympathetic adrenomedullary (SAM) system activity, during the Strange Situation (SS) procedure in a sample of more than 100 healthy infants, aged 12 to 18 months. Results: Individual differences in alpha amylase response to separation were predicted by security of attachment in interaction with 5-HTTLPR and GABRA6 genetic polymorphisms, whereas alpha amylase basal levels were predicted by COMT x attachment interaction. No significant effect of attachment, genetics and their interaction on cortisol activity emerged. Conclusions: These results help to disentangle the role played by both genetic and environmental factors in determining individual differences in stress response in infancy. The results also shed light on the suggestion that HPA and SAM systems are likely to have different characteristic responses to stress.

Control of a compliant two-axis robotic arm

In order to ease control, the links between actuators and robotic limbs are generally made to be as stiff as possible. This is in contrast to natural limbs, where compliance is present. Springs have been added to the drive train between the actuator and load to imitate this natural compliance. The majority of these springs have been in series between the actuator and load. However, a more biologically inspired approach is taken, here springs have been used in parallel to oppose each other. The paper will describe the application of parallel extension springs in a robot arm in order to give it compliance. Advantages and disadvantages of this application are discussed along with various control strategies.

Control of a compliant two-axis robotic arm

It is common to make the links between actuators and robotic limbs as stiff as possible, in complete contrast to natural systems, where compliance is present. In the past, to create some compliance in a drive, springs have been added to the link between the actuator and load. Many of these springs have been in series with the drive, but recently a more 'biological' approach has been taken where two springs have been used in parallel to counteract each other. This paper describes the application of parallel extension springs in a robot arm in order to give it compliance. Advantages and disadvantages of this application are discussed, along with various control strategies.

Dynamic stall for a Vertical Axis Wind Turbine in a two-dimensional study

The last few years have proved that Vertical Axis Wind Turbines (VAWTs) are more suitable for urban areas than Horizontal Axis Wind Turbines (HAWTs). To date, very little has been published in this area to assess good performance and lifetime of VAWTs either in open or urban areas. At low tip speed ratios (TSRs<5), VAWTs are subjected to a phenomenon called 'dynamic stall'. This can really affect the fatigue life of a VAWT if it is not well understood. The purpose of this paper is to investigate how CFD is able to simulate the dynamic stall for 2-D flow around VAWT blades. During the numerical simulations different turbulence models were used and compared with the data available on the subject. In this numerical analysis the Shear Stress Transport (SST) turbulence model seems to predict the dynamic stall better than the other turbulence models available. The limitations of the study are that the simulations are based on a 2-D case with constant wind and rotational speeds instead of considering a 3-D case with variable wind speeds. This approach was necessary for having a numerical analysis at low computational cost and time. Consequently, in the future it is strongly suggested to develop a more sophisticated model that is a more realistic simulation of a dynamic stall in a three-dimensional VAWT.