Age-related changes in upper airway muscles morphological and oxidative properties.

Obstructive sleep apnea (OSA) is a common disorder of the middle aged and elderly. It results from the decrease in upper airway muscle (UAM) tone that occurs during sleep. It is unclear whether age-related changes in UAM could constitute a contributory mechanism to the increased prevalence of OSA with increasing age, and previous papers evaluating the effects of aging on UAM in rats reported conflicting results. In the present study, we compared, in four age groups of Wistar rats (6-24 months), fiber-type distribution, mean cross-sectional fiber area and succinate dehydrogenase optical density of dilating and non-dilating UAM, and the diaphragm. Succinate dehydrogenase optical density, a marker of oxidative capacity, decreased significantly after the age of 6 months in all muscles (except for the sternohyoid), particularly in the genioglossus, the main tongue protrudor. In this muscle, we also found a significant decrease in type IIa and an increase in IIb fibers after the age of 18 months. Age-related changes in fiber-type distribution in other muscles were mostly insignificant. Dilating UAM could not be distinguished from their non-dilating neighboring muscles by their histochemical properties or aging-related changes. The aging-related changes observed in the present study may decrease UAM endurance, particularly that of the main tongue protrudor, the genioglossus.

Head stabilization in herons.

We examined head stabilization in relation to body mass and length of legs in four heron species (little egrets, Egretta garzetta; night herons, Nycticorax nycticorax; squacco herons, Ardeola ralloides; and cattle egrets, Bubulcus ibis: Aves: Ardeidae). Head stabilization, under controlled, sinusoidal, perch perturbations was mostly elicited at frequencies lower than 1 Hz. Maximal perturbation amplitudes sustained were positively correlated with leg length and maximal perturbation frequencies sustained were negatively correlated with body mass and with leg length. The species differed significantly in average maximal perturbation amplitudes sustained. Combinations of amplitude and frequency for which stabilization was achieved were bounded by a decreasing concave "envelope" curve in the frequency-amplitude plane, with inter specific differences in "envelope". As physical constraints, we tested maximal vertical acceleration, which translates into a line defined by the product of frequency2 x amplitude, and maximal vertical velocity, which translates into a line defined by the product of frequency x amplitude. Both relations were in good agreement with the experimental results for all but squacco herons. The results support predictions based on mechanical considerations and may explain the predominance of motor patterns employed by herons while foraging.

Characterization of a DNA-cleaving deoxyribozyme.

A copper-dependent self-cleaving DNA that was isolated by in vitro selection has been minimized to its smallest active domain using both in vitro selection and rational design methods. The minimized 46-nucleotide deoxyribozyme forms duplex and triplex substructures that flank a highly conserved catalytic core. This self-cleaving construct can be converted into a bimolecular complex that comprises separate substrate and enzyme domains. Substrate cleavage is directed at one of two adjacent nucleotides and proceeds via an oxidative cleavage mechanism that is unique to the position cleaved. The structural, kinetic and mechanistic characteristics of this DNA-cleaving deoxyribozyme are reported.

Fracture of the clavicle in the newborn following normal labor and delivery.

OBJECTIVE: Earlier works have associated neonatal clavicular fracture (0.2-3.5% of all deliveries) with a range of procedural, fetal and maternal risk factors; more recent studies, however, have failed to firmly identify any one or a combination of them. In the present work we sought to determine possible ante/intra-partum risk factors for this condition. STUDY DESIGN: Using a retrospective case-controlled approach, we examined a series of maternal, fetal and pregnancy or delivery-related variables in 87 cases (out of 403) of fractured clavicle of the newborn diagnosed in our department from 1986 to 1994. All infants were delivered vaginally (in the occipito-anterior position) at term by a specialist obstetrician and underwent peripartum sonographic fetal weight estimation. All variables were compared with those of an equal number of infants born immediately before or after each affected infant and delivered by the same obstetrical team. RESULTS: Fractured clavicles were found in 1.65% of the total number of deliveries during the study period. Neonatal clavicular fracture was significantly and directly related to the duration of the second stage of labor, peripartum sonographic fetal weight estimation, and neonatal length, and inversely related to maternal height; nevertheless, all values in both the study and control groups were within normal range. Logistic regression analysis showed that these antenatal variables significantly affect the chances of clavicular fracture, but due to the high false-positive rate they cannot serve clinically as a comprehensive antenatal prediction index. CONCLUSIONS: The majority of clavicular fractures occur in normal newborns following normal labor and delivery. The risk factors we identified statistically do not offer a method for clinical prenatal prediction. This work provides statistical evidence of the nature of this complication of early newborn life.

Cleaving DNA with DNA.

A DNA structure is described that can cleave single-stranded DNA oligonucleotides in the presence of ionic copper. This "deoxyribozyme" can self-cleave or can operate as a bimolecular complex that simultaneously makes use of duplex and triplex interactions to bind and cleave separate DNA substrates. Bimolecular deoxyribozyme-mediated strand scission proceeds with a kobs of 0.2 min-1, whereas the corresponding uncatalyzed reaction could not be detected. The duplex and triplex recognition domains can be altered, making possible the targeted cleavage of single-stranded DNAs with different nucleotide sequences. Several small synthetic DNAs were made to function as simple "restriction enzymes" for the site-specific cleavage of single-stranded DNA.

In vitro selection of self-cleaving DNAs.

BACKGROUND: Ribozymes catalyze an important set of chemical transformations in metabolism, and 'engineered' ribozymes have been made that catalyze a variety of additional reactions. The possibility that catalytic DNAs or 'deoxyribozymes' can be made has only recently been addressed. Specifically, it is unclear whether the absence of the 2' hydroxyl renders DNA incapable of exhibiting efficient enzyme-like activity, making it impossible to discover natural or create artificial DNA biocatalysts. RESULTS: We report the isolation by in vitro selection of two distinct classes of self-cleaving DNAs from a pool of random-sequence oligonucleotides. Individual catalysts from 'class I' require both Cu2+ and ascorbate to mediate oxidative self-cleavage. Individual catalysts from class II use Cu2+ as the sole cofactor. Further optimization of a class II individual by in vitro selection yielded new catalytic DNAs that facilitate Cu2+-dependent self-cleavage with rate enhancements exceeding 1 000 000-fold relative to the uncatalyzed rate of DNA cleavage. CONCLUSIONS: Despite the absence of 2' hydroxyls, single-stranded DNA can adopt structures that promote divalent-metal-dependent self-cleavage via an oxidative mechanism. These results suggest that an efficient DNA enzyme might be made to cleave DNA in a biological context.

Plasma volume conservation in pigeons: effects of air temperature during dehydration.

We assessed the effects of the ambient air temperature prevailing during dehydration, which included complete water and food deprivation, on plasma volume (PV) conservation in pigeons (Columba livia) exposed to air temperatures of 25 degrees C (n = 7), 36 degrees C (n = 12), and 40 degrees C (n = 24). The pigeons were dehydrated for 65.4, 32.3, and 27.7 h, on average, at 25, 36, and 40 degrees C, respectively. Dehydration rates averaged 5, 10, and 15.2% of initial total body water (TBW) per day at the three air temperatures, in ascending order. Birds exposed to 25 and 36 degrees C maintained PV despite the fact that they lost, on average, 14 and 17.3% of their TBW, respectively. In contrast, PV in pigeons exposed to 40 degrees C decreased by 8.9%, even though the reduction in TBW (17.7%) was similar to that incurred at 36 degrees C. Mean plasma osmolalities reached 347.7, 345.6, and 374.8 mosmol/kgH2O at 25, 36, and 40 degrees C, respectively. No significant changes occurred in hematocrit (Hct) and hemoglobin concentrations (Hb) during dehydration at 25 and 36 degrees C. However, at 40 degrees C Hb increased by 8.2% with no change in Hct, indicating a decrease in red blood cell volume (RBCV). The results of this study suggest that maintenance of PV and RBCV is affected not only by the dehydration level attained but also by the ambient conditions under which dehydration is induced and the rate at which dehydration takes place.