Action of the diaphragm on the rib cage inferred from a force-balance analysis

Displacements of the rib cage are determined by the intrinsic passive properties of the rib cage, rib cage musculature, pleural and abdominal pressures, and the diaphragm. The diaphragm's mechanical actions on the rib cage are inferred from a force-balance analysis in which the diaphragm is seen to cause expansion of the rib cage by pulling cephalad at its insertions on the lower ribs (insertional component) and by raising intra-abdominal pressure, which pushes outward on the diaphragm's zone of apposition to the rib cage (appositional component). Goldman and Mead suggested that the diaphragm, acting alone, could drive both the rib cage and abdomen on their passive characteristics. The force-balance analysis shows that the diaphragm's inspiratory action on the rib cage is less than predicted by Goldman and Mead, but that in the special circumstances of their experiment (low lung volumes), the appositional component is large and the rib cage can be driven close to its passive characteristics. The force-balance analysis is consistent with recent observations by other investigations and is incompatible with the model proposed by Macklem and colleagues and with the Goldman-Mead hypothesis. Experiments on three subjects produced data consistent with the force-balance analysis, showing that the inspiratory action of the diaphragm on the rib cage is greatest at low lung volumes.     

Stability of unsaturated methyl esters of fatty acids on surfaces

The stability of unsaturated methyl esters is greater when they are adsorbed on silica gel than when a glass surface is used. Storage of small samples adsorbed on silica gel may be a convenient addition to conventional methods of protecting labile fats against autoxidation.     

The source of progesterone in preimplantation rabbit blastocysts.

In vitro and in vivo synthesis of progesterone, sequestration of progesterone from the surrounding medium, and its subsequent conversion to metabolites was investigated in 146 hr post coitus preimplantation rabbit blastocysts. No significant conversion of 3H-pregnenolone to 3H-progesterone was observed throughout the 8 hr incubation. Progesterone content in blastocysts and culture medium did not change during the course of an 8 hr incubation. This suggests that the failure to detect incorporation of label into progesterone was not due to the presence of a large endogenous pool of pregnenolone. Significant uptake (p less than 0.05) of 3H-progesterone from the incubation medium was observed as was significant conversion of the 3H-progesterone to unidentified metabolites. Therefore it would appear that the preimplantation rabbit blastocyst is not capable of de novo synthesis of progesterone from pregnenolone prior to implantation but sequesters progesterone from the surrounding medium and converts it to progesterone metabolites.     

Changes of time constants during infancy and early childhood

We used respiratory inductance plethysmography to record tidal respiration in 27 healthy unsedated infants and children 1 mo to 8 yr of age during sleep. Rib cage and abdominal outputs were present at approximately equal gains and summed to obtain an estimate of volume. Flow-volume curves were generated from the uncalibrated volume signal and its flow derivative. Expiratory time constants (tau) were obtained by visually drawing a line through the linear portion of the expiratory flow-volume relationship. tau increased significantly during the first 10 mo of life. After 10 mo, the estimated rate of increase of tau for older children was less than 5% of the estimated initial rate and not significantly different from zero. Prolongation of tau was paralleled by an increase in expiratory time (Te), and no changes in Te/tau were observed in the first 2 yr of life. These changes in tau likely reflect the increase in lung compliance induced by rapid alveolar growth during infancy. After the first year, expiratory time constants appear to remain relatively constant and may be consistent with balanced changes in compliance and resistance beyond infancy.     

Injection-mediated transposon transgenesis in Xenopus tropicalis and the identification of integration sites by modified extension primer tag selection (EPTS) linker-mediated PCR

The generation of transgenic lines is vital to many genetic strategies and provides useful reagents for cell labeling and lineage-tracing experiments. Transposon-based systems offer simple, yet robust, platforms for transgenesis in the frog. Here, we provide a protocol for a microinjection-based transposon transgenesis method using a 'natural breeding' strategy for the collection of Xenopus tropicalis embryos. This method uses co-injection of a plasmid containing a transposon substrate together with synthetic mRNA encoding the transposase to achieve efficient integration of the transgene in the frog genome. We also describe a modified extension primer tag selection linker-mediated PCR technique to identify transposon integration sites within the host genome. This cloning strategy allows rapid identification of genomic sequences flanking the integration sites and multiple independently segregating transposon integration events in a single tadpole can be cloned simultaneously.