Elastic moduli of excised constricted rat lungs

When airways constrict, the surrounding parenchyma undergoesstretch and distortion. Because of the mechanical interdependence between airways and parenchyma, the material properties of the parenchyma are important factors that modulate the degree ofbronchoconstriction. The purpose of this study was to investigate theeffect of changes in transpulmonary pressure (Ptp) and inducedconstriction on parenchymal bulk (k)and shear (µ) moduli. In excised rat lungs, pressure was measured atthe airway opening, and pressure-volume curves were obtained byimposing step decreases in volume with a calibrated syringe from totallung inflation. Calculation was made ofk during small-volume oscillations (1 Hz). Absolute lung volume at 0 cmH₂O Ptp was obtained bysaline displacement. To calculate µ, a lung-indentation test wasperformed. The lung surface was deformed with a cylindrical punch(diameter = 0.45 cm) in 0.25-mm increments, and the force required toeffect this displacement was measured by a weight balance. Measurementsof k and µ were obtained at 4 and 10 cmH₂O Ptp, and again at 4 cmH₂O Ptp, after delivery ofmethacholine aerosol (100 mg/ml) into the trachea. Values ofk and µ in rat lungs were similar tothose reported in other species. In addition, k and µ were dependent on Ptp. Afterinduced constriction, k and µ increased significantly. That k and µ can increase after induced constriction has important implicationsvis a vis the factors modulating airway narrowing.

     

Midkine expression is associated with postnatal development of the lungs

A heparin-binding growth factor, midkine, is the product of a retinoic acid-responsive gene. Since retinol plays critical roles in lung development and treatment of bronchopulmonary dysplasia, and midkine has been implicated in the maturation of lung explants and in cytoprotection, we herein examined midkine expression during postnatal development of the lungs and hyperoxic lung injury. Midkine protein transiently increased to a maximum level at around 4 days postnatal. Immunohistochemistry revealed that the amounts of midkine increased in resident alveolar cells, but not in smooth muscle cells or the large airway epithelium. If neonatal mice were exposed to >95% oxygen, lung development was impaired and midkine expression was suppressed. In contrast, when adult mouse lungs as well as in vitro cultured lung adenocarcinoma cells were exposed to hyperoxia, midkine expression was not affected. Furthermore, a pronounced induction of midkine by retinoic acid was observed in neonatal lungs. The results indicate that midkine expression is associated with postnatal lung development, but not necessarily with hyperoxic cell damage.     

Weight of the skeleton during postnatal development

The weight of all bones and the length of humeri, radii, femora and tibiae have been determined in a series of 150 dry, fat-free skeletons from American Whites and Negroes of both sexes, ranging in age from 23 days to 22 years. Six skeletons were eliminated from the series because of evidence of previous illness. A comparison of the lengths of femur plus tibia of this series with the mean statures of a large series of living children at given ages indicates similarity in the growth patterns. Statistical analyses of the data show that the skeletal weight cannot be estimated reliably from age by cither an exponential growth equation or by a logistic function. The weight of the skeleton, however, is related to the lengths of the measured limb bones by allometric equations, and such equations involving each of the four bones are presented for estimation of skeletal weight in the living. Although the standard errors of estimate of the equations based on lengths of each of these four bones differ very little, the radius is recommended over the other three because it is more readily accessible in the living for a roentgenogram and its shadow on the film shows least distortion.     

Changes of the caecal villi during postnatal development in rats

Summary The villi of the caecal mucosa in postnatal rats were studied using both scanning electron and light microscopy.On the day of birth, numerous villi of various sizes and shapes were present on the caecal mucosa. After the 5th day, the villi decreased very rapidly in length and in number. A strong constriction was observed at the basal region of the caecal villi. During postnatal days 5 9 the villi probably separated and disappeared from the caecal mucosa. No villi were observed in rats that were over 10 days of age.     

Polysomes during early postnatal development of brain in the rat

We have attempted to show eventual modifications in the brain protein synthesis apparatus of rat during the first three weeks after birth. Through this time we noted a steady decrease (about 60%) in the free polysomes, when expressed relative to tissue weight. This decrease does not correlate with changes in the polysome profile, indicating that no loss in the efficiency of protein synthesis was involved. Translation in a reticulocyte lysate also failed to reveal differences.     

The septal organ of the rat during postnatal development

The septal organ of Masera (SO) is a small, isolated patch of olfactory epithelium, located in the ventral part of the nasal septum. We investigated in this systematic study the postnatal development of the SO in histological sections of rats at various ages from the day of birth (P1) to P666. The SO-area increases to a maximum at P66-P105, just as the animals reach sexual maturity, and decreases thereafter, significantly however only in males, indicating a limited neurogenetic capacity for regeneration. In contrast, the main olfactory epithelium area continues to expand beyond P300. The modified respiratory epithelium ('zwischen epithelium') separating the SO and the main olfactory epithelium contains a few olfactory neurons up to age P66. Its length increases postnatally so that the SO becomes more ventral to the OE. Although the position of the SO relative to other anatomical landmarks changes with development it is consistently located just posterior to the opening of the nasopalatine duct (NPAL). Thus, a possible function of the SO is in sensing chemicals in fluids entering the mouth by licking and then delivered to the nasal cavity via the NPAL; therefore the SO may be involved in social/sexual behavior as is the vomeronasal organ (VNO). We suggest that the SO is a separate accessory olfactory organ with properties somewhat different from both OE and VNO and may exist only in species where the NPAL does not open into the VNO.     

NMDA receptors in GABAergic synapses during postnatal development

GABA (gamma-aminobutyric-acid), the main inhibitory neurotransmitter in the adult brain, exerts depolarizing (excitatory) actions during development and this GABAergic depolarization cooperates with NMDARs (N-methyl-D-aspartate receptors) to drive spontaneous synchronous activity (SSA) that is fundamentally important for developing neuronal networks. Although GABAergic depolarization is known to assist in the activation of NMDARs during development, the subcellular localization of NMDARs relative to GABAergic synapses is still unknown. Here, we investigated the subcellular distribution of NMDARs in association with GABAergic synapses at the developmental stage when SSA is most prominent in mice. Using multiple immunofluorescent labeling and confocal laser-scanning microscopy in the developing mouse hippocampus, we found that NMDARs were associated with both glutamatergic and GABAergic synapses at postnatal day 6-7 and we observed a direct colocalization of GABA(A)- and NMDA-receptor labeling in GABAergic synapses. Electron microscopy of pre-embedding immunogold-immunoperoxidase reactions confirmed that GluN1, GluN2A and GluN2B NMDAR subunits were all expressed in glutamatergic and GABAergic synapses postsynaptically. Finally, quantitative post-embedding immunogold labeling revealed that the density of NMDARs was 3 times higher in glutamatergic than in GABAergic synapses. Since GABAergic synapses were larger, there was little difference in the total number of NMDA receptors in the two types of synapses. In addition, receptor density in synapses was substantially higher than extrasynaptically. These data can provide the neuroanatomical basis of a new interpretation of previous physiological data regarding the GABA(A)R-NMDAR cooperation during early development. We suggest that during SSA, synaptic GABA(A)R-mediated depolarization assists NMDAR activation right inside GABAergic synapses and this effective spatial cooperation of receptors and local change of membrane potential will reach developing glutamatergic synapses with a higher probability and efficiency even further away on the dendrites. This additional level of cooperation that operates within the depolarizing GABAergic synapse, may also allow its own modification triggered by Ca(2+)-influx through the NMDA receptors.     

Tectorial membrane changes in hypothyroid rats during postnatal development

The morphological changes of the tectorial membrane (TM) during the postnatal development (0, 3, 6, 12 and 25 day old) of the organ of Corti were studied by light microscopy in 20 control and hypothyroid rats. Hypothyroidism was induced by daily administration of propylthioruracil (PTU) until the end of lactation. The auditive receptor in the cochlea of the hypothyroid animals shows serious structural alterations compared with those of normal ones: abnormal persistence of K?lliker's organ, immaturity of sensory cells and supporting cells and a specific distortion of the TM. Differences with controls were first observed on the sixth postnatal day of the hypothyroid rats. The inner spiral sulcus was not shaped and the TM was attached to the K?lliker's organ. In older stages (12 and 25 days), K?lliker's organ was still present. The TM acquired a shap hump with an abnormal fibrillar arrangement in its middle part. It was still attached to the outer supporting cells by a remnant of the marginal net. It was suggested that the TM is secreted by the inner spiral limbus and K?lliker's organ. An abnormal persistence of these structures in the hypothyroidism results in a retardation of Corti's organ development. However, this conclusion does not explain the absence of the outer portion of the TM. Our study confirms the hypothesis that the secretion of any components of the marginal zone of TM is made by outer supporting cells which in PTU-treated animals appear very immature and with hypoplasia.     

Fiber-type proportions in mammalian soleus muscle during postnatal development

We analyzed the fiber-type composition of the soleus muscle in rats and mice to determine whether the adult proportion of fiber types is fixed soon after birth or whether it changes during postnatal maturation. We examined muscles from animals varying in age from 1 week to 1 year using monoclonal antibodies that distinguish between fast and slow isoforms of myosin heavy chains. In cross sections of unfixed muscle containing profiles of all myofibers in the muscle, we counted the fibers that stained with antibodies to fast myosin, and in adjacent sections, those that stained positive with an antibody to slow myosin. We also counted the total number of fibers in each section. Rat soleus contained about 2500 myofibers, and mouse about 1000 at all ages studied, suggesting that myogenesis ceases in soleus by 1 week after birth or sooner. In mouse soleus, the relative proportions of fibers staining positive with fast and slow myosin antibodies were similar at all ages studied, about 60%–70% being fast and 30%–40% slow. In rat soleus, however, the proportions of fast antibody-positive and slow antibody-positive fibers changed dramatically during postnatal maturation. At 1 week after birth, about 50% of rat soleus fibers stained with fast myosin antibodies, whereas between 1 and 2 months this value fell to about 10%. In mouse, about 10% of fibers at 1 week, but none at 1 year, reacted with both fast and slow antibodies, whereas in rat, fewer than 3% bound both antibodies to a significant degree at 1 week. It is puzzling why, in rat soleus, the majority of apparently fast fibers present at 1 week is converted to a slow phenotype, whereas in mouse soleus the predominant change appears to be the suppression of fast myosin expression in a subset of fibers that expresses both myosin types at 1 week. It is possible that this may be related to differences in size and the amount of body growth between these two species.     

The vaginal surface epithelium during postnatal development in gerbils

The postnatal development of the gerbil vagina has been investigated and special attention has been paid to the luminal surface epithelium structures. Different types of microvilli and solitary cilia are discussed.     

Retinoid dynamics in chicken eye during pre-and postnatal development

Changes in the steady state level of retinols, retinaldehydes and retinyl esters in the trans and 11-cis forms and trans retinoic acid were measured in whole chicken eye during development from day 6in ovo to day 3 post-hatch. These retinoids, quantified by different HPLC systems, were detected in this time sequence: trans-retinol and trans-retinyl esters in the first weekin ovo, 11-cis-retinol in the second week. The highest level of 11-cis-retinaldehyde and 11-cis-retinyl esters was reached at the end of developmentin ovo; however, their levels increased further after hatching. The retinoic acid level decreased at the end of the first week, rising again at the end of the second week.The enzyme activities involved in the metabolism of these retinoids-acyl-CoA: retinol acyltransferase, trans-retinol dehydrogenase, 11-cis-retinol dehydrogenase, trans-retinyl ester hydrolase and trans: 11-cis-retinol isomerase were also estimated and they were detectable already in the first week of developmentin ovo.At day 6 of the biosynthesis of retinoic acid by the retinaldehyde dehydrogenase activity from retina cytosol was also shown.     

Plasma testosterone concentrations during postnatal development in the male common marmoset

Repeated measurements of plasma testosterone (T) were made in 56 male marmosets from the day of birth until 300 days of age and in 44 adults (greater than 3 years). The resulting profile of plasma T during postnatal development shows higher levels during infancy (1-90 days) followed by a nadir between 100 and 170 days and then a progressive rise in T during puberty. Although T levels of up to 21 ng/ml were measured in infant males, mean levels (+/- SEM) were 5.4 +/- 0.6 ng/ml (days 1-10), declining gradually to 1.7 +/- 0.1 ng/ml (days 100-110). No increase in mean T levels between 15 and 100 days was identified, and the onset of puberty was earlier in some males than measured previously in this species.