Population dynamics of clock-controlled biological species: models and why circadian rhythms are circadian

The endolymph flow inside the semicircular ducts is analytically investigated by considering a system of two hydrodynamically interconnected ducts. Rotation of this system adds an amount of motion (momentum) to parts of it. This results in an endolymph flow in generally all vestibular parts. The "external impulses" are the impulses which emerge by rotation of exclusively a particular vestibular part. The real impulses can be calculated from a set of equations which contain the external impulses. Analytical expressions are derived for the initial velocities in the ducts and for the maximum endolymph displacements. These formulae contain the external impulses and the ratios of: (1) the radii of crus commune and ducts (gamma), (2) the lengths of crus commune and ducts (lambda). It was proven that an interconnected system composed of two ducts, and also a system composed of two such semicircular duct systems, behaves as a pure rotation transducer (like a single duct does), also when it is rotated excentrically. Duct systems with polygonal and circular geometries were used to evaluate whether an optimal value of lambda would exist (gamma was already considered elsewhere). Optimum values of lambda in a range of about 0.10-0.52 were found. This rather wide range of values agrees with values from measurements. Optimization of an interconnected duct system appeared to be equal to optimization of a system composed of separate ducts.     

A new quantitative model of total endolymph flow in the system of semicircular ducts

1. A new concept of endolymph flow in the vertebrate vestibular system is presented. This approach describes quantitatively the flow in the entire system of three semicircular ducts interconnected by the utriculus and the crus commune. This approach is quite distinct from the classical theory in which the labyrinth is generally conceived to consist of three separate duct circuits. 2. The present approach shows the following set of distinct differences to the classical view: (a) In a labyrinth composed of three ducts perpendicular to each other the flow is non-zero in the other ducts when the labyrinth is rotated in the plane of a particular duct. (b) In a labyrinth with two equal ducts and with the duct planes under approximately 73 degrees the flow in one duct is zero when the rotation takes place in the plane of the other duct. Previous measurements of duct angles reflect this value surprisingly well. An obtuse or sharp angle between duct planes can lead to better performance of a particular labyrinth because the "external impulses" in the different ducts may amplify or compensate each other. (c) The behaviour of the flow in the entire labyrinth is a non-linear function of direction or rotation (cf. points (d), (e]. (d) Six time constants for the entire labyrinth can be distinguished (three long, three short); the flow in a particular duct is composed of six terms with these time constants. The composition of this flow and thus the relative importance of the terms depends on the positioning of the labyrinth with respect to the rotation vector. (e) The time constants also depend, for different labyrinths, on a shared influence of the dimensions of the ducts and the elastic properties of all three cupulae. (f) The forces in a particular duct depend also on the amount of motion the fluid will acquire in the other ducts. (g) The sensitivity of a particular duct depends also on the dimensions of the other parts in the vestibular system. 3. Equations for a system consisting of two ducts and for the classical single duct system are also given. Both systems are special cases of the three-duct system. The single duct equations are equivalent with equations given by Oman (1980) and Oman et al. (1987) which include the contribution of a wide utriculus. 4. The present theory of endolymph flow is mainly supported by the outcome of previously performed experiments concerning time constants and rotation of human subjects in different planes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Optimization of the mechanical performance of a two-duct semicircular duct system--part 3: the positioning of the ducts in the head

In the majority of vertebrates, the horizontal duct of the vestibular system lies approximately in the yawing plane of the head. The positioning of the vertical ducts, however, is not in the pitch- and roll planes but the vertical ducts generally lie under an angle of about 30-45 degrees relative to the medial plane. Using the equations for a hydrodynamically interconnected two-duct system, optimal positions of the vertical and horizontal ducts in different vertebrate groups can be derived. It was stated that the mean response of the vertical ducts should be optimized. This leads to a symmetrical positioning of the vertical ducts with respect to the medial plane. In all observed vertebrate groups, a solution of mu =(pi-alpha)/2 is found (mu is the angle of the vertical ducts relative to the medial plane, alpha is the angle between the vertical duct planes). For alpha=90 degrees, this provides an equal sensitivity for pitch- and roll- movements. For alpha>90 degrees, a larger sensitivity for pitch movements is obtained, at the expense of a lower sensitivity for roll movements. It is argued that the angle alpha between the vertical ducts may vary from 90 to 120 degrees. In most vertebrates, the centre of mass is stabilized by e.g. fins, tri- or quadrupedal stability, a crawling body or upside-down resting positions (e.g. bats). Birds are generally biped, so in walking they are also rather sensitive to roll. These features are related to labyrinth positioning in the head.     

Microscopic vs. macroscopic deformation of the pulmonary alveolar duct.

The stretch of the perimeters of alveolar ducts was measured at the surface of saline-filled specimens of human and dog lung parenchyma that were stretched biaxially. The microscopic stretch of these ducts was measured at several levels of isotropic biaxial macroscopic stretch of the parenchyma with stretch ratio (lambda x = lambda y) in the range of 1.20-1.40, which roughly corresponds to tidal breathing in humans and dogs. Alveolar walls were found to be load-carrying elements in the saline-filled lung, as seen by their straightness at all levels of stretch. Quantitatively, let l, A, L, and S denote, respectively, the duct perimeter length and area and the parenchymal target perimeter and area in the deformed state and lo, Ao, Lo, and So the corresponding variables in the undeformed state. The microscopic stretch ratio of the ducts (l/lo) was found to be approximately 4% larger than the macroscopic stretch ratio (L/Lo) in human lung and approximately 10% larger in dog lung. The microscopic area ratio of the ducts (A/Ao) was found to be approximately 10% larger than the macroscopic area ratio (S/So) in human lung and approximately 22% larger in dog lung. Ducts within human parenchyma were seen to be about twice as stiff as ducts within dog parenchyma over the range of macroscopic stretch studied. This correlates with the volume fractions of collagen and elastin being higher in the human lung than in dog lung. The observed nonuniformity in strain field at the microstructural level suggests the need to include a force balance between alveolar ducts and septal walls when modeling the mechanics of saline-filled parenchyma.     

The ultrastructure of the duct system in the rat extraorbital lacrimal gland

Summary The duct system of the rat exorbital lacrimal gland consists of intercalated ducts, interlobular ducts and excretory ducts. The morphological changes from one type of duct to the next are gradual. At the light microscopical level this consists of a change from a bilaminar epithelium in the intercalated ducts to an epithelium, consisting of approximately three layers — which may be pseudostratified — in the excretory ducts. The basal layer of the intercalated ducts consists of myoepithelial cells, whereas the inner epithelial cells may have both a secretory and an electrolyte transporting function. The interlobular duct epithelium contains many cells with deep infoldings of the basolateral plasma membranes and associated mitochondria, suggesting a similar function to the striated duct epithelium in salivary glands. Numerous basal cells in this epithelium have tentatively been interpreted as unusual myoepithelial cells. Nerve terminals have been observed in the ductal epithelium.This work was supported by the National Health and Medical Research Council of Australia. — We wish to thank Mrs. Eva Vasak for her expert technical assistance.     

The importance of the spermathecal duct in bumblebees

The elongated spermathecal duct of bumblebees has been studied in hibernating queens, queens shortly after hibernation, mature egg-laying queens and uninseminated queens captured during summer, and workers. Only rather small size differences are found when comparing spermathecae of queens and workers. Clear differences between bumblebee queens and workers are found when comparing the histochemistry of the spermathecal ducts. Adult queens, regardless of age and reproductive status have spermathecal ducts that contain PAS positive material, whereas workers do not. It is suggested that the polysaccharides in the spermathecal ducts of queens are necessary as a source of energy for the rapid activation of spermatozoa passing through the duct prior to oocyte fertilization. An ultrastructural investigation revealed the presence of high glycogen content in the cells lining the duct of queens. Assuming that sperm cells are kept in a rather inactive state in the reservoir, the carbohydrate (glycogen) probably serves as an energy source for the sperm. The comparatively increased spermathecal duct length of bumblebees may increase the retention time of sperm inside the lumen.     

Morphology of the antennary gland exit duct in ecological and phylogenetic series of talitroid Amphipoda (Crustacea)

The form of the proximal segments of antenna two peduncle and of the antennary gland exit duct on peduncle article two has been examined in 16 species of amphipod crustaceans (including 14 species of Talitridae). Gammarus duebeni (Gammaridae), regarded as exemplifying the norm for aquatic amphipods, has a very distinctive fluted exit duct emanating from a pronounced gland cone. The talitroid Hyale nilssoni was regarded as a typical representative of the hyalid-like ancestors of the Talitridae. It also has a gland cone, but the exit duct of the antennary gland is a thin-walled, collapsible cone. The two proximal articles of antenna two peduncle are much reduced in Talitridae. Only the second may retain a degree of mobility. No gland cone remains. The structure of the urinary exit duct in seven species of simplidactylate landhoppers (Bousfield's Gp IVa) was very similar to the hyalid condition. Beachfleas (Gp II) have strengthened, often sculpted ducts. whilst sandhoppers (Gp III) have no protruding exit duct at all. Only one species of Gp IVb (cuspidactylate) landhopper ( Tasmanorchestia sp.) was investigated and it has an exit duct similar in form to that of the beachfleas (Gp II). Neorchestia plicibranchiata (a Gp IVa species), however, already known to be an anomalous species, has unusually elongate urinary ducts (for a Gp IVa species). These observations lend support to the notion that the landhoppers are a polyphyletic grouping and that the sandhoppers are a very isolated ecomorphological grouping within the family.     

A general pre-steady-state solution to complex kinetic mechanisms

We have developed a general method for solving transient kinetic equations using Laplace transforms. Laplace transforms can be used to transform systems of differential equations that describe pre-steady-state kinetics to systems of linear algebraic equations. The general form of the pre-steady-state solution is (formula; see text) where I(t) is the time dependence of the physically observed property of the system, n is the number of intermediates, lambda i are the observed rate constants (reciprocals of the relaxation times), t is time, and Ii are the amplitude coefficients associated with each observed rate constant. We have written a program in compiled BASIC to run on a personal computer to evaluate Ii and lambda i. The program will evaluate the rate constants and coefficients of a mechanism with eight intermediates and seven relaxation times in 4 s on an 8-MHz PC-XT equipped with a math coprocessor. The most complex mechanism that we have solved, a mechanism containing 20 intermediates and 19 relaxation times, required approximately 5 min. We believe that this method will be useful to evaluate the differences in transient properties of complex biochemical mechanisms.     

Wound-induced traumatic resin duct development in stems of Norway spruce (Pinaceae): anatomy and cytochemical traits

Wounding of Norway spruce by inoculation with sterile agar, or agar containing the pathogenic fungus Ceratocystis polonica, induced traumatic resin duct formation in the stem. Visible anatomical responses occurred in the cambium 6-9 d post-inoculation. Near the inoculation site cellular proliferation, polyphenolic accumulation, and lignification were induced as a wound reaction to seal the damaged area. Five centimetres from the inoculation site cells in the cambial zone swelled and divided to form clusters. By 18 d post-inoculation, these cells began to differentiate into resin duct epithelial cells surrounding incipient schizogenous lumens. Mature axial traumatic ducts appeared by 36 d as a row of ducts in the xylem centripetal to the cambium. The ducts formed an interconnected network continuous with radial resin ducts. Parenchyma cells surrounding the ducts accumulated polyphenols that disappeared as the cells differentiated into tracheids. These polyphenols appeared to contain fewer sugar residues compared to those accumulating in the secondary phloem, as indicated by the periodic acid-Schiff's staining. The epithelial cells did not accumulate polyphenols but contained immunologically detectable phenylalanine ammonia lyase (EC 4.3.1.5), indicating synthesis of phenolics as a possible resin component. These findings may represent a defense mechanism in Norway spruce against the pathogenic fungus Ceratocystis polonica.     

In vitro induction of the pronephric duct in Xenopus explants

The earliest form of embryonic kidney, the pronephros, consists of three components: glomus, tubule and duct. Treatment of the undifferentiated animal pole ectoderm of Xenopus laevis with activin A and retinoic acid (RA) induces formation of the pronephric tubule and glomus. In this study, the rate of induction of the pronephric duct, the third component of the pronephros, was investigated in animal caps treated with activin A and RA. Immunohistochemistry using pronephric duct-specific antibody 4A6 revealed that a high proportion of the treated explants contained 4A6-positive tubular structures. Electron microscopy showed that the tubules in the explants were similar to the pronephric ducts of normal larvae, and they also expressed Gremlin and c-ret, molecular markers for pronephric ducts. These results suggest that the treatment of Xenopus ectoderm with activin A and RA induces a high rate of differentiation of pronephric ducts, in addition to the differentiation of the pronephric tubule and glomus, and that this in vitro system can serve as a simple and effective model for analysis of the mechanism of pronephros differentiation.     

The duct system of the lachrymal salt gland of the green sea turtle,Chelonia mydas

Summary The duct system of the lachrymal salt gland of the green sea turtle comprises central canals, secondary ducts and a sac-like main duct. Distally the central canals consist of large columnar cells with lateral membranes folded into plicae which interdigitate in adjacent cells to form complex intercellular spaces. More proximally the central canals, secondary ducts and main duct consist of epithelia which are stratified or pseudostratified. The cells of these epithelia are separated by wide and complex inter-cellular spaces: they are joined by frequent maculae adherentes junctions. Complex intracellular webs of tonofilaments are associated with these junctions. At the luminal border of the epithelia of the secondary and main ducts is a layer of mucocytes. The mucocytes increase in density towards the proximal extremity of the main duct and secrete a thick luminal layer of mucus. The duct system is very well vascularised. It is suggested that it is unlikely to be merely a passive conduit and that it may have a role in the modification of the fluid secreted by the gland.     

Experimental studies on pancreatic duct occlusion with prolamine

The effect of the occlusion of the pancreatic duct system with prolamine (Ethibloc) has been studied in animal experiments with dogs and mini-pigs. The solution becomes solid in the duct system and becomes disintegrated again within 11 days. This time, however, is sufficient to keep a high-grade atrophy of the exocrine parenchyma. With this method one doesn't risk the provocation of an acute pancreatitis. The endocrine function of the atrophied glands is satisfactory, no animal became diabetic. The basal jugular vein insulin shows no difference to that of the control group, but nevertheless the mean whole pancreas hormone content is reduced for insulin and somatostatin, but not for glucagon.     

The duct system of the avian salt gland as a transporting epithelium: structure and morphometry in the duck Anas platyrhynchos

Summary The duct system of the nasal salt gland of the duck comprises central canals, secondary ducts and main ducts. The secondary and main ducts consist of a layer of columnar cells overlying a layer of small cuboidal cells. The columnar cells have complex intercellular spaces showing evidence of Na⁺ K⁺ -ATPase at the apical regions. Approximately 70% of surface area of the duct system is external to the gland. During adaptation to salt water the duct system increases in size as does the gland. Although the components of the gland of adapted ducks, including the duct system within the gland, increase in size compared with normal ducks, the percentage volume densities of the components remain similar in both categories of ducks, i.e. the duct system increases in size in proportion to the glandular tissue. The volume of the duct system external to the gland is six to seven times larger than the volume within the gland. Thus, if ductal modification of secreted fluid occurs, it will be most likely to take place in the ducts external to the gland.Total surface areas of the duct system were measured from serial sections of glands and ducts from one normal and one adapted duck. These were used to calculate possible flux rates of water and sodium across the duct epithelium, assuming the occurrence of either water reabsorption or sodium secretion. Although these flux rates are high it is shown that they are similar to calculated flux rates across the luminal surface of the secretory tubules.     

Distribution of aquaporin 1 in the rat pancreatic duct system examined with light- and electron-microscopic immunohistochemistry

The pancreatic duct is the major site for the secretion of pancreatic fluid, but the pathway of water transport in this system is not known. Recently, intense signal for mRNA of aquaporin 1 (AQP1) water channels was detected in isolated rat interlobular ducts. Therefore, we performed light- and electron-microscopic (EM) immunohistochemistry for AQP1 in the rat pancreatic ducts. AQP1 immunoproducts were not observed in the acinar cells, centroacinar cells or intercalated ducts. In the smaller intralobular ducts less than 10 microm in diameter (the lumen plus duct cells), most cells were immunonegative. AQP1-positive cells appeared in intralobular ducts 10-15 microm in diameter. In small and medium-sized interlobular ducts 15-70 microm in diameter surrounded by periductal connective tissue 2-40 microm thick, most cells were AQP1 positive with various degrees of immunoreactivity. In the larger interlobular ducts, the expression of AQP1 was variable, ranging from immunopositive to negative. In the main pancreatic duct, most cells were negative for AQP1. EM immunohistochemistry of the intralobular and small interlobular ductal epithelial cells showed that the AQP1 immunoproducts were more abundant in the basolateral membrane than in the apical membrane, though they were present in both membranes. In the medium-sized interlobular ducts, AQP1 immunoproducts were distributed densely along the apical, lateral interdigitation and basal membrane of the epithelial cells. In the various sizes of interlobular ducts, immunoproducts were associated not only with the plasma membrane, but also with the caveolae and vesicle-like structures. Secretin did not induce any significant difference in AQP1 expression and cellular and subcellular localization. These results indicate that the expression and subcellular localization of AQP1 vary considerably depending on the duct size, which may reflect water transport characteristics in the different divisions of the pancreatic duct system.     

Cell proliferation kinetics of the bile duct epithelium of the rat

Abstract. Cell proliferation kinetics of the extrahepatic bile duct were studied by flash and cumulative labelling methods and immunohistochemical techniques. We compared the cell kinetics of the epithelium of the intra- and extra-pancreatic bile ducts and of the bile duct of the ampulla in rats administered intraperitoneally with bromodeoxyuridine (BrdUrd). After a single injection of BrdUrd (flash labelling), labelled cells appeared in the lower portion of the downgrowths of the epithelium in the intra-and extra-pancreatic bile ducts. A gradual accumulation of the labelled cells at the surface epithelium was observed during the cumulative labelling. After cumulative labelling the labelled cells gradually decreased in number and were finally confined to the degenerative cell zone of the surface epithelium 30 days later. Similarly, after a single injection of BrdUrd, the labelled cells in the bile duct of the ampulla appeared at the lower half of the crypt from where they migrated to the upper portion during cumulative labelling. These findings indicate that epithelial cells of the bile duct are renewed at the lower portion of the downgrowths of the epithelium, or crypt, and shed from the surface epithelium or upper portion of the fold. The labelling indices reached 23.83 ± 7.47% in the intra-pancreatic bile duct, 14.74 ± 7.99% in the extra-pancreatic bile duct and 43.42 ± 4.40% in the bile duct of the ampulla at the end of 70 h cumulative labelling. The fluctuating values of the labelling index were higher in the bile duct of the ampulla than in the intra- or extra-pancreatic bile ducts. These results indicate that the bile-duct epithelium undergoes a slower renewal rate than the other parts of the gastrointestinal tract, and that the renewal time of the epithelial cells is shorter at the bile duct of the ampulla than at the intra- or extra-pancreatic bile ducts.     

Wolffian duct differentiation by physiological concentrations of androgen delivered systemically

In developing mammalian males, conversion of the Wolffian ducts into the epididymides and vasa deferentia depends on androgen secretion by the testes, whereas in females these ducts remain in a vestigial form or regress. However, there is continuing uncertainty whether the androgen needs to be delivered locally, either by diffusion from the adjacent testis or, by secretion into the lumen of the duct, or whether circulating androgens maintain and virilize the Wolffian ducts. To resolve this uncertainty, we transplanted either day 0-2 or day 8-9 post-partum testes beneath the flank skin of three groups of neonatal (days 0-1) female tammar wallabies, where they developed and secreted physiological levels of hormones. The Wolffian ducts of all these females were retained and had formed extensive epididymides when examined at days 25, 34 and 87 after birth. In the two older groups of females, sampled after the time of prostatic bud formation, the urogenital sinus was virilized and there was extensive prostatic development similar to that of normal males of the same age, showing that androgen secretion had occurred. Virilization of the Wolffian ducts occurred during an early but short-lived window of sensitivity. This study provides the first clear evidence that under physiological conditions virilization can be mediated by circulating androgen.     

Ephrin-B2 governs morphogenesis of endolymphatic sac and duct epithelia in the mouse inner ear

Control over ionic composition and volume of the inner ear luminal fluid endolymph is essential for normal hearing and balance. Mice deficient in either the EphB2 receptor tyrosine kinase or the cognate transmembrane ligand ephrin-B2 (Efnb2) exhibit background strain-specific vestibular-behavioral dysfunction and signs of abnormal endolymph homeostasis. Using various loss-of-function mouse models, we found that Efnb2 is required for growth and morphogenesis of the embryonic endolymphatic epithelium, a precursor of the endolymphatic sac (ES) and duct (ED), which mediate endolymph homeostasis. Conditional inactivation of Efnb2 in early-stage embryonic ear tissues disrupted cell proliferation, cell survival, and epithelial folding at the origin of the endolymphatic epithelium. This correlated with apparent absence of an ED, mis-localization of ES ion transport cells relative to inner ear sensory organs, dysplasia of the endolymph fluid space, and abnormally formed otoconia (extracellular calcite-protein composites) at later stages of embryonic development. A comparison of Efnb2 and Notch signaling-deficient mutant phenotypes indicated that these two signaling systems have distinct and non-overlapping roles in ES/ED development. Homozygous deletion of the Efnb2 C-terminus caused abnormalities similar to those found in the conditional Efnb2 null homozygote. Analyses of fetal Efnb2 C-terminus deletion heterozygotes found mis-localized ES ion transport cells only in the genetic background exhibiting vestibular dysfunction. We propose that developmental dysplasias described here are a gene dose-sensitive cause of the vestibular dysfunction observed in EphB–Efnb2 signaling-deficient mice.     

Focal expression of insulin-like growth factor I in rat kidney collecting duct

To address the question of insulin-like growth factor (IGF) I localization and synthesis in kidney, we used two complementary experimental approaches: immunohistochemistry of fixed paraffin-embedded rat kidney sections; and measurement of IGF I mRNA in isolated components of the rat nephron, using a highly sensitive and specific solution hybridization assay. Immunostainable IGF I was localized exclusively to principal cells of cortical and medullary collecting ducts. Administration of growth hormone to hypophysectomized rats for 8 d resulted in enhanced immunohistochemical staining of IGF I within collecting ducts, but no detectable IGF I in other portions of the nephron. The abundance of IGF I mRNA was 7-12-fold higher in isolated papillary collecting ducts than in proximal tubules or glomeruli, and was enriched 10-fold compared with whole kidney. Our data demonstrate colocalization of IGF I and IGF I mRNA in the collecting duct, consistent with focal expression of the IGF I gene at this site.     

Immunohistochemical localization of senescence marker protein-30 (SMP30) in the submandibular gland and ultrastructural changes of the granular duct cells in SMP30 knockout mice

Senescence Marker Protein-30 (SMP30) is a calcium-regulating protein that decreases in an androgen-independent manner as aging occurs. An enzyme-labeled antibody technique has demonstrated that SMP30 localized to the ducts (granular, intercalated, and striated ducts) of mouse submandibular glands. Immunoelectronmicroscopy demonstrated that the granular duct cells were strongly positive for SMP30, but that pillar cells in the granular duct were negative for the protein. In SMP30-knockout (KO) mice, the granular ducts were smaller in diameter. Swelling of mitochondria in the granular duct cells was observed; however, this phenomenon was not observed in the pillar cells. After administration of alpha-isoproterenol, a beta-adrenergic stimulant, a large numbers of small secretory granules were present in the granular duct cells and an expansion of the rough endoplasmic reticulum in SMP30-wild type (WT) mice; in contrast, little change was observed in SMP30-KO mice. These results suggest that SMP30 may be closely related to a signal transduction pathway in the granular duct cells of submandibular glands.