Active Growth Centers Research Articles

The chondrocranial key: Fetal and perinatal morphogenesis of the sphenoid bone in primates

The sphenoid bone articulates with multiple basicranial, facial, and calvarial bones, and in humans its synchondroses are known to contribute to elongation of the skull base and possibly to cranial base angulation. Its early development (embryological, early fetal) has frequently been studied in a comparative context. However, the perinatal events in morphogenesis of the sphenoid have been explored in very few primates. Using a cross-sectional age sample of non-human primates (n=39; 22 platyrrhines; 17 strepsirrhines), we used microcomputed tomographic (µCT) and histological methods to track age changes in the sphenoid bone. In the midline, the sphenoid expands its dimensions at three growth centers, including the sphenooccipital, intrasphenoidal (ISS) and presphenoseptal (PSept) synchondroses. Bilaterally, the alisphenoid is enlarged via appositional bone growth that radiates outward from cartilaginous parts of the alisphenoid during midfetal stages. The alisphenoid remains connected to the basitrabecular process of the basisphenoid via the alibasisphenoidal synchondrosis (ABS). Reactivity to proliferating cell-nuclear antigen is observed in all synchondroses, indicating active growth perinatally. Between mid-fetal and birth ages inSaguinus geoffroyi, all synchondroses decrease in the breadth of proliferating columns of chondrocytes. In most primates, the ABS is greatly diminished by birth, and is likely the earliest to fuse, although at least some cartilage may remain by at least one-month of age. Unlike humans, no non-human primate in our sample exhibits perinatal fusion of ISS. A dichotomy among primates is the orientation of the ABS, which is more rostrally directed in platyrrhines. Based on fetalSaguinus geoffroyispecimens, the ABS was initially oriented within a horizontal plane, and redirects inferiorly during late fetal and perinatal stages. These changes occur in tandem with forward orientation of the orbits in platyrrhines, combined with downward growth of the midface. Thus, we postulate that active growth centers direct the orientation of the midface and orbit before birth.

Cranial synchondroses of primates at birth.

Cranial synchondroses are cartilaginous joints between basicranial bones or between basicranial bones and septal cartilage, and have been implicated as having a potential active role in determining craniofacial form. However, few studies have examined them histologically. Using histological and immunohistochemical methods, we examined all basicranial joints in serial sagittal sections of newborn heads from nine genera of primates (five anthropoids, four strepsirrhines). Each synchondrosis was examined for characteristics of active growth centers, including a zonal distribution of proliferating and hypertrophic chondrocytes, as well as corresponding changes in matrix characteristics (i.e., density and organization of Type II collagen). Results reveal three midline and three bilateral synchondroses possess attributes of active growth centers in all species (sphenooccipital, intrasphenoidal, presphenoseptal). One midline synchondrosis (ethmoseptal) and one bilateral synchondrosis (alibasisphenoidal synchondrosis [ABS]) are active growth centers in some but not all newborn primates. ABS is oriented more anteriorly in monkeys compared to lemurs and bushbabies. The sphenoethmoidal synchondrosis (SES) varies at birth: in monkeys, it is a suture-like joint (i.e., fibrous tissue between the two bones); however, in strepsirrhines, the jugum sphenoidale is ossified while the mesethmoid remains cartilaginous. No species possesses an SES that has the organization of a growth plate. Overall, our findings demonstrate that only four midline synchondroses have the potential to actively affect basicranial angularity and facial orientation during the perinatal timeframe, while the SES of anthropoids essentially transitions toward a "suture-like" function, permitting passive growth postnatally. Loss of cartilaginous continuity at SES and reorientation of ABS distinguish monkeys from strepsirrhines.

Anticalcification potential of heparin on hydroxyapatite seeds using a constant composition in vitro model

Calcification is among the principal causes of biological heart valve substitute failure. Glycosaminoglcans (GAGs) are negatively charged molecules, possessing anticoagulation and anti-inflammatory activity that make them a potential solution against calcification. In the present work, the anticalcification potential of heparin was investigated under constant supersaturation conditions with respect to hydroxyapatite (Ca5(PO4)3OH; HAP). Heparin concentration in the supersaturated solutions was in the range between 0.25 and 3 ppm, at pH 7.40 and 37 °C. Heparin showed inhibitory activity, which was attributed to adsorption at the active crystal growth centres. Heparin concentration as low as ca. 50 μM, reduced the rate of HAP crystal growth by more than 80%, while further increase (up to 200 μM) failed to completely inhibit the process beyond 90%. Heparin uptake studies at equilibrium conditions and analysis of the kinetics data in the presence of heparin, strongly suggest that the inhibition is due to the adsorption of heparin onto the HAP crystals, which resulted in the poisoning of the active growth sites.

Bone scintigraphy as a diagnostic tool in condylar hyperplasia

Unilateral condylar hyperplasia (UCH) is a pathological condition characterized by unrestrained growth of condyle unilaterally and is of idiopathic in nature. It is often diagnosed clinically but more frequently if not always is augmented by planar and single photon emission computed tomography bone scans to confirm the finding. Hence, bone scintigraphy using technetium-99 m methylene diphosphonate is the diagnostic tool to identify these active growth centers. Detection and excision of active growth center are the line of management for condylar hyperplasia. This article highlights the importance of using these radioactive scans to diagnose as well as to monitor the prognosis of UCH in two such cases.

Cell longevity and sustained primary growth in palm stems

Longevity, or organismal life span, is determined largely by the period over which constituent cells can function metabolically. Plants, with modular organization (the ability continually to develop new organs and tissues) differ from animals, with unitary organization (a fixed body plan), and this difference is reflected in their respective life spans, potentially much longer in plants than animals. We draw attention to the observation that palm trees, as a group of monocotyledons without secondary growth comparable to that of lignophytes (plants with secondary growth from a bifacial cambium), retain by means of sustained primary growth living cells in their trunks throughout their organismal life span. Does this make palms the longest-lived trees because they can grow as individuals for several centuries? No conventional lignophyte retains living metabolically active differentiated cell types in its trunk for this length of time, even though the tree as a whole can exist for millennia. Does this contrast also imply that the long-lived cells in a palm trunk have exceptional properties, which allows this seeming immortality? We document the long-life of many tall palm species and their inherent long-lived stem cell properties, comparing such plants to conventional trees. We provide a summary of aspects of cell age and life span in animals and plants. Cell replacement is a feature of animal function, whereas conventional trees rely on active growth centers (meristems) to sustain organismal development. However, the long persistence of living cells in palm trunks is seen not as evidence for unique metabolic processes that sustain longevity, but is a consequence of unique constructional features. This conclusion suggests that the life span of plant cells is not necessarily genetically determined.

Chemical deposition of nanostructured tungsten and tungsten-alloy coatings from gas phase

The historical overview of the fluoride method for the low-temperature deposition of tungsten, its alloys, and compounds in Russia is presented. The physicochemical fundamentals (thermodynamics, kinetics) of the deposition process are given. The most probable rout for homogeneous and heterogeneous reactions resulting in the formation of the tungsten metal at the substrate surface is theoretically substantiated. Based on the experimental study of the initial crystallization stages, a basic mechanism of the active growth centers formation is formulated. Kinetic characteristics of the processes of tungsten codeposition with refractory transition metals, as well as the coatingsí physical-mechanical properties are given. Data on the deposition of solid tungsten-carbide films from gas phase onto low-temperature substrate are reported. Possible applications of the tungsten, tungsten alloys with transition metals, and tungsten carbide coatings are discussed.

PET as a Diagnositic Tool in Unilateral Condylar Hyperactivity

PET as a Diagnositic Tool in Unilateral Condylar Hyperactivity

Study of the Propagation Center in the Anionic Polymerization of (Meth)acrylic Monomers: NMR and MO LCAO Study of the Interaction of Di-tert-butyl 2-Lithio-2,4,4-trimethylglutarate and the Living Poly(tert-butyl methacrylate) Oligomers with Lithium 2-(2-Methoxyethoxy)ethoxide in Tetrahydrofuran

Interactions of lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM) with the model dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) and the living poly(tert-butyl methacrylate) oligomers (B) were studied in tetrahydrofuran-d8 at 203−273 K using 1H, 13C, 7Li, and 6Li, 1D and 2D, NMR and ab initio SCF 3-21G and MNDO quantum chemical calculations. LiOEEM is shown to have a strong tendency to self-aggregation, producing dimeric, trimeric, and tetrameric aggregates and competing with its mixed aggregation (or complexation) with A and, in particular, B. When dissolved in THF, LiOEEM as well as its mixtures with A form metastable systems which relax in several days at 258 K into equilibrium. Interaction of LiOEEM with A leads to a system of mixed aggregates LiOEEM1A1, LiOEEM3A1, and possibly LiOEEM2A1 along with the original components, in relative populations depending on the LiOEEM/A molar ratio, temperature, time, and probably other factors of preparation. Probable structures of these complexes are proposed, and the nature of the prevalent bonding is suggested. Experimental results indicate that LiOEEM is unable to convert A completely at moderate excess (up to 4/1 mol/mol). Interaction of LiOEEM with B leads to quite analogous complexes but with even lower yields. There appear to be traces of uncomplexed B even at the LiOEEM/B ratio of 10 mol/mol. This is suggested to produce at least two different kinds of active growth centers in the corresponding ligated anionic polymerization of tert-butyl methacrylate and, consequently, the observed bimodality of the polymeric product. The difference with respect to methyl methacrylate, where LiOEEM ensures an almost ideal living polymerization, is suggested to be due to the steric hindrance of efficient complexation exerted by the tert-butyl group.

Basic mechanisms in craniofacial growth.

Bone growth is controlled by growth areas, not active growth centers as stated earlier. Conversion of cartilage, sutural deposition, and periosteal remodeling are the basic phenomena involved in growth mechanisms. The principles of bone growth will result in changes in the size and shape of the mandible and the nasomaxillary complex in the three dimensions. The growth rate varies at different times during the development of the child. The processes of facial growth and changes in the dental arches continue to a much later age than had previously been realized. Although our knowledge of craniofacial growth has increased during recent times, it is still incomplete with regard to the explanation for the regulation of craniofacial growth.

Axial ‘anchor’ screw (lag screw with biconcave washer) or ‘slanted-screw’ plate for osteosynthesis of fractures of the mandibular condylar process

Almost a quarter of all mandibular fractures are located in the condylar neck region and generally lead to disturbances of occlusion. Because they still possess active growth centres, children and adolescents can take advantage of the joint's remodelling capacity following conservative treatment of these fractures. Fractures with displacement of the condylar head in adults can interfere with function if they are not surgically reduced (Krenkel and Strobl, 1989). In addition, a compensatory overloading of the non-fractured side, which originally goes unnoticed, can bring about disc pathology and chronic pain years later. For this reason, a surgical technique was developed for the management of mandibular condylar neck fractures. A new axial/oblique-axial lag screw (anchor screw) with biconcave washers (anchor washer) makes it possible to carry out standardized osteosynthesis in the region of the thin mandibular condyle neck. Functional exercises can be initiated immediately after the operation. There are three operative procedures using an extraoral approach (1-3) and two using an intraoral approach (4-5), depending on the type and severity of the fracture: 1. Direct anchor screw osteosynthesis with closed gliding hole. 2. Indirect anchor screw osteosynthesis with open gliding groove and safety plates. 3. Osteosynthesis with a 'slanted-screw' plate for longer oblique fractures. 4. Intraoral anchor screw method. 5. Intraoral anchor screw method with intraoral 'slanted-screw' plate. The functional long-term results of conservatively and surgically treated mandibular condylar neck fractures were objectively documented by means of mechanical and electronic axiography. The functional long-term results of the condylar neck fractures treated surgically were significantly better than those treated conservatively.(ABSTRACT TRUNCATED AT 250 WORDS)

The crystal growth of silicon in Al-Si alloys

Some crystallographic observations of primary silicon and unmodified eutectic silicon in aluminium-silicon alloys are summarized and used to support the theory that sodium modification is due to the poisoning of active growth centres. The implications of endogenous growth in unmodified aluminium-silicon sand castings are explored and mechanisms are proposed for the flake-fibre transition in chill-modified and sodium-modified alloys.

Ultrastructure of lipoma.

Eleven benign lipogenic tumors comprising ten ordinary lipomas and one fibroblastic lipoma were studied by light and electron microscopy. The former, which contained only a few inconspicuous septa, were composed of univacuolar mature adipocytes. No young forms of adipocytic differentiation were seen reflecting the slow growth of the ordinary lipomas. Small spindle cells accompanying capillaries located in the triangular confluence of the adipocytes are thought to be potential precursors of adipocytes. By contrast, the fibroblastic lipoma contained many younger forms which closely resembled those seen during maturation of normal adipose tissue. These younger forms are located in and about prominent trabeculae which therefore are considered to constitute active growth centers.

Callus Initiation and Plant Regeneration from Triticale Embryos1

This study was conduced to determine optimal concentrations of sucrose and combinations of growth regulators required for callus initiation and plant regeneration from immature embryos of 'Councill' and other triticales (X Triticosecale Wittmack) and to make histological observations of triticale callus during differentiation and organogenesis. Immature triticale embryos were cultured on a basal medium containing the salts of Murashige and Skoog and vitamins plus selected concentrations of sucrose and different auxins or cytokinins, alone or in combination. The optimal concentration of sucrose for increasing fresh weight of callus derived from hexaploid embryos was 20 g/liter. The addition of 2, 4‐D [(2, 4 dichlorophenoxy) acetic acid] to the basal medium was superior to the addition of IAA (indoleacetic acid), kinetin (6‐furfurylaminopurine) and auxin/cytokinin combinations for both callus initiation and growth. higher concentrations of 2, 4‐D (6 mg/liter) promoted callus initiation and growth, but prevented plant regeneration on callus subsequently subcultured to a medium without growth regulators. Histological observations gave evidence of formation of active growth centers or meristemoids in callus. These subsequently led to differentiated root primordia. Our study showed that triticale embryos behaved similar to other cereals in their callus initiation and plant regeneration traits.

Dislocations in NaClO 3 crystals in relation to growth mechanism from aqueous solution

The normal growth rates of {100} faces of NaClO 3 crystals have been measured under well controlled supersaturation ranging from 0.029 to 0.063. The growth mechanisms are investigated based on the growth rate versus supersaturation relation, together with the results of Bennema and Hosoya et al. Seven crystals grown in different supersaturation ranges are selected for X-ray topographic investigation, and the defect configurations are studied. Two types of growth defects are observed: straight line defects originating at the centres of seed surfaces are found in the crystals grown in the whole supersaturation range, whereas curved line defects are mainly found in the crystals grown in a lower supersaturation range. The latter defects are mostly screw dislocations, and the formers are dislocations with edge component, together with some screw dislocations. It is concluded that the straight dislocations are formed as a result of mismatch between the growth layers spreading inward from the edges and do not play the role of active growth centres, whereas the curved dislocations appear when spiral growth starts to operate, and play the role of active growth centres.

Anionic Polymerization of Methyl Methacrylate in the Presence of Piperidine

Abstract Anionic polymerization of methyl methacrylate (MMA) initiated by lithium tert-butoxide (t-BuOLi) was investigated in different mixtures of benzene and piperidine. The latter compound activates the associated alkoxide, as evidenced by the observed increase in the rate of polymerization, proportional to piperidine concentration and also by the lowering of the overall kinetic order of the polymerization reaction with respect to initial monomer concentration. However, at higher piperidine concentration the rate of the polymer growth significantly decreases after a short period of time; a probable reason for this retardation or termination effect is the decay of active growth centers by a termination reaction with the methacrylate carbonyl group. The molecular weight of the polymer is significantly lowered by even a small addition of piperidine as a result of increased initiator efficiency that leads to a higher absolute concentration of active centers and approaches the theoretical limit given by the...

Glucocorticoid-induced alterations in collagen of neonatal mouse condylar cartilage.

Neonatal mice were treated with a single dose of triamcinolone hexacetonide, a long-acting synthetic analogue of cortisol, and their mandibular condyles were studied ultrastructurally ten days thereafter. A pronounced decrease in the number and size of matrix granules (proteoglycans) was found in the cartilaginous matrix of triamcinolone-treated condyles. In contrast, a marked increase concomitant with significant structural changes was noted in collagen fibrils. An obvious enhancement of collagen fibrillogenesis was noticed in the pre-mineralizing extracellular matrix. Atypical, wider than normal, banded collagen fibrils were found to form dense meshworks which appeared to lack any specific orientation or organization. It is proposed that glucocorticoid hormones, given systemically to neonatal mice, interfere with regulatory mechanisms involved with the biosynthesis of cartilaginous matrical macromolecules, i.e., proteoglycans and collagen and thereby promote certain aging processes within active growth centers.

Patterns of Carbon Allocation in an Arctic Tundra Grass, Dupontia fischeri (Gramineae), at Barrow, Alaska

In Dupontia fischeri R. Br. the pattern of translocation of photosynthetically incorporated 14C was established within six hr after treatment in situ at Barrow, Alaska. More radiocarbon went to younger rather than older tillers. The most effective sinks were root, lateral root, and rhizome primordia and nonemergent tillers which were actively growing. Substantial amounts of radiocarbon appeared in the stem base and rhizome of the treated tiller. Although relatively little appeared in other plant parts, except for the sinks mentioned above, interdependence of tillers appeared to be maintained until flowering occurred. This pattern of distribution was established early in the season once the soil thawed, and growth began and was maintained until mid-August. Some translocation to active growth centers occurred even while the soil was thawing. Redistribution of radiocarbon to new root and leaf tissues produced after the time of treatment was observed. There was no autoradiographic evidence during the season to indicate storage of large amounts of mobilizable photosynthate in the stem base or rhizome of a tiller at the time these field studies were carried out.

PATTERNS OF CARBON ALLOCATION IN AN ARCTIC TUNDRA GRASS, DUPONTIA FISCHERI (GRAMINEAE), AT BARROW, ALASKA

In Dupontia fischeri R. Br. the pattern of translocation of photosynthetically incorporated 14C was established within six hr after treatment in situ at Barrow, Alaska. More radiocarbon went to younger rather than older tillers. The most effective sinks were root, lateral root, and rhizome primordia and nonemergent tillers which were actively growing. Substantial amounts of radiocarbon appeared in the stem base and rhizome of the treated tiller. Although relatively little appeared in other plant parts, except for the sinks mentioned above, interdependence of tillers appeared to be maintained until flowering occurred. This pattern of distribution was established early in the season once the soil thawed, and growth began and was maintained until mid‐August. Some translocation to active growth centers occurred even while the soil was thawing. Redistribution of radiocarbon to new root and leaf tissues produced after the time of treatment was observed. There was no autoradiographic evidence during the season to indicate storage of large amounts of mobilizable photosynthate in the stem base or rhizome of a tiller at the time these field studies were carried out.

The histochemistry of the human nail

The histological divisions of the nail suggested by Lewis have been confirmed by histochemical methods. Definite differences have been demonstrated between the dorsal, intermediate, and ventral nail plates. The upper or dorsal nail plate appears to have the hardest physical structure, and this is probably related to its high calcium content rather than to its disulfide bonding. The intermediate plate is formed from a different matrix and the cells undergo less cytolysis prior to keratinization than those of the dorsal plate. This region forms the main bulk of the nail and lies between the forward-growing dorsal plate and the upward-growing ventral plate. The latter appears to be formed directly from the cells of the nail bed, and as these grow upward they are simultaneously carried forward by the ventral and dorsal portions. Diseases of the nail may primarily affect one, two, or all of the active growth centers, and it is probably because of this that the diverse morphological clinical appearances are produced.

The Histochemistry of the Human Nail

The histological divisions of the nail suggested by Lewis have been confirmed by histochemical methods. Definite differences have been demonstrated between the dorsal, intermediate, and ventral nail plates. The upper or dorsal nail plate appears to have the hardest physical structure, and this is probably related to its high calcium content rather than to its disulfide bonding. The intermediate plate is formed from a different matrix and the cells undergo less cytolysis prior to keratinization than those of the dorsal plate. This region forms the main bulk of the nail and lies between the forward-growing dorsal plate and the upward-growing ventral plate. The latter appears to be formed directly from the cells of the nail bed, and as these grow upward they are simultaneously carried forward by the ventral and dorsal portions. Diseases of the nail may primarily affect one, two, or all of the active growth centers, and it is probably because of this that the diverse morphological clinical appearances are produced.