Autoradiographic studies on postnatal growth of the skull in young rats injected with tritiated glycine

The role of sutures in normal and abnormal craniofacial growth

The paper is a shortened version of a paper read at the symposium on craniofacial growth, in which the literature on various aspects of sutures was reviewed. Suture development, structure, growth, and closure are covered, and the response of sutures to orthopedic forces and their role in craniosynostosis exemplified. Rather than being an extensive review, references are included preferably to present diversity in results and methods within the subtitle of the symposium, 'mechanisms and study methods'.

Static magnetic field effects on the sagittal suture in Rattus norvegicus

Twenty-day-old Wistar albino rats were exposed to static magnetic fields by placing a neodymium-iron-boron magnetic over their sagittal suture. Cellular activity was monitored by the uptake of tritiated thymidine in control, north, south, and unoperated animals at 1, 3, 5, and 10 days (n = 10 per group). A total of 160 animals were used for this part of the study, with the animals examined 1, 3, 5, and 10 days after surgery. Bone remodeling was examined by tetracycline fluorescence with 10 animals allocated to 5- and 10-day periods for north and south poles (n = 10 per group) and control experiments. This consisted of the placement of unmagnetized alloy, similar in size and shape to the magnets, and also included unoperated animals (n = 5 per group). A total of 60 animals were used for the tetracycline study and were examined at 5 and 10 days after surgery. While the tetracycline examination revealed very little change, the thymidine reflected a reduction in thymidine uptake subsequent to placement of the magnet, reaching a maximal effect at 3 days and returning to a normal value thereafter. This questions the potential of static magnetic fields affecting cell mitotic activity as previously reported.

Candida myositis manifesting as a discrete neck mass

Endochondral osteogenesis was studied autoradiographically in ribs and tibiae of 32 Long-Evans rats injected with 1 µc/gm H³-thymidine at 6 days of age and sacrificed at intervals between 1 hour and 2 weeks later. Proliferation and specialization of bone cells were studied by analyses of (a) the percentage of mitoses which were labeled, (b) the percentage of labeled nuclei in bone cells, and (c) grain counts. The following conclusions were derived: The various types of bone cells represent different functional states of the same cell. Cell division is usually restricted to cells in the morphologically unspecialized "osteoprogenitor" state. Specialized bone cells arise by modulation of osteoprogenitor cells. The average cell generation time is shortest in the metaphysis, longest in the periosteum, and intermediate in the endosteum. The average duration of DNA synthesis is relatively constant (about 8 hours). With increasing length of generation time there is a slight increase in G₂ + mitosis, but the major change is a lengthening of G₁. After dividing, cells in the osteoprogenitor state may remain within the progenitor pool or undergo modulation of cell type, specializing as osteoblasts or becoming incorporated in osteoclasts.

The effect of sutural growth rate on collagen phenotype synthesis

We determined the ratio of newly-synthesized type III collagen to the total of type I and type III collagen in mouse interparietal sutural tissue at selected ages between birth and adulthood (36 weeks old). We incubated mouse calvaria explants in Trowell-type organ culture dishes for one h and then added [14C]-glycine for two h. We dissected the interparietal sutural tissues for collagen solubilization by limited pepsin digestion. Fluorographic visualization of separated radiolabeled collagens, after SDS-PAGE, found the ratio of collagen type III alpha-chains to the total type I and type III alpha-chains to be age-dependent. The proportion of type III alpha-chains at birth was quite high, but there was a significant drop (p less than 0.05) during the first two days of life, probably because of the sudden environmental change from in utero. The proportion of type III alpha-chains rose significantly from day 2 to day 4, reaching a maximum and then dropping significantly to about the same proportion as at birth by day 7. A further significant drop took place during the second week of life, with the proportion stabilized at around 3.5% at two weeks to ten weeks of age. A final significant drop during the eleventh week of life led to no detectable synthesis of type III collagen after 12 weeks of age. The changes in the collagen phenotype ratio did not relate to changes in body weight during growth and development, which suggests that the interparietal suture may have an independent maturing pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Sutures and forces: a review

This review gives a description of the biologic significance of craniofacial sutures with respect to growth and to growth corrections. Sutural growth and its regulation are discussed briefly. Morphogenesis of sutures, sutural morphology, both microscopic and macroscopic, the structure and function of the sutural periosteum and secondary cartilages, and the biochemical composition of sutures are described. Furthermore, in vivo and in vitro experiments, including transplantation experiments, are discussed. The relationship between extrinsic mechanical forces and the resulting tissue responses in sutures is given special attention. The present article describes the state of our knowledge on the interaction between sutures and forces, and indicates problems that need to be investigated.

A radioautographic study of the effect of age on the protein-synthetic and bone-deposition activity in interparietal sutures of male white mice

Groups of male white mice were killed at 4, 5, 6, 7, 8, 9 and 10 weeks of age 2 h after intraperitoneal injection with [3H]-proline. Radioautographic analysis of sections of the interparietal suture demonstrated significantly greater protein-synthetic activity in the para-osseous zones relative to the middle zone (p less than 0.01) and a plateau of lower protein-synthetic activity by 7-8 weeks of age (p less than 0.05). Groups of mice were selected at 4, 6, 8 and 10 weeks of age. Each mouse was injected intraperitoneally with [3H]-proline three times at one-week intervals. Sutural growth rate was determined from incremental lines revealed by radioautographs prepared from serial paraffin sections of the interparietal suture and demonstrated a stabilization of growth by 8 weeks of age. This, together with the grain counting data, suggested that a mouse of 7-8 weeks would provide a suitable model for experimental studies in sutural remodelling response without masking effects by normal growth.

Ossification of the skull of the growing hamster. Autoradiographic observations

Desmal ossification of the roof of the skull and of the alveolus of the incisor teeth of the mandible of growing hamsters and secondary ossification of the mandible were followed by autoradiography. Matrix production patterns as known from chondral ossification can be confirmed for desmal ossification as well. The secondary cartilage of the mandible shows an extremely low glycine turnover. These cells and the surrounding intercellular substance show different incorporation patterns as known for the epiphyseal cartilage of long bones. Secondary cartilage does not have growth functions for the mandible.

Characteristics of growing bone surfaces

Both bone-forming and bone-destructing cells may appear in different forms. This conclusion has been drawn as a result of compared observations from histomorphologic, histochemical and vital staining studies. The bone-forming cells may be cuboidal and situated in one or more rows along the bone surfaces, or may be flat. The type of cell reflects the rate of bone formation. The bone-resorbing cells may be big multinucleated cells or small mononucleated cells. The latter cell type is well-known from the literature although not referred to in textbooks of histology. Flat bone-forming cells and small mononucleated bone-resorbing cells resemble each other in the light microscope. Studies of bone growth with the aid of histomorphologic descriptions of cell types have to take this fact into account. Otherwise, erroneous conclusions may easily be drawn.

Comparison of whole calvarial bones and long bones during early growth in rats. II. Turnover of calcified and uncalcified collagen masses

The increase of total collagen and its destruction were compared for whole calvaria and long bones from young growing rats prelabeled in utero with 3H-L-proline. Rats were compared from birth to 16 weeks of age. Long bones and calvaria were isolated as intact anatomical units for autoradiography or separated by collagenase into calified and uncalcified collagens. Autoradiography using 14C-L-proline demonstrated eccentric modeling of bone collagen. With growth the mass of calcified collagen (bone) increased rapidly in calvaria and long bones. A similar increase in the mass of uncalcified collagen (mainly cartilage) occured in the long bones; a very small increase occurred in the fibrous tissue of calvaria. Total and specific radioactivities of collagens at each age were compared to that present at birth. With growth remodeling an almost complete loss of pre-existing radioactive collagen occurred from uncalcified fibrous tissue of calvaria as compared to a smaller but substantial loss from the uncalcified cartilage of long bones. A marked loss of calcifed collagen occurred in long bones as compared to a smaller loss from calvarial bones. The istopic data indicate a large turnover of fibrous tissue (type I collagen) with growth remodeling as compared to a smaller turnover of bone (calcified, type I collagen) and cartilage (typc I collagen). The turnover rate of skeletal collagens depends upon whether the collagen is calcified or not, and not upon the type of collagen.

An anatomical, histochemical, and autoradiographic study of the ever-growing molar dentition of Microtus with comments on the role of structure in growth and eruption

An analysis of the microanatomy of the molar dentition of Microtus utilizing histological, histochemical and autoradiographic techniques reveals a complex architecture with distinctive morphogenic mechanisms which respond to the functional requirements of the organism. These mechanisms include; the maintenance of continued growth and eruption of the molars to compensate for continued hard tissue loss from wear at the occlusal surface of the crown throughout the entire lifespan of the orgainism and a positive feedback repair mechanism to protect the growth systems from the potential destruction this normal occlusal wear could initiate. An awareness and understanding of these phenomena is of significant value for interpreting palentological specimens and formulating a theoretical model for interpreting the evolution of Microtine molar dentitions.

Comparison of whole calvarial bones and long bones during early growth in rats. Histology and collagen composition

The distribution of ossified collagen (bone) and uncalcified collagen (fibrous tissue and cartilage) was compared histologically for rat and dog calvaria at birth. The relative amount of bone and uncalcified collagen was quantitated morphologically for rat calvaria during the first four weeks of rapid growth. Whereas dog calvaria are essentially ossified at birth, rat calvaria at birth consist mostly of fibrous tissue but rapidly become ossified with growth. Bacterial collagenase was used to separate uncalcified collagen from calcified collagen of whole membranous bones (frontal and parietal) and long bones (femur and humerus) at birth from man, monkey, dog, guinea pig, rabbit and rat. By this means quantitative changes in the relative fractions of the two forms of collagen were determined during the first eight weeks of postnatal growth for each type of rat bone. Quantitative biochemical data on whole rat bones (calvarium, femur, humerus) confirmed measurements based on histology which showed that at birth rat calvaria are mostly uncalcified as compared to other species whose bones are mostly ossified at birth. With growth rat membranous bones ossify more rapidly than long bones.