Edgar A. Tonna

Cellular Response to Fracture Studied with Tritiated Thymidine

An autoradiographic study of femoral-fracture repair using tritiated thymidine was made on forty-two female mice, five weeks of age. Assessment of the periosteal labeling index was obtained from one hour to fourteen days after fracture. Results showed that the initial proliferative response is seen in the periosteum and adjacent soft tissues sixteen hours after fracture. No increase in proliferation was observed at eight hours. The reaction was not limited to the fracture site but extended along the entire femoral diaphysis. The maximum increase of the labeled periosteal population (25.4 per cent) was observed at thirty-two hours after fracture. After thirty-two hours, the size of the labeled population decreased with increasing time. The decrease was more apparent away from the fracture site, so that within five days of fracture the proliferative potential was similar to that of the non-fractured control femur. Fourteen days after fracture, the labeled population of periosteal cells at the fracture site was still above the value of the controls. The course of fracture repair was followed autoradiographically.

Autoradiographic Studies of Cell Proliferation in the Periosteum of Intact and Fractured Femora of Mice Utilizing DNA Labeling with H3-Thymidine.∗†

Summary An autoradiographic study of cell proliferation in intact and fractured femoral periosteum of mice using H3-thymidine showed that osteogenic cells are a relatively quiescent cell population awaiting a signal for proliferation and transformation as in fracture repair. Osteogenic cells constitute a self-sustaining cell population, which becomes diminished in size with increasing age. Osteoblasts are in part self-reproducing and in part are produced by transformation of pre-osteoblasts. The authors wish to thank Miss M. Pavelec for her technical assistance and Mr. Robert F. Smith for the photomicrography.

Functional Demands on the Cell Proliferative Activity of the Rat Periodontium Studied Autoradiographically

Functional demands on the cell proliferative activity of the rat periodontium were studied autoradiographically with tritiated thymidine. Labeling indexes were assessed for fibroblasts, osteoblasts, and cementoblasts in the regions of the first molars of the maxilla and the mandible. Fibroblasts had the highest labeling index.

Changes in the Skeletal Cell Proliferative Response to Trauma Concomitant with Aging

An autoradiographic study of femoral-fracture repair using tritiated thymidine was made on thirty-five female mice, eighteen months of age. Assessment of the periosteal labeling index was obtaibed from eight hours to fourteen days after fracture. Results showed that the intial proliferative response to trauma occurs after eight hours and that the response extends throughout the shaft. After forty-eight hours the periosteal response away from the fracture site, having reached a maximum labeling index of 0.110, decreases rapidly so that the non-fractured level (0.005) is reached by the fourth day. At the fracture site the labeling index continues to increase to a maximum labeling index of 0.180 at four days, then decreases rapidly, reaching a plateau of approximately 0.045. In comparing the present results with those of young mice it is apparent that the difference in fracture healing is quantitative and not qualitative. Some old-looking, flat periosteal osteogenic cells are still capable of desoxyribonucleic acid synthesis and respond to trauma at the same time as similar cells in five-week-old mice. Flat, elongated periosteal cells, in response to trauma, altered their morphological characteristics so that in many instances they were indistinguishable from cells of younger mice. In older mice the formation of the internal callus progresses more rapidly than the formation of the external callus. This appears to be largely due to the proliferative response of the osteogenic cells within the intertrabecular spaces near the fractured ends. The over-all labeling of periosteal cells in older mice is less than that encountered in young mice.

The cell proliferative activity of parodontal tissues in aging mice

Abstract One hundred and thirty-eight short-lived mice of the Brookhaven National Laboratory inbred strain of Swiss albino 5, 26, 52, 78 weeks of age were used to determine the normal proliferative activity of the parodontal tissues comprising the mesial aspects of the maxillary 1st molars and the associated changes concomitant with aging. Labelling indices were obtained following grain-counting of autoradiographs. Each animal received 1 μCi of tritiated thymidine per gram body weight 1 hr prior to death. Five micron sections were cut from paraffin blocks prepared routinely following EDTA decalcification. Results showed that the order of proliferative activity was similar at all ages. The proliferative activity was highest in gingival epithelium while all other tissue compartments were significantly lower. In lessening order, these were 4 connective tissue compartments, 2 osteogenic layers and lastly the cementoblastic layer. A progressive decrease in labelling indices to 52 weeks of age was generally observed with increasing age. This was subsequently followed by a rise in the number of labelled cells, especially in the gingival epithelium and connective tissue below the crevicular region. A survey of the tissues for inflammatory reactions revealed increased incidence with advancing age, especially at 78 weeks of age. The crevicular region of the epithelium, the connective tissue below and the periapical periodontium were the usual inflammatory sites. It was concluded that increased labelling observed in animals older than 52 weeks of age was associated with increased incidence of inflammation at susceptible sites coincidental with histological age changes in parodontal tissues.

An autoradiographic study of the mouse incisor using tritiated histidine

Abstract An autoradiographic study of the mouse incisor after tritiated histidine administration revealed a rapid turnover of the radioactivity of ameloblasts. The enamel matrix was rapidly and intensively labelled within 1 hr. Odontoblasts and dentinal matrix were much less labelled. The distribution of the silver grains over the enamel matrix at different time intervals can be correlated with the growth of the incisor. The observation that histidine is an important component of enamel matrix was confirmed autoradiographically.

Cell Proliferation Kinetics of the Internal Enamel Epithelium of Mouse Incisors

SYNOPSIS IN INTERLINGUA CINETICA DEL PROLIFERATION CELLULAR IN LE EPITHELIO INTERO-ADAMANTIN DEL INCISORES DE MUSES.-Un analyse cinetic del proliferation de preameloblastos in le incisores de muses esseva effectuate a base de autoradiographias post le administration a thymidina a tritium. Le minime tempore generatori estimate a base del curva de mitosis esseva 14,2 horas. Le minime tempore del synthese de acido deoxyribonucleic, le minime tempore postsynthetic, le minime tempore mitotic e le minime tempore presynthetic esseva 5,5, 0,82, 0,5, e 7,4 horas, respectivemente. Le total tempore generatori medie de 24,0 horas esseva calculate a base del proportion de tempore medie del synthese de acido deoxyrobonucleic (7,2 horas) al indice de marcage (0,30). Esseva trovate que durante le processo de maturation preameloblastic quatro successive divisiones cellular occurre ante que le cellulas deveni ameloblastos functional. Le minime tempore de transito del preameloblastos es approximativemente 56,8 horas.

A SERIAL AUTORADIOGRAPHIC ANALYSIS OF H3-GLYCINE UTILIZATION AND DISTRIBUTION IN THE FEMORA OF GROWING MICE

The localization, distribution and cellular turnover of tritium labeled-glycine were followed and quantitatively assessed autoradiographically in the femora of young mice. Initially the labeled amnino acid was taken up by the cellular phase of the skeletal system, and was observed within cells 15 minutes after isotope administration. Thirty minutes after H3-glycine injection represented the peak of cellular uptake (assessed by autoradiographic grain density over cells). Shortly after cells incorporated H3-gycine, silver grains appeared over newly deposited bone and cartilage matrices. At the surfaces of bone, silver grains were arranged in bands which were followed up to 14 days after H3-glycine administration. These growth bands were found over deeper layers of bone with increasing time. The movement of these bands was illustrated and discussed. Labeling of cartilage matrix was diffuse.

AN AUTORADIOGRAPHIC STUDY OF THE LOCALIZATION AND DISTRIBUTION OF TRITIATED HISTIDINE IN BONE

The localization, distribution and cellular turnover of tritium labeled-histidine was followed autoradiographically in the femora of young mice. Initially the labeled amino acid was taken up by the cellular phase of the skeletal system within the first hour after isotope administration. From 1 to 4 hours, intracellular histidine appeared within newly deposited cartilage and bone matrix. By 14 days skeletal cells had lost their label, however, red blood cells were still labeled at 14 days.

A [3H]-thymidine autoradiographic study of cell proliferative activity of injured parodontal tissues of 5-week-old mice

Abstract Evaluation of the cell proliferative changes which occur in response to trauma in young mice was investigated autoradiographically. Forty-four 5 week-old female mice of the short-lived Brookhaven National Laboratory (BNL) strain were gingivectomized surgically, removing the papilla mesial to the maxillary first molar. One hour prior to death, each animal received 1.0 μCi of tritiated thymidine per g of body weight by subcutaneous injection. Following death, the maxillae were removed, and the appropriate tissues were prepared for histologic and autoradiographic studies. Labelling indices were determined of various parodontal tissue cell compartments. The results were compared with previously published control values and rat data. Response of the mouse parodontal tissues to injury was, by and large, similar to that of the rat, with the exception that the proliferative activity of mouse tissues was significantly lower and occurred sooner following injury. The differences do not appear to be biologically significant in young animals. On the basis of the present findings, it was concluded that the size of the normal proliferative activity cannot be taken as (1) an index of the rate of repair, (2) an indication of the required length of repair, or (3) a measure of the proliferative capacity of the tissue. Normal labelling indices reflect only the level of cell turnover occurring in a given cell compartment, at a given anatomical site, in response to current physiological demands of the organism.