Computer simulations of chondrocytic clone behaviour in rabbit growth plates.

The growth behaviour of chondrocytic clones in the cell columns of the proximal tibial growth plates of young rabbits was modelled in computer simulations. Simulations were performed, modelling either clones in large groups of columns or clones in one single column. The former were based on morphological data and measurements of cell columns from an earlier study while the latter utilised previous findings of cellular kinetics in rabbit growth plates.

Comparative cell kinetics of avian growth plates.

New data on the cell kinetics of the cartilage growth plates in the chicken, budgerigar and rhea derived from studies with tritiated thymidine labelling are given. Quantitative histological measurements on growth plates from leg bones (tibiotarsus, tarsometatarsus and a phalangeal bone) in a further five species of birds are presented. Counts of flat cells and measurements of the average diameter of hypertrophic cells were made for each growth plate.

Cell kinetics and longitudinal bone growth in birds.

The theory that links cell division in epiphyseal cartilage plates to overall growth of long bones has been extended from linear growth systems to those in which proliferating and hypertrophied cells are not arranged in columns. Consideration has also been given to the analysis of non-parallel growth systems. The theory is illustrated by examples from the growth of chicken bones.

In vitro thymidine labelling in human and porcine growth plates.

An in vitro technique has been used to label dividing cells in the growth plates of human bones with tritiated thymidine. The patterns of labelling in autoradiographs of human plates are described and values given for the labelling index, the number of cells in the proliferation zones and the heights of hypertrophied cells. In two of the four subjects no labelled cells were found in the growth plates and possible causes for these failures are discussed.

Cell kinetics of growth cartilage in spondylo-metaphyseal chondrodysplasia (smc) mice.

The gene for spondylo-metaphyseal chondrodysplasia (smc) in the mouse disrupts the formation of growth plate cartilage. No cartilage columns are found in the head of the tibia and secondary centres of ossification appear very late. The number of cells labelled with tritiated thymidine is sharply reduced at 16, 18 and 21 days of age but hypertrophic cell height is normal.

Cell kinetics of growth cartilage of achondroplastic (cn) mice.

Mice homozygous for the recessive gene achondroplasia (cn) aged 16 and 17 days and some homozygotes aged 22-34 days have disruptions in the growth of the proximal tibial growth plate which are due solely to reduced hypertrophic cell height. A second class of homozygote, distinguishable at 22 days, has a greater disruption due to much reduced hypertrophic cell height, reduced labelling index and reduction of the number of cells in the effective proliferative zone.

Cell kinetics of growth cartilage in stumpy: a new chondrodystrophic mutant in the mouse.

The proximal growth plates of the tibiae in normal and stumpy mice aged 10-41 days were studied. Autoradiographic studies using tritiated thymidine enabled the size of the proliferating cell population and the labelling indices of the growth plates to be determined. Hypertrophic cell heights were also measured.

Physical measurements with a high-energy proton beam using liquid and solid tissue substitutes.

The measurement of the physical parameters of a high-energy proton beam, using a range of liquid and solid tissue substitutes, is described. The system, the detectors used and the experimental verification of the tissue equivalence of the new tissue substitutes is presented. The measurements with the scattered but uncollimated proton beam in muscle- and brain-equivalent liquids and in water are compared to similar data obtained from the scattered but collimated beam.

Irregular radiation response of a chondrosarcoma.

The DC II mouse chondrosarcoma is a potentially valuable radiobiological tumour system since it has been observed to recover from radiation injury by regrowth from clones that may be counted in histological sections. Unfortunately, the normal growth of this tumour following s.c.

Cell kinetics and the control of growth in long bones.

The cell kinetics of the cartilage growth plate are outlined and discussed in terms of the probable levels of control on the system. Possible mechanisms of growth control at the cellular level are examined for (i) the rate of cell division in the proliferation zone, (ii) the command to differentiate that limits the size of the proliferation zone and (iii) the ageing process in the cartilage plate. The evidence of cell kinetics does not point unequivocally to any particular mechanism.

Longitudinal bone growth of the human femur.

A study is presented of the histological structure and growth rate of the growth plate at the distal end of the femur in normal children. From a comparison of quantitative histological information from post-mortem specimens with measurements on serial radiographs it is estimated that the distal growth plate contributes about 66% of the total longitudinal growth of the bone. The marked differences between rodent and man indicate that caution is required in extrapolating data from these animals to man.

Quantitative histology of the human growth plate.

This paper describes a study in the human femur of the relationship between cell division in growth cartilage and overall bone growth. Growth rates for the distal femur from birth to eighteen years were determined from serial radiographs available from the Harpenden Growth Study; An average of 1-4 cm/year was found for the ages of five to eight years. The development of the growth plate is illustrated in a series of photomicrographs of femur sections.

Cell kinetics of a chondrosarcoma.

The cell kinetics of the transplantable DC-II mouse chondrosarcoma have been studied by the pulse labelled mitoses method. The analysis gave the following estimates for the phases of the cell cycle: G1, 10-5 hr; S, 9-5 hr; G2, 4 hr with an intermitotic time of 23-5 hr. Consideration of the overall growth of the tumour indicated that the growth fraction and cell loss factor both had values of about 0-5.

An approach to microdosimetry in a pi- meson beam using nuclear emulsions.

K5 emulsions 10 mum thick were exposed at various depths in a perspex phantom to a 70 MeV pi- meson beam and counts taken of the tracks in emulsion volumes 7x7x10 mum3. Data are presented on the number of track events and also the total number of grains associated with each event in each of four categories spanning the LET range of the secondary particles. The number of heavy tracks (category 4) shows an increased incidence in the region of the stopping pi- mesons (14-5 cm in perspex) while the number of single grains (category 1) decreases with depth.