Long bone lengthening occurs at the growth plate (GP) by well-regulated chondrocyte proliferation, hypertrophy and terminal matrix deposition. GP chondrocyte (GPC) hypertrophy has been implicated to be the main determinant of bone growth rate; however the mechanism is poorly understood. The work of this thesis examined some of the cellular process that drives the chondrocyte swelling or hypertrophy particularly in a mammalian post natal GPs using living in situ GPC and fixed GP tissues. Confocal scanning microscopy (CLSM) was used to determine living in situ GPC volume and dimension changes in proliferative zone (PZ) through to hypertrophic zone (HZ) chondrocytes of different GPs of various bones. While PZ cells showed similar volumes and dimensions, HZ cells varied in different GPs, even within the same long bone but at opposite ends. However, the hypertrophic cell volume measured at a single post natal age (day 7) was independent of the corresponding bone length. This could reflect a complex interplay between local and systemic factors in different GPs, which occurs throughout the active phase of bone growth. Maintaining GPC morphology was critical in studying GPC hypertrophy using fixed tissues. This work highlighted a problem caused by conventional fixative solutions, which caused up to 44% hypertrophic GPC shrinkage following GP fixation. This artifact appeared to be associated with the hyperosmotic nature of the fixatives used and could be abolished by adjusting the fixative osmolarity close to physiological level (280 mOsm), or could be significantly reduced by bisecting bone tissues prior to tissue fixation. This thesis proposed roles for plasma membrane transporter(s) in mediating GPC hypertrophy. This hypothesis was tested by examining roles of sodium-hydrogen exchanger (NHE) and anion exchanger (AE) in GPC hypertrophy using an ex vivo bone growth inhibition model. Inhibition of bone growth by inhibitors of NHE (EIPA) and AE (DIDS) respectively was shown to be dose-dependent. The histology of bones demonstrated that the late HZ width was significantly reduced in GPs treated with EIPA or DIDS. Although in situ GPC volumes in the PZ and HZ were not notably different in DIDS-treated GP, the cell volumes in both zones were significantly reduced by EIPA treatment. Fluorescence immunohistochemistry revealed distinctive cellular localisations of NHE1 and AE2 in the PZ and early HZ. These results suggest a possible role of AE in mediating GPC volume increase in PZ chondrocytes and those in the early stages of cell hypertrophy, whereas NHE could possibly maintain intracellular pH of GPC throughout all GP zones. This thesis has characterized various changes in volume and dimensions of living in situ GPC from PZ through to HZ of different GPs of postnatal rats. This work emphasized the importance of fixative osmolarity in order to accurately preserve the normal volume/morphology of cells within tissues. Most importantly, this thesis confirmed a potential role of the plasma membrane transporters, AE and NHE in GPC hypertrophy of growing bones.

Mechanical stress exerted on long bones stimulate ossification and it has been shown that the mechanical variable frequency promotes osteogenesis. This ex-vivo study aimed to investigate how compressive and cyclic loading frequency impacts longitudinal growth of long bones. Three separate experiments were performed utilizing fetal Sprague-Dawley rat bones as experimental model. In the first two trials metatarsals where used while tibias were tested in the third trial. The bones were loaded once with a material testing system, cultured in an incubator and had their length measured on several occasions throughout their growth period. Loading protocol and days of length measurement differed between the trials. The first trial failed, since all of the control bones decreased in length in relation to the day of loading, while they should at least have grown 30% on the fifth day after loading. The results obtained from the second trial indicate that the frequency 0.4 Hz has a great impact on longitudinal growth, with a length increase of 50%-60% in relation to the day of loading. A conclusion regarding the other frequencies studied could not be made due to high spread of length alteration data. The tibias from the last trial did not show any significant results. Moreover, it was concluded that compressive and cyclic loading do promote longitudinal growth, despite the great variation in length alteration for most of the bones, including the control bones. The findings of this study could serve as a foundation for a research study further investigating the relation between frequency and longitudinal growth.

abstract: The process of combining data is one in which information from disjoint datasets sharing at least a number of common variables is merged. This process is commonly referred to as data fusion, with the main objective of creating a new dataset permitting more flexible analyses than the separate analysis of each individual dataset. Many data fusion methods have been proposed in the literature, although most utilize the frequentist framework. This dissertation investigates a new approach called Bayesian Synthesis in which information obtained from one dataset acts as priors for the next analysis. This process continues sequentially until a single posterior distribution is created using all available data. These informative augmented data-dependent priors provide an extra source of information that may aid in the accuracy of estimation. To examine the performance of the proposed Bayesian Synthesis approach, first, results of simulated data with known population values under a variety of conditions were examined. Next, these results were compared to those from the traditional maximum likelihood approach to data fusion, as well as the data fusion approach analyzed via Bayes. The assessment of parameter recovery based on the proposed Bayesian Synthesis approach was evaluated using four criteria to reflect measures of raw bias, relative bias, accuracy, and efficiency. Subsequently, empirical analyses with real data were conducted. For this purpose, the fusion of real data from five longitudinal studies of mathematics ability varying in their assessment of ability and in the timing of measurement occasions was used. Results from the Bayesian Synthesis and data fusion approaches with combined data using Bayesian and maximum likelihood estimation methods were reported. The results illustrate that Bayesian Synthesis with data driven priors is a highly effective approach, provided that the sample sizes for the fused data are large enough to provide unbiased estimates. Bayesian Synthesis provides another beneficial approach to data fusion that can effectively be used to enhance the validity of conclusions obtained from the merging of data from different studies. / Dissertation/Thesis / Doctoral Dissertation Psychology 2017

In vivo studies of mechanical loading on bone have suggested that load magnitude is one of the parameters that play a vital role in bone adaptation. This study examined how longitudinal growth of immature rat metatarsals is affected by different load magnitudes. The main hypotheses were that the longitudinal growth of immature bone would decrease with increased compressive load magnitude, and that the longitudinal growth would be more decelerated the higher the load mag- nitude. The three middle metatarsal bones in the back paws of 19-20 days old Sprague-Dawley rat fetuses were extracted. Metatarsal bones were loaded with 0.05 N, 0.25 N, 1.25 N and 6.25 N. Loading rate and number of cycles were constant at 0.01 mm/sec and 10 cycles respectively. Length measurements occurred every 2-3 day. Concluded from the study was that a load magni- tude of 0.05 N resulted in an increased longitudinal growth, compared to unloaded bones. For the other load magnitudes the results were insufficient and inconsistent and therefore nothing could be suggested for them. The problem remained as before and further studies are needed.

Objectives: To determine if temporomandibular joint (TMJ) compressive stresses during incisor biting (1) differed between growing children over time, and (2) were correlated with Frankfort Horizontal-mandibular plane angle (FHMPA, 8) and ramus length (Condylion-Gonion (Co-Go), mm). Materials and Methods: Three-dimensional anatomical geometries, FHMPA and Co-Go, were measured longitudinally from lateral and posteroanterior cephalographs1 of children aged 6 (T1), 12 (T2), and 18 (T3) years. Geometries were used in numerical models to estimate subject-specific TMJ eminence shape and forces for incisor bite-forces of 3, 5, and 8 Newtons at T1, T2, and T3, respectively. TMJ compressive stresses were estimated via two steps: First, TMJ force divided by age-dependent mandibular condylar dimensions, and second, modified by loading surfaces' congruency. Analysis of variance and Tukey honest significant difference post-hoc tests, plus repeated measures and mixed effects model analyses were used to evaluate differences in variables between facial groups. Regression analyses tested for correlation between agedependent compressive stresses, FHMPA, and Co-Go. Results: Sixty-five of 842 potential subjects had T1-T3 cephalographs and were grouped by FHMPA at T3. Dolichofacial (FHMPA ≥ 27°, n=36) compared to meso-brachyfacial (FHMPA, 27°, n=29) subjects had significantly larger FHMPA at T1-T3, shorter Co-Go at T2 and T3 (all P < .01), and larger increases in TMJ compressive stresses with age (P < .0001). Higher compressive stresses were correlated with larger FHMPA (all R2 ≥ 0.41) and shorter Co-Go (all R2 ≥ 0.49). Conclusions: Estimated TMJ compressive stress increases from ages 6 to 18 years were significantly larger in dolichofacial compared to meso-brachyfacial subjects and correlated to FHMPA and Co-Go.