Secondary Osteons Research Articles

Dose-Dependent Impact of Bee Pollen Supplementation on Macroscopic and Microscopic Structure of Femoral Bone in Rats.

Simple SummaryBee pollen is considered an interesting feed supplement with beneficial health impacts. It contains many basic nutritional compounds that improve growth performance, development and immune response of animals. However, its effect on bone structure has been studied to a limited extent and the results published so far are ambiguous. Therefore, the impact of bee pollen supplementation on selected bone characteristics of rats was investigated in our study. We determined a dose-dependent effect of bee pollen administration on macroscopic and microscopic structure of femoral bone. Several negative effects of bee pollen supplementation at the level of 0.75% on bone features have been demonstrated, while the level of 0.5% did not influence these properties in rats.Bee pollen has been successfully used as a feed additive with beneficial impacts on productive, reproductive, and immune conditions of animals. However, its effect on bone structure and bone health remains controversial. Therefore, the purpose of our study was to examine the impact of bee pollen supplementation on macroscopic and microscopic structure of a femoral bone using rats as suitable animal models. Male rats (1 month-old) were assigned into three groups: control (C group) that was fed a standard diet without bee pollen and two bee pollen supplemented groups (P1 and P2 groups) that received an experimental diet including 0.5% and 0.75% of bee pollen, respectively, for 3 months. A number of unfavorable effects of 0.75% bee pollen administration on bone weight, cortical bone thickness, calcium content, alkaline phosphatase activity, sizes of primary osteons’ vascular canals, Haversian canals and secondary osteons in the cortical bone have been recorded, whereas these bone parameters were significantly decreased in the P2 group versus the C group. On the contrary, the concentration of 0.5% did not affect any of bone features mentioned above. In conclusion, the impact of bee pollen supplementation on femoral bone structure of rats depends on the dose used.

Age-related changes of the histological structure in the limb bones of the domestic fowl

To assess the possibility of using the bird bone tissue as a recording structure, the histomorphological parameters of the bone tissue of laying hens of the lohman brown cross from the Kirov region (9 females and 1 male) aged from 1 month to 7.5 years were investigated. The comparison of the cross-sections of the humerus and femur, the phalanx of the toe and tibiotarsus of a 6-year-old individual revealed that tibiotarsus is the least susceptible to resorption. For further research in 7 individuals, this bone was divided into 3 sections (T1, T2 and T3), for each of which the description and measurement of the microstructure of the cross sections was carried out. It was revealed that the process of resorption of the periosteum begins at 2.5 years of age with the appearance of primary osteons. At the age of 3.5 years and later they penetrate into all layers of the periosteum, locating in chains between the lines of arrested growth. At 4.5 years of age, secondary osteons appear in the place of the primary ones, and areas of resorption are formed at the intersection of the Haversian and Volkmann canals. At the age of 5.5 years the medullary bone disappears from the bone cavity, rounded cavities filled with centripetal deposition of new bone tissue at the edges appear within the resorption sites. At the age of 6-7 years, bone tissue degeneration occurs, when the small cavities enlarge and merge into large resorption cavities, up to the complete resorption of the mesost. In the distal part of tibiotarsus (T3), a prolonged apposition of the layers of the periosteum and the latest resorption were recorded. The increase of the thickness of the periosteum and a decrease in the density of the osteon population was revealed by the morphometry of cross sections of the center of diaphysis. The sites of tibiotarsus where the age of females corresponds to the lines of growth layer of the periosteum were determined. The sites with additional lines of the arrested growth were demarcated. It was concluded that the periosteal layer of the domestic fowl tibiotarsus in the distal and proximal sites are suitable as a recording structure.

Intraskeletal Osteohistovariability Reveals Complex Growth Strategies in a Late Cretaceous Enantiornithine

Most crown-birds experience rapid growth, reaching adult size within a year. Rapid growth strategies evolved within Aves multiple times during the Cretaceous, documented in the Confuciusornithiformes and the Ornithuromorpha. In contrast, osteohistological data suggest the Enantiornithes, the dominant clade of Cretaceous terrestrial birds, were characterized by much slower growth rates that were sustained longer into adulthood. Here we provide evidence for a unique growth strategy involving relatively rapid growth in the Late Cretaceous avisaurid enantiornithine,Mirarce eatoni. Multiple appendicular skeletal elements were sectioned for osteohistological analysis. These show remarkable intraskeletal variation, and high levels of variation even between individual sections. The radius is composed of parallel-fibered bone, similar to histological descriptions in other enantiornithines. Other elements, in contrast, differ markedly from other members of the clade. The humerus is composed of parallel-fibered bone with a middle layer of incipient fibrolamellar bone and several growth lines in the outer circumferential layer and near the endosteal border. The endosteal and periosteal layers of slow-growing bone indicate cyclical variation in growth rates. The femur shows regions of coarse compact cancellous bone and parallel-fibered bone with numerous secondary osteons, and only a single growth line. The tarsometatarsus is predominantly fibrolamellar in texture, with several asymmetrical growth lines located throughout the cortex; this element exhibits strong cortical drift. Growth lines in both the endosteal and periosteal portions of the cortex indicate that, like the humerus, growth rates of this bone varied cyclically. The two phalanges studied here are composed of parallel-fibered bone with extensive evidence of and remodeling over possible regions of coarse compact cancellous bone. AlthoughMirarceis one of the largest known enantiornithines, slow and protracted growth documented in similarly-sized taxa suggests this bone texture is not merely a size-related scaling effect. These findings indicate that by the Late Cretaceous, some enantiornithines had evolved absolutely higher growth rates and more complex life history strategies, in which growth rates varied across the skeleton. Furthermore, a variety of strategies were employed to achieve adult size and morphology, including cycles of slow and fast growth, asymmetrical growth within a single element, and extensive remodeling.

An examination of histomorphometric relationships in the anterior and posterior human femoral cortex.

Static cortical bone histomorphometry utilised in forensic age-at-death estimation generally examines only the anterior femoral mid-shaft, as biomechanical strain at the posterior femur is thought to result in increased bone remodelling, osteon density and adversely affect age-at-death estimates. As osteon density increases there is a corresponding decrease in geometric variables, such as osteon area and Haversian canal diameter. The present study tests whether the inverse relationship between osteon density and osteon geometry is reflected in a modern documented Australian sample, and if this relationship differs between the anterior and posterior femoral mid-shaft. The study sample comprises 215 femoral microradiographs (117♂ 98♀) of recorded age (18‒97years) from the Melbourne Femur Reference Collection (MFRC). The following variables were measured in Image J across six 1mm2 regions of interest (ROIs) from the anterior and posterior; mean intact and fragmentary secondary osteon count, osteon population density, osteon and Haversian canal area, perimeter, and diameter. Osteon area was positively correlated with Haversian canal size and shape metrics, and negatively correlated with osteon density. Chronological age was significantly correlated with most variables. There were significant between-group effects between the youngest (18‒34years) and all other age groups (35‒49, 50-74 and 75 + years) for both regions. Our findings support an increased rate of remodelling associated with decreases in osteon geometry in the anterior and posterior femur. Future studies should examine static osteon histomorphometry using anterior and posterior measurements in larger samples of documented age and sex.

Bone remodeling in the longest living rodent, the naked mole-rat: Interelement variation and the effects of reproduction.

The pattern of bone remodeling of one of the most peculiar mammals in the world, the naked mole-rat (NMR), was assessed. NMRs are known for their long lifespans among rodents and for having low metabolic rates. We assessed long-term in vivo bone labeling of subordinate individuals, as well as the patterns of bone resorption and bone remodeling in a large sample including reproductive and non-reproductive individuals (n=70). Over 268 undecalcified thin cross-sections from the midshaft of humerus, ulna, femur and tibia were analyzed with confocal fluorescence and polarized light microscopy. Fluorochrome analysis revealed low osteogenesis, scarce bone resorption and infrequent formation of secondary osteons (Haversian systems) (i.e., slow bone turnover), thus most likely reflecting the low metabolic rates of this species. Secondary osteons occurred regardless of reproductive status. However, considerable differences in the degree of bone remodeling were found between breeders and non-breeders. Pre-reproductive stages (subordinates) exhibited quite stable skeletal homeostasis and bone structure, although the attainment of sexual maturity and beginning of reproductive cycles in female breeders triggered a series of anabolic and catabolic processes that up-regulate bone turnover, most likely associated with the increased metabolic rates of reproduction. Furthermore, bone remodeling was more frequently found in stylopodial elements compared to zeugopodial elements. Despite the limited bone remodeling observed in NMRs, the variation in the pattern of skeletal homeostasis (interelement variation) reported here represents an important aspect to understand the skeletal dynamics of a small mammal with low metabolic rates. Given the relevance of the remodeling process among mammals, this study also permitted the comparison of such process with the well-documented histomorphology of extinct therapsids (i.e., mammalian precursors), thus evidencing that bone remodeling and its endocortical compartmentalization represent ancestral features among the lineage that gave rise to mammals. It is concluded that other factors associated with development (and not uniquely related to biomechanical loading) can also have an important role in the development of bone remodeling.

Microanatomy and histology of frontal bones in two species of Albanerpeton sensu lato (Lissamphibia: Albanerpetontidae) from the Upper Cretaceous Oldman Formation in southeastern Alberta, Canada

ABSTRACT Albanerpetontids are an extinct clade of salamander-like lissamphibians characterised by features such as fused frontals and sculptured skull roof bones. Here we provide a histological analysis of the fused and sculptured frontals in two Late Cretaceous species of the type genus Albanerpeton sensu lato that differ in body size: moderate-sized ‘Al.’ gracile and larger-sized ‘Al.’ nexuosum. Despite general similarities in microanatomy/histology (no sutural trace remains between left and right frontals; sculpture formed by appositional growth of bone; predominance of parallel-fibred bone; and lack of growth marks, secondary osteons, and Sharpey’s fibres) and the presence of sub-ventrolateral crest canals (possible albanerpetontid synapomorphy), ‘Al.’ nexuosum differs from ‘Al.’ gracile in exhibiting: a distinct three-layered diploë structure; bone remodelling; a higher degree of vascularisation; and more numerous osteocytic lacunae. We suggest that (1) histological differences between ‘Al.’ gracile and ‘Al.’ nexuosum are related to differences in absolute body sizes and relative development of sculpture and robustness of frontals and (2) the sub-ventrolateral crest canals in albanerpetontids are homologous to the canalis arteriae orbitonasalis in modern anurans. Two features (internal vascularisation and lack of Sharpey’s fibres) support a recent suggestion that albanerpetontids may have relied entirely on cutaneous respiration.

Study of ossification in long bones of aborted human fetuses of various weeks of gestation by Alcian blue stain

Bone consists of bone cells and interstitial matrix, which is further divided into organic and inorganic. Four types of bone cells are present- osteoprogenitor cells, osteoblasts, osteocytes & osteoclasts. The bones are arranged in Haversian system or secondary osteons, which consists of central Haversian canal surrounded by concentric lamellae of bony tissue. These Haversian canals or the canals of Havers are in direct communication with medullary cavity also communicate with the surface of bone via Volkmann’s canal. Bone ossification in human foetuses is not widely studied. The information on primates is considered for comparison. In the present study attempts have been made to study the long bone ossification pattern in aborted human foetus between gestational ages 10 weeks to 32 weeks of gestation by Alcian Blue stain. The stages of cartilage transformation to bones are seen in six stages. The present study was aimed to evidence the human foetus long bones ossification at various weeks of gestation. The emanated information may enrich the existing global information on human foetuses ossification. From each foetus of different gestational weeks longitudinal and transverse sections of 7 long bones (clavicle, humerus, radius, ulna, femur, tibia, and fibula) were taken into study. All of them were stained by Alcian Blue stain. Keywords: Osteoprogenitor cells, Osteoblasts, Alcian Blue, Haversian canal, Volkmann’s canal.

Long bone histomorphogenesis of the naked mole-rat: Histodiversity and intraspecific variation.

Lacking fur, living in eusocial colonies and having the longest lifespan of any rodent, makes naked mole-rats (NMRs) rather peculiar mammals. Although they exhibit a high degree of polymorphism, skeletal plasticity and are considered a novel model to assess the effects of delayed puberty on the skeletal system, scarce information on their morphogenesis exists. Here, we examined a large ontogenetic sample (n=76) of subordinate individuals to assess the pattern of bone growth and bone microstructure of fore- and hindlimb bones by using histomorphological techniques. Over 290 undecalcified thin cross-sections from the midshaft of the humerus, ulna, femur, and tibia from pups, juveniles and adults were analyzed with polarized light microscopy. Similar to other fossorial mammals, NMRs exhibited a systematic cortical thickening of their long bones, which clearly indicates a conserved functional adaptation to withstand the mechanical strains imposed during digging, regardless of their chisel-tooth predominance. We describe a high histodiversity of bone matrices and the formation of secondary osteons in NMRs. The bones of pups are extremely thin-walled and grow by periosteal bone formation coupled with considerable expansion of the medullary cavity, a process probably tightly regulated and adapted to optimize the amount of minerals destined for skeletal development, to thus allow the female breeder to produce a higher number of pups, as well as several litters. Subsequent cortical thickening in juveniles involves high amounts of endosteal bone apposition, which contrasts with the bone modeling of other mammals where a periosteal predominance exists. Adults have bone matrices predominantly consisting of parallel-fibered bone and lamellar bone, which indicate intermediate to slow rates of osteogenesis, as well as the development of poorly vascularized lamellar-zonal tissues separated by lines of arrested growth (LAGs) and annuli. These features reflect the low metabolism, low body temperature and slow growth rates reported for this species, as well as indicate a cyclical pattern of osteogenesis. The presence of LAGs in captive individuals was striking and indicates that postnatal osteogenesis and its consequent cortical stratification most likely represents a plesiomorphic thermometabolic strategy among endotherms which has been suggested to be regulated by endogenous rhythms. However, the generalized presence of LAGs in this and other subterranean taxa in the wild, as well as recent investigations on variability of environmental conditions in burrow systems, supports the hypothesis that underground environments experience seasonal fluctuations that may influence the postnatal osteogenesis of animals by limiting the extension of burrow systems during the unfavorable dry seasons and therefore the finding of food resources. Additionally, the intraspecific variation found in the formation of bone tissue matrices and vascularization suggested a high degree of developmental plasticity in NMRs, which may help explaining the polymorphism reported for this species. The results obtained here represent a valuable contribution to understanding the relationship of several aspects involved in the morphogenesis of the skeletal system of a mammal with extraordinary adaptations.

The effects of eggshell calcium (Biomin H® ) and its combinations with alfacalcidol (1α-hydroxyvitamin D3) and menaquinone-7 (vitamin K2) on ovariectomy-induced bone loss in a rat model of osteoporosis.

The purpose of this study was to investigate the impact of eggshell calcium (Biomin H® dietary supplement) and its combinations with alfacalcidol (1α-hydroxyvitamin D3 ) and menaquinone-7 (vitamin K2 ) on ovariectomy-induced bone loss in rats. Adult female rats (n=48) were divided into 6 groups of 8 individuals each: sham-operated rats (SHAM); ovariectomized (OVX) rats untreated; OVX rats treated with Biomin H® (BIO); OVX rats simultaneously receiving Biomin H® , vitamin D3 (BIO+D3 ); OVX rats simultaneously treated with Biomin H® , vitamin K2 (BIO+K2 ) and OVX rats treated with Biomin H® , vitamin D3 , vitamin K2 (BIO+D3 +K2 ) during 8weeks. Biochemical parameters, bone mineral density (BMD), bone mineral content (BMC) and femoral bone microstructure were determined. Plasma calcium and phosphate were increased in BIO+D3 and BIO+D3 +K2 groups as compared to OVX. Alkaline phosphatase was elevated in OVX, BIO versus SHAM, BIO+D3 +K2 groups. When compared to OVX group, decreased urine deoxypyridinoline was observed in all treated groups and femoral BMD, BMC were higher in BIO, BIO+D3 , BIO+D3 +K2 groups. The BIO+K2 rats had similar densitometrical values than OVX individuals. Microcomputed tomography revealed increased trabecular relative bone volume (due to an increase in trabecular number) in BIO+D3 , BIO+D3 +K2 as compared to OVX. The higher relative bone volume in BIO+D3 , BIO+D3 +K2 groups was also accompanied by an increase in bone surface. In the cortical bone, an enhanced periosteal bone apposition was identified in BIO, BIO+D3 , BIO+K2 , BIO+D3 +K2 groups. The rats from BIO+D3 +K2 group had a higher area of primary osteon's vascular canals. In BIO+D3 , BIO+K2 , BIO+D3 +K2 groups, an increased area of secondary osteons was determined in comparison with OVX. Our results indicate the beneficial effect of triple application of Biomin H® , vitamin D3 , vitamin K2 , as well as simultaneous administration of Biomin H® , vitamin D3 on the inhibition of ovariectomy-induced bone loss in a rat model of osteoporosis.

Humerus midshaft histology in a modern and fossil wombat

The common wombat (Vombatus ursinus) is equipped with a set of physiological and morphological adaptations suited to a fossorial lifestyle. These allow wombats to engage in efficient scratch-digging and maintaining a low basal metabolic rate while living underground. While bone microstructure has been described for several subterranean animals, wombat bone histology has received very little attention to date. Here, we present preliminary insights into bone histology in modern adult V. ursinus (Mt Fairy, New South Wales) and Pleistocene fossil Vombatus sp. (Bakers Swamp, New South Wales) midshaft humeri. The modern sample was well preserved, allowing us to identify varying bone tissue types (woven, parallel-fibred, lamellar). The sample showed vascularity composed of primary and secondary osteons, and simple longitudinal and radial vessels. We also observed evidence for Haversian remodelling (i.e. localised replacement of pre-existing bone) and coarse compact cancellous bone within the inner cortex of the diaphysis. The fossil histology was poorly preserved, but likely showed bone matrix organisation similar to the modern specimen. We use these preliminary data to discuss hypotheses for wombat forelimb biomechanical and physiological microscopic adaptation to a burrow environment. We encourage future intraskeletal examination of microstructure in wombat populations to better inform their ecological adaptations and behaviour in palaeontological contexts.

Aging-related histomorphometric changes in cortical bone tissue of bottlenose dolphins (Tursiops truncatus)

Morphological characteristics of bones have shaped as a result of adaptation to life in the aquatic environment and whale diving habits. This study deals with the postnatal bone development and microscopic characteristics of bones of bottlenose dolphins (Tursiops truncatus). Bone sections of the right humerus and the fifth right rib of 106 dolphins aged less than 1–21 years were used to determine the density of the primary, secondary and remodelling osteons, the magnitude of the area occupied by the osteons, and the number of osteon lamellae. Bone sections were analysed using a compound microscope with standard and polarized light. Our study showed the primary osteons of bones to occupy a smaller area than the secondary ones. The secondary osteon area in the humerus is significantly larger than that in the rib. All rib osteons are significantly denser than those of the humerus. In both bones, the number of osteon lamellae is higher in secondary than in primary osteons. The number of secondary and remodelling osteons and the areas occupied by them increase with age, as opposed to primary osteons in which a decrease was noted. The number of lamellae in primary osteons decreases with age, while in secondary osteons their number increases. Within the study frame, morphometric osteon values of the bottlenose dolphin were determined, to the best of our knowledge, for the first time ever as concerns the aquatic mammals.

Secondary osteon structural heterogeneity between the cranial and caudal cortices of the proximal humerus in white-tailed deer.

Cortical bone remodeling is an ongoing process triggered by microdamage, where osteoclasts resorb existing bone and osteoblasts deposit new bone in the form of secondary osteons (Haversian systems). Previous studies revealed regional variance in Haversian systems structure and possibly material, between opposite cortices of the same bone. As bone mechanical properties depend on tissue structure and material, it is predicted that bone mechanical properties will vary in accordance with structural and material regional heterogeneity. To test this hypothesis, we analysed the structure, mineral content and compressive stiffness of secondary bone from the cranial and caudal cortices of the white-tailed deer proximal humerus. We found significantly larger Haversian systems and canals in the cranial cortex but no significant difference in mineral content between the two cortices. Accordingly, we found no difference in compressive stiffness between the two cortices and thus our working hypothesis was rejected. As the deer humerus is curved and thus likely subjected to bending during habitual locomotion, we expect that similar to other curved long bones, the cranial cortex of the deer humerus is likely subjected primarily to tensile strains and the caudal cortex is subject primarily to compressive strains. Consequently, our results suggest that strain magnitude (larger in compression) and sign (compression versus tension) affect the osteoclasts and osteoblasts differently in the basic multicellular unit. Our results further suggest that osteoclasts are inhibited in regions of high compressive strains (creating smaller Haversian systems) while the osteoid deposition and mineralization by osteoblasts is not affected by strain magnitude and sign.

Effect of cortical bone micro-structure in fragility fracture patients on lamellar stress

This work investigates how changes in cortical bone microstructure alter the risk of fragility fractures. The secondary osteons of non-osteoporotic (by DXA) women with fragility fractures have reduced lamellar width and greater areas of birefringent brightness in transverse sections, a pathological condition. We used hierarchical finite element (FE) models of the proximal femur of two women aged 67 and 88 (younger and older) during one-legged stance. At specific locations of the anterior-inferior neck (ROI), we analyzed micro-models containing osteons comprised of alternating birefringent extinct and bright lamellae. The plane of lamellar isotropy (XY) was transverse to the osteon longitudinal axis (Z) which was parallel to the femoral neck axis. To evaluate changes in fracture risk with changes in microstructure, we investigated principal and von Mises stresses, and planar stress measures that accounted for transverse isotropy. For both younger and older femurs, 48% to 100% of stress measures were larger in models with healthy architecture than in models with pathological architecture, while controlling for type of lamella and osteon. These findings suggest that bone adaptation reduces stress at most pathological lamellar sites. However, in the bright lamellae of the younger femur, the pathological tensile, compressive and distortional stresses in the transverse plane and distortional stress in the longitudinal planes were larger than the non-negligible corresponding stresses in 6 of the 28 osteon models with healthy architecture, in 5 of the 7 locations. Therefore, a minority of sites with pathological architecture present greater stress, and therefore, greater fracture risk.

Ontogenetic changes to bone microstructure in an archaeologically derived sample of human ribs

There is considerable variation in the gross morphology and tissue properties among the bones of human infants, children, adolescents, and adults. Using 18 known-age individuals (nfemale =8, nmale =9, nunknown =1; birth to 21years old), from a well-documented cemetery collection, Spitalfields Christ Church, London, UK, this study explores growth-related changes in cortical and trabecular bone microstructure. Micro-CT scans of mid-shaft middle thoracic ribs are used for quantitative analysis. Results are then compared topreviously quantified conventional histomorphometry of the same sample. Total area (Tt.Ar), cortical area (Ct.Ar), cortical thickness (Ct.Th), and the major (Maj.Dm) and minor (Min.Dm) diameters of the rib demonstrate positive correlations with age. Pore density (Po.Dn) increases, but age-related changes to cortical porosity (Ct.Po) appear to be non-linear. Trabecular thickness (Tb.th) and trabecular separation (Tb.Sp) increase with age, whereas trabecular bone pattern factor (Tb.Pf), structural model index (SMI), and connectivity density (Conn.D) decrease with age. Sex-based differences were not identified for any of the variables included in this study. Some samples display clear evidence of diagenetic alteration without corresponding changes in radiopacity, which compromises the reliability of bone mineral density (BMD) data in the study of past populations. Cortical porosity data are not correlated with two-dimensional measures of osteon population density (OPD). This suggests that unfilled resorption spaces contribute more significantly to cortical porosity than do the Haversian canals of secondary osteons. Continued research using complementary imaging techniques and a wide array of histological variables will increase our understanding of age- and sex-specific ontogenetic patterns within and among human populations.

Long-term peroral administration of bitter apricot seeds influences cortical bone microstructure of rabbits.

Apricot seeds due to the presence of cyanogenic glycoside amygdalin belong to the popular "alternative cancer cures", although anticancer effect of amygdalin remains controversial. This in vivo study points to the effect of long-term peroral administration of bitter apricot seeds on bone microstructure of rabbits since chronic amygdalin toxicity in relation to bone parameters has not been investigated yet. Rabbits (n=16) were randomly divided into four experimental groups of 4 animals each. Three experimental groups S1, S2 and S3 received commercial feed for rabbits mixed with crushed bitter apricot seeds at doses 60, 300 and 420mg/kg bw during five months, respectively. The control (C) group received no apricot seeds. The long-term consumption of apricot seeds had no impact on total body weight, femoral weight and femoral length of rabbits. Also, microcomputed tomography (3D analysis) of cortical and trabecular bone tissues did not reveal any significant impact of amygdalin toxicity on relative bone volume, BMD, cortical bone thickness, bone surface, trabecular number, thickness, and their separation. On the other hand, histological (2D) analysis demonstrated evident changes in cortical bone microstructure consistent with a decreased density of secondary osteons in the middle part of substantia compacta due to a replacement of Haversian bone tissue by plexiform bone tissue, vasoconstriction in the primary osteons' vascular canals, Haversian canals, and decreased sizes of secondary osteons in rabbits from S1, S2 and S3 groups. These negative changes are associated with different vascularization and biomechanical properties of cortical bones.

Microanatomy and growth of the mesosaurs <i>Stereosternum tumidum</i> and <i>Brazilosaurus sanpauloensis</i> (Reptilia, Parareptilia)

Abstract. Histology and microanatomy of vertebrae, ribs, haemal arch, and humeri and femora of 10 individuals of Stereosternum and two dorsal ribs of 1 individual of Brazilosaurus were studied. All individuals had achieved a body length of 50 cm (equal to 65 % of the maximum known body length) or larger. All sampled bones are highly osteosclerotic due to the reduction of medullary cavities and the filling of medullary regions by endosteal bone. Calcified cartilage occurs – if at all – only locally in small clusters in the medullary regions of midshaft and in higher amounts only in non-midshaft sections of long bones and towards the medio-distal rib shaft, respectively. The primary bone tissue consists of highly organized parallel-fibred tissue and/or lamellar tissue, which is in most samples relatively lightly vascularized or even avascular. If present, vascular canals are mainly longitudinally oriented; some show a radial orientation. Simple vascular canals as well as primary osteons occur. Some of the latter are secondarily altered, i.e. widened. Remodelling of the periosteal cortex is only documented by few scattered erosion cavities and secondary osteons. The tissue is regularly stratified by lines of arrested growth (LAGs), which usually appear as double or multiple rest lines, indicating strong dependence on exogenous and endogenous factors. Because of the inhibition of periosteal remodelling the growth record is complete and no inner cycles are lost. Individuals of Stereosternum show a poor correlation of body size and number of growth marks, which might be the result of developmental plasticity. Brazilosaurus shows a highly organized, avascular lamellar tissue and a high number of regularly deposited rest lines throughout the cortex of the ribs. The medullary region in the ribs of Brazilosaurus is distinctly larger when compared to ribs of Stereosternum. However, strong osteosclerosis is obvious in both taxa, pointing to a high degree of aquatic adaption. Ribs of Stereosternum, Brazilosaurus, and Mesosaurus are clearly distinguishable from each other by the distribution of the periosteal and endosteal territory. Furthermore, Brazilosaurus differs in its growth pattern (i.e. spacing of rest lines) when compared to Stereosternum and Mesosaurus.

Fossildiagenesis and ontogenetic insights of crocodyliform bones from the Adamantina Formation, Bauru Basin, Brazil

The histological analysis of fossil bones allows a taphonomic approach, especially to fossildiagenesis. We studied the femur, vertebra, and osteoderm of the crocodyliform Montealtosuchus arrudacamposi (Adamantina Formation; Late Cretaceous), to make inferences of the sequence of the diagenetic processes. Cross-sections of the bones and the rock matrix that fills the medullar cavity were analyzed under a scanning electron microscopy with compositional analysis (SEM/EDS) and μ-X-Ray fluorescence (μ-XRF). The microstructural pattern of the femur and vertebra was similar, with a transition from vascularized fibrolamellar internal cortex, with reticular and longitudinal canals to zonal lamellar in the outer, and a medullary cavity portion filled with quartz and other mineral grains. The osteoderm, however, presented a less vascularized cortex. In all samples were found the External Fundamental System (EFS), secondary osteons in the internal cortex and spongy tissue, and the transition from a fibrolamellar to a lamellar tissues, indicating that the individual reached ontogenetic maturity (adult/senescent) before they died. The compositional results showed that the samples mainly comprised calcium and phosphorus, which were homogeneously distributed. However, we inferred that these elements occurred during the formation of recrystallized and authigenic minerals. Iron, vanadium, and cerium are the elements found that occurred in the composition of the fossil remains during early diagenesis, and this process was observed to extend to the late diagenesis. Cerium was homogeneously distributed and incorporated to authigenic apatite. Iron and vanadium were restricted to the cortex. The presence of authigenic apatite and Rare Earth Elements (REEs) in the samples supported that the diagenetic environment of the Adamantina Formation was alkaline. Furthermore, it suggested an association with a groundwater environment that have allowed and facilitated the well preservation of fossil vertebrates in this geological formation.

The impact of flavonoid epicatechin on compact bone microstructure in rabbits

Epicatechin is one of the dozens of potent natural antioxidants with beneficial activities on many biological systems. However, its impact on bone structure has not been sufficiently investigated. The purpose of our study was to examine the effect of pure epicatechin on compact bone microstructure in five-month-old female rabbits. Twelve rabbits were intramuscularly (i.m.) injected with various doses of epicatechin: 10 μg kg−1 body weight (bw) (Epi10 group; n = 4), 100 μg kg−1 bw (Epi100 group; n = 4) and 1000 μg kg−1 bw (Epi1000 group; n = 4) for 30 days, 3 times per week. Four individuals from the control (C) group were i.m. administrated with physiological saline solution. Compact bone arrangement in all epicatechin-exposed groups was similar to the C group. We identified only intensive apposition of primary vascular longitudinal bone tissue under periosteum in Epi10, Epi100 and Epi1000 groups. On the contrary, significantly increased sizes of the primary osteons’ vascular canals were observed in rabbits from Epi10 group in comparison with C group. Interestingly, females from the Epi100 and Epi1000 groups had significantly decreased values of primary osteons’ vascular canals as compared to C and Epi10 groups. Haversian canals’ parameters were decreased in all rabbits exposed to epicatechin. Sizes of secondary osteons did not differ significantly among all analysed groups. Our results demonstrate that subacute intramuscular exposure to epicatechin influences bone vascularization (higher doses lead to vasoconstriction of blood vessels) and did not cause any demonstrable changes in compact bone arrangement.

Haversian remodeling corresponds to load frequency but not strain magnitude in the macaque (Macaca fascicularis) skeleton.

One way bone adapts to its mechanical environment is by Haversian remodeling, a repair process in which existing bone is resorbed and replaced by new bone. Haversian remodeling forms interconnected, cylindrical structures called secondary osteons. The amount of remodeling that occurs is related to the nature of mechanical loading and accrual of microdamage, but it is uncertain whether habitual loads of high magnitude versus high frequency result in more remodeling. The answer to this question is important if remodeling is to be a tool for inferring loading environments, and thus behavior, in past populations. Here, secondary osteon population density (OPD), osteon cross-sectional area (On.Ar), and percent Haversian bone (%HAV) were compared among mid-diaphysis femora, tibia, fibulae, and mid-level ribs of five adult crab-eating macaques (Macaca fascicularis). Ribs experience relatively low strains but have a high daily loading frequency (~33 times per minute). Limb bones are loaded for fewer cycles per day, but the femur and tibia have high load magnitudes due to gravitational forces. Strain magnitudes in the fibula are a fraction of those in the femur and tibia. Analyses of variance demonstrated significant differences in OPD (P = 0.010) and On.Ar (P < 0.001) among the bones. Pairwise t-tests revealed greater OPD but lower On.Ar in the rib than all other bones. The high rib OPD suggests that Haversian remodeling is more responsive to load frequency than strain magnitude. The fact that osteons are smaller in ribs than any other bone may be an effect of remodeling in comparatively narrow cortices.

Microanatomical Record of Cortical Bone Remodeling and High Vascularity in a Fossil Giant Rat Midshaft Femur.

Rat cortical bone does not typically undergo secondary (Haversian) remodeling. Haversian organization of rat bone has been mainly observed in experimental settings following biomechanical or dietary manipulation. Here, we report an observation of cortical secondary osteons within a histological femur cross-section from an extinct (late Quaternary) form of Timorese giant rat (Murinae gen. et sp. indet). The medio-lateral midshaft diameter of its femur, used as a measure of bone size, is 6.15 mm and indicates a heavier than normal skeletal frame. We compare this sample to bone histology in a small rat's midshaft femur of 2.33 mm diameter. A complete lack of Haversian bone remodeling characteristics is noted for the smaller sample, which is dominated by radial vascular canals. The giant rat shows clear secondary osteons and diffuse vascularity mainly composed of tightly packed longitudinal canals across its cortex. It appears that rat cortical bone can undergo bone remodeling, and is organized in a highly vascularized manner, in insular giant cases. Our findings from Timor align with results reported in experimental rat model skeletal biology literature and other insular fossil rat material. Where macroanatomical examination is limited, histological observations on fossil rat limb bones have the potential to aid reconstructions of life history and skeletal growth aspects in these rodents. Anat Rec, 302:1934-1940, 2019. © 2019 American Association for Anatomy.