Examining bone surfaces across puberty: a 20-month pQCT trial.

This follow-up study assessed sex differences in cortical bone growth at the tibial midshaft across puberty. In both sexes, periosteal apposition dominated over endosteal resorption. Boys had a greater magnitude of change at both surfaces, and thus, a greater increase in bone size across puberty. Relative increase in cortical bone area was similar between sexes. INTRODUCTION: Generally, sex differences in bone size become most evident as puberty progresses. This was thought to be caused, in part, by greater periosteal apposition in boys, whereas endosteal apposition prevailed in girls. However, this premise is based on evidence from cross-sectional studies and planar measurement techniques. Thus, our aim was to prospectively evaluate sex-specific changes in cortical bone area across puberty. MATERIALS AND METHODS: We used pQCT to assess the tibial midshaft (50% site) at baseline and final (20 months) in girls (N = 68) and boys (N = 60) across early-, peri-, and postpuberty. We report total bone cross-sectional area (ToA, mm2), cortical area (CoA, mm2), marrow cavity area (CavA, mm2), and CoA/ToA ratio. RESULTS: Children were a mean age of 11.9 +/- 0.6 (SD) years at baseline. At the tibia, CoA ranged from 230 +/- 44, 261 +/- 50, and 258 +/- 46 in early-, peri-, and postpubertal girls. In boys, comparable values were 223 +/- 36 (early), 264 +/- 38 (peri), and 281 +/- 77 (postpubertal). There was no sex difference for ToA or CoA at baseline. Increase in ToA and CoA was, on average, 10% greater for boys than girls across maturity groups. The area of the marrow cavity increased in all groups, but with considerable variability. The increase in CavA was significantly less for girls than boys in the early- and postpubertal groups. Change in CoA/ToA was similar between sexes across puberty. CONCLUSION: Both sexes showed a similar pattern of change in CoA at the tibial midshaft, where periosteal apposition dominated over endosteal resorption. Boys showed a greater magnitude of change at both surfaces, and thus, showed a greater increase in bone size across puberty. The relative increase in cortical area was similar between sexes. These pQCT findings provide no evidence for endosteal apposition in postmenarchal girls.     

Site- and compartment-specific changes in bone with hindlimb unloading in mature adult rats

The purpose of this study was to examine site- and compartment-specific changes in bone induced by hindlimb unloading (HU) in the mature adult male rat (6 months old). Tibiae, femora, and humeri were removed after 14, 21, and 28 days of HU for determination of bone mineral density (BMD) and geometry by peripheral quantitative computed tomography (pQCT), mechanical properties, and bone formation rate (BFR), and compared with baseline (0 day) and aging (28 day) controls. HU resulted in 20%-21% declines in cancellous BMD at the proximal tibia and femoral neck after 28 day HU vs. 0 day controls (CON). Cortical shell BMD at these sites was greater (by 4%-6%) in both 28 day HU and 28 day CON vs. 0 day CON animals, and nearly identical to that gain seen in the weight-bearing humerus. Mechanical properties at the proximal tibia exhibited a nonsignificant decline after HU vs. those of 0 day CON rats. At the femoral neck, a 10% decrement was noted in ultimate load in 28 day HU rats vs. 28 day CON animals. Middiaphyseal tibial bone increased slightly in density and area during HU; no differences in structural and material properties between 28 day HU and 28 day CON rats were noted. BFR at the tibial midshaft was significantly lower (by 90%) after 21 day HU vs. 0 day CON; this decline was maintained throughout 28 day HU. These results suggest there are compartment-specific differences in the mature adult skeletal response to hindlimb unloading, and that the major impact over 28 days of unloading is on cancellous bone sites. Given the sharp decline in BFR for midshaft cortical bone, it appears likely that deficits in BMD, area, or mechanical properties would develop with longer duration unloading.     

Histomorphometric, physical, and mechanical effects of spaceflight and insulin-like growth factor-I on rat long bones

Previous experiments have shown that skeletal unloading resulting from exposure to microgravity induces osteopenia in rats. In maturing rats, this is primarily a function of reduced formation, rather than increased resorption. Insulin-like growth factor-I (IGF-I) stimulates bone formation by increasing collagen synthesis by osteoblasts. The ability of IGF-I to prevent osteopenia otherwise caused by spaceflight was investigated in 12 rats flown for 10 days aboard the Space Shuttle, STS-77. The effect IGF-I had on cortical bone metabolism was generally anabolic. For example, humerus periosteal bone formation increased a significant 37.6% for the spaceflight animals treated with IGF-I, whereas the ground controls increased 24.7%. This increase in humeral bone formation at the periosteum is a result of an increased percent mineralizing perimeter (%Min.Pm), rather than mineral apposition rate (MAR), for both spaceflight and ground control rats. However, IGF-I did inhibit humerus endocortical bone formation in both the spaceflight and ground control rats (38.1% and 39.2%, respectively) by limiting MAR. This effect was verified in a separate ground-based study. Similar histomorphometric results for spaceflight and ground control rats suggest that IGF-I effects occur during normal weight bearing and during spaceflight. Microhardness measurements of the newly formed bone indicate that the quality of the bone formed during IGF-I treatment or spaceflight was not adversely altered. Spaceflight did not consistently change the structural (force-deflection) properties of the femur or humerus when tested in three-point bending. IGF-I significantly increased femoral maximum and fracture strength.     

Implant placement increases bone remodeling transiently in a rat model

To examine bone remodeling following implant placement, 88 female Sprague–Dawley rats underwent either sham ovariectomy (sham‐ovx) or ovariectomy (ovx) at 4.5 months. At 11 months, 17 baseline control animals were euthanized, while 71 rats received bilateral intramedullary femoral implants. Implanted rats were randomized to 4‐, 8‐, or 12‐week follow‐up times. Microcomputed tomography was used to assess cortical area and trabecular architecture in all rats. Dynamic and static histomorphometry were performed in a subset to examine the trabecular and endocortical bone in the distal femoral metaphysis adjacent to the implant and the periosteal surface at the midshaft superior to the implant (n = 59). Implantation did not affect bone volume in either sham‐ovx or ovx rats compared to baseline controls. Implant placement significantly increased mineralizing surface, mineral apposition rate, and bone formation rate in both sham‐ovx and ovx rats at the trabecular and endocortical surfaces at four and sometimes 8 weeks, with a return to baseline values by 12 weeks. At the periosteal surface, implant placement increased bone formation at 4 weeks with a return to baseline levels by 8 weeks. Thus, implant placement increases bone remodeling transiently without affecting bone volume in sham‐ovx and ovx rats. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 800–806, 2013     

Adaptations in Cortical and Trabecular Bone in Response to Mechanical Loading with and without Weight Bearing

Exercise that imparts rapid, high-magnitude mechanical loading is considered to be advantageous to bone health. Previous rodent studies have suggested that swimming may also be beneficial to bone. We investigated the differential effects of exercise with and without weight bearing on cortical and trabecular bone. Forty female Sprague-Dawley rats (120 days) were weight-stratified and randomized into four groups: swim control (Cs, n = 10), swim (S, n = 10), treadmill control (Ct, n = 10), and treadmill (T, n = 10). Treadmill speed was adjusted to match the average limb loading frequency used for swimming, and all training progressed to 1 hour/day, 5 days/week, for 12 weeks. Femurs and humeri were assessed for cortical morphometry by peripheral quantitative computed tomography, areal bone mineral density (BMD) by peripheral dual-energy X-ray absorptiometry, mineral content by ashing, strength by three-point bending, and trabecular volume (BV/TV) by micro-computed tomography. Swimming was associated with increases in cortical thickness and BMD in the humerus midshaft and trabecular BV/TV in the distal femur and proximal humerus compared with age-matched controls. Compared to swimming, treadmill training was associated with increases in percent ash of the femur and humerus and Young’s modulus of the femur. Swimming appears to engender novel bone strains and osteogenic adaptations in the humerus and femur, which are different from those induced by normal cage activity. In summary, our findings suggest that when limb loading frequency is matched, swimming may afford greater benefits to cortical and trabecular bone than uphill treadmill work in rats.     

Quantitative measurements of periosteal and cortical-endosteal bone formation and resorption in the midshaft of male rat femur

Morphologic and modeling parameters have been studied in the femoral diaphysis of male rats between 60 days and 840 days of age. The modeling rates were measured by use of a vital labeling technique with calcein. The mathematical bone model that was developed for the midshaft of female rats was used also for male rats. The two ellipses, defined by four time-dependent functions of the radii, and one drift function that describes the movement of the whole diaphysis in the transverse direction have been adapted to the new data sets obtained for male rats. With increasing age the apposition(MF), forming(BF), and resorbing(BR) rates decrease continuously from 5.4 mm/year(MF), 960%/year(BF), and 540%/year(BR) at age 60 days to 0.038 mm/year(MF), 8.4%/year(BF), and 6.3%/year(BR) at age 850 days, whereas the endosteal and periosteal diameters increase. Between age 60 days and 550 days, formation rate, resorption rate, apposition rate, and the growth rate of the bone volume and body weight are greater in male than in female rats, but after this age they are comparable. The average cumulative radiation dose near bone surfaces after contamination with alpha-emitting bone surface-seeking radionuclides is greater in the diaphysis of female rats than in the corresponding male rats. In young animals it is greater initially on the cortical-endosteal surfaces, but after age 250 days the dose on the periosteal surface becomes predominant.     

Short-Term effects of high dose estrogen on tibiae of growing male rats

The short-term effects of estrogen at a single high dose (4 mg/kg body weight/day for 14 days) were determined on tibiae in the normal (noncastrate) growing male rat. In cortical periosteal bone, at a middiaphyseal site devoid of resorbing activity, estrogen suppressed periosteal bone formation and apposition rates, resulting in a smaller cross-sectional area. In middiaphyseal endocortical bone, estrogen had no effect on apposition and formation rates and, because medullary area was unchanged, probably had no effect on endocortical bone resorption. In the proximal tibial metaphysis, estrogen greatly suppressed longitudinal growth rate. In a site within the metaphysis adjusted for the effects of growth, cancellous mineral apposition was greatly reduced by the hormone. Estrogen-treated rats retained more of a fluorochrome label deposited in cancellous bone at the beginning of the study than vehicle-treated animals, indicating a reduced net bone loss. As a result of the lowered resorption induced by estrogen, cancellous bone mass (area and perimeter) were both significantly higher in estrogen-treated rats. No evidence was found for an anabolic action of the hormone in the male rat; indeed, estrogen reduced indices of bone formation. Received: 31 December 1995 / Accepted: 3 May 1996     

Intrathecal bupivacaine protects against extension of lesions in an acute contusive spinal cord injury model

BACKGROUND AND OBJECTIVE: We recently demonstrated that intrathecal bupivacaine before or after acute photochemical spinal injury improved functional outcome in rats. However, the closest model to spinal trauma is the contusive weight-drop method. The aim of this study was to evaluate functional, electrophysiological and anatomical consequences of a contusive spinal-cord lesion in rats with or without an intrathecal injection of bupivacaine. METHODS: Fifteen minutes before a contusive spinal lesion, 18 rats received intrathecally either 0.5% bupivacaine (Group T) or saline (Group C). During an 18-days period, motor and sensory functions were evaluated, and bladder voiding dysfunction was noted. Somatosensory evoked potential testings were performed at day 18. Then, the intact spinal cord area at the epicentre of the lesion and the extent of the lesion were measured. RESULTS: Motor deficit was less and inclined-plane stability was better in treated animals at all times, the scores were statistically different from day 7. There were no differences concerning the sensory test. Despite no significant difference, there were less spinal bladders in the T group from day 7. Somatosensory evoked potential latencies were longer in T group, but only the first negative component (N1) was statistically significant. Amplitudes were higher in T group, but were not statistically different. The spinal cord intact area at the epicentre of the lesion was higher in the T group (1.23 +/- 0.8 mm(2) vs. 0.81 +/- 0.39 mm(2); P < 0.05). The extent of the lesion was higher in the C group (9.4 +/- 2.9 mm vs. 6.4 +/- 3.4 mm; P < 0.05). CONCLUSION: Intrathecal 0.5% bupivacaine provide a neuroprotective effect by decreasing functional, electrophysiological and anatomical consequences after a contusive spinal cord injury.     

Spinal cord injury causes rapid osteoclastic resorption and growth plate abnormalities in growing rats (SCI-induced bone loss in growing rats)

Summary

Spinal cord injury causes severe bone loss. We report osteoclast resorption with severe trabecular and cortical bone loss, decreased bone mineral apposition, and growth plate abnormalities in a rodent model of contusion spinal cord injury. These findings will help elucidate the mechanisms of osteoporosis following neurological trauma.

Introduction

Limited understanding of the mechanism(s) that underlie spinal cord injury (SCI)-induced bone loss has led to few treatment options. As SCI-induced osteoporosis carries significant morbidity and can worsen already profound disability, there is an urgency to advance knowledge regarding this pathophysiology.

Methods

A clinically relevant contusion model of experimental spinal cord injury was used to generate severe lower thoracic SCI by weight-drop (10 g?×?50 mm) in adolescent male Sprague-Dawley rats. Body weight and gender-matched naïve (no surgery) rats served as controls. Bone microarchitecture was determined by micro-computed tomographic imaging. Mature osteoclasts were identified by TRAP staining and bone apposition rate was determined by dynamic histomorphometry.

Results

At 10 days post-injury we detected a marked 48% decrease in trabecular bone and a 35% decrease in cortical bone at the distal femoral metaphysis by micro-CT. A 330% increase in the number of mature osteoclasts was detected at the growth plate in the injured animals that corresponded with cellular disorganization at the chondro-osseous junction. Appositional growth studies demonstrated decreased new bone formation with a mineralization defect indicative of osteoblast dysfunction.

Conclusions

Contusion SCI results in a rapid bone loss that is the result of increased bone resorption and decreased bone formation.     

Bone mineral content in the senescent rat femur: an assessment using single photon absorptiometry

The single photon absorptiometry technique was evaluated for measuring bone mineral content (BMC) of the excised femurs of the rat, and the system was used to examine the changes in cortical and trabecular bone from young adult (6 mo), mature adult (12 mo), and senescent (24 mo) male and female animals. BMC of the femur midshaft, representing cortical bone, apparently increased progressively with advancing age. The width of the femur at the scan site also increased with age. Normalizing the midshaft BMC by width partially compensated for the age-associated increase. However, when bone mineral values were normalized by the cortical area at the scan site, to take into account the geometric differences in the femurs of different aged animals, maximum bone densities were found in the mature adult and these values decreased slightly in the femurs from senescent rats. In contrast, the BMC of the femur distal metaphysis, representing trabecular bone, decreased markedly in the aged rat. The loss of trabecular bone was also evident from morphological examination of the distal metaphysis. These findings indicated that bone mineral loss with age was site specific in the rat femur. These studies provided additional evidence that the rat might serve as a useful animal model for specific experiments related to the pathogenesis of age-associated osteopenia.     

Effects of human parathyroid hormone (1-34), LY333334, on bone mass, remodeling, and mechanical properties of cortical bone during the first remodeling cycle in rabbits

We have previously shown that parathyroid hormone (PTH) increases cortical bone mass and mechanical strength of female rabbits after 140 days of treatment. However, cortical porosity was also shown to increase. If cortical porosity increases prior to the change in geometry, there may be a transient decrease in cortical bone strength that could make the bone more susceptible to fracture in the early phase of treatment. The purpose of this study is to examine the effects of PTH on the remodeling dynamics and mechanical properties of cortical bone in rabbits, which exhibit haversian remodeling, during the first remodeling cycle after the initiation of treatment. Fifty 9-month-old intact female New Zealand white rabbits were randomized into five groups. A baseline control group was killed at the start of the experiment. The two PTH-treated groups were given human PTH(1-34) at 10 microg/kg daily subcutaneously for 35 (P35) or 70 (P70) days. Two respective age-matched control groups (V35, V70) were injected with vehicle. Histomorphometry of the cortical bone in the tibial midshaft showed that, although intracortical activation frequency was significantly increased by PTH at 35 days, there was no significant increase of cortical porosity in the first remodeling cycle (70 days). Moreover, stimulation of cortical surface bone formation in the treated animals led to significantly greater cortical area and greater bone strength in both P35 and P70. We conclude that, although intracortical remodeling increases within the first remodeling period (70 days) in animals treated with 10 microg/kg PTH, the greater cortical area due to acceleration of bone formation on cortical surfaces increases cortical bone strength. There is no mechanical risk during the first remodeling cycle associated with intermittent PTH treatment in animals with normal bone mass.     

BBB评分评估脊髓损伤大鼠后肢运动功能的探讨

目的：探讨大鼠脊髓损伤后和修复中如何评估人鼠后肢运动的BBB评分。方法：对4组大鼠分别行T10脊髓背侧半切断(A组)、T10脊髓全切断(B组)、T10脊髓节段全切除(C组)、T10以下脊髓全切除(D组)，制成不同损伤程度的大鼠脊髓损伤模型，对所有动物的后肢运动功能进行BBB评分和脊髓组织学观察。结果：A组大鼠BBB评分存损伤后5崩达到20分或21分，B组和C组大鼠存术后2周以后BBB评分维持在8分．D组大鼠BBB评分维持在0。B组和C组大鼠脊髓顺行追踪显示脊髓损伤区和尾侧无追踪剂分布．连续矢状冰冻切片抗神经丝(NF)染色未见连续NF通过损伤区，结论：大鼠脊髓损伤模型的后肢运动功能BBB评分如果在8分以下，就需要慎重评价，这种运动有可能完全是或包括有自发的后肢运动。     

Restriction of axonal retraction and promotion of axonal regeneration by chronically injured neurons after intraspinal treatment with glial cell line-derived neurotrophic factor (GDNF)

The response of supraspinal neurons to acute or delayed treatment with GDNF following a spinal cord injury was examined. A cervical level 3 hemisection lesion cavity was created by tissue aspiration in adult, female rats. In one experiment gel foam saturated with GDNF was placed into the lesion cavity immediately after injury to determine if the extent of axonal retraction was affected by neurotrophic factor treatment. One week prior to sacrifice animals received a microinjection of biotinylated dextran amine (BDA) into the red nucleus and reticular formation to label descending spinal pathways by anterograde transport mechanisms. Animals were sacrificed 1 or 4 weeks after injury and treatment with GDNF. The terminal end of injured BDA-labeled rubrospinal and reticulospinal tract axons was identified and the distance from the lesion was measured. In comparison to PBS-treated animals, GDNF-treatment resulted in a significant decrease in the extent of axonal retraction of both rubrospinal and reticulospinal tract axons at 1 week after spinal cord injury for both tracts. At 4 weeks after injury the mean distance from the lesion was less than 240 microm following GDNF-treatment for both tracts, compared to over 480 microm following PBS-treatment. In the second experiment injured supraspinal neurons were labeled by retrograde transport of True Blue that had been placed into the lesion cavity. One month later scar tissue was removed from the cavity by aspiration to enlarge the cavity by approximately 500 microm in a rostral direction. GDNF-saturated gel foam was placed into the cavity for 60 min prior to apposition of an autologous peripheral nerve (PN) graft to the rostral cavity wall. One month later Nuclear Yellow was applied to the distal end of the PN graft and animals were sacrificed after 2 days. The number of supraspinal neurons containing both True Blue and Nuclear Yellow was counted as a measure of axonal regeneration by chronically injured neurons. There was a seven-fold increase in the number of regenerating neurons after GDNF-treatment, with the majority (65%) of dual-labeled neurons located within the reticular formation. These results indicate that GDNF has neuroprotective effects when provided acutely after injury and promotes axonal regeneration when provided in a chronic injury situation.     

Departments

Abstract

This study was conducted to determine the effects of chronic phrenicotomy on spinal hemisection-induced morphological plasticity occurring in the phrenic nucleus. Young adult rats were divided into a hemisection-alone and two hemisection-plus-phrenicotomy (HPP) groups. HPP animals received a left phrenicotomy two or four weeks prior to sacrificing; whereas hemisection-alone animals did not. All animals received a left C2 spinal hemisection 24 hours prior to death. Quantitative morphometric analysis of the phrenic nucleus showed significant reductions in phrenic dendritic size and the number of dendrodendritic appositions in HPP (two week) animals and in the length of dendrodendritic appositions in HPP (four week) animals. Significant increases in microglial area fraction in HPP (two week) animals and in astroglia area fraction in HPP (four week) animals were also detected. The results suggest that the alterations in the spinal hemisection-induced dendrodendritic apposition formation is most likely influenced by the different stages of the glial reactions induced by the chronic phrenicotomy/spinal hemisection. (J Spinal Cord Med: 19:58–70)     

The effect of hyperbaric oxygen on glucose utilization in a freeze-traumatized rat brain

Local cerebral glucose utilization was measured with the autoradiographic 2-deoxyglucose technique in rats injured by a focal parietal cortical freeze lesion then treated with hyperbaric oxygen (HBO). The cold lesion depressed glucose utilization in the contralateral as well as in the ipsilateral hemisphere. The largest decreases were observed in ipsilateral cortical areas. Treatment of lesioned animals with HBO at 2 atm for 90 minutes on each of 4 consecutive days tended to increase the overall cerebral glucose utilization measured 5 days after injury when compared to animals exposed to normobaric air. This improvement reached statistical significance in five of the 21 structures studied: the auditory cortex, medial geniculate body, superior olivary nucleus, and lateral geniculate body ipsilateral to the lesion, and the mammillary body. The data indicate that changes in lesioned rats exposed to HBO are not restricted to the period of time that the animals are in the hyperbaric chamber but are persistent.     

Changes in Geometry and Cortical Porosity in Adult, Ovary-Intact Rabbits after 5 Months Treatment with LY333334 (hPTH 1-34)

The purpose of this study was to determine if the increased cortical bone porosity induced by intermittently administered parathyroid hormone (PTH) reduces bone strength significantly. Mature ovary-intact New Zealand white rabbits were treated with once daily injections of vehicle, or PTH(1-34), LY333334, at 10 or 40 μg/kg/day for 140 days. Geometry of the femoral midshaft was measured to evaluate changes in the cross-sectional moment of inertia (CSMI). Cortical porosity was measured in the midshaft of the tibia by dividing cortical area into three zones based on equal divisions of cortical diameter: near endocortical (Zone I), near intermediate (Zone II), and near periosteal (Zone III) regions. Total cortical porosity significantly increased after PTH treatment from 1.4% in the controls to 6.3% in the higher dose group, but the location of the new porosities was not randomly distributed. In the controls, porosity of Zones I and II (both 1.7%) was almost twice as much as that of Zone III (0.9%). In the lower dose group, cortical porosity of Zone I (5.5%) and II (1.8%) was greater than in Zone III (0.9%), but these differences were not statistically significant. In the higher dose group, cortical porosity of Zone I (11.5%) and II (6.1%) significantly increased compared with Zone III (1.4%) (P < 0.0005). Histomorphometric measurements showed that bone formation rate on both periosteal and endocortical surfaces increased, resulting in increased bone area and cortical area in the higher dose group. A model was developed to evaluate the effect of the changes in geometry and porosity on CSMI in the different zones. This simulation model indicated that CSMI in the higher dose group was significantly greater than in the other two groups, despite the increased porosity. We speculate the reason to be that porosity increased near the endocortical surface, where its mechanical effect is small. This increase was more than offset by apposition of new bone on the periosteal surface. These data suggest that (1) PTH increases cortical porosity in a dose-dependent manner, primarily near endocortical surfaces; (2) because of this nonhomogeneous distribution, the mechanical effect of increased porosity is small; (3) the increased cortical porosity associated with PTH treatment is more than offset by periosteal apposition of new bone, causing an overall increase in the bending rigidity of cortical bone; and (4) these changes cannot be accurately evaluated using noninvasive methods of bone densitometry, which cannot account for the location of bone gain and bone loss. Received: 20 May 1999 / Accepted: 10 January 2000     

Effects of 4-amino-1-hydroxybutylidene bisphosphonate on bone biomechanics in rats.

Bisphosphonates inhibit osteoclast-mediated bone resorption, but their effects on the mechanical behavior of bone remain uncertain. This study investigated the effects of 4-amino-1-hydroxybutylidene bisphosphonate (AHBuBP) on the biomechanical and morphologic properties of bone in ovariectomized rats. Sprague-Dawley rats (four groups, n = 6) were ovariectomized at 3 months of age. From 7 to 13 months, the groups received vehicle or 0.28, 2.8, or 28 micrograms/kg of AHBuBP twice weekly through subcutaneous injection. An additional group of control animals (n = 6) received neither surgery nor drug. We determined the stiffness, yield, and ultimate loads of the femoral midshaft, the sixth lumbar (L6) vertebra, and the femoral neck. Geometric properties of the cortical bone were measured from digitized images of the tibial diaphysis at the level of the synostosis. The area fraction of trabecular bone was determined through the midsagittal plane of the fifth lumbar (L5) vertebra. There were no significant differences in the structural properties of the femoral neck and midshaft, with the exception that the medium-dose group had a greater ultimate load than the vehicle group for the femoral midshaft in bending. Cross-sectional analysis of the tibia did not show significant differences in the inertial properties or area. Ovariectomy caused a significant reduction in the stiffness and ultimate load of L6 and in the area fraction of trabecular bone of L5.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fluoro-jade B stains quiescent and reactive astrocytes in the rodent spinal cord

In an attempt to label dying neurons in the injured spinal cord, we used the novel fluorescein derivative Fluoro-Jade B, which has been reported to specifically label dead or dying neurons in the brain. Rats and mice were subjected to a moderate level of spinal cord injury using an IH impact device and sacrificed at 1, 2, 4, 7, 14, and 21 days post injury. Spinal cord tissue was processed for Fluoro-Jade B histochemistry and included sections throughout the injured region of the cord. No Fluoro-Jade positive neurons were observed in sections from any time point postinjury at any level of the spinal cord. Instead, Fluoro-Jade labeled astrocytes in uninjured control animals and injured animals. The specificity of astrocytic staining was confirmed by co-localizaton of Fluoro-Jade with glial fibrillary acidic protein. We also subjected a group of rats to a sequential cortical contusion injury and spinal cord injury. Sections from these animals showed numerous Fluoro-Jade positive neurons in the hippocampal formation and thalamus underlying the cortical contusion; however, the staining pattern in the spinal cord was identical to those animals that had received spinal cord injury alone.     

Effects of spinal cord injury and hindlimb immobilization on sublesional and supralesional bones in young growing rats

Both spinal cord injury (SCI) and hindlimb cast immobilization (HCI) cause reduction in maturation-related bone gain in young rats, but the effects of the two interventions on bone pathophysiology may be different. The objective of this study was to compare the effects of SCI and HCI on the sublesional/supralesional bones and bone turnover indicators in young rats. Forty male Sprague-Dawley rats (six-week-old) were randomized into four groups, with ten rats in each group. The groups were classified as follows: base-line control, age-matched intact control, HCI, and SCI groups. Bone tissues, blood, and urine samples were studied at 4 weeks after treatments. The tibial dry weights and ash weights in SCI were remarkably reduced by 7.5% (dry weights) and 8.2% (ash weights) compared with HCI. SCI rats showed lower areal bone mineral density in the proximal tibiae compared with HCI rats (- 14%). Cortical thickness and cortical area of the tibial midshaft in SCI were lower than HCI (- 23%, - 33% respectively). The bone surface/bone volume, trabecular separation, trabecular number, connectivity of the trabecular network, and structure model index of the proximal tibiae were remarkably different between SCI and HCI groups. In SCI tibiae, the mineralizing surface, mineral apposition rate, and surface-based bone formation rate were significantly higher than HCI groups (12%, 47%, and 29% respectively). In the compression test, the ultimate load, the energy of ultimate load, and Young's modulus of the proximal tibiae in SCI rats were significantly lower than HCI rats. The serum levels of osteocalcin and the urinary levels of deoxypyridinoline in SCI were higher than those in HCI. There were no significant changes in supralesional bones between SCI and HCI rats. SCI results in a rapid bone loss with more deterioration of trabecular microstructure and cortical bone geometric structure in sublesional bones. High bone turnover rate and low biomechanics strength were found in tibiae in SCI rats. This might be the result of the imbalance of bone resorption and bone formation induced by the impaired neuronal function.     

Intermittently administered human parathyroid hormone(1-34) treatment increases intracortical bone turnover and porosity without reducing bone strength in the humerus of ovariectomized cynomolgus monkeys.

Cortical porosity in patients with hyperparathyroidism has raised the concern that intermittent parathyroid hormone (PTH) given to treat osteoporotic patients may weaken cortical bone by increasing its porosity. We hypothesized that treatment of ovariectomized (OVX) cynomolgus monkeys for up to 18 months with recombinant human PTH(1-34) [hPTH(1-34)] LY333334 would significantly increase porosity in the midshaft of the humerus but would not have a significant effect on the strength or stiffness of the humerus. We also hypothesized that withdrawal of PTH for 6 months after a 12-month treatment period would return porosity to control OVX values. OVX female cynomolgus monkeys were given once daily subcutaneous (sc) injections of recombinant hPTH(1-34) LY333334 at 1.0 microg/kg (PTH1), 5.0 microg/kg (PTH5), or 0.1 ml/kg per day of phosphate-buffered saline (OVX). Sham OVX animals (sham) were also given vehicle. After 12 months, PTH treatment was withdrawn from half of the monkeys in each treatment group (PTH1-W and PTH5-W), and they were treated for the remaining 6 months with vehicle. Double calcein labels were given before death at 18 months. After death, static and dynamic histomorphometric measurements were made intracortically and on periosteal and endocortical surfaces of sections from the middiaphysis of the left humerus. Bone mechanical properties were measured in the right humeral middiaphysis. PTH dose dependently increased intracortical porosity. However, the increased porosity did not have a significant detrimental effect on the mechanical properties of the bone. Most porosity was concentrated near the endocortical surface where its mechanical effect is small. In PTH5 monkeys, cortical area (Ct.Ar) and cortical thickness (Ct.Th) increased because of a significantly increased endocortical mineralizing surface. After withdrawal of treatment, porosity in PTH1-W animals declined to sham values, but porosity in PTH5-W animals remained significantly elevated compared with OVX and sham. We conclude that intermittently administered PTH(1-34) increases intracortical porosity in a dose-dependent manner but does not reduce the strength or stiffness of cortical bone.