To elucidate mechanisms of bone loss after spinal cord injury (SCI), we evaluated the time-course of cancellous and cortical bone microarchitectural deterioration via microcomputed tomography, measured histomorphometric and circulating bone turnover indices, and characterized the development of whole bone mechanical deficits in a clinically relevant experimental SCI model. 16-weeks-old male Sprague-Dawley rats received T laminectomy (SHAM, n = 50) or moderate-severe contusion SCI (n = 52). Outcomes were assessed at 2-weeks, 1-month, 2-months, and 3-months post-surgery. SCI produced immediate sublesional paralysis and persistent hindlimb locomotor impairment. Higher circulating tartrate-resistant acid phosphatase 5b (bone resorption marker) and lower osteoblast bone surface and histomorphometric cancellous bone formation indices were present in SCI animals at 2-weeks post-surgery, suggesting uncoupled cancellous bone turnover. Distal femoral and proximal tibial cancellous bone volume, trabecular thickness, and trabecular number were markedly lower after SCI, with the residual cancellous network exhibiting less trabecular connectivity. Periosteal bone formation indices were lower at 2-weeks and 1-month post-SCI, preceding femoral cortical bone loss and the development of bone mechanical deficits at the distal femur and femoral diaphysis. SCI animals also exhibited lower serum testosterone than SHAM, until 2-months post-surgery, and lower serum leptin throughout. Our moderate-severe contusion SCI model displayed rapid cancellous bone deterioration and more gradual cortical bone loss and development of whole bone mechanical deficits, which likely resulted from a temporal uncoupling of bone turnover, similar to the sequalae observed in the motor-complete SCI population. Low testosterone and/or leptin may contribute to the molecular mechanisms underlying bone deterioration after SCI.

Diminished bone perfusion develops in response to disuse and has been proposed as a mechanism underlying bone loss. Bone blood flow (BF) has not been investigated within the unique context of severe contusion spinal cord injury (SCI), a condition that produces neurogenic bone loss that is precipitated by disuse and other physiologic consequences of central nervous system injury. Herein, 4-mo-old male Sprague-Dawley rats received T9 laminectomy (SHAM) or laminectomy with severe contusion SCI (N=20/group). Time course assessments of hindlimb bone microstructure and bone perfusion were performed in vivo at 1- and 2-wks post-surgery via microCT and intracardiac microsphere infusion, respectively, and bone turnover indices were determined via histomorphometry. Both groups exhibited cancellous bone loss beginning in the initial post-surgical week, with cancellous and cortical bone deficits progressing only in SCI thereafter. Trabecular bone deterioration coincided with uncoupled bone turnover after SCI, as indicated by signs of ongoing osteoclast-mediated bone resorption and a near-complete absence of osteoblasts and cancellous bone formation. Bone BF was not different between groups at 1-wk, when both groups displayed bone loss. In comparison, femur and tibia perfusion was 30-40% lower in SCI vs SHAM at 2-wks, with the most pronounced regional BF deficits occurring at the distal femur. Significant associations existed between distal femur BF and cancellous and cortical bone loss indices. Our data provide the first direct evidence indicating bone BF deficits develop in response to SCI and temporally coincide with suppressed bone formation and with cancellous and cortical bone deterioration.

Loading and testosterone may influence musculoskeletal recovery after spinal cord injury (SCI). Our objectives were to determine (a) the acute effects of bodyweight‐supported treadmill training (TM) on hindlimb cancellous bone microstructure and muscle mass in adult rats after severe contusion SCI and (b) whether longer‐term TM with adjuvant testosterone enanthate (TE) delivers musculoskeletal benefit. In Study 1, TM (40 min/day, 5 days/week, beginning 1 week postsurgery) did not prevent SCI‐induced hindlimb cancellous bone loss after 3 weeks. In Study 2, TM did not attenuate SCI‐induced plantar flexor muscles atrophy nor improve locomotor recovery after 4 weeks. In our main study, SCI produced extensive distal femur and proximal tibia cancellous bone deficits, a deleterious slow‐to‐fast fiber‐type transition in soleus, lower muscle fiber cross‐sectional area (fCSA), impaired muscle force production, and levator ani/bulbocavernosus (LABC) muscle atrophy after 8 weeks. TE alone (7.0 mg/week) suppressed bone resorption, attenuated cancellous bone loss, constrained the soleus fiber‐type transition, and prevented LABC atrophy. In comparison, TE+TM concomitantly suppressed bone resorption and stimulated bone formation after SCI, produced near‐complete cancellous bone preservation, prevented the soleus fiber‐type transition, attenuated soleus fCSA atrophy, maintained soleus force production, and increased LABC mass. 75% of SCI+TE+TM animals recovered voluntary over‐ground hindlimb stepping, while no SCI and only 20% of SCI+TE animals regained stepping ability. Positive associations between testosterone and locomotor function suggest that TE influenced locomotor recovery. In conclusion, short‐term TM alone did not improve bone, muscle, or locomotor recovery in adult rats after severe SCI, while longer‐term TE+TM provided more comprehensive musculoskeletal benefit than TE alone.

Spinal cord injury (SCI) is associated with obesity and is a risk factor for type 2 diabetes mellitus (T2DM). Immobilization, muscle atrophy, obesity, and loss of sympathetic innervation to the liver are believed to contribute to risks of these abnormalities. Systematic study of the mechanisms underlying SCI-induced metabolic disorders has been limited by a lack of animal models of insulin resistance following SCI. Therefore, the effects of a high-fat diet (HFD), which causes weight gain and glucose intolerance in neurologically intact mice, was tested in mice that had undergone a spinal cord transection at thoracic vertebra 10 (T10) or a sham-transection. At 84 days after surgery, Sham-HFD and SCI-HFD mice showed impaired intraperitoneal glucose tolerance when compared with Sham control (Sham-Con) or SCI control (SCI-Con) mice fed a standard control chow. Glucose tolerance in SCI-Con mice was comparable to that of Sham-Con mice. The mass of paralyzed skeletal muscle, liver, and epididymal, inguinal, and omental fat deposits were lower in SCI versus Sham groups, with lower liver mass present in SCI-HFD versus SCI-Con animals. SCI also produced sublesional bone loss, with no differences between SCI-Con and SCI-HFD groups. The results suggest that administration of a HFD to mice after SCI may provide a model to better understand mechanisms leading to insulin resistance post-SCI, as well as an approach to study pathogenesis of glucose intolerance that is independent of obesity.

OBJECTIVE:Angiogenesis inhibitors (AgI) are commonly used in combination chemotherapy protocols to treat cancer, and have been linked to osteonecrosis of the jaw (ONJ). However, it is unknown if AgI therapy alone is sufficient to induce ONJ. We have previously established an ONJ model in rice rats with localized periodontitis that receive zoledronic acid (ZOL). The purpose of this study was to use this model to determine the role of anti-vascular endothelial growth factor A (anti-VEGF) antibody treatment of rice rats with localized maxillary periodontitis. We hypothesized that rice rats with localized maxillary periodontitis given anti-VEGF monotherapy will develop oral lesions that resemble ONJ, defined by exposed, necrotic alveolar bone. METHODS:At age 4 wks, 45 male rice rats were randomized into three groups (n=15): 1) VEH (saline), 2) ZOL (80 μg/kg body weight, intravenously once monthly), and 3

Periodontitis is an important public health concern worldwide. Because rodents from the genus Rattus are resistant to spontaneous periodontitis, experimental periodontitis must be initiated by mechanical procedures and interventions. Due to their exacerbated Th1 response and imbalanced Th17 regulatory T-cell responses, Lewis rats are highly susceptible to inducible inflammatory and autoimmune diseases. We hypothesized that feeding Lewis rats a diet high in sucrose and casein (HSC) would alter the oral microenvironment and induce inflammation and the development of periodontitis lesions without mechanical intervention. A baseline group (BSL, n = 8) was euthanized at age 6 wk. Beginning at 6 wk of age, 2 groups of Lewis rats were fed standard (STD, n = 12) or HSC (n = 20) chow and euthanized at 29 wk of age. We evaluated the degree of periodontitis through histology and μCT of maxillae and mandibles. The HSC-induced inflammatory response of periodontal tissues was assessed by using immunohistochemistry. Gene expression analysis of inflammatory cytokines associated with Th1 and Th17 responses, innate immunity cytokines, and tissue damage in response to bacteria were assessed also. The potential systemic effects of HSC diet were evaluated by assessing body composition and bone densitometry endpoints; serum leptin and insulin concentrations; and gene expression of inflammatory cytokines in the liver. Placing Lewis rats on HSC diet for 24 wk induced a host Th1-immune response in periodontal tissues and mild to moderate, generalized periodontitis characterized by inflammatory cell infiltration (predominantly T cells and macrophages), osteoclast resorption of alveolar bone, and hyperplasia and migration of the gingival epithelium. HSC-fed Lewis rats developed periodontitis without mechanical intervention in the oral cavity and in the absence of any noteworthy metabolic abnormalities. Consequently, the rat model we described here may be a promising approach for modeling mild to moderate periodontitis that is similar in presentation to the human disease.

BACKGROUND 3D image registration is a technique where in‐vivo microCT scans are collected at different timepoints and regions of interest (ROI) are constructed and aligned to improve the precision of determining bone microstructure. In the rodent spinal cord injury (SCI) model, the rapid bone loss occurring at the distal femur precludes the use of standard 3D registration strategies. PURPOSE To (1) adapt a microCT‐based 3D registration protocol to our rodent SCI model, (2) determine the degree of cancellous bone loss at the distal femoral epiphysis after SCI, and (3) assess the effects of bodyweight‐supported treadmill training (TM) or passive bicycle training (PBT) on bone loss after SCI. METHODS 16‐wk old male Sprague‐Dawley rats were stratified to receive: 1) T9 laminectomy (SHAM) (n=9), 2) severe T9 contusion (SCI) (n=10), 3) SCI+TM (n=10), or 4) SCI+PBT (n=14). TM and PBT began 1‐wk post‐surgery (post‐sx, two 20‐min bouts/day, 5‐d/wk for 3‐wks). In‐vivo microCT scans were performed pre‐sx and 2‐ and 4‐wks post‐sx. Images were aligned with a 3D registration protocol. ROIs were developed to assess cancellous bone microstructure at the distal femoral epiphysis using two separate protocols that either included or excluded new bone formed by periosteal bone expansion over the 4‐wk experiment. RESULTS Differences were noted between the ROI protocols, with the ROI that included periosteal bone growth underestimating SCI‐induced bone loss. As such, the results reported hereafter were derived from the ROI that excluded new bone resulting from periosteal bone expansion. No differences in bone outcomes were present in SHAMs at any timepoint except for a slightly higher trabecular separation (Tb.Sp) at 4‐wks (p<.05). At 2‐wks, SCI displayed 14% lower cancellous bone volume (BV/TV) than pre‐sx (p<.01), characterized by 13% lower trabecular number (Tb.N) (p<.05) and 7% higher Tb.Sp (p<.05). Bone loss was more pronounced at 4‐wks after SCI, evidenced by lower trabecular thickness (Tb.Th) and higher Tb.Sp vs 2‐wks (both p<.01). SCI+TM and SCI+PBT displayed a similar magnitude of bone loss to SCI at 2‐wks (1‐wk after starting exercise). Thereafter, SCI+TM displayed no further bone loss, resulting in 9% less BV/TV loss than SCI (p<.01). In comparison, PBT increased BV/TV 15% from 2‐ to 4‐wks (p<.01), due to 5% higher Tb.Th (p<.01) and 12% higher Tb.N (p<.05), ultimately restoring BV/TV to pre‐sx levels. Structural model index (SMI) and trabecular pattern factor (Tb.Pf) increased in SCI (p<0.05) and SCI+TM at 4‐wks (p<.05 to <.01), signifying transition from rod‐like to weaker plate‐like trabeculae and a less connected trabecular network, respectively. In comparison, SMI (p<.05) and Tb.Pf (p<.01) increased in SCI+PBT at 2‐wks before returning to pre‐sx levels by 4‐wks. CONCLUSION Using our 3D registration protocol, we determined that SCI causes severe cancellous bone loss and changes indicative of an overall weakening of bone architecture at the distal femoral epiphysis. TM attenuated bone loss at this skeletal site, while PBT...

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