Androgen administration protects against musculoskeletal deficits in models of sex-steroid deficiency and injury/disuse. It remains unknown, however, whether testosterone prevents bone loss accompanying spinal cord injury (SCI), a condition that results in a near universal occurrence of osteoporosis. Our primary purpose was to determine whether testosterone-enanthate (TE) attenuates hindlimb bone loss in a rodent moderate/severe contusion SCI model. Forty (n=10/group), 14 week old male Sprague-Dawley rats were randomized to receive: (1) Sham surgery (T9 laminectomy), (2) moderate/severe (250 kdyne) SCI, (3) SCI+Low-dose TE (2.0 mg/week), or (4) SCI+High-dose TE (7.0 mg/week). Twenty-one days post-injury, SCI animals exhibited a 77-85% reduction in hindlimb cancellous bone volume at the distal femur (measured via μCT) and proximal tibia (measured via histomorphometry), characterized by a >70% reduction in trabecular number, 13-27% reduction in trabecular thickness, and increased trabecular separation. A 57% reduction in cancellous volumetric bone mineral density (vBMD) at the distal femur and a 20% reduction in vBMD at the femoral neck were also observed. TE dose dependently prevented hindlimb bone loss after SCI, with high-dose TE fully preserving cancellous bone structural characteristics and vBMD at all skeletal sites examined. Animals receiving SCI also exhibited a 35% reduction in hindlimb weight bearing (triceps surae) muscle mass and a 22% reduction in sublesional non-weight bearing (levator ani/bulbocavernosus [LABC]) muscle mass, and reduced prostate mass. Both TE doses fully preserved LABC mass, while only high-dose TE ameliorated hindlimb muscle losses. TE also dose dependently increased prostate mass. Our findings provide the first evidence indicating that high-dose TE fully prevents hindlimb cancellous bone loss and concomitantly ameliorates muscle loss after SCI, while low-dose TE produces much less profound musculoskeletal benefit. Testosterone-induced prostate enlargement, however, represents a potential barrier to the clinical implementation of high-dose TE as a means of preserving musculoskeletal tissue after SCI.

The purpose of this study is two-fold: (1) to examine skeletal muscle function in a rat model of midthoracic contusion spinal cord injury (SCI) and (2) to evaluate the therapeutic influence of a short bout (1 week) of treadmill locomotor training on soleus muscle function (peak force, fatigability, contractile properties, fiber types), size (fiber area), and motor deficit and recovery (BBB scores) after SCI. The rats were injured with a moderate T8 spinal cord contusion and were assigned to either receive treadmill locomotor training (TM), starting 1 week after SCI for 5 consecutive days (20 min/trial, 2 trials/day) or not to receive any exercise intervention (no TM). Locomotor training resulted in a significant improvement in overall locomotor function (32% improvement in BBB scores) when compared to no TM. Also, the injured animals that trained for 1 week had 38% greater peak soleus tetanic forces (p < 0.05), a 9% decrease in muscle fatigue (p < 0.05), 23% larger muscle fiber CSA (p < 0.05), and decreased immunoexpression of fast heavy chain fiber types than did rats receiving no TM. In addition, there was a good correlation (0.704) between the BBB scores of injured animals and peak soleus muscle force regardless of group assignment. No significant differences were seen in twitch or time to peak tension values across groups. Collectively, these results indicate that 1 week of treadmill locomotor training, initiated early after SCI, can significantly improve motor recovery following SCI. The magnitude of these changes is remarkable considering the relatively short training interval and clearly illustrates the potential that initiating treadmill locomotor training shortly after injury may have on countering some of the functional deficits resulting from SCI.

Study design: Experimental rat model of spinal cord contusion injury (contusion SCI).Objective: The objectives of this study were (1) to characterize the longitudinal changes in rat lower hindlimb muscle morphology following contusion SCI by using magnetic resonance imaging and (2) to determine the therapeutic potential of two types of locomotor training, treadmill and cycling. Setting: University research setting. Methods: After moderate midthoracic contusion SCI, Sprague-Dawley rats were assigned to either treadmill training, cycle training or an untrained group. Lower hindlimb muscle size was examined prior to SCI and at 1-, 2-, 4-, 8-, and 12-week post injury. Results: Following contusion SCI, we observed significant atrophy in all rat hindlimb muscles with the posterior muscles (triceps surae and flexor digitorum) showing greater atrophy than the anterior muscles (tibialis anterior and extensor digitorum). The greatest amount of atrophy was measured at 2-week post injury (range from 11 to 26%), and spontaneous recovery in muscle size was observed by 4 weeks post-SCI. Both cycling and treadmill training halted the atrophic process and accelerated the rate of recovery. The therapeutic influence of both training interventions was observed within 1 week of training and no significant difference was noted between the two interventions, except in the tibialis anterior muscle. Finally, a positive correlation was found between locomotor functional scores and hindlimb muscle size following SCI. Conclusions: Both treadmill and cycle training diminish the extent of atrophy and facilitate muscle plasticity after contusion SCI.

Spinal cord injury (SCI) results in rapid and extensive sublesional bone loss. Sclerostin, an osteocyte-derived glycoprotein that negatively regulates intraskeletal Wnt signaling, is elevated after SCI and may represent a mechanism underlying this excessive bone loss. However, it remains unknown whether pharmacologic sclerostin inhibition ameliorates bone loss subsequent to SCI. Our primary purposes were to determine whether a sclerostin antibody (Scl-Ab) prevents hindlimb cancellous bone loss in a rodent SCI model and to compare the effects of a Scl-Ab to that of testosterone-enanthate (TE), an agent that we have previously shown prevents SCI-induced bone loss. Fifty-five (n ¼ 11-19/group) skeletally mature male Sprague-Dawley rats were randomized to receive: (A) SHAM surgery (T8 laminectomy), (B) moderate-severe (250 kilodyne) SCI, (C) 250 kilodyne SCI þ TE (7.0 mg/wk, im), or (D) 250 kilodyne SCI þ Scl-Ab (25 mg/kg, twice weekly, sc) for 3 weeks. Twenty-one days post-injury, SCI animals exhibited reduced hindlimb cancellous bone volume at the proximal tibia (via mCT and histomorphometry) and distal femur (via mCT), characterized by reduced trabecular number and thickness. SCI also reduced trabecular connectivity and platelike trabecular structures, indicating diminished structural integrity of the remaining cancellous network, and produced deficits in cortical bone (femoral diaphysis) strength. Scl-Ab and TE both prevented SCI-induced cancellous bone loss, albeit via differing mechanisms. Specifically, Scl-Ab increased osteoblast surface and bone formation, indicating direct bone anabolic effects, whereas TE reduced osteoclast surface with minimal effect on bone formation, indicating antiresorptive effects. The deleterious microarchitectural alterations in the trabecular network were also prevented in SCI þ Scl-Ab and SCI þ TE animals, whereas only Scl-Ab completely prevented the reduction in cortical bone strength. Our findings provide the first evidence indicating that sclerostin inhibition represents a viable treatment to prevent SCI-induced cancellous and cortical bone deficits and provides preliminary rationale for future clinical trials focused on evaluating whether Scl-Ab prevents osteoporosis in the SCI population.

The objective of this study was to determine the impact of treadmill locomotor training on the expression of insulin-like growth factor I (IGF1) and changes in myogenic regulatory factors (MRFs) in rat soleus muscle following spinal cord injury (SCI). Moderate, midthoracic (T(8)) contusion SCIs were produced using a NYU (New York University) impactor. Animals were randomly assigned to treadmill training or untrained groups. Rats in the training group were trained starting at 1 week after SCI, for either 3 bouts of 20 min over 1.5 days or 10 bouts over 5 days. Five days of treadmill training completely prevented the decrease in soleus fiber size resulting from SCI. In addition, treadmill training triggered increases in IGF1, MGF and IGFBP4 mRNA expression, and a concurrent reduction of IGFBP5 mRNA in skeletal muscle. Locomotor training also caused an increase in markers of muscle regeneration, including small muscle fibers expressing embryonic myosin and Pax7 positive nuclei and increased expression of the MRFs, myogenin and MyoD. We concluded that treadmill locomotor training ameliorated muscle atrophy in moderate contusion SCI rats. Training-induced muscle regeneration and fiber hypertrophy following SCI was associated with an increase in IGF1, an increase in Pax7 positive nuclei, and upregulation of MRFs.

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.

Spasticity is an important problem that complicates daily living in many individuals with spinal cord injury (SCI). While previous studies in human and animals revealed significant improvements in locomotor ability with treadmill locomotor training, it is not known to what extent locomotor training influences spasticity. In addition, it would be of considerable practical interest to know how the more ergonomically feasible cycle training compares with treadmill training as therapy to manage SCI-induced spasticity and to improve locomotor function. Thus the main objective of our present studies was to evaluate the influence of different types of locomotor training on measures of limb spasticity, gait, and reflex components that contribute to locomotion. For these studies, 30 animals received midthoracic SCI using the standard Multicenter Animal Spinal cord Injury Studies (MASCIS) protocol (10 g 2.5 cm weight drop). They were divided randomly into three equal groups: control (contused untrained), contused treadmill trained, and contused cycle trained. Treadmill and cycle training were started on post-injury day 8. Velocity-dependent ankle torque was tested across a wide range of velocities (612–49°/s) to permit quantitation of tonic (low velocity) and dynamic (high velocity) contributions to lower limb spasticity. By post-injury weeks 4 and 6, the untrained group revealed significant velocity-dependent ankle extensor spasticity, compared to pre-surgical control values. At these post-injury time points, spasticity was not observed in either of the two training groups. Instead, a significantly milder form of velocity-dependent spasticity was detected at postcontusion weeks 8–12 in both treadmill and bicycle training groups at the four fastest ankle rotation velocities (350–612°/s). Locomotor training using treadmill or bicycle also produced significant increase in the rate of recovery of limb placement measures (limb axis, base of support, and open field locomotor ability) and reflex rate-depression, a quantitative assessment of neurophysiological processes that regulate segmental reflex excitability, compared with those of untrained injured controls. Light microscopic qualitative studies of spared tissue revealed better preservation of myelin, axons, and collagen morphology in both locomotor trained animals. Both locomotor trained groups revealed decreased lesion volume (rostro-caudal extension) and more spared tissue at the lesion site. These improvements were accompanied by marked upregulation of BDNF, GABA/GABAb, and monoamines (e.g., norepinephrine and serotonin) which might account for these improved functions. These data are the first to indicate that the therapeutic efficacy of ergonomically practical cycle training is equal to that of the more labor-intensive treadmill training in reducing spasticity and improving locomotion following SCI in an animal model.

Progressive neurophysiological changes in the excitability of the pathways that subserved ankle extensor stretch reflexes were observed following midthoracic contusion. The purpose of the present study was to determine the nature and time course of velocity-dependent changes in the excitability of the ankle stretch reflex following T(8) contusion injury. These studies were conducted in adult Sprague-Dawley rats using a 10-g 2.5-cm weight drop onto the exposed thoracic spinal cord (using an NYU injury device and a MASCIS protocol). Velocity-dependent ankle torques and triceps surae EMGs were measured in awake animals over a broad range of rotation velocities (49-612 deg/sec) using instrumentation and protocol previously reported. EMGs and ankle torques were measured before and at weekly intervals following injury. Statistical tests of the data included within group repeated measures ANOVA and between group one-way ANOVA comparisons with time-matched control animals. An alternating pattern of significant increase followed by significant decrease in velocity-dependent ankle torque was observed during the first postinjury month. An increase of 33% in the peak torque and 24% in peak EMG magnitude at 612 deg/sec was observed in the first week. EMG burst amplitudes, that were timed-locked to the dynamic phase of the rotation, were observed to increase and decrease in a manner, which indicated that the changes in torque included stretch-evoked active contractions of the ankle extensors. During the second and third postinjury months, consistent 24-40% increases in the peak torques and 17-107% increases in the EMG magnitudes at the highest velocity were observed. No significant increases in torques were observed in the slowest rotation velocity in these periods.