Dynamic Weight Bearing Research Articles

Correlation between μCT imaging, histology and functional capacity of the osteoarthritic knee in the rat model of osteoarthritis

BackgroundTo acquire the most meaningful understanding of human arthritis, it is essential to select the disease model and methodology translatable to human conditions. The primary objective of this study was to evaluate a number of analytic techniques and biomarkers for their ability to accurately gauge bone and cartilage morphology and metabolism in the medial meniscal tear (MMT) model of osteoarthritis (OA).MethodsMMT surgery was performed in rats to induce OA. A dynamic weight bearing system (DWB) system was deployed to evaluate the weight-bearing capacity of the front and hind legs in rats. At the end of a 10-week study cartilage pathology was evaluated by micro computed tomography (μCT), contrast enhanced μCT (EPIC μCT) imaging and traditional histology. Bone tissue was evaluated at the tibial metaphysis and epiphysis, including the subchondral bone. Histological techniques and dynamic histomorphometry were used to evaluate cartilage morphology and bone mineralization.ResultsThe study results showed a negative impact of MMT surgery on the weight-bearing capacity of the operated limb. Surgery caused severe and extensive deterioration of the articular cartilage at the medial tibial plateau, as evidenced by elevated CTX-II in serum, EPIC μCT and histology. Bone analysis by μCT showed thickening of the subchondral bone beneath the damaged cartilage, loss of cancellous bone at the metaphysis and active osteophyte formation.ConclusionsThe study emphasizes the need for using various methodologies that complement each other to provide a comprehensive understanding of the pathophysiology of OA at the organ, tissue and cellular levels. Results from this study suggest that use of histology, μCT and EPIC μCT, and functional DWB tests provide powerful combination to fully assess the key aspects of OA and enhance data interpretation.

Identification of a novel target, FoxA2, in the onset and development of osteoarthritis

Identification of a novel target, FoxA2, in the onset and development of osteoarthritis

Evaluation of dynamic weight bearing for measuring nonevoked inflammatory hyperalgesia in mice.

Animal models in pain research have suggested that inclusion of both evoked and nonevoked behavioral measures is needed to better reflect the human pain experience. Individuals with chronic pain are known to experience spontaneous pain, in addition to pain after exposure to an external stimulus. Recently, the dynamic weight bearing (DWB) apparatus was developed to assess for nonevoked hyperalgesia by capturing weight bearing and surface distribution in the paws of mice after acute inflammation. The aim of this study was to evaluate the DWB test as a measure of nonevoked hyperalgesia. The experimental group received an intraplantar injection in the left hind paw of the inflammatory agent--complete Freund's adjuvant (CFA)--whereas the vehicle control group received a saline injection and the naive control group had no treatment. Calipers and a plethysmometer were used to verify inflammation and the hot-plate test was used as a measure for stimulus-evoked hyperalgesia. Data were collected at baseline; 3 hours; and 1, 3, and 7 days after injection. Mice injected with CFA showed a statistically significant higher mean paw thickness and volume displacement compared with the vehicle and naive control groups. In the hot-plate testing, CFA-treated mice showed lower response temperature at 7 days compared with the other groups. On the DWB test, CFA-treated mice showed a reduction in the ipsilateral paw load and surface area compared with the contralateral paw load at Days 1, 3, and 7. Mice with inflammation showed alterations in weight bearing as well as increased thermal hyperalgesia in comparison with control groups. These findings support the use of the DWB test as a tool for measuring nonevoked inflammatory hyperalgesia in a mouse model.

Orthopedic surgery and bone fracture pain are both significantly attenuated by sustained blockade of nerve growth factor.

The number of patients suffering from postoperative pain due to orthopedic surgery and bone fracture is projected to dramatically increase because the human life span, weight, and involvement in high-activity sports continue to rise worldwide. Joint replacement or bone fracture frequently results in skeletal pain that needs to be adequately controlled for the patient to fully participate in needed physical rehabilitation. Currently, the 2 major therapies used to control skeletal pain are nonsteroidal anti-inflammatory drugs and opiates, both of which have significant unwanted side effects. To assess the efficacy of novel therapies, mouse models of orthopedic and fracture pain were developed and evaluated here. These models, orthopedic surgery pain and bone fracture pain, resulted in skeletal pain-related behaviors that lasted 3 weeks and 8 to 10 weeks, respectively. These skeletal pain behaviors included spontaneous and palpation-induced nocifensive behaviors, dynamic weight bearing, limb use, and voluntary mechanical loading of the injured hind limb. Administration of anti-nerve growth factor before orthopedic surgery or after bone fracture attenuated skeletal pain behaviors by 40% to 70% depending on the end point being assessed. These data suggest that nerve growth factor is involved in driving pain due to orthopedic surgery or bone fracture. These animal models may be useful in developing an understanding of the mechanisms that drive postoperative orthopedic and bone fracture pain and the development of novel therapies to treat these skeletal pains.

Long-term functional outcome after surgical repair of cranial cruciate ligament disease in dogs.

BackgroundCranial cruciate ligament (CCL) rupture is a very common cause of pelvic limb lameness in dogs. Few studies, using objective and validated outcome evaluation methods, have been published to evaluate long-term (>1 year) outcome after CCL repair. A group of 47 dogs with CCL rupture treated with intracapsular, extracapsular, and osteotomy techniques, and 21 healthy control dogs were enrolled in this study. To evaluate long-term surgical outcome, at a minimum of 1.5 years after unilateral CCL surgery, force plate, orthopedic, radiographic, and physiotherapeutic examinations, including evaluation of active range of motion (AROM), symmetry of thrust from the ground, symmetry of muscle mass, and static weight bearing (SWB) of pelvic limbs, and goniometry of the stifle and tarsal joints, were done.ResultsAt a mean of 2.8 ± 0.9 years after surgery, no significant differences were found in average ground reaction forces or SWB between the surgically treated and control dog limbs, when dogs with no other orthopedic findings were included (n = 21). However, in surgically treated limbs, approximately 30% of the dogs had decreased static or dynamic weight bearing when symmetry of weight bearing was evaluated, 40-50% of dogs showed limitations of AROM in sitting position, and two-thirds of dogs had weakness in thrust from the ground. The stifle joint extension angles were lower (P <0.001) and flexion angles higher (P <0.001) in surgically treated than in contralateral joints, when dogs with no contralateral stifle problems were included (n = 33). In dogs treated using the intracapsular technique, the distribution percentage per limb of peak vertical force (DPVF) in surgically treated limbs was significantly lower than in dogs treated with osteotomy techniques (P =0.044).ConclusionsThe average long-term dynamic and static weight bearing of the surgically treated limbs returned to the level of healthy limbs. However, extension and flexion angles of the surgically treated stifles remained inferior to healthy joints, and impairment of AROM and weakness in thrust from the ground in the surgically treated limbs were frequently present. Ground reaction forces may be inadequate as a sole method for assessing functional outcome after cranial cruciate ligament repair.

Abstract 3687: Analgesic effects of capsazepine on a mouse model of bone cancer pain

Abstract Breast cancer has the highest incidence rate in women, accounting for more than 22% of all cancers and possessing a strong disposition to metastasize to bone. Discovered in 70% of advanced breast cancer patients and over 90% prevalence in patients who die from breast cancer, the affinity of this disease to metastasize bone has become overwhelming. These skeletal metastases become a significant cause of morbidity and mortality in patients with the primary symptom being pain. Pain is a major concern in determining a patient's quality of life and there have been many attempts to understand and control bone pain with little success. Capsazepine was identified during a high throughput screen to be a potent inhibitor of breast cancer cell-mediated glutamate release, a neurotransmitter with known associations in both neural communication and pain. This drug also has antagonistic effects on transient receptor potential vanilloid type 1 (TRPV-1) receptors which act as key players in both heat and vanilloid-induced nociception. Studies have shown that glutamate plays a role in bone cancer pain, with an excess in free glutamate able to cause pain either directly through excitotoxic pathways or indirectly though the dysregulation of osteoclasts and osteoblasts, causing bone dysregulation. TRPV-1 receptors have also has been implicated in the mechanisms of bone cancer pain, as osteoclasts release protons during bone remodeling which can elicit a TRPV-1-related nociceptive response from neurons in the surrounding periosteum. These findings suggest that Capsazepine may provide a powerful multi-pronged approach to treating cancer pain. A model of breast cancer-induced bone pain has been established using human MDA-MB-231 breast adenocarcinoma cells injected into the femurs of BALB/c nude mice. Behavioural tests are then preformed using the dynamic plantar aesthesiometer (DPA) and the dynamic weight bearing (DWB) devices on the affected limb for both movement-evoked and spontaneous pain-related behaviours. Using Capsazepine, delivered intraperitoneally via mini-osmotic drug pumps (5kg/mg and 10kg/mg), we demonstrate a dose-dependent attenuation of pain behaviours in vivo. While confirming tumour presence using immunohistochemistry (IHC) we show that TRPV-1 and glutamate play an important role in the onset and severity of bone cancer pain. The use of Capsazepine was able to attenuate these pain-related behaviours without the side effects of common analgesics. (This work is supported by the Canadian Institutes of Health Research (CIHR)) Citation Format: Matthew D. Balenko, Eric Seidlitz, Gurmit Singh. Analgesic effects of capsazepine on a mouse model of bone cancer pain. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3687. doi:10.1158/1538-7445.AM2014-3687

Immediate effects of single-leg stance exercise on dynamic balance, weight bearing and gait cycle in stroke patients

Methods: Eighteen patients with hemiplegia participated in this study. There were twelve males and six females. This study investigated the effects of the single-leg stance exercise on dynamic balance, weight bearing, and gait ability compared with four conditions. Dynamic balance and weight bearing were measured using the step test (ST) of the affected side in stroke patients. In addition, gait parameters were measured using the optogait system for analysis of the spatial and temporal parameters of walking in stroke patients. Results: This study investigated the effect of the single leg stance exercise on the paralysis side. The ST showed significant findings for all conditions (p<0.05). Therefore, knee extension and flexion exercise on the affected side single-leg stance (condition 4) significantly improved dynamic balance and weight bearing on the affected side (p<0.05). In the condition of moving the knee joint in a single-leg stance was discovered that the stance phase time significantly increased more than in the condition of supporting the maximal voluntary weight on the affected side (p<0.05). Conclusions: Single-leg stance on the paralysis side with knee flexion and extension increased symmetry in weight bearing during stance phase time. This study suggests that single-leg stance exercises augments improved gait function through sufficient weight bearing in the stance phase of the affected side.

Use of dynamic weight bearing as a novel end-point for the assessment of abdominal pain in the LPS-induced peritonitis model in the rat.

Chronic pelvic pain (CPP) is defined as long-lasting and severe pelvic pain persisting over six months in cyclic or non-cyclic chronic manner. Various pathologic conditions like endometriosis, abdominal infections, intra-peritoneal adhesions or infection, underlie CPP which is often the leading symptom of the associated diseases. Pharmacological approaches addressing CPP are hampered by the absence of a straight-forward, objective, and reliable method for the assessment of CPP in rodents. In the presented study, the dynamic weight bearing system (DWB) was employed for the first time for the evaluation of pelvic pain in a rat model of LPS-induced peritonitis. Rats were pretreated with the COX-2 inhibitor rofecoxib and PGE2 levels were evaluated in peritoneal lavage. DWB analysis revealed that rats treated with LPS showed a relief posture by a significantly increased weight distribution to the front when compared to vehicle-treated animals. This effect was prevented by rofecoxib treatment indicating the sensitivity of the model for pelvic pain related to peritonitis. Analysis of the PGE2 levels in the peritoneal fluid indicated a correlation with the relief posture intensity. In contrast to others weight bearing approaches, the use of DWB allows evaluation of spontaneous posture changes as a consequence of pelvic pain. Taken together, we were able to show, that DWB combined with LPS-induced peritonitis may deliver a new reliable animal model addressing pelvic pain with high construct validity (peritoneal inflammation), and face validity (pain related relief posture).

Repair of the injured spinal cord by implantation of a synthetic degradable block copolymer in rat

The present study is designed to assess the properties of a new degradable PLA-b-PHEMA block copolymer hydrogel and its therapeutic effectiveness after implantation following a thoracic spinal cord hemisection on rats. Degradable characteristics and porous aspect of the scaffold are respectively analyzed by the evaluation of its mass loss and by electron microscopy. The biomaterial toxicity is measured through in vitro tests based on motoneuron survival and neurite growth on copolymer substrate. Functional measurements are assessed by the Basso, Beattie and Bresnahan (BBB) and the Dynamic Weight Bearing (DWB) tests during 8 weeks post-surgery. Histological analyses are achieved to evaluate the presence of blood vessels and axons, the density of the glial scar, the inflammatory reaction and the myelination at the lesion site and around it. The results indicate that the synthetic PLA-b-PHEMA block copolymer is a non-toxic and degradable biomaterial that provides support for regenerating axons and seems to limit scar tissue formation. Additionally, the implantation of the porous PLA-b-PHEMA scaffold enhances locomotor improvement. The observed functional recovery highlights the potential benefits of plain tissue engineering material, which can further be optimized by bioactive molecule functionalization or transplanted cell encapsulation.

The effect of resiniferatoxin pretreatment on pain measured by dynamic weight bearing and evoked pain responses in an acute inflammatory murine arthritis model

s / Osteoarthritis and Cartilage 22 (2014) S57–S489 S421 withdrawal threshold (PWT: g) using calibrated Von Frey hairs) at 0, 3, 7, 9, 14, 16 and 20 days post-injection. Alterations in knee joint structure (cartilage and synovium) were examined by macroscopic visualisation of articular surfaces (Guingamp classification), histology or immunohistochemistry. Differences between groups were analysed using Kruskal Wallis test followed by post hoc Dunn’s test. Data are presented as mean (95% confidence interval). Data for correlations between pain and pathology were obtained using pain behaviour scores observed at day of sacrifice. Data are presented as Spearman’s correlation coefficients. Results: Saline 0.1 mg MIA 1 mg MIA Associations between

Are static and dynamic kinematics comparable after total knee arthroplasty?

Knee kinematics provide information about how the femoral, tibial and patellar bones or prosthetic components move relative to each other. Accurate knowledge of kinematics is valuable for implant design, comparisons between designs or surgical techniques, and to identify differences between patients with good and poor outcomes. Both static and dynamic imaging techniques have been used to evaluate kinematics. In general, static imaging is used to capture better quality images or to capture views that cannot be acquired by dynamic imaging, whereas dynamic imaging is used to capture real-life movements. How well static kinematics represent dynamic kinematics is subject to frequent debate and has not been adequately addressed, especially after total knee arthroplasty (TKA). We compared the static and dynamic weightbearing kinematics of 10 female subjects after TKA. Using the same clinical scanner for both methods, static images were taken using our standard protocol, sequential-biplane radiographs at multiple flexion angles, as well as with dynamic video fluoroscopy during a step up activity. The static method can reliably measure all 12 degrees of freedom (DOF) after TKA, however only seven were compared due to the poorer out-of-plane reliability in the single-plane dynamic imaging. No differences were found between the static and dynamic kinematics for nine out of ten subjects. For one subject, however, a difference of 5–8° in internal/external tibial rotation was found. The research question, study purpose and the advantages and disadvantages of each method need to be considered when determining which imaging method to use.

Use of dynamic weight bearing as a novel end-point for the assessment of Freund's Complete Adjuvant induced hypersensitivity in mice

Animal models are an integral part of pain research. However, current models tend to rely on evoked responses and there is a belief that non-evoked responses may be a more relevant behavioural readout as the animal responds in a more natural manner. Here, dynamic weight bearing (DWB), a novel method for assessing mechanical hypersensitivity, was evaluated using the Freund's Complete Adjuvant (FCA) model of inflammatory pain in mice. DWB enables the measurement of weight placed through all four paws of a freely moving animal. The data obtained from DWB was compared with data acquired using the standard static weight bearing (incapacitance) test. In both tests reversal of FCA induced mechanical hypersensitivity was investigated using the selective COX2 inhibitor celecoxib. Mice treated with FCA placed less weight through the ipsilateral hindpaw compared to vehicle controls. This reduction was reversed by celecoxib (30mg/kg p.o.) in the dynamic and static weight bearing tests. The data presented here suggests that dynamic weight bearing may provide a novel end point for the development of new analgesics.

Dynamic effect of the tibialis posterior muscle on the arch of the foot during cyclic axial loading

BackgroundThe most common cause of acquired flatfoot deformity is tibialis posterior tendon dysfunction. The present study compared the change in medial longitudinal arch height during cyclic axial loading with and without activated tibialis posterior tendon force. MethodsFourteen normal, fresh frozen cadaveric legs were used. A total of 10,000 cyclic axial loadings of 500N were applied to the longitudinal axis of the tibia. The 32-N tibialis posterior tendon forces were applied to the specimens of the active group (n=7). Specimens of another group (non-active group, n=7) were investigated without the tibialis posterior tendon force. The bony arch index was calculated from the displacement of the navicular height. FindingsThe mean initial bony arch indexes with maximal weightbearing were 0.239 (SD 0.009) in active group and 0.239 (SD 0.014) in non-active group. After 7000cycles, the bony arch indexes with maximal weightbearing were significantly greater in the active group (mean 0.214, SD 0.013) than in the non-active group (mean 0.199, SD 0.013). The mean bony arch indexes with maximal weightbearing after 10,000cycles were 0.212 (SD 0.011) in the active group and 0.196 (SD 0.015) in the non-active group. InterpretationThe passive supportive structures were inadequate, and the tibialis posterior muscle was essential to maintain the medial longitudinal arch of the foot in the dynamic weightbearing condition. The findings underscore that physical therapy and arch supportive equipments are important to prevent flatfoot deformity in the condition of weakness or dysfunction of the tibialis posterior muscle.

Analgesic effects of lidocaine, morphine and diclofenac on movement-induced nociception, as assessed by the Knee-Bend and CatWalk tests in a rat model of osteoarthritis

Pain is the major symptom of osteoarthritis (OA) and the main reason for patients seeking medical care, but its treatment is not optimal. Animal studies are necessary to elucidate mechanisms underlying OA-induced pain and assess analgesics' efficacy. Previously, we showed that the Knee-Bend test and dynamic weight bearing by the CatWalk test are clinically relevant methods for assessing movement-induced nociception in the mono-iodoacetate (MIA) OA model. Using the same tests, in the present study we investigate the effects of lidocaine (5mg, 10% solution, intra-articular), morphine (6mg/kg, subcutaneous) and diclofenac (30mg/kg per os) on nociceptive behavior in OA animals, on days 3 and 20 of OA evolution.Morphine reduced nociceptive behavior in both tests at both time-points. Lidocaine also decreased nociceptive behavior in both tests on day 3, but on day 20 only reduced the Knee-Bend score. Diclofenac was highly effective in both tests on day 3, while on day 20 it induced a less pronounced decrease in the Knee-Bend score and was ineffective in the CatWalk test.The results showed that the Knee-Bend and CatWalk tests are reliable alternative methods for evaluating movement-induced nociception in OA animals, and measure nociception in a clinically relevant way, since an analgesic profile similar to the one described in humans was observed. Therefore, these tests might be important as good predictors of drug efficacy.

In Vivo Analysis of the Isolated Posterior Cruciate Ligament–Deficient Knee During Functional Activities

Background: Most patients with isolated posterior cruciate ligament (PCL) injuries have minimal symptoms, and nonoperative treatment is recommended. However, over time, these patients can develop significant degenerative changes in their knees. Historically, PCL laxity is graded by nonweightbearing anteroposterior measuring techniques that do not reproduce the true, dynamic weightbearing conditions in the injured knee. The purpose of this study was to determine the patholaxity in patients with isolated PCL deficiency during functional weightbearing activities (running, walking, and stair ascent). Hypothesis: Patients with unilateral, isolated PCL deficiency will demonstrate dynamic anteroposterior and rotational instability in their affected knees during functional activities of level running and stair ascent compared with their unaffected, contralateral knees. Study Design: Controlled laboratory study. Methods: Nine asymptomatic patients with isolated grade II PCL injury underwent Dynamic Stereo X-Ray (DSX) of both knees during level running and stair ascent. Three-dimensional reconstructions of the patients’ bilateral distal femurs and proximal tibias were created from high-resolution computed tomography (CT) scans. Three-dimensional joint kinematics were determined using a model-based tracking approach to align the radiographic images with CT-derived bone models. The resulting tibiofemoral rotations and translations for the PCL-deficient and PCL-intact knees were then compared. Results: During level running, the tibia of the PCL-deficient knee was approximately 2 mm posteriorly subluxated and had an anterior velocity relative to the femur approximately 40 mm/s greater than the contralateral, uninjured knee; however, this was only during the swing phase. No significant differences were found during the stance phase of running. During stair ascent, the tibia of the PCL-deficient knee was approximately 4 mm posteriorly subluxated compared with the intact limb during the terminal swing phase and early stance phase. Between foot strike and the time of peak ground-reaction force (GRF), the tibia of the PCL-deficient knee translated anteriorly relative to the femur with velocities 3 to 4 times greater than in the intact limb. Level walking was also evaluated in 3 patients, but no differences were seen, and it was not tested in the remaining 6 patients. Conclusion: Changes in knee kinematics due to isolated PCL injuries were highly activity dependent. During running, small differences were identified only during the swing phase when the knee was unloaded. However, during stair ascent, significant differences extended from the late swing into early stance phase. During the swing phase of stair ascent, the tibia in the PCL-deficient joint subluxated posteriorly. Then, as load was transferred to the ascending limb, the tibia reduced anteriorly with high velocity relative to the femur. The resulting shear motion may expose the loaded joint to abnormal and potentially damaging forces. Clinical Relevance: During functional activities, patients with isolated PCL injuries experience significant knee instability that cannot be identified by standard nonweightbearing static laxity measurements. The finding that different activities create different degrees of instability may have important implications for rehabilitation and activity limitations for PCL-deficient individuals.

Use of bathroom scales in measuring asymmetry of hindlimb static weight bearing in dogs with osteoarthritis

The study assessed the use and reliability of bathroom scales as an objective measurement tool, and setting a normal variance of static weight bearing between hindlimbs. Two groups of dogs were tested: a healthy control group (n = 21) and a group (n = 43) of dogs with confirmed osteoarthritis in at least one stifle joint, with or without hip joint osteoarthritis. Static weight bearing was evaluated manually and measured with two bathroom scales. An orthopaedic examination was done and dynamic weight bearing was measured using a force platform. Radiographs were taken to confirm the presence of osteoarthritis, and dogs were divided into groups of severe and non-severe osteo- arthritic changes. Reliability by repeatability was tested using analysis of variance, and the congruity between static weight bearing and other evaluation methods with Kappa statistics and proportion of agreement. The difference between the hindlimbs proportional to the body weight in control dogs was 3.3% (± 2.7%). The repeatability of measuring static weight bearing in the hindlimbs of osteoarthritic dogs with bathroom scales was 81% with osteoarthritic limbs, and 70% for unaffected limbs. The sensitivity of static weight bearing measurements using bathroom scales was 39% and specificity 85%. Bathroom scales are a reliable, simple, and cost-effective objective method for measuring static weight bearing and can be used as an outcome measure when rehabilitating dogs with osteoarthritic changes in the hindlimbs.

Nav1.9 Channel Contributes to Mechanical and Heat Pain Hypersensitivity Induced by Subacute and Chronic Inflammation

Inflammation is known to be responsible for the sensitization of peripheral sensory neurons, leading to spontaneous pain and invalidating pain hypersensitivity. Given its role in regulating neuronal excitability, the voltage-gated Nav1.9 channel is a potential target for the treatment of pathological pain, but its implication in inflammatory pain is yet not fully described. In the present study, we examined the role of the Nav1.9 channel in acute, subacute and chronic inflammatory pain using Nav1.9-null mice and Nav1.9 knock-down rats. In mice we found that, although the Nav1.9 channel does not contribute to basal pain thresholds, it plays an important role in heat pain hypersensitivity induced by subacute paw inflammation (intraplantar carrageenan) and chronic ankle inflammation (complete Freund's adjuvant-induced monoarthritis). We showed for the first time that Nav1.9 also contributes to mechanical hypersensitivity in both models, as assessed using von Frey and dynamic weight bearing tests. Consistently, antisense-based Nav1.9 gene silencing in rats reduced carrageenan-induced heat and mechanical pain hypersensitivity. While no changes in Nav1.9 mRNA levels were detected in dorsal root ganglia (DRGs) during subacute and chronic inflammation, a significant increase in Nav1.9 immunoreactivity was observed in ipsilateral DRGs 24 hours following carrageenan injection. This was correlated with an increase in Nav1.9 immunolabeling in nerve fibers surrounding the inflamed area. No change in Nav1.9 current density could be detected in the soma of retrolabeled DRG neurons innervating inflamed tissues, suggesting that newly produced channels may be non-functional at this level and rather contribute to the observed increase in axonal transport. Our results provide evidence that Nav1.9 plays a crucial role in the generation of heat and mechanical pain hypersensitivity, both in subacute and chronic inflammatory pain models, and bring new elements for the understanding of its regulation in those models.

Weight bearing evaluation in inflammatory, neuropathic and cancer chronic pain in freely moving rats

Preclinical pain assessment remains a key step for the development of new and potent painkillers. Significant progress in pain evaluation has been achieved with the development of non-reflexive tools. Seeking efficient and clinically relevant devices for pain-related quality of life assessment, we evaluated a new Dynamic Weight Bearing (DWB) device based on pressure captors in three different preclinical chronic pain models. Inflammatory (CFA), neuropathic (CCI) and bone cancer pain (femoral tumor) models were evaluated in Sprague Dawley rats for mechanical allodynia using dynamic von Frey for pain-related behaviors and DWB for discomfort. We observed similar impairment patterns in all of the models for both von Frey (allodynia) and DWB (weight balance) during the complete observation period, starting at day 3 in CCI- and CFA-affected limbs and at day 14 in bone cancer-afflicted rats, indicating that the DWB could be a useful tool for supporting pain assessment. Interestingly, we demonstrated that the main compensation, when animals experienced pain, was seen in the forepaws, ranging from 46% to 69% of increased load compared to normal. Other pain-related coping behaviors were also measured, such as the time spent on each paw and the contact surface. Our results revealed that CFA, CCI and cancerous rats decreased the use of their ipsilateral hind paws by 30% and showed a 50% reduction in paw surface pressed against the floor. In conclusion, this new device improves methods for preclinical evaluation of discomfort and quality of life proxies and could be helpful in screening putative analgesics.

Abstract P1-03-08: Targeting Neurotensinergic Receptors for Bone Cancer Pain Relief

Abstract Metastatic breast cancer spreads principally to long bones like femur. The presence of breast cancer metastasis in bone microenvironment results in severe pain increasing with disease progression. Opioids, including morphine, are a standard for bone cancer pain management despite their adverse effects at high doses. Our aim here was to examine the effects of opioidergic-independent neurotensin (NT) receptor (NTS1, NTS2) activation in alleviating bone cancer pain in a new clinically relevant mouse model. To this end, neurotensinergic agonists (PD149163, JMV-2012 or JMV-431) were intrathecally administrated to C57BL/6 mice implanted with syngenic E0771 metastatic breast cancer cells in the femoral intramedullary canal. Compounds were analysed for touch-evoked (von Frey), forced movement-evoked (Rotarod) and ambulatory (dynamic weight bearing) pain 18 days following E0771 implantation. The intrathecal injection of PD149163, a NTS1-selective agonist, induced a marked decrease of touch-evoked pain reaching 64 ± 9%. On the Rotarod, PD149163 treatment failed to improve either time spent on the rotating cylinder or the visual pain score. The injection of a non-selective agonist, JMV-2012, reduced touch-evoked pain of 16 ± 5%, but was not efficient in reversing pain under a physical effort on the Rotarod. JMV-431, a NTS2-selective agonist, produced a significant reduction of touch-evoked pain of 70 ± 9% in cancer mice, which also spent more time (10 ± 13%) on the Rotarod and expressed less movement-evoked pain (97 ± 20%) than saline-treated cancer mice. However, acute spinal JMV-431 failed to restore ipsilateral weight bearing toward basal values. The analysis of spinal neuronal activity of mice injected with JMV-431 showed a significant reduction of 55 ± 6% of c-Fos expression in laminae V-VII of the ipsilateral horn 18 days post implantation. In conclusion, these results indicate that the NTS2 receptor represents a promising target for treating bone cancer pain. Further investigations of continuous delivery of NTS2-selective agonists at the central and peripheral levels are under way to evaluate the real potential of these compounds for prophylactic and curative treatments against cancer pain. Supported by CIHR/Canadian Pain Society/AstraZeneca and Cancer Research Society grants. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-03-08.

Hypolocomotion, Asymmetrically Directed Behaviors (Licking, Lifting, Flinching, and Shaking) and Dynamic Weight Bearing (Gait) Changes are Not Measures of Neuropathic Pain in Mice

BackgroundSpontaneous (non-evoked) pain is a major clinical symptom of neuropathic syndromes, one that is understudied in basic pain research for practical reasons and because of a lack of consensus over precisely which behaviors reflect spontaneous pain in laboratory animals. It is commonly asserted that rodents experiencing pain in a hind limb exhibit hypolocomotion and decreased rearing, engage in both reflexive and organized limb directed behaviors, and avoid supporting their body weight on the affected side. Furthermore, it is assumed that the extent of these positive or negative behaviors can be used as a dependent measure of spontaneous chronic pain severity in such animals. In the present study, we tested these assumptions via blinded, systematic observation of digital video of mice with nerve injuries (chronic constriction or spared nerve injury), and automated assessment of locomotor behavior using photocell detection and dynamic weight bearing (i.e., gait) using the CatWalk® system.ResultsWe found no deficits in locomotor activity or rearing associated with neuropathic injury. The frequency of asymmetric (ipsilaterally directed) behaviors were too rare to be seriously considered as representing spontaneous pain, and in any case did not statistically exceed what was blindly observed on the contralateral hind paw and in control (sham operated and unoperated) mice. Changes in dynamic weight bearing, on the other hand, were robust and ipsilateral after spared nerve injury (but not chronic constriction injury). However, we observed timing, pharmacological, and genetic dissociation of mechanical allodynia and gait alterations.ConclusionsWe conclude that spontaneous neuropathic pain in mice cannot be assessed using any of these measures, and thus caution is warranted in making such assertions.