Inhibiting nerve growth factor or its receptors downregulates calcitonin gene‐related peptide expression in rat lumbar dorsal root ganglia innervating injured intervertebral discs

Nerve growth factor (NGF) and its dual structurally unrelated receptors, tropomyosin‐related kinase A (TrkA) or p75 neurotrophin receptor (p75^NTR), cause the pathogenesis of discogenic pain. To investigate the sensory innervation of injured rat lumbar intervertebral disc (IVD), we examined the expression of neuropeptides such as calcitonin gene‐related peptide (CGRP) at dorsal root ganglia (DRG) by inhibiting NGF or its dual receptors. Sprague–Dawley rats with multiply punctured L5–L6 IVD were used. Six experimental groups were prepared: naïve, sham control, and four agent‐treated groups with punctured IVD (vehicle, anti‐NGF antibody, anti‐TrkA antibody, and anti‐p75^NTR antibody). Retrograde neurotracer Fluoro‐Gold (FG) was applied together except for the naïve group. Their lumbar DRG were harvested and immunolabeled for CGRP. FG‐labeled DRG neurons were most prevalent at L1 and L2 DRG, and the proportion of FG‐labeled CGRP‐immunoreactive DRG neurons in the vehicle group was significantly elevated (p < 0.05) compared with the sham group, while those of antibody‐treated groups, especially in the anti‐p75^NTR group, significantly decreased compared with the vehicle group (p < 0.05). Direct intradiscal application of antibody to NGF or its receptors suppressed CGRP expression, and p75^NTR antagonism induced the most profound suppression. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1614–1620, 2010     

Dorsal root ganglion neurons with dichotomizing axons projecting to the hip joint and the knee skin in rats: possible mechanism of referred knee pain in hip joint disease

BackgroundPatients who have hip joint diseases sometimes complain of knee pain as well as hip joint area pain. However, the precise sensory innervation pattern and correlation of the sensory nerves of the hip joint and knee are unknown. The purpose of this study was to investigate dorsal root ganglion (DRG) neurons with dichotomizing axons projecting to both the hip joint and the knee skin in rats using double fluorescent labeling techniques, and to examine characteristics of the DRG neurons with dichotomizing axons using immunohistochemical staining for inflammatory neuropeptides such as calcitonin gene-related peptide (CGRP).MethodsFor 20 rats, two kinds of neurotracers, Fluor-o-Gold (FG) and 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl-indocarbocyanine perchlorate (DiI), were used in the double-labeling study. FG was injected into the left hip joint, and DiI was applied to the left medial portion of knee skin. Ten days after application, bilateral DRGs were harvested and immunohistochemically stained for CGRP.ResultsDRG neurons double labeled with FG and DiI were observed only from L2 to L4 on the left side. Approximately 1.6% of all DRG neurons innervating the hip joints had other axons that extended to the medial portion of knee skin, and 35% of double-labeled neurons were CGRP positive.ConclusionsOur results showed that the double-labeled neurons had peripheral axons that dichotomized into both the hip joint and the knee skin. CGRP-positive neurons of these dichotomizing fibers may play some role in the manifestation of referred knee pain with hip joint pain.     

神经生长因子对老年退变性膝骨关节炎疼痛模型的影响

目的:探讨体外模型评价神经生长因子(nerve growth factor,NGF)抗体在膝骨关节炎(knee osteoarthritis,KOA)疼痛模型中的作用。方法:选取30只8周龄雄性SPF大鼠,分为空白组10只;其余20只行右膝关节单碘乙酸 (monoiodoacetate,MIA) 注射,制备骨性关节炎疼痛模型。造模成功后,再根据干预方法不同分为对照组(生理盐水腹腔注射)、治疗组(抗NGF 腹腔注射),每组10只。所有动物右膝关节进行荧光金 (fluorogold,FG) 逆行神经示踪剂注射。分别在治疗前,治疗后1、2周使用猫道步态分析系统评估步态。治疗后3周,从L₃-L₅水平切除右背根神经节(dorsal root ganglia,DRG),进行降钙素基因相关肽 (calcitonin gene-related peptide,CGRP) 免疫染色,并计算DRG数量。结果:在使用猫道系统的步态分析中,与空白组相比,对照组、治疗组占空比、摆动速度和触地面积比率明显降低(P<0.05);与对照组相比,治疗组占空比、摆动速度明显改善(P<0.05),触地面积比率与空白组比较,差异无统计学意义(P>0.05)。对照组中FG标记的DRG神经元数量高于治疗组和空白组(P<0.05);对照组CGRP表达上调,与治疗组比较,差异有统计学意义(P<0.05)。结论:腹腔注射抗 NGF抗体抑制了步态损伤和 DRG 神经元中CGRP 的上调。这些发现提示抗神经生长因子治疗可能对治疗膝关节疼痛有价值。NGF可能是治疗KOA疼痛的重要靶点。     

Characterization and comparison of rat monosodium iodoacetate and medial meniscal tear models of osteoarthritic pain

Osteoarthritis (OA) is a degenerative form of arthritis that can result in loss of joint function and chronic pain. The pathological pain state that develops with OA disease involves plastic changes in the peripheral and central nervous systems, however, the cellular mechanisms underlying OA are not fully understood. We characterized the medial meniscal tear (MMT) surgical model and the intra‐articular injection of monosodium iodoacetate (MIA) chemical model of OA in rats. Both models produced histological changes in the knee joint and associated bones consistent with OA pathology. Both models also increased p38 activation in the L3, but not L4 dorsal root ganglia (DRG), increased tyrosine hydroxylase immunostaining in the L3 DRG indicating sympathetic sprouting, and increased phosphorylated (p)CREB in thalamic neurons. In MIA‐OA, but not MMT‐OA rats, p38 and pERK were increased in the spinal cord, and pCREB was enhanced in the prefrontal cortex. Using in vivo electrophysiology, elevated spontaneous activity and increased responsiveness of wide dynamic range neurons to stimulation of the knee was found in both models. However, a more widespread sensitization was observed in the MIA‐OA rats as neurons with paw receptive fields spontaneously fired at a greater rate in MIA‐OA than MMT‐OA rats. Taken together, the MIA and MMT models of OA share several common features associated with histopathology and sensitization of primary somatosensory pathways, but, observed differences between the models highlights unique consequences of the related specific injuries, and these differences should be considered when choosing an OA model and when interpreting data outcomes. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2109–2117, 2018.

     

Inflammatory pain-related traits of sensory DRG neurons innervating the hip joints

Background

Hip pain is transmitted to the dorsal horn of the spinal cord via the dorsal root ganglion (DRG), which contains two types of neurons with differential sensitivity to neurotrophic factors. If either type predominantly innervates the hip joint, it may represent a good target for hip joint pain treatment.

Altered Spinal MicroRNA‐146a and the MicroRNA‐183 Cluster Contribute to Osteoarthritic Pain in Knee Joints

The objective of this study was to examine whether altered expression of microRNAs in central nervous system components is pathologically linked to chronic knee joint pain in osteoarthritis. A surgical animal model for knee joint OA was generated by medial meniscus transection in rats followed by behavioral pain tests. Relationships between pathological changes in knee joint and development of chronic joint pain were examined by histology and imaging analyses. Alterations in microRNAs associated with OA‐evoked pain sensation were determined in bilateral lumbar dorsal root ganglia (DRG) and the spinal dorsal horn by microRNA array followed by individual microRNA analyses. Gain‐ and loss‐of‐function studies of selected microRNAs (miR‐146a and miR‐183 cluster) were conducted to identify target pain mediators regulated by these selective microRNAs in glial cells. The ipsilateral hind leg displayed significantly increased hyperalgesia after 4 weeks of surgery, and sensitivity was sustained for the remainder of the 8‐week experimental period (F = 341, p < 0.001). The development of OA‐induced chronic pain was correlated with pathological changes in the knee joints as assessed by histological and imaging analyses. MicroRNA analyses showed that miR‐146a and the miR‐183 cluster were markedly reduced in the sensory neurons in DRG (L4/L5) and spinal cord from animals experiencing knee joint OA pain. The downregulation of miR‐146a and/or the miR‐183 cluster in the central compartments (DRG and spinal cord) are closely associated with the upregulation of inflammatory pain mediators. The corroboration between decreases in these signature microRNAs and their specific target pain mediators were further confirmed by gain‐ and loss‐of‐function analyses in glia, the major cellular component of the central nervous system (CNS). MicroRNA therapy using miR‐146a and the miR‐183 cluster could be powerful therapeutic intervention for OA in alleviating joint pain and concomitantly regenerating peripheral knee joint cartilage. © 2013 American Society for Bone and Mineral Research.     

Calcitonin gene-related peptide immunoreactive neurons with dichotomizing axons projecting to the lumbar muscle and knee in rats

Dorsal root ganglion (DRG) neurons with dichotomizing axons have been reported in several species and are thought to be related to referred pain. However, these neurons, which have dichotomizing axons to the lumbar muscles and to the knee, have not been investigated. Clinically, pain from the lumbar muscles is sometimes referred to the lower extremities. Two kinds of neurotracers [1,1-dioctadecyl-3,3,3,3-tetramethyl-indocarbocyanine perchlorate (DiI) and fluoro-gold (FG)] were used in the present double-labelling study. DiI crystals were placed in the left lower back muscle, and FG was applied to the medial side of the knee. Bilateral DRGs from L1 through L6 were immunoreacted with calcitonin gene-related peptide (CGRP) antibodies and observed under a fluorescence microscope. DRG neurons double-labelled with DiI and FG were recognized only in the ipsilateral DRGs from levels L1 to L6. Approximately 1% of DRG neurons innervating the low back muscles had other axons to the medial side of the knee. In double-labelled neurons, the ratio of CGRP-immunoreactive DRG neurons was 60%. This finding provides a possible neuroanatomical explanation for referred knee pain from the lower back since CGRP is a marker of sensory neurons typically involved with pain perception. However, these neurons are rare, and mechanisms of referred pain may be explained by the convergence–projection hypothesis.     

Interleukin‐6 and interleukin‐6 receptor expression,localization, and involvement in pain‐sensing neuron activation in a mouse intervertebral disc injury model

The pathological mechanism of intractable low back pain is unclear. However, intervertebral disc (IVD) degeneration is a primary cause of low back pain, and pain‐related mediators, such as interleukin‐6 (IL‐6), have been correlated with discogenic pain. The objective of this study is to elucidate the mechanism of local IL‐6 and IL‐6 receptor (IL‐6R) expression after IVD injury as well as determine the involvement of IL‐6/IL‐6 signaling in discogenic pain. To do this, quantitative and immunohistological analyses in a mouse model of IVD injury were performed. Firstly, we measured the local expression levels of IL‐6 and IL‐6R in IVDs by enzyme‐linked immunosorbent assay (ELISA). Secondly, we immunohistochemically confirmed their localization in injured IVDs. Lastly, we evaluated the effects of intradiscal injection of an IL‐6 inhibitor by evaluating pain‐related protein, calcitonin gene‐related peptide (CGRP), expression in dorsal root ganglia (DRG) neurons that innervate IVDs. Injured IVDs showed increased production of IL‐6 and IL‐6R. IL‐6 and IL‐6R expression in the injured IVD were predominantly localized in the annulus fibrosus and endplate, and intradiscal injection of the IL‐6 inhibitor suppressed CGRP expression in the DRG neurons. These results show that IL‐6 and IL‐6R expression levels are responsive to IVD injury and that inhibition of IL‐6/IL‐6R signaling may be a promising analgesic treatment for degenerative disc diseases. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1508–1514, 2015.     

Effect of applying p75NTR saporin to a punctured intervertebral disc on calcitonin gene-related peptide expression in rat dorsal root ganglion neurons

Background

Recent studies have revealed that the low-affinity nerve growth factor receptor, p75 neurotrophin receptor (p75NTR), is important in inflammatory pain. Moreover, p75NTR immunoreactive sensory nerve and dorsal root ganglion (DRG) neurons have been found to innervate lumbar intervertebral discs. The purpose of the current study was to investigate the effect of p75NTR saporin, a toxin used to destroy p75NTR, on calcitonin gene-related peptide (CGRP), an inflammatory neuropeptide associated with pain, in DRG neurons innervating punctured intervertebral discs in rats.

Methods

The neurotracer fluorogold (FG) was applied to the surfaces of L5/6 discs to label their innervating DRG neurons (n = 30). Of 30 rats, 10 were in a nonpunctured disc sham surgery control group (nonpuncture group), and the other 20 were in experimental groups in which intervertebral discs were punctured with a 23-gauge needle. p75NTR saporin was applied to the discs of 10 rats (puncture + p75NTR saporin group) and the other 10 received the same volume of saline (puncture + saline group). At 14 days after surgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP, and the proportions of CGRP-immunoreactive DRG neurons was evaluated.

Results

Of the FG-labeled neurons innervating the L5/6 disc, the proportion of CGRP-immunoreactive neurons was 32% ± 6% (mean ± SE) in the nonpuncture group, 47.2% ± 8% in the puncture + saline group, and 34.6% ± 9% in the puncture + p75NTR saporin group. The proportion of CGRP-immunoreactive neurons was significantly greater in the puncture + saline group compared with the nonpuncture and puncture + p75NTR saporin groups (P < 0.01).

Conclusions

Half of the DRG neurons innervating the discs were positive for CGRP in the puncture + saline group. CGRP is important for mediating inflammatory and nerve-injured pain and may be important in discogenic pain. However, p75NTR saporin suppressed CGRP expression in DRG neurons. Therefore, p75NTR may be an important receptor for mediating discogenic pain via CGRP expression.     

背根神经节内P物质、降钙素基因相关肽免疫阳性神经元与阴茎包皮系带感觉信息的传递

目的:探讨背根神经节(DRG)内P物质(SP)、降钙素基因相关肽(CGRP)免疫阳性神经元与阴茎包皮系带感觉信息传递之间的关系。方法:通过荧光金(FG)逆行标记对大鼠阴茎包皮系带内神经末梢的来源作追踪定位,并结合SP、CGRP免疫荧光标记法,研究大鼠DRG内FG标记阳性神经元中SP、CGRP免疫阳性神经元的形态和分布。结果:FG逆行标记结果发现,大鼠阴茎包皮系带内的神经末梢起源于第6腰髓对应的背根神经节(L6-DRG)和第1骶髓对应的背根神经节(S1-DRG)的神经元。对这些神经元分别作SP、CGRP免疫荧光标记后发现,标记细胞大小不等,分别呈深红色和深绿色,沿神经束成行排列或散在分布。FG/SP、FG/CGRP双标记阳性细胞均为中小型,其数量分别占FG逆行标记阳性细胞总数的1/3和1/2,FG/SP/CGRP三标记阳性细胞占FG逆行标记阳性细胞总数的1/5。结论:大鼠L6-DRG和S1-DRG内的SP、CGRP免疫阳性神经元可能参与阴茎包皮系带感觉信息的传递。     

Characteristics of sensory DRG neurons innervating the lumbar facet joints in rats

The rat L5/6 facet joint, from which low-back pain can originate, is multisegmentally innervated from the L1 to L5 dorsal root ganglions (DRGs). Sensory fibers from the L1 and L2 DRGs are reported to non-segmentally innervate the paravertebral sympathetic trunks, whilst those from the L3 to L5 DRGs segmentally innervate the L5/6 facet joint. In the current study, characteristics of sensory DRG neurons innervating the L5/6 facet joint were investigated in rats, using a retrograde neurotransport method, lectin affinity- and immuno-histochemistry. We used four markers: (1) calcitonin gene-related peptide (CGRP) as a marker of small peptide containing neurons, (2) the glycoprotein binding the isolectin from Griffonia simplicifolia (IB4) or (3 the purinergic P2X₃ receptor for small, non-peptide containing neurons, and (4) neurofilament 200 (NF200) for small and large myelinated fibers. IB4-binding and CGRP and P2X₃ receptor containing neurons are typically involved in pain sensation, whereas NF200 is associated with pain and proprioception. Neurons innervating the L5/6 facet joints, retrogradely-labeled with fluoro-gold (FG), were distributed throughout DRGs from L1 to L5. Of FG-labeled neurons, the ratios of NF200 immunoreactive (IR) neurons and CGRP-IR neurons were 37% and 35% respectively. The ratio of IB4-binding and P2X₃ receptor-IR neurons was 10%, significantly less than the ratio of CGRP-IR neurons to FG-labeled neurons. The ratios of IB4-binding and P2X₃ receptor-IR neurons were significantly higher, and that of CGRP-IR neurons was significantly less in L1 and L2 DRGs than those in L3, L4 or L5 DRGs. Under physiological conditions in rats, DRG neurons transmit several types of sensations, such as proprioception or nociception of the facet joint. Most neurons transmitting pain are CGRP-IR peptide-containing neurons. They may have a more significant role in pain sensation in the facets via peptidergic DRG neurons.Tetsuhiro Ishikawa, Masayuki Miyagi, and Seiji Ohtori contributed equally to this work.     

Primary sensory neurons with dichotomizing axons projecting to the facet joint and the low back muscle in rats

Background

Clinically, the origin of low back pain is unknown. The pain may originate from the lumbar muscles directly, or it may be referred pain from the spine. Dorsal root ganglion (DRG) neurons with dichotomizing axons have been reported in several species and are thought to be related to referred pain. However, these neurons, which have dichotomizing axons to the lumbar facet joints and to the lumbar muscle, have not been fully investigated.

Methods

Two neurotracers — 1,1′-dioctadecyl-3,3,3′,3′- tetramethyl-indocarbocyanine perchlorate (DiI) and fluorogold (FG) — were used in the present double-labeling study. DiI crystals were placed in the right L5/6 facet joint, and FG was applied to right multifidus muscles at the L5 level in 10 rats. Two weeks later, bilateral DRGs from L1 through L6 were harvested, sectioned, and observed under a fluorescence microscope.

Results

DiI-labeled DRG neurons innervating the L5/6 facet joint (5.17% of the total DRG neurons) were distributed from L1 to L6. FG-labeled DRG neurons innervating the lower back muscle (15.9% of the total) were also distributed from L1 to L6. Double-labeled DRG neurons were found from L1 to L6. The ratio of total double-labeled/total DiI-labeled DRG neurons was 17% and that of total double-labeled/total FG-labeled DRG neurons was 7%. Approximately 17% of all DRG neurons innervating the facet joints had other axons that extended to the lower back muscle.

Conclusions

This finding provides a possible neuroanatomical explanation for referred low back muscle pain from the lower facet joints.     

Up-regulation of p55 TNF alpha-receptor in dorsal root ganglia neurons following lumbar facet joint injury in rats

The rat L5/6 facet joint is multisegmentally innervated from the L1 to L6 dorsal root ganglia (DRG). Tumor necrosis factor (TNF) is a known mediator of inflammation. It has been reported that satellite cells are activated, produce TNF and surround DRG neurons innervating L5/6 facet joints after facet injury. In the current study, changes in TNF receptor (p55) expression in DRG neurons innervating the L5/6 facet joint following facet joint injury were investigated in rats using a retrograde neurotransport method followed by immunohistochemistry. Twenty rats were used for this study. Two crystals of Fluorogold (FG; neurotracer) were applied into the L5/6 facet joint. Seven days after surgery, the dorsal portion of the capsule was cut in the injured group (injured group n = 10). No injury was performed in the non-injured group (n = 10). Fourteen days after the first application of FG, bilateral DRGs from T13 to L6 levels were resected and sectioned. They were subsequently processed for p55 immunohistochemistry. The number of FG labeled neurons and number of FG labeled p55-immunoreactive (IR) neurons were counted. FG labeled DRG neurons innervating the L5/6 facet joint were distributed from ipsilateral L1 to L6 levels. Of FG labeled neurons, the ratio of DRG neurons immunoreactive for p55 in the injured group (50%) was significantly higher than that in the non-injured group (13%). The ratio of p55-IR neurons of FG labeled DRG neurons was significantly higher in total L1 and L2 DRGs than that in total L3, 4, 5 and 6 DRGs in the injured group (L1 and 2 DRG, 67%; L3, 4, 5 and 6 DRG, 37%, percentages of the total number of p55-IR neurons at L1 and L2 level or L3–6 level/the total number of FG-labeled neurons at L1 and L2 level or L3–6 level). These data suggest that up-regulation of p55 in DRG neurons may be involved in the sensory transmission from facet joint injury. Regulation of p55 in DRG neurons innervating the facet joint was different between upper DRG innervated via the paravertebral sympathetic trunks and lower DRG innervated via other direct routes. Y. Sakuma and S. Ohtori contributed equally to this work.     

Low affinity NGF receptor (p75 neurotrophin receptor) inhibitory antibody reduces pain behavior and CGRP expression in DRG in the mouse sciatic nerve crush model

Nerve growth factor (NGF) and its low‐affinity receptor, p75 neurotrophin receptor (p75NTR), are important mediators of pain. To explore further the mechanisms involved, we examined suppression of pain behavior and expression of neuropeptides such as calcitonin gene‐related peptide (CGRP) using a p75 NTR inhibitory antibody, in a mouse sciatic nerve crush model. In the nerve‐injured model, 150 µg of a p75 NTR inhibitory antibody or 10 µl of saline were applied. The sciatic nerve in the sham‐operated group was uninjured. Mechanical allodynia was measured for 2 weeks. CGRP and p75NTR expression in L5 dorsal root ganglions (DRGs) was examined immunohistochemically. Mechanical allodynia was found in the two nerve injured groups, but not in the sham‐operated group (p < 0.05). However, the magnitude of the mechanical allodynia was significantly decreased after application of p75 NTR inhibitory antibody (p < 0.05). CGRP and p75NTR immunoreactivity in the L5 DRG neurons was upregulated in the injured nerve groups compared with the sham‐operated group; however, p75 NTR inhibitory antibody decreased the CGRP and p75NTR expression (p < 0.01). Application of the p75 NTR inhibitory antibody to the pinched sciatic nerve suppressed CGRP and p75NTR expression and pain behavior. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:279–283, 2010     

Extracorporeal shock wave therapy improves motor dysfunction and pain originating from knee osteoarthritis in rats

OBJECTIVE: Although there have been several reports on the use of extracorporeal shock wave therapy (ESWT), the efficacy of ESWT for knee osteoarthritis (OA) has not been clarified. The aim of this study is to investigate the effect of ESWT on OA in a rat knee model. METHODS: The rats were divided into three groups: (1) control, (2) OA, and (3) ESWT (knee OA+shock wave therapy). Behavioral analysis consisted of measuring the duration of walking on a treadmill. The expression of calcitonin gene-related peptide (CGRP) in dorsal root ganglion (DRG) neurons innervating the knee using immunohistochemistry was examined in the three groups at their peak time point on the treadmill. RESULTS: Walking duration was significantly extended 4, 7 and 14 days after ESWT in rats with knee OA (peak time point: 4 days), again decreasing by days 21 and 28. Immunohistochemical studies revealed that the OA group had significantly higher percentages of CGRP positive neurons in the DRG than were found in the control group. In addition, ESWT reduced the ratio of CGRP positive DRG neurons in the OA model. CONCLUSION: The improvement in walking ability and the reduction of CGRP positive neurons in DRG indicates that ESWT is a useful treatment for knee OA.     

Expression and activity of COX‐1 and 2 and 5‐LOX in joint tissues from dogs with naturally occurring coxofemoral joint osteoarthritis

Understanding the neurobiology of pain in naturally occurring models of osteoarthritis (OA) may improve the understanding of human OA pain. Both COX and LOX have been associated with joint pain. This study evaluated COX‐1, COX‐2, and 5‐LOX expression and activity in a naturally occurring canine model of secondary OA. Hip joint capsule with synovial tissue (HJC) and femoral head subchondral bone (FH) was collected from normal dogs and dogs undergoing total hip replacement for coxofemoral joint OA. Tissues were analyzed for COX‐1, COX‐2, and LOX protein, and PGE₂ and LTB₄. Significantly more COX‐2 protein was present in OA HJC than normal joints (p = 0.0009). There was no significant difference in COX‐1 or LOX protein, although LOX protein was increased (p = 0.069). PGE₂ concentration in normal and OA HJC was similar (p = 1.0). LTB₄ concentration in OA HJC was significantly greater than normal HJC (p = 0.028). Significantly more COX‐1 (p = 0.0098), COX‐2 (p = 0.0028), and LOX (p = 0.0095) protein was present in OA FH tissue compared to normal FH tissue. There were no differences in PGE₂ or LTB₄ concentration in normal and OA FH tissue (p = 0.77 and p = 0.11). Together, these data suggest both COX‐2 and 5‐LOX are appropriate targets for the management of pain associated with naturally occurring OA. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

The quantitative and functional relation between insulin‐like growth factor‐I (IGF) and IGF‐binding proteins during human osteoarthritis

A previous hypothesis stated that during osteoarthritis (OA) increased insulin‐like growth factor (IGF) binding proteins (IGFBPs) sequester IGFs and limit their access to the cell. The objective of this article was to test this by: (1) quantifying IGF and IGFBP‐3 as well as their ratios in human OA cartilages, and (2) measuring the metabolic responses of diseased cartilage to IGF‐I and its IGFBP‐insensitive analogs. Knee or hip OA cartilages were staged for OA by histology. Cartilage slices were either extracted for assays of IGF proteins, or maintained intact as organ cultures. Proteoglycan (PG) metabolism ± IGFs was measured by use of the ³⁵S‐sulfate precursor. IGFBP‐3 (ng/mg protein) was weakly correlated with OA score by regression analysis (R² = 0.122; p = 0.040; n = 35). IGF‐I (ng/mg protein) was constant across all OA groups (ANOVA; p = .428, n = 18) and the IGF‐I/IGFBP‐3 ratios were > 1 in most samples. All OA cartilages responded to hrIGF‐I by increasing PG synthesis [average 2.29‐fold ± 0.55 (±SD) at saturation, n = 12] irrespective of OA score. The des (1–3) IGF‐I analog (which lacks the three N‐terminal amino acids) had similar maximal effects (average 2.23‐fold stimulation ± 0.71, n = 10), but it was more effective in two out of three samples at suboptimal doses. The effect of hrIGF‐I, des (1–3) IGF‐I, or the B‐chain analog on degradation was minimal. In summary, catabolism was insensitive to IGF‐I, and this was probably not due to IGFBPs. By contrast, IGF‐I exerted a robust stimulation of anabolism at sufficiently high doses, even though IGFBPs could tone down the ligand effect at low doses. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:465–474, 2008     

Primary sensory neurons with dichotomizing axons projecting to the facet joint and the sciatic nerve in rats.

STUDY DESIGN: Dorsal root ganglion (DRG) neurons that have dichotomizing axons to the lumbar facet joint and to the sciatic nerve were investigated in rats using a double fluorescent labeling technique. OBJECTIVES: To clarify the existence of DRG neurons with dichotomizing axons projecting to the lumbar facet joint and to the sciatic nerve in rats. SUMMARY OF BACKGROUND DATA: DRG neurons having dichotomizing axons have been reported in several species and are considered to be related to referred pain. However, such DRG neurons have not been investigated in the lumbar spine. Clinically, pain from the lumbar facet joint is sometimes referred to the lower extremities innervated by the sciatic nerve. METHODS: Two kinds of neurotracers (DiI and FG) were used in the present double-labeling study. DiI crystals were placed in the left L5-L6 facet joint, and FG was applied to the ipsilateral sciatic nerve or along the midline of the L5 dermatome. Bilateral DRGs T13-S1 were observed by fluorescence microscope. RESULTS: DRG neurons double labeled with DiI and FG were recognized only in the ipsilateral DRGs from L3 to L6 levels. Approximately 3% of DRG neurons innervating the L5-L6 facet joint had other axons to the sciatic nerve. By contrast, no double-labeled neurons were observed after FG was applied to the L5 dermatome. CONCLUSIONS: In rats approximately 3% of DRG neurons innervating the lumbar facet joints have dichotomized axons projecting to the sciatic nerve.