Neuropeptide Y, tyrosine hydroxylase and vasoactive intestinal polypeptide-immunoreactive nerve fibers in the vertebral bodies, discs, dura mater, and spinal ligaments of the rat lumbar spine

Immunohistochemical and histological study of human uncovertebral joints: a preliminary investigation

STUDY DESIGN

A descriptive cadaveric study.

OBJECTIVE

To investigate the anatomy and innervation of the uncovertebral joint to determine if it is synovial in nature and capable of generating pain.

SUMMARY OF BACKGROUND DATA

There is controversy with regard to the anatomic and histological makeup of the uncovertebral interface with some authors considering it a joint and others disc tissue. No research has investigated the presence of pain generating neurotransmitters within the uncovertebral cartilaginous and capsular tissue.

METHODS

Tissue from uncovertebral capsule and cartilage was harvested for each uncovertebral surface starting at the C2-C3 to the C6-C7 cervical segment. The tissue was placed in 4% paraformaldehyde fixative, then dehydrated and embedded in paraffin. Ten micron sections were cut through the tissue blocks and mounted on slides. The tissue was rehydrated and either stained with hematoxylin and eosin (H and E) or immunostained with antisera against protein gene product 9.5 (PGP 9.5), substance P (SP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP).

RESULTS

The sample consisted of 2 unembalmed fresh male human cadavers of a mean age of 83 years. Chondrocytes and synoviocytes were identified at the capsular tissue of each uncovertebral interface from C2-C3-C6-C7. Immunoreactivity for PGP 9.5, SP, CGRP, and NPY was observed at all uncovertebral interface levels in capsular tissue.

CONCLUSION

The presence of both synoviocytes and chondrocytes has been recorded in the present study, suggesting that the uncovertebral interface is synovial in nature. Immunoreactivity to PGP 9.5, SP, CGRP, and NPY indicates the presence of nerve fibers from both the somatic and autonomic nervous systems. These findings suggest that the uncovertebral joints are potential pain generators in the cervical spine.

The density of nociceptive SP- and CGRP-immunopositive nerve fibers in the dura mater lumbalis of rats is enhanced after laminectomy, even after application of autologous fat grafts

A considerable number of patients complain about pain after lumbar surgery. The spinal dura mater has been debated as a possible source of this pain. However, there is no information if laminectomy influences the nociceptive sensory innervation of the dura. Therefore, we quantitatively evaluated the density of SP- and CGRP-immunopositive nerve fibers in the dura mater lumbalis in an animal model of laminectomy. Twelve adult Lewis rats underwent laminectomy, in six of them the exposed dura was covered by an autologous fat graft. Further six animals without surgical treatment served as controls. Six weeks after surgery, the animals were perfused and the lumbar dura was processed immunohistochemically for the detection of CGRP- and SP-containing nerve fibers. In controls, the peptidergic nerve fibers were found predominantly in the ventral but rarely in the dorsal dura mater lumbalis. After laminectomy, the density of SP- and CGRP-immunopositive neurons significantly increased in ventral as well as in dorsal parts of the dura. Axonal spines could be observed in some cases at the site of laminectomy. The application of autologous fat grafts failed to inhibit the significant increase in the density of peptidergic afferents. Thus, we have provided the first evidence that laminectomies induce an increase in the density of putative nociceptive SP- and CGRP-immunopositive neurons in the lumbar dura mater ascribable to an axonal sprouting of fine nerve fibers. This effect was not prevented by using autologous fat grafts. It is conceivable that the neuronal outgrowth of nociceptive afferents is a cause of low back pain observed after lumbar surgery.

Interventional techniques for back pain

Most Americans will be afflicted by some form of spine-related pain in their lifetime. In older patients, the most frequent source of back pain is lumbar spinal stenosis or vertebral compression fracture. Although most back pain is self-limited, some patients will require interventional techniques. This article reviews minimally invasive techniques for treating back pain, lumbosacral radicular pain, lumbar spinal stenosis, and compression fractures.

Relationship between the histological findings of spondylolytic tissue, instability of the loose lamina, and low back pain

STUDY DESIGN

We investigated the histomorphological features of the tissue occupying the spondylolytic defect (spondylolytic tissue), which was similar to ligament, and then graded the complete enthesis structure and the density of the fibrous portion. The relationships between the features, instability of the loose lamina against the affected vertebra, and the severity of low back pain were studied.

OBJECTIVE

To elucidate the histomorphological features of spondylolytic tissue and the associations between the features, instability of the loose lamina, and low back pain.

SUMMARY OF BACKGROUND DATA

Spondylolysis is thought to be caused primarily by a fatigue fracture and spondylolytic tissue has been recognized as being a fibrocartilaginous mass. Recently, innervation of the spondylolytic tissue was reported to be one of the sources of low back pain.

METHODS

The spondylolytic tissue from 17 patients who underwent microscopic decompression of the pars defect was observed for histology including hematoxylin and eosin, elastica van Gieson, and immunohistochemical staining for S100 protein. Instability of the loose lamina against the affected vertebra was evaluated by flexion/extension radiographs.

RESULTS

The spondylolytic tissue had a ligamentous structure without innervation. The histomorphological findings, instability of the loose lamina, and low back pain had no relationship to one another.

CONCLUSION

Spondylolysis is a pseudarthorosis of the pars interarticularis and the spondylolytic tissue tends to develop noninnervated ligament-like tissue with an enthesis structure. The histomorphological features, instability of the loose lamina, and low back pain have no relationship to one another.

The nerve supply of the lumbar intervertebral disc

The anatomical studies, basic to our understanding of lumbar spine innervation through the sinu-vertebral nerves, are reviewed. Research in the 1980s suggested that pain sensation was conducted in part via the sympathetic system. These sensory pathways have now been clarified using sophisticated experimental and histochemical techniques confirming a dual pattern. One route enters the adjacent dorsal root segmentally, whereas the other supply is non-segmental ascending through the paravertebral sympathetic chain with re-entry through the thoracolumbar white rami communicantes. Sensory nerve endings in the degenerative lumbar disc penetrate deep into the disrupted nucleus pulposus, insensitive in the normal lumbar spine. Complex as well as free nerve endings would appear to contribute to pain transmission. The nature and mechanism of discogenic pain is still speculative but there is growing evidence to support a 'visceral pain' hypothesis, unique in the muscloskeletal system. This mechanism is open to 'peripheral sensitisation' and possibly 'central sensitisation' as a potential cause of chronic back pain.

The significance of substance P in physiological and malignant haematopoiesis

The role of substance P (SP) in physiological haematopoiesis is well established. However, it also seems to be important in the neoplastic transformation of bone marrow, leading to the development of acute leukaemia in children, and also metastases to bone marrow of solid tumours (particularly neuroblastoma and breast cancer) in early stages of these diseases. This review summarises the available data on SP involvement in both processes. In the future, SP antagonists may be used as anti-neoplastic drugs, for example by direct or indirect blocking of tumour cell proliferation through inhibition of growth factor production and interleukin-1b synthesis.

Sensory innervation of lumbar vertebral bodies in rats

STUDY DESIGN

Using a retrograde neurotracing method with Fluoro-Gold (FG), the level at which dorsal root ganglions (DRGs) innervate the L2 and L5 vertebral bodies and the innervation pathways were investigated in rats.

OBJECTIVE

To clarify the levels at which DRGs innervate the lumbar vertebral bodies and to determine the pathways from the L2 and L5 vertebral bodies to DRGs.

SUMMARY OF BACKGROUND DATA

Elderly patients with osteoporosis sometimes experience lumbar vertebral fracture and may also feel diffuse nonlocalized pain in the back, lateral portion of the trunk, and area surrounding the iliac crest. However, the pattern of sensory innervation of vertebral bodies remains unclear.

METHODS

Forty female Sprague-Dawley rats were used. FG crystals were applied to the L2 (L2 vertebra group) or L5 (L5 vertebra group) vertebral bodies via an anterior approach, and numbers of labeled neurons in DRGs from T10 to L6 were counted. To determine sensory pathways, bilateral sympathectomy was performed.

RESULTS

In nonsympathectomy animals, FG-labeled neurons were present in DRGs from T11 through L3 in the L2 vertebra group and from T13 through L6 in the L5 vertebra group. The number of labeled neurons following sympathectomy was not significantly different in L1, L2, and L3 DRGs in the L2 vertebra group or in L3, L4, L5, and L6 DRGs in the L5 vertebra group from those in nonsympathectomy animals. In contrast, fewer labeled DRG neurons were present in sympathectomy animals at T11, T12, and T13 in the L2 vertebra group, and at T13, L1, and L2 in the L5 vertebra group than in nonsympathectomy animals (P < 0.01).

CONCLUSION

Sensory nerve fibers in the L2 and L5 vertebral bodies are derived from the T11-L3 and T13-L6 DRGs, respectively. Some sensory nerves from the L2 and L5 vertebral bodies enter the paravertebral sympathetic trunks and reach the DRGs at multisegmental levels. The present findings regarding multisegmental innervation to vertebral bodies may explain the diffuse pain that originates within osteoporotic vertebral fractures in elderly patients.

Characteristics of Sensory Dorsal Root Ganglia Neurons Innervating the Lumbar Vertebral Body in Rats

Characteristics of sensory dorsal root ganglia (DRG) neurons innervating the L5 vertebral body were investigated in rats by using a retrograde neurotransport method, lectin affinity- and immuno-histochemistry to further elucidate the causes of diffuse pain suffered by some elderly patients in their back, lateral trunk, and iliac crest, after lumbar osteoporotic vertebral fracture. We used calcitonin gene-related peptide (CGRP) as a marker of small peptide-containing neurons and the glycoprotein binding the isolectin from Griffonia simplicifolia (IB4) as a marker of small non-peptide-containing neurons. Neurons innervating the L5 vertebral bodies, retrogradely labeled with fluoro-gold (FG), were distributed throughout DRGs from T13 to L6. The proportion of CGRP-immunoreactive (IR) FG-labeled neurons was 32%. The proportion of IB4-binding FG-labeled neurons was significantly smaller, at 4%. Other neurons that were non-CGRP-IR and non-IB4-binding were mostly large neurons, and they may transmit proprioception from vertebral bodies. Most neurons transmitting pain are CGRP-IR peptide-containing neurons. They may have a more significant role in pain sensation in the vertebral bodies as peptidergic DRG neurons.

PERSPECTIVE

This article shows that vertebral bodies are innervated by CGRP-IR neurons. CGRP-IR neurons may play a role in pain sensation through peptidergic DRG neurons. These findings contribute to an understanding of pain associated with the vertebral body such as tumor, infection, or osteoporotic fracture.

Greater bone formation of Y2 knockout mice is associated with increased osteoprogenitor numbers and altered Y1 receptor expression

Germ line or hypothalamus-specific deletion of Y2 receptors in mice results in a doubling of trabecular bone volume. However, the specific mechanism by which deletion of Y2 receptors increases bone mass has not yet been identified. Here we show that cultured adherent bone marrow stromal cells from Y2(-/-) mice also demonstrate increased mineralization in vitro. Isolation of two populations of progenitor cell types, an immature mesenchymal stem cell population and a more highly differentiated population of progenitor cells, revealed a greater number of the progenitor cells within the bone of Y2(-/-) mice. Analysis of Y receptor transcripts in cultured stromal cells from wild-type mice revealed high levels of Y1 but not Y2, Y4, Y5, or y6 receptor mRNA. Interestingly, germ line Y2 receptor deletion causes Y1 receptor down-regulation in stromal cells and bone tissue possibly due to the lack of feedback inhibition of NPY release and subsequent overstimulation of Y1 receptors. Furthermore, deletion of Y1 receptors resulted in increased bone mineral density in mice. Together, these findings indicate that the greater number of mesenchymal progenitors and the altered Y1 receptor expression within bone cells in the absence of Y2 receptors are a likely mechanism for the greater bone mineralization in vivo and in vitro, opening up potential new treatment avenues for osteoporosis.

Arthritis and pain. Neurogenic origin of joint pain

Arthritis pain affects millions of people worldwide yet we still have only a limited understanding of what makes our joints ache. This review examines the sensory innervation of diarthroidal joints and discusses the neurophysiological processes that lead to the generation of painful sensation. During inflammation, joint nerves become sensitized to mechanical stimuli through the actions of neuropeptides, eicosanoids, proteinase-activated receptors and ion channel ligands. The contribution of immunocytes to arthritis pain is also reviewed. Finally, the existence of an endogenous analgesic system in joints is considered and the reasons for its inability to control pain are postulated.

The control of bone remodeling by neuropeptide Y receptors

An important role for the neuropeptide Y receptor system in the regulation of bone formation was recently revealed with a significant elevation in trabecular bone formation and bone volume following germline or hypothalamus-specific deletion of neuropeptide Y2 receptors in mice. Subsequent studies have now demonstrated that this central pathway is distinct from that of the other centrally regulated bone formation pathway mediated by leptin. This review discusses these recent findings and outlines how these new pathways could translate into potential novel targets for the treatment of bone disease.

Estudo comparativo dos mecanorreceptores dos discos intervertebrais normais e degenerados da coluna lombar de humanos pela radiografia, ressonância magnética e estudo anatomopatológico

Os autores fizeram um estudo da coluna lombar de humanos, objetivando avaliar e determinar os diferentes tipos de fibras nervosas no disco intervertebral normal e no degenerado. Foram usadas dez colunas lombares de cadáveres com aproximadamente 48 a 72 horas de óbito. As peças foram submetidas a exames de radiografia simples e ressonância magnética. Após os exames, os discos foram classificados em normais e degenerados. Em seguida, foram dissecados, divididos em regiões anterior e posterior, incluídos em parafina e realizado estudo de imuno-histoquímica com a proteína S100. Com o auxílio de um programa de computador Image-Pro Plus (media cybernetics®), as fibras nervosas tiveram seu diâmetro medidos em micrômetros e classificadas em quatro tipos de fibras. Foram encontrados quatro tipos de fibras nervosas nas diferentes regiões discais. O número e o tipo de fibras variaram de acordo com a região e grau de degeneração do disco intervertebral. Concluíram que as fibras do tipo III são mais freqüentes na região anterior; as fibras dos tipos II e IV são mais freqüentes na região posterior, e as fibras do tipo I não apresentaram diferenças entre a região anterior e a posterior; além disso, o disco degenerado tem mais fibras nervosas que o disco normal.

Sensory neurons and fibers from multiple spinal cord levels innervate the rabbit lumbar disc

OBJECTIVE

To establish the neurotransmission pathway from the lumbar L5/6 intervertebral disc (IVD) to the spinal cord in the rabbit.

DESIGN

Fluorogold particles injected into the posterior portion of the rabbit L5/6 IVD were traced by examining gold-positive neurons and fibers in the dorsal root ganglion (DRG) and spinal cord at various root levels.

RESULTS

Fluorogold-labeled neurons were observed bilaterally in primary afferent DRG neurons from the L3 through L5 segments; a small number of gold-labeled neurons were found at the L1 level. Fluorogold-labeled neurons were predominantly present in the ipsilateral DRG (the side of the injection) at the L5 level, but they were more equally distributed (on both sides) at the L4 and L3 levels. In the posterior horn of the spinal cord, Fluorogold particles were found in nerve fibers as rostral as the T12 level.

CONCLUSIONS

Our study has shown that Fluorogold particles injected into the rabbit L5/6 IVD are taken up by primary sensory neurons in the DRGs and primary sensory fibers in the posterior horn of the spinal cord at multiple levels. This diffuse innervation pattern of the lumbar disc may help explain why discogenic back pain in humans is often poorly localized.

Projection field of primary afferent fibers innervating the ventral portion of the lumbar intervertebral disc in the spinal cord dorsal horn

In the present study, we investigated the central projection of afferent fibers innervating the lumbar intervertebral disc using the fluorescent neurotracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). The tracer Dil was applied to the ventrolateral portion of the L5-L6 intervertebral disc in 11 adult rats. Fluorescent sites were observed microscopically on spinal cord transverse sections. Fluorescent spots in laminae I-III were plotted on the central projection map of cutaneous afferents. In six of 11 rats, Dil was restricted to the application site. Of these six rats, three showed no evident fluorescent sites. In the remaining three rats, small fluorescent spots were scattered in the dorsal horn. Fluorescent spots in dorsal horn lamina I were located in the central projection fields of the low back and groin skin. Fluorescent spots were observed, also sporadically, in Clarke's column in T12-L1 segments. The central projection of afferent fibers innervating the rat lumbar intervertebral disc was indistinct with Dil labeling. We presumed this was due to the scarcity of central terminal arbors of disc afferent fibers. Spotty projections in laminae I-IllIIere present near the central projection fields of the loin and groin, indicating that pain would be perceived in the groin.

Complications of percutaneous vertebroplasty and their prevention

Vertebroplasty is an efficient treatment of vertebral collapses of malignant or benign origin but also carries a risk of complications. Cement extravasation is a frequent occurrence in vertebroplasty. It is well tolerated in the large majority of cases but is also the main source of complications especially nerve root compression in case of cement leakage into the intervertebral foramen and pulmonary embolism of cement complicating venous cement leakage. Rate of these complications are much higher in malignant than in osteoporotic collapses. The risk of neurological complication also increases at the cervical level. In addition, incidence of new vertebral fractures in adjacent vertebrae may be increased by vertebroplasty. General reactions possibly due to a reflex reaction to intramedullary bone injection and fat embolism may also occur. This article reviews the safety measures to reduce the risk of cement extravasation including high quality permanent radiological guidance enabling early detection of cement extravasation, use of conscious sedation, bilateral transpedicular approach at the thoracic and lumbar levels, careful selection of the bone penetration site in order to make a single vertebral needle path, careful needle placement to avoid the risk of cortical breakthrough, use of a well-opacified and refrigerated cement with a toothpaste consistency.

Immunohistochemical demonstration of lumbar intervertebral disc innervation in the dog

Low back pain is a common ailment in dogs, particularly in specific breeds such as the German shepherd dog. A number of structures such as facet joint capsules, ligaments, dorsal root ganglia, periosteum, vertebral endplates and meninges have been associated with this condition. Yet, in spite of all diagnostic efforts, the origin of pain remains obscure in a substantial proportion of all cases. A further structure often being involved in vertebral column disorders is the intervertebral disc. The presence of nerves, however, is a precondition for pain sensation and, consequently, structures lacking innervation can be left out of consideration as a cause for low back pain. Nerve fibres have been demonstrated at the periphery of the intervertebral disc in man, rabbit and rat. With regard to the dog, however, the extent of intervertebral disc innervation is still being disputed. The goal of the present study, therefore, was to substantiate and expand current knowledge of intervertebral disc innervation. Protein gene product (PGP) 9.5 was used for immunohistochemical examination of serial transversal and sagittal paraffin sections of lumbar discs from adult dogs. This general marker revealed nerve fibres to be confined to the periphery of the intervertebral discs. These results indicate that even limited pathological processes affecting the outer layers of the intervertebral disc are prone to cause low back pain.

The pathogenesis of discogenic low back pain

Discogenic low back pain is a common cause of disability, but its pathogenesis is poorly understood. We collected 19 specimens of lumbar intervertebral discs from 17 patients with discogenic low back pain during posterior lumbar interbody fusion, 12 from physiologically ageing discs and ten from normal control discs. We investigated the histological features and assessed the immunoreactive activity of neurofilament (NF200) and neuropeptides such as substance P (SP) and vasoactive-intestinal peptide (VIP) in the nerve fibres. The distinct histological characteristic of the painful disc was the formation of a zone of vascularised granulation tissue from the nucleus pulposus to the outer part of the annulus fibrosus along the edges of the fissures. SP-, NF- and VIP-immunoreactive nerve fibres in the painful discs were more extensive than in the control discs. Growth of nerves deep into the annulus fibrosus and nucleus pulposus was observed mainly along the zone of granulation tissue in the painful discs. This suggests that the zone of granulation tissue with extensive innervation along the tears in the posterior part of the painful disc may be responsible for causing the pain of discography and of discogenic low back pain.

The sensory and sympathetic nerve supply within the cervical spine: review of recent observations

The purpose of this review is to identify recently observed features of the sympathetic and sensory systems and their pathways which characterize cervical spine innervation and their potential relevance to the clinical pain syndromes. The results of studies examining the innervation patterns of the zygoapophysial joints serve to demonstrate that structures in the cervical spine, as in other spinal regions, are partly innervated by sensory nerves traveling along sympathetic pathways. These studies also demonstrate that the neuropeptide levels in the cell bodies located within the dorsal root ganglion of these sensory nerves fluctuate according to the physiological state of the zygoapophysial joint. Additional to the sympathetic nerves accompanying the vertebral artery, the innervation patterns of dura and posterior longitudinal ligament in the upper cervical spine are distinctive features of cervical spine innervation. The possible clinical implications of cervical innervation patterns are considered with reference to referred pain, the pain patterns associated with a dissecting vertebral artery and cervicogenic headaches.

Autonomic innervation of immune organs and neuroimmune modulation

1. Increasing evidence indicates the occurrence of functional interconnections between immune and nervous systems, although data available on the mechanisms of this bi-directional cross-talking are frequently incomplete and not always focussed on their relevance for neuroimmune modulation. 2. Primary (bone marrow and thymus) and secondary (spleen and lymph nodes) lymphoid organs are supplied with an autonomic (mainly sympathetic) efferent innervation and with an afferent sensory innervation. Anatomical studies have revealed origin, pattern of distribution and targets of nerve fibre populations supplying lymphoid organs. 3. Classic (catecholamines and acetylcholine) and peptide transmitters of neural and non-neural origin are released in the lymphoid microenvironment and contribute to neuroimmune modulation. Neuropeptide Y, substance P, calcitonin gene-related peptide, and vasoactive intestinal peptide represent the neuropeptides most involved in neuroimmune modulation. 4. Immune cells and immune organs express specific receptors for (neuro)transmitters. These receptors have been shown to respond in vivo and/or in vitro to the neural substances and their manipulation can alter immune responses. Changes in immune function can also influence the distribution of nerves and the expression of neural receptors in lymphoid organs. 5. Data on different populations of nerve fibres supplying immune organs and their role in providing a link between nervous and immune systems are reviewed. Anatomical connections between nervous and immune systems represent the structural support of the complex network of immune responses. A detailed knowledge of interactions between nervous and immune systems may represent an important basis for the development of strategies for treating pathologies in which altered neuroimmune cross-talking may be involved.

ISSLS prize winner: The innervation of the intervertebral disc: a quantitative analysis

OBJECTIVE

The first quantitative analysis of the innervation of the lumbar intervertebral disc is presented.

METHODS

A sheep model was used allowing evaluation of the whole motion segment. Four sheep spines were used. One was processed for PGP 9.5 immunofluorescence and three were processed for PGP 9.5 immunoperoxidase histochemistry. A count was made of the densities of innervation of the endplate and anulus, and these were compared.

RESULTS

There is no significant difference between endplate and anulus innervation densities. The endplate innervation is concentrated centrally adjoining the nucleus. The richest area of innervation is in the perianular connective tissue.

DISCUSSION

The lumbar intervertebral disc has a meager innervation. This is concentrated in the perianular connective tissue and the central endplate. Although receptor threshold is more closely related to nociceptive function than innervation density, these findings have important implications for any treatment of discogenic pain.

Stereoscopic structure of sensory nerve fibers in the lumbar spine and related tissues

STUDY DESIGN

Neurotracer was applied to various sites in the rat lumbar spine and related tissues. The segmental distribution of labeled neurons in dorsal root ganglia (DRG) was investigated.

OBJECTIVES

To clarify the stereoscopic structure of afferent fibers innervating the lumbar spine and related tissues.

SUMMARY OF BACKGROUND DATA

Afferent fibers in the rat L5-L6 lumbar intervertebral disc are reported to originate from neurons in L1 and L2 DRG. However, anatomic studies determined that each dorsal ramus of the spinal nerve sends nerves to dorsal elements of the corresponding lumbar vertebra.

METHODS

Fluorescent neurotracer DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) was applied to various sites of the lumbar spine and related tissues in the L2, L5, and L6 levels in rats. DRG were sectioned 3 weeks after DiI application. Rostrocaudal distribution of DiI-labeled neurons was investigated.

RESULTS

At L5, DiI-labeled neurons were prominent in DRG L3 for the lamina, L2 for the spinous process, L2 for the back muscle fascia, and L1 for the skin. Dorsal elements are therefore innervated by neurons in more rostral DRG. In the transverse plane, the more distant from the DRG a site was, the more rostral the DRG innervating the site. This structure suggested a concentric innervation pattern in the transverse plane.

CONCLUSION

Stereoscopically, the peripheral innervation territory of a lumbar DRG is conical, with the apex at the ganglion and the base circumference located on the dermatome. The lumbar spine itself is involved in the conical innervation territories of DRG.

Substance P-containing nerves within the human vertebral body. an immunohistochemical study of the basivertebral nerve

BACKGROUND CONTENT

The basivertebral nerve provides innervation to the trabecular bone of the vertebral body. The function of this nerve is not known.

PURPOSE

The study was undertaken to better define the anatomic origin of this intraosseous nerve and to determine if this nerve contains substance P.

METHODS

The basivertebral nerve, which enters the vertebral body by means of the large posterior vascular foramen was studied anatomically by dissection and then histologically characterized. Sixty-two specimens of the basivertebral nerve were harvested from within the bone by microscopically aided dissection. Specimens were harvested from cervical, thoracic and lumbar vertebrae. These specimens were then stained for the presence of protein S-100 and substance P.

RESULTS

All 62 specimens stained positively for both S-100 and substance P.

CONCLUSION

The presence of substance P within these nerves is strong evidence that these nerves have the potential to transmit signals of nociception. The basivertebral nerve may play a role in some forms of clinical back and neck pain.

Origins of skeletal pain: sensory and sympathetic innervation of the mouse femur

Although skeletal pain plays a major role in reducing the quality of life in patients suffering from osteoarthritis, Paget's disease, sickle cell anemia and bone cancer, little is known about the mechanisms that generate and maintain this pain. To define the peripheral fibers involved in transmitting and modulating skeletal pain, we used immunohistochemistry with antigen retrieval, confocal microscopy and three-dimensional image reconstruction of the bone to examine the sensory and sympathetic innervation of mineralized bone, bone marrow and periosteum of the normal mouse femur. Thinly myelinated and unmyelinated peptidergic sensory fibers were labeled with antibodies raised against calcitonin gene-related peptide (CGRP) and the unmyelinated, non-peptidergic sensory fibers were labeled with the isolectin B4 (Bandeira simplicifolia). Myelinated sensory fibers were labeled with an antibody raised against 200-kDa neurofilament H (clone RT-97). Sympathetic fibers were labeled with an antibody raised against tyrosine hydroxylase. CGRP, RT-97, and tyrosine hydroxylase immunoreactive fibers, but not isolectin B4 positive fibers, were present throughout the bone marrow, mineralized bone and the periosteum. While the periosteum is the most densely innervated tissue, when the total volume of each tissue is considered, the bone marrow receives the greatest total number of sensory and sympathetic fibers followed by mineralized bone and then periosteum. Understanding the sensory and sympathetic innervation of bone should provide a better understanding of the mechanisms that drive bone pain and aid in developing therapeutic strategies for treating skeletal pain.

Discography interpretation and techniques in the lumbar spine

The authors provide an indepth analysis of discography, a provocative diagnostic tool to determine the origin of low-back pain. Injecting the intervertebral disc with radiopaque dye provides physicians with several useful pieces of information. First, the modality provides radiographic evaluation of the integrity of the nucleus pulposus and annular rings to determine tears or other lesions that could be creating low-back pain. Second, and very important, is its measure of disc nociception. A normal disc should not cause pain when injected; however, a disc that is physiologically compromised can mimic the pain previously experienced by a patient. The authors review the indications, technique, and interpretation of discography to allow a better understanding of when to use this diagnostic test and what to do with the results.

Mast cells in the pathogenesis of chronic back pain: a hypothesis

The pathophysiology of chronic low back pain is poorly understood, mainly because it is difficult to study experimentally or objectively. Recently it has been found that there is a relationship between neovascularization and innervation of the usually avascular and aneural intervertebral disc at the sites of discogenic pain. These data, together with the recognized involvement of mast cells in tissue repair, in the induction of angiogenesis, and in the production of and response to neurotrophic stimuli such as nerve growth factor, has suggested the hypothesis that mast cells may have a causative role in chronic low back pain. If so, the mast cell may represent an attractive therapeutic target.

Increased nerve and blood vessel ingrowth associated with proteoglycan depletion in an ovine anular lesion model of experimental disc degeneration

STUDY DESIGN

Nerves and blood vessel distribution in discs were localized immunohistochemically and correlated with the proteoglycan contents of normal and degenerate disc tissues.

OBJECTIVE

The aim of the present study was to systematically evaluate whether nerve and blood vessel ingrowth was associated with depletion of disc proteoglycans and degenerative changes in an established experimental model of disc degeneration.

SUMMARY OF BACKGROUND DATA

Animal models of disc degeneration, allowing longitudinal study of pathogenic mechanisms, are limited. The ovine model enables systematic monitoring of blood vessel and nerve ingrowth during the development of disc degeneration after injury to the anulus fibrosus.

METHODS

Merino sheep received a controlled left anterolateral surgical defect in the outer anulus fibrosus of the L1-L2 and L3-L4 discs (lesion group); sham-operated controls received the retroperitoneal anterolateral approach only. Animals were killed 3, 6, 12, and 26 months postoperation, and the discs were collected for histology and compositional and morphologic analyses. Sagittal tissue sections were stained with toluidine blue and hematoxylin and eosin; Type IV collagen immunolocalization visualized blood vessel ingrowth, and nerves were immunolocalized using monoclonal antibodies to growth-associated protein (GAP-43), protein gene product 9.5, and glial fibrillary acidic protein.

RESULTS

Compositional and histologic results demonstrated early focal depletion 3-12 months postoperation of glycosaminoglycan associated with lesion development, increased blood vessel and nerve ingrowth, and infiltration of cells from the outer anulus fibrosus along the plane of the original defect. Blood vessel numbers in the outer to mid third of the anulus fibrosus were elevated in the lesion discs 3-6 months postoperation reaching a maximum at 12 months postoperation; nerves immunoreactive with protein gene product 9.5 (also maximal at 12 months postoperation) were often found associated (but not exclusively) with blood vessels, and some nerves were also reactive with GAP-43 and glial fibrillary acidic protein, but only at 12 months postoperation.

CONCLUSIONS

Nerve and blood vessel ingrowth into the anulus fibrosis were strongly associated with proteoglycan depletion. The ovine anular lesion model of disc degeneration is a useful experimental model for the systematic evaluation of nerve and blood vessel development after anular injury.

Fat embolism and acute hypotension during vertebroplasty: an experimental study in sheep

STUDY DESIGN

An experimental study of cardiovascular complications that arise during vertebroplasty was conducted.

OBJECTIVE

To investigate the sequential occurrence of fat embolism and hypotension during vertebroplasty.

SUMMARY OF BACKGROUND DATA

Vertebroplasty, the augmentation of vertebrae with polymethylmethacrylate, is a technique for treating osteoporotic compression fractures and achieving prophylactic stabilization of osteoporotic vertebral bodies at risk of fracture. However, there is concern that fat embolism and acute hypotension could occur as in a variety of other orthopedic procedures.

METHODS

In six sheep, 6 mL of polymethylmethacrylate was injected unilaterally into L1. Transesophageal echocardiography monitored the pulmonary artery for echodense particles. Heart rate, arterial and venous pressures, and blood gas values were recorded before and for 25 minutes after injection. The lungs were subjected to postmortem histologic evaluation and compared with lung specimens from two sheep that had not undergone vertebroplasty.

RESULTS

Injection of cement elicited a very rapid decrease in heart rate (within 2 +/- 1 seconds) and a rapid increase in venous pressure (within 3 +/- 1 seconds), which was followed by a fall in arterial pressure (within 5 +/- 2 seconds) (phase 1). Thereafter, showers of echogenic material appeared (within 6 +/- 1 seconds) and lasted for 138 +/- 36 seconds. A second more severe fall in arterial pressure was observed beginning at 18 +/- 2 seconds (phase 2). The injection resulted in an increase in partial pressure of carbon dioxide and a decrease in pH. The histology showed intravascular fat globules and bone marrow cells in lung tissue.

CONCLUSIONS

The results suggest that immediately after cement injection, there was a reflex fall in heart rate and arterial pressure. The second fall in arterial pressure was a consequence of fat emboli passing through the heart and getting trapped in the lungs.

Induction of cholinergic function in cultured sympathetic neurons by periosteal cells: cellular mechanisms

Periosteum, the connective tissue surrounding bone, alters the transmitter properties of its sympathetic innervation during development in vivo and after transplantation. Initial noradrenergic properties are downregulated and the innervation acquires cholinergic and peptidergic properties. To elucidate the cellular mechanisms responsible, sympathetic neurons were cultured with primary periosteal cells or osteoblast cell lines. Both primary cells and an immature osteoblast cell line, MC3T3-E1, induced choline acetyltransferase (ChAT) activity. In contrast, lines representing marrow stromal cells or mature osteoblasts did not increase ChAT. Growth of periosteal cells with sympathetic neurons in transwell cultures that prevent direct contact between the neurons and periosteal cells or addition of periosteal cell-conditioned medium to neuron cultures induced ChAT, indicating that periosteal cells release a soluble cholinergic inducing factor. Antibodies against LIFRbeta, a receptor subunit shared by neuropoietic cytokines, prevented ChAT induction in periosteal cell/neuron cocultures, suggesting that a member of this family is responsible. ChAT activity was increased in neurons grown with periosteal cells or conditioned medium from mice lacking either leukemia inhibitory factor (LIF) or LIF and ciliary neurotrophic factor (CNTF). These results provide evidence that periosteal cells influence sympathetic neuron phenotype by releasing a soluble cholinergic factor that is neither LIF nor CNTF but signals via LIFRbeta.

Comparison of sensory and sympathetic innervation of the dura mater and posterior longitudinal ligament in the cervical spine after removal of the stellate ganglion

Although cervical spinal tissues are rich in sensory and sympathetic fibers, which play a significant role in clinical phenomena, there is little information available regarding their anatomical characteristics. In this study, we compared the innervation of the cervical dura mater and the posterior longitudinal ligament (PLL) to that after removal of the stellate ganglion to determine whether the anatomical background plays a significant role in clinical manifestations. Immunoreactivities for calcitonin gene-related peptide (CGRP) and substance P (SP) were used as sensory markers, and immunoreactivity for neuropeptide Y (NPY) was used as a sympathetic marker. Sensory fibers in the cervical dura mater were distributed within each cervical segment, but those in the PLL extended beyond the segmental borders. A dense sensory fiber network forming a single layer was seen at the intervertebral disc region in the cervical PLL, whereas sympathetic fibers in this region were sparsely distributed. Sympathetic fibers were distributed not only around the vascular wall but also in the region independent from vessels, and some occasionally ran together with sensory fibers in both the dura mater and the PLL. Removal of the stellate ganglion had little effect on the distribution of sensory fibers but denervated the sympathetic fiber networks in the region independent from vessels of the upper ipsilateral cervical PLL. In conclusion, the cervical dura mater and the PLL have different sensory and sympathetic innervations. Sympathetic fibers pass through the stellate ganglion to project to the region independent from vessels in the upper cervical PLL. Clinical symptoms may be attributed to this characteristic innervation of the cervical spine.

Autonomic innervation of tendons, ligaments and joint capsules. A morphologic and quantitative study in the rat

We analyzed the neuronal occurrence of autonomic transmitters; noradrenaline (NA), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), in the Achilles tendon, medial and lateral collateral ligaments and knee joint capsule in the rat--by immunohistochemistry (IHC). In addition, the tissue concentrations of the sympathetic neuropeptide, NPY, and the parasympathetic peptide, VIP, were determined by radioimmunoassay (RIA). IHC demonstrated nerve fibers containing sympathetic vasoconstrictors--NA and NPY--and the parasympathetic vasodilator, VIP, in all tissues. NPY- and NA-positive nerve fibers were predominantly observed in larger blood vessels, whereas, nerve fibers immunoreactive to VIP were found in smaller vessels. In many nerve fibers a co-localization of the transmitters was seen. RIA showed that the concentration of NPY compared to VIP was 15-times higher in ligaments and twice as high in tendons and capsules. The differences noted may reflect a difference in vulnerability to degenerative conditions. In pathological conditions, dysregulation of autonomic transmitters in hypovascularized tissues subjected to repetitive mechanical load may contribute to tissue hypoxia leading to degeneration and rupture of tendons and ligaments.

Sensory innervation of the lumbar dura mater passing through the sympathetic trunk in rats

STUDY DESIGN

Sensory innervation of the lumbar dura mater passing through the sympathetic trunk was investigated by neuronal tracing and immunohistochemical methods.

OBJECTIVE

To assess an anatomic basis indicating that sympathetic block in the higher lumbar region is effective for patients with low back pain.

SUMMARY OF BACKGROUND DATA

Low back pain is elicited by disorder or mechanical stimulation of the lumbar dura mater. Clinically, the authors often have observed patients in whom root block at the responsible level or sympathetic block at the higher level could relieve low back pain. Therefore, there may be two different sensory routes, the segmental innervation at the same level and nonsegmental fibers from higher dorsal root ganglia.

METHODS

The tracers were injected into the sympathetic trunk between L3 and L4 of rats. The lumbar dorsal root ganglia and dura mater were examined, and labeled cells were measured in size and the distribution. To establish the sensory property, the materials were processed in immunohistochemistry for calcitonin gene-related peptide.

RESULTS

Many small- to medium-sized neurons were retrogradely labeled L1 and L2 dorsal root ganglia after injection into the sympathetic trunk. The anterogradely labeled fibers were found in the dura mater at L4 and L5. Some of the labeled neurons and fibers were immunoreactive for calcitonin gene-related peptide.

CONCLUSION

Sensory fibers from the upper lumbar ganglia innervated the lower lumbar dura mater directly. These sensory nerves may mediate low back pain and possibly interact with sympathetic nerves.

Sensory innervation of the dorsal portion of the lumbar intervertebral disc in rats

STUDY DESIGN

The vertebral levels of dorsal root ganglia innervating the dorsal portion of the L5-L6 intervertebral disc were investigated in rats using a retrograde transport method. The pathways and functions of nerve fibers supplying the dorsal portion of the disc were determined by denervation and immunohistochemistry.

OBJECTIVES

The dorsal portion of the lumbar intervertebral disc has been reported to be innervated segmentally, but anesthetic block of the paravertebral sympathetic trunks and the L2 spinal nerve can relieve discogenic low back pain. In the current study, the sensory innervation of the dorsal portion of the L5-L6 intervertebral disc was investigated, because the disc anatomically corresponds to the L4-L5 disc in humans, and the dorsal portion of the human L4-L5 disc is frequently subject to injury that causes low back pain.

METHODS

A retrograde transport of Fluoro-Gold (F-G; Fluorochrome, Denver, CO) was used. Subjects included nontreated control (n = 32) and sympathectomized rats in which paravertebral sympathetic trunks were removed from L2 to L3 (n = 9). In a ventral approach, Fluoro-Gold crystals were placed on the dorsal portion of the L5-L6 disc, and labeled neurons in the bilateral dorsal root ganglia from T10 to L6 were counted.

RESULTS

Fluoro-Gold crystals did not leak from the dorsal portion of the L5-L6 disc in 14 of the 32 nontreated rats and in 5 of the 9 sympathectomized rats. These rats were used for analysis. Fluro-Gold-labeled neurons were found in dorsal root ganglia from T13 to L6 in the 14 control rats but only from L2 to L6 in the 5 sympathectomized rats.

CONCLUSION

The dorsal portion of the L5-L6 disc of rats was shown to be multisegmentally innervated by the T13 to L6 dorsal root ganglia. The sensory fibers from T13, L1, and L2 dorsal root ganglia were shown to innervate the dorsal portion of the L5-L6 disc through the paravertebral sympathetic trunks. In contrast, those from the L3-L6 dorsal root ganglia may innervate the dorsal portion of the L5-L6 disc through the sinuvertebral nerves.

An immunohistochemical study of innervation of lumbar spinal dura and longitudinal ligaments

STUDY DESIGN

An immunocytochemical study of nerve fibers in lumbar spinal dura and longitudinal ligaments was conducted in New Zealand white rabbits.

OBJECTIVES

To demonstrate the presence of nerve fibers and to establish the presence of nociceptive and sympathetic nerve fibers in lumbar dura and longitudinal ligaments.

SUMMARY OF BACKGROUND DATA

The role of dura as a source of low back pain is still unclear, and the data present a somewhat conflicting picture of the nature of nociceptive innervation in this tissue.

METHODS

An immunocytochemical method was used to study dura and longitudinal ligaments from New Zealand White rabbits.

RESULTS

Numerous fine nerve fibers and some small bundles were demonstrated in both the dura and the longitudinal ligaments. In dorsal dura, the fibers were seen at lateral margins running toward midline. In ventral dura and longitudinal ligaments, the fibers were seen throughout the substance of these tissues. A population of substance P, calcitonin gene-related peptide, and tyrosine hydroxylase-reactive nerve fibers were observed in all the tissues. In addition, fibers exhibiting nicotinamide adenine dinucleotide phosphate diaphorase activity were also observed, indicating the presence of nitric oxide in dura.

CONCLUSIONS

The results clearly demonstrate an extensive distribution of nerve fibers in dura and longitudinal ligaments. The presence of a significant number of putative nociceptive fibers supports a possible role for these structures as a source of low back pain and radicular pain.

An ultrastructural study of calcitonin gene-related peptide-immunoreactive nerve fibers innervating the rat posterior longitudinal ligament. A morphologic basis for their possible efferent actions

STUDY DESIGN

The present study investigated ultrastructural characteristics of calcitonin gene-related peptide-immunoreactive nerve fibers in the posterior longitudinal ligament of the rat lumbar spine.

OBJECTIVES

To provide a morphologic basis for assessment of the afferent and, in particular, efferent functions of calcitonin gene-related peptide immunoreactive nerves in the posterior longitudinal ligament and their eventual role in degenerative spondylarthropathies and low back pain.

SUMMARY OF BACKGROUND DATA

Previous studies using light-microscopic localization of sensory neuronal markers such as calcitonin gene-related peptide have reported the presence of sensory fibers in the supporting structures of the vertebral column. Meanwhile, accumulating research data have suggested efferent properties for calcitonin gene-related peptide, i.e., a trophic action that alters the intrinsic properties of target cells not through transient action of synaptic transmission, but through long-lasting signal transmission by the secreted neuropeptides. To verify such trophic, paracrine actions of the calcitonin gene-related peptide-containing fibers in the posterior longitudinal ligament, however, ultrastructural details of the terminals and their spatial relationship to their eventual target structures have to be elucidated.

METHODS

Rat posterior longitudinal ligaments were stained immunohistochemically for calcitonin gene-related peptide. Light-microscopic analysis of the semithin sections facilitated subsequent electron microscopy of specific sites of the posterior longitudinal ligament to determine ultrastructural details and nerve fiber-target relationships.

RESULTS

The rat lumbar posterior longitudinal ligament was found to be innervated by two distinctive calcitonin gene-related peptide immunoreactive nerve networks. In immunoelectronmicroscopy, the fibers of the deep network had numerous free nerve endings, whereas those of the superficial network showed spatial associations with other non-calcitonin gene-related peptide immunoreactive components of the network. In both systems, naked axons not covered by the Schwann cells made close spatial contact with smooth muscle cells: of blood vessels and resident posterior longitudinal ligament fibroblasts.

CONCLUSIONS

The ultrastructural characteristics of the innervation of the rat posterior longitudinal ligament would be compatible not only with a nociceptive function, but also with neuromodulatory, vasoregulatory, and trophic functions, as has already been established in some visceral organs.

Nerve ingrowth into diseased intervertebral disc in chronic back pain

BACKGROUND

In the healthy back only the outer third of the annulus fibrosus of the intervertebral disc is innervated. Nerve ingrowth deeper into diseased intervertebral disc has been reported, but how common this feature is and whether it is associated with chronic pain are unknown. We examined nerve growth into the intervertebral disc in the pathogenesis of chronic low back pain.

METHODS

We collected 46 samples of intervertebral discs from 38 patients during spinal fusion for chronic back pain. 30 samples were from pain levels clinically established by discography and 16 samples were from adjacent vertebral levels with no pain. We obtained 34 control samples of intervertebral disc from previously healthy individuals with normal histology within 8 h of recorded death. We used standard immunohistochemical techniques to test for a general nerve marker, a nociceptive neurotransmitter (substance P), and a protein expressed during axonogenesis (growth-associated protein 43 [GAP43]).

FINDINGS

We identified nerve fibres in the outer third of the annulus fibrosus in 48 (60%) of the 80 samples of intervertebral discs. Nerves were restricted to the outer or middle third of the annulus fibrosus in the 34 control samples. Among the patients with chronic low back pain, nerves extended into the inner third of the annulus fibrosus and into the nucleus pulposus in 21 (46%) and ten (22%) samples, respectively. Nerves usually accompanied blood vessels, but in 14 of the samples from back-pain patients, isolated nerve fibres were seen in the discal matrix. Both types of nerve fibres expressed substance P, but only non-vessel-associated fibres expressed GAP43. Deep nerve ingrowth into the inner third of the annulus fibrosus, the nucleus pulposus, or both was seen in four (25%) of 16 biopsy samples from non-pain levels and in 17 (57%) samples from pain levels. Of the 16 paired samples from both pain and non-pain levels, five pain-level samples and one non-pain-level sample showed deep nerve ingrowth.

INTERPRETATION

Our finding of isolated nerve fibres that express substance P deep within diseased intervertebral discs and their association with pain suggests an important role for nerve growth into the intervertebral disc in the pathogenesis of chronic low back pain.

Morphological and immunohistochemical examination of nerves in normal and injured collateral ligaments of rat, rabbit, and human knee joints

BACKGROUND

Knee joints possess an abundant nerve supply that relays sensory and motor information on such aspects as proprioception, nociception, and vasoregulation. Although synovial innervation has been well documented, little is known of the nerves that supply the collateral ligaments.

METHODS

The morphology of rabbit and human collateral ligament nerves was examined by silver impregnation. Immunohistochemistry was performed on rabbit and rat collateral ligaments to determine the presence of peptidergic nerves in these tissues. A 6-week gap injury was performed on three rabbit medial collateral ligaments, and the localisation of peptidergic nerves in these tissues was determined.

RESULTS

Irrespective of species or type of ligament examined, the greatest density of nerve fibres was found in the epiligament. Nerve fibres commonly accompanied blood vessels along the long axis of the ligament and then entered the substance of the tissue before ramifying in the deeper layers. Substance P and calcitonin gene-related peptide-immunoreactive nerve fibres were found in the collateral ligaments of the rat and rabbit. Injured ligaments showed a higher than normal level of immunoreactivity in and around the healing zone; however, the nerve fibres appeared tangled and truncated.

CONCLUSIONS

Like other structures in knee joints, collateral ligaments possess a complex nerve supply. The presence of peptidergic nerves suggests that ligaments may be susceptible to neurogenic inflammation and may be centres of articular nociception.

Tyrosine hydroxylase-immunoreactive nerve fibres in rat posterior longitudinal ligament

The nerve supply to the posterior longitudinal ligament (PLL) of the lumbar vertebrae has been the focus of considerable interest to gain insight into the pathogenesis of low back pain. The present study aimed to characterize the sympathetic fibres in the PLL by immuno-electronmicroscopy for tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis. The posterior central branches of the segmental lumbar arteries received numerous communicating fibres from the sinuvertebral nerve (SVN), but only shortly after their entrance to the spinal canal. The non-vessel-associated branches of the SVN formed transverse bundles, which met fibres from the opposite side in a plexus-like mid-sagittal network. As these fibres approached the midline, they gradually lost their Schwann cell cover. The free and naked fibres contained numerous terminal-like varicosities. The TH-ir and 6-hydroxydopamine (6-OH-DA) sensitive fibres were intermingled with non-TH-ir fibres. The TH-ir sympathetic fibres had no obvious target structures except for the numerous, intermingled, closely related and communicating terminal-like axons in the mid-sagittal network in contact with non-TH-ir fibres. This may represent a neuroanatomical equivalent reflecting modulatory functions, which could participate in the pathogenesis of low back pain.

Identification of the location, extent, and pathway of sensory neurologic feedback after mechanical stimulation of a lateral spinal ligament in chickens

STUDY DESIGN

This study traced the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens. The pathway was traced by locating the sites of Fos protein production in neuronal cell bodies at various sites in the nervous system.

OBJECTIVES

To trace the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens.

SUMMARY OF BACKGROUND DATA

The innervation of ligaments is thought to form part of a protective feedback mechanism to provide stability for joints. The precise pathway and extent of the feedback for spinal ligaments is currently unknown. Such information would provide a clear focus for future studies, especially for diseases such as scoliosis where it has been suggested that there is abnormality in perception of sensory feedback.

METHODS

The intertransverse ligament on the right side at T3-T4 in 4-week-old chickens was exposed by blunt dissection. After Fos production resulting from the surgery had been stopped, the ligament was stretched mechanically and repeatedly for 60 minutes using a 300-g weight. Various areas of the nervous system then were sectioned and processed immunohistochemically to identify areas of Fos production in nerve cell bodies. The presence of Fos indicated neurons that had been stimulated by the stretching the ligament, including interneurons along the feedback pathway.

RESULTS

Fos protein was identified in nerve cell bodies in the dorsal root ganglia and intermediate gray matter of the spinal cord at the level of stimulation as well as at several spinal cord levels above and below the site of stimulation. Identification was made on the ipsilateral and the contralateral sides, although the extent of Fos production was less on the contralateral side. Fos presence also was identified in sympathetic ganglia at these sites. Nerve cell bodies in the combined nucleus cuneatus and gracilis in the medulla oblongata, the vestibular nuclei, and the thalamus also contained Fos-positive particles.

CONCLUSIONS

Stretching a single lateral ligament of the spine produces a barrage of sensory feedback from several spinal cord levels on both sides of the spinal cord. This sensory information also is transferred to higher levels in the brain, including the nucleus gracilis and cuneatus, the vestibular nuclei, and the thalamus. These sites of Fos production suggest the locations of pathways for this sensory information, which include the dorsal columns and the spinocerebellar tracts. The information obtained from this study provides a clear focus for future studies in this area, particularly for diseases such as scoliosis where it is thought that incorrect perception of sensory information from the ligaments might be a major contributing factor.

Vertebral body MRI related to lumbar fusion results

The evaluation of continued pain after a technically successful posterolateral lumbar spine fusion is often challenging. Although the intervertebral disc is often a source of low back pain, abnormal endplates may also be a focus of pain, and possibly a source of continued pain after a posterolateral fusion. MRI allows noninvasive evaluation for disc degeneration, as well as for abnormal endplates and adjacent vertebral body marrow. Previous studies have found inflammatory marrow changes, adjacent to abnormal endplates, associated with disc degeneration in low back pain patients. In this study, preoperative MRI scans in 89 posterolateral lumbar fusion patients were reviewed, by an independent radiologist, to determine whether vertebral body marrow changes adjacent to the endplates were related to continued pain. Independent chart review and follow-up telephone interview of all patients at a 4-year follow-up (mean) formed the basis for the clinical results. Vertebral body MRI signals consistent with inflammatory or fatty changes were found in 38% of patients, and always occurred adjacent to a degenerated disc. Inflammatory MRI vertebral body changes were significantly related to continued low back pain at P = 0.03. We conclude that posterolateral lumber fusion has a less predictable result for the subset of degenerative disc patients with abnormal endplates and associated marrow inflammation. More research is needed to determine the biological and biomechanical effects of posterolateral fusion upon the endplate within the fused segments. If indeed further study supports the hypothesis that abnormal endplates associated with inflammation are a source of pain, then treating the endplates directly by anterior fusion may be a preferred treatment for this subset of degenerative patients.

Origin of nerves supplying the posterior portion of lumbar intervertebral discs in rats

STUDY DESIGN

The authors studied the origin of nerves supplying the posterior portion of lumbar intervertebral discs in rats by resection of the sympathetic trunks.

OBJECTIVE

To understand discogenic low back pain from the innervation of the lumbar intervertebral discs.

SUMMARY OF BACKGROUND DATA

The afferent pathways of discogenic low back pain have not been studied thoroughly. It has been reported that stimulation of an inflamed lower spinal nerve root elicits leg pain but not low back pain and that stimulation of the posterior portion of lumbar intervertebral discs evokes only low back pain. These facts suggest that pain sensation from the posterior portion of lumbar discs is not transmitted via the lower spinal nerve roots.

METHODS

Forty-five Wistar rats were used. Seven days after the resection of sympathetic trunks with ganglia at different levels, the whole lumbar spine was stained by an acetylcholinesterase histochemical method. The posterior portions of lumbar intervertebral discs were observed.

RESULTS

The dense nerve network on the posterior portion of lumbar intervertebral discs had disappeared almost completely after total resection of bilateral sympathetic trunks at L2-L6. However, there was a slight decrease in the network after bilateral single-level resection or unilateral multisegmental resection.

CONCLUSIONS

The results showed that the posterior portion of lumbar intervertebral discs was innervated by the sympathetic nerves multisegmentally and bilaterally.

An anatomic study of neuropeptide immunoreactivities in the lumbar dura mater after lumbar sympathectomy

STUDY DESIGN

The distribution and density of nerve innervation in the lumbar dura mater after lumbar sympathectomy were assessed in wistar rats.

OBJECTIVE

To provide basic information on the interaction between sympathetic and sensory nerves in patients with low back pain.

SUMMARY OF BACKGROUND DATA

Many studies have indicated that the sinuvertebral nerve has an important role in innervating the tissues around the vertebrae. However, the origin, innervating pattern, and connections between the nerves are still controversial. It is well known that pain is often accompanied with sympathetic symptoms and exaggerated by sympathetic stimuli. Occasionally, anesthetic block at the L2 or L3 sympathetic ganglion relieves low back pain or symptoms associated with low back pain. The authors assessed the changes of the density and distribution of nerve innervation of the lumbar dura mater after lumbar sympathectomy.

METHODS

Normal adult rats were sympathectomized at L2-L3. The threshold for thermal noxious pain by hot-plate analgesia test and changes in neuropeptides in the lumbar dura mater and dorsal root ganglia using light microscopic immunohistochemistry were assessed and compared with control rats.

RESULTS

In the hot-plate analgesia test, sympathectomized rats increased their hot-plate latency time compared with that of sham-operated rats. Density of calcitonin gene-related peptide immunoreactive fibers in sympathectomy side of the lumbar dura mater decreased to 45.5% compared with the contralateral side. The number and size of calcitonin gene-related peptide immunoreactive cells in dorsal root ganglia showed no difference between sympathectomized and contralateral side.

CONCLUSION

Sympathectomy increased the pain threshold and made the sympathectomized rats hypesthetic. A large numbers of sensory fibers innervated the lumbar dura mater via L2-L3 sympathetic nerve in rats. Sympathectomy reduced the number of these nerve fibers in the lumbar dura mater. Sympathetic nerves may play an important role for low back pain involving the lumbar dura mater.

Innervation of the spinal dura. Myth or reality?

STUDY DESIGN

Cranial and spinal dura from nine Sprague Dawley male rats were examined immunocytochemically for the presence of nerve fibers and mast cells and for innervation. The posterior longitudinal ligament and peridural membrane were also examined for these elements.

OBJECTIVE

To examine the pattern of sensory innervation and the presence of mast cells in rat spinal dura.

SUMMARY OF BACKGROUND DATA

The cranial dura is richly innervated and has a robust population of mast cells, which have been implicated in the pathogenesis of vascular headache. Moskowitz's explanation for vascular headache focused on the dura mater and neurogenic inflammation. Essential to his model are dural trigeminovascular fibers and mast cells. Previous studies provide contradictory and inconclusive results regarding spinal dural innervation.

METHODS

Immunocytochemical techniques using antibodies to calcitonin gene-related peptide and substance P were used to identify sensory nerve fibers and antibodies to serotonin were used to identify mast cells. Specimens dissected included dura of the cranial vault in continuity with the dorsal cervical dura, dura of the skull base in continuity with the ventral cervical dura, lumbar dura, and posterior longitudinal ligament from the cervical and lumbar regions.

RESULTS

A rich neural network and an abundant mast cell population were identified in the supratentorial and infratentorial cranial dura, both dorsally and ventrally. A paucity of nerve fibers and mast cells was observed in the cervical and lumbar dura; in contrast, these elements were prominent in the posterior longitudinal ligament and peridural membrane.

CONCLUSIONS

Spinal dura does not have a rich innervation of calcitonin gene-related peptide- and substance P-positive nerve fibers or a robust population of mast cells. The spinal dura may serve as a protective covering. Unlike the cranial dura, it may not be implicated in the pathogenesis of pain. Additional studies on primate and human spinal dura are warranted to corroborate findings that the spinal dura may be relatively insensitive.

A mechanism for sympathectomy-induced bone resorption in the middle ear

BACKGROUND

Recent investigations have demonstrated a link between sympathectomy and osteoclast-mediated bone resorption. The exact nature of this link, however, is unknown. We hypothesize that substance P, a potent vasoconstrictive neuropeptide found in peripheral sensory fibers, including those innervating bone, is the mediator of this phenomenon. To test this theory, the effects of substance P on in vitro calcium release from cultured neonatal mouse calvaria were assessed. In addition, an in vivo study was conducted whereby gerbils were injected with capsaicin to eliminate substance P-containing fibers before sympathectomy with 6-hydroxydopamine. If the effects of 6-hydroxydopamine were eliminated by prior administration of capsaicin, the role of sensory nerves in sympathectomy-induced resorption would be strongly implicated.

IN VITRO STUDY

Substance P at 10(-8) mol/L was incubated with eight newborn Swiss-Webster mouse hemicalvarial explants and compared with explants incubated in control media alone. The neonatal mice were euthanized at day 3, and their hemicalvaria were preincubated in 2 ml of stock media without treatment for 24 hours at 36.5 degrees C as a stabilization period. After the stabilization period, the stock media were replaced with 2 ml of fresh control media or media containing substance P at 10(-8) mol/L. A similar experiment was performed with the addition of indomethacin at 5 x 10(-7). The explants were then incubated for 72 hours with gassing every 12 hours with a mixture of O2, N2, and CO2. At the end of the 72-hour period, the media were analyzed for calcium content by atomic absorption spectrophotometry and compared by one-way analysis of variance with Bonferroni-corrected post hoc tests.

IN VIVO STUDY

Forty-eight Mongolian gerbils were placed into four groups: group 1 received intraperitoneal injections of 6-hydroxydopamine at 75 micrograms/gm body weight on days 1, 2, 6, 7, and 8; group 2 received identical injections of hydroxydopamine, but 12 hours after receiving subdermal injections of capsaicin at 50 micrograms/gm body weight; group 3 received only subdermal injections of capsaicin; and group 4 received only saline injections to serve as controls. Seven days after treatment, the animals were euthanized, and the ventral wall of each animal's right bulla was resected and quantified for osteoclast number and surface with a computer-based histomorphometry system. Analysis was then made by one-way analysis of variance with Bonferroni-corrected post hoc tests.

RESULTS

The results of the in vitro study revealed that substance P at 10(-8) mol/L (11.05 +/- 3.37 micrograms/ml) induced significant calcium release from cultured neonatal mouse calvaria when compared with control bone incubated in base media alone (0.92 +/- 2.85 micrograms/ml, p < 0.01). The process was completely inhibited by 5.0 x 10(-7) indomethacin. The results of the in vivo study showed 6-hydroxydopamine treatment significantly increased both the osteoclast number (NOc/TL = 3.14 +/- 1.33/mm) and the osteoclast surface (OcS/BS = 16.04% +/- 6.95%) of bone when compared with bone from saline-treated controls (NOc/TL = 1.77 +/- 0.79/mm, p < 0.01; OcS/BS = 8.88% +/- 4.15%, p < 0.01). These 6-hydroxydopamine-induced increases were eliminated, however, in animals pretreated with capsaicin before sympathectomy (NOc/TL = 1.86 +/- 0.68/mm, p > 0.05; OcS/BS = 9.92 +/- 3.73, p > 0.05), whereas treatment with capsaicin alone had no effect when compared with bone from saline-treated controls (NOc/TL = 2.02 +/- 0.50/mm, p > 0.05; OcS/BS = 10.28% +/- 2.62%, p > 0.05). Substance P has thus been shown to induce calcium release from membranous bone in vitro, whereas capsaicin, a substance P-specific sensory neurolytic chemical, eliminates the in vivo osteoclast-inductive effects of 6-hydroxydopamine when given 12 hours before treatment. The results indicate that substance P is capable of inducing resorption and that substance P-containing sensory ne