Immunoreactivity of brain-derived neurotrophic factor in rat dorsal root ganglion and spinal cord dorsal horn following exposure to herniated nucleus pulposus

Inflammatory interactions between degenerated intervertebral discs and microglia: Implication of sphingosine-1-phosphate signaling

The etiology of intervertebral disc degeneration is largely unknown, but local neuroinflammation may exert a crucial role through activation of cells as microglia and pro-inflammatory cytokines production. We aimed to compare the effect of degenerated and normal intervertebral disc microenvironment on microglial cells and the potential role of sphingosine-1-phosphate, a pro-inflammatory sphingolipid, in their crosstalk. Human degenerated intervertebral discs (Pfirrmann grade IV) were obtained at surgery for spondylolisthesis. Normal intervertebral discs were collected from cadaveric normal lumbar spines. Normal and degenerated-intervertebral discs were kept in culture to obtain media conditioning. Then, microglial cells were cocultured with conditioned media and viability, proliferation, migration, chemotaxis, and inflammatory gene expression were evaluated. The results demonstrate that conditioned media from degenerated intervertebral discs activate microglial cells, increasing chemotaxis, migration, and pro-inflammatory mediators release to a great extent than normal discs. In addition, we show that the administration of sphingosine-1-phosphate to normal intervertebral disc/microglia coculture mimicked degenerative effects. Interestingly, sphingosine-1-phosphate content in conditioned media from degenerated discs was significantly higher than that from normal ones. In addition, FTY720, a functional antagonist of sphingosine-1-phosphate, potently inhibited the effect of degenerated intervertebral discs on microglial inflammatory factor transcription and migration. Our data report, for the first time, that sphingosine-1-phosphate is involved as signal in the microenvironment of human degenerated intervertebral discs. Sphingosine-1-phosphate signaling modulation by FTY720 may induce beneficial effects in counteracting microglial activation during intervertebral disc degeneration.

Pulsed Electromagnetic Fields Accelerate Sensorimotor Recovery Following Experimental Disc Herniation

STUDY DESIGN

An experimental animal study.

OBJECTIVE

The aim of this study was to investigate the effect of pulsed electromagnetic fields (PEMF) on recovery of sensorimotor function in a rodent model of disc herniation (DH).

SUMMARY OF BACKGROUND DATA

Radiculopathy associated with DH is mediated by proinflammatory cytokines. Although we have demonstrated the anti-inflammatory effects of PEMF on various tissues, we have not investigated the potential therapeutic effect of PEMF on radiculopathy resulting from DH.

METHODS

Nineteen rats were divided into three groups: positive control (PC; left L4 nerve ligation) (n = 6), DH alone (DH; exposure of left L4 dorsal root ganglion [DRG] to harvested nucleus pulposus and DRG displacement) (n = 6), and DH + PEMF (n = 7). Rodents from the DH + PEMF group were exposed to PEMF immediately postoperatively and for 3 hours/day until the end of the study. Sensory function was assessed via paw withdrawal thresholds to non-noxious stimuli preoperatively and 1 and 3 days postoperatively, and every 7 days thereafter until 7 weeks after surgery. Motor function was assessed via DigiGait treadmill analysis preoperatively and weekly starting 7 days following surgery until 7 weeks following surgery.

RESULTS

All groups demonstrated marked increases in the left hindlimb response threshold postoperatively. However, 1 week following surgery, there was a significant effect of condition on left hindlimb withdrawal thresholds (one-way analysis of variance: F = 3.82, df = 2, P = 0.044) where a more rapid recovery to baseline threshold was evident for DH + PEMF compared to PC and DH alone. All groups demonstrated gait disturbance postoperatively. However, DH + PEMF rodents were able to regain baseline gait speeds before DH and PC rodents. When comparing gait parameters, DH + PEMF showed consistently less impairment postoperatively suggesting that PEMF treatment was associated with less severe gait disturbance.

CONCLUSION

These data demonstrate that PEMF accelerates sensorimotor recovery in a rodent model of DH, suggesting that PEMF may be reasonable to evaluate for the clinical management of patients with herniation-associated radiculopathy.Level of Evidence: N/A.

Effect of an Acid-sensing Ion Channels Inhibitor on Pain-related Behavior by Nucleus Pulposus Applied on the Nerve Root in Rats

STUDY DESIGN

Controlled, interventional animal study.

OBJECTIVE

To examine the effect of an inhibitor of acid-sensing ion channel 3 (ASIC3) on pain-related behavior induced by application of the nucleus pulposus (NP) onto the dorsal root ganglion (DRG) in rats.

SUMMARY OF BACKGROUND DATA

ASIC3 is associated with acidosis pain in inflamed or ischemic tissues and is expressed in sensory neurons and NP cells. The ASIC3 inhibitor, APETx2, increases the mechanical threshold of pain in models of knee osteoarthritis or postoperative pain. However, the efficacy of APETx2 for pain relief in the NP application model remains unknown.

METHODS

Autologous NP was applied to the left L5 nerve root of 183 adult female Sprague-Dawley rats. The DRGs were treated with NP plus one of the following four treatments: saline solution (SM), low (0.01 μg: LD), medium (0.1 μg: MD), or high dose (1.0 μg: HD) of APETx2. Behavioral testing was performed to investigate the mechanical withdrawal threshold using von Frey hairs. Expression of nerve growth factor, hypoxia-inducible factor-1α (HIF1α), activating transcription factor-3, and ionized calcium-binding adaptor molecule-1 was evaluated using immunohistochemistry. Statistical differences among multiple groups were assessed using the Steel test, the Tukey-Kramer test, and the Dunnett test. P < 0.05 were considered significant.

RESULTS

The thresholds in the HD group were higher than those in the SM group at Days 14 and 21 (P < 0.05). In the MD group, the threshold was higher than in the SM group at Day 14 (P < 0.05). High doses of APETx2 reduced the expression of HIF1α after Day 14 compared with the SM group (P < 0.05).

CONCLUSION

APETx2 significantly improved pain-related behavior in a dose-dependent manner. APETx2 may inhibit ASIC3 and partly inhibit Nav1.8 channels. This ASIC3 channel inhibitor may be a potential therapeutic agent in early-stage lumbar disc herniation.

LEVEL OF EVIDENCE

N/A.

Role of vitamin D3 in treatment of lumbar disc herniation--pain and sensory aspects: study protocol for a randomized controlled trial

BACKGROUND

Vitamin D receptors have been identified in the spinal cord, nerve roots, dorsal root ganglia and glial cells, and its genetic polymorphism association with the development of lumbar disc degeneration and herniation has been documented. Metabolic effects of active vitamin D metabolites in the nucleus pulposus and annulus fibrosus cells have been studied. Lumbar disc herniation is a process that involves immune and inflammatory cells and processes that are targets for immune regulatory actions of vitamin D as a neurosteroid hormone. In addition to vitamin D's immune modulatory properties, its receptors have been identified in skeletal muscles. It also affects sensory neurons to modulate pain. In this study, we aim to study the role of vitamin D3 in discogenic pain and related sensory deficits. Additionally, we will address how post-treatment 25-hydroxy vitamin D3 level influences pain and sensory deficits severity. The cut-off value for serum 25-hydroxy vitamin D3 that would be efficacious in improving pain and sensory deficits in lumbar disc herniation will also be studied.

METHODS/DESIGN

We will conduct a randomized, placebo-controlled, double-blind clinical trial. Our study population will include 380 cases with one-level and unilateral lumbar disc herniation with duration of discogenic pain less than 8 weeks. Individuals who do not have any contraindications, will be divided into three groups based on serum 25-hydroxy vitamin D3 level, and each group will be randomized to receive either a single-dose 300,000-IU intramuscular injection of vitamin D3 or placebo. All patients will be under conservative treatment. Pre-treatment and post-treatment assessments will be performed with the McGill Pain Questionnaire and a visual analogue scale. For the 15-day duration of this study, questionnaires will be filled out during telephone interviews every 3 days (a total of five times). The initial and final interviews will be scheduled at our clinic. After 15 days, serum 25-hydroxy vitamin D3 levels will be measured for those who have received vitamin D3 (190 individuals).

TRIAL REGISTRATION

Iranian Registry for Clinical Trials ID: IRCT2014050317534N1 (trial registration: 5 June 2014).

[Neurotrophins and pain]

Neurotrophins are a family of trophic factors well known for their effects on neuronal survival, growth and neuronal differentiation. During the last decade, a large literature has shown in humans and in animal models that nerve growth factor (NGF) is a peripheral mediator of pain, especially in the states of inflammatory pain. NGF synthesis is indeed increased in a wide variety of inflammatory diseases and NGF neutralizing molecules are effective analgesic agents in these models of persistent pain. Therapeutical strategies targeting the sequestering of NGF did yield very encouraging results in clinical trials (stages II and III) but have been on hold since 2010 due to potential harmful effects in combination with non-steroid anti-inflammatory drug. NGF regulates the expression of a second neurotrophin, Brain Derived Neurotrophic Factor (BDNF), in nociceptors. BDNF is released where nociceptors are activated, and it acts as a modulator of pain in the central nervous system and is involved in central sensitization.

Tumor necrosis factor-α-dependent infiltration of macrophages into the dorsal root ganglion in a rat disc herniation model

STUDY DESIGN

A prospective molecular mechanism of macrophages infiltration in experimental disc herniation.

OBJECTIVE

To investigate the mechanisms of macrophages infiltration into the dorsal root ganglion (DRG) in a rat model of disc herniation.

SUMMARY OF BACKGROUND DATA

Macrophages infiltrate the DRG after application of nucleus pulposus (NP) on the DRG, and may play an important role in radiculopathy. However, the mechanisms of macrophages infiltration after NP application remain poorly understood.

METHODS

After experimental disc herniation in this study, we investigated changes in the expression of ED1 (a marker of macrophages) and vascular cell adhesion molecule-1 (VCAM-1) in DRG using immunofluorescence. We also investigated the expression of ED1 and VCAM-1 in DRG by treatment with tumor necrosis factor-α (TNF-α) inhibitor at the time of surgery.

RESULTS

We found a massive ED1-positive macrophages infiltrated the DRG, and VCAM-1-like immunoreactivity vessels became evident after NP application. Furthermore, both macrophage infiltration and VCAM-1 expression were prevented by treatment with TNF-α inhibitor at the time of surgery.

CONCLUSION

These findings indicated that macrophages infiltration into the DRG was TNF-α-dependent, and might be partly mediated by VCAM-1 in the early stage of experimental lumbar disc herination. Taken together, this study provides important preliminary data suggesting that TNF-α plays an important role in the macrophage infiltration.

LEVEL OF EVIDENCE

N/A.

Kinematic and dynamic gait compensations in a rat model of lumbar radiculopathy and the effects of tumor necrosis factor-alpha antagonism

Introduction

Tumor necrosis factor-α (TNFα) has received significant attention as a mediator of lumbar radiculopathy, with interest in TNF antagonism to treat radiculopathy. Prior studies have demonstrated that TNF antagonists can attenuate heightened nociception resulting from lumbar radiculopathy in the preclinical model. Less is known about the potential impact of TNF antagonism on gait compensations, despite being of clinical relevance. In this study, we expand on previous descriptions of gait compensations resulting from lumbar radiculopathy in the rat and describe the ability of local TNF antagonism to prevent the development of gait compensations, altered weight bearing, and heightened nociception.

Methods

Eighteen male Sprague-Dawley rats were investigated for mechanical sensitivity, weight-bearing, and gait pre- and post-operatively. For surgery, tail nucleus pulposus (NP) tissue was collected and the right L5 dorsal root ganglion (DRG) was exposed (Day 0). In sham animals, NP tissue was discarded (n = 6); for experimental animals, autologous NP was placed on the DRG with or without 20 μg of soluble TNF receptor type II (sTNFRII, n = 6 per group). Spatiotemporal gait characteristics (open arena) and mechanical sensitivity (von Frey filaments) were assessed on post-operative Day 5; gait dynamics (force plate arena) and weight-bearing (incapacitance meter) were assessed on post-operative Day 6.

Results

High-speed gait characterization revealed animals with NP alone had a 5% decrease in stance time on their affected limbs on Day 5 (P ≤0.032). Ground reaction force analysis on Day 6 aligned with temporal changes observed on Day 5, with vertical impulse reduced in the affected limb of animals with NP alone (area under the vertical force-time curve, P <0.02). Concordant with gait, animals with NP alone also had some evidence of affected limb mechanical allodynia on Day 5 (P = 0.08) and reduced weight-bearing on the affected limb on Day 6 (P <0.05). Delivery of sTNFRII at the time of NP placement ameliorated signs of mechanical hypersensitivity, imbalanced weight distribution, and gait compensations (P <0.1).

Conclusions

Our data indicate gait characterization has value for describing early limb dysfunctions in pre-clinical models of lumbar radiculopathy. Furthermore, TNF antagonism prevented the development of gait compensations subsequent to lumbar radiculopathy in our model.

Intervertebral disc, sensory nerves and neurotrophins: who is who in discogenic pain?

The normal intervertebral disc (IVD) is a poorly innervated organ supplied only by sensory (mainly nociceptive) and postganglionic sympathetic (vasomotor efferents) nerve fibers. Interestingly, upon degeneration, the IVD becomes densely innervated even in regions that in normal conditions lack innervation. This increased innervation has been associated with pain of IVD origin. The mechanisms responsible for nerve growth and hyperinnervation of pathological IVDs have not been fully elucidated. Among the molecules that are presumably involved in this process are some members of the family of neurotrophins (NTs), which are known to have both neurotrophic and neurotropic properties and regulate the density and distribution of nerve fibers in peripheral tissues. NTs and their receptors are expressed in healthy IVDs but much higher levels have been observed in pathological IVDs, thus suggesting a correlation between levels of expression of NTs and density of innervation in IVDs. In addition, NTs also play a role in inflammatory responses and pain transmission by increasing the expression of pain-related peptides and modulating synapses of nociceptive neurons at the spinal cord. This article reviews current knowledge about the innervation of IVDs, NTs and NT receptors, expression of NTs and their receptors in IVDs as well as in the sensory neurons innervating the IVDs, the proinflammatory role of NTs, NTs as nociception regulators, and the potential network of discogenic pain involving NTs.

Gene expression changes in dorsal root ganglion of rat experimental lumber disc herniation models

STUDY DESIGN

Comprehensive overviews of gene expression changes in dorsal root ganglion (DRG) were obtained using microarrays in 2 rat models of experimental lumbar disc herniation (LDH).

OBJECTIVE

To clarify the mechanisms of painful radiculopathy caused by LDH from the viewpoint of gene expression changes in DRG of 2 rat models of LDH.

SUMMARY AND BACKGROUND DATA

Mechanical compression and chemical irritation are considered to be the 2 major causative factors of radiculopathy associated with LDH. Several basic studies have revealed histologic and functional changes in the nerve root and DRG induced by mechanical compression or application of nucleus pulposus. However, the effects of the 2 major factors have not been investigated in detail. METHODS.: The effects of mechanical and chemical factors were assessed in 2 models and in sham-operated rats. The mechanical compression model had a stainless steel rod inserted through a drill hole in the L5 lamina; the nucleus pulposus model had autologous nucleus pulposus placed in the drill hole, and only a drill hole was made in the L5 lamina of sham-operated rats. Samples from the left L5 DRG were harvested from the models with mechanical allodynia and from sham rats and analyzed using microarrays at 3 and 7 days after surgery.

RESULTS

The gene expression profiles differed in the 2 models at 7 days, but were similar at 3 days after surgery. Expression of the growth factor gene, insulin-like growth factor 1, and of the cyclinD1, cell division cycle 2 homolog A, and cyclinA2 genes related to the cell cycle was significantly upregulated in the DRG of the mechanical compression group at 7 days after surgery.

CONCLUSION

Mechanical and chemical factors caused altered gene expression in the DRG at 7 days after surgery, suggesting that the mechanisms of nerve injury induced by these factors differ. The upregulation of IGF-1 might be a key factor in painful radiculopathy induced by mechanical factors.

BDNF in RA: downregulated in plasma following anti-TNF treatment but no correlation with inflammatory parameters

The involvement of brain-derived neurotrophic factor (BDNF) in rheumatoid arthritis (RA) is largely unknown. The distribution of BDNF and its associated receptors, TrkB and p75, in the synovial tissue of patients with RA was examined and contrasted with that in patients with osteoarthritis (OA). Additionally, levels of BDNF in both synovial tissue and synovial fluid were measured. Furthermore, the effects of anti-tumour necrosis factor (anti-TNF; infliximab) treatment on BDNF levels in the plasma of RA patients were analysed. Cells in the synovium showed immunoreactivity for BDNF and BDNF-, p75- and TrkB-receptor immunoreactions were seen in nerve fibres of nerve fascicles and in association with sensory corpuscles. The levels of BDNF in synovial tissue were not correlated with the number of inflammatory cells observed microscopically or with levels of TNFalpha. Nor did the BDNF levels in synovial fluid correlate with erythrocyte sedimentation rate (ESR) or white blood cell counts. Anti-TNF treatment lead to a decrease in plasma levels of BDNF 14 weeks after the initiation of anti-TNF therapy, i.e., 8 weeks after the last infusion. Higher levels of BDNF were observed in RA patients at baseline compared with those for healthy individuals. However, the levels of BDNF in plasma of patients treated with anti-TNF did not correlate with the changes in ESR or a disease activity score. The clinical significance of this study is that anti-TNF treatment influences plasma levels of BDNF although there was no evidence that BDNF levels correlate with inflammatory parameters in either infliximab-treated or non-infliximab-treated patients with RA. Instead it is likely that sources other than inflammatory cells, including nerve structures, are important sources of BDNF and that the effects of anti-TNF treatment on BDNF levels may be related to effects on circulating and various local cells and/or BDNF-containing neurons.

An injectable and in situ-gelling biopolymer for sustained drug release following perineural administration

STUDY DESIGN

This study evaluated whether the aggregation behavior of a thermally responsive elastin-like polypeptide (ELP) prolongs protein residence time at the dorsal root ganglion (DRG). This work involves development of a sustained-release drug delivery vehicle to provide high and sustained levels of biologic therapeutics to the dorsal root ganglion while minimizing systemic exposure.

OBJECTIVE

To study the potential of the ELP biopolymer to sustain release and lower systemic exposure of bioactive peptides following perineural administration.

SUMMARY OF BACKGROUND DATA

Anticytokine treatment for lumbar radiculopathy may offer clinical improvement, but exposes patients to systemic toxicities of immunosuppression. ELPs are environmentally responsive polypeptides that undergo a phase transition on heating to form an insoluble aggregate. Drug conjugates with ELP exhibit both temperature-sensitivity and in vitro bioactivity. Monomer resolubilization yields solution-phase molecules, and this reversible aggregation behavior may create a perineural drug depot to sustain drug delivery to an inflamed nerve.

METHODS

This experiment involved 48 rats in which radiolabeled ELPs (aggregating or soluble) were injected overlying the L5 dorsal root ganglion. Animals were killed at 6 different time points, and radioactivity associated with the injected segment, serum, and other tissues was evaluated.

RESULTS

The aggregating ELP demonstrated a 7-fold longer perineural half-life compared with the soluble ELP. This supports the hypothesis that the aggregating ELP forms a depot from which slow resolubilization and clearance provides sustained, local protein release. Furthermore, serum radioactivity reached a lower peak for the aggregating group, demonstrating slower absorption of the aggregating protein into the systemic circulation.

CONCLUSION

These results suggest that ELP aggregation confer the benefit of perineural compartment longevity for bioactive therapeutics delivered fused with this carrier. This may sustain release of potent immunomodulator therapeutics to treat local neuroinflammation. Desirable features include delivery of high local doses and protection against systemic exposure and associated toxicity.

Thalamic activation in a disc herniation model

STUDY DESIGN

A novel approach combining a rodent disc herniation model with electrophysiologic recordings of thalamic evoked responses.

OBJECTIVE

To assess short-term effects of nucleus pulposus (NP) application on dorsal root ganglions (DRG) on high threshold afferent fiber evoked activation in the thalamus.

SUMMARY OF BACKGROUND DATA

Epidural application of NP in combination with mechanical compression induces pain related behavior in rats associated with enhanced activity of pain-processing neurons in the dorsal horn of the spinal cord. However, possible effects on neuronal activity in the pain processing ventral posterior lateral (VPL) thalamic nucleus following NP application on DRG have not been investigated.

METHODS

Responses in the contralateral VPL evoked by electrical stimulation of the sciatic nerve and of the fourth lumbar (L4) DRG were recorded in adult Sprague-Dawley rats. Records were obtained before and during application (5, 10, and 20 minutes) of NP or of adipose tissue (AT) to the L4 DRG. AT was used as control for mechanical effects of NP application.

RESULTS

Application of NP resulted in an increase of evoked thalamic responses to 138% +/- 10% of control after 20 minutes (P < 0.01), whereas AT application for 20 minutes resulted in a reduction of evoked responses to 77% +/- 4% (P < 0.05). Recordings in control animals (i.e., with no application) demonstrated stable evoked neuronal thalamic activity for up to 40 minutes.

CONCLUSION

The study demonstrates that NP application onto DRG increases afferent fiber evoked responses in the thalamus and in view of the opposite effects of AT application suggests that these effects may be specific for NP. The results show that NP affects sensory transmitting pathways within a few minutes, possibly due to rapid and reversible alterations in the neuronal excitability. The study thus introduces a rodent model for studying sensory afferent evoked thalamic activity related to DRG injury which may be used to evaluate analgesics and anti-inflammatory drugs used for pain relief in disc herniation and neuropathic pain patients.

Neurotrophins: mediators and modulators of pain

The neurotrophin family of neurotrophic factors are well-known for their effects on neuronal survival and growth. Over the past decade, considerable evidence has accumulated from both humans and animals that one neurotrophin, nerve growth factor (NGF), is a peripheral pain mediator, particularly in inflammatory pain states. NGF is upregulated in a wide variety of inflammatory conditions, and NGF-neutralizing molecules are effective analgesic agents in many models of persistent pain. Such molecules are now being evaluated in clinical trials. NGF regulates the expression of a second neurotrophin, brain-derived neurotrophic factor (BDNF), in nociceptors. BDNF is released when nociceptors are activated, and it acts as a central modulator of pain. The chapter reviews the evidence for these roles (and briefly the effects of other neurotrophins), the range of conditions under which they act, and their mechanism of action.

BDNF in sensory neurons and chronic pain

Neurotrophic factors, which support neuronal survival and growth during development of the nervous system, have been shown to play significant roles in the transmission of physiologic and pathologic pain. Brain-derived neurotrophic factor (BDNF), synthesized in the primary sensory neurons, is anterogradely transported to the central terminals of the primary afferents in the spinal dorsal horn, where it is involved in the modulation of painful stimuli. In models of inflammatory and neuropathic pain, BDNF synthesis is greatly increased in different populations of dorsal root ganglion (DRG) neurons. Furthermore, it is now known that the activation of mitogen-activated protein kinases occurs in these sensory neurons and contributes to persistent inflammatory and neuropathic pain by regulating BDNF expression. The recent discovery that BDNF upregulation in the DRG and spinal cord contributes to chronic pain hypersensitivity indicates that blocking BDNF in sensory neurons could provide a fruitful strategy for the development of novel analgesics.

Pathophysiology of disk-related low back pain and sciatica. II. Evidence supporting treatment with TNF-alpha antagonists

Strong evidence suggests that TNF-alpha may be among the chemical factors involved in disk-related sciatica. TNF-alpha is involved in the genesis of nerve pain in animal models and may promote pain-signal production from nerve roots previously subjected to mechanical deformation. In animal experiments, TNF-alpha has been identified in nucleus pulposus and Schwann cells. Local production of endogenous TNF-alpha may occur early in the pathogenic process. Exposure to exogenous TNF-alpha induces electrophysiological, histological, and behavioral changes similar to those seen after exposure to nucleus pulposus, and these changes are more severe when mechanical compression is applied concomitantly. TNF-alpha antagonists diminish or abolish abnormalities in animal models. Other cytokines may be involved also, as suggested by the potent inhibitory effects of compounds such as doxycycline. Two open-label studies in humans suggest dramatic efficacy of TNF-alpha antagonists in alleviating disk-related sciatica. In contrast, the results of the only controlled study available to date do not support a therapeutic effect of TNF-alpha antagonists. Thus, whether TNF-alpha antagonist therapy is warranted in patients with disk-related sciatica remains an open question, and further randomized controlled studies are needed.

Nerve growth factor content in dorsal root ganglion as related to changes in pain behavior in a rat model of experimental lumbar disc herniation

STUDY DESIGN

The time courses of nerve growth factor content and pain-related behavior were examined using experimental disc herniation models.

OBJECTIVES

To investigate a relationship between nerve growth factor level and pain behavior.

SUMMARY OF BACKGROUND DATA

An induction of nerve growth factor in the periphery is regarded as a major contributor of inflammatory hyperalgesia and neuropathic pain. However, it has not been clarified quantitatively whether disc herniation induces changes in nerve growth factor levels in the dorsal root ganglion in relation to pain-related behavior.

METHODS

A total of 140 rats were used in this study. The animals had their left L4 nerve roots and associated dorsal root ganglion exposed and were equally divided into 4 groups: L4-L5 disc puncture, displacement of L4 nerve roots/dorsal root ganglion, the combination of disc puncture and displacement, and sham exposure. The content of nerve growth factor in the affected dorsal root ganglion was assessed by enzyme-linked immunosorbent assay as well as pain behavior during a postoperative 21-day period.

RESULTS

Disc puncture resulted in nerve growth factor induction at postoperative day 3, but not apparent behavioral changes. Mechanical displacement induced nerve growth factor at postoperative day 1 and mechanical allodynia at postoperative day 3, respectively (P < 0.05). In the combination model, there were more pronounced changes in nerve growth factor induction and both mechanical and thermal threshold during 7 days after surgery (P < 0.05).

CONCLUSIONS

These data suggest the possibilities that elevated nerve growth factor level is partly involved in pain behavior and further the combined model mimicking the clinical situation, which causes the marked neuronal responses, is helpful to advance the understanding of the mechanisms underlying sciatica due to lumbar disc herniation.

Evidence for brain-derived neurotrophic factor-like neuropeptide in brain of the silk moth Bombyx mori during postembryonic periods

Brain-derived neurotrophic factor-like neuropeptide is produced in the brain of the silk moth, Bombyx mori. Immunocytochemical studies of brain and retrocerebral complex of larvae, prepupae, pupae and adults showed that four pairs of median neurosecretory cells and six pairs of lateral neurosecretory cells which had different immunoreactivities to BDNF peptide. Day-1 adult brains showed no evidence of neurons stained by anti-BDNF antibodies. Those reactivities, which were much stronger in median cells than in lateral cells, were the weakest in an earliest larval stage and a latest pupal stage but the strongest in late larval stage. Median neurosecretory cells projected their axons into the contralateral corpora allata by decussation in the median region, nerve corpora cardiaca (NCC) I, and nerve corpora allata (NCA) I, whereas lateral neurosecretory cells extended their axons to the ipsilateral corpora allata via NCC II and NCA I.