Synapse involvement of the dorsal horn in experimental lumbar nerve root compression: a light and electron microscopic study

The role of spinal thrombin through protease-activated receptor 1 in hyperalgesia after neural injury

OBJECTIVE Painful neuropathic injuries induce blood-spinal cord barrier (BSCB) breakdown, allowing pro-inflammatory serum molecules to cross the BSCB, which contributes to nociception. The goal of these studies was to determine whether the blood-borne serine protease thrombin also crosses a permeable BSCB, contributing to nociception through its activation of protease-activated receptor-1 (PAR1). METHODS A 15-minute C-7 nerve root compression, which induces BSCB breakdown and painful behaviors by Day 1, was administered in the rat (n = 10); sham operation (n = 11) and a 3-minute compression (n = 10) that does not induce sensitivity were administered as controls. At Day 1 after root compression, spinal cord tissue was co-immunolabeled for fibrin/fibrinogen, the enzymatic product of thrombin, and IgG, a serum protein, to determine whether thrombin acts in areas of BSCB breakdown. To determine whether spinal thrombin and PAR1 contribute to hyperalgesia after compression, the thrombin inhibitor hirudin and the PAR1 antagonist SCH79797, were separately administered intrathecally before compression injuries (n = 5-7 per group). Rat thrombin was also administered intrathecally with and without SCH79797 (n = 6 per group) to determine whether spinal thrombin induces hypersensitivity in naïve rats through PAR1. RESULTS Spinal fibrin(ogen) was elevated at Day 1 after root compression in regions localized to BSCB breakdown and decreased in those regions by Day 7. Blocking either spinal thrombin or PAR1 completely prevented compression-induced hyperalgesia for 7 days. Intrathecal thrombin induced transient pain that was prevented by blocking spinal PAR1 before its injection. CONCLUSIONS The findings of this study suggest a potent role for spinal thrombin and its activation of PAR1 in pain onset following neuropathic injury.

Changes in the Expressions of Iba1 and Calcitonin Gene-Related Peptide in Adjacent Lumbar Spinal Segments after Lumbar Disc Herniation in a Rat Model

Lumbar disc herniation is commonly encountered in clinical practice and can induce sciatica due to mechanical and/or chemical irritation and the release of proinflammatory cytokines. However, symptoms are not confined to the affected spinal cord segment. The purpose of this study was to determine whether multisegmental molecular changes exist between adjacent lumbar spinal segments using a rat model of lumbar disc herniation. Twenty-nine male Sprague-Dawley rats were randomly assigned to either a sham-operated group (n=10) or a nucleus pulposus (NP)-exposed group (n=19). Rats in the NP-exposed group were further subdivided into a significant pain subgroup (n=12) and a no significant pain subgroup (n=7) using mechanical pain thresholds determined von Frey filaments. Immunohistochemical stainings of microglia (ionized calcium-binding adapter molecule 1; Iba1), astrocytes (glial fibrillary acidic protein; GFAP), calcitonin gene-related peptide (CGRP), and transient receptor potential vanilloid 1 (TRPV1) was performed in spinal dorsal horns and dorsal root ganglions (DRGs) at 10 days after surgery. It was found immunoreactivity for Iba1-positive microglia was higher in the L5 (P=0.004) dorsal horn and in the ipsilateral L4 (P=0.009), L6 (P=0.002), and S1 (P=0.002) dorsal horns in the NP-exposed group than in the sham-operated group. The expression of CGRP was also significantly higher in ipsilateral L3, L4, L6, and S1 segments and in L5 DRGs at 10 days after surgery in the NP-exposed group than in the sham-operated group (P<0.001). Our results indicate that lumbar disc herniation upregulates microglial activity and CGRP expression in many adjacent and ipsilateral lumbar spinal segments.

Thoracic Radiculopathy Resulting From Retrograde Neuronal Degeneration

We report a case of thoracic radiculopathy caused by retrograde degeneration from an intercostal nerve mass. A 74-year-old woman presented with thoracic radicular pain in the T4 dermatome. Needle electromyography revealed abnormal spontaneous activity in the left paraspinal muscle. Magnetic resonance imaging of the thoracic spine showed no signs of a herniated thoracic disk or root compression but revealed a mass along the intercostal space. The pathologic findings included perineural infiltration. A mass located along the intercostal space approximately 1.8 cm from the dorsal root ganglion may cause thoracic radiculopathy via retrograde degeneration.

Diffusion-Weighted Imaging for Pretreatment Evaluation and Prediction of Treatment Effect in Patients Undergoing CT-Guided Injection for Lumbar Disc Herniation

OBJECTIVE

To determine whether a change in apparent diffusion coefficient (ADC) value could predict early response to CT-guided Oxygen-Ozone (O2-O3) injection therapy in patients with unilateral mono-radiculopathy due to lumbar disc herniation.

MATERIALS AND METHODS

A total of 52 patients with unilateral mono-radiculopathy received a single intradiscal (3 mL) and periganglionic (5 mL) injection of an O2-O3 mixture. An ADC index of the involved side to the intact side was calculated using the following formula: pre-treatment ADC index = ([ADC involved side - ADC intact side] / ADC intact side) × 100. We analyzed the relationship between the pre-treatment Oswestry Disability Index (ODI) and the ADC index. In addition, the correlation between ODI recovery ratio and ADC index was investigated. The sensitivity and specificity of the ADC index for predicting response in O2-O3 therapy was determined.

RESULTS

Oswestry Disability Index and the ADC index was not significantly correlated (r = -0.125, p = 0.093). The ADC index and ODI recovery ratio was significantly correlated (r = 0.819, p < 0.001). When using 7.10 as the cut-off value, the ADC index obtained a sensitivity of 86.3% and a specificity of 82.9% for predicting successful response to therapy around the first month of follow-up.

CONCLUSION

This preliminary study demonstrates that the patients with decreased ADC index tend to show poor improvement of clinical symptoms. The ADC index may be a useful indicator to predict early response to CT-guided O2-O3 injection therapy in patients with unilateral mono-radiculopathy due to lumbar disc herniation.

The relationship between the duration of acute cauda equina compression and functional outcomes in a rat model

STUDY DESIGN

Immunohistochemical and behavioral study using a rat model of acute cauda equina syndrome (CES).

OBJECTIVE

To determine the effect of duration of extradural cauda equina compression (CEC) on bladder, sensory, and motor functions.

SUMMARY OF BACKGROUND DATA

Cauda equina syndrome is a devastating injury treated with surgical decompression. Controversy exists regarding the optimal timing of surgery. Animal models of CES have focused on motor recovery but have not evaluated pain behavior or bladder function.

METHODS

A 4-mm balloon-tipped Fogarty catheter was inserted between the fifth and sixth lumbar lamina into the dorsal epidural space and inflated to compress the nerve roots at the L5 level. Maximal inflation was maintained at a constant balloon pressure of 304 Kpa for 1 or 4 hours. The catheter was inserted but not inflated in sham animals. During a 4-week period, pain behavior, bladder function, and locomotor function were assessed. Postmortem bladders and the lesion site were collected for analysis.

RESULTS

Mechanical allodynia was 2-fold greater in 1-hour CEC rats than 4-hour CEC (P=0.002) and sham-operated (P=0.001) rats at 4 weeks after injury. Hind limb locomotor function was not different between groups at 4 weeks after injury. Both the 1-hour and 4-hour CEC group rats retained greater volumes of urine than the sham-operated rats throughout the 4-week period (P<0.05). At 4 weeks, bladder weight and volume were 2-fold greater in the 4-hour CEC group than in the 1-hour CEC group (P=0.006 and P=0.01, respectively). Histology of the bladder wall revealed an overall thinning after 4-hour CEC. Histology of the lesion site revealed a greater overall severity of injury after 4-hour CEC than after 1-hour CEC (P=0.04) and sham operation (P=0.002).

CONCLUSION

Our data suggest that recovery of motor function is less affected by the timing of decompression compared with bladder function and pain behavior. Early decompression preserved bladder function but was associated with allodynia.

LEVEL OF EVIDENCE

N/A.

Riluzole effects on behavioral sensitivity and the development of axonal damage and spinal modifications that occur after painful nerve root compression

Object

Cervical radiculopathy is often attributed to cervical nerve root injury, which induces extensive degeneration and reduced axonal flow in primary afferents. Riluzole inhibits neuro-excitotoxicity in animal models of neural injury. The authors undertook this study to evaluate the antinociceptive and neuroprotective properties of riluzole in a rat model of painful nerve root compression.

Methods

A single dose of riluzole (3 mg/kg) was administered intraperitoneally at Day 1 after a painful nerve root injury. Mechanical allodynia and thermal hyperalgesia were evaluated for 7 days after injury. At Day 7, the spinal cord at the C-7 level and the adjacent nerve roots were harvested from a subgroup of rats for immunohistochemical evaluation. Nerve roots were labeled for NF200, CGRP, and IB4 to assess the morphology of myelinated, peptidergic, and nonpeptidergic axons, respectively. Spinal cord sections were labeled for the neuropeptide CGRP and the glutamate transporter GLT-1 to evaluate their expression in the dorsal horn. In a separate group of rats, electrophysiological recordings were made in the dorsal horn. Evoked action potentials were identified by recording extracellular potentials while applying mechanical stimuli to the forepaw.

Results

Even though riluzole was administered after the onset of behavioral sensitivity at Day 1, its administration resulted in immediate resolution of mechanical allodynia and thermal hyperalgesia (p < 0.045), and these effects were maintained for the study duration. At Day 7, axons labeled for NF200, CGRP, and IB4 in the compressed roots of animals that received riluzole treatment exhibited fewer axonal swellings than those from untreated animals. Riluzole also mitigated changes in the spinal distribution of CGRP and GLT-1 expression that is induced by a painful root compression, returning the spinal expression of both to sham levels. Riluzole also reduced neuronal excitability in the dorsal horn that normally develops by Day 7. The frequency of neuronal firing significantly increased (p < 0.045) after painful root compression, but riluzole treatment maintained neuronal firing at sham levels.

Conclusions

These findings suggest that early administration of riluzole is sufficient to mitigate nerve root–mediated pain by preventing development of neuronal dysfunction in the nerve root and the spinal cord.

Efficacy of diffusion-weighted magnetic resonance imaging in diagnosing spinal root disorders in lumbar disc herniation

STUDY DESIGN

Prospective study based on magnetic resonance imaging for lumbar disc herniation.

OBJECTIVE

In this study, we captured diffusion-weighted imaging (DWI) of dorsal root ganglion (DRG) of the affected nerve root in lumbar disc herniation and examined the relationship between apparent diffusion coefficient (ADC) and clinical symptoms to evaluate the efficacy of DWI in the diagnosis of lumbar spinal disorders.

SUMMARY OF BACKGROUND DATA

DWI captures diffusion of water molecules in intracellular or extracellular fluid, allowing visualization of edematous changes, and is therefore used in diagnosis of hyper-acute cerebral infarction. In addition, it is possible to quantify the degree of diffusion using ADC calculated from the DWI data. Meanwhile in lumbar disc herniation, edematous changes occur in DRG of affected nerve root. If DWI enables visualization of these edematous changes, it will be possible to diagnose objectively the affected level.

METHODS

The subjects were 30 patients who underwent surgery of unilateral radiculopathy and a single level lumbar disc herniation. We analyzed the relationship between morbidity duration, visual analogue scale (VAS) score of leg symptoms, and ADC. In addition, we investigated any correlation between VAS recovery ratio (i.e., VAS preoperative - VAS postoperative)/VAS preoperative × 100) with ADC.

RESULTS

When compared with the contralateral side, ADC of the affected DRG was observed to increase in 18 and decrease in 12 subjects, and thus no definite trend was observed. The relationship between morbidity duration, VAS score, and ADC had no observed correlation. A positive correlation between ADC and VAS recovery ratio was statistically observed (P < 0.01, leg pain: r = 0.707, leg numbness: r = 0.738).

CONCLUSION

This study showed that patients with decreased ADC tended to show poor improvement of leg symptoms, which may suggest the possibility that ADC of DRG is related to neuronal plasticity.

LEVEL OF EVIDENCE

2.

Experimental syringohydromyelia induced by adhesive arachnoiditis in the rabbit: changes in the blood-spinal cord barrier, neuroinflammatory foci, and syrinx formation

There are many histological examinations of syringohydromyelia in the literature. However, there has been very little experimental work on blood permeability in the spinal cord vessels and ultrastructural changes. We prepared an animal model of spinal adhesive arachnoiditis by injecting kaolin into the subarachnoid space at the eighth thoracic vertebra of rabbits. The animals were evaluated 4 months later. Of the 30 rabbits given kaolin injection into the cerebrospinal fluid, 23 showed complete circumferential obstruction. In the 7 animals with partial obstruction of the subarachnoid space, intramedullary changes were not observed. However, among the 23 animals showing complete obstruction of the subarachnoid space, dilatation of the central canal (hydromyelia) occurred in 21, and intramedullary syrinx (syringomyelia) was observed in 11. In animals with complete obstruction, fluorescence microscopy revealed intramedullary edema around the central canal, extending to the posterior columns. Electron microscopy of hydromyelia revealed a marked reduction of villi on the ependymal cells, separation of the ependymal cells, and cavitation of the subependymal layer. The dilated perivascular spaces indicate alterations of fluid exchange between the subarachnoid and extracellular spaces. Syringomyelia revealed that nerve fibers and nerve cells were exposed on the surface of the syrinx, and necrotic tissue was removed by macrophages to leave a syrinx. Both pathologies differ in their mechanism of development: hydromyelia is attributed to disturbed reflux of cerebrospinal fluid, while tissue necrosis due to disturbed intramedullary blood flow is considered to be involved in formation of the syrinx in syringomyelia.

Development of a duration threshold for modulating evoked neuronal responses after nerve root compression injury

Cervical nerve roots are susceptible to compression injuries of various durations. The duration of an applied compression has been shown to contribute to both the onset of persistent pain and also the degree of spinal cellular and molecular responses related to nociception. This study investigated the relationship between peripherally-evoked activity in spinal cord neurons during a root compression and the resulting development of axonal damage. Electrically-evoked spikes were measured in the spinal cord as a function of time during and after (post-compression) a 15 minute compression of the C7 nerve root. Compression to the root significantly (p=0.035) reduced the number of spikes that were evoked over time relative to sham. The critical time for compression to maximally reduce evoked spikes was 6.6±3.0 minutes. A second study measured the post- compression evoked neuronal activity following compression applied for a shorter, sub-threshold time (three minutes). Ten minutes after compression was removed, the discharge rate remained significantly (p=0.018) less than baseline by 58±25% relative to sham after the 15 minute compression, but returned to within 3±33% of baseline after the three minute compression. Axonal damage was evident in the nerve root at day seven after nerve root compression only after a 15 minute compression. These studies demonstrate that even a transient mechanical insult to the nerve root is sufficient to induce sustained neuronal dysfunction and axonal pathology associated with pain, and results provide support that such minor neural tissue traumas can actually induce long-lasting functional deficits.

Pathomechanisms of sciatica in lumbar disc herniation: effect of periradicular adhesive tissue on electrophysiological values by an intraoperative straight leg raising test

STUDY DESIGN

This study is aimed to investigate the changes of nerve root functions during the straight leg raising (SLR) test in vivo.

OBJECTIVE

To investigate the relationship between nerve root movement and the electrophysiological values during an intraoperative SLR test.

SUMMARY OF BACKGROUND DATA

The SLR test is one of the most significant signs for making a clinical diagnosis of lumbar disc herniation. A recent study showed that intraradicular blood flow apparently decreased during the SLR test in patients with disc herniation.

METHODS

The study included 32 patients who underwent microdiscectomy. During the surgery, the nerve root motion affected by the hernia was observed during the SLR test. The patients' legs were allowed to hang down to the angle at which sciatica had occurred and the change of nerve root action potentials was measured. After removal of the hernia, a similar procedure was repeated. The periradicular specimens collected during surgery were examined by light and electron microscope.

RESULTS

In all patients intraoperative microscopy revealed that the hernia was adherent to the dura mater of the nerve roots. During the SLR test, the limitation of nerve root movement occurred by periradicular adhesive tissue and amplitude of action potential showed a sharp decrease at the angle that produced sciatica. After removal of the hernia, all the patients showed smooth gliding of the nerve roots during the test, and there was no marked decrease of amplitude. Our data suggest that temporary ischemic changes in the nerve root cause transient conduction disturbances. Pathologic examination showed that the periradicular tissue consisted of the granulation with vascularization and many inflammatory cell infiltrations.

CONCLUSION

The presence of periradicular fibrosis will compound the nerve root pain by fixing the nerve in one position, thereby increasing the susceptibility of the nerve root to tension or compression.

Changes in blood flow, oxygen tension, action potentials, and vascular permeability induced by arterial ischemia or venous congestion on the lumbar dorsal root ganglia in dogs

It is generally believed that radiculopathy associated with the degenerative conditions of the spine may result from both mechanical compression and circulatory disturbance. However, the basic pathophysiology of circulatory disturbance induced by ischemia and congestion is not fully understood. This study investigated the effect of ischemia and congestion on the dorsal root ganglion (DRG) using an in vivo model. The sixth and seventh lumbar laminae were removed and the seventh lumbar DRG was exposed using adult dogs. The aorta was clamped as an ischemic model in the DRG, and the inferior vena cava was clamped as a congestion model at the sixth costal level for 30 min using forceps transpleurally. Measurements of blood flow, partial oxygen pressure, and action potentials in the DRG were recorded over a period of 1 h after clamp release. Finally, we examined the status of intraganglionic blood permeability under a fluorescence microscope following injection of Evans blue albumin into the cephalic vein to determine the type of circulatory disturbance occurring in the DRG. Immediately after inferior vena cava clamping, the central venous pressure increased approximately four times and marked extravasation of protein tracers was induced in the lumbar DRG. Blood flow, partial oxygen pressures, and action potentials within the DRG were more severely affected by the aorta clamping; however, this ischemic model did not reveal any permeability changes in the DRG. The permeability change in the DRG was more easily increased via venous congestion than by arterial ischemia. The intraganglionic venous flow was stopped with compression at much lower pressures than that needed to impact arterial flow. From a clinical perspective, intraganglionic edema formation, rather than arterial ischemia, may be an earlier phenomenon inducing DRG dysfunction.

Intramuscular oxygen-ozone therapy in the treatment of acute back pain with lumbar disc herniation: a multicenter, randomized, double-blind, clinical trial of active and simulated lumbar paravertebral injection

STUDY DESIGN

Multicenter randomized, double-blind, simulated therapy-controlled trial in a cohort of patients with acute low back pain (LBP) due to lumbar disc herniation (LDH).

OBJECTIVE

To assess the benefit of intramuscular-paravertebral injections of an oxygen-ozone (O2O3) mixture.

SUMMARY OF BACKGROUND DATA

Recent findings have shown that O2O3 therapy can be used to treat LDH that fails to respond to conservative management. However, these findings are based on intradiscal/intraforaminal O2O3 injection, whereas intramuscular-paravertebral injection is the technique used most in clinical practice in Italy and other Western countries.

METHODS

Sixty patients suffering from acute LBP caused by LDH was randomized to an intramuscular O2O3 or control group. Patients were observed up to assess pain intensity, LBP-related disability, and drug intake (15 [V2] and 30 [V3] days after treatment started, and 2 weeks [V4], and 3 [V5] and 6 [V6] months after treatment ended).

RESULTS

A significant difference between the 2 groups in the percentage of cases who had become pain-free (61% vs. 33%, P < 0.05) was observed at V6. Patients who received O2O3 had a lower mean pain score than patients who received simulated therapy throughout the observation period. A significant improvement was observed in LBP-related disability in the study group patients when compared with the control group patients. Active O2O3 therapy was followed by a significantly lower number of days on nonsteroidal anti-inflammatory drugs at V2 and V3 and by a lower number of days at V4. No adverse events were reported.

CONCLUSION

Treatment of LBP and sciatica is a major concern. Although the natural history of acute LBP is often self-limiting, conservative therapies are not always effective; in such cases, O2O3 intramuscular lumbar paravertebral injections, which are minimally invasive, seem to safely and effectively relieve pain, as well as reduce both disability and the intake of analgesic drugs.

Effects of clotrimazole on experimental spinal cord ischemia/reperfusion injury in rats

OBJECTIVE

The effect of clotrimazole was examined using a spinal cord ischemia/reperfusion model.

METHODS

Twenty albino Wistar rats weighing 234 +/- 12.3 g were used in this study. Rats were anesthetized intraperitoneally with 50 mg/kg ketamine HCl. All animals underwent laparotomy under aseptic conditions. Abdominal aortas of the animals in all but the sham group were exposed. After opening the retroperitoneum, the infrarenal abdominal aorta was clipped for 45 minutes to produce ischemia/reperfusion injury. Polyethylene glycol (PEG, 1 mL) was administrated to the vehicle group. PEG (1 mL) and clotrimazole (30 mg/kg) were administered intraperitoneally in the clotrimazole group. Total laminectomy of T8-T12 was performed on all rats under a microscope. Spinal cords were excised for a length of 2-cm rostrally and 1-cm caudally to the injury site and deep frozen at -76 degrees C for biochemical studies. The levels of malondialdehyde, glutathione-peroxidase, superoxide dismutase, and catalase were measured as an indicator of ischemia level. The most cranial part of the specimens was evaluated morphologically.

RESULTS

Treatment with clotrimazole significantly decreased malondialdehyde, glutathione-peroxidase, superoxide dismutase, and catalase levels in comparison with other groups (P = 0.008). Morphologic evaluation revealed that clotrimazole protected the axons and their myelin sheaths from ischemic damage.

CONCLUSION

This study showed the neuroprotective effects of clotrimazole on spinal cord ischemia/reperfusion injury.