Search

Long-term administration of D-galactose induces oxidative stress and accelerates normal age-related changes. Hence, the D-galactose-treated rodent model has been widely used for aging research. In this study, we examined the immunological characteristics, especially CD4+ T-cell subset composition, of D-galactose-induced aging model mice to evaluate the model’s utility in immunosenescence studies. The spleens of aging model mice subjected to repeated subcutaneous injections of D-galactose exhibited significant increases in T cells with the memory phenotype (CD62Llow CD44high) and individual T-cell subsets (Th1, Th2, Th17 and Treg). Furthermore, cells with the phenotype of T follicular helper (Tfh) cells were spontaneously increased. The features of T-cell subset composition in D-galactose-treated mice were in close agreement with those observed in normal aged mice and appeared to mimic the currently known normal aging processes associated with T-cell homeostasis. Our results suggest that D-galactose-induced aging models would be useful for immunosenescence studies focusing on T-cell homeostasis and give valuable insight into age-related immune system dysregulation.

Cauda equina compression (CEC) is a major cause of neurogenic claudication and progresses to neuropathic pain (NP). A lipid mediator, lysophosphatidic acid (LPA), is known to induce NP via the LPA1 receptor. To know a possible mechanism of LPA production in neurogenic claudication, we determined the levels of LPA, lysophosphatidylcholine (LPC) and LPA-producing enzyme autotaxin (ATX), in the cerebrospinal fluid (CSF) and spinal cord (SC) using a CEC as a possible model of neurogenic claudication. Using silicon blocks within the lumbar epidural space, we developed a CEC model in rats with motor dysfunction. LPC and LPA levels in the CSF were significantly increased from day 1. Importantly, specific LPA species (16:0, 18:2, 20:4) were upregulated, which have been shown to produce by ATX detected in the CSF, without changes on its level. In SC, the LPC and LPA levels did not change, but mass spectrometry imaging analysis revealed that LPC was present in a region where the silicon blocks were inserted. These results propose a model for LPA production in SC and CSF upon neurogenic claudication that LPC produced locally by tissue damages is converted to LPA by ATX, which then leak out into the CSF.

Psychological and social factors are involved in the disability and chronicity of pain. Our study aim was to investigate whether social defeat stress (SDS) as a psychophysical stress affected mechanical withdrawal thresholds in the lumbar disk herniation (LDH) rat model. Changes in microglia and astrocytes, which play important roles in neuropathic pain states, were also investigated. For the LDH model, nucleus pulposus (NP) was applied to the L5 dorsal root ganglion (DRG) in adult female Sprague–Dawley rats. SDS was performed 15 min daily for 8 days. Mechanical withdrawal thresholds were measured, and immunoreactive cells of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (Iba-1), which were used as markers of microglia, satellite glial cells, and astrocytes, were assessed in the DRG, spinal cord (SC), and ventrolateral periaqueductal gray matter (VLPAG). Mechanical withdrawal thresholds decreased in the NP group for 21 days and for 35 days in the NP + SDS group. Expression of GFAP and Iba-1 in the DRG and SC increased up to day 21 in the NP and NP + SDS groups. In the sham + SDS and NP + SDS groups, expression of GFAP in the VLPAG decreased until day 35. SDS prolongs mechanical allodynia induced by NP. Changes of GFAP expression in the VLPAG were associated with mechanical allodynia of the NP + SDS group during the late phase. These results suggest that psychological chronic stress might delay recovery from mechanical allodynia induced by the LDH model.

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

Various drugs are used to treat patients with neuropathic pain; however, optimal treatment using acetaminophen (A) and/or tramadol (T) remains unclear. The evidence supporting the drug choice and the timing of administration is insufficient. Therefore, the objective of the present study was to investigate the effect of T and/or A on pain-related behavior in a nucleus pulposus (NP) rat model. Sprague–Dawley rats (n = 180) were divided into NP-A (52 mg/kg), NP-T (6 mg/kg), NP-AT (combined A and T), NP-S (saline), and sham groups (n = 36 per group). The rats received 0.2 mL of treatment solution orally once daily for 7 days after application of NP on the left L5 dorsal root ganglion (DRG). Behavioral testing and immunohistochemistry analysis for some markers’ expressions in DRGs and the spinal cord were performed. Pain thresholds in the NP-AT group did not significantly differ from the sham at all time points, while those were significantly lower in the NP-A and in the NP-T groups at D7 and/or D14 (p

Controlled, interventional, animal study.To investigate the spatial and temporal changes of μ-opioid receptor (MOR) expression in a rat lumbar disc herniation (LDH) model.MORs widely express in the peripheral and central nervous systems, and opioid drugs produce an analgesic effect through their activation. However, the efficacy of opioid drugs is sometimes inadequate in several pathological conditions of pain. MORs in the brain as well as the spinal cord (SC) and dorsal root ganglion (DRG) are thought to be associated with pain-related behavior, but the underlying mechanisms are not completely understood.In all, 91 adult female Sprague-Dawley rats were used. Autologous nucleus pulposus (NP) was applied onto the left L5 DRG in the NP group rats. Rats were divided into two surgical groups, the NP and the sham group. The von Frey test of left hind paw was performed before surgery, and 2, 7, 14, 21 and 28 days after surgery. Immunohistochemistry and immunoblotting in the DRG, SC, Caudate putamen, nucleus accumbens (NAc) and periaqueductal grey matter were performed before surgery, and 2, 7, 14, 21 and 28 days after surgery.The thresholds in the NP group were significantly lower than those in the sham group from day 2 onwards. At days 7 and 14, MOR expression in the injured-side SC and DRG were significantly lower than those in the sham group. At day 21, MOR in the NAc was significantly decreased compared to that in the sham group.Changes of MOR expression in the NAc, SC and DRG were associated with pain-related behavior. This result might show the underling pathogenesis of the resistance to MOR agonists in the patient with LDH.N/A.

Neuropathic pain, commonly related to intervertebral disk (IVD) degeneration, responds poorly to standard pain treatments. Serotonin–noradrenaline reuptake inhibitors (SNRIs) have been reported to reduce neuropathic pain; however their effect on radiculopathy induced by lumbar disk herniation remains unclear. The aim of this study was to investigate the effect of SNRI duloxetine in rat model of IVD-related neuropathic pain. Effects of SNRI duloxetine were tested in Sprague–Dawley rats (n = 135). Neuropathic pain was induced by applying autologous nucleus pulposus (NP) on the left L5 dorsal root ganglion (DRG). Duloxetine in concentrations 0.4 mg/kg (low dose) and 1.2 mg/kg (high dose) or saline were administered orally for 10 days. Von Frey test was carried out on post-operative days 2, 7, 14, 21, and 28 to test pain sensitivity. Immunohistochemistry of L5 DRG and L5 segment of spinal cord (SC) was performed on days 7 and 21 to examine expressions of tumor necrosis factor alpha (TNF), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and ionized calcium-binding adapter molecule 1 (Iba1). On days 14, 21, and 28, expressions of TNF in DRG as well as NGF and BDNF in SC were tested by immunoblotting. Sham-operated rats and naive rats were used as controls. Duloxetine in both concentrations significantly improved pain threshold from postoperative day 21 onward, compared to the NP + saline group (p

A controlled, interventional animal study.The aim of this study was to evaluate the effect of diabetes mellitus (DM) on radiculopathy due to lumbar disc herniation (LDH), by investigating pain-related behavior and the expression of tumor necrosis factor-alpha (TNF-α) and growth-associated protein 43 (GAP43) in type 2 diabetic rats following application of nucleus pulposus (NP) to the dorsal root ganglion (DRG).Previous clinical studies suggested negative effects of DM on radiculopathy due to LDH, and that inflammation and nerve regeneration could interact with DM and radiculopathy.We applied autologous NP to the left L5 DRG of adult male Wistar rats and Goto-Kakizaki rats. Behavioral testing measured the mechanical withdrawal threshold of rats. We immunohistochemically evaluated the localization of ionized calcium-binding adapter molecule-1 (Iba-1), receptor of advanced glycation end products (RAGE), and TNF-α in DRGs. TNF-α and GAP43 expression levels in DRG were determined by quantitative real-time PCR and western blotting.The mechanical withdrawal threshold significantly declined in the non-DM NP group compared with the non-DM sham group for 28 days, whereas the decline in threshold extended to 35 days in the DM NP group compared with the DM sham group. RAGE and TNF-α expression in DRGs was colocalized in Iba-1 positive cells. The non-DM NP rats had higher TNF-α protein expression levels versus the non-DM sham rats on day 7, and the DM NP group had higher levels versus the DM sham group on days 7 and 14. The non-DM NP group had higher GAP43 mRNA expression than the non-DM sham group for 28 days, while the DM NP group had a higher level than the DM sham group for 35 days.DM prolongs the pain-related behavior caused by NP. The prolonged inflammation and nerve regeneration could elucidate the pathogenesis of continuous pain of radiculopathy initiated by LDH.N /A.

Isoflurane is a widely used anesthetic, but its effects with increase in inspired concentration on cardiovascular function have not yet been clarified in rodents. Additionally, there are only a few studies comparing isoflurane-induced cardiorespiratory effects between rat strains. Thus, we investigated the differences in cardiorespiratory responsiveness to increasing concentration of inspired isoflurane in SHR/Izm, WKY/Izm and Crl:CD (SD) rats, by increasing the setting values of vaporizer's dial indicator. The rats were anesthetized with 1.5% isoflurane, and electrocardiograms, blood pressure, and respiratory rate were recorded simultaneously. Thereafter, the inspired concentration was increased stepwise to 2%, 3%, 4%, and 5%, and cardiorespiratory parameters were obtained at each concentration. Under anesthesia at more than 4%, although prolongation of the RR and PR intervals was observed in all strains, shortening of the QTC interval was found only in SHR/Izm rats. From frequency domain analysis of heart rate variability, an increase in LF/HF ratio and a decrease of HF components were observed in SHR/Izm and WKY/Izm rats, respectively, with 5% isoflurane anesthesia. Blood pressure and heart rate were remarkably reduced in SHR/Izm rats at higher concentrations, whereas the reduction was smallest in WKY/Izm rats among the three strains examined. Respiratory rate was inspired concentration-dependently decreased in all strains. These results suggested that SHR/Izm rats are more sensitive to suppressive effects of isoflurane anesthesia on cardiovascular function among these rat strains.

A magnitude 9.0 great earthquake, the 2011 off the Pacific coast of Tohoku Earthquake, occurred on March 11, 2011, and subsequent Fukushima Daiichi Nuclear Power Station (Fukushima NPS) accidents stirred up natural radiation around the campus of Fukushima Medical University (FMU). FMU is located in Fukushima City, and is 57 km to the northwest of Fukushima NPS. Due to temporary failure of the steam boilers, the air conditioning system for the animal rooms, all autoclaves, and a cage washer could not be used at the Laboratory Animal Research Center (LARC) of FMU. The outside air temperature dropped to zero overnight, and the temperature inside the animal rooms fell to 10°C for several hours. We placed sterilized nesting materials inside all cages to encourage rodents to create nests. The main water supply was cut off for 8 days in all, while supply of steam and hot water remained unavailable for 12 days. It took 20 days to restore the air conditioning system to normal operation at the facility. We measured radiation levels in the animal rooms to confirm the safety of care staff and researchers. On April 21, May 9, and June 17, the average radiation levels at a central work table in the animal rooms with HEPA filters were 46.5, 44.4, and 43.4 cpm, respectively, which is equal to the background level of the equipment. We sincerely hope our experiences will be a useful reference regarding crisis management for many institutes having laboratory animals.

The P2X(3) receptor is a ligand-gated cation channel that is activated by extra cellular adenosine triphosphate (ATP) found in the dorsal root, trigeminal and nodose ganglia. It is one of the receptors transmitting nociceptive information of injuries and inflammation of the periphery by endogenous ATP released from damaged cells. The present study was performed in order to evaluate if there was an increased expression of P2X(3)-immunoreactivity in dorsal root ganglion (DRG) neurons after experimental disc herniation. There were four groups: exposure of the left L4 dorsal root ganglion and incision of the L4-L5 disc, exposure and slight displacement of the left L4 dorsal ganglion, sham exposure of the L4 dorsal root ganglion, and normal. Seven days after surgery, the DRG's were collected, sectioned and stained immunohistochemically for the P2X(3) receptor. The expression of P2X(3) increased significantly following incision of the L4-5 disc compared to the normal group. Sham surgery induced a minor, although statistically significant increase. Mechanical displacement did not induce any increased expression of the receptors. The study demonstrates that expression of the P2X(3)receptors in the DRG may be induced by local application of nucleus pulposus. This may increase our understanding of the pathophysiologic mechanisms related to disc herniation and sciatica.

Chronic pain has an impact on psychological and social factors. It is known that stress influences physiological and behavioral changes and affects several neurotransmitter and hormonal systems. It is also known that corticosterone is increased by stress. The role of chronic stress in sciatica in lumbar disc herniation (LDH) in rats has not been investigated. The aim of this study was to investigate the effect of the restraint stress (RS) on pain-related behavior induced by application of nucleus pulposus (NP) in rats.Adult female Sprague-Dawley rats were divided into six experimental groups (naive group; naive + RS; sham group; sham + RS; autologous nucleus pulposus [NP] applied on the left L5 nerve root [NP group]; and NP + RS group). Von Frey tests were used to test pain-related behavior. Concentrations of plasma corticosterone were measured to assess changes in levels of endogenous corticosterone caused by RS. Expression of ATF-3 in the left L5 DRG was examined by immunohistochemical analyses in each group.Mechanical withdrawal thresholds of the NP and NP + RS groups were significantly decreased after surgery compared with the naive group. Although the thresholds in the NP group recovered after 28 days, the thresholds in the NP + RS group were significantly decreased during the 42 days after surgery. RS increased the concentration of plasma corticosterone at 21 and 42 days after surgery. In the NP and the NP + RS groups, the expression of ATF-3 was significantly increased at 7 days after surgery. The expression of ATF-3 was sustained for 21 days by RS.Concentrations of plasma corticosterone were increased in three groups that underwent RS. The pain-related behavior persisted for the long term in the LDH model. The expression of ATF-3 in DRG neurons increased for 21 days by RS. These results suggest that RS plays a role in the chronicity of pain-related behavior in the LDH rats.

Study design Controlled, interventional, animal study. Objective To examine the involvement of high-mobility group box 1 (HMGB1) in the neuropathic pain state induced by the application of nucleus pulposus onto the dorsal root ganglion (DRG) and to investigate the effect of HMGB1 neutralization antibody in the pathogenesis. Summary of background data HMGB1 is a potent proinflammatory mediator when present extracellularly, and anti-HMGB1 neutralization antibody inhibits inflammation, cytokine expression, and macrophage activation. Methods Thirty-nine adult female Sprague-Dawley rats (200-300 g) were used. The left L5/6 facet joint was removed, and the L5 DRG was exposed. Nucleus pulposus harvested from the tail was applied to the left L5 DRG. Then, 400 μg of anti-HMGB1 neutralization antibody was administered intraperitoneally after surgery. Behavioral testing using von Frey hairs was performed to investigate the mechanical withdrawal threshold. Neuronal damage was investigated by counting the number of activating transcription factor 3 (ATF3) neurons. The expressions of tumor necrosis factor-α (TNF-α) and HMGB1 were measured by double-labeled immunohistochemistry and immunoblotting. Results Immunoblotting of harvested nucleus pulposus revealed HMGB1 in the nucleus pulposus. Double-labeled immunohistochemistry revealed that macrophages in the applied nucleus pulposus expressed HMGB1 and TNF-α. Administration of anti-HMGB1 neutralization antibody significantly reduced the TNF-α expression in the DRG and improved the pain-related behavior from day 2 to day 14. Conclusion HMGB1 appears to play an important role in the development of pain-related behavior induced by the application of nucleus pulposus onto the DRG. HMGB1 from applied nucleus pulposus and actively secreted from macrophages would act as a proinflammatory mediator together with proinflammatory cytokines. HMGB1 blocking therapy might become a new treatment method for neuropathic pain.

Study design The effects of exogenous 5-hydroxytryptamine (5-HT), tumor necrosis factor(TNF)-α, 5-HT + TNF in combination, and autologous nucleus pulposus (NP) at dorsal root ganglion (DRG) were examined using rat models. Objective To examine the interaction of 5-HT with TNF for pain-related behavior in a rat lumbar disc herniation (LDH) model. Summary of background data 5-HT and TNF have been shown to play roles in sciatica in lumbar disc herniation as chemical factors. Methods Adult female Sprague-Dawley rats were divided into six groups: 5-HT group, TNF group, 5-HT + TNF (combination) group, NP group, control group, and naive group. Von Frey tests were used for pain-related behavior testing. Expressions of activating transcription factor 3 and calcitonin gene-related peptide (CGRP) were evaluated immunohistochemically. Expressions of TNF, TNF receptor 1 (TNFR1), and 5-HT2A receptors in the left L5 DRG were examined using western blotting. Plasma levels of 5-hydroxyindole acetic acid, a metabolite of 5-HT, were measured. Results Mechanical withdrawal thresholds were significantly decreased in the 5-HT, TNF, combination, and NP groups compared with controls. Thresholds recovered after 14 days in the 5-HT and TNF groups, and after 28 days in the combination group. Exogenous 5-HT and TNF to the nerve root induced pain-related behavior and lasted for a shorter period compared with combination and NP groups. Activating transcription factor 3- and calcitonin gene-related peptide-immunoreactive DRG neurons were significantly increased only in the early phase in 5-HT, TNF, combination, and NP groups. TNF induced 5-HT2A receptor expressions in the DRG, while 5-HT induced TNF and TNF receptor 1 expressions. Conclusion The present findings suggest that both 5-HT and TNF induce pain-related behavior and interact with each other to prolong pain-related behavior in a rat LDH model.

Symptomatic induction of disc herniation involves both mechanical compression and chemical factors. Inhibitors of tumor necrosis factor-alpha (TNF-α) are known to reduce pain-related behavior in experimental models. Animals were divided into mechanical compression (MC) group; a stainless steel rod was inserted on the dorsal root ganglion, nucleus pulposus (NP) group: NP was harvested from the coccygeal vertebral disc, MC and NP group; rats were received stainless rod and NP, and sham group; rats were received neither rod nor NP. Rats in the MC group received a TNF-α antibody (10 mg/kg) (antibody group) or were not treatment (untreated group). The withdrawal thresholds of the MC, NP and MC+NP groups decreased significantly compared with the sham group. In the antibody group, the threshold was significantly higher than that of the untreated group. An anti-TNF-α antibody reduced allodynia caused by DRG compression.

STUDY DESIGN Controlled, interventional, animal study. OBJECTIVE To observe the reaction of glial cells and endoneurial macrophages in the dorsal root ganglion (DRG) after application of nucleus pulposus (NP) and investigate whether activated DRG glial cells play a role in the pathogenesis of neuropathic pain. SUMMARY OF BACKGROUND DATA Peripheral nerve injury activated DRG and spinal cord glial cells and several cytokines and neurotrophins released from these activated glial cells might induce pain hypersensitivity. METHODS Adult male Sprague-Dawley rats were used. NP harvested from the tail was applied to the left L5 DRG. Behavioral testing was performed to investigate the mechanical withdrawal threshold. The numbers of activated satellite glial cells and endoneurial macrophages were counted, and the expressions of tumor necrosis factor-alpha (TNF-alpha) and glial cell-line derived neurotrophic factor (GDNF) were examined by double-labeled immunohistochemistry and immunoblotting. RESULTS The mechanical withdrawal threshold was significantly decreased for 28 days and then gradually recovered (P < 0.05). Long-term activation of endoneurial macrophages and satellite glial cells in the DRG was observed, and the reactions of these cells correlated well with pain-related behavior. TNF-alpha was expressed in both endoneurial macrophages and activated satellite glial cells, and TNF-alpha expression was significantly increased in the early stage (P < 0.05). Activated satellite glial cells also expressed GDNF, and its expression was significantly increased and persisted for 28 days (P < 0.05). CONCLUSION Activation of DRG glial cells and endoneurial macrophages plays an important role in the pathogenesis of the neuropathic pain state. TNF-alpha actively released from activated glial cells and endoneurial macrophages in the DRG might initiate and maintain the neuropathic pain together with TNF-alpha derived from the applied NP. In the recovery phase, persistent expression of GDNF from activated satellite glial cells might play an important role to restore the function of damaged neurons and recover from neuropathic pain.

The role of 5-hydroxytryptamine (5-HT) in sciatica in lumbar disc herniation (LDH) in rats was investigated.We evaluated the effects of exogenous 5-HT applied on the nerve root on pain-related behavior, the release of endogenous 5-HT in plasma, and the expression of 5-HT2A receptors in dorsal root ganglion (DRG) in a rat LDH model.In previous studies, 5-HT2A receptor antagonists improved sciatica in patients with LDH and attenuated pain-related behavior induced by nucleus pulposus applied to the nerve root in rats.Adult female Sprague-Dawley rats were divided into four experimental groups [control group; low-dose (10 microg) 5-HT-group; high-dose (30 microg) 5-HT-group; and autologous nucleus pulposus (NP) and saline group] and each drug was applied to the L5 nerve root. Von Frey tests were used for pain-behavior testing. To assess levels of endogenous 5-HT released in capillaries surrounding inflamed nerve roots, we measured 5-hydroxyindole acetic acid (5-HIAA), a metabolite of 5-HT. Expression of 5-HT2A receptors in the left L5 DRG was examined by immunohistochemical and immunoblotting analyses in the control and NP groups.Mechanical withdrawal thresholds of the high-dose 5-HT and the NP groups were significantly decreased after surgery compared with the control group and recovered after 14 days in the high-dose 5-HT group. 5-HIAA in plasma was increased by nucleus pulposus applied on the nerve root for 7 days after surgery. The expression of 5-HT2A receptors was enhanced in a time-dependent manner by nucleus pulposus.Exogenous 5-HT to the nerve root induced pain-related behavior with short-lasting effects compared with the nucleus pulposus application. 5-HIAA content in plasma and expression of 5-HT2A receptors in DRG neurons increased early time points after the nucleus pulposus application. These results suggest that 5-HT plays a role in the early phase of the chemical pathogenesis of sciatica in LDH in rats.

Study design An analysis of pain behavior and neuronal apoptosis in the dorsal root ganglion (DRG) following crush injury to the L5 nerve root, with or without surgical sympathectomy. Objectives To determine whether sympathectomy prevents pain behavior and to compare pain behavior with expression of tumor necrosis factor (TNF)-alpha and apoptosis in the DRG. Summary of background data Sympathetic block is used to relieve symptoms in radiculopathy patients. One effect of the block is improvement of blood flow to the nerve. However, this beneficial effect continues longer than the expected duration of local anesthesia, suggesting an unknown neuroprotective effect involving interference with sympathetic activity. Methods Sprague-Dawley rats (n = 102) were used and divided into 4 experimental groups. In the crush group, animals received a crush injury to the L5 nerve root. In the sympathectomy group, animals received sympathectomy (Syx) on the left side. In the Syx + crush group, both sympathectomy and crush injury were performed. In the sham group, the surgical procedure was the same, but neither sympathectomy nor crush injury took place. Mechanical allodynia was determined in 4 groups. Expression of TNF-alpha was compared in rats with crush injury, with and without sympathectomy. Using immunostaining for caspase 3, NeuN, and GFAP, localization of apoptotic cells was observed. In addition, we compared the percentage of neurons undergoing apoptosis in the DRG. Results Sympathectomy prevented mechanical allodynia throughout the 14-day experimental period. TNF-alpha expression was increased in the DRG following crush-only injury, whereas it was decreased in animals undergoing sympathectomy after the crush injury. DRG apoptosis in the crush group was significantly higher than in the sympathectomy group at day 7 (P Conclusion Surgical sympathectomy reduced mechanical allodynia for 14 days after nerve root crush injury, and that DRG apoptosis was decreased in injured animals that underwent sympathectomy. Sympathetic block may not only cause an increase in nerve blood flow, but may also prevent the development of significant TNF-alpha elevation, DRG apoptosis, and neuropathic pain.

Study design The association between lumbar facet joint inflammation and radiculopathy was investigated using behavioral, histologic, and immunohistochemical testing in rats. Objectives To develop a rat model of lumbar facet joint inflammation and ascertain whether facet joint inflammation induces radiculopathy using this model. Summary of background data Both mechanical and chemical factors have been identified as important for inducing radiculopathy. In lumbar spondylosis, facet joint osteophytes may contribute to nerve root compression, which may induce radiculopathy. Furthermore, inflammation may occur in the facet joint, as in other synovial joints. Inflamed synovium may thus release inflammatory cytokines and induce nerve root injury with subsequent radiculopathy. Methods A piece of gelatin sponge containing complete adjuvant was inserted into the L5-L6 facet joint in rats (arthritis group). Saline was used in the control group. Mechanical allodynia was determined using the von Frey test. Inflammatory cells infiltrating the epidural space were counted, and changes in cartilage were assessed histologically. Tumor necrosis factor (TNF)-alpha-immunoreactive cells in the L5 dorsal root ganglion were counted. Results Mechanical allodynia was observed in the arthritis group from day 3, gradually recovering during the observation period. Significantly larger numbers of inflammatory cells had infiltrated the epidural space by days 3 and 7 in the arthritis group than in controls. Numbers of TNF-alpha-immunoreactive cells were significantly increased at days 1 and 3 in the arthritis group compared with controls. Predominantly small nociceptive neurons were stained. Conclusions When inflammation was induced in a facet joint, inflammatory reactions spread to nerve roots, and leg symptoms were induced by chemical factors. These results support the possibility that facet joint inflammation induces radiculopathy.

Study design Controlled, interventional, animal study. Objective To evaluate the effect of a 5-HT2A receptor antagonist on pain-related behavior, endogenous 5-hydroxytryptamine (5-HT) plasma levels, and expression of 5-HT2A receptors in dorsal root ganglia (DRGs) in a rat lumbar disc herniation model. Summary of background data Application of nucleus pulposus on the nerve root induces immediate peripheral 5-HT production and the expression of 5-HT2A receptors in the adjacent DRG. However, the efficacy of a 5-HT2A receptor antagonist for pain relief in this situation and the mechanism remain unknown. Methods Autologous nucleus pulposus was applied to the left L5 nerve root of 91 adult female Sprague-Dawley rats. The selective 5-HT2A receptor antagonist sarpogrelate hydrochloride (SPG; 1 mg/kg or 10 mg/kg) or vehicle was administered orally once a day from 1 to 21 days postoperatively. Von Frey tests were used to test pain behavior before and after surgery. To assess the effect of SPG on endogenous 5-HT release surrounding the inflamed nerve root, we measured levels of 5-hydroxyindole acetic acid, a 5-HT metabolite, in plasma. Expression of 5-HT2A receptors in the left L5 DRG was examined with immunoblotting. Results The higher dose (10 mg/kg) of SPG significantly improved the mechanical withdrawal thresholds from 5 to 21 days after surgery compared with vehicle treatment. 5-hydroxyindole acetic acid in plasma was not significantly different among any groups at any time points. Both doses of SPG inhibited the expression of 5-HT2A receptors after surgery compared with vehicle treatment. Conclusion A selective 5-HT2A receptor antagonist attenuated pain-related behavior and suppressed 5-HT2A receptor expression in the DRG, but did not affect peripheral 5-HT production. Selective 5-HT2A receptor antagonists may attenuate sciatica by blocking and downregulating 5-HT2A receptors in DRGs in lumbar disc herniation. Level of evidence NA.

Neurogenic intermittent claudication (NIC) can be caused by compression of the cauda equina by spinal stenosis and is a major clinical problem. A reduction of blood flow is an important mechanism for inducing NIC and may be caused by a vasoconstrictive effect mediated by the serotonin 5-HT2A receptor in chronic cauda equina compression lesions. This study assessed the effects of the 5-HT2A receptor antagonist on nerve vasculature in chronically compressed nerve roots. A plastic balloon was placed under the lamina of L7 and inflated to 10 mmHg and left for 1 week in several cauda equina compression models. All experimental animals received an acute administration of serotonin. One group received sarpogrelate hydrochloride (5-HT2A receptor antagonist: 5-HTRA) before administration of serotonin, and another group was administered 5-HTRA after administration of serotonin. Diameters and blood flow in the vasculature of S2 or S3 nerve roots were measured after injection of serotonin. In animals without compression of the cauda equina (sham), blood vessels contracted and the blood flow was reduced after administration of serotonin. In sham and compression animals receiving both serotonin and 5-HTRA, blood vessel diameter was not reduced and was significantly larger than that in the compression group receiving only serotonin (p

Low doses of methotrexate (MTX) are safe and effective for treating adult and juvenile rheumatoid arthritis. However, because this powerful anti-inflammatory drug might negatively influence the healing of wounds and fractures, MTX administration is often stopped during surgical procedures. The present study assesses the effects of low- and high-dose MTX on early inflammatory processes and bone healing in an experimental model of fracture. Thirty male Sprague-Dawley rats were assigned to low- and high-dose MTX and control groups. A femur was cut using a reciprocating saw and a 2-mm fracture gap was made using a fixator. One or four weeks thereafter, macrophages were immunostained and new bone formation was histomorphometrically measured. Significantly less new bone was formed in the high-dose MTX, than in the control group (p< 0.01), whereas bone formation did not significantly differ between the low-dose MTX and control groups. These results suggested that a low dose of MTX does not affect the early process of endochondral bone formation during fracture healing, whereas a high dose might delay the progress of new periosteal bone formation. Although more macrophages were found in the groups treated with MTX, their impact on surrounding inflammatory processes remains unclear.

TNFα is an inflammatory mediator related to neuropathic pain including sciatica. Much basic research suggests that anti-TNFα therapy may be useful for the treatment of sciatica. The purpose of this study was to clarify the effects of etanercept in a dorsal root ganglion (DRG) compression model.Adult male Sprague-Dawley rats (200-250 g, n = 60) were used. An L-shaped stainless rod was used to compress the left L5 DRG in the saline and etanercept groups. No rod was used in the sham group. In the etanercept group, 1 mg of etanercept was applied locally onto the DRG at the end of surgery. Saline was applied in the saline and sham groups. On day 3 and day 7 after surgery, the number of ED1-immunoreactive (IR) cells (macrophages) in the DRG was calculated by immunohistochemical methods (n = 6). In addition, double-immunofluorescence labeling for ED1 and TNFα was performed. Behavioral testing with von Frey filaments and a heat stimulator was performed (n = 12).ED1-IR cells in the DRG significantly increased in the control group compared with the sham group (p 0.05). Some ED1-IR cells were co-labeled for TNFα. In the etanercept group, decrease in mechanical threshold was significantly inhibited compared with the saline group (p 0.05). Thermal hyperalgesia was observed in the control group, but in neither the sham nor etanercept group (p 0.05).Etanercept attenuated the pain-related behavior induced by DRG compression. These findings suggest that mechanical effects on the DRG might be reduced by etanercept in addition to the effects on nucleus pulposus in lumbar disc herniation.

Study design Descriptive and mechanistic investigation of the anti-inflammatory and anticatabolic effect of resveratrol in intervertebral discs (IVDs) in vitro and of the analgetic effect in vivo. Objective To determine whether resveratrol may be useful in treating nucleus pulposus (NP)-mediated pain. Summary of background data Proinflammatory cytokines seem to be key mediators in the development of NP-mediated pain. Patients with discogenic or radiculopathic pain may substantially benefit from anti-inflammatory substances that could be used in a minimal-invasive treatment approach. Resveratrol, a polyphenolic phytoalexin found in red wine exhibits anti-inflammatory effects in various cell types and tissues, but no data exists so far with regards to the IVD in the context of low back and leg pain. Methods In part 1, the anti-inflammatory and anticatabolic effect of resveratrol was investigated in a cell culture model on interleukin 1β (IL-1β) prestimulated human IVD cells on the gene and protein expression level. In part 2, the molecular mechanisms underlying the effects observed upon resveratrol treatment were investigated (toll-like receptors, nuclear factor κB, sirtuin 1 (SIRT1), mitogen-activated protein (MAP) kinases p38/ERK/JNK). In part 3, the analgetic effects of resveratrol were investigated in vivo using a rodent model of radiculopathy and von Frey filament testing. All quantitative data were statistically evaluated either by Mann-Whitney U test or by one-way analysis of variance and Bonferroni post hoc testing (P Results In vitro, resveratrol exhibited an anti-inflammatory and anticatabolic effect on the messenger RNA and protein level for IL-6, IL-8, MMP1, MMP3 and MMP13. This effect does not seem to be mediated via the MAP kinase pathways (p38, ERK, JNK) or via the NF-κB/SIRT1 pathway, although toll-like receptor 2 was regulated to a minor extent. In vivo, resveratrol significantly reduced pain behavior triggered by application of NP tissue on the dorsal root ganglion for up to 14 days. Conclusion Resveratrol was able to reduce levels of proinflammatory cytokines in vitro and showed analgetic potential in vivo. A decrease in proinflammatory cytokines may possibly be the underlying mechanism of pain reduction observed in vivo. Resveratrol seems to have considerable potential for the treatment of NP-mediated pain and may thus be an alternative to other currently discussed (biological) treatment options.

Study design An experimental animal study. Objective We evaluated the efficacy of lactoferrin (LF) compared with diclofenac to reduce the pain, using a rat lumbar disc herniation model. Summary of background data LF is a multifunctional protein that is found in milk. Recent studies have reported that LF reduces nociception in various experimental models. Methods Rats were operated on the left L5 vertebral arch. The left L5 nerve root and dorsal root ganglion (DRG) were exposed by a L5 partial laminectomy. An L-shaped stainless steel rod was inserted from the laminectomy toward the intervertebral foramen to compress the nerve root. In addition, nucleus pulposus from coccygeal discs was applied on the nerve root. At 1 day before operation, all rats were tested regarding the withdrawal threshold of the left plantar surface using von Frey filaments to determine baseline values. Additional von Frey tests were performed on postoperative days 3, 7, 14, and 21. Thirty minutes before each test except for baseline, the rats received LF (100 mg/kg), diclofenac (10 mg/kg), or saline by intraperitoneal injection (n = 6). Results As compared with the control group, thresholds of rats in the diclofenac group were significantly higher on postoperative days 3 and 7. However, on postoperative days 14 and 21, there were no significant differences. Thresholds of rats in the LF group were significantly higher on all postoperative days compared with the control group. Conclusion Analgesic effect of diclofenac reduced with time. However, the effect of LF continued during the whole experimental period. LF might become useful as pain-killer.

STUDY DESIGN The effect of an EP1 receptor antagonist on pain-related behavior induced by nucleus pulposus (NP) applied to the dorsal root ganglion (DRG) in rats was investigated. OBJECTIVE We investigated pain-related behavior, the amount of prostaglandin E2 (PGE2), and neural damage to the DRG after application of NP to the DRG after administration of an EP1 receptor antagonist. SUMMARY OF BACKGROUND DATA PGE2 induces mechanical allodynia and hyperalgesia, which are mediated by PGE2 receptors. EP1 is one of the PGE2 receptor subtypes. An EP1 antagonist reduces hyperalgesia, allodynia, and c-fos expression in the rat chronic nerve constriction model. METHODS Sprague-Dawley rats (n = 103) were used. Animals receiving NP were divided into three experimental groups (n = 12 in each group): saline, high-dose (5 mg/kg) EP1 receptor antagonist (RA), and low-dose (2.5 mg/kg) EP1-RA (orally once daily for 5 days). Animals in the sham group did not receive NP. Von Frey tests were used for pain-behavior testing. The amount of PGE2 in DRG and the number of activating transcription factor-3 (ATF3) immunoreactive positive cells were compared among groups. RESULTS The mechanical thresholds in the three groups decreased 7 days after surgery (just before treatment). The threshold in both the high- and low-dose EP1-RA groups increased at 11 days (5 days after treatment) and continued for 14 days. The thresholds in both the low- and high-dose EP1-RA groups increased significantly compared with the saline group (P < 0.05). The amount of PGE2 was significantly increased in the NP group compared with the sham and naive animals after application of NP. ATF3 expression was increased by NP but was not increased after administration of the EP1-RA. CONCLUSION An EP1 receptor antagonist improves pain-related behavior in the rat model and might be a potential agent to improve pain-related behavior in patients with lumbar disc herniation.

STUDY DESIGN An experimental rat study. OBJECTIVE To assess pain-related behavior and vascular endothelial growth factor (VEGF) expression induced by nucleus pulposus (NP) applied to nerve roots in rats. SUMMARY OF BACKGROUND DATA Radiculopathy from disc herniation is caused by nerve compression and chemical inflammation. In experimental studies, a decrease in mechanical withdrawal threshold, blood flow, and nerve root dysfunction was reported when the NP was applied to nerve roots. However, neuron reproduction and changes in nerve root blood vessels have not been clearly understood. METHODS NP harvested from the tail was applied to the left L5 dorsal root ganglion (NP group; n = 77). As a control, sham-operated animals were used (n = 77). Behavioral testing with von Frey hairs was performed for 35 days. Immunoreactivity (IR) for VEGF, activating transcription factor-3, growth-associated protein-43 (GAP-43), factor VIII, and hypoxia-inducible factor-1[alpha] (HIF-1 a) were studied by immunohistochemistry. Western blot analyses of VEGF and GAP-43 were also performed. RESULTS The mechanical withdrawal threshold significantly decreased from 7 to 28 days in the NP group versus the sham group (P < 0.05). In the NP group, activating transcription factor-3-IR cells increased from 3 to 14 days (P < 0.05), hypoxia-inducible factor-1[alpha]-IR cells increased at 14 days (P < 0.05), and blood vessels with Factor VII-IR cells increased at 28 days (P < 0.05) compared with the sham group. The expression levels of VEGF and GAP-43 in the NP group significantly increased at 14 and 28 days (P < 0.05). CONCLUSION Neuron damage induced by NP applied to the nerve root at the early stage, and axon extension occurred from 14 days. VEGF increased at 14 and 28 days, and the numbers of blood vessels increased 28 days after surgery. The mechanical withdrawal threshold improved at 35 days. Regeneration and vascularization by VEGF might be associated with pain-related behavior.

STUDY DESIGN this study was designed to examine the neuroprotective effects of asialo-erythropoietin (A-EPO) in a rat model of lumbar disc herniation. OBJECTIVE to investigate the effects of A-EPO on pain-related behavior, the expression of phosphorylated-p38 (p-p38) mitogen activated kinase, and the expression of tumor necrosis factor alpha (TNF-α) induced by nucleus pulposus (NP) application on the nerve root. SUMMARY OF BACKGROUND DATA erythropoietin (EPO) has neuroprotective effects in a variety of models of central and peripheral nerve injuries. However, EPO is a hematopoietic growth factor and can therefore cause significant side effects such as thicker blood and promotion of blood clotting. A-EPO is a neuroprotective derivative of EPO that is not hematopoietic. METHODS female Sprague-Dawley rats (n = 149) were used in this study. NP harvested from the tail was applied to the left L5 nerve root and the rats were then divided into four groups: NP + nontreatment group, no further treatment; NP + A-EPO group, 13.4 microg/kg A-EPO; NP + EPO group, 13.4 microg/kg EPO; and NP + vehicle group, received vehicle. The substances were administered subcutaneously 1 day before surgery and daily for 2 weeks. In the sham group of animals, the L5 nerve root was exposed and NP was not applied. Withdrawal thresholds were determined by the von-Frey test 28 days after surgery. The expressions of p-p38 and TNF-α were assessed by immunohistochemical and immunoblotting analysis. Data were analyzed by unpaired Student t test and Dunnett t test (significance level, P < 0.05). RESULTS in the NP + nontreatment and NP + vehicle groups, withdrawal thresholds were decreased significantly for 28 days compared with the sham group (P < 0.05). In the NP + A-EPO group, the thresholds were significantly increased on day 28, and in the NP + EPO group, the thresholds were significantly increased on days 21 and 28 (P < 0.05) compared with the NP + nontreatment and NP + vehicle groups. The expression of p-p38 in the NP + A-EPO group was significantly lower than that in the NP + vehicle group on day 1 (P < 0.05). The expression of TNF in the NP + A-EPO and NP + EPO groups was significantly lower than that in the NP + vehicle group on days 1 and 7 (P < 0.05). CONCLUSIONS A-EPO improved pain-related behavior and reduced the expression of p-p38 and TNF-α. The effect of A-EPO may be related to the inhibitory action of p-p38 and TNF-α in the dorsal root ganglion.

Study design we investigated the localization of insulin-like growth factor 1 (IGF-1) using immunohistochemistry and the effects of small interfering RNA (siRNA) on IGF-1 in dorsal root ganglions (DRG) in a rat lumbar disc herniation (LDH) model. Objective to determine the localization and function of IGF-1 in DRG of an experimental model of LDH. Summary of background data mechanical compression and chemical irritation are 2 major causative factors of radiculopathy in LDH. IGF-1, Ccnd1, Cdc2a, and CyclinA2 genes have been shown to be significantly upregulated in the mechanical model, but not in the chemical model. However, the localization and function of IGF-1 in DRG remain unknown in the mechanical compression animals. Methods twenty-six adult female Sprague-Dawley rats were used in this study. A mechanical compression model was prepared by inserting a stainless rod. The rod was not inserted in the sham model. Expression of IGF-1 and Neuronal Nucli (NeuN) or glial fibrillary acidic protein was determined using double-fluorescence 7 days after mechanical compression (n = 5). Rats were randomly separated into 3 groups for the siRNA study (n = 7 in each group): (1) vehicle group; (2) siRNA group; and (3) sham group. The mechanical withdrawal threshold of the plantar food pad was examined using von Frey filaments for 35 days. Results IGF-1 was localized particularly in the neuronal cell body, and revealed that it colocalized with NeuN but not with glial fibrillary acidic protein. The threshold was reduced in the vehicle and siRNA groups compared with the sham group. The threshold of the siRNA group significantly recovered from reduction compared with the vehicle group at 5 days after surgery, and this effect persisted throughout the experimental period. CONCLUSION.: IGF-1 was localized with neuronal cell bodies in DRG. IGF-1 knockdown caused a reduction in mechanical allodynia. The upregulation of IGF-1 might be a key factor in painful radiculopathy induced by mechanical factors.

The association between intramuscular pressure and low back pain was investigated by measuring intramuscular pressure and blood flow, assessing histologic appearance, and performing immunohistochemical testing in rats.To develop an experimental rat model of increased intramuscular pressure (IMP) in the lumbar paraspinal muscles accompanied by reduced intramuscular blood flow (IMBF). The expression of neuropeptides in the dorsal root ganglion of the experimental model was also investigated.Studies have reported that IMP in the lumbar paraspinal muscles is one of the causes of chronic low back pain. However, the pathology of low back pain accompanied by IMP has not been sufficiently clarified.A balloon was inflated below the vertebral fascia of rats (balloon group) and intramuscular pressure and blood flow in the lumbar paraspinal muscles were measured. Intramuscular pressure was measured using a pressure transducer, whereas IMBF was measured using a contact-type laser Doppler flowmeter. Compared with the sham operation group, intramuscular pressure was higher and IMBF was lower for the balloon group at 1 hour and 1 day after insertion. In addition, at 1 hour and 1 day after insertion, IMBF and pressure were continuously measured while rats were positioned in flexion for 1 hour.Intramuscular pressure was significantly higher and IMBF was significantly lower in the balloon group at 1 day after insertion (P0.05). Expression of substance P, a neuropeptide, was also observed in the dorsal root ganglion of the first lumbar vertebra.These findings suggest that IMP and decreased IMBF in the lumbar paraspinal muscles induce inflammation and pain in the lower back.

The purpose of this study was to clarify the mechanism of tendon regeneration by investigating macroscopically, histologically, and biomechanically.Fifty, adult, female Sprague-Dawley rats were used. The Achilles tendon in the left hind limb was removed totally by use of the tendon-stripping device. Rats were killed at 2, 7, 30, 90, and 180 days after surgery, and the regenerate tendons were dissected. Contralateral Achilles tendons were used as normal controls. Gross anatomic changes, microscopic remodeling, and recovery of biomechanical properties of regenerate tendons were investigated. The expressions of type I collagen, type III collagen, and transforming growth factor β1 were also investigated by immunohistochemistry.The regenerate tendons formed in all specimens. In the early phase, hematoma and soft granulation tissue were observed at the harvest defect. These gradually matured with time, and the microscopic structure became quite similar to normal at 180 days after surgery. These findings occurred uniformly along the entire length of the regenerate tendon. However, the biomechanical properties were significantly inferior to the normal tendons (P.05). Transforming growth factor β1 was well co-localized with inflammatory cells and fibroblasts in the regenerate tendons. The type I-type III collagen ratio in the regenerate tendon was significantly decreased in the early phase (P.05) but gradually increased with time.Tendon regeneration and maturation occurred uniformly along the length of regenerate tendons. The hematoma that initially occupies the harvest defect acted as a scaffold for fibroblast precursor cells from the surrounding peritendinous tissue and tendon sheath. The mechanical properties of regenerate tendon were significantly inferior to contralateral control even at 180 days after surgery, and the alteration of the collagen composition would have an influence on mechanical properties of regenerate tendon.Clinicians should be cautious about using reharvested hamstring tendons for ligament reconstruction surgery.

Background Calcitonin is used as a treatment to reduce the blood calcium concentration in hypercalcemia and to improve bone mass in osteoporosis. An analgesic effect of calcitonin has been observed and reported in clinical situations. Ovariectomaized (OVX) rats exhibit the same hormonal changes as observed in humans with osteoporosis and are an animal model of postmenopousal osteoporosis. The aim of this study to investigate antinociceptive effect of calcitonin in OVX rats using the immunohistochemical study. Methods We assessed the antinociceptive effects of calcitonin in an ovariectomized (OVX) rat model, which exhibit osteoporosis and hyperalgesia, using the immunohistochemical method. Fifteen rats were ovariectomized bilaterally, and ten rats were received the same surgery expected for ovariectomy as a sham model. We used five groups: the OVX-CT (n = 5), the sham-CT (n = 5), and the OVX-CT-pcpa (n = 5) groups recieved calcitonin (CT: 4 U/kg/day), while OVX-vehi (n = 5) and the sham-vehi (n = 5) groups received vehicle subcutaneously 5 times a week for 4 weeks. The OVX-CT-pcpa-group was given traperitoneal injection of p-chlorophenylalanine (pcpa; an inhibitor of serotonin biosynthesis) (100 mg/kg/day) in the last 3 days of calcitonon injection. Two hours after 5% formalin (0.05 ml) subcutaneously into the hind paw, the L5 spinal cord were removed and the number of Fos-immunoreactive (ir) neurons were evaluated using the Mann-Whitney-U test. Results The numbers of Fos-ir neurons in the OVX-CT and sham-CT groups were significantly less than in the OVX-vehi and sham-vehi groups, respectively (p = 0.0090, p = 0.0090). The number of Fos-ir neurons in the OVX-CT-pcpa-group was significantly more than that of the OVX-CT-group (p = 0.0283), which means pcpa inhibits calcitonin induced reduction of c-Fos production. Conclusion The results in this study demonstrated that 1) the increase of c-Fos might be related to hyperalgesia in OVX-rats. 2) Calcitonin has an antinociceptive effect in both OVX and sham rats. 3) The central serotonergic system is involved in the antinociceptive properties of calcitonin.

Altered dorsal root ganglion (DRG) function is associated with neuropathic pain following spinal nerve injury. However, compression of the cauda equina and dorsal rhizotomy proximal to the DRG do not induce significant pain, whereas in the spinal nerve and peripheral nerve, injury distal to the DRG does induce neuropathic pain. Caspase signaling induces apoptosis, and caspase inhibitors prevent pain-related behavior. The degree of DRG neuronal apoptosis is thought to play a role in pain behavior. We suggest that differences in pain behavior according to the injury sites within the DRG may be related to imbalances in apoptotic injuries. The aim of this study was to determine which compression injury was more painful and to compare behavior with expression of tumor necrosis factor (TNF)-alpha in DRG and apoptosis in the DRG following crush injury to the L5 nerve root or L5 spinal nerve. Sprague–Dawley rats received a crush injury to the L5 spinal nerve (distal to the DRG), crush injury to the L5 nerve root (proximal to the DRG), or no crush injury (sham). Mechanical allodynia was determined by the von Frey test. Expression of TNF-alpha was compared among three groups using immunoblot findings. Furthermore, we compared the percentage of neurons injured in the DRG using immunostaining for apoptotic cells and localization of activated caspase 3. Mechanical allodynia was observed in both crush injury groups. The duration of mechanical allodynia in the distal crush group was significantly longer than in the proximal crush group (P

STUDY DESIGN Analyses of improvements in nerve conduction velocity (NCV) and blood flow after administering cilostazol in a dog model of experimental acute and chronic cauda equina compression. OBJECTIVE To determine whether cilostazol improves NCV and blood flow, and cilostazol inhibits blood clots in capillaries of nerve roots after cauda equina compression. SUMMARY AND BACKGROUND DATA Reduction in blood flow is an important factor in neurogenic intermittent claudication for lumbar spinal stenosis. Prostaglandin E1 (PGE1) and calcitonin have been reported to improve blood flow and neurogenic intermittent claudication in clinical and experimental studies. Cilostazol affects vasodilator and antiplatelet activity, and protects endothelial cells in blood vessels. METHODS Experimental groups in the acute compression study (n = 40) were divided into 4 treatment groups. Low-dose (3 microg/kg/min), medium-dose (10 microg/kg/min), or high-dose (30 microg/kg/min) cilostazol or a control vehicle were administered intravenously after cauda equina compression. NCV and blood flow were measured during the observation period (n = 20 measurements for each). Another 12 animals were used to evaluate chronic compression. Cilostazol was administered for 6 days orally 1 day after compression treatment group (n = 6); the nontreatment group (n = 6) did not receive any drug. NCV was measured immediately after and 7 days after compression. Blood flow was measured 7 days after compression. RESULTS In the acute compression study, NCV in the medium-dose group was significantly higher than that in the other groups during the compression period (P < 0.05). During the recovery period, there was no significant difference in NCV among groups. In the chronic compression study, NCV and blood flow in the cilostazol group were significantly higher than those in the control group (P < 0.05). CONCLUSION Cilostazol improved NCV and blood flow to the cauda equina in this dog model. Cilostazol might be a potential agent to improve symptoms due to compression of cauda equina and/or cauda equina dysfunction.

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.

STUDY DESIGN The contralateral pain-related behavioral and immunohistochemical changes after hemilateral spinal nerve injury in rats were investigated. OBJECTIVES We evaluated the longitudinal changes in contralateral mechanical allodynia, expression of tumor necrosis factor (TNF)-alpha and glial fibrillary acidic protein (GFAP)-positive satellite cells in the contralateral dorsal root ganglion (DRG), and expression of astrocytes and microglia in the contralateral spinal dorsal horn after hemilateral spinal nerve injury in rats. SUMMARY OF BACKGROUND DATA In previous studies, hemilateral nerve injury has sometimes induced contralateral neuropathic pain. TNF-alpha expression and glial cell reactions in the DRG and spinal cord play an important role in the neuropathic pain state, and TNF-alpha is released from glial cells in the nervous system. METHODS Adult male Sprague-Dawley rats were used. The spinal L5 nerve distal to the DRG was crushed once for 3 seconds. At days 2, 7, 14, and 21 after surgery, mechanical allodynia was determined in bilateral hind paws by the von Frey test. Expression of TNF-alpha and GFAP in bilateral L5 DRGs and expression of GFAP and ionized calcium-binding adaptor molecule-1 (Iba-1) in bilateral L5 spinal dorsal horns were studied using immunohistochemistry and immunoblotting. RESULTS Mechanical withdrawal threshold of the ipsilateral hind paw was significantly decreased for 21 days. Conversely, mechanical withdrawal threshold of the contralateral hind paw was significantly decreased from 5 to 10 g for 7 days, and was

STUDY DESIGN: An experimental study of compensatory neovascularization after cauda equina compression in rats. OBJECTIVE: To explore the possibility that cauda equina compression induces compensatory neovascularization accompanied by an increase in the expression of vascular endothelial growth factor (VEGF). SUMMARY OF BACKGROUND DATA: VEGF is a potent promoter of neovascularization that follows ischemia. Studies suggest that compression of the cauda equina causes ischemic changes that in turn cause an increase in VEGF expression that induces neovascularization. The mechanisms by which neovascularization develops in a compressed cauda equina are unknown. METHODS: Two rectangular-solid pieces of silicone rubber were implanted in the fourth and sixth epidural spaces of rats (1 piece in each space); in the sham control group, no rubber was implanted. VEGF expression in the compressed cauda equina was assessed by immunohistochemistry and Western blotting. Ischemia and neovascularization of the cauda equina were assessed by immunostaining for hypoxia-inducible factor-1 alpha (HIF-1 alpha) and 5-bromodeoxyuridine (BrdU). The unpaired Student t test was used for statistical analysis (P < 0.05). RESULTS: At 14 and 21 days after surgery, ischemic changes were observed, as indicated by expression of HIF-1 alpha. In the compression group at 21 and 28 days after surgery, Western blot analysis showed a significant increase in VEGF expression (P < 0.05). VEGF was localized to pericytes, Schwann cells, and macrophages. In the compression group at 21 days after surgery, neovascularization was observed, as indicated by an increase in the number of proliferating endothelial cells (which stained positive for BrdU). CONCLUSION: Cauda equina compression seems to induce compensatory neovascularization of the cauda equina accompanied by an increase in VEGF expression.

Study design We investigated involvement of EphB/ephrinB system in neuropathic pain. Objective Using immunoblotting, immunohistochemistry, and RNA interference techniques, we examined the expression levels of EphB receptors and ephrinB ligands in neuropathic pain. We also explored the effect of ephrinB siRNA for neuropathic pain. Summary of background data It has been reported that EphB2 regulates the development of synaptic plasticity in the hippocampus by interacting with N-methyl-D-aspartate (NMDA) receptors. In acute pain models, it has been clear that EphB1/ephrinB2 interactions via the NMDA receptor modulates synaptic efficacy in spinal cord. Methods Adult female Sprague-Dawley rats were used in this study. A crush injury model was prepared by crushing the left L5 spinal nerve distal to dorsal root ganglions (DRG) under deep anesthesia. The sham operation was subjected as control. Expression of ephrinB2 and EphB1 were examined by immunoblotting and immunohistochemical analyses with anti-EphB and anti-ephrinB antibodies. To assess involvement of ephrinB in neuropathic pain, we examined the effect of small interference RNA (siRNA) on mechanical allodynia. Results Among EphB and ephrinB isoforms tested, ephrinB2 and EphB1 were predominant in DRG and spinal cord. Results showed that the expression of ephrinB2 was enhanced in neurons in DRG and spinal cord by the injury in a time-dependent manner. EphB1 was expressed in neurons of spinal cord. Administration of ephrinB2 siRNA reduced the expression of ephrinB2 and mechanical allodynia. Conclusion Expression of ephrinB2 is enhanced by nerve injury in neurons in DRG and spinal cord, while its receptor EphB1 is expressed in spinal cord. These results suggest that induction of ephrinB2 might activate EphB1/ephrinB2 signaling pathway to regulate synaptic plasticity and reorganization, and that ephrinB2 siRNA could be a potential therapeutic agent for neuropathic pain.

Reduction of blood flow in compressed nerve roots is considered as one important mechanism of induction of neurogenic intermittent claudication in lumbar spinal canal stenosis. Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis, and is increased in expression in hypoxic conditions. The objective of this study was to examine if cauda equina compression affects motor function and induces expression of VEGF and angiogenesis. The cauda equina was compressed by placing a piece of silicone rubber into the L5 epidural space. Walking duration was examined by rota-rod testing. The compressed parts of the cauda equina and L5 dorsal root ganglion (DRG) were removed at 3, 7, 14, or 28 days after surgery, and processed for immunohistochemistry for VEGF and Factor VIII (marker for vascular endothelial cells). Numbers of VEGF-immunoreactive (IR) cells and vascular density were examined. Walking duration was decreased after induction of cauda equina compression. The number of VEGF-IR cells in the cauda equina and DRG was significantly increased at 3, 14, and 28 days after cauda equina compression, compared with sham-operated rats (P

Study Design. An experimental study on mechanical allodynia, c-Fos expression, and 200-kDa-neurofilament immunoreactive (IR) afferent expression in the substantia gelatinosa related to compression of dorsal root ganglion (DRG). Objectives. To evaluate the presence of allodynia in DRG compression model and to demonstrate that the structural changes of spinal dorsal horn related to DRG compression. Summary of Background Data. A previous experimental report has demonstrated that the peripheral nerve injury may trigger some structural changes of the superficial spinal dorsal horn. These changes of the spinal dorsal horn were thought to be important for the modulation of pain sensations such as allodynia. Methods. Sixty-eight male rats were used. The left L5 lamina was exposed and a drill hole was made in it. A stainless rod was placed close to the left L5 DRG through the drill hole. Behavioral testing with von Frey filament was performed. On day 28 after surgery, c-Fos expression in the spinal dorsal horn by non-noxious stimulation was examined. L5 spinal cord and bilateral L5 DRG specimens were stained with antibody for 200-kDa neurofilament (RT97). In addition, 2 or 3 spinal cord sections per rats were processed for immunoelectron microscopy. Results. In the DRG compression group, the mechanical withdrawal threshold was decreased, c-Fos expression by non-noxious stimulation was observed in the spinal dorsal horn, and there were many RT97-IR afferents in the superficial spinal dorsal horn. Immunoelectron microscopic observations showed that RT97-IR terminals made synaptic contact with neurons in the superficial spinal dorsal horn. There were no significant differences in the distribution of RT97-IR neurons in DRG between compression and sham group. Conclusions. DRG compression induced allodynia and that RT97-IR afferents increased in the superficial dorsal horn of the spinal cord. The increase of RT97-IR afferents may be related to the mechanisms for the observed allodynia.

Background External medication that is absorbed percutaneously may be used to reduce inflammation and relieve pain from acute injuries such as ankle sprains and bruises. The plaster method of percutaneous absorption for non-steroidal anti-inflammatory drugs (NSAIDs) was established in Japan in 1988. However, due to the possibility of a placebo effect, the efficacy of this method remains unclear. This experimental study was conducted to control for the placebo effect and to study the efficacy of the plaster method in relieving pain by using a rat model of inflammation. Methods Male Wistar-Imamichi rats were used. A yeast suspension was injected into the right hind paw to induce inflammation. A sheet (2.0 × 1.75 cm) containing the drug was adhered to the inflamed paw. Five treatment groups were used, and each sheet contained a single drug: loxoprofen sodium (loxoprofen-Na) (2.5 mg); felbinac (1.75 mg); indomethacin (1.75 mg); ketoprofen (0.75 mg); or base only (control, 0 mg). Mechanical pain threshold, expression of c-Fos in the dorsal horn, and amount of prostaglandin (PG) E2 in the inflamed paw were evaluated. Results Pain threshold increased after treatment, and was significantly increased in the loxoprofen-Na group compared with the control group (p < 0.05). Amounts of PGE2 were significantly decreased in the loxoprofen-Na and indomethacin groups compared with the control group (p < 0.05). Expression of c-Fos was significantly decreased in the loxoprofen-Na group compared with the control group (p < 0.05). Conclusion Percutaneously absorbed NSAIDs have an analgesic effect, inhibit expression of c-Fos in the dorsal horn, and reduce PGE2 in inflamed tissue, indicating the efficacy of this method of administration for acute inflammation and localized pain.

Study design An experimental animal study. Objective To study if antitumor necrosis factor-alpha (TNF-alpha) antibody, which is administered at different times, reduces the pain behavior induced by application of nucleus pulposus (NP) to the nerve root. Summary of background data Treatment with TNF-alpha inhibitor reduces the pain-related behavior induced by epidural application of NP in rats. Methods Left L5 partial laminectomy was performed and NP was applied to the L5 nerve root in 24 rats. The rats were divided into 4 groups. In 3 groups, anti-rat TNF-alpha antibody was intravenously administered immediately after, or 6 or 20 days after NP application. The fourth group was not treated with anti-rat TNF-alpha antibody (untreated rats). The withdrawal threshold of the plantar surface was determined 1 day before up through 28 days after NP application. Results The withdrawal threshold of rats that had been treated with anti-rat TNF-alpha antibody immediately after or 6 days after, but not 20 days after, NP application, was significantly higher than that of the untreated rats. Conclusions Anti-TNF-alpha antibody reduced allodynia only when it was administered soon after the onset of allodynia. Late administration of anti-TNF-alpha antibody did not have an antiallodynic effect.

Blood vessel clots are found around the nerve root in patients with lumbar disc herniation. Thrombosis formation in the experimental application of nucleus pulposus to the nerve root has been shown in histological studies. In addition, reduction of blood flow and nerve conduction velocity are induced by the application of nucleus pulposus, which mimics lumbar disc herniation. In patients with lumbar disc herniation, nerve root block, which is thought to increase nerve blood flow, improves radiculopathy. 5-HT(2A) receptor antagonists are used in chronic arterial occlusive diseases to improve blood flow and have been reported to work as well as nonsteroidal anti-inflammatory drugs in improving radiculopathy due to lumbar disc herniation in clinical studies. This study investigated the effects of a 5-HT(2A) receptor antagonist on blood vessel diameter and blood flow in a canine experimental model of lumbar disc herniation. A total of 13 dogs were used. The animals were divided into three experimental groups and surgery was performed 1 week before measurements. In the nucleus pulposus group (NP; n = 5), the nucleus pulposus was applied to the nerve roots from the ventral side. In the sham group (n = 5), nucleus pulposus was not applied. In the naive group (n = 3), the animals did not undergo surgery. Measurements of vessel diameter and blood flow were done before and after administration of saline and drugs. The diameters and blood flow volume of the observed blood vessels were measured on video-recordings every 10 min for 65 min. In all groups, vessel diameter and blood flow did not change before or after administration of saline. In the NP and sham groups, vessel diameter and blood flow increased significantly after administration of 5-HTRA compared with the naive group. 5-HTRA improved blood vessel diameter and blood flow in the nerve roots inflamed by the application of nucleus pulposus but not in the intact nerve roots. 5-HTRA might be a potential agent to improve blood flow in the nerve roots of patients with lumbar disc herniation.

Study Design. Vasodilatation was studied in a model of experimental chronic cauda equina compression using measurements of vessel diameter on video recordings. Objective. The vasodilative effect was compared between a prostaglandin E 2 receptor (EP) subtype agonists (EP 4 agonist) and a prostaglandin E 1 (PGE 1 ) derivate. and Background Data. Reduction of blood flow is one important pathogenic factor of neurogenic intermittent claudication (NIC) for lumbar spinal canal stenosis. It is known that PGE 1 improves the mean walking distance in patients with cauda equina compression type of NIC. There are four subtypes of EP: EP 1 , EP 2 , EP 3 , and EP 4 . EP 4 is located in vessels of pigs and rabbits. A highly selective EP 4 agonist, which has effects on dilatation of pig and rabbit vessels, has recently been developed. One may therefore assume that this agonist may improve blood flow in the chronically compressed cauda equina. Methods. A total of 25 dogs were used. A plastic balloon inflated to 10 mm Hg was placed under the lamina of the seventh lumbar vertebra for 1 week. OP-1206 cyclodextrin clathrate (OP-1206 CD: prostaglandin E 1 derivate) and ONO-4819 CD (a highly selective EP 4 agonist) were intravenously administrated. The following 5 experimental groups were assigned: animals in group OP (3) (n = 5) and Group OP (10) (n = 5) received 3 η g/kg per minute and 10 η g/kg per minute of OP-1206 CD, respectively; those in Group EP (3) (n = 5) and Group EP (10) (n = 5) received 3 η g/kg per minute and 10 η g/kg per minute of ONO-4819 CD, respectively; and those in the control group (n = 5) received saline. After 7 days, the cauda equina was exposed and blood vessels of the second or third sacral nerve root were identified using a specially designed operation microscope equipped with a video camera. The diameters of the observed blood vessels were measured on video-recordings every 10 minutes until 60 minutes after administrating OP-1206 CD or ONO-4819CD. Results. In the Groups OP (3), OP (10), and EP (10), the blood vessels were dilated and blood flow increased after injection of the agents. In the Group EP (10), the vessel diameter and blood flow increased significantly compared with that in the other four groups. In contrast, the blood vessels contracted and the blood flow was reduced in the Group EP (3). Conclusions. Our results suggested that the EP 4 agonist at high concentrations might be a potential therapeutic agent since it is expected to increase blood flow in nerve roots In patients with spinal canal stenosis.

Neurophysiologic function and ischemia causes neurogenic symptoms in lumbar spinal stenosis. Neurophysiologic function and potential therapeutic agents were investigated using a chronic cauda equina compression model that was developed according to a clinical pathogenesis. In the chronic cauda equina compression model, nerve conduction velocity and blood flow in spinal nerves decreased but mechanical allodynia was not induced. Prostaglandins and 5-HT receptor antagonist effected to improve blood flow in nerve roots after cauda equina compression;therefore, they might be potential agents for lumbar spinal stenosis.

STUDY DESIGN An analysis of pathologic changes after different degrees of cauda equina compression. OBJECTIVES To explore the association between the degree of the cauda equina compression and the extent of pathologic change, expression of tumor necrosis factor (TNF-alpha), and neuropathic pain. To compare with distal nerve compression injury. SUMMARY OF BACKGROUND DATA Compression of the cauda equina reduces blood flow in compressed nerve roots and causes TNF-alpha expression and neuropathological change. In peripheral nerve, expression of TNF-alpha in Schwann cells is associated with primary demyelination without pain while TNF-alpha expression by macrophages is associated with axonal (Wallerian) degeneration and pain. METHODS Two square-shaped pieces of silicon were placed into the fourth and sixth epidural space in rats. Various sized silicon was used in each group (mild, moderate, and strong compression groups), while no silicon was used in the sham-operated group. Mechanical allodynia was determined by the von Frey test. Comparisons of the number of TNF-alpha- and apoptosis-positive cells were made using immunohistochemistry. RESULTS There was no significant mechanical allodynia observed in any group. Some nerve roots showed demyelination following mild cauda equina compression. Axonal degeneration was observed in the moderate and strong cauda equina compression groups. TNF-alpha-immunoreactive cells were increased in all compression groups. Apoptosis of dorsal root ganglion cells was less than apoptosis in the spinal cord. CONCLUSION Mild cauda equina compression induces TNF-alpha expression and demyelination. Moderate and strong cauda equina compression induces TNF-alpha expression and degeneration associated with macrophage invasion. Neither demyelination nor degeneration in the cauda equina induced mechanical allodynia. Nerve lesions proximal to the dorsal root ganglion do not produce significant mechanical allodynia. Dorsal root ganglion apoptosis may be important for pain.

STUDY DESIGN An analysis of nerve vascular changes in nerve roots induced by serotonin in chronically compressed nerve roots. OBJECTIVES To assess the hypotheses that serotonin might have a vasoconstrictive effect in chronically compressed nerve roots. SUMMARY OF BACKGROUND DATA The 5-hydroxytryptamine 2A receptor is involved in serotonin-induced activation or sensitization of sensory nerve terminals. Serotonin exerts complex effects on pain and hyperalgesia through various receptor subtypes located at various levels of the pain transmission system. Serotonin induces endothelium-dependent contraction in vascular diseases. However, there is no knowledge regarding a response of nerve vasculature induced by serotonin in chronically compressed nerve roots. METHODS A total of 45 dogs were used. A plastic balloon was placed under the lamina L7 and inflated to 10 mm Hg and left for 1 week. Four experimental groups were used: no operation (Group A, n = 15), the balloon was placed under the lamina but not inflated (Group B, n = 10), the balloon was inflated to 10 mm Hg for 1 week and the pressure was released just before the measurement (Group C, n = 10), and the balloon was inflated to 10 mm Hg for 1 week and inflation was maintained during the measurements (Group D, n = 10). The blood vessels of the second or third sacral nerve were defined after an intra-arterial injection of 0.5 micromol/L or 1.0 micromol/L serotonin using a specially designed operation microscope equipped with a video camera. In all groups 0.5 micromol/L serotonin (each group, n = 5) or 1.0 micromol/L serotonin (each group, n = 5) was injected. In Group A (n = 5) saline was injected. The measurements of diameter of observed blood vessels and blood flow index were performed on video recordings. All statistical assessments were performed by Wilcoxon signed-ranks test and Fisher's PLSD. RESULTS In Group A, the diameter of blood vessels and blood flow did not change after administration of saline. In the noncompression groups (Groups A and B) the diameter of blood vessels and blood flow increased after injection of 0.5 micromol/L serotonin. In compression groups (Groups C and D) the blood vessels contracted after injecting 0.5 micromol/L serotonin and blood flow decreased. There was a significant difference in the diameter of blood vessels and blood flow between noncompression and compression groups (P < 0.01). There was no difference regarding diameter of blood vessels between released compression (Group C) and maintained compression during measurement group (Group D). In all groups blood vessels contracted and blood flow decreased after injecting 1.0 micromol/L. In electron microscopic observation tight junction of endothelial cells was destroyed in chronically compression nerve roots. DISCUSSION The present study demonstrated that serotonin had a vasodilative effect on the intact nerve roots, whereas there was a vasoconstrictive effect to the chronically compressed nerve roots. There was no difference in the diameter of blood vessels between released compression and maintained compression during measurement group. Results suggested that dysfunction of endothelial cells induced by serotonin rather than mechanical compression itself might lead to contraction of blood vessels under chronic compression. CONCLUSION Serotonin had a vasoconstrictive effect on the chronically compressed nerve roots.

The 32-kDa galectin (LEC-1) of the nematode Caenorhabditis elegans (C. elegans) is composed of two tandemly repeated homologous sequences, each containing a carbohydrate-recognition domain (CRD). Using the polymerase chain reaction (PCR) with LEC-1 cDNA as a template and “megaprimers”, we performed site-directed mutagenesis to substitute conserved amino acid residues in these domains. The resultant mutated LEC-1s were produced in E. coli, and their binding abilities were estimated by affinity chromatography. When one of the conserved amino acid residues in the first lectin domain was substituted, the binding ability of the mutant protein to asialofetuin-agarose was reduced but still remained. The binding ability of such mutants was similar to that of the recombinant half molecule containing the second lectin domain (Ch). However, when mutations were introduced into the second lectin domain, the binding ability of these mutant lectins to asialofetuin-agarose was significantly reduced just like the half recombinant molecule containing the first lectin domain (Nh). The different effects of the substitution of amino acid residues on the two lectin domains suggest that the binding properties of the two sites are different and that LEC-1 acts as a “heterobifunctional crosslinker.”

Background Reduction of blood flow is important in the induction of neurogenic intermittent claudication (NIC) in lumbar spinal canal stenosis. PGE1 improves the mean walking distance in patients with NIC type cauda equina compression. PGE1 derivate might be effective in dilating blood vessels and improving blood flow in nerve roots with chronically compressed cauda equina. The aim of this study was to assess whether PGE1 derivate has vasodilatory effects on both arteries and veins in a canine model of chronic cauda equina compression. Methods Fourteen dogs were used in this study. A plastic balloon inflated to 10 mmHg was placed under the lamina of the 7th lumbar vertebra for 1 week. OP-1206-cyclodextrin clathrate (OP-1206-CD: prostaglandin E1 derivate) was administered orally. The blood vessels of the second or third sacral nerve root were identified using a specially designed surgical microscope equipped with a video camera. The diameter of the blood vessels was measured on video-recordings every 15 minutes until 90 minutes after the administration of the PGE1 derivate. Results We observed seven arteries and seven veins. The diameter and blood flow of the arteries was significantly increased compared with the veins at both 60 and 75 minutes after administration of the PGE1 derivate (p < 0.05). Blood flow velocity did not change over 90 minutes in either the arteries or veins. Discussion The PGE1 derivate improved blood flow in the arteries but did not induce blood stasis in the veins. Our results suggest that the PGE1 derivate might be a potential therapeutic agent, as it improved blood flow in the nerve roots in a canine model of chronic cauda equina compression.