• The Korean Journal of Pain
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• v.27 no.3
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• pp.239-245
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• 2014

Background: Neuropathic pain induced by spinal or peripheral nerve injury is very resistant to common pain killers, nerve block, and other pain management approaches. Recently, several studies using stem cells suggested a new way to control the neuropatic pain. In this study, we used the spinal nerve L5 ligation (SNL) model to investigate whether intrathecal rat mesenchymal stem cells (rMSCs) were able to decrease pain behavior, as well as the relationship between rMSCs and reactive oxygen species (ROS). Methods: Neuropathic pain of the left hind paw was induced by unilateral SNL in Sprague-Dawley rats (n = 10 in each group). Mechanical sensitivity was assessed using Von Frey filaments at 3, 7, 10, 12, 14, 17, and 24 days post-ligation. rMSCs ($10{\mu}l$, $1{\times}10^5$) or phosphate buffer saline (PBS, $10{\mu}l$) was injected intrathecally at 7 days post-ligation. Dihydroethidium (DHE), an oxidative fluorescent dye, was used to detect ROS at 24 days post-ligation. Results: Tight ligation of the L5 spinal nerve induced allodynia in the left hind paw after 3 days post-ligation. ROS expression was increased significantly (P < 0.05) in spinal dorsal horn of L5. Intrathecal rMSCs significantly (P < 0.01) alleviated the allodynia at 10 days after intrathecal injection (17 days post-ligation). Intrathecal rMSCs administration significantly (P < 0.05) reduced ROS expression in the spinal dorsal horn. Conclusions: These results suggest that rMSCs may modulate neuropathic pain generation through ROS expression after spinal nerve ligation.

• The Korean Journal of Pain
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• v.21 no.3
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• pp.187-196
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• 2008

Background: Upregulation of one type of the pro-inflammatory chemokine (CCL2) and its receptor (CCR2) following peripheral nerve injury contributes to the induction of neuropathic pain. Here, we examined whether another type of chemokine (CCL3) is involved in neuropathic pain. Methods: We measured changes in mechanical and thermal sensitivity in the hind paws of naïve rats or rats with an L5 spinal nerve ligation (SNL) after intra-plantar injection of CCL3 or met-RANTES, an antagonist of the CCL3 receptor, CCR1. We also measured CCL3 levels in the sciatic nerve and the hind paw skin as well as CCR1 expression in dorsal root ganglion (DRG) cells from the lumbar spinal segments. Results: Intra-plantar injection of CCL3 into the hind paw of naive rats mimicked L5 SNL-produced hyperalgesia. Intra-plantar injection of met-RANTES into the hind paw of rats with L5 SNL attenuated hyperalgesia. L5 SNL increased CCL3 levels in the sciatic nerve and the hind paw skin on the affected side. The number of CCR1-positive DRG cells in the lumbar segments was not changed following L5 SNL. Conclusions: Partial peripheral nerve injury increases local CCL3 levels along the degenerating axons during Wallerian degeneration. This CCL3 binds to its receptor, CCR1, located on adjacent uninjured afferents, presumably nociceptors, to induce hyperalgesia in the neuropathic pain state.

• The Korean Journal of Pain
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• v.24 no.4
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• pp.185-190
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• 2011

Background: Spinal nerve ligation (SNL) injury in rats produces a pain syndrome that includes mechanical and thermal allodynia. Previous studies have indicated that proinflammatory cytokines such as tumor necrosis factor-${\alpha}$ (TNF-${\alpha}$) play an important role in peripheral mediation of neuropathic pain, and that altered dorsal root ganglion (DRG) function and degree of DRG neuronal apoptosis are associated with spinal nerve injury. The present study was conducted to evaluate the expression of TNF-${\alpha}$ and the extent of apoptosis in the dorsal root ganglion after SNL in rats. Methods: Sprague-Dawley rats were subjected to SNL of the left L5 and L6 spinal nerves distal to the DRG and proximal to the formation of the sciatic nerve. At postoperative day 8, TNF-${\alpha}$ protein levels in the L5.6 DRG were compared between SNL and naive groups using ELISA. In addition, we compared the percentage of neurons injured in the DRG using immunostaining for apoptosis and localization of activated caspase-3. Results: SNL injury produced significant mechanical and cold allodynia throughout the 7-day experimental period. TNF-${\alpha}$ protein levels were increased in the DRG in rats that had undergone SNL ($12.7{\pm}3.2$ pg/100 ${\mu}g$, P < 0.001) when compared with naive rats ($4.1{\pm}1.4$ pg/100 ${\mu}g$). The percentage of neurons or satellite cells co-localized with activated caspase-3 were also significantly higher in rats with SNL than in naive rats (P < 0.001, P < 0.05, respectively). Conclusions: SNL injury produces mechanical and cold allodynia, as well as TNF-${\alpha}$ elevation and apoptosis in the DRG.

• Biomolecules & Therapeutics
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• v.21 no.2
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• pp.126-131
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• 2013

Neuropathic pain is a chronic pain disorder caused by nervous system lesions as a direct consequence of a lesion or by disease of the portions of the nervous system that normally signal pain. The spinal nerve ligation (SNL) model in rats that reflect some components of clinical pain have played a crucial role in the understanding of neuropathic pain. To investigate the direct effects of gabapentin on differential gene expression in cultured dorsal root ganglion (DRG) cells of SNL model rats, we performed a differential display reverse transcription-polymerase chain reaction analysis with random priming approach using annealing control primer. Genes encoding metallothionein 1a, transforming growth factor-${\beta}1$ and palmitoyl-protein thioesterase-2 were up-regulated in gabapentin-treated DRG cells of SNL model rats. The functional roles of these differentially expressed genes were previously suggested as neuroprotective genes. Further study of these genes is expected to reveal potential targets of gabapentin.

• Molecules and Cells
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• v.25 no.2
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• pp.242-246
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• 2008

To assess the role of $\alpha_{1G}$ T-type $Ca^{2+}$ channels in neuropathic pain after L5 spinal nerve ligation, we examined behavioral pain susceptibility in mice lacking $Ca_{V}3.1$ (${\alpha}_{1G}{^{-/-}}$), the gene encoding the pore-forming units of these channels. Reduced spontaneous pain responses and an increased threshold for paw withdrawal in response to mechanical stimulation were observed in these mice. The ${{\alpha}_{1G}}^{-/-}$ mice also showed attenuated thermal hyperalgesia in response to both low-(IR30) and high-intensity (IR60) infrared stimulation. Our results reveal the importance of ${\alpha}_{1G}$ T-type $Ca^{2+}$ channels in the development of neuropathic pain, and suggest that selective modulation of ${\alpha}_{1G}$ subtype channels may provide a novel approach to the treatment of allodynia and hyperalgesia.

• The Korean Journal of Pain
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• v.26 no.4
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• pp.356-360
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• 2013

Background: Nerve injury sometimes leads to chronic neuropathic pain associated with neuroinflammation in the nervous system. In the case of chronic neuropathic pain, the inflammatory and algesic mediators become predominant and result in pain hypersensitivity following nervous system damage. It is well known that urinary trypsin inhibitor (ulinastatin, UTI) has an anti-inflammatory activity. Recently, the neuroprotective action of UTI on the nervous system after ischemic injury has been reported. Thus, we evaluated the neuroprotective effect of ulinastatin in a rat model of neuropathic pain. Methods: Neuropathic pain was induced with L5 spinal nerve ligation (SNL) in male Sprague-Dawley rats weighing 100-120 g. The rats were divided into 3 groups, with n = 8 in each group. The rats in the control group (group 1) were administered normal saline and those in group 2 were administered UTI (50,000 U/kg) intravenously through the tail vein for 3 days from the day of SNL. Rats in group 3 were administered UTI (50,000 U/kg) intravenously from the $5^{th}$ day after SNL. The paw withdrawal threshold was measured using the von Frey test for 3 days starting from the $5^{th}$ day after SNL. Results: The paw withdrawal thresholds were significantly increased in the rats of group 2 compared to the other groups (P < 0.05). Conclusions: Ulinastatin, which was administered for 3 days after SNL, increased the paw withdrawal threshold and it could have a neuroprotective effect in the rat model of neuropathic pain.

• The Korean Journal of Pain
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• v.21 no.3
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• pp.179-186
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• 2008

Background: The adrenergic nervous system in the spinal cord contributes to the development of neuropathic pain after nerve injury. Brain derived neurotrophic factor may facilitate the sympathetic change in the spinal cord and influence the state of neuropathic pain. We probed the effect of chronic repetitive administration of systemic 4-methylcatechol, which is known to be a neurotrophic factor inducer, in a spinal nerve ligation model. Methods: We made the rat neuropathic pain model by the ligation of the L5 spinal nerve. Intraperitoneal 4-methylcatechol ($10{\mu}g/kg$) or the same volume of saline wasadministrated twice daily just after the operation for 7 days. The tactile allodynia was measured by using von Frey filaments and its change was followed up from 3 days after SNL. The lumbosacral enlargement of the spinal cord was taken out and the mRNA contents of the ${\alpha}_2-adrenoceptor$ subtypes were measured by real time polymerase chain reaction and this was then compared with the control groups. The antiallodynic effect of intrathecal clonidine (3, 10, $30{\mu}g$) was evaluated and compared in the 4-methylcatechol treated rats and the control rats. Results: The expression of the ${\alpha}_{2A}$ and ${\alpha}_{2C}$ adrenoceptor subtypes did not change after 4-methylcatechol treatment. Intrathecal clonidine showed an earlier and better effect at the highest dose ($30{\mu}g$ intrathecal), but not with any other doses. Conclusions: Chronic intraperitoneal administration of 4-methylcatechol may improve the effect of intrathecal clonidine, but we could not prove the increase of ${\alpha}_{2A}$ and ${\alpha}_{2C}$ adrenoceptors in the spinal cord of 4-methylcatechol treated rats.

• The Korean Journal of Pain
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• v.36 no.4
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• pp.441-449
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• 2023

Background: Hypertonic saline is used for treating chronic pain; however, clinical studies that aid in optimizing therapeutic protocols are lacking. We aimed to determine the concentration of intrathecally injected hypertonic saline at which the effect reaches its peak as well as the underlying γ-aminobutyric acid (GABA) receptor-related antinociceptive mechanism. Methods: Spinal nerve ligation (SNL; left L5 and L6) was performed to induce neuropathic pain in rats weighing 250-300 g. Experiment 1: one week after implanting the intrathecal catheter, 60 rats were assigned randomly to intrathecal injection with 0.45%, 0.9%, 2.5%, 5%, 10%, and 20% NaCl, followed by behavioral testing at baseline and after 30 minutes, 2 hours, 1 day, and 1 week to determine the minimal concentration which produced maximal analgesia. Experiment 2: after determining the optimal intrathecal hypertonic saline concentration, 60 rats were randomly divided into four groups: Sham, hypertonic saline without pretreatment, and hypertonic saline after pretreatment with one of two GABA receptor antagonists (GABA_A [bicuculline], or GABA_B [phaclofen]). Behavioral tests were performed at weeks 1 and 3 following each treatment. Results: Hypertonic saline at concentrations greater than 5% alleviated SNL-induced mechanical allodynia and had a significant therapeutic effect, while showing a partial time- and dose-dependent antinociceptive effect on thermal and cold hyperalgesia. However, pretreatment with GABA receptor antagonists inhibited the antinociceptive effect of 5% NaCl. Conclusions: This study indicates that the optimal concentration of hypertonic saline for controlling mechanical allodynia in neuropathic pain is 5%, and that its analgesic effect is related to GABA_A and GABA_B receptors.

• The Korean Journal of Pain
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• v.33 no.1
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• pp.30-39
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• 2020

Background: This study examined the effects of gabexate mesilate on spinal nerve ligation (SNL)-induced neuropathic pain. To confirm the involvement of gabexate mesilate on neuroinflammation, we focused on the activation of nuclear factor-κB (NF-κB) and consequent the expression of proinflammatory cytokines and inducible nitric oxide synthase (iNOS). Methods: Male Sprague-Dawley rats were used for the study. After randomization into three groups: the sham-operation group, vehicle-treated group (administered normal saline as a control), and the gabexate group (administered gabexate mesilate 20 mg/kg), SNL was performed. At the 3rd day, mechanical allodynia was confirmed using von Frey filaments, and drugs were administered intraperitoneally daily according to the group. The paw withdrawal threshold (PWT) was examined on the 3rd, 7th, and 14th day. The expressions of p65 subunit of NF-κB, interleukin (IL)-1, IL-6, tumor necrosis factor-α, and iNOS were evaluated on the 7th and 14th day following SNL. Results: The PWT was significantly higher in the gabexate group compared with the vehicle-treated group (P < 0.05). The expressions of p65, proinflammatory cytokines, and iNOS significantly decreased in the gabexate group compared with the vehicle-treated group (P < 0.05) on the 7th day. On the 14th day, the expressions of p65 and iNOS showed lower levels, but those of the proinflammatory cytokines showed no significant differences. Conclusions: Gabexate mesilate increased PWT after SNL and attenuate the progress of mechanical allodynia. These results seem to be involved with the antiinflammatory effect of gabexate mesilate via inhibition of NF-κB, proinflammatory cytokines, and nitric oxide.

• The Korean Journal of Pain
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• v.34 no.4
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• pp.405-416
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• 2021

Background: This study investigated the effect of intrathecal Sec-O-glucosylhamaudol (SOG) on the p38/c-Jun N-terminal kinase (JNK) signaling pathways, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-related inflammatory responses, and autophagy in a spinal nerve ligation (SNL)-induced neuropathic pain model. Methods: The continuous administration of intrathecal SOG via an osmotic pump was performed on male Sprague-Dawley rats (n = 50) with SNL-induced neuropathic pain. Rats were randomized into four groups after the 7th day following SNL and treated for 2 weeks as follows (each n = 10): Group S, sham-operated; Group D, 70% dimethylsulfoxide; Group SOG96, SOG at 96 ㎍/day; and Group SOG192, SOG at 192 ㎍/day. The paw withdrawal threshold (PWT) test was performed to assess neuropathic pain. Western blotting of the spinal cord (L5) was performed to measure changes in the expression of signaling pathway components, cytokines, and autophagy. Additional studies with naloxone challenge (n = 10) and cells were carried out to evaluate the potential mechanisms underlying the effects of SOG. Results: Continuous intrathecal SOG administration increased the PWT with p38/JNK mitogen-activated protein kinase (MAPK) pathway and NF-κB signaling pathway inhibition, which induced a reduction in proinflammatory cytokines with the concomitant downregulation of autophagy. Conclusions: SOG alleviates mechanical allodynia, and its mechanism is thought to be related to the regulation of p38/JNK MAPK and NF-κB signaling pathways, associated with autophagy during neuroinflammatory processes after SNL.