Analgesic effects of electroacupuncture via the EphBs-p38 MAPK signaling pathway and microglial suppression in the chronic constriction injury rat model of neuropathic pain.

IntroductionNeuropathic pain is pretty common in modern society, and the treatment effect is far from satisfactory. This study aimed to find evidence of the neuroprotective effect of erythropoietin (EPO) in the treatment of neuropathic pain in a rat model of chronic constriction injury (CCI).MethodsA total of 30 rats were randomly divided into sham operation group, CCI group, or CCI+EPO group. The mechanical and thermal nociception thresholds are evaluated as behavioral assessments. The dorsal root ganglion cells were morphologically evaluated by hematoxylin and eosin staining, and AMPK, p-AMPK, mTOR, p70S6K, and AQP-2 proteins were compared and analyzed by Western blotting. Compared with the sham operation group, rats in the CCI group had shorter paw withdrawal threshold and paw withdrawal latency, abnormal morphology, and increased satellite glial cells.ResultsAfter treatment with EPO, these changes were significantly reversed. In vivo administration of erythropoietin seems to be able to regulate the expression of AQP-2 through the AMPK/mTOR/p70S6K pathway. Our study provides behavioral, morphological, and immunoblot evidence to prove the neuroprotective effect of EPO in the treatment of chronic neuropathic pain in the CCI rat model.ConclusionOur results indicate that EPO has the potential to treat neuropathic pain caused by peripheral nerve injury, although further verification is needed.

Purpose: To investigate the role of RAS-like protein A (RalA) in lipopolysaccharide-induced inflammatory regulation in primary microglia of chronic constriction injury (CCI)-induced neuropathic pain in rat models.
 Methods: In vitro, overexpression (OE) of RalA was performed in rat microglia using transfection procedure, and then LPS was used to provoke the inflammatory phenotype. In vivo, the rat model of neuropathic pain was induced using CCI and treated with LV-RalA. Neuroinflammatory levels including the expressions of IL-1β, IL-6, and TNF-α were detected. Moreover, the expressions of NF-κB p65, thioredoxin-interacting protein (TXNIP) and NLR family pyrin domain-containing 3(NLRP3)were examined in CCI rats and microglial cells. Finally, the functional evaluation was determined via mechanical allodynia and thermal hyperalgesia assays.
 Results: The level of RalA decreased in the dorsal horn following CCI. OE of RalA in microglia after LPS insult and CCI-induced rat model significantly decreased the expressions of inflammation promoters (p < 0.05). Mechanistically, OE of RalA mitigated inflammatory response by inhibiting NF-κB/TXNIP/NLRP3 signaling pathway, thus attenuating neuropathic pain in microglial cells and CCI rats.
 Conclusion: These results indicate that the OE of RalA plays a protective role in CCI-induced neuropathic pain via NF-κB/TXNIP/ NLRP3 axis. These findings may provide a promising therapeutic target for neuropathic pain.

To study the effects of electroacupuncture (EA) in chronic constrictive injury (CCI) rat model and the expression of N-methyl-D-aspartate receptor type 2B (NR2B) in ipsilateral spinal dorsal horn in rats to explore the analgesic mechanisms of EA. According to the random number table, totally 180 rats were evenly divided into a sham group, a CCI group, and an EA group. CCI model was conducted with four 4-0 chromic gut ligatures loosely ligated around the left sciatic nerve 1 cm above the trifurcation. Rats in the EA group received 2 Hz EA therapy bilaterally at acupoints of Zusanli (ST 36) and Sanyinjiao (SP 6) once daily (30 min/d) for 30 days after surgery. Paw withdrawal thresholds (PWTs) were measured on 0 (baseline), 1, 3, 7, 15, 30 days after surgery. Rats were sacrificed on 0, 1, 3, 7, 15 and 30 days after surgery, and the L4-5 segments of spinal cord were removed to detect the expression of NR2B by immunohistochemistry and quantitative polymerase chain reaction. PWTs in the CCI group were significantly lower than the sham group at Day 1-30 after surgery, and reached its lowest at Day 1 (P<0.01). After EA treatment, the PWTs recovered rapidly and were significantly higher than those in the CCI group on 3, 7, 15 and 30 days after surgery (P<0.01). The numbers of NR2B-immunoreactive cells of the CCI group significantly increased after CCI surgery compared with the sham group (P<0.01). Compared with the CCI group, stimulation of EA markedly decreased the numbers of NR2B-immunoreactive cells at Day 3, 7, 15 and 30 (P<0.05). In the sham group, NR2B mRNA was expressed at a low level. It increased after CCI surgery, which increased rapidly at Day 7 (P<0.01) and reached its peak value at Day 15 (P<0.01). After EA stimulation, relative quantity of NR2B mRNA expression was less than that in the CCI group at Day 15 and 30 (P<0.05). Low frequency of EA had antinociceptive effect in CCI rat model. The analgesic effects of EA might be through the inhibition of NR2B.

Objective To investigate the effect of sufentanil on chemokine receptors and p38 mitogen activated protein kinase(MAPK) in neuropathic pain (NP) rats. Methods Fifty-four adult Sprague Dawley (SD) rats were divided into the sham operation group (S group), chronic constriction injury (CCI) group (CCI group) and sufentanil group (Suf group) by random number table method, with 18 rats in each group. In CCI group and Suf group, NP rat models were made by CCI. Suf group received daily intraperitoneal injection of sufentanil (10 μg/kg) after operation, while S group and CCI group received the same volume of physiological saline. Paw mechanical withdrawal threshold (PMWT) and paw withdraw thermal latency (PWTL) were measured at 1 d before operation (T0), 3 d (T1), 7 d (T2), and 14 d (T3) after operation. The expression of C-C chemokine receptor type 2 (CCR2), C-X3-C motif chemokine receptor 1 (CX3CR1), total p38MAPK (t-p38), phosphorylated p38MAPK (p-p38) and nuclear factor-κB (NF-κB) p65 protein in the dorsal horn of the spinal cord were detected by Western blot. Results Compared with S group, PMWT and PWTL were significantly decreased in CCI group and Suf group at T1-T3 (P<0.05). The levels of CCR2, CX3CR1, p-p38 and NF-κB p65 protein were significantly increased (P<0.05). Compared with CCI group, PMWT and PWTL were significantly increased in Suf group at T1-T3 (P<0.05), while the levels of CCR2, CX3CR1, p-p38 and NF-κB p65 protein were significantly decreased in Suf group (P<0.05). Conclusions Sufentanil can reduce the expression of chemokine receptors CCR2 and CX3CR1, inhibit the activation of spinal dorsal horn p38MAPK and NF-κB, and alleviate the pain response of NP rats. Key words: Sufentanil; Neuropathic pain; Chemokine receptor; p38 mitogen activated protein kinase

Objective To observe the effect of early use of 0.25 MPa hyperbaric oxygen (HBO) on pain behavior in model rat of neuropathic pain (NP) and explore the mechanism. Methods Fifty-four male Sprague⁃Dawley (SD) rats were randomly divided into 3 groups (18 rats per group) including sham operation, sciatic nerve ligation with chronic constriction injury (CCI) and HBO early⁃treatment groups. The rat model of neuropathic pain was established, and CCI + HBO group received 0.25 MPa HBO treatment for 60 min per day at early stage, continuing for 5 d. The changes in general state of health, the number of paw withdrawal responses, paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were assessed at different time points after operation. Results Compared with sham-operated group, the body weight of rats in CCI group decreased significantly (t = 4.772, P = 0.000) on the 14th day; the body weight of rats in CCI + HBO group was significantly higher than that in CCI group (t = 2.411, P = 0.029). Compared with sham-operated group, reduced PWL immediately after operation (t = 28.345, P = 0.000), and more paw withdrawal responses (t = 12.541, P = 0.000) and decreased PWT (t = 4.032, P = 0.001) from the 3rd day after operation were observed in CCI group. Compared with CCI group, the number of paw withdrawal responses decreased (t = 8.077, P = 0.000), and PWT and PWL increased (t = 2.114, P = 0.049; t = 7.715, P = 0.000) in CCI + HBO group. Conclusion 0.25 MPa HBO treatment at early stage can ameliorate the mechanical and thermal hyperalgesia. HBO may provide a new convenient and effective way for the treatment of neuropathic pain in clinic.

In this study, we examined the relationships between p38 mitogen-activated protein kinase (MAPK) activation in the cuneate nucleus (CN) and behavioral hypersensitivity after chronic constriction injury (CCI) of the median nerve. We further investigated effects of melatonin administration and pinealectomy on p38 MAPK activation and development of hypersensitivity. Using immunohistochemistry and immunoblotting, low levels of phosphorylated p38 (p-p38) MAPK were detected in CN of normal rats. As early as 1day after CCI, p-p38 MAPK levels in the ipsilateral CN were significantly increased (1.4±0.2-fold, P<0.05), which reached a maximum at 7days (5.1±0.4-fold, P<0.001). Double immunofluorescence labeling with cell-specific markers showed that p-p38 MAPK immunoreactive cells co-expressed OX-42, a microglia activation maker, suggesting the expression of p-p38 MAPK in microglia. Microinjection of SB203580, a p38 MAPK inhibitor, into the CN 1day after CCI attenuated injury-induced behavioral hypersensitivity in a dose-dependent manner. Furthermore, animals received melatonin treatment at daily doses of 37.5, 75, 150, or 300mg/kg from 30min before until 3days after CCI. Melatonin treatment dose-dependently attenuated p-p38 MAPK levels, release of pro-inflammatory cytokines, and behavioral hypersensitivity following CCI; conversely, pinealectomy that resulted in a reduction in endogenous melatonin levels exacerbated these effects. In conclusion, median nerve injury-induced microglial p38 MAPK activation in the CN modulated development of behavioral hypersensitivity. Melatonin supplementation eased neuropathic pain via inhibition of p38 MAPK signaling pathway; contrarily, reducing endogenous blood melatonin levels by pinealectomy promoted phosphorylation of p38 MAPK and made rats more vulnerable to nerve injury-induced neuropathic pain.

Objective To investigate the effect of tramadol on the expression of 5-HT1A receptor in the distal'cerebrospinal fluid contacting neurons (CSF-CNs) in mid-brain in a rat model of neuropathic pain. Methods Forty male SPF SD rats weighing 220-280 g were randomly divided into 5 groups (n = 8 each): group Ⅰ normal control (group C); group Ⅱ normal saline (group NS); group Ⅲ tramodol (group T); group Ⅳ neuropathic pain + normal saline (group NP+ NS) and group Ⅴ neuropathic pain + tramadol (group NP + T). Neuropathic pain was induced by chronic constrictive injury (CCI) in group Ⅳ and Ⅴ . Four silk ligatures were placed on the sciatic nerve at 1 mm intervals. In group Ⅱ (NS) and group Ⅲ (T) the sciatic nerve was exposed but not ligated and NS 2 ml/kg and tramadol 10 mg/kg were injected IP respectively, while in group Ⅳ and Ⅴ NS 2 ml/kg and tramadol 10 mg/kg were injected IP respectively on the 7th day after CCI. Paw withdrawal threshold (PWT) to von Frey filament stimulation and paw withdrawal latency (PWL) to noxious thermal stimuli were measured before (T1) and after IP NS or tramadol injection (T2) in group Ⅱ-Ⅴ. The distal CSF-CNs in the mid-brain was labelled with 30% cholera toxin subunit B and horseradish peroxidase compound (CB-HRP) 3 μl injected in left lateral cerebral ventricle. The expression of 5-HT1A receptors was measured by immuno-histochemistry. Results PWT and PWL were significantly decreased after CCI in group Ⅳ (NP + NS) and tramadol significantly inhibited the mechanical and thermal hyperalgesia in group Ⅴ (NP + T). There was no significant difference in the number of distal CSF-CNs among the 5 groups. CCI significantly down-regulated the expression of 5-HT1A in distal CSF-CNs in group Ⅳ(NP+ NS) as compared with group Ⅰ , Ⅱ and Ⅲ and tramadol significantly inhibited the CCI-induced downregulation of 5-HT1A receptor expression. Conclusion Tramadol can ease neuropathic pain by down-regulating the expression of 5-HT1A receptor in distal CSF-CNs in mid-brain. Key words: Tramadol; Neurons; Receptor, serotonin, 5-HT1A; Neuralgia

Qisheng wan decoction alleviates the inflammation of CCI rats via TRP channels

Background &amp; Objective: Neuropathic pain (NP) is a pain due to a somatosensory lesion. NP leads to disruption of health, work, social relationships, hobbies, sleep, mood, and cognitive function. Up till now, the treatment of NP remains unsatisfactory. It makes many patients seek alternative therapies, including wet cupping therapy (WCT). We aimed to analyze the effects of WCT against NP in chronic constriction injury (CCI) in a rat model by assessing the increase in time withdrawal latency (TWL) and GABA-A receptors expression in the spinal cord.&#x0D; Methodology: We used CCI as one of the NP models in Rattus norvegicus species of rats and treated with WCT. We used 21 four months old male rats, divided into 3 groups (n = 7); P1 (sham CCI group), P2 (CCI group), and P3 (CCI plus WCT group). WCT was given two times every week for three weeks with 5 min of first cupping using −200 mmHg, and followed by ten punctures and then 5 min of second cupping using −200 mmHg. TWL assesment was conducted by using hotplate. Expresion of GABA-A receptor was evaluated with immunohistochemistry.&#x0D; Results: WCT significantly increased TWL with P = 0.0001 and decreased expresion of GABA-A receptors in the spinal cord of CCI rat model.&#x0D; Conclusion: This research concluded that wet cupping therapy could increase time withdrawal latency and decrease the expression of GABA-A receptors in the spinal cord in chronic constriction injury rat model. This result suggests a promising method in controlling neuropathic pain. However, further investigations are required to understand the mechanism.&#x0D; Abbreviations: CCI: Chronic Constriction Injury; CT: Cupping Therapy; DCT: Dry Cupping Therapy; NP: Neuropathic Pain; TWL: Time Withdrawal Latency; WCT: Wet Cupping Therapy;&#x0D; Key words: Chronic constriction injury; CCI rat model; GABA-A receptors; Neuropathic pain; Pain; Time withdrawal latency; TWL; Wet cupping therapy.&#x0D; Citation: Hidayati HB, Qurnianingsih E, Widjiati, Khaerunnisa S, Puspamaniar VA, Susetyo RD. Wet cupping therapy increases the time withdrawal latency (TWL) and decreases GABA-A receptor expression in the spinal cord in a rat model of neuropathic pain. Anaesth. pain intensive care 2022;27(1):97−103; DOI: 10.35975/apic.v27i1.2124&#x0D; Received: July 05, 2022; Reviewed: July 08,2022; Accepted: December 12, 2022

The present study observed the effects of repeated electroacupuncture of Zusanli (ST36) and Yanglingquan (GB34) on expression of hippocampal acetylcholinesterase, vesicular acetylcholine transporter, and muscarinic M1 receptor mRNA in chronic constrictive injury (neuropathic pain) and/or ovariotomy rats. Results demonstrated increased expression of hippocampal acetylcholinesterase, vesicular acetylcholine transporter, and muscarinic M1 receptor mRNA, as well as decreased pain threshold, in a rat model of chronic neuropathic pain after electroacupuncture. The effects of electroacupuncture increased with prolonged time, but the above-mentioned effects decreased in memory-deficient animals. Results indicated that repeated electroacupuncture has a cumulative analgesic effect, which is closely associated with upregulation of acetylcholinesterase and vesicular acetylcholine transporter activity, as well as M1 receptor mRNA expression and memory.

Activation of mitogen-activated protein kinases (MAPKs), especially p38 MAPK, plays an important role in the development of central sensitization related to persistent inflammatory pain. Electroacupuncture (EA) is well known to relieve persistent inflammatory pain. However, little is known about relationship between EA and p38 MAPK. Inflammatory pain rat model was induced by intraplantar injection of complete Freund's adjuvant (CFA). Male adult SD rats were randomly divided into the saline group, CFA group, and CFA + EA group. EA (constant saquare wave, 2 Hz and 100 Hz alternating frequencies, intensities ranging from 1 to 2 mA) was applied to bilateral “Zusanli” (ST 36) and “Kunlun” acupoints (BL 60) for 30 min, once per day. The paw edema and paw withdrawal threshold (PWT) were measured at preinjection and days postinjection 1, 3, and 14. Spinal p-p38MAPK- immunoreactivty (p-p38MAPK-IR) cells were detected by immunohistochemistry at postinjection day 3 and 14. EA significantly inhibited paw edema at postinjection days 14 and increased PWT at postinjection days 3 and 14. Moreover, the increasing number of spinal p-p38MAPK-IR cells which was induced by CFA injection was suppressed by EA stimulation. These results indicate that anti-inflammatory and analgesic effect of EA might be associated with its inhibition of spinal p38 MAPK activation and thereby provide a potential mechanism for the treatment of inflammatory pain by EA.

To observe the effect of electroacupuncture (EA) on the expression of Toll like receptor 4(TLR4)and heat shock protein 90(HSP90) in the spinal cord of rats with chronic constriction injury (CCI) of sciatic nerve, so as to explore the mechanism of spinal cord TLR4 and HSP90 in alleviating chronic neuropathic pain by EA. Male Wistar rats were randomized into control, model, EA, HSP90 inhibitor (inhibitor) and EA+ inhibitor groups (n=10 in each group). The neuropathic pain model was established by ligature of the right sciatic nerve to induce CCI. EA (1 mA，2 Hz/15 Hz)was applied at bilateral "Zusanli"(ST36) and "Yanglingquan"(GB34) for 30 min, once daily for 5 days. Rats of the inhibitor and EA+inhibitor groups were given a subcutaneous injection of HSP90 inhibitor geldanamycin (50 μg/kg) at the neck before daily EA. The paw withdrawal latency (PWL) of the bilateral hind-limbs was detected by using an algesia-detector. The contents of interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) in the lumbar spinal cord (L2-L4) tissue were detected by enzyme-linked immunosorbent assay. The relative expression levels of HSP90 and TLR4 proteins in the lumbar spinal cord (L2-L4) were detected using Western blot and immunofluorescence double labeling, respectively. Following CCI, a strong thermal hyperalgesia, an apparent up-regulation of expression of HSP90 and TLR4 proteins and TLR4 in microglia, and increasing levels of IL-1β and TNF-α in the spinal cord were induced in the model group relevant to the control group (P<0.01，P<0.05). Five sessions of EA intervention or inhibitor injection significantly attenuated hyperalgesia, reversed the increase of IL-1β and TNF-α, and down-regulated the expression of TLR4 in microglia (P<0.05). Compared with the model group, the expression of HSP90 was further increased (P<0.05), and those of TLR4 in microglia and neurons were significantly decreased and increased, respectively in the EA group (P<0.05). Compared with the EA group, the levels of PWLD,TLR4 and HSP90 expression, and the proportions of neuronal nuclei antigen（NeuN） and TLR4, and ionized calcium binding adapter molecule （Iba1） and TLR4 co-expressed cells were significantly decreased in the inhibitor group and EA+inhibitor group (P<0.05). The proportion of NeuN and TLR4 co-expression cells in the EA+inhibitor group was significantly higher than that of the inhibitor group (P<0.05). EA stimulation of ST36 and GB34 can alleviate thermal hyperalgesia in CCI rats, which is closely associated with its effect in regulating the expression of TLR4 in the spinal cord neurons and microglia. HSP90 in the spinal cord may be a co-stimulatory molecule for EA induced relief of neuropathic pain by regulating TLR4.

Objective To investigate the effects of adenovirus containing human beta-nerve growth factor (Ad-hNGFβ) gene on substance P (SP) and calcitonin gene-related peptide (CGRP) content of the spinal cord in a rat model of neuropathic pain by chronic constrictive injury (CCI). Methods Forty-eight male SD rats weighing 200-250 g were randomly divided into 3 groups (n=16 each) : group Ⅰ sham operation; group Ⅱ CCI and group Ⅲ CCI + Ad-hNGFβ gene IT. The animals were anesthetized with intraperitoneal choral hydrate 300-350 mg/kg. The right sciatic nerve was exposed and 4 ligatures were placed on the sciatic nerve at 1-2 nun intervals as described by Bennet and Xie[5]. In sham operation group, right sciatic nerve was exposed but not ligated. In group Ⅰ and Ⅱ artificial cerebrnspinal fluid was injected IT instead of Ad-hNGFβ gene. The behavior score and the paw-withdrawal latency (PWL) to radiant heat and mechanical stimulus were measured one day before operation and every 4 days within the 28 days after gene transfection. Four animals were killed at 4, 7, 14 and 28 day after IT gene transfection in each group and lumbar segment (L4-6 ) of the spinal cord was removed for determination of SP and CGRP content by immunohistochemistry. Results The behavior scores were significantly higher and PWL to radiant heat and mechanical stimulus were significantly lower in group Ⅱ and Ⅲ than in group Ⅰ. There was no significant difference in the behavior score and PWL to mechanical stimulus between group Ⅱ and Ⅲ while the PWL to radiant heat was significantly higher in group Ⅲ than in group Ⅱ. After operation SP and CGRP content were significantly higher in group Ⅱ and group Ⅲ than in group Ⅰ , and significangly lower in group Ⅲ than in group Ⅱ 7-28 days after operation. Conclusion The recomhinant Ad-hNGFβ gene transfection can attenuate heat hyperalgesia by reducing SP and CGRP content of the spinal cord in a rat model of neuropathic pain induced by CCI. Key words: Nerve growth factor; Injections, spinal; Transfection; Neuropathic pain; Substance P; Calcitonin gene-related peptide

The p21-activated kinases (PAKs) contain an N-terminal Cdc42/Rac interactive binding domain, which in the group 1 PAKs (PAK1, 2, and 3) regulates the activity of an adjacent conserved autoinhibitory domain. In contrast, the group 2 PAKs (PAK4, 5, and 6) lack this autoinhibitory domain and are not activated by Cdc42/Rac binding, and the mechanisms that regulate their kinase activity have been unclear. This study found that basal PAK6 kinase activity was repressed by a p38 mitogen-activated protein (MAP) kinase antagonist and could be strongly stimulated by constitutively active MAP kinase kinase 6 (MKK6), an upstream activator of p38 MAP kinases. Mutation of a consensus p38 MAP kinase target site at serine 165 decreased PAK6 kinase activity. Moreover, PAK6 was directly activated by MKK6, and mutation of tyrosine 566 in a consensus MKK6 site (threonine-proline-tyrosine, TPY) in the activation loop of the PAK6 kinase domain prevented activation by MKK6. PAK6 activation by MKK6 was also blocked by mutation of an autophosphorylated serine (serine 560) in the PAK6 activation loop, indicating that phosphorylation of this site is necessary for MKK6-mediated activation. PAK4 and PAK5 were similarly activated by MKK6, consistent with a conserved TPY motif in their activation domains. The activation of PAK6 by both p38 MAP kinase and MKK6 suggests that PAK6 plays a role in the cellular response to stress-related signals.

Neuropathic pain is related to the sustained activation of neuroglial cells and the production of proinflammatory cytokines in the spinal dorsal horn. Ghrelin, the endogenous ligand for growth hormone secretagogue receptor 1a (GHSR-1a), has been shown to inhibit the activation of microglia and the release of proinflammatory cytokines. The purpose of this study was to investigate the role of ghrelin/GHSR-1a signaling in neuropathic pain and to understand the associated mechanisms. A rat model of neuropathic pain was established by chronic constriction injury (CCI) of the sciatic nerve. Hyperalgesia and allodynia were evaluated by observing the mechanical withdrawal threshold and the thermal withdrawal latency. The expression levels of ghrelin and GHSR-1a were detected by semiquantitative reverse transcriptase-polymerase chain reaction and Western blot analysis. The levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α were detected using an enzyme-linked immunosorbent assay. The expression levels of p-p38 mitogen-activated protein kinases (p38 MAPK) and nuclear factor-κB (NF-κB) p65 were determined by Western blot and immunohistochemistry analysis. Both ghrelin and GHSR-1a were expressed in the spinal dorsal horns of normal rats and were not significantly different from that of sham rats. However, rats in the CCI model group developed severe hyperalgesia and allodynia, as well as significantly downregulated expression of ghrelin and GHSR-1a. Compared with CCI model rats, intrathecal injection of ghrelin clearly delayed thermal hyperalgesia and mechanical allodynia at 3, 5, and 7 days after CCI; reduced the levels of IL-1β, IL-6, and tumor necrosis factor-α; and inhibited the phosphorylation of p38 MAPK and the activation of NF-κBp65 in the spinal dorsal horn. In addition, the effect of ghrelin could be blocked by [D-Lys]-GHRP-6, a GHSR-1a antagonist. Our present study demonstrated that ghrelin alleviated neuropathic pain through a GHSR-1a-mediated suppression of the p38 MAPK/NF-κB pathway.