The Effect of Tramadol Versus Sufentanil on Controlling Postoperative Pain for Men Who Smoke and Do Not Smoke: A Randomized Clinical Trial.

BACKGROUND: Smoking behavior alters the analgesic threshold, which challenges postoperative pain management for patients who smoke. OBJECTIVES: We aimed to assess the analgesic efficacy of tramadol versus sufentanil in relieving postoperative pain for patients who do and do not smoke who underwent a partial hepatectomy. STUDY DESIGN: Double-blinded randomized controlled trial. SETTING: Eastern Hepatobiliary Surgery Hospital, Shanghai, China. METHODS: All patients in this study were men. A total of 66 patients who smoke were randomly assigned to receive tramadol or sufentanil (n = 33 each). In addition, a total of 66 patients who do not smoke were randomly assigned to receive tramadol or sufentanil (n = 33 each). The primary outcome was the consumption of additional analgesics within the first 48 hours to control postoperative pain. Secondary outcomes included the postoperative pain level, the frequency of postoperative nausea and vomiting, the sedation score, and the frequency of fever within 48 hours postsurgery. RESULTS: A significant interaction between "analgesic strategy" and "smoking history" was detected on the consumption of additional analgesics. In those who smoke, the requests for additional doses of analgesics were significantly less in those receiving tramadol than those receiving sufentanil; such a difference was not observed in those who do not smoke. The postoperative pain level was not significantly different between the tramadol group and the sufentanil group within patients who smoke within 48 hours postsurgery. The incidence of treatment-related adverse events was not significantly different between the tramadol group and the sufentanil group within both those who do and do not smoke. LIMITATIONS: Only men patients were included. Also, the superior analgesic effect and the incidence of adverse events of tramadol in patients who smoke were only assessed within the first 48 hours postsurgery. CONCLUSIONS: Our data suggest that tramadol has a better analgesic effect than sufentanil in relieving postoperative pain in patients who smoke.

Corrigendum: Role of MicroRNA-143 in Nerve Injury-Induced Upregulation of Dnmt3a Expression in Primary Sensory Neurons.

[This corrects the article DOI: 10.3389/fnmol.2017.00350.].

Differentially Expressed Genes in the Brain of Aging Mice With Cognitive Alteration and Depression- and Anxiety-Like Behaviors.

Despite the great increase in human lifespan with improved medical care, the physiological and pathological changes such as memory and cognitive disorders and associated anxiety and depression are major concern with aging. Molecular mechanisms underlying these changes are little known. The present study examined the differentially expressed genes (DEGs) and the genes with differentially expressed isoforms in three brain regions, anterior cingulate cortex (ACC), amygdala and hippocampus, throughout the lifespan of mice. Compared to 2-month old mice, both 12- and 24-month old mice displayed memory and cognitive impairments in the Morris water maze, Y-maze, and novel object recognition tests and depression- and anxiety-like behaviors in the tail suspension, forced swimming, open field, and elevated plus maze tests. RNA sequencing analysis identified 634 and 1078 DEGs in ACC, 453 and 1015 DEGs in the amygdala and 884 and 1054 DEGs in hippocampus in the 12- and 24-month old mice, respectively. Similarly, many genes with differentially expressed isoforms were also identified in these three brain regions in the 12- and 24-month old mice. Further functional analysis revealed that many DEGs and the genes with differentially expressed isoforms in the ACC and amygdala were mapped to depression- and anxiety-related genes, respectively and that a lot of DEGs and the genes with differentially expressed isoforms in hippocampus were mapped to cognitive dysfunction-related genes from both 12- and 24-month old mice. All of these mapped DEGs and the genes with differentially expressed isoforms were closely related to neuroinflammation. Our findings indicate that these neuroinflammation-related DEGs and the genes with differentially expressed isoforms are likely new targets in the management of memory/cognitive impairment and emotional disorders during the aging.

MicroRNA-330 Directs Downregulation of the GABABR2 in the Pathogenesis of Pancreatic Cancer Pain.

Pancreatic cancer is one of the most aggressive and deadly malignancies with a very poor prognosis. Pancreatic cancer-induced visceral pain is very common and is generally presented among the initial symptoms in patients; such pain is strongly associated with poor quality of life, impaired functional activity, and decreased survival. However, the principal neurobiological mechanisms of pain caused by pancreatic cancer have not been fully elucidated. Accumulating studies have shown that miRNAs play a major role in chronic pain by suppressing key molecules involved in nociception. In the present study, we report that microRNA (miR)-330 is highly expressed in the spinal dorsal horn (SDH) of nude mice with pancreatic cancer pain. Mimicking pancreatic carcinoma-induced SDH miR-330 upregulation by microinjection of miR-330 mimic into the SDH significantly induced abdominal mechanical allodynia in normal nude mice. Additionally, we found that the expression of GABABR2 was significantly decreased in the SDH of nude mice with pancreatic cancer pain and was regulated directly by miR-330 both in vitro and in vivo. Furthermore, inhibition of miR-330 rescued the expression of GABABR2 and alleviated pancreatic carcinoma-induced abdominal pain hypersensitivity in nude mice with pancreatic carcinoma. These results show that miR-330 participates in the genesis of pancreatic carcinoma-induced pain hypersensitivity by inhibiting GABABR2 expression in the SDH and might be a potential therapeutic target for pancreatic cancer pain.

Wrist-ankle acupuncture attenuates cancer-induced bone pain by regulating descending pain-modulating system in a rat model.

BACKGROUND: Cancer-induced bone pain (CIBP) presents a multiple-mechanism of chronic pain involving both inflammatory and neuropathic pain, and its pathogenesis is closely related to endogenous descending system of pain control. However, the action mechanism underlying the effects of wrist-ankle acupuncture (WAA) versus electroacupuncture (EA) on CIBP remains unknown. METHODS: Thirty-two Wistar rats were divided into sham, CIBP, EA-treated and WAA-treated groups. CIBP was induced in rats of the latter three groups. Time courses of weight and mechanical hyperalgesia threshold (MHT) were evaluated. After 6 days of EA or WAA treatment, the expressions of 5-hydroxytryotamine type 3A receptor (5-HT3AR) and µ-opioid receptor (MOR) in rostral ventromedial medulla (RVM) and/or spinal cord, as well as the levels of 5-HT, ß-endorphin, endomorphin-1 and endomorphin-2 in RVM and spinal cord, were detected. RESULTS: Injection of cancer cells caused decreased MHT, which was attenuated by EA or WAA (P < 0.05). WAA had a quicker analgesic effect than EA (P < 0.05). No significant difference of MOR in RVM was found among the four groups. EA or WAA counteracted the cancer-driven upregulation of 5-HT3AR and downregulation of MOR in spinal cord (P < 0.05), and upregulation of 5-HT and downregulation of endomorphin-1 in both RVM and spinal cord (P < 0.05). ß-endorphin and endomorphin-2 in RVM and spinal cord decreased in CIBP group compared with sham group (P < 0.05), but EA or WAA showed no significant effect on them, although a tendency of increasing effect was observed. CONCLUSION: WAA, similar to EA, alleviated mechanical hyperalgesia in CIBP rats by suppressing the expressions of 5-HT and 5-HT3AR, and increasing the expressions of MOR and endomorphin-1 in RVM-spinal cord pathway of the descending pain-modulating system. However, WAA produced a quicker analgesic effect than EA, the mechanisms of which need further investigation.

Intravenous Dexmedetomidine Combined with Ultrasound-Guided Rectus Sheath Block for Open Gastrectomy: a Prospective Randomized Trial.

PURPOSE: To compare the incidences of positive hemodynamic response (HR > 100 beats min-1 or SBP > 160 mmHg) during abdominal exploration and moderate pain after surgery, when using dexmedetomidine infusion and rectus sheath block. METHODS: One hundred patients undergoing open gastrectomy were randomized to receive rectus sheath block with ropivacaine (Group B, n = 25), initial loading dose of 0.6 µg kg-1 dexmedetomidine, followed by a continuous infusion of 0.2 µg kg-1 h-1 throughout surgery (Group D, n = 25), both rectus sheath block and dexmedetomidine (Group BD, n = 25), or neither rectus sheath block nor dexmedetomidine (Group C, n = 25). General anesthesia techniques were standardized. HR, SBP, and positive hemodynamic response at peritoneum incision (TPI), 5 min (TAE-5), 10 min (TAE-10), and 15 min (TAE-15) after the start of abdominal exploration, and incidences of moderate postoperative pain were recorded. RESULTS: Positive hemodynamic responses during abdominal exploration were more common in Groups B (82%) and C (74%) than in Groups D (14%) and BD (9%) (all P = 0.000). HR and SBP were lower in Groups D and BD, compared with those in Groups C and B (all P < 0.05). Compared with TPI, HR and SBP increased significantly in Groups B and C during abdominal exploration (all P < 0.05), but not in Group BD (except HR at TAE-15). The incidences of moderate pain in Groups B and BD were noticeably lower than in Groups C and D at 1 h, 2 h, and 6 h after surgery (all P < 0.0083). CONCLUSION: Dexmedetomidine infusion combined with rectus sheath block provided more hemodynamic stability during abdominal exploration and better analgesia after surgery.

Inhibition of Mast Cell Degranulation Relieves Visceral Hypersensitivity Induced by Pancreatic Carcinoma in Mice.

Cancer pain induced by pancreatic carcinoma is one of the most common symptoms and is difficult to endure, especially in the advanced stage. Evidence suggests that mast cells are recruited and degranulate in enteric disease-related visceral hypersensitivity. However, whether mast cells promote the visceral pain induced by pancreatic carcinoma remains unclear. Here, using toluidine blue staining and western blotting, we observed that mast cells were dramatically recruited to tissues surrounding pancreatic carcinoma, but not inside the carcinoma in patients with severe visceral pain. The levels of mast cell degranulation products, including tryptase, histamine, and nerve growth factor, were significantly increased in pericarcinoma tissues relative to their levels in normal controls, as evidenced by enzyme-linked immunosorbent assay. We determined that systemic administration of mast cell secretagogue compound 48/80 exacerbated pancreatic carcinoma-induced visceral hypersensitivity in a male BALB/c nude mouse model as assessed by measuring the hunching behavior scores and mechanical withdrawal response frequency evoked by von Frey stimulation. In contrast, the mast cell stabilizer ketotifen dose-dependently alleviated pancreatic cancer pain. In addition, we observed incomplete development of abdominal mechanical hyperalgesia and hunching behavior in mast cell-deficient mice with pancreatic carcinoma. However, ketotifen did not further attenuate visceral hypersensitivity in mast cell-deficient mice with carcinoma. Finally, we confirmed that intraplantar injection of pericarcinoma supernatants from BALB/c nude mice but not mast cell-deficient mice caused acute somatic nociception. In conclusion, our findings suggest that mast cells contribute to pancreatic carcinoma-induced visceral hypersensitivity through enrichment and degranulation in pericarcinoma tissues. The inhibition of mast cell degranulation may be a potential strategy for the therapeutic treatment of pancreatic carcinoma-induced chronic visceral pain.

TET1 Overexpression Mitigates Neuropathic Pain Through Rescuing the Expression of µ-Opioid Receptor and Kv1.2 in the Primary Sensory Neurons.

Peripheral nerve injury downregulates the expression of the µ-opioid receptor (MOR) and voltage-gated potassium channel subunit Kv1.2 by increasing their DNA methylation in the dorsal root ganglion (DRG). Ten-eleven translocation methylcytosine dioxygenase 1 (TET1) causes DNA demethylation. Given that DRG MOR and Kv1.2 downregulation contribute to neuropathic pain genesis, this study investigated the effect of DRG TET1 overexpression on neuropathic pain. Overexpression of TET1 in the DRG through microinjection of herpes simplex virus expressing full-length TET1 mRNA into the injured rat DRG significantly alleviated the fifth lumbar spinal nerve ligation (SNL)-induced pain hypersensitivities during the development and maintenance periods, without altering acute pain or locomotor function. This microinjection also restored morphine analgesia and attenuated morphine analgesic tolerance development after SNL. Mechanistically, TET1 microinjection rescued the expression of MOR and Kv1.2 by reducing the level of 5-methylcytosine and increasing the level of 5-hydroxymethylcytosine in the promoter and 5' untranslated regions of the Oprml1 gene (encoding MOR) and in the promoter region of the Kcna2 gene (encoding Kv1.2) in the DRG ipsilateral to SNL. These findings suggest that DRG TET1 overexpression mitigated neuropathic pain likely through rescue of MOR and Kv1.2 expression in the ipsilateral DRG. Virus-mediated DRG delivery of TET1 may open a new avenue for neuropathic pain management.

Posttraumatic stress disorder: from diagnosis to prevention.

Posttraumatic stress disorder (PTSD) is a chronic impairment disorder that occurs after exposure to traumatic events. This disorder can result in a disturbance to individual and family functioning, causing significant medical, financial, and social problems. This study is a selective review of literature aiming to provide a general outlook of the current understanding of PTSD. There are several diagnostic guidelines for PTSD, with the most recent editions of the DSM-5 and ICD-11 being best accepted. Generally, PTSD is diagnosed according to several clusters of symptoms occurring after exposure to extreme stressors. Its pathogenesis is multifactorial, including the activation of the hypothalamic-pituitary-adrenal (HPA) axis, immune response, or even genetic discrepancy. The morphological alternation of subcortical brain structures may also correlate with PTSD symptoms. Prevention and treatment methods for PTSD vary from psychological interventions to pharmacological medications. Overall, the findings of pertinent studies are difficult to generalize because of heterogeneous patient groups, different traumatic events, diagnostic criteria, and study designs. Future investigations are needed to determine which guideline or inspection method is the best for early diagnosis and which strategies might prevent the development of PTSD.

Role of MicroRNA-143 in Nerve Injury-Induced Upregulation of Dnmt3a Expression in Primary Sensory Neurons.

Peripheral nerve injury increased the expression of the DNA methyltransferase 3A (Dnmt3a) mRNA and its encoding Dnmt3a protein in injured dorsal root ganglia (DRG). This increase is considered as an endogenous instigator in neuropathic pain genesis through epigenetic silencing of pain-associated genes (such as Oprm1) in injured DRG. However, how DRG DNMT3a is increased following peripheral nerve injury is still elusive. We reported here that peripheral nerve injury caused by the fifth spinal nerve ligation (SNL) downregulated microRNA (miR)-143 expression in injured DRG. This downregulation was required for SNL-induced DRG Dnmt3a increase as rescuing miR-143 downregulation through microinjection of miR-143 mimics into injured DRG blocked the SNL-induced increase in Dnmt3a and restored the SNL-induced decreases in Oprm1 mRNA and its encoding mu opioid receptor (MOR) in injured DRG, impaired spinal cord central sensitization and neuropathic pain, and improved morphine analgesic effects following SNL. Mimicking SNL-induced DRG miR-143 downregulation through DRG microinjection of miR143 inhibitors in naive rats increased the expression of Dnmt3a and reduced the expression of Oprm1 mRNA and MOR in injected DRG and produced neuropathic pain-like symptoms. These findings suggest that miR-143 is a negative regulator in Dnmt3a expression in the DRG under neuropathic pain conditions and may be a potential target for therapeutic management of neuropathic pain.

Trypsin-protease activated receptor-2 signaling contributes to pancreatic cancer pain.

Pain treatment is a critical aspect of pancreatic cancer patient clinical care. This study investigated the role of trypsin-protease activated receptor-2 (PAR-2) in pancreatic cancer pain. Pancreatic tissue samples were collected from pancreatic cancer (n=22) and control patients (n=22). Immunofluorescence analyses confirmed colocalization of PAR-2 and neuronal markers in pancreatic cancer tissues. Trypsin levels and protease activities were higher in pancreatic cancer tissue specimens than in the controls. Supernatants from cultured human pancreatic cancer tissues (PC supernatants) induced substance P and calcitonin gene-related peptide release in dorsal root ganglia (DRG) neurons, and FS-NH2, a selective PAR-2 antagonist, inhibited this effect. A BALB/c nude mouse orthotopic tumor model was used to confirm the role of PAR-2 signaling in pancreatic cancer visceral pain, and male Sprague-Dawley rats were used to assess ambulatory pain. FS-NH2 treatment decreased hunch scores, mechanical hyperalgesia, and visceromotor reflex responses in tumor-bearing mice. In rats, subcutaneous injection of PC supernatant induced pain behavior, which was alleviated by treatment with FS-NH2 or FUT-175, a broad-spectrum serine protease inhibitor. Our findings suggest that trypsin-PAR-2 signaling contributes to pancreatic cancer pain in vivo. Treatment strategies targeting PAR-2 or its downstream signaling molecules might effectively relieve pancreatic cancer pain.

DNMT3a contributes to the development and maintenance of bone cancer pain by silencing Kv1.2 expression in spinal cord dorsal horn.

Abstract: Metastatic bone tumor-induced changes in gene transcription and translation in pain-related regions of the nervous system may participate in the development and maintenance of bone cancer pain. Epigenetic modifications including DNA methylation regulate gene transcription. Here, we report that intrathecal injection of decitabine, a DNA methyltransferase (DNMT) inhibitor, dose dependently attenuated the development and maintenance of bone cancer pain induced by injecting prostate cancer cells into the tibia. The level of the de novo DNMT3a, but not DNMT3b, time dependently increased in the ipsilateral L4/5 dorsal horn (not L4/5 dorsal root ganglion) after prostate cancer cells injection. Blocking this increase through microinjection of recombinant adeno-associated virus 5 (AAV5) expressing Dnmt3a shRNA into dorsal horn rescued prostate cancer cells-induced downregulation of dorsal horn Kv1.2 expression and impaired prostate cancer cells-induced pain hypersensitivity. In turn, mimicking this increase through microinjection of AAV5 expressing full-length Dnmt3a into dorsal horn reduced dorsal horn Kv1.2 expression and produced pain hypersensitivity in the absence of prostate cancer cells injection. Administration of neither decitabine nor virus affected locomotor function and acute responses to mechanical, thermal, or cold stimuli. Given that Dnmt3a mRNA is co-expressed with Kcna2 mRNA (encoding Kv1.2) in individual dorsal horn neurons, our findings suggest that increased dorsal horn DNMT3a contributes to bone cancer pain through silencing dorsal horn Kv1.2 expression. DNMT3a may represent a potential new target for cancer pain management.

G9a participates in nerve injury-induced Kcna2 downregulation in primary sensory neurons.

Nerve injury-induced downregulation of voltage-gated potassium channel subunit Kcna2 in the dorsal root ganglion (DRG) is critical for DRG neuronal excitability and neuropathic pain genesis. However, how nerve injury causes this downregulation is still elusive. Euchromatic histone-lysine N-methyltransferase 2, also known as G9a, methylates histone H3 on lysine residue 9 to predominantly produce a dynamic histone dimethylation, resulting in condensed chromatin and gene transcriptional repression. We showed here that blocking nerve injury-induced increase in G9a rescued Kcna2 mRNA and protein expression in the axotomized DRG and attenuated the development of nerve injury-induced pain hypersensitivity. Mimicking this increase decreased Kcna2 mRNA and protein expression, reduced Kv current, and increased excitability in the DRG neurons and led to spinal cord central sensitization and neuropathic pain-like symptoms. G9a mRNA is co-localized with Kcna2 mRNA in the DRG neurons. These findings indicate that G9a contributes to neuropathic pain development through epigenetic silencing of Kcna2 in the axotomized DRG.

Contribution of the Suppressor of Variegation 3-9 Homolog 1 in Dorsal Root Ganglia and Spinal Cord Dorsal Horn to Nerve Injury-induced Nociceptive Hypersensitivity.

BACKGROUND: Peripheral nerve injury-induced gene alterations in the dorsal root ganglion (DRG) and spinal cord likely participate in neuropathic pain genesis. Histone methylation gates gene expression. Whether the suppressor of variegation 3-9 homolog 1 (SUV39H1), a histone methyltransferase, contributes to nerve injury-induced nociceptive hypersensitivity is unknown. METHODS: Quantitative real-time reverse transcription polymerase chain reaction analysis, Western blot analysis, or immunohistochemistry were carried out to examine the expression of SUV39H1 mRNA and protein in rat DRG and dorsal horn and its colocalization with DRG µ-opioid receptor (MOR). The effects of a SUV39H1 inhibitor (chaetocin) or SUV39H1 siRNA on fifth lumbar spinal nerve ligation (SNL)-induced DRG MOR down-regulation and nociceptive hypersensitivity were examined. RESULTS: SUV39H1 was detected in neuronal nuclei of the DRG and dorsal horn. It was distributed predominantly in small DRG neurons, in which it coexpressed with MOR. The level of SUV39H1 protein in both injured DRG and ipsilateral fifth lumbar dorsal horn was time dependently increased after SNL. SNL also produced an increase in the amount of SUV39H1 mRNA in the injured DRG (n = 6/time point). Intrathecal chaetocin or SUV39H1 siRNA as well as DRG or intraspinal microinjection of SUV39H1 siRNA impaired SNL-induced allodynia and hyperalgesia (n = 5/group/treatment). DRG microinjection of SUV39H1 siRNA also restored SNL-induced DRG MOR down-regulation (n = 6/group). CONCLUSIONS: The findings of this study suggest that SUV39H1 contributes to nerve injury-induced allodynia and hyperalgesia through gating MOR expression in the injured DRG. SUV39H1 may be a potential target for the therapeutic treatment of nerve injury-induced nociceptive hypersensitivity.

Identification of Early RET+ Deep Dorsal Spinal Cord Interneurons in Gating Pain.

The gate control theory (GCT) of pain proposes that pain- and touch-sensing neurons antagonize each other through spinal cord dorsal horn (DH) gating neurons. However, the exact neural circuits underlying the GCT remain largely elusive. Here, we identified a new population of deep layer DH (dDH) inhibitory interneurons that express the receptor tyrosine kinase Ret neonatally. These early RET+ dDH neurons receive excitatory as well as polysynaptic inhibitory inputs from touch- and/or pain-sensing afferents. In addition, they negatively regulate DH pain and touch pathways through both pre- and postsynaptic inhibition. Finally, specific ablation of early RET+ dDH neurons increases basal and chronic pain, whereas their acute activation reduces basal pain perception and relieves inflammatory and neuropathic pain. Taken together, our findings uncover a novel spinal circuit that mediates crosstalk between touch and pain pathways and suggest that some early RET+ dDH neurons could function as pain "gating" neurons.

Dorsal root ganglion transcriptome analysis following peripheral nerve injury in mice.

BACKGROUND: Peripheral nerve injury leads to changes in gene expression in primary sensory neurons of the injured dorsal root ganglia. These changes are believed to be involved in neuropathic pain genesis. Previously, these changes have been identified using gene microarrays or next generation RNA sequencing with poly-A tail selection, but these approaches cannot provide a more thorough analysis of gene expression alterations after nerve injury. METHODS: The present study chose to eliminate mRNA poly-A tail selection and perform strand-specific next generation RNA sequencing to analyze whole transcriptomes in the injured dorsal root ganglia following spinal nerve ligation. Quantitative real-time reverse transcriptase polymerase chain reaction assay was carried out to verify the changes of some differentially expressed RNAs in the injured dorsal root ganglia after spinal nerve ligation. RESULTS: Our results showed that more than 50 million (M) paired mapped sequences with strand information were yielded in each group (51.87 M-56.12 M in sham vs. 51.08 M-57.99 M in spinal nerve ligation). Six days after spinal nerve ligation, expression levels of 11,163 out of a total of 27,463 identified genes in the injured dorsal root ganglia significantly changed, of which 52.14% were upregulated and 47.86% downregulated. The largest transcriptional changes were observed in protein-coding genes (91.5%) followed by noncoding RNAs. Within 944 differentially expressed noncoding RNAs, the most significant changes were seen in long interspersed noncoding RNAs followed by antisense RNAs, processed transcripts, and pseudogenes. We observed a notable proportion of reads aligning to intronic regions in both groups (44.0% in sham vs. 49.6% in spinal nerve ligation). Using quantitative real-time polymerase chain reaction, we confirmed consistent differential expression of selected genes including Kcna2, Oprm1 as well as lncRNAs Gm21781 and 4732491K20Rik following spinal nerve ligation. CONCLUSION: Our findings suggest that next generation RNA sequencing can be used as a promising approach to analyze the changes of whole transcriptomes in dorsal root ganglia following nerve injury and to possibly identify new targets for prevention and treatment of neuropathic pain.

Inhibition of GAP-43 by propentofylline in a rat model of neuropathic pain.

Neural plasticity within the spinal nociceptive network may be fundamental to the chronic nature of neuropathic pain. The relation of growth-associated protein-43 (GAP-43), a protein involved in the nerve fiber growth and sprouting, to pain hypersensitivity has been investigated. Glial activation and inflammatory cytokines released by microglia and astrocytes are considered to be involved in the neural sprouting and plasticity. In the present study, the anti-nociception effect of propentofylline, a glial modulating agent, was investigated in a rat chronic constriction injury (CCI) model aiming to explore the role of GAP-43 expression. Our results demonstrated that propentofylline could attenuate the CCI-induced mechanical allodynia and thermal hyperalgesia and inhibit the astrocyte activation and production of IL-1ß. GAP-43 expression was also down-regulated by intrathecal propentofylline. These findings suggest that astrocyte activation is involved in the regulation of GAP-43 expression and propentofylline might be used in the treatment of neuropathic pain.

Effect of recombinant adenovirus coding for endomorphin-2 on neuropathic pain in rats.

OBJECTIVE: To construct a transgene expressing human endomorphin-2 by linking the signal peptide of mouse nerve growth factor (PN) to a human endomorphin-2 DNA sequence containing a short linker recognized by the protease FURIN and test the analgesic effect of endomorphin-2 on neuropathic pain. METHODS: The transgene was inserted into the cosmid pAxCAwt to generate PN-EM-2-pAxCAwt. The recombinant adenovirus Ad-PNEM2 was packaged and propagated in HEK293 cells. After the Ad-PNEM2-infected NIH3T3 cells had been cultured, protein expression was examined by immunofluorescence and ELISA. A CCI rat model was constructed and the Ad-PNEM2 was administered intrathecally. The rats' pain thresholds (PWL) were measured and the presence of endomorphin-2 in the cerebrospinal fluid was confirmed through ELISA. RESULTS: The Ad-PNEM2 expressed endomorphin-2 smoothly and abundantly in NIH3T3 cells at a significantly higher rate than the viral control (P<0.01) or blank control (P<0.01). The expressed endomorphin-2 was mainly observed in the cytoplasm. The concentration of endomorphin-2 in the cerebrospinal fluid increased 1 day after injection and peaked between 7 and 14 days after injection. After injection, PWL approached normal levels in the operated study group. No significant change was observed in the control groups. There was a significant correlation between PWL and endomorphin-2 level (r = 0.944, P<0.001). CONCLUSION: The constructed human endomorphin-2 transgene was expressed effectively, and endomorphin-2 expressed by the recombinant adenovirus altered the threshold to thermal stimulus and showed good analgesic effect.

Down-regulation of GAP-43 by inhibition of caspases-3 in a rat model of neuropathic pain.

BACKGROUND: Neuropathic pain remains a prevalent and persistent clinical problem due to incomplete understanding of its pathogenesis. OBJECTIVE: The present study aimed to investigate the role of caspase-3 in the neuropathic pain in rats with chronic constriction injury (CCI). METHODS: SD rats were randomly assigned four groups (n=18 per group): sham group, normal saline group (NS group), Z-DEVD-FMK group (DEVD group) and RNA interference group (siRNA group). Z-DEVD-FMK (1 U/30 µl), siRNA targeting caspase-3 (10 µg/30 µl) and NS of equal volume were intrathecally administered once daily for 5 days starting 1 day before surgery in the DEVD, siRNA and NS group, respectively. Thermal hyperalgesia was assessed at one day before and 1, 2, 4, 5, 6, 7 and 10 days after surgery. The mRNA and protein expressions of caspase-3 were measured by real time PCR and immunofluorescence assay. Apoptosis was detected by TUNEL staining. GAP-43 expression was measured by immunofluorescence and western blot assays. RESULTS: The right paw withdrawal latency (PWL) was decreased after CCI (P<0.05). TUNEL-positive neurons and the mRNA and protein expressions of caspase-3 in the spinal cord were increased significantly. After Z-DEVD-FMK or siRNA treatment, TUNEL-positive neurons were decreased, PWLs increased (P<0.05) and the mRNA and protein expressions of caspase-3 decreased. The expression of GAP-43, a sprouting related protein, was decreased in the DEVD and siRNA group as compared to NS group (P<0.05). Up-regulation of GAP-43 following CCI was decreased following caspase-3 inhibition. Following sciatic nerve ligation, the gene expression, translation and transcription are significantly changed in the neurons which finally results in neuron apoptosis. The neuron apoptosis induce the up-regulation of GAP-43 expression leading to hyperalgesia. CONCLUSION: Caspase-3 mediated neuron apoptosis is probably responsible for the neuropathic pain in CCI rats. Inhibition of caspase-3 may serve as a treatment of neuropathic pain.