Incisional Pain Model Research Articles

The anti-nociceptive effect of BPC-157 on the incisional pain model in rats.

BackgroundThe pentadecapeptide BPC-157 has been shown to have anti-inflammatory and wound healing effects on multiple target tissues and organs. Peptides have potent anti-inflammatory effects on periodontal tissues in rats with periodontitis. Few studies have investigated the effect of BPC-157 on pain after dental procedures or oral surgeries. The purpose of the present study was to investigate the antinociceptive effects of BPC-157 on postoperative incisional pain in rats.MethodsSprague–Dawley rats were randomly divided into five groups: control (saline with the same volume), BPC10 (10 µg/kg of BPC-157), BPC20 (20 µg/kg of BPC-157), BPC40 (40 µg/kg of BPC-157), and morphine (5 mg/kg of morphine). A 1-cm longitudinal incision was made through the skin, fascia, and muscle of the plantar aspect of the hind paw in isoflurane-anesthetised rats. Withdrawal responses were measured using von Frey filaments at 0, 2, 6 h and 4, 7 d after incision. The formalin test was also performed to differentiate its anti-nociceptive effect from an inflammatory reaction or central sensitization. Pain behavior was quantified periodically in phases 1 and 2 by counting the number of flinches in the ipsilateral paw after injection with 30 µL of 5% formalin.ResultsThe threshold of mechanical allodynia was significantly increased in the BPC10, BPC20, BPC40 and morphine groups compared with that in the control group at 2 h. These increasing thresholds then returned to the levels of the control group. The BPC-157 group showed a much higher threshold at 4 days after incision than the control group. The thresholds of the BPC groups, except the morphine group, were normalized 7 days after incision.The flinching numbers of the BPC10, BPC20, BPC40 and morphine groups were significantly decreased in phase 1, but there was no decrease in the BPC-157 groups except the morphine group in phase 2.ConclusionsBPC-157 was effective only for a short period after incision. It was also effective during phase 1 but not during phase 2, as determined by the formalin test. BPC-157 might have a short antinociceptive effect, even though it has anti-inflammatory and wound healing effects.

Extended-release Buprenorphine, an FDAindexed Analgesic, Attenuates Mechanical Hypersensitivity in Rats (Rattus norvegicus).

A new extended-release buprenorphine (XR), an FDA-indexed analgesic, has recently become available to the laboratory animal community. However, the effectiveness and dosing of XR has not been extensively evaluated for rats. We investigated XR's effectiveness in attenuating postoperative hypersensitivity in a rat incisional pain model. We hypothesized that high dose of XR would attenuate mechanical and thermal hypersensitivity more effectively than the low dose of XR in this model. We performed 2 experiments. In experiment 1, male adult Sprague-Dawley rats (n = 31) were randomly assigned to 1 of the 4 treatment groups: 1) saline (saline, 0.9% NaCl, 5 mL/kg, SC, once); 2) sustained-release buprenorphine (Bup-SR; 1.2 mg/kg, SC, once), 3) low-dose extended-release buprenorphine (XR-Lo; 0.65 mg/kg, SC, once), and 4) high-dose extended-release buprenorphine (XR-Hi; 1.3 mg/kg, SC, once). After drug administration, a 1 cm skin incision was made on the plantar hind paw under anesthesia. Mechanical and thermal hypersensitivity were evaluated 1 d before surgery (D-1), 4 h after surgery (D0), and for 3 d after surgery (D1, D2, and D3). In experiment 2, plasma buprenorphine concentration (n = 39) was measured at D0, D1, D2, and D3. Clinical observations were recorded daily, and a gross necropsy was performed on D3. Mechanical and thermal hypersensitivity were measured for 3 d (D0-D3) in the saline group. Bup-SR, XR-Lo, and XR-Hi effectively attenuated mechanical hypersensitivity for D0-D3. Plasma buprenorphine concentrations remained above 1 ng/mL on D0 and D1 in all treatment groups. No abnormal clinical signs were noted, but injection site reactions were evident in the Bup-SR (71%), XR-Lo (75%), and XR-Hi (87%) groups. This study indicates that XR-Hi did not attenuate hypersensitivity more effectively than did XR-Lo in this model. XR 0.65 mg/kg is recommended to attenuate postoperative mechanical hypersensitivity for up to 72 h in rats in an incisional pain model.

Electroacupuncture Alleviates Hyperalgesia by Regulating CB1 Receptor of Spinal Cord in Incisional Neck Pain Rats.

Acupuncture therapy is effective in relieving postoperative pain of neck surgery, but its underlying mechanisms remain largely unknown. This study, in the incisional neck pain rat model, was designed to explore whether the endocannabinoid receptor 1 (CB1) in the cervical spinal cord is involved in the analgesic effect of electroacupuncture (EA) or not.The incisional neck pain model was established by making a longitudinal incision and applied EA treatment of Futu (LI18), Hegu-Neiguan (LI4-PC6), or Zusanli-Yanglingquan (ST36-GB34) for pain relief. The results showed that EA LI18 and EA LI4-PC6 effectively relieve allodynia caused by neck incision, which was obviously better than EA ST34-GB34 (P < 0.05). After EA, the expression levels of CB1 mRNA at 4h in the EALI18 group, and 24 and 48h in both EALI18 and EALI4-PC6 groups, and those of CB1 protein at 4, 24, and 48h in the EALI18 group, and the immunoactivity of CB1 in both EALI18 and EALI4-PC6 groups at 4h were significantly upregulated in contrast to those of the model group (P < 0.05). EA of either acupoint group had no effect on the expression of CB2 protein (P > 0.05). Moreover, the antinociceptive effect of EA was reversed by AM251 (CB1 antagonist). Immunofluorescence dual staining showed that CB1 expressed in astrocytes in the superficial layer (laminae I and II) of dorsal horns of the cervical spinal cord. Therefore, the findings of this study revealed that upregulation of CB1 expression in the cervical spinal cord contributes to the analgesic effect of EA in incisional neck pain rats. The CB1 receptor expresses on astrocytes.

The Effect of Fluoxetine and Ibuprofen on BCG-Induced Alteration in Pain Sensitivity in Mice

Abstract Clinical observations recognized the co-existence and interactions of pain and depression a long time, ago. The aim of this work was to study the effect of ibuprofen and fluoxetine on BCGinduced depressive-like behaviour, on formalin-induced pain, as well as on mechanical allodynia after planter incision in mice. BCG induced a depressive behaviour that was seen in the forced swim test (FST) and the tail suspension test (TST). It also induced a decrease in pain-related behaviour in the formalin test, and an increase in the baseline in mechanical allodynia test compared to the control group. Fluoxetine (80 mg/L of drinking water) showed a significant decrease in the immobility time in the FST and TST and enhanced pain related behaviour in formalin test in the BCG-inoculated group. However, it did not affect the increase in the pain threshold in the planter incision allodynia model. Adding ibuprofen to drinking water (0.2 g/L of drinking water), reversed the depressive like behaviour induced by BCG and enhanced pain-related behaviour in formalin test, in both the total pain-related behaviour and phase 2. It also prevented the increase in the base line induced by BCG. On the other hand, the incisional pain model was not affected by BCG inoculation except at the 2-hour time point, where it showed hypoalgesia, as well.

Effects of a BMI1008 mixture on postoperative pain in a rat model of incisional pain.

The purpose of this study was to evaluate the analgesic effect of BMI1008 (a new drug containing lidocaine, methylene blue, dexamethasone and vitamin B complex) and to investigate the analgesic effect of lidocaine and BMI-L (other components of BMI1008 except lidocaine) at different concentrations in a rat model of incisional pain. Male Sprague-Dawley rats (250-300 g) were used for the incisional pain model simulating postoperative pain. After the operation, normal saline, various concentrations of BMI1008, lidocaine with a fixed concentration of BMI-L, and BMI-L with a fixed concentration of lidocaine were injected at the incision site. The preventive analgesic effect was evaluated using BMI1008 administered 30 min before and immediately after the operation. In addition, BMI1008 was compared with positive controls using intraperitoneal ketorolac 30 mg/kg and fentanyl 0.5 μg/kg. The mechanical withdrawal threshold was measured with a von Frey filament. The analgesic effect according to the concentration of BMI1008, lidocaine with a fixed concentration of BMI-L, and BMI-L with a fixed concentration of lidocaine showed a concentration-dependent response and statistically significant difference among the groups (P <0.001, P <0.001, and P <0.001, respectively). The analgesic effect according to the time point of administration (before and after the operation) showed no evidence of a statistically significant difference between the groups (P = 0.170). Compared with the positive control groups, the results showed a statistically significant difference between the groups (P = 0.024). BMI1008 showed its analgesic effect in a rat model of incisional pain in a concentration-dependent manner. Moreover, BMI-L showed an additive effect on the analgesic effect of lidocaine.

Osmotically balanced, large unilamellar liposomes that enable sustained bupivacaine release for prolonged pain relief in in vivo rat models

To efficiently prolong analgesic effects, we developed osmotically balanced, large unilamellar liposomes (~ 6 μm in diameter) in which highly concentrated bupivacaine (up to 30 mg/mL) was encapsulated, and their sustained bupivacaine release was highly effective in relieving postoperative pain over 24 h in a rat model. Our reverse-phase evaporation method based on non-toxic alcohol, ethanol, enabled simple and cost-effective production of bupivacaine-loaded liposomes, of which osmotic pressure was readily balanced to improve the structural stability of the enlarged unilamellar liposomes along with extension of their shelf life (> a month). The in vitro release profile verified that the release duration of the bupivacaine-loaded liposomes extended up to 6 days. For the in vivo study, male Sprague–Dawley rats were used for the incisional pain model, simulating postoperative pain, and the mechanical withdrawal threshold (MWT) was measured using a von Frey filament. Compared to the control group that received intraplantar administration of normal saline, the group of liposomal bupivacaine showed that the initially increased MWT gradually decreased up to 24 h, and importantly, the analgesic effect of the liposomal bupivacaine was maintained 6 times longer than that of bupivacaine only, proving the potential of effective long-acting anesthetics.

Effect of pregabalin on nociceptive thresholds and immune responses in a mouse model of incisional pain.

BackgroundIt is known that some analgesics as well as pain can affect the immune system. The aim of this study was to investigate the analgesic effect and immunomodulation of pregabalin (PGB) in a mouse incisional pain model.MethodsA postoperative pain model was induced by hind paw plantar incision in male BALB/c mice. Mice were randomly divided into four groups (n = 8) a saline-treated incision (incision), PGB-treated incision (PGB-incision), sham controls without incision or drug treatment (control), and a PGB-treated control (PGB-control). In the PGB treated groups, PGB was administered intraperitoneally (IP) 30 minutes before and 1 hour after the plantar incision. Changes of the mechanical nociceptive thresholds following incision were investigated. Mice were euthanized for spleen harvesting 12 hours after the plantar incision, and natural killer (NK) cytotoxicity to YAC 1 cells and lymphocyte proliferation responses to phytohemagglutinin were compared among these four groups.ResultsMechanical nociceptive thresholds were decreased after plantar incision and IP PGB administration recovered these decreased mechanical nociceptive thresholds (P < 0.001). NK activity was increased by foot incision, but NK activity in the PGB-incision group was significantly lower than that in the Incision group (P < 0.001). Incisional pain increased splenic lymphocyte proliferation, but PGB did not alter this response.ConclusionsIncisional pain alters cell immunity of the spleen in BALB/c mice. PGB showed antinocieptive effect on mouse incisional pain and attenuates the activation of NK cells in this painful condition. These results suggest that PGB treatment prevents increases in pain induced NK cell activity.

Lipid bound extended release buprenorphine (high and low doses) and sustained release buprenorphine effectively attenuate post-operative hypersensitivity in an incisional pain model in mice (Mus musculus).

BackgroundExtended‐release buprenorphine (XR) is indicated for pain management in rodents, but little is known about its use in mice. This study aimed to investigate whether high dose XR effectively attenuates post‐operative hypersensitivity better than low dose XR in a mouse model of incisional pain.MethodsMice (n = 44) were randomly assigned to 1 of 4 treatment groups: (a) saline (1 ml/kg SC, once); (b) sustained release buprenorphine (Bup‐SR, 1 mg/kg SC, once); (c) low dose extended‐release buprenorphine (XR‐lo, 3.25 mg/kg SC, once); (d) high dose extended‐release buprenorphine (XR‐hi, 6.5 mg/kg SC, once). On days −1, 0 (4 hours), 1, 2, and 3, mechanical and thermal hypersensitivities were evaluated, and plasma buprenorphine concentrations were measured.ResultsMechanical (days 0‐2) and thermal (days 0‐1) hypersensitivities were observed in the saline group. Bup‐SR, XR‐lo, and XR‐hi attenuated mechanical hypersensitivity on days 0, 1, and 2. None of the treatment groups, except XR‐Lo on day 0, attenuated thermal hypersensitivity on days 0 or 1. Plasma buprenorphine concentration peaked at 4 hours (day 0) in all treatment groups and remained greater than 1 ng/mL on days 0‐2. No abnormal clinical observations or gross pathologic findings were seen in any groups.ConclusionThe results indicate XR‐hi did not effectively attenuate post‐operative hypersensitivity better than XR‐lo. Thus both 3.25 and 6.5 mg/kg XR are recommended for attenuating post‐operative hypersensitivity for at least up to 48 hours in mice.

Antinociceptive Effects of Sinomenine Combined With Ligustrazine or Paracetamol in Animal Models of Incisional and Inflammatory Pain.

The management of postoperative and inflammatory pain has been a pressing challenge in clinical settings. Sinomenine (SN) is a morphinan derived alkaloid with remarkable analgesic properties in various kinds of pain models. The aim of the current study is to investigate if SN can enhance the effect of ligustrazine hydrochloride (LGZ) or paracetamol (PCM) in animal models of postoperative and inflammatory pain. And to determine if the combined therapeutic efficacies can be explained by pharmacokinetics changes. Pharmacological studies were performed using a rat model of incisional pain, and a mouse model of carrageenan induced inflammatory pain. Pharmacokinetic studies were performed using a microdialysis sampling and HPLC-MS/MS assay method to quantify SN, LGZ, and PCM levels in blood and extracellular fluid in brain. We found that SN plus LGZ or SN plus PCM produced marked synergistic analgesic effects. However, such synergy was subjected to pain modalities, and differed among pain models. Pharmacological discoveries could be partially linked to pharmacokinetic alterations in SN combinations. Though further evaluation is needed, our findings advocate the potential benefits of SN plus LGZ for postoperative pain management, and SN plus PCM for controlling inflammatory pain.

Sustained release buprenorphine effectively attenuates postoperative hypersensitivity in an incisional pain model in neonatal rats (Rattus norvegicus)

Despite the need for safe and effective postoperative analgesia in neonates, research regarding pain management in neonatal rodents is relatively limited. Here, we investigate whether sustained release buprenorphine (Bup SR) effectively attenuates thermal hypersensitivity in a neonatal rat model of incisional pain. Male and female postnatal day 3 Sprague Dawley rat pups (n = 34) were randomly assigned to one of four treatment groups: 1) saline (control), 0.1 mL, once subcutaneously (SC); 2) buprenorphine HCl (Bup HCl), 0.05 mg/kg, once SC; 3) low dose Bup SR (low-SR), 0.5 mg/kg, once SC; 4) high dose Bup SR (high-SR), 1 mg/kg, once SC. Pups were anesthetized with sevoflurane and a 0.5-cm long skin incision was made over the left lateral thigh. The underlying muscle was dissected and closed using surgical glue. Thermal hypersensitivity testing was performed at 24 h prior to surgery and subsequently at 1, 4, 8, 24, and 48 h post-surgery using an infrared diode laser. Thermal hypersensitivity was attenuated at 1 h post-surgery in the Bup HCl group, while it was attenuated through the entire postoperative period in both low-SR and high-SR groups. This data suggests that a single dose of low-SR (0.5 mg/kg) or high-SR (1 mg/kg) effectively attenuates thermal hypersensitivity for at least 8 h in neonatal rat pups.

Nociceptive Sensitization by Activation of Protease-Activated Receptor 2 in a Rat Model of Incisional Pain

Postoperative pain and consequent inflammatory responses after tissue incision adversely affects many surgical patients due to complicated mechanisms. In this study, we examined whether activation of protease-activated receptor 2 (PAR-2), which is stimulated by tryptase from mast cells, elicits nociception and whether the PAR-2 antagonist could reduce incisional nociceptive responses in vivo and in vitro. The effects of a selective PAR-2 antagonist, N3-methylbutyryl-N-6-aminohexanoyl-piperazine (ENMD-1068), pretreatment on pain behaviors were assessed after plantar incision in rats. The effects of a PAR-2 agonist, SLIGRL-NH2, on nociception was assessed after the injection into the hind paw. Furthermore, the responses of C-mechanosensitive nociceptors to the PAR-2 agonist were observed using an in vitro skin–nerve preparation as well. Intraplantar injection of SLIGRL-NH2 elicited spontaneous nociceptive behavior and hyperalgesia. Local administration of ENMD-1068 suppressed guarding behaviors, mechanical and heat hyperalgesia only within the first few hours after incision. SLIGRL-NH2 caused ongoing activity in 47% of C-mechanonociceptors in vitro. This study suggests that PAR-2 may support early nociception after incision by direct or indirect sensitization of C-fibers in rats. Moreover, PAR-2 may play a regulatory role in the early period of postoperative pain together with other co-factors to that contribute to postoperative pain.

Tiletamine/zolazepam and dexmedetomidine with tramadol provide effective general anesthesia in rats.

BackgroundTiletamine/zolazepam is a dissociative anesthetic combination commonly used in small animals but information is limited in rats. The alpha‐2 agonist, dexmedetomidine, has gained popularity in laboratory animal anesthesia. Tramadol is a weak opioid mu agonist. The aim of this study was to assess whether the tiletamine/zolazepam/dexmedetomidine (ZD) combination effectively provides a surgical anesthesia plane comparable to tiletamine/zolazepam/dexmedetomidine with tramadol (ZDT) in a minor procedure in rats.MethodsRats were induced with ZD or ZDT. After the loss of paw withdrawal, a small incision was made on the rats’ left thighs as a surgical stimulus. Rats were maintained under a surgical anesthesia plane by assessing the loss of the paw withdrawal reflex for 45 minutes, then atipamezole was administered. Monitored anesthesia parameters included: (a) physiological parameters – pulse rate (PR), respiratory rate (RR), tissue oxygen saturation (%SpO2), and body temperature; (b) duration parameters – induction time, onset and duration of surgical anesthesia plane, onset of recovery, and recovery time.ResultsPR was significantly lower at 10 minutes in ZD and 5 minutes in ZDT groups. No difference was observed for RR, %SpO2, and body temperature. Likewise, there were no differences for duration parameters: induction time was less than 3 minutes; onset and duration of surgical anesthesia plane were approximately 5 and 45 minutes, respectively; onset of recovery (time to move) was 51 minutes; and recovery time was 52 minutes, respectively.ConclusionThese data suggest the ZD combination provides a surgical anesthesia plane comparable to ZDT in a rat incisional pain model.

GABAergic Inhibition of Spinal Cord Dorsal Horns Contributes to Analgesic Effect of Electroacupuncture in Incisional Neck Pain Rats.

BackgroundAcupuncture has shown to be effective in relieving post-surgical pain. Nonetheless, its underlying mechanisms remain largely unknown. In the present study, we investigated the effect of electroacupuncture (EA) on the expression of GABA, GABA-A receptor (R) and GABA-BR in the spinal cord dorsal horns (DHs), and the involved neural cells in rats with incisional neck pain.Materials and MethodsMale SD rats were randomly divided into control, model, Futu (LI18), Hegu-Neiguan (LI4-PC6), and Zusanli-Yanglingquan (ST36-GB34) groups. The incisional neck pain model was established by making a longitudinal incision and repeated mechanical separation along the thyroid gland region. EA (2Hz/100Hz, 1mA) was applied to LI18, LI4-PC6, ST36-GB34 separately for 30min, once at 4, 24 and 48h after incision. The local thermal pain threshold (TPT) of the focus was measured and the expression of GABA, and GABAR proteins and mRNAs detected by immunofluorescence stain and quantitative RT-PCR, respectively.ResultsThe analgesic effect of LI18 and LI4-PC6 was superior to that of ST36-GB34 in incisional neck pain rats. Moreover, the EA stimulation of LI18 or LI4-PC6 increased the expression of GABA and GABA-Aα2 and GABA-Aβ3, GABA-B1, and GABA-B2 mRNAs in spinal DHs 4h after surgery, while GABA-A and GABA-B antagonists inhibited the analgesic effect of LI18. Immunofluorescence double staining showed that GABA was expressed on astrocytes and neurons, and GABA-B expressed only on neurons.ConclusionEA of both LI18 and LI4-PC6 has a good analgesic effect in incisional neck pain rats, which is closely related to their effects in upregulating the expression of GABA and its receptors in spinal DHs. The effects of LI18 and LI4-PC6 EA are obviously better that those of ST36-GB34 EA, and GABA is expressed on neurons and astrocytes.

Approach Behavior Induced by 10.6-μm Laser Stimulation at Acupoint ST36 in a Rat Model of Incisional Pain.

Objective: Laser stimulation (LS) at both the injury site and specific acupoints may induce analgesic effects. The purpose of this study is to investigate the effects of LS at injury site or acupoint on analgesic-associated approach behavior and determine whether opioid receptors in the anterior cingulate cortex (ACC) were involved. Methods: The left hindpaw incision was established in rats. LS (10.6 μm) was performed at the ipsilateral (left) acupoint ST36 (Zusanli) or locally to the incision site. Characteristic guarding pain behavior was measured to assess incision-induced pain. A two-chamber conditioned place preference (CPP) paradigm was used to measure approach behavior induced by pain relief. To inhibit opioid receptors, naloxone was microinjected into the ACC before LS. Results: A delayed analgesic effect (24 h after treatment) was induced in both the LS groups (ST36 and incision site) as compared with the sham control or model groups (p < 0.05). An immediate (30 min after the end of the LS) decrease in guarding pain (p < 0.001) and CPP for the LS chamber (p < 0.001) were observed only in the ST36 LS group. The administration of naloxone in ACC inhibited the LS-induced analgesic effect and CPP (p < 0.05). Conclusions: Our results highlight the novel approach behavior of pain relief induced by 10.6-μm LS at ST36 in a rat model of incisional pain, and implicate ACC opioid receptor signaling in these actions.

Use of Flavored Tablets of Gabapentin and Carprofen to Attenuate Postoperative Hypersensitivity in an Incisional Pain Model in Rats (Rattus norvegicus).

Providing postoperative analgesia to rats by oral administration, compared with injections, reduces stress from frequent handling and is technically easier for investigators. The purpose of this study was to investigate whether bacon-flavored tablets containing gabapentin, carprofen or a combination of both drugs effectively attenuates postoperative mechanical and thermal hypersensitivity in a rat model of incisional pain. Forty-eight Sprague-Dawley rats were randomly assigned to 1 of 5 treatment groups: placebo tablet; a single, subcutaneous injection of buprenorphine sustained release at 1.2 mg/kg; gabapentin 90 mg/tablet; carprofen 5 mg/tablet; gabapentin 90 mg and carprofen 5 mg/tablet (gabapentin/carprofen). Tablets were given to rats on days -3, -2, -1, 0 (surgery), 1, and 2. Rats were anesthetized using isoflurane. A 1 cm skin incision was made aseptically on the plantar surface of the left hindpaw and closed by using suture. Mechanical (von Frey monofilament) and thermal (Hargreaves method) hypersensitivity were tested daily, and analyzed on days -1, 1, 2, and 3. The amount of tablet consumed was recorded daily; postoperatively rats consumed 101 to 133 mg/kg of gabapentin, 5.5 to 5.8 mg/kg of carprofen, and 86-137/1.9-3 mg/kg of gabapentin/carprofen, respectively. Both the gabapentin and carprofen groups displayed attenuated mechanical hypersensitivity on all 3 postsurgical days and decreased thermal hypersensitivity on Day 3. The gabapentin/ carprofen group showed attenuated mechanical hypersensitivity on Day 2 and 3, but no significant reduction of thermal hypersensitivity. These data suggest that both gabapentin and carprofen, given orally by flavored tablet, effectively attenuate postoperative mechanical hypersensitivity for 3 d after surgery in a rat model of incisional pain.

Global transcriptome analysis of rat dorsal root ganglia to identify molecular pathways involved in incisional pain.

To develop non-opioid therapies for postoperative incisional pain, we must understand its underlying molecular mechanisms. In this study, we assessed global gene expression changes in dorsal root ganglia neurons in a model of incisional pain to identify pertinent molecular pathways. Male, Sprague–Dawley rats underwent infiltration of 1% capsaicin or vehicle into the plantar hind paw (n = 6–9/group) 30 min before plantar incision. Twenty-four hours after incision or sham (control) surgery, lumbar L4–L6 dorsal root ganglias were collected from rats pretreated with vehicle or capsaicin. RNA was isolated and sequenced by next generation sequencing. The genes were then annotated to functional networks using a knowledge-based database, Ingenuity Pathway Analysis. In rats pretreated with vehicle, plantar incision caused robust hyperalgesia, up-regulated 36 genes and downregulated 90 genes in dorsal root ganglias one day after plantar incision. Capsaicin pretreatment attenuated pain behaviors, caused localized denervation of the dermis and epidermis, and prevented the incision-induced changes in 99 of 126 genes. The pathway analyses showed altered gene networks related to increased pro-inflammatory and decreased anti-inflammatory responses in dorsal root ganglias. Insulin-like growth factor signaling was identified as one of the major gene networks involved in the development of incisional pain. Expression of insulin-like growth factor -2 and IGFBP6 in dorsal root ganglia were independently validated with quantitative real-time polymerase chain reaction. We discovered a distinct subset of dorsal root ganglia genes and three key signaling pathways that are altered 24 h after plantar incision but are unchanged when incision was made after capsaicin infiltration in the skin. Further exploration of molecular mechanisms of incisional pain may yield novel therapeutic targets.

Upregulation of spinal glucose-dependent insulinotropic polypeptide receptor induces membrane translocation of PKCγ and synaptic target of AMPA receptor GluR1 subunits in dorsal horns in a rat model of incisional pain

It is unclear whether glucose-dependent insulinotropic polypeptide receptor (GIPR) signaling plays an important role in spinal nociception. We hypothesized that the spinal GIPR is implicated in central sensitization of postoperative pain. Our data showed that the cumulative pain scores peaked at 3 h, kept at a high level at 1 d after incision, gradually decreased afterwards and returned to the baseline values at 5 d after incision. Correspondingly, the expression of GIPR in spinal cord dorsal horn peaked at 1 d after incision, and returned to the baseline value at 5 d after incision. The double-labeling immunofluorescence demonstrated that spinal GIPR was expressed in dorsal horn neurons, but not in astrocyte or microglial cells. At 1 d after incision, the effects of intrathecal saline, GIPR antagonist (Pro3)GIP on pain behaviors were investigated. Our data showed that at 30 min and 60 min following intrathecal treatments of 300 ng (Pro3)GIP, the cumulative pain scores were decreased and paw withdrawal thresholds to mechanical stimuli were increased when compared to those immediately before intrathecal treatments. Accordingly, at 30 min after intrathecal injections, the membrane translocation levels of PKCγ and the GluR1 expression in postsynaptic membrane in ipsilateral dorsal horns to the incision were significantly upregulated in rats with intrathecal saline injections, as compared to normal control group. At 30 min after intrathecal treatment, (Pro3)GIP inhibited the membrane translocation levels of PKCγ and the GluR1 expression in postsynaptic membrane in ipsilateral dorsal horns. Our study indicates that upregulation of spinal GIPR may contribute to pain hypersensitivity through inducing membrane translocation level of PKCγ and synaptic target of AMPA receptor GluR1 subunits in ipsilateral dorsal horns of rats with plantar incision.

Dezocine attenuates the remifentanil-induced postoperative hyperalgesia by inhibition of phosphorylation of CaMKⅡα

Remifentanil, ultra-short-acting μ-opioid receptor agonist, has the greatest advantage in analgesia but could increase postoperative pain scores and induces postoperative hyperalgesia. Dezocine is a mixed opioid receptor partial agonist/antagonist and has been used for postoperative hyperalgesia management in clinical patients,but the potential molecular mechanism is still unclear. Ca2+/calmodulin-dependent protein kinase Ⅱ(CaMKⅡ) has been reported involved in remifentanil-induced hyperalgesia (RIH) in previous studies, but the relationship between CaMKⅡ and dezocine in RIH is still unclear. To investigate the mechanism of dezocine in RIH, we used a remifentanil induced postoperative hyperalgesia (RIPH) in incisional pain model of mouse. We subcutaneously infused remifentanil (40 μg/kg) to induce postoperative hyperalgesia. Dezocine (1.5 mg/kg, 3.0 mg/kg, and 6.0 mg/kg) was infused subcutaneously with remifentanil using the apparatus pump for 30 min. Paw withdrawal thermal latency (PWTL) and paw withdrawal mechanical threshold (PWMT) were used to assess thermal hyperalgesia and mechanical allodynia. Western blotting analysis and immunohistochemistry analysis were used to assess the expression of phosphorylated CaMKⅡα (p-CaMKⅡα) in somatosensory cortex, hippocampus and spinal cord. Subcutaneous infusion of remifentanil enhanced postoperative pain induced by surgical incision and increased PWTL and PWMT. Dezocine dose-dependently decreased the PWTL and PWMT in RIPH model. Correlating with behavioral effects, dezocine inhibited remifentanil-induced up-regulation of p-CaMKⅡα expression in somatosensory cortex, hippocampus and spinal cord. Dezocine could attenuate RIPH by suppressing p-CaMKⅡα.

Electroacupuncture alleviated incisional neck pain possibly by suppressing TNF-α expression and increasing IL-4/IL-4 receptor signaling in cervical dorsal part of spinal cord in incisio-nal neck pain rats

To observe the effect of electroacupuncture (EA) on incisional pain and expression of tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10) and interleukin-4 (IL-4) of cervical dorsal part of spinal cord in rats with incisional neck pain, so as to explore its analgesic mechanisms. Eighty-four male SD rats were randomly divided into normal control, model, EA-Futu(LI18) and EA-Zusanli(ST36)-Yanglingquan(GB34, EA-ST36-GB34) groups (n=21 in each group). The incisional neck pain model was established by making a longitudinal incision along the bilateral cervical thyroid regions and repeated mechanical separation stimulation. For rats of the EA groups, EA (2 Hz/100 Hz, 1 mA) was applied to bilateral LI18 or ST36-GB34 for 30 min/ time during the surgery, and 20 and 44 h after surgery, respectively. The thermal pain threshold (TPT) of the incisional region was detected. The immunoactivity of TNF-α and IL-10 of the dorsal portion of the cervical spinal cord (C2-C5) was detected by immunofluorescence, and the expression of TNF-α, IL-10, IL-4 and IL-4 receptor (IL-4R) mRNAs was determined by quantitative real-time PCR. Compared with the normal group, the TPT of the incisional area was significantly decreased at 4, 24 and 48 h after neck-incision (P<0.05), the levels of TNF-α mRNA, IL-10 mRNA and TNF-α IL-10 immunoactivity at 24 h were remarkably increased (P<0.05), and the expression of IL-4R mRNA was considerably decreased at 24 h in the model group (P<0.05). Following EA intervention, the TPT, and expression levels of IL-4 mRNA and IL-4R mRNA were significantly increased at 24 h after surgery in the EA-LI18 group relevant to the model group (P<0.05), while the expression level of TNF-α(coexpressed with microgliacytes) in the EA-LI18 group, and TNF-α mRNA expression at 24 h in both EA-LI18 and EA-ST36-GB34 groups, as well as the expression of IL-10 and IL-10 mRNA at 24 h in both EA-LI18 and EA-ST36-GB34 groups were significantly decreased (P<0.05). The effect of EA LI18 was significantly superior to that of EA ST36-GB34 in up-regulating TPT and expression of IL-4 mRNA and IL-4R mRNA at 24 h (P<0.05). EA of LI18 has an analgesic effect in incisional neck pain rats, which may be related to its effect in down-regulating the expression of TNF-α, IL-10 and promoting IL-4 /IL-4R signaling in dorsal portions of the cervical spinal cord. The analgesic effect of EA LI18 is better than that of EA ST36-GB34.

Propentofylline reduces mechanical allodynia and induces mitogen-activated protein kinase phosphatase-1: An experimental study in a rat model of acute incisional pain

ABSTRACTBackground: Acute postoperative pain can lead to long hospital stays, dysfunction, and even chronic pain. Mitogen-activated protein kinases (MAPKs) are important in pain signaling. The activity of MAPKs are negatively regulated by dual specificity phosphatases such as mitogen- activated protein kinase phosphatase-1 (MKP-1), which specifically dephosphorylates MAPK p38. Since, propentofylline (PPF) can reduce pain by inhibiting MAPKs, we hypothesized that PPF relieves acute pain by inducing MKP-1 levels.Objective: Investigating the anti-nociception effect of an intrathecal injection of PPF in a rat model of acute incisional pain and the role of MKP-1 and phospho-p38 in the mechanism by which PPF ameliorates acute pain.Methods: We assessed the mechanical withdrawal threshold (MWT) response before and after incisional pain surgery between a control group and a group receiving PPF, and also assessed the effect of pre-treatment with Ro 31–8220, an MKP-1 inhibitor, on PPF effects. Following the MWT, lumbar spinal cord samples were also analyzed by western blot analysis to determine MKP-1 and p-p38 levels.Results: Following surgery, the MWT response was decreased over 5 h–3 d accompanied by decreased expression of MKP-1 and increased p-p38 levels. An intrathecal injection of PPF increased the MWT response and increased spinal cord MKP-1 expression, but decreased p-p38 levels. Pre-treatment of rats with Ro31-8220 partly reversed the analgesic effect of PPF and its effect on MKP-1/p-p38 levels.Conclusions: This study suggests that an increase in MKP-1 levels and a corresponding decrease in p-p38 levels may be the mechanism by which PPF ameliorates acute pain.