Animal Model Of Postoperative Pain Research Articles

Epigallocatechin-3-Gallate Modulates Postoperative Pain by Regulating Biochemical and Molecular Pathways

Treating postoperative (PO) pain is a clinical challenge. Inadequate PO pain management can lead to worse outcomes, for example chronic post-surgical pain. Therefore, acquiring new information on the PO pain mechanism would increase the therapeutic options available. In this paper, we evaluated the role of a natural substance, epigallocatechin-3-gallate (EGCG), on pain and neuroinflammation induced by a surgical procedure in an animal model of PO pain. We performed an incision of the hind paw and EGCG was administered for five days. Mechanical allodynia, thermal hyperalgesia, and motor dysfunction were assessed 24 h, and three and five days after surgery. At the same time points, animals were sacrificed, and sera and lumbar spinal cord tissues were harvested for molecular analysis. EGCG administration significantly alleviated hyperalgesia and allodynia, and reduced motor disfunction. From the molecular point of view, EGCG reduced the activation of the WNT pathway, reducing WNT3a, cysteine-rich domain frizzled (FZ)1 and FZ8 expressions, and both cytosolic and nuclear β-catenin expression, and the noncanonical β-catenin–independent signaling pathways, reducing the activation of the NMDA receptor subtype NR2B (pNR2B), pPKC and cAMP response element-binding protein (pCREB) expressions at all time points. Additionally, EGCG reduced spinal astrocytes and microglia activation, cytokines overexpression and nuclear factor kappa-light-chain-enhancer of activated B cells (NFkB) pathway, downregulating inducible nitric oxide synthase (iNOS) activation, cyclooxygenase 2 (COX-2) expression, and prostaglandin E2 (PGE2) levels. Thus, EGCG administration managing the WNT/β-catenin signaling pathways modulates PO pain related neurochemical and inflammatory alterations.

Propofol attenuates postoperative hyperalgesia via regulating spinal GluN2B-p38MAPK/EPAC1 pathway in an animal model of postoperative pain.

Total intravenous anesthesia with propofol has been shown to reduce postoperative pain in some clinical studies, but knowledge of its underlying analgesic mechanism remains limited. In this study, we compared the analgesic effects of propofol versus isoflurane in an animal model of postoperative pain and evaluated its underlying molecular mechanisms. Plantar incision was made in the hind paws of rats under general anesthesia with 2.5% of inhalational isoflurane (isoflurane group) or intravenous infusion of propofol (1.5mgkg-1 min-1 , propofol group). Mechanical allodynia was assessed by paw withdrawal threshold before and after incision. Spinal dorsal horns (L3-L5) were harvested 1hr after incision to assess the level of phosphorylated GluN2B, p38MAPK, ERK, JNK, and EPAC using Western blot and immunofluorescence. Mechanical allodynia induced by plantar incision peaked at 1hr and lasted for 3days after incision. It was significantly less in the propofol group compared with the isoflurane group in the first 2hr following incision. The incision-induced increases in phosphorylated GluN2B, p38MAPK, and EPAC1 were significantly reduced in the propofol group. The number of spinal dorsal neurons co-expressed with EPAC1 and c-Fos after the incision was significantly lower in the propofol group. Propofol reduced pain responses in an animal model of postoperative pain and suppressed the spinal GluN2B-p38MAPK/EPAC1 signaling pathway. Since the p38MAPK/EPAC pathway plays a critical role in the development of postoperative hyperalgesia, our results provide evidence-based behavioral, molecular, and cellular mechanisms for the analgesic effects of propofol when used for general anesthesia. These findings may provide a new mechanism for the postsurgical analgesic effect of propofol, which is particularly interesting during the subacute period after surgery as it is the critical period for the development of persistent postsurgical pain.

(303) - The mast cell receptor mrgprb2 contributes to inflammatory pain via immune cell modulation

Although the mechanisms of postoperative pain are still incompletely understood, research has shed light on one potentially important immune cell. As one of the key effector cells in the inflammatory process, mast cells are an important contributor to pain pathophysiology. The role of mast cells in mediating postoperative pain is incompletely understood, although studies using mast cell stabilizers demonstrate that this immune cell is involved in contributing to nociception in animal models of postoperative pain. Thus, there is a compelling need for fundamental research aimed at understanding the mechanisms of mast cells in postoperative pain. Towards this objective, our lab has previously published data identifying a novel mast cell specific receptor, Mas-related G-protein-coupled receptor B2 (MRGB2) and its human orthologue, MRGX2, in non-allergenic activation of mast cells. To evaluate the role of MRGB2 in postoperative pain we utilized a hindpaw incision model. After baselines were measured, mice were anesthetized and a 5-mm incision beginning 2 mm from the proximal edge of the right heel was made. Curved forceps elevated the underlying muscle. A mattress suture of 8–0 nylon on a TG175-8 needle were then used to close the incision. Antibiotic ointment (Bacitracin Zinc Ointment) was then applied. Male C57bl/6 wild-type (WT) or MRGB2KO (n = 6/group) were tested 24 h after incision surgery. Behavioral testing was done utilizing the radiant heat test and Von Frey filaments. At 24 hours post-surgery we saw significant reduction in both mechanical and thermal allodynia in MRGB2 KO mice but not WT, indicating that mast cells contribute to postoperative allodynia via MRGB2. Further study of the mechanisms underlying the role of this receptor in mediating incision induced pain may provide potential strategies for the development of novel analgesics to treat debilitating postoperative pain.

Ameliorative Potential of Standardized Extract of Condalia buxifolia Reissek in Attenuating the Postoperative Pain: Evidence for the Inhibition of AMPA and Kainate in the Spinal Cord

Acute pain post-surgery is one of the major problems of public health, and its treatment is still a challenge. In this study, it was investigated the analgesic effect of a standardized methanolic extract of Condalia buxifolia (MECb) (30 and 100 mg/kg, i.g.) in a plantar incision surgery (PIS) model in mice, and the possible mechanism that underlying its effect. The effect of MECb was evaluated on the hyperalgesia (mechanical, cold and heat stimuli), and in this same model, it was analyzed the effect of MECb (100 mg/kg, i.g.) on the concentration of cytokines (TNF-α, IL-1β, IL-10) and nerve growth factor (NGF) in the paw and spinal cord. Further we investigated the effects of MECb (100 mg/kg, i.g.) on the nocifensive behaviour (spontaneous pain and hyperalgesia) induced by AMPA and kainate. Moreover, the safety profile of prolonged treatment with MECb (100 and 300 mg/kg, i.g.) and involvement of C fibers sensitive to capsaicin in its effect (100 mg/kg, i.g.) was evaluated. MECb showed a marked reduction on mechanical and heat hyperalgesia, and reduced the concentrations of TNF-α, IL-1β, and NGF. The treatment with MECb prevented the nocifensive behaviour and central sensitization caused by AMPA and kainate. Moreover, the analgesic effect of MECb was not affected by the ablation of the central afferent C fibers, and it showed reduced toxicity, indicating good safety and efficacy. The current data showed, for the first time, the analgesic and anti-inflammatory effect of MECb in an animal model of postoperative pain. The results support and suggest the use of MECb as an alternative treatment and a possible source of analgesics substances to postoperative pain.

(296) MRGB2 contributes to mechanical and thermal allodynia in an animal model of postoperative pain

Although the mechanisms of postoperative pain are still incompletely understood, research has shed light on one potentially important immune cell. As one of the key effector cells in the inflammatory process, mast cells are an important contributor to pain pathophysiology. The role of mast cells in mediating postoperative pain is incompletely understood, although studies using mast cell stabilizers demonstrate that this immune cell is involved in contributing to nociception in animal models of postoperative pain. Thus, there is a compelling need for fundamental research aimed at understanding the mechanisms of mast cells in postoperative pain. Towards this objective, our lab has previously published data identifying a novel mast cell specific receptor, Mas-related G-protein-coupled receptor B2 (MRGB2) and its human orthologue, MRGX2, in non-allergenic activation of mast cells.1 To evaluate the role of MRGB2 in postoperative pain we utilized a hindpaw incision model. After baselines were measured, mice were anesthetized and a 5-mm incision beginning 2 mm from the proximal edge of the right heel was made. Curved forceps elevated the underlying muscle. A mattress suture of 8–0 nylon on a TG175-8 needle were then used to close the incision. Antibiotic ointment (Bacitracin Zinc Ointment) was then applied. Male C57bl/6 wild-type (WT) or MRGB2KO (n=6/group) were tested 24 h after incision surgery. Behavioral testing was done utilizing the radiant heat test and Von Frey filaments. At 24 hours post-surgery we saw significant reduction in both mechanical and thermal allodynia in MRGB2 KO mice but not WT, indicating that mast cells contribute to postoperative allodynia via MRGB2. Further study of the mechanisms underlying the role of this receptor in mediating incision induced pain may provide potential strategies for the development of novel analgesics to treat debilitating postoperative pain. (1. McNeil B, et al. Nature 2015.)

Development and Characterization of a Novel, Anatomically Relevant Rat Model of Acute Postoperative Pain

Acute postoperative pain remains a significant health care issue. Development of anatomically relevant animal models of postoperative pain, with improved predictive validity, would advance understanding of postoperative pain mechanisms and improve treatment outcomes. This study aimed to develop, characterize, and validate a rat model of acute postoperative pain associated with inguinal hernia repair based on the Lichtenstein inguinal hernia repair procedure (without hernia induction). We hypothesized that the surgery would result in reduced spontaneous locomotor activity, which would represent a pain-related phenotype. Postsurgical characterization involved extensive monitoring of home cage and open field locomotor activity, as well as mechanical hypersensitivity and assessment of c-Fos expression in the dorsal horn of the spinal cord. In pharmacologic validation studies, rats received morphine, carprofen, or paracetamol 1 hour before, and/or immediately after, surgery. Rats that underwent hernia repair surgery exhibited significantly lower horizontal and vertical activities in the home cage and open field in the early postsurgical period, compared with sham rats or rats that underwent skin incision only. Morphine, carprofen, and paracetamol attenuated the surgery-induced reductions in locomotor activity, to varying degrees. Surgery was associated with significantly increased c-Fos expression in the ipsilateral dorsal horn of the spinal cord, an effect attenuated by carprofen treatment. These results support the development and characterization of a novel, anatomically relevant animal model of acute postoperative pain that may facilitate development of improved treatment regimens. PerspectiveAcute pain following inguinal hernia repair can be difficult to treat. Here we report, for the first time, the development of a novel, anatomically relevant rat model to facilitate improved understanding and treatment of acute postoperative pain following inguinal hernia repair.

Surgical incision induces phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites and GluR1 trafficking in spinal cord dorsal horn via a protein kinase Cγ-dependent mechanism

Spinal α-amino-3-hydroxy-5-methy-4-isoxazole propionate (AMPA) receptor plays an important role in acute pain induced by surgical tissue injuries. Our previous study has shown that the enhanced phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites by protein kinase C (PKC) in the spinal cord dorsal horn is involved in post-surgical pain hypersensitivity. However, which isoforms of PKC are responsible for the phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites remains to be established. In the present study, using an animal model of postoperative pain, we found that surgical tissue injuries enhanced the membrane translocation level of PKCγ, but not PKCα, βI, and βII, and induced the trafficking of GluR1, but not GluR2 into neuronal plasma membrane. Intrathecal (i.t.) pretreatment of small interfering RNA targeting PKCγ to reduce the PKCγ expression in the spinal cord significantly attenuated the pain hypersensitivity and inhibited the phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites as well as GluR1 membrane trafficking. Our study indicates that the surgical incision-induced phosphorylation of AMPA receptor GluR1 subunits at Serine-831 sites and GluR1 trafficking are regulated by a PKCγ-dependent mechanism.

Effect of pentoxiflline on the spinal cord glial cells activation in a rat model of postoperative pain

Objective To investigate the effect of intraperitoneal administration of pentoxifylline on the development of hyperalgesia and the activation of glial cells in a rat model of postoperative pain. Methods Sixty male SD rats weight 190 g-220 g were randomly divided into 2 groups: control group (NS group) and treatment group (PTX group), in which 50 mg/kg saline vehicle or pentoxifylline (n=30) was given intraperitoneally 15 min before surgery and continued once a day to the 5th day after the operation, respectively.The animal model of postoperative pain was established by incision hind paw. Cumulative pain score and paw withdrawal threshold were measured at 1 d before operation and then at 1, 2, 3, and 5 h and 1, 2, 3, and 5 d after operation.Spinal cord tissue samples from rats were taken for analysis of glial fibrillary acid protein (GFAP) and ionized calcium bindingadaptor molecule-1 (Iba-1) expression by means of immunohistochemistry at the following times after operation: 1, 2, 3, and 0.8, 6.6±0.5, 8.6±0.7, 10.2±0.4, 7.0±0.6 and 5.6±0.5 in the PTX group respectively, less than the NS group with 4.0±0.6, 6.0±and 3 d, the PWT were (5.8±1.6), (5.2±1.1), (4.4±0.6), (4.9±0.4), (5.2±1.1), (7.6±1.8) and (10.4±1.6) g in the PTX group respectively, more than the NS group with (2.4 ±0.8), (2.1±0.5), (2.0±0.5), (2.1±0.3), (2.3±0.5), (4.5±0.9)and(8.1±1.4) g 205.6±4.2 and 230.2±3.2 in the PTX group respectively, lower than the NS group with 244.1±4.9, 258.6±4.12 and 276.2±3.4 (P＜the PTX group respectively, lower than the NS group with 230±3 and 205±4 (P＜0.05). Conclusion Pentoxifylline can attenuate the process of mechanical allodynia in a rat model of postoperative pain, its main mechanism may be related to the inhibition of glial cells activation in the spinal cord. Key words: Pentoxifylline; Postoperative pain; Astrocyte; Microglia

Interleukin-1 signaling is required for induction and maintenance of postoperative incisional pain: Genetic and pharmacological studies in mice

Postoperative incisional pain is characterized by persistent acute pain in the area of the cut, and is associated with release of proinflammatory cytokines, including interleukin-1 (IL-1), which play important hyperalgesic and allodynic roles in various inflammatory conditions. In the present study, we tested the role of IL-1 signaling in postoperative incisional pain using three mouse strains impaired in IL-1 signaling due to deletion of the IL-1 type I receptor on a mixed genetic background (IL-1rKO) or congenic background (IL-1rKOCog), or due to transgenic over-expression of IL-1 receptor antagonist (IL-1raTG). We used the relevant wild-type (WT) mice both as controls for the mutant strains, and for assessing the effects of pharmacological blockade of IL-1-signaling. Mechanosensitivity was assessed using the von-Frey filament test before, and up to 4 days following plantar incision, an animal model of postoperative pain. WT mice developed significant allodynia in the incised, compared with the intact, hind-paw beginning 3h after the incision and lasting up to 48h postoperatively. In contrast, IL-1rKO, IL-1rKOCog, and IL-1raTG mice, as well as WT mice chronically treated with IL-1ra, did not display increased mechanical pain sensitivity in either hind-paw. To test the hypothesis that IL-1-signaling is also involved in the maintenance of postoperative pain, WT mice were acutely treated with IL-1ra 24h following the incision, when allodynia was already evident. This treatment reversed the allodynic response throughout the observation period. Together, these findings suggest that IL-1 plays a critical role in the development and maintenance of postoperative incisional pain.

Effect of male hypogonadism on mechanical hyperalgesia and spinal clonidine analgesia in a validated animal model of postoperative pain

Effect of male hypogonadism on mechanical hyperalgesia and spinal clonidine analgesia in a validated animal model of postoperative pain

Room A, 10/17/2000 2: 00 PM - 4: 00 PM (PS) Contribution of Peripheral Capsaicin Receptors to Thermal Hyperalgesia in an Animal Model of Postoperative Pain

Room A, 10/17/2000 2: 00 PM - 4: 00 PM (PS) Contribution of Peripheral Capsaicin Receptors to Thermal Hyperalgesia in an Animal Model of Postoperative Pain

Effect of continuous spinal remifentanil infusion on behaviour and spinal glutamate release evoked by subcutaneous formalin in the rat

Injection of formalin into the hind paw of the rat evokes a biphasic nociceptive behavioural response, which is considered to be an animal model of postoperative pain in humans. The initial response (phase 1) is caused by activation of peripheral nociceptors and is followed by a second phase attributed to ongoing activity in primary afferents and increased sensitivity of dorsal horn neurones. The latter effect is thought to result from glutamate-mediated N-methyl-D-aspartate receptor activation. In studies to date it has been difficult to discriminate mechanisms underlying phase 1 and phase 2 events because of the long-lasting half-times of intrathecally administered opioids. To further understanding of the opioid pharmacology of the two different phases of the formalin test, we have studied behavioural activity and spinal glutamate release after intrathecal administration of remifentanil, a new short-lasting mu opioid. Intrathecal remifentanil 3 micrograms microliter-1 min-1 delivered during phase 1 inhibited behavioural response during phase 1 (100%), but did not abolish subsequent phase 2 behavioural activity completely (67 (12) %). Intrathecal remifentanil administered separately in phase 1 and phase 2 revealed a similar ED50 (0.2 microgram microliter-1 min-1) for inhibition of the behavioural responses. In vivo, spinal microdialysis showed incomplete reduction in glutamate concentrations in response to intrathecal remifentanil administration; this in turn inhibited phase 1 behavioural responses. Therefore we contend that supramaximal doses of intrathecal remifentanil sufficient to inhibit phase 1 activity still permitted sufficient glutamate release to allow spinal facilitation. Incomplete suppression of spinal excitatory neurotransmitter release by intrathecal opioids is consistent with spinal wind-up that is triggered during phase 1 and results in phase 2 afferent drive. This might reflect one of the mechanisms underlying post-operative pain.