Hindpaw Mechanical Withdrawal Thresholds Research Articles

Effects of electroacupuncture on ethology, microglia activation and P2X7 receptor expression in periaqueductal gray in rats with migraine

To observe the effects of electroacupuncture(EA) at "Fengchi"(GB20) on the ethology, microglia activation and P2X7 receptor(P2X7R) expression in the periaqueductal gray(PAG) in recurrent migraine rat model, so as to explore the underlying mechanism of EA reducing central sensitization of migraine. Thirty-six male SD rats were randomly divided into control, model and EA groups, with 12 rats in each group. Recurrent migraine model was induced using repea-ted dural electrical stimulation once another day(the 1st, 3rd, 5th, 7th and 9th days), for a total of 5 times; rats in the EA group received EA treatment(2 Hz/15 Hz, 0.8-1 mA) at GB20 after dural electrical stimulation, for 10 min every time, once a day for 9 days; rats in the control group only received electrode placement. The facial and hindpaw mechanical withdrawal threshold was detected by using an electronic von-Frey on the 0th(baseline), 2nd, 4th, 6th, and 8th days. Microglia activation in the PAG was evaluated by using immunofluorescence staining to detect the number of ionized calcium binding adaptor molecule-1(Iba-1)-labeled microglia. Expression levels of microglia marker Iba-1, inflammatory factor interleukin(IL)-1β and P2X7R were detected by Western blot. Compared with the control group, the facial and hindpaw mechanical withdrawal threshold of rats were significantly reduced on the 2nd, 4th, 6th, and 8th days(P<0.01，P<0.001); the microglia in the PAG area were significantly activated, with the number of Iba-1-positive microglia, and the expression levels of Iba-1, IL-1β and P2X7R proteins significant increased(P<0.001, P<0.05) in the model group. Compared with the model group, the facial and hindpaw mechanical withdrawal threshold of rats were significantly increased on the 4th, 6th, and 8th days(P<0.05，P<0.001，P<0.01), and the above indicators were significantly reversed (P<0.05) in the EA group. EA at GB20 can significantly improve facial and hindpaw mechanical withdrawal threshold of migraine rats, and its possible mechanism may be related to inhibiting microglia activation mediated by P2X7R in the PAG.

Effect of electroacupuncture on spontaneous pain during the synovial inflammatory response stage and allodynia at the later stage in rats with knee osteoarthritis

To observe the effect of electroacupuncture (EA) on pain behavior, synovial inflammatory response and demyelination of saphenous nerve in the rats modeled with knee osteoarthritis (KOA) and explore the effect mechanism of EA for reliving allodynia. Eighty-four male SD rats were randomly divided into a control group, a model group and an EA group, 28 rats in each one. Intra-articular injection of sodium monoiodoacetate (MIA) was administered in right knee joint of each rat in the model group and the EA group to establish the KOA model. In the EA group, separately, on day 5, 7 and 9 after modeling, EA was applied at "Zusanli" (ST 36) and "Yanglingquan" (GB 34) on the right side, with disperse-dense wave (2 Hz/15 Hz), 1 mA in current intensity, for 30 min in one intervention, once a day, and 3 interventions were required. On the 9th day after modeling, the weight-bearing rate was calculated for the affected limbs of the rats in each group, the synovial morphological changes were observed using HE and Masson staining, flow cytometry was adopted to detect the synovial immunocyte counts, and MSD multi-spot assay was used to detected the synovial inflammatory cytokine content. On the 14th day after modeling, the hind-paw mechanical withdrawal threshold was observed in each group and the ultrastructure of the saphenous nerve was observed under transmission electron microscopy. On the 9th day after modeling, compared with the control group, the weight-bearing rate of the affected limb was reduced (P<0.01), the synovial hyperplasia, inflammatory cell infiltration and synovial fibrosis occurred in the affected limb; the counts of synovial CD11b+ cells and M1 macrophages (CD11b+CD86+) were increased (P<0.01), the contents of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-1β, IL-10 and IL-13 in the synovial tissue were elevated (P<0.01, P<0.05) for the rats of the model group. Compared with the model group, the weight-bearing rate of the affected limb was increased (P<0.05), the synovial hyperplasia, inflammatory cell infiltration and synovial fibrosis were mitigated, the counts of CD11b+ cells and M1 macrophages (CD11b+CD86+) in the synovial tissue, and the contents of TNF-α and IL-6 were reduced (P<0.01, P<0.05) in the EA group. On the 14th day after modeling, the hind-paw mechanical withdrawal threshold was reduced in the model group when compared with the control group (P<0.01), and it was increased in the EA group when compared with the model group (P<0.05). Besides, in the model group, obviously, the myelin sheath structure was destroyed, the myelin layer was disintegrated and loosened, the axon was extruded or the layer thicken and cracked. Compared with the model group, the injury of saphenous nerve was alleviated remarkably in the EA group. The intervention with EA may attenuate the synovial inflammatory response and the injury of saphenous nerve in the affected limb of the rat with KOA, so that the spontaneous pain during the synovial inflammatory response stage and allodynia at the later stage are relieved.

Yaobishu Regulates Inflammatory, Metabolic, Autophagic, and Apoptosis Pathways to Attenuate Lumbar Disc Herniation.

Objective Here, we aimed to explore the main mechanism of Yaobishu (YBS) in lumbar disc herniation (LDH). Methods and Results Eighteen compounds that might act on LDH were obtained through a combination of network pharmacology prediction and identification by high-performance liquid chromatography-mass spectrometry. The key compounds were palmitic acid and trans-4-hydroxy-3-methoxycinnamate (cinnamate). KEGG analysis demonstrated that palmitic acid target genes mainly regulate the PPAR signaling pathway, Ras signaling pathway, and fatty acid metabolism. Cinnamate target genes were primarily involved in chemical carcinogenesis-receptor activation, lipid and atherosclerosis, the HIF-1 signaling pathway, and nitrogen metabolism. The rat LDH model was constructed using autologous nucleus pulposus tissue implantation. Differential expression gene (DEGs) related to metabolism (CDKN1A and UHRF1), inflammation (S100A9 and SOCS3), autophagy (DCN and LEPR), and apoptosis (CTSW and BCL2A1) in dorsal root ganglion (DRG) tissues of the control and LDH groups was evaluated by RNA-Seq. TNF-α stimulated DRG neuronal cells were used to establish an in vitro LDH model. YBS, palmitic acid, and cinnamate reduced the expression of substance P, CGRP, S100A9, CTSW, and cleaved caspase-3, while enhancing the expression of CDKN1A, UHRF1, PCNA, Ki67, SOCS3, DCN, LEPR, and BCL2A1, as well as telomerase activity. Pearson's correlation analysis confirmed that DCN was positively correlated with BCL2A1, indicating that autophagy might be negatively correlated with apoptosis in LDH. YBS, palmitic acid, and cinnamate reduced the Siegal neurological score and serum IL-1β and IL-18 levels, while increasing changes in the hind paw mechanical withdrawal threshold. The RNA-Seq results further showed that YBS downregulated S100A9 and CTSW expression, while upregulating SOCS3, CDKN1A, UHRF1, DCN, LEPR, and BCL2A1 expression. Conclusion YBS and its compounds, palmitic acid, and cinnamate, attenuated LDH by regulating the inflammatory, metabolic, autophagic, and apoptotic pathways. Our results might improve the theoretical and experimental basis for clinical applications of LDH disease treatment.

The Impact of Long-term High-fat Diet on Co-morbid Disorders in an Early Life Stress Mouse Model

Exposure to stress early in life has been associated with adult-onset co-morbidities such as chronic pain, obesity, and metabolic disorders. We have established a mouse model of early life stress using neonatal maternal separation (NMS) that results in urogenital hypersensitivity and increased body weight and adiposity compared to naive (non-separated) mice. In this study we tested the hypothesis that consumption of a high fat/high sucrose (HFS) diet will worsen NMS-related outcomes. Male and female naive and NMS mice were pair-housed with a sex matched littermate. At 4-weeks of age mice were assigned to either control diet or HFS diet and weight gain and food intake were measured weekly. Mechanical sensitivity and body composition were measured at 22-weeks of age. At 25-29 weeks of age mice were subject to a glucose tolerance test. Mice were then sacrificed, and tissues were fixed and frozen. Adipose tissue was analyzed via RT-PCR and fixed liver tissue was stained and analyzed for steatosis. NMS mice on a HFS diet were found to have increased body weight and percent body fat compared to naive mice on a HFS diet and to NMS mice on a control diet. Additionally, both NMS and the HFS diet resulted in significantly lower hind paw mechanical withdrawal thresholds indicative of hypersensitivity. Both NMS and HFS diet consumption were found to result in impaired glucose homeostasis. Upon histological examination of the liver, HFS diet fed NMS mice were observed to have increased steatosis and hepatocyte ballooning. Our results suggest that HFS diet exacerbates the outcomes of NMS in both males and females, resulting in widespread hypersensitivity, weight gain, glucose intolerance, and steatosis. Future work will explore possible underlying mechanisms for the increased weight gain and sensitivity associated with stress and diet. Grant support from RO1DK099611 (JAC), RO1DK103872 (JAC), T32HD057850 (OCE), COBRE grant P20GM104936, IDeA grant P20GM103418, core support from IDDRC grant P30HD002528.

Postoperative pain facilitates rat C-fibre activity-dependent slowing and induces thermal hypersensitivity in a sex-dependent manner

BackgroundPostoperative pain is a common clinical problem that, in preclinical studies, has almost exclusively been studied in males. Altered C-fibre activity-dependent slowing (ADS) is a potential underlying mechanism, given it is altered after tissue inflammation and nerve injury, but this has not been explored post-incision. We therefore investigated the effect of hind-paw incision on C-fibre ADS in both sexes and the involvement of voltage-gated sodium channels (NaV) as they contribute to ADS. We also assessed mechanical and thermal sensitivity post-incision in both sexes. MethodsDorsal roots were isolated from hind-paw incision (2–4 days post-surgery) or naive (control) juvenile rats of both sexes. Compound action potential recordings were made to assess C-fibre ADS in response to ×40 stimuli at 2 and 10 Hz and repeated in the presence of 20 nM tetrodotoxin/vehicle. Data were quantified by the normalised change in latency (negative peak) and width (positive-to-positive peak) of the triphasic C-fibre response. Hind-paw mechanical withdrawal thresholds and thermal withdrawal latencies were measured pre- and post-incision. ResultsIncision facilitates C-fibre ADS in both sexes, with more pronounced facilitation in females. Tetrodotoxin induces sex- and injury-dependent changes in C-fibre ADS that were distinct between latency and width measures. Hind-paw incision induced comparable mechanical hypersensitivity in both sexes but less peak heat hypersensitivity in females. ConclusionsHind-paw incision induces sex-dependent changes in C-fibre activity-dependent slowing, which likely contribute to the observed sex difference in peak thermal hypersensitivity. This may reflect sex- and incision-induced differences in functional expression of NaV channels that differs by C-fibre subtype.

Dexamethasone-Loaded Thermosensitive Hydrogel Suppresses Inflammation and Pain in Collagen-Induced Arthritis Rats.

PurposeTo overcome negative adverse effects and improve therapeutic index of dexamethasone (Dex) in rheumatoid arthritis (RA), we developed a novel sustained release formulation-intra-articular injectable dexamethasone-loaded thermosensitive hydrogel (DLTH) with chitosan-glycerin-borax as carrier for the remission of inflammation and pain. The focus of this article is to explore both anti-inflammatory and pain-relieving effects of DLTH joint injection in bovine type-II collagen-induced arthritis (CIA) rats.MethodsWistar rats were randomized into three groups, including the normal group (n=6), the model group (n=6) and the DLTH group (n=10). Joint injection of DLTH (1mg/kg Dex per rat) was injected on day 12 in the DLTH group twice a week for three weeks. Clinical signs of body weight, paw swelling and arthritis scores, histologic analysis, hind paw mechanical withdrawal threshold (MWT), plantar pressure pain threshold (PPT) were taken into consideration. Serum contents of IL-17A, prostaglandin E2 (PGE2), prostacyclin 2 (PGI2) and prostaglandin D2 (PGD2), real-time polymerase chain reaction (PCR) analysis of inflammatory factors and pain-related mediators in synovium and dorsal root ganglia (DRG), Western blotting of NF-κB in synovium were all evaluated.ResultsPaw swelling, arthritis scores and joint inflammation destruction were all attenuated in the DLTH-treated group. Results showed that DLTH not only down-regulated serum IL-17A, but also mRNA levels of inflammatory factors and NGF, and key proteins contents of the NF-κB pathway in synovium. Increases of MWT and PPT in DLTH-treated rats elucidated pain-reducing effects of DLTH. Elevated serum PGD2 levels and declines of serum PGE2 and PGI2, and inflammatory and pain-related genes in DRGs in the DLTH group were also recorded.ConclusionThese data elucidated that DLTH joint injection impeded synovial inflammation processes through down-regulating transcription activity of NF-κB pathway, and intra-articular DLTH may aid in the regulation of RA pain through regulating inflammation and pain conduction process.

Contribution of salidroside to the relieve of symptom and sign in the early acute stage of osteoarthritis in rat model

Ethnopharmacological relevanceThe genus Rhodiola has been used to treat cough, hemoptysis, fever, pain, bruise and other symptoms which are related to injury and inflammation over a thousand years in traditional Tibetan medicine. Salidroside (p-hydroxyphenethyl-β-D-glucoside) is one of the most potent bioactive ingredients of the genus Rhodiola. Aim of studyThe present study aimed to explore whether salidroside could alleviate the clinical symptom and sign in the early acute stage of osteoarthritis (OA) in monosodium iodoacetate (MIA) rat model, and its underlying mechanisms. Materials and methodsOsteoarthritis (OA) was induced in rat knees by intra-articular injection of MIA; simultaneously salidroside was administered by intravenous injection. Pain behaviors were evaluated by knee-bend test, hind limb weight-bearing asymmetry and hind paw mechanical withdrawal threshold. The joint swelling was determined by the difference of knee joint diameter. Inflammatory exudates in synovial fluid were evaluated by leukocyte counting and protein content. Cytokines, chemokines, reactive oxygen species (ROS) and reactive nitrogen species (RNS) markers were determined by Enzyme-linked immunosorbent assay (ELISA) and colorimetric assay in synovial fluid. Pro-inflammatory gene expressions in synovial tissue were detected by quantitative real time RT-PCR (qRT-PCR). Nuclear factor kappa-B (NF-κB) DNA binding assay and western blot were used to determine NF-κB activation and ROS marker protein expression in synovial tissue. Glycosaminoglycan (GAG) content in the cartilage was measured by dimethylmethylene blue method. Hematoxylin and eosin (H&E), Safranin O-fast green and a modified Mankin grading system were used to evaluate the histology of articular cartilage. ResultsSalidroside could alleviate pain and joint swelling in the early acute stage of OA in rat model, reduced the number of leukocytes, total protein content, proinflammatory mediators and ROS/RNS markers in synovial fluid, down regulated the expression of proinflammatory genes in synovium, inhibited the activation of NF- κ B and oxidative stress response in synovium, promoted the synthesis of cartilage GAG, prevented the loss of proteoglycan and chondrocyte degeneration. ConclusionsSalidroside effectively alleviates acute symptom and sign of OA in rat model by its anti-inflammatory and antioxidant affects to inhibit synovial inflammation, which provides a new strategy to prevent the onset and progression of OA.

ALGX‐XC20, a Novel Transient Receptor Potential Ankyrin 1 (TRPA1) Antagonist Attenuates Joint Pain and Articular Cartilage Damage in an Osteoarthritis Rat Model

Currently, there are no approved disease‐modifying drugs for osteoarthritis (OA). OA patients depend upon analgesic drugs such as nonsteroidal anti‐inflammatory drugs (NSAIDs) and opioid analgesics for pain management. Despite existing therapies, pain relief in OA remains largely inadequate. Recently, the functional role for TRPA1 receptor‐channels which are expressed on nociceptor sensory nerves and other non‐neuronal cells within the joint has been identified, although studies of the role of TRPA1 in the pathogenesis of OA pain are limited. TRPA1 represents a promising target for the development of novel therapeutic agent for managing OA pain. This study investigated the effects of ALGX‐XC20, a highly selective and potent TRPA1 antagonist with a long in‐vivo half‐life on pain behaviors and cartilage damage in a rat model of monosodium iodoacetate (MIA)‐induced OA. The analgesic effect of a single dose (30 mg/kg; oral) of ALGX‐XC20 was evaluated for a period of 14 days post‐OA induction and compared to celecoxib (30 mg/kg; oral), a selective cyclooxygenase‐2 (COX‐2) inhibitor by using pain‐related behavior assessments, including hindlimb weight distribution and von Frey tests. The histological scoring of cartilage damage was also determined according to the Mankin grading system. The MIA‐induced OA rat group displayed a large reduction in the weight bearing distribution on the ipsilateral hindlimb (p&lt;0.01–0.05) and hind paw mechanical withdrawal thresholds compared to saline control group, which was maintained for 14 days. The MIA‐evoked reduction in weight bearing distribution was significantly reversed (~50%) in the MIA‐induced group treated with ALGX‐XC20 compared to the MIA‐treated group for the 2‐week duration, while the antiallodynic effect of ALGX‐XC20 was less pronounced. In addition, histopathology studies showed that ALGX‐XC20 was also effective in reducing the severe cartilage damage in the MIA‐injected knee joint as shown by a significant improvement in the Mankin score in the ALGX‐XC20 treated group at 14 days (p&lt;0.05). The magnitude of the effect on spontaneous weight bearing behavior due to ALGX‐XC20 treatment is closely comparable to the effects observed for the MIA‐celecoxib group and reported for TRPA1‐KO animals. The positive analgesic effects in this OA model due to pharmacological inhibition of TRPA1 by ALGX‐XC20 occur without any adverse behavioral effects. These in vivo data suggest that ALGX‐XC20 may be used as a novel therapeutic analgesic/anti‐inflammatory drug for the treatment of chronic arthritis, such as OA pain. This TRPA1 antagonist drug may also represent a new class of disease‐modifying drug by providing a chondroprotective effect on articular cartilage.

Proliferator-Activated Receptor-Gamma Coactivator-1α Haploinsufficiency Promotes Pain Chronification After Burn Injury.

Tissue injuries such as surgery and trauma are usually accompanied by simultaneous development of acute pain, which typically resolves along with tissue healing. However, in many cases, acute pain does not resolve despite proper tissue repair; rather, it transitions to chronic pain. In this study, we examined whether proliferator-activated receptor-gamma coactivator-1α (PGC-1α), a master regulator of mitochondria biogenesis, is implicated in pain chronification after burn injury in mice. We used PGC-1α and littermates PGC-1α mice of both sex. Burn injury was induced on these mice. Hindpaw mechanical withdrawal thresholds and thermal withdrawal latency were examined. Hindpaw mechanical withdrawal thresholds and thermal withdrawal latencies were comparable at baseline between PGC-1α and PGC-1α mice. After burn injury, both PGC-1α and PGC-1α mice exhibited an initial dramatic decrease of withdrawal parameters at days 3 and 5 after injury. While PGC-1α mice fully recovered their withdrawal parameters to preinjury levels by days 11-14, PGC-1α mice failed to recover those parameters during the same time frame, regardless of sex. Moreover, we found that PGC-1α mice resolved tissue inflammation in a similar fashion to PGC-1α mice using a chemiluminescence-based reactive oxygen species imaging technique. Taken together, our data suggest that PGC-1α haploinsufficiency promotes pain chronification after burn injury.

A Traditional Clinic Chinese Medicine Prescription Qu-Zhuo-Tong-Bi (QZTB) Alleviates Gouty Arthritis in Model Rats.

Qu-Zhuo-Tong-Bi (QZTB) is an empirical traditional Chinese medicine prescription for treating acute gouty arthritis clinically without serious adverse effects in mainland China. However, the biochemical mechanism underlying the therapeutic action produced by QZTB treatment against acute gouty arthritis and the effect on recurrent attack remain unknown. In this study, we investigated the anti-inflammatory and analgesic effects of QZTB on acute gouty arthritis and the recurrent attack in rats, as well as the underlying mechanisms. The gouty arthritis model was established by intra-articular injection of monosodium urate (MSU) crystal suspension (2 mg/50 μL) into the right ankle joint of Sprague Dawley (SD) male rats. QZTB (500 mg/kg) and the positive control drug meloxicam were administrated by gavages twice a day for 7 days before, or 3 days after, first MSU injection in different experiments, respectively. The analgesic effects were evaluated by pain-like behaviors and hind paw mechanical withdrawal threshold testing. The anti-inflammatory activities were evaluated by ankle swelling measurement, histologic examination, NLRP3 inflammasome, and inflammatory cytokine expression. Western blot and quantitative real-time PCR were used to detect the protein and mRNA expressions of NLRP3. IL-1β and TNF-α level in the blood serum were detected by enzyme-linked immunosorbent assay (ELISA). QZTB can suppress ankle swelling and synovial inflammation in the MSU-induced gouty arthritis rat model. QZTB alleviated the acute attack and prevented the recurrent attack of gouty arthritis. In addition, QZTB treatment significantly decreased both mRNA and protein levels of NLRP3, as well as the production of IL-1 and TNF-α in the ankle joint of model rats. Taken together, these results suggest that QZTB may be a promising herbal formula for the prevention and treatment of gouty arthritis in humans.

Effect of Electroacupuncture on Hyperalgesia and Vasoactive Neurotransmitters in a Rat Model of Conscious Recurrent Migraine.

Migraine onset is associated with the abnormal release of vasoactive neurotransmitters from perivascular nerves, and these neurotransmitters are involved in the pathophysiology of migraine. Hyperalgesia is a key feature of migraine, and accumulating evidence indicates that electroacupuncture (EA) at the single acupuncture point (Fengchi [GB20]) is effective in ameliorating hyperalgesia. In clinical practice, multiple acupuncture points are widely used, especially GB20 and Yanglingquan (GB34). However, the role played by vasoactive neurotransmitters in acupuncture antihyperalgesic effect at the single or multiple acupuncture points remains unknown. We aimed to determine whether EA would exert its antihyperalgesic effects by modulating vasoactive neurotransmitter release from the perivascular nerves. Furthermore, we examined whether targeting multiple acupuncture points would be more effective than targeting a single point in reducing hyperalgesia. The mechanical and thermal hyperalgesia were evaluated by measuring the facial and hind-paw mechanical withdrawal thresholds, tail-flick and hot-plate latencies. Plasma concentrations of vasoactive neurotransmitters were determined using rat-specific ELISA kits from jugular vein, including calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), pituitary adenylate cyclase-activating polypeptide (PACAP), nitric oxide (NO), and endothelin-1 (ET-1). The result suggested that EA significantly ameliorated the mechanical and thermal hyperalgesia, reduced c-Fos levels in the trigeminal ganglion, and attenuated plasma and dural levels of vasoactive neurotransmitters, especially in the multiple acupuncture points group (GB20+GB34). In conclusion, EA exerts antihyperalgesic effect in a rat model of conscious recurrent migraine, possibly via modulation of the vasoactive neurotransmitters. Furthermore, targeting multiple acupuncture points is more effective than targeting a single point in reducing hyperalgesia.

Mechanical allodynia corresponds to Oprm1 downregulation within the descending pain network of male and female rats exposed to neonatal immune challenge

Exposure to painful procedures and/or stressors during the early neonatal period can reprogram the underlying neurocircuitry involved in nociception and neuropathic pain perception. The reprogramming of these systems can result in an enduring elevation in sensitivity towards mechanical and thermal stimuli. Recent evidence suggests that exposure to mild inflammatory mediators during the neonatal period can induce similar pain responses in both adolescent and adult rats. Therefore, we sought to profile changes in the expression of several genes across brain areas involved in the active modulation of nociception and neuropathic pain using a well-recognized model of neonatal inflammation. In the present study male and female Sprague-Dawley rats were administered either the inflammatory endotoxin lipopolysaccharide (LPS; 0.05mg/kg, i.p.) or saline (equivolume) on postnatal days (PND) 3 and 5. During adolescence, hind paw mechanical withdrawal thresholds were evaluated using an electronic von Frey anesthesiometer. Animals challenged neonatally with LPS (nLPS) had increased pain sensitivity on this measure which was associated with decreased Oprm1 expression in the prefrontal cortex (PFC) and periaqueductal gray (PAG) of both male and female rats. Although a ‘second hit’ with LPS in adolescence (aLPS) did not confer protection or reveal additional vulnerabilities, aLPS given to animals treated neonatally with saline was associated with increased pain sensitivity, but only in females. Interestingly, adolescent inflammatory challenge decreased Hcrt2 mRNA in the PAG and elevated Trpv1 in the PAG and PFC of both sexes. There was no effect of inflammatory treatment on either anxiety or depressive-like behavior suggesting that affective functioning did not account for differences in mechanical pain sensitivity. Finally, a preliminary investigation demonstrated that administration of a broad spectrum antibiotic cocktail attenuated the mechanical sensitivity that followed nLPS. Together, these data extend upon evidence that inflammation imparts long term changes in quality of life and pain responses via interference within the descending pain network. Moreover, they highlight a potential window of opportunity to target the microbiota-gut-brain axis and reverse pain processing disturbances following perinatal inflammation.

The local effect of octreotide on mechanical pain sensitivity is more sensitive in DA rats than DA.1U rats.

A recent study by the authors indicated that major histocompatibility complex (MHC) genes are associated with the differences in basal pain sensitivity and in formalin model between Dark-Agouti (DA) and novel congenic DA.1U rats, which have the same genetic background as DA rats except for the u alleles of MHC. The objective of the present study is to investigate whether there is a difference in the pristane-induced arthritis (PIA) model and local analgesic effect of octreotide (OCT) between DA and DA.1U rats. The hindpaw mechanical withdrawal threshold (MWT) and heat withdrawal latency (HWL) were observed. The C unit firings of the tibial nerve evoked by non-noxious and noxious toe movements were recorded by electrophysiological methods in normal and PIA models in DA and DA.1U rats before and after local OCT administration. The expression of somatostatin receptor 2A (SSTR2A) was observed by immunohistochemistry. The results demonstrate that DA rats have a higher mechanical sensitivity than DA.1U rats after PIA. Local OCT administration significantly elevated MWT in DA rats under normal and PIA sate, but not in DA.1U rats. The electrophysiological experiments showed OCT significantly attenuated the firings of C units evoked by non-noxious and noxious stimulation in DA rats more than those in DA.1U rats both in normal and PIA states. In addition, the expression of SSTR2A in the dorsal horn of the spinal cord was significantly higher in DA than in DA.1U rats. All of the findings suggest a higher local analgesic effect of OCT in DA rats than DA.1U rats, which might be associated with the MHC genes.

Effect of pulsed radiofrequency on rat sciatic nerve chronic constriction injury: a preliminary study.

Background:Pulsed radiofrequency (PRF) application to the dorsal root ganglia can reduce neuropathic pain (NP) in animal models, but the effect of PRF on damaged peripheral nerves has not been examined. We investigated the effect of PRF to the rat sciatic nerve (SN) on pain-related behavior and SN ultrastructure following chronic constriction injury (CCI).Methods:The analgesic effect was measured by hindpaw mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL). Twenty rats with NP induced by ligating the common SN were then randomly divided into a PRF treatment group and a sham group. The contralateral SN served as a control. The MWT and TWL were determined again 2, 4, 6, 8, 10, 12, and 14 days after the PRF or sham treatment. On day 14, ipsilateral and contralateral common SNs were excised and examined by electron microscopy.Results:Ipsilateral MWT was significantly reduced and TWL significantly shorter compared to the contralateral side 14 days after CCI (both P = 0.000). In the PRF group, MWT was significantly higher and TWL significantly longer 14 days after the PRF treatment compared to before PRF treatment (both P = 0.000), while no such difference was observed in the sham group (P > 0.05). Electron microscopy revealed extensive demyelination and collagen fiber formation in the ipsilateral SN of sham-treated rats but sparse demyelination and some nerve fiber regrowth in the PRF treatment group.Conclusions:Hyperalgesia is relieved, and ultrastructural damage ameliorated after direct PRF treatment to the SN in the CCI rat model of NP.

Characterisation of pain responses in the high fat diet/streptozotocin model of diabetes and the analgesic effects of antidiabetic treatments.

Chronic pain is a common complication of diabetes. The aim of the present study was to characterise pain behaviour in a high fat diet/streptozotocin (HFD/STZ) model of diabetes in the rat, investigate spinal mechanisms, and determine the effects of antidiabetic interventions. Three-week consumption of a high fat diet followed by single injection of STZ (45 mgkg−1) produced sustained changes in plasma insulin and glucose until day 120. Hindpaw mechanical withdrawal thresholds were significantly lowered in the model, but mechanically evoked responses of spinal neurones were unaltered, compared to HFD/vehicle rats. HFD/STZ rats had significantly lower numbers of spinal Iba-1 positive cells (morphologically identified as activated microglia) and spinal GFAP immunofluorescence (a marker of astrogliosis) in the spinal cord at day 50, compared to time-matched controls. The PPARγ ligand pioglitazone (10 mgkg−1) did not alter HFD/STZ induced metabolic changes or hindpaw withdrawal thresholds of HFD/STZ rats. Daily linagliptin (3 mgkg−1) and metformin (200 mgkg−1) from day 4 after model induction did not alter plasma glucose or insulin in HFD/STZ rats but significantly prevented changes in the mechanical withdrawal thresholds. The demonstration that currently prescribed antidiabetic drugs prevent aberrant pain behaviour supports the use of this model to investigate pain mechanisms associated with diabetes.

Nerve injury induces a new profile of tactile and mechanical nociceptor input from undamaged peripheral afferents

Chronic pain after nerve injury is often accompanied by hypersensitivity to mechanical stimuli, yet whether this reflects altered input, altered processing, or both remains unclear. Spinal nerve ligation or transection results in hypersensitivity to mechanical stimuli in skin innervated by adjacent dorsal root ganglia, but no previous study has quantified the changes in receptive field properties of these neurons in vivo. To address this, we recorded intracellularly from L4 dorsal root ganglion neurons of anesthetized young adult rats, 1 wk after L5 partial spinal nerve ligation (pSNL) or sham surgery. One week after pSNL, hindpaw mechanical withdrawal threshold in awake, freely behaving animals was decreased in the L4 distribution on the nerve-injured side compared with sham controls. Electrophysiology revealed that high-threshold mechanoreceptive cells of A-fiber conduction velocity in L4 were sensitized, with a seven-fold reduction in mechanical threshold, a seven-fold increase in receptive field area, and doubling of maximum instantaneous frequency in response to peripheral stimuli, accompanied by reductions in after-hyperpolarization amplitude and duration. Only a reduction in mechanical threshold (minimum von Frey hair producing neuronal activity) was observed in C-fiber conduction velocity high-threshold mechanoreceptive cells. In contrast, low-threshold mechanoreceptive cells were desensitized, with a 13-fold increase in mechanical threshold, a 60% reduction in receptive field area, and a 40% reduction in instantaneous frequency to stimulation. No spontaneous activity was observed in L4 ganglia, and the likelihood of recording from neurons without a mechanical receptive field was increased after pSNL. These data suggest massively altered input from undamaged sensory afferents innervating areas of hypersensitivity after nerve injury, with reduced tactile and increased nociceptive afferent response. These findings differ importantly from previous preclinical studies, but are consistent with clinical findings in most patients with chronic neuropathic pain.

SAT0554 Intra-Articular Injection of Mesenchymal Stem Cells Improves Pain Behaviour in A Model of OA Pain

BackgroundOsteoarthritis (OA) is a degenerative joint disease affecting around 8 million people in the UK. Pain is a prominent and often disabling feature of OA, the relationship between pain and...

Augmented pain behavioural responses to intra-articular injection of nerve growth factor in two animal models of osteoarthritis

ObjectivesNerve growth factor (NGF) is a promising analgesic target, particularly in osteoarthritis (OA) where existing therapies are inadequate. We hypothesised that pain responses to NGF are increased in OA joints....

Hind Paw Incision in the Rat Produces Long-Lasting Colon Hypersensitivity

Visceral injury has been shown to alter somatic sensitivity, but little is known about the effect of somatic insult on the viscera. In the present study, we examined (1) the effect of colon inflammation on somatic sensitivity and (2) the affect of hind paw incision on colon sensitivity. After intracolonic administration of trinitrobenzene sulfonic acid (TNBS) or zymosan, visceromotor responses to colorectal distension were increased to post-treatment day 8. Mechanical withdrawal thresholds in the hind paw were decreased in TNBS- and in zymosan-treated rats until post-intracolonic treatment day 2. There was no change in hind paw heat withdrawal latency in either group. Plantar incision of the hind paw resulted in a decrease in both hind paw mechanical withdrawal threshold and heat withdrawal latency and significantly increased the visceromotor response to colorectal distension from postincision days 1 to 8. The colon hypersensitivity was of longer duration than hyperalgesia at the site of hind paw incision. These results support the hypothesis that somatic injury and visceral inflammation can alter central processing of visceral and somatic inputs, respectively. Surgical procedures are common and typically associated with hyperalgesia at and around the site of incision. This report establishes in a model of postsurgical pain and hyperalgesia that a long-lasting visceral hypersensitivity may also accompany postsurgical hyperalgesia.

Hyperexcitability of Axotomized and Neighboring Unaxotomized Sensory Neurons Is Reduced Days After Perineural Clonidine at the Site of Injury

Hyperexcitability after peripheral nerve injury occurs in axotomized and neighboring unaxotomized dorsal root ganglion (DRG) neurons and contributes to hypersensitivity. Previous studies have focused on proximal nerve injury and have not examined unaxotomized neurons innervating the site of sensory testing. The current study used a distal nerve injury (partial sciatic nerve ligation [PSNL]), and identified, using fluorescent tracers, axotomized and unaxotomized neurons innervating the site of hypersensitivity. We hypothesized that reduced hypersensitivity after perineural clonidine was associated with reduced hyperexcitability of DRG neurons. Rats underwent sham or PSNL surgery, followed 2 wk later by a single injection at the injury site of clonidine or saline. PSNL, but not sham surgery, reduced hindpaw mechanical withdrawal threshold, and clonidine, but not saline, partially reversed this effect 3 days after injection. Intracellular recording of neurons in whole DRG demonstrated similar changes in membrane properties and excitability in unaxotomized and axotomized neurons after PSNL compared with sham surgery, primarily depolarized resting membrane potential, reduced rheobase, presence of oscillations, and capability to fire repetitively. Most of these changes were present in small-, medium-, and large-diameter neurons. Perineural clonidine 3 days later significantly reversed many of these effects, whereas saline was without effect. We speculate that perineural clonidine reduces signals, likely proinflammatory cytokines and prostaglandins produced during Wallerian degeneration after nerve injury, which drive changes in ion channel expression in DRG somata leading to hyperexcitability and hypersensitivity.