Diabetic Neuropathic Pain In Rats Research Articles

Salidroside Ameliorates Diabetic Neuropathic Pain in Rats by Inhibiting Neuroinflammation.

More than half of diabetic patients suffer from intractable neuropathic pain. As inflammation plays an important role in diabetic neuropathic pain, anti-inflammatory drugs might have therapeutic potentials for neuropathic pain. Salidroside (SAL), a phenylpropanoid glucoside, modulates a variety of cell functions, including inflammation. Here, we explored anti-nociceptive and anti-inflammatory effects of SAL on Zucker diabetic fatty rats with type 2 diabetes (DM rats). DM rats were tested for mechanical and thermal hyperalgesia using von Frey filament and plantar hot box test, respectively. The anti-nociceptive effect of chronic SAL (25-100mg/kg, per oral) treatment was tested. The expression of inflammatory cytokines (TNF-α and IL-1β) and P2X7 receptors in spinal cord and sciatic nerve were measured with ELISA. SAL alleviated mechanical and thermal hyperalgesia and reduced TNF-α and IL-1β in sciatic nerve and spinal cord in DM rats. Furthermore, SAL reduced P2X7 receptor upregulation in spinal cord of DM rats and directly inhibited P2X7 receptors expressed in HEK293 cells. This study provides evidence that SAL attenuated nociception in diabetic neuropathic pain rat models probably through inhibiting neuroinflammation and P2X7 receptors.

Influences of intraperitoneal injection of dexmedetomidine on activation of spinal glial cells in diabetic neuropathic pain rats

Objective Exploring the influences of intraperitoneal injection of dexmedetomidine(Dex) on activation of spinal glial cells and expression of inflammatory factors in rats with diabetic neuropathic pain(DNP). Methods Thirty two health male SD rats, weight 180-200 g, were divided into four groups (n=8) according the random number table method. The four groups included the control group(group C), diabetic neuropathic pain group(group DNP), group Dex and α2 receptor antagonist group(group YOH). Streptozotocin(STZ) was used to establish the DNP model in rats. Starting from 28 d after STZ injection, Dex group was given intraperitoneal injection of Dex(50 μg/kg) for consecutive 7 d, while group YOH was given intraperitoneal injection of Yohimbine(0.1 mg/kg) 30 min before intraperitoneal injection of Dex(50 μg/kg) for consecutive 7 d. Mechanical withdrawal threshold (MWT) was determined in each group of rats 29-35 d after STZ injection. Rats were sacrificed after MWT detection on 35 d. Immunofluorescence double-staining was used to detect activation of microglia and astrocytes in rat spinal cord of each group. ELISA was used to measure TNF-α and IL-1 expression in rat spinal cord of each group. Results Compared with group C, rat body weights were decreased while blood glucose values were increased in group DNP, group Dex and group YOH(P 0.05). Compared with group C, MWT at all time points decreased in group DNP and group YOH(P 0.05). Conclusions Dex can relieve hyperalgesia in rats with diabetic neuropathy pain. The underlying mechanism may be related to inhibition of microglia activation and reduction of the inflammatory reaction in spinal cord. Key words: Dexmedetomidine; Diabetic neuropathic pain; Microglia; Astrocyte; Inflammatory reaction

Decreased spinal endomorphin-2 contributes to mechanical allodynia in streptozotocin-induced diabetic rats

Diabetic neuropathic pain (DNP) plays a major role in decreased life quality of diabetes patients, however, the neural mechanisms underlying DNP remain unclear. Endomorphins are the endogenous ligands for mu-opioid receptor. There is increasing evidence implicating the involvement of spinal endomorphin-2 (EM2) in neuropathic pain. In this study, using a streptozotocin induced diabetic rat model that displayed obvious mechanical allodynia, it was found that the expression of spinal EM2 was significantly decreased in DNP rats. While intrathecal administration of exogenous EM2 attenuated mechanical allodynia in DNP rats, the mu-opioid receptor antagonist β-funaltrexamine facilitated these events. It was found that the reduction in spinal EM2 was mediated by increased activity of dipeptidylpeptidase IV, possibly as a consequence of diabetes-induced oxidative stress. Taken together, our results provide the first evidence that the reduction in the level of an endogenous opioid in primary afferents was significantly associated with DNP. This indicates that the chronic pain associated with DNP might be due to the loss of an inhibitory effect on pain signal transmission.

Effects of hyperbaric factors on lidocaine-induced apoptosis in spinal neurons and the role of p38 mitogen-activated protein kinase in rats with diabetic neuropathic pain.

The application of lidocaine can lead to nerve damage. Evidence suggests that patients with diabetic neuropathy are at a higher risk for neurotoxicity. In the present study, the successful induction of diabetic neuropathic pain (DNP) in rats via a high-sugar, high-fat diet and intraperitoneal injection of 1% streptozotocin was verified and pronounced tactile allodynia was observed. It was found that intrathecal injections of hyperbaric lidocaine produced motor blocks of longer durations in the DNP model rats than in nondiabetic rats, or in DNP model rats injected with isobaric lidocaine. Histology of the lumbar 4–5 spinal cord revealed a significant difference in neuropathology between the DNP and nondiabetic rats. Moreover, edematous neurons and TUNEL-positive cells were observed in the hyperbaric lidocaine group. It was also found that the inhibition of p38 mitogen-activated protein kinase (p38MAPK) played a neuroprotective role in response to hyperbaric lidocaine-induced apoptosis in DNP rats, which indicates that p38MAPK plays a key role in the regulation of hyperbaric lidocaine-induced apoptosis in DNP rats. These findings suggest that hyperbaric lidocaine can promote spinal cord neuronal apoptosis in rats with DNP. Furthermore, p38MAPK might play a key role in the regulation of hyperbaric lidocaine-induced apoptosis in rats with DNP.

The mechanism of RvD1 alleviates type 2 diabetic neuropathic pain by influencing microglia polarization in rats

To study the relationship between microglia polarization in the spinal dorsal horn and type 2 diabetic neuropathic pain (DNP). And explore the mechanism of RvD1 alleviating type 2 diabetic neuropathic pain. Type 2 diabetes mellitus (T2DM) rats came from the male SD rats which were fed by high-fat and high-sucrose diet and given intraperitoneal streptozotocin(STZ), then detected fa sting blood glucose level, the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL), which was to prepare the type 2 DNP model rats. And they were randomly divided into 3 groups:type 2 DNP group (group D), type 2 DNP and RvD1 group (group R), type 2 DNP and solvent control group (group S), 36 rats in each group. After being given STZ 14 days, the rats of group D, R, S were placed a catheter in subarachnoid cavity. Three days later, the RvD1 10μl (10 ng/μl) and 100% ethanol 10μl were injected into subarach-noid cavity through the catheter once a day for 14 consecutive days. Another 36 normal rats were served as normal control group (group N) and were fed with common forage. MWT and TWL were measured at 1, 3, 7, 14 days after Subarachnoid injection, then the nine rats'spinal cord of the lumbar segment 4~6 were removed to detect the expression of inducible nitric oxide synthase(iNOS) and arginase 1(Arg1) by Western blot, the marker of microglia M1 and M2 polarization. Compared with group N, MWT was decreased significantly and TWL was shortened, the expression of Arg1 was down-regulated and the expression of iNOS was up-regulated in spinal dorsal horn at the 1, 3, 7, 14 days in groups D and S (P < 0.05). Compared with group D, MWT was significantly increased and TWL was prolonged, the expression of Arg1 was up-regulated and the expression of iNOS was down-regulated in spinal dorsal horn at the 7, 14 days in group R (P < 0.05). There was no significant difference in the MWT, TWL and expression of Arg1 and iNOS between D and S groups. RvD1 promotes mi-croglia toward M2 polarization and alleviates type 2 diabetic neuropathic pain in rats.

Endomorphin-2 Inhibition of Substance P Signaling within Lamina I of the Spinal Cord Is Impaired in Diabetic Neuropathic Pain Rats.

Opiate analgesia in the spinal cord is impaired in diabetic neuropathic pain (DNP), but until now the reason is unknown. We hypothesized that it resulted from a decreased inhibition of substance P (SP) signaling within the dorsal horn of the spinal cord. To investigate this possibility, we evaluated the effects of endomorphin-2 (EM2), an endogenous ligand of the μ-opioid receptor (MOR), on SP release within lamina I of the spinal dorsal horn (SDH) in rats with DNP. We established the DNP rat model and compared the analgesic efficacy of EM2 between inflammation pain and DNP rat models. Behavioral results suggested that the analgesic efficacy of EM2 was compromised in the condition of painful diabetic neuropathy. Then, we measured presynaptic SP release induced by different stimulating modalities via neurokinin-1 receptor (NK1R) internalization. Although there was no significant change in basal and evoked SP release between control and DNP rats, EM2 failed to inhibit SP release by noxious mechanical and thermal stimuli in DNP but not in control and inflammation pain model. We also observed that EM2 decreased the number of FOS-positive neurons within lamina I of the SDH but did not change the amount of FOS/NK1R double-labeled neurons. Finally, we identified a remarkable decrease in MORs within the primary afferent fibers and dorsal root ganglion (DRG) neurons by Western blot (WB) and immunohistochemistry (IHC). Taken together, these data suggest that reduced presynaptic MOR expression might account for the loss of the inhibitory effect of EM2 on SP signaling, which might be one of the neurobiological foundations for decreased opioid efficacy in the treatment of DNP.

Diosgenin ameliorates development of neuropathic pain in diabetic rats: Involvement of oxidative stress and inflammation.

Neuropathic pain is one of the prevalent complications of diabetes mellitus (DM). Oxidative stress and inflammation are the principal determinants for its development. Pharmacological interventions targeted at alleviating or suppressing these pathways are clinically promising. Diosgenin is a natural steroidal saponin with anti-diabetic and multiple protective properties. This study was designed to study the efficacy of chronic diosgenin administration on alleviation of hyperalgesia in streptozotocin (STZ)-diabetic rats. Rats were allocated to control, diosgenin-treated control, diabetic, and diosgenin-treated-diabetic groups. Diosgenin was daily administered at a dose of 40mg/kg for 5 weeks. Nociceptive behavior was assessed using paw pressure, hot tail immersion, and formalin tests. In addition, some oxidative stress and inflammation markers were measured. Diosgenin treatment of diabetic group increased mechanical and thermal nociceptive thresholds and lowered pain score at late phase of the formalin test, but not at its early phase. Biochemical analysis of serum samples and sciatic nerve and dorsal root ganglion (DRG) lysates showed restoration or improvement of nuclear factor-<kappa>B (NF-κB), malondialdehyde (MDA) level, activity of superoxide dismutase (SOD), catalase, tumor necrosis factor α (TNFα), and interleukin 1β (IL-1β) upon diosgenin treatment of diabetic rats. The obtained results exhibited antinociceptive potential of diosgenin in diabetic rats through lowering oxidative stress and inflammation and improving antioxidant defense system. This suggests possible therapeutic potential of diosgenin for alleviation and management of diabetic neuropathic pain.

SIRT1 attenuates neuropathic pain by epigenetic regulation of mGluR1/5 expressions in type 2 diabetic rats.

Accumulating evidence has demonstrated that epigenetic modification-mediated changes in pain-related gene expressions play an important role in the development and maintenance of neuropathic pain. Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, is involved in the development of chronic pain. Moreover, SIRT1 may be a novel therapeutic target for the prevention of type 2 diabetes mellitus (T2DM). But the role of SIRT1 in T2DM-induced neuropathic pain remains unknown. In this study, we found that spinal SIRT1 expression and activity were downregulated significantly in high-fat-fed/low-dose streptozotocin-induced neuropathic pain rats. SIRT1 localized in spinal neurons but not in astrocytes or microglia. Furthermore, the expressions of metabotropic glutamate receptor (mGluR1) and mGluR5, which play a key role in central sensitization and neuropathic pain, and H3 acetylation levels at Grm1/5 (encoding mGluR1/5) promoter regions were increased in diabetic neuropathic pain rats. SIRT1 activator SRT1720 reversed thermal hyperalgesia and mechanical allodynia and spinal neuronal activation in diabetic neuropathic pain rats. Concurrently, increased expressions of mGluR1/5 and H3 acetylation levels at Grm1/5 promoter regions were reversed by SIRT1 activation. In addition, knockdown of SIRT1 by Ad-SIRT1-shRNA induced pain behaviors and spinal neuronal activation in normal rats, which was accompanied by the increased expressions of mGluR1/5 and H3 acetylation levels at Grm1/5 promoter regions. Therefore, we concluded that SIRT1-mediated epigenetic regulation of mGluR1/5 expressions was involved in the development of neuropathic pain in type 2 diabetic rats.

Role of PTEN protein in spinal cord neurons in diabetic neuropathic pain in rats

Objective To investigate the role of phosphatase and tensin homologue deleted on chromosome 10(PTEN)protein in the spinal cord neurons in diabetic neuropathic pain(DNP)in rats. Methods Male Sprague-Dawley rats, aged 2 months, weighing 180-200 g, were studied.Diabetes mellitus was induced by single intraperitoneal injection of streptozotocin(STZ)60 mg/kg.Sixteen rats with DNP were randomly divided into 2 groups(n=8 each)using a random number table: DNP group and DNP+ PTEN inhibitor bpv(pic)group(DPN-bpv group). Another 16 rats were equally and randomly divided into either control group(group C)or bpv group.In DNP-bpv and bpv groups, bpv(pic)0.2 mg/kg was injected intraperitoneally once a day within 14-28 days after injection of STZ.Before STZ injection(T1), and at 2, 7, 14, 2l and 28 days after STZ injection(T2-6), the mechanical paw withdrawal threshold(MWT)was measured.After measurement of MWT, the rats were sacrificed, and the lumbar segments of the spinal cord(L4, 5)were removed for determination of PTEN protein activity(by ELISA)and Akt(s473)phosphorylation(by Western blot). Results Compared with group C, the MWT was significantly decreased at T4-6, and the PTEN protein activity and Akt(s473)phosphorylation were significantly increased in DNP and DNP-bpv groups(P<0.05 or 0.01). Compared with group DNP, the MWT was significantly increased at T6, and the PTEN protein activity and Akt(s473)phosphorylation were significantly decreased in group DNP-bpv(P<0.05). Conclusion PTEN protein in the spinal cord neurons is involved in the maintenance of DNP in rats. Key words: Chromosomes, human, pair 10; Genes, tumor suppressor; Spinal cord; Neuralgia; Diabetes mellitus

Galanin and its receptor system promote the repair of injured sciatic nerves in diabetic rats.

Various studies have reported that galanin can promote axonal regeneration of dorsal root ganglion neurons in vitro and inhibit neuropathic pain. However, little is known about its effects on diabetic peripheral neuropathy, and in vivo experimental data are lacking. We hypothesized that repeated applications of exogenous galanin over an extended time frame may also repair nerve damage in diabetic peripheral neuropathy, and relieve pain in vivo. We found that neuropathic pain occurred in streptozotocin-induced diabetic rats and was more severe after sciatic nerve pinch injury at 14 and 28 days than in diabetic sham-operated rats. Treatment with exogenous galanin alleviated the neuropathic pain and promoted sciatic nerve regeneration more effectively in diabetic rats than in non-diabetic rats after sciatic nerve pinch injury. This was accompanied by changes in the levels of endogenous galanin, and its receptors galanin receptor 1 and galanin receptor 2 in the dorsal root ganglia and the spinal dorsal horn when compared with nerve pinch normal rats. Our results show that application of exogenous galanin daily for 28 days can promote the regeneration of injured sciatic nerves, and alleviate neuropathic pain in diabetic rats.

Reduction of spinal glycine receptor-mediated miniature inhibitory postsynaptic currents in streptozotocin-induced diabetic neuropathic pain

Diabetic neuropathic pain (DNP) is a common clinical problem, and the mechanisms underlying the onset and progression of this complication are poorly understood. The present study examined the glycine receptors (GlyR) in the control of synaptic input to dorsal horn neurons in diabetes. Male Sprague-Dawley rats with or without streptozotocin (STZ) intraperitoneal injections were used. Tactile sensitivities were assessed by measuring paw withdrawal thresholds to von Frey filaments for four weeks. The extent of GlyR-mediated inhibition controlling primary afferent-evoked excitation in dorsal horn neurons was examined by using the whole cell patch clamp recording technique in isolated adult rat spinal cord slices. The content of the spinal dorsal horn glycine levels was measured by microdialysis. An intrathecal glycine agonist injection was used to test whether mimicking endogenous glycine-receptor-mediated inhibition reduces DNP. We found that persistent hyperglycemia induced by the administration of STZ caused a decrease in the paw withdrawal latency to mechanical stimuli. The miniature inhibitory post-synaptic current (mIPSC) rise, decay kinetics and mean GlyR-mediated mIPSC amplitude were not affected in DNP. The mean frequency of GlyR-mediated mIPSC of lamina I neurons from DNP rats was, however, significantly reduced when compared with neurons from control rats. Principal passive and active membrane properties and the firing patterns of spinal lamina I neurons were not changed in DNP rats. Spinal microdialysis rats had a significantly decreased glycine level following its initial elevation. The intrathecal administration of glycine diminished tactile pain hypersensitivity in DNP rats. In conclusion, these results indicate that long-lasting hyperglycemia induced by STZ injections leads to a reduced glycinergic inhibitory control of spinal lamina I neurons through a presynaptic mechanism.

Effects of curcumin on TTX-R sodium currents of dorsal root ganglion neurons in type 2 diabetic rats with diabetic neuropathic pain

Type 2 diabetic mellitus (T2DM) has reached pandemic status and shows no signs of abatement. Diabetic neuropathic pain (DNP) is generally considered to be one of the most common complications of T2DM, which is also recognized as one of the most difficult types of pain to treat. As one kind of peripheral neuropathic pain, DNP manifests typical chronic neuralgia symptoms, including hyperalgesia, allodynia, autotomy, and so on. The injured dorsal root ganglion (DRG) is considered as the first stage of the sensory pathway impairment, whose neurons display increased frequency of action potential generation and increased spontaneous activities. These are mainly due to the changed properties of voltage-gated sodium channels (VGSCs) and the increased sodium currents, especially TTX-R sodium currents. Curcumin, one of the most important phytochemicals from turmeric, has been demonstrated to effectively prevent and/or ameliorate diabetic mellitus and its complications including DNP. The present study demonstrates that the TTX-R sodium currents of small-sized DRG neurons isolated from DNP rats are significantly increased. Such abnormality can be efficaciously ameliorated by curcumin.

Role of spinal MCP-1-ERK-KIF17/NR2B signaling pathway in maintenance of type 2 diabetic neuropathic pain in rats

Objective To explore the role of spinal monocyte chemoattractant protein-1 (MCP-1) -extracellular signal-regulated protein kinase (ERK) -kinesin superfamily motor protein 17 (KIF17) /N-methyl-D-aspartate receptor subunit 2B (NR2B) signaling pathway in the maintenance of type 2 diabetic neuropathic pain (DNP) in rats. Methods Type 2 diabetes mellitus was induced by a high-fat and high-sucrose diet and intraperitoneal streptozotocin (STZ) 35 mg/kg, and confirmed by fasting blood glucose level≥16.7 mmol/L 3 days later in male Sprague-Dawley rats aged 6 weeks.Type 2 DNP was confirmed when the mechanical paw withdrawal threshold (MWT) and thermal paw withdrawl latency (TWL) measured on day 14 after STZ administration decreased to < 80% of the baseline value.The rats with type 2 DNP were randomly divided into 4 groups (n=36 each) using a random number table: type 2 DNP group (group DNP) , type 2 DNP + MCP-1 neutralizing antibody group (group DM) , type 2 DNP + ERK inhibitor group (group DE) and type 2 DNP + dimethyl sulfoxide group (group DD) . In DM, DE and DD groups, 0.1 ng/μl MCP-1 neutralizing antibody 10 μl, 0.5 μg/μl U0126 10 μl and 5 % dimethyl sulfoxide 10 μl were injected intrathecally, respectively, once a day for 14 consecutive days starting from 14 days after administration of STZ.Another 36 normal rats fed a common forage diet were adopted as control group (group C) . MWT and TWL were measured before STZ injection and at 1, 3, 7 and 14 days after STZ injection (T0-4) . Nine rats were sacrificed after measurement of pain thresholds at T1-4, and the lumbar segments (L4-6) of the spinal cord were removed for determination of the expression of phosphorylated ERK (p-ERK) , KIF17 and phosphorylated NR2B (p-NR2B) by Western blot. Results Compared with group C, the MWT was significantly decreased, the TWL was shortened, and the expression of p-ERK, KIF17 and p-NR2B was up-regulated at T1-4 in DNP, DM, DE and DD groups.Compared with group DNP, the MWT at T3-4 in group DM and at T2-4 in group DE was significantly increased, the TWL at T3-4 in group DM and at T2-4 in group DE was prolonged, and the expression of p-ERK, KIF17 and p-NR2B was down-regulated at T2-4 in DM and DE groups, and no significant changes were found in the parameters mentioned above in group DD. Conclusion Spinal MCP-1-ERK-KIF17/NR2B signaling pathway is involved in the maintenance of type 2 DNP in rats. Key words: Diabetes mellitus, type 2; Neuropathic pain; Chemokine CCL2; Extracellular Signal-Regulated MAP Kinases; Receptors, N-Methyl-D-Aspartate; Kinesin; Spinal cord

Activated autophagy in spinal cord contributes to maintaining diabetic neuropathic pain in rats model

To observe the role of autophagy in maintaining diabetic neuropathic pain in rats model. A total of 44 male Sprague-Dawley rats were randomly divided into diabetic neuropathic (n = 36) and normal control (n = 8) groups. Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ) (60 mg/kg body weight, i.p) freshly dissolved in citrate buffer (pH = 4.5). For assessing the presence of mechanical hyperalgesia in diabetic rats, mechanical paw-withdrawal threshold (MWT) in response to punctuate mechanical stimuli was measured. At Week 4 post-injection, the rats with mechanical pain threshold decreasing over 50% as compared to baseline were designated as diabetic neuropathic pain rats. They were randomly divided into three groups of neuropathic pain (DP), neuropathic pain plus rapamycin (DR) and neuropathic pain plus 3-methyladenine (3-MA) (DA). The DR group received an intraperitoneal injection of rapamycin (1 mg/kg body weight) for Day 1 to Day 14 after grouping. At the same timepoint, the DA group had an intraperitoneal injection of 3-MA (2 mg/kg body weight) and the other group phosphate buffered saline (PBS) (1 ml/kg body weight). MWT was measured at week 1, 2, 3, 4 after STZ injection and at day 1, 3, 5, 7, 9, 14 after rapamycin, 3-MA or PBS injections. Spinal cord tissues were used to examine the expression of LC3, Beclin-1 and P62 protein by Western blot at Day 14 after medication. The mechanical threshold of group DR decreased further from Day 3 to Day 14 after rapamycin injection compared to baseline [(4.8±0.8), (4.3±0.7), (4.1±0.6), (3.6±0.5), (3.3±0.6) vs (5.3±0.9) g, P<0.05]. The mechanical threshold of group DA began to increase from Day 5 to Day 14 after 3-MA injection [(7.0±0.8), (7.7±1.0), (9.1±0.9), (9.6±1.1) vs (5.3±0.6) g, P<0.05]. The expressions of LC3-II and Beclin-1 protein in spinal cord of rapamycin-treated rats was significantly higher than those of non-supplemented diabetics (1.32±0.12 vs 1.02±0.11; 1.03±0.08 vs 0.80±0.06, P<0.05). Otherwise the expressions of these protein in spinal cord of 3-MA-treated rats were significantly lower than those of non-supplemented diabetics (0.70±0.09 vs 1.02±0.11; 0.55±0.05 vs 0.80±0.06, P<0.05). Up-regulated autophagy in spinal cord partially contributes to the maintenance of diabetic neuropathic pain.

Effect of Hydroethanolic Extract of Rubus fruticosus on Neuropathic Pain in Wistar Diabetic Rats

Article type: Original Article Background: Diabetes mellitus is the most common metabolic disorder with many complications such as neuropathic pain which relief from it is a dilemma. Objectives: To investigate the effect of hydroethanolic extract of Rubus fruticosus on neuropathic pain in diabetic rats. Materials and Methods: In this experimental case –control study, forty eight male Wistar rats (250±20 g) were divided randomly to non-diabetic and diabetic groups. Streptozotocin (60 mg/kg, intra-peritoneal) was used to induce experimental diabetes. Each group was divided into three groups: receiving orally normal saline, 100 and 200 mg/kg doses of Rubus fruticosus extract for 30 days. At the end; the rats were subjected to Tail-Flick test. The data were analyzed by one-way and two-way ANOVA followed by Tukey’s test in SPSS 21. Results: In a paired comparison, all diabetic groups had shorter latency of tailflicking time (p < 0.01) and lower pain tolerance threshold. Also among diabetic rats, significant differences existed between saline group and group receiving the extract at a dose of 100 mg/Kg (p < 0.01), between saline group and the group receiving the extract at a dose of 200 mg/Kg (p < 0.001) and also between the groups receiving extract at two different doses (p < 0.001). But, only diabetic group receiving the extract at a dose of 200 mg/Kg showed positive significant difference with non-diabetic control group (p < 0.01). Conclusions: The hydroethanolic extract of Rubus fruticosus can heighten the pain tolerance threshold and reduce the neuropathic pain induced by diabetes mellitus.

Protective Effect of Ethanol Extracts of Hericium erinaceus on Alloxan-Induced Diabetic Neuropathic Pain in Rats.

We investigated the effects of Hericium erinaceus (HEE) on alloxan induced diabetic neuropathic pain in laboratory rats. Alloxan induced diabetic rats were administered orally HEE. After 6 weeks of treatments, treatment with HEE 40 mg/kg in diabetic animals showed significant increase in pain threshold and paw withdrawal threshold and significant decrease in serum glucose and urine glucose. We also observed a significant increase in lactate dehydrogenase (LDH), Lipid peroxidation (LPO), glutathione peroxidase (GPx) activity, glutathione reductase (GR) activity, catalase (CAT) activity, Na+K+ATPase activity, and glutathione S transferase (GST) activity along with significant decreased levels of glutathione (GSH) content in diabetic rats. The total antioxidant status (TAOS) in the HEE-treated groups was significantly lower than that in the alloxan-treated group. HEE can offer pain relief in diabetic neuropathic pain. The improvement in diabetic state after HEE treatment along with the antioxidant activity could be the probable way by which it had alleviated diabetic neuropathy.

Effects of nefopam on streptozotocin-induced diabetic neuropathic pain in rats.

BackgroundNefopam is a centrally acting non-opioid analgesic agent. Its analgesic properties may be related to the inhibitions of monoamine reuptake and the N-methyl-D-aspartate (NMDA) receptor. The antinociceptive effect of nefopam has been shown in animal models of acute and chronic pain and in humans. However, the effect of nefopam on diabetic neuropathic pain is unclear. Therefore, we investigated the preventive effect of nefopam on diabetic neuropathic pain induced by streptozotocin (STZ) in rats.MethodsPretreatment with nefopam (30 mg/kg) was performed intraperitoneally 30 min prior to an intraperitoneal injection of STZ (60 mg/kg). Mechanical and cold allodynia were tested before, and 1 to 4 weeks after drug administration. Thermal hyperalgesia was also investigated. In addition, the transient receptor potential ankyrin 1 (TRPA1) and TRP melastatin 8 (TRPM8) expression levels in the dorsal root ganglion (DRG) were evaluated.ResultsPretreatment with nefopam significantly inhibited STZ-induced mechanical and cold allodynia, but not thermal hyperalgesia. The STZ injection increased TRPM8, but not TRPA1, expression levels in DRG neurons. Pretreatment with nefopam decreased STZ-induced TRPM8 expression levels in the DRG.ConclusionsThese results demonstrate that a nefopam pretreatment has strong antiallodynic effects on STZ-induced diabetic rats, which may be associated with TRPM8 located in the DRG.

Role of transient receptor potential ankyrin 1 in dorsal root ganglion neurons in development of diabetic neuropathic pain in rats

Objective To evaluate the role of transient receptor potential ankyrin 1 (TRPA1) in the dorsal root ganglion neurons in the development of diabetic neuropathic pain (DNP) in rats.Methods Twenty-four Sprague-Dawley rats with DNP were randomly divided into 3 groups (n-=8 each) using a random number table:DNP group,TRPA1-specific siRNA group (siRNA group) and TRPA1-negative siRNA group (NC group).Another 8 Sprague-Dawley rats with normal blood glucose served as control group (C group).In siRNA group,TRPA1-specific siRNA 45 μl was injected intrathecally.In NC group,TRPA1-negative siRNA 45 μl was injected intrathecally.In DNP and C groups,normal saline 45 μl was injected intrathecally.On 2nd day after intrathecal administration,the lumbar segment (L4-6) of the dorsal root ganglions was removed for determination of the expression of TRPA1 mRNA.On 7,14,21 and 28 days after intrathecal administration (T1-4),MWT was measured.Results Compared with DNP group,TRPA1 mRNA expression was down-regulated in siRNA and C groups.Compared with DNP group,and MWT was significantly decreased at T1.2 in siRNA group,MWT was decreased at T1-3 in NC group,MWT was increased at T1-4 in group C.Compared with siRNA group,MWT was significantly increased at T1-4 in group C.MWT was significantly higher at T1~ in group C than in NC group.Conclusion TRPA1 in the dorsal root ganglion neurons is involved in the development of DNP in rats. Key words: Transient receptor potential channels; Posterior horn cells; Diabetic neuropathies

Intrathecal baclofen, a GABAB receptor agonist, inhibits the expression of p-CREB and NR2B in the spinal dorsal horn in rats with diabetic neuropathic pain.

This study aimed to investigate the effect of baclofen, a γ-aminobutyric acid B (GABAB) receptor agonist, on the expression of p-CREB and NR2B in the spinal dorsal horn of rats with diabetic neuropathic pain (DNP). The DNP rats, which were successfully induced with streptozocin, were distributed among 3 groups that were treated with saline (D1 group), baclofen (D2 group), or CGP55845 + baclofen (D3 group) continuously for 4 days. The rats induced with saline and subsequently treated with saline were used as controls (C group). The times for the paw withdrawal threshold and thermal withdrawal latency of the D1 group were lower than those for the C group, and were significantly increased after baclofen treatment, but not when GABA receptor was pre-blocked with CGP55845 (D3 group). Increased protein expression levels of NR2B and p-CREB and mRNA levels of NR2B were found in the D1 group when compared with the controls. Baclofen treatment significantly suppressed their expression, bringing it close to the levels of controls. However, in the D3 group, the expression of p-CREB and NR2B were still significantly higher than that of the controls. Activation of GABAB receptor by baclofen attenuates diabetic neuropathic pain, which may partly be accomplished via down-regulating the expression of p-CREB and NR2B.

Effects of hydrogen-rich saline on early diabetic neuropathic pain in rats

Objective To evaluate the effects of hydrogen-rich saline on the early diabetic neuropathic pain (DPN) in rats.Methods Healthy male Sprague-Dawley rats,aged 8 weeks,weighing 180-220 g,were used in the study.DPN model was made by intraperitoneal injection of 1％ streptozocin (STZ) 65 mg/kg.Twelve diabetic rats were randomly divided into 2 groups (n =6 each) using a random number table:DPN group and hydrogen-rich saline group (HRS group).Another 6 normal rats were randomly collected as control group (group C).At 14 days after STZ injection,hydrogen-rich saline 5 ml/kg was injected intraperitoneally once a day for 14 consecutive days in HRS group,while C and DNP groups received the equal volume of normal saline.Mechanical paw withdrawal threshold to yon Frey stimuli (MWT) and paw withdrawal latency to nociceptive thermal stimulation (TWL) were measured at 2 days before STZ injection (To) and 7,14,21 and 28 days after STZ injection (T1-4).The motor nerve conduction velocity (MNCV) of the right hindlimb and distal motor latency was measured after pain threshold was measured at T4.After measurement of neurological function was completed,tumor necrosis factor-α (TNF-α) and i nterleukin-6 (IL-6) contents (by ELISA) and nuclear factor kappa B (NF-κB) activity (by immuno-histochemistry) were detected.Results Compared with group C,MNCV was significantly decreased,the motor latency was prolonged,MWT was decreased at T1-T4,TWL was shortened at T2-T4,TNF-a and IL-6 contents were increased,and NF-κB activity was enhanced in DNP and HRS groups (P ＜ 0.05).Compared with group DNP,MNCV was significandy increased,the motor latency was shortened,MWT was increased at T3.4,TWL was prolonged at T4,TNF-a and IL-6 contents were decreased,and NF-κB activity was weakened in group HRS (P ＜ 0.05).Conclusion Hydrogen-rich saline can relieve the early DPN through inhibiting NF-κB signaling pathway in rats. Key words: Hydrogen; Diabetes mellitus; Neuralgia