Selective activation of AKAP150/TRPV1 in ventrolateral periaqueductal gray GABAergic neurons facilitates conditioned place aversion in male mice.

Aversion refers to feelings of strong dislike or avoidance toward particular stimuli or situations. Aversion can be caused by pain stimuli and has a long-term negative impact on physical and mental health. Aversion can also be caused by drug abuse withdrawal, resulting in people with substance use disorder to relapse. However, the mechanisms underlying aversion remain unclear. The ventrolateral periaqueductal gray (vlPAG) is considered to play a key role in aversive behavior. Our study showed that inhibition of vlPAG GABAergic neurons significantly attenuated the conditioned place aversion (CPA) induced by hindpaw pain pinch or naloxone-precipitated morphine withdrawal. However, activating or inhibiting glutamatergic neurons, or activating GABAergic neurons cannot affect or alter CPA response. AKAP150 protein expression and phosphorylated TRPV1 (p-TRPV1) were significantly upregulated in these two CPA models. In AKAP150flox/flox mice and C57/B6J wild-type mice, cell-type-selective inhibition of AKAP150 in GABAergic neurons in the vlPAG attenuated aversion. However, downregulating AKAP150 in glutamatergic neurons did not attenuate aversion. Knockdown of AKAP150 in GABAergic neurons effectively reversed the p-TRPV1 upregulation in these two CPA models utilized in our study. Collectively, inhibition of the AKAP150/p-TRPV1 pathway in GABAergic neurons in the vlPAG may be considered a potential therapeutic target for the CPA response.

Distinct roles of srGAP3-Rac1 in the initiation and maintenance phases of neuropathic pain induced by paclitaxel.

KEY POINTS: Spinal cord dorsal horn srGAP3 (slit-robo GTPase activating protein 3) increases in the initiation phase of neuropathic pain and decreases in the maintenance phase. However, Rac1 activity, which can be reduced by srGAP3, decreases in the initiation phase and increases in the maintenance phase. The increased srGAP3 in the initiation phase promotes new immature dendritic spines instigating neuropathic pain. Decreased srGAP3 in the maintenance phase enhances Rac1 activity facilitating maturation of dendritic spines and the persistence of neuropathic pain. SrGAP3 small interfering RNA can ameliorate neuropathic pain only when administrated in the initiation phase. The Rac1 inhibitor can ameliorate neuropathic pain only when administrated in the maintenance phase. Combined targeting of srGAP3 in the initiation phase and Rac1 in the maintenance phase can produce optimal analgesic efficacy. ABSTRACT: Neuropathic pain includes an initiation phase and maintenance phase, each with different pathophysiological processes. Understanding the synaptic plasticity and molecular events in these two phases is relevant to exploring precise treatment strategies for neuropathic pain. In the present study, we show that dendritic spine density increases in the spinal dorsal horn in the initiation phase of neuropathic pain induced by paclitaxel and that the spine maturity ratio increases in the maintenance phase. Increased srGAP3 (slit-robo GTPase activating protein 3) facilitates dendritic spine sprouting in the initiation phase. In the maintenance phase, srGAP3 decreases to upregulate Rac1 activity, which facilitates actin polymerization and dendritic spine maturation and thus the persistence of neuropathic pain. Knockdown of srGAP3 in the initiation phase or inhibition of Rac1 in the maintenance phase attenuates neuropathic pain. Combined intervention of srGAP3 in the initiation phase, and Rac1 in the maintenance phase shows better analgesic efficacy against neuropathic pain. The present study demonstrates the role of srGAP3-Rac1 in dendritic spine plasticity in the two phases of neuropathic pain and, accordingly, provides treatment strategies for different phases of neuropathic pain.

AKAP150 involved in paclitaxel-induced neuropathic pain via inhibiting CN/NFAT2 pathway and downregulating IL-4.

Antitubulin chemotherapeutics agents, such as paclitaxel, are effective chemotherapy drugs for cancer treatment. However, painful neuropathy is a major adverse effect limiting the wider application of chemotherapeutics. In this study, we found that A-kinase anchor protein 150 (AKAP150) was significantly upregulated after paclitaxel injection. Inhibition of AKAP150 via siRNA or AKAP150flox/flox in rodents alleviated the pain behavior induced by paclitaxel, and partly restored the decreased calcineurin (CN) phosphatase activity after paclitaxel treatment. Paclitaxel decreased the expression of anti-inflammatory cytokine interleukin-4 (IL-4), and intrathecal injections of IL-4 effectively alleviated paclitaxel-induced hypersensitivity and the frequency of dorsal root ganglion (DRG) neurons action potential. The decreased CN enzyme activity, resulted in reduced protein expression of nuclear factor of activated T cells 2 (NFAT2) in cell nuclei. Chromatin immunoprecipitation showed that, NFAT2 binds to the IL-4 gene promoter regulating the protein expression of IL-4. Overexpression of NFAT2 by intrathecal injection of the AAV5-NFAT2-GFP virus alleviated the pain behavior induced by paclitaxel via increasing the expression of IL-4. Knocked down AKAP150 by siRNA or AAV5-Cre-GFP partly restored the expression of IL-4 in DRG. Our results indicated that regulation of IL-4 via the CN/NFAT2 pathway mediated by AKAP150 could be a pivotal treatment target for paclitaxel-induced neuropathic pain and or other neuropsychiatric disorders.

Synergistic Interaction Between Dexmedetomidine and Ulinastatin Against Vincristine-Induced Neuropathic Pain in Rats.

Antimicrotubulin chemotherapeutic agents such as vincristine (VCR), often induce peripheral neuropathic pain. It is usually permanent and seriously harmful to cancer patients' quality of life and can result in the hampering of clinical treatments. Currently, there is no definitive therapy, and many of the drugs approved for the treatment of other neuropathic pain have shown little or no analgesic effect. It is therefore vital to find new and novel therapeutic strategies for patients suffering from chemotherapeutic agent-induced neuropathic pain to improve patients' quality of life. This study shows that intrathecal injections of dexmedetomidine (DEX), or intraperitoneally administered ulinastatin (UTI) significantly reduces Sprague Dawley rats' mechanical allodynia induced by VCR via upregulation of interleukin-10 expression and activating the α2-adrenergic receptor in dorsal root ganglion (DRG). Moreover, when combined there is a synergistic interaction between DEX and UTI, which acts against VCR-induced neuropathic pain. This synergistic interaction between DEX and UTI may be partly attributed to a common analgesic pathway in which the upregulation of interleukin -10 plays an important role via activating α2-adrenergic receptor in rat dorsal root ganglion. The combined use of DEX and UTI does not affect the rat's blood pressure, heart rate, sedation, motor score, spatial learning, or memory function. All of these show that the combined use of DEX and UTI is an effective method in relieving VCR-induced neuropathic pain in rats. PERSPECTIVE: This article documents the synergistic interaction between 2 widely used drugs, DEX and UTI, against VCR-induced neuropathic pain. The results provide a potential target and novel drug administrated method for the clinical treatment of chemotherapy-induced peripheral neuropathic pain.

Epigenetic upregulation of CXCL12 expression mediates antitubulin chemotherapeutics-induced neuropathic pain.

Clinically, Microtubule-targeted agents-induced neuropathic pain hampers chemotherapeutics for patients with cancer. Here, we found that application of paclitaxel or vincristine increased the protein and mRNA expression of CXCL12 and frequency and amplitude of miniature excitatory post synaptic currents (mEPSCs) in spinal dorsal horn neurons. Spinal local application of CXCL12 induced the long-term potentiation of nociceptive synaptic transmission and increased the amplitude of mEPSCs. Inhibition of CXCL12 using the transgenic mice (CXCL12) or neutralizing antibody or siRNA ameliorated the mEPSC's enhancement and mechanical allodynia. In addition, paclitaxel and vincristine both could increase the phosphorylation of signal transducer and activator of transcription 3 (STAT3) and the acetylation of histone H4 in the CXCL12-expressing neurons. Immunoprecipitation and chromatin immunoprecipitation assays demonstrated that antitubulin chemotherapeutics increased the binding of STAT3 to the CXCL12 gene promoter and the interaction between STAT3 and p300, and contributed to the enhanced transcription of CXCL12 by increasing the acetylation of histone H4 in CXCL12 gene promoter. Inhibition of STAT3 by intrathecal injection of adeno-associated virus encoding Cre and green fluorescent protein into STAT3 mice or inhibitor S3I-201 into rats suppressed the CXCL12 upsurge by decreasing the acetylation of histone H4. Finally, blockade of CXCR4 but not CXCR7 ameliorated the paclitaxel- or vincristine-induced mechanical allodynia. Together, these results suggested that enhanced interaction between STAT3 and p300 mediated the epigenetic upregulation of CXCL12 in dorsal horn neurons, which contributed to the antitubulin chemotherapeutics-induced persistent pain.

Corrigendum to "Spinal Antinociceptive Action of Amiloride and Its Interaction with Tizanidine in the Rat Formalin Test".

[This corrects the article DOI: 10.1155/2015/902914.].

Ulinastatin attenuates neuropathic pain induced by L5-VRT via the calcineurin/IL-10 pathway.

Previous studies have shown that ulinastatin, an effective inhibitor of the inflammatory response in clinical applications, can attenuate hyperalgesia in rodents. However, the underlying mechanism remains unclear. In the present study, we first examined the change in the calcineurin level, which plays an important role in regulating cytokine release in the nervous system, following lumbar 5 ventral root transection in the rat. Furthermore, we determined whether intraperitoneal (i.p.) injection of ulinastatin attenuated pain behavior via inhibition of the calcineurin-mediated inflammatory response induced by lumbar 5 ventral root transection. The results showed that the paw withdrawal threshold and paw withdrawal latency were significantly decreased following lumbar 5 ventral root transection compared to the sham group. Neuropathic pain induced by lumbar 5 ventral root transection significantly decreased the expression of calcineurin in the DRG, and calcineurin was mostly located with NF-200-positive cells, IB4-positive cells, and CGRP-positive cells and less with GFAP-positive satellite cells. Furthermore, intrathecal (i.t.) injection of exogenous calcineurin attenuated the pain behavior induced by lumbar 5 ventral root transection. Importantly, intraperitoneal injection of ulinastatin alleviated the pain behavior and calcineurin downregulation induced by lumbar 5 ventral root transection. Lastly, the cytokine IL-10 was significantly decreased following lumbar 5 ventral root transection, and application of calcineurin (intrathecal) or ulinastatin (intraperitoneal) inhibited the IL-10 downregulation induced by lumbar 5 ventral root transection. These results suggested that ulinastatin, by acting on the CN/IL-10 pathway, might be a novel and effective drug for the treatment of neuropathic pain.

Spinal antinociceptive action of amiloride and its interaction with tizanidine in the rat formalin test.

BACKGROUND: Amiloride has been reported to produce a wide variety of actions, thereby affecting several ionic channels and a multitude of receptors and enzymes. Intrathecal α2-adrenergic receptor agonists produce pronounced analgesia, and amiloride modulates α2-adrenergic receptor agonist binding and function, acting via the allosteric site on the α2A-adrenergic receptor. OBJECTIVES: To investigate the antinociceptive interaction of intrathecal amiloride and the α2-adrenoceptor agonist tizanidine using a rat formalin test. METHODS: Sprague-Dawley rats were chronically implanted with lumbar intrathecal catheters and were tested for paw flinching using formalin injection. Biphasic painful behaviour was recorded. Amiloride, tizanidine or an amiloride-tizanidine mixture was administered 10 min before formalin injection. To characterize any interactions, isobolographic analysis was performed. The effects of a pretreatment using intrathecally administered yohimbine was also tested. RESULTS: Intrathecally administered amiloride (12.5 µg to 100 µg) and tizanidine (0.5 µg to 5 µg), given separately, produced a significant dose-related suppression of the biphasic responses in the formalin test. Isobolographic analysis revealed that the combination of intrathecal amiloride and tizanidine synergistically reduced phase I and II activities. Intrathecally administered yohimbine antagonized or attenuated the antinociceptive effect of amiloride, tizanidine and the amiloride-tizanidine mixture. Intrathecally administered amiloride synergistically interacts with tizanidine to reduce the nociceptive response in the formalin test, most likely by activating α2-adrenoceptors in the spinal cord. CONCLUSIONS: Although intrathecal tizanidine produced pronounced analgesia, antinociceptive doses of intrathecal tizanidine also produced several side effects, including bradycardia and sedation. Amiloride produced antinociceptive action against the thermal nociceptive test without side effects in rats.