http://www.molecularpain.com The latest research articles published by Molecular Pain 2013-06-17T00:00:00Z Background: We previously reported that nerve injury-induced neuropathic pain is initiated by newly produced lysophosphatidic acid (LPA). Results: In this study, we developed a quantitative mass spectrometry for detecting LPA species by using Phos-tag. Following nerve injury, the levels of 18:1, 16:0 and 18:0 LPA in the spinal dorsal horn significantly increased at 3 h and declined at 6 h. Among them, 18:1 LPA level was the most abundant. In the same preparation, there were significant elevations in the activities of cytosolic phospholipase A2 (cPLA2) and calcium-independent phospholipase A2 (iPLA2), key enzymes for LPA synthesis, at 1 h, while there was no significant change in phospholipase A1 activity. Pharmacological studies revealed that NMDA and neurokinin 1 receptors, cPLA2, iPLA2 and microglial activation, as well as LPA1 and LPA3 receptors were all involved in the nerve injury-induced LPA production, and underlying cPLA2 and iPLA2 activations. In the cells expressing LPA1 or LPA3 receptor, the receptor-mediated calcium mobilization was most potent with 18:1 LPA, compared with 16:0 or 18:0 LPA. Moreover, the intrathecal injection of 18:1 LPA, but not 16:0 or 18:0 LPA, caused a spinal LPA production and neuropathic pain-like behavior. Conclusion: These results suggest that 18:1 LPA is the predominant ligand responsible for LPA1 and LPA3 receptors-mediated amplification of LPA production through microglial activation. http://www.molecularpain.com/content/9/1/29 Lin Ma Jun Nagai Jerold Chun Hiroshi Ueda Molecular Pain 2013, null:29 2013-06-17T00:00:00Z doi:10.1186/1744-8069-9-29 /content/figures/1744-8069-9-29-toc.gif Molecular Pain 1744-8069 ${item.volume} 29 2013-06-17T00:00:00Z PDF Both spinal and trigeminal somatosensory systems use the TRPM8 channel as a principal transducer for detecting cold stimuli. It is currently unclear whether this cold transducer may play a role in trigeminal neuropathic pain manifesting cold allodynia and hyperalgesia. In the present study, trigeminal neuropathy was induced by chronic constrictive nerve injury of the infraorbital nerve (ION-CCI). Behavioral responses to cold stimuli in orofacial regions were assessed by the newly developed orofacial operant test in the ION-CCI rats. We tested menthol and capsazepine, two compounds that can activate and inhibit TRPM8 respectively, on orofacial operant responses to cold stimuli in ION-CCI rats. Testing animals performed operant tasks by voluntarily contacting their orofacial regions to a cold stimulation module in order to access sweetened milk as a reward, and contact time and number of the operant behaviors were automatically recorded. Total contact time was significantly reduced at the cooling temperatures of 17 [degree sign]C and 12 [degree sign]C in ION-CCI group in comparison with sham group, indicating the presence of cold allodynia and hyperalgesia in ION-CCI rats. When menthol was administered to ION-CCI rats, total contact time was further reduced and total contact number increased at the cooling temperatures. In contrast, after administration of capsazepine to ION-CCI rats, total contact time was significantly increased at the cooling temperatures. The behavioral outcomes support the idea that TRPM8 plays a role in cold allodynia and hyperalgesia following chronic trigeminal nerve injury. http://www.molecularpain.com/content/9/1/28 Xiaozhuo Zuo Jennifer Ling Guang-Yin Xu Jianguo Gu Molecular Pain 2013, null:28 2013-06-14T00:00:00Z doi:10.1186/1744-8069-9-28 /content/figures/1744-8069-9-28-toc.gif Molecular Pain 1744-8069 ${item.volume} 28 2013-06-14T00:00:00Z PDF Background: Extracellular acidosis is a prominent feature of multiple pathological conditions, correlating with pain sensation. Acid-sensing ion channels (ASICs), a family of proton-gated cation channels, are distributed throughout the central and peripheral nervous systems. Activation of ASICs, particularly ASIC3 and ASIC1a channels, by acidic pH and the resultant depolarization of nociceptive primary sensory neurons, participates in nociception. Agents that inhibit the activation of ASICs are thus expected to be analgesic. Here, we studied the effect of local anesthetic tetracaine on ASIC currents. Results: Tetracaine inhibited the peak ASIC3 current in a concentration-dependent manner with an IC50 of 9.96 +/- 1.88 mM. The degree of inhibition by tetracaine was dependent on the extracellular pH but independent of the membrane potential. Furthermore, 3 mM tetracaine also inhibited 29.83% of the sustained ASIC3 current. In addition to ASIC3, tetracaine inhibited the ASIC1a and ASIC1beta currents. The inhibition of the ASIC1a current was influenced by the frequency of channel activation. In contrast to ASIC3, ASIC1a, and ASIC1beta currents, ASIC2a current was not inhibited by tetracaine. In cultured mouse dorsal root ganglion neurons, 1--3 mM tetracaine inhibited both the transient and sustained ASIC currents. At pH4.5, 3 mM tetracaine reduced the peak ASIC current to 60.06 +/- 4.51%, and the sustained current to 48.24 +/- 7.02% of the control values in dorsal root ganglion neurons. In contrast to ASICs, voltage-gated sodium channels were inhibited by acid, with 55.15% inhibition at pH6.0 and complete inhibition at pH5.0. Conclusions: These findings disclose a potential new mechanism underlying the analgesic effects of local anesthetics, particularly in acidic conditions where their primary target (i.e. voltage-gated Na+ channel) has been suppressed by protons. http://www.molecularpain.com/content/9/1/27 Tiandong Leng Jun Lin James Cottrell Zhi-Gang Xiong Molecular Pain 2013, null:27 2013-06-10T00:00:00Z doi:10.1186/1744-8069-9-27 /content/figures/1744-8069-9-27-toc.gif Molecular Pain 1744-8069 ${item.volume} 27 2013-06-10T00:00:00Z PDF Background: Although a number of clinical and preclinical studies have demonstrated analgesic effects of cannabinoid treatments, there are also instances when cannabinoids have had no effect or even exacerbated pain. The observed pro-nociceptive effects appear to be due to cannabinoid-induced disinhibition of afferent synaptic input to nociceptive circuits. To better understand how cannabinoid-mediated plasticity can have both pro- and anti-nociceptive effects, we examined the possibility that cannabinoids differentially modulate nociceptive vs. non-nociceptive synapses onto a shared postsynaptic target. These experiments were carried out in the central nervous system (CNS) of the medicinal leech, in which it is possible to intracellularly record from presynaptic nociceptive (N-cell) or pressure-sensitive (P-cell) neurons and their shared postsynaptic targets. Results: The endocannabinoid 2-arachidonoyl glycerol (2AG) elicited significant long-lasting synaptic depression in nociceptive (N-cell) synapses. However, non-nociceptive (P-cell) synapses were potentiated following 2AG treatment. 2AG-induced potentiation of non-nociceptive synapses was blocked by the TRPV antagonist SB366791, suggesting involvement of the same TRPV-like receptor that has already been shown to mediate endocannabinoid-dependent depression in nociceptive inputs. Treatment with the GABA receptor antagonist bicuculline also blocked 2AG-induced potentiation, consistent with the idea that increased synaptic signaling was the result of endocannabinoid-mediated disinhibition. Interestingly, while bicuculline by itself increased non-nociceptive synaptic transmission, nociceptive synapses were depressed by this GABA receptor antagonist indicating that nociceptive synapses were actually excited by GABAergic input. Consistent with these observations, GABA application depolarized the nociceptive afferent and hyperpolarized the non-nociceptive afferent. Conclusions: These findings show that endocannabinoids can differentially modulate nociceptive vs. non-nociceptive synapses and that GABAergic regulation of these synapses plays an important role in determining whether endocannabinoids have a potentiating or depressing effect. http://www.molecularpain.com/content/9/1/26 Alexandra Higgins Sharleen Yuan Yanqing Wang Brian Burrell Molecular Pain 2013, null:26 2013-06-01T00:00:00Z doi:10.1186/1744-8069-9-26 /content/figures/1744-8069-9-26-toc.gif Molecular Pain 1744-8069 ${item.volume} 26 2013-06-01T00:00:00Z PDF Background: The quantification of pain intensity in vivo is essential for identifying the mechanisms of various types of pain or for evaluating the effects of different analgesics. A variety of behavioral tests for pain measurement have been devised, but many are limited because animals are physically restricted, which affects pain sensation. In this study, pain assessment was attempted with minimal physical restriction, and voluntary movements of unrestrained animals were used to evaluate the intensities of various types of pain. Results: The number of times animals reared or total distances traveled was measured using a motion-tracking device and found to be markedly reduced in carrageenan-induced inflammatory, acetic acid-induced visceral, and streptozotocin-induced neuropathic pain tests. These two voluntary movement parameters were found to be highly correlated with paw withdrawal latency from irradiating heat. In addition, these parameters were markedly reversed by morphine and by non-steroidal anti-inflammatory drugs in inflammatory pain models. These parameters were also useful to detect hypoalgesia in TRPV1-/- mice. Conclusions: These results suggest that parameters of voluntary movement, such as, number of rearing and total distance moved, are effective indicators of pain intensity for many types of pain and that they can be used to evaluate degree of pain perception. http://www.molecularpain.com/content/9/1/25 Hawon Cho Yongwoo Jang Byeongjun Lee Hyeyoun Chun Jooyoung Jung Sung Kim Sun Hwang Uhtaek Oh Molecular Pain 2013, null:25 2013-05-20T00:00:00Z doi:10.1186/1744-8069-9-25 /content/figures/1744-8069-9-25-toc.gif Molecular Pain 1744-8069 ${item.volume} 25 2013-05-20T00:00:00Z PDF Background: Odontoblasts are specialized cells that form dentin and they are believed to be sensors for tooth pain. Transforming growth factor-β1 (TGF-β1), a pro-inflammatory cytokine expressed early in odontoblasts, plays an important role in the immune response during tooth inflammation and infection. TGF-β1 is also known to participate in pain signaling by regulating cyclin-dependent kinase 5 (Cdk5) in nociceptive neurons of the trigeminal and dorsal root ganglia. However, the precise role of TGF-β1 in tooth pain signaling is not well characterized. The aim of our present study was to determine whether or not in odontoblasts Cdk5 is functionally active, if it is regulated by TGF-β1, and if it affects the downstream pain receptor, transient receptor potential vanilloid-1 (TRPV1). Results: We first determined that Cdk5 and p35 are indeed expressed in an odontoblast-enriched primary preparation from murine teeth. For the subsequent analysis, we used an odontoblast-like cell line (MDPC-23) and found that Cdk5 is functionally active in these cells and its kinase activity is upregulated during cell differentiation. We found that TGF-β1 treatment potentiated Cdk5 kinase activity in undifferentiated MDPC-23 cells. SB431542, a specific inhibitor of TGF-β1 receptor 1 (Tgfbr1), when co-administered with TGF-β1, blocked the induction of Cdk5 activity. TGF-β1 treatment also activated the ERK1/2 signaling pathway, causing an increase in early growth response-1 (Egr-1), a transcription factor that induces p35 expression. In MDPC-23 cells transfected with TRPV1, Cdk5-mediated phosphorylation of TRPV1 at threonine-407 was significantly increased after TGF-β1 treatment. In contrast, SB431542 co-treatment blocked TRPV1 phosphorylation. Moreover, TGF-β1 treatment enhanced both proton- and capsaicin-induced Ca2+ influx in TRPV1-expressing MDPC-23 cells, while co-treatment with either SB431542 or roscovitine blocked this effect. Conclusions: Cdk5 and p35 are expressed in a murine odontoblast-enriched primary preparation of cells from teeth. Cdk5 is also functionally active in odontoblast-like MDPC-23 cells. TGF-β1 sensitizes TRPV1 through Cdk5 signaling in MDPC-23 cells, suggesting the direct involvement of odontoblasts and Cdk5 in dental nociceptive pain transduction. http://www.molecularpain.com/content/9/1/24 Elias Utreras Michaela Prochazkova Anita Terse Jacklyn Gross Jason Keller Michael Iadarola Ashok Kulkarni Molecular Pain 2013, null:24 2013-05-13T00:00:00Z doi:10.1186/1744-8069-9-24 /content/figures/1744-8069-9-24-toc.gif Molecular Pain 1744-8069 ${item.volume} 24 2013-05-13T00:00:00Z XML Background: An inositol 1,4,5-trisphosphate binding protein, comprising 2 isoforms termed PRIP-1 and PRIP-2, was identified as a novel modulator for GABAA receptor trafficking. It has been reported that naive PRIP-1 knockout mice have hyperalgesic responses.FindingsTo determine the involvement of PRIP in pain sensation, a hind paw withdrawal test was performed before and after partial sciatic nerve ligation (PSNL) in PRIP-1 and PRIP-2 double knockout (DKO) mice. We found that naive DKO mice exhibited normal pain sensitivity. However, DKO mice that underwent PSNL surgery showed increased ipsilateral paw withdrawal threshold. To further investigate the inverse phenotype in PRIP-1 KO and DKO mice, we produced mice with specific siRNA-mediated knockdown of PRIPs in the spinal cord. Consistent with the phenotypes of KO mice, PRIP-1 knockdown mice showed allodynia, while PRIP double knockdown (DKD) mice with PSNL showed decreased pain-related behavior. This indicates that reduced expression of both PRIPs in the spinal cord induces resistance towards a painful sensation. GABAA receptor subunit expression pattern was similar between PRIP-1 KO and DKO spinal cord, while expression of K+-Cl--cotransporter-2 (KCC2), which controls the balance of neuronal excitation and inhibition, was significantly upregulated in DKO mice. Furthermore, in the DKD PSNL model, an inhibitor-induced KCC2 inhibition exhibited an altered phenotype from painless to painful sensations. Conclusions: Suppressed expression of PRIPs induces an elevated expression of KCC2 in the spinal cord, resulting in inhibition of nociception and amelioration of neuropathic pain in DKO mice. http://www.molecularpain.com/content/9/1/23 Tomoya Kitayama Katsuya Morita Rizia Sultana Nami Kikushige Keisuke Mgita Shinya Ueno Masato Hirata Takashi Kanematsu Molecular Pain 2013, null:23 2013-05-02T00:00:00Z doi:10.1186/1744-8069-9-23 /content/figures/1744-8069-9-23-toc.gif Molecular Pain 1744-8069 ${item.volume} 23 2013-05-02T00:00:00Z XML Background: Noxious stimulation and nerve injury induce an increase in intracellular Ca2+ concentration ([Ca2+]i) via various receptors or ionic channels. While an increase in [Ca2+]i excites neurons, [Ca2+]i overload elicits cytotoxicity, resulting in cell death. Intracellular Ca2+ is essential for many signal transduction mechanisms, and its level is precisely regulated by the Ca2+ extrusion system in the plasma membrane, which includes the Na+-Ca2+ exchanger (NCX). It has been demonstrated that Ca2+-ATPase is the primary mechanism for removing [Ca2+]i following excitatory activity in trigeminal ganglion (TG) neurons; however, the role of NCXs in this process has yet to be clarified. The goal of this study was to examine the expression/localization of NCXs in TG neurons and to evaluate their functional properties. Results: NCX isoforms (NCX1, NCX2, and NCX3) were expressed in primary cultured rat TG neurons. All the NCX isoforms were also expressed in A-, peptidergic C-, and non-peptidergic C-neurons, and located not only in the somata, dendrites, axons and perinuclear region, but also in axons innervating the dental pulp. Reverse NCX activity was clearly observed in TG neurons. The inactivation kinetics of voltage-dependent Na+ channels were prolonged by NCX inhibitors when [Ca2+]i in TG neurons was elevated beyond physiological levels. Conclusions: Our results suggest that NCXs in TG neurons play an important role in regulating Ca2+-homeostasis and somatosensory information processing by functionally coupling with voltage-dependent Na+ channels. http://www.molecularpain.com/content/9/1/22 Hidetaka Kuroda Ubaidus Sobhan Masaki Sato Maki Tsumura Tatsuya Ichinohe Masakazu Tazaki Yoshiyuki Shibukawa Molecular Pain 2013, null:22 2013-04-29T00:00:00Z doi:10.1186/1744-8069-9-22 /content/figures/1744-8069-9-22-toc.gif Molecular Pain 1744-8069 ${item.volume} 22 2013-04-29T00:00:00Z XML Background: Peripheral nerve injury can have long-term consequences including pain-related manifestations, such as hypersensitivity to cutaneous stimuli, as well as affective and cognitive disturbances, suggesting the involvement of supraspinal mechanisms. Changes in brain structure and cortical function associated with many chronic pain conditions have been reported in the prefrontal cortex (PFC). The PFC is implicated in pain-related co-morbidities such as depression, anxiety and impaired emotional decision-making ability. We recently reported that this region is subject to significant epigenetic reprogramming following peripheral nerve injury, and normalization of pain-related structural, functional and epigenetic abnormalities in the PFC are all associated with effective pain reduction.In this study, we used the Spared Nerve Injury (SNI) model of neuropathic pain to test the hypothesis that peripheral nerve injury triggers persistent long-lasting changes in gene expression in the PFC, which alter functional gene networks, thus providing a possible explanation for chronic pain associated behaviors. Results: SNI or sham surgery where performed in male CD1 mice at three months of age. Six months after injury, we performed transcriptome-wide sequencing (RNAseq), which revealed 1147 differentially regulated transcripts in the PFC in nerve-injured vs. control mice. Changes in gene expression occurred across a number of functional gene clusters encoding cardinal biological processes as revealed by Ingenuity Pathway Analysis. Significantly altered biological processes included neurological disease, skeletal muscular disorders, behavior, and psychological disorders. Several of the changes detected by RNAseq were validated by RT-QPCR and included transcripts with known roles in chronic pain and/or neuronal plasticity including the NMDA receptor (glutamate receptor, ionotropic, NMDA; grin1), neurite outgrowth (roundabout 3; robo3), gliosis (glial fibrillary acidic protein; gfap), vesicular release (synaptotagmin 2; syt2), and neuronal excitability (voltage-gated sodium channel, type I; scn1a). Conclusions: This study used an unbiased approach to document long-term alterations in gene expression in the brain following peripheral nerve injury. We propose that these changes are maintained as a memory of an insult that is temporally and spatially distant from the initial injury. http://www.molecularpain.com/content/9/1/21 Sebastian Alvarado Maral Tajerian Magali Millecamps Mathew Suderman Laura Stone Moshe Szyf Molecular Pain 2013, null:21 2013-04-18T00:00:00Z doi:10.1186/1744-8069-9-21 /content/figures/1744-8069-9-21-toc.gif Molecular Pain 1744-8069 ${item.volume} 21 2013-04-18T00:00:00Z XML Background: Pain tolerance is subject to considerable inter-individual variation, which may be influenced by a number of genetic and non-genetic factors. The mu, delta and kappa opioid receptors play a role in pain perception and are thought to mediate different pain modalities. The aim of this study was to explore associations between pain thresholds and gender and genetic variants in the three opioid receptor genes (OPRM, OPRD and OPRK). Experimental multi-modal pain data from previously published studies carried out in healthy Caucasian volunteers were used in order to limit the number of confounders to the study outcome. Data on thermal skin pain (n=36), muscle pressure pain (n=31) and mechanical visceral pain (n=50)) tolerance thresholds were included. Results: Nineteen genetic polymorphisms were included in linear regression modeling. Males were found to tolerate higher thermal and muscle pressure pain than females (p=0.003 and 0.02). Thirty four percent of variability in thermal skin pain was accounted for by a model consisting of OPRK rs6473799 and gender. This finding was just outside significance when correction for multiple testing was applied. Variability in muscle pressure pain tolerance was associated with OPRK rs7016778 and rs7824175. These SNPs accounted for 43% of variability in muscle pressure pain sensitivity and these findings remained significant after adjustment for multiple testing. No association was found with mechanical visceral pain. Conclusion: This is a preliminary and hypothesis generating study due to the relatively small study size. However, significant association between the opioid receptor genes and experimental pain sensitivity supports the influence of genetic variability in pain perception. These findings may be used to generate hypotheses for testing in larger clinical trials of patients with painful conditions. http://www.molecularpain.com/content/9/1/20 Hiroe Sato Joanne Droney Joy Ross Anne Olesen Camilla Staahl Trine Andresen Ruth Branford Julia Riley Lars Arendt-Nielsen Asbjørn Drewes Molecular Pain 2013, null:20 2013-04-09T00:00:00Z doi:10.1186/1744-8069-9-20 /content/figures/1744-8069-9-20-toc.gif Molecular Pain 1744-8069 ${item.volume} 20 2013-04-09T00:00:00Z XML