http://www.molecularpain.com The latest research articles published by Molecular Pain 2010-02-08T00:00:00Z This is an RSS newsfeed from BioMed Central It is intended to be used with an RSS reader. For more information about RSS newsfeeds from BioMed Central, visit http://www.biomedcentral.com/info/about/rss/ Calcitonin gene-related peptide (CGRP) plays an important role in peripheral and central sensitization. CGRP also is a key molecule in the spino-parabrachial-amygdaloid pain pathway. Blockade of CGRP1 receptors in the spinal cord or in the amygdala has antinociceptive effects in different pain models. Here we studied the electrophysiological mechanisms of behavioral effects of CGRP in the amygdala in normal animals without tissue injury.Whole-cell patch-clamp recordings of neurons in the latero-capsular division of the central nucleus of the amygdala (CeLC) in rat brain slices showed that CGRP (100 nM) increased excitatory postsynaptic currents (EPSCs) at the parabrachio-amygdaloid (PB-CeLC) synapse, the exclusive source of CGRP in the amygdala. Consistent with a postsynaptic mechanism of action, CGRP increased amplitude, but not frequency, of miniature EPSCs and did not affect paired-pulse facilitation. CGRP also increased neuronal excitability. CGRP-induced synaptic facilitation was reversed by an NMDA receptor antagonist (AP5, 50 uM) or a PKA inhibitor (KT5720, 1 uM), but not by a PKC inhibitor (GF109203X, 1 uM). Stereotaxic administration of CGRP (10 uM, concentration in microdialysis probe) into the CeLC by microdialysis in awake rats increased audible and ultrasonic vocalizations and decreased hindlimb withdrawal thresholds. Behavioral effects of CGRP were largely blocked by KT5720 (100 uM) but not by GF109203X (100 uM).The results show that CGRP in the amygdala exacerbates nocifensive and affective behavioral responses in normal animals through PKA- and NMDA receptor-dependent postsynaptic facilitation. Thus, increased CGRP levels in the amygdala might trigger pain in the absence of tissue injury. http://www.molecularpain.com/content/6/1/10 Jeong Han Hita Adwanikar Zhen Li Guangchen Ji Volker Neugebauer Molecular Pain 2010, 6:10 2010-02-08T00:00:00Z doi:10.1186/1744-8069-6-10 Molecular Pain 1744-8069 6 10 2010-02-08T00:00:00Z PDF Background: In order to evaluate the neural mechanisms underlying the abnormal facial pain that may develop following regeneration of the injured inferior alveolar nerve (IAN), the properties of the IAN innervated in the mental region were analyzed. Results: Fluorogold (FG) injection into the mental region 14 days after IAN transection showed massive labeling of trigeminal ganglion (TG). The escape threshold to mechanical stimulation of the mental skin was significantly lower (i.e. mechanical allodynia) at 11-14 days after IAN transection than before surgery. The background activity, mechanically evoked responses and afterdischarges of IAN A delta -fibers were significantly higher in IAN-transected rats than naive. The small/medium diameter TG neurons showed an increase in both tetrodotoxin (TTX)-resistant (TTX-R) and -sensitive (TTX-S) sodium currents (INa) and decrease in total potassium current, transient current (IA) and sustained current (IK) in IAN-transected rats. The amplitude, overshoot amplitude and number of action potentials evoked by the depolarizing pulses after 1 micro M TTX administration in TG neurons were significantly higher, whereas the threshold current to elicit spikes was smaller in IAN-transected rats than naive. Resting membrane potential was significantly smaller in IAN-transected rats than that of naive. Conclusions: These data suggest that the increase in both TTX-S INa and TTX-R INa and the decrease in IA and Ik in small/medium TG neurons in IAN-transected rats are involved in the activation of spike generation, resulting in hyperexcitability of A delta -IAN fibers innervating the mental region after IAN transection. http://www.molecularpain.com/content/6/1/9 Kazuharu Nakagawa Mamoru Takeda Yoshiyuki Tsuboi Masahiro Kondo Junichi Kitagawa Shigeji Matsumoto Azusa Kobayashi Barry Sessle Masamichi Shinoda Koichi Iwata Molecular Pain 2010, 6:9 2010-02-03T00:00:00Z doi:10.1186/1744-8069-6-9 Molecular Pain 1744-8069 6 9 2010-02-03T00:00:00Z PDF Background: The dynorphin-kappa opioid receptor (KOR) system regulates glial proliferation after sciatic nerve injury. Here, we investigated its role in cell proliferation following partial ligation of infraorbital nerve (pIONL), a model for trigeminal neuropathic pain. Mechanical allodynia was enhanced in KOR gene deleted mice (KOR-/-) compared to wild type mice. Using bromodeoxyuridine (BrdU) as a mitotic marker, we assessed cell proliferation in three different areas of the trigeminal afferent pathway: trigeminal nucleus principalis (Vp), trigeminal root entry zone (TREZ), and trigeminal ganglion (TG). Results: In KOR-/- mice or norBNI-treated mice, the number of proliferating cells in the Vp was significantly less than in WT mice, whereas cell proliferation was enhanced in TREZ and TG. The majority of the proliferating cells were nestin positive stem cells or CD11b positive microglia in the Vp and macrophages in the TG. GFAP-positive astrocytes made a clear borderline between the CNS and the PNS in TREZ, and phosphorylated KOR staining (KOR-p) was detectable only in the astrocytes in CNS in WT mice but not in KOR-/- or norBNI-treated mice. Conclusions: These results show that kappa opioid receptor system has different effects after pIONL in CNS and PNS: KOR activation promotes CNS astrocytosis and microglial or stem cell proliferation but inhibits macrophage proliferation in PNS. The trigeminal central root has a key role in the etiology and treatment of trigeminal neuralgia, and these newly identified responses may provide new targets for developing pain therapies. http://www.molecularpain.com/content/6/1/8 Aita Megumi Margaret Byers Charlse Chavkin Mei Xu Molecular Pain 2010, 6:8 2010-01-29T00:00:00Z doi:10.1186/1744-8069-6-8 Molecular Pain 1744-8069 6 8 2010-01-29T00:00:00Z PDF Background: Unilateral constrictive sciatic nerve injury (uCCI) is a common neuropathic pain model. However, the bilateral constrictive injury (bCCI) model is less well studied, and shows unique characteristics. In the present study, we sought to correlate effects of bCCI on nocifensive responses to cold and mechanical stimuli with selected dorsal horn anatomic markers. bCCI or sham ligation of both rat sciatic nerves were followed for 45 days of behavioral testing. Additional rats sacrificed at 15, 30 and 90 days were used for anatomic analyses. Behavioral tests included hindpaw withdrawal responses to topical acetone, cold plate testing, an operant thermal preference task and hindpaw withdrawal thresholds to mechanical probing. Results: All nocifensive responses to cold increased and remained enhanced for >45 days. Mechanical withdrawal thresholds decreased for 25 days only. Densitometric analyses of immunoperoxidase staining in the superficial dorsal horn at L4-5 revealed decreased cholecystokinin (CCK) staining at all times after bCCI, decreased mu opiate receptor (MOR) staining, maximal at 15 days, increased neuropeptide Y (NPY) staining only at days 15 and 30, and increased neurokinin-1 receptor (NK-1R) staining at all time points, maximal at 15 days. Correlation analyses at 45 days post-bCCI, were significant for individual rat nocifensive responses in each cold test and CCK and NK-1R, but not for MOR or NPY. Conclusions: These results confirm the usefulness of cold testing in bCCI rats, a new approach using CCI to model neuropathic pain, and suggest a potential value of studying the roles of dorsal horn CCK and substance P in chronic neuropathic pain. Compared to human subjects with neuropathic pain, responses to cold stimuli in rats with bCCI may be a useful model of neuropathic pain. http://www.molecularpain.com/content/6/1/7 Sukdeb Datta Koel Chatterjee Robert Kline Ronald Wiley Molecular Pain 2010, 6:7 2010-01-27T00:00:00Z doi:10.1186/1744-8069-6-7 Molecular Pain 1744-8069 6 7 2010-01-27T00:00:00Z PDF Background: ATP-sensitive potassium (KATP) channels in neurons mediate neuroprotection, they regulate membrane excitability, and they control neurotransmitter release. Because loss of DRG neuronal KATP currents is involved in the pathophysiology of pain after peripheral nerve injury, we characterized the distribution of the KATP channel subunits in rat DRG, and determined their alterations by painful axotomy using RT-PCR, immunohistochemistry and electron microscopy. Results: PCR demonstrated Kir6.1, Kir6.2, SUR1 and SUR2 transcripts in control DRG neurons. Protein expression for all but Kir6.1 was confirmed by Western blots and immunohistochemistry. Immunostaining of these subunits was identified by fluorescent and confocal microscopy in plasmalemmal and nuclear membranes, in the cytosol, along the peripheral fibers, and in satellite glial cells. Kir6.2 co-localized with SUR1 subunits. Kir6.2, SUR1, and SUR2 subunits were identified in neuronal subpopulations, categorized by positive or negative NF200 or CGRP staining. KATP current recorded in excised patches was blocked by glybenclamide, but preincubation with antibody against SUR1 abolished this blocking effect of glybenclamide, confirming that the antibody targets the SUR1 protein in the neuronal plasmalemmal membrane.In the myelinated nerve fibers we observed anti-SUR1 immunostaining in regularly spaced funneled-shaped structures. These structures were identified by electron microscopy as Schmidt-Lanterman incisures (SLI) formed by the Schwann cells. Immunostaining against SUR1 and Kir6.2 colocalized with anti-Caspr at paranodal sites.DRG excised from rats made hyperalgesic by spinal nerve ligation exhibited similar staining against Kir6.2, SUR1 or SUR2 as DRG from controls, but showed decreased prevalence of SUR1 immunofluorescent NF200 positive neurons. In DRG and dorsal roots proximal to axotomy SLI were smaller and showed decreased SUR1 immunofluorescence. Conclusions: We identified Kir6.2/SUR1 and Kir6.2/SUR2 KATP channels in rat DRG neuronal somata, peripheral nerve fibers, and glial satellite and Schwann cells, in both normal state and after painful nerve injury. This is the first report of KATP channels in paranodal sites adjacent to nodes of Ranvier and in the SLI of the Schwann cells. After painful axotomy KATP channels are downregulated in large, myelinated somata and also in SLI, which are also of smaller size compared to controls.Because KATP channels may have diverse functional roles in neurons and glia, further studies are needed to explore the potential of KATP channels as targets of therapies against neuropathic pain and neurodegeneration. http://www.molecularpain.com/content/6/1/6 Vasiliki Zoga Takashi Kawano Mei-Ying Liang Martin Bienengraeber Dorothee Weihrauch Bruce McCallum Geza Gemes Quinn Hogan Constantine Sarantopoulos Molecular Pain 2010, 6:6 2010-01-26T00:00:00Z doi:10.1186/1744-8069-6-6 Molecular Pain 1744-8069 6 6 2010-01-26T00:00:00Z PDF The functional properties of alpha-amino-3-hydroxy-5-methy-4-isoxazole propionate (AMPA) receptors in different brain regions, such as hippocampus and cerebellum, have been well studied in vitro and in vivo. The AMPA receptors present a unique characteristic in the mechanisms of subunit regulation during LTP (long-term potentiation) and LTD (long-term depression), which are involved in the trafficking, altered composition and phosphorylation of AMPA receptor subunits. Accumulated data have demonstrated that spinal AMPA receptors play a critical role in the mechanism of both acute and persistent pain. However, less is known about the biochemical regulation of AMPA receptor subunits in the spinal cord in response to painful stimuli. Recent studies have shown that some important regulatory processes, such as the trafficking of AMPA receptor subunit, subunit compositional changes, phosphorylation of AMPA receptor subunits, and their interaction with partner proteins may contribute to spinal nociceptive transmission. Of all these regulation processes, the phosphorylation of AMPA receptor subunits is the most important since it may trigger or affect other cellular processes. Therefore, these study results may suggest an effective strategy in developing novel analgesics targeting AMPA receptor subunit regulation that may be useful in treating persistent and chronic pain without unacceptable side effects in the clinics. http://www.molecularpain.com/content/6/1/5 Yun Wang Jing Wu Zhiguo Wu Qing Lin Yun Yue Li Fang Molecular Pain 2010, 6:5 2010-01-21T00:00:00Z doi:10.1186/1744-8069-6-5 Molecular Pain 1744-8069 6 5 2010-01-21T00:00:00Z PDF Background: The cooling agents menthol and icilin act as agonists at TRPM8 and TRPA1. In vitro, activation of TRPM8 by icilin and cold, but not menthol, is dependent on the activity of a sub-type of phospholipase A2, iPLA2. Lysophospholipids (e.g. LPC) produced by PLA2 activity can also activate TRPM8. The role of TRPA1 as a primary cold sensor in vitro is controversial, although there is evidence that TRPA1 plays a role in behavioural responses to noxious cold stimuli. In this study, we have investigated the roles of TRPM8 and TRPA1 and the influence of iPLA2 on noxious cold sensitivities in naive animals and after local administration of menthol, icilin and LPC. The roles of the channels in cold sensitivity were investigated in mice lacking either TRPM8 (Trpm8-/-) or TRPA1 (Trpa1-/-). Results: Intraplantar administration of icilin evoked a dose-dependent increase in sensitivity to a 10oC stimulus that was inhibited by iPLA2 inhibition with BEL. In contrast the cold hypersensitivities elicited by intraplantar menthol and LPC were not inhibited by BEL treatment. BEL had no effect on basal cold sensitivity and mechanical hypersensitivities induced by the TRPV1 agonist, capsaicin, and the P2X3 agonist alpha/beta-methylene ATP. Both Trpm8-/- and Trpa1-/- mice showed longer latencies for paw withdrawal from a 10oC stimulus than wild-type littermates. Cold hypersensitivities induced by either icilin or LPC were absent in Trpm8-/- mice but were retained in Trpa1-/- mice. In contrast, cold hypersensitivity evoked by menthol was present in Trpm8-/- mice but was lost in Trpa1-/- mice. Conclusions: The findings that iPLA2 inhibition blocked the development of cold hypersensitivity after administration of icilin but failed to affect menthol-induced hypersensitivity agree well with our earlier in vitro data showing a differential effect of iPLA2 inhibition on the agonist activities of these agents. The ability of LPC to induce cold hypersensitivity supports a role for iPLA2 in modulating TRPM8 activity in vivo. Studies on genetically modified mice demonstrated that the effects of icilin and LPC were mediated by TRPM8 and not TRPA1. In contrast, menthol-induced cold hypersensitivity was dependent on expression of TRPA1 and not TRPM8. http://www.molecularpain.com/content/6/1/4 Clive Gentry Natalie Stoakley David Andersson Stuart Bevan Molecular Pain 2010, 6:4 2010-01-21T00:00:00Z doi:10.1186/1744-8069-6-4 Molecular Pain 1744-8069 6 4 2010-01-21T00:00:00Z PDF Background: Analgesics, including opioids and non-steroid anti-inflammatory drugs reduce postoperative pain. However, little is known about the quantitative effects of these drugs on cortical activity induced by nociceptive stimulation. The aim of the present study was to determine the neural activity in response to a nociceptive stimulus and to investigate the effects of fentanyl (an opioid agonist) and parecoxib (a selective cyclooxygenase-2 inhibitor) on this nociception-induced cortical activity evoked by tail pinch. Extracellular recordings (electroencephalogram and multi-unit signals) were performed in the area of the anterior cingulate cortex while intracellular recordings were made in the primary somatosensory cortex. The effects of parecoxib and fentanyl on induced cortical activity were compared. Results: Peripheral nociceptive stimulation in anesthetized rats produced an immediate electroencephalogram (EEG) desynchronization resembling the cortical arousal (low-amplitude, fast-wave activity), while the membrane potential switched into a persistent depolarization state. The induced cortical activity was abolished by fentanyl, and the fentanyl's effect was reversed by the opioid receptor antagonist, naloxone. Parecoxib, on the other hand, did not significantly affect the neural activity. Conclusion: Cortical activity was modulated by nociceptive stimulation in anesthetized rats. Fentanyl showed a strong inhibitory effect on the nociceptive-stimulus induced cortical activity while parecoxib had no significant effect. http://www.molecularpain.com/content/6/1/3 Yuan-Zhi Peng Xiao-Xi Li Ying-Wei Wang Molecular Pain 2010, 6:3 2010-01-21T00:00:00Z doi:10.1186/1744-8069-6-3 Molecular Pain 1744-8069 6 3 2010-01-21T00:00:00Z PDF Background: This study demonstrates a critical role in CNS innate immunity of the microglial Toll-like receptor 4 (TLR4) in the induction and maintenance of behavioral hypersensitivity in a rat model of bone cancer pain with the technique of RNA interference (RNAi). We hypothesized that after intramedullary injection of Walker 256 cells (a breast cancer cell line) into the tibia, CNS neuroimmune activation and subsequent cytokine expression are triggered by the stimulation of microglial membrane-bound TLR4. Results: We assessed tactile allodynia and spontaneous pain in female Sprague-Dawley (SD) rats after intramedullary injection of Walker 256 cells into the tibia. In a complementary study, TLR4 small interfering RNA(siRNA) was administered intrathecally to bone cancer pain rats to reduce the expression of spinal TLR4. The bone cancer pain rats treated with TLR4 siRNA displayed significantly attenuated behavioral hypersensitivity and decreased expression of spinal microglial markers and proinflammatory cytokines compared with controls. Only intrathecal injection of TRL4 siRNA at post-inoculation day 4 could prevent initial development of bone cancer pain; intrathecal injection of TRL4 siRNA at post-inoculation day 9 could attenuate, but not completely block, well-established bone cancer pain. Conclusions: TLR4 might be the main mediator in the induction of bone cancer pain. Further study of this early, specific, and innate CNS/microglial response, and how it leads to sustained glial/neuronal hypersensitivity, might lead to new therapies for the prevention and treatment of bone cancer pain syndromes. http://www.molecularpain.com/content/6/1/2 Liu Lan Yang Ping Wang Na Jiang Miao Qiu Cheng Ma Ni Liu Lei Li Fang Ren Guang Zhou Jing Li Wei Molecular Pain 2010, 6:2 2010-01-20T00:00:00Z doi:10.1186/1744-8069-6-2 Molecular Pain 1744-8069 6 2 2010-01-20T00:00:00Z PDF Background: Our previous study demonstrated that nitric oxide (NO) contributes to long-term potentiation (LTP) of C-fiber-evoked field potentials by tetanic stimulation of the sciatic nerve in the spinal cord in vivo. Ryanodine receptor (RyR) is a down-stream target for NO. The present study further explored the role of RyR in synaptic plasticity of the spinal pain pathway. Results: By means of field potential recordings in the adult male rat in vivo, we showed that RyR antagonist reduced LTP of C-fiber-evoked responses in the spinal dorsal horn by tetanic stimulation of the sciatic nerve. Using spinal cord slice preparations and field potential recordings from superficial dorsal horn, high frequency stimulation of Lissauer's tract (LT) stably induced LTP of field excitatory postsynaptic potentials (fEPSPs). Perfusion of RyR antagonists blocked the induction of LT stimulation-evoked spinal LTP, while Ins(1,4,5)P3 receptor (IP3R) antagonist had no significant effect on LTP induction. Moreover, activation of RyRs by caffeine without high frequency stimulation induced a long-term potentiation in the presence of bicuculline methiodide and strychnine. Further, in patch-clamp recordings from superficial dorsal horn neurons, activation of RyRs resulted in a large increase in the frequency of miniature EPSCs (mEPSCs). Immunohistochemical study showed that RyRs were expressed in the dorsal root ganglion (DRG) neurons. Likewise, calcium imaging in small DRG neurons illustrated that activation of RyRs elevated [Ca2+]i in small DRG neurons. Conclusions: These data indicate that activation of presynaptic RyRs play a crucial role in the induction of LTP in the spinal pain pathway, probably through enhancement of transmitter release. http://www.molecularpain.com/content/6/1/1 Long-Zhen Cheng Ning Lu Yu-Qiu Zhang Zhi-Qi Zhao Molecular Pain 2010, 6:1 2010-01-20T00:00:00Z doi:10.1186/1744-8069-6-1 Molecular Pain 1744-8069 6 1 2010-01-20T00:00:00Z PDF