Inflammatory Pain Sensitivity Research Articles

Neuropeptides and Microglial Activation in Inflammation, Pain, and Neurodegenerative Diseases.

Microglial cells are responsible for immune surveillance within the CNS. They respond to noxious stimuli by releasing inflammatory mediators and mounting an effective inflammatory response. This is followed by release of anti-inflammatory mediators and resolution of the inflammatory response. Alterations to this delicate process may lead to tissue damage, neuroinflammation, and neurodegeneration. Chronic pain, such as inflammatory or neuropathic pain, is accompanied by neuroimmune activation, and the role of glial cells in the initiation and maintenance of chronic pain has been the subject of increasing research over the last two decades. Neuropeptides are small amino acidic molecules with the ability to regulate neuronal activity and thereby affect various functions such as thermoregulation, reproductive behavior, food and water intake, and circadian rhythms. Neuropeptides can also affect inflammatory responses and pain sensitivity by modulating the activity of glial cells. The last decade has witnessed growing interest in the study of microglial activation and its modulation by neuropeptides in the hope of developing new therapeutics for treating neurodegenerative diseases and chronic pain. This review summarizes the current literature on the way in which several neuropeptides modulate microglial activity and response to tissue damage and how this modulation may affect pain sensitivity.

A Chemogenetic Receptor That Enhances the Magnitude and Frequency of Glycinergic Inhibitory Postsynaptic Currents without Inducing a Tonic Chloride Flux.

The gene transfer-mediated expression of inhibitory ion channels in nociceptive neurons holds promise for treating intractable pain. Chemogenetics, which involves expressing constructs activated by biologically inert molecules, is of particular interest as it permits tunable neuromodulation. However, current chloride-permeable chemogenetic constructs are problematic as they mediate a tonic chloride influx which over time would deplete the chloride electrochemical gradient and reduce inhibitory efficacy. Inflammatory pain sensitization can be caused by prostaglandin E2-mediated inhibition of glycinergic inhibitory postsynaptic currents in spinal nociceptive neurons. We developed a highly conducting (100 pS) inhibitory chemogenetic construct based on a human glycine receptor (α1Y279F,A288G) with high ivermectin sensitivity. When virally infected into spinal neurons, 10 nM ivermectin increased the magnitude and frequency of glycinergic postsynaptic currents without activating a tonic chloride flux. The construct should thus produce analgesia. Its human origin and the well-established biocompatibility of its ligand suggest it may be suited to human use.

Expression patterns of T-type Cav3.2 channel and insulin-like growth factor-1 receptor in dorsal root ganglion neurons of mice after sciatic nerve axotomy.

Substantial evidence indicates that T-type Cav3.2 channel and insulin-like growth factor-1 (IGF-1) contribute to pain hypersensitivity within primary sensory nerves. A recent study suggested that activation of IGF-1 receptor (IGF-1R) could increase Cav3.2 channel currents and further contribute to inflammatory pain sensitivity. However, the expression patterns of Cav3.2 and IGF-1R and their colocalization in dorsal root ganglion (DRG) in chronic neuropathic pain condition remain unknown. In this study, we explored expression patterns of Cav3.2, IGF-1R and their colocalization, and whether phenotypic switch occurs in a subpopulation of Cav3.2 or IGF-1R neurons in mouse DRGs after sciatic nerve axotomy with immunofluorescence, real-time reverse transcription-PCR, and western blot assays. We found that expressions of Cav3.2 and IGF-1R, and their colocalization were not increased in DRGs of mice following axotomy. In addition, Cav3.2 or IGF-1R subpopulation neurons did not acquire significant switch in expression phenotype after sciatic nerve axotomy. Our findings argue for an upregulation of Cav3.2 and IGF-1R expression in lumbar DRGs post-sciatic nerve axotomy and provided an insight for understanding the functions of peripheral afferent Cav3.2 channel and IGF-1/IGF-1R signaling in chronic neuropathic pain.

Colocalization of insulin-like growth factor-1 receptor and T type Cav3.2 channel in dorsal root ganglia in chronic inflammatory pain mouse model.

Insulin-like growth factor-1 (IGF-1) is a neurotrophic factor and plays important roles in the nervous system. Increasing evidence supports that IGF-1 contributes to pain hypersensitivity through its insulin-like growth factor-1 receptor (IGF-1R) by activating IGF-1R/Akt or MAPK signaling pathways, whereas T-type Cav3.2 channel can facilitate and amplify pain signals originating from the sensory periphery. A recent study showed that activated IGF-1R can increase T-type Cav3.2 channel currents and further activate the G protein-dependent PKCα pathway to contribute to inflammatory pain sensitivity. However, the colocalization of IGF-1R and Cav3.2 in mouse dorsal root ganglion (DRG) under chronic inflammatory pain conditions remains elusive. In this study, we investigated changes in the expression of IGF-1R and the Cav3.2 channel, and their colocalization in mouse DRGs in chronic inflammatory pain condition (induced by complete Freund's adjuvant intraplanter injection) using real-time RT-PCR and immunohistochemistry approaches to confirm that Cav3.2 channel can mediate pain facilitation following IGF-1/IGF-1R signaling. We found that IGF-1R was expressed extensively in DRG neurons including small-, medium-, and large-sized neurons, whereas Cav3.2 channel was expressed exclusively in small-sized DRG neurons of naive mice. Expression of Cav3.2, but not IGF-1R, and colocalization of Cav3.2 and IGF-1R were increased in lumbar (L)4-L6 primary sensory neurons in DRGs of mice in chronic inflammatory pain. Moreover, the increased colocalization of IGF-1R and Cav3.2 is exclusively localized in small- and medium-sized primary sensory neurons. Our findings provided morphological evidence that T-type Cav3.2 channel, at least partially, mediates the pain facilitation of IGF-1/IGF-1R signaling in chronic inflammatory pain condition.

Lulling immunity, pain, and stress to sleep with cortistatin.

Cortistatin is a neuropeptide isolated from cortical brain regions, showing high structural homology and sharing many functions with somatostatin. However, cortistatin exerts unique functions in the central nervous and immune systems, including decreasing locomotor activity, inducing sleep-promoting effects, and deactivating inflammatory and T helper (TH )1/TH 17-driven responses in preclinical models of sepsis, arthritis, multiple sclerosis, and colitis. Besides its release by cortical and hippocampal interneurons, cortistatin is produced by macrophages, lymphocytes, and peripheral nociceptive neurons in response to inflammatory stimuli, supporting a physiological role of cortistatin in the immune and nociceptive systems. Cortistatin-deficient mice have been shown to have exacerbated nociceptive responses to neuropathic and inflammatory pain sensitization. However, a paradoxical effect has been observed in studies of immune disorders, in which, despite showing competent inflammatory/autoreactive responses, cortistatin-deficient mice were partially resistant to systemic autoimmunity and inflammation. This unexpected phenotype was associated with elevated circulating glucocorticoids and anxiety-like behavior. These findings support cortistatin as a novel multimodal therapeutic approach to treat autoimmunity and clinical pain and identify it as a key endogenous component of the neuroimmune system related to stress responses.

Control of ethanol sensitivity of the glycine receptor α3 subunit by transmembrane 2, the intracellular splice cassette and C-terminal domains.

Previous studies have shown that the effect of ethanol onglycine receptors (GlyRs) containing the a1 subunit is affected by interaction with heterotrimeric G proteins (Gβγ). GlyRs containing the α3 subunit are involved in inflammatory pain sensitization and rhythmic breathing and have received much recent attention. For example, it is unknown whether ethanol affects the function of this important GlyR subtype. Electrophysiologic experiments showed that GlyR α3 subunits were not potentiated by pharmacologic concentrations of ethanol or by Gβγ. Thus, we studied GlyR α1–α3 chimeras and mutants to determine the molecular properties that confer ethanol insensitivity. Mutation of corresponding glycine 254 in transmembrane domain 2 (TM2) found in a1 in the α3(A254G) –α1 chimera induced a glycine-evoked current that displayed potentiation during application of ethanol (46 ± 5%, 100 mM) and Gβγ activation (80 ± 17%). Interestingly,insertion of the intracellular α3L splice cassette into GlyR α1 abolished the enhancement of the glycine-activated current by ethanol (5 ± 6%) and activation by Gβγ (21 6 7%). In corporation of the GlyR α1 C terminus into the ethanol-resistant α3S(A254G) mutant produced a construct that displayed potentiation of the glycine-activated current with 100 mM ethanol (40 ± 6%)together with a current enhancement after G protein activation (68 ± 25%). Taken together, these data demonstrate that GlyRα3 subunits are not modulated by ethanol. Residue A254 in TM2, the α3L splice cassette, and the C-terminal domain of α3GlyRs are determinants for low ethanol sensitivity and form the molecular basis of subtype-selective modulation of GlyRs by alcohol.

Annexin A2 regulates TRPA1-dependent nociception.

The transient receptor potential A1 (TRPA1) channel is essential for vertebrate pain. Even though TRPA1 activation by ligands has been studied extensively, the molecular machinery regulating TRPA1 is only poorly understood. Using an unbiased proteomics-based approach we uncovered the physical association of Annexin A2 (AnxA2) with native TRPA1 in mouse sensory neurons. AnxA2 is enriched in a subpopulation of sensory neurons and coexpressed with TRPA1. Furthermore, we observe an increase of TRPA1 membrane levels in cultured sensory neurons from AnxA2-deficient mice. This is reflected by our calcium imaging experiments revealing higher responsiveness upon TRPA1 activation in AnxA2-deficient neurons. In vivo these findings are associated with enhanced nocifensive behaviors specifically in TRPA1-dependent paradigms of acute and inflammatory pain, while heat and mechanical sensitivity as well as TRPV1-mediated pain are preserved in AnxA2-deficient mice. Our results support a model whereby AnxA2 limits the availability of TRPA1 channels to regulate nociceptive signaling in vertebrates.

Altered formalin-induced pain and Fos induction in the periaqueductal grey of preadolescent rats following neonatal LPS exposure.

Animal and human studies have demonstrated that early pain experiences can produce alterations in the nociceptive systems later in life including increased sensitivity to mechanical, thermal, and chemical stimuli. However, less is known about the impact of neonatal immune challenge on future responses to noxious stimuli and the reactivity of neural substrates involved in analgesia. Here we demonstrate that rats exposed to Lipopolysaccharide (LPS; 0.05 mg/kg IP, Salmonella enteritidis) during postnatal day (PND) 3 and 5 displayed enhanced formalin-induced flinching but not licking following formalin injection at PND 22. This LPS-induced hyperalgesia was accompanied by distinct recruitment of supra-spinal regions involved in analgesia as indicated by significantly attenuated Fos-protein induction in the rostral dorsal periaqueductal grey (DPAG) as well as rostral and caudal axes of the ventrolateral PAG (VLPAG). Formalin injections were associated with increased Fos-protein labelling in lateral habenula (LHb) as compared to medial habenula (MHb), however the intensity of this labelling did not differ as a result of neonatal immune challenge. These data highlight the importance of neonatal immune priming in programming inflammatory pain sensitivity later in development and highlight the PAG as a possible mediator of this process.

Altered nociceptive, endocrine, and dorsal horn neuron responses in rats following a neonatal immune challenge

The neonatal period is characterized by significant plasticity where the immune, endocrine, and nociceptive systems undergo fine-tuning and maturation. Painful experiences during this period can result in long-term alterations in the neurocircuitry underlying nociception, including increased sensitivity to mechanical or thermal stimuli. Less is known about the impact of neonatal exposure to mild inflammatory stimuli, such as lipopolysaccharide (LPS), on subsequent inflammatory pain responses. Here we examine the impact of neonatal LPS exposure on inflammatory pain sensitivity and HPA axis activity during the first three postnatal weeks. Wistar rats were injected with LPS (0.05mg/kg IP, Salmonella enteritidis) or saline on postnatal days (PNDs) 3 and 5 and later subjected to the formalin test at PNDs 7, 13, and 22. One hour after formalin injection, blood was collected to assess corticosterone responses. Transverse spinal cord slices were also prepared for whole-cell patch clamp recording from lumbar superficial dorsal horn neurons (SDH). Brains were obtained at PND 22 and the hypothalamus was isolated to measure glucocorticoid (GR) and mineralocorticoid receptor (MR) transcript expression using qRT-PCR. Behavioural analyses indicate that at PND 7, no significant differences were observed between saline- or LPS-challenged rats. At PND 13, LPS-challenged rats exhibited enhanced licking (p<.01), and at PND 22, increased flinching in response to formalin injection (p<.05). LPS-challenged rats also displayed increased plasma corticosterone at PND 7 and PND 22 (p<.001) but not at PND 13 following formalin administration. Furthermore, at PND 22 neonatal LPS exposure induced decreased levels of GR mRNA and increased levels of MR mRNA in the hypothalamus. The intrinsic properties of SDH neurons were similar at PND 7 and PND 13. However, at PND 22, ipsilateral SDH neurons in LPS-challenged rats had a lower input resistance compared to their saline-challenged counterparts (p<.05). These data suggest neonatal LPS exposure produces developmentally regulated changes in formalin-induced behavioural responses, corticosterone levels, and dorsal horn neuron properties following noxious stimulation later in life. These findings highlight the importance of immune activation during the neonatal period in shaping pain sensitivity later in life. This programming involves both spinal cord neurons and the HPA axis.

142. Neonatal endotoxin exposure alters inflammatory pain sensitivity and HPA axis activity in a sex and age-dependent manner

Neonatal exposure to Lipopolysaccharide (LPS) is known to program neuroendocrine-immune function. How this affects pain sensitivity later in life is the focus of this study. Rats were subjected to either LPS ( salmonella enteriditis , 0.05 mg/kg, ip) or saline (equivolume) on postnatal days (PND) 3 and 5. At PND 22 and PND 80–92, rats were subjected to the formalin test. Brains and plasma were obtained 1hr post behavioural testing. IL1b was measured in plasma and hippocampus. Hypothalamic mineralocorticoid (MR) and glucocorticoid receptors (GR) expression was also assessed. Preadolescent rats treated neonatally with LPS displayed significant hyperalgesia during the late phase of the formalin test ( p p p

Phosphorylation of α3 Glycine Receptors Induces a Conformational Change in the Glycine-Binding Site

Inflammatory pain sensitization is initiated by prostaglandin-induced phosphorylation of α3 glycine receptors (GlyRs) that are specifically located in inhibitory synapses on spinal pain sensory neurons. Phosphorylation reduces the magnitude of glycinergic synaptic currents, thereby disinhibiting nociceptive neurons. Although α1 and α3 subunits are both expressed on spinal nociceptive neurons, α3 is a more promising therapeutic target as its sparse expression elsewhere implies a reduced risk of side-effects. Here we compared glycine-mediated conformational changes in α1 and α3 GlyRs to identify structural differences that might be exploited in designing α3-specific analgesics. Using voltage-clamp fluorometry, we show that glycine-mediated conformational changes in the extracellular M2-M3 domain were significantly different between the two GlyR isoforms. Using a chimeric approach, we found that structural variations in the intracellular M3-M4 domain were responsible for this difference. This prompted us to test the hypothesis that phosphorylation of S346 in α3 GlyR might also induce extracellular conformation changes. We show using both voltage-clamp fluorometry and pharmacology that Ser346 phosphorylation elicits structural changes in the α3 glycine-binding site. These results provide the first direct evidence for phosphorylation-mediated extracellular conformational changes in pentameric ligand-gated ion channels, and thus suggest new loci for investigating how phosphorylation modulates structure and function in this receptor family. More importantly, by demonstrating that phosphorylation alters α3 GlyR glycine-binding site structure, they raise the possibility of developing analgesics that selectively target inflammation-modulated GlyRs.

The Yin and Yang of pain: variability in formalin test nociception and morphine analgesia produced by the Yin Yang 1 transcription factor gene

We recently observed a reliable phenotypic difference in the inflammatory pain sensitivity of a congenic mouse strain compared to its background strain. By constructing and testing subcongenic strains combined with gene-expression assays, we provide evidence for the candidacy of the Yy1 gene - encoding the ubiquitously expressed and multifunctional Yin Yang 1 transcription factor - as responsible. To confirm this hypothesis, we used a Cre/lox strategy to produce mutant mice in which Yy1 expression was ablated in Nav 1.8-positive neurons of the dorsal root ganglion. These mutants also displayed reduced inflammatory pain sensitivity on the formalin test. Further testing of pain-related phenotypes in these mutants revealed robustly increased sensitivity to systemic and spinal (but not supraspinal) morphine analgesia, and greatly increased endogenous (swim stress-induced) opioid analgesia. None of the known biological roles of Yin Yang 1 were suggestive of such a phenotype, and thus a novel player in pain modulatory systems has been identified.

Dietary Supplementation with Docosahexanoic Acid (DHA) Improves RBC Flexibility and Reduces Cold Hypersensitivity in Mice with Sickle Cell Disease.

AbstractAbstract 2116Humans and mice with sickle cell disease (SCD) have RBC stiffness, multiorgan and vascular pathology, and complex pain syndromes. Omega-3 fatty acids, such as docosahexanoic acid (DHA), are essential fatty acids that have anti-inflammatory and anti-thrombotic activities. As dietary supplements, omega-3 fatty acids are beneficial in many cardiovascular diseases. Several studies demonstrate that dietary supplementation with omega-3 fatty acids results in increased incorporation of these fatty acids into the RBC membrane, which can influence RBC deformability. In this study, SCD mice were fed natural ingredient rodent diets supplemented with 3% DHA (DHA diet) or a control matched in total fat with a similar distribution of saturated, monounsaturated, and polyunsaturated fatty acids (CTRL diet). After 8 weeks of feeding, we examined the RBCs for: 1) deformability, as measured by ektacytometry; 2) stiffness, as measured by atomic force microscopy; 3) osmotic fragility, using a flow cytometric method; and 4) percent irreversibly sickled RBCs on peripheral blood smears. Consistent with other studies, RBCs from SCD mice fed Control diet exhibit low deformability by ektacytometry as compared to RBCs from wild-type mice (0.075 Max EI, SCD mice Control Diet, versus 0.285 Max EI, wild-type mice). Correspondingly, RBC stiffness, as measured by atomic force microscopy, is increased in SCD mice fed Control diet as compared to wild-type mice (1911 Pa, SCD mice Control Diet, versus 831 Pa, wild-type mice). In contrast, RBCs from SCD mice fed DHA diet had improved deformability (0.135 Max EI) compared to RBCs from SCD mice fed Control diet (p<0.02). Furthermore, RBCs from DHA diet-fed SCD mice had markedly decreased stiffness (798 Pa) to nearly normal levels compared to RBCs from Control diet-fed SCD mice (p<0.0001). In addition, RBCs from SCD mice fed DHA diet had decreased osmotic fragility as compared to RBCs from SCD mice fed Control diet (p<0.001). Examination of peripheral blood smears also revealed less irreversibly sickled RBCs in SCD mice fed DHA diet as compared to Control Diet (2.5% versus 4.1%, p<0.04). These results suggest that DHA supplementation has modified RBC membrane properties of SCD mice. Individuals with SCD as well as murine models of SCD display increased sensitivity to pain. Stiffened RBCs are thought to contribute to pain in SCD by stimulating vasoocclusive events. Importantly, a small-scale human SCD trial indicated that dietary supplementation with omega-3 fatty acids reduced pain episodes by almost 50% (Tomer, et al, 2001). Therefore, we measured sensitivity of SCD mice to mechanical and cold stimuli both prior to dietary feeding and after 8 weeks of feeding on Control or DHA diet. Mechanical hypersensitivity was assessed using von Frey filaments, with the paw withdrawal threshold assessed using the up-down method of Dixon (1980). Mechanical hypersensitivity thresholds are reduced in SCD mice (Hillery, et al, 2011), and were not altered by either the Control or DHA diet. Cold hypersensitivity was assessed using a 2-temperature choice assay and measuring the amount of time spent on the colder plate (23°C) versus the warmer plate (30°C). Similar to our previous findings, SCD mice exhibit hypersensitivity to cold. There was no change in pre- versus post-diet cold hypersensitivity in SCD mice fed Control diet. In contrast, post-diet cold hypersensitivity was improved compared to pre-diet cold hypersensitivity in SCD mice fed DHA diet (p<0.007). In summary, our findings indicate that DHA supplementation improves RBC flexibility, decreases osmotic fragility and irreversibly sickled cells, and reduces cold hypersensitivity in a murine model of SCD. The reduction in cold hypersensitivity may reflect the increased flexibility of the RBCs, making them less likely to cause vasoocclusive events that can activate inflammatory pain mechanisms. Additionally, resolvins D1 and D2, anti-inflammatory lipid mediators derived from DHA, inhibit the activity of the transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) channels, which contribute importantly to inflammatory pain sensitivity to mechanical and thermal stimuli. Disclosures:Mickelson:Harlan Laboratories, Inc.: Employment. Stucky:Purdue Pharma: Research Funding. Hillery:Purdue Pharma: Research Funding; Bayer Pharmaceuticals: Consultancy.

Exercise-induced Pain Intensity Predicted by Pre-exercise Fear of Pain and Pain Sensitivity

Our primary goals were to determine whether preexisting fear of pain and pain sensitivity contributed to post-exercise pain intensity. Delayed-onset muscle pain was induced in the trunk extensors of 60 healthy volunteers using an exercise paradigm. Levels of fear of pain and experimental pain sensitivity were measured before exercise. Pain intensity in the low back was collected at 24 and 48 hours post-exercise. Participants were grouped based on pain intensity. Group membership was used as the dependent variable in separate regression models for 24 and 48 hours. Predictor variables included fear, pain sensitivity, torque lost during the exercise protocol, and demographic variables. The final models predicting whether a participant reported clinically meaningful pain intensity at 24 hours only included baseline fear of pain at each level of pain intensity tested. The final model at 48 hours included average baseline pain sensitivity and the loss of muscle performance during the exercise protocol for 1 level of pain intensity tested (greater than 35 mm of 100 mm). Combined, these findings suggest that the initial reports of pain after injury may be more strongly influenced by fear whereas the inflammatory process and pain sensitivity may play a larger role for later pain intensity reports.

Presynaptic α2-GABAAReceptors in Primary Afferent Depolarization and Spinal Pain Control

Spinal dorsal horn GABA(A) receptors are found both postsynaptically on central neurons and presynaptically on axons and/or terminals of primary sensory neurons, where they mediate primary afferent depolarization (PAD) and presynaptic inhibition. Both phenomena have been studied extensively on a cellular level, but their role in sensory processing in vivo has remained elusive, due to inherent difficulties to selectively interfere with presynaptic receptors. Here, we address the contribution of a major subpopulation of GABA(A) receptors (those containing the α2 subunit) to spinal pain control in mice lacking α2-GABA(A) receptors specifically in primary nociceptors (sns-α2(-/-) mice). sns-α2(-/-) mice exhibited GABA(A) receptor currents and dorsal root potentials of normal amplitude in vitro, and normal response thresholds to thermal and mechanical stimulation in vivo, and developed normal inflammatory and neuropathic pain sensitization. However, the positive allosteric GABA(A) receptor modulator diazepam (DZP) had almost completely lost its potentiating effect on PAD and presynaptic inhibition in vitro and a major part of its spinal antihyperalgesic action against inflammatory hyperalgesia in vivo. Our results thus show that part of the antihyperalgesic action of spinally applied DZP occurs through facilitated activation of GABA(A) receptors residing on primary nociceptors.

Monoacylglycerol Lipase Activity Is a Critical Modulator of the Tone and Integrity of the Endocannabinoid System

Endocannabinoids are lipid molecules that serve as natural ligands for the cannabinoid receptors CB1 and CB2. They modulate a diverse set of physiological processes such as pain, cognition, appetite, and emotional states, and their levels and functions are tightly regulated by enzymatic biosynthesis and degradation. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid in the brain and is believed to be hydrolyzed primarily by the serine hydrolase monoacylglycerol lipase (MAGL). Although 2-AG binds and activates cannabinoid receptors in vitro, when administered in vivo, it induces only transient cannabimimetic effects as a result of its rapid catabolism. Here we show using a mouse model with a targeted disruption of the MAGL gene that MAGL is the major modulator of 2-AG hydrolysis in vivo. Mice lacking MAGL exhibit dramatically reduced 2-AG hydrolase activity and highly elevated 2-AG levels in the nervous system. A lack of MAGL activity and subsequent long-term elevation of 2-AG levels lead to desensitization of brain CB1 receptors with a significant reduction of cannabimimetic effects of CB1 agonists. Also consistent with CB1 desensitization, MAGL-deficient mice do not show alterations in neuropathic and inflammatory pain sensitivity. These findings provide the first genetic in vivo evidence that MAGL is the major regulator of 2-AG levels and signaling and reveal a pivotal role for 2-AG in modulating CB1 receptor sensitization and endocannabinoid tone.

L-Proline as a modulator of ectodermal differentiation in ES cells. Focus on “l-Proline induces differentiation of ES cells: a novel role for an amino acid in the regulation of pluripotent cells in culture

current research is focusing on defining the control of pluripotency and lineage determination of pluripotent cells, particularly of embryonic stem (ES) cells. ES cells are usually produced from the inner cell mass (ICM) of the blastocyst and are considered equivalent to ICM cells captured during a

The influence of juvenile capsaicin desenzitization on different sensory processes

Event Abstract Back to Event The influence of juvenile capsaicin desenzitization on different sensory processes Gábor Tuboly1*, Gabriella Kékesi1, Gabor Adam1, Gyorgy Benedek1 and Gyöngyi Horváth1 1 Department of Physiology, University of Szeged, Hungary Introduction: Several data suggest that neonatal versus adult capsaicin desensitization leads to different phenotypes in some respects. The goal of this study was to reveal the effects of high dose capsaicin treatment on different parameters (pain sensitivity, thermoregulation, visceral function) in young but not neonate animals. Methods: 21 days old male Wistar rats, after weaning, were injected for 4 days with capsaicin in increasing doses of 10, 20 50 and 100 mg/kg intraperitoneally. Control animals received physiological saline. The animals were followed up for 3 months and we determined the body weight, the blepharosmasm and paw wiping reflex of the eye exposed to diluted capsaicin, changes in acute and inflammatory pain sensitivity, volume of the urinary bladder and body temperature. Results: The body weight of capsaicin-treated animals decreased temporarily compared to the control group. Capsaicin-treated animals had complete abolishment of eye-wipe responses and blepharospasm, suggesting that desensitization prevented the painful effects of capsaicin eye drops. Both heat and mechanical acute pain sensitivity augmented while pain threshold in inflamed limbs diminished. Ultrasound examination of urinary bladder revealed that the volume was significantly larger compared to untreated animals. Disturbance in thermoregulation has been also observed since desensitized rats had higher body temperature. Our results suggest that juvenile capsaicin desensitization produced sustained changes in several physiological parameters, and these changes are similar to alterations observed after adult capsaicin desensitization. This work was supported by the National Research and development Office, Hungary (OMFB-0066/2005/DNT) and a Hungarian Research Grant (OTKA, K60278). Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Pathophysiology and neurology - non-degenerative disorders Citation: Tuboly G, Kékesi G, Adam G, Benedek G and Horváth G (2009). The influence of juvenile capsaicin desenzitization on different sensory processes. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.042 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Feb 2009; Published Online: 27 Feb 2009. * Correspondence: Gábor Tuboly, Department of Physiology, University of Szeged, Szeged, Hungary, corp120@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Gábor Tuboly Gabriella Kékesi Gabor Adam Gyorgy Benedek Gyöngyi Horváth Google Gábor Tuboly Gabriella Kékesi Gabor Adam Gyorgy Benedek Gyöngyi Horváth Google Scholar Gábor Tuboly Gabriella Kékesi Gabor Adam Gyorgy Benedek Gyöngyi Horváth PubMed Gábor Tuboly Gabriella Kékesi Gabor Adam Gyorgy Benedek Gyöngyi Horváth Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

ThermoTRP channels in nociceptors: taking a lead from capsaicin receptor TRPV1.

Nociceptors with peripheral and central projections express temperature sensitive transient receptor potential (TRP) ion channels, also called thermoTRP’s. Chemosensitivity of thermoTRP’s to certain natural compounds eliciting pain or exhibiting thermal properties has proven to be a good tool in characterizing these receptors. Capsaicin, a pungent chemical in hot peppers, has assisted in the cloning of the first thermoTRP, TRPV1. This discovery initiated the search for other receptors encoding the response to a wide range of temperatures encountered by the body. Of these, TRPV1 and TRPV2 encode unique modalities of thermal pain when exposed to noxious heat. The ability of TRPA1 to encode noxious cold is presently being debated. The role of TRPV1 in peripheral inflammatory pain and central sensitization during chronic pain is well known. In addition to endogenous agonists, a wide variety of chemical agonists and antagonists have been discovered to activate and inhibit TRPV1. Efforts are underway to determine conditions under which agonist-mediated desensitization of TRPV1 or inhibition by antagonists can produce analgesia. Also, identification of specific second messenger molecules that regulate phosphorylation of TRPV1 has been the focus of intense research, to exploit a broader approach to pain treatment. The search for a role of TRPV2 in pain remains dormant due to the lack of suitable experimental models. However, progress into TRPA1’s role in pain has received much attention recently. Another thermoTRP, TRPM8, encoding for the cool sensation and also expressed in nociceptors, has recently been shown to reduce pain via a central mechanism, thus opening a novel strategy for achieving analgesia. The role of other thermoTRP’s (TRPV3 and TRPV4) encoding for detection of warm temperatures and expressed in nociceptors cannot be excluded. This review will discuss current knowledge on the role of nociceptor thermoTRPs in pain and therapy and describes the activator and inhibitor molecules known to interact with them and modulate their activity.

Kinetics and functional characterization of the glycine receptor α2 and α3 subunit

In recent studies one serine residue (Ser-346) within the protein-kinase-A (R-E-S-R) consensus sequence of the GlyRalpha3 intracellular loop has proven to be an essential target for prostaglandin-E(2)-mediated phosphorylation, which further modulates spinal nociceptive transmission and central inflammatory pain sensitization. In the present study we investigated the effect of Ser-346 phosphorylation and Ser-346 mutation on receptor kinetics and function using whole-cell patch-clamp recordings in transfected HEK 293 T cells. We compared biophysical properties of wild type GlyRalpha3 and two site-directed mutants, where Ser-346 was replaced by alanine or aspartate, in the absence and presence of prostaglandin-E(2). The mutation to alanine was accompanied by significantly altered dose-response and desensitization properties. Mutation to aspartate had only minor effects on receptor kinetics and function. Phosphorylation of Ser-346 slowed desensitization and decreased glycinergic currents in GlyRalpha3/mEP2 transfected cells. In addition, we demonstrated that prostaglandin-E(2) also had an effect on the GlyRalpha2 subunit. Exposure to prostaglandin-E(2) decreased the maximum peak current amplitude of glycinergic currents in GlyRalpha2/mEP2 transfected cells in the same manner as phosphorylation of the GlyRalpha3 subunit. It led to a significant increase of the desensitization time constants and thus significantly affected the desensitization behaviour. These results indicate that the GlyRalpha2 and the GlyRalpha3 subunits act as important subunits for the modulation of glycine receptor kinetics and function.