Pain. 2010 Aug;150(2):340-50. Epub 2010 Jun 12.

TRPM8, but not TRPA1, is required for neural and behavioral responses to acute noxious cold temperatures and cold-mimetics in vivo.

Knowlton WM, Bifolck-Fisher A, Bautista DM, McKemy DD.

Source

Neuroscience Graduate Program, Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA.

Abstract

Somatosensory neurons detect environmental stimuli, converting external cues into neural activity that is relayed first to second-order neurons in the spinal cord. The detection of cold is proposed to be mediated by the ion channels TRPM8 and TRPA1. However, there is significant debate regarding the role of each channel in cold-evoked pain, complicating their potential as drug targets for conditions such as cold allodynia and hyperalgesia. To address this debate, we generated mice lacking functional copies of both channels and examined behaviors and neural activity in response to painful cold and noxious cooling compounds. Whereas normal mice display a robust preference for warmth over cold, both TRPM8-null (TRPM8(-/-)) and TRPM8/TRPA1 double-knockout mice (DKO) display no preference until temperatures reach the extreme noxious range. Additionally, in contrast to wildtype mice that avoid touching cold surfaces, mice lacking TRPM8 channels display no such avoidance and explore noxious cold surfaces, even at 5 degrees C. Furthermore, nocifensive behaviors to the cold-mimetic icilin are absent in TRPM8(-/-) and DKO mice, but are retained in TRPA1-nulls (TRPA1(-/-)). Finally, neural activity, measured by expression of the immediate-early gene c-fos, evoked by hindpaw stimulation with noxious cold, menthol, or icilin is reduced in TRPM8(-/-) and DKO mice, but not in TRPA1(-/-) animals. Thus our results show that noxious cold signaling is exclusive to TRPM8, mediating neural and behavioral responses to cold and cold-mimetics, and that TRPA1 is not required for acute cold pain in mammals.

Journal club 2012-11-30 Read More »

2012-11-26 고려인삼학회포스터

somi2388

고려인삼학회포스터

A particular ginsenoside has a potential to inhibit itch transduction

Wook-Joo Lee, Dasom Choi, Won-Sik Shim^*

College of Pharmacy, Gachon University, Incheon, 406-799, South Korea

Purpose:

Korean red ginseng (the steamed root of Panax ginseng C.A. Meyer, family Araliaceae) has been used as a remedy for wide variety of disorders, and recent studies have identified its beneficial use in itch-related diseases such as atopic dermatitis. Although its anti-pruritic effect was mostly revealed by animal scratching tests, its underlying molecular mechanism has never been investigated. Because the itch transduction in peripheral nervous system could be initiated via histamine-dependent (H1R/TRPV1), or -independent (MrgprA3/TRPA1) pathway, the putative inhibitory effect of various ginsenosides were investigated in the present study.

Method:

cDNA combinations of H1R/TRPV1 or MrgprA3/TRPA1 were transiently expressed in human embryonic kidney (HEK) 293T cells, and calcium influx was monitored with Fluo3-AM, a calcium-specific fluorescent dye. To test the inhibitory effect, 11 ginsenosides were pretreated for 10 min, and either histamine (for H1R/TRPV1) or chloroquine (for MrgprA3/TRPA1) was treated and changes were recorded for 1 min.

Result:

It was found that one particular ginsenoside strongly inhibited the calcium influx on both H1R/TRPV1- and MrgprA3/TRPA1-expressing cells even after histamine or chloroquine was treated, suggesting that the ginsenoside may have a potential anti-pruritic activity. Furthermore, it seems that the inhibitory effect is mediated by directly blocking the action of ion channels (TRPV1, TRPA1) rather than interfering with receptors (H1R, MrgprA3), implying other possible roles especially in nociception.

2012-11-26 고려인삼학회포스터 Read More »

Journal club 2012-11-09

WOOK-JOO LEE

Piezo1 and Piezo2 Are Essential Components of Distinct Mechanically Activated Cation Channels

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Bertrand Coste,1 Jayanti Mathur,2 Manuela Schmidt,1 Taryn J. Earley,1 Sanjeev Ranade,1 Matt J. Petrus,2 Adrienne E. Dubin,1 Ardem Patapoutian1,2*

Mechanical stimuli drive many physiological processes, including touch and pain sensation, hearing, and blood pressure regulation. Mechanically activated (MA) cation channel activities have been recorded in many cells, but the responsible molecules have not been identified.
We characterized a rapidly adapting MA current in a mouse neuroblastoma cell line. Expression profiling and RNA interference knockdown of candidate genes identified Piezo1 (Fam38A) to be required for MA currents in these cells. Piezo1 and related Piezo2 (Fam38B) are vertebrate multipass transmembrane proteins with homologs in invertebrates, plants, and protozoa. Overexpression of mouse Piezo1 or Piezo2 induced two kinetically distinct MA currents. Piezos are expressed in several tissues, and knockdown of Piezo2 in dorsal root ganglia neurons specifically reduced rapidly adapting MA currents. We propose that Piezos are components of MA cation channels.

Journal club 2012-11-09 Read More »

Journal club 2012-11-09

WOOK-JOO LEE

TRPA1 contributes to specific mechanically activated currents and sensory neuron mechanical hypersensitivity

Stuart M. Brierley1,2,3, Joel Castro1,2, Andrea M. Harrington1,2, Patrick A. Hughes1,2, Amanda J. Page1,2,3, Grigori Y. Rychkov3 and L. Ashley Blackshaw1,2,3

1Nerve-Gut Research Laboratory, Department of Gastroenterology and Hepatology, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia, Australia 5000
Disciplines of 2Medicine and 3Physiology, Faculty of Heath Sciences, University of Adelaide, Adelaide, South Australia, Australia 5000

tjp0589-3575

Abstract
The mechanosensory role of TRPA1 and its contribution to mechanical hypersensitivity in sensory neurons remains enigmatic. We elucidated this role by recording mechanically activated currents in conjunction with TRPA1 over- and under-expression and selective pharmacology. First, we established that TRPA1 transcript, protein and functional expression are more abundant in smaller-diameter neurons than larger-diameter neurons, allowing comparison of two different neuronal populations. Utilising whole cell patch clamping, we applied calibrated displacements to neurites of dorsal root ganglion (DRG) neurons in short-term culture and recorded mechanically activated currents termed intermediately (IAMCs), rapidly (RAMCs) or slowly adapting (SAMCs). Trpa1 deletion (–/–) significantly reduced maximum IAMC amplitude by 43% in small-diameter neurons compared with wild-type (+/+) neurons. All other mechanically activated currents in small- and large-diameter Trpa1−/− neurons were unaltered. Seventy-three per cent of Trpa1+/+ small-diameter neurons responding to the TRPA1 agonist allyl-isothiocyanate (AITC) displayed IAMCs to neurite displacement, which were significantly enhanced after AITC addition. The TRPA1 antagonist HC-030031 significantly decreased Trpa1+/+ IAMC amplitudes, but only in AITC responsive neurons. Using a trans- fection system we also showed TRPA1 over-expression in Trpa1+/+ small-diameter neurons increases IAMC amplitude, an effect reversed by HC-030031. Furthermore, TRPA1 introduction into Trpa1−/− small-diameter neurons restored IAMC amplitudes to Trpa1+/+ levels, which was subsequently reversed by HC-030031. In summary our data demonstrate TRPA1 makes a contribution to normal mechanosensation in a specific subset of DRG neurons. Furthermore, they also provide new evidence illustrating mechanisms by which sensitisation or over-expression of TRPA1 enhances nociceptor mechanosensitivity. Overall, these findings suggest TRPA1 has the capacity to tune neuronal mechanosensitivity depending on its degree of activation or expression.

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Journal club 2012-11-02

somi2388

nihms225332

Enhanced scratching evoked by PAR-2 agonist and 5-HT but not histamine in a mouse model of chronic dry skin itch.

Akiyama T, Carstens MI, Carstens E.

Source

Department of Neurobiology, Physiology and Behavior, University of California, Davis, CA 95616, USA.

Abstract

Chronic itch is a symptom of many skin conditions and systemic disease, and it has been hypothesized that the chronic itch may result from sensitization of itch-signaling pathways. We induced experimental chronic dry skin on the rostral back of mice, and observed a significant increase in spontaneous hindlimb scratches directed to the dry skin. Spontaneous scratching was significantly attenuated by a PAR-2 antibody and 5-HT2A receptor antagonist, indicating activation of these receptors by endogenous mediators released under dry skin conditions. We also observed a significant increase in the number of scratch bouts evoked by acute intradermal injections of a protease-activated receptor (PAR)-2 agonist and serotonin (5-HT), but not histamine. We additionally investigated if pruritogen-evoked activity of dorsal root ganglion (DRG) neurons is enhanced in this model. DRG cells from dry skin mice exhibited significantly larger responses to the PAR-2 agonist and 5-HT, but not histamine. Spontaneous scratching may reflect ongoing itch, and enhanced pruritogen-evoked scratching may represent hyperknesis (enhanced itch), both potentially due to sensitization of itch-signaling neurons. The correspondence between enhanced behavioral scratching and DRG cell responses suggest that peripheral pruriceptors that respond to proteases and 5-HT, but not histamine, may be sensitized in dry skin itch.

Journal club 2012-11-02 Read More »