QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: mol.106.026740v1 71/1/12    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Endres-Becker, J. Articles by Zöllner, C. Search for Related Content PubMed PubMed Citation Articles by Endres-Becker, J. Articles by Zöllner, C.

µ-Opioid Receptor Activation Modulates Transient Receptor Potential Vanilloid 1 (TRPV1) Currents in Sensory Neurons in A Model of Inflammatory Pain

Klinik für Anaesthesiologie und operative Intensivmedizin (J.E.-B., P.A.H., S.A.M., D.L., M.S., C.S., C.Z.) and Institut für Pharmakologie (A.O.), Charité Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany

Current therapy for inflammatory pain includes the peripheral application of opioid receptor agonists. Activation of opioid receptors modulates voltage-gated ion channels, but it is unclear whether opioids can also influence ligand-gated ion channels [e.g., the transient receptor potential vanilloid type 1 (TRPV1)]. TRPV1 channels are involved in the development of thermal hypersensitivity associated with tissue inflammation. In this study, we investigated µ-opioid receptor and TRPV1 expression in primary afferent neurons in the dorsal root ganglion (DRG) in complete Freund's adjuvant (CFA)-induced paw inflammation. In addition, the present study examined whether the activity of TRPV1 in DRG neurons can be inhibited by µ-opioid receptor (µ-receptor) ligands and whether this inhibition is increased after CFA inflammation. Immunohistochemistry demonstrated colocalization of TRPV1 and µ-receptors in DRG neurons. CFA-induced inflammation increased significantly the number of TRPV1- and µ-receptor-positive DRG neurons, as well as TRPV1 binding sites. In whole-cell patch clamp studies, opioids significantly decreased capsaicin-induced TRPV1 currents in a naloxone- and pertussis toxinsensitive manner. The inhibitory effect of morphine on TRPV1 was abolished by forskolin and 8-bromo-cAMP. During inflammation, an increase in TRPV1 is apparently rivaled by an increase of µ-receptors. However, in single dissociated DRG neurons, the inhibitory effects of morphine are not different between animals with and without CFA inflammation. In in vivo experiments, we found that locally applied morphine reduced capsaicin-induced thermal allodynia. In summary, our results indicate that µ-receptor activation can inhibit the activity of TRPV1 via G_i/o proteins and the cAMP pathway. These observations demonstrate an important new mechanism underlying the analgesic efficacy of peripherally acting µ-receptor ligands in inflammatory pain.

Address correspondence to: Christian Zöllner, MD, Klinik für Anaesthesiologie und operative Intensivmedizin, Charité - Universitätsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany. E-mail: christian.zoellner{at}charite.de

This article has been cited by other articles:

				Y. Chen, C. Geis, and C. Sommer Activation of TRPV1 Contributes to Morphine Tolerance: Involvement of the Mitogen-Activated Protein Kinase Signaling Pathway J. Neurosci., May 28, 2008; 28(22): 5836 - 5845. [Abstract] [Full Text] [PDF]