PAR-2 agonists activate trigeminal nociceptors and induce functional competence in the delta opioid receptor.
The role of protease activated receptor-2 (PAR-2) activation in trigeminal nociception and in induction of functional competence in the delta opioid receptor (DOR) is not known. In this study, we evaluated whether agonists of PAR-2 activate the capsaicin-sensitive subclass of trigeminal nociceptors in a PLC-PKC-dependent manner and induce functional competence in the DOR. Adult male rat trigeminal ganglion (TG) cultured neurons were treated with the PAR-2 agonist (SL-NH2) or an enzyme activator of PAR (trypsin) and the activation of TG nociceptors was assessed using three independent methods: neuropeptide release, calcium influx, and whole cell patch-clamp. The specificity of SL-NH2 and trypsin responses was evaluated using TG cultures transfected with siRNA against PAR-2. The in vivo role of PAR-2 activation was determined measuring SL-NH2 and trypsin-evoked nocifensive behavior and increase in blood flow. Trigeminal neurons were treated with SL-NH2/vehicle and then the DOR agonist to determine DOR inhibition of evoked neuropeptide release and cAMP accumulation. The results showed that SL-NH2 (100 microM) and trypsin (1-600 nM) activate TG nociceptors, which is partly reversible by the PKC inhibitor bisindolylmaleimide (500 nM) and by ruthenium red (10 microM). In cultures treated with siRNA against PAR-2, both SL-NH2 and trypsin responses were significantly diminished. Both SL-NH2 and trypsin evoke nocifensive behavior and increases in blood flow in an orofacial pain model. Application of SL-NH2 rapidly produced functional competence of DOR for inhibiting nociceptor function. In inflamed tissue, endogenous proteases may activate TG nociceptors and generate pain. Moreover, activation of PAR-2 can also induce functional competence in DOR.
Patwardhan
Amol M
AM
Department of Pharmacology, University of Texas Health Science Center, San Antonio, TX 78229, USA.
Diogenes
Anibal
A
Berg
Kelly A
KA
Fehrenbacher
Jill C
JC
Clarke
William P
WP
Akopian
Armen N
AN
Hargreaves
Kenneth M
KM
D000818:Animals; D002478:Cells, Cultured; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism*; D009842:Oligopeptides / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044464:Receptor, PAR-2 / Q000819:agonists* / Q000378:metabolism*; D017465:Receptors, Opioid, delta / Q000378:metabolism*; D014278:Trigeminal Nuclei / Q000187:drug effects / Q000378:metabolism*; D014357:Trypsin / Q000008:administration & dosage*
D009842:Oligopeptides; D044464:Receptor, PAR-2; D017465:Receptors, Opioid, delta; C112356:seryl-leucyl-isoleucyl-glycyl--arginyl-leucinamide; D014357:Trypsin