title: Activation of transient receptor potential vanilloid 2-expressing primary afferents stimulates synaptic transmission in the deep dorsal horn of the rat spinal cord and elicits mechanical hyperalgesia.
abstract: Probenecid, an agonist of transient receptor vanilloid (TRPV) type 2, was used to evaluate the effects of TRPV2 activation on excitatory and inhibitory synaptic transmission in the dorsal horn (DH) of the rat spinal cord and on nociceptive reflexes induced by thermal heat and mechanical stimuli. The effects of probenecid were compared with those of capsaicin, a TRPV1 agonist. Calcium imaging experiments on rat dorsal root ganglion (DRG) and DH cultures indicated that functional TRPV2 and TRPV1 were expressed by essentially non-overlapping subpopulations of DRG neurons, but were absent from DH neurons and DH and DRG glial cells. Pretreatment of DRG cultures with small interfering RNAs against TRPV2 suppressed the responses to probenecid. Patch-clamp recordings from spinal cord slices showed that probenecid and capsaicin increased the frequencies of spontaneous excitatory postsynaptic currents (sEPSCs) and spontaneous inhibitory postsynaptic currents in a subset of laminae III-V neurons. In contrast to capsaicin, probenecid failed to stimulate synaptic transmission in lamina II. Intrathecal or intraplantar injections of probenecid induced mechanical hyperalgesia/allodynia without affecting nociceptive heat responses. Capsaicin induced both mechanical hyperalgesia/allodynia and heat hyperalgesia. Activation of TRPV1 or TRPV2 in distinct sets of primary afferents increased the sEPSC frequencies in a largely common population of DH neurons in laminae III-V, and might underlie the development of mechanical hypersensitivity following probenecid or capsaicin treatment. However, only TRPV1-expressing afferents facilitated excitatory and/or inhibitory transmission in a subpopulation of lamina II neurons, and this phenomenon might be correlated with the induction of thermal heat hyperalgesia.
authors.affiliation: Institut des Neurosciences Cellulaires et Integratives, UPR 3212 Centre National de la Recherche Scientifique, Strasbourg, France; Universite de Strasbourg, 5 rue Blaise Pascal, F-67084, Strasbourg, France.
authors.forename: Hugues
authors.initials: H
authors.lastname: Petitjean
authors.forename: Sylvain
authors.initials: S
authors.lastname: Hugel
authors.forename: Florent
authors.initials: F
authors.lastname: Barthas
authors.forename: Yohann
authors.initials: Y
authors.lastname: Bohren
authors.forename: Michel
authors.initials: M
authors.lastname: Barrot
authors.forename: Ipek
authors.initials: I
authors.lastname: Yalcin
authors.forename: Rémy
authors.initials: R
authors.lastname: Schlichter
mesh_terms: D000344:Afferent Pathways; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D002478:Cells, Cultured; D005727:Ganglia, Spinal / Q000187:drug effects / Q000502:physiology; D006930:Hyperalgesia / Q000139:chemically induced; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D059225:Nociception / Q000187:drug effects / Q000502:physiology; D011339:Probenecid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D066148:Spinal Cord Dorsal Horn / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects; D050916:TRPV Cation Channels / Q000819:agonists / Q000502:physiology*
chemical_list: D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; C476722:Trpv2 protein, rat; D011339:Probenecid; D002211:Capsaicin
keywords: TRPV1; dorsal root ganglion; excitatory postsynaptic current; inhibitory postsynaptic current; pain