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.

Pannexin 1 Modulates Axonal Growth in Mouse Peripheral Nerves

“…0.05% nerve growth factor (NGF-7S, N0513, Sigma-Aldrich) was included in the growth media unless otherwise stated. To further investigate purinergic signaling pathways, WT DRG were also treated with media containing 2.5 units/ml apyrase (from potatoes, A7646, Sigma-Aldrich) or 50 μM probenecid (20061, Bioquest), 1 mg/mL 10 Panx peptide, or 1 μM ATP for 7 days (Zhang et al, 2007 ; Kim et al, 2012 ; Petitjean et al, 2014 ). For all drug treatment groups, contralateral control explants were harvested and seeded in normal media, to confirm successful tissue culture for a given round of dissections.…”

Thermosensitive Transient Receptor Potential (TRP) Channel Agonists and Their Role in Mechanical, Thermal and Nociceptive Sensations as Assessed Using Animal Models

“…Conversely, neurons lacking TRPV1 and TRPV2 have been reported to exhibit normal responses to noxious heating (Woodbury et al, 2004). Unlike capsaicin, which rapidly induces mechanical allodynia and thermal heat hyperalgesia after intrathecal or intraplantar application, probenecid only enhanced mechanical hypersensitivity (Petitjean et al, 2014). Therefore it is postulated that TRPV2 may have a large role in mechanotranduction, rather than in processing nociceptive heat information.…”

Loss of SLC9A6/NHE6 impairs nociception in a mouse model of Christianson syndrome

“…In every recording event, KCl was applied to neurons at the end of the recording session and only those that responded to KCl were analyzed for their responses to 5-μM capsaicin. 27 …”