Extracts of Helleborus roots were traditionally used in the Balkan area for their analgesic action. We report that the pure natural product MCS-18 isolated from this source is a potent, specific and reversible antagonist of the capsaicin receptor, TRPV1, expressed in rat dorsal root ganglion (DRG) neurons. TRPV1 is a nonselective cation channel expressed in a subset of cutaneous and visceral sensory nerve endings and activated by noxious heat, acidity and fatty acid metabolites of arachidonic acid, with a decisive role in inflammatory heat hyperalgesia. MCS-18 inhibited the increase in intracellular calcium concentration evoked in DRG neurons by capsaicin (300 nM) and low pH (5.5) but not by heat (43 ºC). The substance had no effect on the responses mediated by acid-sensing ion channels (ASICs) or the irritant receptor TRPA1. Whole-cell patch-clamp was used to confirm the inhibition of capsaicin-induced currents by MCS-18 which was dose-dependent. The mechanism of inhibition does not require an intact cell, as capsaicin-induced currents were also inhibited in the excised outside-out configuration. The antagonism of the capsaicin and proton action on native TRPV1 by MCS-18 may be of interest for pain therapy., C. Neacsu ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
Protease-activated receptors (PARs) belong to the G-proteincoupled receptor family, that are expressed in many body tissues especially in different epithelial cells, mast cells and also in neurons and astrocytes. PARs play different physiological roles according to the location of their expression. Increased evidence supports the importance of PARs activation during nociceptive signaling and in the development of chronic pain states. This short review focuses on the role of PAR2 receptors in nociceptive transmission with the emphasis on the modulation at the spinal cord level. PAR2 are cleaved and subsequently activated by endogenous proteases such as tryptase and trypsin. In vivo, peripheral and intrathecal administration of PAR2 agonists induces thermal and mechanical hypersensitivity that is thought to be mediated by PAR2-induced release of pronociceptive neuropeptides and modulation of different receptors. PAR2 activation leads also to sensitization of transient receptor potential channels (TRP) that are crucial for nociceptive signaling and modulation. PAR2 receptors may play an important modulatory role in the development and maintenance of different pathological pain states and could represent a potential target for new analgesic treatments., P. Mrozkova, J. Palecek, D. Spicarova., and Obsahuje bibliografii
Theta burst stimulation (TBS) is a modified form of highfrequency repetitive transcranial magnetic stimulation (rTMS) with promising effect in chronic pain. The aim of our doubleblind, sham-controlled, parallel-group, randomized study was to assess an efficacy of intermittent TBS (iTBS) in the treatment of patients with chronic orofacial pain. Nineteen patients (twelve females) with chronic orofacial pain were prospectively included and randomly assigned to single session of an active (iTBS) or sham (intermediate TBS; imTBS) stimulation delivered to the primary motor cortex (M1) contralateral to painful side. The primary outcome was pain relief assessed using a visual analogue scale (VAS) after stimulation and at the end of two-week followup. The secondary outcomes were changes in the quantitative sensory testing (QST). QST set the threshold for thermal and tactile (touch) sensation in the affected facial area. Intermittent TBS, compared with the sham, showed significant improvement in VAS after stimulation, but not at the end of two-week followup. Regarding the secondary outcomes (QST), we failed to find any significant difference between iTBS and sham. Our findings demonstrate that iTBS of M1 transiently provides transient and modest subjective pain relief in chronic orofacial pain.