Transient receptor potential vanilloid 1 (TRPV1) channels contribute to the development of several chronic pain states and represent a possible therapeutic target in many painful disease treatment. Proinflammatory mediator bradykinin (BK) sensitizes TRPV1, whereas noxious peripheral stimulation increases BK level in the spinal cord. Here, we investigated the involvement of spinal TRPV1 in thermal and mechanical hypersensitivity, evoked by intrathecal (i.t.) administration of BK and an endogenous agonist of TRPV1, N-oleoyldopamine (OLDA), using behavioral tests and i.t. catheter implantation, and administration of BK-induced transient thermal and mechanical hyperalgesia and mechanical allodynia. All these hypersensitive states were enhanced by co-administration of a low dose of OLDA (0.42 µg i.t.), which was ineffective only under the control conditions. Intrathecal pretreatment with TRPV1 selective antagonist SB366791 prevented hypersensitivity induced by i.t. co-administration of BK and OLDA. Our results demonstrate that both thermal and mechanical hypersensitivity evoked by co-administration of BK and OLDA is mediated by the activation of spinal TRPV1 channels.

• Keywords
• OLDA, TRPV1, allodynia, bradykinin, hyperalgesia, spinal cord,
• MeSH
• Bradykinin MeSH
• Dopamine analogs & derivatives   MeSH
• Hyperalgesia metabolism   MeSH
• TRPV Cation Channels agonists   metabolism   MeSH
• Rats MeSH
• Spinal Cord metabolism   MeSH
• Rats, Wistar MeSH
• Injections, Spinal MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Bradykinin MeSH
• Dopamine MeSH
• TRPV Cation Channels MeSH
• N-oleoyldopamine MeSH Browser
• TRPV1 protein, mouse MeSH Browser

The mechanisms of inflammatory pain need to be identified in order to find new superior treatments. Protease-activated receptors 2 (PAR2) and transient receptor potential vanilloid 1 (TRPV1) are highly co-expressed in dorsal root ganglion neurons and implicated in pain development. Here, we examined the role of spinal PAR2 in hyperalgesia and the modulation of synaptic transmission in carrageenan-induced peripheral inflammation, using intrathecal (i.t.) treatment in the behavioral experiments and recordings of spontaneous, miniature and dorsal root stimulation-evoked excitatory postsynaptic currents (sEPSCs, mEPSCs and eEPSCs) in spinal cord slices. Intrathecal PAR2-activating peptide (AP) administration aggravated the carrageenan-induced thermal hyperalgesia, and this was prevented by a TRPV1 antagonist (SB 366791) and staurosporine i.t. pretreatment. Additionally, the frequency of the mEPSC and sEPSC and the amplitude of the eEPSC recorded from the superficial dorsal horn neurons were enhanced after acute PAR2 AP application, while prevented with SB 366791 or staurosporine pretreatment. PAR2 antagonist application reduced the thermal hyperalgesia and decreased the frequency of mEPSC and sEPSC and the amplitude of eEPSC. Our findings highlight the contribution of spinal PAR2 activation to carrageenan-induced hyperalgesia and the importance of dorsal horn PAR2 and TRPV1 receptor interactions in the modulation of nociceptive synaptic transmission.

• Keywords
• PAR2, TRPV1, inflammatory pain, nociception, peripheral inflammation, spinal cord, superficial dorsal horn, synaptic transmission, thermal hyperalgesia,
• MeSH
• Anilides pharmacology   MeSH
• Posterior Horn Cells drug effects   metabolism   physiology   MeSH
• Cinnamates pharmacology   MeSH
• Excitatory Postsynaptic Potentials MeSH
• Hyperalgesia etiology   metabolism   physiopathology   MeSH
• Carrageenan pharmacology   toxicity   MeSH
• TRPV Cation Channels antagonists & inhibitors   metabolism   MeSH
• Rats MeSH
• Miniature Postsynaptic Potentials MeSH
• Nociception MeSH
• Rats, Wistar MeSH
• Receptor, PAR-2 metabolism   MeSH
• Staurosporine pharmacology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anilides MeSH
• Cinnamates MeSH
• Carrageenan MeSH
• TRPV Cation Channels MeSH
• N-(3-methoxyphenyl)-4-chlorocinnamanilide MeSH Browser
• Receptor, PAR-2 MeSH
• Staurosporine MeSH
• Trpv1 protein, rat MeSH Browser

Peripheral neuropathy is dose limiting in paclitaxel cancer chemotherapy and can result in both acute pain during treatment and chronic persistent pain in cancer survivors. The hypothesis tested was that paclitaxel produces these adverse effects at least in part by sensitizing transient receptor potential vanilloid subtype 1 (TRPV1) through Toll-like receptor 4 (TLR4) signaling. The data show that paclitaxel-induced behavioral hypersensitivity is prevented and reversed by spinal administration of a TRPV1 antagonist. The number of TRPV1(+) neurons is increased in the dorsal root ganglia (DRG) in paclitaxel-treated rats and is colocalized with TLR4 in rat and human DRG neurons. Cotreatment of rats with lipopolysaccharide from the photosynthetic bacterium Rhodobacter sphaeroides (LPS-RS), a TLR4 inhibitor, prevents the increase in numbers of TRPV1(+) neurons by paclitaxel treatment. Perfusion of paclitaxel or the archetypal TLR4 agonist LPS activated both rat DRG and spinal neurons directly and produced acute sensitization of TRPV1 in both groups of cells via a TLR4-mediated mechanism. Paclitaxel and LPS sensitize TRPV1 in HEK293 cells stably expressing human TLR4 and transiently expressing human TRPV1. These physiological effects also are prevented by LPS-RS. Finally, paclitaxel activates and sensitizes TRPV1 responses directly in dissociated human DRG neurons. In summary, TLR4 was activated by paclitaxel and led to sensitization of TRPV1. This mechanism could contribute to paclitaxel-induced acute pain and chronic painful neuropathy. Significance statement: In this original work, it is shown for the first time that paclitaxel activates peripheral sensory and spinal neurons directly and sensitizes these cells to transient receptor potential vanilloid subtype 1 (TRPV1)-mediated capsaicin responses via Toll-like receptor 4 (TLR4) in multiple species. A direct functional interaction between TLR4 and TRPV1 is shown in rat and human dorsal root ganglion neurons, TLR4/TRPV1-coexpressing HEK293 cells, and in both rat and mouse spinal cord slices. Moreover, this is the first study to show that this interaction plays an important role in the generation of behavioral hypersensitivity in paclitaxel-related neuropathy. The key translational implications are that TLR4 and TRPV1 antagonists may be useful in the prevention and treatment of chemotherapy-induced peripheral neuropathy in humans.

• Keywords
• DRG, cancer, dorsal horn, neuropathy,
• MeSH
• Excitatory Postsynaptic Potentials drug effects   MeSH
• Antineoplastic Agents, Phytogenic antagonists & inhibitors   pharmacology   MeSH
• HEK293 Cells MeSH
• Hyperalgesia chemically induced   physiopathology   MeSH
• TRPV Cation Channels antagonists & inhibitors   MeSH
• Rats MeSH
• Humans MeSH
• Pain Measurement drug effects   MeSH
• Patch-Clamp Techniques MeSH
• Spinal Cord drug effects   MeSH
• Mice, Inbred C57BL MeSH
• Mice MeSH
• Sensory Receptor Cells drug effects   MeSH
• Paclitaxel antagonists & inhibitors   pharmacology   MeSH
• Rats, Sprague-Dawley MeSH
• Signal Transduction drug effects   MeSH
• Ganglia, Spinal cytology   drug effects   MeSH
• Toll-Like Receptor 4 antagonists & inhibitors   drug effects   MeSH
• Calcium metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Antineoplastic Agents, Phytogenic MeSH
• TRPV Cation Channels MeSH
• Paclitaxel MeSH
• Toll-Like Receptor 4 MeSH
• TRPV1 receptor MeSH Browser
• Calcium MeSH

BACKGROUND: The cytokine tumor necrosis factor α (TNFα) is an established pain modulator in both the peripheral and central nervous systems. Modulation of nociceptive synaptic transmission in the spinal cord dorsal horn (DH) is thought to be involved in the development and maintenance of several pathological pain states. Increased levels of TNFα and its receptors (TNFR) in dorsal root ganglion (DRG) cells and in the spinal cord DH have been shown to play an essential role in neuropathic pain processing. In the present experiments the effect of TNFα incubation on modulation of primary afferent synaptic activity was investigated in a model of peripheral neuropathy. METHODS: Spontaneous and miniature excitatory postsynaptic currents (sEPSC and mEPSCs) were recorded in superficial DH neurons in acute spinal cord slices prepared from animals 5 days after sciatic nerve transection and in controls. RESULTS: In slices after axotomy the sEPSC frequency was 2.8 ± 0.8 Hz, while neurons recorded from slices after TNFα incubation had significantly higher sEPSC frequency (7.9 ± 2.2 Hz). The effect of TNFα treatment was smaller in the slices from the control animals, where sEPSC frequency was 1.2 ± 0.2 Hz in slices without and 2.0 ± 0.5 Hz with TNFα incubation. Tetrodotoxin (TTX) application in slices from axotomized animals and after TNFα incubation decreased the mEPSC frequency to only 37.4 ± 6.9% of the sEPSC frequency. This decrease was significantly higher than in the slices without the TNFα treatment (64.4 ± 6.4%). TTX application in the control slices reduced the sEPSC frequency to about 80% in both TNFα untreated and treated slices. Application of low concentration TRPV1 receptors endogenous agonist N-oleoyldopamine (OLDA, 0.2 μM) in slices after axotomy induced a significant increase in mEPSC frequency (175.9 ± 17.3%), similar to the group with TNFα pretreatment (158.1 ± 19.5%). CONCLUSIONS: Our results indicate that TNFα may enhance spontaneous transmitter release from primary afferent fibres in the spinal cord DH by modulation of TTX-sensitive sodium channels following sciatic nerve transection. This nerve injury also leads to enhanced sensitivity of presynaptic TRPV1 receptors to endogenous agonist. Modulation of presynaptic receptor activity on primary sensory terminals by TNFα may play an important role in neuropathic pain development.

• MeSH
• Excitatory Postsynaptic Potentials MeSH
• Rats MeSH
• Patch-Clamp Techniques MeSH
• Spinal Cord pathology   physiology   ultrastructure   MeSH
• Peripheral Nervous System Diseases chemically induced   pathology   physiopathology   MeSH
• Synaptic Transmission physiology   MeSH
• Neurons, Afferent cytology   drug effects   physiology   MeSH
• Nociception drug effects   physiology   MeSH
• Rats, Wistar MeSH
• Sodium Channels metabolism   MeSH
• Ganglia, Spinal cytology   physiology   MeSH
• Synapses physiology   MeSH
• Tumor Necrosis Factor-alpha pharmacology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Sodium Channels MeSH
• Tumor Necrosis Factor-alpha MeSH