Transient receptor potential ion channel, vanilloid subfamily, type 1 (TRPV1) cation channel, and cannabinoid receptor 1 (CB1) are essential in the modulation of nociceptive signaling in the spinal cord dorsal horn that underlies different pathological pain states. TRPV1 and CB1 receptors share the endogenous agonist anandamide (AEA), produced from N-arachidonoylphosphatidylethanolamine (20:4-NAPE). We investigated the effect of the anandamide precursor 20:4-NAPE on synaptic activity in naive and inflammatory conditions. Patch-clamp recordings of miniature excitatory postsynaptic currents (mEPSCs) from superficial dorsal horn neurons in rat acute spinal cord slices were used. Peripheral inflammation was induced by subcutaneous injection of carrageenan. Under naive conditions, mEPSCs frequency (0.96 ± 0.11 Hz) was significantly decreased after 20 μM 20:4-NAPE application (55.3 ± 7.4%). This 20:4-NAPE-induced inhibition was blocked by anandamide-synthesizing enzyme N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD) inhibitor LEI-401. In addition, the inhibition was prevented by the CB1 receptor antagonist PF 514273 (0.2 μM) but not by the TRPV1 receptor antagonist SB 366791 (10 μM). Under inflammatory conditions, 20:4-NAPE (20 μM) also exhibited a significant inhibitory effect (74.5 ± 8.9%) on the mEPSCs frequency that was prevented by the TRPV1 receptor antagonist SB 366791 but not by PF 514273 application. Our results show that 20:4-NAPE application has a significant modulatory effect on spinal cord nociceptive signaling that is mediated by both TRPV1 and CB1 presynaptic receptors, whereas peripheral inflammation changes the underlying mechanism. The switch between TRPV1 and CB1 receptor activation by the AEA precursor 20:4-NAPE during inflammation may play an important role in nociceptive processing, hence the development of pathological pain.

• Keywords
• 20:4-NAPE, CB1, NAPE-PLD, TRPV1, anandamide, inflammation, spinal cord,
• Publication type
• Journal Article MeSH

The development of painful paclitaxel-induced peripheral neuropathy (PIPN) represents a major dose-limiting side effect of paclitaxel chemotherapy. Here we report a promising effect of duvelisib (Copiktra), a novel FDA-approved PI3Kδ/γ isoform-specific inhibitor, in preventing paclitaxel-induced pain-like behavior and pronociceptive signaling in DRGs and spinal cord dorsal horn (SCDH) in rat and mouse model of PIPN. Duvelisib blocked the development of mechanical hyperalgesia in both males and females. Moreover, duvelisib prevented paclitaxel-induced sensitization of TRPV1 receptors, and increased PI3K/Akt signaling in small-diameter DRG neurons and an increase of CD68+ cells within DRGs. Specific optogenetic stimulation of inhibitory neurons combined with patch-clamp recording revealed that duvelisib inhibited paclitaxel-induced weakening of inhibitory, mainly glycinergic control on SCDH excitatory neurons. Enhanced excitatory and reduced inhibitory neurotransmission in the SCDH following PIPN was also alleviated by duvelisib application. In summary, duvelisib showed a promising ability to prevent neuropathic pain in PIPN. The potential use of our findings in human medicine may be augmented by the fact that duvelisib is an FDA-approved drug with known side effects.SIGNIFICANCE STATEMENT We show that duvelisib, a novel FDA-approved PI3Kδ/γ isoform-specific inhibitor, prevents the development of paclitaxel-induced pain-like behavior in males and females and prevents pronociceptive signaling in DRGs and spinal cord dorsal horn in rat and mouse model of paclitaxel-induced peripheral neuropathy.

• Keywords
• PI3K, TRPV1, dorsal horn, glycine, neuropathy, pain,
• MeSH
• Pain MeSH
• Phosphatidylinositol 3-Kinases MeSH
• Antineoplastic Agents, Phytogenic * pharmacology   MeSH
• Hyperalgesia chemically induced   drug therapy   prevention & control   MeSH
• Isoquinolines MeSH
• Rats MeSH
• Mice MeSH
• Peripheral Nervous System Diseases MeSH
• Neuralgia * chemically induced   drug therapy   prevention & control   MeSH
• Paclitaxel adverse effects   MeSH
• Purines MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• duvelisib MeSH Browser
• Antineoplastic Agents, Phytogenic * MeSH
• Isoquinolines MeSH
• Paclitaxel MeSH
• Purines MeSH

BACKGROUND: Opioid analgesics remain widely used for pain treatment despite the related serious side effects. Some of those, such as opioid tolerance and opioid-induced hyperalgesia may be at least partially due to modulation of opioid receptors (OR) function at nociceptive synapses in the spinal cord dorsal horn. It was suggested that increased release of different chemokines under pathological conditions may play a role in this process. The goal of this study was to investigate the crosstalk between the µOR, transient receptor potential vanilloid 1 (TRPV1) receptor and C-C motif ligand 2 (CCL2) chemokine and the involvement of spinal microglia in the modulation of opioid analgesia. METHODS: Patch-clamp recordings of miniature excitatory postsynaptic currents (mEPSCs) and dorsal root evoked currents (eEPSC) in spinal cord slices superficial dorsal horn neurons were used to evaluate the effect of µOR agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO), CCL2, TRPV1 antagonist SB366791 and minocycline. Paw withdrawal test to thermal stimuli was combined with intrathecal (i.t.) delivery of CCL2 and DAMGO to investigate the modulation in vivo. RESULTS: Application of DAMGO induced a rapid decrease of mEPSC frequency and eEPSC amplitude, followed by a delayed increase of the eESPC amplitude, which was prevented by SB366791. Chemokine CCL2 treatment significantly diminished all the DAMGO-induced changes. Minocycline treatment prevented the CCL2 effects on the DAMGO-induced eEPSC depression, while mEPSC changes were unaffected. In behavioral experiments, i.t. injection of CCL2 completely blocked DAMGO-induced thermal hypoalgesia and intraperitoneal pre-treatment with minocycline prevented the CCL2 effect. CONCLUSIONS: Our results indicate that opioid-induced inhibition of the excitatory synaptic transmission could be severely attenuated by increased CCL2 levels most likely through a microglia activation-dependent mechanism. Delayed potentiation of neurotransmission after µOR activation is dependent on TRPV1 receptors activation. Targeting CCL2 and its receptors and TRPV1 receptors in combination with opioid therapy could significantly improve the analgesic properties of opioids, especially during pathological states.

• Keywords
• CCL2, Hyperalgesia, MOR, Microglia, Spinal cord, Synaptic transmission, TRPV1,
• MeSH
• Anilides pharmacology   MeSH
• Chemokine CCL2 pharmacology   MeSH
• Cinnamates pharmacology   MeSH
• Enkephalin, Ala(2)-MePhe(4)-Gly(5)- pharmacology   MeSH
• Excitatory Postsynaptic Potentials drug effects   MeSH
• Rats MeSH
• Spinal Cord drug effects   MeSH
• Miniature Postsynaptic Potentials drug effects   MeSH
• Synaptic Transmission drug effects   MeSH
• Neurons drug effects   MeSH
• Nociception drug effects   MeSH
• Analgesics, Opioid pharmacology   MeSH
• Rats, Wistar MeSH
• Spinal Cord Dorsal Horn drug effects   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anilides MeSH
• Chemokine CCL2 MeSH
• Cinnamates MeSH
• Enkephalin, Ala(2)-MePhe(4)-Gly(5)- MeSH
• N-(3-methoxyphenyl)-4-chlorocinnamanilide MeSH Browser
• Analgesics, Opioid MeSH

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

Paclitaxel-induced peripheral neuropathy (PIPN) is often associated with neuropathic pain and neuroinflammation in the central and peripheral nervous system. Antihypertensive drug losartan, an angiotensin II receptor type 1 (AT1R) blocker, was shown to have anti-inflammatory and neuroprotective effects in disease models, predominantly via activation of peroxisome proliferator-activated receptor gamma (PPARγ). Here, the effect of systemic losartan treatment (100 mg/kg/d) on mechanical allodynia and neuroinflammation was evaluated in rat PIPN model. The expression of pro-inflammatory markers protein and mRNA levels in dorsal root ganglia (DRGs) and spinal cord dorsal horn (SCDH) were measured with Western blot, ELISA and qPCR 10 and 21 days after PIPN induction. Losartan treatment attenuated mechanical allodynia significantly. Paclitaxel induced overexpression of C-C motif chemokine ligand 2 (CCL2), tumour necrosis alpha (TNFα) and interleukin-6 (IL-6) in DRGs, where the presence of macrophages was demonstrated. Neuroinflammatory changes in DRGs were accompanied with glial activation and pro-nociceptive modulators production in SCDH. Losartan significantly attenuated paclitaxel-induced neuroinflammatory changes and induced expression of pro-resolving markers (Arginase 1 and IL-10) indicating a possible shift in macrophage polarization. Considering the safety profile of losartan, acting also as partial PPARγ agonist, it may be considered as a novel treatment strategy for PIPN patients.

• Keywords
• losartan, macrophage, neuroinflammation, neuropathic pain, paclitaxel,
• MeSH
• Biomarkers MeSH
• Enzyme-Linked Immunosorbent Assay MeSH
• Antineoplastic Agents, Phytogenic adverse effects   MeSH
• Rats MeSH
• Losartan pharmacology   MeSH
• Macrophages drug effects   metabolism   MeSH
• Pain Management MeSH
• Disease Models, Animal MeSH
• Neuralgia diagnosis   drug therapy   etiology   metabolism   MeSH
• Paclitaxel adverse effects   MeSH
• Ganglia, Spinal drug effects   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
• Biomarkers MeSH
• Antineoplastic Agents, Phytogenic MeSH
• Losartan MeSH
• Paclitaxel MeSH

BACKGROUND AND PURPOSE: Endocannabinoids play an important role in modulating spinal nociceptive signalling, crucial for the development of pain. The cannabinoid CB1 receptor and the TRPV1 cation channel are both activated by the endocannabinoid anandamide, a product of biosynthesis from the endogenous lipid precursor N-arachidonoylphosphatidylethanolamine (20:4-NAPE). Here, we report CB1 receptor- and TRPV1-mediated effects of 20:4-NAPE on spinal synaptic transmission in control and inflammatory conditions. EXPERIMENTAL APPROACH: Spontaneous (sEPSCs) and dorsal root stimulation-evoked (eEPSCs) excitatory postsynaptic currents from superficial dorsal horn neurons in rat spinal cord slices were assessed. Peripheral inflammation was induced by carrageenan. Anandamide concentration was assessed by mass spectrometry. KEY RESULTS: Application of 20:4-NAPE increased anandamide concentration in vitro. 20:4-NAPE (20 μM) decreased sEPSCs frequency and eEPSCs amplitude in control and inflammatory conditions. The inhibitory effect of 20:4-NAPE was sensitive to CB1 receptor antagonist PF514273 (0.2 μM) in both conditions, but to the TRPV1 antagonist SB366791 (10 μM) only after inflammation. After inflammation, 20:4-NAPE increased sEPSCs frequency in the presence of PF514273 and this increase was blocked by SB366791. CONCLUSIONS AND IMPLICATIONS: While 20:4-NAPE treatment inhibited the excitatory synaptic transmission in both naive and inflammatory conditions, peripheral inflammation altered the underlying mechanisms. Our data indicate that 20:4-NAPE application induced mainly CB1 receptor-mediated inhibitory effects in naive animals while TRPV1-mediated mechanisms were also involved after inflammation. Increasing anandamide levels for analgesic purposes by applying substrate for its local synthesis may be more effective than systemic anandamide application or inhibition of its degradation. LINKED ARTICLES: This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

• MeSH
• Posterior Horn Cells drug effects   metabolism   MeSH
• Phosphatidylethanolamines chemical synthesis   chemistry   pharmacology   MeSH
• Mass Spectrometry MeSH
• Carrageenan MeSH
• Rats MeSH
• Spinal Cord drug effects   metabolism   MeSH
• Synaptic Transmission drug effects   MeSH
• Rats, Wistar MeSH
• Dose-Response Relationship, Drug MeSH
• Structure-Activity Relationship MeSH
• Inflammation chemically induced   metabolism   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
• Phosphatidylethanolamines MeSH
• Carrageenan MeSH

Protease-activated receptors 2 (PAR2) and transient receptor potential vanilloid 1 (TRPV1) receptors in the peripheral nerve endings are implicated in the development of increased sensitivity to mechanical and thermal stimuli, especially during inflammatory states. Both PAR2 and TRPV1 receptors are co-expressed in nociceptive dorsal root ganglion (DRG) neurons on their peripheral endings and also on presynaptic endings in the spinal cord dorsal horn. However, the modulation of nociceptive synaptic transmission in the superficial dorsal horn after activation of PAR2 and their functional coupling with TRPV1 is not clear. To investigate the role of spinal PAR2 activation on nociceptive modulation, intrathecal drug application was used in behavioural experiments and patch-clamp recordings of spontaneous, miniature and dorsal root stimulation-evoked excitatory postsynaptic currents (sEPSCs, mEPSCs, eEPSCs) were performed on superficial dorsal horn neurons in acute rat spinal cord slices. Intrathecal application of PAR2 activating peptide SLIGKV-NH2 induced thermal hyperalgesia, which was prevented by pretreatment with TRPV1 antagonist SB 366791 and was reduced by protein kinases inhibitor staurosporine. Patch-clamp experiments revealed robust decrease of mEPSC frequency (62.8 ± 4.9%), increase of sEPSC frequency (127.0 ± 5.9%) and eEPSC amplitude (126.9 ± 12.0%) in dorsal horn neurons after acute SLIGKV-NH2 application. All these EPSC changes, induced by PAR2 activation, were prevented by SB 366791 and staurosporine pretreatment. Our results demonstrate an important role of spinal PAR2 receptors in modulation of nociceptive transmission in the spinal cord dorsal horn at least partially mediated by activation of presynaptic TRPV1 receptors. The functional coupling between the PAR2 and TRPV1 receptors on the central branches of DRG neurons may be important especially during different pathological states when it may enhance pain perception.

• MeSH
• Hypersensitivity metabolism   pathology   MeSH
• Anilides pharmacology   MeSH
• Posterior Horn Cells drug effects   physiology   MeSH
• Behavior, Animal drug effects   MeSH
• Cinnamates pharmacology   MeSH
• Excitatory Postsynaptic Potentials drug effects   MeSH
• Hyperalgesia etiology   prevention & control   MeSH
• Protein Kinase Inhibitors pharmacology   MeSH
• TRPV Cation Channels antagonists & inhibitors   metabolism   MeSH
• Rats MeSH
• Patch-Clamp Techniques MeSH
• Spinal Cord metabolism   MeSH
• Synaptic Transmission physiology   MeSH
• Oligopeptides pharmacology   MeSH
• Rats, Wistar MeSH
• Receptor, PAR-2 agonists   metabolism   MeSH
• Staurosporine pharmacology   MeSH
• In Vitro Techniques MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anilides MeSH
• Cinnamates MeSH
• Protein Kinase Inhibitors MeSH
• TRPV Cation Channels MeSH
• N-(3-methoxyphenyl)-4-chlorocinnamanilide MeSH Browser
• Oligopeptides MeSH
• Receptor, PAR-2 MeSH
• seryl-leucyl-isoleucyl-glycyl-lysyl-valinamide MeSH Browser
• Staurosporine MeSH
• TRPV1 receptor MeSH Browser

BACKGROUND: Acute postoperative pain is one of the frequent reasons for pain treatment. However, the exact mechanisms of its development are still not completely clear. Transient receptor potential vanilloid 1 (TRPV1) receptors are involved in nociceptive signaling in various hypersensitive states. Here we have investigated the contribution of TRPV1 receptors expressed on cutaneous peripheral nociceptive fibers and in the spinal cord on the development and maintenance of hypersensitivity to thermal and mechanical stimuli following surgical incision. A rat plantar incision model was used to test paw withdrawal responses to thermal and mechanical stimuli. The effect of the TRPV1 receptor antagonist SB366791 was investigated 1) by intrathecal injection 15 min before incision and 2) intradermal injection before (30 min) and immediately after the surgery. Vehicle-injected rats and naïve animals treated identically were used as controls. RESULTS: Plantar incision induced mechanical allodynia and hyperalgesia and thermal hyperalgesia. A single intrathecal administration of SB366791 significantly reduced postincisional thermal hyperalgesia and also attenuated mechanical allodynia, while mechanical hyperalgesia remained unaffected. Local intradermal SB366791 treatment reduced thermal hyperalgesia and mechanical allodynia without affecting mechanical hyperalgesia. CONCLUSIONS: Our experiments suggest that both peripheral and spinal cord TRPV1 receptors are involved in increased cutaneous sensitivity following surgical incision. The analgesic effect of the TRPV1 receptor antagonist was especially evident in the reduction of thermal hyperalgesia. The activation of TRPV1 receptors represents an important mechanism in the development of postoperative hypersensitivity.

• MeSH
• Anilides pharmacology   therapeutic use   MeSH
• Time Factors MeSH
• Cinnamates pharmacology   therapeutic use   MeSH
• Physical Stimulation adverse effects   MeSH
• Touch MeSH
• Hyperalgesia drug therapy   etiology   MeSH
• TRPV Cation Channels antagonists & inhibitors   metabolism   MeSH
• Rats MeSH
• Pain Measurement drug effects   MeSH
• Spinal Cord drug effects   metabolism   MeSH
• Disease Models, Animal MeSH
• Pain, Postoperative complications   drug therapy   MeSH
• Rats, Wistar MeSH
• Pain Threshold drug effects   MeSH
• Reaction Time drug effects   MeSH
• Hot Temperature MeSH
• Drug Administration Routes 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
• Anilides MeSH
• Cinnamates MeSH
• TRPV Cation Channels MeSH
• N-(3-methoxyphenyl)-4-chlorocinnamanilide MeSH Browser
• Trpv1 protein, rat MeSH Browser