capsazepine and Neuralgia

The endocannabinoid system modulates a wide variety of pain conditions. Systemically administered AM404, an endocannabinoid reuptake inhibitor, exerts antinociceptive effects via activation of the endocannabinoid system. However, the mechanism and site of AM404 action are not fully understood. Here, we explored the effect of AM404 on neuropathic pain at the site of the spinal cord.. Male Sprague-Dawley rats were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of intrathecal administration of AM404 on mechanical and cold hyperalgesia were examined using the electronic von Frey test and cold plate test, respectively. Motor coordination was assessed using the rotarod test. To understand the mechanisms underlying the action of AM404, we tested the effects of pretreatment with the cannabinoid type 1 (CB. AM404 attenuated mechanical and cold hyperalgesia with minimal effects on motor coordination. AM251 significantly inhibited the antihyperalgesic action of AM404, whereas capsazepine showed a potentiating effect.. These results indicate that AM404 exerts antihyperalgesic effects primarily via CB

Topics: Animals; Arachidonic Acids; Capsaicin; Constriction; Disease Models, Animal; Endocannabinoids; Hyperalgesia; Indoles; Male; Neuralgia; Pain Measurement; Piperidines; Pyrazoles; Rats; Rats, Sprague-Dawley; Receptor, Cannabinoid, CB1; Receptor, Cannabinoid, CB2; Rotarod Performance Test; Spinal Cord; TRPV Cation Channels

The antiallodynic effect of PhAR-DBH-Me was evaluated on two models of neuropathic pain, and the potential roles of CB1, CB2, and TRPV1 receptors as molecular targets of PhAR-DBH-Me were studied. Female Wistar rats were submitted to L5/L6 spinal nerve ligation (SNL) or repeated doses of cisplatin (0.1 mg/kg, i.p.) to induce experimental neuropathy. Then, tactile allodynia was determined, and animals were treated with logarithmic doses of PhAR-DBH-Me (3.2-100 mg/kg, i.p.). To evaluate the mechanism of action of PhAR-DBH-Me, in silico studies using crystallized structures of CB1, CB2, and TRPV1 receptors were performed. To corroborate the computational insights, animals were intraperitoneally administrated with antagonists for CB1 (AM-251, 3 mg/kg), CB2 (AM-630, 1 mg/kg), and TRPV1 receptors (capsazepine, 3 mg/kg), 15 min before to PhAR-DBH-Me (100 mg/kg) administration. Vagal stimulation evoked on striated muscle contraction in esophagus, was used to elicited pharmacological response of PhAR-DBH-ME on nervous tissue. Systemic administration of PhAR-DBH-Me reduced the SNL- and cisplatin-induced allodynia. Docking studies suggested that PhAR-DBH-Me acts as an agonist for CB1, CB2, and TRPV1 receptors, with similar affinity to the endogenous ligand anandamide. Moreover antiallodynic effect of PhAR-DBH-Me was partially prevented by administration of AM-251 and AM-630, and completely prevented by capsazepine. Finally, PhAR-DBH-Me decreased the vagally evoked electrical response in esophagus rat. Taken together, results indicate that PhAR-DBH-Me induces an antiallodynic effect through partial activation of CB1 and CB2 receptors, as well as desensitization of TRPV1 receptors. Data also shed light on the novel vanilloid nature of the synthetic compound PhAR-DBH-Me.

Topics: Animals; Antineoplastic Agents; Arachidonic Acids; Azabicyclo Compounds; Cannabinoid Receptor Antagonists; Capsaicin; Cisplatin; Endocannabinoids; Female; Hyperalgesia; Injections, Intraperitoneal; Ligation; Models, Animal; Neuralgia; Oleic Acids; Polyunsaturated Alkamides; Rats; Rats, Wistar; Spinal Nerves; TRPV Cation Channels; Vagus Nerve Stimulation

Clinical studies indicate that cannabidiol (CBD), the primary nonaddictive component of cannabis that interacts with the serotonin (5-HT)1A receptor, may possess analgesic and anxiolytic effects. However, its effects on 5-HT neuronal activity, as well as its impact on models of neuropathic pain are unknown. First, using in vivo single-unit extracellular recordings in rats, we demonstrated that acute intravenous (i.v.) increasing doses of CBD (0.1-1.0 mg/kg) decreased the firing rate of 5-HT neurons in the dorsal raphe nucleus, which was prevented by administration of the 5-HT1A antagonist WAY 100635 (0.3 mg/kg, i.v.) and the TRPV1 antagonist capsazepine (1 mg/kg, i.v.) but not by the CB1 receptor antagonist AM 251 (1 mg/kg, i.v.). Repeated treatment with CBD (5 mg/kg/day, subcutaneously [s.c.], for 7 days) increased 5-HT firing through desensitization of 5-HT1A receptors. Rats subjected to the spared nerve injury model for 24 days showed decreased 5-HT firing activity, mechanical allodynia, and increased anxiety-like behavior in the elevated plus maze test, open-field test, and novelty-suppressed feeding test. Seven days of treatment with CBD reduced mechanical allodynia, decreased anxiety-like behavior, and normalized 5-HT activity. Antiallodynic effects of CBD were fully prevented by capsazepine (10 mg/kg/day, s.c., for 7 days) and partially prevented by WAY 100635 (2 mg/kg/day, s.c., for 7 days), whereas the anxiolytic effect was blocked only by WAY. Overall, repeated treatment with low-dose CBD induces analgesia predominantly through TRPV1 activation, reduces anxiety through 5-HT1A receptor activation, and rescues impaired 5-HT neurotransmission under neuropathic pain conditions.

Topics: Action Potentials; Animals; Anxiety; Cannabidiol; Capsaicin; Disease Models, Animal; Exploratory Behavior; Feeding Behavior; Ganglia, Spinal; Hyperalgesia; Lysergic Acid Diethylamide; Male; Maze Learning; Neuralgia; Piperazines; Piperidines; Pyrazoles; Pyridines; Rats; Rats, Wistar; Serotonin; Serotonin Antagonists; Swimming

The clinical anti-cancer efficacy of vincristine is limited by the development of dose-dependent peripheral neuropathy. Up-regulation of transient receptor potential vanilloid 1 (TRPV1) is correlated with peripheral neuropathy following anti-cancer drug treatment. To analyze the contribution of TRPV1 to the development of vincristine-induced mechanical allodynia/hyperalgesia, TRPV1 expression in the rat dorsal root ganglion (DRG) was analyzed after vincristine treatment. Mechanical allodynia/hyperalgesia was tested with von Frey filaments 14 days after intraperitoneal administration of 0.1 mg/kg vincristine in rats. TRPV1 expression in DRGs following vincristine treatment was assessed with western blot analysis and in situ hybridization histochemistry. Vincristine-induced mechanical allodynia/hyperalgesia after day 14 was significantly inhibited by the TRP antagonist ruthenium red (3 mg/kg, s.c.) and the TRPV1 antagonist capsazepine (30 mg/kg, s.c.). Vincristine treatment increased the expression of TRPV1 protein in DRG neurons. In situ hybridization histochemistry revealed that most of the TRPV1 mRNA-labeled neurons in the DRG were small in size. Immunohistochemistry showed that isolectin B4-positive small DRG neurons co-expressed TRPV1 protein 14 days after treatment. These results suggest that vincristine treatment increases TRPV1 expression in small DRG neurons. TRPV1 expression may contribute to the development of vincristine-induced painful peripheral neuropathy.

Topics: Animals; Antineoplastic Agents, Phytogenic; Capsaicin; Disease Models, Animal; Dose-Response Relationship, Drug; Ganglia, Spinal; Gene Expression; Humans; Male; Neuralgia; Neurons; Rats, Wistar; Ruthenium Red; TRPV Cation Channels; Up-Regulation; Vincristine

The aim of this research was to assess the antinociceptive activity of the transient receptor potential (TRP) channel TRPV1, TRPM8, and TRPA1 antagonists in neurogenic, tonic, and neuropathic pain models in mice. For this purpose, TRP channel antagonists were administered into the dorsal surface of a hind paw 15 min before capsaicin, allyl isothiocyanate (AITC), or formalin. Their antiallodynic and antihyperalgesic efficacies after intraperitoneal administration were also assessed in a paclitaxel-induced neuropathic pain model. Motor coordination of paclitaxel-treated mice that received these TRP channel antagonists was investigated using the rotarod test. TRPV1 antagonists, capsazepine and SB-366791, attenuated capsaicin-induced nociceptive reaction in a concentration-dependent manner. At 8 µg/20 µl, this effect was 51% (P<0.001) for capsazepine and 37% (P<0.05) for SB-366791. A TRPA1 antagonist, A-967079, reduced pain reaction by 48% (P<0.05) in the AITC test and by 54% (P<0.001) in the early phase of the formalin test. The test compounds had no influence on the late phase of the formalin test. In paclitaxel-treated mice, they did not attenuate heat hyperalgesia but N-(3-aminopropyl)-2-{[(3-methylphenyl)methyl]oxy}-N-(2-thienylmethyl) benzamide hydrochloride salt (AMTB), a TRPM8 antagonist, reduced cold hyperalgesia and tactile allodynia by 31% (P<0.05) and 51% (P<0.01), respectively. HC-030031, a TRPA1 channel antagonist, attenuated tactile allodynia in the von Frey test (62%; P<0.001). In conclusion, distinct members of TRP channel family are involved in different pain models in mice. Antagonists of TRP channels attenuate nocifensive responses of neurogenic, tonic, and neuropathic pain, but their efficacies strongly depend on the pain model used.

Topics: Acetanilides; Analgesics; Animals; Benzamides; Capsaicin; Cold Temperature; Disease Models, Animal; Formaldehyde; Hyperalgesia; Isothiocyanates; Male; Mice; Neuralgia; Oximes; Paclitaxel; Pain Measurement; Purines; Thiophenes; Touch; Transient Receptor Potential Channels; TRPA1 Cation Channel; TRPM Cation Channels; TRPV Cation Channels

A novel series of N-aryl-3,4-dihydro-1'H-spiro[chromene-2,4'-piperidine]-1'-carboxamides was identified as transient receptor potential melastatin 8 (TRPM8) channel blockers through analogue-based rational design, synthesis and screening. Details of the synthesis, effect of aryl groups and their substituents on in-vitro potency were studied. The effects of selected functional groups on the 4-position of the chromene ring were also studied, which showed interesting results. The 4-hydroxy derivatives showed excellent potency and selectivity. Optical resolution and screening of alcohols revealed that (R)-(-)-isomers were in general more potent than the corresponding (S)-(+)-isomers. The isomer (R)-(-)-10e (IC50: 8.9nM) showed a good pharmacokinetic profile upon oral dosing at 10mg/kg in Sprague-Dawley (SD) rats. The compound (R)-(-)-10e also showed excellent efficacy in relevant rodent models of neuropathic pain.

Topics: Administration, Oral; Amides; Analgesics; Animals; Disease Models, Animal; Half-Life; Male; Mice; Mice, Inbred C57BL; Neuralgia; Piperidines; Protein Binding; Rats; Rats, Sprague-Dawley; Spiro Compounds; Stereoisomerism; Structure-Activity Relationship; TRPM Cation Channels

Both spinal and trigeminal somatosensory systems use the TRPM8 channel as a principal transducer for detecting cold stimuli. It is currently unclear whether this cold transducer may play a role in trigeminal neuropathic pain manifesting cold allodynia and hyperalgesia. In the present study, trigeminal neuropathy was induced by chronic constrictive nerve injury of the infraorbital nerve (ION-CCI). Behavioral responses to cold stimuli in orofacial regions were assessed by the newly developed orofacial operant test in the ION-CCI rats. We tested menthol and capsazepine, two compounds that can activate and inhibit TRPM8 respectively, on orofacial operant responses to cold stimuli in ION-CCI rats. Testing animals performed operant tasks by voluntarily contacting their orofacial regions to a cold stimulation module in order to access sweetened milk as a reward, and contact time and number of the operant behaviors were automatically recorded. Total contact time was significantly reduced at the cooling temperatures of 17°C and 12°C in ION-CCI group in comparison with sham group, indicating the presence of cold allodynia and hyperalgesia in ION-CCI rats. When menthol was administered to ION-CCI rats, total contact time was further reduced and total contact number increased at the cooling temperatures. In contrast, after administration of capsazepine to ION-CCI rats, total contact time was significantly increased at the cooling temperatures. The behavioral outcomes support the idea that TRPM8 plays a role in cold allodynia and hyperalgesia following chronic trigeminal nerve injury.

Topics: Animals; Behavior, Animal; Capsaicin; Cold Temperature; Conditioning, Operant; Facial Nerve; Facial Pain; Hyperalgesia; Male; Menthol; Neuralgia; Pain Measurement; Physical Stimulation; Rats; Rats, Sprague-Dawley; Trigeminal Nerve; Trigeminal Nerve Injuries; TRPM Cation Channels

Paclitaxel chemotherapy is limited by a long-lasting painful neuropathy that lacks an effective therapy. In this study, we tested the hypothesis that paclitaxel may release mast cell tryptase, which activates protease-activated receptor 2 (PAR2) and, subsequently, protein kinases A and C, resulting in mechanical and thermal (both heat and cold) hypersensitivity. Correlating with the development of neuropathy after repeated administration of paclitaxel, mast cell tryptase activity was found to be increased in the spinal cord, dorsal root ganglia, and peripheral tissues in mice. FSLLRY-amide, a selective PAR2 antagonist, blocked paclitaxel-induced neuropathic pain behaviors in a dose- and time-dependent manner. In addition, blocking downstream signaling pathways of PAR2, including phospholipase C (PLC), protein kinase A (PKA), and protein kinase Cε (PKC), effectively attenuated paclitaxel-induced mechanical, heat, or cold hypersensitivity. Furthermore, sensitized pain response was selectively inhibited by antagonists of transient receptor potential (TRP) V1, TRPV4, or TRPA1. These results revealed specific cellular signaling pathways leading to paclitaxel-induced neuropathy, including the activation of PAR2 and downstream enzymes PLC, PKCε, and PKA and resultant sensitization of TRPV1, TRPV4, and TRPA1. Targeting one or more of these signaling molecules may present new opportunities for the treatment of paclitaxel-induced neuropathy.

Topics: Analysis of Variance; Anilides; Animals; Ankyrins; Antineoplastic Agents, Phytogenic; Capsaicin; Carbazoles; Central Nervous System; Cinnamates; Cyclic AMP-Dependent Protein Kinases; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Estrenes; Gene Expression Regulation; Hyperalgesia; Male; Mice; Mice, Inbred ICR; Neuralgia; Oligopeptides; Paclitaxel; Pain Measurement; Physical Stimulation; Protein Kinase C; Pyrroles; Pyrrolidinones; Receptor, PAR-2; Sulfonamides; Time Factors; TRPV Cation Channels; Tryptases; Type C Phospholipases

VR1 receptors, present on Adelta- and C-fibres and post-synaptic sites within the spinal cord dorsal horn, is an integrator of noxious stimuli. Here, the contribution of spinal VR1 receptors to spinal nociceptive processing in nerve injured (selective spinal nerve ligated SNL) and sham anaesthetised rats was studied. Spinal capsazepine (0.5-30 microM), a competitive VR1 antagonist, reduced noxious evoked responses of spinal neurones to a greater extent in sham operated rats, compared to SNL rats. Significant differences between the effect of spinal capsazepine on the non-potentiated component of the C-fibre evoked response of SNL and sham operated rats are reported (p< 0.01, two-way ANOVA). Our data suggest there is a functional plasticity of the spinal VR1 receptor following nerve injury.

Topics: Action Potentials; Animals; Capsaicin; Denervation; Dose-Response Relationship, Drug; Down-Regulation; Hyperalgesia; Ligation; Nerve Fibers; Nerve Fibers, Myelinated; Neuralgia; Neuronal Plasticity; Nociceptors; Pain Threshold; Peripheral Nerve Injuries; Peripheral Nerves; Peripheral Nervous System Diseases; Physical Stimulation; Posterior Horn Cells; Rats; Receptors, Drug