Neuropathic-like Nociception and Spinal Cord Neuroinflammation Are Dependent on the TRPA1 Channel in Multiple Sclerosis Models in Mice.

Background: Transient receptor potential ankyrin 1 (TRPA1) activation is implicated in neuropathic pain-like symptoms. However, whether TRPA1 is solely implicated in pain-signaling or contributes to neuroinflammation in multiple sclerosis (MS) is unknown. Here, we evaluated the TRPA1 role in neuroinflammation underlying pain-like symptoms using two different models of MS. Methods: Using a myelin antigen, Trpa1+/+ or Trpa1-/- female mice developed relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE) (Quil A as adjuvant) or progressive experimental autoimmune encephalomyelitis (PMS)-EAE (complete Freund's adjuvant). The locomotor performance, clinical scores, mechanical/cold allodynia, and neuroinflammatory MS markers were evaluated. Results: Mechanical and cold allodynia detected in RR-EAE, or PMS-EAE Trpa1+/+ mice, were not observed in Trpa1-/- mice. The increased number of cells labeled for ionized calcium-binding adapter molecule 1 (Iba1) or glial fibrillary acidic protein (GFAP), two neuroinflammatory markers in the spinal cord observed in both RR-EAE or PMS-EAE Trpa1+/+ mice, was reduced in Trpa1-/- mice. By Olig2 marker and luxol fast blue staining, prevention of the demyelinating process in Trpa1-/- induced mice was also detected. Conclusions: Present results indicate that the proalgesic role of TRPA1 in EAE mouse models is primarily mediated by its ability to promote spinal neuroinflammation and further strengthen the channel inhibition to treat neuropathic pain in MS.

Acetaldehyde via CGRP receptor and TRPA1 in Schwann cells mediates ethanol-evoked periorbital mechanical allodynia in mice: relevance for migraine.

BACKGROUND: Ingestion of alcoholic beverages is a known trigger of migraine attacks. However, whether and how ethanol exerts its pro-migraine action remains poorly known. Ethanol stimulates the transient receptor potential vanilloid 1 (TRPV1) channel, and its dehydrogenized metabolite, acetaldehyde, is a known TRP ankyrin 1 (TRPA1) agonist. METHODS: Periorbital mechanical allodynia following systemic ethanol and acetaldehyde was investigated in mice after TRPA1 and TRPV1 pharmacological antagonism and global genetic deletion. Mice with selective silencing of the receptor activated modifying protein 1 (RAMP1), a component of the calcitonin gene-related peptide (CGRP) receptor, in Schwann cells or TRPA1 in dorsal root ganglion (DRG) neurons or Schwann cells, were used after systemic ethanol and acetaldehyde. RESULTS: We show in mice that intragastric ethanol administration evokes a sustained periorbital mechanical allodynia that is attenuated by systemic or local alcohol dehydrogenase inhibition, and TRPA1, but not TRPV1, global deletion, thus indicating the implication of acetaldehyde. Systemic (intraperitoneal) acetaldehyde administration also evokes periorbital mechanical allodynia. Importantly, periorbital mechanical allodynia by both ethanol and acetaldehyde is abrogated by pretreatment with the CGRP receptor antagonist, olcegepant, and a selective silencing of RAMP1 in Schwann cells. Periorbital mechanical allodynia by ethanol and acetaldehyde is also attenuated by cyclic AMP, protein kinase A, and nitric oxide inhibition and pretreatment with an antioxidant. Moreover, selective genetic silencing of TRPA1 in Schwann cells or DRG neurons attenuated periorbital mechanical allodynia by ethanol or acetaldehyde. CONCLUSIONS: Results suggest that, in mice, periorbital mechanical allodynia, a response that mimics cutaneous allodynia reported during migraine attacks, is elicited by ethanol via the systemic production of acetaldehyde that, by releasing CGRP, engages the CGRP receptor in Schwann cells. The ensuing cascade of intracellular events results in a Schwann cell TRPA1-dependent oxidative stress generation that eventually targets neuronal TRPA1 to signal allodynia from the periorbital area.

Non-neuronal TRPA1 encodes mechanical allodynia associated with neurogenic inflammation and partial nerve injury in rats.

BACKGROUND AND PURPOSE: The pro-algesic transient receptor potential ankyrin 1 (TRPA1) channel, expressed by a subpopulation of primary sensory neurons, has been implicated in various pain models in mice. However, evidence in rats indicates that TRPA1 conveys nociceptive signals elicited by channel activators, but not those associated with tissue inflammation or nerve injury. Here, in rats, we explored the TRPA1 role in mechanical allodynia associated with stimulation of peptidergic primary sensory neurons (neurogenic inflammation) and moderate (partial sciatic nerve ligation, pSNL) or severe (chronic constriction injury, CCI) sciatic nerve injury. EXPERIMENTAL APPROACH: Acute nociception and mechanical hypersensitivity associated with neurogenic inflammation and sciatic nerve injury (pSNL and CCI) were investigated in rats with TRPA1 pharmacological antagonism or genetic silencing. TRPA1 presence and function were analysed in cultured rat Schwann cells. KEY RESULTS: Hind paw mechanical allodynia (HPMA), but not acute nociception, evoked by local injection of capsaicin or allyl isothiocyanate, the TRP vanilloid 1 (TRPV1) or the TRPA1 activators was mediated by CGRP released from peripheral sensory nerve terminals. CGRP-evoked HPMA was sustained by a ROS-dependent TRPA1 activation, probably in Schwann cells. HPMA evoked by pSNL, but not that evoked by CCI, was mediated by ROS and TRPA1 without the involvement of CGRP. CONCLUSIONS AND IMPLICATIONS: As found in mice, TRPA1 mediates mechanical allodynia associated with neurogenic inflammation and moderate nerve injury in rats. The channel contribution to mechanical hypersensitivity is a common feature in rodents and might be explored in humans.

miRNA-203b-3p Induces Acute and Chronic Pruritus through 5-HTR2B and TRPV4.

Growing evidence indicates that transient receptor potential (TRP) channels contribute to different forms of pruritus. However, the endogenous mediators that cause itch through transient receptor potential channels signaling are poorly understood. In this study, we show that genetic deletion or pharmacological antagonism of TRPV4 attenuated itch in a mouse model of psoriasis induced by topical application of imiquimod. Human psoriatic lesions showed increased expression of several microRNAs, including the miR-203b-3p, which induced a calcium ion response in rodent dorsal root ganglion neurons and scratching behavior in mice through 5-HTR2B activation and the protein kinase C‒dependent phosphorylation of TRPV4. Computer simulation revealed that the miR-203b-3p core sequence (GUUAAGAA) that causes 5-HTR2B/TRPV4-dependent itch targets the extracellular side of 5-HTR2B by interacting with a portion of the receptor pocket consistent with its activation. Overall, we reveal the unconventional pathophysiological role of an extracellular microRNA that can behave as an itch promoter through 5-HTR2B and TRPV4.

Oxidative stress mediates thalidomide-induced pain by targeting peripheral TRPA1 and central TRPV4.

BACKGROUND: The mechanism underlying the pain symptoms associated with chemotherapeutic-induced peripheral neuropathy (CIPN) is poorly understood. Transient receptor potential ankyrin 1 (TRPA1), TRP vanilloid 4 (TRPV4), TRPV1, and oxidative stress have been implicated in several rodent models of CIPN-evoked allodynia. Thalidomide causes a painful CIPN in patients via an unknown mechanism. Surprisingly, the pathway responsible for such proalgesic response has not yet been investigated in animal models. RESULTS: Here, we reveal that a single systemic administration of thalidomide and its derivatives, lenalidomide and pomalidomide, elicits prolonged (~ 35 days) mechanical and cold hypersensitivity in C57BL/6J mouse hind paw. Pharmacological antagonism or genetic deletion studies indicated that both TRPA1 and TRPV4, but not TRPV1, contribute to mechanical allodynia, whereas cold hypersensitivity was entirely due to TRPA1. Thalidomide per se did not stimulate recombinant and constitutive TRPA1 and TRPV4 channels in vitro, which, however, were activated by the oxidative stress byproduct, hydrogen peroxide. Systemic treatment with an antioxidant attenuated mechanical and cold hypersensitivity, and the increase in oxidative stress in hind paw, sciatic nerve, and lumbar spinal cord produced by thalidomide. Notably, central (intrathecal) or peripheral (intraplantar) treatments with channel antagonists or an antioxidant revealed that oxidative stress-dependent activation of peripheral TRPA1 mediates cold allodynia and part of mechanical allodynia. However, oxidative stress-induced activation of central TRPV4 mediated the residual TRPA1-resistant component of mechanical allodynia. CONCLUSIONS: Targeting of peripheral TRPA1 and central TRPV4 may be required to attenuate pain associated with CIPN elicited by thalidomide and related drugs.

Brain Histamine Modulates the Antidepressant-Like Effect of the 3-Iodothyroacetic Acid (TA1).

3-iodothyroacetic acid (TA1), an end metabolite of thyroid hormone, has been shown to produce behavioral effects in mice that are dependent on brain histamine. We now aim to verify whether pharmacologically administered TA1 has brain bioavailability and is able to induce histamine-dependent antidepressant-like behaviors. TA1 brain, liver and plasma levels were measured by LC/MS-MS in male CD1 mice, sacrificed 15 min after receiving a high TA1 dose (330 µgkg-1). The hypothalamic mTOR/AKT/GSK-ß cascade activation was evaluated in mice treated with 0.4, 1.32, 4 µgkg-1 TA1 by Western-blot. Mast cells were visualized by immuno-histochemistry in brain slices obtained from mice treated with 4 µgkg-1 TA1. Histamine release triggered by TA1 (20-1000 nM) was also evaluated in mouse peritoneal mast cells. After receiving TA1 (1.32, 4 or 11 µgkg-1; i.p.) CD1 male mice were subjected to the forced swim (FST) and the tail suspension tests (TST). Spontaneous locomotor and exploratory activities, motor incoordination, and anxiolytic or anxiogenic effects, were evaluated. Parallel behavioral tests were also carried out in mice that, prior to receiving TA1, were pre-treated with pyrilamine (10 mgkg-1; PYR) or zolantidine (5 mgkg-1; ZOL), histamine type 1 and type 2 receptor antagonists, respectively, or with p-chloro-phenylalanine (100 mgkg-1; PCPA), an inhibitor of serotonin synthesis. TA1 given i.p. to mice rapidly distributes in the brain, activates the hypothalamic mTOR/AKT and GSK-3ß cascade and triggers mast cells degranulation. Furthermore, TA1 induces antidepressant effects and stimulates locomotion with a mechanism that appears to depend on the histaminergic system. TA1 antidepressant effect depends on brain histamine, thus highlighting a relationship between the immune system, brain inflammation and the thyroid.

The acyl-glucuronide metabolite of ibuprofen has analgesic and anti-inflammatory effects via the TRPA1 channel.

Ibuprofen is a widely used non-steroidal anti-inflammatory drug (NSAID) that exerts analgesic and anti-inflammatory actions. The transient receptor potential ankyrin 1 (TRPA1) channel, expressed primarily in nociceptors, mediates the action of proalgesic and inflammatory agents. Ibuprofen metabolism yields the reactive compound, ibuprofen-acyl glucuronide, which, like other TRPA1 ligands, covalently interacts with macromolecules. To explore whether ibuprofen-acyl glucuronide contributes to the ibuprofen analgesic and anti-inflammatory actions by targeting TRPA1, we used in vitro tools (TRPA1-expressing human and rodent cells) and in vivo mouse models of inflammatory pain. Ibuprofen-acyl glucuronide, but not ibuprofen, inhibited calcium responses evoked by reactive TRPA1 agonists, including allyl isothiocyanate (AITC), in cells expressing the recombinant and native human channel and in cultured rat primary sensory neurons. Responses by the non-reactive agonist, menthol, in a mutant human TRPA1 lacking key cysteine-lysine residues, were not affected. In addition, molecular modeling studies evaluating the covalent interaction of ibuprofen-acyl glucuronide with TRPA1 suggested the key cysteine residue C621 as a probable alkylation site for the ligand. Local administration of ibuprofen-acyl glucuronide, but not ibuprofen, in the mouse hind paw attenuated nociception by AITC and other TRPA1 agonists and the early nociceptive response (phase I) to formalin. Systemic ibuprofen-acyl glucuronide and ibuprofen, but not indomethacin, reduced phase I of the formalin response. Carrageenan-evoked allodynia in mice was reduced by local ibuprofen-acyl glucuronide, but not by ibuprofen, whereas both drugs attenuated PGE2 levels. Ibuprofen-acyl glucuronide, but not ibuprofen, inhibited the release of IL-8 evoked by AITC from cultured bronchial epithelial cells. The reactive ibuprofen metabolite selectively antagonizes TRPA1, suggesting that this novel action of ibuprofen-acyl glucuronide might contribute to the analgesic and anti-inflammatory activities of the parent drug.

Anticonvulsant and Neuroprotective Effects of the Thyroid Hormone Metabolite 3-Iodothyroacetic Acid.

BACKGROUND: 3-Iodothyroacetic acid (TA1) is among the thyroid hormone (T3) metabolites that can acutely modify behavior in mice. This study aimed to investigate whether TA1 is also able to reduce neuron hyper-excitability and protect from excitotoxic damage. METHODS: CD1 male mice were treated intraperitoneally with saline solution or TA1 (4, 7, 11, or 33 µg/kg) before receiving 90 mg/kg pentylenetrazole subcutaneously. The following parameters were measured: latency to first seizure onset, number of mice experiencing seizures, hippocampal levels of c-fos, and PI3K/AKT activation levels. Organotypic hippocampal slices were exposed to vehicle or to 5 µM kainic acid (KA) in the absence or presence of 0.01-10 µM TA1. In another set of experiments, slices were exposed to vehicle or 5 µM KA in the absence or presence of 10 µM T3, 3,5,3'-triiodothyroacetic acid (TRIAC), T1AM, thyronamine (T0AM), or thyroacetic acid (TA0). Neuronal cell death was measured fluorimetically. The ability of TA1 and T3, TRIAC, T1AM, T0A, and TA0 to activate the PI3K/AKT cascade was evaluated by Western blot. The effect of TA1 on KA-induced currents in CA3 neurons was evaluated by patch clamp recordings on acute hippocampal slices. RESULTS: TA1 (7 and 11 µg/kg) significantly reduced the number of mice showing convulsions and increased their latency of onset, restored pentylenetrazole-induced reduction of hippocampal c-fos levels, activated the PI3K/AKT, and reduced GSK-3ß activity. In rat organotypic hippocampal slices, TA1 reduced KA-induced cell death by activating the PI3K/AKT cascade and increasing GSK-3ß phosphorylation levels. Protection against KA toxicity was also exerted by T3 and other T3 metabolites studied. TA1 did not interact at KA receptors. Both the anticonvulsant and neuroprotective effects of TA1 were abolished by pretreating mice or organotypic hippocampal slices with pyrilamine, an histamine type 1 receptor antagonist (10 mg/kg or 1 µM, respectively). CONCLUSIONS: TA1 exerts anticonvulsant activity and is neuroprotective in vivo and in vitro. These findings extend the current knowledge on the pharmacological profile of TA1 and indicate possible novel clinical use for this T3 metabolite.

3-Iodothyroacetic acid (TA1), a by-product of thyroid hormone metabolism, reduces the hypnotic effect of ethanol without interacting at GABA-A receptors.

3-iodothyroacetic acid (TA1) is among the by-products of thyroid hormone metabolism suspected to mediate the non-genomic effects of the hormone (T3). We aim to investigate whether TA1 systemically administered to mice stimulated mice wakefulness, an effect already described for T3 and for another T3 metabolite (i.e. 3-iodothryonamine; T1AM), and whether TA1 interacted at GABA-A receptors (GABA-AR). Mice were pre-treated with either saline (vehicle) or TA1 (1.32, 4 and 11 µg/kg) and, after 10 min, they received ethanol (3.5 g/kg, i.p.). In another set of experiments, TA1 was administered 5 min after ethanol. The latency of sleep onset and the time of sleep duration were recorded. Voltage-clamp experiments to evaluate the effect of 1 µM TA1 on bicuculline-sensitive currents in acute rat hippocampal slice neurons and binding experiments evaluating the capacity of 1, 10, 100 µM TA1 to displace [3H]flumazenil from mice brain membranes were also performed. 4 µg/kg TA1 increases the latency of onset and at 1.32 and 4 µg/kg it reduces the duration of ethanol-induced sleep only if administered before ethanol. TA1 does not functionally interact at GABA-AR. Overall these results indicate a further similarity between the pharmacological profile of TA1 and that of T1AM.

The impact of scopolamine pretreatment on 3-iodothyronamine (T1AM) effects on memory and pain in mice.

We previously demonstrated that 3-iodothyronamine (T1AM), a by-product of thyroid hormone metabolism, pharmacologically administered to mice acutely stimulated learning and memory acquisition and provided hyperalgesia with a mechanism which remains to be defined. We now aimed to investigate whether the T1AM effect on memory and pain was maintained in mice pre-treated with scopolamine, a non-selective muscarinic antagonist expected to induce amnesia and, possibly, hyperalgesia. Mice were pre-treated with scopolamine and, after 20min, injected intracerebroventricularly (i.c.v.) with T1AM (0.13, 0.4, 1.32µg/kg). 15min after T1AM injection, the mice learning capacity or their pain threshold were evaluated by the light/dark box and by the hot plate test (51.5°C) respectively. Experiments in the light/dark box were repeated in mice receiving clorgyline (2.5mg/kg, i.p.), a monoamine oxidase (MAO) inhibitor administered 10min before scopolamine (0.3mg/kg). Our results demonstrated that 0.3mg/kg scopolamine induced amnesia without modifying the murine pain threshold. T1AM fully reversed scopolamine-induced amnesia and produced hyperalgesia at a dose as low as 0.13µg/kg. The T1AM anti-amnestic effect was lost in mice pre-treated with clorgyline. We report that the removal of muscarinic signalling increases T1AM pro learning and hyperalgesic effectiveness suggesting T1AM as a potential treatment as a "pro-drug" for memory dysfunction in neurodegenerative diseases.

TRPA1 mediates trigeminal neuropathic pain in mice downstream of monocytes/macrophages and oxidative stress.

Despite intense investigation, the mechanisms of the different forms of trigeminal neuropathic pain remain substantially unidentified. The transient receptor potential ankyrin 1 channel (encoded by TRPA1) has been reported to contribute to allodynia or hyperalgesia in some neuropathic pain models, including those produced by sciatic nerve constriction. However, the role of TRPA1 and the processes that cause trigeminal pain-like behaviours from nerve insult are poorly understood. The role of TRPA1, monocytes and macrophages, and oxidative stress in pain-like behaviour evoked by the constriction of the infraorbital nerve in mice were explored. C57BL/6 and wild-type (Trpa1(+/+)) mice that underwent constriction of the infraorbital nerve exhibited prolonged (20 days) non-evoked nociceptive behaviour and mechanical, cold and chemical hypersensitivity in comparison to sham-operated mice (P < 0.05-P < 0.001). Both genetic deletion of Trpa1 (Trpa1(-/-)) and pharmacological blockade (HC-030031 and A-967079) abrogated pain-like behaviours (both P < 0.001), which were abated by the antioxidant, α-lipoic acid, and the nicotinamide adenine dinucleotide phosphate oxidase inhibitor, apocynin (both P < 0.001). Nociception and hypersensitivity evoked by constriction of the infraorbital nerve was associated with intra- and perineural monocytic and macrophagic invasion and increased levels of oxidative stress by-products (hydrogen peroxide and 4-hydroxynonenal). Attenuation of monocyte/macrophage increase by systemic treatment with an antibody against the monocyte chemoattractant chemokine (C-C motif) ligand 2 (CCL2) or the macrophage-depleting agent, clodronate (both P < 0.05), was associated with reduced hydrogen peroxide and 4-hydroxynonenal perineural levels and pain-like behaviours (all P < 0.01), which were abated by perineural administration of HC-030031, α-lipoic acid or the anti-CCL2 antibody (all P < 0.001). The present findings propose that, in the constriction of the infraorbital nerve model of trigeminal neuropathic pain, pain-like behaviours are entirely mediated by the TRPA1 channel, targeted by increased oxidative stress by-products released from monocytes and macrophages clumping at the site of nerve injury.

Observation of an improved healing process in superficial skin wounds after irradiation with a blue-LED haemostatic device.

The healing process of superficial skin wounds treated with a blue-LED haemostatic device is studied. Four mechanical abrasions are produced on the back of 10 Sprague Dawley rats: two are treated with the blue-LED device, while the other two are left to naturally recover. Visual observations, non-linear microscopic imaging, as well as histology and immunofluorescence analyses are performed 8 days after the treatment, demonstrating no adverse reactions neither thermal damages in both abraded areas and surrounding tissue. A faster healing process and a better-recovered skin morphology are observed: the treated wounds show a reduced inflammatory response and a higher collagen content. Blue LED induced photothermal effect on superficial abrasions.

The pro-healing effect of exendin-4 on wounds produced by abrasion in normoglycemic mice.

Experimental evidence suggested that Exendin-4 (Exe4), an agonist at glucagon like receptor-1 (GLP-1R), promoted tissue regeneration. We aimed to verify the effect of Exe4, in the absence or in the presence of Exendin-4(9-39), an antagonist at GLP-1R, on the healing of abraded skin. Two wounds (approximately 1.1×1.1 cm(2); namely "upper" and "lower" in respect of the head) were produced by abrasion on the back of 12 mice, which were then randomly assigned to receive an intradermal injection (20 µl) of Group 1: saline (NT) or Exe4 (62 ng) in the upper and lower wound respectively; Group 2: Exendin-4(9-39) (70 ng) in the upper and Exendin-4(9-39) (70 ng) and, after 15 min, Exe4 (62 ng) in the lower wound. Wounds were measured at the time of abrasion (T0) and 144 h (T3) afterward taking pictures with a ruler and by using a software. The inflammatory cell infiltrate, fibroblasts/myofibroblasts, endothelial cells and GLP-1R expression, were each labeled by immunofluorescence in each wound, pERK1/2 was evaluated by Western-blot in wound lysates. At T3, the percentage of healing surface was 53% and 92% for NT and Exe4 wounds respectively and 68% and 79% for those treated with Exendin-4(9-39) and Exendin-4(9-39)+Exe4 respectively. Exe4, but not Exendin-4(9-39) induced quantitative increase in fibroblasts/myofibroblasts and vessel density when compared to NT wounds. This increase was not evident in wounds treated with Exendin-4(9-39)+Exe4. Exe4 promotes wound healing opening to the possible dermatological use of this incretin analogue.

Ureteral relaxation through calcitonin gene-related peptide release from sensory nerve terminals by hypotonic solution.

OBJECTIVES: To evaluate the influence of hypotonic solutions on ureteral relaxation mediated by the release of calcitonin gene-related peptide from intramural sensory nerve endings. METHODS: Urine osmolarity of Sprague-Dawley rats drinking water low in salt content (Fiuggi water) or a reference water for 7 days was measured. Release of calcitonin gene-related peptide-like immunoreactivity from slices of rat ureter and urinary bladder by hypotonic solutions was assessed by an immunometric assay. The mechanism through which hypotonic solutions inhibit neurokinin A-induced phasic contractions of isolated rat ureters was evaluated by organ bath studies. RESULTS: A 7-day consumption of Fiuggi water in rats reduced urine osmolarity by ~40%. Exposure to hypotonic solutions released calcitonin gene-related peptide-like immunoreactivity from slices of rat ureter. This response was abated in a calcium-free medium, after capsaicin desensitization, and in the presence of the unselective transient receptor potential channel antagonist, ruthenium red. Exposure of isolated rat ureteral preparations to a hypotonic solution inhibited neurokinin A-evoked phasic contraction. This response was attenuated by capsaicin desensitization and in the presence of the calcitonin gene-related peptide receptor antagonist, calcitonin gene-related peptide8-37 . Transient receptor potential vanilloid 1 or transient receptor potential vanilloid 4 antagonists did not affect the neurogenic and calcitonin gene-related peptide-dependent relaxation. CONCLUSION: Present data show that hypotonic solution evokes calcitonin gene-related peptide release from capsaicin-sensitive intramural sensory nerves, thus inhibiting ureteral contractility, through a transient receptor potential-dependent mechanism. However, this mechanism does not involve transient receptor potential vanilloid 1 or transient receptor potential vanilloid 4. Future studies with appropriate in vivo models should investigate the hypothesis that hypostenuric urine diffusing into the ureteral tissue might favor ureteral relaxation through this novel mechanism.

In the brain of mice, 3-iodothyronamine (T1AM) is converted into 3-iodothyroacetic acid (TA1) and it is included within the signaling network connecting thyroid hormone metabolites with histamine.

3-iodothyronamine (T1AM) and its oxidative product, 3-iodotyhyroacetic acid (TTA1A), are known to stimulate learning and induce hyperalgesia in mice. We investigated whether i)TA1 may be generated in vivo from T1AM, ii) T1AM shares with TA1 the ability to activate the histaminergic system. Tandem mass spectrometry was used to measure TA1 and T1AM levels in i) the brain of mice following intracerebroventricular (i.c.v.) injection of T1AM (11µgkg(-1)), with or without pretreatment with clorgyline, (2.5mgkg(-1) i.p.), a monoamine oxidase inhibitor; ii) the medium of organotypic hippocampal slices exposed to T1AM (50nM). In addition, learning and pain threshold were evaluated by the light-dark box task and the hot plate test, respectively, in mice pre-treated subcutaneously with pyrilamine (10mgkg(-1)) or zolantidine (5mgkg(-1)), 20min before i.c.v. injection of T1AM (1.32 and 11µgkg(-1)). T1AM-induced hyperalgesia (1.32 and 11µgkg(-1)) was also evaluated in histidine decarboxylase (HDC(-/-)) mice. T1AM and TA1 brain levels increased in parallel in mice injected with T1AM with the TA1/T1AM averaging 1.7%. Clorgyline pre-treatment reduced the increase in both T1AM and TA1. TA1 was the main T1AM metabolite detected in the hippocampal preparations. Pretreatment with pyrilamine or zolantidine prevented the pro-learning effect of 1.32 and 4µgkg(-1) T1AM while hyperalgesia was conserved at the dose of 11µgkg(-1) T1AM. T1AM failed to induce hyperalgesia in HDC(-/-) mice at all the doses. In conclusion, TA1 generated from T1AM, but also T1AM, appears to act by modulating the histaminergic system.

3-iodothyroacetic acid, a metabolite of thyroid hormone, induces itch and reduces threshold to noxious and to painful heat stimuli in mice.

BACKGROUND AND PURPOSE: Itch is associated with increased sensitization to nociceptive stimuli. We investigated whether 3-iodothyroacetic acid (TA1), by releasing histamine, induces itch and increases sensitization to noxious and painful heat stimuli. EXPERIMENTAL APPROACH: Itch was evaluated after s.c. administration of TA1 (0.4, 1.32 and 4 µg·kg(-1) ). Mice threshold to noxious (NHT) and to painful heat stimuli were evaluated by the increasing-temperature hot plate (from 45.5 to 49.5°C) or by the hot plate (51.5°C) test, respectively, 15 min after i.p. injection of TA1 (0.4, 1.32 and 4 µg·kg(-1) ). Itch, NHT and pain threshold evaluation were repeated in mice pretreated with pyrilamine. Itch and NHT were also measured in HDC(+/+) and HDC(-/-) following injection of saline or TA1 (1.32, 4 and 11 µg·kg(-1) ; s.c. and i.p.). pERK1/2 levels were determined by Western blot in dorsal root ganglia (DRG) isolated from CD1 mice 15 min after they received (i.p.): saline, saline and noxious heat stimulus (46.5°C), TA1 (0.1, 0.4, 1.32, 4 µg·kg(-1) ) or TA1 1.32 µg·kg(-1) and noxious heat stimulus. KEY RESULTS: TA1 0.4 and 1.32 µg·kg(-1) induced itch and reduced NHT; pyrilamine pretreatment prevented both of these effects. TA1 4 µg·kg(-1) (i.p.) reduced pain threshold without inducing itch or modifying NHT. In HDC(-/-) mice, TA1 failed to induce itch and to reduce NHT. In DRG, pERK1/2 levels were significantly increased by noxious heat stimuli and by TA1 0.1, 0.4 and 1.32 µg·kg(-1) ; i.p. CONCLUSIONS AND IMPLICATIONS: Increased TA1 levels induce itch and an enhanced sensitivity to noxious heat stimuli suggesting that TA1 might represent a potential cause of itch in thyroid diseases.

Histamine mediates behavioural and metabolic effects of 3-iodothyroacetic acid, an endogenous end product of thyroid hormone metabolism.

BACKGROUND AND PURPOSE: 3-Iodothyroacetic acid (TA1) is an end product of thyroid hormone metabolism. So far, it is not known if TA1 is present in mouse brain and if it has any pharmacological effects. EXPERIMENTAL APPROACH: TA1 levels in mouse brain were measured by HPLC coupled to mass spectrometry. After i.c.v. administration of exogenous TA1 (0.4, 1.32 and 4 µg·kg(-1) ) to mice, memory acquisition-retention (passive avoidance paradigm with a light-dark box), pain threshold to thermal stimulus (51.5°C; hot plate test) and plasma glucose (glucorefractometer) were evaluated. Similar assays were performed in mice pretreated with s.c. injections of the histamine H1 receptor antagonist pyrilamine (10 mg·kg(-1) ) or the H2 receptor antagonist zolantidine (5 mg·kg(-1) ). TA1 (1.32 and 4 µg·kg(-1) ) was also given i.c.v. to mice lacking histidine decarboxylase (HDC(-/-) ) and the corresponding WT strain. KEY RESULTS: TA1 was found in the brain of CD1 but not of HDC mice. Exogenous TA1 induced amnesia (at 0.4 µg·kg(-1) ), stimulation of learning (1.32 and 4 µg·kg(-1) ), hyperalgesia (0.4, 1.32 and 4 µg·kg(-1) ) and hyperglycaemia (1.32 and 4 µg·kg(-1) ). All these effects were modulated by pyrilamine and zolantidine. In HDC(-/-) mice, TA1 (1.32 and 4 µg·kg(-1) ) did not increase plasma glucose or induce hyperalgesia. CONCLUSIONS AND IMPLICATIONS: Behavioural and metabolic effects of TA1 disclosed interactions between the thyroid and histaminergic systems.

Parthenolide inhibits nociception and neurogenic vasodilatation in the trigeminovascular system by targeting the TRPA1 channel.

Although feverfew has been used for centuries to treat pain and headaches and is recommended for migraine treatment, the mechanism for its protective action remains unknown. Migraine is triggered by calcitonin gene-related peptide (CGRP) release from trigeminal neurons. Peptidergic sensory neurons express a series of transient receptor potential (TRP) channels, including the ankyrin 1 (TRPA1) channel. Recent findings have identified agents either inhaled from the environment or produced endogenously that are known to trigger migraine or cluster headache attacks, such as TRPA1 simulants. A major constituent of feverfew, parthenolide, may interact with TRPA1 nucleophilic sites, suggesting that feverfew's antimigraine effect derives from its ability to target TRPA1. We found that parthenolide stimulates recombinant (transfected cells) or natively expressed (rat/mouse trigeminal neurons) TRPA1, where it, however, behaves as a partial agonist. Furthermore, in rodents, after initial stimulation, parthenolide desensitizes the TRPA1 channel and renders peptidergic TRPA1-expressing nerve terminals unresponsive to any stimulus. This effect of parthenolide abrogates nociceptive responses evoked by stimulation of peripheral trigeminal endings. TRPA1 targeting and neuronal desensitization by parthenolide inhibits CGRP release from trigeminal neurons and CGRP-mediated meningeal vasodilatation, evoked by either TRPA1 agonists or other unspecific stimuli. TRPA1 partial agonism, together with desensitization and nociceptor defunctionalization, ultimately resulting in inhibition of CGRP release within the trigeminovascular system, may contribute to the antimigraine effect of parthenolide.

Pharmacological effects of 3-iodothyronamine (T1AM) in mice include facilitation of memory acquisition and retention and reduction of pain threshold.

BACKGROUND AND PURPOSE: 3-Iodothyronamine (T1AM), an endogenous derivative of thyroid hormones, is regarded as a rapid modulator of behaviour and metabolism. To determine whether brain thyroid hormone levels contribute to these effects, we investigated the effect of central administration of T1AM on learning and pain threshold of mice either untreated or pretreated with clorgyline (2.5 mg·kg(-1) , i.p.), an inhibitor of amine oxidative metabolism. EXPERIMENTAL APPROACH: T1AM (0.13, 0.4, 1.32 and 4 µg·kg(-1) ) or vehicle was injected i.c.v. into male mice, and after 30 min their effects on memory acquisition capacity, pain threshold and curiosity were evaluated by the following tests: passive avoidance, licking latency on the hot plate and movements on the hole-board platform. Plasma glycaemia was measured using a glucorefractometer. Brain levels of triiodothyroxine (T3), thyroxine (T4) and T1AM were measured by HPLC coupled to tandem MS. ERK1/2 activation and c-fos expression in different brain regions were evaluated by Western blot analysis. RESULTS: T1AM improved learning capacity, decreased pain threshold to hot stimuli, enhanced curiosity and raised plasma glycaemia in a dose-dependent way, without modifying T3 and T4 brain concentrations. T1AM effects on learning and pain were abolished or significantly affected by clorgyline, suggesting a role for some metabolite(s), or that T1AM interacts at the rapid desensitizing target(s). T1AM activated ERK in different brain areas at lower doses than those effective on behaviour. CONCLUSIONS AND IMPLICATIONS: T1AM is a novel memory enhancer. This feature might have important implications for the treatment of endocrine and neurodegenerative-induced memory disorders.