RESUMEN
BACKGROUND: The α1 -adrenoceptor agonist, phenylephrine, is used at high concentrations as a mydriatic agent and for the treatment of nasal congestion. Among its adverse side-effects transient burning sensations are reported indicating activation of the trigeminal nociceptive system. METHODS: Neuropeptide release, calcium imaging and meningeal blood flow recordings were applied in rodent models of meningeal nociception to clarify possible receptor mechanisms underlying these pain phenomena. RESULTS: Phenylephrine above 10 mM dose-dependently released calcitonin gene-related peptide (CGRP) from the dura mater and isolated trigeminal ganglia, whereas hyperosmotic mannitol at 90 mM was ineffective. The phenylephrine-evoked release was blocked by the transient receptor potential vanilloid 1 (TRPV1) antagonist BCTC and did not occur in trigeminal ganglia of TRPV1-deficient mice. Phenylephrine at 30 mM caused calcium transients in cultured trigeminal ganglion neurons responding to the TRPV1 agonist capsaicin and in HEK293T cells expressing human TRPV1. Local application of phenylephrine at micromolar concentrations to the exposed rat dura mater reduced meningeal blood flow, whereas concentrations above 10 mM caused increased meningeal blood flow. The flow increase was abolished by pre-application of the CGRP receptor antagonist CGRP8-37 or the TRPV1 antagonist BCTC. CONCLUSIONS: Phenylephrine at high millimolar concentrations activates TRPV1 receptor channels of perivascular afferents and, upon calcium inflow, releases CGRP, which increases meningeal blood flow. Activation of TRPV1 receptors may underlie trigeminal nociception leading to cranial pain such as local burning sensations or headaches caused by administration of high doses of phenylephrine. SIGNIFICANCE: Phenylephrine is used at high concentrations as a mydriaticum and for treating nasal congestion. As adverse side-effects burning sensations and headaches have been described. Phenylephrine at high concentrations causes calcium transients in trigeminal afferents, CGRP release and increased meningeal blood flow upon activation of TRPV1 receptor channels, which is likely underlying the reported pain phenomena.
Asunto(s)
Péptido Relacionado con Gen de Calcitonina , Calcitonina , Animales , Péptido Relacionado con Gen de Calcitonina/metabolismo , Células HEK293 , Humanos , Ratones , Fenilefrina/farmacología , Ratas , Ratas Wistar , Canales Catiónicos TRPVRESUMEN
We demonstrate a novel dual strategy against inflammation and pain through body-wide desensitization of nociceptors via TRPA1. Attenuation of experimental colitis by capsazepine (CPZ) has long been attributed to its antagonistic action on TRPV1 and associated inhibition of neurogenic inflammation. In contrast, we found that CPZ exerts its anti-inflammatory effects via profound desensitization of TRPA1. Micromolar CPZ induced calcium influx in isolated dorsal root ganglion (DRG) neurons from wild-type (WT) but not TRPA1-deficient mice. CPZ-induced calcium transients in human TRPA1-expressing HEK293t cells were blocked by the selective TRPA1 antagonists HC 030031 and A967079 and involved three cysteine residues in the N-terminal domain. Intriguingly, both colonic enemas and drinking water with CPZ led to profound systemic hypoalgesia in WT and TRPV1(-/-) but not TRPA1(-/-) mice. These findings may guide the development of a novel class of disease-modifying drugs with anti-inflammatory and anti-nociceptive effects.
Asunto(s)
Analgésicos/farmacología , Antiinflamatorios/farmacología , Señalización del Calcio/efectos de los fármacos , Capsaicina/análogos & derivados , Dolor/tratamiento farmacológico , Aceites de Plantas/farmacología , Canal Catiónico TRPA1/metabolismo , Acetanilidas/farmacología , Animales , Capsaicina/farmacología , Células HEK293 , Humanos , Inflamación/tratamiento farmacológico , Inflamación/genética , Inflamación/metabolismo , Ratones , Ratones Noqueados , Planta de la Mostaza , Oximas/farmacología , Dolor/genética , Dolor/metabolismo , Purinas/farmacología , Canal Catiónico TRPA1/antagonistas & inhibidores , Canal Catiónico TRPA1/genéticaRESUMEN
The primary afferent nociceptive neuron has recently attracted major research interest because of the cloning of very selectively expressed and well-conserved ion channel genes. All parts of the neuron, sensory terminals, axon and cell body, are accessible to validated research techniques in vitro using various isolated tissues or cells taken from laboratory animals. Single-unit recording and measuring stimulated calcitonin gene-related peptide (CGRP) release as well as patch-clamping and calcium imaging of cultured sensory neurons provide different kinds of information, and no model alone answers all questions. In combination, however, consistent results and complementary evidence form a solid basis for translational research to follow.
Asunto(s)
Electrofisiología , Nociceptores , Animales , Péptido Relacionado con Gen de Calcitonina/metabolismo , Calcio/metabolismo , Señalización del Calcio/fisiología , Células Cultivadas , Electrofisiología/instrumentación , Electrofisiología/métodos , Ganglios Espinales/citología , Humanos , Canales Iónicos/metabolismo , Ratones , Nociceptores/química , Nociceptores/citología , Nociceptores/metabolismo , RatasRESUMEN
Cold sensing in mammals is not completely understood, although significant progress has been made recently with the cloning of two cold-activated ion channels, TRPM8 and TRPA1. We have used rat DRG neurons in primary culture and calcium fluorimetry to identify distinct populations of cold-sensitive neurons, which may underlie different functions. Menthol sensitivity clearly separated two classes of cold-responding neurons. One group was menthol-sensitive (MS), was activated at warmer temperatures and responded faster and with a larger increase in intracellular calcium concentration during cooling; the fraction of MS neurons in culture and their cold sensitivity were both increased in the presence of nerve growth factor. Neurons in the menthol-insensitive (MI) group required stronger cooling for activation than MS cells and neither their proportion nor their cold sensitivity were significantly altered by nerve growth factor. The two groups of cold-sensitive neurons also had different pharmacology. A larger fraction of MS cells were capsaicin-sensitive and coexpression of menthol and capsaicin sensitivity was observed in the absence of NGF. MI neurons were not stimulated by the super-cooling agent icilin or by the irritant mustard oil. Taken together these findings support a picture in which TRPM8 is the major player in detecting gentle cooling, while TRPA1 does not seem to be involved in cold sensing by MI neurons, at least in the temperature range between 32 and 12 degrees C.