The non-peptide NK1 receptor antagonist SR140333 produces long-lasting inhibition of neurogenic inflammation, but does not influence acute chemo- or thermonociception in rats

Nociceptive afferent phenotyping reveals that transient receptor potential ankyrin 1 promotes cold pain through neurogenic inflammation upstream of the neurotrophic factor receptor GFRα3 and the menthol receptor transient receptor potential melastatin 8

ABSTRACT

The proper detection and behavioral response to painfully cold temperatures is critical for avoiding potentially harmful tissue damage. Cold allodynia and hyperalgesia, pain associated with innocuous cooling and exaggerated pain with noxious cold, respectively, are common in patients with chronic pain. In peripheral somatosensory afferents, the ion channels transient receptor potential melastatin 8 (TRPM8) and transient receptor potential ankyrin 1 (TRPA1) are candidate receptors for innocuous and noxious cold temperatures, respectively. However, the role of TRPA1 as a cold sensor has remained controversial, and recent evidence suggests that TRPM8 channels and afferents mediate the detection of both pleasant and painful cold. To determine the role of TRPA1 afferents in cold-induced mouse behaviors in vivo, we used functional phenotyping by targeted nerve conduction block with the cell-impermeant lidocaine derivative QX-314. Surprisingly, we find that injection of QX-314 with TRPA1 agonists reduces cold-induced behaviors in mice, but does so in a TRPM8-dependent manner. Moreover, this effect is sexually dimorphic and requires the glial cell line-derived neurotrophic factor receptor GFRα3, as does cold hypersensitivity produced by the activation of TRPA1 channels. Taken together, these results suggest that under conditions of neurogenic inflammation, TRPA1 works upstream of GFRα3 and TRPM8 to produce cold hypersensitivity, providing novel insights into the role of TRPA1 channels in cold pain.

TRPM8: A Therapeutic Target for Neuroinflammatory Symptoms Induced by Severe Dry Eye Disease

Dry eye disease (DED) is commonly associated with ocular surface inflammation and pain. In this study, we evaluated the effectiveness of repeated instillations of transient receptor potential melastatin 8 (TRPM8) ion channel antagonist M8-B on a mouse model of severe DED induced by the excision of extra-orbital lacrimal and Harderian glands. M8-B was topically administered twice a day from day 7 until day 21 after surgery. Cold and mechanical corneal sensitivities and spontaneous ocular pain were monitored at day 21. Ongoing and cold-evoked ciliary nerve activities were next evaluated by electrophysiological multi-unit extracellular recording. Corneal inflammation and expression of genes related to neuropathic pain and inflammation were assessed in the trigeminal ganglion. We found that DED mice developed a cold allodynia consistent with higher TRPM8 mRNA expression in the trigeminal ganglion (TG). Chronic M8-B instillations markedly reversed both the corneal mechanical allodynia and spontaneous ocular pain commonly associated with persistent DED. M8-B instillations also diminished the sustained spontaneous and cold-evoked ciliary nerve activities observed in DED mice as well as inflammation in the cornea and TG. Overall, our study provides new insight into the effectiveness of TRPM8 blockade for alleviating corneal pain syndrome associated with severe DED, opening a new avenue for ocular pain management.

TRPV1 activity and substance P release are required for corneal cold nociception

As a protective mechanism, the cornea is sensitive to noxious stimuli. Here, we show that in mice, a high proportion of corneal TRPM8⁺ cold-sensing fibers express the heat-sensitive TRPV1 channel. Despite its insensitivity to cold, TRPV1 enhances membrane potential changes and electrical firing of TRPM8⁺ neurons in response to cold stimulation. This elevated neuronal excitability leads to augmented ocular cold nociception in mice. In a model of dry eye disease, the expression of TRPV1 in TRPM8⁺ cold-sensing fibers is increased, and results in severe cold allodynia. Overexpression of TRPV1 in TRPM8⁺ sensory neurons leads to cold allodynia in both corneal and non-corneal tissues without affecting their thermal sensitivity. TRPV1-dependent neuronal sensitization facilitates the release of the neuropeptide substance P from TRPM8⁺ cold-sensing neurons to signal nociception in response to cold. Our study identifies a mechanism underlying corneal cold nociception and suggests a potential target for the treatment of ocular pain.

The eye shows protective responses to noxious stimuli including cold. Here, the authors show that TRPV1, found co-expressed on TRPM8 + fibres in the cornea, is necessary for cold nociception in the eye.

Prenatal nicotinic exposure upregulates pulmonary C-fiber NK1R expression to prolong pulmonary C-fiber-mediated apneic response

Prenatal nicotinic exposure (PNE) prolongs bronchopulmonary C-fiber (PCF)-mediated apneic response to intra-atrial bolus injection of capsaicin in rat pups. The relevant mechanisms remain unclear. Pulmonary substance P and adenosine and their receptors (neurokinin-A receptor, NK1R and ADA1 receptor, ADA1R) and transient receptor potential cation channel subfamily V member 1 (TRPV1) expressed on PCFs are critical for PCF sensitization and/or activation. Here, we compared substance P and adenosine in BALF and NK1R, ADA1R, and TRPV1 expression in the nodose/jugular (N/J) ganglia (vagal pulmonary C-neurons retrogradely labeled) between Ctrl and PNE pups. We found that PNE failed to change BALF substance P and adenosine content, but significantly upregulated both mRNA and protein TRPV1 and NK1R in the N/J ganglia and only NK1R mRNA in pulmonary C-neurons. To define the role of NK1R in the PNE-induced PCF sensitization, the apneic response to capsaicin (i.v.) without or with pretreatment of SR140333 (a peripheral and selective NK1R antagonist) was compared and the prolonged apnea by PNE significantly shortened by SR140333. To clarify if the PNE-evoked responses depended on action of nicotinic acetylcholine receptors (nAChRs), particularly α7nAChR, mecamylamine or methyllycaconitine (a general nAChR or a selective α7nAChR antagonist) was administrated via another mini-pump over the PNE period. Mecamylamine or methyllycaconitine eliminated the PNE-evoked mRNA and protein responses. Our data suggest that PNE is able to elevate PCF NK1R expression via activation of nAChRs, especially α7nAChR, which likely contributes to sensitize PCFs and prolong the PCF-mediated apneic response to capsaicin.

Induction of the neurokinin 1 receptor by TNFα in endometriotic tissue provides the potential for neurogenic control over endometriotic lesion growth

CONTEXT

Endometriosis is characterized by the growth of ectopic endometrial tissue. Nerve fibers are frequently associated with ectopic lesions, and neurogenic inflammation may play a role in endometriosis.

OBJECTIVE

The purpose of this study was to determine the presence of tachykinin receptors in endometriotic lesions and the role of TNFα on their expression.

DESIGN

This study was an assessment of matching eutopic and ectopic endometrial tissue and peritoneal fluid from patients with endometriosis and an in vitro analysis of primary endometrial cells.

SETTING

The setting was a university hospital.

PATIENTS

Participants were premenopausal women undergoing laparoscopy.

INTERVENTIONS

Endometriotic lesions were removed surgically.

MAIN OUTCOME MEASURES

Tachykinin mRNA (TACR1/2) and protein (neurokinin 1 receptor [NK1R]) expression in both eutopic and ectopic endometrial tissue from patients with endometriosis and the correlation to peritoneal fluid TNFα were measured. Primary endometrial epithelial and stromal cells were assessed in vitro to determine the induction of TACR1/2 and NK1R expression after TNFα treatment. Cell viability of endometrial stromal cells after substance P exposure was also assessed.

RESULTS

Expression of both TACR1 and TACR2 mRNA was significantly higher in the ectopic than in the eutopic tissue. Both TACR1 mRNA and NK1R protein expression was significantly correlated with peritoneal fluid TNFα, and in vitro studies confirmed that TNFα treatment induced both TACR1 mRNA and NK1R protein expression in endometrial stromal cells. In endometrial stromal cells, substance P treatment enhanced cell viability, which was inhibited by a specific NK1R antagonist.

CONCLUSIONS

NK1R expression is induced in ectopic endometrial tissue by peritoneal TNFα. Induction of NK1R expression may permit endometriotic lesion maintenance via exposure to substance P.

Neurokinin-1 receptor antagonist treatment protects mice against lung injury in polymicrobial sepsis

Earlier work from our laboratory has suggested a role for the neuropeptide substance P (SP) in inducing lung injury in sepsis. In that study, mice lacking the preprotachykinin-A gene, which encodes for SP, were protected against lung injury in sepsis. To further substantiate the role of SP in sepsis and to study its mechanism, we have evaluated the effect of SR140333, a SP receptor antagonist, on lung injury in sepsis, which was induced in male Swiss mice by cecal ligation and puncture (CLP). Sham-operated animals received the same surgical procedure, except CLP. Vehicle or SR140333 (1 mg/kg, s.c.) was administered to CLP mice 30 min before or 1 h after the CLP. Eight hours after surgery, lung tissue was collected and analyzed for myeloperoxidase (MPO) activity, chemokines, cytokines, and adhesion molecules. The CLP procedure alone caused a significant increase in the lung levels of MIP-2, MCP-1, IL-1beta, IL-6, ICAM-1, E- and P-selectin, and MPO activity when compared with sham-operated mice. SR140333 injected 30 min before or 1 h after CLP significantly attenuated the increased lung MPO activity and levels of MIP-2, MCP-1, IL-1beta, IL-6, ICAM-1, and E- and P-selectin compared with CLP-operated mice injected with the vehicle. Histological evaluation of the lung sections further supported the beneficial effect of SR140333 on lung inflammation. Therefore, SP receptor antagonism can be a potential therapeutic target in polymicrobial sepsis, and this effect is brought about via reduction in leukocyte recruitment.

Neurokinin 1 receptor signaling mediates sex differences in μ and κ opioid-induced enhancement of contact hypersensitivity

Contact hypersensitivity (CHS) is a type of cutaneous inflammation that is exacerbated by neurogenic factors. Both mu- and kappa-opioids enhance CHS to a greater extent in females than males. It was hypothesized that potentiated neurokinin 1 (NK1) receptor signaling following opioid treatment accounts for sex differences in the magnitude of CHS. Following morphine or spiradoline treatment the NK1 receptor antagonist SR140,333 significantly attenuated the magnitude of CHS in females but not males. By contrast, the NK2 antagonist SR48968 had no effect on morphine modulation of CHS. Taken together, these data indicate that NK1 receptor signaling is a key mediator of sex differences in opioid-induced enhancement of CHS.

Immunohistochemical localization of histamine H3 receptors in rodent skin, dorsal root ganglia, superior cervical ganglia, and spinal cord: potential antinociceptive targets

Activation of histamine H3 receptors (H3Rs) reduces inflammation and nociception, but the existence of H3Rs on peripheral innervation has never been demonstrated. Here we use antibodies to locate H3Rs in whisker pads, hairy and glabrous hind paw skin, dorsal root ganglia (DRGs), and spinal cords of rats, wild type mice, and H3R knockout (H3KO) mice. Although H3Rs have been hypothesized to be on C and sympathetic fibers, H3R-like immunoreactivity (H3R-LI) was only detected on presumptive periarterial A delta fibers and on A beta fibers that terminated in Meissner's corpuscles and as lanceolate endings around hair follicles. The H3R-positive periarterial fibers were thin-caliber and coexpressed immunoreactivity for calcitonin gene-related peptide (CGRP), substance P, acid sensing ion channel 3, and 200 kDa neurofilament protein (NF). H3R-LI was also detected on epidermal keratinocytes and Merkel cells, but not on Merkel endings, C fibers, any other A delta fibers, or sympathetic fibers. In DRGs, H3R-LI was preponderantly on medium to large neurons coexpressing NF-LI and mostly CGRP-LI. In dorsal horn, CGRP-positive fibers with and without H3R-LI ramified extensively in lamina II; many of the former formed a plexus in lamina V. Low levels of H3R-LI were also present on A beta fibers penetrating superficial and into deeper laminae. The distribution of H3R-LI was similar in rats and wild type mice, but was eliminated or strongly reduced in A delta fibers and A beta fibers, respectively, in H3KO mice. Taken with recently published behavioral results, the present findings suggest that periarterial, peptidergic, H3R-containing A delta fibers may be sources of high threshold mechanical nociception.

The NK1 Receptor Antagonist SR140333 Inhibits Capsaicin-Induced ERK Phosphorylation in Sensory Neurons

Primary sensory neurons respond to a vigorous excitation via the capsaicin receptor/TRPV1 cation channel by a phosphorylation of the Jak/STAT pathway as measured by phospho-STAT3, and of the Ras/Raf-MAPK pathway as measured by phospho-MAPK/ERK1/2. In the present investigation a possible involvement of NK1 receptors in the capsaicin-induced activation of these signal transduction pathways was investigated by protein extraction and Western immunoblotting. Phospho-MAPK/ERK1/2 and phospho-STAT3 were determined in the dorsal root ganglia (DRG) and in the sciatic nerve of rats at 3 and 6 h following a systemic capsaicin treatment without or with the pretreatment of the selective NK1 receptor antagonist SR140333 (1 mg/kg s.c.; 3 h before capsaicin). Capsaicin evoked a threefold increase in phospho-ERK in the sciatic nerve and a two- to threefold increase in the DRG at 3 h and 6 h after the treatment. SR140333 markedly attenuated the capsaicin-induced increase in phosphorylated ERK. In the sciatic nerve the difference was significant at each individual time point (3 and 6 h, p < 0.001). In the DRG the difference was significant when the data at 3 h and 6 h were combined (p < 0.05), but not when individual time points were considered. Capsaicin evoked a four- to fivefold increase in phospho-STAT3 in the sciatic nerve and a twofold increase in the DRG at 3 and 6 h after the treatment. SR140333 less markedly attenuated the capsaicin-induced increase in phosphorylated STAT3: whereas in the sciatic nerve the difference was significant when the data at 3 h and 6 h were combined (p < 0.05), no such treatment effect of SR140333 was observed in the DRG. The expression of TRPV1 mRNA, a specific marker of capsaicin-sensitive small sensory neurons, was investigated by RT-PCR 4 days after the capsaicin treatment. Treatment of rats with SR140333 had no influence on the long-term downregulation of TRPV1 mRNA by capsaicin. Based on the present results and previous findings it can be postulated that the capsaicin-induced ERK phosphorylation in sensory neurons is not a direct effect by capsaicin, but that rather substance P release from the stimulated sensory neurons with an NK1-mediated nerve growth factor (NGF) production is involved.

Effects of the novel TRPV1 receptor antagonist SB366791 in vitro and in vivo in the rat

The TRPV1 capsaicin receptor is a non-selective cation channel localized in the cell membrane of a subset of primary sensory neurons and functions as an integrator molecule in nociceptive/inflammatory processes. The present paper characterizes the effects of SB366791, a novel TRPV1 antagonist, on capsaicin-evoked responses both in vitro and in vivo using rat models. SB366791 (100 and 500 nM) significantly inhibited capsaicin-evoked release of the pro-inflammatory sensory neuropeptide substance P from isolated tracheae, while it did not influence electrically induced neuropeptide release. It also decreased capsaicin-induced Ca2+ influx in cultured trigeminal ganglion cells in a concentration-dependent manner (0.5-10 microM) with an IC50 of 651.9 nM. In vivo 500 microg/kg i.p. dose of SB366791 significantly inhibited capsaicin-induced hypothermia, wiping movements and vasodilatation in the knee joint, while 2 mg/kg capsazepine was ineffective, its effect lasted for 1h. However, neither antagonist was able to inhibit capsaicin-evoked hypothermia in Balb/c mice. Based on these data SB366791 is a more selective and in vivo also a more potent TRPV1 receptor antagonist than capsazepine in the rat therefore, it may promote the assessment of the therapeutic utility of TRPV1 channel blockers.

Pharmacological characterization of the TRPV1 receptor antagonist JYL1421 (SC0030) in vitro and in vivo in the rat

The TRPV1 capsaicin receptor is an integrator molecule on primary afferent neurones participating in inflammatory and nociceptive processes. The present paper characterizes the effects of JYL1421 (SC0030), a TRPV1 receptor antagonist, on capsaicin-evoked responses both in vitro and in vivo in the rat. JYL1421 concentration-dependently (0.1-2 microM) inhibited capsaicin-evoked substance P, calcitonin gene-related peptide and somatostatin release from isolated tracheae, while only 2 microM resulted in a significant inhibition of electrically induced neuropeptide release. Capsazepine (0.1-2 microM), as a reference compound, similarly diminished both capsaicin-evoked and electrically evoked peptide release. JYL1421 concentration-dependently decreased capsaicin-induced Ca(2+) accumulation in cultured trigeminal ganglion cells, while capsazepine was much less effective. In vivo 2 mg/kg i.p. JYL1421, but not capsazepine, inhibited capsaicin-induced hypothermia, eye wiping movements and reflex hypotension (a component of the pulmonary chemoreflex or Bezold-Jarisch reflex). Based on these data JYL1421 is a more selective and in most models also a more potent TRPV1 receptor antagonist than capsazepine, therefore it may promote the assessment of the (patho)physiological roles of the TRPV1 receptor.

Substance P released from sensory nerve endings influences tear secretion and goblet cell function in the rat

The aim of this study was to present morphological and functional evidence to evaluate whether tear secretion is influenced by neuropeptides released from sensory nerve endings of the conjunctiva. Following unilateral electrical stimulation of the trigeminal ganglion, tears were collected at both sides and assessed for volume and protein concentration; as well as gel electrophoresis and luminol chemiluminescence with immunostaining to immunoglobulin A and lysozyme measurements. Goblet cell density (goblet cells/100 basal cells) was recorded during histopathological examination of removed lids. Rats were pretreated with atropine to block parasympathetic; guanethidine to block sympathetic neuronal pathways; or hexamethonium to block synaptic transmission in ganglia. Capsaicin was used to deplete neurotransmitters from sensory nerve endings or SR140333 to block substance P tachykinin NK1 receptor mediated responses. Effects of inadequate electrode position or incidental lesion of trigeminal ganglion were examined by placing the electrode in false position, or no stimulation at a correct position. Electrical stimulation resulted in 380% increase of tear secretion (p < 0.001) and 30% decrease of goblet cell density (p < 0.001) on the the stimulated side compared to the unstimulated side. Atropine, guanethidine and hexamethonium pretreatments had no effect (p > 0.05), but capsaicin and SR140333 inhibited the effect of stimulation (by 96% and 72%, respectively, p < 0.001). Inadequate stimulation did not increase the tear secretion (p < 0.05). Protein concentration decreased, whilst tear volume and total secreted protein increased (p < 0.005) after stimulation. Electrophoresis showed no difference in protein pattern between stimulated and control side and analysis of equivalent amount of tear protein with luminol chemiluminescence indicated no difference in immunoglobulin A and lysozyme ratio following stimulation (p>0.05). We conclude that antidromic electrical activation of conjunctival sensory nerve endings significantly increases water, mucus and protein phases of tear. It is suggested that the sensory neuropeptide substance P plays a pivotal role in this neurogenic regulatory mechanism.

Beta adrenergic inhibition of capsaicin-induced, NK1 receptor-mediated nerve growth factor biosynthesis in rat skin

Excitation of primary afferent neurons stimulates the expression of cytokines and nerve growth factor (NGF) in innervated tissues. Since NGF is a neurotrophic and immunomodulatory factor contributing to inflammatory hyperalgesia and tissue response to injury, this study was conducted in order to investigate the mechanisms by which afferent neuron stimulation by topical application of capsaicin increases NGF in the rat skin. Thereby it was sought to identify possible targets for pharmacological modulation of NGF biosynthesis. Topical capsaicin (>1 mg/ml ethanol) caused a concentration- and time-dependent increase in the concentration of NGF in rat skin. The capsaicin-induced increase of NGF was not significantly affected by indomethacin administered at a dose (2 mg/kg) that abolishes prostaglandin E2 biosynthesis. The NGF increase was suppressed by treatment of rats with the selective tachykinin NK1 receptor antagonist SR140333 (0.1 mg/kg), and by the beta adrenergic agonist terbutaline (0.3 mg/kg). The effect of terbutaline was reversed by the beta adrenergic antagonist propranolol (1 mg/kg). Terbutaline also inhibited the increase in NGF caused by intraplantar injection of the NK1 receptor agonist substance P (SP), but did not significantly affect that caused by carrageenan. The results show that topical administration of capsaicin causes a primarily NK1 receptor-dependent increase in the NGF content of rat skin, which is susceptible to inhibition by beta adrenergic agonists. These observations not only suggest regulation of skin NGF biosynthesis by afferent neuronal and adrenergic mechanisms, but also indicate possible targets for pharmacological modulation of skin NGF biosynthesis.

A role for proteinase-activated receptor-1 in inflammatory bowel diseases

Proteinase-activated receptor-1 (PAR1), a G protein-coupled receptor activated by thrombin, is highly expressed in different cell types of the gastrointestinal tract. The activity of thrombin and of other proteinases is significantly increased in the colon of inflammatory bowel disease (IBD) patients. Since PAR1 activation in tissues other than the gut provoked inflammation, we hypothesized that PAR1 activation in the colon is involved in the pathogenesis of IBD. Here, we demonstrate that PAR1 is overexpressed in the colon of IBD patients. In mice, intracolonic administration of PAR1 agonists led to an inflammatory reaction characterized by edema and granulocyte infiltration. This PAR1 activation-induced inflammation was dependent on B and T lymphocytes. Moreover, PAR1 activation exacerbated and prolonged inflammation in a mouse model of IBD induced by the intracolonic administration of trinitrobenzene sulfonic acid (TNBS), while PAR1 antagonism significantly decreased the mortality and severity of colonic inflammation induced by TNBS and dextran sodium sulfate. In these 2 models, colitis development was strongly attenuated by PAR1 deficiency. Taken together, these results imply an important role for PAR1 in the pathogenesis of experimental colitis, supporting the notion that PAR1 inhibition may be beneficial in the context of IBD and possibly in other chronic intestinal inflammatory disorders.

Colitis induced by proteinase-activated receptor-2 agonists is mediated by a neurogenic mechanism

Proteinase-activated receptor-2 (PAR2) activation induces colonic inflammation by an unknown mechanism. We hypothesized that PAR2 agonists administered intracolonically in mice induce inflammation via a neurogenic mechanism. Pretreatment of mice with neurokinin-1 and calcitonin-gene-related peptide (CGRP) receptor antagonists or with capsaicin showed attenuated PAR2-agonist-induced colitis. Immunohistochemistry demonstrated a differential expression of a marker for the type-1 CGRP receptor during the time course of PAR2-agonist-induced colitis, further suggesting a role for CGRP. We conclude that PAR2-agonist-induced intestinal inflammation involves the release of neuropeptides, which by acting on their receptors cause inflammation. These results implicate PAR2 as an important mediator of intestinal neurogenic inflammation.

Mustard oil induces a transient receptor potential vanilloid 1 receptor-independent neurogenic inflammation and a non-neurogenic cellular inflammatory component in mice

A neurogenic component has been suggested to play a pivotal role in a range of inflammatory/immune diseases. Mustard oil (allyl-isothiocyanate) has been used in studies of inflammation to mediate neurogenic vasodilatation and oedema in rodent skin. The aim of the present study was to analyse mustard oil-induced oedema and neutrophil accumulation in the mouse ear focussing on the roles of neurokinin 1 (NK(1)) and vanilloid (TRPV1) receptors using normal (BALB/c, C57BL/6) as well as NK(1) and TRPV1 receptor knockout mice. A single or double treatment of 1% mustard oil on the BALB/c mouse ear induced ear oedema with responses diminished by 6 h. However a 25-30% increase in ear thickness was maintained by the hourly reapplication of mustard oil. Desensitisation of sensory nerves with capsaicin, or the NK(1) receptor antagonist SR140333, inhibited oedema but only in the first 3 h. Neutrophil accumulation in response to mustard oil was inhibited neither by SR140333 nor capsaicin pre-treatment. An activating dose of capsaicin (2.5%) induced a large oedema in C57BL/6 wild-type mice that was minimal in TRPV1 receptor knockout mice. By comparison, mustard oil generated ear swelling was inhibited by SR140333 in wild-type and TRPV1 knockout mice. Repeated administration of mustard oil maintained 35% oedema in TRPV1 knockout animals and the lack of TRPV1 receptors did not alter the leukocyte accumulation. In contrast repeated treatment caused about 20% ear oedema in Sv129+C57BL/6 wild-type mice but the absence of NK(1) receptors significantly decreased the response. Neutrophil accumulation showed similar values in both groups. This study has revealed that mustard oil can act via both neurogenic and non-neurogenic mechanisms to mediate inflammation in the mouse ear. Importantly, the activation of the sensory nerves was still observed in TRPV1 knockout mice indicating that the neurogenic inflammatory component occurs via a TRPV1 receptor independent process.

Passive smoke effects on cough and airways in young guinea pigs: role of brainstem substance P

Children raised with extended exposure to environmental tobacco smoke (ETS) experience increased cough and wheeze. This study was designed to determine whether extended ETS exposure enhances citric acid-induced cough and bronchoconstriction in young guinea pigs via a neurokinin-1 (NK-1) receptor mechanism at the first central synapse of lung afferent neurons, the nucleus tractus solitarius. Guinea pigs were exposed to ETS from 1 to 6 weeks of age. At 5 weeks of age, guide cannulae were implanted bilaterally in the medial nucleus tractus solitarius at a site that produced apnea in response to the glutamate agonist D,L-homocysteic acid. At 6 weeks of age, either vehicle or a NK-1 receptor antagonist, SR 140333, was injected into the nucleus tractus solitarius of the conscious guinea pigs who were then exposed to citric acid aerosol. ETS exposure significantly enhanced citric acid-induced cough by 56% and maximal Penh (a measure of airway obstruction) by 43%, effects that were attenuated by the NK-1 receptor antagonist in the nucleus tractus solitarius. We conclude that in young guinea pigs extended exposure to ETS increases citric acid-induced cough and bronchoconstriction in part by an NK-1 receptor mechanism in the nucleus tractus solitarius.

Postexercise hypotension in conscious SHR is attenuated by blockade of substance P receptors in NTS

In hypertensive subjects, a single bout of dynamic exercise results in an immediate lowering of blood pressure back toward normal. This postexercise hypotension (PEH) also occurs in the spontaneously hypertensive rat (SHR). In both humans and SHRs, PEH features a decrease in sympathetic nerve discharge, suggesting the involvement of central nervous system pathways. Given that substance P is released in the nucleus tractus solitarius (NTS) by activation of baroreceptor and skeletal muscle afferent fibers during muscle contraction, we hypothesized that substance P acting at neurokinin-1 (NK-1) receptors in the NTS might contribute to PEH. We tested the hypothesis by determining, in conscious SHRs, whether NTS microinjections of the NK-1 receptor antagonist SR-140333 before exercise attenuated PEH. The antagonist, in a dose (60 pmol) that blocked substance P- and spared D,L-homocysteic acid-induced depressor responses, significantly attenuated the PEH by 37%, whereas it had no effect on blood pressure during exercise. Vehicle microinjection had no effect. The antagonist also had no effect on heart rate responses during both exercise and the PEH period. The data suggest that a substance P (NK-1) receptor mechanism in the NTS contributes to PEH.

[Nociceptors and mediators in acute inflammatory pain]

OBJECTIVE

To bring together the most recent data concerning the physiology of nociceptors at a time when there has been significant progress in the understanding of these.

DATA SOURCES

References were obtained from computerised bibliographic data banks (Medline and others) and the authors' personal documents.

DATA SYNTHESIS

Nociceptive impulses are generated at the periphery in unmyelinated fibres called nociceptors, the responses of which depend on the tissue environment. Numerous mediators can activate, sensitise or "wake up" nociceptor: kinins (bradykinin, kallidin and their metabolites), pro-inflammatory cytokines (TNF alpha, IL-6, IL-1 beta, IL-8), anti-inflammatory cytokines (IL-4, IL-6, IL-10, IL-12, IL-13), prostanoids (PGE2, PGI2), lipo-oxygenases (leucotrienes such LTB4 or 15-HETE), the "central mediators of the immune response" (NF-kappa B), growth factors such as neurotrophins (NGF, BDNF, NT-3 and NT-4/5), peptides (substance P, CGRP, Neurokinin A), nitric oxide, histamine, serotonin, proteases, excitatory amino acids, adrenergic amines and opioids. The release of neuromediators by primary afferent fibres in the spinal cord may be summarised by successively considering calcium channels, presynaptic receptors, excitatory amino acids and peptides.

CONCLUSION

Sensitisation phenomena are not exclusively peripheral but also central in origin and these are interlinked.

Proteinases and proteinase-activated receptor 2: a possible role to promote visceral hyperalgesia in rats

BACKGROUND & AIMS

PAR-2s are highly expressed throughout the gastrointestinal tract. These receptors are cleaved by trypsin and mast cell tryptase and can be activated by peptides corresponding to the tethered ligand of the receptor (SLIGRL-NH2 for rat). The aim of this study was to determine whether colonic administration of PAR-2 agonists affects visceral sensitivity to rectal distention in conscious rats.

METHODS

Abdominal contractions (a criteria of visceral pain) were recorded in rats equipped with intramuscular electrodes. Rectal distention was performed at various times after intracolonic infusion of SLIGRL-NH2 and trypsin. Inflammation parameters and permeability were followed in the colon after the intracolonic injections. Fos expression at a spinal level (L4-L6) was also studied 2 hours after intracolonic injection of SLIGRL-NH2.

RESULTS

Rectal distention significantly increased abdominal contractions starting at the RD volume of 0.8 mL. Intracolonic injection of SLIGRL-NH2 (200 microg/rat) and trypsin (200 U/rat), but not vehicle, LRGILS-NH2 (control peptide), boiled trypsin, or SLIGRL-NH2 injected IP, significantly increased (P < 0.05) abdominal contractions for high volumes of distention, 10- and 24-hour postinfusion. SLIGRL-NH2-induced hyperalgesia was inhibited by a NK1 receptor antagonist (SR 140333) but not by indomethacin. Intracolonic injection of SLIGRL-NH2 elevated spinal Fos expression and caused increased intestinal permeability but did not cause detectable inflammation.

CONCLUSIONS

Intracolonic infusion of subinflammatory doses of PAR-2 agonists activated spinal afferent neurons and produced a delayed rectal hyperalgesia that involves changes in intestinal permeability and the activation of NK1 receptors. These results identify a possible role for proteinases and PAR-2 in the genesis of visceral hyperalgesia.

Proteinase-activated receptor-2 and hyperalgesia: A novel pain pathway

Using a combined pharmacological and gene-deletion approach, we have delineated a novel mechanism of neurokinin-1 (NK-1) receptor-dependent hyperalgesia induced by proteinase-activated receptor-2 (PAR2), a G-protein-coupled receptor expressed on nociceptive primary afferent neurons. Injections into the paw of sub-inflammatory doses of PAR2 agonists in rats and mice induced a prolonged thermal and mechanical hyperalgesia and elevated spinal Fos protein expression. This hyperalgesia was markedly diminished or absent in mice lacking the NK-1 receptor, preprotachykinin-A or PAR2 genes, or in rats treated with a centrally acting cyclooxygenase inhibitor or treated by spinal cord injection of NK-1 antagonists. Here we identify a previously unrecognized nociceptive pathway with important therapeutic implications, and our results point to a direct role for proteinases and their receptors in pain transmission.

The tachykinin NK(1) receptor antagonist SR140333 prevents the increase of nerve growth factor in rat paw skin induced by substance P or neurogenic inflammation

Target-derived nerve growth factor provides trophic support for adult primary afferent neurons containing calcitonin gene-related peptide and tachykinins. Noxious chemical or thermal stimuli cause the release of these mediators from peripheral afferent nerve endings. However, little is known of the extent to which these mediators, in turn, influence nerve growth factor expression in the innervated tissue. The aim of this study was therefore to investigate the possible effect of exogenous substance P, or neurogenic inflammation on the nerve growth factor concentration in the skin of the rat hindpaw. Our results show that substance P as well as topical application of mustard oil cause a significant increase in detectable nerve growth factor, an effect that was prevented by treatment of rats with the tachykinin NK(1) receptor antagonist SR140333. We did not observe a significant inhibitory effect of SR140333 on the nerve growth factor content in non-treated skin, or the nerve growth factor increase caused by carrageenan or allergic inflammation. The results provide evidence that substance P as well as neurogenic inflammation cause a rapid increase in detectable nerve growth factor in the paw skin and suggest the involvement of NK(1) receptors in this effect. We obtained no evidence for the participation of a NK(1) receptor-mediated nerve growth factor increase in models of inflammation induced by non-neurogenic stimuli.

Mechanisms of the cutaneous vasodilator response to local external pressure application in rats: involvement of CGRP, neurokinins, prostaglandins and NO

1. Local pressure-induced vasodilation (PIV) is a neural vasodilator response to non-nociceptive externally applied pressure in the skin, previously described in humans. We first determined whether PIV exists in rats and depends on capsaicin-sensitive fibres as it does in humans. We then examined the mediators involved in the efferent pathway of PIV. 2. Cutaneous blood flow was measured by laser Doppler flowmetry during 11.1 Pa s(-1) increases in local applied pressure in anaesthetized rats. The involvement of capsaicin-sensitive fibres in PIV was tested in rats treated neonatally with capsaicin. To antagonize CGRP, neurokinin-1, -2, or -3 receptors, different groups of rats were treated with CGRP(8 - 37), SR140333, SR48968 or SR142801, respectively. Prostaglandins involvement was tested with indomethacin treatment. To inhibit nitric oxide synthase (NOS) activity or specific neuronal NOS, rats were treated with N(G)-nitro-L-arginine or 7-nitroindazole, respectively. 3. PIV was found in rats, as in humans. PIV was abolished by neonatal treatment with capsaicin and by administration of CGRP(8 - 37) but remained unchanged with SR140333, SR48968 and SR142801 treatments. Prostaglandin inhibition resulted in a significant decrease in PIV. Inhibition of NOS abolished PIV, whereas inhibition of neuronal NOS caused a diminution of PIV. 4. These data suggest that PIV depends on capsaicin-sensitive fibres in rats, as in humans. It appears that CGRP plays a major role in the PIV, whereas neurokinins have no role. Furthermore, PIV involves a contribution from prostaglandins and depends on endothelial NO, whereas neuronal NO has a smaller role.

Oral anti-hyperalgesic and anti-inflammatory activity of NK(1) receptor antagonists in models of inflammatory hyperalgesia of the guinea-pig

The oral analgesic and anti-inflammatory activity of NK(1) antagonists with species preference for the human receptor were assessed in (1) the carrageenan-induced inflammatory hyperalgesia and (2) Freund's complete adjuvant (FCA)-induced extravasation in the knee joint models of the guinea-pig, respectively. Mechanical hyperalgesia was determined by measuring the withdrawal threshold to a noxious mechanical stimulus applied to the paw and thermal hyperalgesia as the withdrawal latency to a noxious thermal stimulus applied to the plantar surface. A concentration of 1.0% carrageenan (intraplantar) reduced mechanical thresholds from 124+/-5 to 63+/-3 g and thermal latencies from 19+/-0.4 to 4.7+/-0.9 s as determined 4 h after injection. The hyperalgesia persisted for over 24 h. The NK(1) receptor antagonists, SDZ NKT 343, RPR100893 and SR140333, reduced mechanical hyperalgesia by 68, 36 and 27% at a dose of 30 mg kg(-1) p.o., respectively. No further reduction was noted at higher doses (maximum 100 mg kg(-1) p.o.). The anti-hyperalgesic effect of SDZ NKT 343 and RPR100893 peaked at 3 h while SR140333 produced maximal reversal at 1 h after oral administration. D(30) values indicated significant differences between the potency of these compounds. SDZ NKT 343 was by far the most potent anti-hyperalgesic agent (D(30): 1.1 mg kg(-1)). The D(30) values for RPR100893 and SR140333 were estimated to be 17 and >100 mg kg(-1), respectively. In thermal hyperalgesia, SDZ NKT 343 produced a significantly weaker anti-hyperalgesic effect with a peak of 25% reversal. The D(30) value for SDZ NKT 343 was 3.89 mg kg(-1). For comparison, morphine inhibited the carrageenan-induced mechanical and thermal hyperalgesia with an ED(50) of 1.85 and 2.51 mg kg(-1) s.c., respectively. When tested up to 300 mg kg(-1) p.o., aspirin reduced carrageenan-induced mechanical and thermal hyperalgesia by 55.0 and 45.2%, respectively. In addition to the anti-hyperalgesic effects of NK(1) receptor antagonists, the effects of SDZ NKT 343 and RPR100893 on plasma protein extravasation were measured in the FCA-treated knee joint of the guinea-pig. SDZ NKT 343 reversed plasma protein extravasation 2 h after administration by 60% at the oral dose of 30 mg kg(-1). RPR100893 was significantly less effective with a maximum reversal of 30% at 100 mg kg(-1). In comparison, indomethacin produced a 50% reversal at a 10 mg kg(-1) dose. These experiments indicate that the carrageenan-induced hyperalgesia in the guinea-pig may be predictive of analgesic activity of NK(1) receptor antagonists in man. NK(1) receptor antagonists are active anti-hyperalgesic drugs in both mechanical and thermal hyperalgesia in the guinea-pig. In addition they inhibit plasma protein extravasation in the same species. The variability of in vivo potency and efficacy of the NK(1) receptor antagonists in the mechanical hyperalgesia model is difficult to interpret as all compounds are highly effective at blocking the NK(1) receptor in guinea-pig tissues. Amongst several possibilities, differences in pharmacokinetics may explain discrepancies.

Substance P-induced airway hyperreactivity is mediated by neuronal M(2) receptor dysfunction

Neuronal muscarinic (M(2)) receptors inhibit release of acetylcholine from the vagus nerves. Hyperreactivity in antigen-challenged guinea pigs is due to blockade of these M(2) autoreceptors by eosinophil major basic protein (MBP) increasing the release of acetylcholine. In vivo, substance P-induced hyperactivity is vagally mediated. Because substance P induces eosinophil degranulation, we tested whether substance P-induced hyperreactivity is mediated by release of MBP and neuronal M(2) receptor dysfunction. Pathogen-free guinea pigs were anesthetized and ventilated. Thirty minutes after intravenous administration of [Sar(9),Met(O(2))(11)]- substance P, guinea pigs were hyperreactive to vagal stimulation and M(2) receptors were dysfunctional. The depletion of inflammatory cells with cyclophosphamide or the administration of an MBP antibody or a neurokinin-1 (NK(1)) receptor antagonist (SR-140333) all prevented substance P-induced M(2) dysfunction and hyperreactivity. Intravenous heparin acutely reversed M(2) receptor dysfunction and hyperreactivity. Thus substance P releases MBP from eosinophils resident in the lungs by stimulating NK(1) receptors. Substance P-induced hyperreactivity is mediated by blockade of inhibitory neuronal M(2) receptors by MBP, resulting in increased release of acetylcholine.

Effects of neurokinin receptor antagonists in virus-infected airways

We investigated the effects of a neurokinin-1 (NK(1)) receptor antagonist (SR-140333) and a NK(2) receptor antagonist (SR-48968) on airway responsiveness and on the function of neuronal M(2) muscarinic receptors, which normally inhibit vagal acetylcholine release, in guinea pigs infected with parainfluenza virus. Antagonists were given 1 h before infection and daily thereafter. Four days later, bronchoconstriction induced by either intravenous histamine (which is partly vagally mediated) or electrical stimulation of the vagus nerves was increased by viral infection compared with control. In addition, the ability of the muscarinic agonist pilocarpine to inhibit vagally induced bronchoconstriction was lost in virus-infected animals, demonstrating loss of neuronal M(2) receptor function. Macrophage influx into the lungs was inhibited by pretreatment with both antagonists. However, only the NK(1) receptor antagonist prevented M(2) receptor dysfunction and inhibited hyperresponsiveness (measured as an increase in either vagally induced or histamine-induced bronchoconstriction). Thus virus-induced M(2) receptor dysfunction and hyperresponsiveness are prevented by a NK(1) receptor antagonist, but not by a NK(2) receptor antagonist, whereas both antagonists had similar anti-inflammatory effects.

Lack of evidence for tachykinin NK1 receptor-mediated neutrophil accumulation in the rat cutaneous microvasculature by thermal injury

The effect of the non-peptide selective tachykinin NK1 receptor antagonist SR140333 has been investigated on oedema formation and neutrophil accumulation induced by thermal injury (50 degrees C for 5 min), mustard oil, substance P, the tachykinin NK1 agonist GR73632, and interleukin-1beta in the abdominal skin of the anaesthetised rat. SR140333 significantly inhibited (120 nmol/kg i.v.) or prevented (240 nmol/kg i.v.) the early oedema formation (0-10 min) induced by thermal injury. However, a dosing strategy which blocked NK1 receptors for 5 h (SR140333, 240 nmol/kg i.v. + 240 nmol/kg s.c.) failed to influence neutrophil accumulation measured 5 h after thermal injury. Thus, the neurogenic component mediated by NK1 receptors is important to elicit the early oedema formation, but does not influence subsequent neutrophil accumulation. Topical application of mustard oil (2%), a neurogenic inflammation stimulant, caused NK1 receptor-mediated early neurogenic plasma extravasation, but did not induce cutaneous neutrophil accumulation over 5 h. Substance P and GR73632 at high doses (1 nmol/site) also failed to elicit neutrophil accumulation. Neutrophil accumulation induced by interleukin-1beta (0.03-3 pmol i.d.) was not affected by SR140333 pretreatment. In conclusion, despite an early pronounced tachykinin NK1 receptor-dependent oedema response after thermal injury, the results suggest that subsequent neutrophil accumulation is not mediated by NK1 receptors. Furthermore, we have not obtained any evidence to suggest that either endogenous or exogenous tachykinins can directly induce neutrophil accumulation in the rat cutaneous microvasculature.

Gastric acid-evoked c-fos messenger RNA expression in rat brainstem is signaled by capsaicin-resistant vagal afferents

BACKGROUND & AIMS

Gastric acid is known to contribute to ulcer pain, but the mechanisms of gastric chemonociception are poorly understood. This study set out to investigate the pathways and mechanisms by which gastric acid challenge is signaled to the brain.

METHODS

Neuronal excitation in the rat brainstem and spinal cord after intragastric administration of HCl (0.35-0.7 mol/L) was examined by in situ hybridization autoradiography for the immediate early gene c-fos.

RESULTS

Gastric acid challenge did not induce c-fos transcription in the spinal cord but caused many neurons in the nucleus tractus solitarii and area postrema to express c-fos messenger RNA (mRNA). The HCl concentration-dependent excitation of medullary neurons was in part associated with behavioral manifestations of pain but not directly related to the acid-induced injury and contraction of the stomach. Subdiaphragmatic vagotomy suppressed the c-fos mRNA response to intragastric acid, and morphine inhibited it in a naloxone-reversible manner, whereas pretreatment of rats with capsaicin was without effect.

CONCLUSIONS

Gastric acid challenge is signaled to the brainstem, but not the spinal cord, through vagal afferents that are sensitive to acid but resistant to capsaicin. It is hypothesized that the gastric acid-induced c-fos transcription in the brainstem is related to gastric chemonociception.

Effects of tachykinin NK1 receptor antagonists on vagal hyperreactivity and neuronal M2 muscarinic receptor function in antigen challenged guinea-pigs

1. The role of tachykinin NK1 receptors in the recruitment of eosinophils to airway nerves, loss of inhibitory neuronal M2 muscarinic receptor function and the development of vagal hyperreactivity was tested in antigen-challenged guinea-pigs. 2. In anaesthetized guinea-pigs, the muscarinic agonist, pilocarpine (1-100 microg kg(-1), i.v.), inhibited vagally induced bronchoconstriction, in control, but not in antigen-challenged guinea-pigs 24 h after antigen challenge. This indicates normal function of neuronal M2 muscarinic receptors in controls and loss of neuronal M2 receptor function in challenged guinea-pigs. Pretreatment of sensitized guinea-pigs with the NK1 receptor antagonists CP99994 (4 mg kg(-1), i.p.), SR140333 (1 mg kg(-1), s.c.) or CP96345 (15 mg kg(-1), i.p.) before antigen challenge, prevented M2 receptor dysfunction. 3. Neither administration of the NK1 antagonists after antigen challenge, nor pretreatment with an NK2 receptor antagonist, MEN10376 (5 micromol kg(-1), i.p.), before antigen challenge, prevented M2 receptor dysfunction. 4. Electrical stimulation of the vagus nerves caused a frequency-dependent (2-15 Hz, 10 V, 0.2 ms for 5 s) bronchoconstriction that was significantly increased following antigen challenge. Pretreatment with the NK1 receptor antagonists CP99994 or SR140333 before challenge prevented this increase. 5. Histamine (1-20 nmol kg(-1), i.v.) caused a dose-dependent bronchoconstriction, which was vagally mediated, and was significantly increased in antigen challenged guinea-pigs compared to controls. Pretreatment of sensitized animals with CP99994 before challenge prevented the increase in histamine-induced reactivity. 6. Bronchoalveolar lavage and histological studies showed that after antigen challenge significant numbers of eosinophils accumulated in the airways and around airway nerves. This eosinophilia was not altered by pretreatment with the NK1 receptor antagonist CP99994. 7. These data indicate that pretreatment of antigen-sensitized guinea-pigs with NK1, but not with NK2 receptor antagonists before antigen challenge prevented the development of hyperreactivity by protecting neuronal M2 receptor function. NK1 receptor antagonists do not inhibit eosinophil accumulation around airway nerves.

Primary afferent tachykinins are required to experience moderate to intense pain

The excitatory neurotransmitter glutamate coexists with the peptide known as substance P in primary afferents that respond to painful stimulation. Because blockers of glutamate receptors reliably reduce pain behaviour, it is assumed that 'pain' messages are mediated by glutamate action on dorsal horn neurons. The contribution of substance P, however, is still unclear. We have now disrupted the mouse preprotachykinin A gene (PPT-A), which encodes substance P and a related tachykinin, neurokinin A. We find that although the behavioural response to mildly painful stimuli is intact in these mice, the response to moderate to intense pain is significantly reduced. Neurogenic inflammation, which results from peripheral release of substance P and neurokinin A, is almost absent in the mutant mice. We conclude that the release of tachykinins from primary afferent pain-sensing receptors (nociceptors) is required to produce moderate to intense pain.

The tachykinin NK1 receptor. Part II: Distribution and pathophysiological roles

The tachykinin NK1 receptor is widely distributed in both the central and peripheral nervous system. In the CNS, NK1 receptors have been implicated in various behavioural responses and in regulating neuronal survival and degeneration. Moreover, central NK1 receptors regulate cardiovascular and respiratory function and are involved in activating the emetic reflex. At the spinal cord level, NK1 receptors are activated during the synaptic transmission, especially in response to noxious stimuli applied at the receptive field of primary afferent neurons. Both neurophysiological and behavioural evidences support a role of spinal NK1 receptors in pain transmission. Spinal NK1 receptors also modulate autonomic reflexes, including the micturition reflex. In the peripheral nervous system, tachykinin NK1 receptors are widely expressed in the respiratory, genitourinary and gastrointestinal tracts and are also expressed by several types of inflammatory and immune cells. In the cardiovascular system, NK1 receptors mediate endothelium-dependent vasodilation and plasma protein extravasation. At respiratory level, NK1 receptors mediate neurogenic inflammation which is especially evident upon exposure of the airways to irritants. In the carotid body, NK1 receptors mediate the ventilatory response to hypoxia. In the gastrointestinal system, NK1 receptors mediate smooth muscle contraction, regulate water and ion secretion and mediate neuro-neuronal communication. In the genitourinary tract, NK1 receptors are widely distributed in the renal pelvis, ureter, urinary bladder and urethra and mediate smooth muscle contraction and inflammation in response to noxious stimuli. Based on the knowledge of distribution and pathophysiological roles of NK1 receptors, it has been anticipated that NK1 receptor antagonists may have several therapeutic applications at central and peripheral level. At central level, it is speculated that NK1 receptor antagonists could be used to produce analgesia, as antiemetics and for treatment of certain forms of urinary incontinence due to detrusor hyperreflexia. In the peripheral nervous system, tachykinin NK1 receptor antagonists could be used in several inflammatory diseases including arthritis, inflammatory bowel diseases and cystitis. Several potent tachykinin NK1 receptor antagonists are now under evaluation in the clinical setting, and more information on their usefulness in treatment of human diseases will be available in the next few years.

Plasma extravasation and neuropeptide release in human skin as measured by intradermal microdialysis

Time course of plasma extravasation in neurogenic inflammation elicited by histamine iontophoresis and topical capsaicin application was measured in vivo by a modified intradermal microdialysis technique in humans. Single linear plasmapheresis fibers were inserted intracutaneously at the volar forearm and perfused with Ringer's solution (4 microl/min) with one microdialysis fiber located at the planned stimulation site and a second inside the axon reflex area. Protein concentration in the dialysate increased by 300% in the histamine wheal but no increase was found in the surrounding flare area. There was no protein extravasation in the skin treated with capsaicin nor in the surrounding flare region. Inside the histamine-induced flare reaction a significant increase of calcitonin gene related peptide (CGRP) was found, whereas the increase of substance P (SP) was not significant.