Upregulation of extraneuronal TRPV1 expression in chronic rhinosinusitis with nasal polyps.

BACKGROUND: Chronic rhinosinusitis (CRS) is a multifactorial upper airway disease with unclear etiology. Neuronal Transient Receptor Potential Vanilloid 1 (TRPV1) and Ankyrin 1 (TRPA1) channels have been implicated in the pathogenesis of CRS. We aimed to detect the expression of extraneuronal TRPV1 and TRPA1 receptors in nasal polyp (NP) tissue samples. METHODOLOGY: Samples were obtained from fourty-two CRS pateints with nasal polyp and sixteen healthy controls to measure receptor gene expression by quantitative PCR, protein localization by immunohistochemistry and cytokine profile by multiplex bead immunoassay. RESULTS: Non-neuronal TRPV1, TRPA1 receptors were expressed in biopsy samples of NP. A population of mast cells and macrophages were immunopositive for TRPV1 and TRPA1. A fraction of plasma cells expressed TRPV1 but not TRPA1 and neither receptor was present on eosinophils. The local gene expression of extraneuronal TRPV1, TRPA1 receptors was also proven. TRPV1 mRNA levels were significantly increased in CRSwNP patients with asthma and allergic rhinitis compared to their NP counterparts. CONCLUSIONS: Elevated TRPV1 levels in comorbid asthma and allergy may have a function in CRSwNP. Subpopulation-specific TRPV1 presence on plasma and mast cells can indicate delicate roles in regulating activation and release of inflammatory mediators.

Marijuana smoke induces severe pulmonary hyperresponsiveness, inflammation, and emphysema in a predictive mouse model not via CB1 receptor activation.

Sporadic clinical reports suggested that marijuana smoking induces spontaneous pneumothorax, but no animal models were available to validate these observations and to study the underlying mechanisms. Therefore, we performed a systematic study in CD1 mice as a predictive animal model and assessed the pathophysiological alterations in response to 4-mo-long whole body marijuana smoke with integrative methodologies in comparison with tobacco smoke. Bronchial responsiveness was measured with unrestrained whole body plethysmography, cell profile in the bronchoalveolar lavage fluid with flow cytometry, myeloperoxidase activity with spectrophotometry, inflammatory cytokines with ELISA, and histopathological alterations with light microscopy. Daily marijuana inhalation evoked severe bronchial hyperreactivity after a week. Characteristic perivascular/peribronchial edema, atelectasis, apical emphysema, and neutrophil and macrophage infiltration developed after 1 mo of marijuana smoking; lymphocyte accumulation after 2 mo; macrophage-like giant cells, irregular or destroyed bronchial mucosa, goblet cell hyperplasia after 3 mo; and severe atelectasis, emphysema, obstructed or damaged bronchioles, and endothelial proliferation at 4 mo. Myeloperoxidase activity, inflammatory cell, and cytokine profile correlated with these changes. Airway hyperresponsiveness and inflammation were not altered in mice lacking the CB1 cannabinoid receptor. In comparison, tobacco smoke induced hyperresponsiveness after 2 mo and significantly later caused inflammatory cell infiltration/activation with only mild emphysema. We provide the first systematic and comparative experimental evidence that marijuana causes severe airway hyperresponsiveness, inflammation, tissue destruction, and emphysema, which are not mediated by the CB1 receptor.

Energetics of fasting heterothermia in TRPV1-KO and wild type mice.

To learn the possible role of TRPV1 in the changes of temperature regulation induced by short-term energy lack, TRPV1-KO and wild type mice were exposed to complete fasting for 2 or 3 days while their core temperature and locomotor activity were recorded using a biotelemetry method. In both types of mice, fasting led to progressive daytime hypothermia with night-time core temperature being maintained at normothermia (collectively called heterothermia). During fasting rises of locomotor activity were observed parallel to night-time normothermia with occasional increases of both parameters recorded every 2 to 3 hours (ultradian rhythms). The daytime fall of core temperature was significantly greater in wild type than in TRPV1-KO mice, in the former an advance of the temperature/activity rhythm having been observed in spite of the presence of a 12/12 hour light/darkness schedule. Re-feeding applied at the beginning of the light-period led to rapid reappearance of normothermia in both types of mice without a large increase in locomotor activity. It is concluded that the TRPV1-gene may have a role in the development of adaptive daytime hypothermia (and hence saving some energy) in mice during complete fasting but still allowing normothermia maintained at night, a strategy probably serving survival under natural conditions in small size rodents such as the mouse. The possible role of muscle thermogenesis either with or without gross bodily movement during fasting or on re-feeding, respectively, may be based on different mechanisms yet to be clarified.

Inhibitory action of endomorphin-1 on sensory neuropeptide release and neurogenic inflammation in rats and mice.

Substance P (SP) and calcitonin gene-related peptide (CGRP) released from capsaicin-sensitive sensory nerves induce local neurogenic inflammation in the innervated area. The aim of the present study was to investigate the effects of an endogenous opioid peptide, endomorphin-1, on sensory neuropeptide release in vitro and acute neurogenic and non-neurogenic inflammatory reactions in vivo. Electrical field stimulation (EFS; 40 V, 0.1 ms, 10 Hz, 120 s; 1200 impulses) was performed to evoke SP and CGRP release from peptidergic afferents of the isolated rat tracheae which was determined from the incubation medium with radioimmunoassay. Neurogenic inflammation in the skin of the acutely denervated rat hind paw was induced by topical application of 1% mustard oil and detected by Evans Blue leakage. Mustard oil-induced ear swelling of the mouse was determined with a micrometer during 3 h and myeloperoxidase activity as an indicator of granulocyte accumulation was measured with spectrophotometry at 6 h. EFS evoked about a twofold elevation in the release of both pro-inflammatory sensory neuropeptides. Endomorphin-1 (5 nM-2 microM) diminished the release of SP and CGRP in a concentration-dependent manner, the EC50 values were 39.45 nM and 10.84 nM, respectively. The maximal inhibitory action was about 80% in both cases. Administration of endomorphin-1 (1-100 microg/kg i.p.) dose-dependently inhibited mustard oil-evoked neurogenic plasma protein extravasation in the rat skin as determined by microg Evans Blue per g wet tissue. Repeated i.p. injections of the 10 microg/kg dose three times per day for 10 days did not induce desensitization in this model. Neurogenic swelling of the mouse ear was also dose-dependently diminished by 1-100 microg/kg i.p. endomorphin-1, but non-neurogenic neutrophil accumulation was not influenced. These results suggest that endomorphin-1 is able to inhibit the outflow of pro-inflammatory sensory neuropeptides. Based on this mechanism of action it is also able to effectively diminish neurogenic inflammatory responses in vivo.

Inhibitory effect of PACAP-38 on acute neurogenic and non-neurogenic inflammatory processes in the rat.

Inhibitory actions of pituitary adenylate cyclase activating polypeptide (PACAP) have been described on cellular/vascular inflammatory components, but there are few data concerning its role in neurogenic inflammation. In this study we measured PACAP-like immunoreactivity with radioimmunoassay in the rat plasma and showed a two-fold elevation in response to systemic stimulation of capsaicin-sensitive sensory nerves by resiniferatoxin, but not after local excitation of cutaneous afferents. Neurogenic plasma extravasation in the plantar skin induced by intraplantar capsaicin or resiniferatoxin, as well as carrageenan-induced paw edema were significantly diminished by intraperitoneal PACAP-38. In summary, these results demonstrate that PACAP is released from activated capsaicin-sensitive afferents into the systemic circulation. It diminishes acute pure neurogenic and mixed-type inflammatory reactions via inhibiting pro-inflammatory mediator release and/or by acting at post-junctional targets on the vascular endothelium.

Chronic stress-induced mechanical hyperalgesia is controlled by capsaicin-sensitive neurones in the mouse.

BACKGROUND: Clinical studies demonstrated peripheral nociceptor deficit in stress-related chronic pain states, such as fibromyalgia. The interactions of stress and nociceptive systems have special relevance in chronic pain, but the underlying mechanisms including the role of specific nociceptor populations remain unknown. We investigated the role of capsaicin-sensitive neurones in chronic stress-related nociceptive changes. METHOD: Capsaicin-sensitive neurones were desensitized by the capsaicin analogue resiniferatoxin (RTX) in CD1 mice. The effects of desensitization on chronic restraint stress (CRS)-induced responses were analysed using behavioural tests, chronic neuronal activity assessment in the central nervous system with FosB immunohistochemistry and peripheral cytokine concentration measurements. RESULTS: Chronic restraint stress induced mechanical and cold hypersensitivity and increased light preference in the light-dark box test. Open-field and tail suspension test activities were not altered. Adrenal weight increased, whereas thymus and body weights decreased in response to CRS. FosB immunopositivity increased in the insular cortex, dorsomedial hypothalamic and dorsal raphe nuclei, but not in the spinal cord dorsal horn after the CRS. CRS did not affect the cytokine concentrations of hindpaw tissues. Surprisingly, RTX pretreatment augmented stress-induced mechanical hyperalgesia, abolished light preference and selectively decreased the CRS-induced neuronal activation in the insular cortex. RTX pretreatment alone increased the basal noxious heat threshold without influencing the CRS-evoked cold hyperalgesia and augmented neuronal activation in the somatosensory cortex and interleukin-1α and RANTES production. CONCLUSIONS: Chronic restraint stress induces hyperalgesia without major anxiety, depression-like behaviour or peripheral inflammatory changes. Increased stress-induced mechanical hypersensitivity in RTX-pretreated mice is presumably mediated by central mechanisms including cortical plastic changes. SIGNIFICANCE: These are the first data demonstrating the complex interactions between capsaicin-sensitive neurones and chronic stress and their impact on nociception. Capsaicin-sensitive neurones are protective against stress-induced mechanical hyperalgesia by influencing neuronal plasticity in the brain.

Effect of pituitary adenylate cyclase activating polypeptide-38 on sensory neuropeptide release and neurogenic inflammation in rats and mice.

Substance P (SP) and calcitonin gene-related peptide (CGRP), released from capsaicin-sensitive sensory nerves induce local neurogenic inflammation, while somatostatin exerts systemic anti-inflammatory actions. The aim of the present study was to investigate the release of pituitary adenylate cyclase activating polypeptide-38 (PACAP-38) and its effects on sensory neuropeptide release in vitro and acute neurogenic ear swelling in vivo. Capsaicin (10(-6) M) or electrical field stimulation (EFS; 40 V, 0.1 ms, 10 Hz, 120 s; 1200 impulses)-induced release of PACAP-38, SP, CGRP and somatostatin from isolated rat tracheae was measured with radioimmunoassay. Mustard oil-induced neurogenic inflammation in the mouse ear was determined with a micrometer and in the rat hind paw skin by the Evans Blue leakage technique. Capsaicin and EFS evoked 27% and more than twofold elevation of PACAP-38 release respectively, compared with the prestimulated basal values from isolated trachea preparation. Exogenously administered PACAP-38 (20-2000 nM) diminished both capsaicin- and EFS-evoked sensory neuropeptide release in a concentration-dependent manner. The maximal inhibitory effects of PACAP on capsaicin-induced substance P, CGRP and somatostatin release amounted to 75.4%, 73.3% and 90.0%, while EFS-evoked release of these peptides was 80.03%, 87.7% and 67.7%. In case of capsaicin stimulation the EC50 values for substance P, CGRP and somatostatin were 82.9 nM, 60.1 nM and 66.9 nM, respectively. When EFS was performed, these corresponding EC50 data were 92.1 nM, 67.8 nM and 20.9 nM. PACAP-38 (10, 100 and 1000 microg/kg i.p. in 200 microl volume) inhibited neurogenic ear swelling in the mouse. Furthermore, 100 microg/kg i.p. PACAP also significantly diminished mustard oil-evoked plasma protein extravasation in the rat skin. These results suggest that PACAP-38 is released from the stimulated peripheral terminals of capsaicin-sensitive afferents and it is able to inhibit the outflow of sensory neuropeptides. Based on this mechanism of action PACAP is also able to effectively diminish/abolish neurogenic inflammatory response in vivo after systemic administration.

Relative roles of protein kinase A and protein kinase C in modulation of transient receptor potential vanilloid type 1 receptor responsiveness in rat sensory neurons in vitro and peripheral nociceptors in vivo.

The function of the transient receptor potential vanilloid type 1 capsaicin receptor is subject to modulation by phosphorylation catalyzed by various enzymes including protein kinase C and cAMP-dependent protein kinase. The aim of this study was to compare the significance of the basal and stimulated activity of protein kinase C and cAMP-dependent protein kinase in transient receptor potential vanilloid type 1 receptor responsiveness in the rat in vitro by measurement of the intracellular calcium concentration in cultured trigeminal ganglion neurons and in vivo by determination of the behavioral noxious heat threshold. KT5720, a selective inhibitor of cAMP-dependent protein kinase, reduced the calcium transients induced by capsaicin or the other, much more potent transient receptor potential vanilloid type 1 receptor agonist resiniferatoxin in trigeminal sensory neurons and diminished the drop of the noxious heat threshold (heat allodynia) evoked by intraplantar resiniferatoxin injection. Chelerythrine chloride, a selective inhibitor of protein kinase C, failed to alter either of these responses, although it inhibited the effect of phorbol 12-myristate 13-acetate in the in vitro assay. Staurosporine, a rather nonselective protein kinase inhibitor, failed to reduce the capsaicin- and resiniferatoxin-induced calcium transients but inhibited the resiniferatoxin-evoked heat allodynia. Dibutyryl-cAMP and phorbol 12-myristate 13-acetate, activator(s) of cAMP-dependent protein kinase and protein kinase C, respectively, enhanced the effect of capsaicin in the calcium uptake assay while forskolin, an activator of adenylyl cyclase, augmented that of resiniferatoxin in the heat allodynia model. None of the protein kinase inhibitors or activators altered the calcium transients evoked by high potassium, a nonspecific depolarizing stimulus. It is concluded that basal activity of cAMP-dependent protein kinase, unlike protein kinase C, is involved in the maintenance of transient receptor potential vanilloid type 1 receptor function in somata of trigeminal sensory neurons but stimulation of either cAMP-dependent protein kinase or protein kinase C above the resting level can lead to an enhanced transient receptor potential vanilloid type 1 receptor responsiveness. Similar mechanisms are likely to operate in vivo in peripheral terminals of nociceptive dorsal root ganglion neurons.

Effects of the somatostatin receptor subtype 4 selective agonist J-2156 on sensory neuropeptide release and inflammatory reactions in rodents.

BACKGROUND AND PURPOSE: Substance P (SP) and calcitonin gene-related peptide (CGRP) released from capsaicin-sensitive sensory nerves induce local neurogenic inflammation; somatostatin exerts systemic anti-inflammatory actions presumably via sst4/sst1 receptors. This study investigates the effects of a high affinity, sst4-selective, synthetic agonist, J-2156, on sensory neuropeptide release in vitro and inflammatory processes in vivo. EXPERIMENTAL APPROACH: Electrically-induced SP, CGRP and somatostatin release from isolated rat tracheae was measured with radioimmunoassay. Mustard oil-induced neurogenic inflammation in rat hindpaw skin was determined by Evans blue leakage and in the mouse ear with micrometry. Dextran-, carrageenan- or bradykinin-induced non-neurogenic inflammation was examined with plethysmometry or Evans blue, respectively. Adjuvant-induced chronic arthritis was assessed by plethysmometry and histological scoring. Granulocyte accumulation was determined with myeloperoxidase assay and IL-1beta with ELISA. KEY RESULTS: J-2156 (10-2000 nM) diminished electrically-evoked neuropeptide release in a concentration-dependent manner. EC50 for the inhibition of substance P, CGRP and somatostatin release were 11.6 nM, 14.3 nM and 110.7 nM, respectively. J-2156 (1-100 microg kg(-1) i.p.) significantly, but not dose-dependently, inhibited neurogenic and non-neurogenic acute inflammatory processes and adjuvant-induced chronic oedema and arthritic changes. Endotoxin-evoked myeloperoxidase activity and IL-1beta production in the lung, but not IL-1beta- or zymosan-induced leukocyte accumulation in the skin were significantly diminished by J-2156. CONCLUSIONS AND IMPLICATIONS: J-2156 acting on sst4 receptors inhibits neuropeptide release, vascular components of acute inflammatory processes, endotoxin-induced granulocyte accumulation and IL-1beta synthesis in the lung and synovial and inflammatory cells in chronic arthritis. Therefore it might be a promising lead for the development of novel anti-inflammatory drugs.

Sensory neuron-specific actions of capsaicin: mechanisms and applications.

Capsaicin acts specifically on a subset of primary afferent sensory neurons to open cation-selective ion channels, probably by interacting directly with a membrane receptor-ion channel complex. Another plant product--resiniferatoxin--has structural similarities to capsaicin and opens the same channels, but is up to 10,000 times as potent. Capsaicin-sensitive neurons are involved in nociception, are responsible for the neurogenic component of the inflammatory response and may also have efferent actions in the peripheral target tissues. In addition to its excitatory actions, capsaicin can have subsequent antinociceptive and anti-inflammatory effects. For these reasons Stuart Bevan and János Szolcsányi argue that drugs based on capsaicin and resiniferatoxin may have important clinical uses.

Plasma extravasation in the skin and pelvic organs evoked by antidromic stimulation of the lumbosacral dorsal roots of the rat.

Electrical stimulation of the distal stump of cut peripheral nerves is a commonly accepted way to evoke neurogenic inflammation. Nevertheless, the modulatory effect of biogenic amines and vasoactive peptides released from efferent fibres can be excluded only if the dorsal roots are stimulated. The present study was focussed to investigate plasma extravasation in the appropriate skin and mucosal areas as well as in the genito-urinary organs in response to antidromic stimulation of the lumbar and sacral dorsal roots of the rat. Plasma extravasation was detected by quantitative measurement of the accumulated Evans Blue tracer in tissue pieces. Two unilateral posterior roots were stimulated simultaneously (20 V, 0.5 ms, 5 Hz, 5 min) in each anaesthetized rat. Intensive blueing response occurred in the following tissues: plantar glabrous skin, L4-L5 (L6); dorsum of the hindpaw and ankle joint, L2-L4; ventral surface of the thigh, L2-L4 (L1); abdominal skin, L1-L4; caudal nipples, L1-L2; root of the tail, S1 orifice of the vagina, S1 (L6); vagina, L2-L3, L5-S1; cervix and corpus uteri, L2-L3, L5-S1; lower two-thirds of the uterine horns, L1-L3; urinary bladder, L1-L3, L6-S1; rectum, L5-S1; scrotum (dorsal surface and lower pole), L6-S1; scrotum (ventral surface), L3-L5. No significant dye accumulation was observed in the muscles, testicles, vas deferens and prostate. Plasma extravasation caused by antidromic activation of the dorsal roots was absent or highly reduced after systemic capsaicin pretreatment of the rats. Neurogenic inflammation evoked by antidromic stimulation of the dorsal roots makes this method suitable for mapping the organs where capsaicin-sensitive sensory nerve endings exert their "efferent functions". This first functional description of segmental innervation of capsaicin-sensitive afferent fibres is in agreement with retrograde tracing studies and immunohistochemical localization of substance P in the dorsal root ganglia and peripheral tissues.

Neonatal capsaicin treatment results in prolonged mitochondrial damage and delayed cell death of B cells in the rat trigeminal ganglia.

Capsaicin acts on the vanilloid receptor subtype 1, a noxious heat-gated cation channel located on a major subgroup of nociceptive primary afferent neurons. Following the systemic capsaicin treatment of neonatal rats, the loss of B-type sensory neurons in trigeminal ganglion of adult rats with chemoanalgesia and abolition of neurogenic inflammation was investigated. Our quantitative morphometric analysis revealed that in the trigeminal ganglion of neonatal rats treated with 50 mg/kg s.c. capsaicin, the total number of neurons, morphology of B-type cells and cell-size histograms did not differ from that of the controls 1 or 5 days after treatment. These observations indicate that early cell death does not play a significant part in the loss of B-type cells, which in our sample was 39.4% on the 19th day. However under the electron microscope pronounced selective mitochondrial swelling with disorganized cristae was observed in B-type neurons at 1-20 weeks after capsaicin treatment. Daily treatment with nerve growth factor (NGF, 10 x 100 microg/kg s.c.), started 1 day after capsaicin injection, prevented the loss of B-type cells but did not counteract the development of long-lasting mitochondrial damage. After NGF treatment, partial restitution of chemonociception to capsaicin instillation into the eye occurred but capsaicin-induced inhibition of neurogenic plasma extravasation in the hindpaw evoked by topical application of mustard oil remained unaltered. We conclude, that capsaicin treatment in neonatal rats, as in the adults, destroys terminal parts of the sensory neurons supplied by vanilloid receptors and induces long-lasting mitochondrial swelling in the soma. We hypothesize that loss of NGF uptake results in delayed cell death of B-type neurons in neonates.

Neonatal anandamide treatment results in prolonged mitochondrial damage in the vanilloid receptor type 1-immunoreactive B-type neurons of the rat trigeminal ganglion.

Capsaicin acting on the vanilloid type 1 receptor (VR1) excites a subset of primary sensory neurons. Systemic capsaicin treatment of adult or neonatal rats results in selective damage of the B-type neurons in the rat sensory ganglia by causing a long-lasting mitochondrial lesion that has been described in detail in previous studies. The endocannabinoid, anandamide, exhibits an agonist effect on VR1 receptors. The physiological role of anandamide as a VR1 agonist is still uncertain. This study addresses whether high doses of anandamide induce similar ultrastructural changes to those described for capsaicin. The effect of neonatally administered anandamide (1 mg/kg) on neurons of the trigeminal ganglia and the hippocampal formation was examined in the light and electron microscope from the first day after injections to the 20th week after treatment. Anandamide was found to cause mitochondrial damage of the B-type neurons of trigeminal ganglia similar to what has been described for capsaicin. The time course of damage was also comparable. In addition to the cells of the trigeminal ganglia, B-type cells of dorsal root ganglia were also damaged. A-type neurons and satellite glial cells were not affected either in the trigeminal or in the dorsal root ganglia. In the hippocampal formation, where a subpopulation of local circuit neurons is known to contain cannabinoid type 1 (CB1) but not VR1 receptors, anandamide did not cause morphological changes of mitochondria either in the dentate gyrus or in Ammon's horn. At 3 weeks of age, all VR1-immunoreactive neurons in the trigeminal ganglia of animals treated neonatally with anandamide displayed swollen mitochondria. The results suggest that anandamide, at pharmacologically relevant doses, acts on the VR1 receptor and causes prolonged and selective mitochondrial damage of B-type sensory neurons, as has previously been described for capsaicin.

Effect of intrathecal capsaicin analogues on the immunofluorescence of peptides and serotonin in the dorsal horn in rats.

The intrathecal administration of capsaicin, a homovanillylamide derivative, has been demonstrated to cause analgesia in response to thermal stimuli. This analgesia has been correlated with a profound depletion of spinal substance P, a putative primary afferent transmitter. We studied the effects of capsaicin, a series of capsaicin analogues, piperine and kainic acid on the immunohistochemical staining of substance P, cholecystokinin, somatostatin, methionine-enkephalin and serotonin. Capsaicin and an analogue 1-nonenoyl-vanillylamide significantly elevated the tail flick latency and when the spinal cords of the rats were analyzed immunohistochemically, a profound depletion of substance P and cholecystokinin was observed. The spinal somatostatin-immunoreactivity of these rats was slightly reduced. Piperine also depleted substance P and reduced somatostatin staining but did not alter the staining intensity or density of cholecystokinin, methionine-enkephalin or serotonin. Kainate-depleted methionine-enkephalin but did not alter any other neuropeptides studied or serotonin. These results may indicate a link between capsaicin-induced analgesia and the concomitant depletion of cholecystokinin and substance P.

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.

The mechanism of the motor response to periarterial nerve stimulation in the small intestine of the rabbit.

In the presence of guanethidine, periarterial nerve stimulation caused a frequency-dependent motor response in the rabbit isolated ileum. Tachyphylaxis to capsaicin greatly diminished the effect of periarterial stimulation; the remaining portion of the contractile response was susceptible to hexamethonium. The motor effect of periarterial stimulation is mediated by two different mechanisms: one via parasympathetic preganglionic nerves and the other sensitive to capsaicin.

Inhibition by nociceptin of neurogenic inflammation and the release of SP and CGRP from sensory nerve terminals.

Pretreatment with the novel neuropeptide nociceptin (20 micrograms kg-1, i.p.) caused an inhibition of plasma extravasation evoked by antidromic stimulation of the saphenous nerve or by topical application of 1% mustard oil on the skin of the acutely denervated hindleg of the rat. In contrast, it did not affect non-neurogenic inflammation evoked by s.c. injection of bradykinin after chronic denervation. Release of substance P (SP) and calcitonin gene-related peptide (CGRP) from rat isolated tracheae in response to electrical field stimulation was diminished by nociceptin (100 nM). It is concluded that nociceptin inhibits the release of sensory neuropeptides from terminals of nociceptive neurones.

Release of somatostatin and its role in the mediation of the anti-inflammatory effect induced by antidromic stimulation of sensory fibres of rat sciatic nerve.

1. The effect of antidromic stimulation of the sensory fibres of the sciatic nerve on inflammatory plasma extravasation in various tissues and on cutaneous vasodilatation elicited in distant parts of the body was investigated in rats pretreated with guanethidine (8 mg kg(-1), i.p.) and pipecuronium (200 microg kg(-1), i.v.). 2. Antidromic sciatic nerve stimulation with C-fibre strength (20 V, 0.5 ms) at 5 Hz for 5 min elicited neurogenic inflammation in the innervated area and inhibited by 50.3 +/- 4.67% the development of a subsequent plasma extravasation in response to similar stimulation of the contralateral sciatic nerve. Stimulation at 0.5 Hz for 1 h also evoked local plasma extravasation and inhibited the carrageenin-induced (1%, 100 microl s.c.) cutaneous inflammation by 38.5 +/- 10.0% in the contralateral paw. Excitation at 0.1 Hz for 4 h elicited no local plasma extravasation in the stimulated hindleg but still reduced the carrageenin-induced oedema by 52.1 +/- 9.7% in the paw on the contralateral side. 3. Plasma extravasation in the knee joint in response to carrageenin (2%, 200 microl intra-articular injection) was diminished by 46.1 +/- 12.69% and 40.9 +/- 4.93% when the sciatic nerve was stimulated in the contralateral leg at 0.5 Hz for 1 h or 0.1 Hz for 4 h, respectively. 4. Stimulation of the peripheral stump of the left vagal nerve (20 V, 1 ms, 8 Hz, 10 min) elicited plasma extravasation in the trachea, oesophagus and mediastinal connective tissue in rats pretreated with atropine (2 mg kg(-1), i.v.), guanethidine (8 mg kg(-1), i.p.) and pipecuronium (200 microg kg(-1), i.v.). These responses were inhibited by 37.8 +/- 5.1%, 49.7 +/- 9.9% and 37.6 +/- 4.2%, respectively by antidromic sciatic nerve excitation (5 Hz, 5 min) applied 5 min earlier. 5. Pretreatment with polyclonal somatostatin antiserum (0.5 ml/rat, i.v.) or the selective somatostatin depleting agent cysteamine (280 mg kg(-1), s.c.) prevented the anti-inflammatory effect of sciatic nerve stimulation (5 Hz, 5 min) on a subsequent neurogenic plasma extravasation of the contralateral paw skin. The inhibitory effect of antidromic sciatic nerve excitation on plasma extravasation in response to vagal nerve stimulation was also prevented by somatostatin antiserum pretreatment. 6. Cutaneous blood flow assessment by laser Doppler flowmetry indicated that antidromic vasodilatation induced by sciatic nerve stimulation was not inhibited by excitation of the sciatic nerve of the contralateral leg (1 Hz, 30 min) or by somatostatin (10 microg/rat, i.v.) injection. 7. Plasma levels of somatostatin increased more than 4 fold after stimulation of both sciatic nerves (5 Hz, 5 min) but the stimulus-evoked increase was not observed in cysteamine (280 mg kg(-1), s.c.) pretreated rats. 8. These results suggest that somatostatin released from the activated sensory nerve terminals mediates the systemic anti-inflammatory effect evoked by stimulating the peripheral stump of the sciatic nerve.

Systemic anti-inflammatory effect induced by counter-irritation through a local release of somatostatin from nociceptors.

1. Neurogenic plasma extravasation evoked by topical application of 1% vv(-1) mustard oil on the skin of the acutely denervated rat hindleg (primary reaction) inhibited the development of a subsequent oil-induced plasma extravasation induced in the skin of the contralateral hindleg by 49.3+/-7.06% (n=9) and in the conjunctival mucosa due to 0.1% wv(-1) capsaicin instillation by 33.5+/-10.05% (n=6). The primary reaction also inhibited the non-neurogenic hindpaw oedema evoked by s.c. injection of 5% wv(-1) dextran into the chronically denervated hindpaw by 48.0+/-4.6% (n= 5). 2. Capsaicin injection (100 microg ml(-1) in 50 microl, s.c.) into the acutely denervated hindleg caused 56.5+/-4.0% (n=5) inhibition in the intensity of plasma extravasation elicited by 1% vv(-1) mustard oil smearing on the contralateral side. After chronic denervation, subplantar injection of 5% wv(-1) dextran elicited a non-neurogenic inflammatory response with intensive tissue oedema without causing any systemic anti-inflammatory effect. Bilateral adrenalectomy did not inhibit the mustard oil-induced anti-inflammatory effect in the contralateral hindleg. 3. Pretreating the rats with polyclonal somatostatin antiserum (0.5 ml rat(-1), i.v.) or with the somatostatin depleting agent cysteamine (280 mg kg(-1), s.c.) prevented the inhibitory action of mustard oil-induced inflammation on subsequent neurogenic plasma extravasation and strongly diminished the inhibition of non-neurogenic oedema formation evoked by dextran. 4. Exogenous somatostatin (10 microg kg(-1), i.p.) caused a 30.3+/-8.3% (n=6) inhibition of plasma extravasation caused by mustard oil smearing on the acutely denervated hindleg and this inhibitory effect was abolished by somatostatin antiserum (0.5 ml rat(-1), i.v.). The plasma level of somatostatin-like immunoreactivity (SST-LI) increased by 40.03+/-6.8% (n= 6) 10 min after topical application of 1% vv(-1) mustard oil on the acutely denervated hindpaws compared to the paraffin oil treated control group. Chronic denervation of the hindlegs or cysteamine (280 mg kg(-1), s.c.) pretreatment prevented the mustard oil-induced elevation of SST-LI in plasma. 5. It is concluded that chemical excitation of the capsaicin-sensitive sensory receptors not only induces local neurogenic plasma extravasation but also inhibits the development of a subsequent inflammatory reaction at remote sites of the body in the rat. A role for somatostatin in this systemic anti-inflammatory effect is suggested.

Capsaicin-insensitive sensory-efferent meningeal vasodilatation evoked by electrical stimulation of trigeminal nerve fibres in the rat.

1. Antidromic vasodilatation and plasma extravasation to stimulation of the trigeminal ganglion or its perivascular meningeal fibres was investigated by laser-Doppler flowmetry and 125I-labelled bovin serum albumin in the dura mater and in exteroceptive areas (nasal mucosa, upper eyelid) of anaesthetized rats pretreated with guanethidine and pipecuronium. 2 Trigeminal stimulation at 5 Hz for 20 s elicited unilateral phasic vasodilatation in the dura and lasting response in the nasal mucosa. Resiniferatoxin (1-3 microg kg(-1) i.v.), topical (1%) or systemic capsaicin pretreatment (300 mg kg(-1) s.c. plus 1 mg kg(-1) i.v.) did not inhibit the meningeal responses but abolished or strongly inhibited the nasal responses. Administration of vinpocetine (3 mg kg(-1) i.v.) increased both basal blood flow and the dural vasodilatation to perivascular nerve stimulation. 3. Dural vasodilatation to trigeminal stimulation was not inhibited by the calcitonin gene-related peptide-1 receptor (CGRP-1) antagonist hCGRP8-37 (15 or 50 microg kg(-1) i.v), or the neurokinin-1 receptor antagonist RP 67580 (0.1 mg kg(-1) i.v.) although both antagonists inhibited the nasal response. Neither mucosal nor meningeal responses were inhibited by atropine (5 mg kg(-1) i.v.), hexamethonium (10 mg kg(-1) i.v.) or the vasoactive intestinal polypeptide (VIP) antagonist (p-chloro-D-Phe6-Leul7)VIP (20 microg kg(-1) i.v.). 4. Plasma extravasation in the dura and upper eyelid elicited by electrical stimulation of the trigeminal ganglion was almost completely abolished in rats pretreated with resiniferatoxin (3 microg kg(-1) i.v.). 5. It is concluded that in the rat meningeal vasodilatation evoked by stimulation of trigeminal fibres is mediated by capsaicin-insensitive primary afferents, while plasma extravasation in the dura and upper eyelid and the vasodilatation in the nasal mucosa are mediated by capsaicin-sensitive trigeminal fibres.