Substance P Content Research Articles

Substance P and Neurokinin 1 receptor - expression is affected in the ileum of mice with mutation in the W locus

The tachykinin substance P (SP) acts on the gut muscle coat via its preferred receptor, neurokinin 1 (NK1r). In the mouse ileum, NK1r-immunoreactivity (NK1r-IR) was detected in neurons, in the interstitial cells of Cajal at the deep muscular plexus (ICC-DMP) and the myoid cells of the villi. SP-IR was detected in neurons and varicose nerve fibers, which were especially numerous at the DMP and closely associated with the ICC-DMP. In mice with a mutation in the W locus (c-kit mutant animals), innervation is suggested to be normal although few studies have actually tested this hypothesis. Indeed, studies demonstrating ICC-DMP integrity are lacking and whether SP- and NK1r-IR are normal in these animals has not been investigated. Our aim was to perform an immunohistochemical study on the ileum of a strain of heterozygous mice with a mutation in the W locus, the We/+ mice, to test this hypothesis. SP-IR nerve fibers were significantly more numerous than in wild type mice; NK1r-IR was clustered on the plasma membrane and also intracytoplasmatic in the neurons, but absent in the ICC-DMP. The richness in SP-IR nerve fibers and the NK1r-IR distribution in the neurons, similar to that of activated cells, might be attempts to compensate for the SP preferred receptor absence at the ICC-DMP. In conclusion, SP content and NK1r expression are noticeably different in c-kit mutants with respect to wild type mice, and probably causing an anomalous tachykininergic control of intestinal motility. Physiological studies on W mutant mice have to take into account that innervation in this animal model is affected by the c-kit mutation.

Role of substance P in stress-derived degranulation of dermal mast cells in mice

The interaction between nerves and mast cells can effect regulation of the immune system and inflammatory responses. Recent studies have shown that various stressors can induce degranulation of dermal mast cells in animals. This study was conducted to confirm that substance P (SP) was involved in the degranulation of dermal mast cells in stress conditions. Using a communication box system, foot shock stress (FS) and psychological stress (PS) were administered to mice and the degranulation rate of dermal mast cells, the number of SP-positive nerve fibers and changes in SP content were determined. The inhibitory effect of a non-peptide NK1-receptor antagonist on these changes was investigated. Both FS and PS significantly enhanced the degranulation of dermal mast cells and increased the number of SP-positive nerve fibers. FS significantly decreased dermal SP content whereas SP was increased by PS. These changes were inhibited by intraperitoneal injection of NK(1) receptor antagonist. It was considered that SP released from the nerve ending, had an important role in the degranulation of dermal mast cells. Results of this study suggest that the tachykinin receptor antagonist exhibited an inhibitory effect on aggravated stress-induced dermatitis.

A study of neuropeptides related to headaches in children with meningeal irritation signs

Purpose : The headache, one of the symptoms of meningitis, is related to abrupt elevation of intracranial pressure(ICP) or stimulation of intracranial nociceptive structure. However, in cases of mild elevation of ICP or normal findings of cerebrospinal fluid(CSF) analysis, patients sometimes complain of headaches. Therefore, other pathways may contribute to the occurrence of headaches in aseptic meningitis or meningismus. We intend to investigate the role of substance P(SP) and calcitonin gene-related peptide(CGRP) in aseptic meningitis or meningismus. Methods : We measured leukocyte count, the concentration of protein and glucose in CSF and ICP of patients with meningeal irritation sign. We also measured SP and CGRP levels by using immunoassay. We analyzed the relationship between the presence of headache and the value of SP and CGRP. Results : The concentrations of CGRP(18.8±10.5 ng/mL) in CSF and ICP(14.8±4.5 cmH2O) in aseptic meningitis group were significantly higher than in those(14.1±7.4 ng/mL and 12.0±5.1 cmH2O, respectively) of the meningismus group(P<0.05). There was no significant difference in the SP levels between the two groups. In the aseptic meningitis group, the concentrations of SP and CGRP were significantly higher in the normal ICP group than in the elevated ICP group(P<0.05). Conclusion : Headaches in children with aseptic meningitis or meningismus is considered to be related to the elevation of the CSF levels of SP and CGRP. (Korean J Pediatr 2006;49:533-538)

The effect of neuropeptides on secretion of Interleukin-8 (IL-8)

We investigated the secretion of Interleukin-8 (IL-8) from ginviva and periodontal ligament stimulated with Substance P (SP) and Calcitonin Gene-related Peptide (CGRP). Gingiva (GF), periodontal ligament (PDLF) and pu)p (PF) tissues were collected from extracted intact 3rd molars. Cultured cells were stimulated with different concentrations of SP for 4 hrs, and stimulated with SP, CGRP and Tumor Necrosis Factor- (TNF-) for 8 hrs. Then RNase Protection Assay was carried out. ELISA was performed using supernatants of stimulated cells for quantitative analysis of IL-8. Results were assessed using student t-test with significance of P) and SP () compared with Mock stimulation in all type of cells studied. 3. IL-8 mRNA expression was not increased after stimulating 8 hrs with SP () and CGRP () compared with Mock stimulation in all type or cells studied. 4. TNF- (2 ng/ml) increased the expression of IL-8 mRNA in all kind of cells studied. 5. The secretion of IL-8 from GF was increased 8 hrs after the stimulation with CGRP ()(p)(p

The effect of CP96,345 on the expression of tachykinins and neurokinin receptors in acute pancreatitis

Acute pancreatitis (AP) is a life-threatening condition that involves an acute inflammatory process in the pancreas. The involvement of tachykinins and neurokinin receptors in acute pancreatitis has been described only recently, despite their long-established role in inflammatory conditions. Among these, substance P (SP) is believed to play a central role in exacerbating the inflammatory process by acting through neurokinin-1 receptor (NK1R). Treatment with the NK1R antagonist, CP96,345, results in protection against caerulein-induced acute pancreatitis in mice. However, the mechanism by which NK1R and SP worsen the condition is still unclear. In the present study, we have investigated the effect of NK1R blockage on the expression of preprotachykinin genes and neurokinin receptors in acute pancreatitis. In the pancreas, CP96,345 treatment resulted in suppression of the elevation of SP concentration, preprotachykinin-A gene (PPT-A) mRNA expression, and NK1R mRNA and protein expression. In the lungs, the antagonist was found to suppress the increase in SP concentration, PPT-A mRNA expression and preprotachykinin-C gene (PPT-C) mRNA expression. However, the antagonist treatment further promoted the accumulation of pulmonary NK1R mRNA and protein expression. Neurokinin-2 receptor (NK2R) mRNA expression was not detected in normal pancreas. However, up-regulated expression of the mRNA for this receptor was observed during acute pancreatitis and treatment with CP96,345 further increased this expression. Pulmonary NK2R mRNA expression was found to be reduced during acute pancreatitis and CP96,345 treatment normalized this reduction. Neurokinin-3 receptor (NK3R) mRNA expression was absent in both pancreas and lung. These data have provided valuable information regarding the regulation of tachykinins and neurokinin receptors during acute pancreatitis.

Increased substance P content in nerve fibers associated with mesenteric veins from deoxycorticosterone acetate (DOCA)-salt hypertensive rats

This study examined sensory nerves associated with mesenteric arteries and veins in sham and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Reactivity of arteries and veins to substances released from sensory nerves was also studied in vitro using computer-assisted video microscopy. Co-localization of substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactivity (ir) was used to evaluate perivascular sensory nerves. Radioimmunoassay was used to quantify SP-and CGRP-ir content. Immunohistochemical studies revealed a plexus of SP/CGRP-ir nerves associated with arteries and veins. The intensity of SP-ir, but not CGRP-ir labeling was greater in arteries and veins from DOCA-salt compared to sham rats. RIA measurements revealed that the CGRP-ir content of arteries and veins was higher than the SP-ir content but there was a significant increase in SP-ir, but not CGRP-ir, content in arteries and veins from DOCA-salt rats. SP (0.03–1 μM) contracted veins and the NK-3 receptor agonist, senktide, mimicked this effect. There were no differences in SP or senktide reactivity of veins from sham or DOCA-salt rats. SP, but not senktide, relaxed KCl (40 mM) preconstricted arteries. CGRP (0.3 μM), acetylcholine (10 μM) and capsaicin (1 μM) relaxed KCl-preconstricted arteries and veins. The NK-1 receptor agonist, substance P methyl ester relaxed arteries but not veins. These data indicate that DOCA-salt hypertension is associated with upregulation of SP content in perivascular nerves. NK-3 receptors mediate venoconstriction which is unchanged in DOCA-salt hypertension. Increased release of SP from perivenous nerves might contribute to the increased venomotor tone in DOCA-salt hypertension.

CD26 modulates nociception in mice via its dipeptidyl-peptidase IV activity

Background CD26 is a multifunctional cell surface glycoprotein expressed by T and B cells. It exhibits a dipeptidyl-peptidase activity (DPP-IV) that cleaves the penultimate proline from the N-terminus of polypeptides, thereby regulating their activity and concentration. Methods Using CD26−/− mice resulting from targeted inactivation of the gene, we examined the consequences of a DPP-IV defect on behavioural response to nociceptive stimuli and concentration of the pain modulator peptides substance P (SP) and endomorphin 2, two DPP-IV substrates. Results CD26 inactivation induced a three-fold decrease in circulating endopeptidase activity while that found in brain extracts was normal, albeit very weak. CD26−/− mice had high SP concentrations in plasma (3.4 ± 1 pg/ml versus 1.5 ± 0.3 pg/ml, P < 10 −3) but not in brain extracts (35 ± 12 pg/ml versus 32 ± 9 pg/ml, P > 0.05). Endomorphin-2 levels in the two groups were in the same range for plasma and brain extracts. CD26−/− mice displayed short latencies to nociceptive stimuli (hot plate test: 6.6 ± 1.2 s versus 8.6 ± 1.5 s, P < 10 −4; tail pinch test: 3.1 ± 0.6 s versus 4.2 ± 0.8 s, P < 10 −3). Administration of an SP (NK1) receptor antagonist or DPP-IV to CD26−/− mice normalised latencies. DPP-IV inhibitors decreased latencies only in CD26+/+ mice. Conclusions Our observations represent the first fundamental evidence showing that DPP-IV influences pain perception via modulation of the peripheral SP concentration. Our work also highlights the role of peripheral NK1 receptors in nociception.

Changes of the neuropeptides content and gene expression in spinal cord and dorsal root ganglion after noxious colorectal distension

Visceral pain/hypersensitivity is a cardinal symptom of functional gastrointestinal disorders. With their peripheral and central (spinal) projections, sensory neurons in the dorsal root ganglia (DRG) are the “gateway” for painful signals emanating from both somatic and visceral structures. In contrast to somatic pain, the neurochemical pathways involved in visceral pain/hypersensitivity have not been well studied. We hypothesized the neuropeptide changes in spinal cord and DRG during visceral pain would mirror similar changes in somatic nociception. Noxious (painful) colorectal distension (CRD) was done by distending a rectal balloon up to 60 mm Hg phasically for 1 h in Sprague–Dawley rats. The spinal content of calcitonin gene-related peptide (CGRP), substance P (SP), galanin and vasoactive intestinal peptide (VIP) as well as their mRNAs in DRG were measured at 0, 4 and 24 h after the CRD. Visceromotor reflex (VMR) was measured by recording the electromyogram at the abdominal muscle in response to CRD. Distal colorectum was removed for evaluating the presence of inflammation. No significant evidence of histological inflammation was seen in the colonic mucosa/submucosa after repeated CRD, which is confirmed by myeloperoxidase assay. The spinal content of CGRP and SP decreased significantly 4 h after CRD, while galanin and VIP levels increased gradually and reached highest level at 24 h ( p < 0.05). The mRNAs in DRG of the neuropeptides were significantly upregulated after CRD ( p < 0.05). VMR recording showed the rat's colon became hypersensitive 4 h after CRD, a sequence parallel to the spinal changes of CGRP and SP in timeframe. Noxious mechanical distension of the colorectum causes an acute change in the spinal levels of excitatory neurotransmitters (CGRP and SP), probably reflecting central release of these peptides from sensory neurons and contributing to the hypersensitivity following the noxious CRD. This is followed by a slower change in the levels of the inhibitory neurotransmitter galanin and VIP. Such stimulation results in significant alternation of the gene expression in DRG, reflecting the plasticity of the neuronal response. In the absence of visceral inflammation, the aforementioned neuropeptides are important mediators in the processing of visceral pain/hypersensitivity.

Substance P in serum and cerebrospinal fluid of depressed patients: No effect of antidepressant treatment

The neuropeptide substance P (SP) and its receptor, the neurokinin receptor-1 (NK-1), have been associated with some aspects of the pathophysiology of depression. There is limited information available about the effects of antidepressant treatment on serum and cerebrospinal fluid (CSF) concentrations of SP. We measured serum levels of SP in 78 depressed patients after a 6-day medication washout period, as well as after 14 and 35 days of antidepressant treatment with either paroxetine or amitriptyline. In 11 patients, SP was determined in CSF both before and after treatment. Eleven healthy male subjects served as controls. Baseline SP concentrations were independent of age, gender and severity of depression. Neither the total group nor subgroups showed significant differences in SP serum concentrations. SP concentrations in CSF did not change significantly in the patients during treatment, but there was a trend for an increase in paroxetine-treated patients. Serum SP concentrations were not related to treatment response or the class of antidepressant administered. Our data do not support the hypothesis that changes in SP levels in serum or CSF are related to antidepressant response.

Gastric Perception Thresholds Are Low and Sensory Neuropeptide Levels High in Helicobacter pylori-Positive Functional Dyspepsia

Background and Aims: In functional dyspepsia (FD) decreased perception levels can be shown on gastric distension. Substance P (SP) and calcitonin gene-related peptide (CGRP) are involved in the sensitization of afferent neuronal pathways due to chronic inflammation. The role of Helicobacter pylori-induced gastric mucosal inflammation in the pathogenesis of FD is controversial. The aim of this study was to assess whether FD patients have altered mucosal concentrations of CGRP and SP, and to investigate whether this is associated with visceral hypersensitivity or H. pylori infection. Methods: Gastrointestinal symptoms, H. pylori status, perception thresholds at gastric balloon distension, and gastric mucosal concentrations of CGRP and SP were determined in 13 FD patients and 18 healthy controls (HC). Results: In H. pylori-positive FD patients discomfort and pain thresholds on gastric distension were lower compared to other groups. Antral mucosal levels of CGRP and SP were higher in H. pylori-positive subjects. In FD significantly negative correlations between discomfort and pain thresholds and antral mucosal concentrations of CGRP and SP were observed. Conclusions: In FD low perception thresholds on gastric distension are associated with high levels of CGRP and SP in the antrum, suggesting that sensory neuropeptides are involved in FD pathophysiology.

Substance P Receptor Antagonists in Psychiatry

Increasing evidence suggests that substance P (SP) and its receptor (neurokinin [NK]-1 receptor [NK1R]) might play an important role in the modulation of stress-related, affective and/or anxious behaviour. First, SP and NK1R are expressed in brain regions that are involved in stress, fear and affective response (e.g. amygdala, hippocampus, hypothalamus and frontal cortex). Second, the SP content in these areas changes upon application of stressful stimuli. Third, the central administration of SP produces a range of fear-related behaviours. In addition, the SP/NK1R system shows significant spatial overlap with neurotransmitters such as serotonin and noradrenaline (norepinephrine), which are known to be involved in the regulation of stress, mood and anxiety. Therefore, it was hypothesised that blockade of the NK1R might have anxiolytic as well as antidepressant effects. Preclinical studies investigating the effects of genetic or pharmacological NK1R inactivation on animal behaviour in assays relevant to depression and anxiety revealed that the behavioural changes resemble those seen with reference antidepressant or anxiolytic drugs. Furthermore, antagonism or genetic inactivation of the NK1R causes alterations in serotonin and norepinephrine neuronal transmission that are likely to contribute to the antidepressant/anxiolytic activity of NK1R antagonists but that are--at least partially--distinct from those produced by established antidepressant drugs. This underlines the conceivable unique mechanism of action of this new class of compounds. In three independent clinical trials with three different compounds (aprepitant [MK-869], L-759274 and CP-122721), an antidepressant effect of NK1R antagonists could be demonstrated. These results, however, have been challenged by recent failed studies with aprepitant. There are numerous indications from preclinical studies that, in addition to SP and NK1R, other neurokinins and/or neurokinin receptors might also be involved in the modulation of stress-related behaviour and that exclusive blockade of the NK1R might not be sufficient to produce consistent anxiolytic and antidepressant effects. One such candidate is the neurokinin-2 receptor (NK2R), and clinical trials to assess the antidepressant effects of NK2R antagonists are currently underway. Of special interest might also be substances that block more than one receptor type such as NK1/2R antagonists or NK1/2/3R antagonists. These compounds may be more efficacious in antagonising the effects of SP than compounds that only block the NK1R.

Levels of gastrin-releasing peptide and substance P in synovial fluid and serum correlate with levels of cytokines in rheumatoid arthritis

It is well known that cytokines are highly involved in the disease process of rheumatoid arthritis (RA). Recently, targeting of neuropeptides has been suggested to have potential therapeutic effects in RA. The aim of this study was to investigate possible interrelations between five neuropeptides (bombesin/gastrin-releasing peptide (BN/GRP), substance P (SP), vasoactive intestinal peptide, calcitonin-gene-related peptide, and neuropeptide Y) and the three cytokines tumour necrosis factor (TNF)-α, IL-6, and monocyte chemoattractant protein-1 in synovial fluid of patients with RA. We also investigated possible interrelations between these neuropeptides and soluble TNF receptor 1 in serum from RA patients. Synovial fluid and sera were collected and assayed with ELISA or RIA. The most interesting findings were correlations between BN/GRP and SP and the cytokines. Thus, in synovial fluid, the concentrations of BN/GRP and SP grouped together with IL-6, and SP also grouped together with TNF-α and monocyte chemoattractant protein-1. BN/GRP and SP concentrations in synovial fluid also grouped together with the erythrocyte sedimentation rate. In the sera, BN/GRP concentrations and soluble TNF receptor 1 concentrations were correlated. These results are of interest because blocking of SP effects has long been discussed in relation to RA treatment and because BN/GRP is known to have trophic and growth-promoting effects and to play a role in inflammation and wound healing. Furthermore, the observations strengthen a suggestion that combination treatment with agents interfering with neuropeptides and cytokines would be efficacious in the treatment of RA. In conclusion, BN/GRP and SP are involved together with cytokines in the neuroimmunomodulation that occurs in the arthritic joint.

Age-related changes in the oestrous cycle and reproductive hormones in senescence-accelerated mouse

To investigate age-related changes in the oestrous cycle and reproductive hormone levels in senescence-accelerated mouse (SAM), we examined these parameters in 3-, 5-, 7-, 9- and 11-month-old female SAM-prone/8 (SAMP8) and SAM-resistant/1 (SAMR1) strains. Levels of beta-endorphin (beta-EP) and substance P (SP) in the hypothalamus were also measured. The oestrous cycle and dioestrus of 9-month-old SAMP8 mice were significantly prolonged compared with age-matched SAMR1 mice. Furthermore, the concentration of serum oestradiol was lower and the level of pituitary luteinising hormone was higher in SAMP8 mice compared with SAMR1 mice. This characterises the hypothalamus-pituitary-ovary (HPO) axis of the SAMP8 strain as hypergonadotropic-hypogonad. The levels of beta-EP and SP in the SAMP8 hypothalamus were lower than in the SAMR1 hypothalamus. These results indicate that the function of the HPO axis in SAMP8 mice declines early and this may be attributed, in part, to the decline in beta-EP and SP concentrations in the hypothalamus.

Increase in sensory neuropeptides surrounding the Achilles tendon in rats with adjuvant arthritis

The Achilles tendon in rats with adjuvant arthritis was analyzed by radioimmunoassay (RIA) and semi-quantitative immunohistochemistry for the occurrence of two sensory neuropeptides, substance P (SP) and calcitonin gene related peptide (CGRP), and a sensory modulating peptide, galanin (GAL). The tissue concentration of SP and CGRP in the Achilles tendon and its envelope, i.e. the paratenon and bony insertion, as assessed by RIA was increased by 22% and 71%, respectively, compared to normal controls, whereas the level of GAL was unchanged. Semi-quantitative immunohistochemistry applied to different regions of the tendon in arthritic rats disclosed an increased occurrence of SP and CGRP positive nerve fibers in the paratenon and bone tendinous junction, whereas GAL fibers were only increased at the bone tendinous junction. Notably, neither neuropeptides nor inflammatory cells were seen in the tendon proper. The increased occurrence of SP and CGRP in the tendon envelope presumably reflects inflammatory actions, whereas that of GAL implies an endogenous anti-inflammatory response. The observed SP and CGRP upregulation in the paratenon and bony insertion suggests a pathophysiological role in paratenonitis and enthesitis often seen in patients with rheumatoid arthritis. Presumably Achillodynia originates in the tendon envelope rather than the tendon proper. The observations could be used to define new pharmacological targets for mitigating symptoms from tendons in rheumatoid arthritis and possibly also in other disorders. Whether a neuronal pathogenic mechanism underlies tendon overuse disorders in non-arthritic tendinopathies and the development of degeneration, i.e. tendinosis, remains to be studied.

Depletion of mucosal substance P in acute otitis media

ObjectiveThe neuropeptide substance P (SP) is an inducer of neurogenic inflammation and bone resorption in the middle ear. Resorption of the bone tissue structures surrounding the middle ear cavity is a distinct feature of the initial stage of acute otitis media (AOM), which may be due to nerve fiber release of SP.Material and methodsTo investigate possible release of SP in the middle ear mucosa during AOM, we used a well-established rat model of AOM caused by Streptococcus pneumoniae. Following tissue extraction on Days 1, 3 and 6 post-inoculation, the mucosal concentration of SP was measured using a radioimmunoassay.ResultsCompared to sham-inoculated control ears, the concentration of SP was significantly reduced on Day 1 and even further reduced on Day 3, whereas partial replenishment was found on Day 6.ConclusionSP seems to be depleted in the rat middle ear mucosa in the hyperacute phase of AOM. This depletion is followed by replenishment and the concentration of SP approaches its normal level 6 days post-inoculation. The release of SP may be the trigger of the concurrent bone resorption and may further augment the inflammatory response to the bacterial colonization.

Influence of maternal pineal gland on the developmental pattern of neurokinin A (NKA) and substance P (SP) in male-rat-offspring: relationship to the season of the year

The present study examines the influence of maternal pineal gland on the frontal cortex, striatal and testicular concentrations of the tachykinins, neurokinin A (NKA) and substance P (SP). Control, pinealectomized (PIN-X) and PIN-X plus melatonin-treated (PIN-X + MEL) mother rats were prepared. Male offspring rats were studied at 21, 31 and 60 days of age, during the four seasons of the year. In control-offspring tachykinin concentrations in frontal cortex were found at their highest levels in 21-day-old rats with a moderate decrease up to 60 days of age. This developmental pattern was season-dependent, observed only during summer and fall. Maternal PIN-X or PIN-X + MEL resulted in alterations in the offspring, showing during spring and summer significantly higher concentrations ( P < 0.01) and during fall significantly lower concentrations of tachykinins in the frontal cortex ( P < 0.05, P < 0.01) as compared to control-offspring. The tachykinin concentration in the striatum of control-offspring showed no major modifications throughout the ages studied in the four seasons of the year. With very few exceptions, PIN-X- and PIN-X + MEL did not alter tachykinin concentrations in striatum. Testicular SP concentrations showed a decrease from 21 to 60 days of age. PIN-X or PIN-X + MEL only caused minor and inconsistent modifications in testicular SP levels. In conclusion, our data clearly indicate for the first time that the maternal pineal gland participates in the regulation of the postnatal tachykinin development in some areas of the central nervous system. This effect was more evident in the frontal cortex than in the striatum and testes.

Capsaicin-evoked substance P release in rat dorsal horn increases after peripheral inflammation: a microdialysis study

Numerous in vitro studies suggest that inflammation is associated with enhanced release of substance P (SP) in the dorsal horn. To test the hypothesis that inflammation increases the evoked concentration of SP in the intact animal, we used in vivo microdialysis with a highly sensitive radioimmunoassay to monitor SP-like immunoreactivity (SP-LI) in the dorsal horn. Seven days after the induction of persistent unilateral inflammation with hindpaw injection of complete Freund’s adjuvant, perfusion of the microdialysis probe with 10 μM capsaicin (a concentration which failed to induce SP-LI release in rats without inflammation) induced a significant increase of microdialysate SP-LI. Inclusion of an NMDA antagonist in the perfusion fluid completely blocked this capsaicin-evoked SP release. Administration of a five-fold higher dose of capsaicin did not further increase SP release. These results in a rat model of chronic arthritis suggest that persistent inflammatory signaling facilitates capsaicin-evoked SP release in the dorsal horn in vivo.

Greater Involvement of Neurokinins Found in Guinea Pig Models of Severe Asthma Compared with Mild Asthma

Background: Involvement of neurokinins in asthma has been previously pointed out by several reports. However, the relationship between neurokinins and the severity of asthma has remained unclear. We developed a model of mild asthma (model I) and severe asthma (model II) in guinea pigs, and investigated the function of neurokinins in both models. Methods: In models I and II, systemically sensitized guinea pigs were made to inhale ovalbumin once and three times, respectively. Substance P (SP) and neurokinin A (NKA) concentrations in the bronchoalveolar lavage fluid (BALF) were measured in models I and II. Then, the effects of a capsaicin pretreatment, which depletes neurokinins, in both animal models on airway narrowing induced by the last ovalbumin inhalation, airway hyperresponsiveness to inhaled methacholine, and eosinophil accumulation in BALF, were investigated. Results: SP concentration tended to increase and the NKA concentration increased significantly in model II, but not in model I. Capsaicin pretreatment significantly inhibited the late bronchial response that was observed 2–6 h after the last ovalbumin inhalation, airway hyperresponsiveness and eosinophil accumulation in model II. On the other hand, it had no effects on the responses in model I. Conclusion: It is suggested that the more severe the disease, the greater the involvement of neurokinins.

Recycling and Resensitization of the Neurokinin 1 Receptor: INFLUENCE OF AGONIST CONCENTRATION AND Rab GTPASES

Substance P (SP) induces endocytosis and recycling of the neurokinin 1 receptor (NK1R) in endothelial cells and spinal neurons at sites of inflammation and pain, and it is thus important to understand the mechanism and function of receptor trafficking. We investigated how the SP concentration affects NK1R trafficking and determined the role of Rab GTPases in trafficking. NK1R trafficking was markedly influenced by the SP concentration. High SP (10 nM) induced translocation of the NK1R and beta-arrestin 1 to perinuclear sorting endosomes containing Rab5a, where NK1R remained for >60 min. Low SP (1 nM) induced translocation of the NK1R to early endosomes located immediately beneath the plasma membrane that also contained Rab5a and beta-arrestin 1, followed by rapid recycling of the NK1R. Overexpression of Rab5a promoted NK1R translocation to perinuclear sorting endosomes, whereas the GTP binding-deficient mutant Rab5aS34N caused retention of the NK1R in superficial early endosomes. NK1R translocated from superficial early endosomes to recycling endosomes containing Rab4a and Rab11a, and Rab11aS25N inhibited NK1R recycling. Rapid NK1R recycling coincided with resensitization of SP-induced Ca2+ mobilization and with the return of surface SP binding sites. Resensitization was minimally affected by inhibition of vacuolar H(+)-ATPase and phosphatases but was markedly suppressed by disruption of Rab4a and Rab11a. Thus, whereas beta-arrestins mediate NK1R endocytosis, Rab5a regulates translocation between early and sorting endosomes, and Rab4a and Rab11a regulate trafficking through recycling endosomes. We have thus identified a new function of Rab5a as a control protein for directing concentration-dependent trafficking of the NK1R into different intracellular compartments and obtained evidence that Rab4a and Rab11a contribute to G-protein-coupled receptor recycling from early endosomes.

Study of visceral hypersensitivity in irritable bowel syndrome

Visceral hypersensitivity is highly prevalent in most functional bowel disorders, such as irritable bowel syndrome (IBS), and activation of intestinal mast cells (MC) may play a role because they have been found in close proximity to gastrointestinal mucosal sensory nerve terminals containing neuropeptides and a bi-directional pathway connecting the central nervous system, gut, and MC has been demonstrated. The current study appraised the status of rectal visceral perception, as well as the changes in the MC and substance P (SP) in the intestinal mucosa of patients with IBS. The study group comprised 42 patients with IBS and 19 healthy subjects who underwent anorectal manometry and rectal perception thresholds to balloon distension. The MC and the SP-ergic terminals in the mucosa were stained for respective histochemical and immunohistochemical investigations. The results were presented both qualitatively and quantitatively by color image analyzer, based on analysis of the intensity and area of stained fibrils. The structural relationship between the MC and nerve terminals was studied by electron microscopy, using an in situ embedding technique. The anorectal resting pressure, squeezing pressure and relaxation pressure were normal in both groups. The sensation threshold, defecation threshold and pain threshold in diarrhea-predominant IBS and the pain thresholds in constipation-predominant IBS were much lower than in the controls. Rectal compliance decreased in IBS. The number of MC in the terminal ileum, the ileocecal junction and the ascending colon was significantly elevated in IBS (P < 0.01), and the MC showed great variation. A significantly increased concentration of SP was found in the colon of the IBS patients compared with the controls. There was a positive correlation between the profiles of mucosal MC and the SP-ergic terminals, and MC were closely adjacent to SP-ergic terminals in the lamina propria. As altered rectal perception is present in almost all patients with IBS, it might be a reliable biological characteristic of the disease. Alterations in the MC and SP of the intestinal mucosa may be important factors in visceral hypersensitivity.