Capsaicin-sensitive Sensory Neurons Research Articles

The role of capsaicin-sensitive sensory neurons in autonomic dysreflexia in the spinal cord injured-rat

Background: A subpopulation of sensory neurons express the transient receptor potential cation channel subfamily V member 1 (TRPV1). It is activated by heat (>43°C), low pH, and capsaicin (the pungent ingredient in hot chili peppers), and has emerged as a promising target for the treatment of pain. Both pain and autonomic dysreflexia that develop in the wake of SCI have been attributed to maladaptive sensory plasticity. We hypothesize that TRPV-1-positive afferents contribute to the development of autonomic dysreflexia (AD).

Impact of Obesity on Ulcerative Colitis Phenotype

induced intestinal lesions were examined in rats. The role of intestinal motility, capsaicinsensitive sensory neurons (CSSNs) and nitric oxide (NO) in the effects of the drugs was also examined. METHODS: Male Wistar rats were treated with IND (10 mg/kg, p.o.) after a 16 h-fast (for gastric ulcers) or without fasting (for intestinal ulcers). The animals were autopsied 24 h after IND administration, and the stomach and small intestine were examined for lesions. Intestinal motility was measured using a balloon method in anesthetized rats. RESULTS: 1. Gastric lesions: IND produced many linear lesions in the corpus mucosa, and the lesion index (LI, total length) in the vehicle-treated group was 25.6±5.3 mm (n=7). The LI was significantly (P<0.05) decreased by pretreatment with oral doses (mg/kg) of CIM (100), RAN (30), FAM (10), OPZ (30), LPZ (30) and RPZ (30). 2. Small intestinal lesions: IND produced many lesions in the middle and lower parts of the small intestine. The LI in the vehicle-treated group was 57.0±10.0 mm (n=10). (a) Effects of H2-RAs: CIM, RAN and FAM increased the LI by 94% (P<0.01), 82% (P<0.01), and 68% (P<0.05), respectively. H2-RAs (3-30, i.v.) did not directly affect intestinal motility, but they did increase the motility induced by IND (10, s.c.). (b) Effects of PPIs: OPZ (100) and RPZ (100) significantly (P<0.05) increased the LI by 48% and 33%, respectively, whereas LPZ (30) significantly (P<0.01) decreased the LI by 61%. The inhibitory effect of LPZ was abolished by functional ablation of CSSNs (20, 30 and 50 mg/kg of capsaicin was administered s.c. for 3 consecutive days 2 weeks before the experiment) or pretreatment with L-NAME (a NO synthase inhibitor). CONCLUSIONS: Though H2-RAs and PPIs markedly inhibited the formation of gastric lesions induced by IND, they (except for LPZ) increased the formation of small intestinal lesions. The results suggest that antisecretory drugs aggravate intestinal lesions induced by NSAIDs, probably by increasing the amount of indigestive foods in the intestine and by increasing intestinal motility. LPZ, though having a potent antisecretory action, inhibited the formation of intestinal lesions, and this action can be explained by its protective action on the mucosa via CSSNs and NO.

Dietary Long Chain Triglycerides Protect Against Oral Sensitization to Peanut Protein and Promote Oral Tolerance in Mice in a Chylomicron-Dependent Manner

induced intestinal lesions were examined in rats. The role of intestinal motility, capsaicinsensitive sensory neurons (CSSNs) and nitric oxide (NO) in the effects of the drugs was also examined. METHODS: Male Wistar rats were treated with IND (10 mg/kg, p.o.) after a 16 h-fast (for gastric ulcers) or without fasting (for intestinal ulcers). The animals were autopsied 24 h after IND administration, and the stomach and small intestine were examined for lesions. Intestinal motility was measured using a balloon method in anesthetized rats. RESULTS: 1. Gastric lesions: IND produced many linear lesions in the corpus mucosa, and the lesion index (LI, total length) in the vehicle-treated group was 25.6±5.3 mm (n=7). The LI was significantly (P<0.05) decreased by pretreatment with oral doses (mg/kg) of CIM (100), RAN (30), FAM (10), OPZ (30), LPZ (30) and RPZ (30). 2. Small intestinal lesions: IND produced many lesions in the middle and lower parts of the small intestine. The LI in the vehicle-treated group was 57.0±10.0 mm (n=10). (a) Effects of H2-RAs: CIM, RAN and FAM increased the LI by 94% (P<0.01), 82% (P<0.01), and 68% (P<0.05), respectively. H2-RAs (3-30, i.v.) did not directly affect intestinal motility, but they did increase the motility induced by IND (10, s.c.). (b) Effects of PPIs: OPZ (100) and RPZ (100) significantly (P<0.05) increased the LI by 48% and 33%, respectively, whereas LPZ (30) significantly (P<0.01) decreased the LI by 61%. The inhibitory effect of LPZ was abolished by functional ablation of CSSNs (20, 30 and 50 mg/kg of capsaicin was administered s.c. for 3 consecutive days 2 weeks before the experiment) or pretreatment with L-NAME (a NO synthase inhibitor). CONCLUSIONS: Though H2-RAs and PPIs markedly inhibited the formation of gastric lesions induced by IND, they (except for LPZ) increased the formation of small intestinal lesions. The results suggest that antisecretory drugs aggravate intestinal lesions induced by NSAIDs, probably by increasing the amount of indigestive foods in the intestine and by increasing intestinal motility. LPZ, though having a potent antisecretory action, inhibited the formation of intestinal lesions, and this action can be explained by its protective action on the mucosa via CSSNs and NO.

Ras signaling pathways mediate NGF-induced enhancement of excitability of small-diameter capsaicin-sensitive sensory neurons from wildtype but not Nf1+/− mice

Nerve growth factor (NGF) activates multiple downstream effectors, including Ras, phosphoinositide-3 kinase, and sphingomyelins. However, pathway mediating the NGF-induced augmentation of sensory neuronal excitability remains largely unknown. We previously reported that small-diameter sensory neurons with a heterozygous mutation of the Nf1 gene ( Nf1+/−) exhibited increased excitability. The protein product of the Nf1 gene is neurofibromin, a guanosine triphosphatase-activating protein (GAP) for p21ras (Ras) that accelerates the conversion of active Ras-GTP to inactive Ras-GDP. Thus, Nf1+/− cells have augmented basal and stimulated Ras activity. To investigate whether NGF-induced increases in excitability of small-diameter sensory neurons are dependent on Ras signaling, an antibody that blocks the activation of Ras, Y13-259, was perfused into the cell. Under these conditions, the enhanced excitability produced by NGF was suppressed in wildtype neurons but the excitability of Nf1+/− neurons was unaltered. In addition, expression of a dominant-negative form of Ras abolished the ability of NGF to increase the excitability of small-diameter sensory neurons. These results demonstrate that NGF enhances excitability of small-diameter sensory neurons in a Ras-dependent manner while the consequences of decreased expression of neurofibromin cannot be restored by blocking Ras signaling; suggesting that Ras-initiated signaling pathways can regulate both transcriptional and posttranslational control of ion channels important in neuronal excitability.

PE-11, a peptide derived from chromogranin B, in the rat eye

The aim of the study was to investigate the presence and distribution of PE-11, a peptide derived from chromogranin B, in the rat eye. For this purpose, newborn rats were injected with a single dosage of 50 mg/kg capsaicin subcutaneously under the neck fold and after three months, particular eye tissues were dissected and the concentration of PE-11-like immunoreactivity was determined by radioimmunoassay. Furthermore, PE-11-like immunoreactivities were characterized in an extract of the rat eye by reversed phase HPLC. Then, the distribution pattern of PE-11 was investigated in the rat eye and rat trigeminal ganglion by immunofluorescence. As a result, PE-11 was present in each tissue of the rat eye and capsaicin pretreatment led to a 88.05% (±7.07) and a 64.26% (±14.17) decrease of the levels of PE-11 in the cornea and choroid/sclera, respectively, and to a complete loss in the iris/ciliary body complex. Approximately 70% of immunoreactivities detected by the PE-11 antiserum have been found to represent authentic PE-11. Sparse nerve fibers were visualized in the corneal and uveal stroma, surrounding blood vessels at the limbus, ciliary body and choroid and in association with the dilator and sphincter muscle. Furthermore, immunoreactivity was present in the corneal endothelium. In the retina and optic nerve, glia was labeled. In the rat trigeminal ganglion, PE-11-immunoreactivity was visualized in small and medium sized ganglion cells with a diameter of up to 30 μm. In conclusion, there is unequivocal evidence that PE-11 is a constituent of capsaicin-sensitive sensory neurons innervating the rat eye and the distribution pattern is typically peptidergic in the peripheral innervation but in the retina completely atypical for neuropeptides and unique.

The role of transient receptor potential ankyrin 1 (TRPA1) receptors in the H2S-evoked calcitonin gene-related peptide (CGRP) release from isolated rat trachea

Event Abstract Back to Event The role of transient receptor potential ankyrin 1 (TRPA1) receptors in the H2S-evoked calcitonin gene-related peptide (CGRP) release from isolated rat trachea G. Pozsgai1, T. Bagoly1, Z. Hajna1, M. Boros1, Z. Helyes1, J. Szolcsányi1 and E. Pintér1* 1 University of Pécs, Department of Pharmacology, Hungary TRPA1 ion channels are expressed by capsaicin-sensitive peptidergic primary sensory neurons. TRPA1 activators, such as allylisothiocyanate (mustard oil), airway irritants, cold temperature stimulate these receptors, thus causing inflammatory neuropeptide release (SP, CGRP) and subsequent airway neurogenic inflammation. It has been established that hydrogen sulfide (H2S) like NO exerts neuromediator function and stimulates the capsaicin-sensitive sensory neurons. The aim of the present study was to investigate the effect of H2S on CGRP release from isolated tracheae comparing the action of the TRPA1 agonist mustard oil. Isolated rat tracheae were perfused in organ bath (37 oC, pH 7.2) containing oxygenized Krebs solution. H2S donor NaHS and mustard oil were applied in different doses to elicit neurotransmitter release. CGRP concentrations of the perfusion fluid were determined by radioimmunoassay. Selective TRPA1 antagonist HC030031 was added into the incubation medium to test the involvement of TRPA1 receptors in the CGRP release. Both NaHS and mustard oil induced dose dependent peptide release from the tracheal tissue which was inhibited by the TRPA1 antagonist. On the basis of these data we conclude that H2S may induce neurogenic airway inflammation by activation of TRPA1 ion channels. Acknowledgements OTKA CNK77793, NNF78917 Keywords: Neurophysiology, Neuroscience Conference: 13th Conference of the Hungarian Neuroscience Society (MITT), Budapest, Hungary, 20 Jan - 22 Jan, 2011. Presentation Type: Abstract Topic: Neurophysiology Citation: Pozsgai G, Bagoly T, Hajna Z, Boros M, Helyes Z, Szolcsányi J and Pintér E (2011). The role of transient receptor potential ankyrin 1 (TRPA1) receptors in the H2S-evoked calcitonin gene-related peptide (CGRP) release from isolated rat trachea. Front. Neurosci. Conference Abstract: 13th Conference of the Hungarian Neuroscience Society (MITT). doi: 10.3389/conf.fnins.2011.84.00022 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2011; Published Online: 23 Mar 2011. * Correspondence: Dr. E. Pintér, University of Pécs, Department of Pharmacology, Pécs, Hungary, erika.pinter@aok.pte.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers G. Pozsgai T. Bagoly Z. Hajna M. Boros Z. Helyes J. Szolcsányi E. Pintér Google G. Pozsgai T. Bagoly Z. Hajna M. Boros Z. Helyes J. Szolcsányi E. Pintér Google Scholar G. Pozsgai T. Bagoly Z. Hajna M. Boros Z. Helyes J. Szolcsányi E. Pintér PubMed G. Pozsgai T. Bagoly Z. Hajna M. Boros Z. Helyes J. Szolcsányi E. Pintér Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Transient Receptor Potential Vanilloid 1 Agonists as Candidates for Anti-inflammatory Agents

The transient receptor potential vanilloid-1 (TRPV1) cation channel is a receptor that is activated by heat, acidosis and a variety of chemicals, including capsaicin. With these properties, TRPV1 has emerged as a polymodal nocisensor of nociceptive afferent neurons. As many proalgesic pathways converge on TRPV1 and it is upregulated and sensitized by inflammation and injury, TRPV1 is thought to be a central transducer of hyperalgesia and a prime target for the pharmacological control of pain. However, there is conflicting evidence to date as to whether TRPV1 agonists promote or inhibit inflammation. We recently demonstrated that SA13353 [1-[2-(1-adamantyl)ethyl]-1-pentyl-3-[3-(4-pyridyl)propyl]urea], a novel TRPV1 agonist, inhibits tumor necrosis factor-α production through the activation of capsaicin-sensitive afferent neurons and reduces the severity of symptoms of kidney injury, lung inflammation, arthritis and encephalomyelitis in disease models. These results suggest that TRPV1 agonists may act in an anti-inflammatory manner in vivo in certain inflammatory diseases.

Stimulation of duodenal HCO3− secretion by hydrogen sulphide in rats: relation to prostaglandins, nitric oxide and sensory neurones

We examined the effect of H₂S on duodenal HCO₃⁻ secretion in rats and investigated the mechanism involved in this response. Animals were fasted for 18 h and anaesthetized with urethane. A duodenal loop was perfused with saline, and HCO₃⁻ secretion was measured at pH 7.0 using a pH stat-method. The loop was perfused at a rate of 0.2 mL min⁻¹ with NaHS (H₂S donor: 0.1-1 mm) for 5 min or 10 mm HCl for 10 min. Indomethacin or l-NAME [nitric oxide (NO) synthase inhibitor) was given s.c. 30 min or 3 h, respectively, before NaHS or acidification, while glibenclamide (K(ATP) channel blocker) or propargylglycine (cystathionine-g-lyase inhibitor) was given i.p. 30 min before. Mucosal perfusion with NaHS dose dependently increased the HCO₃⁻ secretion, and this effect was significantly attenuated by indomethacin and l-NAME as well as by sensory deafferentation, but not by glibenclamide. Mucosal prostaglandin E₂ (PGE₂) production and luminal release of NO were both increased by NaHS perfusion. Mucosal acidification stimulated HCO₃⁻ secretion concomitant with an increase in PGE₂ and NO production, and these responses were mitigated by propargylglycine. The duodenal damage induced by acid (100 mm HCl for 4 h) was aggravated by pre-treatment with propargylglycine. These results suggest that H₂S increases HCO₃⁻ secretion in the rat duodenum, and that this action is partly mediated by PG and NO as well as by capsaicin-sensitive afferent neurones. It is assumed that endogenous H₂S is involved in the regulatory mechanism of acid-induced HCO₃⁻ secretion and mucosal protection in the duodenum.

The role of the transient receptor potential (TRP) superfamily of cation‐selective channels in the management of the overactive bladder

• The pathophysiology of lower urinary tract symptoms (LUTS), detrusor overactivity (DO), and the overactive bladder (OAB) syndrome is multifactorial and remains poorly understood. • The transient receptor potential (TRP) channel superfamily has been shown to be involved in nociception and mechanosensory transduction in various organ systems, and studies of the LUT have indicated that several TRP channels, including TRPV1, TRPV2, TRPV4, TRPM8, and TRPA1, are expressed in the bladder, and may act as sensors of stretch and/or chemical irritation. • However, the roles of these individual channels for normal LUT function and in LUTS/DO/OAB, have not been established. • TRPV1 is the channel best investigated. It is widely distributed in LUT structures, but despite extensive information on morphology and function in animal models, the role of this channel in normal human bladder function is still controversial. Conversely, its role in the pathophysiology and treatment of particularly neurogenic DO is well established. • TRPV1 is co-expressed with TRPA1, and TRPA1 is known to be present on capsaicin-sensitive primary sensory neurones. Activation of this channel can induce DO in animal models. • TRPV4 is a Ca(2+)-permeable stretch-activated cation channel, involved in stretch-induced ATP release, and TRPV4-deficient mice exhibit abnormal frequencies of voiding and non-voiding contractions in cystometric experiments. • TRPM8 is a cool receptor expressed in the urothelium and suburothelial sensory fibres. It has been implicated in the bladder-cooling reflex and in idiopathic DO. • The occurrence of other members of the TRP superfamily in the LUT has been reported, but information on their effects on LUT functions is scarce. There seem to be several links between activation of different members of the TRP superfamily and LUTS/DO/OAB, and further exploration of the involvement of these channels in LUT function, normally and in dysfunction, may be rewarding.

The Role of Capsaicin in Spontaneous Pacemaking Activity in Gastrointestinal Tract

Interstitial cells of Cajal (ICCs) are the pacemaking cells in the gastrointestinal (GI) tracts that generate the rhythmic oscillations in the membrane potential which were known as slow waves recorded in native smooth muscle tissue preparations in the past. Auto-rhythmicity in GI tracts is an exclusive property of ICCs and the spread of slow waves through GI tracts occurs electrically, and not by the active regeneration properties of ICCs and smooth muscles. Pacemaking ICCs are organized into electrically coupled networks within discrete areas of the stomach, small intestine, and colon.1,2 ICCs were originally identified by Santiago Ramon y Cajal and were characterized by morphological criteria until the discovery that these cells express the receptor tyrosine kinase Kit.3 Subsequent studies determined that Kit immunoreactivity in the muscularis propria of the GI tract is restricted to 2 cell types: mast cells4 and ICCs. Kit-positive ICCs are distributed throughout the GI tract as well as in other smooth muscle tissues.5 All regions of the GI tract contain ICCs but the location within the muscularis propria varies according to region or species.6 In the myenteric plexus region, ICCs form a network between the muscle layers forming a mesh around the ganglia and are considered as major pacemaker cells. A network of deep muscular plexus ICCs is present in the small intestine between the inner and outer circular muscle layers.6 In the colon and parts of the gastric antrum, submuscular ICCs are located outside the circular muscle layer.7 Intramuscular ICCs are distributed through the longitudinal and circular muscle layers and are considered to be involved in neurotransmission from nerve terminals. Septal ICCs are found between the fascicles of muscle in humans and other large species. These can be considered as one type of intramuscular ICCs.8 Stellate, subserosal ICCs are observed on the boundary between the longitudinal muscle and the serosa in the colon of mice.9 Capsaicin (8-methyl-N-vanillyl-6-ninenamide) activates afferent fiber endings and capsaicin sensitive primary afferent neurons participate in the regulation of GI motility.10 Furthermore, capsaicin induces contraction in the guinea-pig ileum11 and relaxation in human small and large intestines.10 Namely, it is known that capsaicin may have excitatory action on animal GI motility but inhibitory on human. However, information about the effect of capsaicin on human GI motility is somewhat controversial. Some reports showed the oral administration of capsaicin to fail in showing a significant effect on GI motility in human12-14 but there are reports that capsaicin could contribute to protection of the esophagus and could promote retention of the irritant in the stomach and faster transit through the small bowel.15 However, there are no reports on the direct effect of the capsaicin on ICCs that have important roles for regulation of GI motility as pacemaker cells. In this issue of the Journal of Neurogastroenterology and Motility, Choi et al examined the role of capsaicin on ICC in mouse small intestine. They showed that capsaicin inhibited the pacemaker activity of ICC dose-dependently. The effect of capsaicin, however, is not through the transient receptor potential of the vanilloid type 1 (TRPV1) channel because capsazepine did not block the effect of capsaicin. Consistently with this result, they also showed in their previous study that TRPV1-immunopositive cells were not co-localized with c-Kit positive tissue layer.16 The effect of capsaicin was not through nitric oxide release from ICCs, because there was no influence on capsaicin-induced action by L-NAME, an inhibitor of nitric oxide synthase in their study. Choi et al. proposed that further studies are needed to investigate the direct effect of capsaicin on pacemaker ion channels like TRPC4 or TRPM7 responsible for pacemaking activity in ICCs.17 Interestingly, when the action of capsaicin was examined in the intracellular calcium oscillation, capsaicin completely abolished the calcium oscillation in ICCs. Recently, 3 research groups showed simultaneously the calcium activated Cl channels to be required for pacemaking activity using TMEM16A knockout mice.18-20 Capsaicin might inhibit pacemaking activity of ICCs through the decreased activity of calcium activated Cl channels due to completely abolished calcium oscillations by application of capsaicin to ICCs. The effect of capsaicin seems more complicated because capsaicin acts on ICCs as well as afferent nerve endings of GI tract. In the future, more sophisticated studies are needed to clarify the role of capsaicin in GI tract considering ICCs and species differences.

Role of Capsaicin-Sensitive Primary Afferent Neurons and Non-protein Sulphydryl Groups on Gastroprotective Effect of Amifostine Against Ethanol-Induced Gastric Damage in Rats

Amifostine has been widely tested as a cytoprotective agent against a number of aggressors in different organs. Recently, a gastroprotective effect was observed for this drug in a model of indomethacin-induced gastric injury. Our objective was to investigate the effect of amifostine on ethanol-induced gastric injury and the role played in this mechanism by afferent sensory neurons, non-protein sulfhydryl groups, nitric oxide, ATP-sensitive potassium channels, and cyclooxygenase-2. Rats were treated with amifostine (22.5, 45, 90, or 180 mg/kg, PO or SC). After 30 min, the rats received absolute ethanol (5 ml kg(-1), PO). One hour later, gastric damage was quantified with a planimeter. Samples from the stomach were also taken for histopathological assessment and for assays of non-protein sulfhydryl groups. The other groups were pretreated with L-NAME (10 mg kg(-1), IP), glibenclamide (10 mg kg(-1), PO), or celecoxib (10 mg kg(-1), PO). After 30 min, the animals were given amifostine (90 mg kg(-1), PO or SC), followed 30 min later by gavage with absolute ethanol (5 ml kg(-1)). Other rats were desensitized with capsaicin (125 mg kg(-1), SC) 8 days prior to amifostine treatment. Amifostine administration PO and SC significantly and dose-dependently reduced ethanol-induced macroscopic and microscopic gastric damage by restoring glutathione levels in the stomach mucosa. Amifostine-promoted gastroprotection against ethanol-induced stomach injury was reversed by pretreatment with neurotoxic doses of capsaicin, but not by L-NAME, glibenclamide, or celecoxib. Amifostine protects against ethanol-induced gastric injury by increasing glutathione levels and stimulating the afferent sensory neurons in the stomach.

Pre-treatment with capsaicin in a rat osteoarthritis model reduces the symptoms of pain and bone damage induced by monosodium iodoacetate

A rat model of osteoarthritis was used to investigate the effect of pre-treatment with capsaicin on the symptoms of osteoarthritis induced by the injection of monosodium iodoacetate. This model mimics both histopathology and symptoms associated of human osteoarthritis. Injection of monosodium iodoacetate, an inhibitor of glycolysis, into the femorotibial joints of rodents promotes loss of articular trabecular bone and invokes pain symptoms similar to those noted in human osteoarthritis. Twenty rats were divided in two groups either receiving placebo or monosodium iodoacetate. Each group was subdivided in two groups either receiving pre-treatment with capsaicin two weeks before monosodium iodoacetate injection or not, resulting in four groups of five rats each. The impact of a single intra-articular administration of capsaicin (0.5%) on the generation of evoked mechanical pain (hind limb weight bearing, automated von Frey monofilament and RotaRod tests) and bone lesions (micro-CT scan radiographic analyses of bone structure) following monosodium iodoacetate-induced osteoarthritis in rats was determined. Evoked mechanical pain as monitored over a period of 4 weeks after monosodium iodoacetate injection was abolished in capsaicin pre-treated animals and pain values are comparable to those of capsaicin controls. Chronic joint pathological changes such as bone erosion and trabecular damage were significantly reduced by pre-treatment with a single administration of capsaicin. Decrease of bone volume was considerably ameliorated and trabecular connectivity was substantially better in capsaicin pre-treated animals. Capsaicin, an agonist activator of the vanilloid nociceptors (TRPV1), appears to be effective in protecting bone from arthritic damage. The present results support the hypothesis that capsaicin-sensitive sensory neurons contribute to bone lesions in the monosodium iodoacetate-induced osteoarthritis rat model.

Lafutidine prevents low‐dose aspirin and loxoprofen induced gastric injury: A randomized, double‐blinded, placebo controlled study

The concomitant use of non-steroidal anti-inflammatory drugs is a risk factor for low-dose aspirin (LDA)-associated upper gastrointestinal toxicity. Lafutidine is an H2-receptor antagonist with gastroprotective activity, produced by acting on capsaicin-sensitive afferent neurons. To evaluate the preventive effect of lafutidine on gastric damage caused by LDA alone and by the combination of both LDA and loxoprofen, we conducted a clinical study using healthy volunteers. A randomized, double-blinded, placebo-controlled, crossover study was carried out. Sixteen healthy volunteers without Helicobacter pylori infection were randomly assigned to two groups. Both groups received 81 mg of aspirin once daily for 14 days (on days 1 to 14) and 60 mg of loxoprofen three times daily for the last 7 days (on days 8 to 14). Placebo or 10 mg of lafutidine was administered twice daily for 14 days in each group. After a 2-week washout period, placebo and lafutidine were crossed over. Endoscopic findings of gastric mucosal damage were evaluated according to the modified Lanza score. The mean modified Lanza score was 2.19 ± 1.06 (SD) for aspirin plus placebo as compared with 0.50 ± 0.77 for aspirin plus lafutidine (P < 0.001), and 3.00 ± 1.56 for aspirin plus loxoprofen and placebo as compared with 1.25 ± 1.37 for aspirin plus loxoprofen and lafutidine (P < 0.01). The addition of loxoprofen to LDA increases gastric mucosal damage. Standard-dose lafutidine significantly prevents gastric mucosal damage induced by LDA alone or LDA plus loxoprofen in H. pylori-negative volunteers. Larger controlled studies are needed to strengthen these findings.

Protective effect of lafutidine, a histamine H2 receptor antagonist, against loxoprofen‐induced small intestinal lesions in rats

We examined the effect of lafutidine, a histamine H(2) receptor antagonist with a mucosal protective action mediated by capsaicin-sensitive sensory neurons (CSN), on intestinal lesions produced by loxoprofen administration in rats. Animals were given loxoprofen (10-100 mg/kg p.o.) and killed 24 h later. Lafutidine (10 and 30 mg/kg), cimetidine (100 mg/kg) or famotidine (30 mg/kg) was given twice p.o. at 0.5 h before and 6 h after loxoprofen. Omeprazole (100 mg/kg) was given p.o. once 0.5 h before. Ampicillin (800 mg/kg) was given p.o. twice at 24 h and 0.5 h before loxoprofen, while 16,16-dimethyl prostaglandin E(2) (dmPGE(2); 0.01 mg/kg) was given i.v. twice at 5 min before and 6 h after. Loxoprofen dose-dependently produced hemorrhagic lesions in the small intestine, accompanied by invasion of enterobacteria and increased inducible nitric oxide synthase (iNOS) expression as well as myeloperoxidase activity in the mucosa. The ulcerogenic response to loxoprofen (60 mg/kg) was significantly prevented by lafutidine (30 mg/kg), similar to dmPGE(2) and ampicillin, and the effect of lafutidine was totally attenuated by ablation of CSN. Neither cimetidine, famotidine nor omeprazole had a significant effect against these lesions. Lafutidine alone increased mucus secretion and reverted the decreased mucus response to loxoprofen, resulting in suppression of bacterial invasion and iNOS expression. In addition, loxoprofen downregulated Muc2 expression, and this response was totally reversed by lafutidine mediated by CSN. Lafutidine protects the small intestine against loxoprofen-induced lesions, essentially mediated by the CSN, and this effect may be functionally associated with increased Muc2 expression/mucus secretion, an important factor in the suppression of bacterial invasion.

Pituitary Adenylate Cyclase-Activating Polypeptide Deficiency Enhances Oxazolone-Induced Allergic Contact Dermatitis in Mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is present in capsaicin-sensitive sensory neurons and inflammatory/immune cells, therefore it is suggested to play a role in neuro-immune interactions. Our aim was to investigate the role of PACAP in oxazolone-induced delayed-type hypersensitivity reaction in the skin using deficient mice (PACAP(-/-)). Sensitization was induced by 2% oxazolone application on the shaved abdomen on two consecutive days; inflammation was elicited by oxazolone smearing on the ears 6days later. Ear thickness was measured by micrometry. Histological examination, cytokine profile [IL-2, IL-4, IL-5, and monocyte chemoattractant protein-1: MCP-1, IFN-γ, tumor necrosis factor alpha (TNF-α)] and myeloperoxidase activity correlating with the number of neutrophils/macrophages were determined 24 and 48h later. Oxazolone induced a 110-130% swelling after 24-48h in wild-type mice, which was significantly greater in PACAP-deficient mice. Histological analysis confirmed markedly increased edema in PACAP(-/-) mice, but the moderately enhanced inflammatory cell accumulation was not statistically significant compared with the wild-types. There was no difference in myeloperoxidase activity of the ear homogenates. Elevation of MCP-1, but not the levels of the other cytokines, was significantly higher in the samples of the PACAP-deficient mice. These results suggest that PACAP exerts anti-inflammatory, particularly edema-inhibiting effects in allergic contact dermatitis.

Augmented Sodium Currents Contribute to the Enhanced Excitability of Small Diameter Capsaicin-Sensitive Sensory Neurons Isolated From Nf1+/− Mice

Neurofibromin, the product of the Nf1 gene, is a guanosine triphosphatase activating protein (GAP) for p21ras (Ras) that accelerates conversion of active Ras-GTP to inactive Ras-GDP. Sensory neurons with reduced levels of neurofibromin likely have augmented Ras-GTP activity. We reported previously that sensory neurons isolated from a mouse model with a heterozygous mutation of the Nf1 gene (Nf1+/⁻) exhibited greater excitability compared with wild-type mice. To determine the mechanism giving rise to the augmented excitability, differences in specific membrane currents were examined. Consistent with the enhanced excitability of Nf1+/⁻ neurons, peak current densities of both tetrodotoxin-resistant sodium current (TTX-R I(Na)) and TTX-sensitive (TTX-S) I(Na) were significantly larger in Nf1+/⁻ than in wild-type neurons. Although the voltages for half-maximal activation (V(0.5)) were not different, there was a significant depolarizing shift in the V(0.5) for steady-state inactivation of both TTX-R and TTX-S I(Na) in Nf1+/⁻ neurons. In addition, levels of persistent I(Na) were significantly larger in Nf1+/⁻ neurons. Neither delayed rectifier nor A-type potassium currents were altered in Nf1+/⁻ neurons. These results demonstrate that enhanced production of action potentials in Nf1+/⁻ neurons results, in part, from larger current densities and a depolarized voltage dependence of steady-state inactivation for I(Na) that potentially leads to a greater availability of sodium channels at voltages near the firing threshold for the action potential.

Transient receptor potential vanilloid 1 agonists as candidates for anti-inflammatory and immunomodulatory agents

We recently demonstrated that SA13353 [1-[2-(1-adamantyl)ethyl]-1-pentyl-3-[3-(4-pyridyl)propyl]urea], a novel transient receptor potential vanilloid 1 (TRPV1) agonist, inhibits TNF-alpha production through the activation of capsaicin-sensitive afferent neurons. In the present study, we investigated the effects of SA13353 on lipopolysaccharide (LPS)-induced cytokine production and a murine model of experimental autoimmune encephalomyelitis (EAE). SA13353 inhibited LPS-induced TNF-alpha and interleukin (IL)-1beta production while augmenting IL-10 production in mice. It also inhibited TNF-alpha and IL-1beta mRNA expression, and increased IL-10 mRNA expression in LPS-treated murine liver. These effects were not observed in TRPV1 KO and sensory denervated mice. Capsaicin and SA13353 increased serum neuropeptide levels, and calcitonin gene-related peptide fragment 8-37 (CGRP(8)(-)(37)), a CGRP antagonist, partially blocked the inhibitory effects of capsaicin and SA13353 on LPS-induced TNF-alpha production. These results suggest that the TPPV1 agonistic effects inhibit TNF-alpha production, at least partially, via neuropeptide release. SA13353 did not directly affect LPS-induced cytokine production in vitro using RAW264.7 macrophages, which do not express TRPV1. Therefore, we consider SA13353 to be a good tool for the investigation of the value of TRPV1 agonists for the treatment of chronic inflammation. In a murine EAE model, SA13353 attenuated clinical signs and histopathological changes. SA13353 attenuated cytokine levels, including TNF-alpha, IL-1beta, IL-12p40, IL-17, and interferon (IFN)-gamma, after proteolipid protein (PLP) immunization. In addition, SA13353 attenuated the increase of IL-17-producing cells. These results suggest that TRPV1 agonists may act as anti-inflammatory and immunomodulatory agents in vivo in certain inflammatory diseases.

The effects of desensitization of capsaicin-sensitive afferent neurons on the microcirculation in the stomach in rats depend on the blood glucocorticoid hormone level

The effects of densensitization of capsaicin-sensitive afferent neurons on the microcirculation in the stomach were studied before and after administration of indomethacin at an ulcerogenic dose in adrenalectomized rats receiving and not receiving replacement therapy with corticosterone and in sham-operated animals. Measures of the microcirculation consisted of blood flow rates in microvessels in the submucous layer of the stomach and the diameter and permeability of microvessels in the mucosa. Desensitization of capsaicin-sensitive afferent neurons was performed by administration of capsaicin at a dose of 100 mg/kg for two weeks and adrenalectomy one week before the experiment. Blood flow rates in microvessels and microvessel diameters were assessed in non-anesthetized rats by direct video recording methods using a special optical system with a contact dark-field epiobjective. Administration of indomethacin at an ulcerogenic dose led to decreases in blood flow rate in microvessels in the submucous layer, dilation of superficial microvessels in the mucosa of the stomach, and an increase in their permeability. Desensitization of capsaicin-sensitive neurons potentiated indomethacin-induced impairments to the microcirculation in the submucous layer and the mucosa of the stomach. These effects of densensitization were significantly enhanced in conditions of glucocorticoid hormone deficiency. Thus, glucocorticoid hormones have favorable effects on the gastric microcirculation in rats with desensitization of capsaicin-sensitive afferent neurons.

Hydrogen Sulfide Prevents Ethanol-Induced Gastric Damage in Mice: Role of ATP-Sensitive Potassium Channels and Capsaicin-Sensitive Primary Afferent Neurons

The aim of this study was to evaluate the protective effect of hydrogen sulfide (H(2)S) on ethanol-induced gastric lesions in mice and the influence of ATP-sensitive potassium (K(ATP)) channels, capsaicin-sensitive sensory afferent neurons, and transient receptor potential vanilloid (TRPV) 1 receptors on such an effect. Saline and L-cysteine alone or with propargylglycine, sodium hydrogen sulfide (NaHS), or Lawesson's reagent were administrated for testing purposes. For other experiments, mice were pretreated with glibenclamide, neurotoxic doses of capsaicin, or capsazepine. Afterward, mice received L-cysteine, NaHS, or Lawesson's reagent. After 30 min, 50% ethanol was administrated by gavage. After 1 h, mice were sacrificed, and gastric damage was evaluated by macroscopic and microscopic analyses. L-cysteine, NaHS, and Lawesson's reagent treatment prevented ethanol-induced macroscopic and microscopic gastric damage in a dose-dependent manner. Administration of propargylglycine, an inhibitor of endogenous H(2)S synthesis, reversed gastric protection induced by L-cysteine. Glibenclamide reversed L-cysteine, NaHS, or Lawesson's reagent gastroprotective effects against ethanol-induced macroscopic damage in a dose-dependent manner. Chemical ablation of sensory afferent neurons by capsaicin reversed gastroprotective effects of L-cysteine or H(2)S donors (NaHS or Lawesson's reagent) in ethanol-induced macroscopic gastric damage. Likewise, in the presence of the TRPV1 antagonist capsazepine, the gastroprotective effects of L-cysteine, NaHS, or Lawesson's reagent were also abolished. Our results suggest that H(2)S prevents ethanol-induced gastric damage. Although there are many mechanisms through which this effect can occur, our data support the hypothesis that the activation of K(ATP) channels and afferent neurons/TRPV1 receptors is of primary importance.

Capsaicin-sensitive primary sensory neurons in the mouse express N-Acyl phosphatidylethanolamine phospholipase D

Our previous finding, that the capsaicin- and KCl-induced Ca2+-dependent production of the intra- and intercellular signaling molecule N-arachidonoyl ethanolamine (anandamide) in cultured primary sensory neurons could be abolished and reduced by ∼2/3 by capsaicin-induced degeneration of capsaicin-sensitive neurons, respectively suggests that a major sub-population of capsaicin-sensitive cells together with a group of non-capsaicin-sensitive cells should express enzymes involved in Ca2+-dependent anandamide synthesis. N-acyl phosphotidylethanolamine phospholipase D (NAPE-PLD) is known to be involved in Ca2+-dependent anandamide production. Hence, here, we used reverse transcriptase and quantitative real time polymerase chain reaction to study NAPE-PLD expression in dorsal root ganglia and to clarify the sub-population of cells expressing this enzyme. Cultures prepared from mouse dorsal root ganglia were grown either in the absence or presence of the neurotoxin, capsaicin (10 μM) overnight. We report, that NAPE-PLD is expressed both in dorsal root ganglia and cultures prepared from dorsal root ganglia and grown in the absence of capsaicin. Furthermore, we also report that capsaicin application downregulates the expression of NAPE-PLD as well as the capsaicin receptor, transient receptor potential vanilloid type 1 ion channel, by about 70% in the cultures prepared from dorsal root ganglia. These findings indicate that a major sub-population of capsaicin-sensitive primary sensory neurons expresses NAPE-PLD, and suggest that NAPE-PLD is expressed predominantly by capsaicin-sensitive neurons in dorsal root ganglia. These data also suggest that NAPE-PLD might be a target to control the activity and excitability of a major sub-population of nociceptive primary sensory neurons.