5-HT acts on nociceptive primary afferents through an indirect mechanism to induce hyperalgesia in the subcutaneous tissue

The roles of 5-HT in orofacial pain

OBJECTIVES

Acute and chronic orofacial pain are very common and remain a vexing health problem that has a negative effect on the quality of life. Serotonin (5-HydroxyTryptamine, 5-HT) is a kind of monoamine neurotransmitter that is involved in many physiological and pathological processes. However, its role in orofacial pain remains inconclusive. Therefore, this review aims to summarize the recent advances in understanding the effect exerted by 5-HT on the modulation of orofacial pain.

SUBJECTS AND METHODS

An extensive search was conducted on PubMed and Web of Science for pertinent studies focusing on the effects of 5-HT on the modulation of orofacial pain.

RESULTS

In this review, we concisely review how 5-HT mediates orofacial pain, how 5-HT is regulated and how we can translate these findings into clinical applications for the prevention and/or treatment of orofacial pain.

CONCLUSIONS

5-HT plays a key role in the modulation of orofacial pain, implying that 5-HT modulators may serve as effective treatment for orofacial pain. However, further research on the precise mechanisms underlying the modulation of orofacial pain is still warranted.

Therapeutic strategies focusing on immune dysregulation and neuroinflammation in rosacea

Rosacea is a complex inflammatory condition characterized by papulopustular lesions and erythema on the central face for which there is no cure. The development of rosacea is influenced by both external triggers and genetics, but the common pathophysiology is overactivation of the immune system. Here, we review the current data on proinflammatory cytokines and dysregulation of the neurovascular system as targetable components of rosacea. Amelioration of cutaneous and gastrointestinal dysbiosis and other external factors impacts the immune state and has been observed to improve rosacea. While multiple treatments exist, many patients do not achieve their goals for rosacea control and highlights an unmet need for dermatologic care. Current interventions encompass topical/oral drugs, light devices, and avoidance of triggers management. Additional understanding of the underlying pathogenesis may help us develop novel targeted therapeutic strategies to improve rosacea.

Fucoidan as a Promising Drug for Pain Treatment: Systematic Review and Meta-Analysis

Fucoidan is a polymer of L-fucose and L-fucose-4-sulphate naturally found in marine sources that inhibits p-selectin, preventing neutrophil recruitment to the site of injury. Fucoidan is employed in many studies as a tool to investigate the contribution of neutrophils to pain, showing analgesic effects. We performed a systematic review and meta-analysis to quantify the analgesic effects of pretreatment with fucoidan reported in the available preclinical studies. In addition, we summarized the articles which have studied the therapeutic effects of fucoidan in pathological pain at preclinical and clinical levels. The results of this systematic review reveal that pretreatment with fucoidan is a powerful tool which reduces neutrophil infiltration by 70-90% at early time points. This meta-analysis showed that preventative treatment with fucoidan produced a significant pain reduction. In addition, several preclinical studies have observed that fucoidan treatment reduces the pain that is associated with various pathologies. Finally, fucoidan has also been tested in several clinical trials, with some degree of analgesic efficacy, but they were mostly small pilot studies. Considering all the above information, it can be concluded that fucoidan is not only a preclinical tool for studying the role of neutrophils in pain but also a promising therapeutic strategy for pain treatment.

Neutrophil biology in injuries and diseases of the central and peripheral nervous systems

The role of inflammation in nervous system injury and disease is attracting increased attention. Much of that research has focused on microglia in the central nervous system (CNS) and macrophages in the peripheral nervous system (PNS). Much less attention has been paid to the roles played by neutrophils. Neutrophils are part of the granulocyte subtype of myeloid cells. These cells, like macrophages, originate and differentiate in the bone marrow from which they enter the circulation. After tissue damage or infection, neutrophils are the first immune cells to infiltrate into tissues and are directed there by specific chemokines, which act on chemokine receptors on neutrophils. We have reviewed here the basic biology of these cells, including their differentiation, the types of granules they contain, the chemokines that act on them, the subpopulations of neutrophils that exist, and their functions. We also discuss tools available for identification and further study of neutrophils. We then turn to a review of what is known about the role of neutrophils in CNS and PNS diseases and injury, including stroke, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, spinal cord and traumatic brain injuries, CNS and PNS axon regeneration, and neuropathic pain. While in the past studies have focused on neutrophils deleterious effects, we will highlight new findings about their benefits. Studies on their actions should lead to identification of ways to modify neutrophil effects to improve health.

Paroxetine is an effective treatment for refractory erythema of rosacea: Primary results from the Prospective Rosacea Refractory Erythema Randomized Clinical Trial

BACKGROUND

Patients with refractory erythema of rosacea have limited treatment options.

OBJECTIVE

To evaluate the efficacy and safety of a 12-week course of paroxetine for moderate-to-severe erythema of rosacea.

METHODS

In a multicenter, randomized, double-blinded, placebo-controlled trial, patients with refractory erythema of rosacea were randomly assigned (1:1) to receive paroxetine 25 mg daily or placebo for 12 weeks.

RESULTS

Overall, 97 patients completed the study (paroxetine: 49; placebo: 48). The primary end point was the proportion of participants achieving Clinical Erythema Assessment success (defined as Clinical Erythema Assessment score of 0, 1, or ≥2-grade improvement from baseline) at week 12; this was significantly greater in the paroxetine group than in the placebo group (42.9% vs 20.8%, P = .02). Some secondary end points were met, such as flushing success with point reductions ≥2 (44.9% vs 25.0%, P = .04) and improvement in overall flushing (2.49 ± 3.03 vs 1.68 ± 2.27, P = .047), burning sensation (46.9% vs 18.8%, P = .003), and depression (P = .041). The most reported adverse events associated with paroxetine were dizziness, lethargy, nausea, dyspepsia, and muscle tremors.

LIMITATIONS

Only a single-dosage regimen of paroxetine within a 12-week study was evaluated.

CONCLUSIONS

Paroxetine is an effective and well-tolerated alternative treatment for moderate-to-severe erythema of rosacea.

Role of peripheral 5-HT1D, 5-HT3 and 5-HT7 receptors in the mechanical allodynia induced by serotonin in mice

Serotonin (5-HT) acts as a neurotransmitter in the central nervous system (CNS) and as a mediator released by enterochromaffin cells to regulate intestinal motility. However, this amine also plays an important role as an inflammatory mediator and induces phenotypic changes of nociceptors. Despite the wide knowledge of the role of 5-HT in nociception, most studies have focused on its role in the CNS, while a clear information about its role in peripheral tissues is still lacking. In the present study, we investigated the role of peripheral 5-HT receptors in the nociceptive response induced by 5-HT or carrageenan in mice by using antagonists that target different 5-HT receptors. Mechanical nociceptive threshold was measured with an analgesimeter and evaluated after intraplantar (i.pl.) injection of 5-HT or carrageenan. 5-HT antagonists were injected via the i.pl. route. 5-HT (10, 20, 40 or 80 μg/paw) or carrageenan (100 μg/paw) induced mechanical allodynia. Pretreatment with isamoltane (5 μg; 5-HT_1B antagonist) or ketanserine (1 μg; 5-HT_2A antagonist) did not affect the mechanical allodynia induced by 5-HT. This response was inhibited by BRL 15572 (10 μg; 5-HT_1D antagonist) or SB 269970 (25 μg; 5-HT₇ antagonist). On the other hand, mechanical allodynia induced by 5-HT or carrageenan was exacerbated by ondansetron (10, 20 or 40 μg; 5-HT₃ antagonist). The results indicate that activation of 5-HT_1D and 5-HT₇ receptors plays a role in the mechanical allodynia induced by 5-HT in mice. This study also demonstrates the inhibitory role of peripheral 5-HT₃ receptors in the nociceptive response induced by 5-HT or carrageenan.

Pharmacodynamic and Metabolomics Studies on the Effect of Kouyanqing Granule in the Treatment of Phenol-Induced Oral Ulcer Worsened by Sleep Deprivation

Oral ulcers are the most prevalent oral mucosal diseases globally, and no specific treatment schemes are currently available due to the complexity of oral ulcer diseases. Sleep deprivation increases the risk of a deterioration in oral health. Kouyanqing Granule (KYQG) has been used for decades in China to treat inflammatory diseases of the mouth and throat associated with the hyperactivity of fire due to yin deficiency syndrome. However, the mechanisms underlying the effects of KYQG in the treatment of oral ulcers are still unclear. The aims of this study were to investigate whether KYQG treatment could attenuate the symptoms of oral ulcers worsened by sleep deprivation and identify the involved metabolic pathways. First, we conducted chemical profiling of KYQG via UPLC–MS analysis. We then combined pharmacological and metabolomics approaches in a phenol-induced rat model of oral ulcers worsened by sleep deprivation. A total of 79 compounds were initially identified. Our observations showed that KYQG treatment induced a significantly higher healing rate in oral ulcers worsened by sleep deprivation. KYQG significantly reduced the levels of 5-HT and GABA in serum, and only decreased the 5-HT level in brain tissue after phenol injury followed by sleep deprivation. Moreover, KYQG administration significantly suppressed systemic inflammation by inhibiting TNF-α, IL-1β, IL-6, IL-18, and MCP-1. Immunohistochemical analysis further revealed that KYQG inhibited IL-6 expression in buccal mucosa tissues. KYQG treatment also significantly decreased the serum levels of ACTH, CORT, IgM, and 8-OHdG. Serum metabolomics analysis showed that a total of 30 metabolites showed significant differential abundances under KYQG intervention, while metabolic pathway analysis suggested that the altered metabolites were associated with the dysregulation of eight metabolic pathways. Taken together, our results indicated that KYQG attenuates the symptoms of oral ulcers worsened by sleep deprivation probably through the regulation of the neuroimmunoendocrine system, oxidative stress levels, and tryptophan metabolism. This study also provides a novel approach for addressing the increased health risks resulting from sleep deficiency using an herbal medicine formula.

Expression of Cutaneous Beta-2 Adrenoceptors Is Similar in Patients with Complex Regional Pain Syndrome and Pain-Free Controls

OBJECTIVE

Studies in rodents suggest that cutaneous beta-2 adrenoceptors (β2-ARs) mediate inflammation and pain after tissue injury and that inflammation and peripheral nerve injury trigger increases in neuronal β2-AR expression. Hence, the aim of this study was to investigate the expression of β2-ARs on keratinocytes and dermal nerves in patients with complex regional pain syndrome (CRPS).

DESIGN, SETTING, AND SUBJECTS

Fifty-eight patients with CRPS were recruited for this study. In addition, skin biopsies were obtained from 13 pain-free women and three pain-free men of similar age and sex distribution as the patients.

METHODS

Quantitative sensory tests for assessing sensitivity to pressure, pinprick, light touch, heat, and cold were administered, and skin biopsies were obtained from the affected and contralateral limbs. Skin biopsies were also obtained from a similar site on the dorsal hand or foot of pain-free controls. Immunohistochemistry and confocal microscopy were used to identify β2-ARs on keratinocytes, dermal nerves, and blood vessels in the skin samples.

RESULTS

The distribution of β2-ARs in keratinocytes and nerves was similar in the affected and contralateral limbs of patients and was similar for target cells in patients and controls. However, elevated β2-AR expression in reticular nerve bundles was associated with heightened sensitivity to heat pain.

CONCLUSIONS

These findings do not support a major role of cutaneous β2-ARs in CRPS. However, activation of neuronal β2-ARs may contribute to thermal hyperalgesia in a subgroup of patients. Whether activation of β2-ARs on keratinocytes mediates inflammation early in the course of CRPS requires further investigation.

Sleep deprivation worsened oral ulcers and delayed healing process in an experimental rat model

AIMS

Sleep deficiency has been reported to be associated with some oral health problems. Oral ulcers are very common lesions of the oral mucosa, which severely impact patients' quality of life. However, the association between sleep deficiency and the oral ulcer remains unknown. The present study aims to explore the effects of sleep deficiency on oral ulcers.

MAIN METHODS

Rats were divided into normal control group (n = 30) and oral ulcer group (OU group, n = 50). Model rats with phenol-induced oral ulcers were deprived of sleep for 72 h by using the modified multiple platform technique.

KEY FINDINGS

Sleep deprivation worsened oral ulcers and delayed healing process in rats. In addition, sleep deprivation increased the γ-aminobutyric acid (GABA, P < 0.01) and 5-hydroxytryptamine (5-HT, P < 0.05) levels in serum and brain, the corticotrophin (ACTH, P < 0.05), corticosterone (CORT, P < 0.01), immunoglobulin (Ig)M (P < 0.01), tumor necrosis factor-alpha (TNF-α) (P < 0.01), interleukin (IL)-1β (P < 0.01), IL-6 (P < 0.01), IL-8 (P < 0.01), monocyte chemoattractant protein-1 (MCP-1) (P < 0.01), and 8-hydroxy-deoxyguanosine (8-OHdG, P < 0.01) levels in serum. Sleep deprivation also up-regulated malonaldehyde (MDA) (P < 0.05), TNF-α (P < 0.05), and IL-1β (P < 0.01) levels in oral mucosa tissue and delayed superoxide dismutase (SOD, P < 0.05) activity recovery.

SIGNIFICANCE

These data suggest that sleep deprivation impaired the oral ulcer healing in rat oral mucosa, and the mechanisms of this effect are probably related to neuro-immuno-endocrine system and oxidative stress.

Mast cells are important regulator of acupoint sensitization via the secretion of tryptase, 5-hydroxytryptamine, and histamine

Mast cells (MCs) play a crucial role in mediating the establishment of networks among the circulatory, nervous and immune system at acupoints. However, the changes which occur in MCs during acupoint sensitization, i.e. the dynamic transformation of an acupoint from a "silenced" to an "activated" status, remain uncharacterized. To investigate the morphological and functional changes of MCs as an aid to understanding the cellular mechanism underlying acupoint sensitization, a rat model of knee osteoarthritis (OA) was induced by an injection of mono-iodoacetate (MIA) on day 0. On day 14, toluidine blue and immunofluorescence staining were used to observe the recruitment and degranulation of MCs and the release of mast cell co-expressed mediators: tryptase, 5-hydroxytryptamine (5-HT) and histamine (HA) at the acupoints Yanglingquan (GB34), Heding (EX-LE2) and Weizhong (BL40). Results showed that the number of MCs as well as the percentages of degranulated and extensively degranulated MCs at the acupoints GB34 and EX-LE2 in the light (A), mild (B), heavy (C) osteoarthritis groups were larger than those in the normal control (N) and normal saline (NS) groups (p < 0.01). Comparisons among the A, B and C groups suggested that the number and the degranulation extent of the MCs at the acupoints GB34 and EX-LE2 were positively correlated with the severity of the disease. Some MCs in the A, B and C group showed the release of 5-HT, HA, and tryptase in degranulation at the acupoints GB34 and EX-LE2. Such changes in MCs were not observed at the acupoint BL40. In conclusion, this study confirmed that acupoint sensitization is associated with the increase in recruitment and degranulation levels of MCs on a acupoint-specific and disease severity-dependent manner. The release of tryptase, 5-HT, and HA during MC degranulation is likely to be one of the cellular mechanisms occurring during acupoint sensitization.

Insights into the sand fly saliva: Blood-feeding and immune interactions between sand flies, hosts, and Leishmania

Background

Leishmaniases are parasitic diseases present worldwide that are transmitted to the vertebrate host by the bite of an infected sand fly during a blood feeding. Phlebotomine sand flies inoculate into the mammalian host Leishmania parasites embedded in promastigote secretory gel (PSG) with saliva, which is composed of a diverse group of molecules with pharmacological and immunomodulatory properties.

Methods and findings

In this review, we focus on 3 main aspects of sand fly salivary molecules: (1) structure and composition of salivary glands, including the properties of salivary molecules related to hemostasis and blood feeding, (2) immunomodulatory properties of salivary molecules and the diverse impacts of these molecules on leishmaniasis, ranging from disease exacerbation to vaccine development, and (3) use of salivary molecules for field applications, including monitoring host exposure to sand flies and the risk of Leishmania transmission. Studies showed interesting differences between salivary proteins of Phlebotomus and Lutzomyia species, however, no data were ever published on salivary proteins of Sergentomyia species.

Conclusions

In the last 15 years, numerous studies have characterized sand fly salivary proteins and, in parallel, have addressed the impact of such molecules on the biology of the host–sand fly–parasite interaction. The results obtained shall pave the way for the development of field-application tools that could contribute to the management of leishmaniasis in endemic areas.

The Diversity of Yellow-Related Proteins in Sand Flies (Diptera: Psychodidae)

Yellow-related proteins (YRPs) present in sand fly saliva act as affinity binders of bioamines, and help the fly to complete a bloodmeal by scavenging the physiological signals of damaged cells. They are also the main antigens in sand fly saliva and their recombinant form is used as a marker of host exposure to sand flies. Moreover, several salivary proteins and plasmids coding these proteins induce strong immune response in hosts bitten by sand flies and are being used to design protecting vaccines against Leishmania parasites. In this study, thirty two 3D models of different yellow-related proteins from thirteen sand fly species of two genera were constructed based on the known protein structure from Lutzomyia longipalpis. We also studied evolutionary relationships among species based on protein sequences as well as sequence and structural variability of their ligand-binding site. All of these 33 sand fly YRPs shared a similar structure, including a unique tunnel that connects the ligand-binding site with the solvent by two independent paths. However, intraspecific modifications found among these proteins affects the charges of the entrances to the tunnel, the length of the tunnel and its hydrophobicity. We suggest that these structural and sequential differences influence the ligand-binding abilities of these proteins and provide sand flies with a greater number of YRP paralogs with more nuanced answers to bioamines. All these characteristics allow us to better evaluate these proteins with respect to their potential use as part of anti-Leishmania vaccines or as an antigen to measure host exposure to sand flies.

Spinal 5-HT3 receptor mediates nociceptive effect on central neuropathic pain; possible therapeutic role for tropisetron

OBJECTIVES

To test the analgesic effect of 5-HT-3 receptor antagonist, tropisetron, in a clip compression injury model of spinal cord pain in rats.

METHODS

Four weeks post compression of the spinal cord at lumbar level, tropisetron was administered intrathecally at 100 μg and 150 μg dosages. Behavioral tests were assessed before administration. Fifteen minutes after injection, behavioral tests were repeated. Randall-Sellitto and plantar test was used for mechanical and thermal hyperalgesia, respectively. Mechanical and cold allodynia were evaluated by Von Frey filament and acetone droplets, respectively. The analgesic effect of tropisetron was compared with intrathecal administration of salicylate. Locomotor score was evaluated by Basso, Beattie and Bresnahan (BBB) test every week after spinal cord injury.

RESULTS

Intrathecal administration of tropisetron, decreased hyperalgesia and mechanical allodynia, but not cold allodynia were observed after compression of the spinal cord.

CONCLUSION

Blockade of 5-HT-3 receptors by tropisetron at the spinal level induces an antinociceptive effect on chronic central neuropathic pain and suggests that this compound may have potential clinical utility for the management of central neuropathic pain, particularly in patients with hyperalgesia and tactile allodynia.

Peripheral P2X7 receptor-induced mechanical hyperalgesia is mediated by bradykinin

P2X7 receptors play an important role in inflammatory hyperalgesia, but the mechanisms involved in their hyperalgesic role are not completely understood. In this study, we hypothesized that P2X7 receptor activation induces mechanical hyperalgesia via the inflammatory mediators bradykinin, sympathomimetic amines, prostaglandin E2 (PGE2), and pro-inflammatory cytokines and via neutrophil migration in rats. We found that 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate triethylammonium salt (BzATP), the most potent P2X7 receptor agonist available, induced a dose-dependent mechanical hyperalgesia that was blocked by the P2X7 receptor-selective antagonist A-438079 but unaffected by the P2X1,3,2/3 receptor antagonist TNP-ATP. These findings confirm that, although BzATP also acts at both P2X1 and P2X3 receptors, BzATP-induced hyperalgesia was mediated only by P2X7 receptor activation. Co-administration of selective antagonists of bradykinin B1 (Des-Arg(8)-Leu(9)-BK (DALBK)) or B2 receptors (bradyzide), β1 (atenolol) or β2 adrenoceptors (ICI 118,551), or local pre-treatment with the cyclooxygenase inhibitor indomethacin or the nonspecific selectin inhibitor fucoidan each significantly reduced BzATP-induced mechanical hyperalgesia in the rat hind paw. BzATP also induced the release of the pro-inflammatory cytokines tumor necrosis factor α (TNF-α), interleukin (IL)-1β, IL-6 and cytokine-induced neutrophil chemoattractant-1 (CINC-1), an effect that was significantly reduced by A-438079. Co-administration of DALBK or bradyzide with BzATP significantly reduced BzATP-induced IL-1β and CINC-1 release. These results indicate that peripheral P2X7 receptor activation induces mechanical hyperalgesia via inflammatory mediators, especially bradykinin, which may contribute to pro-inflammatory cytokine release. These pro-inflammatory cytokines in turn may mediate the contributions of PGE2, sympathomimetic amines and neutrophil migration to the mechanical hyperalgesia induced by local P2X7 receptor activation.

The contribution of transient receptor potential ankyrin 1 (TRPA1) to the in vivo nociceptive effects of prostaglandin E₂

AIMS

Although evidence suggest that TRPA1 mediates some effects of prostaglandins, it is not known whether TRPA1 contributes to the in vivo nociceptive effects of prostaglandin E2 (PGE2), a key mediator of inflammatory pain.

MAIN METHODS

To address this issue, the effect of the pharmacological blockade of TRPA1 or of its gene silencing on the hyperalgesia induced in the rat paw by PGE2 or its downstream signaling molecules, protein kinase A (PKA) or protein kinase C-epsilon (PKCε), was evaluated. TRPA1 expression on dorsal root ganglia cells was assessed by western blot.

KEY FINDINGS

The pharmacological blockade of local TRPA1 by its selective antagonist, HC 030031 decreased and reversed PGE2-induced hyperalgesia. The TRPA1 gene silencing induced by intrathecal pre-treatment with antisense oligodeoxynucleotide blocked PGE2-induced hyperalgesia and strongly reduced TRPA1 expression in dorsal root ganglia cells (L5 and L6). PGE2 injection into the hind paw did not significantly increase TRPA1 expression in dorsal root ganglia cells. Treatment with either HC 030031 or antisense oligodeoxynucleotide significantly decreased the hyperalgesia induced by PKA or PKCε. Since both kinases are the major components of PGE2-induced intracellular signal transduction, the modulation of TRPA1 function by PGE2 may be downstream PKA and PKC-epsilon.

SIGNIFICANCE

These findings show that TRPA1 is essential to the in vivo nociceptive effects induced by one of the most important mediators of inflammatory pain, PGE2. This is one of the crucial findings necessary to support TRPA1 as a promising target for the development of future drugs to pain treatment and control.

New insights into rosacea pathophysiology: a review of recent findings

Rosacea is a common, chronic inflammatory skin disease of poorly understood origin. Based on its clinical features (flushing, chronic inflammation, fibrosis) and trigger factors, a complex pathobiology involving different regulatory systems can be anticipated. Although a wealth of research has shed new light over recent years on its pathophysiology, the precise interplay of the various dysregulated systems (immune, vascular, nervous) is still poorly understood. Most authors agree on 4 major clinical subtypes of rosacea: erythematotelangiectatic rosacea, papulopustular rosacea, phymatous rosacea, and ocular rosacea. Still, it needs to be elucidated whether these subtypes develop in a consecutive serial fashion or if any subtypes may occur individually as part of a syndrome. Because rosacea often affects multiple family members, a genetic component is also suspected, but the genetic basis of rosacea remains unclear. During disease manifestation and early stage, the innate immune system and neurovascular dysregulation seem to be driving forces in rosacea pathophysiology. Dissection of major players for disease progression and in advanced stages is severely hampered by the complex activation of the innate and adaptive immune systems, enhanced neuroimmune communication, profound blood vessel and possibly lymphatic vessel changes, and activation of almost every resident cell in the skin. This review discusses some of the recent findings and aims to build unifying hypotheses for a modern understanding of rosacea pathophysiology.

Association of temporomandibular dysfunction with the 102T-C polymorphism in the serotonin receptor gene in Brazilian patients

INTRODUCTION

Serotonin is a key neurotransmitter in the central nervous system. It has been suggested that serotoninergic dysfunction mediates the pathophysiology of temporomandibular dysfunction (TMD). Polymorphisms in the serotonin receptor gene (HTR2A) can alter its transcription, affecting the number of receptors in the serotoninergic system, altering nociceptive pain and hyperalgesia in TMD. The aim of this study is to investigate the association of the 102T-C polymorphism in the HTR2A gene in Brazilian patients with TMD.

MATERIAL AND METHODS

This cross-sectional study examined 100 patients, of both genders, with TMD as index cases and 100 healthy volunteers as controls, also of both genders. DNA was extracted from peripheral blood leukocytes, and the site that encompassed the polymorphism in the HTR2A gene was amplified by polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP).

RESULTS

Our results revealed that there were significantly more females among index cases compared with the control group (p < 0.05). The CC genotype of the 102T-C polymorphism was more frequent in patients with TMD vs. controls (OR: 2.25; 95% CI: 1.13-4.46; p < 0.05).

CONCLUSIONS

The present study supports the view that the 102T-C polymorphism in the HTR2A gene is associated with TMD in this studied Brazilian population.

P-selectin is required for neutrophils and macrophage infiltration into injured site and contributes to generation of behavioral hypersensitivity following peripheral nerve injury in mice

Growing evidence suggests that leukocyte extravasation is initiated by the interaction of selectins with their ligands; as well as an essential role for P-selectin in the initial recruitment of inflammatory cells to sites of inflammation. In this study, P-selectin-deficient (P-sel-/-) mice were used to test the hypothesis that lack of P-selectin would attenuate the recruitment of inflammatory cells to the site of inflammation, thereby modulating pain in a murine chronic neuropathic pain model. Nociceptive sensitization and the microenvironment of the peripheral injury site were studied in wild-type (P-sel+/+) and P-selectin-deficient (P-sel-/-) mice after partial sciatic nerve ligation (PSNL). Variables measured included myeloperoxidase (MPO) activity, several inflammatory cell infiltration profiles, cytokines, and endogenous opioid peptide expression in damaged nerves. Results indicate that behavioral hypersensitivity, MPO activity, and infiltration of neutrophils and macrophages were attenuated in P-sel-/- mice after PSNL. Proinflammatory cytokines, tumor necrosis factor α, and interleukin (IL)-6, were reduced in damaged nerves following PSNL; however, several antiinflammatory cytokines - IL-1Ra, IL-4, and IL-10 - were significantly increased in P-sel-/- mice. In addition, endogenous opioid peptides mRNA was significantly lower in P-sel-/- mice compared with P-sel +/+ mice. The current results demonstrated that the absence of P-selectin in mice leads to an altered microenvironment that attenuated behavioral hypersensitivity. The specific role of P-selectin could have been a result of decreased neutrophils, as well as the accumulation of macrophages at the site of injury, which may subsequently modulate the inflammatory cytokine expression and impact behavioral hypersensitivity within the injured nerve.

Effect of transcutaneous electrical stimulation on nociception and edema induced by peripheral serotonin

Transcutaneous electrical nerve stimulation (TENS) is defined as the application of an electrical current to the skin through surface electrodes for pain relief. Various theories have been proposed in order to explain the analgesic mechanism of TENS. Recent studies have demonstrated that part of this analgesia is mediated through neurotransmitters acting at peripheral sites. The aim of this study was to investigate the effects of low frequency (LF: 10 HZ) TENS and high frequency (HF: 130 HZ) TENS on hyperalgesia and edema when applied before the serotonin (5-HT) administered into the rat paw. LF and HF TENS were applied to the right paw for 20 min, and 5-HT was administered immediately after TENS. The Hargreaves method was used to measure nociception, while the hydroplethysmometer (Ugo Basile®) was used to measure edema. Neither HF nor LF TENS inhibited 5-HT-induced edema. However, LF TENS, but not HF TENS, completely reduced 5-HT-induced hyperalgesia. Pre-treatment of the paw with naltrexone, prior to application of TENS, (Nx: 50 μg; I.pl.) showed a complete blockade of the analgesic effect induced by low frequency TENS. Thus, our results confirmed the lack of an anti-inflammatory effect through the use of TENS as well as the participation of peripheral endogenous opioid receptors in LF TENS analgesia in addition to its central action.

Evidence for the participation of peripheral 5-HT₂A, 5-HT₂B, and 5-HT₂C receptors in formalin-induced secondary mechanical allodynia and hyperalgesia

The role of 5-HT₂A/₂B/₂C receptors in formalin-induced secondary allodynia and hyperalgesia in rats was assessed. Formalin produced acute nociceptive behaviors (flinching and licking/lifting) followed by long-term secondary mechanical allodynia and hyperalgesia. Pre-treatment for five consecutive days with compound 48/80 (1, 3, 10, 10, and 10 μg/paw) prevented formalin-induced secondary allodynia and hyperalgesia. Ipsilateral, but not contralateral, peripheral pre-treatment (nmol/paw) with the 5-HT₂ receptor agonist DOI (3-30), 5-HT (10-100) or fluoxetine (0.3-3) significantly increased 0.5% formalin-induced secondary allodynia and hyperalgesia in both paws. The pronociceptive effect of DOI (10 nmol/paw), 5-HT (100 nmol/paw) and fluoxetine (1 nmol/paw) was blocked by selective 5-HT₂A (ketanserin), 5-HT₂B (RS-127445), and 5-HT₂C (RS-102221) receptor antagonists. Furthermore, ipsilateral pre-treatment (nmol/paw) with ketanserin (1, 10, and 100), RS-127445 (0.01, 0.1 and 1) or RS-102221 (1, 10 and 100) prevented while post-treatment reversed 1% formalin-induced secondary allodynia and hyperalgesia in both paws. In marked contrast, contralateral injection of the greatest tested dose of 5-HT₂A/₂B/₂C receptor antagonists did not modify long-lasting secondary allodynia and hyperalgesia. These results suggest that 5-HT released from mast cells after formalin injection sensitizes primary afferent neurons via 5-HT₂A/₂B/₂C receptors leading to the development and maintenance of secondary allodynia and hyperalgesia.

Anti-inflammatory and antinociceptive effects of salbutamol on acute and chronic models of inflammation in rats: involvement of an antioxidant mechanism

The possible role of β-2 adrenergic receptors in modulation of inflammatory and nociceptive conditions suggests that the β-2 adrenergic receptor agonist, salbutamol, may have beneficial anti-inflammatory and analgesic effects. Therefore, in this study, we induced inflammatory and nociceptive responses with carrageenan-induced paw edema or cotton-pellet-induced granuloma models, both of which result in oxidative stress. We hypothesized that salbutamol would prevent inflammatory and nociceptive responses by stimulating β-2 adrenergic receptors and the prevention of generation of ROS during the acute inflammation process in rats. Both doses of salbutamol used in the study (1 and 2 mg/kg) effectively blocked the acute inflammation and inflammatory nociception induced by carrageenan. In the cotton-pellet-induced granuloma test, both doses of salbutamol also significantly decreased the weight of granuloma tissue on the cotton pellets when compared to the control. Anti-inflammatory and analgesic effects of salbutamol were found to be comparable with those of indomethacin. Salbutamol decreased myeloperoxidase (MPO) activity and lipid peroxidation (LPO) level and increased the activity of superoxide dismutase (SOD) and level of glutathione (GSH) during the acute phase of inflammation. In conclusion, salbutamol can decrease acute and chronic inflammation, possibly through the stimulation of β-2 adrenergic receptors. This anti-inflammatory effect may be of significance in asthma treatment, where inflammation also takes part in the etiopathology. This study reveals that salbutamol has significant antioxidative effects, which at least partially explain its anti-inflammatory capabilities. These findings presented here may also shed light on the roles of β-2 adrenergic receptors in inflammatory and hyperalgesic conditions.

Blockade of β₁-, β₂- and β₃-adrenoceptors in the temporomandibular joint induces antinociception especially in female rats

BACKGROUND

Temporomandibular joint (TMJ) receives rich sympathetic innervations that may contribute to TMJ pain through the local release of sympathomimetic amines. The aim of this study was to determine whether blockade of β-adrenoceptors in the TMJ of male and female rats reduces formalin-induced TMJ nociceptive behaviour.

METHODS

We co-administrated each one of the selective β(1) -, β(2) - and β(3) -adrenoceptors antagonists, atenolol, ICI 118.551 and SR59230A, respectively, with formalin in the TMJ of male and proestrus and dioestrus female rats. Because intra-temporomandibular joint formalin induces significantly different concentration-dependent responses among the three groups, with dioestrus females showing greater responses than males or proestrus females, equi-nociceptive formalin concentrations were used to test the effects of the β-adrenoceptor antagonists.

RESULTS

We found that atenolol, ICI 118.551 and SR59230A significantly reduced formalin-induced TMJ nociception in a dose response fashion in both males and females. However, a lower dose of each β-adrenoceptor antagonist was sufficient to significantly reduce nociceptive responses in females than in males. Administration of the highest doses of each β-adrenoceptor antagonist in the TMJ contralateral to that receiving formalin did not affect formalin-induced nociception in males and females, confirming the local action of the β-adrenoceptor antagonists.

CONCLUSIONS

We conclude that blockade of β-adrenoceptors in the temporomandibular joint suppresses formalin-induced TMJ nociceptive behaviour in both males and females but females are more responsive. These findings suggest that the use of β-blockers in the treatment of TMJ pain might be of benefit, especially in females.

Propofol reduces early post-operative pain after gynecological laparoscopy

BACKGROUND

There is some evidence that propofol may reduce post-operative pain. However, the results on the analgesic effects of propofol are inconsistent. Thus, we hypothesized that propofol reduces acute pain if confounding factors like opioids are avoided.

METHODS

In this prospective, randomized, subject- and assessor-blind, parallel-group, head-to-head comparative study, 90 American Society of Anesthesiologists I or II females underwent elective laparoscopies were randomized to receive either propofol-based (PR), or sevoflurane-based (SR), or sevoflurane-propofol-based anesthesia (SPR). Pain score at rest assessed by a numerical rating scale at 0.5 h after surgery was the primary outcome. The secondary outcomes included pain score at 1 and 24 h post-operatively, duration of post-anesthesia care units stay (PACU), incidence of post-operative nausea and vomiting, incidence of shivering, and post-operative quality of recovery score (QoR-40) within the first 24 h post-operatively.

RESULTS

No patients received rescue analgesia. The pain score at 0.5 h post-operatively was less in group PR when compared with group SR (0.7 ± 1.4 vs. 2.1 ± 1.8; P = 0.010) or group SPR (0.7 ± 1.4 vs. 2.1 ± 2.2; P = 0.008). Group PR was also associated with shorter PACU stay than group SR (21.8 ± 5.7 vs. 26.2 ± 6.9; P = 0.050) or group SPR (21.8 ± 5.7 vs. 27.8 ± 8.9; P = 0.005). Intraoperative bispectral index values, hemodynamic values and post-operative QoR-40 scores did not differ among the three groups.

CONCLUSIONS

Propofol anesthesia was associated with significantly less pain at 0.5 and 1 h after surgery in patients undergoing gynecological laparoscopies with planned opioid-free post-operative analgesia.

Neurovascular and neuroimmune aspects in the pathophysiology of rosacea

Rosacea is a common skin disease with a high impact on quality of life. Characterized by erythema, edema, burning pain, immune infiltration, and facial skin fibrosis, rosacea has all the characteristics of neurogenic inflammation, a condition induced by sensory nerves via antidromically released neuromediators. To investigate the hypothesis of a central role of neural interactions in the pathophysiology, we analyzed molecular and morphological characteristics in the different subtypes of rosacea by immunohistochemistry, double immunofluorescence, morphometry, real-time PCR, and gene array analysis, and compared the findings with those for lupus erythematosus or healthy skin. Our results showed significantly dilated blood and lymphatic vessels. Signs of angiogenesis were only evident in phymatous rosacea. The number of mast cells and fibroblasts was increased in rosacea, already in subtypes in which fibrosis is not clinically apparent, indicating early activation. Sensory nerves were closely associated with blood vessels and mast cells, and were increased in erythematous rosacea. Gene array studies and qRT-PCR confirmed upregulation of genes involved in vasoregulation and neurogenic inflammation. Thus, dysregulation of mediators and receptors implicated in neurovascular and neuroimmune communication may be crucial at early stages of rosacea. Drugs that function on neurovascular and/or neuroimmune communication may be beneficial for the treatment of rosacea.

Sertraline inhibits formalin-induced nociception and cardiovascular responses

The objective of the present study was to determine the antihyperalgesic effect of sertraline, measured indirectly by the changes of sciatic afferent nerve activity, and its effects on cardiorespiratory parameters, using the model of formalin-induced inflammatory nociception in anesthetized rats. Serum serotonin (5-HT) levels were measured in order to test their correlation with the analgesic effect. Male Wistar rats (250-300 g) were divided into 4 groups (N = 8/per group): sertraline-treated group (Sert + Saline (Sal) and Sert + Formalin (Form); 3 mg·kg-1·day-1, ip, for 7 days) and saline-treated group (Sal + Sal and Sal + Form). The rats were injected with 5% (50 µL) formalin or saline into the right hind paw. Sciatic nerve activity was recorded using a silver electrode connected to a NeuroLog apparatus, and cardiopulmonary parameters (mean arterial pressure, heart rate and respiratory frequency), assessed after arterial cannulation and tracheotomy, were monitored using a Data Acquisition System. Blood samples were collected from the animals and serum 5-HT levels were determined by ELISA. Formalin injection induced the following changes: sciatic afferent nerve activity (+50.8 ± 14.7%), mean arterial pressure (+1.4 ± 3 mmHg), heart rate (+13 ± 6.8 bpm), respiratory frequency (+4.6 ± 5 cpm) and serum 5-HT increased to 1162 ± 124.6 ng/mL. Treatment with sertraline significantly reduced all these parameters (respectively: +19.8 ± 6.9%, -3.3 ± 2 mmHg, -13.1 ± 10.8 bpm, -9.8 ± 5.7 cpm) and serum 5-HT level dropped to 634 ± 69 ng/mL (P < 0.05). These results suggest that sertraline plays an analgesic role in formalin-induced nociception probably through a serotonergic mechanism.

Structure and function of a "yellow" protein from saliva of the sand fly Lutzomyia longipalpis that confers protective immunity against Leishmania major infection

LJM11, an abundant salivary protein from the sand fly Lutzomyia longipalpis, belongs to the insect "yellow" family of proteins. In this study, we immunized mice with 17 plasmids encoding L. longiplapis salivary proteins and demonstrated that LJM11 confers protective immunity against Leishmania major infection. This protection correlates with a strong induction of a delayed type hypersensitivity (DTH) response following exposure to L. longipalpis saliva. Additionally, splenocytes of exposed mice produce IFN-γ upon stimulation with LJM11, demonstrating the systemic induction of Th1 immunity by this protein. In contrast to LJM11, LJM111, another yellow protein from L. longipalpis saliva, does not produce a DTH response in these mice, suggesting that structural or functional features specific to LJM11 are important for the induction of a robust DTH response. To examine these features, we used calorimetric analysis to probe a possible ligand binding function for the salivary yellow proteins. LJM11, LJM111, and LJM17 all acted as high affinity binders of prohemostatic and proinflammatory biogenic amines, particularly serotonin, catecholamines, and histamine. We also determined the crystal structure of LJM11, revealing a six-bladed β-propeller fold with a single ligand binding pocket located in the central part of the propeller structure on one face of the molecule. A hypothetical model of LJM11 suggests a positive electrostatic potential on the face containing entry to the ligand binding pocket, whereas LJM111 is negative to neutral over its entire surface. This may be the reason for differences in antigenicity between the two proteins.

5-hydroxytryptamine type 3 receptor modulates opioid-induced hyperalgesia and tolerance in mice

BACKGROUND

Opioid-induced hyperalgesia (OIH) and tolerance are challenging maladaptations associated with opioids in managing pain. Recent genetic studies and the existing literature suggest the 5-hydroxytryptamine type 3 (5-HT3) receptor participates in these phenomena. The location of the relevant receptor populations and the interactions between the 5-HT3 system and other systems controlling OIH and tolerance have not been explored, however. We hypothesized that 5-HT3 receptors modulate OIH and tolerance, and that this modulation involves the control of expression of multiple neurotransmitter and receptor systems.

METHODS

C57BL/6 mice were exposed to a standardized 4-day morphine administration protocol. The 5-HT3 antagonist ondansetron was administered either during or after the conclusion of morphine administration. Mechanical testing was used to quantify OIH, and thermal tail-flick responses were used to measure morphine tolerance. In other experiments spinal cord and dorsal root ganglion tissues were harvested for analysis of messenger RNA concentrations by real-time polymerase chain reaction or immunochemistry analysis.

RESULTS

The results showed that (1) systemic or intrathecal injection of ondansetron significantly prevented and reversed OIH, but not local intraplantar injection; (2) systemic or intrathecal injection of ondansetron prevented and reversed tolerance; and (3) ondansetron blocked morphine-induced increases of multiple genes relevant to OIH and tolerance in dorsal root ganglion and spinal cord.

CONCLUSIONS

Morphine acts via a 5-HT3-dependent mechanism to support multiple maladaptations to the chronic administration of morphine. Furthermore, the use of 5-HT3 receptor antagonists may provide a new avenue to prevent or reverse OIH and tolerance associated with chronic opioid use.

Facial injections of pruritogens or algogens elicit distinct behavior responses in rats and excite overlapping populations of primary sensory and trigeminal subnucleus caudalis neurons

In the present study, we investigated whether intradermal cheek injection of pruritogens or algogens differentially elicits hindlimb scratches or forelimb wipes in Sprague-Dawley rats, as recently reported in mice. We also investigated responses of primary sensory trigeminal ganglion (TG) and dorsal root ganglion (DRG) cells, as well as second-order neurons in trigeminal subnucleus caudalis (Vc), to pruritic and algesic stimuli. 5-HT was the most effective chemical to elicit dose-dependent bouts of hindlimb scratches directed to the cheek, with significantly less forelimb wiping, consistent with itch. Chloroquine also elicited significant scratching but not wiping. Allyl isothiocyanate (AITC; mustard oil) elicited dose-dependent wiping with no significant scratching. Capsaicin elicited equivalent numbers of scratch bouts and wipes, suggesting a mixed itch and pain sensation. By calcium imaging, ∼ 6% of cultured TG and DRG cells responded to 5-HT. The majority of 5-HT-sensitive cells also responded to chloroquine, AITC, and/or capsaicin, and one-third responded to histamine. Using a chemical search strategy, we identified single units in Vc that responded to intradermal cheek injection of 5-HT. Most were wide dynamic range (WDR) or nociceptive specific (NS), and a few were mechanically insensitive. The large majority additionally responded to AITC and/or capsaicin and thus were not pruritogen selective. These results suggest that primary and second-order neurons responsive to pruritogens and algogens may utilize a population coding mechanism to distinguish between itch and pain, sensations that are behaviorally manifested by distinct hindlimb scratching and forelimb wiping responses.

P2X3 and P2X2/3 receptors mediate mechanical hyperalgesia induced by bradykinin, but not by pro-inflammatory cytokines, PGE₂ or dopamine

Activation of peripheral P2X3 and P2X2/3 receptors by endogenous ATP is essential to the development of inflammatory hyperalgesia. We have previously demonstrated that this essential role of P2X3 and P2X2/3 receptors in the development of mechanical hyperalgesia induced by the inflammatory agent carrageenan is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of tumor necrosis factor alpha (TNF-α) and by a direct sensitization of the primary afferent nociceptors. Therefore, in this study we asked whether activation of P2X3 and P2X2/3 receptors contribute to the mechanical hyperalgesia induced by the inflammatory mediators involved in carrageenan-induced mechanical hyperalgesia, such as bradykinin, tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), chemokine-induced chemoattractant-1 (CINC-1), prostaglandin E₂ (PGE₂) and dopamine. Co-administration of the non-selective P2X3 receptor antagonist TNP-ATP or the selective P2X3 and P2X2/3 receptor antagonist A-317491 with bradykinin, but not with TNF-α, IL-1β, IL-6, CINC-1, PGE₂ or dopamine, prevented in a dose-dependent manner the mechanical hyperalgesia. We also verified whether the activation of P2X3 and P2X2/3 receptors by endogenous ATP contributes to bradykinin-induced mechanical hyperalgesia via neutrophil migration and/or cytokine release. Co-administration of TNP-ATP or A-317491 did not affect either neutrophil migration or the increased concentration of TNF-α, IL-1β, IL-6 and CINC-1 induced by bradykinin. These findings demonstrate that the activation of P2X3 and P2X2/3 receptors by endogenous ATP mediates bradykinin-induced mechanical hyperalgesia by a mechanism that does not depend on neutrophil migration or cytokines release.

The improvement of the anti-hyperalgesic effect of ketamine and of its isomers by the administration of ifenprodil

Intrathecal or epidural administration of NMDA (N-methyl-D-aspartate) receptors antagonists, in special ketamine and ifenprodil are used to control moderate to severe hyperalgesia in humans. Activation of NMDA receptor usually requires binding of two agonists, glutamate and glycine, in different receptor subunits. Ketamine is a NMDA receptor antagonist and acts at phencyclidine site in NR1 subunit while ifenprodil is a selective NR2B subunit antagonist of NMDA receptor. The aim of this study was to investigate the pharmacological interactions between ketamine or its isomers and ifenprodil, when intrathecally co-administrated, to reduce prostaglandin E(2)-induced hyperalgesia in rat's hind paw. The intrathecal administration of ketamine, its isomers R(-) or S(+), or ifenprodil-induced anti-hyperalgesic effects in a dose-related manner. Ifenprodil, in a dose that did not induce significant effect when administrated alone, significantly improved the anti-hyperalgesic effect of ketamine or its isomers. The other way round, ketamine or S(+) ketamine, but not R(-) ketamine, in a dose that did not induce significant effect when administrated alone, improved the anti-hyperalgesic effect of ifenprodil. However, by comparing ED(50)s (half maximal effective doses), ifenprodil-induced potentiation of ketamine was significantly greater than ketamine-induced potentiation of ifenprodil. The findings of this present study suggest that intrathecal administration of very small doses of ifenprodil, just before and ketamine significantly improves its anti-hyperalgesic effect and this association could be useful to control inflammatory pain with less undesirable effects.

Peripheral mechanisms underlying the essential role of P2X7 receptors in the development of inflammatory hyperalgesia

Activation of P2X7 receptors by endogenous ATP contributes to the development of inflammatory hyperalgesia. Given the clinical importance of mechanical hyperalgesia in inflammatory states, we hypothesized that the activation of the P2X7 receptor by endogenous ATP contributes to carrageenan-induced mechanical hyperalgesia, and that this contribution is mediated by an indirect sensitization of the primary afferent nociceptors. Co-administration of the selective P2X7 receptor antagonist, A-438079, or the P2X7 receptor antagonist, oATP, with carrageenan blocked the mechanical hyperalgesia induced by carrageenan and significantly reduced the increased concentration of TNF-alpha, IL-6 and CINC-1, but not of IL-1beta induced by carrageenan in the subcutaneous tissue of the rat's hind paw. We concluded that the activation of P2X7 receptors by endogenous ATP is essential to the development of the mechanical hyperalgesia induced by carrageenan in the subcutaneous tissue. It is suggested that this essential role of P2X7 receptors in the development of carrageenan-induced mechanical hyperalgesia is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of TNF-alpha, IL-6 and CINC-1, but not of IL-1beta.

Acute and persistent nociceptive paw sensitisation in mice: the involvement of distinct signalling pathways

AIMS

Many fundamental pharmacological studies in pain and inflammation have been performed on rats. However, the pharmacological findings were generally not extended to other species in order to increase their predictive therapeutic value. We studied acute and chronic inflammatory nociceptive sensitisation of mouse hind paws by prostaglandin E(2) (PGE(2)) or dopamine (DA), as previously described in rats. We also investigated the participation of the signalling pathways in acute and persistent sensitisation.

MAIN METHODS

Mechanical sensitisation (hypernociception) induced by intraplantar administrations of PGE(2) or DA was evaluated with an electronic pressure meter. The signalling pathways were pharmacologically investigated with the pre-administration of adenylyl cyclase (AC), cAMP-dependent protein kinase (PKA), protein kinase Cepsilon (PKCepsilon), and the extracellular signal-related kinase (ERK) inhibitors.

KEY FINDINGS

Single or 14days of successive intraplantar injections of PGE(2) or DA-induced acute and persistent hypernociception (lasting for more than 30days), respectively. The involvement of AC, PKA or PKCepsilon was observed in the acute hypernociception induced by PGE(2), while PKA or PKCepsilon were continuously activated during the period of persistent hypernociception. The acute hypernociception induced by DA involves activation of ERK, PKCepsilon, AC or PKA, while persistent hypernociception implicated ERK activation, but not PKA, PKCepsilon or AC.

SIGNIFICANCE

In mice, acute and persistent paw sensitisation involves the different activation of kinases, as previously described for rats. This study opens the possibility of comparing pharmacological approaches in both species to further understand acute and chronic inflammatory sensitisation, and possibly associated genetic manipulations.

Role of sensory innervation in the rat pulmonary neutrophil recruitment induced by staphylococcal enterotoxins type A and B

Rat airways exposure to Staphylococcal enterotoxin A (SEA) and B (SEB) induces marked neutrophil influx. Since sensory neuropeptides play important roles in cell infiltration, in this study we have investigated its contribution in triggering SEA- and SEB-induced pulmonary neutrophil infiltration. Male Wistar rats were exposed intratracheally with SEA (3 ng/trachea) or SEB (250 ng/trachea). Animals received different in vivo pretreatments, after which the neutrophil counts and levels of substance P and IL-1 in bronchoalveolar lavage fluid were evaluated. Alveolar macrophages and peritoneal mast cells were incubated with SEA and SEB to determine the IL-1 and TNF-alpha levels. Capsaicin pretreatment significantly reduced SEA- and SEB-induced neutrophil influx in bronchoalveolar lavage fluid, but this treatment was more effective to reduce SEA responses. Treatments with SR140333 (tachykinin NK(1) receptor antagonist) and SR48968 (tachykinin NK(2) receptor antagonist) decreased SEA-induced neutrophil influx, whereas SEB-induced responses were inhibited by SR140333 only. Cyproheptadine (histamine/5-hydroxytriptamine receptor antagonist) and MD 7222 (5-HT(3) receptor antagonist) reduced SEA- and SEB-induced neutrophil influx. The substance P and IL-1 levels in bronchoalveolar lavage fluid of SEA-exposed rats were significantly higher than SEB. In addition, SEA (but not SEB) significantly released mast cell TNF-alpha. Increased production of TNF-alpha and IL-1 in alveolar macrophages was observed in response to SEA and SEB. In conclusion, sensory neuropeptides contribute significantly to SEA- and SEB-induced pulmonary neutrophil recruitment, but SEA requires in a higher extent the airways sensory innervation, and participation of mast cells and alveolar macrophage products.

Multifunctionality and mechanism of ligand binding in a mosquito antiinflammatory protein

The mosquito D7 salivary proteins are encoded by a multigene family related to the arthropod odorant-binding protein (OBP) superfamily. Forms having either one or two OBP domains are found in mosquito saliva. Four single-domain and one two-domain D7 proteins from Anopheles gambiae and Aedes aegypti (AeD7), respectively, were shown to bind biogenic amines with high affinity and with a stoichiometry of one ligand per protein molecule. Sequence comparisons indicated that only the C-terminal domain of AeD7 is homologous to the single-domain proteins from A. gambiae, suggesting that the N-terminal domain may bind a different class of ligands. Here, we describe the 3D structure of AeD7 and examine the ligand-binding characteristics of the N- and C-terminal domains. Isothermal titration calorimetry and ligand complex crystal structures show that the N-terminal domain binds cysteinyl leukotrienes (cysLTs) with high affinities (50-60 nM) whereas the C-terminal domain binds biogenic amines. The lipid chain of the cysLT binds in a hydrophobic pocket of the N-terminal domain, whereas binding of norepinephrine leads to an ordering of the C-terminal portion of the C-terminal domain into an alpha-helix that, along with rotations of Arg-176 and Glu-268 side chains, acts to bury the bound ligand.

Current evidence for a modulation of low back pain by human genetic variants

The manifestation of chronic back pain depends on structural, psychosocial, occupational and genetic influences. Heritability estimates for back pain range from 30% to 45%. Genetic influences are caused by genes affecting intervertebral disc degeneration or the immune response and genes involved in pain perception, signalling and psychological processing. This inter-individual variability which is partly due to genetic differences would require an individualized pain management to prevent the transition from acute to chronic back pain or improve the outcome. The genetic profile may help to define patients at high risk for chronic pain. We summarize genetic factors that (i) impact on intervertebral disc stability, namely Collagen IX, COL9A3, COL11A1, COL11A2, COL1A1, aggrecan (AGAN), cartilage intermediate layer protein, vitamin D receptor, metalloproteinsase-3 (MMP3), MMP9, and thrombospondin-2, (ii) modify inflammation, namely interleukin-1 (IL-1) locus genes and IL-6 and (iii) and pain signalling namely guanine triphosphate (GTP) cyclohydrolase 1, catechol-O-methyltransferase, mu opioid receptor (OPMR1), melanocortin 1 receptor (MC1R), transient receptor potential channel A1 and fatty acid amide hydrolase and analgesic drug metabolism (cytochrome P450 [CYP]2D6, CYP2C9).

Peripheral mechanisms underlying the essential role of P2X3,2/3 receptors in the development of inflammatory hyperalgesia

Activation of P2X3,2/3 receptors by endogenous ATP contributes to the development of inflammatory hyperalgesia. Given the clinical importance of mechanical hyperalgesia in inflammatory states, we hypothesized that the activation of P2X3,2/3 receptors by endogenous ATP contributes to carrageenan-induced mechanical hyperalgesia and that this contribution is mediated by an indirect and/or a direct sensitization of the primary afferent nociceptors. Co-administration of the selective P2X3,2/3 receptors antagonist A-317491, or the non-selective P2X3 receptor antagonist, TNP-ATP, with carrageenan blocked the mechanical hyperalgesia induced by carrageenan, and significantly reduced the increased concentration of tumor necrosis factor alpha (TNF-alpha) and chemokine-induced chemoattractant-1 (CINC-1) but not of interleukin-1 beta (IL-1 beta) induced by carrageenan. Co-administration of the selective P2X3,2/3 receptors antagonist A-317491 with carrageenan did not affect the neutrophil migration induced by carrageenan. Intrathecal administration of oligonucleotides antisense against P2X3 receptors for seven days significantly reduced the expression of P2X3 receptors in the saphenous nerve and significantly reduced the mechanical hyperalgesia induced by carrageenan. We concluded that the activation of P2X3,2/3 receptors by endogenous ATP is essential to the development of the mechanical hyperalgesia induced by carrageenan. Furthermore, we showed that this essential role of P2X3,2/3 receptors in the development of carrageenan-induced mechanical hyperalgesia is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of TNF-alpha and by a direct sensitization of the primary afferent nociceptors.

Alarm or curse? The pain of neuroinflammation

The nociceptive nervous system and the immune system serve to defend and alarm the host of imminent or actual damage. However, persistent or recurring exposure of neurons to activated immune cells is associated with an increase in painful behavior following experimental neuropathic injuries. Our understanding of the functional consequences of immune cell-neuron interaction is still incomplete. The purpose of this review is to focus on a seriously detrimental consequence of chronic activation of these two systems, by discussing the contributions of microglia and polymorphonuclear neutrophils to neuropathic pain following experimental spinal cord injury or peripheral nerve injury. Identification of molecules mediating pro-nociceptive signaling between immune cells and neurons, as well as the distinction between neuroprotective versus neuroexcitatory effects of activated immune cells, may be useful in the development of pharmacotherapy for the management of chronic pain and restoration of the beneficial alarm function of pain.

Activated polymorphonuclear cells promote injury and excitability of dorsal root ganglia neurons

Therapies aimed at depleting or blocking the migration of polymorphonuclear leukocytes (PMN or neutrophils) are partially successful in the treatment of neuroinflammatory conditions and in attenuating pain following peripheral nerve injury or subcutaneous inflammation. However, the functional effects of PMN on peripheral sensory neurons such as dorsal root ganglia (DRG) neurons are largely unknown. We hypothesized that PMN are detrimental to neuronal viability in culture and increase neuronal activity and excitability. We demonstrate that isolated peripheral PMN are initially in a relatively resting state but undergo internal oxidative burst and activation by an unknown mechanism within 10 min of co-culture with dissociated DRG cells. Co-culture for 24 h decreases neuronal count at a threshold<0.4:1 PMN:DRG cell ratio and increases the number of injured and apoptotic neurons. Within 3 min of PMN addition, fluorometric calcium imaging reveals intracellular calcium transients in small size (<25 microm diam) and large size (>25 microm diam) neurons, as well as in capsaicin-sensitive neurons. Furthermore, small size isolectin B4-labeled neurons undergo hyperexcitability manifested as decreased current threshold and increased firing frequency. Although co-culture of PMN and DRG cells does not perfectly model neuroinflammatory conditions in vivo, these findings suggest that activated PMN can potentially aggravate neuronal injury and cause functional changes to peripheral sensory neurons. Distinguishing the beneficial from the detrimental effects of PMN on neurons may aid in the development of more effective drug therapies for neurological disorders involving neuroinflammation, including painful neuropathies.

Indirect mechanism of histamine-induced nociception in temporomandibular joint of rats

A considerable amount of evidence suggests that temporomandibular joint (TMJ) pain associated with temporomandibular disorder results, at least in part, from an inflammatory episode. Although histamine can cause pain, it is not clear whether this mediator induces nociception in the TMJ. In this study, we investigated the contribution of endogenous histamine to formalin-induced nociception in the TMJ of rats. We also investigated whether the administration of histamine induces nociception in the TMJ and, if so, whether this effect is mediated by an indirect action on primary afferent nociceptors. Local administration of the H1-receptor antagonist pyrilamine prevented formalin-induced nociception in the TMJ in a dose-dependent manner. Local administration of histamine (250 microg) in the TMJ induced nociceptive behavior that was inhibited by co-administration of the lidocaine N-ethyl bromide quaternary salt QX-314 (2%) or the selective H1-receptor antagonist pyrilamine (400 microg). Nociception induced by histamine was also inhibited by pre-treatment with sodium cromoglycate (800 microg) and by co-administration of the 5-HT(3) receptor antagonist tropisetron (400 mug), while pyrilamine (400 mug) did not inhibit nociception induced by 5-hydroxytryptamine (5-HT, 250 microg) in the TMJ. Furthermore, histamine, in a dose that did not induce nociception by itself, strongly enhanced 5-HT-induced nociception. Finally, the administration of a sub-threshold dose of 5-HT (100 microg), but not of histamine (100 microg), elicited nociception in the TMJ previously challenged with the inflammatory agent carrageenan (100 microg). In conclusion, these data suggest that histamine induces TMJ nociception by an indirect mechanism involving endogenous release of 5-HT and activation of 5-HT(3) receptors on sensory afferents. It is proposed that histamine activates the H1 receptor to induce the release of 5-HT which depolarizes the nociceptor by activating 5-HT(3) receptor.

Serotonin (5-HT) excites rat masticatory muscle afferent fibers through activation of peripheral 5-HT3 receptors

In the present study, we combined immunohistochemical experiments with in vivo single unit recordings to examine whether 5-HT(3) receptors are expressed by masticatory (masseter and temporalis) sensory ganglion neurons and to investigate the effects of intramuscular injection of 5-HT on the excitability and mechanical threshold of rat masticatory muscle afferent fibers. The expression of 5-HT(3) receptors by masticatory ganglion neurons was examined using immunohistochemical techniques. In vivo extracellular single unit recording techniques were used to assess changes in the excitability of individual masticatory muscle afferent fibers. Immunohistochemical experiments detected a relatively high frequency (52%) of 5-HT(3) receptor expression by masticatory ganglion neurons. Injection of 5-HT (10(-4), 10(-3), 10(-2)M) evoked concentration-related increases in the magnitude of afferent discharge, but did not significantly sensitize muscle afferent fibers to mechanical stimuli. No significant sex-related differences in 5-HT-evoked afferent discharge were identified. Afferent discharge evoked by 5-HT was significantly attenuated by co-injection with the selective 5-HT(3) receptor antagonist tropisetron (10(-3)M). Afferent discharge was also evoked by the selective 5-HT(3) receptor agonist 2-methyl-5-HT. Unexpectedly, a significant concentration-related decrease in median blood pressure in response to 5-HT injection was found. This 5-HT-induced decrease in blood pressure was not antagonized by tropisetron or mimicked by 2-methyl-5-HT, indicating that the drop in blood pressure was not 5-HT(3) receptor-mediated. The present results indicate that 5-HT excites slowly conducting masticatory muscle afferent fibers through activation of peripheral 5-HT(3) receptors, and suggest that similar mechanisms may contribute to 5-HT-evoked muscle pain in human subjects.