The role of neuropeptides and capsaicin-sensitive fibres in glutamate-induced nociception and paw oedema in mice

Bradykinin Receptors Play a Critical Role in the Chronic Post-ischaemia Pain Model

Complex regional pain syndrome type-I (CRPS-I) is a chronic painful condition resulting from trauma. Bradykinin (BK) is an important inflammatory mediator required in acute and chronic pain response. The objective of this study was to evaluate the association between BK receptors (B₁ and B₂) and chronic post-ischaemia pain (CPIP) development in mice, a widely accepted CRPS-I model. We assessed mechanical and cold allodynia, and paw oedema in male and female Swiss mice exposed to the CPIP model. Upon induction, the animals were treated with BKR antagonists (HOE-140 and DALBK); BKR agonists (Tyr-BK and DABK); antisense oligonucleotides targeting B₁ and B₂ and captopril by different routes in the model (7, 14 and 21 days post-induction). Here, we demonstrated that treatment with BKR antagonists, by intraperitoneal (i.p.), intraplantar (i.pl.), and intrathecal (i.t.) routes, mitigated CPIP-induced mechanical allodynia and oedematogenic response, but not cold allodynia. On the other hand, i.pl. administration of BKR agonists exacerbated pain response. Moreover, a single treatment with captopril significantly reversed the anti-allodynic effect of BKR antagonists. In turn, the inhibition of BKRs gene expression in the spinal cord inhibited the nociceptive behaviour in the 14th post-induction. The results of the present study suggest the participation of BKRs in the development and maintenance of chronic pain associated with the CPIP model, possibly linking them to CRPS-I pathogenesis.

Antinociceptive and anti-inflammatory effects of 1,2-bis-(4 methoxyphenylselanyl) styrene in mice: involvement of the serotonergic system

BACKGROUND

Pain is one of the most prevalent, costly and disabling conditions that reduces quality of life. Although there are many analgesics available, there is some concern regarding their efficacy, safety and side effects. Organic selenium compounds are attractive targets of various research groups due to their pharmacological properties.

OBJECTIVES

The aim of this study was to evaluate the antinociceptive and anti-inflammatory activity of 1,2-bis-(4-methoxyphenylselanyl) styrene (BMOSE) in mice, as well as to investigate the mechanism involved in the antinociceptive effect.

METHODS

The animals were submitted to the formalin and glutamate tests. The assessment of the possible involvement of the serotonergic system in BMOSE antinociceptive activity was performed using the glutamate test. Also, we investigated the possible toxicity of the compound.

KEY FINDINGS

1,2-bis-(4-methoxyphenylselanyl) styrene (0.1-50 mg/kg, i.g.) was efficient in avoiding nociception induced by glutamate and formalin and also reduced paw oedema. The possible involvement of 5-HT₃ serotoninergic receptor antagonist ondansetron blocked the antinociceptive effect of BMOSE. The acute toxicity assays did not show any toxicity related to the administration of BMOSE (200 mg/kg).

CONCLUSIONS

It is possible to conclude that BMOSE has both antinociceptive and anti-inflammatory activity, and the serotoninergic system, more specifically, the 5-HT₃ receptor, is involved in the effect.

Anti-inflammatory and analgesic effects of Bi-yuan-ling granules

Bi-yuan-ling granule (BLG) is a traditional Chinese medicine compound composed mainly of baicalin and chlorogenic acid. It has been demonstrated to be clinically effective for various inflammatory diseases such as acute rhinitis, chronic rhinitis, atrophic rhinitis and allergic rhinitis. However, the underlying mechanisms of BLG against these diseases are not fully understood. This study aimed to explore the anti-inflammatory and analgesic activities of BLG, and examine its protective effects on mouse acute lung injury (ALI). The hot plate test and acetic acid-induced writhing assay in Kunming mice were adopted to evaluate the pain-relieving effects of BLG. The anti-inflammatory activities of BLG were determined by examining the effects of BLG on xylene-caused ear swelling in Kunming mice, the cotton pellet-induced granuloma in rats, carrageenan-induced hind paw edema and lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. The results showed that BLG at 15.5 mg/g could significantly relieve the pain by 82.5% (P<0.01) at 1 h after thermal stimulation and 91.2% (P<0.01) at 2 h after thermal stimulation. BLG at doses of 7.75 and 15.5 mg/g reduced the writhing count up to 33.3% (P<0.05) and 53.4% (P<0.01), respectively. Additionally, the xylene-induced edema in mice was markedly restrained by BLG at 7.75 mg/g (P<0.05) and 15.5 mg/g (P<0.01). BLG at 5.35 and 10.7 mg/g significantly reduced paw edema by 34.8% (P<0.05) and 37.9% (P<0.05) at 5 h after carrageenan injection. The granulomatous formation of the cotton pellet was profoundly suppressed by BLG at 2.68, 5.35 and 10.7 mg/g by 15.4%, 38.2% (P<0.01) and 58.9% (P<0.001), respectively. BLG also inhibited lung W/D ratio and the release of prostaglandin E2 (PGE2) in ALI mice. In addition, the median lethal dose (LD50), median effective dose (ED50) and half maximal inhibitory concentration (IC50) of BLG were found to be 42.7, 3.2 and 12.33 mg/g, respectively. All the findings suggest that BLG has significantly anti-inflammatory and analgesic effects and it may help reduce the damage of ALI.

Antinociceptive, anti-inflammatory and smooth muscle relaxant activities of the pyrrolo[3,4-d]pyridazinone derivatives: Possible mechanisms of action

The aim of this study was to evaluate the analgesic as well as anti-inflammatory activities of the new pyrrolo[3,4-d]pyridazinone derivatives. Moreover, the present study attempted to assess some of the mechanisms involved in the pharmacological activity of these compounds. In the previous studies it was shown that these compounds were highly active in the phenylbenzoquinone-induced 'writhing syndrome' test and had much lower activity in the hot plate, which indicates that mainly peripheral mechanisms of analgesia are involved in their effects. In these extended studies the analgesic activity of two tested compounds (4c, 4f) was confirmed in some animal models of pain. The studied compounds showed a significant and dose-related antinociceptive effect in the models of pain induced by formalin, capsaicin and glutamic acid. Both compounds decreased the edema formation and one of them (4c) attenuated mechanical hyperalgesia in carrageenan-induced paw inflammation in rats. Furthermore, both compounds inhibited cell migration, plasma exudation and nociceptive reaction in zymosan A-induced mouse peritonitis. In the subsequent studies, including experiments on isolated organs (ileum, trachea, aorta), radioligand assays and biochemical tests, it was demonstrated that analgesic and anti-inflammatory effects of the investigated structures are largely due to their competitive antagonism for histamine H1 receptor. The influence on the level of cAMP in inflammatory cells (shown in RAW 264.7 macrophages) and subsequent inhibition of cytokine (TNFα, IL-1β) release can also be one of the important mechanisms of their action. Moreover some additional mechanisms may also be involved in the eventual analgesic effect of tested pyrrolo[3,4-d]pyridazinone derivatives.

Cellular prion protein protects from inflammatory and neuropathic pain

Cellular prion protein (PrP^C) inhibits N-Methyl-D-Aspartate (NMDA) receptors. Since NMDA receptors play an important role in the transmission of pain signals in the dorsal horn of spinal cord, we thus wanted to determine if PrP^C null mice show a reduced threshold for various pain behaviours.

We compared nociceptive thresholds between wild type and PrP^C null mice in models of inflammatory and neuropathic pain, in the presence and the absence of a NMDA receptor antagonist. 2-3 months old male PrP^C null mice exhibited an MK-801 sensitive decrease in the paw withdrawal threshold in response both mechanical and thermal stimuli. PrP^C null mice also exhibited significantly longer licking/biting time during both the first and second phases of formalin-induced inflammation of the paw, which was again prevented by treatment of the mice with MK-801, and responded more strongly to glutamate injection into the paw. Compared to wild type animals, PrP^C null mice also exhibited a significantly greater nociceptive response (licking/biting) after intrathecal injection of NMDA. Sciatic nerve ligation resulted in MK-801 sensitive neuropathic pain in wild-type mice, but did not further augment the basal increase in pain behaviour observed in the null mice, suggesting that mice lacking PrP^C may already be in a state of tonic central sensitization. Altogether, our data indicate that PrP^C exerts a critical role in modulating nociceptive transmission at the spinal cord level, and fit with the concept of NMDA receptor hyperfunction in the absence of PrP^C.

Glutamate pharmacology and metabolism in peripheral primary afferents: physiological and pathophysiological mechanisms

In addition to using glutamate as a neurotransmitter at central synapses, many primary sensory neurons release glutamate from peripheral terminals. Primary sensory neurons with cell bodies in dorsal root or trigeminal ganglia produce glutaminase, the synthetic enzyme for glutamate, and transport the enzyme in mitochondria to peripheral terminals. Vesicular glutamate transporters fill neurotransmitter vesicles with glutamate and they are shipped to peripheral terminals. Intense noxious stimuli or tissue damage causes glutamate to be released from peripheral afferent nerve terminals and augmented release occurs during acute and chronic inflammation. The site of action for glutamate can be at the autologous or nearby nerve terminals. Peripheral nerve terminals contain both ionotropic and metabotropic excitatory amino acid receptors (EAARs) and activation of these receptors can lower the activation threshold and increase the excitability of primary afferents. Antagonism of EAARs can reduce excitability of activated afferents and produce antinociception in many animal models of acute and chronic pain. Glutamate injected into human skin and muscle causes acute pain. Trauma in humans, such as arthritis, myalgia, and tendonitis, elevates glutamate levels in affected tissues. There is evidence that EAAR antagonism at peripheral sites can provide relief in some chronic pain sufferers.

The nociception induced by glutamate in mice is potentiated by protons released into the solution

In this study we compare the effect of a glutamate solution with pH adjusted to 7 (3-30 micromol/paw), a non-pH-adjusted glutamate solution (.3-30 micromol/paw, pH range 2.24-1.14), and an acid solution (2% acetic acid, pH 1.4-7) in terms of causing licking behavior in mice. The sum of licking seconds was recorded in the first 15 minutes following the intraplantar (i.pl.) injection of the solutions. Protons potentiated the nociception induced by glutamate. The ED(50) values were 2.5 (1.5-4.2) and 15.1 (11.5-19.9) micromol/paw for the non-pH-adjusted and pH-adjusted glutamate solutions, respectively. The acid solutions at pH 1.4, 2 and 4 induced a similar nociception. The blocking of the acid-sensitive ion channels (ASICs) by amiloride and the antagonism of the transient receptor potential vanilloid subtype-1 (TRPV1) by capsazepine, injected via i.pl., significantly decreased the nociception mediated by acid and by non-pH-adjusted glutamate solutions, but did not affect the nociception caused by the pH-adjusted glutamate solution. The pretreatment with the NMDA-receptor antagonist (MK-801, i.pl.), with the cyclooxygenase inhibitor (indomethacin, i.pl.) or the disruption of the sensorial C fibers by capsaicin, decreased the nociceptive effect of the 3 algogen tested. In summary, the protons present in aqueous solution of glutamate can cause nociception per se or can potentiate the nociception caused by glutamate. These effects are related to the activation of ASICs, TRPV1 and NMDA receptors, inhibition of the synthesis of prostanoids, and disruption of the C fibers.

PERSPECTIVE

The nociception induced by glutamate is a useful method for investigation of the mechanisms of nociception and the effects of new analgesic drugs. Our findings showed that the protons released from glutamic acid have to be removed from the solution to avoid misinterpretation of results in the search for new analgesic drugs.

Peripheral inhibition of glutaminase reduces carrageenan-induced Fos expression in the superficial dorsal horn of the rat

In inflamed tissue, the levels of the excitatory amino acid glutamate are increased. Glutamate sensitizes peripheral axons of primary afferent neurons during inflammation leading to decreased firing threshold and hyperexcitability. One proposed source of glutamate is the primary afferent. Antagonizing glutamate receptors on peripheral axons of primary afferents during inflammation provides analgesia in animals and humans. The enzyme glutaminase is used by primary sensory neurons to convert glutamine to glutamate, and peripheral inhibition of glutaminase with 6-diazo-5-oxo-l-norleucine (DON) provides long-lasting analgesia during inflammation. In this study, we measured the effects of glutaminase inhibition on carrageenan-induced spinal Fos expression. Rats were given intraplantar injections of carrageenan and treated locally with either vehicle or DON. After 3h of inflammation, hind paw swelling and spinal expression of Fos were examined. CellProfiler was used to automate Fos nuclei counting in five laminar groupings in the spinal cord (I-II, III-IV, V-VI, VII-IX, X). Carrageenan increased hind paw thickness by approximately 70% and spinal Fos expression in superficial (I-II) and deep (V-VI) laminae by 10-fold and 5-fold, respectively. Treatment with DON reduced hind paw swelling by approximately 13% and suppressed Fos expression in the laminae I-II by approximately 54%, but not the deep laminae. Our results further support the notion of glutamate as a peripheral inflammatory mediator and indicate that glutaminase should be considered as a novel therapeutic target for treatment of inflammatory pain.

Evidence of TRPV1 receptor and PKC signaling pathway in the antinociceptive effect of amyrin octanoate

Previous studies from our group investigated the antinociceptive property of amyrin octanoate, a synthetic compound derivative from natural precursor alpha, beta-amyrin, against nociceptive response induced by acetic acid and formalin. Here, we investigated some of the mechanisms of action underlying the antinociceptive effects of amyrin octanoate. Amyrin octanoate given intraperitoneally (0.001-1 mg /kg) or intrathecally (10-1000 ng /site) caused dose-dependent and long-lasting inhibition of acetic acid-induced visceral nociception, with mean ID(50) values of 0.003 (0.001-0.005) mg/kg and 122.4 (60.8-246.6) ng/site, respectively. In the capsaicin- and glutamate-induced paw licking, amyrin octanoate caused significant and dose-dependent inhibition of both nociceptive responses, with ID(50) values of 1.36 and 0.04 mg/kg, respectively. Furthermore, amyrin octanoate also reduced significantly the nociception caused by intrathecal injection of glutamate, substance P and capsaicin, with inhibitions of 36+/-11%, 67+/-10% and 78+/-5%, respectively. The antinociception caused by amyrin octanoate in the acetic acid test was significantly attenuated by neonatal pretreatment of mice with capsaicin, but seems to involve mechanisms independent of G(i/o) protein, opioidergic, serotonergic, noradrenergic and cholinergic system, since it was not affected by pertussis toxin, naloxone, yohimbine, mecamylamine or atropine. In addition, amyrin octanoate reduced thermal and mechanical hyperalgesia induced by bradykinin and phorbol myristate acetate in rats, without affecting similar responses caused by prostaglandin E(2). Taken together, the present results shown that octanoate amyrin produces antinociceptive and antihyperalgesic effects, through an interaction with capsaicin-sensitive fibers and the inhibition of the PKC signaling pathway.

Further analysis of the antinociceptive action caused by p-methoxyl-diphenyl diselenide in mice

The objective of this study was to extend our previous findings by investigating in greater detail the mechanisms that might be involved in the antinociceptive action of p-methoxyl-diphenyl diselenide, (MeOPhSe)(2), in mice. The pretreatment with nitric oxide precursor, l-arginine (600 mg/kg, intraperitoneal, i.p.), reversed antinociception caused by (MeOPhSe)(2) (10 mg/kg, p.o.) or N(G)-nitro-l-arginine (l-NOARG, 75 mg/kg, i.p.) in the glutamate test. Ondansetron (0.5 mg/kg, i.p., a 5-HT(3) receptor antagonist) and SCH23390 (0.05 mg/kg, i.p.., a D(1) receptor antagonist) blocked the antinociceptive effect caused by (MeOPhSe)(2). Conversely, pindolol (1 mg/kg, i.p., a 5-HT(1A)/(1B) receptor/beta adrenoceptor antagonist), WAY 100635 (0.7 mg/kg, i.p., a selective 5-HT(1A) receptor antagonist), ketanserin (0.3 mg/kg, i.p., a selective 5-HT(2A) receptor antagonist), prazosin (0.15 mg/kg, i.p., an alpha(1)-adrenoreceptor antagonist), yohimbine (1.0 mg/kg, i.p., an alpha(2)-adrenoreceptor antagonist), sulpiride (5 mg/kg, i.p., a D(2) receptor antagonist), naloxone (1 mg/kg, i.p., a non-selective opioid receptor antagonist) and caffeine (3 mg/kg, i.p., a non-selective adenosine receptor antagonist) did not change the antinociceptive effect of (MeOPhSe)(2). (MeOPhSe)(2) significantly inhibited nociception induced by intraplantar (i.pl.) injection of bradykinin (10 nmol/paw) and Des-Arg(9)-bradykinin (10 nmol/paw, a B(1) receptor agonist). (MeOPhSe)(2) significantly inhibited phorbol myristate acetate (PMA, 0.03 mug/paw, a protein kinase C (PKC) activator)-induced licking response. These results indicate that (MeOPhSe)(2) produced antinociception in mice through mechanisms that involve an interaction with nitrergic system, 5-HT(3) and D(1) receptors. The antinociceptive effect is related to (MeOPhSe)(2) ability to interact with kinin B(1) and B(2) receptors and PKC pathway mediated mechanisms.

The role of kinin B1 receptors in the nociception produced by peripheral protein kinase C activation in mice

The peripheral injection of phorbol myristate acetate (PMA) into the mouse paw induces nociception mediated through activation of protein kinase C (PKC). In the present study, we examine the contribution of kinin B1 receptor to PMA-induced nociception. Nociception was assessed after intraplantar injection of PMA or the B1 receptor agonist des-Arg9-bradykinin in mice. Mechanisms of nociception were studied using the combination of knockout mice, selective drugs, and measurement of B1 receptor mRNA and protein levels. Peripheral injection of PMA (50 pmol/paw) induced a nociceptive behaviour that was abolished by selective B1 receptor antagonist des-Arg9-Leu8-bradykinin or by the B1 receptor gene deletion. Moreover, PMA treatment did not alter B1 receptor mRNA levels, but greatly increased B1 receptor protein levels in the mouse paw. The injection of des-Arg9-bradykinin did not cause nociception in naive mice, but produced marked nociception in animals previously treated with a low dose of PMA (0.5 nmol/paw). The co-treatment of PMA with selective PKC or protein synthesis inhibitors, but not with p38 mitogen activated protein kinase (MAPK) or transcription inhibitors significantly reduced des-Arg9-bradykinin-induced nociception. On the other hand, the co-administration of selective PKC or p38 MAPK inhibitors, but not of protein synthesis or transcription inhibitors, reduced des-Arg9-bradykinin-induced nociception when evaluated in PMA pre-injected animals. These results suggest that the B1 receptor exerts a critical role in the nociception caused by PKC activation in peripheral tissues. Since the PKC pathway is downstream of several pro-inflammatory mediators, B1 receptor stimulation appears to contribute to the acute inflammatory pain process.

Involvement of cellular prion protein in the nociceptive response in mice

The role of the cellular prion protein (PrP(c)) in neuronal functioning includes neuronal excitability, cellular adhesion, neurite outgrowth and maintenance. Here we investigated the putative involvement of the PrP(c) function on the nociceptive response using PrP(c) null (Prnp(0/0)) and wild-type (Prnp(+/+)) mice submitted to thermal and chemical models of nociception. PrP(c) null mice were more resistant than wild-type mice to thermal nociception of the tail-flick test. However, no significant difference was found on the hot plate test. In the acetic acid-induced visceral nociception, PrP(c) null mice showed an enhanced response when compared to wild-type mice. However, there was no difference between Prnp(0/0) and wild-type mice on glutamate- and formalin-induced licking behaviour and Freund's Complete Adjuvant (FCA)-induced mechanical allodynia. PrP(c) null mice developed significantly lower paw edema than wild-type mice. In addition, the visceral conditioning stimuli produced by a previous injection of acetic acid (20 days before testing) significantly reduced early and late phases of formalin-induced nociception in wild-type mice. In contrast, the same pre-treatment did not alter the formalin response in PrP(c) null mice. These results indicate a role of PrP(c) in the nociceptive transmission, including the thermal tail-flick test and visceral inflammatory nociception (acetic acid-induced abdominal constriction). Our findings show that PrP(c) is involved with a response mediated by inflammation (paw edema) and by visceral conditioning stimuli.

Effects of subcutaneous administration of glutamate on pain, sensitization and vasomotor responses in healthy men and women

The present study aimed to investigate if (1) subcutaneous injection of glutamate induces pain, sensitization and vasomotor responses in humans and (2) if sex differences exist in these responses. Thirty healthy volunteers (men-15 and women-15) were included. Each subject received four subcutaneous injections (0.1ml; glutamate 100, 10, 1mM and isotonic saline 0.9%) into the forehead skin in two sessions separated by one week. Assessments of pain intensity (VAS), quality, distribution; area of pinprick hyperalgesia; pressure pain threshold (PPT) at the injection site; surface skin temperature and local blood flow were performed at predetermined time points. The highest concentration of glutamate evoked the highest pain intensity, the longest duration of pain and the largest pain area under the VAS-time curve (P<0.001) in both men and women, although responses in women were larger than in men (P<0.05). The face-chart pain area was the largest for the highest concentration of glutamate (P<0.001) and women drew a larger pain area than men (P=0.024). The area of pinprick hyperalgesia was the largest for glutamate 100mM (P<0.001) and women indicated a larger area than men (P<0.001). Concentration-dependent local vasomotor responses were found following the subcutaneous injection of glutamate but there was no sex difference in this effect. Glutamate 100mM significantly reduced the PPT values (P<0.001) without sex-related differences. The present study demonstrates for the first time that subcutaneous injection of glutamate evokes pain, vasomotor responses and pinprick hyperalgesia in human volunteers and that there are sex-related differences in some of these responses.

Sensitivity of rat temporalis muscle afferent fibers to peripheral N-methyl-D-aspartate receptor activation

The temporalis muscle is a common source of pain in headache and chronic craniofacial pain conditions such as temporomandibular disorders, which have an increased prevalence in women. The characteristics of slowly conducting temporalis afferent fibers have not been investigated. Therefore, the aim of the present study was to examine the characteristics of slowly conducting temporalis muscle afferent fibers and to determine whether these fibers are excited by activation of peripheral N-methyl-D-aspartate receptors. The response properties of a total of 117 temporalis afferent fibers were assessed in male and female rats. A majority of these fibers had high mechanical thresholds and slow conduction velocities (<10 m/s). The mechanical threshold of the temporalis afferent fibers was inversely correlated with afferent conduction velocity, however, no sex-related differences in mechanical threshold were identified. There were also no sex-related differences in N-methyl-D-aspartate-evoked afferent discharge. Indeed, injection of a high concentration (1600 mM) of N-methyl-D-aspartate into the temporalis muscle was necessary to evoke significant afferent discharge. Thirty minutes after the initial injection of N-methyl-D-aspartate into the temporalis muscle, a second injection of N-methyl-D-aspartate produced a response only about 50% as large as the initial injection. Co-injection of ketamine (20 mM) with the second injection of N-methyl-D-aspartate significantly decreased N-methyl-D-aspartate-evoked afferent discharge in both sexes. This concentration of ketamine is greater than that needed to attenuate afferent discharge evoked by injection of glutamate into the masseter muscle. These results suggest that unlike masseter afferent fibers, temporalis afferent fibers are relatively insensitive to peripheral N-methyl-D-aspartate receptor activation.

The sesquiterpenes polygodial and drimanial in vitro affect glutamatergic transport in rat brain

Natural products including those derived from plants, have over the years greatly contributed to the development of therapeutic drugs. Polygodial and drimanial are sesquiterpenes isolated from the bark of the plant Drymis Winteri (Winteraceae) that exhibit antinociceptive properties. Since peripheral glutamate presents nociceptive actions, in this study it was investigated the effects of hydroalcooholic extracts from Drymis winteri (polygodial and drimanial) on the glutamatergic system in rat brain. Polygodial and drimanial inhibited glutamate uptake by astrocytes, as well as by cortical, hippocampal and striatal slices, and increased synaptosomal glutamate release. These concurrent effects would predispose to an increase in the extracellular glutamate concentrations, leading to possible neurotoxic effects (excitotoxicity) of these natural compounds, which would suggest the need for some caution in their therapeutic application.

Pharmacological and molecular characterization of the mechanisms involved in prostaglandin E2-induced mouse paw edema

The present study evaluated some of the mechanisms underlying prostaglandin E2 (PGE2)-induced paw edema formation in mice. Intraplantar (i.pl.) injection of PGE2 (0.10-10.0 nmol/paw) into the hindpaw elicited a dose-related edema formation, with a mean ED50 value of 0.42 nmol/paw. The coinjection of selective E-prostanoid (EP)3 [(2E)-N-[(5-bromo-2-methoxyphenyl)-sulfonyl]-3-[5-chloro-2-(2-naphthylmethyl)phenyl]acrylamide; L826266), but not EP2 or EP4 (all 10 nmol/paw), receptor antagonists significantly inhibited PGE2-induced paw edema. Like L826266, the PGE2-induced paw edema was markedly reduced by treatment with pertussis toxin and phospholipase C (PLC) inhibitor 1-[6-[[17beta-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U-73122). Likewise, the selective neurokinin (NK)1 receptor antagonist N-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl)carbonyl-l-prolyl]-N-methyl-N-phenyl-methyl-3-(2-aphthyl)-l-alaninamide (FK888) and the antagonist of vanilloid receptor (TRPV1) receptors 4'-chloro-3-methoxycinnamanilide (SB366791) (both 1 nmol/paw) also significantly inhibited PGE2-mediated paw edema. Conversely, the selective NK2, NK3, and calcitonin gene-related peptide (CGRP) CGRP(8-37) receptor antagonists all failed to interfere with PGE2-induced paw edema. The neonatal treatment of mice with capsaicin was also able to reduce PGE2-induced paw edema. The inhibitors of protein kinase C (PKC) 3-[1-[3-(dimethylaminopropyl]-1H-indol-3-yl]-4-(1H-indol-3-yl)-1H-pyrrole-2,5-dione monohydrochloride (GF109203X) and mitogen protein-activated kinases (MAPKs; 30 nmol/paw) c-Jun NH2-terminal kinase (JNK) (anthra[1,9-cd]pyrazol-6(2H)-one; SP600125), extracellular signal-regulated kinase (PD98059), and p38 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole; SB203580], but not protein kinase A, markedly decreased the PGE2-mediated edema formation. The i.pl. injection of PGE2 (3 nmol/paw) induced a significant activation of MAPKs, namely, JNK and p38, an effect that was largely prevented by the selective EP3 receptor antagonist L826266 (10 nmol/paw). Collectively, these findings indicate that edematogenic responses elicited by PGE2 are mediated by EP3 receptor activation, also involving the stimulation of PLC, PKC, and MAPKs pathways and the participation of TRPV1 and NK1 receptors. These results make a considerable contribution to our comprehension of the mechanisms involved in PGE2-mediated inflammatory responses in mice.

Ketamine attenuates glutamate-induced mechanical sensitization of the masseter muscle in human males

The purpose of the present study was to determine whether glutamate-induced mechanical sensitization of the masseter muscle in human volunteers involves activation of peripheral N-methyl-D-aspartate (NMDA) receptors. Healthy male volunteers (n=18) participated in this randomized, two-session study. During each session, the volunteers received two injections into the right masseter muscle. An initial injection of glutamate (1 M, 0.2 ml) alone was followed 30 min later by a second injection of glutamate alone or glutamate combined with ketamine (10 mM). Pressure pain threshold (PPT) was assessed over the right masseter muscle at and 2 cm above the injection site, as well as over the right temporalis muscle and left masseter muscle prior to the first injection. The PPT was reassessed at all four sites every 5 min from 10 to 30 min after the second injection and once again 60 min after the second injection. Glutamate-evoked muscle pain, pain area and the sensory pain response index of the McGill pain questionnaire were all significantly reduced by co-injection of ketamine. The mean PPT values were significantly decreased by approximately 10%, 10, 15 and 25 min after injection of glutamate, but only over the site of injection. Co-injection of ketamine with glutamate also completely blocked the glutamate-induced mechanical sensitization 15 min post-injection as compared with glutamate alone. The lack of spread of mechanical sensitization outside the area of glutamate injection is consistent with the view that glutamate-induced mechanical sensitization results from a peripheral mechanism. The attenuation of glutamate-induced mechanical sensitization by ketamine suggests that this effect is mediated, in part, through activation of peripheral NMDA receptors.

Antinociceptive effect of proanthocyanidins from Croton celtidifolius bark

The chemical composition of the chromatography 63 subfraction (63SF) from the ethyl acetate soluble fraction of the crude extract of Croton celtidifolius bark presented a high content of total proanthocyanidins (75.0+/-2.3%). HPLC analysis of 63SF revealed a dimeric profile (e.g.catechin-(4alpha-->8)-catechin and gallocatechin-(4alpha-->8)-catechin) and polymeric proanthocyanidins. In pharmacological investigations, 63SF administered intraperitoneally exhibited dose-dependent antinociceptive activity against several chemical stimuli, including the intraperitoneal injection of acetic acid (ID50 (the dose of 63SF which was able to reduce the nociceptive response by 50% relative to the control value)=0.9 (0.5-1.6)) and the intraplantar injection of capsaicin (ID50=13.0 (10.0-17.0)), glutamate (ID50=4.0 (2.0-7.0)) and formalin (ID50 first phase=36.0 (24.0-53.0) and late phase=11.0 (8.0-14.0)). 63SF administered orally exhibited an antinociceptive effect in the formalin test (ID50 first phase=125.0 (89.0-177.0) and late phase=65.0 (33.0-95.0)). In the same test, 63SF was effective when given soon after the first phase, as well as exhibiting therapeutic activity. Furthermore, 63SF was effective in models of thermal nociception including tail-flick and hot-plate tests. When the mice were treated in the neonatal period with capsaicin, the antinociceptive effect of 63SF in the first phase of the formalin test was abolished, but pretreatment with naltrexone did not change the antinociceptive effect of 63SF. Together, these results provide evidence that 63SF exerted a pronounced systemic antinociception against chemical (acetic acid, formalin, glutamate and capsaicin tests) and thermal (hot-plate and tail-flick tests) nociceptive models of pain in mice at a dose that did not interfere with the locomotor activity. The mechanism by which this sub-fraction produced antinociception remains unclear, but it is unlikely to involve the activation of the opioid system. However, unmyelinated C-fibres sensitive to treatment with capsaicin are likely to participate in antinociception caused by 63SF.

Mechanisms involved in the antinociception caused by agmatine in mice

The present study examined the antinociceptive effects of agmatine in chemical behavioural models of pain. Agmatine (1-30 mg/kg), given by i.p. route, 30 min earlier, produced dose-dependent inhibition of acetic acid-induced visceral pain, with mean ID50 value of 5.6 mg/kg. Given orally, 60 min earlier, agmatine (10-300 mg/kg) also produced dose-related inhibition of the visceral pain caused by acetic acid, with mean ID50 value of 147.3 mg/kg. Agmatine (3-100 mg/kg, i.p.) also caused significant and dose-dependent inhibition of capsaicin- and glutamate-induced pain, with mean ID50 values of 43.7 and 19.5 mg/kg, respectively. Moreover, agmatine (1-100 mg/kg, i.p.) caused marked inhibition of both phases of formalin-induced pain, with mean ID50 values for the neurogenic and the inflammatory phases of 13.7 and 5.6 mg/kg, respectively. The antinociception caused by agmatine in the acetic acid test was significantly attenuated by i.p. treatment of mice with L-arginine (precursor of nitric oxide, 600 mg/kg), naloxone (opioid receptor antagonist, 1 mg/kg), p-chlorophenylalanine methyl ester (PCPA, an inhibitor of serotonin synthesis, 100 mg/kg once a day for 4 consecutive days), ketanserin (a 5-HT2A receptor antagonist, 0.3 mg/kg), ondansetron (a 5-HT3 receptor antagonist, 0.5 mg/kg), yohimbine (an alpha2-adrenoceptor antagonist, 0.15 mg/kg) or by efaroxan (an I1 imidazoline/alpha2-adrenoceptor antagonist, 1 mg/kg). In contrast, agmatine antinociception was not affected by i.p. treatment of animals with pindolol (a 5-HT1A/1B receptor antagonist, 1 mg/kg) or idazoxan (an I2 imidazoline/alpha2-adrenoceptor antagonist, 3 mg/kg). Likewise, the antinociception caused by agmatine was not affected by neonatal pre-treatment with capsaicin. Together, these results indicate that agmatine produces dose-related antinociception in several models of chemical pain through mechanisms that involve an interaction with opioid, serotonergic (i.e., through 5-HT2A and 5-HT3 receptors) and nitrergic systems, as well as via an interaction with alpha2-adrenoceptors and imidazoline I1 receptors.

Kinin B1 receptors: key G-protein-coupled receptors and their role in inflammatory and painful processes

Kinins are a family of peptides implicated in several pathophysiological events. Most of their effects are likely mediated by the activation of two G-protein-coupled receptors: B(1) and B(2). Whereas B(2) receptors are constitutive entities, B(1) receptors behave as key inducible molecules that may be upregulated under some special circumstances. In this context, several recent reports have investigated the importance of B(1) receptor activation in certain disease models. Furthermore, research on B(1) receptors in the last years has been mainly focused in determining the mechanisms and pathways involved in the process of induction. This was essentially favoured by the advances obtained in molecular biology studies, as well as in the design of selective and stable peptide and nonpeptide kinin B(1) receptor antagonists. Likewise, development of kinin B(1) receptor knockout mice greatly helped to extend the evidence about the relevance of B(1) receptors during pathological states. In the present review, we attempted to remark the main advances achieved in the last 5 years about the participation of kinin B(1) receptors in painful and inflammatory disorders. We have also aimed to point out some groups of chronic diseases, such as diabetes, arthritis, cancer or neuropathic pain, in which the strategic development of nonpeptidic oral-available and selective B(1) receptor antagonists could have a potential relevant therapeutic interest.

Role of kinin B1 and B2 receptors in the development of pilocarpine model of epilepsy

The tissue sclerosis found in epilepsy of limbic origin is characterized by shrunken gliotic hippocampus, granule cell loss in the dentate gyrus and extensive pyramidal cell loss in Ammon's horn. Evidence has indicated that sprouting of dentate granule cell axons into the inner molecular layer of the dentate gyrus is related to hyperexcitability. Trying to understand the role of kinin B1 and B2 receptors in the physiopathology of temporal lobe epilepsy (TLE), the present work was delineated to study the development of the epilepsy model induced by pilocarpine in B1 and B2 knockout mice (B1KO and B2KO, respectively). Behavior parameters, cell death and mossy fiber sprouting were analyzed. B1KO mice showed increased latency for the first seizure, associated to a decreased frequency of spontaneous seizures, when compared with wild-type mice. In addition, B1KO mice showed less cell death in all hippocampal formation associated to a reduced grade of mossy fiber sprouting. Furthermore, B2KO mice presented minor duration of the silent period and an increased frequency of spontaneous seizures, when compared with wild-type mice. B2KO and their control lineage showed similar pattern of cell death in the hippocampus, which was very intense when compared with saline-treated animals. The mossy fiber sprouting was also increased in B2KO mice, when compared to wild-type mice and saline-treated animals. Taken together, these data suggest a deleterious effect for kinin B1 receptor and a protective effect for kinin B2 receptor during the development of the temporal lobe epilepsy.

Evidence for the involvement of metabotropic glutamatergic, neurokinin 1 receptor pathways and protein kinase C in the antinociceptive effect of dipyrone in mice

This study aimed to investigate further the mechanisms involved in the antinociception caused by dipyrone, given by intraperitoneal (i.p.) or intrathecal (i.t.) routes. The intraperitoneal administration of dipyrone to mice 30 min prior resulted in a significant and dose-related inhibition of the biting responses induced by i.t. injection of glutamate, trans-ACPD or substance P (SP). In addition, dipyrone given by i.t. route, 15 min before glutamate, trans-ACPD or SP, also produced a significant reduction in their nociceptive effects. In addition, dipyrone given by i.t. route, 15 min before glutamate, trans-ACPD or SP, also produced a significant reduction in their nociceptive effects. Dipyrone, given either systemically (i.p.) or by i.t. route also caused a dose-dependent inhibition of phorbol myristate acetate (PMA)-induced nociception. Given by systemic route, dipyrone inhibited PMA-induced paw oedema formation. Collectively, these results extend previous data from our group indicating that glutamatergic-mediated pain responses, specifically those mediated by metabotropic receptor subtype, together with inhibition of neurokinin NK(1)-mediated response, account for the antinociceptive action of dipyrone in mice. Furthermore, we have also produced experimental evidence indicating that the activation of the protein kinase C-dependent pathway plays a role in the dipyrone antinociceptive action.

Sensory neuropeptide mRNA up-regulation is bilateral in periodontitis in the rat: a possible neurogenic component to symmetrical periodontal disease

Periodontal disease is a common multifactorial chronic inflammatory disease in humans. In inflammatory conditions that are known to be associated with changes in nociception, such as arthritis, the neuronal expression of the proinflammatory neuropeptides, substance P and calcitonin gene-related peptide is altered. In this study the expression of these neuropeptides' mRNAs has been studied in an inflammatory model that shows no behavioural evidence of altered nociception. Periodontitis was induced in male rats by intragingival injection of lipopolysaccharide adjacent to the second right mandibular molar. The animals were killed at various times after lipopolysaccharide injection and right and left trigeminal ganglia and brain were processed for in situ hybridization for beta-preprotachykinin and alpha-calcitonin gene-related peptide mRNAs. Expression of both neuropeptide mRNAs was significantly increased only in small neurons in the mandibular division of the trigeminal ganglion ipsilateral to the LPS injection from 3 to 10 days postinjection. Neuropeptide mRNA expression was also significantly increased in the contralateral trigeminal ganglion at day 10. No significant changes in neuropeptide mRNA levels were seen in the maxillary and ophthalmic divisions of the trigeminal ganglia or in the trigeminal mesencephalic nucleus. The up-regulation of substance P and CGRP mRNAs in periodontal disease suggests that this is associated with the inflammatory process rather than nociception, as this disease does not appear to result in altered nociception in either rats or humans. The contralateral alteration in neuropeptide mRNA expression suggests a role for neurogenic mechanisms in the development of periodontal disease.