The phthalimide analogues N-3-hydroxypropylphthalimide and N-carboxymethyl-3-nitrophthalimide exhibit activity in experimental models of inflammatory and neuropathic pain.

BACKGROUND: Phthalimide analogues devoid of the glutarimide moiety exhibit multiple biological activities, thus making them candidates for the treatment of patients with different diseases, including those with inflammatory and painful disorders. In the present study, the activities of five phthalimide analogues devoid of the glutarimide moiety (N-hydroxyphthalimide, N-hydroxymethylphthalimide, N-3-hydroxypropylphthalimide, N-carboxy-3-methylphthalimide, N-carboxymethyl-3-nitrophthalimide) were evaluated in experimental models of acute and chronic inflammatory and neuropathic pain. METHODS: The phthalimide analogues were administered per os (po) in Swiss mice or Wistar rats. Nociceptive response induced by formaldehyde and mechanical allodynia induced by chronic constriction injury (CCI) of the sciatic nerve or intraplantar (ipl) injection of complete Freund's adjuvant (CFA) were used as experimental models of pain. RESULTS: N-carboxymethyl-3-nitrophthalimide (700 mg/kg, -1 h) inhibited the second phase of the nociceptive response induced by the intraplantar injection of formaldehyde in mice. N-3-hidroxypropylphthalimide (546 mg/kg, -1 h) inhibited both phases of the nociceptive response induced by formaldehyde. Treatment of rats with N-carboxymethyl-3-nitrophthalimide (700 mg/kg) or N-3-hydroxypropylphthalimide (546 mg/kg) inhibited the mechanical allodynia induced by CCI of the sciatic nerve or ipl injection of CFA in rats. Intraperitoneal administration of the opioid antagonist naltrexone (10 mg/kg, -1.5 h) attenuated the antinociceptive activity of N-carboxymethyl-3-nitrophthalimide (700 mg/kg) in the model of nociceptive response induced by formaldehyde. CONCLUSIONS: N-3-hydroxypropylphthalimide and N-carboxymethyl-3-nitrophthalimide, two phthalimide analogues devoid of the glutarimide moiety, exhibited activities in different experimental models of pain, including models of chronic inflammatory and neuropathic pain.

Antiallodynic activity of leflunomide is partially inhibited by naltrexone and glibenclamide and associated with reduced production of TNF-α and CXCL-1.

Leflunomide, an immunosuppressive drug approved for the treatment of patients with rheumatoid arthritis, exhibits many mechanisms which may affect the nociceptive processing. Therefore, the present study aimed to evaluate the effect induced by leflunomide on the mechanical allodynia in models of inflammatory and neuropathic pain in mice and investigate mechanisms mediating such effects. Per os (p.o.) administration of leflunomide (25, 50 or 100mg/kg) inhibited the inflammatory edema and mechanical allodynia induced by intraplantar carrageenan. Even ongoing inflammatory edema and mechanical allodynia were reduced by leflunomide. Previous administration of naltrexone (10mg/kg, intraperitoneal) or glibenclamide (40mg/kg, p.o.) partially attenuated leflunomide antiallodynic activity. A single administration of leflunomide (50 or 100mg/kg, p.o.) also partially inhibited ongoing mechanical allodynia induced by chronic constriction injury (CCI) or repeated administrations of paclitaxel. The antiallodynic effect induced by leflunomide (50 or 100mg/kg, p.o.) in the model of neuropathic pain induced by CCI was associated with reduced production of tumor necrosis factor-α both at the injury site and ipsilateral paw. Leflunomide also reduced production of the chemokine CXCL-1 at the paw ipsilateral to the injury site. Concluding, leflunomide partially inhibited ongoing mechanical allodynia in models of inflammatory and neuropathic pain. The antiallodynic effect was associated with activation of opioidergic receptors and ATP-sensitive potassium channels and reduced production of inflammatory mediators. These data indicate leflunomide as a drug that should be further investigated aiming to identify a new analgesic pharmacotherapy and reinforces repositioning as an important strategy to identify new uses for approved drugs.

Thiamine and riboflavin inhibit production of cytokines and increase the anti-inflammatory activity of a corticosteroid in a chronic model of inflammation induced by complete Freund's adjuvant.

BACKGROUND: The effects induced by thiamine and riboflavin, isolated or in association with corticosteroids, in models of chronic inflammation are not known. Thus, we evaluated the effect induced by these B vitamins, isolated or in association with dexamethasone, on the mechanical allodynia, paw edema and cytokine production induced by complete Freund's adjuvant (CFA) in rats. METHODS: Chronic inflammation was induced by two injections of CFA. Nociceptive threshold, paw volume and body temperature were evaluated for 21days. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) contents were determined in paw tissue. Riboflavin (125, 250 or 500mg/kg) or thiamine (150, 300 or 600mg/kg) were administered per os (po), twice daily. Dexamethasone (0.5mg/kgday, po) was administered every three days. RESULTS: CFA induced long lasting mechanical allodynia and paw edema. Elevation of body temperature was observed for a short period. Riboflavin reduced neither paw edema nor mechanical allodynia. Thiamine did not change paw edema, but partially inhibited mechanical allodynia. Riboflavin (500mg/kg) and thiamine (600mg/kg) exacerbated the anti-inflammatory activity of dexamethasone. Riboflavin, thiamine and dexamethasone reduced TNF-α and IL-6 production. The association of dexamethasone with thiamine induced greater inhibition of IL-6 production when compared with that induced by dexamethasone. CONCLUSIONS: Riboflavin and thiamine exacerbate the anti-inflammatory activity of dexamethasone and reduce production of TNF-α and IL-6.

2-Phthalimidethanol and 2-phthalimidethyl nitrate inhibit mechanical allodynia, neutrophil recruitment and cytokine and chemokine production in a murine model of articular inflammation.

BACKGROUND: Phthalimide analogs have been shown to exhibit anti-inflammatory, analgesic and immunomodulatory activities in different preclinical assays. This study aimed to investigate the potential role of 2-phthalimidethanol (PTD-OH) and 2-phthalimidethyl nitrate (PTD-NO) in a murine model of antigen-induced articular inflammation. METHODS: Articular inflammation was induced by intra-articular injection of methylated bovine serum albumin (mBSA) in the knee joint of immunized male C57BL/6J mice. The animals were pre-treated with PTD-OH or PTD-NO (500mg/kg, per os, - 1h). Nociceptive threshold was measured using an electronic von Frey apparatus. The total number of leukocytes in the synovial cavity was determined. Concentrations of tumor necrosis factor (TNF)-α and CXCL-1 and myeloperoxidase (MPO) activity were determined in periarticular tissue. RESULTS: Both PTD-OH and PTD-NO inhibited at similar extent the mechanical allodynia, neutrophil recruitment to the synovial cavity and periarticular tissue and TNF-α and CXCL-1 production induced by intra-articular challenge with mBSA in immunized mice. CONCLUSIONS: PTD-OH and PTD-NO exhibit a marked activity in a murine model of antigen-induced articular inflammation in immunized animals. These results reinforce the interest in the investigation of phthalimide analogs devoid of the glutarimide ring as candidates to analgesic and anti-inflammatory drugs.

Nicorandil inhibits neutrophil recruitment in carrageenan-induced experimental pleurisy in mice.

Nicorandil is a drug characterized by the coupling of a nitric oxide (NO) donor to nicotinamide. We have previously demonstrated that nicotinamide exhibits activity in different models of pain and inflammation. Now, we investigated the effects induced by per os (p.o.) administration of nicorandil (25, 50 or 100mg/Kg) on neutrophil recruitment in a carrageenan-induced model of pleurisy in mice. Effects induced by nicorandil (100mg/kg) were compared with those induced by equimolar doses of nicotinamide (58mg/kg) and N-(2-hydroxyethyl)-nicotinamide (NHN; 79mg/kg). We also investigated whether effects on the production of inflammatory mediators play a role in the activity of nicorandil. P.o. nicorandil, 0.5h before and 1h after the i.pl. injection of carrageenan, reduced neutrophil recruitment. However, equimolar doses of nicotinamide or NHN failed to induce such effect. Single treatment (previous or late) with nicorandil (100mg/Kg, p.o.) also reduced neutrophils recruitment, although to a lesser extent when compared to the double treatment. Nicorandil reduced the concentrations of interleukin-1ß, CXCL-1 and prostaglandin E2 in the pleural exudate. Concluding, we demonstrated the activity of nicorandil in a model of pleurisy induced by carrageenan. This activity was characterized by reduction of the neutrophil accumulation and inhibition of production of inflammatory mediators. The effects induced by nicorandil on the leukocytes recruitment and production of inflammatory mediators contribute to a better understanding of its clinical benefits and indicate that these benefits may be due to its vasodilating and anti-inflammatory activities.

Opioid pathways activation mediates the activity of nicorandil in experimental models of nociceptive and inflammatory pain.

We have previously demonstrated that nicorandil inhibits the second phase of the nociceptive response induced by formaldehyde. In the present study, we evaluated the effects induced by nicorandil in other models of nociceptive and inflammatory pain in mice and also whether opioid pathways activation mediates its activity. As we have previously demonstrated, per os (p.o.) administration of nicorandil (50, 100 or 150mg/kg; -1h) inhibited the second phase of the nociceptive response induced by intraplantar (i.pl.) injection of formaldehyde. Nicorandil (50, 100 or 150mg/kg; p.o., -1h) also exhibited activity in models of inflammatory pain induced by i.pl. injection of carrageenan (300µg) and nociceptive pain induced by exposure to noxious heat (50°C). Intraperitoneal (i.p.) administration of the opioid antagonist naltrexone (1, 5 or 10mg/kg, -30min) attenuated or abolished the antinociceptive activity of nicorandil (100mg/kg, p.o.) in the three experimental pain models. In conclusion, we demonstrate that nicorandil exhibits activity in different models of nociceptive and inflammatory pain. The demonstration that the antinociceptive effect induced by nicorandil is markedly attenuated by an opioid antagonist provides solid information about an important mechanism mediating the activity of this antianginal drug. Altogether, our data suggest that the clinical pain relief induced by nicorandil in heart ischemic conditions may result from both vasodilation and intrinsic analgesic activity.

Activities of 2-phthalimidethyl nitrate and 2-phthalimidethanol in the models of nociceptive response and edema induced by formaldehyde in mice and preliminary investigation of the underlying mechanisms.

The activities of 2-phthalimidethyl nitrate (PTD-NO) and 2-phthalimidethanol (PTD-OH) were recently demonstrated in models of pain and inflammation. We expanded our investigation by evaluating their activities in models of nociceptive and inflammatory pain and inflammatory edema, the preliminary pharmacokinetic parameter for PTD-NO and the role of opioid and cannabinoid pathways in the activity of analogs. Per os (p.o.) administration of PTD-NO or PTD-OH, 1h before intraplantar injection of formaldehyde, inhibited both phases of the nociceptive response (500 and 750 mg/kg) and paw edema (125, 250, 500 and 750 mg/kg). After p.o. administration of PTD-NO, peak plasma concentrations of PTD-NO and PTD-OH were found 0.92 and 1.13 h, respectively. The plasma concentrations of PTD-NO were higher than those of PTD-OH. Intraperitoneal (i.p.) administration of CB1 (AM251) or CB2 (AM630) cannabinoid receptor antagonists (4 or 8 mg/kg, -30 min) or opioid antagonist naltrexone (5 or 10mg/kg, -30 min) did not affect the antinociceptive activities of the analogs. AM251 (8 mg/kg, i.p., -30 min) attenuated the antiedematogenic activity of both analogs, while naltrexone (10mg/kg, i.p., -30 min) only attenuated the antiedematogenic activity of PTD-NO. The antiedematogenic activities of both analogs were not affected by the CB2 cannabinoid antagonist AM630 (4 or 8 mg/kg, i.p., -30 min). Concluding, we expanded the knowledge on the activities of PTD-NO and PTD-OH by showing that these phthalimide analogs also exhibit marked activity in models of nociceptive and inflammatory pain and inflammatory edema. Opioid and cannabinoid mechanisms partially mediate the anti-inflammatory, but not the antinociceptive activity.

Activities of 2-phthalimidethanol and 2-phthalimidethyl nitrate, phthalimide analogs devoid of the glutarimide moiety, in experimental models of inflammatory pain and edema.

The reintroduction of thalidomide in the pharmacotherapy greatly stimulated the interest in the synthesis and pharmacological evaluation of phthalimide analogs with new and improved activities and also greater safety. In the present study, we evaluated the activities of two phthalimide analogs devoid of the glutarimide ring, namely 2-phthalimidethanol (PTD-OH) and 2-phthalimidethyl nitrate (PTD-NO), in experimental models of inflammatory pain and edema in male C57BL/6J mice. Intraplantar (i.pl.) injection of carrageenan (300 µg) induced mechanical allodynia and this response was inhibited by previous per os (p.o.) administration of PTD-OH and PTD-NO (750 mg/kg) and also by thalidomide (500 or 750 mg/kg). The edema induced by carrageenan was also inhibited by previous p.o. administration of PTD-OH (500 and 750 mg/kg) and PTD-NO (125, 250, 500 or 750 mg/kg), but not by thalidomide. Carrageenan increased tumor necrosis factor (TNF)-α and CXCL1 concentrations and also the number of neutrophils in the paw tissue. Previous p.o. administration of PTD-NO (500 mg/kg) reduced all the parameters, while PTD-OH (500 mg/kg) reduced only the accumulation of neutrophils. Thalidomide, on the other hand, was devoid of effect on these biochemical parameters. Plasma concentrations of nitrite were increased after p.o. administration of the phthalimide analog coupled to a NO donor, PTD-NO (500 mg/kg), but not after administration of PTD-OH or thalidomide. In conclusion, our results show that small molecules, structurally much simpler than thalidomide or many of its analogs under investigation, exhibit similar activities in experimental models of pain and inflammation. Finally, as there is evidence that the glutarimide moiety contributes to the teratogenic effect of many thalidomide analogs, our results indicate that phthalimide analogs devoid of this functional group could represent a new class of analgesic and anti-inflammatory candidates with potential greater safety.

Anti-inflammatory and antinociceptive activities of azadirachtin in mice.

Azadirachta indica (Meliaceae) extracts have been reported to exhibit anti-inflammatory and antinociceptive properties. However, the activities of azadirachtin, a limonoid and the major bioactive compound found in the extracts, have been poorly investigated in animal models. In the present study, we investigated the effects induced by azadirachtin in experimental models of pain and inflammation in mice. Carrageenan-induced paw edema and fibrovascular tissue growth induced by subcutaneous cotton pellet implantation were used to investigate the anti-inflammatory activity of azadirachtin in mice. Zymosan-induced writhing and hot plate tests were employed to evaluate the antinociceptive activity. To explore putative mechanisms of action, the level of tumor necrosis factor-α in inflammatory tissue was measured and the effect induced by opioidergic and serotonergic antagonists was evaluated. Previous per os (p. o.) administration of azadirachtin (120 mg/kg) significantly reduced the acute paw edema induced by carrageenan. However, the concomitant increase of the paw concentration of tumor necrosis factor-α induced by this inflammatory stimulus was not reduced by azadirachtin. In addition to inhibiting the acute paw edema induced by carrageenan, azadirachtin (6, 60, and 120 mg/kg) inhibited the proliferative phase of the inflammatory response, as demonstrated by the reduced formation of fibrovascular tissue growth. Azadirachtin (120 mg/kg) also inhibited the nociceptive response in models of nociceptive (hot plate) and inflammatory (writhing induced by zymosan) pain. The activity of azadirachtin (120 mg/kg) in the model of nociceptive pain was attenuated by a nonselective opioid antagonist, naltrexone (10 mg/kg, i. p.), but not by a nonselective serotonergic antagonist, cyproheptadine. In conclusion, this study demonstrates the activity of azadirachtin in experimental models of nociceptive and inflammatory pain, and also in models of acute and chronic inflammation. Finally, multiple mechanisms, including the inhibition of the production of inflammatory mediators and activation of endogenous opioid pathways, may mediate azadirachtin activities in experimental models of inflammation and pain.

Synthesis, antinociceptive activity and pharmacokinetic profiles of nicorandil and its isomers.

Nicorandil (N-(2-hydroxyethyl)nicotinamide nitrate) is an antianginal drug, which activates guanylyl cyclase and opens the ATP-dependent K(+) channels, actions that have been suggested to mediate its vasodilator activity. We synthesized nicorandil and its two isomers, which vary in the positions of the side chain containing the nitric oxide (NO) donor, and also their corresponding denitrated metabolites. The activities of these compounds were evaluated in an experimental model of pain in mice. Pharmacokinetic parameters of nicorandil and its isomers, as well as the plasma concentrations of the corresponding denitrated metabolites and also nicotinamide and nitrite were determined. Nicorandil exhibited the highest antinociceptive activity, while the ortho-isomer was the least active. Nicorandil and para-nicorandil, which induced higher plasma concentrations of nitrite, exhibited higher antinociceptive activity, which suggests that the release of NO may mediate this activity.

A minocycline derivative reduces nerve injury-induced allodynia, LPS-induced prostaglandin E2 microglial production and signaling via toll-like receptors 2 and 4.

Many studies have shown that minocycline, an antibacterial tetracycline, suppresses experimental pain. While minocycline's positive effects on pain resolution suggest that clinical use of such drugs may prove beneficial, minocycline's antibiotic actions and divalent cation (Ca(2+); Mg(2+)) chelating effects detract from its potential utility. Thus, we tested the antiallodynic effect induced by a non-antibacterial, non-chelating minocycline derivative in a model of neuropathic pain and performed an initial investigation of its anti-inflammatory effects in vitro. Intraperitoneal minocycline (100mg/kg) and 12S-hydroxy-1,12-pyrazolinominocycline (PMIN; 23.75 mg/kg, 47.50mg/kg or 95.00 mg/kg) reduce the mechanical allodynia induced by chronic constriction injury of mouse sciatic nerve. PMIN reduces the LPS-induced production of PGE2 by primary microglial cell cultures. Human embryonic kidney cells were transfected to express human toll-like receptors 2 and 4, and the signaling via both receptors stimulated with PAM3CSK4 or LPS (respectively) was affected either by minocycline or PMIN. Importantly, these treatments did not affect the cell viability, as assessed by MTT test. Altogether, these results reinforce the evidence that the anti-inflammatory and experimental pain suppressive effects induced by tetracyclines are neither necessarily linked to antibacterial nor to Ca(2+) chelating activities. This study supports the evaluation of the potential usefulness of PMIN in the management of neuropathic pain, as its lack of antibacterial and Ca(2+) chelating activities might confer greater safety over conventional tetracyclines.

Activity of nicorandil, a nicotinamide derivative with a nitrate group, in the experimental model of pain induced by formaldehyde in mice.

Nicorandil (2-nicotinamide ethyl nitrate), an antianginal drug characterized by the coupling of nicotinamide with a nitric oxide (NO) donor, activates guanylyl cyclase and opens ATP-dependent K(+) channels. In the present study, we investigated the effects induced by per os (p.o.) administration of nicorandil (12.5, 25 or 50 mg/kg) or equimolar doses (corresponding to the highest dose of nicorandil) of N-(2-hydroxyethyl) nicotinamide (NHN), its main metabolite, or nicotinamide in the model of nociceptive response induced by formaldehyde in mice. Nicorandil, but not NHN or nicotinamide, inhibited the second phase of the nociceptive response. This activity was observed when nicorandil was administered between 30 and 120 min before the injection of formaldehyde. Ipsilateral intraplantar injection of nicorandil (125, 250 or 500 µg/paw) did not inhibit the nociceptive response. After p.o. administration of nicorandil (50 mg/kg), peak plasma concentrations of this compound and NHN were observed 0.63 and 4 h later, respectively. Nicotinamide concentrations were not increased after administration of nicorandil. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 1 or 2 mg/kg), a guanylyl cyclase inhibitor, partially attenuated the antinociceptive activity of nicorandil. However, this activity was not changed by glibenclamide (30 or 60 mg/kg), an inhibitor of ATP-dependent K(+) channels. In conclusion, we demonstrated the antinociceptive activity of nicorandil in a model of pain that exhibits both a nociceptive and an inflammatory profile. This activity is not mediated by nicotinamide or NHN. The coupling of an NO-donor to nicotinamide results in a compound with an increased potency. The NO-cGMP pathway, but not ATP-dependent K(+) channels, partially mediates the antinociceptive activity of nicorandil.

Neutrophil recruitment is inhibited by nicotinamide in experimental pleurisy in mice.

Several emerging lines of evidence support an anti-inflammatory role for nicotinamide and other vitamin B components. However, the mechanisms underlying their activity remain unclear. In the present study, we investigated the ability of nicotinamide to inhibit both neutrophil recruitment in IL-8-, LTB(4)- or carrageenan-induced pleurisy in mice and the rolling and adherence of neutrophils. Nicotinamide inhibited IL-8-, LTB(4)- and carrageenan-induced neutrophil migration, KC production and carrageenan-induced neutrophil rolling and adherence. We propose that the effects of nicotinamide in inhibiting neutrophil recruitment in carrageenan-induced pleurisy may be due to the ability of nicotinamide to inhibit the action of IL-8 and LTB(4), decrease KC production, and inhibit early events that regulate leukocyte migration from blood vessels into tissue.

Nicotinic acid induces antinociceptive and anti-inflammatory effects in different experimental models.

Although in vitro studies have shown that nicotinic acid inhibits some aspects of the inflammatory response, a reduced number of in vivo studies have investigated this activity. To the best of our knowledge, the effects induced by nicotinic acid in models of nociceptive and inflammatory pain are not known. Per os (p.o.) administration of nicotinic acid (250, 500 or 1000 mg/kg, -1 h) inhibited the first and the second phases of the nociceptive response induced by formalin in mice. Nicotinic acid (250 or 500 mg/kg, -1 and 3 h) also inhibited the mechanical allodynia induced by carrageenan in rats, a model of inflammatory pain. However, in a model of nociceptive pain, exposure of mice to a hot-plate, nicotinic acid was devoid of activity. In addition to inhibiting the nociceptive response in models of inflammatory pain, nicotinic acid (250 or 500 mg/kg, p.o., -1 and 3 h) inhibited paw edema induced by carrageenan in mice and rats. Picolinic acid (62.5 or 125 mg/kg, p.o., -1 h), a nicotinic acid isomer, inhibited both phases of the nociceptive response induced by formalin, but not paw edema induced by carrageenan in mice. The other nicotinic acid isomer, isonicotinic acid, was devoid of activity in these two models. In conclusion, our results represent the first demonstration of the activity of nicotinic acid in experimental models of nociceptive and inflammatory pain and also provide further support to its anti-inflammatory activity. It is unlikely that conversion to nicotinamide represents an important mechanism to explain the antinociceptive and anti-inflammatory activities of nicotinic acid. The demonstration of new activities of nicotinic acid, a drug that has already been approved for clinical use and presents a positive safety record, may contribute to raise the interest in conducting clinical trials to investigate its usefulness in the treatment of painful and inflammatory diseases.

Antinociceptive and anti-inflammatory activities of nicotinamide and its isomers in different experimental models.

Although there is evidence for the anti-inflammatory activity of nicotinamide, there is no evaluation of its effects in models of nociceptive and inflammatory pain. In addition, there is no information about the potential anti-inflammatory and antinociceptive activities of the nicotinamide isomers, picolinamide and isonicotinamide. Per os (p.o.) administration of nicotinamide (1000 mg/kg, -1h) inhibited the first and second phases of the nociceptive response induced by formalin in mice. In the model of nociceptive pain, exposure of mice to a hot-plate (50°C), nicotinamide (1000 mg/kg, -1h) also presented antinociceptive activity. Nicotinamide (500 mg/kg, -1 and 3h) also inhibited the mechanical allodynia induced by carrageenan in rats, a model of inflammatory pain. In addition to inhibiting the nociceptive response, nicotinamide (500 or 1000 mg/kg, -1 and 3h) inhibited the paw edema induced by carrageenan in mice and rats. P.o. administration of picolinamide (125 mg/kg, -1h) and isonicotinamide (500 or 1000 mg/kg, -1h) inhibited the second phase of the nociceptive response induced by formalin in mice. The paw edema induced by carrageenan in mice was also inhibited by isonicotinamide (500 or 1000 mg/kg, -1h) and picolinamide (125 mg/kg, -1h and 3h). The results represent the first demonstration of the activity of nicotinamide and its isomers in models of nociceptive and inflammatory pain and provide support to their anti-inflammatory activity. The demonstration of new activities for nicotinamide is important as it may contribute to expand its use in the treatment of other pathological conditions.

Peripheral 5-HT1B and 5-HT2A receptors mediate the nociceptive response induced by 5-hydroxytryptamine in mice.

While the role of 5-hydroxytryptamine (5-HT, serotonin) in the nociceptive processing has been widely investigated in the central nervous system, information regarding its role in peripheral tissues is still lacking. Noteworthy, 5-HT induces phenotypic changes of nociceptors and peripheral injection induces pain in humans and nociceptive response in rodents. However, local receptors involved in 5-HT effects are not well characterized. Thus, we aimed to investigate the role of 5-HT and some of its receptors in the peripheral nociceptive processing in mice. Intraplantar injection of 5-HT (10, 20 or 40 µg) into the hind-paw of mice induced paw licking behavior, which was inhibited by previous intraplantar treatment with cyproheptadine (5-HT(1) and 5-HT(2) antagonist; 0.5 or 5 µg), mianserin (5-HT(2) and 5-HT(6) antagonist; 0.1 µg), isamoltane (5-HT(1B) antagonist; 0.5 or 5 µg) and ketanserin (5-HT(2A) antagonist; 0.1 or 1 µg), but not by BRL 15572 (5-HT(1D) antagonist; 1 or 10 µg), ondansetron (5-HT(3) antagonist; 1, 5, 10 or 20 µg) and SB 269970 (5-HT(7) antagonist; 2.5 and 25 µg). Altogether, these results indicate the local involvement of 5-HT(1), 5-HT(2) and 5-HT(6), especially 5-HT(1B) and 5-HT(2A), in the nociceptive response induced by 5-HT in mice, thus contributing to a better understanding of 5-HT role in the peripheral nociceptive processing. In addition, they also point to important species differences and the need of a wide evaluation of the peripheral nociceptive processing in mice as these animals have been increasingly used in studies investigating the cellular and molecular mechanisms mediating the nociceptive response.

Effects induced by Apis mellifera venom and its components in experimental models of nociceptive and inflammatory pain.

The effects induced by Apis mellifera venom (AMV), melittin-free AMV, fraction with molecular mass < 10 kDa (F<10) or melittin in nociceptive and inflammatory pain models in mice were investigated. Subcutaneous administration of AMV (2, 4 or 6 mg/kg) or melittin-free AMV (1, 2 or 4 mg/kg) into the dorsum of mice inhibited both phases of formaldehyde-induced nociception. However, F<10 (2, 4 or 6 mg/kg) or melittin (2 or 3 mg/kg) inhibited only the second phase. AMV (4 or 6 mg/kg), but not F<10, melittin-free AMV or melittin, induced antinociception in the hot-plate model. Paw injection of AMV (0.05 or 0.10 mg), F<10 (0.05 or 0.1 mg) or melittin (0.025 or 0.050 mg) induced a nociceptive response. In spite of inducing nociception after paw injection, scorpion (Tityus serrulatus) or snake (Bothrops jararaca) venom injected into the dorsum of mice did not inhibit formaldehyde-induced nociception. In addition, AMV (6 mg/kg), but not F<10 (6 mg/kg) or melittin (3 mg/kg), inhibited formaldehyde paw oedema. Concluding, AMV, F<10 and melittin induce two contrasting effects: nociception and antinociception. AMV antinociception involves the action of different components and does not result from non-specific activation of endogenous antinociceptive mechanisms activated by exposure to noxious stimuli.