Differential sensitivity of models of antinociception in the rat, mouse and guinea-pig to mu- and kappa-opioid receptor agonists.

1 A range of opioid receptor agonists were tested for activity in five antinociceptive models: the acetylcholine-induced abdominal constriction, tail-flick and hot plate tests in the mouse and the paw pressure test in the rat and guinea-pig. 2 Agonists acting preferentially at the kappa-opioid receptor were significantly more potent in the guinea-pig than in the rat paw pressure test, whereas mu-receptor preferring agonists were equipotent in the two tests. The mouse abdominal constriction test was of equal sensitivity to the guinea-pig pressure test for both types of agonist. 3 The mouse tail-flick and hot plate tests were progressively less sensitive than the other three tests, particularly to kappa-receptor preferring agonists. 4 The efficacy of an agonist can also markedly affect its activity in antinociceptive tests. Thus, partial kappa-agonists were weak or inactive in the rat paw pressure test, and partial agonists at both mu- and kappa-opioid receptors were relatively weak in the tests in which heat was the noxious stimulus, particularly the mouse hot plate test. 5 The mouse abdominal constriction test is suggested as the most appropriate antinociceptive model for testing a broad range of opioid agonists, whilst the relative potency of a drug in the rat and guinea-pig paw pressure tests may indicate the degree to which it is selective for kappa-opioid receptors in vivo.     

Synergistic and additive interactions of the cannabinoid agonist CP55,940 with mu opioid receptor and alpha2-adrenoceptor agonists in acute pain models in mice

1. Cannabinoid receptor agonists elicit analgesic effects in acute and chronic pain states via spinal and supraspinal pathways. We investigated whether the combination of a cannabinoid agonist with other classes of antinociceptive drugs exerted supra-additive (synergistic) or additive effects in acute pain models in mice. 2. The interactions between the cannabinoid agonist CP55,940, alpha2-adrenoceptor agonist dexmedetomidine and mu-opioid receptor agonist morphine were evaluated by isobolographic analysis of antinociception in hot plate (55 degrees C) and tail flick assays in conscious male Swiss mice. Drug interactions were examined by administering fixed-ratio combinations of agonists (s.c.) in 1:1, 3:1 and 1:3 ratios of their respective ED50 fractions. 3. CP55,940, dexmedetomidine and morphine all caused dose-dependent antinociception. In the hot plate and tail flick assays, ED50 values (mg kg(-1)) were CP55,940 1.13 and 0.51, dexmedetomidine 0.066 and 0.023, and morphine 29.4 and 11.3, respectively. Synergistic interactions existed between CP55,940 and dexmedetomidine in the hot plate assay, and CP55,940 and morphine in both assays. Additive interactions were found for CP55,940 and dexmedetomidine in the tail flick assay, and dexmedetomidine and morphine in both assays. 4. Thus, an alpha2-adrenoceptor agonist or mu opioid receptor agonist when combined with a cannabinoid receptor agonist showed significant synergy in antinociception in the hot plate test. However, for the tail flick nociceptive response to heat, only cannabinoid and mu opioid receptor antinociceptive synergy was demonstrated. If these results translate to humans, then prudent selection of dose and receptor-specific agonists may allow an improved therapeutic separation from unwanted side effects.     

Sex differences in opioid antinociception: kappa and 'mixed action' agonists.

A number of investigators have shown that male animals are more sensitive than females to the antinociceptive effects of mu-opioid agonists. The present study was conducted to examine sex differences in opioid antinociception in the rat using agonists known to differ in selectivity for and efficacy at kappa- versus mu-receptors. Dose- and time-effect curves were obtained for s.c. U69593, U50488, ethylketazocine, (-)-bremazocine, (-)-pentazocine, butorphanol and nalbuphine on the 50 or 54 degrees C hotplate and warm water tail withdrawal assays; spontaneous locomotor activity was measured 32-52 min post-injection in the same rats. On the hotplate assay, only butorphanol (54 degrees C) and nalbuphine (50 degrees C) were significantly more potent in males than females. On the tail withdrawal assay, all agonists were significantly more potent or efficacious in males than females at one or both temperatures. In contrast, no agonist was consistently more potent in one sex or the other in decreasing locomotor activity. Estrous stage in female rats only slightly influenced opioid effects, accounting for an average of 2.6% of the variance in females' antinociceptive and locomotor responses to drug (50 degrees C experiment). These results suggest that (1) sex differences in antinociceptive effects of opioids are not mu-receptor-dependent, as they may occur with opioids known to have significant kappa-receptor-mediated activity; (2) the mechanisms underlying sex differences in kappa-opioid antinociception may be primarily spinal rather than supraspinal; (3) sex differences in antinociceptive effects of opioid agonists are not secondary to sex differences in their sedative effects.     

Rat cold water tail-flick: a novel analgesic test that distinguishes opioid agonists from mixed agonist-antagonists

The models currently used to assess antinociceptive efficacy in animals are far from ideal. Those procedures that detect both opioid agonists and mixed agonist-antagonists fail to differentiate between them unless the noxious stimulus is adjusted. Furthermore, changes in the sensitivity of the test often result in positive responses being elicited from agents that are either not analgesics or only weak ones, at best. The technique described in this report uses cold water as the noxious stimulus in rats. It is simple, requires no complicated instrumentation or training, correlates well with clinical efficacy in man, and allows separation of opioid agonists from mixed agonist-antagonists without detecting non-opioid agents.     

Reversal by beta-funaltrexamine and 16-methyl cyprenorphine of the antinociceptive effects of opioid agonists in the mouse and guinea-pig

The present study compared the effects of two opioid antagonists, beta-funaltrexamine (beta-FNA) and 16-methyl cyprenorphine (RX8008M) on the antinociception produced by a range of opioid agonists in the abdominal constriction test in the mouse and the paw pressure test in the guinea-pig. Both antagonists produced large shifts in the dose-response curves to the mu-agonists, morphine and fentanyl, confirming their mu-antagonist activity. Neither antagonist produced any antagonism of the antinociceptive effects of the selective kappa-agonists U50488, U69593 and tifluadom, in the mouse. However, RX8008M produced small shifts in the dose-response curves to these agonists in the guinea-pig, which seems more likely to reflect mu-receptor activity of the agonists in the guinea-pig than lack of selectivity of the antagonists. Both beta-FNA and RX8008M produced some antagonism of bremazocine, ethyl-ketocyclazocine, proxorphan and butorphanol, indicating that these agonists have a prominent mu-receptor component to their antinociceptive actions.     

Stereospecific inhibition of oxotremorine-induced antinociception by (+)-isomers of opioid antagonists: comparison with opioid receptor agonists

The antagonistic effects of the two benzomorphan opioid antagonists, Mr-1452 and Mr-2266 and their respective (+)-isomers Mr-1453 and Mr-2267 upon morphine, ethylketocyclazocine (EKC), D-ala2-D-leu5-enkephalinamide (BW 180-C) and oxotremorine (OTMN) antinociceptive activity in mice were investigated. Pretreatment with either Mr-1452 (2.0 mg Kg-1 i.p.) or Mr-2266 (2.0 mg kg-1 i.p.) significantly antagonized the antinociceptive effects of the three opioid agonists in the hot plate test, but were ineffective against OTMN, which in contrast was antagonized by the (+)-isomers. Interaction between the antagonists and submaximal analgesic doses of the opioids or OTMN produced similar results in the tail immersion assay. However, the effect of Mr-2267 on OTMN was biphasic and this contrasted with Mr-1453 which produced consistent and graded antagonism.     

Air-induced writhing: A rapid broad spectrum assay for analgesics

The injection of air into the peritoneal cavity of rats produces reliable and quantifiable behavioral responses. These responses are blocked by compounds known to have analgesic properties, including opioid agonists, opioid agonist-antagonists, cyclo-oxygenase inhibitors, and amine potentiators. However, psychotropic agents were generally inactive at reasonable doses. The ability of this assay to identify a wide spectrum of analgesic agents in rats was superior to the hot plate, warm plate, and tail immersion assays.     

Studies on o-methylflavinantine

The antinociceptive effects of O-methylflavinantine (OMF), a morphinandienone alkaloid, were investigated in the mouse hot plate and abdominal constriction tests (nociceptive agents: 5-Hydroxytryptamine, acetylcholine, bradykinin, prostaglandin, E (1) (PGE (1), formic acid and phenylquinone). The potency of OMF in the hot plate test was approximately 10 times less than that of morphine and the effect was naloxone reversible. In the abdominal constriction test, morphine was 78-650 times more potent than OMF, depending on the nociceptive agent used, but a higher dose of naloxone was necessary to reverse the response to formic acid. Pretreatment of mice with reserpine (1 mg/kg, s.c., 24 h) reduced and alpha-methyl-p-tyrosine (200 mg/kg, i.p., 3 h) potentiated the antinociceptive effects of both morphine and OMF in the hot plate test. The results are considered to indicate that OMF possesses centrally mediated antinociceptive activity which is similar to that of morphine.     

A series of novel, highly potent and selective agonists for the kappa-opioid receptor.

1. This paper describes the opioid receptor pharmacology and in vivo activity of several novel benzene-acetamidopiperidine and benzeneacetamidopiperazine analogues. 2. These compounds all showed potent, naloxone-reversible, full agonist activity in the field-stimulated rabbit vas deferens, indicating that they are kappa-opioid agonists; but showed very little activity in the rat or hamster vas deferens, indicating good selectivity with regard to mu- and delta-opioid receptors. 3. They were all potent antinociceptive agents, the most potent compound, GR 103545, having an ED50 value in the mouse abdominal constriction test of 0.25 micrograms kg-1 s.c. The compounds also produced sedation and diuresis, but had little effect on respiration rate or gastrointestinal motility. 4. It is concluded that the seven novel compounds described are all potent and selective agonists for the kappa-opioid receptor.     

Differentiation of potent mu and kappa-opiate agonists using heat and pressure antinociceptive profiles and combined potency analysis

The antinociceptive profiles of strong mu- and kappa-opiate agonists were determined in the tail clip, hot plate (55 degrees C) and tail immersion (48 degrees C and 55 degrees C) tests in mice. All mu- and kappa-agonists produced steep dose-response lines in all the tests. Using a combined analysis of potencies for pressure against heat noxia it was possible to differentiate between mu- and kappa-agonists and this paralleled findings in other laboratories using isolated tissue preparations. It was also concluded that qualitative rather than quantitative differences between noxia were responsible for the observed differentiation since potency differences for mu- and kappa-agonists between tests were maintained even after the intensity of heat and pressure noxia were equated. It was also proposed that use of the combined tail clip and immersion tests may be useful for rapid behavioural classification of novel synthetic mu- and kappa-opiate analgesics.     

Antinociceptive activity of carvacrol (5‐isopropyl‐2‐methylphenol) in mice

Objectives Carvacrol (5‐isopropyl‐2‐methylphenol) is a monoterpenic phenol which is present in the essential oil of oregano and thyme. We have investigated the behavioural effects of carvacrol in animal models of pain, such as acetic acid‐induced abdominal constriction, formalin and hot‐plate tests in mice. The spontaneous motor activity of animals treated with carvacrol was investigated using open‐field and rotarod tests. Methods Carvacrol was administered orally, at single doses of 50 and 100 mg/kg while indometacin (5 mg/kg), morphine (7.5 mg/kg) and diazepam (2 mg/kg) were used as standard drugs. Naloxone (1 mg/kg) and l ‐arginine (150 mg/kg) were used to elucidate the possible antinociceptive mechanism of carvacrol on acetic acid‐induced abdominal constriction and formalin tests. Key findings The results showed that carvacrol produced significant inhibitions on nociception in the acetic acid‐induced abdominal constriction, formalin and hot‐plate tests. In the open‐field and rotarod tests carvacrol did not significantly impair the motor performance. The effect of the highest dose of carvacrol in mice in the acetic acid‐induced abdominal constriction and formalin tests were not reversed by naloxone or l ‐arginine. Conclusions Based on these results, it has been suggested that carvacrol presents antinociceptive activity that may not act through the opioid system nor through inhibition of the nitric oxide pathway.     

A comparison of the antinociceptive responses to the GABA-receptor agonists THIP and baclofen

The antinociceptive action of the gamma-aminobutyric acid (GABA) agonists THIP and baclofen was evaluated in mice using hot-plate (48 and 55 degrees C) and tail-immersion (50 degrees C) procedures. It was found that atropine reversed antinociception induced by THIP but not that induced by baclofen in the 48 degrees C test, whereas the anticholinergic drug blocked the response to both GABA agonists when the stimulus was provided by a 55 degrees C hot-plate. Atropine methylnitrate, mecamylamine, picrotoxin and bicuculline had no effect on antinociception induced by THIP or baclofen. Prior treatment with haloperidol enhanced only the response to baclofen on the 55 degrees C hot-plate. A reciprocal cross-tolerance was found between THIP and baclofen in the tail-immersion assay, although only THIP exhibited cross-tolerance to morphine. These results suggest that while the analgesic response to THIP and baclofen is partially mediated by a common system, the two agents act by independent mechanisms as well.     

The effect of naloxone on restraint-induced antinociception in mice.

Restraint for a period from 15-60 min induced significant antinociceptive effect in both male and female mice. The restraint animals all showed an increase in response time to the hot plate test at 55 degrees C. The antinociceptive activity was still apparent one hour after restraint. In the male animals, prior administration of naloxone s.c. 15 min before restraint for 60 min did not affect the degree of antinociceptive activity induced by restraint. In addition, naloxone administered s.c. immediately after restraint for 60 min also did not affect the degree of antinociceptive activity in male mice. These findings indicate that in male animals the endogenous opioid mechanism is most likely not involved in the restraint-induced antinociception. However, for the female mice naloxone administered s.c. either before or immediately after restraint for 60 min dose-dependently suppressed the antinociceptive activity induced by restraint. It is concluded that restraint can induce antinociceptive activity in mice; however, different mechanisms may be involved in the antinociception observed. In male mice the endogenous opioid systems do not seem to play a significant role in restraint-induced antinociception, while for female animals blockade of opioid receptors would greatly diminish the antinociception observed after restraint.     

Evaluation of analgesic and anti-inflammatory activities of Nectandra megapotamica (Lauraceae) in mice and rats

The bioactivity-guided phytochemical investigation of the crude hydralcoholic extract of Nectandra megapotamica was carried out using the abdominal constriction test in mice, which led to the isolation of three active compounds: alpha-asarone (1), galgravin (2) and veraguensin (3). The crude extract (EBCA, 300 mg kg(-1)) and isolated compounds 1,2, and 3, at different doses, were evaluated using the acetic acid-induced abdominal constriction test in mice, carrageenan-induced paw oedema in rats, and hot plate tests in rats. The EBCA showed a significant effect in the abdominal constriction and hot plate tests, but did not show activity in the rat paw oedema assay. All isolated compounds displayed activity in the abdominal constriction test, but only compound 1 was active in the hot plate test. Compounds 2 and 3 displayed activity in the anti-inflammatory assay. It was suggested that the analgesic effects obtained for EBCA could be due mainly to the presence of its major compound, alpha-asarone (1).     

Antinociceptive and anti-inflammatory activities of Dicranopteris linearis leaves chloroform extract in experimental animals

The present study was carried out to establish the antinociceptive and anti-inflammatory properties of Dicranopteris linearis leaves chloroform extract in experimental animals. The antinociceptive activity was measured using the abdominal constriction, formalin and hot plate tests, while the anti-inflammatory activity was measured using the carrageenan-induced paw edema. The extract, obtained after 72 h soaking of the air-dried leaves in chloroform followed by evaporation under vacuo (40 degrees C) to dryness, was dissolved in dimethyl sulfoxide to the doses of 20, 100 and 200 mg/kg and administered subcutaneously 30 min prior to subjection to the above mentioned assays. The extract, at all doses used, was found to exhibit significant (p<0.05) antinociceptive activity in a dose-dependent manner. However, the significant (p<0.05) anti-inflammatory activity observed occur in a dose-independent manner. As a conclusion, the chloroform extract of D. linearis possesses antinociceptive and anti-inflammatory activity and thus justify its traditional uses by the Malays to treat various ailments.     

The influences of temperature and naloxone on the antinociceptive activity of Corchorus olitorius L. in mice

A series of preliminary studies was carried out to evaluate the antinociceptive (pain relief) activity of the aqueous extract of Corchorus olitorius L. leaves (COAE) and to determine the influence of temperature and opioid receptors on COAE activity using the abdominal constriction and hot plate tests in mice. COAE, at concentrations of 10, 25, 50, 75, and 100%, showed both peripheral and central antinociception that are non-concentration- and concentration-dependent respectively. The peripheral activity was clearly observed at a concentration of 25% and diminished at a concentration of 100%, while the central activity was observed at all the concentrations of COAE used. Furthermore, the insignificant results obtained indicated that this peripheral activity (at concentrations of 25 and 50%) was comparable to that of morphine (0.8 mg/kg). Pre-heating COAE at a temperature of 80°C and 100°C, or 60°C and 80°C was found to enhance its peripheral and central antinociception respectively. Pre-treatment with naloxone (10 mg/kg), a general opioid receptor antagonist, for 5 min, followed by COAE, was found to completely block its peripheral, but not central, antinociceptive activity. Based on this observation, we conclude that the antinociceptive activity exhibited by C. olitorius is enhanced by the increase in temperature and may be mediated peripherally, but not centrally, at least in part, via an opioid receptor.     

Effects of yohimbine on the antinociceptive and place conditioning effects of opioid agonists in rodents

1. The pharmacological modulation of opioid actions by drugs acting on heterologous mechanisms could be useful to overcome some of the main problems associated with the use of opiate agonists. Based on previous findings on the interactions between yohimbine and opioid drugs, we have further studied the effects of yohimbine on the antinociceptive and positive-negative reinforcing effects of morphine (mu opioid receptor-preferring agonist), U-50,488 (kappa agonist) and SNC80 (delta agonist). 2. Pretreatment with yohimbine completely blocked the antinociception provided by the three opioid agonists in the mouse tail-immersion test. 3. A similar blockade of SNC80 and U-50,488-induced antinociception was observed with yohimbine in the mouse hot plate test at the same doses. In this paradigm, the effect of the kappa agonist was very slight and the actions of yohimbine rather variable. 4. In place conditioning experiments with SD (Sprague -- Dawley) male rats, yohimbine alone was inactive but it limited the preference induced by morphine and SNC80 and the aversive effect of U-50,488. Impaired novelty preference was also observed with the combination of yohimbine and U-50,488. 5. It is concluded that yohimbine tends to limit opioid antinociception and the addictive potential of mu and delta opioid agonists. More selective drugs could help to understand the mechanisms involved in these actions.     

Modulatory effects of dopamine D3/2 agonists on kappa opioid-induced antinociception and diuresis in the rat

RATIONALE: The dopamine (DA) D3/2 agonist 7-OH-DPAT has been shown to attenuate the behavioral effects of the mu agonist morphine as well as the development of morphine tolerance. OBJECTIVES: To evaluate the effects of DA D3/2 agonists [7-OH-DPAT, (+)-PD128,907, quinelorane, (-)-quinpirole], a D1 agonist (SKF38393), a D1 antagonist [(+)-SCH23390], a DA antagonist (spiperone), and an indirect DA agonist (cocaine) on the antinociceptive effects of kappa agonists (spiradoline, U69,593, bremazocine) as well as the effects of D3/2 agonists on the diuretic effects of spiradoline. METHODS: Antinociception was determined using a warm water (50-55 degrees C) tail-withdrawal procedure and urine output was collected over a 2-h interval. RESULTS: The antinociceptive effects produced by the kappa agonists varied with the intensity of the nociceptive stimulus (water), as maximal or near maximal effects were obtained with spiradoline at 55 degrees C, U69,593 at 52 degrees C, and bremazocine at 50 degrees C water. 7-OH-DPAT produced a dose-dependent attenuation of the antinociceptive effects of spiradoline, U69,593, and bremazocine. Spiperone completely reversed the effects of 7-OH-DPAT on spiradoline antinociception. (+)-PD128,907 and quinelorane, but not (-)-quinpirole or the other DAergic agents examined, attenuated the antinociceptive effects of spiradoline in a dose- and time-dependent manner. The diuretic effects of spiradoline were attenuated by 7-OH-DPAT, (+)-PD128,907, quinelorane, and (-)-quinpirole, and this attenuation was reversed by spiperone. CONCLUSIONS: The present study demonstrated that some D3/2 agonists can modulate both the antinociceptive and diuretic effects of kappa agonists. These modulatory actions are similar to those obtained against the effects of mu agonists.     

Role of histamine in rodent antinociception.

1. Effects of substances which are able to alter brain histamine levels on the nociceptive threshold were investigated in mice and rats by means of tests inducing three different kinds of noxious stimuli: mechanical (paw pressure), chemical (abdominal constriction) and thermal (hot plate). 2. A wide range of i.c.v. doses of histamine 2HCl was studied. Relatively high dose were dose-dependently antinociceptive in all three tests: 5-100 micrograms per rat in the paw pressure test, 5-50 micrograms per mouse in the abdominal constriction test and 50-100 micrograms per mouse in the hot plate test. Conversely, very low doses were hyperalgesic: 0.5 microgram per rat in the paw pressure test and 0.1-1 microgram per mouse in the hot plate test. In the abdominal constriction test no hyperalgesic effect was observed. 3. The histamine H3 antagonist, thioperamide maleate, elicited a weak but statistically significant dose-dependent antinociceptive effect by both parenteral (10-40 mg kg-1) and i.c.v. (1.1-10 micrograms per rat and 3.4-10 micrograms per mouse) routes. 4. The histamine H3 agonist, (R)-alpha-methylhistamine dihydrogenomaleate was hyperalgesic, with a rapid effect (15 min after treatment) following i.c.v. administration of 1 microgram per rat and 3 microgram per mouse, or i.p. administration of 100 mg kg-1 in mice. In rats 20 mg kg-1, i.p. elicited hyperalgesia only 4 h after treatment. 5. Thioperamide-induced antinociception was completely prevented by pretreatment with a non-hyperalgesic i.p. dose of (R)-alpha-methylhistamine in the mouse hot plate and abdominal constriction tests. Antagonism was also observed when both substances were administered i.c.v. in rats. 6. L-Histidine HCl dose-dependently induced a slowly occurring antinociception in all three tests. The doses of 250 and 500 mg kg-1, i.p. were effective in the rat paw pressure test, and those of 500 and 1500 mg kg-1, i.p. in the mouse hot plate test. In the mouse abdominal constriction test 500 and 1000 mg kg-1, i.p. showed their maximum effect 2 h after treatment. 7. The histamine N-methyltransferase inhibitor, metoprine, elicited a long-lasting, dose-dependent antinociception in all three tests by both i.p. (10-30 mg kg-1) and i.c.v. (50-100 micrograms per rat) routes. 8. To ascertain the mechanism of action of the antinociceptive effect of L-histidine and metoprine, the two substances were also studied in combination with the histamine synthesis inhibitor (S)-alpha-fluoromethylhistidine and with (R)-alpha-methylhistamine, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antinociceptive activity of a synthetic curcuminoid analogue, 2,6-bis-(4-hydroxy-3-methoxybenzylidene)cyclohexanone, on nociception-induced models in mice

Abstract: This study investigated the potential antinociceptive efficacy of a novel synthetic curcuminoid analogue, 2,6‐bis‐(4‐hydroxy‐3‐methoxybenzylidene)cyclohexanone (BHMC), using chemical‐ and thermal‐induced nociception test models in mice. BHMC (0.03, 0.1, 0.3 and 1.0 mg/kg) administered via intraperitoneal route (i.p.) produced significant dose‐related inhibition in the acetic acid‐induced abdominal constriction test in mice with an ID₅₀ of 0.15 (0.13–0.18) mg/kg. It was also demonstrated that BHMC produced significant inhibition in both neurogenic (first phase) and inflammatory phases (second phase) of the formalin‐induced paw licking test with an ID₅₀ of 0.35 (0.27–0.46) mg/kg and 0.07 (0.06–0.08) mg/kg, respectively. Similarly, BHMC also exerted significant increase in the response latency period in the hot‐plate test. Moreover, the antinociceptive effect of the BHMC in the formalin‐induced paw licking test and the hot‐plate test was antagonized by pre‐treatment with the non‐selective opioid receptor antagonist, naloxone. Together, these results indicate that the compound acts both centrally and peripherally. In addition, administration of BHMC exhibited significant inhibition of the neurogenic nociception induced by intraplantar injections of glutamate and capsaicin with ID₅₀ of 0.66 (0.41–1.07) mg/kg and 0.42 (0.38–0.51) mg/kg, respectively. Finally, it was also shown that BHMC‐induced antinociception was devoid of toxic effects and its antinociceptive effect was associated with neither muscle relaxant nor sedative action. In conclusion, BHMC at all doses investigated did not cause any toxic and sedative effects and produced pronounced central and peripheral antinociceptive activities. The central antinociceptive activity of BHMC was possibly mediated through activation of the opioid system as well as inhibition of the glutamatergic system and TRPV1 receptors, while the peripheral antinociceptive activity was perhaps mediated through inhibition of various inflammatory mediators.