Opioid, cannabinoid CB1 and NOP receptors do not mediate APAP-induced hypothermia in rats

Acetaminophen (APAP) produces antinociception and hypothermia. Because the antinociceptive effect in rats is partially dependent on opioid and cannabinoid CB₁ receptor activation, we determined if activation of these receptors also contributes to the hypothermic effect of APAP. Rats injected with APAP (100, 250, 375 or 500 mg/kg, i.p.) displayed dose-related hypothermia. For combined administration, the hypothermic effect of APAP (400 mg/kg, i.p.) was not altered by pretreatment with: naltrexone (10 mg/kg, s.c.), a non-selective opioid antagonist; naltrindole (1 mg/kg, s.c.), a delta opioid antagonist; nor-binaltorphimine (10 mg/kg, i.p.), a kappa opioid antagonist; SR 141716A (3 mg/kg, i.m.), a cannabinoid CB₁ receptor antagonist; or JTC-801(1 mg/kg, i.p.), a nociceptin/orphanin FQ peptide (NOP) receptor antagonist. The demonstration that APAP produces hypothermia independent of opioid, cannabinoid CB₁ or NOP receptor activation is contrary to its antinociceptive effect, which requires opioid and cannabinoid CB₁ receptor activation.     

Antinociceptive Effects of Racemic AM1241 and Its Chirally Synthesized Enantiomers: Lack of Dependence upon Opioid Receptor Activation

Cannabinoid CB₂ receptors represent a therapeutic target that circumvents unwanted central side effects (e.g., psychoactivity and/or addiction) associated with activation of CB₁ receptors. One of the primary investigative tools used to study functions of the CB₂ receptor is the aminoalkylindole (R,S)-AM1241. However, (R,S)-AM1241 has been described as an atypical CB₂ agonist which produces antinociception mediated indirectly by opioid receptors. (R,S)-AM1241 and its enantiomers, (R)-AM1241 and (S)-AM1241, were evaluated for antinociception in response to thermal (Hargreaves) and mechanical (von Frey) stimulation. Pharmacological specificity was established using antagonists for CB₁ (rimonabant [SR141716]) and CB₂ (SR144528). The opioid antagonist naloxone was administered locally in the paw or systemically to evaluate the contribution of opioid receptors to CB₂-mediated antinociception produced by (R,S)-AM1241, (R)-AM1241, and (S)-AM1241. Comparisons were made with the opioid analgesic morphine. (R,S)-AM1241, (R)-AM1241, and (S)-AM1241 (0.033–10 mg/kg i.p.) produced antinociception to thermal, but not mechanical, stimulation of the hindpaw in naive rats. Antinociception produced by (R,S)-AM1241 and (S)-AM1241 exhibited an inverted U-shaped dose response curve. (R)-AM1241 produced greater antinociception than either (S)-AM1241 or (R,S)-AM1241 at the lowest (0.033 and 0.1 mg/kg i.p.) and highest (10 mg/kg i.p.) doses. Similar levels of antinociception were observed at intermediate doses. (R,S)-AM1241, (R)-AM1241, and (S)-AM1241 each produced CB₂-mediated antinociception that was blocked by SR144528 but not by rimonabant. Local and systemic naloxone blocked morphine-induced antinociception but did not block antinociceptive effects of (R,S)-AM1241, (R)-AM1241, or (S)-AM1241. The antinociceptive effects of the CB₂-selective cannabinoid (R,S)-AM1241 and its enantiomers, (R)-AM1241 and (S)-AM1241, are not dependent upon opioid receptors.     

Modulation of opioids via protection of anandamide degradation by fatty acid amide hydrolase

Lack of involvement of the opioid system with the endocannabinoid, arachidonylethanolamide (anandamide) was possibly due to hydrolysis by fatty acid amide hydrolase (FAAH). Cyclohexylcarbamic acid 3′-carbamoyl-biphenyl-3-yl ester (URB597) is an inhibitor of FAAH, increases brain anandamide levels and enhances anandamide-induced antinociception in male ICR mice (25–30 g). The combination of URB597 (10 mg/kg, i.p.) and anandamide (40 mg/kg, i.p.) produced maximal antinociception in the mouse tail-flick test [68.7 ± 16.8 percent maximum possible effect (%MPE)], versus either substance alone (27.3 ± 7.9%MPE and 4.6 ± 2.3%MPE, respectively) and is significantly blocked (p < 0.05) by the cannabinoid CB₁ receptor antagonist, SR141716A (rimonabant), the kappa opioid receptor-selective antagonist, nor-Binaltorphimine (10 μg i.t.; 12.7 ± 4.0%MPE) and the mu opioid receptor antagonist, naloxone (1 mg/kg, s.c.; 6.0 ± 3.8%MPE), but not by the delta opioid receptor-selective antagonist, naltrindole (2 mg/kg, s.c.; 29.7 ± 8.2%MPE) or the cannabinoid CB₂ receptor antagonist, SR144528. In addition, nor-BNI (10 μg i.t) administration to FAAH^−/− knockout mice produced a nociceptive response. The URB597/anandamide combination was not active in the CB₁^−/− knockout mice, but retained activity in the MOR^−/− knockout mice. The sub-active combination of (URB597 10 mg/kg, i.p/anandamide 10 mg/kg, i.p.; 15.5 ± 4.3%MPE) shifted the dose response curve of morphine to the left (morphine alone ED₅₀ = 4.6 mg/kg [3.7–5.6] versus morphine/URB597/anandamide (ED₅₀ = 2.5 mg/kg [1.9–3.4]). These data are the first demonstration that anandamide, if protected from degradation, acts via the CB₁ receptor to interact with kappa opioid receptor systems in opioid analgesia.     

Implication of NGF and endocannabinoid signaling in the mechanism of action of sesamol: a multi-target natural compound with therapeutic potential

Rationale

Sesamol, a natural compound with anti-inflammatory, antioxidant and neuroprotective properties, has shown promising antidepressant-like effects. However, its molecular target(s) have not been well defined, which merits further investigation.

Objectives

Based on the interaction between the neurotrophin and endocannabinoid (eCB) systems and their contribution to emotional reactivity and antidepressant action, we aimed to investigate the involvement of nerve growth factor (NGF) and eCB signalling in the mechanism of action of sesamol.

Methods

Following acute and 4-week intraperitoneal (i.p.) administration of sesamol (40, 80 and 100 mg/kg), the classical antidepressant amitriptyline (2.5, 5 and 10 mg/kg) or the benzodiazepine flurazepam (5, 10 and 20 mg/kg), brain regional levels of NGF and eCB contents were quantified in rats by Bio-Rad protein assay and isotope-dilution liquid chromatography/mass spectrometry, respectively. In the case of any significant change, the cannabinoid CB₁ and CB₂ receptor antagonists (AM251 and SR144528) were administered i.p. 30 min prior to the injection of sesamol, amitriptyline or flurazepam.

Results

Following the chronic treatment, sesamol, similar to amitriptyline, resulted in the sustained elevation of NGF and eCB contents in dose-dependent and brain region-specific fashion. Neither acute nor chronic treatment with flurazepam altered brain NGF or eCB contents. Pretreatment with 3 mg/kg AM251, but not SR144528, prevented the elevation of NGF protein levels. AM251 exerted no effect by itself.

Conclusions

Sesamol, similar to amitriptyline, is able to affect brain NGF and eCB signalling under the regulatory drive of the CB₁ receptors.     

Cannabinoid CB1 receptors mediate the effects of dipyrone

Dipyrone is a non‐steroidal anti‐inflammatory drug used primarily as an analgesic and antipyretic. Some hypothesize that dipyrone activity can modulate other pathways, including endocannabinoid signalling. Thus, the aim of the present study was to evaluate the possible role of endocannabinoids in mediating dipyrone activity. This study is based on the tetrad effects of cannabinoids, namely an antinociceptive and cataleptic state, hypolocomotion and hypothermia. Dipyrone (500 mg/kg, i.p.) treatment decreased locomotor activity, increased the latency to a thermal analgesic response and induced a cataleptic and hypothermic state. These reactions are similar to the tetrad effects caused by the cannabinoid agonist WIN 55,212‐2 (3 mg/kg, i.p.). The cannabinoid CB₁ receptor antagonist AM251 (10 mg/kg, i.p.) reversed the effects of dipyrone on locomotor activity, the cataleptic response and thermal analgesia. Both AM251 (10 mg/kg, i.p.) and the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine (10 mg/kg, i.p.) accentuated the reduction in body temperature caused by dipyrone. However, the CB₂ receptor antagonist AM630 did not alter the hypothermic response to dipyrone. These results indicate involvement of the endocannabinoid system, especially CB₁ receptors, in the analgesic and cataleptic effects of dipyrone, as well as hypolocomotion. However, cannabinoid receptors and TRPV1 were not involved in the hypothermic effects of dipyrone. We hypothesize that the mechanism of action of dipyrone may involve inhibition of cyclo‐oxygenase and fatty acid amide hydrolase, which together provide additional arachidonic acid as substrate for endocannabinoid synthesis or other related molecules. This increase in endocannabinoid availability enhances CB₁ receptor stimulation, contributing to the observed effects.     

Agmatine enhances cannabinoid action in the hot-plate assay of thermal nociception

Agmatine–cannabinoid interactions are supported by the close association between cannabinoid CB₁ receptors and agmatine immunoreactive neurons and evidence that shared brain mechanisms underlie the pharmacological effects of agmatine and cannabinoid agonists. In the present study, we used the hot-plate assay of thermal nociception to determine if agmatine alters cannabinoid action through activation of imidazoline sites and/or alpha₂-adrenoceptors. WIN 55212-2 (1, 2 or 3 mg/kg, i.p.) or CP55,940 (1, 2 or 3 mg/kg, i.p.) administration increased hot-plate response latency. Agmatine (50 or 100 mg/kg, i.p.) was ineffective. Administration of agmatine (50 mg/kg, i.p.) with WIN 55212-2 (1, 2 or 3 mg/kg, i.p.) or CP55,940 (1, 2 or 3 mg/kg, i.p.) produced response-latency enhancement. Regression analysis indicated that agmatine increased the potency of WIN 55212-2 and CP55,940 by 3- and 4.4-fold, respectively, indicating synergy for both drug interactions. Idazoxan, a mixed imidazoline site/alpha₂-adrenoceptor antagonist, but not yohimbine (5 mg/kg, i.p.), a selective alphia₂-adrenoceptor antagonist, blocked response-latency enhancement produced by a combination of WIN 55212-2 (2 mg/kg) and agmatine. Response-latency enhancement produced by WIN 55212-2 (2 mg/kg) was blocked by SR 141716A (5 mg/kg, i.p.), a cannabinoid CB₁ receptor antagonist; attenuated by idazoxan (2 and 5 mg/kg); and not affected by yohimbine (5 mg/kg). These results demonstrate a synergistic interaction between agmatine and cannabinoid agonists and suggest that agmatine administration enhances cannabinoid action in vivo.     

Diacerein decreases visceral pain through inhibition of glutamatergic neurotransmission and cytokine signaling in mice

The present study evaluated the antinociceptive effect of the pro-inflammatory cytokines inhibitor diacerein in mice and its possible mechanism of action. The antinociception produced by diacerein was tested at different sites of action, moreover selective antagonists or agonists were used to identify the mechanism that may be involved in its antinociceptive action against acetic acid-induced visceral pain. Diacerein administered systemically (intraperitoneal [i.p.] or intra-gastric [i.g.] routes), supra-spinally (i.c.v.), spinally (i.t.) or peripherally (in association with the irritant agent) inhibited the visceral nociception induced by acetic acid in mice. Interestingly, diacerein treatment (25 mg/kg, i.p. or 50 mg/kg, i.g.) produced long-lasting (for up to 4 h) inhibition of acetic acid-induced nociception. Intraperitoneal treatment of mice with diacerein (25.0 mg/kg) inhibited somatic nociception induced by i.t. injection of glutamate, NMDA, kainate, and trans-ACPD but not that caused by AMPA. Diacerein (5.0-25.0 mg/kg) also produced dose related inhibition of interleukin-1β (IL-1β) and tumor necrosis factor alpha (TNF-α) induced nociception. These results indicate that diacerein produces antinociception by inhibiting glutamatergic transmission through both ionotropic and metabotropic receptors as well as activity of pro-inflammatory cytokines.     

Involvement of the neurotrophin and cannabinoid systems in the mechanisms of action of neurokinin receptor antagonists

The anxiolytic- and antidepressant-like effects of the neurokinin (NK) receptor antagonists have been shown in behavioral studies. According to the involvement of neurotrophin signaling in the mechanisms of action of psychotropic agents, we aimed to investigate whether the selective NK₁, NK₂, or NK₃ receptor antagonists (GR-205171, SR48968, and SR142801, respectively) affect nerve growth factor (NGF) contents in the brain regions involved in the modulation of emotions. To gain a mechanistical insight into the process by which the NK antagonists regulate brain NGF levels, we evaluated the role of the cannabinoid system which is linked to depression and/or antidepressant effects and appears to interact with neurotrophin signaling. According to the results, single injection of the NK receptor antagonists (3, 5, and 10 mg/kg, i.p.) into gerbils did not alter NGF or endocannabinoid (eCB) levels quantified by Bio-Rad protein assay and isotope-dilution liquid chromatography/mass spectrometry, respectively. Three-week administration of 10 mg/kg NK antagonists significantly elevated both NGF and eCB levels in brain-region specific fashion. Pre-application of the CB₁ receptor neutral antagonist AM4113 (5.6 mg/kg) prevented the elevation of NGF or eCB induced by the NK antagonists. AM4113 showed no effect by itself. We conclude that the cannabinoid system is implicated in the mechanisms of action of NK receptor antagonists including the upregulation of brain NGF levels.     

The antinociceptive effect of Delta9-tetrahydrocannabinol in the arthritic rat involves the CB(2) cannabinoid receptor

Cannabinoid CB₂ receptors have been implicated in antinociception in animal models of both acute and chronic pain. We evaluated the role both cannabinoid CB₁ and CB₂ receptors in mechanonociception in non-arthritic and arthritic rats. The antinociceptive effect of Δ⁹-tetrahydrocannabinol (Δ⁹THC) was determined in rats following administration of the cannabinoid CB₁ receptor-selective antagonist, SR141716A, the cannabinoid CB₂ receptor-selective antagonist, SR144528, or vehicle. Male Sprague–Dawley rats were rendered arthritic using Freund’s complete adjuvant and tested for mechanical hyperalgesia in the paw-pressure test. Arthritic rats had a baseline paw-pressure of 83 ± 3.6g versus a paw-pressure of 177 ± 6.42g in non-arthritic rats. SR144528 or SR141716A (various doses mg/kg; i.p.) or 1:1:18 (ethanol:emulphor:saline) vehicle were injected 1 h prior to Δ⁹THC (4mg/kg; i.p) or 1:1:18 vehicle and antinociception determined 30min post Δ⁹THC. AD₅₀'s for both antagonists were calculated with 95% confidence limits. In addition, midbrain and spinal cord were removed for determination of cannabinoid CB₁ and CB₂ receptor protein density in the rats. SR144528 significantly attenuated the antinociceptive effect of Δ⁹THC in the arthritic rats [AD₅₀ = 3.3 (2.7–4) mg/kg], but not in the non-arthritic rats at a dose of 10/mg/kg. SR141716A significantly attenuated Δ⁹THC-induced antinociception in both the non-arthritic [AD₅₀ = 1.4 (0.8–2) mg/kg] and arthritic rat [AD₅₀ = 2.6 (1.8–3.1) mg/kg]. SR141716A or SR144528 alone did not result in a hyperalgesic effect as compared to vehicle. Our results indicate that the cannabinoid CB₂ receptor plays a critical role in cannabinoid-mediated antinociception, particularly in models of chronic inflammatory pain.     

Defaecation, intestinal fluid accumulation and motility in rodents: implications of cannabinoid CB1 receptors

We have studied the effect of SR141716A (0.1–5 mg/kg, i.p.), a cannabinoid CB₁ receptor antagonist, and WIN (0.1–5 mg/kg, i.p.), a cannabinoid receptor agonist, on acute defaecation and gastrointestinal transit in mice and on intraluminal fluid accumulation in the rat small intestine. SR141716A increased while WIN 55,212-2 decreased defaecation, gastrointestinal transit and fluid accumulation. A per se non-effective dose of SR141716A (0.3 mg/kg) counteracted the inhibitory effect of WIN 55,212-2 (1 mg/kg) on gastrointestinal functions studied. The effect of SR141716 on both intestinal fluid accumulation in rats and gastrointestinal transit in mice was inhibited by atropine (1 mg/kg, i.p.), but not by hexamethonium (1 mg/kg, s.c.), SR140333 (20 μg/kg, i.p.) or SR48968 (20 μg/kg, i.p.), antagonists of NK₁ and NK₂ receptors, respectively. These results suggest that intestinal fluid accumulation and motility are inhibited by endogenous cannabinoid(s) acting at the cannabinoid CB₁ receptors. This effect may be mediated by mechanisms involving muscarinic cholinoceptors. Received: 13 July 1998 / Accepted: 25 September 1998     

The involvement of central cholinergic system in (+)-matrine-induced antinociception in mice

The antinociceptive effect of (+)-matrine was examined in mice by writhing, tail-pressure and hot-plate tests. (+)-Matrine (5, 10 and 20 mg/kg s.c.) produced antinociception in a dose-dependent manner. In hot-plate test, the antinociception produced by (+)-matrine (10 mg/kg s.c.) was attenuated by muscarinic receptor antagonists atropine (5 mg/kg i.p.) and pirenzepine (0.1 mug/mouse i.c.v.) and acetylcholine depletor hemicholinium-3 (HC-3) (1 mug/mouse i.c.v.), but not by opioid receptor antagonist naloxone (2 mg/kg i.p.), dopamine D(2) receptor agonist (-)-quinpirole (0.1 mg/kg i.p.) or catecholamine depletor reserpine (2.5 mg/kg i.p.). Radioligand binding assay demonstrated that (+)-matrine had no affinity for mu-, kappa- or delta-opioid receptors in a wide concentration range (1 x 10(-11)-1 x 10(-3) M). The results suggest that (+)-matrine exerts its antinociceptive effect through multiple mechanism(s) such as increasing cholinergic activation in the CNS rather than acting on opioid receptors directly.     

Agmatine enhances cannabinoid action in the hot-plate assay of thermal nociception

Agmatine–cannabinoid interactions are supported by the close association between cannabinoid CB₁ receptors and agmatine immunoreactive neurons and evidence that shared brain mechanisms underlie the pharmacological effects of agmatine and cannabinoid agonists. In the present study, we used the hot-plate assay of thermal nociception to determine if agmatine alters cannabinoid action through activation of imidazoline sites and/or alpha₂-adrenoceptors. WIN 55212-2 (1, 2 or 3 mg/kg, i.p.) or CP55,940 (1, 2 or 3 mg/kg, i.p.) administration increased hot-plate response latency. Agmatine (50 or 100 mg/kg, i.p.) was ineffective. Administration of agmatine (50 mg/kg, i.p.) with WIN 55212-2 (1, 2 or 3 mg/kg, i.p.) or CP55,940 (1, 2 or 3 mg/kg, i.p.) produced response-latency enhancement. Regression analysis indicated that agmatine increased the potency of WIN 55212-2 and CP55,940 by 3- and 4.4-fold, respectively, indicating synergy for both drug interactions. Idazoxan, a mixed imidazoline site/alpha₂-adrenoceptor antagonist, but not yohimbine (5 mg/kg, i.p.), a selective alphia₂-adrenoceptor antagonist, blocked response-latency enhancement produced by a combination of WIN 55212-2 (2 mg/kg) and agmatine. Response-latency enhancement produced by WIN 55212-2 (2 mg/kg) was blocked by SR 141716A (5 mg/kg, i.p.), a cannabinoid CB₁ receptor antagonist; attenuated by idazoxan (2 and 5 mg/kg); and not affected by yohimbine (5 mg/kg). These results demonstrate a synergistic interaction between agmatine and cannabinoid agonists and suggest that agmatine administration enhances cannabinoid action in vivo.     

Filicene obtained from Adiantumcuneatum interacts with the cholinergic, dopaminergic, glutamatergic, GABAergic, and tachykinergic systems to exert antinociceptive effect in mice

In the present study, we describe the antinociceptive effect of filicene, a triterpene isolated from Adiantumcuneatum (Adiantaceae) leaves, in several models of pain in mice. When evaluated against acetic acid-induced abdominal constrictions, filicene (10, 30 and 60 mg/kg, i.p.) produced dose-related inhibition of the number of constrictions, being several times more potent [ID₅₀ = 9.17 (6.27-13.18) mg/kg] than acetaminophen [ID₅₀ = 18.8 (15.7-22.6) mg/kg], diclofenac [ID₅₀ = 12.1(9.40-15.6) mg/kg] and acetylsalicylic acid [ID₅₀ = 24.0(13.1-43.8) mg/kg] in the same doses as those used for the standard drugs. Filicene also produced dose-related inhibition of the pain caused by capsaicin and glutamate, with mean ID₅₀ values of 11.7 (8.51-16.0) mg/kg and < 10 mg/kg, respectively. Its antinociceptive action was significantly reversed by atropine, haloperidol, GABA_A and GABA_B antagonists (bicuculline and phaclofen, respectively), but was not affected by L-arginine-nitric oxide, serotonin, adrenergic and the opioid systems. Together, these results indicate that the mechanisms involved in its action are not completely understood, but seem to involve interaction with the cholinergic, dopaminergic, glutamatergic, GABAergic and tachykinergic systems.     

Cannabinoid CB1 receptor antagonist rimonabant disrupts nicotine reward-associated memory in rats

Exposure to cues previously associated with drug intake leads to relapse by activating previously acquired memories. Based on previous findings, in which cannabinoid CB₁ receptors were found to be critically involved in specific aspects of learning and memory, we investigated the role of CB₁ receptors in nicotine reward memory using a rat conditioned place preference (CPP) model. In Experiment 1, rats were trained for CPP with alternating injections of nicotine (0.5 mg/kg, s.c.) and saline to acquire the nicotine-conditioned memory. To examine the effects of rimonabant on the reconsolidation of nicotine reward memory, rats were administered rimonabant (0, 0.3, and 3.0 mg/kg, i.p.) immediately after reexposure to the drug-paired context. In Experiment 2, rats were trained for CPP similarly to Experiment 1. To examine the effects of rimonabant on the reinstatement of nicotine reward memory, rimonabant (0, 0.3, and 3.0 mg/kg, i.p.) was administered before the test of nicotine-induced CPP reinstatement. In Experiment 3, to evaluate whether rimonabant itself produces a reward memory, rats were trained for CPP with alternating injections of different doses of rimonabant (0, 0.3, and 3.0 mg/kg) and saline. Rimonabant at a dose of 3.0 mg/kg significantly disrupted the reconsolidation of nicotine memory and significantly blocked the reinstatement of nicotine-induced CPP. However, rimonabant itself did not produce CPP. These findings provide clear evidence that CB₁ receptors play a role in nicotine reward memory, suggesting that CB₁ receptor antagonists may be a potential target for managing nicotine addiction.     

Mechanisms involved in the antinociception caused by ethanolic extract obtained from the leaves of Melissa officinalis (lemon balm) in mice

The present study examined the antinociceptive effect of the ethanolic extract from Melissa officinalis L. and of the rosmarinic acid in chemical behavioral models of nociception and investigates some of the mechanisms underlying this effect. The extract (3-1000 mg/kg), given orally (p.o.) 1 h prior to testing, produced dose-dependent inhibition of acetic acid-induced visceral pain, with ID50 value of 241.9 mg/kg. In the formalin test, the extract (30-1000 mg/kg, p.o.) also caused significant inhibition of both, the early (neurogenic pain) and the late (inflammatory pain), phases of formalin-induced licking. The extract (10-1000 mg/kg, p.o.) also caused significant and dose-dependent inhibition of glutamate-induced pain, with ID50 value of 198.5 mg/kg. Furthermore, the rosmarinic acid (0.3-3 mg/kg), given p.o. 1 h prior, produced dose-related inhibition of glutamate-induced pain, with ID50 value of 2.64 mg/kg. The antinociception caused by the extract (100 mg/kg, p.o.) in the glutamate test was significantly attenuated by intraperitoneal (i.p.) treatment of mice with atropine (1 mg/kg), mecamylamine (2 mg/kg) or l-arginine (40 mg/kg). In contrast, the extract (100 mg/kg, p.o.) antinociception was not affected by i.p. treatment with naloxone (1 mg/kg) or d-arginine (40 mg/kg). It was also not associated with non-specific effects, such as muscle relaxation or sedation. Collectively, the present results suggest that the extract produced dose-related antinociception in several models of chemical pain through mechanisms that involved cholinergic systems (i.e. through muscarinic and nicotinic acetylcholine receptors) and the l-arginine-nitric oxide pathway. In addition, the rosmarinic acid contained in this plant appears to contribute for the antinociceptive property of the extract. Moreover, the antinociceptive action demonstrated in the present study supports, at least partly, the ethnomedical uses of this plant.     

Combined use of tertiary amine parasympathomimetics with a quaternary amine parasympatholitic--a new perspective to use parasympathomimetic drugs for systemic analgesia

The interactions on antinociception between a muscarinic agonist arecoline (arec), an anticholinesterase physostigmine (physo) which both cross CNS, and a peripherally acting antimuscarinic hyoscine-N-butyl bromide (hyo), were assessed by tail flick test in mice. All drugs were administered intraperitoneally (i.p.). While hyoscine-N-butyl bromide (0.15 and 4.00 mg/kg, i.p.) did not produce antinociception, physostigmine salicylate (0.3 mg/kg, i.p.) and arecoline hydrobromide (8.00 mg/kg, i.p.) exerted significant antinociceptive effect. In combined applications, physo + hyo (0.075 + 0.15; 0.15 + 0.30; 0.30 + 0.60 mg/kg) and arec + hyo (1.00 + 0.50; 2.00 + 1.00; 4.00 + 2.00; 8.00 + 4.00 mg/kg), respectively, produced significant antinociception and the tail flick latencies produced by physo 0.30 + hyo 0.60 mg/kg and arec 8.00 + hyo 4.00 mg/kg were not significantly different from those of physo 0.30 mg/kg and arec 8.00 mg/kg, respectively, showing that hyo did not antagonise the antinociceptive effects of physo and arec. We believe that combining an centrally acting cholinergic drug applied systemically with a peripherally acting (quaternary amine) antimuscarinic compound might be used as an effective analgesic in clinical practice.     

Hesperidin produces antinociceptive response and synergistic interaction with ketorolac in an arthritic gout-type pain in rats

Hesperidin occurs in greatest concentration in plants from the Rutaceae and Lamiaceae families. In human nutrition it contributes to the integrity of blood vessels and its deficiency in the diet has been linked to abnormal capillary leakiness as well as pain. In this study, the bioflavonoid hesperidin was identified as an active compound in an ethanol extract of the Rosmarinus officinalis aerial parts tested in the pain-induced functional impairment model in the rat (PIFIR) as an assay of inflammatory and chronic nociception similar to that observed in clinical gout. Hesperidin produced a dose-dependent and significant response with an ED₂₅ = 1666.72 mg/kg in comparison to an ED₂₅ = 302.90 mg/kg for the extract or an ED₂₅ = 0.47 mg/kg for the reference drug ketorolac in the PIFIR model. Although the antinociceptive response of R. officinalis was reverted in presence of the opioid antagonist naloxone (10 mg/kg, s.c.) and the 5HT_1A antagonist WAY100635 (0.12 mg/kg, s.c.), the hesperidin response was not modified by naloxone (10 mg/kg), WAY100635 (0.12 mg/kg), bicuculline (1 mg/kg, s.c.), flumazenil (10 mg/kg, i.p.) or caffeine (1 mg/kg, s.c.). Nevertheless, it was reduced in presence of capsazepine (10 or 20 mg/kg, s.c.) suggesting the participation of the TRPV1 receptor, which was reinforced when hesperidin significantly reduced the capsaicin-induced nociceptive response. A synergistic interaction was also observed when antinociceptive doses of hesperidin were combined with those of ketorolac producing 15 combinations mainly in additive and supra-additive responses. These results provide evidence for the antinociceptive activity of hesperidin and demonstrate synergistic response when combined with ketorolac, possibly by involvement of the TRPV1 receptor, suggesting their clinical potential in pain therapy.     

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-HT₃ receptor antagonist) and SCH23390 (0.05 mg/kg, i.p.., a D₁ receptor antagonist) blocked the antinociceptive effect caused by (MeOPhSe)₂. Conversely, pindolol (1 mg/kg, i.p., a 5-HT_1A/_1B receptor/β 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 α₁-adrenoreceptor antagonist), yohimbine (1.0 mg/kg, i.p., an α₂-adrenoreceptor antagonist), sulpiride (5 mg/kg, i.p., a D₂ 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-Arg⁹-bradykinin (10 nmol/paw, a B₁ receptor agonist). (MeOPhSe)₂ significantly inhibited phorbol myristate acetate (PMA, 0.03 μg/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-HT₃ and D₁ receptors. The antinociceptive effect is related to (MeOPhSe)₂ ability to interact with kinin B₁ and B₂ receptors and PKC pathway mediated mechanisms.     

Yohimbine produces antinociception in the formalin test in rats: involvement of serotonin1A receptors

Rationale: Previous studies have suggested that the α₂-adrenergic receptor antagonist yohimbine produced antinociceptive effects in the formalin test in rats. However, yohimbine is also an agonist at serotonin (5-HT)_1A receptors, suggesting the possibility that the antinociceptive effects of yohimbine might be mediated via these receptors. Objective: The purpose of the present studies was to evaluate the potential role of 5-HT_1A receptors in mediating the antinociceptive effects of yohimbine. Methods: The antinociceptive effects of yohimbine were evaluated using the formalin test in rats. Results: Yohimbine (2.5–10 mg/kg s.c.) produced dose-related antinociception during both phase I and phase II of the formalin test, and was approximately equipotent and equiefficacious to morphine. The selective 5-HT_1A receptor antagonist WAY 100,635 (0.03–3.0 mg/kg s.c.) produced a partial reversal of yohimbine. In comparison, the selective 5-HT_1A receptor agonist (±)8-hydroxy- dipropylaminotetralin HBr (8OH-DPAT; 1.0 mg/kg s.c.) also produced a dose-related antinociception in the formalin test, although 8OH-DPAT was completely reversed by WAY 100,635 (3.0 mg/kg s.c.). The antinociceptive effects of yohimbine were not antagonized by the 5-HT_1B/1D antagonist GR 127935 (1.0 mg/kg and 3.0 mg/kg s.c.), the 5-HT₂ antagonist LY53857 (1.0 mg/kg s.c.), or the 5-HT₃ antagonist zatosetron (3.0 mg/kg s.c.). Conclusions: The present results demonstrate that yohimbine produces a dose-related antinociception in the formalin test in rats which is mediated in part by the agonistic actions at 5-HT_1A receptors. Received: 10 September 1999 / Final version: 5 November 1999     

Antinociceptive effects of haloperidol and its metabolites in the formalin test in mice

Rationale Formalin-induced pain is reduced in sigma-1 (σ₁) receptor knockout mice; therefore, we hypothesized that haloperidol and its metabolites I and II, which have affinity for σ₁ receptors, may modulate formalin-induced pain. Results Intraplantar administration of formalin (2.5%) to CD-1 mice produced a biphasic period of pain. Haloperidol (0.03–1 mg/kg, s.c.) and reduced haloperidol (metabolite II, 0.25–8 mg/kg, s.c.) dose-dependently inhibited both phases of formalin-induced pain. Haloperidol metabolite I (4–128 mg/kg, s.c.) also produced dose-dependent antinociception in the second phase of the formalin test, but was less potent and effective against first-phase pain. Haloperidol metabolite III (16 and 128 mg/kg) and (−)sulpiride (200 mg/kg), which have no affinity for σ₁ receptors, did not produce significant antinociception in either phase of the formalin test. The order of potency of the drugs to produce their antinociceptive effect [haloperidol > metabolite II > metabolite I ≫ metabolite III= (−)sulpiride=inactive] correlated with their affinity for σ₁ receptors, but not with their affinity for σ₂ or dopamine D₂ receptors. Naloxone (1 mg/kg, s.c.) did not antagonize the antinociception induced by haloperidol and its metabolites. None of the antinociceptive drugs in the formalin test produced any antinociception in the tail flick test. Conclusion These results suggest that the antinociceptive effect of haloperidol and its metabolites in the formalin test is not due to unspecific/generalised inhibition of nociception or modulation of opioid receptors, and that it may be related, at least partially, to the ability of these drugs to interact with σ₁ receptors.