Inhibitory effect of salvinorin A, from Salvia divinorum, on ileitis-induced hypermotility: cross-talk between kappa-opioid and cannabinoid CB(1) receptors

Background and purpose:

Salvinorin A, the active component of the hallucinogenic herb Salvia divinorum, inhibits intestinal motility through activation of κ-opioid receptors (KORs). However, this compound may have target(s) other than the KORs in the inflamed gut. Because intestinal inflammation upregulates cannabinoid receptors and endogenous cannabinoids, in the present study we investigated the possible involvement of the endogenous cannabinoid system in salvinorin A-induced delay in motility in the inflamed gut.

Experimental approach:

Motility in vivo was measured by evaluating the distribution of a fluorescent marker along the small intestine; intestinal inflammation was induced by the irritant croton oil; direct or indirect activity at cannabinoid receptors was evaluated by means of binding, enzymic and cellular uptake assays.

Key results:

Salvinorin A as well as the KOR agonist U-50488 reduced motility in croton oil treated mice. The inhibitory effect of both salvinorin A and U-50488 was counteracted by the KOR antagonist nor-binaltorphimine and by the cannabinoid CB₁ receptor antagonist rimonabant. Rimonabant, however, did not counteract the inhibitory effect of salvinorin A on motility in control mice. Binding experiments showed very weak affinity of salvinorin A for cannabinoid CB₁ and CB₂ and no inhibitory effect on 2-arachidonoylglycerol and anandamide hydrolysis and cellular uptake.

Conclusions and implications:

The inhibitory effect of salvinorin A on motility reveals a functional interaction between cannabinoid CB₁ receptors and KORs in the inflamed—but not in the normal—gut in vivo.     

Peripheral interactions between cannabinoid and opioid systems contribute to the antinociceptive effect of crotalphine

Background and Purpose

Crotalphine is an antinociceptive peptide that, despite its opioid-like activity, does not induce some of the characteristic side effects of opioids, and its amino acid sequence has no homology to any known opioid peptide. Here, we evaluated the involvement of the peripheral cannabinoid system in the crotalphine effect and its interaction with the opioid system.

Experimental Approach

Hyperalgesia was evaluated using the rat paw pressure test. Involvement of the cannabinoid system was determined using a selective cannabinoid receptor antagonist. Cannabinoid and opioid receptor activation were evaluated in paw slices by immunofluorescence assays using conformation state-sensitive antibodies. The release of endogenous opioid peptides from skin tissue was measured using a commercial enzyme immunoassay (EIA).

Key Results

Both p.o. (0.008–1.0 μg·kg⁻¹) and intraplantar (0.0006 μg per paw) administration of crotalphine induced antinociception in PGE₂-induced hyperalgesia. Antinociception by p.o. crotalphine (1 μg·kg⁻¹) was blocked by AM630 (50 μg per paw), a CB₂ receptor antagonist, and by antiserum anti-dynorphin A (1 μg per paw). Immunoassay studies confirmed that crotalphine increased the activation of both κ-opioid (51.7%) and CB₂ (28.5%) receptors in paw tissue. The local release of dynorphin A from paw skin was confirmed by in vitro EIA and blocked by AM630.

Conclusions and Implications

Crotalphine-induced antinociception involves peripheral CB₂ cannabinoid receptors and local release of dynorphin A, which is dependent on CB₂ receptor activation. These results enhance our understanding of the mechanisms involved in the peripheral effect of crotalphine, as well as the interaction between the opioid and cannabinoid systems.     

Central antinociception induced by μ-opioid receptor agonist morphine,but not δ- or κ-, is mediated by cannabinoid CB1 receptor

Background and purpose:

It has been demonstrated that cannabinoids evoke the release of endogenous opioids to produce antinociception; however, no information exists regarding the participation of cannabinoids in the antinociceptive mechanisms of opioids. The aim of the present study was to determine whether endocannabinoids are involved in central antinociception induced by activation of µ-, δ- and κ-opioid receptors.

Experimental approach:

Nociceptive threshold to thermal stimulation was measured according to the tail-flick test in Swiss mice. Morphine (5 µg), SNC80 (4 µg), bremazocine (4 µg), AM251 (2 and 4 µg), AM630 (2 and 4 µg) and MAFP (0.1 and 0.4 µg) were administered by the intracerebroventricular route.

Key results:

The CB₁-selective cannabinoid receptor antagonist AM251 completely reversed the central antinociception induced by morphine in a dose-dependent manner. In contrast, the CB₂-selective cannabinoid receptor antagonist AM630 did not antagonize this effect. Additionally, the administration of the anandamide amidase inhibitor, MAFP, significantly enhanced the antinociception induced by morphine. In contrast, the antinociceptive effects of δ- and κ-opioid receptor agonists were not affected by the cannabinoid antagonists. The antagonists alone caused no hyperalgesic or antinociceptive effects.

Conclusions and implications:

The results provide evidence for the involvement of cannabinoid CB₁ receptors in the central antinociception induced by activation of µ-opioid receptors by the agonist morphine. The release of endocannabinoids appears not to be involved in central antinociception induced by activation of κ- and δ-opioid receptors.     

Antidepressant-like effects of cannabidiol in mice: possible involvement of 5-HT1A receptors

Background and purpose:

Cannabidiol (CBD) is a non-psychotomimetic compound from Cannabis sativa that induces anxiolytic- and antipsychotic-like effects in animal models. Effects of CBD may be mediated by the activation of 5-HT_1A receptors. As 5-HT_1A receptor activation may induce antidepressant-like effects, the aim of this work was to test the hypothesis that CBD would have antidepressant-like activity in mice as assessed by the forced swimming test. We also investigated if these responses depended on the activation of 5-HT_1A receptors and on hippocampal expression of brain-derived neurotrophic factor (BDNF).

Experimental approach:

Male Swiss mice were given (i.p.) CBD (3, 10, 30, 100 mg·kg⁻¹), imipramine (30 mg·kg⁻¹) or vehicle and were submitted to the forced swimming test or to an open field arena, 30 min later. An additional group received WAY100635 (0.1 mg·kg⁻¹, i.p.), a 5-HT_1A receptor antagonist, before CBD (30 mg·kg⁻¹) and assessment by the forced swimming test. BDNF protein levels were measured in the hippocampus of another group of mice treated with CBD (30 mg·kg⁻¹) and submitted to the forced swimming test.

Key results:

CBD (30 mg·kg⁻¹) treatment reduced immobility time in the forced swimming test, as did the prototype antidepressant imipramine, without changing exploratory behaviour in the open field arena. WAY100635 pretreatment blocked CBD-induced effect in the forced swimming test. CBD (30 mg·kg⁻¹) treatment did not change hippocampal BDNF levels.

Conclusion and implications:

CBD induces antidepressant-like effects comparable to those of imipramine. These effects of CBD were probably mediated by activation of 5-HT_1A receptors.     

Differential effect of opioid and cannabinoid receptor blockade on heroin-seeking reinstatement and cannabinoid substitution in heroin-abstinent rats

BACKGROUND AND PURPOSE

Opioids and cannabinoids interact in drug addiction and relapse. We investigated the effect of the opioid receptor antagonist naloxone and/or the cannabinoid CB₁ receptor antagonist rimonabant on cannabinoid-induced reinstatement of heroin seeking and on cannabinoid substitution in heroin-abstinent rats.

EXPERIMENTAL APPROACH

Rats were trained to self-administer heroin (30 µg·kg⁻¹ per infusion) under a fixed-ratio 1 reinforcement schedule. After extinction of self-administration (SA) behaviour, we confirmed the effect of naloxone (0.1–1 mg·kg⁻¹) and rimonabant (0.3–3 mg·kg⁻¹) on the reinstatement of heroin seeking induced by priming with the CB₁ receptor agonist WIN55,212-2 (WIN, 0.15–0.3 mg·kg⁻¹). Then, in a parallel set of heroin-trained rats, we evaluated whether WIN (12.5 µg·kg⁻¹ per infusion) SA substituted for heroin SA after different periods of extinction. In groups of rats in which substitution occurred, we studied the effect of both antagonists on cannabinoid intake.

KEY RESULTS

Cannabinoid-induced reinstatement of heroin seeking was significantly attenuated by naloxone (1 mg·kg⁻¹) and rimonabant (3 mg·kg⁻¹) and fully blocked by co-administration of sub-threshold doses of the two antagonists. Moreover, contrary to immediate (1 day) or delayed (90 days) drug substitution, rats readily self-administered WIN when access was given after 7, 14 or 21 days of extinction from heroin, and showed a response rate that was positively correlated with the extinction period. In these animals, cannabinoid intake was increased by naloxone (1 mg·kg⁻¹) and decreased by rimonabant (3 mg·kg⁻¹).

CONCLUSIONS AND IMPLICATIONS

Our findings extend previous research on the crosstalk between cannabinoid and opioid receptors in relapse mechanisms, which suggests a differential role in heroin-seeking reinstatement and cannabinoid substitution in heroin-abstinent rats.

LINKED ARTICLES

This article is part of a themed issue on Cannabinoids in Biology and Medicine. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2011.163.issue-7     

Liguzinediol improved the heart function and inhibited myocardial cell apoptosis in rats with heart failure

Aim:

Liguzinediol is a novel derivative of ligustrazine isolated from the traditional Chinese medicine Chuanxiong (Ligusticum wallichii Franch), and produces significant positive inotropic effect in isolated rat hearts. In this study we investigated the effects of liguzinediol on a rat model of heart failure.

Methods:

To induce heart failure, male SD rats were injected with doxorubicin (DOX, 2 mg/kg, ip) once a week for 4 weeks. Then the rats were administered with liguzinediol (5, 10, 20 mg·kg⁻¹·d⁻¹, po) for 2 weeks. Hemodynamic examination was conducted to evaluate heart function. Myocardial cell apoptosis was examined morphologically. The expression of related genes and proteins were analyzed using immunohistochemical staining and Western blot assays, respectively.

Results:

Oral administration of liguzinediol dose-dependently improved the heart function in DOX-treated rats. Electron microscopy revealed that liguzinediol (10 mg·kg⁻¹·d⁻¹) markedly attenuated DOX-induced injury of cardiomyocytes, and decreased the number of apoptotic bodies in cardiomyocytes. Furthermore, liguzinediol significantly decreased Bax protein level, and increased Bcl-2 protein level in cardiomyocytes of DOX-treated rats, led to an increase in the ratio of Bcl-2/Bax. Moreover, liguzinediol significantly decreased the expression of both cleaved caspase-3 and NF-κB in cardiomyocytes of DOX-treated rats. Administration of digitalis (0.0225 mg·kg⁻¹·d⁻¹) also markedly improved the heart function and the morphology of cardiomyocytes in DOX-treated rats.

Conclusion:

Liguzinediol improves the heart function and inhibits myocardial cell apoptosis in the rat model of heart failure, which is associated with regulating Bcl-2, Bax, caspase-3 and NF-κB expression.     

Cannabidivarin-rich cannabis extracts are anticonvulsant in mouse and rat via a CB1 receptor-independent mechanism

BACKGROUND AND PURPOSE

Epilepsy is the most prevalent neurological disease and is characterized by recurrent seizures. Here, we investigate (i) the anticonvulsant profiles of cannabis-derived botanical drug substances (BDSs) rich in cannabidivarin (CBDV) and containing cannabidiol (CBD) in acute in vivo seizure models and (ii) the binding of CBDV BDSs and their components at cannabinoid CB₁ receptors.

EXPERIMENTAL APPROACH

The anticonvulsant profiles of two CBDV BDSs (50–422 mg·kg⁻¹) were evaluated in three animal models of acute seizure. Purified CBDV and CBD were also evaluated in an isobolographic study to evaluate potential pharmacological interactions. CBDV BDS effects on motor function were also investigated using static beam and grip strength assays. Binding of CBDV BDSs to cannabinoid CB₁ receptors was evaluated using displacement binding assays.

KEY RESULTS

CBDV BDSs exerted significant anticonvulsant effects in the pentylenetetrazole (≥100 mg·kg⁻¹) and audiogenic seizure models (≥87 mg·kg⁻¹), and suppressed pilocarpine-induced convulsions (≥100 mg·kg⁻¹). The isobolographic study revealed that the anticonvulsant effects of purified CBDV and CBD were linearly additive when co-administered. Some motor effects of CBDV BDSs were observed on static beam performance; no effects on grip strength were found. The Δ⁹-tetrahydrocannabinol and Δ⁹-tetrahydrocannabivarin content of CBDV BDS accounted for its greater affinity for CB₁ cannabinoid receptors than purified CBDV.

CONCLUSIONS AND IMPLICATIONS

CBDV BDSs exerted significant anticonvulsant effects in three models of seizure that were not mediated by the CB₁ cannabinoid receptor and were of comparable efficacy with purified CBDV. These findings strongly support the further clinical development of CBDV BDSs for the treatment of epilepsy.     

Cannabidiolic acid prevents vomiting in Suncus murinus and nausea-induced behaviour in rats by enhancing 5-HT1A receptor activation

Background and Purpose

To evaluate the ability of cannabidiolic acid (CBDA) to reduce nausea and vomiting and enhance 5-HT_1A receptor activation in animal models.

Experimental Approach

We investigated the effect of CBDA on (i) lithium chloride (LiCl)-induced conditioned gaping to a flavour (nausea-induced behaviour) or a context (model of anticipatory nausea) in rats; (ii) saccharin palatability in rats; (iii) motion-, LiCl- or cisplatin-induced vomiting in house musk shrews (Suncus murinus); and (iv) rat brainstem 5-HT_1A receptor activation by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and mouse whole brain CB₁ receptor activation by CP55940, using [³⁵S]GTPγS-binding assays.

Key Results

In shrews, CBDA (0.1 and/or 0.5 mg·kg⁻¹ i.p.) reduced toxin- and motion-induced vomiting, and increased the onset latency of the first motion-induced emetic episode. In rats, CBDA (0.01 and 0.1 mg·kg⁻¹ i.p.) suppressed LiCl- and context-induced conditioned gaping, effects that were blocked by the 5-HT_1A receptor antagonist, WAY100635 (0.1 mg·kg⁻¹ i.p.), and, at 0.01 mg·kg⁻¹ i.p., enhanced saccharin palatability. CBDA-induced suppression of LiCl-induced conditioned gaping was unaffected by the CB₁ receptor antagonist, SR141716A (1 mg·kg⁻¹ i.p.). In vitro, CBDA (0.1–100 nM) increased the E_max of 8-OH-DPAT.

Conclusions and Implications

Compared with cannabidiol, CBDA displays significantly greater potency at inhibiting vomiting in shrews and nausea in rats, and at enhancing 5-HT_1A receptor activation, an action that accounts for its ability to attenuate conditioned gaping in rats. Consequently, CBDA shows promise as a treatment for nausea and vomiting, including anticipatory nausea for which no specific therapy is currently available.     

Cannabinoid CB(2) receptor attenuates morphine-induced inflammatory responses in activated microglial cells

BACKGROUND AND PURPOSE

Among several pharmacological properties, analgesia is the most common feature shared by either opioid or cannabinoid systems. Cannabinoids and opioids are distinct drug classes that have been historically used separately or in combination to treat different pain states. In the present study, we characterized the signal transduction pathways mediated by cannabinoid CB₂ and µ-opioid receptors in quiescent and LPS-stimulated murine microglial cells.

EXPERIMENTAL APPROACH

We examined the effects of µ-opioid and CB₂ receptor stimulation on phosphorylation of MAPKs and Akt and on IL-1β, TNF-α, IL-6 and NO production in primary mouse microglial cells.

KEY RESULTS

Morphine enhanced release of the proinflammatory cytokines, IL-1β, TNF-α, IL-6, and of NO via µ-opioid receptor in activated microglial cells. In contrast, CB₂ receptor stimulation attenuated morphine-induced microglial proinflammatory mediator increases, interfering with morphine action by acting on the Akt-ERK1/2 signalling pathway.

CONCLUSIONS AND IMPLICATIONS

Because glial activation opposes opioid analgesia and enhances opioid tolerance and dependence, we suggest that CB₂ receptors, by inhibiting microglial activity, may be potential targets to increase clinical efficacy of opioids.     

Cue-conditioned alcohol seeking in rats following abstinence: involvement of metabotropic glutamate 5 receptors

Background and purpose:

The current study was designed to: (i) examine whether functional interactions occur between receptors known to regulate alcohol self-administration; and (ii) characterize relapse to alcohol seeking following abstinence.

Experimental approach:

The selective cannabinoid CB₁ receptor antagonist SR141716A (0.03–1.0 mg·kg⁻¹ i.p.) resulted in a dose-dependent reduction in ethanol self-administration in ethanol-preferring Indiana-preferring rats. SR141716A was then co-administered with either the selective glutamate metabotropic glutamate 5 (mGlu₅) receptor antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) or the selective adenosine A_2A receptor antagonist {"type":"entrez-protein","attrs":{"text":"SCH58261","term_id":"1052882304","term_text":"SCH58261"}}SCH58261.

Key results:

When administered at individually sub-threshold doses, a combination of SR141716A (0.1 mg·kg⁻¹) and {"type":"entrez-protein","attrs":{"text":"SCH58261","term_id":"1052882304","term_text":"SCH58261"}}SCH58261 (0.5 mg·kg⁻¹ i.p.) produced a reduction (28%) in ethanol self-administration. Combinations of threshold doses of SR141716A (0.3 mg·kg⁻¹) and {"type":"entrez-protein","attrs":{"text":"SCH58261","term_id":"1052882304","term_text":"SCH58261"}}SCH58261 (2.0 mg·kg⁻¹, i.p.) caused an essentially additive reduction (68%) in alcohol self-administration. A combination of individually sub-threshold doses of CB₁ and mGlu₅ receptor antagonists did not affect alcohol self-administration; however, combined threshold doses of SR141716A (0.3 mg·kg⁻¹) and MTEP (1.0 mg·kg⁻¹ i.p.) did reduce ethanol self-administration markedly (80%). Cue-conditioned alcohol seeking was attenuated by pretreatment with MTEP (1.0 mg·kg⁻¹) co-administered with SR141716A (0.3 mg·kg⁻¹ i.p.). In contrast, {"type":"entrez-protein","attrs":{"text":"SCH58261","term_id":"1052882304","term_text":"SCH58261"}}SCH58261 (2.0 mg·kg⁻¹) co-administered with SR141716A (0.3 mg·kg⁻¹ i.p.) did not reduce cue-conditioned alcohol seeking.

Conclusions and implications:

Adenosine A_2A and cannabinoid CB₁ receptors regulated alcohol self-administration additively, but combined low-dose antagonism of these receptors did not prevent cue-conditioned alcohol seeking after abstinence. In contrast, combined low-dose antagonism of mGlu₅ and CB₁ receptors did prevent relapse-like alcohol seeking after abstinence, suggesting a prominent role for mGlu₅ receptors in this paradigm.     

Novel κ-opioid receptor agonist MB-1C-OH produces potent analgesia with less depression and sedation

Aim:

To characterize the pharmacological profiles of a novel κ-opioid receptor agonist MB-1C-OH.

Methods:

[³H]diprenorphine binding and [³⁵S]GTPγS binding assays were performed to determine the agonistic properties of MB-1C-OH. Hot plate, tail flick, acetic acid-induced writhing, and formalin tests were conducted in mice to evaluate the antinociceptive actions. Forced swimming and rotarod tests of mice were used to assess the sedation and depression actions.

Results:

In [³H]diprenorphine binding assay, MB-1C-OH did not bind to μ- and δ-opioid receptors at the concentration of 100 μmol/L, but showed a high affinity for κ-opioid receptor (K_i=35 nmol/L). In [³⁵S]GTPγS binding assay, the compound had an E_max of 98% and an EC₅₀ of 16.7 nmol/L for κ-opioid receptor. Subcutaneous injection of MB-1C-OH had no effects in both hot plate and tail flick tests, but produced potent antinociception in the acetic acid-induced writhing test (ED₅₀=0.39 mg/kg), which was antagonized by pretreatment with a selective κ-opioid receptor antagonist Nor-BNI. In the formalin test, subcutaneous injection of MB-1C-OH did not affect the flinching behavior in the first phase, but significantly inhibited that in the second phase (ED₅₀=0.87 mg/kg). In addition, the sedation or depression actions of MB-1C-OH were about 3-fold weaker than those of the classical κ agonist (−)U50,488H.

Conclusion:

MB-1C-OH is a novel κ-opioid receptor agonist that produces potent antinociception causing less sedation and depression.     

A cannabinoid receptor, sensitive to O-1918, is involved in the delayed hypotension induced by anandamide in anaesthetized rats

Background and purpose:

Intravenous injection of the endocannabinoid anandamide induces complex cardiovascular changes via cannabinoid CB₁, CB₂ and vanilloid TRPV1 receptors. Recently, evidence has been accumulating that in vitro, but not in vivo, anandamide relaxes blood vessels, via an as yet unidentified, non-CB₁ vascular cannabinoid receptor, sensitive to O-1918 (1,3-dimethoxy-5-2-[(1R,6R)-3-methyl-6-(1-methylethenyl)-2-cyclohexen-1-yl]-benzene). We here examined whether the anandamide-induced hypotension in urethane-anaesthetized rats was also mediated via a non-CB₁ vascular cannabinoid receptor.

Experimental approach:

Effects of two antagonists (O-1918 and cannabidiol) of the non-CB₁ vascular cannabinoid receptor on anandamide-induced changes in mean, systolic and diastolic blood pressure (MBP, SBP, DBP), mesenteric (MBF) and renal (RBF) blood flow and heart rate (HR) in urethane-anaesthetized rats was examined.

Key results:

In anaesthetized rats, anandamide (1.5–3 µmol·kg⁻¹) and its stable analogue methanandamide (0.5 µmol·kg⁻¹) caused a delayed and prolonged decrease in MBP, SBP, DBP, MBF and RBF by about 10–30% of the respective basal values without changing HR. In pithed rats, anandamide (3 µmol·kg⁻¹) decreased blood pressure by about 15–20% of the basal value without affecting HR, MBF and RBF. All vascular changes were reduced by about 30–70% by cannabidiol and O-1918 (3 µmol·kg⁻¹, each).

Conclusions and implications:

Non-CB₁ cannabinoid vascular receptors, sensitive to O-1918, contribute to the hypotensive effect of anandamide in anaesthetized rats. Activation of these receptors may be therapeutically important as the endocannabinoid system could be activated as a compensatory mechanism in various forms of hypertension.     

Palmitoylethanolamide,a naturally occurring lipid,is an orally effective intestinal anti-inflammatory agent

BACKGROUND AND PURPOSE

Palmitoylethanolamide (PEA) acts via several targets, including cannabinoid CB₁ and CB₂ receptors, transient receptor potential vanilloid type-1 (TRPV1) ion channels, peroxisome proliferator-activated receptor alpha (PPAR α) and orphan G protein-coupled receptor 55 (GRR55), all involved in the control of intestinal inflammation. Here, we investigated the effect of PEA in a murine model of colitis.

EXPERIMENTAL APPROACH

Colitis was induced in mice by intracolonic administration of dinitrobenzenesulfonic acid (DNBS). Inflammation was assessed by evaluating inflammatory markers/parameters and by histology; intestinal permeability by a fluorescent method; colonic cell proliferation by immunohistochemistry; PEA and endocannabinoid levels by liquid chromatography mass spectrometry; receptor and enzyme mRNA expression by quantitative RT-PCR.

KEY RESULTS

DNBS administration caused inflammatory damage, increased colonic levels of PEA and endocannabinoids, down-regulation of mRNA for TRPV1 and GPR55 but no changes in mRNA for CB₁, CB₂ and PPARα. Exogenous PEA (i.p. and/or p.o., 1 mg·kg⁻¹) attenuated inflammation and intestinal permeability, stimulated colonic cell proliferation, and increased colonic TRPV1 and CB₁ receptor expression. The anti-inflammatory effect of PEA was attenuated or abolished by CB₂ receptor, GPR55 or PPARα antagonists and further increased by the TRPV1 antagonist capsazepine.

CONCLUSIONS AND IMPLICATIONS

PEA improves murine experimental colitis, the effect being mediated by CB₂ receptors, GPR55 and PPARα, and modulated by TRPV1 channels.     

Cannabinoid CB1 receptors mediate the effects of corticotropin-releasing factor on the reinstatement of cocaine seeking and expression of cocaine-induced behavioural sensitization

BACKGROUND AND PURPOSE

The endocannabinoid and corticotropin-releasing factor (CRF) systems have been implicated in several long-lasting behavioural effects of prior cocaine experience. The present experiments were designed to probe functional interactions between endocannabinoids and CRF by testing the role of cannabinoid CB₁ receptors in cocaine-related behaviours induced or mediated by CRF.

EXPERIMENTAL APPROACH

In Experiment 1, rats trained to self-administer cocaine were pretreated with the CB₁ receptor antagonist, AM251 (0, 10, 100 or 200 µg, i.c.v.), before tests for reinstatement in response to CRF (0, 0.5 µg, i.c.v.), intermittent footshock stress (0, 0.9 mA) or cocaine (0, 10 mg·kg⁻¹, i.p.). In Experiment 2, rats pre-exposed to cocaine (15–30 mg·kg⁻¹, i.p.) or saline for 7 days were pretreated with AM251 (0, 10 or 100 µg, i.c.v.) before tests for locomotion in response to CRF (0.5 µg, i.c.v.), cocaine (15 mg·kg⁻¹, i.p.) or saline (i.c.v.).

KEY RESULTS

Pretreatment with AM251 selectively interfered with CRF-, but not footshock- or cocaine-induced reinstatement. AM251 blocked the expression of behavioural sensitization induced by challenge injections of both CRF and cocaine.

CONCLUSIONS AND IMPLICATIONS

These findings reveal a mediating role for CB₁ receptor transmission in the effects of CRF on cocaine-related behaviours.     

Tetrahydrocannabinolic acid reduces nausea-induced conditioned gaping in rats and vomiting in Suncus murinus

BACKGROUND AND PURPOSE

We evaluated the anti-emetic and anti-nausea properties of the acid precursor of Δ⁹-tetrahydrocannabinol (THC), tetrahydrocannabinolic acid (THCA), and determined its mechanism of action in these animal models.

EXPERIMENTAL APPROACH

We investigated the effect of THCA on lithium chloride- (LiCl) induced conditioned gaping (nausea-induced behaviour) to a flavour, and context (a model of anticipatory nausea) in rats, and on LiCl-induced vomiting in Suncus murinus. Furthermore, we investigated THCA''s ability to induce hypothermia and suppress locomotion [rodent tasks to assess cannabinoid₁ (CB₁) receptor agonist-like activity], and measured plasma and brain THCA and THC levels. We also determined whether THCA''s effect could be blocked by pretreatment with SR141716 (SR, a CB₁ receptor antagonist).

KEY RESULTS

In rats, THCA (0.05 and/or 0.5 mg·kg⁻¹) suppressed LiCl-induced conditioned gaping to a flavour and context; the latter effect blocked by the CB₁ receptor antagonist, SR, but not by the 5-hydroxytryptamine-1A receptor antagonist, WAY100635. In S. murinus, THCA (0.05 and 0.5 mg·kg⁻¹) reduced LiCl-induced vomiting, an effect that was reversed with SR. A comparatively low dose of THC (0.05 mg·kg⁻¹) did not suppress conditioned gaping to a LiCl-paired flavour or context. THCA did not induce hypothermia or reduce locomotion, indicating non-CB₁ agonist-like effects. THCA, but not THC was detected in plasma samples.

CONCLUSIONS AND IMPLICATIONS

THCA potently reduced conditioned gaping in rats and vomiting in S. murinus, effects that were blocked by SR. These data suggest that THCA may be a more potent alternative to THC in the treatment of nausea and vomiting.     

Evidence that the plant cannabinoid cannabigerol is a highly potent α2-adrenoceptor agonist and moderately potent 5HT1A receptor antagonist

Background and purpose:

Cannabis is the source of at least seventy phytocannabinoids. The pharmacology of most of these has been little investigated, three notable exceptions being Δ⁹-tetrahydrocannabinol, cannabidiol and Δ⁹-tetrahydrocannabivarin. This investigation addressed the question of whether the little-studied phytocannabinoid, cannabigerol, can activate or block any G protein-coupled receptor.

Experimental approach:

The [³⁵S]GTPγS binding assay, performed with mouse brain membranes, was used to test the ability of cannabigerol to produce G protein-coupled receptor activation or blockade. Its ability to displace [³H]CP55940 from mouse CB₁ and human CB₂ cannabinoid receptors and to inhibit electrically evoked contractions of the mouse isolated vas deferens was also investigated.

Key results:

In the brain membrane experiments, cannabigerol behaved as a potent α₂-adrenoceptor agonist (EC₅₀= 0.2 nM) and antagonized the 5-HT_1A receptor agonist, R-(+)-8-hydroxy-2-(di-n-propylamino)tetralin (apparent K_B= 51.9 nM). At 10 µM, it also behaved as a CB₁ receptor competitive antagonist. Additionally, cannabigerol inhibited evoked contractions of the vas deferens in a manner that appeared to be α₂-adrenoceptor-mediated (EC₅₀= 72.8 nM) and displayed significant affinity for mouse CB₁ and human CB₂ receptors.

Conclusions and implications:

This investigation has provided the first evidence that cannabigerol can activate α₂-adrenoceptors, bind to cannabinoid CB₁ and CB₂ receptors and block CB₁ and 5-HT_1A receptors. It will now be important to investigate why cannabigerol produced signs of agonism more potently in the [³⁵S]GTPγS binding assay than in the vas deferens and also whether it can inhibit noradrenaline uptake in this isolated tissue and in the brain.     

Histamine mediates behavioural and metabolic effects of 3-iodothyroacetic acid,an endogenous end product of thyroid hormone metabolism

BACKGROUND AND PURPOSE

3-Iodothyroacetic acid (TA1) is an end product of thyroid hormone metabolism. So far, it is not known if TA1 is present in mouse brain and if it has any pharmacological effects.

EXPERIMENTAL APPROACH

TA1 levels in mouse brain were measured by HPLC coupled to mass spectrometry. After i.c.v. administration of exogenous TA1 (0.4, 1.32 and 4 μg·kg⁻¹) to mice, memory acquisition-retention (passive avoidance paradigm with a light-dark box), pain threshold to thermal stimulus (51.5°C; hot plate test) and plasma glucose (glucorefractometer) were evaluated. Similar assays were performed in mice pretreated with s.c. injections of the histamine H₁ receptor antagonist pyrilamine (10 mg·kg⁻¹) or the H₂ receptor antagonist zolantidine (5 mg·kg⁻¹). TA1 (1.32 and 4 μg·kg⁻¹) was also given i.c.v. to mice lacking histidine decarboxylase (HDC^−/−) and the corresponding WT strain.

KEY RESULTS

TA1 was found in the brain of CD1 but not of HDC mice. Exogenous TA1 induced amnesia (at 0.4 μg·kg⁻¹), stimulation of learning (1.32 and 4 μg·kg⁻¹), hyperalgesia (0.4, 1.32 and 4 μg·kg⁻¹) and hyperglycaemia (1.32 and 4 μg·kg⁻¹). All these effects were modulated by pyrilamine and zolantidine. In HDC^−/− mice, TA1 (1.32 and 4 μg·kg⁻¹) did not increase plasma glucose or induce hyperalgesia.

CONCLUSIONS AND IMPLICATIONS

Behavioural and metabolic effects of TA1 disclosed interactions between the thyroid and histaminergic systems.     

Stimulation of angiotensin AT2 receptors by the non-peptide agonist,Compound 21, evokes vasodepressor effects in conscious spontaneously hypertensive rats

Background and purpose:

Angiotensin type 2 receptor (AT₂ receptor) stimulation evokes vasodilator effects in vitro and in vivo that oppose the vasoconstrictor effects of angiotensin type 1 receptors (AT₁ receptors). Recently, a novel non-peptide AT₂ receptor agonist, Compound 21, was described, which exhibited high AT₂ receptor selectivity.

Experimental approach:

Functional cardiovascular effects of the drug candidate Compound 21 were assessed, using mouse isolated aorta and rat mesenteric arteries in vitro and in conscious spontaneously hypertensive rats (SHR).

Key results:

Compound 21 evoked dose-dependent vasorelaxations in aortic and mesenteric vessels, abolished by the AT₂ receptor antagonist, PD123319. In vivo, Compound 21 administered alone, at doses ranging from 50 to 1000 ng·kg⁻¹·min⁻¹ over 4 h did not decrease blood pressure in conscious normotensive Wistar-Kyoto rats or SHR. However, when given in combination with the AT₁ receptor antagonist, candesartan, Compound 21 (300 ng·kg⁻¹·min⁻¹) lowered blood pressure in SHR only. Further analysis in separate groups of conscious SHR revealed that, at a sixfold lower dose, Compound 21 (50 ng·kg⁻¹·min⁻¹) still evoked a significant depressor response in adult SHR (∼30 mmHg) when combined with different doses of candesartan (0.01 or 0.1 mg·kg⁻¹). Moreover, the Compound 21-evoked depressor effect was abolished when co-infused (50 µg·kg⁻¹·min⁻¹ for 2 h) with the AT₂ receptor antagonist PD123319.

Conclusion and implications:

Collectively, our results indicate that acute administration of Compound 21 evoked blood pressure reductions via AT₂ receptor stimulation. Thus Compound 21 can be considered an excellent drug candidate for further study of AT₂ receptor function in cardiovascular disease.     

Kappa opioid mediation of cannabinoid effects of the potent hallucinogen, salvinorin A, in rodents

Rationale

Salvinorin A, the primary psychoactive derivative of the hallucinogenic herb Salvia divinorum, is a potent and highly selective kappa-opioid receptor (KOR) agonist. Several recent studies, however, have suggested endocannabinoid system mediation of some of its effects.

Objectives

This study represents a systematic examination of this hypothesis.

Methods

Salvinorin A was isolated from S. divinorum and was evaluated in a battery of in vitro and in vivo procedures designed to detect cannabinoid activity, including CB₁ receptor radioligand and [³⁵S]GTPγS binding, calcium flux assay, in vivo cannabinoid screening tests, and drug discrimination.

Results

Salvinorin A did not bind to nor activate CB₁ receptors. In vivo salvinorin A produced pronounced hypolocomotion and antinociception (and to a lesser extent, hypothermia). These effects were blocked by the selective KOR antagonist, JDTic, but not by the CB₁ receptor antagonist rimonabant. Interestingly, however, rimonabant attenuated KOR activation stimulated by U69,593 in a [³⁵S]GTPγS assay. Salvinorin A did not substitute for Δ⁹-tetrahydrocannabinol (THC) in mice trained to discriminate THC.

Conclusions

These findings suggest that similarities in the pharmacological effects of salvinorin A and those of cannabinoids are mediated by its activation of KOR rather than by any direct action of salvinorin A on the endocannabinoid system. Further, the results suggest that rimonabant reversal of salvinorin A effects in previous studies may be explained in part by rimonabant attenuation of KOR activation.     

A new coumarin derivative,IMM-H004, attenuates okadaic acid-induced spatial memory impairment in rats

Aim:

A novel coumarin derivative 7-hydroxy-5-methoxy-4-methyl-3-(4-methylpiperazin-1-yl)-coumarin (IMM-H004) has shown anti-apoptotic, anti-inflammatory and neuroprotective activities. In this study we investigated the effects of IMM-H004 on spatial memory in rats treated with okadaic acid (OKA), which was used to imitate Alzheimer''s disease (AD)-like symptoms.

Methods:

SD rats were administered IMM-H004 (8 mg·kg⁻¹·d⁻¹, ig) or donepezil (positive control, 1 mg·kg⁻¹·d⁻¹, ig) for 25 d. On d 8 and 9, OKA (200 ng) was microinjected into the right ventricle. Morris water maze test was used to evaluate the spatial memory impairments. Tau and β-amyloid (Aβ) pathology in the hippocampus was detected using Western blot and immunohistochemistry. TUNEL staining was used to detect cell apoptosis.

Results:

OKA-treated rats showed significant impairments of spatial memory in Morris water maze test, which were largely reversed by administration of IMM-H004 or donepezil. Furthermore, OKA-treated rats exhibited significantly increased phosphorylation of tau, deposits of Aβ protein and cell apoptosis in the hippocampus, which were also reversed by administration of IMM-H004 or donepezil.

Conclusion:

Administration of IMM-H004 or donepezil protects rats against OKA-induced spatial memory impairments via attenuating tau or Aβ pathology. Thus, IMM-H004 may be developed as a therapeutic agent for the treatment of AD.