The ameliorating effects of 5,7-dihydroxy-6-methoxy-2(4-phenoxyphenyl)-4H-chromene-4-one, an oroxylin A derivative, against memory impairment and sensorimotor gating deficit in mice

We previously reported that oroxylin A, a γ-aminobutyric acid A (GABA_A) receptor antagonist, ameliorates drugs-induced memory impairments. We synthesized several oroxylin A derivatives in efforts to find a substance that has pro-cognitive effects as well as improves sensorimotor gating. The aim of the present study is to investigate the effect of a novel oroxylin A derivative, 5,7-dihydroxy-6-methoxy-2(4-phenoxyphenyl)-4H-chromene-4-one (DMPC), on pharmacological models of schizophrenia, which exhibit memory impairment and sensorimotor gating deficit. Memory impairment was induced by scopolamine, a muscarinic receptor antagonist, or MK-801, an N-methyl-d-aspartate receptor antagonist. Sensorimotor gating deficits were induced by MK-801 and measured by prepulse inhibition (PPI) of the acoustic startle response task. DMPC treatment (20 mg/kg) significantly attenuated scopolamine- or MK-801-induced memory impairment and it even enhanced cognitive performance of normal animals. Furthermore, DMPC significantly ameliorated MK-801-induced PPI deficits in the acoustic startle response task. In an in vitro study, DMPC (20 μM) inhibited intracellular Cl^? influx induced by muscimol, a selective GABA_A receptor agonist. These results suggest that DMPC would be a potential candidate for alleviating cognitive dysfunction and sensorimotor gating deficits in schizophrenia, and that its effects may be mediated, in part, via blockade of the GABAergic neurotransmitter system.     

Long-term effects of neonatal MK-801 treatment on prepulse inhibition in young adult rats

Rationale

Blockade of N-methyl-d-asparate (NMDA) receptors has been shown to produce some of the abnormal behaviors related to symptoms of schizophrenia in rodents and human. Neonatal treatment of rats with non-competitive NMDA antagonists has been shown to induce behavioral abnormality in a later period.

Objectives

The aim of this study was to determine whether brief disruption of NMDA receptor function during a critical stage of development is sufficient to produce sensorimotor-gating deficits in the late adolescence or early adulthood in the rat.

Methods

Male pups received the NMDA receptor blocker MK-801 (0.13 or 0.20 mg/kg), or an equal volume of saline on postnatal day (PD) 7 through 10. The animals were tested twice for prepulse inhibition (PPI) and locomotor activity in pre- (PD 35-38) and post- (PD 56-59) puberty.

Results

Neonatal exposure to both doses MK-801 disrupted PPI in the adolescence and early adulthood. Low-dose MK-801 elicited long-term effects on startle amplitudes, whereas high-dose MK-801 did not. Neither dose of MK-801 showed a significant effect on spontaneous locomotor activity, whereas the high dose attenuated rearing.

Conclusions

The results of this study suggest neonatal exposure to MK-801 disrupted sensorimotor gating in the adolescence and early adulthood stages. These findings indicate that rats transiently exposed to NMDA blockers in neonatal periods are useful for the study of the pathophysiology and treatment of schizophrenia.     

Chronic blockade of cannabinoid CB2 receptors induces anxiolytic-like actions associated with alterations in GABA(A) receptors

BACKGROUND AND PURPOSE

The aim of this study was to explore the effects of CB₂ receptor agonist and antagonist in the regulation of anxiety-like behaviours.

EXPERIMENTAL APPROACHES

Effects of acute and chronic treatment with the CB₂ receptor agonist JWH133 and CB₂ receptor antagonist AM630 were evaluated in the light-dark box (LDB) and elevated plus maze (EPM) tests in Swiss ICR mice. CB₂ receptor, GABA_Aα₂ and GABA_Aγ₂ gene and protein expression in the cortex and amygdala of mice chronically treated with JWH133 or AM630 were examined by RT-PCR and Western blot. Effects of chronic AM630 treatment were evaluated in spontaneously anxious DBA/2 mice in LDB.

KEY RESULTS

Acute JWH133 treatment failed to produce any effect. Acute AM630 treatment increased anxiety and was blocked by pre-treatment with JWH133. Chronic JWH133 treatment increased anxiety-like behaviour whereas chronic AM630 treatment was anxiolytic in LDB and EPM tests. Chronic AM630 treatment increased gene and reduced protein expression of CB₂ receptors, GABA_Aα₂ and GABA_Aγ₂ in cortex and amygdala. Chronic JWH133 treatment resulted in opposite gene and protein alterations. In addition, chronic AM630 administration decreased the anxiety of DBA/2 mice in the LDB test.

CONCLUSIONS AND IMPLICATIONS

The opposing behavioural and molecular changes observed after chronic treatment with AM630 or JWH133 support the key role of CB₂ receptors in the regulation of anxiety. Indeed, the efficacy of AM630 in reducing the anxiety of the spontaneously anxious DBA/2 strain of mice strengthens the potential of the CB₂ receptor as a new target in the treatment of anxiety-related disorders.     

Co-administration of 5-HT6 receptor antagonists with clozapine, risperidone, and a 5-HT2A receptor antagonist: effects on prepulse inhibition in rats

Rationale

Some novel antipsychotics manifest antagonistic activity at serotonin-6 receptors; however, little is known about the role of 5-HT6 receptors in ameliorating sensory gating deficits.

Objective

We evaluated the effects of the combined administration of the 5-HT6 receptor antagonist SB 271046 with clozapine and haloperidol, as well as the co-administration of SB 271046 or SB 399885 with risperidone and the 5-HT2A antagonist M100907, to overcome the deficits induced by MK-801 in the prepulse inhibition (PPI) test.

Results

MK-801 (0.1 mg/kg) produced reliable PPI deficits. Administration of SB 271046 (6 and 9 mg/kg), SB 399885 (3 and 6 mg/kg), clozapine (2.5 mg/kg), haloperidol (0.1 and 0.2 mg/kg), risperidone (0.25–1 mg/kg), and M100907 (0.5 and 1 mg/kg) did not affect the MK-801-induced deficits, but the administration of clozapine (5 mg/kg) did reverse the effects of MK-801. In MK-801-treated rats, the co-administration of inactive doses of clozapine (2.5 mg/kg) and SB 271046 (6 mg/kg) reversed the PPI impairments compared to animals that were administered inactive doses of either clozapine or SB 271046 alone. Co-administration of risperidone (1 mg/kg) or M100907 (0.5 mg/kg) with SB 271046 (6 mg/kg) or SB 399885 (3 mg/kg) also attenuated the MK-801-induced PPI deficits. In contrast, joint administration of haloperidol and SB 271046 had no effect on the PPI deficit.

Conclusion

The present results suggest that the 5-HT6 receptors may play adjunctive roles in antipsychotic drug action, and that the combination of 5-HT2A and 5-HT6 antagonism may represent an important element in the pharmacological profile of antipsychotic drugs.     

CRF1 receptor antagonists do not reverse pharmacological disruption of prepulse inhibition in rodents

Rationale

As enhanced corticotropin-releasing factor (CRF) transmission is associated with induction of sensorimotor gating deficits, CRF₁ receptor antagonists may reverse disrupted prepulse inhibition (PPI), an operational measure of sensorimotor gating.

Objectives

To determine the effects of CRF₁ receptor antagonists in pharmacological models of disrupted PPI and to determine if long-term elevated central CRF levels alter sensitivity towards PPI disrupting drugs.

Methods

CP154,526 (10–40 mg/kg), SSR125543 (3–30 mg/kg) and DMP695 (40 mg/kg) were tested on PPI disruption provoked by d-amphetamine (2.5, 3 mg/kg), ketamine (5, 30 mg/kg) and MK801 (0.2, 0.5 mg/kg) in Wistar rats, C57Bl/6J and CD1 mice, and on spontaneously low PPI in Iffa Credo rats and DBA/2J mice. PPI-disrupting effects of d-amphetamine (2.5–5 mg/kg) and MK801 (0.3–1 mg/kg) were examined in CRF-overexpressing (CRFtg) mice, which display PPI deficits. Finally, we determined the influence of CP154,526 on d-amphetamine-induced dopamine outflow in nucleus accumbens and prefrontal cortex of CRFtg mice using in vivo microdialysis.

Results

No CRF_1?antagonists improved PPI deficits in any test. CRFtg mice showed blunted PPI disruption in response to MK801, but not d-amphetamine. Further, d-amphetamine-induced dopamine release was less pronounced in CRFtg versus wild-type mice, a response normalized by pretreatment with CP154,526.

Conclusion

The inability of CRF₁ receptor antagonists to block pharmacological disruption of sensorimotor gating suggests that the involvement of CRF1 receptors in the modulation of dopaminergic and glutamatergic neurotransmission relevant for sensory gating is limited. Furthermore, the alterations observed in CRFtg mice support the notion that long-term elevated central CRF levels induce changes in these neurotransmitter systems.     

Combined administration of an mGlu2/3 receptor agonist and a 5-HT2A receptor antagonist markedly attenuate the psychomotor-activating and neurochemical effects of psychostimulants

Rationale

It was recently reported that administration of the metabotropic glutamate 2 and 3 (mGlu2/3) receptor agonist prodrug LY2140023 to schizophrenic patients decreased positive symptoms. However, at the single, potentially suboptimal, dose that was tested, LY2140023 trended towards being inferior to olanzapine on several indices of efficacy within the Positive and Negative Syndrome Scale.

Objectives

In this study, we examined whether the antipsychotic potential of mGlu2/3 receptor agonism can be enhanced with 5-HT_2A receptor antagonism.

Materials and methods

Specifically, we characterized the effects of coadministering submaximally effective doses of the 5-HT_2A receptor antagonist M100907 (0.2 mg/kg) and the mGlu2/3 receptor agonist LY379268 (1 mg/kg) on amphetamine-induced and MK-801-induced psychomotor activity in rats, an assay sensitive to antipsychotics. We also determined the effects of coadministering these two compounds on MK-801-induced dopamine and norepinephrine efflux in the nucleus accumbens (NAc).

Results

At the submaximally effective doses tested, the effects of M100907 and LY379268 on amphetamine-induced and MK-801-induced psychomotor activity were significantly greater when given together than when given separately. Furthermore, coadministration of these doses of M100907 and LY379268 reduced MK-801-induced dopamine efflux in the NAc. This effect on dopamine release was not observed with the administration of either compound alone, even at higher doses that attenuated MK-801-induced psychomotor activity.

Conclusions

Our results suggest that a single compound having both mGlu2/3 receptor agonist and 5-HT_2A receptor antagonist activity, or coadministration of two compounds selective for these receptors, could be superior in terms of efficacy and/or reduced side-effect liability relative to an mGlu2/3 receptor agonist alone.     

Chronic blockade of CB1 receptors reverses startle gating deficits and associated neurochemical alterations in rats reared in isolation

BACKGROUND AND PURPOSE

Pharmacological interventions aimed at restoring the endocannabinoid system functionality have been proposed as potential tools in the treatment of schizophrenia. Based on our previous results suggesting a potential antipsychotic-like profile of the CB₁ receptor inverse agonist/antagonist, AM251, here we further investigated the effect of chronic AM251 administration on the alteration of the sensorimotor gating functions and endocannabinoid levels induced by isolation rearing in rats.

EXPERIMENTAL APPROACH

Using the post-weaning social isolation rearing model, we studied its influence on sensorimotor gating functions through the PPI paradigm. The presence of alterations in the endocannabinoid levels as well as in dopamine and glutamate receptor densities was explored in specific brain regions following isolation rearing. The effect of chronic AM251 administration on PPI response and the associated biochemical alterations was assessed.

KEY RESULTS

The disrupted PPI response in isolation-reared rats was paralleled by significant alterations in 2-AG content and dopamine and glutamate receptor densities in specific brain regions. Chronic AM251 completely restored normal PPI response in isolated rats. This behavioural recovery was paralleled by the normalization of 2-AG levels in all the brain areas analysed. Furthermore, AM251 partially antagonized isolation-induced changes in dopamine and glutamate receptors.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate the efficacy of chronic AM251 treatment in the recovery of isolation-induced disruption of PPI. Moreover, AM251 counteracted the imbalances in the endocannabinoid content, specifically 2-AG levels, and partially reversed the alterations in dopamine and glutamate systems associated with the disrupted behaviour. Together, these findings support the potential antipsychotic-like activity of CB₁ receptor blockade.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8     

Effects of cannabinoid receptor ligands on psychosis-relevant behavior models in the rat

Abstract Rationale. Marijuana is known to have psychotropic effects in humans. In this study, we used rat models of sensorimotor gating, hyperactivity and stereotypy to explore whether CB₁ receptor stimulation or blockade induces behavioral changes consistent with psychotomimetic or antipsychotic agents, respectively. Objectives. We determined whether (a) the cannabinoid agonist CP 55940 decreased pre-pulse inhibition (PPI) as might be expected from a psychotomimetic agent, and (b) the selective CB₁ receptor antagonist, SR 141716A, had any effect on PPI on its own or following disruptions by psychotomimetic agents. In addition, we investigated the effects of SR 141716A on elevated levels of hyperactivity and stereotypy elicited by d-amphetamine. Methods. These studies were conducted in rats using standard methodologies for determination of PPI following acoustic stimuli, and d-amphetamine-induced hyperactivity and stereotypies. Results. Decreased startle responses to 120 dB stimuli were observed in rats treated with CP 55940 (0.1 mg/kg IP) in the absence and presence of a 73 dB pre-pulse. These effects were reversed by SR 141716A (5 and 10 mg/kg, respectively). SR 141716A (0.1, 5, 10 mg/kg) had no effect on PPI on its own or following disruptions by apomorphine, d-amphetamine or MK-801. Conversely, in separate experiments different antipsychotic agents reversed disruptions in PPI induced by d-amphetamine (haloperidol), apomorphine (haloperidol or clozapine) or MK-801 (clozapine or olanzapine). In addition, unlike haloperidol, SR 141716A (5 mg/kg) did not reverse d-amphetamine-mediated increases in hyperactivity or stereotypy. Conclusions. The CP 55940-mediated decreases in startle amplitude confound assessment of the effects of CB₁ receptor activation on PPI. The failure of SR 141716A to reverse disruptions in PPI, hyperactivity or stereotypy induced by non-cannabinoid psychotomimetic agents suggests that blockade of the CB₁ receptor on its own is not sufficient for antipsychotic therapy. Electronic Publication     

Efficacy of 3,5-dibromo-L-phenylalanine in rat models of stroke,seizures and sensorimotor gating deficit

Background and purpose:

Abnormal glutamatergic activity is implicated in neurologic and neuropsychiatric disorders. Selective glutamate receptor antagonists were highly effective in animal models of stroke and seizures but failed in further clinical development because of serious side effects, including an almost complete set of symptoms of schizophrenia. Therefore, the novel polyvalent glutamatergic agent 3,5-dibromo-L-phenylalanine (3,5-DBr-L-Phe) was studied in rat models of stroke, seizures and sensorimotor gating deficit.

Experimental approach:

3,5-DBr-L-Phe was administered intraperitoneally as three boluses after intracerebral injection of endothelin-1 (ET-1) adjacent to the middle cerebral artery to cause brain injury (a model of stroke). 3,5-DBr-L-Phe was also given as a single bolus prior to pentylenetetrazole (PTZ) injection to induce seizures or prior to the administration of the N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK-801) to cause disruption of prepulse inhibition (PPI) of startle (sensorimotor gating deficit).

Key results:

Brain damage caused by ET-1 was reduced by 52%, which is comparable with the effects of MK-801 in this model as reported by others. 3,5-DBr-L-Phe significantly reduced seizures induced by PTZ without the significant effects on arterial blood pressure and heart rate normally caused by NMDA antagonists. 3,5-DBr-L-Phe prevented the disruption of PPI measured 3 days after the administration of ET-1. 3,5-DBr-L-Phe also eliminated sensorimotor gating deficit caused by MK-801.

Conclusion and implications:

The pharmacological profile of 3,5-DBr-L-Phe might be beneficial not only for developing a therapy for the neurological and cognitive symptoms of stroke and seizures but also for some neuropsychiatric disorders.     

Inhibition of phosphodiesterase 10A has differential effects on dopamine D1 and D2 receptor modulation of sensorimotor gating

Rationale

Inhibitors of phosphodiesterase 10A (PDE10A), an enzyme highly expressed in medium spiny neurons of the mammalian striatum, enhance activity in direct (dopamine D1 receptor-expressing) and indirect (D2 receptor-expressing striatal output) pathways. The ability of such agents to act to potentiate D1 receptor signaling while inhibiting D2 receptor signaling suggest that PDE10A inhibitors may have a unique antipsychotic-like behavioral profile differentiated from the D2 receptor antagonist-specific antipsychotics currently used in the treatment of schizophrenia.

Objectives

To evaluate the functional consequences of PDE10A inhibitor modulation of D1 and D2 receptor pathway signaling, we compared the effects of a PDE10A inhibitor (TP-10) on D1 and D2 receptor agonist-induced disruptions in prepulse inhibition (PPI), a measure of sensorimotor gating disrupted in patients with schizophrenia.

Results

Our results indicate that, in rats: (1) PDE10A inhibition (TP-10, 0.32–10.0 mg/kg) has no effect on PPI disruption resulting from the mixed D1/D2 receptor agonist apomorphine (0.5 mg/kg), confirming previous report; (2) Yet, TP-10 blocked the PPI disruption induced by the D2 receptor agonist quinpirole (0.5 mg/kg); and attenuated apomorphine-induced disruptions in PPI in the presence of the D1 receptor antagonist SCH23390 (0.005 mg/kg).

Conclusions

These findings indicate that TP-10 cannot block dopamine agonist-induced deficits in PPI in the presence of D1 activation and suggest that the effect of PDE10A inhibition on D1 signaling may be counterproductive in some models of antipsychotic activity. These findings, and the contribution of TP-10 effects in the direct pathway on sensorimotor gating in particular, may have implications for the potential antipsychotic efficacy of PDE10A inhibitors.     

LSD but not lisuride disrupts prepulse inhibition in rats by activating the 5-HT2A receptor

Rationale

Compounds that activate the 5-HT_2A receptor, such as lysergic acid diethylamide (LSD), act as hallucinogens in humans. One notable exception is the LSD congener lisuride, which does not have hallucinogenic effects in humans even though it is a potent 5-HT_2A agonist. LSD and other hallucinogens have been shown to disrupt prepulse inhibition (PPI), an operational measure of sensorimotor gating, by activating 5-HT_2A receptors in rats.

Objective

We tested whether lisuride disrupts PPI in male Sprague–Dawley rats. Experiments were also conducted to identify the mechanism(s) responsible for the effect of lisuride on PPI and to compare the effects of lisuride to those of LSD.

Results

Confirming a previous report, LSD (0.05, 0.1, and 0.2 mg/kg, s.c.) reduced PPI, and the effect of LSD was blocked by pretreatment with the selective 5-HT_2A antagonist MDL 11,939. Administration of lisuride (0.0375, 0.075, and 0.15 mg/kg, s.c.) also reduced PPI. However, the PPI disruption induced by lisuride (0.075 mg/kg) was not blocked by pretreatment with MDL 11,939 or the selective 5-HT_1A antagonist WAY-100635 but was prevented by pretreatment with the selective dopamine D₂/D₃ receptor antagonist raclopride (0.1 mg/kg, s.c).

Conclusions

The effect of LSD on PPI is mediated by the 5-HT_2A receptor, whereas activation of the 5-HT_2A receptor does not appear to contribute to the effect of lisuride on PPI. These findings demonstrate that lisuride and LSD disrupt PPI via distinct receptor mechanisms and provide additional support for the classification of lisuride as a non-hallucinogenic 5-HT_2A agonist.     

Cannabidiol reverses MK-801-induced disruption of prepulse inhibition in mice.

Cannabidiol, a nonpsychoactive constituent of the Cannabis sativa plant, has been reported to act as an agonist of the vanilloid 1 channel in the transient receptor potential family (TRPV1) and also to inhibit the hydrolysis and cellular uptake of the endogenous cannabinoid anandamide. Cannabidiol has also been reported to have potential as an antipsychotic. We investigated the effect of cannabidiol on sensorimotor gating deficits in mice induced by the noncompetitive NMDA receptor antagonist, MK-801. Sensorimotor gating is deficient in psychotic disorders such as schizophrenia and may be reliably measured by prepulse inhibition (PPI) of the startle response in rodents and humans. MK-801 (0.3-1 mg/kg i.p.) dose dependently disrupted PPI while cannabidiol (1-15 mg/kg i.p.), when administered with vehicle, had no effect on PPI. Cannabidiol (5 mg/kg i.p.) successfully reversed disruptions in PPI induced by MK-801 (1 mg/kg i.p.), as did the atypical antipsychotic clozapine (4 mg/kg i.p.). Pretreatment with capsazepine (20 mg/kg i.p.) prevented the reversal of MK-801-induced disruption of PPI by cannabidiol, providing preliminary evidence that TRPV1 receptors are involved in the reversal of MK-801-induced sensorimotor gating deficits by cannabidiol.     

Cannabinoid CB₂ receptor-mediated regulation of impulsive-like behaviour in DBA/2 mice

BACKGROUND AND PURPOSE

This study evaluated gene expression differences between two mouse strains, characterized by opposite impulsivity-like traits and the involvement of the cannabinoid CB₂ receptor in the modulation of impulsivity.

EXPERIMENTAL APPROACH

Behavioural tests were conducted to compare motor activity, exploration and novelty seeking, attention and cognitive and motor impulsivity (delayed reinforcement task: session duration 30 min; timeout 30 s) between A/J and DBA/2 mice. Expression of genes for dopamine D₂ receptors, CB₁ and CB₂ receptors were measured in the cingulate cortex (CgCtx), caudate-putamen (CPu), accumbens (Acc), amygdala (Amy) and hippocampus (Hipp). Involvement of CB₂ receptors in impulsivity was evaluated in DBA/2 mice with a CB₂ receptor agonist (JWH133) and an antagonist (AM630).

KEY RESULTS

DBA/2 mice presented higher motor and exploratory activity, pre-pulse inhibition impairment and higher cognitive and motor impulsivity level than A/J mice. In addition, DBA/2 mice showed lower (CgCtx, Acc, CPu) D₂ receptor, lower (Amy) and higher (CgCtx, Acc, CPu, Hipp) CB₁ receptor and higher (CgCtx, Acc, Amy) and similar (CPu, Hipp) CB₂ receptor gene expressions. Treatment with JWH133 (0.5, 1, 3 mg·kg⁻¹, i.p.) reduced cognitive and motor impulsivity level, accompanied by CB₂ receptor down-regulation (CgCtx, Acc, Amy) but did not modify other behaviours. In contrast, AM630 (1, 2, 3 mg·kg⁻¹, i.p.) improved pre-pulse inhibition and reduced novelty seeking behaviour in DBA/2 mice.

CONCLUSIONS AND IMPLICATIONS

CB₂ receptors might play an important role in regulating impulsive behaviours and should be considered a promising therapeutic target in the treatment of impulsivity-related disorders.     

JWH018, a common constituent of ��Spice�� herbal blends, is a potent and efficacious cannabinoid CB1 receptor agonist

Background and purpose:

‘Spice’ is an herbal blend primarily marketed in Europe as a mild hallucinogen with prominent cannabis-like effects and as a legal alternative to cannabis. However, a recent report identified a number of synthetic additives in samples of ‘Spice’. One of these, the indole derivative JWH018, is a ligand for the cannabinoid receptor 1 (CB₁) cannabinoid receptor and inhibits cAMP production in CB₁ receptor-expressing CHO cells. Other effects of JWH018 on CB₁ receptor-mediated signalling are not known, particularly in neurons. Here we have evaluated the signalling pathways activated by JWH018 at CB₁ receptors.

Experimental approach:

We investigated the effects of JWH018 on neurotransmission in cultured autaptic hippocampal neurons. We further analysed its activation of ERK1/2 mitogen activated protein kinase (MAPK) and internalization of CB₁ receptors in HEK293 cells stably expressing this receptor.

Key results:

In cultured autaptic hippocampal neurons, JWH018 potently inhibited excitatory postsynaptic currents (IC₅₀= 14.9 nM) in a concentration- and CB₁ receptor-dependent manner. Furthermore, it increased ERK1/2 MAPK phosphorylation (EC₅₀= 4.4 nM). We also found that JWH018 potently induced rapid and robust CB₁ receptor internalization (EC₅₀= 2.8 nM; t_1/2= 17.3 min).

Conclusions and implications:

JWH018, a prominent component of several herbal preparations marketed for their psychoactivity, is a potent and effective CB₁ receptor agonist that activates multiple CB₁ receptor signalling pathways. Thus, it is likely that the subjective effects of ‘Spice’ are due to activation of cannabinoid CB₁ receptors by JWH018, added to this herbal preparation.     

A novel peripherally restricted cannabinoid receptor antagonist, AM6545, reduces food intake and body weight, but does not cause malaise, in rodents

BACKGROUND AND PURPOSE

Cannabinoid CB₁ receptor antagonists reduce food intake and body weight, but clinical use in humans is limited by effects on the CNS. We have evaluated a novel cannabinoid antagonist (AM6545) designed to have limited CNS penetration, to see if it would inhibit food intake in rodents, without aversive effects.

EXPERIMENTAL APPROACH

Cannabinoid receptor binding studies, cAMP assays, brain penetration studies and gastrointestinal motility studies were carried out to assess the activity profile of AM6545. The potential for AM6545 to induce malaise in rats and the actions of AM6545 on food intake and body weight were also investigated.

KEY RESULTS

AM6545 binds to CB₁ receptors with a K_i of 1.7 nM and CB₂ receptors with a K_i of 523 nM. AM6545 is a neutral antagonist, having no effect on cAMP levels in transfected cells and was less centrally penetrant than AM4113, a comparable CB₁ receptor antagonist. AM6545 reversed the effects of WIN55212-2 in an assay of colonic motility. In contrast to AM251, AM6545 did not produce conditioned gaping or conditioned taste avoidance in rats. In rats and mice, AM6545 dose-dependently reduced food intake and induced a sustained reduction in body weight. The effect on food intake was maintained in rats with a complete subdiaphragmatic vagotomy. AM6545 inhibited food intake in CB₁ receptor gene-deficient mice, but not in CB₁/CB₂ receptor double knockout mice.

CONCLUSIONS AND IMPLICATIONS

Peripherally active, cannabinoid receptor antagonists with limited brain penetration may be useful agents for the treatment of obesity and its complications.     

The cannabinoid CB2 receptor is necessary for nicotine-conditioned place preference, but not other behavioral effects of nicotine in mice

Rationale

Whereas cannabinoid CB₁ receptors have long been known to contribute to the rewarding effects and dependence liability of many drugs of abuse, recent studies have implicated the involvement of cannabinoid CB₂ receptors.

Objective

Here, we evaluated the role of CB₂ receptors in the rewarding properties of nicotine, as assessed in the conditioned place preference (CPP) paradigm and mecamylamine-precipitated withdrawal in nicotine dependent mice.

Methods

Using complementary pharmacological and genetic approaches, we investigated the involvement of CB₂ receptors in nicotine- and cocaine-induced CPP in mice and mecamylamine-precipitated withdrawal in nicotine-dependent mice. We also determined whether deletion of CB₂ receptors affects nicotine-induced hypothermia and hypoalgesia.

Results

Nicotine-induced (0.5 mg/kg) CPP was completely blocked by selective CB₂ antagonist, SR144528 (3 mg/kg) in wild-type mice, and was absent in CB₂ (?/?) mice. Conversely, the CB₂ receptor agonist, O-1966 (1, 3, 5, 10, 20 mg/kg) given in combination with a subthreshold dose of nicotine (0.1 mg/kg) elicited a place preference. In contrast, O-1966 (20 mg/kg) blocked cocaine (10 mg/kg)-induced CPP in wild type mice, while CB₂ (?/?) mice showed unaltered cocaine CPP. CB₂ (+/+) and (?/?) nicotine-dependent mice showed almost identical precipitated withdrawal responses and deletion of CB₂ receptor did not alter acute somatic effects of nicotine.

Conclusions

Collectively, these results indicate that CB₂ receptors are required for nicotine-induced CPP in the mouse, while it is not involved in nicotine withdrawal or acute effects of nicotine. Moreover, these results suggest that CB₂ receptors play opposing roles in nicotine- and cocaine-induced CPP.     

Spinal and peripheral analgesic effects of the CB2 cannabinoid receptor agonist AM1241 in two models of bone cancer-induced pain

Background and purpose:

The activation of CB₂ receptors induces analgesia in experimental models of chronic pain. The present experiments were designed to study whether the activation of peripheral or spinal CB₂ receptors relieves thermal hyperalgesia and mechanical allodynia in two models of bone cancer pain.

Experimental approach:

NCTC 2472 osteosarcoma or B16-F10 melanoma cells were intratibially inoculated to C3H/He and C57BL/6 mice. Thermal hyperalgesia was assessed by the unilateral hot plate test and mechanical allodynia by the von Frey test. AM1241 (CB₂ receptor agonist), AM251 (CB₁ receptor antagonist), SR144528 (CB₂ receptor antagonist) and naloxone were used. CB₂ receptor expression was measured by Western blot.

Key results:

AM1241 (0.3–10 mg·kg⁻¹) abolished thermal hyperalgesia and mechanical allodynia in both tumour models. The antihyperalgesic effect was antagonized by subcutaneous, intrathecal or peri-tumour administration of SR144528. In contrast, the antiallodynic effect was inhibited by systemic or intrathecal, but not peri-tumour, injection of SR144528. The effects of AM1241 were unchanged by AM251 but were prevented by naloxone. No change in CB₂ receptor expression was found in spinal cord or dorsal root ganglia.

Conclusions and implications:

Spinal CB₂ receptors are involved in the antiallodynic effect induced by AM1241 in two neoplastic models while peripheral and spinal receptors participate in the antihyperalgesic effects. Both effects were mediated by endogenous opiates. The use of drugs that activate CB₂ receptors could be a useful strategy to counteract bone cancer-induced pain symptoms.     

Characterization of cannabinoid receptor ligands in tissues natively expressing cannabinoid CB2 receptors

Background and Purpose

Although cannabinoid CB₂ receptor ligands have been widely characterized in recombinant systems in vitro, little pharmacological characterization has been performed in tissues natively expressing CB₂ receptors. The aim of this study was to compare the pharmacology of CB₂ receptor ligands in tissue natively expressing CB₂ receptors (human, rat and mouse spleen) and hCB₂-transfected CHO cells.

Experimental Approach

We tested the ability of well-known cannabinoid CB₂ receptor ligands to stimulate or inhibit [³⁵S]GTPγS binding to mouse, rat and human spleen membranes and to hCB₂-transfected CHO cell membranes. cAMP assays were also performed in hCB₂-CHO cells.

Key Results

The data presented demonstrate that: (i) CP 55,940, WIN 55,212-2 and JWH 133 behave as CB₂ receptor full agonists both in spleen and hCB₂-CHO cells, in both [³⁵S]GTPγS and cAMP assays; (ii) JWH 015 behaves as a low-efficacy agonist in spleen as well as in hCB₂-CHO cells when tested in the [³⁵S]GTPγS assay, while it displays full agonism when tested in the cAMP assay using hCB₂-CHO cells; (iii) (R)-AM 1241 and GW 405833 behave as agonists in the [³⁵S]GTPγS assay using spleen, instead it behaves as a low-efficacy inverse agonist in hCB₂-CHO cells; and (iv) SR 144528, AM 630 and JTE 907 behave as CB₂ receptor inverse agonists in all the tissues.

Conclusion and Implications

Our results demonstrate that CB₂ receptor ligands can display differential pharmacology when assays are conducted in tissues that natively express CB₂ receptors and imply that conclusions from recombinant CB₂ receptors should be treated with caution.     

Cannabinoid receptor agonists modulate oligodendrocyte differentiation by activating PI3K/Akt and the mammalian target of rapamycin (mTOR) pathways

BACKGROUND AND PURPOSE

The endogenous cannabinoid system participates in oligodendrocyte progenitor differentiation in vitro. To determine the effect of synthetic cannabinoids on oligodendrocyte differentiation, we exposed differentiating cultures of oligodendrocytes with cannabinoid CB₁, CB₂ and CB₁/CB₂ receptor agonists and antagonists. The response of the PI3K/Akt and the mammalian target of rapamycin (mTOR) signalling pathways were studied as effectors of cannabinoid activity.

EXPERIMENTAL APPROACH

Purified oligodendrocyte progenitor cells (OPC) obtained from primary mixed glial cell cultures were treated for 48 h with CB₁, CB₂ and CB₁/CB₂ receptor agonists (ACEA, JWH133 and HU210, respectively) in the presence or absence of the antagonists AM281 (CB₁ receptor) and AM630 (CB₂ receptor). Moreover, inhibitors of the phosphatidylinositol 3-kinase (PI3K)/Akt and mTOR pathways ({"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 and rapamycin, respectively) were used to study the involvement of these pathways on cannabinoid-induced OPC maturation.

KEY RESULTS

ACEA, JWH133 and HU-210 enhanced OPC differentiation as assessed by the expression of stage specific antigens and myelin basic protein (MBP). Moreover, this effect was blocked by the CB receptor antagonists. ACEA, JWH133 and HU210 induced a time-dependent phosphorylation of Akt and mTOR, whereas the inhibitors of PI3K/Akt ({"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002) or of mTOR (rapamycin) reversed the effects of HU-210 on oligodendrocyte differentiation and kinase activation.

CONCLUSIONS AND IMPLICATIONS

Activation of cannabinoid CB₁ or CB₂ receptors with selective agonists accelerated oligodendrocyte differentiation through the mTOR and Akt signalling pathways.

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     

The effect of nicotine on sensorimotor gating is modulated by a CHRNA3 polymorphism

Rationale

Prepulse inhibition (PPI) of the acoustic startle response, a measure of sensorimotor gating, can be enhanced by nicotine. Moreover, the TT genotype of the nicotinic acetylcholine receptor (nAChR) α3-subunit (CHRNA3) rs1051730 polymorphism has previously been associated with diminished PPI and nicotine dependence.

Objectives

We tested whether this CHRNA3 polymorphism also modulates the nicotine-induced enhancement of PPI.

Methods

We assessed the effect of nicotine on PPI, startle reactivity, and habituation in 52 healthy nonsmoking volunteers genotyped for CHRNA3 rs1051730 in a double-blind, placebo-controlled, counterbalanced, within-subjects design. Additionally, cotinine plasma levels were measured.

Results

Nicotine significantly enhanced PPI in TT homozygotes only and tended to worsen PPI in TC and CC carriers. Additionally, nicotine significantly reduced startle habituation.

Conclusions

The present findings imply that the effect of nicotine on sensorimotor gating is modulated by nAChR α3-subunits. Thus, genetic variation in nicotinic receptor genes might be an important connecting link between early attentional processes and smoking behavior.