Inhibition of forebrain μ-opioid receptor signaling by low concentrations of rimonabant does not require cannabinoid receptors and directly involves μ-opioid receptors.

Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvari krt. 62, H-6726 Szeged, Hungary.
Neurochemistry International (Impact Factor: 2.66). 05/2012; 61(3):378-88. DOI: 10.1016/j.neuint.2012.05.015
Source: PubMed

ABSTRACT Increasing number of publications shows that cannabinoid receptor 1 (CB(1)) specific compounds might act in a CB(1) independent manner, including rimonabant, a potent CB(1) receptor antagonist. Opioids, cannabinoids and their receptors are well known for their overlapping pharmacological properties. We have previously reported a prominent decrease in μ-opioid receptor (MOR) activity when animals were acutely treated with the putative endocannabinoid noladin ether (NE). In this study, we clarified whether the decreased MOR activation caused by NE could be reversed by rimonabant in CB(1) receptor deficient mice. In functional [(35)S]GTPγS binding assays, we have elucidated that 0.1mg/kg of intraperitoneal (i.p.) rimonabant treatment prior to that of NE treatment caused further attenuation on the maximal stimulation of Tyr-d-Ala-Gly-(NMe)Phe-Gly-ol (DAMGO), which is a highly specific MOR agonist. Similar inhibitory effects were observed when rimonabant was injected i.p. alone and when it was directly applied to forebrain membranes. These findings are cannabinoid receptor independent as rimonabant caused inhibition in both CB(1) single knockout and CB(1)/CB(2) double knockout mice. In radioligand competition binding assays we highlighted that rimonabant fails to displace effectively [(3)H]DAMGO from MOR in low concentrations and is highly unspecific on the receptor at high concentrations in CB(1) knockout forebrain and in their wild-type controls. Surprisingly, docking computational studies showed a favorable binding position of rimonabant to the inactive conformational state of MOR, indicating that rimonabant might behave as an antagonist at MOR. These findings were confirmed by radioligand competition binding assays in Chinese hamster ovary cells stably transfected with MOR, where a higher affinity binding site was measured in the displacement of the tritiated opioid receptor antagonist naloxone. However, based on our in vivo data we suggest that other, yet unidentified mechanisms are additionally involved in the observed effects.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: What is known There is a growing number of evidence showing, that the cannabinoid receptor 1 (CB1) antagonist rimonabant has many non-cannabimimetic actions, such as affecting the opioid system. The direct effect of rimonabant on opioid receptors has been studied so far mainly on μ-opioid receptors. However recently the δ-opioid receptor (DOR) receives much more attention as before, due to its potential therapeutic applications, such as nociception or treatment for psychiatric disorders. Objectives To investigate the direct effect of rimonabant on DOR specific ligand binding and on the DOR mediated G-protein activation. Results Micromolar concentrations of rimonabant directly inhibited the DOR specific agonist binding in radioligand competition binding experiments using Chinese hamster ovary cells stably transfected with mouse DOR (CHO-mDOR). However the inhibition occurred also in the subnanomolar range during DOR specific antagonist binding in similar experimental conditions. In functional [35S]GTPγS binding assays rimonabant significantly decreased the basal receptor activity in CHO-mDOR but also in parental CHO cell membranes. During DOR agonist stimulation, micromolar concentration of rimonabant attenuated the DOR G-protein activation and the potency of the activator ligand in [35S]GTPγS binding assays performed in CHO-mDOR, in wild type and also in CB1/CB2 double knock-out mouse forebrain membranes. Yet again this inhibitory action was DOR specific, since it did not occur during other specific GPCR agonist mediated G-protein activation. Conclusion Rimonabant directly inhibited DOR function in the micromolar concentrations. The inhibitory actions indicate an antagonistic behaviour towards DOR which was established by the followings: (i) rimonabant inhibited DOR antagonist binding more effectively than agonist binding, (ii) the inverse agonistic, agonistic effect of the compound can be excluded, (iii) additionally according to previous findings the allosteric mechanism can also be foreclosed.
    Neurochemistry International 02/2014; · 2.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Application of cannabinoids and endocannabinoids to perfused vascular beds or individual isolated arteries results in changes in vascular resistance. In most cases, the result is vasorelaxation, although vasoconstrictor responses are also observed. Cannabinoids also modulate the actions of vasoactive compounds including acetylcholine, methoxamine, angiotensin II and U46619 (thromboxane mimetic). Numerous mechanisms of action have been proposed including receptor activation, potassium channel activation, calcium channel inhibition and the production of vasoactive mediators such as calcitonin gene-related peptide, prostanoids, nitric oxide, endothelial-derived hyperpolarising factor and hydrogen peroxide. The purpose of this review is to examine the evidence for the range of receptors now known to be activated by cannabinoids. Direct activation by cannabinoids of CB1 , CBe , TRPV1 (and potentially other TRP channels) and PPARs in the vasculature has been observed. A potential role for CB2, GPR55 and 5HT1A has also been identified in some studies. Indirectly, activation of prostanoid receptors (TP, IP, EP1 and EP4 ) and the CGRP receptor are involved in the vascular responses to cannabinoids. The majority of this evidence has been obtained through animal research, but recent work has confirmed some of these targets in human arteries. Vascular responses to cannabinoids are enhanced in hypertension and cirrhosis, but are reduced in obesity and diabetes, both due to changes in the target sites of action. Much further work is required to establish the extent of vascular actions of cannabinoids and the application of this research in physiological and pathophysiological situations.
    British Journal of Pharmacology 12/2013; · 5.07 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Though the underlying mechanism remains unknown, several studies have suggested benefits of n-3 long-chain polyunsaturated fatty acid (PUFA) for patients with anxiety disorders. Elevated fear is thought to contribute to the pathogenesis of particular anxiety disorders. The aim of the present study was to evaluate whether the dietary n-3 to n-6 PUFA (3/6) ratio influences fear memory. For this purpose, the effects of various dietary 3/6 ratios on fear memory were examined in mice using contextual fear conditioning, and the effects of these diets on central synaptic transmission were examined to elucidate the mechanism of action of PUFA. We found that fear memory correlated negatively with dietary, serum and brain 3/6 ratios in mice. The low fear memory in mice fed a high 3/6 ratio diet was increased by the cannabinoid CB1 receptor antagonist rimonabant, reaching a level seen in mice fed a low 3/6 ratio diet. The agonist-sensitivity of CB1 receptor was enhanced in the basolateral nucleus of the amygdala (BLA) of mice fed a high 3/6 ratio diet, compared with that of mice fed a low 3/6 ratio diet. Similar enhancement was induced by pharmacological expulsion of cholesterol in the neuronal membrane of brain slices from mice fed a low 3/6 ratio diet. CB1 receptor-mediated short-term synaptic plasticity was facilitated in pyramidal neurons of the BLA in mice fed a high 3/6 ratio diet. These results suggest that the ratio of n-3 to n-6 PUFA is a factor regulating fear memory via cannabinoid CB1 receptors.Neuropsychopharmacology accepted article preview online, 12 February 2014; doi:10.1038/npp.2014.32.
    Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 02/2014; · 8.68 Impact Factor


Available from
May 22, 2014