The Endogenous Cannabinoid Anandamide Inhibits α₇Nicotinic Acetylcholine Receptor-Mediated Responses inXenopusOocytes

Abstract

The effect of the endogenous cannabinoid ligand anandamide on the function of the cloned ␣ 7 subunit of the nicotinic acetylcholine (ACh) receptor expressed in Xenopus oocytes was investigated by using the two-electrode voltage-clamp technique. Anandamide reversibly inhibited nicotine (10 M) induced-currents in a concentration-dependent manner (10 nM to 30 M), with an IC 50 value of 229.7 Ϯ 20.4 nM. The effect of anandamide was neither dependent on the membrane potential nor meditated by endogenous Ca 2ϩ dependent Cl Ϫ channels since it was unaffected by intracellularly injected BAPTA and perfusion with Ca 2ϩ -free bathing solution containing 2 mM Ba 2ϩ . Anandamide decreased the maximal nicotine-induced responses without significantly affecting its potency, indicating that it acts as a noncompetitive antagonist on nicotinic acetylcholine (nACh) ␣ 7 receptors. This effect was not mediated by CB 1 or CB 2 receptors, as neither the selective CB 1 receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride (SR 141716A) nor CB 2 receptor antagonist N-((1S)-endo-1,3,3-trimethyl-bicyclo-heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR 144528) reduced the inhibition by anandamide. In addition, inhibition of nicotinic responses by anandamide was not sensitive to either pertussis toxin treatment or to the membrane permeable cAMP analog 8-Br-cAMP (0.2 mM). Inhibitors of enzymes involved in anandamide metabolism including phenylmethylsulfonyl fluoride, superoxide dismutase, and indomethacin, or the anandamide transport inhibitor AM404 did not prevent anandamide inhibition of nicotinic responses, suggesting that anandamide itself acted on nicotinic receptors. In conclusion, these results demonstrate that the endogenous cannabinoid anandamide inhibits the function of nACh ␣ 7 receptors expressed in Xenopus oocytes in a cannabinoid receptor-independent and noncompetitive manner.

Differential Effects of Endogenous and Synthetic Cannabinoids on α7-Nicotinic Acetylcholine Receptor-Mediated Responses in Xenopus Oocytes

“…Biochemical and behavioral studies support the idea that functional interactions between nicotine receptors and cannabinoid receptor ligands exist (Pryor et al, 1978;Valjent et al, 2002). In addition, we have shown that the endogenous cannabinoid, anandamide, inhibits ion currents mediated by the activation of nACh ␣ 7 receptors expressed in Xenopus oocytes (Oz et al, 2003). Another receptor that shares a high degree of homology with nACh ␣ 7 receptors is the serotonin 5-HT 3 receptor (for reviews, see Jackson and Yakel, 1995;Reeves and Lummis, 2002).…”

“…However, several reports also indicate that endocannabinoids and the psychoactive active ingredient of marijuana, ⌬ 9 -THC, can produce effects that are not mediated by the activation of the cloned CB 1 and/or CB 2 receptors. For example, it has been demonstrated that endocannabinoids such as anandamide and/or 2-AG can inhibit the function of gap junctions (Venance et al, 1995), voltage-dependent Ca 2ϩ channels (Oz et al, 2000;Chemin et al, 2001), Na ϩ channels (Nicholson et al, 2003), various types of K ϩ channels (Poling et al, 1996;Van den Bossche and Vanheel, 2000;Maingret et al, 2001), 5-HT 3 receptor function (Barann et al, 2002;Oz et al, 2002a;Godlewski et al, 2003), and nicotinic ACh receptors (Oz et al, 2003). This suggests that additional molecular targets for certain classes of cannabinoids exist in the central nervous system, and that these targets may represent important sites for cannabinoids to alter neuronal function.…”

Hippocampal interneurons co-express transcripts encoding the α7 nicotinic receptor subunit and the cannabinoid receptor 1

“…Functional interactions between the nicotinic and cannabinoid systems have been documented (for reviews see, Castañe et al, 2005;Viveros et al, 2006), and results from recent in vitro (Oz et al, 2003(Oz et al, , 2004 and in vivo (Solinas et al, 2007) studies provide evidence for possible functional interactions between the α7 nACh and the cannabinoid systems. These interactions may occur, in part, by direct actions of endogenous cannabinoids on α7 nACh receptormediated neurotransmission.…”

“…Electrophysiological studies, using hippocampal cultures (Ohno-Shosaku et al, 2001) and hippocampal slices (Wilson and Nicoll, 2001), demonstrated that endogenous cannabinoids produced in postsynaptic neurons act on presynaptic CB1 receptors on terminals of interneurons to suppress GABA release. In addition, it has been shown that CB1 receptor activation by synthetic CB1 agonists (Katona et al, 1999;Hajos et al, 2000;Hoffman and Lupica, 2000) or endogenous cannabinoids (OhnoShosaku et al, 2001;Wilson and Nicoll, 2001) inhibits hippocampal GABA neurotransmission, and that hippocampal neurons that express high levels of the CB1 mRNA are mostly GABAergic .Functional interactions between the nicotinic and cannabinoid systems have been documented (for reviews see, Castañe et al, 2005;Viveros et al, 2006), and results from recent in vitro (Oz et al, 2003(Oz et al, , 2004 and in vivo (Solinas et al, 2007) studies provide evidence for possible functional interactions between the α7 nACh and the cannabinoid systems. These interactions may occur, in part, by direct actions of endogenous cannabinoids on α7 nACh receptormediated neurotransmission.…”

“…These interactions may occur, in part, by direct actions of endogenous cannabinoids on α7 nACh receptormediated neurotransmission. Previously, we showed that endogenous cannabinoids inhibit α7 nACh receptor-mediated responses in Xenopus oocytes (Oz et al, 2003(Oz et al, , 2004. Recent studies with rats demonstrated that systemic administration of a selective α7 nACh receptor antagonist diminishes the discriminative and reinforcing effects of cannabinoids and their ability to increase dopamine levels in the nucleus accumbens (Solinas et al, 2007).…”