Cannabinoid-1 receptor neutral antagonist reduces binge-like alcohol consumption and alcohol-induced accumbal dopaminergic signaling

Abstract

Binge alcohol (ethanol) drinking is associated with profound adverse effects on our health and society. Rimonabant (SR141716A), a CB1 receptor inverse agonist, was previously shown to be effective for nicotine cessation and obesity. However, studies using rimonabant were discontinued as it was associated with an increased risk of depression and anxiety. In the present study, we examined the pharmacokinetics and effects of AM4113, a novel CB1 receptor neutral antagonist on binge-like ethanol drinking in C57BL/6J mice using a two-bottle choice drinking-in-dark (DID) paradigm. The results indicated a slower elimination of AM4113 in the brain than in plasma. AM4113 suppressed ethanol consumption and preference without having significant effects on body weight, ambulatory activity, preference for tastants (saccharin and quinine) and ethanol metabolism. AM4113 pretreatment reduced ethanol-induced increase in dopamine release in nucleus accumbens. Collectively, these data suggest an important role of CB1 receptor-mediated regulation of binge-like ethanol consumption and mesolimbic dopaminergic signaling, and further points to the potential utility of CB1 neutral antagonists for the treatment of binge ethanol drinking.

Keywords: AM4113; Binge drinking; Cannabinoid receptor; Neutral antagonist; Nucleus accumbens.

Figure 1

Drinking in the dark (DID) paradigm was used to model binge-like ethanol consumption in mice. Mice were habituated to reverse light-dark cycle for a week and offered two bottles containing water and 20% ethanol 3 hours into the dark phase for 2 hours for five days a week (Monday to Friday) with two days of abstinence.

Figure 2

Effect of AM4113 on ethanol consumption and preference was examined using a two-bottle choice paradigm. AM4113 significantly suppressed ethanol consumption at dose 1 mg/kg on day 1 (***p<0.0001) and 2 (*p<0.05), and at dose 3 mg/kg on day 1 (***p<0.0001), day 2(***p<0.0001), day 3 (*p<0.05) and day 4 (*p<0.05). A marked reduction in ethanol preference was observed at dose 1 mg/kg on day 1 (***p<0.0001) and 2 (*p<0.05), and at dose 3 mg/kg on day 1 (***p<0.0001), day 2 (***p<0.0001), day 3 (*p<0.05) and day 4 (*p<0.05). Data are presented as mean ± SEM. (p values are relative to the vehicle treated group (Vehicle = 10; 1 mg/kg =10; 3 mg/kg = 11); Two-way mixed ANOVA with Bonferroni post-hoc test).

Figure 3

Effect of AM4113 treatment on the body weight, ambulatory activity and preference for tastants. The body weight, measured before and 24 hour after the last injections, was presented as change in body weight. Home cage ambulatory activity (beams broken X-Y) and preference for tastants were measured for 2 hour in the dark-cycle 3 hour after AM4113 and vehicle injections. Treatment of AM4113 for 4 days did not significantly alter (A) body weight [F(2,15) = 0.06; p=0.94; n=6 per group), (B) ambulatory activity [F(2,12) = 0.32; p=0.73; n = 5 per group] and (C) preference for saccharin [F(2,15) = 1.79; p=0.20; n=6 per group] or quinine [F(2,15) = 0.34; p = 0.71; n=6 per group] compared to their respective vehicle treated mice (n = 6 per group). Data are presented as mean ± SEM.

Figure 4

Microdialysis studies were conducted to examine the effect of AM4113 on ethanol-induced on dopamine (DA) release in nucleus accumbens shell (NAcS). Ethanol (1.5 g/kg, i.p.) was administered 120 min after the injections of either vehicle (n=5) or AM4113 (1 mg/kg, i.p.; n=8). Ethanol significantly increased DA release at 20 min (**p<0.001), 40 min (***p<0.0001) and 60 min (*p<0.05) post-injections compared to vehicle treated group (A). Ethanol-induced DA level was suppressed by AM4113 treatment after 40 min of ethanol injection (^#p=0.0012; A). The placements of microdialysis probes were verified histologically. A representative image with arrow indicate a probe placement in NAcS (B). Data are presented as mean ± SEM.

Figure 5

Effect of AM4113 treatment on ethanol metabolism. Blood ethanol concentration (BEC) was measured at 40, 80 and 120 min following ethanol administration (1.5 g/kg., i.p.). There was a significant effect of time on BEC [F(2,24) =2 21.9; p<0.0001]. However, no significant effects of either AM4113 treatment [F(2,12) = 0.17; p = 0.84] or interaction between time and AM4113 treatment [F(4,24)= 0.80; p = 0.53] were observed compared to vehicle treated group. Data are presented as mean ± SEM (n = 5 per group).

Figure 6

The concentrations of AM4113 in brain and plasma were analyzed by liquid chromatography-mass spectrometry (LC-MS) following intraperitonial injection of mice at dose of 1 mg/kg. Plasma (A; ***p<0.0001 at 20 min [n=4] compared to 40 min [n=5], 60 min [n=5], 90 min [n=5], 180 min [n=5], 300 min [n=4] and 420 min [n=3] post-injection time points) and brain (B; *p<0.05; **p<0.001;***p<0.0001 compared to 10 min post-injection time point) concentrations of AM4113 were significantly higher at 20 min and 60 min, respectively.