Greater inhibition of female rat binge alcohol intake by adrenergic receptor blockers using a novel Two-Shot rat binge drinking model

Abstract

Binge drinking (BD) contributes strongly to the harms of alcohol use disorder. Most rodent models do not result in binge-level blood alcohol concentrations (BACs), and to better understand individual and sex differences in neurobiological mechanisms related to BD, the use of outbred rat strains would be valuable. Here, we developed a novel BD model where after 3+ months of intermittent access to 20% alcohol Wistar rats drank, twice a week, with two 5-minute intake (what we called Two-shot) separated by a 10-minute break. Our findings showed during Two-Shot that most animals reached ≥ 80mg% BAC levels (when briefly food-restricted). However, when increasing alcohol concentrations from 20% to 30%, 40%, or 50%, rats titrated to similar intake levels, suggesting rapid sensing of alcohol effects even when front-loading. Two-Shot drinking was reduced in both sexes by naltrexone (1mg/kg), validating intake suppression by a clinical therapeutic agent. Further, both propranolol (β adrenergic receptor antagonist) and prazosin (α1 adrenergic receptor antagonist) reduced female but not male BD at the lower dose. Thus, our results provide a novel model for BD in outbred rats and suggest that female binging is more sensitive to adrenergic modulation than males, perhaps providing a novel sex-related therapy.

Figure 1. Schematic representation of the novel Two-Shot model.

After 3+ months of IA2BC, rats started to drink twice a week in the Two-Shot model. In each session of the Two-Shot, rats drank for 5min (Shot-1), followed by 10 min of break, and then a second 5-min drinking (Shot-2).

Figure 2. Two-Shot model with 20% alcohol leads to binge-level BACs.

(A) BAC was greater than 80mg% with 20% alcohol drinking in females (purple) and males (green) and (B) alcohol intake >1g/kg. Also, alcohol intake level (g/kg) and BACs were significantly correlated in females (C) and males (D). * p<0.05; **p<0.01; ***p<0.001.

Figure 3. Female and male rats maintained similar intake levels as alcohol concentration increased.

(A,B) During Shot-1, females consumed more alcohol than males and, for both sexes, there was no difference in intake levels between 20%, 30%, 40%, or 50% alcohol. (C,D). For Shot-2, there were no differences by sex or alcohol concentrations. (E,F) During the full Two-Shots intake period, females consumed more alcohol, and there was no difference between the alcohol concentrations. n=20 per sex *p<0.05

Figure 4. Relation of 20% alcohol intake to intake of other alcohol concentrations.

(A-C) Relation of female intake level for 20% alcohol to higher alcohol concentrations, for (A)Two-Shot, (B) Shot-1 alone, and (C) Shot-2 alone. (D-F) Relation of male intake level for 20% alcohol to higher alcohol concentrations, for (D)Two-Shot, (E) Shot-1 alone, and (F) Shot-2 alone. (G,H) Relation between Shot-1 and Shot-2 intake, for each alcohol concentration separately, in (G) females and (H) males. * p<0.05; **p<0.01; ***p<0.001.

Figure 5. Two-Shot intake was inhibited by naltrexone in both sexes, and females drinking was inhibited by lower concentrations of propranolol.

(A) Cartoon of injection timing. (B-E) Impact of 1mg/kg naltrexone or 5mg/kg propranolol in (B,C) female and (D,E) male rats. (F-I) Impact of 10mg/kg propranolol in (F,G) female and (H,I) male rats. * p<0.05; **p<0.01; ***p<0.001, vs group control.

Figure 6. Female drinking was inhibited by lower concentrations of prazosin relative to males.

(A) Cartoon of injection timing. (B-E) Impact of 0.75mg/kg or 1.5mg/kg prazosin on (B,C) female and (D,E) male rat Two-Shot drinking. (F,G) Relationship between basal intake levels and impact of (F) 0.75mg/kg prazosin or(G) 5mg/kg propranolol on drinking (change in drinking determined as drug/vehicle intake and expressed as percent). * p<0.05; **p<0.01.