Modeling Aversion Resistant Alcohol Intake in Indiana Alcohol-Preferring (P) Rats

Abstract

With the substantial social and medical burden of addiction, there is considerable interest in understanding risk factors that increase the development of addiction. A key feature of alcohol use disorder (AUD) is compulsive alcohol (EtOH) drinking, where EtOH drinking becomes “inflexible” after chronic intake, and animals, such as humans with AUD, continue drinking despite aversive consequences. Further, since there is a heritable component to AUD risk, some work has focused on genetically-selected, EtOH-preferring rodents, which could help uncover critical mechanisms driving pathological intake. In this regard, aversion-resistant drinking (ARD) takes >1 month to develop in outbred Wistar rats (and perhaps Sardinian-P EtOH-preferring rats). However, ARD has received limited study in Indiana P-rats, which were selected for high EtOH preference and exhibit factors that could parallel human AUD (including front-loading and impulsivity). Here, we show that P-rats rapidly developed compulsion-like responses for EtOH; 0.4 g/L quinine in EtOH significantly reduced female and male intake on the first day of exposure but had no effect after one week of EtOH drinking (15% EtOH, 24 h free-choice paradigm). Further, after 4−5 weeks of EtOH drinking, males but not females showed resistance to even higher quinine (0.5 g/L). Thus, P-rats rapidly developed ARD for EtOH, but only males developed even stronger ARD with further intake. Finally, rats strongly reduced intake of quinine-adulterated water after 1 or 5 weeks of EtOH drinking, suggesting no changes in basic quinine sensitivity. Thus, modeling ARD in P-rats may provide insight into mechanisms underlying genetic predispositions for compulsive drinking and lead to new treatments for AUDs.

Keywords: addiction; alcohol preference; alcoholism; compulsive drinking; gender studies; genetic model; selected lines.

Figure 1

In alcohol naïve female P-rats (n = 6), using a daily escalation paradigm of increasing quinine concentration in 15% EtOH, 0.4 g/L quinine significantly reduced 24 h intake of 15% EtOH compared to intake of 0.1, 0.2, or 0.3 g/L quinine (* p < 0.01; p < 0.05 and p < 0.05, respectively, Tukey’s posthoc test). For comparison, the mean 4-day intake of EtOH in a separate set of control female P-rats drinking 15% quinine without EtOH is presented (n = 5).

Figure 2

Quinine Effect on First Day of EtOH Drinking. Black bars: intake on the first day of exposure to 15% EtOH containing 0.4 g/L quinine; white bars: intake of 15% EtOH without quinine on the following day; hashed bars: intake of control rats (15% EtOH only) on the first day of EtOH access. Adulteration with 0.4 g/L quinine robustly reduced intake of EtOH in males (A) (n = 5; t = 11.09, * p < 0.001, paired t-test vs. white bar; * p < 0.001 vs. control group—hatched bar; unpaired t-test) and females (B) (n = 7; * p < 0.03, paired t-test vs. white bar; * p < 0.03 vs. control group—hatched; unpaired t-test).

Figure 3

Quinine resistance after 1 week EtOH drinking: Male and female P-rats had one week 24 h continuous access to 15% EtOH. Average EtOH intake for that week is depicted in the open bar (zero quinine condition). The following day, 0.4 g/L quinine was added to EtOH (black bars), with no significant effect of 0.4 g/L quinine on EtOH intake in either male (A) or female (B) P-rats (n = 11, 12/group, p > 0.05, paired t-tests).

Figure 4

Quinine resistance to higher quinine (0.5 g/L) after 3–5 weeks EtOH drinking. (A) In male P-rats (n = 12), EtOH drinking was sensitive to 0.5 g/L quinine after 3 weeks intake (W3) (* p < 0.05). However, after 4 weeks (W4) or 5 weeks (W5) of EtOH drinking, male intake persisted despite 0.5 g/L quinine in EtOH. (B) In contrast to males, female (n = 12) EtOH drinking was significantly reduced by 0.5 g/L quinine at W3 (*** p < 0.001), W4 (** p < 0.01), and W5 (*** p < 0.001).

Figure 5

Adding one week of Limited Access Drinking does not alter Quinine Sensitivity. After (A) one week (n = 8) or (B) 5 weeks (n = 12) of continuous EtOH drinking, male P-rats had 5 days of limited access drinking (1 h/day), then were tested for sensitivity to 0.5 g/L quinine in EtOH using the 24 h free-choice protocol. (A) Rats with 1 week EtOH drinking history prior to daily limited access retained sensitivity to 0.5 g/L quinine in EtOH (* p < 0.05; paired t-test; n = 8). (B) However, rats with 5 weeks drinking history were resistant to 0.5 g/L quinine in EtOH after limited access drinking (p > 0.05; paired t-test; n.s.).

Figure 6

Quinine sensitivity in water. Male P-rats consumed EtOH under free-choice conditions for 1 week (left, n = 8) or 5 weeks (right, n = 7), then were tested under two-bottle choice conditions, with one bottle containing water, and the second bottle with 0.1 g/L quinine in water. Rats in both groups highly preferred water alone compared to the water adulterated with 0.1 g/L quinine (t-values > 16; **** p < 0.0001).