Assessing initial/early aversion-resistant drinking across male and female alcohol-preferring and non-preferring rats

Abstract

Background: One trait of alcohol use disorder (AUD) is continuing to drink despite negative consequences. The current study investigated initial/early aversion-resistant drinking (ARD) across selectively bred alcohol-preferring lines to assess aversion resistance with minimal ethanol history and subsequent ethanol-seeking and drinking profiles. Additionally, ARD was assessed in alcohol-preferring and non-preferring rats using a sucrose reinforcer to determine if ARD may be a genetic risk factor for AUD.

Methods: Male and female alcohol-preferring rats were given four concentrations of quinine (0.03, 0.10, 0.30, and 1.00 g/L-in random order) in an ethanol solution in the homecage for 30 min daily across 12 days. Seeking and drinking were then assessed in the operant chambers. Additional groups of alcohol-preferring and non-preferring rats were given access to the same concentrations of quinine-adulterated sucrose using the same daily, random-order presentation.

Results: In ethanol, all preferring lines performed similarly, showing resistance to quinine at the lowest concentration. In the homecage, high-alcohol-drinking (HAD)1 rats drank high levels of ethanol similar to alcohol-preferring (P) rats, whereas in an operant task were more similar to the HAD2 rats. In sucrose, P and HAD2 rats were shown to be aversion resistant at low concentrations of quinine compared to baseline. Overall, the non-preferring lines all demonstrated sensitivity to quinine-adulterated sucrose.

Conclusions: This study demonstrates alcohol-preferring lines show similar ARD when ethanol is the reinforcer. Regarding motivated responding, P rats show high-seeking and drinking behaviors as previously observed. In the homecage, HAD1 rats drink similarly to P rats indicating that different conditions (i.e., free vs. operant access) influence drinking behaviors between these lines. Importantly, in a sucrose reinforcer, alcohol-preferring rats are more aversion-resistant than non-preferring lines, while non-preferring lines show high sensitivity to aversion, suggesting an overall tendency to demonstrate a low level of compulsive behavior.

Keywords: alcohol; aversion‐resistant drinking; compulsive drinking; quinine; rat.

FIGURE 1

Example timeline for ethanol ARD. E = 10% ethanol; h = hours; numbers refer to g/L quinine concentration. Note that actual quinine concentrations were presented in random order for each 2‐day period by subject (indicated by italics).

FIGURE 2

Ethanol intake baseline across preferring lines collapsed by sex. P and HAD1 rats drank significantly more 10% ethanol than HAD2 rats. There were no sex differences found between females and males within any of the lines. * indicates p < 0.05.

FIGURE 3

Ethanol ARD across baseline and increasing quinine concentrations in alcohol‐preferring lines split by sex. P rats displayed no significant differences between baseline and the lowest (0.03 g/L) concentration of quinine (A). Overall, HAD1 females drank significantly more than males collapsed across concentrations. No significant difference was found between baseline and the lowest concentration. Additionally, no significant difference was found between 0.3 and 1.0 g/L (B). HAD2 rats also displayed no difference in intake between baseline and the 0.03 g/L of quinine. There was also no significant difference between 0.03 and 0.1 g/L as well as 0.1 g/L was not significantly different than both 0.3 g/L or 1.0 g/L (C). ^a p < 0.05 from baseline, ^b p < 0.05 from 0.03 g/L, ^c p < 0.05 from 0.1 g/L, ^d p < 0.05 from 0.3 g/L, ^f p < 0.05 from 1.0 g/L.

FIGURE 4

Operant behavioral testing. Male rats are represented by square data points on graphs. P rats pressed significantly more than HAD1 and HAD2 rats during extinction sessions. HAD1 and HAD2 rats were not significantly different (A). Averaged across the 12 reinforced sessions, P rats drank significantly more ethanol than both HAD1 and HAD2 rats during the 20 min of access each session. HAD1 and HAD2 rats did not significantly differ from each other (B).

FIGURE 5

Sucrose baseline across alcohol‐preferring and non‐preferring lines split by sex. P rats drank more sucrose at baseline than all other strains. Male P rats drank significantly more than female P rats. HAD1 rats drank significantly more sucrose than HAD2 rats. HAD1 and LAD1 rats did not differ in sucrose intake. However, LAD1 females drank significantly more sucrose than LAD1 males. HAD2 and LAD2 rats also did not significantly differ in sucrose intake. ** indicates p < 0.05 compared to all other strains, * indicates p < 0.05 between HAD1 and HAD2 rats, # indicates a significant sex difference within one strain.

FIGURE 6

Sucrose ARD across baseline and increasing concentrations of quinine in preferring and non‐preferring lines split by sex. Overall, male P rats drank significantly more than female P rats at baseline. Collapsed by sex, baseline and 0.03 g/L of quinine did not significantly differ. Baseline was significantly different than all other concentrations (A). NP rats showed a significant difference between baseline and all quinine concentrations but no differences between quinine concentrations (B). HAD1 rats displayed a significant difference between baseline and all quinine concentrations as well as a significant difference between 0.03 g/L of quinine and all other concentrations of quinine (C). In LAD1 rats, overall females drank more than male rats. Collapsed by sex, there was a significant difference between baseline and all other concentrations of quinine (D). In HAD2 rats, baseline was not significantly different than 0.03 or 0.1 g/L concentrations of quinine (E). LAD2 female rats drank significantly more than male rats. Collapsed by sex, LAD2 rats showed a significant difference between baseline and all other concentrations of quinine (F). ^a p < 0.05 from baseline, ^b p < 0.05 from 0.03 g/L, ^c p < 0.05 from 0.1 g/L, ^d p < 0.05 from 0.3 g/L, ^f p < 0.05 from 1.0 g/L, * indicated p < 0.05, # indicates a significant sex difference.