Housing Condition Differentially Impacts Escalation of Alcohol Intake, Relapse-Like Drinking, Anxiety-Like Behavior, and Stress History Effects by Sex

Abstract

Background: Stress triggers alcohol use and relapse to drinking, with different effects by sex. Women are more susceptible to stress-related alcohol misuse, and most stressors in rodents produce sexually divergent effects. Female rodents are particularly sensitive to the stress produced by solitary housing, yet the impact of housing conditions on the establishment, escalation, and post-abstinence potentiation of intermittent access alcohol drinking in male and female rats, and the interaction of these factors with stress history are not well described.

Methods: Male (n = 62) and female (n = 64) Wistar rats were housed individually or in pairs separated by a perforated divider. Rats were exposed to light-cued footshock stress (stress history), or cues alone (control), once daily for 3 days, followed by 8 weeks' drinking under intermittent access to a 2-bottle choice (IA2BC), with 20% alcohol (v/v in water) available in addition to water for 24 hours on alternate days. After a 2-week forced abstinence, anxiety-like behavior was assessed via defensive withdrawal testing; then, IA2BC alcohol access was renewed for 2 weeks to model relapse-like behavior.

Results: Pair-housed female rats did not increase their alcohol intake across the 8-week drinking period, unlike all other groups, and stress history did not significantly change alcohol consumption. After abstinence, anxiety-like behavior was greatest in pair-housed stress history males, whereas alcohol intake was significantly elevated only in female rats, particularly those in solitary housing.

Conclusions: Together, these findings suggest that paired housing differentially contributes to behavior in male and female rats, blunting alcohol intake in females, and unmasking stress history effects on anxiety-like behavior in males.

Keywords: Footshock; Housing; Sex Differences; Stress History.

Figure 1.. Experimental timeline.

Pre-exposure: To acquaint rats with the taste of alcohol prior to stress exposure, rats were given 48-h access to 2 bottles, one containing 20% alcohol (v/v in water) and the other containing water. FS Stress: At least 24 h after cessation of alcohol pre-exposure, rats experienced 3, ~30-min sessions of 60 light-cued footshocks (stress history) or light cues alone (control). IA2BC: 24-h access to 2-bottle choice (20% alcohol and water) was provided on alternate days (Monday, Wednesday, Friday) for 8 weeks. A single water bottle was available on the other days. Forced abstinence: Access to alcohol ceased for 2 weeks. Rats were tested for anxiety-like behavior in 10-min defensive withdrawal sessions at the end of the abstinence period. IA2BC “Relapse”: Alcohol access returned under IA2BC conditions for an additional 2 weeks.

Figure 2.. Escalation of intermittent access drinking differs by housing condition and sex.

Solo- and pair-housed rats consumed 20% alcohol in the home cage under intermittent access 2-bottle choice (IA2BC) availability. Solo-housed rats (A-C): Alcohol intake in males (A) and females (B) increased across the 8-week access period, as did alcohol preference (C), with preference also differing by sex. Pair-housed rats (D-F): Alcohol intake in males (D) escalated similarly to solo-housed animals, whereas females’ (E) alcohol intake did not change significantly across the 8-week access period. Alcohol preference (F) paralleled intake, with preference increasing in males but not females. Data are expressed as mean ± S.E.M. weekly averages for each measure, with intake calculated as (g alcohol consumed) / (kg body weight) and preference calculated as (ml alcohol consumed) / (total ml fluid intake)*100. * p < 0.05 vs. Week 1, collapsed across groups; ^ p < 0.05 vs. Week 1 across groups for males only; ^& p <0.001, main effect of Sex. n = 14-16.

Figure 3.. Anxiety-like behavior in defensive withdrawal differs by housing condition and sex.

At the end of 2 weeks’ forced abstinence from intermittent alcohol access, rats explored an arena containing a dark chamber for 10 min, with all rats beginning in the chamber. (A) Solo-housed rats displayed no stress history or sex-specific differences in latency to emerge from the beaker (exit latency). (B) For pair-housed rats, stress history increased exit latency in males but not females. (C) Solo-housed rats did not differ by sex or stress history in total time spent in the dark chamber. (D) Pair-housed rats differed by sex but not stress history in total time spent in the dark chamber, with all males spending more time in the beaker than all females. Data are expressed as mean ± S.E.M. time in seconds, or as the base 10 logarithm of those times where indicated. * p < 0.05, vs. all other groups or comparisons as indicated, ^@ p < 0.05 vs. control by Mann-Whitney U test. n = 8-10, as indicated in (A) and (B).

Figure 4.. Forced abstinence increases relapse-like drinking in females.

(A) Renewed access to alcohol after 2 weeks’ forced abstinence consistently increased alcohol intake across all 24-h access periods in solo-housed female, but not male, rats, regardless of stress history. (B) Pair-housed female, but not male, rats displayed modest elevations in 24-h alcohol intake after the abstinence period, regardless of sex or stress history. (C) Solo-housed female rats increased alcohol consumption during the first hour of access, relative to pre-abstinence 1-h intake, without effect in males or based on stress history. (D) No significant changes in alcohol intake by sex or stress history were observed during the first hour of access, relative to pre-abstinence intakes, in pair-housed rats. Data are presented as mean ± S.E.M. alcohol intake normalized to pre-abstinence baseline, calculated as [(weight-normalized alcohol intake post-abstinence)/(average weight-normalized alcohol intake in the last week pre-abstinence)], averaged over single sessions (A,B) or the 2-week post—abstinence period (C,D). * p < 0.05, female vs. male. n = 8-10, as indicated in (C) and (D).