Chronic Intermittent Ethanol Exposure Increases Ethanol Consumption Following Traumatic Stress Exposure in Mice

Abstract

Individuals with post-traumatic stress disorder (PTSD) often use alcohol to cope with their distress. This aberrant use of alcohol often develops into alcohol use disorder (AUD) leading to high rates of PTSD-AUD co-occurrence. Individuals with comorbid PTSD-AUD have more intense alcohol cravings and increased relapse rates during withdrawal than those with AUD alone. Also, individuals with PTSD or AUD alone often show similar psychological behaviors, such as impulsivity and anhedonia. Extensive clinical studies on the behavioral effects of PTSD-AUD comorbidity, namely alcohol use, have been performed. However, these effects have not been well studied or mechanistically explored in animal models. Therefore, the present study evaluated the effects of traumatic stress comorbid with alcohol exposures on ethanol intake, impulsivity, and anhedonia in mice. Adult male C57Bl/6 mice were first exposed to either mouse single-prolonged stress (mSPS), an animal model that has been validated for characteristics akin to PTSD symptoms, or control conditions. Baseline two-bottle choice ethanol consumption and preference tests were conducted after a 7-day isolation period, as part of the mSPS exposure. Next, mice were exposed to air or chronic intermittent ethanol (CIE), a vapor-induced ethanol dependence and withdrawal model, for 4 weeks. Two-bottle choice ethanol drinking was used to measure dependence-induced ethanol consumption and preference during periods intervening CIE cycles. The novelty suppressed feeding (NSF) test was used to evaluate impulsivity and anhedonia behaviors 48 h after mSPS and/or repeated CIE exposure. Results showed that, compared to control conditions, mSPS did not affect baseline ethanol consumption and preference. However, mSPS-CIE mice increased Post-CIE ethanol consumption compared to Control-Air mice. Mice exposed to mSPS had a shorter latency to feed during the NSF, whereas CIE-exposed mice consumed less palatable food reward in their home cage after the NSF. These results demonstrate that mice exposed to both mSPS and CIE are more vulnerable to ethanol withdrawal effects, and those exposed to mSPS have increased impulsivity, while CIE exposure increases anhedonia. Future studies to examine the relationship between behavioral outcomes and the molecular mechanisms in the brain after PTSD-AUD are warranted.

Keywords: alcohol use disorder; anhedonia; chronic intermittent ethanol; ethanol consumption; impulsivity; mouse single-prolonged stress; post-traumatic stress disorder.

Figure 1

Schematic overview of (A) the mouse single-prolonged stress (mSPS) paradigm, (B) mSPS, and chronic intermittent ethanol (CIE) exposure with two-bottle choice drinking test. After the mSPS paradigm, mice were exposed to two-bottle choice for five nights. Mice were then exposed to CIE exposure every other week, with a Post-CIE drinking test in between the weeks of CIE exposure.

Figure 2

Average of Pre-CIE (A) ethanol intake and (B) ethanol preference on the 8th day after 7-day of incubation. A student’s two-tailed t-test revealed no significant impact on ethanol consumption and preference after mSPS (n = 14). However, a three-way ANOVA with repeated measures and post hoc Fisher-LSD test showed the results in (C) that vapor-induced ethanol intake was significantly increased in mSPS-CIE (n = 5) compared to Control-Air (n = 5; ^∧p < 0.05) and Control-CIE mice (n = 4; *p < 0.05) in the 1st and 4th Post-CIE ethanol intake test sessions (Test 1 and 4). Mice exposed to mSPS and air control (mSPS-Air: n = 4) showed increased ethanol consumption in the 1st post-CIE ethanol intake session (Test 1; ^∧p < 0.05) compared to Control-Air mice, but not in subsequent Post-CIE ethanol intake test sessions. The results in (D) showed no significant impact on ethanol preference among groups in either test session. A three-way ANOVA with repeated measures showed that neither the (E) average total fluid consumption among groups nor the (F) mouse body weights were affected in Test 1 and 4. Data are mean ± SEM.

Figure 3

Average blood ethanol concentrations (BECs; mg/dl) across four cycles of CIE vapor exposure. Average BECs in mSPS-CIE mice (n = 5) over four cycles of CIE vapor exposure did not differ from the Control-CIE mice (n = 4). Data are mean ± SEM.

Figure 4

Average of (A) latency to feed during the novelty suppressed feeding (NSF) test and (B) percent sweetened fruit cereal consumed in the home cage, after the 4th cycle of CIE (before Test 4). mSPS increased impulsivity behavior (A), and CIE exposure decreased home cage sweetened cereal intake in mice (n = 5–6; B). A two-way ANOVA revealed that mSPS-exposed mice, either exposed to CIE or Air, had a shorter latency to take the first bite of a sweetened fruit cereal (*p < 0.05) compared to mSPS controls. A two-way ANOVA also revealed that CIE-exposed mice, either exposed to mSPS or Control (non-mSPS) conditions previously, consumed less sweetened cereal in their home cages compared to Air-exposed mice. Data are mean ± SEM.